WO2025114790A1

WO2025114790A1 - Conductive adhesive compositions and electrically conductive articles

Info

Publication number: WO2025114790A1
Application number: PCT/IB2024/060698
Authority: WO
Inventors: Claire Hartmann-Thompson; Tamuka CHIDANGURO; Jing Fang; Shane P. WHITE; Marina M. KAPLUN; Wei Zhou
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2023-12-01
Filing date: 2024-10-30
Publication date: 2025-06-05
Anticipated expiration: 2026-06-01
Also published as: CN120082306A

Abstract

A conductive adhesive composition is provided. The composition includes a pressure sensitive adhesive matrix including at least one non-linear block copolymer having aromatic end blocks and aliphatic elastomeric blocks, at least one hydrocarbon-based tackifying resin, at least one aromatic reinforcing resin, and electrically conductive particles dispersed within the matrix. In some cases, the composition further includes an adhesion promoter including an alkyl alkoxysilane, an alkenyl alkoxysilane, an alkyl phosphonic acid, or an alkyl carboxylic acid, and optionally a non-functional dipodal alkoxysilane. When the adhesion promoter contains an alkyl alkoxysilane or an alkenyl alkoxysilane, the non-functional dipodal alkoxysilane is present. In other cases, the composition further includes an adhesion promoter including an organic molecule selected from classes of organic compounds that can form a bond with a metal oxide surface. An electrically conductive article is also provided including a substrate and an electrically conductive adhesive disposed on the substrate.

Description

CONDUCTIVE ADHESIVE COMPOSITIONS AND ELECTRICALLY CONDUCTIVE ARTICLES

BACKGROUND

[0001] Electrically conductive adhesives are preferred to combine good electrical performance, adhesive performance, and resistance to heat and humidity aging. Further developments in electrically conductive adhesives would be desirable.

SUMMARY

[0002] In a first aspect, a conductive adhesive composition is provided. The conductive adhesive composition comprises a pressure sensitive adhesive matrix comprising at least one non-linear block copolymer comprising aromatic end blocks and aliphatic elastomeric blocks; at least one hydrocarbonbased tackifying resin; at least one aromatic reinforcing resin; and electrically conductive particles dispersed within the matrix. The conductive adhesive composition further comprises an adhesion promoter comprising an alkyl alkoxysilane, an alkenyl alkoxysilane, an alkyl phosphonic acid, or an alkyl carboxylic acid; and optionally a non-functional dipodal alkoxysilane, with the proviso that when the adhesion promoter comprises an alkyl alkoxysilane or an alkenyl alkoxysilane, the non-functional dipodal alkoxysilane is present.

[0003] In a second aspect, another conductive adhesive composition is provided. The conductive adhesive composition comprises a pressure sensitive adhesive matrix comprising at least one non-linear block copolymer comprising aromatic end blocks and aliphatic elastomeric blocks; at least one hydrocarbon-based tackifying resin; at least one aromatic reinforcing resin; an adhesion promoter comprising an organic molecule selected from classes of organic compounds that can form a bond with a metal oxide surface; and electrically conductive particles dispersed within the matrix.

[0004] In a third aspect, an electrically conductive article is provided. The electrically conductive article comprises a substrate with a first major surface and a second major surface: and an electrically conductive adhesive layer disposed on at least a portion of the second major surface of the substrate. The electrically conductive adhesive comprises any conductive adhesive composition according to the first aspect or the second aspect.

[0005] The above Summary is not intended to describe each illustrated embodiment or every implementation of the present certain exemplary embodiments of the present disclosure. The Drawings and the Detailed Description that follow more particularly exemplify certain preferred embodiments using the principles disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying figures, in which:

[0007] FIG. 1 is a generalized schematic cross-sectional view of an exemplary electrically conductive article, according to various embodiments disclosed herein; and

[0008] FIG. 2 is a cross sectional view of a device for testing PIM (passive intermodulation) of adhesives.

[0009] In the drawings, like reference numerals indicate like elements. While the above-identified drawings, which may not be drawn to scale, set forth various embodiments of the present disclosure, other embodiments are also contemplated, as noted in the Detailed Description. In all cases, this disclosure describes the presently disclosed disclosure by way of representation of exemplary embodiments and not by express limitations. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this disclosure.

DETAILED DESCRIPTION

[0010] In electronic assembly devices such as smart phones and tablets, there are many applications that need conductive tapes and conductive gaskets to work as grounding and/or shielding materials.

Conductive pressure sensitive adhesives (CPSAs) and articles that contain CPSAs are among the components used in the electronic devices. These CPSAs are used not only to adhere elements of the devices together (the typical role of PSAs), but also are called upon to provide additional roles within the device. Conductive PSAs have contradictory requirements, typically they need to have high electrical conductivity for grounding performance and adhere strongly to electrical components without adversely affecting the electrical components. Since the electrical components are often subject to corrosion and degradation (such as layers of copper and conductive fabrics for example), many typical materials used in pressure sensitive adhesives are not optimal (such as acid- or base-functional materials, or traces of acid or base impurities in the CPSA components) for use in CPSAs.

[0011] One desire in electronic devices is for a reduction in passive intermodulation (PIM). PIM is generated when two or more signals at different frequencies mix with each other due to electrical nonlinearities. In some cases, the PIM signal resulting from wireless transmission of a signal can occur at a frequency inside a receiving band of the wireless communication or data device, thereby causing undesired signal interference. A method for measuring PIM is described below and shown in the Figures. Therefore, the need remains for conductive PSAs that have and maintain good PSA properties (such as peel and shear properties) even when aged at elevated temperatures and humidity levels, good conductive properties, and provide a low level of PIM.

[0012] In this disclosure, conductive PSAs are described that have and maintain good PSA properties (such as peel and shear properties), good conductive properties, and provide a low level of PIM. The conductive PSAs comprise a pressure sensitive adhesive matrix comprising at least one non-linear block copolymer comprising aromatic end blocks and aliphatic elastomeric blocks, at least one hydrocarbonbased tackifying resin, at least one aromatic reinforcing resin, and electrically conductive particles dispersed within the matrix. Also disclosed are articles prepared using this conductive pressure sensitive adhesive.

[0013] For the following Glossary of defined terms, these definitions shall be applied for the entire application, unless a different definition is provided in the claims or elsewhere in the specification.

Glossary

[0014] Certain terms are used throughout the description and the claims that, while for the most part are well known, may require some explanation. It should be understood that:

[0015] The term “adhesive” as used herein refers to polymeric compositions useful to adhere together two adherends. Examples of adhesives are pressure sensitive adhesives.

