JPH09187722A - Method for forming coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a coating film by which a metallic coating film with excellent clearness and improved whiteness is obtained. SOLUTION: This method involves steps of applying a base clear coating A, a metallic coating B, and a top clear coating C successively by a wet-on-wet way and cross-linking and hardening the coatings A, B, and C simultaneously by heating. In the method, the contact angle (a) of the dried coating film of the coating A against water is made smaller than the contact angle (b) of the dried coating film of the coating B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a multi-layer coating film, and more particularly to a coating film forming method capable of obtaining a metallic coating film having excellent image clarity and improved whiteness.

[0002]

2. Description of the Related Art Conventionally, the coating of automobile bodies, especially metallic finish coating, has conventionally been carried out by applying an electrodeposition paint and an intermediate coating paint, followed by heating and curing, and then applying a metallic paint and a clear paint wet-on-wet. Then, it is cured by heating.

In such a metallic finish, an excellent metallic feeling can be obtained by orienting the scaly metallic pigment in the metallic coating film in parallel and uniformly on the entire surface to be coated. However, when a clear coating was applied on the metallic coating surface by wet-on-wet, there was a problem that even if the metallic pigment flowed, unevenness occurred. For this reason, for example, by increasing the viscosity at the time of application of the metallic paint to prevent the flow of the metallic pigment, or by increasing the difference in the film thickness after application and after heat curing, the metallic pigment is applied to the coated surface. However, the former method does not provide sufficient smoothness on the coated surface, and the latter method increases the amount of organic solvent, which is desirable from the standpoint of working environment. It wasn't something.

If the thickness of the metallic coating film can be made smaller than the average particle size of the metallic pigment such as aluminum powder, it is considered that the metallic pigment is inevitably hard to move and oriented parallel to the coated surface. If the coating amount of the coating material is reduced in order to reduce the coating film thickness, there is a problem that a continuous film cannot be formed on the intermediate coating film which is a cured film.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a clear coating film layer having a higher surface tension than the coating film is wet-on-wet under the metallic coating film. It has been found that the metallic coating can be made very thin and the orientation of the metallic pigment can be improved by arranging the coating and further forming a top coat of the clear coating layer to form a 3-coat 1-bake. Reached

That is, according to the present invention, the base clear coating (A), the metallic coating (B), and the top clear coating (C) are sequentially applied wet-on-wet, and then the coating is heated to apply the coating (A), ( A method of simultaneously crosslinking and curing the coating films of B) and (C), wherein the water contact angle a in the dry coating film of the coating material (A) is smaller than the water contact angle b in the dry coating film of the coating material (B). The present invention provides a method for forming a coating film.

The present invention will be described in detail below.

In the present invention, the base clear coating material (A)
Is a liquid composition obtained by mixing a thermosetting resin composition and a solvent, and forms a transparent coating film.

Examples of the thermosetting resin composition include:
A composition in which a base resin such as an acrylic resin, a polyester resin or an alkyd resin having a crosslinkable functional group is mixed with a crosslinker such as an amino resin such as a melamine resin or a urea resin or a polyisocyanate is suitable. As the solvent, an organic solvent and / or water can be used, and the above components can be mixed and dispersed therein.

If necessary, the base clear coating material (A) may further contain pigments such as extender pigments and coloring pigments, and additives for coating materials.

The above-mentioned base clear coating material (A) is a substrate obtained by forming an electrodeposition coating film and an intermediate coating material on a material such as metal or plastic by a coating method such as electrostatic coating, air spraying or airless spraying. 5 to 15 μm in dry film thickness,
It is preferable to apply the coating so that the film thickness is 5 to 10 μm. The coating film made of such a base clear coating material (A) is not crosslinked and cured at room temperature or by heating (10
The temperature is preferably 0 ° C. or lower) and dried, and then the metallic paint (B) is applied.

In the present invention, the metallic paint (B) is
It is a liquid coating composition which is applied onto the uncured Besk rear coating film obtained above and which comprises a thermosetting resin composition, a metallic pigment and a solvent.

Examples of the thermosetting resin composition include:
A composition prepared by mixing a base resin such as an acrylic resin, a polyester resin, or an alkyd resin having a crosslinkable functional group with a melamine resin, an amino resin such as a urea resin, or a crosslinking agent such as polyisocyanate is suitable.

The metallic pigment is preferably a scaly particle pigment having a light interference effect or a glittering sensation, and examples thereof include aluminum, mica, mica coated with a metal oxide, mica-like iron oxide, and metal iron oxide. Examples thereof include coated mica-like iron oxide. The average particle size of the metallic pigment is generally 10 μ or more, preferably 10 to 50 μ. The blending amount of the metallic pigment is appropriately 1 to 50 parts by weight per 100 parts by weight of the thermosetting resin composition.
Depending on the thickness of the metallic coating film, it is preferably 10 parts by weight or more in terms of concealment.

As the solvent, an organic solvent and / or water can be used, and the above components can be mixed and dispersed therein.

