Electroconductive composition, conductor using same, laminated structure, and electronic component

Abstract

[Problem] To provide an electroconductive composition capable of forming a conductor endowed with the high electroconductivity and stretchability that are required for a wearable device. [Solution] An electroconductive composition wherein: a binder resin, electroconductive particles, and a solvent are blended; and the proton spin-spin relaxation time measured by the CPMG method of pulsed NMR is 10-500 milliseconds.

Description

Conductive composition, and conductor, laminate structure, and electronic component using the same

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

[0002] Conventionally, a paste-like conductive composition comprising a metal powder mixed with an organic binder has been used as a material for forming a patterned conductor such as an electrode of a printed wiring board. Such a conductive composition can be applied in a pattern and then solidified to form a desired conductor, but the resulting conductor generally has high hardness. Therefore, it has been difficult to say that such a conductive composition can fully function in wiring boards that require flexibility, such as flexible printed wiring boards. Therefore, there is a need for a conductive composition that can form a conductor suitable for wiring boards that require flexibility, such as flexible printed wiring boards, and that can stably and fully function even when bent together with the wiring board.

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

[0004] However, for example, when a wearable device is attached to clothing, the pattern and degree of shape change of the wearable device will vary depending on the shape and size of the clothing, the physique and movement patterns (tendencies) of the wearer of the clothing, etc. In other words, when different subjects wear the same clothing and perform the same movement, the pattern and degree of shape change of the clothing will vary greatly depending on the subject, and therefore the pattern and degree of shape change of the wearable device attached to the clothing will also vary greatly depending on the subject. In such cases, the wearable device may not be able to adequately follow the changes in the shape of the clothing due to insufficient stretchability, and as a result, the wearable device may not operate stably.

[0005] Furthermore, because conductive compositions tend to deteriorate over time after preparation, long-term storage typically involves storing them in a sealed container to prevent this deterioration. However, once the container is opened, the deterioration of the conductive composition progresses over time. Therefore, if the entire amount of 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 film may deteriorate, resulting in a malfunction in which the device does not operate stably. In such cases, the remaining conductive composition must be discarded, necessitating the preparation of a new conductive composition, resulting in a decrease in the utilization efficiency of the conductive composition and an increase in costs. Furthermore, discarding the conductive composition before it is fully used may increase the environmental burden. Therefore, from the perspective of improving utilization efficiency (reducing costs and minimizing environmental burden), there is a demand for a conductive composition whose utilization efficiency over time after preparation is suppressed.

[0006] International Publication No. 2015 / 005204

[0007] Therefore, a technical challenge exists to provide a conductive composition that can form a conductor that has stable high conductivity whether it is stretched greatly or only slightly (i.e., regardless of the degree of stretching).

[0008] Another technical challenge is to provide a conductive composition that can be reused as a conductive composition that suppresses deterioration over time after preparation and, as a result, can form a conductor that combines high conductivity and stretchability even after a long period of time has passed since the storage container was opened.

[0009] Therefore, an object of the present invention is to provide a conductive composition that can form a conductor that has stable high conductivity regardless of the degree of stretching required for wearable devices and that is inhibited from deteriorating over time after preparation, as well as a conductor obtained by solidifying the conductive composition, a laminate structure including a layer of the conductor, and an electronic component including the conductor or laminate structure. Another object of the present invention is to provide a method for producing a conductor, a laminate structure including a layer of the conductor, or an electronic component including the conductor or laminate structure, using the conductive composition.

[0010] As a result of extensive research, the present inventors have discovered that the above-mentioned problems can be solved by adjusting the proton spin-spin relaxation time, measured by the CPMG method of pulsed NMR, to 10 to 500 milliseconds in a conductive composition containing a binder resin, conductive particles, and a solvent. The present invention is based on this discovery. Specifically, the gist of the present invention is as follows.

[0011] [1] A conductive composition comprising a binder resin, conductive particles, and a solvent, wherein the proton spin-spin relaxation time measured by the CPMG method of pulsed NMR is 10 to 500 milliseconds. [2] The conductive composition according to [1], wherein a dispersion of the conductive particles in the solvent has an Rsp value of 0.02 to 1.0 measured by pulsed NMR. [3] The conductive composition according to [1] or [2], wherein the proton spin-spin relaxation time measured by the CPMG method of pulsed NMR is 100 to 300 milliseconds. [4] The conductive composition according to any of [1] to [3], wherein the conductive particles are metal particles. [5] The conductive composition according to any of [1] to [4], further comprising silica. [6] The conductive composition according to any of [1] to [5], further comprising a fatty acid. [7] The conductive composition according to any of [1] to [6], which is used to form a conductor. [8] A conductor obtained by solidifying the conductive composition according to any of [1] to [7]. [9] The conductor according to [8], which has a resistance change of 50 times or less at 30% elongation.

[10] A laminated structure comprising a substrate and a layer of the conductor according to [8] or [9] laminated on the substrate.

[11] The laminated structure according to

[10] , wherein the substrate is a stretchable substrate having a tensile elongation at break of 200% or more.

[12] An electronic component comprising the layer of the conductor according to [8] or [9], or the laminated structure according to

[10] or

[11] .

[13] A method for producing an electronic component comprising a layer of a conductor, the method comprising a step of forming the layer of the conductor by solidifying the conductive composition according to any one of [1] to [7].

[0012] According to the present invention, it is possible to provide a conductive composition capable of forming a conductor having both high conductivity and stretchability required for wearable devices, a conductor obtained by solidifying the conductive composition, a laminate structure including a layer of the conductor, and an electronic component including the conductor or laminate structure. Furthermore, according to the present invention, it is possible to provide a method for manufacturing a conductor, a laminate structure including a layer of the conductor, or an electronic component including the conductor or laminate structure, using the conductive composition.

