TW201946988A - Method for forming multilayer coating film - Google Patents

Abstract

Provided is a method for forming a multilayer coating film having excellent distinctness of image with respect to a metal member and a plastic member used in an automotive body. The method for forming a multilayer coating film includes sequentially performing: (1) a step of forming a primer coating film; (2) a step of forming a coating film based on a solvent-based first colored coating composition (X) on the coating film formed in the step (1); (3) a step of forming a coating film based on a solvent-based second colored coating composition (Y) on the coating film formed in the step (2); (4) a step of forming a clear coating film based on a solvent-based two-component clear coating composition (Z) on the coating film formed in the step (3); and (5) heat-curing these coating films. The coating composition (X) contains a hydroxyl group-containing resin (A) and a polyisocyanate compound (I), and the coating composition (Y) contains a hydroxyl group-containing resin (B). Solubility parameter [delta]A of the hydroxyl group-containing resin (A) and solubility parameter [delta]B of the hydroxyl group-containing resin (B) have a relationship of 0.6 < [delta]A-[delta]B < 1.2.

Description

Method for forming multilayer coating film

The present invention relates to a method for forming a multilayer coating film, which can form a multilayer coating film that is excellent in image clarity for both metal and plastic members used in automobile bodies.

Generally, an automobile body includes a metal member and a plastic member such as a bumper forming the body.

In the application of such a car body in the related field, the following steps are widely used: a step of applying a coating composition suitable for a metal member to a metal member, and applying a different coating composition suitable for a plastic member to a plastic member The steps are performed separately, and then the plastic member is attached to the metal member.

However, in recent years, an application method in a state where a plastic member is attached to a metal member is required in order to reduce the equipment cost in the manufacturing process of an automobile body or to match the hue of the metal member and the plastic member.

For example, Patent Document 1 discloses a method for coating an automobile outer panel, in which a metal member and a plastic member to which a cationic electrodeposition coating composition has been previously applied are assembled to form an automotive outer plate, and An aqueous barrier coating of a composition composed of an olefin resin and a urethane resin (as a main component of a carrier) is applied to the two members, and then an intermediate coating composition is applied thereon as necessary, followed by protection thereon. Layer coating composition.

Patent Document 2 discloses a method for forming a coating film, in which an electrodeposited metal member and a plastic member are assembled and integrated, and a coating film capable of forming a static glass transition temperature of -100 ° C to 0 ° C and containing as a main component an isocyanate modified Quality polybutadiene resin, a polyol component having a number average molecular weight of 150 to 50,000, and a solvent-based coating composition of a conductive filler are applied to the surface of the two members, and then, if necessary, An intermediate coating composition is applied thereon, followed by a protective layer coating composition.
However, in any of the coating methods described in Patent Documents 1 and 2, the obtained multilayer coating film has insufficient impact resistance in a low-temperature environment (-30 ° C).

Regarding the physical properties obtained in a low-temperature environment, for example, Patent Document 3 discloses a method for forming a multilayer coating film, in which an electrodeposition coating film, an intermediate coating film, a primer coating film, and a transparent coating film are sequentially laminated on a substrate. On / above the coated object, the tensile strength of the transparent coating film at -20 ° C is 60 MPa or higher and the elongation at break is 5% or higher.
Prior Technical Documents Patent Documents

Patent Document 1: JP-A-H04-122474
Patent Document 2: JP-A-H01-288372
Patent Document 3: JP-A-2011-020104

The design nature of the car is very important, as well as the finishing quality after coating, especially excellent image sharpness. However, in Patent Documents 1 to 3, the image clarity of the formed coating film is not considered, and its effect is unknown.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for forming a multilayer coating film having excellent image sharpness with respect to metal members and plastic members used in automobile bodies.

After intensive research in order to achieve the above purpose, the inventors of the present case have found that these problems can be solved by the following method for forming a multilayer coating film, and the present invention has been completed.

That is, this invention relates to the following <1> to <3>.
<1> A method for forming a multi-layer coating film, comprising:
(1) A primer coating composition (P) is applied to the surface of an automotive outer plate including at least one of a metal member and a plastic member to form an uncured primer coating film (uncured primer coating film);
(2) applying a solvent-based first colored coating composition (X) to the uncured base coating film obtained in step (1) to form an uncured first colored coating composition Coating step
(3) a step of applying a solvent-based second colored coating composition (Y) to the uncured first colored coating film obtained in step (2) to form an uncured second colored coating film;
(4) a step of applying the solvent-based two-component transparent coating composition (Z) to the uncured second colored coating film obtained in step (3) to form an uncured transparent coating film; and
(5) heating the uncured base coating film formed in step (1), the uncured first colored coating film formed in step (2) at 75 ° C to 95 ° C, and Forming the uncured second colored coating film and the uncured transparent coating film formed in step (4) to simultaneously cure the coating films,
The solvent-based first colored coating composition (X) is a two-component coating composition containing a hydroxyl-containing resin (A) and a polyisocyanate compound (I).
Wherein, the solvent-based second colored coating composition (Y) is a single-component coating composition containing a hydroxyl-containing resin (B), and wherein a solubility parameter (solubility parameter) of the hydroxyl-containing resin (A) δA and the solubility parameter δB of the hydroxyl-containing resin (B) have a relationship of 0.6 <δA-δB <1.2.
<2> The method according to <1>, wherein the hydroxyl group-containing resin (A) has a weight average molecular weight ranging from 29,000 to 47,000.
<3> The method according to <1> or <2>, wherein the hydroxyl-containing resin (B) has a weight average molecular weight ranging from 15,000 to 40,000.

According to the method for forming a multi-layer coating film in the present invention, a multi-layer coating film having excellent image clarity for both metal members and plastic members used in automobile bodies can be formed.
In addition, according to the method for forming a multilayer coating film in the present invention, a multilayer coating film having excellent flip-flop properties and high hardness can be formed.

Hereinafter, the method for forming a multilayer coating film in the present invention is described in more detail.
In the present invention, (meth) acrylate means acrylate or methacrylate, (meth) acrylic means (acrylic) or methacrylic, and (meth) acryloyl ( (meth) acryloyl) means acryloyl or methacryloyl, and (meth) acrylo means (acrylo) or methacrylo.

In the method for forming a multilayer coating film in the present invention, the following steps (1) to (5) are sequentially performed.
The automobile outer panel is a member constituting the outer surface of the automobile, and examples thereof include opening / closing members such as a front door, a rear door, and a hood, a fender panel, and the like other than a top plate.

[step 1)]
In step (1) of the present invention, an undercoating composition (P) is applied to a surface of an automobile outer panel including at least one of a metal member and a plastic member to form an uncured undercoating film.

(Metal and plastic components)
Examples of the metal member include, for example, iron, aluminum, brass, copper, tin, stainless steel, galvanized steel, and zinc alloy (for example, Zn-Al, Zn-Ni, Zn-Fe, and the like) plated steel.

The surface of the above-mentioned metal member may be subjected to a surface treatment such as a phosphate treatment, a chromate treatment, or a complex oxide treatment, and the base coating composition may be applied.
An undercoating composition is further formed thereon. Examples of the undercoating composition include an electrodeposition coating composition, and among them, a cationic electrodeposition coating composition is preferred.

As the plastic member, for example, a polyolefin formed by (co) polymerizing one or two or more olefins (such as ethylene, propylene, butene, and hexene) having 2 to 10 carbon atoms is particularly preferable, and Examples of the plastic member other than polyolefin include polycarbonate, ABS resin, urethane resin, polyamide and the like.

These plastic components are used, for example, in bumpers, spoilers, grills, or fenders. Before applying the undercoating composition (P), if appropriate, the plastic members may be subjected to degreasing treatment, water washing treatment, etc. by a method known per se.

