Conductive compositions and conductors, multilayer structures, and electronic components using the same

Abstract

To provide a conductive composition from which a conductor having both high conductivity and elasticity required for a wearable device can be formed, and in which a dispersion state of components suitable for the conductor to be formed to stably and sufficiently exhibit such performance is formed and maintained.SOLUTION: In a conductive composition, an elastomer, conductive particles, silica and a solvent are compounded, the conductive particles are made to be chain-like conductive particles, a content of the conductive particles is made to be 60-95 mass% in terms of solid content based on the total mass of the conductive composition, and the particle density value of the conductive particles measured by a grind gauge is made to be 10-40 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive composition, a conductor obtained by solidifying the conductive composition, a laminated structure comprising a layer of the conductor, and an electronic component comprising the conductor or the laminated structure. [Background technology]

[0002] Conventionally, a paste-like conductive composition, obtained by mixing metal powder with an organic binder, has been used as a material to form patterned conductors such as electrodes on printed circuit boards. While such conductive compositions can form the desired conductor by solidifying them after being applied in a pattern, the resulting conductor generally has high hardness. Therefore, it has been difficult to say that such conductive compositions can adequately perform their function in circuit boards where flexibility is required, such as flexible printed circuit boards. Thus, there is a need for a conductive composition that can form a conductor that is suitable for circuit boards where flexibility is required, such as flexible printed circuit boards, and that can stably and adequately perform its function even when bent together with the circuit board.

[0003] Furthermore, with the recent growth of the wearable device field, there is a growing demand for imparting elasticity to conductors. In particular, wearable devices that adhere closely to the body require a high degree of elasticity. To meet these demands, a conductive composition has been proposed that uses an elastomer as an organic binder containing metal powder, thereby imparting not only flexibility but also elasticity to the resulting conductor (for example, Patent Document 1).

[0004] However, when a wearable device is attached to clothing, for example, the pattern and degree of change in the shape of the wearable device will differ depending on the shape and size of the clothing, the wearer's physique, and their movement patterns (tendencies). In other words, when the same clothing is worn by different people performing the same actions, the pattern and degree of change in the shape of the clothing will differ greatly depending on the person, and similarly, the pattern and degree of change in the shape of a wearable device attached to clothing will also differ greatly depending on the person. In such cases, the wearable device may not be able to adequately follow the changes in the shape of the clothing due to insufficient stretching, and as a result, the wearable device may not operate stably.

[0005] Furthermore, conductive compositions tend to deteriorate over time after preparation. Therefore, when storing them for extended periods, it is common practice to seal them in appropriate storage containers to suppress this deterioration. However, once the storage container is opened, the deterioration of the conductive composition progresses over time. If the entire amount of the conductive composition sealed in the container is not used at once after opening, the remaining conductive composition may deteriorate and become unusable when used again. Specifically, the conductivity and elasticity of the conductive composition coating may worsen, potentially leading to malfunctions such as unstable device operation. In such cases, the remaining conductive composition must be discarded, necessitating the preparation of a new conductive composition, which reduces the efficiency of using the conductive composition and increases costs. Moreover, discarding conductive compositions without using them completely can increase the environmental burden. Therefore, from the perspective of improving efficiency (reducing costs and minimizing environmental impact), there is a need for conductive compositions that suppress deterioration over time after preparation. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2015 / 005204 brochure [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, a technical challenge exists in providing a conductive composition that can form a conductor that exhibits consistently high conductivity regardless of whether it is stretched or contracted significantly or only slightly (i.e., regardless of the degree of stretching or contraction).

[0008] Furthermore, another technical challenge is to provide a reusable conductive composition that suppresses deterioration over time after preparation, and as a result, can form a conductor that possesses both high conductivity and elasticity even after a long period of time has passed since opening the storage container.

[0009] Therefore, the present invention aims to provide a conductive composition that can form a conductor that has stable and high conductivity regardless of the degree of stretching, which is required for wearable devices, and which has suppressed degradation over time after preparation, as well as a conductor obtained by solidifying the conductive composition, a laminated structure having a layer of the conductor, and an electronic component having the conductor or laminated structure. Another object of the present invention is to provide a method for manufacturing a conductor, a laminated structure having a layer of the conductor, or an electronic component having the conductor or laminated structure using the above conductive composition. [Means for solving the problem]

[0010] As a result of diligent research, the inventors have found that the above problems can be solved in a conductive composition containing an elastomer, conductive particles, silica, fatty acids, and a solvent, by using chain-shaped conductive particles, setting the conductive particle content to 60-95% by mass on a solid content basis relative to the total mass of the conductive composition, and setting the particle density of the conductive particles, as measured by a grind gauge, to 10-40 μm. The present invention is based on this finding. In other words, the gist of the present invention is as follows.

[0011] [1] A conductive composition comprising an elastomer, conductive particles, silica, fatty acid, and solvent, The conductive particles are conductive particles in a collapsed state, The content of the conductive particles is 60 to 95% by mass in terms of solid content relative to the total mass of the conductive composition. A conductive composition characterized in that the conductive particles have a particle density of 10 to 40 μm as measured by a grind gauge. [2] The conductive composition according to [1], wherein the conductive particles are metal particles. [3] The conductive composition according to [1] or [2], wherein the average particle diameter (D50) of the conductive particles is 10 μm or more. [4] The tap density of the conductive particles is 2.0 g / cm³ 3 A conductive composition as described in any of the following [1] to [3]. [5] The BET specific surface area of ​​the silica is 100 to 1000 m² 2 A conductive composition according to any one of [1] to [4], wherein the amount is / g. [6] The conductive composition according to any one of [1] to [5], wherein the fatty acid comprises a fatty acid having 10 to 18 carbon atoms. [7] The conductive composition according to any one of [1] to [6], wherein the elastomer is a block copolymer consisting of hard blocks and soft blocks. [8] A conductive composition according to any one of [1] to [7], used for forming a conductor. A conductor obtained by solidifying one of the conductive compositions described in [9][1] to [8].

