Conductive member including insulating film

Abstract

To provide a conductive member including an insulating film capable of preventing reduction of the insulation resistance of the insulating film.SOLUTION: A conductive member includes an insulating film served as a sintered smectite clay mineral film on the surface of a conductive base material and capable of preventing reduction of insulation resistance by processing the surface of the sintered film with a silane coupling agent having a structural formula (1), where, in the structural formula (1), X represents a 6-18C straight chain alkyl group or a 6-10C straight chain fluoro alkyl group, and R1-R3 independently represent a methyl group or an ethyl group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a conductive member having an insulating film, and more particularly to a conductive member having an insulating film derived from a clay mineral on the surface of which an electric circuit can be formed. [Background technology]

[0002] To fabricate electronic devices such as solar cells and strain sensors on conductive substrates such as steel, it is necessary to prevent short circuits between the electronic devices and the conductive substrate, and an insulating film is formed on the surface of the conductive substrate.

[0003] Resin insulating films have been known as insulating films that can be applied by a wet process and are easy to form. However, insulating films formed from resin generally have low heat resistance due to the physical properties of the resin that forms the insulating film, which limits the types of electronic devices that can be formed on the insulating film and the manufacturing methods thereof.

[0004] Although silicon oxide insulating films are heat-resistant, forming them by CVD or thermal oxidation is time-consuming and costly. Furthermore, when silicon oxide insulating films are formed by wet processes such as the sol-gel method, cracks tend to occur during firing of the coating film, making it difficult to form a dense insulating film, resulting in a decrease in production yield.

[0005] In Patent Document 1, the present inventors disclosed that by using an insulating coating composition in which smectite clay minerals are dispersed using a viscosity reducing agent, an insulating film that does not contain resin components can be formed on the surface of a conductive substrate by a wet process. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-037368 Summary of the Invention [Problem to be solved by the invention]

[0007] However, it was later discovered that the conductive member described in Patent Document 1 had a problem in that the insulation resistance of the insulating film decreased over time when used under high temperature and high humidity conditions.

[0008] The present invention has been made in view of the problems associated with the prior art, and an object of the present invention is to provide a conductive member having an insulating film that can prevent a decrease in the insulation resistance of the insulating film. [Means for solving the problem]

[0009] In order to achieve the above object, the inventors suspected that the decrease in the insulation resistance of the insulating film was caused by the intrusion of water molecules into the insulating film due to the absorption of moisture by cations such as sodium (Na) present between the layers of the clay mineral. They found that the above object could be achieved by preventing the intrusion of water molecules into the insulating film, and thus completed the present invention.

[0010] That is, the above problems are solved by the conductive members of the present invention as set forth in the following items (1) to (3). (1) A conductive member having an insulating film on the surface of a conductive substrate, the insulating film is a fired film of a smectite clay mineral, a conductive member characterized in that the surface of the fired film is treated with a silane coupling agent represented by the following structural formula (1):

[0011] [ka] In the structural formula (1), X represents a linear alkyl group having 6 to 18 carbon atoms or a linear fluoroalkyl group having 6 to 10 carbon atoms, and R 1 ~R 3 each independently represents a methyl group or an ethyl group. (2) The conductive member according to (1) above, wherein the conductive substrate is made of a metal material. (3) The conductive member according to (1) above, wherein the smectite clay mineral is a synthetic hectorite clay mineral. [Effects of the Invention]

[0012] According to the present invention, a fired film of smectite clay mineral is treated with a silane coupling agent, so that a conductive member having an insulating film that can prevent a decrease in the insulation resistance of the insulating film can be provided. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a state in which smectite clay minerals are stacked in an insulating film. DETAILED DESCRIPTION OF THE INVENTION

[0014] The conductive member of the present invention will now be described in detail. The conductive member includes an insulating film on the surface of a conductive substrate. The insulating film is a fired film of a smectite clay mineral, The surface of the fired film is treated with a linear alkylsilane coupling agent or a linear fluoroalkylsilane coupling agent represented by the following structural formula (1).

[0015] [ka] In the structural formula (1), X represents a linear alkyl group having 6 to 18 carbon atoms or a linear fluoroalkyl group having 6 to 10 carbon atoms, and R 1 ~R 3 each independently represents a methyl group or an ethyl group.