[0016] Pressure sensitive adhesive compositions are well known to those of ordinary skill in the art to possess properties including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be cleanly removable from the adherend. Materials that have been found to function well as pressure sensitive adhesives are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power. Obtaining the proper balance of properties is not a simple process.

[0017] The terms “room temperature” and “ambient temperature” are used interchangeably to mean temperatures in the range of 20°C to 25°C.

[0018] The term “adjacent” as used herein when referring to two layers means that the two layers are in proximity with one another with no intervening open space between them. They may be in direct contact with one another (e.g., laminated together) or there may be intervening layers.

[0019] The terms “polymer” and “macromolecule” are used herein consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeated subunits. The term “polymer” is used to describe the resultant material formed from a polymerization reaction.

[0020] As used herein, “essentially free” with respect to a component of a composition means that the component is present in amount of less than 0.1 weight percent (wt.%), based on the total weight of the composition, such as less than 0.09 wt.%, 0.08 wt.%, 0.07 wt.%, 0.06 wt.%, or even less than 0.05 wt.% of the total weight of the composition.

[0021] The term “alkenyl” refers to a monovalent group that is a radical of an alkene, which is a hydrocarbon with at least one carbon-carbon double bond. The alkenyl can be linear, branched, cyclic, or combinations thereof and typically contains 2 to 20 carbon atoms. In some embodiments, the alkenyl contains 2 to 18, 2 to 12, 2 to 10, 4 to 10, 4 to 8, 2 to 8, 2 to 6, or 2 to 4 carbon atoms. Exemplary alkenyl groups include ethenyl, 1 -propenyl, and 1-butenyl.

[0022] The term “alkyl” refers to a monovalent group that is a radical of an alkane, which is a saturated hydrocarbon. The alkyl can be linear, branched, cyclic, or combinations thereof and typically has 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1 to 12, 1 to 10, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, ethylhexyl, and octadecyl.

[0023] The term “alkylene” refers to a divalent group that is a radical of an alkane. The alkylene can be straight-chained, branched, cyclic, or combinations thereof. The alkylene often has 1 to 20 carbon atoms. In some embodiments, the alkylene contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. The radical centers of the alkylene can be on the same carbon atom (i.e., an alkylidene) or on different carbon atoms.

[0024] The term “alkoxy” refers to a monovalent group of formula -OR where R is an alkyl group. The term “akoxysilane” refers to a monovalent group of formula -Si(OR)n where R is an alkyl group and n is an integer of 1 to 3.

[0025] The term “dipodal alkoxy silane” refers to a component that has two sets of alkoxy silane groups. [0026] The term “non-functional” refers to lacking any functional group exhibiting reactivity or polymerizable reactivity with another functional group including a hydroxyl group, a silanol group, a Sill group, a vinyl group, an allyl group, an acrylic group, a methacrylic group, an epoxy group, an amino group, and a mercapto group. Examples of non-functional groups include an alkyl group or an aryl group consisting of a carbon, a hydrogen, and in some embodiments, a halogen atom (for example, a chlorineatom).

[0027] The term “phosphonic acid” as used herein refers to a group having the formula -P(=O)(OH)₂ attached directly to a carbon atom.

[0028] The term “carboxylic acid” as used herein refers to a group having the formula -C(=O)(OH) attached directly to a carbon atom.

[0029] The terms “about” or “approximately” with reference to a numerical value or a shape means +/- five percent of the numerical value or property or characteristic, but expressly includes the exact numerical value.

[0030] The term “substantially” with reference to a property or characteristic means that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited.

[0031] As used in this specification and the appended embodiments, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to “a compound” includes a mixture of two or more compounds. As used in this specification and the appended embodiments, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

[0032] Unless otherwise indicated, all numbers expressing quantities or ingredients, measurement of properties and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached listing of embodiments can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claimed embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0033] By definition, the total weight percentages of all ingredients in a composition equals 100 weight percent.

[0034] Various exemplary embodiments of the disclosure will now be described. Exemplary embodiments of the present disclosure may take on various modifications and alterations without departing from the spirit and scope of the present disclosure. Accordingly, it is to be understood that the embodiments of the present disclosure are not to be limited to the following described exemplary embodiments but are to be controlled by the limitations set forth in the claims and any equivalents thereof.

[0035] In a first aspect, a conductive adhesive composition is provided. The conductive adhesive composition comprises:

[0036] a pressure sensitive adhesive matrix comprising at least one non-linear block copolymer comprising aromatic end blocks and aliphatic elastomeric blocks;

[0037] at least one hydrocarbon-based tackifying resin;

[0038] at least one aromatic reinforcing resin;

[0039] an adhesion promoter comprising an alkyl alkoxy silane, an alkenyl alkoxy silane, an alkyl phosphonic acid, or an alkyl carboxylic acid;

[0040] optionally a non-functional dipodal alkoxysilane, with the proviso that when the adhesion promoter comprises an alkyl alkoxysilane or an alkenyl alkoxysilane, the non-functional dipodal alkoxysilane is present; and

[0041] electrically conductive particles dispersed within the matrix.

[0042] In a second aspect, another conductive adhesive composition is provided. The conductive adhesive composition comprises:

[0043] a pressure sensitive adhesive matrix comprising at least one non-linear block copolymer comprising aromatic end blocks and aliphatic elastomeric blocks;

[0044] at least one hydrocarbon-based tackifying resin;

[0045] at least one aromatic reinforcing resin;

[0046] an adhesion promoter comprising an organic molecule selected from classes of organic compounds that can form a bond with a metal oxide surface; and [0047] electrically conductive particles dispersed within the matrix.

[0048] Various classes of organic compounds are suitable as adhesion promoters for the conductive adhesives disclosed herein, including certain alkoxysilanes (e.g., alkyl alkoxysilanes, alkenyl alkoxysilanes), phosphonic acids (e.g., alkyl phosphonic acids), carboxylic acids (e.g., alkyl carboxylic acids), hydroxamic acids (i.e., N-hydroxy -amides), and phosphate esters. [0049] It was unexpectedly discovered that adhesion promoters according to the present disclosure provide an improvement in clean removal of conductive adhesives when peeled from a substrate, as compared to using an amino alkoxy silane adhesion promoter.

[0050] Although it is possible to employ a combination of an amino alkoxysilane adhesion promoter and the adhesion promoters described herein, in some embodiments, the conductive adhesive composition is essentially free of an amino alkoxysilane (i.e., contains less than 0.1 wt.% of an amino alkoxysilane).

