JP7767907B2 - Conductive composition, conductor, stretchable conductive material, electronic device - Google Patents

Description

The present invention relates to conductive compositions, conductors, stretchable conductive materials, and electronic devices.

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, it is necessary to apply a conductive composition such as a paste to a stretchable substrate to form a printed pattern. However, depending on the conductive composition used, aggregates may be generated, which can lead to a problem of reduced printability on various stretchable film substrates.

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 effectively suppresses the occurrence of cracks during stretching, thereby exhibiting excellent resistance to repeated stretching, and that also has good electrical conductivity, moist heat resistance, and printability on stretchable film substrates.

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 provides a polymer having a weight average molecular weight of 20,000 or more and 500,000 or less.
a block copolymer (E) mainly composed of structural units derived from an ethylenically unsaturated monomer;
A conductive composition comprising:
the content of the conductive fine particles (F) is 60 to 95 mass% based on the total solid content of the conductive composition, and the content of the chain-like silver powder (f1) in the conductive fine particles (F) is 20 mass% or more and less than 70 mass% based on the total solid content of the conductive composition,
The conductive composition relates to the chain-like silver powder (f1) having a tap density of 2.0 g/cm3 ^or less.

The present invention also relates to the above-mentioned conductive composition, which further contains flaky silver powder (f2), and the content of the flaky silver powder (f2) is 1 to 75 mass% based on the total solid content of the conductive composition.

The present invention also relates to the above-mentioned conductive composition, wherein the structure of the block copolymer (E) is a triblock structure represented by the following formula (1) or a starblock structure represented by the following formula (2):
Formula (1)...polymer block A-polymer block B-polymer block A
Formula (2)... [polymer block A-polymer block B] _q X
(In the above formula (1), the glass transition temperature of polymer block A is 20°C or higher, and the glass transition temperature of polymer block B is lower than 20°C. In the above formula (2), the glass transition temperature of polymer block A is 20°C or higher, and the glass transition temperature of [polymer block B] _qX is lower than 20°C, q is an integer of 2 or more and 6 or less, and X is an initiator residue and/or a coupling agent residue, or a derivative thereof.)

The present invention also relates to the above-mentioned conductive composition, wherein the block copolymer (E) has 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.

The present invention also relates to the above-mentioned conductive composition, which further contains a crosslinking agent (D) capable of forming crosslinks with the reactive functional groups possessed by the block copolymer (E).

The present invention also relates to the above-mentioned conductive composition, wherein the block copolymer (E) contains sulfur atoms.

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

The present invention also relates to a conductor formed by forming a cured product of the above-mentioned conductive composition on a stretchable 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 comprising the above-mentioned conductor or the above-mentioned stretchable conductive material.

The present invention has the excellent effect of providing conductive compositions, conductors, stretchable conductive materials, and electronic devices that have excellent resistance to repeated stretching by effectively suppressing the occurrence of cracks during stretching, and that also have good electrical conductivity, moist heat resistance, and printability on stretchable film substrates.

The conductive composition, conductor, stretchable conductive material, and electronic device according to this embodiment will be described in detail below.
In the present embodiment, 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 block copolymer (E) having a weight-average molecular weight of 20,000 or more and 500,000 or less, the block copolymer (E) being composed mainly of structural units derived from an ethylenically unsaturated monomer; and conductive fine particles (F), wherein the conductive fine particles (F) account for 60 to 95 mass% of the total solid content contained in the conductive composition; and further, among the conductive fine particles (F), chain-like silver powder (f1), in which fine particles are aggregated to form aggregate particles, accounts for 20 to less than 70 mass% of the total solid content of the conductive composition; and the chain-like silver powder (f1) has a tap density of 2.0 g/cm3 or ^less .

<Block copolymer (E)>
The conductive composition of this embodiment contains a binder block copolymer (E) to impart film-forming properties and adhesion to a stretchable substrate film. Furthermore, in this embodiment, the inclusion of the block copolymer (E) can impart flexibility and stretchability to the conductive layer. Therefore, the inclusion of the block copolymer (E) suppresses breakage of the conductive layer due to stretching or shrinkage.

The block copolymer (E) is a block copolymer primarily composed of structural units derived from ethylenically unsaturated monomers, and has a weight-average molecular weight of 20,000 or more and 500,000 or less.

In this specification, "ethylenically unsaturated monomer" refers to a monomer having one or more polymerizable ethylenically unsaturated groups in the molecule. Furthermore, "mainly composed of" means that the block copolymer contains 70% by mass or more of structural units derived from ethylenically unsaturated monomers, based on the total mass of the block copolymer.

Specific examples of the ethylenically unsaturated group in the ethylenically unsaturated monomer include an ethylene group, a propenyl group, a butenyl group, a vinylphenyl group, a (meth)acrylic group, an allyl ether group, a vinyl ether group, a maleyl group, a maleimide group, a (meth)acrylamide group, an acetylvinyl group, and a vinylamide group. The "ethylenically unsaturated monomer" is preferably a (meth)acrylic group. "(Meth)acrylic" encompasses both "acrylic," "methacrylic," and mixtures thereof. "(Meth)acrylate" encompasses both "acrylate," "methacrylate," and mixtures thereof.

In addition, 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 residue of an ethylenically unsaturated monomer with a reactive compound during or after polymerization of the block copolymer. For example, it also includes structural units in which a functional group and/or substituent not originally contained in the monomer is introduced into a portion of the residue of an ethylenically unsaturated monomer. Note that the monomer itself may contain functional groups and/or substituents. It also includes structures in which side groups, side chains, or side groups and side chains within a block copolymer are bonded to each other or via a reactive compound to form a ring.

[Configuration of block copolymer (E)]
The block copolymer (E) of this embodiment preferably contains a soft segment and a hard segment. The soft segment is a block component made of a flexible and highly flexible polymer chain, and the hard segment is a block component made of a polymer chain that is prone to crystallization or aggregation and has higher rigidity than the soft segment. The block copolymer of this embodiment preferably has a configuration in which the 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).

