JP7768074B2 - Conductive composition, conductor, stretchable conductive material, and electronic device - Google Patents

Description

The present invention relates to a conductive composition, a conductor, a stretchable conductive material, and an electronic device.

Conductive materials are used in a variety of industrial fields, and various 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 their use in actuators and wearable sensors.
Patent Document 1 discloses a low-cost, highly durable, stretchable conductive coating, and discloses that by using silver-coated particles that have not been surface-treated and further combining them with specific additives, high conductivity can be obtained when the coating is stretched.
Patent Document 2 discloses a conductive composition that can provide a conductor with significantly improved stretchability by combining a block copolymer with a specific silver powder.

International Publication No. 2018/159374 International Publication No. 2017/026130

With advances in fields such as healthcare devices like biosensors, wearable devices, and robotics, conductive materials are now required to not only have the conductivity that has traditionally been required, but also to have the flexibility to conform to curved or moving surfaces during processing and use.

Furthermore, when conductive materials are used in curved or movable parts, repeated expansion and contraction can cause structural damage to the resin, leading to the problem of cracks occurring in the resin. In particular, conductive fine particles are often added to conductive materials, and when the resin is expanded or contracted, the conductive material peels off from the resin, creating voids in the resin, which can easily become the starting point for cracks. This results in a decrease in conductivity with each expansion and contraction.
Furthermore, to form a stretchable conductive material, a conductive composition such as a paste is applied to a stretchable substrate to form a printed pattern. However, depending on the conductive composition used, aggregates may form, resulting in a decrease in (continuous) printability on various stretchable film substrates. Furthermore, the affinity (compatibility) between various stretchable film substrates and conductive compositions such as a paste is poor, and the substrate adhesion, particularly with silicone substrates and olefin substrates, is insufficient, preventing the conductive composition from exhibiting its inherent material properties.

The present invention has been made in light of the above background, and aims to provide a conductive composition, conductor, stretchable conductive material, and electronic device that has excellent resistance to repeated stretching, conductivity, moist heat resistance, substrate adhesion to stretchable film substrates such as silicone substrates, and continuous printability.

After extensive research, the inventors discovered that the problems of the present invention could be solved in the following manner, leading to the completion of the present invention.

That is, the present invention relates to a conductive composition comprising a silicone resin (A) and conductive fine particles (F), wherein the conductive fine particles (F) comprise chain-like silver powder (f1) having a tap density of 2.5 g/cm3 or ^less .

The present invention also relates to the above-mentioned conductive composition, in which the content of the conductive fine particles (F) is 60 to 95 mass% based on the total solid content of the conductive composition.

The present invention also relates to the above-mentioned conductive composition, in which the content of the chain-like silver powder (f1) is 20 to 69 mass% based on the total solid content of the conductive composition.

The present invention also relates to the above-mentioned conductive composition, wherein the conductive fine particles (F) contain flaky silver powder (f2).

The present invention also relates to the above-mentioned conductive composition, in which the silicone resin (A) includes an addition-curable silicone resin (a1).

The present invention also relates to the above-mentioned conductive composition, in which the silicone resin (A) contains a (meth)acrylic block copolymer (a2) having a siloxane bond.

The present invention also relates to the above-mentioned conductive composition, in which the (meth)acrylic block copolymer (a2) having a siloxane bond has structural units derived from an acrylic monomer having a siloxane bond.

The present invention also relates to the above-mentioned conductive composition, which further contains a (meth)acrylic block copolymer (B) that does not have a siloxane bond.

The present invention also relates to a conductor containing the above-mentioned conductive composition.

The present invention also relates to a conductor having a cured product of the above-mentioned conductive composition on a stretchable substrate.

The present invention also relates to the above-mentioned conductor, wherein the stretchable substrate is a silicone substrate.

The present invention also relates to a stretchable conductive material comprising the above-mentioned conductor.

The present invention also relates to an electronic device equipped with the above-mentioned stretchable conductive material.

The present invention has the excellent effect of providing a conductive composition, conductor, stretchable conductive material, and electronic device that has excellent resistance to repeated stretching, conductivity, moist heat resistance, substrate adhesion to stretchable film substrates such as silicone substrates, and continuous printability.

The conductive composition, conductor, stretchable conductive material, and electronic device according to the present invention will be described in detail below.
In the present invention, the term "cured product" includes not only products cured by chemical reaction but also products cured by methods other than chemical reaction, such as evaporation of a solvent.

<Conductive composition>
The conductive composition of the present invention is a conductive composition comprising a silicone resin (A) and conductive fine particles (F), wherein the conductive fine particles (F) comprise chain-like silver powder (f1) having a tap density of 2.5 g/cm3 or ^less .

<Silicone Resin (A)>
The conductive composition of the present invention contains a binder silicone resin (A) to impart film-forming properties and adhesion and printability to stretchable substrate films such as silicone substrates. Furthermore, in the present invention, the inclusion of the silicone resin (A) can impart flexibility and stretchability to the conductive layer, particularly adhesion to silicone substrates and printability. Therefore, breakage of the conductive layer during stretching or shrinkage is suppressed. Furthermore, adhesion to stretchable films such as stretchable silicone substrates and continuous printability are improved.

The content of silicone resin (A) is preferably 8 to 40% by mass relative to the total solid content in the conductive composition. It is more preferably 10 to 38% by mass, and even more preferably 15 to 35% by mass. By having the content of silicone resin (A) within this range, sufficient flexibility is imparted to the conductive layer, effectively suppressing the occurrence of cracks in the conductive layer when stretched, and the inclusion of a sufficient amount of conductive fine particles (F) enables the production of a conductive layer with excellent conductivity.

The silicone resin (A) may be used alone or in combination of two or more types.

Examples of the silicone resin (A) 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 have organopolysiloxane as their main component (base polymer), but the curing method is not particularly limited, and examples include conventionally known condensation curing, addition curing, organic peroxide curing, and radiation curing. In the conductive composition of the present invention, addition curing silicone resin (a1) is particularly preferred, as it results in less shrinkage after curing and improves elastic conductivity.

(Addition-curable silicone resin (a1))
The addition-curable silicone resin (a1) is a silicone resin produced by reacting a polysiloxane resin component having at least two unsaturated groups per molecule with a polysiloxane resin component having at least two hydrosilyl groups per molecule, where the hydrosilyl group is a functional group in which a hydrogen atom is directly bonded to a silicon atom.

Examples of addition-curable silicone resins (a1) include KE-1820, KE-1823, KE-1800T-A/B, KE-1031-A/B, KE103, KE-1051J-A/B, KE-1012-A/B, KE106, KE-1282-A/B, and KE-1283-A/B manufactured by Shin-Etsu Chemical Co., Ltd.; SILPOT184 manufactured by DuPont-Toray Specialty Materials Co., Ltd.; and YSR-3022, TPR-6700, TPR-6720, and TPR-6721 manufactured by Toshiba Silicones Co., Ltd.

(Condensation curing type silicone resin)
Condensation curing type silicone resins include, for example, KE-441, KE-471, and KE-47.

<(Meth)acrylic Block Copolymer (a2) Having Siloxane Bond>
A preferred embodiment of the silicone resin (A) is a (meth)acrylic block copolymer (a2) having a siloxane bond. The (meth)acrylic block copolymer (a2) having a siloxane bond can be synthesized using, for example, an initiator or monomer having a siloxane bond, and from the viewpoint of elasticity, it is preferable to synthesize the copolymer using an acrylic monomer having a siloxane bond.
In the present invention, (meth)acrylic is a general term for acrylic and methacrylic, and (meth)acrylate is a general term for acrylate and methacrylate.

