Cationic electrodeposited paint composition and method for forming cured electrodeposited coating

Abstract

A cationic electrodeposited paint composition according to the present invention contains an amine-modified epoxy resin (A), a blocked polyisocyanate curing agent (B), and a coordination polymer catalyst (C) having, as a constituent unit, a metal complex containing metal ions (C1) and an organic ligand (C2). The metal ions (C1) include ions of at least one metal element selected from the group consisting of Bi, Zn, Zr, Cs, and lanthanoid. The organic ligand (C2) contains at least one substance selected from the group consisting of amine compounds represented by general formulas (1)-(5).

Description

Cationic electrodeposition coating composition and method for forming cured electrodeposition coating film

[0001] The present invention relates to a cationic electrodeposition coating composition and a method for forming a cured electrodeposition coating film.

[0002] Cationic electrodeposition coating compositions are generally used as undercoats for automobiles, etc. Cationic electrodeposition coating compositions form coatings with high corrosion resistance.

[0003] Patent Document 1 discloses a cationic electrodeposition coating composition containing a bismuth compound as a catalyst, and Patent Document 2 discloses an electrodeposition coating composition containing a cyclic guanidine.

[0004] JP 2015-187198 A U.S. Patent Application Publication No. 2011 / 0005937

[0005] Bismuth compounds can lose their catalytic activity over time due to hydrolysis, whereas organic amine catalysts such as cyclic guanidines are highly water-soluble and have poor electrodeposition efficiency, making them difficult to incorporate into the deposited film and therefore difficult to demonstrate their catalytic activity.

[0006] An object of the present invention is to provide a cationic electrodeposition coating composition which gives a cured electrodeposition coating film having excellent corrosion resistance and appearance.

[0007] In order to solve the above problems, the present invention provides the following aspects: [1] A coordination polymer catalyst (C) comprising an amine-modified epoxy resin (A), a blocked polyisocyanate curing agent (B), and a metal complex containing a metal ion (C1) and an organic ligand (C2) as a constituent unit, wherein the metal ion (C1) contains an ion of at least one metal element selected from the group consisting of Bi, Zn, Zr, Cs, and a lanthanoid, and the organic ligand (C2) is represented by the following general formula (1): (wherein R11, R21, and R31 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group), an amine compound (C2-1) represented by the following general formula (2): (wherein R12 and R22 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group), an amine compound (C2-2) represented by the following general formula (3): (wherein R13 and R23 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group), an amine compound (C2-3) represented by the following general formula (4): (wherein R14, R24, R34, R44, and R54 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group), and an amine compound (C2-4) represented by the following general formula (5): (wherein R15 to R125 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group). [2] The cationic electrodeposition coating composition of [1] above, which contains the coordination polymer catalyst (C) in an amount of 0.1 part by mass or more and 3 parts by mass or less per 100 parts by mass of the resin solid content of the cationic electrodeposition coating composition. [3] The cationic electrodeposition coating composition of [1] above, wherein in the coordination polymer catalyst (C), the molar ratio of the metal ion (C1) to the organic ligand (C2) (metal ion:organic ligand) is 1:0.5 to 1:5. [4] The cationic electrodeposition coating composition of the above [1] or [2], wherein in the coordination polymer catalyst (C), the molar ratio of the metal ion (C1) to the organic ligand (C2) (metal ion:organic ligand) is 1:1 to 1:2.8. [5] The cationic electrodeposition coating composition of any of the above [1] to [4], wherein the coordination polymer catalyst (C) is a solid. [6] The cationic electrodeposition coating composition of any of the above [1] to [5], further comprising an inorganic pigment (D). [7] The cationic electrodeposition coating composition of any of the above [1] to [6], wherein the blocked polyisocyanate curing agent (B) comprises a reaction product of a blocking agent and an aromatic polyisocyanate. [8] A method for forming a cured electrodeposition coating film, comprising: immersing an object to be coated in any of the cationic electrodeposition coating compositions [1] to [7] above to perform electrodeposition coating, thereby forming an uncured electrodeposition coating film; and heating the uncured electrodeposition coating film to form a cured electrodeposition coating film on the object to be coated.

[0008] According to the present invention, it is possible to provide a cationic electrodeposition coating composition which can give a cured electrodeposition coating film having excellent corrosion resistance and appearance.

[0009] In the present disclosure, a polymer having as a constituent unit a metal complex in which one or more amine compounds are coordinated to a metal ion is used as a catalyst. Coordinating an amine compound to a catalytically active metal inhibits its hydrolysis and enhances its stability. Fixing a catalytically active amine compound to a metal reduces its water solubility. The polymer catalyst can maintain high catalytic activity (high stability). Furthermore, the polymer catalyst is uniformly and finely present in the deposit film, allowing the deposit film to harden densely and smoothly. The resulting cured electrodeposition coating film has excellent corrosion resistance and appearance.

[0010] Hereinafter, the number average molecular weight and weight average molecular weight can be measured by gel permeation chromatography (GPC) using a polystyrene standard sample after removing water by drying under reduced pressure or the like.

[0011] The average particle size is the 50% average particle size (D50) in a volumetric particle size distribution measured using a laser diffraction / scattering particle size distribution measuring device, such as UPA-150 (Microtrack particle size distribution measuring device, manufactured by Nikkiso Co., Ltd.).

[0012] The solid content is the component remaining as a solid after the solvent is removed. The solid content of the resin emulsion (i) described below is specifically the amine-modified epoxy resin (A), the curing agent (B), and other solid components added as needed. The solid content of the pigment dispersion paste (ii) is specifically the coordination polymer catalyst (C), the inorganic pigment (D), the pigment dispersion resin (E), and other solid components added as needed.

[0013] The resin solid content is the resin component of the above solid content. The resin solid content of the resin emulsion (i) is specifically the amine-modified epoxy resin (A) and the curing agent (B). The resin solid content of the pigment dispersion paste (ii) is specifically the pigment dispersion resin (E). The resin solid content of the cationic electrodeposition coating composition is specifically all the resin solid content contained in the resin emulsion (i) and the pigment dispersion paste (ii).

[0014] Cationic Electrodeposition Coating Composition The cationic electrodeposition coating composition contains an amine-modified epoxy resin (A), a blocked polyisocyanate curing agent (B), and a coordination polymer catalyst (C).

[0015] The cationic electrodeposition coating composition may further contain an inorganic pigment (D). The cationic electrodeposition coating composition may further contain a pigment dispersing resin (E). The cationic electrodeposition coating composition may be a mixture of a resin emulsion (i) and a pigment dispersing paste (ii). The resin emulsion (i) contains an amine-modified epoxy resin (A) and a blocked polyisocyanate curing agent (B). The pigment dispersing paste (ii) contains a coordination polymer catalyst (C), an inorganic pigment (D), and a pigment dispersing resin (E).

[0016] Hereinafter, a cationic electrodeposition coating composition (hereinafter, sometimes simply referred to as electrodeposition coating) which is a mixture of a resin emulsion (i) and a pigment dispersion paste (ii) will be described as an example. However, the cationic electrodeposition coating composition used in the present disclosure is not limited to this. First, the coordination polymer catalyst (C) will be described.