The object to be coated in the present invention includes at least one of the two types of members described above, and the coated surface is preferably configured to at least partially contain the two types of members described above. There are no restrictions on the structure and individual content ratio of these two components. However, it is preferable that 20% or more of the coated surface is constituted such that the metal member accounts for 5% to 95% and the plastic member accounts for 95% to 5%.
The metal and plastic components described above can be assembled by known methods.

(Bottom coating composition (P))
The undercoating composition (P) is preferably an aqueous coating composition, and its use purpose is mainly to make the colored coating composition to be laminated on at least one of a plastic member and a metal member have adhesiveness.
Examples of the undercoating composition (P) include, for example, a coating composition containing as a main component a base resin such as an aqueous polyolefin resin that can be chlorinated, an aqueous polyurethane resin, an aqueous polyester resin, and Water-based acrylic resins; cross-linking agents such as block polyisocyanate compounds and melamine resins; and water; and, if necessary, further additives such as rheology control agents for coating compositions commonly used in the field of coating compositions (agen), organic solvents, coloring pigments, extender pigments, conductive pigments, anticorrosive pigments, pigment dispersants, and plasticizers. One of these additives for coating composition may be used alone, or two or more of them may be used in combination.

The primary coating film is obtained by a method known per se such as air spraying, airless spraying, rotary atomization coating, curtain-coating (curtain- (coat coating) The base coating composition (P) is applied to the above-mentioned object to be coated, and an electrostatic charge may be applied during coating. Among these methods, air spray coating, spin spray coating, and the like are preferred.

The coating amount of the undercoating composition (P) is an amount that provides a thickness of the thermosetting film in the range of preferably 2 to 15 μm, and particularly preferably 5 to 10 μm.

If necessary, the obtained base coating film may be preheated or air blown, for example, at a temperature of about 50 ° C to about 90 ° C for 1 to 60 minutes.

(Step (2))
In step (2) of the present invention, a solvent-based first colored coating composition (X) is applied to the uncured base coating film obtained in step (1) to form an uncured first colored coating film. .

<Solvent-based first colored coating composition (X)>
The solvent-based first colored coating composition (X) is a two-component coating composition containing a hydroxyl group-containing resin (A) and a polyisocyanate compound (I). The solvent-based first colored coating composition (X) includes a main agent containing a hydroxyl group-containing resin (A) and a curing agent containing a polyisocyanate compound (I). The state of the solvent-based first colored coating composition (X) may be a state where the above-mentioned main agent and the above-mentioned curing agent are not mixed, or a state where they are mixed.
A solvent-based coating composition is a term that is opposed to an aqueous coating composition, and is a coating composition that does not substantially contain water as a solvent.

(Hydroxy-containing resin (A))
The hydroxyl group-containing resin (A) is a resin having at least one hydroxyl group in one molecule. Examples of the hydroxyl-containing resin (A) include, for example, resins having a hydroxyl group, such as acrylic resins having a hydroxyl group, polyester resins having a hydroxyl group, polycarbonate resins having a hydroxyl group, polyurethane resins having a hydroxyl group, having Hydroxyl epoxy resin, and alkyd resin with hydroxyl group. One of them may be used alone or two or more of them may be used in combination. Among these, in view of the thickness of the coating film and weather resistance, the hydroxyl-containing resin (A) is preferably a hydroxyl-containing acrylic resin and / or a hydroxyl-containing polyester resin.

In view of the reactivity with the polyisocyanate compound (I) described later, the hydroxyl value range of the hydroxyl-containing resin (A) is preferably 30 to 300 mgKOH / g, and particularly preferably 40 to 250 mgKOH / g.

In this specification, the hydroxyl value of a resin (mgKOH / g) is expressed in mg of potassium hydroxide equivalent to the hydroxyl content of 1 g of resin. The molecular weight of potassium hydroxide is 56.1.

In view of the sharpness of the image of the obtained coating film, the acid value range of the hydroxyl-containing resin (A) is preferably 20 mgKOH / g or less, particularly preferably 1 to 15 mgKOH / g.

In this specification, the acid value of the resin (mgKOH / g) is the value when the mass of potassium hydroxide required to neutralize the protonic acid contained in 1 g of resin is expressed in mg. The measurement can be based on JIS-K-2501-2003.

Considering the sharpness of the obtained coating film
(distinctness of image), the weight-average molecular weight range of the hydroxyl-containing resin (A) is preferably 29,000 to 47,000, more preferably 29,000 to 45,000, and still more preferably 29,000 to 40,000.

In this specification, weight average molecular weight (weight
average molecular weight) and number average molecular weight (number
average molecular weight) is the conversion of retention time (retention capacity) measured by gel permeation chromatography (GPC) into the molecular weight of polystyrene (based on standard polystyrene with a known molecular weight) Retention time (retention capacity) (measured under the same conditions)).

The weight average molecular weight can be obtained by using "HLC-8120GPC" (trade name, manufactured by Tosoh Corp.) as a gel permeation chromatography device and using a column "TSKgel GMHHR-L" (trade name, manufactured by Tosoh Corp.). And using a differential refractometer as a detector, at a mobile phase of N, N-dimethylformamide (containing 10 mM lithium bromide and phosphoric acid), and a measurement temperature of 25 ° C And 1 mL / min flow rate.

In addition, the number-average molecular weight can be obtained by using "HLC-8120GPC" (trade name, manufactured by Tosoh Corp.) as a gel permeation chromatography device, using four-column columns "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL" and "TSKgel G-2000HXL" (commercial names, both manufactured by Tosoh Corp.), and using a differential refractometer as a detector, in a mobile phase of tetrahydrofuran, a measurement temperature of 40 ° C, and 1 mL / min flow rate.

In view of the sharpness of the image of the obtained coating film, the solubility parameter δA of the hydroxyl-containing resin (A) is in the range of preferably 10.5 to 11.0, and more preferably 10.5 to 10.7.

In this specification, the "solubility parameter value" (SP value) of the hydroxyl-containing resin represents the scale of the intermolecular interaction of liquid molecules, and can be calculated by the method shown below.
The solubility parameter value (SP value) of the hydroxyl group-containing resin obtained by copolymerizing at least two polymerizable monomers can be calculated by the following formula.

SP value = SP1 × fW1 + SP2 × fW2 + ... + SPn × fWn
In the above formula, SP1, SP2, ... SPn represent SP values of homopolymers of individual polymerizable monomers, and fW1, fW2, ... fWn represent weight fractions of individual monomers relative to the total amount of monomers . The SP values of homopolymers of polymerizable monomers are described in J. Paint Technology, vol 42, 176 (1970).

In view of the sharpness of the image of the obtained coating film, the blending amount (solid content) of the hydroxyl-containing resin (A) was 100 parts by mass of the solvent-based first colored coating composition (X) with a total solid content of The basis is preferably in the range of 18 to 30 parts by mass, more preferably 20 to 25 parts by mass.

The hydroxyl-containing acrylic resin is generally a copolymer of a hydroxyl-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl-containing polymerizable unsaturated monomer. Examples of the method of obtaining the copolymer include known methods such as a solution polymerization method in an organic solvent.

The hydroxyl-containing polymerizable unsaturated monomer is a compound having one or more hydroxyl groups and one or more polymerizable unsaturated bonds per molecule. Specific examples thereof include, for example, a monoesterified product of (meth) acrylic acid and a dihydric alcohol having 2 to 8 (preferably 2 to 4) carbon atoms, such as 2-hydroxy (meth) acrylic acid Ethyl ester, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, (methyl ) 6-hydroxyhexyl acrylate, 7-hydroxyheptyl (meth) acrylate, and 8-hydroxyoctyl (meth) acrylate; monomers of (meth) acrylic acid and glycols having 2 to 8 carbon atoms Esterification product, which is modified by ε-caprolactone; N-hydroxymethyl (meth) acrylamide; allyl alcohol; (Meth) acrylic acid ester of a hydroxyl polyoxyethylene chain.