An example of a block copolymer containing a soft segment and a hard segment is a block copolymer represented by the following formula (3).
Polymer block A - polymer block B (3)
In formula (3), 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 20°C. By using the block copolymer represented by formula (3), 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 (3) may be abbreviated as "AB".

An example of a block copolymer with a triblock structure is a block copolymer represented by the following formula (1):

Polymer block A - polymer block B - polymer block A (1)
In formula (1), the polymer block A and the polymer block B can be defined by the same description as for formula (3).
In this specification, formula (1) 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 (3) and formula (1), 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 (3) and formula (1), it is preferable to use the block copolymer of formula (1) 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.

In addition to the block structures represented by the above formulas (3) and (1), the block copolymer (E) may also have a star block structure represented by the following formula (2):

[Polymer block A-Polymer block B] _q X (2)
In formula (2), q is an integer of 2 or more and 6 or less. For polymer block A and polymer block B, the description of formula (3) 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 (2) may be abbreviated as "[AB] _q X".

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.

The Tg of polymer block A in this specification is the Tg of <polymer block A> _Total observed in a curve obtained by differential scanning calorimetry (DSC) measurement at the stage of obtaining the block copolymer, and is a value obtained by measurement based on JIS K7121:2012, Measurement of Transition Temperature of Plastics, and 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 can therefore be easily distinguished from the Tg of polymer block B in the case of a diblock structure or triblock structure, and 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 change significantly depending on the chain end of the block copolymer, i.e., the structure of the chain end of the polymer block A. Therefore, in this specification, the Tg of each polymer block A and the Tg of <polymer block A> _total are determined by including the chain end of the 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 _{the total} <polymer block A>. 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] _q X 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] _q X 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 block copolymer preferably has a block structure of an A-B diblock structure, an A-B-A triblock structure, or an [A-B] _q X star block structure, and the polymer block A may have an initiator residue or a derivative thereof, a functional group, an inactive group, a crosslinkable group, a substituent, or the like at the chain end.

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 read as the Tg of <polymer block A> _Total (the same applies hereinafter). 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 a triblock structure, and the Tg of [polymer block B] _q X in the case of a star block structure, 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, and 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) referred to in this specification is a value determined by the method described in the Examples section below. The Mw of the block copolymer (E) is 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 for a stretchable conductive material, both tensile strength and conductive stability can be achieved. The preferred range of 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 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 form of the block copolymer (E) is preferably an A-B-A triblock structure, a bibranched structure where q = 2 in [A-B] _q X, or a tribranched structure where q = 3. The polymer block A and the polymer block B each independently have structural units derived from one type of monomer alone or two or more types of monomers.

The content of structural units derived from ethylenically unsaturated monomers in block copolymer (E) is 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 a microphase-separated structure of polymer block A and polymer block B, a block copolymer consisting of structural units (100% by mass) derived from ethylenically unsaturated monomers, other than X (initiator residue and/or coupling agent residue, or derivative thereof) and the terminal structure of the block copolymer, is preferred.

Polymer block A satisfies the above-mentioned Tg and is a block that functions as a hard segment, primarily composed of structural units derived from ethylenically unsaturated monomers. Monomers can be used alone or in combination of two or more. Specific examples of monomers include methacrylic acid esters, acrylamides, N-alkylacrylamides, styrene, styrene derivatives, maleimides, and acrylonitrile. Examples of methacrylic acid esters include those having an alkyl group containing 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Examples of styrene derivatives include α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene. Furthermore, the monomers exemplified for polymer block B, described below, can be suitably included as part of the polymer block.

Polymer block B satisfies the above-mentioned Tg and is a block that functions as a soft segment, primarily composed of structural units derived from ethylenically unsaturated monomers. Monomers may be used singly or in combination. Specific examples of monomers include acrylic acid esters, olefin compounds, diene compounds, and alkylene oxides. Examples of acrylic acid esters include alkyl acrylates having an alkyl group containing 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Examples of olefin compounds and diene compounds include olefin compounds and diene compounds having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Examples of alkylene oxides include alkylene oxides having an alkylene group containing 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. In addition, the monomers exemplified above for polymer block A can be suitably included as part of the polymer block.

A suitable example of block copolymer (E) is a block copolymer in which polymer block A contains 50% by mass or more of structural units derived from methacrylic acid esters and polymer block B contains 70% by mass or more of structural units derived from acrylic acid esters. The structural units derived from methacrylic acid esters 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. Furthermore, the structural units derived from methacrylic acid esters may 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.
Also, hydroxyalkyl methacrylates having a hydroxyalkyl group of 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 having an alkoxy group of 1 to 4 carbon atoms and an alkyl group of 1 to 4 carbon atoms, such as methoxymethyl methacrylate, methoxyethyl methacrylate, methoxypropyl methacrylate, ethoxymethyl methacrylate, ethoxyethyl methacrylate, and ethoxypropyl methacrylate;
Monomethacrylates of (polyalkylene) glycol monoalkyls, alkylenes, alkyne ethers, or esters; methacrylic acid monomers having an acid group (carboxy group, sulfonic acid, phosphoric acid) including acrylic acid or acrylic acid dimers; oxygen atom-containing methacrylic acid monomers; methacrylic acid monomers having an amino group; nitrogen atom-containing methacrylic acid monomers, etc. can be used. Other examples include monomethacrylates having three or more hydroxyl groups, halogen atom-containing methacrylates, silicon atom-containing methacrylic acid monomers, methacrylic acid monomers having a group that absorbs ultraviolet light, and acrylates with a hydroxyl group methyl substituted at the α-position. Also usable are 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.

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.

A suitable example of block copolymer (E) 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 for block copolymer (E) 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 block copolymer (E), 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), cylinder (hexagonal), gyroid, or lamellar phase. Forming a microphase-separated structure can provide a conductive composition that imparts excellent elasticity and effectively suppresses cracking (disconnection) associated with stretching. From the perspective of more effectively enhancing elasticity, 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).

