JP2000073007A - Coating composition and coated metal plate produced by using the composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a matte coating agent having good processability, free from the generation of crack even after the aging of a processed coating film and capable of forming a coating film having excellent acid resistance and weatherability and high corrosion-resistance of the processed part. SOLUTION: This coating composition is a crepe coating composition giving a coating film having a glass transition temperature of 20-65 deg.C and containing (A) 29-93 pts.wt. of a hydroxyl-containing polyester resin having a number- average molecular weight of 10,000-30,000, a glass transition temperature of -30 to +20 deg.C and a hydroxyl value of 3-40 mgKOH/g, (B) 0-56 pts.wt. of a hydroxyl-containing polyester resin having a number-average molecular weight of 1,000-7,000 and a hydroxyl value of 20-100 mgKOH/g, (C) 7-35 pts.wt. of a low-nuclear methylated melamine resin and (D) 0.1-3 pts.wt. (in terms of sulfonic acid based on 100 pts.wt. of A+B+C) of a reaction mixture of 1 equivalent of a sulfonic acid with 1.5-40 equivalent of a secondary or tertiary amine compound having a boiling point of 30-250 deg.C. The coated metal plate is produced by forming a cured coating film of the coating composition on a metal plate interposing a primer coating layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition which can form a coating film having excellent workability, corrosion resistance of a processed portion and weather resistance and has excellent coatability, and is particularly suitable as a precoated steel sheet for building materials. The present invention relates to a coated paint composition and a coated metal sheet obtained by applying the paint composition.

[0002]

2. Description of the Related Art In recent years,
In snowy areas, there has been raised a problem that red rust is generated on a molded part such as a roof of a house molded from a precoated steel sheet. This phenomenon occurs especially on the roofs of houses on the Sea of Japan side of the Tohoku region.

[0003] The above phenomenon is caused by the fact that acidic substances such as sulfur dioxide gas generated by coal combustion in China are mixed with snow to form acidic snow. It is thought to be caused by contact with the roof of the resulting house. Acid snow has a strong acidity, and the galvanized layer of the galvanized steel sheet, which is the base material, is melted in areas where cracks occur in the coating film such as the processed part of the precoated steel sheet in contact with the acid snow and iron The iron part is exposed, and this iron part gradually changes to red rust in the presence of water and oxygen. When red rust occurs on the roof, the appearance of the roof is impaired, and the strength of the roof decreases.

[0004] Conventionally, precoated steel sheets used for roofing materials for construction materials mainly include a hot-dip galvanized steel sheet as a base material and a hard matte finish coating film formed through a primer coating film. There are many used. For this reason, processability is poor, and weather resistance is poor because it contains a large amount of matting agent. Therefore, the conventional precoated steel sheet is apt to generate red rust due to acidic snow as described above.

[0005] Due to the above-mentioned problems of acid snow and the like, functions such as workability, acid resistance, and weather resistance have been regarded as important for precoated steel sheets for building materials.

[0006] However, polyester resin-based paints are mainly used as a topcoat paint for precoated steel sheets for building materials. Generally, when workability is improved, acid resistance and weather resistance tend to decrease. Above all, in the case of a low gloss matte finish having a 60-degree specular reflectance (60-degree gloss) of 15 or less, which is strongly demanded for roofs, it is difficult to achieve all of the above functions, and it has not yet been achieved. . Further, with regard to workability, even if the initial workability is good, there is also a problem that cracks are likely to occur over time after processing (cooling / heating cycle test which is this accelerated test).

The present invention is suitable for producing a precoated steel sheet for building materials which has good workability, does not crack even after aging after processing, is excellent in acid resistance and weather resistance, and has excellent corrosion resistance in a processed part. The purpose of the present invention is to obtain a top coat having good roll coater coatability.

[0008]

Means for Solving the Problems The present inventors have found that a polyester resin-based coating contains a specific amount of a polyester resin having a high molecular weight and a low glass transition temperature as a polyester resin, and a low-nucleated methylated melamine as a crosslinking agent. It has been found that the above object can be achieved by using a resin and containing a sulfonic acid amine neutralized product and a secondary or tertiary amine compound, and the present invention has been completed.

