JPH03131370A - Method and composition for surface treatment of zinc plated steel material - Google Patents

Abstract

PURPOSE:To enhance the corrosion resistance of a steel material by environmental pollution reducing treatment by applying an aqueous composition based on an alpha-olefine/alpha,beta-ethylenic unsaturated carboxylic acid copolymer resin to the surface of a zinc plated steel material to heat the coated steel material. CONSTITUTION:A surface treatment composition for a zinc plated steel material is prepared by compounding a 60-120 pts.wt. of water-dispersible silica and 1-40 pts.wt. of a water-dispersible chrominum compound with 100 pts.wt. of a dispersion of an alpha-olefin/alpha,beta-ethylenic unsaturated carboxylic acid copolymer resin on a solid basis. An aqueous solution of the prepared surface treatment composition for the zinc plated steel material is applied to the surface of the zinc plated steel material and heated to improve the corrosion resistance of the surface of the steel material. It is pref. to further add 1-10 pts.wt. (per 100 pts.wt. of the resin solid) of a trialkoxysilane compound to the aforementioned surface treatment composition.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has an α-olefin-α-β ethylenically unsaturated carboxylic acid copolymer resin dispersion as a main component,
An aqueous composition prepared by mixing water-dispersible silica and a water-dispersible chromium compound is applied to the galvanized steel surface or after phosphate treatment or chromate treatment, and The present invention relates to a surface treatment method for galvanized steel, which comprises drying at a low temperature to form a hardened film with excellent corrosion resistance and hardness, and a surface treatment composition used therein.

[Prior art and its problems] In recent years, there has been a strong demand for surface-treated materials with particularly excellent corrosion resistance as electroplated steel materials used in applications such as automobile parts, light electrical appliances, and general equipment. This trend is likely to increase in the future. Conventionally, zinc plating has been generally used as a metal plating to improve the corrosion resistance of steel materials, and alloyed zinc plating has also been applied to further improve the corrosion resistance. This zinc plating suppresses corrosion of steel materials by sacrificial corrosion protection of zinc, and in order to obtain high corrosion resistance, the amount of zinc deposited must be increased. Therefore, there are problems such as a decrease in workability, weldability, and productivity. As a method of improving the corrosion resistance of electrogalvanized steel materials, alloyed galvanizing in which metals other than zinc are contained in the galvanized film, such as Zn-Ni, Zn-Ni, etc.
-Co, Zn-Fe, etc. plating is performed. Furthermore, after plating, chromate treatment is applied to improve corrosion resistance and coatability.

In the case of these alloyed zinc platings, as a result of forming a passivation film and suppressing the dissolution of zinc, the corrosion resistance is significantly improved compared to normal zinc plating. However, even with these alloyed zinc platings, there is a problem that white rust and red rust easily occur when used outdoors or when sprayed with water or salt water.
It cannot be said that it is sufficient to satisfy the demands of consumers.

On the other hand, in order to improve the corrosion resistance of galvanized steel, paints mainly composed of water-soluble resins or emulsion quives that dry at room temperature are coated with a sufficient thickness, and baking paints (for example, acrylic A method is used in which a film of 20 to 40 P is formed by applying a melamine-based material, an alkyd-melamine-based material, etc., and baking and drying the film at a high temperature of 120° C. or higher. However, paints that dry at room temperature are inferior in corrosion resistance, water resistance, and organic solvent resistance, while baked paints require high temperature baking to form a film, and insufficient curing results in poor water resistance and chemical resistance of the film. However, since there are disadvantages such as poor resistance to organic solvents, it is necessary to install a baking furnace at a relatively high temperature. In addition, when such high-temperature treatment is performed, cracks occur in the chromate film, and hexavalent chromium becomes insoluble due to high temperatures, which reduces the self-healing effect inherent in the chromate film and significantly reduces corrosion resistance. Such problems arise.

Furthermore, the above-mentioned paints generally have problems in adhesion to zinc plating, and the paint film sometimes peels off when in contact with water or salt water, so they do not exhibit sufficient corrosion resistance.

Means for Solving Problem E] Therefore, the present inventors have developed a surface treatment method and surface treatment for solving the above-mentioned problems and further obtaining a galvanized steel material with excellent corrosion resistance compared to conventionally known methods. As a result of extensive research aimed at providing a composition, the present invention has been completed.