[10] A laminated structure comprising a substrate and a layer of the conductive material described in [9] laminated on the substrate. An electronic component comprising a conductive layer as described in

[11] [9], or a laminated structure as described in

[10] .

[12] A method for manufacturing an electronic component comprising a conductive layer, comprising the step of forming the conductive layer by solidifying a conductive composition according to any one of [1] to [8]. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a conductive composition that can form a conductor possessing both high conductivity and stretchability required for wearable devices, a conductor obtained by solidifying the conductive composition, a laminated structure having a layer of the conductor, and an electronic component comprising the conductor or the laminated structure. Furthermore, according to the present invention, it is possible to provide a method for manufacturing a conductor, a laminated structure having a layer of the conductor, or an electronic component comprising the conductor or the laminated structure using the above conductive composition.

[0013] Furthermore, the present invention provides a conductive composition in which deterioration over time after preparation is suppressed. Such a conductive composition can be reused as a conductive composition that can form a conductor possessing both high conductivity and elasticity, even after a long period of time has elapsed since preparation, for example, after a long period of time has elapsed since opening the sealed storage container containing the conductive composition. Therefore, the efficiency of use of the conductive composition can be improved, resulting in reduced costs and a reduced environmental impact. [Modes for carrying out the invention]

[0014] [Conductive composition] The conductive composition of the present invention contains an elastomer, conductive particles, silica, a fatty acid, and a solvent, wherein the conductive particles are chain-like conductive particles, and the content of the conductive particles and the grain density value measured by a grind gauge are adjusted within a specific range. In such a conductive composition of the present invention, it is considered that an appropriate dispersion state of the components is formed and maintained, and thus a conductor having both high conductivity and stretchability required for wearable devices can be formed. Although the reason why an appropriate dispersion state of the components is formed and maintained in the conductive composition of the present invention, and a conductor having both high conductivity and stretchability can be formed is not clear, it can be inferred as follows. That is, the fatty acid contained in the conductive composition promotes the dissociation of the conductive particles in the aggregated state, forms a dispersion state within a specific range, and further, the fatty acid and silica maintain the dispersion state over time. It is considered that the dispersion state of the conductive particles formed and maintained in this way changes depending on the grain density value of the conductive particles measured by a grind gauge, and when the grain density value is 10 to 40 μm, a dispersion state of the conductive particles suitable for forming a conductor having both high conductivity and stretchability is formed and maintained in the conductive composition. As a result, the conductive composition of the present invention can form and maintain a dispersion state of the conductive particles suitable for forming a conductor having both high conductivity and stretchability, and it is considered that a conductor formed by solidifying such a conductive composition can have both high conductivity and stretchability.

[0015] The conductive composition of the present invention preferably has a proton spin-spin relaxation time measured by the CPMG method (Carr Purcell Meiboom-Gill method) of pulsed NMR of 10 to 500 milliseconds. When the proton spin-spin relaxation time measured by the CPMG method of pulsed NMR is within such a range, a conductor having high conductivity and stretchability required for wearable devices can be formed. As the CPMG method using pulsed NMR for measuring the proton spin-spin relaxation time T2 of the conductive composition, a known method can be used. For example, the spin-spin relaxation time T2 can be measured using Spin Track manufactured by Resonance Systems. Specifically, the conductive composition is sufficiently stirred using a spatula, stirred for 1 minute using Awatoritenro (ARE-310, manufactured by Shinki Co., Ltd.), and using Spin Track manufactured by Resonance System, with the measurement nucleus being a proton, the measurement temperature being 30 °C, the frequency being 20 MHz, the 90° pulse, the pulse width being 2.5 μs, and the number of integrations being 16 times, an attenuation curve Y(t) is obtained by the CPMG method, and the following formula (1) corresponding to the obtained attenuation curve Y(t): Y(t)=A2exp(-t / T2)+Y2 Formula (1)<明 [In the formula, A2 and Y2 are constants, T2 is the relaxation time, and t is the measurement time.] Based on this, the relaxation time (spin-spin relaxation time) T2 of protons can be calculated.

[0016] According to the conductive composition of the present invention, by utilizing the above characteristics, it can be suitably used for forming conductors for wearable devices such as worn-on-body devices, extracorporeal devices, body surface devices, electronic skin devices, and intracorporeal devices. Hereinafter, each component contained in the conductive composition of the present invention will be described in detail.

[0017] <Elastomer> The conductive composition of the present invention contains an elastomer. The elastomer contained in the conductive composition can be used without particular limitations as long as it is a material that has rubber elasticity at room temperature. For example, rubber, thermoplastic elastomers, functional group-containing elastomers, block copolymers, etc., can be suitably used. The elastomer may be used alone or in combination of two or more types.

[0018] Any known and commonly used type of rubber can be used, such as diene-based rubber and non-diene-based rubber.

[0019] Any known or commonly used thermoplastic elastomer can be used, such as styrene elastomers, olefin elastomers, urethane elastomers, polyester elastomers, polyamide elastomers, acrylic elastomers, and silicone elastomers.

[0020] Any known or commonly used functional group-containing elastomer can be used, but from the viewpoint of elasticity, urethane-based and olefin-based elastomers are preferred, and from the viewpoint of solvent resistance, those having functional groups such as (meth)acryloyl groups, acid anhydride groups, carboxyl groups, and epoxy groups are preferred.

[0021] Any known and conventional block copolymer can be used, but preferably a block copolymer consisting of a hard segment and a soft segment is used.

