JP2000007984A - Coating material composition and coated steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating material composition capable of affording a precoated steel plate excellent in resistance to corrosion, acid and boiling water and in processibility without using a chromate rustproof pigment. SOLUTION: The objective coating material composition comprises film- forming resin components comprising (A) 20-90 pts.wt. of a hydroxyl group- containing polyester resin having a glass transition temperature of 10-100 deg.C and a number average mol.wt. of 2,000-25,000, (B) 5-70 pts.wt. of a novolak type epoxy resin and (C) 5-40 pts.wt. of at least one curing agent selected from amino resins and blocked polyisocyanates, and (D) 30-100 pts.wt., based on 100 pts.wt. of the total of the film forming resin components, of calcium ion- exchanged amorphous silica particulates. This coating material composition forms a cured coating film having a glass transition temperature of 40-80 deg.C. The coated steel plates are obtained by forming an undercoating from the above coating material composition on various steel plates and then forming thereon an overcoating film having a glass transition temperature of 20-80 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to acid resistance, corrosion resistance,
The present invention relates to a coating composition suitable for obtaining a coated steel sheet having excellent workability and boiling water resistance, and a coated steel sheet having a cured coating film of the coating composition provided with an overcoat film.

[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) 20 to 90 parts by weight of a hydroxyl group-containing polyester resin having a glass transition temperature of 10 to 100 ° C. and a number average molecular weight of 2,000 to 25,000, (B) 5 to 70 parts by weight of a novolak type epoxy resin, and (C) (D) calcium ion-exchanged amorphous based on 100 parts by weight of a total amount of a film-forming resin component comprising 5 to 40 parts by weight of at least one curing agent selected from an amino resin and a blocked polyisocyanate compound A paint composition containing 30 to 100 parts by weight of silica fine particles, wherein a cured coating film obtained by heating and curing the paint has a glass transition temperature of 40 to 90 ° C. Things.

Further, the present invention provides an undercoat film of the above-mentioned coating composition 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. With a glass transition temperature of 20
It is intended to provide a coated steel sheet provided with an overcoating film at -80 ° C.

[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 polyester resin (A) The hydroxyl-containing polyester resin as the component (A) of the composition of the present invention has a glass transition temperature of 10 to 100 ° C, preferably 20 to 80 ° C, and a number average molecular weight of 2, 000-25,
000, preferably in the range of 3,000 to 20,000, having a hydroxyl group, preferably a hydroxyl value of 2 to 100.
KOH mg / g. By having the characteristic value in the above range, a coating film having good workability, chemical resistance, workability, and coating workability can be formed. In the present invention, the glass transition temperature (Tg) is determined by differential thermal analysis (DTA).
And the number average molecular weight is by gel permeation chromatography (GPC).

Examples of the hydroxyl group-containing polyester resin (A) include oil-free polyester resins, oil-modified alkyd resins, and modified products of these resins, such as urethane-modified polyester resins, urethane-modified alkyd resins, and epoxy-modified polyester resins. No.

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.

Novolak type epoxy resin (B) The novolak type epoxy resin which is the component (B) in the composition of the present invention includes phenol novolak type epoxy resin, cresol novolak type epoxy resin and phenol having a large number of epoxy groups in the molecule. Various novolak type epoxy resins such as a glyoxal type epoxy resin can be exemplified. The novolak type epoxy resin preferably has a number average molecular weight of 2,000 or less.

Representative examples of the novolak type epoxy resin include resins represented by the following general formulas [1], [2] and [3].

[0019]

Embedded image

In the above formula, R ¹ represents a hydrogen atom or a methyl group; R ² represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a phenyl group or an aralkyl group having 7 to 10 carbon atoms; Represents an integer of 2 to 12.

[0021]

Embedded image

In the above formula, R ³ and R ⁴ are the same or different and each represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and m represents an integer of 1 to 5.

