JPH09271714A - Coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for applying a base coating and a clear coating of 2 coat 1 bake (2C1B) by utilizing an 1 coat bake coating (1C1B) line. SOLUTION: After an organic solvent based base coating (A) containing a hydroxide group-containing resin, a full etherified methyl melamine, a color pigment and substantially no curing agent, or an organic solvent based base coating (C) containing the hydroxide group-containing resin, the curing agent and the color pigment is applied and heated in a coating film baking furnace, an organic solvent based clear coating (B) containing the hydroxide group- containing resin, the full etherified methyl melamine and the curing agents is applied on the coated surface of the base coating (A) on a material to be coated or an organic solvent based clear coating (D) containing the hydroxide group-containing resin and a polyisocyanate compound is applied to the coated surface of the base coating (C) on the material to be coated in a coating booth of the 1C1B coating line again and is heated in the coating film baking furnace.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a 1C1B coating line, in which a base coat and a clear coat are provided in two coats.
The present invention relates to a method of applying a baking method (hereinafter referred to as 2C1B).

[0002]

2. Description of the Related Art Organic solvent-based base coats such as metallic paints and organic solvent-based clear coats are sequentially applied by wet-on-wet, and then heated to simultaneously cure both coating films. 2C1B multi-layer coating film,
It has excellent gloss, sharpness, metallic appearance, and weather resistance, so it is often used as a top coat for automobile exterior panels that require these properties.

The 2C1B coating line comprises a coating boot for coating both coatings and at least two coating stages, and a baking oven for curing a multilayer coating film. The boot is a space more than twice as long as 1C1B.
It is necessary. On the other hand, the coating booth is less than half 1
If you try to use the 2 coat 2 bake method (2C2B) by using the C1B coating line twice, the base coat coating is already cross-linked and cured before the clear coat coating. There arises a problem that the smoothness, interlayer adhesion, etc. of the multilayer coating film formed in step 2) are significantly reduced as compared with the multilayer coating film of 2C1B.

[0004]

SUMMARY OF THE INVENTION The present invention uses a 1C1B coating line twice to apply a base coat and a clear coat to an object to be coated with 2C1B to smooth a multilayer coating film. It is intended to provide a novel method for preventing the deterioration of the adhesiveness and interlayer adhesion. The feature is that the base coat is applied in the first 1C1B coating line, but the basecoat coating is not cured in the coating baking furnace, and the base coat is not cleared in the second 1C1B coating line. After coating the coat, both the base coat and the clear coat are simultaneously cured in a coat baking oven.

According to the first aspect of the present invention, however,
Using a 1-coat 1-bake type coating line (hereinafter referred to as 1C1B coating line) consisting of a coating boot and a coating baking oven, a base coat and a clear coat are applied to an object to be coated. A two-coat, one-bake coating method (1)
First, in a coating booth of a 1C1B coating line, an object to be coated is an organic solvent-based base containing a hydroxyl group-containing resin, a fluorinated methyl melamine and a coloring pigment and substantially not containing a curing catalyst (a). After coating the coat (A), it is heated in a coating baking oven (2) and then again in the coating boot of the 1C1B coating line, on the coated surface of the base coat (A) of the object to be coated. After coating an organic solvent-based clear coat (B) containing a hydroxyl group-containing resin, a fluorinated methyl melamine and a curing catalyst (a), the base coat is heated in a coating film baking oven. (A) and clear coat (B)
There is provided a coating method (hereinafter referred to as coating method I), characterized in that both coating films are cross-linked and cured at the same time.

According to the second aspect of the present invention, a 1C1B coating line consisting of a coating boot and a coating baking oven is used to apply a base coat and a clear coat to an object to be coated. 2
A method of coating by a coat 1-bake method, wherein (1) first, an organic substance containing a hydroxyl group-containing resin, a curing catalyst (b) and a color pigment on an object to be coated in a coating boot of a 1C1B coating line. After coating the solvent-based base coat (C), it is heated in a coating film baking oven (2) and then again in the coating boot of the 1C1B coating line, the base coat (C) of the article to be coated. After coating an organic solvent-based clear coat (D) containing a hydroxyl group-containing resin and a polyisocyanate compound on the coated surface of the above, the base coat is heated by a coating baking oven.
There is provided a coating method (hereinafter referred to as coating method II), which comprises simultaneously crosslinking and curing both the coating film (C) and the clear coating film (D).

The method of the present invention will be described in more detail below.

