JP2892052B2 - How to paint galvanized steel - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for coating galvanized steel, and more particularly, to α-olefin-α · β on a galvanized steel surface.
An aqueous composition containing an ethylenically unsaturated carboxylic acid copolymer resin dispersion, water-dispersible silica and a water-dispersible chromium compound is applied and dried, and then a low-temperature-curable topcoat is applied and dried. The present invention relates to a method for coating a galvanized steel material having excellent corrosion protection and aesthetic properties.

[Conventional technology and its problems] In recent years, surface-treated materials with particularly excellent corrosion resistance have been strongly demanded as electroplated steel materials used for automobile parts, light electrical appliances, general equipment, and the like. It will tend to increase in the future. Conventionally, zinc plating is generally performed as metal plating for improving the corrosion resistance of steel materials, and alloyed zinc plating is also performed for improving the corrosion resistance. This galvanization suppresses the corrosion of the steel material by sacrificial corrosion prevention of zinc. In order to obtain high corrosion resistance, the amount of zinc deposition must be increased. For this reason, there are problems such as deterioration in workability, weldability, and productivity. As a method for improving the corrosion resistance of electrogalvanized steel, alloyed zinc plating containing a metal other than zinc in a galvanized film, for example, Zn-Ni, Zn-Ni-Co,
Plating such as Zn-Fe is performed. Further, after plating, a chromate treatment is performed to improve the corrosion resistance and the paint base.

In the case of these alloyed zinc platings, a passivation film is formed and the dissolution of zinc is suppressed. As a result, the corrosion resistance is greatly improved as compared with ordinary zinc plating. However, even with these alloyed zinc platings, there is a problem that white rust and red rust are easily generated by outdoor use or spraying of water or salt water, which is not sufficient to satisfy the demands of customers.

On the other hand, in order to improve the corrosion resistance of galvanized steel,
A coating mainly composed of a water-soluble resin or an emulsion type resin which is dried at room temperature is applied with a sufficient film thickness, or a baking coating (for example, an acryl-melamine type or an alkyd-melamine type) is applied. A method of baking and drying at a high temperature of not less than ° C. to form a film of 20 to 40 μm is performed. However, cold-drying paints are inferior in corrosion resistance, water resistance, and organic solvent resistance. On the other hand, baking paints require high-temperature baking to form the film. In addition, since a drawback such as poor organic solvent resistance occurs, it is necessary to install a relatively high-temperature baking furnace. In addition, when such high-temperature treatment is performed, cracks occur in the chromate film, and hexavalent chromium is inactivated by high temperatures, so that the self-healing action inherent to the chromate film is reduced, and the corrosion resistance is significantly reduced. Problems occur.

Furthermore, the above-mentioned paints generally have a problem in adhesion to galvanization, and in some cases, the coating film is peeled off by contact with water or salt water, and is not a paint showing sufficient corrosion resistance.

In order to solve this problem, the surface of a galvanized steel sheet is mainly composed of an α-olefin-α-βethylenically unsaturated carboxylic acid copolymer resin dispersion, which contains water-dispersible silica and water-dispersible chromium. A high degree of corrosion resistance can be obtained by drying the aqueous composition obtained by mixing the compounds at a low temperature of 100 ° C. or less, but sufficient to satisfy the requirements in terms of weather resistance and aesthetics requiring various colorings. Not.

[Means for Solving the Problems] Accordingly, the present inventors have solved the above-mentioned problems, and furthermore, compared with a conventionally known method, zinc having excellent corrosion resistance and having both weather resistance and cosmetics. As a result of intensive studies for the purpose of providing a surface treatment method and a coating method for obtaining a plated steel material, the present invention has been completed.

Thus, according to the present invention, the water-dispersible silica is solidified on the surface of the galvanized steel material based on 100 parts by weight of the solid content of the α-olefin-α-βethylenically unsaturated carboxylic acid copolymer resin resin. An aqueous composition containing 5 to 120 parts by weight and a water-dispersible chromium compound in a solid content of 1 to 40 parts by weight in minutes is then applied, and then heated and dried to form an undercoat film, and further thereon. A method of coating a galvanized steel material, which comprises applying and drying a paint that cures at a temperature of 140 ° C. or less to form a top coat.

Next, the surface treatment method for a galvanized steel material having excellent corrosion resistance according to the present invention will be described in detail.

The galvanized steel material to which the surface treatment method of the present invention is applied may be itself or may be subjected to a phosphate treatment or a chromate treatment on the surface. If a high degree of corrosion resistance is desired, a chromate treatment is applied.

