JPH11148047A - Coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating composition excellent in coating film performances such as processability, coating film hardness, blocking resistance and weather resistance and capable of forming uniform coating films which look like the citrus skin. SOLUTION: This coating composition comprises 100 pts.wt. of a resin component comprising (A) 20-80 pts.wt. of a polyester resin having a number-average mol.wt. of 2,000-18,000, a glass transition temperature of -20 deg.C to <5 deg.C, and a hydroxyl group value of 5-60 mgKOH/g, (B) 5-65 pts.wt. of a polyester resin having a number-average mol.wt. of 13,000-30,000, a glass transition temperature of 5-35 deg.C and a hydroxyl group value of 2-25 mgKOH/g, and (C) 15-35 pts.wt. of a melamine resin cross-linking agent, and (D) 1-20 pts.wt. of polybutylene terephthalate particles having an average particle diameter of 15-70 μm. Therein, the component B has a larger number-average mol.wt. by >=1,000 than that of the component A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition capable of forming a yuzu skin coating and capable of forming a coating excellent in low-temperature processability, coating hardness and blocking resistance, in particular, precoat coating for container processing. The present invention relates to a coating composition suitable for a steel sheet and a coated metal plate obtained by applying the coating composition.

[0002]

2. Description of the Related Art In recent years,
While a smooth finish is required for the finish of the coating film of a painted metal plate processed into a container such as a home appliance such as a VTR, a radio cassette player, and a microwave oven, the so-called skin looks similar to the so-called post-coat finish. The appearance of a coated film is required in terms of inconspicuous surface defects and ease of use in combination with a post-coated member.

[0003] As a coating material for forming a so-called citrus skin-like painted metal plate coating film, JP-A-4-370164 contains a vehicle resin and a thermoplastic resin powder having an average particle size of 10 to 50 µm. A coating composition is disclosed.

However, since the coating film formed from this coating composition contains a thermoplastic resin powder, it is difficult to balance coating film hardness, processability of the coating film and blocking resistance. When the thermoplastic resin is melted by the method, a foam like foam is easily generated around the thermoplastic resin powder, and there is a problem that a coated surface appearance is deteriorated. Also,
There is a problem that the weather resistance tends to be insufficient when used outdoors, because the coating has unevenness in the form of yuzu skin and the thickness of the coating in the recesses is reduced.

Accordingly, the present inventors have obtained a coating material which has a good balance between coating film hardness, workability and blocking resistance, has good weather resistance, and is capable of forming a concavo-convex pattern having an excellent surface appearance. As a result of intensive studies, a polyester-melamine resin paint is a composition in which a specific polyester resin and a crosslinking agent are combined, and the dynamic elastic modulus and the molecular weight between crosslinks of a cured coating film obtained from the composition are as follows. It has been found that the above object can be achieved by using a material having a specific range, and the present invention has been completed.

[0006]

That is, the present invention provides:
(A) a number average molecular weight of 2,000 to 18,000, a glass transition temperature of −20 ° C. to less than 5 ° C., and a hydroxyl value of 5 to 60 m
20 to 80 parts by weight of a polyester resin which is gKOH / g, (B) a number average molecular weight of 13,000 to 30,000,
Glass transition temperature 5-35 ° C, hydroxyl value 2-25 mg KO
In 100 parts by weight of a resin component comprising 5 to 65 parts by weight of a polyester resin which is H / g and 15 to 35 parts by weight of a (C) melamine resin curing agent, (D) an average particle diameter of 15 to 7 parts
A coating composition comprising 1 to 20 parts by weight of a 0 μm polybutylene terephthalate fine powder, wherein the polyester resin (B) has a number average molecular weight of the polyester resin (A).
And a coating composition capable of forming a yuzu skin-like coating film having a number average molecular weight of 1,000 or more larger than the number average molecular weight.

Further, the present invention is characterized in that a cured coating of the coating composition according to the above item 1 is formed on a metal plate via a polyester-based primer coating or an epoxy-based primer coating. A painted metal plate is provided.

