JPH08120149A - Curable resin composition, coating composition and method for coating film formation - Google Patents

Abstract

PURPOSE: To obtain the subject composition excellent in weatherability and tape adhesivity, useful for e.g. automotive face coatings, comprising a melamine resin and an acrylic copolymer as a copolymer of at least two kinds of ethylenic unsaturated monomer. CONSTITUTION: This composition comprises (A) 40-90wt.% of an acrylic copolymer 20-400mgKOH/g in hydroxyl value, 1-100mgKOH/g in acid value and 500-50000 in average molecular weight, produced by copolymerization between (i) 1-80wt.% of at least one kind of ethylenic unsaturated monomer selected from hydroxyl-contg. ethylenic unsaturated monomers of formulas I and II (R1 is H or methyl; R2 is cyclohexylene or phenylene; (m) and (n) are each an integer of 1-4) and (ii) 20-99wt.% of another copolymerizable ethylenic unsaturated monomer and (B) 10-60wt.% of a melamine resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a curable resin composition which can be suitably used as a topcoat paint for automobiles and a paint for coil coating, and a coating film forming method using the same.

[0002]

2. Description of the Related Art It is common to use a combination of a hydroxyl group-containing polymer and a melamine resin curing agent in a binder used as a top coating for automobiles. However, when such a melamine resin is used as a curing agent, the cured coating film obtained generally has poor acid resistance. Therefore, such a coating film is particularly likely to be deteriorated by acid rain, which has been a problem in recent years, and causes a defect in appearance.

Therefore, many attempts have been made to reduce the amount of melamine resin used and to improve the acid resistance of the topcoat paint by changing the curing agent to a material other than melamine resin. However, generally, even if the amount of the melamine resin used is reduced, it is not effective in improving the acid resistance, and for example, there is a problem that other curing systems such as an acid-epoxy curing system have poor storage stability.

On the other hand, a curing system using a melamine resin has advantages such as excellent storage stability. Therefore, improvement of acid resistance in the melamine resin curing system is desired.

Further, in recent years, car body decoration using an adhesive tape has become widespread. With this method, it is possible to easily decorate the car body without performing complicated operations such as making holes in the car body, but the strength with which the ornament is fixed to the car body depends on the adhesion of the adhesive tape to the painted surface. And fluctuate. Therefore, there is a demand for a clear coating film having excellent tape adhesion that can firmly fix parts such as ornaments to a vehicle body using an adhesive tape.

[0006]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned conventional problems, and an object thereof is to provide a melamine which forms a coating film excellent in weather resistance, particularly acid rain resistance and tape adhesion. A curable resin composition, a coating film forming method using the same, and a coated article.

[0007]

The present invention is based on the formula (A) (1)

[0008]

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[Wherein R ₁ is a hydrogen atom or a methyl group, and R ₂ is independently a cyclohexylene group or a phenylene group, and l, m and n are integers of 1 to 4. ] 1 to 80% by weight of at least one ethylenically unsaturated monomer selected from the group consisting of hydroxyl group-containing ethylenically unsaturated monomers and (2) 20 to 99% by weight of other copolymerizable ethylenically unsaturated monomers Obtained by copolymerizing, the hydroxyl value is from 20 to 400 mgKOH / g, the acid value is from 1 to 100 mgKOH / g, and the number average molecular weight is from 500 to 500.
The present invention provides a clear coating composition containing 40 to 90% by weight of an acrylic polymer of 00; and 10 to 60% by weight of (B) a melamine resin, thereby achieving the above object.

The acrylic polymer (A) used in the curable resin composition of the present invention is a copolymer of at least two kinds of ethylenically unsaturated monomers.

The first ethylenically unsaturated monomer has the formula

[0012]

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[Wherein R ₁ is a hydrogen atom or a methyl group, and R ₂ is independently a cyclohexylene group or a phenylene group, and l, m and n are integers of 1 to 4. ] One or more hydroxyl group-containing ethylenically unsaturated monomers (A) (1) shown below. These compounds are near the hydroxyl group (C ₁
To C ₄ ) has a benzene ring or a cyclohexane ring and is a primary hydroxyl group, which makes the vicinity of the hydroxyl group (near the cross-linking point) hydrophobic and improves the acid resistance of the cured coating film. When the distance between the hydroxyl group and the benzene ring or the cyclohexane ring exceeds C ₄ and becomes far, the acid resistance of the cured coating film decreases.

