Electroconductive ink compositions and electroconductive film

Abstract

An electroconductive ink composition comprising a (meth)acrylic polymer (A) and silver particles (B), wherein the (meth)acrylic polymer (A) has a glass transition temperature of 0°C or lower, a weight-average molecular weight of 500,000 or higher, and a hydroxyl value exceeding 50 mgKOH / g and the silver particles (B) have a specific surface area of 0.5-3.0 m2 / g, a 50% average particle diameter of 0.5-14.0 μm, and a maximum particle diameter of 8 μm or larger, the electroconductive ink composition having a solid content of 50-80 mass%; and an electroconductive ink composition comprising a (meth)acrylic polymer (A) and carbon black (CB), wherein the (meth)acrylic polymer (A) has a glass transition temperature of 0°C or lower, a weight-average molecular weight of 500,000 or higher, and a hydroxyl value exceeding 50 mgKOH / g and the carbon black (CB) has a specific surface area of 50 m2 / g or larger and an aggregate diameter of 400 nm or less, the electroconductive ink composition having a solid content of 15-30 mass%.

Description

Conductive ink composition and conductive film

[0001] The present invention relates to a conductive ink composition and a conductive film using the conductive ink composition. This application claims priority based on Japanese Patent Application Nos. 2021-191276 and 2021-191277, filed on November 25, 2021, the contents of which are incorporated herein by reference.

[0002] In recent years, printed electronics (PE), which uses conductive ink to form conductive films by printing, has been attracting attention in the field of electronic device manufacturing. By using PE, for example, it is possible to form conductive films on thin substrates and manufacture flexible devices.

[0003] Patent Document 1 aims to make electrodes and wiring in a flexible wiring board stretchable and to reduce changes in electrical resistance due to stretching, and proposes a method in which metal filler particles of a specific shape are filled into an elastomer that has functional groups capable of hydrogen bonding and has a glass transition temperature of −10°C or lower, and the flake-shaped or needle-shaped metal filler particles are oriented in the stretching direction of the film and brought into contact with the chunk-shaped metal filler particles to ensure conductivity.

[0004] Japanese Patent Application Publication No. 2010-153364

[0005] According to the findings of the present inventors, there are cases where sufficient elongation cannot be achieved by the method described in Patent Document 1. An object of the present invention is to provide a conductive ink composition that can form a conductive film that is stretchable and has excellent conductivity when stretched.

[0006] The present invention has the following aspects: [1-1] A (meth)acrylic polymer (A) and silver particles (B), wherein the (meth)acrylic polymer (A) has a glass transition temperature of 0°C or lower, a weight-average molecular weight of 500,000 or higher, and a hydroxyl value of more than 50 mgKOH / g, and the silver particles (B) have a specific surface area of ​​0.5 to 3.0 m ２ / g, a 50% average particle size of 0.5 to 14.0 μm, a maximum particle size of 8 μm or more, and a solid content of 50 to 80 mass %. [1-2] The conductive ink composition of [1-1], wherein the (meth)acrylic polymer (A) has a glass transition temperature of more than -50°C and less than -30°C, and a weight average molecular weight of 500,000 to 990,000. [1-3] The conductive ink composition of [1-1] or [1-2], wherein the content of units (a1) derived from a hydroxyl group-containing monomer is 20 to 40 mass % with respect to all units constituting the (meth)acrylic polymer (A). [1-4] The conductive ink composition of any of [1-1] to [1-3], wherein the viscosity at 23°C is 20 to 50 Pa s. [1-5] A conductive film obtained by drying a coating of the conductive ink composition of any of [1-1] to [1-4]. [1-6] The conductive film according to [1-5], which is used for electrodes or wiring that require stretchability in electronic devices. [1-7] The conductive film according to [1-5], which is used for a detection unit, electrode, or wiring of a resistance change sensor. [2-1] A conductive film comprising a (meth)acrylic polymer (A) and carbon black (CB), wherein the (meth)acrylic polymer (A) has a glass transition temperature of 0°C or lower, a weight average molecular weight of 500,000 or higher, a hydroxyl value of more than 50 mgKOH / g, and a specific surface area of ​​the carbon black (CB) of 50 m ２ / g or more, an aggregate diameter of 400 nm or less, and a solid content of 15 to 30 mass %. [2-2] The conductive ink composition of [2-1], wherein the (meth)acrylic polymer (A) has a glass transition temperature of more than -50°C and less than -30°C and a weight average molecular weight of 500,000 to 990,000. [2-3] The conductive ink composition of [2-1] or [2-2], wherein the content of units (a1) derived from a hydroxyl group-containing monomer is 20 to 40 mass % relative to all units constituting the (meth)acrylic polymer (A). [2-4] The conductive ink composition of any of [2-1] to [2-3], wherein the viscosity at 23°C is 20 to 100 Pa s. [2-5] A conductive film obtained by drying a coating of the conductive ink composition of any of [2-1] to [2-4]. [2-6] The conductive film of [2-5], which is used for electrodes or wiring that require stretchability in electronic devices. [2-7] The conductive film of [2-5] used in the detection unit, electrode, or wiring of a resistance change sensor.

[0007] The conductive ink composition of the present invention can form a conductive film that is stretchable and has excellent conductivity when stretched.

[0008] The following definitions of terms apply throughout this specification and the claims. A numerical range expressed as "to" means a range of numerical values ​​with the numerical values ​​before and after "to" as the lower and upper limits. "(Meth)acrylate" is a general term for acrylate and methacrylate, and "(meth)acrylic" is a general term for "acrylic" and "methacrylic." A "unit" of a polymer means an atomic group (monomer unit) formed from one monomer molecule.

[0009] The weight average molecular weight (Mw) of the polymer is a polystyrene-equivalent molecular weight obtained by measuring by gel permeation chromatography using a calibration curve prepared using standard polystyrene samples of known molecular weight. More specifically, for example, it can be determined by measuring in polystyrene equivalent value under the following GPC measurement conditions using a GPC measurement device, such as "Alliance E2695 Separation Module" manufactured by Nihon Waters Co., Ltd. (GPC measurement conditions) Sample concentration: 0.5 wt % (tetrahydrofuran solution) Sample injection amount: 20 μL Eluent: tetrahydrofuran (THF) Flow rate (flow rate): 0.3 mL / min Column temperature (measurement temperature): 40° C. Column: trade name "TSKguard column HSPgel RT-MB-H+ HSPgel RT-2.0" (manufactured by Tosoh Corporation) Detector: differential refractometer (RI), trade name "Alliance 2414" (manufactured by Nihon Waters K.K.)

[0010] The hydroxyl value (unit: mgKOH / g) of the polymer is a theoretical value calculated from the following formula (1). In the following formula (1), the "copolymerization amount of the monomer having a hydroxyl group" means the ratio (unit: mass %) of the monomer having a hydroxyl group to all the monomers constituting the polymer.

[0011]

[0012] The glass transition temperature of the copolymer obtained by polymerizing the monomer mixture is Tg (theoretical value) calculated by the Fox equation of the following formula (2) using the known glass transition temperatures of the homopolymers of each monomer. The glass transition temperature of the homopolymer of the monomer can be, for example, the value described in the Polymer Handbook Fourth Edition (Wiley-Interscience 2003). In the following formula (2), Tg is the glass transition temperature of the copolymer (unit: K), Tg １ is the glass transition temperature of the homopolymer of Monomer 1 (unit: K), Tg ２ is the glass transition temperature of the monomer 2 homopolymer (unit: K), Tg ｎis the glass transition temperature of the homopolymer of monomer n (unit: K), W １ is the weight fraction of monomer 1 in the monomer mixture, W ２ is the weight fraction of monomer 2 in the monomer mixture, W ｎ represents the weight fraction of monomer n in the monomer mixture.