[0023]

Embedded image

In the above formula, R ¹ has the same meaning as described above.

In R ² in the above formula [1], examples of the alkyl group having 1 to 4 carbon atoms include methyl, ethyl, isopropyl, t-butyl and the like. Examples of the aralkyl group include benzyl, α-methylbenzyl, α, α-dimethylbenzyl, and a phenethyl group.

In R ³ and R ⁴ in the above formula [2],
Examples of the alkyl group having 1 to 3 carbon atoms include a methyl, ethyl, n-propyl, and isopropyl group.

As a commercially available product of the above novolak type epoxy resin, phenol novolak type is available as Epicoat 1
52 and 154 (all of which are manufactured by Yuka Shell Epoxy Co., Ltd.), EPPN-201 (manufactured by Nippon Kayaku Co., Ltd.),
Epototo YDPN-638 (manufactured by Toto Kasei Co., Ltd.) and the like, and as cresol novolak type, Epicoat 180S65 and 180H65 (all of which are manufactured by Yuka Shell Epoxy Co., Ltd.), EOCN-102S, EO
CN-103S, EOCN-104S (all manufactured by Nippon Kayaku Co., Ltd.), Epototo YDCN-701, -702, -703, -704 (Toto Kasei Co., Ltd.)
And epotote ZX-107.
1T, ZX-1015, ZX-1247, YDG
And -414S (both manufactured by Toto Kasei Co., Ltd.).

Curing Agent (C) The curing agent (C) can react with the hydroxyl group-containing polyester resin (A) and optionally the novolak type epoxy resin (B) by heating to cure the coating film. , An amino resin and a blocked polyisocyanate compound.

Examples of the amino resin include methylolated amino resins 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.

Of the above-mentioned amino resins, melamine resins are preferred. 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.), 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.

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

Examples of the polyisocyanate compound before blocking include aliphatic diisocyanates such as hexamethylene diisocyanate or trimethylhexamethylene diisocyanate; cycloaliphatic diisocyanates such as hydrogenated xylylene diisocyanate or isophorone diisocyanate; tolylene diisocyanate Or an organic diisocyanate itself such as an aromatic diisocyanate such as 4,4'-diphenylmethane diisocyanate, or an adduct of each of these organic diisocyanates with a polyhydric alcohol, a low molecular weight polyester resin or water, or each organic diisocyanate as 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 (C) may be composed of one kind of crosslinking agent or a mixture of two or more kinds of crosslinking agents.

In the composition of the present invention, the mixing ratio of the hydroxyl group-containing polyester resin (A), the novolak type epoxy resin (B) and the curing agent (C) is as follows:
It is as follows based on 100 parts by weight of the total solid content of the components (B) and (C).

Component (A): 20 to 90 parts by weight, preferably 20 to 70 parts by weight, Component (B): 5 to 70 parts by weight, preferably 10 to 50 parts by weight, Component (C): 5 to 40 parts by weight Parts, preferably 10 to 30 parts by weight.

When the amount of the component (A) is less than 20 parts by weight, the processability of the obtained coating film is apt to deteriorate, while when it exceeds 90 parts by weight, the corrosion resistance and boiling water resistance of the obtained coating film are lowered. It tends to decrease, and the coating workability also decreases. When the amount of the component (B) is less than 5 parts by weight, the component (B)
The effect of the components is not sufficient, and the corrosion resistance, especially when the salt spray test is performed, the corrosion resistance of the end face which is the cut surface of the coated plate, the boiling water resistance is inferior.
When a type of topcoat that cures by the catalytic action of an acid catalyst is applied on the resulting coating film, it causes curing inhibition,
The curability of the overcoat film becomes insufficient, and the solvent resistance and the processability of the paint film are liable to decrease. If the amount of the component (C) is less than 5 parts by weight, the curability of the coating film tends to decrease, while if it exceeds 40 parts by weight, the processability of the resulting coating film tends to decrease.

