JP7200444B1 - HIGH-SOLID COATING COMPOSITION AND MULTIPLE-LAYER COATING METHOD - Google Patents

Abstract

An object of the present invention is to provide a high-solids coating composition capable of forming a coating film having excellent coating performance and finished appearance. (A) a hydroxyl group-containing acrylic resin having a weight average molecular weight within the range of 3,000 to 10,000 and a hydroxyl value within the range of 130 to 220 mgKOH/g, (B) castor oil, (C) a melamine resin and (D) A high-solids coating composition containing a catalyst and having a solids content of 50% by mass or more at the time of coating can solve the problems of the present invention.

Description

TECHNICAL FIELD The present invention relates to a high-solids coating composition and a method for forming a multi-layer coating film.

In recent years, from the viewpoint of global environmental protection, it is required to reduce volatile organic compounds (VOC) emitted from paints, and solvent-based paints are rapidly replacing water-based paints in various fields.

In the past, large amounts of solvent-based paints were used in automobile painting, and there was an urgent need to reduce VOCs emitted from these paints. Concerning, organic solvent-based paints are being replaced with water-based paints, and at present, water-based paints are the mainstream.

However, since topcoat clear paints are required to have particularly high levels of coating film performance (recoat adhesion, curability, etc.) and finished appearance, solvent-based clear paints are still mainly used today.
One technique for reducing VOCs that does not rely on water-based clear paints is to increase the solid content of the paint (increase the solid content concentration).

For example, Patent Document 1 discloses a high-solids coating composition containing 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. things are disclosed.
However, although this coating composition has good finished appearance and curability, it sometimes has insufficient recoat adhesion.

Further, Patent Document 2 discloses (A) a carboxyl group-containing compound, (B) a polyepoxide, and (C) (a) 30 to 50% by weight of vinyltrimethoxysilane and/or vinyltriethoxysilane, and (b) N-methylol. A heat characterized by containing a copolymer obtained by polymerizing a monomer component consisting of 5 to 15% by weight of (meth)acrylamide alkyl ether and (c) 35 to 65% by weight of other polymerizable unsaturated monomer. A curable high solids coating composition is disclosed.
However, although this coating composition has good finished appearance and good recoat adhesion, it sometimes has insufficient curability.

Japanese Patent Application Laid-Open No. 2002-201430 WO99/03939

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

The present inventors have made intensive studies to achieve the above objects, and found that (A) the weight average molecular weight is in the range of 3,000 to 10,000 and the hydroxyl value is 130 to 220 mgKOH / g High solid content paint containing hydroxyl group-containing acrylic resin, (B) castor oil, (C) melamine resin and (D) catalyst within the range, and having a solid content of 50% by mass or more at the time of coating It has been found that a composition can achieve the above objects.

According to the present invention, a high solids coating composition is provided which includes the following aspects.
Item 1. (A) a hydroxyl group-containing acrylic resin having a weight average molecular weight within the range of 3,000 to 10,000 and a hydroxyl value within the range of 130 to 220 mgKOH/g, (B) castor oil, (C) a melamine resin and (D) A high-solids coating composition containing a catalyst and having a solids content of 50% by mass or more at the time of coating.
Section 2. Item 2. The high-solids coating composition according to Item 1, wherein the hydroxyl group-containing acrylic resin (A) contains a secondary hydroxyl group-containing acrylic resin (A').
Item 3. 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.
Section 4. 4. The high-solids coating composition according to any one of Items 1 to 3, wherein the catalyst (D) comprises a sulfonic acid catalyst (D-1).
Item 5. Item 5. The high-solids coating composition according to any one of items 1 to 4, further comprising a blocked polyisocyanate compound (E).
Item 6. Step (1): A step of applying an intermediate coating composition onto an object to be coated to form an intermediate coating film;
Step (2): A step of applying a base coat paint composition onto the intermediate coat film formed in step (1) to form a base coat paint film;
Step (3): A step of applying the high solid content coating composition according to any one of Items 1 to 5 on the base coat film formed in the step (2) to form a clear coat film. ,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) all at once;
A method for forming a multilayer coating film comprising:

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

The high-solids coating composition of the present invention (hereinafter sometimes abbreviated as "the present coating material") will be described in more detail below.

The high solid content coating composition of the present invention comprises (A) a hydroxyl group-containing acrylic resin having a weight average molecular weight within the range of 3,000 to 10,000 and a hydroxyl value within the range of 130 to 220 mgKOH/g; A high-solids coating composition containing (B) castor oil, (C) a melamine resin and (D) a catalyst, and having a solids content of 50% by mass or more at the time of coating.
In this 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 within the range of 3,000 to 10,000 and a hydroxyl value within the range of 130 to 220 mgKOH/g.

When the weight average molecular weight of the hydroxyl group-containing acrylic resin (A) is 3,000 or more, the curability of the coating film formed is good, and when the weight average molecular weight is 10,000 or less, it is formed The finished appearance of the coating film is improved. Among them, the weight-average molecular weight of the hydroxyl group-containing acrylic resin (A) is preferably in the range of 4,000 to 9,000, and preferably 5,000, from the viewpoint of the curability and finished appearance of the coating film to be formed. It is more preferably in the range of ~8,000.

In this specification, the average molecular weight is a value calculated based on the molecular weight of standard polystyrene from a chromatogram measured by gel permeation chromatography. "HLC8120GPC" (manufactured by Tosoh Corporation) was used as the gel permeation chromatograph. As the columns, four of "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000HXL" (all manufactured by Tosoh Corporation, trade names) are used, Mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 cc/min, detector: RI.

When the hydroxyl value of the hydroxyl-containing acrylic resin (A) is 130 mgKOH/g or more, the resulting coating film has good recoat adhesion and curability, and when the hydroxyl value is 220 mgKOH/g or less, formation The finished appearance of the coated film is improved. Among them, the hydroxyl value of the hydroxyl-containing acrylic resin (A) is preferably in the range of 140 to 210 mgKOH/g, from 150 to More preferably within the range of 200 mg KOH/g.