The surface treatment composition for undercoating used in the surface treatment method of the present invention is an α-olefin-α · β ethylenically unsaturated carboxylic acid copolymer resin dispersion, water-dispersible silica, a water-dispersible chromium compound and preferably Is an aqueous composition containing a trialkoxy (or alkoxyalkoxy) silane compound, and the α-olefin-α · β ethylenically unsaturated carboxylic acid copolymer resin is an α-olefin such as ethylene, propylene, butene, It is a copolymer of a monomer such as butylene and isobutylene with a monomer such as an α / β ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, and maleic acid.

The amount of the carboxylic acid group in the copolymer resin may be an amount necessary for dispersing in water, and the amount of the α · β ethylenically unsaturated carboxylic acid is in the range of 5 to 40% by weight, preferably 5 to 20% by weight. May be copolymerized. The aqueous dispersion of the copolymer resin is performed by converting a carboxylic acid group introduced into the resin skeleton to an amine compound (for example, aliphatic amines represented by monoethylamine,
It can be achieved by neutralization with a basic substance such as alkanolamines represented by diethanolamine, cyclic amines such as pyridine) and aqueous ammonia.

Next, the water-dispersible silica is a so-called colloidal silica, preferably having a particle diameter of 7 to 100 mμ, particularly preferably in the range of 10 to 80 mμ, and a known one usually supplied as an aqueous dispersion may be used as it is. it can. For example, it is represented by Snowtex (trade name) manufactured by Nissan Chemical Industries, Ltd. The amount of the water-dispersible silica is α-olefin-α
5 to 120 parts by weight, preferably 20 to 100 parts by weight, based on 100 parts by weight of β-ethylenically unsaturated carboxylic acid copolymer resin, and when the amount is less than 5 parts by weight, adhesion to steel material On the other hand, when the amount exceeds 120 parts by weight, the mechanical strength is poor.

Next, regarding the particle size and blending amount of the water-dispersible silica, for those having a particle size in the range of 10 to 30 mμ,
The proper amount is 20 to 60 parts by weight, and for particles having a particle size in the range of 30 to 80 mμ, the appropriate amount is
40 to 100 parts by weight. When a water-dispersible silica having a relatively large particle size is used, the suitable amount of the silica increases.

The next water-dispersible chromium compound, strontium chromate (SrCrO _4), barium chromate (BaCrO _4), lead chromate (P ₆ CrO _4), calcium chromate (CaCrO _4),
Basic zinc chromate _{(ZnCrO 4 · 4Zn (OH)} 2) , etc. can be used. The compounding amount of the chromium compound is the same as that of the copolymer resin.
1 to 40 parts by weight, preferably 3 to 15 parts by weight, per 100 parts by weight
If the amount is less than 1 part by weight, the corrosion resistance is poor, and if it exceeds 40 parts by weight, the storage stability of the paint is inferior.

As the trialkoxy (or alkoxyalkoxy) silane compound to be added as needed, a conventionally known compound can be used. Among them, amino-functional silane compounds such as N-β (aminoethyl) γ-aminopropylmethyl Dimethoxysilane, N-β (aminoethyl) γ
-Aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane and the like can be suitably used. The compounding amount of the silane compound is in the range of 1 to 10 parts by weight, preferably 2 to 6 parts by weight based on 100 parts by weight of the copolymer resin. When the compounding amount is less than 1 part by weight, the corrosion resistance is inferior. If the amount exceeds 10 parts by weight, no remarkable effect is observed.
Less than 10 parts by weight is desirable from economic considerations.

Next, in the aqueous liquid of the composition containing the above-described components, an alcohol-based or ether-based water-soluble organic solvent is added, if necessary, to adjust the viscosity of the aqueous liquid, defoam, or reduce the surface tension. Is added in order to obtain various advantages such as ease of wetting and lowering of the freezing point. The amount of the organic solvent to be added is not more than 20% by weight of the surface treatment composition, preferably in the range of 5 to 15% by weight. If the amount exceeds 20% by weight, the flash point is lowered and the properties as a water-based paint are lost. As alcohol solvents, polyhydric alcohols (e.g., ethylene glycol, propylene glycol, etc.) have excellent stability with respect to copolymer resin dispersion and water-dispersible silica, and furthermore have high storage stability and freezing point. Serves as an effective diluent that causes a drop. As the ether-based solvent, cellosolve and butyl cellosolve can be used, and butyl cellosolve is particularly effective because it has a high defoaming effect. Squid, these cellosolve systems and n
-Some solvents of monohydric alcohols such as butanol and isopropyl alcohol impair the stability of the copolymer resin dispersion and the water-dispersible silica, cause agglomeration, and cause a decrease in storage properties. It is important to keep the amount.

If necessary, a combination of a chelate compound such as titanium, zirconium, or aluminum, a metal salt, or the like with the aqueous composition described above can further obtain low-temperature curability.

