JP2021133316A - Method for producing multilayered coating film - Google Patents

Abstract

To provide a method for producing a multilayered coating film which is excellent in appearance and resistance.SOLUTION: A method for producing a multilayered coating film onto a molding for an automobile component composed of a plastic base material includes: a step of coating a first coating composition onto the molding, and forming a first uncured coating film; a step of forming a second uncured coating film onto the first uncured coating film; a step of forming an uncured clear coating film onto the second uncured coating film; and a step of baking and curing the first uncured coating film, the second uncured coating film and the uncured clear coating film, and forming a multilayered coating film. The first coating composition contains a polyester resin (A) and a carbodiimide compound (B), the polyester resin (A) has predetermined Tg, number average molecular weight, hydroxyl value and acid value, and a predetermined functional group, and has at least one selected from the group consisting of a hydroxyl group, a ketone group, a carboxy group, an amino group and a sulfo group, and the second uncured coating film is a mica base coating film.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a multi-layer coating film.

In recent years, molded products for automobile parts made of plastic materials have been used. This molded product for automobile parts is usually required to be painted and have excellent designability.
For example, a multi-layer coating film is formed on a molded product for an automobile part to impart excellent designability.

Japanese Patent Application Laid-Open No. 2005-905 (Patent Document 1) describes a step of applying a water-based white primer coating having a water content of 15 to 48% by weight on a plastic base material, and preheating the coating coating of the primer coating. Then, in the step of adjusting the water content in the coating film within the range of 1 to 10% by weight and the surface electrical resistance value of the coating film to less than 109Ω / □, and on the above-mentioned adjusting coating film of the primer paint, The process of electrostatically applying a heat-curable transparent colored paint,
The process of electrostatically coating a thermosetting clear paint on the uncured paint of the colored paint and then simultaneously baking the three-layer paint made of the above paint to obtain the Munsell color system specified in JIS Z 8721. A method for producing a coating film of a plastic base material including a step of obtaining a multi-layer coating film having a lightness (N value) of 8.5 or more based on the lightness (N value) is disclosed.

Japanese Unexamined Patent Publication No. 2005-905

Such a multi-layer coating film is required to have high resistance in addition to being excellent in appearance, but at present, it cannot be said that the technique for improving the appearance and resistance is sufficient.

The present invention solves such a technical problem, and an object of the present invention is to provide a method for producing a multi-layer coating film having excellent appearance and resistance.

In order to solve the above problems, the present invention provides the following aspects.
[1] A method for manufacturing a multi-layer coating film on a molded product for automobile parts made of a plastic material.
A step of coating a first coating composition on a molded product to form an uncured first coating film.
A step of forming an uncured second coating film on an uncured first coating film,
A step of forming an uncured clear coating film on an uncured second coating film, and baking and curing the uncured first coating film, the uncured second coating film, and the uncured clear coating film. Including the step of forming a multi-layer coating film
The first coating composition contains a polyester resin (A) and a carbodiimide compound (B).
The polyester resin (A) is
The glass transition temperature Tg is 40 ° C. or higher and 120 ° C. or lower.
The number average molecular weight Mn is 6000 or more and 20000 or less.
The hydroxyl value is 12 mgKOH / g or less,
The acid value is 20 mgKOH / g or less,
It has at least one selected from the group consisting of a hydroxyl group, a ketone group, a carboxy group, an amino group and a sulfo group.
The uncured second coating film is a method for producing a multi-layer coating film which is a mica-based coating film.
[2] The method for producing a multi-layer coating film according to [1], wherein the baking curing temperature is 100 ° C. or higher and 130 ° C. or lower.
[3] The method for producing a multi-layer coating film according to [1] or [2], wherein the glass transition temperature Tg of the polyester resin (A) is 40 ° C. or higher and 80 ° C. or lower.
[4] The method for producing a multilayer coating film according to any one of [1] to [3], wherein the polyester resin (A) has a hydroxyl value of 1 mgKOH / g or more and 10 mgKOH / g or less.
[5] The method for producing a multilayer coating film according to any one of [1] to [4], wherein the acid value of the polyester resin (A) is 1.0 mgKOH / g or more and 8.0 mgKOH / g or less.

The method for producing a multi-layer coating film according to the present disclosure provides a method for producing a multi-layer coating film having excellent appearance and resistance.

The method for producing a multi-layer coating film according to the present disclosure is as follows.
A process of coating a first coating composition on a molded product for automobile parts (hereinafter sometimes referred to as "molded product for automobile parts") made of a plastic material to form an uncured first coating film.
A step of forming an uncured second coating film on an uncured first coating film,
A step of forming an uncured clear coating film on the uncured second coating film, and baking and curing the uncured first coating film, the uncured second coating film, and the uncured clear coating film are performed. Including the step of forming a layer coating film
The first coating composition contains a polyester resin (A) and a carbodiimide compound (B).
The polyester resin (A) is
The glass transition temperature Tg is 40 ° C. or higher and 120 ° C. or lower.
The number average molecular weight Mn is 6000 or more and 20000 or less.
The hydroxyl value is 12 mgKOH / g or less,
The acid value is 20 mgKOH / g or less,
It has at least one selected from the group consisting of a hydroxyl group, a ketone group, a carboxy group, an amino group and a sulfo group.
The uncured second coating film is a mica-based coating film.

The method for producing a multi-layer coating film according to the present disclosure is superior to a molded product for automobile parts made of a plastic material (hereinafter, may be referred to as "molded product for automobile parts" in the present specification). It is possible to form a multi-layer coating film having a good appearance and high resistance. For example, it is possible to form a multi-layer coating film having an excellent appearance even for a molded product for an automobile part having a complicated flat shape, a three-dimensional shape such as unevenness.

Further, by using the first coating composition, a coating film having a stable hue can be formed. Therefore, the first coating film can form a coating film having good adhesion to a molded product made of a plastic material and having a stable hue, so that the first coating film formed from the first coating composition can be formed. Can function as a color-based coating film in addition to the function as a primer coating film. Therefore, in one embodiment, the method for producing a multi-layer coating film according to the present disclosure can reduce the step of forming a color-based coating film, and can bring about reduction of environmental load such as energy saving and reduction of carbon dioxide emissions. can.

In addition, in the method for producing a multi-layer coating film according to the present disclosure, the first coating composition is the same on an object to be coated made of a steel material such as an automobile body, in addition to a molded product for an automobile part made of a plastic material. It is possible to form a multi-layer coating film by coating in the above process. Therefore, in one embodiment, it is not necessary to coat the object to be coated made of steel material and the object to be coated made of plastic material in separate steps. Furthermore, it can bring about a reduction in environmental load.

Further, in the method for producing a multi-layer coating film according to the present disclosure, since the second coating film is a mica-based coating film, high designability can be obtained. Excellent design can be obtained.

Hereinafter, each step in the method for producing a multi-layer coating film according to the present disclosure will be described.

[Step of forming an uncured first coating film]
The method for producing a multi-layer coating film according to the present disclosure includes a step of coating a first coating composition on a molded product for automobile parts made of a plastic material to form an uncured first coating film.

(First paint composition)
The first coating composition contains a polyester resin (A) and a carbodiimide compound (B).
The polyester resin (A) is
The glass transition temperature Tg is 40 ° C. or higher and 120 ° C. or lower.
The number average molecular weight Mn is 6000 or more and 20000 or less.
The hydroxyl value is 12 mgKOH / g or less,
The acid value is 20 mgKOH / g or less,
It has at least one selected from the group consisting of a hydroxyl group, a ketone group, a carboxy group, an amino group and a sulfo group.

(Polyester resin (A))
The polyester resin (A) is
The glass transition temperature Tg is 40 ° C. or higher and 120 ° C. or lower.
The number average molecular weight Mn is 6000 or more and 20000 or less.
The hydroxyl value is 12 mgKOH / g or less,
The acid value is 20 mgKOH / g or less,
It has at least one selected from the group consisting of a hydroxyl group, a ketone group, a carboxy group, an amino group and a sulfo group.
In one embodiment, the polyester resin (A) may be an emulsion or dispersion.

Although it should not be interpreted only in a specific theory, by using the polyester resin (A), it is possible to prevent the water contained in the uncured second coating film from permeating into the uncured first coating film. It is possible to suppress the mixed phase of the uncured first coating film and the uncured second coating film. In addition, the first coating film containing the polyester resin (A) can have a high surface free energy and can exhibit good wettability. Further, the surface roughness of the uncured second coating film can be reduced by the first coating film containing the polyester resin (A). Therefore, the multi-layer coating film obtained by the method for producing a multi-layer coating film according to the present disclosure can exhibit an excellent coating film appearance. Further, by using the polyester resin (A) together with the carbodiimide compound (B), a multi-layer coating film exhibiting excellent resistance can be formed.

The glass transition temperature Tg of the polyester resin (A) may be 40 ° C. or higher and 120 ° C. or lower, for example, 40 ° C. or higher and 80 ° C. or lower. In one embodiment, the glass transition temperature Tg of the polyester resin (A) may be 55 ° C. or higher and 75 ° C. or lower.
The glass transition temperature may be measured by a differential scanning calorimetry (DSC) device, for example, in accordance with JIS K 7121: 1987.

The number average molecular weight Mn of the polyester resin (A) may be, for example, 6000 or more and 20000 or less. In one embodiment, the number average molecular weight Mn of the polyester resin (A) may be 8500 or more and 20000 or less.
The measurement of the number average molecular weight can be calculated from the measurement result of gel permeation chromatography (GPC) using, for example, polystyrene as a standard.

The hydroxyl value of the polyester resin (A) may be, for example, 0.1 mgKOH / g or more and 12 mgKOH / g or less. In one embodiment, the hydroxyl value of the polyester resin (A) may be 1 mgKOH / g or more and 10 mgKOH / g or less, for example, 1 mgKOH / g or more and 8 mgKOH / g or less.
The hydroxyl value can be measured by a titration method according to, for example, JIS K 0070: 1992.

The acid value of the polyester resin (A) may be, for example, 0.1 mgKOH / g or more and 20 mgKOH / g or less. In one embodiment, the acid value of the polyester resin (A) may be 1 mgKOH / g or more and 8 mgKOH / g or less, for example, 1 mgKOH / g or more and 6 mgKOH / g or less.
The acid value can be measured by a titration method according to, for example, JIS K 0070: 1992.

The polyester resin (A) has at least one selected from the group consisting of a hydroxyl group, a ketone group, a carboxy group, an amino group and a sulfo group as a functional group. In one embodiment, the polyester resin (A) may have a sulfo group as a functional group.

The solid content of the polyester resin (A) may be 10 parts by mass or more and 35 parts by mass or less with respect to a total of 100 parts by mass of the resin solid content of the first coating composition, for example, 15 parts by mass or more and 25 parts by mass or less. be.
Here, the resin solid content of the first coating composition refers to the solid content of the resin component contained in the first coating composition, the solid content of the carbodiimide compound (B), and the curing agent when the curing agent is contained. It means the total with the solid content.

Examples of the polyester resin (A) include a condensate of a polybasic acid and a polyhydric alcohol. Examples of the polybasic acid include phthalic anhydride, isophthalic acid, terephthalic acid, adipic acid, succinic anhydride and the like. Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,6-hexanediol, polyethylene glycol, polypropylene glycol and the like.

In the embodiment in which the polyester resin (A) is an emulsion, as a method for obtaining the dispersion of the polyester resin (A), for example, the resin component is neutralized with a base, and water is gradually added under stirring to invert the phase. Examples include a method of emulsifying, a method of forcibly emulsifying a resin component in water using a high-speed homogenizer, and the like.

Commercially available products can be used as the polyester resin emulsion, and examples thereof include Bironal MD1100, MD1200, MD2000 (Toyobo Ltd.), and KT-8803 (Unitika Ltd.).

(Carbodiimide compound (B))
The first coating composition contains a carbodiimide compound (B). When the first coating composition contains the carbodiimide compound (B) together with the polyester resin (A), a multi-layer coating film having excellent resistance can be formed.
In one embodiment, the carbodiimide compound (B) may be an emulsion.

