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

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 multilayer coating film forming method

Technical Field

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

Background Art

In recent years, from the viewpoint of protecting the global environment, there has been a demand for reducing volatile organic compounds (VOC) emitted from paints, and the replacement of solvent-based paints with water-based paints has been rapidly advancing in various fields.

In the past, a large amount of solvent-based paints were used in automobile painting, and the reduction of VOCs emitted from these paints has become a top priority. However, with regard to the various paints used in the base coat, mid coat, and top coat painting processes of automobiles, the replacement of organic solvent-based paints with water-based paints is being promoted, and painting using water-based paints has become the mainstream.

However, in the top-coat clear coating, particularly high coating film properties (recoat adhesion, curability, etc.) and a level of finished product appearance are required, and therefore solvent-based clear coatings are also mainly applied at present.

One method of reducing VOC that is not related to the water-based nature of the clear coating material is to increase the solid content of the coating material (increase the solid content concentration).

For example, Patent Document 1 discloses a high-solid coating composition comprising a reaction product of a specific carboxyl group-containing compound and an epoxy group-containing compound, a polyisocyanate compound and a melamine resin, and a specific hydroxyl group-containing resin.

However, the coating composition has good finished product appearance and curability, but sometimes has insufficient recoatability.

In addition, Patent Document 2 discloses a thermosetting high-solid content coating composition, characterized in that it contains: (A) a carboxyl group-containing compound; (B) a polyepoxide; and (C) a copolymer obtained by polymerizing a monomer component consisting of (a) 30 to 50 wt % of vinyltrimethoxysilane and/or vinyltriethoxysilane, (b) 5 to 15 wt % of N-hydroxymethyl (meth) acrylamide alkyl ether, and (c) 35 to 65 wt % of other polymerizable unsaturated monomers.

However, the coating composition has good finished product appearance and recoatability, but sometimes has insufficient curability.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2002-201430

Patent Document 2: International Publication No. 99/03939

Summary of the invention

Problem that the invention aims to solve

An object of the present invention is to provide a high-solid coating composition capable of forming a coating film having excellent coating film properties and finished product appearance.

Technical Solution

The present inventors have repeatedly conducted intensive studies to achieve the above-mentioned object, and as a result, found that the above-mentioned object can be achieved according to the following high-solid content coating composition, which contains: (A) a hydroxyl-containing 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, (B) castor oil, (C) a melamine resin and (D) a catalyst, and the solid content during coating is 50% by mass or more.

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

Item 1. A high-solid content coating composition comprising: (A) a hydroxyl-containing 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, (B) castor oil, (C) a melamine resin and (D) a catalyst, wherein the solid content during coating is 50% by mass or more.

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

Item 3. The high-solid 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.

Item 4. The high-solid coating composition according to any one of Items 1 to 3, wherein the catalyst (D) comprises a sulfonic acid catalyst (D-1).

Item 5. The high-solid coating composition according to any one of Items 1 to 4, further comprising a blocked polyisocyanate compound (E).

Item 6. A method for forming a multilayer coating film, comprising: step (1): applying a mid-coat coating composition on a coated object to form a mid-coat coating film; step (2): applying a base coating coating composition on the mid-coat coating film formed in the step (1) to form a base coating film; step (3): applying a high-solid coating composition as described in any one of items 1 to 5 on the base coating film formed in the step (2) to form a clear coating film; and step (4): heating and curing the mid-coat coating film, base coating film and clear coating film formed in the steps (1) to (3) together.

Beneficial Effects

The high-solid content coating composition of the present invention can form a coating film having excellent recoatability, curability and finished product appearance.

DETAILED DESCRIPTION

Hereinafter, the high-solid coating composition of the present invention (hereinafter, sometimes simply referred to as "the present coating") 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-containing 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, (B) castor oil, (C) a melamine resin, and (D) a catalyst, and the solid content during coating is 50% by mass or more.

In addition, in this specification, a high-solid coating composition refers to a coating composition having a solid content of 50% or more during coating.

Hydroxyl-containing acrylic resin (A)

The hydroxyl-containing acrylic resin (A) is an acrylic resin having a weight average molecular weight in the range of 3,000 to 10,000 and a hydroxyl value in the range of 130 to 220 mgKOH/g.

When the weight average molecular weight of the hydroxyl-containing acrylic resin (A) is 3000 or more, the curability of the formed coating film becomes good, and when the weight average molecular weight is 10000 or less, the finished appearance of the formed coating film becomes good. Among them, from the viewpoint of the curability of the formed coating film and the finished appearance, the weight average molecular weight of the hydroxyl-containing acrylic resin (A) is preferably in the range of 4000 to 9000, and more preferably in the range of 5000 to 8000.

It should be noted that in this specification, the average molecular weight is a value calculated based on the molecular weight of standard polystyrene according to the chromatogram measured by gel permeation chromatography. The gel permeation chromatograph used is "HLC8120GPC" (manufactured by Tosoh Corporation). As chromatographic columns, four columns "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000HXL" (all manufactured by Tosoh Corporation, trade names) were used, and the mobile phase was tetrahydrofuran, the measurement temperature was 40°C, the flow rate was 1cc/min, and the detector was RI.

When the hydroxyl value of the hydroxyl-containing acrylic resin (A) is 130 mgKOH/g or more, the recoatability and curability of the formed coating film become good, and when the hydroxyl value is 220 mgKOH/g or less, the finished product appearance of the formed coating film becomes good. Among them, from the viewpoint of the recoatability and curability of the formed coating film and the finished product appearance, the hydroxyl value of the hydroxyl-containing acrylic resin (A) is preferably in the range of 140 to 210 mgKOH/g, and more preferably in the range of 150 to 200 mgKOH/g.

