JPH03229674A - Method for forming film - Google Patents

Abstract

PURPOSE:To obtain a film having good repairing properties by applying the first clear coat paint on the film of thermosetting base coat paint to cure the same under heating and applying the second clear coat paint thereon to cure the same under heating. CONSTITUTION:Thermosetting base coat paint compounded with a colorant and a brightening agent is applied to an object to be coated and the first clear coat paint is applied thereon to be cured under heating. Next, the second clear coat paint is applied thereon to be cured under heating. The first clear coat paint is prepared by compounding 50-80wt.% of an acrylic resin having a hydroxyl value of 100-200mgKOH/g, an acid value of 3-40mgKOH/g and glass transition temp. of -20-40 deg.C and 15-50wt.% of an alkyl-etherified melamine resin. The obtained film is excellent in scratch resistance, acid resistance or weatherability and useful as the film of a car body.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for forming a coating film in a 6-coat, 2-bake coating system, and more specifically, for coating films on automobile bodies that require a high level of aesthetics and performance. The present invention relates to a method for forming a coating film that is used in the field of application and has excellent scratch resistance, acid resistance, gloss retention during outdoor exposure, and stain resistance.

[Prior art]

When painting automobile bodies, after electrocoating and intermediate coating, a base coat containing coloring pigments and metallic pigments and a top clear coat are applied in a wet-on-wet manner. Heat and cure at the same time. The so-called 2-coat, 1-base method is generally used, but attempts have been made to make the clear coat paint thicker in order to achieve even higher cosmetics, but the coating tends to suffer from wrinkles and sagging. This caused film defects, and there was a limit to how thick the film could be made. Therefore, on top of the base coat film,
A clear coat paint is applied and cured by heating, and then a second clear coat paint is applied and cured by heating. It has long been known that using the so-called 3-coat, 2-bake painting method and applying two coats of clear coat paint results in a high-quality appearance, but the adhesion between the first clear coat and second clear coat can be reduced. Due to its poor properties, there was a problem of delamination during outdoor exposure or water resistance tests.

In addition, in recent years, the durability of coating films has become a problem, particularly the deterioration of the appearance of the coating due to scratches.

When a dark base coat paint such as black, navy blue, or red is used, scratches on the surface of the clear coat film caused by car wash brushes and sand particles thrown up during driving are likely to be noticeable. In particular, there is a strong desire both domestically and internationally to solve the problem of scratches caused by the car wash plans of automatic car wash machines.

As a solution to this problem, it has been proposed to provide scratch resistance by coating with UV-curable or silicone-based paints, etc., but this method provides a good balance of repairability, weather resistance, etc. It was difficult to form a coating.

[Problem to be solved by the invention]

It is an object of the present invention to provide a first clear coat while obtaining a higher level of cosmetic properties than the coating obtained by the conventional two coat/one bake method. A coating film that maintains the weather resistance, water resistance, and other properties of an acrylic urethane thermosetting coating film without the problem of peeling of the second clear coating film, and that can obtain a coating film with excellent scratch resistance. The object of the present invention is to provide a forming method.

[Means to solve the problem]

That is, the method for forming a coating film of the present invention is to apply a base coat paint containing a coloring agent or a brightening agent, then overcoat a first clear coat paint, and then heat-cure the first clear coat paint, and further apply A three-coat/two-bake coating method in which a second clear coat paint is applied and cured by heating is a method of forming a coating film in which the first clear coat paint and the second clear coat paint have the following compositions.

