TW202140154A - Method for forming multilayer coating film - Google Patents

Abstract

Provided is a method for forming a multilayer coating film that has good shock absorption and adhesion properties. In this method for forming a multilayer coating film, a primer coating composition is applied to an item to be coated to form an uncured primer coating film, an intermediate coating composition is applied on top of the obtained uncured primer coating film to form an uncured intermediate coating film, a base coating composition is applied on top of the obtained uncured intermediate coating film to form an uncured base coating film, a clear coating composition is applied on top of the obtained uncured base coating film to form an uncured clear coating film, and these uncured coating films are heated and cured. The primer coating composition includes a coating film forming resin, and the coating film forming resin includes 10 mass% or more of a polyolefin resin (A) in relation to the resin solid content of the coating film forming resin, 20 mass% or more of a polyurethane resin (B), and 5 mass% or more of a polyester resin (C).

Description

Multilayer coating film forming method

The present invention relates to a method for forming a multi-layer coating film including a coating primer coating composition.

Generally, a multi-layer coating film is provided on the surface of a coated object such as a car body. The above-mentioned multi-layer coating film is formed by sequentially forming multiple layers of coating films with various functions. The multi-layer coating film can protect the object to be coated and give a specific design at the same time. In the formation of the multi-layer coating film, primer coating is sometimes performed. The primer coating composition used in the primer coating may include, for example, a conductive primer coating composition and an anti-knock primer coating composition. The conductive primer coating composition coats resin members such as polyolefin (especially polypropylene). By coating the resin member with a conductive primer coating composition, conductivity can be imparted, and subsequent coatings such as electrostatic coating can be performed. In addition, in particular, resin members such as polyolefins have low polarity, but by coating the primer, the adhesion between the coating film formed by subsequent coating and the member can be improved.

The anti-knock primer coating composition is generally used for metal substrates. For example, the coating film that protects the surface of metal coatings such as car bodies, residential building materials, guardrails, and road signs may crack or peel due to the bouncing of stones that may occur when driving on the road. This phenomenon is generally called chipping. If water enters the cracked or peeled part of the coating, it will rust on the original surface of the coated object, resulting in corrosion of the coated object. In order to prevent the advancement of the above-mentioned knocking and the resulting corrosion, coating with a knock-resistant primer coating composition will be carried out.

The common point of the conductive primer coating composition and the anti-knock primer coating composition is that they are all primers that are coated before the formal coating. However, as described above, the functions required for the conductive primer coating composition and the knock-resistant primer coating composition are different from each other. In addition, since these primer coating compositions differ in coating objects and required functions, most of the coating forms are also different.

For example, Japanese Patent Application Laid-Open No. 2012-067197 (Patent Document 1) discloses a common coating composition that can be used for two purposes, a knock-resistant primer and a bumper primer. In addition, it is described that the common paint composition of Patent Document 1 contains a non-chlorinated polyolefin, a melamine resin, and an aqueous primer paint composition of a carbonate-based urethane resin (claims 1, 2, etc.). Prior art literature Patent literature

Patent Document 1: Japanese Patent Application Publication No. 2012-067197

The problem to be solved by the invention As described above, Patent Document 1 describes a common coating composition that can be used for two purposes of anti-knock primer and bumper primer. On the other hand, in recent years, from the viewpoint of further improving automobile fuel consumption, energy saving, and reducing carbon dioxide emissions, further weight reduction of automobile parts and the like is required. As one of the methods to reduce the weight of automobile parts, the thinning of parts can be exemplified. In order to ensure the strength of the thinned parts, the primer is required to have more excellent knock-out resistance (impact mitigation performance) and adhesion.

The subject of the present invention is to solve the above-mentioned technical problems. To be more specific, the subject of the present invention is to provide a method for forming a multi-layer coating film that has good impact mitigation performance and adhesion.

Means to solve the problem In order to solve the above-mentioned problems, the present invention provides the following aspects. [1] A method for forming a multi-layer coating film, comprising: The primer coating film formation step is to coat the primer coating composition on the object to be coated to form an unhardened primer coating film; The intermediate coating film forming step is to coat the intermediate coating composition on the obtained unhardened primer film to form an unhardened intermediate coating film; The base coating film formation step is to coat the base coating composition on the obtained unhardened intermediate coating film to form an unhardened base coating film; The step of forming a clear coating film is to apply a clear coating composition on the resulting unhardened base coating film to form an unhardened clear coating film; and The hardening step is to heat the obtained unhardened primer coating film, intermediate coating film, base coating film and clear coating film to harden them; The aforementioned primer coating composition includes a coating film forming resin; The coating film forming resin includes polyolefin resin (A), polyurethane resin (B) and polyester resin (C), The aforementioned polyolefin resin (A) has a resin solid content of 10% by mass or more relative to the resin solid content of the coating film forming resin, The aforementioned polyurethane resin (B) is 20% by mass or more of the resin solid content of the coating film forming resin, The said polyester resin (C) is 5 mass% or more with respect to the resin solid content of a coating film formation resin. [2] A method for forming a multi-layer coating film, including: The primer coating film formation step is to coat the primer coating composition on the object to be coated to form an unhardened primer coating film; The base coating film formation step is to coat the base coating composition on the obtained unhardened primer coating film to form an unhardened base coating film; The step of forming a clear coating film is to apply a clear coating composition on the resulting unhardened base coating film to form an unhardened clear coating film; and The hardening step is to heat the obtained unhardened primer coating film, base coating film and clear coating film to harden them; The aforementioned primer coating composition includes a coating film forming resin; The aforementioned coating film forming resin includes polyolefin resin (A), polyurethane resin (B), and polyester resin (C), The aforementioned polyolefin resin (A) has a resin solid content of 10% by mass or more relative to the resin solid content of the coating film forming resin, The aforementioned polyurethane resin (B) is 20% by mass or more of the resin solid content of the coating film forming resin, The said polyester resin (C) is 5 mass% or more with respect to the resin solid content of a coating film formation resin. [3] The method for forming a multi-layer coating film as described in [1] or [2], wherein the content of the polyester resin (C) is 20 relative to the resin solid content of the coating film forming resin contained in the primer coating composition Mass% or more and 70% by mass or less. [4] The method for forming a multi-layer coating film according to any one of [1] to [3] above, wherein the heating temperature in the curing step is in the range of 70 to 150°C. [5] The method for forming a multi-layer coating film according to any one of the above [1] to [4], wherein the polyester resin (C) is a condensation reaction product of an aromatic dicarboxylic acid and a polyhydric alcohol. [6] The method for forming a multi-layer coating film according to any one of [1] to [5] above, wherein the glass transition temperature of the polyester resin (C) is in the range of -50 to 20°C, The acid value is in the range of 1~50mgKOH/g, and The hydroxyl value is in the range of 10~200mgKOH/g. [7] The method for forming a multi-layer coating film according to any one of [1] to [6] above, wherein the primer coating composition further contains a conductive pigment (D). [8] The method for forming a multi-layer coating film according to any one of the above [1] to [7], wherein the polyester resin (C) contained in the primer coating composition is relative to the polyolefin resin (A) And the mass ratio of the total mass of the resin solid content of the polyurethane resin (B) is in the range of (C): ((A)+(B))=1:0.4~1:4.5. [9] The method for forming a multi-layer coating film according to any one of [1] to [8] above, wherein the object to be coated includes a steel plate part and a resin part. [10] The method for forming a multi-layer coating film according to any one of [1] to [9] above, wherein the primer coating composition is a solvent-based primer coating composition. [11] A primer coating composition comprising a coating film forming resin; The coating film forming resin includes polyolefin resin (A), polyurethane resin (B) and polyester resin (C), The aforementioned polyolefin resin (A) has a resin solid content of 10% by mass or more relative to the resin solid content of the coating film forming resin, The aforementioned polyurethane resin (B) is 20% by mass or more of the resin solid content of the coating film forming resin, The aforementioned polyester resin (C) is 20% by mass or more and 70% by mass or less relative to the resin solid content of the coating film forming resin; and The above-mentioned polyester resin (C) is a condensation reaction product of aromatic dicarboxylic acid and polyhydric alcohol. [12] Like the primer coating composition of [11], the primer coating composition further contains a conductive pigment (D).

Invention effect By using the above primer coating composition to form a multi-layer coating film, a multi-layer coating film with good impact mitigation performance and adhesion can be obtained. The above-mentioned multi-layer coating film forming method can be suitably used, for example, for a to-be-coated article including a steel plate part and a resin part.

The form used to implement the invention The method for forming a multi-layer coating film of this embodiment includes the following steps: The primer coating film formation step is to coat the primer coating composition on the object to be coated to form an unhardened primer coating film; The intermediate coating film forming step is to coat the intermediate coating composition on the obtained unhardened primer film to form an unhardened intermediate coating film; The base coating film formation step is to coat the base coating composition on the obtained unhardened intermediate coating film to form an unhardened base coating film; The step of forming a clear coating film is to apply a clear coating composition on the resulting unhardened base coating film to form an unhardened clear coating film; and The curing step is to heat the obtained uncured primer coating film, intermediate coating film, base coating film and clear coating film to harden them.

In addition, the method for forming a multi-layer coating film of this embodiment includes the following steps: The primer coating film formation step is to coat the primer coating composition on the object to be coated to form an unhardened primer coating film; The base coating film formation step is to coat the base coating composition on the obtained unhardened primer coating film to form an unhardened base coating film; The step of forming a clear coating film is to apply a clear coating composition on the resulting unhardened base coating film to form an unhardened clear coating film; and The curing step is to heat the obtained uncured primer coating film, base coating film, and clear coating film to harden them. Hereinafter, the coating composition used in each step is described.

Primer coating composition The primer coating composition used in the above-mentioned multi-layer coating film forming method contains a coating film forming resin. In addition, the coating film-forming resin is characterized by comprising polyolefin resin (A), polyurethane resin (B), and polyester resin (C). The aforementioned polyolefin resin (A) is relative to the resin of the coating film-forming resin. The solid content is 10% by mass or more, the resin solid content of the polyurethane resin (B) relative to the coating film forming resin is 20% by mass or more, and the polyester resin (C) is relative to the resin resin forming the coating film The solid content is 5% by mass or more.

