JPWO2018235734A1 - Conductive composition, conductor using the same, and laminated structure - Google Patents

Abstract

[Problem] To provide a conductive composition capable of obtaining a conductor having excellent stability of electric resistance even when expansion and contraction are repeated or expansion is increased. [Solution] A conductive composition containing an elastomer and silver powder, wherein the silver powder is surface-treated, and the silver powder has an average primary particle diameter of 1.0 μm or less and an apparent porosity. 50 to 95%, and the cumulative 95% particle diameter (D95 particle diameter) in the particle size distribution of the secondary particles of the silver powder in the conductive composition is 3.0 to 25.0 μm. ..

Description

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

  As a material for forming a patterned conductor such as an electrode of a printed wiring board or the like, a paste-like conductive composition in which a metal powder is mixed with an organic binder is used. According to the conventional conductive composition, a desired conductor can be formed by applying it in a pattern and then solidifying it, but the obtained conductor generally has high hardness. Therefore, in a flexible printed wiring board, there is a demand for a conductive composition in which a solidified conductor has bending resistance.

  On the other hand, along with the recent growth in the field of wearable devices, it is required to impart elasticity to the conductor. In particular, a wearable device having a higher degree of close contact with the body is required to have higher elasticity.

  In response to such a demand, for example, a conductive composition has been proposed in which an elastomer is used as an organic binder containing a metal powder, and a conductor has stretchability as well as flexibility (see Patent Document 1). etc).

International Publication No. 2015/005204 Pamphlet

  However, even a conductor using the above-mentioned conductive composition may repeatedly expand and contract, or the resistance value may sharply increase when the conductor is stretched to some extent, or in some cases, the wire may be broken. Therefore, there is a demand for a conductive composition capable of obtaining a conductor having excellent stability of electric resistance even when it is repeatedly stretched and stretched.

  Therefore, an object of the present invention is to provide a conductive composition capable of obtaining a conductor excellent in stability of electric resistance even when repeated stretching and expansion are increased.

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

  The inventors repeated expansion and contraction by making a surface-treated silver powder having a specific average primary particle diameter, which is a conductive metal powder to be mixed with an elastomer, into a specific agglomerated state in the composition. It has been found that a conductive composition that can obtain a conductor having excellent stability of electric resistance can be realized even in the case where it is greatly expanded to 400% or more. The present invention is based on such findings.

That is, the conductive composition of the present invention is a conductive composition containing an elastomer and silver powder,
The silver powder is surface-treated,
The silver powder has an average primary particle size of 1.0 μm or less and an apparent porosity of 50 to 95%,
In the conductive composition, the cumulative 95% particle size (D95 particle size) in the particle size distribution of the secondary particles of the silver powder is 3.0 to 25.0 μm.

  In the embodiment of the present invention, it is preferable that the silver powder is contained in an amount of 60 to 95 mass% in terms of solid content with respect to the entire conductive composition.

  Further, a conductor according to another embodiment of the present invention is obtained by solidifying the above-mentioned conductive composition.

  A laminated structure according to another embodiment of the present invention has the above-mentioned conductor layer on a base material.

  An electronic component according to another embodiment of the present invention includes the conductor layer or the laminated structure.

  According to the conductive composition of the present invention, as the conductive metal powder to be blended with the elastomer, the surface-treated silver powder having a specific average primary particle diameter is brought into a specific agglomerated state in the composition. Even when the expansion and contraction are repeated or the expansion is increased, a conductor having excellent stability of electric resistance can be obtained.

  The conductive composition of the present invention contains an elastomer and silver powder, and by blending a specific silver powder in the elastomer, the electrical resistance is not limited to the case of bending but also the case of stretching or greatly expanding. It is possible to obtain a conductor having excellent stability. As a result, the conductive composition of the present invention can be suitably used for forming a conductor for a wearable device such as an extracorporeal device, a body surface device, an electronic skin device, and an internal device by utilizing such characteristics. it can. Hereinafter, each component contained in the conductive composition of the present invention will be described in detail.

