JPH02245268A - Method for finish coating - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the finished appearance by applying a thermosetting paint contg. pigment of a surface to be coated, applying a topcoat clear paint contg. specified amts. of specified monomer and a cross- linking agent, heating and curing the paints. CONSTITUTION:From 20 to 90wt.% of the 4-24C monohydric alcohol ester of (meth)acrylic acid 5-50wt.% 4-butanediol (meta)acrylate monomer, 0-45wt.% of the <=3C dihydric alcohol ester of (meth)acrylic acid and 0-70wt.% of vinyl monomer are previously copolymerized to prepare an overcoat clear paint contg. acryl polyol having 3000-30,000 weight average mol.wt. and a cross-linking agent. The overcoat clear paint is applied on the pigment-contg. thermosetting paint layer formed on the surface to be coated, and then both paint layers are simultanoeusly heated and cured.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides an excellent painted finish appearance and improves the adhesion between the base coat and top clear coat after curing, and the adhesion between the layers during recoating. This invention relates to an excellent so-called two-coat-one-bake (2CIB) painting finishing method.

(Prior art and its problems) The so-called 2CIB painting method, in which a base coat containing blood marks is applied to the surface to be painted, then a top clear coat is applied, and both coatings are simultaneously heated and cured, is used in the painting equipment for automotive metallic paints. It is widely used mainly for painting. 2C
The important requirements for painting using the IB method are: ■ No or minimal mixing of layers between the base coat and top clear coat, ■ Excellent recoat adhesion, and ■ Good bonding between the base coat and top clear coat. Three points are mentioned: excellent interlayer adhesion.

Looking at the three points above, firstly, if there is a lot of mixing between the base coat and top coat, the pigment in the base coat, especially if it contains metallic powder, will move, resulting in an excellent painted finish appearance. I won't be able to do it.

Next, ■On the painting line, painting using the 2CIB method,
After baking, it is often necessary to apply two CIBs of the same base coat and top clear coat to repair paint defects such as dust, smudges, smudges, and glossy pixel marks. In this case, the first top clear coat and the second one for repair.
Adhesion with the second base coat (recoat adhesion)
It is necessary to be good.

In addition, it is necessary that the interlayer adhesion between the base coat film and the top clear coat film be excellent, and the base coat film must contain certain pigments, especially dark pigments such as red pigments such as perylene pigments and blue pigments. Adhesion between the wet-on-wet base coat and the top clear coat is often a problem.

Until now, acrylic polyol/amino aldehyde resin systems and acrylic polyol/polyisocyanate systems have been used because of their excellent weather resistance in the 2CIB coating system, base coat, and top clear coat. It is difficult to satisfy all of the following items at the same time. For example, if the hydroxyl value of the acrylic polyol used for the top clear coat is increased to improve recoat adhesion, a mixed layer between the base coat and top clear coat is likely to occur. There were problems such as a tendency for the finished appearance to deteriorate.

(Means for solving the problem) The present inventors applied the 2CIB coating method using a top clear coat using acrylic polyol as a base resin.
As a result of extensive research to satisfy all of the above items, we found that 1,4-butanediol monoacrylate and 1゜4-pukundiol monomethacrylate were used as the hydroxyl group source for the acrylic polyol for the top clear coat. As a result, they discovered that there is a 2CIB coating method that satisfies the above objectives and completed the present invention.

That is, the present invention applies a thermosetting paint containing a pigment (base coat) to the surface to be coated, and then overcoats a clear top coat (top clear coat) to form a two-layer uncured paint film. In a two-coat l-bake finishing method in which the clear paint is heated and cured at the same time, the clear paint is (A) (at m alcohols having 4 to 24 carbon atoms, (
20-90% by weight of meth)acrylic acid ester monomer, 5-50% by weight of (bl), 4-butanediol mono(meth)acrylate monomer.

(c) Mono (meth) of dihydric alcohol having 3 or less carbon atoms
0 to 45% by weight of an acrylic acid ester monomer and 0 to 70% by weight of a copolymerizable monomer other than fd) monomer (aJ, (b), and (c)), and (bl monomer and (C ) A weight average molecular weight of 3000 to 3 with a total weight of 10 to 50% with monomers.
0000 acrylic polyol and (B) a crosslinking agent as main components.

The painting finishing method of the present invention will be specifically explained below.

The surface to be coated in the present invention is not particularly limited to metal materials, plastic materials, wood, etc. Specific examples of metal materials include iron, copper, aluminum, zinc, or alloys thereof, and surface treatments thereof. Board (iron phosphate treatment,
Examples include zinc phosphate treatment, chromate treatment, etc.

Specifically, the plastic materials include polyurethane,
Examples include polypropylene and polycarbonate. In addition, primer coating, electrical! Surfaces that have been painted, etc., and surfaces that have been further coated with intermediate coatings can also be used as surfaces to be coated.

In the present invention, the thermosetting paint containing pigment, which is the first layer of a two-coat one-bake finish, has, for example, finished appearance (sharpness, smoothness, gloss, etc.), weather resistance (glossy retention, color retention, etc.). Known paints for plastics or metals that can form coatings with excellent chemical resistance, water resistance, moisture resistance, hardening properties, etc.) can be used. Specifically, acrylic paints can be used. Examples include paints containing resins, alkyd resins, polyester resins, etc. as vehicle main components and crosslinking agents that crosslink with these vehicle main components. Of these,
Acrylic/aminoaldehyde-based paints, acrylic/polyisocyanate-based paints, and the like are suitable. The forms of these thermosetting paints are organic solution type, non-aqueous dispersion type, aqueous solution type,
Although any aqueous dispersion type can be used, organic solution type and non-aqueous dispersion type are more preferable.

Examples of pigments to be contained in the paint include aluminum powder, mica powder, titanium dioxide-coated mica, iron oxide-coated mica, flaky iron oxide, stainless steel powder, organic colored pigments, and inorganic colored pigments.

The above thermosetting paint is preferably applied by spray painting, electrostatic painting, etc., and the coating film thickness is 10~
A range of 30μ is preferred.

Therefore, after semi-curing, that is, while the coating film is not yet cured (including semi-cured), the top clear paint is applied.

The clear top coating in the present invention contains the TAI acrylic polyol and the fBl crosslinking agent as main components.

(The Al component is an acrylic polyol obtained by copolymerizing the above (a), (b) and optionally (C), (dl monomer), and (a) a monohydric alcohol with 4 to 24 carbon atoms. , (meth)acrylic acid ester monomers include, for example, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, n- Octyl (meth)acrylate, lauryl (meth)acrylate, )・
Examples include lysosyl (meth)acrylate and stearyl (meth)acrylate.

(Examples of the bl monomer include 1.4-butanediol monoacrylate and 1.4-butanediol monomethacrylate.

(C) Mono (meth) of dihydric alcohol having 3 or less carbon atoms
Examples of acrylic acid ester monomers include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, and 2-hydroxyethyl acrylate.
-Hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, and the like.

fd) Monomer fat, (bl, (as copolymerizable vinyl monomers other than cl), for example, styrene, vinyltoluene, p-chlorostyrene, pt-butylstyrene, α-methylstyrene, methyl (meth)acrylate, Ethyl (meth)acrylate, propyl (meth)acrylate, (meth)acrylonitrile, (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N-methylolacrylamide, glycidyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, Diethylaminoethyl (meth)acrylate, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid (anhydride), fumaric acid, adduct of phthalic anhydride and 2-hydroxyethyl (meth)acrylate, succinic anhydride and Examples include an adduct of 2-hydroxyethyl (meth)acrylate, an adduct of ε-caprolactone and 2-hydroxyethyl (meth)acrylate, and the like.

(In the Al component, (a), (b), (c), (d
+The blending ratio of each monomer is (a), fb), (C1
, (d) fa) monomers 220 to 90% by weight, preferably 25 to 90% by weight, based on the total amount of monomers
85% by weight, fbl monomer: 5-50% by weight, preferably 10-4
0% by weight, (20-45% by weight of cl monomer, preferably 5-35% by weight)
% by weight, (di-7 sonomer 0-70% by weight, preferably 0-60
% by weight, and the total of (bl monomer and (cl monomer) must be in the range of 10 to 50% by weight.

If the amount of FAL is less than 20% by weight, the finished appearance of the paint and the weather resistance of the coating film will deteriorate, while if it exceeds 9.0% by weight, the amount of hydroxyl groups necessary for crosslinking will be insufficient and the curability will be poor. In addition, if the (bl monomer content is less than 5% by weight, the finished appearance of the paint will deteriorate, while if it exceeds 50% by weight, the interlayer adhesion between the base coat film and the top clear coat film and water resistance will deteriorate. If the total amount of BL monomer and ICL monomer is less than 10% by weight, the amount of hydroxyl groups necessary for crosslinking will be insufficient, resulting in poor curability, while if it exceeds 50% by weight, interlayer adhesion between the base coat film and the top clear film will occur. properties and water resistance will decrease.

By using not only the (b) monomer as a hydroxyl group-containing monomer, but also the (Cl monomer), it becomes easier to balance the appearance of the painted finish, the glabella adhesion during recoating, and the glabella adhesion between the base coat and top clear coat.

The monomer compositions (a1 to (di) above can be copolymerized according to a known polymerization method such as a solution polymerization method to obtain an acrylic polyol as the component (A).

The weight average molecular weight of the acrylic polyol (At component) of the present invention must be 3000 to 30000.
If it is less than 00, the weather resistance will deteriorate, and if it is more than 30,000, the finished appearance of the paint will be poor.

This product can be used as it is as an organic solvent type polyol. Alternatively, a carboxyl group may be introduced into this product, and the product may be neutralized with an amine to make it aqueous, and used as an aqueous solution or an aqueous dispersion. Furthermore, it can be used as a non-aqueous dispersion type (NAD type) obtained by using the organic solvent type acrylic polyol as a dispersion stabilizer and copolymerizing an acrylic monomer in the presence of the organic solvent type acrylic polyol.

Used in the top clear coat used in the method of the present invention
(As the crosslinking agent which is the Bl component, one that crosslinks and hardens the TAIAl component is used, but melamine resins and polyisocyanate compounds are suitable.

As the melamine resin used as a crosslinking agent, for example, butylated melamine resin (manufactured by Mitsui Toatsu: x, -han 20)
SE-60, Super: / 225, Super Beckamin G340, manufactured by Dainippon Ink, Superl 303, Sumimaru M-100, manufactured by Sumitomo Chemical, Suru 235. An alkyl etherified melamine resin that is widely used in conventional thermosetting acrylic resin paints such as SUMIMAR M66B manufactured by Sumitomo Chemical Co., Ltd.) can be used. The ratio of acrylic polyol/melamine resin is usually 80/20 to 501 by weight.
A range of 50 is preferred.

The polyisocyanate compound used as a crosslinking agent may be a polyisocyanate compound having free isocyanate groups, a polyisocyanate compound having blocked incyanate groups, or a polyisocyanate compound having free inocyanate groups. Isocyanate compounds include aliphatic diisocyanates such as hexamethylene diisocyanate or trimethylhexamethylene diisocyanate; cycloaliphatic diisocyanates such as xylylene diisocyanate or isophorone diisocyanate; aromatic diisocyanates such as nitolylene diisocyanate or 4.4'-diphenylmethane diisocyanate; Organic diisocyanates themselves, such as the above, or adducts of excess amounts of each of these organic diisocyanates with polyhydric alcohols, low molecular weight polyester resins, water, etc., or polymers of each of the organic diisocyanates as listed in 1 above, and furthermore, isocyanates.・Biuret bodies, etc. can be mentioned, but examples of typical commercially available products include “Burnock D-750, -8”.
00, DN-950, -970 or 15-455J
(The above are products of Dainippon Ink and Chemicals), "Desmodule L, N, HL, or N3390J (product of Bayer, West Germany),""Takene"-D-102
゜-202, -1) ON or -123NJ (product for Shikinichi Pharmaceutical Industries), [Coronate L, HL, EH or 203J (product of Nippon Polyurethane Industries) or [Duranate 24A-90CXJ (product of Asahi Kasei Industries), etc.] Can be mentioned. As the polyisocyanate compound having a blocked isocyanate group, the above-mentioned,
Examples of typical commercially available products include polyisocyanate compounds having free incyanate groups blocked with known blocking agents such as oximes, phenols, alcohols, lactams, malonic acid esters, and mercaptans. “Burnock D-550J
(Dainippon Ink and Chemicals (ceramic products).

“Takenate B-815-NJ (Shikinichi Yakuhin Kogyo ((
7) Product), [ADDITOL VXL
-80J (product of Hoechst, West Germany) or "Coronate 2507J (Japan Polyurethane Industry ((7)
) products), etc. The molar ratio of hydroxyl groups/isocyanate groups in the acrylic polyol is usually 1. O/2.
0 to 1.010.5 is appropriate.

In the top clear coat used in the method of the present invention, a small amount of a modified resin such as cellulose acetate butyrate, epoxy resin, polyester resin, alkyd resin, or acrylic resin may be used in combination in addition to the fAl component and the fB) component. Various known and commonly used additives such as a curing catalyst, a fluid FIN agent, a color separation inhibitor, an antioxidant, an ultraviolet absorber, or a silane coupling agent may also be incorporated.

Among these, when the curing agent is a polyisocyanate compound, dibutyltin diacetate, dibutyltin dioctate, dibutyltin dilaurate,
Examples include triethylamine or jetanolamine, and when the curing agent is a melamine resin, p-toluenesulfonic acid, phosphoric acid or an alkyl ester of phosphoric acid, "Neiku 7155.2500X, X-49-
1) The dinonylnac range represented by 0,5225 or 3525J (product of King Company, USA) can also be used within the range not exceeding the middle diameter.

(Function) The reason why the method of the present invention exhibits the above-mentioned features is not clear, but the top clear coat (
Since 1,4-butanediol mono(meth)acrylate is used as a hydroxyl group-containing upper layer in the Al component, the hydroxyl group exists apart from the main chain, and the hydroxyl group and the middle chain of the acrylic polyol concatenate (CH,)
This seems to be related to the hydrophobicity of 4. In other words, since the hydroxyl group exists far away from the acrylic polyol main chain, it is less susceptible to steric hindrance, and the hydroxyl group has high reactivity.Also, since 4cHJ- is connected to the hydroxyl group, the polarity of the hydroxyl group is relaxed, making it suitable for highly polar base coats. It is estimated that mixed layers are less likely to occur.

1,4-Pukundi is mentioned as a hydroxyl group-containing monomer. In addition, the interlayer adhesion between the base coat film and the top clear coat film is improved by using the pigment together with the building (meth)acrylate of the color clear paint.
It is presumed that this is because the overall reactivity of the hydroxyl groups in the acrylic polyol is moderately reduced, and the crosslinking agent in the top clear coat reacts very slightly with the hydroxyl groups of the base coat polyol on the surface of the base coat.

The reason why a coating film with excellent recoat adhesion can be obtained by the method of the present invention is that the crosslinking agent in the second coated base coat remains in the lower layer top coat due to the highly reactive 1.
It is presumed that this is due to a very small amount of reaction with the hydroxyl group derived from 4-butanediol mono(meth)acrylate.

Omame Ω four presentations According to the invention, in the 2CIB coating system.

Suppresses mixed layer between base coat and top clear coat,
By the method of the present invention, the above three items can be improved by the method of the present invention, which provides an excellent painted finish appearance and at the same time provides a coating film with excellent recoat adhesion and interlayer adhesion between the base coat film and the top clear coat film. It can be achieved at a level far superior to the 2CIB painting method.

The present invention will be explained in more detail with reference to Examples below. Unless otherwise specified, "r parts" and "r%" respectively refer to "parts by weight."
, means "% by weight".

[1] Sample Preparation Production Example 1 (Production to Acrylic Polyol Resin Solution) Swazol 1ooo [manufactured by Cosmo Oil ■,
150 parts of an aromatic solvent and 15 parts of butyl acetate were charged, heated and stirred, and when the temperature reached 132°C, the following monomer mixture was added over a period of 3 hours.

°Styrene 20 parts n-butyl methacrylate 382-ethylhexyl methacrylate 201.4-butanediol
2゜Monoacrylate acrylic acid 2AIBN (Note 1) 5 (Note 1) AIBN is α,
α′-Azobisisobutyronitrile.

After addition of the above monomer mixture, for another 1 hour at 132°C.
A mixture of 1 part of t-butyl peroctoate and 100,010 parts of Sufuzol was added over a period of 1 hour. Thereafter, stirring was continued while maintaining the temperature at 132° C. for 1 hour, and then the mixture was cooled. Swasol 1000 was added to this to obtain an acrylic resin solution A with a solid content concentration of 50%.

The weight average molecular weight (vIW) of this acrylic resin is 820
It was 0.

Production Examples 2 to 6 (Production of Acrylic Polyol Resin Solutions B to F) Acrylic resin solutions B to F were produced in the same manner as Production Example 1. All solids concentrations ranged from 49.0 to 51.0% by weight. Table 1 shows the compositions of acrylic resin solutions A-F and their weight average molecular weights (Mw).

Production Example 7 (Production of acrylic resin solution G) 25 parts of xylene and 15 parts of n-butanol were charged into a normal acrylic resin reaction tank equipped with a stirrer, a thermometer, a reflux condenser, etc., and heated and stirred. After reaching ℃, add 3 of the following monomer mixture.
Added over time.

After the addition was completed, the mixture was maintained at 5° C. for an additional hour (1), and then a mixture of 0.5 parts of t-butyl peroctoate and 10 parts of xylene was added over a period of 1 hour. 1 hour after that 1) 5
Stirring was continued while maintaining the temperature at °C, and then the mixture was cooled. Xylene was added to this to obtain an acrylic resin solution G having a solid content concentration of 50%. This acrylic resin had an Mw of 25,400 and a hydroxyl value of 52.

° Refuria S, I Used acrylic resin solutions A-F to prepare top-coat clear paints I to ■ of the compositions shown in Table 2.6 Next, the top-coat clear paint was mixed with Swasol 1000 (Note 2)/n-butanol. = 9/1 or Sufuzol 1000/butyl acetate = 8
72 mixed solvent, viscosity approximately 30 seconds (Ford Cup #4
The viscosity was adjusted to 20°C) and used for coating.

Swazol 1 when using melamine resin as a crosslinking agent
When a polyisocyanate compound was used as a crosslinking agent, a mixed solvent of Swasol 1000 and butyl acetate was used. Moreover, all the compounding amounts in Table 2 indicate the solid content or the amount of active ingredients.

(Note 2) Swazol l 000: Manufactured by Cosmo Oil ■, aromatic solvent.

Base coat; H 1. ' Base coat A was prepared using acrylic resin solution G with the following formulation. The blending amount is indicated by the solid content or the amount of active ingredient.

Acrylic resin G 75 knee pants 2
8S, E (Note 6) 25 Alpaste #491
9 (Note 7), 6.5 Full Paste #55-51
9 (Note 8) 6.5 (Note 6) Kneepan 28SE: n-butylated melamine resin manufactured by Mitsui Toatsu Chemical ■ (solid content 60%) (Note 7) Alpaste #4919: Toyo Aluminum ■
Aluminum paste (solid content 65%) (Note 8) Alpaste #55-519: Same as above, then
Add this penis coat to 40 parts of toluene and 10 parts of Swazol.
o [Cosmo Oil Co., Ltd. 130 parts, butyl acetate 20 parts and n
- A mixed solvent consisting of 10 parts of butanol with a viscosity of 14 seconds ()
Aud cup #4/20°C) was prepared and used for painting.

Amount of base coat CoJ.

Basecoat J was prepared in the same manner as Basecoat H using the following formulation.

Acrylic resin G 75 knee pants 2
8SE 25 Al Paste #491
9 3Perindo Marroon R-6434 (Note 9) 20 Power-Bonn MA (
Note 10) 0.5 (Note 9) West Germany, manufactured by Bayer ■, perylene-based red pigment (Note 1O) manufactured by Mitsubishi Kasei f@, carbon black-based black pigment [Examples and comparative examples] Example 1 Zinc phosphate chemical Epoxy-based cationic electrodeposition paint was electrodeposited onto the treated dull steel plate with a thickness of 0.8+n+++ to a dry coating thickness of approximately 20 microns, and then heated at 170℃ for 20 minutes.
After baking for a minute, it was sanded with #400 sandpaper, wiped with petroleum benzine to degrease it, and then air-sprayed with an automotive intermediate coating, Surf Acer, to a dry film thickness of about 25 microns, and heated at 140°C for 30 minutes. After baking.

Sand with #400 sandpaper, drain and dry.
The material was then degreased with petroleum benzene and used as a test material.

A base coat with adjusted viscosity, Air Spray Gun Wider W71 (manufactured by Iwata Yaiki Kogyo Co., Ltd.) was applied on this material to a dry film thickness of approximately 15 microns, and after being left at room temperature for 2 minutes, the viscosity was approximately 30 seconds. After applying the top coat clear paint of Preparation Example 1, which had a viscosity of
Table 3 lists the test results of the obtained coated plate, which was left to stand at room temperature for 30 minutes and then cured by baking at 140° C. for 30 minutes in an electric hot air dryer.

Examples 2 to 5, Comparative Examples 1 to 3 Examples 2 to 5, Comparative Example 1 were prepared in the same manner as in Example 1, except that the combinations of base coat and top coat clear paint were as shown in Tables 3 and 4. - 3 was carried out to obtain each coated plate. The test results are listed in Tables 3 and 4.

In addition, each test in Tables 3 and 4 was conducted according to the fertilization method.

(Notice): Appearance of paint film The finished appearance of the paint film was evaluated based on gloss and texture.

0: Very good △; Poor (Note 12): Measurement of sharpness The angle was fixed at 55° using a sharpness measuring device JCRI-GGD-166 type Gd meter (sold by Bhon Color Research Institute). It was measured using

(Note 13): The coating film was observed and evaluated after being exposed for 1600 hours using a weather resistant sunshine weatherometer.

0: No abnormality △: Some small cracks occurred (Note 14) Recoat adhesion Coated plates prepared according to the procedures of each example and comparative example (140 ° C.
X30'7? After further baking at 160°C for 30 minutes, the same base coat and top clear paint used in each example and comparative example were applied again, and baking was performed at 140°C for 30 minutes. After that, make incisions on the painted surface parallel to the substrate at 1 mm intervals using a force/v knife to reach the substrate.1) Then make incisions perpendicular to these.
A total of lOO 1 mm square goblets were created by making incisions at 1 mm intervals on the book. After that, a peeling test was performed using cellophane tape on the grid area, and the number of strands that remained without peeling out of 100 strands was indicated in the numerator.
For example, 100/100 means that there is no peeling and good adhesion.) (Note 15) 2CIB interlayer adhesion The coated plate was immersed in 40°C warm water for 24 hours, and then air-dried at room temperature for 1 hour. (Note 14) In the same way, add gobang eyes,
A peel test was conducted using cellophane tape to evaluate the adhesion between the base coat and the clear coat. The results were displayed in the same manner as in (Note 14).

Claims (2)

[Claims] (1) After applying a thermosetting paint containing pigments (base coat) to the surface to be coated, a clear top coat (top clear coat) is applied on top of this, resulting in two layers of uncured paint being heated at the same time. In a two-coat, one-bake finishing method for curing, the clear paint comprises (A) 20 to 90% by weight of a (meth)acrylic acid ester monomer of a monohydric alcohol having 4 to 24 carbon atoms, (b) 1, 4-butanediol mono(meth)acrylate monomer 5 to 50% by weight, (c) mono(meth) of dihydric alcohol having 3 or less carbon atoms
0 to 45% by weight of an acrylic ester monomer and (d) 0 to 70% by weight of a copolymerizable vinyl monomer other than monomers (a), (b), and (c), and (b) the monomer and (c) a monomer having a total weight average molecular weight 3 of 10 to 50% by weight.
A painting finishing method characterized in that the main components are an acrylic polyol of 000 to 30,000 and (B) a crosslinking agent. (2) (b) the amount of monomer is 10-40% by weight; (c)
2. A method according to claim 1, wherein the amount of monomer is 5 to 35% by weight.