A preferred specific example is (meth) acrylic acid.
(4-hydroxymethylcyclohexyl) methyl may be mentioned.

As the second ethylenically unsaturated monomer, a copolymerizable ethylenically unsaturated monomer (A) (2) other than the monomer (A) (1) can be used. The monomer (A) (2) is not particularly limited as long as it is a monomer having a functional group that is copolymerizable with the monomer (A) (1) and can coexist with a hydroxyl group, but preferably an ethylenically unsaturated bond is used. One carbon number 3
-15, especially 3-12 monomers.

Such monomer (A) (2) which can be preferably used
Specific examples of (meth) acrylic acid; styrene derivatives such as styrene, α-methylstyrene and p-tert-butylstyrene; methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylic acid Such as propyl, (meth) acrylate-n, i, and t-butyl, 2-ethylhexyl (meth) acrylate and isobornyl (meth) acrylate
(Meth) acrylic acid ester; and Veova-made by Shell
There are vinyl esters such as 9 and Veova-10.

In addition, a hydroxyl group-containing ethylenically unsaturated monomer different from the monomer (A) (1) can be used as the monomer (A) (2).

For example, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and
Included are compounds such as 6-hydroxyhexyl (meth) acrylate, and their reactants with ε-caprolactone. Such compounds are commercially available, for example,
“Plaxel FM1” and “Plaxel FA1” manufactured by Daicel Chemical Industries, Ltd. may be mentioned. Particularly preferred specific examples
2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate are mentioned.

Monomers prepared by mixing two or more kinds of monomers
It can also be used as (A) (2). This is because it is effective in improving the compatibility between resins.

The acrylic polymer (A) is a monomer (A) (1)
1-80% by weight, preferably 3-70% by weight, more preferably 5-50% by weight; monomer (A) (2) 20-99% by weight, preferably 30-97% by weight, more preferably 50- 95% by weight; and is obtained by copolymerization. When the amount of the monomer (A) (1) is 1% by weight or less, the acid resistance decreases, and when it is 80% by weight or more, the flexibility, stability and water resistance decrease. monomer
If the amount of (A) (2) is 20% by weight or less, the stability is reduced, and if it is 99% by weight or more, the acid resistance is reduced.

Particularly, the monomer (A) (2) is used as the monomer (A).
When a hydroxyl group-containing monomer other than (1) is used, the amount thereof used is preferably up to 40% by weight based on the total monomers for preparing the acrylic polymer (A). This is because if the amount of the hydroxyl group-containing monomer other than the monomer (A) (1) used exceeds 40% by weight, the acid resistance decreases.

Polymerization can be carried out by solution radical polymerization, which is well known to those skilled in the art. It is preferable to carry out polymerization at a temperature of 100 to 150 ° C. for a polymerization time of 3 to 8 hours using an azo or peroxide type initiator at atmospheric pressure or under pressure. The radical polymerization initiator is preferably used in an amount of 0.5 to 15% by weight based on all the monomers.

The resulting acrylic polymer (A) has a hydroxyl value of 20 to 400, preferably 35 to 350, more preferably 50 to 350.
250 mgKOH / g, acid value 1-100, preferably 2-8
It is adjusted to 0, more preferably 5 to 50 mgKOH / g, and the number average molecular weight is 500 to 50,000, preferably 1,000 to 30,000, more preferably 1,500 to 25,000. If the hydroxyl value is less than 20, the acid resistance, adhesion and curability will decrease, and if it exceeds 400, the flexibility and water resistance will decrease. When the acid value is less than 1, the curability is lowered, and when it exceeds 100, the water resistance is lowered. If the molecular weight is less than 500, the curability is deteriorated to deteriorate the appearance of the coating film, and if it exceeds 50,000, the solubility in a solvent is decreased to deteriorate the appearance of the coating film. In addition,
The molecular weight of the polymer used in the present invention is determined by the GPC method.