[0051] It is noted that certain classes of organic compounds can form a bond with a metal oxide surface, for instance and without limitation, alkoxysilanes, phosphonic acids, phosphate esters, carboxylic acids and hydroxamic acids. In some cases, the adhesion promoter does form a bond with a metal oxide surface, such as a hydrogen bond or a covalent bond. The adhesion promoter may form a single bond or two bonds with a metal oxide surface. Typical metal oxides include, for instance and without limitation, nickel oxide, copper oxide, silver oxide, aluminum oxide, chromium oxide, iron oxide, and titanium oxide.

[0052] In some embodiments, an alkyl alkoxy silane is present as and the alkyl group of the alkyl alkoxysilane is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl. In certain cases, the alkyl group of the alkyl alkoxysilane is n-butyl. Often, suitable alkoxy groups of the alkyl alkoxysilane have 1 to 6 carbon atoms, 1 to 4 carbon atoms, 1 to 3 carbon atoms, or 1 to 2 carbon atoms. The alkoxy group is often methoxy or ethoxy. In some embodiments, the alkyl alkoxysilane comprises a dialkoxysilane or a trialkoxysilane. Exemplary alkyl alkoxysilanes include for instance and without limitation, n- butyltrimethoxysilane, n-decyltrimethoxysilane, n-octyltrimethoxysilane, n-butyldimethoxysilane, n- decyldimethoxysilane, and n-octyldimethoxysilane.

[0053] In some embodiments, the alkenyl alkoxy silane is present and the alkenyl group of the alkenyl alkoxy silane is selected from the group consisting of ethenyl, 1 -propenyl, 1-butenyl, and a polybutadiene oligomer. The polybutadiene oligomer is not particularly limited and may have a weight average molecular weight of up to 5,000 g/mol, such as up to 4,500 g/mol, 4,000 g/mol, 3,500 g/mol, or up to 3,000 g/mol. The weight average molecular weight (Mw) can be determined by gel permeation chromatography. In select cases, the alkenyl group of the alkenyl alkoxysilane is polybutadiene. Exemplary alkenyl alkoxy silanes include for instance and without limitation, trimethoxy vinylsilane, allyltrimethoxysilane, trimethoxyoctenylsilane, dimethoxyvinylsilane, allyldimethoxysilane, dimethoxyoctenylsilane and trimethoxy- or triethoxy -modified polybutadienes.

[0054] As noted above, when the adhesion promoter comprises an alkyl alkoxysilane or an alkenyl alkoxysilane, the non-functional dipodal alkoxysilane is present. It has been discovered that the combination of non-functional dipodal alkoxysilane and either alkyl alkoxysilane or alkenyl alkoxysilane provides a synergistic effect of cleaner removal of the conductive adhesive when peeled than when any of those materials are used alone in the conductive adhesive. Without wishing to be bound by theory, it is believed that the additional alkoxy silane groups of the non-functional dipodal alkoxy silanes improve interaction of the conductive adhesive with a substrate surface. In some embodiments, the alkyl alkoxy silane and the non-functional dipodal alkoxy silane are present in a weight ratio of 9 : 1 to 1 : 1, such as 8 : 1 to 1 : 1, 7 : 1 to 1 : 1, 6 : 1 to 1 : 1, or even 5 : 1 to 1 : 1. Exemplary suitable non-functional dipodal alkoxysilanes include for instance and without limitation, 1,2-bistrimethoxy silylethane, 1,2- bistrimethoxysilylmethane 1,2-bistrimethoxy silyloctane, 1,2-bistriethoxy silylethane, 1,2- bistriethoxy silylmethane, 1,2-bistriethoxy silyloctane, 1,2-bisdimethoxy silylethane, 1,2- bisdimethoxy silylmethane, 1,2-bisdimethoxy silyloctane, 1,2-bisdiethoxy silylethane, 1,2- bisdiethoxysilylmethane and,l,2-bisdiethoxysilyloctane.

[0055] In some embodiments, the alkyl phosphonic acid is present and the alkyl group of the alkyl phosphonic acid is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl. In select cases, the alkyl group is n-butyl. Optionally, a second alkyl phosphonic acid may be added. Exemplary suitable alkyl phosphonic acids include for instance and without limitation, 1-butylphosphonic acid, 1,2- ethylenediphosphonic acid, methylphosphonic acid, ethylphosphonic acid, and 1,8-octanediphosphonic acid.

[0056] In some embodiments, the alkyl carboxylic acid is present and the alkyl group of the alkyl carboxylic acid is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl. In select cases, the alkyl group is n-butyl or n-pentyl. Exemplary suitable alkyl carboxylic acids include for instance and without limitation, butanoic acid, pentanoic acid, and octanoic acid. In some cases, the alkyl carboxylic acid may also include at least one acrylate or vinyl group that can react into the PSA, such as betacarboxyethyl acrylate.

[0057] In some embodiments, the adhesion promoter comprises a phosphate ester. Exemplary suitable phosphate esters include for instance and without limitation, propyl phosphate, isopropyl phosphate, butyl phosphate, 2-ethylhexyl phosphate, dipropyl phosphate, diisopropyl phosphate, dibutyl phosphate, and bis(2 -ethylhexyl) phosphate.

[0058] In some embodiments, the adhesion promoter comprises a hydroxamic acid. Exemplary suitable hydroxamic acid include for instance and without limitation, N-hydroxybutanamide, N- hydroxypentanamide, and N-hydroxyhexanamide.

[0059] The conductive adhesive can be tested for PIM (passive intermodulation) as described in greater detail below, in the Examples section and in the Figures. The method involves forming a tape, the tape comprising a layer of the conductive adhesive and an electrically conductive layer such as a conductive woven or non-woven layer. The tape is placed in a test fixture comprising gold conductive surfaces. When first and second electrical signals of magnitude 30 dBm propagate in the thickness direction of the conductive adhesive layer between the gold surfaces at respective frequencies Fl and F2, any intermodulation signal generated from the first and second electrical signals having a frequency F3 equal to nFl+mF2, m and n positive or negative integers, has a power of less than about -60 dBm. It is to be understood that “less than” a particular negative number refers to a larger negative number, e.g., -70 dBm is less than -60 dBm. [0060] It should be noted that properties of the adhesive such as 180° Peel Adhesion, DC resistance, and PIM are properties of the conductive adhesive. While the conductive adhesive is, for example formed into a tape by disposing the adhesive onto a 50-micrometer PET backing for 180° Peel Adhesion testing, the property is a property of the adhesive itself and does not mean that the adhesive can only be used in the form of a tape. The method of testing involves the formation of a tape to carry out the testing, but the properties listed are of the adhesive itself.