First Clear Coat Paint Composition> (1) (a) A polyester selected from (meth)acrylic acid esters containing secondary hydroxyl groups represented by the following general formulas (1), (II) and (III). Seed monomer 10 to 50 wt.
1 to 10 weight (C) Represented by the general formula (■) (
meth) acrylic acid ester 15 to 60 weight range (a) The hydroxyl value obtained by copolymerizing at least one of the above components (h) to (c) with another vinyl monomer that can be copolymerized is I D O ~ 2 Q QqKoH/1.Acid value is 3
~4owIgKOH/v, acrylic copolymer (A
) SO ~ 85 weight (2) 7 *s, etherified melamine resin (B) 15 ~ 50 weight (weight) 1st part Rear coat coating composition> (1) (e) Represented by general formula (V) hydroxyl group-containing (meth)acrylic ester 10 to 60 parts OH, =O-
c-o-R7 (V) R8-○-(c-ct horse t-0)k-H(Vi') (f) Hydroxyl group-containing (meth)acrylic acid ester represented by general formula (■) 2 to 5 0 weight CH = O-C-0-R 4-0H (■) (g) 30 to 80 weight parts of other vinyl monomers that can be copolymerized with the above components (e) and (t). Hydroxyl value obtained by copolymerization 2>1100-2501yKOIII/1
, an acrylic copolymer (
0 and (2) polyisocyanate compound (j, and present in the acrylic copolymer (c). A composition having a ratio X/Y of 1/1L5 to 171.5.

In the present invention, 2 represented by general formula (I), (n) or (II), which is one of the constituent elements of the acrylic copolymer (A) used in the first clear coat paint,
The hydroxyl group-containing (meth)acrylic acid ester (a) of
It is used for the purpose of improving the interlayer adhesion between the first clear coating film and the second clear coating film.
Hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxypentyl (meth)acrylate, 5-hydroxyhexyl (meth)acrylate, Premer manufactured by NOF ■ PP1000,
Examples include acrylic oligomer HP-20 manufactured by Nippon Shokubai Kagaku ■.

The vinyl monomer (b), which is one of the monomers constituting the acrylic copolymer ((trans)), has one or more carboxyl groups, sulfonic acid groups, and phosphoric acid groups in the molecule. Monomers containing at least one kind of functional group, examples of monomers containing carboxyl groups include (meth)acrylic acid,
Itaconic acid, maleic acid, fumaric acid, crotonic acid, monomethyl itaconate, monobutyl itaconate, monomethyl maleate, motuptyl maleate, and monooctyl maleate. Specific examples of sulfonic acid group-containing monomers include 2-sulfoethyl (meth)acrylate and vinylbenzenesulfonic acid, and examples of phosphoric acid group-containing monomers include Kayamer manufactured by Nippon Kayaku ■. PM21, Light Ester PM, Light Ester P manufactured by Kyoeisha Yushi ■
Examples include. The amount of the vinyl monomer (Tsuru) having these acidic substituents is 11 to 10% by weight.

The (meth)acrylic acid ester represented by the general formula (W), which is one of the monomers constituting the acrylic copolymer (A), is essential in terms of weather resistance, cosmetic properties, and flexibility. It is used in a range of 15 to 60% by weight. If the weight is less than 15%, the weather resistance and cosmetic properties will deteriorate, and if it exceeds 60% by weight, the adhesion to the second clear coating will be undesirable. Specific examples include n-butyl (meth)acrylate, 1-butyl (meth)acrylate, 5ec-butyl (meth)acrylate, t-butyl (meth)acrylate, V-chlorohexyl (meth)acrylate, phenyl (meth)acrylate, Benzyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate
Examples include acrylate, isobornyl (meth)acrylate, FA-511A manufactured by Hitachi Chemical, and Pmu-513M.

Other vinyl monomers copolymerizable with components (a) to (c), which are one of the monomers constituting the acrylic copolymer (A), are used in an amount of 0 to 50% by weight. Specifically, styrene 11 conductors such as styrene, α-methylstyrene, and vinyltoluene; 7 Polymerizable unsaturated nitriles such as crylonitrile and methacrylonitrile; vinyl acetate,
Vinyl esters such as vinyl propionate; N-alkoxy substituted amides such as N-methoxymethyl (meth)acrylamide and N-butoxymethyl (meth)acrylamide; glycidyl (meth)acrylate, (meth)allyl glycidyl ether, metaglycidyl Epoxy group-containing monomers such as (meth)acrylate; basic monomers such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; methyl (meth)acrylate;
Acrylate, alkyl (meth)acrylate such as ethyl (meth)acrylate, propyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate, 2
- Hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, Plaxel FM-1, Plaxel FA-2, Plaxel FM-4, etc. with primary hydroxyl groups at the end (meth) ) Acrylic acid esters are mentioned.