<Silver dust>
The silver powder constituting the conductive composition of the present invention is surface-treated and has an average primary particle diameter of 1.0 μm or less, preferably 0.1 to 1.0 μm and an apparent porosity of 50 to 50 μm. 95%, preferably 60 to 95% is used. When such silver powder is used, the expansion and contraction are repeated and the expansion is increased by forming an aggregated state in which the particle size distribution of the secondary particles of the silver powder in the composition is within the range described below. Also, the stability of electric resistance can be maintained. In the present invention, the average primary particle diameter of the silver powder means that the silver powder in a powder state is observed with a scanning electron microscope at a magnification of 10,000 times, and 10 primary particles are randomly extracted. It means the average value of the particle diameters when the particle diameters are measured. Further, the apparent porosity of silver powder is an index showing the state of an agglomeration structure (secondary particles) in which primary particles of silver powder are connected to each other and have appropriate voids, and can be measured as follows. it can.
That is,
The density of silver is ρ ₀ (g / cm ³ ),
When the volume of silver powder when a load of 1 kg is applied to the silver powder of mass M (g) is V (cm ³ ), the apparent density ρ (g / cm ³ ) is
ρ = M / V
The apparent porosity (P) can be calculated from the apparent density by the following formula.
P = (1-ρ / ρ ₀ ) × 100
The silver density ρ ₀ is 10.49 g / cm ³ , and the silver powder volume V under a heavy load of 1 kg is the silver powder volume 1 hour after the load is applied.

  In the present invention, the above-mentioned apparent porosity P is an index representing the state of aggregation of the primary particles of the silver powder before mixing with the elastomer. When a constant load is applied to the silver powder, the compression of the filled silver powder proceeds. At this time, when the silver powder is not in an aggregated state but the primary particles are separated from each other, the apparent porosity after compression is small. On the other hand, when the silver powder forms an aggregated state, the apparent porosity increases due to the voids inside the aggregate. Thereby, the aggregation state of the primary particles of the silver powder can be evaluated as the apparent porosity.

  Further, in the present invention, the shape of the silver powder primary particles is preferably substantially spherical, and the substantially spherical primary particles are present in the conductive composition in the form of secondary particles in which they are three-dimensionally and randomly linked. Thus, as described above, the silver powder can follow the extension deformation of the elastomer in the solidified material of the conductive composition without reducing the contact points between the primary particles even when the solidified material of the conductive composition greatly expands.

  The shape of the primary particles of the silver powder is not limited to the one having a substantially spherical shape, and it goes without saying that a silver powder having a shape other than a substantially spherical shape may be included within a range not impairing the effects of the present invention. .

  As the silver powder having an average primary particle diameter and an apparent porosity in the above range, a commercially available one can be used, and the commercially available silver powder can be a specific average primary particle using a classifier or the like. It may be obtained by classifying into a silver powder having a diameter and an apparent porosity.

  The silver powder used in the present invention (that is, the silver powder before being prepared as a conductive composition) preferably has an average secondary particle diameter of 5.0 to 40.0 μm, more preferably more than 10.0. ˜40.0 μm, and more preferably more than 15.0 to 40.0 μm. When the average secondary particle diameter is within the above range, when the silver powder is dispersed in the composition, it becomes easy to adjust the particle diameter within a specific range as described later. The average secondary particle size of the silver powder before being prepared as a conductive composition means the average value (D50) of the particle sizes of the silver powder in a powder state measured by a laser diffraction scattering type particle size distribution measuring method. To do.

  The silver powder (silver powder before being prepared as a conductive composition) used in the present invention has a DBP oil absorption of 30 to 200 ml / 100 g measured according to JIS K 6217-4 (2017). Is preferred. The DBP oil absorption of silver powder means a value obtained by measuring the amount of dibutyl phthalate absorbed by 100 g of silver powder in accordance with JIS K 6217-4, and in the present invention, the degree of connection of primary particles of silver powder. It is used as an index showing the degree of aggregation. By using the silver powder having the DBP oil absorption in the above range, it becomes easy to adjust the particle diameter to a specific range as described later when the silver powder is dispersed in the composition.

  The conductive composition of the present invention is obtained by dispersing the above-mentioned silver powder in an elastomer, and the cumulative 95% particle size (D95 particle size) in the particle size distribution of the secondary particles of the silver powder in the conductive composition. Is in the range of 3.0 to 25.0 μm. The present invention is a silver powder having a surface-treated specific average primary particle diameter as described later, and in a specific aggregation state (that is, specific apparent porosity), preferably a specific DBP oil absorption amount. Controlling the aggregation state of the silver powder in the composition when the silver powder is mixed with the elastomer to form a composition (that is, the cumulative 95% particle size in the particle size distribution of the secondary particles is within a specific range). According to the present invention, the conductivity of the cured product obtained by solidifying the conductive composition is improved, and even when the expansion and contraction are repeated or the expansion is made large, it is possible to obtain a conductor having excellent stability of electric resistance. it can.

