JPH11256099A - Coating composition and coated steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating compsn. which can form a coating film which exhibits excellent process adhesion and scratch resistance in the initial and secondary stages and is excellent in corrosion resistance. SOLUTION: This coating compsn. contains (A) a hydroxyl-group-contg. resin comprising at least one resin selected from among polyester resins and epoxy resins and having a glass transition temp. of 10-100 deg.C and a number average mol.wt. of 2,000-25,000, (B) at least one curative selected from among amino resins and blocked polyisocyanate compds., (C) a chromium-free rustproof pigment, and (D) a conductive high-molecular compd., the wt. ratio of A/B being (65/35)-(95/5). Various steel sheets are coated with the compsn. as an undercoating and then with a topcoating compsn. to give coated steel sheets.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to scratch resistance,
The present invention relates to a coating composition for a steel sheet which is suitable for obtaining a coated steel sheet having excellent processing adhesion and corrosion resistance, and a coated steel sheet provided with an overcoat film on a cured coating film of the coating composition.

[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.

[0004] In the case of a pre-coated steel sheet, from the viewpoint of durability, the coated film has good working adhesion when processed by pressing or the like, and the coated film does not have a good impact when a shock is applied to the surface of the coated film. It is very important that the material is not easily peeled off from the substrate, that is, it has good scratch resistance. These performances are required in both the initial performance and the secondary performance (the performance after the boiling water immersion treatment). However,
In general, those with good workability tended to have poor scratch resistance, and those with good scratch resistance tended to have poor workability.

[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 generates hexavalent chromium, which has a problem in safety and hygiene.

Accordingly, the present inventors have solved the above problems, and have developed a precoat having excellent initial and secondary performances in processing adhesion and scratch resistance and excellent corrosion resistance without using a chromate rust preventive pigment. As a result of intensive studies to develop a coating composition capable of obtaining steel sheets, the use of a paint that combines a non-chromium-based antirust pigment and a conductive polymer compound with a specific film-forming resin component As a result, the present inventors have found that the above object can be achieved, and have completed the present invention.

[0007]

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,
000, a coating containing (B) at least one curing agent selected from an amino resin and a blocked polyisocyanate compound, (C) a chromium-free rust preventive pigment, and (D) a conductive polymer compound. In the total amount of 100 parts by weight of the resin (A) and the curing agent (B), 65 to 95 parts by weight of the resin (A) and 5 to 35 parts by weight of the curing agent (B).
It is intended to provide a coating composition characterized by being within the range of parts by weight.

The present invention also provides an undercoating film of the above 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. An object of the present invention is to provide a coated steel sheet wherein a top coat is provided on the film.

[0009]

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 by a method known per se in addition to the acid component and the alcohol component of the above-mentioned oil-free polyester resin. Soybean oil fatty acids, linseed oil fatty acids, safflower oil fatty acids, tall oil fatty acids, dehydrated castor oil fatty acids, kiri oil fatty acids and the like can be mentioned. The oil length of the alkyd resin is preferably 30% or less, particularly preferably about 5 to 20%.

As the urethane-modified polyester resin,
The oil-free polyester resin, or a low-molecular-weight oil-free polyester resin obtained by reacting an acid component and an alcohol component used in the production of the oil-free polyester resin, reacts with a polyisocyanate compound by a method known per se. Examples include: Further, the urethane-modified alkyd resin, the alkyd resin, or a low molecular weight alkyd resin obtained by reacting each component used in the production of the alkyd resin was reacted with a polyisocyanate compound by a method known per se. Things are included. Examples of polyisocyanate compounds that can be used when producing urethane-modified polyester resin and urethane-modified alkyd resin include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate,
4,4'-methylenebis (cyclohexyl isocyanate), 2,4,6-triisocyanatotoluene, and the like. In general, as the urethane-modified resin, those having a modification degree in which the amount of the polyisocyanate compound forming the urethane-modified resin is 30% by weight or less based on the urethane-modified resin can be suitably used.

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 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 the 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 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; 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 a mixture of two or more types of crosslinking agents.

