CN117178038A

CN117178038A - High solid content coating composition and method for forming multilayer coating film

Info

Publication number: CN117178038A
Application number: CN202280029158.4A
Authority: CN
Inventors: 大西康平; 伊藤弘高; 吉原秀树
Original assignee: Kansai Paint Co Ltd
Current assignee: Kansai Paint Co Ltd
Priority date: 2021-05-18
Filing date: 2022-03-31
Publication date: 2023-12-05
Also published as: WO2022244538A1; JP7200444B1; JPWO2022244538A1

Abstract

The present invention has an object to provide a high-solid-content coating composition capable of forming a coating film excellent in coating film properties and finished appearance. The problem of the present invention can be solved by a high-solid-content coating composition comprising: (A) a hydroxyl group-containing acrylic resin having a weight average molecular weight of 3000 to 10000 and a hydroxyl value of 130 to 220mgKOH/g, (B) castor oil, (C) a melamine resin, and (D) a catalyst, and the solid content at the time of coating is 50 mass% or more.

Description

High solid content coating composition and method for forming multilayer coating film

Technical Field

The present invention relates to a high-solid-content coating composition and a multilayer coating film forming method.

Background

In recent years, from the viewpoint of global environment protection, it has been demanded to reduce Volatile Organic Compounds (VOC) released from paints, and in various fields, substitution from solvent-based paints to water-based paints has been rapidly advanced.

In the coating of automobiles, a large amount of solvent-based paint has been used, and reduction of VOC discharged from these paints has become urgent, but with respect to various paints used in the steps of undercoating, intermediate coating and top coating of automobiles, replacement of water-based paint with organic solvent-based paint is advanced, and currently, coating with water-based paint is becoming mainstream.

However, in the overcoating of a clear coating, particularly, a high level of film properties (recoatability, curability, etc.) and finished appearance is required, so that a solvent-based clear coating is also mainly applied at present.

One method of VOC reduction that is not related to the water-based development of clear paints is to differentiate the paint into a high solid content (increase the solid content).

For example, patent document 1 discloses a high-solid-content coating composition comprising a specific hydroxyl-containing resin in which a polyisocyanate compound and a melamine resin are used in combination in a reaction product of a specific carboxyl-containing compound and an epoxy-containing compound.

However, the coating composition has good finished appearance and curability, but may have insufficient recoatability.

Patent document 2 discloses a thermosetting high-solid-content coating composition comprising: (a) a carboxyl group-containing compound; (B) polyepoxides; and (C) a copolymer obtained by polymerizing a monomer component comprising (a) 30 to 50% by weight of vinyltrimethoxysilane and/or vinyltriethoxysilane, (b) 5 to 15% by weight of N-methylol (meth) acrylamide alkyl ether, and (C) 35 to 65% by weight of another polymerizable unsaturated monomer.

However, the coating composition has good finished appearance and recoatability, but may have insufficient curability.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2002-201430

Patent document 2: international publication No. 99/03939

Disclosure of Invention

Problems to be solved by the invention

The present invention has an object to provide a high-solid-content coating composition capable of forming a coating film excellent in coating film properties and finished appearance.

Technical proposal

As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by a high-solid-content coating composition comprising: (A) a hydroxyl group-containing acrylic resin having a weight average molecular weight of 3000 to 10000 and a hydroxyl value of 130 to 220mgKOH/g, (B) castor oil, (C) a melamine resin, and (D) a catalyst, and the solid content at the time of coating is 50 mass% or more.

According to the present invention, there is provided a high-solid-content coating composition comprising the following aspects.

Item 1. A high solids coating composition comprising: (A) a hydroxyl group-containing acrylic resin having a weight average molecular weight of 3000 to 10000 and a hydroxyl value of 130 to 220mgKOH/g, (B) castor oil, (C) a melamine resin, and (D) a catalyst, and the solid content at the time of coating is 50 mass% or more.

Item 2. The high solids coating composition according to item 1, wherein the hydroxyl group-containing acrylic resin (A) comprises a secondary hydroxyl group-containing acrylic resin (A').

Item 3. The high solids coating composition according to item 1 or 2, wherein the castor oil (B) has a hydroxyl value in the range of 80 to 230 mgKOH/g.

The high-solid content coating composition according to any one of items 1 to 3, wherein the catalyst (D) comprises a sulfonic acid catalyst (D-1).

The high solids coating composition according to any one of items 1 to 4, further comprising a blocked polyisocyanate compound (E).

Item 6. A multilayer coating film forming method comprising: step (1): a step of forming an intercoat coating film by applying an intercoat coating composition to a substrate; step (2): a step of forming a base coating film by applying a base coating composition to the base coating film formed in the step (1); step (3): a step of forming a clear coat film by applying the high-solid-content coating composition according to any one of claims 1 to 5 to the base coat film formed in the step (2); and (4) a step of: and (3) a step of heating and curing the intercoat coating film, the base coating film and the clear coating film formed in the steps (1) to (3) together.

Advantageous effects

The high-solid-content coating composition of the present invention can form a coating film excellent in recoating adhesion, curability and finished appearance.

Detailed Description

Hereinafter, the high-solid-content coating composition (hereinafter, may be simply referred to as "the present coating") of the present invention will be described in further detail.

The high-solid-content coating composition of the present invention is a high-solid-content coating composition comprising: (A) a hydroxyl group-containing acrylic resin having a weight average molecular weight of 3000 to 10000 and a hydroxyl value of 130 to 220mgKOH/g, (B) castor oil, (C) a melamine resin, and (D) a catalyst, and the solid content at the time of coating is 50 mass% or more.

In the present specification, the high-solid-content coating composition means a coating composition having a solid content of 50% or more at the time of coating.

Hydroxyl group-containing acrylic resin (A)

The hydroxyl group-containing acrylic resin (A) is an acrylic resin having a weight average molecular weight in the range of 3000 to 10000 and a hydroxyl value in the range of 130 to 220 mgKOH/g.

The hydroxyl group-containing acrylic resin (a) has a weight average molecular weight of 3000 or more, so that the resulting coating film has good curability, and the coating film has a finished appearance of 10000 or less. Among them, the weight average molecular weight of the hydroxyl group-containing acrylic resin (a) is preferably in the range of 4000 to 9000, more preferably in the range of 5000 to 8000, from the viewpoints of curability of the formed coating film and appearance of the finished product.

In the present specification, the average molecular weight is a value calculated based on the molecular weight of standard polystyrene based on a chromatogram measured by gel permeation chromatography. As a gel permeation chromatograph, "HLC8120GPC" (manufactured by Tosoh corporation) was used. As the column, four columns, "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", "TSKgel G-2000HXL" (all manufactured by Tosoh Co., ltd., trade name) were used in the mobile phase: tetrahydrofuran, determination temperature: 40 ℃, flow rate: 1 cc/min, detector: RI.

The hydroxyl value of the hydroxyl group-containing acrylic resin (A) is 130mgKOH/g or more, so that the coating film formed has good recoatability and curability, and the coating film formed has good finished appearance when the hydroxyl value is 220mgKOH/g or less. Among them, the hydroxyl value of the hydroxyl group-containing acrylic resin (A) is preferably in the range of 140 to 210mgKOH/g, more preferably in the range of 150 to 200mgKOH/g, from the viewpoints of the recoatability, curability and finished appearance of the formed coating film.

The hydroxyl group-containing acrylic resin (a) can be obtained, for example, by copolymerizing a hydroxyl group-containing polymerizable unsaturated monomer with another polymerizable unsaturated monomer (a polymerizable unsaturated monomer other than the hydroxyl group-containing polymerizable unsaturated monomer).