The types and amounts of the monomers shown in components (1)(a) to (1)(d) used in the production of the acrylic copolymer (-) are as follows: Transition temperature: 120℃~40℃, hydroxyl value: 100~20
0■KOH/f, acid value 3-40119KOH/l
should be selected so that

Further, the glass transition temperature of the acrylic copolymer can be calculated from the glass transition temperature (Tg) of a known homopolymer using the following formula.

If the hydroxyl value is less than 100 WKOH/f, non-sanding with the second clear coating will be required, and adhesion during recoating will decrease.
Exceeding this is not preferable because water resistance decreases, the coating film becomes brittle, and scorchability decreases. Also, the acid value is 3 Misaki KO
If it is less than H/f, the crosslinking reaction with miramin resin, which is a crosslinking agent, will not proceed sufficiently, and the hardness and solvent resistance of the coating will be low, and if it exceeds a o Mqxoa/r, the water resistance will decrease. .

Furthermore, if the glass transition temperature is less than 120°C, the adhesion with the second clear coating film will be low, and if it exceeds 40°C, the cosmetic properties will deteriorate, which is not preferable.

The first clear coat coating material of the present invention contains an alkyl etherified melamine resin (B) in an amount of 15 to 50 by weight. If it is less than 15% by weight, the crosslinking density of the coating film will be low, resulting in poor weather resistance and water resistance.On the other hand, if it exceeds 50% by weight, the coating film will become brittle, have reduced flammability, and
This is not preferable because it reduces adhesion to the clear coating film.

A specific example of the alkyl etherified melamine resin c-th is one obtained by methylolizing aminotrisulfuric acid and alkyl etherifying it with cyclohexanol or an alkanol having 1 to 6 carbon atoms. Specific examples include methyl etherified melamine resin, ethyl etherified melamine resin, butyl etherified melamine resin, butyl methyl mixed melamine resin, etc. Specific examples include Kneepan 2osx (manufactured by Mitsui Toatsu Chemical Co., Ltd.), Super Beckamine (
As a specific example of methyl etherified melamine resin, Cymel (Mitsui Suyanamide) is manufactured by Dainippon Ink Chemical Co., Ltd.
(manufactured by).

The acrylic copolymer (c) used in the second clear coat paint in the present invention includes the acrylic copolymer (A
)K The hydroxyl group-containing (meth)acrylic acid ester used as the component (6) is an essential component from the viewpoint of scratch resistance, 10~
It is used in a range of 60 weight ginseng. If the weight is less than 10%,
The improvement in abrasion resistance is insufficient, and if the weight exceeds the reverse 4C60 weight, the hardness of the coating film will decrease and the water resistance will also decrease, which is not preferable. A specific example is 2-hydroxyethyl (
1 mole adduct of E-caprolactone to meth)acrylate, C to 2-hydroxyethyl(meth)acrylate
Examples include adducts of 2-hydroxyethyl (meth)acrylate and organic lactones, such as a 2-mole adduct of -caprolactone and a 3-mole adduct of f-caprolactone to 2- and droxyethyl (meth)acrylate. Further, adducts of 2-hydroxypropyl (meth)acrylate and organic lactones can also be used. Also, 2- and droxyethyl (meth)acrylate or 2-hydroxypropyl (meth)
Ring-opening adducts of ethylene oxide and propylene oxide to acrylates, dimers of 2-t:l'oxyethyl (meth)acrylate or 2-tl'$/propyl (meth)acrylate, and 3 mer, and two or more of these may be used in combination.

The hydroxyl group-containing (meth)acrylic ester (f), which is one of the monomers constituting the acrylic copolymer (c), is combined with the hydroxyl group-containing (meth)acrylic ester (e'l component) Acrylic copolymer (c) + 7) in combination
It is contained in an amount of 2 to 50% by weight so that the hydroxyl value is 100 to 25[IMfKOH/f].

