Coating composition and coating film forming method

Abstract

Provided are a coating composition including: (A) a hydroxyl group-containing resin, (B) a polyisocyanate compound, (C) an organometallic catalyst composed of a zinc compound and an amidine compound, and (D) a compound containing a phosphoric acid group; and a coating film forming method including coating a coating target with the coating composition to form a coating film on the coating target, and then heating and curing the coating film.

Description

Technical Field

[0001] This invention relates to coating compositions and methods for forming coating films. Background Technology

[0002] In recent years, from the perspective of saving energy and reducing environmental impact, there has been active development in the painting of automobile bodies and other products to shorten the baking and curing process.

[0003] In shortening the baking and curing process, there is a growing demand for reducing the temperature and time of the curing step. As coating compositions that meet this requirement of low temperature and short curing time, hydroxyl / isocyanate-based crosslinked coating compositions have been investigated, in which hydroxyl-containing resins are cured using polyisocyanate compounds as curing agents.

[0004] Organotin compounds are commonly used as catalysts to accelerate the curing reaction of the above-mentioned hydroxy / isocyanate crosslinked coating compositions (Patent Document 1).

[0005] However, despite the extremely high catalytic performance of organotin compounds, their toxicity has become a concern in recent years. Therefore, alternative catalysts to organotin compounds are needed.

[0006] Furthermore, hydroxyl / isocyanate-crosslinked coating compositions are typically used by mixing a base agent containing a hydroxyl-containing resin and a curing agent containing a polyisocyanate compound. Excellent pot life is required to ensure a good working time after mixing.

[0007] Patent Document 2 describes a coating composition with the following characteristics that achieves excellent low-temperature and short-time curing properties and pot life, and provides a cured coating film with excellent finished appearance: the composition contains (A) a secondary hydroxyl-containing acrylic resin, which is a copolymer of monomer components formed from 20% to 50% by mass of (a) a secondary hydroxyl-containing polymerizable unsaturated monomer and 50% to 80% by mass of (b) any other polymerizable unsaturated monomer, (B) a polyisocyanate compound, and (C) an organometallic catalyst formed from (C1) a metal compound and (C2) an amidine compound, wherein the metal of the metal compound is selected from one of the following: zinc; tin; zirconium; bismuth; lead; cobalt; manganese; titanium; aluminum; and molybdenum; and the equivalent ratio (NCO / OH) of the isocyanate groups in the polyisocyanate compound (B) to the hydroxyl groups in the secondary hydroxyl-containing acrylic resin (A) falls within the range of 0.8 to 1.8. However, in recent years, there has been a desire for coating compositions with even better pot life.

[0008] Reference List

[0009] Patent documents

[0010] PTL 1:JP 2002-338885 A

[0011] PTL 2:WO 2013 / 047208 A1 Summary of the Invention

[0012] Technical issues

[0013] The objective of this invention is to provide a coating composition that exhibits excellent low-temperature and short-time curing properties and an excellent pot life without the use of any organotin compounds.

[0014] Solution to the problem

[0015] In order to achieve the above objectives, the inventors of the present invention conducted extensive research and found that the above objectives can be achieved by a coating composition comprising: (A) a hydroxyl-containing resin; (B) a polyisocyanate compound; (C) an organometallic catalyst formed from a zinc compound and an amidine compound; and (D) a compound containing a phosphate ester group.

[0016] According to the present invention, a coating composition and a method for forming a coating film are provided, comprising the following aspects.

[0017] Item 1. A coating composition comprising: (A) a hydroxyl-containing resin; (B) a polyisocyanate compound; (C) an organometallic catalyst formed from a zinc compound and an amidine compound; and (D) a compound containing a phosphate ester group.

[0018] Item 2. The coating composition according to Item 1, wherein the hydroxyl-containing resin (A) contains a hydroxyl-containing acrylic resin (A1).

[0019] Item 3. The coating composition according to Item 2, wherein the hydroxyl-containing acrylic resin (A1) contains an acrylic resin (A11) containing primary hydroxyl groups.

[0020] Item 4. The coating composition according to any one of items 1 to 3, wherein the compound (D) containing a phosphate ester group contains an alkyl phosphate ester (D1) and / or a resin (D2) containing a phosphate ester group.

[0021] Item 5. A method for forming a coating film, comprising: applying a coating composition according to any one of items 1 to 4 to a top of a workpiece to form a coating film; and then heating the coating film to cure the coating film.

[0022] Beneficial effects of the invention

[0023] The coating composition of the present invention has excellent low-temperature and short-time curing properties, and excellent pot life without the use of any organotin compounds. Detailed Implementation Plan

[0024] In this specification, except where explicitly described alone or where there is obvious contradiction in the context, the singular form (e.g., a(a), a(an), or described) includes both the singular and plural forms. The coating composition of the present invention (hereinafter sometimes simply referred to as "the coating") is described in more detail below.

[0025] The coating composition of the present invention comprises the following: (A) a hydroxyl-containing resin; (B) a polyisocyanate compound; (C) an organometallic catalyst formed from a zinc compound and an amidine compound; and (D) a compound containing a phosphate ester group.

[0026] Hydroxyl-containing resin (A)

[0027] A hydroxyl-containing resin (A) is a resin having at least one hydroxyl group in its molecule. Various known resins can be used as hydroxyl-containing resins (A), examples of which include hydroxyl-containing acrylic resins, hydroxyl-containing polyester resins, hydroxyl-containing acrylic-modified polyester resins, hydroxyl-containing polyether resins, hydroxyl-containing polycarbonate resins, hydroxyl-containing polyurethane resins, hydroxyl-containing epoxy resins, and hydroxyl-containing alkyd resins. These resins can be used alone or in combination. In particular, from the viewpoint of the water resistance of the coating to be formed, the hydroxyl-containing resin (A) preferably contains a hydroxyl-containing acrylic resin (A1).

[0028] Hydroxyl-containing acrylic resin (A1)

[0029] Hydroxyl-containing acrylic resins (A1) can be obtained, for example, by copolymerizing a hydroxyl-containing polymerizable unsaturated monomer with any other polymerizable unsaturated monomer (a polymerizable unsaturated monomer other than the hydroxyl-containing polymerizable unsaturated monomer).

[0030] The aforementioned hydroxyl-containing polymerizable unsaturated monomers are compounds having one or more hydroxyl groups and one or more polymerizable unsaturated bonds in their molecules. Examples of hydroxyl-containing polymerizable unsaturated monomers may include: monoester compounds of (meth)acrylic acid and diols each having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylic acid, 2-hydroxypropyl (meth)acrylic acid, 3-hydroxypropyl (meth)acrylic acid, and 4-hydroxybutyl (meth)acrylic acid; ε-caprolactone-modified products of monoester compounds of (meth)acrylic acid and diols each having 2 to 8 carbon atoms; adducts of (meth)acrylic acid and compounds containing epoxy groups (e.g., "CARDURAE10P" (product name), manufactured by Hexion, Inc., glycidyl neodecanoate); N-hydroxymethyl (meth)acrylamide; allyl alcohol; and (meth)acrylic acid esters each having a polyoxyethylene chain with a hydroxyl group at the end of its molecule.

[0031] For example, the monomers described in items (1) through (6) below can each be used as other polymerizable unsaturated monomers that can be copolymerized with the above-described hydroxyl-containing polymerizable unsaturated monomers. These polymerizable unsaturated monomers can be used alone or in combination.

[0032] (1) Polymerizable unsaturated monomers containing acid groups

[0033] Acid-containing polymerizable unsaturated monomers are compounds having one or more acid groups and one or more polymerizable unsaturated bonds in their molecules. Examples of monomers may include: carboxyl-containing monomers, such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, and maleic anhydride; and sulfonic acid-containing monomers, such as vinylsulfonic acid and 2-sulfoethyl (meth)acrylic acid. These monomers may be used alone or in combination. When using acid-containing polymerizable unsaturated monomers, the amount is set such that the acid value of the hydroxyl-containing acrylic resin (A1) is preferably from 0.5 mg KOH / g to 15 mg KOH / g, more preferably from 1 mg KOH / g to 12 mg KOH / g.

