Aqueous dispersion, anionic electrodeposition coating composition and coated article

Abstract

To provide an aqueous dispersion which is excellent in storage stability, gives an excellent coating film appearance even in thick film coating, and gives a coating film excellent in thermal shock resistance, insulation properties, heat resistance, and adhesion to a substrate, an anionic electrodeposition coating, and a coated article.SOLUTION: The aqueous dispersion contains a polyimide resin (A), a basic compound (B), an organic solvent (C), and water, wherein the polyimide resin (A) has a bisphenol skeleton, a hydroxyl group, and an anionic group, and the ratio of the hydroxyl value to the anionic group value of the polyimide resin (A), [hydroxyl value] / [anionic group value], is 0.1 to 10.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to aqueous dispersions, anionic electrodeposition paints and coated articles. [Background technology]

[0002] Polyimide resins, which have excellent heat resistance and chemical resistance, are widely used in a wide range of fields, including electrical insulation and electronics. Polyimide resins are typically converted into varnishes using organic solvents to produce films, sheets, molded products, etc. However, from the perspectives of reducing environmental impact and economic efficiency, or for use as electrodeposition coatings, aqueous dispersion compositions based on organic solvent / water mixtures have been proposed. For example, Patent Document 1 discloses an aqueous polyimide resin dispersion containing water and a polyimide resin (I) having carboxy groups and an acid value of 5 to 80. Patent Document 2 also discloses an aqueous dispersion composition containing a polyimide resin (A) having alkylene glycol bisanhydrotrimellitate residues and diisocyanate residues and an acid value of 15 to 100 mgKOH / g, and an amine (B) in an amount of 1 to 10 equivalents relative to the acid value of the polyimide resin (A).

[0003] Patent Document 3 discloses a suspension-type polyimide electrodeposition paint in which block copolymer polyimide particles having siloxane bonds in the molecular skeleton, anionic groups in the molecule, and a specific range of average particle size and particle size distribution are dispersed. Patent Document 4 also discloses an electrodeposition paint composition containing a polyimide block copolymer having siloxane bonds in the molecular skeleton and anionic groups in the molecule, a basic compound, a water-soluble polar solvent, and a poor solvent for the polyimide block copolymer in specific ratios. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-116874 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-199749 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-256318 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-234257 Summary of the Invention [Problem to be solved by the invention]

[0005] As aqueous dispersions of polyimide resins are applied to a variety of fields, including coatings, adhesives, and molded products (e.g., coating materials), the market demands highly reliable materials that combine electrical insulation, heat resistance, substrate adhesion, and storage stability. For example, coating materials used in electric vehicles (EVs) and hybrid vehicles (HVs) and component coating materials require not only electrical insulation but also long-term heat resistance to withstand the high temperatures encountered during driving. Furthermore, thermal shock resistance is also required for use in cold climates. Furthermore, for electrodeposition coating, materials with excellent coating appearance are required when applied to thick films.

[0006] The present disclosure has been made in view of the above background, and aims to provide an aqueous dispersion, an anionic electrodeposition paint, and a coated article that have excellent storage stability, can provide an excellent coating film appearance even when a thick film is applied, and have excellent coating film thermal shock resistance, insulating properties, heat resistance, and substrate adhesion. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that the problems of the present disclosure can be solved in the following aspects, and have thus completed the present disclosure. [1]: An aqueous dispersion containing a polyimide resin (A), a basic compound (B), an organic solvent (C), and water, The polyimide resin (A) has a bisphenol skeleton, a hydroxyl group, and an anionic group, An aqueous dispersion, wherein the ratio of the hydroxyl value to the anionic value of the polyimide resin (A), [hydroxyl value] / [anionic value], is 0.1 to 10. [2]: The polyimide resin (A) is a polyimide containing a repeating structural unit obtained by reacting an acid dianhydride (X) with a diamine (Y), at least one of the acid dianhydride (X) and the diamine (Y) has the bisphenol skeleton; The aqueous dispersion according to [1], wherein the total amount of the acid dianhydride (X1) having a bisphenol skeleton and the diamine (Y1) is 40 mol % or more relative to the total amount of the acid dianhydride (X) and the diamine (Y). [3]: The aqueous dispersion according to [2], wherein the polyimide resin (A) contains 5 to 55 mol % of a diamine having a hydroxyl group based on the total amount of the diamine components. [4] The aqueous dispersion according to any one of [1] to [3], wherein the basic compound (B) is an alkanolamine compound. [5]: Contains a water-soluble solvent as the organic solvent (C), The aqueous dispersion according to any one of [1] to [4], wherein the water-soluble solvent is contained in an amount of 30 to 80% by mass relative to 100% by mass of the aqueous dispersion. [6]: The aqueous dispersion according to any one of [1] to [5], wherein the polyimide resin (A) has a number average molecular weight of 7,500 to 50,000. [7]: An anionic electrodeposition paint comprising the aqueous dispersion according to any one of [1] to [6]. [8]: A coated article obtained by electrodeposition coating of a substrate using the anionic electrodeposition coating material according to [7]. [Effects of the Invention]

[0008] The present disclosure has the excellent effect of providing an aqueous dispersion, an anionic electrodeposition paint, and a coated article that have excellent storage stability, provide excellent coating film appearance even when applied to a thick film, and provide coating films with excellent thermal shock resistance, insulating properties, heat resistance, and substrate adhesion. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present disclosure will be described in detail below. Needless to say, other embodiments are also included within the scope of the present disclosure as long as they are consistent with the spirit of the present disclosure. In this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the lower and upper limits. Unless otherwise noted, the various components in this specification may be used independently, either singly or in combination of two or more types. The numerical values ​​described in this specification refer to values ​​obtained by the methods described in the Examples below, etc.

[0010] 1.Aqueous dispersion The aqueous dispersion of the present disclosure (hereinafter also referred to as the present aqueous dispersion) contains a polyimide resin (A), a basic compound (B), an organic solvent (C), and water. The polyimide resin (A) has a bisphenol skeleton, a hydroxyl group, and an anionic group. The ratio of the hydroxyl value to the anionic group value in the polyimide resin (A), i.e., [hydroxyl value] / [anionic group value], is 0.1 to 10. The hydroxyl value and the anionic group value can be determined by the methods described in the Examples below.

[0011] In this specification, the aqueous dispersion refers to a dispersion containing an organic solvent (C) and water, in which dispersed particles of polyimide resin (A) having a particle size of 0.03 μm or more are observed when the particle size of the dispersed particles is measured by dynamic light scattering. Polyimide resin (A) having a particle size of less than 0.03 μm may also be contained.

[0012] The average particle size of the polyimide resin (A) in the aqueous dispersion is preferably 0.03 to 5 μm, more preferably 0.04 to 3 μm, and even more preferably 0.05 to 1 μm, from the viewpoints of dispersion stability of the aqueous dispersion and uniform dispersibility when formed into a coating. The average particle size of the polyimide resin (A) can be adjusted by the type and content of the water-soluble solvent and the type and content of the basic compound.

[0013] This aqueous dispersion exhibits excellent storage stability. The main reason for this is believed to be that the dispersibility of the polyimide resin (A) in the aqueous dispersion is enhanced by combining the polyimide resin (A) with a basic compound (B) having a hydroxyl value / anionic value ratio of 0.1 to 10. Furthermore, the use of a polyimide resin having a relatively large molecular weight and a bisphenol skeleton that is both rigid and flexible reduces the number of imide bonds in the molecule, resulting in excellent solvent solubility and ease of aqueous dissolution, resulting in an aqueous dispersion with excellent storage stability.

[0014] Furthermore, this aqueous dispersion exhibits excellent thermal shock resistance, heat resistance, electrical insulation, and substrate adhesion. The main reason for this is believed to be that the hydroxyl groups and anionic groups moderately inhibit the interaction between the bisphenol skeleton, which has excellent heat resistance and electrical insulation, and the imide ring, thereby imparting stress relaxation properties and thereby enhancing thermal shock resistance. Furthermore, the use of a polyimide resin (A) having a bisphenol skeleton that combines rigidity and flexibility and a [hydroxyl value] / [anionic group value] ratio of 0.1 to 10 is believed to enhance the adhesion of the polyimide resin (A) to substrates. These factors are believed to have resulted in an aqueous dispersion capable of forming a coating film that combines excellent thermal shock resistance, heat resistance, electrical insulation, and substrate adhesion.

[0015] Furthermore, this aqueous dispersion provides excellent coating appearance even when applied in thick films. The main reason for this is believed to be that the use of a polyimide resin (A) with a bisphenol skeleton and a hydroxyl value / anionic value ratio of 0.1 to 10 as a blending component of the aqueous dispersion allows water and organic solvents to be adequately retained in the coating film, improving film-forming properties during application and drying. Furthermore, by preventing excessive drying of the coating surface, it is possible to prevent pinholes, popping, and loss of smoothness that tend to occur during thick-film application, resulting in a highly uniform and excellent coating appearance.