In the present invention, a polymerizable unsaturated monomer having a UV-absorbing functional group, such as 2-hydroxy-4- (3-methacryloxy-2-hydroxypropoxy) benzophenone described later (2-hydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone) is not a polymerizable unsaturated monomer containing a hydroxyl group, but is regarded as belonging to another polymerizable unsaturated monomer containing a hydroxyl group. Range of polymerizable polymerizable unsaturated monomers.

Examples of another polymerizable unsaturated monomer copolymerizable with the hydroxyl-containing polymerizable unsaturated monomer include an alkyl (meth) acrylate or a cycloalkyl (meth) acrylate ( cycloalkyl (meth) acrylate), such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate , Isobutyl (meth) acrylate, third butyl (meth) acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, ( Nonyl methacrylate, tridecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, "Isostearyl acrylate" (trade name, manufactured by Osaka Organic Chemical Industry Ltd), Cyclohexyl (meth) acrylate, methyl cyclohexyl (meth) acrylate, tertiary butyl cyclohexyl (meth) acrylate, and cyclododecyl (meth) acrylate ; Polymerizable unsaturated monomers with isobornyl group, such as isoamyl (meth) acrylate; with adamantyl group ) Polymerizable unsaturated monomers, such as adamantane (meth) acrylate; vinyl aromatic compounds, such as styrene, α-methylstyrene, and vinyl toluene; and polymerizable alkoxysilyl-containing groups Unsaturated monomers, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, γ- (methyl ) Acrylic methoxypropyltrimethoxysilane (γ- (meth)
acryloyloxypropyltrimethoxysilane) and γ- (meth) acryloxypropyltriethoxysilane; perfluoroalkyl (meth) acrylate, such as perfluorobutyl ethyl (meth) acrylate And perfluorooctyl ethyl (meth) acrylate; polymerizable unsaturated monomers containing fluorinated alkyl groups, such as fluoroolefins; polymerizable unsaturated monomers containing photopolymerizable functional groups, such as those containing cis Polymerizable unsaturated monomer of butene difluorenimide; vinyl compounds such as N-vinyl pyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate And vinyl acetate; polymerizable unsaturated monomers containing carboxyl groups, such as (meth) acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate; containing Polymerizable unsaturated monomers of nitrogen, such as (meth) acrylonitrile, (meth) acrylamide, N, N-dimethylamine (meth) acryl (N, N-dimethylaminoethyl (meth) acrylate), N, N-dimethylaminopropyl (meth) acrylate (N, N-dimethylaminopropyl (meth) acrylamide), and adduct of glycidyl (meth) acrylate and amine compounds; each molecule has two or more polymerizable compounds Polymerizable unsaturated monomers of saturated groups, such as allyl (meth) acrylate, 1,6-hexanediol-di (meth) acrylate; polymerizable unsaturated monomers containing epoxy groups, such as Glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-cyclo (meth) acrylate 3,4-epoxycyclohexylmethyl (meth) acrylate, 3,4-epoxycyclohexylethyl (meth) acrylate (3,4-
epoxycyclohexylethyl (meth) acrylate), 3,4-epoxycyclohexylpropyl (meth)
acrylate), and allyl glycidyl ether; (meth) acrylates with polyoxyethylene chains whose molecular ends are alkoxy groups; polymerizable unsaturated monomers with sulfonic acid groups , Such as 2-acrylamide-2-methylpropanesulfonic acid, allylsulfonic acid, sodium styrenesulfonate
styrenesulfonate), sulfoethyl methacrylate
methacrylate), and its sodium and ammonium salts; polymerizable unsaturated monomers having a phosphate group, such as 2-acrylic acid oxyethyl phosphate (2-
acryloyloxyethyl acid phosphate), 2-methacryloyloxyethyl acid phosphate, 2-acryloyloxypropyl acid phosphate, and acid 2 -Methacryloxypropyl (2-
methacryloyloxypropyl acid phosphate); a polymerizable unsaturated monomer having a UV-absorbing functional group, such as 2-hydroxy-4- (3-methacryloxy-2-hydroxypropoxy) benzophenone (2-hydroxy -4- (3-
methacryloyloxy-2-hydroxypropoxy) benzophenone), 2-hydroxy-4- (3-propenyloxy-2-hydroxypropoxy) benzophenone (2-hydroxy-4- (3-acryloyloxy-2-hydroxypropoxy) benzophenone), 2,2'-dihydroxy-4- (3-methacryloxy-2-hydroxypropoxy) benzophenone (2,2'-dihydroxy-4- (3-methacryloyloxy-2 -hydroxypropoxy)
benzophenone), 2,2'-dihydroxy-4- (3-propenyloxy-2-hydroxypropoxy) benzophenone (2,2'-dihydroxy-4- (3-acryloyloxy-2-
hydroxypropoxy) benzophenone) and 2- (2'-hydroxy-5'-methacryloxyethylphenyl) -2H-benzotriazole (2- (2'-hydroxy-5'-
methacryloyloxyethyl phenyl) -2H-benzotriazol); UV-stabilizable polymerizable unsaturated monomers, such as 4- (meth) propenyloxy-
1,2,2,6,6-pentamethylpiperidine (4- (meth) acryloyloxy-1,2,2,6,6-
pentamethylpiperidine), 4- (meth) acryloxy-2,2,6,6-tetramethylpiperidine (4- (meth) acryloyloxy-2,2,6,6-tetramethylpiperidine), 4-cyano 4- (meth) acrylfluorenylamino-2,2,6,6-tetramethylpiperidine (4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine), 1 -(Meth) acrylfluorenyl-4- (meth) acrylfluorenylamino-2,2,6,6-tetramethylpiperidine (1- (meth) acryloyl-4- (meth) acryloylamino-2 , 2,6,6-tetramethylpiperidine), 1- (meth) acrylfluorenyl-4-cyano-4- (meth) acrylfluorenylamino-2,2,6,6-tetramethylpiperidine (1- (meth) acryloyl-4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine), 4-crotonyloxy-2,2,6,6-tetramethylpiperidine (4-crotonoyloxy-2,2,6,6-tetramethylpiperidine), 4-crotonoylamino-2,2,6,6-tetramethylpiperidine (4-crotonoylamino-2,2,6,6- tetramethylpiperidine), 1-crotonoyl-4-crotonyloxy-2,2,6,6-tetramethylpiperidine (1-crotonoyl-4-crotonoyloxy-2,2,6,6-
tetramethylpiperidine); and carbonyl-containing polymerizable unsaturated monomers, such as acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate
methacrylate), formylstyrol, and vinyl alkyl ketone (e.g. vinyl methyl ketone, vinyl ethyl ketone, and vinyl butyl ketone) having 4 to 7 carbon atoms ). One of them may be used alone or two or more of them may be used in combination.

In view of reactivity with the polyisocyanate compound (I) described later, the hydroxyl value of the hydroxyl-containing acrylic resin is preferably in the range of 30 to 300 mgKOH / g, and particularly preferably 40 to 250 mgKOH / g.

In view of the sharpness of the image of the obtained coating film, the acid value range of the hydroxyl-containing acrylic resin is preferably 20 mgKOH / g or less, particularly preferably 1 to 15 mgKOH / g.

In view of the sharpness of the image of the obtained coating film, the weight average molecular weight range of the hydroxyl-containing acrylic resin is preferably 29,000 to 47,000, more preferably 29,000 to 45,000, and still more preferably 29,000 to 40,000.

In view of the sharpness of the image of the obtained coating film, the solubility parameter δA of the hydroxyl-containing acrylic resin is preferably 10.5 to 11.0, and more preferably 10.5 to 10.7.

The above-mentioned hydroxyl-containing polyester resin can usually be obtained by an esterification reaction of a polybasic acid and a polyhydric alcohol in the case of an excess of a hydroxyl group by a method known per se.

As the polybasic acid, a compound commonly used as an acid component in the production of a polyester resin can be used. Examples of this acid component include, for example, an aliphatic polyacid, an alicyclic polyacid, and an aromatic polyacid.