[0022] Among the elastomers described above, block copolymers have low crystallinity and weak intermolecular forces, resulting in a lower glass transition temperature (Tg) compared to other rubbers. Therefore, even when mixed with conductive particles, they exhibit high flexibility and good elongation. Consequently, block copolymers are suitable for forming conductors for wearable devices. In this specification, a block copolymer refers to one that possesses rubber elasticity at room temperature (25°C). Any known or conventional block copolymer that satisfies the above conditions can be used. In particular, block copolymers of hard segments and soft segments are more preferable. In this specification, a hard segment refers to one with a Tg of 30°C or higher, while a soft segment refers to one with a Tg of 0°C or lower. The Tg is measured using the starting point method in accordance with the provisions of JIS K7121. However, regarding the heating rate and temperature, the Tg observed above 40°C is specifically obtained from a stabilized DSC curve obtained by repeatedly heating approximately 10 mg of sample from 25°C to 200°C at a heating rate of 10°C per minute using a differential scanning calorimeter (DSC-6100, manufactured by Hitachi High-Tech Science Corporation) under a nitrogen gas atmosphere. α-alumina is used as the reference. Furthermore, the Tg observed below 40°C is obtained from a stabilized DSC curve obtained by repeatedly heating approximately 10 mg of sample from -100°C to 100°C at a heating rate of 20°C per minute using a differential scanning calorimeter (DSC-6100, manufactured by Hitachi High-Tech Science Corporation) under a nitrogen gas atmosphere. The reference material used is α-alumina, as described above.

[0023] The ratio of hard segments to soft segments (mass of hard segments:mass of soft segments) in the block copolymer is not particularly limited as long as the curing of the present invention is achieved, but is preferably 10:90 to 70:30, and more preferably 10:90 to 40:60. When the ratio of hard segments to soft segments is within the above range, it is preferable because it suppresses wire breakage when the conductive material obtained by solidifying the conductive composition is stretched.

[0024] The block copolymers described above include X-block-Y-block diblock copolymers, X-block-Y-block-X-block types, X-block-Y-block-X-block types, X-block-Y-block-X'-block types, Y-block-X-block-Y-block types, and Y-block-X-block-Y'-block types. However, from the viewpoint of superior compatibility with other components and flexibility, X-block-Y-block-X-block triblock copolymers are preferred.

[0025] The unit structures constituting the hard segments in the block copolymer are not particularly limited as long as the effects of the present invention are achieved, and examples include methyl (meth)acrylate units and styrene units. Similarly, the unit structures constituting the soft segments are not particularly limited as long as the effects of the present invention are achieved, and examples include n-butyl acrylate units and butadiene units. As the block copolymer, for example, a triblock copolymer of polymethyl (meth)acrylate / poly-n-butyl (meth)acrylate / polymethyl (meth)acrylate can be used. In this specification, (meth)acrylate is a general term for acrylate and methacrylate, and the same applies to other similar expressions.

[0026] Commercially available block copolymers can be used. Examples of commercially available block copolymers include acrylic triblock copolymers manufactured by Arkema, Inc. using living polymerization. More specifically, SBM type copolymers represented by polystyrene-polybutadiene-polymethyl methacrylate, MAM type copolymers represented by polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate, and acrylic triblock copolymers of carboxylic acid-modified or hydrophilic group-modified MAM N type or MAM A type copolymers can be used. Examples of SBM type copolymers include E41, E40, E21, and E20. Examples of MAM type copolymers include M51, M52, M53, and M22. Examples of MAM N type copolymers include 52N and 22N. Examples of MAM A type copolymers include SM4032XM10. Another example of a commercially available block copolymer is Clarity®, an acrylic block copolymer manufactured by Kuraray Co., Ltd. Clarity® is a block copolymer derived from methyl methacrylate and butyl acrylate.

[0027] In addition to the commercially available products mentioned above, synthetic products prepared as appropriate may also be used as block copolymers. Examples of synthetic block copolymers containing (meth)acrylate polymer blocks include block copolymers synthesized by the methods described in Japanese Patent Publication No. 2007-516326 or Japanese Patent Publication No. 2005-515281.

[0028] The weight-average molecular weight of the block copolymer is preferably 20,000 to 400,000, and more preferably 50,000 to 300,000. When the weight-average molecular weight is 20,000 or more, toughness and flexibility can be imparted to the conductive material formed by solidifying the conductive composition, and excellent tackiness can be obtained when the conductive composition is molded and dried into a film or when it is applied to a substrate and dried. When the weight-average molecular weight is 400,000 or less, the conductive composition has good viscosity, and higher printability and processability can be achieved. Furthermore, when the weight-average molecular weight is 50,000 or more, excellent mitigation effects against external impacts can be obtained.

[0029] The tensile elongation at break of a block copolymer, measured according to the International Organization for Standardization (ISO) standard ISO 37, is preferably 100-600%. When the tensile elongation at break is 100-600%, the elasticity and electrical resistance stability of the conductor formed by solidifying the conductive composition are superior. More preferably, the tensile elongation at break of the block copolymer is 300-600%. The tensile elongation at break can be calculated according to the following formula. Tensile elongation at break (%) = (Elongation at break (mm) - Initial dimension (mm)) / (Initial dimension (mm)) × 100

[0030] When rubber or functional group-containing elastomers are used as elastomers, sulfur-based vulcanizing agents or non-sulfur-based vulcanizing agents are usually added to them. However, since metal particles such as silver powder may be oxidized or sulfurized and corroded by sulfur-based vulcanizing agents, it is preferable not to add sulfur-based vulcanizing agents to the elastomer when metal particles are used as conductive particles, and it is preferable to add non-sulfur-based vulcanizing agents as needed.

[0031] The conductive composition of the present invention may contain a small amount of sulfur compound, as long as it does not impair the effects of the present invention.

[0032] Furthermore, the elastomer may contain known additives such as softeners and plasticizers. Examples of softeners include mineral oil-based softeners and vegetable oil-based softeners. Examples of mineral oil-based softeners include various oils such as paraffinic process oils, naphthenic process oils, and aromatic process oils. Examples of vegetable oil-based softeners include castor oil, linseed oil, flaxseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, pine oil, and tall oil. These softeners may be used individually or in combination of two or more. The desired rubber elasticity and stretchability can be adjusted by the amount of softener added.

