Conductive paint and circuit formation body

Abstract

A conductive coating material according to the present invention comprises a silicone resin (A) and a conductive powder (B) at a specific mass ratio and satisfies expression (1) below, wherein the conductive powder (B) contains, at a specific mass ratio, a flaky conductive powder (B1) having an average particle size of 1-7 μm and an irregular conductive powder (B2) having an average particle size of 1-6 μm.　(1): 100≤X1+X2≤260 X1=(average particle size of conductive powder (B1) / tap density of conductive powder (B1))×(content of conductive powder (B1) on basis of total mass of conductive powder (B)) X2=(average particle size of conductive powder (B2) / tap density of conductive powder (B2))×(content of conductive powder (B2) on basis of total mass of conductive powder (B))

Description

[Technical Field]

[0001] The present invention relates to a conductive paint and a circuit-forming body. This application claims priority based on Japanese Patent Application No. 2022-073168, filed on April 27, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, efforts have been intensifying to popularize devices that require flexibility and stretchability, such as wearable devices, flexible printed circuit boards, and displays. These devices are usually formed by applying a conductive paint containing conductive particles and a binder resin onto a flexible and stretchable substrate, but the coating film formed from the conductive paint may also be required to have stretchability. As an example of a conductive member having stretchable wiring, Patent Document 1 discloses a conductive member having wiring formed by drying a conductive paste of polyurethane dispersion and conductive particles, and a plastic substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-54192 Summary of the Invention [Problem to be solved by the invention]

[0004] However, coating films formed from conventional conductive paints suffer from disconnection or an increase in resistance when repeatedly stretched and contracted, and therefore have a problem with the stability of electrical resistance. An object of the present invention is to provide a conductive coating material that can form a coating film that is excellent in durability even when stretched and contracted repeatedly and has a small rate of change in resistance value. [Means for solving the problem]

[0005] The present invention has the following aspects. [1] A silicone resin (A) and a conductive powder (B), a mass ratio (A / B) of the silicone resin (A) to the conductive powder (B) is 10 / 90 to 35 / 65; the conductive powder (B) comprises a flake-shaped conductive powder (B1) having an average particle size of 1 to 7 μm and an irregularly shaped conductive powder (B2) having an average particle size of 1 to 6 μm; the mass ratio (B1 / B2) of the conductive powder (B1) to the conductive powder (B2) is 40 / 60 to 90 / 10; A conductive paint that satisfies the following formula (1): 100≦X1+X2≦260 (1) X1 = (average particle size of conductive powder (B1) / tap density of conductive powder (B1)) x (content of conductive powder (B1) relative to the total mass of conductive powder (B)) X2 = (average particle size of conductive powder (B2) / tap density of conductive powder (B2)) x (content of conductive powder (B2) relative to the total mass of conductive powder (B)) [2] The conductive coating material according to [1], wherein the silicone resin (A) contains a curable silicone resin, and preferably contains at least one of an addition reaction curable silicone resin and a condensation reaction curable silicone resin. [3] The silicone resin (A) includes the addition reaction curable silicone resin, The conductive paint according to [2], further comprising one or more catalysts selected from a platinum-based metal catalyst, a rhodium-based metal catalyst, a palladium-based metal catalyst, a cobalt-based metal catalyst, a nickel-based metal catalyst, and an iron-based metal catalyst. [4] The conductive coating material according to any one of [1] to [3], wherein each of the conductive powder (B1) and the conductive powder (B2) contains one or more selected from gold, silver, copper, platinum, nickel, graphite, and materials composed of two or more elements (for example, alloys, metals, or resins coated with metal). [5] The conductive coating material according to any one of [1] to [4] above, wherein the conductive powder (B1) has an average particle size of 1.5 to 6.7 μm, more preferably 2 to 6.5 μm, and even more preferably 2 to 5 μm. [6] The conductive coating material according to any one of the above [1] to [5], wherein the conductive powder (B2) has an average particle size of 1.5 to 5.5 μm, more preferably 2 to 5.5 μm, and even more preferably 2.5 to 5 μm. [7] The conductive coating material according to any one of the above [1] to [6], wherein the mass ratio (A / B) of the silicone resin (A) to the conductive powder (B) is 15 / 85 to 30 / 70, more preferably 15 / 85 to 25 / 75. [8] The conductive coating material according to any one of [1] to [7], wherein the total content of the silicone resin (A) and the conductive powder (B) is 70 mass % or more, more preferably 80 mass % or more, even more preferably 90 mass % or more, and particularly preferably 100 mass %, relative to the total mass of the conductive coating material. [9] The conductive coating material according to any one of the above [1] to [8], wherein the mass ratio (B1 / B2) is 45 / 55 to 85 / 15, and more preferably 45 / 55 to 80 / 20.