[0013] Furthermore, according to the present invention, a conductive composition can be provided in which deterioration over time after preparation is suppressed. Such a conductive composition can be reused as a conductive composition capable of forming a conductor having both high conductivity and stretchability even if a long period of time has passed since preparation, for example, even if a long period of time has passed since the opening of a storage container in which the conductive composition is sealed. Therefore, the use efficiency of the conductive composition can be improved, resulting in cost reduction and environmental load reduction.

[0014] [Conductive Composition] The conductive composition of the present invention comprises a binder resin, conductive particles, and a solvent, and is a conductive composition in which the proton spin-spin relaxation time measured by the CPMG method (CarrPurcell Meiboom-Gill method) of pulsed NMR is adjusted to 10 to 500 milliseconds, preferably 100 to 300 milliseconds. With such a conductive composition of the present invention, a conductor having both high conductivity and stretchability required for wearable devices can be formed. The reason why a conductor having both high conductivity and stretchability can be formed with the conductive composition of the present invention is not clear, but can be inferred as follows. Generally, the proton spin-spin relaxation time (hereinafter simply referred to as "spin-spin relaxation time T") measured by the CPMG method of pulsed NMR is adjusted to 10 to 500 milliseconds, preferably 100 to 300 milliseconds. ２ "," "T ２ ") is considered to be an index of the dispersion state of particles. In the conductive composition of the present invention, this spin-spin relaxation time T ２ When the specific range is set as described above, it is believed that the components of the conductive composition, particularly the conductive particles, will be appropriately dispersed in the conductive composition. More specifically, it is believed that the conductive particles will be appropriately dispersed in the conductive composition so that the conductive particles have an appropriate distribution so that the conductor has both high conductivity and elasticity. As a result, it is believed that the conductor formed by solidifying the conductive composition of the present invention will have both high conductivity and elasticity.

[0015] The spin-spin relaxation time T of the protons in the conductive composition ２As the CPMG method using pulsed NMR for measuring the spin-spin relaxation time T ２ Specifically, the conductive composition is thoroughly stirred with a spatula, and stirred for 1 minute with a mixer (ARE-310, manufactured by Thinky Corporation), and an attenuation curve Y(t) is obtained by the CPMG method using a Spin Track manufactured by Resonance Systems under the following measurement conditions: proton as the measurement nucleus, measurement temperature 30°C, frequency 20 MHz, 90° pulse, pulse width 2.5 μsec, and number of accumulations 16. The following equation (1) corresponding to the obtained attenuation curve Y(t): Y(t)=A ２ exp(-t / T ２ ) + Y ２ Formula (1) [wherein, A ２ and Y ２ are constants, T ２ is the relaxation time, and t is the measurement time.] Based on this, the proton relaxation time (spin-spin relaxation time) T ２ can be calculated.

[0016] By utilizing the above-described properties, the conductive composition of the present invention can be suitably used to form conductors for wearable devices such as clothing devices, external devices, surface devices, electronic skin devices, and internal devices. Each component contained in the conductive composition of the present invention will be described in detail below.

[0017] <Binder Resin> The conductive composition of the present invention contains a binder resin. The binder resin in the conductive composition can be any material that has rubber elasticity at room temperature without any particular limitation, and for example, a thermoplastic resin, an elastomer, or the like can be suitably used. One type of binder resin may be used alone, or two or more types may be used in combination.

[0018] Any known or commonly used thermoplastic resin can be used, such as polyester resin, polyether resin, polyamide resin, polyamideimide resin, polyimide resin, polyvinyl butyral resin, polyvinyl formal resin, phenoxy resin, polyhydroxypolyether resin, acrylic resin, polystyrene resin, butadiene resin, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, styrene-butadiene copolymer, acrylic acid copolymer, etc. The thermoplastic resin may be saturated or unsaturated. Of these thermoplastic resins, saturated polyester resin and unsaturated polyester resin are preferably used from the viewpoint of adhesion to the substrate.

[0019] As the elastomer, for example, rubber, thermoplastic elastomer, functional group-containing elastomer, block copolymer, etc. can be suitably used.

[0020] Any known and commonly used rubber can be used, including, for example, diene rubber and non-diene rubber.

[0021] Any known and commonly used thermoplastic elastomer can be used, such as a styrene-based elastomer, an olefin-based elastomer, a urethane-based elastomer, a polyester-based elastomer, a polyamide-based elastomer, an acrylic-based elastomer, and a silicone-based elastomer.

[0022] Any known and commonly used functional group-containing elastomer can be used, but from the viewpoint of elasticity, urethane-based, olefin-based, and the like are preferred, and from the viewpoint of solvent resistance, those having a functional group such as a (meth)acryloyl group, an acid anhydride group, a carboxyl group, or an epoxy group are preferred.

[0023] Any known and commonly used block copolymer can be used, but a block copolymer comprising a hard segment and a soft segment is preferably used.

