JPH036903B2 - - Google Patents

Description

[Detailed description of the invention]

(1) Industrial application field The present invention is suitable for use in automobile body parts, equipment parts placed in corrosive environments, building materials, etc. that require welding during assembly and joining. Concerning zinc-rich welded multilayer coated steel sheets. (2) Prior art As a weldable coated steel sheet with excellent corrosion resistance, the steel sheet contains a total of 60% by weight or more of zinc powder and zinc-magnesium-based alloy powder via a chromate film or a phosphate film and a chromate film. Some have a zinc-rich coating. This steel sheet has a zinc-rich coating film that contains zinc-magnesium-based alloy powder, which has high hardness and excellent corrosion resistance, in addition to zinc powder to improve the powdering resistance and corrosion resistance of the coating film. The base alloy powder is
The ratio of Zn powder/Zn-Mg based alloy powder is approximately 50/50 to 98/2. (3) Problems to be solved by the invention However, in the above-mentioned weldable coated steel sheet, the pretreatment coating is a chromate coating or a phosphate coating, and the zinc-rich coating is made of zinc powder or zinc-magnesium-based alloy powder with a total weight of 60%. % or more, there were problems with the secondary adhesion and water resistance of the paint film, and there was also the problem that if the chromate film was made thicker to improve corrosion resistance, the paint film adhesion would decrease. In order to solve this problem, it is possible to interpose a thin resin film containing hexavalent chromium between the chromate film or phosphate film of the pretreatment film and the zinc-rich coating, but the formation of the resin film is 6
Since an aqueous solution must be used due to the relationship with the chromium supplying agent, a monomer or a low molecular weight polymer having a hydrophilic group (for example, a hydroxyl group or an amino group) must be used as the resin for the resin film. However, in the case of such a resin, when a hexavalent chromium supplying agent (chromic anhydride, chromate) coexists, the hydrophilic groups are easily oxidized and gelatinized, making it impossible to apply the resin. (4) Means for solving the problem As a result of various studies on resins that are not oxidized by the hexavalent chromium supply agent, the present inventors found that (A) general formula

[Formula] (in the formula, R ₁ is H, CH ₃ , R ₂ is a C1-8 alkyl group) and one or two monomers
(B) 3-20% by weight of an α,β-unsaturated carboxylic acid monomer; and (C) 0-50% by weight of a monomer copolymerizable with these monomers. [However, the total of (A), (B) and (C) is 100% by weight] It was found that it is sufficient to use a copolymer resin with an acid value of 100 to 200 per solid content obtained by emulsion polymerization. Ta. Since this copolymer resin does not have hydrophilic groups that are easily oxidized such as hydroxyl groups or amino groups, it will not be oxidized even if a hexavalent chromium co-supplying agent is added to the treatment liquid, and since it is a water-dispersible resin, Even if the molecular weight is increased, it can be made into an aqueous solution. In the present invention, those copolymerized to have a molecular weight of 100,000 or more are usually used. The acid value of this copolymer resin is 10 to 10 per solid content.
The reason for setting it to 200 is that if the acid value is less than 10, the water resistance will be good, but the adhesion with the pretreatment film and zinc-rich coating will decrease, and if it exceeds 200, the water resistance will decrease and the corrosion resistance will deteriorate. It is from. General formula constituting the above copolymer resin