[0061] The conductive adhesive comprises a pressure sensitive adhesive matrix. The pressure sensitive adhesive matrix comprises at least one non-linear block copolymer comprising aromatic end blocks and aliphatic elastomeric blocks, at least one hydrocarbon-based tackifying resin, and at least one aromatic reinforcing resin.

[0062] A wide range of non-linear block copolymers comprising aromatic end blocks and aliphatic elastomeric blocks are suitable. The non-linear block copolymers are not simple A-B-A block copolymers. In some embodiments, at least one non-linear block copolymer comprises a star or comb copolymer. Star block copolymers are also sometimes referred to as radial block copolymers. An example of a commercially available radial styrene-famesene-styrene block copolymers includes SF902 from Kuraray, Tokyo, Japan.

[0063] In some embodiments of the block copolymer, the aromatic end blocks comprise styrene blocks, and the aliphatic elastomeric blocks comprise isoprene, famesene, or a combination thereof. Particularly suitable polymers include radial styrene-isoprene-styrene block copolymers and styrene-famesene- styrene block copolymers. Examples of commercially available radial styrene-isoprene-styrene block copolymers include those available from Kraton Polymers, Houston, TX under the trade names, D1340KT, and DL1124KT. A particularly suitable radial block copolymer comprises a star copolymer with styrene end blocks and isoprene elastomeric blocks wherein the end blocks comprise styrene that is 9-10% by weight of the total polymer.

[0064] The pressure sensitive adhesive matrix further comprises at least one hydrocarbon tackifying resin. The hydrocarbon tackifying resin comprises a hydrogenated or partially hydrogenated hydrocarbon resin. A wide range of hydrogenated or partially hydrogenated hydrocarbon resins are suitable.

Examples of commercially available hydrogenated or partially hydrogenated hydrocarbon resin include the resins ARKON P100, ARKON P125, and ARKON PHO from Arakawa Chemical, Inc. Chicago, IL. [0065] The pressure sensitive adhesive matrix further comprises at least one aromatic reinforcing resin. In some embodiments, the aromatic reinforcing resin comprises a thermoplastic aromatic co-polymer with a Tg (glass transition temperature) of greater than 100°C. A wide range of aromatic resins are suitable. An example of a commercially available aromatic reinforcing resin is END EX 160 from Eastman Chemical Company, Kingsport, TN.

[0066] The conductive adhesive further comprises electrically conductive particles dispersed within the pressure sensitive adhesive matrix. A wide range of electrically conductive particles are suitable. The electrically conductive filler particles can be in the form of metallic particles or metal coated insulative (e.g., polymeric) particles or combinations thereof. In some embodiments, the electrically conductive particles comprise particles of nickel-coated graphite. The amount of electrically conductive particles present in the conductive adhesive can vary as will be described below. One particularly suitable conductive particle is the nickel-coated graphite particle “E-Fill #2806 Ni” commercially available from Oerlikon Metco, Westbury, NY.

[0067] The conductive adhesive may optionally include at least one additive. Particularly suitable additives include conductive nanoparticles. Examples of suitable conductive nanoparticles include carbon nanotubes, metallic nanoparticles including nanowires, nanoflakes, nanograins, and nanospheres. [0068] The conductive adhesive matrix formulations can have a wide range of component compositions. In some embodiments, the conductive adhesive comprises: a pressure sensitive adhesive matrix, where the pressure sensitive adhesive matrix comprises: 40-70 parts by weight of at least one non-linear block copolymer; 30-60 parts by weight of hydrocarbon-based tackifying resin; 2-8 parts by weight of aromatic reinforcing resin; 0.1-5 parts by weight of adhesion promoter; 0-2.5 parts of by weight of non-functional dipodal alkoxysilane; and 15-30 parts by weight of electrically conductive particles. In select embodiments, the 0.1-5 parts by weight of adhesion promoter comprises 0.2-5 parts by weight of alkyl phosphonic acid. In select embodiments, the 0.1 -5 parts by weight of adhesion promoter comprises 0.5-5 parts by weight of alkyl carboxylic acid. In select embodiments, the 0.1-5 parts by weight of adhesion promoter comprises 0.1-4.5 parts by weight of alkenyl alkoxysilane. In select embodiments, the 0.1-5 parts by weight of adhesion promoter comprises 0.1-4.5 parts by weight of alkyl alkoxysilane, in which case the pressure sensitive adhesive matrix further comprises 0.02-2.5 parts by weight of non-functional dipodal alkoxy silane. Parts by weight are used to describe these formulations instead of weight % as the weight components do not necessarily add up to 100.

[0069] As was mentioned above, the conductive adhesives have a wide range of desirable properties. Among these properties are adhesive properties (180° Peel Adhesion) and electrical properties (DC resistance and PIM). Each of these properties is described below.

[0070] The conductive adhesive is a pressure sensitive adhesive, meaning that has the features characteristic of a pressure sensitive adhesive: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be cleanly removable from the adherend. One test commonly used to measure the adhesive properties of a pressure sensitive adhesives is 180° Peel Adhesion. In this test the adhesive is disposed on a backing and peeled from a test surface as described in the test method in the Examples section. In some embodiments, the conductive adhesive has a 180° Peel Adhesion of at least 15.0 Newtons/decimeter (0.15 N/mm) at Room Temperature. In other embodiments, the conductive adhesive has a 180° Peel Adhesion of at least 20.0 Newtons/decimeter at Room Temperature (0.20 N/mm), 30 N/dm (0.3 N/mm), 40 N/dm (0.4 N/mm), 50 N/dm (0.5 N/mm), 60 N/dm (0.6 N/mm), 70 N/dm (0.7 N/mm) or even at least 80 N/dm (0.8 N/mm).

[0071] The conductive adhesive also has desirable electrical properties. Among these properties are DC resistance and PIM. The conductive adhesive has a DC Resistance of less than 0.4 ohms as measured by ETM-12. The test method ETM-12 is described in the Examples section below. In some embodiments, the conductive adhesive has a DC Resistance of less than 0.35 ohms, 0.3 ohms, 0.25 ohms, 0.2 ohms, 0.15 ohms, 0.1 ohms, or even less than 0.05 ohms.