  The silver powder constituting the conductive composition of the present invention, even when mixed or kneaded with an elastomer, while maintaining a constant agglomerated state in which a plurality of primary particles are three-dimensionally and randomly linked, in the conductive composition It is thought to be dispersed. That is, when silver powder having a specific apparent porosity is mixed or kneaded with the elastomer, among the secondary particles obtained by aggregating the primary particles of the silver powder, the secondary particles having a large particle size collapse and become small to some extent. By adjusting so that the cumulative 95% particle size in the particle size distribution of the secondary particles at that time is 3.0 to 25.0 μm, apparent voids appropriately remain in the secondary particles of the silver powder. It is considered that since the elastomer enters the above, the effect peculiar to the present invention can be exhibited.

  Although the detailed mechanism by which the effect peculiar to the present invention is exhibited is not clear, it is considered as follows. That is, a silver powder having a surface-treated average primary particle diameter of 1.0 μm or less as described below, and an apparent porosity of 50 to 95%, preferably a DBP oil absorption amount in the above range. When the composition is prepared by blending and dispersing in an elastomer, by appropriately disintegrating the aggregation of the silver powder and stirring or kneading the composition so that the D95 particle diameter becomes 3.0 to 25.0 μm. In the secondary particles of silver powder, apparent voids are appropriately present, and the elastomer sufficiently enters the voids, so that the contact points between the primary particles are reduced even when the solidified material of the conductive composition is greatly expanded. It is considered that the silver powder can follow the elongation deformation of the elastomer without doing so.

  The cumulative 95% particle size (D95 particle size) in the particle size distribution of the secondary particles of the silver powder in the conductive composition is the laser diffraction scattering particle size of the conductive composition obtained by mixing or kneading the silver powder and the elastomer. It can be measured by a distribution measuring method. Specifically, propylene glycol monomethyl ether acetate is used as the measurement solvent, the conductive composition is diluted with the measurement solvent (propylene glycol monomethyl ether acetate) to 3000% by mass, and the secondary particles of silver powder are separated with a spatula or the like. Immediately after stirring appropriately so as not to disintegrate, the particle size distribution was measured immediately with a measurement range of 0.020 μm to 1000.00 μm, a particle refractive index of 1.33, and a solvent refractive index of 1.40. The value calculated as the cumulative 95% particle diameter of is defined as the D95 particle diameter.

  As described above, according to the conductive composition of the present invention, the silver powder surface-treated so that the D95 particle diameter is within the above range is dispersed in the conductive composition, and thus the conductive composition is formed. It is considered that even when the solidified product repeats expansion and contraction or greatly expands, it is possible to obtain a conductor having excellent stability of electric resistance.

  When ordinary silver powder is dispersed in an elastomer, the aggregated state of the silver powder in the conductive composition collapses too much, so when the solidified material of the conductive composition is greatly expanded, the primary deformation of the silver powder is caused by this expansion deformation. The points of contact between particles are reduced. In this respect, according to the characteristic configuration of the present invention as described above, apparent voids are appropriately present in the secondary particles of the silver powder in the conductive composition, and the elastomer sufficiently enters the voids. It is considered that the silver powder can follow the elongation deformation of the elastomer without reducing the contact points between the primary particles even when the solidified product of such a conductive composition is greatly expanded.

  In the conductive composition of the present invention, in order for the silver powder to be present in the form as described above, the silver powder has a high affinity with the elastomer by the surface treatment, and the primary particles of the silver powder are connected to each other and the voids are appropriately present. Must have an aggregate structure (secondary particles) to

  Therefore, in the present invention, the surface-treated silver powder is used in order to adjust the DBP oil absorption and the affinity between the silver powder and the elastomer described above. Examples of the surface treatment of the silver powder include a wet method in which the silver powder is put into a solution containing the dispersion liquid and stirred, and a dry method in which the solution containing the dispersion liquid is sprayed while stirring the silver powder. Further, the surface treatment may be carried out by using a surfactant together.

  As the dispersant used for such a surface treatment, for example, a protective colloid such as a fatty acid, an organic metal, or gelatin can be used. However, considering the possibility of contamination of impurities and the improvement of the adsorption property with a hydrophobic group, the fatty acid is Alternatively, it is preferably a salt thereof. As the dispersant, a fatty acid or salt thereof emulsified with a surfactant may be used. Preferred dispersants are fatty acids having 6 to 24 carbon atoms, and stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, linolenic acid and the like can be more preferably used. It is considered that these fatty acids have little adverse effect on the wiring layer and the electrode using the conductive composition. The above fatty acids may be used alone or in combination of two or more.