[0016] This aqueous dispersion has excellent heat resistance, electrical insulation, thermal shock resistance, and substrate adhesion, making it suitable for use as a wall coating for building materials, an exterior coating for automobiles, and a coating for sliding parts. It is also suitable as an anionic electrodeposition coating. It also has excellent substrate adhesion and insulating properties, making it suitable for various adhesive applications, including electronic materials such as circuit boards. Furthermore, it has excellent electrical insulation properties, making it suitable as an insulating coating for electric wires, etc. It also has excellent coatability, making it suitable for coating various articles. Each component is described in detail below.

[0017] 1-1. Polyimide resin (A) As described above, the polyimide resin (A) has a bisphenol skeleton, a hydroxyl group, and an anionic group. The ratio of the hydroxyl value to the anionic group value of the polyimide resin (A), i.e., [hydroxyl value] / [anionic group value], is 0.1 to 10. The polyimide resin (A) is a resin having an imide group, and includes polyimide resins, polyamideimide resins, polyesterimide resins, polyetherimide resins, and polyurethaneimide resins.

[0018] By combining a polyimide resin (A) having a [hydroxyl value] / [anionic group value] ratio of 0.1 to 10 with a basic compound (B), the aqueous dispersion exhibits excellent dispersibility. The lower limit of the [hydroxyl value] / [anionic group value] ratio is more preferably 0.5, and even more preferably 1.0. The upper limit of the [hydroxyl value] / [anionic group value] ratio is more preferably 8, and even more preferably 6.

[0019] The hydroxyl value of the polyimide resin (A) is preferably from 3 to 70 mgKOH / g, more preferably from 5 to 60 mgKOH / g, and even more preferably from 10 to 50 mgKOH / g, from the viewpoint of further improving thermal shock resistance.

[0020] The bisphenol skeleton refers to a skeleton represented by the following formula (1). [ka] Each "O" in the formula independently bonds to a hydrogen atom to form an OH group, or to an organic group to form an ether bond. The "O" is independently located in the ortho, meta, or para position relative to "A" in the formula. "A" is a divalent linking group. Of the carbon atoms constituting the two benzene skeletons in the formula, the carbon atoms other than those bonded to "A" and "O" are independently bonded to a hydrogen atom, an organic group, or a heteroatom.

[0021] A suitable example of A is C(R 1 )(R 2 ), C(R 1 )(R 2 )-Ar-C(R 1 )(R 2 ), C(CF3)2, and SO2. 1 , R 2 represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 6 to 12 carbon atoms, or an aromatic ring having 6 to 12 carbon atoms. Ar represents a divalent aryl group which may have a substituent. C(R 1 )(R 2 Specific examples of C(R) include C(CH), CH(CH), CH, C(CH)(Ph (phenyl group)), and C(CH)(CHCH). 1 )(R 2 )-Ar-C(R 1 )(R 2 Specific examples of C(CH3)2-Ph(phenylene group)-C(CH3)2 include C(CH3)2-Ph(phenylene group)-C(CH3)2. Among these, from the viewpoint of the solvent solubility of the polyimide resin (A) and the heat resistance, thermal shock resistance, and substrate adhesion of the resulting coating film, A in formula (1) is preferably C(CH3)2 or SO2.

[0022] Specific examples of bisphenol skeletons include bisphenol A (2,2-bis(4-hydroxyphenyl)propane), bisphenol AF (2,2-bis(4-hydroxyphenyl)hexafluoropropane), bisphenol S (bis(4-hydroxyphenyl)sulfone), bisphenol E (1,1-bis(4-hydroxyphenyl)ethane) skeleton, bisphenol F (bis(4-hydroxyphenyl)methane) skeleton, bisphenol AP (1,1-bis(4-hydroxyphenyl)-1-phenylethane) skeleton, bisphenol B (2,2-bis(4-hydroxyphenyl)butane) skeleton, bisphenol M (1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene) skeleton, and bisphenol P (1,4-bis(2-(4 Examples of suitable polyimide resins include bisphenol A (bis(4-hydroxyphenyl)-2-propyl)benzene), bisphenol BP (bis(4-hydroxyphenyl)diphenylmethane), bisphenol C (2,2-bis(3-methyl-4-hydroxyphenyl)propane), bisphenol C (bis(4-hydroxyphenyl)-2,2-dichloroethylene), bisphenol G (2,2-bis(4-hydroxy-3-isopropylphenyl)propane), bisphenol PH (5,5'-(1-methylethylidene)-bis(1,1'-(bisphenyl)-2-ol)propane), bisphenol TMC (1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane), and bisphenol Z (1,1-bis(4-hydroxyphenyl)cyclohexane). Among these, bisphenol A and bisphenol S skeletons are preferred from the viewpoints of the solvent solubility of the polyimide resin (A) and the heat resistance, thermal shock resistance, and substrate adhesion of the resulting coating film.

[0023] The hydroxyl groups in the polyimide resin (A) can be introduced into side groups, side chains, and molecular chain terminals. The hydroxyl groups may be hydroxyl groups of a bisphenol skeleton or hydroxyl groups of other skeletons. The type of hydroxyl group is not limited, but from the viewpoint of improving the storage stability of the aqueous dispersion, substrate adhesion, etc., phenolic hydroxyl groups are preferred. Furthermore, from the viewpoint of improving the thermal shock resistance of the coating film, hydroxyl groups of a bisphenol skeleton are preferred, and phenolic hydroxyl groups of a bisphenol skeleton are more preferred.

[0024] An anionic group is a group that exhibits anionic properties by ionization in water. Specific examples of anionic groups include a carboxy group, a sulfo group, a phosphate group, and salts thereof. Among these, a carboxy group or a salt of a carboxy group is preferred in terms of ease of synthesis. By having an acid anhydride group at the molecular chain terminal, two equivalents of carboxy groups generated by ring-opening the acid anhydride group can be easily neutralized with a basic compound (B) to make the dispersion water-soluble, thereby improving dispersibility and providing an aqueous dispersion with excellent storage stability.

[0025] By preparing an aqueous dispersion using a polyimide resin (A) having a bisphenol skeleton, a hydroxyl group, and an anionic group, and having a [hydroxyl group value] / [anionic group value] ratio of 0.1 to 10, it is possible to obtain a coating film with excellent appearance even when applied in a thick film, and to obtain a coating film with excellent thermal shock resistance, insulating properties, heat resistance, and substrate adhesion.

[0026] A suitable example of the polyimide resin (A) is a polyimide containing a repeating structural unit obtained by the reaction of an acid dianhydride (X) with a diamine (Y). The repeating structural unit obtained by the reaction of the acid dianhydride (X) with the diamine (Y) preferably accounts for 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, and may even be 100 mol% of the total repeating structural units of the polyimide resin (A). Diisocyanate may be used instead of the diamine (Y). Furthermore, a tetracarboxylic acid derivative such as a tetracarboxylic acid or a tetracarboxylic acid diester may be used as a monomer instead of the acid dianhydride (X). While examples using the acid dianhydride (X) and the diamine (Y) as monomers will be described below, the polyimide resin (A) of the present disclosure also includes polyimides in which the "acid dianhydride (X)" is replaced with a tetracarboxylic acid derivative such as a "tetracarboxylic acid" or a "tetracarboxylic acid diester." Similarly, the polyimide resin (A) of the present disclosure also includes polyimides in which the "diamine (Y)" is replaced with a "diisocyanate."

[0027] In order to easily introduce a bisphenol skeleton into the main chain skeleton of the polyimide resin (A), it is preferable that at least one of the acid dianhydride (X) and the diamine (Y) has a bisphenol skeleton. From the viewpoint of improving the thermal shock resistance and substrate adhesion of the resulting coating film, the total of the acid dianhydride (X1) having a bisphenol skeleton (hereinafter also referred to as acid dianhydride (X1) or simply (X1)) and the diamine (Y1) having a bisphenol skeleton (hereinafter also referred to as diamine (Y1) or simply (Y1)) is preferably 40 mol% or more relative to the total amount of the acid dianhydride (X) and the diamine (Y). The lower limit is more preferably 50 mol%, even more preferably 55 mol%, and may even be 100 mol%.

[0028] From the viewpoint of further improving the thermal shock resistance and substrate adhesion of the resulting coating film, it is preferable to use a diamine (Y1) having a bisphenol skeleton, it is more preferable to use an acid dianhydride (X1) having a bisphenol skeleton, and it is even more preferable to use an acid dianhydride (X1) having a bisphenol skeleton and a diamine (Y1) having a bisphenol skeleton in combination.

[0029] From the viewpoint of improving the storage stability of the aqueous dispersion, the amount of the diamine (Y2) having a hydroxyl group (hereinafter also referred to as diamine (Y2) or (Y2)) is preferably 5 to 55 mol % relative to the total amount of diamine (Y). The lower limit is more preferably 7 mol %, and even more preferably 10 mol %. The upper limit is more preferably 50 mol %, and even more preferably 45 mol %.

