Method for producing insulating electrodeposition coating material and insulating electrodeposition coating material

Abstract

Provided is a method for producing an insulating electrodeposition coating material that includes a step for mixing: a resin solution containing a polyimide-based resin and a liquid medium containing water and an organic solvent; and an acidic to weakly alkaline silica sol containing silica particles and water, to prepare an insulating electrodeposition coating material.

Description

Manufacturing method of insulating electrodeposition paint and insulating electrodeposition paint

[0001] The present disclosure relates to a method for producing an insulating electrodeposition paint and an insulating electrodeposition paint.

[0002] Insulating electrodeposition paints for forming insulating films on objects by electrodeposition coating are known. Patent Document 1 discloses a suspension (electrodeposition liquid) in which resin particles and heat-resistant particles are dispersed in a dispersion medium.

[0003] JP 2016-15295 A

[0004] As a result of intensive research, the inventors have found that there is still room for improvement in the coating films formed using paints prepared based on conventional techniques such as those described in Patent Document 1, in terms of achieving both heat resistance and long-term insulation stability.

[0005] The present disclosure has been made in view of the above circumstances, and aims to provide a method for producing an insulating electrodeposition paint for forming a coating film that is heat resistant and has excellent long-term insulating stability, and also aims to provide an insulating electrodeposition paint produced by the method.

[0006] The method for producing an insulating electrodeposition paint comprises a step of preparing an insulating electrodeposition paint by mixing a resin liquid containing a liquid medium including a polyimide resin, water, and an organic solvent with a silica sol containing silica particles and water and having an acidic to weakly alkaline liquid property.

[0007] According to the present disclosure, it is possible to provide a method for producing an insulating electrodeposition paint for forming a coating film that has heat resistance and excellent long-term insulating stability, and also to provide an insulating electrodeposition paint produced by the method.

[0008] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments.

[0009] One aspect of the present disclosure provides a method for producing an insulating electrodeposition paint, comprising the step of mixing a resin liquid containing a polyimide resin and a liquid medium containing water and an organic solvent with a silica sol containing silica particles and water and having an acidic to weakly alkaline liquid property to prepare an insulating electrodeposition paint. This production method can provide an insulating electrodeposition paint for forming a coating film that has heat resistance and excellent long-term insulation stability.

[0010] In one embodiment, the organic solvent may contain N-methyl-2-pyrrolidone and 1-methoxy-2-propanol, which makes it easier to maintain good dispersibility of the polyimide resin and silica particles.

[0011] In one embodiment, the insulating electrodeposition paint may contain 0.01 to 22 parts by mass of silica particles per 100 parts by mass of polyimide resin, which makes it easier to maintain the dispersibility of the polyimide resin and silica particles.

[0012] In one embodiment, the silica sol is prepared by the addition of NaOH and NH ４ OH, which makes it easier to maintain the dispersibility of the polyimide resin and silica particles.

[0013] In one embodiment, the average particle size of the silica particles may be 1 to 60 nm, which makes it easier to maintain the dispersibility of the silica particles.

[0014] In one embodiment, the pH of the silica sol may be 2.0 to 10.0, which makes it easier to maintain the dispersibility of the silica particles and to form a coating film that is heat resistant and has excellent long-term insulation stability.

[0015] In one embodiment, the liquid medium may contain 70 to 95% by mass of an organic solvent, which makes it easier to maintain the dispersibility of the polyimide resin and silica particles.

[0016] Another aspect of the present disclosure provides an insulating electrodeposition paint comprising a mixture of a resin liquid containing a polyimide resin and a liquid medium containing water and an organic solvent, and a silica sol containing silica particles and water and having an acidic to weakly alkaline liquid property. The insulating electrodeposition paint can form a coating film that is heat resistant and has excellent long-term insulating stability.

[0017] <Method for Producing Insulating Electrodeposition Paint> The method for producing an insulating electrodeposition paint according to the present disclosure comprises the step of preparing an insulating electrodeposition paint by mixing a resin liquid containing a polyimide resin and a liquid medium containing water and an organic solvent with a silica sol containing silica particles and water, the silica sol having an acidic to weakly alkaline liquid property. By dispersing a polyimide resin in a system using both water and an organic solvent as the liquid medium and mixing this with a silica sol having an acidic to weakly alkaline liquid property to prepare an insulating electrodeposition paint (hereinafter sometimes simply referred to as "paint"), it is possible to form a coating film (insulating film) that is heat resistant and has excellent long-term insulating stability. While the reason for this is unclear, the inventors speculate that the polyimide resin and silica particles are well dispersed in the paint prepared as described above, resulting in the formation of a uniform coating film.

