WO2025241057A1

WO2025241057A1 - Bonded structure comprising an electrochemically debondable adhesive film

Info

Publication number: WO2025241057A1
Application number: PCT/CN2024/094168
Authority: WO
Inventors: Lucas STRICKER; Philipp Huehnergarth; Stefanie Stapf; Fangqi TAO; Christian TAPLAN; Carla NEGELE; Jing Yang; Mo XUN
Original assignee: Henkel China Co Ltd; Henkel China Investment Co Ltd; Henkel AG and Co KGaA
Current assignee: Henkel China Co Ltd; Henkel China Investment Co Ltd; Henkel AG and Co KGaA
Priority date: 2024-05-20
Filing date: 2024-05-20
Publication date: 2025-11-27
Anticipated expiration: 2026-11-20
Also published as: WO2025242379A1

Abstract

A bonded structure comprising: a first substrate provided with a first electrically conductive surface; a second substrate provided with a second electrically conductive surface; and, a cured, electrochemically debondable adhesive film interposed between said first and second electrically conductive surfaces, said electrochemically debondable adhesive film having one or more constituent layers, wherein at least one layer of the cured adhesive film comprises a non-polymerizable electrolyte and at least one polyurethane polymer; wherein at least one of said first and second electrically conductive surfaces is provided by a ink film which is obtained by the evaporative removal of solvent from an ink composition, said ink film comprising:a matrix of a polymeric resin (F^R);and, electrically conductive particles.

Description

BONDED STRUCTURE COMPRISING AN ELECTROCHEMICALLY DEBONDABLE ADHESIVE FILM

FIELD OF THE INVENTION

The present disclosure is directed to bonded structure comprising an electrochemically debondable adhesive film. More particularly, the present disclosure is directed to a bonded structure comprising an electrochemically debondable adhesive film which is disposed between electrically conductive surfaces, of which at least one electrically conductive surface is provided by a dried ink film comprising a polymeric resin and electrically conductive particles.

BACKGROUND TO THE INVENTION

Adhesive bonds and polymeric coatings are commonly used in the assembly and finishing of manufactured goods. They are used in place of mechanical fasteners, such as screws, bolts and rivets, to provide bonds with reduced machining costs and greater adaptability in the manufacturing process. Adhesive bonds distribute stresses evenly, reduce the possibility of fatigue and seal the joints from corrosive species.

Whilst adhesive bonds thus offer many advantages over mechanical fasteners, it tends to be difficult to disassemble adhesively bonded objects where this is required in practical applications. The removal of the adhesive through mechanical processes –such as by sand blasting or by wire brushing –is often precluded, in part because the adhesive is disposed between substrates and is thus either inaccessible or difficult to abrade without corrupting the substrate surfaces. Disassembly through the application of chemicals and /or high temperature –such as disclosed in US Patent No. 4,171,240 (Wong) and US Patent No. 4,729,797 (Linde et al. ) -might be effective but can be time consuming and complex to perform: moreover, the aggressive chemicals and /or harsh conditions required can damage the substrates being separated, rendering them unsuitable for subsequent applications.

Noting these problems, certain authors have sought to develop electrochemically debondable adhesive compositions, wherein the passage of an electrical current through the cured compositions acts to disrupt the bonding at the interface of the adhesive and the substrate.

US Patent No. 7,465,492 (Gilbert) describes an electrochemically disbondable composition comprising: a matrix functionality comprising a monomer selected from the group consisting of acrylics, methacrylics and combinations thereof; a free radical initiator; and, an electrolyte, wherein the electrolyte provides sufficient ionic conductivity to said composition to support a faradaic reaction at a bond formed between the composition and an electrically conductive surface and thus allows the composition to disbond from the surface.

US 2007/0269659 (Gilbert) describes an adhesive composition disbondable at two interfaces, the composition: (i) comprising a polymer and an electrolyte; (ii) facilitating joinder of two surfaces; and, (iii) in response to a voltage applied across both surfaces so as to form an anodic interface and a cathodic interface, disbonding from both the anodic and cathodic surfaces.

US2020/195025A (Yoder et al. ) describes a system comprising: an electronic device; a battery coupled to the electronic device; and, an electro-adhesive layer included within a coupling between the battery and the electronic device. The electro-adhesive layer is composed of a material that chemically reacts to weaken a bond at an interface between the battery and the electronic device when a current of predetermined magnitude is directed through the electro-adhesive layer between a first electrode and a second electrode, the weakened bond facilitating separation of the battery from the electronic device.

EP 3 835 383 A1 (Henkel AG & Co. KGaA) discloses a bonded structure comprising a first material layer having an electrically conductive surface; and, a second material layer having an electrically conductive surface; wherein a curable and debondable one component (1 K) adhesive composition is disposed between the first and second material layers. The curable and one component (1 K) debondable adhesive composition comprises: a) epoxy resin; b) a curing agent for said epoxy resin; c) an electrolyte; and, d) an electrically non-conductive filler; wherein said composition comprises at least one of: e) a combination of a solubilizer and a toughener; and, f) electrically conductive particles.

EP 3 835 378 A1 (Henkel AG & Co. KGaA) discloses a bonded structure comprising a first material layer having an electrically conductive surface; a second material layer having an electrically conductive surface; wherein a cured debondable two-part hybrid adhesive composition is disposed between the first and second material layers. The curable and debondable two-part hybrid adhesive composition comprises a first part comprising: a) epoxy resin; b) (meth) acrylate monomer; c) an electrolyte; d) a solubilizer; and, e) a filler. The composition further comprises a second part comprising: a) a curing agent consisting of at least one compound possessing at least two epoxide reactive groups per molecule; b) an accelerator; and, c) a filler.

EP 3 835 386 A1 (Henkel AG & Co. KGaA) discloses a bonded structure comprising a first material layer having an electrically conductive surface; a second material layer having an electrically conductive surface; wherein a cured debondable two-part (2K) adhesive composition is disposed between the first and second material layers. The curable and debondable two-part (2K) adhesive composition comprise a first part comprising: a) epoxy resin; b) an electrolyte; and, c) optionally, a solubilizer. The second part comprises: a) a curing agent consisting of at least one compound possessing at least two epoxide reactive groups per molecule; and, b) an accelerator. The composition still further comprises an electrically non-conductive filler and, optionally a toughener.

WO 2016/135341 (Henkel AG & Co. KGaA) discloses an electrically debondable reactive hot melt adhesive composition, comprising: a) at least one isocyanate-functional polyurethane polymer; and, b) at least one organic or inorganic salt. The fact that the pre-formed polyurethane polymer is applied within a hot melt adhesive is considered to present the disadvantage that the application of the polyurethane adhesive requires specialized equipment and the efficacy of the adhesive is sensitive to application temperature.

WO 2022/207300 A1 (Henkel AG & Co. KGaA) discloses a curable and electrochemically debondable two-component (2K) adhesive composition comprising: a first component comprising: i) at least one polyol selected from the group consisting of fatty alcohols, polyester polyols, polyether polyols, polyether-polyester polyols and polycarbonate polyols; ii) optionally further active hydrogen compounds; and, iii) non-polymerizable electrolyte; and, a second component comprising at least one polyisocyanate, wherein said composition is characterized in that the molar equivalents ratio of NCO groups to active hydrogen atoms is at least 1: 1.

The adhesives of such disclosures are applied to the surfaces to be bonded in liquid form, typically in molten form or as solvent-borne compositions. Whilst the bonding of surfaces using dry adhesive films –including but not limited to B-staged or partially cured adhesive films -is broadly known in the art, a dry-to-touch film of an electrochemically debondable composition having this utility is not known to the present inventors. In addition to permitting bonded structures to be disassembled by the application of a potential difference across the film, further advantages of such films would be realized, including the control of the thickness of the debondable adhesive and the capacity to generated bonded structures in a clean, hazard-free manner with minimum waste.

Furthermore, it is a common feature of these references that two metallic substrates must be provided, in between the surfaces of which the debondable adhesives are disposed. This imposes a significant limitation on the utility of the debondable adhesives given the ubiquity of bonded structures which should be candidates for disassembly and recycling but which comprise at least one substrate which either is not electrically conductive per se or does not present an electrically conductive surface.

STATEMENT OF THE INVENTION

In accordance with a first aspect of the disclosure there is provided a bonded structure comprising:

a first substrate provided with a first electrically conductive surface;

a second substrate provided with a second electrically conductive surface; and,

a cured, electrochemically debondable adhesive film interposed between said first and second electrically conductive surfaces, said electrochemically debondable adhesive film having one or more constituent layers, wherein at least one layer of the cured adhesive film comprises a non-polymerizable electrolyte and at least one polyurethane polymer;

wherein at least one of said first and second electrically conductive surfaces is provided by a ink film which is obtained by the evaporative removal of solvent from an ink composition, said ink film comprising: a matrix of a polymeric resin (F^R) ; and, electrically conductive particles.

The dried ink film (s) may serve to render electrically conductive the surface of at least one substrate which possesses bulk electrical non-conductivity. The term “bulk electrical (non-) conductivity” refers to the electrical (non-) conductivity of a matrix material on the macroscale as opposed to localized electrical conductivity that can occur through, herein, surface modification. Thus, in an important embodiment of the bonded structure, said first substrate possesses bulk electrical non-conductivity and the first electrically conductive surface thereof is provided by a first dried ink film comprising: a) a matrix of polymeric resin (F^R) ; and, electrically conductive particles. It is preferred that said first dried ink film providing the first electrically conductive surface is disposed on and in direct contact with said first substrate.

Whilst the second substrate may possess both volume and surface electrical conductivity, it is also envisaged that the second substrate may be an insulating material. Thus, it is considered that the second substrate may also possess bulk electrical non-conductivity and that the second electrically conductive surface may be provided by a second dried ink film comprising: a) a matrix of polymeric resin (F^R) ; and, electrically conductive particles. And preferably said dried ink film providing the second electrically conductive surface is disposed on and in direct contact with said second substrate.

Good results have been obtained where the polymeric resin (F^R) of each dried ink film of the bonded structure is chosen from: nitrocellulose; epoxy resins; phenolic resins; and, mixtures thereof. Further, it is preferred that the electrically conductive particles of each dried ink film of the bonded structure be chosen from: carbon black; graphite; carbon nanotubes; carbon fibers; silver; silver coated copper; silver coated graphite; silver coated polymers; silver coated aluminium; silver coated glass; and, mixtures thereof. A particular preference for the use as the conductive particles of graphite, carbon black and mixtures thereof might be noted: any mixtures thereof may, in certain embodiments, be characterized by a ratio by weight of graphite to carbon black of from 1: 1 to 5: 1.

In an important embodiment, the non-polymerizable electrolyte of the cured, electrochemically debondable film adhesive comprises or consists of a non-polymerizable salt of chosen from: ammonium salts; pyridinium salts; pyrrolidinium salts; phosphonium salts; imidazolium salts; oxazolium salts; guanidinium salts; sulfonium salts; sulfonium salts; sulfonium salts; thiazolium salts; and, mixtures thereof.

The cured, electrochemically debondable adhesive film is interposed between -and is conventionally in direct contact with -said first and second electrically conductive surfaces of the substrate. The cured, electrochemically debondable adhesive film is preferably obtained from a precursor curable film, in particular a curable transfer film. And, as noted, the cured electrochemically debondable adhesive film has one or more constituent layers, typically from 1 to 3 layers and preferably either 1 or 2 layers.

In an interesting embodiment, at least one layer of the electrochemically debondable adhesive film consists of a film (F^a) which is obtained by:

drying a solvent-borne composition (a) to obtain a curable film therefrom, said solvent-borne composition (a) comprising: a1) at least one thermoplastic polyurethane polymer; a2) at least one polyester polyol; a3) at least one polyisocyanate compound having at least two isocyanate groups and at least one uretdione group; a4) non-polymerizable electrolyte; optionally a5) rheology control agent comprising electrically non-conductive fillers, electrically conductive fillers or mixtures thereof; and, a6) at least one organic solvent, wherein the molar ratio of -N=C=O groups to hydroxyl groups in the composition (a) is from 0.1: 1 to 10: 1;

transferring said curable film to interpose it between said first and second electrically conductive surfaces; and,

curing the transferred film by heating said film.

In another embodiment, which is not mutually exclusive of that given above, at least one layer of the electrochemically debondable adhesive film consists of a film (F^b) which is obtained by:

drying a water-borne composition (b) to obtain a curable film therefrom, said water-borne composition (b) comprising: water; b1) at least one first polyurethane polymer having at least one active hydrogen group, wherein said first polyurethane polymer is obtained by the reaction of at least one polyisocyanate compound with at least one polyol (POHA) which has a number average molecular weight (Mn) of at least 500 g/mol. and which further has one or more structural units chosen from structural units of Formula (I) , Formula (II) , Formula (III) described herein; b2) at least one second polyurethane polymer which is distinct from said first polyurethane polymer, said second polyurethane polymer having at least one isocyanate reactive functional group; b3) at least one surface-deactivated solid polyisocyanate compound; b4) non-polymerizable electrolyte; and, optionally b5) rheology control agent comprising electrically non-conductive fillers, electrically conductive fillers or mixtures thereof, wherein the molar ratio of -N=C=O groups to active hydrogen atoms in the composition (a) is from 0.1: 1 to 10: 1;

curing the obtained film by heating said film.

The type of substrates which may be bonded within –and electrochemically disbonded from -the above captioned structure are not particularly limited. However, the bonding of electronic components -including but not limited to batteries –within encasements or to supportive structures is particularly envisaged.

In an embodiment of the bonded structure: said first substrate is furnished by an electronic component and said first electrically conductive surface is provided on the exterior of said electronic component; and, said second substrate is furnished by a frame disposed about the exterior of said electronic component, wherein: said frame comprises an integrant (I^F) of a material possessing a volume electrical conductivity of less than 1 Sm^-1 and having an outer surface and an inner surface; and, a dried ink film is disposed on the inner surface of said integrant (I^F) , the dried ink film providing said frame with the second electrically conductive surface of the structure.

The present disclosure also provides a method of disbonding a bonded structure as defined hereinabove and in the appended claims, the method comprising the steps of:

i) applying a voltage across said first electrically conductive surface and said second electrically conductive surface to form an anodic interface and a cathodic interface; and,

ii) disbonding said first and second substrates.

In important embodiments of this method, the voltage applied in step i) is from 0.5 to 200 V and it is preferably applied for a duration of from 1 second to 60 minutes.

Where the aspects of the disclosure are described above as having certain embodiments, any one or more of those embodiments can be implemented in or combined with any one of the further embodiments, even if that combination is not explicitly described. Expressed differently, the described embodiments are not mutually exclusive, and permutations thereof remain within the scope of this disclosure.

DEFINITIONS

As used herein, the singular forms "a" , "an" and "the" include plural referents unless the context clearly dictates otherwise.

The terms “comprising” , “comprises” and “comprised of” as used herein are synonymous with “including” , “includes” , “containing” or “contains” , and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. As used herein, the term “consisting of” excludes any element, ingredient, member or method step not specified. For completeness, the term “comprising” encompasses “consisting of” .

The words "preferred" , "preferably" , “desirably” and “particularly” are used frequently herein to refer to embodiments of the disclosure that may afford particular benefits, under certain circumstances. However, the recitation of one or more preferable, preferred, desirable or particular embodiments does not imply that other embodiments are not useful and is not intended to exclude those other embodiments from the scope of the disclosure.

The word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion.

As used throughout this application, the word “may” is used in a permissive sense –that is meaning to have the potential to -rather than in the mandatory sense.

Spatially relative terms, such as “inner” , “outer” , "top" , "back" , "above" , "below" , "left" , "right" and the like may be applicable herein to describe an component’s relationship to another component (s) as illustrated in the figures. Obviously all such spatially relative terms refer to the orientation shown in the figures only for ease of illustration and are not necessarily limiting given that an assembly can assume orientations and configurations different from those illustrated in the figures when in use.

The term “fraction” as used herein refers to a numerical quantity which defines a part up to but not including 100 percent or the entirety of the thing in question.

When amounts, concentrations, dimensions and other parameters are expressed in the form of a range, a preferable range, an upper limit value, a lower limit value or preferable upper and limit values, it should be understood that any ranges obtainable by combining any upper limit or preferable value with any lower limit or preferable value are also specifically disclosed, irrespective of whether the obtained ranges are clearly mentioned in the context.

Further, in accordance with standard understanding, a weight range represented as being “from 0 to x” specifically includes 0 wt. %: the ingredient defined by said range may be absent from the material or may be present in the material in an amount up to x wt. %.

As used herein, room temperature is 23℃ plus or minus 2℃. As used herein, “ambient conditions” means the temperature and pressure of the surroundings in which the curable film is located or in which a coating layer or the substrate for said coating layer is located.

The molecular weights referred to in this specification can be measured with gel permeation chromatography (GPC) using linear polystyrene calibration standards, such as is done according to ASTM 3536. An exemplary device for such measurement is a Waters 2695 Separation Module with a Waters 2414 Differential Refractometer (RI detector) .

Viscosities of the coating compositions described herein are, unless otherwise stipulated, measured using the Brookfield Viscometer, Model RVT at standard conditions of 20℃ and 50%Relative Humidity (RH) . The viscometer is calibrated using silicone oils of known viscosities, which vary from 5,000 cps to 50,000 cps. A set of RV spindles that attach to the viscometer are used for the calibration. Measurements of the coating compositions are done using the No. 6 spindle at a speed of 20 revolutions per minute for 1 minute until the viscometer equilibrates. The viscosity corresponding to the equilibrium reading is then calculated using the calibration.

Where mentioned, a calculated glass transition temperature ( “T_g” ) of a polymer or co-polymer is that temperature which may be calculated by using the Fox equation (T. G. Fox, Bull. Am. Physics Soc., Volume 1, Issue No. 3, page 123 (1956) ) . Conversely, the actual glass transition temperature (T_g) of a polymer can be determined by dynamic mechanical thermal analysis (DMTA) in accordance with ASTM E1640: DMA Testing: Standard Test Method for Assignment of the Glass Transition Temperature By Dynamic Mechanical Analysis.

The term “liquid” herein means in a liquid state at room temperature and at atmospheric pressure. Analogously, the term “solid” means in a solid state at room temperature and at atmospheric pressure.

As used herein, the term "metallic" encompasses elemental metal, metal alloys and metal composites. As used herein, the term “alloy” refers to a substance composed of two or more metals or of a metal and a non-metal which have been intimately united, usually by being fused together and dissolved in each other when molten.

As exemplary metals and metallic alloys, mention may be made of: aluminum; aluminum alloys; bronze; beryllium; beryllium alloys; chromium; chromium alloys; cobalt; cobalt alloys; copper; copper alloys; gold; iron; iron alloys; steels; magnesium; magnesium alloys; nickel; nickel alloys; lead; lead alloys; tin; tin alloys, such as tin-bismuth and tin-lead; zinc; zinc alloys; and, superalloys, such as International Nickel 100 (IN-100) or International Nickel 718 (IN-718) . Representative steels include: crucible steel; carbon steel; spring steel; alloy steel; maraging steel; and, stainless steel, inclusive of austenitic stainless steel, ferritic stainless steel, duplex stainless steel, and Martensitic stainless steel.

The term "electrically conductive" as used herein references materials, such as fillers, which have a bulk resistivity of less than 10 ohm-cm, in particular less than 1.0 ohm-cm or less than 0.1 ohm-cm. The terms “surface electrical conductivity” and “volume electrical conductivity” are used in accordance with their standard meanings given in ASTM D1711–22 Standard Terminology Relating to Electrical Insulation. Electrical conductivity may be measured in accordance with ASTM 257-14 (2021) Standard Test Methods for DC Resistance or Conductance of Insulating Materials.

The term “electrically non-conductive substrate” as used herein references a substrate which possesses bulk electrical non-conductivity: the substrate may be exemplified by a volume electrical conductivity of less than 1 Sm^-1, typically less than 1 x 10^-5 Sm^-1 or less than 1 x 10^-8 Sm^-1.

The term “carbon nanostructures” refers to structures such as nanotubes, nanorods, nanocubes and nanodiamonds. The term also encompasses polymeric structures formed by nantotubes which are interdigitated and /or which share common walls: in such polymeric structures, carbon nanotubes may be deemed to represent the basic monomeric unit.

The term “water-borne” means that the solvent or medium of the composition primarily or principally comprises water, in particular that water constitutes at least 50%by weight, for example at least 60%by weight or at least 70%by weight, of the liquid continuous phase of the composition. The term “solvent-borne” as used herein means that the medium of the composition primarily or principally comprises organic solvent, in particular that organic solvent constitutes at least 50%by weight, for example at least 60%by weight or at least 70%by weight, of the liquid continuous phase of the composition.

The term “heat-activatable” , as used herein to characterize the adhesive films (F^a, F^b) and the compositions (a, b) from which said films are obtained by drying, equates to thermally activatable or thermally curable. It is understood to mean that the composition or film obtained therefrom have latent adhesive properties which are activated after having heated said composition or said film above a given temperature, the “activation temperature” . It is during this thermal activation stage that a film will develop its adhesive properties.

The term “film” as used herein denotes a material sample having at least two surfaces that at least generally oppose each other and are separated by the thickness of the sample. The term “film” herein may include one or more layers or lamina. Formation of samples into films may be accomplished by a variety of art disclosed techniques of which coating and casting may be mentioned as examples.

As used herein, the term "release liner" refers to a thin flexible sheet which, after being placed in intimate contact with an adhesive surface may be subsequently removed without damaging the adhesive coating. Release liners may typically have a thickness of from 20 to 500 microns, such as from 20 to 250 microns or from 20 to 200 microns. Illustrative materials of which the release liner may comprise or consist include: polyethylene; polypropylene; polyesters, such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) ; cellulose acetate; polyvinylchloride; polyvinylidene fluoride; and, paper substrates coated or laminated with the aforementioned thermoplastics. For completeness, the coated papers or thermoplastic materials are often siliconized or otherwise treated with a release agent to impart improved release characteristics.

As is known in the art, release liners are typically left in place for storage and transport and only removed when a bonding operation is to be performed. The release liners thereby perform a number of functions, including preventing contamination of the composition, facilitating handling thereof, providing support thereto and providing for the conveyance of information or identifying data.

As used herein, the term “carrier” refers to a material onto which a curable film of an adhesive composition can be coated so as to stabilize the film. The carrier can add thickness to the article so as to improve handling. The carriers itself may typically have a thickness of from 20 to 500 microns, such as from 20 to 250 microns or from 20 to 200 microns. The carrier substrate differs from a release liner in that it cannot be physically removed from the curable film without deleteriously effecting the integrity of the curable film. The carrier may be flexible and may conventionally be selected from: polymeric films, such as polyester, polypropylene and polyethylene films; electrically conductive films, such as metallic films; foams; paper; cloths; and, combinations thereof. In the present disclosure, it is typical for a carrier which is disposed upon an electrochemically debondable adhesive film to be an electrically conductive film.

As used herein, the term "transfer adhesive film" references the adhesive film per se, in particular the adhesive film considered independently from: any backing, such as a release liner or carrier on which the film or layer may be disposed in an article of manufacture; and, any substrate on which the film or layer may be disposed in forming a bonded structure.

The term “frame” as used herein encompasses any rigid structure that provides structural support to an object, in particular an electronic component. Whilst a frame may be configured in a variety of different shapes and configurations, the term encompasses rigid structures which may at least partially surround or enclose said objects.

An “integrant” of a frame or electronic component refers herein to a designated region thereof which is selected for the bonding of an adherend thereto. Whilst it is not precluded that the integrant may be disposed at the edge or corner of the frame or component, the integrant will more typically be a planer region. The integrant should possess structural integrity and thereby have the ability to bear load, including its own weight, whilst resisting breakage, bending or collapse.

The term “electronic component” denotes any component, member or apparatus which fulfils any electric, magnetic and/or electronic functionality. This means that electric, magnetic and/or electromagnetic signals may be applied to and/or generated by the electronic component during regular use. Exemplary electronic components include but are not limited to: batteries; battery cells; (micro) processors; signal processors; displays; capacitors; resistors; transistors; medical application devices, such as a glucose delivery device or an automatic defibrillator; global positioning system (GPS) receivers; sensors, such as biometric sensors, temperature sensors, moisture sensors, velocity sensors and accelerometers; and, antennas. The present disclosure has particular utility for the housing or framing of battery cells.

