Cationic electrodeposition coating composition, electrodeposition coated product, and method for producing electrodeposition coated product

Abstract

Provided is a cationic electrodeposition coating composition capable of forming a coating film excellent in rust prevention properties and coating film appearance.　This cationic electrodeposition coating composition comprises (A) an aminated epoxy resin, (B) an aminated acrylic resin, (C) a blocked polyisocyanate curing agent, (D) a pigment, and (E) a polyamidine compound or hydrophobized modified body thereof, wherein the polyamidine compound or hydrophobized modified body thereof (E) has a structural unit represented by general formula (I) (in the formula, R1 and R2 are each independently a hydrogen atom or a hydrocarbon group having 1-3 carbon atoms, and X is an anion).

Description

Cationic electrodeposition coating composition, electrodeposition coated article, and method for producing electrodeposition coated article

[0001] The present invention relates to a cationic electrodeposition coating composition, an electrodeposition-coated article, and a method for producing an electrodeposition-coated article.

[0002] Cationic electrodeposition paints are widely used as primers to impart rust prevention to industrial products such as automobiles. From the viewpoint of rust prevention, it is necessary for the coating film to be formed uniformly on the substrate. However, it is difficult to cover edges with a sufficiently thick coating film, making them susceptible to corrosion. Therefore, increasing the viscosity of the paint has been proposed. In this regard, Patent Document 1 teaches the addition of polyvinyl formamide polymer to cationic electrodeposition paints. Patent Document 2 teaches the addition of polyvinyl compounds to cationic electrodeposition paints.

[0003] JP 2011-524934 A International Publication No. 2020 / 262549

[0004] However, even if the above-mentioned viscosity-improving agents are added, the effect of inhibiting edge corrosion is insufficient. Furthermore, when edge corrosion is inhibited, the appearance of the coating film is usually deteriorated. The present invention solves the above-mentioned conventional problems, and aims to provide a cationic electrodeposition coating composition that can provide a coating film with excellent rust prevention, particularly edge rust prevention, and excellent appearance.

[0005] In order to solve the above problems, the present invention provides the following aspects: [1] A composition comprising an aminated epoxy resin (A), an aminated acrylic resin (B), a blocked polyisocyanate curing agent (C), a pigment (D), and a polyamidine compound or a hydrophobically modified polyamidine compound (E), wherein the polyamidine compound or a hydrophobically modified polyamidine compound (E) is represented by the following general formula (I): (In the formula, R １ and R ２ are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and X is an anion. [2] A cationic electrodeposition coating composition having a structural unit represented by the following general formula (X): (In the formula, R １ and R ２ are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and R ３ is a hydrophobic structural unit containing at least one of a substituted or unsubstituted, linear or branched alkyl group having 3 to 12 carbon atoms, or a substituted or unsubstituted aromatic group having 6 to 12 carbon atoms.) [3] The cationic electrodeposition coating composition according to [1] or [2], wherein the solids mass of the polyamidine compound or its hydrophobically modified product (E) is 0.2 ppm or more and 1,200 ppm or less of the solids mass of the cationic electrodeposition coating composition. [4] The cationic electrodeposition coating composition according to [1] or [2], wherein the weight-average molecular weight of the polyamidine compound or its hydrophobically modified product (E) is 50,000 or more. [5] The cationic electrodeposition coating composition according to [1] or [2], wherein the pigment (D) includes an extender pigment. [6] The cationic electrodeposition coating composition according to [1] or [2], wherein the cationic electrodeposition coating composition does not contain an organotin compound or the content of the organotin compound is 0.25 mass % or less. [7] The aminated epoxy resin (A) is an aminated epoxy resin obtained by reacting an amine compound with an epoxy resin, the amine compound being a combination of two amines, a primary amine and a secondary amine, and the primary amine is a amine represented by the formula: NH ２ - (CH ２ ) n-NR １１ R １２ (In the formula, R １１ and R １２ are the same or different and represent an alkyl group having 1 to 6 carbon atoms which may have a terminal hydroxyl group, and n represents an integer of 2 to 4, and the secondary amine has the formula: R １３ R １４ NH (wherein, R １３ and R １４are the same or different and represent an alkyl group having 1 to 4 carbon atoms and a hydroxyl group at its terminal.), or the amine compound comprises one or more compounds selected from the group consisting of ketimine compounds and diketimine compounds. [8] The cationic electrodeposition coating composition according to [1] or [2], wherein the blocked polyisocyanate curing agent (C) comprises an oxime-blocked isocyanate curing agent which is a blocked reaction product of a blocking agent containing an oxime compound with a polyisocyanate, and the polyisocyanate in the blocking reaction comprises one or more compounds selected from the group consisting of aromatic polyisocyanate compounds, aliphatic polyisocyanate compounds, and alicyclic polyisocyanate compounds. [9] An electrodeposition-coated article comprising: a substrate; and an electrodeposition coating film formed on the substrate using the cationic electrodeposition coating composition according to [1] or [2].

[10] A method for producing an electrodeposition coated article, comprising the steps of: immersing an article to be coated in the cationic electrodeposition coating composition according to [1] or [2], and then applying a voltage between the article to be coated and a counter electrode to form an uncured electrodeposition coating film on the article to be coated; and heating the uncured electrodeposition coating film at a temperature of 75°C or higher and 200°C or lower to obtain a cured electrodeposition coating film.

[0006] According to the present invention, it is possible to provide a cationic electrodeposition coating composition which can give a coating film having excellent rust prevention properties, particularly edge rust prevention properties, and excellent appearance, as well as an electrodeposition-coated article and a method for producing the same.

[0007] The polymeric viscous agent interacts with the film-forming resin and pigment to increase the viscosity of the cationic electrodeposition coating composition. This increased viscosity of the coating composition prevents the coating composition from flowing when heated. However, it is difficult to cure the coating composition while covering the edges.

[0008] In this embodiment, a polyamidine compound having a cyclic amidine skeleton (hereinafter referred to as a cyclic polyamidine compound) is added to the paint composition. This significantly improves edge rust prevention. The reason why the cyclic polyamidine compound improves edge rust prevention is unclear, but it is thought to be because the polyamidine compound has an electric charge. Charged polyamidine compounds tend to precipitate at edge portions. In addition, the cyclic structure increases the viscosity of the paint composition, allowing the paint composition to harden while covering the edge portions, improving edge rust prevention. From the perspective of paint stability, cyclic polyamidine compounds may be modified to introduce hydrophobic groups. Compounds with hydrophobic groups introduced are referred to herein as "hydrophobized modified compounds."

[0009] The film-forming resin flows to some extent when heated, so the surface of the resulting cured film is leveled, giving it a good appearance.

[0010] Furthermore, the cationic electrodeposition coating composition according to this embodiment contains, in addition to the aminated epoxy resin (A), an aminated acrylic resin (B) as a film-forming resin component that cures upon reaction with a curing agent, which has the advantage of enabling better weather resistance to be obtained.

[0011] [Cationic Electrodeposition Coating Composition] The cationic electrodeposition coating composition according to this embodiment (hereinafter sometimes simply referred to as the coating composition) contains an aminated epoxy resin (A), an aminated acrylic resin (B), a blocked polyisocyanate curing agent (C), a pigment (D), and a polyamidine compound or a hydrophobically modified polyamidine compound (E) represented by the following general formula: (In the formula, R １ and R ２ are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and X is an anion.

[0012] <Aminized Epoxy Resin (A)> The aminated epoxy resin (A) is a film-forming resin. In the aminated epoxy resin (A), at least one oxirane ring (also referred to as an "epoxy group") of the epoxy resin is aminated. The aminated epoxy resin (A) is preferably contained in the electrodeposition coating composition in the form of a resin emulsion together with the blocked polyisocyanate curing agent (C).

[0013] The number average molecular weight of the aminated epoxy resin (A) is, for example, 1,000 or more and 7,000 or less. When the number average molecular weight is 1,000 or more, the rust prevention and solvent resistance of the resulting cured electrodeposition coating film are likely to be improved. When the number average molecular weight is 7,000 or less, the viscosity of the aminated epoxy resin (A) is easily adjusted, allowing for smooth synthesis, and in addition, the resulting aminated epoxy resin (A) is easily emulsified and dispersed. The number average molecular weight of the aminated epoxy resin (A) may be 1,500 or more and 4,000 or less.

[0014] The number average molecular weight of the aminated epoxy resin (A) is a value calculated as a styrene homopolymer, measured by gel permeation chromatography.

[0015] The amine value of the aminated epoxy resin (A) is, for example, 20 mgKOH / g or more and 100 mgKOH / g or less. When the amine value of the aminated epoxy resin (A) is 20 mgKOH / g or more, the stability of the emulsion dispersion of the aminated epoxy resin (A) in the coating composition is good. When the amine value is 100 mgKOH / g or less, the amount of amino groups in the cured electrodeposition coating film is appropriate, and a decrease in the water resistance of the coating film is suppressed. The amine value of the aminated epoxy resin (A) may be 20 mgKOH / g or more and 80 mgKOH / g or less.

[0016] The amine value can be determined in accordance with ASTM D2073 by the following method. (1) Accurately weigh out 500 mg of aminated epoxy resin into a 200 ml Erlenmeyer flask. (2) Add approximately 50 ml of glacial acetic acid and dissolve uniformly. (3) Add 5 to 6 drops of indicator (methyl violet solution) and stir uniformly. (4) Titrate with 0.1 N perchloric acid / acetic acid solution, and the endpoint is the point at which the color turns bright green. (The above steps (3) and (4) can also be replaced with potentiometric titration.)

[0017] The aminated epoxy resin (A) may have a hydroxyl group, and the hydroxyl value of the aminated epoxy resin (A) is, for example, 150 mgKOH / g or more and 650 mgKOH / g or less. When the hydroxyl value is 150 mgKOH / g or more, the curability of the coating composition is enhanced and the appearance of the coating film is improved. When the hydroxyl value is 650 mgKOH / g or less, the amount of hydroxyl groups remaining in the cured electrodeposition coating is appropriate, and the water resistance of the coating film is easily improved. In one embodiment, the hydroxyl value of the aminated epoxy resin (A) is 150 mgKOH / g or more, 180 mgKOH / g or more, 200 mgKOH / g or more, 250 mgKOH / g or more, 300 mgKOH / g or more, 350 mgKOH / g or more, 400 mgKOH / g or more, 450 mgKOH / g or more, 500 mgKOH / g or more, 550 mgKOH / g or more, or 600 mgKOH / g or more. In another embodiment, the hydroxyl value of the aminated epoxy resin (A) component is 650 mgKOH / g or less, 600 mgKOH / g or less, 550 mgKOH / g or less, 500 mgKOH / g or less, 450 mgKOH / g or less, 400 mgKOH / g or less, 350 mgKOH / g or less, 300 mgKOH / g or less, 250 mgKOH / g or less, or 200 mgKOH / g or less. In yet another embodiment, the hydroxyl value of component (A) is 180 to 300 mgKOH / g.