[0072] As mentioned above, an important feature of the current conductive adhesives is their stability when exposed to heat and humidity, especially when the adhesive is in contact with a conductive substrate such as a conductive fabric. In some embodiments, the conductive adhesive 180° Peel Adhesion changes by 25% or less after aging on a conductive fabric substrate for at least 1 week at 85°C and 85% Relative Humidity.

[0073] Layers of adhesive are generally described as having length and width in the x-y plane and have a thickness along the z-axis. The conductive adhesives of this disclosure are generally “z-axis conductive adhesives”. By this it is meant that a layer of the adhesive conducts in the z-axis, which is the thickness of the layer of adhesive, and does not necessarily conduct in the x-y plane of the layer of adhesive.

[0074] The adhesive layers of this disclosure can be prepared from the conductive adhesive compositions. The layers can be prepared by disposing the adhesive composition on the surface of a substrate such as a release liner. The adhesive layers can be provided in a variety of ways such as a sheet or as a roll, where the roll can be rolled upon itself for shipment or storage and unrolled when used.

[0075] In a third aspect, an electrically conductive article is provided. The electrically conductive article comprises a substrate with a first major surface and a second major surface: and an electrically conductive adhesive layer disposed on at least a portion of the second major surface of the substrate. The electrically conductive adhesive comprises any electrically conductive adhesive composition according to the first aspect or the second aspect, described in detail herein.

[0076] Referring to FIG. 1, a generalized schematic cross-sectional view of an electrically conductive article 100 is provided. The article 100 includes a substrate 110 having a first major surface 112 and an opposing second major surface 114. An electrically conductive adhesive 120 is disposed on (at least a portion of) the second major surface 114 of the substrate 110. In this embodiment, an optional second layer of electrically conductive adhesive 130 is disposed on (at least a portion of) the first major surface 112 of the substrate 110.

[0077] A wide variety of substrates are suitable. In some embodiments, the substrate comprises an electrically conductive substrate. These embodiments can be described as “single-sided tapes” as they have a single side of exposed adhesive. A wide range of electrically conductive substrates are suitable. Examples of suitable conductive substrates include a non-woven layer comprising metal coated polymer fibers, a woven fabric layer comprising metal coated polymer fibers, a film layer with metal coated surface(s), or a metal foil. Metal can be deposited on fibers or films in a wide variety of ways such as by coating, sputtering, electroplating, or chemical vapor deposition.

[0078] In other embodiments, the substrate comprises a release liner. In these embodiments, the conductive adhesive layer is a free-standing adhesive layer where both surfaces of the adhesive layer are exposed. These free-standing adhesive layers can be used in a wide variety of ways. The exposed adhesive surface can be laminated to a conductive substrate to form a single-sided tape as described above. The free-standing adhesive layer can be used as it is and laminated to a surface, the release liner can be removed to expose the second surface of the adhesive and a substrate or surface can be adhered to the newly exposed surface. The free-standing adhesive layer can also be laminated to the opposite surface of a single-sided adhesive tape as described above to form a double-sided adhesive tape.

[0079] Release liners are well understood in the adhesive arts as being a film from which adhesive compositions or coatings can be readily removed. Exemplary release liners include those prepared from paper (e.g., Kraft paper) or polymeric material (e.g., polyolefins such as polyethylene or polypropylene, ethylene vinyl acetate, polyurethanes, polyesters such as polyethylene terephthalate, and the like, and combinations thereof). At least some release liners are coated with a layer of a release agent such as a silicone, a fluorosilicone-containing material or a fluorocarbon-containing material.

[0080] Another important feature of the conductive adhesives of this disclosure is the relatively low PIM (passive intermodulation). PIM can be tested as shown in FIG. 2, in which a double-sided tape is used that comprises two layers of conductive adhesive with a conductive interlayer disposed between. The conductive interlayer may be a variety of conductive layers such as a metallic layer or a layer of conductive woven or non-woven. Samples of the double-sided tape are disposed on the gold portions of the PIM board, and a conductive bridge connects the samples. In FIG. 2, PIM test board 200 has gold portions 210 and wires 240. The test sample includes adhesive layer 220 with conductive bridge 230. Adhesive layer 220 has sublayers, these sublayers are sublayer 221 that is the adhesive sample, sublayer 222 is a conductive interlayer, and sublayer 223 is the adhesive sample.

[0081] It should be understood that the method of testing of the adhesive for PIM is not limiting on articles that can be made from the conductive adhesive but that regardless of how the PIM is measured, the property is that of the conductive adhesive and not of articles of the adhesive (such a single-sided tapes, double-sided tapes and the like). When first and second electrical signals of magnitude 30 dBm propagate in the thickness direction (z-axis) of the conductive adhesive layer at respective frequencies Fl and F2, any intermodulation signal generated has a frequency F3 equal to nFl+mF2, m and n positive or negative integers. When measured in this way, the PIM has a power of less than about -60 dBm.

[0082] Also disclosed herein are electrically conductive articles. In some embodiments, the electrically conductive article comprises a substrate with a first major surface and a second major surface, and an electrically conductive adhesive layer disposed on at least a portion of the second major surface of the substrate. The electrically conductive adhesive has been described in detail above. In some embodiments, the conductive adhesive comprises a pressure sensitive adhesive matrix and electrically conductive particles dispersed within the matrix. The pressure sensitive adhesive matrix comprises at least one non-linear block copolymer comprising aromatic end blocks and aliphatic elastomeric blocks, at least one hydrocarbon-based tackifying resin, and at least one aromatic reinforcing resin. The conductive adhesive is a pressure sensitive adhesive and when disposed on a 50-micrometer thick PET (polyethylene terephthalate) backing has a 180° Peel Adhesion of at least 30.0 Newtons/decimeter at Room Temperature (0.3 N/mm), and when disposed on a copper foil backing has a DC Resistance of less than 0.3 ohms as measured by ETM-12 Optionally, the 180° Peel Adhesion changes by 25% or less after aging on a conductive fabric substrate for at least 1 week at 85°C and 85% Relative Humidity. [0083] Listing of Exemplary Embodiments

[0084] In a first embodiment, the present disclosure provides a conductive adhesive composition. The conductive adhesive composition comprises a pressure sensitive adhesive matrix comprising at least one non-linear block copolymer comprising aromatic end blocks and aliphatic elastomeric blocks; at least one hydrocarbon-based tackifying resin; at least one aromatic reinforcing resin; and electrically conductive particles dispersed within the matrix. The conductive adhesive composition further comprises an adhesion promoter comprising an alkyl alkoxysilane, an alkenyl alkoxysilane, an alkyl phosphonic acid, or an alkyl carboxylic acid; and optionally a non-functional dipodal alkoxysilane, with the proviso that when the adhesion promoter comprises an alkyl alkoxysilane or an alkenyl alkoxysilane, the nonfunctional dipodal alkoxysilane is present.