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

The above-mentioned hydroxyl-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-containing polymerizable unsaturated monomer include: monoesters of (meth)acrylic acid and a diol 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; ε-caprolactone-modified monoesters of (meth)acrylic acid and a diol having 2 to 8 carbon atoms; adducts of (meth)acrylic acid and epoxy-containing compounds (e.g., "Cardura E10P" (trade name), manufactured by Momentive Specialty Chemicals, glycidyl neodecanoate); N-hydroxymethyl (meth)acrylamide; allyl alcohol; and (meth)acrylates having a polyoxyethylene chain with a hydroxyl group at the molecular end.

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

(1) Acid group-containing polymerizable unsaturated monomers

The polymerizable unsaturated monomer containing an acid group 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-containing monomers such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, and maleic anhydride; sulfonic acid-containing monomers such as vinyl sulfonic acid and 2-sulfoethyl (meth)acrylate; acidic phosphate monomers such as 2-(meth)acryloyloxyethyl phosphate, 2-(meth)acryloyloxypropyl phosphate, 2-(meth)acryloyloxy-3-chloropropyl phosphate, and 2-methacryloyloxyethylphenyl phosphate. One or more of these monomers can be used. When using a polymerizable unsaturated monomer containing an acid group, it is preferably set to an amount such that the acid value of the hydroxyl-containing acrylic resin (A) becomes 0.5 to 30 mgKOH/g, particularly 1 to 20 mgKOH/g.

(2) Esterification products of acrylic acid or methacrylic acid and monohydric alcohol having 1 to 20 carbon atoms

Specifically, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isotetradecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl acrylate (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 can be cited.

(3) Aromatic vinyl monomers

Specifically, styrene, α-methylstyrene, vinyltoluene, etc. can be cited. By using an aromatic vinyl monomer as a constituent component, the glass transition temperature of the obtained resin increases, and a coating film with a high refractive index and hydrophobicity can be obtained, so that the gloss of the coating film can be improved to improve the appearance of the finished product. When an aromatic vinyl monomer is used as a constituent component, its mixing ratio is preferably in the range of 3 to 50% by mass, particularly preferably in the range of 5 to 40% by mass, relative to the total amount of the monomer component.

(4) Glycidyl-containing polymerizable unsaturated monomers

The glycidyl group-containing polymerizable unsaturated monomer is a compound having one or more glycidyl groups and one or more polymerizable unsaturated bonds in one molecule, and specific examples thereof include glycidyl acrylate and glycidyl methacrylate.

(5) Nitrogen-containing compounds containing polymerizable unsaturated bonds

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, vinylimidazole, acrylonitrile, methacrylonitrile, and the like can be mentioned.

(6) Other vinyl compounds

Examples thereof include vinyl acetate, vinyl propionate, vinyl chloride, and vinyl versatate. Examples of vinyl versatate include commercially available products such as "VEOVA 9" and "VEOVA 10" (trade names, manufactured by JAPAN EPOXY RESIN CO., LTD.).

As other polymerizable unsaturated monomers, the monomers shown in (1) to (6) above may be used alone or in combination of two or more.

In the present invention, a polymerizable unsaturated monomer refers to a monomer having one or more (e.g., 1 to 4) polymerizable unsaturated groups. A polymerizable unsaturated group refers to an unsaturated group that can undergo free radical polymerization. Examples of the polymerizable unsaturated group include vinyl, (meth)acryloyl, (meth)acrylamide, vinyl ether, allyl, propenyl, isopropenyl, and maleimide.

In addition, in this specification, "(meth)acrylate" means acrylate or methacrylate. "(meth)acrylic acid" means acrylic acid or methacrylic acid. In addition, "(meth)acryloyl" means acryloyl or methacryloyl. In addition, "(meth)acrylamide" means acrylamide or methacrylamide.

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

As a copolymerization method for obtaining the hydroxyl-containing acrylic resin (A) by copolymerizing the above-mentioned polymerizable unsaturated monomer mixture, 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, xylene, and "Swazol 1000" (a trade name of a high-boiling-point petroleum solvent manufactured by COSMO Petroleum Corporation); 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 ethyl ether acetate, and propylene glycol methyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; and alcohol solvents such as isopropyl alcohol, n-butanol, isobutyl alcohol, and 2-ethylhexanol.

These organic solvents may be used alone or in combination of two or more, and from the viewpoint of solubility of acrylic resin, ester solvents and ketone solvents are preferably used, and aromatic solvents may also be preferably used in combination.

Examples of the polymerization initiator that can be used in the copolymerization of the hydroxyl-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, 2,2'-azobis(2-methylbutyronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile).

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

From the viewpoint of water resistance of the formed coating film and finished product appearance, the glass transition temperature of the hydroxyl-containing acrylic resin (A) is preferably in the range of 0 to 70°C, particularly preferably 10 to 60°C, and even more particularly preferably 20 to 55°C.

In this specification, the glass transition temperature (° 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 each formula, W1, W2, ... represent the mass fraction of each monomer used for copolymerization, and T1, T2, ... represent the Tg (K) of the homopolymer of each monomer. It should be noted that T1, T2, ... are values of pages III-139 to 179 of Polymer Hand Book (Second Edition, edited by J. Brandup·E.H. Immergut). In addition, the glass transition temperature (°C) when the Tg of the homopolymer of the monomer is unclear is set as the static glass transition temperature. For example, a differential scanning calorimeter "DSC-220U" (manufactured by Seiko Instrument Co., Ltd.) is used to take the sample into a measuring cup, vacuum suction is performed to completely remove the solvent, and then the heat change is measured in the range of -20°C to +200°C at a heating rate of 3°C/min, and the initial change point of the baseline on the low temperature side is set as the static glass transition temperature.

From the viewpoint of the recoatability of the formed coating film and the appearance of the finished product, the hydroxyl-containing acrylic resin (A) preferably includes a secondary hydroxyl-containing acrylic resin (A'). The secondary hydroxyl-containing acrylic resin (A') can be produced, for example, by using a secondary hydroxyl-containing polymerizable unsaturated monomer as one of the hydroxyl-containing polymerizable unsaturated monomers in the production method of the hydroxyl-containing acrylic resin (A).