[0034] (2) Ester compounds of acrylic acid or methacrylic acid and monohydric alcohols having 1 to 20 carbon atoms.

[0035] Ester compounds of acrylic acid or methacrylic acid and monohydric alcohols having 1 to 20 carbon atoms may specifically include, for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, isomyristyl methacrylate, stearyl methacrylate, isostearyl methacrylate (manufactured by Osaka Organic Chemicals Co., Ltd., product name), lauryl methacrylate, tridecyl methacrylate, tetrahydrofurfuryl methacrylate, cyclohexyl methacrylate, or isobornyl methacrylate.

[0036] (3) Aromatic vinyl monomers

[0037] Aromatic vinyl monomers can specifically be, for example, styrene, α-methylstyrene, or vinyltoluene.

[0038] When aromatic vinyl monomers are used as components, the glass transition temperature of the resin increases, and a hydrophobic coating with a high refractive index can be obtained. Therefore, an improved appearance of the finished product can be achieved by enhancing the gloss of the coating.

[0039] When aromatic vinyl monomers are used as components, the mixing ratio is preferably in the range of 3% to 50% by mass relative to the total amount of monomer components, more preferably in the range of 5% to 40% by mass.

[0040] (4) Polymerizable unsaturated monomers containing glycidyl groups

[0041] A polymerizable unsaturated monomer containing a glycidyl group is a compound having one or more glycidyl groups and one or more polymerizable unsaturated bonds in its molecule. Specific examples may include glycidyl acrylate and glycidyl methacrylate.

[0042] (5) Compounds containing nitrogen atoms with polymerizable unsaturated bonds

[0043] Compounds containing nitrogen atoms with polymerizable unsaturated bonds can be, for example, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-[3-(dimethylamino)propyl](meth)acrylamide, N-butoxymethyl(meth)acrylamide, diacetone(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylate, vinylpyridine, vinylimidazolium, acrylonitrile, or methacrylonitrile.

[0044] (6) Other vinyl compounds

[0045] Any other vinyl compound may be, for example, vinyl acetate, vinyl propionate, vinyl chloride, or vinyl tert-carbonate. Examples of vinyl tert-carbonate may include the commercial products “VeoVa 9” and “VeoVa 10” (which are product names manufactured by Hexion, Inc.).

[0046] As used herein, the term "polymerizable unsaturated monomer" refers to a monomer having one or more (e.g., 1 to 4) polymerizable unsaturated groups. The term "polymerizable unsaturated group" means an unsaturated group that can undergo free radical polymerization. Examples of such polymerizable unsaturated groups include vinyl, (meth)acryloyl, (meth)acrylamido, vinyl ether, allyl, propenyl, isopropenyl, and maleimide.

[0047] Furthermore, as used herein, the term "(meth)acrylate" means acrylate or methacrylate. The term "(meth)acrylic acid" means acrylic acid or methacrylic acid. The term "(meth)acryloyl" means acryloyl or methacryloyl. The term "(meth)acrylamide" means acrylamide or methacrylamide.

[0048] From the viewpoints of pot life, low temperature and short curing time of the coating composition, the hydroxyl value of the above-mentioned hydroxyl-containing acrylic resin (A1) falls within the range of preferably 20 mg KOH / g to 200 mg KOH / g, more preferably 25 mg KOH / g to 180 mg KOH / g, and particularly preferably 30 mg KOH / g to 160 mg KOH / g.

[0049] Furthermore, from the viewpoints of pot life, low temperature and short time curing properties of the coating composition, the weight average molecular weight of the above-mentioned hydroxyl-containing acrylic resin (A1) falls within the range of preferably 2,000 to 50,000, more preferably 3,000 to 40,000, and particularly preferably 4,000 to 30,000.

[0050] The term "weight-average molecular weight" as used in this article refers to the value calculated relative to the molecular weight of standard polystyrene from a chromatogram measured by gel permeation chromatography. The HLC-8120GPC (manufactured by Tosoh Corporation) was used as the gel permeation chromatograph. Four columns, "TSKgel G-4000HXL," "TSKgel G-3000HXL," "TSKgel G-2500HXL," and "TSKgel G-2000HXL" (all manufactured by Tosoh Corporation), were used as columns, and measurements were performed under the following conditions: tetrahydrofuran was used as the mobile phase; the measurement temperature was set to 40°C; the flow rate was set to 1 cc / min; and an RI detector was used as the detector.

[0051] Furthermore, from the viewpoint of the hardness and final appearance of the coating to be formed, the glass transition temperature of the hydroxyl-containing acrylic resin (A1) falls within the range of -30°C to 85°C, more preferably -10°C to 80°C, and particularly preferably 10°C to 75°C.

[0052] In this specification, the glass transition temperature (°C) of acrylic resin is calculated using the following equation.

[0053] 1 / Tg(K)=(W1 / T1)+(W2 / T2)+……(1)

[0054] Tg (℃)=Tg (K)-273 (2)

[0055] In the corresponding equations, W1, W2, ... represent the corresponding mass fractions of the monomers used for copolymerization, and T1, T2, ... represent the Tg(K) of the homopolymers of the corresponding monomers.

[0056] T1, T2, ... are values ​​based on pages 139-179 of "Polymer Handbook (Second Edition, edited by J. Brandup and EHImmergut)" III. Furthermore, when the Tg of the homopolymer of the monomer is unknown, the static glass transition temperature (°C) is used as the glass transition temperature. For example, the sample is placed in a measuring cup of a differential scanning calorimeter "DSC-220U" (manufactured by Seiko Instruments Inc.), and vacuum is applied to completely remove the solvent. The change in heat is then measured using the calorimeter at a heating rate of 3°C / min within the range of -20°C to +200°C. The first baseline change point at the lower temperature is used as the static glass transition temperature.

[0057] There are no particular limitations on the copolymerization method for obtaining hydroxyl-containing acrylic resins (A1) by copolymerizing the mixture of the above monomers, and each copolymerization method known in itself can be used. In particular, solution polymerization methods including polymerization in an organic solvent in the presence of a polymerization initiator can be suitably used.

[0058] Examples of organic solvents used in solution polymerization methods may include: aromatic solvents, such as toluene, xylene, and SWASOL 1000 (manufactured by Maruzen Petrochemical Co., Ltd., product name, high-boiling-point petroleum solvent); ester-based solvents, such as ethyl acetate, butyl acetate, propyl propionate, butyl propionate, 1-methoxy-2-propyl acetate, 2-ethoxyethyl propionate, 3-methoxybutyl acetate, ethylene glycol ethyl ether acetate, and propylene glycol methyl ether acetate; ketone-based solvents, such as methyl ethyl ketone, methyl isobutyl ketone, and methyl pentyl ketone; and alcohol-based solvents, such as isopropanol, n-butanol, isobutanol, and 2-ethylhexanol.

[0059] Although these organic solvents can be used alone or in combination, ester-based or ketone-based solvents are preferred for their solubility in acrylic resins. Furthermore, aromatic solvents can be suitably used in combination with them.

[0060] Examples of polymerization initiators that can be used for copolymerization of hydroxyl-containing acrylic resins (A1) may include known free radical polymerization initiators such as 2,2′-azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, di-tert-pentyl peroxide, tert-butyl peroctanoate, 2,2′-azobis(2-methylbutyronitrile), and 2,2′-azobis(2,4-dimethylpentanonitrile).

[0061] Hydroxyl-containing acrylic resins (A1) can be used alone or in combination.

