JPH1119583A - Method for coating metal plate and metal plate coated by method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a double-layer upper coating film with excellent decorative property and coating property by applying a top coat color base coating material containing a coloring pigment and having specified constituents and a top coat clear coating material to a long metal plate coated with a primer-cured coating film and forming a top coat clear coating film on the top coat color base coating film by burning the resultant substrate. SOLUTION: A top coat color base coating material containing 60-90 pts.wt. of OH group- containing polyester resin and 5-40 pts.wt. of a melamine resin type cross-linking agent as coating film-formable resin components together with a coloring pigment and a top coat clear coating material containing 60-90 pts.wt. of OH group-containing polyester resin and 10-40 pts.wt. of melamine resin type cross-linking agent as coating film-formable resin components are formed on a primer-cured coating film formed on a long metal plate which is continuously moved and then burned to form a top coat clear coating film. The polyester resin for the top coat color coating material has number average molecular weight 1,500-35,000, glass transition temperature within a range from -30 to 60 deg.C, and hydroxyl value 3-100 mgKOH/g and the polyester resin for the top coat clear coating material has number average molecular weight 1,500-25,000, glass transition temperature within a range from 0 to 70 deg.C, and hydroxyl value 8-100 mgKOH/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for coating a continuously moving long metal plate, wherein the number of overcoat layers is two and the number of baking of the overcoat layer is one. The present invention relates to a method for coating a metal plate capable of forming a two-layer coating film having excellent film performance, and a coated metal plate.

[0002]

2. Description of the Related Art
In the field of pre-coated metal sheets for building materials and equipment processing, a so-called two-coat method is used in which a primer paint is applied and baked on a metal sheet, and then a colored top coat is applied and baked on the primer coat. -A two-bake method is generally used.

In recent years, for the purpose of further improving the coating performance and aesthetics of a precoated metal sheet, an intermediate coating has been applied and baked on the primer coating, and a top coating has been applied and baked on the intermediate coating. In other words, a so-called three-coat, three-bake method is used in some cases. However, in this method, since the baking is performed three times each, the conventional two-coat
This cannot be performed using a 2-bake type line, and a significant line remodeling is required.

[0004] In the field of precoated metal sheets, paints have been applied on metal sheets or cured coating layers so that the two paint layers are in contact with each other in a wet-on-wet manner. Painting has not been put to practical use.

[0005] In the field of precoated metal sheets, the present inventors have proposed a method in which a top coat is formed into two layers, and the two top coats are coated so as to be in contact with each other by wet-on-wet.
The intense research was carried out on the simultaneous baking of the overcoating layers to form a coating film having excellent aesthetics and coating performance.
As a result, by forming a top coat clear paint layer on the uncured top coat coloring base paint layer by a curtain coating method or a die coating method, on a long metal plate that moves continuously without increasing the number of baking times. Furthermore, they have found that a two-layer coating film having excellent aesthetics and coating performance can be formed, and the present invention has been completed.

[0006]

That is, the present invention provides a top-coating base paint containing a color pigment on a continuously moving long metal plate, with or without a primer-cured coating film. A method of applying a topcoat clear paint and baking to form a topcoat clearcoat on the topcoat basecoat, wherein the topcoat basecoat (A) has a number average molecular weight of 1,5.
00 to 35,000, glass transition temperature -30 to 60 ° C,
A film-forming resin component comprising 60 to 95 parts by weight of a hydroxyl group-containing polyester resin having a hydroxyl value of 3 to 100 mgKOH / g and 5 to 40 parts by weight of at least one crosslinking agent selected from (B) a melamine resin and a blocked polyisocyanate compound. And (C) a paint containing a color pigment,
When the clear top coating is (D) a number average molecular weight of 1,500 to 2,
5,000, glass transition temperature 0 to 70 ° C, hydroxyl value 8 to
100 mg KOH / g hydroxyl-containing polyester resin 6
0 to 90 parts by weight and (E) melamine resin crosslinking agent 10 to 40
Parts by weight and a clear paint having a film-forming resin component, and the top clear paint film is formed on a top-colored base paint film by a curtain coating method or a die coating method in a wet-on-wet manner. A method for coating a metal plate is provided.

[0007] The present invention also provides a coated metal plate coated by the above coating method.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the method of the present invention will be described in more detail.

The object to be coated in the method of the present invention is a long metal plate used in the field of a precoated steel sheet. Examples of the material include a cold-rolled steel sheet, a galvanized steel sheet, an aluminum sheet and a stainless steel sheet. Can be. Examples of the galvanized steel sheet include hot-dip galvanized steel sheet, electro-galvanized steel sheet, iron-zinc alloy-plated steel sheet, nickel-zinc alloy-plated steel sheet, and aluminum-zinc alloy-plated steel sheet (for example, trade names such as “Galvalume” and “Galphan”). Plated steel sheet). These metal plates may be those whose surfaces have been subjected to a chemical conversion treatment such as a phosphate treatment, a composite oxide film treatment, and a chromate treatment.

In the method of the present invention, a top-coating colored base coating and a top-coat clear coating may be applied directly or via a primer-cured coating on the long metal plate.

The primer-cured coating film can be formed, for example, by applying a primer on a metal plate by a roll coater or the like so as to have a dry film thickness of about 1 to 15 μm, and baking and drying. The primer coating film is formed for the purpose of improving the corrosion resistance of the resulting coated metal plate, improving the adhesion of the coating film, and the like. Examples of the primer include polyester primers and epoxy primers.These primers contain rust preventive pigments such as strontium chromate, calcium chromate, zinc chromate, barium chromate, and zinc phosphate. You may.

The top-colored base paint used in the method of the present invention is:
A paint containing a coloring pigment (C) using a hydroxyl group-containing polyester resin (A) and a crosslinking agent (B) as a film-forming resin component.