The melamine resin (B) used in the curable resin composition of the present invention generally refers to a resin obtained by adding an aliphatic aldehyde to melamine to form an ether, and particularly melamine-
Etherification of the formaldehyde addition reaction product is preferred. Melamine resins obtained by etherifying an addition reaction product of melamine and an aliphatic aldehyde include condensates such as methyletherified melamine, methylbutyletherified melamine, and butyletherified melamine.

In particular, in order to achieve high solidification and scratch resistance, it is desirable to use a highly alkylated melamine resin having a high alkyl etherification in combination with an acid catalyst described later,
The highly alkylated melamine resin is a melamine resin in which a methylolated amino group is completely or considerably alkylated and has an amount of alkyl ether groups per triazine nucleus of 50% or more. Here, the amount of alkyl ether group is 100% when all the hydrogen atoms of the amino group in the melamine resin are replaced with alkanol and then all the terminal OH groups are replaced with an alkoxy group, and the actually added alkyl The average ratio of ether groups is expressed in%. Since the number of amino groups per triazine nucleus is 3, 50% or more of alkyl ether groups means that an average of 3 or more alkyl ether groups are added per triazine nucleus.

Examples of the alkyl etherified melamine resin include H of a methylol group added to an amino group.
Is substituted with an alkyl group, and examples of the alkyl group include a methyl group, an ethyl group, an n-butyl group and an isobutyl group.

Acrylic polymer thus obtained
The curable resin composition of the present invention can be obtained by blending (A) and the melamine resin (B).

The blending amount can be calculated from the hydroxyl value and acid value of each polymer by a calculation method well known to those skilled in the art. It is preferable to mix them in an equivalence ratio, but it is not strict and slight variations are allowed.

Generally, the curable resin composition of the present invention comprises an acrylic polymer (A) of 40 to 90% by weight, preferably 50 to 80% by weight and a melamine resin (B) of 10 to 60% by weight, preferably 2%.
It is obtained by blending in an amount of 0 to 50% by weight. If the amount of the acrylic polymer (A) is more than 90% by weight, the curability will be lowered, and if it is less than 40% by weight, the flexibility and the acid resistance will be lowered. When the melamine resin (B) is more than 60% by weight, flexibility and acid resistance are lowered, and when it is less than 10% by weight, curability is lowered.

In addition to the above polymers (A) and (B), the curable resin composition of the present invention may be a curing resin usually used for acrylic-melamine curable resin compositions such as p-toluenesulfonic acid. A catalyst may be included. Specific examples of other catalysts that can be used in the curable resin composition of the present invention include dodecylbenzene sulfonic acid and dinonyl naphthalene disulfonic acid. These catalysts may be mixed and used. The amount of this catalyst blended is 0.1 to the resin composition solids.
It is preferably 5% by weight.

The resin used in the present invention has an acidic group as a functional group. Therefore, by neutralizing with an amine, it is possible to obtain an aqueous resin composition using water as a medium.

The curable resin composition of the present invention can be suitably used as a binder component of a clear coating composition. In that case, the curable resin composition of the present invention is an additive such as an ultraviolet absorber, a hindered amine light stabilizer and an antioxidant for improving the weather resistance of a coating film; alcohol-based.
(For example, methanol, ethanol, propanol, and butanol), hydrocarbon-based and ester-based diluents for viscosity adjustment; crosslinked resin particles as a rheology control agent; and surface preparation for appearance control It is blended with the drug product.

Such clear coating compositions are generally
It is used to form a top coat when forming a composite coat consisting of a plurality of layers on a substrate. The composite coating film is, for example, a step of forming an undercoat on a substrate and, if necessary, a coating film of an intermediate coating, a step of forming a coating film of a base coating thereon, and a clear coating composition of the same. The method includes the step of forming a coating film.

In this case, a color pigment-containing aqueous paint or a color pigment-containing organic solvent type paint is preferably used as the base paint as the base of the clear paint composition. At the time of coating, it is possible to use a two-coat one-bake curing method in which a base coating surface is not cured and a clear coating material containing the curable resin composition of the present invention is applied to the surface of the base coating material, and then both coating films are cured. preferable.