The hydroxyl-containing acrylic resin (A) is obtained, for example, by copolymerizing a hydroxyl-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers (polymerizable unsaturated monomers other than hydroxyl-containing polymerizable unsaturated monomers). be able to.

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 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and the like. Monoesterified product of (meth)acrylic acid and a dihydric alcohol having 2 to 8 carbon atoms; ε-caprolactone modified product of the monoesterified product of (meth)acrylic acid and a dihydric alcohol having 2 to 8 carbon atoms; adduct of meth)acrylic acid and an epoxy group-containing compound (e.g., "Cardura E10P" (trade name), manufactured by Momentive Specialty Chemicals, neodecanoic acid glycidyl ester); N-hydroxymethyl (meth)acrylamide; allyl alcohol; , a (meth)acrylate having a polyoxyethylene chain with a hydroxyl group at the molecular end, and the like.

As other polymerizable unsaturated monomers copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer, for example, the following monomers (1) to (6) can be used. These polymerizable unsaturated monomers can be used alone 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. 2-(meth)acryloyloxyethyl acid phosphate, 2-(meth)acryloyloxypropyl acid phosphate, 2-(meth)acryloyloxy-3-chloropropyl acid phosphate, 2-methacryloyloxyethyl phenyl phosphoric acid, etc. Phosphate ester-based monomers and the like can be mentioned. These can be used alone or in combination of two or more. When the acid group-containing polymerizable unsaturated monomer is used, it is preferably used in such an amount that the hydroxyl group-containing acrylic resin (A) has an acid value of 0.5 to 30 mgKOH/g, particularly 1 to 20 mgKOH/g.

(2) Esterified products of acrylic acid or methacrylic acid and monohydric alcohols 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, isomyristyl (meth) acrylate, stearyl (meth) acrylate, isostearyl acrylate (Osaka organic Kagaku Kogyo Co., Ltd., trade name), lauryl (meth)acrylate, tridecyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and the like.

(3) Aromatic Vinyl Monomer Specific examples include styrene, α-methylstyrene, vinyltoluene, and the like. By using an aromatic vinyl monomer as a constituent component, the glass transition temperature of the resin obtained increases, and a hydrophobic coating film with a high refractive index can be obtained. improvement effect can be obtained. When the aromatic vinyl monomer is used as the constituent component, the blending ratio thereof is preferably in the range of 3 to 50% by mass, particularly 5 to 40% by mass, based on the total amount of the monomer components.

(4) Glycidyl Group-Containing Polymerizable Unsaturated Monomer A 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. Acrylate, glycidyl methacrylate and the like can be mentioned.

(5) polymerizable unsaturated bond-containing nitrogen atom-containing compounds such as (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.

(6) Other Vinyl Compounds Examples include vinyl acetate, vinyl propionate, vinyl chloride, and vinyl versatate. Versatic acid vinyl esters include commercially available products such as "Veova 9" and "Veova 10" (both trade names, manufactured by Japan Epoxy Resin Co., Ltd.).

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

In the present invention, the polymerizable unsaturated monomer refers to a monomer having one or more (eg, 1 to 4) polymerizable unsaturated groups. A polymerizable unsaturated group means an unsaturated group capable of undergoing radical polymerization. Examples of such polymerizable unsaturated groups include vinyl groups, (meth)acryloyl groups, (meth)acrylamide groups, vinyl ether groups, allyl groups, propenyl groups, isopropenyl groups, and maleimide groups.

Moreover, in this specification, "(meth)acrylate" means acrylate or methacrylate. "(Meth)acrylic acid" means acrylic acid or methacrylic acid. Moreover, "(meth)acryloyl" means acryloyl or methacryloyl. "(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 used is the total amount of the copolymerized monomer components from the viewpoint of recoat adhesion, curability, and finished appearance of the coating film to be formed. It is preferably in the range of 25 to 60% by mass, more preferably 30 to 55% by mass.

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

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

These organic solvents can be used alone or in combination of two or more. From the viewpoint of the solubility of the acrylic resin, it is preferable to use an ester-based solvent or a ketone-based solvent. Further, it is also possible to use an aromatic solvent in suitable combination.

Examples of polymerization initiators that can be used in copolymerizing the hydroxyl group-containing acrylic resin (A) include 2,2'-azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, and di-t-amyl. Peroxide, t-butyl peroctoate, 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile) and other known radical polymerization initiators be able to.

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 in the range of 0 to 70°C, particularly 10 to 60°C, more particularly 20 to 55°C, from the viewpoint of the water resistance and finished appearance of the coating film to be formed. is preferably

In this specification, the glass transition temperature (°C) of the acrylic resin was calculated by the following formula.
1/Tg(K)=(W1/T1)+(W2/T2)+ (1)
Tg (°C) = Tg (K) - 273 (2)
In each formula, W1, W2, . T1, T2, . Further, when the Tg of the homopolymer of the monomer is not clear, the glass transition temperature (° C.) is the static glass transition temperature. Take the sample in a measuring cup, vacuum aspirate to completely remove the solvent, then measure the calorific value change in the range of -20 ° C to +200 ° C at a heating rate of 3 ° C / min, and the first baseline on the low temperature side. The change point was taken as the static glass transition temperature.

The hydroxyl-containing acrylic resin (A) preferably contains a secondary hydroxyl-containing acrylic resin (A') from the viewpoint of the recoat adhesion of the coating film to be formed and the finished appearance. The secondary hydroxyl group-containing acrylic resin (A′) is, for example, a secondary hydroxyl group-containing polymerizable unsaturated monomer as one of the hydroxyl group-containing polymerizable unsaturated monomers in the method for producing the hydroxyl group-containing acrylic resin (A). can be manufactured by using

Examples of the secondary hydroxyl group-containing polymerizable unsaturated monomer include, for example, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, etc. Polymerizable unsaturated monomer having 2 to 8 carbon atoms, preferably 3 to 6 carbon atoms, more preferably 3 or 4 secondary hydroxyl groups; name), manufactured by Momentive Specialty Chemicals, neodecanoic acid glycidyl ester), and the like. These can be used individually or in combination of 2 or more types. Among them, 2-hydroxypropyl (meth)acrylate can be preferably used from the viewpoint of recoating adhesion of the coating film to be formed, finished appearance, 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 used is the coating film to be formed. From the viewpoint of curability, finished appearance, etc., it is preferably in the range of 25 to 60% by mass, more preferably in the range of 30 to 55% by mass, based on the total amount of the copolymerizable monomer components.