If the hydroxyl value is less than 100'll9KOH/l, the scratch resistance is insufficient, and if it exceeds 250 wyKaH/l,
It is not preferred because the coating film is brittle and visibility is reduced.

Specific examples include #i2-hydroxyethyvmeth)acrylate, 2-hydroxypropyl(meth)acrylate,
Examples include hydroxyalkyl (meth)acrylates such as 3-hydroxypropyl (meth)acrylate, 4-hydroxy(meth)acrylate, and 6-hydroxyhexyl (meth)acrylate, and two or more of these may be used in combination.

Other vinyl monomers that can be copolymerized with components (e) and (f), which are one of the monomers constituting the acrylic copolymer (C), are used in a weight range of 30 to 80%. . In other words, the glass transition temperature of the acrylic copolymer (a) produced within a range that does not completely impair the scratch resistance, which is a feature of this Komei, is 15.
It is used at a temperature of 0°C to 50°C and an acid value of 0 to 40 K Oalt.

Examples of 8 types include styrene derivatives such as styrene, α-methylstyrene, and vinyltoluene; polymerizable unsaturated nitrites such as acrylonitrile and methacrylonitrile; vinyl esters such as vinyl acetate and vinyl propionate;
N-alkoxy substituted amides such as methoxymethyl (meth)acrylamide and N-butoxymethyl (meth)acrylamide; glycidyl (meth)acrylate, (meth)
Ebony V1 & containing monomers such as allyl glycidyl ether and metaglycidyl (meth)acrylate; Basic monomers such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; (meth)acrylic acid, itaconic acid, fumaric acid , crotonic acid,
Carboxyl group-containing vinyl monomers such as maleic acid, maleic anhydride, itaconic anhydride, monomethyl itaconate, motubutyl itaconate, monomethyl maleate, monobutyl maleate; 2-sulfoethyl (meth)acrylate, vinylbenzenesulfone alcohol, etc. Sulfonic acid group-containing vinyl monomers include phosphoric acid group-containing vinyl monomers such as Light Ester FA, Light Ester PM (manufactured by Kyoeisha Yushi ■), and Kayamer PM21 (manufactured by Nippon Kayaku ■).

Also, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, amyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, Benzyl (
Examples include (meth)acrylic acid esters such as meth)acrylate.

In order to satisfy the above-mentioned quality performance in the automobile paint, which is the main application of the second clear coat paint in the present invention, it contains a polyisocyanate compound as a curing agent.The isocyanate prepolymer constituting the polyisocyanate compound is A compound containing two or more free or blocked isocyanate groups in the molecule, specifically, tetramethylene diisonanate,
Aliphatic diisocyanates such as hexamethylene diisonanate and trimethylhexane diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate and 44'-methylenebis(cyclohexyl isocyanate); aromatic diisocyanates such as xylylene diisocyanate and tolylene diisocyanate -based diisocyanates; polyhydric alcohol adducts such as ethylene glycol, fluoropylene gellicol, neopentyl glycol, and trimethylolpropane to polyisocyanate; low molecular weight polyester resins having functional groups that react with isocyanate groups or water and polyisocyanate and biuret forms; polymers of diisocyanates; and polyisocyanates in which isocyanate groups are blocked with known blocking agents such as lower monomer alcohols and methyl ethyl ketone oxime. The amount of the polyisocyanate compound used is less than 1/1.5 expressed as the equivalent ratio X/Y of the OH group equivalent X of the acrylic copolymer (a) and the Nco group equivalent Y of the polyisocyanate compound (Tsuru). The membrane becomes brittle,
Weather resistance decreases. On the other hand, if X/Y exceeds 1/α5, the crosslinking density of the coating film will be low and the solvent resistance and water resistance will be reduced, which is not preferable. Polyisocyanate compound (Ijl
Noyoshi prefers the amount used when the above X/Y is 1/18 to 1/
The range is 1.2. Furthermore, if necessary, a tin-based curing accelerating catalyst such as diptyltin dilaurate can also be used.