Examples of acrylic monomers having siloxane bonds used in the polymerization of the (meth)acrylic block copolymer (a2) having siloxane bonds include reactive silicones (Silaplane) FM-0711, FM-0721, FM-0725, and TM-0701T manufactured by JNC Corporation. Furthermore, the acrylic monomers having siloxane bonds may be copolymerized with either or both of the soft and hard segments, but from the standpoint of elasticity, it is more preferable to copolymerize them only with the soft segments.

Furthermore, examples of initiators having a siloxane bond that can be used in the polymerization of the (meth)acrylic block copolymer (a2) having a siloxane bond include the polymeric azo initiators "VPS-1001" and "VPS-1001N" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

When the silicone resin (A) is a (meth)acrylic block copolymer (a2) having a siloxane bond, the content of structural units derived from an acrylic monomer having a siloxane bond in the block copolymer (a2) is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more. It may also be 100% by mass.

The (meth)acrylic block copolymer (a2) having a siloxane bond preferably contains a soft segment and a hard segment, as described below. The soft segment is a block component made of a flexible, highly flexible polymer chain, while the hard segment is a block component made of a polymer chain that is prone to crystallization or aggregation and is more rigid than the soft segment. It is more preferable that the (meth)acrylic block copolymer (a2) having a siloxane bond has a configuration in which a soft segment is sandwiched between hard segments (i.e., a "hard segment-soft segment-hard segment" triblock structure or a star-shaped block structure described below).

<(Meth)acrylic Block Copolymer (B) Having No Siloxane Bond>
The conductive composition of the present invention preferably further contains a (meth)acrylic block copolymer (B) having no siloxane bond.
The (meth)acrylic block copolymer (B) having no siloxane bond means a (meth)acrylic block copolymer that does not contain a siloxane bond in the polymer component. Specific examples thereof include triblock copolymers such as polymethyl(meth)acrylate/poly-n-butyl(meth)acrylate/polymethyl(meth)acrylate and polystyrene/poly-n-butyl(meth)acrylate/polystyrene.

The (meth)acrylic block copolymer (B) having no siloxane bonds preferably contains soft segments and hard segments, as described below. It is more preferable that the (meth)acrylic block copolymer (B) having no siloxane bonds has a configuration in which a soft segment is sandwiched between hard segments (i.e., a "hard segment-soft segment-hard segment" triblock structure or a star block structure described below).

The (meth)acrylic block copolymer (B) without siloxane bonds may be a commercially available product. An example of a commercially available product is an acrylic triblock copolymer manufactured by Arkema using living polymerization. Specifically, SBM types such as polystyrene-polybutadiene-polymethyl methacrylate, MAM types such as polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate, and MAMN or MAMA types that have been modified with a carboxylic acid or hydrophilic group can be used. Another example of a commercially available product is a block copolymer derived from methyl methacrylate and butyl acrylate manufactured by Kuraray Co., Ltd.

From the viewpoint of forming a conductive layer that exhibits excellent adhesion to the substrate and excellent conductivity, the content of the (meth)acrylic block copolymer (B) that does not have a siloxane bond is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, of the total resin components.

The (meth)acrylic block copolymer (B) not having a siloxane bond may be used alone or in combination of two or more types.

<Block copolymer containing soft segments and hard segments>
Hereinafter, a block copolymer containing a soft segment and a hard segment, which is a preferred embodiment of the (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) not having a siloxane bond, will be described in detail.
Examples of the block copolymer containing a soft segment and a hard segment include a block copolymer represented by the following formula (1).
Polymer block A - polymer block B (1)
In formula (1), polymer block A is a block (hard segment) having a glass transition temperature Tg of 20°C or higher, and polymer block B is a block (soft segment) having a glass transition temperature Tg of less than 200°C. By using the block copolymer represented by formula (1), the cured product of the conductive composition according to this embodiment exhibits toughness. The glass transition temperature Tg can be measured using differential scanning calorimetry (DSC).
In this specification, formula (1) may be abbreviated as "AB".

An example of a block copolymer with a triblock structure is a block copolymer represented by the following formula (2):

Polymer block A - polymer block B - polymer block A (2)
In formula (2), the polymer block A and the polymer block B can be defined in the same manner as in formula (1).
In this specification, formula (2) may be abbreviated as "ABA."

Polymer block A is preferably a block having a Tg of 50°C or higher, and polymer block B is preferably a block having a Tg of -20°C or lower.

In the block copolymers represented by formula (1) and formula (2), it is preferred that the polymer block B having a lower glass transition temperature Tg corresponds to the soft segment, and the polymer block A having a higher glass transition temperature Tg corresponds to the hard segment.
Comparing formula (1) and formula (2), it is preferable to use the block copolymer of formula (2) from the viewpoint of tensile elongation at break.

Furthermore, it is preferable that the block copolymer is solid at least in the range of 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.

Furthermore, the mass ratio of polymer block A to polymer block B is preferably in the range of 15:85 to 40:60. When the mass ratio of polymer block A to polymer block B is within this range, the polymer conforms to the substrate when stretched, making breakage less likely to occur. A ratio of 20:80 to 35:75 is more preferable.

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. Note that in this application, (meth)acrylate is a general term that refers to acrylate and methacrylate, and the same applies to other similar expressions.

Furthermore, the (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) not having a siloxane bond may have a star block structure represented by the following formula (3) in addition to the block structures represented by the above-mentioned formulas (1) and (2).

[Polymer block A-polymer block B]qX (3)
In formula (3), q is an integer of 2 or more and 6 or less. For polymer block A and polymer block B, the description of formula (1) can be applied.
The term "star block structure" refers to a structure of [polymer block A-polymer block B]qX in which a plurality of (2 to 6) diblock units of polymer block A-polymer block B are bonded together starting from X (X is bonded to polymer block B). X is a residue of an initiator and/or a residue of a coupling agent, or a derivative thereof.
In this specification, formula (3) may be abbreviated as "[AB]qX".

Furthermore, "initiator residue" refers to a partial structure derived from an initiator, meaning a residue derived from the initiator in the block copolymer. Furthermore, "coupling agent residue" refers to a partial structure derived from a coupling agent, meaning a residue derived from the coupling agent in the block copolymer. Furthermore, "derivative thereof" refers to a structure in which a portion of the initiator residue and/or coupling agent residue has been chemically converted. For example, this includes a structure in which a portion of the initiator residue and/or coupling agent residue has been substituted or added during the synthesis of the block copolymer.

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 as long as it does not deviate from the spirit of the present invention. For example, it can be approximately 50 to 2,500. The molecular weight of the initiator residue or its derivative, which may optionally be present at the chain end of polymer block A, is likewise not particularly limited as long as it does not deviate from the spirit of the present invention, and can be, for example, approximately 50 to 2,500.

In this specification, the Tg of polymer block A refers to the Tg of <polymer block A> Total observed in the curve obtained by differential scanning calorimetry (DSC) measurement of the block copolymer obtained, and is the value obtained by measurement in accordance with JIS K7121:2012, Method for Determining Transition Temperature of Plastics, using the extrapolated glass transition onset temperature (Tig) described in JIS 9.3. The Tg derived from <polymer block A> Total is the same as or close to the Tg of a non-block polymer having a similar chemical structure, and therefore can be easily distinguished from the Tg of polymer block B in the case of a diblock or triblock structure, or from the Tg of [polymer block B]qX in the case of a star block structure. The above Tg of <Polymer Block A> Total and the Tg of each polymer block A do not vary significantly depending on the chain end of the block copolymer, i.e., the structure of the chain end of polymer block A. Therefore, in this specification, the Tg of each polymer block A and the Tg of <Polymer Block A> Total will be determined including the chain end of polymer block (A).

