Electrodeposition liquid and method for producing insulating film

Abstract

An electrodeposition liquid for electrodepositing an electrodeposition film on a conductive substrate by anionic electrodeposition, the electrodeposition liquid containing water, an organic solvent, a solid component, a neutralizing agent, and an organic acid, the solid component containing at least a polyimide resin. A method for producing an insulating coating film in which an insulating coating film is formed on the surface of a base material, the method comprising: an electrodeposition film formation step (S02) in which the base material and a counter electrode are immersed in the electrodeposition liquid, the base material is used as an anode, the counter electrode is used as a cathode, a voltage is applied between the anode and the cathode, and an electrodeposition film is formed on the surface of the base material; an electrodeposition film is formed on the base material; and a baking step (S03) in which the electrodeposited film is baked.

Description

Technical Field

[0001] This invention relates to an electrodeposition solution used in electrodeposition of an electrodeposition film onto a conductive substrate by anion electrodeposition and a method for manufacturing an insulating coating.

[0002] This application claims priority based on Japanese Patent Application No. 2023-070843 filed on April 24, 2023 and Japanese Patent Application No. 2024-017133 filed on February 7, 2024, the contents of which are incorporated herein by reference. Background Technology

[0003] Insulated conductors, which are made by coating a conductive substrate with an insulating film composed of insulating resin, are widely used as conductive materials or heat sink materials for various electrical equipment that require insulation.

[0004] As a constituent material of insulating coatings, various resins are being used. For example, Patent Document 1 discloses a technology using polyimide resins such as polyamide-imide resin, and Patent Document 2 proposes a technology using a mixed resin of polyimide resin and fluorine resin.

[0005] Electrodeposition is a known method for forming an insulating film made of such insulating resin on the surface of a conductive substrate.

[0006] Electrodeposition is a method in which a substrate and a counter electrode for forming an insulating coating are immersed in an electrodeposition solution containing a material with an insulating coating. A voltage is applied between the substrate and the counter electrode to form an electrodeposited film, which deposits the insulating coating material on the surface of the substrate. Furthermore, the formed electrodeposited film is heated to bake it onto the substrate, thereby forming the insulating coating.

[0007] Furthermore, electrodeposition methods include anion electrodeposition and cation electrodeposition. Anion electrodeposition is a method in which a voltage is applied to the substrate as an anode to form an insulating coating on the surface of the substrate, while cation electrodeposition is a method in which a voltage is applied to the substrate as a cathode to form an insulating coating on the surface of the substrate.

[0008] Patent Document 1: Japanese Patent Application Publication No. 2017-115120 (A)

[0009] Patent Document 2: Japanese Patent Application Publication No. 2018-070663 (A)

[0010] However, the anion electrodeposition solution used in the anion electrodeposition method contains solid components including the aforementioned resin, water, organic solvents, and a neutralizing agent. By applying voltage, the pH near the surface of the anode (substrate) decreases, and the solid components precipitate on the surface of the anode (substrate) to form an electrodeposited film.

[0011] Here, when baking the electrodeposited film formed on the anode surface, microcracks may be generated, which may make it impossible to ensure the insulation of the insulating coating. Summary of the Invention

[0012] The present invention was made in view of the above circumstances, and its object is to provide an electrodeposition solution that can suppress the generation of microcracks and form an insulating coating with excellent insulation properties when baking an electrodeposited film, and a method for manufacturing an insulating coating using the electrodeposition solution.

[0013] In order to solve the above problems, the inventors conducted in-depth research and found that the micro-cracks generated during the baking of the electrodeposited film are caused by insufficient organic solvent in the electrodeposited film. However, if an appropriate amount of organic acid is added to the electrodeposition solution, the insufficient amount of organic solvent in the electrodeposited film can be eliminated.

[0014] Therefore, the following insights were obtained: if an appropriate amount of organic acid is added to the electrodeposition solution, the amount of organic solvent contained in the electrodeposited film can be optimized when the solid components are deposited on the surface of the anode (substrate), thereby suppressing the generation of microcracks during baking.

