Method for manufacturing a cationic electrodeposition coating composition

Abstract

This invention provides a method for producing a cationic electrodeposition coating composition containing a modified acrylic resin without using polycaprolactone-modified monomers. [Solution] A method for producing a cationic electrodeposition coating composition, Step 1: A process to produce a modified acrylic resin (A) by reacting a hydroxyl group-containing (meth)acrylic acid ester (a-1) with other polymerizable unsaturated group-containing monomers (a-2) and a lactone (a-3). Step 2: A step of preparing a resin emulsion comprising the modified acrylic resin (A), an amino group-containing epoxy resin (B), an acidic compound (C), and water (D). Step 3: A step of mixing the resin emulsion and the pigment dispersion paste, A method for producing a cationic electrodeposition coating composition containing the above.

Description

Technical Field

[0001] The present disclosure relates to a method for producing a cationic electrodeposition coating composition.

Background Art

[0002] Cationic electrodeposition coatings are widely used in automotive parts, electrical equipment parts, and other industrial equipment that require these performances, due to their excellent coating workability and the good corrosion resistance of the formed coating films.

[0003] As cationic electrodeposition coatings, those containing an epoxy resin and an acrylic resin that achieve both weather resistance and corrosion resistance are known. For example, Patent Document 1 discloses a technique using an amino group-containing epoxy resin as the epoxy resin, and a modified acrylic resin obtained by polymerizing a polylactone-modified monomer and other monomers as the acrylic resin.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the technique described in Patent Document 1, a polycaprolactone-modified monomer is used as a raw material for the acrylic resin for compatibility with the epoxy resin, but the polycaprolactone-modified monomer has the disadvantages of poor versatility, high cost, and difficult handling due to its high crystallinity.

[0006] An object of the present invention is to provide a method for producing a cationic electrodeposition coating composition containing a modified acrylic resin without using a polycaprolactone-modified monomer.

Means for Solving the Problems

[0007] In order to solve the above problems, the inventors conducted extensive research and found that a modified acrylic resin can be obtained by reacting a hydroxyl group-containing (meth)acrylic acid ester with other polymerizable unsaturated group-containing monomers and lactones, and that a cationic electrodeposition coating composition can be manufactured using this modified acrylic resin.

[0008] This invention was completed based on these findings and includes the following broad embodiments of the invention.

[0009] [Section 1] A method for producing a cationic electrodeposition coating composition, Step 1: A process to produce a modified acrylic resin (A) by reacting a hydroxyl group-containing (meth)acrylic acid ester (a-1) with other polymerizable unsaturated group-containing monomers (a-2) and a lactone (a-3). Step 2: A step of preparing a resin emulsion comprising the modified acrylic resin (A), an amino group-containing epoxy resin (B), an acidic compound (C), and water (D). Step 3: A step of mixing the resin emulsion and the pigment dispersion paste, A method for producing a cationic electrodeposition coating composition containing the above. [Section 2] The manufacturing method according to item 1, wherein in step 2, the resin emulsion further comprises blocked polyisocyanate (E). [Section 3] The method for producing a product according to claim 1 or 2, wherein in step 1, a mixture containing a hydroxyl group-containing (meth)acrylic acid ester (a-1) and another polymerizable unsaturated group-containing monomer (a-2) is added dropwise to a solution containing a lactone (a-3). [Section 4] The manufacturing method according to any one of items 1 to 3, wherein in step 1, 100 to 1000 mol% of lactone (a-3) is used based on 100 mol% of hydroxyl group-containing (meth)acrylic acid ester (a-1). [Section 5] The manufacturing method according to any one of items 1 to 4, wherein in step 1, 15 to 50 parts by mass of hydroxyl group-containing (meth)acrylic acid ester (a-1), 20 to 80 parts by mass of other polymerizable unsaturated group-containing monomers (a-2), and 5 to 40 parts by mass of lactone (a-3) are used per 100 parts by mass of the solid content of the modified acrylic resin (A). [Section 6] The manufacturing method according to any one of items 1 to 5, wherein in step 2, the modified acrylic resin (A) is 5 to 20% by mass and the amino group-containing epoxy resin (B) is 80 to 95% by mass, relative to the total solid content mass of the modified acrylic resin (A) and the amino group-containing epoxy resin (B). [Section 7] The manufacturing method according to any one of items 2 to 6, wherein in step 2, the modified acrylic resin (A) is 5 to 30% by mass, the amino group-containing epoxy resin (B) is 40 to 75% by mass, and the blocked polyisocyanate (E) is 20 to 40% by mass, relative to the total solid content mass of the modified acrylic resin (A), amino group-containing epoxy resin (B), and blocked polyisocyanate (E). [Section 8] The manufacturing method according to any one of claims 1 to 7, wherein the solid content of the modified acrylic resin (A) in the reaction mixture obtained in step 1 is 50% by mass or more. [Effects of the Invention]

[0010] According to the present invention, a method for producing a cationic electrodeposition coating composition containing a modified acrylic resin without using a polycaprolactone-modified monomer can be provided. [Modes for carrying out the invention]

[0011] In this specification, the singular form includes both singular and plural forms unless otherwise explicitly stated herein or the context clearly contradicts it.

[0012] In this specification, "contains" is a concept that also includes "substantially consists only of" and "consists only of."

[0013] In the numerical ranges described stepwise in the present specification, the upper limit value or lower limit value of a numerical range at one step can be arbitrarily combined with the upper limit value or lower limit value of a numerical range at another step. Further, in the numerical ranges described in the present specification, the upper limit value or lower limit value of the numerical range may be replaced with a value shown in the Examples or a value that can be uniquely derived from the Examples. Furthermore, in the present specification, numerical values connected by "to" mean a numerical range including the numerical values before and after "to" as the lower limit value and the upper limit value, respectively.

[0014] In the present specification, "(meth)acrylate" means acrylate, methacrylate, or both thereof, "(meth)acrylic acid" means acrylic acid, methacrylic acid, or both thereof, "(meth)acryloyl" means acryloyl, methacryloyl, or both thereof, and "acrylic polymerization" means (co)polymerization of a polymerizable unsaturated group-containing monomer.

[0015] Hereinafter, the embodiments included in the present disclosure will be further described. The embodiments described below show an example of representative embodiments of the present disclosure, and the scope of the invention is not limited thereby.

[0016] The present invention provides a method for producing a cationic electrodeposition coating composition. The method for producing a cationic electrodeposition coating composition of the present invention includes the following Step 1 to Step 3. Other steps may be included between, before, and after Step 1 to Step 3. Step 1: a step of reacting a hydroxyl group-containing (meth)acrylic acid ester (a-1), another polymerizable unsaturated group-containing monomer (a-2), and a lactone (a-3) to produce a modified acrylic resin (A). Step 2: a step of preparing a resin emulsion containing the modified acrylic resin (A), an amino group-containing epoxy resin (B), an acidic compound (C), and water (D). Step 3: a step of mixing at least the resin emulsion and a pigment dispersion paste.

[0017] <Step 1> Step 1 is a step for producing the modified acrylic resin (A). The modified acrylic resin (A) is produced by reacting a hydroxyl group-containing (meth)acrylate ester (a-1), another polymerizable unsaturated group-containing monomer (a-2), and a lactone (a-3). Hereinafter, each component used in Step 1 will be described.

[0018] Hydroxyl group-containing (meth)acrylic acid ester (a-1) The hydroxyl group-containing (meth)acrylate ester is a compound having one or more hydroxyl groups in one molecule and one or more (meth)acryloyl groups in one molecule. It is preferably a compound having one hydroxyl group in one molecule and one (meth)acryloyl group in one molecule. In the present specification, the hydroxyl group-containing (meth)acrylate ester (a-1) preferably does not include a lactone-modified hydroxyl group-containing (meth)acrylate ester (for example, a caprolactone-modified hydroxyl group-containing (meth)acrylate which is a monomer obtained by adding ε-caprolactone to a hydroxyl group-containing (meth)acrylate).