The above-mentioned aliphatic polybasic acid is usually an aliphatic compound having two or more carboxyl groups per molecule, an anhydride of the aliphatic compound, or an esterification product of the aliphatic compound.

Examples of the aliphatic polybasic acid include, for example, an aliphatic polyvalent carboxylic acid such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, eleven Undecanedioic acid, dodecanedioic acid, brasylic acid, octadecanedioic acid, citric acid, and butanetetracarboxylic acid An anhydride of an aliphatic polyvalent carboxylic acid; and an esterification product of an aliphatic polyvalent carboxylic acid and a lower carbon alkyl group having about 1 to 4 carbon atoms. One of these aliphatic polybasic acids may be used alone or two or more of them may be used in combination.

As the aliphatic polybasic acid, adipic acid and / or adipic acid anhydride is preferably used in view of the smoothness of the obtained coating film, the sharpness of the image, and the like.

An alicyclic polybasic acid is generally a compound having one or more alicyclic structures and two or more carboxyl groups per molecule, an anhydride of the compound, or an esterification product of the compound. The alicyclic structure is mainly a 4- to 6-membered ring structure.

Examples of the alicyclic polyacid include, for example, alicyclic polyvalent carboxylic acid, such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid Formic acid (1,3-cyclohexanedicarboxylic acid), 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid acid), 3-methyl-1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid ,2-
cyclohexanedicarboxylic acid), 1,2,4-cyclohexanetricarboxylic acid, and 1,3,5-cyclohexanetricarboxylic acid; alicyclic Anhydrides of polyvalent carboxylic acids of the Group; and esterification products of alicyclic polyvalent carboxylic acids with lower carbon alkyl groups having about 1 to 4 carbon atoms. One of these alicyclic polybasic acids may be used alone or two or more of them may be used in combination.

As the alicyclic polybasic acid, in view of the smoothness and image clarity of the obtained coating film, it is preferable to use 1,2-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic anhydride, 1 , 3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, and 4-cyclohexene-1,2-dicarboxylic anhydride. Among these, 1,2-cyclohexanedicarboxylic acid and / or 1,2-cyclohexanedicarboxylic anhydride are more preferably used.

The aromatic polybasic acid is generally an aromatic compound having at least two carboxyl groups per molecule, an anhydride of the aromatic compound, or an esterification product of the aromatic compound, and examples thereof include, for example, an aromatic polyvalent carboxylic acid such as phthalic acid ( phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, benzene partial Trimellitic acid and pyromellitic acid; the anhydride of the aromatic polyvalent carboxylic acid; and the aromatic polyvalent carboxylic acid with a lower carbon alkyl group having about 1 to 4 carbon atoms Esterification product. One of these aromatic polybasic acids may be used alone or two or more of them may be used in combination.

As the aromatic polybasic acid, phthalic acid, phthalic anhydride, isophthalic acid, trimellitic acid, trimellitic anhydride, and the like are preferably used.

Examples of the fatty acid component used in the production of alkyd resin include, for example, fatty acids such as palm oil fatty acid, cottonseed oil fatty acid, hempseed oil fatty acid, rice bran oil fatty acid, fish oil fatty acid, pine Oil fatty acids, soybean oil fatty acids, linseed oil fatty acids, tung oil fatty acids, rapeseed oil fatty acids, castor oil fatty acids, dehydrated castor oil fatty acids, and safflower oil fatty acids; monocarboxylic acids such as laurel Acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-tert-butylbenzoic acid (p -tert-butylbenzoic acid), cyclohexanoic acid, and 10-phenyloctadecanoic acid; and hydroxycarboxylic acids such as lactic acid, 3-hydroxybutanoic acid, and 3-hydroxy-4-ethyl 3-hydroxy-4-ethoxybenzoic acid. One of these fatty acid components may be used alone or two or more of them may be used in combination.

Examples of fats and oils may include glycerol esterified products of the above-mentioned fatty acids, and the like.

Examples of polyhydric alcohols include, for example, glycols such as ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, Dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, 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-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol , 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1, 4-hexanediol, 2,5-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, hydroxypivalic acid neopentyl glycol ester), hydrogenated bisphenol A, hydrogenated bisphenol F, and dimethylolpropionic acid; by adding a lactone compound such as ε-caprolactone to the above-mentioned glycol obtain Polylactone diol; ester diol compound, such as bis (hydroxyethyl) terephthalate; polyether diol compound , Such as alkylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, and polybutylene glycol; trihydric or higher alcohols, such as glycerol, trimethylolethane ), Trimethylolpropane, diglycerin, triglycerin, 1,2,6-hexanetriol, neopentaerythritol, dipentaerythritol, ginseng (2-hydroxyethyl Tris (2-hydroxyethyl) isocyanuric acid, sorbitol and mannitol; obtained by adding a lactone compound such as ε-caprolactone to the above trihydric or higher alcohol Polylactone polyol compounds; and esterification products of glycerin fatty acids.

Monoalcohol is not particularly limited, and examples thereof include monoalcohols such as methanol, ethanol, propanol, butanol, stearyl alcohol, and 2-phenoxyethanol.

As another alcohol component, it is also possible to synthesize a hyperbranched saturated fatty acid ring by using an acid and a single epoxy compound such as propylene oxide, butylene oxide, "Cardura E 10" (trade name, manufactured by Momentive Specialty Chemicals) Oxypropyl ester).

The method for producing a hydroxyl-containing polyester resin is not particularly limited, and can be performed according to a conventional method. For example, a hydroxyl-containing polyester resin can be manufactured by heating the polybasic acid and the alcohol component in a nitrogen stream at a temperature of about 150 to about 250 ° C for about 5 to about 10 hours, thereby performing polybasic acid and Esterification or transesterification of alcohol components.

When the polybasic acid and the alcohol component undergo an esterification reaction or a trans-esterification reaction, the polybasic acid component and the alcohol component may be added to the reaction container all at once, or one or both of them may be added in portions. In addition, after first synthesizing the hydroxyl-containing polyester resin, the obtained hydroxyl-containing polyester resin can be reacted with an acid anhydride to thereby semi-esterify to obtain a carboxyl- and hydroxyl-containing polyester resin, and the alcohol group can be further It is added to form a polyester resin containing a hydroxyl group.

In esterification or trans-esterification reactions, catalysts can be used to accelerate the reaction. Examples of the catalyst include, for example, catalysts known per se, such as dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate And tetraisopropyl titanate.

In addition, the hydroxyl-containing polyester resin may be modified with a polyisocyanate compound or the like during or after the resin preparation.

Examples of the polyisocyanate compound include, for example, aliphatic diisocyanate compounds such as lysine diisocyanate, hexamethylene diisocyanate
diisocyanate) and trimethylhexane diisocyanate; alicyclic diisocyanate compounds, such as hydrogenated xylene diisocyanate, isophorone diisocyanate, methylcyclohexane Methylcyclohexane-2,4-diisocyanate, methylcyclohexane-2,6-diisocyanate, methylcyclohexane-2,6-diisocyanate, 4,4'-methylenebis ( Cyclohexyl isocyanate) (4,4'-methylenebis (cyclohexylisocyanate)) and 1,3- (isocyanatomethyl) cyclohexane (1,3- (isocyanatomethyl) cyclohexane); aromatic diisocyanate compounds such as di Tolylene diisocyanate, xylylene diisocyanate, and diphenylmethane diisocyanate; organic polyisocyanates themselves, such as trivalent or higher polyisocyanates, For example, lysine triisocyanate; adduct of organic polyisocyanate with polyol, low molecular weight polyester resin, water, etc .; and cyclized polymer (Eg, isocyanurate) or biuret-type adduct of organic polyisocyanate. One of these polyisocyanate compounds may be used alone or two or more of them may be used in combination.

In view of the water resistance of the obtained coating film, the hydroxyl value of the hydroxyl-containing polyester resin is preferably 30 to 300 mgKOH / g, more preferably 40 to 250 mgKOH / g, and still more preferably 50 to 200 mgKOH / g.

