Conductive compositions, conductors, stretchable conductive materials, and electronic devices

Abstract

To provide a conductive composition, a conductor, a stretchable conductive material, and an electronic device having excellent conductivity, repeated expansion / contraction tolerance, moisture-heat resistance and adhesiveness.SOLUTION: A conductive composition includes elastomer (A) and conductive microparticles (B), where a particle diameter (rtop) at the peak top in a particle size distribution curve of the conductive microparticles (B) measured by a laser diffraction / scattering particle size distribution measuring method after the composition is allowed to pass through a screen mask having 400 mesh, a wire diameter 23 μm and numerical aperture 41% is 2.0 μm or more and 20.0 μm or less, and frequency (ftop) of the peak top is 1.5% or more and 9.0% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to conductive compositions, conductors, stretchable conductive materials, and electronic devices. [Background technology]

[0002] Conductive materials are used in various industrial fields, and numerous proposals have been made to further enhance the functionality of these materials. In particular, in recent years, the development of stretchable conductive materials with flexibility and elasticity has progressed, and proposals have been made for applications such as actuators and wearable sensors.

[0003] Furthermore, with the advancement of healthcare equipment such as biosensing, wearable devices, and robotics, conductive materials are now required not only to possess the conductivity that was previously demanded, but also to have the flexibility to conform to curved and movable parts during processing and use.

[0004] On the other hand, when conductive materials are used in curved or movable parts, there is a problem that the resin is prone to cracking due to structural damage caused by repeated expansion and contraction. In particular, in the case of conductive materials, conductive fine particles are usually added, and when deformation occurs due to expansion and contraction, the conductive material peels off from the resin, creating voids in the resin, from which cracks are likely to start. As a result, there is a problem that the conductivity decreases with each expansion and contraction.

[0005] Furthermore, in order to form stretchable conductive materials, it is necessary to apply a conductive composition, such as a paste made by kneading elastomers, conductive fine particles, and other components, to a stretchable substrate and form a printed pattern. However, depending on the elastomer, conductive composition, dispersion method, and printing pattern formation method used, aggregates may form, overdispersion may occur, or the viscoelastic behavior of the paste may change, resulting in problems such as a decrease in (continuous) printability on various stretchable film substrates and a decrease in stretchability conductivity during (continuous) printing. In addition, in the process of dispersing resin and conductive fine particles and coating the resulting conductive composition to create a printed material, there is a problem that the aggregation state and particle size distribution of the conductive fine particles in the conductive composition change, resulting in a decrease in stretchability conductivity.

[0006] Patent Document 1 discloses that by bringing silver powder having a specific average primary particle size, which has undergone surface treatment, into a specific aggregation state in a composition, it exhibits excellent stability in electrical resistance even when subjected to repeated expansion and contraction or when the elongation rate is increased.

[0007] Patent Document 2 discloses that by using a combination of two types of conductive metal powders to be blended into an elastomer—one silver powder having a specific apparent porosity with an average primary particle diameter on the order of submicrons, and another silver powder having a specific apparent porosity with an average primary particle diameter on the order of microns—it is possible to obtain a conductor with a low initial electrical resistance value before stretching and excellent stability of electrical resistance value even during stretching. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 7077316 [Patent Document 2] Japanese Patent Publication No. 2020-132756

[0009] However, while the inventions described in Patent Documents 1 and 2 specify the particle size of silver powder before it is incorporated into the conductive composition or the silver powder in the conductive composition, the particle size distribution of the conductive material changes during the process of dispersing and coating the conductive composition to make a conductor (for example, the process of passing it through a screen mask). This can lead to a decrease in stretch conductivity, or a decrease in the tack of the conductive composition and reduced adhesion depending on the change in the particle size of the conductive material and, consequently, the specific surface area. [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The present invention has been made in view of the above background, and aims to provide a conductive composition, conductor, stretchable conductive material, and electronic device that are excellent in conductivity, resistance to repeated stretching and shrinking, resistance to moisture and heat, and adhesion. [Means for solving the problem]

[0011] After diligent research by the inventors, it was discovered that the problems of the present invention can be solved in the following embodiment, and thus the present invention was completed.

[0012] In other words, the present invention relates to the following [1] to [6]. [1] A conductive composition comprising an elastomer (A) and conductive fine particles (B), After passing through a screen mask with 400 mesh, wire diameter 23 μm, and aperture ratio 41%, In the particle size distribution curve of conductive fine particles (B) measured by laser diffraction scattering particle size distribution measurement, the peak top particle diameter (rtop) is between 2.0 μm and 20.0 μm. A conductive composition having a peak top frequency (ftop) of 1.5% or more and 9.0% or less. [2] When passing through a screen mask with 400 mesh, wire diameter of 23 μm, and aperture ratio of 41%, in the particle size distribution curve measured by the laser diffraction scattering method of the conductive fine particles (B), the cumulative 95% particle diameter (r95) is 10.0 μm or more, and the cumulative 10% particle diameter (r10) is 0.1 μm or more and 5.0 μm or less, the conductive composition according to [1]. [3] When passing through a screen mask with 400 mesh, wire diameter of 23 μm, and aperture ratio of 41%, the particle diameter ratio before and after passing through the screen mask (cumulative 95% particle diameter (R95) in the particle size distribution curve of the conductive fine particles (B) before passing / cumulative 95% particle diameter (r95) in the particle size distribution curve of the conductive fine particles (B) after passing) is 5.0 or less, the conductive composition according to [1] or [2]. [4] A conductor containing the conductive composition according to [1] or [2]. [5] A stretchable conductive material having a cured product of the conductive composition according to [1] or [2] provided on a stretchable base material. [6] An electronic device including the conductor according to [4]. [Effects of the Invention]

[0013] According to the present invention, there is an excellent effect that a conductive composition, a conductor, a stretchable conductive material, and an electronic device excellent in conductivity, repeated stretch resistance, moisture and heat resistance, and adhesion can be provided. [Embodiments for Carrying Out the Invention]

[0014] Hereinafter, the conductive composition, conductor, stretchable conductive material, and electronic device according to the present invention will be described in detail in order. In the present invention, the cured product includes not only those cured by a chemical reaction but also those cured by a method other than a chemical reaction such as volatilization of a solvent. Other embodiments are also included in the scope of the present invention, insofar as they are consistent with the spirit of the present invention. Furthermore, unless otherwise specified, each component can be used independently, alone, or in combination of two or more types.

[0015] <Conductive composition> The conductive composition of the present invention is a conductive composition comprising an elastomer (A) and conductive fine particles (B), wherein the particle size of the peak top (rtop) in the particle size distribution curve measured by laser diffraction scattering particle size distribution measurement method when passing through a screen mask of 400 mesh, wire diameter 23 μm, and aperture ratio 41% is 2.0 μm or more and 20.0 μm or less, and the frequency of the peak top (ftop) is 1.5% or more and 9.0% or less.

[0016] The conductive composition of the present invention, by defining the particle size distribution of conductive fine particles (B) after passing through a screen mask, maintains conductive path formation even during expansion and contraction when a printed material is produced through any process, suppresses the decrease in expansion and contraction conductivity, and provides good adhesion.

[0017] The detailed mechanism by which this unique effect of the present invention manifests is not clear, but it is thought to be as follows. Note that the following mechanism is merely a consideration and does not limit the present invention in any way.

[0018] In the process of dispersing and coating a conductive composition to produce a printed material (the method is not limited, but for example, the process involves passing the material through a screen mask with a 400-mesh screen, a wire diameter of 23 μm, and an aperture ratio of 41%), there are several factors that can change the particle size distribution of the conductive material in the conductive composition. These include the dispersion method, the shear applied during printing, the formulation of the conductive composition, the particle size, and combinations thereof.

[0019] In dispersion methods, the particle size distribution of conductive microparticles can be adjusted by various conditions, such as the mixing means itself, the scale of the mixing machine, the shape of the device, the shape of the stirring spring, the rotation speed and time of mixing, the mixing temperature, the bead filling rate, and the roll spacing.

[0020] During printing, repeated shearing, such as during continuous printing, is expected to excessively loosen the aggregation of conductive fine particles in the conductive composition. On the other hand, if the degree of loosening of the aggregation of conductive fine particles is within the optimal range (i.e., the range defined in this invention), sufficient contact points are formed between the conductive fine particles when the material is not stretched or when it is stretched, improving conductivity and resistance to repeated stretching.

[0021] Furthermore, if the particle size distribution of the conductive fine particles is within the range defined in this invention, the specific surface area of ​​the conductive fine particles will not become too large, and the amount of elastomer that penetrates between the particles will decrease, thereby improving the adhesion of the conductive composition.

[0022] <Elastomer (A)> The conductive composition of the present invention contains a binder elastomer (A) to impart film-forming properties and adhesion to stretchable substrate films. Furthermore, in the present invention, the inclusion of elastomer (A) imparts flexibility, stretchability, adhesion to stretchable substrate films, and printability to the conductive layer. As a result, wire breakage of the conductive layer during stretching or shrinking is suppressed. Moreover, adhesion to stretchable substrate films is improved.

[0023] Examples of the elastomer (A) include hydrocarbon-based elastomers such as natural rubber, isoprene rubber, nitrile rubber (NBR), ethylene propylene rubber (EPDM), styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR), as well as their hydrogenated versions, silicone elastomers, fluorine elastomers, urethane elastomers, acrylic elastomers, polyester elastomers, polyamide elastomers, and polyimide elastomers. These may be used individually or in combination of two or more. Alternatively, a composite elastomer may be formed by chemically bonding two or more elastomers. The composite elastomer may be used individually or in combination of two or more. The structure of the composite elastomer is not limited, but examples include random copolymers, diblock copolymers, triblock copolymers, graft copolymers, and star-shaped block copolymers. Among these, silicone elastomers, urethane elastomers, acrylic elastomers, and polyester elastomers are preferred in terms of elasticity, and further, in terms of adhesion to the substrate, silicone elastomers, urethane elastomers, and acrylic elastomers are preferred, with acrylic elastomers being more preferred. In this context, elastomers refer to polymeric materials with remarkable elasticity. These materials rapidly stretch when subjected to tension without generating heat due to energy dissipation, and return to their original length when the tension is removed.