The method for applying the undercoating surface treatment composition according to the present invention includes:
Methods such as dip coating, brush coating, and shower coating can be used. When a large number of small articles are processed, a dip-spin coating method can also be used. The coating dry film thickness is 2-10μ
m. Drying of the film after application is achieved at 100 ° C. or less, preferably at 60 to 100 ° C. in 15 to 25 minutes, and a cured film can be obtained at a relatively low temperature. Does not impair the corrosion protection of

Next, the surface treatment composition described above is used as an undercoat, and a low-temperature-curable surface treatment composition that is excellent in weather resistance and aesthetic properties applied thereon and that does not impair the corrosion resistance of the galvanized layer is as follows. Things.

That is, acrylic resin, polyester resin, phenol resin, epoxy resin, urethane resin, vinyl resin, alkyd resin, and phthalic acid resin are used.

The reason why the galvanized steel material obtained by the surface treatment coating system of the present invention has both excellent corrosion resistance and excellent weather resistance and is excellent in cosmetics and the like which can be variously colored will be described. First, regarding corrosion resistance, the cause of imparting excellent corrosion resistance to galvanized steel has not yet been sufficiently clarified, but is presumed as follows.

The α-olefin α-β ethylenically unsaturated carboxylic acid copolymer resin has the property of an ionomer (ionic copolymer), and a metal ion (for example, divalent) formed by dissolving a chromium compound in water. Strontium ion, barium ion, calcium ion, etc.), the molecular chains are crosslinked by using carboxylic acid groups in the resin skeleton. In addition, a molecule utilizing a carboxylic acid group also by trivalent chromium (Cr ⁺³ ) generated by a redox reaction between a chromate ion (CrO ₄ ^-2 ) generated by dissolving a chromate compound in water and a resin. Interchain crosslinking occurs. Thus, an insolubilized film having excellent solvent resistance is obtained.

Also, between the copolymer resin and colloidal silica,
The hydrogen bond between the silanol group of the colloidal silica and the carboxylic acid group in the copolymer resin forms a copolymer resin / colloidal silica composite. When an alkoxysilane compound is further added, a strong siloxane bond is easily formed by a dehydration-condensation reaction between a silanol group generated by hydrolysis of the silane compound and a silanol group on the surface of the colloidal silica particles. The bond forms a colloidal silica-silane compound complex.

Still further, the bond between the colloidal silica-silane compound composite and the copolymer resin is a van der Waals-like bond between the organic group contained in the silane compound and the copolymer resin and the bond in the composite. A complex is formed with a relatively weak bonding force due to a hydrogen bond between the silanol group and the carboxylic acid group in the copolymer resin.

In this manner, the crosslinking reaction proceeds at a relatively low temperature, the formed film is densified, the film becomes a barrier film that blocks corrosion-forming substances, and the excellent film-forming and coating properties of the copolymer resin, It is supposed that excellent corrosion resistance is imparted by having both the advantages such as flexibility and the excellent hardness of silica or the inorganic composite, such as corrosion resistance against metals. Further, it is considered that a passivation film is formed on the metal surface by the chromium compound, and it is considered that a more excellent corrosion resistance is exhibited by a synergistic effect with the barrier film.

Although the galvanized steel itself has considerable corrosion resistance, when a topcoat composition is applied directly on the galvanized steel, the corrosion resistance is increased by the corrosion resistance of the galvanized itself and the corrosion resistance of the topcoat composition, and shows some corrosion resistance. However, this cannot be sufficiently satisfied in a field where the use conditions are severe. For this reason, weather resistance and aesthetics cannot be sufficiently satisfied in connection with this.However, according to the coating method of the present invention, the undercoat composition shows excellent corrosion resistance, and the topcoat composition has weather resistance and Since it is responsible for cosmetics, it is possible to impart excellent corrosion resistance, weather resistance and cosmetics by a synergistic effect of the undercoat and the top coat.

As this top coat, a commonly used colorant having good weather resistance may be used, but the chromate film on the galvanized steel material cracks when a high temperature is applied, and hexavalent. As the chromium becomes insoluble at high temperatures, the self-healing action inherent to the chromate film is reduced, and the corrosion resistance is prevented from being significantly reduced. If so, more corrosion resistance is expected. As the overcoat composition, acrylic resin, urethane resin, alkyd melamine resin, acrylic melamine resin, polyester resin,
By applying a low-temperature curable coating composition consisting of amide resin, phenol resin, epoxy resin, etc., the corrosion resistance of the chromate-treated galvanized steel sheet is not impaired, and the corrosion resistance and weather resistance are excellent. A coating method for Zn-plated steel material which has various characteristics and is capable of being colored variously and has excellent aesthetic properties is established.