Further, in the secondary hydroxyl group-containing acrylic resin (A′), the content ratio of the secondary hydroxyl group-containing polymerizable unsaturated monomer in the total amount of the hydroxyl group-containing polymerizable unsaturated monomer is determined by recoating adhesion of the formed coating film. , From the viewpoint of curability and finished appearance, it is preferably in the range of 50 to 100% by mass, more preferably in the range of 55 to 100% by mass, and in the range of 60 to 100% by mass. is more preferred.

The content of the hydroxyl group-containing acrylic resin (A) in the high solid content coating composition of the present invention is determined from the viewpoint of recoat adhesion, curability and finished appearance of the coating film to be formed. It is preferably in the range of 20 to 70 parts by mass, more preferably 25 to 65 parts by mass, and even more preferably 30 to 60 parts by mass based on 100 parts by mass of the resin solid content.

Castor oil (B)
Castor oil (B) is a vegetable oil made from castor beans 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) shall include natural castor oil and synthetic castor oil.

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

A commercially available product can be used as the castor oil-based polyol (B′). Commercially available product names include, for example, "URIC H-30", "URIC H-31", "URIC H-52", "URIC H-57", "URIC H-62", and "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 POLYCATOR #10", "URIC POLYCATOR #30" (manufactured by Ito Oil Co., Ltd.), "TLM", "LM-R", "ELA- DR", "HS CM", "HS 2G-120", "HS 2G-160R", "HS 2G-270B", "HS KA-001", "HS CM-025P", "HS CM-075P", "HS 3G-500B" (manufactured by Toyokuni Oil Co., Ltd.) and the like.
The above castor oil-based polyols (B') can be used either alone or in combination of two or more.

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, from the viewpoint of recoat adhesion, curability, and finished appearance of the formed coating film. more preferably within the range of 100 to 200 mgKOH/g.

The content of castor oil (B) in the high solid content coating composition of the present invention is determined from the viewpoint of recoat adhesion, curability, finished appearance, etc. of the coating film formed, the resin solid content of the high solid content coating composition Based on 100 parts by mass, it 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.

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

Moreover, the methylol group of the above methylolated melamine resin may be partially or completely etherified with a suitable alcohol. Examples of alcohols used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethyl-1-butanol, 2-ethyl-1 - hexanol and the like.

The melamine resin (C) includes a methyl-etherified melamine resin in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with methyl alcohol, and a methylol group of a partially or completely methylolated melamine resin with butyl alcohol. butyl-etherified melamine resins partially or fully etherified with methyl alcohol and methyl-butyl mixed-etherified melamine resins partially or fully etherified with methyl alcohol and butyl alcohol preferable.

Further, the melamine resin (C) preferably has a weight average molecular weight in the range of 400 to 6,000, preferably 500 to 5,000, more preferably 800 to 4,000.

Commercial products can be used as the melamine resin (C). Commercial product names 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), " U-Van 120", "U-Van 20HS", "U-Van 20SE60", "U-Van 2021", "U-Van 2028", and "U-Van 28-60" (manufactured by Mitsui Chemicals, Inc.).

The melamine resin (C) can be used either 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 determined from the viewpoint of recoat adhesion, curability and finished appearance of the coating film to be formed. It is preferably in the range of 5 to 50 parts by mass, more preferably 10 to 45 parts by mass, even more preferably 15 to 40 parts by mass, based on 100 parts by mass per minute.

Catalyst (D)
As the catalyst (D), conventionally known ones can be used, for example, sulfonic acid catalyst (D-1) such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid; , dibutyl phosphate, mono(2-ethylhexyl) phosphate, di(2-ethylhexyl) phosphate and other alkyl phosphoric acid esters (D-2); tin octylate, dibutyltin diacetate, dibutyltin Di(2-ethylhexanoate), dibutyltin dilaurate, dioctyltin diacetate, dioctyltin di(2-ethylhexanoate), dibutyltin oxide, dibutyltin sulfide, dioctyltin oxide, dibutyltin fatty acid salt, 2- Lead ethylhexanoate, zinc octoate, zinc naphthenate, zinc fatty acids, bismuth octoate, bismuth 2-ethylhexanoate, bismuth oleate, bismuth neodecanoate, bismuth versatate, bismuth naphthenate, cobalt naphthenate, octylic acid Organometallic compound catalysts such as calcium, copper naphthenate, tetra(2-ethylhexyl) titanate; amine catalysts such as tertiary amines; From the viewpoint of properties and finished appearance, it preferably contains at least one selected from a sulfonic acid catalyst (D-1) and a phosphoric acid catalyst (D-2), and the sulfonic acid catalyst (D-1) may be contained. More preferred.

The content of the catalyst (D) in the high solid content coating composition of the present invention is determined from the viewpoint of the recoat adhesion, curability and finished appearance of the coating film to be formed, the resin solid content of the high solid content coating composition Based on 100 parts by mass, it 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. .

High solid content coating composition The high solid content coating composition of the present invention has (A) a weight average molecular weight within the range of 3,000 to 10,000 and a hydroxyl value within the range of 130 to 220 mgKOH/g. A high-solids coating composition containing a hydroxyl group-containing acrylic resin, (B) castor oil, (C) a melamine resin, and (D) a catalyst, and having a solids content of 50% by mass or more at the time of coating. be.

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

As used herein, "solid content" means non-volatile components such as resins, curing agents, and pigments contained in the coating composition that remain after the coating composition is dried at 110°C for 1 hour. For this reason, for example, the total solid content of the coating composition is measured by weighing the coating composition into a heat-resistant container such as an aluminum foil cup, spreading the coating composition on the bottom surface of the container, drying at 110 ° C. for 1 hour, It can be calculated by weighing the mass of the components remaining after drying in the coating composition and determining the ratio of the mass of the components remaining after drying to the total mass of the coating composition before drying.