That is, the present invention provides (A) a number average molecular weight of 1
0000-30,000, glass transition temperature -30 to 2
0 ° C., 29 to 93 parts by weight of a hydroxyl group-containing polyester resin having a hydroxyl value of 3 to 40 mg KOH / g, (B) a number average molecular weight of 1,000 to 7,000, and a hydroxyl value of 20 to 100 mg K
With respect to 100 parts by weight of 0 to 56 parts by weight of an OH / g hydroxyl group-containing polyester resin and 7 to 35 parts by weight of (C) a low nucleated methylated melamine resin, 1 equivalent of (D) sulfonic acid and a boiling point of 30 to A reaction mixture of a secondary or tertiary amine compound at 250 ° C. and 1.5 to 40 equivalents of sulfonic acid in an amount of 0.1 to 3 parts by weight, and An object of the present invention is to provide a fine paint composition wherein the glass transition temperature of the formed coating film is in the range of 20 to 65 ° C.

[0010] The present invention also provides a coated metal plate wherein a cured coating film of the above-mentioned coating composition is formed on a metal plate via a primer coating film.

[0011]

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

Polyester Resin (A) The polyester resin as the component (A) in the composition of the present invention is a polyester resin containing a hydroxyl group, and is an oil-free polyester resin, an oil-modified alkyd resin, or a modified product of these resins. Examples thereof include urethane-modified polyester resins, urethane-modified alkyd resins, epoxy-modified polyester resins, and acryl-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 in a manner 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 silicone-modified polyester resin,
A reaction product obtained by using a polyester resin produced from each component used in the production of the above polyester resin and reacting a hydroxyl group in the polyester resin with a silicon intermediate to bond thereto is used. In general, the degree of modification with the silicon intermediate is preferably such that the amount of the silicon intermediate is 0.1 to 35% by weight based on the silicon-modified polyester resin.

As the acrylic-modified polyester resin,
Using a polyester resin produced from each component used in the production of the polyester resin, a functional group in the polyester resin, for example, a reactive group having a reactivity with a carboxyl group, for example, a polymerizable unsaturated monomer having an epoxy group (for example, , Glycidyl methacrylate) to introduce a polymerizable unsaturated group into the polyester resin, to which an acrylic monomer is graft-reacted. The degree of modification by the acrylic monomer is based on the acrylic-modified polyester resin,
The amount is preferably 0.1 to 20% by weight.

Among the polyester resins described above, oil-free polyester resins and oil-modified alkyd resins are preferred, and oil-free polyester resins are particularly preferred.

The polyester resin (A) has a number average molecular weight of 10,000 to 30,000, preferably 12,000.
~ 25,000, glass transition temperature (Tg point) -30 ~ 2
0 ° C, preferably -10 ° C to 10 ° C, hydroxyl value 3 to 40
mgKOH / g, preferably 5 to 15 mgKOH / g. As the polyester resin (A),
The above polyester resins can be used alone or in combination of two or more.

In the present invention, the glass transition temperature (Tg) of the resin is determined by differential scanning calorimetry (DSC), and the number average molecular weight is determined by gel permeation chromatography (GPC) using a calibration curve of standard polystyrene. Measured.

When the number average molecular weight of the polyester resin (A) is less than 10,000, the processability is liable to decrease,
On the other hand, when it exceeds 30,000, the degree of cross-linking of the obtained coating film is lowered, so that the acid resistance is apt to be lowered, and the coating workability is liable to be lowered. If the Tg is lower than -30 ° C, the acid resistance of the obtained coating film tends to decrease, while if it exceeds 20 ° C, the processability of the obtained coating film tends to decrease. Further, when the hydroxyl value is less than 3 mgKOH / g, the degree of crosslinking of the obtained coating film is reduced, and the acid resistance and the solvent resistance are reduced.
If it exceeds 40 mgKOH / g, the obtained coating film becomes large, and the workability tends to decrease.

Polyester Resin (B) The polyester resin which is the component (B) in the composition of the present invention is a component which is added as necessary for the purpose of improving the coatability of the composition of the present invention with a roll coater.

The polyester resin (B) 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, acryl-modified polyester resin and the like can be mentioned.

The polyester resin (B) has a number average molecular weight of 1,000 to 7,000, preferably 2,000 to 5,
000, the hydroxyl value is 20 to 100 mgKOH / g, preferably 30 to 60 mgKOH / g, and the glass transition temperature (Tg point) is preferably -30 to 40C, more preferably -20 to 20C.