When a water-based paint is used as the base paint, it is preferable to heat the base coat at 60 to 100 ° C. for 2 to 10 minutes before applying the clear paint in order to obtain a good finished coating film. . As the base paint, those specifically described in US Pat. Nos. 5,151,125 and 5,183,504 can be used. In particular, U.S. Pat.
The aqueous coating composition described in No. 3,504 is most suitable in terms of finish, appearance and performance.

The method for producing the curable resin composition of the present invention is not particularly limited, and any method known to those skilled in the art can be used. For example, in the case of an enamel paint, the compound such as a pigment may be kneaded and dispersed using a kneader or a roll.

The coating composition of the present invention can be applied by spray coating, brush coating, dip coating, roll coating, flow coating or the like. The substrate may be undercoated or intermediate coated, if desired. Known undercoat paints and intermediate paints can be used.

The coating composition according to the invention can advantageously be used on any substrate, such as wood, metal, glass, cloth, plastics, foams, etc., especially on plastics and metal surfaces such as steel, aluminum and their alloys.

In general, the film thickness will vary depending on the desired application. In most cases 0.5-3 mils are useful.

After coating the substrate, the coating film is cured. Curing gives a cured coating film having a high degree of crosslinking at 100 to 180 ° C, preferably 120 to 160 ° C. The curing time varies depending on the curing temperature and the like, but curing at 120 to 160 ° C for 10 to 30 minutes is suitable.

[0041]

The present invention will be further described by the following examples, but the present invention is not limited thereto. Unless otherwise specified, the blending amount is indicated by weight.

The relationship between the abbreviations of various hydroxyl group-containing ethylenically unsaturated monomers (hereinafter referred to as "OH monomers") and the structures used in this example is shown in the following table.

OH monomers a1 to a8

[0044]

[Chemical 4]

[0045]

[Table 1] OH Monomers No. m and n R ₁ R ₂ a1 1 hydrogen atom cyclohexylene group a2 2 methyl group cyclohexylene group a3 1 methyl group phenylene group a4 2 hydrogen atom phenylene group a5 3 hydrogen atom cyclohexylene group a6 4 Methyl group Cyclohexylene group a7 3 Methyl group Phenylene group a8 4 Hydrogen atom Phenylene group

OH monomer a9 to a16

[0047]

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[0048]

[Table 2] OH Monomer Nos. M and n R ₁ R ₂ a9 1 hydrogen atom cyclohexylene group a10 2 methyl group cyclohexylene group a11 1 methyl group phenylene group a12 2 hydrogen atom phenylene group a13 3 hydrogen atom cyclohexylene group a14 4 Methyl group Cyclohexylene group a15 3 Methyl group Phenylene group a16 4 Hydrogen atom Phenylene group

Production Example 1 A 200 ml reaction vessel equipped with a thermometer, a stirrer, a cooling tube, a nitrogen introducing tube and a dropping funnel was charged with xylol, S-100 and
n-Butanol was added at the blending amount shown in Table 3 below, and 130
The temperature was raised to ° C. Then, various monomers having the compositions shown in Table 3 were added, and 5.00 parts of a xylol solution containing 5.00 parts of t-butylperoxy-2-ethylhexanoate as an initiator was added dropwise over 3 hours, and the mixture was heated at 130 ° C. for 30 minutes. Held in. After dropping 1.00 parts of t-butylperoxy-2-ethylhexanoate and 10.00 parts of xylol over 30 minutes,
The stirring was continued for another 90 minutes, and the mixture was cooled to 70 ° C. Thus, acrylic polymer A-1 was obtained. Table 3 shows the nonvolatile content (%), number average molecular weight, acid value and hydroxyl value of the obtained polymer composition.

[0050]

Table 3 Obtained Polymer No. A-1 Solvent Xylol 22.2 S-100 22.2 n-Butanol 22.2 OH monomer a1 17.6 a2 21.4 Acid monomer Acrylic acid 2.6 Neutral monomer Styrene 20 Ethyl acrylate 10 Ethyl methacrylate 10 Isobutyl acrylate 10 Isobutyl methacrylate 8.4 Nonvolatile matter (%) 60 Number average molecular weight 15000 Acid value 20 Hydroxyl value 100

Production Example 2 An acrylic polymer A-2 was obtained in the same manner as in Production Example 1 except that the composition shown in Table 4 below was used. The properties of the obtained polymer composition are also shown in Table 4.