[0024] Examples of the silicone elastomer include curable silicone resins, and resins synthesized using initiators or monomers having siloxane bonds. Examples of curable silicone resins include silicone elastomers obtained by curing organopolysiloxane compositions. Organopolysiloxane compositions mainly consist of organopolysiloxanes (base polymers), but the curing method is not particularly limited. Examples include conventionally known condensation curing, addition curing, organic peroxide curing, and radiation curing. In the conductive composition of the present invention, the use of an addition-curing silicone resin is particularly preferable from the viewpoint of elastic conductivity because it exhibits less shrinkage after curing.

[0025] The acrylic elastomer can be formed by polymerizing an ethylenically unsaturated monomer containing a (meth)acrylic monomer in the presence of a polymerization initiator, although the method of its production is not limited, and it has constituent units derived from the (meth)acrylic monomer. In this specification, "ethylenically unsaturated monomer" means a monomer having one or more polymerizable ethylenically unsaturated groups in its molecule.

[0026] This reaction may be carried out entirely with a solvent or without one. If a solvent is used, it may be removed under reduced pressure or atmospheric pressure during or after the reaction. In the case of solution polymerization, the polymerization solvent may be ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, xylene, acetone, hexane, methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol monoethyl ether acetate, tetraethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol dimethyl ether, diacetone alcohol, cyclohexanone, isophorone, etc., but is not limited to these. Two or more of these polymerization solvents may be used in mixture form, but it is preferable that the solvent used is the one used in the final application.

[0027] <Ethylene-unsaturated monomers> Examples of ethylenically unsaturated monomers constituting acrylic elastomers include linear or branched alkyl(meth)acrylates such as methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, tertiary-butyl(meth)acrylate, isoamyl(meth)acrylate, octyl(meth)acrylate, isooctyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, cetyl(meth)acrylate, decyl(meth)acrylate, isodecyl(meth)acrylate, lauryl(meth)acrylate, tridecyl(meth)acrylate, isomiristyl(meth)acrylate, stearyl(meth)acrylate, and isostearyl(meth)acrylate; Cyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, and other cyclic alkyl (meth)acrylates; Fluoroalkyl (meth)acrylates such as trifluoroethyl (meth)acrylate, octafluoropentyl (meth)acrylate, perfluorooctylethyl (meth)acrylate, and tetrafluoropropyl (meth)acrylate; Heterocyclic (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate and 3-methyl-3-oxetanyl (meth)acrylate; (Meth)acrylates having aromatic rings, such as benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, paracumylphenoxyethyl (meth)acrylate, paracumylphenoxypolyethylene glycol (meth)acrylate, or nonylphenoxypolyethylene glycol (meth)acrylate; (Meth)acrylates having alkyl ether groups, such as methoxypolyethylene glycol mono(meth)acrylate, octoxypolyethylene glycol polypropylene glycol mono(meth)acrylate, lauroxypolyethylene glycol mono(meth)acrylate, stearoxypolyethylene glycol mono(meth)acrylate, phenoxypolyethylene glycol mono(meth)acrylate, phenoxypolyethylene glycol polypropylene glycol mono(meth)acrylate, polyethylene glycol monomethyl ether (meth)acrylate, lauroxypolyethylene glycol mono(meth)acrylate, nonylphenoxypolyethylene glycol mono(meth)acrylate, nonylphenoxypolypropylene glycol mono(meth)acrylate, nonylphenoxypolyethylene glycol polypropylene glycol mono(meth)acrylate, phenoxypolyethylene glycol mono(meth)acrylate, methoxypolyethylene glycol (meth)acrylate, n-butoxyethyl (meth)acrylate, n-butoxydiethylene glycol (meth)acrylate, 2-methoxyethyl (meth)acrylate, and 2-ethoxyethyl (meth)acrylate; (Meth)acrylates having an oxetanyl group, such as 3-(acryloyloxymethyl)3-methyloxetane, 3-(methacryloyloxymethyl)3-methyloxetane, 3-(acryloyloxymethyl)3-ethyloxetane, 3-(methacryloyloxymethyl)3-ethyloxetane, 3-(acryloyloxymethyl)3-butyloxetane, 3-(methacryloyloxymethyl)3-butyloxetane, 3-(acryloyloxymethyl)3-hexyloxetane, and 3-(methacryloyloxymethyl)3-hexyloxetane; Vinyl compounds such as styrene, α-methylstyrene, vinyl acetate, vinyl (meth)acrylate, or allyl (meth)acrylate; Vinyl ethers having an ether group, such as ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, or isobutyl vinyl ether; Examples include (meth)acrylates having siloxane bonds, such as the reactive silicones (Sylaplane) FM-0711, FM-0721, FM-0725, and TM-0701T manufactured by JNC Corporation. These may be used individually or in combination of two or more types.

[0028] Specific examples of ethylenically unsaturated groups in ethylenically unsaturated monomers include ethylene, propenyl, butenyl, vinylphenyl, (meth)acrylic, allyl ether, vinyl ether, maleyl, maleimide, (meth)acrylamide, acetylvinyl, and vinylamide groups. The (meth)acrylic group is more preferred among the "ethylenically unsaturated monomers." Note that "(meth)acrylic" includes both "acrylic," "methacrylic," and mixtures thereof. Similarly, "(meth)acrylate" includes both "acrylate," "methacrylate," and mixtures thereof.

[0029] Furthermore, in this specification, "structural units derived from ethylenically unsaturated monomers" include not only residues of ethylenically unsaturated monomers, but also derivatives of residues of ethylenically unsaturated monomers obtained by reacting a portion of the residues of ethylenically unsaturated monomers with a reactive compound during or after polymerization of the block copolymer. For example, this also includes structural units in which a functional group and / or substituent not originally present in the monomer is introduced into a portion of the residues of the ethylenically unsaturated monomer. Note that the monomer itself may contain a functional group and / or substituent. It also includes structures in which side groups, side chains, or side groups and side chains within the block copolymer are bonded to each other or via a reactive compound to form a ring.

[0030] Furthermore, the acrylic elastomer may have constituent units derived from ethylenically unsaturated monomers having one or more crosslinking groups within the molecule. The presence of crosslinking groups promotes aggregation by crosslinking, thereby improving the toughness, stretchability, solvent resistance, and heat resistance of the resulting conductive composition. Moreover, from the viewpoint of reactivity with the crosslinking agent, it is more preferable that the crosslinking group is one or more selected from the group consisting of hydroxyl groups, carboxyl groups, epoxy groups, isocyanate groups and their blocks, amino groups, (meth)acrylate groups, hydrolyzable silyl groups, and nitrile groups; even more preferable that it is one or more selected from the group consisting of hydroxyl groups, carboxyl groups, epoxy groups, isocyanate groups and their blocks; and particularly preferable that it is a hydroxyl group.

[0031] Examples of ethylenically unsaturated monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-hydroxy-3-allyloxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, or caprolactone adducts of these monomers (1 to 5 moles added), polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, and glycerin mono(meth)acrylate.

[0032] A preferred form of acrylic elastomer is a (meth)acrylic block copolymer (hereinafter sometimes simply referred to as a block copolymer). Furthermore, it is preferable that the (meth)acrylic block copolymer includes soft segments and hard segments. The soft segments are block components consisting of flexible and highly pliable polymer chains, while the hard segments are block components consisting of polymer chains that are easily crystallized or aggregated and have higher rigidity than the soft segments. In the acrylic block copolymer according to the present invention, it is preferable that the soft segments are sandwiched between hard segments (i.e., a triblock structure of "hard segment-soft segment-hard segment" or a star-shaped block structure described later).

[0033] Examples of block copolymers containing soft segments and hard segments include block copolymers represented by the following formula (3). Polymer block A - Polymer block B...(3) In formula (3), polymer block A is a block (hard segment) with a glass transition temperature Tg of 20°C or higher, and polymer block B is a block (soft segment) with a glass transition temperature Tg of less than 20°C. By using the block copolymer represented by formula (3), the cured product of the conductive composition according to the embodiment of the present invention exhibits toughness. The glass transition temperature Tg can be measured using differential scanning calorimetry (DSC). In this specification, formula (3) may be abbreviated as "AB".

[0034] Furthermore, an example of a triblock block copolymer is the block copolymer represented by the following formula (1).

[0035] Polymer block A - Polymer block B - Polymer block A...(1) In formula (1), polymer block A and polymer block B can be described by referring to the description for formula (3). In this specification, formula (1) may be abbreviated as "ABA".

[0036] Furthermore, polymer block A is preferably a block with a Tg of 50°C or higher, and polymer block B is preferably a block with a Tg of -20°C or lower.

[0037] Furthermore, in the block copolymers shown in formulas (3) and (1), it is preferable that polymer block B, which has a smaller glass transition temperature Tg, corresponds to the soft segment, and polymer block A, which has a larger glass transition temperature Tg, corresponds to the hard segment. Furthermore, comparing formula (3) and formula (1), it is preferable to use the block copolymer of formula (1) from the viewpoint of tensile break elongation.

[0038] Furthermore, the block copolymer is preferably solid in the temperature range of at least 20°C to 30°C. Being solid in this temperature range ensures good tackiness when applied to a flexible substrate or when dried after application.