The content of polymer block A relative to polymer block A and polymer block B in block copolymer (E) is not particularly limited, but from the viewpoint of easily obtaining a microphase-separated structure of a sea-island structure, it is preferably 1 to 50% by mass, more preferably 15 to 30% by mass. Furthermore, from the viewpoint of effectively obtaining adhesiveness, 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, 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-separated structure, the content ratio of polymer block A and polymer block B relative to the total mass of the block copolymer is preferably 90.0 to 99.9 mass%, and more preferably 98.0 to 99.9 mass%.

From the viewpoint of maintaining good electrical conductivity, it is preferable that 90% by mass or more of the ethylenically unsaturated monomers in the block copolymer (E) 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 block copolymer (E) may 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]
Among the functional groups, the block copolymer (E) preferably has 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. By combining the functional group as a reactive functional group with a crosslinking agent (D) described later and chemically crosslinking the block copolymer (E), the block copolymer (E) can be three-dimensionally crosslinked, making it suitable for use in applications where hardness is required for the conductive layer.

[Sulfur atom]
From the viewpoint of effectively suppressing the occurrence of cracks when a conductive filler such as a metal filler is contained, the block copolymer (E) preferably contains a sulfur atom, and more preferably the sulfur atom is derived from a sulfide group, a disulfide group, a mercapto group, or the like.

When block copolymer (E) contains sulfur atoms in its molecule, polymer block A and polymer block B constituting block copolymer (E) form a microphase-separated structure, and physical crosslinks can be formed that can form a structure including stress relaxation points. Block copolymer (E) has a microphase-separated structure, and the formation of physical crosslinks can provide excellent elasticity. Furthermore, self-organization (aggregation of segments) can bring sulfur atoms closer to each other. Such a distribution of sulfur atoms further imparts cohesive strength and stress relaxation, thereby providing block copolymer (E) with excellent elasticity, heat resistance, and moist heat resistance.

Examples of methods for incorporating sulfur atoms into the block copolymer (E) include a method of directly introducing sulfur atoms using a monomer having a sulfur atom, a method of copolymerizing a monomer using a polymerization initiator having a sulfur atom, a method of producing the block copolymer (E) using a coupling agent having a sulfur atom, and a method of introducing sulfur atoms by modification (chemical conversion). Examples of the polymerization initiator having a sulfur atom include commercially available sulfur-based RAFT initiators.
Another example is a method of obtaining a polymer using a chain transfer agent having a mercapto group such as mercaptohexanol, etc. Still another example is a method of directly introducing a sulfur atom such as a mercapto group by adding 1,2-ethanedithiol or the like to the block copolymer (E) obtained after polymerization.

[Method for producing block copolymer (E)]
An example of a method for producing the block copolymer (E) of the present embodiment will be described below, but the present invention is not limited thereto.

The method for producing block copolymer (E) is not particularly limited, but production 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, after obtaining a reactive terminal diblock structure, a block copolymer can be obtained using a coupling agent.

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] _q X, which includes a step of obtaining a polymer block B and a polymer block A in this order by sequential polymerization 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.

There is also a method for producing a block copolymer represented by [polymer block A-polymer block B]qX, which includes the steps of obtaining an A-B type diblock structure by sequentially polymerizing a polymer block B and a polymer block _A in any order, introducing a reactive terminal into a molecular terminal of the A-B type diblock structure as needed, and carrying out a coupling reaction with any coupling agent having 3 to 6 linking units reactive with the reactive terminal.

The block copolymer (E) may also be a commercially available product. An example of a commercially available product is an acrylic triblock copolymer manufactured by Arkema using living polymerization. Specifically, the SBM type, represented by polystyrene-polybutadiene-polymethyl methacrylate, the MAM type, represented by polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate, and the MAMN or MAMA type, which have been modified with a carboxylic acid or a 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.

In this embodiment, the content of the block copolymer (E) is 8% by mass or more and 40% by mass or less, based on the total amount of solids contained in the conductive composition. It is more preferably 10% by mass or more and 38% by mass or less, and even more preferably 15% by mass or more and 35% by mass or less. Having the content of block copolymer (E) within this range imparts sufficient flexibility to the conductive layer, effectively suppressing the occurrence of cracks in the conductive layer during elongation, and by including a sufficient amount of conductive fine particles (F), a conductive layer with excellent conductivity can be obtained.

The block copolymer used in block copolymer (E) may be used alone or in combination of two or more types.

If necessary, other binder resins may be used in combination as resin components other than block copolymer (E). From the viewpoint of forming a conductive layer with excellent conductivity, the amount of resin components other than block copolymer (E) 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.

<Conductive fine particles (F)>
The conductive fine particles (F) are particles that exhibit conductivity when a plurality of conductive fine particles come into contact with each other in the conductive layer, and in this embodiment, they are appropriately selected from those that can obtain conductivity without heating at high temperatures. Examples of the conductive fine particles used in this embodiment include metal fine particles, carbon fine particles, conductive oxide fine particles, etc.
Examples of metal fine particles include powders of simple metals such as gold, silver, copper, nickel, chromium, palladium, rhodium, ruthenium, indium, aluminum, tungsten, malbutene, 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 this embodiment, 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 (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 this example, 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. The solution was then irradiated with 40 W ultrasonic waves for 180 seconds while stirring, and then measurement was performed. The determined median diameter (D50) was taken as the average particle size of the conductive fine particles (F).

In this embodiment, the conductive fine particles (F) can be used alone or in combination of two or more types. The content of the conductive fine particles (F) in the conductive composition in this embodiment is 60% by mass or more and 95% by mass or less, based on the total solid content of the conductive composition. Furthermore, from the viewpoints of conductivity and elasticity, the content is preferably 65% by mass or more and 90% by mass or less, and more preferably 70% by mass or more and 85% by mass or less, based on 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 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 upper limit, the content of the block copolymer (E) can be increased, improving film-forming properties and adhesion to elastic films and imparting flexibility and elasticity to the conductive layer.