[0018] The hydroxyl value can be determined by the neutralization titration method described in JIS K 0070 using an aqueous potassium hydroxide solution.

[0019] In particular, when the number average molecular weight of the aminated epoxy resin (A) is within the range of 1,000 to 7,000, the amine value is 20 to 100 mgKOH / g, and the hydroxyl value is 150 to 650 mgKOH / g (preferably 150 to 400 mgKOH / g), the rust prevention properties of the coated object are more likely to be improved.

[0020] The coating composition may contain multiple aminated epoxy resins (A) with different amine values ​​and / or hydroxyl values. In this case, the average amine value and average hydroxyl value calculated based on the mass ratio of the multiple aminated epoxy resins (A) preferably fall within the above-mentioned ranges. In particular, the multiple aminated epoxy resins (A) preferably include an aminated epoxy resin having an amine value of 20 to 50 mgKOH / g and a hydroxyl value of 50 to 300 mgKOH / g, and an aminated epoxy resin having an amine value of 50 to 200 mgKOH / g and a hydroxyl value of 200 to 500 mgKOH / g. This makes the core of the emulsion more hydrophobic and the shell more hydrophilic, thereby further improving the rust prevention properties of the coated object.

[0021] The aminated epoxy resin (A) can be prepared, for example, by reacting the oxirane ring of the epoxy resin with an amine compound. The amine compound used is one that is commonly used in producing aminated epoxy resins. Examples of commonly used amine compounds include primary amines such as butylamine, octylamine, and monoethanolamine; secondary amines such as diethylamine, dibutylamine, methylbutylamine, diethanolamine, and N-methylethanolamine; and complex amines such as diethylenetriamine. The primary amine can form a ketimine group using a ketone compound, thereby controlling the reaction through so-called blocking. Usable amine compounds having a ketimine or diketimine group include the ketimine of aminoethylethanolamine and the diketimine of diethylenetriamine. Examples of ketone compounds that generate ketimine groups include methyl isopropyl ketone (MIPK), diisobutyl ketone (DIBK), methyl isobutyl ketone (MIBK), diethyl ketone (DEK), ethyl butyl ketone (EBK), ethyl propyl ketone (EPK), dipropyl ketone (DPK), and methyl ethyl ketone (MEK), with methyl isobutyl ketone (MIBK) being preferred. Tertiary amines may also be used as amine compounds, and specific examples thereof include triethylamine, N,N-dimethylbenzylamine, and N,N-dimethylethanolamine. These amines may be used alone or in combination of two or more.

[0022] During the conversion to amination, the amine compound is preferably used in an amount of 0.9 to 1.2 equivalents per equivalent of epoxy groups in the raw material epoxy resin. The reaction conditions for the conversion to amination can be appropriately selected depending on the reaction scale, etc. For example, the reaction may be carried out at 80°C to 150°C for 0.1 to 5 hours, or at 120°C to 150°C for 0.5 to 3 hours.

[0023] In one embodiment of the present invention, an amine compound having at least one of a primary amino group, a secondary amino group, and a tertiary amino group, excluding ketimine (including diketimine), is used as the amine compound that modifies the oxirane ring (also referred to as an "epoxy group") of the epoxy resin.

[0024] When it is necessary to narrowly control the molecular weight distribution of the aminated epoxy resin, particularly when it is necessary to control the molecular weight distribution to 2.7 or less, selecting a specific amine compound has the advantage of facilitating control. Specifically, for example, the amine compound may be a combination of two types of amines, a primary amine and a secondary amine, and the primary amine is a compound represented by the formula: NH ２ - (CH ２ ) n-NR １１ R １２ (1) (In formula (1), R １１ and R １２ are the same or different and represent an alkyl group having 1 to 6 carbon atoms which may have a terminal hydroxyl group, and n represents an integer of 2 to 4, and the secondary amine has the formula: R １３ R １４ NH (2) (In formula (2), R １３ and R １４ represents an alkyl group having 1 to 4 carbon atoms and a terminal hydroxyl group.) When these amine compounds are used, the primary amino group of the primary amine first reacts with the epoxy resin and is consumed, leaving only secondary amino groups, which then react with the epoxy groups of the epoxy resin. This is thought to ensure that the reaction proceeds evenly without any difference in reactivity, making it possible to control the molecular weight distribution. It is also conceivable that the tertiary amino group present in the primary amine, or the tertiary amino group produced by the reaction of the secondary amino group, may also react with the epoxy group to form a quaternary ammonium group, but this reaction is thought to be infrequent.

[0025] The primary amine has the formula (1) above, and R １１ and R １２is specifically methyl, ethyl, propyl or butyl, and may have a hydroxyl group at the terminal. Furthermore, n is 2 to 4, preferably 3. Specific examples of the primary amine include aminopropyldiethanolamine, dimethylaminopropanediamine, diethylaminopropanediamine, and dibutylaminopropanediamine. The secondary amine is a secondary amine having the above formula (2), but does not have R attached to a nitrogen atom. １３ and R １４ is bonded to R ３ and R ４ and each have a hydroxyl group-containing alkyl group having 1 to 4 carbon atoms. Specific examples of secondary amines include dimethanolamine and diethanolamine.

[0026] In another embodiment of the present invention, the amine compound used for the amination may include an amine compound having a ketimine group or a diketimine group.

[0027] <Amino acrylic resin (B)> The aminated acrylic resin (B) is a film-forming resin. The aminated acrylic resin (B) functions as a film-forming resin and also functions to impart weather resistance mainly to the electrodeposition coating film.

[0028] The aminated acrylic resin (B) can be obtained by copolymerizing (i) an amino group-containing acrylic monomer, (ii) a hydroxyl group-containing acrylic monomer, and (iii) other ethylenically unsaturated monomers. Furthermore, it can also be obtained by copolymerizing an epoxy group-containing acrylic monomer (iv) in place of the amino group-containing acrylic monomer with a hydroxyl group-containing acrylic monomer and other ethylenically unsaturated monomers, and then ring-opening the epoxy groups of the resulting copolymer with an amine.

[0029] Examples of the amino group-containing acrylic monomer (i) include N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, and N,N-diethylaminopropyl (meth)acrylate.

[0030] Preferred examples of the hydroxyl group-containing acrylic monomer (ii) include mono(meth)acrylates of alkylene diols such as 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate, polypropylene glycol mono(meth)acrylate, and 1,6-hexanediol mono(meth)acrylate.

[0031] Also preferred are (meth)acrylamides such as N-hydroxyethyl(meth)acrylamide and N-hydroxypropyl(meth)acrylamide. Furthermore, a reaction product of a hydroxyalkyl mono(meth)acrylate with ε-caprolactone or a reaction product of a hydroxyalkyl mono(meth)acrylate with a six-membered cyclic carbonate can also be suitably used as the hydroxyl group-containing acrylic monomer (ii).

[0032] Examples of other ethylenically unsaturated monomers (iii) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, styrene, vinyl toluene, α-methyl styrene, (meth)acrylonitrile, (meth)acrylamide, and vinyl acetate.

[0033] As an alternative method for preparing the aminated acrylic resin (B), as described above, an acrylic monomer having a hydroxyl group and other ethylenically unsaturated monomers may be copolymerized with an epoxy group-containing acrylic monomer (iv) such as glycidyl (meth)acrylate, followed by reaction of the epoxy group with a secondary amine. Secondary amines that can be used in the reaction with the epoxy group include diethylamine, dibutylamine, dicyclohexylamine, morpholine, diethanolamine, and N-methylethanolamine, with amines containing a hydroxyl group and a secondary amino group in the molecule being particularly preferred. Also usable are methyl isobutyl ketone diketimine products of diethylenetriamine and methyl isobutyl ketone monoketimine products of 2-(2-aminoethylamino)ethanol. Examples of the epoxy group-containing acrylic monomer (iv) include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, and 3,4-epoxycyclohexylmethyl (meth)acrylate.

[0034] The polymerization of the acrylic monomers (i) to (iv) can be carried out by a conventional method such as solution polymerization. The number average molecular weight of the copolymer may be, for example, 1,000 or more, 1,500 or more, or 2,000 or more, and may be 50,000 or less, 40,000 or less, 30,000 or less, or 20,000 or less. During the preparation of the aminated acrylic resin (B), the degree of polymerization can be adjusted, if necessary, using a chain transfer agent such as dodecyl mercaptan or 2-ethylhexyl thioglycolate.

[0035] A half-blocked diisocyanate may be added to an amino group-containing acrylic polymer via a urethane bond to impart self-crosslinking properties. In this case, it is preferable to use an alicyclic diisocyanate such as isophorone diisocyanate (IPDI), 4,4'-methylenebis(cyclohexyl isocyanate) (hydrogenated MDI), or norbornane diisocyanate (NBDI).

[0036] A known blocking agent can be used to block one of the isocyanate groups of the diisocyanate to form a half-blocked diisocyanate. Examples of the blocking agent include alcohols such as n-butanol, 2-ethylhexanol, ethylene glycol monobutyl ether, and cyclohexanol; phenols such as phenol, nitrophenol, cresol, and nonylphenol; oximes such as dimethyl ketoxime, methyl ethyl ketoxime, and methyl isobutyl ketoxime; and lactams such as ε-caprolactam.

[0037] In one aspect of this embodiment, the aminated acrylic resin (B) can be designed to have a lower SP value than the aminated epoxy resin (A). By using the aminated epoxy resin (A) in combination with the aminated acrylic resin (B) having a lower SP value than the aminated epoxy resin (A), at least a portion of the aminated epoxy resin (A) migrates to the metal substrate during baking after electrodeposition coating, thereby improving corrosion resistance, and at least a portion of the aminated acrylic resin (B) migrates to the coating film surface, thereby improving, for example, the weather resistance of the cured electrodeposition coating film as a single film.

[0038] The SP values ​​of the aminated epoxy resin (A) and the aminated acrylic resin (B) can be determined by calculation based on the SP values ​​of homopolymers of the constituent monomers that make up the resins and the weight fractions of each constituent monomer in the monomer mixture.