In view of the sharpness of the image of the obtained coating film, the number average molecular weight range of the hydroxyl-containing polyester resin is preferably 29,000 to 47,000, more preferably 29,000 to 45,000, and still more preferably 29,000 to 40,000.

In view of the storage stability of the coating composition, the acid value range of the hydroxyl-containing polyester resin is preferably 0 to 10 mgKOH / g, and more preferably 0 to 5 mgKOH / g.

In view of the sharpness of the image of the obtained coating film, the solubility parameter δA of the hydroxyl-containing polyester resin is preferably 10.5 to 11.0, and more preferably 10.5 to 10.7.

(Polyisocyanate compound (I))
The polyisocyanate compound (I) is a compound having two or more free isocyanate groups per molecule and the isocyanate groups are not blocked by a blocking agent.

Specifically, those conventionally used for polyurethane production can be used. Examples of this polyisocyanate include aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, aromatic aliphatic polyisocyanate compounds, aromatic polyisocyanate compounds, crude products thereof, modified products of these polyisocyanate compounds (containing amines Urethane group, carbodiimide group, allophanate group, urea group, biuret group, uretdione group, uremine group Modified products such as uretimine group, isocyanurate group, or oxazolidone group), and mixtures of two or more thereof.

Specific examples of the aliphatic polyisocyanate compound include, for example, ethylene diisocyanate, tetramethylene diisocyanate, and diisocyanate adipate
(hexamethylene diisocyanate) (HDI), dodecamethylene diisocyanate, 1,6,11-undecantriisocyanate, 2,2 diisocyanate 2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanate methylcaproate, bis (2-isocyanatoethyl) fumarate, bis (2-isocyanatoethyl) carbonate, and 2-isocyanatoethyl-2,6-diisocyanatohexanoate.

Specific examples of the alicyclic polyisocyanate compound include, for example, isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI) Cyclohexanediisocyanate
(cyclohexylene diisocyanate), methylcyclohexylene diisocyanate (hydrogenated TDI), bis (2-isocyanatoethyl) -4-cyclohexene-1,2-dicarboxylate (bis (2-isocyanatoethyl) -4-cyclohexene-1,2-dicarboxylate), and 2,5- and / or 2,6-norbornene diisocyanate.

Specific examples of the aromatic aliphatic polyisocyanate compound include m-xylylene diisocyanate or p-xylylene diisocyanate (XDI), and diisocyanate α , α, α ', α'-tetramethylxylylene diisocyanate (TMXDI).

Specific examples of the aromatic polyisocyanate compound include, for example, 1,3-phenylene diisocyanate or 1,4-phenylene diisocyanate, 2,4-diisocyanate Toluene diester or 2,6-tolylene diisocyanate (TDI), crude TDI (crude TDI), 2,4'-biphenylmethane diisocyanate or 4,4 ' -4,4'-biphenylmethane diisocyanate (MDI), 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl- 4,4'-diisocyanatobiphenyl (3,3'-dimethyl-4,4'-diisocyanatobiphenyl), 3,3'-dimethyl-4,4'-diisocyanatodiphenylmethane (3,3'-dimethyl-4,4'-diisocyanatodiphenylmethane), crude MDI, 1,5-naphthylene diisocyanate, 4,4 ', 4 ”-triphenylmethane Triisocyanate (4,4 ', 4 ”-triphenylmethane triisocyanate), and m-isocyanatophenylsulfonyl isocyanate or p-isocyanatophenylsulfonyl isocyanate ).

1. polyisocyanate compound
Examples of the modified product of compound (I) include, for example, modified products of polyisocyanate, such as modified MDI (urethane-modified MDI), carbodiimide modified Carbodiimide-modified MDI, trihydrocarbylphosphate modified MDI), urethane-modified TDI, biuret-modified HDI (biuret modified HDI), isocyanurate modified HDI, and isocyanurate modified IPDI; and mixtures of two or more of them (e.g., modified MDI and modified HDDI) A combination of urethane-modified TDI (prepolymer containing isocyanate groups). Among them, trimeric isocyanate-modified HDI is preferred.

In view of chemical resistance and corrosion resistance, an aliphatic polyisocyanate compound and an alicyclic polyisocyanate compound are preferably used as the polyisocyanate compound (I). The number average molecular weight range of the polyisocyanate compound (I) is preferably 3,000 or less, and particularly preferably 100 to 1,500.

Examples of commercially available products of this polyisocyanate compound (I) include, for example, Bayhydur TP-LS2550, Sumidur N3300 (manufactured by Sumika Bayer Urethane Co., Ltd.), TPA 100 (manufactured by Asahi Kasei Chemicals Corp.), and BASONAT HI100 (Manufactured by BASF).

In view of the sharpness of the image of the obtained coating film, the blending amount of the polyisocyanate compound (I) is based on 100 parts by mass of the total solid content of the hydroxyl-containing resin (A), and is preferably 60 to 90 It is more preferably 65 to 85 parts by mass.

The amount of the polyisocyanate compound (I) is appropriately selected so that the equivalent ratio of the isocyanate group (NCO) contained therein to the hydroxyl group (OH) in the hydroxyl group-containing resin (A) ), That is, NCO / OH, is usually in the range of 1.0 to 2.5, preferably 1.0 to 2.0.

The solvent-based first colored coating composition (X) preferably further contains a pigment. Examples of the pigment include, for example, a color pigment, an extender pigment, and an effect pigment. One of them may be used alone or two or more of them may be used in combination.

When the solvent-based first colored coating composition (X) contains the pigment, the total blending amount of the pigment is 100 parts by mass of the total resin in the solvent-based first colored coating composition (X). The solid content is based on a range of preferably 1 to 170 parts by mass, more preferably 5 to 165 parts by mass, and still more preferably 10 to 160 parts by mass.

Examples of the coloring pigment include, for example, titanium oxide, zinc oxide, carbon black, molybdenum red, Prussian blue, cobalt blue, and azo pigments (azo -based pigment), phthalocyanine-based pigment, quinacridone-based pigment, iso indoline-based pigment, three-based pigment ), Perylene-based pigments, dioxazine-based pigments, and diketopyrrolopyrrole-based pigments. Among them, titanium oxide and carbon black are preferred.

When the solvent-based first colored coating composition (X) contains the above-mentioned colored pigment, the blending amount of the colored pigment is based on the total resin solid content in 100 parts by mass of the solvent-based first colored coating composition (X). In general, it is preferably in the range of 1 to 180 parts by mass, more preferably 3 to 160 parts by mass, and still more preferably 5 to 140 parts by mass.

Examples of extender pigments include, for example, talc, clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, silica, and alumina white.

When the solvent-based first colored coating composition (X) contains the above-mentioned filler pigment, the blending amount of the filler pigment is based on the total resin solid content in 100 parts by mass of the solvent-based first colored coating composition (X). In general, it is preferably in the range of 1 to 150 parts by mass, more preferably 5 to 130 parts by mass, and still more preferably 10 to 110 parts by mass.

Examples of effect pigments include, for example, aluminum (including deposited aluminum), copper, zinc, brass, nickel, aluminum oxide, mica, titanium oxide-coated alumina, iron oxide-coated oxidation Aluminum, titanium oxide-coated mica, iron oxide-coated mica, glass flake, and holographic pigment. One of these effect pigments may be used alone or two or more of them may be used in combination. Non-leafing type aluminum and leafing type aluminum can be used as the aluminum pigment, and either one can be used.

When the solvent-based first colored coating composition (X) contains the above-mentioned effect pigment, the blending amount of the effect pigment is based on the total resin solid content in 100 parts by mass of the solvent-based first colored coating composition (X). In general, it is preferably in the range of 1 to 50 parts by mass, more preferably 2 to 30 parts by mass, and still more preferably 3 to 20 parts by mass.