The 1C1B coating line used in the coating methods I and II of the present invention usually has substantially one coating boot and one coating baking oven.
It is for painting a type of paint and baking it to form a single layer coating. A single-layer heat-cured coating film is formed on the article to be coated that has passed through this 1C1B coating line, but the coating method I, which is the first embodiment of the present invention, cures as the first base coat. By using a coating material which does not substantially contain the catalyst (a), even if the base coat is coated on a 1C1B coating line and baked, a crosslinked cured coating film is not substantially formed. There is.

In the coating method I, however, as the base coat (A), a hydroxyl group-containing resin, a fluorinated methyl melamine, a color pigment and an organic solvent are used as main components, and the curing catalyst (a) is used. An organic solvent-based paint that does not substantially contain is used. Here, the "curing catalyst (a)" refers to a substance that catalyzes the cross-linking curing reaction between the hydroxyl group-containing resin and the fluorinated methyl melamine.

The hydroxyl group-containing resin used in the base coat (A) is a film-forming resin having two or more hydroxyl groups in one molecule and contains, for example, a hydroxyl group usually used in the decomposition of paint. Acrylic resin, polyester resin,
Examples thereof include alkyd resins, and hydroxyl group-containing acrylic resins are particularly preferable. The resin has a hydroxyl value in the range of 30 to 200, particularly 40 to 170, and 3,000 to
Those having a number average molecular weight in the range of 50,000, especially 5,000 to 30,000 are suitable.

The hydroxyl group-containing acrylic resin is usually prepared by using a hydroxyl group-containing unsaturated monomer and an acrylic unsaturated monomer, and if necessary, in combination with another copolymerizable unsaturated monomer. It can be obtained by polymerization.

The hydroxyl group-containing unsaturated monomer is a compound having at least one hydroxyl group and at least one polymerizable unsaturated bond in one molecule, and examples thereof include hydroxyethyl (meth) acrylate and hydroxypropyl (meth). Examples thereof include monoesters of (meth) acrylic acid such as acrylate and a divalent alcohol having 2 to 20 carbon atoms and allyl alcohol. Examples of the acrylic unsaturated monomer include (meth) acrylic acid, monoester products of (meth) acrylic acid and monovalent alcohols having 1 to 22 carbon atoms, and glycidyl (meth) acrylate. And so on. Further, the other copolymerizable unsaturated monomer is a compound other than these having one or more polymerizable unsaturated bond, and examples thereof include styrene, alkyl-substituted styrene, acrylonitrile, acrylamide, and N-methylolacrylamide. Examples thereof include alkyl ether, vinyl chloride, vinyl acetate, ethylene and propylene.

The amount of hydroxyl groups introduced into the acrylic resin can be easily adjusted by adjusting the amount of the above-mentioned unsaturated monomer containing a hydroxyl group. It may further contain a functional group of.

Examples of the hydroxyl group-containing polyester resin and the hydroxyl group-containing alkyd resin include esterified products of polybasic acids and polyhydric alcohols and those obtained by modifying the esterified products with higher fatty acids. As the polybasic acid, a compound having two or more carboxyl groups in one molecule can be used, and examples thereof include phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, Tetrahydrophthalic acid, hexahydrophthalic acid, het acid, hymic acid, maleic acid, fumaric acid,
Examples thereof include itaconic acid, trimellitic acid, pyromellitic acid and their anhydrides. On the other hand, as the polyvalent alcohol, a compound having two or more hydroxyl groups in one molecule is used, and for example, ethylene glycol, propylene glycol, butylene glycol, hexanediol,
Diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, hydrogenated bisphenol, glycerin, trimethylolethane,
Examples include trimetol propane and pentaerythritol.

The amount of hydroxyl groups introduced into the polyester resin and the alkyd resin can be adjusted by adjusting the amount of polyvalent alcohol, particularly trivalent or higher polyvalent alcohol used. It may contain other functional groups such as groups.

Flue used for base coat (A)
Tellurized methyl melamine serves as a cross-linking agent for the hydroxyl group-containing resin. For example, melamine is methylated with formaldehyde or the like, and if necessary, methylolated melamine is dimerized or trimerized. Subsequent to monomerization, and substantially all of the methylol groups present are alkyl etherified with monovalent alcohols having 1 to 6 carbon atoms. 1 to 1 carbon atoms used for etherification
Examples of the monovalent alcohol of 6 include, for example, methyl alcohol.
, Ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-
Butyl alcohol, n-amyl alcohol, isoamyl alcohol, sec-amyl alcohol, tert-amyl alcohol, n-hexyl alcohol, sec-hexyl alcohol, tert-hexyl alcohol and the like. To be Of these, methyl alcohol, ethyl alcohol, n-propyl alcohol, isobutyl alcohol
A monohydric alcohol having 1 to 4 carbon atoms, such as ruble, is suitable.