[0039] The aminated acrylic resin (B) also preferably contains hydroxyl groups. The hydroxyl value of the aminated acrylic resin (B) may be, for example, 20 to 250 mgKOH / g or more. The hydroxyl value of the aminated acrylic resin (B) may be 40 mgKOH / g or more, 50 mgKOH / g or more, or 55 mgKOH / g or more, and may be 200 mgKOH / g or less, 180 mgKOH / g or less, or 160 mgKOH / g or less. The monomer composition can be configured so that the hydroxyl value falls within the above range by methods well known to those skilled in the art.

[0040] The amine value of the aminated acrylic resin (B) may be, for example, 20 to 100. The amine value of the aminated acrylic resin (B) may be 20 or more, 30 or more, or 35 or more, and may be 95 or less, 90 or less, 85 or less, or 80 or less. The monomer composition can be configured so that the amine value of the aminated acrylic resin (B) falls within the above range by methods well known to those skilled in the art.

[0041] The aminated acrylic resin (B) may have a resin solids mass ratio of aminated epoxy resin (A) to aminated acrylic resin (B) of (A):(B) in the range of 5:95 to 30:70, or in the range of 10:90 to 40:60. By setting the resin solids mass ratio of aminated epoxy resin (A) to aminated acrylic resin (B) in the above range, there is an advantage in that the weather resistance of the electrodeposition coating film single layer can be further improved.

[0042] (Other Film-Forming Resins) The coating composition may optionally contain an aminated resin other than the aminated epoxy resin (A) and the aminated acrylic resin (B), such as an aminated polyester resin. The coating composition may also contain a film-forming resin other than the above aminated resins. Examples of other film-forming resins include hydroxyl-containing acrylic resins, hydroxyl-containing polyester resins, urethane resins, butadiene resins, phenolic resins, and xylene resins. Of the film-forming resins contained in the coating composition that react with a curing agent to form a coating film, 80% by mass or more, even 90% by mass or more, and particularly 100% by mass may be composed of the aminated epoxy resin (A) and the aminated acrylic resin (B).

[0043] <Blocked Polyisocyanate Curing Agent (C)> The blocked polyisocyanate curing agent (C) (hereinafter sometimes simply referred to as curing agent (C)) also constitutes an electrodeposition coating film. The blocked polyisocyanate curing agent (C) reacts preferentially with the amine groups of the aminated epoxy resin (A) and the aminated acrylic resin (B), and further reacts with the hydroxyl groups, thereby curing the aminated epoxy resin (A) and the aminated acrylic resin (B). The blocked polyisocyanate curing agent (C) can be prepared by blocking a polyisocyanate compound with a blocking agent.

[0044] Examples of polyisocyanate compounds include aliphatic polyisocyanate compounds having 3 to 12 carbon atoms, such as hexamethylene diisocyanate (including trimer), 2,2,4-trimethylhexane diisocyanate, and lysine diisocyanate; and alicyclic polyisocyanate compounds, such as 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isopropylidenedicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, and 2,5- or 2,6-bis(isocyanatomethyl)-bicyclo[2.2.1]heptane (also referred to as norbornane diisocyanate); Examples of suitable diisocyanate compounds include aromatic polyisocyanate compounds such as tolylene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI), polymethylene polyphenyl polyisocyanate (MDI polymer, polymeric MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; aliphatic polyisocyanate compounds having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); and modified products of these diisocyanates (urethane compounds, carbodiimides, uretdione, uretoimine, biuret, isocyanurate modified products, etc.). In this specification, polyisocyanate compounds (particularly aliphatic polyisocyanate compounds) also include their isocyanurate forms. For example, in this specification, the isocyanurate of hexamethylene diisocyanate is included in the aliphatic polyisocyanate compounds. The polyisocyanate compound may be used alone or in combination with two or more thereof. Furthermore, an adduct or prepolymer obtained by reacting the above polyisocyanate compound with a polyhydric alcohol such as ethylene glycol, propylene glycol, trimethylolpropane, or hexanetriol at an NCO / OH ratio of 2 or more may also be used to prepare the blocked isocyanate curing agent (C).

[0045] 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; oximes 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.

[0046] In one preferred embodiment of the cationic electrodeposition coating composition of the present disclosure, the blocked polyisocyanate curing agent (C) comprises an oxime-blocked isocyanate curing agent, which is a blocked reaction product of a blocking agent containing an oxime compound and a polyisocyanate, and the polyisocyanate in the blocking reaction comprises one or more compounds selected from the group consisting of aromatic polyisocyanate compounds, aliphatic polyisocyanate compounds, and alicyclic polyisocyanate compounds. As mentioned above, blocking with oximes has the effect of lowering the curing temperature of the electrodeposition coating composition. In the examples of the present invention, the curability of the electrodeposition coating film (single-layer coating film) was specifically evaluated by baking at 135°C for 25 minutes. High curability after 25 minutes of curing at 135°C can be determined to be high low-temperature curing ability.

[0047] One embodiment of the cationic electrodeposition coating composition of the present disclosure is one in which the blocked polyisocyanate curing agent (C) contains an oxime-blocked isocyanate curing agent, which is a blocked reaction product of a blocking agent containing an oxime compound and a polyisocyanate, and the polyisocyanate in the blocking reaction contains an aliphatic polyisocyanate compound and / or an alicyclic polyisocyanate compound.

[0048] Another embodiment of the cationic electrodeposition coating composition of the present disclosure is one in which the blocked polyisocyanate curing agent (C) contains an oxime-blocked isocyanate curing agent, which is a blocked reaction product of a blocking agent containing an oxime compound and a polyisocyanate, and the polyisocyanate in the blocking reaction contains at least an aliphatic polyisocyanate compound and an alicyclic polyisocyanate compound.

[0049] The above-mentioned configuration has the advantage of ensuring low-temperature curing properties and maintaining a favorable balance of the physical properties of the resulting electrodeposition coating film. In the above-mentioned embodiment, the blocked polyisocyanate curing agent is preferably a combination of an aliphatic polyisocyanate compound and an alicyclic polyisocyanate compound as the polyisocyanate curing agent before blocking, since this alleviates internal stress in the curing agent. When an aliphatic polyisocyanate compound and an alicyclic polyisocyanate compound are used in combination, the mass ratio of aliphatic polyisocyanate compound / alicyclic polyisocyanate compound is 5 / 95 to 95 / 5, preferably 20 / 80 to 80 / 20, and more preferably 30 / 70 to 70 / 30.

[0050] The content of the blocked polyisocyanate curing agent (C) is set taking into consideration the structure of the curable resin (specifically, the combination of the aminated epoxy resin (A) and the aminated acrylic resin (B)). Specifically, a sufficient amount of curing agent is used to react with the active hydrogen-containing functional groups, such as primary amino groups, secondary amino groups, and hydroxyl groups, possessed by the curable resin. The curing agent is blended, for example, so that the solids mass ratio of the curable resin to the blocked polyisocyanate curing agent (C) (referred to as curable resin / curing agent) is 90 / 10 to 50 / 50, more preferably 80 / 20 to 65 / 35. The fluidity and curing speed of the electrodeposition coating composition are controlled by the solids mass ratio of the curable resin to the curing agent.

[0051] The content of the curing agent (typically, curing agent (C)) is set taking into consideration the amount, structure, etc. of the film-forming resin (typically, the aminated epoxy resin (A) and the aminated acrylic resin (B)). Specifically, a sufficient amount of curing agent is used to react with the active hydrogen-containing functional groups, such as primary amino groups, secondary amino groups, and hydroxyl groups, possessed by the film-forming resin. The curing agent is blended, for example, so that the solids mass ratio of the film-forming resin to the curing agent (film-forming resin / curing agent) is 90 / 10 to 50 / 50, more preferably 80 / 20 to 65 / 35. The fluidity and curing speed of the coating composition are controlled by the solids mass ratio of the film-forming resin to the curing agent.

[0052] The coating composition may contain a curing agent other than the blocked polyisocyanate curing agent (C) as needed. Examples of other curing agents include organic curing agents such as melamine resins or phenolic resins, silane coupling agents, and metal curing agents. Of all the curing agents contained in the coating composition, 80% by mass or more, even 90% by mass or more, and particularly 100% by mass may be the blocked polyisocyanate curing agent (C).

[0053] <Pigment (D)> The pigment is a pigment commonly used in coating compositions. Examples of pigments include coloring 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. The coating composition may contain an extender pigment to further improve edge rust prevention. The extender pigment can interact appropriately with the cyclic polyamidine compound.

[0054] The solid content of the coating composition refers to all components contained in the coating composition that remain in the form of a solid even after removal of the solvent, specifically, the solid components contained in the coating composition, such as the aminated epoxy resin (A), aminated acrylic resin (B), blocked polyisocyanate curing agent (C), pigment (D), and cyclic polyamidine compound or its hydrophobic modified product (E), as well as any pigment dispersing resin that is contained as needed.

[0055] Pigments are usually added to coating compositions as a pigment dispersion paste comprising a pigment dispersing resin and a pigment.

[0056] (Pigment Dispersion Resin) The pigment dispersion resin is a resin for dispersing pigments. Examples of the pigment dispersion resin include pigment dispersion resins having a cationic group, such as modified epoxy resins having at least one group selected from a quaternary ammonium group, a tertiary sulfonium group, and a primary amino group. Specific examples of the pigment dispersion resin include quaternary ammonium group-containing epoxy resins and tertiary sulfonium group-containing epoxy resins. Examples of the aqueous solvent include ion-exchanged water and ion-exchanged water containing a small amount of alcohol.

[0057] <Cyclic Polyamidine Compound or Hydrophobically Modified Product thereof (E)> The cyclic polyamidine compound or hydrophobically modified product thereof (E) is a compound represented by the following general formula: (In the formula, R １ and R ２are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and X is an anion.

[0058] Such polyamidine compounds having a cyclic structure are easily deposited on the edge because they have an electric charge, and further increase the viscosity of the coating composition, which is thought to improve the edge rust prevention properties.

[0059] R １ and R ２ may each independently be a hydrogen atom. X represents an anion, for example, a halogen ion. Examples of the halogen ion include F － , Cl － ,Br － , I － Among them, halogen ions are Cl because they are easily available. － It may be.

[0060] The cyclic polyamidine compound (E) can be synthesized, for example, by hydrolyzing a copolymer of N-vinylcarboxylic acid amide and unsaturated nitrile in the presence of an acid. During the hydrolysis in the presence of an acid, the amide group derived from the N-vinylcarboxylic acid amide is hydrolyzed and reacts with the cyano group of the unsaturated nitrile to form a cyclic amidine skeleton.

[0061] Examples of N-vinylcarboxylic acid amides include N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinylformamide, N-methyl-N-vinylformamide, N-vinylpropionic acid amide, and N-vinylbutyric acid amide. These may be used alone or in combination of two or more.