The solvent-based first colored coating composition (X) contains a hydroxyl group-containing resin (A) and a polyisocyanate compound (I) as basic resin components. If necessary, the solvent-based first colored coating composition (X) further contains the above-mentioned pigments, other resin components, organic solvents, thickeners, antisettling agents, curing catalysts, pigment dispersants, UV absorption Agents, light stabilizers, surface conditioners, defoamers, plasticizers, etc. These can be dissolved or dispersed in an organic solvent to form a coating composition.

The above-mentioned solvent-based first colored coating composition (X) can be obtained by a method known per se, for example, by air spray coating, airless spray coating, or a rotary atomizing coater. atomization coating machine) and applied to the uncured base coating film obtained in step (1). During coating, an electrostatic charge can be applied. Among them, electrostatic coating by air spraying and electrostatic coating by a rotary atomizing coater are preferred, and electrostatic coating by a rotary atomizing coater is particularly preferred.

In terms of the thickness of the cured film, the thickness of the coating film of the solvent-based first colored coating composition (X) is preferably generally 10 to 100 μm, more preferably 10 to 50 μm, and still more preferably 15 to 35 μm. range.

The method for forming a multilayer coating film in the present invention has the advantage that a multilayer coating film having excellent image sharpness can be formed without preheating.

In this specification, the cured coating film is in a cured dry state as defined in JIS-K-5600-1-1, that is, it is strongly sandwiched between the thumb and forefinger through the center of the coated surface. The dents caused by fingerprints are not left on the coated surface, no movement of the coating film is felt, and rapid and repeated rubbing with the fingertip through the center of the coated surface does not leave friction marks on the coated surface. On the other hand, the uncured coating film is a state in which the coating film has not reached the above-mentioned cured and dried state, and the touch dry state and semi-cured and dried state (defined in JIS-K-5600-1-1) semi-cured dry state) refers to the state of the uncured coating film.

[Step (3)]
In step (3) of the present invention, a solvent-based second colored coating composition (Y) is applied to the uncured first colored coating film obtained in step (2) to form an uncured second colored coating. Coating film.

<Solvent-based second colored coating composition (Y)>
The solvent-based second colored coating composition (Y) is a one-component coating composition containing a hydroxyl group-containing resin (B), and is used for the purpose of generally imparting excellent appearance to an object to be coated.

(Hydroxy-containing resin (B))
The hydroxyl group-containing resin (B) is a resin having at least one hydroxyl group per molecule. Examples of the hydroxyl-containing resin (B) include, for example, a resin having a hydroxyl group, such as an acrylic resin having a hydroxyl group, a polyester resin having a hydroxyl group, a polycarbonate resin having a hydroxyl group, a polyurethane resin having a hydroxyl group, having Hydroxyl epoxy resin, and alkyd resin with hydroxyl group. One of them may be used alone or two or more of them may be used in combination. Among these, in view of the thickness of the coating film and weather resistance, the hydroxyl-containing resin (B) is preferably a hydroxyl-containing acrylic resin and / or a hydroxyl-containing polyester resin.

In view of the water resistance of the obtained coating film (water
resistance), and the hydroxyl value of the hydroxyl-containing resin (B) is preferably in the range of 30 to 300 mgKOH / g, particularly preferably 40 to 250 mgKOH / g.

In view of the sharpness of the image of the obtained coating film, the acid value range of the hydroxyl-containing resin (B) is preferably 20 mgKOH / g or less, particularly preferably 1 to 15 mgKOH / g.

In view of the sharpness of the image of the obtained coating film, the weight-average molecular weight of the hydroxyl-containing resin (B) is in the range of preferably 15,000 to 40,000, and more preferably 16,000 to 35,000.

In view of the sharpness of the image of the obtained coating film, the solubility parameter δB of the hydroxyl-containing resin (B) is preferably 9.0 to 10, and more preferably 9.2 to 9.9.

In view of the sharpness of the image of the obtained coating film, the blending amount (solid content) of the hydroxyl-containing resin (B) was 100 parts by mass of the solvent-based second colored coating composition (Y) as the total solid content The reference meter is preferably in the range of 40 to 97 parts by mass, and more preferably 50 to 90 parts by mass.

The hydroxyl-containing acrylic resin can be obtained by using the above-mentioned method and the monomer described for the hydroxyl-containing acrylic resin in the hydroxyl-containing resin (A).

In view of the water resistance of the obtained coating film, the hydroxyl value of the hydroxyl-containing acrylic resin is preferably 30 to 300 mgKOH / g, and particularly preferably 40 to 250 mgKOH / g.

In view of the sharpness of the image of the obtained coating film, the acid value range of the hydroxyl-containing acrylic resin is preferably 20 mgKOH / g or less, particularly preferably 1 to 15 mgKOH / g.

In view of the sharpness of the image of the obtained coating film, the weight average molecular weight of the hydroxyl-containing acrylic resin is in the range of preferably 25,000 to 40,000, and more preferably 26,000 to 33,000.

In view of the sharpness of the image of the obtained coating film, the solubility parameter δB of the hydroxyl-containing acrylic resin is preferably 9.0 to 10, more preferably 9.2 to 9.9.

The hydroxyl-containing polyester resin can be obtained by using the above-mentioned method and the monomer described for the hydroxyl-containing polyester resin in the hydroxyl-containing resin (A).

In view of the water resistance of the obtained coating film, the hydroxyl value of the hydroxyl-containing polyester resin is preferably 30 to 300 mgKOH / g, more preferably 40 to 250 mgKOH / g, and still more preferably 50 to 200 mgKOH / g.

In view of the sharpness of the image of the obtained coating film, the number average molecular weight of the hydroxyl-containing polyester resin is preferably in the range of 15,000 to 20,000 and particularly preferably 15,000 to 18,000.

In view of the storage stability of the coating composition, the acid value range of the hydroxyl-containing polyester resin is preferably 0 to 10 mgKOH / g, and more preferably 0 to 5 mgKOH / g.

In view of the image clarity of the obtained coating film, the solubility parameter δB of the hydroxyl-containing polyester resin is preferably 9.0 to 10, and more preferably 9.2 to 9.9.

The solvent-based second colored coating composition (Y) may contain a curing agent. Examples of the curing agent include, for example, a melamine resin, a polyisocyanate compound, a blocked polyisocyanate compound, and a carbodiimide group-containing compound.

The solvent-based second colored coating composition (Y) contains a hydroxyl group-containing resin (B) as a basic resin component. If necessary, the solvent-based second colored coating composition (Y) may further contain pigments, other resin components, organic solvents, thickeners, anti-settling agents, curing catalysts, pigment dispersants, UV absorbers, and light stabilizers. Agents, surface modifiers, defoamers, plasticizers, etc., and these can be dissolved or dispersed in an aqueous medium to form a coating composition.

As the pigment, a coloring pigment, an effect pigment, or the like can be used.
Examples of the coloring pigment include, for example, titanium oxide, zinc oxide, carbon black, molybdenum red, Prussian blue, cobalt blue, azo-based pigments, phthalocyanine-based pigments, quinacridone-based pigments, isoindoline-based pigments, and threate-based pigments (Anthraquinone-based pigment), fluorene-based pigment, difluorene-based pigment, and diketopyrrolopyrrole-based pigment, and one of these may be used alone or two or more of them may be used in combination.

Examples of effect pigments include, for example, aluminum (including deposited aluminum), copper, zinc, brass, nickel, alumina, mica, titanium oxide coated coated alumina, iron oxide coated alumina, titanium oxide coated Mica, iron oxide-coated mica, glass flakes, and holographic pigments, and one of these may be used alone or two or more of them may be used in combination. The effect pigment is preferably scaly.

The solvent-based second colored coating composition (Y) can be applied to the uncured first colored coating film by a method known per se such as air spraying, airless spraying, spin spray coating, curtain coating, and coating Static charges can be applied during this period. Among these methods, air spray coating, spin spray coating, and the like are preferred.