Thus, according to the present invention, α
・With respect to 100 parts by weight of the solid content of the olefin-α/β ethylenically unsaturated carboxylic acid copolymer resin dispersion, the solid content of water-dispersible silica is more than 60 parts by weight and 120 parts by weight.
Parts by weight or less and water-dispersible chromium compounds in solid content of 1 to 1
Provided is a method for surface treatment of galvanized steel, which comprises applying an aqueous composition containing 40 parts by weight and then heating and drying, and a surface treatment composition for galvanized steel comprising the aqueous composition described above. Ru.

Since the above-mentioned surface treatment composition is a waterless application type, there are no problems such as leakage, scattering, drainage, or sludge generation of hexavalent chromium, which is a harmful component, and it has advantages such as low pollution and labor saving in the treatment process. It has the following characteristics.

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

The galvanized steel materials to which the surface treatment method of the present invention is applied are:
It may be used as such, or its surface may be subjected to phosphate treatment, chromate treatment, or the like. Chromate treatment is applied when a high degree of corrosion resistance is desired.

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

The amount of carboxylic acid groups in the copolymer resin may be any amount necessary for water dispersion, 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. Copolymerization can be carried out using Water dispersion of this copolymer resin is carried out by converting the carboxylic acid groups introduced into the resin skeleton into amine compounds (
For example, this can be achieved by neutralizing with a basic substance such as aqueous ammonia (aliphatic amines such as monoethylamine, alkanolamines such as jetanolamine, cyclic amines such as pyridine), and aqueous ammonia. .

Next, the water-dispersible silica is so-called colloidal silica, and preferably has a particle size in the range of 7 to 100 mμ, particularly 30 to 80 mμ, and known ones that are usually supplied as an aqueous dispersion can be used as they are. can. For example, it is typified by Cataloid (trade name) manufactured by Catalysts and Chemicals Industrial Steel. The amount of water-dispersible silica is more than 60 parts by weight and less than 120 parts by weight, preferably from 60 to 100 parts by weight, based on 100 parts by weight of the α-olefin-α-β ethylenically unsaturated carboxylic acid copolymer resin. It is. Regarding the particle size and appropriate blending amount of water-dispersible silica, the following knowledge has been obtained. For particles with a diameter of 10 to 30 mμ, the appropriate amount is 5 to 60 parts by weight, and for particles with a diameter of 30 to 80 mμ, the appropriate amount is 60 to 10 parts by weight.
A loading of 0 parts by weight is most preferred. Particularly particle size 30-8
It was found that using 60 to 100 parts by weight of particles with a particle diameter of 10 to 30 mμ provides even better corrosion resistance than using 5 to 60 parts by weight of particles with a particle diameter of lO to 30 mμ.

This is presumed to be the result of water-dispersible silica exhibiting the highest adhesion to metals. Next, the particle size is 8
If it exceeds 0 mμ, the gloss of the coating film will be significantly impaired by adding 20 parts by weight or more. Also, regarding corrosion resistance, no effect of particle size can be obtained.

Next, as water-dispersible chromium compounds, strontium chromate (SrCr04), barium chromate (BaCr
OJ, lead chromate (PbCr04), calcium chromate (CaCr04), basic zinc chromate (ZnCrO
4.4Zn (OH) 2), etc. can be used. The blending amount of the chromium compound is in the range of 1 to 40 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the copolymer resin. If the blending amount is less than 1 part by weight, corrosion resistance is poor.
If it exceeds 40 parts by weight, the storage stability of the paint will be poor.

Next, as the trialkoxy (or alkoxyalkoxy) silane compound added as needed, conventionally known ones can be used, and 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 blending 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.If the blending amount is less than 1 part by weight, corrosion resistance will be poor; Even if the amount exceeds 10 parts by weight, no significant effect is observed. From economical considerations, it is desirable to use 10 parts by weight or less.