[0017] Coordination Polymer Catalyst (C) The coordination polymer catalyst (C) is a polymer having, as a constituent unit, a metal complex containing a metal ion (C1) and an organic ligand (C2).

[0018] The coordination polymer catalyst (C) has a structure similar to that of a material known as MOF (Metal Organic Frameworks). MOFs are metal complexes containing metal ions and organic ligands, and are highly regular, porous structures in which metal ions (or metal clusters) serving as nodes are cross-linked by organic ligands.

[0019] The coordination polymer catalyst (C) has a large surface area and high catalytic activity. In addition, the coordination polymer catalyst (C) has excellent stability, so this high catalytic activity can be maintained. Since the coordination polymer catalyst (C) exists in a solid (powder) form in the electrodeposition coating, it is easily electrodeposited and can be present uniformly and finely in the deposited film. Therefore, the coordination polymer catalyst (C) can harden the deposited film densely and smoothly.

[0020] With regard to MOFs, reference can be made to, for example, (1) Kitagawa Susumu (editor), "Porous Materials Made by Nanoscience," CMC Publishing, March 2010, and (2) Japan Chemical Society (ed.), "Creation of Functional Substances with Innovative Porous Material Spaces," Kagaku Dojin, December 2010.

[0021] The coordination polymer catalyst (C) may have a one-dimensional structure, a two-dimensional structure, or a three-dimensional structure, and typically has a three-dimensional structure.

[0022] The coordination polymer catalyst (C) can be dispersed using a pigment dispersing resin (E) in the same manner as the inorganic pigment (D).

[0023] The size of the coordination polymer catalyst (C) before being blended into the electrodeposition coating is not particularly limited. The average particle size of the coordination polymer catalyst (C) is, for example, 0.001 μm or more and 10 μm or less. The average particle size of the coordination polymer catalyst (C) may be 0.01 μm or more. The average particle size of the coordination polymer catalyst (C) may be 5 μm or less.

[0024] The organic ligand (C2) is coordinately bonded to the metal ion (C1) via an amino group. The coordination number of the organic ligand (C2) is not particularly limited. The molar ratio of the metal ion to the organic ligand (metal ion:organic ligand) may be, for example, 1:0.5 to 1:5. When the number of moles of organic ligand per mole of metal ion is 0.5 or more, stability can be further improved. When the number of moles of organic ligand per mole of metal ion is 5 or less, the appearance of the coating film can be further improved. The number of moles of organic ligand per mole of metal ion may be 1.0 or more, 1.5 or more, or 2.0 or more. The number of moles of organic ligand per mole of metal ion may be 2.8 or less, or 2.5 or less. In one embodiment, the molar ratio (metal ion:organic ligand) is, for example, 1:1 to 1:2.8.

[0025] The molar ratio (metal ion / organic ligand) is calculated from the amounts of raw materials (e.g., metal salts as raw materials for the metal ions (C1) and amine compounds as raw materials for the organic ligands (C2)) charged when producing the coordination polymer catalyst (C), the yield, atomic weights (or molecular weights), and the like.

[0026] The content of the coordination polymer catalyst (C) may be 0.1 parts by mass or more and 3.0 parts by mass or less, relative to 100 parts by mass of the resin solid content of the cationic electrodeposition coating composition. When the content of the coordination polymer catalyst (C) is 0.1 parts by mass or more, curability is improved. When the content of the coordination polymer catalyst (C) is 3.0 parts by mass or less, the appearance of the coating film is improved. The content of the coordination polymer catalyst (C) may be 0.5 parts by mass or more, or may be 1.0 part by mass or more. The content of the coordination polymer catalyst (C) may be 2.5 parts by mass or less, or may be 2.0 parts by mass or less.

[0027] The coordination polymer catalyst (C) can be obtained by reacting a metal salt with an amine compound at room temperature or under heating. Examples of the metal salt include nitrates, acetates, and hydrochlorides. Examples of the amine compound include the amine compounds (C2-1) to (C2-5) described below.

[0028] Metal ion (C1) The metal ion (C1) contains an ion of at least one metal element selected from the group consisting of Bi (bismuth), Zn (zirconium), Zr (zirconium), Cs (cesium), and lanthanoids. The metal element may be Bi (bismuth) or Zn (zinc).

[0029] Lanthanoids is a general term for 15 elements with atomic numbers from 57 to 71 (lanthanum to lutetium on the periodic table). Examples of lanthanoids include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0030] The metal element may be contained as a cluster, which is an aggregate of metal atoms having metal-metal bonds.

[0031] Organic Ligand (C2) The organic ligand (C2) includes at least one selected from the group consisting of amine compounds (C2-1) to (C2-5) represented by the following general formulas (1) to (5).

[0032] In general formulas (1) to (5), some or all of the hydrogen atoms of the alkyl group, aryl group, and alkoxy group may be substituted with halogen atoms or may be unsubstituted. Some or all of the hydrogen atoms of the aryl group may be substituted with alkyl groups and / or alkoxy groups or may be unsubstituted. Some or all of the hydrogen atoms of the amino group may be substituted with at least one group selected from the group consisting of alkyl groups, aryl groups, and alkoxy groups or may be unsubstituted.

[0033] In the general formulas (1) to (5), the alkyl group, aryl group and alkoxy group may have, for example, one or more N, O or carbonyl groups at the end or in the molecular chain.

[0034] In the general formulas (1) to (5), the alkyl group may be linear or branched, and may contain one or more ring structures. The number of carbon atoms in the alkyl group is not particularly limited and may be, for example, 1 to 20.

[0035] In the general formulas (1) to (5), the aryl group is not particularly limited as long as it has at least one aromatic ring. The number of carbon atoms in the aryl group is not particularly limited, and is, for example, 6 to 20.

[0036] In the general formulas (1) to (5), the alkyl group constituting the alkoxy group may be linear or branched, and may contain one or more ring structures. The number of carbon atoms in the alkyl group is not particularly limited, and may be, for example, 1 to 20.

[0037] Examples of the alkyl group include unsubstituted alkyl groups such as methyl, ethyl, propyl, isopropyl, n-butyl, and isobutyl groups; and substituted alkyl groups such as chloromethyl groups.

[0038] The organic ligand (C2) may not contain an S atom. A group containing an S atom (for example, an —SH group) may reduce the corrosion resistance of the cured electrodeposition coating film.

[0039] Amine Compound (C2-1) The amine compound (C2-1) is represented by the following general formula (1): Specifically, the amine compound (C2-1) is imidazole or a derivative thereof.

[0040] (In the formula, R11, R21, and R31 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group.)

[0041] At least one of R11, R21, and R31 may be a hydrogen atom or a methyl group. R11, R21, and R31 may all be hydrogen atoms. R11 and R21 may be hydrogen atoms, and R31 may be an alkyl group having 1 to 3 carbon atoms.

[0042] Amine Compound (C2-2) The amine compound (C2-2) is represented by the following general formula (2): Specifically, the amine compound (C2-2) is triazole or a derivative thereof.

[0043] (In the formula, R12 and R22 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group.)

[0044] At least one of R12 and R22 may be a hydrogen atom. Both R12 and R22 may be hydrogen atoms.