As used herein the term “electrochemically debondable” means that, after curing of the adhesive, the bond strength can be weakened by at least 50%upon application of an electrical potential of 30V for a duration of 20 minutes. The adhesive is applied between two substrates which are bonded by said adhesive so that an electric current is running through the adhesive bond line. Bond strength is measured by Tensile Lap Shear (TLS) test performed at room temperature and based upon ASTM D3163-01 Standard Test Method for Determining Strength of Adhesively Bonded Rigid Plastic Lap-Shear Joints in Shear by Tension Loading. The bond overlapping area for this determination should be 2.5 cm x 2.5 cm with a bond thickness of 60-150 microns.

The term “electrolyte” is used herein in accordance with its standard meaning in the art as a substance containing free ions which can conduct electricity by displacement of charged carrier species. The term is intended to encompass molten electrolytes, liquid electrolytes, semi-solid electrolytes and solid electrolytes wherein at least one of the cationic or anionic components of their electrolyte structure is essentially free for displacement, thus acting as charge carrier.

The curable film adhesive of the present invention and the cured adhesive film obtained therefrom possess "electrolyte functionality" in that the adhesive material permits the conduction of ions, either anions, cations or both. The electrolyte functionality is understood to derive from the ability of the compositions and curable adhesives to solvate ions of at least one polarity.

The term "faradaic reaction" means an electrochemical reaction in which a material is oxidized or reduced.

The term “hydroxyl number” as used herein is defined as the mass in milligrams of potassium hydroxide required to neutralize the acetic acid taken up on acetylation of one gram of a chemical substance that contains free hydroxyl groups. Where stated, the hydroxyl number is analyzed in accordance with according to the standard test method ASTM D4274-11.

Unless otherwise stated, the term “particle size” refers to the largest axis of the particle. In the case of a generally spherical particle, the largest axis is the diameter.

The term “mean volume particle size” (Dv50) , as used herein, refers to a particle size corresponding to 50%of the volume of the sampled particles being greater than and 50%of the volume of the sampled particles being smaller than the recited Dv50 value. Particle size is determined herein by laser diffraction using Anton Paar Particle Size Analyzer (PSA) 1190.

As used herein, the term “monomer” refers to a substance that can undergo a polymerization reaction to contribute constitutional units to the chemical structure of a polymer. The term “monomer” herein encompasses macromonomers which, in accordance with IUPAC Gold Book are polymeric or oligomeric molecules possessing at least one reactive functional group: the macromonomer participates in a polymerization reaction and contributes a single monomer unit to the chain of the product polymer.

The term “ethylenically unsaturated monomer” as used herein, refers to any monomer containing a terminal double bond capable of polymerization under normal conditions of free-radical addition polymerization.

As used herein, " (meth) acryl" is a shorthand term referring to "acryl" and/or "methacryl" . Thus the term " (meth) acrylate" refers collectively to acrylate and methacrylate.

As used herein, "C₁-C_n alkyl" group refers to a monovalent group that contains 1 to n carbons atoms, that is a radical of an alkane and includes straight-chain and branched organic groups. As such, a "C₁-C₄ alkyl" group refers to a monovalent group that contains from 1 to 4 carbons atoms, that is a radical of an alkane and includes straight-chain and branched organic groups. Examples of alkyl groups include, but are not limited to: methyl; ethyl; propyl; isopropyl; n-butyl; isobutyl; sec-butyl; and, tert-butyl. In the present invention, such alkyl groups may be unsubstituted or may be substituted with one or more halogen. Where applicable for a given moiety (R) , a tolerance for one or more non-halogen substituents within an alkyl group will be noted in the specification.

The terms “alkylene group" refers to a divalent radical divalent radical derived from an alkyl group, as defined above.

The term “C₁-C_n hydroxyalkyl” as used herein refers to an HO- (alkyl) group having from 1 to n carbon atoms, where the point of attachment of the substituent is through the oxygen-atom and the alkyl group is as defined above.

The term “C₃-C₁₈ cycloalkyl” as used herein means a saturated cyclic hydrocarbon having from 3 to 18 carbon atoms. In the present invention, such cycloalkyl groups may be unsubstituted or may be substituted with one or more halogen. Where applicable for a given moiety (R) , a tolerance for one or more non-halogen substituents within a cycloalkyl group will be noted in the specification. Exemplary cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl groups.

As used herein, an “C₆-C₁₈ aryl” group used alone or as part of a larger moiety -as in “aralkyl group” -refers to monocyclic, bicyclic and tricyclic ring systems in which the monocyclic ring system is aromatic or at least one of the rings in a bicyclic or tricyclic ring system is aromatic. The bicyclic and tricyclic ring systems include benzofused 2-3 membered carbocyclic rings. In the present disclosure, such aryl groups may be unsubstituted or may be substituted with one or more halogen. Where applicable for a given moiety (R) , a tolerance for one or more non-halogen substituents within an aryl group will be noted in the specification. Exemplary aryl groups include: phenyl; (C₁-C₄) alkylphenyl, such as tolyl and ethylphenyl; indenyl; naphthalenyl, tetrahydronaphthyl, tetrahydroindenyl; tetrahydroanthracenyl; and, anthracenyl.

The term “arylene” as used herein refers to a divalent radical counterpart of an aryl group. Further, as used herein, "alkylaryl" refers to alkyl-substituted aryl groups as set forth above. Moreover, as used herein "aralkyl" means an alkyl group substituted with an aryl radical as defined above.

The term "hetero" as used herein refers to groups or moieties containing one or more heteroatoms, such as N, O, Si, P or S. Thus, for example "heterocyclic" refers to cyclic groups having, for example, N, O, Si or S as part of the ring structure. "Heteroalkyl" , "heterocycloalkyl" , “heteroaryl” and “heteroalkylaryl” moieties are alkyl, cycloalkyl and aryl groups as defined hereinabove, respectively, containing N, O, Si, P or S as part of their structure.

The term "heterocyclyl" refers to a monovalent chain of carbon and heteroatoms, wherein the heteroatoms are selected from N, O, Si, P or S, a portion of which, including at least one heteroatom, form a ring.

The term “substituted” refers to substitution with at least one suitable substituent. For completeness: the substituents may connect to the specified group or moiety at one or more positions; and, multiple degrees of substitution are allowed unless otherwise stated. Further, the terms “substitution” or “substituted with” include the implicit proviso that such substitution is in accordance with permitted valence of the substituted atom and the substituent, and that the substitution results in a stable compound that does not spontaneously undergo transformation by, for instance, rearrangement, cyclization or elimination.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure provides a bonded structure comprising:

a first substrate provided with a first electrically conductive surface;

a second substrate provided with a second electrically conductive surface; and,

a cured, electrochemically debondable adhesive film interposed between –and typically in direct contact with -said first and second electrically conductive surfaces, said electrochemically debondable adhesive film having one or more constituent layers, wherein at least one layer of the cured adhesive film comprises a non-polymerizable electrolyte and at least one polyurethane polymer;

BONDED STRUCTURE

The bonded structure of the present disclosure will be described with reference to the appended drawings in which:

Figure 1a illustrates a bonded structure in accordance with a first embodiment of the present disclosure.

Figure 1b illustrates the initial debonding of the structure of the first embodiment upon passage of a current across that structure.

Figure 2a illustrates a bonded structure in accordance with a second embodiment of the present disclosure.

Figure 2b illustrates the initial debonding of the structure of the second embodiment upon passage of a current across that structure.

Figure 3a illustrates a bonded structure in accordance with a third embodiment of the present disclosure.

Figure 3b illustrates the initial debonding of the structure of the second embodiment upon passage of a current across that structure.

For each illustrated structure of Figures 1 and 3, the illustrated conductive substrate (13) is shown in the form of a layer which is a non-composite material which may be constituted by inter alia: a metallic film; a metallic mesh or grid; deposited metal particles; or, a conducting oxide. As exemplary conducting oxides there may be mentioned: doped indium oxides, such as indium tin oxide (ITO) ; doped zinc oxide; antimony tin oxide; cadmium stannate; and, zinc stannate. The selection of the conductive substrate (13) aside, the skilled artisan will recognize that the efficacy of the debonding operation may be diminished where the conductive substrates (13) are in the form of a grid or mesh which offers limited contact with the illustrated layers of cured electrochemically debondable adhesive film (10) .

As shown in Figure 1a appended hereto, a bonded structure is provided in which a layer of electrochemically debondable adhesive film (10) is disposed between an electrically conductive substrate (13) and an electrically non-conductive substrate (12) : such a layer of electrochemically debondable adhesive film (10) may, for example, have a thickness of from 15 to 500 μm, for instance from 50 to 250 μm or from 50 to 200 μm. A dried ink film (11) as described herein is disposed upon the non-conductive substrate (12) to form the depicted bonded structure. The dried ink film (11) and the electrically conductive substrate (13) are in electrical contact with an electrical power source (14) .

The composition of the electrically non-conductive substrate (12) is not particularly limited. Exemplary substrates (12) include polymeric substrates of which mention may be made of: polyolefins such as polyethylene and polypropylene; polyesters, such as polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) ; polyamides; polyacrylonitrile; polyvinyl chloride; polyacrylates, such as polymethyl methacrylate; conjugated diene homopolymers, such as polychloroprene, polybutadiene and polyisoprene; copolymers of conjugated dienes; copolymers of conjugated dienes with aromatic vinyl compounds, such as copolymers of butadiene or isoprene with styrene; silicones; and, polyurethanes. It is also possible that the electrically non-conductive substrate (12) may be constituted by a polymer-wrapped metallic material. Further, the use of mineral and lignocellulosic materials in or as the electrically non-conductive substrate (12) is not precluded.

A more complex bonded structure is depicted in Figure 2a wherein dried ink films (11) are respectively disposed upon two electrically non-conductive substrates (12) . The layer of electrochemically debondable adhesive film (10) is interposed between said dried ink films (11) . Further, each dried ink film (11) is in electrical contact with an electrical power source (14) . In this structure, the compositions of each dried ink film (11) may be the same or different. In the latter circumstance, the dried ink films may differ in one or more of: the composition of the matrix of polymeric resin; the composition of the electrically conductive particles; the physical properties of the electrically conductive particles; or, the loading of said particles within the dried ink film, as defined by weight or by volume.

Figure 3a depicts a bonded structure in accordance with a still further embodiment of the present disclosure. A dried ink film (11) is disposed between a layer of electrochemically debondable adhesive film (10) and a layer of a fixative (15) . That layer of fixative (15) provides adherence of the dried ink film (11) to the electrically non-conductive substrate (12) to form the depicted bonded structure. Similarly, the layer of cured electrochemically debondable adhesive film (10) provides adherence to the conductive substrate (13) . The dried ink film (11) and the conductive substrate (13) are in electrical contact with an electrical power source (14) .

The fixative of layer (15) of Figures 3a and 3b should not be electrochemically debondable: save for this condition, the fixative of layer (15) is not particularly limited in composition but it should be operable or effective in the bonding of polymeric and other non-metallic substrates. Good results have been obtained where the fixative of layer (15) is obtained by the curing of a composition selected from: two-part (2K) polyurethane adhesive compositions; two-part (2K) epoxy adhesive compositions; or, thermally conductive adhesive compositions. In certain embodiments, the fixative layer (15) should have a thickness of from 10 to 300 μm, for instance from 10 to 200 μm or from 15 to 150 μm.

For completeness, it is noted that the curable electrochemically debondable adhesive film from which layer (10) is derived and the composition from which the fixative layer (15) is derived may be independently cured. Alternatively, the respective compositions may be simultaneously cured where the operable curing conditions for each composition are compatible.

In certain embodiments, spacers (not shown) may be interposed between the dried ink film (11) and the electrically non-conductive substrate (12) . Any spacer should conventionally be detachable from the adherends without damaging said elements of the bonded structure. For surety, such spacers are optional and may be absent in certain variants of the bonded structure. However, spacers can serve to firmly fix the spatial relationship between the non-conductive substrate (12) and the dried ink film (11) and, in doing so, moderate the effects of vibrations and impacts to which a bonded structure might be subjected either per se or when included as a component of a larger article of manufacture. This is particularly germane for structures which are to be disposed within portable electronic devices or within vehicles where vibration and jolting can displace adherends.

Where more than one spacer is present, the two spacers may be identical but it is not precluded that individual spacers may possess different geometries and /or be comprised of different materials. Moreover, a given spacer need not be unitary but may comprise a plurality of elements provided this does not compromise the mechanical strength of the spacer or diminish the support role thereof. Still further, the number of spacers and the disposal of the spacers within the fixative layer (15) may be moderated to optimize that support function. The spacers may be disposed at the extremities of the fixative layer (15) ; alternatively or additionally said spacers may interrupt the fixative layer (15) .

The spacers should preferably be formed from electrically insulating materials which are flame retardant, which possess a suitable hardness and which are suited to meet impact strain requirements, for example by providing shock absorption or flexure for a support system. A Shore A hardness of from 20 to 95, for instance from 30 to 90 might be mentioned in this context. Exemplary polymeric materials having utility as spacers include but are not limited to: polyvinyl chloride; polyalkylenes, such as polyethylene and polypropylene; polyacrylates such as polymethyl methacrylate; conjugated diene homopolymers, such as polychloroprene, polybutadiene and polyisoprene; copolymers of conjugated dienes; copolymers of conjugated dienes with aromatic vinyl compounds, such as copolymers of butadiene or isoprene with styrene; silicones; and, polyurethanes. A preference for injection moldable polymeric materials may be noted.

The electrical power source (14) may be a battery or an AC-driven source of direct current (DC) . The positive and negative terminals of that power source (14) are shown in Figures 1 to 3 in one fixed position but the skilled artisan will of course recognize that the polarity of the system can be reversed.

When an electrical voltage is applied either between the electrically conductive substrate (13) and the dried ink film (11) -as depicted in Figure 1b and 3b -or between the two dried ink films (11) as depicted in Figure 2b, current is supplied to the electrochemically debondable adhesive film (10) disposed therebetween. This induces electrochemical reactions at the interface of either the conductive substrate (13) or the dried ink film (11) and the adhesive film (10) , which electrochemical reactions are understood as oxidative at the positively charged or anodic interface and reductive at the negatively charged or cathodic interface. The reactions are considered to weaken the adhesive bond therebetween allowing the easy removal of the debondable composition from the substrate.

As depicted in Figures 1b, 2b and 3b, the debonding occurs at the negative interface, that interface between the adhesive film (10) and either the dried ink film (11) or the electrically conductive substrate (13) that is in electrical contact with the negative electrode. By reversing current direction prior to separation of the substrates, the adhesive bond may be weakened at both interfaces of the cured adhesive film (10) .

It is however noted that the composition of the layer (10) of adhesive film may be moderated so that debonding occurs at either the positive or negative interface or simultaneously from both. For some embodiments, a voltage applied across both surfaces so as to form an anodic interface and a cathodic interface will cause debonding to occur simultaneously at both the anodic and cathodic adhesive /substrate interfaces. In an alternative embodiment, reversed polarity may be used to simultaneously disbond both substrate /adhesive interfaces if the composition does not respond at both interfaces to direct current. The current can be applied with any suitable waveform, provided that sufficient total time at each polarity is allowed for debonding to occur. Sinusoidal, rectangular and triangular waveforms might be appropriate in this regard and may be applied from a controlled voltage or a controlled current source.

Without intention to limit the present invention, it is considered that the debonding operation may be performed effectively where at least one and preferably both of the following conditions are instigated: a) an applied voltage of from 0.5 to 200 V, for example from 5 to 100 V or from 5 to 50 V; and, b) the voltage being applied for a duration of from 1 second to 120 minutes, for example from 1 second to 30 minutes. Where the release of the substrates from the cured adhesive film is to be facilitated by the application of a force –exerted via a weight or a spring, for instance –the potential might only need to be applied for the order of seconds.

As discussed above, the illustrated bonded structure may have utility in the bonding of electronic components either to one another or to a frame, which frame may optionally be disposed within an assembly comprising a plurality of electronic components in order to position or constrain one or more of said electronic components. Such an assembly may, for example, be provided with an encasement or other supporting arrangement in order to mitigate impacts or compressive, tensile, torsional, shear or bending stresses imposed thereon. The assembly will contain electrical interconnects which enable a voltage to be applied across electrically conductive surfaces provided on the frame and electronic component (s) thereof. The requisite power source to provide this potential difference may be disposed within the encasement or external to the encasement.

By way of example, it is envisaged that the bonded structure may serve to debondably fix one or more electronic components to a frame disposed within a phone encasement. The debondable fixing of a battery within such a phone encasement may be specifically mentioned.

Having regard to Figure 1a, the non-conductive substrate (12) may be provided by an integrant (I^F) of the frame of an article of manufacture: that article further comprises at least one electronic component which provides the conductive substrate (13) . A dried ink film (11 ^F) may be disposed on that integrant (I^F) to provide that frame with an electrically conductive surface. The debondable adhesive film (10) is disposed between the dried ink film (11 ^F) and the electrically conductive substrate (13) provided by the electronic component. Moreover, optionally –and as depicted in Figure 3a –a layer of fixative may be provided on the frame to provide adherence between the integrant (I^F) thereof and the dried ink film (11^F) .

Extending this utility of the bonded structure to Figure 2a, a second non-conductive substrate (12) may be provided by an integrant (I^C) of an electronic component provided within the article. A dried ink film (11^C) may be disposed on that integrant (I^C) to provide the electronic component with an electrically conductive exterior surface. The debondable adhesive film (10) is disposed between the dried ink films respectively provided by the frame (11 ^F) and electronic component (11^C) .

DRIED INK FILM (11)

Each dried ink film (11) comprises: a) a matrix of a polymeric resin; and, b) electrically conductive particles. The disposal of the electrically conductive particles within the polymeric resin matrix should form semi-continuous or continuous conductive pathways which extend through the body of the dried ink film (11) . These pathways should thereby provide a low resistance route by which electrons and, in some instances thermal phonons, can travel through the dried ink film (11) . The dried ink film (11) itself should be continuous, by which is meant that there are no discontinuities or gaps in the film within the two-dimensional area to which the film is applied.

It is preferred for the dried ink film (11) to be electrically conductive in all three dimensions and thus across its width, length and thickness: as is known in the art, electrical resistance measurements may be taken on a surface of the dried ink film using a probe, such as a 4-point probe, connected to an ohmmeter. Independently of or additional to this dimensional conductivity preference, it is preferred that the dried ink film (11) has a sheet resistance less than 100 Ohm/sq/mil, preferably less than 50 Ohm/sq/mil, and more preferably from less than 30 Ohm/sq/mil, wherein the sheet resistance is measured according to ASTM D257-14 (2021) .

The formation of conductive pathways in the dried ink film should be determinative of the loading of the electrically conductive particulates within that film. In addition, the loading of said particulates may be selected to attain operable density, and operable rheological and adhesive properties of the dried ink film (11) .

In certain embodiments, the dried ink film may comprise, based on the total weight of the film: a matrix of polymeric resin; and, from 0.5 to 75 wt. %of electrically conductive particles disposed in said matrix, wherein said electrically conductive particles are characterized by a bulk resistivity of less than 50 microohm-centimeters (μΩ-cm) . For example, the dried ink film may comprise, based on the weight of the film: a matrix of polymeric resin; and, from 5 to 75 wt. %, preferably from 15 to 75 wt. %of said electrically conductive particles.

In an alternate expression which is not intended to be mutually exclusive of that given above, the dried ink film may comprise, based on the volume of the film: a matrix of polymeric resin; and, from 5 to 90 vol. %of electrically conductive particles disposed in said matrix, wherein said electrically conductive particles are characterized by a bulk resistivity of less than 50 microohm-centimeters (μΩ-cm) . For example, the dried ink film may comprise, based on the volume of the film: a matrix of polymeric resin; and, from 10 to 75 vol. %, preferably from 30 to 70 vol. %of said electrically conductive particles.

The distribution of the electrically conductive particles within the matrix resin may be homogeneous or non-homogeneous. In certain situation, it may be beneficial for the concentration of particulates to vary across a dimension, in the particular the thickness, of the dried ink film. The variation may permit specific loci of the dried ink film to exhibit higher relative electrical conductivity and, potentially, thermal conductivity. Such variation should not however compromise the structural integrity of the dried ink film by, for instance, reducing hardness or tensile strength of the film.

Broadly, there is no particular intention to limit the shape of the electrically conductive particles in the dried ink film: particles that are fibrous, acicular, spherical, ellipsoidal, cylindrical, bead-like, cubic or platelet-like may be used alone or in combination. Moreover, it is envisaged that agglomerates of more than one particle type may be used.

Equally, there is no particular intention to limit the size of the particles employed as conductive fillers. And, for surety, it is noted that suitable electrically conductive particles for use in the present invention may be a mixture of particles having a small particle size and particles having a larger particle size. However, such electrically conductive particles will conventionally have a median particle size by volume (D_v50) , as measured by laser diffraction /scattering methods, of from 300 nm to 50 μm, for example from 500 nm to 40 μm or from 500 nm to 30 μm. In the aforementioned measurement method, the particle size is measured by particle size analyser and the particle shape is analysed by scanning electron microscope. In short, scattered laser lights from the particles are detected an array of detectors. Theoretical calculation is carried out to fit the measured distribution of scattered light intensity. During the fitting process, the particle size distribution is deduced and inter alia D_v50 and D_v90 values are calculated accordingly.

Additionally or alternatively to the aforementioned median particle size, said electrically conductive particles should typically be characterized by a density of less than 5 g/cm³.

In a further independent characterization of the electrically conductive particles, which may or may not compliment the aforementioned median particle size and /or density characterizations, it is preferred that the electrically conductive particles have a tap density of from 0.5 to 6.0 g/cm³, preferably from 0.5 to 5.5 g/cm³ and more preferably from 0.5 to 5.0 g/cm³ as determined in accordance to ISO 3953 using a 25 cm³ graduated glass cylinder. The principle of the method specified is tapping a specified amount of powder in a container by means of a tapping apparatus until no further decrease in the volume of the powder takes place. The mass of the powder divided by its volume after the test gives its tap density.

Exemplary non-fibrous, electrically conductive particles which may be present in the dried ink film, either alone or in combination, include: metallic flakes; metallic powders; milled or ground metallized glass; silicon; silicon dioxide; germanium; selenium; carbon black; graphene; fullerene; graphite; and, carbon nanostructures.

In an embodiment, at least a portion of the electrically conductive particles of the dried ink film are selected from the group consisting of: silver, silver coated copper; silver coated graphite; silver coated polymers; silver coated aluminium; silver coated glass; and, mixtures thereof. Silver is particularly preferred because of its good electrical performance. Conversely, silver coated particles might gain preference because of their lower cost as compared to silver per se. However, in such silver coated or silver plated particles, the silver coating or plating should substantially and preferably wholly coat the underlying particulate material. Alternatively or additional to that requirement, the quantity of silver in the silver coated particle should preferably be from 10 to 70 wt. %, for example from 10 to 65 or 60 wt. %based on the total weight of the electrically conductive particles.

By way of illustration only, suitable commercially available electrically conductive particles based on silver include, but are not limited to: AA3462, AA-5124, AA-192N, C-1284P, C-0083P and P543-14 silver particles, available from Metalor; KP84, KP74 and KP29 silver particles, available from Ames Goldsmidth; CGF-DAB-121 B silver coated copper particles, available from Dowa; AgCu0810 or AgCu0305 silver coated copper particles, available from Ames Goldsmidth; CONDUCT-O-FIL^TMSG15F35 silver coated glass, available from Potters Industries Inc.; the silver coated polymers Spherica^TM Ag-30-01, Spherica^TM Ag-10-01 and Spherica^TM Ag-4-01 available from Conpart AS; silver coated graphite available as P594-5 from Metalor; and, silver coated aluminium available as CONDUCT-O-FIL^TM SA325S20 from Potters Industries Inc.

