JP7659376B2 - Conductive composition, and conductor, laminate structure, and electronic component using the same - Google Patents

Description

The present invention relates to a conductive composition, a conductor formed by solidifying the conductive composition, a laminated structure having a layer of the conductor, and an electronic component having the conductor or laminated structure.

A paste-like conductive composition in which metal powder is mixed with an organic binder is used as a material for forming patterned conductors such as electrodes on printed wiring boards. Conventional conductive compositions can be applied in a pattern and then solidified to form the desired conductor, but the resulting conductor generally has high hardness. For this reason, there is a demand for conductive compositions in which the solidified conductor has bending resistance for flexible printed wiring boards.

In addition, with the recent growth of the wearable device field, there is a demand for imparting elasticity to conductors. In particular, the closer the wearable device is to the body, the higher the degree of elasticity required. In response to such demands, for example, a conductive composition has been proposed that uses an elastomer as an organic binder containing metal powder, giving the conductor not only flexibility but also elasticity (Patent Document 1, etc.).

On the other hand, in wearable devices, the materials used in the wiring and electrodes are expensive, so attempts are being made to reuse them, and there is a demand for technology to easily peel and recover conductors from the base substrate. From the standpoint of cost and environmental impact, washing with water is considered to be the most desirable method for peeling conductors from the base substrate, but the conductive composition proposed in Patent Document 1 and elsewhere is not soluble in water, making it difficult to peel the conductors from the base substrate by washing with water.

Incidentally, Patent Document 2 proposes that, in a conductive composition capable of forming electrodes by screen printing, a water-soluble thermosetting resin is used as a binder resin, and that water and a dihydric alcohol solvent are used in combination to dissolve the resin, so that printing tools, containers, etc. to which the conductive composition is attached can be removed by washing with water.

International Publication No. 2015/005204 Japanese Patent Application Publication No. 9-282937

However, in the conductive composition using the water-soluble thermosetting resin as a binder described in Patent Document 2, the resulting conductor does not have sufficient elasticity, and the conductor cannot follow when the wearable device expands and contracts, resulting in cracks and a significant increase in resistance. In addition, although the conductive composition using the water-soluble thermosetting resin as a binder is water-soluble before solidification, it does not dissolve in water in the solidified state (when the solvent has evaporated), and it is considered difficult to peel the conductor from the base substrate. Furthermore, the conductive composition described in Patent Document 2 contains water to dissolve the water-soluble thermosetting resin, and the water in the composition evaporates during the device production process, causing a deterioration in fluidity, and continuous printability and processability are significantly reduced.

Therefore, there is a demand for conductive compositions that are soluble in water even when they are conductors (solidified conductive compositions), can be easily peeled off from the base substrate by washing with water, and have the conductivity and elasticity required for wearable devices, and have excellent continuous printability and processability required for device manufacturing processes.

The object of the present invention is therefore to provide a conductive composition that, even when solidified into a conductor, dissolves in water and can be easily peeled off from the base substrate by washing with water, can produce a conductor that combines the conductivity and elasticity required for wearable devices, and has excellent continuous printability and processability required for device manufacturing processes.

Another object of the present invention is to provide a conductor formed by solidifying such a conductive composition, a laminated structure having a layer of the conductor, and an electronic component having the conductor or laminated structure.

The present inventors have found that by using a water-soluble thermoplastic resin and a block copolymer in combination as binder components in a conductive composition, even if the conductive composition is solidified to form a conductor, it dissolves in water and can be easily peeled off from the base substrate by washing with water, and a conductor having both the conductivity and elasticity required for wearable devices can be obtained, and a conductive composition with excellent printability and processability required for device manufacturing processes can be realized. The present invention is based on such findings. That is, the gist of the present invention is as follows.

[1] An electrochemical device comprising at least (A) a water-soluble thermoplastic resin, (B) a block copolymer, and (C) conductive particles;
The conductive composition, wherein the block copolymer has an SP value within ±5 (J/cm ³ ) ^1/2 of the SP value of the water-soluble thermoplastic resin.
[2] The conductive composition according to [1], wherein the block copolymer (B) has a hard segment block and a soft segment block.
[3] The conductive composition according to [1] or [2], wherein the ratio of the water-soluble thermoplastic resin (A) to the block copolymer (B) is in the range of 15:85 to 95:5 on a mass basis.
[4] The conductive composition according to any one of [1] to [3], wherein the water-soluble thermoplastic resin (A) is at least one resin selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetal, polyethylene oxide, polyethylene glycol, polypropylene glycol, polybutylene glycol, polyoxazoline, and polyamide, and has an SP value of 12 (J/cm ³ ) ^1/2 or more and 15 (J/cm ³ ) ^1/2 or less.
[5] The conductive composition according to any one of [1] to [4], which is used to form a conductor.
[6] A conductor obtained by solidifying the conductive composition according to any one of [1] to [5].
[7] A laminated structure comprising a substrate and a layer made of the conductor according to [6] provided on the substrate.
[8] An electronic component comprising a layer made of the conductor according to [6] or the laminated structure according to [7].

According to the conductive composition of the present invention, by using a combination of (B) the block copolymer and (A) the water-soluble thermoplastic resin as the binder components, even if the conductive composition is solidified to form a conductor, it dissolves in water and can be easily peeled off from the base substrate by washing with water, and a conductor having both the conductivity and elasticity required for wearable devices can be obtained, and a conductive composition with excellent printability and processability required for the device manufacturing process can be realized.