[0033] The elastomer content in the conductive composition is preferably 5 to 40% by mass, more preferably 14 to 28% by mass, based on the total solid content in the conductive composition. Furthermore, from the viewpoint of the elasticity of the formed conductor, the block copolymer content in the total elastomer is preferably 85 to 100% by mass. When the block copolymer content is within the above range, the elasticity of the conductor formed by solidifying the conductive composition is better. Note that the conductive composition of the present invention may contain other organic binders such as thermoplastic resins other than elastomers, as long as it does not impair the effects of the present invention. In the present invention, solid content refers to the conductive composition excluding the solvent.

[0034] <Conductive particles> The conductive composition of the present invention contains conductive particles. The conductive particles included in the conductive composition can be conventionally known materials used in conductive compositions, such as carbon particles like graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; metal particles like copper powder, nickel powder, and silver powder; metal carbides like WC, B4C, ZrC, NbC, MoC, TiC, and TaC; metal nitrides like TiN, ZrN, and TaN; and metal silicides like WSi2 and MoSi2. These conductive particles may be used individually or in combination of two or more. Preferably, metal particles, and more preferably silver powder, are used as conductive particles because they yield a conductive composition with low electrical resistance. Furthermore, in the conductive composition of the present invention, the conductive particles are in a chain-like (aggregated) state (i.e., chain-shaped conductive particles). Therefore, it is particularly preferable to use chain-like (aggregated) silver powder as the conductive particles.

[0035] The conductive composition of the present invention has an Rsp value, measured by pulsed NMR of a dispersion of conductive particles in a solvent described later, for example, measured by a Spin Track from Resonance Systems, which is preferably 0.02 to 1.0, more preferably 0.03 to 0.5, and even more preferably 0.05 to 0.2. This Rsp value is an indicator of the compatibility (affinity) between the conductive particles and the solvent in the conductive composition. A larger Rsp value indicates higher compatibility between the conductive particles and the solvent (i.e., higher dispersibility of the conductive particles in the conductive composition), while a smaller Rsp value indicates lower compatibility between the conductive particles and the solvent (i.e., lower dispersibility of the conductive particles in the conductive composition). Furthermore, a larger Rsp value means that even if the conductive particles dispersed in the conductive composition settle, they can be easily redispersed by stirring. The Rsp value is calculated using pulsed NMR using the following formula (2): Rsp = (Rav - Rb) / (Rb) (1) Equation (2) [In the formula, Rav is the reciprocal of the spin-spin relaxation time when measuring a dispersion of 1% by mass of conductive particles in the same organic solvent as the conductive composition, and Rb is the reciprocal of the spin-spin relaxation time when measuring only the same organic solvent as the conductive composition.] This can be calculated based on the above.

[0036] The conductive particles have a particle density of 10-40 μm, as measured by a grind gauge. Although the detailed mechanism is not clear, it is believed that when conductive particles have a particle density within this range, they are properly dispersed in the conductive composition, and as a result, the conductor formed by solidifying the conductive composition can achieve both high conductivity and elasticity. The particle density of conductive particles can be measured using a grind gauge (SU2050MHJ, manufactured by Daiichi Sokuhan Seisakusho Co., Ltd.). Specifically, the conductive composition is thoroughly stirred using a spatula, stirred for 1 minute using an Awatori Rentaro (ARE-310, manufactured by Shinky Co., Ltd.), diluted by adding 0.3 grams of propylene glycol monomethyl ether acetate per gram of conductive composition to obtain a dilution, and the obtained dilution is applied to a grind gauge (SU2050MHJ, manufactured by Daiichi Sokuhan Seisakusho Co., Ltd.) using a scraper (SK9225, manufactured by Daiichi Sokuhan Seisakusho Co., Ltd.). The upper limit of the interval in which 20 or more particles are observed when reading the scale at 5.0 μm intervals is defined as the particle density value. Therefore, with respect to conductive particles, "a particle density value of 10 to 40 μm measured by the grind gauge" means that conductive particles are present in the conductive composition such that the particle density value of conductive particles measured by the method described above is in the range of 10 to 40 μm. The particle density value of conductive particles is preferably 15 to 40 μm, more preferably 20 to 40 μm.

[0037] The conductive particles, when measured in accordance with ISO 3953 with 1000 taps, preferably have a tap density of 2.0 g / cm³. 3 More preferably, 0.3 to 1.5 g / cm³ 3 More preferably 0.3 to 1.0 g / cm³ 3Although the detailed mechanism is not clear, it is thought that the conductive particles having a tap density within this range increases the volume per unit mass of the conductive particles, resulting in many contact points between the conductive particles, thus achieving high conductivity. As a result, it is thought that the increase in resistance can be sufficiently suppressed whether the conductor is strongly or weakly stretched.

[0038] The shape of each particle (primary particle) constituting the conductive particles is not particularly limited as long as the effects of the present invention are achieved. Examples include spherical, substantially spherical, needle-shaped, ellipsoidal, flake-shaped, flaky, irregularly shaped, etc., and is preferably spherical or substantially spherical. As conductive particles, one type of particle having the same shape may be used alone, or two or more types of particles having different shapes may be used in combination.

[0039] The average particle diameter (average primary particle diameter) of each conductive particle (primary particle) constituting the chain-like conductive particles is preferably 0.1 to 10 μm, more preferably 0.1 to 5 μm. The average particle diameter (average secondary particle diameter) of the chain-like conductive particles (secondary particles) is preferably 1 to 100 μm, more preferably 10 to 50 μm. For example, if the conductive particles are chain-like silver powder, the average primary particle diameter of each silver powder particle constituting the chain-like silver powder is preferably 1.0 μm or less, more preferably 0.1 to 1.0 μm. Furthermore, the average secondary particle diameter (D50) of the chain-like silver powder is preferably 10 μm or more, more preferably 10 to 50 μm. When the average secondary particle diameter is within this range, the conductive particles in the conductive composition will have many contact points with each other, which is thought to result in high conductivity. As a result, it is thought that the increase in resistance can be sufficiently suppressed whether the conductor is strongly or weakly stretched.

