HK1234768A - Dual crosslinked tackified pressure sensitive adhesive - Google Patents

Description

Dual-crosslinked tackified pressure sensitive adhesives

The application is a divisional application, the application date of the original application is 09/13 2010, the application number is 201080050913.4(PCT/US2010/048598), and the invention name is 'double-crosslinking tackifying pressure sensitive adhesive'.

Cross Reference to Related Applications

This application claims the benefit of U.S. provisional patent application No. 61/241,553, filed on 9, 11, 2009, which is hereby incorporated by reference in its entirety.

Technical Field

The present invention relates to pressure sensitive adhesives, and more particularly to acrylic-based pressure sensitive adhesives that are tackified after in-line (in-line) mixing with an aziridine crosslinking agent and tackified by dual cure (dual cured).

Background

The automotive, consumer appliance, consumer electronics, and other industries require adhesives with a combination of properties such as long term durability, resistance to sustained exposure to high temperatures, and good peel adhesion (peel adhesion) to a wide range of substrates such as metals, plastics, paints, and the like. Although rubber/resin based adhesives exhibit excellent peel adhesion to many substrates, they perform poorly at high temperatures. In contrast, acrylic-based adhesives have outstanding peel adhesion and poor high temperature performance, or have low peel adhesion and outstanding high temperature performance. What is desired is a durable adhesive with good peel adhesion to Low Surface Energy (LSE) substrates, high shear adhesive failure temperature, good stress relief properties, and excellent conversion properties.

It is known that if an acrylic pressure-sensitive adhesive is mixed with a low-molecular weight tackifying resin, the peel adhesion to various substrates is generally improved. For example, japanese patent 8569180 (assigned to Nitto) teaches the use of terpene phenol resins as tackifiers in photocurable pressure sensitive adhesives. The Japanese journal "Setchaku" (Vol.23, 489-504, 1984) describes the use of other types of resins, including rosin resins. The use of cyclohexene resins is described in DE 323122 (1983).

U.S. Pat. No. 4,418,120 to Kealy et al discloses crosslinked tackifying polymers based on isooctyl acrylate and 3% to 7% by weight acrylic acid. The polymer is stated to have an inherent viscosity of 0.75 to 1.5dl/g prior to curing. The cured product is stated to have a shear value (shear value) of at least 5,000 minutes at 70 ℃. The incorporation of low molecular weight resins into adhesive formulations typically results in adhesives with poor high temperature shear adhesion.

The choice of monomers comprising the copolymer and the type of cure employed also affect the durability, adhesion, and other properties of the pressure sensitive adhesive. Japanese patent No. 84-18774 discloses a radiation curable pressure sensitive composition containing a terpene phenol resin and a glycidyl methacrylate monomer. Curing is via carbon-carbon double bonds and is activated by radiation.

Melancon et al, U.S. patent No. 6893718B2, discloses PSA compositions comprising a bisamide crosslinker that provides high temperature resistance and adhesion, but these types of PSAs do not adhere well to low surface energy substrates such as polypropylene-based substrates. Likewise, Ames, U.S. patent No. 4,456,741, discloses hot melt acrylic adhesives comprising tackifiers having good peel adhesion and permanent tack back, but low shear adhesion.

U.S. Pat. No. 4,726,982 to Traynor et al discloses tackified acrylic-based pressure sensitive compositions containing N-vinyl-2-pyrrolidone and which are described as being beneficial in adhesion to high solids automotive paints.

U.S. patent No. 7,109,266 to Isiguro et al discloses an acrylic pressure sensitive adhesive composition containing an acrylic polymer and a tackifier obtained by acid-modifying a tackifier resin inherently free of an acid component, which results in a PSA composition having high initial adhesive strength.