(Polyolefin resin (A)) The above-mentioned polyolefin resin (A) is one type of coating film forming resin. By including the polyolefin resin (A) as the coating film forming resin, the adhesion to the resin part can be improved particularly in the coating material. Examples of polyolefin resins include radical homopolymers or copolymers of at least one olefin selected from ethylene, propylene, butene, methylbutene, isoprene, etc.; and, the above-mentioned olefins and vinyl acetate Free radical copolymers of esters, butadiene, acrylate, methacrylate, etc.

The polyolefin resin (A) may also be chlorinated. Examples of the polychlorinated olefin resin include chlorinated polyethylene, chlorinated polypropylene, chlorinated ethylene-propylene copolymer, and chlorinated ethylene-vinyl acetate copolymer. The polychlorinated olefin resin can also use what is obtained by graft-polymerizing a polymerizable monomer to a polychlorinated olefin. The above-mentioned polymerizable monomers for graft polymerization include, for example, alkyl (meth)acrylate, alkoxyalkyl (meth)acrylate, glycidyl (meth)acrylate, and epoxy (meth)acrylate. The adduct of propyl ester and monocarboxylic acid, hydroxyalkyl (meth)acrylate, acrylic acid, methacrylic acid, etc.

For the above-mentioned polyolefin resin (A), monomers having functional groups such as hydroxyl groups or acid groups (for example, polymerizable unsaturated dicarboxylic acids or anhydrides thereof) can also be graft-polymerized by known methods as needed. The above-mentioned polymerizable unsaturated dicarboxylic acid or its anhydride is a compound having one polymerizable unsaturated bond and two or more carboxyl groups or anhydrous groups in one molecule, such as maleic acid and its anhydride, itaconic acid and its Anhydride, citraconic acid and its anhydride, etc. The graft polymerization can be carried out by a method commonly used by those skilled in the art.

The weight average molecular weight of the polyolefin resin (A) is preferably 10,000 or more and 200,000 or less, preferably 30,000 or more and 150,000 or less.

As for the polyolefin resin (A), a commercially available product can also be used. Commercial products include, for example, SUPERCHLON 930 (manufactured by Nippon Paper Co., Ltd., non-volatile content 20%), SUPERCHLON 892L (manufactured by Nippon Paper Co., Ltd., non-volatile content 20%), and SUPERCHLON 822 (manufactured by Nippon Paper Co., Ltd., non-volatile content 20%) , SUPERCHLON 842LM (manufactured by Nippon Paper Co., Ltd., non-volatile content 20%), SUPERCHLON 851L (manufactured by Nippon Paper Co., Ltd., non-volatile content 20%), etc.

The content of the polyolefin resin (A) is 10% by mass or more with respect to the resin solid content of the coating film forming resin contained in the primer coating composition. The content of the polyolefin resin (A) is preferably 10% by mass or more and 60% by mass or less, preferably 10% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less. Since the content of the polyolefin resin (A) satisfies the above conditions, it has the advantage of obtaining good adhesion to the coated object.

(Polyurethane resin (B)) The above-mentioned polyurethane resin (B) is one of coating film forming resins. Since the polyurethane resin (B) is contained as the coating film forming resin, it has the advantage of good solvent resistance of the primer coating film. The polyurethane resin (B) can be prepared by, for example, reacting a polyol compound, a polyisocyanate compound, and a compound having an active hydrogen group in the molecule.

The polyol compound is not particularly limited as long as it has two or more hydroxyl groups. Specific examples of polyol compounds include the following: ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 3-methylpentanediol, 2-ethyl-1, 3-Hexanediol, trimethylolpropane, glycerin and other polyols; polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol and other polyether polyols; composed of adipic acid, sebacic acid, itaconic acid, Polyester polyols derived from dicarboxylic acids such as maleic anhydride, phthalic acid and isophthalic acid and glycols such as ethylene glycol, triethylene glycol, propylene glycol, butylene glycol, tripropylene glycol, and neopentyl glycol; Polycaprolactone polyol; polybutadiene polyol; polycarbonate polyol; polysulfide polyol. The above-mentioned polyol compounds may be used alone, or two or more of them may be used in combination. The number average molecular weight of the polyol compound is preferably 500 or more and 5000 or less.

The polyisocyanate compound is not particularly limited as long as it has two or more isocyanate groups in the molecule. Specific examples of polyisocyanate compounds include, for example, the following: hexamethylene diisocyanate, 2,2,4-trimethylhexane diisocyanate, lysine diisocyanate, and other aliphatic diisocyanates with 2 to 12 carbon atoms ; 1,4-cyclohexane diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, methylcyclohexyl diisocyanate, isopropylidene cyclohexyl-4,4'-di Alicyclic diisocyanates with 4 to 18 carbon atoms such as isocyanates; 2,4-stilbene diisocyanate, 2,6-stilbene diisocyanate, diphenylmethane-4,4'-diisocyanate, 1,5' -Naphthenic diisocyanate, toluidine diisocyanate, diphenylmethylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, stubborn diisocyanate, tetramethyl stubborn diisocyanate, 4,4'- Aromatic diisocyanates such as benzhydryl diisocyanate and 1,3-phenylene diisocyanate; lysine triisocyanate, triphenylmethane triisocyanate, 1,6,11-undecane triisocyanate, 1,8 -Triisocyanates such as diisocyanate-4,4-isocyanate methyl octane, 1,3,6-hexamethylene triisocyanate, and bicycloheptane triisocyanate. The polyisocyanate compound may be a dimer or trimer (trimer isocyanate bond) of the above-mentioned polyisocyanate compound, or it may be used by reacting the above-mentioned polyisocyanate compound with an amine to form a biuret. In addition, polyisocyanates having urethane bonds formed by reacting these polyisocyanate compounds with polyols can also be used.

The polyisocyanate compound is more preferably an aromatic aliphatic diisocyanate compound, such as isophorone diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, methyl Cyclohexylene diisocyanate, isopropylidene cyclohexyl-4,4'-diisocyanate, etc. By using the above isocyanate compound to prepare the polyurethane resin (B), there is an advantage that a coating film with good flexibility can be obtained through the balance between the hard segment and the soft segment.

Compounds having active hydrogen groups in the molecule can generally be used to block isocyanate groups in the above-mentioned polyisocyanate compounds. Specific examples of the compound include, for example, the following: monohydric alcohols such as methanol, ethanol, and diethylene glycol monobutyl ether; monocarboxylic acids such as acetic acid and propionic acid; monohydric mercaptans such as ethyl mercaptan; Primary amines such as amines and monoethanolamine; secondary amines such as diethylamine; oximes such as methyl ethyl ketoxime.

When preparing the polyurethane resin (B), a chain extender can also be used as needed. The chain extender is not particularly limited as long as it contains two or more active hydrogen groups, and examples thereof include polyamines and the like. Specific examples of polyamines include, for example, ethylene diamine, hexamethylene diamine, diethylene triamine, hydrazine, diamine, isophorone diamine, and the like.

When preparing the polyurethane resin (B), a monoisocyanate compound may be used as needed. Monoisocyanate compounds include, for example, methyl isocyanate, ethyl isocyanate, propyl isocyanate, butyl isocyanate, lauryl isocyanate, cyclohexyl isocyanate, phenyl isocyanate, isocyanate Toluene cyanate and so on.

The reaction method for producing polyurethane resin (B) can be a single-shot method in which each component reacts at once, or a multi-stage method in which each component is reacted step by step (a part of an active hydrogen-containing compound (such as a polymer Alcohol) reacts with polyisocyanate to form an NCO terminal prepolymer, and then reacts the remaining part of the active hydrogen-containing compound). The synthesis reaction of the polyurethane resin (B) is usually 40°C or higher and 140°C or lower, preferably 60°C or higher and 120°C or lower. In order to promote the reaction, tin-based catalysts such as dibutyltin laurate and tin octoate, or amine-based catalysts such as triethylenediamine, which are usually used in urethane reactions, can also be used. In addition, the above-mentioned reaction may be carried out for isocyanate in an inert organic solvent (for example, acetone, toluene, dimethylformamide, etc.), and a solvent may be added during the reaction or after the reaction.

A commercially available product can also be used for the polyurethane resin (B). Commercial products include, for example, NBC300 (manufactured by Sanyo Chemical Co., Ltd., non-volatile content 30%), NBC100 (manufactured by Sanyo Chemical Co., Ltd., non-volatile content 40%), IB-465 (manufactured by Sanyo Chemical Co., Ltd., non-volatile content 30%), IB-940 (manufactured by Sanyo Chemical Co., Ltd., non-volatile content 40%), IB-700 (manufactured by Sanyo Chemical Co., Ltd., non-volatile content 30%), etc.

The content of the polyurethane resin (B) is 20% by mass or more with respect to the resin solid content of the coating film forming resin contained in the primer coating composition. The content of the polyurethane resin (B) is preferably 20% by mass or more and 70% by mass or less, preferably 25% by mass or more and 60% by mass or less. Since the content of the polyurethane resin (B) satisfies the above conditions, it has the advantage of improving the knock resistance of the primer coating film.

In addition, the mass ratio of the resin solid content of the polyolefin resin (A) and the polyurethane resin (B) contained in the primer coating composition (=(A):(B)) is preferably 12.5: 87.5~ Within the range of 75:25, and preferably within the range of 16.7:83.3~67:33.

(Polyester resin (C)) Polyester resin (C) is one of coating film forming resins. By including polyester resin (C) as the coating film forming resin, the compatibility of the above-mentioned polyolefin (A) and polyurethane resin (B) can be improved, and the stability of the obtained primer coating composition can be improved sex.