Next, an alcohol-based or ether-based water-soluble organic solvent is added to the aqueous liquid of the composition containing the above-mentioned components as necessary to adjust the viscosity of the aqueous liquid, defoaming it, and lowering the surface tension of the coating material. It is added to obtain various benefits such as easier wettability and lower freezing point. The amount of the organic solvent added is 20% by weight or less, preferably in the range of 5 to 15% by weight of the surface treatment composition. If the amount added exceeds 20% by weight, the flash point will be low (and the characteristics as a water-based paint will be lost). It has excellent stability for resin dispersions and water-dispersible silica, and acts as an effective diluent that improves storage stability and lowers the freezing point.Cellosolve and butyl cellosolve can also be used as ether solvents. However, some of these cellosolve-based solvents and monohydric alcohol solvents such as n-butanol and isopropyl alcohol are effective for copolymer resin dispersion and water dispersion. It is important to limit the amount to an appropriate amount because it impairs the stability of silica, causes aggregation, and causes a decrease in storage stability.

It is also possible to further obtain low-temperature curability by using a chelate compound such as titanium, zirconium, aluminum, metal salts, etc. in combination with the above-mentioned aqueous composition as required. Furthermore, it is also possible to disperse a pigment or the like in the composition to obtain a coating composition having optical dioptric properties.

The method of applying the surface treatment composition according to the present invention includes dip coating,
Methods such as brushing and shower coating can be used, and when processing a large amount of small items such as bolts, dip coating can be used.
A spin coating method is also available. The coating dry film thickness is 2
~lopm range. Drying of the film after application is 1
This is achieved in 15 to 25 minutes at a temperature of 00°C or less, preferably 60 to 100°C, and a hardened film can be obtained at a relatively low temperature, so the corrosion protection of chromate-treated galvanized steel is not impaired.

The surface treatment composition according to the present invention forms a film as water evaporates, and the surface drying of the coating film after painting is relatively fast. For example, at 20℃ for 10 to 13 minutes and at 30℃ for 5 to 8 minutes,
The surface becomes dry to the extent that even if you touch it with your hand, you won't even get a finger mark (dry to the touch). Therefore, in the case of dip painting, areas that do not need to be painted or should not be painted are masked using an appropriate jig, but since they dry to the touch in a short time, it is important to allow enough time for them to dry to the touch. For example, the masking jig can be removed before baking and drying. By removing the jig before baking and drying, the finished appearance of the boundary line area is greatly improved. If you want to remove the jig after baking and drying, remove it along the boundary line.
Pali (a jagged, torn paint film) occurs, impairing the finished appearance. Next, when processing small items such as screw parts in large quantities, a method of centrifuging the remaining droplets after dip coating (dip spin method) is generally used.

Small screw parts have a large number of edges. Taking a bolt as an example in particular, there are edges everywhere, including around the bolt head and threads. According to the dip-spin coating method, when residual droplets are removed by centrifugation, the coating liquid adhering to these edges is shaken off, resulting in an extremely thin film with a dry coating thickness of 1 micron or less. Or it will be in a state where it is not coated at all. On the other hand, coating defects such as scratches on the coating may occur due to contact between the objects to be coated in the centrifuge, contact between the objects to be coated and the basket, or after the objects are removed from the centrifuge. be.

These poor coating of the edges and scratches due to contact, etc. cause a significant decrease in corrosion resistance and impair the commercial value in terms of finished appearance. Here, the above-mentioned coating defects can be overcome by repeating the dip spin twice using the surface treatment composition according to the present invention. That is, the film after the first dip spin treatment has the above-mentioned coating defects, but by reducing the volatile content in the coating film to 30% by weight or less,
It will be in a semi-hardened state. After reaching this state,
The dip spin treatment is carried out again using the same bath solution as the -th time, and the sample is dried at a temperature of 100° C. or lower. - If the film obtained in the second treatment is made into a semi-cured state, it will not be redissolved even if it is immersed in a bath liquid again, and it will not become soft and fluid. Therefore, the substrate will not be exposed due to damage caused by contact during processing, and by the -th processing,
Because a semi-cured film that does not flow is formed around the edge, the radius of curvature of the edge becomes large, and the edge structure allows the second coating to cover the edge. Excellent heat coverage.

Next, regarding the equipment used for dip-spin coating, centrifugation after immersion is preferably performed above the liquid level in the immersion bath from the economical point of view of increasing the recovery rate of residual droplets. However, when centrifuging in a bathtub, droplets of the processing liquid inevitably adhere to the walls of the bathtub. When the surface treatment composition according to the present invention is formed into a coating film, the surface dries relatively quickly, so that the coating liquid adhering to the wall surface is likely to form a film. Therefore, by repeating the painting process, a deposited layer of paint is formed on the wall inside the tank, so frequent cleaning is necessary.
This is not preferable from the point of view of effective use of the processing liquid. Therefore, by keeping the walls of the bathtub constantly wet with the processing liquid, that is, by allowing the processing liquid to overflow from the upper end of the wall to the entire surface of the wall, and covering the wall with the processing liquid that flows down in a bay shape, the adhesion of droplets caused by centrifugation can be prevented. The recovery rate of the processing liquid is further increased, and the economic effect can be greatly enhanced.

