JPH11222575A - Coating composition and coated steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating composition which can be used for producing a precoated steel having excellent corrosion resistance, processability and acid resistance without using a chromate anticorrosive pigment. SOLUTION: This coating composition comprises a coating which contains, relative to 100 pts.wt. of the total amount of a film-forming resin component consisting of (A) 65-95 pts.wt. at least one hydroxyl group-containing resin selected from a polyester resin and an epoxy resin, which has a glass transition temperature of 10-100 deg.C and a number average molecular weight of 2,000-25,000, and (B) 5-35 pts.wt. curing agent selected from an amino-aldehyde resin and a blocked polyisocyanate compound, (C) 30-100 pts.wt. calcium ion-exchanged noncrystalline silica fine particles, wherein a cured film of the coating has a glass transition temperature of 40-115 deg.C. A top coating film having a glass transition temperature of 20-80 deg.C is applied on a prime coating film formed with the above coating composition on various kinds of steel sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a coating composition for a steel sheet which is suitable for obtaining a coated steel sheet having excellent acid resistance, corrosion resistance and workability, and a top coating film formed on a cured coating film of the coating composition. It relates to the provided painted steel plate.

[0002]

2. Description of the Related Art
In the coating of home appliances, so-called post-coating, in which the steel sheet is molded and then painted by the home appliance manufacturer, has been performed in many cases.However, the evaporation of solvent vapor and formalin during the baking of paint has caused a deterioration in the work environment, especially in the global environment. It has a negative effect on air pollution.

[0003] In recent years, in order to eliminate adverse effects on the working environment and the global environment, and to reduce the complexity of painting on the home appliance maker side, steel sheet is coated on the steel sheet maker side by a coil coating method, a sheet coating method, or the like. A so-called pre-coat method has been adopted in which a coated steel sheet (hereinafter sometimes abbreviated as “pre-coated steel sheet”) is obtained by baking in a closed system, and the coated steel sheet is molded by a home appliance manufacturer.

In the case of precoated steel sheets, the glass transition temperature (hereinafter sometimes abbreviated as “Tg”) of the overcoat film is usually in the range of 20 to 80 ° C., and severe processing such as press molding is particularly performed during processing. In this case, the workability must be excellent, and the Tg of the overcoat film is generally 20
A material as low as about 65 ° C. is used.

[0005] In a precoated steel sheet, the corrosion resistance of the above-mentioned processed portion and the corrosion resistance of the scratched portion when the coating film surface is scratched are very important. In order to satisfy such corrosion resistance, countermeasures such as improvement of the resin composition of the paint and increase of the amount of chromate rust preventive pigment are generally taken. However, sufficient corrosion resistance cannot be obtained only by improving the resin composition, and the chromate rust preventive pigment has a problem in terms of safety and health because it generates hexavalent chromium.

[0006] Further, precoated steel sheets are increasingly used for outdoor applications such as outdoor units for air conditioners and the like, and there is an increasing demand for acid resistance outdoors due to the problem of acid rain. However, as described above, in general, a pre-coated steel sheet has a high concentration of chromate rust-preventive pigment that is easy to elute in a base coat, and the Tg of a top coat is generally low,
Furthermore, since the total coating film thickness is thin,
When it comes into contact with an acidic solution having a low acidity, the acidic solution easily penetrates through the coating film, dissolving the steel sheet surface, easily causing blisters, and has a problem of poor acid resistance.

Accordingly, the present inventors have solved these problems and obtained a precoated steel sheet having excellent corrosion resistance, workability, and acid resistance in a worked portion or a scratched portion without using a chromate rust preventive pigment. As a result of intensive studies to develop a coating composition capable of performing the above, it was found that the above object can be achieved by using a coating in which calcium ion-exchanged silica fine particles are combined with a specific film-forming resin component. Was completed.