The use of conductive carbon blacks as at least a portion of the electrically conductive particles of the dried ink film is of particular interest. Additionally or alternatively, the use of graphite as at least a portion of the electrically conductive particles of the dried ink film is of interest. And in certain embodiments, the electrically conductive particles of the dried ink film comprise a mixture of graphite and carbon black, preferably wherein the ratio by weight of graphite to carbon black is from 1: 1 to 5: 1 or from 2: 1 to 4: 1. A particular preference may be noted for the use of a mixture of graphite and carbon black, wherein the ratio by weight of graphite to carbon is 2.5: 1 to 3.5: 1, for example 3: 1.

The combination of graphite and carbon black as the electrically conductive particles is considered to provide good conductivity at the conventional thickness of dried ink film.

Suitable carbon blacks having utility in the present disclosure should be characterized by at least one of:

i) a specific surface area of from 30 to 1400 m²/g, preferably from 100 to 700 m²/g and more preferably from 150 to 350 m²/g, as determined by low temperature nitrogen absorption in accordance with ASTM D 3037-78;

ii) a pore volume of from 1 to 4 ml/g as determined by mercury porosimetry;

iii) a pore diameter of from 25 to 1000 Angstroms, as determined by mercury porosimetry; and,

iv) an oil absorption number from 70 to 500 ml/100g, preferably from 100 to 300 ml/100g and more preferably from 150 to 200 ml/100g, as determined in accordance with ASTM D2414.

These characterizations are not mutually exclusive and one, two three or four of them may be applicable to a given carbon black having utility in the present disclosure.

Exemplary commercial conductive carbon blacks which may have utility herein include: Black Pearls andC available from Cabot Corporation; Ensaco 250G, available from from Imerys and; available from Nouryon.

Particulate graphite having utility in the present disclosure should possess a D_v90 particle size by volume, as measured by laser diffraction /scattering methods, of from 1 μm to 75 μm, preferably from 2 μm to 45 μm, more preferably from 3 μm to 25 μm and even more preferably 3 μm to 10 μm. Additionally, or alternatively to the aforementioned particle size, the particulate graphite should possess a specific surface area, as determined by low temperature nitrogen absorption in accordance with ASTM D 3037-78, of from 0.25 to 25 m²/g, preferably from 4 to 22 m²/g and more preferably from 7 to 21 m²/g.

Exemplary commercially available graphites for use in the present disclosure invention include but are not limited to: Timrex SFG6 from TIMCAL Graphite & Carbon; and, Graphite Pure 200-09 available from Asbury.

The use of carbon nanotubes as at least a portion of the electrically conductive particles is also of interest. As used herein, the term “carbon nanotube” refers to carbon fullerene, a synthetic graphite, which typically has a molecular weight of greater than 840 g/mole. The term is intended to encompass roped carbon nanotubes, single-walled carbon nanotubes (SWNT) , multiple walled carbon nanotubes (MWNT) : single walled carbon nanotubes typically have diameters of from 1 to 5 nm whilst multi-walled carbon nanotubes typically have diameters of from 5 to 200 nm. It is further envisaged that carbon nanotubes having utility herein may be opened or chopped, for which US Patent No. 7,641,829 B2 provides an instructive reference. And still further, the present invention does not preclude the use of carbon nanotubes which have been chemically modified through, for example doping with thionyl chloride (SOCl₂) or carbon nanotubes which have been coated with, for example metallic materials which enhance the conductivity of the nanotubes. For completeness, exemplary commercial providers of carbon nanotubes are: Unidym Inc.; and, Carbon Nanotechnologies, Inc.

It is not precluded that the electrically conductive particles of the dried ink film may comprise or consist of conductive fibers. It is preferred that the conductive fibers are characterized by least one of the following parameters: an aspect ratio of from 5 to 2000, preferably from 20 to 2000; a mean length of from 1 to 20 mm, for instance from 1 to 15 mm; and, a mean diameter of from 1 to 50 μm, preferably from 5 to 25 μm. These characterizations of the conductive fiber are not mutually exclusive: the fibers may meet one, two or three thereof.

Examples of electrically conductive fibers, which may be present in the dried ink film alone or in combination, include but are not limited to:

a) Fibers of conductive metals such as copper (Cu) , iron (Fe) , nickel (Ni) , cobalt (Co) , aluminum (Al) , silver (Ag) , gold (Au) , palladium (Pd) , platinum (Pt) , ruthenium (Ru) , rhodium (Rh) , alloys thereof and combinations thereof. Exemplary alloys include nickel alloys and iron alloys and specific mention may be made of the use of stainless steel fibers and monel fibers. Moreover, exemplary combinations of the metals and alloys include but are not limited to: multifilament fibers in which individual filaments comprise different metals or alloys; and, fibers in which a metal or alloy is used to plate or coat a distinct metal or alloy. As regards the latter combination, mention may be made of: silver-plated copper fibers; nickel-clad copper fibers; tin-plated, copper-clad steel fibers; and tin-clad copper fibers.

b) Electrically conductive fibers obtained by modifying electrically insulating polymeric fibers through, for example, incorporating a conductivity-imparting agent into the polymeric fiber or imparting a metallic plating or coating onto a polymeric fiber core. The constituent polymer (s) of the fibers should be characterized by a softening point that is higher -and preferably at least 10℃ or at least 20℃ higher -than the softening point of the polymer which forms the matrix of the dried ink film. This enables the matrix to be subjected to a temperature above its softening point, in a molding operation for instance, without melting the metallized polymeric fibers.

c) Carbon fibers. in particular graphite fibers.

d) Fibers obtained by imparting a metallic plating or coating to a non-polymeric, non-metal fiber core, such as a graphite or glass fiber core. Mention in this regard may be made of: nickel plated graphite fibers of which a commercial example isfiber available from Solvay; and silver coated glass fibers of which a commercial example includes CONDUCT-O-FIL SF82TF20 available from Potters Industries.

The aforementioned metals and alloys (a) ) are candidate conductivity imparting agents for incorporation within or coating of non-metallic fibers: the choice of metal or alloy may be based on both functionality or economy, noting that the cost of precious metals may limit or preclude their use. In those embodiments where a conductive fiber is obtained by applying a metal or alloy coating to a non-metallic core, it is preferred the coating is continuous on the surface of the fiber. Further, the metal or alloy coating should preferably have a thickness of from 0.1 to 100 microns, for example from 0.1 to 50 microns.

The electrically insulating polymeric fibers (b) ) may comprise natural polymers, synthetic polymers or combinations thereof. Illustrative synthetic insulating polymeric fibers include: polyolefin fibers, such as polyethylene and polypropylene fibers; polyester fibers; polyacrylate fibers; polyamide fibers, such as nylon and aramid fibers; and, polyimide fibers. Illustrative natural insulating polymeric fibers include polysaccharide fibers, such as fibers of cellulose, starch and fibroin. As regards fibers of type b) , mention may be made of coated nylon fibers, coated polyacrylate fibers and coated polyethylene fibers, wherein the coating is selected from silver, gold, nickel, aluminium, iron or steel.

The term “carbon fiber” (c) above) herein refers to a fiber of which carbon constitutes at least 95 wt.%, based on the weight of the fiber. As is known in the art, carbon fibers may be classified by the precursors from which are they are derived. Polyacrylonitrile (PAN) , pre-oxidized polyacrylonitrile, isotropic-pitch-and mesophase-pitch-based carbon fibers are produced by the wet (solution) spinning of each precursor followed by oxidative stabilization and carbonization (or graphitization) at a temperature up to 1300℃. Vapor-grown carbon fibers are prepared by thermal decomposition of a hydrocarbon vapor, such as methane (CH₄) , in which method oxidative stabilization is not needed. There is no intention in the present disclosure to limit the precursor from which the carbon fibers are obtained.

Irrespective of precursor, carbon fibers having utility in the dried ink film should be characterized by a diameter of from 5 to 25 μm. At diameters above 25 μm, the specific surface area of the fiber may be reduced to the extent that it compromises the compositing of the fibers.

Exemplary commercial carbon fibers having utility herein include: III carbon fibers, available from Pyrograf Products Inc; and, carbon fibers, available from Solvay.

As noted above, the dried ink film of the present disclosure comprises a matrix of polymeric resin. It is preferred that this polymeric resin has a melting temperature of at least 100℃, preferably at least 125℃.

Exemplary polymeric resins from which the matrix may be formed -and which may be used alone or in combination -include but are not limited to: nitrocellulose resins; epoxy resins; phenolic resins; polycarbonate; polystyrene; acrylonitrile butadiene styrene copolymers (ABS) ; styrene acryloniitrile copolymers (SAN) ; styrene butadiene styrene copolymers; styrene ethylene propylene styrene copolymers; polyvinyl chloride; polyvinylidene fluoride (PVDF) ; polyolefins, such as polypropylene, polyethylene, and polybutylene; polyamide; polyimide; polyamideimide; polyether imide; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polyacrylates, such as polymethyl methacrylate; ethylene butyl acrylate copolymers; polyacrylonitrile; polyetherketone; polyarylketone; polyethersulfone (PES) ; polyarylsulfone; polysulfone; polyphenylene sulfide; polyurethane; polyurea; polybenzoxazole; polyoxadiazol; polybenzothiazole; polybenzimidazole; polypyridine resin; polytriazole; polypyrrolidone; polydibenzofuran resin; and, polyphosphazene.

In an embodiment, the matrix resin of the dried ink film is chosen from: nitrocellulose; epoxy resins; phenolic resins; polyurethane; polyacrylates; and, mixtures thereof.

As illustrated in the appended drawings, the dried ink film is disposed upon an electrically non-conductive substrate (12) . Typically, such disposal will be effected by the application of a solvent-borne composition comprising the matrix resin and the electrically conductive particles onto the non-conductive substrate followed by the evaporative drying of the applied composition. The constituent solvent of the solvent-borne composition will be selected to both dissolve the matrix resin well and to lead to a uniform layer formation upon evaporation.

The amount of solvent is in part determined by the mode of application of the composition, in particular the viscosity tolerance of that mode. Conventionally, the solvent-borne composition should have a viscosity from 0.1 to 30 Pa·sas measured according with ISO 3219 using a rheometer at a constant shear rate of 15-swith a 20 mm plate-plate configuration (0.2 mm gap, 60 sec., 25℃) . A particularly suitable viscosity for screen-and roto-screen printing is from 2 to 30 Pa·s. A particularly suitable viscosity for rotogravure or flexographic printing is from 0.5 to 4 Pa·s.

Viscosity aside, it is also considered that significant dilution of the matrix resin may adversely affect the conductivity of the dried ink film obtained from the solvent-borne composition. Thus conventionally, the solvent content will be from 40 to 90 wt. %, based on the weight of the composition.

The solvent-borne composition may be prepared by mixing the components together. Preferably the mixing is performed in a pebble mill or a tri-roll mill to prevent aggregation of the electrically conductive particles through the action of either grinding with pebbles or passage through the three rolls turning against one other.

Prior to applying the solvent-borne ink compositions, it is often advisable to pre-treat the relevant surfaces to remove foreign matter therefrom: this step can, if applicable, facilitate the subsequent adhesion of the compositions thereto. The ink compositions are then applied to the preferably pre-treated surfaces of the non-conductive substrate (12) by conventional application methods such as: bar coating; doctor-blade application; printing methods, including pad printing, stencil printing, screen printing, rotogravure printing, roto screen printing and flexographic printing; and, spraying methods, including but not limited to air-atomized spray, air-assisted spray, airless spray and high-volume low-pressure spray.

It is recommended that the ink compositions be applied to a surface at a wet film thickness of from 10 to 500 μm. The application of thinner films within this range is more economical and provides for a reduced likelihood of deleterious thick cured regions. However, great control must be exercised in applying thinner coatings so as to avoid the formation of discontinuous layers.

The drying and, if applicable, the curing of the applied solvent-borne ink compositions typically occurs at a temperature of from 20℃ to 120℃, preferably from 40℃ to 80℃. The temperature that is suitable depends on the non-conductive substrate (12) and the specific compounds, particularly solvents, present. That said, the temperature required to ensure a desired drying rate can be determined in the individual case by the skilled artisan, using simple preliminary tests if necessary. Of course, drying and, if applicable, curing at lower temperatures within the aforementioned ranges is advantageous as it obviates the requirement to substantially heat or cool the non-conductive substrate (12) and therefore permits the use of more delicate substrates.

For completeness, the term “dried ink film” references the partial or complete removal of the solvent from an ink composition to form a film therefrom. In particular, drying should comprise at least 90 wt.%or at least 95 wt. %of the total weight of solvent being removed from an ink composition. Drying is associated with coalescence of the polymeric resin (s) of the ink composition. It is not precluded that drying may be associated with curing and interpenetration of the polymeric resins, wherein curing refers to a chemical alteration of the constituent polymeric resins. The degree of coalescence of the polymeric resin (s) can be affected by the pressure and heat which is applied during drying.

It is considered that the dried ink film may be applied in either a single stage or multi-stage manner to obtain an overall thickness of the dried ink film of from 10 to 200 μm, for example from 20 to 100 μm.In the multi-stage application, the dried ink film will be constituted by a plurality of thin sub-layers having, for instance, a dry-layer thickness of from 5 to 50 μm. It is considered, however, that intra-layer cohesion forces may be more practicable within a dried ink film provided as a single layer.

ADHESIVE FILM (10)

As described above said cured electrochemically debondable adhesive film (10) has one or more constituent layers, wherein at least one layer of the cured adhesive film comprises a non-polymerizable electrolyte and at least one polyurethane polymer.

Without intention to limit the present disclosure, the adhesive film (10) is typically disposed within the bonded structure described above using a precursor curable film which is cured in situ when interposed between the first and second electrically conductive surfaces. In particular, the cured electrochemically debondable adhesive film (10) may be disposed within the bonded structure by a transfer method using an article of manufacture (A) which comprises the precursor curable film.

Thus, in important embodiments, the bonded structure is obtained by a method comprising: (i) providing an article (A) comprising a curable adhesive film, wherein the curable film is disposed on a release liner and /or a carrier; (ii) attaching the curable film of the article (A) to at least one of the conductive surfaces of the structure (11, 13) ; (iii) mating said conductive surfaces (11, 13) to dispose the curable film therebetween; and, (iv) curing the adhesive film, wherein the release liner of the article (A) , if present, is removed before and/or after step (ii) . The mating of the substrate surfaces, to interpose the curable film of the adhesive therebetween, may occur under the application of pressure.

Prior to the aforementioned bonding operation, it is often advisable to pre-treat the surfaces (11, 13) to be mated to remove foreign matter there from: this step can, if applicable, facilitate the subsequent adhesion of the films thereto. Such treatments are known in the art and can be performed in a single or multi-stage manner constituted by, for instance, the use of one or more of: an etching treatment with an acid suitable for the substrate and optionally an oxidizing agent; sonication; plasma treatment, including chemical plasma treatment, corona treatment, atmospheric plasma treatment and flame plasma treatment; immersion in a waterborne alkaline degreasing bath; treatment with a waterborne cleaning emulsion; treatment with a cleaning solvent, such as acetone, carbon tetrachloride or trichloroethylene; and, water rinsing, preferably with deionized or demineralized water. In those instances where a waterborne alkaline degreasing bath is used, any of the degreasing agent remaining on the surface should desirably be removed by rinsing the substrate surface with deionized or demineralized water.

In some embodiments, the adhesion of the transfer films to the preferably pre-treated substrate may be facilitated by the application of a primer thereto. Indeed primer compositions may be necessary to ensure efficacious fixture and /or cure times of the curable adhesive film on inactive substrates. Whilst the skilled artisan will be able to select an appropriate primer, instructive references for the choice of primer include but are not limited to: US Patent No. 3,855,040; US Patent No. 4,731,146; US Patent No. 4,990,281; US Patent No. 5,811,473; GB 2502554; and, US Patent No. 6,852,193.

Where applicable, the curing of the transfer film depends on the specific compounds, including accelerators, present in the curable film. That said, the temperature required to ensure a desired curing rate can be determined in the individual case by the skilled artisan, using simple preliminary tests if necessary.

For surety, it is noted that a curable adhesive film from which layer (10) may be derived and the composition from which a fixative layer (15) –when present -is derived may be independently cured. Alternatively, the respective compositions may be simultaneously cured where the operable curing conditions for each composition are compatible.

Article of Manufacture (A)

The aforementioned article of manufacture (A) will be described with reference to the appended drawings in which:

Figure 4 illustrates a single-sided tape absent a release liner according to an embodiment of the article of manufacture.

Figure 5 illustrates an embodiment of the article of manufacture that may correspond to a single-sided tape or a label with a release liner.

Figure 6 illustrates a transfer tape with one release liner according to an embodiment of the article of manufacture.

Figure 7 illustrates a transfer tape with two release liners according to an embodiment of the article of manufacture.

Figure 8 illustrates a double-sided tape with one release liner according to an embodiment of the article of manufacture.

Figure 9 illustrates a double-sided tape with two release liners according to an embodiment of the article of manufacture.

Figure 10 is an expanded view of a monolayer transfer film according to a first variant of the transfer films disposed in the tapes of Figures 4 to 9.

Figure 11 is an expanded view of a bilayer transfer film according to a second variant of the transfer films disposed in the tapes of Figures 4 to 9.

Figure 12 is an expanded view of a trilayer transfer film according to a third variant of the transfer films disposed in the tapes of Figures 4 to 9.

In Figure 4, a single sided tape (101) is shown which consists of a carrier (102) and a curable adhesive transfer film (103) having at least one layer which comprises or consists of the heat-activatable adhesive film of the present disclosure, as cast or otherwise formed from a heat-activatable adhesive composition (a, b) as described below. The carrier (102) should be an electrically conductive film.

The embodiment depicted in Figure 5 could be either a single sided tape or a label (201) , which tape or label consists of a carrier (102) -which should be an electrically conductive film -and an adhesive transfer film (103) as described above: the adhesive transfer film (103) is covered with a release liner (104) to protect the curable film adhesive thereof and prevent unwanted adhesion of the adhesive transfer film (103) .

Figures 6 and 7 depict transfer tapes which have particular utility for transferring the heat-activatable film adhesive from a release liner to a target surface (S¹, S²) . In Figure 6, the transfer tape (301) consists of a release liner (104) coated with an adhesive transfer film (103) as described above. The release liner (104) should have release properties on both sides but should not possess equivalent release properties on those sides: consequently, when winding and unwinding the transfer tape (301) from a roll -there will be a differentiation between the release effects on the two sides of the release liner (104) .

In Figure 7, the transfer tape (401) consists of an adhesive transfer film (103) interposed between first (104) and second (105) release liners. The first (104) and second (105) release liners may have different release properties relative to the adhesive transfer layer which allows these liners (104, 105) to be removed therefrom independently of one another.

A double-sided adhesive tape (501) is depicted in Figure 8 and consists of a carrier (102) having a first adhesive transfer film (103) on a first side of the carrier (102) and a second adhesive film (106) on a second side of the carrier (102) . The first (103) and second (106) adhesive transfer films may be the same of different in that they may be obtained from the same or different compositions, subject to the proviso that at least one of said adhesive transfer films (103, 106) is provided in accordance with the present disclosure and is thereby preferably constituted by at least one layer which comprises or consists of the heat-activatable adhesive film as cast or otherwise formed from the solvent-based heat-activatable adhesive composition (a) or a water-borne, heat-activated adhesive composition (b) . Given this, the carrier (102) should be an electrically conductive film. A release liner (104) covers and protects the second curable film (106) , which liner (104) should have release properties on both sides but should not possess equivalent release properties on those sides. In these circumstances -when winding and unwinding the transfer tape (501) from a roll -there will be a differentiation between the release effects on the two sides of the release liner (104) .

A second embodiment of a double-sided adhesive tape (601) is provided in Figure 9. The depicted tape (601) consists of a carrier (102) having a first adhesive transfer film (103) on a first side of the carrier (102) and a second adhesive transfer film (106) on a second side of the carrier (102) . The first (103) and second (106) adhesive transfer films may be the same of different, that is they may be obtained from the same or different compositions, subject to the aforementioned proviso that at least one of said adhesive transfer films (103, 106) is provided in accordance with the present disclosure. Given this, the carrier (102) should be an electrically conductive film. A first release liner (104) covers and protects the first adhesive transfer film (103) . A second release liner (105) covers and protects the second adhesive transfer film (106) . The first (104) and second (105) release liners may have different release properties relative to the adhesive transfer layers (103, 106) .

As depicted in Figure 10, it is envisaged that the adhesive transfer film (103) –as disposed in any one of the articles of manufacture illustrated in Figure 4 to 9 -may consist of a single layer (1030) which preferably consists of the heat-activatable adhesive film cast or otherwise obtained from a heat-activatable adhesive composition (a, b) . In an alternative embodiment, such an adhesive transfer film (103) may be a multi-layer film of which at least one said layer (1031) comprises or consists of the heat-activatable adhesive film of the present disclosure: as exemplars thereof, a bilayer (1031, 1032) film is depicted in Figure 11 and a trilayer (1031, 1032, 1033) film is depicted in Figure 12. Such multi-layer films may, in certain embodiments, include film adhesives which are distinct from those of the present disclosure. Mention may, however, be made of multi-layer transfer films (103) comprising: at least one layer which consists of the curable precursor of film (F^a) ; and, at least one layer which consists of the curable precursor of film (F^b) discussed herein below.

Independently of whether said transfer films (103, 106) have a monolayer or multilayer structure, it is preferred that said transfer films (103, 106) have a total thickness of from 15 to 500 microns, such as from 50 to 500 microns, from 50 to 250 microns or from 50 to 200 microns.

CURABLE ADHESIVE TRANSFER FILMS (103, 106)

The curable transfer film (103) which is to be transposed from the article of manufacture to a position which is interposed between the first and second electrically conductive substrates of the bonded structure is typically obtained from the casting of a water-or solvent borne composition, followed by the drying of said composition.

In important embodiments of the present disclosure: a solvent borne, heat-activatable composition (a) as described below; and /or, a water-borne, heat-activatable composition (b) as described below may be independently cast and dried to form the curable transfer film (103) .

(A) Solvent-borne heat-activatable adhesive composition

According to the present disclosure, the solvent-based heat-activatable adhesive composition (a) comprises: a1) at least one thermoplastic polyurethane polymer; a2) at least one polyol; a3) at least one polyisocyanate compound having at least two isocyanate groups and at least one uretdione group in one molecule; a4) electrolyte; optionally a5) rheology control agent; and, a6) at least one organic solvent.

(a1) Thermoplastic Polyurethane Polymer

The solvent-based heat-activatable adhesive composition (a) of the present disclosure comprises a1) at least one thermoplastic polyurethane polymer. Typically, the solvent-based heat-activatable adhesive composition (a) may comprise, based on the total weight of said composition (a) , from 5 to 50 wt. %of a1) said at least one thermoplastic polyurethane polymer. For instance, the solvent-based heat-activatable adhesive composition (a) may comprise from 5 to 40 wt. %, from 10 to 30 wt. %or from 10 to 25 wt. %of a1) said at least one thermoplastic polyurethane polymer, based on the total weight of said composition (a) .

Without a thermoplastic polyurethane polymer, the adhesive film derived therefore cannot be self-supporting. A thermoplastic polymer is distinct from a thermosetting polymer: the latter polymer solidifies via crosslinking or curing when subjected to heat whilst a thermoplastic polymer is pliable at elevated temperatures and solidifies when cooled.

It is preferred that the or each thermoplastic polyurethane polymer of substituent a1) has a weight-average molecular weight (Mw) of at least 10,000 g/mol, for example from 10,000 to 200,000 g/mol, from 10,000 to 150,000 g/mol or from 20,000 to 100,000 g/mol.

Independently of, or additional to the molecular weight characterization, it is desired that the or each thermoplastic polyurethane polymer of substituent a1) exhibits an optimum activation temperature of at most 100℃., preferably at most 85℃. For instance, the or each thermoplastic polyurethane polymer may have an activation temperature of from 30 to 80℃, from 30 to 70℃ or from 30 to 60℃. Within the preferred range, the heat-activatable adhesive film derived from the solvent-based heat-activatable adhesive composition (a) can be self-supporting and can exhibit efficacious bond strength when cured at a low temperature, such as a temperature of less than 90℃.