[0052]

[Table 4] Obtained polymer No. A-2 solvent Xylol 33.3 S-100 33.3 OH monomer a3 9.2 a4 9.8 acid monomer methacrylic acid 0.8 neutral monomer styrene 20 2-ethylhexyl acrylate 20 2-ethylhexyl methacrylate 20 cyclohexyl acrylate 20.2 non-volatile Min (%) 60 Number average molecular weight 1500 Acid value 5 Hydroxyl value 50

Production Example 3 An acrylic polymer A-3 was obtained in the same manner as in Production Example 1 except that the composition shown in Table 5 below was used. The characteristics of the obtained polymer composition are also shown in Table 5.

[0054]

[Table 5] Obtained polymer No. A-3 Solvent Xylol 33.3 n-Butanol 33.3 OH monomer a5 22.6 a6 26.4 Acid monomer Acrylic acid 3.2 Methacrylic acid 3.8 Neutral monomer Styrene 20 Cyclohexyl methacrylate 24 Nonvolatile matter (%) 60 Number average molecular weight 5000 Acid value 50 Hydroxyl value 100

Production Example 4 An acrylic polymer A-4 was obtained in the same manner as in Production Example 1 except that the composition shown in Table 6 below was used. The properties of the obtained polymer composition are also shown in Table 6.

[0056]

Table 6 Obtained polymer No. A-4 solvent S-100 33.3 n-butanol 33.3 OH monomer a7 23.3 a8 24.6 2-hydroxypropyl acrylate 11.6 2-hydroxypropyl methacrylate 12.8 2-hydroxyethyl acrylate 10.3 acid monomer acrylic acid 1.3 Methacrylic acid 1.5 Neutral monomer Styrene 10 n-Butyl acrylate 4.6 Nonvolatile matter (%) 60 Number average molecular weight 10000 Acid value 20 Hydroxyl value 250

Production Example 5 An acrylic polymer A-5 was obtained in the same manner as in Production Example 1 except that the composition shown in Table 7 below was used. The properties of the obtained polymer composition are also shown in Table 7.

[0058]

[Table 7] Obtained polymer No. A-5 solvent Xylol 44.4 S-100 22.2 OH monomer a9 10.2 a10 11.9 2-hydroxyethyl methacrylate 5.8 "Plaxel FA-1" manufactured by Daicel Chemical Industries Ltd. 10.2 Acid monomer Acrylic acid 2.6 Neutral Monomer Styrene 30 n-Butyl methacrylate 10 t-Butyl acrylate 19.3 Nonvolatile matter (%) 60 Number average molecular weight 15000 Acid value 20 Hydroxyl value 100

Production Example 6 An acrylic polymer A-6 was obtained in the same manner as in Production Example 1 except that the composition shown in Table 8 below was used. The properties of the obtained polymer composition are also shown in Table 8.

[0060]

[Table 8] Obtained polymer No. A-6 solvent Xylol 44.4 n-butanol 22.2 OH monomer a11 10.6 a12 11.2 Daicel Chemical Industries "Plaxel FM-1" 10.9 Daicel Chemical Industries "Plaxel FA-2" 15.3 Acid Monomer Methacrylic acid 3.1 Neutral monomer Styrene 20 t-Butyl acrylate 10 t-Butyl methacrylate 18.9 Nonvolatile matter (%) 60 Number average molecular weight 25000 Acid value 20 Hydroxyl value 100

Production Example 7 An acrylic polymer A-7 was obtained in the same manner as in Production Example 1 except that the composition shown in Table 9 below was used. The properties of the obtained polymer composition are also shown in Table 9.