[0062] From the viewpoint of low temperature and short curing time, the above-mentioned hydroxyl-containing acrylic resin (A1) preferably includes acrylic resin (A11) containing primary hydroxyl groups.

[0063] The aforementioned acrylic resin (A11) containing primary hydroxyl groups can be prepared, for example, by using a polymerizable unsaturated monomer containing primary hydroxyl groups as a polymerizable unsaturated monomer containing hydroxyl groups in the aforementioned method for producing acrylic resin (A1).

[0064] Examples of the aforementioned polymerizable unsaturated monomers containing primary hydroxyl groups include: polymerizable unsaturated monomers having primary hydroxyl groups, wherein the alkyl group of the ester moiety has 2 to 8, preferably 2 to 6, more preferably 2 to 4 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, or 4-hydroxybutyl (meth)acrylate; and adducts of (meth)acrylate and epoxy-containing compounds (e.g., "CARDURA E10P" (product name), manufactured by Hexion, Inc., glycidyl neodecanoate). These monomers can be used alone or in combination. In particular, 2-hydroxyethyl (meth)acrylate is suitable for use from the perspective of the hardness, etc., of the coating to be formed.

[0065] From the perspective of low temperature and short curing time of the coating film to be formed, in the production of the above-mentioned acrylic resin (A11) containing primary hydroxyl groups, the amount of the polymerizable unsaturated monomer containing primary hydroxyl groups is preferably in the range of 10% to 60% by mass relative to the total amount of the monomer component to be copolymerized, and more preferably in the range of 5% to 50% by mass relative to it.

[0066] Furthermore, in the aforementioned acrylic resin (A11) containing primary hydroxyl groups, from the viewpoint of low temperature and short curing time, the content of the polymerizable unsaturated monomer containing primary hydroxyl groups in the total amount of polymerizable unsaturated monomers containing hydroxyl groups is preferably in the range of 50% by mass to 100% by mass, more preferably in the range of 55% by mass to 100% by mass, and even more preferably in the range of 60% by mass to 100% by mass.

[0067] From the viewpoints of pot life, low temperature and short curing time of the coating composition, the content of the above-mentioned hydroxyl-containing acrylic resin (A1) in the coating composition of the present invention is preferably 40% to 85% by mass, more preferably 45% to 75% by mass, and even more preferably 50% to 70% by mass relative to the resin solids content of the coating composition.

[0068] Polyisocyanate compounds (B)

[0069] A polyisocyanate compound (B) is a compound having at least two isocyanate groups in its molecule, and examples of such compounds may include aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, aromatic-aliphatic polyisocyanate compounds, aromatic polyisocyanate compounds, and derivatives of polyisocyanate compounds.

[0070] Examples of aliphatic polyisocyanate compounds may include: aliphatic diisocyanate compounds, such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate or 2,2,4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and 2,6- Methyl diisocyanate (common name: lysine diisocyanate); and aliphatic triisocyanate compounds, such as 2,6-diisocyanate hexanoate 2-isocyanate ethyl ester, 1,6-diisocyanate-3-isocyanate methyl hexane, 1,4,8-triisocyanate octane, 1,6,11-triisocyanate undecane, 1,8-diisocyanate-4-isocyanate methyl octane, 1,3,6-triisocyanate hexane, and 2,5,7-trimethyl-1,8-diisocyanate-5-isocyanate methyl octane.

[0071] Examples of alicyclic polyisocyanate compounds may include: alicyclic diisocyanate compounds, such as 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), 4-methyl-1,3-cyclohexyl diisocyanate (common name: hydrogenated TDI), 2-methyl-1,3-cyclohexene... Hydroxymethyl diisocyanate, 1,3-bis(methyl isocyanate)cyclohexane or 1,4-bis(methyl isocyanate)cyclohexane (common name: hydrogenated xylene diisocyanate) or mixtures thereof, methylene bis(4,1-cyclohexanediyl) diisocyanate (common name: hydrogenated MDI), and norbornene diisocyanate; and alicyclic triisocyanate compounds, such as 1,3,5-triisocyanocyclohexane, 1,3,5-trimethylisocyanocyclohexane. 2-(3-isocyanopropyl)-2,5-di(isocyanomethyl)-bicyclo(2.2.1)heptane, 2-(3-isocyanopropyl)-2,6-di(isocyanomethyl)-bicyclo(2.2.1)heptane, 3-(3-isocyanopropyl)-2,5-di(isocyanomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanoethyl)-2-isocyanomethyl-3-(3-isocyanopropyl)-bicyclo(2.2.1)heptane Cyclo(2.2.1)heptane, 6-(2-isocyanoethyl)-2-isocyanomethyl-3-(3-isocyanopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanoethyl)-2-isocyanomethyl-2-(3-isocyanopropyl)-bicyclo(2.2.1)heptane, and 6-(2-isocyanoethyl)-2-isocyanomethyl-2-(3-isocyanopropyl)-bicyclo(2.2.1)heptane.

[0072] Examples of aromatic-aliphatic polyisocyanate compounds may include: aromatic-aliphatic diisocyanate compounds, such as methylene bis(4,1-phenylene) diisocyanate (common name: MDI), 1,3-xylene diisocyanate or 1,4-xylene diisocyanate or mixtures thereof, ω,ω′-diisocyanate-1,4-diethylbenzene, and 1,3-bis(1-isocyanate-1-methylethyl)benzene or 1,4-bis(1-isocyanate-1-methylethyl)benzene (common name: tetramethylxylene diisocyanate or mixtures thereof); and aromatic-aliphatic triisocyanate compounds, such as 1,3,5-triisocyanomethylbenzene.

[0073] Examples of aromatic polyisocyanate compounds may include: aromatic diisocyanate compounds, such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolyl diisocyanate (common name: 2,4-TDI) or 2,6-tolyl diisocyanate (common name: 2,6-TDI) or mixtures thereof, 4,4′-toluidine diisocyanate, and 4,4′-diphenyl ether diisocyanate; aromatic triisocyanate compounds, such as triphenylmethane-4,4′,4″-triisocyanate, 1,3,5-triisocyanophenylbenzene, and 2,4,6-triisocyanotoluene; and aromatic tetraisocyanate compounds, such as 4,4′-diphenylmethane-2,2′,5,5′-tetraisocyanate.

[0074] In addition, examples of derivatives of polyisocyanate compounds may include dimers, trimers, biuret, urethane, urea diketone, uretimine, isocyanurate, oxadiazine trione, polymethylene polyphenyl polyisocyanate (crude MDI and polymerized MDI), and crude TDI of the above polyisocyanate compounds.

[0075] The aforementioned polyisocyanate compounds and their derivatives can be used alone or in combination.

[0076] From the viewpoint of the weather resistance of the coating film to be formed, it is preferable to use at least one selected from aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds and their derivatives as polyisocyanate compound (B), and from the viewpoint of the final appearance of the coating film formed from the coating composition to be obtained, it is more preferable to use aliphatic polyisocyanate compound and / or its derivatives.

[0077] In particular, from the viewpoint of, for example, the final appearance, curability and weather resistance of the coating to be formed, the aliphatic diisocyanate compounds and / or their isocyanurate forms are preferably used as the aforementioned aliphatic polyisocyanate compounds and / or their derivatives, and more preferably hexamethylene diisocyanate and / or their isocyanurate forms.

[0078] From the viewpoint of, for example, the pot life of the coating composition, low temperature and short curing time, the content of polyisocyanate compound (B) in the coating composition of the present invention is preferably 5% to 60% by mass, more preferably 10% to 55% by mass, and even more preferably 15% to 50% by mass relative to the resin solids content of the coating composition.

[0079] Organometallic catalysts formed from zinc compounds and amidine compounds (C)

[0080] The organometallic catalyst (C) formed from zinc compounds and amidine compounds has both the function of a catalyst that promotes the curing reaction of the coating when heated and the function of an inhibitor that inhibits catalysis at room temperature.