[0085] In a second embodiment, the present disclosure provides a conductive adhesive composition according to the first embodiment, wherein the adhesive composition is essentially free of an amino alkoxysilane.

[0086] In a third embodiment, the present disclosure provides a conductive adhesive composition according to the first embodiment or the second embodiment, wherein the alkyl alkoxysilane is present and the alkyl group of the alkyl alkoxy silane is selected from the group consisting of methyl, ethyl, n- propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl.

[0087] In a fourth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through third embodiments, wherein the alkyl alkoxy silane is present and the alkyl group of the alkyl alkoxysilane is n-butyl.

[0088] In a fifth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through fourth embodiments, wherein the alkyl alkoxy silane is present and the alkyl alkoxysilane comprises a dialkoxysilane or a trialkoxysilane.

[0089] In a sixth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through fifth embodiments, wherein the alkyl alkoxysilane is present and the alkyl alkoxysilane and the non-functional dipodal alkoxysilane are present in a weight ratio of 9 : 1 to 1 : 1.

[0090] In a seventh embodiment, the present disclosure provides a conductive adhesive composition according to the first embodiment or the second embodiment, wherein the alkenyl alkoxysilane is present and the alkenyl group of the alkenyl alkoxy silane is selected from the group consisting of ethenyl, 1- propenyl, 1-butenyl, and a polybutadiene oligomer.

[0091] In an eighth embodiment, the present disclosure provides a conductive adhesive composition according to the first embodiment, the second embodiment, or the seventh embodiment, wherein the alkenyl alkoxysilane is present and the alkenyl group of the alkenyl alkoxysilane is polybutadiene. [0092] In a ninth embodiment, the present disclosure provides a conductive adhesive composition according to the first embodiment or the second embodiment, wherein the alkyl phosphonic acid is present and the alkyl group of the alkyl phosphonic acid is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl.

[0093] In a tenth embodiment, the present disclosure provides a conductive adhesive composition according to the ninth embodiment, wherein the alkyl group is n-butyl.

[0094] In an eleventh embodiment, the present disclosure provides a conductive adhesive composition according to the tenth embodiment, further comprising 1,2-ethylenediphosphonic acid.

[0095] In a twelfth embodiment, the present disclosure provides a conductive adhesive composition according to any of the ninth through eleventh embodiments, comprising 40-70 parts by weight of the at least one non-linear block copolymer; 0-60 parts by weight of the at least one hydrocarbon-based tackifying resin; 2-8 parts by weight of the at least one aromatic reinforcing resin; 0.2-5 parts by weight of the alkyl phosphonic acid; and 15-30 parts by weight electrically conductive particles.

[0096] In a thirteenth embodiment, the present disclosure provides a conductive adhesive composition according to the first embodiment or the second embodiment, wherein the alkyl carboxylic acid is present and the alkyl group of the alkyl carboxylic acid is selected from the group consisting of methyl, ethyl, n- propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl.

[0097] In a fourteenth embodiment, the present disclosure provides a conductive adhesive composition according to the thirteenth embodiment, wherein the alkyl carboxylic acid comprises butanoic acid, pentanoic acid, or beta-carboxyethyl acrylate.

[0098] In a fifteenth embodiment, the present disclosure provides a conductive adhesive composition according to the thirteenth embodiment or the fourteenth embodiment, comprising 40-70 parts by weight of the at least one non-linear block copolymer; 30-60 parts by weight of the at least one hydrocarbonbased tackifying resin; 2-8 parts by weight of the at least one aromatic reinforcing resin; 0.5-5 parts by weight of the alkyl carboxylic acid; and 15-30 parts by weight electrically conductive particles.

[0099] In a sixteenth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through fifteenth embodiments, wherein the at least one non-linear block copolymer comprises a star or comb copolymer.

[00100] In a seventeenth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through sixteenth embodiments, wherein the aromatic end blocks comprise styrene blocks, and the aliphatic elastomeric blocks comprise isoprene, famesene, or a combination thereof.

[00101] In an eighteenth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through seventeenth embodiments, wherein the non-linear block copolymer comprises a star copolymer with styrene end blocks and isoprene elastomeric blocks wherein the styrene end blocks comprise 9-10% by weight of the total polymer. [00102] In a nineteenth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through eighteenth embodiments, wherein the at least one hydrocarbon tackifying resin comprises a hydrogenated or partially hydrogenated hydrocarbon resin.

[00103] In a twentieth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through nineteenth embodiments, wherein the at least one aromatic reinforcing resin comprises a thermoplastic aromatic co-polymer with a Tg of greater than 100°C.

[00104] In a twenty -first embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through twentieth embodiments, wherein the electrically conductive particles comprise particles of nickel-coated graphite.

[00105] In a twenty-second embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through sixth embodiments, comprising 40-70 parts by weight of the at least one non-linear block copolymer; 30-60 parts by weight of the at least one hydrocarbonbased tackifying resin; 2-8 parts by weight of the at least one aromatic reinforcing resin; 0.1 -4.5 parts by weight of the alkyl alkoxy silane or alkenyl alkoxy silane; 0.02-2.5 parts by weight of the non-functional dipodal alkoxysilane; and 15-30 parts by weight electrically conductive particles.

[00106] In a twenty -third embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through twenty-second embodiments, further comprising conductive nanoparticles comprising at least one of carbon nanotubes, metallic nanowires, metallic nanoflakes, metallic nanograins, or metallic nanospheres.

[00107] In a twenty -fourth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through twenty -third embodiments, wherein the conductive adhesive composition can be tested for passive intermodulation by forming a tape, the tape comprising a layer of the conductive adhesive composition and an electrically conductive layer, and placing the tape in a test fixture comprising one gold conductive surface and one stainless steel conductive surface, according to the PIM Test Method, wherein when first and second electrical signals of magnitude 30 dBm propagate in the thickness direction of the conductive adhesive layer between the gold surfaces at respective frequencies Fl and F2, any intermodulation signal generated from the first and second electrical signals having a frequency F3 equal to nFl+mF2, m and n positive or negative integers, has a power of less than about -60 dBm.