<Chained silver powder (f1)>
The conductive composition of the present invention contains, as the conductive fine particles (F), chain-like silver powder (f1) having a tap density of 2.0 g/ ^cm3 or less. Here, the chain-like silver powder is silver powder in which fine particles are aggregated to form aggregated particles, and has a granular or aggregated shape. Specific examples include aggregated silver powder (reduced silver powder) and silver powder in which silver particles branch out like branches, i.e., dendritic silver powder. Furthermore, the chain-like silver powder (f1) is preferably 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 2.0 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 stretching. 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 chain-like silver powder (f1) preferably has an average particle size (D50) of 3 to 15 μm as measured by a laser analysis scattering particle size distribution measurement method.

The amount of chain-like silver powder (f1) is 20% by mass or more and less than 70% by mass, based on the total solid content of the conductive composition. Within this range, both low resistance and stable conductivity during stretching are possible. In particular, when the amount of chain-like silver powder (f1) is less than 70% by mass, based on the total solid content of the conductive composition, a conductor with good printability (adhesion) to stretchable film substrates can be obtained. The amount is preferably 30% by mass or more and less than 70% by mass, more preferably 40% by mass or more and less than 70% by mass, even more preferably 50% by mass or more and less than 70% by mass, and particularly preferably 50% by mass or more and less than 65% by mass. While the detailed mechanism of this effect is unclear, it is speculated as follows: By incorporating the chain-like silver powder (f1) in the above amount, the polymer block A and polymer block B constituting the block copolymer (E) described above are more likely to form a microphase-separated structure. As a result, the stretchability of the block copolymer (E) can be improved. Furthermore, it is believed that the self-organization (aggregation of segments) of the optimized microphase separation structure further improves the affinity between the block copolymer (E) and the chain-like silver powder (f1), improving the dispersibility of the conductive fine particles (F). This makes it possible to create a conductive composition with an ideal conductive path design that can withstand expansion and contraction (elastic deformation) and excellent printability (ideal dispersion design).

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-shaped silver powder includes shapes such as flat, thin flakes, and scales, and also includes shapes obtained by crushing three-dimensional silver powder such as spherical or lumpy shapes in one direction. Specifically, it preferably includes leaf-shaped silver powder in which the thickness of a single silver powder particle 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. In the present invention, the length of a single silver powder particle in the longitudinal direction of the flat portion and the length in the transverse direction of the flat portion are each independently preferably 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 flexibility is also excellent 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.

The flaky silver powder of the present invention may be, for example, in the general flake, scale, or plate shape.

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 amount of the flake silver powder, in terms of mass %, based on the total solid content in the conductive composition is preferably 1 to 75 mass %, and more preferably 5 to 60 mass %.

Furthermore, the conductive composition of the present invention may contain other conductive fine particles as long as the effects of the present invention are not impaired.

<Crosslinking agent (D)>
The conductive composition of the present invention may further contain other components as necessary. In particular, when the block copolymer (E) contained in the conductive composition of the present invention has the above-described reactive functional group, it is preferable that the conductive composition further contains a crosslinking agent (D).

The crosslinking agent (D) is used to crosslink the block copolymer (E). The crosslinking reaction between the block copolymer (E) and the crosslinking agent (D) can be accelerated by heat and/or irradiation with active energy rays such as ultraviolet rays. Examples of active energy rays include ultraviolet rays, electron beams, alpha rays, beta rays, and gamma rays. At the conductive composition stage, the crosslinking agent and a portion of the block copolymer may already be crosslinked.

By using a resin composition containing a combination of crosslinking agent (D) and block copolymer (E), a crosslinked structure can be constructed while maintaining elasticity, promoting cohesive force and increasing elasticity, and providing a component with excellent solvent resistance and elastic conductivity.

When the block copolymer (E) has the reactive functional group described above, the crosslinking agent (D) preferably has a functional group capable of crosslinking with the reactive functional group. The type of crosslinking agent varies depending on the type of functional group in the block copolymer (E). When the functional group is a hydroxyl group or an amino group, the crosslinking agent is preferably an isocyanate compound, an epoxy compound, or a metal chelate compound. When the functional group is a carboxyl group or a phosphate group, the crosslinking agent is preferably a metal chelate compound or an isocyanate compound. When the functional group is an epoxy group or an oxetane group, the crosslinking agent is preferably an amine-based compound. When the functional group is an isocyanate group or a blocked isocyanate group, the crosslinking agent is preferably a hydroxyl-based compound. When the functional group is a vinyl group, a furyl group, or an acetoacetyl group, the crosslinking agent is preferably a polyfunctional acrylate-based monomer compound. When the functional group is a hydrolyzable silyl group, the crosslinking agent is preferably a silane coupling agent-based compound. When the functional group is a nitrile group, the crosslinking agent is preferably a phenolic resin-based compound.

The isocyanate compound is preferably a compound having two or more isocyanate groups, and examples include isocyanate monomers such as aromatic polyisocyanates, aliphatic polyisocyanates, araliphatic polyisocyanates, and alicyclic polyisocyanates, as well as biuret compounds, nurate compounds, and adduct compounds.

Specific examples of the isocyanate compound include aromatic polyisocyanates such as 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, and 4,4',4"-triphenylmethane triisocyanate;
Aliphatic polyisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (also known as HMDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate;
Aromatic aliphatic polyisocyanates such as ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate;
Examples of the polyisocyanate include alicyclic polyisocyanates such as 3-isocyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI, isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanatemethyl)cyclohexane.

The biuret form refers to a self-condensation product having a biuret bond formed by the self-condensation of an isocyanate monomer. Specific examples include the biuret form of hexamethylene diisocyanate.

The nurate form refers to a trimer of an isocyanate monomer, such as a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, or a trimer of tolylene diisocyanate.

The adduct refers to a difunctional or higher isocyanate compound obtained by reacting an isocyanate monomer with a difunctional or higher low-molecular-weight active hydrogen-containing compound. Examples include a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with tolylene diisocyanate, a compound obtained by reacting trimethylolpropane with xylylene diisocyanate, a compound obtained by reacting trimethylolpropane with isophorone diisocyanate, and a compound obtained by reacting 1,6-hexanediol with hexamethylene diisocyanate.