The fluetherated methylmelamine may preferably have a molecular weight in the range of from about 300 to about 1,500, especially 400 to 1,000, and the methylo-
A partially etherified melamine having a residual group may be mixed, but the amount thereof is preferably 50% by weight or less based on the fluetherified methylmelamine.

Further, the base coat (A) may be made of, for example, titanium oxide, zinc oxide, or a carbon in order to impart a color and / or metallic feeling to the coating film formed therefrom.
Bon Black, Yellow Lead, Hansaelo, Chrome Orange,
Iron oxide, permanent red, fast violet,
For ordinary paints such as coloring pigments such as chrome green and phthalocyanine blue, and flakes of aluminum, mica, metallic pigments such as mica surface-coated with metal oxides such as titanium oxide, metallic pigments such as mica iron oxide. A pigment is added.

The coating material for the base coat (A) can be prepared by dissolving or dispersing the above-mentioned hydroxyl group-containing resin, fluorinated methyl melamine and color pigment in an organic solvent. As the organic solvent,
For example, a usual solvent for coating materials such as hydrocarbon type (aliphatic type or aromatic type), ketone type, alcohol type, ester type and ether type may be used.

The composition ratio of each of these components in the base coat (A) is not particularly limited and can be changed according to the application of the coated article, but usually, the hydroxyl group-containing resin 1
1 part by weight of fluterated methylmelamine per 100 parts by weight
The range of 5 to 100 parts by weight, particularly 25 to 65 parts by weight, and the range of the color pigment of 2 to 200 parts by weight, especially 3 to 150 parts by weight are suitable. If necessary, the base coat (A) may further contain a viscosity modifier such as non-aqueous dispersion type resin particles and an ultraviolet absorber. The solid content of the base coat (A) during coating is usually 15
It is preferable to adjust the content within the range of 60 to 60% by weight, particularly 20 to 45% by weight.

In the coating method I, first, the above-mentioned base is used.
The coat (A) is applied to the object to be coated in a coating boot built into the 1C1B coating line. A preferred example of the article to be coated is a metal or plastic automobile outer panel, but is not limited thereto. If necessary, an undercoat paint such as an electrodeposition paint or an intermediate paint can be applied to the object to be coated in advance, and these paint films are applied prior to the base coat (A). It is preferable to cure by curing.

The coating of the base coat (A) with the coating boot can be performed by atomization coating such as air spraying, airless spraying, electrostatic coating, etc., and the film thickness thereof. Is generally 5 to 40 μm, especially 1 based on the cured coating film.
The range of 0 to 30 μm is suitable. And 1C1B
The substrate to which the base coat (A) is applied in the above coating line is then heated to a temperature of about 120 to about 150 ° C. or higher installed in the same line. It is transported into the furnace. In the furnace, the base scoot (A)
Since the coating film of No. 1 does not contain the curing catalyst (a), the organic solvent is volatilized, and the hydroxyl group-containing resin and the fluorinated methyl melamine may be melted, but substantially cross-linked. In this state, the article to be coated passes through the furnace and is carried out to the outside. After passing through the furnace, the coated surface is melted and fluidized and has excellent smoothness.

In the coating method I, 1C1 was further added to the uncured coating surface of the base coat (A) thus coated.
The clear coat (B) is painted on the B paint line.

The clear coat (B) is an organic solvent-based clear coating composition containing a hydroxyl group-containing resin, a fluorinated methyl melamine, a curing catalyst (a) and an organic solvent as main components. Thermosetting paints that form transparent coatings that are substantially free can be used.

The hydroxyl group-containing resin, the fluorinated methylmelamine and the organic solvent in the clear coat (B) can be appropriately selected from those described above for the base coat (A). . The hydroxyl group-containing resin, the fluorinated methyl melamine and the organic solvent used in the clear coat (B) may be the same as or different from those used in the base coat (A). It may be.

As the curing catalyst (a) to be blended with the clear coat (B), usually, a sulfonic acid type catalyst is suitable, for example, paratoluene sulfonic acid, dodecylbenzene sulfonic acid, diether. Examples thereof include nonylnaphthalene sulfonic acid, dinonyl naphthalene disulfonic acid; those obtained by neutralizing these acids with an amino compound; adducts of these acids with an epoxy compound.

