WO2025129600A1

WO2025129600A1 - Conductive adhesive compositions, crosslinked conductive adhesive compositions, and electrically conductive articles

Info

Publication number: WO2025129600A1
Application number: PCT/CN2023/140842
Authority: WO
Inventors: Jing Fang; Tamuka CHIDANGURO; Claire Hartmann-Thompson; Marina Markovna KAPLUN; Shane Paul WHITE
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2023-12-22
Filing date: 2023-12-22
Publication date: 2025-06-26
Anticipated expiration: 2026-06-22

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. The composition further includes a crosslinker having acrylate groups and an optional aliphatic olefin group and optionally an aliphatic olefin component that has a glass transition temperature (Tg) of less than -5 degrees C. The crosslinker has a Tg of less than -5 degrees C. When the crosslinker lacks an aliphatic olefin group, the aliphatic olefin component is present. Also, a crosslinked conductive adhesive composition is provided that is a free-radically cured reaction product of the conductive adhesive composition. Further provided is an electrically conductive article including a substrate and a crosslinked electrically conductive adhesive disposed on the substrate.

Description

CONDUCTIVE ADHESIVE COMPOSITIONS, CROSSLINKED CONDUCTIVE ADHESIVE COMPOSITIONS, AND ELECTRICALLY CONDUCTIVE ARTICLES

BACKGROUND

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

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 hydrocarbon-based tackifying resin; and at least one aromatic reinforcing resin. The composition further includes a crosslinker having acrylate groups and an optional aliphatic olefin group and optionally an aliphatic olefin component that has a glass transition temperature (Tg) of less than -5 degrees Celsius. The crosslinker has a Tg of less than -5 degrees Celsius. When the crosslinker lacks an aliphatic olefin group, the aliphatic olefin component is present. The conductive adhesive composition further comprises electrically conductive particles dispersed within the pressure sensitive adhesive matrix.

In a second aspect, a crosslinked conductive adhesive composition is provided. The crosslinked conductive adhesive composition comprises a free-radically cured reaction product of any conductive adhesive composition according to the first aspect.

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 a crosslinked electrically conductive adhesive layer disposed on at least a portion of the second major surface of the substrate. The crosslinked electrically conductive adhesive comprises any crosslinked electrically conductive adhesive composition according to the second aspect.

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

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:

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

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

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

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.

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.

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 hydrocarbon-based tackifying resin, at least one aromatic reinforcing resin, and electrically conductive particles dispersed within the matrix. Also disclosed are crosslinked conductive adhesive compositions and articles prepared using a crosslinked conductive pressure sensitive adhesive.

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

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:

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

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.

The terms “room temperature” and “ambient temperature” are used interchangeably to mean temperatures in the range of 20℃ to 25℃.

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.

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.

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.

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.

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.

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.

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.

The term “dipodal alkoxysilane” refers to a component that has two sets of alkoxysilane groups.

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 Si-H 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 chlorine atom) .

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

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

As used herein, the terms “glass transition temperature” and “Tg” are used interchangeably and refer to the glass transition temperature of a material or a mixture. Unless otherwise indicated, glass transition temperature values are determined by Differential Scanning calorimetry (DSC) , such as at a heating rate of 10℃. per minute in a nitrogen stream. When the Tg of a monomer is mentioned, it is the Tg of a homopolymer of that monomer or crosslinker. The homopolymer must be sufficiently high molecular weight such that the Tg reaches a limiting value, as it is generally appreciated that a Tg of a homopolymer will increase with increasing molecular weight to a limiting value. The homopolymer is also understood to be substantially free of moisture, residual monomer, solvents, and other contaminants that may affect the Tg. A suitable DSC method and mode of analysis is as described in Matsumoto, A. et al., J. Polym. Sci. A., Polym. Chem. 1993, 31, 2531-2539.

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.

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.

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.

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.

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

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.

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 hydrocarbon-based tackifying resin;

at least one aromatic reinforcing resin;

a crosslinker comprising acrylate groups and an optional aliphatic olefin group, wherein the crosslinker has a glass transition temperature (Tg) of less than -5 degrees Celsius;

optionally an aliphatic olefin component that has a Tg of less than -5 degrees Celsius, with the proviso that when the crosslinker lacks an aliphatic olefin group, the aliphatic olefin component is present; and

electrically conductive particles dispersed within the matrix.