In the resin solid content of the first coating composition, the carbodiimide compound (C) may be 0.5 parts by mass or more and 10 parts by mass or less, for example, 1 part by mass or more and 5 parts by mass or less, and 1 part by mass or more. It may be 3 parts by mass or less.
When the solid content of the carbodiimide compound (B) is within such a range, the water resistance of the multi-layer coating film can be improved more easily, and further, the shrinkage of the coating film generated after the water resistance test can be more easily performed. It can be suppressed.

The carbodiimide compound (B) may be, for example, a modified carbodiimide compound. The carbodiimide compound (B) is intracellularly
-OCONH-X-NHCOOY
[X is a bifunctional organic group containing at least one carbodiimide group, and Y is a structure obtained by removing a hydroxyl group from a polyalkylene glycol monoalkyl ether. ]
It has one or more structural units K represented by.
It is considered that having the structural unit K provides both excellent water dispersibility and excellent curability.

Three types of modified carbodiimide compounds are exemplified: those having one structural unit K, those having two structural units, and those having three structural units K.
Examples of those having two structural units K include those represented by the following general formula (I).

In the general formula (I), X is a bifunctional organic group containing at least one carbodiimide group, Y is a structure obtained by removing hydroxyl groups from the same or different polyalkylene glycol monoalkyl ethers, and Z is a number. It has a structure in which hydroxyl groups are removed from a bifunctional polyol having an average molecular weight of 200 to 5000.

Here, the above X may be represented by the following general formula (a).

In the general formula (a), R ² is preferably a hydrocarbon group having 6 or more and 15 or less carbon atoms. Specific examples thereof include a phenylene group, a diphenylene methyl group, a diphenylene (dimethyl) methyl group, a methylphenylene group, a dimethylphenylene group, a tetramethylxylylene group, a hexylene group, a cyclohexylene group, a dicyclohexylenemethyl group and the like. be able to. Preferred is a dicyclohexylenemethyl group. Further, the above p is 1 or more and 10 or less. p is the number of carbodiimide groups present in the structural unit, preferably 2 or more from the viewpoint of curability, and further preferably 8 or less.

In this specification, the number of repetitions is expressed as an average value, not limited to the above p.

The Y can be represented by the following general formula (b) or (c).

In formula (b) and (c), ^{R 3} is preferably an alkyl group having 1 to 20 carbon atoms. Specific examples thereof include a methyl group, an ethyl group, a butyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a stearyl group and the like. Further, R ⁴ is a hydrogen atom or a methyl group, and is preferably a hydrogen atom. q is 4 or more and 40 or less. In the general formulas (b) and (c), when R ⁴ is hydrogen, the general formulas (b) and (c) show the same structure.

The Z is a polymer structure composed of an ether bond, an ester bond, or a carbonate bond.

The parent-modified carbodiimide compound (C) having two structural units K has a raw material carbodiimide compound containing at least two isocyanate groups in one molecule and a hydroxyl group at the molecular terminal, and has a number average molecular weight of 200 or more and 5000 or less. A polyalkylene glycol monoalkyl ether is further reacted with a reaction product obtained by reacting a bifunctional polyol with a reaction product in which the molar amount of isocyanate groups of the raw material carbodiimide compound exceeds the molar amount of hydroxyl groups of the polyol. Can be obtained.

The raw material carbodiimide compound containing at least two isocyanate groups in the molecule preferably has isocyanate groups at both ends from the viewpoint of reactivity. The method for producing a raw material carbodiimide compound having isocyanate groups at both ends is well known to those skilled in the art, and for example, a condensation reaction involving decarbonization of organic diisocyanate can be utilized.

As the organic diisocyanate, specifically, aromatic diisocyanate, aliphatic diisocyanate, alicyclic diisocyanate, and a mixture thereof can be used, and specifically 1,5-naphthylene diisocyanate and 4,4-diphenylmethane. Diisocyanate, 4,4-diphenyldimethylmethane diisocyanate, 1,3-phenylenediocyanate, 1,4-phenylenediocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate and 2 , 6-Torylene diisocyanate, hexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4-diisocyanate, methylcyclohexane diisocyanate, tetramethylxylylene diisocyanate and the like. be able to. From the viewpoint of reactivity, dicyclohexylmethane-4,4-diisocyanate is preferable.

A carbodiimidization catalyst is usually used for the condensation reaction. Specific examples of the carbodiimidation catalyst include 1-phenyl-2-phospholene-1-oxide, 3-methyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, and 3-. Examples thereof include methyl-1-phenyl-2-phospholene-1-oxide, phosphorene oxides such as these 3-phosphorene isomers, and the like. From the viewpoint of reactivity, 3-methyl-1-phenyl-2-phospholene-1-oxide is preferable.

Next, the bifunctional polyol having a hydroxyl group at the molecular terminal is not particularly limited, but from the viewpoint of reaction efficiency, the number average molecular weight is preferably 200 or more and 5000 or less. Specific examples of the bifunctional polyol having a hydroxyl group at the molecular end include polyether diol, polyester diol, and polycarbonate diol. For example, polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, and poly. Polyalkylene glycols such as hexamethylene ether glycol and polyoctamethylene ether glycol, polyethylene adipate, polybutylene adipate, polyhexamethylene adipate, polyneopentyl adipate, poly-3-methylpentyl adipate, polyethylene / butylene adipate, polyneopentyl / Examples thereof include polyester diols such as hexyl adipate, polycaprolactone diols, polylactone diols such as poly-3-methylvalerolactone diols, polycarbonate diols such as polyhexamethylene carbonate diols, and mixtures thereof.

The reaction between the raw material carbodiimide compound containing at least two isocyanate groups in one molecule and the bifunctional polyol having a hydroxyl group at the molecular terminal and having a number average molecular weight of 200 or more and 5000 or less is the reaction of the isocyanate group of the raw material carbodiimide compound. The reaction is carried out at a ratio in which the molar amount exceeds the molar amount of the hydroxyl group of the polyol. When the molar amount of the isocyanate group is less than or the same as the molar amount of the hydroxyl group, the reaction of the polyalkylene glycol monoalkyl ether described later cannot be sufficiently carried out.

The ratio of the molar amount of the isocyanate group of the raw material carbodiimide compound to the molar amount of the hydroxyl group of the polyol having a hydroxyl group at the molecular terminal is 1.1: 1.0 to 2.0: from the viewpoint of reaction efficiency and economy. It is preferably 1.0. The degree of polymerization of the raw material carbodiimide compound and the bifunctional polyol having a hydroxyl group at the molecular terminal in the reaction product obtained by this step is preferably 1 or more and 10 or less from the viewpoint of reaction efficiency.

By further reacting the reaction product thus obtained with a polyalkylene glycol monoalkyl ether, a hydrophilized modified carbodiimide compound (C) having two of the above structural units can be obtained. As the polyalkylene glycol monoalkyl ether, those represented by the following general formula (b') or (c') are used.

In the general formula (b ') and ^{(c'), R 3,} R 4, and q is contents described at the previous general formula (b) and (c) is directly applied. Type and q of R ⁴ in the above units, storage stability, water-dispersible and water in consideration of the reactivity after the volatilization, it is respectively appropriately set within the above range. From the viewpoint of water dispersibility, ^{it is preferable that R 3} in the monoalkoxy polyalkylene glycol is a methyl group and R ⁴ is a hydrogen atom. Further, the q is preferably 4 or more and 20 or less, and more preferably 6 or more and 12 or less, from the viewpoint of water dispersibility and reactivity after water volatilization.

As the polyalkylene glycol monoalkyl ether, a polyalkylene glycol monoalkyl ether having a number average molecular weight of 200 or more and 5000 or less is preferably used. The alkyl group of this polyalkylene glycol monoalkyl ether is preferably an alkyl group having 1 to 20 carbon atoms. Specific examples of the polyalkylene glycol monoalkyl ether include polyethylene glycol, polypropylene glycol, or a mixture thereof, in which one end is sealed with an alkyl group having 1 to 20 carbon atoms. As a more detailed specific example of such a polyalkylene glycol monoalkyl ether, for example, polyethylene glycol monomethyl ether, polyethylene glycol mono-2-ethylhexyl ether, polyethylene glycol monolauryl ether, polypropylene having a number average molecular weight of 200 or more and 5000 or less. Examples thereof include glycol monomethyl ether, polypropylene glycol mono-2-ethylhexyl ether, and polypropylene glycol monolauryl ether.

The reaction product and the polyalkylene glycol monoalkyl ether are reacted at a ratio in which the molar amount of the isocyanate group of the reaction product is equal to or greater than the molar amount of the hydroxyl group of the polyalkylene glycol monoalkyl ether. When the molar amount of the isocyanate group is less than the molar amount of the hydroxyl group, the reaction of the polyalkylene glycol monoalkyl ether with the reaction product cannot be sufficiently carried out. The molar amount of the isocyanate group of the reaction product can be obtained by direct measurement, or a value calculated from the preparation formulation may be adopted.

A catalyst can be used in the reaction between the raw material carbodiimide compound and the bifunctional polyol having a hydroxyl group at the molecular terminal, and in the reaction between the reaction product and the polyalkylene glycol monoalkyl ether. The temperature at the time of the reaction is not particularly limited, but is preferably 60 ° C. or higher and 120 ° C. or lower from the viewpoint of controlling the reaction system and reaction efficiency. Further, in the above reaction, it is preferable to use an organic solvent that does not contain active hydrogen.

By undergoing such a two-step reaction, a carbodiimide compound (B) having two structural units K can be obtained. The carbodiimide compound (B) thus produced does not have only the structure of the general formula (I) shown above, but is a mixture containing various other reaction products derived from the raw materials used. be. However, in general, it can be regarded as having the structure of the general formula (I).

Further, as the carbodiimide compound (B), a compound having three structural units K is represented by the following general formula (II).

In the general formula (II), the above description of X and Y can be directly applied to X and Y having two structural units K. Further, R ⁰ is a hydrogen, a methyl group, or an ethyl group. R ¹ is an alkylene group having 4 or less carbon atoms, and may be the same or different. Specific examples of the alkylene group include a methylene group, an ethylene group, a propylene group and a butylene group. n is 0 or 1, and m is 0 or more and 60 or less.

R ⁰ , R ¹ , n and m are determined by the trifunctional polyol used in the production of the carbodiimide compound (B).

When m is 11 or more, the ratio of the hydrophilic portion to the hydrophobic portion is preferably 2.0 to 6.3. The ratio of the hydrophilic portion to the hydrophobic portion can be determined by dividing the molecular weight of the portion of the oxymethylene group or the oxyethylene group present in the carbodiimide compound by the molecular weight of the carbodiimide compound.

The carbodiimide compound (B) having three structural units K is composed of a raw material carbodiimide compound containing at least two isocyanate groups in one molecule and a polyalkylene glycol monoalkyl ether, and the equivalent of the isocyanate groups of the raw material carbodiimide compound is It can be obtained by further reacting a trifunctional polyol with a reaction product obtained at a ratio exceeding the equivalent of the hydroxyl groups of the polyalkylene glycol monoalkyl ether.

As the raw material carbodiimide compound containing at least two isocyanate groups in one molecule, the above description for the raw material carbodiimide compound of the carbodiimide compound (B) having two structural units K is applied as it is.

In the reaction between the raw material carbodiimide compound and the polyalkylene glycol monoalkyl ether, the isocyanate group needs to remain because it is further reacted with the trifunctional polyol after the reaction. Therefore, in the above reaction, the equivalent of the isocyanate group needs to be larger than the equivalent of the hydroxyl group, and the equivalent ratio of the isocyanate group to the hydroxyl group is preferably 1/2. The reaction can usually be carried out under conditions well known to those skilled in the art, and tin-based catalysts can be used as needed.

As the polyalkylene glycol monoalkyl ether, the above description for the polyalkylene glycol monoalkyl ether of the carbodiimide compound (B) having two structural units K is applied as it is.