[0081] This is likely due to the following reasons. The organometallic catalyst (C) formed by the zinc compound and the amidine compound forms a complex structure, with the amidine compound acting as a blocker. The amidine compound, acting as a blocker, dissociates at low temperatures, and after dissociation, the inherent catalytic ability of the zinc compound—its excellent ability to improve low-temperature curing properties—becomes active. Therefore, low-temperature and short-time curing properties, as well as a long pot life, can be achieved in this coating.

[0082] Examples of the zinc compounds described above may include zinc carboxylate compounds and zinc acetylacetone complexes. In particular, zinc carboxylate compounds may be suitably used.

[0083] Specific examples of the aforementioned zinc carboxylic acid compounds may include zinc 2-ethylhexanoate, zinc acetate, zinc cyclonaphthenate, zinc octanoate, zinc stearate, zinc neodecanoate, and zinc oleate. In particular, zinc octanoate may be suitably used because it possesses excellent catalytic activity and is readily available industrially.

[0084] Amidine compounds are organic compounds having a structure represented by the following formula (1).

[0085] R 1 -C(=NR 2 )-NR 3 R 4 …(1)

[0086] In equation (1), one nitrogen atom is bonded to a carbon (C) atom via a double bond, and the other nitrogen atom is bonded to it via a single bond.

[0087] R 1 It can represent a hydrogen atom, a substituted organic group, or an amino group, and can specifically represent, for example, a substituted hydrocarbon group or a etherified hydroxyl group.

[0088] R 2 and R 3 Each can independently represent a hydrogen atom or an organic group, or a heterocycle with a structure in which heterocycles are bonded together (each heterocycle is a monocyclic ring with one or two or more heteroatoms, or a bonded bicyclic ring with one or two or more heteroatoms).

[0089] R 4 It represents a hydrogen atom, a substituted organic group or a etherifiable hydroxyl group, and may preferably represent, for example, a substituted hydrocarbon group having eight or more carbon atoms.

[0090] When R 1 or R 4 When referring to an organic group, the group may be, for example, a group having 1 to 40 carbon atoms, or, for example, a polymer group having a molecular weight of 500 to 50,000.

[0091] By R 1 R 2 R 3 and R 4 The groups represented can each independently contain alcohol hydroxyl groups as substituents.

[0092] Where R 2 and R 3 Specific examples of interamidinium compounds represented by formula (1) that are not bonded to each other may include N′-cyclohexyl-N,N-dimethylformamidinium, N′-methyl-N,N-di-n-butylacetamidine, N′-octadecyl-N,N-dimethylformamidinium, N′-cyclohexyl-N,N-dimethylpentanetamidine, 1-methyl-2-cyclohexyliminopyrrolidine, 3-butyl-3,4,5,6-tetrahydropyrimidine, N-(hexyliminomethyl)morpholine, N-(α-(decyliminoethyl)ethyl)pyrrolidine, N′-decyl-N,N-dimethylformamidinium, N′-decyl-N,N-dimethylformamidinium, and N′-cyclohexyl-N,N-acetamidine.

[0093] In addition, the following amidine compounds are included in the amidine compounds: those having R 2 -R 3 In its amidine structure, a five- to seven-membered ring containing two nitrogen atoms is formed, and R 1 -R 3 or R 1 -R 4 One of them is an amidine compound that forms a five- to nine-membered ring with one nitrogen atom and multiple carbon atoms in the amidine structure.

[0094] Specific examples of amidine compounds having this structure may include 1,5-diazabicyclo(4.3.0)non-5-ene, 1,8-diazabicyclo(5.4.0)undec-7-ene, 1,4-diazabicyclo(3.3.0)oct-4-ene, 2-methyl-1,5-diazabicyclo(4.3.0)non-5-ene, 2,7,8-trimethyl-1,5-diazabicyclo(4.3.0)non-5-ene, 2-butyl-1,5-diazabicyclo(4.3.0)non-5-ene, and 1,9-diazabicyclo(6.5.0)tridec-8-ene.

[0095] Furthermore, examples of amidine compounds may include each having R in formula (1). 2 and R 3Heterocyclic compounds with interconnected structures, such as imidazoles, imidazolines, tetrahydropyrimidines, dihydropyrimidines, and compounds containing pyrimidine rings.

[0096] Specific examples of imidazole compounds may include N-(2-hydroxyethyl)imidazolium, N-(3-aminopropyl)imidazolium, 4-(hydroxymethyl)imidazolium, 1-(tert-butoxycarbonyl)imidazolium, imidazolium-4-propionic acid, 4-carboxyimidazole, 1-butylimidazolium, 1-methylimidazolium, 2-methyl-4-imidazolium carboxylic acid, 4-formylimidazolium, 1-(ethoxycarbonyl)imidazolium, reactants of propylene oxide with imidazolium and 2-methylimidazolium, 1-trimethylsilylimidazolium, 4-(hydroxymethyl)imidazolium hydrochloride, and 1-chloro-2,3-propylene oxide with imidazolium. The copolymers of 1-(p-toluenesulfonyl)imidazolium, 1,1-carbonylbisimidazole, 1-(2-cyanoethyl)-2-ethyl-4-methylimidazolium, 2-phenyl-2-imidazoline pyromellitic acid ester, 4-(hydroxymethyl)imidazolium picrate, disodium salts of 2-acrylic acid with 4,5-dihydro-2-nonyl-1H-imidazolium-1-ethanol and 2-heptyl-4,5-dihydro-1H-imidazolium-1-ethanol, 1-(cyanoethyl)-2-undecylimidazolium trimellitate, 1-(2-hydroxypropyl)imidazolium carbamate, imidazolium sodium, and imidazolium silver.

[0097] Amidine compounds can be used alone or in combination.

[0098] Specifically, in this coating, the organometallic catalyst formed by the zinc compound and the amidine compound is a metal complex, and the complex can be prepared, for example, by heating one mole of zinc carboxylate and two moles of amidine compound in a solvent such as methanol.

[0099] In the above production process, the metal complex can be produced by maintaining the mixture at about 50°C for about 2 hours until the mixture becomes a transparent solution. The transparent solution is then filtered and dried. From the viewpoints of pot life, low temperature and short-time curing properties of the coating composition, the molar ratio of the amidine compound to the zinc compound (the ratio of the number of moles of the amidine compound to the number of moles of the zinc compound) is preferably set in the range of 1.3 to 8.0, more preferably in the range of 1.6 to 5.0, and even more preferably in the range of 1.8 to 4.0.

[0100] Organometallic catalysts formed from zinc and amidine compounds can be used by dissolving them in solvents. There are no particular limitations on the solvents, but examples may include solvents comprising: alcohols, such as ethylene glycol, diethylene glycol, dipropylene glycol, propylene glycol, and butanediol; hydrocarbons, such as toluene, xylene, mineral turpentine, and mineral oil; esters, such as ethyl acetate, butyl acetate, methyl ethylene glycol acetate, and cellolytic esters; ketones, such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; glycol ethers, such as ethyl 3-ethoxypropionate and 3-methoxybutyl acetate; organic solvents for amides, such as N,N-dimethylformamide and N,N-dimethylacetamide; β-diketones, such as acetylacetone and its fluorinated products; and ketone esters, such as methyl acetoacetate and ethyl acetoacetate.

[0101] From the viewpoint of pot life, low temperature and short curing time of the coating composition, the content of the organometallic catalyst (C) formed by zinc compound and amidine compound is preferably in the range of 0.01 parts by mass to 5 parts by mass relative to 100 parts by mass of the resin solids content of the coating composition of the present invention, more preferably in the range of 0.03 parts by mass to 4 parts by mass, and even more preferably in the range of 0.05 parts by mass to 3 parts by mass.