Although it is not clear why the high solid content coating composition of the present invention can form a coating film having excellent recoat adhesion, curability and finished appearance, the hydroxyl group-containing acrylic resin (A) has a weight average molecular weight of Since it is low in the range of 3,000 to 10,000, the viscosity during heat flow is lowered, and a coating film with excellent finished appearance can be formed despite the high solid content. Since (A) has a high hydroxyl value in the range of 130 to 220 mgKOH/g and contains a catalyst (D), it has high reactivity with the melamine resin (C) and good curability. , is inferred. Furthermore, since it contains a low-polarity alkyl chain derived from a fatty acid and castor oil (B) having a secondary hydroxyl group, it is presumed that the concentration of hydroxyl groups in the surface layer is increased and the recoat adhesion 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 recoat adhesion, curability and finished appearance.

Block polyisocyanate compound (E)
The blocked polyisocyanate compound (E) is a polyisocyanate compound in which isocyanate groups are blocked with a blocking agent.
A polyisocyanate compound is a compound having at least two isocyanate groups in one molecule. Examples of polyisocyanate compounds include aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic 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 -aliphatic diisocyanates such as butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate and methyl 2,6-diisocyanatohexanoate (common name: lysine diisocyanate); , 2-isocyanatoethyl 2,6-diisocyanatohexanoate, 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. isocyanate, and the like.

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)cyclohexane (common name: hydrogenated xylylene diisocyanate) or mixtures thereof, cycloaliphatic diisocyanates such as methylenebis(1,4-cyclohexanediyl) diisocyanate (common name: hydrogenated MDI) and norbornane diisocyanate; and 1,3,5-triisocyanatocyclohexane, 1,3,5- trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 2-(3-isocyanatopropyl)-2,6- Di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 3-(3-isocyanatopropyl)-2,5-di(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 cycloaliphatic triisocyanates such as 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, etc. can be mentioned.

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

Examples of the aromatic polyisocyanate include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4- or 2,6-tolylene diisocyanate, and mixtures thereof. , 4,4′-toluidine diisocyanate and 4,4′-diphenyl ether diisocyanate; triphenylmethane-4,4′,4″-triisocyanate, 1,3,5-triisocyanatobenzene and 2 ,4,6-triisocyanatotoluene and other aromatic triisocyanates; and 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate and other aromatic tetraisocyanates. .

Examples of the polyisocyanate derivative include dimers, trimers, biuret, allophanate, uretdione, uretimine, isocyanurate, oxadiazinetrione, and polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI) of the polyisocyanate compound. and crude TDI.

Examples of the blocking agent include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; ε-caprolactam, δ-valerolactam, Lactams such as γ-butyrolactam and β-propiolactam; Aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol and lauryl alcohol; Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono Ethers such as butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, methoxymethanol; benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, lactic acid alcohols such as butyl, methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate; oxime series; dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, active methylene series such as acetylacetone; Mercaptans such as phenol, methylthiophenol, ethylthiophenol; acid amides such as acetanilide, acetanisidide, acetotolide, acrylamide, methacrylamide, acetic acid amide, stearamide, benzamide; succinimide, phthalimide, maleic acid imide, etc. imides; amines such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, butylphenylamine; imidazoles such as imidazole and 2-ethylimidazole; urea, thio Urea, ethylene urea, ethylenethiourea, diphenyl urea compounds such as urea; carbamic acid ester compounds such as phenyl N-phenylcarbamate; imine compounds such as ethyleneimine and propyleneimine; sulfite compounds such as sodium bisulfite and potassium bisulfite; . 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, pyrazole or pyrazole derivatives such as 5-dimethylpyrazole, 3-methyl-5-phenylpyrazole; imidazole or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole; 2-methylimidazoline , 2-phenylimidazoline and other imidazoline derivatives.

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

Other Components The high solid content coating composition of the present invention may further contain resins other than the above, cross-linking agents other than the above, pigments, organic solvents, dispersants, anti-settling agents, anti-foaming agents, and thickeners, if necessary. , an ultraviolet absorber, a light stabilizer, a surface control agent, and the like.

Examples of resins other than the above include acrylic resins that do not contain hydroxyl groups, polyester resins that may contain hydroxyl groups, polyurethane resins that may contain hydroxyl groups, polyether resins that may contain hydroxyl groups, and hydroxyl group-containing resins. Polycarbonate resins that may contain hydroxyl groups, epoxy resins that may contain hydroxyl groups, and the like can be mentioned, and among them, hydroxyl group-containing polyester resins (F) can be preferably used.

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

Examples of the polyhydric alcohol 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, 3-methyl-4,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, Dihydric alcohols such as 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, and neopentyl glycol hydroxypivalate; Polylactone diols obtained by adding lactones such as ε-caprolactone to functional alcohols; Ester diols such as bis(hydroxyethyl) terephthalate; Polyethers such as alkylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, and polybutylene glycol Diols; α-olefin epoxides such as propylene oxide and butylene oxide; monoepoxy compounds such as Cardura E10 [manufactured by Shell Chemical Co., trade name, glycidyl ester of synthetic highly branched saturated fatty acid]; glycerin, trimethylolpropane, trimethylolethane , diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, sorbitol, mannitol and other trihydric or higher alcohols; these trihydric or higher alcohols and lactones such as ε-caprolactone polylactone polyols added with; 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, hydrogenated bisphenol A and hydrogenated bisphenol F, etc. Cyclic polyolization having a nurate structure such as tris(hydroxyalkyl)isocyanurate, ε-caprolactone-modified tris(hydroxyalkyl)isocyanurate, tris(hydroxyethyl)isocyanurate compounds; and the like.
The above polyhydric alcohols may be used alone or in combination of two or more.

