Conductive adhesive composition, crosslinked conductive adhesive composition, and conductive article

Abstract

The invention provides a conductive adhesive composition. The present invention relates to a pressure sensitive adhesive composition comprising: a pressure sensitive adhesive matrix comprising at least one non-linear block copolymer comprising an aromatic terminal block and an aliphatic elastomer block; at least one hydrocarbon-based tackifying resin; at least one aromatic reinforced resin; and conductive particles dispersed within the matrix. The composition further comprises a crosslinker having an acrylate group and optionally an aliphatic olefin group, and optionally an aliphatic olefin component having a glass transition temperature (Tg) of less than-5 degrees Celsius. The crosslinking agent has a Tg of less than-5 degrees Celsius. When the crosslinker lacks aliphatic olefin groups, an aliphatic olefin component is present. Further, a crosslinked conductive adhesive composition is provided that is a free radical cure reaction product of the conductive adhesive composition. Also provided is a conductive article comprising a substrate and a crosslinked conductive adhesive disposed on the substrate.

Description

BACKGROUND OF THE INVENTION

[0001] Conductive adhesives tend to have good electrical properties, adhesive properties, and heat and moisture aging resistance. Further development of conductive adhesives would be desirable. SUMMARY OF THE INVENTION

[0002] In a first aspect, there is provided a conductive adhesive composition. The conductive adhesive composition comprises: a pressure-sensitive adhesive matrix comprising at least one non-linear block copolymer, the at least one non-linear block copolymer comprising aromatic end blocks and an aliphatic elastomeric block; at least one hydrocarbon-based tackifying resin; and at least one aromatic reinforcing resin. The composition further comprises a crosslinking agent having acrylate groups and optionally aliphatic olefin groups, and optionally an aliphatic olefin component having a glass transition temperature (Tg) of less than -5 degrees Celsius. The crosslinking agent has a Tg of less than -5 degrees Celsius. When the crosslinking agent lacks aliphatic olefin groups, the aliphatic olefin component is present. The conductive adhesive composition further comprises conductive particles dispersed within the pressure-sensitive adhesive matrix.

[0003] In a second aspect, there is provided a crosslinked conductive adhesive composition. The crosslinked conductive adhesive composition comprises the free radical curing reaction product of any of the conductive adhesive compositions according to the first aspect.

[0004] In a third aspect, there is provided a conductive article. The conductive article comprises: a substrate having a first major surface and a second major surface; and a crosslinked conductive adhesive layer disposed on at least a portion of the second major surface of the substrate. The crosslinked conductive adhesive comprises any of the crosslinked conductive adhesive compositions according to the second aspect.

[0005] The above Summary of the Invention is not intended to describe every illustrated embodiment or every implementation of the present disclosure's current exemplary embodiments. The following drawings and Detailed Description more particularly illustrate certain preferred embodiments that utilize the principles disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present disclosure may be more fully understood in view of the following detailed description of various embodiments of the present disclosure in conjunction with the accompanying drawings, in which:

[0007] Figure 1 is a general schematic cross-sectional view of an exemplary conductive article according to various embodiments disclosed herein; and

[0008] Figure 2 is a cross-sectional view of a device for testing the PIM (passive intermodulation) of an adhesive.

[0009] In the drawings, like reference numerals indicate like elements. Although the above-described drawings, which may not be drawn to scale, illustrate various embodiments of the present disclosure, other embodiments are also contemplated, as pointed out in the detailed description. In all cases, the present disclosure describes the presently disclosed disclosure in terms of representations of exemplary embodiments rather than by way of limitation. It should be understood that many other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the present disclosure. Detailed Description

[0010] In electronic component devices such as smart phones and tablet computers, there are many applications that require conductive tapes and conductive gaskets for use as grounding and / or shielding materials. Conductive pressure-sensitive adhesives (CPSAs) and articles containing CPSAs are used in components within electronic devices. These CPSAs are not only used to adhere the components of the device together (the typical role of a PSA), but are also required to provide additional functions within the device. Conductive PSAs have conflicting requirements, typically requiring high electrical conductivity for grounding performance and strong adhesion to electronic components without adversely affecting the electronic components. Since electronic components are typically subject to corrosion and degradation (such as, for example, layers of copper and conductive fabric), many of the typical materials used in pressure-sensitive adhesives are not the best options for CPSAs (such as acidic or basic functional materials, or trace acidic or basic impurities in the CPSA components).

[0011] One desire in electronic devices is to reduce passive intermodulation (PIM). When two or more signals at different frequencies mix with each other, PIM is generated due to electrical non-linearity. In some cases, PIM signals generated by the wireless transmission of signals can occur at frequencies within the receive band of a wireless communication or data device, thereby causing undesirable signal interference. Methods for measuring PIM are described below and illustrated in the drawings. Accordingly, there is still a need for such a conductive PSA that has and maintains good PSA properties (such as peel and shear properties), has and maintains good conductive properties, and provides a low level of PIM even when aged at elevated temperature and humidity levels.

[0012] In the present disclosure, a conductive PSA is described that has and maintains good PSA properties (such as peel and shear properties), good conductive properties, and provides a low level of PIM. The conductive PSA comprises a pressure-sensitive adhesive matrix that comprises at least one non-linear block copolymer containing an aromatic end block and an aliphatic elastomeric block, at least one hydrocarbon-based tackifying resin, at least one aromatic reinforcing resin, and conductive particles dispersed within the matrix. Also disclosed are crosslinked conductive adhesive compositions and articles prepared using the crosslinked conductive pressure-sensitive adhesive.

[0013] For the glossary of terms defined below, unless a different definition is provided elsewhere in the claims or the specification, the entire application shall be construed in accordance with these definitions.

[0014] Glossary

[0015] Certain terms are used throughout the specification and claims, and although most are well known, some explanation may still be required. It should be understood that:

[0016] As used herein, the term "adhesive" refers to a polymeric composition that can be used to adhere two adherends together. Examples of adhesives are pressure-sensitive adhesives.

[0017] Those of ordinary skill in the art are familiar with the properties of pressure-sensitive adhesive compositions, which include: (1) strong and durable adhesion, (2) the ability to adhere by finger pressure, (3) sufficient ability to adhere to the adherend, and (4) sufficient cohesive strength to be cleanly removed from the adherend. Materials that have been found to function well as pressure-sensitive adhesives are polymers that are designed and formulated to exhibit the desired viscoelastic properties, such that the tack, peel adhesion, and shear retention are balanced as desired. Achieving the proper balance of properties is not a simple matter.

[0018] The terms "room temperature" and "ambient temperature" are used interchangeably and mean a temperature in the range of 20°C to 25°C.

[0019] As used herein, the term "adjacent" when referring to two layers means that the two layers are adjacent to each other with no intervening open space. They may be in direct contact with each other (e.g., laminated together) or there may be an intervening layer.