U.S. patent No. 5,639,811 to platthottam et al teaches tackified pressure sensitive adhesives and tapes comprising copolymers based on an acrylic backbone, glycidyl monomers, unsaturated carboxylic acid monomers and preferably vinyl lactam monomers and tackifiers that are dual-cured and have outstanding peel adhesion and high temperature shear properties. However, the molecular weight is not high enough to pass the extreme high temperature shear requirements.

WO2008/116033 teaches a pressure sensitive adhesive formed from a mixture comprising: a) an acrylate polymer having a Tg of less than 20 ℃ and a molecular weight of greater than 20,000, b) an oligomer having at least one crosslinkable functional group, wherein the oligomer is liquid at room temperature, and c) at least one crosslinker, wherein at least one of a) and b) is crosslinked in the presence of the other.

U.S. patent 2005/0061435A 1 to Evererts et al discloses a latent over-tackified adhesive (latentover-blocked adhesive) that can be activated with a plasticizer to form a pressure sensitive adhesive when desired. The formulation uses an aziridine crosslinking agent, but does not enhance high temperature shear during product use.

Peloquin et al, U.S. patent 5,874,143, discloses the incorporation of plasticizer materials into tackified acrylic PSAs. The resulting PSAs have been shown to provide improved adhesion of marking films and labels to low energy surfaces such as high density polyethylene plastics.

Despite all attempts, PSAs having a combination of high peel adhesion to low surface energy substrates, high temperature shear, excellent stress relief properties, and excellent conversion properties are not available. For many industrial tape bonding applications with new materials, there is still a need for PSAs with a combination of properties such as high bond strength, adhesion to low surface energy substrates, and stress relief properties.

Disclosure of Invention

The present invention provides high molecular weight acrylic-based pressure sensitive adhesives in which pendant epoxy functional groups and pendant carboxylic acid functional groups are incorporated into an acrylic-based copolymer that, when combined with a tackifier in conjunction with an in-line mixed aziridine crosslinking agent, provides a dual cure adhesive with high bond strength, good adhesion to low surface energy substrates, and good stress relief properties.

The acrylic copolymer is based on a backbone of polymerized alkyl acrylate and/or alkyl methacrylate monomers and further includes a polymerized glycidyl monomer containing the desired epoxy functionality and a positive amount (positive amount) of an unsaturated carboxylic acid. The copolymer is combined with a tackifier along with an in-line mixed aziridine crosslinking agent to produce a "dual cure" tackified pressure sensitive adhesive. When the adhesive is initially (or first) cured by exposure to heat, the result is an adhesive that exhibits a good balance of excellent tack and peel properties, as well as high temperature shear. When the adhesive is subsequently exposed to high temperatures under service conditions (secondary curing), an intrinsic interaction occurs between adjacent copolymer chains. Without being bound by any particular theory, the epoxy moiety of the glycidyl monomer appears to interact with the carboxylic acid moiety, thereby completing the intrinsic secondary cure of the further crosslinked copolymer.

The adhesive of the present invention may further comprise other conventional adjuvants such as fillers, pigments, diluents and the like. The invention also provides for the use of the adhesive according to the invention, for example in transfer tapes (transfer tapes) and single-or double-sided tapes consisting of a core and at least one skin layer of the adhesive according to the invention. The adhesives and tapes of the invention exhibit good adhesion to a variety of substrates and can be used for structural bonding and other applications.

Detailed Description

The pressure sensitive adhesives of the present invention are prepared by combining certain high molecular weight acrylic-based copolymers ("copolymers") with tackifiers along with in-line mixed aziridines (aziridienes), and initially curing the combination by exposure to heat. Referred to herein as the first (or initial) cure.

Preparing a copolymer by copolymerizing a monomer mixture: the monomer mixture includes at least one monomer selected from the group consisting of alkyl acrylates and mixtures thereof; a glycidyl monomer selected from the group consisting of allyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, and mixtures thereof; and an unsaturated carboxylic acid.