The epoxy compound is preferably a compound having two or more epoxy groups, such as a compound having a glycidyl group, a bisphenol-type epoxy resin, or a novolac-type epoxy resin.
Specific examples include bisphenol-type epoxy resins such as bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, and bisphenol A/bisphenol F copolymer epoxy resin;
Novolac epoxy resins such as cresol novolac epoxy resins and phenol novolac epoxy resins;
Examples of compounds having a glycidyl group include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidylaminophenylmethane, triglycidylaminophenol, biphenyl diglycidyl ether, triglycidyl isocyanurate, polyglycidyl (meth)acrylate, and copolymers of glycidyl (meth)acrylate and vinyl monomers copolymerizable therewith.

Examples of the metal chelate compounds include coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium with acetylacetone or ethyl acetoacetate. Specific examples include aluminum ethylacetoacetate diisopropylate, aluminum trisacetylacetonate, aluminum bisethylacetoacetate monoacetylacetonate, and aluminum alkylacetoacetate diisopropylate.

Examples of the polyfunctional acrylate monomer compounds include bifunctional monomers such as 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentyl glycol adipate di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, caprolactone-modified dicyclopentenyl di(meth)acrylate, ethylene oxide-modified phosphate di(meth)acrylate, di(acryloxyethyl)isocyanurate, allylated cyclohexyl di(meth)acrylate, ethoxylated bisphenol A diacrylate, and 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene; trifunctional types such as dimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, propionic acid-modified dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, tris(acryloxyethyl)isocyanurate, ε-caprolactone-modified tris-(2-(meth)acryloxyethyl)isocyanurate; tetrafunctional types such as diglycerin tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate; pentafunctional types such as propionic acid-modified dipentaerythritol penta(meth)acrylate; and hexafunctional types such as dipentaerythritol hexa(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate.
The polyfunctional acrylate monomer compound can form crosslinks by an enethiol reaction with the reactive functional groups of the block copolymer (E).

Among crosslinking agents, isocyanate compounds and epoxy compounds are more preferred from the standpoints of storage stability and curing ability.

From the viewpoint of promoting the formation of a microphase-separated structure, the molar ratio of the reactive functional group of the block copolymer (E) to the functional group capable of reacting with the functional group in the crosslinking agent (crosslinking agent) (reactive functional group (block copolymer (E))/functional group (crosslinking agent)) is preferably 0.01 to 10.0, and more preferably 0.5 to 2.0.

For example, the crosslinking agent can be contained in an amount of 0.01 to 50.0 parts by mass per 100 parts by mass of block copolymer (E). More preferably, the amount is 0.1 to 10.0 parts by mass, and even more preferably, 0.5 to 1.5 parts by mass per 100 parts by mass of block copolymer.

From the perspective of more effectively utilizing the stretchability of the block copolymer (E) and the stretchable conductivity of the stretchable conductive material, it is more preferable that the crosslinking agent have high affinity with polymer block A, which may have a reactive functional group, or polymer block B. For example, the affinity (compatibility) can be selected with reference to the solubility parameter value.

When a crosslinking agent is added to the conductive composition of the present invention, a crosslinking accelerator may be added to accelerate the crosslinking reaction. Examples of crosslinking accelerators include organotin catalysts, inorganic metal catalysts, inorganic tin compounds, acid catalysts, organic base catalysts, and acid anhydride catalysts.

<Solvent>
The solvent that the conductive composition may contain is not particularly limited, and examples thereof include 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, and isophorone.
These solvents may be used alone or in combination of two or more. Among them, in order to adapt the conductive paste to screen printing, it is preferable to use a solvent with a boiling point of 180° C. or higher and 270° C. or lower, in order to prevent the paste from drying inside the mesh of the printing plate and clogging the mesh.

<Other ingredients>
The conductive composition of the present invention may further contain other components, such as the above-mentioned crosslinking agent (D), dispersant, friction resistance improver, infrared absorber, ultraviolet absorber, fragrance, antioxidant, organic pigment, inorganic pigment, antifoaming agent, silane coupling agent, plasticizer, flame retardant, and 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 this embodiment, 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 (D), it is further heated to cause a crosslinking reaction and harden the composition. When the crosslinking agent is not contained, the heating temperature is preferably 80 to 230°C, and the heating time is preferably 10 to 120 minutes, in order to ensure sufficient volatilization of the solvent, and when the crosslinking agent is contained, in order to ensure sufficient volatilization of the solvent and crosslinking reaction. This allows a patterned conductive layer to be obtained. If necessary, the patterned conductive layer may be provided with an insulating layer so as to cover the conductive pattern. The insulating layer is not particularly limited, and any known insulating layer can 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 this embodiment is made of 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 standpoint of stretchability, polyurethane, silicone rubber, ethylene propylene rubber, styrene rubber, acrylic rubber, and epoxy rubber are particularly preferred as stretchable film substrates.

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.

[Measurement of glass transition temperature]
The glass transition temperature was measured in accordance with JIS K 7121 (2012) Method for Measuring Transition Temperature of Plastics, and the glass transition temperature was determined as the temperature obtained from the extrapolated glass transition onset temperature (Tig) described in JIS 9.3. For the measurement, a differential scanning calorimeter (DSC Q2000, manufactured by TA Instruments) was used.
By the above method, the Tg of <polymer block A> _Total , the Tg of polymer block B in the case of a triblock structure, and the Tg of [polymer block (B)] _q X in the case of a star block structure can be determined.

