JP7170484B2 - Conductive composition, conductor and laminated structure using the same - Google Patents

Description

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

As a material for forming a patterned conductor such as a wiring circuit, a pasty conductive composition obtained by mixing metal powder with an organic binder is conventionally known. According to such a conductive composition, it is possible to form a desired conductor by applying it in a pattern and then solidifying it.

However, with a general conductive composition, the hardness of the obtained conductor is high, so in the use of flexible printed wiring boards, sufficient flexibility of the conductor cannot be obtained, and a conductor with excellent bending resistance can be formed. There is a demand for development of a conductive composition suitable for In particular, in the field of wearable devices, which has grown remarkably in recent years, it is required to impart stretchability to conductors in addition to bending resistance.

In response to such demands, conventionally, a conductive composition has been proposed in which an elastomer is used as an organic binder containing a metal powder to give the conductor not only flexibility but also stretchability (see Patent Document 1). ). However, even when a conductive composition such as that proposed in Patent Document 1 is used, repeated expansion and contraction, or when the conductor is stretched to some extent, the resistance value increases sharply, and in some cases disconnection occurs. The electrical conductivity during expansion and contraction was still insufficient.

On the other hand, there is a demand for the development of conductive compositions suitable for devices that are used in direct contact with a living body, such as bioelectrodes used for electrocardiographic measurement.

International Publication No. 2015/005204 pamphlet

Therefore, an object of the present invention is to provide a conductive material suitable for device applications such as bioelectrodes, which can obtain a conductor with excellent stability in electrical resistance even when stretching is repeated or when stretching is increased. The object is to provide a composition.

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 comprising the conductor or laminated structure, especially An object of the present invention is to provide a device such as a bioelectrode.

Now, the present inventors used silver powder having a specific average primary particle size that has been subjected to surface treatment as the conductive metal powder to be blended in the elastomer, and by making it in a specific aggregation state in the composition, it is possible to expand and contract. or, for example, even when greatly stretched to 400% or more, it is possible to realize a conductive composition that can obtain a conductor with excellent stability in electrical resistance. In addition, we proposed a conductive composition that can obtain a conductor with excellent electrical resistance stability even when stretching is repeated or stretched greatly (International Application No.: PCT / JP2018 / 022909).

The present inventors further conducted extensive research on conductive compositions suitable for devices used in direct contact with a living body as described above. Even when combined with silver chloride particles and blended with an elastomer, a conductor made of the conductive composition has stable electrical resistance even when it is repeatedly stretched or stretched greatly, for example, by 400% or more. We have found that it can be realized as a device application such as a bioelectrode that is excellent in The present invention is based on such findings.

That is, the conductive composition of the present invention is a conductive composition containing an elastomer, silver powder and silver chloride particles,
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 and the silver chloride particles is 3.0 to 25.0 μm. be.

In an embodiment of the present invention, the total amount of the silver powder and the silver chloride particles is preferably 60 to 95% by mass based on the total solid content of the conductive composition.

Further, in the conductor according to another embodiment of the present invention, the silver chloride particles may be contained up to 70% by mass with respect to the total amount of the silver powder and the silver chloride particles.

In the conductor according to another embodiment of the present invention, the average primary particle size of the silver chloride particles is preferably 0.1 to 10 μm.

A conductor according to another embodiment of the present invention is obtained by solidifying the conductive composition.

A laminated structure according to another embodiment of the present invention has the conductor layer on a substrate.

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

Moreover, in the embodiment of the present invention, it is preferable that the electronic component is used as a bioelectrode.

According to the conductive composition of the present invention, in a composition in which silver powder and silver chloride particles are blended with an elastomer, silver powder having a specific average primary particle size subjected to surface treatment is added as the silver powder in the composition. A conductor with excellent stability in electrical resistance even when it is repeatedly stretched or stretched to a large extent, for example, 400% or more, by making it into a specific aggregation state, especially a conductor suitable for a bioelectrode. can be obtained.