[0008]

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

Polyester resin (A) and polyester
Resin (B) The polyester resin as the component (A) and the component (B) 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, and a modified product of these resins. Products, such as urethane-modified polyester resin, urethane-modified alkyd resin,
Epoxy-modified polyester resin and the like can be mentioned.

The above-mentioned 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%.

The urethane-modified polyester resin includes:
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.

In the coating composition of the present invention, two types of polyester resins (A) and (B) are used in combination as the polyester resin from the viewpoint of the low-temperature processability and the high-temperature blocking resistance of the obtained coating film.

The polyester resin (A) has a number average molecular weight of 2,000 to 18,000, preferably 8,000 to 1
7,000, glass transition temperature (Tg point) -20 ° C or higher and lower than 5 ° C, preferably -10 ° C or higher and lower than 5 ° C, hydroxyl value 5 to 60 mgKOH / g, preferably 7 to 30 mgK
OH / g polyester resin. The polyester resin (B) has a number average molecular weight of 13,000 to 30,000.
0, preferably 14,000 to 28,000, a glass transition temperature of 5 to 35 ° C, preferably 5 to 32 ° C, and a hydroxyl value of 2
２５25 mg KOH / g, preferably 3-20 mg KOH
/ G of polyester resin.

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.

In the polyester resin (A), if the number average molecular weight is less than 2,000, processability and weather resistance are inferior. On the other hand, if it exceeds 18,000, the degree of cross-linking of the obtained coating film is lowered and the blocking resistance is lowered. I do. Tg point is -20 ° C
If the temperature is lower than 5 ° C., the hardness of the obtained coating film is low. On the other hand, if the temperature is 5 ° C. or higher, the balance between the processability and the blocking resistance of the obtained coating film cannot be obtained. In addition, the hydroxyl value is 5 mg KO
If it is less than H / g, the degree of crosslinking of the obtained coating film will be low, and the blocking resistance will be low. On the other hand, if it exceeds 60 mgKOH / g, the processability of the obtained coating film will be deteriorated.

When the number average molecular weight of the polyester resin (B) is less than 13,000, the processability of the obtained coating film is improved.
The weather resistance is not sufficiently improved, and the weather resistance cannot be sufficiently improved. On the other hand, when it exceeds 30,000, the degree of cross-linking of the obtained coating film is low, and the blocking resistance is low. Tg
If the point is less than 5 ° C., the balance between workability and blocking resistance of the obtained coating film cannot be obtained. On the other hand, when the temperature exceeds 35 ° C., the workability of the obtained coating film deteriorates. When the hydroxyl value is less than 2 mgKOH / g, the degree of crosslinking of the obtained coating film is reduced and the blocking resistance is reduced.
If it exceeds KOH / g, the processability of the obtained coating film will be deteriorated.

In the coating composition of the present invention, the polyester resins (A) and (B) are used in combination. The number average molecular weight of the polyester resin (B) is 1,000 or more, preferably 3, It is necessary to use a resin larger than 000. Polyester resin (B) with high molecular weight in addition to polyester resin (A)
When used together, the coating film hardness, blocking resistance and weather resistance can be improved while maintaining the practical level of workability of the obtained coating film.

Melamine Resin Curing Agent (C) The melamine resin curing agent, which is the component (C) in the composition of the present invention, includes an addition reaction product of melamine with an aldehyde component such as formaldehyde and paraformaldehyde (a monomer and a monomer). Or a part of the methylol groups of the methylolated melamine resin, which is any of the following compounds: methanol, ethanol, isopropanol, n-
Examples thereof include those etherified with a lower alcohol having 1 to 6 carbon atoms such as propanol, n-butanol, and isobutanol.

Representative examples of the melamine resin curing agent include a methyletherified melamine resin in which some or all of the methylol groups of the methylolated melamine resin are etherified with methyl alcohol, and a butyletherified melamine resin in which butylether is butyletherified with butylalcohol. Or a mixed etherified melamine resin of methyl ether and butyl ether etherified with both methyl alcohol and butyl alcohol.