[0024] Among the elastomers mentioned above, block copolymers have low crystallinity and weak intermolecular forces, resulting in a lower glass transition temperature (Tg) than other rubbers. Therefore, even when mixed with conductive particles, they have high flexibility and good elongation. Therefore, block copolymers are suitable for forming conductors for wearable devices. In this specification, the term "block copolymer" refers to a copolymer that has rubber elasticity at room temperature (25°C). Any known or commonly used block copolymer that satisfies the above conditions can be used. Block copolymers composed of hard and soft segments are particularly suitable. In this specification, the term "hard segment" refers to a copolymer with a Tg of 30°C or higher. The term "soft segment" refers to a copolymer with a Tg of 0°C or lower. The Tg is a value measured by the initial point method in accordance with JIS K7121. However, with regard to the heating rate and temperature, the Tg observed at 40°C or higher is specifically obtained from a stabilized DSC curve by repeatedly heating approximately 10 mg of a sample from 25°C to 200°C at a heating rate of 10°C per minute under a nitrogen gas atmosphere using a differential scanning calorimeter (DSC-6100, manufactured by Hitachi High-Tech Science Corporation). α-alumina is used as the reference. Furthermore, the Tg observed at temperatures below 40°C is obtained from a stabilized DSC curve by repeatedly heating approximately 10 mg of a sample from -100°C to 100°C at a heating rate of 20°C per minute under a nitrogen gas atmosphere using a differential scanning calorimeter (DSC-6100, manufactured by Hitachi High-Tech Science Corporation). α-alumina is used as the reference, as above.

[0025] The ratio of the hard segment to the soft segment in the block copolymer (mass of hard segment: mass of soft segment) is not particularly limited as long as the curing of the present invention is achieved, but is preferably 10:90 to 70:30, more preferably 10:90 to 40:60. When the content ratio of the hard segment to the soft segment is within the above range, disconnection of the conductor obtained by solidifying the conductive composition when stretched is suppressed, which is preferable.

[0026] When the hard segment is represented as an X block and an X' block and the soft segment is represented as a Y block and a Y' block, the block copolymer may be an X block-Y block diblock copolymer, an X block-Y block-X block type, an X block-Y block-X block type, an X block-Y block-X' block type, an Y block-X block-Y block type, or an Y block-X block-Y' block type triblock copolymer. From the viewpoint of excellent compatibility with other components and flexibility, an X block-Y block-X block triblock copolymer is preferred.

[0027] The unit structure constituting the hard segment in the block copolymer is not particularly limited as long as the effects of the present invention are achieved, and examples thereof include methyl (meth)acrylate units, styrene units, etc. Furthermore, the unit structure constituting the soft segment is not particularly limited as long as the effects of the present invention are achieved, and examples thereof include n-butyl acrylate units, butadiene units, etc. As the block copolymer, for example, a triblock copolymer of polymethyl (meth)acrylate / poly n-butyl (meth)acrylate / polymethyl (meth)acrylate can be used. Note that, in this specification, "(meth)acrylate" is a general term referring to acrylate and methacrylate, and the same applies to other similar expressions.

[0028] 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 types, such as polystyrene-polybutadiene-polymethyl methacrylate, MAM types, such as polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate, and carboxylic acid-modified or hydrophilic group-modified MAM N or MAM A types, can be used. Examples of SBM types include E41, E40, E21, and E20. Examples of MAM types include M51, M52, M53, and M22. Examples of MAM N types include 52N and 22N. Examples of MAM A types include SM4032XM10. Another example of a commercially available block copolymer is Kuralyte (registered trademark), an acrylic block copolymer manufactured by Kuraray Co., Ltd. Kuralyte (registered trademark) is a block copolymer derived from methyl methacrylate and butyl acrylate.

[0029] In addition to the above-mentioned commercially available block copolymers, appropriately prepared synthetic products can also be used. Examples of synthetic block copolymers containing a (meth)acrylate polymer block include block copolymers synthesized by the methods described in JP-A-2007-516326 and JP-A-2005-515281.

[0030] 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 conductor formed by solidifying the conductive composition can be imparted with toughness and flexibility, and excellent tackiness can be obtained when the conductive composition is formed into a film and dried, or when applied to a substrate and dried. Furthermore, when the weight-average molecular weight is 400,000 or less, the conductive composition has good viscosity, achieving higher printability and processability. Furthermore, when the weight-average molecular weight is 50,000 or more, excellent effects can be obtained in terms of mitigating external impacts.

[0031] The tensile elongation at break of the block copolymer, measured according to 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 conductor formed by solidifying the conductive composition will have better stretchability and stable electrical resistance. The tensile elongation at break of the block copolymer is more preferably 300 to 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)) x 100

[0032] When rubber or a functional group-containing elastomer is used as the elastomer, it is usually blended with a sulfur-based vulcanizing agent, a non-sulfur-based vulcanizing agent, etc. However, since metal particles such as silver powder may be oxidized or sulfurized by a sulfur-based vulcanizing agent and corrode, when metal particles are used as conductive particles, it is preferable not to blend a sulfur-based vulcanizing agent into the elastomer, and it is preferable to blend a non-sulfur-based vulcanizing agent as needed.

[0033] The conductive composition of the present invention may contain a small amount of a sulfur compound as long as the effect of the present invention is not impaired.

[0034] The elastomer may also 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 oil, naphthenic process oil, and aromatic process oil. Examples of vegetable oil-based softeners include castor oil, corn kernel oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, pine oil, and tall oil. These softeners may be used alone or in combination of two or more. The desired rubber elasticity and extensibility can be adjusted by the amount of softener added.

[0035] The content of the elastomer in the conductive composition is preferably 5 to 40 mass %, more preferably 14 to 28 mass %, calculated as solids, based on the total solid content in the conductive composition. Furthermore, from the viewpoint of the elasticity of the formed conductor, the content of the block copolymer in the entire elastomer is preferably 85 to 100 mass %. When the content of the block copolymer is within the above range, the elasticity of the conductor formed by solidifying the conductive composition is improved. The conductive composition of the present invention may contain other organic binders, such as thermoplastic resins, other than the elastomer, as long as the effects of the present invention are not impaired. In the present invention, the solid content refers to the conductive composition excluding the solvent.