[0030] Examples of the acid dianhydride (X1) having a bisphenol skeleton include 4,4'-(4,4'-isopropylidenediphenoxy)bisphthalic dianhydride, 4,4'-(4,4'-methylenediphenoxy)bisphthalic dianhydride, and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride. Substituents may be introduced into any position of these compounds. The same applies to the following compounds.

[0031] Examples of diamines (Y1) having a bisphenol skeleton include 4,4'-isopropylidenebis[(4-aminophenoxy)benzene], 4,4'-(hexafluoroisopropylidene)bis[(4-aminophenoxy)benzene], bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)phenylsulfone, and 6,6'-[(1-methylethylidene)-bis(-4,1-phenyleneoxy)]-bis-3-pyridine-amine.

[0032] Among the diamines (Y2) having a hydroxyl group, examples of diamines corresponding to the diamine (Y1) having a bisphenol skeleton include bis(3-amino-4-hydroxyphenyl)hexafluoropropane, bis(3-amino-4-hydroxyphenyl)sulfone, bis(3-amino-4-hydroxyphenyl)propane, bis(3-amino-4-hydroxyphenyl)methylene, bis(3-amino-4-hydroxyphenyl)fluorene, bis(3-amino-4-hydroxyphenyl)ether, and 4,4'-diamino-4''-hydroxytriphenylmethane.

[0033] Among the diamines (Y2) having a hydroxyl group, diamines that do not fall under the category of diamine (Y1) include aromatic diamines such as 2,2'-ditrifluoromethyl-5,5'-dihydroxyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-5,5'-dihydroxybenzidine, and 4,4'-diamino-3,3'-dihydroxybiphenyl.

[0034] The acid dianhydride (X2) other than (X1) is not particularly limited. For example, pyromellitic anhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 3,3',4 aromatic tetracarboxylic acid dianhydrides such as 4'-diphenylsulfonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, p-phenylenebis(trimellitic acid monoester acid anhydride), and ethylene glycol bisanhydrotrimellitate; Cyclobutane-1,2,3,4-tetracarboxylic acid, cyclopentane-1,2,3,4-tetracarboxylic acid, cyclohexane-1,2,3,4-tetracarboxylic acid, cyclohexane-1,2,4,5-tetracarboxylic acid, 1-carboxymethyl-2,3,5-cyclopentanetricarboxylic acid, 3-carboxymethyl-1,2,4-cyclopentanetricarboxylic acid, rel-dicyclohexyl-3,3',4,4'-tetracarboxylic acid, tricyclo[4.2.2.02,5]de carboxymethylbicyclo[2.2.1]heptane-2,3,6-tricarboxylic acid, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic acid, bicyclo[2.2.2]octane-7-ene-2,3,6,7-tetracarboxylic acid, bicyclo[3.3.0]octane-2,4,6,7-tetracarboxylic acid, 7,8-diphenylbicyclo[2.2.2]octane-7-ene-2,3,5,6-tetracarboxylic acid, Cyclo-, bicyclo-, and tricyclotetracarboxylic acids such as 4,8-diphenyl-1,5-diazabicyclooctane-2,3,6,7-tetracarboxylic acid, 9-oxatricyclo[4.2.1.02,5]nonane-3,4,7,8-tetracarboxylic acid, and 9,14-dioxopentacyclo[8.2.11,11.14,7.02,10.03,8]tetradecane-5,6,12,13-tetracarboxylic acid; and 2,8-dioxaspiro[4.5]decane-1,3,7,9-tetradecane. Pyrocyclic tetracarboxylic acids; alicyclic tetracarboxylic dianhydrides such as 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 1,3,3a,4,5,9b-hexahydro-5(tetrahydro-2,5-dioxo-3-furanyl)naphtho[1,2-c]furan-1,3-dione, and 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride; Examples include aliphatic tetracarboxylic acid dianhydrides such as 1,2,3,4-butanetetracarboxylic acid, 1,2,3,4-pentanetetracarboxylic acid, 1,2,4,5-pentanetetracarboxylic acid, 1,2,3,4-hexanetetracarboxylic acid, and 1,2,5,6-hexanetetracarboxylic acid. From the viewpoint of the heat resistance and thermal shock resistance of the coating film, aromatic tetracarboxylic acid dianhydrides are preferred.

[0035] Examples of diamines (Y4) having an anionic group (hereinafter also referred to as diamine (Y4) or (Y4)) include 3,5-diaminobenzoic acid, 2,4-diaminophenylacetic acid, 2,5-diaminoterephthalic acid, 3,3'-dicarboxy-4,4'-diaminodiphenylmethane, 3,5-diamino-p-toluic acid, 3,5-diamino-2-naphthalenecarboxylic acid, 1,4-diamino-2-naphthalenecarboxylic acid, 2,5-diaminobenzenesulfonic acid, 4,4'-diamino-2,2'-stilbenedisulfonic acid, and o-tolidinedisulfonic acid.

[0036] Other diamines (Y3) not falling under (Y1), (Y2), and (Y4) include 1,4-diaminobenzene, 1,3-diaminobenzene, 1,2-diaminobenzene, 1,5-diaminonaphthalene, 1,8-diaminonaphthalene, 2,3-diaminonaphthalene, 2,6-diaminotoluene, 2,4-diaminotoluene, 3,4-diaminotoluene, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diamino-1,2-diphenylethane, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, and 3,3'-diaminodiphenyl sulfone; alicyclic diamines such as isophoronediamine, norbornanediamine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 4,4'-diaminodicyclohexylmethane, and piperazine; Aliphatic diamines such as ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,9-nonanediamine, 1,12-dodecamethylenediamine, metaxylenediamine, and dimer diamine are included. Aromatic diamines are preferred from the viewpoint of the heat resistance and thermal shock resistance of the resulting coating film.

[0037] The polyimide resin (A) may have a siloxane skeleton for the purpose of improving the insulating properties, thermal shock resistance, etc. of the coating film. Examples of diamines having a siloxane skeleton include KF-8010, X-22-161A, X-22-161B, KF-8012, X-22-9409, and X-22-1660B-3 manufactured by Shin-Etsu Chemical Co., Ltd., BY-16-853U and BY-16-853 manufactured by Dow-Toray, and Silaplane FM-3311 manufactured by JNC Corporation.

[0038] The molecular chain terminals of the polyimide resin (A) are not limited. From the viewpoint of improving the coating appearance, polyimide resins (A) having anionic groups at the molecular chain terminals are preferred. From the viewpoint of ease of synthesis, a method in which the molecular chain terminals are acid anhydride groups and then carboxy groups are obtained by ring-opening is preferred. The molecular chain terminals refer to the repeating structural units that constitute the molecular chain of the polyimide resin (A) at the terminals, or non-repeating structures connected to the terminals. The molecular chain terminals of the polyimide resin (A) may be converted to amino groups, hydroxyl groups, alkyl groups, alkylene groups, aryl groups, etc.

[0039] The number average molecular weight Mn of the polyimide resin (A) is not particularly limited, but from the viewpoint of improving the film uniformity and reliability of the mechanical properties, Mn is preferably 7,500 to 50,000. The lower limit of Mn is more preferably 10,000, and even more preferably 15,000. The upper limit of Mn is more preferably 45,000, and even more preferably 40,000.

[0040] From the viewpoint of achieving better heat resistance and thermal shock resistance, the polyimide resin (A) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the total solid content in the aqueous dispersion.

[0041] The polyimide resin (A) can be produced by known methods. For example, a polyimide precursor, a polyamic acid resin or a polyamic acid ester resin, is cyclized by heating to convert it to an imide group. For example, a polyamic acid resin can be synthesized by dissolving a monomer containing an acid dianhydride and a diamine in a solvent and stirring the mixture at a temperature of 60 to 120°C for 0.1 to 2 hours to polymerize the monomer. Synthesis conditions are preferably such that 90% or more of each monomer is consumed, more preferably 95% or more. To introduce an anionic group into the molecular chain terminal, the amount of acid dianhydride is preferably greater than the amount of diamine. The equivalent ratio (molar ratio) of the acid dianhydride to the diamine, etc., can be, for example, 0.9 to 1, preferably 0.94 to 1. Another method involves reacting an acid dianhydride with a diisocyanate to obtain a polyimide precursor, followed by the production of a polyimide resin.

[0042] Examples of methods for synthesizing polyamic acid ester resins include a method in which a diester is obtained from a tetracarboxylic dianhydride and an alcohol, and then the diester is reacted with a diamine in the presence of a condensing agent, and a method in which a diester is obtained from a tetracarboxylic dianhydride and an alcohol, and then the remaining dicarboxylic acid is converted into an acid chloride and reacted with a diamine.

[0043] Examples of organic solvents used in polymerization include N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, and cresol. Solvents can be used alone or in combination. Aromatic hydrocarbons such as xylene and toluene can also be used in combination.