In view of the image clarity of the obtained multilayer coating film, the coating amount of the solvent-based second colored coating composition (Y) to be applied is preferably 6 to 20 µm, more preferably 8 to 20, to provide a cured film thickness. 15 μm range. In particular, in the case where the aqueous second colored coating composition (Y) contains an effect pigment, when the coating amount is within the above range, the effect pigment is oriented in the second colored coating film, making it possible to obtain Appearance of excellent design properties of gloss or optical interference.

The relationship between the solubility parameter δA of the hydroxyl-containing resin (A) contained in the solvent-based second colored coating composition (Y) and the solubility parameter δB of the hydroxyl-containing resin (B) is "0.6 <δA-δB <1.2 ", And preferably" 0.6 <δA-δB ≤ 1.1 ".

When the value of "δA-δB" exceeds 0.6, the hydroxyl group-containing resin (A) in the solvent-based first colored coating composition (X) and the solvent-containing second colored coating composition (Y) can be prevented. By mixing the hydroxyl resin (B), a coating film having excellent image clarity, flip-flop (FF) properties, and hardness can be obtained.
When the value of "δA-δB" is less than 1.2, in the following step (4), the solvent-based two-component transparent coating composition (Z) can be uniformly spread on the second colored coating film, and can be spread on the second colored coating film. The entire surface of the colored coating film forms a transparent coating film.

[Step (4)]
In step (4) of the present invention, a solvent-based two-component transparent coating composition (Z) is applied to the uncured second colored coating film obtained in step (3) to form an uncured clear coating. membrane.

(Solvent-based two-component transparent coating composition (Z))
As the solvent-based two-component transparent coating composition (Z), any solvent-based two-component thermosetting transparent coating composition known for coating of automobile bodies and the like can be used. Examples of the thermosetting transparent coating composition include, for example, an organic solvent-based thermosetting coating composition containing a crosslinkable functional group-containing base resin and a crosslinking agent.

Examples of the crosslinkable functional group included in the base resin include, for example, a carboxyl group, a hydroxyl group, an epoxy group, and a silanol group.

Examples of the kind of the base resin include, for example, acrylic resin, polyester resin, alkyd resin, urethane resin, epoxy resin, and fluororesin.

Examples of the cross-linking agent include, for example, a polyisocyanate compound, a blocked polyisocyanate compound, a melamine resin, a urea resin, a carboxyl group-containing compound, a carboxyl group-containing resin, and an epoxy resin. Based resins, and epoxy-containing compounds.

As the combination of the base resin and the crosslinking agent in the solvent-based two-component transparent coating composition (Z), a combination of a hydroxyl-containing resin and a polyisocyanate compound is preferred.

If necessary, coloring pigments, effect pigments, dyes, etc. may be included in the solvent-based two-component transparent coating composition (Z) to the extent that transparency is not impaired, and filler pigments, UV absorbers, and light stabilizers may be appropriately contained. , Defoamer, thickener, rust inhibitor, surface conditioner.

The solvent-based two-component transparent coating composition (Z) may be applied to the second colored coating film by a method known per se such as airless spraying, air spraying, rotary atomizing coater, and an electrostatic charge may be applied during coating.

In terms of cured film thickness, the coating film thickness of the solvent-based two-component transparent coating composition (Z) is preferably usually 10 to 80 μm, more preferably 15 to 70 μm, and still more preferably 20 to 60 μm Range.

After applying the solvent-based two-component transparent coating composition (Z), if necessary, it is preferably set at an interval of 1 to 60 minutes at room temperature, or preheated at a temperature of 40 to 80 ° C for about 1 to 60 minute.

[Step (5)]
In step (5) of the method for forming a multilayer coating film in the present invention, the formed in step (1) is simultaneously cured by heating at a temperature of 75 ° C to 95 ° C, preferably 80 ° C to 90 ° C. Uncured base coating film, uncured first colored coating film formed in step (2), uncured second colored coating film formed in step (3), and uncured substrate formed in step (4) Clear coating film.

When the heating temperature is 75 ° C or higher, a multilayer coating film having excellent hardness can be obtained, and when the heating temperature is 95 ° C or lower, a multilayer coating film having excellent image clarity can be obtained.

The curing of the base coating film, the first colored coating film, the second colored coating film, and the transparent coating film can be performed by a common coating film baking method, for example, hot-air heating, infrared heating heating) or high-frequency heating.
The range of the heating time is preferably 10 to 60 minutes, and more preferably 15 to 40 minutes.

Examples

Hereinafter, the present invention will be described in more detail by referring to examples, but the scope of the present invention is not limited to these examples. In the embodiment, "part" and "%" represent "mass part" and "mass%", respectively.

[Manufacturing test board]
On a cold rolled steel plate (450 mm × 300 mm × 0.8 mm) treated with zinc phosphate, a thermosetting epoxy resin-based cationic electrodeposition coating composition was applied by electrodeposition. resin-based cationic electrodeposition coating composition) (trade name, "Elecron GT-10", manufactured by Kansai Paint Co., Ltd.) to a film thickness of 20 µm, and then cured by heating at 170 ° C for 30 minutes to prepare Metal components.

A 2 mm polypropylene plate (350 mm × 10 mm × 2 mm) was prepared as a plastic member.

Then, the surface of the metal member and the plastic member prepared as described above was wiped with a gauze including petroleum benzine and degrease, and they were placed next to each other to form a test board. plate).

[Production of hydroxyl-containing resins (A) and (B)]
(Production example 1)
In a reaction vessel equipped with a stirring device, a thermometer, a reflux condenser, a thermostat, and a dropping pump, add 60 parts of xylene, and blow the nitrogen while stirring the temperature. Raise to 145 ° C. Then, using a dropping pump, the following monomer and polymerization initiator mixture was added dropwise to the reaction vessel at a fixed rate for 3 hours:
52 parts of methyl methacrylate,
22 parts of ethyl acrylate,
10 parts of methoxyethyl acrylate,
15 parts of 2-hydroxyethyl methacrylate
methacrylate), and
1 part of acrylic acid.
Then, a mixture of 0.5 parts of 2,2'-azobisisobutyronitrile (2,2'-azobisisobutyronitrile) and 10 parts of xylene was added dropwise at a fixed rate over 1 hour. After the dropwise addition was completed, the mixture was aged at the same temperature for 3 hours to terminate the reaction to obtain a hydroxyl-containing acrylic resin (A-1) solution.

The obtained hydroxyl-containing acrylic resin (A-1) solution was a uniform transparent solution having a solid content of 50%. In addition, the hydroxyl group-containing acrylic resin (A-1) had a solubility parameter δA of 10.6, a weight average molecular weight of 29,000, and a hydroxyl value of 65 mgKOH / g.

(Production Examples 2 to 5)
The hydroxyl group-containing resins (A-2) to (A-5) were obtained in the same manner as in Production Example 1 except that the monomer composition was changed as shown in Table 1. The solubility parameters δA, the weight average molecular weight, and the hydroxyl value of the hydroxyl-containing resins (A-2) to (A-5) are shown in Table 1.

(Production Examples 6 to 10)
The hydroxyl group-containing resins (B-1) to (B-5) were obtained in the same manner as in Production Example 1 except that the monomer composition was changed as shown in Table 2. The solubility parameters δB, the weight average molecular weight, and the hydroxyl value of the hydroxyl-containing resins (B-1) to (B-5) are shown in Table 2.
The hydroxyl-containing resins (A-1) to (A-5) and the hydroxyl-containing resins (B-1) to (B-5) obtained as described above are "hydroxyl-containing acrylic resins".