[Examples] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the example of the undercoat composition, α-olefin-α
-Ethylene-acrylic acid copolymer resin dispersion [manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Nipporan 3202"] as β-ethylenically unsaturated carboxylic acid copolymer resin dispersion, solid as water-dispersible silica 50% colloidal silica [Cataloid Si-50, trade name, manufactured by Catalyst Chemical Industry Co., Ltd.], N-β (aminoethyl) γ-aminopropyltrimethoxysilane [Shin-Etsu Chemical Co., Ltd. Co., Ltd., trade name “KBM-603”].

Examples of the overcoat composition include specially modified alkyd resin-based paint [Lastite NC No. 2 manufactured by Kansai Paint Co., Ltd.]
0], specially modified epoxy resin paint [Kansai Paint Co., Ltd., 1 coat enamel No. 500], aminoalkyd resin paint [Kansai Paint Co., Ltd., Amirac No. 30]
0, Amirac TM-13], urethane resin paint [Kansai Paint Co., Ltd., urethane PG-60, urethane PG-80], urethane resin marking film [Kansai Paint Co., Ltd.]
Manufactured by FANTAC Ltd.].

Example (1) Based on 100 parts by weight of the solid content of the ethylene-acrylic acid copolymer resin dispersion, 4% of butyl cellosolve was added to an aqueous liquid containing 30 parts by weight of colloidal silica as a solid and 7.5 parts by weight of strontium chromate. The product added with 4% ethylene glycol was applied to a chromate-treated electrogalvanized steel sheet having a zinc adhesion amount of 20 g / m ² (one side), and dried at 80 ° C. for 20 minutes. The film thickness at that time is 3-5μ
m.

This was used as an undercoat, and a urethane resin-based paint [Rethane PG-60, manufactured by Kansai Pent Co., Ltd.] was applied thereon in an amount of 30 to 40 μm.
It was spray painted and dried at 80 ° C for 30 minutes. Table of test results
It is shown in FIG.

Examples (2) to (4) and Comparative Examples (1) to (6) Undercoat compositions (solid content ratio) used in Examples (2) to (4) and Comparative Examples (1) to (6) and Table 1
Shown in

The undercoat aqueous liquid used in Examples (2) to (4) and Comparative Examples (1) to (3) and (6) contains 4% butyl cellosolve and 4% ethylene glycol as in Example (1).
Was added, and the material subjected to the test was the same electrogalvanized steel sheet (gin coat EG-C) as in Example (1). Drying conditions and film thickness after coating are the same. Examples (2) to (3) and Comparative Examples (4) to (5)
The top coat was spray-coated to a film thickness of 30 to 40 μm, and the drying conditions were drying at 80 ° C. for 30 minutes. Example (4)
The urethane resin-based marking film was directly adhered on the aqueous liquid coating film. The epoxy-modified polyester melamine resin-based paint of Comparative Example (6) was spray-coated to a film thickness of 30 μm, and was baked at 150 ° C. for 30 minutes.
Table 2 shows the test results.

1. Salt spray test The test is based on the JIS-Z-2371 salt spray test method.

2. Water resistance After immersion in deionized water at 40 ° C for 240 hours, the painted surface condition and the 2mm square goban test were performed.

Display method 3. Solvent resistance Perform a rubbing test with gauze impregnated with methyl ethyl ketone (MEK).

：: No abnormality △: Swelling, scuffing occurred ×: Burned off 4. Accelerated weathering test (sunshine weatherometer) According to JIS D 0205-1976.

[Effects of the Invention] As is clear from the above description, according to the present invention, 10
At a low temperature of 0 ° C or less, the excellent effect on galvanized steel material is due to the synergistic effect of the barrier function against corrosion-forming substances due to the fully crosslinked cured film and the formation of a passivation film on the metal surface by the chromium compound. A surface treatment method showing rust prevention can be provided. Further, since the surface treatment composition of the present invention is a coating and anhydrous washing type composition, it is possible to reduce pollution and save labor in the treatment process.

In addition, by applying a top coat on this aqueous composition, it is possible to provide a coating film having excellent weather resistance and a variety of colorings and an excellent cosmetic property and a coating method. It is suitable as a coating method.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification code FI C23C 2/06 C23C 2/06 // C09D 123/02 C09D 123/02 (58) Fields surveyed (Int.Cl. ⁶ , DB Name) B05D 7 / 14,7 / 24 C09D 5/00-5/02 C09D 123 / 02,133 / 02 C23C 2/06

Claims (1)

(57) [Claims] 1. A water-dispersible silica in a solid content of 5 parts by weight per 100 parts by weight of a solid content of an α-olefin-α-β ethylenically unsaturated carboxylic acid copolymer resin resin on a surface of a galvanized steel material. To 120 parts by weight and an aqueous composition containing a water-dispersible chromium compound at a solid content of 1 to 40 parts by weight, and then dried by heating to form an undercoat film,
A method for coating a galvanized steel material, further comprising applying and drying a paint that cures at a temperature of 140 ° C. or less to form a top coat.