JPH1190322A - Coating of metal sheet and coated metal sheet excellent in scratching resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent adhesion property between layers by applying a specified overcoat base coating material and a specified overcoat clear coating material in a wet-on-wet process and baking. SOLUTION: An overcoat clear coating material is applied and baked on a primer hardened coating film on a long-length metal sheet to form an overcoat clear coating film on the overcoat color base coating film. The film forming resin component of the overcoat color base coating material consists of 60 to 95 pts.wt. hydroxyl group-contg. polyester resin and 5 to 40 pts.wt. crosslinking agent such as melamine resin. The film forming resin component of the overcoat clear coating material consists of 55 to 90 pts.wt. hydroxyl group-contg. org. resin having -20 to 80 deg.C glass transition temp. and 10 to 45 pts.wt. crosslinking agent such as melamine resin. The overcoat clear coating material contains 1 to 20 pts.wt. org. resin powder comprising org. resin particles of 5 to 80 μm average particle size or particles having 2 to 50 μm average diameter, 30 to 5000 μm length and 1/2 to 1/100 diameter to length ratio to 100 pts.wt. of the film forming resin component. The hardened coating film formed has 150 to 700 mol.wt. of inter crosslink molecules.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a metal plate capable of forming a multi-layer coating film having excellent scratch resistance and excellent adhesion between two top coating films on a continuously moving long metal plate. The present invention relates to a coating method and a coated metal plate coated by the method.

[0002]

2. Description of the Related Art
A pre-coated steel sheet for object processing or building material coated by continuous coating such as coil coating or the like may be abbreviated as a 2 coat 2 bake (undercoat-bake-overcoat-bake) method (hereinafter, "2C2B"). ) Is the mainstream, and 3 coats and 3 bake (undercoating-baking-intermediate coating or topcoat base coating-baking-topcoat or clearcoat-baking) for the purpose of improving the aesthetics of the painted surface and improving the coating film performance (Hereinafter, may be abbreviated as "3C3B") in some cases. In the field of precoated steel sheets,
A two-coat one-bake method (hereinafter sometimes abbreviated as “2C1B”) or a three-coat two-bake method (hereinafter “3C2B”)
B) may not be used at present.

[0003] When performing 3C3B, there is a problem that the number of times of coating and the number of times of baking of the coating film are each one more than that of 2C2B, thereby increasing the burden on equipment. There is also a problem that the occupied area of the equipment is greatly increased. Further, since a precoated steel sheet is generally cut and formed, it is necessary to achieve both workability and scratch resistance. In a coated steel sheet coated with 3C3B, if the glass transition temperature of the coating resin is increased or the crosslinking density of the coating is increased in order to improve the scratch resistance,
There is a problem that the adhesion between the layers of the top coat base coat and the top coat clear coat is reduced. Further, there is a problem that the scratch is generally conspicuous in the clear top coat layer.

[0004] It is an object of the present invention to provide a two-layer top coat having good adhesion between the top coat base coat and the clear top coat, excellent aesthetics of the coated surface, excellent workability and scratch resistance. Is obtained in a method with a small burden on facilities.

The present inventors used a specific top coat base paint and a specific top coat clear paint containing an organic resin powder,
The inventors have found that the above object can be achieved by applying a topcoat base coating film and a topcoat clear coating film in a wet-on-wet manner and baking them, and have completed the present invention.

[0006]

That is, the present invention provides a method for applying a top-coating colored base coating and a top-coating clear coating on a continuously moving long metal plate with or without a primer-cured coating film. And baking to form a topcoat clear coating on the topcoat basecoat, wherein the topcoat clearcoat is formed wet-on-wet on the topcoat basecoat and the topcoat The film-forming resin component of the base paint is (A) a hydroxyl group-containing polyester resin 6
0 to 95 parts by weight and (B) 5 to 40 parts by weight of at least one crosslinking agent selected from a melamine resin and a blocked polyisocyanate compound, and the film-forming resin component of the top clear coating composition comprises (C) Glass transition temperature -2
55 to 90 parts by weight of a hydroxyl group-containing organic resin at 0 to 80 ° C and at least one crosslinking agent 10 to 45 selected from (D) a melamine resin and a blocked polyisocyanate compound.
(E) having an average particle diameter of 5 to 80 μm with respect to 100 parts by weight of the film-forming resin component of the top clear paint.
m organic resin particles and an average diameter of 2 to 50 μm and a length of 30
1 to 20 parts by weight of at least one kind of organic resin powder selected from organic resin fibers having a diameter / length ratio of 1/2 to 1/100, and a curing formed from a top clear paint. The coating has a molecular weight between crosslinks of 150 to 70
The present invention provides a method for coating a metal plate characterized by having a value of 0.