Next, the reaction product thus obtained is reacted with a trifunctional polyol. The amount of the trifunctional polyol used in the reaction is preferably an amount having a hydroxyl group equivalent equal to or higher than the isocyanate equivalent of the reaction product, and more preferably the isocyanate equivalent is equal to the hydroxyl group equivalent. The isocyanate equivalent of the reaction product can be obtained by calculation from the compounding ratio of the diisocyanate compound and the polyalkylene glycol monoalkyl ether in the previous step, in addition to the direct measurement. The reaction can be carried out in the same manner as the reaction of the raw material carbodiimide compound and the polyalkylene glycol monoalkyl ether.

The trifunctional polyol is preferably trimethylolpropane, glycerin, or an alkylene oxide adduct thereof, because it is easily available. Examples of the alkylene oxide include ethylene oxide and propylene oxide. The alkylene oxide adduct of glycerin is commercially available from Sanyo Chemical Industries, Ltd. as a GP series. Considering the curing reactivity of the obtained 3-chain hydrophilic carbodiimide compound, those having a structure in which an alkylene oxide is added to one hydroxyl group are particularly preferable. Among the GP series, those having such a structure include GP-250, GP-3000 and the like.

By undergoing such a two-step reaction, a carbodiimide compound (B) having three structural units K can be obtained. As described above, the carbodiimide compound (B) produced in this manner does not have only the structure of the general formula (II), but is considered to have the structure of the general formula (II). It doesn't matter.

As the carbodiimide compound (B), a compound having one structural unit K is represented by the following general formula (III).

［Ｘは、少なくとも１個のカルボジイミド基を含有する２官能性有機基であり、Ｙは、同一又は異種のポリアルキレングリコールモノアルキルエーテルから水酸基を除いた構造である。］

[X is a bifunctional organic group containing at least one carbodiimide group, and Y is a structure in which a hydroxyl group is removed from the same or different polyalkylene glycol monoalkyl ether. ]

X in the general formula (III) is a group that can be represented by the formula (a) in the above general formula (I).

Y in the general formula (III) has a structure in which the hydroxyl group is removed from the same or different polyalkylene glycol monoalkyl ether. This Y can represent the same as Y in the above general formula (I). By using the hydrophilized modified carbodiimide compound (C) represented by the general formula (III), there is an advantage that the cross-linking is maintained at a higher level. Possible reasons are that the general formulas (I) and (II) having a plurality of carbodiimide units have a low acid value of the aqueous resin, but the reaction efficiency with the acid is low, and the general formula (III) is general. Since it does not have a bulky structure like the formulas (I) and (II), it does not inhibit the cross-linking between the hydroxyl group and the isocyanate of the aqueous resin, so that the carbodiimide compound (B) represented by the general formula (III) is not inhibited. I think that the cross-linking of the

Y in the general formula (III) is preferably the following (i) or (ii):
(I) A structure in which a hydroxyl group is removed from a polyethylene glycol monoalkyl ether in which an alkyl group having 1 or more carbon atoms and 3 or less carbon atoms is ether-bonded to the end of a polyethylene oxide unit having 6 or more repetitions and 20 or less repetitions (ii) Number of repetitions 4 or more. A structure in which a hydroxyl group is removed from a polypropylene glycol monoalkyl ether in which an alkyl group having 1 to 8 carbon atoms is ether-bonded to the end of a polypropylene oxide unit having 60 or less carbon atoms.
It is more preferable that the structure is the same or different from the above.
More preferably, the number of repetitions of the polypropylene oxide unit of (ii) is 15 to 60.
By using the carbodiimide compound (B) represented by the general formula (III) having the above (i) and (ii), the water dispersibility is excellent, the stability is improved, and the cross-linking is maintained at a higher level. There is an advantage that

In the carbodiimide compound (B) represented by the general formula (III), the same or different polyalkylene glycol monoalkyl ethers are reacted with the raw material carbodiimide compound obtained by the condensation reaction involving decarbonization of the organic diisocyanate described above. Can be prepared by

The polyalkylene glycol monoalkyl ether is
-Polyethylene glycol monoalkyl ether or polyethylene glycol monoalkyl ether in which an alkyl group having 1 to 3 carbon atoms is ether-bonded to the end of a polyethylene oxide unit having 6 to 20 repetitions.
A polypropylene glycol monoalkyl ether in which an alkyl group having 1 to 8 carbon atoms is ether-bonded to the end of a polypropylene oxide unit having 4 to 60 repetitions.
Is more preferable. In the preparation of the carbodiimide compound (B) represented by the general formula (III), these polyethylene glycol monoalkyl ethers and polypropylene glycol monoalkyl ethers may be used alone or in combination.

Specific examples of the polyethylene glycol monoalkyl ether include polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether, and polyethylene glycol monopropyl ether, and polyethylene glycol monomethyl ether is particularly preferable.
Specific examples of the polypropylene glycol monoalkyl ether include polypropylene glycol monomethyl ether, polypropylene glycol monoethyl ether, polypropylene glycol monobutyl ether, polypropylene glycol 2-ethylhexyl ether, and the like, and polypropylene glycol monobutyl ether is particularly preferable. be.

In the carbodiimide compound (B) represented by the general formula (III), one Y is (i) and the other Y is (ii), and (i) the number of repetitions is 6 or more and 20 or less. Polyethylene glycol monoalkyl ether in which an alkyl group having 1 or more and 3 or less carbon atoms is ether-bonded to the end of the polyethylene oxide unit of the above, and (ii) a polypropylene oxide unit having 4 or more and 60 or less repetitions. The ratio of the structure in which the hydroxyl group is removed from the polypropylene glycol monoalkyl ether in which an alkyl group having 1 to 8 carbon atoms is bonded to the end with an ether is (i) :( ii) = 1: 0.7 to 1: 8. It is more preferable that it is within the range of.
In the carbodiimide compound (B) represented by the general formula (III), it is preferable that the periphery of the carbodiimide group is hydrophobic to some extent in order to improve the water resistance when the coating film is formed. Further, in order to suppress the deactivation of carbodiimide by water and maintain the stability, it is preferable that the periphery of the carbodiimide group is hydrophobic to some extent and the contact with water molecules is kept low. On the other hand, in the carbodiimide compound represented by the general formula (III), it is necessary to have a certain amount of polyethylene glycol structure in order to maintain hydrophilicity. Here, when the structures (i) and (ii) are present in the range of (i) :( ii) = 1: 0.7 to 1: 8, while ensuring the hydrophilicity of the carbodiimide compound. On the other hand, the hydrophobicity can be maintained to some extent around the carbodiimide group. This has the advantage that a primer coating composition having better low-temperature curability and more excellent coating stability can be obtained. The ratio (i): (ii) is more preferably in the range of (i): (ii) = 1: 0.7 to 1: 1.5.
Examples of commercially available products of the carbodiimide compound (B) include carbodilite E02, carbodilite E03A, and carbodilite E05 (all manufactured by Nisshinbo).

In addition to the polyester resin (A) and the carbodiimide compound (B), the first coating composition contains other resins such as acid-modified polypropylene, acid-modified chlorinated polyolefin, epoxy resin, polyurethane resin, and aqueous alkyd resin. , Water-soluble acrylic resin and the like may be included. In one embodiment, these resins may be included as pigment dispersion resins. Also, in one embodiment, these resins may be included in the form of an emulsion.

For example, the first coating composition may contain a maleic anhydride-modified polyolefin resin.

The maleic anhydride-modified polyolefin resin may be any derivative synthesized from the polyolefin resin and maleic anhydride, and is not particularly limited. The maleic anhydride-modified polyolefin resin may be only one kind or two or more kinds.

The maleic anhydride-modified polyolefin resin may be in an emulsion state, and such a resin may be referred to as a maleic anhydride-modified polyolefin resin emulsion. In this embodiment, the maleic anhydride-modified polyolefin resin means the maleic anhydride-modified polyolefin resin emulsion itself, and does not contain other emulsion resins.

The weight average molecular weight of the maleic anhydride-modified polyolefin resin is preferably in the range of 20,000 or more and 200,000 or less, and more preferably in the range of 50,000 or more and 120,000 or less. The weight average molecular weight can be calculated from the measurement result of gel permeation chromatography (GPC) using polystyrene as a standard. When the weight average molecular weight is within such a range, for example, in the embodiment in which the first coating composition is used as the primer coating composition, the strength required as the primer coating film and the adhesion to the object to be coated are further improved. It can be easily enhanced, and further, coagulation failure in the coating film can be suppressed more easily. In addition, the maleic anhydride-modified polyolefin resin can be emulsified by a known method, and the stabilization of the coating composition can be more easily exhibited.
Further, for example, in the embodiment in which the polyolefin material is used for the object to be coated, the decrease in wettability can be more easily suppressed, and the adhesion of the material can be more easily enhanced.

The maleic anhydride-modified polyolefin resin may be, for example, 15% by mass or more and 40% by mass or less, and 20% by mass or more and 35% by mass or less in the resin solid content of the first coating composition.

When the amount of the maleic anhydride-modified polyolefin resin is within such a range, for example, in the embodiment in which the polyolefin material is used for the object to be coated, the adhesiveness can be more easily and well maintained. In addition, poor appearance can be more easily suppressed, and for example, poor adhesion to the underlying coating film at the time of recoating can be more easily suppressed.

As a method for emulsifying the maleic anhydride-modified polyolefin resin, a commonly used emulsification method such as a mechanical emulsification method, a method using an emulsifier or a basic substance, and a combination thereof can be used. When an emulsifier is used, the amount of the emulsifier can be appropriately set depending on the amount of maleic anhydride-modified polyolefin resin, basic substance, water and the like. When a basic substance is used, it can be appropriately set depending on the amount of maleic anhydride-modified polyolefin resin, water, etc., and in particular, the amount is such that the acid functional groups of the maleic anhydride-modified polyolefin resin and the emulsifier are sufficiently neutralized. It is preferable to set the pH of the obtained emulsion in consideration of 7 or more and 11 or less, more preferably 7.5 or more and 10.5 or less. When the pH value of the obtained maleic anhydride-modified polyolefin resin emulsion is within the above range, the stabilization of the emulsion can be maintained, for example, the release of basic substances can be suppressed, and the water resistance can be improved.

The average particle size of the maleic anhydride-modified polyolefin resin in the emulsion is not particularly limited. For example, in one embodiment, the average particle size is preferably 0.01 μm or more and 10 μm or less. Since the average particle size is within such a range, a large amount of emulsifier is not required.
For example, if a large amount of emulsifier is contained, the water resistance of the coating film may be slightly inferior. On the other hand, by having the above average particle size, it is possible to suppress a decrease in water resistance of the coating film. In addition, the stability of the emulsion may be kept good.

In one embodiment, the mass ratio of the structure derived from maleic anhydride (acid anhydride) in the maleic anhydride-modified polyolefin resin is preferably 1% by mass or more and 10 or less by mass, more preferably 1.2. It is preferably mass% or more and 5 mass% or less. When the mass ratio is within the above range, the maleic anhydride-modified polyolefin resin can be appropriately emulsified, and the coating composition can be stabilized. In addition, it is possible to suppress a decrease in the water resistance of the coating film.

In one embodiment, the maleic anhydride-modified polyolefin resin may be a chlorinated maleic anhydride-modified polyolefin resin. In the present specification, such a chlorinated resin may be referred to as a maleic anhydride-modified chlorinated polyolefin resin.
By using the maleic anhydride-modified chlorinated polyolefin resin, for example, in the embodiment of using the coating composition according to the present disclosure as a primer coating composition, the strength required as a primer coating film can be maintained, and the strength with which it is coated can be maintained. High adhesion can be maintained.
In addition, it is possible to suppress cohesive failure in the coating film, and in addition, it is possible to show stabilization of the coating composition.
Further, by chlorination, the melting point is lowered while maintaining the crystallinity of the crystalline polyolefin, and handling such as emulsification becomes easy.