[00108] In a twenty -fifth embodiment, another conductive adhesive composition is provided. The conductive adhesive composition comprises: a pressure sensitive adhesive matrix comprising at least one non-linear block copolymer comprising aromatic end blocks and aliphatic elastomeric blocks; at least one hydrocarbon-based tackifying resin; at least one aromatic reinforcing resin; an adhesion promoter comprising an organic molecule selected from classes of organic compounds that can form a bond with a metal oxide surface; and electrically conductive particles dispersed within the matrix.

[00109] In a twenty-sixth embodiment, the present disclosure provides an electrically conductive article. The electrically conductive article comprises a substrate with a first major surface and a second major surface: and an electrically conductive adhesive layer disposed on at least a portion of the second major surface of the substrate. The electrically conductive adhesive comprises any electrically conductive adhesive composition according to any of the first through twenty -fifth embodiments.

[00110] In a twenty-seventh embodiment, the present disclosure provides an electrically conductive article according to the twenty-sixth embodiment, wherein the substrate comprises an electrically conductive substrate.

[00111] In a twenty -eighth embodiment, the present disclosure provides an electrically conductive article according to the twenty-seventh embodiment, wherein the electrically conductive substrate comprises a non-woven layer comprising metal coated polymer fibers, a woven fabric layer comprising metal coated polymer fibers, a film layer with a metal coated surface, or a metal foil.

[00112] In a twenty -ninth embodiment, the present disclosure provides an electrically conductive article according to the twenty-seventh embodiment or the twenty -eighth embodiment, wherein the article further comprises a second layer of conductive adhesive disposed on the first major surface of the electrically conductive substrate.

[00113] In a thirtieth embodiment, the present disclosure provides an electrically conductive article according to the twenty-sixth embodiment, wherein the substrate comprises a release liner.

EXAMPLES

[00114] Unless otherwise noted or readily apparent from the context, all parts, percentages, ratios, etc., in the Examples and the rest of the specification are by weight.

Materials Used in the Examples

Static Shear Test

[00115] The test was conducted at 70°C. An adhesive sample was laminated on a 50 pm thick PET film. Test specimens were cut out of the sample material having a dimension of 12.7 mm by 175 mm. The liner was then removed, and the adhesive was adhered onto to stainless steel plate with an overlap of 12.7 mm x 25.4 mm. A loop was prepared at the end of the test strip to hold a specified weight. Next, the test samples were rolled four times with a standard FINAT test roller (weight 2 kg) at a speed of approximately 10 mm per second to obtain intimate contact between the adhesive and the surface. The test samples are allowed to dwell for 24 hours at ambient room temperature (23 °C +/- 2°C, 50% relative humidity +/-5%) prior to testing.

[00116] Each sample was then placed into a vertical shear-stand (+2° disposition) at 70°C with automatic time logging. After ten minutes dwell time in the oven, a 500 g weight was hung into the loop. The time until failure was measured and recorded in minutes. Target value was 10.000 minutes. Two samples were measured for each construction. A recorded time of “>10,000” indicates that the adhesive did not fail after 10,000 minutes. Failure modes were given as followed: PO for pop-off, AT for adhesive transfer and CF for cohesive failure.

Double Coated Tape Preparation

[00117] Two sheets of 20 pm thick 17.8 cm * 17.8 cm samples were laminated onto a 22 pm thick nickeFcopper coated fabric using a seam roller. Each of the fabric samples was passed through a laminator with a rubber roller at the bottom and a steel roller at the top (Chemlnstruments Hot Roll Laminator, HL-200) at room temperature and a pressure of 0.34 MPa (50 psi, controlled by an air regulator). After lamination, the samples were annealed in an oven at 40°C for four days before measurement.

Peel Test

[00118] ASTM D3330/D3330M was followed. Some samples were laminated onto either side of a conductive fabric to make a double coated tape construction. Release liners were removed, and the adhesive samples were laminated onto a 50 pm thick PET film. The adhesives were then applied to a Stainless-Steel substrate and allowed to dwell at room temperature for 20 minutes (RT 20 min) or 72 hours (RT 72 hrs), after which they were peeled at 30.5 cm per minute at 180°. Three measurements were taken, and average peel values were noted. Peel failure modes were also noted (clean or 2-bond).

Passive Intermodulation (PIM) test

[00119] A test fixture, comprised of a 50 Ohm microstrip test board and mechanically connected coaxial cables, was used to measure PIM of the samples. The test board was 50 mm x 80 mm x 60 mil (1.52 mm) FR-4 dielectric with 1 oz copper having an ENIG (electroless nickel, immersion gold) finish. The microstrip line was 3 mm wide with a 10 mm gap centered along the board length to break the circuit. Two 3 mm x 15 mm adhesive samples were adhered manually (by finger pressure) on either side of the 10 mm gap in the microstrip line. A 40 mm x 3 mm x 1 mm stainless steel 316L bridge was aligned to the samples and gap and connected using 0.103 MPa (15 psi) pressure, completing the electrical circuit. The samples were left to dwell for at least twenty minutes before measurement. A Rosenberger desktop PIM analyzer (Tittmoning, Germany) was connected to the test fixture to perform the measurement. Two frequency signals between 729 - 758 MHz of 30 dBm (1 W) were swept over the LTE700L cellular band and the maximum reflected third-order (IM3) value was recorded.

ETM-12, DC Resistance through the PSA, Z-axis test

[00120] A double-coated tape sample was cut into 10 mm x 10 mm pieces and two pieces were placed with one adhesive side down on the center of each of the electrodes on a 3M ETM-7 board (St. Paul, MN, United States). After initial hand lamination and removal of the liners, a 3M ETM-12-SUS316L (stainless steel) plate (50 mm x 10 mm x 1 mm), (Cheil Technology, Seoul, South Korea) was placed with the metal side down on the tapes, then a 2 kg rubber roller was applied across the ETM-12 board. After 20 minutes of dwell time, the DC resistance between the electrodes was measured with a microohm meter.

Formulations [00121] Quantities of materials (in grams) listed in Table 1 were added to a glass jar after which a 3 : 1 mixture of HEP with EA was added to make a 30% solids solution. The jars were rolled for 12 hours under heat lamps to form homogenous solutions. The solutions were then coated on a RL-1 (50 pm thick) using a knife coater with a gap of 63.5 pm (2.5 mil). The coated samples were placed in an oven set at 70°C for 15 minutes. RL-2 (50 pm thick) was then laminated onto each of the dried samples.

Table 2: Compositions (in grams)

[00122] Peel Adhesion testing was performed, and the results are represented in Table 3. Electrical testing was conducted, and the results are represented in Table 4. It is noted that a more negative PIM value indicates better performance. Static Shear testing was performed, and the results are represented in Table 5.