[10] The conductive coating material according to any one of [1] to [9], wherein the total content of the conductive powder (B1) and the conductive powder (B2) is 80 mass% or more, more preferably 90 mass% or more, even more preferably 95 mass% or more, and particularly preferably 100 mass%, based on the total mass of the conductive powder (B).

[11] The conductive coating material according to any one of [1] to

[10] above, wherein X1+X2 is 120 to 250, and more preferably 130 to 210.

[12] A circuit-formed body, comprising a substrate on which a circuit is formed by a coating film obtained by using the conductive coating material according to any one of [1] to

[11] above. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a conductive coating material capable of forming a coating film that is excellent in durability even when stretched and contracted repeatedly and has a small rate of change in resistance value. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view schematically showing a circuit forming body according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] The following definitions of terms apply throughout the specification and claims. The term "conductive" is used to distinguish it from the general term "insulating," and in the case of a circuit pattern, it preferably means that the electrical resistance is less than 150 Ω. The "coating film" refers to a coating film formed from the conductive coating material of the present invention. The symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. The numerical ranges of the contents, various physical property values, and property values ​​disclosed in this specification can be arbitrarily combined with the lower and upper limits to form new numerical ranges.

[0009] [Conductive paint] The conductive coating material according to one embodiment of the present invention contains the following silicone resin (A) and conductive powder (B). The conductive paint may further contain components other than the silicone resin (A) and the conductive powder (B) (hereinafter also referred to as "optional components") as needed, as long as the effects of the present invention are not impaired.

[0010] <Silicone resin (A)> The silicone resin (A) is a resin that is excellent in durability and flexibility. Among the silicone resins (A), curable silicone resins are preferred. Examples of the curable silicone resin include addition reaction curable silicone resin, condensation reaction curable silicone resin, radical reaction curable silicone resin, ultraviolet or electron beam curable silicone resin, etc. Among these, addition reaction curable silicone resin and condensation reaction curable silicone resin are preferred, with addition reaction curable silicone resin being more preferred, since they can form not only thin coating films but also thick coating films and the film thickness can be easily adjusted depending on the required application. The silicone resin (A) may be used alone or in combination of two or more kinds.

[0011] Addition reaction curing silicone resins are constructed by crosslinking two types of organopolysiloxanes through the addition reaction of their functional groups. Condensation reaction curable silicone resins are constructed by crosslinking functional groups in two types of organopolysiloxanes, or functional groups in an organopolysiloxane and a silicon compound such as silica or silane, by condensation reaction.

[0012] As the silicone resin (A), commercially available products can be used. Examples of commercially available addition reaction curing silicone resins include those manufactured by Shin-Etsu Chemical Co., Ltd. under the trade names "KE-1820" and "KE-1823"; those manufactured by Momentive Performance Materials Japan, LLC under the trade names "TSE-3221," "TSE-3250," and "TSE-3251"; those manufactured by Dow-Toray Industries, Inc. under the trade names "SE-1750" and "SE-4450"; and those manufactured by Wacker Asahi Kasei Silicones Co., Ltd. under the trade names "SEMICOSIL 987 GR," "SEMICOSIL 988 / 1K GRAY," and "SEMICOSIL 989 / 1K." Commercially available condensation reaction curing silicone resins include those manufactured by Shin-Etsu Chemical Co., Ltd. under the trade names "KE-441," "KE-471," and "KE-47"; those manufactured by Mentive Performance Materials Japan, LLC under the trade names "TSE-387" and "TSE-397"; and those manufactured by Dow-Toray Industries, Inc. under the trade names "SE-917G," "SE-9186," and "SE-9184."