[0062]

[Table 9] Obtained polymer No. A-7 solvent S-100 44.4 n-butanol 22.2 OH monomer a13 12.7 a14 14.6 "Plaxel FM-2" manufactured by Daicel Chemical Industries, Ltd. 16.0 2-hydroxybutyl acrylate 6.4 acid monomer acrylic acid 2.6 Neutral monomer Ethyl acrylate 10 Ethyl methacrylate 10 Isobutyl acrylate 10 Isobutyl methacrylate 17.7 Nonvolatile matter (%) 60 Number average molecular weight 15000 Acid value 20 Hydroxyl value 100

Production Example 8 An acrylic polymer A-8 was obtained in the same manner as in Production Example 1 except that the composition shown in Table 10 below was used. The properties of the obtained polymer composition are also shown in Table 10.

[0064]

Table 10 Obtained Polymer No. A-8 Xylol 22.2 n-Butanol 44.4 OH Monomer a15 13.1 a16 13.7 2-Hydroxybutyl Methacrylate 4.7 4-Hydroxybutyl Methacrylate 4.3 4-Hydroxybutyl Methacrylate 4.7 Acid Monomer Methacrylic Acid 3.1 Neutral Monomer 2-Ethylhexyl acrylate 10 2-Ethylhexyl methacrylate 10 Cyclohexyl acrylate 10 Cyclohexyl methacrylate 10 n-Butyl acrylate 16.4 Nonvolatile matter (%) 60 Number average molecular weight 15000 Acid value 20 Hydroxyl value 100

Production Example 9 An acrylic polymer A-9 was obtained in the same manner as in Production Example 1 except that the composition shown in Table 11 below was used. The properties of the obtained polymer composition are also shown in Table 11.

[0066]

Table 11 Obtained Polymer No. A-9 Solvent Xylol 22.2 S-100 22.2 n-Butanol 22.2 OH monomer 2-hydroxypropyl acrylate 11.6 2-Hydroxypropyl methacrylate 12.8 Acid monomer Acrylic acid 1.3 Methacrylic acid 1.5 Neutral monomer Styrene 30 Ethyl acrylate 10 Ethyl methacrylate 10 Isobutyl acrylate 10 Isobutyl methacrylate 12.8 Nonvolatile content 60 Number average molecular weight 15000 Acid value 20 Hydroxyl value 100

Production Example 10 An acrylic polymer A-10 was obtained in the same manner as in Production Example 1 except that the composition shown in Table 12 below was used. The properties of the obtained polymer composition are also shown in Table 12.

[0068]

Table 12 Obtained Polymer No. A-10 Xylol 22.2 S-100 22.2 n-Butanol 22.2 OH Monomer 2-hydroxyethyl acrylate 25.8 2-Hydroxyethyl methacrylate 29.0 Acid monomer Acrylic acid 3.2 Methacrylic acid 3.8 Neutral monomer Styrene 102 -Ethylhexyl acrylate 10 2-Ethylhexyl methacrylate 5 Cyclohexyl acrylate 5 Cyclohexyl methacrylate 8.2 Nonvolatile content 60 Number average molecular weight 1500 Acid value 50 Hydroxyl value 250

[0069] In the formulation shown in Example 1 in Table 13, the acrylic polymer obtained in Production Example 1 A-
1, melamine resin ("Uban-128" manufactured by Mitsui Toatsu), p-
Toluenesulfonic acid (Wako Pure Chemical Industries, Ltd.), triethylamine, UV absorber (Ciba Geigy's "Tinuvin 90
0 ”), an antioxidant (“ Sanol LS-292 ”manufactured by Sankyo Co.) and n
-Butanol was added while stirring with a disper to prepare a curable resin composition. The obtained resin composition was treated with a solvent consisting of butyl acetate / xylene = 1/1 in a Ford cup No. 4
The viscosity was adjusted to 0 seconds to obtain a clear coating composition.

On the other hand, a 0.8 mm thick phosphoric acid-treated steel sheet was coated with an electrodeposition coating (Nippon Paint Co., Ltd., Power Top pu-50) and an intermediate coating (Nippon Paint Co., Ltd., Olga P-2) to dry thickness. A solvent-type melamine-based base paint ("Superlac M-90" manufactured by Nippon Paint Co., Ltd.) was applied to a process test plate coated to a thickness of 25 μm and 40 μm.
A base coating film was formed by air-spray coating so as to have a thickness of μm and setting for about 7 minutes.