[Production of solvent-based first colored coating composition (X)]
(Production Example 11)
A solution of 10.6 parts (solid content) of a hydroxyl-containing resin (A-1) with a solid content of 50%, and 2.6 parts (solid content) of a hydroxyl-containing polyester resin (A-6) with a solid content of 60% ( Hydroxyl value: 105, solubility parameter value: 10.6), 9.5 parts (solid content) of "Sumidur N3300" (commercial name, manufactured by Sumika Covestro Urethane Co., Ltd., polyisocyanate compound), 28.3 parts (solid content) "JR-806" (commercial name, manufactured by Tayca Corp., titanium oxide pigment), 0.2 parts of "MA-100" (commercial name, manufactured by Mitsubishi Chemical Corp., carbon black), and 7.4 parts of "Balifine BF "-20" (trade name, manufactured by Sakai Chemical Industry Co., Ltd., barium sulfate with an average particle diameter of 0.03 μm) was uniformly mixed.
In addition, the solid content was adjusted by butyl acetate to obtain a solvent-based first colored coating composition (X-1), so that the "viscosity cup NK-2 (viscosity cup NK)" manufactured by Anest Iwata Corp. was used at 20 ° C. -2) "The measured viscosity is 20 ± 1 second.

(Production Examples 12 to 15)
The solvent-based first colored coating compositions (X-2) to (X-5) were obtained in the same manner as in Production Example 11 except that the monomer composition was changed as shown in Table 3.

[Production of solvent-based second colored coating composition (Y)]
(Production Example 16)
21.6 parts (solid content) of a hydroxyl-containing acrylic resin (B-1) solution having a solid content of 50%, and 4.5 parts (solid content) of a hydroxyl-containing polyester resin (B-6) having a solid content of 70% ) (Hydroxyl value: 60, solubility parameter value: 9.9), 5.4 parts (solid content) of "GX 180A" (trade name, manufactured by Asahi Kasei Corp., aluminum paste), and 3.1 parts of "Balifine "BF-20" (trade name, manufactured by Sakai Chemical Industry Co., Ltd., barium sulfate with an average particle diameter of 0.03 μm, filled with pigment) was uniformly mixed.
In addition, the solid content was adjusted by butyl acetate to obtain a solvent-based second colored coating composition (Y-1), so that it was measured at 20 ° C with a "viscosity cup NK-2" manufactured by Anest Iwata Corp. The viscosity is 10 ± 1 second.

(Production Examples 17 to 20)
The solvent-based second colored coating compositions (Y-2) to (Y-5) were obtained in the same manner as in Production Example 16 except that the monomer composition was changed as shown in Table 4.

[Manufacturing test coated board]
(Example 1)
The obtained test board was spray-coated with a water-based primer coating composition "Soflex 3100" (trade name, manufactured by Kansai Paint Co., Ltd.) to a thickness of 10 μm (in terms of the thickness of the cured film) and at room temperature. After standing for 6 minutes, the solvent-based first colored coating composition (X-1) produced above was electrostatically applied to a thickness of 20 μm (in terms of the thickness of the cured film) and allowed to stand at room temperature. For 6 minutes, the solvent-based second colored coating composition (Y-1) produced as described above was then electrostatically applied to a thickness (in terms of the thickness of the cured film) of 10 μm.

Next, a solvent-based two-component transparent coating composition (Z) "Soflex 7500" (trade name, manufactured by Kansai Paint Co., Ltd.) was electrostatically applied to a thickness (in terms of dry film thickness) of 35 μm. , And allowed to stand at room temperature for 5 minutes, and then heated in an oven at 85 ° C. for 30 minutes to form a test coated plate on which a multilayer coating film was formed.
The obtained multilayer coating films were subjected to various coating film performance tests described below. The results are shown in Table 5.

(Examples 2 to 5 and Comparative Examples 1 to 4)
The test coating plate on which the multilayer coating film was formed was the same as in Example 1, except that the solvent-based first colored coating composition (X) and the solvent-based second colored coating composition (Y) were changed as shown in Table 5. , And baking temperature. Each of the obtained multilayer coating films was subjected to various coating film performance tests described below.
In Comparative Example 2, the solvent-based two-component transparent coating composition (Z) "Soflex 7500" (trade name, manufactured by Kansai Paint Co., Ltd.) was not evenly spread on the coating film, and Since a transparent coating film cannot be formed on the entire surface of the coating film, various coating film performance tests have not been performed. The results are shown in Table 5.

[Coating film performance test]
(Image sharpness)
The Wb value of each test coated plate obtained in the foregoing was measured with a "Determination of Image Clarity (DOI)" analyzer "Wave Scan DOI" (trade name, manufactured by BYK, Gardner).
A smaller Wb value indicates higher image sharpness on the coated surface. A smaller Wb value is better, and the Wb value needs to satisfy the condition of less than 20.

(Flip-flop (FF) properties)
For each of the test coated plates obtained above, a laser type metallic feeling analyzer (Alcoop LMR-200) (trade name, manufactured by Kansai Paint Co., Ltd.) was used to measure 15 ° The Y value "a" of the light receiving angle and the Y value "b" of the light receiving angle of 110 ° are obtained by the following formula.
FF value = (a--b) / [(a + b) / 2]

A large FF value indicates a large change in Y value (brightness) due to a viewing angle (light receiving angle), and it indicates that the angular heterochromatic property is excellent. The upper limit of the FF value is 2.00.

(Pencil Hardness)
The pencil hardness of the coated surface of each of the test coated plates obtained previously was measured in accordance with JIS-K-5600-5-4 (1999) "scratch hardness (pencil method)".
When the pencil hardness is F or H, the hardness is good.

As can be seen from Table 5, the test coated plates of Examples 1 to 5 were excellent in image sharpness, chromaticity (FF) properties, and hardness.

On the other hand, the test coated plate of Comparative Example 1 with δA-δB of 0.5 was inferior to those of Examples 1 to 5 in terms of image sharpness and angular heterochromatic (FF) properties.
In Comparative Example 2 in which δA-δB was 1.4, the solvent-based two-component transparent coating composition (Z) "Soflex 7500" (trade name, manufactured by Kansai Paint Co., Ltd.) did not spread evenly. Various coating film performance tests have not been performed on the coating film, and a transparent coating film cannot be formed on the entire surface of the coating film.

In addition, in the test coated plate of Comparative Example 3 in which the baking temperature of the coating film was 60 ° C., the angle-dependent color (FF) properties and hardness were worse than those of the test coated plates of Examples 1 to 5.
In addition, in the test coated plate of Comparative Example 4 in which the baking temperature of the coating film was 110 ° C., the angle-dependent color (FF) properties and hardness were inferior to those of the test coated plates of Examples 1 to 5.

Claims (3)

A method for forming a multilayer coating film, comprising: (1) a step of applying a primer coating composition (P) to a surface of an automotive outer plate including at least one of a metal member and a plastic member to form an uncured primer coating film ; (2) applying a solvent-based first colored coating composition (X) to the uncured base coating film obtained in step (1) to form an uncured first colored coating film step; (3) a step of applying a solvent-based second colored coating composition (Y) to the uncured first colored coating film obtained in step (2) to form an uncured second colored coating film; (4) a step of applying a solvent-based two-component transparent coating composition (Z) to the uncured second colored coating film obtained in step (3) to form an uncured transparent coating film; and (5) heating the uncured base coating film formed in step (1), the uncured first colored coating film formed in step (2) at 75 ° C to 95 ° C, and Forming the uncured second colored coating film and the uncured transparent coating film formed in step (4) to simultaneously cure the coating films, The solvent-based first colored coating composition (X) is a two-component coating composition containing a hydroxyl-containing resin (A) and a polyisocyanate compound (I). Wherein, the solvent-based second colored coating composition (Y) is a single-component coating composition containing a hydroxyl-containing resin (B), and The solubility parameter δA of the hydroxyl-containing resin (A) and the solubility parameter δB of the hydroxyl-containing resin (B) have a relationship of 0.6 <δA-δB <1.2. For example, the method of claim 1, wherein the hydroxyl group-containing resin (A) has a weight average molecular weight ranging from 29,000 to 47,000. For example, the method of claim 1 or 2, wherein the hydroxyl-containing resin (B) has a weight average molecular weight ranging from 15,000 to 40,000.