[0020] As used herein, the terms "polymer" and "macromolecule" are consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeating subunits. The term "polymer" is used to describe the resulting material formed by a polymerization reaction.

[0021] As used herein, "substantially free of" with respect to a component of a composition means that, based on the total weight of the composition, the amount of that component present is less than 0.1 weight percent (wt%), such as less than 0.09 wt%, 0.08 wt%, 0.07 wt%, 0.06 wt% of the total weight of the composition, or even less than 0.05 wt%.

[0022] The term "alkenyl" refers to a monovalent group that is an olefinic group, where the olefin is a hydrocarbon having at least one carbon-carbon double bond. The alkenyl can be straight-chain, branched-chain, cyclic, or a combination 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 vinyl, 1-propenyl, and 1-butenyl.

[0023] The term "alkyl" refers to a monovalent group that is an alkyl group, where the alkane is a saturated hydrocarbon. The alkyl can be straight-chain, branched-chain, cyclic, or a combination 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.

[0024] The term "alkylene" refers to a divalent group that is a group of an alkane. The alkylene can be straight-chain, branched-chain, cyclic, or a combination thereof. The alkylene typically 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 group center of the alkylene can be on the same carbon atom (i.e., alkylidene) or on different carbon atoms.

[0025] The term "alkoxy" refers to a monovalent group having the formula -OR, where R is an alkyl group. The term "alkoxysilane" refers to a monovalent group having the formula -Si(OR)n, where R is an alkyl group and n is an integer from 1 to 3.

[0026] The term "bidentate alkoxysilane" refers to a component having two sets of alkoxysilyl groups.

[0027] The term "non-functionalized" means not having any functional group that exhibits reactivity or polymerizable reactivity with another functional group, where the other functional group includes hydroxyl group, silanol group, Si-H group, vinyl group, allyl group, acrylic group, methacrylic group, epoxy group, amino group, and mercapto group. Examples of non-functional groups include alkyl groups or aryl groups composed of carbon, hydrogen, and (in some embodiments) halogen atoms (e.g., chlorine atom).

[0028] As used herein, the term "phosphonic acid" refers to a group having the formula -P(=O)(OH)2 directly attached to a carbon atom.

[0029] As used herein, the term "carboxylic acid" refers to a group of the formula -C(=O)(OH) directly attached to a carbon atom.

[0030] As used herein, the terms "glass transition temperature" and "Tg" are used interchangeably and refer to the glass transition temperature of a material or mixture. Unless otherwise specified, glass transition temperature values are measured by differential scanning calorimetry (DSC) at a heating rate of 10 °C / minute in a nitrogen stream. When referring to the Tg of a monomer, it is the Tg of the homopolymer of that monomer or crosslinker. The homopolymer must have a high enough molecular weight such that the Tg reaches a limiting value, as it is generally believed that the Tg of a homopolymer will increase to a limiting value with increasing molecular weight. The homopolymer should also be understood to be substantially free of moisture, residual monomers, solvents, and other contaminants that may affect the Tg. Suitable DSC methods and analysis modes are described in the following reference: Matsumoto, A. et al., Journal of Polymer Science, Part A: Polymer Chemistry, 1993, Vol. 31, pp. 2531-2539 (Matsumoto, A. et al., J. Polym. Sci. A., Polym. Chem. 1993, 31, 2531-2539).

[0031] The term "about" or "approximately" with respect to a numerical value or shape means + / - 5% of that numerical value or property or characteristic, but expressly includes the exact numerical value.

[0032] The term "substantially" with respect to a property or characteristic means that the degree to which that property or characteristic is exhibited is greater than the degree to which the opposite of that property or characteristic is exhibited.

[0033] As used in this specification and the appended embodiments, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" include plural referents. Thus, for example, reference to "a compound" includes a mixture of two or more compounds. As used in this specification and the appended embodiments, unless the context clearly dictates otherwise, the term "or" is generally used in its meaning that includes "and / or".

[0034] Unless otherwise specified, all numbers expressing quantities or ingredients, properties measurements, etc. used in this specification and the embodiments are to be understood in all instances as being modified by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the above specification and the list of appended embodiments can vary depending upon the desired properties sought to be obtained by those of ordinary skill in the art utilizing the teachings of this disclosure. At the very least, and without attempting to limit the application of the doctrine of equivalents to the scope of the embodiments claimed, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0035] By definition, the total weight percentage of all components in the composition equals 100 weight %.

[0036] Various exemplary embodiments of the present disclosure will now be described. Various modifications and changes can be made to the exemplary embodiments of the present disclosure without departing from the essence and scope of the present disclosure. Therefore, it should be understood that the embodiments of the present disclosure are not limited to the exemplary embodiments described below, but are controlled by the limiting factors shown in the claims and any equivalents thereof.

[0037] In a first aspect, a conductive adhesive composition is provided. The conductive adhesive composition comprises:

[0038] a pressure-sensitive adhesive matrix that comprises at least one non-linear block copolymer, the at least one non-linear block copolymer comprising an aromatic end block and an aliphatic elastomeric block;

[0039] at least one hydrocarbon-based tackifying resin;

[0040] at least one aromatic reinforcing resin;

[0041] a crosslinking agent, the crosslinking agent comprising acrylate groups and optionally aliphatic olefin groups, wherein the crosslinking agent has a glass transition temperature (Tg) of less than -5 degrees Celsius;

[0042] an optional aliphatic olefin component having a Tg of less than -5 degrees Celsius, provided that when the crosslinking agent lacks aliphatic olefin groups, the aliphatic olefin component is present; and

[0043] conductive particles, the conductive particles being dispersed within the matrix.

[0044] Surprisingly, it has been found that by using certain crosslinking agents to crosslink the conductive adhesive composition, a low resistance can be better maintained after the crosslinked conductive adhesive composition is aged on a conductive fabric substrate at 85 °C and 85% relative humidity for 72 hours. The crosslinking agent comprises acrylate groups and has a glass transition temperature (Tg) of less than -5 degrees Celsius. In some cases, the crosslinking agent further comprises aliphatic olefin groups. When the crosslinking agent lacks aliphatic olefin groups, a separate aliphatic olefin component having a Tg of less than -5 degrees Celsius is also included in the conductive adhesive composition.

[0045] In some embodiments where aliphatic olefin groups are present in the crosslinker, the crosslinker comprises at least one of polyisoprene groups, butadiene groups, or polymerizable terpenes (such as farnesene or myrcene). In selected cases, the crosslinker comprises isoprene groups. In selected cases, the crosslinker comprises butadiene groups. In selected cases, the crosslinker comprises polymerizable terpenes. In selected cases, the crosslinker comprises farnesene. In selected cases, the crosslinker comprises myrcene. In selected cases, the crosslinker comprises (e.g., other) polymerizable terpenes. Such aliphatic olefin groups tend to be compatible with at least the aliphatic elastomeric blocks of the non-linear block copolymer of the binder matrix.