[0013] When an addition reaction curing type silicone resin is used as the silicone resin (A), it is preferable to use a catalyst in combination to promote the addition reaction. Examples of the catalyst include platinum-based metal catalysts, rhodium-based metal catalysts, palladium-based metal catalysts, cobalt-based metal catalysts, nickel-based metal catalysts, iron-based metal catalysts, etc. Among these, platinum-based metal catalysts are preferred because they are the most widely used and are more likely to improve the addition reaction rate. The catalyst may be used alone or in combination of two or more.

[0014] <Conductive powder (B)> The conductive powder (B) contains a flake-shaped conductive powder (B1) having an average particle size of 1 to 7 μm and an irregularly shaped conductive powder (B2) having an average particle size of 1 to 6 μm. By containing the flake-shaped conductive powder (B1) and the irregularly shaped conductive powder (B2), the conductive powder (B) can form a coating film that is excellent in durability even when stretched and contracted repeatedly and has a small rate of change in resistance value. The conductive powder (B) may further contain a conductive powder other than the conductive powder (B1) and the conductive powder (B2) (hereinafter also referred to as "conductive powder (B3)") as needed, as long as the effects of the present invention are not impaired.

[0015] (Conductive powder (B1)) The conductive powder (B1) is a flake-shaped conductive powder having an average particle size of 1 to 7 μm. The average thickness of the flakes is usually 1 / 10 to 1 / 2 of the average particle size. The conductive powder (B1) imparts conductivity to the coating film. The conductive powder (B1) is not particularly limited as long as it is one that can be used in conductive coating materials, and examples thereof include metals such as gold, silver, copper, platinum, nickel, etc.; graphite, etc. Among these, silver is preferred from the viewpoints of excellent conductivity and resistance to oxidation. The conductive powder (B1) may be composed of two or more elements, for example, an alloy, a metal, or a resin coated with the metals listed above. Among these, a metal other than silver or a resin coated with silver is preferred from the viewpoints of excellent conductivity and resistance to oxidation. The conductive powder (B1) may be used alone or in combination of two or more kinds. In the present invention, the term "flake-like" can be rephrased as "scale-like," "flat-like," "plate-like," or "thin-like."

[0016] The conductive powder (B1) has an average particle size of 1 to 7 μm, preferably 1.5 to 6.7 μm, more preferably 2 to 6.5 μm, and even more preferably 2 to 5 μm. When the average particle size of the conductive powder (B1) is at least the above lower limit, the conductivity can be maintained at a good level. When the average particle size of the conductive powder (B1) is at most the above upper limit, the durability of the coating film is excellent even when the powder is repeatedly stretched and contracted. The average particle size of the conductive powder (B1) is a value measured as follows. That is, the arithmetic mean diameter calculated from the volume distribution measured by a laser diffraction / scattering particle size distribution measurement method is taken as the average particle size of the conductive powder (B1). Note that, when a catalog value is available, the catalog value may be used as a simple measurement value for the average particle size of the conductive powder (B1).

[0017] (Conductive powder (B2)) The conductive powder (B2) is a conductive powder having an irregular shape of 1 to 6 μm. The conductive powder (B2) imparts conductivity to the coating film. The conductive powder (B2) is not particularly limited as long as it is one that can be used in conductive coating materials, and examples thereof include metals such as gold, silver, copper, platinum, nickel, etc.; graphite, etc. Among these, silver is preferred from the viewpoints of excellent conductivity and resistance to oxidation. The conductive powder (B2) may be composed of two or more elements, for example, an alloy, a metal, or a resin coated with the above-mentioned metals. Among these, a metal other than silver or a resin coated with silver is preferred from the viewpoint of excellent conductivity and resistance to oxidation. The conductive powder (B2) may be used alone or in combination of two or more kinds. In the present invention, "irregular shape" refers to a shape other than flake-like, and refers to a mixture of two or more different shapes, such as spherical, cubic, needle-like, beaded, and shapes with surface protrusions like sugar candy, and the shape cannot be limited; or refers to an aggregate formed by the aggregation of primary particles having one or more shapes selected from spherical, cubic, needle-like, beaded, and shapes with surface protrusions like sugar candy.