[0045] Amine Compound (C2-3) The amine compound (C2-3) is represented by the following general formula (3): Specifically, the amine compound (C2-3) is triazole or a derivative thereof.

[0046] (In the formula, R13 and R23 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group.)

[0047] At least one of R13 and R23 may be a hydrogen atom, and both R13 and R23 may be hydrogen atoms.

[0048] Amine Compound (C2-4) The amine compound (C2-4) is represented by the following general formula (4): Specifically, the amine compound (C2-4) is benzimidazole or a derivative thereof.

[0049] (In the formula, R14, R24, R34, R44, and R54 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group.)

[0050] At least one of R14, R24, R34, R44 and R54 may be a hydrogen atom. R14, R24, R34, R44 and R54 may all be hydrogen atoms.

[0051] Amine Compound (C2-5) The amine compound (C2-5) is represented by the following general formula (5): Specifically, the amine compound (C2-5) is 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) or a derivative thereof.

[0052] (In the formula, R15 to R125 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group.)

[0053] At least one of R15, R25, R35, R45, R55, R65, R75, R85, R95, R105, R115, and R125 may be a hydrogen atom. All of R15, R25, R35, R45, R55, R65, R75, R85, R95, R105, R115, and R125 may be a hydrogen atom.

[0054] Resin emulsion (i) The resin emulsion (i) contains an amine-modified epoxy resin (A) and a blocked polyisocyanate curing agent (B). The resin emulsion (i) may further contain other components, as necessary.

[0055] Amine-modified epoxy resin (A) The amine-modified epoxy resin (A) is a film-forming resin that constitutes the electrodeposition coating film.

[0056] The amine-modified epoxy resin (A) may have an oxirane ring in the epoxy resin skeleton modified with an amine compound. The amine-modified epoxy resin (A) can be prepared, for example, by ring-opening the oxirane ring in the raw material epoxy resin skeleton through a reaction with an amine compound such as a primary amine, a secondary amine, or a tertiary amine and / or an acid salt thereof.

[0057] A typical example of the starting epoxy resin is a polyphenol polyglycidyl ether type epoxy resin, which is obtained by reacting a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolac, or cresol novolac with epichlorohydrin.

[0058] Other raw material epoxy resins include, for example, the oxazolidone ring-containing epoxy resins described in JP-A-5-306327. These epoxy resins are prepared by reacting epichlorohydrin with a diisocyanate compound or a bis-urethane compound obtained by blocking the isocyanate groups of a diisocyanate compound with a lower alcohol such as methanol or ethanol.

[0059] The raw material epoxy resin may be chain-extended with a difunctional polyester polyol, polyether polyol, bisphenol, dibasic carboxylic acid, or the like.

[0060] The starting epoxy resin may have an oxirane ring to which a monohydroxy compound such as 2-ethylhexanol, nonylphenol, ethylene glycol mono-2-ethylhexyl ether, ethylene glycol mono-n-butyl ether, or propylene glycol mono-2-ethylhexyl ether, or a monocarboxylic acid compound such as octylic acid, is added. This allows the molecular weight or amine equivalent of the epoxy resin to be adjusted, and the thermal flow properties to be improved.

[0061] Examples of amine compounds include primary amines and secondary amines. Reaction of a raw epoxy resin with a secondary amine produces an amine-modified epoxy resin having a tertiary amino group. Reaction of a raw epoxy resin with a primary amine produces an amine-modified epoxy resin having a secondary amino group. Use of a secondary amine having a blocked primary amine produces an amine-modified epoxy resin having a primary amino group. For example, to prepare an amine-modified epoxy resin having primary and secondary amino groups, a ketimine in which the primary amino group is blocked with a ketone can be used as the amine compound. After introducing the ketimine into the raw epoxy resin, deblocking produces primary and secondary amino groups. If necessary, a tertiary amine may be used in combination as the amine to react with the oxirane ring.

[0062] Specific examples of primary amines and secondary amines include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, and N-methylethanolamine. Specific examples of secondary amines having a blocked primary amine include the ketimine of aminoethylethanolamine and the diketimine of diethylenetriamine. Specific examples of tertiary amines include triethylamine, N,N-dimethylbenzylamine, and N,N-dimethylethanolamine. These may be used alone or in combination of two or more.

[0063] As the amine compound, a combination of 50 to 100% by mass of a secondary amine, 0 to 30% by mass of a secondary amine having a blocked primary amine, and 0 to 20% by mass of a primary amine may be used.

[0064] The number average molecular weight of the amine-modified epoxy resin (A) is, for example, 1,000 to 5,000. When the number average molecular weight is 1,000 or more, solvent resistance and corrosion resistance are further improved. When the number average molecular weight is 5,000 or less, viscosity adjustment of the amine-modified epoxy resin (A) becomes easy, and synthesis proceeds smoothly. In addition, the amine-modified epoxy resin (A) is easily emulsified and dispersed, improving handleability. The number average molecular weight of the amine-modified epoxy resin (A) may be 2,000 or more. The number average molecular weight of the amine-modified epoxy resin (A) may be 3,500 or less.

[0065] The amine value of the amine-modified epoxy resin (A) may be 20 to 100 mgKOH / g. When the amine value is 20 mgKOH / g or more, the dispersion stability of the amine-modified epoxy resin (A) in the electrodeposition coating is improved. When the amine value is 100 mgKOH / g or less, the water resistance of the electrodeposition coating film is enhanced. The amine value of the amine-modified epoxy resin (A) may be 80 mgKOH / g or less.

[0066] The hydroxyl value of the amine-modified epoxy resin (A) may be 150 to 650 mgKOH / g. When the hydroxyl value is 150 mgKOH / g or more, the curability and appearance of the electrodeposition coating film are improved. When the hydroxyl value is 650 mgKOH / g or less, the water resistance of the electrodeposition coating film is enhanced. The hydroxyl value of the amine-modified epoxy resin (A) may be 180 mgKOH / g or more. The hydroxyl value of the amine-modified epoxy resin (A) may be 300 mgKOH / g or less.

[0067] The amine-modified epoxy resin (A) may have a number average molecular weight of 1,000 to 5,000, an amine value of 20 to 100 mgKOH / g, and a hydroxyl value of 150 to 650 mgKOH / g, which further improves corrosion resistance.

[0068] Two or more amine-modified epoxy resins having different amine values ​​and / or hydroxyl values ​​may be used in combination as the amine-modified epoxy resin (A). In this case, the average amine value and average hydroxyl value calculated based on the mass ratio of the amine-modified epoxy resins used should be within the above-mentioned ranges.

[0069] The electrodeposition paint may contain other film-forming resins, such as acrylic resins, polyester resins, urethane resins, olefin resins, phenolic resins, and xylene resins.

[0070] As the coating film-forming resin, for example, an amino group-containing acrylic resin and an amino group-containing polyester resin may be used together with the amine-modified epoxy resin (A) as needed.

[0071] Blocked Polyisocyanate Curing Agent (B) The blocked polyisocyanate curing agent (B) (hereinafter sometimes simply referred to as "curing agent (B)") is also a film-forming resin. The curing agent (B) reacts preferentially with the amino groups of the amine-modified epoxy resin (A) and then with the hydroxyl groups to form a crosslinked structure.