Examples of the polybasic acid include aromatic polybasic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, and diphenylmethane-4,4′-dicarboxylic acid, and anhydrides thereof. ; alicyclic dicarboxylic acids such as hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrophthalic acid, tetrahydrophthalic acid and their anhydrides; adipic acid, sebacic acid, suberic acid, succinic acid, glutaric acid, maleic acid, chloro Aliphatic polybasic acids such as maleic acid, fumaric acid, dodecanedioic acid, pimelic acid, azelaic acid, itaconic acid, citraconic acid and dimer acid, and their anhydrides; lower alkyls such as methyl and ethyl esters of these dicarboxylic acids; Esters; trivalent or higher polybasic acids such as trimellitic acid, trimellitic anhydride, pyromellitic acid, pyrometic anhydride, trimesic acid, methylcyclohexene tricarboxylic acid, tetrachlorohexene polybasic acid and anhydrides thereof; .
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 100 to 210 mgKOH/g, from the viewpoint of the finished appearance of the coating film to be formed.

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

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

When the high solid content coating composition of the present invention contains the hydroxyl group-containing polyester resin (F), the content thereof is determined from the viewpoint of recoat adhesion, curability and finished appearance of the coating film to be formed. Based on 100 parts by mass of resin solid content of the high solid content coating composition, it is preferably in the range of 1 to 30 parts by mass, more preferably 2 to 20 parts by mass, 3 to 15 parts by mass. is more preferred.

Examples of the pigment include coloring pigments, luster pigments, and extender pigments. The pigments may be used alone or in combination of two or more.
Examples of coloring pigments include titanium oxide, zinc white, carbon black, cadmium red, molybdenum red, chrome yellow, chromium oxide, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, threne pigments, Perylene pigments and the like can be mentioned.
Examples of luster pigments include aluminum powder, mica powder, mica powder coated with titanium oxide, and the like.
Examples of extender pigments include talc, clay, kaolin, baryta, 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 paint composition of the present invention is used as a clear paint and contains a pigment, the amount of the pigment to be blended should be an amount that does not impair the transparency of the resulting paint film. Preferably, for example, it is usually in the range of 0.1 to 20% by mass, particularly 0.3 to 10% by mass, and more particularly 0.5 to 5% by mass, relative to the total solid content in the high solid content coating composition. is preferred.

In addition, when the high solid content paint composition of the present invention is used as a colored paint and contains a pigment, the blending amount of the pigment is, relative to the total solid content in the high solid content paint composition, It is preferably in the range of usually 1 to 200% by mass, particularly 2 to 100% by mass, more particularly 5 to 50% by mass.

Organic solvents include, for example, toluene, xylene, aromatic solvents such as "Swasol 1000" (manufactured by Cosmo Oil Co., Ltd., trade name, high boiling point petroleum solvents); 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 , ester solvents such as propylene glycol monomethyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone and methyl amyl ketone; alcohol solvents such as isopropanol, n-butanol, isobutanol and 2-ethylhexanol. can. These can be used individually or in combination of 2 or more types.

Conventionally known thickeners can be used, for example, clay minerals (e.g., metal silicates, montmorolilonite), acrylics (e.g., acrylic acid ester or methacrylic acid ester in the molecule). including structures consisting of polymers and oligomers), polyolefins (e.g. polyethylene, polypropylene, etc.), amides (higher fatty acid amides, polyamides, oligomers, etc.), polycarboxylic acids (having at least two or more carboxyl groups in the molecule derivatives), cellulose (including various derivatives such as nitrocellulose, acetylcellulose, cellulose ether, etc.), urethane (polymers, oligomers, etc. containing a urethane structure in the molecule), urea (a polymer containing a urea structure in the molecule, oligomers, etc.), urethane urea (polymers, oligomers, etc. containing a urethane structure and a urea structure in the molecule), and the like.

As the ultraviolet absorber, conventionally known ones can be used, and examples include ultraviolet absorbers such as benzotriazole-based absorbers, triazine-based absorbers, salicylic acid derivative-based absorbers, and benzophenone-based absorbers. can. These can be used alone 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 is usually 0.1 to 10% by mass with respect to the total solid content in the high solid content coating composition. , particularly 0.2 to 5% by weight, more particularly 0.3 to 3% by weight.

As the light stabilizer, conventionally known ones can be used, and examples thereof include hindered amine light stabilizers.
As the hindered amine light stabilizer, a hindered amine light stabilizer with low basicity can be preferably used from the viewpoint of pot life. Examples of such hindered amine light stabilizers include acylated hindered amines and amino ether hindered amines. , manufactured by BASF) and the like.

The high solid content paint composition of the present invention may be either a one-component paint or a multi-component paint, but it has excellent productivity without a paint mixing process, and can simplify maintenance of coating machines. From this point of view, it is preferable to use a one-component paint.

The coating method of 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 atomization coating, and curtain coating. A wet coating film can be formed by the method of In these coating methods, static electricity may be applied as necessary. Among these, air spray coating or rotary atomization coating is particularly preferred. It is preferable that the coating amount of the present coating material is such that the cured film thickness is usually 10 to 60 μm, particularly 25 to 50 μm.

When air spray coating, airless spray coating, or rotary atomization coating is performed, the viscosity of the present coating is adjusted to a viscosity range suitable for the coating, usually Ford Cup No. 4 viscometer, at 20 ° C. 20 to 60 seconds, it is preferable to adjust the viscosity appropriately using a solvent such as an organic solvent and a thickener so that the viscosity range of 25 to 50 seconds in particular.

Curing of a wet coating film obtained by applying the present coating material to an object to be coated can be performed by heating, and the heating can be performed by a known heating means such as a hot air oven, an electric oven, and infrared induction heating. A drying oven such as an oven can be used. The heating temperature is not particularly limited, and is preferably in the range of 120 to 160°C, preferably 130 to 150°C. The heating time is not particularly limited, and is preferably in the range of 10 to 60 minutes, preferably 15 to 30 minutes.

Since the high-solids coating composition of the present invention can form a coating film having excellent recoat adhesion, curability and finished appearance, it can be suitably used as a topcoat top clearcoat. The present paint can be particularly suitably used as an automotive paint.