[0040] The average primary particle diameter of conductive particles can be measured by observing conductive particles in powder form with a scanning electron microscope at a magnification of 10,000x, randomly selecting 10 primary particles, and measuring their particle diameters. The average of these particle diameters is then used to determine the average value of the measured particle diameters.

[0041] The average secondary particle diameter (D50) of the conductive particles can be measured according to the following procedure. First, dilute the conductive composition with 3000% by mass of propylene glycol monomethyl ether acetate to obtain a solution. Using a laser diffraction scattering particle size distribution analyzer (TM3000, manufactured by Microtrac Bell Corporation), measure the particle size distribution in reflection mode within a measurement range of 0.020 μm to 1000.00 μm with the refractive index of the solvent set to 1.40. From this particle size distribution, obtain the particle diameter at 50% cumulative percentage, and use it as the average secondary particle diameter (D50) of the conductive particles.

[0042] The apparent porosity of the chain-like conductive particles is preferably 50 to 95%, more preferably 60 to 90%. The apparent porosity of the chain-like conductive particles is an index representing the state of an aggregated structure (secondary particles) in which the primary particles of the conductive particles are connected and appropriate voids exist. For example, when the conductive particles are chain-like silver powder, its apparent porosity is preferably 50 to 95%, more preferably 60 to 95%.

[0043] The apparent porosity of the chain-like conductive particles can be measured as follows. That is, Let the density of the conductive particles be ρ0 (g / cm 3 ), When a load of 1 kg is applied to conductive particles with a mass of M (g), and after 1 hour has passed, the volume of the conductive particles is V (cm 3 ), the apparent density ρ (g / cm 3 ) is defined as ρ = M / V From the apparent density, the apparent porosity (P) can be calculated by the following formula. P = (1 - ρ / ρ0) × 100 For example, when the conductive particles are chain-like silver powder, the density ρ0 is 10.49 g / cm 3 .

[0044] The DBP oil absorption of chain-shaped conductive particles, as measured in accordance with JIS K 6217-4:2017, is preferably 30 to 300 ml / 100 g, more preferably 50 to 200 ml / 100 g. For example, if the conductive particles are chain-shaped silver powder, the DBP oil absorption of the chain-shaped silver powder, as measured in accordance with JIS K 6217-4:2017, is preferably 50 to 150 ml / 100 g.

[0045] The content of conductive particles in the conductive composition is 60 to 95% by mass, preferably 65 to 85% by mass, and more preferably 70 to 80% by mass, based on the total amount of solids contained in the conductive composition. When the content of conductive particles in the conductive composition is within this range, a conductor can be obtained that has a low initial electrical resistance value before stretching and maintains a stably low electrical resistance value even when stretched, as a conductor formed by solidifying the conductive composition.

[0046] <Fatty acid> The conductive composition of the present invention contains fatty acids. It is believed that the inclusion of fatty acids in the conductive composition promotes the dissociation of aggregated conductive particles and further stabilizes the dispersion state of the conductive particles. When the conductive particles have a particle density within the range described above, it is believed that the fatty acids stably maintain the dissociation and dispersion state of the conductive particles in a state suitable for forming a conductor that combines high conductivity and elasticity. Furthermore, because the inclusion of fatty acids in the conductive composition stably maintains the dispersion state of the conductive particles, an additional effect is achieved in that the deterioration of the performance of the conductive composition over time can be suppressed.

[0047] Any type of fatty acid can be used, including straight-chain fatty acids, branched-chain fatty acids, and cyclic fatty acids, and either saturated or unsaturated fatty acids can be used.

[0048] The number of carbon atoms in the fatty acid is not particularly limited as long as the effects of the present invention are achieved, but for example, it is 10 to 18. From the viewpoint of suppressing adverse effects on wiring layers and electrodes using conductive compositions, stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, linolenic acid, etc. are particularly preferred. One type of fatty acid may be used alone, or two or more types may be used in combination.

[0049] The fatty acid content in the conductive composition is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, and even more preferably 0.1 to 1% by mass, based on the total amount of solids contained in the conductive composition.

[0050] <Silica> The conductive composition of the present invention contains silica. It is believed that the inclusion of silica in the conductive composition allows for the stable maintenance of the dispersion state of conductive particles within the conductive composition. Furthermore, when the conductive particles have a particle density within the range described above, it is believed that silica stably maintains the dispersion state of the conductive particles in a manner suitable for forming a conductor that combines high conductivity and elasticity. In addition, because the inclusion of silica in the conductive composition allows for the stable maintenance of the dispersion state of conductive particles, there is also the incidental effect of suppressing the deterioration of the performance of the conductive composition over time. In particular, it is believed that the combination of the fatty acid and silica described above allows for particularly stable maintenance of the dissociation and dispersion state of conductive particles.

[0051] Examples of silica types that can be used include fused silica, spherical silica, amorphous silica, and crystalline silica. Furthermore, silica with various surface treatments can also be used. Silica may be used individually or in combination of two or more types.

[0052] The surface area of ​​silica is not particularly limited as long as the effects of the present invention are achieved, but the BET specific surface area is preferably 100 to 1000 m². 2 / g, more preferably 100-800m 2 / g, more preferably 100-500m 2 The value is / g. It is believed that silica having a BET specific surface area within this range allows for the stable maintenance of the dispersion state of silica in the conductive composition. Furthermore, when silica has a BET specific surface area within the above range, it is believed that silica stably maintains the dispersion state of conductive particles in a state suitable for forming a conductor that combines high conductivity and elasticity. In addition, because silica can stably maintain the dispersion state of conductive particles in this way, there is also the incidental effect of suppressing the deterioration of the performance of the conductive composition over time. The BET specific surface area can be measured by the gas adsorption method in accordance with JIS Z8831.