The above-mentioned polyester resin (C) can be prepared by, for example, an esterification reaction or a transesterification reaction between a polybasic acid and a polyhydric alcohol. The polybasic acid is a compound having two or more carboxyl groups in one molecule, and examples include the following: terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 4,4'-diphthalic acid, and diphthalic acid Aromatic dicarboxylic acids such as phenylmethane-4,4'-dicarboxylic acid and their anhydrides; alicyclic dicarboxylic acids such as hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrophthalic acid, tetrahydrophthalic acid, etc. Anhydride; adipic acid, sebacic acid, suberic acid, succinic acid, glutaric acid, maleic acid, chloromaleic acid, fumaric acid, dodecanedioic acid, pimelic acid, azelaic acid, Ikon Aliphatic dicarboxylic acids and anhydrides such as acid, citraconic acid, dibasic acid, etc.; lower alkyl esters such as methyl and ethyl esters of these dicarboxylic acids; trimellitic acid, trimellitic anhydride, pyromellitic acid Acid, pyromellitic anhydride, trimesic acid, methylcyclohexene tricarboxylic acid, tetrachlorohexene tricarboxylic acid and its anhydride, etc. are polybasic acids with trivalent or more.

The polybasic acid used to prepare the polyester resin (C) preferably contains aromatic dicarboxylic acid. In addition, the polyester resin (C) is preferably a condensation reaction product of aromatic dicarboxylic acid and polyol. Preferably, isophthalic acid is contained as the above-mentioned aromatic dicarboxylic acid. By using the polybasic acid, there is an advantage that a primer coating film with better knock-out resistance can be obtained.

Polyols are compounds having two or more hydroxyl groups in one molecule, and examples include the following: 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, 2-butyl- 2-Ethyl-1,3-propanediol, 1,2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyl Trimethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol, 3-methyl-4,5-pentanediol, 2,2,4-trimethyl-1,3 -Pentylene glycol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, hydroxytrimethylacetic acid, neopentyl Diols such as glycol esters; polylactone diols obtained by adding lactones such as ε-caprolactone to these diols; ester diols such as bis(hydroxyethyl) terephthalate Class; bisphenol A alkylene oxide adducts, polyethylene glycol, polypropylene glycol, polybutylene glycol and other polyether glycols; glycerin, trimethylolpropane, trimethylolethane, diglycerin, triglycerin , 1,2,6-hexanetriol, neopentylerythritol, dineopentaerythritol, sorbitol, mannitol and other alcohols with more than 3 valences; add ε-caprolactone to these alcohols with more than 3 valences Polylactone polyols such as lactones; alicyclic polyols such as 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, etc. In addition, α-olefin epoxides such as propylene oxide and butylene oxide, monoepoxy compounds such as "Cardura E10" (trade name, manufactured by Japan Epoxy Resins, which synthesizes glycidyl esters of hyperbranched saturated fatty acids), etc. It reacts with an acid to introduce the obtained alcohol compound into the polyester resin.

The said polybasic acid and polyhydric alcohol may be used individually by 1 type, respectively, and may use 2 or more types together. In addition, the above-mentioned esterification reaction of polybasic acid and polyhydric alcohol can be carried out under the conditions commonly used by those skilled in the art.

The glass transition temperature of the above-mentioned polyester resin (C) is preferably -50°C or more and 20°C or less. Since the glass transition temperature of the polyester resin (C) is within the above range, a better compatibility improvement effect of the polyolefin resin (A) and polyurethane resin (B) can be obtained, and it can be used in the primer It has the advantages of better knock-out resistance and adhesion in the coating film.

The glass transition temperature can be measured, for example, by using a differential scanning calorimeter to detect the thermal change accompanying the glass transition of the resin. The differential scanning calorimeter that can be used includes, for example, DSC220C manufactured by Seiko Instruments Inc., etc.

The acid value of the polyester resin (C) is preferably 1 mgKOH/g or more and 50 mgKOH/g or less, preferably 5 mgKOH/g or more and 30 mgKOH/g or less. The hydroxyl value of the polyester resin (C) is preferably 10 mgKOH/g or more and 200 mgKOH/g or less, preferably 50 mgKOH/g or more and 150 mgKOH/g or less. Since the hydroxyl value and acid value of the polyester resin (C) are within the above ranges, there is an advantage that the physical properties of the obtained primer coating film can be adjusted to a more favorable range.

The SP value of the above-mentioned polyester resin (C) is preferably 9.5 or more and 11.0 or less. Here, the SP value is an abbreviation of solubility parameter, and it is a criterion of solubility. The larger the value of SP value, the higher the polarity, on the contrary, the smaller the value, the lower the polarity.

For example, the SP value can be actually measured using the following method [Reference: SUH, CLARKE, J.P.S.A-1, 5, 1671~1681 (1967)].

Weigh 0.5 g of organic solvent in a 100 ml flask, add 10 ml of acetone using a full pipette, and dissolve it with a magnetic stirrer, and use the obtained substance as a sample. To this sample, 50 ml of biuret was used to drop a poor solvent at a measurement temperature of 20°C, and the point at which turbidity occurred was used as the dropping amount. For the poor solvent system, ion-exchanged water was used as a high-SP poor solvent, and n-hexane was used as a low-SP poor solvent, and the cloud point measurement was performed respectively. The SP value δ of organic solvents can be given according to the following calculation formula. δ=(V _ml ^{1 /2} δ _ml +V _mh ^{1 /2} δ _mh )/(V _ml ^{1 /2} +V _mh ^{1 /2} ) V _m =V ₁ V ₂ /(φ ₁ V ₂ +φ ₂ V ₁ ) δ _m =φ ₁ δ ₁ +φ ₂ δ ₂ Vi: molecular volume of solvent (ml/mol) φi: volume fraction of each solvent at the cloud point δi: SP value of solvent ml: low SP poor solvent System mh: High SP poor solvent system

When the SP value of the polyester resin (C) is within the above range, the compatibility with the polyolefin resin (A) and the polyurethane resin (B) will be further improved in terms of the polarity of the polyester resin. Therefore, it has the advantage of achieving better knock resistance and adhesion.

Commercial products can also be used for the polyester resin (C). Commercial products include, for example, BECKOLITE 46-118 (manufactured by Dainippon Ink Chemical Industry Co., Ltd., non-volatile content 60%), BECKOLITE 46-119 (manufactured by Dainippon Ink Chemical Industry Co., Ltd., non-volatile content 60%), BECKOLITE M6205-50 (Made by Dainippon Ink Chemical Industry Co., Ltd., non-volatile content 50%), BECKOLITE M6401-52 (manufactured by Dainippon Ink Chemical Industry Co., Ltd., non-volatile content 52%), PRS-1015 (manufactured by Nitto Motor Co., Ltd., non-volatile content) 70%) etc.

The content of the polyester resin (C) is 5% by mass or more relative to the resin solid content of the coating film forming resin contained in the primer coating composition. The content of the polyester resin (C) is preferably 5% by mass or more and 70% by mass or less, preferably 20% by mass or more and 70% by mass or less. Since the content of the polyester resin (C) satisfies the above conditions, the compatibility with the polyolefin resin (A) and polyurethane resin (B) will be further improved. Therefore, the primer coating film has the advantages of improved knock-out resistance and adhesion.

In addition, the mass ratio of the polyester resin (C) contained in the primer coating composition to the total mass of the resin solid content of the polyolefin resin (A) and the polyurethane resin (B) (=(C) ：((A)+(B)) should be in the range of 1:0.4~1:4.5, and preferably in the range of 1:0.5~1:4.0, more preferably in the range of 1:1.5~1:4.0 Good. Since the mass ratio (=(C):((A)+(B)) is within the above range, it can maintain the performance of polyolefin resin (A) and polyurethane resin (B) At the same time, the compatibility of polyester resin (C) with polyolefin resin (A) and polyurethane resin (B) can be further improved.

(Conductive Pigment (D)) The aforementioned primer coating composition preferably further contains a conductive pigment (D). The conductive pigment (D) is not particularly limited as long as it can impart conductivity to the primer coating film. The conductive pigment (D) can also be used in any shape such as particles, flakes, and fibers (including whiskers). Specific examples of the conductive pigment (D) include conductive carbon such as conductive carbon black, carbon nanotubes, carbon nanofibers, and carbon micro-coil; silver, nickel, copper, graphite, aluminum, etc. The metal powder. In addition, tin oxide doped with antimony, tin oxide doped with phosphorus, acicular titanium oxide whose surface is coated with tin oxide and/or antimony, antimony oxide and other pigments coated with conductive metal oxides, etc. can be mentioned. These can be used individually, respectively, and can also be used in combination of 2 or more types. As the conductive pigment (D), conductive carbon can be suitably used in terms of performance and price.

From the viewpoint of imparting conductivity and primer coating film adhesion, water resistance, etc., the content of the conductive pigment (D) is relative to 100 parts by mass of the resin solid content of the coating film forming resin contained in the primer coating composition. It is preferably 1 part by mass or more and 60 parts by mass or less, preferably 1 part by mass or more and 50 parts by mass or less, and more preferably 1 part by mass or more and 45 parts by mass or less.

The aforementioned primer coating composition may further contain pigments other than the aforementioned conductive pigment (D) as required, such as coloring pigments such as titanium dioxide, iron oxide, aluminum paste, azo series, phthalocyanine series, etc.; talc, silica , Calcium carbonate, barium sulfate, zinc oxide and other extender pigments.

The aforementioned primer coating composition is preferably solvent-based. In addition, the aforementioned primer coating composition may also contain an organic solvent as required. The organic solvent is preferably inactive to the above-mentioned components (for example, isocyanate groups, etc.). Preferable organic solvents include, for example, the following: propylene glycol dimethyl ether, dipropylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether and other ether solvents; methyl ethyl Ketone solvents such as ketone and methyl isobutyl ketone; ethyl acetate, propylene glycol methyl ether acetate (2-methoxy-1-methylethyl acetate), amyl acetate, isoamyl acetate, isobutyl acetate, isoacetate Ester solvents such as propyl acetate, octyl acetate, n-butyl acetate, secondary butyl acetate, tertiary butyl acetate, propyl acetate, heptyl acetate, etc.

The resin solid content concentration of the primer coating composition is preferably 15% by mass or more and 60% by mass or less, preferably 20% by mass or more and 50% by mass or less.

The aforementioned primer coating composition may also contain other components as required. Other components may include, for example, the following: viscosity modifiers, film forming aids, surface modifiers, ultraviolet absorbers, light stabilizers, antioxidants, and other additives commonly used in coating compositions.