[0015] The present invention is based on the above insights. The electrodeposition solution of aspect 1 of the present invention is an electrodeposition solution for electrodepositing an electrodeposition film on a conductive substrate by anion electrodeposition, characterized in that the electrodeposition solution contains water, an organic solvent, a solid component containing at least a polyimide resin, a neutralizing agent and an organic acid.

[0016] According to aspect 1 of the present invention, the electrodeposition solution contains organic acids, thus allowing the amount of organic solvent contained in the electrodeposited film to be adjusted by utilizing the pH buffering effect of the organic acids and their effect on the compatibility of the resin and the organic solvent. That is, it can suppress a sharp drop in pH near the surface of the anode (substrate) and ensure that the electrodeposited film is sufficiently rich in organic solvent. Therefore, the generation of microcracks can be suppressed during baking of the electrodeposited film, and a highly insulating coating can be formed.

[0017] The electrodeposition solution of aspect 2 of the present invention is characterized in that, in the electrodeposition solution of aspect 1 of the present invention, the organic acid includes any one of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, benzoic acid, phthalic acid, trimellitic acid, glycolic acid, hydroxypropionic acid, and hydroxybutyric acid. Furthermore, since hydroxypropionic acid or hydroxybutyric acid, etc., exert their effect regardless of the position of the functional group, even positional isomers will produce an effect.

[0018] According to aspect 2 of the present invention, the electrodeposition solution contains the aforementioned organic acid, thus reliably suppressing the sharp drop in pH near the anode (substrate) surface and enabling the electrodeposition film to be sufficiently contained in the organic solvent, thereby effectively suppressing the generation of cracks when the electrodeposition film is baked.

[0019] The electrodeposition solution of aspect 3 of the present invention is characterized in that, in the electrodeposition solution of aspect 1 or aspect 2 of the present invention, the organic acid is selected from two or more of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, benzoic acid, phthalic acid, trimellitic acid, glycolic acid, hydroxypropionic acid, and hydroxybutyric acid.

[0020] According to aspect 3 of the present invention, the electrodeposition solution contains two or more of the aforementioned organic acids, thus enabling more effective suppression of the sharp drop in pH near the anode (substrate) surface and enabling the electrodeposition film to be sufficiently contained in organic solvent, thereby effectively suppressing the generation of cracks when the electrodeposition film is baked.

[0021] The electrodeposition solution of aspect 4 of the present invention is characterized in that, in the electrodeposition solution of any one of aspects 1 to 3 of the present invention, the organic acid includes a hydroxy acid.

[0022] According to aspect 4 of the invention, the electrodeposition solution, since the organic acid includes hydroxy acid, can more effectively suppress the sharp drop in pH near the anode (substrate) and can make the electrodeposition film sufficiently contain organic solvent, thus effectively suppressing the formation of cracks when the electrodeposition film is baked.

[0023] The electrodeposition solution of aspect 5 of the present invention is characterized in that, in the electrodeposition solution of any one of aspects 1 to 4 of the present invention, the concentration of the organic acid is in the range of 5 mg / L or more and 500 mg / L or less.

[0024] According to aspect 5 of the present invention, the electrodeposition solution, since the concentration of the organic acid is in the range of 5 mg / L or more and 500 mg / L or less, can exert an appropriate pH buffering effect, can sufficiently suppress the generation of cracks when the electrodeposition film is baked, and can stably form the electrodeposition film.

[0025] The electrodeposition solution of aspect 6 of the present invention is characterized in that, in the electrodeposition solution of any one of aspects 1 to 5 of the present invention, the ratio A / B of the concentration A of the neutralizing agent to the concentration B of the organic acid is in the range of 5 or more and 500 or less.

[0026] According to aspect 6 of the present invention, since the ratio A / B of the concentration A of the neutralizing agent to the concentration B of the organic acid is in the range of 5 or more and 500 or less, the generation of microcracks during baking can be suppressed by the effect of the organic acid without hindering the action of the neutralizing agent.

[0027] The electrodeposition solution of aspect 7 of the present invention is characterized in that, in the electrodeposition solution of any one of aspects 1 to 6 of the present invention, the solid component further contains a fluoropolymer.