The polyester resin (B) has the above properties, and can be produced by the same method as that for producing the polyester resin (A).

The polyester resin (B) preferably has a number average molecular weight within the above range from the viewpoint of the effect of improving the coatability of the roll coater and processability, and has a hydroxyl value within the above range from the viewpoint of curability. Is appropriate.

Low Nucleated Methylated Melamine Resin (C) The low nucleated methylated melamine resin as the component (C) in the composition of the present invention is a melamine resin having a methoxy group by methyl etherification, and has an average degree of condensation. 3.0 or less,
A melamine resin containing 4 or more alkyl ether groups and 2.5 or more methyl ether groups per nucleus of a triazine ring, and particularly preferably a melamine resin containing 30% by weight or more of a mononuclear hexamethoxymethylmelamine. . As the alkyl ether group which can be contained in addition to the methyl ether group, a group having 2 to 4 carbon atoms is preferable, and examples thereof include an ethoxy group, an n-butoxy group, and an isobutoxy group.

Commercially available products of the above low nucleated methylated melamine resin (C) include, for example, Cymel 300, 303, 327, 350, 370, and 712 (all of which are manufactured by Mitsui Cytec Co., Ltd.). Nikarac MW30, MW22A, MX430, MX650 [all, manufactured by Sanwa Chemical Co., Ltd.], Sumimar M-55, M-100, [all, manufactured by Sumitomo Chemical Co., Ltd.], REGIMIN 745 And 747 (all of which are manufactured by Monsanto); Cymel 232, 235, 238, 266, and 202 (all of which are manufactured by Mitsui Cytec Co., Ltd.);
Mixed etherified melamine resin of methyl ether and butyl ether such as MX600 and MS95 (all of which are manufactured by Sanwa Chemical Co., Ltd.), Rezmin 753 and 755 (all of which are manufactured by Monsanto Co.) Can be.

Reaction mixture of sulfonic acid and amine compound
(D) The composition of the present invention contains a reaction mixture (D) of a sulfonic acid and an amine compound in the composition.

Representative examples of the sulfonic acid include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid. The sulfonic acid in the reaction mixture (D) functions as a curing catalyst for accelerating the reaction between the polyester resin (A) or the polyester resin (B) and the melamine resin (C). As the sulfonic acid, p-toluenesulfonic acid and dodecylbenzenesulfonic acid are particularly preferred from the viewpoints of the stability of the paint, the effect of accelerating the reaction, and the physical properties of the obtained coating film. In the composition of the present invention, when the coating film is baked, the amine compound in the reaction mixture (D) evaporates and the sulfonic acid is regenerated, whereby the sulfonic acid can effectively function as a catalyst.

The amine compound constituting the reaction mixture (D) is a secondary or tertiary amine compound having a boiling point of 30 to 250 ° C. As the secondary amine compound, for example,
Diethylamine, diisopropylamine, di-n-propylamine, diallylamine, diamylamine, di-n-butylamine, diisobutylamine, disec-butylamine, N-ethyl-1,2-dimethylpropylamine,
N-methylhexylamine, di-n-octylamine, piperidine, 2-pipecoline, 4-pipecoline, 2,4
-, 2,5- or 3,5-lupetidine, dimethyloxazolidine, 3-piperidinemethanol, and the like. Examples of the tertiary amine compound include, for example, triethylamine, tributylamine, N-methylmorpholine, N, N -Dimethylallylamine, N-methyldiallylamine, triallylamine, N, N, N ', N'-tetramethyl-1,2-diaminoethane, N, N, N',
N'-tetramethyl-1,3-diaminopropane, N-
Examples include methylpiperidine, 4-ethylpiperidine, pyridine and the like. Further, a compound having both a secondary amino group and a tertiary amino group such as N-methylpiperazine can be used as a secondary or tertiary amine compound.

The mixing ratio of the sulfonic acid and the amine compound in the reaction mixture (D) is such that the amine compound is 1.5 to 40 equivalents, preferably 5 to 20 equivalents, per 1 equivalent of the sulfonic acid. is there. The sulfonic acid and the amine compound easily react by mixing to produce a neutralized sulfonic acid amine. Therefore, the reaction mixture (D) is a mixture of an amine neutralized sulfonic acid and an amine compound.