[0039] Furthermore, it is preferable that the mass ratio of polymer block A to polymer block B is in the range of 15:85 to 40:60. When the mass ratio of polymer block A to polymer block B is within the above range, it follows the substrate during elongation, making it less likely for wires to break. More preferably, it is 20:80 to 35:75.

[0040] Examples of polymer block A include polymethyl methacrylate (PMMA) and polystyrene (PS). Examples of polymer block B include poly-n-butyl acrylate (PBA) and polybutadiene (PB). The block copolymer is preferably a triblock copolymer of polymethyl (meth)acrylate / poly-n-butyl (meth)acrylate / polymethyl (meth)acrylate. In this application, (meth)acrylate is a general term for acrylate and methacrylate, and the same applies to other similar expressions.

[0041] Furthermore, the block copolymer may have a star-shaped block structure represented by formula (2) below, in addition to the block structure represented by formulas (3) and (1) described above.

[0042] [Polymer Block A - Polymer Block B] q X···(2) In equation (2), q is an integer between 2 and 6. Polymer block A and polymer block B can be described using the same method as for equation (3). A "star-shaped block structure" is formed when multiple (2-6) diblocks of polymer block A and polymer block B are linked together starting from X (X is linked to polymer block B) [polymer block A - polymer block B]. q This refers to the structure of X. X is an initiator residue and / or a coupling agent residue, or a derivative thereof. In this specification, formula (2) is defined as "[AB] q It is sometimes abbreviated as "X".

[0043] Furthermore, "initiator residue" refers to a substructure derived from the initiator, meaning a residue derived from the initiator in the block copolymer. Similarly, "coupling agent residue" refers to a substructure derived from the coupling agent, meaning a residue derived from the coupling agent in the block copolymer. Finally, "derivative thereof" refers to a structure in which part of the initiator residue and / or coupling agent residue has been chemically modified. For example, this includes structures in which part of the initiator residue and / or coupling agent residue has been substituted or added during the synthesis of the block copolymer.

[0044] In the case of a star-shaped block structure, the molecular weight of the initiator residue and / or coupling agent residue, or its derivative X, is not particularly limited within the scope of the present invention. For example, it can be about 50 to 2,500. Similarly, the molecular weight of the initiator residue or its derivative, which may optionally be present at the chain end of polymer block A, is not particularly limited within the scope of the present invention, and can be about 50 to 2,500.

[0045] The Tg of polymer block A in this specification is the Tg observed in the curve obtained by differential scanning calorimetry (DSC) measurement at the stage when the block copolymer is obtained <polymer block A> Total and is measured based on JIS K7121:2012 Method for Measuring Transition Temperature of Plastics, and the value is determined by the extrapolated glass transition onset temperature (Tig) described in JIS 9.3. <polymer block A> Total Since the Tg derived from Total is the same as or close to the Tg of a polymer having a block with a similar chemical structure, in the case of a diblock structure or triblock structure, it is the Tg of polymer block B, and in the case of a star block structure, it is [polymer block B] q and can be easily distinguished from the Tg of X. <polymer block A> Total The above-mentioned Tg and the Tg of each polymer block A do not vary significantly depending on the structure of the chain ends of the block copolymer, that is, the chain ends of polymer block A. Therefore, in this specification, including the chain ends of polymer block (A), the Tg of each polymer block A and <polymer block A> Total are used to judge the Tg.

[0046] However, in cases where the structural units derived from the monomers of each polymer block A are different for each block, and multiple Tgs are observed in the curve obtained by DSC measurement, <polymer block A> Total instead of the Tg of Total , the Tg of each polymer block A is used for judgment. In that case, sampling is performed at the time when the polymerization of each polymer block A is completed to determine the Tg. Alternatively, since there is a correlation between the Tg of each polymer block (A) and the Tg of a polymer having a similar chemical structure, the Tg of each corresponding polymer can be determined from Fox's equation, and it can be judged whether the Tg is 20 °C or higher. Fox's equation is the value obtained from the following equation (4). 1 / (TgA + 273.15) = Σ[Wa / (Tga + 273.15)] ··· (4) In equation (4), TgA is the Tg (°C) of polymer block A, Wa is the mass fraction of monomer a constituting polymer block A, and Tga is the Tg (°C) of the homopolymer of monomer a. Note that Tga is a widely known characteristic value of homopolymers, and values ​​such as those listed in "POLYMER HANDBOOK, THIRD EDITION" or manufacturer catalog values ​​can be used.

[0047] In this specification, the Tg of polymer block B is the Tg of polymer block B itself when the block copolymer has a diblock or triblock structure, and [polymer block B] when it has a star-shaped block structure. q Let Tg be X. Here, polymer block B has a diblock structure, a triblock structure, and polymer block B has a star-shaped block structure. q X is collectively referred to as <polymer block B[X]>. The Tg of polymer block B[X] is the Tg of polymer block B[X] observed in the curve obtained by DSC measurement at the stage when the block copolymer is obtained. The measurement is performed according to JIS K7121:2012 Method for measuring transition temperatures of plastics, and the value is determined by the extrapolation glass transition onset temperature (Tig) described in JIS 9.3. The Tg of polymer block B[X] will be the same as or close to the Tg of polymers having a similar chemical structure, so it can be easily distinguished from the Tg derived from polymer block A.

[0048] Block copolymers have a block structure that is either a diblock structure of AB, a triblock structure of ABA, or [AB] q It is preferable that X has a star-shaped block structure, and polymer block A may have initiator residues or derivatives thereof, functional groups, inert groups, crosslinkable groups, substituents, etc. at the chain ends.

[0049] The Tg of polymer block A is 20°C or higher, preferably 40°C or higher, more preferably 60°C or higher, even more preferably 80°C or higher, and particularly preferably 100°C or higher. The upper limit of the Tg of polymer block A is not particularly limited, but can be, for example, 300°C, 250°C, or 200°C. As mentioned above, the Tg of polymer block A is <polymer block A> Total This can be interpreted as Tg (and the same applies hereafter). That is, <polymer block A> Total The temperature is 20°C or higher, preferably 40°C or higher, more preferably 60°C or higher, even more preferably 80°C or higher, and particularly preferably 100°C or higher. Similarly, <polymer block A> Total The upper limit is not particularly limited, but it can be, for example, 300°C, 250°C, or 200°C.

[0050] Tg of polymer block B in the case of diblock structure, triblock structure, and [polymer block B] in the case of star-shaped block structure q The Tg of X, i.e., the Tg of <polymer block B[X]>, is less than 20°C, preferably -10°C or lower, and particularly preferably -20°C or lower. The lower limit of the Tg of <polymer block (B)[X]> is not particularly limited, but can be, for example, -100°C, -90°C, or 80°C.

[0051] The temperature difference between the Tg of polymer block A and the Tg of polymer block B[X] is not particularly limited, but is preferably 75°C or higher, more preferably 100°C or higher, even more preferably 125°C or higher, and most preferably 150°C or higher. Setting it to 75°C or higher promotes the formation of microphase separation structures, allowing for a more effective extraction of the effects of physical crosslinking.

[0052] The weight-average molecular weight (Mw) as used herein is the value obtained by the method described in the examples below. The Mw of the block copolymer is 20,000 to 500,000. By setting it within this range, both stretchability and conductivity stability can be achieved when the block copolymer is used as a conductive composition for stretchable conductive materials. The preferred range for Mw is 25,000 to 400,000, and the more preferred range is 30,000 to 300,000. The polydispersity (Mw / Mn) is not particularly limited, but is preferably 1 to 2.5, more preferably 1 to 2.0, and even more preferably 1 to 1.8. From the viewpoint of promoting the formation of microphase separation structures that affect stretchability, a polydispersity of 1 to 1.5 or 1 to 1.3 is particularly preferred.

[0053] The Mw of each polymer block A may be different, but from the viewpoint of elasticity, it is preferable that they be substantially the same. Similarly, the Mw of each polymer block B may be different, but from the viewpoint of elasticity, it is preferable that they be substantially the same.

[0054] The structural units derived from monomers in each polymer block A may consist of structural units derived from different monomers for each block, or they may consist of structural units derived from the same monomer across all blocks. It is preferable that polymer blocks A share 60% or more by mass of the monomer-derived structural units, more preferably 70% by mass, and even more preferably 80% or more by mass. Similarly, each polymer block B may consist of structural units derived from different monomers for each block, or they may consist of structural units derived from the same monomer across all blocks. Preferably, polymer blocks B share 60% or more by mass of the monomer-derived structural units, more preferably 70% by mass, and even more preferably 80% or more by mass. Here, "shared" means that the components are common, without regard to the order of the monomers.

[0055] From the viewpoint of more effectively enhancing the properties of stretchability and stretch conductivity, which are characteristics of stretchable conductive materials, the bond structure of the block copolymer is an ABA-type triblock structure, [AB] q A bifurcated structure with q=2 and a trifurcated structure with q=3 are preferred for X. Polymer block A and polymer block B each independently have structural units derived from one or more monomers.

[0056] The content of structural units derived from ethylenically unsaturated monomers in the block copolymer is preferably 70% by mass or more, preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the total mass of the block copolymer. From the viewpoint of more effectively promoting the formation of microphase separation structures of polymer block A and polymer block B, it is preferable that the block copolymer consists of structural units derived from ethylenically unsaturated monomers (100% by mass) except for X (initiator residues and / or coupling agent residues, or derivatives thereof) and the terminal structures of the block copolymer.

[0057] Polymer block A satisfies the aforementioned Tg and is a block that functions as a hard segment, mainly consisting of structural units derived from ethylenically unsaturated monomers. Monomers are used individually or in combination of two or more. Specific examples of monomers include methacrylic acid esters, acrylamides, N-alkylacrylamides, styrene, styrene derivatives, maleimides, and acrylonitriles. Examples of methacrylic acid esters include those having alkyl groups with 1 to 20, 1 to 16, 1 to 12, 1 to 8, or 1 to 4 carbon atoms. Examples of styrene derivatives include α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene. Furthermore, monomers exemplified in polymer block B, which will be described next, can be suitably included as part of the block.