[0019] Examples of the hydroxyl group-containing (meth)acrylate ester (a-1) include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate; hydroxyl group-containing (meth)acrylates containing one (meth)acrylic group such as 2-hydroxy-3-phenoxypropyl (meth)acrylate, dipropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, and polypropylene glycol mono(meth)acrylate; hydroxyl group-containing (meth)acrylates containing two (meth)acrylic groups such as glycerin di(meth)acrylate; and hydroxyl group-containing (meth)acrylates containing three or more (meth)acrylic groups such as pentaerythritol tri(meth)acrylate and dipentaerythritol penta(meth)acrylate. These can be used singly or in combination of two or more kinds.

[0020] The amount of hydroxyl group-containing (meth)acrylic acid ester (a-1) used in step 1 is preferably 15 to 50 parts by mass, and more preferably 20 to 45 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A). This range is preferable because it allows for a balance between controlling the hydrophilicity / hydrophobicity of the resin and the amount of modification.

[0021] Other polymerizable unsaturated group-containing monomers (a-2) Other polymerizable unsaturated group-containing monomers refer to polymerizable unsaturated group-containing monomers other than the hydroxyl group-containing (meth)acrylic acid ester (a-1) described above. They are not particularly limited as long as they do not contain a hydroxyl group and have one or more polymerizable unsaturated groups in one molecule. It is preferable that the other polymerizable unsaturated group-containing monomers also do not contain polycaprolactone-modified monomers. Examples of polymerizable unsaturated groups include vinyl group, vinyloxy group, 1-chlorovinyl group, isopropenyl group, 4-vinylphenyl group, allyloxy group, acryloyl group, methacryloyl group, oxyranyl group, and oxetanyl group. Among these, acryloyl group, methacryloyl group, and vinyl group are preferred.

[0022] Other polymerizable unsaturated group-containing monomers (a-2) include, for example, alkyl(meth)acrylates such as methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, and octyl(meth)acrylate; cycloalkyl(meth)acrylates such as cyclohexyl(meth)acrylate; aryl(meth)acrylates such as phenyl(meth)acrylate; benzyl(meth)acrylate, phenyl Rubenzyl (meth)acrylate; isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate; methoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate, nonylphenoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate (e.g., methoxytriethylene glycol (meth)acrylate), butoxydiethylene glycol (meth)acrylate, ether group-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate; glycidyl (meth)acrylate; amino group-containing (meth)acrylates such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexane Difunctional (meth)acrylates such as diol di(meth)acrylate, neopentyl glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, neopentyl glycol adipate di(meth)acrylate, hydroxypivalate neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, ethylene oxide modified phosphate di(meth)acrylate, allylated cyclohexyl di(meth)acrylate, and isocyanurate di(meth)acrylate;Examples include trifunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, and tris(acryloxyethyl) isocyanurate; tetrafunctional or more (meth)acrylates such as ditrimethylolpropane tetra(meth)acrylate, propionic acid-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; and aromatic vinyl monomers such as styrene, p-methylstyrene, o-methylstyrene, and vinylnaphthalene. These may be used individually or in combination of two or more.

[0023] The amount of other polymerizable unsaturated group-containing monomer (a-2) used in step 1 is preferably 20 to 80 parts by mass, and more preferably 30 to 70 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A). This range facilitates control of the resin's hydrophobicity and compatibility with epoxy resins.

[0024] Lactone (a-3) Lactone (a-3) is a compound that can react with hydroxyl groups such as hydroxyl group-containing (meth)acrylic acid esters (a-1) by ring-opening polymerization.

[0025] Examples of lactones (a-3) include β-propiolactone, β-butyrolactone, γ-butyrolactone, γ-valerolactone, γ-caprolactone, γ-heptalactone, γ-octaractone, γ-nonalactone, γ-decanolactone, δ-valerolactone, β-methyl-δ-valerolactone, δ-hexanolactone, δ-octanolactone, δ-decanolactone, δ-nonalactone, ε-caprolactone, etc., with ε-caprolactone being preferred. These may be used individually or in combination of two or more.

[0026] The amount of lactone (a-3) used in step 1 is preferably 5 to 40 parts by mass, and more preferably 10 to 35 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A). This range is preferable because it results in good compatibility of the resulting modified acrylic resin (A) with the amino group-containing epoxy resin (B), and thus a good coating film appearance.

[0027] Furthermore, the amount of lactone (a-3) used in step 1 is preferably 100 to 1000 mol%, more preferably 100 to 800 mol%, even more preferably 150 to 600 mol%, and particularly preferably 200 to 500 mol%, based on 100 mol% of hydroxyl group-containing (meth)acrylic acid ester (a-1).

[0028] Polymerization initiator In the reaction of step 1, it is preferable to use a polymerization initiator.

[0029] Examples of polymerization initiators include organic peroxides such as benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, cumene hydroperoxide, tert-butyl peroxide, tert-butyl peroxylaurate, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyacetate, and diisopropylbenzene hydroperoxide; azobisisobutyronitrile, azobis(2,4-dimethylvaleronitrile), azobis(2-methyl propyl nitrile). Examples of polymerization initiators include azo compounds such as ropionnitrile, azobis(2-methylbutyronitrile), 4,4'-azobis(4-cyanobutanoic acid), dimethylazobis(2-methylpropionate), azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], azobis{2-methyl-N-[2-(1-hydroxybutyl)]-propionamide}, and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamide]; and persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate. These polymerization initiators can be used individually or in combination of two or more. In addition, a reducing agent such as sugar, sodium formaldehyde sulfoxylate, or an iron complex can be used in combination with the above polymerization initiator as needed to form a redox initiator.

[0030] Ring-opening polymerization catalyst In the reaction of step 1, it is preferable to use a ring-opening polymerization catalyst. The ring-opening polymerization catalyst is not particularly limited as long as it is a catalyst that is normally used in ring-opening polymerization. Examples include organozinc compounds (e.g., zinc alkylate, zinc halide, zinc oxide, etc.), organotin compounds (e.g., tin octoate, dibutyltin oxide, dibutyltin laurate, stannous chloride, stannous bromide, etc.), organotitanium compounds (e.g., tetrabutyl titanate, tetrapropyl titanate, tetraethyl titanate, etc.), organoaluminum compounds, calcium compounds, lithium compounds, iron compounds, quaternary ammonium salts, quaternary phosphonium salts, etc. Among these, organozinc compounds are preferred from the viewpoint of reaction efficiency. The ring-opening polymerization catalyst may be used alone or in combination of two or more types.

[0031] solvent In the reaction of Step 1, it is preferable to use a solvent. Examples of solvents that can be used in Step 1 include ketone solvents such as methyl isobutyl ketone, cyclohexanone, diisobutyl ketone, and methyl ethyl ketone; ether solvents such as oxane, 1,2-dimethoxyethane, tetrahydrofuran, cyclopentyl methyl ether, and ethylene glycol dimethyl ether; aromatic hydrocarbon solvents such as toluene, benzene, and xylene; aliphatic hydrocarbon solvents such as n-pentane, n-hexane, and n-heptane; halogenated hydrocarbon solvents such as dichloromethane, chloroform, carbon tetrachloride, and 1,2-dichloroethane; amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; nitrile solvents such as acetonitrile and benzonitrile; and ester solvents such as ethyl acetate, isopropyl acetate, and butyl acetate. A single solvent may be used, or two or more solvents may be used in combination.