  The silver powder as described above is adjusted so that the D95 particle diameter of the secondary particles of the silver powder is in the range of 3.0 to 25.0 μm by mixing the elastomer described below and a solvent as necessary and stirring or kneading. To do. For example, stirring or kneading can be performed using a stirrer such as a dissolver or a butterfly mixer, or a kneader such as a roll mill or a bead mill. At that time, the stirring speed of the stirrer and / or the kneader, stirring blades, or a kneading device The shape, the stirring or kneading time, the temperature during stirring or kneading, the bead filling rate, the roll interval, and the like can be adjusted according to various conditions.

The content of silver powder in the conductive composition is preferably 60 to 95 mass% based on the total solid content of the conductive composition. When it is 60% by mass or more, a conductor having a low resistance value can be easily obtained. When the content is 95% by mass or less, disconnection is less likely to occur during expansion and contraction.
The conductive composition of the present invention may be used in combination with other conductive powder such as carbon other than silver powder as long as the effect of the present invention is not impaired.

<Elastomer>
The elastomer contained in the conductive composition according to the present invention can be used without particular limitation as long as it is a material having rubber elasticity at room temperature, and examples thereof include rubber, thermoplastic elastomers, functional group-containing elastomers and block copolymers. It can be used preferably.

  As the rubber, any of diene rubber and non-diene rubber may be used, and known and commonly used rubber may be used alone or in combination of two or more kinds.

  Examples of the thermoplastic elastomer include styrene-based elastomers, olefin-based elastomers, urethane-based elastomers, polyester-based elastomers, polyamide-based elastomers, acrylic-based elastomers, silicone-based elastomers, etc., which may be used alone or in combination of two or more. be able to.

  As the functional group-containing elastomer, urethane type and olefin type are preferable from the viewpoint of elasticity, and (meth) acryloyl group, acid anhydride group, carboxyl group, epoxy group and other functional groups are preferable from the viewpoint of solvent resistance. Those are preferable.

  As the block copolymer, any block copolymer of a hard segment and a soft segment can be used, and they can be used alone or in combination of two or more kinds.

  Among the above-mentioned elastomers, the block copolymer has low crystallinity and weak intermolecular force, and therefore has a low glass transition point (hereinafter abbreviated as Tg) as compared with other rubbers, and when mixed with silver powder. Is preferable because it is flexible and has good elongation. Therefore, the block copolymer is suitable for forming a conductor for wearable devices. In particular, a block copolymer of a hard segment having a Tg of less than 150 ° C. and a soft segment having a Tg of less than 0 ° C. is more preferable. The glass transition point Tg is measured by differential scanning calorimetry (DSC).

  The ratio of hard segment to soft segment in such a block copolymer is preferably in the range of 20:80 to 50:50. Within this range, wire breakage is less likely to occur during the expansion of the conductor obtained by solidifying the conductive composition, which is preferable. More preferably, it is 25:75 to 40:60.

  Here, examples of the hard segment in the block copolymer include a methyl (meth) acrylate unit and a styrene unit. Examples of soft segment units include n-butyl acrylate and butadiene units. The block copolymer is preferably a triblock copolymer of polymethyl (meth) acrylate / polyn-butyl (meth) acrylate / polymethyl (meth) acrylate. The block copolymers may be used alone or in combination of two or more. In addition, in this specification, (meth) acrylate is a general term for acrylate and methacrylate, and the same applies to other similar expressions.

  The block copolymer may be a commercially available product. An example of a commercially available product is an acrylic triblock copolymer manufactured using living polymerization manufactured by Arkema. Specifically, SBM type represented by polystyrene-polybutadiene-polymethylmethacrylate, MAM type represented by polymethylmethacrylate-polybutylacrylate-polymethylmethacrylate, and carboxylic acid modification treatment or hydrophilic group modification treatment. MAM N type or MAM A type can be used. Examples of SBM types are E41, E40, E21 and E20. Examples of MAM types are M51, M52, M53 and M22. Examples of MAM N types are 52N and 22N. An example of a MAM A type is SM4032XM10. Another example of a commercial product is Clarity manufactured by Kuraray. This clarity is a block copolymer derived from methyl methacrylate and butyl acrylate.

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

  The weight average molecular weight of the block copolymer is preferably 20,000 to 400,000, 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 are obtained, and it is excellent when the conductive composition is formed into a film and dried, and when applied to a substrate and dried. The tackiness is obtained. Further, when the weight average molecular weight is 400,000 or less, the conductive composition has a good viscosity, and higher printability and processability can be achieved. Further, when the weight average molecular weight is 50,000 or more, an excellent effect is obtained in the relaxation property against external impact.