However, when multiple Tg's are observed in the curve obtained by DSC measurement, for example, when the structural units derived from the monomers of each polymer block A are different for each block, the Tg of each polymer block A is used for judgment instead of the Tg of <polymer block A> total. In such cases, the Tg is determined by sampling at the time when the polymerization of each polymer block A is completed. Alternatively, since there is a correlation with the Tg of a polymer having the same chemical structure as each polymer block (A), the Tg of each corresponding polymer may be calculated using the Fox equation, and judgment may be made based on whether the Tg is 20°C or higher. The Fox equation is a value calculated from the following equation (4):
1/(TgA+273.15)=Σ[Wa/(Tga+273.15)] (4)
In formula (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 a homopolymer of monomer a. Note that Tga is widely known as a characteristic value of homopolymers, and for example, the value described in "POLYMER HANDBOOK, THIRDEDITION" or the value in a manufacturer's catalog can be used.

In this specification, the Tg of polymer block B refers to the Tg of polymer block B itself when the block copolymer has a diblock structure or a triblock structure, and refers to the Tg of [polymer block B]qX when the block copolymer has a star block structure. Here, polymer block B of a diblock structure or a triblock structure and [polymer block B]qX of a star block structure are collectively referred to as <polymer block B[X]>.
The Tg of the <polymer block B[X]> is the Tg of the <polymer block B[X]> observed in a curve obtained by DSC measurement of the obtained block copolymer, and is measured in accordance with JIS K7121:2012, Measurement of Transition Temperature of Plastics, and is the value obtained from the extrapolated glass transition onset temperature (Tig) described in JIS 9.3. The Tg of the <polymer block B[X]> is the same as or close to the Tg of a polymer having a similar chemical structure, and therefore can be easily distinguished from the Tg derived from the polymer block A.

The (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) not having a siloxane bond preferably have a block structure of an A-B diblock structure, an A-B-A triblock structure, or an [A-B]qX star block structure, and the chain end of the polymer block A may contain an initiator residue or a derivative thereof, a functional group, an inactive group, a crosslinkable group, a substituent, or the like.

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 described above, the Tg of polymer block A can be interpreted as the Tg of <polymer block A> Total (this applies hereinafter as well). That is, <polymer block A> Total 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, the upper limit of <polymer block A> Total is not particularly limited, but can be, for example, 300°C, 250°C, or 200°C.

The Tg of polymer block B in the case of a diblock structure or triblock structure, and the Tg of [polymer block B]qX in the case of a star block structure, i.e., the Tg of <polymer block B[X]>, is less than 0.20°C, preferably -10°C or less, and particularly preferably -20°C or less. 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.

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 particularly preferably 150°C or higher. A temperature of 75°C or higher promotes the formation of a microphase-separated structure, and the effects of physical crosslinking can be more effectively achieved.

The weight-average molecular weight (Mw) in the present invention is a value determined by the method described in the Examples below. The Mw of the (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) not having a siloxane bond is preferably 20,000 or more and 500,000 or less. By setting the Mw within this range, when the block copolymer is used as a conductive composition, both tensile strength and conductive stability can be achieved. The preferred range of Mw is 25,000 to 400,000, and more preferably 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 a microphase-separated structure that affects tensile strength, a polydispersity of 1 to 1.5 or 1 to 1.3 is particularly preferred.

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

The structural units derived from the monomers of each polymer block A may be composed of structural units derived from different monomers for each block, or may be composed of structural units derived from the same monomer across the blocks. Preferably, 60% by mass or more of the structural units derived from the monomers of the polymer blocks A are common to each other, more preferably 70% by mass or more, and even more preferably 80% by mass or more. Similarly, each polymer block B may be composed of structural units derived from different monomers for each block, or may be composed of structural units derived from the same monomer across the blocks. Preferably, 60% by mass or more of the structural units derived from the monomers of the polymer blocks B are common to each other, more preferably 70% by mass or more, and even more preferably 80% by mass or more. Here, "common" means that the components are common, regardless of the monomer sequence.

From the viewpoint of more effectively enhancing the stretchability and stretchable conductivity, which are the properties of a stretchable conductive material, the bonding structure of the (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) not having a siloxane bond is preferably an A-B-A triblock structure, a bibranched structure where q = 2 in [A-B]qX, or a tribranched structure where q = 3. Polymer block A and polymer block B each independently have structural units derived from one type of monomer or two or more types of monomers.

Preferred examples of the (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) not having a siloxane bond include block copolymers in which polymer block A contains 50% by mass or more of structural units derived from a methacrylic acid ester and polymer block B contains 70% by mass or more of structural units derived from an acrylic acid ester. The structural units derived from a methacrylic acid ester in polymer block A are more preferably 60% by mass or more, even more preferably 70% by mass or more, 80% by mass or more, or 90% by mass or more. The structural units derived from a methacrylic acid ester may also be taken as 100% by mass.

Furthermore, the structural units derived from acrylic acid ester in polymer block B are more preferably 80% by mass or more, even more preferably 85% by mass or more, 90% by mass or more, or 95% by mass or more. Furthermore, the structural units derived from acrylic acid ester may be 100% by mass. When 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 polymer can exhibit more excellent stretchability and stable stretchable conductivity.

Examples of monomers forming the methacrylate ester-derived structural units of polymer block A include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, normal butyl methacrylate, isobutyl methacrylate, tertiary butyl methacrylate, isoamyl methacrylate, pentyl methacrylate, normal hexyl methacrylate, isohexyl methacrylate, isoheptyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, normal octyl methacrylate, isononyl methacrylate, isodecyl methacrylate, and lauryl methacrylate. Examples of the alkyl methacrylate include aliphatic, alicyclic, and aromatic alkyl methacrylates such as benzotriazole, tetradecyl methacrylate, octadecyl methacrylate, behenyl methacrylate, isostearyl methacrylate, cyclohexyl methacrylate, t-butylcyclohexylmethyl methacrylate, isobornyl methacrylate, trimethylcyclohexyl methacrylate, cyclodecyl methacrylate, cyclodecylmethyl methacrylate, benzyl methacrylate, t-butylbenzotriazole phenylethyl methacrylate, phenyl methacrylate, naphthyl methacrylate, and allyl methacrylate.
Other examples that can be used include hydroxyalkyl methacrylates in which the hydroxyalkyl group has 2 to 4 carbon atoms, such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate, and hydroxyl group-containing methacrylic acid monomers such as glycerin acrylate and glycerin methacrylate; alkoxyalkyl methacrylates such as alkoxyalkyl methacrylates in which the alkoxy group has 1 to 4 carbon atoms and the alkyl group has 1 to 4 carbon atoms, such as methoxymethyl methacrylate, methoxyethyl methacrylate, methoxypropyl methacrylate, ethoxymethyl methacrylate, ethoxyethyl methacrylate, and ethoxypropyl methacrylate; (polyalkylene)glycol monoalkyl, alkylene, alkyne ether or ester monomethacrylates; methacrylic acid monomers having an acid group (carboxy group, sulfonic acid, phosphoric acid) including acrylic acid and acrylic acid dimer; oxygen atom-containing methacrylic acid monomers; amino group-containing methacrylic acid monomers; and nitrogen atom-containing methacrylic acid monomers. Other examples include monomethacrylates having three or more hydroxyl groups, halogen-containing methacrylates, silicon-containing methacrylic acid monomers, methacrylic acid monomers having a group that absorbs ultraviolet light, and acrylates with a methyl-substituted hydroxyl group at the α-position.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.