[0013]

[0014] The viscosity of the conductive ink composition is a value measured using a rheometer. The viscosity is measured at a shear rate of 5.1 (unit: 1 / s). The viscosity measurement temperature is 23°C unless otherwise specified.

[0015] - First embodiment - <<Conductive ink composition>> A conductive ink composition of a first embodiment (hereinafter also referred to as "first composition") contains a (meth)acrylic polymer (A) and silver particles (B). In this specification, the specific surface area of ​​the silver particles is a value measured by the BET method, in which a mixed gas of helium and nitrogen is adsorbed onto the silver particles and the specific surface area of ​​the silver particles is measured from the amount of the adsorbed mixed gas. In this specification, the maximum particle size and 50% average particle size of the silver particles are the maximum particle size and the median diameter at 50% cumulative volume in a particle size distribution curve measured by laser diffraction particle size measurement.

[0016] <(Meth)acrylic polymer (A)> The (meth)acrylic polymer (A) is a polymer containing units based on (meth)acrylate. The content of units based on (meth)acrylate relative to all units constituting the (meth)acrylic polymer (A) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It may be 100% by mass.

[0017] The (meth)acrylic polymer (A) preferably contains one or more units (a1) derived from a hydroxyl group-containing monomer. The units (a1) contribute to the hydroxyl value of the (meth)acrylic polymer (A). The units (a1) are preferably units derived from a (meth)acrylate having a hydroxyl group. Specific examples of the hydroxyl group-containing monomer (a1) corresponding to the units (a1) include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, and 2-hydroxyethyl methacrylate. The content of the units (a1) relative to the total units of the (meth)acrylic polymer (A) is preferably 20 to 40% by mass, more preferably 22 to 38% by mass, and even more preferably 24 to 36% by mass. When the content of the units (a1) is equal to or greater than the lower limit of the above range, a hydroxyl value of more than 50 mgKOH / g is easily obtained, and the affinity with silver particles is increased, resulting in excellent elasticity. When the content is equal to or less than the upper limit, the self-cohesion of the meth(acrylic) polymer is not too strong, and good dispersibility and good stretchability are likely to be obtained during ink production.

[0018] The (meth)acrylic polymer (A) preferably contains one or more units (a2) based on a (meth)acrylate having an alkyl group having 4 to 12 carbon atoms. The units (a2) do not contain units (a1). The alkyl group having 4 to 12 carbon atoms in the units (a2) may be linear or branched. Specific examples of the (meth)acrylate (a2) corresponding to the units (a2) include n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. The content of the units (a2) relative to the total units of the (meth)acrylic polymer (A) is preferably 46 to 64% by mass, more preferably 48 to 62% by mass, and even more preferably 50 to 60% by mass. When the content of the units (a2) is equal to or greater than the lower limit of the above range, good durability during stretching is likely to be obtained. When the content is equal to or less than the upper limit, the polymer is less likely to become rigid and good stretchability is likely to be obtained.

[0019] The (meth)acrylic polymer (A) preferably contains one or more units (a3) ​​based on a (meth)acrylate having an alkyl group having 1 to 3 carbon atoms. The units (a3) ​​do not contain units (a1) or units (a2). The alkyl group having 3 carbon atoms in the units (a3) ​​may be linear or branched. Specific examples of the (meth)acrylate (a3) ​​corresponding to the units (a3) ​​include methyl (meth)acrylate and ethyl (meth)acrylate. The content of the units (a3) ​​relative to the total units of the (meth)acrylic polymer (A) is preferably 6 to 19% by mass, more preferably 8 to 17% by mass, and even more preferably 10 to 15% by mass. When the content of the units (a3) ​​is equal to or greater than the lower limit of the above range, excellent flexibility and sufficient stretchability are likely to be obtained. When the content is equal to or less than the upper limit, excellent adhesion to the substrate and good durability during stretching are likely to be obtained.

[0020] The (meth)acrylic polymer (A) preferably contains one or more units (a4) derived from a carboxyl group-containing monomer. The units (a4) do not include units (a1), (a2), or (a3). Specific examples of the carboxyl group-containing monomer (a4) corresponding to the units (a4) include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and acid anhydride group-containing monomers (maleic anhydride, itaconic anhydride, etc.). The content of the units (a4) relative to the total units of the (meth)acrylic polymer (A) is preferably 0.05 to 0.35% by mass, more preferably 0.10 to 0.30% by mass, and even more preferably 0.15 to 0.25% by mass. When the content of the units (a4) is equal to or greater than the lower limit of the above range, excellent affinity with silver particles is achieved, and sufficient stretchability is easily obtained. When the content is equal to or less than the upper limit, the cohesive force of the (meth)acrylic acid is not too high, and good stretchability is easily obtained.

[0021] The (meth)acrylic polymer (A) may contain one or more units (a5) based on other monomers copolymerizable with the units (a1) to (a4) other than the above units (a1) to (a4). Examples of the other monomers (a5) corresponding to the units (a5) include (meth)acrylates having a linear or branched alkyl group with 13 to 20 carbon atoms, (meth)acrylates having an aromatic ring, (meth)acrylates having a non-aromatic cyclic hydrocarbon group, epoxy group-containing (meth)acrylates, vinyl ester-based monomers, styrene-based monomers, olefin-based monomers, vinyl ether-based monomers, and polyfunctional monomers. For example, vinyl ester-based monomers such as vinyl acetate and vinyl propionate are preferred. The content of the units (a5) relative to the total units of the (meth)acrylic polymer (A) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. It may even be zero.

[0022] The glass transition temperature of the (meth)acrylic polymer (A) is 0°C or lower, preferably lower than -30°C, and more preferably lower than -32°C. When the glass transition temperature is equal to or lower than the above upper limit, drying properties during the production of a conductive film can be ensured, and a good elongation rate can be obtained. The lower limit of the glass transition temperature is preferably higher than -50°C, and more preferably higher than -45°C. When the glass transition temperature of the (meth)acrylic polymer (A) is higher than -50°C, the conductive film has excellent durability and is likely to have sufficient stretchability.

[0023] The weight-average molecular weight of the (meth)acrylic polymer (A) is 500,000 or more, preferably 520,000 or more, and more preferably 540,000 or more. When the weight-average molecular weight is equal to or greater than the lower limit, the durability of stretchability is excellent. The upper limit of the weight-average molecular weight is preferably 990,000 or less, more preferably 950,000 or less, and even more preferably 900,000 or less, from the viewpoint of ensuring flexibility and exhibiting conductivity.

[0024] The hydroxyl value of the (meth)acrylic polymer (A) is greater than 50 mgKOH / g, preferably 75 mgKOH / g or greater, and more preferably 100 mgKOH / g or greater. When the hydroxyl value exceeds 50 mgKOH / g, the affinity between the silver particles and the (meth)acrylic polymer is moderately high, and the elasticity is excellent. The upper limit of the hydroxyl value is preferably 200 mgKOH / g or less, more preferably 175 mgKOH / g or less, and even more preferably 150 mgKOH / g or less, from the viewpoint of not impairing the conductivity of the silver particles.

[0025] The (meth)acrylic polymer (A) may be produced by a conventional method, or a commercially available product may be used. The (meth)acrylic polymer (A) may be used in the form of a (meth)acrylic polymer composition containing the (meth)acrylic polymer (A) and an optional solvent. The solid content of the (meth)acrylic polymer composition is not particularly limited, but from the viewpoint of handling during blending, a viscosity that imparts appropriate fluidity is desirable. For example, a solid content of 10% by mass or more to 50% by mass is preferred, and 20% by mass or more to 40% by mass is more preferred.