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 based on 100 parts by weight of the total solid content of the hydroxyl group-containing polyester resin (A), the novolak type epoxy resin (B) and the curing agent (C). On the other hand, 30 to 10
0 parts by weight, preferably in the range of 40 to 70 parts by weight.

The coating composition of the present invention comprises a hydroxyl group-containing polyester resin (A), a novolak type epoxy resin (B),
It can consist essentially of a curing agent (C) and an ion-exchanged silica (D), but usually contains an organic solvent and, if necessary, a curing catalyst and pigments such as titanium white; It may contain additives known per se, such as antifoaming agents, coating surface conditioners, and anti-settling agents.

The above-mentioned organic solvent is blended as required for improving the coating property of the composition of the present invention and the like.
Those which can dissolve or disperse the hydroxyl group-containing resin (A), the novolak type epoxy resin (B) and the curing agent (C) can be used. Specifically, for example, toluene, xylene,
Hydrocarbon solvents such as high boiling petroleum hydrocarbons, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and isophorone, and ester solvents such as ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate, and diethylene glycol monoethyl ether acetate Solvent, methanol, ethanol,
Examples thereof include alcohol solvents such as isopropanol and butanol, and ether alcohol solvents such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether and diethylene glycol monobutyl ether. These may be used alone or as a mixture of two or more. can do.

The curing catalyst is added as necessary to promote the reaction between the curing agent (C) and other film-forming resin components, and depends on the type of the curing agent (C). It is appropriately selected and used.

When the curing agent (C) contains a melamine resin, particularly a low-molecular-weight melamine resin of methyl etherification or a mixed etherification of methyl ether and butyl ether, a sulfonic acid compound or 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 (C) is a blocked polyisocyanate compound, a curing catalyst that promotes the dissociation of the blocking agent of the blocked polyisocyanate compound as the curing agent is preferable. 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, the blending amount of the curing catalyst is usually based on 100 parts by weight of the total amount of the film-forming resin component composed of the components (A), (B) and (C). Usually, it is preferable to be in the range of 0.1 to 2.0 parts by weight. Curing catalyst amount, when the curing catalyst is a sulfonic acid compound or an amine neutralized sulfonic acid compound,
It means the amount of sulfonic acid, and when the curing catalyst is an organometallic catalyst, it means the amount of 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 80 ° C., preferably 50 to 70 ° C., for example, acid resistance, corrosion resistance and workability of the coating film. It is preferable from the point of. The glass transition temperature of the coating film was determined by DINAMIC VISCOELASTOMETE
R MODEL VIBRON (Dynamic Visco Elastometer Model Vibron) DDV-II E
This is the maximum temperature determined from the change in tan δ by temperature dispersion measurement at a frequency of 110 Hz using a type A (manufactured by Toyo Baldwin Co., Ltd., automatic dynamic viscoelasticity analyzer).

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. The drying of the coating film may be appropriately set according to the type of the resin to be used and the like, but when continuously coated by a coil coating method or the like, the material reaching maximum temperature is usually 160 to 250. C., preferably 180 to 230.degree. C. for 15 to 60 seconds. When baking is performed in a batch system, baking can be performed at 80 to 140 ° C. for 10 to 30 minutes.

The coated steel sheet of the present invention is provided with an undercoat film of the above-described undercoat paint composition 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 80 ° C, preferably 30 to 70 ° C. 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 50 μm, preferably 10 to 25 μm.

The 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 excellent coating performance in acid resistance, corrosion resistance, workability, and boiling water resistance.