The hydroxyl group-containing polymerizable unsaturated monomer is a compound having one or more hydroxyl groups and one or more polymerizable unsaturated bonds in one molecule. Examples of the hydroxyl group-containing polymerizable unsaturated monomer include: monoesters of (meth) acrylic acid with a glycol having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate; an epsilon-caprolactone modified product of a monoester of (meth) acrylic acid and a glycol having 2 to 8 carbon atoms; an adduct of (meth) acrylic acid and an epoxy group-containing compound (for example, "Cardura E10P" (trade name), manufactured by Momentive Specialty Chemicals company, glycidyl neodecanoate); n-methylol (meth) acrylamide; allyl alcohol; and (meth) acrylic acid esters having polyoxyethylene chains with hydroxyl groups at the molecular terminals.

As the other polymerizable unsaturated monomer copolymerizable with the above-mentioned hydroxyl group-containing polymerizable unsaturated monomer, for example, monomers shown in the following (1) to (6) and the like can be used. These polymerizable unsaturated monomers may be used singly or in combination of two or more.

(1) Acid group-containing polymerizable unsaturated monomer

The acid group-containing polymerizable unsaturated monomer is a compound having one or more acid groups and one or more polymerizable unsaturated bonds in one molecule. Examples of the monomer include: carboxyl group-containing monomers such as (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid and maleic anhydride; sulfonic acid group-containing monomers such as vinylsulfonic acid and 2-sulfoethyl (meth) acrylate; acid phosphate monomers such as acid phosphoric acid 2- (meth) acryloyloxyethyl ester, acid phosphoric acid 2- (meth) acryloyloxypropyl ester, acid phosphoric acid 2- (meth) acryloyloxy-3-chloropropyl ester, and phosphoric acid 2-methacryloyloxyethyl phenyl ester. One or two or more kinds of them may be used. When the acid group-containing polymerizable unsaturated monomer is used, the acid value of the hydroxyl group-containing acrylic resin (A) is preferably set to 0.5 to 30mgKOH/g, particularly 1 to 20 mgKOH/g.

(2) Esters of acrylic acid or methacrylic acid with monohydric alcohols having 1 to 20 carbon atoms

Specifically, there may be mentioned: methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, isotetradecyl (meth) acrylate, stearyl (meth) acrylate, isostearyl (trade name manufactured by Osaka organic chemical industry Co., ltd.), lauryl (meth) acrylate, tridecyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and the like.

(3) Aromatic vinyl monomer

Specifically, there may be mentioned: styrene, alpha-methylstyrene, vinyltoluene, and the like. By using an aromatic vinyl monomer as a constituent component, the glass transition temperature of the obtained resin increases, and a coating film having a high refractive index and being hydrophobic can be obtained, so that the effect of improving the appearance of the finished product due to the improvement in the gloss of the coating film can be obtained. When an aromatic vinyl monomer is used as a constituent component, the blending ratio thereof is preferably in the range of 3 to 50% by mass, particularly preferably 5 to 40% by mass, relative to the total amount of the monomer components.

(4) Glycidyl group-containing polymerizable unsaturated monomer

The polymerizable unsaturated monomer containing a glycidyl group is a compound having one or more glycidyl groups and one or more polymerizable unsaturated bonds in one molecule, and specifically, glycidyl acrylate, glycidyl methacrylate, and the like are exemplified.

(5) Nitrogen atom-containing Compound containing polymerizable unsaturated bond

Examples include: (meth) acrylamide, N-dimethyl (meth) acrylamide, N- [3- (dimethylamino) propyl ] (meth) acrylamide, N-butoxymethyl (meth) acrylamide, diacetone (meth) acrylamide, N-dimethylaminoethyl (meth) acrylate, vinylpyridine, vinylimidazole, acrylonitrile, methacrylonitrile, and the like.

(6) Other vinyl Compounds

Examples include: vinyl acetate, vinyl propionate, vinyl chloride, vinyl versatate, and the like. Examples of vinyl versatate include commercially available products such as "VEOVA 9" and "VEOVA 10" (trade name, manufactured by JAPAN EPOXY RESIN Co., ltd.).

As the other polymerizable unsaturated monomer, one or two or more kinds of the monomers described in the above (1) to (6) may be used alone.

In the present invention, the polymerizable unsaturated monomer means a monomer having one or more (for example, 1 to 4) polymerizable unsaturated groups. The polymerizable unsaturated group means an unsaturated group capable of undergoing radical polymerization. Examples of the polymerizable unsaturated group include: vinyl, (meth) acryl, (meth) acrylamido, vinyl ether, allyl, propenyl, isopropenyl, maleimide, and the like.

In addition, in the present specification, "(meth) acrylate" means acrylate or methacrylate. "(meth) acrylic" refers to acrylic or methacrylic. In addition, "(meth) acryl" means acryl or methacryl. In addition, "(meth) acrylamide" means acrylamide or methacrylamide.

In the production of the hydroxyl group-containing acrylic resin (a), the amount of the hydroxyl group-containing polymerizable unsaturated monomer to be used is preferably in the range of 25 to 60 mass%, more preferably in the range of 30 to 55 mass% relative to the total amount of the comonomer components, from the viewpoints of recoatability, curability and finished appearance of the formed coating film.

As a copolymerization method for copolymerizing the polymerizable unsaturated monomer mixture to obtain the hydroxyl group-containing acrylic resin (a), a solution polymerization method in which polymerization is performed in an organic solvent in the presence of a polymerization initiator can be preferably used.

Examples of the organic solvent used in the solution polymerization method include: aromatic solvents such as toluene and xylene, and "Swazol 1000" (trade name, high boiling point petroleum solvent, manufactured by COSMO Petroleum Co.); ester solvents such as ethyl acetate, butyl acetate, propyl propionate, butyl propionate, 1-methoxy-2-propyl acetate, 2-ethoxyethyl propionate, 3-methoxybutyl acetate, ethylene glycol monoethyl ether acetate, and propylene glycol methyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; alcohol solvents such as isopropyl alcohol, n-butanol, isobutyl alcohol, and 2-ethylhexanol.

These organic solvents may be used singly or in combination of two or more, and from the viewpoint of solubility of the acrylic resin, an ester-based solvent and a ketone-based solvent are preferably used. In addition, it is also preferable to use an aromatic solvent in combination.

Examples of the polymerization initiator that can be used in the copolymerization of the hydroxyl group-containing acrylic resin (a) include: known radical polymerization initiators such as 2,2' -azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, di-t-amyl peroxide, t-butyl peroctoate, 2' -azobis (2-methylbutyronitrile), and 2,2' -azobis (2, 4-dimethylvaleronitrile).

The hydroxyl group-containing acrylic resin (A) may be used alone or in combination of two or more.

The glass transition temperature of the hydroxyl group-containing acrylic resin (a) is preferably in the range of 0 to 70 ℃, particularly preferably 10 to 60 ℃, and even more particularly preferably 20 to 55 ℃ from the viewpoint of water resistance of the formed coating film, appearance of the finished product, and the like.

In the present specification, the glass transition temperature (. Degree. C.) of the acrylic resin is calculated according to the following formula.