[0058] Polymer block B satisfies the aforementioned Tg and is a block that functions as a soft segment, mainly consisting of structural units derived from ethylenically unsaturated monomers. Monomers are used individually or in combination of two or more. Specific examples of monomers include acrylic acid esters, olefin compounds, diene compounds, and alkylene oxides. Examples of acrylic acid esters include alkyl acrylates having alkyl groups with 1 to 20, 1 to 16, 1 to 12, 1 to 8, or 1 to 4 carbon atoms. Examples of olefin compounds and diene compounds include olefin compounds and diene compounds with 1 to 20, 1 to 16, 1 to 12, 1 to 8, or 1 to 4 carbon atoms. Examples of alkylene oxides include alkylene oxides having alkylene groups with 1 to 20, 1 to 16, 1 to 12, 1 to 8, or 1 to 4 carbon atoms. Furthermore, the monomer exemplified in the aforementioned polymer block A can preferably be included as part of it.

[0059] A suitable example of a block copolymer is a block copolymer in which polymer block A contains 50% by mass or more of structural units derived from methacrylic acid ester, and polymer block B contains 70% by mass or more of structural units derived from acrylic acid ester. The amount of structural units derived from methacrylic acid ester in polymer block A is more preferably 60% by mass or more, and even more preferably 70% by mass or more, 80% by mass or more, or 90% by mass or more. Alternatively, the amount of structural units derived from methacrylic acid ester may be 100% by mass.

[0060] Furthermore, the amount of structural units derived from acrylic acid esters in polymer block B is more preferably 80% by mass or more, and even more preferably 85% by mass or more, 90% by mass or more, or 95% by mass or more. Alternatively, the amount of structural units derived from acrylic acid esters may be 100% by mass. By polymer block A containing 50% by mass or more of structural units derived from methacrylic acid esters, and polymer block B containing 70% by mass or more of structural units derived from acrylic acid esters, it is possible to achieve superior elasticity and stable stretch conductivity.

[0061] The monomers that form structural units derived from methacrylate esters in polymer block A include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isoamyl methacrylate, pentyl methacrylate, n-hexyl methacrylate, isohexyl methacrylate, isoheptyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, n-octyl methacrylate, isononyl methacrylate, isodecyl methacrylate, and lauric acid. Examples of aliphatic, alicyclic, and aromatic alkyl methacrylates include methyl methacrylate, tetradecyl methacrylate, octadecyl methacrylate, behenyl methacrylate, isostearyl methacrylate, cyclohexyl methacrylate, t-butylcyclohexylmethyl methacrylate, isoboronyl methacrylate, trimethylcyclohexyl methacrylate, cyclodecyl methacrylate, cyclodecylmethyl methacrylate, benzyl methacrylate, t-butylbenzotriazolephenylethyl methacrylate, phenyl methacrylate, naphthyl methacrylate, and allyl methacrylate. Furthermore, hydroxyl group-containing methacrylic acid monomers such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate, where the hydroxyalkyl group has 2 to 4 carbon atoms, glycerin acrylate, and glycerin methacrylate; alkoxyalkyl methacrylates such as methoxymethyl methacrylate, methoxyethyl methacrylate, methoxypropyl methacrylate, ethoxymethyl methacrylate, ethoxyethyl methacrylate, and ethoxypropyl methacrylate, where the alkoxy group has 1 to 4 carbon atoms and the alkyl group has 1 to 4 carbon atoms; Monomethacrylates of (polyalkylene) glycol monoalkyls, alkylenes, alkyne ethers, or esters; methacrylic acid monomers having acidic groups (carboxyl groups, sulfonic acid, phosphoric acid) including acrylic acid or acrylic acid dimers; methacrylic acid monomers containing oxygen atoms; methacrylic acid monomers having amino groups; methacrylic acid monomers containing nitrogen atoms, etc. can be used. Furthermore, other examples include monomethacrylates having three or more hydroxyl groups, halogen atom-containing methacrylates, silicon atom-containing methacrylic acid monomers, methacrylic acid monomers having ultraviolet-absorbing groups, and α-hydroxyl group-substituted methyl acrylates. In addition, methacrylic acid monomers having two or more addition polymerizable groups, such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and methacrylic acid esters of polyalkylene glycol adducts of trimethylolpropane, may also be used.

[0062] Other monomers that can polymerize with methacrylic acid ester can be used as monomers that form structural units of polymer block A other than those derived from methacrylic acid ester. Specifically, examples include styrene and acrylonitrile.

[0063] A preferred example of polymer block A is an embodiment containing 50% by mass or more of structural units derived from methyl methacrylate. More preferably, the structural units derived from methyl methacrylate are 60% by mass or more, and even more preferably 80% by mass or more. Alternatively, 100% by mass of polymer block A may be structural units derived from methyl methacrylate.

[0064] The monomers that form the structural units derived from acrylic acid esters in polymer block B are methyl acrylate, ethyl acrylate, propyl methacrylate, isopropyl methacrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, isoamyl acrylate, pentyl acrylate, n-hexyl acrylate, isohexyl acrylate, isoheptyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, n-octyl acrylate, isononyl acrylate, isodecyl acrylate, and lau Examples of aliphatic, alicyclic, and aromatic alkyl acrylates include lyl acrylate, tetradecyl acrylate, octadecyl acrylate, behenyl acrylate, isostearyl acrylate, cyclohexyl acrylate, t-butylcyclohexylmethyl acrylate, isoboronyl acrylate, trimethylcyclohexyl acrylate, cyclodecyl acrylate, cyclodecylmethyl acrylate, benzyl acrylate, t-butylbenzotriazolephenylethyl acrylate, phenyl acrylate, naphthyl acrylate, and allyl acrylate. Furthermore, acrylic acid monomers containing hydroxyl groups; acrylic acid monomers having glycol groups; monoacrylates of (polyalkylene) glycol monoalkyl, alkylene, alkyne ether or ester; acrylic acid monomers having acidic groups (carboxyl groups, sulfonic acid, phosphoric acid) including acrylic acid or acrylic acid dimers; acrylic acid monomers containing oxygen atoms; acrylic acid monomers having amino groups; acrylic acid monomers containing nitrogen atoms, etc. can also be used. In addition, monoacrylates having three or more hydroxyl groups, halogen atom-containing acrylates, silicon atom-containing acrylic acid monomers, acrylic acid monomers having ultraviolet-absorbing groups, and α-hydroxyl group-substituted methyl acrylates can also be used. Furthermore, acrylic acid monomers having two or more addition polymerizable groups, such as ethylene glycol diacrylate, diethylene glycol diacrylate, and acrylic acid esters of polyalkylene glycol adducts of trimethylolpropane, may also be used.

[0065] As structural units other than those derived from acrylic acid esters in polymer block B, other monomers that can polymerize with acrylic acid esters can be used. Examples include maleic acid, itaconic acid, and crotonic acid.

[0066] A preferred example of polymer block B is an embodiment containing 70% by mass or more of structural units derived from butyl acrylate. More preferably, the structural units derived from butyl acrylate are 80% by mass or more, and even more preferably 90% by mass or more. Alternatively, 100% by mass of polymer block B may be structural units derived from butyl acrylate.

[0067] A suitable example of a block copolymer is one in which polymer block A contains 50% by mass or more of structural units derived from methyl methacrylate, and polymer block B contains 70% by mass or more of structural units derived from butyl acrylate. Using such a block copolymer provides an excellent stretchable conductive material. The amount of structural units derived from methyl methacrylate in polymer block A may be 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 100% by mass or more. The amount of structural units derived from butyl acrylate in polymer block B may be 80% by mass or more, 90% by mass or more, or 100% by mass.

[0068] By using block copolymers, polymer block A and polymer block B can form molecular-level phase separation structures (microphase separation structures) such as sea-island structures (body-centered cubic), cylinders (hexagonal), gyroids, and lamellar phases. By forming microphase separation structures, a conductive composition can be provided that offers excellent stretchability and effectively suppresses crack generation (disconnection) associated with stretching. From the viewpoint of more effectively enhancing stretchability, it is more preferable that polymer block A forms an island and polymer block B forms the sea in a sea-island structure. The microphase separation structure can be confirmed by observation using an atomic force microscope (AFM).

[0069] The content of polymer block A relative to polymer block A and polymer block B in the block copolymer is not particularly limited, but from the viewpoint of easily obtaining a microphase separation structure of sea-island structure, it is preferably 1 to 50% by mass, and more preferably 15 to 30% by mass. Furthermore, from the viewpoint of effectively eliciting tackiness, the total content of polymer block A relative to polymer block A and polymer block B in the block copolymer is preferably 1 to 35% by mass, and more preferably 5 to 30% by mass. The content ratio of polymer block A and polymer block B in the block copolymer is not particularly limited, but from the viewpoint of easily obtaining a microphase separation structure, it is preferable that the content ratio of polymer block A and polymer block B is 90.0 to 99.9% by mass, and more preferably 98.0 to 99.9% by mass, relative to the total mass of the block copolymer.

[0070] From the viewpoint of maintaining good conductivity, it is preferable that 90% or more by mass of the ethylenically unsaturated monomers of the block copolymer are hydrophobic ethylenically unsaturated monomers. Here, "hydrophobic ethylenically unsaturated monomers" refers to monomers whose solubility in water at 20°C is 6.5 g / 100 mL or less. Examples of hydrophobic ethylenically unsaturated monomers include the alkyl (meth)acrylates mentioned above, olefins such as butadiene and isoprene, vinyls such as vinyl acetate and vinyl chloride, and aromatics such as styrene.