[0062] The unsaturated nitrile may have, for example, 3 to 18 carbon atoms, or 3 to 9 carbon atoms. Specific examples of the unsaturated nitrile include acrylonitrile; α-alkyl acrylonitriles such as methacrylonitrile and ethacrylonitrile; fumaronitrile; and α-halogeno acrylonitriles such as α-chloro acrylonitrile and α-bromo acrylonitrile. These may be used alone or in combination of two or more.

[0063] The acid used for the hydrolysis is, for example, a strong inorganic acid, and specific examples thereof include hydrochloric acid, nitric acid, and p-toluenesulfonic acid.

[0064] The cyclic polyamidine compound (E) may be a partially hydrolyzed copolymer of N-vinylcarboxylic acid amide and unsaturated nitrile, which can be explained using the following chemical formula:

[0065] For example, N-vinylcarboxylic acid amide can be ２ =CR ４ -NH-CO-R ６ and unsaturated nitrile is represented by CH ２ =CR ５ When R is represented by —CN, the copolymerized polymer is usually represented by the following general formula (II). １ or R ２ However, R ４ ~R ６ is used because general formula (I) and general formula (II) represent different parts of the copolymer. (In the above general formula (II), R ４ , R ５ and R ６ are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms.) The copolymer of general formula (II) represents a state in which each monomer is polymerized alternately, but in reality it is composed of the following N-vinylcarboxylic acid amide structural unit (III) and unsaturated nitrile structural unit (IV) bonded randomly: (In the above formulas (III) and (IV), R ４ ~R ６ has the same meaning as above.)

[0066] When such a copolymer has a structure in which the structural unit (III) and the structural unit (IV) are arranged side by side, as in the above general formula (II), upon hydrolysis in the presence of an acid, the amide group derived from the N-vinylcarboxylic acid amide (amide group of formula (III)) is hydrolyzed and reacts with the cyano group of the unsaturated nitrile (cyano group of formula (IV)), forming a cyclic amidine skeleton and resulting in the cyclic amidine structure of general formula (I).

[0067] The ratio of the number of structural units (I) to the total number of structural units (I) and structural units (II) in one molecule of the cyclic polyamidine compound (E): I / (I+II) may be 5% or more, 10% or more, or 20% or more. The ratio: I / (I+II) may be 100%, 90% or less, or 80% or less.

[0068] In another preferred embodiment of the present invention, the cyclic polyamidine compound is modified to introduce a hydrophobic moiety into the polyamidine compound. Hydrophobization offers the advantage of improving the stability of the coating material (cationic electrodeposition coating composition) when it is formed. More specifically, hydrophobizing the polyamidine compound has the advantage of improving the storage stability when the polyamidine compound is mixed with a resin emulsion containing an aminated epoxy resin (A) and a curing agent. Hydrophobization is primarily carried out by the following two methods. In the first hydrophobization method, when the unsaturated nitrile structural units (IV) are arranged adjacent to each other, a cyclization reaction between the nitrile groups occurs with an acid, producing a cyclized structural unit.

[0069] Taking acrylonitrile as an example, the formation of the nitrile cyclized structural unit can be expressed by the following chemical reaction formula: As is clear from this reaction formula, two nitrile groups (CN) are cyclized to form the above-mentioned nitrogen atom-containing six-membered ring structure (aminopyridine structure or six-membered ring pyridine derivative-like structure), and this nitrile cyclized structural unit has higher hydrophobicity than the other parts, so it can be hydrophobized.

[0070] The first method of hydrophobic modification involves heating the reaction in the presence of an acid. The acid is preferably a weak acid such as acetic acid, formic acid, lactic acid, phosphoric acid, oxalic acid, or hydrogen sulfide, and the heating temperature is preferably 70 to 98°C. The amount of acid added is preferably 5 to 40 parts by weight, more preferably 8 to 25 parts by weight, per 100 parts by weight of the polyamidine compound. The reaction time can be appropriately selected depending on the heating conditions and the amount of acid added, and can be selected from the range of, for example, 3 to 80 hours, more preferably 6 to 46 hours. Pressurized conditions may be applied to accelerate the reaction.

[0071] The second method of hydrophobic modification is to further react the amidine ring represented by the above formula (I) with an alkyl halide compound to bond an alkyl group to the amidine ring, thereby imparting hydrophobicity. This reaction is represented by the following reaction formula: (In the above reaction formula, R １ ~R ３ and X are as defined above, and Hal represents a halogen atom.

[0072] The second method of hydrophobic modification involves heating the reaction in the presence of an alkali. Reaction conditions include, for example, pH 4.0 to 6.5 and the addition of an alkaline substance such as sodium hydroxide, potassium hydroxide, or aqueous ammonia. Heating conditions are preferably 80°C to 98°C. The reaction time can be appropriately selected depending on the heating conditions, pH conditions, and the type of alkaline substance used, and can be selected within the range of, for example, 2 to 36 hours, more preferably 10 to 24 hours. Pressurization may be applied to accelerate the reaction.

[0073] Alkyl halide (R ３ -Hal), R ３ contains at least one of a substituted or unsubstituted linear or branched alkyl group having 3 to 12 carbon atoms, or a substituted or unsubstituted aromatic group having 6 to 12 carbon atoms. ３is an alkyl group (e.g., n-propyl, sec-propyl, n-butyl, sec-butyl, hexyl, n-pentyl, sec-pentyl, neopentyl, heptyl, pentyl, octyl, etc.); or an aromatic group (e.g., benzyl, naphthalene, etc.). As the substituent of these groups, any substituent that does not affect the hydrophobic modification can be used without any particular limitation. Examples of the substituent include alkenyl groups having 3 to 6 carbon atoms and alkyl ether groups having 3 to 6 carbon atoms. The above alkyl groups and aromatic groups preferably have no substituent. Examples of the halogen atom in the alkyl halide include a chlorine atom, a bromine atom, and a fluorine atom. The alkyl halide (R ３ -Hal) is more specifically chlorohexane, bromohexane, chloropentane, bromopentane, iodohexane, iodopentane, chloroheptane, bromoheptane, iodoheptane, chlorooctane, bromooctane, iodooctane, and the like.

[0074] The weight-average molecular weight of the cyclic polyamidine compound or its hydrophobically modified product (E) is, for example, 50,000 or more. This allows a small amount to be used to achieve the effect of improving edge rust prevention. The weight-average molecular weight of the cyclic polyamidine compound or its hydrophobically modified product (E) may be 80,000 or more, 100,000 or more, or 300,000 or more. The weight-average molecular weight of the cyclic polyamidine compound or its hydrophobically modified product (E) may be 4,000,000 or less, 3,500,000 or less, 3,200,000 or less, or 3,000,000 or less. In one aspect, the weight-average molecular weight of the cyclic polyamidine compound or its hydrophobically modified product (E) may be 50,000 or more and 4,000,000 or less, or 80,000 or more and 3,200,000 or less.

[0075] In the present disclosure, the weight average molecular weight of the cyclic polyamidine compound or its hydrophobically modified product (E) is measured by a molecular weight measuring device (such as DLS-7000 manufactured by Otsuka Electronics Co., Ltd.) using a static light scattering method.

[0076] The solids mass of the cyclic polyamidine compound or its hydrophobized modified product (E) may be 0.2 ppm or more of the solids mass of the cationic electrodeposition coating composition. The solids mass of the cyclic polyamidine compound or its hydrophobized modified product (E) may be 1,200 ppm or less. Even with such a small amount of the cyclic polyamidine compound or its hydrophobized modified product (E) added, the effect of improving edge rust prevention can be obtained. The solids mass of the cyclic polyamidine compound or its hydrophobized modified product (E) may be 1 ppm or more, 2 ppm or more, or 50 ppm or more. The solids mass of the cyclic polyamidine compound or its hydrophobized modified product (E) may be 1,000 ppm or less, 700 ppm or less, or 200 ppm or less. In one embodiment, the solids mass of the cyclic polyamidine compound or its hydrophobized modified product (E) is 20 ppm or more and 1,200 ppm or less, and may be 25 ppm or more and 1,000 ppm or less, 25 ppm or more and 700 ppm or less, or 50 ppm or more and 200 ppm or less.

[0077] <Curing Catalyst> The coating composition may contain a curing catalyst. The curing catalyst is not particularly limited, and any known catalyst in the coating field can be used. Examples of curing catalysts include organotin compounds and bismuth compounds. Examples of organotin compounds include dibutyltin oxide, dioctyltin oxide, dioctyltin dilaurate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dibenzoate, and dioctyltin dibenzoate. Examples of bismuth compounds include bismuth oxide, bismuth hydroxide, bismuth subsalicylate, and bismuth subnitrate. In a preferred embodiment of the cationic electrodeposition coating composition of the present disclosure, a curing catalyst containing a bismuth compound can be used.

[0078] From the viewpoint of environmental load, the content of the curing catalyst (particularly, the organotin compound) may be 0.5 mass % or less, or 0.25 mass % or less, of the solid content of the coating composition.

[0079] <Metal Nitrite> The coating composition may further contain a metal nitrite. The metal nitrite can further improve edge rust prevention. As the metal nitrite, a nitrite of an alkali metal or a nitrite of an alkaline earth metal is preferred, and a nitrite of an alkaline earth metal is more preferred. Examples of the metal nitrite include calcium nitrite, sodium nitrite, potassium nitrite, magnesium nitrite, strontium nitrite, barium nitrite, and zinc nitrite.

[0080] The content of the metal nitrite is, for example, 0.001% by mass or more and 0.2% by mass or less in terms of the metal element of the metal component relative to the total mass of the coating film-forming resin and the curing agent.

[0081] (Other Components) The coating composition may contain additives commonly used in the coating field, such as organic solvents, surfactants such as drying inhibitors and antifoaming agents, viscosity modifiers such as acrylic resin microparticles, anti-repellent agents, and inorganic rust inhibitors, as needed. Examples of organic solvents include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and propylene glycol monophenyl ether. Examples of inorganic rust inhibitors include vanadium salts, copper salts, iron salts, manganese salts, magnesium salts, and calcium salts.

[0082] Furthermore, in addition to the above, known auxiliary complexing agents, buffering agents, smoothing agents, stress relaxation agents, glossing agents, semi-glossing agents, antioxidants, ultraviolet absorbers, etc. may be included depending on the purpose.