It was unexpectedly discovered that it is possible to better maintain low electrical resistance after aging of a crosslinked conductive adhesive composition on a conductive fabric substrate for 72 hours at 85℃ and 85%Relative Humidity, by using certain crosslinkers to crosslink the conductive adhesive composition. The crosslinker comprises acrylate groups and has a glass transition temperature (Tg) of less than -5 degrees Celsius. In certain cases, the crosslinker further comprises an aliphatic olefin group. When the crosslinker lacks an aliphatic olefin group, a separate aliphatic olefin component having a Tg of less than -5 degrees Celsius is also included in the conductive adhesive composition.

In some embodiments in which an aliphatic olefin group is present in the crosslinker, the crosslinker comprises at least one of poly-isoprene groups, butadiene groups, or polymerizable terpenes, such as farnesene or myrcene. In select cases, the crosslinker comprises isoprene groups. In select cases, the crosslinker comprises butadiene groups. In select cases, the crosslinker comprises a polymerizable terpene. In select cases, the crosslinker comprises farnesene. In select cases, the crosslinker comprises myrcene. In select 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 adhesive matrix.

Exemplary suitable crosslinkers having both acrylate groups and aliphatic olefin groups include for instance and without limitation, an acrylate functionalized isoprene rubber commercially available under the trade designation “UC-102M” from Kuraray (Houston, TX) .

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 of less than -5 degrees Celsius include for instance and without limitation, a multifunctional acrylate ester commercially available under the trade designations “CN307, CN308, and CN309” from Arkema Sartomer Americas (Exton, PA) . When a crosslinker is employed that does not contain any aliphatic olefin groups, the aliphatic olefin component having a Tg of less than -5 degrees Celsius is present in the conductive adhesive composition. Exemplary suitable aliphatic olefin components include for instance and without limitation, copolymers of styrene and butadiene such as one commercially available under the trade designation “L-SBR-820” from Kuraray (Houston, TX) .

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

Suitable exemplary photoinitiators are those available under the trade designations OMNIRAD from IGM Resins (Waalwijk, The Netherlands) and include 1-hydroxy cyclohexyl phenyl ketone (OMNIRAD 184) , 2, 2-dimethoxy-l, 2-diphenylethan-l-one (OMNIRAD 651) , bis (2, 4, 6 trimethylbenzoyl) phenylphosphineoxide (OMNIRAD 819) , l- [4- (2-hydroxyethoxy) phenyl] -2-hydroxy-2-methyl-l-propane-1-one (OMNIRAD 2959) , 2-benzyl-2-dimethylamino-l- (4-morpholinophenyl) butanone (OMNIRAD 369) , 2-dimethylamino-2- (4-methyl-benzyl) -l- (4-morpholin-4-yl-phenyl) -butan-l-one (OMNIRAD 379) , 2-methyl-l- [4- (methylthio) phenyl] -2-morpholinopropan-l-one (OMNIRAD 907) , Oligo [2 -hydroxy-2 -methyl-1- [4- (l-methylvinyl) phenyl] propanone] ESACURE ONE (Lamberti S. p. A., Gallarate, Italy) , 2-hydroxy-2-methyl-1-phenyl propan-l-one (DAROCUR 1173) , 2, 4, 6-trimethylbenzoyldiphenylphosphine oxide (OMNIRAD TPO) , and 2, 4, 6-trimethylbenzoylphenyl phosphinate (OMNIRAD TPO-L) . Additional suitable photoinitiators include for example and without limitation, benzyl dimethyl ketal, 2-methyl-2-hydroxypropiophenone, benzoin methyl ether, benzoin isopropyl ether, anisoin methyl ether, aromatic sulfonyl chlorides, photoactive oximes, and combinations thereof.

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 crosslinked 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 crosslinked conductive adhesive layer between the gold surfaces at respective frequencies F1 and F2, any intermodulation signal generated from the first and second electrical signals having a frequency F3 equal to nF1+mF2, m and n positive or negative integers, has a power of less than about -70 dBm. It is to be understood that “less than” a particular negative number refers to a larger negative number, e.g., -80 dBm is less than -70 dBm.

It should be noted that properties of the adhesive such as 180° Peel Adhesion, DC resistance, and PIM are properties of the crosslinked 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.

The crosslinked 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.

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-Ablock copolymers. In some embodiments, at least one non-linear block copolymer comprises a star or comb copolymer. An example of a commercially available comb styrene-farnesene-styrene block copolymers includes SF902 from Kuraray, Tokyo, Japan.

In some embodiments of the block copolymer, the aromatic end blocks comprise styrene blocks, and the aliphatic elastomeric blocks comprise isoprene, farnesene, or a combination thereof. Star block copolymers are also sometimes 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 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.