[0071] [Functional group] The block copolymer may have functional groups. Examples of functional groups include mercapto groups, hydroxyl groups, amino groups, carboxyl groups, glycidyl groups, (meth)acrylic groups, hydrolyzable silyl groups, nitrile groups, and isocyanate groups.

[0072] [Reactive functional groups] The block copolymer preferably has one or more reactive functional groups selected from the group consisting of mercapto groups, hydroxyl groups, amino groups, and carboxyl groups. By chemically crosslinking these functional groups with a crosslinking agent described later, the block copolymer can be crosslinked in three dimensions, making it suitable for use in applications where hardness is required for the conductive layer.

[0073] [Sulfur atom] Block copolymers preferably contain sulfur atoms, and more preferably, these sulfur atoms originate from sulfide groups, disulfide groups, mercapto groups, etc., in order to effectively suppress the occurrence of cracks when conductive fillers such as metal fillers are included.

[0074] By containing sulfur atoms within the molecule, the block copolymer can form a microphase separation structure between polymer block A and polymer block B, creating physical crosslinks that include stress relaxation points. The presence of a microphase separation structure and the formation of physical crosslinks in the block copolymer enhance its elasticity. Furthermore, self-assembly (assembly of segments) can bring sulfur atoms closer together. This distribution of sulfur atoms further imparts cohesive force and stress relaxation, resulting in superior elasticity, heat resistance, and moisture resistance of the block copolymer.

[0075] Methods for incorporating sulfur atoms into block copolymers include, for example, direct introduction using a monomer containing sulfur atoms, copolymerization of monomers using a polymerization initiator containing sulfur atoms, production of block copolymers using a coupling agent containing sulfur atoms, and introduction of sulfur atoms by modification (chemical transformation). Examples of polymerization initiators containing sulfur atoms include commercially available sulfur-based RAFT initiators. Another method involves obtaining polymers using chain transfer agents containing mercapto groups, such as mercaptohexanol. Furthermore, another method involves directly introducing sulfur atoms, such as mercapto groups, by adding 1,2-ethanedithiol or the like to the block copolymer obtained after polymerization.

[0076] [Method for manufacturing block copolymer] The following describes, but is not limited to, an example of a method for producing block copolymers.

[0077] The method for producing block copolymers is not particularly limited, but methods using radical polymerization and ionic polymerization are preferred. Ionic polymerization includes anionic polymerization and cationic polymerization. The type of radical polymerization is not particularly limited, but living radical polymerization is preferred. Alternatively, a block copolymer can be obtained by first obtaining a reactive terminal diblock structure and then using a coupling agent.

[0078] Examples of anionic polymerization include methods using an organo-rare-earth metal complex or organo-alkali metal compound as a polymerization initiator in the presence of an inorganic salt, and methods using an organo-alkali metal compound as a polymerization initiator in the presence of an organo-aluminum compound. Examples of living radical polymerization include polymerization using nitroxide-based catalysts (NMP method), atom transfer radical polymerization using transition metal complex-based catalysts (ATRP method), reversible addition-cleavage chain transfer polymerization using reversible addition-cleavage chain transfer agents (RAFT method), polymerization using organotellurium-based catalysts (TERP method), and iodine transfer polymerization using iodine-based compounds as catalysts (RCMP method (reversible coordination-mediated polymerization) or RTCP method (reversible transfer catalytic polymerization)).

[0079] Alternatively, the process includes obtaining polymer block B and polymer block A by sequential polymerization in the following order using a polymerization initiator having 2 to 6 polymerization initiators [polymer block A - polymer block B]. q There is a method for producing block copolymers represented by X.

[0080] Another method involves a step-by-step polymerization process starting with a polymerization initiator to obtain polymer block A, polymer block B, and polymer block A in that order, thereby producing a block copolymer represented by a triblock structure of polymer block A-polymer block B-polymer block A.

[0081] Furthermore, the process includes obtaining an AB-type diblock structure by sequentially polymerizing polymer block B and polymer block A in any order, introducing reactive ends to the molecular ends of the AB-type diblock structure as needed, and carrying out a coupling reaction using a coupling agent having 3 to 6 linking units that react with these reactive ends, [polymer block A - polymer block B] q There is a method for producing block copolymers represented by X.

[0082] Furthermore, the block copolymer may be a commercially available product. An example of a commercially available product is an acrylic triblock copolymer manufactured using living polymerization by Arkema. Specifically, SBM type represented by polystyrene-polybutadiene-polymethyl methacrylate, MAM type represented by polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate, and MAMN or MAMA type that have been treated with carboxylic acid modification or hydrophilic group modification can be used. Another example of a commercially available product is a block copolymer derived from methyl methacrylate and butyl acrylate, manufactured by Kuraray.

[0083] The block copolymer may be used alone or in combination of two or more types.

[0084] Elastomer (A) may contain additives other than resin components, such as plasticizers, antioxidants, anti-aging agents, and colorants.

[0085] <Conductive fine particles (B)> Conductive fine particles (B) exhibit conductivity through contact between multiple conductive fine particles within a conductive layer. In the present invention, conductive fine particles are appropriately selected and used from those that can be made conductive without heating at high temperatures. Examples of conductive fine particles used in the present invention include metal fine particles, carbon fine particles, and conductive oxide fine particles.

[0086] Examples of metal nanoparticles include elemental metal powders such as gold, silver, copper, nickel, chromium, palladium, rhodium, ruthenium, indium, aluminum, tungsten, molarbutene, and platinum, as well as alloy powders such as copper-nickel alloys, silver-palladium alloys, copper-tin alloys, silver-copper alloys, and copper-manganese alloys, and metal coated powders in which the surface of the elemental metal powders or alloy powders is coated with silver, etc. Examples of carbon nanoparticles include carbon black, graphite, and carbon nanotubes. Examples of conductive oxide nanoparticles include silver oxide, indium oxide, tin oxide, zinc oxide, and ruthenium oxide.

[0087] In the present invention, it is preferable to include one or more conductive fine particles selected from the group consisting of silver powder, copper powder, silver-coated powder, copper alloy powder, conductive oxide powder, and carbon fine particles. By using these conductive fine particles (B), a conductive layer with excellent conductivity can be formed without undergoing sintering.

[0088] The shape of the conductive fine particles (B) is not particularly limited, and irregular shapes, aggregates, flakes, microcrystalline, spherical, flakes, wires, dendrites, etc., can be used as appropriate. From the viewpoint of maintaining conductivity during molding and the adhesion of the conductive pattern to the substrate, aggregates, flakes, wires, and dendrites are preferred.

[0089] (Average particle size) The average particle size of conductive fine particles before preparation as a conductive composition is not particularly limited, but from the viewpoint of dispersibility in the conductive composition and conductivity when formed as a conductive layer, it is preferably 0.1 μm to 50 μm, and more preferably 0.5 μm to 30 μm.

[0090] In this invention, the average particle size of conductive fine particles (B) before being prepared as a conductive composition is calculated as follows. In accordance with the laser diffraction and scattering method described in JIS M8511 (2014), a laser diffraction and scattering particle size distribution analyzer (Nikkiso Co., Ltd.: Microtrac 9220FRA) was used. An appropriate amount of conductive fine particles (B) was added to an aqueous solution containing 0.5 volume% of a commercially available surfactant, polyoxyethylene octylphenyl ether (Roche Diagnostics K.K.: Triton X-100), as a dispersant. After irradiating with 40W ultrasonic waves for 180 seconds while stirring, the measurement was performed. The obtained median diameter (D50) value was taken as the average particle size of conductive fine particles (B) before being prepared as a conductive composition.

[0091] (particle size distribution) The particle size distribution of conductive fine particles (B) in the conductive composition, when passed through a screen mask with a 400-mesh, 23 μm wire diameter, and 41% aperture ratio, is such that the peak top particle size (rtop) is between 2.0 μm and 20.0 μm, and the peak top frequency (ftop) is between 1.5% and 9.0%. As a result, as described above, when a printed material is produced through any process, the conductive path formation is maintained even during expansion and contraction, the decrease in expansion and contraction conductivity is suppressed, and a conductive composition with good adhesion is obtained.

[0092] The particle size of the peak top (rtop) in the particle size distribution of conductive fine particles (B) in the conductive composition after passing through the above-mentioned 400-mesh, 23 μm wire diameter, and 41% aperture ratio screen mask is preferably 2.75 μm or more and 18.5 μm or less, and more preferably 7.5 μm or more and 17.0 μm or less. The frequency of ftops in the particle size distribution of conductive fine particles (B) in the conductive composition after passing through the above-mentioned 400-mesh, 23 μm wire diameter, and 41% aperture ratio screen mask is preferably 2.0% to 7.0%, and more preferably 2.2% to 4.0%.

[0093] Furthermore, when the conductive fine particles (B) in the conductive composition are passed through a screen mask with a 400-mesh, 23 μm wire diameter, and 41% aperture ratio, it is preferable that the cumulative 95% particle size (r95) is 10.0 μm or larger, and the cumulative 10% particle size (r10) is 0.1 μm or larger and 5.0 μm or smaller. When the cumulative 95% particle size (r95) and the cumulative 10% particle size (r10) meet this range, the degree of silver aggregation is appropriate, the number of contact points between silver particles is sufficiently large both when not stretched and when stretched, and the conductivity and resistance to repeated stretching are excellent. In addition, the amount of elastomer that penetrates between the silver powders and the amount of elastomer that is exposed at the substrate interface are both appropriate, resulting in excellent adhesion.