[0032] Manufacturing of modified acrylic resin (A) In the reaction of step 1, the reaction order of the hydroxyl group-containing (meth)acrylic acid ester (a-1), the other polymerizable unsaturated group-containing monomer (a-2), and the lactone (a-3) is not particularly limited. (1) An acrylic polymer may be synthesized by acrylic polymerization of a hydroxyl group-containing (meth)acrylic acid ester (a-1) and another polymerizable unsaturated group-containing monomer (a-2), and then a modified acrylic resin (A) may be produced by ring-opening polymerization of a lactone (a-3). (2) A modified acrylic resin (A) may be produced by adding lactone (a-3) during the acrylic polymerization of a hydroxyl group-containing (meth)acrylic acid ester (a-1) and another polymerizable unsaturated group-containing monomer (a-2), thereby simultaneously carrying out the acrylic polymerization of the hydroxyl group-containing (meth)acrylic acid ester (a-1) and the other polymerizable unsaturated group-containing monomer (a-2) and the ring-opening polymerization by lactone (a-3). (3) A modified acrylic resin (A) may be produced by adding a hydroxyl group-containing (meth)acrylic acid ester (a-1) and other polymerizable unsaturated group-containing monomers (a-2) to a solution containing lactone (a-3), thereby simultaneously carrying out acrylic polymerization of the hydroxyl group-containing (meth)acrylic acid ester (a-1) and other polymerizable unsaturated group-containing monomers (a-2) and ring-opening polymerization by lactone (a-3). Other methods may also be used. From the viewpoint of producing the modified acrylic resin (A) inexpensively and easily, it is preferable to use any of the methods (1) to (3) above. It is more preferable to use method (3) above because it allows for the production of the modified acrylic resin (A) in a shorter time, and because lactone (a-3) can be used as a solvent, it is easy to produce a modified acrylic resin (A) with a high solid content, and the amount of solvent brought in from the modified acrylic resin (A) can be reduced as much as possible (the subsequent desolventing process can be streamlined).

[0033] In the reaction method described in (1) above, first, acrylic polymerization is carried out between a hydroxyl group-containing (meth)acrylic acid ester (a-1) and another polymerizable unsaturated group-containing monomer (a-2). It is preferable not to use polycaprolactone-modified monomers in the acrylic polymerization. The polymerization reaction can be carried out by conventionally known methods. It is preferable to use the above polymerization initiator in the reaction.

[0034] The amount of polymerization initiator used is preferably 0.1 to 10 parts by mass, and more preferably 2 to 5 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A).

[0035] The method of adding the polymerization initiator is not particularly limited and can be appropriately selected depending on its type and amount. For example, it can be included in a mixture with a hydroxyl group-containing (meth)acrylic acid ester (a-1) and other polymerizable unsaturated group-containing monomers (a-2) beforehand, or it can be added all at once during polymerization, or it can be added dropwise, continuously or discontinuously.

[0036] Acrylic polymerization is preferably carried out in the presence of an inert gas such as nitrogen. The reaction temperature is preferably 80 to 150°C, and more preferably 100 to 120°C. The reaction time is preferably 0.1 to 12 hours, and more preferably 0.5 to 6 hours. It is preferable to use a solvent in the reaction. The solvents listed above can be preferably used. The amount of solvent used is preferably 10 to 150 parts by mass, and more preferably 25 to 75 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A).

[0037] In the reaction method described in (1) above, ring-opening polymerization of lactone (a-3) is carried out after acrylic polymerization. In the reaction method described in (1) above, the reaction may be carried out in one pot, or the acrylic polymer obtained by acrylic polymerization may be obtained first and then the ring-opening polymerization reaction may be carried out, but from the viewpoint of saving labor, it is preferable to carry it out in one pot.

[0038] The ring-opening polymerization reaction can be carried out by conventionally known methods. It is preferable to use the above-mentioned ring-opening polymerization catalyst in the reaction.

[0039] The amount of ring-opening polymerization catalyst used is preferably 0.01 to 10 parts by mass, and more preferably 0.4 to 3 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A).

[0040] In one embodiment, in the reaction method of (1) above, acrylic polymerization is carried out by dropwise adding a mixture of a hydroxyl group-containing (meth)acrylic acid ester (a-1), another polymerizable unsaturated group-containing monomer (a-2), and a polymerization initiator to the solvent, which is preferably maintained at 80 to 150°C, more preferably at 100 to 120°C, in the presence of an inert gas such as nitrogen, and mixing for 0.1 to 12 hours, preferably 0.5 to 6 hours. Subsequently, a lactone (a-3) and a ring-opening polymerization catalyst are added to the acrylic polymer solution obtained by acrylic polymerization, preferably at 80 to 150°C, more preferably at 100 to 120°C, and ring-opening polymerization is carried out by mixing for 0.1 to 12 hours, preferably 0.5 to 6 hours to obtain a modified acrylic resin (A).

[0041] The solid content of the modified acrylic resin (A) in the reaction mixture obtained by the reaction method described in (1) above is preferably 50% by mass or more, more preferably 65% ​​by mass or more, and particularly preferably 80% by mass.

[0042] In the reaction method described in (2) above, lactone (a-3) is added during the acrylic polymerization of a hydroxyl group-containing (meth)acrylic acid ester (a-1) and another polymerizable unsaturated group-containing monomer (a-2).

[0043] In one embodiment, a monomer mixture of a hydroxyl group-containing (meth)acrylic acid ester (a-1) and another polymerizable unsaturated group-containing monomer (a-2) is first added dropwise to a solvent preferably maintained at 80 to 150°C, more preferably 100 to 120°C, in the presence of an inert gas such as nitrogen. The solvent can preferably be the one described above, and the amount of solvent used is preferably 10 to 150 parts by mass, and more preferably 25 to 75 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A). Furthermore, it is preferable that the monomer mixture does not contain polycaprolactone-modified monomers. After the dropwise addition of the monomer mixture is complete, lactone (a-3) is further added and mixed for 0.1 to 12 hours, preferably 0.5 to 6 hours, to obtain the modified acrylic resin (A).

[0044] The acrylic polymerization reaction preferably includes a polymerization initiator. The above-mentioned materials can preferably be used as polymerization initiators. The method of adding the polymerization initiator is not particularly limited and can be appropriately selected depending on the type and amount. For example, it may be added simultaneously with the monomer mixture, added after the monomer mixture, or a portion of the polymerization initiator may be added simultaneously with the monomer mixture and the remainder added after the monomer mixture. The amount of polymerization initiator used is preferably 0.1 to 10 parts by mass, and more preferably 2 to 5 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A).

[0045] It is preferable to use a ring-opening polymerization catalyst for the ring-opening polymerization reaction of lactone. The above-mentioned catalysts can be preferably used as ring-opening polymerization catalysts. The method of adding the ring-opening polymerization catalyst is not particularly limited; for example, it may be added simultaneously with the monomer mixture, or simultaneously with lactone (a-3). The amount of ring-opening polymerization catalyst used is preferably 0.01 to 10 parts by mass, and more preferably 0.4 to 3 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A).

[0046] The solid content of the modified acrylic resin (A) in the reaction mixture obtained by the reaction method described in (2) above is preferably 50% by mass or more, more preferably 65% ​​by mass or more, and particularly preferably 80% by mass.

[0047] In the reaction method described in (3) above, a hydroxyl group-containing (meth)acrylic acid ester (a-1) and other polymerizable unsaturated group-containing monomers (a-2) are added to the lactone (a-3).