[Conductive composition]
The conductive composition of the present invention contains (A) a water-soluble thermoplastic resin, (B) a block copolymer, and (C) conductive particles, and thus dissolves in water and can be easily peeled off from the base substrate by washing with water, and can provide a conductor or the like that combines conductivity and elasticity. It is not necessarily clear that a conductive composition that is particularly excellent in printability and processability can be obtained by using (B) a block copolymer having an SP value close to that of (A) the water-soluble thermoplastic resin in combination, but it is presumed that this is due to the good compatibility between (A) the water-soluble thermoplastic resin and (B) the block copolymer.

The conductive composition of the present invention can be used to form conductors for wearable devices such as external devices, surface devices, electronic skin devices, and internal devices by utilizing the above-mentioned properties, and when the device is disposed of, expensive conductors used in wiring and electrodes can be dissolved in water and easily peeled off and recovered from the base substrate. Each component contained in the conductive composition of the present invention is described in detail below.

<(A) Water-soluble thermoplastic resin>
The water-soluble thermoplastic resin (A) contained in the conductive composition according to the present invention can be any material that has water solubility and thermoplasticity at room temperature without any particular limitation. For example, a water-soluble thermoplastic resin, a water-soluble protein, a water-soluble block copolymer, etc. can be suitably used.

(A) The water-soluble thermoplastic resin may be any of polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetal, polyethylene oxide, polyethylene glycol, polypropylene glycol, polybutylene glycol, polyoxazoline, polyamide, polyacrylamide, polyacrylic acid, cellulose ether, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and copolymers thereof, and any of the well-known and commonly used resins may be used alone or in combination of two or more.

Among the above-mentioned (A) water-soluble thermoplastic resins, polyvinylpyrrolidone is preferred because it has particularly good compatibility with the (B) block copolymer described below and good solubility in organic solvents, and therefore the resulting conductive composition has excellent printability and processability, and the resulting conductor has excellent elasticity and solubility in water.

(A) The water-soluble thermoplastic resin may be a commercially available product. Examples of commercially available products include Gohsenol manufactured by Mitsubishi Chemical Corporation, Kuraray Poval and Elvanol manufactured by Kuraray Co., Ltd., PEO (polyethylene oxide) manufactured by Sumitomo Seika Chemical Co., Ltd., S-LEC manufactured by Sekisui Chemical Co., Ltd., polyvinylpyrrolidone (powder product) manufactured by Nippon Shokubai Co., Ltd., CMC (carboxymethyl cellulose) and HEC (hydroxyethyl cellulose) manufactured by Daicel FineChem Ltd., and AQ nylon (pellets) manufactured by Toray Industries, Inc.

The weight-average molecular weight of the water-soluble thermoplastic resin (A) is preferably 20,000 to 400,000, and more preferably 50,000 to 300,000. When the weight-average molecular weight is 20,000 or more, the desired effects of toughness and flexibility can be obtained. When the weight-average molecular weight is 400,000 or less, the conductive composition has good viscosity and can achieve higher printability and processability. When the weight-average molecular weight is 50,000 or more, an excellent effect in terms of mitigation against external impacts can be obtained. The weight-average molecular weight means a standard polystyrene equivalent value measured by gel permeation chromatography (GPC).

The SP value of the (A) water-soluble thermoplastic resin is preferably 12 (J/cm ³ ) ^1/2 or more and 15 (J/cm ³ ) ^1/2 or less. When the (A) water-soluble thermoplastic resin has an SP value of 12 (J/cm ³ ) ^1/2 or more, the solubility of the conductor in water is improved, and the conductor is dissolved in water by water washing and easily peeled off from the base substrate. In addition, when the (A) water-soluble thermoplastic resin has an SP value of 15 (J/cm ³ ) ^1/2 or less, the solubility in organic solvents and the compatibility with the (B) block copolymer are improved, and the conductive composition can obtain printability and processability that are easy to apply to device manufacturing processes. The SP value is a value calculated by the Fedors method described in Polymer Engineering and Science, February, 1974, Vol. 14, No. 2, 147-154P, and can be calculated by the following formula.
SP value = (△H/V) ^1/2
(In the formula, ΔH represents the molar heat of vaporization (cal), and V represents the molar volume (cm ³ ).)

<(B) Block Copolymer>
The (B) block copolymer contained in the conductive composition according to the present invention has rubber elasticity at room temperature (25°C). Rubber elasticity means a property that can undergo reversible deformation, such as that seen in rubber-like substances, where the deformation occurs due to an external force and returns to the original shape when the external force is removed, and for example, refers to a property that does not cause breakage or plastic deformation at an elongation of 20% at room temperature. By including such a (B) block copolymer in the conductive composition, it is possible to impart elasticity to the solidified product of the conductive composition. As the block copolymer, any known and commonly used one can be used without any particular restriction as long as it has rubber elasticity at room temperature, but a block copolymer of a hard segment and a soft segment can be preferably used. The block copolymer can be used alone or in a mixture of two or more types.