The composition ratio of each of these components in the clear coat (B) is not particularly limited and can be changed according to the application of the coated article, etc., but usually the hydroxyl group-containing resin 1
1 part by weight of fluterated methylmelamine per 100 parts by weight
5 to 100 parts by weight, especially 25 to 80 parts by weight, and the curing catalyst (a) may be 0.5 to 5 parts by weight, especially 1 to 3 parts by weight. If necessary, the clear coat (B) may further contain a viscosity modifier such as non-aqueous dispersion type resin particles and an ultraviolet absorber.
The solid content concentration of the clear coat (B) during coating is usually 20 to 80% by weight, preferably 35 to 65% by weight.

The curing catalyst (a) contained in the clear coat (B) promotes a cross-linking reaction between the hydroxyl group-containing resin and the fluorinated methyl melamine.
When the coating film of the coat (B) is heated at a temperature of about 120 to about 150 ° C., the organic solvent volatilizes, the hydroxyl group-containing resin and the fluorinated methylmelamine melt, and the catalyst (a) causes Both components crosslink and harden.

In the coating method I, an object to be coated on which the base coat (A) has been coated as described above is the same or different one.
It is transported to the coating booth of the C1B coating line, where it is delivered to the coating booth.
The clear coat (B) is applied to the coated surface of the coat (A). The coating of the clear coat (B) with a coating boot can be performed by an atomizing method such as air spray, airless spray, electrostatic coating, etc., and the film thickness is based on the cured coating film. In general, the range of 20 to 100 μm, particularly 25 to 60 μm is suitable.

After coating the clear coat (B), the object to be coated is placed in the same line in a coating film baking oven heated to a temperature of about 120 to about 150 ° C. or higher. When the multi-layer coating film composed of the base coat (A) and the clear coat (B) is heated therein, both coating films are simultaneously crosslinked and cured. The exact reason why both coatings crosslink simultaneously at the same time, although the curing catalyst (a) is not contained in the single coating of the base coat (A), is not clear, but probably the clear coating. -(B) coating film, the cross-linking reaction between the hydroxyl group-containing resin and the fluoretherized methyl melamine is promoted by the curing catalyst (a) which coexists, and the clear coat coating film is cross-linked and cured. In the coating film of the base coat (A) in the lower layer, a part of the curing catalyst (a) in the clear coat (B) in the upper layer is a base coat (A).
It is presumed that the base coat film is cross-linked and cured by promoting the cross-linking and hardening of the hydroxyl group-containing resin and the full-etherified melamine in the base coat (A) film by permeating into the coating film. The degree of cross-linking and hardening of the multilayer coating film formed by the coating method I of the present invention is generally 95% by weight or more for both coating films, when the gel fraction is measured.

Coating method II, which is the second aspect of the present invention
Is basically the base in the coating method I described above.
An organic solvent-based base coat (C) comprising a scot (A) containing a hydroxyl group-containing resin, a curing catalyst (b) and a color pigment.
And the clear coat (B) of Coating Method I
Can be carried out according to the above-mentioned coating method I, except that each is replaced with an organic solvent-based clear coat (D) containing a hydroxyl group-containing resin and a polyisocyanate compound.

The base coat (C) used in the coating method II is an organic solvent system containing a hydroxyl group-containing resin, a curing catalyst (b) and a color pigment and containing substantially no polyisocyanate compound. It is paint. Among these, as the hydroxyl group-containing resin, the color pigment and the organic solvent,
What was mentioned above about the scoot (A) can be used similarly.