[0048] In one embodiment, lactone (a-3) is preferably mixed with a solvent and heated to the reaction temperature in the presence of an inert gas such as nitrogen. The solvent can preferably be one of the above, and the amount of solvent used is preferably 10 to 150 parts by mass, more preferably 15 to 65 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A). A monomer mixture containing a hydroxyl group-containing (meth)acrylic acid ester (a-1) and other polymerizable unsaturated group-containing monomers (a-2) is then added. Addition is preferably done dropwise. Furthermore, it is preferable that the monomer mixture does not contain polycaprolactone-modified monomers. After adding the monomer mixture, the mixture is maintained at the reaction temperature for 0.1 to 12 hours, preferably 0.5 to 6 hours, to obtain the modified acrylic resin (A). As described above, since lactone (a-3) can be used as a solvent when adding the monomer mixture, the amount of solvent used in the reaction can be reduced, and the solid content concentration of the reaction product containing the modified acrylic resin (A) can be increased. This makes it possible to reduce the labor involved in the solvent removal process when preparing resin emulsions.

[0049] The reaction temperature is preferably 80 to 150°C, and more preferably 100 to 120°C.

[0050] It is preferable to use a ring-opening polymerization catalyst for the ring-opening polymerization reaction of lactone. The above-mentioned catalysts can be preferably used as ring-opening polymerization catalysts. The method of adding the ring-opening polymerization catalyst is not particularly limited; for example, it may be pre-mixed with lactone (a-3) before adding the above mixture, added before adding the above monomer mixture, or added simultaneously with the above monomer mixture. The amount of ring-opening polymerization catalyst used is preferably 0.01 to 10 parts by mass, and more preferably 0.4 to 3 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A).

[0051] It is preferable to use a polymerization initiator in the acrylic polymerization reaction. The above-mentioned materials can preferably be used as polymerization initiators. The method of adding the polymerization initiator is not particularly limited and can be appropriately selected depending on the type and amount. For example, it may be added at the same time as the monomer mixture, or added after the monomer mixture, or a portion of the polymerization initiator may be added at the same time as the monomer mixture and the remainder added after the monomer mixture. The amount of polymerization initiator used is preferably 0.1 to 10 parts by mass, and more preferably 2 to 5 parts by mass, per 100 parts by mass of the solid content of the modified acrylic resin (A).

[0052] The solid content of the modified acrylic resin (A) in the reaction mixture obtained by the reaction method described in (3) above is preferably 50% by mass or more, more preferably 65% ​​by mass or more, and particularly preferably 80% by mass.

[0053] The weight-average molecular weight of the modified acrylic resin (A) is preferably 1,000 to 100,000, more preferably 1,000 to 20,000, and even more preferably 2,000 to 5,000. In this specification, unless otherwise specified, the weight-average molecular weight and number-average molecular weight are values ​​obtained by converting the retention time (retention capacity) measured using gel permulation chromatography (GPC) to the molecular weight of polystyrene using the retention time (retention capacity) of standard polystyrene with a known molecular weight measured under the same conditions. Specifically, the measurement can be performed using the "HLC8120GPC" (product name, manufactured by Tosoh Corporation) as the gel permument chromatograph, and four columns: "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000HXL" (product names, all manufactured by Tosoh Corporation) as the columns, under the conditions of tetrahydrofuran as the mobile phase, a measurement temperature of 40°C, a flow rate of 1 mL / min, and a radioisotope detector.

[0054] The hydroxyl value of the modified acrylic resin (A) is preferably 100 to 180 mgKOH / g, and more preferably 120 to 160 mgKOH / g. In this specification, the hydroxyl value can be measured in accordance with JIS K1557.

[0055] <Process 2> Step 2 is the step of preparing a resin emulsion. The resin emulsion contains a modified acrylic resin (A), an amino group-containing epoxy resin (B), an acidic compound (C), and water (D).

[0056] The following describes each component used in step 2.

[0057] Modified acrylic resin (A) The modified acrylic resin (A) used is the one manufactured in step 1 described above. The modified acrylic resin (A) may be used in step 2 without purification after being manufactured in step 1, or it may be purified by a known and conventional method before use. However, from the viewpoint of saving labor, it is preferable to use it without purification.

[0058] Amino group-containing epoxy resin (B) An amino group-containing epoxy resin is an epoxy resin having one or more (preferably two or more) amino groups per molecule. Examples include: (1) adducts of epoxy resin with primary mono- and polyamines, secondary mono- and polyamines, or mixed primary and secondary polyamines (see, for example, U.S. Patent No. 3,984,299); (2) adducts of epoxy resin with secondary mono- and polyamines having ketiminated primary amino groups (see, for example, U.S. Patent No. 4,017,438); and (3) reaction products obtained by etherification of epoxy resin with a hydroxy compound having ketiminated primary amino groups (see, for example, Japanese Patent Publication No. 59-43013).

[0059] Examples of primary mono- and polyamines, secondary mono- and polyamines, or primary and secondary mixed polyamines used in the production of the amino group-containing epoxy resin described in (1) above include mono- or di-alkylamines such as monomethylamine, dimethylamine, monoethylamine, diethylamine, monoisopropylamine, diisopropylamine, monobutylamine, and dibutylamine; alkanolamines such as monoethanolamine, diethanolamine, mono(2-hydroxypropyl)amine, and monomethylaminoethanol; and alkylene polyamines such as ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, diethylenetriamine, and triethylenetetramine.

[0060] Examples of ketiminated secondary mono- and polyamines having primary amino groups used in the production of the amino group-containing epoxy resin described in (2) above include, for example, ketiminated products produced by reacting a ketone compound with a primary or secondary mixed polyamine such as diethylenetriamine, which is used in the production of the amine-added epoxy resin described in (1) above.

[0061] Examples of ketiminated hydroxy compounds having a primary amino group used in the production of the amino group-containing epoxy resin described in (3) above include hydroxyl group-containing ketiminated compounds obtained by reacting a ketone compound with a compound having a primary amino group and a hydroxyl group, such as monoethanolamine, mono(2-hydroxypropyl)amine, etc., among the primary mono- and polyamines, secondary mono- and polyamines, or primary and secondary mixed polyamines used in the production of the amino group-containing epoxy resin described in (1) above.

[0062] Examples of polyphenol compounds used for forming the epoxy resin mentioned above include bis(4-hydroxyphenyl)-2,2-propane [bisphenol A], bis(4-hydroxyphenyl)methane [bisphenol F], bis(4-hydroxycyclohexyl)methane [hydrogenated bisphenol F], 2,2-bis(4-hydroxycyclohexyl)propane [hydrogenated bisphenol A], 4,4'-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-ethane, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-3-tert-butyl-phenyl)-2,2-propane, bis(2-hydroxynaphthyl)methane, tetra(4-hydroxyphenyl)-1,1,2,2-ethane, 4,4'-dihydroxydiphenylsulfone, phenol novolac, cresol novolac, and the like.

[0063] Furthermore, among epoxy resins obtained by the reaction of polyphenol compounds with epihalohydrins, resins derived from bisphenol A, as shown in the following formula, are particularly preferred.

[0064] [ka] Here, values ​​shown for n = 0 to 8 are preferred.

[0065] Examples of commercially available epoxy resins include those sold by Mitsubishi Chemical Corporation under the product names jER828EL, jER1002, jER1004, and jER1007.

[0066] Furthermore, as the above-mentioned amino group-containing epoxy resin, an epoxy resin containing a polyalkylene oxide chain in the resin backbone can be used. Typically, such an epoxy resin can be obtained by (α) reacting an epoxy resin having at least one, preferably two or more epoxy groups with an alkylene oxide or polyalkylene oxide to introduce a polyalkylene oxide chain, or by (β) reacting the above-mentioned polyphenol compound with a polyalkylene oxide having at least one, preferably two or more epoxy groups to introduce a polyalkylene oxide chain. Alternatively, an epoxy resin that already contains a polyalkylene oxide chain may be used. (See, for example, Japanese Patent Publication No. 8-337750)

[0067] The alkylene group in the polyalkylene oxide chain is preferably an alkylene group having 2 to 8 carbon atoms, more preferably an ethylene group, a propylene group, or a butylene group, and particularly preferably a propylene group.