The above-mentioned (B) block copolymer has low crystallinity and weak intermolecular forces, and therefore has a lower glass transition temperature (Tg) than other rubbers, is flexible and stretchable when mixed with conductive particles, and has good compatibility with (A) water-soluble thermoplastic resins and highly polar solvents such as alcohol, making it preferable. Therefore, the (B) block copolymer is suitable for forming a conductor for wearable devices, and even if the conductive composition is solidified to form a conductor, it dissolves in water and can be easily peeled off from the base substrate by washing with water, and a conductor having both the conductivity and elasticity required for wearable devices can be obtained. In particular, a block copolymer of a hard segment and a soft segment is more suitable. In this specification, the term "hard segment" refers to a segment having a glass transition temperature (Tg) of 30° C. or more, and the term "soft segment" refers to a segment having a Tg of 0° C. or less. The Tg is a value measured by the starting point method in accordance with the provisions of JIS K7121.
However, regarding the heating rate and temperature, the Tg observed at 40° C. or higher is specifically obtained from a stabilized DSC curve obtained by repeatedly heating about 10 mg of a sample from 25° C. to 200° C. at a heating rate of 10° C. per minute in a nitrogen gas atmosphere using a differential scanning calorimeter (DSC-6100, manufactured by Hitachi High-Tech Science Corporation). α-alumina is used as a reference.
The Tg observed at less than 40° C. is obtained from a stabilized DSC curve obtained by repeatedly heating about 10 mg of a sample from −100° C. to 100° C. at a heating rate of 20° C. per minute in a nitrogen gas atmosphere using a differential scanning calorimeter (DSC-6100, manufactured by Hitachi High-Tech Science Corporation). As a reference, α-alumina is used as above.

The ratio of hard segments to soft segments in such block copolymer (B) is preferably in the range of 10:90 to 70:30. If it is within this range, disconnection is less likely to occur when the conductor formed by solidifying the conductive composition expands and contracts, which is preferable. More preferably, it is 10:90 to 40:60.

The above-mentioned block copolymer (B), where the hard segment is represented as X block and X' block, and the soft segment is represented as Y block and Y' block, may be a diblock copolymer of X block-Y block type, a triblock copolymer of X block-Y block-X block type, X block-Y block-X' block type, Y block-X block-Y block type, or a triblock copolymer of Y block-X block-Y' block type, among others. However, from the viewpoint of excellent compatibility with other components and flexibility, a triblock copolymer of X block-Y block-X block type is preferable.

Here, examples of the hard segment in the (B) block copolymer include methyl (meth)acrylate units and styrene units. Examples of the soft segment unit include n-butyl acrylate and butadiene units. The (B) block copolymer is preferably a triblock copolymer of polymethyl (meth)acrylate/poly n-butyl (meth)acrylate/polymethyl (meth)acrylate. Such a (B) block copolymer has excellent compatibility with the (A) water-soluble thermoplastic resin and high polarity solvent, so that the obtained conductive composition has good fluidity and excellent continuous printability and processability. The (B) block copolymer may be used alone or in combination of two or more types. In this specification, (meth)acrylate is a general term for acrylate and methacrylate, and the same applies to other similar expressions.

(B) The block copolymer may be a commercially available product. An example of a commercially available product is an acrylic triblock copolymer produced by living polymerization manufactured by Arkema. Specifically, SBM type represented by polystyrene-polybutadiene-polymethyl methacrylate, MAM type represented by polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate, and MAM N type or MAM A type modified with carboxylic acid or hydrophilic group can be used. Examples of SBM type are E41, E40, E21, and E20 manufactured by Arkema. Examples of MAM type are M51, M52, M53, and M22 manufactured by Arkema. Examples of MAM N type are 52N and 22N. An example of MAM A type is SM4032XM10. Another example of a commercially available product is Kuraly manufactured by Kuraray. This Kuraly is a block copolymer derived from methyl methacrylate and butyl acrylate.

A block copolymer containing the above-mentioned (meth)acrylate polymer block can be obtained, for example, by the method described in JP-T-2007-516326 or JP-T-2005-515281.

The weight-average molecular weight of the (B) block copolymer is preferably 20,000 to 400,000, and more preferably 50,000 to 300,000. When the weight-average molecular weight is 20,000 or more, the desired effects of toughness and flexibility can be obtained. Furthermore, when the weight-average molecular weight is 400,000 or less, the conductive composition has good viscosity, and higher printability and processability can be achieved. Furthermore, when the weight-average molecular weight is 50,000 or more, excellent effects in terms of mitigation against external impacts can be obtained.

The tensile elongation at break of the block copolymer (B) is preferably 100 to 600% as measured by the International Organization for Standardization's international standard ISO 37:2017. When the tensile elongation at break is 100 to 600%, the conductor has better elasticity and better stability of electrical resistance. More preferably, it is 300 to 600%.
Tensile elongation at break (%) = (elongation at break (mm) - initial dimension (mm)) / (initial dimension (mm)) x 100

The above-mentioned (B) block copolymer must have an SP value of ±5 (J/cm ³ ) ^1/2 relative to the SP value of the (A) water-soluble thermoplastic resin. In the present invention, the (B) block copolymer has an SP value of ±5 (J/cm ³ ) ^1/2 relative to the SP value of the (A) water-soluble thermoplastic resin, so that even if the conductive composition is solidified to form a conductor, it dissolves in water and can be easily peeled off from the base substrate by washing with water, and a conductor having both the conductivity and elasticity required for a wearable device can be obtained, and a conductive composition having excellent printability and processability required for the device manufacturing process can be obtained. The SP value of the (B) block copolymer is preferably within the range of ±3 (J/cm ³ ) ^1/2 relative to the SP value of the (A) water-soluble thermoplastic resin. More preferably, the SP value of the block copolymer is 9 (J/cm ³ ) ^1/2 or more and less than 12 (J/cm ³ ) ^1/2 . When the SP value of the block copolymer is 9 (J/ ^cm3 ) ^1/2 or more and less than 12 (J/ ^cm3 ) ^1/2 , the compatibility of the block copolymer (B) with the water-soluble thermoplastic resin (A) and the highly polar organic solvent is further improved, and the conductive composition can obtain flowability that makes it easy to apply to device fabrication processes. The SP value can be calculated in the same manner as above.