[0008]

That is, the present invention provides:
(A) at least one resin selected from polyester resins and epoxy resins, having a glass transition temperature of 10 to 100 ° C. and a number average molecular weight of 2,000 to 25,
To a total of 100 parts by weight of a film-forming resin component comprising 65 to 95 parts by weight of a hydroxyl group-containing resin of 000 and 5 to 35 parts by weight of at least one curing agent selected from (B) an amino resin and a blocked polyisocyanate compound. On the other hand, (C) a paint containing 30 to 100 parts by weight of amorphous silica fine particles subjected to calcium ion exchange,
The present invention also provides a coating composition characterized in that a cured coating film obtained by heat-curing the coating has a glass transition temperature of 40 to 115 ° C.

The present invention also provides an undercoating film of the coating composition according to claim 1 on a galvanized steel sheet, a zinc alloy-plated steel sheet or an aluminum-plated steel sheet, which may be subjected to a chemical conversion treatment. It is intended to provide a coated steel sheet wherein a top coat having a glass transition temperature of 20 to 80 ° C is provided on the undercoat.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Each component of the coating composition of the present invention will be described in detail below.

Hydroxyl-containing resin (A) The hydroxyl-containing resin as the component (A) of the composition of the present invention is selected from polyester resins and epoxy resins, and has a glass transition temperature of 10 to 100 ° C, preferably At 25 to 90 ° C, the number average molecular weight is 2,000 to 2,
5,000, preferably 3,000 to 20,000 hydroxyl group-containing resin, preferably a hydroxyl value of 2 to 100
mg KOH / g. In the present invention, the glass transition temperature (Tg) is measured by differential scanning calorimetry (DSC).

The polyester resin, which is one of the hydroxyl group-containing resins (A), is a hydroxyl group-containing polyester resin, and is an oil-free polyester resin, an oil-modified alkyd resin, or a modified product of these resins, for example, a urethane-modified resin. Examples include polyester resins, urethane-modified alkyd resins, and epoxy-modified polyester resins.

The above oil-free polyester resin comprises an esterified product of a polybasic acid component and a polyhydric alcohol component. As the polybasic acid component, for example, one or more selected from phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic acid, fumaric acid, adipic acid, sebacic acid, maleic anhydride, and the like Dibasic acids and lower alkyl esterified products of these acids are mainly used, and if necessary, monobasic acids such as benzoic acid, crotonic acid, pt-butylbenzoic acid, trimellitic anhydride, methylcyclohexenetricarboxylic acid And tribasic or higher polybasic acids such as pyromellitic anhydride. Examples of the polyhydric alcohol component include ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol,
Dihydric alcohols such as neopentyl glycol, 3-methylpentanediol, 1,4-hexanediol, and 1,6-hexanediol are mainly used, and if necessary, glycerin, trimethylolethane, trimethylolpropane, and pentane. A trihydric or higher polyhydric alcohol such as erythritol can be used in combination. These polyhydric alcohols can be used alone or in combination of two or more. In addition, a part of the acid component and the alcohol component can be replaced with oxyacid components such as dimethylolpropionic acid, oxypivalic acid, and paraoxybenzoic acid; lower alkyl esters of these acids; and lactones such as ε-caprolactone. . Esterification or transesterification of these 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 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.

The epoxy resin as one of the hydroxyl group-containing resins (A) is an epoxy resin having a hydroxyl group,
Also included are polymerized fatty acids such as saturated aliphatic monocarboxylic acids, dibasic acids, and dimer acids, and epoxy resins modified with a modifier such as an isocyanate compound.

As the epoxy resin, bisphenol type epoxy resins, novolak type epoxy resins, and modified epoxy resins thereof are preferably used. In the production of the modified epoxy resin, the modification time is not limited, and may be modified during the production of the epoxy resin or may be modified after the production of the epoxy resin.