[0026] A preferred embodiment of the (meth)acrylic polymer (A) is, for example, embodiment (i) below. [Embodiment (i)] A (meth)acrylic polymer having a content of units (a1) of 20 to 40% by mass, a content of units (a2) of 46 to 64% by mass, a content of units (a3) ​​of 6 to 19% by mass, a content of units (a4) of 0.05 to 0.35% by mass, a content of units (a5) of 10% by mass or less, a glass transition temperature of more than -50°C and less than -30°C, a weight-average molecular weight of 500,000 to 990,000, and a hydroxyl value of more than 50 mgKOH / g and not more than 200 mgKOH / g. The total of units (a1) to (a5) does not exceed 100% by mass.

[0027] <Silver particles (B)> The silver particles (B) have a specific surface area of ​​0.5 to 3.0 m ２ / g, a 50% average particle size of 0.5 to 14.0 μm, and a maximum particle size of 8 μm or more. The silver particles (B) preferably have a flat shape in one direction, such as a flake or scale shape. The specific surface area is 0.7 to 3.0 m ２ / g is more preferable. The 50% average particle size is more preferably 1.0 to 12.0 μm. The surfaces of the silver particles (B) may be coated with an organic acid. Specific examples of organic acids include stearic acid, oleic acid, lauric acid, and hexanoic acid. The organic acid is not limited to the above specific examples. When silver particles (B) satisfying the above conditions are used, a conductive film with excellent conductivity when stretched is easily obtained. Furthermore, when a (meth)acrylic polymer (A) is combined with silver particles (B) satisfying the above conditions, a conductive film that is less likely to crack or break when stretched and that can exhibit conductivity even when highly stretched is obtained.

[0028] <Solvent (C)> The first composition may contain one or more solvents (C) as needed. The solvent (C) is not particularly limited as long as it can uniformly disperse the (meth)acrylic polymer (A) and silver particles (B), has low volatility, maintains stable ink viscosity, and can be removed in the drying step during conductive film formation. Examples of the solvent (C) include ester-based solvents such as diethylene glycol monoethyl ether acetate (also known as ethyl carbitol acetate), hydrocarbon-based solvents such as decane, tetradecane, and cyclohexane, and alcohol-based solvents such as 2-ethylhexanol, 2-ethylhexyl ether derivatives, and diethylene glycol monobutyl ether.

[0029] <Optional Components> The first composition may contain optional components other than the (meth)acrylic polymer (A), silver particles (B), and solvent (C) to the extent that the effects of the present invention are not impaired. Components known in the field of conductive ink compositions can be used as the optional components. For example, to improve printability, components that adjust the interfacial tension of the ink (e.g., surfactants, leveling agents, etc.) and components that adjust the viscosity of the ink (e.g., thixotropic agents) may be added. Furthermore, to improve adhesion to each substrate, a binder component different from the (meth)acrylic polymer (A) can be added. Examples of binder components include polyurethane polymers, epoxy polymers, ester polymers, terpene resins, and terpene resin derivatives (e.g., terpene phenol resins, etc.). The binder component can be added in an amount that does not impair elasticity. Furthermore, an ion scavenger can be added to prevent migration.

[0030] The solid content of the first composition is 50 to 80% by mass, preferably 52 to 78% by mass, and more preferably 54 to 76% by mass, based on the total mass of the first composition. When the solid content is within the above range, sufficient extensibility and good conductivity during elongation are likely to be obtained. Furthermore, a viscosity suitable for printing is likely to be obtained. The solid content can be adjusted by the content of the solvent (C).

[0031] The viscosity of the first composition is preferably 20 to 50 Pa·s, more preferably 24 to 46 Pa·s, and even more preferably 28 to 42 Pa·s. When the viscosity is within the above range, good printability is likely to be obtained. For example, properties suitable for screen printing are likely to be obtained. For example, if the viscosity of the first composition is too high, clogging or rubbing may occur during printing, and if the viscosity is too low, printing defects such as bleeding and dripping may occur.

[0032] The content of the (meth)acrylic polymer (A) relative to the solid content of the first composition is preferably 3.0 to 10.5% by mass, more preferably 4.0 to 10.0% by mass, and even more preferably 4.5 to 9.5% by mass. When the content of the (meth)acrylic polymer (A) is equal to or greater than the above-mentioned lower limit, sufficient stretchability is likely to be obtained. When the content is equal to or less than the above-mentioned upper limit, a sufficient content of silver particles (B) is likely to be secured, and good conductivity during stretching is likely to be obtained. When the content of silver particles (B) is equal to or less than the above-mentioned lower limit, good conductivity is likely to be secured, and good properties such as stretchability are likely to be obtained. The content of the optional components relative to the solid content of the first composition is preferably 10% by mass or less, more preferably 5% by mass or less, and may be zero.

[0033] <Method for producing conductive ink composition> The first composition is obtained by uniformly mixing a (meth)acrylic polymer (A), silver particles (B), a solvent (C), and optional components as needed. A (meth)acrylic polymer composition containing the (meth)acrylic polymer (A) and a solvent compatible with (A) may be used as the (meth)acrylic polymer (A). The solvent compatible with the (meth)acrylic polymer (A) may be one of the solvents listed above as examples of the solvent (C), or may be another good solvent (e.g., ethyl acetate). Known mixing methods can be used. For example, the first composition can be produced by premixing all components using a stirrer and kneading the resulting premix multiple times using a three-roll mill.

[0034] <Conductive film> The first composition is applied to a substrate or the like to form a coating film, and the coating film is dried to remove the solvent (C), thereby obtaining a conductive film. The material and shape of the substrate are not particularly limited. A stretchable substrate is preferred. Examples of stretchable materials include polyurethane, ethylene propylene rubber, silicone rubber, and various elastomers.

[0035] A known coating method can be used to apply the first composition to the substrate. Examples include printing, dipping, spraying, and bar coating. Printing is preferred from the viewpoint of versatility and accuracy. Examples of printing methods include inkjet printing, flexographic printing, gravure printing, screen printing, pad printing, and lithography printing. Screen printing is particularly preferred because it can easily reduce costs, is suitable for large-area printing, and can easily increase the thickness of the conductive film.

[0036] The coating film may be heated in the drying process. The heating temperature during drying is preferably a temperature that does not adversely affect the substrate and that can completely remove the solvent in the coating material. Although this temperature varies depending on the type of substrate, for example, 80 to 150°C is preferred. The thickness of the conductive film after drying is not particularly limited, but is preferably, for example, 10 to 100 μm, and more preferably 20 to 80 μm. When the thickness is equal to or greater than the lower limit of the above range, conductivity is easily exhibited, and when it is equal to or less than the upper limit, the device to be fabricated can be made smaller in size.

[0037] The conductive film of the first embodiment is stretchable and conductive, as shown in the examples described below. It also has good adhesion to the substrate. Therefore, the first composition can be suitably used as a conductive material for forming wiring, electrodes, etc. on a stretchable substrate, and can achieve good conformity to the stretching and contraction of the substrate.

[0038] Furthermore, as shown in the examples described below, the conductive film of the first embodiment also has excellent resistance to repeated elongation, and exhibits good stability of conductivity when repeatedly elongated. According to the first embodiment, for example, a conductive film can be realized whose conductivity is detectable even after 100 repeated elongations at an elongation rate of 100%. For example, a conductive film can be realized in which the absolute value of the difference in surface resistance (deviation in surface resistance before and after repeated elongation) between before and after (at the start and end) repeated elongation at an elongation rate of 100% is 100 Ω or less.

[0039] Furthermore, the conductive film of the first embodiment remains conductive even when stretched, as will be shown in the examples described later. For example, a wearable sensor requires 200% stretch when applied to the elbow, which is the maximum range of human movement. According to the first embodiment, a conductive film can be realized that can detect conductivity even when stretched to, for example, 250% elongation.