The method of incorporating a reaction mixture (D) of a sulfonic acid and an amine compound into the composition of the present invention includes:
(1) A method in which a reaction mixture in which a sulfonic acid and an amine compound are reacted in advance and the reaction mixture is blended into a composition; and (2) A sulfonic acid and an amine compound are separately blended into the composition. (3) a method in which a sulfonic acid amine neutralized product obtained by reacting a sulfonic acid with a part of an amine compound and a residual amount of the amine compound are separately incorporated into the composition. it can. In the above method (2), the sulfonic acid and the amine compound react in the composition to form an amine neutralized sulfonic acid, and the reaction mixture (a mixture of the neutralized sulfonic acid and the amine compound) D).

In the reaction mixture (D), sulfonic acid 1
When the amount of the amine compound is less than 1.5 equivalents to the equivalent weight, the curing catalyst action of sulfonic acid is exerted even inside the coating film before the paint is sufficiently formed on the surface of the coating film at the time of baking and the curing is performed. Because it progresses, the desired matte coating film cannot be formed without obtaining a satisfactory shrinking pattern,
In addition, the acid resistance and weather resistance of the coating film are apt to decrease. On the other hand, when the amount of the amine compound exceeds 30 equivalents, the inside of the coating film is not sufficiently cured, or it takes a long time to cure. Problems are more likely to occur.

Preparation of coating composition The coating composition of the present invention comprises the polyester resin (A), polyester resin (B) and melamine resin (C) described above.
And the reaction mixture (D).

The mixing ratio of the polyester resin (A), the polyester resin (B) and the melamine resin (C) based on the weight of the solid content is determined by the sum of the solid contents of the components (A), (B) and (C). The following ranges are based on 100 parts by weight.

Polyester resin (A): 29 to 93 parts by weight, preferably 50 to 88 parts by weight, polyester resin (B): 0 to 56 parts by weight, preferably 2 to 40 parts by weight, melamine resin (C): 7 -35 parts by weight, preferably 10-30 parts by weight.

When the amount of the polyester resin (A) is less than 29 parts by weight in the above mixing ratio, the workability of the cured coating film obtained tends to deteriorate, while the amount of the polyester resin (A) is 93 parts by weight. If the amount exceeds the above range, the curability and acid resistance of the obtained cured coating film are likely to decrease. When the amount of the polyester resin (B) exceeds 56 parts by weight, the workability of the obtained cured coating film tends to deteriorate. Furthermore, when the amount of the melamine resin (C) is less than 7 parts by weight, the curability and acid resistance of the obtained cured coating film are liable to decrease, while when it exceeds 35 parts by weight, the processability of the obtained cured coating film becomes poor. It is easy to deteriorate.

In the coating composition of the present invention, the amount of the reaction mixture (D) is based on 100 parts by weight of the total solid content of the polyester resin (A), the polyester resin (B) and the melamine resin (C). And sulfonic acid amount in the range of 0.1 to 3 parts by weight, preferably 0.2 to 1.5 parts by weight. Here, the “value converted into a sulfonic acid compound” means the amount of the sulfonic acid itself obtained by removing the amine compound from the reaction mixture (D). If the amount of the reaction mixture (D) is less than 0.1 part by weight, as a value converted into a sulfonic acid compound, the effect of promoting the reaction between the polyester resin and the melamine resin is not sufficient.
If the amount exceeds 3 parts by weight, the processability and water resistance of the resulting coating film are reduced.

The coating composition of the present invention can consist essentially of the above polyester resin (A), polyester resin (B), melamine resin (C) and reactive compound (D). From the point of view, an organic solvent is usually contained. As the organic solvent, those capable of dissolving or dispersing the components (A), (B), (C) and (D) can be used. Specifically, for example, toluene, xylene, high boiling petroleum-based Hydrocarbon solvents such as hydrocarbons, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and isophorone, ester solvents such as ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, methanol, Examples thereof include alcohol solvents such as ethanol and butanol, and ether alcohol solvents such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and diethylene glycol monobutyl ether. It can be used as a mixture of two or more.