[0083] <Preparation of Cationic Electrodeposition Coating Composition> The coating composition is prepared by mixing, by a commonly used method, a resin emulsion containing a coating film-forming resin (typically, an aminated epoxy resin (A) and an aminated acrylic resin (B)) and a curing agent (typically, a blocked polyisocyanate curing agent (C)), a pigment dispersion paste containing a pigment (D), and a cyclic polyamidine compound or a hydrophobically modified cyclic polyamidine compound (E; hereinafter, simply referred to as "cyclic polyamidine compound (E)" may also mean "cyclic polyamidine or a hydrophobically modified cyclic polyamidine compound (E)").

[0084] The cyclic polyamidine compound or its hydrophobically modified product (E), other components and additives may be added to the resin emulsion, the pigment dispersion paste, or the resin emulsion and the pigment dispersion paste during or after mixing. The cyclic polyamidine compound or its hydrophobically modified product (E), etc., are added to these, for example, in the form of an aqueous solution.

[0085] (Preparation of Resin Emulsion) In one embodiment of the resin emulsion preparation, the aminated epoxy resin (A), the aminated acrylic resin (B), and optionally other film-forming resins, as well as the blocked polyisocyanate curing agent (C) and other curing agents, are each dissolved in an organic solvent to prepare a solution, and these solutions are mixed and then neutralized with a neutralizing acid. In another embodiment of the resin emulsion preparation, the aminated epoxy resin (A) and the aminated acrylic resin (B) can each be prepared as a resin emulsion. In this embodiment, the aminated epoxy resin (A), and optionally other film-forming resins, as well as the blocked polyisocyanate curing agent (C) and other curing agents, are each dissolved in an organic solvent to prepare a solution, and these solutions are mixed and then neutralized with a neutralizing acid to prepare the epoxy resin emulsion. The aminated acrylic resin (B), and optionally other film-forming resins, as well as the blocked polyisocyanate curing agent (C) and other curing agents, are each dissolved in an organic solvent to prepare a solution, and the solutions are mixed and then neutralized with a neutralizing acid, thereby preparing the acrylic resin emulsion.

[0086] 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 one or more selected from the group consisting of formic acid, acetic acid, and lactic acid.

[0087] The solid content of the resin emulsion may be, for example, 25% by mass or more and 50% by mass or less, or 35% by mass or more and 45% by mass or less, based on the total amount of the resin emulsion. The solid content of the resin emulsion refers to all components contained in the resin emulsion that remain in solid form even after removal of the solvent. Specifically, the solid content of the resin emulsion refers to the aminated epoxy resin (A), aminated acrylic resin (B), blocked polyisocyanate curing agent (C), and other solid components added as needed, contained in the resin emulsion.

[0088] The amount of neutralizing acid used, expressed as the equivalent ratio of the neutralizing acid to the equivalent of the amino groups in the aminated epoxy resin, may be 10% or more and 100% or less, or 20% or more and 70% or less. Hereinafter, the equivalent ratio of the neutralizing acid to the equivalent of the amino groups in the aminated epoxy resin will be referred to as the neutralization rate. A neutralization rate of 10% or more ensures affinity for water and improves water dispersibility.

[0089] (Method for preparing pigment dispersion paste) The pigment dispersion paste is prepared by mixing a pigment dispersion resin and a pigment. The solid content mass of the pigment dispersion resin in the pigment dispersion paste is not particularly limited, and may be, for example, 20 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the pigment.

[0090] The solid content mass of the pigment dispersion paste is, for example, 40% by mass or more and 70% by mass or less, and may be 50% by mass or more and 60% by mass or less.

[0091] The solid content of the pigment dispersion paste refers to all components contained in the pigment dispersion paste that remain solid even after removal of the solvent, specifically, the pigment dispersion resin, pigment, and other solid components added as needed.

[0092] [Method for producing an electrodeposition-coated article] An electrodeposition coating film is formed by electrodeposition coating an article using a coating composition. An electrodeposition-coated article having an electrodeposition coating film is produced by a method (production method 1) comprising the steps of immersing the article in the cationic electrodeposition coating composition according to this embodiment, applying a voltage between the article and a counter electrode to form an uncured electrodeposition coating film on the article, and heating the coating film at a temperature of 75°C or higher and 200°C or lower to obtain a cured electrodeposition coating film.

[0093] As described above, the cationic electrodeposition coating composition contains the aminated epoxy resin (A), the aminated acrylic resin (B), the blocked polyisocyanate curing agent (C), the pigment (D), and the cyclic polyamidine compound or its hydrophobic modified product (E).

[0094] (1) Formation of an uncured electrodeposition coating film After immersing a substrate in a cationic electrodeposition coating composition, a voltage is applied between the substrate as a cathode and a counter electrode (anode), resulting in the deposition of an uncured electrodeposition coating film on the substrate.

[0095] (Application Conditions) The voltage is, for example, 50 V or more and 450 V or less. The bath liquid temperature is, for example, 10° C. or more and 45° C. or less. The time for applying the voltage is not particularly limited, and is, for example, 2 minutes or more and 5 minutes or less.

[0096] (Substrate) The material of the substrate is not particularly limited as long as it is electrically conductive. The shape of the substrate is also not particularly limited, and it may be flat or have a complex three-dimensional shape. Examples of substrates 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, tin-plated steel sheets, and those that have been subjected to a chemical conversion treatment (e.g., a surface treatment using a phosphate, zirconium salt, or the like). When performing a chemical conversion treatment with a phosphate, the substrate may be surface-conditioned with a zinc-, titanium-, or manganese-based surface conditioner prior to the chemical conversion treatment. This makes the crystals of the zinc phosphate coating denser.

[0097] (2) Curing of Electrodeposition Coating Film The formed uncured electrodeposition coating film is washed with water, if necessary, and then heated at a temperature of 75° C. to 200° C. This causes a curing reaction to occur, resulting in a cured electrodeposition coating film.

[0098] (Curing Conditions) The curing temperature may be 100° C. or higher, or may be 110° C. or higher. The curing temperature may be, for example, 180° C. or lower, or may be 150° C. or lower. The heating time is not particularly limited, and is, for example, 10 to 30 minutes.

[0099] [Electrodeposition-coated product] An electrodeposition-coated product has a substrate and an electrodeposition coating film formed on the substrate using the cationic electrodeposition coating composition described above. The electrodeposition coating film is cured. The electrodeposition-coated product is produced, for example, by the method described above. The electrodeposition-coated product has excellent rust prevention properties, particularly edge rust prevention properties. The electrodeposition-coated product also has a good appearance.

[0100] From the viewpoint of rust prevention, the thickness of the cured electrodeposition coating film may be 5 μm or more and 60 μm or less. 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.

[0101] Edge rust prevention is evaluated, for example, by a salt spray test (35°C x 72 hours) in accordance with JIS Z 2371 (2000) performed on a cured electrodeposition coating film with a film thickness of 25 to 50 μm. If the number of rust particles that occur at the edge of the coated object after the salt spray test is less than 5 particles / cm2, the edge rust prevention can be evaluated as excellent.

[0102] [Method 2 for producing electrodeposition-coated article] In consideration of the effects of the cyclic polyamidine compound, the cyclic polyamidine compound may be used as a pretreatment agent for electrodeposition coating (electrodeposition pretreatment agent). An electrodeposition pretreatment layer containing the cyclic polyamidine compound is also deposited on the edge portion, resulting in a coating film with excellent edge rust prevention properties.

[0103] That is, an electrodeposition-coated article having an electrodeposition coating film can also be produced by a method comprising the steps of: applying an electrodeposition pretreatment agent containing a cyclic polyamidine compound or a hydrophobically modified form (E) thereof to an article to be coated; immersing the article to which the electrodeposition pretreatment agent has been applied in a cationic electrodeposition coating composition; and then applying a voltage between the article to be coated and a counter electrode to form an uncured electrodeposition coating film on the article to be coated; and heating the uncured electrodeposition coating film at a temperature of 75°C or higher and 200°C or lower to obtain a cured electrodeposition coating film.

[0104] The cationic electrodeposition coating composition used in Production Method 2 contains an aminated epoxy resin (A), an aminated acrylic resin (B), a blocked polyisocyanate curing agent (C), and a pigment (D). The cyclic polyamidine compound or its hydrophobically modified form (E) is contained in an electrodeposition pretreatment agent, which is applied to the substrate prior to the application of the cationic electrodeposition coating composition. The cationic electrodeposition coating composition containing the aminated epoxy resin (A), the aminated acrylic resin (B), the blocked polyisocyanate curing agent (C), and the pigment (D) and the electrodeposition pretreatment agent containing the cyclic polyamidine compound or its hydrophobically modified form (E) are used in combination as a paint set.

[0105] (1) Application of Electrodeposition Pretreatment Agent An electrodeposition pretreatment agent containing a cyclic polyamidine compound or its hydrophobized modified form (E) is applied to a substrate. The electrodeposition pretreatment agent is, for example, an aqueous solution of the cyclic polyamidine compound or its hydrophobized modified form (E). The concentration of the cyclic polyamidine compound is, for example, 10% by mass.

[0106] The application method is not particularly limited, and the substrate may be immersed in the electrodeposition pretreatment agent, or the electrodeposition pretreatment agent may be applied to the substrate. Application methods include coating and spraying. After the electrodeposition pretreatment agent has been applied, a voltage may be applied to the substrate. The voltage is, for example, 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 time for applying the voltage is not particularly limited, and is, for example, 2 minutes or more and 5 minutes or less. After the electrodeposition pretreatment agent has been applied, the substrate may be subjected to the next step without applying a voltage.

[0107] Examples of substrates that can be coated include those similar to those in Production Method 1. The application of the electrodeposition pretreatment agent is carried out after the above-mentioned surface conditioning treatment and chemical conversion treatment, and before electrodeposition coating.

[0108] (2) Formation of Uncured Electrodeposition Coating Film After immersing a substrate to which an electrodeposition pretreatment agent has been applied in the cationic electrodeposition coating composition, a voltage is applied between the substrate as the cathode and a counter electrode (anode). As a result, an uncured electrodeposition coating film is deposited on the substrate via a film containing the cyclic polyamidine compound or its hydrophobic modified form (E). The application conditions may be the same as those in Production Method 1.

[0109] (3) Curing of Electrodeposition Coating Film The formed uncured electrodeposition coating film is washed with water as needed and heated at a temperature of 75°C or higher and 200°C or lower. This causes a curing reaction to occur, resulting in a cured electrodeposition coating film. The curing conditions may be the same as those in Production Method 1.

[0110] From the viewpoint of rust prevention, the thickness of the cured electrodeposition coating film may be 5 μm or more and 60 μm or less. 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.