[0040] Furthermore, the conductive film of the first embodiment can maintain its conductivity in an elongated state even when repeatedly stretched, as shown in the examples described later. According to the first embodiment, for example, even when repeatedly stretched 100 times at an elongation rate of 100%, it is possible to realize a conductive film whose conductivity can be detected in an elongated state at an elongation rate of 100%.

[0041] Furthermore, according to the first embodiment, a conductive film whose conductivity (resistance value) changes with shape change can be obtained. Specifically, as shown in the examples described below, a conductive film whose surface resistance value increases with increasing elongation can be realized. For example, a conductive film can be realized in which the logarithm of the resistance change (unit: Ω / %) per 1% of elongation when the elongation rate changes from 0% to 250% is 5.0 or less, preferably 4.0 or less. Such a conductive film whose resistance value changes with shape change is suitable for use in a resistance change sensor. Specifically, the conductive film of the first embodiment can be used as a resistor (sensing means) in a resistance change sensor. Specific examples of resistance change sensors include wearable or flexible sensors that detect expansion and contraction through changes in electrical resistance, strain sensors that measure strain through changes in electrical resistance, and pressure-sensitive sensors that can sense and measure deformation through changes in electrical resistance. Furthermore, because the conductive film can exhibit high conductivity even when stretched, it can also be used in conductive components (wiring, electrodes, antennas, heating elements, etc.) that constitute stretchable articles. Specifically, examples of the conductive film include use in conductive members (wiring, electrodes, antennas, etc.) that constitute the wearable sensor, the pressure-sensitive sensor, moving parts of robots, artificial muscles, or flexible displays, wiring for in-mold molded parts, and heating elements for flexible heaters. For example, the conductive film of the first embodiment is suitable for electrodes that require stretchability in electronic devices, or for wiring that requires stretchability in electronic devices. For example, the conductive film of the first embodiment is suitable for the detection unit of a resistance change sensor, the electrode of a resistance change sensor, or the wiring of a resistance change sensor.

[0042] Second Embodiment A conductive ink composition of a second embodiment (hereinafter also referred to as the "second composition") contains a (meth)acrylic polymer (A) and carbon black (CB) (hereinafter also referred to as (CB) particles). In this specification, the specific surface area of ​​the carbon black is a value measured by the BET method, in which nitrogen is adsorbed onto carbon black particles and the specific surface area of ​​the carbon black is measured from the amount of adsorbed nitrogen. The BET specific surface area of ​​the carbon black is measured by a method conforming to ASTM D 3037. In this specification, the aggregate diameter, which is the aggregate diameter of primary particle aggregates of carbon black, is a value measured by the aggregate diameter measurement method described in JIS K6217-6.

[0043] <(Meth)acrylic polymer (A)> The (meth)acrylic polymer (A) in the second embodiment can be the same polymer as the (meth)acrylic polymer (A) in the first embodiment. The (meth)acrylic polymer (A) in the second embodiment can contain the same units (a1) to (a4) as in the first embodiment. It may further contain the unit (a5).

[0044] In the second embodiment, the content of units (a1) relative to all units of the (meth)acrylic polymer (A) is preferably 20 to 40% by mass, more preferably 22 to 38% by mass, and even more preferably 24 to 36% by mass. When the content of units (a1) is at least the lower limit of the above range, a hydroxyl value of more than 50 mgKOH / g is likely to be obtained, and affinity with the (CB) particles is increased, resulting in excellent elasticity. When the content is at most the upper limit, the self-cohesion force of the meth(acrylic) polymer is not too strong, and good dispersibility and good elasticity during ink production are likely to be obtained.

[0045] In the second embodiment, the content of the units (a2) relative to all units of the (meth)acrylic polymer (A) is preferably 46 to 64 mass%, more preferably 48 to 62 mass%, and even more preferably 50 to 60 mass%. When the content of the units (a2) is equal to or greater than the lower limit of the above range, good durability during stretching is likely to be obtained. When it is equal to or less than the upper limit, the polymer is less likely to become rigid and good stretchability is likely to be obtained.

[0046] In the second embodiment, the content of the units (a3) ​​relative to all units of the (meth)acrylic polymer (A) is preferably 6 to 19 mass%, more preferably 8 to 17 mass%, and even more preferably 10 to 15 mass%. When the content of the units (a3) ​​is equal to or greater than the lower limit of the above range, excellent flexibility and sufficient stretchability are likely to be obtained. When the content is equal to or less than the upper limit, excellent adhesion to the substrate and good durability during stretching are likely to be obtained.

[0047] In the second embodiment, the content of the units (a4) relative to all units of the (meth)acrylic polymer (A) is preferably 0.05 to 0.35% by mass, more preferably 0.10 to 0.30% by mass, and even more preferably 0.15 to 0.25% by mass. When the content of the units (a4) is equal to or greater than the lower limit of the above range, the affinity with the (CB) particles is excellent and sufficient stretchability is easily obtained. When the content is equal to or less than the upper limit, the cohesive strength of the (meth)acrylic acid is not too high and good stretchability is easily obtained.

[0048] In the second embodiment, the content of the units (a5) relative to all units of the (meth)acrylic polymer (A) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. It may be zero.

[0049] The glass transition temperature of the (meth)acrylic polymer (A) in the second embodiment is the same as that in the first embodiment. The weight average molecular weight of the (meth)acrylic polymer (A) in the second embodiment is the same as that in the first embodiment.

[0050] In a second embodiment, the hydroxyl value of the (meth)acrylic polymer (A) is greater than 50 mgKOH / g, preferably 75 mgKOH / g or greater, and more preferably 100 mgKOH / g or greater. When the hydroxyl value exceeds 50 mgKOH / g, the affinity between the (CB) particles and the (meth)acrylic polymer is moderately high, and the elasticity is excellent. The upper limit of the hydroxyl value is preferably 200 mgKOH / g or less, more preferably 175 mgKOH / g or less, and even more preferably 150 mgKOH / g or less, from the viewpoint of not impairing the conductivity of the (CB) particles.

[0051] In the second embodiment, the (meth)acrylic polymer (A) may be used in the form of a (meth)acrylic polymer composition containing the (meth)acrylic polymer (A) and an optional solvent. The solid content of the (meth)acrylic polymer composition is not particularly limited, but from the viewpoint of handling during blending, a viscosity that imparts appropriate fluidity is desirable. For example, a solid content of 10% by mass or more and 50% by mass or less is preferred, and 20% by mass or more and 40% by mass or less is more preferred.

[0052] A preferred aspect of the (meth)acrylic polymer (A) in the second embodiment is, for example, the above aspect (i).

[0053] <Carbon black (CB)> Carbon black (CB) has a specific surface area of ​​50 m ２ / g or more, and the aggregate diameter is 400 nm or less. ２ / g is preferred, and 55 to 1000m ２ / g is more preferable. The aggregate diameter is preferably 400 nm or less from the viewpoint of not inhibiting stretchability. The lower limit of the aggregate diameter is not particularly limited, but from the viewpoint of exhibiting conductivity, it is preferably 100 nm or more, more preferably 150 nm or more. When carbon black (CB) satisfying the above conditions is used, a conductive film with excellent conductivity when stretched is easily obtained. Furthermore, when the (meth)acrylic polymer (A) is combined with carbon black (CB) satisfying the above conditions, a conductive film that is less likely to crack or break when stretched is obtained.

[0054] Examples of carbon black (CB) include those commercially available as conductive carbon black. Specific examples include furnace black, channel black, thermal black, and acetylene black. Furnace black is preferred in terms of achieving both elasticity and conductivity. One type of carbon black (CB) may be used, or two or more types may be used in combination.