1/Tg(K)＝(W1/T1)+(W2/T2)+……(1)

Tg(℃)＝Tg(K)-273(2)

In the formulae, W1, W2, … … represent the respective mass fractions of the monomers used for copolymerization, and T1, T2, … … represent Tg (K) of the homopolymers of the respective monomers. T1, T2 and … … are values of pages III-139 to 179 of the Polymer Manual (Polymer Hand Book) (Second Edition, J.Brandup.E.H.Immerout). The glass transition temperature (. Degree.C.) in the case where Tg of the homopolymer of the monomer is not clear is set to a static glass transition temperature, for example, a differential scanning calorimeter "DSC-220U" (manufactured by Seiko Instrument Co., ltd.) is used, a sample is taken into a measuring cup, the solvent is completely removed by vacuum suction, then a change in heat is measured at a temperature rise rate of 3℃per minute in the range of-20℃to +200℃, and the initial change point of the base line at the low temperature side is set to the static glass transition temperature.

From the viewpoints of the recoating property of the formed coating film and the appearance of the finished product, the hydroxyl group-containing acrylic resin (a) preferably contains a secondary hydroxyl group-containing acrylic resin (a'). The secondary hydroxyl group-containing acrylic resin (a') can be produced, for example, as follows: in the above-mentioned method for producing the hydroxyl group-containing acrylic resin (a), a secondary hydroxyl group-containing polymerizable unsaturated monomer is used as one of the hydroxyl group-containing polymerizable unsaturated monomers.

Examples of the secondary hydroxyl group-containing polymerizable unsaturated monomer include: a polymerizable unsaturated monomer having a secondary hydroxyl group, wherein the alkyl group of the ester moiety such as 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, or 3-hydroxybutyl (meth) acrylate has 2 to 8 carbon atoms, preferably 3 to 6 carbon atoms, and more preferably 3 or 4 carbon atoms; an adduct of (meth) acrylic acid and an epoxy group-containing compound (for example, "Cardura E10P" (trade name), manufactured by Momentive Specialty Chemicals company, glycidyl neodecanoate), and the like. They may be used singly or in combination of two or more. Among them, 2-hydroxypropyl (meth) acrylate is preferably used from the viewpoints of the recoatability of the formed coating film, the appearance of the finished product, and the like.

In the production of the secondary hydroxyl group-containing acrylic resin (a'), when the secondary hydroxyl group-containing polymerizable unsaturated monomer is used, the amount of the secondary hydroxyl group-containing polymerizable unsaturated monomer to be used is preferably in the range of 25 to 60 mass%, more preferably in the range of 30 to 55 mass% relative to the total amount of the comonomer components, from the viewpoints of curability of a formed coating film, appearance of a finished product, and the like.

In the secondary hydroxyl group-containing acrylic resin (a'), the content of the secondary hydroxyl group-containing polymerizable unsaturated monomer in the total amount of the hydroxyl group-containing polymerizable unsaturated monomer is preferably in the range of 50 to 100% by mass, more preferably in the range of 55 to 100% by mass, and even more preferably in the range of 60 to 100% by mass, from the viewpoints of the recoatability, curability, and finished appearance of the formed coating film.

The content of the hydroxyl group-containing acrylic resin (a) in the high-solid-content coating composition of the present invention is preferably in the range of 20 to 70 parts by mass, more preferably 25 to 65 parts by mass, still more preferably 30 to 60 parts by mass, based on 100 parts by mass of the resin solid content of the high-solid-content coating composition, from the viewpoints of the recoatability, curability, and finished appearance of the formed coating film.

Castor oil (B)

Castor oil (B) is a vegetable oil prepared from seeds of castor oil, and is a glyceride of unsaturated fatty acids such as ricinoleic acid and oleic acid, and saturated fatty acids such as palmitic acid. In the present specification, castor oil (B) includes natural castor oil and synthetic castor oil.

As the synthetic castor oil, castor oil-based polyol (B') can be preferably used. The castor oil-based polyol (B') is not particularly limited, and examples thereof include castor oil, alkylene oxide adducts of castor oil, esters of castor oil fatty acids and hydroxyl group-containing compounds, and the like.

As the castor oil-based polyol (B'), commercially available ones can be used. The trade names of commercial products include, for example: "URIC H-30", "URIC H-31", "URIC H-52", "URIC H-57", "URIC H-62", "URIC H-73X", "URIC H-81", "URIC H-102", "URIC H-420", "URIC H-854", "URIC H-870", "URIC H-1823", "URIC H-1824", "URIC H-1830", "URIC HF-1300", "URIC POLYCASTOR #10", "URIC POLYCASTOR #30", made by Equisetum oil company, above "," TLM "," LM-R "," ELA-DR "," HS "," CM "," HS 2G-120"," HS2G-160R "," HS2G-270B "," HS KA-001"," HS CM-025P "," HS 3G-500B ", made by Equisetum oil company, and the like.

The castor oil-based polyol (B') may be used alone or in combination of two or more.

The hydroxyl value of the castor oil (B) is preferably in the range of 80 to 230mgKOH/g, more preferably in the range of 90 to 215mgKOH/g, and even more preferably in the range of 100 to 200mgKOH/g, from the viewpoints of the recoatability, curability, and finished appearance of the formed coating film.

The content of castor oil (B) in the high-solid-content coating composition of the present invention is preferably in the range of 1 to 30 parts by mass, more preferably 2 to 20 parts by mass, and even more preferably 3 to 10 parts by mass, based on 100 parts by mass of the resin solid content of the high-solid-content coating composition, from the viewpoints of the recoatability, curability, and finished appearance of the formed coating film.

Melamine resin (C)

As the melamine resin (C), a partially methylolated melamine resin or a fully methylolated melamine resin obtained by the reaction of a melamine component and an aldehyde component can be used. The aldehyde component includes: formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde, and the like.

In addition, a material in which the methylol group of the methylolated melamine resin is partially or completely etherified with an appropriate alcohol may be used. Examples of the alcohol used for etherification include: methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, 2-ethyl-1-butanol, 2-ethyl-1-hexanol, and the like.

The melamine resin (C) is preferably a methyl-etherified melamine resin obtained by partially or completely etherifying the methylol group of a partially or completely methylolated melamine resin with methanol, a butyl-etherified melamine resin obtained by partially or completely etherifying the methylol group of a partially or completely methylolated melamine resin with butanol, or a methyl-butyl mixed etherified melamine resin obtained by partially or completely etherifying the methylol group of a partially or completely methylolated melamine resin with methanol and butanol.

Further, the melamine resin (C) preferably has a weight average molecular weight of 400 to 6000, more preferably 500 to 5000, still more preferably 800 to 4000.

As the melamine resin (C), commercially available ones can be used. The trade names of commercial products include, for example: "CYMEL 202", "CYMEL 203", "CYMEL 211", "CYMEL 238", "CYMEL 251", "CYMEL 303", "CYMEL 323", "CYMEL 324", "CYMEL 325", "CYMEL 327", "CYMEL 350", "CYMEL 385", "CYMEL 1156", "CYMEL 1158", "CYMEL 1116", "CYMEL 1130" (manufactured by Allnex Japan, supra) "," U-VAN 120"," U-VAN 20HS "," U-VAN 20SE60"," U-VAN 2021"," U-VAN 2028"," U-VAN 28-60 "(manufactured by Mitsui chemical Co, supra), and the like.

The melamine resin (C) may be used alone or in combination of two or more.

The content of the melamine resin (C) in the high-solid-content coating composition of the present invention is preferably in the range of 5 to 50 parts by mass, more preferably in the range of 10 to 45 parts by mass, and even more preferably in the range of 15 to 40 parts by mass, based on 100 parts by mass of the resin solid content of the high-solid-content coating composition, from the viewpoints of the recoatability, curability, and finished appearance of the formed coating film.