The above-mentioned primer coating composition can be prepared by mixing the above-mentioned components by a method commonly used by those skilled in the art.

The aforementioned primer coating composition is characterized by good impact mitigation performance and high adhesion to the resin part. Therefore, the above-mentioned primer coating composition has the advantage that it can be suitably used especially when forming a multi-layer coating film on a to-be-coated article including a steel plate part and a resin part. In addition, when the aforementioned primer coating composition contains the conductive pigment (D), there is an advantage that a primer coating film having two properties of a conductive primer and a knock-resistant primer can be provided.

The conventional conductive primer coating composition applied on the resin part must ensure the adhesion to the resin, so it basically contains polyolefin resin. On the other hand, the conductive primer coating composition is inferior in anti-knock performance. In addition, the conventional anti-knock primer coating composition coated on metal or electrodeposition coating film has good impact mitigation performance, but on the other hand, its adhesion to the resin part is basically poor. Therefore, it is difficult to balance the adhesion and impact mitigation performance, and it is difficult to share the conductive primer coating composition and the anti-knock primer coating composition.

In contrast, since the primer coating composition of the present embodiment contains the above-mentioned specific components (A) to (C) in a specific content range, it has high adhesion to the resin portion and has good impact mitigation performance. Therefore, the aforementioned primer coating composition can share the primer coating composition for the resin part (especially the conductive primer coating composition) and the anti-knock primer coating composition. Therefore, for example, a coating film can be formed with a common coating composition (and at the same time) on a coated object containing different materials such as a resin part and a steel plate part. And there will be the advantage of simplification of coating steps and coating equipment.

Intermediate coating composition The intermediate coating composition can be used to form an intermediate coating film. The middle coating film can be set arbitrarily. The intermediate coating composition used in the above-mentioned multi-layer coating film forming method may be a intermediate coating composition commonly used in the coating field. The intermediate coating composition can be a water-based intermediate coating composition or a solvent-based intermediate coating composition.

As the intermediate coating composition, for example, a coating composition containing a coating film-forming resin, organic and/or inorganic various pigments (for example, coloring pigments, extender pigments, etc.) can be used. The coating film forming resin of the intermediate coating composition is not particularly limited, and it is preferable to include a hydroxyl-containing resin and a hardener from the viewpoint of various properties of the intermediate coating film obtained. In particular, a combination of a hydroxyl-containing resin and a hardener can be suitably used. The hydroxyl-containing resin includes a hydroxyl-containing acrylic resin and/or a hydroxyl-containing polyester resin, and the hardener includes at least one of a melamine hardener and an isocyanate hardener.

The coloring pigments contained in the above-mentioned intermediate coatings include, for example, coloring pigments (gray-based intermediate coating composition) based on carbon black and titanium dioxide, and coloring pigments that exhibit a hue similar to that of the surface coating base film (so-called colored pigments). Intermediate coating composition) and so on.

Among the above-mentioned formation of the multi-layer coating film, for example, when the multi-layer coating film is formed under heating at a relatively low temperature, the intermediate coating composition is preferably a two-component solvent intermediate coating composition. The two-component solvent intermediate coating composition preferably consists of a main agent and a hardener. The main agent includes a hydroxyl-containing resin selected from the group consisting of hydroxyl-containing acrylic resin and hydroxyl-containing polyester resin, and the hardener is selected from the group consisting of From the group consisting of polyisocyanate hardener and melamine resin.

(Main agent) The hydroxyl-containing acrylic resin can be obtained, for example, by copolymerizing a monomer mixture containing a hydroxyl-containing α,β-ethylenically unsaturated monomer.

The above-mentioned hydroxyl-containing α,β-ethylenically unsaturated monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and allyl Alcohol, methacrylate alcohol, hydroxyethyl (meth)acrylate and ε-caprolactone adduct. Among them, preferred are 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and an adduct of hydroxyethyl (meth)acrylate and ε-caprolactone. In addition, in this specification, "(meth)acrylic acid" means both acrylic acid and methacrylic acid.

The above-mentioned monomer mixture may further contain a carboxyl group-containing α,β-ethylenically unsaturated monomer. Carboxyl group-containing α, β-ethylenically unsaturated monomers include acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-propenyloxyethyl phthalate, 2-propenyloxyethyl succinate Esters, ω-carboxy-polycaprolactone mono(meth)acrylate, maleic acid, fumaric acid, itaconic acid, etc. Among them, acrylic acid and methacrylic acid are preferred.

In the above copolymerization, other α,β-ethylenically unsaturated monomers can be used as required. The above-mentioned other α,β-ethylenically unsaturated monomers include (meth)acrylates (e.g. methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, (meth) ) N-butyl acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl methacrylate, phenyl acrylate, (methyl) ) Isobornyl acrylate, cyclohexyl methacrylate, tributylcyclohexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, dihydrodicyclopentadi (meth)acrylate Alkenyl esters, etc.), polymerizable amide compounds (e.g. (meth)acrylamide, N-methylol(meth)acrylamide, N-butoxymethyl(meth)acrylamide, etc.) .

The above-mentioned other α,β-ethylenically unsaturated monomers can also be crosslinked monomers. The above-mentioned crosslinkable monomer is a compound having two or more radically polymerizable ethylenic unsaturated groups in the molecule, and examples thereof include divinylbenzene, allyl (meth)acrylate, ethylene glycol bis(methyl) ) Acrylic etc.

The hydroxyl-containing acrylic resin can be prepared by subjecting the above-mentioned monomer mixture to solution polymerization or emulsion polymerization. Solution polymerization or emulsion polymerization can use the above-mentioned monomer mixtures, and are carried out according to procedures commonly used by those skilled in the art.

The hydroxyl-containing polyester resin can be prepared, for example, by condensing a polyhydric alcohol component and a polybasic acid component.

Examples of the above-mentioned polyol components include, for example, ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-Diethyl-1,3-propanediol, neopentyl glycol, 1,9-nonanediol, 1,4-cyclohexanediol, neopentyl glycol hydroxytrimethyl acetate, 2-butane Hydroxycarboxylic acid components such as 2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethylpentanediol.

Examples of the above-mentioned polybasic acid components include, for example, the following: phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, tetrachlorophthalic anhydride, pyromellitic anhydride and other aromatic polycarboxylic acids and acid anhydrides; Hexahydrophthalic anhydride, tetrahydrophthalic anhydride, 1,4- and 1,3-cyclohexanedicarboxylic acid and other alicyclic polycarboxylic acids and anhydrides; maleic anhydride, fumaric acid, succinic anhydride, adipic acid, decane Aliphatic polycarboxylic acids such as diacids and polybasic acid components such as anhydrides and such anhydrides. Monobasic acids such as benzoic acid or tertiary butyl benzoic acid can also be used together as needed.

In addition, as reaction components, monohydric alcohols, monoepoxy compounds such as Cardura E (trade name: manufactured by Shell Chemicals), and lactones (β-propiolactone, dimethylpropiolactone, butyrolactone) may be further used in combination. Ester, γ-valerolactone, ε-caprolactone, γ-caprolactone, etc.).

Fatty acids such as castor oil and dehydrated castor oil and oil components of a mixture of one or more of these fatty acids can also be added to the above-mentioned polybasic acid component and polyol component. In addition, the hydroxyl-containing polyester resin may be grafted with acrylic resin, vinyl resin, etc., or a polyisocyanate compound may be reacted according to requirements.

(hardener) Polyisocyanate hardener and melamine hardener are compounds that cross-link with hydroxyl-containing resin to form a coating film. The polyisocyanate hardener and the melamine hardener are not particularly limited as long as they are usually used as hardeners for paint users. Representative polyisocyanate hardeners include the following: trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), trimethylhexamethylene Aliphatic polyisocyanates such as diisocyanates (especially aliphatic diisocyanates); 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate, isophorone Alicyclic polyisocyanates such as diisocyanate (IPDI) and methyl norbornane diisocyanate (especially alicyclic diisocyanate); XDI, 2,4-toluene diisocyanate (TDI) ), 2,6-toluene diisocyanate and other aromatic polyisocyanates; and trimer isocyanate compounds, uretdione compounds, urethane compounds, allophanate compounds, biuret compounds, and The adduct of trimethylolpropane. Commercially available polyisocyanate hardeners can also be used.

The melamine hardener is not particularly limited, and the Cytec series, MYCOAT series, U-VAN series, etc. manufactured by Mitsui Chemicals Co., Ltd. can be suitably used. For example, the melamine resin is preferably an alkyl etherified melamine resin, preferably a melamine resin substituted with a methoxy group and/or a butoxy group.

The above-mentioned intermediate coating composition may also contain a catalyst as required. Examples of the catalyst include metal catalysts such as organotin catalysts.

The resin solid content concentration of the intermediate coating composition varies depending on the coating conditions. Generally speaking, it can be 15% by mass or more and 60% by mass or less, and can also be 35% by mass or more and 55% by mass or less.

The intermediate coating composition may also contain other components as required. Examples of other components include the following: various resin components, various pigments, dispersing aids, viscosity modifiers, film forming aids, surface modifiers, ultraviolet absorbers, light stabilizers, antioxidants, and coating compositions Other additives commonly used.

The intermediate coating composition can be prepared by mixing the above-mentioned components by a method commonly used by those skilled in the art.

Base coating composition The above-mentioned multi-layer coating film formation method can use a base coating composition commonly used in the coating field. The base coating composition may be water-based or solvent-based.

The base coating composition includes, for example, the following: coating film forming resins, organic and/or inorganic pigments (such as coloring pigments, extender pigments, gloss pigments, etc.). The coating film forming resin of the base coating composition is not particularly limited, but preferably contains a hydroxyl-containing resin and a hardener according to the demand. In particular, a combination of a hydroxyl-containing resin and a hardener can be suitably used. The hydroxyl-containing resin includes a hydroxyl-containing acrylic resin, and the hardener includes at least one of a melamine hardener and an isocyanate hardener (which can also be blocked as required).