In the composition of the present invention, the compounding amount of the hydroxyl group-containing resin (A) and the curing agent (B) is such that the total amount of the solids (A) and (B) is 100 parts by weight. 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.

Non-Chromium Rust Preventive Pigment (C) In the composition of the present invention, the non-chromium rust preventive pigment as the component (C) is a rust preventive pigment containing no chromium atom and contributes to the improvement of the corrosion resistance of the coating film. Components, for example, zinc oxide, zinc phosphate, phosphorous zinc silicate, aluminum zinc phosphate, calcium zinc phosphate, zinc phosphite, calcium phosphite, aluminum phosphite, zinc cyanamide calcium, zinc-treated polyphosphorus Aluminum acid,
Aluminum tripolyphosphate, zinc calcium molybdate, zinc molybdate, zinc phosphomolybdate, aluminum phosphomolybdate, calcium ion-exchanged amorphous silica fine particles (hereinafter sometimes abbreviated as “ion-exchanged silica”), etc. Can be mentioned. Among them, zinc phosphate, zinc calcium molybdate, and ion-exchanged silica can be preferably used.

The above-mentioned ion-exchanged silica is silica fine particles in which calcium ions are introduced into a fine porous silica carrier 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 non-chromium rust preventive pigment (C) is not particularly limited.
Usually, 5 to 90 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),
More preferably, the amount is in the range of 20 to 70 parts by weight.

Conductive Polymer Compound (D) In the composition of the present invention, the conductive polymer compound as the component (D) is used to improve the initial performance and secondary performance of the coating film in terms of scratch resistance and processing adhesion, and corrosion resistance. It is a component that contributes to the improvement of.

The conductive polymer compound (D) in the composition of the present invention has a conductivity of 1.0 × 10 ⁴ Ω · volume specific resistance.
cm or less, and if the paint stability is good when blended in the composition of the present invention,
It can be used without particular limitation.

Examples of the conductive polymer compound (D) include vinyl compounds such as polyacetylene, polyalkene, polycyanoacetylene, polyphenylacetylene, and polyparaphenylene vinylene; polyparaphenylene, polyparaphenylene sulfide, polyphenylene oxide, and the like. Phenylenes such as polyparaphenylene selenide; aromatics containing nitrogen atoms such as polyaniline and polyparaphenylene azophenylene; heterocyclic systems such as polypyrrole, polythiophene, polyfuran, polyselenophene, polyindole and polycarbazole; polyazulene and polypyrene And polycyclic and high molecular compounds such as polyacene. As the derivatives and dopants of these exemplified compounds, those doped with anions and cations are also included in the conductive polymer compound (D) as long as the volume specific resistance is 1.0 × 10 ⁴ Ω · cm or less. Of these,
Polyaniline, polypyrrole, and those obtained by doping these with a dopant can be particularly preferably used. These conductive polymer compounds can be used alone or in combination of two or more.

The amount of the conductive polymer compound (D) is not particularly limited, but is usually 100 parts by weight of the total solid content of the hydroxyl group-containing resin (A) and the curing agent (B). On the other hand, 0.1 to 100 parts by weight, preferably 0.4
It is preferable that the amount is in the range of 40 to 40 parts by weight, more preferably 0.5 to 20 parts by weight.

The coating composition of the present invention can be substantially composed of a hydroxyl group-containing resin (A), a curing agent (B), a chromium-free rust preventive pigment (C), and a conductive polymer compound (D). However, usually, an organic solvent is blended, and if necessary, a curing catalyst, pigments such as titanium white; additives such as antifoaming agents, coating surface adjusters, and anti-settling agents known per se for paints. It may be contained.

The above-mentioned organic solvent is added as necessary for improving the coating property of the composition of the present invention, and the like.
What can dissolve or disperse the hydroxyl group-containing resin (A), the curing agent (B) and the conductive polymer compound (D) can be used,
Specifically, for example, toluene, xylene, hydrocarbon solvents such as high boiling petroleum hydrocarbons, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ketone solvents such as isophorone, ethyl acetate, butyl acetate,
Ester solvents such as ethylene glycol monoethyl ether acetate and diethylene glycol monoethyl ether acetate; alcohol solvents such as methanol, ethanol, isopropanol and butanol; ether alcohols such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether and diethylene glycol monobutyl ether Solvents and the like can be mentioned, and these can be used alone or as a mixture of two or more.