[0018] The conductive powder (B2) has an average particle size of 1 to 6 μm, preferably 1.5 to 5.5 μm, more preferably 2 to 5.5 μm, and even more preferably 2.5 to 5 μm. When the average particle size of the conductive powder (B2) is at least the above lower limit, the conductivity can be maintained at a good level. In addition, the durability of the coating film is excellent even after repeated stretching. When the average particle size of the conductive powder (B2) is at most the above upper limit, the durability of the coating film is excellent even after repeated stretching. The average particle size of the conductive powder (B2) is a value measured as follows. That is, the arithmetic mean diameter calculated from the volume distribution measured by a laser diffraction / scattering particle size distribution measurement method is taken as the average particle size of the conductive powder (B2). Note that, when a catalog value is available, the catalog value may be used as a simple measurement value for the average particle size of the conductive powder (B2).

[0019] (Conductive powder (B3)) The conductive powder (B3) is a conductive powder other than the conductive powder (B1) and the conductive powder (B2). Examples of the conductive powder (B3) include flake-shaped conductive powders having an average particle size of more than 7 μm, irregularly shaped conductive powders having an average particle size of more than 6 μm, and regular shaped conductive powders such as spherical ones. The conductive powder (B3) imparts conductivity to the coating film. The conductive powder (B3) is not particularly limited as long as it is one that can be used in conductive paints, and examples thereof include metals such as gold, silver, copper, platinum, nickel, etc.; graphite, etc. Among these, silver is preferred from the viewpoints of excellent conductivity and resistance to oxidation. The conductive powder (B3) may be composed of two or more elements, for example, an alloy, a metal, or a resin coated with the metals listed above. Among these, a metal other than silver or a resin coated with silver is preferred from the viewpoints of excellent conductivity and resistance to oxidation. The conductive powder (B3) may be used alone or in combination of two or more kinds.

[0020] <Optional ingredients> Optional components include components that can be used in conventionally known conductive coating materials, such as organic solvents, binder resins other than the silicone resin (A), dispersants, surface conditioners, thixotropic agents, adhesion promoters, and resin modifiers. The optional components may be used alone or in combination of two or more. However, among the above optional components, it is preferable not to include insulating components that remain as solids when the coating film is formed, as they reduce the conductive performance of the coating film. Furthermore, when the conductive coating material contains an addition reaction type silicone resin as the silicone resin (A), it is preferable that it does not substantially contain impurities such as sulfur that act as curing inhibitors. Here, "substantially free" means that insulating components or impurities such as sulfur that may be curing inhibitors are not intentionally blended, excluding those that are unintentionally contained.

[0021] If the conductive paint contains an organic solvent, the viscosity can be easily adjusted. The organic solvent is preferably one that can dissolve the silicone resin (A), and for example, a mixture of petroleum-based aliphatic hydrocarbon solvents and petroleum-based aromatic solvents, or a single substance such as toluene, diethylbenzene, decalin, or dodecane can be used. The organic solvent may be used alone or in combination of two or more kinds.

[0022] Examples of binder resins other than the silicone resin (A) (hereinafter also referred to as "other binder resins") include polyester resins, phenoxy resins, polyamide resins, polyamideimide resins, polyimide resins, polyurethane resins, acrylic resins, polystyrene, styrene-acrylic resins, styrene-butadiene copolymers, epoxy resins, phenolic resins, polyether resins, polycarbonate resins, alkyd resins, polysulfone resins, polyethersulfone resins, vinyl chloride-vinyl acetate copolymer resins, ethylene-vinyl acetate copolymers, fluorine-based resins, and silicone-modified resins of these resins. The other binder resins may be used alone or in combination of two or more.