[0044] The method for imidizing a polyimide precursor to obtain a polyimide resin is not particularly limited, but an example is a method in which the polyimide precursor is heated in a solvent at a temperature of 80 to 400°C for 0.5 to 50 hours. A catalyst and / or a dehydrating agent may be used as needed. Examples of reaction catalysts include aliphatic tertiary amines such as triethylamine, aromatic tertiary amines such as dimethylaniline, and heterocyclic tertiary amines such as pyridine, picoline, and isoquinoline. Examples of dehydrating agents include aliphatic acid anhydrides such as acetic anhydride and aromatic acid anhydrides such as benzoic anhydride.

[0045] The imidization rate (the rate of imide ring formation) is not limited, but is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more, from the viewpoint of the heat resistance and thermal shock resistance of the resulting coating film. The imidization rate in this specification can be easily determined by the following method. First, the infrared absorption spectrum of the polyimide resin is measured, and the absorption peak of the imide ring structure (1780 cm -1 Near 1380cm -1 Next, the polyimide resin is heat-treated at 350°C for 1 hour, and the infrared absorption spectrum is measured. This is used as a sample with an imidization rate of 100%, and the 1380cm wavelength of the polyimide resin before and after the heat treatment is measured. -1 By comparing the peak intensity with that of the peaks around the peak, the imide group content in the polyimide resin before heat treatment can be calculated, and the imidization rate can be determined.

[0046] A simple method for introducing hydroxyl groups into the polyimide resin (A) is to synthesize the polyimide resin using a monomer having a hydroxyl group. A preferred method for introducing phenolic hydroxyl groups is to introduce phenolic hydroxyl groups derived from a monomer derived from a bisphenol skeleton. Hydroxyl groups may be introduced into side groups, side chains, and / or molecular chain terminals after the synthesis of the polyimide resin. Hydroxyl groups other than phenolic hydroxyl groups, i.e., alcoholic hydroxyl groups, may be introduced by modifying carboxyl groups or phenolic hydroxyl groups introduced into side groups with a monofunctional epoxy. Examples of monofunctional epoxy compounds include aliphatic monofunctional epoxy compounds such as Denacol EX-121, Denacol EX-171, and Denacol EX-192, all of which are manufactured by Nagase ChemteX Corp., and aromatic monofunctional epoxy compounds such as Denacol EX-141, Denacol EX-142-IM, Denacol EX-145, Denacol EX-146, Denacol EX-146P, and Denacol EX-731, all of which are manufactured by Nagase ChemteX Corp. The hydroxyl value of the polyimide resin (A) can be adjusted by the amount of hydroxyl group-containing monomer charged, and the introduction rate of hydroxyl groups into molecular chain terminals, side groups, and / or side chains.

[0047] Examples of methods for introducing anionic groups into polyimide resin (A) include synthesizing the polyimide resin using a monomer having an anionic group, and synthesizing the polyimide resin (A) and then introducing anionic groups into side groups, side chains, and / or molecular chain terminals. The anionic group value of polyimide resin (A) can be adjusted by the amount of monomer having anionic groups charged, and the introduction rate of anionic groups into molecular chain terminals, side groups, and / or side chains. From the viewpoint of ease of synthesis, the introduction of anionic groups into molecular chain terminals is preferred. A simple method is to convert the molecular chain terminals into acid anhydride groups and introduce carboxyl groups by ring-opening the acid anhydride groups.

[0048] 1-2. Basic compounds (B) The basic compound (B) is used to neutralize the anionic groups present in the polyimide resin (A) and impart hydrophilicity. When the polyimide resin (A) has an acid anhydride group, the acid anhydride group undergoes ring-opening, and the resulting carboxyl group is neutralized by the basic compound (B), thereby imparting hydrophilicity to the polyimide resin (A). Examples of the basic compound (B) include organic amine compounds, ammonia, and alkali metal hydroxides.

[0049] Examples of the organic amine compound include alkylamine compounds such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, tripropylamine, monobutylamine, dibutylamine, tributylamine, benzylamine, N-methylbenzylamine, and dimethylbenzylamine; Alkanolamine compounds such as monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine (also known as dimethylaminoethanol), N,N-diethylethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolamine, monoisopropanolamine, diisopropanolamine, and triisopropanolamine; Examples thereof include heterocyclic amine compounds such as pyrrole, imidazole, oxazole, pyrazole, thiazole, pyridine, pyridazine, pyrimidine, pyrazine, piperidine, piperazine, morpholine, and N-methylmorpholine. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. The basic compound (B) can be used alone or in combination of two or more. The basic compound (B) can be added at any time, either once or in multiple portions.

[0050] The basic compound (B) preferably contains an organic amine compound, and among organic amine compounds, an alkanolamine compound is preferred. By containing the alkanolamine compound, the storage stability of the aqueous dispersion is improved. In addition, the film-forming properties of the aqueous dispersion are improved, resulting in a better coating film appearance.

[0051] The amount of the basic compound (B) is preferably 0.1 to 5.0 equivalents relative to the anionic groups in the polyimide resin (A), more preferably 0.3 to 4.0 equivalents, and particularly preferably 0.5 to 3.0 equivalents. When the amount is 0.1 to 5.0 equivalents, the storage stability of the aqueous dispersion is improved, the film-forming properties of the aqueous dispersion are improved, and a better coating appearance is obtained. As a result, the coating film has better thermal shock resistance, insulating properties, substrate adhesion, etc.

[0052] 1-3. Organic solvent (C) and water The aqueous dispersion contains an organic solvent (C) and water. The inclusion of the organic solvent (C) improves film-forming properties, and can improve the coating appearance, the coating film's adhesion to the substrate, thermal shock resistance, and insulating properties. The organic solvent (C) may be used singly or in combination of two or more.

[0053] The content of the organic solvent (C) is preferably 30 to 80 mass% of 100 mass% of the aqueous dispersion, more preferably 35 to 75 mass%, and even more preferably 40 to 70 mass%, from the viewpoint of improving the thermal shock resistance, insulating properties, substrate adhesion, etc. of the coating film. Also, a better coating film appearance is obtained. The content of water is preferably 5 to 60 mass%, more preferably 10 to 50 mass%, and even more preferably 15 to 40 mass%, from 100 mass% of the aqueous dispersion.

[0054] The organic solvent (C) preferably contains a water-soluble solvent (C-1). 5 A solvent that, when mixed with an equal volume of water at 20°C (at 20°C / Pa), maintains a uniform appearance when visually inspected.

[0055] Examples of the water-soluble solvent (C-1) include cyclic amides such as N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone; acyclic amides such as N,N-dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, and hexamethylphosphoric triamide; cyclic esters such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone; acyclic esters such as methyl lactate, ethyl lactate, and ethylene glycol monomethyl ether acetate; Ureas such as tetramethylurea and 1,3-dimethyl-2-imidazolidinone; Sulfoxides such as dimethyl sulfoxide; alkylene glycol dialkyl ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and triethylene glycol dimethyl ether; cyclic ethers such as tetrahydrofuran and 1,4-dioxane; Alcohols such as methanol, ethanol, isopropyl alcohol, t-butanol, 1-propanol, and diacetone alcohol; alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono(iso)propyl ether, ethylene glycol mono(iso)butyl ether, ethylene glycol mono-tert-butyl ether, 3-methoxybutanol, 3-methyl-3-methoxybutanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono(iso)propyl ether, diethylene glycol mono(iso)butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono(iso)propyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol monoethyl ether; Examples include ketones such as acetone and dihydrolevoglucosenone.

[0056] The water-soluble solvent (C-1) is preferably an aprotic solvent from the viewpoint of the solubility of the polyimide resin (A). Among aprotic solvents, the water-soluble solvent (C-1) is more preferably a cyclic amide, acyclic amide, or cyclic ester from the viewpoint of the storage stability of the aqueous dispersion and the film-forming property during electrodeposition coating, and among these, cyclic esters are even more preferred from the viewpoint of safety.

[0057] The water-soluble solvent (C-1) is preferably present in an amount of 30 to 80 mass %, more preferably 35 to 75 mass %, and even more preferably 40 to 70 mass %, based on 100 mass % of the aqueous dispersion, from the viewpoint of improving the thermal shock resistance, insulating properties, substrate adhesion, etc. of the coating film, and when used as an electrodeposition coating, a better coating film appearance can be obtained.

[0058] The proportion of the water-soluble solvent (C-1) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on 100% by mass of the organic solvent (C). When the content of the water-soluble solvent (C-1) is 50% by mass or more, the storage stability of the aqueous dispersion is superior, and the film-forming properties during coating and baking are improved, resulting in a superior coating appearance. As a result, the coating film has superior thermal shock resistance, insulating properties, substrate adhesion, etc.