[0036] <Conductive Particles> The conductive composition of the present invention contains conductive particles. As the conductive particles contained in the conductive composition, conventionally known materials used in conductive compositions can be used, for example, carbon particles such as graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; metal particles such as copper powder, nickel powder, and silver powder; WC, B ４ Metal carbides such as C, ZrC, NbC, MoC, TiC, and TaC, metal nitrides such as TiN, ZrN, and TaN, and WSi ２ , MoSi ２Examples of the conductive particles include metal silicides such as those mentioned above. One type of these conductive particles may be used alone, or two or more types may be used in combination. As the conductive particles, metal particles are preferably used, and silver powder is more preferably used, since a conductive composition with low electrical resistance can be obtained. Furthermore, in the conductive composition of the present invention, the conductive particles are preferably in a chain (aggregated) state (i.e., chain-like conductive particles). Therefore, it is particularly preferable to use silver powder in a chain (aggregated) state, i.e., chain-like silver powder, as the conductive particles.

[0037] The conductive composition of the present invention has a dispersion obtained by dispersing conductive particles in a solvent described below. The Rsp value, measured by pulse NMR, for example, a Spin Track manufactured by Resonance Systems, 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. The larger the Rsp value, the higher the compatibility between the conductive particles and the solvent (i.e., the higher the dispersibility of the conductive particles in the conductive composition). The smaller the Rsp value, the lower the compatibility between the conductive particles and the solvent (i.e., the lower the dispersibility of the conductive particles in the conductive composition). The larger the Rsp value, the easier it is for the conductive particles to be re-dispersed by stirring, even if the conductive particles dispersed in the conductive composition settle. The Rsp value can be calculated using pulse NMR based on the following formula (2): Rsp=(Rav-Rb) / (Rb)(1) Formula (2) (where Rav is the reciprocal of the spin-spin relaxation time when measuring a dispersion in which 1 mass % of conductive particles are dispersed 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.)

[0038] The conductive particles preferably have a particle density value of 10 to 40 μm as measured with a grind gauge. The particle density value of the conductive particles can be measured using a grind gauge (SU2050MHJ, manufactured by Daiichi Sokhan Co., Ltd.). Specifically, the conductive composition is thoroughly stirred with a spatula, stirred for 1 minute with a mixer (ARE-310, manufactured by Thinky Corporation), and diluted with 0.3 grams of propylene glycol monomethyl ether acetate per gram of the conductive composition to obtain a diluted solution. The resulting diluted solution is applied to a grind gauge (SU2050MHJ, manufactured by Daiichi Sokhan Co., Ltd.) with a scraper (SK9225, manufactured by Daiichi Sokhan Co., Ltd.), and the particle density value is determined by the upper limit of the range in which 20 or more particles are observed when reading the scale at 5.0 μm intervals. Therefore, with respect to conductive particles, "a particle density of 10 to 40 μm as measured by a grind gauge" means that the conductive particles are present in the conductive composition such that the particle density of the conductive particles as measured by the above-mentioned method is in the range of 10 to 40 μm. The particle density of the conductive particles is preferably 15 to 40 μm, and more preferably 20 to 40 μm.

[0039] The conductive particles preferably have a tap density of 2.0 g / cm when measured after 1000 taps in accordance with ISO 3953. ３ or less, more preferably 0.3 to 1.5 g / cm ３ , more preferably 0.3 to 1.0 g / cm ３ Although the detailed mechanism is not clear, it is believed that when the conductive particles have a tap density in this range, the volume per unit mass of the conductive particles increases, resulting in many contact points between the conductive particles, resulting in high conductivity. As a result, it is believed that the increase in resistance value can be sufficiently suppressed whether the conductor is stretched strongly or weakly.

[0040] 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 exhibited, and examples thereof include spherical, approximately spherical, needle-like, oval-spherical, flake-like, scale-like, and irregular shapes, with spherical and approximately spherical shapes being preferred. As the 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.

[0041] The average particle diameter (average primary particle diameter) of the conductive particles (primary particles) is preferably 0.1 to 10 μm, more preferably 0.1 to 5 μm. Furthermore, when the conductive particles are chain-like conductive particles, 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, when 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 have many contact points with each other, which is believed to result in high conductivity. As a result, it is believed that an increase in resistance can be sufficiently suppressed whether the conductor is stretched strongly or weakly.

[0042] The average primary particle diameter of the conductive particles can be measured by observing the conductive particles in a powder state with a scanning electron microscope at a magnification of 10,000 times, randomly extracting 10 primary particles, and measuring their particle diameters, and then determining the average value of the particle diameters.

[0043] The average secondary particle diameter (D50) of the conductive particles can be measured according to the following procedure. First, a conductive composition is diluted with 3000 mass% propylene glycol monomethyl ether acetate to obtain a solution. The particle size distribution of the obtained solution is measured in reflection mode using a laser diffraction / scattering particle size distribution analyzer (TM3000, manufactured by Microtrac-Bell) with a solvent refractive index of 1.40 and a measurement range of 0.020 μm to 1000.00 μm. From the particle size distribution, the particle diameter at 50% of the cumulative total is determined and used as the average secondary particle diameter (D50) of the conductive particles.

[0044] When the conductive particles are chain-like conductive particles, 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 that represents the state of an aggregate structure (secondary particles) in which primary particles of the conductive particles are connected to each other and an appropriate amount of voids are present. For example, when the conductive particles are chain-like silver powder, the apparent porosity is preferably 50 to 95%, more preferably 60 to 95%.

[0045] The apparent porosity of the chain-like conductive particles can be measured as follows: ０ (g / cm ３ ) and the volume of the conductive particles after 1 hour has passed since a load of 1 kg was applied to the conductive particles with a mass M (g) is V (cm ３ ), the apparent density ρ (g / cm ３ ) is defined as ρ=M / V, and the apparent porosity (P) can be calculated from the apparent density by the following formula: P=(1−ρ / ρ ０ ) × 100 For example, when the conductive particles are chain-like silver powder, the density ρ ０ is 10.49 g / cm ３ is.