The above-mentioned bisphenol type epoxy resin can be obtained by reacting, for example, epihalohydrin, bisphenols and, if necessary, a modifier such as a saturated aliphatic monocarboxylic acid, a dibasic acid or a polymerized fatty acid according to a conventional method. As the epihalohydrin used as a raw material, epichlorohydrin is particularly preferred. Examples of bisphenols include, for example, bis (4-hydroxyphenyl) methane [abbreviation: bisphenol F], 1,1
-Bis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxyphenyl) propane [abbreviation, bisphenol A], 2,2-bis (4-hydroxyphenyl) butane [abbreviation, bisphenol B], bis ( 4-hydroxyphenyl) -1,1-isobutane, bis (4-
(Hydroxy-tert-butyl-phenyl) -2,2-propane, p- (4-hydroxyphenyl) phenol, oxybis (4-hydroxyphenyl), sulfonylbis (4-hydroxyphenyl), 4,4'-dihydroxybenzophenone, etc. Can be mentioned.

Examples of the novolak type epoxy resin usable as the epoxy resin include various novolak types such as phenol novolak type epoxy resin, cresol novolak type epoxy resin, and phenol glyoxal type epoxy resin having a large number of epoxy groups in a molecule. Type epoxy resin.

Curing Agent (B) The curing agent (B) is capable of reacting with the hydroxyl group-containing resin (A) to cure the resin (A), and is selected from amino resins and blocked polyisocyanate compounds. At least one of the following.

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

Among the above-mentioned amino resins, melamine resins are preferable. Among them, methyl etherified melamine resin, mixed etherified melamine resin of methyl ether and butyl ether, or methyl etherified melamine resin or the above mixed etherified melamine resin is preferable. It is preferable that the mixed melamine resin contains 60% by weight or more and 40% by weight or less of the butyl etherified melamine resin.

Specific examples of the melamine resin include Cymel 300, 303, 325, 327, 350, 730, 736, and 738 (all of which are manufactured by Mitsui Cytec Co., Ltd.) 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.

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

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

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

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

The curing agent (B) may be composed of one type of crosslinking agent, or may be a mixture of two or more types of crosslinking agents.

In the composition of the present invention, the blending amount of the hydroxyl group-containing resin (A) and the curing agent (B) is such that the total solid content of (A) and (B) is 100 parts by weight of the hydroxyl group-containing resin (B). A) is 65 to 95 parts by weight, preferably 75 to 92 parts by weight, and the curing agent (B) is 35 to 5 parts by weight, preferably 8
２５25 parts by weight.

Calcium ion exchanged amorphous silica
Fine Particles (C) In the composition of the present invention, the (C) component, calcium ion-exchanged amorphous silica fine particles (hereinafter sometimes abbreviated as “ion-exchanged silica”), is a fine porous silica carrier. These are silica fine particles into which calcium ions have been introduced by ion exchange. The ion-exchanged silica compounded in the coating film is ion-exchanged with H ⁺ ions transmitted through the coating film, and calcium ion Ca, which is a rust preventive seed ion,
It is believed that ²⁺ is released to protect the metal surface.
Commercially available ion-exchanged silica is SHIELDEX
(Shielddex, registered trademark) C303, AC-3,
C-5 (both are WR Grace & C
o. And the like).

In the composition of the present invention, the compounding amount of the ion-exchanged silica (C) is 30 parts by weight based on 100 parts by weight of the total solid content of the hydroxyl group-containing resin (A) and the curing agent (B).
To 100 parts by weight, preferably 40 to 70 parts by weight.

The coating composition of the present invention can consist essentially of the hydroxyl group-containing resin (A), the curing agent (B) and the ion-exchange silica (C). Depending on the curing agent, a curing catalyst, pigments such as titanium white, and additives such as antifoaming agents, coating surface conditioners, and anti-settling agents known per se for paints may be contained.