[0059] The organic solvent other than the water-soluble solvent (C-1) is not particularly limited, but it is preferable to use an organic solvent that can dissolve or disperse each component such as the polyimide resin (A). 5It refers to a mixture that, when gently stirred at a pressure of 100 Pa with an equal volume of pure water at a temperature of 20°C, does not maintain a uniform appearance when visually inspected after the flow has subsided. Specific examples include hexane, heptane, octane, decane, amylbenzene, isopropylbenzene, ethylbenzene, o-xylene, m-xylene, p-xylene, 1,2-diethylbenzene, 1,3-diethylbenzene, 1,4-diethylbenzene, cyclohexylbenzene, 2,6-dimethylnaphthalene, p-cymene, styrene, tetralin, α-pinene, β-pinene, dodecylbenzene, toluene, mesitylene, and other hydrocarbons, as well as Swasol 1000, Swasol 1500 (all manufactured by Maruzen Petrochemical Co., Ltd.), T-SOL100FLUID, and T-SOL150FLUID (all manufactured by JXTG Nippon Oil & Energy Corporation); Alcohols such as n-amyl alcohol, s-amyl alcohol, t-amyl alcohol, isoamyl alcohol, isobutyl alcohol, 2-ethylbutanol, 2-ethylhexanol, 2-octanol, n-octanol, neopentyl alcohol, n-butanol, s-butanol, n-hexanol, 2-heptanol, 3-heptanol, n-heptanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-2-butanol, 4-methyl-2-pentanol, cyclohexanol, and benzyl alcohol; alkylene glycol monoalkyl ethers such as ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, propylene glycol mono(iso)butyl ether, dipropylene glycol mono(iso)propyl ether, and dipropylene glycol mono(iso)butyl ether; Ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, methylcyclohexanone, and isophorone; Esters such as ethyl acetate, butyl acetate, dimethyl succinate, dimethyl glutarate, dimethyl adipate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, 3-methoxybutyl acetate, ethylene glycol monobutyl ether acetate, 3-methyl-3-methoxybutyl acetate, and FlexiSolv DBE esters (manufactured by INVISTA); ethers such as dimethyl ether, diethyl ether, diisopropyl ether, and anisole; alkylene glycol dialkyl ethers such as ethylene glycol di(iso)butyl ether, diethylene glycol di(iso)butyl ether, diethylene glycol dihexyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di(iso)propyl ether, propylene glycol di(iso)butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol di(iso)propyl ether, and dipropylene glycol di(iso)butyl ether; Examples include cyclic ethers such as 2-methyltetrahydrofuran, tetrahydropyran, and 4-methyltetrahydropyran.

[0060] 1-4. Hardener The aqueous dispersion may further contain a curing agent for the purpose of improving the thermal shock resistance and substrate adhesion of the coating film. Examples of curing agents that can be used include blocked polyisocyanate compounds, epoxy group-containing compounds, phenolic resins, amino resins, carbodiimide group-containing compounds, maleimide group-containing compounds, metal chelate compounds, and β-hydroxyalkylamide compounds. Among these, blocked polyisocyanate compounds and epoxy group-containing compounds are more preferred, with blocked polyisocyanate compounds being particularly preferred. One or more curing agents may be added. The curing agent can react with the hydroxyl group, acid anhydride group, and carboxyl group in the polyimide resin (A), and may also be one that cures with itself.

[0061] The blocked polyisocyanate compound preferably has three or more isocyanate groups from the viewpoints of thermal shock resistance and substrate adhesion.

[0062] The content of the curing agent is preferably 1 to 40 parts by mass, more preferably 3 to 35 parts by mass, and even more preferably 5 to 30 parts by mass, relative to 100 parts by mass of the polyimide resin (A). By using 1 to 40 parts by mass of the curing agent, the thermal shock resistance and substrate adhesion of the coating film are further improved without impairing the storage stability of the coating material and the heat resistance of the coating film.

[0063] 1-5.Other ingredients A filler may be added to the aqueous dispersion for the purpose of improving the insulating properties, heat resistance, thermal shock resistance, etc. of the coating film. The filler is not particularly limited, and examples thereof include crystalline silica, amorphous silica, hollow silica, porous silica, mica, talc, kaolin, clay, hydrotalcite, pyrophyllite, sericite, vermiculite, smectite, bentonite, stevensite, montmorillonite, nontronite, wollastonite, xonotlite, silicon nitride, boron nitride, aluminum nitride, calcium hydrogen phosphate, calcium phosphate, glass flakes, glass beads, wollastonite, hydrated glass, calcium titanate, sepiolite, magnesium sulfate, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, barium hydroxide, calcium hydroxide, titanium oxide, tin oxide, aluminum oxide, magnesium oxide, and the like. Examples of the filler include magnesium, zirconium oxide, zinc oxide, molybdenum oxide, antimony oxide, nickel oxide, zinc carbonate, magnesium carbonate, calcium carbonate, barium carbonate, zinc borate, aluminum borate, polytetrafluoroethylene and its modified products, tetrafluoroethylene-perfluoroalkyl vinyl ether, tetrafluoroethylene-ethylene, tetrafluoroethylene-hexafluoropropylene, tetrafluoroethylene-vinylidene fluoride, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether, polychlorotrifluoroethylene, chlorotrifluoroethylene-ethylene, chlorotrifluoroethylene-vinylidene fluoride, polyvinylidene fluoride, polyvinyl fluoride, etc. The shape of the filler is not particularly limited, and examples include spherical, powdery, fibrous, needle-like, and scaly shapes.

[0064] If necessary, a lubricant such as wax can be added to the aqueous dispersion to prevent scratches on the coating film. Suitable waxes include animal and vegetable waxes such as carnauba wax, lanolin wax, palm oil, candelilla wax, and rice wax, petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum, and synthetic waxes such as polyolefin wax and polytetrafluoroethylene (PTFE) wax.

[0065] The aqueous dispersion may also contain colorants such as pigments and dyes, as needed. Examples of pigments include chromatic pigments (e.g., quinacridone, phthalocyanine, and azo pigments) and achromatic pigments (e.g., titanium oxide, iron oxide, aluminum, and carbon black).

[0066] Furthermore, for the purpose of improving storage stability, electrodeposition coating properties, and the physical properties of the coating film formed, the aqueous dispersion may contain curing catalysts, leveling agents, antifoaming agents, dispersants, surfactants, preservatives, mildew inhibitors, rust inhibitors, pH adjusters, viscosity adjusters, flame retardants, antioxidants, ion scavengers, antibacterial agents, antistatic agents, antiblocking agents, ultraviolet absorbers, infrared absorbers, electromagnetic wave shielding agents, and the like, depending on the respective purposes and uses.

[0067] <Electrical conductivity> The electrical conductivity of the aqueous dispersion is not particularly limited. When the aqueous dispersion is used as an electrodeposition coating, the electrical conductivity of the aqueous dispersion at a coating temperature of 25°C is usually 10 μS / cm or more and 2500 μS / cm or less, more preferably 10 μS / cm or more and 500 μS / cm or less, and even more preferably 10 μS / cm or more and less than 300 μS / cm. By setting the conductivity within this range, a sudden increase in the electrical resistance value of the coating film can be suppressed, and an excellent coating film appearance can be obtained even when a thick film is applied. The electrical conductivity can be measured using a commercially available electrical conductivity meter in accordance with JIS K 0130 (general rules for measuring electrical conductivity). The electrical conductivity can be controlled by, for example, the amount of the basic compound (B) or organic solvent (C) added to neutralize the carboxyl group, and can be increased by increasing the amount of the basic compound (B) or decreasing the amount of the organic solvent (C).On the other hand, the electrical conductivity decreases by decreasing the amount of the basic compound (B) or increasing the amount of the organic solvent (C).

[0068] The aqueous dispersion can be obtained by neutralizing some or all of the anionic groups present in the polyimide resin (A) with a basic compound (B) and adding water while stirring. When the anionic groups are carboxy groups, some or all of the carboxy groups generated by ring-opening the carboxy groups and / or acid anhydride groups present in the polyimide (A) are neutralized with the basic compound (B), followed by adding water while stirring. Specifically, the polyimide resin (A) is dissolved in an organic solvent (C), and neutralization is carried out by adding the basic compound (B) while stirring at a temperature of 10 to 120°C, preferably 20 to 100°C. Water is then gradually added while stirring, and, if necessary, the organic solvent (C), a curing agent, etc. are added and mixed by stirring. The organic solvent (C) and the curing agent may be added before adding water. The nonvolatile content of the aqueous dispersion is preferably 1 to 20% by mass, more preferably 1 to 15% by mass.

[0069] Any component of the aqueous dispersion can be added at any time. Mixing, dispersing, or dissolving during production of the aqueous dispersion can be carried out using, for example, a mixer, disperser, kneader, or the like, such as a homomixer, homogenizer, disperser, paint shaker, bead mill, sand mill, in-line mixer, or high shear mixer.

[0070] 2. Anionic electrodeposition paints and coated articles The aqueous dispersion can be suitably used as an anionic electrodeposition paint. The coated article of the present disclosure (hereinafter also referred to as the present coated article) is obtained by electrodeposition coating of the present electrodeposition paint on a substrate.