[0111] [Electrodeposition-coated article 2] Production method 2 provides an electrodeposition-coated article comprising a substrate, an electrodeposition pretreatment layer formed on the substrate and containing a cyclic polyamidine compound or a hydrophobized modified product thereof (E), and an electrodeposition coating film formed from a cationic electrodeposition coating composition containing an aminated epoxy resin (A), a blocked polyisocyanate curing agent (C), and a pigment (D).

[0112] Alternatively, an electrodeposition-coated article comprising a substrate and an electrodeposition coating film formed on the substrate can be obtained by Production Method 2. The electrodeposition coating film is formed from a cationic electrodeposition coating composition comprising an aminated epoxy resin (A), an aminated acrylic resin (B), a blocked polyisocyanate curing agent (C), and a pigment (D), and further contains at least a portion of the cyclic polyamidine compound or its hydrophobized modified form (E) contained in the electrodeposition pretreatment agent. These electrodeposition coating films have excellent edge rust prevention and appearance.

[0113] The cationic electrodeposition coating composition according to this embodiment has the advantage of providing good weather resistance by containing an aminated epoxy resin (A) and an aminated acrylic resin (B) as film-forming resins that react with a curing agent, and therefore has the advantage that it can be suitably used in coating applications in which the formation of an intermediate coating film and / or a top coating film, which are generally formed on an electrodeposition coating film, is omitted, such as the coating of specific parts or components of an automobile body.

[0114] 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.

[0115] Production Example 1-1 Production of aminated epoxy resin (A1) 26 parts of butyl cellosolve, 940 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by Dow Chemical Company), 380 parts of bisphenol A, 58 parts of phenol, and 2 parts of dimethylbenzylamine were added to a reaction vessel, and the internal temperature was maintained at 120°C. The reaction was continued until the epoxy equivalent reached 1,100 g / eq, and then the reaction vessel was cooled to a temperature of 110°C. 60 parts of diethanolamine (DETA), 20 parts of N-methylethanolamine (MMA), and 85 parts of diethylenetriamine diketimine (diketimine: methyl isobutyl ketone solution with a solids content of 73%) were added, and the mixture was allowed to react at 140°C for 1 hour to obtain aminated epoxy resin (A1).

[0116] Production Example 1-2: Production of aminated epoxy resin (A2) 12 parts of butyl cellosolve, 940 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by The Dow Chemical Company), 325 parts of bisphenol A, 4.2 parts of phenol, and 2 parts of dimethylbenzylamine were added, and the temperature inside the reaction vessel was maintained at 120° C. while the reaction was carried out until the epoxy equivalent reached 620 g / eq., and then the temperature inside the reaction vessel was cooled to 110° C. Next, a mixture of 110 parts of diethanolamine (DETA) and 70 parts of diethylaminopropanediamine (DEAPA) was added, and the reaction was carried out at 140° C. for 1 hour to obtain aminated epoxy resin (A2).

[0117] Production Example 2-1: Production of blocked polyisocyanate curing agent (C1) 222 parts of isophorone diisocyanate was placed in a reaction vessel equipped with a stirrer, a nitrogen inlet tube, a condenser, and a thermometer, and diluted with 56 parts of methyl isobutyl ketone (MIBK), after which 0.2 parts of butyltin laurate was added and the temperature was raised to 50° C. After which 17 parts of methyl ethyl ketoxime was added so that the temperature of the contents did not exceed 70° C. The mixture was then kept at 70° C. for 1 hour until the absorption of isocyanate residues in the infrared absorption spectrum had substantially disappeared, and then diluted with 43 parts of n-butanol to obtain a blocked polyisocyanate curing agent (C1) with a solids content of 70%.

[0118] Production Example 2-2: Production of Blocked Polyisocyanate Curing Agent (Curing Agent C2) 165 parts of an isocyanurate of hexamethylene diisocyanate (trade name Sumidur N3300, manufactured by Sumika Bayer Urethane Co., Ltd.) and 24 parts of MIBK were charged into a reaction vessel and heated to 60°C. 75 parts of methyl ethyl ketoxime (MEK oxime) were added dropwise over 2 hours. After further heating at 70°C for 2 hours, IR spectroscopy confirmed that absorption due to isocyanate groups had disappeared. Thereafter, 36 parts of butyl cellosolve was added to obtain a blocked polyisocyanate curing agent (C2).

[0119] Production Example 2-3 Production of Blocked Polyisocyanate Curing Agent (C3) 1,400 parts of polymeric MDI (MDI: diphenylmethane diisocyanate) was charged into a reaction vessel and heated to 60°C. A mixture of 330 parts of butyl diglycol ether (BDG) and 950 parts of butyl cellosolve (BC) 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 in IR spectrum measurement that absorption due to isocyanate groups had disappeared. After allowing the mixture to cool, 27 parts of methyl isobutyl ketone (MIBK) was added to obtain a blocked polyisocyanate curing agent (C3).

[0120] Production Example 3: Production of aminated acrylic resin (B1) A five-neck flask equipped with a reflux condenser, a stirrer, a dropping funnel, and a nitrogen inlet tube was charged with 82 parts of MIBK and heated to 115°C under a nitrogen atmosphere. To this was added dropwise from the dropping funnel over 3 hours a mixture of 24 parts of glycidyl methacrylate, 25 parts of hydroxyethyl methacrylate, 40 parts of methyl methacrylate, 25 parts of styrene, 35 parts of n-butyl acrylate, and 8 parts of t-butylperoxy 2-ethylhexanoate. After completion of the dropwise addition, the mixture was maintained at 115°C for approximately 1 hour, and then 3 parts of t-butylperoxy 2-ethylhexanoate was added dropwise, followed by maintaining the temperature at 115°C for approximately 30 minutes to obtain an acrylic resin solution with a solids content of 64%. The mixture was then concentrated under reduced pressure to a nonvolatile content of 73%, cooled, and then 3 parts of N-methylethanolamine and 10 parts of 2-ethylaminoethanol were added, followed by reaction at 120°C for 2 hours under a nitrogen atmosphere to obtain a solution of aminated acrylic resin (B1) with a solids content of approximately 76%. The resulting aminated acrylic resin (B1) had a number average molecular weight (Mn) of 7,000 and a glass transition temperature (Tg) of 30°C.

[0121] Production Example 3-1: Production of aminated acrylic resin emulsion (Em-1) 240 parts of the aminated acrylic resin (B) solution obtained in Production Example 3 and 85 parts of the blocked isocyanate curing agent (C2) obtained in Production Example 2-2 were added and stirred for 30 minutes. Thereafter, 4.5 parts of acetic acid was added, and the mixture was diluted with ion-exchanged water to a nonvolatile content of 24%, and then concentrated under reduced pressure to a nonvolatile content of 30% to obtain aminated acrylic resin emulsion (Em-1).

[0122] Production Example 4 Preparation of Pigment Dispersion Resin 2,220 parts of isophorone diisocyanate and 342.1 parts of methyl isobutyl ketone were charged into a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen inlet tube, and a thermometer. The temperature was raised to 50°C, and 2.2 parts of dibutyltin laurate was added. The temperature was raised to 60°C, and 878.7 parts of methyl ethyl ketone oxime was added. The mixture was then kept at 60°C for 1 hour, and it was confirmed that the NCO equivalent was 348. 890 parts of dimethylethanolamine was then added. The mixture was then kept at 60°C for 1 hour, and it was confirmed by IR that the NCO peak had disappeared. Next, while cooling so as not to exceed 60°C, 1,872.6 parts of 50% lactic acid and 495 parts of deionized water were added to obtain a quaternizing agent.

[0123] 870 parts of tolylene diisocyanate and 49.5 parts of methyl isobutyl ketone were charged into a separate reaction vessel. 667.2 parts of 2-ethylhexanol were added dropwise to the reaction vessel over 2.5 hours while cooling so that the temperature did not exceed 50°C. After completion of the dropwise addition, 35.5 parts of methyl isobutyl ketone were added and the mixture was kept warm for 30 minutes. Thereafter, it was confirmed that the NCO equivalent was 330 to 370, and a half-blocked polyisocyanate was obtained.

[0124] A reaction vessel equipped with a stirrer, a condenser, a nitrogen inlet tube, and a thermometer was charged with 940.0 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by The Dow Chemical Company) and 38.5 parts of methanol, followed by the addition of 0.1 parts of dibutyltin dilaurate. The mixture was heated to 50°C, and then 87.1 parts of tolylene diisocyanate was added. The mixture was further heated to 100°C, and 1.4 parts of N,N-dimethylbenzylamine was added. The mixture was then maintained at 130°C for 2 hours. At this time, methanol was fractionated using a fractionating column. The mixture was cooled to 115°C, and methyl isobutyl ketone was added until the solids concentration reached 90%. Subsequently, 270.3 parts of bisphenol A and 39.2 parts of 2-ethylhexanoic acid were added, followed by heating and stirring at 125°C for 2 hours. Subsequently, 516.4 parts of the half-blocked polyisocyanate was added dropwise over 30 minutes, followed by heating and stirring for 30 minutes. Furthermore, 1506 parts of polyoxyethylene bisphenol A ether was gradually added and dissolved therein. After cooling to 90°C, the quaternizing agent was added, and the temperature was maintained at 70 to 80°C. After confirming that the acid value was 2 or less, a pigment dispersion resin (resin solids content 30%) was obtained.

[0125] [Production Example 5] Preparation of pigment dispersion paste 1,200 parts of the pigment dispersion resin obtained in Production Example 4, 3 parts of carbon black, 620 parts of kaolin, 500 parts of titanium dioxide, 70 parts of bismuth oxide, and 1,100 parts of deionized water were placed in a sand grinding mill and dispersed until the particle size reached 10 μm or less, thereby preparing a pigment dispersion paste (solid content 50%).

[0126] [Example 1] Preparation of cationic electrodeposition coating composition (Preparation of epoxy resin emulsion) 400 g (solids content) of the aminated epoxy resin (A1) obtained in Production Example 1-1, 80 g (solids content) of the blocked polyisocyanate curing agent (C1) obtained in Production Example 2-1, and 80 g (solids content) of the blocked polyisocyanate curing agent (C2) obtained in Production Example 2-2 were mixed, and ethylene glycol mono-2-ethylhexyl ether was added so that the concentration was 3% (15 g) based on the solids content. Next, formic acid was added to achieve a neutralization rate of 40%, and the mixture was slowly diluted with ion-exchanged water to obtain an epoxy resin emulsion.