Specific examples of the melamine resin include Cymel 300, 303, 325, 327, 350, 730, 736, and 738 (all of which are manufactured by Mitsui Cytec Co., Ltd.), and melan. 522, 523
[These are all manufactured by Hitachi Chemical Co., Ltd.], Nicaraq MS
001, MX430, and MX650 (all manufactured by Sanwa Chemical Co., Ltd.), Sumimar M-55, and M-M
100 and M-40S [all of which are Sumitomo Chemical Co., Ltd.]
Methyl etherified melamine resins such as Resin 740 and 747 (all manufactured by Monsanto); Uban 20SE and 225 (all manufactured by Mitsui Toatsu Co., Ltd.), Super Beckamine J820-60 , L
-117-60, L-109-65, 47-508
Butyl etherified melamine resins such as -60, L-118-60, and G821-60 (all manufactured by Dainippon Ink and Chemicals, Ltd.); Cymel 232, 26
6, XV-514 and 1130 (all of which are manufactured by Mitsui Cytec Co., Ltd.), Nikarac MX500, and MX
600, MS35, MS95 [all, all manufactured by Sanwa Chemical Co., Ltd.], Regimin 753, 755 [all, manufactured by Monsanto Co., Ltd.], Sumimar M-66B
Mixed etherified melamine resin of methyl ether and butyl ether such as [manufactured by Sumitomo Chemical Co., Ltd.]. These melamine resins can be used alone or as a mixture of two or more.

As the melamine resin curing agent, those containing at least 50% by weight of a methyl etherified melamine resin or a mixed etherified melamine resin of a mixture of methyl ether and butyl ether are preferred. It is composed of a mixed etherified melamine resin of the ether and butyl ether (the former) and a butyl etherified melamine resin (the latter), and the weight ratio of the former / the latter is 30/1 to 1/1, preferably 15/1 to 1
Those having a ratio of 3/1 are preferred from the viewpoints of blocking resistance, workability, coating film hardness, stain resistance and the like.

Fine powder of polybutylene terephthalate (D) The fine powder of polybutylene terephthalate, which is the component (D) of the present invention, is melted at the time of heating and curing the coating film to give the coating film a wrinkled appearance. Average particle size 15-70 μm
Having. When the average particle diameter is smaller than 15 μm, the obtained coating film has insufficient unevenness, and the desired yuzu skin appearance cannot be obtained.On the other hand, when the particle diameter exceeds 70 μm, when the paint is roll-coated, Coating defects due to streaking tend to occur.

Polybutylene terephthalate fine powder (D)
Preferably has a melt viscosity at 190 ° C. of 50 to 300 Pa · s.

Polybutylene terephthalate fine powder (D)
As a typical commercially available product, for example, Vestamelt 448
1, 4280, 4681, 4380, 448
0, 4280 (all of these are manufactured by Daicel Huels Co., Ltd.), Aronmelt PES-110, PES-
085 (all of which are manufactured by Toagosei Co., Ltd.).

The coating composition of the present invention may optionally contain a curing catalyst in order to accelerate the curing reaction between the polyester resin (A) and the polyester resin (B) and the melamine resin curing agent (C). can do.

The curing catalyst which can be used includes, for example, strong acids and neutralized products of strong acids.
Examples thereof include sulfonic acid compounds which are strong acids such as toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid, and amine neutralized products of these sulfonic acid compounds. Among these, an amine neutralized product of p-toluenesulfonic acid and / or an amine neutralized product of dodecylbenzenesulfonic acid are preferred from the viewpoints of the stability of the paint, the reaction promoting effect, and the physical properties of the obtained coating film. . The amount of the curing catalyst used is generally 2. as a value converted into an acid compound per 100 parts by weight of the total amount of the polyester resin (A), the polyester resin (B) and the melamine resin curing agent (C).
0 parts by weight or less, preferably in the range of 0.1 to 1.5 parts by weight is suitable. Here, when the curing catalyst is a neutralized acid, the “value converted into an acid compound” means the amount of the acid itself after removing the neutralizing agent from the curing catalyst. When the curing catalyst is the acid itself, it means the amount of the acid itself.

Preparation and Coating of Coating Composition The coating composition of the present invention comprises the polyester resin (A), polyester resin (B), melamine resin curing agent (C) and polybutylene terephthalate fine powder (D) described above. ,
Further, if necessary, it can be prepared by mixing a curing catalyst.