As the monomer forming the structural unit of polymer block A other than that derived from methacrylic acid ester, other monomers that can be polymerized with methacrylic acid ester can be used. Specific examples include styrene and acrylonitrile.

A suitable example of polymer block A is one containing 50% by mass or more of structural units derived from methyl methacrylate. More preferably, the structural units derived from methyl methacrylate account for 60% by mass or more, and even more preferably 80% by mass or more. Furthermore, 100% by mass of polymer block A may be structural units derived from methyl methacrylate.

Examples of monomers forming the acrylate ester-derived structural units of polymer block B include methyl acrylate, ethyl acrylate, propyl methacrylate, isopropyl methacrylate, normal butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, isoamyl acrylate, pentyl acrylate, normal hexyl acrylate, isohexyl acrylate, isoheptyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, normal octyl acrylate, isononyl acrylate, isodecyl acrylate, and lauryl acrylate. Examples of the alkyl acrylate include aliphatic, alicyclic, and aromatic alkyl acrylates such as methyl acrylate, tetradecyl acrylate, octadecyl acrylate, behenyl acrylate, isostearyl acrylate, cyclohexyl acrylate, t-butylcyclohexylmethyl acrylate, isobornyl acrylate, trimethylcyclohexyl acrylate, cyclodecyl acrylate, cyclodecylmethyl acrylate, benzyl acrylate, t-butylbenzotriazole phenylethyl acrylate, phenyl acrylate, naphthyl acrylate, and allyl acrylate.
Other examples that can be used include acrylic acid monomers containing hydroxyl groups, acrylic acid monomers containing glycol groups, (polyalkylene) glycol monoalkyl, alkylene, alkyne ether or ester monoacrylates, acrylic acid monomers containing acid groups (carboxyl, sulfonic acid, phosphoric acid) including acrylic acid and acrylic acid dimers, oxygen atom-containing acrylic acid monomers, amino group-containing acrylic acid monomers, and nitrogen atom-containing acrylic acid monomers. Other examples include monoacrylates having three or more hydroxyl groups, halogen atom-containing acrylates, silicon atom-containing acrylic acid monomers, acrylic acid monomers having a group that absorbs ultraviolet light, and acrylates with methyl-substituted hydroxyl groups at the α-position. Also usable are 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.

As structural units of polymer block B other than those derived from acrylic acid esters, other monomers polymerizable with acrylic acid esters can be used. Examples include maleic acid, itaconic acid, and crotonic acid.

A suitable example of polymer block B is one containing 70% by mass or more of structural units derived from butyl acrylate. More preferably, the structural units derived from butyl acrylate account for 80% by mass or more, and even more preferably 90% by mass or more. Furthermore, 100% by mass of polymer block B may be structural units derived from butyl acrylate.

Preferred examples of the (meth)acrylic block copolymer (a2) having siloxane bonds and the (meth)acrylic block copolymer (B) not having siloxane bonds include an embodiment 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 for the (meth)acrylic block copolymer (a2) having siloxane bonds and/or the (meth)acrylic block copolymer (B) not having siloxane bonds can provide an excellent stretchable conductive material. The 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 even 100% by mass or more. The structural units derived from butyl acrylate in polymer block B may be 80% by mass or more, 90% by mass or more, or even 100% by mass.

By using a (meth)acrylic block copolymer (a2) having a siloxane bond and/or a (meth)acrylic block copolymer (B) not having a siloxane bond, polymer block A and polymer block B can form a molecular-level phase-separated structure (microphase-separated structure) such as a sea-island structure (body-centered cubic), a cylindrical (hexagonal), a gyroid, or a lamellar phase. Forming a microphase-separated structure can provide a conductive composition that imparts excellent stretchability and effectively suppresses cracking (disconnection) associated with stretching. From the perspective of more effectively enhancing stretchability, a sea-island structure in which polymer block A corresponds to the islands and polymer block B corresponds to the sea is more preferred. The microphase-separated structure can be confirmed by observation using an atomic force microscope (AFM).

In the (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) not having a siloxane bond, the content of polymer block A relative to the total amount of polymer block A and polymer block B is not particularly limited, but from the viewpoint of easily obtaining a microphase-separated structure with a sea-island structure, it is preferably 1 to 50 mass% and more preferably 15 to 30 mass%. Furthermore, from the viewpoint of effectively obtaining adhesiveness, the content of the entire polymer block A relative to the total amount of polymer block A and polymer block B is preferably 1 to 35 mass% and more preferably 5 to 30 mass%. The total content 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-separated structure, it is preferably 90.0 to 99.9 mass% and more preferably 98.0 to 99.9 mass%.

In order to maintain good conductivity, it is preferable that 90% by mass or more of the ethylenically unsaturated monomers in the (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) not having a siloxane bond be hydrophobic ethylenically unsaturated monomers. Here, "hydrophobic ethylenically unsaturated monomer" refers to a monomer having a solubility in water at 20°C of 6.5 g/100 mL or less. Examples of hydrophobic ethylenically unsaturated monomers include the above-mentioned alkyl (meth)acrylates, olefins such as butadiene and isoprene, vinyls such as vinyl acetate and vinyl chloride, and aromatics such as styrene.

[Functional group]
The (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) not having a siloxane bond may each have a functional group, such as a mercapto group, a hydroxy group, an amino group, a carboxy group, a glycidyl group, a (meth)acrylic group, a hydrolyzable silyl group, a nitrile group, or an isocyanate group.

[Reactive Functional Group]
The (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) not having a siloxane bond preferably have one or more reactive functional groups selected from the group consisting of a mercapto group, a hydroxy group, an amino group, and a carboxy group, among the above functional groups.

[Method of producing block copolymer]
Hereinafter, an example of a method for producing the (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) having no siloxane bond of the present embodiment will be described, but the present invention is not limited thereto.

The (meth)acrylic block copolymer (a2) having a siloxane bond and the (meth)acrylic block copolymer (B) not having a siloxane bond can be produced by any method, but 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 using a coupling agent after obtaining a reactive terminal diblock structure.

Examples of anionic polymerization include a method of polymerization using an organic rare earth metal complex or an organic alkali metal compound as a polymerization initiator in the presence of an inorganic acid salt, and a method of polymerization using an organic alkali metal compound as a polymerization initiator in the presence of an organoaluminum compound.
Examples of living radical polymerization include polymerization using a nitroxide-based catalyst/NMP method, atom transfer radical polymerization/ATRP method using a transition metal complex-based catalyst, reversible addition-fragmentation chain transfer polymerization/RAFT method using a reversible addition-fragmentation chain transfer agent, polymerization using an organotellurium-based catalyst/TERP method, and iodine transfer polymerization using an iodine-based compound as a catalyst/RCMP method (reversible coordination-mediated polymerization) or RTCP method (reversible transfer catalyst polymerization).

Another method is a method for producing a block copolymer represented by [polymer block A-polymer block B]qX, which includes a step of sequentially polymerizing polymer block B and polymer block A in this order using a polymerization initiator having 2 to 6 polymerization initiation sites.