Examples of the hydroxyl group-containing polyester resin (A) include oil-free polyester resins, oil-modified alkyd resins, and modified products of these resins, such as urethane-modified polyester resins, urethane-modified alkyd resins, epoxy-modified polyester resins, and acrylic-modified polyester resins. Modified polyester resin and the like can be mentioned.

The oil-free polyester resin comprises an esterified product of a polybasic acid component and a polyhydric alcohol component. As the polybasic acid component, for example, one or more selected from phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic acid, fumaric acid, adipic acid, sebacic acid, maleic anhydride, and the like Dibasic acids and lower alkyl esterified products of these acids are mainly used, and if necessary, monobasic acids such as benzoic acid, crotonic acid, pt-butylbenzoic acid, trimellitic anhydride, methylcyclohexenetricarboxylic acid And tribasic or higher polybasic acids such as pyromellitic anhydride. Examples of the polyhydric alcohol component include ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol,
Dihydric alcohols such as neopentyl glycol, 3-methylpentanediol, 1,4-hexanediol, and 1,6-hexanediol are mainly used, and if necessary, glycerin, trimethylolethane, trimethylolpropane, and pentane. A trihydric or higher polyhydric alcohol such as erythritol can be used in combination. These polyhydric alcohols can be used alone or in combination of two or more. The esterification or transesterification of both components can be carried out by a method known per se. As the acid component, isophthalic acid, terephthalic acid,
And lower alkyl esters of these acids are particularly preferred.

The alkyd resin is obtained by reacting an oil fatty acid by a method known per se in addition to the acid component and the alcohol component of the above-mentioned oil-free polyester resin. Soybean oil fatty acids, linseed oil fatty acids, safflower oil fatty acids, tall oil fatty acids, dehydrated castor oil fatty acids, kiri oil fatty acids and the like can be mentioned. The oil length of the alkyd resin is preferably 30% or less, particularly preferably about 5 to 20%.

As the urethane-modified polyester resin,
The oil-free polyester resin, or a low-molecular-weight oil-free polyester resin obtained by reacting an acid component and an alcohol component used in the production of the oil-free polyester resin, reacts with a polyisocyanate compound by a method known per se. Examples include: Further, the urethane-modified alkyd resin, the alkyd resin, or a low molecular weight alkyd resin obtained by reacting each component used in the production of the alkyd resin was reacted with a polyisocyanate compound by a method known per se. Things are included. Examples of polyisocyanate compounds that can be used when producing urethane-modified polyester resin and urethane-modified alkyd resin include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate,
4,4'-methylenebis (cyclohexyl isocyanate), 2,4,6-triisocyanatotoluene, and the like. In general, as the urethane-modified resin, those having a modification degree in which the amount of the polyisocyanate compound forming the urethane-modified resin is 30% by weight or less based on the urethane-modified resin can be suitably used.

As the epoxy-modified polyester resin,
Using a polyester resin produced from each component used in the production of the above polyester resin, a reaction product of a carboxyl group of this resin and an epoxy group-containing resin, and a hydroxyl group in the polyester resin and a hydroxyl group in the epoxy resin are polyisocyanate. Reaction products such as addition, condensation, and grafting of a polyester resin and an epoxy resin, such as a product bonded via a compound, can be given.
In general, the degree of modification in such an epoxy-modified polyester resin is preferably such that the amount of the epoxy resin is 0.1 to 30% by weight based on the epoxy-modified polyester resin.

As the acrylic-modified polyester resin,
Using a polyester resin produced from each component used in the production of the polyester resin, a group having a reactivity with these groups to a carboxyl group or a hydroxyl group of the resin, such as an acrylic resin containing a carboxyl group, a hydroxyl group or an epoxy group. And a reaction product obtained by graft polymerization of (meth) acrylic acid or (meth) acrylic ester on a polyester resin using a peroxide-based polymerization initiator. The degree of modification in such an acrylic-modified polyester resin is generally
It is preferable that the amount of the acrylic resin is 0.1 to 50% by weight based on the acrylic-modified polyester resin.

Of the hydroxyl group-containing polyester resins described above, oil-free polyester resins are particularly preferred.

The above-mentioned hydroxyl-containing polyester resin (A)
Has a number average molecular weight of 1,500 to 35,000, preferably 3,000 to 25,000, and a glass transition temperature (Tg).
Point) -30 to 60 ° C, preferably -20 to 35 ° C, hydroxyl value 3 to 100 mgKOH / g, preferably 8 to 70
mg KOH / g. The number average molecular weight is 1,5
When it is less than 00, the processability of the coating film is reduced.
If it exceeds 000, the viscosity becomes high and handling becomes difficult.
When the Tg point is lower than −30 ° C., the hardness of the coating film decreases, while when it exceeds 60 ° C., the processability of the coating film decreases. Further, when the hydroxyl value is less than 3 mgKOH / g, the curability of the coating film is reduced, while 100 mgKOH / g
If it exceeds 300, the processability of the coating film will decrease.

In the present invention, the glass transition temperature (Tg)
Is measured by differential thermal analysis (DTA), and the number average molecular weight is measured by gel permeation chromatography (GPC) using a standard polystyrene calibration curve.

The cross-linking agent (B) constituting the top-coating colored base coating has a function of reacting with the above-mentioned hydroxyl-containing polyester resin (A) to cross-link. Crosslinking agent (B)
Is at least one selected from a melamine resin and a blocked polyisocyanate compound.

Examples of the melamine resin include a methylolated amino resin obtained by reacting melamine with an aldehyde. Examples of the aldehyde used in the above reaction include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde and the like. Further, those obtained by etherifying the above methylolated amino resin with an appropriate alcohol can also be used as the melamine resin. Examples of alcohols used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethylbutanol,
2-ethylhexanol and the like.