[0028] According to aspect 7 of the present invention, the electrodeposition solution contains a fluoropolymer as a solid component in addition to a polyimide-based resin, thus enabling the formation of an insulating coating with particularly excellent insulating and dielectric properties. Furthermore, since the electrodeposition film containing the fluoropolymer is more difficult to crack-suppress compared to the case where a polyimide-based resin is used alone, the addition of an organic acid is effective.

[0029] The method for manufacturing an insulating film according to aspect 8 of the present invention is a method for manufacturing an insulating film by forming an insulating film on the surface of a substrate, characterized by comprising: an electrodeposition film forming step, wherein the substrate and a counter electrode are immersed in an electrodeposition solution of any one of aspects 1 to 7 of the present invention, wherein the substrate is used as an anode and the counter electrode is used as a cathode, and a voltage is applied between the anode and the cathode to form an electrodeposition film on the substrate; and a baking step, wherein the electrodeposition film is baked.

[0030] According to the method for manufacturing an insulating coating of aspect 8 of the present invention, since it includes an electrodeposition film forming step of forming an electrodeposition film using an electrodeposition solution of any one of aspects 1 to 7 of the present invention and a baking step of baking the electrodeposition film, it is possible to suppress the generation of micro-cracks in the electrodeposition film during the baking step, and to stably manufacture an insulating coating with excellent insulating properties.

[0031] According to the present invention, an electrodeposition solution is provided that can suppress the generation of microcracks and form an insulating coating with excellent insulation properties when baking an electrodeposited film, and a method for manufacturing an insulating coating using the electrodeposition solution is provided. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating a method for manufacturing an insulating coating using an electrodeposition solution according to one embodiment of the present invention. Detailed Implementation

[0033] The following describes a method for manufacturing an electrodeposition solution and an insulating coating according to one embodiment of the present invention.

[0034] The electrodeposition solution of this embodiment is used to form an electrodeposition film on the surface of a conductive substrate as a precursor to an insulating coating.

[0035] In addition, in this embodiment, an anion electrodeposition method is used, which forms an insulating coating on the surface of the substrate, which serves as the anode, by applying a voltage to the substrate as the anode.

[0036] The electrodeposition solution in this embodiment contains water, organic solvent, solid components, neutralizing agent, and organic acid.

[0037] Furthermore, the electrodeposition solution of this embodiment contains amine as a neutralizing agent because it is used for anion electrodeposition as described above.

[0038] In this embodiment, the solid component is set to contain at least a polyimide resin, preferably both a polyimide resin and a fluorine resin.

[0039] In this embodiment, examples of polyimide-based resins include polyamide-imide, polyether-imide, and polyimide. Furthermore, examples of fluorine-based resins include polytetrafluoroethylene and perfluoroalkoxyalkanes.

[0040] Furthermore, the average particle size of the solid component is 50 nm or more and 500 nm or less, more preferably 50 nm or more and 450 nm or less, and even more preferably 50 nm or more and 300 nm or less. Furthermore, the standard deviation of the particle size of the solid component is 250 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less.

[0041] Water and organic solvents are used to disperse polyimide and fluorine resins as solid components.

[0042] Examples of organic solvents include N,N-dimethylacetamide, propylene carbonate, dimethyl sulfoxide, N,N-dimethylformamide, 4-butyrolactone, N-methyl-2-pyrrolidone, and N-methyl-2-pyrrolidone.

[0043] Furthermore, the water content in the electrodeposition solution is preferably 15% by mass or more, and more preferably 50% by mass or more. On the other hand, the water content in the electrodeposition solution is preferably 85% by mass or less, and more preferably 75% by mass or less.

[0044] Furthermore, the organic solvent content in the electrodeposition solution is preferably 15% by mass or more, and more preferably 50% by mass or more. On the other hand, the organic solvent content in the electrodeposition solution is preferably 85% by mass or less, and more preferably 75% by mass or less.

[0045] Organic acids have a pH buffering effect and influence the compatibility of resins (as solid components) with organic solvents. By adjusting the type and content of the organic acid, the amount of organic solvent contained in the electrodeposited film can be controlled.