[0127] (Preparation of Cationic Electrodeposition Coating Composition) To a stainless steel container were added 1,800 parts of ion-exchanged water, 700 parts of the epoxy resin emulsion prepared above, 1,200 parts of the acrylic resin emulsion (Em-1) obtained in Production Example 3-1, and 330 parts of the pigment dispersion paste obtained in Production Example 5. The mixture was then aged at 40°C for 16 hours. Furthermore, a 2% aqueous solution of polyamidine compound (E1) (Himoc ZP-700, manufactured by Hymo Co., Ltd., weight-average molecular weight 3,000,000, partial hydrolyzate of acrylonitrile / N-vinylformamide copolymer, ratio of structural unit (I) to structural unit (I+II): I / I+II = 30 to 40%) was added so that the solids content was 100 ppm of the solids mass of the cationic electrodeposition coating composition, thereby obtaining a cationic electrodeposition coating composition.

[0128] The cyclic polyamidine compound (E1) has a structural unit of the following formula:

[0129] Preparation of Electrodeposition Coated Objects Cold-rolled steel sheets (JIS G3141, SPCC-SD) were prepared as substrates. These steel sheets were degreased by immersion in Surf Cleaner EC90 (manufactured by Nippon Paint Surf Chemicals) at 50°C for 2 minutes. Subsequently, they were immersed in Surfdyne EC3200 (manufactured by Nippon Paint Surf Chemicals, a zirconium conversion treatment agent) at 35°C for 90 seconds. Afterwards, they were rinsed with deionized water.

[0130] The viscosity of the cationic electrodeposition coating composition obtained above was adjusted by adding a required amount of 2-ethylhexyl glycol so that the thickness of the electrodeposition coating film after curing would be 20 μm. After all of the steel plates were immersed in the obtained cationic electrodeposition coating composition, voltage application was immediately initiated. The voltage was increased over 30 seconds, and after reaching 180 V, was maintained for 150 seconds. This resulted in the deposition of an uncured electrodeposition coating film on the substrate. The obtained uncured electrodeposition coating film was heat-cured at 135°C for 25 minutes to obtain an electrodeposition-coated product (single-layer coating film) having a cured electrodeposition coating film thickness of 20 μm.

[0131] Example 2 A cationic electrodeposition coating composition was produced in the same manner as in Example 1, except that the aminated epoxy resin (A2) obtained in Production Example 1-2 was used instead of the aminated epoxy resin (A1) obtained in Production Example 1-1. An electrodeposition coated article (single-layer coating film) was produced using the obtained cationic electrodeposition coating composition in the same manner as in Example 1.

[0132] Example 3 Preparation of Hydrophobically Modified Polyamidine Compound (1) Preparation of Aminating Agent 179 parts of diethanolamine were added to a reaction vessel, and the temperature was raised to 50°C. 320 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by The Dow Chemical Company) was added. The temperature was then maintained at 110°C and the reaction was continued until the epoxy equivalent reached 290 g / eq. The mixture was then cooled to 80°C, and 17 parts of 90% acetic acid was added. After stirring for 10 minutes, 420 parts of deionized water was added to obtain an epoxy resin having amine groups introduced therein.

[0133] (2) Hydrophobic Preparation of Polyamidine Compound by Cyclization of Nitrile Groups One part of polyamidine (Himoc ZP-700, manufactured by Hymo Co., Ltd., weight-average molecular weight 3,000,000, partial hydrolyzate of acrylonitrile-N-vinylformamide copolymer, ratio of structural unit (I) to structural unit (I + II): I / I + II = 30-40%) and 499 parts of deionized water were added to a reaction vessel and stirred to prepare a 2% aqueous solution. The temperature inside the reaction vessel was then maintained at 90°C, and 1 part of 90% acetic acid and 30 parts of the epoxy resin with amine groups introduced thereinto as an amine catalyst were added, followed by heating for 46 hours to obtain polyamidine compound E2 (a hydrophobic modified polyamidine compound) having unsaturated nitrile cyclized segment units (two nitrile groups (CN) cyclized).

[0134] Preparation of cationic electrodeposition coating composition and production of electrodeposition-coated article A cationic electrodeposition coating composition was obtained in the same manner as in Example 1, except that the hydrophobic modified polyamidine compound (E2) obtained above was added in place of the polyamidine compound (E1) so that its solid content was 100 ppm based on the solid content mass of the cationic electrodeposition coating composition. Using the obtained cationic electrodeposition coating composition, an electrodeposition-coated article (single-layer coating film) was produced in the same manner as in Example 1.

[0135] [Comparative Example 1] A cationic electrodeposition coating composition was produced in the same manner as in Example 1, except that the aminated acrylic resin (B1) and the polyamidine compound (E1) were not used. Using the obtained cationic electrodeposition coating composition, an electrodeposition coated article (single-layer coating film) was produced in the same manner as in Example 1.

[0136] [Comparative Example 2] A cationic electrodeposition coating composition was produced in the same manner as in Example 2, except that the aminated acrylic resin (B1) and the polyamidine compound (D1) were not used. Using the resulting cationic electrodeposition coating composition, an electrodeposition-coated product (single-layer coating film) was produced in the same manner as in Example 2.

[0137] Comparative Example 3 A cationic electrodeposition coating composition was produced in the same manner as in Example 1, except that the aminated acrylic resin (B1) and the polyamidine compound (D1) were not used and that the polyisocyanate curing agent (C3) was used instead of the polyisocyanate curing agent (C1+C2). Using the obtained cationic electrodeposition coating composition, an electrodeposition coated article (single-layer coating film) was produced in the same manner as in Example 1.

[0138] [Comparative Example 4] A cationic electrodeposition coating composition was produced in the same manner as in Example 1, except that the polyamidine compound (D1) was not used. Using the resulting cationic electrodeposition coating composition, an electrodeposition coated product (single-layer coating film) was produced in the same manner as in Example 1.

[0139] [Comparative Example 5] Except for not using the aminated acrylic resin (B1), a cationic electrodeposition coating composition was produced in the same manner as in Example 1. Using the obtained cationic electrodeposition coating composition, an electrodeposition coated article (single-layer coating film) was produced in the same manner as in Example 1.

[0140] Comparative Example 6 A cationic electrodeposition coating composition was obtained and an electrodeposition coated article (single-layer coating film) was produced in the same manner as in Example 1, except that a commercially available viscosity modifier, poly-N-vinylacetamide (weight average molecular weight 50,000: product name GE191-107, manufactured by Showa Denko K.K.), was added instead of the polyamidine compound (D1).

[0141] [Evaluation of Cationic Electrodeposition Coating Compositions and Electrodeposition Coated Products] The cationic electrodeposition coating compositions and electrodeposition coated products (single-layer coating films) obtained in Examples 1 to 3 and Comparative Examples 1 to 6 above were evaluated for gel fraction, coating appearance, edge rust prevention, and weather resistance (for both single-layer coating films and multi-layer coating films) as described below, and the results are shown in Table 1. Table 1 also shows the amounts of polyamidine compound, polyvinyl formamide, or poly-N-vinyl acetamide blended in the electrodeposition coating.

[0142] (1) Gel Fraction (Curability) The cationic electrodeposition coating compositions according to the above Examples and Comparative Examples were applied to tinplates whose weights had been measured in advance, to deposit a coating film of 20 μm in thickness after drying. The coating film was then cured by baking at 135°C for 25 minutes, forming a cationic electrodeposition coating film on the tinplate. The weight of the resulting test plate was measured, and the plate was then immersed in acetone and refluxed for 6 hours, followed by drying at 105°C for 20 minutes. The dried weight was measured, and the gel fraction was calculated using the following formula (1). Curability was evaluated based on the gel fraction value according to the following criteria, with A being considered acceptable. The results are shown in Table 1. Gel Fraction (%) = (W2 - W0) / (W1 - W0) x 100 (1) In formula (1), W0 is the weight of the tinplate, W1 is the weight of the coated plate after baking, and W2 is the weight of the coated plate after immersion in acetone.

[0143] (Evaluation criteria) A: Gel fraction 90% or more B: Gel fraction less than 90%

[0144] (2) Coating Appearance (Surface Roughness Ra of Single-Layer Coating) The surface roughness of the electrodeposition coated products (single-layer coating) obtained in Examples 1 to 3 and Comparative Examples 1 to 6 was measured in accordance with JIS-B0601 using an evaluation-type surface roughness measuring instrument (Mitsutoyo Corporation, SURFTEST SJ-201P) to measure the arithmetic mean roughness (Ra) of the roughness curve of the cured electrodeposition coating. Seven measurements were made using a sample with a 2.5 mm wide cutoff (5 sections), and the Ra value (μm) was obtained by averaging the top and bottom values. Table 1 lists only the Ra value. The smaller the Ra value, the less unevenness there was and the better the single-layer coating appearance.

[0145] (3) Edge Rust Prevention In Examples 1 to 3 and Comparative Examples 1 to 6, the substrate was changed to an L-type dedicated replaceable blade (LB10K: manufactured by Olfa Corporation, length 100 mm, width 18 mm, thickness 0.5 mm), and test pieces having a cured electrodeposition coating film of 20 μm thickness were prepared using the same procedures as in these Examples and Comparative Examples. These test pieces were subjected to a salt spray test (35°C x 72 hours) in accordance with JIS Z 2371 (2000), and the number of rust spots that occurred on the edge of the coated substrate was counted.

[0146] The edge of the object to be coated is the area extending from the apex of the blade to 5 mm in the direction of the blade body, and is present on both the front and back surfaces of the blade. The total area of ​​the edge is 10 cm, which is the blade length 100 mm x the width of the area (5 mm x 2). ２ Edge part (10 cm ２ If the number of rust spots formed on the edge is less than 50, the edge rust prevention property can be evaluated as good.

[0147] (Evaluation criteria) Best: Less than 10 rust spots Good: 10 to less than 20 rust spots Passable: 20 to less than 50 rust spots Poor: 50 to less than 100 rust spots Unacceptable: 100 or more rust spots

[0148] (4) Weather Resistance (Multi-Layer Coating Film) Formation of Multi-Layer Coating Film Test pieces having the cationic electrodeposition coating films prepared in Examples 1 to 3 and Comparative Examples 1 to 6 above were coated with AR-620#7018 (an intermediate coating paint manufactured by Nippon Paint Automotive Coatings Co., Ltd.) to a dry film thickness of 25 μm, and dried at 80°C for 5 minutes to form an uncured base coating film. AR-3020#7A21 (aqueous base coating paint manufactured by Nippon Paint Automotive Coatings Co., Ltd.) was then air spray coated thereon to a dry film thickness of 15 μm, and dried at 80°C for 5 minutes to form an uncured base coating film. Furthermore, O-1820 (clear coating paint manufactured by Nippon Paint Automotive Coatings Co., Ltd.) was then applied to the test pieces using a thinner consisting of normal butyl acetate / ethyl 3-ethoxypropionate = 1 / 2 (mass ratio). The paint was diluted to 30 seconds / 20°C using a 4 Ford cup and then air sprayed to a dry film thickness of 40 μm to form an uncured clear coating film. After setting for 7 minutes, the coating was baked at 140°C for 25 minutes to cure, forming a multi-layer coating film.