Examples of the above-mentioned polymerizable unsaturated monomers containing secondary hydroxyl groups include: polymerizable unsaturated monomers having secondary hydroxyl groups, such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-hydroxybutyl (meth)acrylate, wherein the carbon number of the alkyl group in the ester portion is 2 to 8, preferably 3 to 6, and more preferably 3 or 4; adducts of (meth)acrylic acid and epoxy-containing compounds (e.g., "Cardura E10P" (trade name), manufactured by Momentive Specialty Chemicals, glycidyl neodecanoate), etc. These can be used alone or in combination of two or more. Among them, 2-hydroxypropyl (meth)acrylate can be preferably used from the viewpoints of the recoatability of the formed coating film and the appearance of the finished product.

In the production of the above-mentioned secondary hydroxyl-containing acrylic resin (A'), when the above-mentioned secondary hydroxyl-containing polymerizable unsaturated monomer is used, from the viewpoints of the curability of the formed coating film, the appearance of the finished product, etc., the usage amount of the secondary hydroxyl-containing polymerizable unsaturated monomer is preferably in the range of 25 to 60% by mass, and more preferably in the range of 30 to 55% by mass relative to the total amount of the copolymerizable monomer components.

Furthermore, in the above-mentioned secondary hydroxyl-containing acrylic resin (A'), from the viewpoints of the recoatability, curability and finished product appearance of the formed coating film, the content ratio of the above-mentioned secondary hydroxyl-containing polymerizable unsaturated monomer in the total amount of the above-mentioned hydroxyl-containing polymerizable unsaturated monomer is preferably in the range of 50 to 100 mass %, more preferably in the range of 55 to 100 mass %, and further preferably in the range of 60 to 100 mass %.

From the viewpoints of the recoatability, curability and finished product appearance of the formed coating film, the content of the hydroxyl-containing acrylic resin (A) in the high-solid 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, and further preferably 30 to 60 parts by mass, based on 100 parts by mass of the resin solid content of the high-solid coating composition.

Castor oil (B)

Castor oil (B) is a vegetable oil made from castor seeds, and is a glyceride of unsaturated fatty acids such as ricinoleic acid and oleic acid and saturated fatty acids such as palmitic acid. In this 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, and esters of castor oil fatty acids and hydroxyl-containing compounds.

As the castor oil-based polyol (B'), a commercially available product can be used. Examples of the trade names of commercially available products include: “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” (all manufactured by Ito Oil Manufacturing Co., Ltd.), “TLM”, “LM-R”, “ELA-DR”, “HS CM”, “HS 2G-120”, “HS2G-160R”, “HS2G-270B”, “HS KA-001”, “HS CM-025P”, “HS CM-075P”, “HS 3G-500B" (made by Fengguo Oil Manufacturing Co., Ltd.), etc.

The castor oil-based polyols (B') described above can be used alone or in combination of two or more.

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

From the viewpoints of the recoatability, curability and finished product 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.

Melamine resin (C)

As the melamine resin (C), a partially methylolated melamine resin or a completely methylolated melamine resin obtained by a reaction between a melamine component and an aldehyde component can be used. Examples of the aldehyde component include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde.

In addition, the methylol groups of the methylolated melamine resin may be partially or completely etherified with a suitable alcohol. Examples of the alcohol used for etherification include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, 2-ethyl-1-butanol, and 2-ethyl-1-hexanol.

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

Furthermore, it is preferred that the weight average molecular weight of the melamine resin (C) is in the range of 400 to 6,000, more preferably 500 to 5,000, and more preferably 800 to 4,000.

As the melamine resin (C), a commercially available product can be used. Examples of the trade names of the commercially available products include: "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" (all manufactured by Allnex Japan Co., Ltd.), "U-VAN 120", "U-VAN 20HS", "U-VAN 20SE60", "U-VAN 2021", "U-VAN 2028", "U-VAN 28-60" (all manufactured by Mitsui Chemicals, Inc.), and the like.

The above melamine resins (C) can be used alone or in combination of two or more.

From the viewpoints of the recoatability, curability and finished product appearance of the formed coating film, the content of the melamine resin (C) in the high-solid 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 further 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 coating composition.

Catalyst (D)

As the catalyst (D), conventionally known catalysts may be used, for example, sulfonic acid catalysts (D-1) such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, and dinonylnaphthalenesulfonic acid; phosphoric acid catalysts (D-2) such as alkyl phosphates such as monobutyl phosphate, dibutyl phosphate, mono(2-ethylhexyl) phosphate, and di(2-ethylhexyl) phosphate; tin octanoate, 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 octanoate, zinc cyclohexaneate, fatty acid zincs, bismuth octanoate, bismuth 2-ethylhexanoate, bismuth oleate, bismuth neodecanoate, bismuth tert-carbonate, bismuth cyclohexaneate, cobalt cyclohexaneate, calcium octanoate, copper cyclohexaneate, tetra(2-ethylhexyl) titanate and other organic metal compound catalysts; amine catalysts such as tertiary amines, etc., wherein, from the viewpoints of the recoat adhesion, curability and finished product appearance of the formed coating film, it is preferred to include at least one selected from the sulfonic acid catalyst (D-1) and the phosphoric acid catalyst (D-2), and it is further preferred to include the sulfonic acid catalyst (D-1).

From the viewpoints of the recoatability, curability and finished product appearance 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.

High solid coating composition

The high-solid content coating composition of the present invention is a high-solid content coating composition comprising: (A) a hydroxyl-containing 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, (B) castor oil, (C) a melamine resin, and (D) a catalyst, and the solid content during coating is 50% by mass or more.

From the viewpoint of reducing VOC, the solid content of the high-solid coating composition of the present invention during coating is preferably 52% or more, more preferably 54% or more.