Method for Forming a Multi-Layer Coating Film As a method for forming a multi-layer coating film in which the present paint is applied as a topcoat top clear coat paint, for example, the following method can be preferably used.
Step (1): A step of applying an intermediate coating composition onto an object to be coated to form an intermediate coating film;
Step (2): A step of applying a base coat paint composition onto the intermediate coat film formed in step (1) to form a base coat paint film;
Step (3): A step of applying the high solid content coating composition of the present invention on the base coat film formed in the step (2) to form a clear coat film, and
Step (4): A method for forming a multi-layer coating film, including a step of heating and curing the intermediate coating film, the base coating film and the cleat coating film formed in the steps (1) to (3) at once.

The object to be coated is not particularly limited, and examples include the outer panel parts of automobile bodies such as passenger cars, trucks, motorcycles, and buses; automotive parts; the outer panel parts of household electrical appliances such as mobile phones and audio equipment. etc. can be mentioned. Among these, outer plate portions of automobile bodies and automobile parts are preferred.

Materials for these objects to be coated are not particularly limited. For example, metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, galvanized steel, zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel; polyethylene resin, polypropylene resin, acrylonitrile- Resins such as butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, plastic materials such as various FRP; inorganic materials such as glass, cement, concrete; wood ; fibrous materials such as paper and cloth; Among these, metal materials and plastic materials are preferred.

In addition, the surface of the object to be coated with a multilayer coating film includes the outer plate of an automobile body, automobile parts, household electrical appliances, and metal surfaces such as metal substrates such as steel plates that constitute these. , chromate treatment, composite oxide treatment, or other surface treatment may be applied.

A coating film may be further formed on the object which may or may not be surface-treated. For example, the article to be coated, which is the base material, may be subjected to a surface treatment, if necessary, and an undercoat film may be formed thereon. For example, when the object to be coated is an automobile body, the undercoat film can be formed using a known undercoat composition that is commonly used in the painting of automobile bodies.

The undercoat paint composition is usually applied for the purpose of imparting anticorrosion properties to an object to be coated.
As the undercoat composition for forming the undercoat film, for example, an electrodeposition paint, preferably a cationic electrodeposition paint, can be used.
Moreover, the undercoat film is preferably a cured coating film from the viewpoint of the finished appearance of the multilayer coating film to be formed.

As the intermediate coating composition, a known thermosetting intermediate coating composition for coating automobile bodies and the like can be used. As the intermediate coating composition, for example, a thermosetting coating containing a base resin having a cross-linkable functional group, a cross-linking agent, a color pigment and an extender pigment can be suitably used.
The intermediate coating composition is usually applied for the purpose of imparting smoothness, chipping resistance, and adhesion between coating films to the object to be coated.
Examples of the crosslinkable functional group of the base resin include carboxyl group, hydroxyl group and epoxy group.
Examples of types of the base resin include acrylic resins, polyester resins, alkyd resins and urethane resins.
Examples of the cross-linking agent include melamine resins, polyisocyanate compounds and blocked polyisocyanate compounds.
As the intermediate coating composition, either a water-based coating composition or an organic solvent-based coating composition may be used.
The amount of the intermediate coating composition to be applied is preferably such that the cured film thickness becomes 5 to 60 μm, more preferably 8 to 50 μm, and further preferably 10 to 40 μm. preferable.

As the base coat paint composition, a known thermosetting base coat paint composition for painting automobile bodies and the like can be used. As the base coat paint composition, for example, a thermosetting paint composition containing a base resin having a crosslinkable functional group, a crosslinking agent, a color pigment, a luster pigment and an extender pigment can be suitably used.
The above-mentioned base coat paint composition is usually applied for the purpose of imparting excellent design properties (eg, color, metallic feeling, gloss, etc.) to the object to be coated.
Examples of the crosslinkable functional group of the base resin include carboxyl group, hydroxyl group and epoxy group.
Examples of types of the base resin include acrylic resins, polyester resins, alkyd resins and urethane resins.
Examples of the cross-linking agent include melamine resins, polyisocyanate compounds and blocked polyisocyanate compounds.
As the base coat coating composition, either a water-based coating composition or an organic solvent-based coating composition may be used.
The coating amount of the base coat coating composition is preferably such that the cured film thickness is 5 to 40 μm, more preferably 6 to 35 μm, even more preferably 7 to 30 μm. .

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

Hereinafter, the present invention will be described more specifically with reference to Production Examples, Examples and Comparative Examples. However, the present invention is not limited by these. In each example, "parts" and "%" are based on mass unless otherwise specified. Also, the film thickness of the coating film is based on the cured coating film.

[1] Preparation of object to be coated A degreased and zinc phosphate-treated steel plate (JIS G3141, size 400 mm × 300 mm × 0.8 mm) was coated with a cationic electrodeposition paint “Electron GT-10” (product name: manufactured by Kansai Paint Co., Ltd.) , epoxy resin polyamine-based cationic resin using a blocked polyisocyanate compound as a curing agent) is electrodeposited so that the film thickness is 20 μm based on the cured coating film, and heated at 170 ° C. for 20 minutes to crosslink. An object to be coated was obtained by curing to form an electrodeposition coating film.

[2] Preparation of paint
Production of hydroxyl group-containing acrylic resin (A)
Production example 1
A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen inlet tube and a dropping device was charged with 27 parts of "Swasol 1000" (trade name, manufactured by Cosmo Oil Co., Ltd., an aromatic organic solvent) and propylene. Five parts of glycol monomethyl ether acetate were charged. While blowing nitrogen gas into the reaction vessel, the charged liquid was stirred at 150° C., and 20 parts of styrene, 32.5 parts of 2-hydroxypropyl acrylate, 46.2 parts of isobutyl methacrylate, 1.3 parts of acrylic acid and jitter were added thereto. A monomer mixture consisting of 3.2 parts of shariamyl peroxide (polymerization initiator) was dropped at a uniform rate over 4 hours. Then, the mixture was aged at 150° C. for 1 hour, cooled, and further diluted with 21 parts of isobutyl acetate to obtain a secondary hydroxyl group-containing acrylic resin (A′-1) solution having a solid concentration of 65% by mass. The obtained secondary hydroxyl group-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 2-4
In Production Example 1, secondary hydroxyl group-containing acrylic resins (A'-2) to (A'-4) having a solid content concentration of 65% were prepared in the same manner as in Production Example 1, except that the formulation composition was as shown in Table 1. ) to give a solution. Table 1 also shows the acid value, hydroxyl value, weight average molecular weight and glass transition temperature of each hydroxyl-containing acrylic resin.