[0094] As described above, after passing through a screen mask with a 400-mesh, 23 μm wire diameter, and 41% aperture ratio, the cumulative 95% particle size (r95) in the particle size distribution of conductive fine particles (B) in the conductive composition is more preferably 12.0 μm or more and 42.0 μm or less, and even more preferably 15.0 μm or more and 40.0 μm or less. The cumulative 10% particle size (r10) in the particle size distribution of conductive fine particles (B) in the conductive composition after passing through the above-mentioned 400-mesh, 23 μm wire diameter, and 41% aperture ratio is more preferably 0.13 μm or more and 4.0 μm or less, and even more preferably 0.15 μm or more and 2.0 μm or less.

[0095] Furthermore, when the conductive fine particles (B) in the conductive composition are passed through a screen mask with a mesh size of 400 mesh, a wire diameter of 23 μm, and an aperture ratio of 41%, the particle size ratio before and after passing through the screen mask (cumulative 95% particle size in the particle size distribution of conductive fine particles (B) before passing through (R95) / cumulative 95% particle size in the particle size distribution of conductive fine particles (B) after passing through (r95)) is preferably 5.0 or less, more preferably 0.85 to 4.0, and even more preferably 0.9 to 2.0. During printing, shearing may be applied, or conductive material equal to or larger than the mesh aperture may be filtered, which may reduce the number of contact points between silver particles in the non-stretched and stretched states. However, within the above range, the number of contact points is sufficiently large, resulting in excellent conductivity and resistance to repeated stretching and shrinking.

[0096] The particle size distribution of conductive fine particles (B) in the conductive composition was measured using the laser diffraction scattering particle size distribution method. The specific measurement conditions are as follows: Equipment: Nikkiso Co., Ltd. Microtrac MT3000II Measurement solvent: Propylene glycol monomethyl ether acetate SetZero time: 20 Measurement time: 60 Transparency: Transparent Particle refractive index: 1.33 Shape: Non-spherical Solvent refractive index: 1.40 After moderately stirring the conductive composition with a spatula or similar tool to prevent the secondary particles of silver powder from disintegrating, the concentration index DV value was quickly adjusted to a range of 0.015-0.020 and the transmittance TR to a range of 0.90-0.95. After confirming that the particle size distribution shape was stable after two scans, the particle size distribution was measured and a particle size distribution curve was obtained. The values ​​calculated as the cumulative 10% and 95% particle sizes of the particle size distribution curve were defined as r10, r95, or R95 particle sizes, respectively. Furthermore, the maximum value of frequency (%) in the particle size distribution curve read from the data analysis view was defined as ftop, and the particle size (μm) at that point was defined as rtop.

[0097] In the present invention, conductive fine particles (B) can be used alone or in combination of two or more types. The content ratio of conductive fine particles (B) in the conductive composition of the present invention is not particularly limited and can be adjusted as appropriate depending on the application, but it is preferably 40 to 99% by mass, and preferably 60 to 95% by mass, based on the total amount of solids contained in the conductive composition. If the content ratio of conductive fine particles (B) is above the lower limit, a conductive layer with excellent conductivity can be formed. If the content ratio of conductive fine particles (B) is below the upper limit, the content ratio of resin (A) can be increased, improving film-forming properties and adhesion to the base film, and also providing flexibility and stretchability to the conductive layer.

[0098] <Other ingredients> The conductive composition in the present invention may contain filler components other than conductive fine particles. Examples include metal chloride fillers such as silver chloride, inorganic fillers such as silica, and organic fillers such as resins. The conductive composition of the present invention may further contain, if necessary, other components such as crosslinking agents, dispersants, friction-resistant agents, infrared absorbers, ultraviolet absorbers, fragrances, antioxidants, organic pigments, inorganic pigments, defoamers, silane coupling agents, plasticizers, flame retardants, and humectants.

[0099] <Method for producing conductive compositions> The method for producing the conductive composition of the present invention is to dissolve or disperse an elastomer (A), conductive fine particles (B), and other components as needed in a solvent, and can be produced by mixing them using known kneading means. Known mixing methods include dissolvers, butterfly mixers, planetary mixers, self-rotating mixers, attritors, three-roll mills, ball mills, bead mills, and sand mills. The particle size of conductive fine particles in a conductive composition can be adjusted by various conditions, such as the mixing method itself, the scale of the mixing machine, the shape of the apparatus, the shape of the stirring spring, the rotational speed and time of mixing, the mixing temperature, the bead filling rate, and the roll spacing.

[0100] <Conductive material> The conductive composition of the present invention can be used as a conductor by forming a cured product through printing or other means. Preferably, the conductor comprises a cured product of the conductive composition of the present invention as a conductive layer.

[0101] The method for forming the conductive layer is not particularly limited, but in the present invention, it is preferable to form it by screen printing, pad printing, stencil printing, screen offset printing, dispenser printing, gravure offset printing, inverted offset printing, or microcontact printing, and it is more preferable to form it by screen printing.

[0102] In screen printing, it is preferable to use a screen with a mesh size of approximately 80 to 650 mesh, from the viewpoint of achieving high resolution of conductive circuit patterns and thickening the film to improve conductivity through repeated stretching. In this case, the open area of ​​the screen is preferably about 20 to 50%. The screen wire diameter is preferably about 10 to 120 μm.

[0103] Types of screens include polyester screens, combination screens, metal screens, and nylon screens. Furthermore, high-tensile stainless steel screens can be used when printing highly viscous paste-like materials. The squeegee for screen printing can be round, rectangular, or square in shape, and a polished squeegee can also be used to reduce the attack angle (the angle between the printing plate and the squeegee during printing). Other printing conditions can be appropriately designed based on conventionally known conditions.

[0104] The method for curing the conductive composition is not particularly limited, but for example, the conductive composition of the present invention can be cured by printing it by screen printing and then heating and drying it. Furthermore, if the conductive composition contains a crosslinking agent, it is further cured by heating to carry out a crosslinking reaction. If the composition does not contain a crosslinking agent, the heating temperature is preferably 80 to 230°C and the heating time is preferably 10 to 120 minutes, in order to allow sufficient evaporation of the solvent if a crosslinking agent is present, and in order to allow sufficient evaporation of the solvent and the crosslinking reaction if a crosslinking agent is present. This allows a patterned conductive layer to be obtained. The patterned conductive layer may be provided with an insulating layer to cover the conductive pattern as needed. The insulating layer is not particularly limited, and known insulating layers can be used.

[0105] The thickness of the conductive layer can be adjusted as appropriate according to the required conductivity, and is not particularly limited, but for example, it can be 0.5 μm or more and 100 μm or less, and preferably 1 μm or more and 50 μm or less.

[0106] <Stretchable conductive material> The present invention can be used as a stretchable conductive material by providing a cured product of the conductive composition of the present invention as a conductive layer on a stretchable substrate. The stretchable conductive material is a conductive material, and by using a cured product of the conductive composition of the present invention as the conductive layer, it possesses both stretchability and conductivity during manufacturing and during product use. Furthermore, this conductive composition suppresses the decrease in conductivity due to repeated stretching and shrinking, improves the printability of the conductor on a stretchable substrate, and enables the manufacture of a stretchable conductive material with excellent adhesion between the conductive layer made of the conductor and the stretchable substrate described later. Furthermore, even when the stretchable conductive material manufactured using this conductive composition is used on a substrate surface that can conform to non-flat curved or movable parts, the decrease in conductivity is suppressed.

[0107] <Stretchable base material> The stretchable substrate is made of natural or synthetic materials that have resistance to damage or cracking during stretching, and is preferably a stretchable film substrate.

[0108] The stretchable substrate is preferably a substrate having a Young's modulus of less than 100 MPa at 23°C. The Young's modulus at 23°C is preferably less than 50 MPa, more preferably less than 10 MPa, and even more preferably less than 1 MPa. Furthermore, the stretchable film substrate is preferably a substrate having a tensile elongation at 150% or more at 23°C. The tensile elongation at 23°C is preferably 200% or more, and more preferably 400% or more. When the stretchable substrate has a Young's modulus of less than 100 MPa and a tensile elongation at 150% or more at 23°C, it is less prone to damage or cracking during stretching, making it suitable as a substrate for stretchable conductive materials.

[0109] The stretchable substrate can be selected from, for example, thermoplastic elastomers, plastics, fibers, nonwoven fabrics, silicone rubber, fluororubber, nitrile rubber, nitrile butadiene rubber, chlorosulfonated polyethylene, polysulfide rubber, acrylic rubber, styrene rubber, styrene-butadiene rubber, chloropyrene rubber, urethane rubber, butyl rubber, ethylene rubber, propylene rubber, ethylene propylene rubber, epoxy rubber, butadiene rubber, natural rubber, and isoprene rubber, and may be a laminated film made of two or more of these materials. Furthermore, the shape of the substrate may be flat, such as a plate or film, or it may be a curved or complex shape.

[0110] Examples of the thermoplastic elastomers include polyurethane-based, polyester-based, polyolefin-based, polyamide-based, polyimide-based, polyester-based, vinyl chloride-based, styrene-based block polymers, and acrylic-based block polymers.

[0111] Examples of the aforementioned plastics include polyolefins such as polyvinyl alcohol, triacetylcellulose, polypropylene, polyethylene, polycycloolefin, and ethylene-vinyl acetate copolymer; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polycarbonate, polynorbornene, polyarylate, polyacrylic, polyphenylene sulfide, polystyrene, epoxy resin, polyamide, and polyimide.

[0112] From the viewpoint of elasticity, polyurethane, silicone rubber, ethylene propylene rubber, styrene rubber, acrylic rubber, and epoxy rubber are particularly preferred as the stretchable base material, and from the viewpoint of adhesion with the conductive composition of the present invention, silicone rubber is even more preferred.

[0113] The thickness of the stretchable substrate is not particularly limited, but it can be, for example, 1 to 500 μm. It can also be 10 to 100 μm or 20 to 50 μm. When the thickness of the stretchable substrate is within the above range, it is superior in terms of windability and processability. On the other hand, if the stretchable substrate is too thin, it tends to lack strength. Also, if the substrate is too thick, its flexibility is poor, and there is a risk that the substrate will not be able to conform to the shape of the adherend.