In one embodiment, the first coating composition can include a maleic anhydride-modified chlorinated polyolefin resin as a maleic anhydride-modified chlorinated polyolefin resin emulsion. The chlorine content of the chlorinated polyolefin resin used for obtaining the maleic anhydride-modified chlorinated polyolefin resin emulsion is 15% by mass or more and 40% by mass or less, more preferably 20% by mass in the maleic anhydride-modified chlorinated polyolefin resin. % Or more and 35% by mass or less.
By containing chlorine in such an amount, emulsification can be easily performed, and further, the adhesion to the object to be coated, for example, the polyolefin material, particularly the adhesion to the polypropylene material can be sufficiently maintained.

The first coating composition may contain a glycidyl group-containing acrylic resin. By using the glycidyl group-containing acrylic resin emulsion, the cohesive force of the coating film can be improved, and the water resistance can be more easily increased. For example, blister generation, delamination due to water swelling, and the like can be more easily suppressed.

The glycidyl group-containing acrylic resin can be obtained by copolymerizing a radically polymerizable monomer containing a glycidyl group with another radically polymerizable monomer. For example, addition of glycidyl methacrylate, glycidyl acrylate and the like with (meth) acrylic acid, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxyethyl acrylate and ε-caprolactone. Functional group-containing monomers such as substances, and further, as (meth) acrylic acid alkyl ester, methyl (meth) acrylic acid, ethyl (meth) acrylic acid, isopropyl (meth) acrylic acid, N-butyl (meth) acrylic acid, T-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, (meth) ) Acrylic resin emulsion containing a glycidyl group can be obtained by copolymerizing with lauryl acrylate to obtain an aqueous emulsion.

Examples of the aqueous emulsion include a method of subjecting to solvent polymerization and then emulsion by forced stirring or using an emulsifier in water, an emulsion polymerization method of copolymerizing in water using an emulsifier, and the like.

The mass ratio of the structure derived from the glycidyl group-containing monomer in the glycidyl group-containing acrylic resin in the emulsion is preferably 30% by mass or more and 60% by mass or less. That is, it is preferable that the amount of the radically polymerizable monomer containing a glycidyl group is 30% by mass or more and 60% by mass or less among all the monomers used for synthesizing the glycidyl group-containing acrylic resin.

In the epoxy emulsion obtained from emulsion polymerization, it is necessary to pay attention to the amount of emulsifier and the like. This is because it may remain in the coating film and reduce water resistance and the like.

Emulsion polymerization can be carried out by heating the monomer mixture in an aqueous solution with stirring in the presence of a radical polymerization initiator and an emulsifier. The reaction temperature is preferably about 30 to 100 ° C., and the reaction time is preferably about 1 to 10 hours. The reaction temperature is adjusted by adding a monomer mixture or a monomer pre-emulsifying solution to a reaction vessel containing water and an emulsifier in a batch or dropping it for a while. It is good to do.

As the radical polymerization initiator, a known initiator usually used in emulsion polymerization of an acrylic resin can be used. Specifically, as a water-soluble free radical polymerization initiator, for example, persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate are used in the form of an aqueous solution. In addition, a so-called redox-based initiator in which an oxidizing agent such as potassium persulfate, sodium persulfate, ammonium persulfate, or hydrogen peroxide is combined with a reducing agent such as sodium hydrogen sulfite, sodium thiosulfite, longalite, or ascorbic acid is an aqueous solution. Used in the form of.

The emulsifier is an anion system selected from micelle compounds having a hydrocarbon group having 6 or more carbon atoms and a hydrophilic moiety such as a carboxylate, a sulfonate or a sulfate partial ester in the same molecule. Alternatively, a nonionic (nonionic) emulsifier is used. Among these, as anionic emulsifiers, alkali metal salts or ammonium salts of sulfuric acid semiesters of alkylphenols or higher alcohols; alkali metal salts or ammonium salts of alkyl or allyl sulfonate; polyoxyethylene alkylphenyl ethers, polyoxyethylenes. Examples thereof include an alkali metal salt or an ammonium salt of a sulfuric acid semi-ester of an alkyl ether or a polyoxyethylene allyl ether. Examples of the nonionic emulsifier include polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether and polyoxyethylene allyl ether. In addition to these general-purpose anionic and nonionic emulsifiers, they also have radically polymerizable unsaturated double bonds in the molecule, that is, acrylic, methacrylic, propenyl, allyl, allyl ether, and maleic acid. Various anionic and nonionic reactive emulsifiers having such groups as appropriate are also used alone or in combination of two or more.

In addition, during emulsion polymerization, the combined use of an auxiliary agent (chain transfer agent) for adjusting the molecular weight, such as a mercaptan compound or a lower alcohol, promotes smooth and uniform formation of the coating film from the viewpoint of promoting emulsion polymerization. From the viewpoint of improving the adhesiveness to the base material, it is often preferable, and it is carried out as appropriate depending on the situation.

The emulsion polymerization includes a normal one-step continuous monomer uniform dropping method, a core-shell polymerization method which is a multi-step monomer feed method, and a power feed polymerization method in which the monomer composition fed during polymerization is continuously changed. It can be legal.

The glycidyl group-containing acrylic resin in the emulsion may be, for example, 5% by mass or more and 25% by mass or less, and 10% by mass or more and 20% by mass or less in the resin solid content of the first coating composition.

The first coating composition may contain a urethane resin dispersion. As the urethane resin dispersion, a polyfunctional isocyanate compound, a polyol having two or more hydroxyl groups in one molecule, and a hydrophilic agent having both a hydroxyl group and a carboxylic acid group such as dimethylolpropanediol or dimethylolbutanediol are dibutyltin. After reacting in the presence of a catalyst such as dilaurylate in an excess of isocyanate groups to obtain a urethane prepolymer, the carboxylic acid is neutralized with an organic base such as amines or an inorganic base such as sodium hydroxide or potassium hydroxide. , Urethane resin dispersion obtained by adding ion-exchanged water to make it aqueous, and further increasing the molecular weight with a chain extender; after synthesizing a urethane prepolymer having no carboxylic acid, carboxylic acid, sulfonic acid, ethylene Urethane obtained by chain extension using a diol or diamine having a hydrophilic group such as glycol, then neutralizing with the above basic substance to make it aqueous, and further increasing the molecular weight with a chain extender if necessary. Resin dispersions and the like; urethane resin dispersions and the like obtained in combination with an emulsifier, if necessary; can be mentioned.

Examples of the polyfunctional isocyanate compound include diisocyanates such as 1,6-hexane diisocyanate, lysine diisocyanate, isophorone diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate, 2,4-tolylene diisocyanate, and 2,6-tolylene diisocyanate. Examples thereof include compounds and polyfunctional isocyanate compounds such as adducts, burettes, and isocyanurates thereof.

Examples of the polyol include polyester polyol, polyether polyol, polycarbonate polyol and the like.

Examples of the chain extender include low molecular weight diol compounds such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, fracidimethanol, diamine glycol, triethylene glycol and tetraethylene glycol, and ethylene oxide and propylene. Polyether diol compound obtained by addition polymerization of oxide, tetrahydrofuran, etc .; Diamine compounds such as the above low molecular weight diol compound, (anhydrous) succinic acid, adipic acid, (anhydrous) futaric acid, and hydroxyl groups at the terminals obtained from these anhydrides. Polyvalent alcohols such as trimethylolethane, trimethylolbropan; aminoalcohols such as monoethanolamine, diethanolamine, triethanolamine; ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, phenylenediamine, toluenediamine, Diamine compounds such as xylene diamine and isophorone diamine; water, ammonia, hydrazine, dibasic acid hydrazide and the like can be mentioned.

The urethane resin in the urethane resin dispersion may be, for example, 15% by mass or more and 40% by mass or less, and 20% by mass or more and 35% by mass or less in the resin solid content of the first coating composition. ..
When the amount of urethane resin in the urethane resin dispersion is within the above range, for example, even under the condition that the coating film is subjected to a water resistance test and then the adhesion of the coating film is evaluated, the coating film is coagulated and broken. -Peeling can be suppressed more easily. Further, it is possible to prevent the degree of cross-linking from becoming too large, for example, it is possible to suppress cross-linking strain, and it is possible to more easily suppress delamination with other coating films and objects to be coated in the initial adhesion.

The first coating composition may contain a curing agent. The curing agent is not particularly limited, but for example, melamine resin, blocked isocyanate, carbodiimide resin and the like are preferable in consideration of stability as a coating composition.
The melamine resin is not particularly limited. For example, methoxy-type melamine and methoxy-butoxy mixed-type melamine can be mentioned.
Butoxy-type melamine can be hydrated and used by a method using an emulsifier, an acrylic resin, an alkyd resin or the like as an emulsifier.
The methoxy-type melamine resin is more preferable because it can be stabilized in water without using an emulsifier or the like. For example, Allnex's Cymel series Cymel 300, 301, 303, 350, 370, 771, 325, 327, 703, 712, 715, 701, 267, 285, 232, 235, 236, 238, 211, 254. , 204, 212, 202, 207 and the like.

Hereinafter, the blocked isocyanate compound will be described. The starting component of the blocked isocyanate compound is a di- or poly-isocyanate compound and a mixture thereof. However, these components react with a blocking agent to obtain a blocked isocyanate compound.

Preferred di- or poly-isocyanate compounds are aliphatic, alicyclic, aromatic aliphatic and heterocyclic polyisocyanates. Polyisocyanate containing carbodiimide group, polyisocyanate containing allophanate group, polyisocyanate containing isocyanurate group, polyisocyanate containing urethane and / or urea group, polyisocyanate containing acylated urea group, polyisocyanate containing burette group, Polyisocyanates produced by the heteropolymerization reaction, polyisocyanates containing an ester group, preferably diisocyanates containing a uretdione group and diisocyanates containing a urea group are also suitable.

Specific examples of the di- or poly-isocyanate compound include the following. p-Xylylene diisocyanate, 1,5-diisocyanatomethylnaphthalene, 1,3-phenylenediocyanate, 1,4-phenylenediocyanate, 1-methylbenzene 2,5-diisocyanate, 1,3 dimethylbenzene 4,6-diisocyanate , 1,4 dimethylbenzene 2,5-diisocyanate, 1-nitrobenzene 2,5-diisocyanate, 1-methoxybenzene 2,4-diisocyanate, 1-methoxybenzene 2,5-diisocyanate, 1,3-dimethoxybenzene 4,6 -Diisocyanate, azobenzene 4,4'-diisocyanate, diphenyl ether 4,4'-diisocyanate, diphenylmethane 4,4'-diisocyanate, diphenyldimethylmethane 4,4'-diisocyanate, naphthalene 1,5-diisocyanate, 3,3'-dimethyl Biphenyl 4,4'-diisocyanate, diphenyl disulfide 4,4'-diisocyanate, diphenyl sulfone 4,4'-diisocyanate, 1-methylbenzene 2,4,6-triisocyanate, 1,3,5-trimethylbenzene 2,4 , 6-Triisocyanate, triphenylmethane 4,4', 4 "-triisocyanate, 4,4'-diisocyanato- (1,2) -diphenylethane, dimer 1-methyl-2,4-phenylenediisocyanate, Dimeric 1-isopropyl-2,4-phenylenediisocyanate, dimer 2,4'diisocyanatodiphenylsulfide, 3,3'-diisocyanato-4,4'-dimethyl-N, N'-diphenylurea, 3 , 3'-Diisocyanato-2,2'-dimethyl-N, N'-diphenylurea, 3,3'-diisocyanate-2,4'-dimethyl-N, N'-diphenylurea, N, N'-bis [ 4 (4-isocyanatophenylmethyl) phenyl] urea, N, N'-bis [4 (2-isocyanatophenylmethyl) phenyl] urea.