Examples of coloring pigments include inorganic coloring pigments such as titanium dioxide, carbon black, iron oxide, and yellow iron oxide; and organic coloring pigments. Examples of organic coloring pigments include phthalocyanine-based pigments such as phthalocyanine blue and phthalocyanine green; azo-based pigments such as azo red, azo yellow, and azo orange; quinacridone red and Cinquasia red , Cinquasia magenta (Cinquasia magenta) and other quinacridone pigments; perylene red, perylene chestnut and other perylene pigments; carbazole violet, anthrapyridine (anthrapyridine), indanthrene yellow, isoindoline yellow , Indanthrene Blue, Dibromo Onion Red, Anthraquinone Red, Pyrrolopyrrole Dione. Glossy pigments can include flake pigments with an average particle size (D50) of 2-50 µm and a thickness of 0.1-5 µm. More specifically, metallic luster pigments such as aluminum, copper, zinc, iron, nickel, tin, alumina, and alloys thereof, interference mica pigments, muscovite pigments, graphite pigments, glass flake pigments, etc. can be cited. Examples of extender pigments include calcium carbonate, barium sulfate, clay, and talc. In addition, pigments other than the above-mentioned pigments may also be included (for example, flat pigments with a long diameter of 1 µm to 10 µm and a number average particle size of 2 µm to 6 µm, etc.).

As the hydroxyl-containing resin, hydroxyl-containing resins (for example, hydroxyl-containing acrylic resins, etc.) that can be suitably used in the intermediate coating composition can be used. As the hardener, melamine hardeners, polyisocyanate hardeners, etc., which can be suitably used in the intermediate coating composition, can be used.

The above-mentioned base coating composition may also contain a catalyst if required. Examples of the catalyst include metal catalysts such as organotin catalysts.

The resin solid content concentration of the base coating composition varies depending on the coating conditions. Generally, it can be 10% by mass or more and 60% by mass or less, or 20% by mass or more and 50% by mass or less.

The base coating composition may also contain other components as required. Other components can include, for example, the following: various resin components, dispersing aids, viscosity modifiers, film forming aids, surface modifiers, ultraviolet absorbers, light stabilizers, antioxidants, and commonly used in coating compositions Other additives.

The base coating composition can be prepared by mixing the above-mentioned components by a method commonly used by those skilled in the art.

Clear coating composition In the above-mentioned multi-layer coating film formation method, a clear coating composition commonly used can be used. Specifically, the clear coating composition includes an acid epoxy hardening clear coating composition containing a polyepoxide and a polyacid, a urethane clear coating composition containing a hydroxyl-containing resin and an isocyanate compound, and the like.

The acid epoxy hardening clear coating composition preferably contains an acid anhydride group-containing acrylic resin, a carboxyl group-containing polyester resin, and an acrylic resin having hydroxyl and epoxy groups. The acid epoxy hardening clear coating composition has a high solid content concentration and also has the advantage of being able to form a coating film with excellent acid resistance. In addition, from the viewpoint of storage stability, the acid anhydride group-containing acrylic resin is preferably half-esterified by the acid anhydride group in the acid anhydride group-containing acrylic resin with a low molecular weight alcohol or the like. In addition, the carboxyl group-containing polyester resin has a hydroxyl group.

The blending of acid anhydride group-containing acrylic resin, carboxyl group-containing polyester resin, and acrylic resin having hydroxyl groups and epoxy groups can be carried out in quantities and methods known to those skilled in the art.

The hardening mechanism of the above-mentioned acid epoxy hardening clear coating composition is as follows. First, by heating, the acid anhydride group in the acid anhydride group-containing acrylic resin reacts with the hydroxyl group of the carboxyl group-containing polyester resin and the hydroxyl group and epoxy group-containing acrylic resin to form a cross-linking point and form a carboxyl group again. The carboxyl group and the carboxyl group present in the carboxyl-containing polyester resin react with the epoxy group present in the hydroxy- and epoxy-containing acrylic resin to form a cross-linking point. In this way, by reacting the three kinds of polymers with each other, the hardening will advance and a high cross-linking density can be provided.

The isocyanate compound contained in the urethane clear coating composition is a hardener. The isocyanate compound is not particularly limited, and examples include the following: trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), trimethylhexamethylene Aliphatic isocyanate such as diisocyanate, 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate, etc. aliphatic cyclic isocyanate, stubborn diisocyanate (XDI), 2,4-toluene diisocyanate (TDI), 2,6-toluene diisocyanate and other aromatic isocyanates, isophorone diisocyanate (IPDI), norbornane diisocyanate methyl ester, etc. Group isocyanates, these biuret bodies, cyanurate bodies, etc. polymers and mixtures.

The content of the isocyanate compound relative to the hydroxyl-containing resin can be appropriately selected within the range usually used by those skilled in the art. For example, it is preferable to use the isocyanate compound in an amount such that the equivalent ratio (NCO/OH) of the isocyanate group (NCO) to the hydroxyl group (OH) is within the range of 0.5 or more and 2.0 or less. The above-mentioned lower limit is preferably 0.7, and the above-mentioned upper limit is preferably 1.7.

The above-mentioned hydroxyl-containing resin is not particularly limited, and examples thereof include acrylic resins, polyester resins, alkyd resins, and polyether resins. One kind of these resins may be used, or two or more kinds may be used in combination. The use of acrylic resin and/or polyester resin as the hydroxyl-containing resin is preferable from the viewpoint of coating film performance such as weather resistance and water resistance.

The clear coating composition may also contain ultraviolet absorbers, hindered amine light stabilizers, antioxidants, cross-linked resin particles as rheology control agents, surface modifiers, hardening catalysts, etc. It is usually used by those who are familiar with the art The additives.

With respect to 100 parts by mass of the resin solid content of the clear coating composition, the crosslinked resin particles are preferably 0.01 parts by mass or more and 15 parts by mass or less, more preferably 0.1 parts by mass or more and 10 parts by mass or less.

The manufacturing method of the clear coating composition is not particularly limited, and any method known to those skilled in the art can be used. In addition, a commercially available product can also be used for the clear coating composition. For example, "MACFLOW O-570 CLEAR" or "MACFLOW O-1820 CLEAR" (both trade names) sold by Nico Automotive Coatings, which contains polyepoxide and polyacid clear coating composition. In addition, "R290S CLEAR" (trade name) or "R2580 CLEAR" (trade name) sold by Nico Automotive Coatings, which contains a urethane clear coating composition containing a hydroxyl-containing resin and a polyisocyanate hardener, can also be cited Wait. In addition, "SUPERLAC O-100 CLEAR" (trade name) sold by Nitu Motor Co., Ltd., which is a clear coating composition containing acrylic resin and melamine hardener, can also be cited.

Multilayer coating film forming method By using the aforementioned primer coating composition, base coating composition and clear coating composition, a multi-layer coating film can be formed. The method of forming a multi-layer coating film includes the following steps: The primer coating film formation step is to coat the primer coating composition on the object to be coated to form an unhardened primer coating film; The base coating film formation step is to coat the base coating composition on the obtained unhardened primer coating film to form an unhardened base coating film; The step of forming a clear coating film is to apply a clear coating composition on the resulting unhardened base coating film to form an unhardened clear coating film; and The curing step is to heat the obtained uncured primer coating film, base coating film, and clear coating film to harden them.

And if necessary, after the primer coating film forming step and before the base coating film forming step, the intermediate coating film forming step is performed, and the intermediate coating composition is applied on the resulting unhardened primer coating film to form an unhardened intermediate coating. Coating.

To be coated Examples of the object to be coated in the above-mentioned method for forming a multi-layer coating film include various steel plates, various resins, and substrates including a steel plate portion and a resin portion. Examples of the steel sheet include metals such as iron, steel, stainless steel, aluminum, copper, zinc, and tin, and alloys thereof. The resin may include, for example, polyethylene resin, EVA resin, polyolefin resin (polyethylene resin, polypropylene resin, etc.), vinyl chloride resin, polystyrene resin, polyester resin (including PET resin, PBT resin, etc.), polycarbonate Resin, acrylic resin, acrylonitrile butadiene styrene (ABS) resin, acrylonitrile styrene (AS) resin, polyamide resin, acetal resin, phenol resin, fluororesin, melamine resin, urethane resin, Epoxy resin, polyphenylene oxide (PPO), etc. These coated objects may also have a three-dimensional shape.

For the above-mentioned steel sheet, a chemical conversion treatment may be performed as required, and an electrodeposited coating film may be further formed. Examples of the chemical conversion treatment include zinc phosphate chemical conversion treatment, zirconium chemical conversion treatment, and chromic acid chemical conversion treatment. In addition, the electrodeposition coating film is formed by, for example, electrodeposition coating using a cationic electrodeposition coating composition or an anionic electrodeposition coating composition.

The above resin can be cleaned with organic solvent vapor, or can be cleaned with neutral detergent.

The aforementioned primer coating composition can be coated by a generally used coating method. For example, in order to improve the appearance of the obtained coating film, multi-stage painting using air non-electrostatic spray coating, preferably one-stage painting, or a combination of air non-electrostatic spray coating and the general term Coating of non-static coating machines such as "µµ (micro) spin cup", "µ (micro) spin cup" or "metabell" etc. The coating of the above-mentioned intermediate coating composition and base coating composition can be coated by a generally used coating method. For example, in order to improve the appearance of the obtained coating film, a multi-stage painting using air electrostatic spray coating, preferably a two-stage painting, or a combination of air electrostatic spray coating and the common name "µµ" can be used. (Micro) Rotary Cup", "µ (Micro) Rotary Cup" or "Metal Rotary Cup" and other rotary atomizing electrostatic coating machines.

The coating film thickness of the primer coating composition can be appropriately selected according to the intended use. The dry film thickness of the coating film of the primer coating composition is preferably 4 µm or more and 30 µm or less, and more preferably 6 µm or more and 20 µm or less. The coating film thickness of the intermediate coating composition can be appropriately selected according to the intended use. The dry film thickness of the coating film of the intermediate coating composition is preferably 8 µm or more and 50 µm or less, and more preferably 15 µm or more and 35 µm or less.

