JP2872761B2 - Coating method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a coating film, and more particularly to a method for forming a coating film which is coated by a wet-on-wet method and simultaneously cured by heating.

[Conventional technology]

In recent years, strong demands for automotive coatings include high appearance quality and high durability.

In order to satisfy these requirements, a two-coat two-bake system in which a clear coat is applied on a base coat containing a pigment and cured at the same time is often used.

Conventionally, acrylic melamine-based thermosetting paints are often used as clear coat paints.

[Problems to be solved by the invention]

However, acrylic melamine-based paints have not yet reached a sufficient level with respect to the requirements for appearance quality, mainly gloss. In addition, resistance to acid rain is insufficient, rain spots are generated, and durability is also insufficient.

On the other hand, as disclosed in JP-A-1-139654, an acrylic resin having an acid group, a resin having an epoxy group,
Paints composed of high-grade phosphonium salts have excellent low-temperature curability,
Although the appearance quality and the durability were satisfied, the reaction proceeded during the preservation of the paint, the viscosity increased, and there was a problem in storage stability.

[Means for solving the problem]

In order to solve the above problems, the present inventors have applied a wet-on-wet coating method and a heat-cured coating film forming method.
As a result of intensive studies in view of durability and storage stability not reaching a sufficient level, a thermosetting solvent-based coating composition using an acrylic resin having an epoxy group and an acrylic resin having an acid group has a low temperature. It has been found that it has excellent curability and appearance quality, has excellent acid resistance, reduces the occurrence of rain spots due to acid rain, and has excellent storage stability by incorporating a curing catalyst into the undercoat paint. The invention has been reached.

That is, in the present invention, after applying an undercoat paint in which a curing catalyst of an epoxy group and an acid group is previously mixed, a solvent-type clear paint composed of an acrylic resin having an epoxy group and an acrylic resin having an acid group is applied to the painted surface. And a method for forming a coating film characterized by being cured by heating.

Examples of the curing catalyst for an epoxy group and an acid group used in the present invention include tertiary phosphine, phosphine oxide, quaternary phosphonium salt, tertiary amine compound, imidazole compound, imidazoline compound, Lewis acid and the like. However, it is preferable to select a catalyst that can transfer from the undercoat paint to the overcoat paint during heat curing.

Such catalysts include, for example, tertiary amines such as triethylamine and dimethylethanolamine; organic acid salts such as triethylamine or dimethylamine paratoluenesulfonic acid and dodecylbenzenesulfonic acid; and Lewis acids such as triethylphosphine and boron trifluoride. Salts.

As the undercoat paint used in the present invention, any paint that can be used in automotive coating can be used.

The undercoat paint contains a resin and a pigment that is a colorant, and useful resin compositions include, for example, acrylic-melamine-based resins,
Polyester (alkyd) -melamine type, water-soluble acryl-melamine type and acrylic polyol and polyester polyol-polyvalent isocyanate type, acrylic emulsion, acrylic lacquer and the like.

Examples of metal pigments and color pigments used in the undercoat paint include aluminum flake, copper bronze flake, and mica.

Color pigments include, for example, inorganic pigments, especially titanium dioxide, iron oxide, chromium oxide, lead chromate and carbon black, and organic pigments include phthalocyanine blue and phthalocyanine green.

Further, the undercoat paint may further use ordinary additives such as a surfactant, a flow control agent, a thixotropic agent, a microgel, an ultraviolet absorber, and a catalyst. Further, a cellulose-based resin can be blended.

Acrylic-melamine-based clear paints that are commonly used can also be used as the undercoat paint. In other words, this is the case where a curing catalyst is blended in advance with the acrylic-melamine-based clear paint, and after application, the solvent-type clear paint of the present invention is applied and cured by heating. At this time, if necessary, an undercoat paint containing a pigment, an acrylic-melamine-based clear paint and the solvent-type clear paint of the present invention may be simultaneously heated and cured.

Examples of the acrylic resin having an epoxy group and the acrylic resin having an acid group used in the present invention include JP-A-1-13996.
54.