The blocked polyisocyanate compound is a compound obtained by blocking free isocyanate groups of a polyisocyanate compound with a blocking agent.

Examples of the polyisocyanate compound before blocking include aliphatic diisocyanates such as hexamethylene diisocyanate or trimethylhexamethylene diisocyanate; cycloaliphatic diisocyanates such as hydrogenated xylylene diisocyanate or isophorone diisocyanate; tolylene diisocyanate Or an organic diisocyanate itself such as an aromatic diisocyanate such as 4,4'-diphenylmethane diisocyanate, or an adduct of each of these organic diisocyanates with a polyhydric alcohol, a low molecular weight polyester resin or water; Cyclic polymers among diisocyanates, and isocyanate / biuret compounds are also included.

Examples of the blocking agent for blocking the isocyanate group include phenols such as phenol, cresol and xylenol; ε-caprolactam;
Lactams such as valerolactam, γ-butyrolactam, β-propiolactam; methanol, ethanol, n-
Or i-propyl alcohol, n-, i- or t-butyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether,
Alcohols such as benzyl alcohol; oximes such as formamidoxime, acetoaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime; dimethyl malonate, diethyl malonate, ethyl acetoacetate, ethyl acetoacetate, methyl acetoacetate, acetylacetone A blocking agent such as an active methylene type can be suitably used.

The free isocyanate group of the polyisocyanate compound can be easily blocked by mixing the polyisocyanate compound with the blocking agent.

The crosslinking agent (B) may be composed of one kind of crosslinking agent, or may be a mixture of two or more kinds of crosslinking agents.

The mixing ratio of the hydroxyl group-containing polyester resin (A) and the crosslinking agent (B) in the top coating base paint is as follows:
The following range is based on 100 parts by weight of the total solid content of the hydroxyl group-containing polyester resin (A) and the crosslinking agent (B). Resin (A): 60 to 95 parts by weight, preferably 70 to 9 parts
0 parts by weight, crosslinking agent (B): 5 to 40 parts by weight, preferably 10 to 30 parts
Parts by weight.

If the amount of the resin (A) is less than 60 parts by weight (the amount of the crosslinking agent (B) exceeds 40 parts by weight), the processability of the coating film is reduced, while the resin (A) The amount of
When the amount exceeds 95 parts by weight [the amount of the crosslinking agent (B) is less than 5 parts by weight], the curability of the coating film is reduced.

The top coating base paint contains a coloring pigment (C) as an essential component in addition to the above-mentioned hydroxyl group-containing polyester resin (A) and a crosslinking agent (B), and usually further contains a solvent.

Examples of the color pigment (C) include color pigments generally used in the field of paints, for example, white pigments such as titanium white and zinc white; blue pigments such as cyanine blue and indathrene blue; cyanine green and patina. Organic pigments such as azo and quinacridone, and red pigments such as bengara; organic yellow pigments such as benzimidazolone, isoindolinone, isoindoline, and quinophthalone; titanium yellow; Yellow pigments; black pigments such as carbon black, graphite, and pine smoke; and glitter pigments such as aluminum powder, copper powder, nickel powder, mica powder coated with titanium oxide, mica powder coated with iron oxide, and glitter graphite. The compounding amount of the color pigment is not particularly limited as long as it is in a range in which good cosmetics can be exhibited, and is usually based on 100 parts by weight of the total film-forming resin component of the base resin and the crosslinking agent. It is used in the range of 1 to 120 parts by weight.

[0033] The solvent to be mixed with the top-colored base paint is
It is blended as needed to improve the paintability, etc., and can use those capable of dissolving or dispersing the above film-forming resin component. Specifically, for example, toluene, xylene, high-boiling petroleum-based carbon Hydrocarbon-based solvents such as hydrogen, ketone-based solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; ester-based solvents such as ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate and diethylene glycol monoethyl ether acetate; methanol and ethanol Alcohol solvents such as butanol, ether glycol solvents such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether and diethylene glycol monobutyl ether, and water. It may be used alone or in combination of two or more.

The top-colored base paint may further comprise, if necessary, a curing catalyst; extender pigments such as talc, clay, silica, mica, and alumina; strontium chromate, calcium chromate, zinc chromate, barium chromate, zinc phosphate. Rust-preventive pigments such as anti-foaming agents and additives known per se for paints, such as antifoaming agents and coating surface conditioners.

The above-mentioned curing catalyst is blended as required in order to accelerate the curing reaction between the hydroxyl group-containing polyester resin (A) and the crosslinking agent (B), and depends on the type of the crosslinking agent (B). It can be appropriately selected and used.

When the crosslinking agent (B) is a melamine resin, particularly a low molecular weight melamine resin of methyl etherification or a mixed etherification of methyl ether and butyl ether, an acid catalyst such as a sulfonic acid compound is used as a curing catalyst. Alternatively, amine neutralized sulfonic acid compounds are preferably used. Representative examples of the sulfonic acid compound include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid. The amine in the amine-neutralized sulfonic acid compound may be any of a primary amine, a secondary amine and a tertiary amine. Among them, an amine neutralized product of p-toluenesulfonic acid and / or an amine neutralized product of dodecylbenzenesulfonic acid are preferable from the viewpoint of the stability of the coating material, the effect of accelerating the reaction, and the properties of the obtained coating film.

When the crosslinking agent (B) is a blocked polyisocyanate compound, a curing catalyst which promotes the dissociation of the blocking agent of the blocked polyisocyanate compound is suitable. As a suitable curing catalyst, for example, octyl Acid tin, dibutyltin di (2-ethylhexanoate),
Examples thereof include organometallic catalysts such as dioctyltin di (2-ethylhexanoate), dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide, and lead 2-ethylhexanoate.