[0055] <Solvent (C)> The second composition may contain one or more solvents (C) as needed. The solvent (C) is not particularly limited as long as it can uniformly disperse the (meth)acrylic polymer (A) and (CB) particles, has low volatility, maintains stable ink viscosity, and can be removed in the drying step during conductive film formation. The solvent (C) in the second embodiment can be the same compound as the solvent (C) in the first embodiment.

[0056] <Graphite Material (D)> The second composition may contain one or more graphite materials (D) as a conductive additive. The graphite material (D) contributes to improving conductivity. Examples of graphite materials include expanded graphite, natural graphite (scale graphite, flake graphite), and artificial graphite. The shape of the graphite material (D) is not particularly limited, but a shape that is flat in one direction, such as a flake or scale shape, is preferred in order not to inhibit stretchability, and the 50% average particle size is preferably 10 μm to 30 μm. The 50% average particle size of the graphite material (D) is the median diameter at 50% cumulative volume in a particle size distribution curve measured by laser diffraction particle size analysis.

[0057] <Optional Components> The second composition may contain optional components other than the (meth)acrylic polymer (A), carbon black (CB), solvent (C), and graphite material (D) to the extent that the effects of the present invention are not impaired. Components known in the field of conductive ink compositions can be used as optional components. For example, to improve printability, components that adjust the interfacial tension of the ink (e.g., surfactants, leveling agents, etc.) and components that adjust the viscosity of the ink (e.g., thixotropic agents) may be added. Furthermore, to improve adhesion to each substrate, a binder component different from the (meth)acrylic polymer (A) can be added. Examples of binder components include polyurethane polymers, epoxy polymers, ester polymers, terpene resins, and terpene resin derivatives (e.g., terpene phenolic resins, etc.). The binder component can be added in an amount that does not impair elasticity.

[0058] The solid content of the second composition is 15 to 30% by mass, preferably 16 to 29% by mass, and more preferably 17 to 28% by mass, based on the total mass of the second composition. When the solid content is within the above range, sufficient extensibility and good conductivity during elongation are likely to be obtained. Furthermore, a viscosity suitable for printing is likely to be obtained. The solid content can be adjusted by the content of the solvent (C).

[0059] The viscosity of the second composition is preferably 20 to 100 Pa·s, more preferably 22 to 98 Pa·s, and even more preferably 24 to 96 Pa·s. When the viscosity is within the above range, good printability is likely to be obtained. For example, properties suitable for screen printing are likely to be obtained. For example, if the viscosity of the second composition is too high, clogging or rubbing may occur during printing, and if the viscosity is too low, printing defects such as bleeding and dripping may occur.

[0060] The content of the (meth)acrylic polymer (A) relative to the solid content of the second composition is preferably 40 to 62% by mass, more preferably 41 to 60% by mass, and even more preferably 42 to 58% by mass. When the content of the (meth)acrylic polymer (A) is equal to or greater than the above-mentioned lower limit, excellent adhesion to the substrate is achieved. Furthermore, sufficient stretchability is easily obtained. When the content is equal to or less than the above-mentioned upper limit, a sufficient content of the (CB) particles is easily ensured, and good conductivity during stretching is easily obtained. The content of the carbon black (CB) relative to the solid content of the second composition is preferably 18 to 50% by mass, more preferably 20 to 48% by mass, and even more preferably 22 to 46% by mass. When the content of the carbon black (CB) is equal to or greater than the above-mentioned lower limit, good conductivity is easily obtained. When the content is equal to or less than the above-mentioned upper limit, a sufficient content of components other than the (CB) particles is easily ensured, and good properties such as stretchability are easily obtained. Furthermore, the viscosity is not too high, and printing defects such as rubbing are less likely to occur. The content of the optional components relative to the solid content of the second composition is preferably 30% by mass or less, more preferably 25% by mass or less, and may be zero.

[0061] When the second composition contains a graphite material (D), the content of the graphite material (D) relative to the solid content of the second composition is preferably 16 to 30 mass%, more preferably 18 to 28 mass%, and even more preferably 20 to 26 mass%. When the content of the graphite material (D) is equal to or greater than the above-mentioned lower limit, the effect of improving conductivity is excellent. When the content of the graphite material (D) is equal to or less than the above-mentioned upper limit, the conductive film is less likely to harden and good stretchability is easily obtained. Furthermore, when the second composition contains a graphite material (D), the proportion of the carbon black (CB) relative to the total mass of the carbon black (CB) and the graphite material (D) is preferably 40 to 80 mass%, more preferably 45 to 70 mass%, and even more preferably 50 to 60 mass%. When the proportion of the carbon black (CB) is equal to or greater than the above-mentioned lower limit, the conductive film is less likely to harden and good stretchability is easily obtained. When the content of the carbon black (CB) is equal to or less than the above-mentioned upper limit, the effect of improving conductivity due to the graphite material (D) is easily obtained. When the second composition contains other conductive carbon materials, the proportion of the other conductive carbon materials is preferably 5 mass% or less, and more preferably 3 mass% or less, based on the total mass of the carbon black (CB), the graphite material (D), and the other conductive carbon materials.

[0062] <Method for producing conductive ink composition> The second composition is obtained by uniformly mixing a (meth)acrylic polymer (A), carbon black (CB), a solvent (C), and, if necessary, a graphite material (D), and optional components. A (meth)acrylic polymer composition containing the (meth)acrylic polymer (A) and a solvent compatible with (A) may be used as the (meth)acrylic polymer (A). The solvent compatible with the (meth)acrylic polymer (A) may be any of the solvents listed above as examples of the solvent (C), or may be another good solvent (e.g., ethyl acetate). The same mixing method as in the first embodiment may be used.

[0063] <Conductive film> The conductive film is obtained by applying the second composition to a substrate or the like to form a coating film, and then drying the coating film to remove the solvent (C). The material and shape of the substrate can be the same as those in the first embodiment.

[0064] The second composition can be applied to the substrate by the same method as in the first embodiment.

[0065] The coating film may be heated in the drying step, as in the first embodiment. The thickness of the conductive film after drying can be the same as in the first embodiment.

[0066] The conductive film of the second embodiment is stretchable and conductive, as shown in the examples below. It also has good adhesion to the substrate. Therefore, the second composition can be suitably used as a conductive material for forming wiring, electrodes, etc. on a stretchable substrate, and good followability to the stretching of the substrate is obtained. For example, the detection limit of the surface resistance value is 1.0 × 10 ７ (Ω) or less, a conductive film can be realized having an elongation at which the surface resistance can be measured of 300% or more, preferably 350% or more.

[0067] Furthermore, as shown in the examples below, the conductive film of the second embodiment is also excellent in resistance to repeated elongation, and exhibits good stability of conductivity when elongated repeatedly. According to the second embodiment, for example, a conductive film can be realized in which conductivity can be detected even after repeated elongation at an elongation rate of 100% 100 times. For example, the absolute value of the difference in surface resistance (deviation in surface resistance before and after repeated elongation) between before and after (start and end) repeated elongation at an elongation rate of 100% is 5.0 × 10 ４ A conductive film with a resistance of Ω or less can be realized.

[0068] Furthermore, the conductive film of the second embodiment remains conductive even when stretched, as will be shown in the examples described later. For example, a wearable sensor requires 200% stretch when applied to the elbow, which is the maximum range of human movement. According to the second embodiment, a conductive film can be realized that can detect conductivity even when stretched to, for example, 300% elongation.

[0069] Furthermore, the conductive film of the second embodiment can maintain its conductivity in an elongated state even when repeatedly elongated, as shown in the examples described later. According to the second embodiment, for example, even when repeatedly elongated 100 times at an elongation rate of 100%, it is possible to realize a conductive film whose conductivity can be detected in an elongated state at an elongation rate of 100%.