Examples of the solvent that can be used in the solvent-type clear coating composition of the present invention include aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as toluene and xylene, and mainly aliphatic hydrocarbons. Petroleum fractions of various boiling ranges containing aromatic hydrocarbons, esters such as butyl acetate, ethylene glycol diacetate, 2-ethoxyethyl acetate, ketones such as acetone and methyl isobutyl ketone, and alcohols such as butyl alcohol. Can be

Preferably, aliphatic and aromatic hydrocarbons are
It is preferably at least 50% by weight.

In addition, solvent-based clear coating, if necessary, other components commonly used, for example, organic montmorillonite, microgel, polyamide, viscosity modifiers such as polyethylene wax,
You may mix | blend silicone, an acrylic organic polymer surface conditioner, an ultraviolet absorber, a melamine resin, a block isocyanate resin, etc.

Furthermore, a small amount of pigment is blended in the solvent type clear paint,
It may be colored to such an extent that complete concealment is not exhibited.

The obtained clear coat composition is adjusted to a predetermined viscosity by using an appropriate solvent as a dilution thinner. In that case, it is preferable to use 50% or more of the aromatic and aliphatic hydrocarbon solvents.

As a method of applying the solvent type clear paint of the present invention, the following method can be typically exemplified.

After applying an undercoat containing a curing catalyst in advance to the substrate, a flash time is allowed, and a solvent-type clear paint is applied. The flash time may be left at room temperature for 1 to 10 minutes, or a suitable heating step at about 80 ° C. may be added.

After the undercoat paint and the solvent-type clear paint are applied to the object to be coated, after a setting time of about 5 to 20 minutes is taken, the object to be coated is about 100 to 180 ° C., preferably 130 to 1
Bake at 60 ° C for about 10-60 minutes. The thickness of a general clear film is 2020 to 60μ.

The method of applying the solvent type clear paint is a normal method,
For example, brush painting, spray painting, dip painting or
Spray coating may be used, but spray coating is preferred for imparting an excellent coating film appearance. Examples of the spray coating method include an air atomization method and a bell atomization method.

According to the method of the present invention, compared with the conventional method, a thermosetting solvent-based coating composition using an acrylic resin having an epoxy group and an acrylic resin having an acid group is excellent in low-temperature curability and appearance quality, and A remarkable effect such as excellent storage stability can be obtained by blending a curing catalyst into the undercoating paint, which has excellent acid resistance, reduces generation of rain spots due to acid rain, and the like.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

In the description, “parts” and “%” are based on weight unless otherwise specified.

Preparation of Undercoat Paint Reference Example 1-1 1-1. Adjustment of Metallic Undercoat Paint 100 parts of xylol was charged into a four-necked flask equipped with a stirrer, a thermometer, and a condenser, and heated to 100 ° C and heated.

Here 10 parts of styrene, 10 parts of methyl methacrylate, 30 parts of butyl acrylate, 35 parts of isobutyl acrylate,
12 parts of 2-hydroxy methacrylate, methacrylic acid 3
Parts, 2 parts of N, N'-azobisbutyronitrile were mixed and added dropwise over 4 hours, and then kept at the same temperature for 6 hours to obtain an acrylic resin having a solid content of about 50%. Obtained.

180 parts of this acrylic resin, 37.5 Uban 20SE-60 (butylated melamine resin, Mitsui Toatsu Chemicals, 60% solids)
Part, aluminum paste 7160N (Toyo Aluminum) 16.
Eight parts were mixed with a stirrer.

The undercoat paint composition obtained above was diluted with the following mixed solvent, and the viscosity was adjusted to 13 seconds / 25 ° C. in Ford Cup # 4 to obtain a metallic undercoat paint (） -1).

Ethyl acetate 15 parts Toluene 40 parts Solvesso # 100 (manufactured by Esso) 35 parts Cellulose acetate 10 parts To 100 parts of the above metallic undercoat (III-1), 3 parts of dodecylbenzenesulfonate of triethylamine is added, and the metallic undercoat is added. (Μ-2) was obtained.

1-2 Preparation of Solid Color Undercoat A solid color undercoat (S-1) was blended as follows.

Acrylic resin for undercoating (solid content: 50%) synthesized in (1-1) 60.7 parts Titanium oxide CR-90 (manufactured by Ishihara Sangyo Co., Ltd.) 52 parts The pigment was dispersed for 1 hour using a paint shaker with the above composition.