Another method is to produce a block copolymer with a polymer block A-polymer block B-polymer block A triblock structure, which includes a step of sequentially polymerizing polymer block A, polymer block B, and polymer block A in this order starting from a polymerization initiator.

In addition, there is a method for producing a block copolymer represented by [polymer block A-polymer block B]qX, which includes the steps of sequentially polymerizing polymer block B and polymer block A in any order to obtain an A-B type diblock structure, optionally introducing a reactive terminal into the molecular end of the A-B type diblock structure, and then carrying out a coupling reaction using any coupling agent having 3 to 6 linking units reactive with the reactive terminal.

<Other binder resins>
If necessary, other binder resins may be used in combination as resin components other than the silicone resin (A) and the (meth)acrylic block copolymer (B) having no siloxane bond. From the viewpoint of forming a conductive layer having excellent conductivity, the content of the resin components other than the silicone resin (A) and the (meth)acrylic block copolymer (B) having no siloxane bond is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10% by mass or less, of the total resin components.
The other binder resins may be used alone or in combination of two or more.

The total content of binder resins, including silicone resin (A), (meth)acrylic block copolymer (B) not having a siloxane bond, which is contained as needed, and other binder resins, is preferably 1 to 90 mass %, more preferably 5 to 60 mass %, and even more preferably 10 to 40 mass %, of the total solids content of the conductive composition.

<Conductive fine particles (F)>
The conductive fine particles (F) exhibit conductivity when multiple conductive fine particles come into contact with each other within the conductive layer. In the present invention, they are appropriately selected from those that can achieve conductivity 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. Examples of metal fine particles include powders of simple metals such as gold, silver, copper, nickel, chromium, palladium, rhodium, ruthenium, indium, aluminum, tungsten, molbutene, 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 gold-coated powders in which the surface of the simple metal powders or alloy powders is coated with silver or the like. Examples of carbon fine particles include carbon black, graphite, and carbon nanotubes. Examples of conductive oxide fine particles include silver oxide, indium oxide, tin oxide, zinc oxide, and ruthenium oxide.

In the present invention, it is preferable to contain 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 (F), a conductive layer with excellent conductivity can be formed without sintering.

The shape of the conductive fine particles (F) is not particularly limited, and amorphous, aggregated, scale-like, microcrystalline, spherical, flake-like, wire-like, etc. can be used as appropriate. From the viewpoint of maintaining conductivity during molding and adhesion of the conductive pattern to the substrate, aggregated, scale-like, flake-like, and wire-like shapes are preferred.

The average particle size of the conductive fine particles (F) is not particularly limited, but from the viewpoints of dispersibility in the conductive composition and conductivity when formed into a conductive layer, it is preferably 0.1 μm or more and 50 μm or less, and more preferably 0.5 μm or more and 30 μm or less.
In the present invention, the average particle size of the conductive fine particles (F) is calculated as follows. According to the laser diffraction/scattering method described in JIS M8511 (2014), a laser diffraction/scattering particle size distribution analyzer (Microtrac 9220FRA manufactured by Nikkiso Co., Ltd.) was used. An appropriate amount of conductive fine particles (F) was added to an aqueous solution containing 0.5% by volume of the commercially available surfactant polyoxyethylene octylphenyl ether (Triton X-100 manufactured by Roche Diagnostics K.K.) as a dispersant, and the solution was irradiated with 40 W ultrasonic waves for 180 seconds while stirring, after which measurement was performed. The determined median diameter (D50) was taken as the average particle size of the conductive fine particles (F).

In the present invention, the conductive fine particles (F) may be used alone or in combination of two or more types. The content of the conductive fine particles (F) in the conductive composition of the present invention is not particularly limited and may be adjusted appropriately depending on the application, etc., but is preferably 40 to 99 mass% and more preferably 60 to 95 mass% relative to the total solid content of the conductive composition. When the content of the conductive fine particles (F) is equal to or greater than the above-mentioned lower limit, a conductive layer with excellent conductivity can be formed. Furthermore, when the content of the conductive fine particles (F) is equal to or less than the above-mentioned upper limit, the content of the silicone resin (A) can be increased, improving film-forming properties and adhesion to stretchable films and imparting flexibility and stretchability to the conductive layer.

<Chained silver powder (f1)>
The conductive composition of the present invention contains, as the conductive fine particles (F), a chain-like silver powder (f1) having a tap density of 2.5 g/ ^cm3 or less. Here, the chain-like silver powder is a silver powder in which fine particles are aggregated to form aggregated particles, and specific examples include agglomerated silver powder and silver particles branched into branches, i.e., dendritic silver powder. Furthermore, the chain-like silver powder (f1) is preferably a chain-like silver powder in which fine particles of 1 μm or less are aggregated to form aggregated particles.

The tap density of the chain-like silver powder (f1) is more preferably 0.3 to 1.5 g/ ^cm3 , and even more preferably 0.3 to 1.0 g/ ^cm3 . Although the detailed mechanism is not clear, it is believed that a tap density of 2.5 g/ ^cm3 or less increases the volume of the silver powder, increasing the number of contact points and making electrical conduction easier. As a result, excellent resistance values can be obtained even when the conductor is subjected to strong expansion and contraction. Note that the tap density in this specification was measured in accordance with ISO 3953, and the number of taps during measurement was 1,000.

The specific surface area of the chain-like silver powder (f1) measured by the BET method is preferably 1.0 to 5.0 m ² /g.

The average particle size (D50) of the chain-like silver powder (f1) measured by a laser analysis scattering particle size distribution measurement method is preferably 3 to 15 μm.

The content of the chain-like silver powder (f1) is preferably 20 to 69 mass% and more preferably 30 to 65 mass% relative to the total solid content of the conductive composition. Within this range, both low resistance and conductive stability during stretching are achieved. In particular, when the content of the chain-like silver powder (f1) is 69 mass% or less relative to the total solid content of the conductive composition, a conductor with good printability (adhesion) to stretchable film substrates can be obtained. The above content is more preferably 50 to 69 mass%. By using the chain-like silver powder (f1) at the above content, the elasticity of the silicone resin (A) described above can be improved. Furthermore, the optimized self-organization (aggregation of segments) of the microphase separation structure is thought to further improve the affinity between the silicone resin (A) and the chain-like silver powder (f1), thereby improving the dispersibility of the conductive microparticles (F). This enables the creation of an ideal conductive path design that can withstand expansion and contraction (elastic deformation) and an ideal dispersion design for improved printability, making it possible to create a conductive composition that has excellent resistance to repeated expansion and contraction, substrate adhesion, and continuous printability.

The chain-like silver powder (f1) may be used alone or in combination of two or more types.

<Flake silver powder (f2)>
The conductive composition of the present invention preferably further contains flaky silver powder (f2) as the conductive fine particles (F).
By using the flake silver powder (f2) in combination with the chain-like silver powder (f1), it is possible to achieve both lower resistance and stable conductivity during stretching. In addition, it is possible to easily obtain a conductor that has better printability (adhesion) to a stretchable film substrate.

Here, flake silver powder refers to leaf-shaped silver powder whose thickness is independently one-tenth or less of the length in the longitudinal direction of the flat portion and the length in the transverse direction of the flat portion of a single silver powder. In the present invention, the length in the longitudinal direction of the flat portion and the length in the transverse direction of the flat portion of a single silver powder in flake silver powder (f2) is preferably independently in the range of 1 μm to 100 μm, and the thickness is more preferably in the range of 0.05 μm to 1 μm.