The composition of the present invention may further comprise, if necessary, a coloring pigment; a glittering pigment such as aluminum powder, copper powder, nickel powder, mica powder coated with titanium oxide, mica powder coated with iron oxide, and glittering graphite; , Clay, silica, mica, alumina and other extender, glass fiber; resin powder;
It may contain additives known per se for coatings, such as antifoaming agents and coating surface conditioners.

Examples of the above-mentioned coloring pigments include coloring pigments usually used in the field of coatings, for example, white pigments such as titanium white and zinc white; organic red pigments such as cyanine blue, cyanine green, azo and quinacridone; Organic yellow pigments such as imidazolones, isoindolinones, isoindolines and quinophthalones; titanium yellow,
Inorganic coloring pigments such as red iron oxide, carbon black, graphite and various calcined pigments are exemplified.

Examples of the resin powder include spherical and fibrous resins made of resins such as nylon resin, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, silicone resin, phenol resin, acrylic resin, polyester resin, polystyrene, and polyacrylonitrile. Various forms of resin powder can be mentioned.

The coating composition of the present invention obtained as described above has a coating film formed from the coating composition of 20 to 65.
It is necessary to have a glass transition temperature in the range of 25 ° C, preferably 25-50 ° C. In the present invention, the "glass transition temperature of the coating film" is applied to a tin plate so as to have a dry film thickness of 20 μm, and after baking for 60 seconds under the condition that the material reaching temperature is 230 ° C., the coating film is peeled off. The cured coating film is obtained from the dynamic viscoelastic behavior measured at a frequency of 110 Hz using an automatic dynamic viscoelasticity meter [Model Toyo Baldwin, Model Leo Vibron DDV-II-EA]. . If the glass transition temperature of the coating film in the coating composition of the present invention is less than 20 ° C., the hardness of the obtained coating film will be insufficient, while if it exceeds 65 ° C., the processability of the coating film tends to decrease.

Coating of Coating Composition The composition of the present invention can be applied to various objects such as metal plates, plastics and glass plates.
When manufacturing a painted metal plate, a metal plate is used as an object to be coated. Examples of the metal plate used as an object to be coated include a cold-rolled steel plate, a zinc-plated steel plate, and an aluminum plate. Among them, a zinc-plated steel plate can be preferably used. Galvanized steel sheets include hot-dip galvanized steel sheets, electro-galvanized steel sheets, iron-zinc alloy-plated steel sheets, nickel-zinc alloy-plated steel sheets, aluminum-zinc alloy-plated steel sheets (for example, trade names such as “Galvalume” and “Galphan”). And zinc-plated steel sheets obtained by subjecting these zinc-based plated steel sheets to a chemical conversion treatment such as a zinc phosphate treatment and a chromate treatment. As the metal plate, among the above-mentioned zinc-based plated steel plates, those obtained by subjecting an aluminum-zinc alloy-plated steel plate to a chromate treatment can be suitably used from the viewpoints of workability, corrosion resistance of a processed portion, and the like.

In producing a coated metal plate, a coated metal plate can be obtained by directly applying the coating composition of the present invention on the above metal plate. However, a primer coating film is provided on the metal plate and the primer coating is performed. It is preferable to coat the coating composition of the present invention on a film from the viewpoint of improving the corrosion resistance of the coated metal plate and the adhesion of the coating. Examples of the primer coating include an epoxy resin-based primer coating, a polyester resin-based primer coating, an epoxy-modified polyester resin-based primer coating, and among others, a polyester resin-based primer coating in terms of processability. It is preferably an epoxy-modified polyester resin-based primer coating, and usually has a thickness of 2 to 10 μm.

The primer coating preferably contains 10 to 35% by weight of a chromium-based rust-preventive pigment based on the weight of the coating, from the viewpoint of corrosion resistance. The temperature is 30-100 ° C, preferably 40
It is preferable that the temperature is in the range of -85 ° C from the viewpoint of workability. As the chromium-based rust preventive pigment, strontium chromate, calcium chromate, zinc chromate, and zinc potassium chromate are suitable, and these can be used alone or in combination of two or more.

The coated metal plate of the present invention can be obtained by forming a cured coating film of the coating composition of the present invention on a metal plate via a primer coating film.