Alkyl acrylates or methacrylates having less than four carbon atoms in the alkyl group can be incorporated into the copolymer if limited to amounts that do not result in a copolymer having a glass transition temperature below about-15 ℃.

The copolymers of the present invention typically comprise, on a copolymerized basis, from about 55% to about 85% by weight of an alkyl acrylate or methacrylate containing from 4 to about 12 carbon atoms in the alkyl group; 0 to about 35% by weight of an alkyl acrylate or methacrylate containing 1 to about 4 carbon atoms in the alkyl group, about 0.01% to about 2% by weight of a glycidyl monomer; and up to about 15% by weight, preferably from about 5% to about 13%, of a positive amount of an unsaturated carboxylic acid.

In one embodiment, the ratio of monomers is selected to give a polymer with a glass transition temperature of less than about-15 ℃. The uncured copolymers of the present invention have a weight average molecular weight of at least about 200,000, preferably from about 200,000 to about 1,000,000 as determined by size exclusion chromatography using polystyrene calibration.

Examples of alkyl acrylates or methacrylates having from 4 to about 12 carbon atoms in the alkyl group include, but are not limited to, 2-ethylhexyl acrylate, isooctyl acrylate, butyl acrylate, sec-butyl acrylate, methylbutyl acrylate, 4-methyl-2-pentyl acrylate, isodecyl methacrylate, methyl acrylate, ethyl acrylate, methyl methacrylate, and the like, and mixtures thereof.

Examples of unsaturated carboxylic acids useful in the present invention include, but are not limited to, acrylic acid, methacrylic acid, fumaric acid, and the like, as well as mixtures thereof.

As described below, the copolymer may also include from 0 to about 30% by weight, preferably from about 0.01% to about 1% by weight, of an activator moiety monomer, the presence of which in the copolymer lowers the temperature at which the adhesive undergoes an internal high temperature post cure, typically under conditions of use.

Copolymers can be synthesized using solution, emulsion, and batch polymerization techniques. According to one embodiment of the invention, the copolymer is prepared in solution using a mixture of solvents. Solution polymerization involves the use of a mixture of ethyl acetate and acetone. The ratio of solvents is adjusted to provide a reflux temperature of about 68 ℃ to about 78 ℃. To achieve the desired weight average molecular weight, and still achieve a manageable viscosity in the reactor, the solids content during polymerization can typically be in the range of about 40% to about 60%. The reaction takes place in the presence of a free radical initiator, preferably of azo type, for example 2, 2' -azo-diisobutyronitrile. Further, the reactor may be purged with nitrogen, which may produce a polymer having a molecular weight typically above 500,000.

Tackifier

Once the copolymer has been prepared, the pressure sensitive adhesive is formulated by combining the copolymer with a tackifier. Various tackifiers may be used to enhance the tack and peel of the adhesive. Such tackifiers include, but are not limited to, rosins and rosin derivatives including rosin materials naturally occurring in the oleoresin of pine trees, as well as derivatives thereof including rosin esters, modified rosins such as fractionated, hydrogenated, dehydrogenated, and polymerized rosins, modified rosin esters, and the like.

A variety of such tackifiers are commercially available, including but not limited to those manufactured and sold by Hercules corporation(glycerides of highly stable rosins),(pentaerythritol esters of hydrogenated rosin), Stabilite ester 10 andPE Estergum et al, manufactured by Arizona Chemical, and Sylvachem40N、And the like.

Terpene resins of the formula C present in most essential oils and oleoresins of plants and phenolic-modified terpene resins may also be used as tackifiers₁₀H₁₆Such as α -pinene, β pinene, dipentene, limonene, myrcene (myrcene), bornene, camphene, etc. various aliphatic hydrocarbon resins such as Escorez manufactured by Exxon Chemical company may also be used^TM1304 and based on C₉、C₅Aromatic resins of dicyclopentadiene, benzofuran, indene, styrene, substituted styrene and styrene derivatives, and the like.