On top of that, the obtained clear coating composition was added,
Use an electrostatic coating machine (“Auto REA” manufactured by Randsburg Gemma) to apply a spraying pressure of 5 kg / cm ² to a dry film thickness of approximately 40 μm, set for approximately 7 minutes, and then set at 140 ° C. for 25 minutes. Baked for a minute.

The above solvent-based base paint was prepared by mixing aluminum flake paste having an aluminum flake content of 65% (“Alpaste 7160N” manufactured by Toyo Aluminum Co., Ltd. 10.9 parts, solid content 4%).
8% thermosetting acrylic resin varnish (Mitsui Toatsu Chemical Co., Ltd. "ALMATEX NT-U-448") 66.85 parts, solid content 60% melamine resin varnish (Mitsui Toatsu Chemical Co., Ltd. "Uban 20N-60") 13.3
7 parts, toluene 6.38 parts, n-butanol 2.0 parts and triethylamine 0.5 parts.

Evaluation of Acid Resistance The obtained cured coating film was brought into contact with 0.2 ml of 0.1N H ₂ SO ₄ aqueous solution at 60 ° C. for 2 hours, and then the coating film surface was visually evaluated according to the following criteria. Table 15 shows the results.

When no change was observed: ○ When a trace was slightly observed △: When a trace was clearly observed ×

Evaluation of Water Resistance After the obtained cured coating film was immersed in ion exchange water at 50 ° C. for 240 hours, the surface of the coating film was visually evaluated according to the following criteria. Table 15 shows the results.

When no change was observed ○ When a slight trace was seen △ When clear trace was seen ×

Evaluation of Adhesion to Tape FIG. 1 schematically shows the evaluation state. First, a coated plate 3 having a cured coating film 2 on a phosphoric acid-treated steel plate 1 was obtained by the above coating film forming operation. The surface of the cured coating film 2 was degreased with isopropyl alcohol, and a 25 mm wide double-sided tape 4 (manufactured by Nichiban Co., Ltd.) was placed on this surface. A PET film 5 having a width of 25 mm (manufactured by Nitto Co., Ltd.) was superposed thereon, and a 5 kg roller was passed back and forth once over the obtained laminated body to uniformly crimp it.

After standing at room temperature for 24 hours, the laminate was fixed vertically as shown in FIG. After being left at 80 ° C. for 30 seconds, 1.5 kg of a weight 6 was attached to the upper end of the PET film 5 under this environmental condition, and 180 ° peeling was tried. The tape adhesion was visually evaluated according to the following criteria. Table 15 shows the results.

No peeling ○ Partial peeling △ Complete peeling ×

Examples 2 to 6 The clear paints of Examples 2 to 8 were prepared in the same manner as in Example 1 except that the formulations shown in Table 13 below were used, and the coating film performance was evaluated. Table 15 shows the evaluation results.

Examples 7 and 8

First, a clear coating composition was obtained in the same manner as in Example 1 with the ingredients shown in Table 14.

On the other hand, a 0.8 mm thick phosphoric acid-treated steel sheet was coated with an electrocoating paint (Nippon Paint Co., Ltd., Power Top pu-50) and an intermediate coating paint (Nippon Paint Co., Ltd., Olga P-2) to a dry thickness. A water-based base coating (Example 1 of US Pat. No. 5,183,504) was applied to a process test plate coated so as to have a thickness of 25 μm and 40 μm so as to have a dry film thickness of 15 μm, and the base was obtained by drying at 80 ° C. for 5 minutes. A coating film was formed.

On top of that, the obtained clear coating composition was added,
Use an electrostatic coating machine (“Auto REA” manufactured by Randsburg Gemma) to apply a spraying pressure of 5 kg / cm ² to a dry film thickness of about 40 μm. After setting for about 7 minutes, set at 140 ° C for 25 minutes. Burned

The above water-based coating composition was prepared by mixing 15 parts of an aluminum pigment paste containing 65% aluminum flake (“Alpaste 7160N” manufactured by Toyo Aluminum Co., Ltd.) and methylated melamine (“Cymel 303 manufactured by Mitsui Toatsu Kagaku Co., Ltd.”). )) 30 parts, isostearic acid phosphate ("Porelex A-180L" manufactured by Sakai Chemical Co., Ltd.), number average molecular weight 12000, hydroxyl value 70, acid value 58 and solid content 50% obtained in Preparation Example 1 of the same document. Of acrylic resin varnish, and 43 parts of urethane emulsion having an acid value of 16.2 and a solid content of 33%.