[0018] In the preparation step, from the viewpoint of easily forming a coating film having heat resistance and excellent long-term insulating stability, the resin liquid and the silica sol are mixed so that the coating material contains preferably 0.01 parts by mass or more of silica particles, more preferably 0.05 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of polyimide resin. Also, from the viewpoint of easily forming a coating film having heat resistance and excellent long-term insulating stability, the resin liquid and the silica sol are mixed so that the coating material contains preferably 22 parts by mass or less of silica particles, more preferably 15 parts by mass or less, and even more preferably 8 parts by mass or less, per 100 parts by mass of polyimide resin.

[0019] As described above, by preparing the resin liquid and silica sol in advance and mixing them, preferably by adding silica sol to the resin liquid and mixing them, it is easy to obtain a coating material in which the polyimide resin and silica particles are suitably dispersed. The method for mixing the two is not particularly limited, but for example, if the amount is small, it can be mixed in a beaker while stirring with a magnetic stirrer or the like, and if the amount is large, it can be mixed by stirring with an emulsifier such as a homodisper.

[0020] (Resin Liquid) Examples of polyimide-based resins include polyimide resins, polyamide-imide resins, polyether-imide resins, polyester-imide resins, etc. Among these, polyimide resins may be used from the viewpoints of dispersibility in the coating material, long-term stability of the coating material, etc.

[0021] The polyimide resin may be present in the coating material as polyimide resin particles. The average particle diameter of the polyimide resin is preferably 10 nm or more, more preferably 100 nm or more, from the viewpoint of facilitating the formation of a uniform coating film. The average particle diameter is preferably 1000 nm or less, more preferably 900 nm or less, from the viewpoint of facilitating the formation of a uniform coating film. The average particle diameter here refers to the median diameter (D50), which can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer.

[0022] The content of the polyimide resin based on the total amount of the resin liquid is preferably 1% by mass or more, more preferably 5% by mass or more, from the viewpoint of easily forming a coating film that has heat resistance and excellent long-term insulating stability, and is preferably 25% by mass or less, more preferably 10% by mass or less, from the viewpoint of easily forming a coating film that has heat resistance and excellent long-term insulating stability.

[0023] By using water and an organic solvent in combination as the liquid medium, good dispersibility of the polyimide resin and silica particles can be maintained when the coating liquid is prepared. The organic solvent is not particularly limited as long as it is one that is used in coating materials for electrodeposition containing polyimide resins, but examples thereof include N-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, etc., and N-methyl-2-pyrrolidone may be used from the viewpoint of good dispersibility of the polyimide resin and silica particles. Furthermore, by using N-methyl-2-pyrrolidone or the like in combination with an alcohol-based solvent as the organic solvent, good dispersibility of the polyimide resin and silica particles can be easily maintained. Examples of alcohol-based solvents include methanol, ethanol, 1-propanol, 2-propanol, t-butyl alcohol, ethylene glycol, propylene glycol, and 1-methoxy-2-propanol, and 1-methoxy-2-propanol is preferred from the viewpoint of good dispersibility of the polyimide resin and silica particles. From the viewpoint of dispersibility of the polyimide resin and silica particles, the organic solvent preferably contains water, N-methyl-2-pyrrolidone, and 1-methoxy-2-propanol, and more preferably consists essentially of these.

[0024] From the viewpoint of good dispersibility of the polyimide resin and silica particles, the liquid medium may mainly contain an organic solvent, i.e., the content of the organic solvent may be greater than the content of water. For example, the liquid medium preferably contains 70 to 95 mass % of the organic solvent, more preferably 75 to 90 mass %.

[0025] The resin liquid may contain, in addition to the polyimide resin, a dispersant such as pyridine as an additive.

[0026] (Silica sol) Silica particles are heat-resistant particles themselves, and when present together with the resin component in the coating film, they can suppress the deterioration of the resin component. This is presumably because the dehydration and endothermic reaction on the surface of the silica particles caused by discharge in the coating film suppresses the deterioration of the resin component due to discharge. When using a polyimide resin, according to the inventors' studies, silica particles have superior properties in this respect compared to metal oxide particles such as alumina and zirconia, which also have heat resistance.

[0027] The silica particles can be used without any particular limitation, and examples thereof include amorphous (non-crystalline) silica particles. Examples of amorphous silica particles include fused silica particles, fumed silica particles, and colloidal silica particles. Among these, colloidal silica particles have high monodispersity and are easy to suppress aggregation in the coating material.

[0028] The shape of the silica particles is not particularly limited, and examples thereof include spherical, cocoon-shaped, and aggregated silica particles. The use of spherical silica particles makes it easier to suppress aggregation in the coating material. Furthermore, the silica particles may have a hollow structure, a porous structure, or the like.