Further, 21.7 parts of Uban 20SE-60 was added, diluted with the following mixed solvent, and the viscosity was adjusted to 13 seconds / 25 ° C. with Ford Cup # 4 to obtain a solid color undercoat.

Toluene 60 parts Solvesso # 100 (manufactured by Esso) 30 parts n-butanol 10 parts To 100 parts of the above solid color undercoat, 2 parts of dimethylethanolamine was added to obtain a solid color undercoat (S-1).

1-3. Preparation of acrylic-melamine-based clear paint In a four-necked flask equipped with a stirrer, a thermometer, and a condenser, 80 parts of Solvesso # 100 and 20 parts of n-butanol were charged and heated to 100 ° C. .

Here, 30 parts of styrene and 40 parts of n-butyl methacrylate
, 12 parts of i-butyl methacrylate, 15 parts of 2-hydroxyethyl acrylate, 3 parts of methacrylic acid, and 3 parts of azobisbutyronitrile, and the mixture was added dropwise over 4 hours. After holding for a time, an acrylic resin having a solid content of about 50% was obtained.

140 parts of this acrylic resin and 50 parts of Uban 20SE-60 were stirred and mixed with a stirrer.

The acrylic-melamine clear paint obtained above was diluted with the following mixed solvent, and the viscosity was adjusted to 30 seconds / 25 ° C. in Ford Cup # 4 to obtain an acrylic-melamine clear paint.

Solvesso # 100 (manufactured by Esso) 50 parts Solvesso # 150 (manufactured by Esso) 50 parts Triethylamine is added to 100 parts of the above acryl-melamine clear paint to obtain an acrylic-melamine clear paint (C-1). Was.

Preparation of Acrylic Resin Having Acid Group Reference Example 2 After purging nitrogen into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, Solvesso # 100 (manufactured by Esso, aromatic carbonization) was added to the flask. 85 parts of hydrogen, boiling point 150 to 177 ° C) and 15 parts of n-butanol
The temperature was raised to ℃.

Here, 5 parts of styrene, 5 parts of methyl methacrylate, n
A raw material comprising 35 parts of -butyl methacrylate, 25 parts of i-butyl methacrylate, 20 parts of 2-ethylhexyl acrylate, 10 parts of acrylic acid, and 3 parts of N, N'-azobisbutyronitrile was added dropwise over 5 hours. And then 100
The mixture was kept at 6 ° C. for 6 hours to obtain an acrylic resin having an acid group with a solid content of about 50%.

Preparation of Acrylic Resin Having Epoxy Group Reference Example 3 After purging with nitrogen into the same reactor as used in Reference Example 2, 150 Solvesso # 100 (manufactured by Esso, aromatic hydrocarbon, boiling point 150-177 ° C.) was added to the flask. And heated to 140 ° C.

Here, 25 parts of styrene, n-butyl methacrylate 5
, 23 parts of 2-ethylhexyl acrylate, 47 parts of glycidyl methacrylate, and 4 parts of N, N'-azobisbutyronitrile were added dropwise over 5 hours, and thereafter, the mixture was kept at 100 ° C for 6 hours. Later, Solvesso # 100 50
The mixture was heated under reduced pressure (~ 30 mmg) and evaporated to remove solids.
% Acrylic resin having an epoxy group was obtained.

REFERENCE EXAMPLE 4 72 parts of the acrylic resin having an acid group of Reference Example 2 and 30 parts of the acrylic resin having an epoxy group of Reference Example 3 were blended, and 0.2% by weight of Resixmix RL-4 based on the resin solid content.
(Leveling agent, manufactured by Mitsui Toatsu Chemicals, Inc.) and stirred with a stirrer. Solvesso # 100 50 parts, Solvesso # 150 50
Diluted with a mixed solvent consisting of Ford C
The viscosity was adjusted to 30 seconds / 25 ° C. in up # 4 to obtain a solvent type clear coating material (A-1).

To 100 parts of the solvent-type clear coating material (A-1), 3 parts of triethylamine was added, and the solvent-type clear coating material (A-
2) was obtained.