The term “optimum activation temperature” described herein means a temperature range or point for a thermoplastic polymer at which coalescence occurs within the thermoplastic polymer (physically) , which polymer has satisfactory strength with a proportion of non-coalescence of less than 10%. The optimum activation temperature of a thermoplastic polymer described herein can be determined according to EN 12961: 2001 Determination of optimum activation temperatures and maximum activation life or solvent-based and dispersion adhesives.

In an embodiment, substituent a1) of the composition comprises or consists of at least one thermoplastic polyurethane polymer which is chemically non-reactive: when subjected to heat, such a polymer coalescences, resulting in a pliable mass having certain adhesive properties. In other embodiments, substituent a1) comprises or consists of at least one thermoplastic polyurethane polymer which has pendant hydroxyl groups that can react with substituent a3) of the composition. As regards these embodiments, it is not precluded that substituent a1) may comprise a mixture of at least one non-reactive thermoplastic polyurethane polymer and at least one thermoplastic polyurethane polymer having pendant hydroxyl groups.

Suitable polyurethane polymers may be obtained from the reaction of: i) at least one non-ionic polyol having a number average molecular weight (Mn) of at least 500 g/mol; ii) optionally further active hydrogen compounds; and, iii) at least one polyisocyanate compound. The equivalence of active hydrogen atoms to -NCO groups of the reactants should be chosen to ensure that no pendant -NCO groups are present in the polyurethane. In those embodiments where the thermoplastic polyurethane polymer has pendant hydroxyl groups, the reaction may be exemplified by a stoichiometric excess of hydroxyl groups to isocyanate functional groups: for example, the molar ratio of hydroxyl groups to isocyanate functional groups may be from 1.1: 1 to 3: 1, from 1.1: 1 to 1.5: 1 or from 1.1: 1 to 2: 1.

As used herein, "polyol" refers to any compound comprising two or more hydroxyl groups: the term is thus intended to encompass diols, triols and compounds containing four or more -OH groups.

The at least one reactant non-ionic polyol i) may typically be chosen from: polyester polyols; polyether polyols; polycarbonate polyols; and, mixtures thereof. The non-ionic polyol may typically have a number average molecular weight (Mn) of from 1000 to 50,000 g/mol, for instance from 1000 to 25,000 g/mol. Alternatively or additionally to this molecular weight property, the hydroxyl number of the reactant non-ionic polyol may typically be from 20 to 850 mg KOH/g, for instance from 25 to 500 mg KOH/g.

Polycarbonate diols may be obtained by reacting carbonic acid derivatives with diols. Exemplary carbonic acid derivatives are diaryl carbonates including but not limited to diphenyl carbonate, di (C₁-C₆) alkyl carbonates and phosgene. Exemplary diols include but are not limited to: ethylene glycol; 1, 2-propanediol; 1, 3-propanediol; 1, 3-butanediol; 1, 4-butanediol; 1, 5-pentanediol; 1, 6-hexanediol; cyclohexane dimethanol; diethylene glycol; dipropylene glycol; neopentylglycol; and, mixtures thereof.

Polyester diols may be obtained by reacting diols with either aliphatic, aromatic or cycloaliphatic dicarboxylic acids or, in some circumstances, the corresponding anhydrides thereof: the reaction may optionally take place in the presence of an esterification catalyst. Examples of suitable dicarboxylic acids include but are not limited to: adipic acid; glutaric acid; pimelic acid; suberic acid; nonanedicarboxylic acid; decanedicarboxylic acid; succinic acid; maleic acid; sebacic acid; azelaic acid; terephthalic acid; isophthalic acid; o-phthalic acid; tetrahydrophthalic acid; hexahydrophthalic acid; trimellitic acid; and, 1, 4-cyclohexanedicarboxylic acid. Examples of suitable anhydrides include succinic, o-phthalic and trimellitic anhydride. It is noted that various commercially available dimeric fatty acids in saturated (hydrogenated) or unsaturated form may also be used as the dicarboxylic acid. And examples of suitable diols for the preparation of the polyester diols are: ethanediol; di-, tri-or tetraethylene glycol; 1, 2-propanediol; di-, tri-, tetrapropylene glycol; 1, 3-propanediol; 1, 4-butanediol; 1, 3-butanediol; 2, 3-butanediol; 1, 6-hexanediol; 1, 5-pentanediol; 2, 2-dimethyl-1, 3-propanediol (neopentylglycol) ; 1, 4-dihydroxycyclohexane; 1, 4-dimethylcyclohexane; 1, 8-octanediol; 1, 10-decanediol; 1, 12-decanediol; 2, 2, 4-and/or 2, 4, 4-trimethyl-1, 3-pentanediol; and, mixtures thereof.

Other useful polyester diols are those obtainable from diol initiated polymerization of hydroxycarboxylic acids containing from 2 to 12 carbon atoms or a lactone thereof. The hydroxycarboxylic acids may be saturated or unsaturated, linear or branched, of which example include: glycolic acid; lactic acid; 5-hydroxy valeric acid; 6-hydroxy caproic acid; ricinoleic acid; 12-hydroxy stearic acid; 12-hydroxydodecanoic acid; 5-hydroxydodecanoic acid; 5-hydroxydecanoic acid; and. 4-hydroxydecanoic acid. Examples of suitable lactones are β-propiolactone, δ-valerolactone, (C₁-C₆) alkyl-valerolactone, ∈-caprolactone and (C₁-C₆) alkyl-∈-caprolactone.

The above aside, in certain embodiments the non-ionic polyol i) from which the polyurethane polymer is derived is a polyether polyol, in particular a polyether polyol having a polydispersity (PD) of less than about 2, for example less than 1.5 or less than 1.3. For completeness, a “polyether” is understood for purpose of the present disclosure as a polymer whose repeating unit contains ether functionalities C-O-C in the main chain. Polymers having lateral ether groups, such as cellulose ethers, starch ethers, and vinyl ether polymers, as well as polyacetals, are therefore not covered by this definition.

Examples of useful polyether polyols for the preparation of the thermoplastic polyurethane polymers of substituent (a1) can be obtained from the polymerization of a cyclic oxide -such as ethylene oxide, propylene oxide or butylene oxide -or by the addition of one or more such oxides to polyfunctional initiators having at least two active hydrogens, such as water, polyhydric alcohols, polythiols, polyamines and alkanolamines. In certain embodiments, the polyether polyol is a polyoxyalkylene, for instance a polyoxy (C₂-C₄) alkylene or a polyoxy (C₂-C₃) alkylene.

As the optional reactant ii) , exemplary further active hydrogen compounds include but are not limited to:low molecular weight low molecular weight polyols, in particular diols; and, polyamines, in particular diamines.

As noted above, the reactants for the derivation of polyurethane polymers include: iii) at least one polyisocyanate compound. As used herein "polyisocyanate compound" means a compound comprising at least two -N=C=O functional groups. The polyisocyanates suitable for the derivation of the (hydroxyl functional) thermoplastic polyurethane means a compound comprising at least two -N=C=O functional groups, for example from 2 to 5 or from 2 to 4 -N=C=O functional groups. Suitable polyisocyanates include aliphatic, cycloaliphatic, aromatic and heterocyclic isocyanates, dimers and trimers thereof, and mixtures thereof.

Aliphatic and cycloaliphatic polyisocyanates can comprise from 6 to 100 carbon atoms linked in a straight chain or cyclized and having at least two isocyanate reactive groups. Examples of suitable aliphatic isocyanates include straight chain isocyanates such as ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, 1, 6-hexamethylene diisocyanate (HDI) , octamethylene diisocyanate, nonamethylene diisocyanate, decamethylene diisocyanate, triisocyanatenonane, 1, 6, 11-undecanetriisocyanate, 1, 3, 6-hexamethylene triisocyanate, bis (isocyanatoethyl) -carbonate, and bis (isocyanatoethyl) ether. Exemplary cycloaliphatic polyisocyanates include dicyclohexylmethane 4, 4′-diisocyanate (H₁₂MDI) , 1-isocyanatomethyl-3-isocyanato-1, 5, 5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI) , cyclohexane 1, 4-diisocyanate, hydrogenated xylylene diisocyanate (H₆XDI) , 1-methyl-2, 4-diisocyanato-cyclohexane, m-or p-tetramethylxylene diisocyanate (m-TMXDI, p-TMXDI) and dimer fatty acid diisocyanate.

The term “aromatic polyisocyanate” is used herein to describe organic isocyanates in which the isocyanate groups are directly attached to the ring (s) of a mono-or polynuclear aromatic hydrocarbon group. In turn the mono-or polynuclear aromatic hydrocarbon group means an essentially planar cyclic hydrocarbon moiety of conjugated double bonds, which may be a single ring or may include multiple condensed (fused) or covalently linked rings. The term aromatic also includes alkylaryl. Typically, the hydrocarbon (main) chain includes 5, 6, 7 or 8 main chain atoms in one cycle. Examples of such planar cyclic hydrocarbon moieties include cyclopentadienyl, phenyl, napthalenyl-, [10] annulenyl- (1, 3, 5, 7, 9-cyclodecapentaenyl-) , [12] annulenyl-, [8] annulenyl-, phenalene (perinaphthene) , 1, 9-dihydropyrene, chrysene (1, 2-benzophenanthrene) . Examples of alkylaryl moieties are benzyl, phenethyl, 1-phenylpropyl, 2-phenylpropyl, 3-phenylpropyl, 1-naphthylpropyl, 2-naphthylpropyl, 3-naphthylpropyl and 3-naphthylbutyl.

Exemplary aromatic polyisocyanates include: all isomers of toluene diisocyanate (TDI) , either in the isomerically pure form or as a mixture of several isomers; naphthalene 1, 5-diisocyanate; diphenylmethane 4, 4′-diisocyanate (MDI) ; diphenylmethane 2, 4′-diisocyanate and mixtures of diphenylmethane 4, 4′-diisocyanate with the 2, 4′isomer or mixtures thereof with oligomers of higher functionality (so-called crude MDI) ; xylylene diisocyanate (XDI) ; diphenyl-dimethylmethane 4, 4′-diisocyanate; di-and tetraalkyl-diphenylmethane diisocyanates; dibenzyl 4, 4′-diisocyanate; phenylene 1, 3-diisocyanate; phenylene 1, 4-diisocyanate; triphenylmethane triisocyanate, 1, 3, 5-benzene triisocyanate; and, 2, 4, 6-toluene triisocyanate.

The polyisocyanates, where required, may have been biuretized, allophanated and /or isocyanurated by generally known methods, such as described in UK Patent No. 889, 050. In use, such derivatives may be substantially free of the parent diisocyanate: the derivatives may have been separated from any excess parent diisocyanate by conventional means, including but not limited to distillation.

For completeness, exemplary commercially available thermoplastic polyurethane polymers having utility in or as substituent (a1) include but are not limited to: Pearlstick series polymers, such as Pearlstick 5707, 5703, 5701, 5714, 5713, 5715, 45-40, 45-50, 45-60, 45-80, 45-90, 48-60, 40-70, 46-10, available from Lubrizol; the HF-4003LH, 3003EH series, HF-3H and 6H series, available from Huafeng Chemicals; and, the WHT-61, 63, 64, 65, 67 series, available from Wanhua Chemicals.

(a2) Polyester Polyol

According to the present adhesive, the solvent-borne heat-activatable adhesive composition (a) comprises (a2) at least one polyester polyol, which polyester polyol can react with substituent a3) described below to form an effective bonding subject to heat. The composition may comprise, based on the total weight of the solvent-based heat-activatable adhesive composition (a) , from 0.1 to 30 wt. %, preferably from 1 to 25 wt. %or from 1 to 20 wt. %, of (a2) said at least one polyester polyol.

Polyester polyols having utility in substituent a2) of the present disclosure may be characterized by at least one of the following: i) a hydroxyl functionality of at least 2, for instance from 2 to 6 or from 3 to 6; ii) a hydroxyl number of at least 10 mg KOH/g, for instance from 10 to 150 mg KOH/g, from 15 to 90 mg KOH/g, such as from 30 to 60 mg KOH/g; iii) having a one or more aromatic groups in the molecule; and, iv) being in the solid state at 20℃. These characterizations are not mutually exclusive and one, two, three or four thereof may be applicable.

In some embodiments, substituent a2) comprises or consists of at least one polyester polyol chosen from amorphous polyester polyols, semi-crystalline polyester polyols, crystalline polyester polyols and mixtures thereof. It is preferred that said at least one polyester polyol has a weight average molecular weight (Mw) of less than 10,000 g/mol. Additionally or alternatively, it is preferred from the perspective of dissolution in the organic solvent of the composition, that said at least one polyester polyol is chosen from amorphous polyester polyols, semi-crystalline polyester polyols and mixtures thereof.

The term “amorphous polyester polyol” used herein means a polyester polyol having no melt transition when measured using Differential Scanning Calorimetry (DSC) . The amorphous polyester polyol should further not have a crystalline form and as such is preferably characterized by a degree of crystallinity by weight of less than 10%, for instance less than 5%, less than 2%or even less than 1%.

The term “semicrystalline polyester polyol” means a polyester polyol comprising crystalline and amorphous regions in its structure. The semi-crystalline polyester polyol may be characterized by a degree of crystallinity by weight of from 20 to 80%, for instance from 30 to 80%or from 40 to 80%.

The term “crystalline polyester polyol” used herein means a polyester polyol having a melt transition when measured using Differential Scanning Calorimetry (DSC) , which has a crystalline form. The crystalline polyester polyol may be characterized by a degree of crystallinity by weight of greater than 80%, for instance at least 85%or at least 90%.

The degree of crystallinity, denoting the proportion of substance in the crystalline state, can be determined by: X-ray diffraction analysis at different angles of incidence; by calorimetric measurements, such as Differential Scanning calorimetry (DSC) ; or, by any other technique that makes it possible to estimate the proportion of crystalline phase of the semicrystalline polyester polyol.

Useful amorphous polyester polyols which may be included in substituent a2) include the product of the polycondensation reaction of: at least one hydroxyl functional compound (a2h) ; at least one carboxyl functional compound or a derivative thereof (a2c) ; and, optionally, at least one hydroxycarboxylic acid compound (a2hc) . Exemplary derivatives of carboxyl functional compounds include esters, anhydrides and acyl halides. In general, the polycondensation reaction can be exemplified by a stoichiometric excess of hydroxyl groups to carboxyl groups. Typically the stoichiometric excess of hydroxyl groups to carboxyl groups may be from 5 to 40 mol. %, such as from 5 to 35 mol. %, from 5 to 30 mol. %or from 5 to 25 mol. %.

The polycondensation reactants can be selected according to type and quantity such that the above-mentioned molecular weight, hydroxyl value and functionality are obtained for the amorphous polyester. Further, at least one of the hydroxyl functional compound (a2h) and the carboxyl functional compound (a2c) may include an aromatic group in some embodiments.

In certain embodiments, the hydroxyl functional substituent (a2h) may comprise at least one diol and optionally at least one at least one polyol having from 3 to 6 hydroxyl groups. The hydroxyl functional substituent (a2h) may in other embodiments consist essentially or consist of at least one diol.

Suitable diols for use in the hydroxyl functional component may be saturated or unsaturated and may be aliphatic, cycloaliphatic or aromatic dihydroxy compounds. The reactant diols may typically have a molecular weight of 250 g/mol. or less. When used herein, the term "diol" can include equivalent ester forming derivatives thereof, provided, however, that the molecular weight requirement pertains to the diol only and not to its derivative. Exemplary ester forming derivatives include the acetates of the diols as well as, for example, ethylene oxide or ethylene carbonate for ethylene glycol.

Typical diols are those having from 2 to 20 carbon atoms. Examples of these diols include: ethylene glycol; propylene glycol; 1, 3-propane diol; 1, 2-butane diol; 2-methyl propanediol; 1, 3-butane diol; 1, 4-butane diol; 2, 3-butanediol; neopentyl glycol; hexanediol; decanediol; hexamethylene glycol; cyclohexane dimethanol; polyoxalkylene glycols, such as diethylene glycol, dipropylene glycol, triethylene glycol, tetraethylene glycol, tripropylene glycol and tetrapropylene glycol; and, aromatic diols such as bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F. Mixtures of such diols may be employed.

Suitable polyols having from 3 to 6 hydroxyl groups may be saturated or unsaturated and may be aliphatic, cycloaliphatic or aromatic compounds: the compounds can typically have a molecular weight of 400 g/mol. or less. Non-limiting examples of aliphatic triols include: 1, 2, 3-propanetriol; 1, 2, 4-butanetriol; 2-ethyl-2-hydroxymethyl-1, 3-propanediol (trimethylolpropane) ; 3-methyl-1, 3, 5-pentanetriol; 1, 2, 3-hexanetriol; 1, 2, 6-hexanetriol; 2, 5-dimethy1-1, 2, 6-hexanetriol; 1, 2, 3-heptanetriol; 1, 2, 3-octanetriol; and, 2-hydroxymethy1-1, 3-propanediol. Non-limiting examples of aliphatic tetrols and aliphatic pentols include: 2, 2-bis (hydroxymethyl) propane-1, 3-diol (pentaerythritol) ; pentose; pentopyranose; 6-deoxyhexopyranose; 2, 5-anhydrohexitol; 1, 5-anhydrohexitol; 6-deoxyhexose; 1-deoxyhexitol; and, pentitol. An exemplary polyol having six hydroxyl groups is D-glucitol (sorbitol) . In embodiments, 2-ethyl-2-hydroxymethyl-1, 3-propanediol (trimethylolpropane) , 2, 2-bis (hydroxymethyl) propane-1, 3-diol (pentaerythritol) or mixtures thereof may be used.

For surety, the present disclosure does not preclude the use -as a reactant polyol having from 3 to 6 hydroxyl groups –of (C₂-C₄) alkylene oxide adducts of the aforementioned diols, triols and higher polyols.

The carboxyl functional substituent (a2c) may comprise at least one dicarboxylic acid; optionally at least one monocarboxylic acid; and, optionally at least one polycarboxylic acid having at least 3 carboxyl groups.

Dicarboxylic acids which are suitable for use herein include aliphatic, cycloaliphatic or aromatic dicarboxylic acids. The dicarboxylic acids can typically have a molecular weight of less than 600 g/mol. The term "dicarboxylic acids" as used herein includes equivalents of dicarboxylic acids having two functional carboxyl groups which perform substantially like dicarboxylic acids in reaction with polyols in forming polyesters. These equivalents include esters and ester forming reactive derivatives, such as acyl halides and anhydrides, provided however that the molecular weight range mentioned above pertains to the acid and not to its equivalent ester or ester-forming derivatives. Thus, an ester of a dicarboxylic acid having a molecular weight greater than 300 g/mol. or an acid equivalent of a dicarboxylic acid having a molecular weight greater than 300 g/mol. are included provided the acid has a molecular weight below 300 g/mol. Additionally, the dicarboxylic acids may contain any substituent groups (s) or combinations which do not substantially interfere with the polymer formation and use of the polymer of this disclosure.

Exemplary dicarboxylic acid or derivatives thereof, which may be used alone or in combination include: aromatic dicarboxylic acids or derivatives thereof, such as terephthalic acid, isophthalic acid, dimethyl terephthalate, diethyl terephthalate, phthalic acid and phthalic anhydride; cycloaliphatic dicarboxylic acids or derivatives thereof, such as tetrahydrophthalic acid, methyl-hexahydrophthalic acid, methyl-hexahydrophthalic anhydride, methyl-tetrahydrophthalic acid, methyl-tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, 1, 3-cyclohexanedicarboxylic acid and 1, 4-cyclohexanedicarboxylic acid; and, aliphatic dicarboxylic acids or derivatives thereof, such as maleic acid, maleic anhydride, maleic acid, maleic anhydride, fumaric acid, succinic acid, succinic anhydride, glutaric acid, glutaric anhydride, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, chlorendic acid, decanedicarboxylic acid and octadecanedicarboxylic acid.

Dimer fatty acids may also be used as dicarboxylic acid reactants for the above described polyester synthesis reaction. Exemplary dimer fatty acids include C₃₆ to C₄₄ aliphatic diacids which may be prepared by the oxidative coupling of C₁₈ to C₂₂ unsaturated monoacids. Dimer acids obtained from the oxidative coupling of oleic acid, linoleic acid or talloil fatty acid may be used.

Monocarboxylic acids which are suitable reactants in the polycondensation reaction include aliphatic, cycloaliphatic or aromatic monocarboxylic acids. These monocarboxylic acids may typically have molecular weight of less than 300 g/mol. Exemplary monocarboxylic acids which may be used alone or in combination include: formic acid; acetic acid; propionic acid; n-butanoic acid; isobutanoic acid; 2-ethylhexanoic acid; octanoic acid; isononanoic acid; decanoic acid, dodecanoic acid; tetradecanoic acid; palmitic acid; and, stearic acid.

A (cyclo) aliphatic hydroxycarboxylic acid substituent (a2hc) may optionally participate in the polycondensation reaction which yields the polyester polyol of substituent a2) . When present, it is typical that the total amount of hydroxycarboxylic acid is at most 10 wt. %, based on the total weight of reactant compounds (a2h, a2c and a2hc) . Exemplary hydroxycarboxylic acids include: 12-hydroxystearic acid; 6-hydroxyhexanoic acid; citric acid; tartaric acid; and, dimethylolpropionic acid. The corresponding lactones may also be employed as a reactant instead of the monohydroxycarboxylic acids.

Specific examples of useful amorphous polyester polyols include: poly (hexanediol phthalate) polyol; poly (neopentyl glycol adipate) polyol; poly (neopentyl glycol phthalate) polyol; poly (neopentyl glycol hexanediol phthalate) polyol; poly (diethylene glycol phthalate) polyol; poly (ethylene glycol adipic acid terephthalate) polyol; polyethylene terephthalate polyols; random copolymer diols of ethylene glycol, hexane diol, neopentyl glycol, adipic acid and terephthalic acid; and, combinations thereof.

It is noted that when the composition comprises a solid amorphous polyester polyol, said polyol should desirably have a softening point of at most 130℃., for example a softening point of at most 120 ℃, at most 110℃ or at most 100℃. Solid amorphous polyester polyol having such softening point promote good bonding strength when fully cured and may moreover be easy to dissolve in the solvent-based heat-activatable adhesive composition (A) .

Suitable crystalline polyester polyols having utility in substituent a2) may be obtained by ring-opening polymerizing a lactone, such as ε-caprolactone, or may be derived from the reaction of diols and dicarboxylic acids. Exemplary diols useful in preparing preferred crystalline polyester polyols include ethylene glycol, diethylene glycol, 1, 3-propylene glycol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 8-octanediol, 1, 10-decanediol, and combinations thereof. Exemplary dicarboxylic acids useful in preparing preferred crystalline polyester polyols include succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, 1, 12-dodecanedioic acid, dimer acid and combinations thereof. The acyl halide, anhydride and ester derivatives of these carboxylic acids, in particular the methyl and ethyl esters thereof may be reacted in some embodiments.

Specific examples of suitable crystalline polyester polyols include but are not limited to: poly (hexanediol adipate) polyol; poly (butanediol adipate) polyol; poly-epsilon-caprolactone polyol; poly (hexanediol dodecanedioate) polyol; poly (hexanediol adipic acid terephthalate) polyol; and, mixtures thereof.

For completeness, exemplary commercially available polyols having utility in or as substituent a2) include: FZPE-A03130, available from Guanzhou FTRT Chemical Co. Ltd; Dynacoll^TM 7110, 7130, 7140, and 7150, available from Evonik Industries AG; and, FLP PA-1000N available from Xuchuan Chemical (Suzhou) Co., Ltd.

(a3) Polyisocyanate

According to the present disclosure, the solvent-based heat-activatable adhesive composition (a) comprises: a3) at least one polyisocyanate compound having at least two isocyanate groups and at least one uretdione group.

The substituent a3) is included in such an amount to satisfy the condition that the molar ratio of -N=C=O groups to hydroxyl groups in the composition (a) is from 0.1: 1 to 10: 1, for instance from 0.1 to 8: 1. The molar ratio of -N=C=O to hydroxyl groups may, for example, be from 0.5: 1 to 5: 1 or from 0.5: 1 to 3: 1. For the clarity, it is noted that the molar ratio of -N=C=O groups to hydroxyl groups in the composition (a) is referring in this context to functional groups of components a2 and a3. In addition, and for surety, the term “-N=C=O groups” includes blocked -N=C=O groups which are therefore included in the molar ratio term.