[0114] Furthermore, if necessary, an anchor coat layer may be provided on the stretchable substrate for purposes such as improving the printability of the conductive composition, and the conductive composition may be printed on the anchor coat layer. The anchor coat layer is not particularly limited as long as it has good adhesion to the substrate and, moreover, to the conductive composition, and conforms to the stretchable substrate during molding. Organic fillers such as resin beads and inorganic fillers such as metal oxides may be added as needed. The method for providing the anchor coat layer is not particularly limited and can be obtained by applying, drying, and curing using conventionally known coating methods.

[0115] Furthermore, if necessary, a hard coat layer may be provided on the stretchable substrate to prevent scratching of the molded surface, and a conductive composition and, if necessary, a decorative layer may be printed on the opposite side. The hard coat layer is not particularly limited as long as it has good adhesion to the stretchable substrate, good surface hardness, and conforms to the stretchable substrate during molding. Organic fillers such as resin beads and inorganic fillers such as metal oxides may also be added as necessary. The method for providing the hard coat layer is not particularly limited and can be obtained by applying, drying, and curing using conventionally known coating methods.

[0116] The stretchable conductive material may be laminated on a support and used as a laminate. The support is not particularly limited, but it is preferably made of a stretchable material in order to take advantage of the stretchability of the stretchable substrate. Specific examples include stretchable plastic film and stretchable fiber. The stretchable fiber may also be textile fabric. Alternatively, a recess may be provided in the support, and the stretchable conductor may be embedded in this recess.

[0117] The stretchable conductive material and the support may be joined by utilizing the adhesive properties of the stretchable conductive material, or by lamination. Alternatively, they can be joined via an adhesive layer or an easy-bonding layer.

[0118] The stretchable conductive material obtained in this way may be a product in itself or may be used as a component. The stretchable conductive material is suitable, for example, as stretchable wiring or stretchable electrodes. Furthermore, the stretchable conductive material can be used as a film such as a stretchable electromagnetic shielding layer or a stretchable heat dissipation layer. It can also be used as a molded body having conductivity in a desired shape.

[0119] <Electronic Devices> Stretchable conductive materials are also suitable for incorporation into electronic devices. Examples of electronic devices incorporating stretchable conductive materials include sensors attached to the body or robots, wearable sensors embedded in clothing, biometric information acquisition devices, flexible displays, flexible circuit boards, flexible transducers, flexible mobile devices, motors and actuators, speakers, vibrators, and ultrasonic generators. [Examples]

[0120] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In the following description, unless otherwise specified, "parts" means "parts by mass" and "%" means "mass%". In addition, values ​​other than solvents are calculated on a non-volatile content basis.

[0121] [Measurement of weight-average molecular weight (Mw), number-average molecular weight (Mn), and Mw / Mn ratio] Using a GPC (product name: GPCV-2000, manufactured by Waters Japan, column: TSKgel, α-3000, mobile phase: 10 mM triethylamine / dimethylformamide solution), a calibration curve was created using polystyrene (molecular weights 427,000, 190,000, 96,400, 37,400, 10,200, 2,630, 440, 92) as standard substances, and the weight-average molecular weight (Mw) and number-average molecular weight (Mn) were measured. From these measurements, the polydispersity index (PDI = Mw / Mn) was calculated.

[0122] <Manufacturing of elastomer (A)> [Acrylic triblock copolymer (a1)] • The resin manufacturing example 1 described later was used. [Acrylic triblock copolymer (a2)] • The resin manufacturing example 2 described later was used. [Acrylic random copolymer (a3)] • The resin manufacturing example 3 described later was used. [Silicone resin (a4)] We used "KE-1800T-A / B" manufactured by Shin-Etsu Chemical Co., Ltd.

[0123] (monomer) MMA: Methyl methacrylate nBA: n-butyl acrylate HEMA: 2-hydroxyethyl methacrylate

[0124] (Polymerization initiator) BM1448: 4-Cyano-4-[(Dodecylsulfanylthiocarbonyl)sulfanyl]pentanosemethyl (manufactured by BORONMOLECULAR) (for RAFT polymerization) • AIBN: 2,2'-Azobis(isobutyronitrile) (manufactured by Wako Pure Chemical Industries, Ltd.)

[0125] <Example of resin production 1: Synthesis of acrylic triblock copolymer (a1)> In a four-necked flask equipped with a stirrer, reflux condenser, gas inlet tube, thermometer, and dropping funnel, 2.0 parts of methyl 4-cyano-4-(dodecylthiocarbonothio)pentanoate, 1 part of AIBN, 60 parts of MMA, and 41 parts of diethylene glycol monoethyl ether acetate (boiling point 218°C) were charged as RAFT initiators, and the mixture was reacted at 80°C for 5 hours. After cooling to 50°C, 253 parts of diethylene glycol monoethyl ether acetate (boiling point 218°C), 454 parts of BA, 19 parts of 2-isocyanatoethyl methacrylate (MOI), and 0.1 parts of AIBN were charged, and the mixture was reacted at 80°C for 12 hours. After cooling to 50°C, 40 parts of diethylene glycol monoethyl ether acetate, 60 parts of MMA, and 0.1 part of AIBN were charged and reacted at 80°C for 5 hours. After cooling to 50°C, 28 parts of butylamine and 300 parts of diethylene glycol monoethyl ether acetate were added and reacted at 50°C for 1 hour, and the disappearance of the 2270 cm-1 peak based on the isocyanate group was confirmed by IR. By adding diethylene glycol monoethyl ether acetate so that the solid content was 30%, an acrylic triblock copolymer (a1) with a number average molecular weight of 100,000 was obtained.

[0126] <Example of resin production 2: Synthesis of acrylic triblock copolymer (a2)> In a four-necked flask equipped with a stirrer, reflux condenser, gas inlet tube, thermometer, and dropping funnel, 2.0 parts of methyl 4-cyano-4-(dodecylthiocarbonothiolthio)pentanoate, 1 part of AIBN, 60 parts of MMA, and 41 parts of diethylene glycol monoethyl ether acetate (boiling point 218°C) were charged as RAFT initiators, and the mixture was reacted at 80°C for 5 hours. After cooling to 50°C, 253 parts of diethylene glycol monoethyl ether acetate (boiling point 218°C), 454 parts of BA, 19 parts of MOI, and 0.1 parts of AIBN were charged, and the mixture was reacted at 80°C for 12 hours. After cooling to 50°C, 40 parts of diethylene glycol monoethyl ether acetate, 60 parts of MMA, and 0.1 parts of AIBN were charged, and the mixture was reacted at 80°C for 5 hours. Subsequently, the mixture was cooled to 50°C, 10 parts of cysteamine were added, and the mixture was reacted at 50°C for 1 hour. IR observation confirmed the disappearance of the 2270 cm-1 peak based on the isocyanate group. By adding diethylene glycol monoethyl ether acetate to achieve a solid content of 30%, an acrylic triblock copolymer (a2) with a number-average molecular weight of 100,000 was obtained.

[0127] <Resin Manufacturing Example 3: Synthesis of Acrylic Random Copolymer (a3)> 2000 parts of acetone (boiling point 56°C) were charged into a four-necked flask equipped with a stirrer, reflux condenser, gas inlet tube, thermometer, and dropping funnel. The temperature was gradually raised, and reflux was started at 56°C. A mixture of 813 parts butyl acrylate (BA), 127 parts methyl methacrylate (MMA), 15 parts 2-hydroxyethyl methacrylate (HEMA), and 2 parts azoisobutyronitrile (AIBN) was added dropwise over approximately 3 hours. One hour after the end of the dropwise addition, 1 part of AIBN was added, and then 1 part of AIBN was added every hour for three more hours, and the reaction was continued for another 3 hours at the reflux temperature of acetone. After cooling to 50°C, the mixture was washed and dried. By adding diethylene glycol monoethyl ether acetate to achieve a solid content of 30%, an acrylic random copolymer (a3) ​​with a number average molecular weight of 146,000 was obtained.

[0128] <Manufacturing of conductive compositions> The following materials were used as conductive fine particles, solvents, and stretchable substrates. <Conductive fine particles (B)> b1: Tap density 1.4 g / cm³ 3 Chain of spherical silver b2: Agglomerated silver with a 50% average particle size of 21.6 μm b3: Flake-shaped silver with a 50% average particle size of 6.0 μm b4: Flake-shaped silver with a 50% average particle size of 8.5 μm b5: Flake-shaped silver with a 50% average particle size of 7.7 μm. <Solvent> • Diethylene glycol monobutyl ether, boiling point 231°C <Stretchable film substrate> We used the TG88-I 70 / 50 manufactured by Takeda Sangyo Co., Ltd. [Dispersion conditions] d1: Awatori Rentaro Atmospheric Pressure Type ARE-310, stirring at 2000 rpm for 1 min, defoaming at 2200 rpm for 0.5 min d2: Awatori Rentaro Atmospheric Pressure Type ARE-310, stirring at 2000 rpm for 15 min, defoaming at 2200 rpm for 1.5 min d3: Awatori Rentaro Atmospheric Pressure Type ARE-310, after 3 mins of pre-mixing at 2000 rpm, using an Imex small 3-roll roller, 1 Pass d4: Awatori Rentaro Atmospheric Pressure Type ARE-310, after 3 minutes of pre-mixing at 2000 rpm, then AIMEX small 3-roll 3-pass mixer. d5: Awatori Rentaro Atmospheric Pressure Type ARE-310, after 3 mins of pre-mixing at 2000 rpm, using an Imex small 3-roll 6-pass mixer. d6: PRIMIX TK Hibiscus Mix 2P-03 / 1 type Rotation 121 rpm, Revolution 50 rpm, 30 min

[0129] [Example 1: Conductive composition (C1)] A conductive paste was obtained by mixing 2.25 parts of a solution of resin (a2) with a solid content of 30%, 2.295 parts of conductive filler (b1), and 0.405 parts of conductive filler (b3) using the dispersion method d2 described above.