[0046] The DBP oil absorption of the conductive particles 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, when the conductive particles are chain silver powder, the DBP oil absorption of the chain silver powder measured in accordance with JIS K 6217-4: 2017 is preferably 50 to 150 ml / 100 g.

[0047] The content of the conductive particles in the conductive composition is 60 to 95 mass %, preferably 65 to 85 mass %, and more preferably 70 to 80 mass %, calculated as solids based on the total solids content in the conductive composition. When the content of the conductive particles in the conductive composition is within this range, a conductor formed by solidifying the conductive composition can be obtained that has a low initial electrical resistance before stretching and maintains a stably low electrical resistance even when stretched.

[0048] <Solvent> The conductive composition of the present invention contains a solvent. As the solvent, an organic solvent is preferably used from the viewpoint of preparing the conductive composition and adjusting the viscosity for applying the conductive composition to a substrate or the like.

[0049] Examples of the organic solvent include ketones, aromatic hydrocarbons, glycol ethers, glycol ether acetates, esters, alcohols, aliphatic hydrocarbons, and petroleum-based solvents. More specific 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 solvents such as petroleum ether, petroleum naphtha, hydrogenated petroleum naphtha, and solvent naphtha. The organic solvents may be used alone or in combination of two or more.

[0050] The boiling point of the organic solvent is not particularly limited, but is preferably 150° C. or higher, and more preferably 200° C. or higher. When an organic solvent having a boiling point in such a range is used, it is possible to prevent the organic solvent from volatilizing during the device production process, thereby preventing a decrease in the continuous printability and processability of the conductive composition.

[0051] The content of the solvent in the conductive composition is preferably 1 to 50 mass %, more preferably 10 to 40 mass %, and even more preferably 15 to 30 mass %, based on the total mass of the conductive composition.

[0052] <Fatty Acid> The conductive composition of the present invention may contain a fatty acid in addition to the above-mentioned components. It is believed that the inclusion of a fatty acid in the conductive composition promotes dissociation of the conductive particles in an aggregated state, and further enables the conductive particles to be stably maintained in a dispersed state. In addition, when the conductive particles have a T in the above-mentioned range, ２ In the case where the conductive composition has the fatty acid, it is believed that the fatty acid stably maintains the dissociated and dispersed state of the conductive particles in a state suitable for forming a conductor having both high conductivity and stretchability. Furthermore, since the conductive composition contains the fatty acid, the dispersed state of the conductive particles can be stably maintained, which also has the additional effect of suppressing deterioration of the performance of the conductive composition over time.

[0053] The type of fatty acid that can be used includes straight-chain fatty acids, branched fatty acids, and cyclic fatty acids, and both saturated and unsaturated fatty acids can be used.

[0054] 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 is, for example, 10 to 18. From the viewpoint of suppressing adverse effects on wiring layers and electrodes using the conductive composition, stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, linolenic acid, etc. are particularly preferably used. One type of fatty acid may be used alone, or two or more types may be used in combination.

[0055] The content of the fatty acid in the conductive composition is preferably 0.01 to 10 mass%, more preferably 0.05 to 5 mass%, and even more preferably 0.1 to 1 mass%, calculated as solid content, based on the total solid content contained in the conductive composition.

[0056] <Silica> The conductive composition of the present invention may contain silica in addition to the above-mentioned components. It is believed that the conductive composition containing silica can stably maintain the dispersed state of the conductive particles in the conductive composition. In addition, when the conductive particles have a T in the above-mentioned range, ２In the case where the conductive composition has the above structure, it is believed that the silica stably maintains the dispersion state of the conductive particles in a state suitable for forming a conductor having both high conductivity and elasticity. Furthermore, since the conductive composition contains silica, the dispersion state of the conductive particles can be stably maintained, which also has the additional effect of suppressing deterioration of the performance of the conductive composition over time. In particular, it is believed that the use of the above-mentioned fatty acid in combination with silica can particularly stably maintain the dissociation and dispersion state of the conductive particles.

[0057] Examples of silica that can be used include fused silica, spherical silica, amorphous silica, and crystalline silica. Silica that has undergone various surface treatments can also be used. Silica may be used alone or in combination of two or more types.

[0058] The surface area of ​​the 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 m ２ / g, more preferably 100 to 800 m ２ / g, more preferably 100 to 500m ２ / g. It is believed that when the silica has a BET specific surface area in this range, the dispersed state of the silica in the conductive composition can be stably maintained. Furthermore, when the silica has a BET specific surface area in the above-mentioned range, it is believed that the silica stably maintains the dispersed state of the conductive particles in a state suitable for forming a conductor that combines high conductivity and elasticity. Furthermore, since the dispersed state of the conductive particles can be stably maintained by the silica in this way, an additional effect of suppressing deterioration of the performance of the conductive composition over time is also achieved. The BET specific surface area can be measured by a gas adsorption method in accordance with JIS Z8831.

[0059] The average particle size (D50) of the silica is preferably 1 to 1,000 nm, more preferably 5 to 500 nm, and even more preferably 10 to 100 nm.

[0060] The content of silica in the conductive composition is preferably 0.01 to 10 mass%, more preferably 0.1 to 5 mass%, and even more preferably 0.5 to 3 mass%, calculated on solids, based on the total solid content contained in the conductive composition.

[0061] <Other Components> The conductive composition of the present invention may contain other components in addition to the above-mentioned components. The other components are not particularly limited and may be any components that are commonly used in the production of conductive compositions and do not impair the effects of the present invention. Examples of the other components include thermosetting components, additives, pigments, etc.