[0029] The average particle size of the silica particles is preferably 1 nm or more, more preferably 5 nm or more, from the viewpoint of more easily maintaining good dispersibility of the polyimide resin and the silica particles. The average particle size is preferably 60 nm or less, more preferably 30 nm or less, from the viewpoint of more easily maintaining good dispersibility of the polyimide resin and the silica particles. The average particle size here refers to the median diameter (D50), and can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer.

[0030] The content of silica particles based on the total amount of silica sol is preferably 5.0% by mass or more, more preferably 10.0% by mass or more, from the viewpoint of easily forming a coating film having heat resistance and excellent long-term insulating stability, and is preferably 30% by mass or less, more preferably 20% by mass or less, from the viewpoint of easily forming a coating film having heat resistance and excellent long-term insulating stability.

[0031] From the viewpoint of forming a uniform coating film and maintaining the dispersibility of silica particles when used as a paint, the liquid pH of the silica sol is acidic to weakly alkaline. Specifically, the pH of the silica sol is preferably 2.0 or higher, more preferably 2.5 or higher, from the viewpoint of more easily maintaining the good dispersibility of the polyimide resin and silica particles in the paint. From the viewpoint of maintaining the dispersibility of silica particles when used as a paint, the pH is preferably 10.0 or lower, more preferably 9.6 or lower. The pH here refers to a value measured at 25°C using a pH meter in accordance with JIS Z 8802.

[0032] The silica sol may contain an alkali or an acid as a stabilizer for the silica particles. The alkali may be NaOH, ammonia (NH ４ Examples of acids include organic acids such as lactic acid and acetic acid, and inorganic acids such as nitric acid. Among these, silica sol is preferably prepared using NaOH, ammonia (NH ４ It is preferable that the alkyl group contains aryl groups such as aryl, ...

[0033] <Insulating Electrodeposition Paint> The insulating electrodeposition paint according to the present disclosure is obtained by mixing the aforementioned resin liquid containing a liquid medium including a polyimide resin, water, and an organic solvent with the aforementioned silica sol containing silica particles and water and having an acidic to weakly alkaline liquid property. By using such a paint, a coating film can be formed that is heat-resistant and has excellent long-term insulating stability. It is believed that the liquid property of the silica sol affects the expression of the coating film's properties (preparation of a desired paint). However, there is a risk that the liquid property may not be accurately reflected in the characteristics of the paint obtained by mixing the silica sol with the resin liquid. In light of this, the insulating electrodeposition paint is described as being obtained by mixing the resin liquid with the silica sol.

[0034] As described above, the coating preferably contains 0.01 to 22 parts by mass, more preferably 0.05 to 15 parts by mass, and even more preferably 1 to 8 parts by mass of silica particles per 100 parts by mass of polyimide resin.

[0035] By applying this paint to an object using an electrodeposition coating device, a heat-resistant coating film (insulating film) can be formed on the surface of the object. Coating conditions can be, for example, an applied voltage of 10 to 200 kV and a voltage application time of 1 second or more, and the thickness of the formed coating film can be, for example, 1 to 200 μm. The object is not particularly limited as long as it is an object that can generally be subjected to insulating electrodeposition coating, but examples include electric high-power density motor stators, power semiconductors, transistors, and other electronic components that require long-term heat resistance and insulating reliability.

[0036] <Outline of this embodiment> [1] A method for producing an insulating electrodeposition paint, comprising a step of mixing a resin liquid containing a liquid medium containing a polyimide resin, water, and an organic solvent with a silica sol containing silica particles and water and having an acidic to weakly alkaline liquid property to prepare an insulating electrodeposition paint. [2] The method according to [1], wherein the organic solvent contains N-methyl-2-pyrrolidone and 1-methoxy-2-propanol. [3] The method according to [1] or [2], wherein the insulating electrodeposition paint contains 0.01 to 22 parts by mass of the silica particles per 100 parts by mass of the polyimide resin. [4] The method according to [1] or [2], wherein the silica sol is a mixture of NaOH and NH ４

[0013] The method for producing an insulating electrodeposition paint according to any one of [1] to [3], wherein the silica particles have an average particle size of 1 to 60 nm.

[0014] The method for producing an insulating electrodeposition paint according to any one of [1] to [3], wherein the silica sol has a pH of 2.0 to 10.0.

[0015] The method for producing an insulating electrodeposition paint according to any one of [1] to [6], wherein the liquid medium contains 70 to 95 mass% of the organic solvent.

[0016] The method for producing an insulating electrodeposition paint according to any one of [1] to [6], wherein the liquid medium contains 70 to 95 mass% of the organic solvent.

[0017] The method for producing an insulating electrodeposition paint according to any one of [1] to [3], wherein the silica sol contains at least one of silica particles, water, and an organic solvent.