The curing catalyst (b) to be added to the base coat (C) has a function of promoting the urethanization reaction between the hydroxyl group of the hydroxyl group-containing resin and the isocyanate group of the polyisocyanate compound. What is used are, for example, lead 2-ethylhexanoate, lead benzoate, lead oleate, sodium propionate, lithium acetate,
Potassium oleate, iron 2-ethylhexanoate (II
I), cobalt benzoate, cobalt 2-ethylhexanoate, aluminum oleate, zinc 2-ethylhexanoate, zinc naphthenate, copper 2-ethylhexanoate, copper acetate, manganese 2-ethylhexanoate, 2-ethylhexane. Organic acid metal salts such as zirconium acid; tetrabutyltin, tributyltin chloride, dibutyltin dichloride, butyltin trichloride, tin chloride, tributyltin-o-phenolate, tributyltin cyanate, tin octylate,
Tin oleate, tin tartrate, dibutyltin di (2-ethylhexylate), dibenzyltin di (2-ethylhexylate), dibutyltin dioctate, dibutyltin dilaurate, dibutyltin oxide, dibutyltin diisooctyl maleate, dibutyltin sulfide, dibutyltin. Dibutoxide, dibutyltin bis (o
-Phenylphenolate), dibutyltin bis (acetylacetonate), di (2-ethylhexyl) tin oxide and other organotin compounds; dibutyltitanium dichloride, tetrabutyltitanate and other organotitanium compounds; sodium trichlorophenolate, ferrocene, trichloride Antimony, cadmium nitrate, thorium nitrate, triphenylaluminum, trioctylaluminum, vanadium trichloride, boron trifluoride-diethyl ether complex, pyridineborane, calcium acetate, barium acetate and the like can be mentioned, among which dibutyltin dioctate. , Dibutyltin dilaurate, dibutyltin dioxide,
Dibutyltin diisooctyl maleate and the like are suitable.

The base coat (C) can be prepared by dissolving or dispersing the above-mentioned hydroxyl group-containing resin, curing catalyst (b) and color pigment in an organic solvent. As the organic solvent, for example, a usual solvent for coating materials such as hydrocarbon type (aliphatic type or aromatic type), ketone type, alcohol type, ester type, ether type or the like can be used.

The composition ratio of each of these components in the base coat (C) is not particularly limited and can be arbitrarily changed according to the use of the coated article. Usually, it is usually 100 parts by weight of the hydroxyl group-containing resin. The curing catalyst (b) is 0.01 to 1 part by weight, particularly 0.05 to 0.5 part by weight, and the coloring pigment is 2 to 2 parts.
Amounts of 00 parts by weight, especially 3 to 150 parts by weight, are suitable. If necessary, the base coat (C) may further contain a viscosity modifier such as non-aqueous dispersion type resin particles and an ultraviolet absorber. The solid content of the base coat (C) during coating is usually 15 to 60.
It is preferable to adjust the content within the range of 20 to 45% by weight, particularly 20 to 45% by weight.

In the coating method II, first, the base coat (C) described above is coated on an object to be coated in a coating boot built into the 1C1B coating line. A preferred example of the article to be coated is a metal or plastic automobile outer panel, but is not limited thereto. If necessary, an undercoat paint such as an electrodeposition paint or an intermediate coat paint can be applied to the object to be coated in advance, and these paint films are applied before the base coat (C) is applied. It is preferable to cure by curing.

The coating of the base coat (C) in the coating boot is carried out by atomization coating such as air spraying, airless spraying, electrostatic coating, etc., and the film thickness is cured. Generally from 5 to 40 μm, especially from 10 to 30 based on the coating film
μm is suitable. The object coated with the base coat (C) on the 1C1B coating line is then heated to a temperature of about 120 to about 150 ° C. or higher installed in the line. It is transported into the coating baking oven. In the furnace, the coating film of the base coat (C) does not contain a polyisocyanate compound, although the organic solvent is volatilized and the hydroxyl group-containing resin may be melted. The material to be coated passes through the furnace without being subjected to a crosslinking reaction and is carried out to the outside. After passing through the furnace
The coated surface of the coat (C) is melted and fluidized and has excellent smoothness.

In the coating method II, the uncured coating surface of the thus coated base coat (C) which has not undergone the crosslinking reaction is further subjected to the clear coat (D) on the 1C1B coating line. Is painted.

The clear coat (D) is an organic solvent-based clear paint containing a hydroxyl group-containing resin and a polyisocyanate compound, and does not substantially contain a coloring pigment, and forms a transparent coating film. Thermosetting paints can be used.

Of these, as the hydroxyl group-containing resin and the organic solvent, the same ones as described above for the base coat (A) can be preferably used, and as the organic solvent, an isocyanate such as a hydroxyl group is particularly preferable. It is desirable to use those which do not have a functional group capable of reacting with the -group.

The polyisocyanate compound blended in the clear coat (D) is a compound having two or more isocyanate groups in one molecule, for example, tolylene diisocyanate, Diphenylmethane diisocyanate
, Xylylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, methylene bis (cyclohexyl isocyanate), isophorone diisocyanate, etc., aromatic, aliphatic or alicyclic System polyisocyanate compounds, dimers or trimers of these polyisocyanates, and polyisocyanates thereof
Free isocyanate group-containing prepolymers obtained by reacting a low-molecular-weight or high-molecular-weight polyol with an excess of isocyanate groups. The trimer (isocyanurate) and the like are preferable.