[0062] 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 are capable of forming films by increasing the molecular weight through a curing reaction and by forming crosslinks.

[0063] Examples of the additives include a coupling agent, a photopolymerization initiator, and a flame retardant.

[0064] The conductive composition of the present invention can be produced, for example, by kneading an elastomer dissolved in a solvent with conductive particles. Examples of kneading methods include a method using a stirring and mixing device such as a roll mill. Specifically, an elastomer solution with a solids content of 50% by mass is prepared by dissolving an elastomer in a solvent, and conductive particles are added to this elastomer solution. The mixture is pre-stirred and mixed with a stirrer, and then kneaded with a three-roll mill to obtain a conductive composition. Depending on the type of elastomer component used and the blending ratio of the solvent, a liquid conductive composition or a paste-like (semi-solid) conductive composition can be produced.

[0065] 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 200 to 1000 dPa s. By adjusting the viscosity of the conductive composition to within this range, a conductive composition with excellent printability and processability required in device fabrication processes can be obtained.

[0066] In the present invention, the conductive composition as described above can be applied in a pattern onto a substrate and then subjected to a heat treatment to form a conductor. Examples of the heat treatment include a drying treatment and a heat curing treatment.

[0067] [Conductor] The conductive composition described above can be solidified to form a conductor. For example, a coating film made of the conductive composition can be formed, dried, and solidified to form a conductor layer. The conductive composition is solidified by drying or heat-treating the conductive composition. Examples of heat treatment include hot air drying and thermal curing. Molding may be performed prior to the heat treatment. For example, a conductor layer can be obtained by applying the conductive composition described above to a substrate in a desired shape and then solidifying it. The conductor layer may have various shapes depending on the intended use. For example, it can be suitably applied to conductor circuits, wiring, anisotropic conductive connections, etc.

[0068] The method for producing a conductor circuit includes a pattern formation step of printing or applying the conductive composition onto a substrate to form a coating pattern, and a step of solidifying the patterned coating. The coating pattern can be formed by a masking method, a method using a resist, or the like.

[0069] Examples of the pattern formation process include a printing method and a dispensing method. Examples of printing methods include gravure printing, offset printing, and screen printing, and screen printing is preferred when forming fine circuits. Gravure printing and offset printing are suitable as large-area coating methods. The dispensing method is a method in which the amount of conductive composition applied is controlled and an extrusion pattern is formed from a needle, and is suitable for forming partial patterns such as earth wiring or patterns on uneven areas.

[0070] The substrate to which the conductive composition is applied can be any electrically insulating material, and examples thereof include paper-phenolic resin, paper-epoxy resin, glass cloth-epoxy resin, glass-polyimide, glass cloth / nonwoven cloth-epoxy resin, glass cloth / paper-epoxy resin, synthetic fiber-epoxy resin, copper-clad laminates of all grades (such as FR-4) made from composites such as fluororesin, polyethylene, polyphenylene ether, and polyphenylene oxide-cyanate ester; sheets or films made from plastics such as polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate, polyimide, polyphenylene sulfide, and polyamide; sheets or films made from crosslinked rubbers such as urethane, silicone rubber, acrylic rubber, and butadiene rubber; and sheets or films made from thermoplastic elastomers such as polyesters, polyurethanes, polyolefins, and styrene-based block copolymers. Among these, not only flexible materials but also stretchable materials (e.g., rubber, thermoplastic elastomers, urethane, etc.) can be used as the substrate, allowing the conductor to be used in applications such as those described below. As the stretchable material, the same materials as those explained above for the elastomer can be used.

[0071] In a preferred embodiment, the substrate to which the conductive composition is applied is a stretchable material (hereinafter referred to as "stretchable substrate"), and in particular, it is preferable that the tensile elongation at break is 200% or more. By using such a stretchable substrate as the substrate, the substrate elongates slightly more than the conductor when it is stretched, and therefore a conductor with stable electrical resistance when stretched can be obtained. The tensile elongation at break of the substrate is measured by the measurement method in accordance with ISO 37 described above.

[0072] In another preferred embodiment, the change in resistance of the conductor when stretched is within a specific range. Specifically, the change in resistance when the conductor is stretched by 30% is preferably more than 20 times and not more than 50 times, more preferably not more than 20 times. By having the change in resistance of the conductor when stretched within the above-mentioned range, the conductor can maintain sufficiently high conductivity when stretched. The change in resistance of the conductor is calculated as the difference between the resistance of the conductor after stretching and the resistance of the conductor before stretching (resistance of the conductor after stretching - resistance of the conductor before stretching). The resistance of the conductor before stretching and in each stretched state are both measured by connecting it to a digital multimeter (PC720M, manufactured by Sanwa Electric Instruments Co., Ltd.).

[0073] [Laminated Structure] The above-described conductor can be formed into a laminated structure by forming multiple layers. There are no particular limitations on the method for forming the laminated structure. For example, a conductor formed by solidifying a conductive composition may be bonded together using heat, pressure, or both, or a conductive composition may be applied to a conductor and then solidified. The laminated structure may also include layers other than the above-described conductor, such as a metal layer, an insulating layer, a protective layer, an adhesive layer, a pressure-sensitive adhesive layer, or a void layer.

[0074] [Electronic Components] Electronic components can be formed using the above-described conductors or laminate structures as constituent elements. There are no particular limitations on the structure, formation method, or use of the electronic components as long as they include the above-described conductors or laminate structures as constituent elements, and examples thereof include sensors, actuators, capacitors, inductors, transistors, converters, thermistors, connectors, transformers, capacitors, diodes, regulators, motors, antennas, and switches, and the like, and electronic components may also have a combination of multiple uses among these uses.