Hydrogenated and partially hydrogenated resins such as Regalrez produced by Hercules corporation^TM1018、Regalrez^TM1033、Regalrez^TM1078、Regalrez^TM1094、Regalrez^TM1126、Regalrez^TM3102、Regalrez^TM6108, etc. may also be used as the tackifier in the present invention. SP 560 type manufactured and sold by Schenectady Chemical, Inc., Nirez 1100 manufactured and sold by Reichold Chemical, Inc., and Nirez manufactured and sold by Hercules, IncThe various terpene phenol resins of (a) are particularly useful tackifiers for the present invention. Further, various mixed aliphatic and aromatic resins such as Hercotex AD 1100 manufactured and sold by Hercules corporation may also be used as tackifiers.

While the resins described above are very useful for tackifying the copolymers of the present invention, the particular tackifying resin and/or amount selected for a given formulation may depend on the type of acrylic polymer being tackified. Some resins such asAre widely compatible with acrylic compositions. Others as Regalrez^TM6108 to tackify a limited number of compositions. The type of tackifying resin, along with the amounts employed, is sufficiently compatible with the acrylic polymer. As used herein, the term "sufficiently compatible" means that when the tackifier and copolymer are combined, the resulting combination is sufficiently transparent to normal vision rather than hazy. Many resins known in the art to be useful in tackifying acrylic-based pressure sensitive adhesives may be effectively used in the practice of the present invention, although the scope of the invention is not limited to only such resins. Resins described in Satas, Handbook of Pressure sensitive adhesive Technology, Von Nostrand Reinhold, Chapter 20, pp 527-584 (1989), which is incorporated herein by reference, may be used. Resins described in U.S. Pat. nos. 4,418,120 and 4,726,983 (incorporated herein by reference) and EP 0,303,430 (incorporated herein by reference) are particularly useful.

Again, the amount of tackifier used in the present invention depends on the type of copolymer and tackifier used. Typically, pressure sensitive adhesive compositions prepared according to the present invention will include from about 5% to about 60% by total weight of one or more tackifiers.

Crosslinking agent

The tackified adhesive may be crosslinked using an aziridine crosslinking agent. Conventional aziridine crosslinking agents may be used. In one embodiment, the aziridine crosslinking agent is CX-100 from DSM NeoResins. Aziridine crosslinking agent CX-100 is a 100% active polyfunctional aziridine liquid crosslinking agent. The crosslinker can be added using an in-line mixer process just prior to coating the mixture on the substrate. The crosslinker level ranges from about 0.05% to about 1% by weight, based on the weight of the dry adhesive.

Other additives

The adhesives of the invention may further comprise one or more conventional adjuvants such as pigments, fillers, plasticizers, diluents and the like. If desired, the pigment is provided in an amount sufficient to impart the desired color to the binder. Examples of pigments include, but are not limited to, solid inorganic fillers such as carbon black, titanium dioxide, and the like, and organic dyes.

If desired, diluents such as plasticizers may be added in place of part of the tackifier to modify the properties of adhesion and bond strength.

The pressure sensitive adhesives of the present invention are first cured by exposure to heat, chemical crosslinkers, actinic radiation, or electron beam radiation. The result is a good balance of excellent adhesion and peel and high temperature shear. The incorporation of glycidyl acrylate and/or glycidyl methacrylate in the copolymerization appears to help produce the desired high molecular weight polymer.

In one embodiment of the invention, the adhesive is first cured by exposure to heat under dry conditions; that is, the adhesive is cured at an elevated temperature sufficient to evaporate the solvent(s) from the composition. Such temperatures typically range from about 70 ℃ to about 120 ℃.