[Function] Although the reason why the surface treatment method of the present invention imparts excellent corrosion resistance to galvanized steel has not yet been fully clarified, it is assumed to be as follows.

α・Olefin-α・β ethylenically unsaturated carboxylic acid copolymer resin has properties as an ionomer (ionic copolymer), and metal ions (for example, 2 (strondium ions, barium ions, calcium ions, etc.) cross-link molecular chains using carboxylic acid groups in the resin skeleton. In addition, molecular silver cross-linking using carboxylic acid groups can also be achieved by trivalent chromium (Cr+8), which is produced by a redox reaction between chromate ions (CrO4-2) produced when a chromate compound is dissolved in water, and the resin. happens. In this way, an insolubilized film with excellent solvent resistance is obtained.

Furthermore, between the copolymer resin and colloidal silica, a copolymer resin/colloidal silica complex is formed due to hydrogen bonding between the silanol groups of the colloidal silica and the carboxylic acid groups in the copolymer resin. . Furthermore, when an alkoxysilane compound is added, the siloxane bond that is easily formed by the dehydration condensation reaction between the silanol group generated by the hydrolysis of the silane compound and the silanol group on the surface of the colloidal silica particles will strengthen the A colloidal silica-silane compound complex is formed through covalent bonds.

Furthermore, the bond between the colloidal silica/silane compound complex and the copolymer resin is a van der Waals bond between the organic group contained in the silane compound and the copolymer resin, and A complex is formed with relatively weak bonding forces due to hydrogen bonds between the silanol groups and the carboxylic acid groups in the copolymer resin.

In this way, the crosslinking reaction progresses at a relatively low temperature, and the formed film becomes dense and becomes a barrier film that blocks corrosion-forming substances, and the copolymer resin has excellent film-forming properties, coating properties, It is presumed that it provides excellent corrosion resistance by combining advantages such as flexibility with the characteristics of silica or inorganic composites such as excellent hardness and corrosion resistance against metals. Furthermore, it is thought that a passivation film is formed on the metal surface by the chromium compound, and the synergistic effect with the barrier film described above is thought to result in superior corrosion resistance.

[Example] Examples and comparative examples are shown below.

In these examples, an ethylene-acrylic acid copolymer resin dispersion [manufactured by Nippon Polyurethane Industries ■, trade name "Niraporan 3202"] was used as the a-olefin-〇-β ethylenically unsaturated carboxylic acid copolymer resin dispersion.
°゛], colloidal silica as water-dispersible silica [manufactured by Catalysts & Chemicals Industry ■, product name °゛Kyacroid i-45P, 5
i80P°"] N-β(aminoethyl)γ-aminopropyltrimethoxysilane [manufactured by Shin-Etsu Chemical Co., Ltd., trade name "K B M2O3"] was used as the trialkoxysilane compound.

Example (1) For 100 parts by weight of solid content of ethylene-acrylic acid copolymer resin dispersion, 70 parts by weight of colloidal silica (particle size = 35 to 55 mμ) as solid content and strontium chromate were added. An aqueous solution containing 7.5 parts by weight, to which 4% butyl cellosolve and 4% ethylene glycol were added, was subjected to chromate treatment on an electrogalvanized steel sheet with a zinc deposit of 20 g/m'' (one side) (Nippon Steel Zincoat EG-C). The film was coated on the film and dried at 80° C. for 20 minutes.The film thickness at that time was 3 to 5 p1n.

Examples (2) to (8) and Comparative Examples (1) to (5) Aqueous liquid composition (solid content ratio) used in Examples (2) to (8) and Comparative Examples (1) to (4) are shown in the table below.