The tensile elongation at break of the block copolymer according to the measuring method of International Standard ISO 37 of the International Organization for Standardization is preferably 100 to 600%. When the tensile elongation at break is 100 to 600%, the stretchability of the conductor and the stability of electric resistance are excellent. More preferably, it is 300 to 600%.
Tensile elongation at break (%) = (elongation at break (mm) -initial dimension mm) / (initial dimension mm) x 100

  Of the above-mentioned elastomers, a sulfur-based vulcanizing agent or a non-sulfur-based vulcanizing agent is usually used for the rubber or the functional group-containing elastomer. In the conductive composition containing the silver powder and the elastomer as in the present invention, the silver contained in the vulcanizing agent in the elastomer may corrode the silver powder in the wiring due to oxidation or sulfidation. In, it is preferable not to include a sulfur-based vulcanizing agent.

  The conductive composition of the present invention may contain a slight amount of a sulfur compound within a range that does not adversely affect the conductivity (a range that does not impair the effects specific to the present invention).

  Further, the elastomer may contain known additives such as a softening agent and a plasticizer. Examples of the softener include mineral oil-based softeners and vegetable oil-based softeners. Examples of the mineral oil-based softeners include various oils such as paraffin-based process oil, naphthene-based process oil, and aromatic-based process oil. Examples of vegetable oil-based softeners include castor oil, brocade oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, pine oil, tall oil, and the like, and these softeners may be used alone or You may use 2 or more types together. Desired rubber elasticity and extensibility can be adjusted by the addition amount of the softening agent.

The elastomer as described above is preferably blended in a proportion of 5 to 40% by mass, and more preferably 14 to 28% by mass, based on the total solid content of the conductive composition. In particular, when the block copolymer as described above is contained, it is preferable that the blending amount of these block copolymers is 85 to 100 mass% with respect to the total elastomer including other elastomers. When the content is within the above range, the stretchability of the formed coating film becomes better.
The conductive composition of the present invention may be used in combination with other organic binders such as thermoplastic resins other than the elastomer, as long as the effects of the present invention are not impaired.

  The conductive composition of the present invention can use an organic solvent for adjusting the composition or for adjusting the viscosity for applying to the substrate.

  Examples of such an organic solvent include ketones, aromatic hydrocarbons, glycol ethers, glycol ether acetates, esters, alcohols, aliphatic hydrocarbons, petroleum-based solvents, and the like. More specifically, ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene, xylene and tetramethylbenzene; cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl. Glycol ethers such as ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, triethylene glycol monoethyl ether; ethyl acetate, butyl acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol methyl ether acetate , Propylene glycol ethyl ether acetate, propylene glycol butyl ether Esters such as cetate; alcohols such as ethanol, propanol, ethylene glycol, propylene glycol; aliphatic hydrocarbons such as octane and decane; petroleum solvents such as petroleum ether, petroleum naphtha, hydrogenated petroleum naphtha, solvent naphtha, etc. is there. Such organic solvents are used alone or as a mixture of two or more kinds. Among these, diethylene glycol monoethyl ether acetate is preferable from the viewpoint of coatability.

  The conductive composition of the present invention may further contain a thermosetting component. Examples of the thermosetting component are polyester resin (urethane modified product, epoxy modified product, acrylic modified product, etc.), epoxy resin, urethane resin, phenol resin, melamine resin, vinyl which can increase the molecular weight by curing reaction and can form a film by cross-linking. Resins and silicone resins.

  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 an elastomer dissolved in a solvent and the above-mentioned silver powder. Examples of the kneading method include a method using a stirring and mixing device such as a roll mill. Specifically, prepare a resin solution having a solid content of 50% by mass in which an elastomer is dissolved in an organic solvent, add silver powder to the resin solution, preliminarily stir and mix with a stirrer, and then knead with a three-roll mill. Then, a conductive composition can be obtained. Depending on the type of elastomer used and the blending ratio of the organic solvent, a liquid conductive composition or a paste (semi-solid) conductive composition can be obtained.

  In the present invention, the conductive composition as described above can be formed into a conductor by, for example, pattern coating on a substrate and heat treatment. Examples of this heat treatment include drying treatment and thermosetting treatment.

  As described above, according to the conductive composition of the present invention, it is possible to obtain a conductor having excellent stretchability and stability of electric resistance. Further, the suitability for coating is also improved by using the silver powder as described above.