The conductive composition of the present invention may be used in combination with other organic binders, such as (A) a water-soluble thermoplastic resin and (B) a water-insoluble thermoplastic resin other than a block copolymer, as long as the effects of the present invention are not impaired.

In addition, a mass ratio of (A) water-soluble thermoplastic resin to (B) block copolymer of 15:85 to 95:5 is preferable in terms of excellent continuous printability. A mass ratio of 30:70 to 80:20 is more preferable.

The water-soluble thermoplastic resin (A) and the block copolymer (B) may contain known additives such as softeners and plasticizers. Examples of the softeners include mineral oil-based softeners and vegetable oil-based softeners. For example, the mineral oil-based softeners include various oils such as paraffin-based process oils, naphthene-based process oils, and aromatic process oils. Examples of the vegetable oil-based softeners include castor oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, pine oil, and tall oil. Examples of the plasticizers include carboxylate esters, phosphate esters, acrylic polymers, and ionic liquids. These softeners and plasticizers may be used alone or in combination. The desired rubber elasticity and extensibility can be adjusted by the amount of the softener or plasticizer added.

<(C) Conductive particles>
The conductive particles (C) used in the conductive composition of the present invention can be any conventional material used in conductive compositions, such as carbon particles such as graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, metal particles such as copper particles, nickel particles, and silver particles, metal carbides such as WC, B ₄ C, ZrC, NbC, MoC, TiC, and TaC, metal nitrides such as TiN, ZrN, and TaN, and metal silicides such as WSi ₂ and MoSi _2. These may be used alone or in combination of two or more. Among the above-mentioned conductive particles (C), silver particles and ketjen black can be preferably used.

(C) The particle shape of the conductive particles is not particularly limited, and examples of such shapes include spherical, needle-like, oval-spherical, flake-like, scale-like, and irregular shapes.

(C) When silver powder is used as the conductive particles, it is preferable to use silver particles having an average primary particle size of 1.0 μm or less, preferably 0.1 to 1.0 μm, and an apparent porosity of 50 to 95%, preferably 60 to 95%. The average primary particle size of silver powder means the average particle size of the silver powder observed in powder form at a magnification of 10,000 times with a scanning electron microscope, randomly extracting 10 primary particles, and measuring their particle size. The apparent porosity of silver powder is an index representing the state of an aggregate structure (secondary particles) in which the primary particles of silver powder are connected to each other to have an appropriate amount of voids, and can be measured as follows.
That is,
The density of silver is ρ ₀ (g/cm ³ ),
When a load of 1 kg is applied to a silver powder having a mass M (g), and the volume of the silver powder is V (cm ³ ), the apparent density ρ (g/cm ³ ) is given by
ρ = M/V
From the apparent density, the apparent porosity (P) can be calculated by the following formula.
P=(1-ρ/ρ ₀ )×100
The density ρ ₀ of silver is 10.49 g/cm ³ , and the silver powder volume V under a 1 kg heavy load is the silver powder volume one hour after the load was applied.

In addition, in the present invention, the shape of the primary particles of the silver powder is preferably approximately spherical. The shape of the primary particles of the silver powder is not limited to being approximately spherical, and it goes without saying that silver powder having a shape other than approximately spherical may be included as long as it does not impair the effects of the present invention.

The silver powder that can be suitably used in the present invention preferably has a DBP oil absorption of 30 to 200 ml/100 g as measured in accordance with JIS K 6217-4:2017.

In the present invention, when Ketjen black is used as the conductive particles (C), from the viewpoints of film-forming properties, conductivity, fluidity, and stability of electrical resistance against expansion and contraction deformation, it is preferable to use particles having an apparent porosity of 50 to 95%, preferably 60 to 95%, and a DBP oil absorption of 300 to 600 ml/100 g. The apparent porosity and DBP oil absorption of Ketjen black can be measured in the same manner as for silver powder described above.

The amount of the (C) conductive particles in the conductive composition can be in the range of 5 to 90% by mass based on the non-volatile components of the conductive composition. More specifically, when silver powder is used as the (C) conductive particles, the amount of the (C) conductive particles is preferably 50 to 90% by mass, more preferably 60 to 85% by mass, based on the non-volatile components of the conductive composition. Furthermore, when Ketjen black is used as the (C) conductive particles, the amount of the (C) conductive particles is preferably 5 to 40% by mass, more preferably 20 to 30% by mass, based on the non-volatile components of the conductive composition.

By mixing the conductive particles (C) with the above characteristics in the above range, it is possible to obtain a conductor that has a low initial electrical resistance before stretching, has excellent electrical conductivity with stable electrical resistance even when stretched, and can be easily peeled off by washing with water.

