JP3951256B2 - Coating method - Google Patents

Description

【００４６】
表１において、「ユーバン２８−６０」（三井東圧（株）製、商品名）は、架橋剤のｎ−ブチルエーテル化メラミン樹脂（トリアジン核を基準に１〜３核体、数平均分子量１，８００）である。また、「アルミペースト７６７９ＮＳ」（東洋アルミニウム（株）製、商品名）は、メタリック顔料のりん片状アルミニウムである。
【００４７】
製造例５ クリヤー塗料の調製
「マジクロンＫＩＮＯ＃１００１Ｔ２」（関西ペイント（株）製、商品名、カルボキシル基含有アクリル樹脂及びエポキシ基含有化合物を含有する「酸−エポキシ型塗料」）を、「ソルベッソ＃１００」（エッソ石油（株）製、商品名、芳香族炭化水素系溶剤）で粘度２２秒（フォードカップ＃４／２０℃）に調整して、クリヤー塗料ｅを得た。
【００４８】
実施例１〜２及び比較例１〜２
製造例１で得た被塗物に、着色塗料を膜厚が硬化塗膜で１５〜２０μｍになるようにスプレー塗装し、室温で５分放置してから、該塗面にクリヤー塗料を膜厚が硬化塗膜で４５〜５０μｍになるようにスプレー塗装し、室温で５分放置してから、１４０℃で３０分加熱して該両塗膜を同時に硬化せしめた。
【００４９】
次に、これらの塗装工程により得られた複層塗膜の性能試験を、下記方法により、調べた。
【００５０】
試験方法
仕上り外観：塗膜を、目視により、次の基準に基づいて評価した。○は平滑性、ツヤ感じが良好で外観に優れることを、△は平滑性、ツヤ感じがやや不良で外観に劣ることを、×は平滑性、ツヤ感じが不良で外観が非常に劣ることを、それぞれ示す。
【００５１】
モドリ現象：「アルコープＬＭＲ２００」（関西ペイント（株）製、商品名、レーザー式メタリック測定器）により、測定して得たＩＶ値で表した。この値が高い程、耐モドリ性が良好であることを示す。
【００５２】
耐チッピング性：「グラベロメータ」（Ｑパネル社製、商品名、飛石試験機）を使用し、７号砕石５００ｇを塗面に対して４５°の角度で、−２０℃において、エアー圧０．３Ｍｐａで吹き付けて塗膜に衝撃を与える。ついで、その塗面に粘着セロハンテープを貼付し、それを急激に剥離した後の、衝撃による塗膜の剥離状態を調べ、次の基準で評価した。○は塗膜剥離が殆ど認められず、耐チッピング性が優れることを、△は塗膜剥離が少し認められ、耐チッピング性が劣ることを、×は塗膜剥離が多く認められ、耐チッピング性が非常に劣ることを、それぞれ示す。
【００５３】
下記表２に、使用塗料及び塗膜性能の試験結果を示す。
【００５４】
【表２】

【００５５】
【発明の効果】
（１）本発明方法で使用する着色塗料は噴霧塗装時の微粒化が改良されており、塗膜の平滑性を向上させることができた。
【００５６】
（２）該着色塗料塗膜を硬化させることなしに該塗面にクリヤー塗料を塗装してから加熱して同時に硬化させても、該両塗膜の混層が全く認められず、モドリ現象が解消され仕上がり外観が向上した。
【００５７】
（３）本発明方法により得られた複層塗膜の耐チッピング性が改善された。
【００５８】
（４）クリヤー塗料として「酸−エポキシ型塗料」を用いた塗装系においても、塗膜の平滑性が優れ、モドリ現象が解消され、しかも耐チッピング性も良好であった。
【００５９】
（５）本発明で使用する着色塗料において、水酸基含有ポリエステル樹脂は水酸基含有アクリル樹脂との相溶性が優れているので、両樹脂の特性を十分に発揮せしめることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel coating film forming method.