[0071] A coating film using this electrodeposition paint can be formed by a known method. Using a typical anionic electrodeposition coating technique, the charged coating film-forming components in this aqueous dispersion are electrophoresed and deposited on the substrate, followed by drying to form a coating film. For example, electrodeposition coating is performed by completely or partially immersing the substrate as the anode in an electrodeposition bath filled with the aqueous dispersion, immersing a counter electrode in the anode, and applying a voltage between them. The substrate, with the aqueous dispersion and its resin component attached, is then removed and the excess aqueous dispersion is washed off in a water bath, followed by drying to obtain a coated article. The coating conditions for anionic electrodeposition coating are not particularly limited and can be adjusted appropriately depending on the type and shape of the substrate, the properties of the aqueous dispersion, the size and shape of the electrodeposition bath, and the intended use and purpose of the substrate. For example, the aqueous dispersion temperature can be 10 to 50°C, the applied voltage can be 1 to 400V, and the electrodeposition time can be 10 seconds to 30 minutes. Drying conditions after coating can be, for example, 140 to 250°C and 3 to 60 minutes. Prior to the above step, preliminary drying can be performed, for example, at 40 to 130°C and for 3 to 60 minutes. The thickness of the coating film is, for example, about 1 to 300 μm.

[0072] The aqueous dispersion is suitable for use in forming a coating film that coats a substrate. The substrate is not particularly limited as long as it is conductive and can be subjected to electrodeposition coating. Examples of substrates include copper materials, iron materials, aluminum or anodized aluminum materials, nickel materials, stainless steel materials, magnesium materials, plated materials or plated articles, die-cast metal materials, and surface-treated metal materials, as well as molded products thereof. Electrodeposition-coated articles have excellent insulation properties, heat resistance, and thermal shock resistance, making them suitable for use as insulating coatings for automobile parts such as motors and powertrains. They are also suitable as coating materials for electric wires such as enameled wires.

[0073] 3. Adhesives, covering materials, etc. The aqueous dispersion can be used as an anionic electrodeposition paint, as well as ordinary paints, coating materials, adhesives, adhesive sheets, covering materials, various substrates such as flexible substrates for electronic circuits, circuit board materials such as cover films and reinforcing plates, carrier materials, release materials, molded products, etc.

[0074] Examples of coating methods other than electrodeposition coating of the present aqueous dispersion include spin coating, roll coating, die coating, flow coating, dip coating, spray coating, and bar coating. The coating method can be appropriately selected depending on the type, shape, and application of the substrate. Drying conditions after coating can be, for example, 140 to 250°C for 3 to 60 minutes. Prior to the above step, pre-drying can be performed under conditions such as 40 to 130°C for 3 to 60 minutes. The thickness of the coating film is, for example, about 1 to 50 μm. [Example]

[0075] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples. In the examples, "parts" and "%" represent "parts by mass" and "% by mass".

[0076] <Measurement method> The numerical values ​​in this example were obtained by the following method. (i) Number average molecular weight (Mn) The Mn of the polyimide resin (A) was determined by dissolving the dried resin in tetrahydrofuran to prepare a 0.5% solution, and then filtering the solution through a membrane filter (13HP045AN manufactured by ADVANTEC, pore size 0.45 μm) using the following equipment and measurement conditions. Apparatus: HLC-8420-GPC system (Tosoh Corporation) Column: TSKgel-Super Multipore HZ-M 4.6 mm I.D. x 15 cm x 3 (molecular weight measurement range: 2,000 to approximately 2,000,000) Elution solvent: tetrahydrofuran Standard material: Polystyrene (manufactured by Tosoh Corporation) Flow rate: 0.6mL / min Amount of sample solution used: 10 μL Column temperature: 40℃

[0077] (ii) Measurement of hydroxyl value The total mass V1 (g) of the monomers used in the synthesis of polyimide resin (A) (hereinafter also referred to as the total amount of monomers) is calculated. Next, the amount of water dehydrated by the imidization reaction is subtracted from the total amount of monomers to determine the mass V2 (g) of polyimide resin (A). V2(g) = V1(g) - diamine monomer amount (mol) × 2 × 18 Thereafter, the amount of hydroxyl groups V3 (mmol) in the polyimide resin (A) is calculated using the following formula: When two or more types of monomers having hydroxyl groups are used, the total value is used. V3 (mmol) = mass of monomer having hydroxyl group (g) / molecular weight of monomer having hydroxyl group (g / mol) × number of hydroxyl groups in monomer having hydroxyl group × 1000 Next, the hydroxyl value in the polyimide resin (A) is calculated. V3(mmol) / V2(g)×56.1(mg / mmol)=V4(mgKOH / g)

[0078] (iii) Measurement of anionic radical value The amount of anionic groups V5 (mmol) in the polyimide resin (A) is determined, for example, as follows. When there are multiple monomers having anionic groups, the total value is used. For V1 and V2, the same explanation as for the hydroxyl value is applied. [α]: Amount of anionic group derived from the monomer (mmol) (group that does not react during synthesis) V5α (mmol) = mass (g) of monomer having an anionic group / molecular weight of monomer having an anionic group × number of anionic groups in monomer having an anionic group × 1000 [β]: Amount (mmol) of anionic groups generated after synthesis of polyimide resin (A) (when the acid anhydride groups are converted to dicarboxylic acid in polyimide resin (A) having acid anhydride groups at both ends of the molecular chain) The number average molecular weight of the polyimide resin (A) is measured, and then the amount of anionic groups (mmol) is calculated using the following formula. V5β (mmol) = 1 (g) / Mn of polyimide resin (A) × 1000 × 2 × 2 V5 (mmol) is calculated as the sum of V5α and V5β. In addition, when polyimide resin (A) is obtained by introducing anionic groups into side chains or the like after obtaining a polyimide resin, V5γ (mmol) is calculated taking into account the amount introduced and the reaction rate, and the sum of V5α and V5β is taken as V5. Next, the anionic group value of the polyimide resin (A) is calculated. V5(mmol) / V2(g)×56.1(mg / mmol)=V6(mgKOH / g)

[0079] (iv) Measurement of average particle size of polyimide resin aqueous dispersion The particle size of the aqueous dispersion was measured by dynamic light scattering. The average particle size is the volume mean diameter (MV) based on the volume. The particle size measuring device used for dynamic light scattering was the Nanotrac WAVE II manufactured by Microtrack Bell Corporation.

[0080] <Additional Notes> The hydroxyl value and anionic group value of the polyimide resin (A) of the present disclosure are values ​​determined by the above methods (ii) and (iii). However, the phenolic hydroxyl value (hydroxyl value) and the acid value (anionic group) of the carboxy group (anionic group) may also be measured by the following method.

[0081] (Method for measuring phenolic hydroxyl value) The phenolic hydroxyl value can be determined, for example, by the method described in JIS K0070 or the Folin-Ciocalteu method. Specifically, approximately 1 g of sample (polyimide resin (A)) is precisely weighed and placed in a stoppered Erlenmeyer flask, and 100 mL of tetrahydrofuran solvent is added for dissolution. Exactly 5 mL of the acetylating agent (25 g of acetic anhydride dissolved in pyridine to a volume of 100 mL) is then added. After stirring for approximately 1 hour, the solution is titrated using an automatic titrator ("COM-A19" manufactured by Hiranuma Sangyo Co., Ltd.) with 0.5 mol / L alcoholic potassium hydroxide solution as the titrant. The inflection point of the resulting titration curve is used as the endpoint, and the phenolic hydroxyl value per unit of nonvolatile content of the resin is calculated using the following equation: Phenolic hydroxyl value (mgKOH / g) = [{(ba) × F × 28.05} / S] + D however, S: Amount of sample collected (g) a: Consumption of 0.5N alcoholic potassium hydroxide solution (mL) b: Amount of 0.5N alcoholic potassium hydroxide solution consumed in the blank experiment (mL) F: Potency of 0.5N alcoholic potassium hydroxide solution D: Acid value (mgKOH / g) The value of b can be determined by titrating 5 mL of the acetylating agent (a solution of 25 g of acetic anhydride dissolved in pyridine to a volume of 100 mL) with 0.5 N alcoholic potassium hydroxide solution.