The curing catalyst is blended as needed 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). 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 preferred. 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, they are usually added in an amount of 0.1 part 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.).

The composition of the present invention can be used, for example, as an undercoat paint or a one-coat finish paint. Examples of objects to be coated with the composition of the present invention include steel plates, copper plates, tin-lead alloy plates, and the like.
Various metal plates such as brass and aluminum plates, among which steel plates can be suitably used.

As the steel sheet to be coated, a cold-rolled steel sheet, a hot-dip galvanized steel sheet, an electro-galvanized steel sheet, a zinc alloy-plated steel sheet (a zinc alloy plating such as iron-zinc, nickel-zinc, aluminum-zinc, etc.) Steel sheet), aluminum-plated steel sheet, stainless steel sheet, copper-plated steel sheet, tin-plated steel sheet, etc., and steel sheets which have been subjected to chemical treatment such as phosphate treatment or chromate treatment. A treated galvanized steel sheet, zinc alloy plated steel sheet, and aluminum plated steel sheet are preferred.

The composition of the present invention is coated on the above-mentioned substrate 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, but when it is used as an undercoat paint, it is usually in the range of 2 to 10 μm, preferably 3 to 6 μm. When used as a coating for finishing the coating of a coat, the thickness is preferably in the range of 3 to 30 μm, preferably 5 to 25 μm. The baking of the coating film from the composition of the present invention may be appropriately set according to the type of the resin to be used, etc. It is baked for 15 to 60 seconds at a temperature of 160 to 250 ° C, preferably 180 to 230 ° C.
It can be carried out by baking at 80C, preferably 100 to 140C for 10 to 30 minutes.

Next, the composition of the present invention is used as an undercoat paint,
A two-coat coated steel sheet in which an overcoat film is formed on an undercoat film will be described.

The two-coat coated steel sheet may be provided with an undercoat film of the coating composition of the present invention on a steel sheet such as 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. And an overcoat film is provided on the undercoat film. 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. The above top coat has a Tg of 20
It is preferably in the range of from 80 to 80C, preferably from 30 to 65C from the viewpoints of acid resistance, corrosion resistance, workability and the like of the coating film.

The coated steel sheet can be suitably obtained by applying and baking the coating composition of the present invention, for example, by a roll coating method, and then coating and baking a top coating composition, for example, by a roll coating method. 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.

[0050]

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.
℃], 250 parts (75 parts by solid content), 20 parts of Shieldex 303 (manufactured by WR Grace & Co., calcium ion-exchanged amorphous silica fine particles, average particle diameter of about 3 μm), titanium white 20 parts and an appropriate amount of a mixed solvent [1/1 (weight basis) mixed solvent of Solvesso 150 (manufactured by Esso Petroleum Co., Ltd., aromatic hydrocarbon solvent) and cyclohexanone] were mixed, and the tub (particle size of pigment coarse particles) was mixed. ) Was reduced to 10 microns or less. Next, 25 parts of Cymel 303 (Methylated Melamine Resin, manufactured by Mitsui Cytec Co., Ltd.) and 10 parts of a 10% solid solution of polyaniline doped with p-toluenesulfonic acid as a dopant were added to the pigment dispersion. At 1.0
Parts) and Nail Cure 5225 (manufactured by King Industries, USA, dodecylbenzenesulfonic acid amine salt,
1.6 parts of active ingredient (about 25%) (0.4 parts of active ingredient)
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 6 and Comparative Examples 1 to 4 Each coating composition having a viscosity of about 80 seconds was 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).