[0046] Herein, the organic acid preferably includes any one of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, benzoic acid, phthalic acid, trimellitic acid, glycolic acid, hydroxypropionic acid, and hydroxybutyric acid, and more preferably includes two or more selected from these.

[0047] Furthermore, hydroxy acids are preferred as organic acids. Examples of hydroxy acids include glycolic acid, hydroxypropionic acid, hydroxybutyric acid, malonic acid, and glyceric acid. Moreover, since hydroxypropionic acid or hydroxybutyric acid exerts its effect regardless of the position of the functional group, even positional isomers will produce an effect.

[0048] In this embodiment, the concentration of the organic acid in the electrodeposition solution is preferably in the range of 5 mg / L or more and 500 mg / L or less. By setting the concentration of the organic acid to 5 mg / L or more, the pH buffering effect can be fully utilized, allowing the organic solvent to be appropriately introduced into the electrodeposition film, thereby effectively suppressing the formation of microcracks during baking. On the other hand, by setting the concentration of the organic acid to 500 mg / L or less, foaming and a decrease in coulombic efficiency caused by excessive organic solvent introduced into the electrodeposition film can be prevented, thereby enabling efficient formation of the electrodeposition film.

[0049] Furthermore, the concentration of organic acid in the electrodeposition solution is preferably 10 mg / L or more, more preferably 20 mg / L or more. Additionally, the concentration of organic acid in the electrodeposition solution is preferably 100 mg / L or less, more preferably 50 mg / L or less.

[0050] In this embodiment, the ratio A / B of the neutralizing agent concentration A mg / L to the organic acid concentration B mg / L is preferably in the range of 5 or more and 500 or less. The organic acid may react with the neutralizing agent, which is composed of amine compounds, in an acid-base reaction, thereby hindering the neutralizing agent's intended function of ionizing the resin. Therefore, to reliably exert their respective effects, the ratio A / B of the neutralizing agent concentration A mg / L to the organic acid concentration B mg / L is preferably set within the above-mentioned range. If the ratio A / B is less than 5, the ionization effect of the neutralizing agent on the resin will be impaired, thus compromising the stability of the liquid. If the ratio A / B exceeds 500, the organic acid will not exert its desired effect, resulting in cracks in the film.

[0051] Furthermore, the ratio A / B of the concentration of the neutralizing agent A mg / L to the concentration of the organic acid B mg / L is more preferably 20 or more, and more preferably 50 or more. Moreover, the ratio A / B of the concentration of the neutralizing agent A mg / L to the concentration of the organic acid B mg / L is more preferably 400 or less, and more preferably 200 or less.

[0052] Next, refer to Figure 1 The method for manufacturing an insulating coating using the electrodeposition solution of this embodiment will be described.

[0053] like Figure 1 As shown, the method for manufacturing the insulating coating in this embodiment includes a surface pretreatment step S01, an electrodeposition film formation step S02, and a baking step S03.

[0054] (Surface pretreatment process S01)

[0055] First, prepare a substrate for forming the electrodeposited film (insulating coating). This substrate is conductive and is made of metallic materials such as copper or copper alloys, aluminum or aluminum alloys.

[0056] Furthermore, surface treatment liquids such as organic solvents or surfactants are used to remove grease or oxidized coatings adhering to the surface of the aforementioned substrate.

[0057] (Electrodeposition film formation process S02)

[0058] Next, in the electrodeposition solution of this embodiment, the substrate and the counter electrode are immersed, with the substrate serving as the anode and the counter electrode as the cathode, and a voltage is applied between the anode (substrate) and the cathode (counter electrode). This causes the pH of the electrodeposition solution around the substrate to decrease, and a solid component (in this embodiment, a mixture of polyimide and fluorine resins) precipitates on the surface of the substrate. Thus, an electrodeposition film is formed on the surface of the substrate. In this embodiment, since an organic acid is added to the electrodeposition solution, the organic solvent can be appropriately contained in the electrodeposition film due to the pH buffering effect of the organic acid.