Blocking agents used to obtain blocked isocyanate compounds include oxime compounds (acetooxime, methylethylketooxime, methylisobutylketooxime, etc.), lactams (ε-caprolactam, etc.), active methylene compounds (diethyl malonate, acetylacetone, etc.). Ethyl acetoacetate, etc.), phenols (phenol, m-cresol, etc.), alcohols (methanol, ethanol, n-butanol, etc.), hydroxyl group-containing ether (methyl cellsolve, butyl cell solution, etc.), hydroxyl group-containing ester (methyl lactate) , Amil lactate, etc.), mercaptans (butyl mercaptan, hexyl mercaptan, etc.), acid amides (acetanilide, acrylic amide, dimer acid amide, etc.), imidazoles (imidazole, 2-ethylimidazole, etc.), acidimides (succinic acid, etc.) Examples thereof include imides (imides of phthalates, etc.), amines (dicyclohexylamines, etc.) and mixtures of two or more of these.

The curing agent may be, for example, 5% by mass or more and 25% by mass or less, and 7% by mass or more and 20% by mass or less in the resin solid content of the first coating composition. When the amount of the curing agent is within such a range, the degree of cross-linking of the coating film can be more easily increased, and a coating film having excellent water resistance and adhesion can be more easily formed.

The first coating composition comprises other components that can be added as the coating composition, such as pigments, surfactants, neutralizers, stabilizers, thickeners, defoamers, surface conditioners, leveling agents, pigment dispersions. Agents, UV absorbers, antioxidants, inorganic fillers such as silica, conductive carbons, conductive fillers, conductive fillers such as metal powders, organic modifiers, plasticizers, etc. shall be blended as necessary. Can be done.

The first coating composition can serve as a color-based coating composition in addition to its role as a primer coating composition. In one embodiment, the first coating composition of the present invention comprises a pigment. The pigment can be used in the form of a pigment dispersion paste.

The pigment dispersion paste is obtained by pre-dispersing a pigment and a pigment dispersant in a small amount of an aqueous medium. The pigment dispersant may be a resin having a structure including a pigment-affinitive portion and a hydrophilic portion. Examples of the pigment-affinitive moiety and the hydrophilic moiety include nonionic, cationic and anionic functional groups. The pigment dispersant may have two or more of the above functional groups in one molecule.

Examples of the nonionic functional group include a hydroxyl group, an amide group, a polyoxyalkylene group and the like. Examples of the cationic functional group include an amino group, an imino group, a hydrazino group and the like. Examples of the anionic functional group include a carboxyl group, a sulfo group, and a phosphoric acid group. Such pigment dispersants can be produced by methods well known to those skilled in the art.

The pigment dispersant is not particularly limited as long as it does not contain a volatile basic substance in its solid content or has a content of 3% by mass or less, but a small amount of pigment dispersant can be used to efficiently pigment the pigment. It is preferable that the substance can be dispersed. For example, commercially available products (all of which are trade names below) can also be used. Specifically, Disperbyk 190, Disperbyk 181 and Disperbyk 182 (polymers), which are anion / nonionic dispersants manufactured by Big Chemie, can be used. Polymer), Disperbyk 184 (polymer copolymer), EFKAPOLYMER4550, an anion-nonionic dispersant manufactured by BASF, Solsparse 27000, a nonionic dispersant manufactured by Abyssia, Solspers 41000, an anion-based dispersant, Solsperse 53095 and the like can be mentioned.

The weight average molecular weight of the pigment dispersant is preferably 1,000 or more and 100,000 or less. The weight average molecular weight is more preferably 2000 or more, and further preferably 4000 or more. Further, the number average molecular weight is more preferably 50,000 or less.

The pigment dispersion paste can be prepared by mixing and dispersing a pigment dispersant and a pigment according to a known method. The ratio of the pigment dispersant during the production of the pigment-dispersed paste is preferably 1% by mass or more and 50% by mass or less with respect to the solid content of the pigment-dispersed paste. When the ratio of the pigment dispersant is within the above range, the pigment dispersion stability and the physical characteristics of the obtained coating film can be kept in a better range. The above ratio of the pigment dispersant is more preferably 3% by mass or more, and more preferably 5% by mass or less.

The pigment is not particularly limited as long as it is a pigment used in an ordinary water-based coating composition, but a colored pigment is preferable from the viewpoint of improving weather resistance and ensuring concealment. In particular, titanium dioxide is more preferable because it has excellent color hiding properties and is inexpensive.

Examples of pigments other than titanium dioxide include azochelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, and isoindolinone. Organic coloring pigments such as system pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and metal complex pigments; inorganic coloring pigments such as yellow lead, yellow iron oxide, red iron oxide, and carbon black can be mentioned. In addition to these pigments, extender pigments such as calcium carbonate, barium sulfate, clay and talc may be used in combination.

Further, as the pigment, a standard gray coating composition containing carbon black and titanium dioxide as main pigments may be used. In addition, a coating composition in which the second coating composition is matched with lightness, hue, etc., and a coating composition in which various coloring pigments are combined may be used.

For the pigment, the ratio of the mass of the pigment to the total mass of the resin solid content and the pigment of the first coating composition (PWC; pigment weight content) is preferably 10% by mass or more and 60% by mass or less. By setting the PWC to 10% by mass, it becomes easier to enhance the concealing property. By setting the PWC to 60% by mass or less, the increase in viscosity during curing can be more easily suppressed, so that it becomes easier to secure the flowability and obtain a good coating film appearance.

Examples of the thickener include an association type nonionic urethane thickener, an alkaline swelling type thickener, and bentonite which is an inorganic interlayer compound.

The first coating composition can be prepared by mixing each component by commonly used means.

The form of the first coating composition is not particularly limited as long as it is aqueous, and may be, for example, a water-soluble, water-dispersible, aqueous emulsion or the like.

The method of applying the first coating composition to a molded product for an automobile part is not particularly limited, and examples thereof include an air spray coating, a bell coating, and the like, which are generally used in the coating field of an automobile body. ..

In one embodiment, the first coating composition according to the present disclosure can form a coating film having both functions of a primer coating film and a color-based coating film. Therefore, in the method for producing a multi-layer coating film according to the present disclosure, the process can be shortened, for example, the process of forming a primer coating film and the process of forming a color-based coating film, which are generally performed, can be integrated. be.

The coating of the first coating composition may be carried out within a range of a dry film thickness of 10 μm or more and 40 μm or less, for example, 20 μm or more and 35 μm or less.

In one embodiment, after coating the first coating composition, it may be allowed to stand at room temperature (room temperature) for an appropriate time to form an uncured first coating film.
In another embodiment, after coating the first coating composition, preheating may be performed in the range of 40 ° C. or higher and 90 ° C. or lower, for example, 50 ° C. or higher and 80 ° C. or lower) for 1 minute or more and 15 minutes or less.
Here, "preheat" in the present specification means that the coated coating composition is heat-dried under conditions such as a temperature and time that do not cause curing.
By performing the preheating, the mixed phase of the uncured first coating film and the uncured second coating film can be suppressed more effectively, and the appearance of the obtained multi-layer coating film can be further improved.

In one embodiment, the surface free energy of the uncured first coating film ^{is preferably 61 mJ / m 2} or more and 70 mJ / m ² or less at 20 ° C. or higher and 23 ° C. or lower. As a result, the water contact angle of the first coating film just before the second coating composition is applied can be 20 ° or more and 30 ° or less at 20 ° C. or higher and 23 ° C. or lower. That is, when the surface free energy of the first coating film is within the above range, the wettability between the uncured first coating film and the second coating composition is high, and the finished appearance of the multi-layer coating film is improved. ..

In one embodiment, the surface free energy of the uncured first coating film may be, for example, 62 mJ / m ² or more and 68 mJ / m ² or less. When the surface free energy of the uncured first coating film is within such a range, the adhesion of the uncured second coating film to the uncured first coating film becomes better.

In the present specification, the surface free energy of the coating film can be measured according to Owens-Wendt's theoretical formula for calculating the surface free energy of a substance. Specifically, the contact angle of the sample substance was measured using a liquid (water, methylene iodide) having a known surface free energy value, and DK Owens and RC Wendt, J. Appl. Polym. Sci., 13, 1741. By using the theoretical formula of (1969), the surface free energy of the sample substance can be calculated.
For example, 2 μl of pure water and diiodomethane were dropped on the surface of the coating layer of the glass test piece, the contact angle (θ) was measured with a contact angle meter, and the surface free energy value γ _s was calculated by the following Owens formula. ..

1 + cos θ = 2 [(γ _s ^d γ _l ^d ) ^1/2 / γ _l + (γ _s ^p γ _l ^p ) ^1/2 / γ _l ]

In the formula, γ _s indicates the surface free energy of a solid, γ _l indicates the surface free energy of a liquid, the subscript d indicates a dispersion force component, and the subscript p indicates a polar force component.

When an uncured second coating film is formed on the uncured first coating film and the uncured first coating film and the uncured second coating film are heat-cured, the surface of the cured second coating film is formed. The roughness Ra is 0.74 μm or less in the horizontal direction with respect to the coated surface and 0.80 μm or less in the vertical direction with respect to the coated surface. In one embodiment, the surface roughness (Ra) is preferably 0.70 μm or less when measured in the horizontal direction. When the surface roughness Ra is within such a range, the multi-layer coating film becomes smooth, and a multi-layer coating film having an excellent appearance can be obtained.

(Molded products for automobile parts made of plastic material)
In the molded product for automobile parts made of a plastic material, the plastic material may include, for example, a polyolefin resin, a polycarbonate resin, a urethane resin, a polyester resin, a polystyrene resin, an ABS resin, a vinyl chloride resin, and a polyamide resin.
In one embodiment, the plastic material may include a polypropylene resin, for example, a modified polypropylene resin. In addition, these resins may contain additives that can be used in molded articles for automobile parts.
Examples of molded products for automobile parts include bumper members, spoiler members, grill members, fender members, and the like.

[Step of forming an uncured second coating film]
The method for producing a multi-layer coating film according to the present disclosure includes a step of forming an uncured second coating film on an uncured first coating film. The uncured second coating film is a mica-based coating film containing mica, and can be formed by a second coating composition containing mica.

The method of coating the second coating composition on the uncured first coating film may be a commonly used coating method, and for example, the coating method described above for the first coating composition may be used.

In the embodiment in which the first coating composition contains a pigment, the formation of a color-based coating film, which has been separately required in the past, can be omitted. Therefore, the second coating composition, that is, mica, is directly applied on the first coating film. Can be coated with a mica-based paint composition containing. The multi-layer coating film thus obtained is excellent in appearance and resistance, and also has high color development property.

The coating film of the second coating composition may be coated within a range of a dry film thickness of 8 μm or more and 20 μm or less, for example, 10 μm or more and 15 μm or less.

In one embodiment, after the second coating composition is coated, it may be allowed to stand at room temperature (room temperature) for an appropriate time to form an uncured second coating film.
In another embodiment, after coating the second coating composition, preheating may be performed for 1 minute or more and 15 minutes or less in the range of 60 ° C. or higher and 100 ° C. or lower, for example, 70 ° C. or higher and 90 ° C. or lower.
By performing the preheating, the mixed phase of the uncured first coating film and the uncured second coating film can be suppressed more effectively, and the appearance of the obtained multi-layer coating film can be further improved.

(Second paint composition)
The second coating composition is a base coating composition containing mica, and forms an uncured second coating film which is a mica-based coating film.

The second coating composition may be, for example, a mica-containing coating composition usually used as an aqueous base coating composition for a molded product for an automobile part made of a plastic material.
Examples of the second coating composition include a second coating composition containing an aqueous resin having a hydroxyl group and a carboxyl group, a carbodiimide compound, a polyisocyanate compound, and an aqueous polyurethane resin.

As an aqueous resin having a hydroxyl group and a carboxyl group contained in the second coating composition, a hydroxyl value of 80 mgKOH / g or more and 200 mgKOH / g or less and an acid value of 10 mgKOH / g or more and 40 mgKOH / g or less in terms of resin solid content. And / or a polyester resin having a hydroxyl value of 80 mgKOH / g or more and 200 mgKOH / g or less and an acid value of 10 mgKOH / g or more and 40 mgKOH / g or less in terms of resin solid content can be used.
As the carbodiimide compound contained in the second coating composition, the carbodiimide compound contained in the first coating composition, for example, a hydrophilized modified carbodiimide compound can be used. For example, the amount of the hydrophilized modified carbodiimide compound can be 1 to 9% by mass with respect to the resin solid content of the second coating composition.