[0016] The insulating film is formed by firing a coating of an insulating film composition whose main component is smectite clay mineral, and as shown in Figure 1, has a structure in which plate-like particles of the smectite clay mineral are oriented and tightly adhered to one another and laminated.

[0017] The fired film is chemically and heat resistant because it contains almost no organic matter. Therefore, it is possible to form an electrical circuit by forming a metal thin film on the insulating film and then etching it with an etching solution into a grid or rosette shape.

[0018] However, the smectite clay mineral has a negative charge throughout the entire layer, and cations such as sodium (Na) penetrate between the layers to neutralize this negative charge. Even if the film is fired, if it is exposed to high temperature and high humidity, water molecules may coordinate with or be hydrated by the cations such as sodium (Na) that have penetrated between the layers, resulting in the incorporation of water molecules between the layers, forming conductive paths in the fired film and reducing the insulation resistance.

[0019] In the present invention, the surface of the fired film of smectite clay mineral is treated with a silane coupling agent to make it hydrophobic, thereby preventing water molecules from penetrating between the layers even under high temperature and humidity conditions, and suppressing a decrease in insulation resistance.

[0020] As the silane coupling agent, a linear alkylsilane coupling agent or a linear fluoroalkylsilane coupling agent represented by the following structural formula (1) is used.

[0021] [ka] In the structural formula (1), X represents a linear alkyl group having 6 to 18 carbon atoms or a linear fluoroalkyl group having 6 to 10 carbon atoms, and R 1 ~R 3 each independently represents a methyl group or an ethyl group. In the present invention, the term "straight-chain fluoroalkyl group" includes both a straight-chain perfluoroalkyl group and a group having a structure in which a straight-chain perfluoroalkyl group is bonded to a straight-chain alkylene group.

[0022] In the present invention, it is necessary not only to prevent wetting by water droplets (liquid) but also to prevent water vapor (gas) from penetrating between the layers. Furthermore, since water molecules are small, it is necessary to minimize localized untreated areas with the silane coupling agent and to form a dense molecular film (moisture-resistant film) of the silane coupling agent on the fired film surface to modify it.

[0023] In the structural formula (1), X is not a bulky alkyl group or fluoroalkyl group having a side chain or a cyclic portion, but a straight-chain alkyl group or a straight-chain fluoroalkyl group. This eliminates steric hindrance between adjacent silane coupling agent molecules, allowing the silane coupling agent to be aligned without gaps, and allows a molecular film in which the silane coupling agent molecules are densely integrated to be formed on the surface. This makes it possible to reduce localized untreated areas on the fired film surface due to the silane coupling agent.

[0024] In other words, because X in the above structural formula (1) has a linear structure, the van der Waals force generated between the linear portions of adjacent silane coupling agent molecules acts in an affinity manner so that the silane coupling agent molecules are more closely aggregated.

[0025] As a result, aggregation of the silane coupling agent molecules is thermodynamically stable, and therefore a molecular film in which the silane coupling agent molecules are densely integrated can be formed.

[0026] In this way, by treating the insulating film with a silane coupling agent in which X in the above structural formula (1) is a straight-chain alkyl group or a straight-chain fluoroalkyl group, a dense molecular film of the silane coupling agent can be formed, which not only repels water droplets (liquid) but also prevents water vapor (gas) from passing through the molecular film and entering between the layers, making it possible to suppress a decrease in the insulation resistance of the insulating film under high temperature and high humidity conditions.

[0027] Among these, a silane coupling agent in which X in the structural formula (1) is a linear alkyl group is preferred.

[0028] In a straight-chain fluoroalkyl group, the van der Waals radius of the fluorine atom is about 20% larger than that of the hydrogen atom in the alkyl group, and the volume is about 70% larger. Therefore, steric repulsion occurs between the fluorine atom, the carbon to which it is bonded, and the fluorine and hydrogen bonded to the adjacent carbon, resulting in a twisted structure in the straight-chain portion.

[0029] In contrast, linear alkyl groups do not have the above-mentioned steric repulsion, and the linear portion forms a planar skeleton. Therefore, linear alkyl groups allow the molecules of the silane coupling agent to be more densely aligned than linear fluoroalkyl groups, allowing a denser molecular film of the silane coupling agent to be formed on the surface of the fired film. This inhibits the passage of water vapor (gas) and prevents it from penetrating between the layers of the smectite clay mineral, thereby better preventing a decrease in insulation properties under high temperature and high humidity.