[0059] The temperature (liquid temperature) of the electrodeposition solution in the electrodeposition film formation process S02 is preferably adjusted to a range of 5°C or higher and 35°C or lower.

[0060] By setting the liquid temperature above 5°C, water contamination in the electrodeposition solution due to condensation can be suppressed. On the other hand, by setting the liquid temperature below 35°C, the storage stability of the electrodeposition solution is improved, enabling the stable formation of the electrodeposition film.

[0061] The applied voltage between the substrate (anode) and the counter electrode (cathode) in the electrodeposition film formation process S02 is preferably in the range of 10V or higher and 600V or lower.

[0062] By setting the applied voltage to 10V or higher, the electrodeposition rate can be ensured, thereby improving productivity. On the other hand, by setting the applied voltage to 600V or lower, the generation of a large number of bubbles on the surface of the substrate can be suppressed, and in the subsequent baking process S03, the rupture of bubbles that would otherwise result in multiple irregularities on the insulating coating can be prevented.

[0063] (Baking process S03)

[0064] In the baking process S03, the substrate on which the electrodeposited film containing solid components (in this embodiment, a mixture of polyimide resin and fluorine resin) is formed, obtained in the electrodeposited film forming process S02, is dried, for example, at a temperature range of 200°C or higher and below the melting point of the solid components, to remove residual electrodepositing liquid. Then, the electrodeposited film is baked onto the substrate to form an insulating coating.

[0065] The baking temperature in baking step S03 can be within a temperature range that allows the electrodeposited film of a solid component (in this embodiment, a mixture of polyimide resin and fluorine resin) to form an insulating coating on the substrate, for example, a range of 200°C or higher and 400°C or lower. Furthermore, the baking time can be, for example, a range of 0.5 minutes or more and 60 minutes or less.

[0066] Through the processes described above, an insulating coating containing solid components (in this embodiment, a mixture of polyimide resin and fluorine resin) can be formed on a conductive substrate. This suppresses the formation of microcracks during baking, resulting in an insulating coating with excellent insulation properties.

[0067] The electrodeposition solution of this embodiment, as described above, contains organic acids. By utilizing the pH buffering effect of organic acids and their effect on the compatibility between the resin and the organic solvent, the amount of organic solvent contained in the electrodeposition film can be adjusted. This allows for sufficient suppression of crack formation during the baking of the electrodeposition film and the formation of an insulating coating with high insulation properties.

[0068] In the electrodeposition solution of this embodiment, when any one of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, benzoic acid, phthalic acid, trimellitic acid, glycolic acid, hydroxypropionic acid, and hydroxybutyric acid is included as an organic acid, the sharp drop in pH near the anode (substrate) surface can be reliably suppressed, and the generation of cracks can be sufficiently suppressed when the electrodeposited film is baked.

[0069] Furthermore, when it contains two or more of the following: formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, benzoic acid, phthalic acid, trimellitic acid, glycolic acid, hydroxypropionic acid, and hydroxybutyric acid, it can further effectively suppress the sharp drop in pH near the anode (substrate) surface and fully suppress the generation of cracks when baking the electrodeposited film.

[0070] Furthermore, when hydroxy acids are present as organic acids, the sharp drop in pH near the anode (substrate) surface can be effectively suppressed, and the generation of cracks can be fully suppressed when the electrodeposited film is baked.

[0071] In the electrodeposition solution of this embodiment, when the concentration of the organic acid is set to 5 mg / L or higher, the pH buffering effect of the organic acid can be reliably exerted, and the generation of cracks can be sufficiently suppressed when the electrodeposited film is baked. On the other hand, when the concentration of the organic acid is set to 500 mg / L or lower, the pH buffering effect can be prevented from being over-exerted, and the electrodeposited film can be formed efficiently without the generation of foam.

[0072] In the electrodeposition solution of this embodiment, when the ratio A / B of the concentration of neutralizing agent A mg / L to the concentration of organic acid B mg / L is in the range of 5 or more and 500 or less, the content of neutralizing agent can be ensured, and the generation of micro-cracks during baking can be suppressed by the pH buffering effect of organic acid without hindering the action of neutralizing agent.