The coating of the coating composition of the present invention is not particularly limited, and can be performed by, for example, roll coating, curtain flow coating, dip coating, spray coating, and the like. Usually has a dry film thickness of 5 to 5.
A range of 30 μm, especially 10 to 25 μm is suitable.
The curing conditions of the coating composition of the present invention can be appropriately selected from the baking conditions under which the coating is cured.
In the case of coil coating in which a long, continuously-moving, primer-coated metal plate is continuously coated by roll coating or the like, the material ultimate temperature (PMT) is usually 1
60-260 ° C. for 15-90 seconds, especially PMT1
Conditions within the range of 90 to 230 ° C and 20 to 60 seconds are suitable.

[0050]

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

Production of Top Coating Examples Examples 1 to 9 and Comparative Examples 1 to 8 Coatings were prepared according to the composition shown in Table 1 below to obtain respective top coatings. In addition, at the time of making the top coats of Examples and Comparative Examples into a paint, titanium white as a white pigment was dispersed. Cyclohexanone / Swazol 1500 (manufactured by Cosmo Oil Co., Ltd., aromatic petroleum-based high boiling point solvent) = 60/40
(Weight ratio) of the mixed solvent was used for adjusting the paint viscosity. When applying these top coats, the paint viscosity was adjusted to about 90 seconds (25 ° C.) with a Ford cup # 4.

The amounts of the polyester resin and the melamine resin in Table 1 are indicated by parts by weight of the solid content.

Table 1 shows the amount of sulfonic acid in each top coat,
It shows the weight ratio of (total amine compound / sulfonic acid) and the glass transition temperature of the coating film obtained from each top coat.

The above-mentioned glass transition temperature is determined by applying the composition to a tin plate so that the dry film thickness becomes 20 μm.
After baking for 60 seconds under the condition of 0 ° C., the coating film was peeled off,
About this cured coating film, an automatic dynamic viscoelasticity meter [Model Leo Vibron DDV-II manufactured by Toyo Baldwin Co., Ltd.]
-EA], obtained from dynamic viscoelastic behavior measured at a frequency of 110 Hz.

[0055]

[Table 1]

[0056]

[Table 2]

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

The polyester resins shown in (* 1) to (* 8) in Table 1 have property values shown in Table 2 below.

[0059]

[Table 3]

(* 9) Cymel 303: low nucleus methyl etherified melamine resin, manufactured by Mitsui Cytec Co., Ltd., having a content of hexakis (methoxymethyl) melamine of 60% by weight or more.

(* 10) Nikarac MW-30: manufactured by Sanwa Chemical Co., Ltd., having a low nucleus methyletherified melamine resin and a content of hexakis (methoxymethyl) melamine of 60% by weight or more.

(* 11) Amine neutralized sulfonic acid
1: A neutralized product of 1 equivalent of paratoluenesulfonic acid and 1 equivalent of diisopropylamine.

Preparation of overcoated steel sheet Examples 10 to 18 and Comparative Examples 9 to 16 Aluminum-zinc alloy-plated steel sheets having a thickness of 0.5 mm and subjected to chromate treatment (the amount of aluminum during plating was about 5
%, Abbreviated as “Zn-Al 5%” in Table 3 below), and “GFP-7 primer” manufactured by Kansai Paint Co., Ltd.
(Polyester primer for pre-coated steel sheet, glass transition temperature of primer coating about 80 ° C)
Painted to a thickness of μm, and the maximum material temperature reached is 225 ° C
Was baked for 40 seconds to obtain a primer-coated steel sheet. On this primer-coated steel sheet, each of the top coats obtained in Examples 1 to 9 and Comparative Examples 1 to 8 was applied using a bar coater so that the dry film thickness was about 20 μm. For 60 seconds to obtain each overcoated steel sheet.

Example 19 In Example 10, instead of "GFP-7 primer", "KP color 8690 primer" (Kansai Paint Co., Ltd., epoxy-modified polyester primer for pre-coated steel sheet, "KP869
Glass transition temperature of about 6 which is abbreviated as "0".
5 ° C.) to obtain a top-coated steel sheet in the same manner as in Example 10.

Example 20 The same procedure as in Example 10 was carried out except that the chromate-treated thickness was 0.1 mm.
Instead of a 5 mm aluminum-zinc alloy-plated steel sheet (the amount of aluminum in the plating is about 5%), a 0.5 mm-thick hot-dip galvanized steel sheet (abbreviated as “HDG” in Table 3 below) is subjected to a chromate treatment. ) Was performed in the same manner as in Example 10 except that (1) was used to obtain a top-coated steel sheet.