Similar to Example (1), 4% butyl cellosolve and 4% ethylene glycol were added to the aqueous liquids used in Examples (2) to (8) and Comparative Examples (1) to (4). The material used was the same electrogalvanized steel sheet (ZINKOTE EG-C) as in Example (1). The drying conditions and film thickness after coating are the same as in Example (1). Comparative Example (5) was an electrogalvanized steel sheet that was not coated with an aqueous liquid. Table 1 shows the test results of Examples (1) to (8) and Comparative Examples (1) to (5).

Examples (9) to (11) and Comparative Example (6) Example (9)
) to (11), the contents of the aqueous liquids used are shown in the table below.

For Examples (9) to (11), the coating was applied to an electrolytically [zinc-nickel] alloy plated steel sheet (Ebara Nishira 2 Ito-Jinloy, plating thickness 5 to 7 coats) that had been chromate-treated, and was heated at 80°C for 20 minutes. Dry for a minute. The film thickness at that time was 3 to 5 meters. The above material to which no aqueous liquid was applied was designated as Comparative Example (6).

Example (12) and Comparative Example (7) The aqueous solution used in Example (1) was applied to a galvanized steel plate (Nissin Steel Pentite 60, zinc coating amount 30 g/m2) and dried at 80 ° C. for 20 minutes. . The film thickness at that time was 3 to 5 units. Comparative Example (7) was Pentite 60, which was not coated with an aqueous liquid.

Example (13) and Comparative Example (8) The aqueous solution used in Example (1) was applied to an electrogalvanized steel sheet that had not been subjected to chromate treatment (Nippon Steel Zincoat EG-C) and heated at 80°C. It was dried for 20 minutes. The film thickness at that time was 3 to 5 meters. The above material to which no aqueous liquid was applied was designated as Comparative Example (8). Examples (9) to (13)
) and the test results of Comparative Examples (6) to (8) are shown in Table 2.

Comparative Example (9) The electrogalvanized steel sheet (Nippon Steel Jinko 1-EG-C) used in Examples (1) to (8) was spray-coated with aqueous air-dry crosslinked acrylic resin paint and heated at 80°C for 30 minutes. Forced drying was performed. The film thickness at that time is 2511? It was +1.

Comparative Example (10) The electrogalvanized steel sheet (Nippon Steel Zincoat EG-C) used in Examples (1) to (8) was spray-coated with an epoxy-modified polyester/melamine resin paint and heated at 150°C for 30 minutes.
Baking drying was performed for 0 minutes. The film thickness at that time was 30F.

The test results of Comparative Examples (9) and (10) are shown in Table 1.

1. Salt spray test According to JIS-Z-2371 salt water spray test method.

2. Water resistance After being immersed in deionized water at 40° C. for 240 hours, the coated surface condition was evaluated and a 2 mm square grid test was performed.

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

○: No abnormality △: Film swelling and scratches occurred ×: Melting falls off 4, film hardness impregnated 7 Pencil hardness 5, impact resistance: DuPont type, impact tester [500g/
50 cm1 [Effect of the invention] As is clear from the above explanation, according to the present invention, 1
At low temperatures below 00°C, the synergistic effect of the sufficiently cross-linked hardened film acting as a barrier against corrosion-forming substances and the formation of a passivation film on the metal surface by the chromium compound provides excellent protection against galvanized steel. A surface treatment method exhibiting rust prevention properties can be provided. Furthermore, since the surface treatment composition of the present invention is a coating-no-rinsing type composition, it is possible to reduce pollution and save labor in the treatment process.

(that's all) \

Claims (3)

[Claims] 1. α・Olefin-α・β on the surface of galvanized steel
With respect to 100 parts by weight of the solid content of the ethylenically unsaturated carboxylic acid copolymer resin dispersion, more than 60 parts by weight of water-dispersible silica and not more than 120 parts by weight of water-dispersible chromium compound in solid content of 1 part by weight A method for surface treatment of galvanized steel, comprising applying an aqueous composition containing up to 40 parts by weight and drying it by heating. 2. α・olefin-α・β ethylenically unsaturated carboxylic acid copolymer Resin dispersion with water-dispersible silica of more than 60 parts by weight and less than 120 parts by weight and water-dispersible A surface treatment composition for galvanized steel, characterized in that it contains a chromium compound in a solid content of 1 to 40 parts by weight. 3. 1 to 10 parts by weight of a trialkoxy (or alkoxyalkoxy) silane compound is further added to the composition according to claim 2, based on 100 parts by weight of the solid content of the copolymer resin dispersion. Surface treatment composition.