[0054]

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

Example 1 Byron EP-2940 (manufactured by Toyobo Co., Ltd., solid content 30)
% Epoxy-modified polyester resin solution, the resin has a number average molecular weight of about 10,000, a glass transition temperature of about 72 ° C.), 133.3 parts (40 parts by solid content), Epicoat 152
(Product name, phenol novolak type epoxy resin, manufactured by Yuka Shell Epoxy Co., Ltd.) 30 parts, Shielddex C3
03 (manufactured by WR Grace & Co., calcium ion-exchanged amorphous silica fine particles, average particle size of about 3 μm), 30 parts of titanium white and 30 parts of a mixed solvent [solvesso 150 (manufactured by Esso Petroleum Co., Ltd., aromatic Group hydrocarbon solvents)
1/1 (weight basis) mixed solvent of hexane and cyclohexanone]
Is mixed, and the tub (particle size of the pigment coarse particles) is 10
Dispersion was carried out until the size became less than micron. Next, 25 parts of Cymel 303 (manufactured by Mitsui Cytec Co., Ltd., methylated melamine resin) and Nailure 5225 (manufactured by King Industries, USA, amine salt of dodecylbenzenesulfonic acid, active ingredient: about 25%) were added to the dispersion. 1.5 parts was added and mixed uniformly, and the mixed solvent was further added to adjust the viscosity to about 80 seconds (Ford cup # 4/25 ° C.) to obtain a coating composition.

Examples 2 to 7 and Comparative Examples 1 to 4 In the same manner as in Example 1, the pigment component was dispersed by using a film-forming resin component other than the curing agent and a mixed solvent. A coating composition was obtained in the same manner as in Example 1 except that the composition was as shown. 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) Byron GK-78CS: manufactured by Toyobo Co., Ltd., a polyester resin solution having a solid content of 40%, the number average molecular weight of the resin is about 10,000, and the glass transition temperature is about 40 ° C. (Note 2) Byron 29CS: manufactured by Toyobo Co., Ltd., solid content 3
A 0% polyester resin solution, the number average molecular weight of the resin is about 20,000, and the glass transition temperature is about 72 ° C. (Note 3) Byron 59CS: manufactured by Toyobo Co., Ltd., solid content 5
0% polyester resin solution, number average molecular weight of resin is about 6,000, glass transition temperature is about 15 ° C. (Note 4) 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 20,000, and the glass transition temperature is about -3 ° C.

(Note 5) Epicoat 154: a phenol novolak type epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd. (Note 6) Epicoat 180S65: manufactured by Yuka Shell Epoxy Co., Ltd., trade name, cresol novolac type epoxy resin. (Note 7) Epicoat 1010: Bisphenol A type epoxy resin solution having a solid content of 40%, 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 8) Coronate 2507: Nippon Polyurethane Co., Ltd., isocyanurate block of hexamethylene diisocyanate, solid content: about 80%. (Note 9) 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. 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.

[0063]

[Table 1]

Example 8 The coating composition obtained in Example 1 was applied to a 0.4 mm-thick hot-dip galvanized steel sheet (galvanized weight: 60 g / m ² ) obtained by chromate treatment to a dry film thickness of 5 μm. It was then coated with a bar coater and baked for 40 seconds so that the maximum temperature of the material reached 220 ° C. to obtain an undercoat film. Then, on each of these undercoat films, Alestec AT2000 White [Kansai Paint Co., Ltd., a polyester resin-based topcoat for advanced processing, white, the glass transition temperature of the cured film is about 3
[1 ° C.] using a bar coater so as to have a film thickness of about 18 μm, and baked for 60 seconds under the condition that the maximum temperature of the material reached 230 ° C. to obtain a coated plate.

Examples 9 to 14 and Comparative Examples 5 to 8 A coated plate was prepared in the same manner as in Example 8 except that the coating composition shown in Table 2 below was used instead of the coating composition of Example 1 as an undercoat. I got

Examples 15 to 17 Except that the following materials were used in place of the chromate-treated 0.4 mm thick hot-dip galvanized steel sheet as the base material, using the paint of Example 2 as the undercoat paint, respectively. A coated plate was prepared in the same manner as in Example 8.

The material types used in Examples 15 to 17 are as follows.