[0102] Compounds containing phosphate ester groups (D)

[0103] Compound (D) containing phosphate ester groups has the function of inhibiting the catalytic ability of organometallic catalysts (C) formed by zinc compounds and amidine compounds at room temperature.

[0104] Examples of compounds (D) containing phosphate ester groups may include: phosphoric acid; monoalkyl phosphoric acid, such as mono-n-propyl phosphoric acid, mono-isopropyl phosphoric acid, mono-n-butyl phosphoric acid, mono-isobutyl phosphoric acid, mono-tert-butyl phosphoric acid, mono-octyl phosphoric acid, and mono-decyl phosphoric acid; dialkyl phosphoric acid, such as di-n-propyl phosphoric acid, di-isopropyl phosphoric acid, di-n-butyl phosphoric acid, di-isobutyl phosphoric acid, di-tert-butyl phosphoric acid, di-octyl phosphoric acid, and di-decyl phosphoric acid; monoalkyl phosphorous acid, such as mono-n-propyl phosphorous acid, mono-isopropyl phosphorous acid, mono-n-butyl phosphorous acid, mono-isobutyl phosphoric acid, mono-tert-butyl phosphoric acid, mono-octyl phosphoric acid, and mono-decyl phosphoric acid; dialkyl phosphorous acid, such as di-n-propyl phosphorous acid, di-isopropyl phosphoric acid, di-n-butyl phosphoric acid, di-isobutyl phosphoric acid, di-tert-butyl phosphoric acid, di-octyl phosphoric acid, and di-decyl phosphoric acid; alkyl ether phosphoric acid; polyoxyethylene alkyl ether phosphoric acid; alkyl phosphate ester (D1); and resins containing phosphate ester groups (D2). In particular, it is preferred to incorporate alkyl phosphate esters (D1) and / or resins containing phosphate ester groups (D2), more preferably alkyl phosphate esters (D1). These compounds can be used alone or in combination.

[0105] In this invention, resins containing phosphate groups and hydroxyl groups are not included in hydroxyl-containing resins (A), but are included in compounds containing phosphate groups (D).

[0106] Alkyl phosphate esters (D1) can be, for example, compounds having a chemical structure represented by the following formula (2).

[0107] O = P(OR) n (OH) 3-n ...Equation (2)

[0108] In the formula, R represents an alkyl group having 4 or more, preferably 6 to 20 carbon atoms. The alkyl group can be straight-chain or branched, preferably branched. Furthermore, "n" represents an integer of 1 to 3. Additionally, the "n" Rs can be the same or different from each other.

[0109] Commercially available products that can be used as the aforementioned alkyl phosphate esters (D1) include, for example, NACURE 4054J (product name, manufactured by King Industries, Inc.), Korantin SMK (product name, manufactured by BASF SE), NIKKOL PHOSTEN HLP (product name, manufactured by Nikko Chemicals Co., Ltd.), PHOSPHANOL RS-410, PHOSPHANOL RS-610, PHOSPHANOL RS-710, PHOSPHANOL RD-510Y, PHOSPHANOL RD-720, PHOSPHANOL RB-410, PHOSPHANOL RL-210, PHOSPHANOL RL-310, PHOSPHANOL ML-200, PHOSPHANOL ML-220, PHOSPHANOL RE-410, PHOSPHANOL PE-510, and PHOSPHANOL. RE-610, PHOSPHANOL RE-960, PHOSPHANOL RM-410, PHOSPHANOL RM-510, PHOSPHANOL RM-710, PHOSPHANOL RE-210, PHOSPHANOL RP-710, or PHOSPHANOL SM-172 (all product names, manufactured by TOHO Chemical Industry Co., Ltd.), or PLYSURF A212C, PLYSURF A215C, PLYSURF A208B, PLYSURF A219B, PLYSURF A210G, PLYSURF A208F, or PLYSURF A212E (all product names, manufactured by DKS Co., Ltd.). Each of these products can be used as is or as a salt neutralized with an alkali metal or organic base. In addition, two or more of them can be used in combination.

[0110] From the viewpoint of pot life, low temperature and short curing time of the coating composition, when the coating composition of the present invention includes the above-mentioned alkyl phosphate ester (D1) as a compound (D) containing a phosphate ester group, its content relative to the resin solids content of 100 parts by weight of the coating composition of the present invention preferably falls within the range of 0.01 parts by weight to 3 parts by weight, more preferably within the range of 0.05 parts by weight to 2.5 parts by weight, and even more preferably within the range of 0.1 parts by weight to 2 parts by weight.

[0111] Examples of the above-mentioned resins containing phosphate groups (D2) may include acrylic resins (D21) containing phosphate groups, polyester resins containing phosphate groups, polyether resins containing phosphate groups, polycarbonate resins containing phosphate groups, polyurethane resins containing phosphate groups, and epoxy resins containing phosphate groups. In particular, acrylic resins (D21) containing phosphate groups are preferred from the viewpoints of pot life, low temperature and short-time curing properties of the coating composition.

[0112] Acrylic resins containing phosphate groups (D21) can be synthesized by conventional methods through copolymerization of polymerizable unsaturated monomers with phosphate groups and any other polymerizable unsaturated monomers.

[0113] Examples of polymerizable unsaturated monomers having phosphate ester groups may include acid phosphoryloxyethyl (meth) acrylate, acid phosphoryloxypropyl (meth) acrylate, acid phosphoryloxypoly(oxyethylene) glycol (meth) acrylate, and acid phosphoryloxypoly(oxypropylene) glycol (meth) acrylate.

[0114] Examples of other polymerizable unsaturated monomers may include the compounds listed in the “Hydroxy-containing acrylic resins (A1)” section.

[0115] In the phosphate ester-containing acrylic resin (D21), the polymerizable unsaturated monomer having the phosphate ester group preferably accounts for 1% to 50% by mass, particularly preferably 5% to 40% by mass, of the total amount of the corresponding monomer component used to form the phosphate ester-containing acrylic resin (D21).

[0116] From the viewpoint of final appearance and coating performance, the weight-average molecular weight of the acrylic resin (D21) containing phosphate ester groups falls within the range of preferably 3,000 to 30,000, more preferably 5,000 to 25,000, and particularly preferably 7,000 to 20,000.

[0117] From the viewpoints of pot life, low temperature and short time curing properties of the coating composition, when the coating composition of the present invention includes the above-mentioned acrylic resin (D21) containing phosphate ester groups as the compound (D) containing phosphate ester groups, its content relative to the resin solids content of the coating composition is preferably 0.01% to 3% by mass, more preferably 0.05% to 2.5% by mass, and even more preferably 0.1% to 2% by mass.

[0118] From the viewpoints of pot life, low temperature and short curing time of the coating composition, when the coating composition of the present invention includes a compound containing a phosphate group other than the above-mentioned alkyl phosphate ester (D1) and the above-mentioned acrylic resin containing a phosphate group (D21) as the compound containing a phosphate group (D), its content relative to the resin solids content of 100 parts by weight of the coating composition of the present invention preferably falls within the range of 0.01 parts by weight to 3 parts by weight, more preferably within the range of 0.05 parts by weight to 2.5 parts by weight, and even more preferably within the range of 0.1 parts by weight to 2 parts by weight.

[0119] From the viewpoints of pot life, low temperature and short-time curing properties of the coating composition, in terms of the molar ratio of the organometallic catalyst (C) formed by zinc compound and amidine compound to the compound containing phosphate ester group (D), in the coating composition of the present invention, the content ratio of the organometallic catalyst (C) formed by zinc compound and amidine compound to the compound containing phosphate ester group (D) preferably falls within the range of 1 / 0.1 to 1 / 10, more preferably within the range of 1 / 0.3 to 1 / 8, and even more preferably within the range of 1 / 0.5 to 1 / 5.