When the adhesive is subsequently exposed to elevated temperatures, typically under conditions of use, a "secondary cure" of the adhesive is performed. While not being bound by theory, it is believed that the inherent interaction occurs primarily between the pendant epoxy functionality of the polymerized glycidyl-containing monomer and the pendant carboxylic acid functionality of the polymerized unsaturated carboxylic acid monomer. It should be understood that when the primary cure is achieved by exposing the adhesive to heat, "secondary cure" may also occur, at least in part, under the primary cure conditions. Thus, some interaction between the epoxy and carboxylic acid functional groups may occur during the first cure. This results in enhanced high temperature performance.

Any chemical species that has the effect of lowering the activation temperature of the secondary cure and is compatible with the tackified acrylic-based adhesives of the present invention may be used. Typically, the activation temperature is no greater than about 120 ℃. By adjusting the amount and type of activator moiety used, it is possible to "dial in" the secondary cure temperature.

In addition to the above adhesive compositions, the present invention further provides transfer tapes and layered structured tapes consisting of a core coated on one or both sides with a skin layer consisting of the tackified acrylic-based copolymer of the present invention.

The transfer tape prepared according to the present invention comprises a self-supporting film of a pressure sensitive adhesive as described above and at least one release liner. Thus, the pressure sensitive adhesive can be coated on a release liner such as silicone release coated paper and stored as a roll.

The adhesives and tapes of the invention exhibit excellent peel adhesion to a variety of substrates such as metals, plastics and paints.

The following tests were used to determine various physical properties of the present invention:

the adhesive was laminated to a 2 mil Mylar film in a manner similar to that described in Test Methods for Pressure Sensitive Adhesives, 8 th edition, PSTC #1, and 90 ° peel was measured.

High temperature shear (232 ℃) was measured at a retention time of 24 hours in a manner similar to that described in Test Methods for Pressure Sensitive Adhesives, 8 th edition, PSTC # 7.

The electronic shear test was performed as follows: the L-shaped stainless steel plate was bonded to a second stainless steel plate having a hole at one end using the pressure-sensitive adhesive under study. A200 g load was hung on the second plate through the hole. The L-shaped plate is fixed to the base so that the laminated portions of the two plates are placed horizontally and the weight is placed vertically. The time taken for the second sheet to fall off the L-shaped sheet at 60 ℃ was measured to characterize the holding power of the adhesive.

The Dome Tent Lift test (Dome Tent Lift test) was performed by placing 1 "x 1" tape with a 2 mil thick aluminum backing over a 13mm diameter hole with an 11mm rivet in the hole. There are 3 holes per panel in the triangular dome tent shape. A 1kg weight was placed in the middle of the hole and the adhesive rise around the bottom of the hole was measured.

Dynamic shear properties (modulus and tan) were measured using a TA Instruments ARES with 8mm parallel plates. Time-temperature superposition was performed with 25 ℃ as reference temperature.

The invention is set forth below, although not limited thereto.

Example 1 HPA HC

A monomer mixture was prepared by mixing 207g of butyl acrylate, 61.2g of 2-ethylhexyl acrylate, 23.1g of acrylic acid and 0.1g of glycidyl methacrylate. 68.5g of this mixture are introduced into a 1.5 l nitrogen-purged reactor equipped with a pitched turbine agitator, a reflux condenser and a thermistor. 29.7g of ethyl acetate and 18g of acetone are also added. The contents of the reactor were heated to reflux and 0.05g of that made and sold by Dupont in 4.5g of ethyl acetate(2-2' -azo-bis-isobutyronitrile) was added. Vigorous reflux was initiated in a short time and the contents of the reactor were allowed to stand for 15 minutes. At this point, the remaining monomer was mixed with 195g ethyl acetate, 40g acetone and 0.24gMixed and added as a single feed mixture over a 3 hour period. At the feed time, the temperature was maintained to keep the reactor contents under reflux. One hour after the end of the feed, in 9g of ethyl acetate and 4g of acetone0.12g ofAnd left for another 1 hour. This step was repeated two more times. At the end of the final addition, a further 1 hour was left standing, after which 178g of toluene and 27g of heptane were added. The final percent solids was 36% and the viscosity was 8000pa.s on a brookfield viscometer using a #4 spindle at 12 rpm. The resulting polymer consisted of 71% by weight of butyl acrylate, 21% by weight of 2-ethylhexyl acrylate, 8.0% of acrylic acid and 0.03% by weight of glycidyl methacrylate. The polymer was formulated with 20 wt% of a Dertophene T tackifier (of terpineol) manufactured by DRT, France. The tackified adhesive was then mixed in-line with 0.1% C X-100, an aziridine crosslinking agent from Neoresins, the NeoResins, Netherlands. Just before example 1, identified as hpac HC, was produced on the coated substrate, the tackifying binder was precisely measured and homogeneously mixed with the aziridine crosslinking agent using a special measuring and mixing system LADO-MIX V-SB manufactured by DOPAG, switzerland.