The above-mentioned organic solvent is blended as required for improving the coating property of the composition of the present invention.
Those which can dissolve or disperse the hydroxyl group-containing resin (A) and the curing agent (B) can be used. Specifically, for example, hydrocarbon solvents such as toluene, xylene, and 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, isopropanol and butanol, ethylene glycol monoethyl Examples thereof include ether alcohol solvents such as ether, ethylene glycol monobutyl ether, and diethylene glycol monobutyl ether, and these can be used alone or as a mixture of two or more.

The curing catalyst is blended as necessary to promote the reaction between the hydroxyl group-containing resin (A) and the curing agent (B), and depends on the type of the curing agent (B) and the like. It is appropriately selected and used.

When the curing agent (B) contains a melamine resin, especially a low-molecular-weight melamine resin of methyl etherification or a mixed etherification of methyl ether and butyl ether, a sulfonic acid compound or a sulfonic acid compound is used as a curing catalyst. Amine neutralized products are preferably used. Representative examples of the sulfonic acid compound include p-toluenesulfonic acid,
Dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid and the like can be mentioned. The amine in the amine-neutralized sulfonic acid compound may be any of a primary amine, a secondary amine and a tertiary amine. Among these, from the viewpoint of the stability of the paint, the reaction promoting effect, and the physical properties of the obtained coating film,
An amine neutralized product of p-toluenesulfonic acid and / or an amine neutralized product of dodecylbenzenesulfonic acid are preferred.

When the curing agent (B) is a blocked polyisocyanate compound, a curing catalyst which promotes the dissociation of the blocking agent of the blocked polyisocyanate compound as a crosslinking agent is suitable. For example, tin octylate, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide, 2-ethyl An organic metal catalyst such as lead hexanoate may be used.

When these curing catalysts are blended, usually 0.1 parts by weight based on 100 parts by weight of the total amount of the film-forming resin component comprising the hydroxyl group-containing resin (A) and the curing agent (B). It is blended in the range of 2.0 parts by weight. When the curing catalyst is a sulfonic acid compound or an amine neutralized sulfonic acid compound, the curing catalyst means an amount converted to the amount of the sulfonic acid, and when the curing catalyst is an organometallic catalyst,
It means the solid content.

In the composition of the present invention, the cured coating film obtained from the composition of the present invention has a glass transition temperature of 40 to 115 ° C., preferably 50 to 105 ° C., for example, acid resistance, corrosion resistance and workability of the coating film. It is preferable from the point of view. The glass transition temperature of the coating film is DINAMIC VISCOELASTOME
TER MODEL VIBRON (Dynamic Visco Elastometer Model Vibron) DDV-II
This is the maximum temperature determined from the change in tan δ by temperature dispersion measurement at a frequency of 110 Hz using an EA type (automatic dynamic viscoelasticity meter manufactured by Toyo Baldwin Co.).

Next, a coated steel sheet using the composition of the present invention will be described.

The composition of the present invention can be used, for example, as an undercoat paint for steel sheets. The steel sheets to be coated include cold-rolled steel sheets, hot-dip galvanized steel sheets, electrogalvanized steel sheets, zinc alloy-plated steel sheets, and aluminum-plated steel sheets. Examples include steel sheets, stainless steel sheets, copper-plated steel sheets, tin-plated steel sheets, and steel sheets obtained by subjecting these steel sheets to a chemical conversion treatment such as a phosphate treatment or a chromate treatment. Steel sheets, zinc alloy plated steel sheets, and aluminum plated steel sheets are preferred.

The composition of the present invention can be coated on the steel plate by a known method such as a roll coating method, a spray method, a brush coating method, and a dipping method. The thickness of the coating film obtained from the composition of the present invention is not particularly limited,
Usually, it is used in the range of 2 to 10 μm, preferably 3 to 6 μm. Drying of the coating film may be appropriately set according to the type of resin used, etc.
Maximum temperature at which the material reaches 160 to 250 ° C, preferably 18
It is baked for 15 to 60 seconds under the condition of 0 to 230 ° C. In the case of baking in a batch mode, 1 to 80 to 140 ° C
It can also be performed by baking for 0 to 30 minutes.