[0120] Other components

[0121] The coating composition of the present invention may optionally further include, for example, resins other than hydroxyl-containing resins (A), crosslinking agents other than polyisocyanate compounds (B), curing catalysts other than organometallic catalysts (C) formed from zinc compounds and amidine compounds, pigments, matting agents, organic solvents, dispersants, antisettling agents, defoamers, thickeners, ultraviolet absorbers, light stabilizers, surface modifiers, or scratch resistance improvers.

[0122] Examples of resins other than the hydroxyl-containing resin (A) mentioned above may include hydroxyl-free acrylic resins, hydroxyl-free polyester resins, hydroxyl-free polyurethane resins, hydroxyl-free polyether resins, hydroxyl-free polycarbonate resins, and hydroxyl-free epoxy resins.

[0123] Examples of pigments can include coloring pigments, gloss pigments, and extender pigments. Pigments can be used alone or in combination.

[0124] Examples of coloring pigments may include titanium oxide, zinc oxide, carbon black, cadmium red, molybdenum red, chrome yellow, chromium oxide, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, threne-based pigments, and perylene pigments.

[0125] Examples of glossy pigments may include aluminum powder, mica powder, and mica powder coated with titanium oxide.

[0126] Examples of extender pigments may include talc, clay, kaolin, barium oxide, barium sulfate, barium carbonate, calcium carbonate, and alumina white.

[0127] The aforementioned pigments can be used alone or in combination.

[0128] When the coating composition of the present invention is used as a transparent coating and includes pigments, the amount of pigment mixed is preferably an amount that does not impair the transparency of the coating film to be obtained. For example, the amount of pigment mixed is preferably in the range of 0.1% by mass to 20% by mass relative to the total amount of resin solids in the coating composition, more preferably in the range of 0.3% by mass to 10% by mass, and particularly preferably in the range of 0.5% by mass to 5% by mass.

[0129] Furthermore, when the coating composition of the present invention is used as a coloring coating and includes pigments, the amount of pigment mixed is preferably in the range of 1% to 200% by mass relative to the total amount of resin solids in the coating composition, more preferably in the range of 2% to 100% by mass, and particularly preferably in the range of 5% to 50% by mass.

[0130] Examples of matting agents include silica particles, alumina particles, titanium dioxide particles, zircon particles, zircon particles, tin oxide particles, magnesium oxide particles, polymethyl methacrylate (PMMA) resin beads, MMA-ethylene glycol dimethacrylate (EGDM) copolymer resin beads, nylon resin beads, and polytetrafluoroethylene resin beads.

[0131] When the coating composition of the present invention is used as a matting coating and includes a matting agent, for example, the amount of matting agent mixed is preferably in the range of 1% to 30% by mass relative to the total amount of resin solids in the coating composition, more preferably in the range of 2% to 25% by mass, and particularly preferably in the range of 3% to 20% by mass.

[0132] Examples of organic solvents may include: aromatic solvents such as toluene, xylene, and "SWASOL 1000" (manufactured by Maruzen Petrochemical Co., Ltd., product name: Aromatic Organic Solvents); ester-based solvents such as ethyl acetate, butyl acetate, propyl propionate, butyl propionate, 1-methoxy-2-propyl acetate, 2-ethoxyethyl propionate, 3-ethoxyethyl propionate, 3-methoxybutyl acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, and propylene glycol monomethyl ether acetate; ketone-based solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl pentyl ketone; and alcohol-based solvents such as isopropanol, n-butanol, isobutanol, and 2-ethylhexanol. These solvents may be used alone or in combination.

[0133] Thickeners known to date can be used as thickeners, and examples of them may include clay minerals (e.g., metal silicates or montmorillonite), acrylic resins (e.g., acrylic resins containing a structure formed by polymers or oligomers of acrylates or methacrylates in their molecules, or non-aqueous dispersion resins), polyolefins (e.g., polyethylene or polypropylene), amides (e.g., higher fatty acid amides, polyamides, or oligomers), polycarboxylic acids (including derivatives having at least two or more carboxyl groups in their molecules), cellulose (including various derivatives such as nitrocellulose, acetylated cellulose, and cellulose ethers), urethanes (e.g., polymers or oligomers having a urethane structure in their molecules), ureas (e.g., polymers or oligomers having a urea structure in their molecules), and urethane ureas (e.g., polymers or oligomers having both urethane and urea structures in their molecules).

[0134] Ultraviolet absorbers known to date can be used as ultraviolet absorbers, and examples of them can include ultraviolet absorbers such as benzotriazole-based absorbers, triazine-based absorbers, salicylic acid derivative-based absorbers, and benzophenone-based absorbers. These absorbers can be used alone or in combination.

[0135] When the coating composition of the present invention contains an ultraviolet absorber, the amount of ultraviolet absorber mixed with respect to the total amount of solids in the coating composition preferably falls within the range of 0.1% by mass to 10% by mass, more preferably within the range of 0.2% by mass to 8% by mass, and particularly preferably within the range of 0.3% by mass to 6% by mass.

[0136] Light stabilizers known to date can be used as light stabilizers, and can be, for example, hindered amine-based light stabilizers.

[0137] From a service life perspective, hindered amine-based light stabilizers with low alkalinity can be suitably used as hindered amine-based light stabilizers. Examples of such hindered amine-based light stabilizers may include acylated hindered amines and amino ether-based hindered amines, and specific examples may include "HOSTAVIN 3058" (product name, manufactured by Clariant AG), "TINUVIN 123" (product name, manufactured by BASF SE), and "HALS292" (product name, manufactured by BASF SE).

[0138] There are no particular limitations on the application method of the coating composition of the present invention, examples of which include coating methods such as air spraying, airless spraying, rotary atomization coating, and curtain coating. Each of these methods is capable of forming a wet film. In each of these coating methods, electrostatic application may optionally be performed. Air spraying or rotary atomization coating is particularly preferred. The coating amount is preferably set to such that its cured thickness is between 5 μm and 50 μm, and this amount is particularly preferably set to such that the cured thickness is between 10 μm and 40 μm.

[0139] Furthermore, when performing each of air spraying, airless spraying, and rotary atomization spraying, it is preferable to adjust the viscosity of the coating appropriately within a suitable viscosity range using solvents such as organic solvents and thickeners. In an Iwata (ANESTIWATA) viscosity cup NK2, the viscosity range at 20°C is typically 5 to 20 seconds, particularly 8 to 15 seconds.

[0140] Coating Formation Method

[0141] The coating composition of the present invention can be suitably used in a coating film forming method comprising: applying the coating composition of the present invention to the top of a workpiece to form a coating film; and then heating the coating film to cure the coating film.

[0142] The coating compositions of the present invention can be used in a variety of industrial applications. The compositions are suitable for use as coating compositions for automotive exterior panels or components, and are particularly suitable for use as clear coating compositions.

[0143] Preferred aspects of the above-described coating formation method may include the following methods (A) to (D).

[0144] Method (A)

[0145] A method for forming a coating film, comprising:

[0146] Step (A1): The step of applying the coating composition of the present invention to the top of the object to form a transparent coating film; and

[0147] Step (A2): Heating the transparent coating film formed in step (A1) to cure the coating film.

[0148] Method (B)

[0149] A method for forming a coating film, comprising:

[0150] Step (B1): Applying a base coating composition to the top of the object to form a base coating film;

[0151] Step (B2): The step of applying the coating composition of the present invention to the top of the base coating film to form a transparent coating film; and

[0152] Step (B3): Heating the base coating film formed in step (B1) and the transparent coating film formed in step (B2) separately or simultaneously to cure the coating films.