In Example 15, a chromate-treated zinc-aluminum alloy-plated steel sheet having a thickness of 0.4 mm (aluminum content in plating: about 5%) [in Table 1, abbreviated as "Zn-5% Al"] ], In Example 16, a 0.4 mm-thick chromate-treated zinc-aluminum alloy-plated steel sheet (aluminum content of about 55% in the plating) [in Table 1, "Zn-55% Al"
In Example 17, a chromated aluminum-plated steel sheet having a thickness of 0.4 mm [abbreviated as “Al steel sheet” in Table 1] was used.

With respect to the coated plates obtained in Examples 8 to 17 and Comparative Examples 5 to 8, the coating properties of the coated plates were evaluated by the following test methods. The test results are shown in Table 2 below.

Test Method Workability: A coated plate was cut into a size of 70 × 150 mm.
At room temperature of 20 ° C. and 0 ° C., the coated plate was bent 180 degrees with a vise with the surface of the coated plate facing outside, and the minimum T number at which no cracks occurred in the bent portion was 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 when 180 ° bending is performed without any pinching inside the bent portion, 1T when one plate with the same thickness as the painted plate is bent, 2T
The number of sheets is 2T, and the number of sheets is 3T.

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.

Rust generation degree in the processed part ：: No rust is generated in the processed part, ：: Rust generation is recognized but less than 10% of the length of the processed part, Δ: Rust 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 processed portion , average blister width of the cross-cut portion ◎: No blister is observed in the cross-cut portion ○: One side from the cut scratch The average blister width 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. X: 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 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.

Water resistance to boiling: After the coated plate was immersed in boiling water at about 100 ° C. for 20 hours, it was pulled up and the appearance of the coating film surface was evaluated.

◎: No abnormality such as swelling is observed in the coating film. ：: Slight swelling is observed in the coating film. Swelling is observed.

[0076]

[Table 2]

[0077]

The coating composition of the present invention can be suitably used as an undercoat coating composition because it can form a coating film having excellent corrosion resistance, processability, acid resistance and boiling water 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 has a coating film excellent in corrosion resistance, workability, acid resistance and boiling water resistance.

The coating composition of the present invention can be suitably used as an undercoat for precoated steel sheets.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 163/04 C09D 163/04 175/04 175/04 C23C 28/00 C23C 28/00 C // C08G 18 / 80 C08G 18/80 F term (reference) 4D075 AE03 BB73X CA33 CA38 CA44 DA03 DB05 DB07 DC18 EA05 EB33 EB35 EB38 EB39 EB45 EB52 EB53 EB56 EC03 EC54 4J034 DA01 DA08 DF01 DF12 DF16 HC12 HC17 HC12 HC22 HC03 HC07 HC07 HC71 HC73 HD03 HD04 HD05 HD12 RA07 4J038 DA192 DA202 DA212 DB072 DD041 DD051 DD111 DD121 DD231 DD241 DG302 GA03 HA446 KA03 KA08 MA13 MA14 NA04 NA12 NA27 PA19 PB09 PC02 4K044 AA02 AB02 BA10 BA14 BA15 BA17 CA21 BB03 BC18 CA05 BB03

Claims (2)

[Claims] 1. A glass transition temperature of (A) 10 to 100 ° C.
A number-average molecular weight of 2,000 to 25,000, 20 to 90 parts by weight of a hydroxyl group-containing polyester resin, (B) 5 to 70 parts by weight of a novolak type epoxy resin, and (C) an amino resin and a blocked polyisocyanate compound. (D) a paint containing 30 to 100 parts by weight of calcium ion-exchanged amorphous silica fine particles based on 100 parts by weight of the total amount of the film-forming resin component comprising 5 to 40 parts by weight of at least one curing agent Wherein the glass transition temperature of a cured coating film obtained by heating and curing the coating material is 40 to 90 ° C. 2. 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.