(Production Example of Block Copolymer (E))
The abbreviations of the raw materials for the block copolymer (E) are as follows:
(monomer)
MMA: methyl methacrylate nBA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate St: styrene HEMA: 2-hydroxyethyl methacrylate MOI: 2-isocyanatoethyl methacrylate MAA: methacrylic acid

(Polymerization initiator)
Synthesis 1: Ethyl 2-methyl-2-n-butyltellanyl propionate (TERP polymerization initiator)
BM1448: 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanemethyl (manufactured by BORON MOLECULAR) (for RAFT polymerization)
CP-I: 2-iodo-2-methylpropionitrile (Tokyo Chemical Industry Co., Ltd.) (for RCMP polymerization)
2f-BiB: Ethylene bis(2-bromoisobutyrate) (manufactured by Aldrich, No. 723177) (for ATRP polymerization)
3f-BiB: 1,1,1-Tris(2-bromoisobutyryloxymethyl)ethane (manufactured by Aldrich, No. 723185)
AIBN: 2,2'-azobis(isobutyronitrile) (manufactured by Wako Pure Chemical Industries, Ltd.)
V65: 2,2'-azobis(2,4-dimethylvaleronitrile) (Wako Pure Chemical Industries, Ltd.)

(Synthesis of TERP Polymerization Initiator)
Synthesis 1: (Ethyl 2-methyl-2-n-butyltellanyl propionate)
This compound was synthesized according to the method disclosed in International Publication No. 2007/119884. Specifically, 6.38 g (50 mmol) of metallic tellurium (manufactured by Aldrich, trade name: Tellurium (-40 mesh)) was suspended in 50 mL of THF, and 34.4 mL (55 mmol) of n-butyllithium (manufactured by Aldrich, 1.6 M hexane solution) was slowly added dropwise at room temperature (10 minutes). This reaction solution was stirred for 20 minutes until the metallic tellurium completely disappeared. 10.7 g (55 mmol) of ethyl 2-bromoisobutyrate was added to this reaction solution at room temperature, and the mixture was stirred for 2 hours. After completion of the reaction, the solvent was concentrated under reduced pressure, followed by vacuum distillation to obtain 7.67 g (46.5% yield) of a yellow oily product, Compound 1. Furthermore, 1H-NMR analysis confirmed the production of the target product.

<Resin Production Example 1: Synthesis of Block Resin (E1)>
The block copolymer used for block copolymer (E) was synthesized by the TERP method. Specifically, in an argon-substituted glove box, 0.25 g of ethyl 2-methyl-2-n-butyltellanyl propionate (Synthesis 1), 0.01 g of AIBN, and 70.3 g of MMA were reacted in 200 g of methyl ethyl ketone solvent at 50°C for 6 hours to obtain a prepolymer. The conversion of MMA calculated from 1H-NMR was 99.5% or higher. Next, 450.0 g of nBA was added to the entire prepolymer solution, and the reaction was carried out at 50°C for 40 hours. The conversion of the second-stage monomer nBA calculated from 1H-NMR was 99.5% or higher. Furthermore, 70.3 g of MMA was added to the entire prepolymer solution, and the reaction was carried out at 50°C for 6 hours. The conversion of the third-stage monomer MMA calculated from 1H-NMR was 99.5% or higher. The mixture was then cooled to room temperature, filtered, washed, and dried to obtain a block copolymer having an A-B-A triblock structure in which the initiator residue X was at the chain end. The physical properties of the block copolymer of Production Example E1 are shown in Table 1 (the same applies to the following Production Examples of block copolymer (E)).

<Resin Production Example 2: Synthesis of Block Resin (E2)>
The block copolymer used for block copolymer (E) was synthesized by the ATRP method. Specifically, 1.0 g of copper(I) bromide, 0.4 g of 3f-BiB, 257.1 g of nBA, and 192.9 g of 2EHA were reacted in 400 g of methyl ethyl ketone solvent at 85°C for 8 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 nBA and 2EHA calculated from 1H-NMR were both 100%. Next, 99.5 g of MMA and 99.8 g of St were added to the total amount of the prepolymer solution, and the reaction was continued at 85°C for 10 hours. The conversion rates of the second-stage monomers MMA and St calculated from 1H-NMR were both 100%. Thereafter, the mixture was cooled to room temperature, filtered, washed and dried to obtain a block copolymer having a three-branched [AB] ₃ X star block structure in which the initiator residue X was located at the branch center of the polymer molecule.

<Resin Production Example 3: Synthesis of Block Resin (E3)>
The block copolymer used for block copolymer (E) was synthesized by the RAFT method. Specifically, 9.1 g of BM1448 (RAFT agent), 0.2 g of AIBN, and 140.6 g of MMA were reacted in 200 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 of MMA calculated from 1H-NMR was 99.5% or higher. Next, 0.3 g of AIBN, 438.3 g of nBA, and 11.7 g of MAA were added to the total amount of the prepolymer solution, and the reaction was carried out at 75°C for 10 hours. The conversions of the second-stage monomers nBA and MAA calculated from 1H-NMR were both 100%. The mixture was then cooled to room temperature, filtered, washed, and dried to obtain a block copolymer with an A-B diblock structure in which the initiator residue X was at the chain end and had a carboxyl group.

<Resin Production Example 4: Synthesis of Block Resin (E4)>
The block copolymer used for block copolymer (E) was synthesized by the RCMP method. Specifically, 2.15 g of CP-I, 0.001 g of iodine, 15.0 g of sodium iodide, 8.6 g of MMA, 42.9 g of St, and 5.7 g of HEMA were reacted in 200 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, St, and HEMA calculated from 1H-NMR were all 99.5% or higher.
Next, 450.0 g of nBA was added to the entire prepolymer solution, and the reaction was carried out at 80°C for 40 hours. The conversion rate of the second-stage monomer nBA calculated from 1H-NMR was 99.5% or higher. Furthermore, 8.6 g of MMA, 42.9 g of St, and 5.7 g of HEMA were added to the entire prepolymer solution, and the reaction was carried out at 75°C for 6 hours. The conversion rates of the third-stage monomers MMA, St, and HEMA calculated from 1H-NMR were all 99.5% or higher. Thereafter, the mixture was cooled to room temperature, filtered, washed, and dried to obtain a block copolymer with an A-B-A triblock structure in which the initiator residue X was located at the chain end and had a hydroxyl group.