[0153] Method (C)

[0154] A method for forming a coating film, comprising:

[0155] Step (C1): Applying the top of the object to the first base coating composition to form a first base coating film;

[0156] Step (C2): Applying the second base coating coating composition to the top of the first base coating film to form the second base coating film;

[0157] Step (C3): The step of applying the coating composition of the present invention to the top of the second base coating film to form a transparent coating film; and

[0158] Step (C4): Heating the first base coating film formed in step (C1), the second base coating film formed in step (C2), and the transparent coating film formed in step (C3) separately or simultaneously to cure the coating films.

[0159] Method (D)

[0160] A method for forming a coating film, comprising:

[0161] Step (D1): Applying a primer coating composition to the top of the substrate to form a primer film;

[0162] Step (D2): Applying the top of the primer film with the first base coating paint composition to form the first base coating film;

[0163] Step (D3): Applying the second base coating coating composition to the top of the first base coating film to form the second base coating film;

[0164] Step (D4): The step of applying the coating composition of the present invention to the top of the second base coating film to form a transparent coating film; and

[0165] Step (D5): Heating the primer film formed in step (D1), the first base coat film formed in step (D2), the second base coat film formed in step (D3), and the transparent coating film formed in step (D4) separately or simultaneously to cure the coatings.

[0166] The objects to be coated are not particularly limited, and examples may include: outer panel portions of automobile bodies for passenger cars, trucks, motorcycles, buses, etc.; automobile parts; and outer panel portions of household appliances such as mobile phones or audio equipment. Among these, outer panel portions of automobile bodies and automobile parts are preferred.

[0167] There are no particular limitations on the material to be coated. Examples may include: metallic materials such as iron, aluminum, brass, copper, tin-plated iron, stainless steel, galvanized steel, and steel plated with zinc alloys (e.g., Zn-Al, Zn-Ni, or Zn-Fe); resins such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, and epoxy resin; plastic materials such as various FRPs; inorganic materials such as glass, cement, and concrete; wood; and fibrous materials such as paper and cloth. Among these, metallic and plastic materials are preferred.

[0168] Furthermore, the surface of the object to which the coating is applied can be a surface obtained by surface treatment of a metal substrate, such as phosphate treatment, chromate treatment, or composite oxide treatment, on a metal substrate (e.g., a metal substrate of steel sheet used to form the outer and inner panels of a car body, automotive parts, and each of household appliances).

[0169] A coating film can be further formed on an object, whether it has undergone surface treatment or not. For example, the following steps can be performed: optionally, the object to be coated, which serves as a substrate, is surface treated, and an undercoat film is formed thereon. For example, when the object to be coated is an automobile body, the aforementioned undercoat film can be formed by using a paint known per se for undercoating, which is commonly used for painting automobile bodies.

[0170] For example, electrodeposited coatings, preferably cationic electrodeposited coatings, can be used as undercoatings to form an undercoating film.

[0171] Products obtained by converting the following materials together with pigments, thickeners and any other optional ingredients into coatings can be used as the above-described primer coating compositions: base resins, such as polyolefin resins, acrylic resins, polyester resins, alkyd resins, urethane resins and epoxy resins having crosslinkable functional groups (e.g. carboxyl or hydroxyl groups); and crosslinking agents, such as amino resins (e.g. melamine resins or urea resins), or end-capped polyisocyanate compounds.

[0172] Products obtained by converting the following materials together with pigments, thickeners and any other optional ingredients into coatings can be used in each of the first and second base coating compositions described above: base resins, such as acrylic resins, polyester resins, alkyd resins, urethane resins, or epoxy resins having crosslinkable functional groups (e.g., carboxyl or hydroxyl groups); and crosslinking agents, such as amino resins (e.g., melamine resins or urea resins), or end-capped polyisocyanate compounds.

[0173] Heating can be carried out by known means, and a drying oven, such as a hot air furnace, an electric furnace, or an infrared induction heating furnace, can be used. The heating temperature falls within the range of 50°C to 110°C, preferably 60°C to 90°C. Although there is no particular limitation on the heating time, it falls within the range of preferably 5 minutes to 40 minutes, more preferably 10 minutes to 35 minutes.

[0174] Example

[0175] The invention is described in more detail below with reference to embodiments and comparative examples. However, the invention is not limited to these embodiments. The terms "parts" and "%" refer to "parts by mass" and "% by mass," respectively.

[0176] Manufacturing of hydroxyl-containing acrylic resins (A1)

[0177] Manufacturing Example 1

[0178] Twenty-seven parts of "SWASOL 1000" (product name, manufactured by Maruzen Petrochemical Co., Ltd., an aromatic organic solvent) and five parts of propylene glycol monomethyl ether acetate were loaded into a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropper. While nitrogen was being purged into the reaction vessel, the loaded liquid was stirred at 150°C, and a monomer mixture consisting of 20 parts styrene, 24.8 parts isobutyl methacrylate, 24 parts ethyl acrylate, 30 parts 2-hydroxyethyl methacrylate, 1.2 parts acrylic acid, and 4.5 parts di-tert-amyl peroxide (polymerization initiator) was added dropwise at a constant rate over 4 hours. The mixture was then aged at 150°C for 1 hour and then cooled. Additionally, 21 parts isobutyl acetate were added to dilute the cooled product. Thus, a solution of a primary hydroxyl-containing acrylic resin (A11-1) with a solids content of 65% by mass was obtained. The resulting acrylic resin (A11-1) containing primary hydroxyl groups has an ester content of 9.3 mg KOH / g, a hydroxyl value of 129 mg KOH / g, a weight-average molecular weight of 6,000, and a glass transition temperature of 39 °C.

[0179] Manufacturing of organometallic catalysts (C) formed from zinc compounds and amidine compounds

[0180] Manufacturing Example 2

[0181] 47 parts of ethyl 3-ethoxypropionate and 81.6 parts of "NIKKA OCTHIX ZINC" (product name, zinc octanoate, manufactured by Nihon Kagaku Sangyo Co., Ltd., zinc content: 8% by mass) were loaded into a reaction vessel containing a stirrer, condenser, temperature controller, nitrogen inlet tube, and dropping funnel. The interior of the reaction vessel was purged with nitrogen and heated to 50°C. Subsequently, 16.4 parts of 1-methylimidazole were added dropwise to the mixture with stirring, and after the addition was complete, the mixture was maintained at 50°C for 2 hours to complete the reaction. The resulting organometallic catalyst (C-1) formed from the zinc compound and the amidine compound was a liquid with a zinc content of 4.5% by mass.

[0182] Manufacturing Examples 3 to 10

[0183] The organometallic catalysts (C-2) to (C-9) formed from the zinc compound and the amidine compound were obtained in the same manner as in Manufacturing Example 2, except that the mixed composition in Manufacturing Example 2 was set as shown in Table 1.

[0184] Table 1

[0185]

[0186]

[0187] "Zinc naphthenate" (Note 1): Zinc content: 10.1%, manufactured by Tokyo Chemical Industry Co., Ltd.

[0188] "Zinc acetylacetone" (Note 2): Zinc content: 25%, manufactured by Showa Chemical Co., Ltd.

[0189] DBN (Note 3): 1,5-diazabicyclo[4.3.0]non-5-ene, and

[0190] DBU (Note 4): 1,8-diazabicyclo[5.4.0]undec-7-ene.

[0191] Preparation of other organometallic catalysts (E)

[0192] Manufacturing Example 11

[0193] 364 parts of ethyl 3-ethoxypropionate and 83.6 parts of "K-KAT 348" (product name, bismuth octanoate, bismuth content: 25%, manufactured by King Industries, Inc.) were loaded into a reaction vessel containing a stirrer, condenser, temperature controller, nitrogen inlet tube, and dropping funnel. The interior of the reaction vessel was purged with nitrogen and heated to 50°C. Subsequently, 16.4 parts of 1-methylimidazole were added dropwise to the mixture with stirring, and after the addition was complete, the mixture was maintained at 50°C for 2 hours to complete the reaction. The resulting other organometallic catalyst (E-1) was a liquid with a bismuth content of 4.5% by mass.