In the present invention, in order to adjust the affinity between the (C) conductive particles and the (A) water-soluble thermoplastic resin or (B) block copolymer, surface-treated (C) conductive particles or a dispersant may be used. Examples of surface treatment of the (C) conductive particles include a wet method in which the (C) conductive particles are put into a solution containing a dispersant and stirred, and a dry method in which a solution containing a dispersant is sprayed onto the (C) conductive particles while stirring them. Furthermore, a surfactant may be used in combination for surface treatment. There are no particular restrictions on the amount or order of blending the dispersant, but the amount of blending may be 0.01 to 30 mass% relative to the (C) conductive particles, and the order of blending may be a method in which the (B) block copolymer and the dispersant are mixed and then the (C) conductive particles are blended.

As the dispersant used in the above-mentioned surface treatment and blending, a conventionally known dispersant can be used. For example, when the conductive particles (C) are silver powder, protective colloids such as fatty acids, organic metals, and gelatin can be used. However, in consideration of the risk of impurities being mixed in and the improvement of the adsorption to the hydrophobic group, fatty acids or their salts are preferable. In addition, as the dispersant, fatty acids or their salts emulsified with a surfactant can be used. Specifically, fatty acids having 6 to 24 carbon atoms, such as stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and linolenic acid, can be more preferably used. These fatty acids are considered to have little adverse effect on the wiring layer and electrodes using the conductive composition. The above-mentioned fatty acids may be used alone or in combination.

When the (C) conductive particles are Ketjen black, the dispersant may be a phosphoric acid ester having an acidic group or a basic group or both, an acrylic copolymer, a polyamine, a polyurethane, a polyester, a polyacrylate, or a phosphate salt or an alkyl ammonium salt thereof. The above-mentioned dispersants may be used alone or in combination.

<Other ingredients>
The conductive composition of the present invention may contain an organic solvent for adjusting the composition or for adjusting the viscosity for application to a substrate.

Such organic solvents include ketones, aromatic hydrocarbons, glycol ethers, glycol ether acetates, esters, alcohols, aliphatic hydrocarbons, and petroleum-based solvents. More specifically, the organic solvents include ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene; glycol ethers such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, and triethylene glycol monoethyl ether; esters such as ethyl acetate, butyl acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, and propylene glycol butyl ether acetate; alcohols such as ethanol, propanol, ethylene glycol, propylene glycol, butylene glycol, and terpineol; aliphatic hydrocarbons such as octane and decane; and petroleum-based solvents such as petroleum ether, petroleum naphtha, hydrogenated petroleum naphtha, and solvent naphtha. These organic solvents are used alone or as a mixture of two or more kinds. Among these, diethylene glycol monoethyl ether acetate and terpineol are preferred from the viewpoints of the solubility, coatability, and continuous printability of the binder resin.

The boiling point of the organic solvent used in the present invention is preferably 150°C or higher, and more preferably 200°C or higher. By using an organic solvent with the above boiling point, it is possible to prevent the organic solvent from volatilizing during the device fabrication process, which would otherwise cause a decrease in the continuous printability and processability of the conductive composition.

The conductive composition of the present invention may further contain a thermosetting component. Examples of thermosetting components include polyester resins (urethane-modified, epoxy-modified, acrylic-modified, etc.) that can form a film by increasing the molecular weight through a curing reaction and by forming crosslinks, epoxy resins, urethane resins, phenolic resins, melamine resins, vinyl resins, silicone resins, and blocked isocyanates.

The conductive composition of the present invention may contain other components as long as the effects of the present invention are not impaired. For example, it may contain additives such as a coupling agent and a photopolymerization initiator.

The conductive composition of the present invention can be produced, for example, by kneading the resin component dissolved in a solvent with the conductive particles (C) described above. Examples of the kneading method include a method using a stirring and mixing device such as a roll mill. Specifically, a resin solution with a solid content of 50% by mass is prepared by dissolving the resin component in an organic solvent, and the conductive particles (C) are mixed into this resin solution, pre-mixed with a stirrer, and then kneaded with a three-roll mill to obtain a conductive composition. Depending on the type of resin component used and the mixing ratio of the organic solvent, a liquid conductive composition or a paste-like (semi-solid) conductive composition can be produced.

The conductive composition of the present invention has no particular limit to its viscosity, but it is preferably 100 to 5000 dPa·s, and more preferably 200 to 1000 dPa·s. By setting the viscosity within this range, a conductive composition with excellent printability and processability required for device manufacturing processes can be obtained.

In the present invention, the conductive composition as described above can be applied in a pattern onto a substrate and then heat-treated to form a conductor. Examples of the heat treatment include drying and heat-curing.

In this way, the conductive composition of the present invention can provide a conductor that is soluble in water, can be peeled off from the base substrate by washing with water, and has excellent elasticity and electrical resistance stability.

<Laminated structure having a conductor and a conductor layer, and uses thereof>
The conductive composition described above can be solidified to form a conductor. For example, a coating film made of the conductive composition can be formed, dried, and solidified to form a conductor layer. The conductive composition is solidified by drying or heat treating the conductive composition. Examples of heat treatment include hot air drying or heat curing. Prior to the heat treatment, molding may be performed. For example, the conductive layer can be obtained by applying the conductive composition to a substrate so as to have a desired shape, and then solidifying the composition. The conductive layer may have various shapes depending on the application. For example, the conductive layer can be suitably applied to conductor circuits and wiring.