[0046] Exemplary suitable crosslinkers having both acrylate groups and aliphatic olefin groups include, for example but not limited to, acrylate-functionalized isoprene rubber commercially available under the trade name "UC-102M" from Kuraray Co., Ltd. (Kuraray (Houston, TX)), Houston, Texas, USA.

[0047] In certain embodiments, a crosslinker having acrylate groups can be used with an olefin that does not have any acrylate groups. Exemplary suitable crosslinkers having acrylate groups and a Tg less than -5 degrees Celsius include, for example but not limited to, polyfunctional acrylates commercially available under the trade names "CN307, CN308, and CN309" from Arkema Sartomer Americas (Exton, PA), Exton, Pennsylvania, USA. When a crosslinker that does not contain any aliphatic olefin groups is employed, an aliphatic olefin component having a Tg less than -5 degrees Celsius is present in the electrically conductive adhesive composition. Exemplary suitable aliphatic olefin components include, for example but not limited to, copolymers of styrene and butadiene commercially available under the trade name "L-SBR-820" from Kuraray Co., Ltd. (Kuraray (Houston, TX)), Houston, Texas, USA.

[0048] In certain embodiments, the electrically conductive adhesive composition further comprises at least one polymerization initiator to assist the crosslinking reaction, such as in an amount of up to about 10 parts by weight of the total electrically conductive adhesive composition, or 8 parts by weight, 5 parts by weight, or even up to 2 parts by weight of the total electrically conductive adhesive composition. The polymerization initiator is a free radical initiator. In selected cases, the polymerization initiator comprises a photoinitiator.

[0049] Suitable exemplary photoinitiators are those that can be purchased from IGM Resins (Waalwijk, The Netherlands) under the trade name OMNIRAD, and include 1-hydroxycyclohexyl phenyl ketone (OMNIRAD 184), 2,2-dimethoxy-1,2-diphenylethan-1-one (OMNIRAD 651), bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide (OMNIRAD 819), 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methylpropan-1-one (OMNIRAD 2959), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one (OMNIRAD 369), 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-ylphenyl)butan-1-one (OMNIRAD 379), 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (OMNIRAD 907), oligomer [2-hydroxy-2-methyl-1-[4-(1-methylethenyl)phenyl]propanone] ESACURE ONE (Lamberti S.p.A., Gallarate, Italy), 2-hydroxy-2-methyl-1-phenylpropan-1-one (DAROCUR 1173), 2,4,6-trimethylbenzoyl diphenyl phosphine oxide (OMNIRAD TPO), and 2,4,6-trimethylbenzoyl phenyl phosphinate (OMNIRAD TPO-L). Additional suitable photoinitiators include, for example and without limitation, benzyl dimethyl ketal, 2-methyl-2-hydroxyacetophenone, benzoin methyl ether, benzoin isopropyl ether, anisoin methyl ether, aromatic sulfonyl chlorides, photoactive oximes, and combinations thereof.

[0050] The electrically conductive adhesive can be subjected to PIM (passive intermodulation) testing as described in more detail in the Examples section and the figures below. The method involves forming a tape that includes a crosslinked electrically conductive adhesive layer and an electrically conductive layer, such as an electrically conductive woven layer or nonwoven layer. The tape is placed in a test fixture that includes a gold electrically conductive surface. When a first electrical signal and a second electrical signal of magnitude 30 dBm propagate between the gold surfaces along the thickness direction of the crosslinked electrically conductive adhesive layer at respective frequencies F1 and F2, any intermodulation signal generated by the first and second electrical signals and having a frequency F3 equal to nF1 + mF2 has a power of less than about -70 dBm, where m and n are positive or negative integers. It should be understood that "less than" a particular negative number means a more negative number, e.g., -80 dBm is less than -70 dBm.

[0051] It should be noted that the properties of the adhesive, such as 180° peel adhesion, DC resistance, and PIM, are properties of the crosslinked conductive adhesive. Although the conductive adhesive is formed into a tape, for example, by setting the adhesive onto a 50-micron PET backing for the 180° peel adhesion test, the properties are properties of the adhesive itself and do not mean that the adhesive can only be used in the form of a tape. The test method involves forming a tape for testing, but the listed properties are properties of the adhesive itself.

[0052] The crosslinked conductive adhesive comprises a pressure-sensitive adhesive matrix. The pressure-sensitive adhesive matrix comprises at least one non-linear block copolymer containing an aromatic end block and an aliphatic elastomeric block, at least one hydrocarbon tackifying resin, and at least one aromatic reinforcing resin.

[0053] A variety of different non-linear block copolymers containing an aromatic end block and an aliphatic elastomeric block are suitable. The non-linear block copolymer is not a simple A-B-A block copolymer. In some embodiments, at least one non-linear block copolymer comprises a star copolymer or a comb copolymer. Examples of commercially available comb styrene-farnesene-styrene block copolymers include SF902 obtained from Kuraray, Tokyo, Japan.

[0054] In some embodiments of the block copolymer, the aromatic end block comprises a styrene block, and the aliphatic elastomeric block comprises isoprene, farnesene, or a combination thereof. Star block copolymers are sometimes also referred to as radial block copolymers. Particularly suitable polymers include radial styrene-isoprene-styrene block copolymers and styrene-farnesene-styrene block copolymers. Examples of commercially available radial styrene-isoprene-styrene block copolymers include those available under the trade names D1340KT and DL1124KT from Kraton Polymers, Houston, TX. Particularly suitable radial block copolymers comprise star copolymers having styrene end blocks and isoprene elastomeric blocks, wherein the end blocks comprise 9 wt% to 10 wt% styrene based on the total polymer.

[0055] 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 variety of different hydrogenated or partially hydrogenated hydrocarbon resins are suitable. Examples of commercially available hydrogenated or partially hydrogenated hydrocarbon resins include resins ARKON P100, ARKON P125, and ARKON P140 obtained from Arakawa Chemical Inc., Chicago, IL.

[0056] The pressure-sensitive adhesive matrix further comprises at least one aromatic reinforcing resin. In some embodiments, the aromatic reinforcing resin comprises a thermoplastic aromatic copolymer having a Tg (glass transition temperature) greater than 100 °C. A variety of different aromatic resins are suitable. An example of a commercially available aromatic reinforcing resin is ENDEX 160 from Eastman Chemical Company, Kingsport, TN.

[0057] The electrically conductive adhesive further comprises electrically conductive particles dispersed within the pressure-sensitive adhesive matrix. A variety of different electrically conductive particles are suitable. The electrically conductive filler particles can be in the form of metal particles or metal-coated insulating (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 electrically conductive adhesive can vary, as will be described below. A particularly suitable electrically conductive particle is the nickel-coated graphite particle "E-Fill #2806Ni", which is commercially available from Oerlikon Metco, Westbury, NY.