Table 3: Peel Adhesion Results

Table 4: ETM-12 and PIM Test Results

Table 5: Static Shear Test Results

[00123] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof. [00124] Furthermore, all publications and patents referenced herein are incorporated by reference in their entirety to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description prevails. Various exemplary embodiments have been described. These and other embodiments are within the scope of the following claims.

Claims

What is claimed is:

1. A conductive adhesive composition comprising: a pressure sensitive adhesive matrix comprising at least one non-linear block copolymer comprising aromatic end blocks and aliphatic elastomeric blocks; at least one hydrocarbon-based tackifying resin; at least one aromatic reinforcing resin; an adhesion promoter comprising an alkyl alkoxysilane, an alkenyl alkoxysilane, an alkyl phosphonic acid, or an alkyl carboxylic acid; optionally a non-functional dipodal alkoxysilane, with the proviso that when the adhesion promoter comprises an alkyl alkoxysilane or an alkenyl alkoxysilane, the non-functional dipodal alkoxysilane is present; and electrically conductive particles dispersed within the matrix.

2. The conductive adhesive composition of claim 1, wherein the adhesive composition is essentially free of an amino alkoxysilane.

3. The conductive adhesive composition of claim 1 or claim 2, wherein the alkyl alkoxy silane is present and the alkyl group of the alkyl alkoxy silane is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n- heptyl, n-octyl, and ethylhexyl.

4. The conductive adhesive composition of any of claims 1 to 3, wherein the alkyl alkoxysilane is present and the alkyl group of the alkyl alkoxysilane is n-butyl.

5. The conductive adhesive composition of any of claims 1 to 4, wherein the alkyl alkoxy silane is present and the alkyl alkoxysilane comprises a dialkoxysilane or a trialkoxysilane.

6. The conductive adhesive composition of any of claims 1 to 5, wherein the alkyl alkoxysilane is present and the alkyl alkoxysilane and the non-functional dipodal alkoxysilane are present in a weight ratio of 9 : 1 to 1 : 1.

7. The conductive adhesive composition of claim 1 or claim 2, wherein the alkenyl alkoxysilane is present and the alkenyl group of the alkenyl alkoxysilane is selected from the group consisting of ethenyl, 1 -propenyl, 1-butenyl, and a polybutadiene oligomer.

8. The conductive adhesive composition of claim 1, claim 2, or claim 7, wherein the alkenyl alkoxysilane is present and the alkenyl group of the alkenyl alkoxysilane is polybutadiene.

9. The conductive adhesive composition of claim 1 or claim 2, wherein the alkyl phosphonic acid is present and the alkyl group of the alkyl phosphonic acid is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n- heptyl, n-octyl, and ethylhexyl.

10. The conductive adhesive composition of claim 9, wherein the alkyl group is n-butyl.

11. The conductive adhesive composition of claim 10, further comprising 1,2-ethylenediphosphonic acid.

12. The conductive adhesive composition of any of claims 9 to 11, comprising:

40-70 parts by weight of the at least one non-linear block copolymer;

30-60 parts by weight of the at least one hydrocarbon-based tackifying resin;

2-8 parts by weight of the at least one aromatic reinforcing resin;

0.2-5 parts by weight of the alkyl phosphonic acid; and

15-30 parts by weight electrically conductive particles.

13. The conductive adhesive composition of claim 1 or claim 2, wherein the alkyl carboxylic acid is present and the alkyl group of the alkyl carboxylic acid is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n- heptyl, n-octyl, and ethylhexyl.

14. The conductive adhesive composition of claim 13, wherein the alkyl carboxylic acid comprises butanoic acid, pentanoic acid, or beta-carboxy ethyl acrylate.

15. The conductive adhesive composition of claim 13 or claim 14, comprising:

40-70 parts by weight of the at least one non-linear block copolymer;

30-60 parts by weight of the at least one hydrocarbon-based tackifying resin;

2-8 parts by weight of the at least one aromatic reinforcing resin;

0.5-5 parts by weight of the alkyl carboxylic acid; and

15-30 parts by weight electrically conductive particles.

16. The conductive adhesive composition of any of claims 1 to 15, wherein the electrically conductive particles comprise particles of nickel-coated graphite.

17. The conductive adhesive composition of any of claims 1 to 6, comprising:

40-70 parts by weight of the at least one non-linear block copolymer;

30-60 parts by weight of the at least one hydrocarbon-based tackifying resin;

2-8 parts by weight of the at least one aromatic reinforcing resin;

0.1-4.5 parts by weight of the alkyl alkoxysilane or the alkenyl alkoxysilane;

0.02-2.5 parts by weight of the non-functional dipodal alkoxy silane; and

15-30 parts by weight electrically conductive particles.

18. The conductive adhesive composition of any of claims 1 to 17, wherein the conductive adhesive composition can be tested for passive intermodulation by forming a tape, the tape comprising a layer of the conductive adhesive composition and an electrically conductive layer, and placing the tape in a test fixture comprising one gold conductive surface and one stainless steel conductive surface, according to the PIM Test Method, wherein when first and second electrical signals of magnitude 30 dBm propagate in the thickness direction of the conductive adhesive layer between the gold surfaces at respective frequencies Fl and F2, any intermodulation signal generated from the first and second electrical signals having a frequency F3 equal to nF l+mF2, m and n positive or negative integers, has a power of less than about -60 dBm.

19. A conductive adhesive composition comprising: a pressure sensitive adhesive matrix comprising at least one non-linear block copolymer comprising aromatic end blocks and aliphatic elastomeric blocks; at least one hydrocarbon-based tackifying resin; at least one aromatic reinforcing resin; an adhesion promoter comprising an organic molecule selected from classes of organic compounds that can form a bond with a metal oxide surface; and electrically conductive particles dispersed within the matrix.

20. An electrically conductive article comprising: a substrate with a first major surface and a second major surface: and an electrically conductive adhesive layer disposed on at least a portion of the second major surface of the substrate; wherein the electrically conductive adhesive comprises the electrically conductive adhesive composition of any of claims 1 to 19.

21. The electrically conductive article of claim 20, wherein the substrate comprises an electrically conductive substrate.

22. The electrically conductive article of claim 21, wherein the electrically conductive substrate comprises a non-woven layer comprising metal coated polymer fibers, a woven fabric layer comprising metal coated polymer fibers, a film layer with a metal coated surface, or a metal foil.

23. The electrically conductive article of claim 21 or claim 22, wherein the article further comprises a second layer of conductive adhesive disposed on the first major surface of the electrically conductive substrate.