[0072] The curing agent (B) is prepared by blocking a polyisocyanate with a blocking agent, for example, by adding the blocking agent dropwise to the polyisocyanate at 40 to 50°C while stirring, optionally in the presence of a curing catalyst (e.g., a tin-based catalyst).

[0073] The polyisocyanate may include at least one selected from the group consisting of aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates. The polyisocyanate may be an aromatic polyisocyanate or an aliphatic polyisocyanate. The polyisocyanate may be an aromatic polyisocyanate. The curing agent (B) may include a reaction product of a blocking agent and an aromatic polyisocyanate.

[0074] Examples of aromatic polyisocyanates include 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate. Examples of aliphatic polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate, tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate. Examples of alicyclic polyisocyanates include alicyclic diisocyanates such as isophorone diisocyanate and 4,4'-methylenebis(cyclohexyl isocyanate).

[0075] In the curing agent (B), the polyisocyanate may form an adduct such as a biuret, uretdione, isocyanurate or allophanate.

[0076] Preferred examples of the blocking agent include monohydric alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol, and methylphenyl carbinol; cellosolves such as ethylene glycol monohexyl ether and ethylene glycol mono-2-ethylhexyl ether; polyether-type both-terminal diols such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol phenol; polyester-type both-terminal polyols obtained from diols such as ethylene glycol, propylene glycol, and 1,4-butanediol and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, and sebacic acid; phenols such as para-t-butylphenol and cresol; oxime compounds such as dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, and cyclohexanone oxime; and lactams represented by ε-caprolactam and γ-butyrolactam. Among others, the blocking agent may be an oxime compound.

[0077] The blocking rate of the curing agent (B) may be 100%, which improves the storage stability of the electrodeposition coating.

[0078] As the curing agent (B), a combination of a blocked aliphatic diisocyanate and a blocked aromatic diisocyanate may be used.

[0079] As the curing agent, at least one selected from the group consisting of organic curing agents (such as melamine resins and phenolic resins), silane coupling agents, and metal curing agents may be used together with the curing agent (B).

[0080] Preparation of Resin Emulsion (i) Resin emulsion (i) can be prepared as follows: The amine-modified epoxy resin (A) and the curing agent (B) are each dissolved in an organic solvent to prepare a solution. These solutions are mixed and then neutralized with a neutralizing acid.

[0081] Examples of the neutralizing acid include organic acids such as methanesulfonic acid, sulfamic acid, lactic acid, dimethylolpropionic acid, formic acid, acetic acid, etc. The neutralizing acid may be at least one selected from the group consisting of formic acid, acetic acid, and lactic acid.

[0082] The ratio of the equivalent weight of the neutralizing acid to the equivalent weight of the amino groups in the amine-modified epoxy resin (A) (neutralization rate) may be 10 to 100%. When the neutralization rate is 10% or more, the affinity of the amine-modified epoxy resin (A) for water is improved, and its water dispersibility is enhanced. The neutralization rate may be 20% or more. The neutralization rate may be 70% or less. The neutralizing acid is used in an amount that satisfies the above neutralization rate.

[0083] The curing agent (B) is used in an amount sufficient to react with active hydrogen-containing functional groups such as primary amino groups, secondary amino groups or hydroxyl groups in the amine-modified epoxy resin (A) during curing.

[0084] The solid mass ratio (A / B) of the amine-modified epoxy resin (A) to the curing agent (B) may be 90 / 10 to 50 / 50. A / B may be 80 / 20 to 65 / 35. By adjusting A / B, the fluidity and curing speed of the deposited film are controlled, improving the appearance of the coating film.

[0085] The solid content of the resin emulsion (i) may be 25% by mass or more and 50% by mass or less, 35% by mass or more, or 45% by mass or less.

[0086] Pigment Dispersion Paste (ii) The pigment dispersion paste (ii) contains a coordination polymer catalyst (C), an inorganic pigment (D), and a pigment dispersing resin (E).

[0087] Inorganic pigment (D) Inorganic pigment (D) is a pigment commonly used in electrodeposition paint, and is not particularly limited. Examples of inorganic pigment (D) include color pigments such as titanium white (titanium dioxide), carbon black, and red iron oxide; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica, and clay; and rust-preventive pigments such as iron phosphate, aluminum phosphate, calcium phosphate, aluminum tripolyphosphate, aluminum phosphomolybdate, and aluminum zinc phosphomolybdate. These pigments may be used alone or in combination of two or more.

[0088] The total content of the inorganic pigment (D) may be 1% by mass or more and 37% by mass or less of the resin solid content of the electrodeposition paint. The content of the inorganic pigment (D) may be 5% by mass or more, 10% by mass or more, 12% by mass or more, 15% by mass or more, or 16% by mass or more. The content of the inorganic pigment (D) may be 30% by mass or less, 27% by mass or less, or 25% by mass or less.

[0089] Pigment Dispersion Resin (E) The pigment dispersing resin is a resin for dispersing pigments and is used by dispersing it in an aqueous medium. For example, a pigment dispersing resin having a cationic group can be used as the pigment dispersing resin. For example, an amine-modified epoxy resin (e) having at least one or more groups selected from a quaternary ammonium group, a tertiary sulfonium group, and a primary amino group can be used as the pigment dispersing resin. Ion-exchanged water or water containing a small amount of alcohol is used as the aqueous solvent.

[0090] The amine-modified epoxy resin (e) can be prepared, for example, by reacting a half-blocked isocyanate with the hydroxyl groups of a raw material epoxy resin having hydroxyl groups to introduce blocked isocyanate groups. The introduction of blocked isocyanate groups is carried out by reacting the raw material epoxy resin having hydroxyl groups with the half-blocked isocyanate at 140°C for about 1 hour.

[0091] Polyepoxides can be used as the raw material epoxy resin. Polyepoxides have an average of two or more 1,2-epoxy groups per molecule. Examples of polyepoxides include the raw material epoxy resins exemplified for the amine-modified epoxy resin (A).

[0092] Half-blocked isocyanates are prepared by blocking some of the isocyanate groups of a polyisocyanate with a blocking agent. Examples of polyisocyanates include the polyisocyanates exemplified as curing agent (B). Examples of blocking agents include lower aliphatic alkyl monoalcohols having 4 to 20 carbon atoms. Specific examples of blocking agents include butyl alcohol, amyl alcohol, hexyl alcohol, 2-ethylhexyl alcohol, and heptyl alcohol.

[0093] The carbon number of the tertiary amine may be 1 to 6. Specific examples of the tertiary amine include dimethylethanolamine, trimethylamine, triethylamine, dimethylbenzylamine, diethylbenzylamine, N,N-dimethylcyclohexylamine, tri-n-butylamine, diphenethylmethylamine, dimethylaniline, and N-methylmorpholine.

[0094] The neutralizing acid is not particularly limited. Examples of the neutralizing acid include inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, and lactic acid, or organic acids. The neutralizing acid may be at least one selected from the group consisting of formic acid, acetic acid, and lactic acid.