[0023] <Content / mass ratio> The mass ratio (A / B) of the silicone resin (A) to the conductive powder (B) is 10 / 90 to 35 / 65, preferably 15 / 85 to 30 / 70, and more preferably 15 / 85 to 25 / 75. When the mass ratio (A / B) is 10 / 90 or more, the durability of the coating film is excellent even after repeated expansion and contraction. When the mass ratio (A / B) is 35 / 65 or less, the conductivity can be well maintained. In addition, the durability of the coating film is excellent even after repeated expansion and contraction. When an addition reaction curable silicone resin is used as the silicone resin (A) and a catalyst is used in combination with the addition reaction curable silicone resin, the mass of the silicone resin (A) used to calculate the mass ratio (A / B) and the content of the silicone resin (A) described below also include the mass of the catalyst. When an addition reaction curable silicone resin is used in combination with a catalyst, the content of the catalyst is preferably 0.01 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the addition reaction curable silicone resin.

[0024] The total content of the silicone resin (A) and the conductive powder (B) is preferably 70 mass% or more, more preferably 80 mass% or more, and even more preferably 90 mass% or more, relative to the total mass of the conductive coating material, and may be 100 mass%. That is, the conductive coating material may consist only of the silicone resin (A) and the conductive powder (B).

[0025] The mass ratio (B1 / B2) of the conductive powder (B1) to the conductive powder (B2) is 40 / 60 to 90 / 10, preferably 45 / 55 to 85 / 15, and more preferably 45 / 55 to 80 / 20. When the mass ratio (B1 / B2) is 40 / 60 or more, the durability of the coating film is excellent even after repeated expansion and contraction, and the rate of change in the resistance value of the coating film is small. When the mass ratio (B1 / B2) is 90 / 10 or less, the durability of the coating film is excellent even after repeated expansion and contraction.

[0026] The total content of the conductive powder (B1) and the conductive powder (B2) is preferably 80 mass% or more, more preferably 90 mass% or more, and even more preferably 95 mass% or more, and may be 100 mass% based on the total mass of the conductive powder (B). That is, the conductive powder (B) may consist only of the conductive powder (B1) and the conductive powder (B2).

[0027] <Formula (1)> The conductive paint satisfies the following formula (1). 100≦X1+X2≦260 (1) X1 = (average particle size of conductive powder (B1) / tap density of conductive powder (B1)) x (content of conductive powder (B1) relative to the total mass of conductive powder (B)) X2 = (average particle size of conductive powder (B2) / tap density of conductive powder (B2)) x (content of conductive powder (B2) relative to the total mass of conductive powder (B))

[0028] X1+X2 is 100 to 260, preferably 120 to 250, and more preferably 130 to 210. When X1+X2 is at least the lower limit above, the coating film has excellent durability and a small rate of change in resistance value even when stretched and contracted repeatedly. When X1+X2 is not more than the upper limit above, the coating film has excellent durability and a small rate of change in resistance value even when stretched and contracted repeatedly.

[0029] The tap density of the conductive powder (B1) and the conductive powder (B2) is measured by a method in accordance with JIS Z 2512: 2012. When a catalog value is available, the catalog value may be used as a simple measurement value for the tap density of the conductive powder (B1) or the conductive powder (B2).

[0030] <Manufacturing method> The conductive coating material can be obtained by mixing the above-mentioned silicone resin (A) and conductive powder (B), and, if necessary, optional components. For mixing, a mixer such as a roll mill or a planetary mixer may be used.

[0031] <Action and effect> The conductive paint of the present embodiment described above satisfies the above formula (1) and contains a silicone resin (A) and a conductive powder (B) in a specific ratio, and the conductive powder (B) contains a flake-shaped conductive powder (B1) having a specific average particle size and an amorphous conductive powder (B2) in a specific ratio, so that a coating film having excellent durability even when repeatedly stretched and contracted and a small rate of change in resistance value can be formed.

[0032] <Application> The conductive paint of this embodiment can be used in circuits for electronic components, etc. Specific examples include touch panel circuits, flexible substrates, and wearable devices. The conductive paint of this embodiment is a conductive paint that can form a coating film that has excellent durability even after repeated stretching and has a small rate of change in resistance value, and is therefore particularly suitable for flexible substrates and wearable devices, which require flexibility and stretchability.