[0149] The test piece having the multilayer coating film prepared above was attached, attached to a Spark Xenon Weather Meter SX2-75 (manufactured by Suga Test Instruments Co., Ltd.), and exposed to simulated sunlight at an illuminance of 180 W / m according to the xenon lamp method of JIS K5600-7-7. ２ Accelerated exposure was carried out for 1000 hours under the conditions of . Thereafter, the test piece was immersed in warm water at 40°C for 24 hours, dried at room temperature for 1 hour, and then a tape peeling test was carried out to visually check for peeling of the intermediate coating film, and judged as ○ (no peeling) or × (peeling confirmed). The tape peeling test was carried out in accordance with JIS K5600. Specifically, the test piece was immersed in pure water and kept at 40°C for 24 hours, and then adhesive cellophane tape (registered trademark) was applied to the test piece, and the tape was rapidly peeled off at 20°C, after which the presence or absence of peeling of the intermediate and topcoat coating film was visually confirmed.

[0150] (5) Weather resistance (single coating film) The following evaluations were carried out on test pieces prepared using the cationic electrodeposition coating compositions obtained in Examples 1 to 3 and Comparative Examples 1 to 6 above. The evaluation results are shown in Table 1. [Weather resistance (single coating film) test] The electrodeposition-coated zinc-treated steel sheet was attached to a Sunshine Weatherometer (specified in JIS B 7753 (Sunshine carbon arc lamp weather resistance tester)) and irradiated for 400 hours. Thereafter, the 60° gloss of the electrodeposition coating surface was measured, and the gloss retention rate relative to the initial 60° gloss was calculated. Evaluation criteria Good: Gloss retention rate ≧80% Poor: Gloss retention rate <80%

[0151]

[0152] As is clear from the results in Table 1, when the cationic electrodeposition coating compositions of the Examples were used, the gel fraction, coating appearance (single-layer coating), edge rust prevention (single-layer coating), and weather resistance (both multi-layer and single-layer coatings) were all evaluated as good. Example 3 is an example using a cationic electrodeposition coating composition that uses a polyamidine compound hydrophobized by the general formula (X), and also has the advantage of good long-term storage stability of the resin emulsion. Comparative Examples 1 to 3 are examples in which the aminated acrylic resin (B) and the polyamidine compound (D) were not used. Comparative Example 1 is a comparison with Example 1, Comparative Example 2 is a comparison with Example 2, and Comparative Example 3 is an example in which the polyisocyanate curing agent in Example 1 was changed to blocked polymeric MDI and the aminated acrylic resin (B) and the polyamidine compound (D) were not used. All of these examples had poor edge rust prevention and weather resistance (single-layer coating). Furthermore, Comparative Example 3 was evaluated as having a gel fraction of B, indicating poor curability. In the example of Comparative Example 3, this is thought to be because the curing temperature increases when blocked polymeric MDI is used. Comparative Example 4 is an example of Example 1 in which the polyamidine compound (E) was not used, and it is clear that the edge rust prevention properties were inferior. Comparative Example 5 is an example of Example 1 in which the aminated acrylic resin (B) was not used, and the weather resistance of a single-layer coating film consisting of only a cationic electrodeposition coating film was poor. Comparative Example 6 is an example in which a commercially available thickener (poly-N-vinylacetamide) was used in place of the polyamidine compound (E), and the coating film appearance (surface roughness Ra of the single-layer coating film) tended to deteriorate.

[0153] The cationic electrodeposition coating composition of the present invention can provide a coating film that is excellent in curability, rust prevention, especially edge rust prevention, as well as in appearance and weather resistance, and is therefore suitable for coating substrates with edges.

[0154] The following aspects are also included in the present invention: [1] A composition comprising an aminated epoxy resin (A), an aminated acrylic resin (B), a blocked polyisocyanate curing agent (C), a pigment (D), and a polyamidine compound or a hydrophobically modified polyamidine compound (E), wherein the polyamidine compound or a hydrophobically modified polyamidine compound (E) is represented by the following general formula (I): (In the formula, R １ and R ２ are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and X is an anion. [2] A cationic electrodeposition coating composition having a structural unit represented by the following general formula (X): (In the formula, R １ and R ２ are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and R ３is a hydrophobic structural unit containing at least one of a substituted or unsubstituted, linear or branched alkyl group having 3 to 12 carbon atoms, or a substituted or unsubstituted aromatic group having 6 to 12 carbon atoms.) [3] The cationic electrodeposition coating composition according to [1] or [2], wherein the solids mass of the polyamidine compound or its hydrophobized modified product (E) is 0.2 ppm or more and 1,200 ppm or less of the solids mass of the cationic electrodeposition coating composition. [4] The cationic electrodeposition coating composition according to any of [1] to [3], wherein the weight-average molecular weight of the polyamidine compound or its hydrophobized modified product (E) is 50,000 or more. [5] The cationic electrodeposition coating composition according to any of [1] to [4], wherein the pigment (D) includes an extender pigment. [6] The cationic electrodeposition coating composition according to any one of [1] to [5], wherein the cationic electrodeposition coating composition does not contain an organotin compound or the content of the organotin compound is 0.25 mass % or less. [7] The aminated epoxy resin (A) is an aminated epoxy resin obtained by reacting an amine compound with an epoxy resin, the amine compound being a combination of two amines, a primary amine and a secondary amine, and the primary amine is a compound represented by the formula: NH ２ - (CH ２ ) n-NR １１ R １２ (In the formula, R １１ and R １２ are the same or different and represent an alkyl group having 1 to 6 carbon atoms which may have a terminal hydroxyl group, and n represents an integer of 2 to 4, and the secondary amine has the formula: R １３ R １４ NH (wherein, R １３ and R １４are the same or different and represent an alkyl group having 1 to 4 carbon atoms and a hydroxyl group at its terminal.), or the amine compound comprises one or more compounds selected from the group consisting of ketimine compounds and diketimine compounds. [8] The cationic electrodeposition coating composition according to any of [1] to [7], wherein the blocked polyisocyanate curing agent (C) comprises an oxime-blocked isocyanate curing agent which is a blocked reaction product of a blocking agent containing an oxime compound with a polyisocyanate, and the polyisocyanate in the blocking reaction comprises one or more compounds selected from the group consisting of aromatic polyisocyanate compounds, aliphatic polyisocyanate compounds, and alicyclic polyisocyanate compounds. [9] An electrodeposition-coated article comprising: a substrate; and an electrodeposition coating film formed on the substrate using the cationic electrodeposition coating composition according to any of [1] to [8].

[10] A method for producing an electrodeposition coated article, comprising the steps of: immersing an article to be coated in the cationic electrodeposition coating composition according to any one of [1] to [8], and then applying a voltage between the article to be coated and a counter electrode to form an uncured electrodeposition coating film on the article to be coated; and heating the uncured electrodeposition coating film at a temperature of 75°C or higher and 200°C or lower to obtain a cured electrodeposition coating film.

Claims

1. A composition comprising an aminated epoxy resin (A), an aminated acrylic resin (B), a blocked polyisocyanate curing agent (C), a pigment (D), and a polyamidine compound or a hydrophobically modified product thereof (E), wherein the polyamidine compound or a hydrophobically modified product thereof (E) is represented by the following general formula (I): (In the formula, R １ and R ２ are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and X is an anion.

2. The hydrophobized modified product of the polyamidine compound contains, in addition to the structural unit (I), a cyclized structural unit derived from an unsaturated nitrile or a cyclic structural unit represented by the following general formula (X): (In the formula, R １ and R ２ are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms; R ３ is a hydrophobic structural unit containing at least one of a substituted or unsubstituted linear or branched alkyl group having 3 to 12 carbon atoms, or a substituted or unsubstituted aromatic group having 6 to 12 carbon atoms.

3. A cationic electrocoating composition according to claim 1 or 2, wherein the solids content by mass of the polyamidine compound or its hydrophobically modified form (E) is 0.2 ppm or more and 1,200 ppm or less of the solids content by mass of the cationic electrocoating composition.

4. A cationic electrodeposition coating composition according to claim 1 or 2, wherein the weight average molecular weight of the polyamidine compound or its hydrophobically modified derivative (E) is 50,000 or more.

5. A cationic electrodeposition coating composition according to claim 1 or 2, wherein the pigment (D) includes an extender pigment.

6. A cationic electrocoating composition according to claim 1 or 2, which does not contain an organotin compound or contains an organotin compound in an amount of 0.25 mass% or less.

7. The aminated epoxy resin (A) is an aminated epoxy resin obtained by reacting an amine compound with an epoxy resin, the amine compound being a combination of two types of amines, a primary amine and a secondary amine, the primary amine being represented by the formula: NH ２ - (CH ２ ) n-NR １１ R １２ (In the formula, R １１ and R １２ are the same or different and each represents an alkyl group having 1 to 6 carbon atoms which may have a hydroxyl group at its terminal, and n represents an integer of 2 to 4; １３ R １４ NH (wherein, R １３ and R １４ and each of the formula (1) and (2) may be the same or different and represents an alkyl group having 1 to 4 carbon atoms and having a hydroxyl group at its terminal. The cationic electrodeposition coating composition according to claim 1 or 2, wherein the amine compound comprises one or more compounds selected from the group consisting of ketimine compounds and diketimine compounds.

8. The cationic electrodeposition coating composition according to claim 1 or 2, wherein the blocked polyisocyanate curing agent (C) contains an oxime-blocked isocyanate curing agent which is a blocked reaction product between a blocking agent containing an oxime compound and a polyisocyanate, and the polyisocyanate in the blocking reaction contains one or more compounds selected from the group consisting of aromatic polyisocyanate compounds, aliphatic polyisocyanate compounds and alicyclic polyisocyanate compounds.

9. An electrocoated article comprising: a substrate; and an electrocoating film formed on the substrate from the cationic electrocoating composition according to claim 1 or 2.

10. A method for producing an electrodeposition coated object, comprising the steps of: immersing an object to be coated in the cationic electrodeposition coating composition according to claim 1 or 2, applying a voltage between the object to be coated and a counter electrode to form an uncured electrodeposition coating film on the object to be coated; and heating the uncured electrodeposition coating film at a temperature of 75°C or higher and 200°C or lower to obtain a cured electrodeposition coating film.

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