[0053] The average particle size (D50) of silica is preferably 1 to 1000 nm, more preferably 5 to 500 nm, and even more preferably 10 to 100 nm.

[0054] The silica content in the conductive composition is preferably 0.01 to 10% by mass, more preferably 0.1 to 5% by mass, and even more preferably 0.5 to 3% by mass, based on the total amount of solids contained in the conductive composition.

[0055] <Solvent> The conductive composition of the present invention contains a solvent. From the viewpoint of preparing the conductive composition and adjusting the viscosity for applying the conductive composition to a substrate, an organic solvent is preferably used as the solvent.

[0056] Examples of organic solvents include ketones, aromatic hydrocarbons, glycol ethers, glycol ether acetates, esters, alcohols, aliphatic hydrocarbons, and petroleum-based solvents. More specifically, examples include ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene; glycol ethers such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, and triethylene glycol monoethyl ether; esters such as ethyl acetate, butyl acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, and propylene glycol butyl ether acetate; alcohols such as ethanol, propanol, ethylene glycol, propylene glycol, butylene glycol, and terpineol; aliphatic hydrocarbons such as octane and decane; and petroleum-based solvents such as petroleum ether, petroleum naphtha, hydrogenated petroleum naphtha, and solvent naphtha. Organic solvents may be used individually or in combination of two or more types.

[0057] The boiling point of the organic solvent is not particularly limited, but is preferably 150°C or higher, more preferably 200°C or higher. When using an organic solvent with a boiling point in this range, it is possible to suppress the evaporation of the organic solvent during the device manufacturing process, which can reduce the continuous printability and processability of the conductive composition.

[0058] The solvent content in the conductive composition is preferably 1 to 50% by mass, more preferably 10 to 40% by mass, and even more preferably 15 to 30% by mass, based on the total mass of the conductive composition.

[0059] <Other ingredients> The conductive composition of the present invention may contain other components in addition to the components described above. These other components are not particularly limited, as they are commonly used in the manufacture of conductive compositions and do not impair the effects of the present invention. Examples of other components include thermosetting components, additives, and pigments.

[0060] Examples of thermosetting components include polyester resins (urethane modified, epoxy modified, acrylic modified, etc.), epoxy resins, urethane resins, phenolic resins, melamine resins, vinyl resins, silicone resins, and blocked isocyanates, which can form films through molecular weight increase and crosslinking by curing reactions.

[0061] Examples of additives include coupling agents, photopolymerization initiators, and flame retardants.

[0062] The conductive composition of the present invention can be manufactured, for example, by kneading an elastomer dissolved in a solvent with conductive particles. Examples of kneading methods include using a stirring and mixing device such as a roll mill. Specifically, an elastomer solution with a solid content of 50% by mass is prepared by dissolving the elastomer in a solvent. Conductive particles are added to this elastomer solution, pre-mixed with a stirrer, and then kneaded with a three-roll mill to obtain the conductive composition. Depending on the type of elastomer component used and the solvent mixing ratio, the conductive composition can be in liquid form or paste form (semi-solid). In the manufacture of the conductive composition of the present invention, preferably by kneading with a three-roll mill four or more times, an appropriate dispersion state of components that allows for the formation of a highly elastic conductor can be achieved in the conductive composition.

[0063] The viscosity of the conductive composition of the present invention is not particularly limited, but is preferably adjusted to 100 to 5000 dPa·s, more preferably to 200 to 1000 dPa·s. By adjusting the viscosity of the conductive composition to this range, a conductive composition with excellent printability and processability required in the device manufacturing process can be obtained.

[0064] In the present invention, the conductive composition described above can be used to form a conductor by, for example, pattern coating it onto a substrate and then heat-treating it. Examples of such heat treatments include drying and thermosetting.

[0065] [conductor] The conductive composition described above can be solidified to form a conductor. For example, a conductive layer can be formed by forming a coating film made of the conductive composition, drying it, and solidifying it. Solidification of the conductive composition is carried out by drying or heat treatment of the conductive composition. Examples of heat treatment include hot air drying and thermosetting. Molding may be performed prior to heat treatment. For example, a conductive layer can be obtained by coating the conductive composition onto a substrate in the desired shape and then solidifying it. The conductive layer may be in various shapes depending on the application. For example, it can be suitably applied to conductive circuits, wiring, etc.

[0066] When manufacturing a conductive circuit, the process includes a pattern formation step of printing or coating the above-mentioned conductive composition onto a substrate to form a coating pattern, and a step of solidifying the patterned coating. Methods such as masking or using a resist can be used to form the coating pattern.

[0067] Pattern formation processes include printing methods and dispensing methods. Printing methods include gravure printing, offset printing, and screen printing, with screen printing being preferred for forming fine circuits. For large-area coating, gravure printing and offset printing are suitable. The dispensing method involves controlling the amount of conductive composition applied and extruding it from a needle to form a pattern. This method is suitable for forming partial patterns such as earth wiring and for forming patterns on uneven surfaces.

[0068] The substrate to which the conductive composition is applied can be any electrically insulating material without particular limitations. Examples include copper-clad laminates of all grades (FR-4, etc.) using composite materials such as paper-phenolic resin, paper-epoxy resin, glass cloth-epoxy resin, glass-polyimide, glass cloth / nonwoven fabric-epoxy resin, glass cloth / paper-epoxy resin, synthetic fiber-epoxy resin, fluororesin / polyethylene / polyphenylene ether, polyphenylene oxide / cyanate ester, etc., sheets or films made of polyester such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polyimide, polyphenylene sulfide, polyamide, etc., sheets or films made of crosslinked rubber such as urethane, silicone rubber, acrylic rubber, butadiene rubber, etc., and sheets or films made of thermoplastic elastomers such as polyester, polyurethane, polyolefin, and styrene block copolymers. Among these, by using not only flexible materials but also stretchable materials (e.g., rubber, thermoplastic elastomers, urethane, etc.) as the substrate, the conductor can be applied to the applications described later. As for the stretchable material, the same material as described above for elastomers can be used.