In this specification, "solid content" refers to non-volatile components such as resin, curing agent, pigment, etc. contained in the coating composition that remain after the coating composition is dried at 110°C for 1 hour. Therefore, 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 of the container, drying at 110°C for 1 hour, weighing the mass of the components in the coating composition remaining after drying, and finding 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 high solid content coating composition of the present invention can form a coating film with excellent recoatability, curability and finished product appearance is not clear, but it is speculated that the weight average molecular weight of the hydroxyl-containing acrylic resin (A) is as low as 3000 to 10000, so the viscosity during heat flow is reduced, and a coating film with excellent finished product appearance can be formed regardless of the high solid content. In addition, the hydroxyl value of the hydroxyl-containing acrylic resin (A) is as high as 130 to 220 mgKOH/g, and it also contains a catalyst (D), so the reactivity with the melamine resin (C) is high and the curability becomes good. In addition, it is speculated that the low polarity alkyl chain derived from fatty acids and castor oil (B) having secondary hydroxyl groups are contained, so the hydroxyl concentration of the surface layer becomes high and the recoatability becomes good.

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

Blocked polyisocyanate compound (E)

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

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

Examples of the aliphatic polyisocyanate include 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- or 2,2,4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and 2,6-diisocyanatohexanoic acid methyl ester (common name: lysine). aliphatic diisocyanates such as 2,6-diisocyanatohexanoic acid 2-isocyanatoethyl ester, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 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 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), alicyclic diisocyanates 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)- Alicyclic triisocyanates such as 5-(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-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

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

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

Examples of the polyisocyanate derivatives include dimers, trimers, biuret, allophanate, uretdione, uretonimine, isocyanurate, oxadiazinetrione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI), and crude TDI of the polyisocyanate compounds.

Examples of the end-capping agent include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxybiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactams such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; aliphatic alcohols such as methanol, ethanol, propanol, butanol, amyl alcohol, and lauryl alcohol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and diethylene glycol; Ethers such as 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, hydroxymethyl urea, hydroxymethyl melamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate; oximes such as formamide oxime, acetamide oxime, acetone oxime, methyl ethyl ketone oxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; dimethyl malonate, diethyl malonate, ethyl acetoacetate esters, methyl acetoacetate and acetylacetone and other active methylene series; butyl mercaptan, tert-butyl mercaptan, hexyl mercaptan, tert-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, ethylthiophenol and other thiol series; acetanilide, acetoanisidine, acetyltoluidine, acrylamide, methacrylamide, acetamide, stearamide, benzamide and other amide series; succinimide, phthalimide, maleimide and other imide series; diphenylamine, phenylnaphthylamine, dimethylamino Amines such as aniline, N-phenyldimethylaniline, carbazole, aniline, naphthylamine, butylamine, dibutylamine, butylaniline, etc.; imidazoles such as imidazole and 2-ethylimidazole, ureas such as urea, thiourea, ethyleneurea, ethylenethiourea, diphenylurea, etc.; carbamates such as N-phenylcarbamate, etc.; imines such as ethyleneimine and propyleneimine, etc.; sulfites such as sodium bisulfite and potassium bisulfite, azole compounds, etc. Examples of the azole compounds include 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 and the like pyrazole or pyrazole derivatives; imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole and the like imidazole or imidazole derivatives; and imidazoline derivatives such as 2-methylimidazoline and 2-phenylimidazoline.

When the high-solid content coating composition of the present invention contains the above-mentioned blocked polyisocyanate compound (E), from the viewpoint of forming a coating film excellent in recoat adhesion, curability and finished product appearance, its content 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 further 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.

Other Ingredients

The high solid coating composition of the present invention may further contain resins other than those mentioned above, crosslinking agents other than those mentioned above, pigments, organic solvents, dispersants, anti-settling agents, defoamers, thickeners, ultraviolet absorbers, light stabilizers, surface conditioners, etc. as necessary.

As resins other than the above, for example, acrylic resins not containing hydroxyl groups, polyester resins optionally containing hydroxyl groups, polyurethane resins optionally containing hydroxyl groups, polyether resins optionally containing hydroxyl groups, polycarbonate resins optionally containing hydroxyl groups, epoxy resins optionally containing hydroxyl groups, etc. can be listed. Among them, polyester resins (F) containing hydroxyl groups are preferably used.

The hydroxyl-containing polyester resin (F) can be generally obtained by esterification reaction of polyol and polyacid in the presence of excess hydroxyl groups by a known method. Polyol is a compound having two or more hydroxyl groups in one molecule, and polyacid is a compound having two or more carboxyl groups in one molecule.

Examples of the polyol include 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, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol, and 3-methyl-4,5-pentanediol. , 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, hydroxypivalate and other diols; polylactone diols obtained by adding lactones such as ε-caprolactone to these diols; ester diols such as bis(hydroxyethyl) terephthalate; alkylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, polybutylene glycol and other polyether diols; α-olefin epoxides such as propylene oxide and butylene oxide, Cardura Monoepoxy compounds such as E10 [manufactured by Shell Chemical Company, trade name, glycidyl ester of synthetic highly branched saturated fatty acid]; trivalent or higher alcohols such as glycerol, trimethylolpropane, trimethylolethane, diglycerol, triglycerol, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, sorbitol, and mannitol; polylactone polyols obtained by adding lactones such as ε-caprolactone to these trivalent or higher alcohols; alicyclic polyols such as 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, hydrogenated bisphenol A, and hydrogenated bisphenol F; cyclic polyol compounds having a urate structure such as tris(hydroxyalkyl)isocyanurate, ε-caprolactone modified form of the tris(hydroxyalkyl)isocyanurate, and tris(hydroxyethyl)isocyanurate; etc.

The above polyols can be used alone or in combination of two or more.