The composition was coated on a release film to give a coating thickness of about 60gsm and the film was dried at 70 ℃ for 15 minutes.

For comparison purposes, existing product FT 2022 was evaluated as shown in table 1.

TABLE 1 high temperature Performance test

TABLE 2 electronic shear test results

TABLE 3 dynamic mechanical Properties

The frequency refers to the frequency of the maximum value of tan d.

As indicated in table 1, the tape formulated according to the present invention demonstrated 1) a higher 90 ℃ peel adhesion on plastic, 2) a higher 80 ℃ (high temperature) peel adhesion, 3) a much higher shear value at 232 ℃, 400g load, and 4) a smaller dome tent lift, showing better stress relief properties.

As indicated in table 2, the adhesive tape formulated according to the present invention exhibited the longest time required for failure at 60 ℃ under a load of 200g, compared to the other two comparative samples.

As indicated in table 3, the tape formulated in accordance with the present invention exhibited much higher G'/tan d values at 100,000rad/s frequency compared to the commercial counterpart 3M300 LSE. This ratio has been used to predict die-cutting performance (die-cutting ability) of adhesives, where the higher the ratio, the better the die-cutting performance of the adhesive.

Claims (8)

1. A tackified pressure sensitive adhesive composition comprising a dual cure acrylic-based copolymer comprising a monomer mixture comprising at least one monomer selected from the group consisting of alkyl acrylates and mixtures thereof, a tackifier, and an aziridine crosslinking agent; a glycidyl monomer selected from the group consisting of allyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, and mixtures thereof; and an unsaturated carboxylic acid.

2. The composition of claim 1 further comprising one or more adjuvants selected from fillers, pigments, diluents, plasticizers, and the like.

3. A tackified pressure sensitive adhesive composition comprising a crosslinked acrylic acid-based copolymer comprising, on a copolymerized basis, 90-50% BA, 5-40% 2-EHA, 0.01% to 0.1% glycidyl methacrylate, up to about 10% of a positive amount of an unsaturated carboxylic acid monomer, 10% to 40% tackifier, and 0.05 to 1% aziridine crosslinking agent.

4. A method of making a dual cure pressure sensitive adhesive, the method comprising:

a) copolymerizing a monomer mixture comprising at least one monomer selected from the group consisting of alkyl acrylates and mixtures thereof to form a copolymer; a glycidyl monomer selected from the group consisting of allyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, and mixtures thereof; and an unsaturated carboxylic acid;

b) adding a tackifier to produce a tackified adhesive; and

c) an aziridine crosslinking agent is added to the tackified adhesive to produce a dual cure pressure sensitive adhesive.

5. The method of claim 4, further comprising adding one or more adjuvants selected from fillers, pigments, diluents, plasticizers, and the like to the dual cure pressure sensitive adhesive.

6. The method of claim 4, further comprising:

d) coating the adhesive formulation on a substrate; and

e) drying the adhesive formulation.

7. An adhesive coated product comprising the pressure sensitive adhesive of claim 1.

8. The product of claim 7, wherein the product is an adhesive tape.