[0068] From the viewpoint of improving paint stability, finish, and corrosion resistance, the content of the polyalkylene oxide chains is usually appropriate in the range of 0.0 to 15% by mass, based on the solid content mass of the amino group-containing epoxy resin.

[0069] Furthermore, the amino group-containing epoxy resin can be modified with a modifying agent as needed. Such modifying agents are not particularly limited as long as they are resins or compounds that react with epoxy resins. For example, polyols, polyether polyols, polyester polyols, polyamidoamines, polycarboxylic acids, fatty acids, polyisocyanate compounds, compounds obtained by reacting polyisocyanate compounds, lactone compounds such as ε-caprolactone, acrylic monomers, compounds obtained by polymerization of acrylic monomers, xyleneformaldehyde compounds, and epoxy compounds can also be used as modifying agents. These modifying agents can be used individually or in combination of two or more.

[0070] The proportion of the modifier used is not strictly limited and can be appropriately changed depending on the application of the paint composition, but from the viewpoint of improving finish and corrosion resistance, it is generally appropriate to use a range of 0 to 50% by mass, preferably 0.1 to 35% by mass, and more preferably 1 to 20% by mass, based on the solid content mass of the amino group-containing epoxy resin.

[0071] The above addition reaction to epoxy resin can usually be carried out in a suitable solvent at a temperature of about 80 to about 170°C, preferably about 90 to about 150°C, for about 1 to 6 hours, preferably about 1 to 5 hours.

[0072] Examples of the solvents mentioned above include hydrocarbons such as toluene, xylene, cyclohexane, and n-hexane; esters such as methyl acetate, ethyl acetate, and butyl acetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; amides such as dimethylformamide and dimethylacetamide; alcohols such as methanol, ethanol, n-propanol, and iso-propanol; ether alcohol compounds such as ethylene glycol monobutyl ether and diethylene glycol monoethyl ether; or mixtures thereof.

[0073] The number-average molecular weight of the amino group-containing epoxy resin (B) is usually in the range of 1,000 to 50,000, more preferably in the range of 1,300 to 20,000, and more preferably in the range of 1,600 to 10,000, from the viewpoint of finish quality, corrosion resistance, etc.

[0074] The amine value of the amino group-containing epoxy resin (B) is usually 20 mgKOH / g or higher, preferably in the range of 30 to 200 mgKOH / g, and more preferably in the range of 35 to 150 mgKOH / g, based on the resin solids content. The amine value in this specification is measured in accordance with JIS K 7237-1995. All values ​​are amine values ​​per resin solids content (mgKOH / g).

[0075] Acidic compound (C) The acidic compound (C) is used as a neutralizing agent, and any known organic acid can be used without particular restriction. Among these, formic acid, lactic acid, acetic acid, or mixtures thereof are preferred.

[0076] Water (D) Water (D) may be deionized water, distilled water, purified water, etc., but is not limited to these.

[0077] Blocked polyisocyanate (E) The resin emulsion preferably contains a blocked polyisocyanate (E). Examples of the blocked polyisocyanate compound (E) include the addition reaction product of a polyisocyanate compound and a blocking agent. Alternatively, if necessary, an active hydrogen-containing compound other than the blocking agent can be used and reacted with the polyisocyanate compound together with the blocking agent.

[0078] Known polyisocyanate compounds can be used as described above. Examples include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic aliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of these polyisocyanates. These may be used individually or in combination of two or more.

[0079] Examples of aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), 1,2-, 2,3- or 1,3-butylene diisocyanate, and 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate.

[0080] Examples of alicyclic polyisocyanates include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate; IPDI), 4,4′-, 2,4′- or 2,2′-dicyclohexylmethane diisocyanate or mixtures thereof (hydrogenated MDI), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane or mixtures thereof (hydrogenated XDI), norbornane diisocyanate (NBDI), and the like.

[0081] Examples of aromatic polyisocyanates include aromatic diisocyanates such as m- or p-phenylenediisocyanate or mixtures thereof, 2,4- or 2,6-tolylenediisocyanate or mixtures thereof (TDI), 4,4′-, 2,4′- or 2,2′-diphenylmethanediisocyanate or mixtures thereof (MDI), 4,4′-toluidinediisocyanate (TODI), 4,4′-diphenyletherdiisocyanate, 4,4′-diphenyldiisocyanate, and 1,5-naphthalenediisocyanate (NDI).

[0082] Furthermore, examples of polyisocyanate derivatives include dimers, trimers, biuretes, allophanates, carbodiimides, uretodiones, uretoimines, isocyanurates, oxadiazinetriones, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), and crude TDI.

[0083] The blocking agent blocks the isocyanate groups of the polyisocyanate compound by adding to them. The blocked polyisocyanate compound (E) produced by this addition is stable at room temperature, but it is desirable that the blocking agent dissociates and regenerates free isocyanate groups when heated to the baking temperature of the coating film (for example, about 80 to 200°C).

[0084] Examples of the above-mentioned blocking agents include oxime compounds, phenolic compounds, alcoholic compounds, lactam compounds, active methylene compounds, pyrazole compounds, mercaptan compounds, acid amide compounds, imide compounds, amine compounds, imidazole compounds, urea compounds, carbamate ester compounds, imine compounds, sulfite compounds, etc. These can be used individually or in combination of two or more.

[0085] Examples of oxime compounds include methyl ethyl ketoxime and cyclohexanone oxime. Examples of phenolic compounds include phenol, para-t-butylphenol, and cresol. Examples of alcohol-based compounds include n-butanol, 2-ethylhexanol, phenylcarbinol, methylphenylcarbinol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, ethylene glycol, propylene glycol, propylene glycol monomethyl ether, and methoxymethanol. Examples of lactam compounds include ε-caprolactam and γ-butyrolactam. Examples of active methylene compounds include dimethyl malonate, diethyl malonate, diisopropyl malonate, ethyl acetoacetate, isopropyl acetoacetate, methyl acetoacetate, isopropyl acetoacetate, and acetylacetone. Examples of pyrazole compounds include pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-bromo-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-benzyl-3,5-dimethylpyrazole, methyl-5-methylpyrazole-3-carboxylate, 3-methyl-5-phenylpyrazole, and 3,5-dimethylpyrazole-4-carboxyanilide. Examples of mercaptan compounds include butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, and ethylthiophenol. Examples of acid amide compounds include acetanilide, acetanisidide, acetotoluid, acrylamide, methacrylamide, acetic acid amide, stearic acid amide, and benzamide. Examples of imide compounds include succinimide, phthalimide, and maleimide. Examples of amine compounds include diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine. Examples of imidazole compounds include imidazole and 2-ethylimidazole. Examples of urea-based compounds include urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea. Examples of carbamic acid ester compounds include phenyl N-phenylcarbamate. Examples of imine compounds include ethyleneimine and propyleneimine. Examples of sulfite compounds include sodium bisulfite and potassium bisulfite.

[0086] Preparation of resin emulsion The preparation of the resin emulsion is not particularly limited, but for example, it can be carried out by mixing the above-mentioned modified acrylic resin (A), amino group-containing epoxy resin (B), acidic compound (C), and optionally blocked polyisocyanate (E) with additives such as surfactants and surface modifiers to form a resin solution, and then dispersing it in water. At the stage of forming the resin solution, the solvent may be removed by vacuum concentration or the like, if necessary.