Example 1 The metallic undercoat (Μ-2) prepared in (1-1) of Reference Example 1 was applied to a copper plate for an automobile body by applying a cationic electrodeposition paint, and then applied to a baked article by air spray.
Minutes after setting, the solvent-based clear paint (A-
1) was wet-on-wet painted by air spray, set for 10 minutes, and then heated at 140 ° C. for 20 minutes to obtain a test plate.

Table 1 shows the film thickness of the clear film and the coating film performance.

Example 2 The same method as in Example 1 except that the metallic undercoat (Μ-2) of Example 1 was changed to the solid color undercoat (S-1) adjusted in (1-2) of Reference Example 1. A test plate was obtained.

Table 1 shows the film thickness of the clear film and the coating film performance.

Example 3 The metallic undercoat (塗 り -1) prepared in (1-1) of Reference Example 1 was applied to a copper plate for an automobile body by applying a cationic electrodeposition paint, and then applied to a baked article by air spraying. After setting for 3 minutes, the acrylic-melamine clear paint (C-1) prepared in (1-3) of Reference Example 1 was wet-on-wet painted by air spray to obtain 1
After setting for 1 minute, solvent type clear paint (A-1)
Was painted by air spray. After setting for 10 minutes, the plate was heated at 140 ° C. for 20 minutes to obtain a test plate.

Table 1 shows the film thickness of the clear film and the coating film performance.

Example 4 A test plate was obtained in the same manner as in Example 1 except that heating at 140 ° C. for 20 minutes in Example 1 was changed to heating at 120 ° C. for 8 minutes.

Table 1 shows the film thickness of the clear film and the coating film performance.

Comparative Example 1 A test plate was obtained in the same manner as in Example 1, except that the metallic undercoat (Μ-2) in Example 1 was changed to the metallic undercoat (Μ-1).

Table 1 shows the film thickness of the clear film and the coating film performance.

Comparative Example 2 The metallic undercoat (Μ-2) of Example 1 was changed to the metallic undercoat (Μ-1), and the solvent-based clear coating (A-1) was changed to the solvent-based clear coating (A-2). Except for the above, a test plate was obtained in the same manner as in Example 1.

Table 1 shows the film thickness of the clear film and the coating film performance.

Comparative Example 3 A test plate was obtained in the same manner as in Comparative Example 1, except that heating at 140 ° C. for 20 minutes in Comparative Example 1 was changed to heating at 120 ° C. for 8 minutes.

Table 1 shows the film thickness of the clear film and the coating film performance.

 The performance evaluation was performed as follows.

Visual appearance The film having excellent coating film appearance was rated as ◎.

Acid-resistant 40 vol% H ₂ SO ₄ was dropped onto the coating film, left at 50 ° C. for 5 hours, and observed by wiping. Those having no trace were evaluated with ◎.

Solvent resistance The coating film surface was rubbed 50 times with gauze impregnated with xylol and then observed.

◎ with no trace at all, ○ with a little trace at ○,
Those with traces were evaluated with x.

Water resistance The coating film was immersed in warm water of 50 ° C. for 48 hours, and the coating film was observed.

No abnormality was evaluated as 異常, slight whitening was evaluated as 、, and whitening and blistering were evaluated as x.

Weather Resistance After 3000 hours of testing with a sunshine weather meter, the gloss retention was indicated.

Storage stability The solvent-type clear paint was stored at 40 ° C. for 7 days, and the change in viscosity was observed.

も の indicates a slight increase in viscosity, and X indicates a marked increase in viscosity.

[Effects of the Invention] According to the method of the present invention, as apparent from Table 1,
It exhibited excellent performance as an automotive paint, and was particularly excellent in low-temperature curability and storage stability.

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁶ identification code FI C09D 163/00 C09D 163/00 (58) Field surveyed (Int.Cl. ⁶ , DB name) B05D 1/02-1/38 B05D 7/24 302 B05D 7/14 C09D 133/14 C09D 163/00

Claims (1)

(57) [Claims] An undercoating composition containing a curing catalyst of an epoxy group and an acid group is applied in advance, and a solvent-type clear coating made of an acrylic resin having an epoxy group and an acrylic resin having an acid group is applied to the coated surface. A method for forming a coating film, which is followed by heat curing.