<Resin Production Example 5: Synthesis of Block Resin (E5)>
The block copolymer used for block copolymer (E) was synthesized by the RAFT method. Specifically, 1.2 g of BM1448 (RAFT agent), 0.2 g of AIBN, and 193.3 g of MMA were reacted in 200 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 of MMA calculated from 1H-NMR was 99.5% or higher. Next, 0.3 g of AIBN, 430.7 g of nBA, and 19.3 g of MOI were added to the total amount of the prepolymer solution, and the reaction was carried out at 75°C for 10 hours. The conversions of the second-stage monomers nBA and MOI calculated from 1H-NMR were both 100%. After cooling to 50°C, 9.6 g of cysteamine and 100.0 g of methyl isobutyl ketone (boiling point 116°C) were added and reacted at 50°C for 1 hour, and the disappearance of the peak at 2270 cm ^-1 due to the isocyanate group was confirmed by IR. 1H-NMR analysis, IR analysis, and mercaptan titration analysis confirmed that the isocyanate group had been converted to a mercapto group. The mixture was then cooled to room temperature, filtered, washed, and dried to obtain a block copolymer with an A-B diblock structure in which the initiator residue X was at the chain end and had a mercapto group.

<Resin Production Example 6: Synthesis of Block Resin (E6)>
The block copolymer used for block copolymer (E) was synthesized by the RAFT method. Specifically, 0.8 g of BM1448 (RAFT agent), 0.2 g of AIBN, 65.7 g of MMA, and 9.0 g of MOI were reacted in 100 g of methyl ethyl ketone solvent in a 2,000 mL flask equipped with a nitrogen gas inlet tube and a stirrer at 75°C for 6 hours to obtain a prepolymer. The conversion rates of MMA and MOI calculated from 1H-NMR were both 99.5% or higher. Next, 0.3 g of AIBN and 450.0 g of nBA were added to the total amount of the prepolymer solution, and the reaction was continued at 75°C for 12 hours. The conversion rate of the second-stage monomer nBA calculated from 1H-NMR was 100%. Furthermore, 0.2 g of AIBN, 65.7 g of MMA, and 9.0 g of MOI 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 monomers MMA and MOI calculated from 1H-NMR were both 99.5% or higher. After cooling to 50°C, 16.4 g of 1,4-bis(aminomethyl)cyclohexane and 100.0 g of methyl isobutyl ketone (boiling point 116°C) were added, and the reaction was carried out at 50°C for 1 hour. IR confirmed the disappearance of the peak at 2270 cm ⁻¹ due to the isocyanate group. 1H-NMR analysis, IR analysis, and amine value measurement confirmed the conversion of the isocyanate group to an amino group. The mixture was then cooled to room temperature, filtered, washed, and dried to obtain a block copolymer with an A-B-A triblock structure in which the initiator residue X was located at the chain end and had an amino group.

<Resin Production Example 7: Synthesis of Block Resin (E7)>
The block copolymer used for block copolymer (E) was synthesized by the RCMP method. Specifically, 2.15 g of CP-I, 0.001 g of iodine, 15.0 g of sodium iodide, and 450.0 g of nBA were reacted in 200 g of methyl ethyl ketone solvent in a 2,000 mL flask equipped with a nitrogen gas inlet tube and a stirrer at 90°C for 24 hours to obtain a prepolymer. The conversion of nBA calculated from 1H-NMR was 99.5% or higher in all cases.
Next, 192.8 g of MMA was added to the entire prepolymer solution, and the mixture was allowed to react at 70°C for 8 hours. The conversion of the second-stage monomer MMA calculated from 1H-NMR was 99.5% or higher. The mixture was then cooled to room temperature, filtered, washed, and dried to obtain a block copolymer with an A-B diblock structure having initiator residue X at the chain end.

<Resin Production Example 8: Synthesis of Block Resin (E8)>
The block copolymer used in block copolymer (E) was synthesized by the RAFT method. Specifically, polymerization was carried out by the RAFT method, similar to Resin Production Example E6, under the conditions shown in Table 1, such as the monomer charging ratio, to obtain a block copolymer having an A-B-A triblock structure in which initiator residue X was at the chain end.

<Block Resin (E9)>
As the block copolymer (E), LA2330 manufactured by Kuraray Co., Ltd. was used.

(Production Example of Comparative Resin (E'))
<Resin Production Example 10: Synthesis of Resin (E′10)>
A block copolymer was synthesized for comparison with block copolymer (E). Specifically, similar to Resin Production Example E2, polymerization was carried out by ATRP under the conditions shown in Table 1, including the monomer charging ratio, to obtain a block copolymer having an A-B-A triblock structure in which initiator residue X was at the chain end.

<Resin Production Example 11: Synthesis of Resin (E′11)>
A block copolymer was synthesized for comparison with block copolymer (E). Specifically, polymerization was carried out by the TERP method, as in Resin Production Example E1, under the conditions shown in Table 1, including the monomer charging ratio, to obtain a block copolymer having an A-B-A triblock structure in which initiator residue X was at the chain end.

<Resin Production Example 12: Synthesis of Resin (E′12)>
A random copolymer was synthesized for comparison with block copolymer (E). Specifically, random polymerization was carried out by the RCMP method in the same manner as in Resin Production Example E4 under the conditions shown in Table 1, such as the monomer charging ratio, to obtain a random copolymer having a random structure in which initiator residue X was located at the chain end.

<Resin Production Example 13: Synthesis of Resin (E'13)>
A urethane resin for comparison with block copolymer (E) 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 urethane resin.

<Resin (E'14)>
Vylon (registered trademark) 290 manufactured by Toyobo Co., Ltd. was used as a polyester resin for comparison with the block copolymer (E).