[0033] [Circuit forming body] A circuit-formed body according to one embodiment of the present invention is formed by forming a circuit on a substrate using a coating film (hereinafter also referred to as "conductive coating film") obtained using the conductive coating material of the present invention. That is, the circuit-formed body has a substrate and a circuit formed on the substrate, and the circuit is formed using the conductive coating material of the present invention. An example of a circuit-formed body of this embodiment is shown in Fig. 1. The circuit-formed body 10 shown in Fig. 1 has a substrate 11 and a circuit 12 formed on the substrate 11.

[0034] As the substrate 11, a conventionally known substrate used as a wiring board can be used, and examples thereof include substrates made of inorganic materials such as glass substrates, ceramic substrates, and silicone substrates; and substrates made of organic materials. Examples of organic materials include polyesters such as polyethylene terephthalate and polyethylene naphthalate; silicones such as polydimethylsiloxane, polydiphenylpolysiloxane and polyfluorosiloxane; urethanes such as thermoplastic polyurethane elastomers; polyimides; polyphenylene sulfide; polyolefins such as polyethylene and polypropylene; polyamides; polystyrenes; acrylics; polyvinyl alcohols; ethylene propylene dienes; epoxies, etc. Among these, substrates formed from silicone (silicone substrates) are preferred because of their good adhesion to the silicone resin in the conductive paint.

[0035] The thickness of the substrate 11 may be set appropriately depending on the application of the circuit-forming body 10, and is preferably, for example, 20 to 600 μm. If the thickness of the substrate 11 is within the above range, the circuit-forming body 10 tends to have good stretchability and durability.

[0036] The method for forming the circuit 12 on the substrate 11 is not particularly limited, but an example is a method in which the conductive paint of the present invention is applied to the substrate 11 to form a desired circuit pattern, and then dried to form the circuit 12 consisting of a coating film. That is, one embodiment of the method for manufacturing the circuit-formed body 10 includes a pattern forming step of applying the conductive paint of the present invention onto the substrate 11 to form a circuit pattern, and a drying step of drying the circuit pattern.

[0037] Examples of methods for applying the conductive paint include screen printing, gravure printing, offset printing, roll coating, bar coating, dispensing, dipping, transfer, ink jet, and aerosol jet. The drying temperature is preferably, for example, 70 to 160°C. The drying time is preferably, for example, 2 to 60 minutes.

[0038] The circuit-formed body of the present embodiment described above has a circuit formed from a coating film obtained using the conductive paint of the present invention, and therefore has excellent durability and a small rate of change in resistance even after repeated stretching. Therefore, the circuit-formed body of the present embodiment is particularly suitable for flexible substrate applications and wearable device applications where flexibility and stretchability are required. [Example]

[0039] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In addition, the following examples 2 6、 Nos. 8, 10, 14, 16 to 19, and 22 to 27 are examples. Example 7 is a reference example. Examples 1, 9, 11 to 13, 15, 20, 21, 28, and 29 are comparative examples. The materials used in each example are as follows:

[0040] [material] A-1: Addition reaction curing silicone resin (manufactured by Wacker Asahi Kasei Silicones Co., Ltd., product name "SEMICOSIL 989 / 1K", contains platinum catalyst). B1-1: Flake-shaped silver powder (manufactured by Tokuriki Chemical Laboratory Co., Ltd., product name "TC-20V", average particle size: 3.6 μm, tap density: 3 g / cm 3 ). B1-2: Flake silver powder (manufactured by Ames Goldsmiths, product name "SF70M", average particle size: 2.1 μm, tap density: 3.15 g / cm 3 ). B1-3: Flake-shaped silver powder (manufactured by Tokuriki Chemical Laboratory Co., Ltd., product name "TC-506", average particle size: 6.7 μm, tap density: 5.5 g / cm 3 ). B1-4: Flake-shaped silver powder (manufactured by Tokuriki Chemical Laboratory Co., Ltd., product name "TC-25A", average particle size: 7.7 μm, tap density: 3.5 g / cm 3). B2-1: Irregular shaped silver powder (manufactured by Yokozawa Chemical Co., Ltd., product name "Y-AF-K", average particle size: 3 μm, tap density: 1.15 g / cm 3 ). B2-2: Irregular silver powder (agglomerate) (manufactured by Ames Goldsmiths, product name "SPK-1", average particle size: 3 μm, tap density: 0.75 g / cm 3 ). B2-3: Irregular shaped silver powder (manufactured by Ames Goldsmiths, trade name "SPG", average particle size: 5.36 μm, tap density: 1 g / cm 3 ). B2-4: Irregular silver powder (agglomerate) (manufactured by Ames Goldsmiths, trade name "SPI", average particle size: 4.54 μm, tap density: 1.1 g / cm 3 ). B2-5: Irregular shaped silver powder (manufactured by Tokuriki Chemical Laboratory Co., Ltd., product name "C-34", average particle size: 0.34 μm, tap density: 2.25 g / cm 3 ). B2-6: Irregular silver powder (aggregate) (Tokuriki Chemical Laboratory Co., Ltd., product name "E-20", average particle size: 10.8 μm, tap density: 2 g / cm 3 ). B2-7: Irregular shaped silver powder (manufactured by Yokozawa Chemical Co., Ltd., product name "Y-AE-K", average particle size: 2 μm, tap density: 1.3 g / cm 3 ). B2-8: Irregular shaped silver powder (Mitsui Mining & Smelting Co., Ltd., product name "SPN10JS", average particle size: 2 μm, tap density: 5.3 g / cm 3 ). B3-1: Spherical silver powder (manufactured by DOWA Electronics Co., Ltd., average particle size: 1.6 μm, tap density: 3.8 g / cm 3 ).

[0041] [Examples 1-29] A total of 100 parts by mass of silicone resin (A) and conductive powder (B) was mixed and dispersed in 11 parts by mass of solvent (dodecane) according to the formulations shown in Tables 1 to 3, to obtain a conductive paint with a solids concentration of 90% by mass. Note that blank spaces in Tables 1 to 3 indicate that the component was not blended. The conductive paint was applied by screen printing to a 1 mm wide, 50 mm long, and 20 μm thick pattern on a 15 mm wide, 70 mm long, and 100 μm thick silicone rubber substrate. The paint was then dried at 160°C for 60 minutes to harden, producing a test piece with a circuit pattern formed on the substrate. The obtained test pieces were evaluated for conductivity, rate of change in resistance value, and durability as follows. The results are shown in Tables 1 to 3.

[0042] (1) Conductivity evaluation The electrical resistance value between both ends of the circuit pattern in the longitudinal direction was measured using a digital multimeter (manufactured by ADC Corporation), and the conductivity was evaluated according to the following evaluation criteria. A: The electrical resistance is less than 10 Ω. B: The electrical resistance is 10 Ω or more and less than 150 Ω. C: The electrical resistance is 150 Ω or more.

[0043] (2) Evaluation of the rate of change of resistance value A circuit pattern with an initial length of 50 mm was stretched to 60 mm and then returned to its initial length of 50 mm. This stretching and contraction was repeated 100 times at a stretching speed of 500 mm / min, and a resistance change test was conducted. The electrical resistance between both ends of the circuit pattern in the longitudinal direction was then measured, and the rate of change in resistance (([electrical resistance after 100 stretches] - [electrical resistance before test]) / [electrical resistance before test] x 100 (%)) was calculated, and the conductivity was evaluated according to the following evaluation criteria. A: The rate of change is less than 2000%. B: The rate of change is 2000% or more and less than 4000%. C: The rate of change is 4000% or more.

[0044] (3) Durability evaluation The resistance change test was carried out in the same manner as in (2). The difference between the rate of change in resistance after the 10th stretch and the rate of change in resistance after the 100th stretch ([rate of change in resistance after the 100th stretch] - [rate of change in resistance after the 10th stretch] (%)) was calculated, and the conductivity was evaluated according to the following criteria. A: The difference in the rate of change is less than 20%. B: The difference in the rate of change is 20% or more and less than 40%. C: The difference in the rate of change is 40% or more.