[0070] Furthermore, according to the second embodiment, a conductive film whose conductivity (resistance value) changes with a change in shape can be obtained. Specifically, as shown in the examples described below, a conductive film whose surface resistance value increases with an increase in elongation can be realized. For example, a conductive film can be realized in which the logarithm of the resistance change (unit: Ω / %) per 1% of elongation when the elongation rate changes from 0% to 300% is 5.0 or less, preferably 4.5 or less. Such a conductive film whose resistance value changes with a change in shape is suitable for use in a resistance change sensor. Specifically, the conductive film of the second embodiment can be used as a resistor (sensing means) in a resistance change sensor. Specific examples of resistance change sensors include wearable or flexible sensors that detect expansion and contraction by changes in electrical resistance, strain sensors that measure strain by changes in electrical resistance, and pressure-sensitive sensors that can sense and measure deformation by changes in electrical resistance. Furthermore, since the conductive film can exhibit high conductivity even when stretched, although not as highly conductive as metal inks using metal fillers, it can also be used for conductive members (wiring, electrodes, heaters, etc.) that constitute stretchable articles. Specific examples include use in conductive members (wiring, electrodes, etc.) that constitute the wearable sensor, the pressure-sensitive sensor, biosensors (e.g., glucose sensors, etc.), and heating elements of flexible heaters. For example, the conductive film of the second embodiment is suitable for electrodes that require stretchability in electronic devices, or for wiring that requires stretchability in electronic devices. For example, the conductive film of the second embodiment is suitable for use in the detection unit of a resistance change sensor, the electrodes of a resistance change sensor, or the wiring of a resistance change sensor.

[0071] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following description. In the following, the unit of content "%" is "% by mass" unless otherwise specified.

[0072] <Production Example of (Meth)acrylic Polymer Composition> The monomers shown in Tables 1 and 7 are as follows: [Hydroxyl group-containing monomer (a1)] 2HPA: 2-hydroxypropyl acrylate 4HBA: 4-hydroxybutyl acrylate 2HEA: 2-hydroxyethyl acrylate 2HEMA: 2-hydroxyethyl methacrylate [C4-12 alkyl (meth)acrylate (a2)] BA: butyl acrylate 2EHA: 2-ethylhexyl acrylate [C1-3 alkyl (meth)acrylate (a3)] MA: methyl acrylate MMA: methyl methacrylate [Carboxy group-containing monomer (a4)] AA: acrylic acid [Other monomers (a5)] Vac: vinyl acetate

[0073] (Production Example 1-1: Production of (meth)acrylic polymer composition (1-1)) The monomer mixture shown in Table 1 was polymerized in a polymerization solvent to synthesize a (meth)acrylic polymer, and a solvent was further added to adjust the solids concentration, thereby obtaining a (meth)acrylic polymer composition. Specifically, 29.8 parts by mass of 2HPA, 57.2 parts by mass of BA, 12.8 parts by mass of MA, and 0.2 parts by mass of AA as monomers, 0.02 parts by mass of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 43 parts by mass of ethyl acetate as a polymerization solvent were placed in a separable flask. Nitrogen gas was introduced to remove oxygen from the polymerization system, and the temperature was raised to 70°C and the mixture was allowed to react for 8 hours to obtain (meth)acrylic polymer A1-1. Ethyl acetate was added to the mixture to adjust the solids concentration to 33% by mass, thereby obtaining (meth)acrylic polymer composition (1-1). The glass transition temperature, weight average molecular weight, and hydroxyl value of the (meth)acrylic polymer are shown in Table 1 (the same applies hereinafter).

[0074] (Production Examples 1-2 to 1-5: Production of (meth)acrylic polymer compositions (1-2) to (1-5)) The composition of the monomer mixture was changed as shown in Table 1, and the monomer mixture was polymerized in the same manner as in Production Example 1 to synthesize (meth)acrylic polymers A1-2 to A1-5. Ethyl acetate was added to each of the resulting mixtures to adjust the solids concentration as shown in Table 1, thereby obtaining (meth)acrylic polymer compositions (1-2) to (1-5).

[0075] (Comparative Composition (1-6)) A polyester resin solution (Mitsubishi Chemical Corporation product name "Nichigo Polyester LP-035") was used as the comparative composition (1-6). The glass transition temperature, weight average molecular weight, and hydroxyl value of the polyester resin (comparative resin P1-6) in the comparative composition (1-6) are shown in Table 1.

[0076]

[0077] <Silver particles (B)> The following silver particles were used. The shape, specific surface area, 50% average particle size, and maximum particle size of each silver particle are shown in Table 2. Silver particles (B1): Tokuriki Kogyo Co., Ltd. product name "Silbestos TC-12", flaky particles. Silver particles (B2): Fukuda Metal Foil & Powder Co., Ltd. product name "AgC-2011", flaky particles. Silver particles (B3): Tokuriki Kogyo Co., Ltd. product name "Silbestos TC-725", flaky particles. Silver particles (B4): Mitsui Mining & Smelting Co., Ltd. product name "SLO2", spherical particles. Silver particles (B5): Tokusen Kogyo Co., Ltd. product name "M612", flaky particles.

[0078] <Solvent (C)> The following solvents were used: Solvent (C1-1): Diethylene glycol monoethyl ether acetate Solvent (C1-2): Polyoxypropylene 2-ethylhexyl ether derivative (Aoki Oil & Fat Co., Ltd. product name "Brownon EHP-4")

[0079] <Optional Components> The following optional components were used. Optional component (1-1): binder, terpene phenol resin (Yasuhara Chemical Co., Ltd. product name "YS Polystar T80") Optional component (1-2): ion scavenger (Toagosei Co., Ltd. product name "IXEPLAS-A2")

[0080]

[0081] (Examples 1-1 to 1-8, Comparative Examples 1-1 to 1-8) Silver particles and a solvent were blended into a (meth)acrylic polymer composition according to the formulations shown in Tables 3 to 6. In Example 1-5, optional component (1-1), silver particles, and a solvent were blended into a (meth)acrylic polymer composition. In Comparative Example 1-4, silver particles and a solvent were blended into a comparative composition (1-6). All of the blended components were premixed using a stirrer and then kneaded using a three-roll mill (Imex Co., Ltd. product name "BR-150VIII") to obtain a conductive ink composition. Kneading was performed twice at a rotation speed of 120 rpm with a roll distance of 40 μm, and then the roll distance was reduced to 10 μm and the kneading was performed two more times. The solids content, (meth)acrylic polymer (A) content, and silver particle (B) content relative to the total mass of the conductive ink composition for each example are shown in the tables. The contents of the (meth)acrylic polymer (A) and the silver particles (B) relative to the solid content are also shown in the table. The viscosities of the conductive ink compositions are also shown in the table. Note that blank spaces in the table indicate that the corresponding component is not blended.

[0082] <Evaluation Method> The obtained conductive films were evaluated by the following methods. The conductive ink composition obtained in each example was applied to a substrate and dried at 130°C for 10 minutes to produce a laminate having a conductive film on the substrate. A stretchable polyurethane sheet (thickness 100 μm) was used as the substrate. The dry thickness of the conductive film was approximately 30 μm. The obtained conductive films were evaluated for the following items. The results are shown in Tables 3 to 6.

[0083] (Measurement of Volume Resistivity) The laminate obtained in each example was used as a sample, and the volume resistivity (unit: Ω cm) of the conductive film was measured using a four-terminal electrode of a resistivity meter (trade name "Loresta" manufactured by Nitto Seiko Analytech Co., Ltd.). The thickness of the conductive film was measured using a microgauge.