[0130] [Examples 2-8 and Comparative Examples 1-6: Conductive compositions (C2-C8, c1-c6)] A laminate was obtained in the same manner as in Example 1, except that the conductive paste formulation and dispersion method were changed as shown in Table 1.

[0131] <Manufacturing of stretchable conductive materials> Next, the conductive compositions (C1) to (C8) and (c1) to (c6) prepared in Examples 1 to 8 and Comparative Examples 1 to 6 were printed and dried on the above substrate under the printing conditions shown below to obtain stretchable conductive materials having conductive layers with a rectangular solid pattern of 20 mm width, 60 mm length, and 10 μm thickness, and linear patterns of 3 mm line width, 60 mm length, and 10 μm thickness.

[0132] [Printing conditions] ·Printing machine: SERIA SSA-PC250-IPP-L-08t12 • Plate: 23μm wire diameter stainless steel 400 mesh, aperture ratio 41%, frame size 550×650mm, emulsion thickness 10μm • Squeegee: Hardness 80°, Angle 75°, Printing pressure 15kgf, Pressing depth 1.5mm, Speed ​​100mm / sec • Scraper: Angle 90°, Printing pressure 8kgf, Pressing depth 0.5mm, Speed ​​100mm / sec • Clearance: 2.5mm Drying conditions: Hot air drying oven, 80°C, 30 minutes

[0133] [Particle size measurement conditions] For conductive compositions before and after passing through a 400-mesh screen mesh with a wire diameter of 23 μm and an aperture ratio of 41%, the particle size distribution of conductive fine particles (B) was measured using the laser diffraction scattering particle size distribution method. The specific measurement conditions are as follows. Furthermore, the conductive composition after passing through the screen mesh was measured by promptly scraping it off the printed pattern using a spatula or the like after printing with the screen mesh. Equipment: Nikkiso Co., Ltd. Microtrac MT3000II Measurement solvent: Propylene glycol monomethyl ether acetate SetZero time: 20 Measurement time: 60 Transparency: Transparent Particle refractive index: 1.33 Shape: Non-spherical Solvent refractive index: 1.40 After moderately stirring the conductive composition with a spatula or similar tool to prevent the secondary particles of silver powder from disintegrating, the concentration index DV value was quickly adjusted to a range of 0.015-0.020 and the transmittance TR to a range of 0.90-0.95. After confirming that the particle size distribution shape was stable after two scans, the particle size distribution was measured and the particle size distribution curve was obtained. The values ​​calculated as the particle diameters at the 10% and 95% cumulative percentages of the particle size distribution curve were defined as the r10, r95, and R95 particle diameters, respectively. Furthermore, the maximum frequency (%) in the particle size distribution curve read from the data analysis view was defined as ftop, and the particle size (μm) at that point was defined as rtop.

[0134] <Rating> (Volume resistivity) The volume resistivity of the stretchable conductive materials according to each example and comparative example was measured. Specifically, a rectangular, solid stretchable conductive material with a width of 20 mm, a length of 60 mm, and a thickness of 10 μm, prepared in the above examples and comparative examples, was used as a test specimen. A surface resistance meter (model number: Loresta® AP MCP-T400, probe: ASP probe (4-probe probe, manufactured by Mitsubishi Chemical Corporation) was used to measure the volume resistivity of the test specimen obtained in accordance with JIS K7194 in an atmosphere at a temperature of 25°C and a relative humidity of 50%. The initial state was evaluated according to the following criteria. +++:2.0×10 -4 Less than Ω·cm ++:2.0×10 -4 Ω cm or more, 9.9×10 -3 Less than Ω·cm +:9.9×10 -3 Ω cm or more, 9.9×10 -1 Less than Ω·cm NG: 9.9×10 -1 Ω cm or more

[0135] (Repeated stretching resistance) For each example and comparative example, a 20mm x 60mm sample of the stretchable conductive material was fixed to a Tensilon tensile testing apparatus. The sample was stretched to 50% at 25°C, 50% relative humidity, and a speed of 4mm / s, then held for 2 seconds, and then unloaded at a speed of 4mm / s. This stretching / unstretching cycle was repeated 1,000 times, and the rate of change after 1,000 cycles was calculated using the following formula. [Percentage change (%)] =[(R1,000)-(R0)]÷[(R0)]×100 Here, R1,000 represents the resistance value immediately after 1,000 stretch cycles, and R0 represents the resistance value using the same film before the start of measurement. The following criteria were used for evaluation. +++: Change rate is 20% or less ++: Rate of change is greater than 20% and less than or equal to 50%. +: Rate of change is greater than 50% and less than or equal to 100%. NG: The rate of change exceeds 100%

[0136] (Adhesion to substrate) For each example and comparative example, a rectangular solid conductive layer measuring 20 mm in width and 60 mm in length was formed on the stretchable conductive material. Using a Gardner 1 mm spaced cross-cut guide, a utility knife was used to make 10 x 10 grid-like cuts that penetrated the conductive layer. Cellophane tape manufactured by Nichiban was then applied, and after removing any trapped air and ensuring good adhesion, the tape was peeled off vertically. The degree of peeling of the coating was evaluated according to the ASTM-D3519 standard based on the following criteria. +++: Rating 5B-4B, and good adhesion. ++: Although the evaluation is 5B to 4B, a portion of the surface of the coating film undergoes cohesive failure. +: Rating 3B, a portion of the coating peels off at the interface along the cut line. NG: Rating 2B or lower, poor adhesion.

[0137] [Table 1]

[0138] The results from Examples 1 to 8 of the present invention show that, even when a printed material is produced by dispersing and coating a conductive composition and forming a printed material, the present invention effectively suppresses the occurrence of cracks and the disconnection of conductive paths during expansion and contraction, thereby obtaining a conductive composition and a stretchable conductive material with excellent conductivity, resistance to repeated expansion and contraction, and adhesion. Due to these properties, these materials are suitable for use in electronic device applications.

Claims

1. A conductive composition comprising an elastomer (A) and conductive fine particles (B), After passing conductive fine particles (B) through a 400-mesh screen mask with a wire diameter of 23 μm and an aperture ratio of 41% under the following printing conditions, the volume-based particle size distribution curve measured by laser diffraction scattering was such that the peak-top particle size (rtop) was between 2.0 μm and 20.0 μm. A conductive composition having a peak top frequency (ftop) of 1.5% or more and 9.0% or less. [Printing conditions] ・Printing machine: SERIA SSA-PC250-IPP-L-08t12 • Plate: 23 μm diameter stainless steel 400 mesh, aperture ratio 41%, frame size 550 x 650 mm, emulsion thickness 10 μm Squeegee: Hardness 80°, Angle 75°, Printing pressure 15kgf, Pressing depth 1.5mm, Speed ​​100mm / sec Scraper: Angle 90°, Printing pressure 8kgf, Pressing depth 0.5mm, Speed ​​100mm / sec • Clearance: 2.5 mm Drying conditions: Hot air drying oven, 80°C, 30 minutes

2. When a screen mask with a 400 mesh, wire diameter of 23 μm, and aperture ratio of 41% was passed through under the following printing conditions, the cumulative 95% particle size (r95) in the volume-based particle size distribution curve measured by the laser diffraction scattering particle size distribution method for conductive fine particles (B) was 10.0 μm or larger. The conductive composition according to claim 1, wherein the cumulative 10% particle size (r10) is 0.1 μm or more and 5.0 μm or less. [Printing conditions] ・Printing machine: SERIA SSA-PC250-IPP-L-08t12 • Plate: 23 μm diameter stainless steel 400 mesh, aperture ratio 41%, frame size 550 x 650 mm, emulsion thickness 10 μm Squeegee: Hardness 80°, Angle 75°, Printing pressure 15kgf, Pressing depth 1.5mm, Speed ​​100mm / sec Scraper: Angle 90°, Printing pressure 8kgf, Pressing depth 0.5mm, Speed ​​100mm / sec • Clearance: 2.5 mm Drying conditions: Hot air drying oven, 80°C, 30 minutes

3. The conductive composition according to claim 1 or 2, wherein when a screen mask with a mesh size of 400, a wire diameter of 23 μm, and an aperture ratio of 41% is passed through the screen mask under the following printing conditions, the particle size ratio before and after passing through the screen mask (cumulative 95% particle size (R95) in the volume-based particle size distribution curve measured by laser diffraction scattering particle size distribution measurement method for conductive fine particles (B) before passing through / cumulative 95% particle size (r95) in the volume-based particle size distribution curve measured by laser diffraction scattering particle size distribution measurement method for conductive fine particles (B) after passing through is 5.0 or less. [Printing conditions] ・Printing machine: SERIA SSA-PC250-IPP-L-08t12 • Plate: 23 μm diameter stainless steel 400 mesh, aperture ratio 41%, frame size 550 x 650 mm, emulsion thickness 10 μm Squeegee: Hardness 80°, Angle 75°, Printing pressure 15kgf, Pressing depth 1.5mm, Speed ​​100mm / sec Scraper: Angle 90°, Printing pressure 8kgf, Pressing depth 0.5mm, Speed ​​100mm / sec • Clearance: 2.5 mm Drying conditions: Hot air drying oven, 80°C, 30 minutes

4. A conductor containing the conductive composition described in claim 1 or 2.

5. A stretchable conductive material comprising a cured product of the conductive composition according to claim 1 or 2 on an expandable substrate.

6. An electronic device comprising the conductor described in claim 4.

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