[0002]
[Prior art]
A so-called two-coat one-bake (hereinafter referred to as “below”) is applied to an object to be coated with a colored paint that is a solid color paint or a metallic paint, a clear paint is applied to the uncured coating surface, and both these coating films are then heat-cured. Forming a multilayer coating film by a method called “2C1B” is widely adopted as a top coating method for automobile outer plates, electrical appliances and the like. Further, as this colored paint, a thermosetting paint mainly composed of a hydroxyl group-containing polyester resin, a crosslinking agent and a colored pigment is used. Conventionally, the introduction of a hydroxyl group into the hydroxyl group-containing polyester resin has been carried out by using a trihydric or higher polyhydric alcohol such as trimethylolethane or trimethylolpropane as a part of the polyhydric alcohol component.
[0003]
However, the colored paint using such a hydroxyl group-containing polyester resin is inferior in smoothness of the coating film due to insufficient atomization at the time of spray coating, and after the clear paint is applied to the uncured coating surface. When heated, the two coating films are mixed to easily cause a mottle phenomenon, and the obtained multilayer coating film has defects that the chipping resistance is not sufficient. Such a mist phenomenon is particularly prominent in a 2C1B system coating system using a so-called “acid-epoxy type paint” which is a paint containing a carboxyl group-containing resin and an epoxy group-containing compound as a clear paint.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a method capable of forming a multilayer coating film excellent in finished appearance, smoothness, chipping resistance, and the like by applying a colored paint and a clear paint in a 2C1B system.
[0005]
[Means for Solving the Problems]
This inventor earnestly researched in order to eliminate the defect of the said prior art in the case of coating the thermosetting coloring paint and clear paint containing a hydroxyl-containing polyester resin by 2C1B system, and forming a multilayer coating film. As a result, by using tris (2-hydroxyethyl) isocyanurate for at least part of the polyhydric alcohol component of the raw material for preparing the hydroxyl group-containing polyester resin used in the colored paint, It has been found that the above object can be achieved by sufficient atomization, excellent smoothness of the coating film, no moist phenomenon, and sufficient chipping resistance of the obtained multilayer coating film. The invention has been completed.
[0006]
That is, the present invention is a method of forming a multilayer coating film by applying a colored paint and a clear paint to an object to be coated by the 2C1B method, and the colored paint contains a base resin, a crosslinking agent and a color pigment. The base resin is a hydroxyl group-containing polyester resin in which a part or all of the starting polyhydric alcohol component is tris (2-hydroxyethyl) isocyanurate.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the method of the present invention will be described in more detail.
[0008]
Examples of the object to be coated in the method of the present invention include a metal or plastic object to be coated such as an automobile outer plate and an electric appliance. The object to be coated is used after being subjected to a chemical conversion treatment or a washing treatment, if necessary. In addition, it is possible to suitably use a material in which an undercoat paint such as a cationic electrodeposition paint is applied to the object to be coated, and a material in which an undercoat and an intermediate paint are applied to the object to be coated.
[0009]
The colored paint in the present invention is a paint that is applied to the surface to be coated prior to the clear paint, and is mainly composed of a hydroxyl group-containing polyester resin that is a base resin, a crosslinking agent, and a colored pigment, and these are usually mixed in an organic solvent. This is a thermosetting liquid paint. Further, it is an essential requirement that the polyester resin is tris (2-hydroxyethyl) isocyanurate as at least a part of the polyhydric alcohol component for preparing the polyester resin.
[0010]
That is, the hydroxyl group-containing polyester resin used as the base resin of the colored paint is prepared by an esterification reaction between a polyhydric alcohol component containing tris (2-hydroxyethyl) isocyanurate and a polybasic acid component.
[0011]
Tris (2-hydroxyethyl) isocyanurate is a compound known per se. Moreover, the thing which carried out addition reaction of the lactone to some or all of the three hydroxyl groups of tris (2-hydroxyethyl) isocyanurate is also included. As tris (2-hydroxyethyl) isocyanurate, “Tanac” (trade name) manufactured by Nissan Chemical Industries, Ltd. can be mentioned as a commercial product.