Examples of the polyacid include aromatic polyacids and their anhydrides such as terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, 4,4'-biphenyl dicarboxylic acid, and diphenylmethane-4,4'-dicarboxylic acid; alicyclic dicarboxylic acids and their anhydrides such as hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrophthalic acid, and tetrahydrophthalic acid; aliphatic polyacids and their anhydrides 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; lower alkyl esters such as methyl esters and ethyl esters of these dicarboxylic acids; trivalent or higher polyacids such as trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, trimesic acid, methylcyclohexenetricarboxylic acid, tetrachlorohexene polyacid and its anhydride, etc.

The above polybasic acids can be used alone or in combination of two or more.

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

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

Furthermore, from the viewpoint of the finished appearance of the formed coating film, the number average molecular weight of the hydroxyl-containing polyester resin (F) is preferably in the range of 500 to 6,000, particularly preferably in the range of 750 to 5,000.

When the high-solid content coating composition of the present invention contains the above-mentioned hydroxyl-containing polyester resin (F), its content 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 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 product appearance of the formed coating film.

Examples of the pigment include coloring pigments, bright pigments, and extender pigments. These pigments may be used alone or in combination of two or more.

Examples of the coloring pigment include titanium dioxide, zinc flower, carbon black, cadmium red, molybdenum red, chrome yellow, chromium oxide, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, threne pigments, and perylene pigments.

Examples of the bright pigment include aluminum pigments, mica pigments, and mica powder coated with titanium oxide.

Examples of the extender pigment include talc, clay, kaolin, heavy earth, barium sulfate, barium carbonate, calcium carbonate, and alumina white.

Each of the above pigments can 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, when it contains a pigment, the amount of the pigment is preferably an amount that does not hinder the transparency of the resulting coating film, for example, usually preferably in the range of 0.1 to 20% by mass, particularly preferably 0.3 to 10% by mass, and further particularly preferably in the range of 0.5 to 5% by mass relative to the total solid content in the high-solid content coating composition.

Furthermore, when the high-solid coating composition of the present invention is used as a colored coating, when it contains a pigment, the amount of the pigment blended is generally preferably in the range of 1 to 200 mass %, particularly preferably 2 to 100 mass %, and even more particularly preferably 5 to 50 mass % relative to the total solid content in the high-solid coating composition.

As the organic solvent, for example, aromatic solvents such as toluene, xylene, and "Swazol 1000" (manufactured by COSMO Oil Co., Ltd., trade name, high boiling point petroleum solvent) can be cited; 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, etc. These can be used alone or in combination of two or more.

As the thickener, conventionally known thickeners can be used, for example, clay minerals (such as metal silicates, montmorillonite), acrylic acid (such as substances containing a structure composed of a polymer or oligomer of acrylate or methacrylate in the molecule), polyolefins (such as polyethylene, polypropylene, etc.), amides (higher fatty acid amides, polyamides, oligomers, etc.), polycarboxylic acids (including derivatives having at least two or more carboxyl groups in the molecule), cellulose (including various derivatives such as nitrocellulose, acetylcellulose, and cellulose ether), and carbamates (polymers, oligomers, etc. containing a carbamate structure in the molecule), ureas (polymers, oligomers, etc. containing a urea structure in the molecule), carbamate ureas (polymers, oligomers, etc. containing a carbamate structure and a urea structure in the molecule), etc.

As the ultraviolet absorber, conventionally known ultraviolet absorbers can be used, and examples thereof include benzotriazole absorbers, triazine absorbers, salicylic acid derivative absorbers, benzophenone absorbers, etc. These can be used alone or in combination of two or more.

When the high-solid content coating composition of the present invention contains a UV absorber, the amount of the UV absorber added is generally 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 solid content in the high-solid content coating composition.

As the light stabilizer, a conventionally known light stabilizer 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 with low basicity can be preferably used. Examples of such hindered amine light stabilizers include acylated hindered amines and aminoether hindered amines, and specifically, "HOSTAVIN 3058" (trade name, manufactured by Clariant) and "TINUVIN 123" (trade name, manufactured by BASF) can be cited.

The high-solid coating composition of the present invention may be either a one-component coating or a multi-component coating, but is preferably a one-component coating from the viewpoints of not requiring a coating mixing step, being excellent in productivity, and being able to simplify the maintenance of coating machinery.

The coating method of the high solid content coating composition of the present invention is not particularly limited, and for example, coating methods such as air spray coating, airless spray coating, rotary atomization coating, curtain coating, etc. can be listed, and wet coating films can be formed by these methods. In these coating methods, electrostatic application can also be performed as needed. Among them, air spray coating or rotary atomization coating is particularly preferred. The coating amount of this coating is usually set to preferably 10 to 60 μm in terms of cured film thickness, and particularly preferably 25 to 50 μm.

In addition, when air spray painting, airless spray painting and rotary atomization painting are performed, the viscosity of the present coating is preferably adjusted appropriately using a solvent such as an organic solvent and a thickener so that it becomes a viscosity range suitable for the painting, usually a viscosity range of 20 to 60 seconds, particularly 25 to 50 seconds at 20°C in a Ford Cup No. 4 viscometer.

The curing of the wet coating formed by applying the present coating to the coated object can be carried out by heating, and the heating can be carried out by a known heating unit, for example, a drying furnace such as a hot air furnace, an electric furnace, an infrared induction heating furnace, etc. Preferably, the heating temperature is not particularly limited, for example, in the range of 120 to 160° C., preferably in the range of 130 to 150° C. Preferably, the heating time is not particularly limited, for example, in the range of 10 to 60 minutes, preferably in the range of 15 to 30 minutes.

The high solid content coating composition of the present invention can form a coating film having excellent recoatability, curability and finished appearance, and can therefore be preferably used as a top clear coating paint. The coating can be particularly preferably used as a coating for automobiles.