In Examples 2 to 4 and Comparative Examples 1, 2 and 4, the dispersion of the pigments of titanium white, shielddex 303, aluminum tripolyphosphate and zinc phosphate was carried out.
Using 30% Byron EP-2940 as a resin solution,
Each coating composition was obtained using a pigment dispersion obtained in the same manner as in Example 1 except that the same amount of the mixed solvent as in Example 1 was used. In Example 5 and Comparative Example 3, the dispersion of the pigment, which is titanium white and Shielddex 303, was used as a resin solution by using Epoxy 820 40CX (manufactured by Mitsui Chemicals, Inc., urethane-modified epoxy resin solution having a solid content of 40%, resin The pigment dispersion obtained in the same manner as in Example 1 except that the number average molecular weight is about 6,000, and the glass transition temperature is about 64 ° C.), and using an appropriate amount of the same mixed solvent as in Example 1. Was used to obtain a coating composition. In Example 6, a dispersion of titanium white and a pigment of Shielddex 303 was used as a resin solution, and a 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 was about 50%). 6,000, glass transition temperature about 1
5 ° C.), and using a pigment dispersion obtained in the same manner as in Example 1 except that the operation was performed using an appropriate amount of the same mixed solvent as in Example 1, to obtain a coating composition.

The glass transition temperature of the cured coating film obtained from each of the coating compositions obtained in Examples 1 to 6 and Comparative Examples 1 to 4 was measured by the following method. The measurement 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.

[0056]

[Table 1]

(Note) in Table 1 is as follows.

(Note 1) Desmodur BL-3175:
A blocked polyisocyanate compound manufactured by Sumitomo Bayer Urethane Co., Ltd. (Note 2) Takenate TK-1: Takeda Pharmaceutical Co., Ltd., organotin-based blocking agent dissociation catalyst, solid content: about 10%.

(Note 3) Doped polypyrrole: a 10% solids resin solution in which polypyrrole is doped with p-toluenesulfonic acid as a dopant.

Application Examples 1 to 6 and Comparative Application Examples 1 to 4 A hot-dip galvanized steel sheet (zinc basis weight 60 g / m ² ) having a thickness of 0.4 mm and subjected to chromate treatment was prepared.
6 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, KP Color 1573 White [manufactured by Kansai Paint Co., Ltd., polyester resin-based top coating, white, glass transition temperature of the cured coating is about 65 ° C.] is applied on each of these undercoat coatings using a bar coater. The coated plate was coated so as to have a thickness of 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.

APPLICATION EXAMPLES 7-9 Except that the following materials were used instead of the 0.4 mm thick hot-dip galvanized steel plate used as the base material and the coating material of Example 1 as the undercoating material, respectively. A coated plate was prepared in the same manner as in Application Example 1.

The material types used in Application Examples 7 to 9 are as follows.

In Application Example 7, 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 2) In the application example 8, 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
5%) steel plate [abbreviated as “Zn-55% Al” in Table 2], and in Application Example 9, a 0.4 mm-thick chromated aluminum-plated steel plate [Table 2 shows “Al-plated steel plate”. Abbreviations] were used.

Each coated plate obtained in each of Application Examples 1 to 9 and Comparative Application Examples 1 to 4 was subjected to various coating film performance tests by the test methods described below. The test results are shown in Table 2 below.

Application Examples 10 to 15 and Comparative Application Examples 5 to 8 A hot-dip galvanized steel sheet having a thickness of 0.4 mm (zinc basis weight 60 g / m ² ) obtained by chromate treatment was prepared.
6 and each of the coating compositions obtained in Comparative Examples 1-4 had a dry film thickness of 1
Paint with a bar coater to a thickness of 5 microns and bake for 40 seconds so that the maximum temperature of the material reaches 220 ° C.
A coated board was obtained.

Application Examples 16 to 18 The following materials are used instead of the chromate-treated hot-dip galvanized steel sheet having a thickness of 0.4 mm, using the paint of Example 1 as a one-coat finish paint. Except for the above, a one-coat finish painted plate was prepared in the same manner as in the case of Application Example 10.