[0030] <Preparation of conductive material> The conductive member can be produced by applying an insulating film composition to the surface of a conductive substrate, drying the composition, baking the composition at 600°C to 750°C for 10 to 60 minutes, treating the composition with the silane coupling agent, and drying the composition by heating.

[0031] The application to the conductive substrate can be carried out by a conventionally known method, such as spin coating, gap coater coating, dip coating, bead coating, or ring coating.

[0032] The firing method may be firing in a firing furnace or oven, and the drying method may be leaving it at room temperature or drying with hot air.

[0033] The insulating film preferably has a thickness of 0.7 μm or more and 20 μm or less. A thickness of 0.7 μm or more allows for the formation of a highly insulating coating without coating defects, while a thickness of 20 μm or less allows for the insulating film to conform to deformations in the conductive substrate, preventing cracks.

[0034] The insulating film can be confirmed to be a fired film by the presence of a solid solution layer containing the constituent elements of the conductive substrate and the constituent elements of the smectite clay mineral on the conductive substrate side.

[0035] The solid solution layer is formed by the diffusion of the constituent elements of the conductive substrate from the conductive substrate side to the fired film side. The presence of such a solid solution layer improves peel resistance.

[0036] The solid solution layer can be confirmed by observing the cross section of the conductive member using TEM-EDS. The concentration of the constituent elements of the conductive base material of the solid solution layer can be confirmed by drilling from the surface of the insulating film with an argon laser and performing elemental analysis using XPS or the like.

[0037] The treatment with the silane coupling agent is carried out on the entire surface of the fired film, which makes it possible to prevent the fired film from absorbing moisture.

[0038] In the silane coupling agent, when X in the structural formula (1) is a linear alkyl group, it has 6 to 18 carbon atoms, and particularly preferably 12 to 16 carbon atoms. If the number of carbon atoms in the linear alkyl group is less than 6, moisture resistance decreases, and if it exceeds 18, the solubility of the silane coupling agent decreases, making it difficult to apply it uniformly to the surface of the conductive substrate.

[0039] Furthermore, when X in the structural formula (1) of the silane coupling agent is a linear fluoroalkyl group having 6 to 10 carbon atoms, such as heptadecafluorodecyl, tridecafluorooctyl, or nonafluorohexyl, is preferred, and tridecafluorooctyl is more preferred in terms of the balance between solubility and moisture resistance.

[0040] The concentration of the silane coupling agent in the silane coupling agent solution used to treat the fired film is preferably 2 to 50 mass %, although it depends on the number of carbon atoms in X in the structural formula (1).

[0041] The conductive substrate is not particularly limited, but examples thereof include substrates formed from metal materials such as stainless steel, iron, copper, and titanium.

[0042] The insulating film composition contains a smectite clay mineral, a viscosity reducer, and a dispersion medium.

[0043] Examples of the smectite clay minerals include saponite, hectorite, sauconite, stevensite, swinholdite, montmorillonite, beidellite, nontronite, and volconstite, but synthetic hectorite with a controlled primary particle size is preferred.

[0044] The viscosity reducer prevents the plate-like particles of the smectite clay mineral from forming a house-of-cards structure and forming a highly viscous gel, thereby enabling the coating and film formation of the insulating film composition.

[0045] Examples of the viscosity reducer include salts of low molecular weight amines, phosphate compounds, phosphonic acid and its derivatives, etidronic acid and / or alkali metal salts of etidronic acid, and ammonium etidronate.

[0046] Among these, etidronic acid and / or alkali metal etidronates and ammonium etidronate are preferably used because they can prevent the smectite clay mineral from forming a house-of-cards structure and gelling over a long period of time.

[0047] Furthermore, ammonium etidronate has a large ionic radius of ammonium ion, and this ammonium ion penetrates between the layers of the smectite clay mineral, displacing the sodium ion (Na + ), which reduces the moisture absorption of the smectite clay mineral itself under high temperature and humidity conditions, thereby preventing a decrease in insulation properties, and is therefore preferably used.

[0048] The dispersion medium improves the affinity between the insulating composition and the surface of the conductive substrate, prevents repelling and uneven coating, and improves the drying properties of the insulating composition.