Multilayer coating film forming method

As a method for forming a multilayer coating film in which the present coating material is applied as a top clear coating material, for example, the following method can be preferably used.

A method for forming a multilayer coating film, comprising: step (1): applying a mid-coat coating composition on a coated object to form a mid-coat coating film; step (2): applying a base coating coating composition on the mid-coat coating film formed in the step (1) to form a base coating film; step (3): applying the high-solid coating composition of the present invention on the base coating film formed in the step (2) to form a clear coating film; and step (4): heating and curing the mid-coat coating film, base coating film and clear coating film formed in the steps (1) to (3) together.

The coated object is not particularly limited, and examples thereof include: outer panels of automobile bodies such as cars, trucks, motorcycles, and buses; automobile parts; outer panels of home appliances such as mobile phones and audio equipment, etc. Among them, outer panels of automobile bodies and automobile parts are preferred.

The materials of these coated objects are not particularly limited. For example, metal materials such as iron, aluminum, brass, copper, tin plate, stainless steel, galvanized steel, zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) steel; resins such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin; plastic materials such as various FRP (fiber reinforced polymer); inorganic materials such as glass, cement, concrete; wood; fiber materials such as paper and cloth, etc. Among them, metal materials and plastic materials are preferred.

In addition, the surface to be coated with the multilayer coating may be a surface treated with phosphate treatment, chromate treatment, composite oxide treatment, etc. on the metal surface of automobile body panels, automobile parts, home appliances, and metal substrates such as steel sheets constituting them.

A coating film may be further formed on an object that has been subjected to or has not been subjected to a surface treatment. For example, a coating object as a substrate may be subjected to a surface treatment as required to form a primer coating film thereon. For example, when the coating object is an automobile body, the primer coating film may be formed using a primer coating composition known per se and commonly used in the coating of automobile bodies.

The above-mentioned primer coating composition is usually applied for the purpose of imparting corrosion resistance to the object to be coated.

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

Furthermore, from the viewpoint of the finished appearance of the multilayer coating film to be formed, the above-mentioned base coating film is preferably a cured coating film.

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

The intermediate coating composition is usually applied to impart smoothness, stone chipping resistance, and adhesion between coating films to the object to be coated.

Examples of the crosslinkable functional group that the base resin has include a carboxyl group, a hydroxyl group, and an epoxy group.

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

Examples of the cross-linking agent include melamine resins, polyisocyanate compounds, and blocked polyisocyanate compounds.

As the intermediate coating composition, any of an aqueous coating composition and an organic solvent-based coating composition can be used.

The amount of the intermediate coating composition applied is preferably an amount that gives a cured film thickness of 5 to 60 μm, more preferably 8 to 50 μm, and still more preferably 10 to 40 μm.

As the base coating composition, a thermosetting base coating composition known for coating automobile bodies, etc. can be used. As the base coating composition, for example, a thermosetting coating composition containing a base resin having a crosslinkable functional group, a crosslinking agent, a coloring pigment, a bright pigment, and a body pigment can be preferably used.

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

Examples of the crosslinkable functional group that the base resin has include a carboxyl group, a hydroxyl group, and an epoxy group.

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

Examples of the cross-linking agent include melamine resins, polyisocyanate compounds, and blocked polyisocyanate compounds.

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

The amount of the base coating composition applied is preferably an amount that gives a cured film thickness of 5 to 40 μm, more preferably 6 to 35 μm, and even more preferably 7 to 30 μm.

The heating can be performed by a known means, for example, a drying furnace such as a hot air furnace, an electric furnace, an infrared induction heating furnace, etc. The heating temperature is preferably 60 to 180° C., more preferably 70 to 170° C., and further preferably 80 to 160° C. The heating time is not particularly limited, but is preferably in the range of 10 to 40 minutes, and more preferably in the range of 20 to 40 minutes.

Example

Hereinafter, manufacturing examples, embodiments and comparative examples are listed to further specifically describe the present invention. However, the present invention is not limited to these examples. In each example, "parts" and "%" are based on mass unless otherwise specified. In addition, the film thickness of the coating is based on the cured coating.

[1] Production of coated objects

On a degreased and zinc phosphate treated steel plate (JIS G3141, size 400 mm × 300 mm × 0.8 mm), a cationic electrodeposition coating "Elecron GT-10" (trade name: manufactured by Kansai Paint Co., Ltd., a coating obtained by using a blocked polyisocyanate compound as a curing agent in an epoxy resin polyamine-based cationic resin) was electro-deposited to a film thickness of 20 μm based on the cured coating film, and heated at 170° C. for 20 minutes to cross-link and cure it to form an electrodeposition coating film, thereby preparing a coated object.

[2] Paint production

Production of hydroxyl-containing acrylic resin (A)

Production Example 1

27 parts of "Swazol 1000" (trade name, manufactured by COSMO FUJIU CO., LTD., aromatic organic solvent) and 5 parts of propylene glycol monomethyl ether acetate were placed in a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen inlet tube and a dropping device. While blowing nitrogen into the reaction vessel, the charged liquid was stirred at 150° C., and a monomer mixture consisting 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-tert-amyl peroxide (polymerization initiator) was dropped therein at a uniform rate over 4 hours. After aging at 150° C. for 1 hour, the mixture was cooled, and 21 parts of isobutyl acetate was further added for dilution to obtain a secondary hydroxyl-containing acrylic resin (A'-1) solution having a solid content concentration of 65% by mass. The obtained secondary hydroxyl-containing acrylic resin (A'-1) had an acid value of 10.1 mgKOH/g, a hydroxyl value of 140 mgKOH/g, a weight average molecular weight of 8,000, and a glass transition temperature of 39°C.

Production Examples 2 to 4

In Production Example 1, except that the blending composition was set as shown in Table 1, secondary hydroxyl-containing acrylic resin (A'-2) to (A'-4) solutions having a solid content concentration of 65% were obtained in the same manner as in Production Example 1. The acid value, hydroxyl value, weight average molecular weight and glass transition temperature of each hydroxyl-containing acrylic resin are collectively shown in Table 1.