[0058] The electrically conductive adhesive can optionally comprise at least one additive. Particularly suitable additives include electrically conductive nanoparticles and / or adhesion promoters. Examples of suitable electrically conductive nanoparticles include carbon nanotubes, metal nanoparticles, and metal nanoparticles include nanowires, nanosheets, nanograins, and nanospheres.

[0059] A variety of adhesion promoters are suitable for the electrically conductive adhesives disclosed herein, including certain alkoxysilanes (e.g., alkylalkoxysilanes, alkenylalkoxysilanes), phosphonic acids (e.g., alkylphosphonic acids), carboxylic acids (e.g., alkylcarboxylic acids), hydroxamic acids (e.g., alkyl N-hydroxyamides), and phosphoric esters. When an adhesion promoter is present, the amount thereof is typically from 0.1 parts by weight to 5 parts by weight.

[0060] Although it is possible to employ a combination of an aminoalkoxysilane adhesion promoter and the adhesion promoters described herein, in some embodiments the electrically conductive adhesive composition is substantially free of aminoalkoxysilane (i.e., contains less than 0.1 wt% aminoalkoxysilane).

[0061] It should be noted that certain classes of organic compounds can form bonds with metal oxide surfaces, such as but not limited to alkoxysilanes, phosphonic acids, phosphoric esters, carboxylic acids, and hydroxamic acids. In some cases, the adhesion promoter does form bonds with the metal oxide surface, such as hydrogen bonds or covalent bonds. The adhesion promoter can form single, double, or triple bonds with the metal oxide surface. Typical metal oxides include, for example but not limited to, nickel oxide, copper oxide, silver oxide, aluminum oxide, chromium oxide, iron oxide, and titanium oxide.

[0062] In some embodiments, an alkylalkoxysilane is present and the alkyl group of the alkylalkoxysilane 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 alkylalkoxysilane is n-butyl. Generally, the suitable alkoxy group of the alkylalkoxysilane has 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 alkylalkoxysilane comprises a dialkoxysilane or a trialkoxysilane. Exemplary alkylalkoxysilanes include, for example but not limited to, n-butyltrimethoxysilane, n-decyltrimethoxysilane, n-octyltrimethoxysilane, n-butyldimethoxysilane, n-decyldimethoxysilane, and n-octyldimethoxysilane.

[0063] In some embodiments, an alkenylalkoxysilane is present and the alkenyl group of the alkenylalkoxysilane is selected from the group consisting of: vinyl, 1-propenyl, 1-butenyl, and polybutadiene oligomers. The polybutadiene oligomer is not particularly limited and its weight average molecular weight can be 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 selected cases, the alkenyl group of the alkenylalkoxysilane is polybutadiene. Exemplary alkenylalkoxysilanes include, for example but not limited to, trimethoxyvinylsilane, allyltrimethoxysilane, trimethoxyoctenylsilane, dimethoxyvinylsilane, allyldimethoxysilane, dimethoxyoctenylsilane, and polybutadiene modified with trimethoxy or triethoxy.

[0064] As described above, when the adhesion promoter contains an alkylalkoxysilane or an alkenylalkoxysilane, a non-functionalized bidentate alkoxysilane is present. In some embodiments, the alkylalkoxysilane and the non-functionalized bidentate alkoxysilane are present in a weight ratio of from 9:1 to 1:1, such as from 8:1 to 1:1, from 7:1 to 1:1, from 6:1 to 1:1 or even from 5:1 to 1:1. Exemplary suitable non-functionalized bidentate alkoxysilanes include, for example but not limited to, 1,2-bis(trimethoxysilyl)ethane, 1,2-bis(trimethoxysilyl)methane, 1,2-bis(trimethoxysilyl)octane, 1,2-bis(triethoxysilyl)ethane, 1,2-bis(triethoxysilyl)methane, 1,2-bis(triethoxysilyl)octane, 1,2-bis(dimethoxysilyl)ethane, 1,2-bis(dimethoxysilyl)methane, 1,2-bis(dimethoxysilyl)octane, 1,2-bis(diethoxysilyl)ethane, 1,2-bis(diethoxysilyl)methane and 1,2-bis(diethoxysilyl)octane.

[0065] In some embodiments, an alkylphosphonic acid is present and the alkyl group of the alkylphosphonic 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 2-ethylhexyl. In a selected case, the alkyl group is n-butyl. Optionally, a second alkylphosphonic acid may be added. Exemplary suitable alkylphosphonic acids include, for example but not limited to, 1-butylphosphonic acid, 1,2-ethylenediphosphonic acid, methylphosphonic acid, ethylphosphonic acid and 1,8-octanediphosphonic acid.

[0066] In some embodiments, an alkylcarboxylic acid is present and the alkyl group of the alkylcarboxylic 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 2-ethylhexyl. In a selected case, the alkyl group is n-butyl or n-pentyl. Exemplary suitable alkylcarboxylic acids include, for example but not limited to, butyric acid, valeric acid and octanoic acid. In some cases, the alkylcarboxylic acid may further include at least one acrylate or vinyl group that can react into the PSA, such as ethyl β-carboxyacrylate.

[0067] In some embodiments, the adhesion promoter contains a phosphate ester. Exemplary suitable phosphate esters include, for example but not limited to, propyl phosphate, isopropyl phosphate, butyl phosphate, 2-ethylhexyl phosphate, dipropyl phosphate, diisopropyl phosphate, dibutyl phosphate and bis(2-ethylhexyl) phosphate.

[0068] In some embodiments, the adhesion promoter contains a hydroxamic acid. Exemplary suitable hydroxamic acids include, for example but not limited to, N-hydroxybutyramide, N-hydroxypentanamide and N-hydroxyhexanamide.

[0069] Conductive adhesive matrix formulations can have various component compositions. In some embodiments, the conductive adhesive comprises: a pressure-sensitive adhesive matrix, wherein the pressure-sensitive adhesive matrix comprises: 40 to 70 parts by weight of at least one non-linear block copolymer; 30 to 60 parts by weight of a hydrocarbon-based tackifying resin; 2 to 8 parts by weight of an aromatic reinforcing resin; 1 to 15 parts by weight of a combination of crosslinking agents, or a combination of a crosslinking agent and an optional aliphatic olefin component if an optional aliphatic olefin component is present; and 15 to 30 parts by weight of conductive particles. Thus, in some cases, there is 1 to 15 parts by weight of a crosslinking agent, while in other cases, there is a combination of 1 to 15 parts by weight of a crosslinking agent and an optional aliphatic olefin component. Parts by weight are used to describe these formulations, rather than weight %, because the weight components are not necessarily added up to 100.

