JPH07265784A - Coat finishing method - Google Patents

Abstract

PURPOSE:To improve the mutual bonding properties by using a thermosetting resin containing styrene, a hydroxyl group-containing acrylic copolymer and melamine as a first clear coat, and a thermosetting resin containing no melamine resin as a second clear coat respectively. CONSTITUTION:First, a thermosetting colored base coating is applied to a material and dried thereon. Then a first thermosetting clear coat is applied, baked and cured together with the base coat. Successively a second thermosetting clear coat is applied, baked and cured. In that case, a thermosetting coating material, containing styrene at 40-60wt.%, a hydroxyl group-containing acryl copolymer prepared by blending a hydroxyl group-containing monomer represented by a general formula shown separately in a manner of setting the hydroxyl value of the copolymer to be 110-160, and melamine resin, is used as a first clear coat. On the other hand, a thermosetting resin material in which melamine resin as a crosslinking agent is not used is used as a second clear coat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel coating finishing method, and more particularly to a coating finishing method using a 3 coat 2 bake system which is particularly excellent in acid rain resistance and finished appearance.

[0002]

2. Description of the Related Art Conventionally, as a paint finishing method for automobile bodies, after coating a colored base coat, a clear coat containing no pigment is applied by wet-on-wetting, and the base coat and the clear coat are baked and cured at the same time. The coat 1 bake (2C1B) coating method is widely practiced. Also, in order to obtain an excellent paint finish appearance, 3C2Bake (3C2Bake) in which 2C1B is applied and then a second clear coat is applied and baked.
A coating finishing method based on the method B) has been proposed (JP-A-1-139179).

In the method disclosed in the above publication, both the clear coat used in 2C1B coating and the second clear coat coated are composed of hydroxyl group-containing acrylic resin and melamine resin.

[0004] On the other hand, in addition to the demand for an excellent finished appearance of automobile bodies and the like, in recent years, with the spread of stains and etching damages on automobile coating films due to acid rain, the development of a top coat paint having excellent acid resistance. Has come to be required. The clear coat used in the 2C1B paint finishing method for top coating of automobile bodies etc. is made of acrylic resin / melamine resin, but it became clear that the melamine resin causes the acid resistance of the coating film to decrease, and melamine A novel resin-free cross-linking method having good storage stability and excellent acid resistance has been proposed (JP-A-63-221).
123, JP-A-63-108048, JP-A-63-108049).

However, these paints have the problems that they are more expensive than the melamine thermosetting paints and that they are inferior in adhesion to the melamine thermosetting paints.

When the 2C1B coating method is used in combination with an acrylic / melamine resin base coat,
It seems that the difference in the cross-linking method is the cause, but in many cases it is difficult to obtain a paint finish with a good appearance because a mixed layer occurs at the interface between the base coat and the clear coat.

3C to obtain an excellent paint finish
In order to obtain the 2B coating finishing method and excellent acid resistance, use of a non-melamine type thermosetting coating is considered. In addition, from the viewpoint of cost, acrylic / melamine resin-based paint that is widely used at present is used for the base coat, cheap acrylic / melamine resin-based paint is used for the first clear coat of 3C2B, and second clear coat of 3C2B is used for the second clear coat. It is possible to use a non-melamine resin type thermosetting clear coat, but in this case, there was a problem that the adhesion between the first clear coat and the second clear coat was poor.

[0008]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to solve the above-mentioned problems, as a result of using the first clear coat having a specific composition, the first clear coat and the non-melamine The present inventors have found that the adhesion to the thermosetting second clear coat is remarkably improved, and have completed the present invention.

That is, in the present invention, a thermosetting colored base coat is applied to a material, and the base coat is air-dried or forcedly dried, and then the thermosetting clear coat (first clear coat).
In the coating method of 3 coat 2 bake (3C2B), which is obtained by coating with a base coat, followed by baking and curing with a base coat, followed by coating with a thermosetting clear coat (second clear coat) and baking and curing, as the first clear coat. , 40-60 wt% styrene and general formula

[0010]

[Chemical 2]

(In the formula, R'represents a hydrogen atom or a methyl group, R is a divalent organic group having 4 or more carbon atoms, and may further contain an oxygen atom). Hydroxyl group-containing monomer having a hydroxyl value of 110 to 16
A hydroxyl group-containing acrylic copolymer obtained by blending in an amount of 0,
And a thermosetting paint containing a melamine resin, and a thermosetting paint which does not use a melamine resin as a cross-linking agent as the second clear coat.

Next, the method of the present invention will be described in detail.

Colored Base Coat As the base coat, any known base coat can be used without particular limitation. For example, the same base coat as that used in the 2 coat 1 bake and 3 coat 2 bake paint finishing methods can be used. it can.

Typical examples of colored base coats include thermosetting paints containing a hydroxyl group-containing resin (acrylic resin, polyester resin, etc.), melamine resin, flake pigments (metal flakes, mica, etc.) and color pigments.

As the base coat, an organic solvent type paint or an aqueous paint using an organic solvent or water as a dispersion medium can be used.

First Clear Coat The first clear coat comprises a hydroxyl group-containing acrylic copolymer having the above specific composition, a melamine resin, an organic solvent, and optionally a curing catalyst. The acrylic copolymer has a styrene content of 40 to 60% by weight, a hydroxyl value of 110 to 160, and a hydroxyl group-containing monomer to be copolymerized to impart such a hydroxyl value.

[0017]

[Chemical 3]

(In the formula, R'and R are the same as defined above). When the styrene content in the acrylic copolymer is lower than 40% by weight, the adhesion to the second clear coat of the present invention is lowered, and when it exceeds 60% by weight, the flexibility of the coating film is lowered too much for practical use. Cause a problem. If the hydroxyl value is less than 110, the adhesion to the second clear coat of the present invention is not sufficient, and if it exceeds 160, the polarity of the copolymer becomes too high, and therefore the compatibility with the melamine resin used as a crosslinking agent is high. This causes problems such as deterioration of the finished appearance and deterioration of water resistance. Also,
As the hydroxyl group-containing monomer, a monomer having 3 or less carbon atoms,
For example, when hydroxyethyl (meth) acrylate or hydroxypropyl (meth) acrylate is used, the adhesion to the second clear coat of the present invention is insufficient. The mechanism by which the above-mentioned hydroxyl group-containing monomer, which is a raw material of the acrylic copolymer used in the present invention, improves the adhesion is not known in detail, but the hydroxyl group of the monomer is located away from the acrylic copolymer main chain, Since it can move freely, it seems to contribute to the improvement of adhesion.

Examples of the divalent organic group represented by R include, for example,

[0020]

[Chemical 4]

And the like.

Specific examples of the hydroxyl group-containing monomer include 4-hydroxybutyl (meth) acrylate and 2-hydroxybutyl (meth) acrylate.
Addition product of 1 mol of hydroxyethyl (meth) acrylate and 1 to 10 mol of ε-caprolactone, addition product of 2-hydroxyethyl (meth) acrylate and γ- (methyl) -valerolactone, methyl (meth) acrylate and poly There are reaction products with alkylene glycol.

As the monomer used in the acrylic copolymer for the first clear coat, in addition to styrene and the above hydroxyl group-containing monomer, for example, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, methacrylic acid are used. Alkyl or cycloalkyl esters of methacrylic acid such as 2-ethylhexyl, cyclohexyl methacrylate, lauryl methacrylate, stearyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate,
Alkyl or cycloalkyl esters of acrylic acid such as 2-ethylhexyl acrylate and cyclohexyl acrylate, α, β-ethylenically unsaturated acids such as acrylic acid and methacrylic acid, n-butoxymethylacrylamide, N
-Methylolacrylamide, acrylamides such as acrylamide, n-butoxymethylmethacrylamide,
Methacrylamides such as N-methylolmethacrylamide and methacrylamide are used.

The molecular weight of the acrylic copolymer is preferably in the range of about 4,000 to 20,000 in terms of weight average molecular weight, from the viewpoint of the balance between the finished appearance of coating and weather resistance.

For the production of the acrylic copolymer, a conventional method for producing an acrylic resin for paint can be applied as it is. That is, it is produced by solution polymerization or dispersion polymerization in an organic solvent at about 50 to 150 ° C. using a peroxide-based or azo-based polymerization catalyst.

As the melamine resin used in the first clear coat of the present invention, a usual melamine resin for paint can be used as it is. That is, melamine, formaldehyde, a monoalcohol having 1 to 4 carbon atoms, and optionally a melamine resin having a condensation degree of about 1.1 to 20 using water as a raw material can be used.

The mixing ratio of the acrylic copolymer and the melamine resin in the first clear coat is 60/40 to 90 /.
About 10 (parts by weight) is preferable. If necessary, an acid catalyst such as a phosphoric acid alkyl ester, p-toluene sulfonic acid, dodecylbenzene sulfonic acid, trichloroacetic acid or the like can be added to the first clear coat as a curing catalyst.

Second Clear Coat As the second clear coat, a thermosetting paint which does not contain a melamine resin or only supplementarily contains a melamine resin can be used. Examples of such a clear coat include the following.

(1) A thermosetting clear paint comprising a resin containing a hydrolyzable group directly bonded to a silanol group and / or a silicon atom, a hydroxyl group and an epoxy group, a curing catalyst and an organic solvent.

(2) A thermosetting clear paint comprising a compound and / or resin containing a carboxyl group and / or an acid anhydride group, a compound and / or resin containing an epoxy group, a curing catalyst and an organic solvent.

(3) A thermosetting clear paint comprising a resin containing a silanol group and / or a hydrolyzable group directly bonded to a silicon atom and optionally a hydroxyl group, a curing catalyst and an organic solvent.

(4) A thermosetting clear paint comprising a compound and / or resin having a blocked isocyanate group, a hydroxyl group-containing resin, a curing catalyst and an organic solvent.

A first clear coat used in the method of the present invention,
An ultraviolet absorber, a light stabilizer, an antioxidant, a fluidity adjusting agent, an anti-sagging agent, a coating surface adjusting agent and the like can be added to the second clear coat and the base coat, if necessary.

In the method of the present invention, for example, a chemical conversion treated steel plate or the like is coated with an electrodeposition paint, an intermediate coating paint (which may be omitted) and a primer suitable for various plastic materials are applied. Using a coating film coated with a coating composition (which may be omitted) as a material, a colored base coat coating composition is coated, then a first clear coat is coated, and once baked and cured, a second clear coat is coated. It is carried out by baking and curing.

The above-mentioned electrodeposition coating composition and intermediate coating composition are usually baked at about 140 to 190 ° C. for about 30 to 90 minutes, depending on the type of coating composition. The pigmented base coat, the first clear coat and the second clear coat coating composition can be coated by a conventional coating method such as electrostatic coating or non-electrostatic coating machine. The thickness of the colored base coat is preferably about 10 to 50 μm (after curing). After applying the paint, leave it at room temperature for several minutes or at 50 to 80 ° C.
After forced drying for several minutes, the first and second clear coat coating compositions are applied. The thickness of the clear coating is 20-
100 μm (after curing) is preferable.

The baking of the base coat and the first clear coat and the baking of the second clear coat are 110 to 110, respectively.
The heating is performed at about 180 ° C. for about 20 to 90 minutes.

[0037]

ACTION AND EFFECTS OF THE INVENTION The details of the reason why the adhesion between the first clear coat and the second clear coat is improved in the present invention are not clear, but the styrene content in the acrylic copolymer of the first clear coat is unknown. A polar effect due to the benzene ring, and a hydroxyl group that is located far from the acrylic copolymer main skeleton and has high reactivity due to less steric hindrance,
It is presumed to be due to the interaction with the first clear coat.

According to the method of the present invention, it is possible to finish the coating finish of an automobile body or the like, which has an extremely excellent coating finish appearance, is extremely excellent in acid resistance (acid rain resistance), and is inexpensive.

[0039]

EXAMPLES The present invention will be described more specifically below with reference to production examples, examples and comparative examples. “Part” and “%” in each example
Means "parts by weight" and "% by weight", respectively.

Production Example 1 Production of Acrylic Resin Solution for Colored Base Coat 10 parts of styrene and 40 parts of methyl methacrylate in an organic solvent consisting of 50 parts of xylene and 10 parts of n-butanol.
Parts, 15 parts of ethyl acrylate, 15 parts of n-butyl acrylate, 18 parts of 2-hydroxyethyl acrylate and 2 parts of acrylic acid are polymerized with α-, α′-azobisisobutyronitrile as a polymerization catalyst, and after completion of the reaction, xylene It was diluted with 30 parts and 10 parts of n-butanol to obtain a hydroxyl group-containing acrylic resin solution A-1 having a weight average molecular weight of 42,000, a resin solid content of 50%, and a Gardner foam viscosity X.

Production Example 2 Production of First Clear Coat Resin (1) Production of Acrylic Resin (Copolymer) Solution B-1 Swazol 1000 (Cosmo Oil Co., Ltd. Petroleum Aromatic Solvent) 50 parts, n 45 parts of styrene, 13 parts of n-butyl methacrylate in 15 parts of butanol in an organic solvent
Parts, 4-hydroxybutyl acrylate 30 parts, Praxel FA2 (note 1) 10 parts and acrylic acid 2 parts were polymerized at 132 ° C. with 4.5 parts of t-butyl peroctoate, and after the reaction was completed Swazol 1000 30 parts And n-
Dilute with 5 parts butanol to give a weight average molecular weight of 1420.
Acrylic resin solution B-1 having 0, a hydroxyl value of 145, a resin solid content of 50%, and a Gardner foam viscosity K was obtained.

(2) Acrylic resin (copolymer) solution B-
2. Production of B-3, B-4 B-2 by the same method as the production of the acrylic resin solution B-1
B-3 and B-4 were manufactured. Table 1 shows the monomer composition, weight average molecular weight, and solid content concentration of each acrylic resin solution.

[0043]

[Table 1]

(Note 1) Praxel FA2: an adduct of 1 mol of 2-hydroxyethyl acrylate and 2 mol of ε-caprolactone, a product of Daicel Corporation.

(Note 2) Praxel FM3: 1 mol of 2-hydroxyethyl methacrylate and ε-caprolactone 3
Mole adduct, a product of Daicel Corporation.

Production Example 3 Production of resin for second clear coat (1) Production of acrylic resin solution C-1 γ-methacryloxypropyltrimethoxysilane 10 parts styrene 15 parts 3,4-epoxycyclohexylmethyl methacrylate 30 parts cyclohexyl methacrylate 20 parts t-butyl methacrylate 15 parts 4-hydroxybutyl acrylate 10 parts α, α′-azobisisobutyronitrile 4 parts The mixture is polymerized at 120 ° C. in a mixed solvent of xylene / n-butanol = 70/30. Conducting resin solids 50
%, Acrylic resin solution C-with a weight average molecular weight of 18,000
Got 1.

(2) Production of Acrylic Resin Solution C-2 A mixture of styrene 30 parts glycidyl methacrylate 30 parts n-butyl methacrylate 30 parts 2-hydroxyethyl acrylate 10 parts α, α′-azobisisobutyronitrile 4 parts was added. Polymerize in xylene at 130 ℃,
An acrylic resin solution C-2 having a resin solid content of 50.3% and a weight average molecular weight of 9,500 was obtained.

(3) Production of Polyester Resin Solution C-3: 134 parts of trimethylolpropane and 462 parts of hexahydrophthalic anhydride were mixed, a condensation reaction was carried out at 220 ° C., the reaction was terminated at an acid value of 250, and xylol / n- It was diluted with a mixed solvent of butanol = 3/7 to obtain a polyester resin solution C-3 having a resin solid content concentration of 60%.

(4) Production of acrylic resin solution C-4 Styrene 30 parts n-Butyl methacrylate 29 parts 2-Ethylhexyl methacrylate 15 parts 2-Hydroxyethyl acrylate 15 parts 4-Hydroxybutyl acrylate 10 parts Acrylic acid 1 part α, α A mixture of 3 parts of'-azobisisobutyronitrile was added to Swazol 1000 / n-butanol = 80.
Polymerization reaction was carried out in a mixed solvent of / 20 at 125 ° C. to obtain an acrylic resin solution C-4 having a resin solid content of 50.1% and a weight average molecular weight of 16200.

(5) Blocked polyisocyanate C-5
Manufacturing of Sumidur N (polyisocyanate manufactured by Sumitomo Bayer Urethane Co., solid content concentration 75%, NCO 16% contained) 10
0 parts and 35 parts of methyl ethyl ketoxime were mixed to produce a blocked polyisocyanate (NCO content 1
2.5%).

Production Example 4 Production of Colored Base Coat a-1 160 Parts of Acrylic Resin Solution A-1, Uban 28SE
(Note 3) 33 parts were mixed, then 20 parts of aluminum paste was added and stirred, and the viscosity of the paint was adjusted to 15 ″ (Ford cup No. 4/20 ° C.) with a mixed solvent of Swasol 1000 / toluene = 1/1. Colored base coat a-1 was obtained.

(Note 3) U-Van 28SE: manufactured by Mitsui Toatsu Chemicals, Inc., butylated melamine resin, resin solid content concentration 60
%.

Production Example 5 Production of first clear coating composition b-1 for clear coat Acrylic resin solution B-1 140 parts, U-Van 20SE
(Note 4) 50 parts were mixed, and it was mixed with Swazol 1000 /
The paint viscosity was adjusted to 25 seconds (Ford cup No. 4/20 ° C.) with a thinner of n-butanol = 9/1 to obtain a clear paint b-1.

(Note 4) U-Van 20SE: Mitsui Toatsu Chemical Co., Ltd., butylated melamine resin, resin solid content concentration 60
%.

Production Example 6 Production of first clear coating composition for clear coat b-2 to b-4 Acrylic resin solution B-1 was replaced with acrylic resin solution B-2, respectively.
~ B-4 except that the first example in the same manner as in Production Example 5
Clear paints b-2 to b-4 for clear coat were manufactured.

Production Example 7 Production of clear coating material c-1 for second clear coat 180 parts of acrylic resin solution C-1 and 10 parts of diphenyldimethoxysilane were mixed with 1 part of tris (acetylacetonato) aluminum, and subsequently squelzeol 1000 was added. The viscosity of the paint was adjusted to 22 seconds (Ford cup No. 4/20 ° C.) to obtain clear paint c-1.

Production Example 8 Production of second clear coat clear coating c-2 140 parts acrylic resin solution C-2, 50 parts polyester resin solution C-3, 0.5 parts tetrabutylammonium bromide, 3 parts methanol were mixed. And then Swazol 1
The paint viscosity was adjusted to 22 seconds (Ford cup No. 4/20 ° C.) with a mixed solvent of 000 / n-butanol = 7/3 to obtain a clear paint c-2.

Production Example 9 Production of second clear coating composition for clear coat c-3 140 parts of acrylic resin solution C-4, 30 parts of blocked polyisocyanate and 1 part of dibutyltin dilaurate were mixed, and Swazol 1000 / n-butanol = 9. Paint viscosity of 22 seconds with 1/1 thinner (Ford Cup No. 4/2
The temperature was adjusted to 0 ° C.) to obtain clear paint c-3.

Production Example 10 Production of Material A dull steel sheet (chemical conversion treatment) was coated with an epoxy resin-based cationic electrodeposition coating (25 μm) and heat-cured at 170 ° C. for 30 minutes, followed by an intermediate coating Lugabak AM (trademark, Kansai Paint Co., Ltd. product of polyester resin / melamine resin for automobiles) was applied to a dry film thickness of 30 μm and baked at 140 ° C. for 30 minutes. Then # 40
0 The coated surface was water-polished with sandpaper, drained and dried, and the coated surface was wiped with petroleum benzine.

Examples 1 to 6 and Comparative Examples 1 to 6 Coating by the 3C2B method was performed using the colored base coat paint, the first clear coat clear paint and the second clear coat clear paint obtained in each production example. It was

After the coating of the colored base coat by air spray coating, the material was left for 3 minutes and then immediately applied with the clear coating for the first clear coat. The film thickness was 15 to 20 μm and 35 to 45 μm, respectively, as a dry film thickness. Then, it was left at room temperature for 10 minutes and baked at the temperature shown in Table 2 for 30 minutes. Then, the second clear coating material for clear coat was air-spray coated so as to have a dry film thickness of 35 to 45 μm, allowed to stand at room temperature for 10 minutes, and then baked at the temperature shown in Table 2 for 30 minutes to obtain a test coated plate.

Next, the appearance (gloss, smoothness, etc.) of the test coated plate obtained above was examined, and the coating film performance was examined by the following test method.

Water resistance: The test coated plate was immersed in warm water at 40 ° C. for 24 hours.
After soaking for 0 hour, the state of the coated surface was observed and evaluated according to the following criteria.

⊚ indicates that there is no abnormality, Δ indicates that there is a little blistering or stinging, and x indicates that there is a blistering or stinging, respectively.

Adhesion: 1 with a cutter knife on the surface of the coated plate
Make 11 vertical and 11 horizontal wefts at 100 mm intervals (100 squares are engraved), then attach cellophane tape to the surface and peel it off abruptly. The first clear coat and the second
The degree of peeling between clear coats was evaluated according to the following criteria.

◎ indicates that the number of peeled squares in 100 squares is 0, and △ indicates that the number of peeled squares in 100 squares is 1 to 50, X is 1
The number of peeled cells out of 00 cells is 51 to 99
XX indicates that the number of peeled squares is 100 out of 100 squares.

The baking temperature of the colored base coat / first clear coat was 160 ° C. The reason why the overbaking 160 ° C. baking was the first clear coat and the second clear coat was higher than the standard condition of 140 ° C. baking. This is because the adhesive force becomes lower and the detectability becomes higher as a test of the adhesiveness.

Solvent resistance: After being immersed in Nisseki Silver Gasoline (manufactured by Nippon Oil Co., Ltd., trade name) for 1 day, the state of the coating film was visually inspected and evaluated according to the following criteria.

⊚ indicates that there is no abnormality, ◯ indicates that slight streaking occurs, Δ indicates that streaking occurs, and × indicates that streaking occurs remarkably.

The test results are also shown in Table 2.

[0071]

[Table 2]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Igarashi 4-17-1, Higashihachiman, Hiratsuka City, Kanagawa Kansai Paint Co., Ltd. Chi Kansai Paint Co., Ltd. (72) Inventor Yutaka Mizutani No. 1 flat land in Kanayo, Miyoshi-cho, Nishikamo-gun, Aichi Kansai Paint Co., Ltd.

Claims (1)

[Claims] 1. A material is coated with a thermosetting colored base coat, the base coat is air-dried or forced dried, and then a thermosetting clear coat (first clear coat) is applied, followed by baking and curing with the base coat, and subsequently, Apply a thermosetting clear coat (second clear coat),
3 coat 2 bake (3C2B) after baking and curing
In the coating method, 40-60 styrene is used as the first clear coat.
% By weight and general formula (In the formula, R'represents a hydrogen atom or a methyl group, R is a divalent organic group having 4 or more carbon atoms, and may further contain an ether bond or an ester bond.). The hydroxyl value of the copolymer is 110 to 110.
A thermosetting paint containing a hydroxyl group-containing acrylic copolymer obtained by blending in an amount of 160 and a melamine resin is used, and the second clear coat is a thermosetting resin which does not use a melamine resin as a crosslinking agent. A paint finishing method characterized by using paint.