The 50% particle size (D50) of the flake silver powder (f2) measured by laser diffraction is preferably 1 μm to 20 μm, and more preferably 3 μm to 15 μm. A 50% particle size (D50) of 1 μm or more facilitates the development of good conductivity, while a 50% particle size (D50) of 20 μm or less prevents the conductive layer from becoming too thick, resulting in good flexibility when used as a stretchable conductive device. Furthermore, using flake silver powder whose 50% particle size (D50) is larger than the thickness of the conductive layer can further improve stretchable conductivity. Note that the 50% particle size (D50) in this specification is a value measured by laser diffraction using a particle size distribution analyzer (Shimadzu Corporation, "SALD-3100") and water as the solvent.

The bulk density of the flaky silver powder (f2) is preferably 0.2 to 0.7 g/ ^cm3 , and more preferably 0.4 to 0.6 g/ ^cm3 . With a bulk density in the above range, good electrical conductivity is likely to be exhibited. Note that the bulk density in the present invention is a value measured by a method in accordance with JIS-Z2504.

As described above, the flaky silver powder (f2) preferably has a 50% particle size (D50) of 1 μm to 20 μm and a bulk density of 0.2 g/cm ³ to 0.7 g/cm ^3. The flaky silver powder exhibits conductivity by overlapping in the conductive layer, and by having the above particle size and bulk density, the overlapping in the conductive layer is improved, and the flaky silver powder also has excellent flexibility when used in a stretchable electronic device.

The flake silver powder in the conductive layer does not necessarily have to be oriented, but orienting the flat parts of the flake silver powder roughly parallel to the coating surface increases the number of contact points between the flake silver powder particles, improving conductivity. On the other hand, if the flake silver powder is irregularly oriented, there will be fewer contact points between the flake silver powder particles, and a larger amount of flake silver powder will be required to achieve the desired conductive properties.

In the present invention, flaky silver powder refers to, for example, general flake, scale, and plate shapes.

The flaky silver powder preferably has a specific surface area of 0.3 to 4.0 m ² /g and a tap density of 1 to 4 g/cm ³ .

The flake silver powder may be used alone or in combination of two or more types. The content of the flake silver powder is preferably 0.5 to 85% by mass, and more preferably 1 to 75% by mass, of the total solid content contained in the conductive composition.

Furthermore, the conductive fine particles (F) may contain other conductive fine particles in addition to the chain-like silver powder (f1) and the flake-like silver powder (f2), as long as the effects of the present invention are not impaired. Examples of other conductive fine particles include silver-coated copper and carbon.

<Other ingredients>
The conductive composition of the present invention may further contain other components, such as a crosslinking agent, a dispersant, a friction resistance improver, an infrared absorber, an ultraviolet absorber, a fragrance, an antioxidant, an organic pigment, an inorganic pigment, an antifoaming agent, a silane coupling agent, a plasticizer, a flame retardant, and a moisturizing agent, as needed.

<Conductor and Conductive Layer>
By printing the conductive composition of the present invention onto a stretchable film by screen printing or the like, a conductor with excellent conductivity can be formed, and a stretchable conductive material having a conductive layer made of the conductor can be easily produced.

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, reverse offset printing, or microcontact printing, and it is more preferable to form it by screen printing.
In the screen printing method, it is preferable to use a fine mesh screen, particularly a fine mesh screen of about 300 to 650 mesh, in order to accommodate the need for high-definition conductive circuit patterns. In this case, the open area of the screen is preferably about 20 to 50%. The screen wire diameter is preferably about 10 to 70 μm.
Types of screens include polyester screens, combination screens, metal screens, nylon screens, etc. When printing highly viscous paste materials, high-tension stainless steel screens can be used.
The squeegee for screen printing may be round, rectangular, or square, and an abrasive squeegee may be used to reduce the attack angle (the angle between the plate and the squeegee during printing). Other printing conditions may be appropriately set based on conventionally known conditions.

The method for curing the conductive composition is not particularly limited. For example, the conductive composition of the present invention can be printed by screen printing, and then heated and dried to cure.
Furthermore, when the conductive composition contains a crosslinking agent, it is further heated to cause a crosslinking reaction and harden. When 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 sufficiently volatilize the solvent, and when the composition contains 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 sufficiently volatilize the solvent and cause the crosslinking reaction. This allows a patterned conductive layer to be obtained. If necessary, an insulating layer may be provided on the patterned conductive layer so as to cover the conductive pattern. The insulating layer is not particularly limited, and any known insulating layer may be used.

The film thickness of the conductive layer can be adjusted appropriately depending on the required conductivity, etc., and is not particularly limited. For example, it can be 0.5 μm or more and 20 μm or less, and preferably 1 μm or more and 15 μm or less.

<Stretchable conductive material>
Furthermore, this conductive composition suppresses the decrease in conductivity that occurs with repeated stretching, improves the printability of the conductor on a stretchable substrate, and makes it possible to produce a stretchable conductive material that has excellent adhesion between a conductive layer made of the conductor and the stretchable film substrate described below.
Furthermore, the stretchable conductive material produced using this conductive composition suppresses a decrease in conductivity even when used on the surface of a substrate that can conform to uneven curved surfaces or movable parts.

[Stretchable base material]
The stretchable film substrate used in the present invention is made from a natural or synthetic material that is resistant to breaking or cracking when stretched.
The stretchable film substrate preferably has 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 preferably has a tensile elongation at break of 150% or more at 23°C. The tensile elongation at break at 23°C is preferably 200% or more, and more preferably 400% or more. When the stretchable film substrate has a Young's modulus of less than 100 MPa and a tensile elongation at break of 150% or more at 23°C, breakage or cracking during stretching is unlikely to occur, and the stretchable film substrate can be used as a substrate suitable for stretchable conductive materials.

The stretchable film 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, chloroprene rubber, urethane rubber, butyl rubber, ethylene rubber, propylene rubber, ethylene propylene rubber, epoxy rubber, butadiene rubber, natural rubber, and isoprene rubber, and may also be a laminate film made of two or more of these materials. Furthermore, the shape of the film substrate may be flat, such as a plate or film, or may be curved or complex.

Examples of the thermoplastic elastomer 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.

Examples of such plastics include polyolefins such as polyvinyl alcohol, triacetyl cellulose, 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.

From the viewpoint of stretchability, polyurethane, silicone rubber, ethylene propylene rubber, styrene rubber, acrylic rubber, and epoxy rubber are particularly preferred as the stretchable film substrate, and silicone rubber is even more preferred from the viewpoint of adhesion to the conductive composition of the present invention.

The thickness of the stretchable film substrate is not particularly limited, but can be, for example, 1 to 500 μm. It may also be 10 to 100 μm or 20 to 50 μm. When the thickness of the stretchable film substrate is within the above range, the film is excellent in terms of windability and processability. On the other hand, if the stretchable film substrate is thin, it tends to lack strength. Furthermore, if the film substrate is too thick, it will have poor flexibility and may not be able to conform to the shape of the adherend.

If necessary, an anchor coat layer may be provided on the stretchable film substrate, and the conductive composition may be printed on the anchor coat layer, for purposes such as improving the printability of the conductive composition. The anchor coat layer is not particularly limited, as long as it has good adhesion to the film substrate and also to the conductive composition, and follows the stretchable film during molding. Organic fillers such as resin beads or inorganic fillers such as metal oxides may also be added as needed. The method for providing the anchor coat layer is not particularly limited, and it can be obtained by applying, drying, and curing using conventional coating methods.