The topcoat clear coating to be used in the topcoat clear coating method of this invention are coating the paint film is formed by wet-on-wet onto the topcoat colored base coating paint film, forming a top layer clear coating film layer Is what you do.

The top clear paint is a thermosetting top clear paint containing a hydroxyl group-containing polyester resin (D) and a melamine resin crosslinking agent (E) as essential components.

The polyester resin (D) has a number average molecular weight of 1,500 to 25,000, preferably 5,000 to 2
000, glass transition temperature (Tg point) 0 to 70 ° C, preferably 10 ° C to 60 ° C, hydroxyl value 8 to 100 mg KO
It is a polyester resin having H / g, preferably 15 to 60 mgKOH / g. The number average molecular weight is 1,5
When it is less than 00, the processability of the coating film is reduced.
If it exceeds 000, the solid content of the paint at the time of coating becomes small, and the coating workability is reduced. Further, when the Tg point is less than 0 ° C., the hardness of the coating film decreases and the surface is easily scratched,
On the other hand, when the temperature exceeds 70 ° C., the processability of the coating film deteriorates. Further, when the hydroxyl value is less than 8 mgKOH / g, the curability of the coating film is reduced and the surface is easily scratched.
If it exceeds mgKOH / g, the processability of the coating film will decrease.

The hydroxyl group-containing polyester resin (D) can be obtained by using the same raw materials and method as in the production of the polyester resin (A) which is the base resin of the above-mentioned top coating base paint. Among the polyester resins, preferred are oil-free polyester resins.

The melamine resin cross-linking agent (E) in the top clear coating composition has a function of reacting with the hydroxyl group-containing polyester resin (D) to cross-link.
The melamine resin described as one of the cross-linking agents (B) in the top coating base paint is suitably used. As a melamine resin crosslinking agent (E), when a coating film having excellent smoothness is to be formed, it is advantageous to use a butyl etherified melamine resin from the viewpoint of heat fluidity.

The blend ratio of the hydroxyl group-containing polyester resin (D) and the melamine resin crosslinking agent (E) in the top clear coating composition is the sum of the hydroxyl group-containing polyester resin (D) and the melamine resin crosslinking agent (E). The range is as follows with respect to 100 parts by weight of the forming resin component (total solid content). Resin (A): 50 to 90 parts by weight, preferably 65 to 8 parts
5 parts by weight, crosslinking agent (B): 10 to 50 parts by weight, preferably 15 to 3 parts
5 parts by weight.

If the amount of the resin (A) is less than 50 parts by weight (the amount of the crosslinking agent (B) exceeds 50 parts by weight), the processability of the coating film is reduced, while the resin (A) The amount of
When the amount exceeds 90 parts by weight (the amount of the crosslinking agent (B) is less than 10 parts by weight), the curability of the coating film decreases, and the scratch resistance of the coating film surface decreases.

In the clear topcoat paint, as the melamine resin crosslinker (E), a melamine resin crosslinker containing at least 80% by weight of a methyletherified or mixed etherified melamine resin of methyl ether and butyl ether is used. The sulfonic acid compound or a neutralized sulfonic acid compound as a curing catalyst (F) is used in an amount of 0.1 to 2 in terms of the amount of the sulfonic acid compound per 100 parts by weight of the coating film-forming resin component of the paint. 0.0 parts by weight and (G) boiling point 3
Secondary or tertiary amine compound at 0 to 250 ° C 0.1 to 10
By including the parts by weight, a uniform shrinkage pattern can be formed on the surface of the clear top coat at the time of baking and curing.

As the melamine resin crosslinking agent (E),
80% by weight of a total of at least one melamine resin selected from a methyl etherified melamine resin and a mixed etherified melamine resin of methyl ether and butyl ether
As described above, the melamine resin containing preferably 90% by weight or more, that is, a methyl etherified melamine resin and a mixed etherified melamine resin of methyl ether and butyl ether in a total of 80% by weight in the melamine resin crosslinking agent (E).
As described above, the melamine resin preferably contains 90% by weight or more, and among them, it is preferable that the melamine resin is composed of a methyl etherified melamine resin.

In the melamine resin crosslinking agent (E),
The melamine resin other than the methyl etherified melamine resin and the mixed etherified melamine resin of methyl ether and butyl ether, which may be contained in an amount of 20% by weight or less, preferably 10% by weight or less, includes methyl ether. A non-esterified melamine resin is exemplified, and a representative example is a butyl etherified melamine resin.

Specific examples of the melamine resin include Cymel 300, 303, 325, 327, 350, 730, 736, and 738 (all of which are manufactured by Mitsui Cytec Co., Ltd.), and melan. 522, 523
[These are all manufactured by Hitachi Chemical Co., Ltd.], Nicaraq MS
001, MX430, and MX650 (all manufactured by Sanwa Chemical Co., Ltd.), Sumimar M-55, and M-M
100 and M-40S [all of which are Sumitomo Chemical Co., Ltd.]
Melamine resins such as Resin 740 and 747 [all of which are manufactured by Monsanto]; Cymel 232, 266, XV-514, 1130.
[The above are all manufactured by Mitsui Cytec Co., Ltd.], Nikarac MX500, MX600, MS35, MS95
[These are all manufactured by Sanwa Chemical Co., Ltd.], Regimin 7
Mixed etherified melamine resin of methyl ether and butyl ether such as 53, 755 [all, manufactured by Monsanto Co., Ltd.] and Sumimar M-66B [Sumitomo Chemical Co., Ltd.]; Uban 20SE, 225 [all, all] Mitsui Toatsu Co., Ltd.], Super Beckamine J820-6
0, L-117-60, L-109-65, 47
-508-60, L-118-60, G821-6
And a butyl etherified melamine resin such as 0 [all manufactured by Dainippon Ink and Chemicals, Inc.].