[0084] (Evaluation of Adhesion) The laminate obtained in each example was used as a sample and a peel test was performed using the cross-cut method based on JIS: K5600-5-6. Specifically, the conductive film of the laminate was cross-cut with a cutter knife so that 100 squares with sides of 1 mm were formed on the conductive film. Cellotape (registered trademark) was attached to this conductive film and peeled off in the vertical direction, and the degree of peeling of the conductive film was evaluated according to the following criteria. When none of the 100 squares peeled off, it was evaluated as "○", when 1 to 99 squares peeled off, it was evaluated as "△", and when all of the 100 squares peeled off, it was evaluated as "×".

[0085] (Elongation Test) The laminate obtained in each example was cut into a No. 3 dumbbell shape and used as a sample, which was set in a tensile tester. The distance between the gauge lines (initial dimension) was 20 mm, and the sample was pulled at a pulling rate of 10 mm / min under conditions of 23°C, and the surface resistance value (unit: Ω) between the gauge lines was measured at each specific elongation using a tester (Custom Co., Ltd., product name "CDM-2000D"). The elongation is a value calculated using the following formula: Elongation (%) = (distance between the gauge lines after elongation (mm) - initial dimension) / initial dimension x 100 The surface resistance value R when the elongation is 200% (at 200% elongation), i.e., when the distance between the gauge lines is 60 mm, is １ The surface resistance R when the elongation rate is 250% (250% elongation), that is, when the distance between the gauge lines is 70 mm, is also shown in the table. ２ The table also shows the logarithm of the change in resistance (unit: Ω / %) per 1% of elongation when the elongation rate changes from 0% to 250%, calculated by the following formula (3). R in formula (3) ０ indicates the surface resistance value when the elongation rate is 0% (0% elongation). When cracks or breaks occur in the film during elongation, it is marked as "x (not achieved)", and when elongation was possible but conductivity could not be detected, it is marked as "x (impossible to measure)".

[0086]

[0087] (Repeated Elongation Test) The laminate obtained in each example was cut into a No. 3 dumbbell shape and set in a tensile tester. The gauge length (initial dimension) was 20 mm, and repeated elongation was performed at 23°C and a tensile speed of 500 mm / min. Specifically, the first cycle consisted of stretching from the initial dimension (0%, gauge length 20 mm) to 100% elongation (40 mm gauge length) and then returning to 0% elongation (20 mm gauge length). The second cycle consisted of stretching from 0% elongation to 100% elongation and then returning to 0% elongation. This cycle was repeated up to 100 times. The surface resistance (unit: Ω) between the gauge lengths was measured every 10 cycles using the resistivity meter. The table shows the surface resistance at the start (0%), the surface resistance at 100% elongation the first time, the surface resistance at 100% elongation the 100th time, and the surface resistance at the end of the 100th elongation and returned to 0% elongation (final elongation 0%). The deviation in surface resistance before and after the repeated elongation test was also evaluated. The difference between the surface resistance at 0% at the end and the surface resistance at 0% at the start is shown in absolute value in the table. If cracks or breaks occurred in the film during elongation at the first elongation or the 100th elongation, this is indicated as "× (not achieved)."

[0088]

[0089]

[0090]

[0091]

[0092] As shown in Tables 3 and 4, the conductive films of Examples 1-1 to 1-8 were excellent in conductivity and adhesion to the substrate, and were stretchable and had excellent conductivity when stretched, with conductivity detectable even at 250% stretch. The conductive films of Examples 1-1 to 1-8 also had excellent resistance to repeated stretching, with conductivity detectable in both the stretched (100)% state and the non-stretched (0%) state even after 100 repeated stretches at 100% elongation. Furthermore, the conductive films exhibited excellent stability of conductivity when repeatedly stretched, with small deviations in surface resistance before and after the repeated stretching test. Furthermore, in Examples 1-1 to 1-8, a tendency for surface resistance to increase with increasing elongation was observed.

[0093] On the other hand, as shown in Tables 5 and 6, Comparative Examples 1-1 to 1-3, in which the glass transition temperature, weight average molecular weight, or hydroxyl value of the (meth)acrylic polymer (A) were outside the ranges of the present invention, and Comparative Example 1-4, in which a comparative resin (polyester) was used instead of the (meth)acrylic polymer (A), exhibited film cracks or breakage during elongation in the elongation test and repeated elongation test. Comparative Example 1-5, in which the maximum particle size of the silver particles was too small, exhibited film cracks or breakage during the elongation test, and surface resistance could not be detected at elongations of 200% or more. Comparative Example 1-6, in which the 50% average particle size and maximum particle size of the silver particles were too small, exhibited film cracks or breakage during the elongation test and repeated elongation test. Comparative Example 1-7, in which the solids content of the conductive ink composition was too low, was able to elongate the conductive film up to 250% in the elongation test, but surface resistance could not be detected. In the repeated elongation test, the film could withstand repeated elongation of 100% x 100 times, but the surface resistance value was not detectable. In Comparative Example 1-8, in which the solid content of the conductive ink composition was too high, cracks or breaks occurred in the film in the elongation test and repeated elongation test.

[0094] (Production Example 2-1: Production of (meth)acrylic polymer composition (2-1)) The monomer mixture shown in Table 7 was polymerized in a polymerization solvent to synthesize a (meth)acrylic polymer, and a solvent was further added to adjust the solids concentration, yielding a (meth)acrylic polymer composition. Specifically, 29.8 parts by mass of 2HPA, 57.2 parts by mass of BA, 12.8 parts by mass of MA, and 0.2 parts by mass of AA as monomers, 0.02 parts by mass of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 43 parts by mass of ethyl acetate as a polymerization solvent were placed in a separable flask. Nitrogen gas was introduced to remove oxygen from the polymerization system, and the temperature was raised to 70°C and the mixture was allowed to react for 8 hours to yield (meth)acrylic polymer A2-1. Ethyl acetate was added to the mixture to adjust the solids concentration to 33% by mass, yielding (meth)acrylic polymer composition (2-1). The glass transition temperature, weight average molecular weight, and hydroxyl value of the (meth)acrylic polymer are shown in Table 7 (the same applies hereinafter).

[0095] (Production Examples 2-2 and 2-3: Production of (meth)acrylic polymer compositions (2-2) and (2-3)) The composition of the monomer mixture was changed as shown in Table 7, and the monomer mixture was polymerized in the same manner as in Production Example 2-1 to synthesize (meth)acrylic polymers A2-2 and A2-3. Ethyl acetate was added to this to adjust the solids concentration as shown in Table 7, to obtain (meth)acrylic polymer compositions (2-2) and (2-3).

[0096] (Comparative Composition (2-4)) A polyester resin solution (Mitsubishi Chemical Corporation product name "Nichigo Polyester LP-035") was used as the comparative composition (2-4). The glass transition temperature, weight average molecular weight, and hydroxyl value of the polyester resin (comparative resin P2-4) in the comparative composition (2-4) are shown in Table 7.

[0097]

[0098] <Carbon Black (CB)> The following (CB) particles were used. The specific surface area and aggregate diameter of each (CB) particle are shown in Table 8. Carbon Black (CB1): Lion Specialty Chemicals product name "Ketjenblack EC300J", furnace black. Carbon Black (CB2): Imerys product name "Ensaco250G", furnace black. Carbon Black (CB3): Denka Company product name "Denka Black HS-100", acetylene black.

[0099] The following raw materials were used. <Solvent (C)> Solvent (C2-1): diethylene glycol monoethyl ether acetate. <Graphite material (D)> Graphite (D2-1): Shin-Etsu Chemical Co., Ltd. product name "BSP-20A", expanded graphite, flaky, average particle size 20 μm. <Dispersant (E)> Dispersant (E2-1): Kusumoto Chemical Co., Ltd. product name "DA-1200", high molecular weight unsaturated polycarboxylic acid.