The coated steel sheet of the present invention is provided with an undercoat film of the undercoat paint composition of the present invention on a galvanized steel sheet, a zinc alloy-plated steel sheet, or an aluminum-plated steel sheet, which may be subjected to a chemical conversion treatment. Tg is 2 on the undercoat
It is provided with a top coat of 0 to 80C, preferably 30 to 65C. The thickness of the undercoat film is usually 2 to 10
μm, preferably 3 to 6 μm, and the thickness of the overcoat film is usually 8 to 30 μm, preferably 10 to 25 μm.

This coated steel sheet can be suitably obtained by applying the undercoat paint of the present invention by a roll coat method and baking, then applying a top coat paint by a roll coat method and baking. Examples of the top coat that forms the top coat include, for example, known top coats for pre-coated steel sheets, such as polyester resin, alkyd resin, silicon-modified polyester resin, silicon-modified acrylic resin, and fluororesin. Can be. When workability is particularly important, a coated steel sheet with particularly excellent workability can be obtained by using a polyester-based topcoat for advanced processing. The coated steel sheet of the present invention can exhibit a coating film excellent in acid resistance, corrosion resistance and workability.

[0045]

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

Example 1 30% Byron EP-2940 [manufactured by Toyobo Co., Ltd., an epoxy-modified polyester resin solution having a solid content of 30%, the number average molecular weight of the resin is about 10,000, and the glass transition temperature is about 72.
° C], 35 parts of Shieldex C303 (manufactured by WR Grace & Co., calcium ion-exchanged amorphous silica fine particles, average particle diameter of about 3 μm), titanium white 30 parts and an appropriate amount of a mixed solvent [1/1 (weight basis) mixed solvent of Solvesso 150 (manufactured by Esso Oil Co., Ltd., aromatic hydrocarbon-based solvent) and cyclohexanone] were mixed, and the tub (particle diameter of pigment coarse particles) was mixed. ) Was reduced to 10 microns or less. Next, Cymer 303 [manufactured by Mitsui Cytec Co., Ltd.
Methylated melamine resin] 25 parts and Nail cure 5225
1.5 parts of an amine salt of dodecylbenzenesulfonic acid (manufactured by King Industry Co., USA, active ingredient: about 25%) were added and mixed uniformly, and the mixed solvent was further added to obtain a viscosity of about 80 seconds (Ford Cup # 4). / 25 ° C) to obtain a coating composition.

Examples 2 to 7 and Comparative Examples 1 to 4 Coating compositions were obtained in the same manner as in Example 1 except that the coating composition was changed to the composition shown in Table 1 below. The blending amounts in Table 1 are indicated by parts by weight (solid content or active ingredient content).

(Note) in Table 1 is as follows.

(Note 1) 40% Byron GK-78CS:
A polyester resin solution having a solid content of 40% manufactured by Toyobo Co., Ltd. The resin has a number average molecular weight of about 10,000 and a glass transition temperature of about 40 ° C. (Note 2) 40% Byron 29CS: a polyester resin solution having a solid content of 30%, manufactured by Toyobo Co., Ltd. The number average molecular weight of the resin is about 20,000, and the glass transition temperature is about 72 ° C. (Note 3) 50% Byron 59CS: manufactured by Toyobo Co., Ltd., a polyester resin solution having a solid content of 50%, the number average molecular weight of the resin is about 6,000, and the glass transition temperature is about 15 ° C. (Note 4) 40% Super Beckolite TF-787: manufactured by Dainippon Ink and Chemicals, Inc., a polyester resin solution having a solid content of 40%, the number average molecular weight of the resin is about 2,000,
Glass transition temperature is about -3 ° C.