In addition, when preparing a paint and using the coating composition of the present invention, if necessary, polycaprolactone polyol Plaxel 208 and Plaxel 22o manufactured by Daicel Chemical Co., Ltd. or Tone D- of Union Carbide Co., Ltd. 1
90, D-225, or the like may be included.

The acrylic copolymer (c) in the first clear coat paint and the acrylic copolymer (c) in the second clear coat paint in the present invention are obtained by polymerizing each of the above monomers, and the polymerization method is as follows: Any known method such as solution polymerization, bulk polymerization, emulsion polymerization, etc. can be used, but solution polymerization is particularly preferred.When using solution polymerization, the monomers are co-produced in the presence of an organic solvent and a polymerization initiator. Polymerization.The solvent used may be a commonly used organic solvent such as isopropyl alcohol, n-butanol, butyl acetate, xylene, Solpetsusona 100 (aromatic petroleum derivative manufactured by Esso), and the polymerization initiator may be azobisisobutylene. Commonly used polymerization initiators such as lonitrile, benzoyl peroxide, and cumene hydroperoxide may be used.

Furthermore, a chain transfer agent such as 2-mercaptoethanol or n-octylmercaptan can be used if necessary.

In addition, in the first clear coat paint of the present invention, an external acid catalyst represented by ni-, para-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, or amine neutralized products thereof may be substituted with an alkyl ether. It may be used as a catalyst for melamine resin (B). In addition, when using any of the first clear coat paint and the second clear coat paint, an ultraviolet absorbing agent and an antioxidant may be added, and an organic solvent for dilution is usually used to adjust the viscosity to an appropriate level. It is diluted and used.

Examples of organic diluting solvents include xylene, which is an aromatic petroleum derivative, Tsurpets÷100, "/Rubetsuso φ15
0 (manufactured by Esso), ketone-based 2-hegtanone (manufactured by Eastman), and the like.

In the present invention, a resin system serving as a vehicle for the base paint may be used together with the clear coat paint, and specific examples of the vehicle include a thermosetting acrylic melamine resin system and a thermosetting alkyd melamine resin system. . For example, in the case of a base coat paint based on acrylic melamine resin, a film-forming acrylic resin with a functional group capable of reacting with an amino resin, a volatile organic liquid diluent, and a curing agent dissolved in the organic liquid diluent are used. A composition consisting of a certain amino resin, a brightening agent such as aluminum paste, mica, and scaly iron oxide, an organic pigment such as titanium oxide, carbon black, and quinacridone, and a non-acrylic resin such as epoxy resin and fiber thread resin; Auxiliary additives such as a surface conditioner, an ultraviolet absorber, an antioxidant, a pigment antisettling agent, etc. are selected as necessary and added by a standard mixing method.

〔Example〕

Hereinafter, the present invention will be explained in more detail according to Examples. In addition, "part" means "part by weight".

A reaction vessel equipped with a stirrer, a temperature controller, and a condenser was charged with 40 parts of toluene and 10 parts of n-butanol. Heat the contents of the reaction vessel with stirring to bring the temperature to 1.
The temperature was raised to 00°C. Next, after dropping 10 tons of a solution consisting of 5 parts of styrene, 2 parts of methacrylic acid, 35 parts of methyl methacrylate, 46 parts of ethyl acrylate, 12 parts of 2-hydroxyethyl acrylate, and 1.5 parts of benzoyl peroxide over 4 hours, A solution consisting of 16 parts of benzoyl peroxide and 20 parts of toluene was added dropwise over 30 minutes. The reaction vessel was further stirred and heated at 100° C. for 2 hours to increase the conversion rate to resin, and then 30 parts of toluene was added to terminate the reaction. The obtained t' acrylic Itoi polymer solution (non-volatile content: 5 on) was used as an acrylic resin face (referred to as Tsuru).The weight average molecule f of this acrylic copolymer was measured by gel permulation chromatography, and it was found to be 7.
It was Q,000.

Put the amounts of each material shown in Table 1 into a stainless steel container,
After stirring thoroughly, adjust the viscosity with a mixed solvent for dilution.
Base coat paints B-1 and B-2 were manufactured.