If desired, the metallic paint (B) may further contain additives for paints such as color pigments, extender pigments, viscosity modifiers and coating surface modifiers.

The metallic coating material (B) is applied by a coating method such as electrostatic coating, air spraying or airless spraying.
It is preferable to apply the coating so that the dry film thickness is 5 to 15 μm, preferably 5 to 10 μm. Without cross-linking and curing the coating film of the metallic paint (B),
The top clear coating composition (C) is applied after drying at room temperature or by heating (preferably 100 ° C. or lower).

In the present invention, top clear paint (C)
Is a liquid composition to be applied on the uncured metallic coating film obtained above, which is a liquid composition prepared by mixing a thermosetting resin composition and a solvent, and forms a transparent coating film.

The thermosetting resin composition comprises, for example, a base resin such as an acrylic resin, a polyester resin or an alkyd resin having a crosslinkable functional group, a melamine resin, an amino resin such as a urea resin, or a crosslink such as polyisocyanate. Examples of the composition include an agent. Further, JP-A-62-8
4137, JP-A-62-87288, JP-A-1-39653, JP-A-2-4577, etc., it is necessary to use the amino resin or the like as a crosslinking agent. A thermosetting resin composition that does not exist can also be preferably used. As the solvent, an organic solvent and / or water can be used, which is adjusted by dissolving or dispersing the thermosetting resin composition therein.

If desired, the top clear coating composition (C) may further contain coating additives such as coloring pigments, metallic pigments, ultraviolet absorbers and light stabilizers to the extent that transparency is not impaired. .

The top clear coating composition (C) is preferably coated by a coating method such as electrostatic coating, air spraying or airless spraying so as to have a dry film thickness of 10 to 50 μm.

The multi-layer coating film of the present invention comprises a base clear coating (A), a metallic coating (B) and a top clear coating (C), which are applied sequentially in a wet-on-wet manner, and then heated to obtain a coating of these coatings. It is obtained by simultaneously curing the coating film. The heating temperature for simultaneously curing the coating films of these paints is generally appropriate in the range of 100 to 180 ° C.

Further, in the present invention, the water contact angle a of the dry coating film of the above-mentioned base clear coating material (A) is smaller than the water contact angle b of the dry coating film of the above metallic coating material (B) (a <b). Is mandatory. Specifically, the difference between the water contact angle a and the water contact angle b is preferably 2 ° or more, more preferably 5 ° or more. When the water contact angle is a ≧ b, the metallic coating material (B) is not preferable because it becomes difficult to form a thin film on the base clear coating film. The water contact angle a in the dried coating film of each paint is such that the water contact angle a is 75 ° or less, preferably 70 ° or less, and the water contact angle b.
Is 70 to 80 °, and the water contact angle c in the dried coating film of the top clear coating material (C) is 75 ° or more, preferably 80.
It is desirable that it is equal to or more than ° and that a <b <c. Here, the water contact angle is 0.03 cc of deionized water on the surface of the coating film after drying, and the contact angle of the water droplet after 1 minute at 20 ° C. is the automatic contact made by Kyowa Interface Science Co., Ltd. It is a numerical value measured by the angle meter CA-Z type.

[0024]

EXAMPLES The present invention will be described in more detail with reference to examples. “Parts” and “%” are “parts by weight” respectively.
And "% by weight".

Preparation of Besk Clear Paint (A) The components and formulations shown in Table 1 were stirred and mixed, and a mixed solvent (xylene / ethyl acetate / isobutanol / Solvesso # 1) was prepared.
50 = 25/50/10/15) to obtain a solid content of 20
% Of the base clear coating materials (A-1) to (A-5) were prepared. The same table shows the water contact angle of the dried coating film of each coating material. The composition of Table 1 is a solid content indication, and (Note 1) in the table
(Note 5) and (* 1) are as follows.

(Note 1) 70 parts of methyl methacrylate, 19 parts of ethyl acrylate, hydroxyethyl acrylate
Acrylic resin obtained by copolymerizing 10 parts of methacrylic acid with 1 part of methacrylic acid (Note 2) 30 parts of methyl methacrylate, 19 parts of n-butyl acrylate, 20 parts of lauryl methacrylate, 2-
Acrylic resin prepared by copolymerizing 20 parts of ethylhexyl methacrylate, 10 parts of hydroxyethyl acrylate and 1 part of acrylic acid (Note 3) Polyester resin of phthalic anhydride / hexahydrophthalic anhydride type (Note 4) Poly 30 parts of an adduct of 12-hydroxystearic acid and glycidyl methacrylate and 10 parts of styrene,
20 parts of methyl methacrylate, 17 parts of 2-ethylhexyl acrylate, 2 parts of 2-hydroxyethyl acrylate
0 part, 30 parts of styrene, 30 parts of methyl methacrylate in the presence of a copolymer with a monomer mixture of 3 parts of acrylic acid.
Part, 2-ethylhexyl acrylate 23 parts, 2-hydroxyethyl acrylate 15 parts, acrylic acid 2 parts monomer mixture prepared by dispersion polymerization in n-heptane (Note 5) "Uban 28-60", manufactured by Mitsui Toatsu Chemicals, Inc. (* 1) Water contact angle: 0.03 cc on the surface of the coating film after drying.
A water drop of deionized water was dropped, and the contact angle of the water drop after 1 minute at 20 ° C. was measured with an automatic contact angle meter CA-Z type manufactured by Kyowa Interface Science Co., Ltd.