(Note 5) 40% Epoch 820 40C
X: a urethane-modified epoxy resin solution having a solid content of 40% manufactured by Mitsui Chemicals, Inc. The number average molecular weight of the resin is about 6,000,
Glass transition temperature is about 64 ° C. (Note 6) 40% epicoat 1010: Bisphenol A type epoxy resin solution, manufactured by Yuka Shell Epoxy Co., Ltd. The resin has a number average molecular weight of about 5,500 and a glass transition temperature of about 70 ° C.

(Note 7) Coronate 2507: Nippon Polyurethane Co., Ltd., isocyanurate block of hexamethylene diisocyanate, solid content: about 80%. (Note 8) Takenate TK-1: Takeda Pharmaceutical Co., Ltd., organotin-based blocking agent dissociation catalyst, solid content: about 10%.

The glass transition temperatures of the cured coating films obtained from the coating compositions obtained in Examples 1 to 7 and Comparative Examples 1 to 4 were measured by the following method. Further, a coating film performance test was performed on each of the coating compositions obtained in the above Examples and Comparative Examples.
The results are shown in Table 1 below.

Glass transition temperature of cured coating film The coating composition of each of the above examples was applied to a tin plate with a dry film thickness of about 15
μm, and the maximum temperature of the tin plate is 2
It was baked for 30 seconds at 20 ° C. to cure. The cured coating film was peeled off from the tin plate by a mercury amalgam method to obtain a free coating film. This free coating film is cut into a predetermined size, and three sheets are stacked, and DINAMIC VISC
OELASTOMETER MODEL VIBRON
(Dynamic Visco Elastometer Model Vibron) Frequency 110 Hz using DDV-II EA type (Toyo Baldwin Co., Ltd., automatic dynamic viscoelasticity measuring instrument)
Is the maximum temperature determined from the change in tan δ by the temperature dispersion measurement at.

Coating performance test A hot-dip galvanized steel sheet (zinc basis weight 60 g / m ² ) having a thickness of 0.4 mm, which had been subjected to a chromate treatment, was prepared in the same manner as in Examples 1 to 4.
7 and each of the coating compositions obtained in Comparative Examples 1-4 had a dry film thickness of 5
It was coated with a bar coater to a micron size and baked for 40 seconds so that the maximum temperature of the material reached 220 ° C. to obtain an undercoat film. Next, on each of these undercoat films, Alestec AT2000 White [manufactured by Kansai Paint Co., Ltd., a polyester resin-based topcoat for advanced processing, white, the glass transition temperature of the cured film is about 31 ° C.] is applied using a bar coater. The coating was applied to a thickness of about 18 microns and baked for 60 seconds under the condition that the maximum temperature of the material reached 230 ° C. to obtain a coated plate. This coated plate was subjected to the following various coating film performance tests to evaluate the overall coating film on the surface. The test results are shown in Table 1 below.

Workability: The coated plate was cut into a size of 70 × 150 mm, and at room temperature of 20 ° C., the coated plate was bent 180 ° with a vise with the surface of the coated plate facing outside, and the bent portion was formed. The minimum T number at which cracking does not occur is indicated.
The T number means the number of plates having the same thickness as the painted plate sandwiched inside the bent portion when performing the bending process, and the smaller the T number, the better the workability. 0T for the case of bending 180 degrees without pinching anything inside the bent part,
When one sheet of the same thickness as the painted board is sandwiched and bent,
T is 2T for two images and 3T for three images.

Corrosion resistance: After the coated plate was cut into a size of 70 × 150 mm, the back surface and the cut surface were sealed with a rust preventive paint. Next, a cross-cut that reaches the base was placed at the approximate center of the coated plate, and a 1T bending process was performed at a position about 1 cm from the end of the coated plate to obtain a test plate. This test plate was subjected to JIS Z-2371. It was subjected to the salt spray test according to it. The salt spray test time was set to 700 hours, the degree of rust generation in the processed portion, and the average blister width in the cross cut portion were visually evaluated according to the following criteria.