[0018] The method for producing an insulating electrodeposition paint according to any one of [1] to [3], wherein the silica sol contains at least one of silica particles, water, and an organic solvent. [0019 ...

[0037] The present disclosure will be explained in more detail by the following examples, but the present disclosure is not limited to these examples.

[0038] (Preparation of Resin Liquid) Resin liquids having the compositions shown in Table 1 were prepared.

[0039]

[0040] (Preparation of Silica Sol) Silica sols (Snowtex series manufactured by Nissan Chemical Industries, Ltd.) shown in Table 2 were prepared.

[0041]

[0042] (Preparation of Alumina Sol) The alumina sols shown in Table 3 were prepared. Clearsol N: manufactured by Kawaken Fine Chemical Co., Ltd. Aluminasol-5F: manufactured by Kawaken Fine Chemical Co., Ltd. Aluminasol-10F: manufactured by Kawaken Fine Chemical Co., Ltd. Aluminasol-10D: manufactured by Kawaken Fine Chemical Co., Ltd.

[0043]

[0044] (Preparation of electrodeposition paint) The resin liquid was placed in a beaker and stirred with a homodisper, and 0.4 parts by mass of the silica sol or alumina sol was added to 100 parts by mass of the resin liquid, as shown in Table 4. The stirring time was 5 minutes or more.

[0045] (Evaluation of Dispersibility of Electrodeposition Paints) The dispersibility of the paints prepared as described above was evaluated as follows. Specifically, the electrodeposition paints prepared by the above method were placed in 100 ml glass bottles, and the state of each electrodeposition paint was visually observed immediately after preparation and one day later. The results are shown in Table 4. A: No sediment or aggregates were present, and electrodeposition coating was possible. B: Sediment and aggregates were present, and electrodeposition coating was not possible.

[0046]

[0047] (Preparation of Test Pieces with Coatings) 500 g of each of the paints Nos. 1 to 6, which were rated A for dispersion stability, was placed in a beaker. While stirring the paint with a magnetic stirrer at 300 rpm, an anode (plated copper test piece) and a cathode (SUS counter electrode) were placed facing each other in the beaker, and an electrodeposition coating film (insulating film) was formed on the surface of the test piece using an electrodeposition coating device SD-EC-800-M manufactured by Takasago Machinery Co., Ltd. The electrodeposition coating conditions were an applied voltage of 60 kV and a voltage application time of 300 seconds. The test piece with the coating film formed thereon was then dried in a dryer. The coating film had a thickness of 50 μm.

[0048] (Evaluation of heat resistance) The test pieces with the coating film obtained as described above were placed in a drying oven at 300° C. and removed after 100 hours. After removal, the appearance of the test pieces with the coating film was visually observed, and no defects such as cracking or peeling were found in the coating of any of the test pieces.

[0049] (Measurement of dielectric breakdown time) Two test pieces (length 180 mm × width 9 mm × thickness 5 mm, length of the portion where the coating was formed 60 mm) with a coating film obtained using paint No. 5 were prepared. The test pieces were stacked so that the portions where the coating was formed faced each other and fixed with Kapton tape. A power source was then connected to the end of each test piece where the coating film was not formed, and a V-t test (test conditions: clock frequency 1 kHz, voltage ±1500 V, atmospheric pressure 1.0 atm) was performed. The coating finally broke down after approximately 71 hours. This indicates that the coating film obtained as described above has excellent long-term insulation stability.

Claims

1. A method for producing an insulating electrodeposition paint, comprising a step of mixing a resin liquid containing a polyimide resin and a liquid medium containing water and an organic solvent with a silica sol containing silica particles and water and having an acidic to weakly alkaline liquid property to prepare an insulating electrodeposition paint.

2. The process of claim 1, wherein the organic solvent comprises N-methyl-2-pyrrolidone and 1-methoxy-2-propanol.

3. The manufacturing method according to claim 1 or 2, wherein the insulating electrocoating contains 0.01 to 22 parts by mass of the silica particles per 100 parts by mass of the polyimide resin.

4. The silica sol is prepared by dissolving NaOH and NH ４ The method according to claim 1 or 2, further comprising at least one of: OH.

5. The method according to claim 1 or 2, wherein the average particle size of the silica particles is 1 to 60 nm.

6. The method according to claim 1 or 2, wherein the pH of the silica sol is 2.0 to 10.

0.

7. The manufacturing method according to claim 1 or 2, wherein the liquid medium contains 70 to 95 mass % of the organic solvent.

8. An insulating electrocoating paint comprising a mixture of a resin liquid containing a polyimide resin and a liquid medium containing water and an organic solvent, and a silica sol containing silica particles and water and having an acidic to weakly alkaline liquid property.