When manufacturing a conductor circuit, the process includes a pattern formation step of printing or applying the conductive composition onto a substrate to form a coating pattern, and a step of solidifying the patterned coating. A masking method or a method using a resist can be used to form the coating pattern.

Examples of pattern formation processes include printing methods and dispensing methods. Examples of printing methods include gravure printing, offset printing, and screen printing. When forming fine circuits, screen printing is preferred. Gravure printing and offset printing are suitable as large-area coating methods. The dispensing method is a method in which the amount of conductive composition applied is controlled and an extrusion pattern is formed from a needle, and is suitable for forming partial patterns such as earth wiring, and for forming patterns on uneven areas.

The substrate to which the conductive composition is applied can be any electrically insulating material, without any particular limitations. Examples of such substrates include paper-phenolic resin, paper-epoxy resin, glass cloth-epoxy resin, glass-polyimide, glass cloth/nonwoven cloth-epoxy resin, glass cloth/paper-epoxy resin, synthetic fiber-epoxy resin, copper-clad laminates of all grades (such as FR-4) using composites such as fluororesin, polyethylene, polyphenylene ether, and polyphenylene oxide-cyanate ester, sheets or films made of plastics such as polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate, polyimide, polyphenylene sulfide, and polyamide, sheets or films made of crosslinked rubbers such as urethane, silicone rubber, acrylic rubber, and butadiene rubber, and sheets or films made of thermoplastic elastomers such as polyesters, polyurethanes, polyolefins, and styrene block copolymers. Among these, not only flexible materials but also elastic materials (e.g., rubber, thermoplastic elastomers, urethane, etc.) can be used as substrates to make it possible to apply the conductor to applications such as those described below. As a material having elasticity, the same material as the block copolymer (B) described above can be used.

<Laminated structure>
The above-mentioned conductor can be made into a laminated structure by forming a plurality of layers. There is no particular limitation on the method of forming the laminated structure, but for example, a conductor obtained by solidifying a conductive composition may be bonded by heat, pressure, or both, or a conductive composition may be applied onto a conductor and then solidified. The laminated structure may include layers other than the above-mentioned conductor, such as a metal layer, an insulating layer, a protective layer, an adhesive layer, an adhesive layer, and a gap layer.

<Electronic Components>
An electronic component can be formed using the above-mentioned conductor or laminate structure as a component. There are no particular limitations on the structure, formation method, or use of the electronic component as long as the electronic component has the above-mentioned conductor or laminate structure as a component, but examples of uses include sensors, actuators, capacitors, inductors, transistors, converters, thermistors, connectors, transformers, capacitors, diodes, regulators, motors, antennas, switches, etc., and electronic components that combine a plurality of these uses are also acceptable.

The conductor obtained by solidifying the conductive composition according to the present invention has excellent stability of electrical resistance even when repeatedly stretched or stretched as described above, and therefore can be suitably used for forming conductors for wearable devices such as external devices, surface devices, electronic skin devices, and internal devices, in addition to conductor circuits and wiring. The conductor layer can also be applied to the electrodes of flexible printed circuit boards. Furthermore, the conductive composition of the present invention is also suitable for forming conductor layers such as actuator electrodes. In addition, since the formed conductor can be dissolved in water, it can be peeled off from the base substrate by washing with water. Therefore, when disposing of the device, the expensive (C) conductive particles can be easily recovered, which is economically rational and has a small environmental impact. It is also suitable for forming conductors with designs that were previously difficult to realize due to insufficient stretchability and stability of electrical resistance. For example, the following can be mentioned.

<Wearable biosensor>
The conductor of the present invention can be applied as a wiring material for a wearable biosensor that is worn to acquire and transmit action potentials/biological information generated by animals and plants, including humans. The sensor must be attached to a location that is in close contact with or close to the surface tissue of animals and plants, including humans, but the surface tissue expands and contracts. Conventional hard and flexible substrates cannot follow the expanding and contracting attachment location, and the location where the sensor can be attached is limited, resulting in limited biological information. According to the conductor of the present invention, the sensor wiring material can be applied to the surface tissue of animals and plants, including humans, so that a wearable biosensor can be made that can be attached to a location where expansion and contraction occurs.

The wiring used in wearable biosensors can be formed by screen printing or dispensing methods, which allows for fine signal wiring, which is thought to contribute to the miniaturization of sensor devices.

<Wiring materials for smart textiles>
In recent years, the field of so-called "smart textiles" using woven fabrics as sensors is expanding. A wiring board or sensor in which wiring is formed on a stretchable substrate that can be thermocompressed using the conductor of the present invention has excellent stability of electrical resistance when stretched, so that by attaching it to the surface of a stretchable woven fabric, it becomes possible to develop a woven fabric with electronic device functions, i.e., a smart textile. As a smart textile, functions such as a pressure-sensitive sensor, a touch sensor, and an antenna wiring can be imparted to the woven fabric.