[0100]

[0101] (Examples 2-1 to 2-5, Comparative Examples 2-1 to 2-7) Carbon black, a graphite material, a dispersant, and a solvent were blended into a (meth)acrylic polymer composition according to the formulations shown in Tables 9 to 11. In Comparative Examples 2-3 and 2-4, carbon black, a graphite material, a dispersant, and a solvent were blended into the comparative composition (2-4). All of the blended components were premixed using a mixer and then kneaded using a three-roll mill (Imex Co., Ltd. product name "BR-150VIII") to obtain a conductive ink composition. Kneading was performed twice at a rotation speed of 120 rpm with a roll distance of 40 μm, and then the roll distance was reduced to 10 μm and the kneading was performed two more times. The solids content, (meth)acrylic polymer (A) content, and carbon black (CB) content relative to the total mass of the conductive ink composition for each example are shown in the tables. The table also shows the content of the (meth)acrylic polymer (A), the content of the carbon black (CB), and the content of the graphite material (D) relative to the solid content. The table also shows the viscosity of the conductive ink composition. Note that blank spaces in the table indicate that the corresponding component is not blended.

[0102] <Evaluation Method> The obtained conductive films were evaluated by the following methods. The conductive ink composition obtained in each example was applied to a substrate and dried at 130°C for 10 minutes to produce a laminate having a conductive film on the substrate. A stretchable polyurethane sheet (thickness 100 μm) was used as the substrate. The dry thickness of the conductive film was approximately 30 μm. The obtained conductive films were evaluated for the following items. The results are shown in Tables 9 to 11.

[0103] (Measurement of volume resistivity) The volume resistivity was measured in the same manner as in Example 1-1. (Evaluation of adhesion) The adhesion was evaluated in the same manner as in Example 1-1.

[0104] (Elongation Test (1)) The laminate obtained in each example was cut into a No. 3 dumbbell shape and used as a sample, which was set in a tensile tester. The distance between the gauge lines (initial dimension) was 20 mm, and the sample was pulled at a pulling rate of 10 mm / min under conditions of 23°C, and the surface resistance value (unit: Ω) between the gauge lines was measured at each specific elongation using a tester (Custom Co., Ltd., product name "CDM-2000D"). The elongation is a value calculated by the following formula: Elongation (%) = (distance between the gauge lines after elongation (mm) - initial dimension) / initial dimension x 100 The surface resistance value R when the elongation is 200% (at 200% elongation), i.e., when the distance between the gauge lines is 60 mm, is １ The table also shows the surface resistance R when the elongation rate is 300% (at 300% elongation), that is, when the distance between the gauge lines is 80 mm. ２ The table also shows the logarithmic value of the resistance change (unit: Ω / %) per 1% elongation when the elongation rate changes from 0% to 300%, calculated by the following formula (4). R in formula (4) ０ indicates the surface resistance value when the elongation rate is 0% (0% elongation). When cracks or breaks occur in the film during elongation, it is marked as "x (not achieved)", and when elongation was possible but conductivity could not be detected, it is marked as "x (impossible to measure)".

[0105]

[0106] (Elongation Test (2)) Using the same measurement method as in Elongation Test (1), the surface resistance (unit: Ω) was measured by increasing the elongation stepwise. The elongation was increased in increments of 25% from 50% to 100%, and then increased in increments of 50% after exceeding 100%. ７ The maximum elongation at which the surface resistance could be measured was 1.0 x 10 ７ The maximum elongation (unit: %) at or below Ω was recorded.

[0107] (Repeated Elongation Test) A repeated elongation test was carried out in the same manner as in Example 1-1, and the items shown in the table were evaluated.

[0108]

[0109]

[0110]

[0111] As shown in Table 9, the conductive films of Examples 2-1 to 2-5 were excellent in conductivity and adhesion to the substrate. They were also stretchable and had excellent conductivity when stretched. Even at 300% stretch, the conductivity was detectable, reaching 1.0 × 10 ７ The maximum elongation value at Ω or less was large. The conductive films of Examples 2-1 to 2-5 also had excellent resistance to repeated elongation, and even after 100 repeated elongations at an elongation rate of 100%, conductivity was detectable in both the elongated state (100)% and the non-elongated state (0%). Furthermore, the stability of conductivity when repeatedly elongated was excellent, and the deviation in surface resistance value before and after the repeated elongation test was small. Furthermore, in Examples 2-1 to 2-5, a tendency for the surface resistance value to increase with increasing elongation rate was observed.

[0112] On the other hand, as shown in Tables 10 and 11, in Comparative Examples 2-1 and 2-2 in which the weight average molecular weight or hydroxyl value of the (meth)acrylic polymer (A) was outside the range of the present invention, and in Comparative Examples 2-3 and 2-4 in which a comparative resin (polyester) was used instead of the (meth)acrylic polymer (A), cracks or breaks occurred in the film during extension in the extension test and repeated extension test. In Comparative Example 2-5 in which the solid content of the conductive ink composition was too low, and in Comparative Example 2-6 in which the solid content was too high, cracks or breaks occurred in the film during the extension test and repeated extension test. In Comparative Example 2-7 in which the specific surface area of ​​the carbon black (CB) was small and the aggregate diameter was large, cracks or breaks occurred in the film during the extension test and repeated extension test.

Claims

1. A conductive ink composition comprising a (meth)acrylic polymer (A) and silver particles (B), wherein the (meth)acrylic polymer (A) has a glass transition temperature of 0 °C or lower, a weight average molecular weight of 500,000 or more, and a hydroxyl value exceeding 50 mg KOH / g, The specific surface area of the silver particles (B) is 0.5 to 3.0 m ２ / g, the 50% average particle diameter is 0.5 to 14.0 μm, and the maximum particle diameter is 8 μm or more, and and a solid content of 50 to 80% by mass.

2. The conductive ink composition according to claim 1, wherein the (meth)acrylic polymer (A) has a glass transition temperature exceeding -50 °C and less than -30 °C, and a weight average molecular weight of 500,000 to 990,000.

3. The conductive ink composition according to claim 1, wherein the content of the unit (a1) based on the hydroxyl group-containing monomer is 20 to 40% by mass with respect to all the units constituting the (meth)acrylic polymer (A).

4. The conductive ink composition according to claim 1, having a viscosity at 23 °C of 20 to 50 Pa·s.

5. A conductive film obtained by drying a coating film of the conductive ink composition according to any one of claims 1 to 4.

6. The conductive film according to claim 5, which is used for an electrode or wiring that requires stretchability in an electronic device.

7. The conductive film according to claim 5, which is used for a detection unit, electrode, or wiring of a resistance change type sensor.

8. A conductive ink composition comprising a (meth)acrylic polymer (A) and carbon black (CB), wherein the (meth)acrylic polymer (A) has a glass transition temperature of 0 °C or lower, a weight average molecular weight of 500,000 or more, and a hydroxyl value exceeding 50 mg KOH / g, The specific surface area of the carbon black (CB) is 50 m ２ / g or more and the aggregate diameter is 400 nm or less, and a solid content of 15 to 30% by mass.

9. The conductive ink composition according to claim 8, wherein the (meth)acrylic polymer (A) has a glass transition temperature exceeding -50 °C and less than -30 °C, and a weight average molecular weight of 500,000 to 990,000.

10. The conductive ink composition according to claim 8, wherein the content of the unit (a1) based on the hydroxyl group-containing monomer is 20 to 40% by mass with respect to all the units constituting the (meth)acrylic polymer (A).

11. The conductive ink composition according to claim 8, having a viscosity at 23 °C of 20 to 100 Pa·s.

12. A conductive film obtained by drying a coating film of the conductive ink composition according to any one of claims 8 to 11.

13. The conductive film according to claim 12, which is used for an electrode or wiring that requires stretchability in an electronic device.

14. The conductive film according to claim 12, which is used for a detection unit, electrode, or wiring of a resistance change type sensor.