Under the condition that the above molar ratio condition is satisfied, the weight percentage of substituent a3) said polyisocyanate compound (s) in the composition is not particularly limited. However, in certain embodiments, the solvent-based heat-activatable adhesive composition (a) may comprise, based on the total weight of said composition (a) , from 0.05 to 10 wt. %, for example from 0.5 to 5 wt. %or from 1 to 5 wt. %of a3) said at least one polyisocyanate compound.

Suitable polyisocyanate compounds include aliphatic, cycloaliphatic, aromatic and heterocyclic polyisocyanate compounds, dimers and trimers thereof, and mixtures thereof. In certain embodiments, substituent a3) may comprise or consist of at least one aromatic polyisocyanate compound having at least two isocyanate groups and at least one uretdione group.

The or each polyisocyanate compound of a3) may in certain embodiments comprise from 1 to 10 uretdione groups. Independently of, or additional to this characterization, the or each polyisocyanate compound of a3) may comprise from 2 to 5 or from 2 to 4 -N=C=O functional groups. In an alternative expression, which is not mutually exclusive of the -N=C=O functionality, the or each polyisocyanate compound of (a3) may be characterized by an -N=C=O content of from 15 to 40 wt. %, for example from 20 to 35 wt. %, based on the weight of said polyisocyanate and as determined according to the testing method of M105-ISO 11909.

Exemplary polyisocyanate (s) (a3) which can be used according to the disclosure may correspond to the following formula (I) :

wherein: R is a divalent group comprising from 6 to 13 carbons; and, n is an integer ranging from 0 to 10. In certain embodiments, R is a divalent aromatic or polyaromatic group. Exemplary divalent groups R include phenylene, tolylene and methylene diphenylene: such groups (R) may be derived respectively from phenylene diisocyanate, toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) .

Specific examples of the polyisocyanate (s) (a3) which can be used according to the disclosure may correspond to Formula (I-1) or Formula (I-2) :

For completeness, suitable commercially available polyisocyanates having utility in or as substituent a3) include: MDI uretdione, available as Grilbond^TM A2bond from EMS-Griltech; and, TDI uretdione, available as Addolink^TM TT from Rhein Chemie or asBL XP2514 available from Covestro.

a4) Non-Polymerizable Electrolyte

The solvent-based heat-activatable adhesive composition (a) comprises: a4) non-polymerizable electrolyte. The term “non-polymerizable” is intended to indicate that the electrolyte, whilst present in the composition, is not incorporated in an amount that can be measured into the polymeric matrix formed from reactive components a2) , a3) and where applicable a1) . The non-polymerizable electrolyte contains no functional groups which are reactive with said substituents.

The solvent-based heat-activatable adhesive composition (a) may comprise, has on the weight of said composition (a) , from 0.5 to 15 wt. %of a4) said non-polymerizable electrolyte. The electrolyte a4) may preferably constitute from 0.5 to 10 wt. %, for example from 0.5 to 5 wt. %, of said composition. These quantities are preferred because a quantity greater than 15 wt. %of electrolyte, based on the weight of said composition (a) , may result in a good debonding effect but cure may be incomplete and /or initial adhesive properties may be adversely affected. Conversely, at amounts less than 0.5 wt. %, based on the weight of said composition, the debonding effect may be compromised.

For completeness, the non-polymerizable electrolyte may be disposed in the first component, the second component or both of the first and second ingredients. It is preferred that at least a portion of the non-polymerizable electrolyte be disposed in the first component of the composition.

Important electrolytes include the non-polymerizable salts of: ammonium; pyridinium; pyrrolidinium; phosphonium; imidazolium; oxazolium; guanidinium; sulfonium; and, thiazolium. In exemplary embodiments, the electrolyte of the present disclosure comprises at least one salt having a Formula selected from the group consisting of:

wherein: R₁, R₂, R₃, R₄, R₅ and R₆ are independently selected from hydrogen, C₁-C₁₈ alkyl, C₃-C₁₈ cycloalkyl, C₆-C₁₈ aryl, C₇-C₂₄ aralkyl, -C (O) R^q, -C (O) OH, -CN or –NO₂;

R^q is C₁-C₆ alkyl; and,

X^-is a counter anion.

Where an ammonium salt is used, it may be subject to the proviso that at most three and desirably at most two of the groups R₁ to R₄ may be hydrogen.

As regards said moieties R₁ to R₆, the terms C₁-C₁₈ alkyl, C₃-C₁₈ cycloalkyl, C₆-C₁₈ aryl, C₇-C₂₄ aralkyl, expressly include groups wherein one or more hydrogen atoms are substituted by halogen atoms (e.g. C₁-C₁₈ haloalkyl) or hydroxyl groups (e. g. C₁-C₁₈ hydroxyalkyl) . In particular, it is preferred that R₁, R₂, R₃, R₄, R₅ and R₆ are independently selected from hydrogen, C₁-C₁₂ alkyl, C₁-C₁₂ haloalkyl, C₁-C₁₂ hydroxyalkyl or C₃-C₁₂ cycloalkyl. For example, R₁, R₂, R₃, R₄, R₅ and R₆ may be independently selected from hydrogen, C₁-C₆ alkyl, C₁-C₆ haloalkyl or C₁-C₆ hydroxyalkyl.

There is no particular intention to limit the counter anion (X-) which may be employed in the non-polymerizable electrolytic salts. Exemplary anions may be selected from:

· Halides;

· Pseudohalides and halogen-containing compounds of the formulae PF₆ ^-, CF₃SO₃ ^-, (CF₃SO₃) ₂N^-, CF₃CO₂ ^-and CCl₃CO₂ ^-,

· CN^-, SCN^-and OCN^-;

· Phenates;

· Sulfates, sulfites and sulfonates of the general formulae SO₄ ^2-, HSO₄ ^-, SO₃ ^2-, HSO₃ ^-, R^aOSO₃ ^-and R^aSO₃ ^-;

· Phosphates of the general formulae PO₄ ^3-, HPO₄ ^2-, H₂PO₄ ^-, R^aPO₄ ^2-, HR^aPO₄ ^-and R^aR^bPO₄ ^-;

· Phosphonates and phosphinates of the general formulae R^aHPO₃ ^-, R^aR^bPO₂ ^-and R^aR^bPO₃ ^-;

· Phosphites of the general formulae: PO₃ ^3-, HPO₃ ^2-, H₂PO₃ ^-, R^aPO₃ ^2-, R^aHPO₃ ^-and R^aR^bPO₃ ^-;

· Phosphonites and phosphinites of the general formulae R^aR^bPO₂ ^-, R^aHPO₂ ^-, R^aR^bPO^-and R^aHPO^-;

· Carboxylic acid anions of the general formula R^aCOO^-;

· Hydroxycarboxylic acids anions and sugar acid anions;

· Saccharinates (salts of o-benzoic acid sulfimide) ;

· Borates of the general formulae BO₃ ^3-, HBO₃ ^2-, H₂BO₃ ^-, R^aR^bBO₃ ^-, R^aHBO₃ ^-, R^aBO₃ ^2-, B (OR^a) (OR^b) (OR^c) (OR^d) ^-, B (HSO₄) ^-and B (R^aSO₄) ^-;

· Boronates of the general formulae R^aBO₂ ^2-and R^aR^bBO^-;

· Carbonates and carbonic acid esters of the general formulae HCO₃ ^-, CO₃ ^2-and R^aCO₃ ^-;

· Silicates and silicic acid esters of the general formulae SiO₄ ^4-, HSiO₄ ^3-, H₂SiO₄ ^2-, H₃SiO₄ ^-, R^aSiO₄ ^3-, R^aR^bSiO₄ ^2-, R^aR^bR^cSiO₄ ^-, HR^aSiO₄ ^2-, H₂R^aSiO₄ ^–and HR^aR^bSiO₄ ^-;

· Alkyl-and arylsilanolates of the general formulae R^aSiO₃ ^3-, R^aR^bSiO₂ ^2-, R^aR^bR^cSiO^-, R^aR^bR^cSiO₃ ^-, R^aR^bR^cSiO₂ ^–and R^aR^bSiO₃ ^2-;

· Pyridinates and pyrimidinates;

· Carboxylic acid imides, bis (sulfonyl) imides and sulfonylimides of the general formulae:

· Methides of the general formula:

· Alkoxides and aryloxides of the general formula R^aO^-; or,

· Sulfides, hydrogen sulfides, polysulfides, hydrogen polysulfides and thiolates of the general formulae S^2-, HS^-, [S_v] ^2-, [HS_v] ^-and [R^aS] ^-

in which general formulae:

v is a whole positive number of from 2 to 10; and,

R^a, R^b, R^c and R^d are independently selected from hydrogen, halogen, C₁-C₁₂ alkyl, C₅-C₁₂ cycloalkyl, C₅-C₁₂ heterocycloalkyl, C₆-C₁₈ aryl, C₇-C₁₈ alkylaryl, C₇-C₁₈ aralkyl or C₅-C₁₈ heteroaryl.

As regards said moieties R^a, R^b, R^c and R^d , the terms C₁-C₁₂ alkyl, C₅-C₁₂ cycloalkyl, C₅-C₁₂ heterocycloalkyl, C₆-C₁₈ aryl, C₇-C₁₈ alkylaryl, C₇-C₁₈ aralkyl and C₅-C₁₈ heteroaryl expressly include groups wherein one or more hydrogen atoms are substituted by halogen atoms. For instance, CH₃, -CH₂F, -CHF₂ and -CF₃ represent exemplary C₁ alkyl groups.

Based on the definitions in the above list, preferred anions of the non-polymerizable electrolytic salts may be selected from the group consisting of: halides; pseudohalides and halogen-containing compounds as defined above; carboxylic acid anions, in particular formate, acetate, propionate, butyrate and octanoate; hydroxycarboxylic acid anions, such as lactate; pyridinates and pyrimidinates; carboxylic acid imides, bis (sulfonyl) imides and sulfonylimides; sulfates, in particular methyl sulfate and ethyl sulfate; sulfites; sulfonates, in particular methanesulfonate and p-toluenesulfonate (tosylate) ; and, phosphates, in particular dimethyl-phosphate, diethyl-phosphate and di- (2-ethylhexyl) -phosphate.

The electrolyte is preferably selected from the group consisting of 1-ethyl-3-methyl-1 H-imidazol-3-um methanesulfonate, 1-ethyl-3-methyl-1 H-imidazol-3-um methyl sulfate, 1-hexyl-3-methylimidazolium 2- (2-fluoroanilino) -pyridinate, 1-hexyl-3-methylimidazolium imide, 1-butyl-1-methyl-pyrrolidinium 2- (2-fluoroanilino) -pyridinate, 1-butyl-1-methyl-pyrrolidinium imide, trihexyl (tetradecyl) phosphonium 2- (2-fluoroanilino) -pyridinate, cyclohexyltrimethylammonium bis (trifluormethylsulfonyl) imide, di (2-hydroxyethyl) ammonium trifluoroacetate, N, N-dimethyl (2-hydroxyethyl) ammonium octanoate, methyltrioctylammonium bis (trifluoromethylsulfonyl) imide, tributylmethylammonium bis (fluorosulfonyl) imide, N-ethyl-N-N-N-N-tetramethylguanidinium trifluoromethanesulfonate, guanidinium trifluoromethanesulfonate, 1-butyl-4-methylpyridinium bromide, 1-butyl-3-methylpyridinium tetrafluoroborate, 1-butyl-3-hydroxymethylpyridinium ethylsulfate, N-propyl-N-methylpyrrolidinium bis (fluorosulfonyl) imide, 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide, 1-butyl-methylpyrrolidinium tris (pentafluoroethyl) trifluorophosphate, 3-methyl imidazolium ethylsulfate, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-ethyl-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium chloride, 1-methyl-3-octylimidazolium chloride, 1-propyl-3-methylimidazolium iodide, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium methyl sulfate, 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3- methylimidazolium bis (fluorosulfonyl) imide, 1-ethyl-3-methylimidazolium bis (fluorosulfonyl) imide, 1-butyl-3-methyl-imidazolium-fluorosulfonate, 1-dodecyl-3-methylimidazolium bis (fluorosulfonyl) imide, 1-butyl-2, 3-dimethylimidazolium tetrafluoroborate, 1-butyl-2, 3-dimethylimidazolium hexafluorophosphate, 1-butylimidazol, 1-methylimidazolium tetrafluoroborate, tributylmethylphosphonium bis (fluorosulfonyl) imide, tetrabutylphosphonium tris (pentafluoroethyl) trifluorophosphate, trihexyl (tetradecyl) phosphonium bis (trifluoromethylsulfonyl) imide, trihexyl (tetradecyl) phosphonium tetrafluoroborate, tributylmethylphosphonium methyl sulfate and mixtures thereof.

A particular preference may be mentioned for the use of at least one of trihexyl (tetradecyl) phosphonium bis (trifluoromethylsulfonyl) imide, tributylmethylphosphonium bis (fluorosulfonyl) imide, tributylmethyl-phosphonium methyl sulfate, tributylmethylammonium bis (fluorosulfonyl) imide, N-propyl-N-methylpyrrolidinium bis (fluorosulfonyl) imide, 1-ethyl-3-methyl-1H-imidazol-3-um methyl sulfate, 1-ethyl-3-methyl-1 H-imidazol-3-um methanesulfonate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-butyl-3-methylimidazolium methyl sulfate, 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methyl-imidazolium-fluorosulfonate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-butyl-3-methylimidazolium bis (fluorosulfonyl) imide and 1-dodecyl-3-methylimidazolium bis (fluorosulfonyl) imide.

a5) Rheology Control Agent

The solvent-based heat-activatable adhesive composition (a) of the present disclosure optionally comprises: a5) a rheology control agent comprising electrically non-conductive fillers, electrically conductive fillers or mixtures thereof.

The desired viscosity of the composition (a) -formed upon mixing its substituents -will generally be determinative of the total amount of rheology control agent added. However, the total amount of rheology control agent present in the solvent-based heat-activatable adhesive composition (a) may typically be from 0.1 to 10 wt. %, such as from 0.1 to 5 wt. %or from 0.5 to 5 wt. %, based on the total weight of the composition.

The presence of electrically non-conductive fillers in the composition may serve to moderate the viscosity of the composition and to reduce the coefficient of thermal expansion of the adhesive. Broadly, there is no particular intention to limit the shape of the particles employed as non-conductive fillers: particles that are acicular, spherical, ellipsoidal, cylindrical, bead-like, cubic or platelet-like may be used alone or in combination. Moreover, it is envisaged that agglomerates of more than one particle type may be used. Equally, there is no particular intention to limit the size of the particles employed as electrically non-conductive fillers. However, such non-conductive fillers will conventionally have a mean volume particle size (Dv50) , as measured by laser diffraction, of from 0.01 to 1500 μm, for example from 0.1 to 1000 μm or from 0.1 to 500 μm.

Exemplary non-conductive fillers include but are not limited to barium sulphate, calcium carbonate, calcium oxide, calcium metasilicate, silica, fumed silica, sand, quartz, zeolites, bentonites, magnesium carbonate, diatomite, alumina, clay, talcum, flint, mica, glass powder, zinc oxide and other ground mineral substances. Short fibres such as glass fibres, glass filament, polyacrylonitrile, carbon fibres, polyethylene fibres can also be added. A preliminary preference may be noted for non-conductive filler selected from the group consisting of: calcium carbonate; calcium oxide; calcium metasilicate; talcum; fumed silica; silica; barium sulphate; and, mixtures thereof. The use of precipitated and /or fumed (pyrogenic) silica as a rheology control agent in the present compositions is particularly preferred: such precipitated or pyrogenic silica should desirably have a BET surface area of from 25 to 500 m²/g, for example from 100 to 250 m²/g as measured by means of nitrogen adsorption according to DIN 66131. A commercial example of such a fumed (pyrogenic) silica is Aerosil 200, available from Evonik Industries.

Also suitable as electrically non-conductive fillers are hollow spheres having a mineral shell or a plastic shell. These can be, for example, hollow glass spheres that are obtainable commercially under the trade names GlassPlastic-based hollow spheres, such asor may be used and are described in EP 0 520 426 B1: they are made up of inorganic or organic substances and each have a diameter of 1 mm or less, preferably 500 μm or less, preferably between 100 μm and 200 μm.

Non-conductive fillers which impart thixotropy to the composition may have utility in certain applications: such fillers are also described as rheological adjuvants, e. g. hydrogenated castor oil, fatty acid amides, or swellable plastics such as PVC.

As noted, the compositions according to the present invention may additionally contain electrically conductive fillers as at least part of the rheology control agent. Broadly, there is no particular intention to limit the shape of the particles employed as conductive fillers: particles that are acicular, spherical, ellipsoidal, cylindrical, bead-like, cubic or platelet-like may be used alone or in combination. Moreover, it is envisaged that agglomerates of more than one particle type may be used. Equally, there is no particular intention to limit the size of the particles employed as conductive fillers. However, such conductive fillers will conventionally have an mean volume particle size (Dv50) , as measured by laser diffraction, of from 1 to 500 μm, for example from 1 to 200 μm.

Exemplary conductive fillers include, but are not limited to: silver; copper; gold; palladium; platinum; nickel; gold or silver-coated nickel; carbon black; carbon fibre; carbon nanotubes; graphite; aluminium; indium tin oxide; silver coated copper; silver coated aluminium; metallic coated glass spheres; metallic coated filler; metallic coated polymers; silver coated fibre; silver coated spheres; antimony doped tin oxide; conductive nanospheres; nano silver; nano aluminium; nano copper; nano nickel; carbon nanotubes; and, mixtures thereof. The use of particulate silver and /or carbon black as the conductive filler is preferred.

a6) Solvent

The solvent-based heat-activatable adhesive composition (a) , from which the heat-activatable films are cast or otherwise formed, comprises: (a6) at least one solvent. The amount of solvent which is present is determined by the desired viscosity of that solvent-borne composition and may be variant depending on the casting method being employed. However, for most casting methods, the solvent-borne compositions should typically possess a viscosity of from 3000 to 20000, preferably from 5,000 to 15000 mPas, as determined at 25℃.

Independently of, or additional to this viscosity condition, the solvent-borne composition may be exemplified by comprising from 30 to 90 wt. %, for instance from 40 to 85 wt. %or from 50 to 80 wt. %of (a6) said at least one solvent, based on the weight of the composition.

The solvent or solvents of substituent a6) are preferably selected to substantially or wholly dissolve a1) said at least one thermoplastic polyurethane and a2) said at least one polyol. The further components of the composition may either be soluble in the solvent or may disperse homogenously within the solvent so as to enable the composition to be readily applied to a substrate.

The or each solvent of the composition should desirably be aprotic. In particular, the or each solvent of substituent a6) may possess: a solubility parameter, delta (δ) of from 6.9 to 10.0 (cal/cm³) ^1/2, as defined inLexikon Lacke and Druckfarben, Georg Thieme Verlag, Stuttgart, New York, 1998, “Solubility Parameters” (pages 361 to 365) ; and, a positive hydrogen bonding index (HBI, γ) , in particular hydrogen bonding index (HBI, γ) , of of from 5.0 to 7.7. These parameters are defined in the literature, such as in sections 38 and 39 of the US2004/0204524. Further, the hydrogen bonding index is determined according to the deviation of the infrared band for the RO-H stretching band as described in Nelson et al. “Treatment of hydrogen bonding in predicting miscibility, ” Journal of Paint Technology, Vol. 42: 550: 636-643 (1970) .

Independently of additionally to being aprotic, it is preferred that the or each solvent of substituent (a6) has a boiling point of less than the optimum activation temperature of the thermoplastic polyurethane (a1) : in this circumstance, the organic solvent may be evaporated to form the thermally curable adhesive film without activating the thermoplastic polymer (a1) . In certain embodiments, the or each solvent may have a boiling point of less than 120℃, such as less than 100℃ or less than 80℃.

Exemplary solvents, which may be used alone or in combination, include: aliphatic and cycloaliphatic hydrocarbons, such as pentane, cyclopentane, n-hexane, cyclohexane and n-heptane; chlorinated aliphatic hydrocarbons, such as dichloromethane and chloroform; ethyl acetate; ketones such as acetone, butan-2-one (methyl ethyl ketone) , 2-pentanone, 3-pentanone and methyl isobutyl ketone; and, ethers such as diethyl ether, methyl-t-butyl ether, 1, 4-dioxane and tetrahydrofuran. In particular, it is preferred that said at least one solvent is selected from the group consisting of tetrahydrofuran, dichloromethane, chloroform, ethyl acetate and mixtures thereof.

(B) Water-borne heat-activatable adhesive composition

The present disclosure provides a water-borne, heat-activatable adhesive composition (b) comprising: water; b1) at least one first polyurethane polymer having at least one isocyanate reactive functional group and comprising at least one residue chosen from residues of the structural units (I) , (II) and (III) described below; b2) at least one second polyurethane polymer which is distinct from said first polyurethane polymer, said second polyurethane polymer having at least one isocyanate reactive functional group; b3) at least one surface-deactivated solid polyisocyanate compound; b4) non-polymerizable electrolyte; and, optionally b5) rheology control agent.

In forming the above described composition (b) , one or more of the substituents (b1) to (b5) may be provided in water, such as a dispersion or solution in water. It is also considered that water may be added to an admixture of two or more substituents chosen from substituents (b1) to (b5) independently of whether said substituents were initially provided in water or not. The amount of water introduced with a given substituent, with a given mixture of substituents and /or as a diluent after admixing all substituents will be moderated to achieve the desired viscosity and solids content of the composition (b) .

b1) First Polyurethane Polymer

The composition (b) comprises: b1) at least one first polyurethane polymer (FPU) . The composition (a) may comprise, based on the total weight of the composition, from 20 to 50 wt. %of b1) said at least one polyurethane polymer (FPU) . It is preferred that said composition comprises from 20 to 40 wt. %or from 25 to 40 wt. %of b1) said at least one first polyurethane polymer, based on the total weight of the composition a) .

The or each first polyurethane polymer (FPU) of the present disclosure has at least one functional group which is reactive with isocyanate groups (-N=C=O) . Examples of reactive functional groups include hydroxyl, amino, carboxyl, amide and thiol (-SH) groups. One or more of such reactive functional groups may be pendant on the first polyurethane polymer.

It is preferred that the weight average molecular weight (Mw) of the first polyurethane polymer (FPU) is at least 2,000 g/mol. The weight average molecular weight (Mw) of the first polyurethane polymer (FPU) may, in certain embodiments, be from 5000 to 250000 g/mol., for example from 5000 to 200000 g/mol.

The first PU polymer (s) of the present disclosure may be obtained from the reaction of: i) at least one polyol having a number average molecular weight (Mn) of at least 500 g/mol.; ii) at least one polyol having a number average molecular weight of less than 500 g/mol. and which either possesses an ionic group or is capable of forming an ionic group; iii) optionally further active hydrogen compounds; and, iv) at least one polyisocyanate compound. The term “polyol” as used herein refers to a compound carrying two or more hydroxyl groups.

To ensure that the polyurethane has no pendant isocyanate (-N=C=O) groups, the equivalence of active hydrogen atoms to -N=C=O groups of the reactants should be chosen to ensure that no free -N=C=O groups are present in the polyurethane. Typically a stoichiometric excess of hydroxyl groups to isocyanate functional groups may be used. For example, the molar ratio of hydroxyl groups to isocyanate functional groups may be from 1.1: 1 to 3: 1, from 1.1: 1 to 1.5: 1 or from 1.1: 1 to 2: 1. In various non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those set forth above are expressly contemplated for use herein.