[0069] [Laminated structure] The conductor described above can be formed into a laminated structure by creating multiple layers. There are no particular restrictions on the method of forming the laminated structure, but for example, conductors formed by solidifying conductive compositions may be bonded together by heat, pressure, or both, or a conductive composition may be applied to the conductor and then solidified. The laminated structure may also include layers other than the conductor described above, such as a metal layer, an insulating layer, a protective layer, an adhesive layer, a bonding layer, and a void layer.

[0070] [Electronic components] Electronic components can be formed using the aforementioned conductors and laminated structures as constituent elements. There are no particular restrictions on the structure, formation method, or application of electronic components that use the aforementioned conductors and laminated structures as constituent elements, but examples include sensors, actuators, capacitors, inductors, transistors, converters, thermistors, connectors, transformers, capacitors, diodes, regulators, motors, antennas, switches, etc., and may have multiple applications among these.

[0071] [Applications in conductors, multilayer structures, and electronic components] As described above, the conductive material formed by solidifying the conductive composition of the present invention exhibits excellent electrical resistance stability even when repeatedly expanding and contracting or when maintaining an extended state. Therefore, it can be suitably used to form conductive materials for wearable devices such as clothing devices, external devices, surface devices, electronic skin devices, and internal devices, in addition to conductive circuits and wiring. Furthermore, the conductive layer can also be applied to electrodes of flexible printed circuit boards. Moreover, the conductive composition of the present invention is also suitable for forming conductive layers such as actuator electrodes. It is also suitable for forming conductive materials with designs that were previously difficult to realize due to insufficient stretchability or electrical resistance stability. Specific applications of the conductive material include, for example, the following.

[0072] <Wearable biosensors> The conductor of the present invention can be applied as a wiring material for wearable biosensors attached to clothing or the body to acquire and transmit action potentials / biological information generated from plants and animals, including humans. The sensor must be attached to a location that is in close contact with or near the surface tissue of plants and animals, including humans, but surface tissues stretch and contract. Furthermore, when attached to clothing, the pattern and degree of change in the shape of the clothing (stretching and contracting) differs depending on the wearer's physique and movement patterns (tendencies). Conventional rigid and flexible substrates lack the ability to follow the stretching and contracting of attachment locations, limiting the locations where sensors can be attached, and consequently limiting the amount of biological information that can be obtained. With the conductor of the present invention, the sensor wiring material can be applied to the surface tissue of plants and animals, including humans, and to clothing, making it possible to create a wearable biosensor that can be attached to locations where stretching and contracting occur, as well as to clothing.

[0073] Since the wiring used in wearable biosensors can be formed by screen printing or dispensing methods, it is possible to miniaturize the signal wiring, which is expected to contribute to the miniaturization of sensor devices.

[0074] <Wiring materials for smart textiles> In recent years, the field of so-called "smart textiles," which uses woven fabrics as sensors, has been expanding. The wiring board or sensor formed on a stretchable, heat-sealable substrate using the conductive material of the present invention exhibits excellent stability of electrical resistance during stretching. Therefore, by attaching it to the surface of a stretchable woven fabric, it becomes possible to develop a woven fabric with the functionality of an electronic device, i.e., a smart textile. As a smart textile, functions such as pressure sensors, touch sensors, and antenna wiring can be added to the woven fabric.

[0075] <Wiring for 3D molded products> Conventional FIM (Film Insert Molding) plastic molded products for electronic equipment casings and the like use a plastic film such as polycarbonate as the base material, which is then heat-pressed after design printing. The conductive wiring of the present invention, which consists of a laminated structure in which a conductor is provided on a stretchable base material, has the characteristics of not breaking when stretched and suppressing changes in resistance. Therefore, by forming the conductive wiring during design printing of the plastic molded product and then performing molding by heat pressing (which causes partial stretching), it is possible to realize electronic devices with built-in 3D-shaped wiring.

[0076] Furthermore, by performing heat pressing using a stretchable substrate such as elastomer as described above, it is possible to realize a stretchable and deformable electronic device with flexible wiring inside a flexible housing. This can be suitably used as a pressure sensor, touch sensor, or for antenna wiring, etc.

[0077] <Stretchable and deformable wiring sheet or wiring board> The conductive wiring of the present invention, comprising a laminated structure in which layers of conductive material are provided on a stretchable substrate, can be used as a stretchable and deformable wiring board sheet. For example, such conductive wiring can be attached to the surface of an object having a three-dimensional shape, such as a molded product, by stretching or deforming it without causing the wiring to break. Therefore, the laminated structure of the present invention, in which layers of conductive material are provided on a stretchable substrate, can be suitably used for pressure sensors, touch sensors, or antenna wiring.

[0078] <Flexible wiring sheet or wiring board> Conventional flexible wiring sheets or circuit boards using conductive pastes can experience wire breakage when subjected to extreme bending, such as clip-folding. However, when using the conductive material of the present invention, because it is a conductive material with elongation properties, it can accommodate bending in areas that conventional conductive pastes could not handle, and a flexible wiring sheet or circuit board can be realized that does not experience wire breakage even when clip-folding is performed. [Examples]

[0079] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, unless otherwise specified, "parts" and "%" all refer to mass.