Catalyst (D)

As the catalyst (D), conventionally known catalysts may be used, and examples thereof include: sulfonic acid catalysts (D-1) such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid and dinonylnaphthalenesulfonic acid; phosphoric acid catalysts (D-2) such as alkyl phosphates (e.g., monobutyl phosphate, dibutyl phosphate, mono (2-ethylhexyl) phosphate, and di (2-ethylhexyl) phosphate); organometallic compound catalysts such as tin octoate, dibutyltin diacetate, dibutyltin di (2-ethylhexanoate), dibutyltin dilaurate, dioctyltin diacetate, dibutyltin di (2-ethylhexanoate), dibutyltin oxide, dibutyltin sulfide, dioctyltin oxide, dibutyltin fatty acid salts, lead 2-ethylhexanoate, zinc octoate, zinc naphthenate, zinc fatty acid, bismuth octoate, bismuth 2-ethylhexanoate, bismuth oleate, bismuth neodecanoate, bismuth versatate, bismuth naphthenate, cobalt naphthenate, calcium octoate, copper naphthenate, and tetra (2-ethylhexyl) titanate; amine catalysts such as tertiary amine, etc., among which at least one selected from the group consisting of sulfonic acid catalysts (D-1) and phosphoric acid catalysts (D-2) is preferably contained, and further preferably the sulfonic acid catalyst (D-1) is contained, from the viewpoints of recoatability, curability, finished appearance, etc., of the formed coating film.

The content of the catalyst (D) in the high-solid-content coating composition of the present invention is preferably in the range of 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, and even more preferably 0.1 to 3 parts by mass, based on 100 parts by mass of the resin solid content of the high-solid-content coating composition, from the viewpoints of the recoatability, curability, and finished appearance of the formed coating film.

High solids coating composition

From the viewpoint of VOC reduction, the solid content at the time of coating of the high solid content coating composition of the present invention is preferably 52% or more, more preferably 54% or more.

In the present specification, the term "solid component" means a nonvolatile component such as a resin, a curing agent, and a pigment contained in the coating composition, which remains after the coating composition is dried at 110 ℃ for 1 hour. For this reason, for example, the total solid content of the coating composition is calculated by measuring the coating composition in a heat-resistant container such as an aluminum foil cup, spreading the coating composition on the bottom surface of the container, drying the container at 110 ℃ for 1 hour, weighing the mass of the components in the coating composition remaining after drying, and determining the ratio of the mass of the components remaining after drying to the total mass of the coating composition before drying.

The reason why the coating composition of the present invention can form a coating film excellent in recoatability, curability and finished appearance is not clear, but it is presumed that the hydroxyl group-containing acrylic resin (a) has a weight average molecular weight in the range of 3000 to 10000, and therefore the viscosity at the time of heat flow is lowered, and a coating film excellent in finished appearance can be formed irrespective of the high solid content, and the hydroxyl group-containing acrylic resin (a) has a hydroxyl value in the range of 130 to 220mgKOH/g, and further contains the catalyst (D), and therefore the reactivity with the melamine resin (C) is high, and the curability becomes good. Further, it is presumed that castor oil (B) having a secondary hydroxyl group and a low polar alkyl chain derived from a fatty acid is contained, and therefore the hydroxyl group concentration of the surface layer is increased and the recoating property is improved.

The high-solid-content coating composition of the present invention preferably further contains a blocked polyisocyanate compound (E) from the viewpoint of forming a coating film excellent in recoatability, curability and finished appearance.

Blocked polyisocyanate compound (E)

The blocked polyisocyanate compound (E) is a polyisocyanate compound obtained by blocking an isocyanate group with a blocking agent.

The polyisocyanate compound is a compound having at least two or more isocyanate groups in one molecule. Examples of the polyisocyanate compound include: aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic aliphatic polyisocyanates, aromatic polyisocyanates, derivatives of these polyisocyanates, and the like. They may be used alone or in combination of two or more.

Examples of the aliphatic polyisocyanate include: aliphatic diisocyanates 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-or 2, 4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and methyl 2, 6-diisocyanato caproate (commonly known as lysine diisocyanate); aliphatic triisocyanates such as 2-isocyanatoethyl 2, 6-diisocyanatohexanoate, 1, 6-diisocyanato-3-isocyanatomethylhexane, 1,4, 8-triisocyanatooctane, 1,6, 11-triisocyanato undecane, 1, 8-diisocyanato-4-isocyanatomethyloctane, 1,3, 6-triisocyanatohexane, and 2,5, 7-trimethyl-1, 8-diisocyanato-5-isocyanatomethyloctane.

Examples of the alicyclic polyisocyanate include: alicyclic diisocyanates such as 1, 3-cyclopentene diisocyanate, 1, 4-cyclohexane diisocyanate, 1, 3-cyclohexane diisocyanate, 3-isocyanatomethyl-3, 5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), methyl-2, 4-cyclohexane diisocyanate, methyl-2, 6-cyclohexane diisocyanate, 1, 3-or 1, 4-bis (isocyanatomethyl) cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, and methylenebis (1, 4-cyclohexanediyl) diisocyanate (common name: hydrogenated MDI); and (2.2.1) such as 1,3, 5-triisocyanatocyclohexane, 1,3, 5-trimethylisocyanatocyclohexane, 2- (3-isocyanatopropyl) -2, 5-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 2- (3-isocyanatopropyl) -2, 6-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 3- (3-isocyanatopropyl) -2, 5-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, and 6- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane.

Examples of the aromatic aliphatic polyisocyanate include: aromatic aliphatic diisocyanates such as methylenebis (1, 4-phenylene) diisocyanate (commonly known as MDI), 1, 3-or 1, 4-xylylene diisocyanate or a mixture thereof, ω' -diisocyanato-1, 4-diethylbenzene, and 1, 3-or 1, 4-bis (1-isocyanato-1-methylethyl) benzene (commonly known as tetramethylxylylene diisocyanate) or a mixture thereof; aromatic aliphatic triisocyanates such as 1,3, 5-triisocyanatotoluene and the like.

Examples of the aromatic polyisocyanate include: aromatic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4' -diphenyl diisocyanate, 1, 5-naphthalene diisocyanate, 2, 4-or 2, 6-tolylene diisocyanate or a mixture thereof, 4' -toluidine diisocyanate, and 4,4' -diphenyl ether diisocyanate; aromatic triisocyanates such as triphenylmethane-4, 4' -triisocyanate, 1,3, 5-triisocyanatobenzene and 2,4, 6-triisocyanatotoluene; aromatic tetraisocyanates such as 4,4' -diphenylmethane-2, 2', 5' -tetraisocyanate, and the like.

Examples of the derivative of the polyisocyanate include: dimers, trimers, biurets, allophanates, uretdiones, uretonimines, isocyanurates, oxadiazinetriones, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like of the polyisocyanate compounds.

Examples of the blocking agent include: phenol systems such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxybiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methylparaben; lactam systems such as epsilon-caprolactam, delta-valerolactam, gamma-butyrolactam and beta-propiolactam; aliphatic alcohols such as methanol, ethanol, propanol, butanol, pentanol, and lauryl alcohol; ether systems such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; alcohols such as benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate; oxime systems such as formamide oxime, acetamide oxime, acetone oxime, methyl ethyl ketoxime, diacetyl monoxime, benzophenone oxime, and cyclohexane oxime; active methylene systems such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; thiol systems such as butyl thiol, t-butyl thiol, hexyl thiol, t-dodecyl thiol, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, and ethylthiophenol; amide systems such as acetanilide, acetotoluidine, acrylamide, methacrylamide, acetamide, stearamide, and benzamide; imide systems such as succinimide and phthalimide and maleimide; amine systems such as diphenylamine, phenylnaphthylamine, dimethylaniline, N-phenyldimethylaniline, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylaniline; imidazole systems such as imidazole and 2-ethylimidazole; urea systems such as urea, thiourea, ethylene urea, ethylene thiourea and diphenylurea; urethane systems such as phenyl N-phenylcarbamate; imine systems such as ethyleneimine (ethyleneimine) and propyleneimine (propyleneimine); sulfite systems such as sodium bisulfite and potassium bisulfite; azole compounds, and the like. The azole compound includes: pyrazole or pyrazole derivatives such as pyrazole, 3, 5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3, 5-dimethylpyrazole, 4-nitro-3, 5-dimethylpyrazole, 4-bromo-3, 5-dimethylpyrazole, 3-methyl-5-phenylpyrazole; imidazole or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, and 2-phenylimidazole; imidazoline derivatives such as 2-methylimidazoline and 2-phenylimidazoline.