As the polyisocyanate compound that can be contained in the second coating composition, aromatics such as tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), and metaxylylene diisocyanate (MXDI). Diisocyanate; aliphatic diisocyanate such as hexamethylene diisocyanate (HDI); alicyclic diisocyanate such as isophorone diisocyanate (IPDI), hydrogenated MDI; Adducts such as burettes, uretdiones, isocyanurates or alohanates of compounds; relatively low molecular weight urethane prepolymers; and other polyisocyanate compounds, and aqueous dispersions (hydrophilic groups) of these polyisocyanates. Examples thereof include those introduced, or those obtained by mixing and emulsifying a surfactant and so-called self-emulsifying).

In another embodiment, as the water-dispersible blocked polyisocyanate compound contained in the second coating composition, the polyisocyanate is reacted with a malonic acid diester, and then the obtained reaction product is reacted with an organic amine compound. The water-dispersible blocked polyisocyanate compound prepared by the above can be used. The amount of the water-dispersible block polyisocyanate compound contained in the second coating composition is preferably 10% by mass or more and 25% by mass or less with respect to the resin solid content of the second coating composition.

As the aqueous polyurethane resin that can be contained in the second coating composition, the aqueous polyurethane resin used in the art can be used. The amount of the aqueous polyurethane resin is preferably 10% by mass or more and 50% by mass or less with respect to the resin solid content of the second coating composition.

In one embodiment, the second coating composition may be a coating composition containing an aqueous resin having a hydroxyl group and a carboxyl group, a melamine resin, a weak acid catalyst, and an aqueous polyurethane resin. As the aqueous resin having a hydroxyl value contained in the second coating composition, an acrylic resin having a hydroxyl value of 80 mgKOH / g or more and 200 mgKOH / g or less in terms of resin solid content, and / or 80 mgKOH in terms of resin solid content. A polyester resin having a hydroxyl value of / g or more and 200 mgKOH / g or less can be used, and the acrylic resin and / or the polyester resin may have an acid value of 10 mgKOH / g or more and 40 mgKOH / g or less. good.

The melamine resin has an average imino group amount of 1.0 or more and an average methylol group of 0.5 or more per melamine nucleus, and is an aqueous resin and a melamine resin contained in the second coating composition. The mass ratio of water-based resin / melamine resin = 0.7 or more and 3 or less in terms of solid content, and the amount of weak acid catalyst is the solid content mass of the water-based resin and melamine resin contained in the second coating composition. It is preferably 0.1 parts by mass or more and 20.0 parts by mass or less with respect to 100 parts by mass of the aqueous resin + melamine resin.
The aqueous polyurethane resin has a glass transition point Tg of −50 ° C. or lower, and a known aqueous polyurethane resin can be used as the aqueous polyurethane resin.
The second coating composition can be prepared by a method commonly used by those skilled in the art.

In addition to the above components, the second coating composition may use a pigment-dispersed resin such as an epoxy resin, an alkyl polyether compound, an acrylic emulsion, an aqueous alkyd resin, or a water-soluble acrylic resin. In one embodiment, the second coating composition may contain some of these.

The mica preferably has an average particle size (D50) of 2 μm or more and 50 μm or less and a thickness of 0.1 μm or more and 5 μm or less. Further, those having an average particle size in the range of 5 μm or more and 35 μm or less are excellent in brilliance and are more preferably used. Examples of mica include interference mica pigments and white mica pigments.

In one embodiment, the second coating composition may include scaly bright pigments in addition to mica. Examples of the scaly bright pigment include metal scaly bright pigments such as metals such as aluminum, copper, zinc, iron, nickel, tin and aluminum oxide or alloys and mixtures thereof. In addition to this, graphite pigments and the like can also be used. These scaly bright pigments may be colored as required.

The average particle size of the scaly bright pigment means the median diameter of the volume-based particle size distribution measured by the laser diffraction / scattering method. The thickness of the scaly bright pigment was measured by observing the cross section of the coating film containing the scaly bright pigment with a microscope and measuring the thickness of the scaly bright pigment using image processing software. It shall be defined as the average value of the measured values.

The method for producing a multi-layer coating film according to the present disclosure has an advantage that better technical effects can be achieved even in an embodiment in which the second coating composition contains at least mica and further contains other scaly bright pigments. There is.

In the second coating composition, the mass ratio (PWC) of mica to the resin solid content contained in the coating composition is 1% or more and 20% or less. When the mass ratio of mica is in the above range, the coating film can have a good appearance.

The second coating composition may contain other components in addition to the above components. Other components include, for example, pigments, viscous agents, film-forming aids, and additives commonly used in coating compositions (eg, UV absorbers, antioxidants, defoamers, surface conditioners, anti-pinhole agents, etc. ) Etc. can be mentioned. These blending amounts are within the range known to those skilled in the art.

[Step of forming an uncured clear coating film]
The method for producing a multi-layer coating film according to the present disclosure includes a step of forming an uncured clear coating film on an uncured second coating film. The uncured clear coating film can be formed by the clear coating composition.

The method of coating the clear coating composition on the uncured second coating film may be a commonly used coating method, and for example, the coating method described above for the first coating composition may be used.

The clear paint can be applied within a range of a dry film thickness of 10 μm or more and 80 μm or less, for example, 20 μm or more and 50 μm or less. When the dry film thickness is within the above range, there is an advantage that the unevenness concealing property of the base is improved and the coating workability can be ensured better.

(Clear paint composition)
An example of a clear coating composition is a urethane clear coating composition. Examples of the urethane clear coating composition include a clear coating composition containing a hydroxyl group-containing resin and an isocyanate compound curing agent. The isocyanate compound as the curing agent is not particularly limited, and for example, aliphatic isocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), and trimethylhexamethylene diisocyanate, 1,3-cyclo. Adicyclic isocyanates such as pentandiisocyanate, 1,4-cyclohexanediisocyanate, 1,2-cyclohexanediisocyanate, xylylene diisocyanate (XDI), 2,4-tolylene diisocyanate (TDI), 2,6-tolylene diisocyanate, etc. Aromatic isocyanates, isophorone diisocyanates (IPDI), alicyclic isocyanates such as norbornandiisocyanate methyl, multimers and mixtures such as bullets and nurates thereof, and the like can be mentioned.

The hydroxyl value of the hydroxyl group-containing resin is preferably in the range of 20 mgKOH / g or more and 200 mgKOH / g or less. When the hydroxyl value is within such a range, the clear coating film can have better water resistance and, moreover, better curability. The hydroxyl value is more preferably 30 mgKOH / g or more, and more preferably 180 mgKOH / g or less.

Further, the weight average molecular weight of the hydroxyl group-containing resin is preferably in the range of 1000 or more and 20000 or less. When the weight average molecular weight is within the above range, good workability and excellent curability can be obtained. The weight average molecular weight is more preferably 2000 or more, and more preferably 15000 or less.

The hydroxyl group-containing resin preferably has an acid value in the range of 2 mgKOH / g or more and 30 mgKOH / g or less. When the acid value is within the above range, the obtained clear coating film can have good water resistance and, moreover, good curability. Oxidation is more preferably 3 mgKOH / g or more, and more preferably 25 mgKOH / g or less.

The content of the isocyanate compound with respect to the hydroxyl group-containing resin can be appropriately selected within a range usually used by those skilled in the art. For example, it is preferable to use an amount such that the equivalent ratio (NCO / OH) of the isocyanate group (NCO) and the hydroxyl group (OH) is in the range of 0.5 or more and 1.7 or less. The equivalent amount ratio is more preferably 0.7 or more, and more preferably 1.5 or less.

The method for producing the clear coating composition is not particularly limited, and any method well known to those skilled in the art can be used. A commercially available product can also be used as the clear coating composition. As commercially available products, for example, R-2500-1, R-2550-2, Polyure Excel O-1100 clear, O-1200 clear (manufactured by Nippon Paint Automotive Coatings Co., Ltd., isocyanate-curable clear paint composition) and the like are available. Can be mentioned.

In the present invention, a clear coating composition other than the urethane clear coating composition may be used depending on the material of the object to be coated. For example, an acid epoxy curing clear coating composition, an acrylic melamine curing clear coating composition, and the like can also be used. As an example of these clear paint compositions, for example, "Mac Flow O-570 Clear" or "Mac" sold by Nippon Paint Automotive Coatings Co., Ltd., which is a clear paint composition containing polyepoxide and polyacid. "Super Rack O-100 Clear" (trade name) sold by Nippon Paint Automotive Coatings Co., Ltd., which is a clear paint composition containing "Flow O-1820 Clear" and the like, and an acrylic resin and a melamine curing agent. And so on. As the heat curing conditions when these clear coating compositions are used, conditions according to the composition of each clear coating composition can be appropriately selected.

[Step of forming a multi-layer coating film]
The method for producing a multi-layer coating film according to the present disclosure includes a step of baking and curing an uncured first coating film, an uncured second coating film and an uncured clear coating film to form a multi-layer coating film. ..
According to the method for producing a multi-layer coating film according to the present disclosure, the uncured coating film can be baked and cured in one step. Therefore, as compared with the conventional method for producing a multi-layer coating film, in which various coating compositions are coated, the coating film is cured, and another coating composition is applied and cured repeatedly. For example, the number of steps can be greatly reduced, which is excellent from the viewpoint of environmental protection and economic efficiency.
Further, it is possible to form a multi-layer coating film having high design property, high color development property, and mirror surface appearance. According to the method for producing a multi-layer coating film according to the present disclosure, for example, excellent color development can be exhibited even in a white mica coating color.

In one embodiment, the baking cure can be performed at 70 ° C. or higher and 150 ° C. or lower, for example, 90 ° C. or higher and 140 ° C. or lower, and 100 ° C. or higher and 130 ° C. or lower. The baking curing time can be 10 minutes or more and 30 minutes or less under such temperature conditions.
By performing baking curing under such conditions, the multi-layer coating film can be sufficiently cured, and the environmental load can be reduced as compared with the conventional high-temperature baking method. Further, there is a possibility that a heat load is generated on the plastic material to be coated.

In the present disclosure, the baking curing time (heating and curing time) means the time during which the surface of the substrate actually keeps the target baking temperature, and more specifically, until the target baking temperature is reached. Time is not taken into consideration and means the time when the target temperature is reached and the temperature is maintained.

Examples of the heating device used for simultaneously baking the uncured film of the coating composition include a drying furnace using a heating source such as hot air, electricity, gas, and infrared rays. Further, it is preferable to use a drying furnace in which two or more of these heating sources are used in combination because the drying time is shortened.

The film thickness of the multi-layer coating film may be, for example, in the range of 28 μm or more and 140 μm or less, and preferably in the range of 50 μm or more and 100 μm or less.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are based on mass unless otherwise specified.

(Polyester resin A-1)
As the polyester resin A-1, a polyester resin having a sulfo group (“MD1200” manufactured by Toyobo Co., Ltd., solid content concentration: 34% by mass) was used. The polyester resin A-1 has a glass transition temperature Tg: 67 ° C., a number average molecular weight Mn: 15000, a hydroxyl value: 6 mgKOH / g, an acid value: less than 3 mgKOH / g, and a pH: 4 to 7. Distilled water and It contained butyl cellosolve.

The glass transition temperature Tg was measured by a differential scanning calorimetry (DSC) device in accordance with JIS K 7121: 1987.
The number average molecular weight Mn is calculated from the measurement results of gel permeation chromatography (GPC) using ram by TSK-gel-supermultipоr HZ-M (manufactured by Tosoh Corporation) and THF as a developing solvent and mpolystyrene as a standard. bottom.
The hydroxyl value and acid value were measured by a titration method in accordance with JIS K 0070: 1992.
The following materials were also measured by these methods.