[0095] The electrodeposition paint may contain an organic solvent, such as ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, or propylene glycol monophenyl ether.

[0096] The electrodeposition paint may contain additives commonly used in the paint field. Examples of the additives include surfactants, viscosity modifiers, anti-repellents, inorganic rust inhibitors, auxiliary complexing agents, buffers, leveling agents, stress relaxation agents, gloss agents, semi-gloss agents, antioxidants, and ultraviolet absorbers. The additives are added during the preparation of the resin emulsion (i) and / or the pigment dispersion paste (ii).

[0097] Formation of cured electrodeposition coating film The cured electrodeposition coating film is formed by a method comprising immersing an object to be coated in the above-mentioned cationic electrodeposition coating composition to perform electrodeposition coating and forming an uncured electrodeposition coating film, and heating the uncured electrodeposition coating film to form a cured electrodeposition coating film on the object to be coated.

[0098] Electrodeposition coating: The object to be coated is immersed in a bath containing electrodeposition paint, and a current is passed between the object as the cathode and a separately installed anode, applying a voltage. This causes the components of the electrodeposition paint to deposit on the object, forming a deposit film (uncured electrodeposition coating film).

[0099] The applied voltage may be 50 V or more and 450 V or less. The bath temperature is, for example, 10° C. or more and 45° C. or less. The application time is, for example, 2 minutes or more and 5 minutes or less.

[0100] The substrate is not particularly limited as long as it is conductive, and examples of the substrate include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrogalvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy-plated steel sheets, zinc-iron alloy-plated steel sheets, zinc-magnesium alloy-plated steel sheets, zinc-aluminum-magnesium alloy-plated steel sheets, aluminum-plated steel sheets, aluminum-silicon alloy-plated steel sheets, and tin-plated steel sheets.

[0101] Heating: The substrate is removed from the bath and heated. This forms a cured electrodeposition coating. The substrate may be rinsed with water before heating.

[0102] The heating temperature is, for example, 120° C. or higher and 260° C. or lower. The heating temperature may be 140° C. or higher. The heating temperature may be 220° C. or lower. The heating time may be, for example, 10 minutes or higher and 30 minutes or lower.

[0103] The thickness of the cured electrodeposition coating film is, for example, 5 μm or more and 40 μm or less. This provides sufficient corrosion resistance. The thickness of the cured electrodeposition coating film may be 10 μm or more. The thickness of the cured electrodeposition coating film may be 25 μm or less.

[0104] The present invention will be described in more detail with reference to the following examples, but is not limited thereto. In the examples, "parts" and "%" are by weight unless otherwise specified.

[0105] [Production Example A] Production of Amine-Modified Epoxy Resin (A) 92 parts of methyl isobutyl ketone (MIBK), 940 parts of bisphenol A epoxy resin (trade name: DER-331J, manufactured by The Dow Chemical Company), 382 parts of bisphenol A, 63 parts of octylic acid, and 2 parts of dimethylbenzylamine were added to a reaction vessel, and the temperature inside the reaction vessel was maintained at 140°C. The reaction was continued until the epoxy equivalent reached 1,110 g / eq, and then the reaction vessel was cooled to 120°C. Next, a mixture of 78 parts of diethylenetriamine diketimine (a methyl isobutyl ketone solution with a solids concentration of 73%) and 92 parts of diethanolamine was added, and the mixture was allowed to react at 120°C for 1 hour to obtain an amine-modified epoxy resin (A).

[0106] [Production Example B1] Production of Blocked Polyisocyanate Curing Agent (B1) 1,680 parts of hexamethylene diisocyanate (HDI) and 732 parts of MIBK were charged into a reaction vessel and heated to 60°C. A solution of 346 parts of trimethylolpropane dissolved in 1,067 parts of methyl ethyl keto (MEK) oxime was added dropwise to the reaction vessel at 60°C over 2 hours. After further heating at 75°C for 4 hours, it was confirmed that the absorption due to the isocyanate group had disappeared in IR spectrum measurement, and the reaction vessel was allowed to cool. 27 parts of MIBK was then added to obtain a blocked polyisocyanate curing agent (B1) with a solids concentration of 80%.

[0107] [Production Example B2] Production of Blocked Polyisocyanate Curing Agent (B2) A reaction vessel was charged with 1,340 parts of 4,4'-diphenylmethane diisocyanate and 277 parts of MIBK, and the mixture was heated to 80°C. A solution of 226 parts of ε-caprolactam dissolved in 944 parts of butyl cellosolve was then added dropwise at 80°C over 2 hours. After further heating at 100°C for 4 hours, IR spectroscopy confirmed that absorption due to isocyanate groups had disappeared, and the mixture was allowed to cool. Subsequently, 349 parts of MIBK was added to obtain a blocked isocyanate curing agent (B2) with a solids concentration of 80%.

[0108] [Preparation Example C1] Preparation of Coordination Polymer Catalyst (C-1) 29.1 parts of a metal salt (bismuth nitrate pentahydrate) was dissolved in 29.1 parts of N,N-dimethylformamide (DMF). Separately, 8.2 parts of an organic compound (imidazole) was dissolved in 25.4 parts of DMF, and then 0.6 parts of triethylamine was added and stirred for 15 minutes. Next, the imidazole solution in DMF was added to the metal salt (bismuth nitrate pentahydrate) solution in DMF, and the mixture was stirred at room temperature for 48 hours. The pH was then adjusted to 9.0 with 10 M aqueous NaOH, and the mixed solution was filtered using a filter with a 1 μm filter diameter. The solid obtained after filtration was dried at 80°C for 12 hours to obtain coordination polymer catalyst (C-1).

[0109] [Production Example C2] Production of Coordination Polymer Catalyst (C-2) Coordination polymer catalyst (C-2) was obtained in the same manner as in Production Example C1, except that 14.3 parts of triazole was used as the organic compound.

[0110] [Production Example C3] Production of Coordination Polymer Catalyst (C-3) Coordination polymer catalyst (C-3) was obtained in the same manner as in Production Example C1, except that 14.2 parts of benzimidazole was used as the organic compound.

[0111] [Production Example C4] Production of Coordination Polymer Catalyst (C-4) A coordination polymer catalyst (C-4) was obtained in the same manner as in Production Example C1, except that 16.7 parts of TBD was used as the organic compound.

[0112] [Production Example C5] Production of Coordination Polymer Catalyst (C-5) A coordination polymer catalyst (C-5) was obtained in the same manner as in Production Example C1, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt.

[0113] [Production Example C6] Production of Coordination Polymer Catalyst (C-6) A coordination polymer catalyst (C-6) was obtained in the same manner as in Production Example C2, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt.

[0114] [Production Example C7] Production of Coordination Polymer Catalyst (C-7) A coordination polymer catalyst (C-7) was obtained in the same manner as in Production Example C3, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt.

[0115] [Production Example C8] Production of Coordination Polymer Catalyst (C-8) A coordination polymer catalyst (C-8) was obtained in the same manner as in Production Example C4, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt.

[0116] [Production Example C9] Production of Coordination Polymer Catalyst (C-9) A coordination polymer catalyst (C-9) was obtained in the same manner as in Production Example C1, except that 13.9 parts of zirconium nitrate hydrate was used as the metal salt.

