JPH0454745B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a highly corrosion-resistant surface-treated steel sheet with improved corrosion resistance and adhesion of the colored resin film, in a surface-treated steel sheet with a colored resin film formed on the surface of the steel sheet and with excellent paintability. (Prior art) Among surface-treated steel sheets in which a cold-rolled steel sheet or a matted steel sheet is treated with a water-dispersible or water-soluble resin containing a colored pigment to form a colored resin film that provides paintability and corrosion resistance on the surface. , which have relatively better paintability and corrosion resistance than conventional ones, have a chromate film formed on the surface of the steel plate, and then a colored resin film alone or a colored resin film containing inorganic substances other than pigments is formed on the chromate film. be. This surface-treated steel sheet has a first layer of chromate film that provides corrosion resistance, and a second layer of colored resin film that provides paintability. Hydrophilic compounds having a hydroxyl group in the upper molecule were used. (Problem to be solved by the invention) However, in the case of the above-mentioned surface-treated steel sheet, its corrosion resistance depends on the first layer of chromate film, so even if an attempt is made to improve the corrosion resistance, there is a limit to the improvement. It was hot. Therefore, in order to further improve the corrosion resistance, it was necessary to improve the corrosion resistance of the colored resin film of the second layer. One possible method for improving the corrosion resistance of colored resin films is to include hexavalent chromium in the colored resin film, but in order to contain hexavalent chromium using this method, a resin film treatment solution containing hexavalent chromium must be used. need to be processed. However, if chromic anhydride or chromate is added to contain hexavalent chromium in the resin coating treatment solution, the hydroxyl groups of the resin molecules will be oxidized, and the treatment solution will become a gel, making it impossible to apply it to the steel plate. It is reduced to valent chromium and no longer exhibits corrosion resistance. For this reason, it has conventionally been difficult to incorporate hexavalent chromium into colored resin films. (Means for Solving the Problems) The present invention provides a highly corrosion-resistant surface-treated steel sheet that makes it possible to incorporate hexavalent chromium into a colored resin film, which has been difficult in the past. The highly corrosion-resistant surface-treated steel sheet of the present invention uses a water-dispersible copolymer that does not have hydroxyl groups as the resin of the colored resin film, so that the resin is not oxidized at the treatment liquid stage, and the acid value of the copolymer is adjusted. By incorporating a silane coupling agent and/or a titanate coupling agent, the water resistance, adhesion and physical properties of the film, as well as the adhesion to the paint film when painted, are improved. That is, the present invention uses (A) the general formula CH ₂ =CR ₁ − as the resin for the colored resin film.
1 to 95% by weight of one or more monomers represented by COOR ₂ (in the formula, R ₁ is H, CH ₃ , R ₂ is an alkyl group having 1 to 8 carbons), (B) α, 3 to 20% by weight of a β-unsaturated carboxylic acid monomer, (C) 0.1 to 50% by weight of a monomer copolymerizable with these monomers [However, (A), (B) and (C) 100% by weight] A copolymer resin obtained by emulsion polymerization and having an acid value of 10 to 200 per solid content is blended with a silane coupling agent and/or a titanate coupling agent. Here, the general formula that constitutes the copolymer resin is CH ₂ =
Examples of CR ₁ -COOR ₂ monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Examples of α, β unsaturated carboxylic acid monomers include acrylic acid, methacrylic acid, itaconic acid, maleic acid, and examples of monomers that can be copolymerized with these monomers include styrene. ,α−
Examples include methylstyrene, vinyl acetate, vinyl chloride, and vinylidene chloride. The reason for using the above-mentioned copolymer resin in the present invention is that a film having the desired physical properties can be obtained and the industrial production of the copolymer resin is easy. The reason why the acid value of the copolymer resin is set to 10 to 200 per solid content is because if it is less than 10, the water resistance is good but the adhesion to the steel plate is poor, and if it exceeds 200, the water resistance is poor. This is because corrosion resistance decreases.
When the acid value is set to 15 to 100, the film will have good water resistance and adhesion, so it is preferable to set it within that range. Even if one or both of the silane coupling agent and the titanate coupling agent are blended, it is preferable to blend them in an amount of 0.05 to 10 parts by weight per 100 parts by weight of the copolymer resin. There are various types of silane coupling agents, but as long as they are water-dispersible or water-soluble, monomer types [e.g. vinyltri(β-methoxyethoxy)silane, γ
-glycidoxypropyltrimethoxysilane],
Oligomer type (e.g. glycide type),
Any resin-modified type (for example, acrylic-modified or epoxy-modified) or cationic type can be used. Further, titanate coupling agents can be used as long as they are water-dispersible or water-soluble, and preferred examples include tetra(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl)phosphite. Titanate, bis(dioctylpyrophosphate)
Examples include oxyacetate titanate and bis(dioctylpyrophosphate) ethylene titanate. In the present invention, the colored resin film is formed as described above, and the film contains chromate as a source of hexavalent chromium, and further contains silica sol to improve the physical properties and corrosion resistance of the film. The chromate to be contained here is preferably water-soluble and inexpensive, such as ammonium chromate, magnesium chromate, potassium dichromate, calcium chromate, zinc chromate, manganese chromate, nickel chromate, and chromate. Cobalt acid, strontium chromate, etc. are suitable. In addition, it is preferable that the thickness of the colored resin film be 0.2 to 10 μm, so the particle size of the pigment should be 1 μm.
Hereinafter, preferably fine particles of 0.1 μm or less are used. The amounts of these chromates, silica sol, and pigments to be contained in the colored resin film are 0.1 to 50 parts by weight for chromate, 0.5 to 100 parts by weight for silica sol, and 0.5 to 100 parts by weight for silica sol per 100 parts by weight of copolymer resin. In this case, it is preferably 0.1 to 50 parts by weight. A colored resin film with such content and film thickness may contain 200 to 400 g of copolymer resin, 0.1 to 40 g of silane coupling agent or/and titanate coupling agent.
It can be formed using a treatment liquid containing 0.2 to 200 g/g of chromate, 1 to 400 g/g of silica sol, and 0.2 to 200 g/g of pigment. Since the colored resin film contains chromate, it exhibits corrosion resistance even when formed directly on a steel plate, but in order to exhibit further corrosion resistance, a chromate film is formed on the steel plate and then formed on it. In this case, the type of chromate film generally does not matter, such as reactive type or coating type, but
The total amount of chromium in the film is preferably 5 to 200 mg/m ² . Steel sheets include cold-rolled steel sheets, galvanized steel sheets (e.g. galvanized steel sheets, aluminum-plated steel sheets,
Various alloy plated steel sheets) may be used. (Example) Acrylic emulsion obtained by emulsion polymerization of 50% by weight of methyl methacrylate, 40% by weight of butyl acrylate, 10% by weight of acrylic acid, and 0.2% by weight of styrene [resin content: 40% by weight, PH2. 3. Viscosity: 25 cps (25°C, B-type viscometer), acid value per solid content: approximately 78, hereinafter the copolymer resin in this emulsion will be referred to as X], and 55% by weight of methyl acrylate.
An acrylic emulsion obtained by emulsion polymerization of 40% by weight of butyl acrylate, 5% by weight of acrylic acid, and 0.3% by weight of vinyl acetate [resin content 40% by weight, PH2.6, viscosity 150cps (same as above), Acid value per solid content of about 40, hereinafter the copolymer resin in this emulsion will be referred to as Y], a silane coupling agent or/and a titanate coupling agent, chromate, silica sol (Snowtex O, Nissan Chemical Products), After preparing a colored resin film treatment solution by adding various particulate pigments, this treatment solution was applied onto a 0.6 mm thick steel plate with a chromate film formed on the surface to produce a surface-treated steel plate. The manufacturing process at this time,
The conditions for forming the chromate film are as follows. (B) Manufacturing process Steel plate → Degreasing → Chromate treatment → Colored resin film treatment solution application → Drying (150℃, 10 seconds) (B) Chromate film formation conditions, treatment of CrO ₃ 20g/, Na ₂ SiF ₆ 1g/ It was immersed in the solution at 40°C for 5 seconds and then rolled squeezed. Table 1 shows the surface-treated steel sheets produced in this manner. Next, a test piece was taken from this surface-treated steel sheet and subjected to a salt spray test and a wet test, and the remaining surface-treated steel sheet was coated with melamine alkyd paint to a dry film thickness of 30 μm and heated at 200°C. After baking for 20 minutes, a coating adhesion test, a salt spray test, and a wetness test were conducted. Table 2 shows the results of these tests. Each of the above tests was conducted in the following manner. (b) Salt spray test: For both unpainted and painted plates, make a cut that reaches the steel plate surface with a knife,
After a period of time, sellotape was applied to the incision and quickly peeled off, and the peeled off portion was evaluated according to the following criteria. ◎...No flaking ○...Flamination width or rust occurrence width is 1mm or less from the notch △...Flamation width or rust occurrence width is more than 1mm and 3mm or less from the notch ×...Flamation width or rust occurrence width is more than 3mm from the notch (b) Moisture test A test piece with the same notch as above for both unpainted and painted boards was placed in an atmosphere with a temperature of 50℃ and a humidity of 98%.
After 1500 hours, sellotape was applied to the incision and rapidly removed, and the removed area was evaluated using the same criteria as in the salt spray test. (c) Paint film adhesion test (a) Dupont impact test A 1/2 inch punch diameter, 500 g weight was used for 50
After dropping the product from a height of 1.5 cm, sellotape was applied to the impact area and rapidly peeled off, and the peeling state of the paint film was evaluated using the following criteria. ◎...No peeling of the paint film ○...Slight peeling of the paint film △...Significant peeling of the paint film ×...More than 30% of the paint film has peeled off (b) Erichsen test for scratches 6 with an Erichsen tester
After extrusion of mm, sellotape was applied to the extruded part and rapidly peeled off, and the peeling state of the coating film was evaluated using the same criteria as in the Dupont impact test. (c) 180-degree close bending test Sellotape was pasted on the outside of the bent portion and rapidly peeled off, and the state of paint film peeling was evaluated using the same criteria as in the Dupont impact test.