Further, the clear coat (D) may be appropriately blended with the above-mentioned curing catalyst (b).

The composition ratio of each of these components in the clear coat (D) is not particularly limited and can be changed depending on the application of the coated article, etc., but usually, a hydroxyl group-containing resin and a polyisocyanate compound are used. The ratio of the former is 1 hydroxyl group
The amount of the latter isocyanate group can be 0.5 to 2 mol, and particularly 0.8 to 1.5 mol per mol, and the curing catalyst (b) is used per 100 parts by weight of the hydroxyl group-containing resin. The amount can be 1 part by weight or less, particularly 0.05 to 0.5 part by weight. If desired, the clear coat (D) may further contain a viscosity modifier such as non-aqueous dispersion type resin particles, an ultraviolet absorber and the like. The solid content concentration of the clear coat (D) during coating is usually 20 to 80% by weight, preferably 35 to 65% by weight.

The curing catalyst (b) contained in the clear coat (D) promotes the urethanization reaction between the hydroxyl group-containing resin and the polyisocyanate compound, and the clear catalyst (D). When the coating film of 1) is heated at a temperature of about 120 to about 150 ° C., the organic solvent is volatilized, the hydroxyl group-containing resin and the like are melted, and the hydroxyl group-containing resin and the polyisocyanate compound are urethanized by the action of the catalyst (b). The reaction is accelerated and a cross-linking reaction is caused to cure.

In the coating method II, the base is applied as described above.
The coated object coated with the coat (C) is conveyed to the coating booth of the same or another 1C1B coating line, and the clear coat (() is applied to the coated surface of the base coat (C) there. Apply D). Painting the clear coat (D) with a paint boot
For example, it can be carried out by an atomization method such as air spray, airless spray, electrostatic coating, and the film thickness thereof is from 20 to 100 μm, especially from 25 to 60, based on the cured coating film.
The range of μm is suitable.

After coating the clear coat (D), the article to be coated is transferred into a coating film baking oven installed in the same line and heated to a temperature of about 120 to 150 ° C. or higher. Then, when the multilayer coating film composed of the base coat (C) and the clear coat (D) is heated there, both coating films are simultaneously crosslinked and cured. Although the base coat (C) alone coat does not contain a polyisocyanate compound as a cross-linking agent, the exact reason why both coats are cross-linked simultaneously is not clear, but probably In the coating film of clear coat (D), the reaction between the hydroxyl group-containing resin and the polyisocyanate compound coexisting by heating proceeds to crosslink and cure, while the base coat in the lower layer is adjacent to it. In the coating film of (C), the polyisocyanate compound in the clear coat (D) of the upper layer permeates into the coating film of the base coat (C) to contain a hydroxyl group in the coating film. It is presumed that the resin reacts with urethane to crosslink and cure the coating film. The base
Since the curing catalyst (b) is also present in the coating film of the coat (C), it is presumed that the above-mentioned urethanization reaction is carried out promptly. The degree of crosslinking and curing of the multilayer coating film formed by the coating method II of the present invention is generally 95% by weight or more for both coating films, as measured by gel fraction.

The above-mentioned coating methods I and I of the present invention
According to I, the following effects can be obtained.

(1) Since it becomes possible to coat the base coat and the clear coat by 2C1B using the 1C1B coating line, the equipment area of the coating line can be reduced.

(2) To form a multilayer coating film having the same or better gloss, sharpness, metallic feel, weather resistance and the like as compared with the conventional multilayer coating film coated on the 2C1B coating line. You can

(3) The formed multilayer coating film is also 1C1
Compared to the multi-layer coating film coated with 2C2B by using the B coating line twice, the smoothness and interlayer adhesion are excellent.

Hereinafter, the present invention will be described in more detail with reference to Examples. "Parts" and "%" in the examples mean "parts by weight" and "% by weight", respectively.

[0052]

【Example】

<Preparation of sample> 1. (X-1) Acrylic resin for hydroxyl group-containing resin base , 30 parts of methyl methacrylate, 20 parts of ethyl acrylate
Parts, 35 parts of n-butyl methacrylate and 15 parts of hydroxyethyl methacrylate were polymerized in xylene at 120 DEG C. for 3 hours in the presence of 1 part of azobisisobutyronitrile.

The obtained resin has a number average molecular weight of 20,000.
0, a hydroxyl value of 65, an acid value of 0 and a solid content of 50%.