[0012]
The polyhydric alcohol component used for the preparation of the polyester resin is composed only of tris (2-hydroxyethyl) isocyanurate, or tris (2-hydroxyethyl) isocyanurate and other polyhydric alcohols coexist. It does not matter.
[0013]
Other polyhydric alcohols are compounds having two or more hydroxyl groups in one molecule, such as ethylene glycol, propylene glycol, butylene glycol, hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol. Glycerin, trimethylolethane, trimethylolpropane, pentaerythritol and the like.
[0014]
In the polyhydric alcohol component, the constituent ratio of both components of tris (2-hydroxyethyl) isocyanurate and other polyhydric alcohol can be arbitrarily selected according to the purpose, for example, based on the total hydroxyl molar amount of both components. , Tris (2-hydroxyethyl) isocyanurate is 1 to 100 mol%, preferably 5 to 70 mol%, more preferably 10 to 50 mol%, and other polyhydric alcohols 99 to 0 mol%, preferably 95 to A suitable range is 30 mol%, more preferably in the range of 90 to 50 mol%.
[0015]
In the preparation of the polyester resin, the polybasic acid component that reacts with the polyhydric alcohol component is a compound having two or more carboxyl groups in one molecule, such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, Examples include adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, hexahydrophthalic acid, het acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, and anhydrides thereof.
[0016]
The hydroxyl group-containing polyester resin is obtained by esterifying a polyhydric alcohol component containing tris (2-hydroxyethyl) isocyanurate and a polybasic acid component. Specifically, these components are obtained by reacting at a temperature of 100 to 200 ° C. for 1 to 24 hours in the presence or absence of an organic solvent. Examples of the organic solvent include hydrocarbon solvents such as hexane, heptane, xylene, toluene, and cyclohexane; ester solvents such as methyl acetate, ethyl acetate, ethylene glycol monomethyl ether, and diethylene glycol monomethyl ether; isopropyl ether, ethylene glycol Examples include ether solvents such as monomethyl ether and diethylene glycol monobutyl ether; alcohol solvents such as ethyl alcohol, butyl alcohol and hexyl alcohol; ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, isophorone and acetophenone.
[0017]
The hydroxyl group-containing polyester resin thus prepared has a hydroxyl value of 30 to 300 mgKOH / g, particularly 60 to 250 mgKOH / g, an acid value of 0 to 30 mgKOH / g, particularly 2 to 10 mgKOH / g, and a number average molecular weight of 500 to 20. In the range of 1,000 to 8,000.
[0018]
Examples of the crosslinking agent in the colored paint include a melamine resin capable of forming a colored coating film that is crosslinked and cured by heating with the polyester resin.
[0019]
Examples of the melamine resin include partially etherified melamine obtained by etherifying a part of methylol group of methylolated melamine with monohydric alcohol having 1 to 8 carbon atoms, or fully etherified melamine obtained by etherifying all of methylol groups. Resins and the like are mentioned, and these are preferably 1 to 5 nuclei based on triazine nuclei and having a number average molecular weight of 300 to 2,000. Further, it may be a melamine resin in which methylol groups and / or imino groups remain.
[0020]
The blending ratio of the polyester resin and the crosslinking agent in the colored paint can be arbitrarily selected according to the purpose. For example, the polyester resin is 50 to 90% by weight, particularly 65 to 80% based on the total solid weight of the two components. The weight percent and the crosslinking agent are preferably in the range of 50 to 10 weight percent, particularly 35 to 20 weight percent.
[0021]
In the colored paint, the color pigment blended with the polyester resin and the crosslinking agent includes a solid color pigment, a metallic pigment exhibiting a metallic feeling or interference color, and the like.