<Conductor layer and its application>
The conductive composition described above can be solidified into a conductor. For example, a conductive film can be formed by forming a coating film of a conductive composition, drying and solidifying. Solidification of the conductive composition is performed by drying or heat-treating the conductive composition. Examples of heat treatment are hot air drying or heat curing. Molding may be performed prior to the heat treatment. For example, as the conductor layer, the conductor layer can be obtained by applying the above-mentioned conductive composition on a base material so as to have a desired shape and then solidifying. The layer of conductor may be of various shapes depending on the application for which it will be used. For example, it can be suitably applied to conductor circuits and wiring.

  In the case of producing a conductor circuit, the method includes a pattern forming step of forming a coating film pattern by printing or applying the above conductive composition on a substrate, and a step of solidifying the patterned coating film. A masking method, a method using a resist, or the like can be used to form the coating film pattern.

  The pattern forming step includes a printing method and a dispensing method. Examples of the printing method include gravure printing, offset printing, screen printing, and the like, and screen printing is preferable when forming a fine circuit. Further, gravure printing and offset printing are suitable as a large area coating method. The dispensing method is a method of forming a pattern extruded from a needle by controlling the coating amount of the conductive composition, and is suitable for partial pattern formation such as ground wiring or pattern formation on an uneven portion.

  The base material to which the conductive composition is applied can be used without particular limitation as long as it is an electrically insulating material. Paper-phenol resin, paper-epoxy resin, glass cloth-epoxy resin, glass-polyimide, glass Cloth / nonwoven fabric-epoxy resin, glass cloth / paper-epoxy resin, synthetic fiber-epoxy resin, fluororesin / polyethylene / phenylene ether, polyphenylene oxide / cyanate ester, etc. Copper clad laminate, sheet or film made of polyester such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polyimide, polyphenylene sulfide, polyamide, urethane, silicone rubber, acrylic rubber, butadiene rubber Sheet or film comprising a crosslinked rubber, such as, polyester, polyurethane, polyolefin, such as a sheet or film made of a thermoplastic elastomer such as styrene-based block copolymer systems. Among these, by using not only a material having flexibility but also a material having elasticity (for example, rubber or thermoplastic elastomer) as a base material, the conductor can be applied to the use described below. As the stretchable material, the same material as the above-mentioned elastomer component can be used.

  Since the conductor layer according to the present invention is excellent in stability of electric resistance even after repeated expansion and contraction or extension as described above, in addition to a conductor circuit and wiring, an extracorporeal device and a body surface device. It can be preferably used for forming a conductor for wearable devices such as electronic skin devices and in-body devices. Further, the conductor layer can be applied to the electrodes of the flexible printed circuit board. Furthermore, the conductive composition of the present invention is also suitable for forming a layer of a conductor such as an actuator electrode. Further, it is also suitable for forming a conductor having a design which has been difficult to realize due to lack of elasticity and stability of electric resistance in the past. For example, the following may be mentioned.

<Wearable biometric sensor>
The conductor of the present invention can be applied as a wiring material for wearable biosensors that can be worn to acquire / transmit action potential / biological information generated from animals and plants including humans. It is essential that the sensor is attached to a place close to or close to the surface tissues of animals and plants including humans, but the surface tissues expand and contract. In conventional hard substrates and flexible substrates, there is no ability to follow the expanding and contracting mounting position, the mounting position of the sensor is limited, and the biometric information obtained as a result is also limited. According to the conductor of the present invention, since the wiring material for a sensor can be applied to the surface layer tissues of animals and plants including humans, it is possible to provide a wearable biosensor that can be attached to a place where expansion and contraction occur.

  The wiring used for the wearable biometric sensor can be formed by screen printing or a dispensing method, so that it is possible to miniaturize the signal wiring and contribute to downsizing of the sensor device.

<Wiring material for smart textiles>
In recent years, the field of so-called "smart textiles" using textile materials as sensors is expanding. A wiring board or a sensor in which wiring is formed on a base material that has elasticity and is capable of thermocompression bonding using the conductor of the present invention has excellent stability of electric resistance during expansion and contraction. By adhering to the surface of the cloth material having the above, it becomes possible to develop the cloth material having the function of the electronic device, that is, the smart textile. As a smart textile, functions such as a pressure sensor, a touch sensor, and antenna wiring can be added to the cloth material.