The conductive composition of the present invention contains an elastomer, silver powder, and silver chloride particles. It is possible to obtain a conductor having excellent electrical resistance stability even when stretched. As a result, the conductive composition of the present invention can be suitably used as a bioelectrode for wearable devices such as extracorporeal devices, body surface devices, electronic skin devices, and intracorporeal devices, utilizing such properties. Each component contained in the conductive composition of the present invention will be described in detail below.

<Silver powder>
The silver powder constituting the conductive composition of the present invention is surface-treated, has 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 1.0 μm. 95%, preferably 60-95% is used. By using such a silver powder, the secondary particles of the silver powder in the composition are aggregated so that the particle size distribution is within the range described later, so that repeated expansion and contraction and expansion are increased. can also maintain the stability of the electrical resistance. In the present invention, the average primary particle size of silver powder is defined by observing silver powder in powder form with a scanning electron microscope at a magnification of 10,000 times, randomly extracting 10 primary particles, It means the average value of those particle sizes when the particle sizes are measured. In addition, the apparent porosity of the silver powder is an index representing the state of the aggregation structure (secondary particles) in which the primary particles of the silver powder are connected to form appropriate voids, and can be measured as follows. can.
i.e.
Let the density of silver be ρ ₀ (g/cm ³ ),
When the silver powder having a mass of M (g) is subjected to a load of 1 kg weight and the volume of the silver powder is V (cm ³ ), the apparent density ρ (g/cm ³ ) is
ρ = M/V
From the apparent density, the apparent porosity (P) can be calculated by the following formula.
P ₌ (1−ρ/ρ0)×100
The density ρ ₀ of silver is 10.49 g/cm ³ , and the silver powder volume V under a heavy load of 1 kg is the silver powder volume one hour after the load is applied.

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

In the present invention, the shape of the primary particles of the silver powder is preferably substantially spherical, and the substantially spherical primary particles are present in the conductive composition in the form of secondary particles that are three-dimensionally and randomly connected. So, as described above, even when the solidified material of the conductive composition is greatly stretched, 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.

It goes without saying that the shape of the primary particles of the silver powder is not limited to being substantially spherical, and silver powder having a shape other than substantially spherical may be included as long as the effects of the present invention are not impaired. .

Commercially available silver powder having an average primary particle size and an apparent porosity within the above ranges can be used. It may be obtained by classifying silver powder having a diameter and an apparent porosity.

The silver powder used in the present invention (that is, silver powder before being prepared as a conductive composition) preferably has an average secondary particle size of 5.0 to 40.0 μm, more preferably more than 10.0. ~40.0 µm, more preferably greater than 15.0 ~ 40.0 µm. When the average secondary particle size is within the above range, when the silver powder is dispersed in the composition, it becomes easier to adjust the particle size to a specific range as described below. 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 particle size distribution measurement method. do.

In addition, 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 the degree of aggregation. By using a silver powder having a DBP oil absorption in the above range, when the silver powder is dispersed in the composition, it becomes easier to adjust the particle size to a specific range as described later.

The conductive composition of the present invention is obtained by dispersing the silver powder and silver chloride particles described above in an elastomer, and the cumulative particle size distribution of the secondary particles of the silver powder and silver chloride particles in the conductive composition is 95%. % particle size (D95 particle size) is in the range of 3.0 to 25.0 μm. The present invention is a silver powder having a specific average primary particle size that has been surface-treated as described later, and is in a specific aggregation state (that is, a specific apparent porosity), and preferably has a specific DBP oil absorption. When the silver powder having silver chloride particles is blended and dispersed in an elastomer together with silver chloride particles to form a composition, the aggregation state of the silver powder and silver chloride particles in the composition is controlled (that is, in the particle size distribution of the secondary particles By setting the cumulative 95% particle size to a specific range), the conductivity of the cured product obtained by solidifying the conductive composition is improved. A conductor having excellent resistance stability can be obtained.