[0075] [Uses of Conductors, Laminated Structures, and Electronic Components] The conductors obtained by solidifying the conductive composition of the present invention exhibit excellent stability of electrical resistance even when repeatedly stretched or maintained in an elongated state, as described above. Therefore, in addition to conductor circuits and wiring, they can be suitably used to form conductors for wearable devices such as clothing devices, extracorporeal devices, body surface devices, electronic skin devices, and intracorporeal devices. Furthermore, a conductor layer can also be applied to electrodes of flexible printed circuit boards. Furthermore, the conductive composition of the present invention is also suitable for forming conductor layers such as actuator electrodes. It is also suitable for forming conductors with designs that have previously been difficult to achieve due to insufficient stretchability or electrical resistance stability. Specific uses of the conductors include, for example, the following.

[0076] <Wearable Biosensor> The conductor of the present invention can be used as a wiring material for a wearable biosensor attached to clothing or the body to acquire and transmit action potentials / biological information generated by animals and plants, including humans. The sensor must be attached in close contact with or close to the surface tissue of animals and plants, including humans, which undergoes stretching and contraction. Furthermore, when attached to clothing, the pattern and extent of changes in the shape of the clothing (stretching and contraction) vary depending on the wearer's physique and movement patterns (tendencies). Conventional rigid and flexible substrates lack the ability to conform to the stretching and contracting of the attachment location, limiting the location where the sensor can be attached and, as a result, limiting the bioinformation obtained. The conductor of the present invention can be used as a wiring material for sensors on the surface tissue and clothing of animals and plants, including humans, enabling a wearable biosensor to be attached to locations that undergo stretching and contraction or on clothing.

[0077] The wiring used in wearable biosensors can be formed by screen printing or dispensing methods, which makes it possible to miniaturize signal wiring, which is thought to contribute to the miniaturization of sensor devices.

[0078] <Wiring Material for Smart Textiles> In recent years, the field of so-called "smart textiles," which use textile fabrics as sensors, has been expanding. Circuit boards or sensors in which wiring is formed on a stretchable substrate that can be thermocompression bonded using the conductor of the present invention exhibit excellent stability of electrical resistance during stretching. Therefore, by attaching the wiring board or sensor to the surface of a stretchable textile fabric, it becomes possible to develop textile fabrics with electronic device functions, i.e., smart textiles. For smart textiles, functions such as pressure-sensitive sensors, touch sensors, and antenna wiring can be imparted to textile fabrics.

[0079] <Wiring for 3D-formed products> Conventional plastic molded products for electronic device housings and the like made using the FIM (film insert molding) method use a plastic film such as polycarbonate as a base substrate, which is printed with a design and then heat-pressed. The conductor wiring of the present invention, which is made of a laminated structure having the conductor of the present invention provided on an elastic substrate, has the properties of being free from disconnection when stretched and suppressing changes in resistance value. Therefore, by forming the conductor wiring during design printing on the plastic molded product and then performing molding processing by heat pressing (which causes partial stretching), it is possible to realize electronic devices with built-in 3D-shaped wiring.

[0080] Furthermore, by performing heat pressing using a stretchable base material such as the elastomer described above, it is possible to realize a stretchable electronics device with soft wiring inside a soft housing. This can be suitably used for pressure-sensitive sensors, touch sensors, antenna wiring, etc.

[0081] <Stretchable Wiring Sheet or Wiring Board> Conductor wiring comprising a laminate structure in which a conductor layer of the present invention is provided on a stretchable substrate can be used as a stretchable wiring board sheet. For example, such conductor wiring can be attached to the surface of a three-dimensional object such as a molded product while being stretched or deformed without causing disconnection of the wiring. Therefore, the laminate structure in which a conductor layer of the present invention is provided on a stretchable substrate can be suitably used for pressure-sensitive sensors, touch sensors, or antenna wiring.

[0082] <Flexible Wiring Sheet or Wiring Board> Flexible wiring sheets or wiring boards using conventional conductive pastes have the problem of wiring breakage when subjected to extreme bending, such as bending with a fingernail. In this regard, when the conductor of the present invention is used, the conductive material has elongation properties, so it can accommodate bending in areas that conventional conductive pastes could not handle, and it is possible to realize a flexible wiring sheet or wiring board in which wiring breakage does not occur even when bending with a fingernail. Example

[0083] 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, "parts" and "%" are all by mass unless otherwise specified.

[0084] [Preparation of Conductive Composition] The following materials were prepared as materials for the conductive composition. Conductive Particles A Conductive Particles B Conductive Particles C Binder Resin A: Acrylic Block Copolymer (LA2250, manufactured by Kuraray Co., Ltd.) Binder Resin B: Polyvinylpyrrolidone (K30, manufactured by Nippon Shokubai Co., Ltd.) Solvent A: Diethylene glycol monoethyl ether acetate Solvent B: Terpineol Solvent C: Propylene glycol Silica: AEROSIL (AEROSIL 200, manufactured by EVONIK, BET specific surface area 200 m) ２ / g) Fatty acid: lauric acid The particle shape, average primary particle diameter, average secondary particle diameter (D50), tap density and apparent porosity of the conductive particles A to C are shown in Table 1 below.

[0085] The tap density of each conductive particle was measured in accordance with ISO 3953 after 1000 taps.

[0086] Each conductive composition was prepared according to the following procedure. First, each of the binder resins described above was dissolved in each solvent according to the composition shown in Table 2 below to prepare a binder resin solution with a solid content of 50% by mass. Next, each of the conductive particles described above and the binder resin solution were mixed to the composition shown in Table 2 below, pre-mixed with a mixer, and then kneaded using a three-roll mill (EXAKT50, manufactured by EXAKT) to obtain the conductive compositions of Examples 1 to 7 and Comparative Examples 1 and 2.