When the high-solid content coating composition of the present invention contains the blocked polyisocyanate compound (E), the content thereof is preferably in the range of 1 to 30 parts by mass, more preferably in the range of 3 to 25 parts by mass, and even more preferably in the range of 5 to 20 parts by mass, based on 100 parts by mass of the resin solid content of the high-solid content coating composition, from the viewpoint of forming a coating film excellent in recoatability, curability and finished appearance.

Other ingredients

The high-solid-content coating composition of the present invention may contain, if necessary, a resin other than the above, a crosslinking agent other than the above, a pigment, an organic solvent, a dispersant, an anti-settling agent, a defoaming agent, a thickener, an ultraviolet absorber, a light stabilizer, a surface conditioner, and the like.

Examples of the resin other than the above include: an acrylic resin containing no hydroxyl group, a polyester resin containing hydroxyl group optionally, a polyurethane resin containing hydroxyl group optionally, a polyether resin containing hydroxyl group optionally, a polycarbonate resin containing hydroxyl group optionally, an epoxy resin containing hydroxyl group optionally, etc., wherein the polyester resin (F) containing hydroxyl group is preferably used.

The hydroxyl group-containing polyester resin (F) can be generally obtained by subjecting a polyhydric alcohol and a polyhydric acid to an esterification reaction in an excess of hydroxyl groups by a method known per se. The polyhydric alcohol is a compound having two or more hydroxyl groups in one molecule, and the polybasic acid is a compound having two or more carboxyl groups in one molecule.

Examples of the polyol include: diols such as ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1, 4-butanediol, 1, 3-butanediol, 2, 3-butanediol, 1, 2-butanediol, 3-methyl-1, 2-butanediol, 1, 2-pentanediol, 1, 5-pentanediol, 1, 4-pentanediol, 2, 3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4, 3-pentanediol, 3-methyl-4, 5-pentanediol, 2, 4-trimethyl-1, 3-pentanediol, 1, 6-hexanediol, 1, 5-hexanediol, 1, 4-hexanediol, 2, 5-hexanediol, neopentyl glycol hydroxypivalate; polylactone diols obtained by adding lactones such as epsilon-caprolactone to these diols; ester diols such as bis (hydroxyethyl) terephthalate; polyether diols such as alkylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like; monoepoxide compounds such as alpha-olefin epoxides (e.g., propylene oxide and butylene oxide), and Cardura E10 (trade name, manufactured by Shell chemical Co., ltd., glycidyl ester of a highly branched saturated fatty acid) are synthesized; tri-or higher alcohols such as glycerin, trimethylolpropane, trimethylolethane, diglycerin, triglycerin, 1,2, 6-hexanetriol, pentaerythritol, dipentaerythritol, sorbitol, mannitol, etc.; polylactone polyols obtained by adding lactones such as epsilon-caprolactone to these ternary or higher alcohols; alicyclic polyols such as 1, 4-cyclohexanedimethanol, tricyclodecanedimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, hydrogenated bisphenol A and hydrogenated bisphenol F; a cyclic polyol compound having a urethane structure such as tris (hydroxyalkyl) isocyanurate, an epsilon-caprolactone modified form of the tris (hydroxyalkyl) isocyanurate, and the like; etc.

The above polyols may be used singly or in combination of two or more.

Examples of the polybasic acid include: aromatic polybasic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, 4 '-biphenyl dicarboxylic acid, and diphenylmethane-4, 4' -dicarboxylic acid, and anhydrides thereof; alicyclic dicarboxylic acids such as hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrophthalic acid and tetrahydrophthalic acid, and anhydrides thereof; aliphatic polybasic acids such as adipic acid, sebacic acid, suberic acid, succinic acid, glutaric acid, maleic acid, chloromaleic acid, fumaric acid, dodecanedioic acid, pimelic acid, azelaic acid, itaconic acid, citraconic acid, and dimer acid, and anhydrides thereof; lower alkyl esters such as methyl and ethyl esters of these dicarboxylic acids; trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, pyromellitic acid, methylcyclohexenetriac acid, tetrachlorohexenepolyacid, and other polyacids having three or more members such as anhydride thereof.

The above polybasic acids may be used singly or in combination of two or more.

The hydroxyl value of the hydroxyl group-containing polyester resin (F) is preferably in the range of 80 to 220mgKOH/g, particularly preferably in the range of 100 to 210mgKOH/g, from the viewpoint of the finished appearance of the formed coating film, etc.

The acid value of the hydroxyl group-containing polyester resin (F) is preferably 10 to 50mgKOH/g, particularly preferably 20 to 40mgKOH/g, from the viewpoint of the appearance of the finished product of the formed coating film, etc.

The hydroxyl group-containing polyester resin (F) preferably has a number average molecular weight of 500 to 6000, particularly preferably 750 to 5000, from the viewpoint of the appearance of the finished product of the formed coating film.

In the case where the high-solid content coating composition of the present invention contains the hydroxyl group-containing polyester resin (F), the content thereof is preferably in the range of 1 to 30 parts by mass, more preferably 2 to 20 parts by mass, still more preferably 3 to 15 parts by mass, based on 100 parts by mass of the resin solid content of the high-solid content coating composition, from the viewpoints of the recoatability, curability, and finished appearance of the formed coating film.

Examples of the pigment include: coloring pigments, luster pigments, extender pigments, and the like. The pigment may be used alone or in combination of two or more.

Examples of the coloring pigment include: titanium dioxide, zinc white, carbon black, cadmium red, molybdenum red, chrome yellow, chromium oxide, prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, reduced (threne) pigments, perylene pigments, and the like.

Examples of the brightening pigment include: aluminum pigments, mica powder covered with titanium oxide, and the like.

As extender pigments, there may be mentioned: talc, clay, kaolin, heavy earth, barium sulfate, barium carbonate, calcium carbonate, alumina white, and the like.

Each of the above pigments may be used alone or in combination of two or more.

When the high-solid-content coating composition of the present invention is used as a clear coating, the amount of pigment blended is preferably an amount that does not inhibit the transparency of the resulting coating film, for example, in the range of usually 0.1 to 20% by mass, particularly preferably 0.3 to 10% by mass, and even more particularly preferably 0.5 to 5% by mass, relative to the total amount of solid components in the high-solid-content coating composition.

In the case where the high-solid-content coating composition of the present invention is used as a colored coating material, the blending amount of the pigment is usually preferably in the range of 1 to 200% by mass, particularly preferably in the range of 2 to 100% by mass, and further particularly preferably in the range of 5 to 50% by mass, relative to the total amount of solid components in the high-solid-content coating composition.