[0087] The dispersion of the resin solution in water may be achieved by adding water to the resin solution while stirring, adding the resin solution to the water while stirring, or mixing the water and resin solution first and then stirring. The solid content concentration of the resin emulsion is preferably 10 to 60% by mass, and more preferably 20 to 45% by mass.

[0088] In a resin emulsion, the preferred blending ratio of modified acrylic resin (A) and amino group-containing epoxy resin (B) is 2 to 35% by mass, preferably 10 to 25% by mass, of the total solid content of the modified acrylic resin (A) and amino group-containing epoxy resin (B), and 60 to 95% by mass, preferably 70 to 90% by mass, of the amino group-containing epoxy resin (B). This is preferable from the viewpoint of corrosion resistance and weather resistance of the coating film.

[0089] Furthermore, when the resin emulsion contains blocked polyisocyanate (E), it is preferable from the viewpoint of corrosion resistance and weather resistance of the coating film that the modified acrylic resin (A) is 5 to 30% by mass, preferably 10 to 20% by mass, the amino group-containing epoxy resin (B) is 40 to 75% by mass, preferably 45 to 70% by mass, and the blocked polyisocyanate (E) is 20 to 40% by mass, preferably 25 to 35% by mass, relative to the total solid content of the modified acrylic resin (A), amino group-containing epoxy resin (B), and blocked polyisocyanate (E).

[0090] The acidic compound (C) in the resin emulsion can be appropriately selected according to the proportion of basic groups (e.g., amino groups, -NH- groups, etc.) that are to be converted to salts (this proportion can be determined, for example, according to the desired water solubility).

[0091] The proportion of water (D) in the resin emulsion is preferably 40 to 90% by mass, and more preferably 55 to 80% by mass, based on 100% by mass of the total components of the resin emulsion.

[0092] <Process 3> Step 3 is a step of mixing the resin emulsion obtained in Step 2 with a pigment dispersion paste to obtain a cationic electrodeposition coating composition.

[0093] Pigment dispersion paste is a paste in which pigments such as coloring pigments, rust-preventive pigments, and extender pigments are pre-dispersed into fine particles. For example, a pigment dispersion paste can be prepared by blending a pigment dispersion resin, a neutralizing agent, and a pigment, and then dispersing them in a dispersion mixer such as a ball mill, sand mill, or pebble mill.

[0094] As the above-mentioned pigment dispersion resin, any known resin can be used without particular limitation. For example, epoxy resins and acrylic resins having hydroxyl groups and cationic groups, surfactants, tertiary amine type epoxy resins, quaternary ammonium salt type epoxy resins, tertiary sulfonium salt type epoxy resins, tertiary amine type acrylic resins, quaternary ammonium salt type acrylic resins, tertiary sulfonium salt type acrylic resins, etc. can be used.

[0095] The above-mentioned pigments can be any known pigments without particular limitation, for example, coloring pigments such as titanium dioxide, carbon black, and red iron oxide; extender pigments such as clay, mica, barita, calcium carbonate, and silica; and rust-preventive pigments such as zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate, and aluminum phosphomolybdate, and zinc phosphomolybdate.

[0096] The amount of pigment added is preferably 1 to 100 parts by mass, and more preferably 10 to 50 parts by mass, per 100 parts by mass of the resin solids of the cationic electrodeposition coating composition.

[0097] Cationic electrodeposition coating compositions may contain a curing catalyst that promotes the curing of the resin component. The curing catalyst is not particularly limited, but may contain, for example, a bismuth compound. Furthermore, in addition to bismuth compounds, one or more curing catalysts selected from the group consisting of, for example, inorganic compounds such as zinc compounds, tin compounds, titanium compounds, zirconium compounds, and yttrium compounds; organic compounds such as phosphazene compounds, amine compounds, and quaternary salt compounds; and composites thereof, can be used in combination. Bismuth compounds are preferred as curing catalysts from an environmental and safety standpoint. Although organotin compounds such as dibutyltin dibenzoate, dioctyl tin oxide, and dibutyltin oxide can be used as curing catalysts to improve the curability of the coating film, it is preferable not to use organotin compounds due to recent environmental regulations on organotin compounds.

[0098] As the bismuth compound, one or more can be selected from the group consisting of inorganic bismuth compounds such as metallic bismuth, bismuth chloride, bismuth oxychloride, bismuth bromide, bismuth oxide, bismuth hydroxide, bismuth nitrate, bismuth nitrite, bismuth silicate, bismuth aluminate, bismuth aluminate, bismuth borate, bismuth phosphate, bismuth carbonate, and bismuth oxycarbonate; and organic bismuth compounds such as bismuth formate, bismuth acetate, bismuth salicylate, bismuth citrate, bismuth benzoate, bismuth gallate, bismuth oxalate, bismuth lactate, bismuth oleate, bismuth methoxyacetate, bismuth dimethylolpropionate, bismuth dialkyldithiocarbamate, bismuth toluenesulfonate, and triphenylbismuth.

[0099] The blending ratio of the curing catalyst in the cationic electrodeposition coating composition is preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 6 parts by mass, per 100 parts by mass of the resin solids content of the cationic electrodeposition coating composition.

[0100] Preparation of cationic electrodeposition coating compositions The preparation of the cationic electrodeposition coating composition is not particularly limited, but for example, it can be obtained by thoroughly mixing the resin emulsion obtained in step 2 with the pigment dispersion paste and other components (the curing agent, water or organic solvent, other additives, etc.).

[0101] The solid content concentration of the cationic electrodeposition coating composition is preferably 10 to 30% by mass, and more preferably 15 to 25% by mass.

[0102] <Cationic electrodeposition coating method> A cationic electrodeposition coating method using the cationic electrodeposition coating composition obtained according to the present invention includes the steps of immersing an object to be coated in an electrodeposition bath consisting of the cationic electrodeposition coating composition, and passing an electric current through the object to be coated with a cathode. A coated article coated with the cationic electrodeposition coating composition can be obtained by immersing an object to be coated in an electrodeposition coating bath containing the cationic electrodeposition coating composition and passing an electric current through the object to form a coating film on the object.

[0103] Examples of substrates to which the cationic electrodeposition coating composition can be applied include automobile bodies, automobile parts, motorcycle parts, household appliances, and other equipment, and there are no particular restrictions as long as the substrate contains metal.

[0104] Examples of metal sheets to be coated include cold-rolled steel sheets, alloyed hot-dip galvanized steel sheets, electro-galvanized steel sheets, electro-galvanized zinc-iron double-layer plated steel sheets, organic composite plated steel sheets, Al material, Mg material, etc., as well as metal sheets that have been cleaned on the surface by alkaline degreasing or the like as needed, and then subjected to surface treatments such as phosphate chlorination, chromate treatment, and composite oxide treatment.

[0105] Cationic electrodeposition coating compositions can be applied to the surface of a desired substrate by cationic electrodeposition coating. The cationic electrodeposition method generally involves using a bath containing a cationic electrodeposition coating composition diluted with deionized water or the like to a solid content concentration of approximately 5 to 40% by mass, preferably 10 to 25% by mass, and further adjusting the pH to within the range of 4.0 to 9.0, preferably 5.5 to 7.0. The bath temperature is usually adjusted to 15 to 35°C, and an electric current is applied with the substrate as the cathode under conditions of a load voltage of 100 to 400V, preferably 150 to 350V. After electrodeposition coating, the substrate is usually thoroughly washed with ultrafiltration solution (UF filtrate), reverse osmosis permeate (RO water), industrial water, pure water, etc., to remove any excess cationic electrodeposition coating.