<Wiring for 3D molded products>
In the conventional FIM (Film / Insert / Mold Molding) method, plastic molded products for housings of electronic devices are made by using a plastic film such as polycarbonate as a base material, design printing, and then hot pressing. ing. Since the conductor wiring of the laminated structure in which the conductor of the present invention is provided on a stretchable base material does not have a disconnection at the time of extension and has the characteristic that the resistance value change is suppressed, it is possible to print the design of a plastic molded product. An electronic device having a 3D-shaped wiring built therein can be realized by forming a conductor wiring and then performing a molding process by hot pressing (expansion partially occurs).

  Further, by performing hot pressing using a stretchable base material such as the elastomer as described above, it is possible to realize a stretchable and deformable electronic device having soft wiring inside a soft casing. It can be suitably used as a pressure sensor, a touch sensor, or for antenna wiring.

<Expandable and deformable wiring sheet or wiring board>
The conductor wiring formed of a laminated structure in which the conductor layer of the present invention is provided on a stretchable base material can be used as a stretchable and deformable wiring board sheet. For example, it is possible to attach such a conductor wiring to the surface of a target object having a three-dimensional shape such as a molded product while stretching or deforming it without causing wire breakage. Therefore, the laminated structure in which the conductor layer of the present invention is provided on the stretchable base material can be suitably used for a pressure-sensitive sensor, a touch sensor, or an antenna wiring.

<Flexible wiring sheet or wiring board>
In a conventional flexible wiring sheet or wiring board using a conductive paste, when an extreme bending such as a claw folding is performed, a phenomenon occurs in which a wire breakage occurs. In this respect, when the conductor of the present invention is used, since it is a conductive material having elongation characteristics, it is possible to deal with the bendability of a region which cannot be separated by the conventional conductive paste. However, it is possible to realize a flexible wiring sheet or a wiring board in which disconnection of wiring does not occur.

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

<Preparation of silver dust>
The following three types of silver powder were prepared as the silver powder for preparing the conductive composition.
Silver powder A: Silver powder having an average primary particle size of 0.3 μm and an apparent porosity of 92%, which has been surface-treated with linolenic acid.
Silver powder B: Silver powder having an average primary particle diameter of 0.5 μm and an apparent porosity of 63%, which has been surface-treated with linolenic acid.
Silver powder C: Silver powder having an average primary particle diameter of 1.3 μm and an apparent porosity of 44%, which has been surface-treated with linolenic acid.

The average primary particle diameter of the silver powder is 10 particles of the silver powder, which are randomly extracted by observing the silver powder at 10,000 times with a scanning electron microscope (JSM-6360L manufactured by JEOL Ltd.). The diameter was measured and used as the average value.
The apparent porosity P of each silver powder was calculated as follows. That is, the silver powder is filled in a cylindrical container, the container is vibrated several times to replenish the silver powder until the upper surface of the silver powder reaches a certain height, and the amount of the silver powder filled in the container is M (g), Using a cylinder with an outer diameter that matches the inner diameter of the container, apply a load of 1 kg to the upper surface of the silver powder, and then leave for 1 hour. The volume of the silver powder (the bottom area of the cylindrical container and the height from the container bottom to the upper surface of the silver powder). (The product of the heights) is V (cm ³ ), the apparent density ρ (g / cm ³ ) defined by ρ = M / V is calculated, and the true density of silver ρ ₀ (10.49 g / cm ³ ) is used. The following formula:
P = (1-ρ / ρ ₀ ) × 100
The apparent porosity P (%) of silver powder represented by

<Preparation of conductive composition>
The following two types were prepared as elastomers for preparing a conductive composition.
Elastomer A (LA2330 manufactured by Kuraray Co., Ltd.)
Elastomer B (LA2250 manufactured by Kuraray Co., Ltd.)
・ Polyester C (Byron 290, manufactured by Toyobo Co., Ltd.)
Regarding the above-mentioned elastomers A and B, the elastomer was dissolved in diethylene glycol monoethyl ether acetate to prepare a resin solution having a solid content of 50% by mass. Further, the polyester C was dissolved in diethylene glycol monoethyl ether acetate to prepare a resin solution having a solid content of 30% by mass.

  The silver powder and the resin solution of the elastomer or polyester were blended according to the composition shown in Table 1 below, and after premixing and stirring with a stirrer, a three roll mill (EXAKT50, manufactured by EXAKT) was used. The conductive composition according to the embodiment was obtained by changing the conditions such as the number of times of kneading, the rotation speed, and the roll interval. In Table 1, the numerical value of the blending amount of the elastomer or polyester and the silver powder represents parts by mass.