[Table 1]

Production of hydroxyl-containing acrylic resin (G)

Production Example 5

27 parts of "Swazol 1000" (trade name, manufactured by COSMO FUJIU CO., LTD., aromatic organic solvent) and 5 parts of propylene glycol monomethyl ether acetate were placed in a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen inlet tube and a dropping device. While blowing nitrogen into the reaction vessel, the charged liquid was stirred at 150° C., and a monomer mixture consisting 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-tert-amyl peroxide (polymerization initiator) was dropped therein at a uniform rate over 4 hours. After aging at 150° C. for 1 hour, the mixture was cooled, and 21 parts of isobutyl acetate was further added for dilution to obtain a secondary hydroxyl-containing acrylic resin (G'-1) solution having a solid content concentration of 65% by mass. The obtained secondary hydroxyl-containing acrylic resin (G'-1) had an acid value of 10.1 mgKOH/g, a hydroxyl value of 177 mgKOH/g, a weight average molecular weight of 11,000, and a glass transition temperature of 39°C.

Production Examples 6 to 8

In Production Example 5, except that the blending composition was set as shown in Table 2, secondary hydroxyl-containing acrylic resin (G'-2) to (G'-4) solutions having a solid content concentration of 65% were obtained in the same manner as in Production Example 5. The acid value, hydroxyl value, weight average molecular weight and glass transition temperature of each hydroxyl-containing acrylic resin are collectively shown in Table 2.

[Table 2]

Production of hydroxyl-containing polyester resin (F)

Production Example 9

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

Production of high solids coating compositions

Example 1

84.6 parts (55 parts solid content) of the secondary hydroxyl-containing acrylic resin (A'-1) solution obtained in Production Example 1, 10 parts (10 parts solid content) of "URIC H-30" (trade name, manufactured by Ito Oil Products, 100% solid content, hydroxyl value 155 to 165 mgKOH/g), 41.7 parts (25 parts solid content) of "U-VAN 20SE60" (trade name, manufactured by Mitsui Chemicals, melamine resin, 60% solid content), 10 parts (10 parts solid content) of "Desmodur BL3575" (trade name, manufactured by Bayer Material Science, pyrazole-terminated polyisocyanate, 100% solid content), 2 parts (0.5 parts solid content) of "NACURE 5528" (trade name, manufactured by KING INDUSTRIES, amine salt of dodecylbenzenesulfonic acid, 25% active ingredient) and 30 parts (25 parts solid content) of "BYK-300" (trade name, BYK 0.4 parts (0.2 parts solid content) of a surface conditioner (manufactured by Chemie Co., Ltd., effective ingredient 52%) were uniformly mixed, and further, butyl acetate was added to adjust the solid content during coating to 55%, thereby obtaining a high-solid content coating composition No. 1.

Examples 2 to 12 and Comparative Examples 1 to 9

High solid coating compositions Nos. 2 to 21 were obtained in the same manner as high solid coating composition No. 1 except that the blending compositions and solid contents during coating were as shown in the following Tables 3 to 6. The blending compositions shown in Tables 3 to 6 are based on the solid content mass of each component.

Preparation of test plate (Preparation of test plate for curing evaluation)

A high-solid coating composition No. 1 was applied to a polypropylene plate using a rotary atomizing electrostatic coating machine so that the cured coating had a film thickness of 35 μm, and the plate was left at room temperature for 7 minutes. The plate was heated at 140° C. in a hot air circulation drying oven for 30 minutes, and the resulting coating was peeled off to prepare a test plate of Example 1.

(Preparation of test plates for product quality evaluation)

Using a rotary atomizing electrostatic coating machine, "ZU-10" (trade name, manufactured by Kansai Paint Co., Ltd., an acrylic resin/melamine resin organic solvent-based mid-coat paint) was electrostatically coated on the coated object prepared in [1] so that the cured film thickness became 15 μm, and then left to stand for 5 minutes to form an uncured mid-coat film.

Next, "Soflex 420" (trade name, manufactured by Kansai Paint Co., Ltd., solvent-based top-coat base coating material) was electrostatically coated on the uncured mid-coat film using a rotary atomizing electrostatic coating machine so as to have a dry film thickness of 12 μm, and the film was left to stand for 3 minutes to form an uncured base coating film.

Next, a rotary atomization type electrostatic coating machine was used to electrostatically coat the uncured base coating film with a high solid content coating composition No. 1 in a manner such that the dry film thickness was 35 μm to form a clear coating film, which was then left to stand for 7 minutes. Next, the intermediate coating film, the base coating film, and the clear coating film were heated and cured at 140° C. for 30 minutes, thereby preparing a test plate of Example 1.

(Preparation of test plate for evaluation of recoating adhesion)

Using a rotary atomizing electrostatic coating machine, "ZU-10" (trade name, manufactured by Kansai Paint Co., Ltd., an acrylic resin/melamine resin organic solvent-based mid-coat paint) was electrostatically coated on the coated object prepared in [1] so that the cured film thickness became 15 μm, and then left to stand for 5 minutes to form an uncured mid-coat film.

Next, "Soflex 420" (trade name, manufactured by Kansai Paint Co., Ltd., solvent-based top-coat base coating material) was electrostatically coated on the uncured mid-coat film using a rotary atomizing electrostatic coating machine so as to have a dry film thickness of 12 μm, and the film was left to stand for 3 minutes to form an uncured base coating film.

Next, a rotary atomization type electrostatic coating machine was used to electrostatically coat the uncured base coating film with a high solid content coating composition No. 1 in a manner such that the dry film thickness was 35 μm to form a clear coating film, which was then left for 7 minutes. Next, the intermediate coating film, the base coating film, and the clear coating film were heated and cured at 160° C. for 60 minutes, and then left at room temperature for 24 hours.