<Wiring for 3D molded products>
In conventional plastic molded products for electronic device housings and the like using the FIM (film insert molding) method, a plastic film such as polycarbonate is used as a base substrate, which is printed with a design and then heat-pressed. The conductor wiring of the present invention, which is made of a laminated structure having a conductor provided on an elastic substrate, has the characteristics of being free from disconnection during stretching and suppressing changes in resistance value, so that the conductor wiring can be formed during design printing of the plastic molded product, and then molded by heat pressing (which causes partial stretching) to realize an electronics device with built-in 3D wiring.

In addition, by performing heat pressing using a stretchable base material such as the block copolymer (B) described above, it is possible to realize a stretchable electronic device with soft wiring inside a soft housing. This device can be suitably used as a pressure sensor, touch sensor, or antenna wiring, etc.

<Stretchable and Deformable Wiring Sheet or Wiring Board>
The conductor wiring made of a laminated structure having a conductor layer of the present invention provided on an elastic substrate can be used as a wiring board sheet that can be stretched and deformed. For example, such a conductor wiring can be attached to the surface of an object having a three-dimensional shape such as a molded product while being stretched or deformed without causing disconnection of the wiring. Therefore, the laminated structure having a conductor layer of the present invention provided on an elastic substrate can be suitably used for pressure-sensitive sensors, touch sensors, or antenna wiring.

<Flexible Wiring Sheet or Wiring Board>
In flexible wiring sheets or wiring boards using conventional conductive pastes, when extreme bending such as bending with a fingernail occurs, the wiring breaks. In this respect, when the conductor of the present invention is used, since it is a conductive material with elongation properties, it can accommodate bending in areas that could not be handled with conventional conductive pastes, and it is possible to realize a flexible wiring sheet or wiring board in which the wiring does not break even when bending with a fingernail.

The present invention will now be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

<(A) Preparation of Water-Soluble Thermoplastic Resin>
The following two types of water-soluble thermoplastic resin (A) for preparing the conductive composition were prepared.
Resin A: Polyvinylpyrrolidone (Polyvinylpyrrolidone K-30, manufactured by Nippon Shokubai Co., Ltd., SP value 13 (J/cm ³ ) ^1/2 , weight average molecular weight 100,000)
Resin B: Polyethylene oxide (PEO-1, manufactured by Sumitomo Seika Chemicals Co., Ltd., SP value 13 (J/cm ³ ) ^1/2 , weight average molecular weight 200,000)
Each resin was dissolved in Terpineol C manufactured by Nippon Terpene Co., Ltd. or water to prepare a resin solution having a solid content of 33% by mass. The weight average molecular weight of each resin was measured by a GPC method (polystyrene standard).
For comparison, a water-soluble thermosetting resin (Shonol BRL-149, manufactured by Aica Kogyo Co., Ltd., SP value 12 (J/cm ³ ) ^1/2 ) was also prepared.

<(B) Preparation of Block Copolymer>
As the block copolymer (B) for preparing the conductive composition, the following was prepared.
Block copolymer: acrylic block copolymer (M52 manufactured by Arkema, SP value 10 (J/cm ³ ) ^1/2 , weight average molecular weight 50,000)
The above block copolymer was dissolved in diethylene glycol monoethyl ether acetate to prepare a resin solution having a solid content of 50% by mass.
For comparison, an amorphous polyester polyol (Vylon-290, manufactured by Toyobo Co., Ltd., SP value 11 (J/cm ³ ) ^1/2 , weight average molecular weight 50,000, Tg = 72°C), which is a non-block copolymer at room temperature, was prepared. The weight average molecular weights of the block copolymer and non-block copolymer were measured by the GPC method (polystyrene standard).

<Calculation of SP value>
The SP values of the above-mentioned resins A and B, the water-soluble thermosetting resin, the block copolymer, and the amorphous polyester polyol are values calculated by the Fedors method described in Polymer Engineering and Science, February, 1974, Vol. 14, No. 2, pp. 147-154, and were calculated according to the following formula.
SP value = (△H/V) ^1/2
(In the formula, ΔH represents the molar heat of vaporization (cal), and V represents the molar volume (cm ³ ).)
The absolute value of the difference in SP value (ΔSP value) between the water-soluble thermoplastic resin (A) and the block copolymer (B) is as shown in Table 1 below.

<(C) Preparation of Conductive Particles>
As the conductive particles (C) for preparing the conductive composition, the following two types of conductive particles were prepared.
Conductive particle A: Silver powder (Sylvest AgC-G, manufactured by Fukuda Metal Foil and Powder Co., Ltd., average primary particle size 0.5 μm, apparent porosity 83%, DBP oil absorption 90 ml/100 g)
Conductive particles B: Carbon black (EC300J, manufactured by Lion Specialty Chemicals Co., Ltd., average primary particle diameter 39.5 μm, apparent porosity 91%, DBP oil absorption 360 ml/100 g)

The average primary particle diameter of each of the conductive particles A and B was obtained by observing the conductive particles A and B with a scanning electron microscope at a magnification of 10,000 times, randomly extracting 10 primary particles, measuring their particle diameters, and calculating the average value. The apparent porosity was calculated from the above formula: P = (1 - ρ/ρ ₀ ) x 100, assuming that the density ρ ₀ of the conductive particles A was 10.49 g/cm ³ and the density of the conductive particles B was 2.2 g/cm ^3. Furthermore, the DBP oil absorption was measured in accordance with JIS K 6217-4:2017.