Examples of the organic solvent include: aromatic solvents such as toluene, xylene, and "Swazol 1000" (trade name, high boiling point petroleum solvent, manufactured by COSMO Petroleum Co.); ester solvents such as ethyl acetate, butyl acetate, propyl propionate, butyl propionate, 1-methoxy-2-propyl acetate, 2-ethoxyethyl propionate, ethyl 3-ethoxypropionate, 3-methoxybutyl acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, and propylene glycol monomethyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; alcohol solvents such as isopropyl alcohol, n-butanol, isobutyl alcohol, and 2-ethylhexanol. They may be used singly or in combination of two or more kinds.

As the thickener, conventionally known thickeners can be used, and examples thereof include: clay minerals (for example, metal silicate, montmorillonite), acrylic acid (for example, a substance having a structure comprising a polymer or oligomer of acrylate or methacrylate in the molecule), polyolefin (for example, polyethylene, polypropylene, etc.), amide (higher fatty acid amide, polyamide, oligomer, etc.), polycarboxylic acid (a derivative having at least two or more carboxyl groups in the molecule), cellulose (various derivatives including nitrocellulose, acetyl cellulose, cellulose ether, etc.), urethane (a polymer or oligomer having a urethane structure in the molecule), urea (a polymer or oligomer having a urea structure in the molecule), urethane urea (a polymer or oligomer having a urethane structure and a urea structure in the molecule), and the like.

As the ultraviolet absorber, conventionally known ultraviolet absorbers can be used, and examples thereof include: ultraviolet absorbers such as benzotriazole-based absorbers, triazine-based absorbers, salicylic acid derivative-based absorbers, and benzophenone-based absorbers. They may be used singly or in combination of two or more.

When the high-solid-content coating composition of the present invention contains an ultraviolet absorber, the amount of the ultraviolet absorber blended is usually preferably in the range of 0.1 to 10% by mass, particularly preferably 0.2 to 5% by mass, and further particularly preferably 0.3 to 3% by mass, relative to the total amount of solid components in the high-solid-content coating composition.

As the light stabilizer, conventionally known light stabilizers can be used, and examples thereof include hindered amine-based light stabilizers.

As the hindered amine light stabilizer, from the viewpoint of pot life, a hindered amine light stabilizer having low basicity can be preferably used. Examples of such hindered amine light stabilizers include: examples of the acylated hindered amide and aminoether-based hindered amide include "HOSTAVIN 3058" (trade name, manufactured by Clariant corporation) and "TINUVIN 123" (trade name, manufactured by BASF corporation).

The high-solid-content coating composition of the present invention may be either a one-pack type coating or a multi-pack type coating, but is preferably a one-pack type coating from the viewpoints of no mixing step of the coating, excellent productivity, and simplification of maintenance of the coating machine.

The method for coating the high-solid-content coating composition of the present invention is not particularly limited, and examples thereof include: coating methods such as air spray coating, airless spray coating, rotary atomizing coating, curtain coating, and the like can form wet coating films by these methods. In these coating methods, electrostatic application may be performed as needed. Among them, air spray coating or rotary atomizing coating is particularly preferable. The coating amount of the present coating material is usually set to an amount of preferably 10 to 60 μm, particularly preferably 25 to 50 μm in terms of the cured film thickness.

In the case of performing air-spray coating, airless spray coating, and rotary atomizing coating, it is preferable that the viscosity of the present paint is suitably adjusted to a viscosity range suitable for the coating, and in general, a Ford cup No.4 viscometer, a solvent such as an organic solvent and a thickener are used so as to have a viscosity range of 20 to 60 seconds, particularly 25 to 50 seconds, at 20 ℃.

The wet coating film obtained by applying the present paint to an object may be cured by heating by a known heating means, and for example, a drying oven such as a hot air oven, an electric oven, or an infrared induction heating oven may be used. The heating temperature is preferably not particularly limited, and is, for example, in the range of 120 to 160 ℃, preferably 130 to 150 ℃. The heating time is preferably not particularly limited, and is, for example, in the range of 10 to 60 minutes, preferably 15 to 30 minutes.

The high-solid-content coating composition of the present invention can form a coating film excellent in recoatability, curability and finished appearance, and therefore can be preferably used as an overcoating top clear coat coating. The coating can be used particularly preferably as an automotive coating.

Method for forming multilayer coating film

As a method for forming a multilayer coating film by applying the top clear coat layer coating material to the present coating material, for example, the following method can be preferably used.

A multilayer coating film forming method comprising: step (1): a step of forming an intercoat coating film by applying an intercoat coating composition to a substrate; step (2): a step of forming a base coating film by applying a base coating composition to the base coating film formed in the step (1); step (3): a step of forming a clear coating film by applying the high-solid-content coating composition of the present invention to the base coating film formed in the step (2); and (4) a step of: and (3) a step of heating and curing the intercoat coating film, the base coating film and the clear coating film formed in the steps (1) to (3) together.

The coating material is not particularly limited, and examples thereof include: an outer panel of a car body of a car, a truck, a motorcycle, a bus, or the like; automobile parts; and an outer panel of home appliances such as mobile phones and audio equipment. Among them, the outer panel portion of the automobile body and the automobile parts are preferable.

The material of the coating material is not particularly limited. Examples include: metallic materials such as iron, aluminum, brass, copper, tin-plated iron (tin plate), stainless steel, galvanized steel, and galvanized alloy (Zn-Al, zn-Ni, zn-Fe, etc.) steel; resins such as polyethylene resins, polypropylene resins, acrylonitrile-butadiene-styrene (ABS) resins, polyamide resins, acrylic resins, vinylidene chloride resins, polycarbonate resins, polyurethane resins, and epoxy resins; plastic materials such as various FRP (fiber reinforced composites: fiber Reinforced Polymer); inorganic materials such as glass, cement, concrete, etc.; wood; and fibrous materials such as paper and cloth. Among them, metallic materials and plastic materials are preferable.

The object surface to be coated to be used for the multilayer coating film may be a surface treated by a surface treatment such as a phosphate treatment, a chromate treatment, or a composite oxide treatment on a metal surface of a metal substrate such as an automobile body outer panel, an automobile part, a home electric appliance, or a steel sheet constituting the same.

The object may be further provided with a coating film. For example, a substrate may be subjected to a surface treatment as needed to form a primer coating film thereon. For example, in the case where the object to be coated is an automobile body, the primer coating film may be formed using a primer coating composition known per se which is generally used for coating an automobile body.

The primer coating composition is usually applied for the purpose of imparting corrosion resistance to a coating object.

As the primer coating composition for forming the above-mentioned primer coating film, for example, an electrodeposition coating material can be used, and a cationic electrodeposition coating material is preferably used.

In addition, the primer coating film is preferably a cured coating film from the viewpoint of the finished appearance of the formed multilayer coating film.

As the intercoat composition, a thermosetting intercoat composition known for coating an automobile body or the like can be used. As the intercoat coating composition, for example, a thermosetting coating material containing a base resin having a crosslinkable functional group, a crosslinking agent, a coloring pigment, and an extender pigment can be preferably used.

The above-mentioned intercoat coating composition is usually applied for the purpose of imparting smoothness, chipping resistance and adhesion between coating films to an object to be coated.

Examples of the crosslinkable functional group of the base resin include: carboxyl, hydroxyl, and epoxy groups.

Examples of the type of the matrix resin include: acrylic resins, polyester resins, alkyd resins, urethane resins, and the like.

Examples of the crosslinking agent include: melamine resins, polyisocyanate compounds, blocked polyisocyanate compounds, and the like.

As the intercoat coating composition, any of an aqueous coating composition and an organic solvent type coating composition can be used.