(Polyester resin A-2)
As the polyester resin A-2, a polyester resin having a sulfo group (“MD1100” manufactured by Toyobo Co., Ltd., solid content concentration: 30% by mass) was used. The polyester resin A-2 has a glass transition temperature Tg: 40 ° C., a number average molecular weight Mn: 20000, a hydroxyl value: 5 mgKOH / g, an acid value: less than 3 mgKOH / g, and a pH: 4 to 6. It contained butyl cellosolve.

(Polyester resin A-3)
As the polyester resin A-3, a polyester resin having a sulfo group (“MD2000” manufactured by Toyobo Co., Ltd., solid content concentration: 40% by mass) was used. The polyester resin A-3 has a glass transition temperature Tg: 67 ° C., a number average molecular weight Mn: 18000, a hydroxyl value: 6 mgKOH / g, an acid value: less than 2 mgKOH / g, and a pH: 4 to 7, and distilled water is used as a solvent. It was included.

(Polyester resin A-4)
As the polyester resin A-4, a polyester resin having a nonionic group (manufactured by DIC Corporation, BCD3120, solid content concentration: 35%) was used. The polyester resin A-2 has a glass transition temperature Tg: −20 ° C. or lower: number average molecular weight Mn: 1800, hydroxyl value: 150 mgKOH / g, acid value: 7 mgKOH / g, pH: 7-9, and distilled water as a solvent. Included.

(Polyester resin A-5)
As the polyester resin A-5, a polyester resin having a sulfo group (“MD1930” manufactured by Toyobo Co., Ltd., solid content concentration: 31% by mass) was used. The polyester resin A-5 has a glass transition temperature Tg: -10 ° C., a number average molecular weight Mn: 20000, a hydroxyl value: 5 mgKOH / g, an acid value: less than 3 mgKOH / g, a pH: 4 to 7, and distilled water as a solvent. And butyl cellosolve.

(Carbodiimide compound B-1)
700 parts of 4,4-dicyclohexylmethane diisocyanate and 7 parts of 3-methyl-1-phenyl-2-phospholene-1-oxide are reacted at 170 ° C. for 7 hours to form 1 of the structure represented by the above general formula (a). A carbodiimide compound having three carbodiimide groups in the molecule and having isocyanate groups at both ends was obtained.
Next, 180 parts of the produced isocyanate-terminated 4,4-dicyclohexylmethanecarbodiimide, PTMG-1000 (polytetramethylene glycol having a number average molecular weight of 1,000 manufactured by Mitsubishi Chemical Corporation, and tetramethylene calculated from the number average molecular weight). Repeating unit of oxide 13.6) 95 parts and 0.2 part of dibutyltin dilaurate were added and heated to 85 ° C., which was kept for 2 hours.
Next, 86.4 parts of methyl polyglycol 130 (polyethylene glycol monomethyl ether manufactured by Nippon Emulsifier Co., Ltd., ethylene oxide repetition number 9 calculated from hydroxyl value 130 mgKOH / g) was added, and the mixture was kept at 85 ° C. for 3 hours. After confirming that the peak of NCO had disappeared by IR measurement, the reaction was terminated, and after cooling to 60 ° C., deionized water was added to make a hydrophilized modified carbodiimide compound (B-) having a resin solid content of 40% by mass. The aqueous dispersion of 1) was obtained. The obtained hydrophilized modified carbodiimide compound was a compound represented by the above general formula (I).

(Carbodiimide compound B-2)
90 parts of 4,4-dicyclohexylmethane carbodiimide having an isocyanate terminal produced in the same manner as carbodiimide compound B-1, 120 parts of polypropylene glycol monobutyl ether having an average number of repetitions of 19, 43.2 parts of methylpolyglycol 130 and dibutyltin 0.07 part of dilaurate was added and kept at 80 ° C. until no absorption of NCO by IR. After cooling to 60 ° C., deionized water was added to obtain an aqueous dispersion of a hydrophilized modified carbodiimide compound (B-2) having a resin solid content of 25%. The obtained hydrophilized modified carbodiimide compound was a compound represented by the above general formula (III).
Further, in the obtained hydrophilized modified carbodiimide compound, the ratio of (i) the structure obtained by removing the hydroxyl group from the polyethylene glycol monoalkyl ether and (ii) the structure obtained by removing the hydroxyl group from the polypropylene glycol monoalkyl ether is (i): (Ii) = 1.0: 1.0.

(Carbodiimide compound B-3)
As the carbodiimide compound B-3, "E-03A" manufactured by Nisshinbo (solid content concentration: 40% by mass, pH: 8 to 11) was used.

(Maleic anhydride-modified chlorinated polyolefin resin)
Maleic anhydride-modified chlorinated polyolefin resin ("Supercron 892LS"; manufactured by Nippon Paper Co., Ltd .: chlorine content 22) in a reaction device equipped with a stirring blade, a thermometer, a temperature control thermister device, a dropping device and a cooling tube. %, Weight average molecular weight 70,000-80,000) 288 parts, surfactant ("Emargen 920" manufactured by Kao Co., Ltd.) 62 parts, aromatic hydrocarbon solvent "Solbesso 100" manufactured by Exxon) 74 parts, carbitol acetate 32 parts were charged, the temperature was raised to 110 ° C., heated at this temperature for 1 hour to dissolve, and then cooled to 100 ° C. or lower. Next, 710 parts of ion-exchanged water in which 6 parts of dimethylethanolamine was dissolved was added dropwise over 1 hour with stirring, and phase inversion emulsification was performed. Then, the mixture was cooled to room temperature and filtered through a 400 mesh wire mesh to obtain a maleic anhydride-modified chlorinated polyolefin (polypropylene) resin emulsion. The non-volatile content of this emulsion was 30% by mass.

(Urethane resin dispersion)
1100 parts of adipic acid and 3methyl-1,5-pentanediol while passing nitrogen gas through a pressure-resistant reaction vessel equipped with a stirring blade, a thermometer, a temperature control, a dropping device, a sampling port, a reflux device with a cooling tube, and a nitrogen introduction tube. 900 parts and 0.5 part of tetrabutyl titanate were charged, the reaction temperature of the liquid in the container was set to 170 ° C., an ester reaction was carried out by dehydration, and the reaction was continued until the acid value became 0.3 mgKOH / g or less. Then, the reaction was carried out for 2 hours under a reduced pressure condition of 180 ° C. and 5 kPa or less to obtain a polyester having a hydroxyl value of 112 mgKOH / g and an acid value of 0.2 mgKOH / g. Then, 500 parts of this polyester polyol, 134 parts of dimethyl sodium 5-sulfoisophthalate and 2 parts of tetrabutyl titanate were charged in another reaction vessel equipped with the same apparatus as the above reaction vessel, and nitrogen was added in the same manner as above. The esterification reaction was carried out by setting the reaction temperature to 180 ° C. while passing through gas to finally obtain a sulfo group-containing polyester resin having a number average molecular weight of 2117, a hydroxyl value of 53 mgKOH / g, and an acid value of 0.3 mgKOH / g. rice field.

280 parts of the obtained sulfo group-containing polyester resin, 200 parts of polybutylene adipate, 35 parts of 1,4-butanediol, 118 parts of hexamethylene diisocyanate and 400 parts of methyl ethyl ketone were mixed with a stirring blade, a thermometer, a temperature control, and a dropping device. , A reaction vessel with a sample collection port and a cooling tube was charged with nitrogen gas, and the urethanization reaction was carried out while maintaining the liquid temperature at 75 ° C. with stirring to obtain a urethane prepolymer having an NCO content of 1%. Subsequently, the temperature in the reaction vessel was lowered to 40 ° C., and 955 parts of ion-exchanged water was uniformly dropped while sufficiently stirring to carry out phase inversion emulsification. Next, the internal temperature was lowered to room temperature, and an aqueous solution of adipic acid hydrazide, which was a mixture of 13 parts of adipic acid hydrazide and 110 parts of ion-exchanged water, was added to carry out amine elongation. Then, the liquid temperature was raised to 60 ° C. under a slight reduced pressure to remove the solvent, and ion-exchanged water was added so that the solid content became 35% at the end, and the sulfo group-containing urethane resin dispersion (2). ) Was obtained. The acid value was 11 mgKOH / g.

(Acrylic resin emulsion containing glycidyl group)
37 parts of ion-exchanged water was charged into a reaction vessel equipped with a stirring blade, a thermometer, a dropping device, a temperature control device, a nitrogen gas introduction tube and a cooling tube, and the temperature was raised to 80 ° C. Each operation was performed while stirring the internal liquid from the temperature rise to the completion of the reaction. On the other hand, an emulsifier (TK Robomix RM type; manufactured by Primix Corporation) contains 21 parts of ion-exchanged water, 1 part of surfactant Newcol 710, and 1 part of Newcol 740 (both are surfactant and Japanese emulsifier). (Manufactured by Co., Ltd.) was charged and uniformly dissolved while stirring.

While continuing to stir, a polymerizable monomer mixed solution consisting of 6 parts of n-butyl acrylate, 8 parts of ethylhexyl methacrylate and 14 parts of glycidyl methacrylate was gradually added dropwise to the emulsifying machine to prepare a preemulsion solution.

On the other hand, a polymerization catalyst solution consisting of 7 parts of ion-exchanged water and 1.1 parts of ammonium persulfate (emulsification polymerization catalyst) was prepared, and the pre-emulsion solution and the polymerization catalyst solution were placed in separate dropping funnels in the reaction vessel. It was added dropwise over 3 hours. Emulsion polymerization was carried out while maintaining the internal temperature of the reaction vessel at 80 ° C. and stirring. The pre-emulsion solution was dropped by directly connecting it to a reaction vessel while maintaining the emulsified state with an emulsifying machine. After 3 hours, only the polymerization catalyst solution consisting of 4 parts of ion-exchanged water and the ammonium persulfate polymerization catalyst was added dropwise over 1 hour while maintaining the internal temperature at 80 ° C. Then, it was aged at 80 ° C. for 1 hour and cooled to obtain a glycidyl group-containing acrylic resin emulsion. The non-volatile content of the glycidyl group-containing acrylic resin emulsion is 30% by mass, and the amount of the glycidyl group-containing monomer in the resin solid content is 50% by mass.

(Melamine resin)
As the melamine resin, "Simel 701" (manufactured by Allnex, non-volatile content 82%) was used.

(Associative thickener)
In a decompressable reaction vessel, 6645 parts by mass of an adduct (number average molecular weight 3320) of cetyl alcohol and 70 mol of ethylene oxide was dehydrated at 100 ° C. under reduced pressure for 3 hours to reduce the water content of the adduct to 0.005%. I did the following.

Then, the mixture was cooled to 70 ° C. under atmospheric pressure, 168 parts of hexamethylene diisocyanate and 0.7 parts by mass of dibutyltin dilaurate were added, the temperature was raised to 80 ° C. under a nitrogen atmosphere, and the mixture was reacted at this temperature for 5 hours. The obtained urethane compound was a viscous liquid, and the weight average molecular weight in GPC measurement in terms of polystyrene was 8000.

A mixture of 15% by mass of this urethane compound, 24% by mass of propylpropylene glycol, and 61% by mass of ion-exchanged water was dispensed and stirred to produce an associative thickener.