[0082] (Acid value measurement) The acid value may be determined, for example, by the method described in JIS K2501 or JIS K0070. A specific example is the following method: 1 g of sample (polyimide resin (A)) is precisely weighed and placed in a stoppered Erlenmeyer flask, and dissolved in 40 mL of N-methyl-2-pyrrolidone and 20 mL of pyridine. 10 mL of water is added, and the mixture is heated at 80°C for 1 hour. After cooling to room temperature, titration is performed using an automatic titrator ("COM-A19" manufactured by Hiranuma Sangyo Co., Ltd.) with a 0.1 mol / L alcoholic potassium hydroxide solution as the titrant. The inflection point of the obtained titration curve is used as the endpoint, and the acid value per unit of nonvolatile content of the resin is calculated using the following formula: Acid value (mgKOH / g)=(5.611×a×F) / S S: Amount of sample collected (g) a: Consumption of 0.1 mol / L alcoholic potassium hydroxide solution (mL) F: Potency of 0.1 mol / L alcoholic potassium hydroxide solution

[0083] <Synthesis of polyimide resin (A)> [Manufacturing Example 1] Into a 1 L separable flask equipped with an oil bath and a stirring rod, 1000.0 parts of N-methyl-2-pyrrolidone was added while introducing nitrogen gas, and 146.8 parts (339 mmol) of Y1-1 (bis[4-(4-aminophenoxy)phenyl]sulfone) as diamine, 11.0 parts (30 mmol) of Y2-1 (bis(3-amino-4-hydroxyphenyl)hexafluoropropane), and 79.4 parts (92 mmol) of Y3-2 (KF-8010, manufactured by Shin-Etsu Chemical Co., Ltd., diamine having a siloxane skeleton) were added with stirring, followed by the addition of 262.7 parts (505 mmol) of X1-1 (4,4'-(4,4'-isopropylidenediphenoxy)bisphthalic dianhydride) as acid dianhydride, and stirring at room temperature for 30 minutes. The mixture was heated to 100°C and stirred for 3 hours, after which the oil bath was removed and the mixture was allowed to cool to room temperature, yielding a polyimide precursor in the form of a varnish.

[0084] The mixture was then heated at 170°C for 10 hours while removing the distilled water from the system using a Dean-Stark trap, resulting in imidization and obtaining a varnish-like polyimide resin. The resulting polyimide resin was dried under reduced pressure to remove volatile components such as the polymerization solvent, yielding a solid polyimide resin (A1). The Mn of the resulting polyimide resin (A1) is shown in Table 1.

[0085] [Manufacturing Examples 2 to 14, 16, 17, 101 to 103] Polyimide resins (A2) to (A14), (A16), (A17), and (A101) to (A103) were obtained in the same manner as in Production Example 1, except that the types and amounts of monomers were changed as shown in Tables 1 and 2.

[0086] [Production Example 15] (Synthesis of Polyimide Resin (A15)) In a 1 L separable flask equipped with an oil bath and a stirring rod, 1000.0 parts of N-methyl-2-pyrrolidone was added while introducing nitrogen gas. 58.2 parts (291 mmol) of Y3-1 (4,4'-diaminodiphenyl ether) as a diamine, 100.0 parts (116 mmol) of Y3-2 (KF-8010 manufactured by Shin-Etsu Chemical Co., Ltd.), and 26.5 parts (174 mmol) of Y4-1 (3,5-diaminobenzoic acid) were added with stirring. 315.2 parts (606 mmol) of X1-1 (4,4'-(4,4'-isopropylidenediphenoxy)bisphthalic dianhydride) were then added and stirred at room temperature for 30 minutes. The mixture was heated to 100 ° C. and stirred for 3 hours. The oil bath was then removed and the mixture was returned to room temperature to obtain a varnish-like polyimide precursor. Thereafter, the mixture was heated at 170° C. for 10 hours while removing the distilled water from the system using a Dean-Stark trap, and imidized to obtain a varnish-like polyimide resin. Next, 500 g of the obtained polyimide resin (resin solids content 33%) and 9.5 g of Denacol EX-141, an aromatic monofunctional epoxy compound, were added to a 1 L separable flask equipped with an oil bath and a stirrer, and the mixture was heated at 130°C for 12 hours. After removing the oil bath and cooling to room temperature, the obtained polyimide resin was dried under reduced pressure to remove volatiles such as the polymerization solvent, thereby obtaining a solid polyimide resin (A15).

[0087] Tables 1 and 2 show the amounts (parts by mass) of the polyimide resins in each production example, the content of the monomer having a bisphenol skeleton, the content of the monomer having a hydroxyl group in the diamine monomer, and values ​​such as [hydroxyl value] / [anionic group value] and Mn. The content of the monomer having a bisphenol skeleton (charge amount) is the total content (mol %) of the acid dianhydride (X1) having a bisphenol skeleton and the diamine (Y1) having a bisphenol skeleton per 100 mol % (charge amount) of the acid dianhydride (X) and the diamine (Y). The content of the monomer having a hydroxyl group is the total content (mol %) of the diamine (Y2) having a hydroxyl group per 100 mol % of the diamine (Y).

[0088] The meanings of the abbreviations in Table 1 etc. are shown below. X1-1: 4,4'-(4,4'-isopropylidenediphenoxy)bisphthalic dianhydride (BPADA) X2-1: 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) X2-2: 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid anhydride (TDA-100) Y1-1: bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS) Y1-2: 4,4'-isopropylidenebis[(4-aminophenoxy)benzene] (BAPP) Y2-1: Bis(3-amino-4-hydroxyphenyl)hexafluoropropane (DABPAF) Y2-2: 4,4'-diamino-4''-hydroxytriphenylmethane (DHTM) Y2-3: 3,3'-dihydroxybenzoic acid (HAB) Y3-1: 4,4'-diaminodiphenyl ether (ODA) Y3-2: KF-8010 (diamine with a siloxane skeleton) manufactured by Shin-Etsu Chemical Co., Ltd. Y3-3: Priamine 1075 (dimer diamine) manufactured by Croda Japan Y4-1: 3,5-diaminobenzoic acid (DABA)

[0089] [Table 1]

[0090] [Table 2]

[0091] <Production of aqueous dispersion> [Example 1] A reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube was charged with 50.0 parts of polyimide resin (A1) and 225.0 parts of N-methyl-2-pyrrolidone (NMP). The mixture was heated to 120°C under a nitrogen gas atmosphere and stirred until the polyimide resin (A1) was completely dissolved. The mixture was then cooled to 70°C, and while maintaining the temperature at 70°C, 1.5 parts of B-1 (dimethylaminoethanol) was added and stirred for 10 minutes. Next, 0.5 parts of Surfynol 420 (a nonionic surfactant manufactured by Shin-Etsu Chemical Co., Ltd.) was added as an additive and stirred for an additional 10 minutes. 223.0 parts of ion-exchanged water was then gradually added dropwise and mixed over 30 minutes to obtain an aqueous dispersion with a nonvolatile content of 10%.

[0092] [Examples 2 to 33], [Comparative Examples 1 to 3] Aqueous dispersions of Examples 2 to 33 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except that the raw materials and blending amounts in Example 1 were changed to those shown in Tables 3 to 6.

[0093] [Example 34] A reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube was charged with 50.0 parts of polyimide resin (A1) and 225.0 parts of gamma-butyrolactone (GBL). The mixture was heated to 120°C under a nitrogen gas atmosphere and stirred until the polyimide resin (A1) was completely dissolved. The mixture was then cooled to 70°C, and while maintaining the temperature at 70°C, 1.5 parts of B-1 (dimethylaminoethanol) were added and stirred for 10 minutes. Next, 0.5 parts of Surfynol 420 (Shin-Etsu Chemical Co., Ltd., nonionic surfactant) were added as an additive, and 5.0 parts of Desmodur BL3272 MPA (Covestro AG, nonvolatile content 72%), a blocked isocyanate, were added as a curing agent, and the mixture was stirred for another 10 minutes. 223.0 parts of ion-exchanged water was then gradually added dropwise and mixed over 30 minutes to obtain an aqueous dispersion with a nonvolatile content of 10%.

[0094] The basic compounds (B) used in the aqueous dispersions are as follows: B-1: Dimethylaminoethanol (alkanolamine compound) B-2: Tripropylamine (alkylamine compound) In Tables 3 to 6, GBL is γ-butyrolactone, DMM is dipropylene glycol dimethyl ether, and CYC is cyclohexanone. The equivalent ratio of the basic compound (B) to the anionic groups of the polyimide resin (A), the content (mass%) of the organic solvent (C) in the aqueous dispersion, the content (mass%) of the water-soluble solvent (C-1) in the aqueous dispersion, and the content (mass%) of water in the aqueous dispersion are shown in Tables 3 to 6. The equivalent ratio is calculated by multiplying the amount (mmol) of the basic compound (B) added by the valence involved in neutralization relative to the amount V5 (mmol) of anionic groups in the polyimide resin (A).

[0095] Using the resulting aqueous dispersion, coated plates (i) and (ii) were prepared by the following method, and the evaluations described below were carried out. [Preparation of coated plate (i)] The resulting aqueous dispersion was placed in an electrodeposition bath, a SUS304 steel plate was used as the cathode, and a copper material (10 cm x 10 cm x 0.30 mm thick) was immersed as the substrate. Anionic electrodeposition coating was performed at a liquid temperature of 25°C, adjusting the voltage and coating time so that the dried coating film would have a thickness of 100 μm. Next, excess paint was washed off in a water bath. After that, the plate was dried at 100°C for 30 minutes and then baked at 200°C for 30 minutes to prepare a coated plate (i) for evaluation.

[0096] [Preparation of coated plate (ii)] 0.5 parts of Adekanol UH-541VF (manufactured by ADEKA Corporation) was blended with 100 parts of the resulting aqueous dispersion as a thickener. The solution was applied to a copper substrate (10 cm x 10 cm x 0.30 mm thick) using a doctor blade in five or more coats to a dry coating thickness of 100 μm, to prepare a coated plate (ii) for evaluation. After each coat, the substrate was dried at 100°C for 30 minutes and then baked at 200°C for 30 minutes.