[0070] In a second aspect, a crosslinked conductive adhesive composition is provided. The crosslinked conductive adhesive composition comprises the free radical curing reaction product of any of the conductive adhesive compositions according to the first aspect described in detail herein. Optionally, a photoinitiated (wherein a photoinitiator is included in the adhesive composition) crosslinking reaction is used, and the conductive adhesive composition is cured using actinic radiation including UV radiation, electron beam radiation, visible light radiation, or a combination thereof to form the crosslinked reaction product. Optionally, a thermally initiated (wherein a thermal initiator is optionally included in the adhesive composition) crosslinking reaction is used, and the conductive adhesive composition is cured using heat (such as at a temperature in the range of about 50 to 150 degrees Celsius) to form the reaction product.

[0071] As described above, the conductive adhesive has various desired properties. Among these properties are adhesive properties (180° peel adhesion) and electrical properties (DC resistance and PIM). Each of these properties is described below.

[0072] The electrically conductive adhesive is a pressure - sensitive adhesive, which means it has the characteristic properties of a pressure - sensitive adhesive: (1) strong and durable adhesion, (2) the ability to adhere by finger pressure, (3) sufficient ability to adhere to the adherend, and (4) sufficient cohesive strength to be cleanly removed from the adherend. A test commonly used to measure the adhesion properties of pressure - sensitive adhesives is the 180° peel adhesion. In this test, the cross - linked adhesive is set on a backing and peeled from the test surface as described in the test methods in the Examples section. In some embodiments, the cross - linked electrically conductive adhesive has a 180° peel adhesion of at least 15.0 Newtons per decimeter (0.15 N / mm) at room temperature. In other embodiments, the cross - linked electrically conductive adhesive has a 180° peel adhesion of at least 20.0 Newtons per decimeter (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) or even at least 60 N / dm (0.6 N / mm) at room temperature.

[0073] As described above, an important characteristic of current electrically conductive adhesives is their stability when exposed to heat and humidity, especially when the adhesive is in contact with an electrically conductive substrate such as an electrically conductive fabric. In some embodiments, after aging on an electrically conductive fabric substrate at 85 °C and 85% relative humidity for at least 72 hours (or even at least 1 week), the change in the 180° peel adhesion of the cross - linked electrically conductive adhesive is 25% or less.

[0074] The cross - linked electrically conductive adhesive also has desirable electrical properties. Among these properties are DC resistance and PIM. The cross - linked electrically conductive adhesive has a DC resistance of less than 0.4 ohms as measured by ETM - 7. The test method ETM - 7 is described in the Examples section below. In some embodiments, the cross - linked electrically conductive adhesive has a DC resistance of less than 0.35 ohms, 0.3 ohms, 0.25 ohms, 0.2 ohms, 0.15 ohms or even less than 0.1 ohm. Advantageously, after aging on an electrically conductive fabric substrate at 85 °C and 85% relative humidity for 72 hours, in some embodiments, the cross - linked electrically conductive adhesive has a DC resistance of less than 0.35 ohms, 0.3 ohms, 0.25 ohms, 0.2 ohms or even less than 0.15 ohm. In some embodiments, after aging on an electrically conductive fabric substrate at 85 °C and 85% relative humidity for at least 72 hours, the change in the DC resistance of the cross - linked electrically conductive adhesive is 65% or less, 60%, 55%, 50%, 45% or even 40% or less.

[0075] The adhesive layer is generally described as having a length and a width in the x - y plane and a thickness along the z - axis. The electrically conductive adhesives of the present disclosure are generally "z - axis electrically conductive adhesives". This means that the electrically conductive adhesive layer conducts along the z - axis, which is the thickness of the adhesive layer, and does not necessarily conduct in the x - y plane of the adhesive layer.

[0076] The adhesive layer of the present disclosure can be prepared from the free radical curing reaction product of a conductive adhesive composition. These layers can be prepared by setting the adhesive composition on the surface of a substrate (such as a release liner) and then subjecting it to curing to effect crosslinking of the pressure-sensitive adhesive matrix. The adhesive layer can be provided in a variety of ways, such as in sheets or rolls, where the roll can roll itself for transportation or storage and be unrolled during use.

[0077] In a third aspect, a conductive article is provided. The conductive article includes: a substrate having a first major surface and a second major surface; and a crosslinked conductive adhesive layer disposed on at least a portion of the second major surface of the substrate. The crosslinked conductive adhesive comprises any of the crosslinked conductive adhesive compositions according to the second aspect described in detail herein.

[0078] Reference Figure 1 , which provides a general schematic cross-sectional view of the conductive article 100. The article 100 includes a substrate 110 having a first major surface 112 and an opposite second major surface 114. The crosslinked 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 130 of the crosslinked conductive adhesive is disposed on at least a portion of the first major surface 112 of the substrate 110.

[0079] A variety of different substrates are suitable. In some embodiments, the substrate includes a conductive substrate. These embodiments can be described as "single-sided tapes" because they have a single-sided exposed adhesive. A variety of different conductive substrates are suitable. Examples of suitable conductive substrates include nonwoven layers comprising metal-coated polymer fibers, woven fabric layers comprising metal-coated polymer fibers, film layers having a metal-coated surface, or metal foils. The metal can be deposited on the fibers or film in a variety of ways, such as by coating, sputtering, electroplating, or chemical vapor deposition.

[0080] In other embodiments, the substrate includes a release liner. In these embodiments, the conductive adhesive layer is a self-standing adhesive layer where both surfaces of the adhesive layer are exposed. These self-standing adhesive layers can be used in a variety of ways. The exposed adhesive surface can be laminated to a conductive substrate to form a single-sided tape as described above. The self-standing adhesive layer can be used because when laminated to a surface, the release liner can be removed to expose the second surface of the adhesive, and the substrate or surface can be adhered to the newly exposed surface. The self-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.

[0081] Release liners are well known in the art of adhesives as films from which an adhesive composition or coating can be readily removed. Exemplary release liners include those made from paper materials (e.g., kraft paper) or polymeric materials (e.g., polyolefins such as polyethylene or polypropylene, ethylene vinyl acetate, polyurethane, polyesters such as polyethylene terephthalate, etc., and combinations thereof). At least some release liners are coated with a release agent layer such as silicone, fluorosilicone-containing materials, or fluorocarbon-containing materials.

[0082] Another important feature of the crosslinked conductive adhesives of the present disclosure is the relatively low PIM (passive intermodulation). PIM can be tested as Figure 2 shown, where a double-sided tape is used that includes two layers of crosslinked conductive adhesive with a conductive intermediate layer disposed therebetween. The conductive intermediate layer can be various conductive layers such as a metal layer or a conductive woven or non-woven layer. A sample of the double-sided tape is disposed on the gold portion of a PIM board, and a conductive bridge connects the sample. In Figure 2 FIG., the PIM test board 200 has a gold portion 210 and wires 240. The test sample includes an adhesive layer 220 having a conductive bridge 230. The adhesive layer 220 has sub-layers that are: sub-layer 221, which is the adhesive sample; sub-layer 222, which is the conductive intermediate layer; and sub-layer 223, which is the adhesive sample.