An important feature of the first polyurethane polymer (FPU) obtained by the aforementioned reaction is that reactant i) comprises at least one polyol which has a number average molecular weight (Mn) of at least 500 daltons and which further has one or more structural units chosen from structural units of formulae (I) to (III) :
-CH (OH) -CH₂-X¹-Y                   (I)
-CH (OH) -CH₂-X²-CH₂-CH (OH) -       (II)
-CH (OH) -CH₂-X¹-Y¹-X³-CH₂-CH (OH) -     (III)

wherein: X¹ represents -OC (=O) -, -S-, -NR¹-, -OP (=O) (OR¹) -O-, -OP (=O) (R¹) -O-, -OP (=O) (R¹) -, -O-P (OR¹) -O-, -O-P (R¹) -O-or -O-P (R¹) -;

X² represents -NR¹-, -OP (=O) (OR¹) -O-, -OP (=O) (R¹) -O-, -O-P (OR¹) -O-or -O-P (R¹) -O-;

X³ represents -C (=O) O-, -S-, -NR¹-, -OP (=O) (OR¹) -O-, -OP (=O) (R¹) -O-, -P (=O) (R¹) -O-, -O-P (OR¹) -O-, -O-P (R¹) -O-; -P (R¹) -O-;

in which groups each R¹ independently represents H or a C₁-C₂₀ organic group;

Y is H or a C₁-C₃₀ monovalent organic group or H; and,

Y¹ is a C₁-C₃₀ divalent organic group, with a proviso that Y¹ is not -CH₂-CH (OH) -.

The polyol comprising one or more structural units selected from formulae (I) to (III) is referred to as polyol POHA in the context of the present application. In certain embodiments said polyol POHA can contain from 1 to 10 structural units, for instance from 1 to 5 structural units chosen from structural units of Formulae (I) to (III) . In various non-limiting embodiments, all values and ranges of value, including and between those set forth above are expressly contemplated for use herein.

Independently of, or additional to the number of said structural units, it is preferred that the polyol (POHA) has a weight average molecular weight (Mw) of from 500 to 5000 g/mol., for example from 500 to 5000 g/mol., of from 1000 to 3000 g/mol. In various non-limiting embodiments, all values and ranges of value, including and between those set forth above are expressly contemplated for use herein.

Preferably, R¹ in formulae (I) to (III) each independently represents: H; an aliphatic group having from 1 to 20 carbon atoms; an alicyclic group having from 3 to 20 carbon atoms; or, an aromatic group having from 6 to 20 carbon atoms, in which one or more carbon atoms of R¹ can optionally be replaced with heteroatoms such as Si, O, N, P or S. Optionally, R¹ can be a bridge group between two X¹s, between two X²s, or between an X¹ and an X². More preferably, R¹ in formulae (I) to (III) each independently represents: H; an aliphatic group having from 1 to 10 carbon atoms; an alicyclic group having from 3 to 10 carbon atoms; or, an aromatic group having from 6 to 10 carbon atoms. For example, R¹ can be methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, phenyl, phenylmethyl or phenylethyl, or their divalent forms, or H.

Preferably, Y in formula (I) represents: H; an aliphatic group having from 1 to 20 carbon atoms; an alicyclic group having from 3 to 20 carbon atoms; an aromatic group having from 6 to 20 carbon atoms, in which one or more carbon atoms of Y can optionally be replaced with heteroatoms such as Si, O, N, P or S. For example, Y can be H, methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, phenyl, phenylmethyl, phenylethyl, or -C₁-C₆ alkylene-Si (O-alkyl) _n (alkyl) _3-n, in which n=0, 1, 2 or 3.

Preferably, Y¹ in formula (III) represents a divalent form of the group Y, for example: a divalent aliphatic group having from 1 to 20 carbon atoms; a divalent alicyclic group having from 3 to 20 carbon atoms; or, a divalent aromatic group having 6 to 20 carbon atoms, in which one or more carbon atoms of Y¹ can optionally be replaced with heteroatoms such as Si, O, N, P or S. For example, Y¹ can be methylene, ethylene, propylene, butylene, pentylene, hexylene, cyclohexylene, phenylene, phenylmethylene or phenylethylene.

Exemplary structural units of formulae (I) to (III) include:

-CH (OH) -CH₂-S-C₁-C₆alkylene-Si (O-C₁-C₆-alkyl) _n (C₁-C₆-alkyl) _3-n, n=0, 1, 2, or 3;

-CH (OH) -CH₂-NR¹-C₁-C₆alkylene-NH₂;

-CH (OH) -CH₂-NR¹-C₁-C₆alkylene-NR¹-CH₂-CH (OH) -;

-CH (OH) -CH₂-O-P (=O) (OH) ₂;

-CH (OH) -CH₂-NR¹-CH₂-CH (OH) -;

-CH (OH) -CH₂-O-P (=O) (OH) -O-CH₂-CH (OH) -; or,

in which each R¹ independently is methyl, ethyl, propyl, butyl, pentyl or hexyl or their divalent forms, or H.

POHA can be obtained by reacting a mono-or poly-functional epoxy resin (ER) with a nucleophilic or electrophilic compound having one or more active hydrogen atoms. It is preferred that the reactant epoxy resin is polyfunctional, in particular difunctional. In structural units of formulae (I) to (III) , the groups Y, Y¹, X¹, X² and X³ , where applicable, are derived from the nucleophilic or electrophilic compound, the groups -CH (OH) -CH₂-and -CH₂-CH (OH) -are derived from the epoxy resin (ER) .

The epoxy resin (ER) can be any known epoxy resins in the art, including, but not limited to: aliphatic epoxy resins; alicyclic epoxy resins; aromatic epoxy resins; or, mixtures thereof. Examples of epoxy resins (ER) include, but not limited to: diglycidyl ethers of dihydric phenols and dihydric alcohols, such as diglycidyl ethers of aliphatic and cycloaliphatic diols, such as 1, 2-ethanediol, 1, 4-butanediol, 1, 6-hexanediol, 1, 8-octanediol, 1, 12–dodecanediol, cyclopentane diol and cyclohexane diol; bisphenol A based diglycidylethers (bisphenol A epoxy resins) ; bisphenol F diglycidyl ethers (bisphenol F epoxy resins) ; polyalkyleneglycol based diglycidyl ethers, in particular polypropyleneglycol diglycidyl ethers; and, polycarbonatediol based glycidyl ethers.

The epoxy resins (ER) useful herein may typically have an epoxy equivalent weight (EEW) of 100 to 700 g/eq., for example from 150 to 600 g/eq. or from 200 to 500 g/eq., as determined according to ISO 3001: 1999. Independently of or additional to this epoxy equivalent weight condition, the epoxy resins (ER) may typically have a weight average molecular weight (Mw) of from 250 to 5000 g/mol., for example from 300 to 3000 g/mol. or from 500 to 2000 g/mol. In various non-limiting embodiments, all values and ranges of value, including and between those set forth above are expressly contemplated for use herein.

For completeness, exemplary commercially available epoxy resins (ER) having utility herein include, but are not limited to: epoxy resin E-54, E-51, E-44, E-42, E-31 and E-20, available from Blue Star New Chemical Material Co., Ltd.

In the aforementioned POHA synthesis reaction, the nucleophilic or electrophilic compound having one or more active hydrogen atom may typically be a compound having pendant -COOH, -OH, -NH₂, -NHR or -SH groups, or organic/inorganic acids containing heteroatom such as N, S or P. For example, the nucleophilic or electrophilic compound may be chosen from: monocarboxylic acids; dicarboxylic acids; phosphorus-containing organic or inorganic acids, such as phosphoric acid, phosphonic acid, phosphinic acid, phosphorous acid, phosphonous acid or phosphinous acid; primary or secondary amines; and, compounds containing at least one -SH group.

Addition reactions between the epoxy resin (ER) and said nucleophilic or electrophilic compound are known in the art, and can proceed, for example, as shown below:

In certain embodiments, the polyol POHA constitutes from 0.1 to 20 wt. %, preferably from 1 to 10 wt. %of the total weight of hydroxyl functional reactants from which the first polyurethane polymer (FPU) is obtained. Independently of or additional to this weight percentage condition, reactant i) from which the first polyurethane polymer (FPU) polymer may be obtained may consist of said polyol POHA or consist essentially of said polyol POHA. In certain embodiments, however, reactant i) may comprise said polyol POHA and one or more further polyols different from the polyol POHA.

The further polyols of reactant i) are referred to hereinafter as polyol POHB. The polyol POHB differs from the polyol POHA in that the polyol POHB does not contain the structural unit of formula (I) or (II) or (III) . Typically the polyol POHB having utility herein may have a weight average molecular weight (Mw) of from 500 to 5000 g/mol., for example from 500 to 2500 g/mol or from 500 to 2000 g/mol. In various non-limiting embodiments, all values and ranges of value, including and between those set forth above are expressly contemplated for use herein.

Examples of the polyol POHB include: polycarbonate polyols; polyester polyols; polyether polyols; or, mixtures thereof. Preferably, the polyol POHB is selected from polycarbonate polyols, polyester polyols or mixtures thereof. More preferably, the polyol POHB is selected from polycarbonate polyols or mixtures thereof. In this regard, a preference may be mentioned for reactant i) to comprise said polyol POHA and at least one polycarbonate polyol.

Suitable polycarbonate polyols having utility as polyol POHB may be produced by reacting a carbonate compound with a diol. Examples of the reactant carbonate compound include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, diethylene carbonate and the like. Examples of the reactant diol include: an aliphatic diol; an alicyclic diol such as cyclohexanediol or a hydrogenated xylene glycol; and, an aromatic diol such as xylylene glycol. Among these diols, preferred is an aliphatic diol, and more preferred is an aliphatic diol having a carbon chain length of not less than 4 and not more than 9. Mention in this regard may be made of: 1, 4-butanediol; 3-methyl-1, 5-pentanediol; 1, 6-hexanediol; heptanediol; octanediol; and, nonanediol.

For completeness, commercially available polycarbonate polyols having utility as said polyol POHB include, but not limited to: DURANOL T4672, DURANOL T4671, DURANOL T4692, DURANOL T4691, DURANOL G3450J, DURANOL G3452, available from Asahi KASEI.

Suitable polyester polyols having utility as polyol POHB may be produced by subjecting a low-molecular diol and a dicarboxylic acid to condensation reaction. Examples of the low-molecular diol include diols having not less than 2 and not more than 6 carbon atoms, such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol and 1, 4-butanediol. Among these low-molecular diols, preferred are ethylene glycol, propylene glycol, 1, 4-butanediol and the like. Examples of the dicarboxylic acid include: aliphatic dibasic acids, such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and brassylic acid; and, aromatic dibasic acids, such as isophthalic acid, terephthalic acid and naphthalene dicarboxylic acid. Amongst these dicarboxylic acids, preferred are aliphatic dibasic acids, and more preferred are dibasic acids having a methylene chain length of not less than 4 and not more than 8, such as adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid.

Commercially available polyester polyols having utility for preparing the first polyurethane polymer (FPU) of the present invention include, but not limited to: Dynacoll 7000, Dynacoll 7380, Dynacoll 7360, Dynacoll 7250, available from Evonik.

Suitable polyether polyols having utility as polyol POHB may be prepared by the reaction of suitable starting compounds which contain reactive hydrogen atoms with alkylene oxides such as, for example, ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran, epichlorohydrin, and mixtures thereof. Suitable starting compounds containing reactive hydrogen atoms include compounds such as, for example, ethylene glycol, propylene glycol, butylene glycol, hexanediol, octanediol, neopentyl glycol, cyclohexanedimethanol, 2-methyl-1, 3-propanediol, 2, 2, 4-trimethyl-1, 3-pentanediol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol, polybutylene glycol, glycerine, trimethylolpropane, pentaerythritol, water, methanol, ethanol, 1, 2, 6-hexane triol, 1, 2, 4-butane triol, trimethylolethane, mannitol, sorbitol, methyl glycoside, sucrose, phenol, resorcinol, hydroquinone and 1, 1, 1-or 1, 1, 2-tris- (hydroxyphenyl) -ethane.

Commercially available polyether polyols for example can be used in preparing the first polyurethane polymer (FPU) of the present invention. Examples thereof include, but are not limited to: Voranol P400, Voranol 2120 and Voranol 2110, available from Dow.

Polyols ii) having a number average molecular weight of less than 500 g/mol. and which either possess an ionic group or are capable of forming an ionic group serve to incorporate said ionic group into the first polyurethane polymer (FPU) via the addition reaction with iv) said polyisocyanate reactant (s) : the ionic group improves the dispersion stability of the PU polymer in an aqueous medium and thereby the storage stability of the aqueous dispersion.

Exemplary ionic polyols ii) include: dihydroxystearic acid; dialkanol di-C₁-C₅-alkanol C₁-C₁₀-carboxylic acids, such as 1, 2-dimethylol acetic acid, dimethylol butanoic acid, dimethylol propionic acid, 2, 2-dimethylolbutanoic acid, 2, 2-dimethylolpentanoic acid, 2, 2-dimethylolhexanoic acid, 2, 2-dimethyloloctanoic acid, di (hydroxyethyl) acetic acid, di (hydroxyethyl) propionic acid, di (hydroxyethyl) butanoic acid, di (hydroxypropyl) acetic acid, di (hydroxypropyl) propionic acid, di (hydroxypropyl) butanoic acid; salts of the aforementioned acids; and, polyols containing sulfonate groups, such as the propoxylated adduct of sodium hydrogen sulfite and 2-butenediol or the polyesters synthesized from salts of sulfoisophthalic acid.

As noted above, the reactants for the derivation of polyurethane (FPU) polymers may optionally include iii) further active hydrogen compounds not corresponding to the aforementioned polyols (i) , ii) . Such further active hydrogen compounds may be classified as for instance: chain extending compounds which possess at least two active hydrogen atoms and of which examples include polyamines and polyols; and, chain terminating compounds which possess one active hydrogen atom of which examples include monoalcohols and monoamines.

Exemplary chain extending compounds having pendant hydroxyl groups include but are not limited to: aliphatic glycols such as ethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 3-butanediol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol and neopentyl glycol; low molecular weight (C₁-C₄) alkylene oxide adducts of said aliphatic glycols, such as diethylene glycol, triethylene glycol, and dipropylene glycol; alicyclic glycols; aromatic glycols; bisphenols; and, alkyldialkanolamines.

Exemplary chain extending compounds having pendant amine groups include but are not limited to: aliphatic diamine compounds, such as ethylene diamine, trimethylenediamine, hexamethylenediamine and octamethylenediamine; aromatic diamine compounds, such as phenylenediamine, 3, 3’-dichloro-4, 4’-diaminodiphenylmethane, 4, 4’-methylenebis (phenylamine) , 4, 4’-diaminodiphenyl ether and 4, 4’-diaminodiphenyl sulfone; alicyclic diamine compounds, such as cyclopentanediamine, cyclohexyldiamine, 4, 4-diaminodicyclohexylmethane, 1, 4-diaminocyclohexane, 1, 3-bisaminomethylcyclohexane, isophorone diamine; and, hydrazines, such as hydrazine, carbodihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide and phthalic acid dihydrazide.

As noted above, the reactants for the derivation of the first polyurethane polymer (FPU) include: iv) at least one polyisocyanate compound. As used herein "polyisocyanate compound" means a compound comprising at least two -N=C=O functional groups. The polyisocyanates suitable for the derivation of the (hydroxyl functional) thermoplastic polyurethane means a compound comprising at least two -N=C=O functional groups, for example from 2 to 5 or from 2 to 4 -N=C=O functional groups. Suitable polyisocyanates include aliphatic, cycloaliphatic, aromatic and heterocyclic isocyanates, dimers and trimers thereof, and mixtures thereof.

As described above, the constituent b1) said at least one first polyurethane polymer (FPU) may be added to the composition (b) as a dispersion in water. In the alternative, at least a part of constituent b1) may be added in solid form, which solid form may be derived from an aqueous suspension of the first polyurethane polymer (s) (FPU) . Any removal of water from such an aqueous suspension, by evaporation for instance, should not trigger the chemical reaction or decomposition of said first polyurethane polymer (s) (FPU) .

To facilitate its inclusion in the compositions of the present disclosure, the or each polyurethane polymer (FPU) may have a particulate form exemplified by a particle size distribution having a mean volume particle size (d_v50) of less than 1 micron, for instance of from 50 to 400 nm, as measured by laser diffraction.

b2) Second Polyurethane Polymer

The composition (a) comprises: b2) at least one second polyurethane polymer (SPU) . The composition (b) may comprise, based on the total weight of the composition, from 30 to 60 wt. %of b2) said at least one second polyurethane polymer (SPU) . It is preferred that said composition comprises from 30 to 55 wt. %or from 30 to 50 wt. %of b2) said least one second polyurethane polymer (SPU) based on the total weight of the composition (b) .

In an alternative expression of composition, which is not intended to be mutually exclusive of that given above, the ratio by weight on a solids basis of substituent b1) to substituent b2) in the composition (b) is preferably from 25: 75 to 60: 40, for example from 30: 70 to 55: 45 or from 35: 65 to 50: 40.

The second polyurethane polymer (SPU) polymer of the present invention can be any conventional polyurethane polymer other than the first PU polymer, as long as the second polyurethane polymer (SPU) has at least one functional group which is reactive with isocyanate groups (-N=C=O) . Examples of reactive functional groups include hydroxyl, amino, carboxyl, amide and thiol (-SH) groups.

In preferred embodiments of the present disclosure, the weight average molecular weight (Mw) of the second polyurethane polymer (SPU) is at least 2000 g/mol. For example, the weight average molecular weight (Mw) of the second polyurethane polymer (SPU) may be from 5000 to 250000 g/mol. or from 20000 to 200000 g/mol.

The second polyurethane polymer (SPU) of the present disclosure may be obtained from the reaction of: si) at least one polyol having a number average molecular weight (Mn) of at least 500 g/mol.; sii) at least one polyol having a number average molecular weight of less than 500 g/mol. and which either possesses an ionic group or is capable of forming an ionic group; siii) optionally further active hydrogen compounds; and, siv) at least one polyisocyanate compound.

To ensure that the or each second polyurethane polymer (SPU) has no pendant isocyanate (-N=C=O) groups, the equivalence of active hydrogen atoms to -N=C=O groups of the aforementioned reactants should be chosen to ensure that no free -N=C=O groups are present in the polyurethane. Typically a stoichiometric excess of hydroxyl groups to isocyanate functional groups may be used. For example, the molar ratio of hydroxyl groups to isocyanate functional groups may be from 1.1: 1 to 3: 1, from 1.1: 1 to 1.5: 1 or from 1.1: 1 to 2: 1. In various non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those set forth above are expressly contemplated for use herein.

The second polyurethane polymer (SPU) differs from the first polyurethane polymer (FPU) polymer in that the second polyurethane polymer (SPU) is not prepared using the polyol POHA: more particularly, polyol POHA is not part of reactant si) . Rather, the second polyurethane polymer (SPU) is prepared using at least one polyol POHB as said reactant si) .

Typically the polyol POHB having utility herein may have a weight average molecular weight (Mw) of from 500 to 5000 g/mol., for example from 500 to 2500 g/mol or from 500 to 2000 g/mol. In various non-limiting embodiments, all values and ranges of value, including and between those set forth above are expressly contemplated for use herein.

Examples of the polyol POHB include: polycarbonate polyols; polyester polyols; polyether polyols; or, mixtures thereof. Preferably, the polyol POHB is selected from polycarbonate polyols, polyester polyols or mixtures thereof. More preferably, the polyol POHB is selected from polycarbonate polyols or mixtures thereof.

Commercially available polyester polyols having utility for preparing the second polyurethane polymer (SPU) of the present invention include, but not limited to: Dynacoll 7000, Dynacoll 7380, Dynacoll 7360, Dynacoll 7250, available from Evonik.

Suitable polyether polyols having utility as polyol POHB may be prepared by the reaction of suitable starting compounds which contain reactive hydrogen atoms with alkylene oxides such as, for example, ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran, epichlorohydrin, and mixtures thereof. Suitable starting compounds containing reactive hydrogen atoms include compounds such as, for example, ethylene glycol, propylene glycol, butylene glycol, hexanediol, octanediol, neopentyl glycol, cyclohexanedimethanol, 2-methyl-1, 3-propanediol, 2, 2, 4-trimethyl-1, 3-pentanediol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol, polybutylene glycol, glycerine, trimethylolpropane, pentaerythritol, water, methanol, ethanol, 1, 2, 6-hexane triol, 1, 2, 4-butane triol, trimethylolethane, mannitol, sorbitol, methyl glycoside, sucrose, phenol, resorcinol, hydroquinone and 1, 1, 1-or 1, 1, 2- tris- (hydroxyphenyl) -ethane.

Commercially available polyether polyols for example can be used in preparing the second polyurethane polymer (SPU) of the present invention. Examples thereof include, but are not limited to: Voranol P400, Voranol 2120 and Voranol 2110, available from Dow.

Polyols sii) having a number average molecular weight of less than 500 g/mol. and which either possess an ionic group or are capable of forming an ionic group serve to incorporate said ionic group into the second polyurethane polymer (SPU) via the addition reaction with siv) said polyisocyanate reactant (s) : the ionic group improves the dispersion stability of the polyurethane polymer in an aqueous medium and thereby the storage stability of the aqueous dispersion.

Exemplary ionic polyols sii) include: dihydroxystearic acid; dialkanol di-C₁-C₅-alkanol C₁-C₁₀-carboxylic acids, such as 1, 2-dimethylol acetic acid, dimethylol butanoic acid, dimethylol propionic acid, 2, 2-dimethylolbutanoic acid, 2, 2-dimethylolpentanoic acid, 2, 2-dimethylolhexanoic acid, 2, 2-dimethyloloctanoic acid, di (hydroxyethyl) acetic acid, di (hydroxyethyl) propionic acid, di (hydroxyethyl) butanoic acid, di (hydroxypropyl) acetic acid, di (hydroxypropyl) propionic acid, di (hydroxypropyl) butanoic acid; salts of the aforementioned acids; and, polyols containing sulfonate groups, such as the propoxylated adduct of sodium hydrogen sulfite and 2-butenediol or the polyesters synthesized from salts of sulfoisophthalic acid.

As noted above, the reactants for the derivation of second polyurethane polymer (SPU) polymers may optionally include siii) further active hydrogen compounds not corresponding to the aforementioned polyols (si) , sii) . Such further active hydrogen compounds may be classified as for instance: chain extending compounds which possess at least two active hydrogen atoms and of which examples include polyamines and polyols; and, chain terminating compounds which possess one active hydrogen atom of which examples include monoalcohols and monoamines.

As noted above, the reactants for the derivation of the second polyurethane polymer (s) (SPU) include: siv) at least one polyisocyanate compound. As used herein "polyisocyanate compound" means a compound comprising at least two -N=C=O functional groups. The polyisocyanates suitable for the derivation of the (hydroxyl functional) thermoplastic polyurethane means a compound comprising at least two -N=C=O functional groups, for example from 2 to 5 or from 2 to 4 -N=C=O functional groups. Suitable polyisocyanates include aliphatic, cycloaliphatic, aromatic and heterocyclic isocyanates, dimers and trimers thereof, and mixtures thereof.

As described above, the constituent a2) said at least one second polyurethane polymer (SPU) may be added to the composition (a) as a dispersion in water. In the alternative, at least a part of constituent a1) may be added in solid form, which solid form may be derived from an aqueous suspension of the second polyurethane polymer (s) (SPU) . Any removal of water from such an aqueous suspension, by evaporation for instance, should not trigger the chemical reaction or decomposition of said second polyurethane polymer (s) (SPU) .

To facilitate its inclusion in the compositions of the present disclosure, the or each second polyurethane polymer (SPU) may have a particulate form exemplified by a particle size distribution having a mean volume particle size (d_v50) of less than 1 micron, for instance of from 50 to 400 nm, as measured by laser diffraction.

For completeness, the second polyurethane polymer (SPU) of the present disclosure can be derived from one or more commercially available aqueous polyurethane dispersions, examples of which include: Adwel 1676, Adwel 1665A, Adwel 1663, Adwel 1630C, available from Wanhua Chemistry; ESACOTE PU 6419 and ESACOTEPU A32D, available from Lamberti; NH-102U, available from Sam Myung Bio Chem Co., Ltd; ESACOTEPU A32D, available from DSM; and, DISPERCOLL U XP 2682, DISPERCOLL U XP 2612, DISPERCOLL U XP 2643, DISPERCOLL U XP 2849, DISPERCOLL U 2824 XP, DISPERCOLL U 53, DISPERCOLL U 56, available from COVESTRO.