The curing catalyst (F) is blended to promote a crosslinking reaction between the hydroxyl group-containing polyester resin (D) and the melamine resin crosslinking agent (E). And the amine-neutralized sulfonic acid compound as the curing catalyst described in the above. The amount of the curing catalyst was converted into the amount of the acid in the curing catalyst, for example, in the case of an amine neutralized sulfonic acid compound, the amount of the sulfonic acid compound with respect to 100 parts by weight of the film-forming resin component. 0.1 to 2.
0 parts by weight, preferably 0.2 to 1.5 parts by weight.

The amine compound (G) is compounded to cause shrinkage on the surface of the clear top coat,
Secondary or tertiary amines having a boiling point of 30 to 250 ° C. are preferably used. Representative examples of the amine compound (G) include diethylamine, diisopropylamine, di-n-propylamine, diallylamine, diamylamine, di-n-butylamine, diisobleamine, disec-butylamine, N
-Ethyl-1,2-dimethylpropylamine, N-methylhexylamine, di-n-octylamine, piperidine, 2-pipecoline, 3-pipecoline, 4-pipecoline, 2,4-, 2,6- or 3,5 -Lupetidine, 3-
Secondary amines such as piperidine methanol; triethylamine, tributylamine, triallylamine, N-methyldiallylamine, N-methylmorpholine, N, N,
N ′, N′-tetramethyl-1,2-diaminoethane,
Tertiary amines such as N-methylpiperidine, pyridine and 4-ethylpyridine; secondary amines such as N-methylpiperazine
One or two such as amines having primary and tertiary amino groups
Mixtures of more than one species. Of these, dialkylamines, particularly diisopropylamine, di-n-propylamine, di-n-butylamine, diisobleamine, and the like are preferable because of their low odor and their ability to form beautiful uniform shrinkage.

The amount of the amine compound (G) is 0.1 to 10 parts by weight, preferably 0.3 to 5 parts by weight, based on 100 parts by weight of the film-forming resin component. In particular, when the amine compound (H) is a tertiary amine, the amine used for neutralizing the acid in the curing catalyst and the amine compound (G) are reacted with 1 mol of the acid in the curing catalyst. It is preferred that the total amount of the amine is in the range of 1.1 to 30 mol,
When the amine compound (G) is a secondary amine, the amine of the amine compound and the amine compound (G) used for neutralization of the acid in the curing catalyst is used per mole of the acid in the curing catalyst. It is preferred that the total amount is in the range from 1.5 to 30 mol.

The clear top coating contains a hydroxyl group-containing resin (D) and a melamine resin crosslinking agent (E) as essential components, and, if necessary, contains a curing catalyst and an amine compound. Accordingly, it may contain a solvent, a glitter powder, a lubricity-imparting agent, an ultraviolet absorber, an ultraviolet stabilizer, an antifoaming agent, a coating surface adjuster, and inorganic fine powder such as silica fine powder.

As the solvent, those capable of dissolving or dispersing coating components such as a base resin and a crosslinking agent can be used. For example, the solvents described in the above-mentioned top coating base paint can also be used.

Examples of the glittering powder to be added to the top clear paint as required include aluminum powder, copper powder, nickel powder, mica powder coated with titanium oxide, mica powder coated with iron oxide, and glittering graphite. . By adding a glitter powder, a glitter can be imparted to the coating film. When the glittering powder is blended, the blending amount may be any amount that gives the glittering appearance to the coated surface and is within the range in which the topcoating colored base coating film can be seen through the topcoating clear coating film. The amount is preferably in the range of 0.005 to 30 parts by weight, more preferably in the range of 0.4 to 10 parts by weight, based on 100 parts by weight of the film-forming resin component in the paint.

As the lubricity-imparting agent, those which can impart lubricity to the surface of the clear top coat without deteriorating the appearance of the coated surface can be used. For example, polyethylene wax, silicone oil, modified silicone oil, paraffin wax,
Examples include petroleum waxes, montan waxes, lanolin waxes, fatty acid sucrose ester waxes, and fatty acid ester waxes such as esters of polyglycerin and fatty acids. The amount of the lubricity-imparting agent to be blended is usually preferably within the range of 0.1 to 10 parts by weight based on 100 parts by weight of the film-forming resin component in the top clear paint.

Examples of the ultraviolet absorber include benzophenones such as 2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone; 2- (2 ′
Examples thereof include benzotriazole-based ultraviolet absorbers such as -hydroxy-5-methylphenyl) benzotriazole. Examples of the ultraviolet stabilizer include a hindered amine-based ultraviolet stabilizer. It is generally preferable that the blending amount of the ultraviolet absorber and the ultraviolet stabilizer is usually 5 parts by weight or less based on 100 parts by weight of the film-forming resin component in the top clear coating composition.

In the coating method of the present invention, in the coating method of the present invention, the top-coating colored base paint and the top-coat clear paint are applied to the continuously moving long metal plate with or without a primer-cured coating film. Painting and baking to form a topcoat colored basecoat and topcoat clearcoat.

In the method of the present invention, baking is performed after the top-coating colored base coating film and the top-coat clear coating film are coated so as to be in contact with each other on a wet-on-wet basis. As a method in which the top-coating colored base coating film and the top-coating clear coating film can be applied so as to be in contact with each other on a wet-on-wet basis, there is a method of coating a top-coating colored base coating film formed on a workpiece by a coating machine such as a roll coater or a roller curtain. A coating method in which a top coat clear paint is formed into a curtain shape by roller curtain coating or slit type curtain coating, a top coat colored base paint layer and a top coat clear paint layer are superposed in two layers, and discharged from a die. An example of the coating method is a die coating method in which two layers, a top coating base coating layer and a top coating clear coating layer, are simultaneously formed on the coating.