[0049] When the dispersion medium is a volatile water-soluble organic solvent, the drying property is improved, and peeling of the coating due to gas generation inside the coating when the coating of the insulating film composition is baked is prevented, and the adhesion between the insulating film and the conductive substrate is improved.

[0050] Examples of the dispersion medium that can be used include water-soluble organic solvents such as alcohol-based solvents such as methyl alcohol, ethyl alcohol, isopropanol, butanol, and 3-methoxy-3-methyl-1-butanol; acetate-based solvents such as methyl acetate, ethyl acetate, and 3-methoxy-3-methyl-1-butyl acetate; glycol ether-based solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, and propylene glycol monomethyl ether; and ketone-based solvents such as acetone and methyl ethyl ketone. These may be used alone or in combination of two or more. Among these, glycol ether solvents are preferred because they have a high flash point, are safe, and have a viscosity-reducing effect, and ethylene glycol monobutyl ether is particularly preferred.

[0051] The content of the dispersion medium in the insulating film composition is preferably 1% by mass to 30% by mass, more preferably 3% by mass to 20% by mass, depending on the dispersion medium used. If it is less than 1% by mass, repelling may occur or drying properties may decrease, while if it exceeds 30% by mass, the dispersibility of the smectite clay mineral may decrease, causing sedimentation.

[0052] <Electronic components> The conductive member of the present invention can be used as an electronic component such as a solar cell or a strain sensor by forming an electronic circuit on the fired film treated with the silane coupling agent as described above. The electronic circuit can be formed by a printing method such as screen printing using a conductive adhesive containing metal particles such as silver particles or carbon particles. [Example]

[0053] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0054] [Example 1] (Preparation of insulating film composition) While stirring the ion-exchanged water at 1000 rpm using a disper, 0.22 mmol of etidronic acid was neutralized with aqueous ammonia for 1 g of smectite clay mineral to prepare ammonium etidronate (4NH4 + ) was added and dispersed, and then 19 parts by mass of synthetic hectorite (BYK Additives & Instruments: Laponite RD: primary particle diameter (median diameter) 60 nm: no viscosity reducer) was added in small amounts to uniformly disperse the smectite clay mineral.

[0055] Next, a mixed solution of 0.1 parts by mass of a nonionic surfactant (polyoxyethylene lauryl ether: DKS NL-40 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 4.0 parts by mass of ethylene glycol monobutyl ether, and 1.5 parts by mass of ethanol was added and homogenized, after which ultrasonic treatment was performed for 20 seconds per 100 g, and further filtered through a 10 μm membrane filter to obtain an insulating film composition with a clay solids content of 19% by mass.

[0056] (Preparation of fired film) After thorough washing with acetone, the above insulating film composition was spin-coated (1000 rpm, 20 seconds) onto the surface of a 50 mm x 50 mm conductive substrate (SUS304) that had been hydrophilized by atmospheric pressure plasma treatment, and then left to dry at room temperature for 1 hour, further dried at 105°C for 1 hour, and then fired at 700°C for 10 minutes to obtain a fired film of smectite clay mineral.

[0057] (Silane coupling treatment) In the structural formula (1), X is a linear alkyl group having 6 carbon atoms, and R1 ~R 3 The silane coupling agent, the moiety of which is a methyl group, was dissolved in ethanol to a concentration of 2.5 mass %, and the pH was adjusted to 5.0 with acetic acid.

[0058] This silane coupling agent solution was applied and spin-coated onto the surface of a fired film of smectite clay mineral that had been hydrophilized by atmospheric pressure plasma treatment, and after leaving it at room temperature for 10 minutes, it was rinsed with ethanol and reacted at 110°C for 10 minutes to obtain a conductive member.

[0059] [Example 2] A conductive member was obtained in the same manner as in Example 1, except that a silane coupling agent solution with a silane coupling agent concentration of 5 mass % was used.

[0060] [Example 3] In the above structural formula (1), X is a linear alkyl group having 12 carbon atoms, and R 1 ~R 3 A conductive member was obtained in the same manner as in Example 1, except that a silane coupling agent in which the group is a methyl group was used.

[0061] [Example 4] A conductive member was obtained in the same manner as in Example 3, except that a silane coupling agent solution with a silane coupling agent concentration of 5 mass % was used.