The performance of the obtained coating film was evaluated in the same manner as in Example 1. Table 15 shows the evaluation results.

Comparative Examples 1 and 2 A clear paint of Comparative Example was prepared in the same manner as in Example 1 except that the formulations shown in Table 14 below were used, and the coating film performance was evaluated. Table 15 shows the evaluation results.

[0088]

[Table 13] Example 1 2 3 4 5 6 A-1 A-2 A-3 A-4 A-5 A-6 No. and amount of acrylic polymer 150 133.3 116.7 100 83.3 66.7 Unit 128 16.7- − − − − Unit 20N-60 − 33.3 25 − − − Unit 225 − − 25 66.7 − − Unit 120 − − − − − 50 − Cymel 303 − − − − − 60 Cymel 267 − − − − − − P-Toluenesulfonic acid − − − − 1 1 Triethylamine − − − − 1 1 Tinubin 900 1 1 1 1 1 1 Sunol LS-292 0.1 0.1 0.1 0.1 0.1 0.1 n-Betanol 5 5 5 5 5 Five

[0089]

[Table 14] Example 7 8 Comparative example 1 Comparative example 2 A-7 A-8 A-9 A-10 No. and amount of acrylic polymer 116.7 116.7 116.7 116.7 unit 128 ----- unit 20N -60 − − 25 − Yuban 225 − − 25 − Yuban 120 − − − − Cymel 303 15 − − 15 Cymel 267 15 30 − 15 p-Toluenesulfonic acid 1 1-1 Triethylamine 1 1-1 Tinubin 900 1 1 1 1 SANOL LS-292 0.1 0.1 0.1 0.1 n-butanol 5 5 5 5

[0090]

[Table 15]

As shown in the results of Table 15, the clear paints of Examples 1 to 8 form coating films having excellent acid resistance, water resistance and tape adhesion as compared with Comparative Examples.

[0092]

The present invention provides a melamine-based curable resin composition which forms a coating film having excellent weather resistance, particularly resistance to acid rain, and excellent tape adhesion.

[Brief description of drawings]

FIG. 1 is a schematic view showing an operation for evaluating tape adhesion.

[Explanation of symbols]

 1 ... Phosphoric acid treated steel plate, 2 ... Hardened coating film, 3 ... Painted plate, 4 ... Double-sided tape, 5 ... PET film.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C09D 161/28 PHK (72) Inventor Yoshitaka Okude 19-17 Ikedanaka-cho, Neyagawa-shi, Osaka Japan Into Inc.

Claims (4)

[Claims] 1. A formula (A) (1) [Wherein R ₁ is a hydrogen atom or a methyl group, and R _{2 is}
Are independently cyclohexylene or phenylene groups and l, m and n are integers from 1 to 4. ] At least one ethylenically unsaturated monomer selected from the group consisting of hydroxyl group-containing ethylenically unsaturated monomers
Obtained by copolymerizing 80% by weight with (2) 20 to 99% by weight of another copolymerizable ethylenically unsaturated monomer,
Hydroxyl value is 20 ~ 400mgKOH / g, acid value is 1 ~ 100mgKOH
A curable resin composition containing 40 to 90% by weight of an acrylic polymer having a number average molecular weight of 500 to 50,000 and (B) 10 to 60% by weight of a melamine resin. 2. A coating composition containing the curable resin composition according to claim 1 as a binder component. 3. A step of (I) forming an undercoat on a base material and optionally a coating film of an intermediate coating, (II) forming a coating film of a base coating thereon, and (III) A method for forming a composite coating film, comprising the step of forming a coating film of the coating composition according to claim 2 above. 4. A coated article obtained by the method according to claim 3.