[0022]
Examples of solid color pigments include inorganic pigments such as titanium oxide, zinc white, carbon black, cadmium red, molybdenum red, chromium yellow, chromium oxide, Prussian blue, cobalt blue; azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments And organic pigments such as selenium pigments and perylene pigments, and the like include flaky aluminum, mica, mica coated with a metal oxide, mica-like iron oxide, and the like as metallic pigments.
[0023]
The colored paint used in the method of the present invention can be prepared by dissolving or dispersing the polyester resin, the crosslinking agent and the color pigment in an organic solvent. Examples of the organic solvent include hydrocarbon solvents such as hexane, heptane, xylene, toluene, and cyclohexane; ester solvents such as methyl acetate, ethyl acetate, ethylene glycol monomethyl ether, and diethylene glycol monomethyl ether; isopropyl ether, ethylene glycol And ether solvents such as monomethyl ether and diethylene glycol monobutyl ether; alcohol solvents such as ethyl alcohol, butyl alcohol and hexyl alcohol; ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, isophorone and acetophenone;
[0024]
In the present invention, a hydroxyl group-containing acrylic resin can be used in combination with the polyester resin as a base resin for the colored paint.
[0025]
As a hydroxyl group-containing acrylic resin, an acrylic ester alkyl ester monomer and a hydroxyl group-containing monomer, if necessary, an alkoxy ester monomer, an amino acrylic monomer, an acrylamide monomer, a carboxyl group-containing A resin obtained by polymerizing by a conventional method using a monomer, a glycidyl group-containing monomer, other monomers, and the like can be used.
[0026]
An acrylic acid alkyl ester monomer is a monoesterified product of (meth) acrylic acid and a monohydric alcohol having 1 to 22 carbon atoms. For example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl Examples include methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate, octyl acrylate, octyl methacrylate, lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, and 2-ethylhexyl methacrylate. A hydroxyl group-containing monomer is a compound having one or more hydroxyl groups and polymerizable unsaturated bonds in one molecule, such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, etc. And monoesterified products of glycols having 2 to 20 carbon atoms and (meth) acrylic acid.
[0027]
Furthermore, the alkoxyester monomer is (meth) acrylic acid and an alkoxyester having 2 to 18 carbon atoms. For example, methoxybutyl acrylate, methoxybutyl methacrylate, methoxyethyl acrylate, methoxyethyl methacrylate and the like are aminoacrylic monomers. Examples of the monomer include N, N-dimethylaminoethyl acrylate, N, N-dimethylaminoethyl methacrylate, N, N-diethylaminoethyl acrylate, N, N-diethylaminoethyl methacrylate, Nt-butylaminoethyl acrylate, Examples of acrylamide monomers include Nt-butylaminoethyl methacrylate, N, N-dimethylaminopropyl acrylate, N, N-dimethylaminopropyl methacrylate, and the like. Methacrylamide, N-methylacrylamide, N-methylmethacrylamide, N-ethylacrylamide, N-ethylmethacrylamide, N-butylacrylamide, N-butylmethacrylamide, N-dimethylacrylamide, N-dimethylmethacrylamide, etc. are carboxyl The group-containing monomer is a compound other than the above having at least one polymerizable unsaturated bond in one molecule, such as monocarboxylic acids such as acrylic acid and methacrylic acid, maleic acid, itaconic acid, and fumaric acid. As glycidyl group-containing monomers, for example, glycidyl acrylate, glycidyl methacrylate, and the like as other monomers include dicarboxylic acids such as mesaconic acid and the like, and anhydrides and half-esterified products thereof, or modified products thereof. For example, styrene, α-methylstyrene, vinyl Nyltoluene, acrylonitrile, vinyl acetate, vinyl chloride and the like can be mentioned.
[0028]
Such a hydroxyl group-containing acrylic resin has a hydroxyl value of 20 to 200 mgKOH / g, particularly 40 to 150 mgKOH / g, an acid value of 0 to 80 mgKOH / g, particularly 4 to 40 mgKOH / g, and a number average molecular weight of 2,000 to 100,000. In particular, the range of 4,000 to 60,000 is preferable.