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

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be described below in detail.

First, the top-colored base paint used in the method of the present invention will be described in detail.

The top coating base paint contains a film-forming resin component comprising a hydroxyl group-containing polyester resin (A) and a crosslinking agent (B), and a coloring pigment.

Hydroxyl-containing polyester resin (A) The hydroxyl-containing polyester resin (A) is a hydroxyl-containing polyester resin such as an oil-free polyester resin, an oil-modified alkyd resin, and a modified product of these resins. Examples thereof include urethane-modified polyester resins, urethane-modified alkyd resins, and epoxy-modified polyester resins.

The above 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.

Among the polyester resins described above, an oil-free polyester resin is particularly preferable.

The polyester resin (A) preferably has a number average molecular weight of 1,000 to 35,000, more preferably 7,000, from the viewpoint of the balance between processability and hardness of the obtained coating film. To 30,000, and the glass transition temperature (Tg point) is preferably from -10 ° C to 80 ° C, more preferably from -5 ° C to 30 ° C.
And the hydroxyl value is preferably from 3 to 160 mgKOH / g, more preferably from 5 to 30 mgKOH / g.
/ G of a polyester resin is preferred.

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.

Crosslinking Agent (B) The crosslinking agent as the component (B) is capable of reacting with the polyester resin (A) to cure the resin (A), and includes a melamine resin and a blocked polyisocyanate compound. At least one crosslinking agent selected from the group consisting of:

Examples of the melamine resin include methylolated melamine resins obtained by reacting melamine with aldehydes such as formaldehyde, paraformaldehyde, acetaldehyde and benzaldehyde.
Further, those obtained by etherifying the above methylolated melamine resin with an appropriate alcohol can also be used as the melamine resin. Examples of the alcohol used for the etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethylbutanol, 2-ethylhexanol and the like.

The blocked polyisocyanate compound used as the crosslinking agent 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 groups 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.

In the top coating base paint, the blending amount of the hydroxyl group-containing polyester resin (A) and the crosslinking agent (B) in 100 parts by weight of the film-forming resin component must be within the following range. Polyester resin (A): 60 to 95 parts by weight, preferably 65 to 85 parts by weight, Crosslinking agent (B): 5 to 40 parts by weight, preferably 15 to 35 parts by weight.

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

The coloring pigment which is added to the top coating base paint of the present invention in addition to the film-forming resin component composed of the polyester resin (A) and the cross-linking agent (B) may be any of the coloring pigments usually used in the paint field. Pigments, for example, white pigments such as titanium white and zinc white; blue pigments such as cyanine blue and induslen blue; green pigments such as cyanine green and green blue; organic red pigments such as azo and quinacridone; Organic yellow pigments such as benzimidazolone, isoindolinone, isoindoline and quinophthalone; yellow pigments such as titanium yellow and graphite; black pigments such as carbon black, graphite and pine smoke; aluminum powder and copper powder , Nickel powder, mica powder coated with titanium oxide, mica powder coated with iron oxide, and glittering pigments such as glittering graphite. It is below. 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.

The top coating base paint of the present invention may further comprise, if necessary, a curing catalyst, an organic solvent;
Extenders such as silica, mica, and alumina; and may contain additives known per se for coatings, such as antifoaming agents and coating surface conditioners.

The curing catalyst is a polyester resin (A)
It is added as needed to promote the curing reaction between the crosslinking agent and the crosslinking agent (B), and can be appropriately selected and used according to the type of the crosslinking agent (B).

When the cross-linking 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, a sulfonic acid compound or an amine of sulfonic acid compound is used as a curing catalyst. A neutralized product is 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. Of these, paint stability,
From the viewpoint of the reaction promoting effect and the physical properties of the obtained coating film, p-
Amine neutralized products of toluenesulfonic acid and / or amine neutralized products of dodecylbenzenesulfonic acid are preferred.

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 as the crosslinking agent is suitable. For example, tin octylate, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanoate), dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide, lead 2-ethylhexanoate, etc. Organic metal catalysts.

The organic solvent is added as necessary to improve the coating properties of the composition of the present invention, and can dissolve or disperse the respective components of the polyester resin (A) and the crosslinking agent (B). What can be used, specifically, for example, toluene, xylene, hydrocarbon solvents such as high-boiling petroleum hydrocarbons, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ketone solvents such as isophorone, ethyl acetate, butyl acetate, Ester solvents such as ethylene glycol monoethyl ether acetate and diethylene glycol monoethyl ether acetate;
Examples thereof include alcohol solvents such as methanol, ethanol, and butanol, and ether alcohol solvents such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and diethylene glycol monobutyl ether. These may be used alone or in combination of two or more. Can be used.

Next, the top clear paint used in the method of the present invention will be described in detail.

The top clear paint used in the method of the present invention is a paint whose paint film is formed on the above-mentioned top colored base paint film by wet-on-wet, and forms the uppermost clear paint film layer. is there. The top clear paint contains, as essential components, a hydroxyl group-containing organic resin (C), a crosslinking agent (D), and an organic resin powder (E).

Hydroxyl-containing organic resin (C) The hydroxyl-containing organic resin (C) contains a hydroxyl group,
There is no particular limitation as long as the organic resin has a glass transition temperature of -20 to 80 ° C. For example, one or a mixture of two or more of polyester resin, silicone polyester resin, acrylic resin, and fluororesin is used. be able to. Among the above-mentioned base resins, a polyester resin can be suitably used. As the polyester resin, those similar to the polyester resin (A) in the above-mentioned top coating base paint can be used as long as the condition that the glass transition temperature is −20 to 80 ° C. is satisfied.

Among the above-mentioned polyester resins, the number average molecular weight is from 1,500 to 5,000, in view of workability, curability and the like.
25,000, preferably 5,000 to 20,000,
Glass transition temperature -20 to 80C, preferably 10C to 6
An oil-free polyester resin having 0 ° C and a hydroxyl value of 8 to 100 mgKOH / g, preferably 15 to 60 mgKOH / g is suitable.

Crosslinking Agent (D) The crosslinking agent (D) to be blended into the top clear coating composition is selected from the melamine resin and the blocked polyisocyanate compound mentioned as the crosslinking agent (B) used in the top coating base paint. The same as the at least one selected crosslinking agent can be used.

In the top clear coating composition, the compounding ratio of the hydroxyl group-containing organic resin (C) and the crosslinking agent (D) is within the following range in terms of the weight of solids based on 100 parts by weight of the total weight of both. Organic resin (C): 55 to 90 parts by weight, preferably 60 to 90 parts by weight
85 parts by weight, crosslinking agent (D): 10 to 45 parts by weight, preferably 15 to 45 parts by weight
40 parts by weight.

When the amount of the organic resin (C) is less than 55 parts by weight [when the amount of the crosslinking agent (D) exceeds 45 parts by weight], the processability of the coating film is reduced and the organic resin (C) is reduced. When the amount of the crosslinking agent exceeds 90 parts by weight, the amount of the crosslinking agent (D) is
Less than 10 parts by weight], the curability of the coating film is reduced and the scratch resistance is also reduced.

Further, the top clear coating composition has a cured coating film formed by curing the coating composition having a molecular weight between crosslinks of 150 to 70.
It is preferred to have 0, preferably 200-500. If the molecular weight between crosslinks is less than 150, the degree of crosslinkage is too high and the workability of the coating film is significantly deteriorated, while if it exceeds 700, the scratch resistance becomes insufficient.

In the present invention, “molecular weight between crosslinks” means
Paint on a tin plate so that the dry coating is about 20 μm,
The coating film baked for 70 seconds under the condition that the maximum temperature of the tin plate is 225 ° C. is peeled off, and the three coating films are stacked to form an automatic dynamic viscoelasticity meter [Toyo Baldwin Co., Ltd., Model Leo Vibron. T [absolute temperature at minimum elastic modulus (弾 性 K)] and E _min [minimum elastic modulus (dy in a high temperature range) when the viscoelasticity of the coating film was measured using DDV-II-EA].
ne / cm)] is a theoretical calculated value obtained by applying the following rubber viscoelasticity theoretical formula by Flory et al.

Cross-linking molecular weight Mc = 3ρRT / E _{min In the} above formula, R = 8.13 × 10 ⁷ (erg / km)
ol) and ρ mean the density (g / cm) of the sample coating film.

Organic resin powder (E) The organic resin powder (E) blended in the top clear paint is an organic resin powder that is not completely melted by baking during the formation of a coating film. The organic resin powder (E) has an average particle diameter of 5 to 80 μm, preferably 1 to 80 μm, from the viewpoint of design properties and coating workability.
5-60 μm particle or average diameter 2-50 μm, length 30-5000 μm, diameter / length ratio 1/2 to 1/10
0, preferably 10 to 30 μm in average diameter and 50 to 2 in length
It has a fibrous form with a diameter / length ratio of 1/3 to 1/20.

As the resin species of the organic resin powder (E), for example, a fluorine resin such as polyvinylidene fluoride or polytetrafluoroethylene, an acrylic resin, a polyurethane,
Phenol resin, silicone resin, polypropylene, and polyamides such as nylon 11 and nylon 12 can be used. Among them, polypropylene and polyamide are preferable.

The compounding amount of the organic resin powder (E) in the top clear paint is 100 parts by weight of the total solid content of the hydroxyl group-containing organic resin (C) and the crosslinking agent (D).
It is 1 to 20 parts by weight, preferably 2 to 15 parts by weight. When the amount of the organic resin powder (E) is less than 1 part by weight, the coating film has insufficient scratch resistance. On the other hand, when the amount exceeds 20 parts by weight, the coating workability deteriorates and the coating film processability deteriorates. I do.

In the top clear coating composition, as the crosslinking agent (D), at least one melamine resin selected from a methyl etherified melamine resin and a mixed etherified melamine resin of methyl ether and butyl ether is used in a total amount of 80% by weight or more. Preferably, a melamine resin crosslinker containing at least 90% by weight is used, and a sulfonic acid compound or a neutralized sulfonic acid compound is used as a curing catalyst with respect to 100 parts by weight of the film-forming resin component. 0.1 to 2.0 parts by weight in terms of the amount of the sulfonic acid compound, and (G) a secondary or tertiary amine compound having a boiling point of 30 to 250 ° C (where the curing catalyst is an amine neutralized product of a sulfonic acid compound. In some cases, by containing 0.1 to 10 parts by weight (as an amount including a secondary or tertiary amine compound in the curing catalyst), Fine shrinkage can be generated and can improve the scratch resistance of the coating film.

Specific examples of the methyl etherified melamine resin and the mixed etherified melamine resin of methyl ether and butyl ether include, for example, Cymel 300, 303, 325, 327, 350, 730, 736, and 736. 738 [all, manufactured by Mitsui Cytec Co., Ltd.], Melan 522, 523 [all, manufactured by Hitachi Chemical Co., Ltd.], Nicaraq MS001, MX4
30, MX650 [all, manufactured by Sanwa Chemical Co., Ltd.], Sumimar M-55, M-100, M
-40S [all, all manufactured by Sumitomo Chemical Co., Ltd.], Regimin 740, 747 [all, manufactured by Monsanto Co., Ltd.]
Methyl etherified melamine resin such as Cymel 23
2, 266, XV-514, 1130 [all, manufactured by Mitsui Cytec Co., Ltd.], Nicaraq MX50
0, MX600, MS35, MS95 [all, manufactured by Sanwa Chemical Co., Ltd.], Regimin 753, 7
55 [all, manufactured by Monsanto], Sumimar M
A mixed etherified melamine resin of methyl ether and butyl ether such as -66B [manufactured by Sumitomo Chemical Co., Ltd.] and the like can be mentioned.

In the melamine resin crosslinking agent, 20% by weight other than the methyl etherified melamine resin and the mixed etherified melamine resin of methyl ether and butyl ether were used.
Hereinafter, as the melamine resin that can be blended in an amount of preferably 10% by weight or less, a melamine resin that has not been methyletherified can be mentioned, and a butyletherified melamine resin can be mentioned as a typical example. Specific examples of the butyl etherified melamine resin include, for example, Uban 20S
E, 225 [all, manufactured by Mitsui Toatsu Co., Ltd.], Super Beckamine J820-60, L-117-6
0, L-109-65, 47-508-60, L
-118-60 and G821-60 [all of which are manufactured by Dainippon Ink and Chemicals, Inc.].

The curing catalyst (F) is compounded to promote a crosslinking reaction between the hydroxyl group-containing organic resin (C) and the melamine resin crosslinking agent, and comprises a sulfonic acid compound or amine neutralization of a sulfonic acid compound. Things. As a typical example of the sulfonic acid compound, p-
Examples thereof include toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid. As the amine in the amine neutralized product of the sulfonic acid compound, a primary amine,
Any of a secondary amine and a tertiary amine may be used.

The amount of the curing catalyst (F) is based on 100 parts by weight of the film-forming resin component in the top clear coating composition.
In the case of an amine neutralized sulfonic acid compound, the amount is 0.1 to 2.0 parts by weight, preferably 0.2 to 1.5 parts by weight in terms of the amount of the sulfonic acid compound.

The secondary or tertiary amine compound (G) having a boiling point of 30 to 250 ° C. is compounded to cause shrinkage on the surface of the clear top coat, and has a boiling point of 50 to 200 ° C.
Is preferable. 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-
Secondary amines such as lupetidine and 3-piperidinemethanol; triethylamine, tributylamine, triallylamine, N-methyldiallylamine, N-methylmorpholine, N, N, N ', N'-tetramethyl-1,2-
Diaminoethane, N-methylpiperidine, pyridine, 4
Tertiary amines such as -ethylpyridine; one or a mixture of two or more such as amines having secondary and tertiary amino groups such as N-methylpiperazine. 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. This amount is an amount including the secondary or tertiary amine compound in the curing catalyst. Above all, the total amount of the secondary or tertiary amine used for neutralizing the sulfonic acid in the curing catalyst and the secondary or tertiary amine compound added separately to the amount of sulfonic acid in the curing catalyst is 1. Preferably it is in the range of 1 to 30 mol.

The top clear coating composition contains a hydroxyl group-containing organic resin (C), a cross-linking agent (D) and an organic resin powder (E) as essential components, and if necessary, a curing catalyst (F) and an amine compound (G). However, if necessary, a solvent, a glittering powder, a lubricity-imparting agent, an ultraviolet absorber, an ultraviolet stabilizer, an antifoaming agent, a coating surface adjusting agent, and an inorganic fine powder such as a silica fine powder. And the like.

As the solvent, those capable of dissolving or dispersing the coating components such as the base resin and the cross-linking agent can be used. For example, the solvents described in the above-mentioned base coating base coating can be used in the same manner.

As the glitter powder, aluminum powder,
Examples thereof include copper powder, nickel powder, mica powder coated with titanium oxide, mica powder coated with iron oxide, and glittering graphite. The blending amount of the glitter powder may be any amount that gives a glitter to the appearance of the coated surface, and is within the range in which the clear coating film can be formed by seeing the top coating base film through the top clear coating film. Is usually 0.005 to 100 parts by weight of the film-forming resin component in the top clear paint.
It is preferably in the range of from 30 to 30 parts by weight, and more preferably in the range of from 0.4 to 10 parts by weight.

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 the top coating base coating film having a viscosity of 40 to 250 seconds and the top coating clear coating film having a viscosity of 50 to 250 seconds 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.

By the coating method of the present invention, a coating film having excellent scratch resistance can be formed on a metal plate.

[0071]

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

Production Example 1 of Topcoat Colored Base Coating 1 75 parts of Byron KS-1460V (polyester resin manufactured by Toyobo Co., Ltd., number average molecular weight 15,000, glass transition temperature 7 ° C., hydroxyl value 11 mg KOH / g) / Solvesso 150 ("Solvesso 150"
Is an aromatic petroleum-based high-boiling solvent manufactured by Esso Oil Co., Ltd.)
It was dissolved in 112.5 parts of a 40/60 (weight ratio) mixed solvent to obtain a resin solution a having a solid content of 40%. To 75 parts of the resin solution a having a solid content of 40%, 75 parts of Taipaque CR-95 (manufactured by Ishihara Sangyo Co., Ltd., titanium white pigment), 3 parts of carbon black pigment and 25 parts of the above mixed solvent were mixed to disperse the pigment. Then, a pigment paste was obtained.

To 178 parts of the obtained pigment paste, 112.5 parts of a resin solution a having a solid content of 40%, and Cymel 303
(Mitsui Cytec Co., Ltd., trade name, low molecular weight methyl etherified melamine resin, hexakis (methoxymethyl)
25 parts of a melamine content of 60% by weight or more, Nailure 5225 (manufactured by King Industries, USA)
A curing catalyst, a trade name, 2 parts of a neutralized solution of dodecylbenzenesulfonic acid in a secondary amine, 25% of an active ingredient) and the above-mentioned solvent mixture for adjusting the viscosity of the coating material were uniformly mixed to obtain a coating viscosity of 90 seconds (Ford cup # 4). , 25 ° C) to obtain a top-coating colored base coating material B-1.

Production Example 2 Byron KS-1640V (a polyester resin manufactured by Toyobo Co., Ltd., having a number average molecular weight of 11,
000, glass transition temperature 20 ° C, hydroxyl value 10mgKO
H / g) 80 parts by weight of cyclohexanone / solvesso 150
("Solvesso 150" is an aromatic petroleum-based high-boiling solvent manufactured by Esso Oil Co., Ltd.) = dissolved in 120 parts of a mixed solvent of 40/60 (weight ratio) to obtain a resin solution b having a solid content of 40%. . 75 parts of a resin solution b having a solid content of 40% was mixed with 75% of Taipaque CR-95 (a titanium white pigment manufactured by Ishihara Sangyo KK)
Parts, 3 parts of carbon black pigment and 25 parts of the above mixed solvent were mixed and dispersed to obtain a pigment paste.

To 178 parts of the obtained pigment paste, 125 parts of a resin solution b having a solid content of 40%, and Desmodur BL-
3175 (Sumitomo Bayer Urethane Co., Ltd., trade name, blocked polyisocyanate compound, solid content: about 75%)
26.7 parts and Formate TK-1 (a curing catalyst which is an organic tin solution manufactured by Takeda Pharmaceutical Co., Ltd., trade name, dissociation catalyst for blocked polyisocyanate compound, solid content of about 1
0%) 2.0 parts and the above-mentioned mixed solvent for paint viscosity adjustment were uniformly mixed, and the paint viscosity was 90 seconds (Ford Cup # 4,
(25 ° C.) to obtain a top-coating colored base coating material B-2.

Production of top clear paints Production Examples 3 to 15 Paints were prepared according to the composition shown in Table 1 below to obtain each top clear paint.

The amounts of the hydroxyl group-containing organic resin and the cross-linking agent in Table 1 are indicated by the weight of the 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. , And tin-based catalysts are indicated by solid content weight. A mixed solvent of cyclohexanone / solvesso 150 = 40/60 (weight ratio) is used for adjusting the viscosity of the paint, etc.
Adjusted to seconds (Ford Cup # 4, 25 ° C.).

[0078]

[Table 1]

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

(* 1) Byron KS-1610V: polyester resin manufactured by Toyobo Co., Ltd., number average molecular weight 3,7
00, glass transition temperature 34 ° C., hydroxyl value 58 mg KOH
/ G. (* 2) Acrylic resin A: the monomer composition is n-butyl methacrylate / 2-hydroxyethyl methacrylate / acrylic acid = 79.5 / 18 / 2.5 (weight ratio of solid content), number average molecular weight about 10,000, An acrylic resin having a glass transition temperature of 28 ° C and a hydroxyl value of 78 mgKOH / g.

(* 3) Olgasol 2002ES-3:
Made by Ato Shimmy, France, trade name, fine resin particles of nylon 12, average particle diameter about 30 μm. (* 4) Olgasol 2002ES-4: Ato, France
Shimmy Co., Ltd., trade name, resin fine particles of nylon 12, average particle diameter of about 40 μm. (* 5) Olgasol 2002EX-D: France, Ato
Shimmy Co., Ltd., trade name, resin fine particles of nylon 12, average particle diameter about 10 μm.

(* 6) Bellpearl R-800: manufactured by Kanebo Co., Ltd., trade name, phenol resin fine particles, average particle diameter of about 20 μm. (* 7) TEXTURE-ULTRAFINE: Texture-Ultrafine, manufactured by Shamrock Chemical Co., Ltd., trade name, polypropylene resin fine particles, average particle diameter of about 18 μm. (* 8) Tuftic FR-14: manufactured by Toyobo Co., Ltd., trade name, polyacrylonitrile resin fiber, average diameter about 14
μm, average length about 500 μm.

(* 9) Tospearl 2000B: trade name, manufactured by Toshiba Silicone Co., Ltd., silicone resin fine particles, average particle diameter of about 6 μm.

(* 10) Molecular weight between crosslinks: Each top clear paint is applied to a tin plate so that the dry coating film becomes about 20 μm, and the maximum temperature of the tin plate is 225 ° C.
The coating film baked for 0 second is peeled off, and the three coating films are stacked to form an automatic dynamic viscoelasticity meter [manufactured by Toyo Baldwin Co., Ltd.
Viscoelasticity was measured using Model Rheovibron DDV-II-EA]. The measured value was applied to the following rubber viscoelasticity theoretical formula by Flory et al. To calculate the molecular weight between crosslinks.

The molecular weight between cross-links Mc = 3ρRT / E _{min The} smaller the molecular weight between cross-links, the higher the degree of cross-linking.

Examples 1 to 22 and Comparative Examples 1 to 8 Preparation of Test Coated Plates Method of preparing test coated plates (1): Examples 1 to 11 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 top-coating colored base paint was applied in a combination of a top-coated colored base paint and a top-coated clear paint shown in Table 2 so that the dry film thickness was about 14 μm. On the uncured coating film of the coating material, the clear top coating material obtained in Production Examples 3 to 15 was applied by a roller curtain coating method so that the dry film thickness was about 10 μm. Then, the coated steel sheet was baked for 70 seconds so that the maximum temperature of the material reached 225 ° C. to obtain each overcoated steel sheet. Viscosity of the top-colored base paint layer immediately before the top clear paint is applied (measured at Ford Cup # 4 at a measurement temperature of 25 ° C.
Viscosity was measured in the same manner as described below) for 100 seconds, and the viscosity of the clear top coating was 110 seconds.

In Example 5, the coating was performed using the above-described hot-dip galvanized steel sheet having no primer coated in place of the primer-coated steel sheet. In Example 6, the top clear paint was applied by a slit curtain coating method instead of the roller curtain coating method.

Method of preparing test coated plate (2): Examples 12 to
22 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 colored base paints obtained in Production Examples 1 and 2 and Production Examples 3 to 15 were used. Each of the resulting clear top coatings was applied in a combination shown in Table 3 below in two layers by a die coating method, extruded from a die, and coated so that the top coating base coating film faced the primer 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 material was baked for 70 seconds so that the maximum temperature at which the material reached reached 225 ° C. to obtain each overcoated steel sheet.

Various tests were performed on the obtained coated steel sheet. The test results are shown in Tables 2 and 3 below.

[0091]

[Table 2]

[0092]

[Table 3]

The tests in Tables 2 and 3 were performed according to the following test methods.

Test Method Appearance of Coated Surface: The appearance of the coating film of the test coated plate was visually evaluated.
も の indicates that the coating film was good without any abnormality, and x indicates that the coating film showed abnormality.

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.

Folding processability: In a room at 20 ° C., the test plate was bent 180 ° with the coated surface outside, and the T number at which no crack was generated 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, and the case of three sheets was set to 3T.