[0106] The thickness of the electrodeposited coating is not particularly limited, but generally it can be in the range of 5 to 40 μm, preferably 10 to 30 μm, based on the dry coating. The coating is then baked and dried using drying equipment such as an electric hot air dryer or a gas hot air dryer, heating the electrodeposited coating at a temperature of 110 to 200°C, preferably 140 to 180°C, on the surface of the coated object for a period of 10 to 180 minutes, preferably 20 to 50 minutes. A cured coating can be obtained by the above baking and drying process.

[0107] All patent applications and document disclosures cited herein are incorporated herein by reference in their entirety. [Examples]

[0108] The present invention will be described in more detail below with reference to manufacturing examples, embodiments, and comparative examples, but the present invention is not limited thereto. In each example, "parts" refers to parts by mass, and "%" refers to mass percent.

[0109] The following examples are for illustrative purposes only and are not intended to limit the technical scope of the present invention in any way. Unless otherwise specified, reagents are obtained or prepared from commercially available sources or according to methods commonly used in the art or procedures described in prior art.

[0110] Manufacturing of modified acrylic resin (A) Manufacturing Example 1: Manufacturing of Modified Acrylic Resin A-1 (as described above) Manufacturing of modified acrylic resin (A) (1) Reaction method in the section "") 256 parts of methyl isobutyl ketone were charged into a 2-liter reaction vessel (minimum stirring capacity of approximately 250 ml) equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropper. After purging with nitrogen, the temperature was maintained at 114°C. The monomer mixture shown below was then added dropwise over 4 hours. Styrene 320 copies n-butyl methacrylate 40 parts 2-Hydroxyethyl methacrylate (molecular weight 130.14) 266 parts 2,2'-Azobis(2-methylbutyronitrile) 32 parts One hour after the dropwise addition was completed, a solution of 2.4 parts 2,2'-azobis(2-methylbutyronitrile) dissolved in 26 parts methyl isobutyl ketone was added dropwise over 40 minutes. After the dropwise addition was completed, the mixture was maintained at 114°C for another hour. Subsequently, a solution of 174 parts ε-caprolactone (molecular weight 114.14) dissolved in 8.4 parts methyl isobutyl ketone and a solution of 6.3 parts zinc hexoate dissolved in 14.4 parts methyl isobutyl ketone were added. Sampling was performed while maintaining the temperature at 114°C, and cooling was started when the solid content reached 72% or more, ultimately yielding a modified acrylic resin A-1 solution with a solid content of approximately 73%. In this case, approximately 2 hours passed between the addition of ε-caprolactone and zinc hexoate and the start of cooling. The obtained modified acrylic resin A-1 had a hydroxyl value of 137 mgKOH / g and a weight-average molecular weight of 4700.

[0111] Manufacturing Example 2: Manufacturing of Modified Acrylic Resin A-2 (as described above) Manufacturing of modified acrylic resin (A) (3) Reaction method in the section "") A 2-liter reaction vessel (with a minimum stirring capacity of approximately 250 ml) equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropper was charged with 153.6 parts methyl isobutyl ketone, 174 parts ε-caprolactone, and 6.3 parts zinc hexoate. After purging with nitrogen, the mixture was maintained at 114°C. The following mixture was then added dropwise over 4 hours. Styrene 320 copies n-butyl methacrylate 40 parts 2-Hydroxyethyl methacrylate 266 parts 2,2'-Azobis(2-methylbutyronitrile) 32 parts One hour after the dropwise addition was completed, a solution of 2.4 parts of 2,2'-azobis(2-methylbutyronitrile) dissolved in 26 parts of methyl isobutyl ketone was added dropwise over 40 minutes. After the dropwise addition was completed, the mixture was maintained at 114°C for another hour, and then cooling was started to obtain a modified acrylic resin A-2 solution with a solid content of approximately 82%. The obtained modified acrylic resin A-2 had a hydroxyl value of 137 mgKOH / g and a weight-average molecular weight of 4700.

[0112] Manufacturing Example 3: Manufacturing of Modified Acrylic Resin A-3 (as described above) Manufacturing of modified acrylic resin (A) (2) Reaction method in the section "") 256 parts of methyl isobutyl ketone were charged into a 2-liter reaction vessel (minimum stirring capacity of approximately 250 ml) equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropper. After purging with nitrogen, the temperature was maintained at 114°C. The monomer mixture shown below was then added dropwise over 4 hours. Styrene 320 copies n-butyl methacrylate 40 parts 2-Hydroxyethyl methacrylate (molecular weight 130.14) 266 parts 2,2'-Azobis(2-methylbutyronitrile) 32 parts After the dropwise addition was complete, a solution of 174 parts ε-caprolactone (molecular weight 114.14) dissolved in 8.4 parts methyl isobutyl ketone and a solution of 6.3 parts zinc hexoate dissolved in 14.4 parts methyl isobutyl ketone were added. One hour after the completion of monomer dropwise addition, a solution of 2.4 parts 2,2'-azobis(2-methylbutyronitrile) dissolved in 26 parts methyl isobutyl ketone was added dropwise over 40 minutes. After the dropwise addition was complete, the mixture was maintained at 114°C for another hour. Sampling was performed while maintaining the temperature at 114°C, and cooling was started when the solid content reached 72% or more, ultimately yielding a modified acrylic resin A-1 solution with a solid content of approximately 73%. In this case, approximately 2 hours passed between the addition of ε-caprolactone and zinc hexoate and the start of cooling. The obtained modified acrylic resin A-3 had a hydroxyl value of 137 mgKOH / g and a weight-average molecular weight of 4700.

[0113] Manufacturing Example 4: Manufacturing of Acrylic Resin A-4 (Unmodified Acrylic Resin) 320 parts of methyl isobutyl ketone were charged into a 2-liter reaction vessel (minimum stirring capacity of approximately 250 ml) equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropper. After purging with nitrogen, the temperature was maintained at 114°C. The following mixture was then added dropwise over 4 hours. Styrene 320 copies n-butyl methacrylate 214 parts 2-Hydroxyethyl methacrylate 266 parts 2,2'-Azobis(2-methylbutyronitrile) 32 parts One hour after the dropwise addition was complete, a solution of 2,2'-azobis(2-methylbutyronitrile) dissolved in 30 parts methyl isobutyl ketone was added dropwise over 40 minutes. After the dropwise addition was complete, the mixture was maintained at 114°C for another hour, and then cooling was started to obtain an acrylic resin A-4 solution with a solid content of approximately 69%. The obtained acrylic resin A-4 had a hydroxyl value of 137 mgKOH / g and a weight-average molecular weight of 3700.

[0114] Manufacturing of amino group-containing epoxy resin (B) Manufacturing Example 5 In a flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux condenser, 1200 parts of jER828EL (trade name, epoxy resin manufactured by Japan Epoxy Resin Co., Ltd., epoxy equivalent 190, number average molecular weight 350) were added to 500 parts of bisphenol A and 0.2 parts of dimethylbenzylamine, and the mixture was reacted at 130°C until the epoxy equivalent reached 850. Next, 160 parts of diethanolamine and 65 parts of a ketimine compound of diethylenetriamine and methyl isobutyl ketone were added, and the mixture was reacted at 120°C for 4 hours. After that, 480 g of ethylene glycol monobutyl ether was added to obtain an amino group-containing epoxy resin B-1 solution with a solid content of 80%. The amino group-containing epoxy resin B-1 had an amine value of 59 mgKOH / g and a number average molecular weight of 2100.