The coating amount of the intercoat coating composition is preferably an amount such that the cured film thickness is 5 to 60. Mu.m, more preferably an amount of 8 to 50. Mu.m, and still more preferably an amount of 10 to 40. Mu.m.

As the primer coating composition, a thermosetting primer coating composition known for coating automobile bodies and the like can be used. As the primer coating composition, for example, a thermosetting coating composition containing a base resin having a crosslinkable functional group, a crosslinking agent, a coloring pigment, a brightening pigment, and an extender pigment can be preferably used.

The base coat paint composition is usually applied for the purpose of imparting excellent design properties (for example, color, metallic feel, gloss, etc.) to a coating object.

As the base coat coating composition, any of an aqueous coating composition and an organic solvent type coating composition can be used.

The coating amount of the base coat coating composition is preferably an amount such that the cured film thickness is 5 to 40. Mu.m, more preferably an amount of 6 to 35. Mu.m, and still more preferably an amount of 7 to 30. Mu.m.

The heating may be performed by a known means, and for example, a drying oven such as a hot air oven, an electric oven, or an infrared induction heating oven may be used. The heating temperature is preferably 60 to 180 ℃, more preferably 70 to 170 ℃, still more preferably 80 to 160 ℃. The heating time is not particularly limited, and is preferably in the range of 10 to 40 minutes, more preferably in the range of 20 to 40 minutes.

Examples

The present invention will be described in more detail below with reference to production examples, examples and comparative examples. However, the present invention is not limited to these examples. In each example, "parts" and "%" are based on mass unless otherwise specified. Further, the film thickness of the coating film is based on the cured coating film.

[1] Manufacture of coated articles

A cationic electrodeposition coating material "Elecron GT-10" (trade name: coating material obtained by using a blocked polyisocyanate compound as a curing agent in an epoxy resin polyamine-based cationic resin, manufactured by Kaposi coating Co., ltd.) was applied by electrodeposition coating to a steel sheet (JISG 3141, size 400 mm. Times.300 mm. Times.0.8 mm) subjected to degreasing and zinc phosphate treatment so that the film thickness was 20 μm based on the cured coating film, and the resultant was heated at 170℃for 20 minutes to crosslink and cure the blocked polyisocyanate compound, thereby forming an electrodeposition coating film, whereby a coating material was produced.

[2] Preparation of the paint

Production of hydroxyl group-containing acrylic resin (A)

Production example 1

27 parts of Swazol 1000 (trade name, product name, aromatic organic solvent manufactured by COSMO Petroleum Co., ltd.) and 5 parts of propylene glycol monomethyl ether acetate were charged into a reaction vessel equipped with a thermometer, a thermostat, a stirring device, a reflux condenser, a nitrogen inlet pipe, and a dropping device. A monomer mixture composed of 20 parts of styrene, 32.5 parts of 2-hydroxypropyl acrylate, 46.2 parts of isobutyl methacrylate, 1.3 parts of acrylic acid and 3.2 parts of di-t-amyl peroxide (polymerization initiator) was added dropwise thereto at a uniform rate over 4 hours while stirring the charge liquid at 150℃while blowing nitrogen gas into the reaction vessel. Then, the mixture was aged at 150℃for 1 hour, cooled, and diluted with 21 parts of isobutyl acetate to obtain a secondary hydroxyl group-containing acrylic resin (A' -1) solution having a solid content of 65% by mass. The secondary hydroxyl group-containing acrylic resin (A' -1) thus obtained had an acid value of 10.1mgKOH/g, a hydroxyl value of 140mgKOH/g, a weight-average molecular weight of 8000 and a glass transition temperature of 39 ℃.

Production examples 2 to 4

In production example 1, acrylic resins (a '-2) to (a' -4) containing secondary hydroxyl groups were obtained in the same manner as in production example 1 except that the blending composition was set as shown in table 1. The acid value, hydroxyl value, weight average molecular weight and glass transition temperature of each hydroxyl group-containing acrylic resin are shown in Table 1.

TABLE 1

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Production of hydroxyl group-containing acrylic resin (G)

Production example 5

27 parts of Swazol 1000 (trade name, product name, aromatic organic solvent manufactured by COSMO Petroleum Co., ltd.) and 5 parts of propylene glycol monomethyl ether acetate were charged into a reaction vessel equipped with a thermometer, a thermostat, a stirring device, a reflux condenser, a nitrogen inlet pipe, and a dropping device. A monomer mixture composed of 20 parts of styrene, 41 parts of 2-hydroxypropyl acrylate, 22.7 parts of isobutyl methacrylate, 15 parts of methyl methacrylate, 1.3 parts of acrylic acid and 2 parts of di-t-amyl peroxide (polymerization initiator) was added dropwise thereto at a uniform rate over 4 hours while stirring the charge liquid at 150℃while blowing nitrogen gas into the reaction vessel. Then, the mixture was aged at 150℃for 1 hour, cooled, and diluted with 21 parts of isobutyl acetate to obtain a secondary hydroxyl group-containing acrylic resin (G' -1) solution having a solid content of 65% by mass. The secondary hydroxyl group-containing acrylic resin (G' -1) thus obtained had an acid value of 10.1mgKOH/G, a hydroxyl value of 177mgKOH/G, a weight average molecular weight of 11000 and a glass transition temperature of 39 ℃.

Production examples 6 to 8

In production example 5, acrylic resins (G '-2) to (G' -4) containing secondary hydroxyl groups were obtained in the same manner as in production example 5 except that the blending composition was set as shown in table 2. The acid value, hydroxyl value, weight average molecular weight and glass transition temperature of each hydroxyl group-containing acrylic resin are shown in Table 2.

TABLE 2

Production of hydroxyl group-containing polyester resin (F)

Production example 9

A reactor equipped with a stirrer, a reflux condenser, a water separator and a thermometer was charged with 79.1 parts of hexahydrophthalic anhydride, 5 parts of adipic acid, 52.1 parts of neopentyl glycol and 25 parts of trimethylolpropane, and the mixture was reacted at 230℃for 6 hours, followed by dilution with butyl acetate to obtain a hydroxyl group-containing polyester resin (F-1) solution having a solid content concentration of 80%. The hydroxyl group-containing polyester resin (F-1) thus obtained had an acid value of 25mgKOH/g, a hydroxyl value of 181mgKOH/g and a number average molecular weight of 1952.

Production of high solids coating compositions

Example 1

84.6 parts (solid content 55 parts) of the secondary hydroxyl group-containing acrylic resin (A' -1) solution obtained in production example 1, 10 parts (solid content 10 parts) of "URIC H-30" (trade name, manufactured by Irvine oil company, solid content 100%, hydroxyl value 155 to 165 mgKOH/g), 41.7 parts (solid content 25 parts) of "U-VAN 20SE60" (trade name, manufactured by Mitsui chemical company, solid content 60%), 10 parts (solid content 10 parts) of "Desmodur BL3575" (trade name, manufactured by Bayer Material Science company, pyrazole-terminated polyisocyanate, solid content 100%), 2 parts (solid content 0.5 parts) of "NACURE 5528" (trade name, manufactured by KING INSTRIES company, amine salt of dodecylbenzenesulfonic acid, active ingredient 25%), 0.4 parts (solid content 0.2 parts) of "BYK-300" (trade name, manufactured by BYK chemie company, surface conditioner, active ingredient 52%) and butyl acetate were uniformly mixed, and then adjusted to obtain a coating composition having a solid content of 55% and a coating composition of high solids content of DUDUU.1.

Examples 2 to 12 and comparative examples 1 to 9

Each of the high-solid-content coating compositions No.2 to 21 was obtained in the same manner as in the high-solid-content coating composition No.1 except that the blending composition and the solid content at the time of coating were set as shown in tables 3 to 6 below. The blending compositions shown in tables 3 to 6 were based on the mass of the solid content of each component.