Example 21 The same procedure as in Example 10 was carried out except that the chromate-treated thickness was 0.1 mm.
Instead of a 5 mm aluminum-zinc alloy-plated steel sheet (about 5% aluminum during plating), a 0.5 mm-thick aluminum-zinc alloy-plated steel sheet (about 55% aluminum during plating, see below) Table 3
In this example, except that "Zn-Al 55%" was used, the same procedure as in Example 10 was carried out to obtain a top-coated steel sheet.

Examples 10 to 21 and Comparative Examples 9 to 16
Various tests were carried out using the top-coated steel sheet obtained in 1) as a test plate. The test results are shown in Table 3 below.

The tests in Table 3 were performed according to the following test methods.

Test Method : Feeling of shrinkage of painted surface: The painted surface was observed with a magnifier of 30 times, and the degree of shrinkage was evaluated. A: A uniform and clear shrinkage pattern is observed on the coated surface. O: A uniform shrinkage pattern is observed on the coated surface, but the shrinkage pattern is not remarkable. X: No shrinkage pattern is observed on the coated surface.

Gloss: JIS K-5400 7.6 (1
990), the 60-degree specular reflectance was measured according to the prescribed 60-degree specular gloss.

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

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.

A: No peeling of the coating film was observed at all. A: The coating film was slightly peeled, but 90 or more squares remained. Δ: The number of remaining squares was 50 or more and less than 90.

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

Folding workability: In a room at 0 ° C., the test plate was bent 180 ° with the coated surface outside, and the T number at which no cracks occurred in the bent portion was visually evaluated and indicated. The T number is 1 without anything inside the bend.
0T when 80 ° bending is performed, 1T when one plate having the same thickness as the test plate is sandwiched and 2T when two plates are bent,... The case was 6T.

Solvent resistance: In a room at 20 ° C., about 1 kg / cm was applied to the coated surface using gauze impregnated with methyl ethyl ketone.
A load of ² was applied and reciprocated between a length of about 5 cm. The number of reciprocations until the primer coating film (steel plate without primer coating) was visible was recorded. Those in which the primer coating film was not visible after 50 reciprocations were designated as 50 <.

Resistance to occurrence of red rust: The test plate subjected to the 2T bending process was left standing at −20 ° C. for 3 hours → 1% of 20 ° C.
The test was immersed in an aqueous sulfurous acid solution for 3 hours, washed with water, and subjected to a 10-cycle test using 1 cycle of the iSuper UV tester SUV-W13 (tested by Iwasaki Electric Co., Ltd. for 18 hours). The degree of occurrence of red rust in the processed part of the test plate after the test was evaluated according to the following criteria.

A: No occurrence of red rust is observed in the processed part. O: Red rust is observed in the processed part, but less than 10% of the length of the processed part. % Or more and less than 50% red rust is observed. ×: Red rust is observed in the processed portion at 50% or more of the length of the processed portion.

Cooling / heat cycling resistance: The test plate subjected to the 2T bending process was subjected to a 5-cycle test in which one cycle was (rest at −20 ° C. for 3 hours → rest at 70 ° C. for 5 hours). The degree of cracking of the coating film in the processed portion after the test was evaluated according to the following criteria.

：: No cracking was observed in the coating film. わ ず か: Cracking occurred slightly in the coating film. Δ: Cracking occurred considerably in the coating film. X: Cracking occurred significantly in the coating film.

Acid resistance: A coated plate is cut into a size of 70 × 150 mm, and the back surface and the cut surface are sealed with an adhesive tape.
The blister area% of the coating film after immersion in a 3% sulfuric acid aqueous solution was examined. The immersion conditions were a liquid temperature of 20 ° C. for 200 hours. ◎: No swelling was observed in the coating film. 塗膜: The coating swelling area was less than 10%. Δ: The coating swelling area was 10% or more and less than 50%. X: The coating swelling area was 50% or more. It is.