[0115] Production of blocked polyisocyanate compound (E) Manufacturing Example 6 270 parts of Cosmonate M-200 (trade name, manufactured by Mitsui Chemicals, crude MDI, NCO group content 31.3%) and 127 parts of methyl isobutyl ketone were added to a reaction vessel and the temperature was raised to 70°C. 236 parts of ethylene glycol monobutyl ether were added dropwise over 1 hour, and the temperature was then raised to 100°C. Samples were taken over time while maintaining this temperature, and infrared absorption spectroscopy was used to confirm that the absorption of unreacted isocyanate groups had disappeared, yielding a blocked polyisocyanate compound E-1 with a resin solids content of 80%.

[0116] Manufacturing of pigment dispersion resins Manufacturing example 7 In a flask equipped with a stirrer, thermometer, dropping funnel, and reflux condenser, 1010 parts of jER828EL (trade name, epoxy resin manufactured by Japan Epoxy Resin Co., Ltd., epoxy equivalent 190, number average molecular weight 350) were added, along with 390 parts of bisphenol A, 240 parts of Praxel 212 (trade name, polycaprolactone diol, Daicel Chemical Industries, Ltd., weight average molecular weight approximately 1250), and 0.2 parts of dimethylbenzylamine. The mixture was reacted at 130°C until the epoxy equivalent was approximately 1090. Next, 134 parts of dimethylethanolamine and 150 parts of a 90% aqueous lactic acid solution were added, and the mixture was reacted at 90°C until the epoxy groups disappeared. Then, propylene glycol monomethyl ether was added to adjust the solid content, yielding a pigment dispersion resin containing a quaternary ammonium base with a solid content of 60%.

[0117] Manufacturing of pigment dispersion paste Manufacturing Example 8 8.3 parts (5 parts solids) of pigment dispersion resin containing a quaternary ammonium base with a solid content of 60% obtained in Production Example 7, 14.5 parts titanium dioxide, 7 parts purified clay, 0.3 parts carbon black, 2 parts bismuth hydroxide, and 20.3 parts deionized water were added and dispersed in a ball mill for 20 hours to obtain pigment dispersion paste P-1 with a solid content of 55%.

[0118] Manufacturing of cationic electrodeposition coating compositions Example 1 21.4 parts (15 parts solids) of modified acrylic resin A-1 obtained in Production Example 1, 68.8 parts (55 parts solids) of amino group-containing epoxy resin B-1 obtained in Production Example 5, and 37.5 parts (30 parts solids) of blocked polyisocyanate compound E-1 obtained in Production Example 6 were mixed, and 13 parts of 10% acetic acid were added and the mixture was uniformly stirred to obtain a resin solution before desolvation. The mixture was then heated to 80°C and desolvated under reduced pressure. Deionized water was then added dropwise over approximately 15 minutes while vigorously stirring to obtain a resin emulsion with a solid content of 34%. 294 parts of the above resin emulsion (100 parts solids), 52.4 parts of the pigment dispersion paste P-1 obtained in Production Example 8, and deionized water were added while stirring to produce a cationic electrodeposition coating composition (X-1) with a solids content of 20%. Subsequently, evaluation tests (corrosion resistance of flat surfaces, finish quality) described later were carried out. The results are shown in Table 1. Note that all amounts in Table 1 are solids.

[0119] Examples 2-4, Comparative Examples 1-2 Cationic electrodeposition coating compositions (X-2) to (X-6) were prepared in the same manner as in Example 1, except for the formulations shown in Table 1 below. Subsequently, evaluation tests (corrosion resistance of flat surfaces, finish quality) were conducted as described later, and the evaluation results are shown in Table 1. Table 1 also lists the percentage of solvent imported from the acrylic resin.

[0120] [Table 1] All resin content values ​​in Table 1 represent the solid content.

[0121] Preparation of test boards Cold-rolled steel sheets (150mm (length) x 70mm (width) x 0.8mm (thickness)) treated with chemical conversion treatment (product name, Palbond #3020, manufactured by Nippon Parkerizing Co., Ltd., zinc phosphate treatment agent) were used as the substrate for electrodeposition coating. Each of the cationic electrodeposition coatings obtained in the examples and comparative examples was electrodeposited to a dry film thickness of 15 μm, and the sheets were baked and dried at 170°C for 20 minutes to obtain test plates.

[0122] <Corrosion resistance of flat parts> Cross-cut scratches were made in the coating of the test board using a utility knife so as to reach the substrate. A 35°C salt spray test was then performed for 840 hours in accordance with JIS Z-2371, and the rust and blister width on one side of the cut area were evaluated according to the following criteria. "◎" and "○" indicate a pass, and "×" indicates a fail. ◎: The maximum width of rust and blistering is 2.0 mm or less on one side from the cut section. ○: The maximum width of rust and blistering exceeds 2.0 mm on one side of the cut section, and is 3.0 mm or less. ×: The maximum width of rust and blistering exceeds 3.0 mm on one side of the cut section.

[0123] <Finish quality (surface roughness)> The surface roughness (Ra) of the obtained test plates was measured using SurfTest 301 (product name, manufactured by Mitutoyo Corporation, surface roughness meter) with a cutoff of 0.8 mm, and evaluated according to the following criteria. "◎" and "○" indicate a pass, and "×" indicates a fail. ◎: Surface roughness value (Ra) is less than 0.2. ○: Surface roughness value (Ra) is 0.2 or higher and less than 0.3. ×: Indicates a surface roughness value (Ra) of 0.3 or higher.

Claims

1. A method for producing a cationic electrodeposition coating composition, Step 1: A step to produce a modified acrylic resin (A) by reacting a hydroxyl group-containing (meth)acrylic acid ester (a-1) with other polymerizable unsaturated group-containing monomers (a-2) and a lactone (a-3). Step 2: A step of preparing a resin emulsion comprising the modified acrylic resin (A), an amino group-containing epoxy resin (B), an acidic compound (C), and water (D). Step 3: A step of mixing the resin emulsion and the pigment dispersion paste, A method for producing a cationic electrodeposition coating composition containing the above.

2. The manufacturing method according to claim 1, wherein in step 2, the resin emulsion further comprises blocked polyisocyanate (E).

3. The method for producing the product according to claim 1, wherein in step 1, a mixture containing a hydroxyl group-containing (meth)acrylic acid ester (a-1) and another polymerizable unsaturated group-containing monomer (a-2) is added dropwise to a solution containing a lactone (a-3).

4. The manufacturing method according to claim 1, wherein in step 1, 100 to 1000 mol% of lactone (a-3) is used based on 100 mol% of hydroxyl group-containing (meth)acrylic acid ester (a-1).

5. The manufacturing method according to claim 1, wherein in step 1, 15 to 50 parts by mass of hydroxyl group-containing (meth)acrylic acid ester (a-1), 20 to 80 parts by mass of other polymerizable unsaturated group-containing monomers (a-2), and 5 to 40 parts by mass of lactone (a-3) are used per 100 parts by mass of the solid content of the modified acrylic resin (A).

6. The manufacturing method according to claim 1, wherein in step 2, the modified acrylic resin (A) is present in an amount of 5 to 20% by mass and the amino group-containing epoxy resin (B) is present in an amount of 80 to 95% by mass, relative to the total mass of solids of the modified acrylic resin (A) and the amino group-containing epoxy resin (B).

7. The manufacturing method according to claim 2, wherein in step 2, the modified acrylic resin (A), amino group-containing epoxy resin (B), and blocked polyisocyanate (E) are present in an amount of 5 to 30% by mass of the total solid content of the modified acrylic resin (A), amino group-containing epoxy resin (B), and blocked polyisocyanate (E), and the amount of the modified acrylic resin (A) is 40 to 75% by mass of the amino group-containing epoxy resin (B), and the amount of the blocked polyisocyanate (E) is 20 to 40% by mass.

8. The manufacturing method according to claim 1, wherein the solid content of the modified acrylic resin (A) in the reaction mixture obtained in step 1 is 50% by mass or more.

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