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[Table] (Effects) As explained above, in the surface-treated steel sheet of the present invention, the resin of the colored resin film does not have hydroxyl groups, so even if the treatment liquid contains chromate during manufacturing,
The resin does not oxidize and does not gel. Since the colored resin film contains chromate, corrosion resistance is improved, and since it also contains a silane coupling agent and/or a titanate coupling agent, and silica sol, the water resistance, adhesion and Physical properties and adhesion to the coating film are improved.

Claims (1)

[Claims] 1 A chromate film is formed on the surface of the steel plate, and (A) general formula CH ₂ = CR ₁ − is formed on the chromate film.
1 to 95% by weight of one or more monomers represented by COOR ₂ (in the formula, R ₁ is H, CH ₃ , R ₂ is an alkyl group having 1 to 8 carbons), (B) α, 3 to 20% by weight of a β-unsaturated carboxylic acid monomer, (C) 0.1 to 50% by weight of a monomer copolymerizable with these monomers [However, (A), (B) and (C) 100% by weight] A resin film made by blending a silane coupling agent and/or a titanate coupling agent with a copolymer resin having an acid value of 10 to 200 per solid content obtained by emulsion polymerization. A highly corrosion-resistant surface-treated steel sheet comprising a chromate, a silica sol, and a finely divided colored pigment.