Next, a rotary atomizing electrostatic coating machine was used to electrostatically coat "ZU-10" (trade name, manufactured by Kansai Paint Co., Ltd., an acrylic resin/melamine resin organic solvent-based mid-coat) on the heat-cured clear coating film so that the cured film thickness became 15 μm, and the film was left to stand for 5 minutes to form an uncured mid-coat film.

Next, "Soflex 420" (trade name, manufactured by Kansai Paint Co., Ltd., solvent-based top-coat base coating material) was electrostatically coated on the uncured mid-coat film using a rotary atomizing electrostatic coating machine so as to have a dry film thickness of 12 μm, and the film was left to stand for 3 minutes to form an uncured base coating film.

Next, a rotary atomization type electrostatic coating machine was used to electrostatically coat the uncured base coating film with a high solid content coating composition No. 1 in a manner such that the dry film thickness was 35 μm to form a clear coating film, which was then left to stand for 7 minutes. Next, the mid-coat film, base coating film, and clear coating film were heated and cured at 130° C. for 20 minutes, thereby preparing a test plate of Example 1.

In the preparation of the test plate of the above-mentioned high-solid coating composition No. 1, except that the high-solid coating composition No. 1 was set to any one of the high-solid coating compositions No. 2 to 21, the test plates of Examples 2 to 12 and Comparative Examples 1 to 9 were prepared in the same manner as the preparation of the test plate of the high-solid coating composition No. 1.

The test plates obtained above were evaluated by the following test methods. The evaluation results are shown in Tables 3 to 6 together with the coating compositions.

(Test method)

Recoat adhesion: According to JIS K 5600-5-6 (1990), 100 2 mm × 2 mm checkerboards were made on the coating surface, and a tape was attached to the surface. After rapid peeling, the number of checkerboard coatings remaining on the coating surface was evaluated. A and B were considered acceptable.

A: Remaining number/total number = 100/100, no edge defects.

B: Number of remaining pieces/total number = 100 pieces/100 pieces, with edge defects.

C: Number of remaining cells/total number = 99 or less.

Curability (crosslinking density): A test piece with a width of 5 mm and a length of 10 mm was prepared, and dynamic viscoelasticity measurement (storage modulus (E'), loss modulus (E"), and loss tangent (tanδ)) was performed under the following conditions. The crosslinking density was measured according to the following formula 1. The smaller the crosslinking density, the higher the curability. 700 or less was considered acceptable.

· Apparatus: Dynamic viscoelasticity measuring apparatus RSA3 (manufactured by TA Instruments).

·Measurement mode: non-resonance forced vibration method.

Heating 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 the peak top of loss tangent (tan δ)): K)

Finished product appearance: The finished product appearance was evaluated based on the long wave (LW) value and short wave (SW) value measured by Wave Scan (trade name, manufactured by BYK Gardner).

LW value: It is an index of smoothness. The smaller the LW value, the higher the smoothness of the coating surface. 15 or less is considered acceptable.

SW value: It is an index of distinctness of image. The smaller the SW value, the higher the distinctness of image of the coating surface. 25 or less is considered acceptable.

[Table 3]

[Table 4]

[Table 5]

[Table 6]

(*1) “URIC H-52”: trade name, manufactured by Ito Oil Manufacturing Co., Ltd., solid content 100%, hydroxyl value 195 to 205 mgKOH/g.

(*2) “URIC H-57”: trade name, manufactured by Ito Oil Manufacturing Co., Ltd., solid content 100%, hydroxyl value 85 to 115 mgKOH/g.

(*3) “URIC H-1824”: trade name, manufactured by Ito Oil Manufacturing Co., Ltd., solid content 100%, hydroxyl value 55 to 77 mgKOH/g.

(*4) “URIC H-62”: trade name, manufactured by Ito Oil Manufacturing Co., Ltd., solid content 100%, hydroxyl value 245 to 275 mgKOH/g.

(*5) Linseed oil: manufactured by Summit-Oilmill, solid content 100%.

(*6) “NACURE 4167”: trade name, manufactured by KING INDUSTRIES, triethylamine salt of alkylphosphoric acid, active ingredient 25%.

As mentioned above, although embodiment and Example of this invention were specifically described, this invention is not limited to the said embodiment, Various deformation|transformation based on the technical idea of this invention is possible.

For example, the structures, methods, processes, shapes, materials, and numerical values listed in the above-mentioned embodiments and examples are merely examples, and different structures, methods, processes, shapes, materials, and numerical values may be used as needed.

Furthermore, the configurations, methods, steps, shapes, materials, numerical values, and the like of the above-described embodiments can be combined with each other as long as they do not depart from the gist of the present invention.

Claims (6)

1. A high solid content coating composition, which contains: (A) a hydroxyl-containing acrylic resin with 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, (B) castor oil, (C) melamine resin, and (D) catalyst, Furthermore, the solid content rate during coating is 50% by mass or more. 2. The high solid content coating composition according to claim 1, wherein The hydroxyl-containing acrylic resin (A) includes a secondary hydroxyl-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-solid coating composition according to any one of claims 1 to 3, wherein: The catalyst (D) contains a sulfonic acid catalyst (D-1). 5. The high-solid coating composition according to any one of claims 1 to 4, further containing a blocked polyisocyanate compound (E). 6. A method for forming a multi-layer coating film, which includes: Step (1): The step of applying an intermediate coating composition on the object to be coated to form an intermediate coating film; Step (2): a step of applying a base coating coating composition on the intermediate coating film formed in the step (1) to form a base coating film; Step (3): Coating the base coat film formed in the step (2) with the high solid content coating composition according to any one of claims 1 to 5 to form a clear coat film process; and Step (4): a step of heating and curing the intermediate coating film, the base coating film, and the clear coating film formed in the steps (1) to (3) together.