The mixing ratio of the polyester resin (A), the polyester resin (B) and the melamine resin curing agent (C) based on the weight of the solid content is determined by the solid content of the components (A), (B) and (C). And the total amount is 100 parts by weight, the range is as follows.

Polyester resin (A): 20 to 80 parts by weight, preferably 30 to 70 parts by weight, polyester resin (B): 5 to 65 parts by weight, preferably 10 to 55 parts by weight, melamine resin curing agent (C) 15 to 35 parts by weight,
Preferably 20 to 30 parts by weight. In the above mixing ratio,
When the amount of the polyester resin (A) is less than 20 parts by weight, the blocking resistance deteriorates, while when it exceeds 80 parts by weight, the processability decreases. When the amount of the polyester resin (B) is less than 5 parts by weight, the processability is deteriorated.
Exceeding the weight part deteriorates the blocking resistance. Further, when the amount of the melamine resin curing agent (C) is less than 15 parts by weight, blocking resistance, coating film hardness, solvent resistance and the like are deteriorated, while when it exceeds 35 parts by weight, processability is reduced.

The compounding amount of the polybutylene terephthalate fine powder (D) in the composition of the present invention is 100% by weight of the total solid content of the polyester resin (A), the polyester resin (B) and the melamine resin curing agent (C). For the department
It is preferably in the range of 1 to 20 parts by weight, preferably 2 to 15 parts by weight.

The coating composition of the present invention comprises the above polyester resin (A), polyester resin (B), melamine resin curing agent (C), polybutylene terephthalate fine powder (D), and, if necessary, a curing catalyst. Although it can be substantial, from the viewpoint of handling and paintability,
Usually, an organic solvent is contained. As the organic solvent, an organic solvent capable of dissolving or dispersing the above (A), (B), and (C) and not dissolving the polybutylene terephthalate fine powder (D) can be used. Specifically, for example, toluene, Xylene, hydrocarbon solvents such as high-boiling petroleum hydrocarbons, methyl ethyl ketone, methyl isobutyl ketone,
Ketone solvents such as cyclohexanone and isophorone, ester solvents such as ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate and diethylene glycol monoethyl ether acetate, alcohol solvents such as methanol, ethanol and butanol,
Examples thereof include ether alcohol solvents such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and diethylene glycol monobutyl ether. These can be used alone or as a mixture of two or more. Above all, boiling point 200
An organic solvent having a temperature of not less than 0 ° C., for example, Solvesso 200 (manufactured by Esso Petroleum Co., high boiling point petroleum solvent, boiling point of about 230 ° C.), diethylene glycol monobutyl ether acetate (boiling point of about 246 ° C.), and the like, may be incorporated in the coating material in an amount of 1% by weight or more. It is suitable for preventing the occurrence of coating film defects such as cracks in the coating film.

The coating composition of the present invention can be used as a coating containing no coloring pigment, but can also be used as an enamel coating containing a coloring pigment. As the coloring pigment, coloring pigments usually used in the field of paints, for example, cyanine blue, cyanine green, organic red pigments such as azo and quinacridone, benzimidazolone, isoindolinone, isoindoline and quinophthalone Organic yellow pigments such as organic yellow pigments; inorganic coloring pigments such as titanium white, titanium yellow, red iron oxide, carbon black, graphite and various calcined pigments.

The composition of the present invention may further comprise, if necessary, a glitter pigment such as aluminum powder, copper powder, nickel powder, mica powder coated with titanium oxide, mica powder coated with iron oxide, and glitter graphite; talc, clay, An extender such as silica, mica, and alumina; may contain additives known per se for coatings, such as an antifoaming agent and a coating surface adjusting agent. Further, the composition of the present invention may contain an amine compound for the purpose of forming a fine shrinkage pattern on the surface of the coating film, improving the surface hardness of the coating film, improving the weather resistance, and the like.
Such amine compounds include, for example, triethylamine, diisopropylamine, diisobutylamine,
Secondary or tertiary amines such as di-n-butylamine can be mentioned. When the amine compound is compounded, the compounding amount is usually 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.
Parts by weight.