[Formula] Examples of monomers include (meth)methyl acrylate, (meth)ethyl acrylate,
Probyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, etc., and examples of α,β unsaturated carboxylic acid monomers include acrylic acid, methacrylic acid, itaconic acid, Examples of monomers that can be copolymerized with maleic acid and the like include styrene, α-methylstyrene, vinyl acetate, vinyl chloride, and vinylidene chloride. The present invention uses the above copolymer resin to form a resin film, contains chromate as a hexavalent chromium supplying agent, and also contains silica sol to improve the physical properties and corrosion resistance of the film. let The chromate to be included is easily soluble in water and inexpensive, such as ammonium chromate, magnesium chromate, potassium dichromate, calcium chromate, zinc chromate, manganese chromate,
Preferred are nickel chromate, cobalt chromate, strontium chromate, and the like. The amount of chromate and silica sol contained in the resin film is preferably 0.1 to 50 parts by weight in the case of chromate and 0.5 to 100 parts by weight in the case of silica sol per 100 parts by weight of the copolymer resin. Further, the thickness of the resin film is preferably 0.1 to 2 μm. A resin film with such content and film thickness consists of copolymer resin 200 to 400 g/, chromate 0.2 to 200 g/, silica sol 1 to 400 g/
It can be formed using a processing liquid containing g/g/. In the case of the present invention, if a resin film having the composition as described above is formed between the pretreatment film and the zinc-rich coating film, the secondary adhesion and water resistance of the coating film will be improved, and the chromate and Silica sol improves corrosion resistance, but adding a coupling agent to the copolymer resin also improves the adhesion of the coating to the pre-treated coating and zinc-rich coating.
Moreover, the water resistance and physical properties of the film can also be improved. It is sufficient to mix the coupling agent in an amount of about 0.05 to 10 parts by weight (0.1 to 40 g/in the treatment liquid) per 100 parts by weight of the copolymer resin in the form of a resin film. As the coupling agent in this case, it is preferable to use a silane coupling agent or a titanate coupling agent. There are various types of silane coupling agents, but those that are water-dispersible or water-soluble are monomeric types [e.g. vinyltri(β-methoxyethoxy)silane, γ-glycidoxypropyltrimethoxysilane]. , oligomer type (e.g. glycide type), resin modified type (e.g. acrylic modified,
(Epoxy-modified type) and cationic type can also be used. Titanate coupling agents can also be used as long as they are water-dispersible or water-soluble; preferred examples include tetra(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl)phosphite titanate. , bis(dioctyl birophosphate) oxyacetate titanate, and bis(dioctyl birophosphate) ethylene titanate. In the case of the present invention, since a pretreatment film exists between the resin film and the steel plate, the resin film is not affected by the type of steel plate. Therefore, the steel sheet may be a cold-rolled steel sheet depending on the purpose, or a galvanized steel sheet (for example, a hot-dip galvanized steel sheet, an electro-galvanized steel sheet, a hot-dip aluminum-galvanized steel sheet, an Al-Zn alloy-galvanized steel sheet, an electric galvanized steel sheet, etc.). It may be an alloy plated steel plate, an electrical multi-layer plated steel plate, an alloyed hot-dip galvanized steel plate, a vapor deposition plated steel plate, etc.). Furthermore, the zinc-rich coating film is not suitable as it contains, in addition to zinc powder and zinc-magnesium based alloy powder, a rust-preventing pigment to improve anti-corrosion properties and a coloring pigment for coloring. (5) Example Acrylic emulsion obtained by emulsion polymerization of 50% by weight of methyl methacrylate, 40% by weight of butyl acrylate, and 10% by weight of acrylic acid [resin content: 40% by weight, PH2.3, viscosity] 25CPS (25℃, B
55% by weight of methyl acrylate, 40% by weight of butyl acrylate, and 5% by weight of acrylic acid. Acrylic emulsion obtained by emulsion polymerization [resin content 40
% by weight, PH 2.6, viscosity 150 CPS (same as above), acid value per solid content approximately 40, hereinafter the copolymer resin in this emulsion will be referred to as Y], chromate and silica sol [Snowtex O, Nissan Chemical] Various resin film treatment solutions were prepared by adding the product] or a coupling agent together with these, and the treatment solutions were applied to a steel plate on which a chromate film or a phosphate film and a chromate film had been formed. Next, on the resin film formed on the chromate film, an epoxy resin zinc-rich paint containing zinc powder and zinc-magnesium-based alloy powder is further applied to reduce the amount of zinc powder and zinc-magnesium-based alloy powder to 85% by weight. (However, Zn powder/Zn-Mg based alloy powder = 85/15)
A zinc-rich coating film with a dry coating thickness of 7 μm was formed. The steel plate used is an alloyed hot-dip galvanized steel plate with a thickness of 0.8 mm (plating weight: 30 g/m ² ).
The manufacturing process and the formation of the phosphate film and chromate film were carried out as follows. (a) Manufacturing process Steel plate → degreasing → (phosphate film) → chromate film → resin film treatment solution application → drying (150℃, 10
seconds) → Apply zinc-rich paint → Dry (250℃,
(60 seconds) (b) Formation of phosphate film Granozin 46N-2 [manufactured by Nippon Paint Co., Ltd.] was sprayed for 3 seconds. (c) Formation of chromate film 10 parts by weight of chromic acid trioxide, 3 parts by weight of phosphoric acid,
A coating type chromate treatment solution consisting of 5 parts by weight of polyacrylic acid, 18 parts by weight of acrylic emulsion polymer solids, 5 parts by weight of polyacrylic acid, 2000 parts by weight of water, and Cr ⁺⁶ /Cr ⁺³ = 1.4 was applied by roll coating. It was coated with Table 1 shows the composition of the coated steel sheet, and Table 2 shows the secondary adhesion, corrosion resistance, and weldability of the coating film. In addition, each test of paint film adhesion, corrosion resistance, and weldability was conducted as follows. (1) Secondary adhesion of coating film After immersing the test piece in boiling water for 2 hours, JIS
A bending test was conducted according to the test method for colored galvanized iron sheets of G.3312. The bending test is 180 with the number of sheets at the inner bending interval of 0 sheets (0t), 1 sheet (1t), and 2 sheets (2t).
After performing the close bending process, cellophane tape was applied to the processed coating film, and cellophane tape was peeled off by rapidly peeling it off, and evaluation was made according to the following criteria.