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 P140 from Arakawa Chemical, Inc. Chicago, IL.

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℃. A wide range of aromatic resins are suitable. An example of a commercially available aromatic reinforcing resin is ENDEX 160 from Eastman Chemical Company, Kingsport, TN.

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.

The conductive adhesive may optionally include at least one additive. Particularly suitable additives include conductive nanoparticles and/or adhesion promoters. Examples of suitable conductive nanoparticles include carbon nanotubes, metallic nanoparticles including nanowires, nanoflakes, nanograins, and nanospheres.

Various adhesion promoters are suitable 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 (e.g, alkyl N-hydroxy-amides) , and phosphate esters. When an adhesion promoter is present it is typically in an amount of 0.1 to 5 parts by weight.

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) .

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, two bonds, or three 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.

In some embodiments, an alkyl alkoxysilane 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.

In some embodiments, 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. 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 alkoxysilanes include for instance and without limitation, trimethoxyvinylsilane, allyltrimethoxysilane, trimethoxyoctenylsilane, dimethoxyvinylsilane, allyldimethoxysilane, dimethoxyoctenylsilane and trimethoxy-or triethoxy-modified polybutadienes.

As noted above, when the adhesion promoter comprises an alkyl alkoxysilane or an alkenyl alkoxysilane, the non-functional dipodal alkoxysilane is present. In some embodiments, the alkyl alkoxysilane and the non-functional dipodal alkoxysilane 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-bistrimethoxysilylethane, 1, 2-bistrimethoxysilylmethane 1, 2-bistrimethoxysilyloctane, 1, 2-bistriethoxysilylethane, 1, 2-bistriethoxysilylmethane, 1, 2-bistriethoxysilyloctane, 1, 2-bisdimethoxysilylethane, 1, 2-bisdimethoxysilylmethane, 1, 2-bisdimethoxysilyloctane, 1, 2-bisdiethoxysilylethane, 1, 2-bisdiethoxysilylmethane and, 1, 2-bisdiethoxysilyloctane.

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.

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 beta-carboxyethyl acrylate.

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.

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.

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; 1-15 parts by weight of a combination of the crosslinker, or if the optional aliphatic olefin component is present, a combination of the crosslinker and the optional aliphatic olefin component; and 15-30 parts by weight of electrically conductive particles. As such, in some cases there are 1-15 parts by weight of the crosslinker, while in other cases there are 1-15 parts by weight of a combination of the crosslinker and the optional aliphatic olefin component. Parts by weight are used to describe these formulations instead of weight %as the weight components do not necessarily add up to 100.

In a second aspect, a crosslinked conductive adhesive composition is provided. The crosslinked conductive adhesive composition comprises a free-radically cured reaction product of any of the conductive adhesive compositions according to the first aspect described in detail herein. The crosslinked reaction product is optionally formed using photoinitiation (in which a photoinitiator is included in the adhesive composition) of the crosslinking reaction, curing the conductive adhesive composition using actinic radiation comprising UV radiation, e-beam radiation, visible radiation, or a combination thereof. The reaction product is optionally formed using thermal initiation (in which a thermal initiator is optionally included in the adhesive composition) of the crosslinking reaction, curing the conductive adhesive composition using heat, such as at a temperature in the range of about 50 to 150 degrees Celsius.

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.

The conductive adhesive is a pressure sensitive adhesive, meaning that it 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 crosslinked 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 crosslinked 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 crosslinked 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) , or even at least 60 N/dm (0.6 N/mm) .

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 crosslinked conductive adhesive 180° Peel Adhesion changes by 25%or less after aging on a conductive fabric substrate for at least 72 hours (or even at least 1 week) at 85℃ and 85%Relative Humidity.

The crosslinked conductive adhesive also has desirable electrical properties. Among these properties are DC resistance and PIM. The crosslinked 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 crosslinked 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 ohms. Advantageously, following aging on a conductive fabric substrate for 72 hours at 85℃and 85%Relative Humidity, some embodiments, the crosslinked 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 ohms. In some embodiments, the crosslinked conductive adhesive DC Resistance changes by 65%or less, 60%, 55%, 50%, 45%or even 40%or less after aging on a conductive fabric substrate for at least 72 hours at 85℃ and 85%Relative Humidity.

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.

The adhesive layers of this disclosure can be prepared from a free-radically cured reaction product of 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) and then subjected to curing to achieve crosslinking of the pressure sensitive adhesive matrix. 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.