[0083] It should be understood that the test method for the adhesive for PIM does not limit the articles that can be made from the conductive adhesive, but rather the properties are those of the crosslinked conductive adhesive regardless of how the PIM is measured, rather than the properties of the articles (such as single-sided tapes, double-sided tapes, etc.) of the adhesive. When a first electrical signal and a second electrical signal of magnitude 30 dBm propagate along the thickness direction (z-axis) of the conductive adhesive layer at respective frequencies F1 and F2, any intermodulation signal generated has a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. When measured in this manner, the PIM has a power of less than about -70 dBm.

[0084] The present disclosure also discloses a conductive article. In some embodiments, the conductive article includes: a substrate having a first major surface and a second major surface; and a crosslinked conductive adhesive layer disposed on at least a portion of the second major surface of the substrate. The conductive adhesive has been described in detail above. In some embodiments, the conductive adhesive comprises a crosslinked pressure-sensitive adhesive matrix and conductive particles dispersed within the matrix. The crosslinked pressure-sensitive adhesive matrix comprises at least one non-linear block copolymer containing an aromatic end block and an aliphatic elastomeric block, at least one hydrocarbon-based tackifying resin, and at least one aromatic reinforcing resin. The conductive adhesive is a crosslinked pressure-sensitive adhesive and, when disposed on a 50-micron-thick PET (polyethylene terephthalate) backing, has a 180° peel adhesion of at least 30.0 Newtons per decimeter (0.3 N / mm) at room temperature and, when disposed on a copper foil backing, has a DC resistance of less than 0.3 ohms as measured by ETM-7. Optionally, after aging for at least 1 week on a conductive fabric substrate at 85 °C and 85% relative humidity, the 180° peel adhesion changes by 25% or less.

[0085] List of Exemplary Embodiments

[0086] 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 an aromatic end block and an aliphatic elastomeric block; at least one hydrocarbon-based tackifying resin; and at least one aromatic reinforcing resin. The conductive adhesive composition further comprises a crosslinking agent comprising acrylate groups and optionally aliphatic olefin groups, wherein the crosslinking agent has a glass transition temperature (Tg) of less than -5 degrees Celsius; and optionally an aliphatic olefin component having a Tg of less than -5 degrees Celsius. When the crosslinking agent lacks aliphatic olefin groups, an aliphatic olefin component is present. The conductive adhesive composition further comprises conductive particles dispersed within the pressure-sensitive adhesive matrix.

[0087] In a second embodiment, the present disclosure provides the conductive adhesive composition according to the first embodiment, wherein the crosslinking agent comprises at least one of a polyisoprene group, a butadiene group, or a polymerizable terpene (such as farnesene or myrcene).

[0088] In a third embodiment, the present disclosure provides the conductive adhesive composition according to the first embodiment or the second embodiment, wherein the crosslinking agent comprises an isoprene group.

[0089] In a fourth embodiment, the present disclosure provides the conductive adhesive composition according to any one of the first to third embodiments, wherein the crosslinking agent comprises a butadiene group.

[0090] In a fifth embodiment, the present disclosure provides a conductive adhesive composition according to any one of the first to fourth embodiments, wherein an aliphatic olefin component is present.

[0091] In a sixth embodiment, the present disclosure provides a conductive adhesive composition according to any one of the first to fifth embodiments, the conductive adhesive composition further comprising at least one polymerization initiator.

[0092] In a seventh embodiment, the present disclosure provides a conductive adhesive composition according to the sixth embodiment, wherein the polymerization initiator comprises a photoinitiator.

[0093] In an eighth embodiment, the present disclosure provides a conductive adhesive composition according to the sixth or seventh embodiment, wherein the polymerization initiator comprises a thermal initiator.

[0094] In a ninth embodiment, the present disclosure provides a conductive adhesive composition according to any one of the first to eighth embodiments, the conductive adhesive composition further comprising at least one adhesion promoter, the at least one adhesion promoter comprising an alkylalkoxysilane, an alkenylalkoxysilane, an alkylphosphonic acid, or an alkylcarboxylic acid; and an optional non-functionalized bidentate alkoxysilane, provided that when the adhesion promoter comprises an alkylalkoxysilane or an alkenylalkoxysilane, a non-functionalized bidentate alkoxysilane is present.

[0095] In a tenth embodiment, the present disclosure provides a conductive adhesive composition according to any one of the first to ninth embodiments, the conductive adhesive composition comprising: 40 to 70 parts by weight of at least one non-linear block copolymer; 30 to 60 parts by weight of the at least one hydrocarbon-based tackifying resin; 2 to 8 parts by weight of the at least one aromatic reinforcing resin; a combination of 1 to 15 parts by weight of a crosslinking agent, or if an optional aliphatic olefin component is present, a combination of a crosslinking agent and an optional aliphatic olefin component; and 15 to 30 parts by weight of conductive particles.

[0096] In an eleventh embodiment, the present disclosure provides a conductive adhesive composition according to any one of the first to tenth embodiments, wherein at least one non-linear block copolymer comprises a star or comb copolymer.

[0097] In a twelfth embodiment, the present disclosure provides a conductive adhesive composition according to any one of the first to eleventh embodiments, wherein the aromatic end block comprises a styrene block, and the aliphatic elastomeric block comprises isoprene, farnesene, or a combination thereof.

[0098] In a thirteenth embodiment, the present disclosure provides a conductive adhesive composition according to any one of the first to twelfth embodiments, wherein the nonlinear block copolymer comprises a star copolymer having styrene end blocks and isoprene elastomeric blocks, and wherein the styrene end blocks account for 9 wt% to 10 wt% of the total polymer.

[0099] In a fourteenth embodiment, the present disclosure provides a conductive adhesive composition according to any one of the first to thirteenth embodiments, wherein the at least one hydrocarbon tackifying resin comprises a hydrogenated or partially hydrogenated hydrocarbon resin.

[0100] In a fifteenth embodiment, the present disclosure provides a conductive adhesive composition according to any one of the first to fourteenth embodiments, wherein the at least one aromatic reinforcing resin comprises a thermoplastic aromatic copolymer having a Tg greater than 100 °C.

[0101] In a sixteenth embodiment, the present disclosure provides a conductive adhesive composition according to any one of the first to fifteenth embodiments, wherein the conductive particles comprise particles of nickel-coated graphite.

[0102] In a seventeenth embodiment, the present disclosure provides a conductive adhesive composition according to any one of the first to sixteenth embodiments, the conductive adhesive composition further comprising conductive nanoparticles comprising at least one of carbon nanotubes, metal nanowires, metal nanosheets, metal nanograins, or metal nanospheres.