Here, the coating method by roller curtain coating is a method in which a coating film formed on a rotating roll is scraped off by a doctor, and the coating film is dropped on a moving object to be coated in a curtain shape and coated. It is. As the roller curtain coating machine, for example, the coating machines described in JP-A-6-7724 and JP-A-6-134385 can be used.

The coating method using the slit type curtain coating is a method in which the coating material is dropped from an elongated slit onto a moving object to be coated in a curtain shape to perform coating.

Further, as a die coating machine which can be used in the above-mentioned die coating method, for example, a die coating machine described in Japanese Patent Application Laid-Open No. 4-100570 can be mentioned. FIG. 1 is a conceptual sectional view of a representative example of a die in a die coating machine.
In FIG. 1, a die 1 is composed of three blades in which an upper blade 2, a middle blade 3 and a lower blade 4 are superimposed, and side plates (not shown) on both sides. The upper blade 2 and the lower blade 4 are provided with paint holding parts 5 and 6, respectively, and paint supply ports 7 and 8 for supplying paint to the paint holding parts. The gap between the upper blade 2 and the middle blade 3 and the gap between the lower blade 4 and the middle blade 3 form slots 9 and 10, respectively. The upper and lower intervals of each slot define the thickness of the paint passing through the slot,
Usually, in the range of 5 to 500 µm, preferably 10 to 120 µm, the paint is set so that the pressure loss of the paint in the slot does not become too large and the paint flows at a uniform flow rate over the entire width of the slot.

The intersection angle a between the slots 9 and 10 is an acute angle, usually 30 degrees or less, so that the upper paint flowing through the slot 9 and the lower paint flowing through the slot 10 smoothly merge to form an overlapping paint layer. In particular, it is preferable to be within the range of 5 to 25 degrees. The tip of the middle blade 3 does not need to be a knife edge.

It is preferable that the slots 9 and 10 join together inside the die as shown in FIG. 1 to form a single slot 11, but they may be independently opened to the outside. The die is provided with a mechanism for supporting the die 1 and adjusting the positions of the lips 12 and 13 of the die, a mechanism for supplying a constant amount of paint to the die, and the like, which are shown in FIG. Absent.

In the die coating method, the paint discharged from the die may be applied directly onto the object to be coated, or may be once received by a rotating roll and then applied to the object from the rotating roll. FIG. 2 shows an example of an apparatus in a case where the paint discharged from the die is directly applied to the object to be coated in FIG. 2, in which the object to be coated 15 is supported by a rotating support roll 14, The slit of the die is arranged perpendicular to the object 15, that is, toward the center of the support roll 14.

When coating is performed using the apparatus shown in FIG.
The lower layer paint is supplied from the paint supply port 8 and the upper layer paint is supplied from the paint supply port 7 to the die by the metering pump according to the application amount while the article 15 is traveling in the direction of the arrow. The paint flows into the paint holding units 5 and 6, flows through the slots 9 and 10, merges in a layer at the slots 11, and is discharged. The paint discharged in two layers adheres uniformly to the object 15 while maintaining the layered state, and forms a coating film having a predetermined thickness.

In the method of the present invention, the thickness of the overcoated base paint film to be formed is not particularly limited, but is usually preferably in the range of 5 to 25 μm in dry film thickness. The thickness of the overcoating clear paint film to be formed is not particularly limited, but is usually preferably in the range of 5 to 25 μm in dry film thickness.

In the coating method in which the top clear coating material is formed into a curtain on the top coating base paint film, the viscosity is 40 to 150 seconds (Ford cup # 4, 2).
(Measurement at 5 ° C., viscosity is measured in the same manner as described below.) It is preferable to apply a topcoat clear paint having a viscosity of 50 to 250 seconds on the topcoat base paint film.

In the above-mentioned coating method using a die coater, it is preferable that a top coating base coating film having a viscosity of 40 to 250 seconds and a top coating clear coating film having a viscosity of 50 to 250 are superposed and discharged from the die.

The conditions for curing the two paint layers, the top paint base paint layer and the top clear paint layer, can be appropriately selected from the baking conditions under which the two paints are cured. Maximum temperature (PMT) 1 at 160-250 ° C
Conditions within the range of 5 to 180 seconds, particularly within the range of 20 to 120 seconds at a PMT of 180 to 230 ° C are suitable.

[0070]

The present invention will be described more specifically with reference to the following examples. Hereinafter, “parts” and “%” are based on weight.

Manufacturing Examples 1 to 12 of Top Coated Base Coatings Coatings were prepared according to the composition shown in Table 1 below to obtain top coating base paints.

The amounts of the polyester resin and the cross-linking agent in Table 1 are indicated by the weight of the solid content.
For the sulfonic acid-based curing catalyst, the amount was converted to the amount of the sulfonic acid compound, and for the organotin-based curing catalyst, the amount was converted to the amount of the organic tin compound, and the weight was expressed. In addition, when making the top-colored base paint in the production example,
After dispersing -95 (Ishihara Sangyo Co., Ltd., titanium white pigment), carbon black and red red iron oxide, the mixture was mixed with the remaining components such as organic resin fine particles and uniformly stirred to form a coating. In addition, cyclohexanone / solvesso 150
("Solvesso 150" is an aromatic petroleum-based high-boiling solvent manufactured by Esso Oil Co., Ltd.) = 40/60 (weight ratio) mixed solvent is used for adjusting the viscosity of the paint, etc. Was adjusted to 90 seconds (Ford Cup # 4, 25 ° C.). The top-colored base paints obtained in Production Examples 11 and 12 are comparative paints.