In Application Example 16, a 0.4 mm-thick chromate-treated zinc-aluminum alloy-plated steel sheet (the aluminum content in the plating is about 5%) [abbreviated as “Zn-5% Al” in Table 3. ], In Application Example 17, a 0.4 mm-thick chromate-treated zinc-aluminum alloy-plated steel sheet (aluminum content of about 55%) [Table 3 shows "Zn-55% Al"]
In the application example 18, a chromate-treated aluminum-plated steel sheet having a thickness of 0.4 mm [abbreviated as “Al-plated steel sheet” in Table 3] was used.

The above application examples 10 to 18 and comparative application examples 5
Each coated plate obtained in 8 was subjected to various coating film performance tests by the following test methods. The test results are shown in Table 3 below.

Test Method Working Adhesion: A coated plate was cut into a size of 70 × 150 mm, and at room temperature of 20 ° C., a 0.4 mm-thick steel plate was placed inside the bent portion with the surface of the coated plate outside. The coated plate is bent 180 degrees with a vise (1T processing)
Then, a cellophane adhesive tape was attached to the bent portion, and the degree of peeling of the coating film in the bent portion when the tape was instantaneously peeled was evaluated according to the following criteria. Two types of coated plates were used: a coated plate that had not been treated after coating (initial stage) and a coated plate that was immersed in boiling water for 20 hours after coating (secondary).

◎: No peeling of the coating film was observed in the processed part. ：: Peeling of the coating film was slightly observed in the processed part. Δ: Peeling of the coating film was considerably observed in the processed part. The peeling of the coating film is remarkably observed.

Scratch resistance: At room temperature of 20 ° C.
Coin Scratch Tester (Automated Giken Co., Ltd.)
With a 3kg load, the edge of the 10-yen coin is pressed against the painted surface of the painted plate at an angle of 45 degrees with a load of 3 kg, and the 10-yen coin is pulled at a speed of 10 mm / sec for about 30 mm to scratch the painted surface. The degree of scratching was evaluated.

：: No metal base is found at the scratched part. ○: Metal base is slightly found at the wounded part. Δ: Metal base is considerably seen at the wounded part. The metal substrate is clearly visible with almost no film remaining.

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 500 hours, the degree of rust generation in the processed part, and the average blister width in the cross cut part were visually evaluated according to the following criteria.

Rust generation degree in the processed part ◎: No rust was generated in the processed part, ：: Rust generation was recognized although 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 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.

[0075]

[Table 2]

[0076]

[Table 3]

[0077]

Industrial Applicability The coating composition of the present invention is a coating composition which is excellent in the initial and secondary performances of processing adhesion and scratch resistance and is capable of forming a coating film having excellent corrosion resistance. It can be suitably used as a one-coat paint finish.

The coated steel sheet having an overcoat film formed on the undercoat film from the coating composition of the present invention is excellent in the initial and secondary performances of work adhesion and scratch resistance, and excellent in corrosion resistance. In particular, the coating composition of the present invention can be suitably used as a primer for a precoated steel sheet.

The coating composition of the present invention is advantageous from the viewpoint of preventing pollution since it does not contain a chromate-based rust preventive pigment.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C09D 163/00 C09D 163/00 175/04 175/04 // C08G 18/42 C08G 18/42 Z 18/58 18/58 18 / 80 18/80

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,
(B) an amino resin and at least one curing agent selected from a blocked polyisocyanate compound, (C) a chromium-free rust preventive pigment, and (D) a conductive polymer compound. It is a paint to be contained, and in a total amount of 100 parts by weight of the resin (A) and the curing agent (B), 65 to 95 parts by weight of the resin (A) and 5 to 35 parts by weight of the curing agent (B).
A coating composition characterized by being in the range of parts by weight. 2. A total of 10 of the resin (A) and the curing agent (B)
The non-chromic rust preventive pigment (C) is contained in an amount of 5 to 90 parts by weight and the conductive polymer compound (D) in an amount of 0.1 to 100 parts by weight based on 0 parts by weight. Paint composition. 3. The coating composition according to claim 1, wherein the conductive polymer compound (D) is at least one selected from polyaniline, polypyrrole, polyaniline doped with a dopant, and polypyrrole doped with a dopant. 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. A coated steel sheet having an overcoat film provided thereon.