(Production of conductive compositions and stretchable conductive materials)
The following conductive particles, solvent, crosslinking agent, 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 μm)
f1-2 (tap density 1.3 g/cm ³ , average particle size 4.2 μm)
(Flake silver powder (f2))
・f2-2 (tap density 3.3 g/cm ³ , average particle size 3.5 μm)
・f2-2 (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
・Acicular conductive tin oxide powder, average particle size 1 μm
Expanded graphite, average particle size 15 μm
<Solvent>
Diethylene glycol monobutyl ether, boiling point 231°C
<Crosslinking Agents (D1) and (D2)>
Crosslinking agent (D1):
Trixe, a blocked isocyanate solution manufactured by Baxeneden Chemicals
neBI7982, containing three blocked isocyanate groups per molecule (functionality value 195 mg KOH/g), non-volatile content 70% (solvent (C17): 2-methoxypropanol)
Crosslinking agent (D2):
Glycidylamine manufactured by Nippon Kayaku Co., Ltd., GOT, containing two epoxy groups per molecule (functional value 4
15 mg KOH/g), non-volatile content 100%
<Stretchable film substrate>
Polyurethane film (TPU):
ES85 manufactured by Okura Kogyo Co., Ltd., having a thickness of 100 μm, a tensile elongation at break of 600%, and a Young's modulus of 0.8 MPa (23° C.), was used.

<Production of conductive composition (K1)>
[Example 1]
20.0 parts of the block copolymer (E1) was dissolved in 30.0 parts of diethylene glycol monobutyl ether, and 60.0 parts of the conductive fine particles (f1) and 20.0 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) for stretchable conductive materials.

<Production of conductive compositions (K2) to (K15)>
[Example 2-15]
Conductive compositions (K2) to (K15) 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 2, and a crosslinking agent was further blended as necessary. Note that the numerical values for each material in Table 2 are all in parts by mass.

<Production of Conductive Compositions (L1) to (L9)>
[Comparative Examples 1-9]
Comparative conductive compositions (L1) to (L9) were obtained in the same manner as in Example 1, except that the types and amounts of resin, solvent, and conductive fine particles were changed as shown in Table 3. The numerical values for each material in Table 3 are all in parts by mass.

<Manufacturing of stretchable conductive material>
[Example 16]
Next, the conductive composition (K1) produced in Example 1 was printed on the polyurethane film (TPU) film using a screen printer (Minomat SR5575 semi-automatic screen printer, manufactured by Minoscreen Co., Ltd.) and then heated at 100°C for 30 minutes in a hot air drying oven to obtain a stretchable conductive material equipped with a conductive layer having a rectangular solid pattern with a width of 20 mm, a length of 60 mm, and a thickness of 10 µm, and a linear pattern with a line width of 3 mm, a length of 60 mm, and a thickness of 10 µm.

[Examples 17-30, Comparative Examples 10-18]
A stretchable conductive material was obtained in the same manner as in Example 16, except that the conductive composition used was changed to that shown in Table 4.

<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 obtained test piece 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 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 is the resistance value immediately after 1,000 repeated extension and contraction cycles, and R0 is 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%

(Repeated stretch resistance | Appearance of conductive film)
The appearance of the stretchable conductive material after the 1000 contractions was compared with the state before the test and evaluated according to the following criteria.
+++: No change in appearance at all ++: Very slight cracks or other fissures have occurred on the appearance +: Cracks or other fissures have occurred on at least part of the appearance NG: Cracks or fissures have clearly occurred on the appearance, and the coating is beginning to peel off

(Printability evaluation)
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 and excellent printability +: Rating 5B to 4B, but the coating film suffered cohesive failure and part of the coating film on the surface side came off NG: Rating 3B or lower, poor adhesion and poor printability

The results of each evaluation are shown in Table 4.

From the results of Examples 1 to 30 of the present invention, it was found that the present invention effectively suppresses the occurrence of cracks during stretching, thereby providing a conductive composition and a stretchable conductive material that are excellent in repeated stretch resistance, and further have good electrical conductivity, moist heat resistance, and printability on a stretchable film substrate. These properties make them suitable for use in electronic devices.

Claims (7)

A conductive composition comprising: a block copolymer (E) having a weight average molecular weight of 20,000 or more and 500,000 or less, the block copolymer mainly comprising structural units derived from an ethylenically unsaturated monomer; and conductive fine particles (F),
the block copolymer (E) has a reactive functional group, and the reactive functional group is a mercapto group;
the conductive fine particles (F) contain chain-like silver powder (f1) and flake-like silver powder (f2),
A conductive composition, wherein the content of the conductive fine particles (F) is 60 to 95 mass% relative to the total solid content of the conductive composition, the content of the chain silver powder (f1) among the conductive fine particles (F) is 20 mass% or more and less than 70 mass% relative to the total solid content of the conductive composition , the content of the flaky silver powder (f2) is 1 to 75 mass% relative to the total solid content of the conductive composition, and the tap density of the chain silver powder (f1) is 2.0 g/ ^cm3 or less. 2. The conductive composition according to claim 1 , wherein the structure of the block copolymer (E) is a triblock structure represented by the following formula (1) or a star block structure represented by the following formula (2):
Formula (1)...polymer block A-polymer block B-polymer block A
Formula (2)... [polymer block A-polymer block B] _q X
(In the above formula (1), the glass transition temperature of polymer block A is 20°C or higher, and the glass transition temperature of polymer block B is lower than 20°C. In the above formula (2), the glass transition temperature of polymer block A is 20°C or higher, and the glass transition temperature of [polymer block B] _qX is lower than 20°C, q is an integer of 2 or more and 6 or less, and X is an initiator residue and/or a coupling agent residue, or a derivative thereof.) 3. The conductive composition according to claim 1 , further comprising a crosslinking agent (D) capable of forming a crosslink with the reactive functional group. A conductor comprising the conductive composition according to any one of claims 1 to 3 . A conductor obtained by forming a cured product of the conductive composition according to any one of claims 1 to 3 on a stretchable substrate. A stretchable conductive material comprising the conductor according to claim 4 or 5 . An electronic device comprising the electrical conductor according to claim 4 or 5 , or the stretchable conductive material according to claim 6 .