Furthermore, if necessary, a hard coat layer may be applied to the stretchable film substrate to prevent scratches on the surface of the molded article, 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 film substrate, as well as good surface hardness, and conforms to the stretchable film during molding. Organic fillers such as resin beads or inorganic fillers such as metal oxides may also be added as needed. There are no particular limitations on the method for applying the hard coat layer, and it can be obtained by applying, drying, and curing using conventional coating methods.

The stretchable conductive material may be laminated on a support and used as a laminate. There are no particular restrictions on the support, but it is preferably a stretchable material to take advantage of the stretchability of the stretchable film substrate. Specific examples include stretchable plastic film and stretchable fiber. The stretchable fiber may also be textile fabric. Alternatively, a recess may be formed in the support, and the stretchable conductor may be embedded in this recess.

The stretchable conductive material and the support may be joined by utilizing the adhesive properties of the stretchable conductive material, or by lamination. They may also be joined via an adhesive layer or an easy-adhesion layer.

The stretchable conductive material obtained in this manner may be a product in itself, or may be used as a component. Stretchable conductive materials are suitable, for example, for stretchable wiring and stretchable electrodes. Stretchable conductive materials can also be used as films such as stretchable electromagnetic wave shielding layers and stretchable heat dissipation layers. They can also be used as conductive molded articles of desired shapes.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these. In the following explanation, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass." Furthermore, values other than solvents are calculated as non-volatile content.

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

[Condensation-curable silicone resin]
"KE-441" manufactured by Shin-Etsu Chemical Co., Ltd. was used.
[Addition-curable silicone resin (a1)]
"KE-1800T-A/B" manufactured by Shin-Etsu Chemical Co., Ltd. was used.
[Block copolymers a2-1 and a2-2]
Resin Production Examples 1 and 2 described below were used.
[Block copolymer (B3) containing no siloxane bond]
- Acrylic block copolymer "LA2330" manufactured by Kuraray Co., Ltd. was used.
[Polyurethane (for comparison)]
Resin Production Example 3 described below was used.
[Polyester (for comparison)]
- Vylon (registered trademark) 290 manufactured by Toyobo Co., Ltd. was used.

(monomer)
MMA: methyl methacrylate DCPMA: dicyclopentanyl methacrylate nBA: n-butyl acrylate

(Polymerization initiator)
BM1448: 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanemethyl (manufactured by BORONMOLECULAR) (for RAFT polymerization)
AIBN: 2,2'-azobis(isobutyronitrile) (manufactured by Wako Pure Chemical Industries, Ltd.)

<Resin Production Example 1: Synthesis of Block Copolymer (a2-1)>
The acrylic-modified block copolymer (a2-1) used in the silicone resin (a2-1) was synthesized by the RAFT method. Specifically, 2.8 g of BM1448 (RAFT agent), 1.2 g of AIBN (azobisisobutyronitrile), and 76.9 g of MMA were reacted in 250 g of methyl ethyl ketone solvent at 75°C for 6 hours in a 2,000 mL flask equipped with a nitrogen gas inlet tube and a stirrer to obtain a prepolymer. The conversion rates of MMA calculated from 1H-NMR were both 99.5% or higher. Next, 0.5 g of AIBN, 350.0 g of FM-0721 (a reactive silicone/Silaplane manufactured by JNC Corporation), and 100.0 g of nBA were added to the total amount of the prepolymer solution, and the reaction was carried out at 75°C for 24 hours. The conversion rates of the second-stage monomers FM-0721 and nBA calculated from 1H-NMR were 99.5%. Furthermore, 1.2 g of AIBN and 76.9 g of MMA were added to the total amount of the prepolymer solution, and the reaction was carried out at 75°C for 6 hours. The conversion rates of the third-stage monomer MMA calculated from 1H-NMR were both 99.5% or higher. The mixture was then cooled to room temperature, filtered, washed, and dried to obtain an acrylic-modified block copolymer (a2-1) with an A-B-A triblock structure in which the soft segments were modified with a silicone component. The resulting block copolymer (a2-1) had an Mw of 95,000 and a molecular weight distribution (Mw/Mn) of 1.3. The content of structural units derived from acrylic monomers having siloxane bonds was approximately 58.0% by mass in the block copolymer.

<Resin Production Example 2: Synthesis of Block Copolymer (a2-2)>
The acrylic-modified block copolymer (a2-2) used in the silicone resin (A) was synthesized by the RAFT method. Specifically, 2.8 g of BM1448 (RAFT agent), 1.2 g of AIBN, and 76.9 g of DCPMA were reacted in 250 g of methyl ethyl ketone solvent in a 2,000 mL flask equipped with a nitrogen gas inlet tube and a stirrer for 6 hours at 75°C to obtain a prepolymer. The conversion rates of DCPMA calculated from 1H-NMR were both 99.5% or higher. Next, 0.5 g of AIBN, 250.0 g of FM-0711 (a reactive silicone/Silaplane manufactured by JNC Corporation), and 200.0 g of nBA were added to the total amount of the prepolymer solution, and the reaction was carried out at 75°C for 24 hours. The conversion rate of the second-stage monomer FM-0711 calculated from 1H-NMR was 99.5%. Furthermore, 1.2 g of AIBN and 76.9 g of DCPMA were added to the total amount of the prepolymer solution, and the reaction was carried out at 75°C for 6 hours. The conversion rates of the third-stage monomer DCPMA calculated from 1H-NMR were 99.5% or higher in both cases. The mixture was then cooled to room temperature, filtered, washed, and dried to obtain an acrylic-modified block copolymer (a2-2) with an A-B-A triblock structure in which the soft segments were modified with a silicone component. The resulting block copolymer (a2-2) had an Mw of 112,000 and a molecular weight distribution (Mw/Mn) of 1.5. The content of structural units derived from acrylic monomers having siloxane bonds was approximately 41.4% by mass in the block copolymer.

<Resin Production Example 3: Synthesis of Polyurethane (for Comparative Example)>
A comparative polyurethane resin was synthesized. Specifically, 783.0 g of polytetramethylene ether glycol (molecular weight 1000) and 200.0 g of IPDI (isophorone diisocyanate) were charged into a 2,000 mL flask equipped with a nitrogen gas inlet tube and a stirrer, and the mixture was gradually heated to 90°C and reacted for 6 hours. The mixture was then cooled to room temperature, filtered, washed, and dried to obtain a comparative polyurethane resin.

(Production of conductive compositions and stretchable conductive materials)
The following conductive particles, solvent, and stretchable film substrate were used.
<Conductive fine particles (F)>
(Chained silver powder (f1))
f1-1 (tap density 0.7 g/cm ³ , average particle size 10.0 μm)
f1-2 (tap density 1.3 g/cm ³ , average particle size 4.2 μm)
(Flake silver powder (f2))
・f2-1 (tap density 1.1 g/cm ³ , average particle size 5.2 μm)
(Other conductive particles)
Silver-coated copper powder, silver coating amount 10%, average particle size 2 μm
Carbon, average particle size 15 μm
<Solvent>
Diethylene glycol monobutyl ether, boiling point 231°C
<Stretchable film substrate>
Silicone rubber base material:
The material used was K-125 manufactured by Togawa Rubber Co., Ltd., with a thickness of 500 μm, a tensile elongation at break of 310%, and a Young's modulus of 1.0 MPa (23° C.).

<Production of conductive composition (K1)>
[Example 1]
41.0 parts of a condensation curable silicone resin was dissolved in 30.0 parts of diethylene glycol monobutyl ether, and 19.0 parts of conductive fine particles (f1-1) and 40.0 parts of silver-coated copper were stirred and mixed, and the mixture was kneaded with a three-roll mill (manufactured by Kodaira Seisakusho) to obtain a conductive composition (K1).