[0062] [Example 5] In the above structural formula (1), X is a linear alkyl group having 16 carbon atoms, and R 1 ~R 3 A conductive member was obtained in the same manner as in Example 1, except that a silane coupling agent in which the group is a methyl group and a silane coupling agent solution in which the concentration of the silane coupling agent was 2.0 mass % were used.

[0063] [Example 6] A conductive member was obtained in the same manner as in Example 5, except that a silane coupling agent solution with a silane coupling agent concentration of 2.5 mass % was used.

[0064] [Example 7] A conductive member was obtained in the same manner as in Example 5, except that a silane coupling agent solution with a silane coupling agent concentration of 5 mass % was used.

[0065] [Example 8] A conductive member was obtained in the same manner as in Example 5, except that a silane coupling agent solution with a silane coupling agent concentration of 50 mass % was used.

[0066] [Example 9] X in the above structural formula (1) is a 1H,1H,2H,2H-tridecafluoro-n-octyl group, R 1 ~R 3 A conductive member was obtained in the same manner as in Example 1, except that a silane coupling agent in which the group is a methyl group and a silane coupling agent solution in which the concentration of the silane coupling agent was 50.0 mass % were used.

[0067] [Example 10] A fired film was prepared in the same manner as in Example 1, except that 0.22 mmol of etidronate (4Na / 2Na:1 / 1) was used as a viscosity reducer per 1 g of smectite clay mineral instead of ammonium etidronate, and a conductive member was obtained in the same manner as in Example 8.

[0068] [Comparative Example 1] In the above structural formula (1), X is a linear alkyl group having 2 carbon atoms, and R 1 ~R 3 A conductive member was obtained in the same manner as in Example 1, except that a silane coupling agent in which the group is a methyl group and a silane coupling agent solution in which the concentration of the silane coupling agent was 2.0 mass % were used.

[0069] Comparative Example 2 A conductive member was obtained in the same manner as in Comparative Example 1, except that a silane coupling agent solution with a silane coupling agent concentration of 4 mass % was used.

[0070] Comparative Example 3 In the above structural formula (1), X is a 3-(phenylamino)propyl group, R 1 ~R 3A conductive member was obtained in the same manner as in Example 1, except that a silane coupling agent in which the group is a methyl group and a silane coupling agent solution in which the concentration of the silane coupling agent was 50.0 mass % were used.

[0071] Comparative Example 4 A conductive member was obtained in the same manner as in Example 1, except that the silane coupling treatment was not carried out.

[0072] <Evaluation> After placing the sample in a high-temperature, high-humidity chamber set at 75°C and 95% RH, the sample was taken out at regular intervals and the resistance value of the insulating film was measured while the sample was left at room temperature. The insulation resistance value was measured at any five points using an insulation resistance meter (manufactured by Hioki E.E. Corporation; SM-8213) at a measurement voltage of 10 V, and the average value was taken as the insulation resistance value. The evaluation results are shown in Table 1. Furthermore, for each of the conductive components of Examples 1 to 10, an electronic circuit was formed using a conductive adhesive on an insulating film treated with a silane coupling agent, and the presence or absence of peeling or breakage of the wiring was checked. No peeling or breakage of the wiring was observed.

[0073] [Table 1]

[0074] The results in Table 1 show that treatment with a silane coupling agent having a linear alkyl group or linear fluoroalkyl group improves moisture resistance under high temperature and humidity conditions and prevents a decrease in insulation resistance. [Explanation of symbols]

[0075] 1 Conductive base material 2. Smectite clay minerals

Claims

1. A conductive member having an insulating film on a surface of a conductive substrate, the insulating film is a fired film of a smectite clay mineral, The conductive member is characterized in that the surface of the fired film is treated with a silane coupling agent represented by the following structural formula (1): 【Chemistry 4】 In the structural formula (1), X represents a linear alkyl group having 6 to 18 carbon atoms or a linear fluoroalkyl group having 6 to 10 carbon atoms, and R １ ~R ３ each independently represents a methyl group or an ethyl group.

2. 2. The conductive member according to claim 1, wherein the conductive substrate is made of a metal material.

3. 2. The conductive member according to claim 1, wherein the smectite clay mineral is a synthetic hectorite clay mineral.

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