[0073]

[Table 1]

(Note) in Table 1 has the following meanings, respectively.

The polyester resins (* 1) to (* 6) in Table 1 are all polyester resins manufactured by Toyobo Co., Ltd., and have the property values shown in Table 2 below.

[0076]

[Table 2]

(* 7) Cymel 303: manufactured by Mitsui Cytec Co., Ltd., having a low molecular weight methyl etherified melamine resin and a content of hexakis (methoxymethyl) melamine of 60% by weight or more. (* 8) Super Beckamine J-820-60: n-butyl etherified melamine resin solution manufactured by Dainippon Ink and Chemicals, Inc. (* 9) Desmodur BL-3175: a blocked polyisocyanate compound manufactured by Sumitomo Bayer Urethane Co., Ltd.

(* 10) Nail Cure 5225: a solution of equimolar neutralized secondary amine of dodecylbenzenesulfonic acid, manufactured by King Industries, USA, curing catalyst. (* 11) Formate TK-1: Takeda Pharmaceutical Company Limited
Catalyst, dissociation catalyst for blocked polyisocyanate compounds, which is an organic tin solution manufactured by Aztec.

Production Examples 13 to 34 of Top Coated Clear Coatings Coatings were prepared according to the composition shown in Table 3 below to obtain respective top coated clear coatings.

In Table 3, the amounts of the base resin and the cross-linking agent are indicated by the weight of solid content, and the amount of the curing catalyst is expressed by weight in terms of the amount of the sulfonic acid compound for the sulfonic acid-based curing catalyst. Cyclohexanone / Solvesso 1
50 ("Solvesso 150" is manufactured by Esso Oil Co., Ltd.)
A mixed solvent of aromatic petroleum-based high-boiling point solvent = 40/60 (weight ratio) is used for adjusting the viscosity of the paint, etc., and the viscosity of the clear top paint is 110 seconds (Ford Cup # 4, 25 ° C.)
Was adjusted.

[0081]

[Table 3]

[0082]

[Table 4]

In (Note) in Table 3, (* 1), (*
3), (* 6), (* 7), (* 8) and (* 10)
Has the same meaning as above. The other notes in Table 3 have the following meanings.

(* 12) Byron KS-1830V: a polyester resin manufactured by Toyobo Co., Ltd., trade name, having a number average molecular weight of 14,000, a Tg point of 45 ° C., and a hydroxyl value of 12 mg KOH / g. (* 13) Resimin 755: a mixed etherified melamine resin of methyl ether and butyl ether, manufactured by Monsanto Co., trade name.

(* 14) Aluminum paste MR-900
0: Asahi Kasei Metals Corporation, trade name “Asahi Kasei Aluminum Paste MR-9000”, brilliant aluminum fine powder having an average particle diameter of about 10 μm. (* 15) Aluminum paste MC-666: manufactured by Asahi Kasei Metals Corporation, trade name "Asahi Kasei Aluminum Paste MC-66"
6 ", a brilliant aluminum fine powder having an average particle size of about 20 µm. (* 16) Iriodin 225R: manufactured by Merck Japan, rutile-type titanium oxide-coated mica fine powder, particle size about 1
0-40 μm, nacreous blue. (* 17) Iriodin 103R: manufactured by Merck Japan Co., Ltd., rutile-type titanium oxide-coated mica fine powder, particle size about 1
0-40 μm, silver white.

Examples 1 to 58 and Comparative Examples 1 to 8 Preparation of Test Coated Plates Method of preparing test coated plates (1): Examples 1 to 29 and Comparative Examples 1 to 4 KP color 863 manufactured by Kansai Paint Co., Ltd. on galvanized steel sheet
0 primer (epoxy-modified polyester primer for pre-coated steel sheet, Tg point of the coating film is 52 ° C.) so that the dry film thickness is about 4 μm,
C. for 30 seconds to obtain a primer-coated steel sheet. On this primer-coated steel sheet, each of the overcoated colored base paints obtained in Production Examples 1 to 12 was applied so that the dry film thickness was about 14 μm, and on the uncured coating film of these overcoated colored base paints, The clear top coatings obtained in the above Production Examples 13 to 34 were applied by a roller curtain coating method so as to have a dry film thickness of about 10 μm using the combinations shown in Table 4 below. Subsequently, each of the steel sheets was baked for 70 seconds so that the maximum temperature of the material reached 235 ° C. to obtain each overcoated steel sheet. The viscosity (measured at a measuring temperature of 25 ° C. in a Ford cup # 4 at a measuring temperature of 25 ° C. and the viscosity is measured in the same manner as described above) of the top-coating colored base coating layer immediately before the top-coat clear coating is applied is 100 seconds, and the top-coat clear coating is applied. Had a viscosity of 110 seconds.

In Example 18, the coating was performed by using the above-mentioned hot-dip galvanized steel sheet without the primer instead of the primer-coated steel sheet. In Example 19, the top clear paint was applied by a slit curtain coating method instead of the roller curtain coating method.

Preparation Method of Test Coated Plate (2): Examples 30 to
58 and Comparative Examples 5 to 8 On the same primer-coated steel sheet as used in the method (1) for preparing the test coated plate, the overcoated base paints obtained in the above Production Examples 1 to 12 and the above-mentioned Production Examples 13 to 34 The resulting clear top coating was applied in a combination shown in Table 5 below by a die coating method and extruded from a die in two layers so that the primer coating faced the top coating base coating film.

The coating film thickness of each paint was such that the dry color base paint layer had a dry film thickness of about 14 μm and the clear paint layer had a dry film thickness of about 7 μm. The viscosity of the paint extruded from the die was 90 seconds for the top colored base paint and 110 seconds for the top clear paint. After the coating, each of the coated steel sheets was baked for 70 seconds so that the maximum temperature of the material reached 220 ° C.