[0029]
The amount of the acrylic resin used is suitably in the range of 0 to 70% by weight, particularly 10 to 60% by weight, based on the total solid weight with the polyester resin.
[0030]
Examples of the clear paint used in the method of the present invention include paints known per se. For example, a thermosetting paint mainly composed of a base resin, a crosslinking agent and an organic solvent is suitable.
[0031]
As the base resin, for example, one or two selected from acrylic resins, vinyl resins, polyester resins, alkyd resins, urethane resins and the like having a crosslinkable functional group (for example, hydroxyl group, epoxy group, carboxyl group, alkoxysilane group, etc.) A mixture of seeds or more can be mentioned. The crosslinking agent for crosslinking and curing the base resin is, for example, selected from alkyl etherified melamine resin, urea resin, guanamine resin, polyisocyanate compound, block polyisocyanate compound, epoxy group-containing compound, carboxyl group-containing compound, etc. 1 type, or 2 or more types of mixtures which are mentioned. The amount of the base resin and the cross-linking agent component used is preferably 50 to 90% by weight for the base resin and 50 to 10% by weight for the cross-linking agent based on the total weight of both components. Of these, the “acid-epoxy type paint” is preferably formed using the carboxyl group-containing resin of the base resin and the epoxy group-containing compound of the crosslinking agent.
[0032]
Examples of the organic solvent include hydrocarbon solvents such as hexane, heptane, xylene, toluene, and cyclohexane; ester solvents such as methyl acetate, ethyl acetate, ethylene glycol monomethyl ether, and diethylene glycol monomethyl ether; isopropyl ether, ethylene glycol And ether solvents such as monomethyl ether and diethylene glycol monobutyl ether; alcohol solvents such as ethyl alcohol, butyl alcohol and hexyl alcohol; ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, isophorone and acetophenone;
[0033]
In addition, the clear pigment can be blended with the color pigment or the like to such an extent that the transparency of the clear coating film is not hindered.
[0034]
The method of the present invention is, for example, applied to a metal or plastic article to be coated such as an automobile outer plate, directly or undercoating with an undercoating paint or an undercoating paint such as a cationic electrodeposition coating, and an intermediate coating, and then curing. Apply a colored paint, if necessary, leave at room temperature for 1 to 20 minutes, then apply a clear paint on the uncured colored paint coating surface, if necessary, leave at room temperature for 1 to 20 minutes, It is carried out by heating at 180 ° C., preferably about 120 to 160 ° C. for about 10 to 40 minutes, so that the two coating films are simultaneously crosslinked and cured.
[0035]
In the method of the present invention, the colored coating is adjusted to a viscosity of 12 to 20 seconds (Ford Cup # 4/20 ° C.) and a solid content of 15 to 50% by weight, airless spray, air spray, electrostatic It is preferable to coat the article to be coated such that the film thickness is about 10 to 50 μm by a method such as painting.
[0036]
In addition, the clear coating is adjusted to a viscosity of 15 to 40 seconds (Ford Cup # 4/20 ° C.) and a solid content of 30 to 65% by weight by airless spray, air spray, electrostatic coating, etc. It is preferable to coat the uncured colored coating surface so that the film thickness is about 20 to 80 μm as a cured coating film.
[0037]
【Example】
Hereinafter, the present invention will be described more specifically with reference to production examples, examples and comparative examples. Unless otherwise specified, “parts” and “%” mean “parts by weight” and “% by weight”, respectively.
[0038]
Production Example 1 Preparation of coating material A steel plate that has been subjected to chemical conversion treatment with phosphate at a size of 150 × 100 × 0.8 mm is electrodeposited with a polyamine-modified epoxy resin cationic electrodeposition coating, heat-cured, and then polyester resin A melamine resin-based intermediate coating was applied and heat-cured to obtain an article to be coated.