(X-2) Acrylic resin 15 parts of styrene, 15 parts of methyl methacrylate, 49 parts of ethyl acrylate, 2 parts of hydroxyethyl acrylate
0 parts and 1 part of acrylic acid were polymerized in xylene in the presence of 1.5 parts of azobisisobutyronitrile for 3 hours at 120 ° C.

The obtained resin has a number average molecular weight of 15,000.
0, hydroxyl value 96, acid value 8 and solid content 50%.

(Y-1) Acrylic resin for clear coat In the presence of 30 parts of styrene, 45 parts of n-butyl methacrylate and 25 parts of hydroxyethyl acrylate and 3 parts of azobisisobutyronitrile. Was polymerized in Solvesso 100 (trade name, aromatic hydrocarbon manufactured by Esso Petroleum) at 120 ° C. for 3 hours.

The resin obtained had a number average molecular weight of 5,000.
0, hydroxyl value 120, acid value 0 and solid content 50%.

(Y-2) Acrylic resin 30 parts of styrene, 20 parts of n-butyl methacrylate, 2
14 parts ethylhexyl methacrylate, 35 parts hydroxyethyl acrylate and 1 part acrylic acid in the presence of 3 parts azobisisobutyronitrile Solvesso 10
12 out of 0 (made by Esso Sekiyu, trade name, aromatic hydrocarbon)
Polymerization was carried out at 0 ° C. for 3 hours.

The resin obtained had a number average molecular weight of 5,000.
0, a hydroxyl value of 168, an acid value of 8 and a solid content of 50%.

2. Base Coat (A) Using the above hydroxyl group-containing resin, a base coat (A) was prepared by mixing the components shown in Table 1 below. The compounding amount in the table is the solid content. An organic solvent (equal weight mixture of xylene and butyl acetate) was added to make the nonvolatile content 30%, and the mixture was subjected to electrostatic air spray coating.

[0061]

[Table 1]

Note 1: Melamine (m-1): Flumethyletherified methylmelamine, Molecular weight 550 (m-2): Flumethylbutyl mixed etherified methylmelamine, Molecular weight 650 Note 2: Metallic pigment aluminum paste : Toyo Aluminum, product name,
Aluminum paste # 55-519 Note 3: Curing catalyst (a) a-1: Equivalent neutralization product of paratoluene sulfonic acid and diisopropanolamine a-2: Equivalent neutralization product of dodecylbenzene sulfonic acid and diisopropanolamine Curing The amount of the catalyst compounded indicates the amount of the active ingredient of sulfonic acid.

3. Clear Coat (B) A clear coat (B) was prepared by using the above-mentioned hydroxyl group-containing resin and mixing with each component shown in Table 2 below. The compounding amount in the table is the solid content. The non-volatile content was adjusted to 55% with an organic solvent (Swazol 1000 (trade name, manufactured by Cosmo Oil Co., Ltd.)) and subjected to electrostatic air spray coating.

[0064]

[Table 2]

4. Base Coat (C) A sample of the above-mentioned hydroxyl group-containing resin was used and mixed with each component shown in Table 3 below to prepare a base coat (C). The compounding amount in the table is the solid content. An organic solvent (equal weight mixture of xylene and butyl acetate) was added to make the nonvolatile content 30%, and the mixture was subjected to electrostatic air spray coating.

[0066]

[Table 3]

Note 4: Polyisocyanate compound n-1: Hexamethylene diisocyanate trimer * The blending amount is the hydroxyl group of the hydroxyl group-containing resin (x-1) and the isocyanate group of (n-1). The ratio is equivalent to that of the base.

Note 5: Curing catalyst (b) b-1: Dioctyl tin dilaurate 5. Clear coat (D-1) Hydroxyl group-containing resin (b-1) and polyisocyanate compound (n-1) (Note 4) were used in a molar ratio of the former hydroxyl group and the latter isocyanate group of 1 Organic solvent (Swazol 1000 (manufactured by Cosmo Oil Co., Ltd., trade name))
Then, the non-volatile content was adjusted to 55% and the product was subjected to electrostatic air spray coating.