[0117] [Production Example C10] Production of Coordination Polymer Catalyst (C-10) A coordination polymer catalyst (C-10) was obtained in the same manner as in Production Example C2, except that 13.9 parts of zirconium nitrate hydrate was used as the metal salt.

[0118] [Production Example C11] Production of Coordination Polymer Catalyst (C-11) Coordination polymer catalyst (C-11) was obtained in the same manner as in Production Example C3, except that 13.9 parts of zirconium nitrate hydrate was used as the metal salt.

[0119] [Preparation Example C12] Preparation of Coordination Polymer Catalyst (C-12) Coordination polymer catalyst (C-12) was obtained in the same manner as in Preparation Example C4, except that 13.9 parts of zirconium nitrate hydrate was used as the metal salt.

[0120] [Production Example C13] Production of Coordination Polymer Catalyst (C-13) A coordination polymer catalyst (C-13) was obtained in the same manner as in Production Example C1, except that 11.7 parts of cesium nitrate was used as the metal salt.

[0121] [Production Example C14] Production of Coordination Polymer Catalyst (C-14) A coordination polymer catalyst (C-14) was obtained in the same manner as in Production Example C2, except that 11.7 parts of cesium nitrate was used as the metal salt.

[0122] [Production Example C15] Production of Coordination Polymer Catalyst (C-15) A coordination polymer catalyst (C-15) was obtained in the same manner as in Production Example C3, except that 11.7 parts of cesium nitrate was used as the metal salt.

[0123] [Production Example C16] Production of Coordination Polymer Catalyst (C-16) A coordination polymer catalyst (C-16) was obtained in the same manner as in Production Example C4, except that 11.7 parts of cesium nitrate was used as the metal salt.

[0124] [Production Example C17] Production of Coordination Polymer Catalyst (C-17) A coordination polymer catalyst (C-17) was obtained in the same manner as in Production Example C1, except that 26.1 parts of cerium nitrate hexahydrate was used as the metal salt.

[0125] [Production Example C18] Production of Coordination Polymer Catalyst (C-18) A coordination polymer catalyst (C-18) was obtained in the same manner as in Production Example C2, except that 26.1 parts of cerium nitrate hexahydrate was used as the metal salt.

[0126] [Production Example C19] Production of Coordination Polymer Catalyst (C-19) A coordination polymer catalyst (C-19) was obtained in the same manner as in Production Example C3, except that 26.1 parts of cerium nitrate hexahydrate was used as the metal salt.

[0127] [Production Example C20] Production of Coordination Polymer Catalyst (C-20) A coordination polymer catalyst (C-20) was obtained in the same manner as in Production Example C4, except that 26.1 parts of cerium nitrate hexahydrate was used as the metal salt.

[0128] [Production Example C21] Production of Coordination Polymer Catalyst (C-21) A coordination polymer catalyst (C-21) was obtained in the same manner as in Production Example C1, except that 26.0 parts of lanthanum nitrate hexahydrate was used as the metal salt.

[0129] [Production Example C22] Production of Coordination Polymer Catalyst (C-22) A coordination polymer catalyst (C-22) was obtained in the same manner as in Production Example C2, except that 26.0 parts of lanthanum nitrate hexahydrate was used as the metal salt.

[0130] [Production Example C23] Production of Coordination Polymer Catalyst (C-23) A coordination polymer catalyst (C-23) was obtained in the same manner as in Production Example C3, except that 26.0 parts of lanthanum nitrate hexahydrate was used as the metal salt.

[0131] [Production Example C24] Production of Coordination Polymer Catalyst (C-24) A coordination polymer catalyst (C-24) was obtained in the same manner as in Production Example C4, except that 26.0 parts of lanthanum nitrate hexahydrate was used as the metal salt.

[0132] [Production Example C25] Production of Coordination Polymer Catalyst (C-25) A coordination polymer catalyst (C-25) was obtained in the same manner as in Production Example C1, except that 26.3 parts of neodymium nitrate hexahydrate was used as the metal salt.

[0133] [Production Example C26] Production of Coordination Polymer Catalyst (C-26) A coordination polymer catalyst (C-26) was obtained in the same manner as in Production Example C2, except that 26.3 parts of neodymium nitrate hexahydrate was used as the metal salt.

[0134] [Production Example C27] Production of Coordination Polymer Catalyst (C-27) A coordination polymer catalyst (C-27) was obtained in the same manner as in Production Example C3, except that 26.3 parts of neodymium nitrate hexahydrate was used as the metal salt.

[0135] [Production Example C28] Production of Coordination Polymer Catalyst (C-28) A coordination polymer catalyst (C-28) was obtained in the same manner as in Production Example C4, except that 26.3 parts of neodymium nitrate hexahydrate was used as the metal salt.

[0136] [Production Example C29] Production of Coordination Polymer Catalyst (C-29) A coordination polymer catalyst (C-29) was obtained in the same manner as in Production Example C1, except that 2.0 parts of imidazole was used as the organic compound.

[0137] [Production Example C30] Production of Coordination Polymer Catalyst (C-30) A coordination polymer catalyst (C-30) was obtained in the same manner as in Production Example C2, except that 3.6 parts of triazole was used as the organic compound.

[0138] [Production Example C31] Production of Coordination Polymer Catalyst (C-31) A coordination polymer catalyst (C-31) was obtained in the same manner as in Production Example C3, except that 3.5 parts of benzimidazole was used as the organic compound.

[0139] [Production Example C32] Production of Coordination Polymer Catalyst (C-32) A coordination polymer catalyst (C-32) was obtained in the same manner as in Production Example C4, except that 4.2 parts of TBD was used as the organic compound.

[0140] [Production Example C33] Production of Coordination Polymer Catalyst (C-33) A coordination polymer catalyst (C-33) was obtained in the same manner as in Production Example C1, except that 20.4 parts of imidazole was used as the organic compound.

[0141] [Production Example C34] Production of Coordination Polymer Catalyst (C-34) A coordination polymer catalyst (C-34) was obtained in the same manner as in Production Example C2, except that 35.7 parts of triazole was used as the organic compound.

[0142] [Production Example C35] Production of Coordination Polymer Catalyst (C-35) A coordination polymer catalyst (C-35) was obtained in the same manner as in Production Example C3, except that 35.4 parts of benzimidazole was used as the organic compound.

[0143] [Production Example C36] Production of Coordination Polymer Catalyst (C-36) A coordination polymer catalyst (C-36) was obtained in the same manner as in Production Example C4, except that 41.8 parts of TBD was used as the organic compound.

[0144] [Production Example C37] Production of coordination polymer catalyst (C-37) A coordination polymer catalyst (C-37) was obtained in the same manner as in Production Example C1, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt and 2.0 parts of imidazole was used as the organic compound.

[0145] [Production Example C38] Production of coordination polymer catalyst (C-38) A coordination polymer catalyst (C-38) was obtained in the same manner as in Production Example C2, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt and 3.6 parts of triazole was used as the organic compound.