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 a crosslinked electrically conductive adhesive layer disposed on at least a portion of the second major surface of the substrate. The crosslinked electrically conductive adhesive comprises any crosslinked electrically conductive adhesive composition according to the second aspect described in detail herein.

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. A crosslinked 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 crosslinked electrically conductive adhesive 130 is disposed on (at least a portion of) the first major surface 112 of the substrate 110.

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.

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.

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.

Another important feature of the crosslinked 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 crosslinked 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.

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 crosslinked 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 F1 and F2, any intermodulation signal generated has a frequency F3 equal to nF1+mF2, m and n positive or negative integers. When measured in this way, the PIM has a power of less than about -70 dBm.

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 a crosslinked 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 crosslinked pressure sensitive adhesive matrix and electrically conductive particles dispersed within the matrix. The crosslinked 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 crosslinked 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-7. Optionally, the 180° Peel Adhesion changes by 25%or less after aging on a conductive fabric substrate for at least 1 week at 85℃ and 85%Relative Humidity.

Listing of Exemplary Embodiments

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; and at least one aromatic reinforcing resin. The conductive adhesive composition further comprises a crosslinker comprising acrylate groups and an optional aliphatic olefin group, wherein the crosslinker has a glass transition temperature (Tg) of less than -5 degrees Celsius; and optionally an aliphatic olefin component that has a Tg of less than -5 degrees Celsius. When the crosslinker lacks an aliphatic olefin group, the aliphatic olefin component is present. The conductive adhesive composition further comprises electrically conductive particles dispersed within the pressure sensitive adhesive matrix.

In a second embodiment, the present disclosure provides a conductive adhesive composition according to the first embodiment, wherein the crosslinker comprises at least one of poly-isoprene groups, butadiene groups, or polymerizable terpenes such as farnesene or myrcene.

In a third embodiment, the present disclosure provides a conductive adhesive composition according to the first embodiment or the second embodiment, wherein the crosslinker comprises isoprene groups.

In a fourth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through third embodiments, wherein the crosslinker comprises butadiene groups.

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

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

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

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

In a ninth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through eighth embodiments, further comprising at least one 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.

In a tenth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through ninth 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 hydrocarbon-based tackifying resin; 2-8 parts by weight of the at least one aromatic reinforcing resin; 1-15 parts by weight of a combination of the crosslinker, or if the optional aliphatic olefin component is present, a combination of the crosslinker and the optional aliphatic olefin component; and 15-30 parts by weight electrically conductive particles.

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

In a twelfth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through eleventh embodiments, wherein the aromatic end blocks comprise styrene blocks, and the aliphatic elastomeric blocks comprise isoprene, farnesene, or a combination thereof.

In a thirteenth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through twelfth 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.

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

In a fifteenth embodiment, the present disclosure provides a conductive adhesive composition according to any of the first through fourteenth embodiments, wherein the at least one aromatic reinforcing resin comprises a thermoplastic aromatic co-polymer with a Tg of greater than 100℃.

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

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

In an eighteenth embodiment, the present disclosure provides a crosslinked conductive adhesive composition. The crosslinked conductive adhesive composition comprises a free-radically cured reaction product of a conductive adhesive composition according to any of the first through seventeenth embodiments.

In a nineteenth embodiment, the present disclosure provides a crosslinked conductive adhesive composition according to the eighteenth embodiment, wherein the crosslinked 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 crosslinked conductive adhesive layer between the gold surfaces at respective frequencies F1 and F2, any intermodulation signal generated from the first and second electrical signals having a frequency F3 equal to nF1+mF2, m and n positive or negative integers, has a power of less than about -70 dBm.

In a twentieth 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 a crosslinked electrically conductive adhesive layer disposed on at least a portion of the second major surface of the substrate. The crosslinked electrically conductive adhesive comprises a crosslinked electrically conductive adhesive composition according to the eighteenth embodiment or the nineteenth embodiment.

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

In a twenty-second embodiment, the present disclosure provides an electrically conductive article according to the twenty-first 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.

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

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

EXAMPLES

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

The test was conducted at 70℃. An adhesive sample was laminated on a 50 μm 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℃ +/-2℃, 50%relative humidity +/-5%) prior to testing.

Each sample was then placed into a vertical shear-stand (+2° disposition) at 70℃ 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

Two sheets of 20 μm thick 17.8 cm × 17.8 cm samples were laminated onto a 22 μm thick nickel/copper 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 (ChemInstruments 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℃ for four days before measurement.

Peel Test

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 μm 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

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

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 Co. Ltd., Hwaseong, 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 micro-ohm meter.