[0045] [Table 1]

[0046] [Table 2]

[0047] [Table 3]

[0048] The conductive coating materials obtained in Examples 2 to 8, 10, 14, 16 to 19, and 22 to 27 were able to form coating films that were excellent in conductivity, had excellent durability even after repeated stretching, and had a small rate of change in resistance value. In contrast, the coating film formed from the conductive coating material of Example 1, in which the mass ratio (B1 / B2) of the conductive powder (B1) to the conductive powder (B2) was 95 / 5, was inferior in durability. The coating film formed from the conductive paint of Example 9, which contained flaky silver powder with an average particle size of 7.7 μm but did not contain flaky conductive powder (B1) with an average particle size of 1 to 7 μm, was inferior in durability. The coating film formed from the conductive paint of Example 11, in which X1+X2 was 281, showed a large change in resistance value due to repeated expansion and contraction. It also had poor durability. The coating film formed from the conductive paint of Example 12, which contained irregular silver powder with an average particle size of 0.34 μm and did not contain irregular conductive powder (B2) with an average particle size of 1 to 6 μm, was poor in conductivity and durability. The coating film formed from the conductive paint of Example 13, which contained irregular silver powder with an average particle size of 10.8 μm and did not contain irregular conductive powder (B2) with an average particle size of 1 to 6 μm, had poor durability. The coating film formed from the conductive paint of Example 15, in which X1+X2 was 92.82, showed a large change in resistance value due to repeated expansion and contraction, and was also poor in durability. The coating film formed from the conductive coating material of Example 20, in which the mass ratio (B1 / B2) of the conductive powder (B1) to the conductive powder (B2) was 35 / 65, showed a large change in resistance value due to repeated expansion and contraction, and also had poor durability. The coating film formed from the conductive coating material of Example 21, in which the mass ratio (A / B) of the silicone resin (A) to the conductive powder (B) was 8 / 92, was poor in durability. The coating film formed from the conductive coating material of Example 28, in which the mass ratio (A / B) of the silicone resin (A) to the conductive powder (B) was 40 / 60, was poor in conductivity and durability. The coating film formed from the conductive paint of Example 29, which contained spherical conductive powder (B3) with an average particle size of 1.6 μm instead of the amorphous conductive powder (B2) with an average particle size of 1 to 6 μm, showed a large change in resistance value with repeated expansion and contraction, and also had poor durability. [Industrial Applicability]

[0049] The conductive paint of the present invention is capable of forming a coating film that is highly durable even after repeated expansion and contraction and has a small rate of change in resistance value, and is therefore useful as a paint for forming circuits in electronic components for touch panel circuits, flexible substrates, wearable devices, etc. [Explanation of symbols]

[0050] 10 Circuit formation body 11 Circuit Board 12 circuits

Claims

1. Contains a silicone resin (A) and a conductive powder (B), a mass ratio (A / B) of the silicone resin (A) to the conductive powder (B) is 10 / 90 to 35 / 65; The conductive powder (B) comprises a flake-shaped conductive powder (B1) having an average particle size of 1 to 7 μm and an irregularly shaped conductive powder (B2) having an average particle size of 1 to 6 μm, the mass ratio (B1 / B2) of the conductive powder (B1) to the conductive powder (B2) is 40 / 60 to 90 / 10; A conductive paint that satisfies the following formula (1) (wherein the term "irregular shape" means an aggregate formed by aggregation of primary particles having one or more shapes selected from the group consisting of spherical, cubic, needle-like, bead-like, and shapes with protrusions on the surface like candy canes). 100≦X1+X2≦260 (1) X1 = (average particle size of conductive powder (B1) / tap density of conductive powder (B1)) x (content of conductive powder (B1) relative to the total mass of conductive powder (B)) X2 = (average particle size of conductive powder (B2) / tap density of conductive powder (B2)) x (content of conductive powder (B2) relative to the total mass of conductive powder (B))

2. A circuit-formed body, comprising a substrate on which a circuit is formed by a coating film obtained by using the conductive coating material according to claim 1.

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