[0146] [Production Example C39] Production of coordination polymer catalyst (C-39) A coordination polymer catalyst (C-39) was obtained in the same manner as in Production Example C3, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt and 3.5 parts of benzimidazole was used as the organic compound.

[0147] [Production Example C40] Production of coordination polymer catalyst (C-40) A coordination polymer catalyst (C-40) was obtained in the same manner as in Production Example C4, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt and 4.2 parts of TBD was used as the organic compound.

[0148] [Production Example C41] Production of coordination polymer catalyst (C-41) A coordination polymer catalyst (C-41) was obtained in the same manner as in Production Example C1, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt and 20.4 parts of imidazole was used as the organic compound.

[0149] [Production Example C42] Production of coordination polymer catalyst (C-42) A coordination polymer catalyst (C-42) was obtained in the same manner as in Production Example C2, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt and 35.7 parts of triazole was used as the organic compound.

[0150] [Production Example C43] Production of coordination polymer catalyst (C-43) A coordination polymer catalyst (C-43) was obtained in the same manner as in Production Example C3, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt and 35.4 parts of benzimidazole was used as the organic compound.

[0151] [Production Example C44] Production of coordination polymer catalyst (C-44) A coordination polymer catalyst (C-44) was obtained in the same manner as in Production Example C4, except that 17.9 parts of zinc nitrate hexahydrate was used as the metal salt and 41.8 parts of TBD was used as the organic compound.

[0152] [Production Example C45] Production of Coordination Polymer Catalyst (C-45) A coordination polymer catalyst (C-45) was obtained in the same manner as in Production Example C1, except that 9.9 parts of 2-methylimidazole was used as the organic compound.

[0153] [Production Example C46] Production of Coordination Polymer Catalyst (C-46) A coordination polymer catalyst (C-46) was obtained in the same manner as in Production Example C1, except that 11.5 parts of 2-ethylimidazole was used as the organic compound.

[0154] [Production Example C47] Production of Coordination Polymer Catalyst (C-47) A coordination polymer catalyst (C-47) was obtained in the same manner as in Production Example C1, except that 1.6 parts of imidazole was used as the organic compound.

[0155] [Production Example C48] Production of Coordination Polymer Catalyst (C-48) A coordination polymer catalyst (C-48) was obtained in the same manner as in Production Example C1, except that 24.5 parts of imidazole was used as the organic compound.

[0156] Comparative Production Example C49 Production of Coordination Polymer Catalyst (C-49) A coordination polymer catalyst (C-49) containing an S atom was obtained in the same manner as in Production Example C1, except that 20.1 parts of 2-mercaptobenzthiazole was used as the organic compound.

[0157] [Production Example E] Production of Pigment Dispersion Resin (E) - Preparation of 2-Ethylhexanol Half-Blocked Isophorone Diisocyanate 222.0 parts of isophorone diisocyanate (IPDI) was placed in a reaction vessel equipped with a stirrer, a condenser, a nitrogen inlet tube, and a thermometer, and diluted with 39.1 parts of MIBK. 0.2 parts of dibutyltin dilaurate was then added. After heating to 50°C, 131.5 parts of 2-ethylhexanol was added dropwise over 2 hours under stirring in a dry nitrogen atmosphere to obtain 2-ethylhexanol half-blocked IPDI (solids concentration 90.0% by mass).

[0158] Preparation of Quaternizing Agent 87.2 parts of dimethylethanolamine, 117.6 parts of a 75% aqueous lactic acid solution, and 39.2 parts of ethylene glycol mono-n-butyl ether were added in this order to a reaction vessel, and the mixture was stirred at 65°C for 30 minutes to prepare a quaternizing agent.

[0159] - Preparation of Pigment Dispersion Resin 10.0 parts of bisphenol A epoxy resin (trade name: DER-331J, manufactured by Dow Chemical Company) and 289.6 parts of bisphenol A were charged into a reaction vessel and reacted for 1 hour at 150 to 160°C under a nitrogen atmosphere. After cooling to 120°C, 498.8 parts of the previously prepared 2-ethylhexanol half-blocked IPDI (MIBK solution) was added. The reaction mixture was stirred for 1 hour at 110 to 120°C. Subsequently, 463.4 parts of ethylene glycol mono-n-butyl ether was added, and the mixture was cooled to 85 to 95°C. After that, 196.7 parts of the previously prepared quaternizing agent was added. The reaction mixture was maintained at 85 to 95°C until the acid value reached 1, and then 964 parts of deionized water was added to obtain a pigment dispersion resin (amine-modified epoxy resin (e)) (solids concentration 50% by mass).

[0160] [Preparation Example 1] Preparation of pigment dispersion paste Ion-exchanged water and 60 parts of a pigment dispersion resin (amine-modified epoxy resin (e)) were mixed and stirred at room temperature for 1 hour. Thereafter, 8.2 parts of a coordination polymer catalyst (C-1), 1 part of carbon, 40 parts of titanium dioxide, and 59 parts of Satenton (calcined kaolin) were added, and the mixture was stirred at 40°C for 1 hour using a sand mill to obtain a pigment dispersion paste (solids concentration: 47% by mass).

[0161] Preparation Example 2: Preparation of Resin Emulsion (Em) 350 parts (solids) of amine-modified epoxy resin (A), 75 parts (solids) of blocked polyisocyanate curing agent (B1), and 75 parts (solids) of blocked polyisocyanate curing agent (B2) were mixed. Ethylene glycol mono-2-ethylhexyl ether was added to the mixture in an amount of 3% (15 parts) based on the solids. Next, formic acid was added to the mixture to a neutralization rate of 40% to neutralize the amine-modified epoxy resin (A), followed by slow dilution with ion-exchanged water. Next, MIBK was removed under reduced pressure until the solids content reached 40%, yielding resin emulsion (Em).

[0162] Example 1 516 parts of ion-exchanged water, 393 parts of resin emulsion (Em), and 91 parts of pigment dispersion paste were added to a stainless steel container, followed by aging at 40°C for 16 hours to obtain a cationic electrodeposition coating composition.

[0163] [Examples 2 to 54, Comparative Example 1] Cationic electrodeposition coating compositions were obtained in the same manner as in Example 1, except that the types of coordination polymer catalysts were as shown in Tables 1 to 9. The content of the coordination polymer catalyst (C) shown in the tables is the value relative to 100 parts by mass of the resin solid content of the cationic electrodeposition coating composition.

[0164] Comparative Example 2 A cationic electrodeposition coating composition was obtained in the same manner as in Example 1, except that a metal compound (C3, bismuth nitrate pentahydrate) and an amine compound (C4, imidazole) were added instead of the coordination polymer catalyst.

[0165] Comparative Example 3 A cationic electrodeposition coating composition was obtained in the same manner as in Example 1, except that a metal compound (C3, zinc nitrate hexahydrate) and an amine compound (C4, imidazole) were added instead of the coordination polymer catalyst.

[0166] Comparative Example 4 A cationic electrodeposition coating composition was obtained in the same manner as in Example 1, except that only a metal compound (C3, bismuth nitrate pentahydrate) was added instead of the coordination polymer catalyst.