The coating composition of the present invention has a dynamic elastic modulus E at 100 ° C. of a cured coating film obtained from the coating composition.
2.0 × 10 ⁸ dyne / cm ² or more, and further 3.0
It is preferably in the range of from 5.5 dyne / cm ^{2 to} the blocking resistance at a high temperature, and the molecular weight between crosslinks is from 300 to 1,300, more preferably from 500 to 1,100.
Is preferable in view of workability at a low temperature and blocking resistance at a high temperature.

In the present invention, the “dynamic elastic modulus E” and the “molecular weight between crosslinks” are such that the average dry film thickness of a tin plate is 20%.
μm, and after baking for 60 seconds under the condition that the temperature at which the material reaches 230 ° C., the coating film is peeled off, and the cured coating film is subjected to an automatic dynamic viscoelasticity measuring device [Model, manufactured by Toyo Baldwin Co., Ltd. Reovibron DDV-II-EA]
And obtained from dynamic viscoelastic behavior measured at a frequency of 110 Hz. “Dynamic elastic modulus E” is a dynamic elastic modulus measured at a measurement temperature of 100 ° C., and “molecular weight between crosslinks” is a dynamic viscoelastic behavior measured as described above by Flor.
This is a theoretical calculation value obtained by applying the following rubber viscoelasticity formula using y and the like.

The molecular weight between cross-links Mc = 3ρRT / Emin [where ρ represents the specific gravity (g / cm ³ ) of the sample coating film, R is a gas constant, and R = 8.31 × 10 ⁷ (erg / cm ³ ) deg ・ mo
l), and T is the temperature (゜ K) at which the dynamic elastic modulus becomes minimum,
Emin indicates the minimum elastic modulus (dyne / cm 2) at the temperature T]. The composition of the present invention comprises the polyester resin (A), the polyester resin (B), the melamine resin curing agent (C) and the polybutylene terephthalate fine powder. (D) by further selecting, if necessary, a curing catalyst, an amine compound and the like at the above-mentioned predetermined ratio, and a resin (B) having a number average molecular weight larger than that of the resin (A) by 1000 or more.
To obtain a coating composition suitable for pre-coated steel sheet, which is excellent in workability and blocking resistance, has good hardness, solvent resistance, stain resistance, weather resistance, etc., can form uneven skin-like coatings. Can be.

The composition of the present invention can be applied to various objects to be coated such as a metal plate, plastics, a glass plate, and the like. Use 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 sheet, hot-dip galvanized steel sheet, electro-galvanized steel sheet, iron
Zinc alloy plated steel sheet, nickel-zinc alloy plated steel sheet,
Aluminum-zinc alloy plated steel sheets (for example, “galvalume”, “galvan” plated steel sheets) and the like, and zinc-treated zinc-coated steel sheets,
A chemical conversion-treated zinc-based plated steel sheet subjected to a chemical conversion treatment such as a chromate treatment can be given. In addition, a primer-coated metal plate provided with a primer coating film on a metal plate for the purpose of improving corrosion resistance and coating adhesion can also be used as an object to be coated. As the primer coating film, a coating film obtained from a polyester-based primer or an epoxy-based primer is preferable, and usually 2 to 10
It has a thickness of μm.

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, or the like. , Usually 5 to 5% by dry coating weight
50 g / m ^2, it is preferred within the scope of particular 10 to 40 g / m ^2. In addition, the curing conditions of the coating composition can be appropriately selected from among the baking conditions under which the coating is cured, but a long metal plate or a primer-coated metal plate that moves continuously is roll-coated or the like. In the case of coil coating to be applied continuously, usually, the maximum material reaching temperature (PMT) is 160 to 260 ° C within a range of 15 to 90 seconds,
In particular, conditions within a range of 20 to 60 seconds at a PMT of 190 to 230 ° C are suitable.