<Examples and Comparative Examples> Examples 1 to 3 and Comparative Examples 1 to 5 base scoot (A-1) to (A-4) or (C-1).
(C-4) is applied to a metal coating object coated with a cationic electrodeposition coating composition and an intermediate coating composition with an electrostatic air spray using a coating boot built into a 1C1B coating line. The film thickness is 10 to 20 μm based on the cured coating film. Then, the object to be coated is installed in the same coating line as about 14
It passes through the baking oven heated to 0 ° C for 30 minutes and is carried out of the oven. Then, the base coat surface of the coated object is cleared by a coating boot on the same coating line. Coat (B-
1) to (B-2) or (D-1) is electrostatic air spray
Paint with. The film thickness of the clear coating film is 40 μm based on the cured coating film. The coated object coated with the clear coat is then conveyed to a baking oven installed in the same line and heated to about 140 ° C., where a base coat and a clear coat are provided. Was heated for 30 minutes.

Table 4 below shows these coating steps and the performance test results of the obtained multilayer coating film.

[0071]

[Table 4]

<Test Method> Gloss : 20 of JISK-5400 7.6 (1990)
According to the specular gloss, the degree of gloss of the coating film is measured by measuring the reflectance when the incident angle and the light receiving angle are 20 degrees, respectively.
The specular gloss is expressed as a percentage when the reference surface is 100.

Smoothness : The state of the coated surface was visually observed and judged according to the following evaluation criteria. ◎ indicates that there is no discoloration or unevenness and that the smoothness is good, △ indicates that some discoloration and unevenness appear, and × indicates that the discoloration or unevenness is observed and the smoothness is inferior. Shown respectively.

Weather resistance : The weather resistance was examined by accelerated weather resistance by a QUV accelerated baculo test using an accelerated weather resistance tester manufactured by Q Panel Co. The test conditions were as follows: ultraviolet irradiation 16 hours / 60 ° C. and water condensation 8 hours / 50 ° C. as one cycle, the coating film after 3,000 hours (125 cycles) test was visually observed, and the following evaluation criteria It was judged by. ◯ indicates that the gloss is almost the same as that of the initial stage, Δ indicates that gloss reduction and whitening phenomenon are observed, and X indicates that gloss reduction, cracking and whitening phenomenon are noticeable, and that the test is unacceptable.

Interlayer adhesion : A weather resistance test was conducted in the same manner as described above, and then the base material was reached with a cutter knife.
Draw 11 parallel lines at 1 mm intervals so that they are orthogonal to the approximate center of the test piece, cut into scratches to make 100 squares in 1 cm ² , and adhere to the coated surface. Cellophane tape was adhered, and after rapidly peeling it off, the coated surface of the burdock was evaluated. ◯ indicates that no peeling of the coating film was observed, Δ indicates that slight peeling was observed between the base coating film and the clear coating film, and x indicates that many interlayer peeling were observed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Yoshikazu Yamamoto, Aichi Prefecture, Miyoshi Town, Nishikamo-gun, Daizai, Hanaji, 1st place, Kansai Paint Co., Ltd. No. 1 Kansai Paint Co., Ltd.

Claims (2)

[Claims] 1. A base coat and a clear for an object to be coated by using a 1-coat 1-bake type coating line (hereinafter referred to as 1C1B coating line) consisting of a coating boot and a coating baking oven. A method of coating a coat by a two-coat / one-bake system, (1) First, in a coating boot of a 1C1B coating line, a hydroxyl group-containing resin, a fluorinated methylmelamine and After coating an organic solvent-based base coat (A) containing a coloring pigment and substantially not containing a curing catalyst, it is heated in a coating film baking oven, and (2) then coated again on the 1C1B coating line. In the above, an organic solvent-based clear coat (B) containing a hydroxyl group-containing resin, a fluorinated methyl melamine and a curing catalyst is provided on the coated surface of the base coat (A) of the coated object. After painting, heat in a coating baking oven Preparative (A) and clear - co - DOO (B) both coating films simultaneously coating method characterized by allowed to crosslink curing of. 2. A 1C comprising a coating boot and a coating baking oven.
A method of coating a base coat and a clear coat on an object by using a 1B coating line in a two-coat / one-bake system. (1) First, a coating coat of a 1C1B coating line. In the second step, an object to be coated is coated with an organic solvent-based base coat (C) containing a hydroxyl group-containing resin, a curing catalyst and a color pigment, and then heated in a coating film baking oven. In a coating boot of 1C1B coating line, an organic solvent-based clear coat (D) containing a hydroxyl group-containing resin and a polyisocyanate compound on the coated surface of the base coat (C) of the object to be coated. After coating, the coating method is characterized in that both the base coat (C) and the clear coat (D) are simultaneously crosslinked and cured by heating in a coating film baking oven.