Coating workability: In reverse roll coater coating with two rolls, each coating composition adjusted to a coating viscosity of 90 seconds (Ford cup # 4/25 ° C.) was coated at a coating speed (peripheral speed of a backup roll) of 70 m /. And baked at 230 ° C. for 60 seconds. The coating workability was evaluated based on the state of the coating surface and the coatable film thickness at that time.

：: Uniform and good coating film can be formed with a dry film thickness of 17 μm or more. ：: Uniform and good coating film can be formed with a dry film thickness of 15 μm or more.
Possibility of forming less than μm ×: A uniform and good coating film having a dry film thickness of 15 μm cannot be formed.

[0084]

[Table 4]

[0085]

[Table 5]

[0086]

The coating composition of the present invention is used as a polyester resin in a polyester-melamine resin-based coating.
Using a polyester resin having a specific range of molecular weight, glass transition temperature and hydroxyl value, using a low nucleated methylated melamine resin as a melamine resin, and preparing a reaction mixture of a sulfonic acid and a secondary or tertiary amine compound. It contains. With the paint composition of the present invention, good workability,
Cracks do not occur even after aging after processing, acid resistance, excellent weather resistance, it is possible to form a low glossy dust coating film excellent in corrosion resistance of the processed part, and the coating composition of the present invention is roll coated Excellent for work.

Although it is not clear why the coating film obtained from the coating composition of the present invention is excellent in processability, acid resistance and weather resistance, the present inventors have found that the polyester resin used has a low glass transition temperature. During the baking and curing of the polyester resin, the amine compound, sulfonic acid, and melamine resin migrate to the surface layer of the coating film, and the sulfonic acid exerts a catalytic ability as the amine compound evaporates from the surface of the coating film. It is considered that the coating proceeds to form a fine coating film and the surface layer of the coating film becomes hard, forming a coating film having excellent acid resistance and weather resistance.

The coating composition of the present invention is particularly suitable as a top coating for a precoated steel sheet for building materials. The pre-coated steel sheet formed by coating the coating composition of the present invention on a metal plate via a primer coating film, even when used for a roof of a house or the like, does not easily generate red rust due to acidic snow even in a molded portion thereof. .

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 161/32 C09D 161/32 163/00 163/00 C23C 28/00 C23C 28/00 C (72) Invention Person Takao Oshima 4-171-1, Higashi-Yawata, Hiratsuka-shi, Kanagawa F-term (reference) in Kansai Paint Co., Ltd. NA03 PB05 PC02 4K044 AA02 AB02 BA10 BA15 BB03 BC02 CA11 CA16 CA18

Claims (5)

[Claims] (A) a number average molecular weight of 10,000 to 3
000, glass transition temperature -30 to 20 ° C., hydroxyl value 3 to 40 mg KOH / g 29 to 93 parts by weight of a hydroxyl group-containing polyester resin, (B) number average molecular weight 1,000 to 7,000, hydroxyl value 20 to 100 mg KOH (D) 1 equivalent of sulfonic acid and a boiling point of 30 to 250 parts by weight based on 100 parts by weight of 0 to 56 parts by weight of a hydroxyl group-containing polyester resin / g and 7 to 35 parts by weight of (C) a low nucleated methylated melamine resin. And a reaction mixture of 1.5 to 40 equivalents of a secondary or tertiary amine compound at 0.1 ° C. in an amount of 0.1 to 3 parts by weight in terms of sulfonic acid, and formed from the coating. A fine paint composition, wherein the glass transition temperature of the coating film is in the range of 20 to 65 ° C. 2. A polyester resin (A) in a total amount of 100 parts by weight of the components (A), (B) and (C).
Is 50 to 88 parts by weight, the amount of the polyester resin (B) is 2 to 40 parts by weight, and the amount of the melamine resin (C) is 10 to
2. The lacquer paint composition according to claim 1, wherein the amount is 30 parts by weight. 3. On a metal plate via a primer coating,
A coated metal sheet comprising a cured coating film of the coating composition according to claim 1. 4. The coated metal plate according to claim 3, wherein the metal plate is a zinc-aluminum alloy-plated steel plate having a surface subjected to chromate treatment. 5. The primer coating film according to claim 3, wherein the primer coating film is a polyester resin-based primer coating film or an epoxy-modified polyester resin-based primer coating film, and the glass transition temperature of the primer coating film is in the range of 30 to 100 ° C. Or 4
Painted metal plate as described.