Production example 5 for production of hydroxyl group-containing acrylic resin (G)
A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen inlet tube and a dropping device was charged with 27 parts of "Swasol 1000" (trade name, manufactured by Cosmo Oil Co., Ltd., an aromatic organic solvent) and propylene. Five parts of glycol monomethyl ether acetate were charged. While blowing nitrogen gas into the reaction vessel, the charged liquid was stirred at 150° C., and 20 parts of styrene, 41 parts of 2-hydroxypropyl acrylate, 22.7 parts of isobutyl methacrylate, 15 parts of methyl methacrylate, and 1.3 parts of acrylic acid were added thereto. and 2 parts of ditertiary mill peroxide (polymerization initiator) were added dropwise at a uniform rate over 4 hours. Then, the mixture was aged at 150° C. for 1 hour, cooled, and further diluted with 21 parts of isobutyl acetate to obtain a secondary hydroxyl group-containing acrylic resin (G′-1) solution having a solid concentration of 65% by mass. The obtained secondary hydroxyl group-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 6-8
In Production Example 5, secondary hydroxyl group-containing acrylic resins (G'-2) to (G'-4) having a solid content concentration of 65% were prepared in the same manner as in Production Example 5, except that the formulations were those shown in Table 2. ) to give a solution. Table 2 also shows the acid value, hydroxyl value, weight average molecular weight and glass transition temperature of each hydroxyl-containing acrylic resin.

Production example 9 for production of hydroxyl group-containing polyester resin (F)
A reactor equipped with a stirrer, reflux condenser, water separator and thermometer is charged with 79.1 parts hexahydrophthalic anhydride, 5 parts adipic acid, 52.1 parts neopentyl glycol and 25 parts trimethylolpropane. , at 230° C. for 6 hours, and then diluted with butyl acetate to obtain a hydroxyl group-containing polyester resin (F-1) solution having a solid concentration of 80%. The resulting 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 1,952.

Production Example 1 of High Solid Content Coating Composition
Secondary hydroxyl group-containing acrylic resin (A'-1) solution obtained in Production Example 1 84.6 parts (solid content 55 parts), "URIC H-30" (trade name, manufactured by Ito Oil Co., Ltd., solid content 100%, Hydroxyl value 155 to 165 mgKOH / g) 10 parts (solid content 10 parts), "Uban 20SE60" (trade name, Mitsui Chemicals, Inc., melamine resin, solid content 60%) 41.7 parts (solid content 25 parts), " Desmodur BL3575" (trade name, manufactured by Bayer Material Science, pyrazole-blocked polyisocyanate, solid content 100%) 10 parts (solid content 10 parts), "NACURE 5528" (trade name, manufactured by KING INDUSTRIES, dodecyl benzene sulfone Amine salt of acid, active ingredient 25%) 2 parts (solid content 0.5 part) and "BYK-300" (trade name, manufactured by BYK-Chemie, surface conditioner, active ingredient 52%) 0.4 part (solid content 0.2 parts) were uniformly mixed, and butyl acetate was added to adjust the solid content at the time of coating to 55%. got 1.

Examples 2-12 and Comparative Examples 1-9
High solid content paint composition No. 1 was used except that the formulation composition and the solid content at the time of coating were as shown in Tables 3 to 6 below. In the same manner as in No. 1, each high solid content coating composition No. 2-21 were obtained. The formulations shown in Tables 3 to 6 are based on the solid mass of each component.

Preparation of test plate (preparation of test plate for curability evaluation)
A high-solids coating composition No. 1 was applied onto a polypropylene plate. 1 was applied using a rotary atomizing electrostatic coating machine so that the cured coating film had a thickness of 35 μm, allowed to stand at room temperature for 7 minutes, and dried at 140° C. for 30 minutes in a hot air circulating drying oven. After heating for 1 minute, the test panel of Example 1 was produced by peeling off the resulting coating.

(Preparation of test plate for finish evaluation)
"ZU-10" (trade name, manufactured by Kansai Paint Co., Ltd., acrylic resin/melamine resin-based organic solvent-based intermediate coating) is applied onto the object to be coated in [1] above by rotary atomization electrostatic coating. Using a machine, electrostatic coating was applied so that the cured film thickness was 15 μm, and left to stand for 5 minutes to form an uncured intermediate coating film.
Next, "Soflex 420" (trade name, manufactured by Kansai Paint Co., Ltd., solvent-based topcoat base coat paint) is applied to the uncured intermediate coating film using a rotary atomizing electrostatic coating machine to dry the film. Electrostatic coating was applied to a thickness of 12 μm and allowed to stand for 3 minutes to form an uncured base coat film.
Next, high solids coating composition No. 1 was applied onto the uncured base coat coating film. 1 was electrostatically coated using a rotary atomization type electrostatic coating machine so as to give a dry film thickness of 35 μm to form a clear coating film, which was left for 7 minutes. Then, by heating at 140° C. for 30 minutes to heat cure the intermediate coating film, the base coating film and the clear coating film, a test panel of Example 1 was produced.