[0042]

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

Examples 1 to 8 and Comparative Examples 1 to 6 Coatings were prepared according to the composition shown in Table 1 below to obtain respective top coatings. On a 0.5 mm thick electrogalvanized steel sheet subjected to chromate treatment, KP Color 8620 primer (polyester primer for pre-coated steel sheet) manufactured by Kansai Paint Co., Ltd. is applied to a dry film thickness of about 4 μm. Then, it was baked for 30 seconds so that the maximum temperature of the material reached 220 ° C. to obtain a primer-coated steel sheet. Each of the top coats obtained as described above was applied on this primer-coated steel sheet by a bar coater so that the dry coating weight was about 29 g / m ^2, and the maximum temperature at which the material reached reached 220 ° C. for 45 seconds. It was baked to obtain each overcoated steel sheet. Various tests were performed on the obtained coated steel sheet.

Table 3 shows the test results. The amounts of the polyester resin and the melamine resin in Table 1 are indicated by the weight of the solid content, and the amounts of the curing catalysts are indicated by weight in terms of the respective sulfonic acid compounds. 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. Also, cyclohexanone / Swazol 1500 (manufactured by Cosmo Oil Co., Ltd., aromatic petroleum solvent) / solvesso 200 (manufactured by Esso Oil Co., Ltd.)
A mixed solvent of (high-boiling-point petroleum solvent) = 60/20/20 (weight ratio) was used for adjusting the paint viscosity. At the time of painting, the paint viscosity was measured with Ford Cup # 4 for about 90 seconds (25
° C).

[0045]

[Table 1]

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

Each of the polyester resins (* 1) to (* 7) in Table 1 is a polyester resin manufactured by Toyobo Co., Ltd. and has the property values shown in Table 2 below.

[0048]

[Table 2]

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

(* 10) Aronmelt PES-085:
Toya Gosei Co., Ltd., polybutylene terephthalate powder,
Average particle size of about 40 μm, melt viscosity at 190 ° C. is 1
50 Pa · s. (* 11) Aronmelt PES-110: manufactured by Toagosei Co., Ltd., polybutylene terephthalate powder, average particle size of about 50 μm, melt viscosity at 190 ° C. of 165 Pa
-S. (* 12) Vestamelt 4681: polybutylene terephthalate powder, manufactured by Daicel Huels Co., Ltd., having an average particle size of about 20 μm or more and 60 μm or less. (* 13) Vestamelt 4580: polybutylene terephthalate powder, manufactured by Daicel Huels Co., Ltd., having an average particle size of about 20 μm or more and 70 μm or less.

(* 14) Olgasol 2002ES-
3: trade name, manufactured by Ato Simmy, France, resin fine particles of nylon 12, average particle diameter of about 30 μm. (* 15) Bellpearl R-800: manufactured by Kanebo Co., Ltd., trade name, phenol resin fine particles, average particle size of about 20 μm.
(* 16) Tuftic A-20: manufactured by Toyobo Co., Ltd., trade name, polyacrylonitrile resin fine particles, average particle diameter of about 26 μm. (* 17) Vestamelt 640: manufactured by Daicel Huels Co., Ltd., nylon fine powder, melting point: about 71 ° C., average particle diameter: about 20 μm or more and 70 μm or less.

(* 18) Nail cure 5225: Aqueous neutralized solution of dodecylbenzenesulfonic acid (manufactured by King Industries, USA) (neutralization equivalent: about 1.0).

[0053]

[Table 3]

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

Test Method Appearance of Coating Film: The appearance of the coating film was observed with the naked eye to evaluate the formability of the yuzu skin pattern and the presence / absence of abnormalities on the coated surface.

The formability of the yuzu skin pattern was evaluated according to the following criteria. ：: Yuzu skin pattern is formed uniformly. Δ: Yuzu skin pattern is formed but is not uniform. The presence or absence of abnormality in the coated surface was evaluated according to the following criteria. ：: Good with no coating surface abnormality such as a crack on the coated surface. ×: Poor with coating surface abnormality such as a crack on the coated surface.

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 scratches 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.

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

Bending workability: In a room at 20 ° C. and 0 ° C., the test plate was bent 180 ° with the painted surface outside,
The T number at which cracking did not occur in the bent portion was visually evaluated and displayed. The T number is defined as 0T when 180 ° bending is performed without putting anything inside the bent portion, and 1T when 2 sheets of the same thickness as the test plate are sandwiched and bent.
The number of sheets was 2T,... (The same applies hereinafter)..., And the number of sheets was 4T.