<Preparation of Conductive Composition>
The conductive particles (C) and each resin solution were mixed according to the composition shown in Table 1 below, pre-mixed with a mixer, and then mixed with a three-roll mill (EXAKT50, manufactured by EXAKT) while varying the conditions such as the number of times of mixing, the rotation speed, and the roll spacing of the three-roll mill, to obtain a conductive composition according to the embodiment. The numerical values of the amounts mixed in Table 1 represent parts by mass converted into solid content.

<Evaluation of Conductive Composition>
(1) Measurement of Continuous Printability When each conductive composition was applied to a PET film substrate (Lumirror manufactured by Toray Industries, Inc.) by screen printing, the number of sheets that could be continuously printed was measured. The continuous printability was evaluated based on the following evaluation criteria.
⊚: Continuous printing of 100 sheets or more was possible. ◯: Continuous printing of 10 sheets or more but less than 100 sheets was possible. ×: Printing was impossible due to separation of the resin component, clogging of the plate, or bleed-through of the conductive composition. The evaluation results are shown in Table 1.

(2) Measurement of specific resistance Each conductive composition was applied to a substrate by screen printing and heat-treated at 80°C for 30 minutes to obtain a conductor. A PET film (Lumirror, manufactured by Toray Industries, Inc.) was used as the substrate. The resistance value at both ends of the obtained conductor was measured by a four-terminal method, and the line width, line length and thickness were also measured to obtain the specific resistance (volume resistivity). The measurement results were as shown in Table 1. In addition, when a conductor could not be formed and measurement could not be performed due to the conductive composition being repelled by the screen plate or the conductive composition causing clogging of the drying screen plate during printing, etc., * was entered.

(3) Measurement of Elasticity Each conductive composition was applied to a substrate by screen printing and heat-treated at 80° C. for 30 minutes to form a conductor having a line width of 1 mm, a thickness of 20 μm, and a length of 40 mm on the substrate. A urethane substrate (manufactured by Okura Kogyo Co., Ltd., ES85, thickness 100 μm) with an elastic modulus of 30 MPa was used as the substrate.
The substrate on which the conductor was formed was stretched at a speed of 5 mm/sec to an elongation degree of 20%, and then held in that state for 15 seconds to measure the resistivity (volume resistivity) of the conductor. The conductivity of the conductor when stretched was evaluated based on the following evaluation criteria.
◎: The resistivity at 20% elongation is 10 times or less than the initial value (when not elongated). ○: The resistivity at 20% elongation is more than 10 times and less than 100 times the initial value (when not elongated). ×: The resistivity at 20% elongation is more than 100 times the initial value (when not elongated) (including breakage).
The evaluation results are shown in Table 1. In addition, when a conductor could not be formed and measurement was not possible due to reasons such as the conductive composition being repelled by the screen or the conductive composition causing clogging of the drying screen during printing, the result is marked with *.

(4) Measurement of solubility in water Each conductive composition was applied to a substrate by screen printing and heat-treated at 80°C for 30 minutes to obtain a conductor. A PET film (Lumirror, manufactured by Toray Industries, Inc.) was used as the substrate. The obtained conductor was immersed in 40°C water for 30 seconds, and the state of change was visually observed. The solubility of the conductor in water was evaluated based on the following evaluation criteria.
: Conductor collapsed naturally : Conductor collapsed when touched with a finger after the test × : Conductor remained even when touched with a finger after the test The evaluation results are as shown in Table 1. Note that in cases where a conductor could not be formed and measurement was not possible due to reasons such as the conductive composition being repelled by the screen or the conductive composition drying during printing causing clogging of the screen, the mark * was entered.

As is clear from the results shown in Table 1, the conductive compositions (Examples 1 to 6) containing (A) a water-soluble thermoplastic resin, (B) a block copolymer, and (C) conductive particles are soluble in water and can be easily peeled off from the base substrate by washing with water, and can produce conductors that combine the conductivity and elasticity required for wearable devices.The conductive compositions have good compatibility with each other, and therefore have excellent continuous printability, which is required for the manufacturing process.

On the other hand, in the conductive composition using a non-block copolymer instead of the (B) block copolymer (Comparative Example 1), it is presumed that the compatibility between the (A) water-soluble thermoplastic resin and the non-block copolymer is low, and it is understood that this is not suitable for preparing a conductive composition. In addition, it is understood that the conductive compositions containing only either the (A) water-soluble thermoplastic resin or the (B) block copolymer as a binder (Comparative Examples 2 and 3) cannot achieve both the elasticity and solubility of the conductor. In addition, it is understood that the conductive composition containing a water-soluble thermosetting resin instead of the (A) water-soluble thermoplastic resin (Comparative Example 4) cannot obtain the elasticity and solubility of the conductor.

Claims (2)

(A) a water-soluble thermoplastic resin (excluding (B) a block copolymer), (B) a block copolymer, and (C) a conductive particle;
the block copolymer (B) has an SP value of ±5 (J/cm ³ ) ^1/2 of the SP value of the water-soluble thermoplastic resin (A);
the ratio of the water-soluble thermoplastic resin (A) to the block copolymer (B) is in the range of 15:85 to 95:5 on a mass basis,
The conductive composition, wherein the blending amount of the conductive particles (C) is in the range of 5 to 90 mass % based on the non-volatile components of the conductive composition. The conductive composition according to claim 1, wherein the block copolymer (B) has a hard segment block and a soft segment block.