[0087]

[0088] The proton spin-spin relaxation time T of each conductive composition ２ The Rsp values ​​were measured by the following method. That is, each conductive composition was thoroughly stirred using a spatula, and then stirred for 1 minute using a mixer (ARE-310, manufactured by Thinky Corporation). An attenuation curve Y(t) was obtained by the CPMG method using a Spin Track manufactured by Resonance Systems, Inc., under the following measurement conditions: proton as the measurement nucleus, measurement temperature 30°C, frequency 20 MHz, 90° pulse, pulse width 2.5 μsec, and accumulation count 16. The following equation (1) corresponding to the obtained attenuation curve Y(t): Y(t)=A ２ exp(-t / T ２ ) + Y ２ Formula (1) [wherein, A ２ and Y ２ are constants, T ２ is the relaxation time, and t is the measurement time.] Based on this, the proton relaxation time (spin-spin relaxation time) T ２ was calculated.

[0089] Next, the Rsp value was calculated based on the following formula (2): Rsp = (Rav - Rb) / (Rb) (1) Formula (2) [where Rav is the reciprocal of the spin-spin relaxation time when measuring a dispersion in which 1 mass % of conductive particles are dispersed 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.] The Rb value was determined by measuring only each solvent used in each conductive composition using the same method as above.

[0090] The particle density value of each conductive particle was measured by the following method: Each conductive composition was thoroughly stirred with a spatula, stirred for 1 minute with a mixer (ARE-310, manufactured by Thinky Corporation), and diluted with 0.3 grams of propylene glycol monomethyl ether acetate per gram of conductive composition to obtain a diluted solution. The diluted solution was applied to a grind gauge (SU2050MHJ, manufactured by Daiichi Sokhan Co., Ltd.) with a scraper (SK9225, manufactured by Daiichi Sokhan Co., Ltd.), and the scale was read at 5.0 μm intervals. The upper limit of the range where 20 or more particles were observed was taken as the particle density value.

[0091] [Evaluation of Conductive Compositions] Immediately after preparation (new), each conductive composition of the Examples and Comparative Examples was applied to a substrate by screen printing and heat-treated at 80°C for 30 minutes to form a conductor with a line width of 1 mm, a thickness of 20 μm, and a length of 40 mm on the substrate. The resistance of the conductor before stretching was measured. A urethane film (TG88-I, manufactured by Takeda Sangyo Co., Ltd., 70 μm thick, 500% tensile elongation at break) was used as the substrate. The conductor was stretched at a rate of 5 mm / sec to a predetermined elongation (2% elongation, 10% elongation, 30% elongation, 50% elongation), and then held in that state for 15 seconds to measure the resistance of the conductor. The conductivity of the conductor during stretching was evaluated according to the following evaluation criteria. The resistance of the conductor was measured using a digital multimeter (PC720M, manufactured by Sanwa Electric Instruments Co., Ltd.). The evaluation results are shown in Table 2. Good: The resistance increased by 20 times or less compared to before stretching, and sufficiently high conductivity was maintained. Δ: The resistance value increases by more than 20 times and not more than 50 times compared to before stretching, and high conductivity is maintained. ×: The resistance value increases by more than 50 times compared to before stretching, and conductivity is not sufficiently maintained.

[0092] Each conductive composition of the Examples and Comparative Examples was prepared by filling and sealing a storage container immediately after preparation, and the conductivity of the conductor when stretched was evaluated for each conductive composition 6 months after the storage container was opened, using the same method as described above. The evaluation results are shown in Table 2.

[0093] The evaluation results shown in Table 2 reveal that when the conductive composition of each Example was used immediately after preparation, high conductivity was maintained even during elongation. That is, for a conductive composition containing a binder resin, conductive particles, and a solvent, the proton spin-spin relaxation time T ２Conductive compositions having a stretch time of 10 to 500 milliseconds can form conductors that combine high conductivity and stretchability. Furthermore, it can be seen that the conductive compositions of each Example almost maintain this high conductivity when stretched, even six months after opening. In other words, it can be said that the conductive compositions of each Example are inhibited from deteriorating over time after preparation. On the other hand, when the conductive compositions of each Comparative Example are used, it can be seen that the high conductivity is not maintained when stretched, whether the conductive compositions are used immediately after preparation or six months after opening.

Claims

1. A conductive composition comprising a binder resin, conductive particles, a solvent, and silica, A conductive composition characterized in that the proton spin-spin relaxation time measured by the CPMG method of pulsed NMR is 10 to 500 milliseconds.

2. 2. The conductive composition according to claim 1, wherein the Rsp value of a dispersion liquid obtained by dispersing the conductive particles in the solvent is 0.02 to 1.0 as measured by pulse NMR.

3. 2. The conductive composition according to claim 1, wherein the proton spin-spin relaxation time measured by the CPMG method of pulsed NMR is 100 to 300 milliseconds.

4. The conductive composition of claim 1 , wherein the conductive particles are metal particles.

5. The conductive composition of claim 1 further comprising a fatty acid.

6. The conductive composition according to claim 1 , which is used to form a conductor.

7. A conductor obtained by solidifying the conductive composition according to claim 1.

8. The conductor according to claim 7, wherein the change in resistance value when stretched by 30% is within 50 times.

9. A laminated structure comprising a substrate and a layer of the conductor according to claim 7 laminated on the substrate.

10. The laminated structure according to claim 9 , wherein the substrate is a stretchable substrate having a tensile elongation at break of 200% or more.

11. An electronic component comprising the conductor layer according to claim 7 or the laminate structure according to claim 9.

12. A method for manufacturing an electronic component having a layer of conductor, the method comprising the step of forming the layer of conductor by solidifying the conductive composition of claim 1.