Blocking resistance: Two test plates were brought into close contact with each other at a temperature of 50 ° C. and a load of 80 kg / cm ² for 24 hours, and then the two test plates were peeled off. The ease of peeling was evaluated.

：: Coated surfaces are not adhered to each other, and the plate can be easily removed. △: Coated surfaces are adhered to each other and force is required to peel the plate, but no abnormality is observed in the peeled coated surface. It sticks strongly, and when peeled off, abnormalities are observed on the painted surface.

Solvent resistance: Approximately 1 kg / cm on the painted surface with gauze impregnated with methyl ethyl ketone in a room at 20 ° C.
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 <.

Accelerated weathering resistance: An accelerated weathering test was conducted for 1000 hours using a sunshine weatherometer, and the gloss was the ratio (%) of the gloss (60-degree specular reflectance) of the coated plate after the test to the coated plate before the test. The retention rate (GR%) is displayed.

Table 3 shows the dynamic elastic modulus E at 100 ° C. of the cured coating film and the molecular weight between crosslinks of the cured coating film of each of the coating materials of Examples and Comparative Examples. These measurements were performed by the above-mentioned measurement method.

[0066]

The coating composition of the present invention comprises two specific types of polyester resin, a melamine resin curing agent and an average particle size of 15%.
And a fine powder of polybutylene terephthalate having a thickness of about 70 μm. The fine powder of polybutylene terephthalate is melted during baking and curing to form a yuzu-skinned coating film. In addition, the cured coating film obtained from the coating composition should form a coating film that satisfies workability in winter, coating film hardness and blocking resistance in summer, and has excellent performance for coated steel sheets such as weather resistance. Can be.
In addition, the obtained coating film has a feature that the coating film surface is in the form of a crumple, so that coating film defects are less noticeable.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C09D 7/12 C09D 7/12 AZ // (C09D 167/00 161: 28)

Claims (6)

[Claims] (A) a number average molecular weight of 2,000 to 18,
Polyester resin having a glass transition temperature of -20 ° C or higher and lower than 5 ° C and a hydroxyl value of 5 to 60 mgKOH / g
20-80 parts by weight, (B) number average molecular weight 13,000-
30,000, glass transition temperature 5-35 ° C, hydroxyl value 2
Polyester resin of 25 mgKOH / g
100 parts by weight of a resin component comprising 5 parts by weight and 15 to 35 parts by weight of (C) a melamine resin curing agent, contains (D) 1 to 20 parts by weight of a polybutylene terephthalate fine powder having an average particle diameter of 15 to 70 μm. It is a coating composition, wherein the number average molecular weight of the polyester resin (B) is 1,000 or more larger than the number average molecular weight of the polyester resin (A). . 2. A cured coating film obtained from a coating composition, comprising:
Dynamic elastic modulus at 0 ° C. is 2.0 × 10 ⁸ dyne / c
and m ² or more, according to claim 1 coating composition according to the molecular weight between crosslinks is characterized in that it is a 300～1,300. 3. A mixed resin of a melamine resin and at least one melamine resin selected from a methyl etherified melamine resin and a mixed etherified melamine resin of methyl ether and butyl ether, wherein the melamine resin curing agent (C) is a mixed resin of butyl amine and melamine resin. The coating composition according to claim 1 or 2, wherein 4. The method of claim 1, wherein the curing catalyst is contained in an amount of 2.0 parts by weight or less in terms of an acid amount based on 100 parts by weight of the components (A), (B) and (C). The coating composition according to claim 3, characterized in that: 5. The method of claim 1, wherein the amine compound is (A)
0.1 to 100 parts by weight of the components (B) and (C)
The coating composition according to claim 4, wherein the coating composition is contained in an amount of 10 parts by weight. 6. A coated metal plate, wherein a cured coating film of the coating composition according to claim 1 is formed on a metal plate via a polyester-based primer coating film or an epoxy-based primer coating film. .