The silver powder constituting the conductive composition of the present invention maintains a certain aggregation state in which a plurality of primary particles are three-dimensionally and randomly connected even when mixed or kneaded with an elastomer. It is considered to be dispersed. That is, when silver powder having a specific apparent porosity is mixed or kneaded with an elastomer, the secondary particles having a large particle size among the aggregated secondary particles of the primary particles of the silver powder collapse to some extent. By adjusting the cumulative 95% particle diameter in the particle size distribution of the secondary particles at that time to 3.0 to 25.0 μm, the apparent voids in the secondary particles of the silver powder are appropriately left, and the voids It is thought that the effect unique to the present invention can be exhibited because the elastomer enters into the .

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, silver powder having an average primary particle diameter of 1.0 μm or less after surface treatment as described later, having an apparent porosity of 50 to 95%, and preferably having a DBP oil absorption in the above range. is mixed with silver chloride particles and dispersed in the elastomer to prepare the composition, the aggregation of the silver powder is appropriately broken down so that the D95 particle size is 3.0 to 25.0 μm. By stirring or kneading, the secondary particles of the silver powder have an appropriate amount of apparent voids, and the elastomer sufficiently enters these voids, so even when the solidified conductive composition is greatly stretched. It is believed that the silver powder can follow the extensional deformation of the elastomer without reducing contact points between primary particles.

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

As described above, according to the conductive composition of the present invention, the silver powder surface-treated so that the D95 particle size is in the above range is dispersed in the conductive composition. It is considered that even when the solidified material is repeatedly expanded and contracted or greatly expanded, a conductor having excellent stability in electrical resistance can be obtained.

When ordinary silver powder is dispersed in an elastomer, the aggregation state of the silver powder in the conductive composition collapses too much. Contact points between particles are reduced. In this respect, according to the characteristic configuration of the present invention as described above, the secondary particles of the silver powder in the conductive composition have an appropriate amount of apparent voids, and the elastomer sufficiently enters these voids. It is thought that the silver powder can follow the elongation deformation of the elastomer without reducing contact points between the primary particles even when the solidified product of such a conductive composition is greatly elongated.

In order for the silver powder to exist in the above-described form in the conductive composition of the present invention, the silver powder must have a high affinity with the elastomer by surface treatment, and the primary particles of the silver powder are connected to each other to form an appropriate amount of voids. It must have an aggregate structure (secondary particles) that

Therefore, in the present invention, a surface-treated silver powder is used in order to adjust the DBP oil absorption and the affinity between the silver powder and the elastomer. Examples of the surface treatment of the silver powder include a wet method in which silver powder is put into a solution containing a dispersion and stirred, and a dry method in which a solution containing a dispersion is sprayed while stirring the silver powder. Furthermore, a surfactant may be used in combination for surface treatment.

Protective colloids such as fatty acids, organic metals, and gelatin can be used as dispersing agents used for such surface treatment. or a salt thereof. As the dispersing agent, an emulsified fatty acid or a salt thereof with a surfactant may be used. Preferable 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 used more preferably. These fatty acids are considered to have little adverse effect on wiring layers and electrodes using the conductive composition. The above fatty acids may be used alone or in combination.

The silver powder described above is mixed with an elastomer described later and a solvent if necessary, and stirred or kneaded so that the D95 particle size of the secondary particles of the silver powder and silver chloride particles is in the range of 3.0 to 25.0 μm. Adjust so that For example, stirring or kneading can be performed using a stirrer such as a dissolver or butterfly mixer or a kneader such as a roll mill or bead mill. shape, stirring or kneading time, temperature during stirring or kneading, bead packing rate, roll interval, and other conditions.

<Silver chloride particles>
The conductive composition according to the present invention contains silver chloride particles in addition to the silver powder described above. By using silver powder and silver chloride particles in combination, an electrode material having excellent biocompatibility can be obtained.