<Production of Conductive Compositions (K2) to (K13) and (L1) to (L5)>
[Examples 2-13, Comparative Examples 1-5]
Conductive compositions (K2) to (K13) and (L1) to (L5) were obtained in the same manner as in Example 1, except that the types and blending amounts of the resin, solvent, and conductive fine particles in Example 1 were changed as shown in Table 1, and the blending ratio was changed as necessary. Note that the numerical values for each material in Table 2 are all in parts by mass.

<Manufacturing of stretchable conductive material>
Next, the conductive compositions (K1) to (K13) and (L1) to (L5) produced in Examples 1 to 13 and Comparative Examples 1 to 5 were printed onto the silicone rubber substrate using a screen printer (Minomat SR5575 semi-automatic screen printer, manufactured by Minoscreen Co., Ltd.) and then heated in a hot air drying oven at 150°C for 30 minutes to obtain stretchable conductive materials each equipped with a conductive layer having a rectangular solid pattern measuring 20 mm in width, 60 mm in length, and 10 μm in thickness, and a linear pattern measuring 3 mm in line width, 60 mm in length, and 10 μm in thickness.

<Evaluation>
(Conductivity | Initial volume resistivity)
The volume resistivity of the stretchable conductive materials according to each of the examples and comparative examples was measured. Specifically, a rectangular, solid stretchable conductive material measuring 20 mm wide, 60 mm long, and 10 μm thick, as produced in the above examples and comparative examples, was used as a test piece. The volume resistivity of the test piece obtained was measured in accordance with JIS K7194 in an atmosphere of 25°C and 50% relative humidity using a surface resistance meter (product number: Loresta (registered trademark) AP MCP-T400, probe: ASP probe (four-point probe, manufactured by Mitsubishi Chemical Corporation)).
The initial state was evaluated according to the following criteria.
+++: Less than 2.0×10 ⁻⁴ Ω·cm ++: 2.0×10 ⁻⁴ Ω·cm or more, less than 9.9×10 ⁻³ Ω·cm +: 9.9×10 ⁻³ Ω·cm or more, less than 9.9×10 ⁻¹ Ω·cm NG: 9.9×10 ⁻¹ Ω·cm or more

(Moisture and heat resistance)
In addition, the volume resistivity of the above stretchable conductive material was measured in the same manner as above after 10 days in an environment of 85°C and 85% relative humidity, and the rate of change from the initial value (change after test) was evaluated according to the following criteria.
[Change rate (%)]
= [(Volume resistivity of test piece before test) - (Volume resistivity of test piece after test)] ÷ [(Volume resistivity of test piece before test)]
+++: Rate of change is 20% or less. ++: Rate of change is more than 20% but not more than 50%. +: Rate of change is more than 50% but not more than 100%. NG: Rate of change is more than 100%.

(Repeated stretch resistance | Resistance change)
For a 20 mm × 60 mm sample of the stretchable conductive material according to each of the Examples and Comparative Examples, its end was fixed to a Tensilon tensile testing device, and the sample was stretched to 50% at a rate of 4 mm/s at 25°C and a relative humidity of 50%, and then held for 2 seconds. This stretching cycle was repeated 1,000 times, and the rate of change after 1,000 times was calculated using the following formula.
[Change rate (%)]
= [(R1,000)-(R0)]÷[(R0)]×100
Here, R1,000 indicates the resistance value immediately after 1,000 repeated extension and contraction cycles, and R0 indicates the resistance value using the same film before starting the measurement. Evaluation was made according to the following criteria.
+++: Rate of change is 20% or less. ++: Rate of change is more than 20% but not more than 50%. +: Rate of change is more than 50% but not more than 100%. NG: Rate of change is more than 100%.

(Adhesion to substrate)
A 20 mm wide, 60 mm long rectangular solid conductive layer formed on the stretchable conductive material of each Example and Comparative Example was cut with a cutter knife using a 1 mm interval cross-cut guide manufactured by Gardner, with a 10 x 10 grid pattern so as to penetrate the conductive layer, and cellophane tape manufactured by Nichiban Co. was attached to the layer to remove trapped air and ensure good adhesion, and then the tape was peeled off vertically. The degree of peeling of the coating was evaluated as follows in accordance with the ASTM-D3519 standard.
+++: Rating 5B to 4B, good adhesion. ++: Rating 5B to 4B, but the coating film suffered cohesive failure and part of the coating film on the surface side came off. +: Rating 4B to 3B, slightly poor adhesion. NG: Rating 3B or below, poor adhesion.

(Continuous printing ability)
Conductive compositions (K1) to (K13) and (L1) to (L5) produced in Examples 1 to 13 and Comparative Examples 1 to 5 were applied to the above silicone rubber substrate in a continuous printing test of 100 sheets using a screen printing machine (Minomat SR5575 semi-automatic screen printing machine, manufactured by Minoscreen Co., Ltd.), and the printed surface of the printed pattern immediately after printing was observed visually and with a stereo microscope, and the dimensions were also measured to confirm whether bleeding or rubbing had occurred.

[Criteria for Judging Smearing or Rubbing]
[Bleeding]: Immediately after printing, there are areas that are 5% or more thicker than the plate dimensions. [Rubbing]: Immediately after printing, there are areas that are 5% or more thinner than the plate dimensions.

[Continuous Printability Evaluation Criteria]
++: 80 or more prints can be made without bleeding or rubbing. +: 25 to 79 prints can be made without bleeding or rubbing. NG: 24 or fewer prints can be made without bleeding or rubbing.

From the results of Examples 1 to 13 of the present invention, it was found that the present invention effectively suppresses the occurrence of cracks and breaks in resistance during stretching, thereby providing a conductive composition and a stretchable conductive material that are excellent in resistance to repeated stretching, and that also have good electrical conductivity, moist heat resistance, and substrate adhesion to stretchable film substrates such as silicone substrates, as well as good continuous printability. These properties make them suitable for use in electronic devices.

Claims (11)

A conductive composition comprising a silicone resin (A), conductive fine particles (F), and a (meth)acrylic block copolymer (B) having no siloxane bond ,
the conductive fine particles (F) contain chain-like silver powder (f1) having a tap density of 2.5 g/cm3 or ^less ,
A conductive composition , wherein the content of the chain-like silver powder (f1) is 20 to 69 mass% based on the total solid content of the conductive composition . The conductive composition according to claim 1, wherein the content of the conductive fine particles (F) is 60 to 95 mass% based on the total solid content of the conductive composition. The conductive composition according to claim 1 or 2, wherein the conductive fine particles (F) further contain flaky silver powder (f2). The conductive composition according to claim 1 or 2, wherein the silicone resin (A) includes an addition-curing silicone resin (a1). The conductive composition according to claim 1 or 2, wherein the silicone resin (A) contains a (meth)acrylic block copolymer (a2) having a siloxane bond. The conductive composition according to claim 5 , wherein the (meth)acrylic block copolymer (a2) having a siloxane bond has a structural unit derived from an acrylic monomer having a siloxane bond. A conductor containing the conductive composition according to claim 1 or 2. A conductor having a cured product of the conductive composition described in claim 1 or 2 on an elastic substrate. The electrical conductor of claim 8 , wherein the stretchable substrate is a silicone substrate. A stretchable conductive material comprising the conductor of claim 7 . An electronic device comprising the stretchable conductive material of claim 10 .