(b3) Polyisocyanate

According to the present disclosure, the water-borne, heat-activatable adhesive composition (b) comprises: b3) at least one surface-deactivated solid polyisocyanate compound.

The term “surface-deactivated” means that reactive -N=C=O groups on the particle surface are blocked with one or more blocking agents. The term “solid polyisocyanate” used herein means that the polyisocyanate is in solid form at room temperature. It is preferred that said solid polyisocyanate is in particulate form, desirably having an mean volume particle size (Dv50) , as determined by laser diffraction of from 0.001 to 100 μm, for example from 0.1 to 80 μm, from 1 to 50 μm or from 1 to 20 μm.

The substituent b3) is included in such an amount to satisfy the condition that the molar ratio of -N=C=O groups to hydroxyl groups in the composition (b) is from 0.1: 1 to 10: 1, for instance from 0.1 to 8: 1. The molar ratio of -N=C=O to hydroxyl groups may, for example, be from 0.5: 1 to 5: 1 or from 0.5: 1 to 3: 1. For surety, the term “-N=C=O groups” includes blocked -N=C=O groups which are therefore included in the molar ratio term.

Under the condition that the above molar ratio condition is satisfied, the weight percentage of substituent b3) said polyisocyanate compound (s) in the composition is not particularly limited. However, in certain embodiments, the water-borne, heat-activatable adhesive composition (b) may comprise, based on the total weight of said composition (b) , from 0.05 to 10 wt. %, for example from 0.5 to 5 wt. %or from 1 to 5 wt. %of b3) said at least one surface-deactivated solid polyisocyanate compound.

The surface-deactivated solid polyisocyanate can be prepared according to known methods in the art. Instructive methods are described in US Patent No. 6,348,548 B1 and US Patent Application Publication No. 2003/0119976A1, the disclosures of which are incorporated herein by its entirety. Without intention to limit the present disclosure, the surface-deactivated solid polyisocyanate is obtainable from a precursor solid polyisocyanate by: dispersing said solid polyisocyanate in a solution of blocking agent; or, adding blocking agent or a solution thereof to said solid polyisocyanate and forming a dispersion from this admixture.

Typically the blocking agent may be chosen from: primary and secondary aliphatic amines, diamines or polyamines; hydrazine derivatives; amidines; guanidines; and, mixtures thereof. Exemplary blocking agents, which may be used alone or in combination, include: ethylene diamine; 1, 3-propylene-diamine; diethylene triamine; triethylene tetramine; 2, 5-dimethyl-piperazine; 3, 3'-dimethyl-4, 4'-diamino dicyloheyl methane; methyl nonane-diamine; isophorone diamine; 4, 4'-diaminodicyclohexyl methane; diamino and triamino polypropylene ether; and, polyamido amine.

Suitable precursor polyisocyanate compounds, to be deactivated, should be solid at room temperature and possess active -N=C=O functional groups on their surface which can react with active hydrogen groups to form crosslinking linkages. The precursor polyisocyanate compounds may comprise from 2 to 5 or from 2 to 4 -N=C=O functional groups. In an alternative expression, which is not mutually exclusive of the -N=C=O functionality, the precursor polyisocyanate compound may be characterized by an -N=C=O content of from 15 to 40 wt. %, for example from 20 to 35 wt. %, based on the weight of said polyisocyanate and as determined according to the testing method of M105-ISO 11909.

Typically said precursor polyisocyanates should have a melting point of at least 40℃, for instance at least 50℃, at least 60℃ or at least 70℃. Such precursor polyisocyanates may be aliphatic, cycloaliphatic, aromatic and heterocyclic polyisocyanate compounds, dimers and trimers thereof, and mixtures thereof. Specific examples thereof include, but are not limited to: diphenyl methane-4, 4'-diisocyanate (4, 4'-MDI) ; dimeric 4, 4'-MDI; napthalene-1, 5-diisocyanate (NDI) ; 1, 4-phenylene diisocyanate; toluene-2, 4-diisocyanate (2, 4-TDI) ; 3, 3'-dimeythyl-biphenyl-4, 4'-diisocyanate (TODI) ; dimeric 1-methyl-2, 4-phenyl-4, 4'-diisocyanate (dimer of 2, 4-TDI) ; 3, 3'-diisocyanate-4, 4'-dimethyl-N, N'-diphenyl urea (TDIH) ; isophorone diisocyanate (IPDI) ; the isocyanurate of isophorone diisoccyanate (trimer of IPDI) ; or, mixtures thereof.

In certain embodiments, precursor polyisocyanate compound, to be deactivated, may comprise or consist of at least one aromatic polyisocyanate compound having at least two isocyanate groups and at least one uretdione group. Exemplary polyisocyanate (s) of this type may correspond to the following formula (I) :

Specific examples of the polyisocyanate (s) in accordance with Formula (I) which can be used according to the disclosure may correspond to Formula (I-1) or Formula (I-2) :

For completeness, suitable commercially available polyisocyanates having utility in or as substituent a3) include: MDI uretdione, available as Grilbond^TM A2bond from EMS-Griltech; and, TDI uretdione, available as Addolink^TM TT from Rhein Chemie or asBL XP2514 available from Covestro; CARMOT BL-1045 CARMOT BL-1041 and CARMOT BL-1042 available from OSIC; and, T9 SuperFine available from TSE.

As described above, the constituent b3) said at least one surface-deactivated solid polyisocyanate compound may be added to the composition (b) as a dispersion in water. In the alternative, this constituent may be added in solid form, which solid form may be derived from an aqueous suspension of the surface-deactivated solid polyisocyanate (s) . Any removal of water from such an aqueous suspension, by evaporation for instance, should not trigger the reaction or decomposition of the surface-deactivated solid polyisocyanate (s) .

b4) Non-Polymerizable Electrolyte

The water-borne heat-activatable adhesive composition (b) comprises: a4) non-polymerizable electrolyte. The term “non-polymerizable” is intended to indicate that the electrolyte, whilst present in the composition, is not incorporated in an amount that can be measured into the polymeric matrix formed from reactive components b1) , b2) and b3) . The non-polymerizable electrolyte contains no functional groups which are reactive with said substituents.

The water-borne, heat-activatable adhesive composition (b) may comprise, has on the weight of said composition (b) , from 0.5 to 15 wt. %of b4) said non-polymerizable electrolyte. The electrolyte b4) may preferably constitute from 0.5 to 10 wt. %, for example from 0.5 to 5 wt. %, of said composition. These quantities are preferred because a quantity greater than 15 wt. %of electrolyte, based on the weight of said composition (b) , may result in a good debonding effect but cure may be incomplete and /or initial adhesive properties may be adversely affected. Conversely, at amounts less than 0.5 wt. %, based on the weight of said composition, the debonding effect may be compromised.

Important electrolytes include the non-polymerizable salts of: ammonium; pyridinium; pyrrolidinium; phosphonium; imidazolium; oxazolium; guanidinium; sulfonium; and, thiazolium. The salts described in section a4) above with respect to the solvent-borne composition (a) , including all statements of preference, are applicable to substituent b4) of the water-borne composition. In the interests of brevity, such discussion will not be repeated at this juncture.

b5) Rheology Control Agent

The water-borne, heat-activatable adhesive composition (b) of the present disclosure may optionally comprise: b5) a rheology control agent comprising electrically non-conductive fillers, electrically conductive fillers or mixtures thereof.

The desired viscosity of the composition (b) -formed upon mixing its substituents -will generally be determinative of the total amount of rheology control agent added. However, the total amount of rheology control agent present in the water-borne, heat-activatable adhesive composition (b) may typically be from 0 to 10 wt. %, such as from 0.1 to 5 wt. %or from 0.5 to 5 wt. %, based on the total weight of the composition.

The elements and compounds and the morphologies of such elements and compounds which described in section a5) above with respect to the solvent-borne composition (a) , including all statements of preference, are applicable to substituent b5) of the water-borne composition. In the interests of brevity, such discussion will not be repeated at this juncture.

Common Additives and Adjunct Materials of the Heat-Activatable Compositions (a, b)

The solvent-borne compositions (a) and the water-borne compositions (b) of the present disclosure will each typically further comprise adjuvants and additives that can impart improved properties to these compositions. For instance, the adjuvants and additives may impart one or more of: improved elastic properties; improved elastic recovery; longer enabled processing time; faster curing time; and, lower residual tack. Included among such adjuvants and additives are: solubilizers; catalysts; tougheners; plasticizers; stabilizers including UV stabilizers; antioxidants; reactive diluents; drying agents; adhesion promoters; wetting agents; defoaming agents; fungicides; flame retardants; color pigments or color pastes; and/or optionally also, to a small extent, non-reactive diluents.

Such adjuvants and additives can be used in such combination and proportions as desired, provided they do not adversely affect the nature and essential properties of the composition, of the curable adhesive film obtained by drying said composition and of the final cured adhesive film. While exceptions may exist in some cases, these adjuvants and additives should not in toto comprise more than 20 wt. %of the total composition and preferably should not comprise more than 10 wt. %of the composition.

Based on the weight of the composition (a, b) , solubilizer may constitute from 0 to 15 wt. %, for example from 0 to 10 wt. %or from 1 to 5 wt. %. The solubilizer has the function of promoting the miscibility of the electrolyte within the composition: the solubilizer may or may not form part of the polymer matrix formed upon curing of the composition but does serve to facilitate ion transfer therein. The solubilizer is, as such, preferably a polar compound and should desirably be liquid at room temperature.

Suitable classes of solubilizer include: polyphosphazenes; polymethylenesulfides; polyoxyalkylene glycols; polyethylene imines; silicone surfactants, such as polyalkylsiloxane and polyoxyalkylene modified polydimethylsiloxanes including but not limited to poly (C₂-C₃) oxyalkylene modified polydimethylsiloxanes; polpolyhydric alcohols; and, sugars. For completeness, fluorinated silicone surfactants, such as fluorinated polysilanes, are intended to be encompassed within the term silicone surfactants.

Polyhydric alcohols and sugars include but are not limited to such as ethylene glycol, 1, 3-propanediol, cyclohexandiol, hydroquinone, catechol, resorcinol, phloroglucinol, pyrogallol, hydroxyhydroquinone, tris (hydroxymethyl) benzene, tris (hydroxymethyl) benzene with three methyl or ethyl substituents bonded to the remaining benzene carbon atoms, isosorbide, isomannide, isoidide, glycerol, cyclohexane-1, 2, 4-triol, 1, 3, 5-cyclohexanetriol, pentane-1, 2, 3-triol, hexane-1, 3, 5-triol, erythritol, 1, 2, 4, 5-tetrahydroxybenzene, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, inositol, fructose, glucose, mannose, lactose, 1, 1, 1-tris (hydroxymethyl) propane, 1, 1, 1-tris (hydroxymethyl) ethane, di (trimethylolpropane) , trimethylolpropane ethoxylate, 2-hydroxymethyl-1, 3-propanediol, pentaerythritol allyl ether and pentaerythritol.

Of the polyoxyalkylene glycols, a particular preference for the use of polyoxy (C₂-C₃) alkylene glycols having a weight average molecular weight of from 200 to 10000 g/mol, for example 200 to 2000 g/mol, may be noted.

The composition (a, b) may, in certain circumstances, comprise a catalyst. For example, the composition may comprise from 0 to 2 wt. %, for instance from 0.1 to 1.0 wt. %of catalyst, based on the total weight of the composition.

Any catalyst conventionally used to promote the reaction between isocyanate groups and active hydrogen groups may have utility in the present composition. Exemplary catalytic compounds, which may be used alone or in combination, include: stannous salts of carboxylic acids, such as stannous octoate, stannous oleate, stannous acetate and stannous laureate; dialkyltin dicarboxylates, such as dibutyltin dilaureate and dibutyltin diacetate; tertiary amines; alkanolamine compounds; 2, 3-dimethyl-3, 4, 5, 6-tetrahydropyrimidine; tetraalkylammonium hydroxides; alkali metal hydroxides; alkali metal alcoholates; tin alkoxides, such as dibutyltin dimethoxide, dibutyltin diphenoxide and dibutyltin diisoproxide; tin oxides, such as dibutyltin oxide and dioctyltin oxide; the reaction products of dibutyltin oxides and phthalic acid esters; tin mercaptides; alkyl titanates; organoaluminum compounds such as aluminum trisacetylacetonate, aluminum trisethylacetoacetate and diisopropoxyaluminum ethylacetoacetate; chelate compounds such as zirconium tetraacetylacetonate and titanium tetraacetylacetonate; organosilicon titanium compounds; bismuth tris-2-ethylhexanoate; acid compounds such as phosphoric acid and p-toluenesulfonic acid; triphenylborane; triphenylphosphine; 1, 8-diazabicycloundec-7-ene (DBU) ; 1, 5-diazabicyclo [4.3.0] non-5-ene; 1, 4-diazabicyclo [2.2.2] octane; 4-dimethylaminopyridine; 1, 5, 7-triazabicyclo [4.4.0] dec-5-ene; 7-methyl-1, 5, 7-triazabicyclo [4.4.0] dec-5-ene; and, 1, 8-bis (tetramethylguanidino) naphthalene; and, 2-tert-butyl-1, 1, 3, 3-tetramethylguanidine.

The optional presence of tougheners -in an amount up to 10 wt. %, based on the weight of the composition (a, b) -can in certain embodiments be advantageous to the debonding of the cured adhesive. Without intention to be bound by theory, tougheners may facilitate phase separation within the cured adhesive under the application of electrical potential. Exemplary tougheners may be selected from: amine functionalized tougheners; C=C double-bond functionalized rubber; and, toughening rubber in the form of core-shell particles.

A "plasticizer" for the purposes of this invention is a substance that decreases the viscosity of the composition and thus facilitates its processability. Herein the plasticizer may constitute up to 10 wt. %or up to 5 wt. %, based on the total weight of the composition (a, b) , and is preferably selected from the group consisting of: diurethanes; ethers of monofunctional, linear or branched C₄-C₁₆ alcohols, such as Cetiol OE (obtainable from Cognis Deutschland GmbH, Düsseldorf) ; esters of abietic acid, butyric acid, thiobutyric acid, acetic acid, propionic acid esters and citric acid; esters based on nitrocellulose and polyvinyl acetate; fatty acid esters; dicarboxylic acid esters; esters of OH-group-carrying or epoxidized fatty acids; glycolic acid esters; benzoic acid esters; phosphoric acid esters; sulfonic acid esters; trimellitic acid esters; polyether plasticizers, such as end-capped polyethylene or polypropylene glycols; polystyrene; hydrocarbon plasticizers; chlorinated paraffin; and, mixtures thereof. It is noted that, in principle, phthalic acid esters can be used as the plasticizer but these are not preferred due to their toxicological potential.

"Stabilizers" for purposes of this invention are to be understood as antioxidants, UV stabilizers, thermal stabilizers or hydrolysis stabilizers. Herein stabilizers may constitute in toto up to 10 wt. %or up to 5 wt. %, based on the total weight of the composition (a, b) . Standard commercial examples of stabilizers suitable for use herein include: sterically hindered phenols; thioethers; benzotriazoles; benzophenones; benzoates; cyanoacrylates; acrylates; amines of the hindered amine light stabilizer (HALS) type; phosphorus; sulfur; and, mixtures thereof.

Exemplary adhesion promoters having utility in the present composition, either alone or in combination, include: γ-aminopropyltrimethoxysilane; γ-aminopropyltriethoxysilane; N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane; N- (β-aminoethyl) -γ-aminopropyltriethoxysilane; bis (γ-trimethoxysilylpropylamine) ; γ-ureidopropyltrimethoxysilane; 4-amino-3, 3-dimethylbutyltrimethoxysilane; 4-amino-3, 3-dimethylbutylmethyldimethoxysilane; N-ethyl-γ-aminoisobutyltrimethoxysilane; γ-methacryloxypropyltrimethoxysilane; γ-methacryloxypropyltriethoxysilane; γ-methacrylamidopropyltrimethoxysilane; and, γ-methacryloxypropyltriisopropoxysilane.

It is noted that compounds having metal chelating properties may be used in the compositions of the present disclosure to help enhance the adhesion of the cured adhesive to a substrate surface. Further, also suitable for use as adhesion promoters are the acetoacetate-functionalized modifying resins sold by King Industries under the trade name K-FLEX XM-B301.

In order to enhance shelf life even further, it is often advisable to further stabilize the compositions of the present disclosure with respect to moisture penetration through using drying agents. A need also occasionally exists to lower the viscosity of an adhesive or sealant composition according to the present invention for specific applications, by using reactive diluent (s) . The total amount of reactive diluents present will typically be from 0 to 15 wt. %, for example from 0 to 5 wt. %, based on the total weight of the composition (a, b) .

Formation of the Compositions (a, b) and of Curable Transfer Films Therefrom

To form the solvent-borne or water-borne compositions, the stated medium and the above-mentioned ingredients are brought together and mixed. It is important that the mixing homogenously distributes the electrolyte within the solvent-borne or water-borne composition: such thorough and effective mixing can be determinative of a homogeneous distribution of the charged species within the polymer matrix of the resultant curable film adhesive and thereby of the provision of sufficient ionic conductivity to support an electrochemical reaction at the interface with the electrically conductive substrate.

The substituents of the composition are brought together and homogeneously mixed under conditions which inhibit or prevent the reactive components from reacting: such conditions would be readily comprehended by the skilled artisan. As such, it will often be preferred that the curative substituents are not mixed by hand but are instead mixed by machine –a static or dynamic mixer, for example -in pre-determined amounts under anhydrous conditions without intentional photo-irradiation and under controlled external heating.

In an embodiment, each composition (a or b) is formed by a multi-stage mixing process comprising: a first stage in which solid substituents are mixed with, respectively, at least a fraction of the solvent (a6) or at least a fraction of the water to form a first stage mixture; and, ii) a second stage in which the first stage mixture is mixed with the remaining substituents of the composition.

It may also be desirable to admix the reactive polyisocyanate compounds (a3, b3) subsequent to the admixture of the other substituents of the compositions. The admixture of those other substituents might be performed at an elevated temperature to ensure sufficient dissolution or dispersion of the substituents: in this circumstance, the admixture should desirably be cooled to room temperature before addition of the reactive polyisocyanate substituent (a3, b3) .

To form curable films (103, 106) therefrom, the so-mixed compositions, which should desirably be bubble-free, are then applied to a surface –in particular the surface of the release liner or carrier of the article of manufacture discussed hereinabove -by conventional application methods such as: dispensing, including but not limited to automatic fine line dispensing or jet dispensing; pouring; brushing; roll coating; bar coating; knife coating; doctor-blade application; printing methods; and, spraying methods, including but not limited to air-atomized spray, air-assisted spray, airless spray and high-volume low-pressure spray.

In an exemplary embodiment, the so-admixed compositions are applied to the surface of a first release liner and either a further release liner or carrier then disposed on the applied composition: the wet film thickness of the interposed composition is then moderated by applying pressure to the obtained structure.

Independently of the method of application, it is recommended that the composition (a, b) be applied to a surface at a wet film thickness of from 15 to 1000 μm, such as from 50 to 750 μm or from 50 to 500 μm. The application of thinner layers within this range is more economical and provides for a reduced likelihood of deleterious thick cured regions in the films. However, great control must be exercised in applying thinner coatings or layers so as to avoid the formation of discontinuous cured films.

After application of the composition (a, b) , the solvent or water, as the case may be, is permitted to evaporate therefrom. Whilst this may be effected at room temperature, the drying may be accelerated by elevating the temperature of the coated substrate, for instance to a temperature of from 40 to 100℃ or from 40 to 80℃. Where applicable, the temperature of the substrate may be raised above the mixing temperature and /or the application temperature of the solvent-borne composition (a) using conventional means, including microwave induction, infrared irradiation, heating plates or by conveying the substrate to an oven.

After drying, the obtained heat-activatable adhesive transfer film (103) should comprise has less than 2.0 wt. %, for instance less than 0.5 wt. %or less than 0.1 wt. %of either solvent or water, based on the total weight of the heat-activatable adhesive film.

As mentioned above, given that the compositions (a, b) each comprise thermally latent hardener, care must be taken in the drying step not to elevate the temperature of the composition to the activation temperature of hardener. However, the present disclosure does not preclude the dried adhesive film obtained therefrom from being in a partially cured state. As used herein, the term "partially cured" means that curing of the composition (a, b) has been initiated and that, for example, cross-linking of ingredients of the composition has commenced but cross-linkable functional groups are pendant within the dried film: the film (103, 106) is not in a fully cross-linked state. Obviously, the rate and mechanism with which a given composition (a, b) cures is contingent on various factors, including the ingredients thereof, functional groups of the ingredients and the parameters of the curing condition.

At least partial solidification of a given composition (a, b) is generally indicative of drying or partial curing. However, both drying and partial cure may be indicated in other ways including, for instance, a viscosity change of the composition, an increased temperature of the composition and /or an opacity change of that composition.

The dried and, where applicable, partially cured composition (a, b) should substantially retain its shape on the application substrate –such as the release liner or carrier -upon exposure to ambient conditions. By "substantially retain its shape" is meant that at least 50%by volume, and more usually at least 80%or 90%by volume of the cast and dried composition retains its shape and does not flow or deform upon exposure to ambient conditions for a period of 5 minutes. Under such circumstances, gravity should not therefore substantially impact the shape of the dried and, where applicable, partially cured composition upon exposure to ambient conditions.

Manufacturing process parameters –including inter alia the particular composition (a, b) used, the applied wet-film thickness thereof and the operating conditions of the manufacturing equipment -can, of course, affect the degree of orientation and, as a result, the anisotropic, tack and peel force properties of the curable adhesive film (103, 106) obtained therefrom.

Multilayer Adhesive Films

As discussed above, the present disclosure also provides for a multi-layer adhesive transfer film (103) . With reference to Figure 11, the multi-layer adhesive film may comprise:

a first layer (1031) having a first major surface (1031f) and a second major surface (1031s) opposite the first major surface; and,

a second layer (1032) disposed on the first major surface (1031f) ;

wherein:

the first layer (1031) is a curable adhesive film prepared by drying a solvent-borne, heat activatable adhesive composition (a) as defined herein above; and, the second layer (1032) is a curable adhesive film prepared by drying a water-borne, heat-activatable composition (b) as defined herein above.

As depicted in Figure 12, the multi-layer adhesive film (103) may, in certain embodiments, further comprise a third layer (1033) in direct contact with the second major surface (1031s) of the layer (1031) , wherein the third layer is a curable adhesive film prepared by drying a water-borne, heat-activatable composition (b) as defined herein above. The third layer (1033) may have the same or different composition and the same of different morphology as the second layer (1032) . More particularly, where layers (1032, 1033) are present, the respective substituents b1) to b5) of the water borne compositions (b) from which the layers are obtained may be independently selected.

When peeling from a substrate, a mono-layer adhesive film (1031) derived from the solvent-based composition (a) may break multiple times, thus resulting in ineffective rework ability. Given that a second layer (1032) and, if present, a third layer (1033) -as derived from water-borne compositions (b) -may be highly resistant, said layer (s) can provide a reliable carrier for the first layer: the multi-layer adhesive film thereby realizes efficacious rework ability and also reinforces the impact resistance of the multi-layer adhesive film when cured.

In forming multi-layer films, each composition (a, b) should be independently cast. In a first illustrative embodiment, the method of forming a multilayer film may comprise the following steps:

i) applying the solvent-based heat-activatable adhesive composition (a) according to the invention onto a release liner;

ii) evaporating the solvent from said applied composition a) to form a first layer (1031) having a first major surface (1031f) and a second major surface (1031s) which is disposed opposite the first major surface and which is further disposed on said release liner;

iii) applying a water-borne composition (b) as defined above onto the first major surface (1031f) of said first layer (1031) ; and,

iv) heating the applied water-borne composition (b) to remove water therefrom and form a second layer (1032) .