Silver chloride grains can be used without any particular limitation, but preferably have an average primary grain size of 0.1 to 10 μm and an apparent porosity of 50 to 95%. The average primary particle size is defined by observing silver chloride particles in a powder state with a scanning electron microscope at a magnification of 10,000, randomly extracting 10 primary particles, and measuring the particle size. Means the average value of those particle sizes when

The amount of silver powder and silver chloride particles in the conductive composition in the present invention is preferably such that the total amount of silver powder and silver chloride particles is 60 to 95% by mass based on the total solid content contained in the conductive composition. . When the amounts of the silver powder and the silver chloride particles are within the above range, a conductor with even lower resistance can be easily obtained. The amount of silver chloride particles in the conductive composition is preferably 70% by mass or less, more preferably 50% by mass or less, based on the total amount of silver powder and silver chloride particles. By using silver chloride particles in combination with silver powder in the above-described range, the stability of electrical resistance is further improved when repeated expansion and contraction and elongation are increased, while making a conductor with high biocompatibility. can be done. The conductive composition of the present invention may contain other conductive powder such as carbon other than the silver powder and the silver chloride particles as long as the effects of the present invention are not impaired.

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

As the rubber, either a diene rubber or a non-diene rubber may be used, and known and commonly used rubbers may be used singly or in combination of two or more.

Examples of thermoplastic elastomers include styrene-based elastomers, olefin-based elastomers, urethane-based elastomers, polyester-based elastomers, polyamide-based elastomers, acrylic-based elastomers, and silicone-based elastomers. be able to.

As the functional group-containing elastomer, urethane-based and olefin-based elastomers are preferable from the viewpoint of elasticity, and functional groups such as (meth)acryloyl groups, acid anhydride groups, carboxyl groups, and epoxy groups are preferred from the viewpoint of solvent resistance. things are preferred.

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.

Among the above-mentioned elastomers, block copolymers have low crystallinity and weak intermolecular forces, so their glass transition point (hereinafter abbreviated as Tg) is lower than other rubbers, and when mixed with silver powder It is flexible and has good elongation, which is preferable. Therefore, block copolymers are suitable for forming conductors for wearable devices. In particular, a block copolymer of a hard segment with a Tg of less than 150°C and a soft segment with a Tg of less than 0°C is more preferred. The glass transition point Tg is measured by differential scanning calorimetry (DSC).

The ratio of hard segments to soft segments in such block copolymers is preferably in the range of 20:80 to 50:50. Within this range, disconnection is less likely to occur during elongation 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 methyl (meth)acrylate units and styrene units. Examples of soft segment units include n-butyl acrylate and butadiene units. The block copolymer is preferably a polymethyl (meth)acrylate/poly n-butyl (meth)acrylate/polymethyl (meth)acrylate triblock copolymer. A block copolymer may be used individually by 1 type, and may be used in combination of 2 or more type. In the present specification, (meth)acrylate is a generic term for acrylate and methacrylate, and the same applies to other similar expressions.

Block copolymers may be commercially available. A commercial example is an acrylic triblock copolymer made using living polymerization from Arkema. Specifically, SBM type represented by polystyrene-polybutadiene-polymethyl methacrylate, MAM type represented by polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate, 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 from Kuraray. This Clarity is a block copolymer derived from methyl methacrylate and butyl acrylate.

A block copolymer containing a (meth)acrylate polymer block as described above 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 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 effect of toughness and flexibility is obtained, and the conductive composition is excellent when formed into a film and dried, or when applied to a substrate and dried. Excellent tackiness is obtained. Further, when the weight average molecular weight is 400,000 or less, the conductive composition has good viscosity, and higher printability and workability can be achieved. Moreover, when the weight average molecular weight is 50,000 or more, an excellent effect can be obtained in terms of relaxation against external impact.

The block copolymer preferably has a tensile elongation at break of 100 to 600% according to the international standard ISO 37 measurement method of the International Organization for Standardization. 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 300 to 600%.
Tensile elongation at break (%) = (elongation at break (mm) - initial dimension mm) / (initial dimension mm) x 100

Among the elastomers described above, sulfur vulcanizing agents and non-sulfur vulcanizing agents are usually used for rubbers and functional group-containing elastomers. In a conductive composition containing silver powder and an elastomer as in the present invention, the sulfur contained in the vulcanizing agent in the elastomer may corrode the silver powder in the wiring due to oxidation or sulfurization. preferably does not contain a sulfur-based vulcanizing agent.

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

The elastomer may also contain known additives such as softeners and plasticizers. Examples of softening agents include mineral oil-based softening agents and vegetable oil-based softening agents. Examples of mineral oil-based softening agents include various oils such as paraffin-based process oils, naphthenic process oils, and aromatic process oils. Vegetable oil softeners include castor oil, broccoli oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, pine oil, tall oil, etc. 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 amount of the softening agent added.

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

An organic solvent can be used in the conductive composition of the present invention to adjust the composition or to adjust the viscosity for application to a substrate.

Examples of such organic solvents include ketones, aromatic hydrocarbons, glycol ethers, glycol ether acetates, esters, alcohols, aliphatic hydrocarbons, and petroleum solvents. 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 Ethers, glycol ethers such as 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 acetate; alcohols such as ethanol, propanol, ethylene glycol, propylene glycol; aliphatic hydrocarbons such as octane and decane; petroleum ether, petroleum naphtha, hydrogenated petroleum naphtha , petroleum-based solvents such as solvent naphtha. Such organic solvents may be used alone or as a mixture of two or more. Among these, diethylene glycol monoethyl ether acetate is preferable from the viewpoint of coatability.

The electrically 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.), epoxy resins, urethane resins, phenolic resins, melamine resins, vinyl based 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, additives such as coupling agents and photopolymerization initiators may be included.

The conductive composition of the present invention can be produced, for example, by kneading an elastomer dissolved in a solvent with the silver powder and silver chloride particles 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 having a solid content of 50% by mass is prepared by dissolving an elastomer in an organic solvent, silver powder and silver chloride particles are blended in the resin solution, pre-stirred and mixed with a stirrer, and then placed in a three-roll mill. A conductive composition can be obtained by kneading with the Depending on the type of elastomer to be used and the blending ratio of the organic solvent, a liquid conductive composition or a pasty (semi-solid) conductive composition can be obtained.

In addition, the method for producing the conductive composition of the present invention is not limited to the above-described method. Two compositions are prepared by separately adding silver powder and silver chloride particles to an elastomer dissolved in a solvent and kneading them, The two may be mixed to produce a conductive composition, or the elastomer previously dissolved in a solvent and silver powder are kneaded to prepare a composition, and silver chloride particles are added to the composition. Alternatively, the elastomer dissolved in a solvent and silver chloride particles are kneaded to prepare a composition, and silver powder is added to the composition and kneaded to produce a conductive composition. may Regardless of which manufacturing method is employed, the cumulative 95% particle diameter (D95 particle diameter) in the particle size distribution of the secondary particles of the silver powder is within the range of 3.0 to 25.0 μm. It is necessary to knead so that

The electrically conductive composition of the present invention contains anti-inflammatory agents, antioxidants, blood circulation promoting agents, antibacterial agents, warming agents, wound healing promoting agents, irritation reducing agents, and analgesics as long as the desired physical properties are not affected. , a cell activator, and other known additives that are blended when used as a bioelectrode may be included.

In the present invention, the conductive composition as described above can be formed into a conductor by, for example, pattern coating on a base material and heat treatment. The heat treatment includes drying treatment, heat curing treatment, and the like.

Thus, according to the conductive composition of the present invention, it is possible to obtain a conductor excellent in stretchability and stability of electrical resistance. Also, by using the silver powder and silver chloride particles as described above, the coatability is improved.

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

When manufacturing a conductive circuit, it includes a pattern forming step of printing or applying the conductive composition on a substrate to form a coating film pattern, 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.

Patterning processes include printing methods and dispensing methods. The printing method includes, for example, gravure printing, offset printing, screen printing, etc. Screen printing is preferable when forming a fine circuit. In addition, gravure printing and offset printing are suitable for large-area coating methods. 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 and pattern formation on uneven portions.

As the substrate to which the conductive composition is applied, any electrically insulating substrate can be used without particular limitation, such as paper-phenol resin, paper-epoxy resin, glass cloth-epoxy resin, glass-polyimide, glass. All grades (FR-4, etc.) using composite materials such as cloth/nonwoven fabric - epoxy resin, glass cloth/paper - epoxy resin, synthetic fiber - epoxy resin, fluororesin/polyethylene/polyphenylene ether, polyphenylene oxide/cyanate ester, etc. sheet or film made of plastic such as polyester such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polyimide, polyphenylene sulfide, polyamide, etc., urethane, silicon rubber, acrylic rubber, butadiene rubber, etc. Sheets or films made of crosslinked rubber, and sheets or films made of thermoplastic elastomers such as polyester, polyurethane, polyolefin, and styrene block copolymers may be used. Among these, by using not only materials with flexibility but also materials with elasticity (for example, rubber and thermoplastic elastomers) as the base material, the conductor can be applied to the applications described later. As the elastic material, the same elastomer component as described above can be used.

The conductor layer according to the present invention has excellent electrical resistance stability even when it is repeatedly stretched or stretched as described above. , electronic skin devices, formation of conductors for wearable devices such as intracorporeal devices, especially bioelectrodes. Also, a conductive 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 layers of conductors such as actuator electrodes. It is also suitable for forming conductors with designs that have been difficult to achieve in the past due to lack of stretchability and stability of electrical resistance. For example:

<Wearable biosensor>
The conductor of the present invention can be applied as a wiring material for wearable biosensors to acquire/transmit action potentials/biological information generated from animals and plants including humans. It is essential that the sensor is attached to a place that is in close contact with or close to the surface tissue of animals and plants, including humans, and the surface tissue expands and contracts. Conventional rigid and flexible substrates do not have the ability to follow the mounting position that expands and contracts, and the mounting position of the sensor is limited, and as a result, the biological information obtained is limited. According to the conductor of the present invention, since the sensor wiring material can be applied to the surface tissue of animals and plants including humans, it can be used as a wearable biosensor that can be attached to a location where expansion and contraction occurs.

Wiring used in wearable biosensors can be formed by screen printing or a dispensing method, so signal wiring can be miniaturized, and it is thought that this will contribute to the miniaturization of sensor devices.

<Wiring materials for smart textiles>
In recent years, the field of so-called "smart textiles" using fabrics as sensors has been expanding. Wiring boards or sensors in which wiring is formed on a stretchable base material that can be thermocompressed using the conductor of the present invention have excellent electrical resistance stability during stretching. By attaching it to the surface of the fabric with the function of electronic devices, it is possible to develop smart textiles. As smart textiles, functions such as pressure sensors, touch sensors, and antenna wiring can be imparted to fabrics.

<Wiring for 3D molded products>
In the conventional FIM (Film-Insert-Molding) method, plastic molded products for electronic equipment housings, etc. use a plastic film such as polycarbonate as the base material, and after the design is printed, the product is heat-pressed. ing. Conductor wiring consisting of a laminated structure in which the conductor of the present invention is provided on an elastic base material does not break when stretched, and has the property of suppressing changes in resistance value. An electronic device with a built-in 3D-shaped wiring can be realized by forming a conductor wiring and then performing molding by hot pressing (partially elongating).

In addition, by performing hot press processing using a stretchable base material such as an elastomer as described above, it is possible to realize an electronic device that can be stretched and deformed and has soft wiring in a soft housing. It can be suitably used as a pressure-sensitive sensor, a touch sensor, antenna wiring, or the like.

<Wiring sheet or wiring board that can be stretched and deformed>
A conductor wiring composed of a laminate structure in which a conductor layer of the present invention is provided on an elastic base material can be used as an elastically deformable wiring board sheet. For example, such 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 breaking the wiring. Therefore, the laminate structure in which the conductor layer of the present invention is provided on a stretchable base material can be suitably used as a pressure-sensitive sensor, a touch sensor, or antenna wiring.

<Flexible wiring sheet or wiring board>
In a conventional flexible wiring sheet or wiring board using a conductive paste, when extreme bending such as nail folding is performed, a phenomenon occurs in which wiring disconnection occurs. In this regard, when the conductor of the present invention is used, since it is a conductive material with elongation properties, it can handle the bending property of the area that could not be handled by the conventional conductive paste. However, it is possible to realize a flexible wiring sheet or wiring board in which disconnection of wiring does not occur.

EXAMPLES 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 powder and silver chloride particles>
The following three types of silver powder were prepared as 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 was surface-treated with linolenic acid.
Silver powder B: Silver powder having an average primary particle size of 0.5 µm and an apparent porosity of 63%, which was surface-treated with linolenic acid.
Silver powder C: Silver powder having an average primary particle size of 1.3 μm and an apparent porosity of 44%, which was surface-treated with linolenic acid.
Silver chloride grain A: silver chloride grain having an average primary particle diameter of 3.8 μm and an apparent porosity of 57%.

The average primary particle size of the silver powder and silver chloride particles was obtained by observing the silver powder at a magnification of 10,000 using a scanning electron microscope (manufactured by JEOL Ltd., JSM-6360L). The particle size of the silver powder particles was measured and the average value was taken.
In addition, the apparent porosity P of each silver powder and silver chloride particles was calculated as follows. That is, silver powder or silver chloride particles are filled in a cylindrical container, the container is vibrated several times, and silver powder or silver chloride particles are replenished until the upper surface of the silver powder or silver chloride particles reaches a certain height, and the container is filled. The amount of silver powder or silver chloride particles applied is M (g), and a cylinder having an outer diameter matching the inner diameter of the container is used to apply a load of 1 kg weight to the upper surface of the silver powder or silver chloride particles, and after standing for 1 hour. The volume of the silver powder or silver chloride particles (the product of the bottom area of the cylindrical container and the height from the bottom of the container to the top surface of the silver powder or silver chloride particles) is defined as V (cm ³ ), and is defined as ρ = M/V. Apparent density ρ (g/cm ³ ) was calculated, and using the true density ρ ₀ of silver (10.49 g/cm ³ ) or the true density ρ ₀ of silver chloride (5.56 g/cm ³ ), the following formula:
P ₌ (1−ρ/ρ0)×100
The apparent porosity P (%) of the silver powder or silver chloride grains represented by was calculated.

<Preparation of conductive composition>
The following two types were prepared as elastomers for preparing the conductive composition.
・Elastomer A (LA2330 manufactured by Kuraray Co., Ltd.)
・Elastomer B (LA2250, manufactured by Kuraray Co., Ltd.)
・Polyester C (Bylon 290 manufactured by Toyobo Co., Ltd.)
For the elastomers A and B described above, the elastomers were dissolved in diethylene glycol monoethyl ether acetate to prepare a resin solution having a solid content of 50% by mass. 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 silver chloride particles described above and the elastomer or polyester resin solution were blended according to the composition shown in Table 1 below, preliminarily stirred and mixed with a stirrer, and then milled using a three-roll mill (manufactured by EXAKT, EXAKT50). A conductive composition according to the embodiment was obtained by kneading while changing the conditions such as the number of times of kneading in a three-roll mill, the rotation speed, and the interval between rolls. In Table 1, the amounts of elastomer or polyester, silver powder and silver chloride particles are expressed in parts by weight.

The secondary particle D95 particle size of the silver powder and silver chloride particles contained in the obtained conductive composition was measured. The D95 particle size was determined as follows. First, the conductive composition was diluted with 3000% by mass of propylene glycol monomethyl ether acetate to prepare a solution. The solution is measured using a laser diffraction scattering particle size distribution analyzer (TM3000, manufactured by Microtrac Bell Co., Ltd.) with a particle refractive index of 1.33 and a solvent refractive index of 1.40. The particle size distribution was measured in the measurement range of 0.00 μm, and the cumulative 95% particle size was determined from the particle size distribution, and was defined as the 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 base material. The resistance value at both ends of the obtained conductor was measured by the four-probe method, and the line width, line length and thickness were measured to obtain the specific resistance (volume resistivity). Table 1 shows the results.

(2) Presence or absence of disconnection in 30% stretch test Each conductive composition is 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. A body was formed on the substrate. A urethane film (TG88-I, manufactured by Takeda Sangyo Co., Ltd., thickness 70 μm) was used as the base material. 100 reciprocations were repeated from a 2.5% stretched state (no bending state) to a 30% stretched state over 250 seconds, and the presence or absence of disconnection was evaluated.

(3) Presence or absence of disconnection in a 50% stretch test Each conductive composition is applied to a substrate by screen printing and heat-treated at 80 ° C. for 30 minutes to obtain a conductive wire with a line width of 1 mm, a thickness of 20 μm, and a length of 40 mm. A body was formed on the substrate. A urethane film (TG88-I, manufactured by Takeda Sangyo Co., Ltd., thickness 70 μm) was used as the base material. 100 reciprocations were repeated over 700 seconds from a 0% non-stretchable state to a 50% stretch state, and the presence or absence of disconnection was evaluated.

As the evaluation of the conductivity during stretching, ⊚ indicates that there was no disconnection in the 50% stretch test, ◯ indicates that there was no disconnection in the 30% stretch test, and x indicates that there was disconnection in the 30% stretch test. The evaluation results were as shown in Table 1 below.

As is clear from the results shown in Table 1, the D95 of silver powder and silver chloride particles using silver powder, silver chloride particles, and an elastomer having an average primary particle size of 1.0 μm or less and an apparent porosity of 50 to 95% The electrically conductive compositions (Examples 1 to 9), which were stirred or kneaded so that the particle size was 3.0 to 25 μm, were excellent in electrical resistance stability even when stretched or stretched repeatedly, and disconnection did not occur. It can be seen that a conductor free of

On the other hand, even when silver powder, silver chloride particles, and an 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 of the silver powder and silver chloride particles is 3. It can be seen that the conductive composition (Comparative Example 1), which is not in the range of 0 to 25 μm, has good electrical conductivity in the initial stage, but the electrical conductivity drops sharply when it is repeatedly stretched or stretched. .
In addition, when using silver powder with an average primary particle size of 1.0 μm or less and an apparent porosity outside the range of 50 to 95% (Comparative Examples 2, 3 and 5), the initial conductivity was also poor. It can be seen that the electrical conductivity is abruptly lowered even when the material is repeatedly stretched or stretched.
Furthermore, a conductive composition using polyester instead of elastomer (Comparative Example 4) comprises silver powder having an average primary particle size of 1.0 μm or less and an apparent porosity of 50 to 95%, silver chloride particles, and an elastomer. Even if it is kneaded so that the D95 particle size of the silver powder and silver chloride particles is in the range of 3.0 to 25 μm, the initial conductivity is good, but when it is repeatedly stretched and stretched, the conductivity decreases. It can be seen that it drops rapidly.

Claims (8)

A conductive composition comprising an elastomer, silver powder and silver chloride particles,
The silver powder is surface-treated with at least one of fatty acids or salts thereof, organic metals, and gelatin ,
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 diameter (D95 particle diameter) in the particle size distribution of the secondary particles of the silver powder and silver chloride particles is 3.0 to 25.0 μm. Composition. 2. The conductive composition according to claim 1, wherein the total amount of said silver powder and said silver chloride particles is 60 to 95% by mass based on the total solid content of said conductive composition. 3. The conductive composition according to claim 1, wherein said silver chloride particles are contained up to 70% by mass with respect to the total amount of said silver powder and said silver chloride particles. The conductive composition according to any one of claims 1 to 3, wherein said silver chloride particles have an average primary particle size of 0.1 to 10 µm. A conductor characterized by being obtained by solidifying the conductive composition according to any one of claims 1 to 3. A laminate structure comprising a base material and a layer of the conductor according to claim 5 provided on the base material. An electronic component comprising the conductor layer according to claim 5 or the laminate structure according to claim 6. The electronic component according to claim 7, which is used as a bioelectrode.