[0080] [Preparation of conductive compositions] The following materials were prepared as components for the conductive composition. Elastomer A: Acrylic block copolymer (product code LA2250, manufactured by Kuraray Co., Ltd.) Elastomer B: Polyester resin (product code Byron 290, manufactured by Toyobo Co., Ltd.) Solvent: Diethylene glycol monoethyl ether acetate Silica: AEROSIL (product code AEROSIL200, manufactured by EVONIK, BET specific surface area 200m²) 2 / g) Fatty acids: Lauric acid Conductive particle A Conductive particles B conductive particles C Conductive particles D The particle shapes, average secondary particle diameter (D50), and tap density of conductive particles A to D are as shown in Table 1 below. [Table 1]

[0081] The tap density of each conductive particle was measured in accordance with ISO 3953, with 1000 taps.

[0082] Each conductive composition was prepared according to the following procedure. First, the elastomers described above were dissolved in a solvent to prepare an elastomer solution with a solid content of 50% by mass. Next, the conductive particles described above and the elastomer solution were mixed to the compositions shown in Table 2 below. After preliminary stirring and mixing with a stirrer, the mixture was kneaded using a three-roll mill (EXAKT50, manufactured by EXAKT) to obtain the conductive compositions of Examples 1-4 and Comparative Examples 1-6.

[0083] [Table 2]

[0084] The particle density of each conductive particle was measured by the following method. Specifically, each conductive composition was thoroughly stirred using a spatula, stirred for 1 minute using an Awatori Rentaro (ARE-310, manufactured by Shinky Co., Ltd.), diluted with 0.3 grams of propylene glycol monomethyl ether acetate per gram of conductive composition to obtain a dilution, applied the obtained dilution to a grind gauge (SU2050MHJ, manufactured by Daiichi Sokuhan Seisakusho Co., Ltd.) using a scraper (SK9225, manufactured by Daiichi Sokuhan Seisakusho Co., Ltd.), and the scale was read at 5.0 μm intervals. The upper limit of the interval in which 20 or more particles were observed was defined as the particle density value.

[0085] [Evaluation of conductive compositions] Each conductive composition of the Examples and Comparative Examples, immediately after preparation (new), was screen-printed onto a substrate and heat-treated at 80°C for 30 minutes to form a conductive material with a line width of 1 mm, a thickness of 20 μm, and a length of 40 mm on the substrate. A urethane film (TG88-I, manufactured by Takeda Sangyo Co., Ltd., 70 μm thick) was used as the substrate. The conductive material was stretched at a speed of 5 mm / second to predetermined degrees of elongation (2% elongation, 10% elongation, 30% elongation, 50% elongation), held in that state for 15 seconds, and the resistivity (volume resistivity) of the conductive material was measured. The conductivity of the conductive material during stretching was evaluated according to the following evaluation criteria. The evaluation results are shown in 2. ○: The increase in resistance is 20 times or less compared to before stretching, and sufficiently high conductivity is maintained. △: The increase in resistance is more than 20 times but less than 50 times compared to before stretching, and high conductivity is maintained. ×: The resistance increased by more than 50 times compared to before extension, indicating insufficient maintenance of conductivity.

[0086] Each conductive composition of the examples and comparative examples was prepared by filling and sealing storage containers immediately after preparation. Six months after opening the storage containers, the conductivity of each conductive composition during extension of the conductor was evaluated according to the same method as described above. The evaluation results are shown in Table 2.

[0087] The evaluation results shown in Table 2 indicate that when the conductive compositions of each example were used immediately after preparation, high conductivity was maintained even during stretching. Specifically, a conductive composition containing an elastomer, conductive particles, silica, fatty acids, and a solvent, wherein the conductive particles are in a chain-like structure, the content of conductive particles is 60-95% by mass in terms of solid content relative to the total mass of the conductive composition, and the particle density of the conductive particles measured by a grind gauge is 10-40 μm, can form a conductor that combines high conductivity and stretchability. Furthermore, it can be seen that even when the conductive compositions of each example were used 6 months after opening, such high conductivity during stretching was almost maintained. In other words, it can be said that deterioration over time after preparation was suppressed in the conductive compositions of each example. On the other hand, when the conductive compositions of each comparative example were used, high conductivity was not maintained during stretching, whether the conductive compositions were used immediately after preparation or 6 months after opening.

Claims

1. A conductive composition comprising an elastomer, conductive particles, silica, fatty acid, and solvent, The conductive particles are conductive particles in a collapsed state, The content of the conductive particles is 60 to 88% by mass in terms of solid content, based on the total amount of solid content contained in the conductive composition. The conductive particles have a particle density of 10 to 40 μm as measured by a grind gauge. The elastomer content is 5 to 40% by mass in terms of solid content, based on the total amount of solids contained in the conductive composition. The silica content is 0.01 to 10% by mass, based on the total amount of solids contained in the conductive composition. The content of the fatty acid is 0.01 to 10% by mass, based on the total amount of solids contained in the conductive composition. A conductive composition characterized by the following features.

2. The conductive composition according to claim 1, wherein the conductive particles are metal particles.

3. The conductive composition according to claim 1 or 2, wherein the average particle diameter (D50) of the conductive particles is 10 μm or more.

4. The conductive composition according to any one of claims 1 to 3, wherein the tap density of the conductive particles is 2.0 g / cm³ or less.

5. The conductive composition according to any one of claims 1 to 4, wherein the BET specific surface area of ​​the silica is 100 to 1000 m² / g.

6. The conductive composition according to any one of claims 1 to 5, wherein the fatty acid comprises a fatty acid having 10 to 18 carbon atoms.

7. The conductive composition according to any one of claims 1 to 6, wherein the elastomer is a block copolymer consisting of a hard block and a soft block.

8. A conductive composition according to any one of claims 1 to 7, used for forming a conductor.

9. A conductor obtained by solidifying the conductive composition according to any one of claims 1 to 8.

10. A laminated structure comprising a base material and a layer of the conductive material according to claim 9 laminated on the base material.

11. An electronic component comprising a conductive layer according to claim 9, or a laminated structure according to claim 10.

12. A method for manufacturing an electronic component comprising a conductive layer, comprising the step of forming the conductive layer by solidifying a conductive composition according to any one of claims 1 to 8.

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