(Preparation of test plate for recoat adhesion evaluation)
"ZU-10" (trade name, manufactured by Kansai Paint Co., Ltd., acrylic resin/melamine resin-based organic solvent-based intermediate coating) is applied onto the object to be coated in [1] above by rotary atomization electrostatic coating. Using a machine, electrostatic coating was applied so that the cured film thickness was 15 μm, and left to stand for 5 minutes to form an uncured intermediate coating film.
Next, "Soflex 420" (trade name, manufactured by Kansai Paint Co., Ltd., solvent-based topcoat base coat paint) is applied to the uncured intermediate coating film using a rotary atomizing electrostatic coating machine to dry the film. Electrostatic coating was applied to a thickness of 12 μm and allowed to stand for 3 minutes to form an uncured base coat film.
Next, high solids coating composition No. 1 was applied onto the uncured base coat coating film. 1 was electrostatically coated using a rotary atomization type electrostatic coating machine so as to give a dry film thickness of 35 μm to form a clear coating film, which was left for 7 minutes. Then, the coating film was heated at 160° C. for 60 minutes to heat cure the intermediate coating film, the base coating film and the clear coating film, and allowed to stand at room temperature for 24 hours.
Next, "ZU-10" (trade name, manufactured by Kansai Paint Co., Ltd., acrylic resin / melamine resin organic solvent type intermediate coating) is applied on the heat-cured clear coat coating film by a rotary atomization type electrostatic coating machine. was electrostatically coated so as to give a cured film thickness of 15 μm and allowed to stand for 5 minutes to form an uncured intermediate coating film.
Next, "Soflex 420" (trade name, manufactured by Kansai Paint Co., Ltd., solvent-based topcoat base coat paint) is applied to the uncured intermediate coating film using a rotary atomizing electrostatic coating machine to dry the film. Electrostatic coating was applied to a thickness of 12 μm and allowed to stand for 3 minutes to form an uncured base coat film.
Next, high solids coating composition No. 1 was applied onto the uncured base coat coating film. 1 was electrostatically coated using a rotary atomization type electrostatic coating machine so as to give a dry film thickness of 35 μm to form a clear coating film, which was left for 7 minutes. Then, by heating at 130° C. for 20 minutes to heat cure the intermediate coating film, the base coating film and the clear coating film, a test panel of Example 1 was produced.

The above high solid content coating composition No. In the preparation of the test plate No. 1, the high solid content coating composition No. 1 was used. 1 to high solid content coating composition No. 1, respectively. 2 to 21, high solid content coating composition No. Test plates of Examples 2 to 12 and Comparative Examples 1 to 9 were prepared in the same manner as the test plate of No. 1.

Each test plate obtained 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)
Recoat adhesion: Make 100 squares of 2 mm x 2 mm on the coating film according to JIS K 5600-5-6 (1990) on the coating surface, attach an adhesive tape to the surface, peel it off rapidly, The number of cross-cut coating films remaining on the coated surface was evaluated. A and B are accepted.
A: Remaining number/total number = 100/100 with no edge chipping B: Remaining number/total number = 100/100 with edge chipping C: Remaining number/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 was measured under the following conditions (storage elastic modulus (E'), loss elastic modulus (E'') and loss tangent (tan δ )), and the crosslink density was measured by the following formula 1. A lower crosslink density indicates higher curability. A score of 700 or less is accepted.
・ Apparatus: dynamic viscoelasticity measuring device RSA3 (manufactured by TA Instruments)
・Measurement mode: non-resonant forced vibration method ・Temperature increase rate: 3.0°C/min
・Measurement interval: 12/min
・Frequency: 1.0Hz
・Temperature range: 30 to 180°C
Formula 1: Crosslink density = E'min/3RT
(Crosslinking density: mol/cm ³ , E′min: Pa, R (gas constant): J/mol·K, T (absolute temperature at peak top of loss tangent (tan δ)): K)

Finished Appearance: The finished 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: An index of smoothness, and the smaller the LW value, the higher the smoothness of the coated surface. A score of 15 or less is accepted.
SW value: An index of sharpness, and the smaller the SW value, the higher the sharpness of the coated surface. A score of 25 or less is accepted.

(* 1) “URIC H-52”: trade name, manufactured by Ito Oil Co., Ltd., solid content 100%, hydroxyl value 195 to 205 mgKOH / g,
(*2) “URIC H-57”: trade name, manufactured by Ito Oil Co., Ltd., solid content 100%, hydroxyl value 85-115 mgKOH/g,
(* 3) “URIC H-1824”: trade name, manufactured by Ito Oil Co., Ltd., solid content 100%, hydroxyl value 55 to 77 mgKOH / g,
(* 4) “URIC H-62”: trade name, manufactured by Ito Oil Co., Ltd., solid content 100%, hydroxyl value 245 to 275 mgKOH / g,
(*5) Flaxseed oil: manufactured by Summit Oil Co., Ltd., solid content 100%,
(*6) “NACURE 4167”: trade name, manufactured by KING INDUSTRIES, triethylamine salt of alkylphosphoric acid, active ingredient 25%.

Although the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications are possible based on the technical idea of the present invention.
For example, the configurations, methods, steps, shapes, materials, numerical values, etc., given in the above-described embodiments and examples are merely examples, and different configurations, methods, steps, shapes, materials, numerical values, etc., may be used if necessary. may be used.
Also, the configurations, methods, steps, shapes, materials, numerical values, etc. of the above-described embodiments can be combined with each other without departing from the gist of the present invention.

Claims (5)

(A) a hydroxyl group-containing acrylic resin having a weight average molecular weight within the range of 3,000 to 10,000 and a hydroxyl value within the range of 130 to 220 mgKOH/g, (B) castor oil, (C) a melamine resin and (D) A high-solids coating composition containing a catalyst and having a solid content of 50% by mass or more during coating , wherein the hydroxyl-containing acrylic resin (A) contains a secondary hydroxyl group. A high-solids coating composition containing an acrylic resin (A') . The high-solids coating composition according to claim 1, wherein the castor oil (B) has a hydroxyl value in the range of 80 to 230 mgKOH/g. The high solids coating composition according to claim 1 or 2 , wherein the catalyst (D) comprises a sulfonic acid catalyst (D-1). 4. The high-solids coating composition according to any one of claims 1 to 3 , further comprising a blocked polyisocyanate compound (E). Step (1): A step of applying an intermediate coating composition onto an object to be coated to form an intermediate coating film;
Step (2): A step of applying a base coat paint composition onto the intermediate coat film formed in step (1) to form a base coat paint film;
Step (3): The high solid content coating composition according to any one of claims 1 to 4 is applied onto the base coat film formed in the step (2) 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) all at once;
A method for forming a multilayer coating film comprising: