JPH11335621A - Clear coating composition giving highly stain-proof coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a clear coating composition giving a clear coating film of greatly improved brightness without damaging coating film properties, e.g. hardness, processability and stain proofness. SOLUTION: This composition contains a resin component composed of (A) 30 to 80 pts.wt. of a polyester resin containing hydroxy group and having a number-average molecular weight of 1,000 to 30,000, glass transition temperature of -10 to 70 deg.C and solubility parameter (sp) of 9.5 to 12.5, (B) 10 to 50 pts.wt. of a polyester of high acid value, having a number-average molecular weight of 400 to 5,000, glass transition temperature of -10 to 70 deg.C and acid value of 50 to 400 mgKOH/g, and (C) 10 to 40 pts.wt. of a hardening agent of melamine resin, and (D) an acidic catalyst at 0.01 to 5 pts.wt. (as the acid quantity) per 100 pts.wt. of the resin component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clear paint composition capable of forming a coating film having excellent stain resistance and sharpness, a method for coating a metal sheet using the clear paint, and a coated metal sheet.

[0002]

2. Description of the Related Art From the viewpoint of productivity and environmental preservation, so-called post-coat coating is used for coating a processed object to be applied to home electric appliances, building materials for indoor and outdoor use, and the like. The pre-coating method, in which a sheet-like material such as a steel sheet is coated by coil coating, etc., and then formed, is being transferred from the method, but the pre-coated sheet-like material is processed into a complex shape. Therefore, high workability is required. Home appliances such as refrigerators, washing machines, and microwave ovens are also required to have hardness, stain resistance, sharpness, and the like.

At present, it has become possible to obtain a coating film having excellent hardness, workability, and stain resistance by using a precoat paint containing a high-molecular polyester resin and an amino resin as main components. However, it has not been possible to obtain a coating film in which the performance of the coating film and the sharpness of the coating film are well balanced.

Conventionally, in the field of pre-coated metal sheets, a one-coat one-bake method in which a top coat is applied and baked on a long metal plate that moves continuously, and a primer paint is applied and baked on a metal plate. Then, a two-coat two-bake system in which a top coat is applied and baked on a primer coating film is generally performed, and the two-coat two-bake system occupies most of the two-bake system. In addition, a three-coat three-bake method is used in which a primer paint is applied and baked on a metal plate, an intermediate coat is applied and baked on the primer coat, and a top coat is applied and baked.

[0005] By forming three coating layers, it is possible to achieve coating performance and coating appearance that cannot be achieved by one or two layers as a total coating film. The number of times of coating and the number of times of baking of the coating film are each one more than those of the two-coat baking method, and there is a problem in that the burden on equipment is increased.

SUMMARY OF THE INVENTION An object of the present invention is to provide a clear paint capable of forming a coating film having significantly improved sharpness without impairing coating film performance such as hardness, workability, and stain resistance of the coating film. is there.

Another object of the present invention is to provide a coating method capable of forming two layers of coating at once on a long metal plate that moves continuously, and with a small load on equipment. An object of the present invention is to provide a method for coating a metal plate capable of forming a coating film having significantly improved sharpness without impairing the coating film performance such as hardness, workability, and stain resistance.

[0008] The present inventors have developed a clear coating composition comprising a combination of a specific acrylic resin having a high styrene content, a polyester resin having a high acid value, and a melamine resin cross-linking agent as a monomer component. Found that it is possible to form a coating film with significantly improved clarity without impairing coating film performance such as processability, stain resistance, etc.In addition, a primer coating film and a top coating coloring coating film are formed on a metal plate. The present inventors have found that a method for coating the above-mentioned object metal plate can be provided by applying a specific clear paint on the top colored base coating film and then baking after coating and baking wet-on-wet, and completed the present invention.

[0009]

That is, the present invention provides:
(A) Number average molecular weight 1,000 to 30,000, glass transition temperature -10 to 70 ° C, solubility parameter (sp value)
9.5 to 12.5, 30 to 80 parts by weight of a hydroxyl group-containing polyester resin having an acid value of less than 50 mgKOH / g, (B) a number average molecular weight of 400 to 5,000, and a glass transition temperature of -10 to -10.
The acid catalyst (D) was added to 100 parts by weight of a resin component composed of 10 to 50 parts by weight of a high acid polyester having an acid value of 50 to 400 mgKOH / g and 70 to 40 parts by weight of a melamine resin curing agent at 70 ° C. An object of the present invention is to provide a clear coating composition containing 0.01 to 5 parts by weight of an acid.

Further, according to the present invention, a primer paint film and a top-coating colored base paint film are applied on a continuously moving long metal plate by wet-on-wet, and the paint films are simultaneously baked to cure the primer. A method for coating a metal plate, comprising forming a coating film and a top-coated colored base cured coating film, and then coating and baking the clear coating composition on the top-coated colored base cured coating film. .

Further, the present invention provides a coated metal plate coated by the above-mentioned coating method.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the clear coating composition of the present invention will be described in detail. First, each component of the clear coating composition of the present invention will be described.

Hydroxyl-containing polyester resin (A) The hydroxyl-containing polyester resin (A) in the composition of the present invention is a hydroxyl-containing polyester resin,
Oil-free polyester resin, oil-modified alkyd resin,
In addition, modified products of these resins, for example, urethane-modified polyester resin, urethane-modified alkyd resin, epoxy-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. Examples of the polybasic acid component include phthalic anhydride, isophthalic acid, tetrahydrophthalic anhydride,
One or more dibasic acids selected from hexahydrophthalic anhydride, succinic acid, fumaric acid, adipic acid, sebacic acid, maleic anhydride and the like, and a lower alkyl ester of these acids are mainly used, and if necessary, benzoic acid acid,
Monobasic acids such as crotonic acid, pt-butylbenzoic acid,
A tribasic or higher polybasic acid such as trimellitic anhydride, methylcyclohexene carboxylic acid, and pyromellitic anhydride is used in combination.

As the polyhydric alcohol component, for example, diethylene glycol, propylene glycol, 1,4-
Butanediol, neopentyl glycol, 3-methylpentanediol, 1,4-hexanediol, 1,6
Dihydric alcohols such as hexanediol are mainly used, and if necessary, trihydric or higher polyhydric alcohols such as glycerin, trimethylolethane, trimethylolpropane and pentaerythritol 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. In addition, terephthalic acid as an acid component and ethylene glycol as an alcohol component tend to deteriorate the solubility of the obtained resin itself in a solvent or reduce the compatibility with other resins. It is better not to use it because it reduces the sharpness of the film.

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.

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

The hydroxyl group-containing polyester resin (A) has a number average molecular weight of 1,0 from the viewpoint of curability, coating film performance and the like.
00 to 30,000, preferably 5,000 to 25.0
00, glass transition temperature is -10 to 70 ° C, preferably 0
-40 ° C, solubility parameter (sp value) 9.5-1
2.5, preferably 10.5-12.0, acid value 50 m
less than gKOH / g, preferably 3 to 40 mgKOH / g
Having a hydroxyl value of 3 to 140 mg.
Suitably, it is in the range of KOH / g, preferably 5-100 mg KOH / g.

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.

High Acid Value Polyester (B) The high acid value polyester (B) used in the composition of the present invention has a number average molecular weight of 400 to 5,000, preferably 1,000 to 4,000, and a glass transition temperature. -10
70 ° C, preferably 10 to 50 ° C, acid value of 50 to 400
mgKOH / g, preferably 100-300 mgKOH
/ G of polyester.

As the polyester (B), for example, a carboxyl group-containing polyester resin, a polyol and 1,2
-Low molecular weight half esters (hereinafter sometimes referred to as "low molecular weight half esters") generated by addition reaction with an acid anhydride.

The carboxyl group-containing polyester resin includes ethylene glycol, 1,2- or 1,3-propanediol, butylene glycol, neopentyl glycol, 1,6-hexanediol, 3,3-dimethylolpentane, 3-dimethylolhexane, glycerin, 1,1,1-trimethylolpropane, 1,2,3
Polyhydric alcohols such as butanetriol, diethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-dimethylolcyclohexane, pentaerythritol and bis (hydroxymethyl) xylene, and adipic acid, sebacic acid, terephthalic acid, and isophthalic acid Acids, polycarboxylic anhydrides (for example, phthalic anhydride, hexahydrophthalic anhydride, succinic anhydride, methylsuccinic anhydride, dodecenylsuccinic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydro Polybasic acids such as phthalic anhydride, endomethylenetetrahydrophthalic anhydride, chlorendic anhydride, itaconic anhydride, citraconic anhydride, maleic anhydride and trimellitic anhydride) and It can be obtained by reaction with a monobasic acid such as benzoic acid in accordance with the requirements.

The carboxyl group-containing polyester resin can be obtained by a one-step reaction in which the polyhydric alcohol and the polybasic acid are subjected to a condensation reaction under conditions in which the carboxyl group is excessive relative to the hydroxyl group, for example. In view of the ease of controlling the molecular weight and the amount of hydroxyl group, the above-mentioned polyhydric alcohol and polybasic acid may be used, for example, if the hydroxyl group is excessive relative to the carboxyl group (one acid anhydride group is two carboxyl groups). After a condensation reaction under the following conditions, it is preferable to obtain a polyester prepolymer obtained by the condensation reaction by a two-step reaction in which the above-mentioned acid anhydride is half-esterified with a hydroxyl group.

In the above half esterification reaction, for example, under the condition that a ring opening reaction of an acid anhydride occurs and a polyester reaction by a generated carboxyl group does not substantially occur, for example,
The reaction can be carried out in a solvent under a nitrogen atmosphere at 70 to 150 ° C, preferably 90 to 120 ° C, for a reaction time of usually 10 minutes to 24 hours. The mixing ratio of the polyester prepolymer and the 1,2-acid anhydride is calculated assuming that the acid anhydride groups are monofunctional, and the equivalent ratio of hydroxyl groups: acid anhydride groups is about 0.8: 1.
A range of -1.2: 1 is preferred.

The low-molecular-weight half ester is prepared by subjecting a polyol and a 1,2-acid anhydride to a half-treatment under conditions in which a ring-opening reaction of the acid anhydride occurs and a polyesterification reaction by a generated carboxyl group does not substantially occur. It is obtained by an esterification reaction. The number average molecular weight of the low molecular weight half ester is usually in the range of 400 to 2,000.

As the polyol used for preparing the low molecular weight half ester, those listed as specific examples of the polyhydric alcohol used for producing the carboxyl group-containing polyester resin can be used. As the 1,2-acid anhydride used for preparing the low-molecular-weight half ester, a 1,2-acid anhydride having about 4 to 32 carbon atoms is preferable. For example, production of the carboxyl group-containing polyester resin is described. Among the polybasic acids used for the above, those listed as specific examples of the polycarboxylic acid anhydride can be suitably used.

The low-molecular-weight half ester is prepared by subjecting the polyol and 1,2-acid anhydride to the same reaction conditions and the same hydroxyl group as in the half-esterification reaction in the two-step reaction for preparing the carboxyl group-containing polyester resin. And an acid anhydride group in an equivalent ratio.

Melamine resin curing agent (C) Melamine resin curing agent (C) used in the present invention
Reacts with a hydroxyl group in the hydroxyl group-containing acrylic resin (A) or a functional group in the polyester resin (B) to form a cured coating film.

The melamine resin curing agent (C) includes a methylolated melamine resin obtained by reacting melamine with an aldehyde. Aldehydes include formaldehyde, paraformaldehyde, acetaldehyde,
Benzaldehyde and the like. Further, those obtained by etherifying the methylolated melamine resin with one or more kinds of alcohols can also be used. Examples of alcohols used for the etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, and n. Monohydric alcohols such as -butyl alcohol, isobutyl alcohol, 2-ethylbutanol and 2-ethylhexanol. Of these, it is preferable melamine resins obtained by etherifying at least part of the methylol groups of inter alia methylolated melamine resin with monohydric alcohol C _{1 to 4.}

Commercial products of the melamine resin curing agent (C) include, for example, Euban 20SE-60, Euban 22
Butyl etherified melamine resin such as No. 5 (all, manufactured by Mitsui Chemicals, Inc.), Super Beckamine G840, and G821 (all, manufactured by Dainippon Ink and Chemicals, Inc.);
Sumimar M-100, M-40S, M-55 (all manufactured by Sumitomo Chemical Co., Ltd.), Cymel 303, 32
5, 327, 350, and 370 (all manufactured by Mitsui Cytec), Nicaraq MS17, and MS15
(The above are all manufactured by Sanwa Chemical Co., Ltd.)
(Manufactured by Monsanto Co.), etc .; methyl etherified melamine resins; Cymel 235, 202, 238, 254;
Mixed etherified melamine resins of methylation and isobutylation, such as 272 and 1130 (all, manufactured by Mitsui Cytec), Sumamir M66B (manufactured by Sumitomo Chemical);
Methylated and n-butylated mixed etherified melamine resins such as Cymel XV805 (manufactured by Mitsui Cytec) and Nicarac MS95 (manufactured by Sanwa Chemical) can be used.

Acid Catalyst (D) The acid catalyst (D) promotes the curing reaction of the composition of the present invention, and includes, for example, paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, phosphoric acid and the like. Specific examples include acid catalysts and amine neutralized products of these acids. Among them, the above-mentioned sulfonic acid compounds or amine-neutralized sulfonic acid compounds are preferred. By blending an acid catalyst, not only the curability of the clear coating film obtained from the composition of the present invention but also the sharpness can be improved. When a curing catalyst is blended, the amount of the curing catalyst depends on the amount of acid (in the case of an amine-neutralized sulfonic acid compound,
0.01 to 5 parts by weight, preferably 100 parts by weight of the total solids of the components (A), (B) and (C), as the amount of the remaining sulfonic acid compound obtained by removing the amine from the neutralized product. Is preferably in the range of 0.05 to 2 parts by weight.

The clear coating composition of the present invention comprises the above-mentioned hydroxyl group-containing polyester resin (A), high acid value polyester resin (B), melamine resin curing agent (C) and acid catalyst (D) as essential components. , The mixing ratio of the above components,
It is in the following range based on a total of 100 parts by weight of the components (A), (B) and (C).

Component (A): 30 to 80 parts by weight, preferably 40 to 70 parts by weight, Component (B): 10 to 50 parts by weight, preferably 15 to 45 parts
Parts by weight, component (C): 10 to 40 parts by weight, preferably 15 to 30 parts by weight
Parts by weight, component (D): 0.01 to 3 parts by weight, preferably 0.05
~ 2 parts by weight.

The clear coating composition of the present invention comprises the above (A)
The components (B), (C) and (D) are essential components,
It contains an organic solvent, and may further contain, if necessary, organic resin fine particles, an ultraviolet absorber, a coating surface adjuster, an antioxidant, a fluidity adjuster, and a lubricity imparting agent such as wax.

The clear coating composition of the present invention is usually an organic solvent type coating composition.
What can dissolve or disperse each component of the paint can be used, for example, hydrocarbon solvents such as heptane, toluene, xylene, octane, mineral spirit; ethyl acetate, n-butyl acetate, isobutyl acetate, ethylene glycol monomethyl ether acetate, Ester solvents such as diethylene glycol monobutyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone and cyclohexanone; methanol, ethanol, isopropanol, n-butanol;
alcohol solvents such as sec-butanol and isobutanol; ethers such as n-butyl ether, dioxane, ethylene glycol monomethyl ether and ethylene glycol monoethyl ether; aromatics such as Swazol 310, Swazol 1000 and Swazol 1500 manufactured by Cosmo Oil Co., Ltd. Petroleum solvents and the like can be mentioned. These organic solvents can be used alone or in combination of two or more. When the clear coating composition of the present invention is applied on a colored base coating film, the organic solvent is preferably one that does not dissolve or swell the colored base coating film, and is preferably a hydrocarbon solvent, an alcohol solvent, or an ether solvent. Solvents, aromatic petroleum solvents, and the like can be suitably used, and the solubility parameter (s) of the solvent composition, which is a mixture of all solvents in the paint, can be used.
(p value) is in the range of 7.5 to 9.5, preferably 8.0 to 9.0.

The coating composition of the present invention is capable of forming a clear coating film having excellent stain resistance and sharpness. It is preferable to paint and bake to form a clear coating film.

The coating composition of the present invention comprises iron, aluminum, brass, copper plate, stainless steel plate, tin plate, galvanized steel plate, alloyed zinc (Zn-Al, Zn-Ni, Zn-
Metals such as plated steel sheets, such as Fe); surface-treated steel sheets, etc. in which these metal surfaces have been subjected to a chemical conversion treatment such as a phosphate treatment or a chromate treatment; plastic, wood, concrete,
It can be applied directly to the material to be coated such as mortar, or onto the coating surface of a film to be coated with a primer and / or a middle coat and / or a top coat colored base, and the hardness is obtained by baking. A clear coating film having good workability, stain resistance, and sharpness can be formed.

The coating thickness of the clear coating composition of the present invention is not particularly limited, but is usually 3 to 5
0 μm, preferably about 5 to 30 μm, and the baking conditions are not particularly limited as long as the clear coating film is cured.
It is preferred that the temperature be in the range of 20 seconds to 40 minutes at ° C.

When the clear coating composition of the present invention is used for clear coating of precoated metal such as for building materials and home appliances, a primer is applied on a metal plate, baked, and then applied on the primer coating film. A so-called three coat 3 in which a colored base paint is applied and baked, and then the clear paint composition of the present invention is applied and baked on the top colored base paint film.
A three-layer coating film can be formed by baking, but also by the following three-coat two-baking method, the hardness, workability, and durability of a coating film consisting of a primer, a top-colored base coating film, and a clear coating film on a metal plate. It is possible to form a three-layer coating film excellent in coating film performance such as stainability and sharpness.

In the above-mentioned three-coat two-bake method, for example, a primer paint film and a top paint base paint film are applied on a long metal plate that moves continuously by wet-on-wet, and both paint films are applied. Simultaneously baking to form a primer-cured coating film and a top-colored base cured film, and then applying and baking the clear coating composition of the present invention onto the top-colored-base cured film.

In the precoat metal coating such as the three-coat three-bake system or the three-coat two-bake system, the clear coating composition can be applied by means such as coil coating or curtain coating. The baking of the film can be performed by heating for about 20 seconds to 2 minutes under the condition that the maximum temperature of the material reaches about 150 to 250 ° C.

In the above-mentioned three-coat two-bake method, a method of applying the primer paint film and the top-coating colored base paint film so as to be in contact with each other in a wet-on-wet manner is as follows. A coating method in which a top coating coloring base coating film is formed in a curtain shape by a roller curtain coating machine or a slit type curtain coating machine on a primer coating film formed by a coating machine such as a coater or a curtain coating machine. A coating method by a die coating method in which a top paint-colored base paint layer is overlaid on two layers and discharged from a die to simultaneously form two layers of a primer paint layer and a top paint-colored base paint layer on an object to be coated. it can.

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 and coated.

Further, as a die coating machine used in the coating method by the die coating method, for example, Japanese Patent Application Laid-Open No.
Die coating machines described in Japanese Patent No. 0570 and the like can be mentioned. The die in the die coating machine includes three blades in which an upper blade, a middle blade, and a lower blade are overlapped, and side plates on both sides. The gap between the upper blade and the middle blade forms a slot for the upper layer paint, and the top coating base paint is extruded from this slot, and the gap between the lower blade and the middle blade forms a slot for the lower layer paint, and the primer is formed from this slot. When the paint is extruded and each paint layer is extruded from each slot, it smoothly merges to form an overlapping paint layer. This overlapping paint layer is extruded from the die, and the overlapped paint layer may be applied directly onto the continuously moving workpiece, or once received by the rotating roll, and then from the rotating roll to the workpiece. It can also be applied.

By coating the pre-coated metal by the three-coat two-bake method, the burden on the equipment in the coating process can be reduced as compared with the three-coat three-bake method.
Energy saving in the baking process can be achieved.

[0049]

EXAMPLES Hereinafter, the present invention will be further clarified with reference to Production Examples, Examples, and Comparative Examples. Unless otherwise specified, “parts” and “%” mean “parts by weight” and “% by weight”, respectively.

Production Example 1 of Hydroxy Group-Containing Polyester Resin (A) The following raw material mixture is placed in a reaction vessel equipped with a stirrer, thermometer, reflux condenser and the like, and the temperature is raised from 160 ° C. to 230 ° C. over 3 hours. It was allowed to warm and the water formed was distilled off through a rectification column. After holding at 230 ° C. for 1 hour, xylol was added and
Dehydration was performed while refluxing xylol at 0 ° C. to carry out an esterification reaction.

1,4-dimethylolcyclohexane 0.3 mol neopentyl glycol 0.6 mol trimethylolpropane 0.1 mol isophthalic acid 0.9 mol When the acid value reaches 5, it is cooled to 140 ° C. and kept for 2 hours. And after cooling, SWASOL 1500 (Cosmo Oil Co., Ltd.)
Was added to obtain a polyester resin (A-1) solution having a solid content of 50%. The obtained resin has a number average molecular weight of 3,000, a glass transition temperature of 32 ° C.,
sp value 11.56, acid value 5 mgKOH / g, hydroxyl value 7
Had 2 mg KOH / g.

Production Example 2 Production Example 2 was carried out in the same manner as in Production Example 1 except that the raw material mixture to be added to the reaction tank was as described below.
A 0% polyester resin (A-2) solution was obtained. The obtained resin had a number average molecular weight of 3,000 and a glass transition temperature −
It had a sp value of 11.38, an acid value of 5 mg KOH / g and a hydroxyl value of 72 mg KOH / g at 5 ° C. 1,4-dimethylolcyclohexane 0.3 mol neopentyl glycol 0.6 mol trimethylolpropane 0.1 mol isophthalic acid 0.6 mol adipic acid 0.3 mol Production Example 3 "Byron KS1430V" manufactured by Toyobo Co., Ltd. (Number average molecular weight 12,000, sp value 11.30, acid value 0.2
mgKOH / g, glass transition temperature 1 ° C, hydroxyl value 11m
(gKOH / g polyester resin) (50 parts) was dissolved in cyclohexanone / swazole 1500 = 1/1 (weight ratio) mixed solvent (50 parts) to obtain a polyester resin (A-3) solution having a solid content of 50%.

Production Example 4 (Comparative) Production Example 4 was carried out in the same manner as in Production Example 1 except that the raw material mixture to be added to the reaction tank was as described below.
A 0% polyester resin (A-4) solution was obtained. The obtained resin had a number average molecular weight of 3,000 and a glass transition temperature of 3
It had a sp value of 12.68, an acid value of 5 mg KOH / g and a hydroxyl value of 77 mg KOH / g at 2 ° C. Ethylene glycol 0.6 mol 1,4-Dimethylolcyclohexane 0.1 mol Neopentyl glycol 0.1 mol Trimethylolpropane 0.2 mol Isophthalic acid 0.85 mol Adipic acid 0.05 mol Production Example 5 (for comparison) In Production Example 1, the same procedure as in Production Example 1 was carried out except that the raw material mixture to be blended in the reaction vessel was as described below, and the solid content was 5%.
A 0% polyester resin (A-5) solution was obtained. The obtained resin had a number average molecular weight of 3,000 and a glass transition temperature −
It had a sp value of 11.42, an acid value of 5 mg KOH / g and a hydroxyl value of 72 mg KOH / g at 20 ° C.

Ethylene glycol 0.6 mol 1,4-Dimethylolcyclohexane 0.2 mol Trimethylolpropane 0.2 mol Isophthalic acid 0.45 mol Adipic acid 0.45 mol Production example of high acid value polyester (B) 6 A mixture of the following components was put into an acrylic resin reaction tank equipped with a stirrer, thermometer, reflux condenser, etc., heated, heated from 160 ° C to 230 ° C over 3 hours, and kept at 230 ° C for 1 hour. The resulting water was distilled off through a rectification column. Then, a small amount of xylene was added, and dehydration was performed while refluxing xylol at 230 ° C. to perform esterification.

Hexahydrophthalic anhydride 0.4 mol Isophthalic acid 0.4 mol Neopentyl glycol 0.2 mol 3,3-Dimethylolpentane 0.2 mol Trimethylolpropane 0.6 mol Resin acid value becomes 3 or less At 140 ° C., and 0.8 mol of hexahydrophthalic anhydride was added at 140 ° C.
After holding at 2 ° C. for 2 hours, the mixture was cooled. After cooling, xylene was added to obtain a polyester (B-1) solution having a solid content of 50%.
The obtained polyester has a number average molecular weight of about 2,500,
Resin acid value 120mgKOH / g, hydroxyl value 30mgKO
H / g, glass transition temperature 30 ° C.

Production Example 7 A mixture of the following components was placed in an acrylic resin reaction tank equipped with a stirrer, thermometer, reflux condenser, and the like, and heated. The temperature was raised from 160 ° C. to 230 ° C. over 3 hours. For 1 hour, and the generated water was distilled off through a rectification column. Then, a small amount of xylene was added, and dehydration was performed while refluxing xylol at 230 ° C. to perform esterification.

Hexahydrophthalic anhydride 0.3 mol Isophthalic acid 0.3 mol Neopentyl glycol 0.2 mol 1,6-hexanediol 0.2 mol Trimethylolpropane 0.7 mol Resin acid value became 3 or less At this point, the mixture was cooled and 1.6 mol of hexahydrophthalic anhydride was added at 140 ° C.
After holding at 2 ° C. for 2 hours, the mixture was cooled. After cooling, xylene was added to obtain a polyester (B-2) solution having a solid content of 50%.
The obtained polyester has a number average molecular weight of about 1,000,
Resin acid value 220mgKOH / g, hydroxyl value 15mgKO
H / g, glass transition temperature 40 ° C.

Production Example 8 A mixture of the following components was placed in an acrylic resin reaction tank equipped with a stirrer, a thermometer, a reflux condenser, and the like, heated, and heated from 160 ° C. to 230 ° C. over 3 hours. For 1 hour, and the generated water was distilled off through a rectification column. Then, a small amount of xylene was added, and dehydration was performed while refluxing xylol at 230 ° C. to perform esterification.

Hexahydrophthalic anhydride 0.62 mol Isophthalic acid 0.22 mol Neopentyl glycol 0.20 mol 3,3-Dimethylolpentane 0.20 mol Trimethylolpropane 0.60 mol Resin acid value becomes 3 or less At 140 ° C., and 0.8 mol of hexahydrophthalic anhydride was added at 140 ° C.
After holding at 2 ° C. for 2 hours, the mixture was cooled. After cooling, xylene was added to obtain a polyester (B-3) solution having a solid content of 50%.
The obtained polyester has a number average molecular weight of about 2,500,
Resin acid value 120mgKOH / g, hydroxyl value 20mgKO
H / g, glass transition temperature 15 ° C.

Production Example 9 A mixture of the following components was placed in an acrylic resin reaction tank equipped with a stirrer, thermometer, reflux condenser, and the like, heated, and heated from 160 ° C. to 230 ° C. over 3 hours. For 1 hour, and the generated water was distilled off through a rectification column. Then, a small amount of xylene was added, and dehydration was performed while refluxing xylol at 230 ° C. to perform esterification.

Hexahydrophthalic anhydride 0.43 mol Isophthalic acid 0.43 mol Neopentyl glycol 0.45 mol Trimethylolpropane 0.50 mol Resin was cooled when the acid value of the resin became 3 or less. 0.3 mole of phthalic anhydride was added and 140
After holding at 2 ° C. for 2 hours, the mixture was cooled. After cooling, xylene was added to obtain a polyester (B-4) solution having a solid content of 50%.
The obtained polyester has a number average molecular weight of about 2,500,
Resin acid value 65mgKOH / g, hydroxyl value 77mgKOH
/ G, glass transition temperature 30 ° C.

Production Example 10 (Comparative) A mixture of the following components was placed in an acrylic resin reaction tank equipped with a stirrer, a thermometer, a reflux condenser, etc. and heated, and the temperature was raised from 160 ° C. to 230 ° C. over 3 hours. Then, water produced by holding at 230 ° C. for 1 hour was distilled off through a rectification column. Then, a small amount of xylene was added, and dehydration was performed while refluxing xylol at 230 ° C. to perform esterification.

Hexahydrophthalic anhydride 0.47 mol Adipic acid 0.48 mol 1,4-dimethylolcyclohexane 0.50 mol 1,6-hexanediol 0.50 mol Cooling when the resin acid value becomes 3 or less Then, at 140 ° C., 0.07 mol of hexahydrophthalic anhydride was added, and 14
After holding at 0 ° C. for 2 hours, the mixture was cooled. After cooling, xylene was added to obtain a polyester (B-5) solution having a solid content of 50%. The obtained polyester has a number average molecular weight of about 5,50.
0, resin acid value 20mgKOH / g, hydroxyl value 10mgK
OH / g, had a glass transition temperature of -27 ° C.

Production Example 11 (Comparative) A mixture of the following components was placed in an acrylic resin reaction tank equipped with a stirrer, a thermometer, a reflux condenser, and the like, heated, and heated from 160 ° C. to 230 ° C. over 3 hours. Then, water produced by holding at 230 ° C. for 1 hour was distilled off through a rectification column. Then, a small amount of xylene was added, and dehydration was performed while refluxing xylol at 230 ° C. to perform esterification.

Hexahydrophthalic anhydride 0.62 mol Isophthalic acid 0.29 mol Neopentyl glycol 0.25 mol 3,3-dimethylolpentane 0.25 mol Trimethylolpropane 0.48 mol Resin acid value becomes 3 or less At that time, the mixture was cooled, and 0.68 mol of hexahydrophthalic anhydride was added at 140 ° C.
After holding at 0 ° C. for 2 hours, the mixture was cooled. After cooling, xylene was added to obtain a polyester (B-6) solution having a solid content of 50%. The obtained polyester has a number average molecular weight of about 4,50.
0, resin acid value 110 mgKOH / g, hydroxyl value 0 mgK
It had an OH / g and a glass transition temperature of 30 ° C.

Production Example 1 of Clear Coating Composition The 50% hydroxyl-containing polyester resin (A) obtained in Production Example 1
-1) 140 parts of the solution (70 parts by solid content), 20 parts of the 50% polyester (B-1) solution obtained in Production Example 6 (10 parts by solid content), 20 parts of Cymel 303 (Note 1) and 0.4 parts (0.1 part in terms of the amount of sulfonic acid) of "Nailure 5225" (Note 2) were mixed and stirred to obtain a clear coating composition.

(Note 1) Cymel 303: manufactured by Mitsui Cytec Co., Ltd., trade name, methyl etherified melamine resin, solid content: about 100%.

(Note 2) Nailure 5225: manufactured by King Industries, USA, trade name, curing catalyst which is an amine neutralized solution of dodecylbenzenesulfonic acid, content of sulfonic acid compound about 25%.

Examples 2 to 11 and Comparative Examples 1 to 9 Each clear coating composition was obtained in the same manner as in Example 1 except that the composition was changed to the composition shown in Table 1 below.

The amount of each component in Table 1 below is based on solid content or parts by weight of the active ingredient. In Table 1, the blending amount of Nail Cure 5225 was indicated by the amount of the sulfonic acid compound. Table 1 shows Examples 1 to 11 and Comparative Example 1.
9 shows the solubility parameter (sp value) of the solvent composition in the coating compositions obtained in Nos. 9 to 9.

(Note) in Table 1 described below has the following meaning.

(* 1) Nikarac MX500: a methyl etherified melamine resin manufactured by Sanwa Chemical Co., Ltd.

Preparation of Test Coated Plate KP Color 8630 Primer (Kansai Paint Co., Ltd., polyester-modified epoxy resin primer for pre-coated steel plate) and topcoat coloring were applied on a 0.5 mm thick hot-dip galvanized steel plate. AT-2000 gray as base paint (manufactured by Kansai Paint Co., Ltd., top-coated polyester resin-based paint for pre-coated steel sheet, gray color) is extruded from the die by superimposing two layers by die coating method,
The coating was performed on a galvanized steel sheet so that the primer coating film faced.

The coating film thickness of each paint was about 5 μm in dry film thickness of the primer paint film, and about 14 μm in dry film thickness of the top colored base paint layer. The viscosity of the paint extruded from the die was 90 seconds for the primer paint and 1 for the top-colored base paint.
00 seconds. After the coating, the steel sheet was baked for 70 seconds so that the maximum temperature of the material reached 220 ° C. to obtain a top-coated colored base-coated steel sheet.

Next, the top coating clear paint obtained in each of the above Examples and Comparative Examples was adjusted to a viscosity of 60 seconds on the top coated colored base coating film of each baked coated steel sheet, and dried with a roll coater. Was about 7 μm, and baked for 50 seconds so that the maximum temperature of the material reached 235 ° C. to obtain each test coated plate. Various tests were performed on the obtained test coated plates. The test results are shown in Table 1 below.

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[Table 1]

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[Table 2]

The tests in Table 1 were performed according to the following test methods.

Test Method Sharpness: Using a sharpness measuring device “PGD-IV” (sold by Nippon Color Research Institute), the angle was fixed at 55 ° and the PGD value of the coating film was measured. The larger the value, the better the sharpness.

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

Bending workability: 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.
Eight sheets, 80T when bent at 80 °, 1T when two sheets of the same thickness as the test plate are bent, 2T when two sheets, 8T when eight sheets If cracks occur in the bent portion even when the sheet is bent by sandwiching it, 8T <is displayed.

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.

Magic stain resistance: In a room at 20 ° C., a line was drawn on the coated surface with a red oil-based ink (Magic Ink Large Red, registered trademark), left for 1 hour, and then gauze impregnated with n-butanol. I wiped it off. The color difference (ΔE) between the trace of wiping off the red oil-based ink and the original plate is measured.
The smaller the color difference, the better the magic stain resistance.

Tobacco stain resistance: A test plate cut into a size of 50 × 50 mm was placed in a desiccator having a capacity of about 4 liters which was allowed to stand in a room at 20 ° C. so that the coating surface was on the top, and a cigarette ( 2 pieces of cans were lit, the smoke was filled in a desiccator, and after leaving for 24 hours, the surface of the test plate was washed with a neutral detergent, and the color difference (Δ
Measure E). The smaller the color difference, the better the resistance to tobacco contamination.

Solvent resistance: In a room at 20 ° C., about 1 kg was applied to the painted surface with gauze impregnated with methyl ethyl ketone.
After applying a load of / cm ² and reciprocating 50 times over a length of about 5 cm, the state of the coated surface was visually evaluated according to the following criteria. ：: No change is observed on the coated surface. ：: Scratch is recognized on the coated surface. X: Whitening or swelling of the coating film is observed.

The test coated plate coated with the clear paint of Comparative Example 4 had poor curability, and no tests other than solvent resistance were performed.

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The clear coating composition of the present invention is a combination of a specific polyester resin, a polyester having a high acid value and a melamine resin crosslinking agent, and can be achieved by the clear coating composition of the present invention. It is possible to form a clear coating film that can achieve both high levels of stain resistance and sharpness, which were not present.

A coated steel sheet having a coating film formed from the clear coating composition of the present invention as a primer coating film, a top coating base coating film and an uppermost coating film on a metal plate has a coating film hardness, workability,
The sharpness can be greatly improved without impairing the coating properties such as stain resistance.

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI C09D 161/28 C09D 161/28

Claims (4)

[Claims] (A) a number average molecular weight of 1,000 to 30,
000, glass transition temperature -10 to 70 ° C, solubility parameter (sp value) 9.5 to 12.5, acid value 50 mgKOH
(B) a high acid polyester having a number average molecular weight of 400 to 5,000, a glass transition temperature of -10 to 70 ° C, and an acid value of 50 to 400 mg KOH / g. (D) an acid catalyst in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of a resin component comprising 10 parts by weight of a melamine resin curing agent and 10 to 40 parts by weight of a melamine resin curing agent. Clear paint composition. 2. The solvent composition in the clear coating composition is 7.
The clear coating composition according to claim 1, wherein the composition has a solubility parameter (sp value) of 5 to 9.5. 3. A primer coating film and a top coating base coating film are applied on a continuously moving long metal plate by wet-on-wet, and both the coating films are simultaneously baked to form a primer-cured coating film. A method for coating a metal plate, comprising: after forming a cured topcoat colored base coating film, coating and baking the clear coating composition according to claim 1 on the cured topcoat colored base coating film. 4. A coated metal plate coated by the coating method according to claim 3.