[0039]
Production Example 2 Preparation of hydroxyl-containing polyester resin for colored paint (A-1): 0.7 mol of hexahydrophthalic anhydride, 0.727 mol of 1,6-hexanediol and tris (2-hydroxyethyl) isocyanurate for Examples 0.273 mol was heated to 230 ° C. in the presence of the esterification catalyst dibutyltin oxide (0.025 phr) and maintained for 1 hour, then xylene was added and water was distilled off at the same temperature for about 6 hours. The mixture was refluxed to obtain a hydroxyl group-containing polyester resin (A-1). This polyester resin had a hydroxyl value of 194 mgKOH / g, an acid value of 2 mgKOH / g, and a number average molecular weight of 1,000.
[0040]
(A-2): 0.875 mol of hexahydrophthalic anhydride for examples, 0.727 mol of 1,6-hexanediol and 0.273 mol of tris (2-hydroxyethyl) isocyanurate were mixed with dibutyltin as an esterification catalyst. After heating to 230 ° C. in the presence of oxide (0.025 phr) and maintaining for 1 hour, xylene was added, and the mixture was refluxed while distilling off water at the same temperature for about 6 hours. ) This polyester resin had a hydroxyl value of 106 mgKOH / g, an acid value of 2 mgKOH / g, and a number average molecular weight of 1,500.
[0041]
(A-3): 0.7 mol of hexahydrophthalic anhydride for comparison, 0.727 mol of 1,6-hexanediol and 0.273 mol of trimethylolpropane were added to dibutyltin oxide (0.025 phr) as an esterification catalyst. The mixture was heated to 230 ° C. in the presence of and maintained for 1 hour, and then xylene was added and refluxed while distilling off water at the same temperature for about 6 hours to obtain a hydroxyl group-containing polyester resin (A-3). This polyester resin had a hydroxyl value of 224 mgKOH / g, an acid value of 2 mgKOH / g, and a number average molecular weight of 1,300.
[0042]
(A-4): 0.875 mol of hexahydrophthalic anhydride for comparison, 0.727 mol of 1,6-hexanediol and 0.273 mol of trimethylolpropane were converted into dibutyltin oxide (0.025 phr) as an esterification catalyst. The mixture was heated to 230 ° C. in the presence of and maintained for 1 hour, and then xylene was added and refluxed while distilling off water at the same temperature for about 6 hours to obtain a hydroxyl group-containing polyester resin (A-4). The polyester resin had a hydroxyl value of 74 mgKOH / g, an acid value of 2 mgKOH / g, and a number average molecular weight of 2,000.
[0043]
Production Example 3 Preparation of Hydroxyl-Containing Acrylic Resin for Colored Paint Copolymerization as usual using a monomer mixture of methyl methacrylate / n-butyl acrylate / hydroxyethyl methacrylate / acrylic acid = 52/32/15/1 (weight ratio) Thus, a hydroxyl group-containing acrylic resin (B-1) was obtained. This acrylic resin had a hydroxyl value of 65 mgKOH / g, an acid value of 7.8 mgKOH / g, and a number average molecular weight of about 32,000.
[0044]
Production Example 4 Preparation of Colored Paint Each component is mixed based on the components and blending amounts (solid content, parts) described in Table 1, and adjusted to a viscosity of 13 seconds (Ford Cup # 4/20 ° C.) with a solvent (xylene). Thus, colored paints a, b, c and d were obtained.
[0045]
[Table 1]

[0046]
In Table 1, “Uban 28-60” (trade name, manufactured by Mitsui Toatsu Co., Ltd.) is an n-butyl etherified melamine resin (1-3 nuclei based on triazine nucleus, number average molecular weight 1, 800). "Aluminum paste 7679NS" (trade name, manufactured by Toyo Aluminum Co., Ltd.) is a metallic pigment flake-like aluminum.