[0073] In the electrodeposition solution of this embodiment, when a fluoropolymer is contained as a solid component in addition to a polyimide resin, an electrodeposition film composed of a mixed resin of a polyimide resin and a fluoropolymer can be formed, resulting in an insulating coating with particularly excellent insulating properties.

[0074] Since the method for manufacturing the insulating coating in this embodiment includes: an electrodeposition film formation step S02, in which a substrate and a counter electrode are immersed in the electrodeposition solution of this embodiment, the substrate is used as the anode and the counter electrode is used as the cathode, and a voltage is applied between the anode and the cathode to form an electrodeposition film on the substrate; and a baking step S03, in which the electrodeposition film is baked, the generation of micro-cracks in the electrodeposition film can be suppressed in the baking step S03, and an insulating coating with excellent insulation properties can be stably manufactured.

[0075] The embodiments of the present invention have been described above, but the present invention is not limited thereto, and appropriate changes can be made without departing from the technical concept of the present invention.

[0076] Example

[0077] The results of the verification experiments conducted to confirm the effectiveness of the present invention will be described below.

[0078] As shown in Tables 1 and 2, water, organic solvent, solid components, neutralizing agent, and organic acid were prepared and mixed according to the mass ratios shown in Tables 1 and 2 to obtain the electrodeposition solution.

[0079] Furthermore, a rectangular rod of oxygen-free copper (1.47mm × 2.94mm × 25cm in length) is prepared as the conductive substrate, and a cylindrical copper plate is prepared as the counter electrode.

[0080] The substrate and the counter electrode were immersed in the electrodeposition solution described above. The temperature of the electrodeposition solution was set to 20°C, the applied voltage was set to 500V, and the holding time was set to 0.5 minutes, thus forming an electrodeposition film.

[0081] Then, the electrodeposited film was baked using a three-stage heating curve, in which the workpiece temperature was maintained at 140-170℃ for 10 minutes, at 240-260℃ for 5 minutes, and at 340-350℃ for 90 seconds followed by rapid cooling, thus forming an insulating coating.

[0082] Here, the concentration of organic acids contained in the electrodeposited film was evaluated as follows.

[0083] After diluting the electrodeposition solution with ultrapure water, the filtrate obtained by removing impurities and passing it through a membrane filter is used as the solution for ion chromatography determination.

[0084] Next, the determination was performed using a Thermo Fisher Scientific ICS-5000+ ion chromatograph. Dionex IonPac AG15 and Dionex IonPac AS15 anion exchange columns were used as the stationary phases for ion chromatography, potassium hydroxide aqueous solution was used as the eluent, Dionex ADRS 600 was used as the suppressor, and conductivity was used as the detector.

[0085] Furthermore, the appearance of the formed insulating film was observed, and cracks and blistering were evaluated.

[0086] The situation where cracks in the Cu substrate can be identified by visual observation is rated as "D", the situation where cracks in the Cu substrate cannot be identified by visual observation is rated as "C", the situation where cracks cannot be identified by visual observation but can be identified by microscopic observation is rated as "B", and the situation where cracks cannot be identified by microscopic observation is rated as "A".

[0087] Furthermore, during visual observation, the presence of blistering in the insulating film was evaluated as "present," while the absence of blistering in the insulating film was evaluated as "absent."

[0088] In addition, the relative permittivity of the insulating coating was determined as follows.

[0089] Silver paste was applied to the insulating film surface at 10 mm from each end and 100 mm from the center to prepare a sample for testing. The capacitance between the conductor and the silver paste in the center was measured using an IM3536 LCR meter manufactured by HIOKI EE CORPORATION, and the relative permittivity was calculated based on the measured capacitance and the thickness of the film.

[0090] Furthermore, the stability of the electrodeposition solution was evaluated. When the electrodeposition solution was kept at 40°C for 5 days, the condition in which separation or precipitation occurred in the electrodeposition solution was rated as "B", and the condition in which no separation or precipitation occurred in the electrodeposition solution was rated as "A".