Test plate production (production of test plate for evaluation of curability)

The test plate of example 1 was produced by coating a polypropylene plate with a high-solid-content coating composition No.1 using a rotary atomizing type electrostatic coater so that the cured coating film had a film thickness of 35. Mu.m, standing at room temperature for 7 minutes, heating at 140℃for 30 minutes in a hot air circulation type drying oven, and then peeling off the obtained coating film.

(production of test plate for evaluation of yield)

The object produced in the above-mentioned [1] was electrostatically coated with "ZU-10" (trade name, acrylic resin/melamine resin type organic solvent type intercoat coating material, manufactured by Guanyi coating Co., ltd.) by using a rotary atomizing type electrostatic coater so that the cured film thickness was 15. Mu.m, and left to stand for 5 minutes to form an uncured intercoat coating film.

Next, "Soflex 420" (trade name, manufactured by the western coating company, solvent-based top coat paint) was electrostatically coated onto the uncured intermediate coating film using a rotary atomizing type electrostatic coater so that the dry film thickness became 12 μm, and left for 3 minutes, to form an uncured intermediate coating film.

Next, a clear coat film was formed by electrostatically coating the high-solid-content coating composition No.1 onto the uncured base coat film using a rotary atomizing type electrostatic coater so that the dry film thickness became 35 μm, and left for 7 minutes. Then, the intermediate coating film, the base coating film and the clear coating film were heated and cured by heating at 140℃for 30 minutes, thereby producing a test board of example 1.

(production of test plate for evaluation of recoatability)

Next, a clear coat film was formed by electrostatically coating the high-solid-content coating composition No.1 onto the uncured base coat film using a rotary atomizing type electrostatic coater so that the dry film thickness became 35 μm, and left for 7 minutes. Then, the intermediate coating film, the base coating film and the clear coating film were cured by heating at 160℃for 60 minutes, and left at room temperature for 24 hours.

Next, "ZU-10" (trade name, manufactured by guan coating company, acrylic resin/melamine resin type organic solvent type intercoat coating material) was electrostatically coated on the heat-cured clear coat film using a rotary atomizing type electrostatic coater so that the cured film thickness became 15 μm, and left for 5 minutes, to form an uncured intercoat film.

Next, a clear coat film was formed by electrostatically coating the high-solid-content coating composition No.1 onto the uncured base coat film using a rotary atomizing type electrostatic coater so that the dry film thickness became 35 μm, and left for 7 minutes. Then, the intermediate coating film, the base coating film and the clear coating film were heated and cured by heating at 130℃for 20 minutes, thereby producing a test board of example 1.

Test panels of examples 2 to 12 and comparative examples 1 to 9 were produced in the same manner as the production of the test panel of high-solid-content coating composition No.1 except that the high-solid-content coating composition No.1 was used as any one of the high-solid-content coating compositions No.2 to 21 in the production of the test panel of the high-solid-content coating composition No. 1.

Each test plate obtained in the above was evaluated by the following test method. The evaluation results are shown in tables 3 to 6 together with the paint compositions.

(test method)

Recoating adhesion: 100 checkerboard patterns of 2mm by 2mm were formed on the coated surface according to JIS K5600-5-6 (1990), an adhesive tape was applied to the surface, and after rapid peeling, the number of checkerboard coating films remaining on the coated surface was evaluated. A and B are considered to be acceptable.

A: number of residues/total number = 100/100, no edge defect.

B: residual number/total number = 100/100, with edge defects.

C: the number of residues/the number of whole bodies=99 or less.

Curability (crosslink density): test pieces having a width of 5mm and a length of 10mm were prepared, and dynamic viscoelasticity was measured (storage modulus (E '), loss modulus (E') and loss tangent (tan. Delta)) under the following conditions, and the crosslink density was measured according to the following formula 1. The smaller the crosslink density, the higher the curability. And the value below 700 is qualified.

Device: dynamic viscoelasticity measuring apparatus RSA3 (manufactured by TA Instruments Co.).

Measurement mode: non-resonant forced vibration method.

Temperature increase rate: 3.0 ℃/min.

Measurement interval: 12/min.

Frequency: 1.0Hz.

Temperature range: 30-180 ℃.

Formula 1: crosslink density = E' min/3RT.

(crosslink Density: mol/cm) ³ E' min: pa, R (gas constant): j/mol·k, T (absolute temperature of peak top of loss tangent (tan δ): k)

Appearance of the finished product: the finished appearance was evaluated based on Long Wave (LW) values and Short Wave (SW) values measured by Wave Scan (trade name, BYK Gardner corporation).

LW value: the smaller the LW value, which is an index of smoothness, the higher the smoothness of the coating surface. And the product is qualified by 15 or less.

SW value: the smaller the SW value is, the higher the distinctness of image of the coated surface is. And 25 or less is qualified.

TABLE 3

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TABLE 4

TABLE 5

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TABLE 6

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(1) "URIC H-52": trade name, solid content 100%, hydroxyl value 195-205 mgKOH/g.

(x2) "URIC H-57": trade name, solid content 100%, hydroxyl value 85-115 mgKOH/g.

(x3) "URIC H-1824": trade name, solid content 100%, hydroxyl value 55-77 mgKOH/g.

(x4) "URIC H-62": trade name, solid content 100%, hydroxyl value 245-275 mgKOH/g.

(x5) linseed oil: summit-Oilmill Co., ltd., solid content 100%.

(x6) "NACURE 4167": trade name, triethylamine salt of alkylphosphoric acid, manufactured by KING INDUSTRIES, 25% of active ingredient.

The embodiments and examples of the present invention have been specifically described above, but the present invention is not limited to the above-described embodiments and may be variously modified based on the technical ideas of the present invention.

For example, the configurations, methods, steps, shapes, materials, numerical values, and the like listed in the embodiments and examples are not always examples, and configurations, methods, steps, shapes, materials, numerical values, and the like different from those described above may be used as needed.

The constitution, method, process, shape, material, numerical value, and the like of the above-described embodiments can be combined with each other without departing from the gist of the present invention.

Claims

1. A high solids coating composition comprising:

(A) a hydroxyl group-containing acrylic resin having a weight average molecular weight of 3000 to 10000 and a hydroxyl value of 130 to 220mgKOH/g, (B) castor oil, (C) a melamine resin, and (D) a catalyst, and the solid content at the time of coating is 50 mass% or more.

2. The high-solids coating composition according to claim 1, wherein,

the hydroxyl group-containing acrylic resin (a) contains a secondary hydroxyl group-containing acrylic resin (a').

3. The high-solid-content coating composition according to claim 1 or 2, wherein,

the hydroxyl value of the castor oil (B) is in the range of 80 to 230 mgKOH/g.

4. The high-solids coating composition according to claim 1 to 3,

the catalyst (D) comprises a sulfonic acid catalyst (D-1).

5. The high solids coating composition according to claim 1 to 4, further comprising a blocked polyisocyanate compound (E).

6. A multilayer coating film forming method comprising:

step (1): a step of forming an intercoat coating film by applying an intercoat coating composition to a substrate;

step (2): a step of forming a base coating film by applying a base coating composition to the base coating film formed in the step (1);

step (3): a step of forming a clear coat film by applying the high-solid-content coating composition according to any one of claims 1 to 5 to the base coat film formed in the step (2); and

step (4): and (3) a step of heating and curing the intercoat coating film, the base coating film and the clear coating film formed in the steps (1) to (3) together.