The coating film thickness of the base coating composition can be appropriately selected according to the intended use. The dry film thickness of the coating film of the base coating composition is, for example, preferably 5 µm or more and 40 µm or less, more preferably 8 µm or more and 30 µm or less.

After coating the above-mentioned intermediate coating composition and base coating composition, they can also be placed as required to remove at least a part of the solvent from the coating film.

The coating of the clear coating composition can be based on the form of the coating composition, and it can be coated by a commonly used method. Specific examples of the method of coating the clear coating composition include, for example, coating using a rotary atomizing electrostatic coating machine called a microbell. In addition, for example, when the clear coating composition is a two-component type, it can also be painted by a method in which each liquid is sent to the spray gun in a two-component mixing spray gun and mixed at the tip of the spray gun. The dry film thickness of the clear coating film formed by applying the above clear coating composition is preferably about 20 μm or more and 60 μm or less. Since the dry film thickness is within the above range, it has the advantages of good coverage of the unevenness of the substrate and good coating workability.

Hardening step In the hardening step, the coating film formed by the above-mentioned primer coating, intermediate coating, base coating, and clear coating is heated and hardened at the same time. The heating temperature in the curing step can be appropriately selected according to the composition of the coating material and the coating composition, for example, it can be 70°C or more and 150°C or less. The heating time can be set arbitrarily according to the shape of the coated object and the heating temperature. The heating time is preferably, for example, 10 minutes or more and 40 minutes or less.

The film thickness of the multi-layer coating film formed as described above is, for example, 20 μm or more and 300 μm or less, preferably 30 μm or more and 250 μm or less.

The multi-layer coating film formed by the above method is characterized by good impact mitigation performance and high adhesion to the resin part. Therefore, it has the advantage that it can be suitably used when forming a multi-layer coating film on a coated article including a steel plate part and a resin part. Moreover, the above method can still form a multi-layer coating film by a common method even for different materials such as resin parts and steel parts, and therefore has the advantage that the color of the obtained multi-layer coating film can be made uniform at a higher level. [Example]

The following examples are used to explain the present invention more specifically, but the present invention is not limited to these. In the embodiment, "parts" and "%" are based on quality standards unless otherwise specified.

Production Example 1-1 Production of primer coating composition (1) In a stainless steel container equipped with a mixer, 14.76 parts of polyurethane resin (B) (manufactured by Sanyo Chemical Co., Ltd. "NBC300", 30% non-volatile content) and carbon black pigment (manufactured by Lion Specialty Chemicals Co., Ltd.) "KETJENBLACK EC-600JD") 0.86 parts, titanium oxide pigment (Ishihara Sangyo Co. "TIPAQUE CR-95") 18.87 parts, aromatic hydrocarbon solvent (Exxon company "Solvesso 100") 26.19 parts, isopropanol 11.80 parts , 7.86 parts of isobutanol and 19.66 parts of methyl ethyl ketone are added in sequence while stirring to mix. This mixture was transferred to a disperser ("DYNO-MILL" manufactured by Will A. Bachofen Ag Maschinenfabrik), and the pigment was dispersed to obtain a dispersion mixture. Transfer 48.50 parts of the obtained dispersion mixture to a stainless steel container equipped with a mixer. Next, 16.80 parts of polyurethane resin (B) ("NBC300" manufactured by Sanyo Chemical Industry Co., Ltd., 30% non-volatile content), and polyester resin (C1) ("BECKOLITE 46-118" manufactured by Dainippon Ink Chemical Industry Co., Ltd.) were added. ", non-volatile content 60%) 6.00 parts and polyolefin resin (A) ("SUPERCHLON 930" manufactured by Nippon Paper Co., Ltd., non-volatile content 20%) 18.00 parts. In addition, 3.6 parts of toluene and 7.1 parts of methyl ethyl ketone were added and mixed to obtain a primer coating composition (1).

Production Example 1-2 Production of primer coating composition (2)~(32) The primer coating composition (2) to (32) was prepared by the same procedure as the production example 1-1 except that the type and amount of each component were changed as shown in the following table.

Production Example 2-1 Production of acrylic latex (AcEm-1) with hydroxyl and carboxyl groups A reaction vessel equipped with a stirrer, a nitrogen introduction tube, a temperature control device, a condenser, and a dropping funnel was fed with 2,000 parts of deionized water, and the temperature was raised to 80°C while stirring in a nitrogen atmosphere. In addition, 103 parts of styrene, 290 parts of n-butyl methacrylate, 280 parts of n-butyl acrylate, 302 parts of hydroxyethyl acrylate, 26 parts of acrylic acid, 3 parts of dodecanethiol and LATEMUL PD-104 as emulsifier 100 parts (manufactured by Kao Corporation, 20% aqueous solution) were added to 1,000 parts of deionized water and emulsified to prepare a pre-emulsion. The pre-emulsion and the initiator aqueous solution in which 3 parts of ammonium persulfate have been dissolved in 300 parts of deionized water were dropped into the above reaction vessel for 2 hours. After the dropping, the reaction was continued at 80°C for 1 hour. 8.2 parts of N,N-dimethylaminoethanol was added to the cooled reactant to obtain an acrylic latex with a resin solid content of 30% by mass. The acrylic latex calculated from the monomer composition has a hydroxyl value of 130 mgKOH/g and an acid value of 20 mgKOH/g in terms of resin solid content. In addition, the number average molecular weight of the acrylic resin in the obtained acrylic latex, measured by GPC after removing moisture, was 45,000.

Production Example 2-2 Production of polyester water dispersion (PE-DP) with hydroxyl and carboxyl groups Add 250 parts of trimethylolpropane, 824 parts of adipic acid and 635 parts of cyclohexanedicarboxylic acid to a reaction vessel equipped with a stirrer, nitrogen inlet pipe, temperature control device, condenser and decanter, and heat to 180°C , The condensation reaction is carried out until the water does not distill out. After cooling to 60°C, 120 parts of phthalic anhydride was added and the temperature was raised to 140°C. The temperature was maintained for 60 minutes to obtain a polyester resin with a number average molecular weight of 2,000 measured by GPC. Then, it was cooled to 80°C, and 59 parts of dimethylaminoethanol (equivalent to 80% of the acid value of the resin (neutralization rate 80%)) was added. Furthermore, 1920 parts of deionized water was added and stirred to obtain a polyester water dispersion with a resin solid content of 45% by mass. The hydroxyl value of the polyester water dispersion in terms of resin solid content is 90 mgKOH/g, and the acid value is 35 mgKOH/g.

Production example 2-3 Production of hydrophilized modified carbodiimide compound 700 parts of 4,4-dicyclohexylmethane diisocyanate and 7 parts of 3-methyl-1-phenyl-2-cyclophosphene-1-oxide were reacted at 170°C for 7 hours to obtain 3 parts per molecule. A carbodiimide compound with a carbodiimide group and an isocyanate group at both ends. Next, PTMG-1000 (polytetramethylene glycol with a number average molecular weight of 1,000 manufactured by Mitsubishi Chemical Corporation) was added to 180 parts of 4,4-dicyclohexylmethane carbodiimide with isocyanate terminal. 13.6) 95 parts of repeating units of tetramethylene oxide calculated by average molecular weight and 0.2 part of dibutyltin dilaurate, heated to 85°C and kept for 2 hours. Next, 86.4 parts of methyl polyglycol 130 (polyethylene glycol monomethyl ether manufactured by Japan Emulsifier Co., Ltd., the number of repetitions of ethylene oxide calculated from the hydroxyl value of 130 mgKOH/g 9) was added, and kept at 85°C for 3 hours . After confirming the disappearance of the NCO peak by IR measurement, the reaction was terminated. After cooling to 60°C, deionized water was added to obtain an aqueous dispersion of a hydrophilized modified carbodiimide compound with a resin solid content of 40% by mass.

Production Example 2-4 Production of colored pigment paste 9.2 parts of a commercially available dispersant "Disperbyk 190" (manufactured by BYK-Chemie), 17.8 parts of ion-exchange water, and 73.0 parts of rutile titanium dioxide were premixed. Then, put it into a paint blender, and mix and disperse it at room temperature with a ball medium until the particle size is 5 µm or less. And the ball medium is removed by filtration to obtain a colored pigment paste.

Production Example 2-5 Production of latex resin with hydroxyl value less than 80mgKOH/g Add ADEKA REASOAP NE-20 (manufactured by ADEKA Corporation, α-[1-[(allyloxy)methyl]-2-(nonylphenoxy) into a reaction vessel fed with 194.1 parts of ion-exchanged water ) Ethyl]-ω-hydroxyoxyethylene, solid content 80% by mass aqueous solution) 0.2 parts, and Aqualon HS-10 (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., polyoxyethylene alkyl propenyl phenyl ether sulfate) 0.2 part, the temperature was raised to 80°C while mixing and stirring in a nitrogen stream. In addition, the first-stage α,β-ethylenically unsaturated monomer mixture and initiator solution were prepared. The first-stage α,β-ethylenically unsaturated monomer mixture was composed of 18.5 parts of methyl acrylate and 31.7 parts of ethyl acrylate. Parts, 5.8 parts of 2-hydroxyethyl acrylate, 10.0 parts of styrene, 4.0 parts of acrylamide, 0.3 parts of ADEKA REASOAP NE-20, 0.2 parts of Aqualon HS-10 and 70 parts of ion exchange water. The initiator solution is It is composed of 0.2 parts of ammonium persulfate and 7 parts of ion exchange water. The α,β-ethylenically unsaturated monomer mixture and the initiator solution were dropped into the above reaction vessel at the same time for 2 hours. After the dripping, the aging was performed at the same temperature for 1 hour. In addition, the second-stage α,β-ethylenically unsaturated monomer mixture and initiator solution were prepared. The second-stage α,β-ethylenically unsaturated monomer mixture was composed of 24.5 parts of ethyl acrylate and 2-hydroxyethyl acrylate. It is composed of 2.5 parts of ester, 3.1 parts of methacrylic acid, 0.3 parts of Aqualon HS-10 and 30 parts of ion exchange water. The initiator solution is composed of 0.1 part of ammonium persulfate and 3 parts of ion exchange water. The α, β-ethylenically unsaturated monomer mixture and the initiator solution were dropped into the above-mentioned reaction vessel maintained at 80° C. at the same time for 0.5 hours. After the dripping is completed, aging is performed at this temperature for 2 hours. Next, the reaction vessel was cooled to 40°C, and the reactant was filtered with a 400-mesh filter. A 10% by mass dimethylaminoethanol aqueous solution was added to the reactant to adjust the pH to 7 to obtain a latex resin. The average particle size of the latex resin is 110nm, the solid content is 24% by mass, and the solid content acid value is 20mgKOH/g. The hydroxyl value is 40 mgKOH/g. The glass transition point was calculated from the total monomer composition, and the result was 0°C.