Various tests were performed on the obtained coated steel sheet. The test results are shown in Tables 4 and 5 below.

[0091]

[Table 5]

[0092]

[Table 6]

[0093]

[Table 7]

[0094]

[Table 8]

The tests in Tables 4 and 5 were performed according to the following test methods.

Test Method Brightness of coated surface: The coated surface was observed at an angle of regular reflection under direct sunlight and the glitter was evaluated according to the following criteria. ◎: Glittering and uniform shining throughout-: Glittering shine is not recognized.

Feeling of shrinkage of painted surface: The painted surface was observed with a magnifying glass of 30 times, and the degree of shrinking pattern was evaluated. A: A uniform and clear shrinkage pattern is observed on the coated surface. O: A uniform shrinkage pattern is observed on the coated surface, but the shrinkage pattern is not remarkable.-: No shrinkage pattern is observed on the coated surface.

Pencil hardness: Regarding the coating film of the coated plate, JIS
A pencil scratch test specified in K-5400 8.4.2 (1990) was performed, and evaluation by tearing of the coating film was performed.

Bending workability: In a room at 20 ° C., the test plate was bent 180 ° with the painted surface outside, and the T number at which no cracks occurred in the bent portion was visually evaluated and indicated. The T number is 1 without anything inside the bend.
The case where 80 ° bending was performed was set to 0T, the case where one plate having the same thickness as the test plate was sandwiched was bent to 1T, the case of two sheets was set to 2T,...

Solvent resistance: In a room at 20 ° C., about 1 kg was applied to the painted surface with gauze impregnated with methyl ethyl ketone.
/ Cm ² was applied and reciprocated for a length of about 5 cm, and the number of reciprocations until the primer coating film was visible was recorded.
Those in which the primer coating film was not visible after 50 reciprocations were indicated as 50 <. The greater the number, the better the curability of the coating film.

Adhesion: JIS K-5400 8.5.
2 (1990) According to the crosscut-tape method, 11 parallel vertical and horizontal straight lines are drawn at 1 mm intervals on the surface of the coating film of the test plate so as to reach the substrate with a cutter knife, and the distance is 1 mm. 100 × 1 mm squares were created. A cellophane adhesive tape was adhered to the surface, and the degree of peeling of the squares when the tape was abruptly peeled was observed and evaluated according to the following criteria. ：: No peeling of the coating film was observed at all. ○: The coating film was slightly peeled, but 90 or more squares remained. Δ: The coating film was peeled, and the number of remaining squares was 50 or more and 90.
Less than pieces.

×: The coating film was peeled off, and the number of remaining squares was less than 50.

[0103]

According to the coating method of the present invention, a top coating base coating film and a top coating clear coating film are formed on a long object to be moved continuously by wet-on-wet, and then both coating films are simultaneously formed. Because of baking and hardening, a larger number of coating layers can be formed without increasing the number of times of baking as compared with the related art. According to the coating method of the present invention, a coating film excellent in coating film performance and cosmetics can be formed.

[Brief description of the drawings]

FIG. 1 is a conceptual sectional view showing an example of a die of a die coating machine used in the present invention.

FIG. 2 is a diagram showing an example of a positional relationship between a die coating machine and a workpiece when a coating material is applied in two layers in the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Die 2 Upper blade of die 3 Middle blade of die 4 Lower blade of die 5, 6 Paint holding part of die 7, 8 Paint supply port to die 9, 10, 11 Slot of die 12, 13 Lip of die 14 Support Roll 15 substrate

Claims (4)

[Claims] 1. A top-coating base paint and a top-coat clear coating containing a color pigment are applied to a continuously moving long metal plate with or without a primer-cured coating film, and baked. A method of forming a topcoat clear coating film on a topcoat coloring base coating film, wherein the topcoat coloring base coating material comprises (A)
Number average molecular weight 1,500-35,000, glass transition temperature -30-60 ° C, hydroxyl value 3-100 mgKOH / g
A hydroxyl group-containing polyester resin of 60 to 95 parts by weight, and (B) at least one kind of crosslinking agent selected from a melamine resin and a blocked polyisocyanate compound in an amount of 5 to 40 parts by weight as a film-forming resin component, and (C) coloring A paint containing a pigment, and the top clear paint is (D) a number average molecular weight of 1,500 to 25,000 and a glass transition temperature of 0.
A clear coating composition comprising 50 to 90 parts by weight of a hydroxyl group-containing polyester resin having a hydroxyl value of 8 to 100 mgKOH / g and 10 to 50 parts by weight of a (E) melamine resin crosslinking agent, In addition, the method for coating a metal sheet is characterized in that the top clear coating film is formed on the top colored base coating film by a curtain coating method or a die coating method on a wet basis. 2. The melamine resin cross-linking agent (E) in the top clear coating composition is a methyl etherified or mixed etherified melamine resin of methyl ether and butyl ether.
A melamine resin crosslinking agent containing at least 100% by weight, based on 100 parts by weight of a film-forming resin component of a top clear paint.
(F) As a curing catalyst, 0.1 to 2.0 parts by weight of a sulfonic acid compound or a neutralized sulfonic acid compound in terms of the amount of the sulfonic acid compound, and (G) a boiling point of 30 to 250.
The coating method according to claim 1, wherein the coating composition contains 0.1 to 10 parts by weight of a secondary or tertiary amine compound at a temperature of 0.1 ° C. 3. The top coat clear coating composition further comprises (H) glitter powder 0.0100 parts by weight based on 100 parts by weight of the film-forming resin component.
The coating method according to claim 1 or 2, wherein the coating method contains 0.5 to 30 parts by weight. 4. A coated metal plate coated by the coating method according to claim 1.