(Water-soluble acrylic resin)
55 parts of propylene glycol monomethyl ether was charged into a reaction vessel equipped with a stirring blade, a dropping device, a temperature control device, a nitrogen gas introduction tube and a cooling tube, and the temperature was raised to 120 ° C. under stirring while introducing nitrogen gas. Next, a polymerizable monomer mixture consisting of 12 parts of 2-hydroxymethylmethacrylate, 9 parts of methacrylic acid, 35 parts of isobutyl methacrylate and 44 parts of n-butyl acrylate and 1 part of t-butylperoxy-2-ethylhexanate are propylene. The solution dissolved in 8 parts of glycol was added dropwise over 3 hours by internal stirring. Then, after completion of the dropping, the aging reaction was carried out at 120 ° C. for 1 hour, and then a solution of 0.1 part of t-butylperoxy-2-ethylhexanolate in 4 parts of propylene glycol was further dissolved for 1 hour. It was added dropwise to the reaction vessel. In each case, the internal stirring state and the liquid temperature of 120 ° C. were maintained. Then, the mixture was aged at 120 ° C. for 2 hours with stirring, then the internal temperature was cooled to 70 ° C., 9.5 parts of dimethylaminoethanol was added dropwise, and the mixture was stirred for 30 minutes. Further, while maintaining the internal temperature at 70 ° C. and stirring, 167 parts of ion-exchanged water was slowly added dropwise and cooled to room temperature (25 ° C.) to obtain a water-soluble acrylic resin solution. The non-volatile content was adjusted to 30% using ion-exchanged water, and this was used as a pigment dispersion resin for a primer in the following pigment dispersion paste. The pH of the obtained pigment-dispersed resin (water-soluble acrylic resin solution) was 8.2, and the weight average molecular weight of the acrylic resin in the GPC measurement in terms of polystyrene was 42000.

(Titanium oxide)
As titanium oxide, "Typake CR95" manufactured by Ishihara Sangyo Co., Ltd. was used.

(Preparation of first paint composition)
Titanium oxide was mill-dispersed with a water-soluble acrylic resin and ion-exchanged water to obtain a titanium oxide paste. In a stainless steel container equipped with a stirrer, the materials were charged so as to have the ratio shown in Table 1, and the rotor No. 1 of the Burgfield type viscometer was charged. Ion-exchanged water was added so that the coating viscosity at 25 ° C. measured at a rotation speed of 6 rpm using No. 3 was 2000 to 2500 mPa · s, and the first coating compositions of Examples 1 to 6 and Comparative Examples 1 to 3 were added. Was prepared. The solid content concentration of the first coating composition was 40 to 45% by mass. The amounts of the components shown in Table 1 are shown in terms of non-volatile content (parts by mass).

(Second paint composition)
As the second paint composition, a water-based mica-based paint composition, water-based base coat AR-3020-1 7A21 (manufactured by Nippon Paint Automotive Coating Co., Ltd.) was used.

(Clear paint composition)
A clear paint composition was prepared by mixing 100.0 parts of an acrylic clear main agent "R-2550-2" manufactured by Nippon Paint Co., Ltd. and 44.0 parts of a curing agent "H-2550" manufactured by Nippon Paint Co., Ltd.

(Measurement of surface free energy)
The first coating composition was spray-coated on the surface of a polypropylene material (70 mm x 150 mm x 3 mm) wiped with isopropyl alcohol by "Wider-71" (manufactured by Anest Iwata Co., Ltd.) in an environment of 25 ° C./70% RH (manufactured by Anest Iwata Co., Ltd.). The dry film thickness was 15 μm), and the mixture was dried at 60 ° C. for 5 minutes to form an uncured first coating film.

Using an automatic contact angle meter (PD-X type manufactured by Kyowa Interface Science Co., Ltd.), the contact angle between the uncured first coating film and DIW (ion exchange water), and the uncured first coating film The contact angle with methylene iodide was measured under the conditions of 20 ° C. or higher and 23 ° C. or lower, 30 seconds after dropping the droplet. The surface free energy of the uncured first coating film was calculated from the obtained measured values based on the above formula.

(Measurement of surface roughness)
An uncured first coating film and an uncured second coating film are formed on the surface of a polypropylene material (70 mm × 150 mm × 3 mm) wiped with isopropyl alcohol in the same manner as for forming a multi-layer coating film described later. Then, after setting for 10 minutes, it was dried at 120 ° C. for 35 minutes, and the uncured first coating film and the uncured second coating film were heat-cured.
The surface roughness Ra value of the obtained laminate of the first coating film and the second coating film is based on JIS-B0601, and an evaluation type surface roughness measuring machine (SURFTEST SJ-201P manufactured by Mitutoyo Co., Ltd.) is used. Was measured. The measurement was performed 7 times using a sample having a 2.5 mm width cutoff (number of sections 5), and the Ra value was obtained by averaging up and down. The smaller Ra is, the smoother the coating film is, and a multi-layer coating film having an excellent finished appearance can be obtained.

(Formation of multi-layer coating film)
The first coating composition of Example 1 by "Wider-71" (manufactured by Anest Iwata Co., Ltd.) on the surface of a polypropylene material (70 mm x 150 mm x 3 mm) wiped with isopropyl alcohol in an environment of 25 ° C./70% RH. Was spray-coated (dry film thickness 25 μm) and dried at 60 ° C. for 5 minutes to form an uncured first coating film.
Subsequently, the second coating composition is coated on the uncured first coating film under the same environment using a new cartridge bell (manufactured by ABB, trade name "new cartridge bell") (gun distance: 200 mm). , Gun speed: 900 mm / s, rotation speed: 35000 rpm, shaping air pressure: 0.15 MPa), spray coating (dry film thickness 15 μm), drying at 80 ° C. for 5 minutes, uncured second coating film ( An uncured mica-based coating film) was formed.
Subsequently, the clear coating composition was applied onto the uncured second coating film using Robobel 951 (gun distance: 200 mm, gun speed: 700 mm / s, rotation speed: 25000 rpm, shaping air pressure: 0. Spray coating (dry film thickness 25 μm) was performed under the condition of 07 MPa). Then, after setting for 10 minutes, it was dried at 120 ° C. for 35 minutes, and the uncured first coating film, the uncured second coating film and the uncured clear coating film were heat-cured to form a multi-layer coating film. ..
The obtained multi-layer coating film had a first coating film, a second coating film and a clear coating film, and the film thickness of the multi-layer coating film was 65 μm.

The multi-layer coating films of Examples 2 to 6 and Comparative Examples 1 to 3 were formed in the same manner as in Example 1 except that the first coating composition of Example 1 was changed.

The obtained multi-layer coating film was evaluated as follows. The evaluation results are shown in Table 2.

(exterior)
Regarding the finished appearance of the multi-layer coating film obtained in Examples and Comparative Examples, L1 (long wavelength) and L4 (short wavelength) were measured using microlо wave scan-T (manufactured by BYK Gardener). The smaller the value, the better the appearance of the coating film.
Those with both L1 and L4 of 10 or less are regarded as acceptable (○), those with either L1 or L4 exceeding 10 are regarded as rejected (Δ), and those with L1 and L4 exceeding 10 are rejected (×). And said.

(water resistant)
Evaluation was made in accordance with JIS K-5600-6-2. Specifically, a test piece having a multi-layer coating film was immersed in water at a temperature of 40 ± 1 ° C. for 240 hours, and then the coating film surface was observed and a grid adhesion test was performed within 1 hour.
The grid adhesion test was conducted as follows. A single-edged cutting tool specified by JIS K-5600-5-6 is applied vertically on the coated surface of the test piece having a multi-layer coating film, and a cut that reaches the base material (polypropylene resin base material) is made. Eleven parallel lines 1 were drawn in parallel. Draw 11 parallel lines 2 that intersect the parallel lines 1 perpendicularly and at the same intervals as the parallel lines 1 with cuts that reach the substrate, and make 100 square grids surrounded by 4 straight lines. rice field. The distance between the parallel lines 1 and 2 was 2 mm. A transparent pressure-bonding tape specified by JIS K-5600-5-6 was adhered to the grid portion so as not to contain air bubbles between the coated surface and the coated surface. Then, the tape was peeled off at once within 0.5 to 1.0 seconds, and the peeled state of the grid portion was visually evaluated (the grid adhesion test).
Then, the case where no abnormality is observed on the coating film surface and no peeling is observed is evaluated as "○", and the case where the coating film surface is abnormal or peeled is evaluated as "x". evaluated.

(Weatherability)
A weather resistance test of a test piece having a multi-layer coating film was performed using a sunshine weather meter (manufactured by Suga Test Instruments Co., Ltd.), and the adhesion and appearance after 1200 hours were evaluated. Adhesion was evaluated by performing a grid adhesion test as described in "Water resistance" above. The appearance was evaluated visually, by color difference, and by gloss value. Then, when no peeling is observed, no significant visual abnormality is observed, the color difference (ΔE) from the initial state (before the weather resistance test) is 3.0 or less, and the gloss is 80 or more, " It was evaluated as "◯", when one of these four items was not satisfied, it was evaluated as "Δ", and when two or more of these four items were not satisfied, it was evaluated as "x".

In addition, as a reference experiment, gloss, hardness and initial adhesion were evaluated as follows.

(Glossy)
The 60 ° glossiness of the test piece having the multi-layer coating film was measured according to JIS K-5600-4-7 using a mirror glossimeter and evaluated according to the following criteria.
"○": The glossiness of 60 ° is 85 or more, and no abnormality on the surface of the coating film such as blisters, cracks, pinholes, and citron skin is observed.
"X": 60 ° glossiness is less than 85, or at least one coating film surface abnormality such as blisters, cracks, pinholes, and citron skin is observed.

(hardness)
The hardness of the multi-layer coating film test piece was measured based on JIS K-5600-5-4. If the measured value is "B" or more, it is evaluated as "○", and it is tested 5 times or more. If there is no superiority difference between "B" and "2B", it is evaluated as "△", and it is "2B" or less. Those that are were evaluated as "x".

(Initial adhesion)
The test piece having the multi-layer coating film before immersion was subjected to a grid adhesion test as described in "Water resistance" above. Then, the case where no peeling was observed was evaluated as "◯", and the case where peeling was observed was evaluated as "x".

As described above, according to the method for producing a multi-layer coating film according to the present disclosure, it is possible to form a multi-layer coating film having an excellent appearance and resistance to a molded product for an automobile part made of a plastic material.

On the other hand, Comparative Examples 1 and 2 were inferior in appearance because the Tg of the polyester resin contained in the first coating composition was as low as 20 ° C. and 17 ° C., respectively.

In Comparative Example 3, since the first coating composition did not contain the carbodiimide compound, the water resistance and weather resistance were low, and the resistance was inferior.

According to the method for producing a multi-layer coating film of the present invention, a multi-layer coating film having an excellent appearance can be formed on a molded product for an automobile part made of a plastic material. Further, according to the method for producing a multi-layer coating film of the present invention, it is possible to form a multi-layer coating film in a smaller number of steps for a molded product for an automobile part made of a plastic material.

Claims (5)

A method for manufacturing a multi-layer coating film on a molded product for automobile parts made of a plastic material.
A step of coating the first coating composition on the molded product to form an uncured first coating film.
A step of forming an uncured second coating film on the uncured first coating film,
A step of forming an uncured clear coating film on the uncured second coating film, and baking the uncured first coating film, the uncured second coating film, and the uncured clear coating film. Includes the steps of curing and forming a multi-layer coating
The first coating composition contains a polyester resin (A) and a carbodiimide compound (B).
The polyester resin (A) is
The glass transition temperature Tg is 40 ° C. or higher and 120 ° C. or lower.
The number average molecular weight Mn is 6000 or more and 20000 or less.
The hydroxyl value is 12 mgKOH / g or less,
The acid value is 20 mgKOH / g or less,
It has at least one selected from the group consisting of a hydroxyl group, a ketone group, a carboxy group, an amino group and a sulfo group.
The uncured second coating film is a method for producing a multi-layer coating film which is a mica-based coating film. The method for producing a multi-layer coating film according to claim 1, wherein the baking hardening temperature is 100 ° C. or higher and 130 ° C. or lower. The method for producing a multilayer coating film according to claim 1 or 2, wherein the glass transition temperature Tg of the polyester resin (A) is 40 ° C. or higher and 80 ° C. or lower. The method for producing a multilayer coating film according to any one of claims 1 to 3, wherein the polyester resin (A) has a hydroxyl value of 1 mgKOH / g or more and 10 mgKOH / g or less. The method for producing a multilayer coating film according to any one of claims 1 to 4, wherein the acid value of the polyester resin (A) is 1 mgKOH / g or more and 8 mgKOH / g or less.