Degree of rust generation in the processed part ◎: No rust is generated in the processed part, ○: Degree of rust is less than 10% of the length of the processed part, but Δ: Rust is generated The degree is 10% or more of the length of the processed part, 30%
Less than: ×: The degree of rust generation is 30% or more of the length of the machined portion , average blister width of the cross cut portion ◎: No blister is observed in the cross cut portion, ○: One side from the cut scratch Is less than 1 mm, Δ: The average blister width on one side from the cut is 1 mm or more and less than 5 mm, ×: The average blister width on one side from the cut is 5 mm or more.

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 is observed in the coating film. ：: The coating swelling area is less than 10%. Δ: The coating swelling area is 10% or more and less than 50%. X: The coating swelling area is 50% or more.

Examples 8 to 10 Except that the following materials were used instead of the chromate-treated hot-dip galvanized steel sheet having a thickness of 0.4 mm using the paint of Example 2 as the undercoat paint, respectively. A coated plate was prepared in the same manner as in Example 2 and subjected to various coating film performance tests in the same manner as described above. The results of these tests are shown in Table 1 below.

The material types used in Examples 8 to 10 are as follows.

In Example 8, a chromate-treated zinc-aluminum alloy-plated steel sheet having a thickness of 0.4 mm (aluminum content in plating: about 5%) [abbreviated as "Zn-5% Al" in Table 1] In Example 9, a zinc-aluminum alloy plating having a thickness of 0.4 mm and subjected to a chromate treatment (the aluminum content in the plating was about 5 mm)
5%) steel sheet [abbreviated as "Zn-55% Al" in Table 1], and in Example 10, a 0.4 mm-thick chromated aluminum-plated steel sheet [abbreviated as "Al steel sheet" in Table 1. Yes] was used for each.

[0062]

[Table 1]

[0063]

The coating composition of the present invention can be suitably used as an undercoat coating composition since it can form a coating film having excellent corrosion resistance, processability and acid resistance. Since the coating composition of the present invention does not require the use of a chromate pigment as a rust preventive pigment, it can solve the problem of hexavalent chromium and is advantageous in terms of safety and health.

The coated steel sheet having an overcoat film formed on the undercoat film from the coating composition of the present invention can form a coating film having excellent corrosion resistance, workability and acid resistance. The composition can be suitably used as a primer for a precoated steel sheet.

Claims (4)

[Claims] (A) at least one resin selected from a polyester resin and an epoxy resin, having a glass transition temperature of 10 to 100 ° C. and a number average molecular weight of 2,
Hydroxyl-containing resin 65-95 having a molecular weight of 2,000-25,000
(C) calcium ion exchange with respect to 100 parts by weight and (B) a total amount of 100 parts by weight of a film-forming resin component comprising 5 to 35 parts by weight of at least one curing agent selected from an amino resin and a blocked polyisocyanate compound. A paint containing 30 to 100 parts by weight of the obtained amorphous silica fine particles, wherein a glass transition temperature of a cured coating film obtained by heating and curing the paint is 40 to 115 ° C. Composition. 2. A paint wherein the hydroxyl group-containing resin (A) is a polyester resin, wherein a cured coating film obtained by heating and curing the paint has a glass transition temperature of 40 to 80 ° C. Item 7. The coating composition according to Item 1. 3. A coating material in which the hydroxyl group-containing resin (A) is an epoxy resin, wherein the cured coating film obtained by heating and curing the coating material has a glass transition temperature of 70 to 115 ° C. Item 7. The coating composition according to Item 1. 4. An undercoat film of the coating composition according to claim 1 is provided on a galvanized steel sheet, a zinc alloy-plated steel sheet or an aluminum-plated steel sheet, which may be subjected to a chemical conversion treatment. Glass transition temperature of 20-8
A coated steel sheet provided with a top coat of 0 ° C.