[0091] [Table 1]

[0092]

[0093] [Table 2]

[0094]

[0095] In Comparative Examples 1 to 3, no organic acid was added to the electrodeposition solution, and cracks were generated in the baked insulating film that allowed the Cu substrate to be identified.

[0096] In contrast, in Examples 1 to 24 of the present invention, an organic acid was added to the electrodeposition solution, and no cracks that could be identified in the Cu substrate were produced in the baked insulating film.

[0097] Furthermore, in Examples 3 to 24 of the present invention, any one of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, benzoic acid, phthalic acid, trimellitic acid, glycolic acid, hydroxypropionic acid, and hydroxybutyric acid was used as an organic acid, and no cracks that could be observed by visual inspection were produced.

[0098] Furthermore, in Examples 1-5 of the present invention, the concentration of the organic acid was less than 5 mg / L. Although microcracks could be identified, no cracks that could be identified in the substrate were produced, and the insulation was not a problem. In Examples 6-9 of the present invention, since the concentration of the organic acid exceeded 500 mg / L, blistering occurred in the coating.

[0099] Furthermore, in Examples 6, 8, 9, 15, and 16 of the present invention, the ratio A / B of the neutralizing agent concentration A mg / L to the organic acid concentration B mg / L was less than 5. When maintained at 40°C for 5 days, separation or precipitation occurred in the electrodeposition solution, resulting in poor stability of the electrodeposition solution. In Examples 10 to 14 of the present invention, even when the organic acid concentration was 5 mg / L or higher, microcracks were generated because the ratio A / B of the neutralizing agent concentration A mg / L to the organic acid concentration B mg / L exceeded 500.

[0100] Furthermore, in Examples 21 and 22 of the present invention, polyimide resin and fluororesin are included as solid components, resulting in a sufficiently low relative permittivity and particularly excellent insulation properties.

[0101] Based on the results of the above confirmation experiments, it has been confirmed that, according to the present invention, an electrodeposition solution capable of suppressing the generation of microcracks and forming an insulating coating with excellent insulation properties during the baking of the electrodeposited film, and a method for manufacturing an insulating coating using the electrodeposition solution, are available.

[0102] Industrial availability

[0103] An electrodeposition solution is provided that can suppress the generation of microcracks and form an insulating coating with excellent insulation properties during the baking of the electrodeposited film, as well as a method for manufacturing an insulating coating using the electrodeposition solution.

Claims

1. An electrodeposition solution, wherein an electrodeposition film is deposited on a conductive substrate by anion electrodeposition, characterized in that, The electrodeposition solution contains water, organic solvent, solid components, neutralizing agent, and organic acid. The solid component contains at least a polyimide resin.

2. The electrodeposition solution according to claim 1, characterized in that, The organic acid includes any one of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, benzoic acid, phthalic acid, trimellitic acid, glycolic acid, hydroxypropionic acid, and hydroxybutyric acid.

3. The electrodeposition solution according to claim 1, characterized in that, The organic acid is selected from two or more of the following: formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, benzoic acid, phthalic acid, trimellitic acid, glycolic acid, hydroxypropionic acid, and hydroxybutyric acid.

4. The electrodeposition solution according to claim 1, characterized in that, The organic acids include hydroxy acids.

5. The electrodeposition solution according to claim 1, characterized in that, The concentration of the organic acid is in the range of 5 mg / L or higher and 500 mg / L or lower.

6. The electrodeposition solution according to claim 1, characterized in that, The ratio A / B of the concentration A of the neutralizing agent to the concentration B of the organic acid is in the range of 5 or higher and 500 or lower.

7. The electrodeposition solution according to claim 1, characterized in that, The solid components also contain fluoropolymers.

8. A method for manufacturing an insulating film, comprising forming an insulating film on the surface of a substrate, characterized in that, have: The electrodeposition film formation process involves immersing the substrate and the counter electrode in the electrodeposition solution according to any one of claims 1 to 7, using the substrate as the anode and the counter electrode as the cathode, and applying a voltage between the anode and the cathode to form an electrodeposition film on the substrate. as well as The baking process involves baking the electrodeposited film.

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