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.

Pencil hardness: Regarding the coating film of the test coated plate, JI
SK-5400 A pencil scratch test specified in 8.4.2 (1990) was performed to evaluate the coating film for scratches.

Scratch resistance: Sand file # 1000 was pressed against the surface of the coating film of the test coated plate to obtain about 70 g /
The state of the coated surface after reciprocating 20 times a distance of about 8 cm in length with a force of cm ² was visually determined at a distance of 20 cm from the coated surface.
The evaluation was performed according to the following criteria. ◎: No scratch is observed on the coating film ○: Slight scratch is slightly detected on the coating film △: Considerable scratch is recognized on the coating film ×: Remarkable scratch is recognized on the coating film

[0101]

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. Since the baking is performed, the number of baking can be increased, and the coating film layer can be formed more without increasing the load on facilities. In the coating method of the present invention,
Since the top coating base coating film and the top clear coating film are coated wet-on-wet, the interlayer adhesion between the two layers is excellent, and the top coating clear coating film has a high degree of crosslinking,
In addition, the uppermost layer coating film containing an organic resin powder and having excellent scratch resistance can be formed. In addition, the resulting overall coating is
Excellent coating film performance such as hardness and curability and coating film appearance can be obtained.

[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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C09D 167/00 C09D 167/00 175/04 175/04 // (C09D 167/00 161: 28)

Claims (6)

[Claims] 1. A top-coating colored base coating and a top-coating clear coating are applied to a continuously moving long metal plate with or without a primer-cured coating and baked. A method of forming a top clear coating film on top, wherein the top clear coating film is formed by wet-on-wet on the top coloring base coating film, and the film-forming resin component of the top coloring base paint is And (A) 60 to 95 parts by weight of a hydroxyl group-containing polyester resin and (B) 5 to 40 parts by weight of at least one crosslinking agent selected from a melamine resin and a blocked polyisocyanate compound,
And the film-forming resin component of the top clear coating composition is (C)
Hydroxyl-containing organic resin having a glass transition temperature of -20 to 80 ° C 5
5 to 90 parts by weight and 10 to 45 parts by weight of (D) at least one crosslinking agent selected from a melamine resin and a blocked polyisocyanate compound, based on 100 parts by weight of the film-forming resin component of the top clear paint. (E) organic resin particles having an average particle diameter of 5 to 80 μm and an average diameter of 2 to 2 μm;
50 μm, length 30-5000 μm, diameter / length ratio 1
/ 1 to 20 parts by weight of at least one organic resin powder selected from organic resin fibers having a molecular weight between crosslinks of 150 to 700. A method for coating a metal plate, comprising: 2. The polyester resin (A) has a number average molecular weight of 1,000 to 35,000 and a glass transition temperature of −10 ° C.
The coating composition according to claim 1, which is a polyester resin having a hydroxyl value of 3 to 160 mgKOH / g at -80 ° C. 3. The cross-linking agent (D) in a top clear paint.
Is a melamine resin containing at least 80% by weight of a melamine resin which is methyletherified or a mixed etherified mixture of methylether and butylether, and the top clear coating composition is based on 100 parts by weight of the film forming resin component of the top coating coating composition. And (F) as a curing catalyst, 0.1 to 2.0 parts by weight of a sulfonic acid compound or a neutralized product of the sulfonic acid compound in terms of the amount of the sulfonic acid compound, and (G) a boiling point of 30 to 250. 0.1 to 10% by weight of a secondary or tertiary amine compound (in the case where the curing catalyst is an amine neutralized sulfonic acid compound, the secondary or tertiary amine compound in the curing catalyst is included) The coating method according to claim 1, wherein the coating method comprises a part. 4. The coating method according to claim 1, wherein the top coating colored base coating and the top coating clear coating are extruded and applied in two layers from a die of a die coater. 5. A top coat clear paint is applied to a continuously moving long metal plate, with or without a primer-cured coating film, on an uncured top coat coloring base paint layer. The coating method according to any one of claims 1 to 3, wherein the coating is performed in a curtain shape using a roller curtain. 6. A coated metal plate coated by the coating method according to claim 1.