[0103] In an eighteenth embodiment, the present disclosure provides a crosslinked conductive adhesive composition. The crosslinked conductive adhesive composition comprises the free radical curing reaction product of a conductive adhesive composition according to any one of the first to seventeenth embodiments.

[0104] In a nineteenth embodiment, the present disclosure provides the crosslinked conductive adhesive composition according to the eighteenth embodiment, wherein the crosslinked conductive adhesive composition can be subjected to a passive intermodulation test according to the PIM test method, the test being performed by forming a tape comprising a layer of the conductive adhesive composition and a conductive layer, and placing the tape in a test fixture comprising a gold conductive surface and a stainless steel conductive surface, wherein when a first electrical signal and a second electrical signal of magnitude 30 dBm propagate between the gold surfaces in the thickness direction of the crosslinked conductive adhesive layer at respective frequencies F1 and F2, any intermodulation signal generated by the first and second electrical signals and having a frequency F3 equal to nF1 + mF2 has a power of less than about -70 dBm, m and n being positive or negative integers.

[0105] In a twentieth embodiment, the present disclosure provides a conductive article. The conductive article includes: a substrate having a first major surface and a second major surface; and a crosslinked conductive adhesive layer disposed on at least a portion of the second major surface of the substrate. The crosslinked conductive adhesive comprises the crosslinked conductive adhesive composition according to the eighteenth embodiment or the nineteenth embodiment.

[0106] In a twenty-first embodiment, the present disclosure provides the conductive article according to the twentieth embodiment, wherein the substrate comprises a conductive substrate.

[0107] In a twenty-second embodiment, the present disclosure provides the conductive article according to the twenty-first embodiment, wherein the conductive substrate comprises a nonwoven layer containing metal-coated polymer fibers, a woven fabric layer containing metal-coated polymer fibers, a film layer having a metal-coated surface, or a metal foil.

[0108] In a twenty-third embodiment, the present disclosure provides the conductive article according to the twenty-first embodiment or the twenty-second embodiment, wherein the article further comprises a second conductive adhesive layer disposed on the first major surface of the conductive substrate.

[0109] In a twenty-fourth embodiment, the present disclosure provides the conductive article according to the twenty-third embodiment, wherein the substrate comprises a release liner.

[0110] Examples

[0111] Unless otherwise specified or readily apparent from the context, all parts, percentages, ratios, etc. in the examples and the remainder of the specification are by weight.

[0112] Materials Used in Examples

[0113]

[0114]

[0115] Static Shear Test

[0116] The tests were conducted at 70 °C. The adhesive samples were laminated onto a 50-μm thick PET film. Test specimens were cut from a sample material measuring 12.7 mm × 175 mm. Then the liner was removed and the adhesive was adhered with an overlap of 12.7 mm × 25.4 mm to a stainless-steel plate. Collars were prepared at the ends of the test strips to hold a specified weight. Next, the test samples were rolled four times with a standard FINAT test roller (weighing 2 kg) at a speed of approximately 10 mm / second to achieve intimate contact between the adhesive and the surface. Before testing, the test samples were left to stand at ambient room temperature (23 °C ± 2 °C, 50% relative humidity ± 5%) for 24 hours.

[0117] Subsequently, each sample was placed in a vertical shear test rig at 70 °C (+2° setting), and the time was automatically recorded at regular intervals. After a ten-minute dwell time in the oven, a 500-g weight was suspended into the collar. The failure time was measured and recorded in minutes. The 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. The failure modes are given as follows: PO for pop-off, AT for adhesive transfer, and CF for cohesive failure.

[0118] Double-Sided Coated Tape Preparation

[0119] Two 20-μm thick samples measuring 17.8 cm × 17.8 cm were laminated to a 22-μm thick nickel / copper-coated fabric using a seam roller. Each fabric sample was passed through a laminator at room temperature and a pressure of 0.34 MPa (50 psi, controlled by an air regulator), which had a rubber roller at the bottom and a steel roller at the top (ChemInstruments Hot Roll Laminator, HL-200). After lamination, the samples were annealed in an oven at 40 °C for four days before measurement.

[0120] Peel Test

[0121] ASTM D3330 / D3330M was followed. Some samples were laminated onto both sides of a conductive fabric to prepare a double-sided coated tape structure. The release liner was removed, and the adhesive samples were laminated onto a 50-μm thick PET film. Then the adhesive was applied to a stainless-steel substrate and left to stand at room temperature for 20 minutes (RT 20 minutes) or 72 hours (RT 72 hours), after which it was peeled at 180° at a rate of 30.5 cm per minute. Three measurements were made, and the average peel value was recorded. The peel failure mode (clean or 2-bond) was also recorded.

[0122] Passive Intermodulation (PIM) Test

[0123] The PIM of the sample was measured using a test fixture consisting of a 50-ohm microstrip test board and a mechanically connected coaxial cable. The test board was a 50 mm × 80 mm × 60 mil (1.52 mm) FR-4 dielectric with 1 ounce of copper and an ENIG (electroless nickel immersion gold) surface finish. The microstrip line was 3 mm wide, with a 10 mm gap centered along the length of the board to break the circuit. Two 3 mm × 15 mm adhesive samples were manually (by finger pressure) adhered to either side of the 10 mm gap in the microstrip line. A 40 mm × 3 mm × 1 mm stainless steel 316L bridge was aligned with the samples and the gap and connected using a pressure of 0.103 MPa (15 psi) to complete the circuit. The samples were allowed to dwell for at least twenty minutes before measurement. A Rosenberger bench-top PIM analyzer (Tittmoning, Germany) was connected to the test fixture to perform the measurements. Two frequency signals between 729 - 758 MHz at 30 dBm (1 W) were swept on the LTE700L cellular band, and the maximum reflected third-order (IM3) value was recorded.

[0124] ETM-12, DC Resistance through PSA, Z-Axis Test

[0125] The double-sided coated tape sample was cut into 10 mm × 10 mm pieces, and two pieces were placed at the center of each electrode on a 3M ETM-7 board (St. Paul, MN, United States) with one adhesive side facing down. After initially removing the liner by hand lamination, a 3M ETM-12-SUS316L (stainless steel) board (50 mm × 10 mm × 1 mm) (Cheil Technology Co., Ltd., Hwaseong, South Korea) was placed on the tape with the metal side facing down, and then a 2 kg rubber roller was applied on the ETM-12 board. After a 20-minute dwell time, the DC resistance between the electrodes was measured using a micro-ohmmeter.