[0027]

[Table 1]

Preparation of metallic paint (B) The components and formulations shown in Table 2 were stirred and mixed to prepare a mixed solvent (xylene / ethyl acetate / isobutanol / solveso # 1).
50 = 25/50/10/15) to obtain a solid content of 20
% Metallic paints (B-1) to (B-3) were prepared. The same table shows the water contact angle of the dried coating film of each coating material. The blending amounts in Table 1 are solid contents, and (Note 6) and (Note 7) in the table are as follows.

(Note 6) 40 parts of methyl methacrylate, 20 parts of ethyl acrylate, 28 parts of 2-ethylhexyl methacrylate, 10 parts of hydroxyethyl acrylate,
Acrylic resin formed by copolymerizing 2 parts of acrylic acid (Note 7) "Aluminum paste # 4919", manufactured by Toyo Aluminum Co., Ltd., average particle size 10 to 13 µm

[0030]

[Table 2]

Example 1 Degreasing and zinc phosphate conversion treatment with a thickness of 0.8 mm
Electrodeposition paint "Electron 200" on dull steel plate
0 "(manufactured by Kansai Paint Co., Ltd., trade name, epoxy resin polyamine / block polyisocyanate compound) is electrodeposited at a dry film thickness of 20 μm and dried at 170 ° C. for 30 minutes.
After heating for a minute to cure the coating, an intermediate coating “TP-37 Primer Surfacer” (manufactured by Kansai Paint Co., trade name, polyester resin / melamine resin) is applied to the electrodeposited surface. Paint to a dry film thickness of 30 μm, 140
The coating was cured by heating at 30 ° C for 30 minutes.

The base coater (A
-1) is 7μm in dry film thickness using a mini bell type electrostatic coating machine
And then left to stand for 5 minutes, and then dried with the REA gun (manufactured by Japan Landsberg Co., electrostatic air spray) on the uncured base clear coating surface. It was coated so that the film thickness would be 7 μm. The metallic coating film was sufficiently obtained as a normal film. After further standing for 5 minutes, top clear paint (C) (“Magiclon Clear TC32F”, manufactured by Kansai Paint Co., Ltd., trade name, acrylic resin / melamine resin-based organic solvent type clear paint on the uncured metallic surface A water contact angle of 78 ° in a dry coating film of the coating material was applied using a minibell type electrostatic coating machine so that the dry film thickness was 35 μm.

This was left for 5 minutes and then heated at 140 ° C. for 30 minutes in a hot-air circulation type drying oven to simultaneously cure the above three-layer coating film to obtain a multilayer coating film.

Examples 2 to 6 and Comparative Examples 1 and 2 The same operation as in Example 1 was carried out except that the paints shown in Table 3 were used as the paints in Example 1 and the paints shown in Table 3 were used. , Each multilayer coating film was obtained.

Each multilayer coating film obtained as described above was subjected to a performance test. The results are shown in Table 3. The test method and evaluation criteria are as follows.

(* 2) Metallic whiteness: L value was measured using "CR200" colorimeter manufactured by Minolta Co., Ltd. and evaluated according to the following criteria. The larger the value, the better the whiteness (○: L value is 75 or more, Δ: 65 or more and less than 75, ×: 6
Less than 5).

(* 3) Finishing property: The metallic feeling was visually evaluated (⊚: there is no unevenness and glittering feeling, ◯: a little inferior metallic feeling, Δ: there is unevenness and inferior metallic feeling).

[0038]

EFFECTS OF THE INVENTION According to the present invention, a clear coating layer having a higher surface tension than that of the metallic coating is provided under the metallic coating by wet-on-wet, thereby improving the wetting and familiarity of the metallic coating. Since the metallic paint can be applied very thinly, the metallic pigment does not move easily, its orientation is improved, and a designed multilayer coating film having a metallic feeling excellent in whiteness of the metal can be formed.

[0039]

[Table 3]

Claims (2)

[Claims] 1. A base clear coating (A), a metallic coating (B), and a top clear coating (C) are applied sequentially in a wet-on-wet manner and then heated to apply the coating (A),
A method for simultaneously crosslinking and curing the coating films of (B) and (C), wherein the water contact angle a in the dry coating film of the coating material (A) is smaller than the water contact angle b of the dry coating film of the coating material (B). A coating film forming method characterized by being small. 2. The coating film forming method according to claim 1, wherein the thickness of the coating film of the metallic coating material (B) is 5 to 15 μm.