Production Example 3 Production of water-based intermediate coating composition The acrylic latex (AcEm-1) 124.7 parts (resin solid content 30.0%) obtained in Production Example 2-1, and 18.7 parts of the polyester water dispersion (PE-DP) obtained in Production Example 2-2 (resin Solid content 45.0%) and 12.5 parts (resin solid content 80%) of "Cymel 202" manufactured by Allnex Japan, which is a melamine resin, are mixed and stirred. 137.7 parts of the coloring pigment paste of Production Example 2-4 was blended therein, and the pH was adjusted to 8.0 with 0.01 part of dimethylethanolamine (manufactured by Kishida Chemical Co., Ltd.). Furthermore, 1.0 part of ADEKANOL UH-814N (urethane associative adhesive, 30% active ingredient, manufactured by ADEKA, trade name) was mixed and stirred, and then the melamine resin made by Allnex Japan was added. "Cymel 202" 10 parts (resin solid content) stir until uniform. In addition, 40.9 parts of Bayhydur 305 (polyisocyanate compound with ethylene oxide made by Sumika Bayer Urethane, ethylene oxide content: 20% by mass, isocyanate group content: 16% by mass) and the hydrophilic modification of Manufacturing Example 2-3 8.3 parts of carbodiimide compounds (resin solid content 40% by mass) were added while stirring and stirred to obtain an aqueous intermediate coating composition. The "Cymel 202" used in this embodiment is an imino-methylol type melamine resin, and the average amount of imine groups per melamine core is 1.5 or more, and the average amount of methylol is 0.5 or more and Less than 1.0.

Production Example 4 To produce an aqueous base coating composition, 116.7 parts of acrylic latex (AcEm-1) obtained in Production Example 2-1 (resin solid content 30.0%) and the hydroxyl value obtained in Production Example 2-5 were less than 80 mgKOH/ 104.2 parts of g latex resin (resin solid content 24%) are mixed. Add 66.7 parts of water-based polyurethane resin (30% resin solid content), 21 parts of Aluminium Paste MH8801 (aluminum pigment manufactured by Asahi Kasei Co., Ltd.) as a gloss pigment (65% solid content), and acrylic acid containing phosphoric acid to the resulting mixture. 5 parts of resin and 0.3 parts of lauric acid phosphate. Next, 30 parts of 2-ethylhexanol, 3.3 parts of ADEKANOL UH-814N (tackifier manufactured by Adeka, solid content 30%), 0.01 part of dimethylethanolamine (manufactured by Kishida Chemical Co., Ltd.), and 150 parts of ion exchange water were added. Parts and 20 parts of "Cymel 701" made by Allnex Japan as a melamine resin (resin solid content). In addition, "Cycat (registered trademark) 296-9" (weak acid phosphate ester, pKa (H ₂ O) 1.8 or more) manufactured by Allnex Japan, which is a weak acid catalyst, is compared to acrylic latex (AcEm-1) and melamine resin The total amount of solid content is 0.5% (solid content = effective amount of catalyst only), add while stirring, then add 0.5 part of N,N-dimethylaminoethanol (neutralizing agent) and stir to obtain an aqueous base Paint composition. The PWC of the obtained coating composition was 12.0%.

Examples 1~14 Form a multi-layer coating (on the hardened electrodeposition coating) Electrodeposition coating of the cationic electrodeposition coating composition "Powernics150" manufactured by Nico Automotive Co., Ltd. on the zinc phosphate treated steel sheet so that the dry film thickness becomes 20µm, and heat and harden at 160°C for 30 minutes, and there is no hardening Electrodeposition coating. On the obtained hardened electrodeposition coating film, air spray coating was performed with the primer coating composition described in the following table so that the dry film thickness became 6 µm. Next, the water-based intermediate coating composition produced in Production Example 3 was coated using a metal spin cup so that the dry film thickness would be 20 µm. Next, the water-based base coating composition prepared in Manufacturing Example 4 was wet-laminated and wet-coated using a metal spin cup so that the dry film thickness became 10 µm. Next, use a micro spin cup to wet-stack the O-1200 CLEAR manufactured by Nitto Automotive Coatings Co., Ltd. so that the dry film thickness becomes 35µm. The obtained wet coating film was baked and cured at 85° C. for 20 minutes to obtain a multi-layer coating film.

Form a multi-layer coating (on the resin substrate) Degrease the polypropylene board with plastic resin base material. Next, the primer coating composition described in the following table was air-sprayed so that the dry film thickness became 8 µm. Next, the water-based intermediate coating composition produced in Production Example 3 was coated using a metal spin cup so that the dry film thickness would be 20 µm. Next, the water-based base coating composition prepared in Manufacturing Example 4 was wet-laminated and wet-coated using a metal spin cup so that the dry film thickness became 10 µm. Next, use a micro spin cup to wet-stack the O-1200 CLEAR manufactured by Nitto Automotive Coatings Co., Ltd. so that the dry film thickness becomes 35µm. The obtained wet coating film was baked and cured at 85° C. for 20 minutes to obtain a multi-layer coating film.

Examples 15, 16 Form a multi-layer coating (on the resin substrate) Degreasing treatment of polypropylene resin board with plastic resin base material. Next, the primer coating composition described in the following table was air-sprayed so that the dry film thickness became 8 µm. Next, the water-based intermediate coating composition produced in Production Example 3 was coated using a metal spin cup so that the dry film thickness would be 20 µm. Next, the water-based base coating composition (2) was wet-laminated and wet-coated so that the dry film thickness became 10 µm using a metal spin cup. Next, use a micro spin cup to wet-stack the O-1200 CLEAR manufactured by Nitto Automotive Coatings Co., Ltd. so that the dry film thickness becomes 35µm. The obtained wet coating film was baked and cured at 85° C. for 20 minutes to obtain a multi-layer coating film.

Examples 17, 18 Form a multi-layer coating (on the hardened electrodeposition coating) Electrodeposition coating of the cationic electrodeposition coating composition "Powernics150" manufactured by Nico Automotive Co., Ltd. on the zinc phosphate treated steel sheet so that the dry film thickness becomes 20µm, and heat and harden at 160°C for 30 minutes, and there is no hardening Electrodeposition coating. On the obtained hardened electrodeposition coating film, air spray coating was performed with the primer coating composition described in the following table so that the dry film thickness became 6 µm. Next, the solvent-based intermediate coating composition (2) was coated using a metal spin cup so that the dry film thickness became 20 µm. Next, the solvent-based base coating composition (3) is wet-laminated and wet-coated so that the dry film thickness becomes 10 µm using a metal spin cup. Next, use a micro spin cup to wet-stack the O-1820 CLEAR made by Nico Automotive Coatings Co., Ltd. so that the dry film thickness becomes 35µm. The obtained wet coating film was baked and cured at 140° C. for 20 minutes to obtain a multi-layer coating film.

Examples 19-21 Except that the intermediate coating composition was not applied, a multi-layer coating film was formed on the hardened electrodeposition coating film and the polypropylene resin plate in the same manner as in Examples 1, 2 or 5, respectively.

Comparative examples 1, 2, 4, 7, 8, 9, 13~15, 18 Using the primer coating composition described in the following table, a multi-layer coating film was formed on the hardened electrodeposition coating film according to the procedure of "Forming a multi-layer coating film (on the hardened electrodeposition coating film)" of Example 1.

Comparative examples 3, 5, 6, 10-12, 16, 17 Using the primer coating composition described in the following table, a multi-layer coating film was formed on the resin substrate according to the procedure of "Forming a multi-layer coating film (on the resin substrate)" of Example 1.

[evaluate] The following evaluation tests were performed using the multi-layer coating films formed in the above-mentioned Examples and Comparative Examples. The evaluation results obtained are listed in the following table.

Knock resistance evaluation (evaluation of multi-layer coating on hardened electrodeposition coating) The test board with the multi-layer coating film on the hardened electrodeposition coating film formed in each of the Examples and Comparative Examples was carried out under the following conditions using a gravel tester KSS-1 (manufactured by Suga Test Instruments Co., Ltd.) Flying stone test. <Test conditions> Blasting material: No. 7 gravel specified in JIS A5001 (road gravel) The amount of spray material: 50g Distance: 35cm Spray pressure: 0.39MPa Spray angle: 90° Test temperature: -20℃

Visually evaluate the test board after the flying stone test based on the following criteria. In the following criteria, a score of 5 or more is judged as ⊚, a score of 4 or more is judged to be practically usable, and it is ○, 3 is judged as △, and 2 or less is judged as x. 5: Almost no peeling of the multi-layer coating film is observed. 4: Although slight peeling can be observed in the multi-layer coating film, almost no peeling from the interface between the hardened electrodeposition coating film and the primer coating film is observed. 3: The peeling area is slightly larger, and peeling from the interface between the hardened electrodeposition coating film and the primer coating film is observed. 2: The peeling area is large, and peeling from the interface between the hardened electrodeposition coating film and the primer coating film can be observed. 1: The peeling area is large, and the damage of the hardened electrodeposition coating film is also observed at the same time as the damage of the multi-layer coating film.

Evaluation of temperature and water resistance (evaluation of multi-layer coatings on hardened electrodeposition coatings and on resin substrates) The test plate was immersed in warm water at 40° C. for 10 days. The test plate was formed with a multi-layer coating film on the hardened electrodeposition coating film and on the polypropylene resin substrate according to the procedures of the above-mentioned Examples and Comparative Examples. The test panel was taken out, and the appearance of the coating film was visually evaluated based on the following criteria. ○: No abnormalities in the coating film such as whitening and swelling were confirmed. △: A decrease in gloss can be confirmed. ×: Abnormal appearance of the coating film such as whitening and swelling can be confirmed.