[0167] Comparative Example 5 A cationic electrodeposition coating composition was obtained in the same manner as in Example 1, except that only an amine compound (C4, imidazole) was added instead of the coordination polymer catalyst.

[0168] [Evaluation] The cationic electrodeposition coating compositions obtained in the Examples and Comparative Examples were evaluated as follows.

[0169] (1) Curability Using the electrodeposition paint immediately after preparation, a coating film was deposited on a tin plate whose mass had been measured in advance so that the dried coating film had a thickness of 20 μm. The plate was then heated at 160°C for 15 minutes to form a cured electrodeposition coating film on the tin plate. After measuring the mass of the coated plate, it was immersed in acetone and refluxed for 6 hours, and then dried at 105°C for 20 minutes. The mass of the coated plate after drying was measured, and the gel fraction was calculated using the following formula (1).

[0170] Gel fraction (%)=(W2−W0) / (W1−W0)×100 In the formula, W0 is the mass of the tin plate, W1 is the mass of the coated plate after curing, and W2 is the mass of the coated plate after immersion in acetone.

[0171] Separately, a coated plate was prepared in the same manner as above using the electrodeposition paint that had been prepared and left to stand at 40°C for 30 days, and the gel fraction was determined. The larger the gel fraction, the higher the curability. A gel fraction of 85% or more can be evaluated as having excellent curability.

[0172] (2) Catalyst Stability The difference between the gel fraction immediately after the preparation and the gel fraction after standing for 40 days was determined and evaluated according to the following criteria: A rating of C or higher indicates that the catalyst has excellent stability.

[0173] (Evaluation criteria) A: The difference in gel fraction is 2% or less. B: The difference in gel fraction is more than 2% and 4% or less. C: The difference in gel fraction is more than 4% and 9% or less. D: The difference in gel fraction is 9% or more.

[0174] (3) Corrosion Resistance A cold-rolled steel sheet (JIS G3141, SPCC-SD) was degreased by immersion in Surf Cleaner EC90 (manufactured by Nippon Paint Co., Ltd.) at 50°C for 2 minutes. Next, the cold-rolled steel sheet was immersed in Surf Fine GL1 (manufactured by Nippon Paint Co., Ltd.) at room temperature for 30 seconds, and then in Surfdyne 6350 (manufactured by Nippon Paint Co., Ltd.) at 35°C for 2 minutes. Thereafter, the sheet was rinsed with deionized water.

[0175] A required amount of 2-ethylhexyl glycol was added to the electrodeposition paint so that the thickness of the cured electrodeposition coating film would be 15 μm. After the above cold-rolled steel sheets were all immersed in the diluted electrodeposition paint, voltage application was immediately initiated. The voltage was increased for 30 seconds, reached 180 V, and then maintained for 150 seconds, depositing an uncured electrodeposition coating film on the cold-rolled steel sheet. The resulting uncured electrodeposition coating film was heat-cured at 140°C for 15 minutes to obtain a coated plate having a cured electrodeposition coating film.

[0176] A cross-cut was made in the cured electrodeposition coating film with a cutter knife so that the cut reached the cold-rolled steel plate. The coated plate was then subjected to a 35°C salt spray test for 1000 hours in accordance with JIS Z-2371. The maximum width of rust or blisters on one side of the cut was measured and evaluated according to the following criteria. A rating of C or higher indicates excellent corrosion resistance.

[0177] (Evaluation criteria) A: 2.0 mm or less B: More than 2.0 mm and 3.5 mm or less C: More than 3.5 mm and 5.0 mm or less D: More than 5.0 mm

[0178] (4) Coating Appearance (Surface Roughness Ra) For coated panels prepared in the same manner as above, the arithmetic mean roughness (Ra) of the roughness curve of the cured electrodeposition coating was measured using an evaluation type surface roughness measuring instrument (Mitsutoyo Corporation, SURFTEST SJ-201P) according to a method in accordance with JIS-B0601. Measurements were made seven times using a sample with a 2.5 mm wide cutoff (number of sections: 5), and the Ra value (μm) was obtained by averaging the values ​​obtained by top and bottom erasure. The obtained average Ra value was evaluated according to the following criteria. A rating of C or higher was considered to be excellent in appearance.

[0179] (Evaluation Criteria) A: Average Ra value is less than 0.20 μm B: Average Ra value is 0.20 μm or more and less than 0.25 μm C: Average Ra value is 0.25 μm or more and less than 0.30 μm D: Average Ra value is 0.30 μm or more

[0180]

[0181]

[0182]

[0183]

[0184]

[0185]

[0186]

[0187]

[0188]

[0189] The present invention can provide a cured electrodeposition coating film having excellent corrosion resistance and appearance, and is particularly suitable for electrodeposition coating of automobile bodies.

[0190] This application claims priority based on Japanese Patent Application No. 2024-084254, filed on May 23, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A method for producing a polymer catalyst comprising: an amine-modified epoxy resin (A); a blocked polyisocyanate curing agent (B); and a coordination polymer catalyst (C) having, as a constituent unit, a metal complex containing a metal ion (C1) and an organic ligand (C2), wherein the metal ion (C1) contains an ion of at least one metal element selected from the group consisting of Bi, Zn, Zr, Cs, and lanthanoids; and the organic ligand (C2) is represented by the following general formula (1): (wherein R11, R21, and R31 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group), an amine compound (C2-1) represented by the following general formula (2): (wherein R12 and R22 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group), an amine compound (C2-2) represented by the following general formula (3): (wherein R13 and R23 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group), an amine compound (C2-3) represented by the following general formula (4): (wherein R14, R24, R34, R44, and R54 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group), and an amine compound (C2-4) represented by the following general formula (5): (wherein R15 to R125 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom, or an amino group).

2. The cationic electrodeposition coating composition according to claim 1, wherein the coordination polymer catalyst (C) is contained in an amount of 0.1 to 3 parts by mass per 100 parts by mass of the resin solid content of the cationic electrodeposition coating composition.

3. The cationic electrodeposition coating composition according to claim 1 or 2, wherein in the coordination polymer catalyst (C), the molar ratio of the metal ion (C1) to the organic ligand (C2) (metal ion:organic ligand) is 1:0.5 to 1:

5.

4. The cationic electrodeposition coating composition according to claim 1 or 2, wherein in the coordination polymer catalyst (C), the molar ratio of the metal ion (C1) to the organic ligand (C2) (metal ion:organic ligand) is 1:1 to 1:2.

8.

5. The cationic electrodeposition coating composition according to any one of claims 1 to 4, wherein the coordination polymer catalyst (C) is a solid.

6. The cationic electrodeposition coating composition according to any one of claims 1 to 5, further comprising an inorganic pigment (D).

7. The cationic electrodeposition coating composition according to any one of claims 1 to 6, wherein the blocked polyisocyanate curing agent (B) comprises a reaction product of a blocking agent and an aromatic polyisocyanate.

8. A method for forming a cured electrodeposition coating film, comprising: immersing an object to be coated in the cationic electrodeposition coating composition according to any one of claims 1 to 7 to perform electrodeposition coating, thereby forming an uncured electrodeposition coating film; and heating the uncured electrodeposition coating film to form a cured electrodeposition coating film on the object to be coated.

Images