JP7077316B2 - Conductive composition and conductors using it and laminated structures - Google Patents

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 such as a printed wiring board, a paste-like conductive composition obtained by mixing a metal powder 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 a 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, with the growth of the wearable device field in recent years, it is also required to impart elasticity to the conductor. In particular, wearable devices with a higher degree of contact with the body are required to have a high degree of elasticity.

In response to such a demand, for example, a conductive composition in which an elastomer is used as an organic binder containing a metal powder and the conductor has not only flexibility but also elasticity has been proposed (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, the resistance value may increase sharply when the conductor is stretched to some extent, and the wire may be broken in some cases. 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 expanded and contracted or stretched.

Therefore, an object of the present invention is to provide a conductive composition capable of obtaining a conductor having excellent stability of electric resistance even when the expansion and contraction are repeated and the expansion and contraction 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 present inventors repeated expansion and contraction by setting a surface-treated silver powder having a specific average primary particle size as a conductive metal powder to be blended in an elastomer into a specific aggregated state in the composition. It has been found that a conductive composition capable of obtaining a conductor having excellent stability of electric resistance can be realized even in the case of a case or, for example, when it is greatly stretched 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 and
The silver powder has an average primary particle diameter 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% by mass based on the total solid content of the conductive composition.

Further, the conductor according to another embodiment of the present invention is a solidified conductive composition.

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

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

According to the conductive composition of the present invention, as the conductive metal powder to be blended in the elastomer, a silver powder having a specific average primary particle size subjected to surface treatment is brought into a specific aggregated state in the composition. Even when the expansion and contraction are repeated or the expansion and contraction 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 with the elastomer, electrical resistance is obtained not only when the elastomer is bent but also when it is expanded or contracted or greatly expanded. It is possible to obtain a conductor or the like 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 a property. can. Hereinafter, each component contained in the conductive composition of the present invention will be described in detail.

<Silver powder>
The silver powder constituting the conductive composition of the present invention is surface-treated, 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. Use 95%, preferably 60-95%. In the case where such silver powder is used to bring the particle size distribution of the secondary particles of the silver powder into the agglomerated state within the range as described later in the composition, the expansion and contraction are repeated and the expansion and contraction are increased. However, the stability of electrical resistance can be maintained. In the present invention, the average primary particle diameter of silver powder is defined as the average primary particle diameter of silver powder, which is obtained by observing silver powder in a powder state at a magnification of 10,000 times with a scanning electron microscope and randomly extracting 10 primary particles thereof. It means the average value of those particle sizes when the particle sizes are measured. In addition, the apparent porosity of silver powder is an index showing the state of the aggregated structure (secondary particles) in which the primary particles of silver powder are connected and an appropriate void is present, and can be measured as follows. 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 silver powder having a mass of 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 showing the aggregated state of the primary particles of silver powder before being mixed with the elastomer. When a constant load is applied to the silver powder, the filled silver powder is compressed. At this time, when the silver powder is not in the aggregated state but in the state where 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 the voids inside the aggregate. This makes it possible to evaluate the agglomerated state of the primary particles of silver powder as the apparent porosity.

Further, 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 in which the substantially spherical primary particles are connected three-dimensionally and randomly. As described above, even when the solidified material of the conductive composition is greatly stretched, the silver powder can follow the stretched deformation of the elastomer in the solidified material of the conductive composition without reducing the contact points between the primary particles.

It is needless to say that the shape of the primary particles of the silver powder is not limited to those having a substantially spherical shape, and silver powder having a shape other than the substantially spherical shape may be contained as long as the effect of the present invention is not impaired. ..

Commercially available silver powder having an average primary particle diameter and apparent porosity within the above ranges can be used, and commercially available silver powder can be used as a specific average primary particle using a classifier or the like. It may be obtained by classifying into 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. It is about 40.0 μm, more preferably more than 15.0 to 40.0 μm. When the average secondary particle size is in the above range, it becomes easy to adjust the particle size to a specific range as described later when the silver powder is dispersed in the composition. The average secondary particle size of the silver powder before being prepared as the conductive composition means the average value (D50) of the particle size of the silver powder in the powder state measured by the laser diffraction / scattering type particle size distribution measurement method. do.