Evaluation of adhesion to polypropylene resin (PP) Regarding the test plate with a multi-layer coating film formed on the polypropylene resin substrate according to the procedures of the above-mentioned examples and comparative examples, the coating film of the test plate will be a single-cut tool specified in JIS K-5600-5-6 Abut vertically, and cut 11 parallel lines 1 as deep as the cut marks of the original material (polypropylene resin base material) in parallel. And it intersects the parallel line 1 perpendicularly and cuts at the same interval as the parallel line 1 to scribe 11 parallel lines 2 as deep as the cut marks of the original material, and make a square surrounded by 4 straight lines. Checkerboard Department. The interval between parallel lines 1 and 2 is set to 2 mm. Make the transparent pressure-sensitive adhesive tape specified in JIS K-5600-5-6 free of air bubbles between the checkerboard part and the coated surface. Then, after peeling off the adhered tape in one go between 0.5 and 1.0 seconds, visually evaluate the peeling state of the checkerboard grid (100 grid adhesion test). ◎: The number of checkerboards with more than 5% peeled off based on the area ratio is 0/100 ○: In terms of area ratio, the number of checkers with more than 5% and less than 50% is 1/100, and the number of checkers with more than 50% is 0/100 ×: The number of checkerboards with 50% or more peeled off based on the area ratio is 1/100 or more

Compatibility evaluation (evaluation of paint stability of primer coating composition) The particle size of the primer coating composition produced according to the procedures of the above-mentioned examples and comparative examples was evaluated using a Hegman particle size meter (Model 232). ○: No paint particles above 10µm have been confirmed △: It can be confirmed that the paint particles are more than 10µm and less than 20µm ×: Paint particles above 20µm can be confirmed

[Table 1]

[Table 2]

[table 3]

[Table 4]

The ingredients shown in the table are as follows. Polyolefin resin (A): SUPERCHLON 930 (manufactured by Nippon Paper Co., Ltd., polyolefin resin) Polyurethane resin (B): NBC300 (manufactured by Sanyo Chemical Co., Ltd., polyurethane resin) Polyester resin (C1): BECKOLITE 46-118 (polyester resin manufactured by Dainippon Ink Industry Co., Ltd., condensation reaction product of aromatic dicarboxylic acid and polyol, glass transition temperature -13°C, acid value 10.8mgKOH/g, hydroxyl Value 100mgKOH/g) Polyester resin (C2): PRS1015 (polyester resin made by Nitto Automotive Co., Ltd., condensation reaction product of aromatic dicarboxylic acid and polyol, glass transition temperature -27°C, acid value 8mgKOH/g, hydroxyl value 92mgKOH/g ) Intermediate coating composition (1): The aqueous intermediate coating composition prepared in Manufacturing Example 3 Intermediate coating composition (2): OTO H885 (manufactured by Nippon Paint Co., Ltd., solvent-based intermediate coating) Base coating composition (1): The water-based base coating composition prepared in Manufacturing Example 4 Base coating composition (2): WB-3060 (manufactured by Nitto Motor Co., Ltd., water-based base coating) Base coating composition (3): H-750 (manufactured by Nippon Paint Co., Ltd., solvent-based base coating) Clear paint composition (1): O-1200 (manufactured by Nitto Motor Co., Ltd., solvent-based clear paint) Clear coating composition (2): O-1820 (manufactured by Nitto Motor Co., Ltd., solvent-based clear coating)

In Examples 1-14, it can be confirmed that by using the above-mentioned specific primer coating composition, a multi-layer coating film with good performance can be formed on both the hardened electrodeposition coating film and on the polypropylene resin. Examples 15 to 18 are examples of using different types of coating compositions for the base coating composition and the clear coating composition. In these examples, it can be confirmed that the above-mentioned specific primer coating composition can be suitably used in a multi-layer coating film forming method using various base coating compositions and clear coating compositions. In Examples 19 to 21, the intermediate coating composition is omitted. In these examples, it can also be confirmed that if the above-mentioned specific primer coating composition is used, both the hardened electrodeposition coating film and the polypropylene resin can form a multi-layer coating film with good performance. Comparative Examples 1, 2, 7-9, 13-15, and 18 are examples in which the content of the polyurethane resin (B) contained in the primer coating composition does not satisfy the above-mentioned range. In these comparative examples, it can be confirmed that when a multi-layer coating film is formed on a hardened electrodeposition coating film, the tapping resistance is poor. Comparative Example 17 is an example in which the content of the polyurethane resin (B) contained in the primer coating composition does not satisfy the above range, and is an example in which a multi-layer coating film is formed on a polypropylene resin. In this case, it can be confirmed that the water resistance is poor. Comparative Examples 3, 10-12, and 16 are examples in which the content of the polyolefin resin (A) contained in the primer coating composition does not satisfy the above-mentioned range. In these comparative examples, it can be confirmed that the adhesion to polypropylene resin is poor. Comparative Examples 4 to 6 are examples in which the polyester resin (C) is not included. In these comparative examples, it can be confirmed that the compatibility (paint stability) of each component is low.

Industrial availability By the above method, a multi-layer coating film with good impact mitigation performance and adhesion can be obtained. The above-mentioned multi-layer coating film forming method can be suitably used, for example, for a to-be-coated article including both a steel plate part and a resin part. Moreover, the above-mentioned multi-layer coating film formation method has the advantage of simplifying the coating steps and coating equipment.

This case is based on the Japanese Special Application No. 2019-238877 filed in Japan on December 27, 2019, and all its contents are quoted in this manual by reference.

(none)

Claims (12)

A method for forming a multi-layer coating film, comprising: The primer coating film formation step is to coat the primer coating composition on the object to be coated to form an unhardened primer coating film; The intermediate coating film forming step is to coat the intermediate coating composition on the obtained unhardened primer film to form an unhardened intermediate coating film; The base coating film formation step is to coat the base coating composition on the obtained unhardened intermediate coating film to form an unhardened base coating film; The step of forming a clear coating film is to apply a clear coating composition on the resulting unhardened base coating film to form an unhardened clear coating film; and The hardening step is to heat the obtained unhardened primer coating film, intermediate coating film, base coating film and clear coating film to harden them; The aforementioned primer coating composition includes a coating film-forming resin; and The aforementioned coating film forming resin includes polyolefin resin (A), polyurethane resin (B), and polyester resin (C), The aforementioned polyolefin resin (A) has a resin solid content of 10% by mass or more relative to the resin solid content of the coating film forming resin, The aforementioned polyurethane resin (B) is 20% by mass or more of the resin solid content of the coating film forming resin, The said polyester resin (C) is 5 mass% or more with respect to the resin solid content of a coating film formation resin. A method for forming a multi-layer coating film, comprising: The primer coating film formation step is to coat the primer coating composition on the object to be coated to form an unhardened primer coating film; The base coating film formation step is to coat the base coating composition on the obtained unhardened primer coating film to form an unhardened base coating film; The step of forming a clear coating film is to apply a clear coating composition on the resulting unhardened base coating film to form an unhardened clear coating film; and The hardening step is to heat the obtained unhardened primer coating film, base coating film and clear coating film to harden them; The aforementioned primer coating composition includes a coating film-forming resin; and The aforementioned coating film forming resin includes polyolefin resin (A), polyurethane resin (B), and polyester resin (C), The aforementioned polyolefin resin (A) has a resin solid content of 10% by mass or more relative to the resin solid content of the coating film forming resin, The aforementioned polyurethane resin (B) is 20% by mass or more of the resin solid content of the coating film forming resin, The said polyester resin (C) is 5 mass% or more with respect to the resin solid content of a coating film formation resin. The method for forming a multi-layer coating film according to claim 1 or 2, wherein the content of the aforementioned polyester resin (C) relative to the resin solid content of the coating film forming resin contained in the primer coating composition is 20% by mass or more and 70% by mass %the following. The method for forming a multi-layer coating film of claim 1 or 2, wherein the heating temperature in the aforementioned curing step is in the range of 70 to 150°C. The method for forming a multi-layer coating film according to claim 1 or 2, wherein the polyester resin (C) is a condensation reaction product of an aromatic dicarboxylic acid and a polyhydric alcohol. Such as the method for forming a multi-layer coating film of claim 1 or 2, wherein the glass transition temperature of the aforementioned polyester resin (C) is in the range of -50 to 20°C, The acid value is in the range of 1~50mgKOH/g, and The hydroxyl value is in the range of 10~200mgKOH/g. The method for forming a multi-layer coating film according to claim 1 or 2, wherein the aforementioned primer coating composition further contains a conductive pigment (D). The method for forming a multi-layer coating film according to claim 1 or 2, wherein the polyester resin (C) contained in the primer coating composition is relative to the polyolefin resin (A) and the polyurethane resin (B) The mass ratio of the total mass of the resin solid content is within the range of (C): ((A) + (B)) = 1:0.4~1:4.5. The method for forming a multi-layer coating film according to claim 1 or 2, wherein the object to be coated includes a steel plate part and a resin part. The method for forming a multi-layer coating film according to claim 1 or 2, wherein the primer coating composition is a solvent-based primer coating composition. A primer coating composition comprising a coating film forming resin; The aforementioned coating film forming resin includes polyolefin resin (A), polyurethane resin (B), and polyester resin (C), The aforementioned polyolefin resin (A) has a resin solid content of 10% by mass or more relative to the resin solid content of the coating film forming resin, The aforementioned polyurethane resin (B) is 20% by mass or more of the resin solid content of the coating film forming resin, The aforementioned polyester resin (C) is 20% by mass or more and 70% by mass or less relative to the resin solid content of the coating film forming resin; and The aforementioned polyester resin (C) is a condensation reaction product of aromatic dicarboxylic acid and polyol. Such as the primer coating composition of claim 11, the aforementioned primer coating composition further contains a conductive pigment (D).