[0097] <Evaluation> a. Storage stability of aqueous dispersions The resulting aqueous dispersion was allowed to stand in an incubator at 25°C for 1 month, 2 months and 3 months, and then the appearance was visually evaluated according to the following criteria. A: No change in appearance after 3 months of standing. Very good. B: No change in appearance after 2 months of standing, but changes in the hue and / or turbidity of the paint after 3 months of standing. Good. C: No change in appearance after 1 month of standing, but changes in the hue and / or turbidity of the paint after 2 months of standing. Can be used. D: After leaving the paint for one month, changes in color and / or turbidity are observed, but there is no separation or sedimentation and the appearance is uniform. Conditional use is permitted. E: Does not fall under any of the above A to D. Abnormalities such as thickening, gelation, separation, and sedimentation are observed. Not suitable for practical use.

[0098] b. Paint appearance of the coating The coating surfaces of the resulting coated plates (i) and (ii) were visually evaluated based on the following criteria. A: A smooth and uniform coating film is obtained. Good. B: There are irregularities in the coating film, but this does not pose any problems in practical use. C: Does not fall under A or B above. Pinholes and / or cracks are observed in the coating film, and the smoothness is reduced. Not suitable for practical use.

[0099] c. Coating adhesion to substrate The coating films of the resulting coated plates (i) and (ii) were scratched with a cutter knife in a grid pattern at 1 mm intervals, so that they intersected at right angles to the substrate. Cellophane tape was then adhered to the scratched coating surfaces, and the cellophane tape was then instantly peeled off by hand, and the peeling state of the scratched coating areas was observed. A: No peeling at all. Good. B: Peeling of more than 0% but less than 5% of the scratched coating area (100%). No practical problems. C: Peeling occurred over an area of ​​more than 5% of the scratched coating area (100%). Not suitable for practical use.

[0100] d. Insulating properties of the coating The dielectric breakdown strength of the resulting coated plates (i) and (ii) was measured according to JIS C 2110-1:2016. Specifically, using an ultra-high voltage withstand voltage tester 7473 (manufactured by Keisoku Gijutsu Kenkyusho Co., Ltd.), coated plates (i) and (ii) were immersed in insulating oil and fixed to the electrodes, and a voltage was applied continuously while increasing the voltage at a rate of 100 V / sec. The voltage at which a current of 2 mA was detected was taken as the dielectric breakdown voltage and evaluated according to the following criteria. A: Dielectric breakdown voltage is 6.0 kV or more. Good. B: Breakdown voltage is 5.0 kV or more and less than 6.0 kV. No practical problems. C: Breakdown voltage is less than 5.0 kV. Not suitable for practical use.

[0101] e. Heat resistance of the coating The resulting coated plates (i) and (ii) were held at 200°C for 500 hours and 1000 hours using an incubator with a safety door, SPHH-202, manufactured by Espec Corp. The coated plates were then measured for dielectric breakdown voltage using the same method as described above, and the heat resistance was evaluated according to the following criteria. A: After 1000 hours of storage, the breakdown voltage is 6.0 kV or more. Very good. B: After 500 hours of holding, the breakdown voltage was 6.0 kV or more, and after 1000 hours of holding, the breakdown voltage was 5.0 kV or more and less than 6.0 kV. Good. C: Dielectric breakdown voltage is 5.0 kV or more and less than 6.0 kV after both 500 hours and 1000 hours of holding. Usable. D: After 500 hours of storage, the breakdown voltage is 5.0 kV or more and less than 6.0 kV. After 1000 hours of storage, the breakdown voltage is less than 5.0 kV. Conditional use is permitted. E: After 500 hours and 1000 hours of holding, the breakdown voltage was less than 5.0 kV. Not suitable for practical use.

[0102] f. Thermal shock resistance 1 Using a thermal shock tester TSE-12-A manufactured by Espec Corporation, the resulting coated plates (i) and (ii) were cooled to -40°C for 15 minutes, then immediately heated to 180°C and held there for 15 minutes. This temperature cycle constitutes one cycle, and thermal shock tests were conducted for 250 and 500 consecutive cycles. After the test, the coated plates were measured for dielectric breakdown voltage using the same method as described above, and thermal shock resistance 1 was evaluated according to the following criteria. A: After 500 cycles, the breakdown voltage is 6.0 kV or more. Very good. B: After 250 cycles, the breakdown voltage is 6.0 kV or more, and after 500 cycles, the breakdown voltage is 5.0 kV or more but less than 6.0 kV. Good. C: After 250 cycles and 500 cycles, the breakdown voltage is 5.0 kV or more and less than 6.0 kV. Usable. D: After 250 cycles, the breakdown voltage is 5.0 kV or more but less than 6.0 kV. After 500 cycles, the breakdown voltage is less than 5.0 kV. Conditional use is permitted. E: After 250 and 500 cycles, the breakdown voltage was less than 5.0 kV. Not suitable for practical use.

[0103] g. Thermal shock resistance 2 Thermal shock tests of 250 and 500 consecutive cycles were carried out using the same method as for thermal shock resistance 1. After the tests, the coated plates were measured using the same method as in "c. Adhesion of the coating to the substrate" above, and thermal shock resistance 2 was evaluated according to the following criteria. A: After 500 cycles, no peeling at all. Very good. B: No peeling at all after 250 cycles. After 500 cycles, peeling occurred in an area of ​​more than 0% but less than 5% of the scratched coating area (100%). Good. C: After 250 and 500 cycles, peeling occurred in an area of ​​more than 0% but less than 5% of the scratched coating area (based on 100%). Usable. D: After 250 cycles, peeling of more than 0% to 5% of the area of ​​the scratched coating film was observed. After 500 cycles, peeling of more than 5% of the area of ​​the scratched coating film was observed. Conditional use permitted. E: After 250 cycles and 500 cycles, peeling occurred in an area exceeding 5% of the area of ​​the scratched coating film, based on 100% of the area. Not suitable for practical use.

[0104] [Table 3]

[0105] [Table 4]

[0106] [Table 5]

[0107] [Table 6]

[0108] It was confirmed that aqueous dispersions using polyimide resins without hydroxyl groups have problems with thermal shock resistance, etc., as shown in Comparative Example 1. It was confirmed that aqueous dispersions using polyimide resins with a [hydroxyl value] / [anionic group value] ratio of more than 10 have problems with storage stability and thermal shock resistance, as shown in Comparative Example 2. Furthermore, it was confirmed that aqueous dispersions using polyimide resins without a bisphenol skeleton have problems with heat resistance, as shown in Comparative Example 3. In contrast, it was confirmed that aqueous dispersions containing a polyimide resin (A) with a bisphenol skeleton and a [hydroxyl value] / [anionic group value] ratio of 0.1 to 10, a basic compound (B), an organic solvent (C), and water have excellent storage stability, provide excellent coating film appearance even when applied to a thick film, and can form aqueous dispersions with excellent coating film thermal shock resistance, insulating properties, heat resistance, and substrate adhesion, as shown in Examples 1 to 34.

Claims

1. An aqueous dispersion containing a polyimide resin (A), a basic compound (B), an organic solvent (C), and water, The polyimide resin (A) has a bisphenol skeleton, a hydroxyl group, and an anionic group, The aqueous dispersion comprises a polyimide resin (A) having a ratio of a hydroxyl value to an anionic value, i.e., [hydroxyl value] / [anionic value], of 0.1 to 10.

2. The polyimide resin (A) is a polyimide containing a repeating structural unit obtained by reacting an acid dianhydride (X) with a diamine (Y), at least one of the acid dianhydride (X) and the diamine (Y) has the bisphenol skeleton; 2. The aqueous dispersion according to claim 1, wherein the total amount of the acid dianhydride (X1) having a bisphenol skeleton and the diamine (Y1) having a bisphenol skeleton is 40 mol % or more relative to the total amount of the acid dianhydride (X) and the diamine (Y).

3. 3. The aqueous dispersion according to claim 2, wherein the diamine (Y2) having a hydroxyl group is contained in an amount of 5 to 55 mol % based on the total amount of the diamine (Y).

4. The aqueous dispersion according to claim 1 , wherein the basic compound (B) is an alkanolamine compound.

5. The organic solvent (C) contains a water-soluble solvent, The aqueous dispersion according to claim 1, wherein the water-soluble solvent is contained in an amount of 30 to 80% by mass relative to 100% by mass of the aqueous dispersion.

6. 2. The aqueous dispersion according to claim 1, wherein the polyimide resin (A) has a number average molecular weight of 7,500 to 50,000.

7. An anionic electrodeposition paint comprising the aqueous dispersion according to any one of claims 1 to 6.

8. A coated article obtained by electrodeposition coating of a substrate with the anionic electrodeposition coating material according to claim 7.

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