[0047]
Production Example 5 Preparation of Clear Paint “Magicron KINO # 1001T2” (trade name, “acid-epoxy type paint” containing carboxyl group-containing acrylic resin and epoxy group-containing compound, manufactured by Kansai Paint Co., Ltd.) The viscosity was adjusted to 22 seconds (Ford Cup # 4/20 ° C.) with “100” (trade name, aromatic hydrocarbon solvent, manufactured by Esso Petroleum Corporation) to obtain a clear paint e.
[0048]
Examples 1-2 and Comparative Examples 1-2
The coated material obtained in Production Example 1 is spray-coated with a colored coating so that the film thickness is 15 to 20 μm as a cured coating film, and is left for 5 minutes at room temperature. Was spray-coated so that the thickness of the cured coating film was 45 to 50 μm, left at room temperature for 5 minutes, and then heated at 140 ° C. for 30 minutes to cure both coating films simultaneously.
[0049]
Next, the performance test of the multilayer coating film obtained by these coating processes was investigated by the following method.
[0050]
Test Method Finished Appearance: The coating film was visually evaluated based on the following criteria. ○ means smoothness and glossiness and good appearance, △ means smoothness and glossiness, slightly poor and poor appearance, × means smoothness and glossiness and poor appearance. , Respectively.
[0051]
Modli phenomenon: It was expressed as an IV value obtained by measurement using “Alcope LMR200” (trade name, laser-type metallic measuring device, manufactured by Kansai Paint Co., Ltd.). The higher this value, the better the anti-moisture resistance.
[0052]
Chipping resistance: Using “Gravelometer” (trade name, manufactured by Q Panel Co., Ltd., stepping stone testing machine), 500g of No. 7 crushed stone at an angle of 45 ° with respect to the coating surface at −20 ° C. and an air pressure of 0.3 Mpa Spray on to impact the coating. Next, an adhesive cellophane tape was affixed to the coated surface, and after peeling it abruptly, the peeled state of the coating film by impact was examined and evaluated according to the following criteria. ○ indicates almost no peeling of the coating film and excellent chipping resistance, Δ indicates that coating film peeling is slightly observed and chipping resistance is inferior, and × indicates that peeling of the coating film is frequently observed and chipping resistance Indicate that they are very inferior.
[0053]
Table 2 below shows the test results of the paint used and the coating film performance.
[0054]
[Table 2]

[0055]
【The invention's effect】
(1) The colored paint used in the method of the present invention has improved atomization at the time of spray coating, and can improve the smoothness of the coating film.
[0056]
(2) Even if a clear paint is applied to the coated surface without curing the colored paint film and then heated and cured at the same time, no mixed layer is observed between the two paint films, eliminating the phenomenon of modding. The finished appearance has been improved.
[0057]
(3) The chipping resistance of the multilayer coating film obtained by the method of the present invention was improved.
[0058]
(4) Even in a coating system using an “acid-epoxy type paint” as a clear paint, the smoothness of the coating film was excellent, the modding phenomenon was eliminated, and the chipping resistance was also good.
[0059]
(5) In the colored paint used in the present invention, since the hydroxyl group-containing polyester resin is excellent in compatibility with the hydroxyl group-containing acrylic resin, the characteristics of both resins can be sufficiently exhibited.

Claims (2)

A method for forming a multilayer coating film by coating a coating material with a colored coating and a clear coating in a two-coat one-bake method, wherein the colored coating contains a base resin, a cross-linking agent, and a coloring pigment. The resin is a hydroxyl group-containing polyester resin in which part or all of the starting polyhydric alcohol component is tris (2-hydroxyethyl) isocyanurate , and the clear paint contains a carboxyl group-containing resin and an epoxy group-containing compound A coating film forming method characterized by being a paint to be applied. The coating film forming method according to claim 1, wherein the colored paint uses, as a base resin, a hydroxyl group-containing acrylic resin in combination with the hydroxyl group-containing polyester resin.