Further, the silver powder used in the present invention (silver powder before being prepared as a conductive composition) has a DBP oil absorption amount of 30 to 200 ml / 100 g measured according to JIS K 6217-4 (2017). Is preferable. The DBP oil absorption amount 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 silver powder having a DBP oil absorption amount in the above range, it becomes easy to adjust the particle size to a specific range as described later when the silver powder is dispersed in the composition.

The conductive composition of the present invention is dispersed in an elastomer using the above-mentioned silver powder, and has a cumulative 95% particle size (D95 particle size) in the particle size distribution of secondary particles of silver powder in the conductive composition. However, it 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 surface-treated as described later, and is in a specific aggregated state (that is, a specific apparent void ratio), preferably a specific DBP oil absorption amount. Controlling the aggregated state of silver powder in the composition when the silver powder to be possessed is blended with an elastomer (that is, the cumulative 95% particle diameter in the particle size distribution of secondary particles is within a specific range). As a result, the conductivity of the cured product obtained by solidifying the conductive composition is improved, and even when the expansion and contraction are repeated and the expansion and contraction are increased, the conductor can be made into a conductor having excellent stability of electrical resistance. can.

The silver powder constituting the conductive composition of the present invention is contained in the conductive composition while maintaining a constant aggregated state in which a plurality of primary particles are three-dimensionally and randomly connected even when mixed or kneaded with the elastomer. It is considered to be dispersed. That is, when silver powder having a specific apparent porosity is mixed or kneaded with an elastomer, among the aggregated secondary particles of the primary particles of the silver powder, the secondary particles having a large particle size are disintegrated and become smaller to some extent. By adjusting the cumulative 95% particle size in the particle size distribution of the secondary particles to be 3.0 to 25.0 μm, apparent voids remain in the secondary particles of silver powder, and the voids remain appropriately. It is considered that the effect peculiar to the present invention can be exhibited because the elastomer enters the particle size.

Although the detailed mechanism by which the effect peculiar to the present invention is exerted is not clear, it is considered as follows. That is, it is a silver powder having an average primary particle diameter of 1.0 μm or less and having an apparent void ratio of 50 to 95%, preferably having a DBP oil absorption amount in the above range, as described later. When preparing a composition by blending and dispersing the above in an elastomer, the agglomeration of silver powder is appropriately disintegrated, and the composition is stirred or kneaded so that the D95 particle size becomes 3.0 to 25.0 μm. In the secondary particles of silver powder, apparent voids are appropriately present, and the elastomer sufficiently penetrates into the voids, so that the contact points between the primary particles are reduced even when the solidified material of the conductive composition is greatly stretched. It is considered that the silver powder can follow the stretch 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 silver powder in the conductive composition is a laser diffraction / scattering type particle size of the conductive composition obtained by mixing or kneading silver powder and an elastomer. It can be measured by the distribution measurement 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) so as to be 3000% by mass, and the secondary particles of silver powder are formed with a spatula or the like. Immediately after stirring appropriately so as not to disintegrate, the particle size distribution was measured in the measurement range of 0.020 μm to 1000.00 μm, with the refractive index of the particles set to 1.33 and the refractive index of the solvent set to 1.40, and the particle size distribution was measured. The value calculated as the cumulative 95% of the particle size of 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 within the above range is dispersed in the conductive composition, and thus it is composed of such a conductive composition. It is considered that a conductor having excellent stability of electric resistance can be obtained even when the solidified material is repeatedly expanded and contracted or greatly expanded.

When ordinary silver powder is dispersed in an elastomer, the aggregated state of the silver powder in the conductive composition collapses too much. Therefore, when the solidified product of the conductive composition is greatly stretched, this stretching deformation causes the silver powder to be primary. The contact points between particles are reduced. In this regard, according to the characteristic configuration of the present invention as described above, the secondary particles of the silver powder in the conductive composition have appropriate apparent voids, and the elastomer sufficiently penetrates into the voids. It is considered that the silver powder can follow the stretch deformation of the elastomer without reducing the contact points between the primary particles even when the solidified product made of such a conductive composition is greatly stretched.

In order for the silver powder to exist in the above-mentioned form in the conductive composition of the present invention, the silver powder has a high affinity with the elastomer by surface treatment, and the primary particles of the silver powder are connected to each other and voids are appropriately present. It is necessary to have an agglomerated structure (secondary particles).

Therefore, in the present invention, a surface-treated silver powder is used in order to adjust the above-mentioned DBP oil absorption amount 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 the silver powder is put into a solution containing the dispersion liquid and stirred, and a dry method in which the silver powder is agitated and sprayed with the solution containing the dispersion liquid. Further, the surface treatment may be performed in combination with a surfactant.

As the dispersant used for such surface treatment, for example, protective colloids such as fatty acids, organic metals and gelatin can be used, but in consideration of the risk of contamination with impurities and the improvement of adsorptivity with hydrophobic groups, fatty acids Or it is preferably a salt thereof. Further, as the dispersant, a fatty acid or a 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 electrodes using the conductive composition. The above-mentioned 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 size of the secondary particles of the silver powder is in the range of 3.0 to 25.0 μm by blending the elastomer described later and a solvent as necessary, stirring or kneading. 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. It can be adjusted according to various conditions such as the shape, stirring or kneading time, temperature at the time of stirring or kneading, bead filling rate and roll interval.

The blending amount of the silver powder in the conductive composition is preferably 60 to 95% by mass based on the total solid content contained in the conductive composition. When it is 60% by mass or more, a conductor having a low resistance value can be easily obtained. When it 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 powders such as carbon other than silver powder 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 particular limitation as long as it is a material having rubber elasticity at room temperature. For example, rubber, thermoplastic elastomer, functional group-containing elastomer, block copolymer and the like can be used. It can be suitably used.

The rubber may be either a diene-based rubber or a non-diene-based rubber, and known and commonly used rubbers may be used alone or in combination of two or more.

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

The functional group-containing elastomer is preferably urethane-based or olefin-based from the viewpoint of elasticity, and has functional groups such as (meth) acryloyl group, acid anhydride group, carboxyl group, and epoxy group from the viewpoint of solvent resistance. The one is preferable.

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

Among the above-mentioned elastomers, block copolymers have low crystallinity and weak intramolecular force, and therefore have a lower glass transition point (hereinafter abbreviated as Tg) as compared with other rubbers, and when mixed with silver powder. It is flexible and stretchable, which is preferable. Therefore, block copolymers are suitable for forming conductors for wearable devices. In particular, a block copolymer having 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 the hard segment to the soft segment in such a block copolymer is preferably in the range of 20:80 to 50:50. When it is within this range, it is preferable because disconnection is less likely to occur when the conductor obtained by solidifying the conductive composition is stretched. 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. Further, examples of the soft segment unit include n-butyl acrylate and butadiene units. The block copolymer is preferably a triblock copolymer of polymethyl (meth) acrylate / poly n-butyl (meth) acrylate / polymethyl (meth) acrylate. One type of block copolymer may be used alone, or two or more types may be used in combination. In addition, in the present 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 commercial product is an acrylic triblock copolymer manufactured by Arkema using living polymerization. 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 MAM A type is SM4032XM10. Another example of a commercial product is Kuraray's Clarity. 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-A-2007-516326 or JP-A-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 toughness and flexibility effects can be obtained, and it is excellent when the conductive composition is formed into a film and dried, or when it is applied to a substrate and dried. Tackiness can be 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 in mitigation against an impact from the outside can be obtained.

The tensile elongation at break of the block copolymer according to the measurement method of the 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 elasticity of the conductor and the stability of the electric resistance are more excellent. More preferably, it is 300 to 600%.
Tensile breaking elongation rate (%) = (breaking point elongation (mm) -initial dimension mm) / (initial dimension mm) x 100

Of the above-mentioned elastomers, sulfur-based vulcanizers, non-sulfur-based vulcanizers, and the like 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, sulfur contained in the vulcanizing agent in the elastomer may cause the silver powder in the wiring to be corroded by oxidation or sulfurization. It is preferable that the sulfur-based vulcanizing agent is not contained in the above.

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

Further, the elastomer may contain known additives such as softeners and plasticizers. Examples of the softening agent include mineral oil-based softeners and vegetable oil-based softeners. For example, mineral oil-based softeners include various oils such as paraffin-based process oils, naphthen-based process oils, and aromatic process oils. Examples of vegetable oil-based softeners include castor oil, brocade oil, linseed oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut oil, pine oil, tall oil, etc., and these softeners may be used alone or. Two or more kinds may be used together. The desired rubber elasticity and extensibility can be adjusted by the amount of the softener added.

The elastomer as described above is 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 block copolymer as described above is contained, it is preferable that the blending amount of these block copolymers is 85 to 100% by mass with respect to all the elastomers including other elastomers. When the blending amount is within the above range, the elasticity 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 elastomers 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 coating on a substrate.

Examples of such organic solvents 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 tetramethyl benzene; cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol and 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 , Esters such as propylene glycol ethyl ether acetate and propylene glycol butyl ether acetate; alcohols such as ethanol, propanol, ethylene glycol and propylene glycol; aliphatic hydrocarbons such as octane and decane; petroleum ether, petroleum naphtha, hydrogenated petroleum naphtha , Solvent naphtha and other petroleum-based solvents. Such organic solvents are used alone or as a mixture of two or more. Of 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 heat-curable components include polyester resins (urethane-modified, epoxy-modified, acrylic-modified, etc.), epoxy resins, urethane resins, phenolic resins, melamine resins, and vinyls that can be formed into films by increasing molecular weight due to curing reaction and forming crosslinks. Phenolic resin and silicone resin.

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 with 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, a resin solution having a solid content of 50% by mass in which an elastomer is dissolved in an organic solvent is prepared, silver powder is mixed with this resin solution, pre-stirring and mixing with a stirrer, and then kneading with a three-roll mill. Therefore, 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-like (semi-solid) conductive composition can be obtained.

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

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

<Conductor layer and its uses>
The above-mentioned conductive composition can be solidified into a conductor. For example, a coating film made of a conductive composition can be formed, dried, and solidified to form a conductive layer. The solidification of the conductive composition is carried out by drying or heat-treating the conductive composition. Examples of heat treatments are hot air drying or thermosetting. Molding may be performed prior to the heat treatment. For example, the conductor layer can be obtained by applying the above-mentioned conductive composition on a substrate so as to have a desired shape and then solidifying the conductor layer. The conductor layer may have various shapes depending on the intended use. For example, it can be suitably applied to conductor circuits and wiring.

The case of manufacturing a conductor circuit includes a pattern forming step of printing or applying the above 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.

Examples of the pattern forming step include 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, as a large area coating method, gravure printing and offset printing are suitable. The dispensing method is a method of forming an extrusion pattern from a needle by controlling the amount of the conductive composition applied, and is suitable for forming a partial pattern such as a ground wiring or forming a pattern on an uneven portion.

As the base material to which the conductive composition is applied, any electrically insulating material can be used without particular limitation, and paper-phenol resin, paper-epoxy resin, glass cloth-epoxy resin, glass-polyimide, and glass. All grades (FR-4, etc.) using composite materials such as cloth / non-woven fabric-epoxy resin, glass cloth / paper-epoxy resin, synthetic fiber-epoxy resin, fluororesin / polyethylene / polyphenylene ether, polyphenylene oxide / cyanate ester, etc. Copper-clad laminate, polyethylene terephthalate (PET), polybutylene terephthalate, polyester such as polyethylene naphthalate, sheet or film made of plastic such as polyimide, polyphenylene sulfide, polyamide, urethane, silicon rubber, acrylic rubber, butadiene rubber, etc. Examples thereof include sheets or films made of crosslinked rubber, sheets or films made of thermoplastic elastomers such as polyester-based, polyurethane-based, polyolefin-based, and styrene-based block copolymers. Among these, by using not only a flexible material but also a stretchable material (for example, rubber or thermoplastic elastomer) as a base material, the conductor can be applied to the applications described later. 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 has excellent stability of electrical resistance even when it is repeatedly expanded and contracted or stretched as described above, it is not only a conductor circuit and wiring, but also an extracorporeal device and a body surface device. , Electronic skin devices, internal devices and the like, can be suitably used for forming conductors for wearable devices. Further, the layer of the conductor can be applied to the electrodes of the flexible printed circuit board. Further, the conductive composition of the present invention is also suitable for forming a layer of a conductor such as an actuator electrode. It is also suitable for forming a conductor with a design that was difficult to realize in the past due to insufficient elasticity and stability of electrical resistance. For example, the following can be mentioned.

<Wearable biosensor>
The conductor of the present invention can be applied as a wiring material for a wearable biological sensor that can be worn 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, but the surface tissue expands and contracts. In the conventional hard substrate and flexible substrate, there is no followability to the mounting location that expands and contracts, the mounting location of the sensor is limited, and the biological information obtained as a result is also limited. According to the conductor of the present invention, since the wiring material for the sensor can be applied to the surface tissue of animals and plants including humans, it is possible to make a wearable biosensor that can be attached to a place where expansion and contraction occurs.

Since the wiring used for the wearable biosensor can be formed by screen printing or the dispense method, it is possible to miniaturize the signal wiring, which is considered to contribute to the miniaturization of the sensor device.

<Wiring material for smart textiles>
In recent years, the field of so-called "smart textiles" that use fabrics as sensors is expanding. The wiring plate or sensor in which wiring is formed on a base material that is elastic and can be thermocompression bonded using the conductor of the present invention is excellent in stability of electrical resistance during expansion and contraction, and therefore is elastic. By sticking it on the surface of the cloth cloth with, it becomes possible to develop a cloth cloth having the function of an electronic device, that is, a smart textile. As a smart textile, functions such as a pressure sensor, a touch sensor, and antenna wiring can be added to the fabric.

<Wiring for 3D molded products>
For plastic molded products for housings of electronic devices by the conventional FIM (film insert mold molding) method, a plastic film such as polycarbonate is used as a base material, and after design printing, heat press processing is adopted. ing. Since the conductor wiring made of a laminated structure in which the conductor of the present invention is provided on an elastic base material has the property that there is no disconnection during elongation and the change in resistance value is suppressed, when printing a design of a plastic molded product. An electronic device having a built-in 3D-shaped wiring can be realized by forming a conductor wiring and then performing a molding process by hot pressing (partially stretching occurs).

Further, by performing heat press working using a stretchable base material such as an elastomer as described above, it is possible to realize a stretchable and deformable electronic device having soft wiring in a soft housing. It can be suitably used for a pressure sensor, a touch sensor, antenna wiring, or the like.

<Wiring sheet or wiring board that can be expanded and contracted>
The conductor wiring made of a laminated structure in which the conductor layer of the present invention is provided on an elastic base material can be used as a wiring board sheet that can be expanded and contracted. For example, such a conductor wiring can be attached to the surface of an object having a three-dimensional shape such as a molded product while being stretched or deformed without causing disconnection of the wiring. Therefore, the laminated structure 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 flexible wiring sheet or wiring board using a conventional conductive paste, a phenomenon occurs in which wiring is broken when an extreme bending such as claw folding is performed. 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 cope with the bendability of a region that cannot be separated by the conventional conductive paste, and when the nail is folded. However, it is possible to realize a flexible wiring sheet or wiring board that does not cause disconnection of wiring.

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>
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 diameter 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 size of the silver powder was 10,000 times by observing the silver powder using a scanning electron microscope (JSM-6360L, manufactured by Nippon Denshi Co., Ltd.), and 10 particles of silver powder particles randomly extracted. 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 leave it for 1 hour. The apparent density ρ (g / cm ³ ) defined by ρ = M / V is calculated with V (cm ³ ) as the product of the container, 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 the silver powder represented by is calculated.

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

The above-mentioned silver powder and an elastomer or polyester resin solution are mixed according to the composition shown in Table 1 below, and after pre-stirring and mixing with a stirrer, a 3-roll mill (EXAKT50 manufactured by EXAKT) is used. The conductive composition according to the embodiment was obtained by kneading while changing the conditions such as the number of kneading times, 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 a part 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 set 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 measuring device (TM3000, manufactured by Microtrac Bell), the solution is 0.020 μm to 1000, with the refractive index of the particles set to 1.33 and the refractive index of the solvent set to 1.40. The particle size distribution was measured within a measurement range of .00 μm, and a cumulative 95% particle size was obtained from the particle size distribution and used 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 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% expansion / contraction test Each conductive composition is applied to a substrate by screen printing and heat-treated at 80 ° C. for 30 minutes to have a line width of 1 mm, a thickness of 20 μm, and a length of 40 mm. Conductor was formed on the substrate. As a base material, a urethane film (manufactured by Takeda Sangyo Co., Ltd., TG88-I, thickness 70 μm) was used. The resistance value of the conductor was measured while repeating 100 reciprocations from a 2.5% expansion / contraction state (no bending state) to a 20% expansion / contraction state over 250 seconds. Table 1 shows the maximum resistance values during that period.

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

(4) Resistance value at 400% elongation Each conductive composition is applied to a substrate by screen printing and heat-treated at 80 ° C. for 30 minutes to form a conductor having a line width of 1 mm, a thickness of 20 μm, and a length of 40 mm. Was formed on the substrate. As a base material, a urethane film (manufactured by Takeda Sangyo Co., Ltd., TG88-I, 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 disconnection. This operation was repeated until the conductor was stretched by 400%. The evaluation results are shown in Table 1.

As is clear from the results shown in Table 1, the D95 particle size is 3.0 to 25 μm by using silver powder having an average primary particle size of 1.0 μm or less and an apparent porosity of 50 to 95% and an elastomer. The conductive compositions (Examples 1 to 4) that have been stirred or kneaded as described above have excellent stability of electrical resistance and can be obtained without disconnection even when they are repeatedly expanded and contracted or stretched. I understand.

On the other hand, even when silver powder having an average primary particle size of 1.0 μm or less and an apparent porosity of 50 to 95% and an elastomer are used, the D95 particle size is not in the range of 3.0 to 25 μm. It can be seen that although the composition (Comparative Example 2) has good initial conductivity, its conductivity drops sharply when it is repeatedly expanded and contracted or stretched. Further, when silver powder having an average primary particle size of 1.0 μm or less and 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 drops sharply even when the expansion and contraction are repeated and the expansion and contraction are repeated.

Claims (4)

A conductive composition containing an elastomer and silver powder.
The silver powder is surface-treated with a dispersant or a surfactant .
The silver powder has an average primary particle diameter of 1.0 μm or less before being prepared as the conductive composition, and an average secondary particle diameter of more than 15.0 μm before being prepared as the conductive composition. It is 0 μm or less and has an apparent porosity of 60 to 95% before being prepared as a conductive composition .
The silver powder is contained in an amount of 60 to 95% by mass in terms of solid content with respect to the entire conductive composition.
A conductive composition having a cumulative 95% particle diameter (D95 particle diameter) of 3.0 to 25.0 μm in the particle size distribution of the secondary particles of the silver powder in the conductive composition. A conductor characterized by solidifying the conductive composition according to claim 1. A laminated structure characterized in that a layer of the conductor according to claim 2 is provided on a base material. An electronic component comprising the layer of the conductor according to claim 2 or the laminated structure according to claim 3.