Table *1) Manufactured by Degutsusa 2) Aluminum paste manufactured by Toyo Aluminum (
Non-volatile content 654) *5) Butyl etherified melamine resin manufactured by Mitsui Toatsu Chemical ■ (non-volatile content 60%) *4) Methyl butyl mixed etherified melamine resin manufactured by Mitsui Suyanamide ■ (non-volatile content 1OO1) *5) KING
*6) Composition of mixed solvent for dilution *1) Aromatic petroleum derivative (manufactured by Esso) For each of the four types of mixtures having the monomer composition shown in Table 2, carry out the polymerization reaction in the following steps. went. First, Solbetu Sona 100 was added to a reaction vessel equipped with a stirrer, a temperature control device, and a condenser.
(manufactured by Etsuso Co., Ltd.) was charged in an amount of 5.53 parts, and the mixture was heated with stirring to raise the temperature to 140°C. Next, a mixture of 100 parts of each monomer mixture listed in Table 2, M parts of 7zobisinbutyronitrile, and 2.5 parts of t-butylperoxyisoglobil carbonate was added dropwise over 6 hours. Next, azobisisobutyronitrile (15 parts) was continuously added little by little to increase the conversion rate to the resin, and then 1 part of n-butanol was added to terminate the reaction. The hydroxyl value and acid value of the acrylic copolymers (P-1 to P-4) and the viscosity and nonvolatile content of the copolymer solution were as shown in Table 2.

Further, regarding the acrylic copolymer (C) contained in the second clear coat paint, a copolymer solution was synthesized using the chemical composition shown in Table 3 according to the polymerization method described above. Hydroxyl value of the obtained acrylic copolymer (P-5 to P-8),
The acid value, viscosity and non-volatile content of the copolymer solution were as shown in Table 3.

Examples 1-7. Comparative Examples 1 to 3 Using each of the acrylic copolymer solutions described above, different types of clear coat paints (τ-1
~T-10) was adjusted.

Formation of coating film and its evaluation A cationic thread electrodeposition paint for automobiles was applied to a Bonply Donna 144 dull steel plate (manufactured by Nippon Test Panel).
Bake the leaves at C for 30 minutes. Next, an amino alkyd intermediate paint was applied and baked at 160° C. for 30 minutes, followed by water polishing and drying. On this coating film, the base coat paints listed in Table 1 and the first clear coat paints listed in Table 2 were coated in combinations shown in Table 4 using a wet-on-wet method. This layering was done as follows. First, apply the base coat paint on the intermediate coating film to a dry film thickness of 20 to 30 μm, and after leaving it for 5 minutes, apply the first clear coat paint to a dry film thickness of 30 μm.
It was painted to look like m. The undried overcoat coating was left at room temperature for 10 minutes and then baked in a hot air dryer at 140°C for 25 minutes. After the coating film was left to cool sufficiently at room temperature, a second clear coat paint was spray-coated to a dry film thickness of 30 μm without sanding the first clear coating film. Similarly, after leaving it at room temperature for 10 minutes, it was heated to 140℃ for 25 minutes.
A so-called 3-coat/2-base laminated coating film was formed by baking separately. Table 5 shows the results of evaluating the coating performance of each of the laminated coating films thus obtained, such as scratch resistance, cosmetic properties, and adhesion between the first clear coating film and the second clear coating film.

However, Comparative Example 1 is a 2-coat, 1-bake laminated coating film in which the second clear coat paint of the present invention is applied over the base coat paint B-2 in a wet-on-wet manner and baked at 140°C for 25 minutes. When evaluated, the glossiness was lower than in the examples.

In addition, in Comparative Example 2, since the first clear coat paint deviated from the claimed range, the adhesion between the first clear coat film and the second clear coat film was poor after the paint film was formed, and the adhesiveness between the layers was determined by the Sellotape peel test. Due to peeling, other performance evaluations were canceled. or,
In Comparative Example 3, the second clear coat paint was outside the claimed range, so the scratch resistance of the paint film was extremely low.