  The secondary particle D95 particle diameter of the silver powder contained in the obtained conductive composition was measured. The D95 particle size was measured as follows. First, the conductive composition was diluted with 3000% by mass of propylene glycol monomethyl ether acetate to prepare a solution. Using a laser diffraction / scattering particle size distribution analyzer (TM3000, manufactured by Microtrac Bell), the solution was set to have a particle refractive index of 1.33 and a solvent refractive index of 1.40, and the solution was 0.020 μm to 1000 μm. The particle size distribution was measured in the measurement range of 0.000 μm, and the cumulative 95% particle size was determined from the particle size distribution, and the particle size was defined as D95 particle size.

<Evaluation of conductive composition>
(1) 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 was used as the substrate. The resistance values at both ends of the obtained conductor were measured by the 4-terminal method, and the line width, line length and thickness were further measured to determine the specific resistance (volume resistivity). The results are shown in Table 1.

(2) Measurement of maximum resistance value in 20% stretch test Each conductive composition was applied to a substrate by screen printing and heat-treated at 80 ° C. for 30 minutes to obtain a line width of 1 mm, a thickness of 20 μm, and a length of 40 mm. Was formed on the base material. As the base material, a urethane film (TG88-I, manufactured by Takeda Sangyo Co., Ltd., thickness 70 μm) was used. The resistance value of the conductor was measured by repeating 100% reciprocation for 250 seconds from the 2.5% expansion / contraction state (no bending) to 250% expansion / contraction. The maximum resistance value in the meantime is shown in Table 1.

(3) Presence or absence of disconnection in 50% expansion / contraction test Each conductive composition was applied to a substrate by screen printing and heat-treated at 80 ° C. for 30 minutes to obtain a conductive line width of 1 mm, thickness of 20 μm, and length of 40 mm. A body was formed on the substrate. As the base material, a urethane film (TG88-I, manufactured by Takeda Sangyo Co., Ltd., thickness 70 μm) was used. The presence or absence of disconnection was evaluated by repeating 100 cycles of 0% non-stretching state and 50% stretching over 700 seconds. The measurement results are shown in Table 1.

(4) Resistance value at 400% extension Each conductive composition was applied to each substrate by screen printing and heat-treated at 80 ° C. for 30 minutes to obtain a conductor having a line width of 1 mm, a thickness of 20 μm and a length of 40 mm. Was formed on the substrate. As the base material, a urethane film (TG88-I, manufactured by Takeda Sangyo Co., Ltd., thickness 70 μm) was used. After stretching 25% at a speed of 5 mm / sec, it was held for 15 seconds to evaluate the presence or absence of wire breakage. This operation was repeated until the conductor stretched 400%. The evaluation results are shown in Table 1.

  As is clear from the results shown in Table 1, using silver powder and elastomer having an average primary particle size of 1.0 μm or less and an apparent porosity of 50 to 95%, the D95 particle size is 3.0 to 25 μm. The electrically conductive compositions (Examples 1 to 4) stirred or kneaded as described above are excellent in stability of electric resistance even when repeated expansion and contraction or elongation, and a conductor free from disconnection can be obtained. I understand.

  On the other hand, even when the silver powder and the elastomer having an average primary particle diameter of 1.0 μm or less and an apparent porosity of 50 to 95% are used, the D95 particle diameter is not in the range of 3.0 to 25 μm. It can be seen that the composition (Comparative Example 2) has good initial conductivity, but the conductivity rapidly decreases when repeated expansion and contraction or elongation. Moreover, when the average primary particle diameter is 1.0 μm or less and the silver powder having an apparent porosity not in the range of 50 to 95% is used (Comparative Example 1 and Comparative Example 3), the initial conductivity is also insufficient, It can be seen that the conductivity decreases sharply even after repeated stretching and stretching.

Claims (5)

A conductive composition comprising an elastomer and silver powder,
The silver powder is surface-treated,
The silver powder has an average primary particle size of 1.0 μm or less and an apparent porosity of 50 to 95%,
In the conductive composition, the cumulative 95% particle size (D95 particle size) in the particle size distribution of the secondary particles of the silver powder is 3.0 to 25.0 μm, the conductive composition.   The conductive composition according to claim 1, wherein the silver powder is contained in a solid content of 60 to 95 mass% with respect to the entire conductive composition.   A conductor obtained by solidifying the conductive composition according to claim 1.   A laminated structure comprising a substrate and a layer of the conductor according to claim 3 provided on the substrate.   An electronic component comprising the conductor layer according to claim 3 or the laminated structure according to claim 4.