[0126] Adhesive Preparation

[0127] The composition of each formulation is summarized in Table 1 below. In a typical procedure, all the components of each formulation are added to a glass jar and then diluted with a mixture of heptane and ethyl acetate (heptane:ethyl acetate 75:25) to prepare a solution with a solids content of 30%. The jar is sealed and the components are mixed on a jar roller overnight until all the materials are completely dissolved. Next, the solution is manually coated onto an RF22N siliconized polyester release liner (thickness 50 μm, SKC Haas, Korea) using a doctor blade coater. The coated sample is placed in an oven at 70 °C for 10 minutes to produce an adhesive sample with a thickness of 20 μm. The sample is crosslinked by exposure to UV radiation with a UVA intensity of 5 J / cm 2 The sample is crosslinked by exposure to UV radiation with a UVA intensity of 5 J / cm

[0128] Table 2: Compositions (in grams)

[0129]

[0130]

[0131] After a 20-minute dwell and after aging for 3 days in an environmental chamber at 85 °C and 85% relative humidity, electrical tests are performed at room temperature. The results are shown in Table 2.

[0132] Table 2: DC Resistance and PIM Test Results

[0133]

[0134] A peel test is performed and the results are shown in Table 3.

[0135] Table 3: Peel Test Results

[0136]

[0137]

[0138] Although specific embodiments have been illustrated and described herein, those of ordinary skill in the art will recognize that many alternative and / or equivalent forms of specific implementation may be used in place of the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any modifications or variations of the specific embodiments discussed herein. Accordingly, the present disclosure is intended to be limited only by the claims and their equivalents.

[0139] In addition, all publications and patents cited herein are hereby incorporated by reference in their entirety as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. In the event of any inconsistency or conflict between the incorporated reference section and the present application, the information in the foregoing description shall prevail. Each of the exemplary embodiments has been described. These embodiments and other embodiments are within the scope of the following claims.

Claims

1. A conductive adhesive composition, the conductive adhesive composition comprising: A pressure - sensitive adhesive matrix, the pressure - sensitive adhesive matrix comprising at least one non - linear block copolymer, the 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; A cross - linker, the cross - linker comprising acrylate groups and optionally aliphatic olefin groups, wherein the cross - linker has a glass transition temperature (Tg) of less than - 5 °C; Optionally an aliphatic olefin component with a Tg less than - 5 °C, provided that when the cross - linker lacks aliphatic olefin groups, the aliphatic olefin component is present; and Conductive particles, the conductive particles being dispersed within the matrix.

2. The conductive adhesive composition according to claim 1, wherein the cross - linker comprises at least one of polyisoprenyl, butadienyl or polymerizable terpenes.

3. The conductive adhesive composition according to claim 1 or claim 2, wherein the cross - linker comprises isoprene groups.

4. The conductive adhesive composition according to any one of claims 1 to 3, wherein the cross - linker comprises butadiene groups.

5. The conductive adhesive composition according to any one of claims 1 to 4, wherein the aliphatic olefin component is present.

6. The conductive adhesive composition according to any one of claims 1 to 5, further comprising at least one polymerization initiator.

7. The conductive adhesive composition according to claim 6, wherein the polymerization initiator comprises a photo - initiator.

8. The conductive adhesive composition according to claim 6 or claim 7, wherein the polymerization initiator comprises a thermal initiator.

9. The conductive adhesive composition according to any one of claims 1 to 8, further comprising at least one adhesion promoter, the at least one adhesion promoter comprising organic molecules selected from the category of organic compounds capable of forming bonds with metal oxide surfaces, the organic compounds optionally comprising alkylalkoxysilanes, alkenylalkoxysilanes, alkylphosphonic acids or alkylcarboxylic acids; and optionally non - functionalized bidentate alkoxysilanes, provided that when the adhesion promoter comprises an alkylalkoxysilane or an alkenylalkoxysilane, the non - functionalized bidentate alkoxysilanes are present.

10. The conductive adhesive composition according to any one of claims 1 to 9, comprising: 40 to 70 parts by weight of the at least one non - linear block copolymer; 30 to 60 parts by weight of the at least one hydrocarbon - based tackifying resin; 2 to 8 parts by weight of the at least one aromatic reinforcing resin; 1 to 15 parts by weight of the cross - linker, or if the optional aliphatic olefin component is present, a combination of the cross - linker and the optional aliphatic olefin component; and 15 to 30 parts by weight of conductive particles.

11. The conductive adhesive composition according to any one of claims 1 to 10, wherein the at least one non - linear block copolymer comprises a star copolymer or a comb copolymer.

12. The electrically conductive adhesive composition according to any one of claims 1 to 11, wherein the aromatic terminal block comprises a styrene block, and the aliphatic elastomeric block comprises isoprene, farnesene, or a combination thereof.

13. The electrically conductive adhesive composition according to any one of claims 1 to 12, wherein the non-linear block copolymer comprises a star copolymer having a styrene terminal block and an isoprene elastomeric block, wherein the styrene terminal block accounts for 9 wt% to 10 wt% of the total polymer.

14. The electrically conductive adhesive composition according to any one of claims 1 to 13, wherein the at least one hydrocarbon tackifying resin comprises a hydrogenated or partially hydrogenated hydrocarbon resin.

15. The electrically conductive adhesive composition according to any one of claims 1 to 14, wherein the at least one aromatic reinforcing resin comprises a thermoplastic aromatic copolymer having a Tg greater than 100 °C.

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

17. The electrically conductive adhesive composition according to any one of claims 1 to 16, further comprising electrically conductive nanoparticles, the electrically conductive nanoparticles comprising at least one of carbon nanotubes, metal nanowires, metal nanosheets, metal nanograins, or metal nanospheres.

18. A crosslinked electrically conductive adhesive composition, the crosslinked electrically conductive adhesive composition comprising a free radical curing reaction product of the electrically conductive adhesive composition according to any one of claims 1 to 17.

19. The crosslinked electrically conductive adhesive composition according to claim 18, wherein the crosslinked electrically conductive adhesive composition is capable of performing a passive intermodulation test according to the PIM test method, the test being performed by forming a tape comprising a layer of the electrically conductive adhesive composition and a conductive layer, and placing the tape in a test fixture comprising a gold conductive surface and a stainless steel conductive surface, wherein when a first electrical signal and a second electrical signal of magnitude 30 dBm propagate between the gold surfaces in the thickness direction of the crosslinked electrically conductive adhesive layer at respective frequencies F1 and F2, any intermodulation signal generated by the first electrical signal and the second electrical signal and having a frequency F3 equal to nF1 + mF2 has a power of less than about -70 dBm, where m and n are positive or negative integers.

20. An electrically conductive article, the electrically conductive article comprising: a substrate having a first major surface and a second major surface; and a crosslinked electrically conductive adhesive layer disposed on at least a portion of the second major surface of the substrate; wherein the crosslinked electrically conductive adhesive comprises the crosslinked electrically conductive adhesive composition according to claim 18 or claim 19.

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

22. The conductive article according to claim 21, wherein the conductive substrate comprises a nonwoven layer containing metal-coated polymer fibers, a woven fabric layer containing metal-coated polymer fibers, a film layer having a metal-coated surface, or a metal foil.

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

24. The conductive article according to claim 23, wherein the substrate comprises a release liner.

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