[0194] Manufacturing Examples 12 and 13

[0195] The other organometallic catalysts (E-2) and (E-3) were obtained in the same manner as in Manufacturing Example 11, except that the mixed composition in Manufacturing Example 11 was set as shown in Table 2.

[0196] Table 2

[0197]

[0198] “NIKKAOCTHIX COBALT” (Note 5): Product name, cobalt octanoate, cobalt content: 8%, manufactured by Nippon Chemical Industries, Ltd.

[0199] “NIKKAOCTHIX MANGANESE” (Note 6): Product name, manganese octanoate, manganese content: 8%, manufactured by Nippon Kagaku Sangyo Co., Ltd.

[0200] Manufacturing of resins containing phosphate ester groups (D2)

[0201] Manufacturing Example 14

[0202] A mixed solvent containing 27.5 parts methoxypropanol and 27.5 parts isobutanol was loaded into a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device, and heated to 110°C. Subsequently, over 4 hours, a mixture of 121.5 parts, consisting of 25 parts styrene, 27.5 parts n-butyl methacrylate, 20 parts isostearyl acrylate (product name, manufactured by Osaka Organic Chemical Industry Ltd., a branched alkyl acrylate), 7.5 parts 4-hydroxybutyl acrylate, less than 15 parts of a polymerizable monomer containing phosphate groups, 12.5 parts 2-methacryloyloxyethyl phosphate, 10 parts isobutanol, and 4 parts tert-butyl peroxyoctanoate, was added to the aforementioned mixed solvent. Furthermore, a mixture consisting of 0.5 parts tert-butyl peroxyoctanoate and 20 parts isopropanol was added to the resulting mixture for 1 hour. The resulting mixture was then stirred and matured for 1 hour to provide an acrylic resin solution (D21-1) containing phosphate ester groups with a solids content concentration of 50%. The resin has an acid value of 83 mg KOH / g for the phosphate ester groups, a hydroxyl value of 29 mg KOH / g, and a weight-average molecular weight of 10,000.

[0203] Polymerizable monomers containing phosphate groups: 57.5 parts monobutylphosphoric acid and 41 parts isobutanol were loaded into a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device, and the temperature of the mixture was increased to 90°C. Then, 42.5 parts glycidyl methacrylate were added dropwise to the mixture over 2 hours, followed by further stirring and aging for 1 hour. Subsequently, 59 parts isopropanol were added to the aged product to provide a solution of polymerizable monomers containing phosphate groups with a solids content concentration of 50%. The acid value of the phosphate groups in the resulting monomer was 285 mg KOH / g.

[0204] Manufacturing of coating compositions

[0205] Examples 1 to 11 and Comparative Examples 1 to 6

[0206] The hydroxyl-containing acrylic resin obtained in Manufacturing Example 1 above, the organometallic catalysts formed from zinc compounds and amidine compounds obtained in Manufacturing Examples 2 to 10 above, the other organometallic catalysts obtained in Manufacturing Examples 11 to 13 above, the phosphate ester-containing resin obtained in Manufacturing Example 14 above, and the raw materials shown in Table 3 below are used. These materials are stirred and mixed using a blade mixer according to the formulations shown in Table 3 below. Furthermore, butyl acetate is added to the mixture to adjust its viscosity, measured using an ANEST IWATA viscosity cup NK2 at 20°C, to 11 seconds. Thus, coating compositions No. 1 to No. 17 are obtained. The formulations for each of the coating compositions shown in Table 3 are the mass ratios of the solid content between the corresponding components.

[0207] Table 3

[0208]

[0209]

[0210]

[0211] Table 3 (continued - 1)

[0212]

[0213]

[0214] Table 3 (continued - 2)

[0215]

[0216]

[0217] (Note 7) "SUMIDUR N3300": Product name, manufactured by Sumika Covestro Urethane Co., Ltd., in the isocyanurate form of hexamethylene diisocyanate, solids content: 100%, and

[0218] (Note 8) "NACURE 4054J": Product name, manufactured by King Industries, Inc., 2-ethylhexyl phosphate.

[0219] Applicable period

[0220] The pot life of each of the coating compositions No. 1 to No. 17 was evaluated by measuring the viscosity at 20°C after standing for 6 hours using an ANEST IWATA viscosity cup NK2. The results are summarized in Table 3. Viscosity after 6 hours (13 seconds or less) was considered acceptable.

[0221] Manufacturing of test panels

[0222] Tin-plated iron sheets were coated with each of coating compositions No. 1 through No. 17 using air spraying to achieve a cured thickness of approximately 30 μm. The sheets were then heated at 80°C for 30 minutes to cure the compositions, followed by standing at 20°C in a constant temperature chamber for 24 hours. This yielded the corresponding test panels.

[0223] NCO reaction rate (%)

[0224] The NCO reaction ratio was evaluated as follows: the isocyanate peak intensity immediately after coating preparation was measured using an FT-IR instrument "FT / IR-420" (manufactured by JASCO Corporation) via the liquid film method; and the isocyanate peak intensity on the test panel surface was measured using the ATR method. The corresponding isocyanate peak intensity was measured (2,271 cm⁻¹). -1 The NCO reaction rate (%) was determined by calculating the ratio between these intensities using the following equation. An NCO reaction rate (%) of 80% or greater was considered acceptable. The measurement results are summarized in Table 3.

[0225] NCO reaction rate (%) = 100 - NCO residual rate (%)

[0226] NCO Residual Ratio (%) = (Isocyanate Peak Intensity of Test Panel) / (Isocyanate Peak Intensity Immediately After Coating Preparation) × 100

[0227] Knoop Hardness

[0228] The Knoop hardness of the coating was measured using a TUKON microhardness tester (manufactured by American Chain & Cable Company, Inc.). Knoop hardness represents the hardness of the coating as measured by the size of the diamond-shaped indentation produced when a pyramidal diamond indenter is pressed into the test surface of the material under a constant test load. A higher value indicates higher hardness. A Knoop hardness of 10 or greater is considered acceptable. The measurement results are summarized in Table 3.

[0229] The embodiments and examples of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments, and various modifications based on the technical concept of the present invention are possible.

[0230] For example, the configurations, methods, steps, shapes, materials, values, etc. listed in the above implementation schemes and embodiments are merely examples, and different configurations, methods, steps, shapes, materials, values, etc. may be optionally used.

Claims

1. A coating composition comprising: (A) Resins containing hydroxyl groups; (B) Polyisocyanate compounds; (C) Organometallic catalysts formed from zinc compounds and amidine compounds; and (D) Compounds containing phosphate groups, The organometallic catalyst described herein has a complex structure. The zinc compounds mentioned above include zinc carboxylate compounds and / or zinc acetylacetone complexes. The compounds containing phosphate groups include one or any combination of phosphoric acid, monoalkyl phosphoric acid, dialkyl phosphoric acid, monoalkyl phosphorous acid, dialkyl phosphorous acid, alkyl ether phosphoric acid, polyoxyethylene alkyl ether phosphoric acid, alkyl phosphate esters, and resins containing phosphate groups.

2. The coating composition according to claim 1, wherein the hydroxyl-containing resin (A) comprises a hydroxyl-containing acrylic resin (A1).

3. The coating composition according to claim 2, wherein the hydroxyl-containing acrylic resin (A1) comprises an acrylic resin (A11) containing primary hydroxyl groups.

4. The coating composition according to any one of claims 1 to 3, wherein the compound (D) containing phosphate ester groups contains alkyl phosphate esters (D1) and / or resins containing phosphate ester groups (D2).

5. A coating film forming method, including: The coating composition according to any one of claims 1 to 4 is applied to the top of the object to form a coating film; as well as The coating is then heated to cure it.

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