Adhesive preparation

The compositions of each formulation are summarized in Table 1 below. In a typical procedure, all the components for each formulation were added to a glass jar and then diluted with a mixture of heptane and ethyl acetate (heptane: Ethyl Acetate 75: 25) to make a solution with 30%solids content. The jar was sealed, and the components mixed overnight on a jar roller until all the materials were completely dissolved. Next, a knife coater was used to manually coat the solution onto an RF22N siliconized polyester release liner (50 μm thickness, SKC Haas, Korea) . The coated sample was placed in an oven at 70 ℃ for 10 minutes yielding adhesive samples with 20 um thickness. Samples were crosslinked via exposure to UV radiation with 5 J/cm² UVA intensity.

Table 2: Compositions (in grams)

Electrical testing was conducted at RT after 20 minutes dwell and after aging in the environmental chamber for 3 days at 85℃ and 85%relative humidity. The results are represented in Table 2.

Table 2: DC resistance and PIM test results

Peel testing was performed, and the results are represented in Table 3.

Table 3: Peel Test Results

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.

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

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;

a crosslinker comprising acrylate groups and an optional aliphatic olefin group, wherein the crosslinker has a glass transition temperature (Tg) of less than -5 degrees Celsius;

optionally an aliphatic olefin component that has a Tg of less than -5 degrees Celsius, with the proviso that when the crosslinker lacks an aliphatic olefin group, the aliphatic olefin component is present; and

electrically conductive particles dispersed within the matrix.
The conductive adhesive composition of claim 1, wherein the crosslinker comprises at least one of poly-isoprene groups, butadiene groups, or polymerizable terpenes.
The conductive adhesive composition of claim 1 or claim 2, wherein the crosslinker comprises isoprene groups.
The conductive adhesive composition of any of claims 1 to 3, wherein the crosslinker comprises butadiene groups.
The conductive adhesive composition of any of claims 1 to 4, wherein the aliphatic olefin component is present.
The conductive adhesive composition of any of claims 1 to 5, further comprising at least one polymerization initiator.
The conductive adhesive composition of claim 6, wherein the polymerization initiator comprises a photoinitiator.
The conductive adhesive composition of claim 6 or claim 7, wherein the polymerization initiator comprises a thermal initiator.
The conductive adhesive composition of any of claims 1 to 8, further comprising at least one adhesion promoter comprising an organic molecule selected from classes of organic compounds that can form a bond with a metal oxide surface, optionally 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.
The conductive adhesive composition of any of claims 1 to 9, 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;

1-15 parts by weight of the crosslinker, or if the optional aliphatic olefin component is present, a combination of the crosslinker and the optional aliphatic olefin component; and

15-30 parts by weight electrically conductive particles.
The conductive adhesive composition of any of claims 1 to 10, wherein the at least one non-linear block copolymer comprises a star or comb copolymer.
The conductive adhesive composition of any of claims 1 to 11, wherein the aromatic end blocks comprise styrene blocks, and the aliphatic elastomeric blocks comprise isoprene, farnesene, or a combination thereof.
The conductive adhesive composition of any of claims 1 to 12, 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.
The conductive adhesive composition of any of claims 1 to 13, wherein the at least one hydrocarbon tackifying resin comprises a hydrogenated or partially hydrogenated hydrocarbon resin.
The conductive adhesive composition of any of claims 1 to 14, wherein the at least one aromatic reinforcing resin comprises a thermoplastic aromatic co-polymer with a Tg of greater than 100℃.
The conductive adhesive composition of any of claims 1 to 15, wherein the electrically conductive particles comprise particles of nickel-coated graphite.
The conductive adhesive composition of any of claims 1 to 16, further comprising conductive nanoparticles comprising at least one of carbon nanotubes, metallic nanowires, metallic nanoflakes, metallic nanograins, or metallic nanospheres.
A crosslinked conductive adhesive composition comprising a free-radically cured reaction product of the conductive adhesive composition of any of claims 1 to 17.
The crosslinked conductive adhesive composition of claim 18, wherein the crosslinked 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 crosslinked conductive adhesive layer between the gold surfaces at respective frequencies F1 and F2, any intermodulation signal generated from the first and second electrical signals having a frequency F3 equal to nF1+mF2, m and n positive or negative integers, has a power of less than about -70 dBm.
An electrically conductive article comprising:

a substrate with 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 of claim 18 or claim 19.
The electrically conductive article of claim 20, wherein the substrate comprises an electrically conductive substrate.
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.
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.
The electrically conductive article of claim 23, wherein the substrate comprises a release liner.