Further, Examples 1 to 7 had excellent coating performance including glossiness, scratch resistance, and weather resistance, and the adhesion between the first clear coating film and the second clear coating film was also good.

〔Effect of the invention〕

According to the method for forming a coating film of the present invention, a coating film having excellent scratch resistance, acid resistance, cosmetic properties represented by gloss, hot water resistance, weather resistance, etc. can be formed, so it can be used especially for automobiles. It is extremely useful in fields such as body coatings that require a high level of cosmetic properties and coating performance.

Claims (1)

[Scope of Claims] A thermosetting base coat containing a coloring agent and a brightening agent is applied, and then a first clear coat is applied, which is then cured by heating, and then a second clear coat is applied thereon. A method for forming a coating film, in which a first clear coat coating and a second clear coat coating have the following compositions, in a three-coat/two-bake coating method in which a coating is applied and cured by heating. <First clear coat coating composition> (1) (a) At least one type selected from (meth)acrylic esters containing a secondary hydroxyl group represented by the following general formulas (I), (II), and (III). Monomer 1 of
0-50% by weight ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) (In the formula, R^1 represents a hydrogen atom or a methyl group, x is an integer from 1 to 5, and y is an integer from 1 to 5. ) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (II) (In the formula, R^2 represents a hydrogen atom or a methyl group, and n represents an integer from 2 to 8.) ▲ Numerical formulas, chemical formulas, tables, etc. etc.▼(III) (In the formula, R^3 represents a hydrogen atom or a methyl group, and m represents an integer from 1 to 3.) (b) Selected from carboxyl group, sulfonic acid group, and phosphoric acid group 0.1 to 10% by weight of vinyl monomer containing at least one kind of functional group (c) 15 to 60% by weight of (meth)acrylic acid ester represented by general formula (IV) ▲ Numerical formula, chemical formula, table, etc. Yes▼(IV) (In the formula, R^4 represents a hydrogen atom or a methyl group, and R^
5 represents substitution with a hydrocarbon having 4 to 20 carbon atoms. ) (d) The hydroxyl value obtained by copolymerizing 0 to 50% by weight of at least one of the above components (a) to (c) and another copolymerizable vinyl monomer is 100 to 200 mgKOH/g,
Acrylic copolymer (A
) 50-85% by weight (2) Alkyl etherified melamine resin (B) 15-5
0% by weight <Second clear coat paint composition> (1) (e) 10 to 60% by weight of hydroxyl group-containing (meth)acrylic acid ester represented by general formula (V) ▲Mathematical formulas, chemical formulas, tables, etc. are available▼( V) (In the formula, R^6 represents a hydrogen atom or a methyl group, and R
^7 is an organic substituent represented by the following general formula (VI), (VII) or (VIII). ) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (VI) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (VII) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (VIII) (In the formula, R^8 is a straight chain Or carbon number 1 with branched structure
~10 alkylene groups, R^9, R^1^0,
R^1^1 and R^1^2 represent a hydrogen atom or a methyl group, l is an integer of 2 to 5, j is an integer of 2 to 10, k is an integer of 1 to 7, p is 1 ~
Represents an integer of 3. (f) Hydroxyl group-containing (meth)acrylic acid ester represented by general formula (IX) 2 to 50% by weight ▲ Numerical formulas, chemical formulas, tables, etc. are available ▼ (IX) (In the formula, R^1^3 is a hydrogen atom or Methyl group, R^1
^4 represents an alkylene group having 2 to 10 carbon atoms. )
(g) A hydroxyl value of 100 to 250 mgKOH/g obtained by copolymerizing 30 to 80% by weight of other vinyl monomers copolymerizable with the components (e) and (f) above,
It consists of an acrylic copolymer (C) having an acid value of 0.1 to 20 mgKOH/g and a glass transition temperature of -50 to 50°C and (2) a polyisocyanate compound (D), and an acrylic copolymer ( C) the equivalent weight of OH groups present in (
A composition in which the ratio X/Y of the equivalent amount (Y) of NCO groups in the polyisocyanate compound (D) and X) is 1/0.5 to 1/1.5.