【table】

【table】

【table】

【table】

[Table] (2) Corrosion resistance (a) Salt spray test A test piece was cross-cut with a knife, bent 2 tons at 180 degrees, and exposed the cut end, and then subjected to salt spray according to JIS Z 2371. The test was conducted to evaluate the time until red rust appeared in each test part. (b) Humidity test The degree of blistering of the coating film after being left in a humid atmosphere of 50°C and 98% RH or higher for 2000 hours was evaluated according to the following criteria.

[Table] (3) Weldability After performing spot welding under the following welding conditions, a tensile test was conducted to investigate the incidence of tensile shear strength of less than 850 Kgf. (a) Welding conditions

【table】 (b) Incidence of tensile shear strength less than 350Kgf

[Table] From Table 2, the coated steel sheets of the present invention are superior to the conventional ones in terms of secondary adhesion and corrosion resistance of the coating film. (6) Effects As explained above, in the coated steel sheet of the present invention, a resin film containing chromate, silica sol, or a coupling agent in addition to these is formed between the pretreatment film and the zinc-rich film. Excellent paint film adhesion and corrosion resistance.

Claims (1)

[Claims] 1. A zinc-rich coating film containing a total of 60% by weight or more of zinc powder and zinc-magnesium-based alloy powder is formed on the surface of a steel sheet via a chromate film or a phosphate film and a chromate film. In the painted steel sheet, between the chromate film and the zinc-rich coating film, (A) a monomer of the general formula [formula] (wherein R ₁ is H, CH ₃ and R ₂ is a C1-8 alkyl group) 1 to 95% by weight of one or more of the following, and (B)
3 to 20% by weight of α,β unsaturated carboxylic acid monomer,
(C) 0 to 50% by weight of a monomer copolymerizable with these monomers [however, the total of (A), (B) and (C) is 100% by weight]
Acid value per solid content obtained by emulsion polymerization: 10 to 200
A weldable multi-layer coated steel sheet with excellent corrosion resistance, characterized in that a copolymer resin film containing chromate and silica sol is formed in the resin film. 2. A painted steel sheet on which a zinc-rich coating film containing a total of 60% by weight or more of zinc powder and zinc-magnesium-based alloy powder is formed on the surface of the steel sheet through a chromate film or a phosphate station film and a chromate film, Between the chromate film and the zinc-rich coating film, (A) one or two monomers with the general formula [formula] (wherein R ₁ is H, CH ₃ , and R ₂ is a C1-8 alkyl group) 1 to 95% by weight or more, and (B)
3 to 20% by weight of α,β unsaturated carboxylic acid monomer,
(C) 0 to 50% by weight of a monomer copolymerizable with these monomers [however, the total of (A), (B) and (C) is 100% by weight]
Acid value per solid content obtained by emulsion polymerization: 10 to 200
Copolymer resin with silane coupling agent or/
A weldable multi-layer coated steel sheet with excellent corrosion resistance, characterized by a resin film containing a titanate coupling agent and a chromate salt and a silica sol.