In preferred embodiments, step ii) of this method is performed at a temperature of from 40℃ to 100℃, for instance from 40 to 80℃ or from 40 to 60℃. Independently of, or additional to this temperature condition, step ii) may be performed for a sufficient duration such that the first layer (1031) comprises less than 2.0 wt. %, for instance less than 0.5 wt. %or less than 0.1 wt. %of solvent, based on the total weight of the layer (1031) . The wet film thickness of the applied solvent-based heat-activatable adhesive composition a) may be one determinant of the required drying time.

It is also preferred that step iv) of this method is performed at a temperature of from 40℃ to 100℃, for instance from 40 to 80℃. Independently of, or additional to this temperature condition, step iv) may be performed for a sufficient duration such that the second layer (1032) comprises less than 2.0 wt.%, for instance less than 0.5 wt. %or less than 0.1 wt. %of water, based on the total weight of the layer (1032) . The wet film thickness of the applied dispersion composition (b¹) may be one determinant of the required drying time.

In some embodiments, the above method may further comprise the steps of:

v) removing the release liner from the second major surface (1031s) of the layer (1031) and applying a second water-borne composition (b) according to the invention onto said second major surface (1031s) ;

vi) heating the applied second water-borne composition (b) to remove water therefrom and form a third layer (1033) ; and, optionally

vii) applying a release liner on said second (1032) and said third (1033) layers’ open surfaces.

It is preferred that step vi) of this method is performed at a temperature of from 40℃ to 100℃, for instance from 40 to 80℃. Independently of, or additional to this temperature condition, step vi) may be performed for a sufficient duration such that the third layer (1033) comprises less than 2.0 wt. %, for instance less than 0.5 wt. %or less than 0.1 wt. %of water, based on the total weight of the layer (1033) . The wet film thickness of the applied second water-borne composition (b) may be one determinant of the required drying time.

In a second illustrative embodiment, the method of forming a multilayer film may comprise the following steps:

α) applying the solvent-based heat-activatable adhesive composition (a) according to the disclosure onto a first release liner;

β) evaporating the solvent from said applied composition a) to form a first layer (1031) having a first major surface (1031f) and a second major surface (1031s) which is disposed opposite the first major surface and which is further disposed on said first release liner;

γ) applying a first water-borne composition (b) according to the disclosure onto a second release liner;

δ) heating the applied first water-borne composition (b) to remove water therefrom and form a second layer (1032) having an open major surface and a further major surface which is disposed opposite said open major surface and which is further disposed on said second release liner; and,

ε) laminating the first major surface (1031f) of the first layer to said open major surface of said second layer (1032) .

The method of this embodiment may further comprise the steps of:

ζ) removing the first release liner from the second major surface (1031s) of said first layer (1031) ;

η) applying a second water-borne composition (b) according to the disclosure onto a third release liner;

θ) heating the applied second water-borne composition (b) to remove water therefrom and form a third layer (1033) having an open major surface and a further major surface which is disposed opposite said open major surface and which is further disposed on said third release liner; and,

ι) laminating the second major surface (1031s) of said first layer (1031) to said open major surface of said third layer (1033) .

The above-described preferred conditions for steps ii) , iv) and vi) of the first method may equally be applied to steps β) , δ) and θ) of this second method. It is further preferred that the or each lamination step (ε) , ι) ) is performed: at a temperature of 40 to 80℃; and /or, at an applied pressure of from 1 to 5 bars.

The following examples are illustrative of the present invention and are not intended to limit the scope of the invention in any way.

EXAMPLES

The following annotations are applied to compounds and materials employed in the Examples:

Dispercoll U42: Anionic polyurethane, dispersion in water available from Covestro.

Dispercoll U56: Anionic polyurethane polymer having a weight average molecular weight of about 73600 g/mol, dispersion in water (solids content: 50%) , available from Covestro.

WH6190A: Thermoplastic polyurethane, available from Wanhua Chemical Group.

FZPE-A03130: Polyester resin, available from FTRT Chemical.

Silquest A-189: γ-mercaptopropyltrimethoxysilane, available from Momentive.

BYK-028: Silicone defoamer, available from BYK.

BYK-349: Polyether modified siloxane, surfactant available from BYK.

PUR80: Thickener, available from Munzing Chemie.

BYK-141: Silicone defoamer, available from BYK.

BYK-3550: Wetting agent based on a silicone acrylate copolymer, available from BYK.

Vulcan PF: Carbon black, available from Cabot Corporation.

Addolink TT: Latent hardener based on dimeric toluene-2, 4-diisocyanate, available from Lanxess AG.

Dispercoll BL XP2514: Latent hardener based on dimeric toluene-2, 4-diisocyanate (NCO Content: 7.5-11 wt. %) , aqueous dispersion (solids content: 40%) , available from Covestro.

BMIM FSI: 1-butyl-3-methylimidazolium bis (fluorosulfonyl) imide, available from Lolitec.

Loctite ECI 1206 E&C: Hereinafter Ink C0: solvent based conductive ink comprising silver particles and epoxy resin, available from Henkel Corporation.

Loctite ECI 7007 E&C: Hereinafter Ink C1: solvent based conductive ink comprising carbon particles, available from Henkel Corporation.

Loctite ECI 1203 E&C: Hereinafter Ink C2: solvent based conductive ink comprising silver particles and epoxy resin, available from Henkel Corporation.

Loctite EDAG SP 413 E&C: Hereinafter Ink C3: solvent based conductive ink comprising silver particles and thermoplastic resin, available from Henkel Corporation.

Primer N: Hereinafter Ink C4: solvent based conductive ink comprising carbon particles, available from Henkel Corporation.

Loctite ECI 1216 E&C: Hereinafter Ink C5: solvent based conductive ink comprising silver particles and epoxy resin, available from Henkel Corporation.

Bonderite C-AD 27B Surface cleaning agent, available from Henkel Corporation.

Kalix: Lap shear substrate, available from Rocholl.

SUS316: Stainless steel lap shear panels, available from Alkemix Corporation.

Alu 6016: Aluminium lap shear panels, available from ACT Test Panels LLC.

Any remaining ingredients not mentioned above are obtainable from Sigma Aldrich.

PREPARATION EXAMPLE: FILM 1

A solvent-borne castable composition was prepared in accordance with Table 1 herein below, wherein the given percentage by weight is stated with respect to the composition in toto. All ingredients of the composition, with the exception of the latent hardener (Addolink TT) were first mixed to dissolve or otherwise homogenously disperse the ingredients in the solvent. The hardener was then added to the obtained mixture within two hours of the intended application or casting of the composition.

Table 1

The obtained composition was bar-coated onto several siliconized-PET liners. The solvent of the composition was permitted to evaporate at room temperature over a period of 24 hours to yield a dry-to-touch transfer curable film adhesive. The transfer film was thus removably disposed on the siliconized liners.

EXAMPLE 1

Ink Preparation

Ink formulation C0 was used in this Example.

Lap Shear Substrate Preparation

Formulation C0 was applied to lap shear substrates of glass by printing coating to a wet film thickness of 30 microns. The substrates were then placed in an oven set at 85℃ for 120 minutes. The substrates were removed from the oven and permitted to cool for 30 minutes: at that time, the dry film thickness of the dried ink film provided to each substrate was determined to be 10-15 μm.

Bonded Assembly Preparation

Bonded assemblies for lap shear testing were prepared using the ink coated glass substrates -as obtained above -which were bonded to stainless steel lap shear substrates (SUS316: Japanese JIS Standard, hereinafter SUS) . The bonded region of the assemblies possessed the configuration depicted in Figure 1a appended hereto. However, within the assembly, a fraction of the ink-coated glass substrate extended from the bonded region. Further, for each combination of ink, film and non-conductive substrate (glass) , five equivalent bonded assemblies were prepared.

To form a singular assembly Film 1, having a thickness of 80 microns, was transferred and applied to the surface of the stainless-steel lap shear substrate. The stainless-steel substrate (SUS) to which the film was thus applied was then mated with the coated glass substrate and clamped to apply pressure (0.4 MPa) thereto: the bond overlapping area for each stated assembly was 2.5 cm x 2.5 cm with a bond thickness of 80 microns. The bonded and clamped assembly was then subjected to a temperature of 70℃ for 10 minutes. The assembly was then declamped and held at room temperature for 24 hours.

Resistance measurements and lap shear strengths were then determined for each assembly, enabling mean values to be recorded for the given combination of ink and non-conductive substrate. Resistance Measurements

A two-point probe (RS Pro RS14 Handheld Multimeter) was employed for determining the resistance of each bonded assembly prior to the application of the potential difference for electrochemical debonding. A first probe was disposed on the external surface of the stainless steel (SUS) lap shear substrate and the second probe was disposed on the fraction of the dried ink film which extended outside of the bonded area. The polarity of the probes is stated in Table 2 below.

Tensile lap shear (TLS) Test

This test was performed at room temperature based upon ASTM D3163-01 Standard Test Method for Determining Strength of Adhesively Bonded Rigid Plastic Lap-Shear Joints in Shear by Tension Loading. For each bonded assembly, tensile lap shear strength was investigated after said 24-hour storage period both prior and subsequent to the application of a constant potential of 30V across the adhesive layer for 20 minutes. Where applicable, the substrate which provides the negative pole has been indicated.

The results of the above-described tests are indicated in Table 2 herein below. The uncertainty of a mean value is provided in parentheses, where applicable. The term primary substrate in Table 2 refers to the substrate to which the conductive ink is applied.

Table 2

PREPARATION EXAMPLE 2: FILM 2

A water-borne castable composition was prepared in accordance with Table 3 herein below, wherein the given percentage by weight is stated with respect to the composition in toto. All ingredients of the composition, with the exception of the latent hardener (Carmot BL-1045) were first mixed to homogenously disperse the ingredients in the solvent. The hardener was then added to the obtained mixture within two hours of the intended application or casting of the composition.

Table 3

The obtained composition was bar-coated onto several siliconized-PET liners. The water of the composition was permitted to evaporate at room temperature over a period of 24 hours to yield a dry-to-touch transfer curable film adhesive. The transfer film was thus removably disposed on the siliconized liners.

EXAMPLE 2

Ink Preparation

Ink formulations C1 to C5 were used in this Example.

Lap Shear Substrate Preparation

Formulations C1-C5 were independently applied to lap shear substrates of Kalix by bar coating to a wet film thickness of 30 microns. The substrates were then placed in an oven set at 85℃ for 120 minutes. The substrates were removed from the oven and permitted to cool for 30 minutes: at that time, the dry film thickness of the dried ink film provided to each substrate was determined to be 10-15 μm, as indicated below.

Bonded Assembly Preparation

Bonded assemblies for lap shear testing were prepared using the ink coated Kalix substrates -as obtained above -which were bonded either to stainless steel lap shear substrates (SUS316: Japanese JIS Standard, hereinafter SUS) or to Aluminium lap shear substrates (Alu 6016) . The bonded region of the assemblies possessed the configuration depicted in Figure 1 a appended hereto. However, within each assembly, a fraction of the ink-coated Kalix substrate extended from the bonded region. Further, for each combination of ink, film, conductive substrate and non-conductive substrate (Kalix) , three equivalent bonded assemblies were prepared.

Films 2 having a thickness of from 130 to 150 microns were independently transferred and applied to the surface of each stainless-steel or aluminium lap shear substrate: the stainless-steel (SUS) or aluminium (Alu 6016) substrates to which the films were thus applied were then respectively mated with the coated Kalix substrate and clamped to apply pressure (0.4 MPa) thereto. The bond overlapping area for each stated assembly was 2.5 cm x 2.5 cm with a bond thickness of 80 microns.

The bonded and clamped assemblies were subjected to temperature of 80℃ for 30 minutes prior to being held at room temperature for 24 hours. Resistance measurements and lap shear strengths were then determined for each assembly, enabling mean values to be recorded for a given combination of ink and non-conductive substrate.

Resistance Measurements

A two-point probe (RS Pro RS14 Handheld Multimeter) was employed for determining the resistance of each bonded assembly prior to the application of the potential difference for electrochemical debonding. A first probe was disposed on the external surface of the stainless steel (SUS) or aluminium (Alu 6016) lap shear substrate and the second probe was disposed on the fraction of the dried ink film which extended outside of the bonded area. The polarity of the probes is stated in Table 4 below.

Tensile lap shear (TLS) Test

Push Out Strength

Where noted in Table 4 below, a test of push-out strength was performed at 23±2 ℃ and 50%±5%relative humidity using a universal testing machine equipped with a punch. The punch applied a compressing force onto the metal substrate of the bonded test assembly at a pushing speed of 10mm/min until the assembly could no longer support the load. The maximum load was recorded in Table 4, and the push-out strength (MPa) was calculated by dividing the total load by the bonding area.

The results of the above-described tests are indicated in Table 4 herein below. The uncertainty deviation of a mean value is provided in parentheses, where applicable. The term primary substrate in Table 4 refers to the substrate to which the conductive ink is applied, where applicable.

Table 4

Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.

Claims

A bonded structure comprising:

a first substrate provided with a first electrically conductive surface;

a second substrate provided with a second electrically conductive surface; and,

a cured, electrochemically debondable adhesive film interposed between said first and second electrically conductive surfaces, said electrochemically debondable adhesive film having one or more constituent layers, wherein at least one layer of the cured adhesive film comprises a non-polymerizable electrolyte and at least one polyurethane polymer;

wherein at least one of said first and second electrically conductive surfaces is provided by a ink film which is obtained by the evaporative removal of solvent from an ink composition, said ink film comprising: a matrix of a polymeric resin (F^R) ; and, electrically conductive particles.
The bonded structure according to claim 1, wherein said first substrate possesses bulk electrical non-conductivity and further wherein the first electrically conductive surface is provided by a first dried ink film comprising: a) a matrix of polymeric resin (F^R) ; and, electrically conductive particles.
The bonded structure according to claim 2, wherein said first dried ink film providing the first electrically conductive surface is disposed on and in direct contact with said first substrate.
The bonded structure according to claim 2 or claim 3, wherein said second substrate possesses bulk electrical non-conductivity and further wherein the second electrically conductive surface is provided by a second dried ink film comprising: a matrix of polymeric resin (F^R) ; and, electrically conductive particles.
The bonded structure according to claim 4, wherein said second dried ink film providing the second electrically conductive surface is disposed on and in direct contact with said second substrate.
The bonded structure according to any one of claims 1 to 5, wherein the polymeric resin (F^R) of said dried ink film is chosen from: nitrocellulose; epoxy resins; phenolic resins; and, mixtures thereof.
The bonded structure according to any of claim 1 to 6, wherein the electrically conductive particles of said dried ink film are chosen from: carbon black; graphite; carbon nanotubes; carbon fibers; silver; silver coated copper; silver coated graphite; silver coated polymers; silver coated aluminium; silver coated glass; and, mixtures thereof.
The bonded structure according to any one of claims 1 to 7, wherein said electrolyte of the electrochemically debondable adhesive film comprises at least one non-polymerizable salt chosen from: ammonium salts; pyridinium salts; pyrrolidinium salts; phosphonium salts; imidazolium salts; oxazolium salts; guanidinium salts; sulfonium salts; sulfonium salts; sulfonium salts; thiazolium salts; and, mixtures thereof.
The bonded structure according to any one of claims 1 to 10, wherein said non-polymerizable electrolyte of the electrochemically debondable adhesive film is chosen from: trihexyl (tetradecyl) phosphonium bis (trifluoromethylsulfonyl) imide, tributylmethylphosphonium bis (fluorosulfonyl) imide, tributylmethyl-phosphonium methyl sulfate, tributylmethylammonium bis (fluorosulfonyl) imide, N-propyl-N-methylpyrrolidinium bis (fluorosulfonyl) imide, 1-ethyl-3-methyl-1 H-imidazol-3-um methyl sulfate, 1-ethyl-3-methyl-1 H-imidazol-3-um methanesulfonate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-butyl-3-methylimidazolium methyl sulfate, 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methyl-imidazolium-fluorosulfonate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-butyl-3-methylimidazolium bis (fluorosulfonyl) imide; 1-dodecyl-3-methylimidazolium bis (fluorosulfonyl) imide; and, mixtures thereof.
The bonded structure according to any one of claims 1 to 9, wherein said electrochemically debondable adhesive film has one or more constituent layers, wherein at least one layer of the electrochemically debondable adhesive film consists of a film (F^a) obtained by:

drying a solvent-borne composition (a) to obtain a curable film therefrom, said solvent-borne composition (a) comprising:

a1) at least one thermoplastic polyurethane polymer;

a2) at least one polyester polyol;

a3) at least one polyisocyanate compound having at least two isocyanate groups and at least one uretdione group;

a4) non-polymerizable electrolyte;

optionally a5) rheology control agent comprising electrically non-

conductive fillers, electrically conductive fillers or mixtures thereof; and,

a6) at least one organic solvent,

wherein the molar ratio of -N=C=O groups to hydroxyl groups in the composition (a) is from 0.1: 1 to 10: 1;

transferring said curable film to interpose it between said first and second electrically conductive surfaces; and,

curing the transferred film by heating said film.
The bonded structure according to claim 10, wherein the solvent-borne composition (a) comprises, based on the total weight of said composition (a) :

from 5 to 50 wt. %of a1) said at least one thermoplastic polyurethane polymer;

from 0.1 to 30 wt. %of a2) said at least one polyester polyol;

from 0.05 to 10 wt. %of a3) said at least one polyisocyanate compound having at least two isocyanate groups and at least one uretdione group;

from 0.5 to 15 wt. %of a4) said non-polymerizable electrolyte;

optionally from 0.1 to 10 wt. %of a5) said rheology control agent; and,

from 30 to 90 wt. %of (a6) said at least one solvent,

wherein the molar ratio of -N=C=O groups to hydroxyl groups in the composition (a) is from 0.5: 1 to 5: 1, preferably from 0.5 to 3: 1.
The bonded structure according to claim 10 or claim 11, wherein the or each thermoplastic polyurethane polymer of substituent a1) is characterized by:

a weight-average molecular weight (Mw) of from 10,000 to 200,000 g/mol; and /or,

an optimum activation temperature of from 30 to 100℃., as determined according to EN 12961: 2001.
The bonded structure according to any one of claims 10 to 12, wherein the or each polyester polyol of substituent a2) is characterized by a hydroxyl functionality of from 2 to 6 and a hydroxyl number of from 10 to 150 mg KOH/g.
The bonded structure according to any one of claims 10 to 13, wherein substituent a2) comprises at least one polyester polyol chosen from amorphous polyester polyols, semi-crystalline polyester polyols and mixtures thereof.
The bonded structure according to any one of claims 10 to 14, wherein substituent a3) comprises or consists of at least one aromatic polyisocyanate compound having at least two isocyanate groups and at least one uretdione group.
The bonded structure according to any one of claims 10 to 15, wherein the or each polyisocyanate compound of a3) is characterized by an -N=C=O content of from 15 to 40 wt.%, based on the weight of said polyisocyanate and as determined according to the testing method of M105-ISO 11909.
The bonded structure according to any one of claims 1 to 16, wherein said electrochemically debondable adhesive film has one or more constituent layers, wherein at least one layer of the electrochemically debondable adhesive film consists of a film (F^b) obtained by:

drying a water-borne composition (b) to obtain a curable film therefrom, said water-borne composition (b) comprising:

water;

b1) at least one first polyurethane polymer having at least one active hydrogen group, wherein said first polyurethane polymer is obtained by the reaction of at least one polyisocyanate compound with at least one polyol (POHA) which has a number average molecular weight (Mn) of at least 500 g/mol. and which further has one or more structural units chosen from structural units of Formula (I) , Formula (II) , Formula (III) or combinations thereof:
-CH (OH) -CH₂-X¹-Y    (I)
-CH (OH) -CH₂-X²-CH₂-CH (OH) -   (II)
-CH (OH) -CH₂-X¹-Y¹-X³-CH₂-CH (OH) -    (III)

wherein: X¹ represents -OC (=O) -, -S-, -NR¹-, -OP (=O) (OR¹) -O-, -OP (=O) (R¹) -O-, -OP (=O) (R¹) -, -O-P (OR¹) -O-, -O-P (R¹) -O-or -O-P (R¹) -;

X² represents -NR¹-, -OP (=O) (OR¹) -O-, -OP (=O) (R¹) -O-, -O-P (OR¹) -O-or -O-P (R¹) -O-;

X³ represents -C (=O) O-, -S-, -NR¹-, -OP (=O) (OR¹) -O-, -OP (=O) (R¹) -O-, -P (=O) (R¹) -O-, -O-P (OR¹) -O-, -O-P (R¹) -O-; -P (R¹) -O-;

in which groups each R¹ independently represents H or a C₁-C₂₀ organic group;

Y is H or a C₁-C₃₀ monovalent organic group or H; and,

Y¹ is a C₁-C₃₀ divalent organic group, with a proviso that Y¹ is not -CH₂-CH (OH) -.

b2) at least one second polyurethane polymer which is distinct from said first polyurethane polymer, said second polyurethane polymer having at least one isocyanate reactive functional group;

b3) at least one surface-deactivated solid polyisocyanate compound;

b4) non-polymerizable electrolyte; and,

optionally b5) rheology control agent comprising electrically non-conductive fillers, electrically conductive fillers or mixtures thereof,

wherein the molar ratio of -N=C=O groups to active hydrogen atoms in the composition (a) is from 0.1: 1 to 10: 1;

transferring said curable film to interpose it between said first and second electrically conductive surfaces; and,

curing the transferred film by heating said film.
The bonded structure according to claim 17, wherein the water-borne composition (b) comprises, based on the total weight of said composition (b) :

water;

from 20 to 50 wt. %of a1) said at least one first polyurethane polymer;

from 30 to 60 wt. %of a2) said at least one second polyurethane polymer;

from 0.05 to 10 wt. %of a3) said at least one surface-deactivated solid polyisocyanate compound;

from 0.5 to 15 wt. %of a4) said non-polymerizable electrolyte; and,

from 0 to 10 wt. %of a5) said rheology control agent,

wherein the molar ratio of -N=C=O groups to active hydrogen atoms in the composition (a)

is from 0.5: 1 to 5: 1, preferably from 0.5 to 3: 1.
The bonded structure according to claim 17 or claim 18, wherein said polyol (POHA) has from 1 to 10, preferably from 1 to 5 structural units chosen from structural units of Formula (I) , Formula (II) , Formula (III) or combinations thereof.
The bonded structure according to any one of claims 17 to 19, wherein structural units of Formula (I) , Formula (II) or Formula (III) are chosen from:
-CH (OH) -CH₂-S-C₁-C₆alkylene-Si (O-C₁-C₆-alkyl) _n (C₁-C₆-alkyl) _3-n;
CH(OH) -CH₂-NR¹-C₁-C₆alkylene-NH₂;
-CH (OH) -CH₂-NR¹-C₁-C₆alkylene-NR¹-CH₂-CH (OH) -;
-CH (OH) -CH₂-O-P (=O) (OH) ₂;
-CH (OH) -CH₂-NR¹-CH₂-CH (OH) -;
-CH (OH) -CH₂-O-P (=O) (OH) -O-CH₂-CH (OH) -; or,

in which: n is 0, 1, 2 or 3; and,

each R¹ independently is H, C₁-C₆ alkyl or C₁-C₆ alkylene.
The bonded structure according to any one of claims 17 to 20, wherein said electrochemically debondable adhesive film has two or more constituent layers of which:

at least one layer consists of a film (F^a) ; and,

at least one layer consists of a film (F^b) .
The bonded structure according to any one of claims 1 to 21, wherein:

said first substrate is furnished by an electronic component and said first electrically conductive surface is provided on the exterior of said electronic component; and,

said second substrate is furnished by a frame disposed about the exterior of said electronic component,

wherein:

said frame comprises an integrant (I^F) of a material possessing a volume electrical conductivity of less than 1 Sm^-1 and having an outer surface and an inner surface;

and,

a dried ink film is disposed on the inner surface of said integrant (I^F) , the dried ink film providing said frame with the second electrically conductive surface of the structure.
A method of disbonding the bonded structure as defined in any one of claims 1 to 22, the method comprising the steps of:

i) applying a voltage across said first electrically conductive surface and said second electrically conductive surface to form an anodic interface and a cathodic interface;

and,

ii) disbonding said first and second substrates.
The method according to claim 23, wherein the applied voltage in step i) is from 0.5 to 200 V and said voltage is applied for a duration of from 1 second to 60 minutes.