JPS637877A - Surface treatment of stainless steel excellent in close adhesiveness of paint - Google Patents

Abstract

PURPOSE:To markedly enhance the close adhesiveness of paint, in painting stainless steel, by forming a silica film on stainless steel by alkyl silicate treatment and applying surface treatment forming a film of a silane coupling agent to said film. CONSTITUTION:For example, ethyl silicate containing 40% of SiO2 is hydrolyzed to be diluted with alcohol and the diluted composition is applied to a stainless steel plate subjected to brightness annealing finish by dripping roll squeezing to form an extremely shin silica film on the surface of the stainless steel plate. A silane coupling agent of an organosilicon monomer having two or more of different reactive groups in the molecule thereof is diluted with alcohol to be applied to said silica film before drying. The electrodeposition film to the stainless steel plate thus surface-treated by acrylic cation paint has excellent close adhesiveness through the silica film and two reactive groups of the silane coupling agent.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention involves forming a silica (SiO2) film on the surface of stainless steel by alkyl silicate treatment in order to improve the adhesion of the paint when painting stainless steel. The present invention relates to a surface treatment method for forming a film of a silane coupling agent.

(Conventional technology) Stainless steel is originally used unpainted, but
Recently, in order to diversify products such as automobiles, building materials, and durable consumer goods, stainless steel has been shot-plast or polished in order to provide color and further improve corrosion resistance.
Alternatively, a method is used in which a corrosive solution such as nitric-hydrofluoric acid or ferric chloride is used to form a rough surface to provide a surface with good paint adhesion.

Further, as in the invention of Japanese Patent Publication No. 60-58819, there is a method of electrolytically treating in a sodium chloride solution to generate pitting corrosion that is wider at the front than at the back, thereby forming a surface with good paint adhesion. Proposed. Generally, chemical conversion treatment using chromate, phosphate, and silicate chemicals is known as a base treatment for metal painting, but when applied to stainless steel, active treatment to remove the passive film is used. oxidation treatment is required in advance.

(Problems to be solved by the invention) The corrosion resistance of stainless steel is maintained by the passive film on the surface, and the bright annealed finish material has a unique oxide film (
BA film) is formed, which helps improve corrosion resistance. These films exhibit resistance to corrosive substances, and at the same time are a factor that inhibits adhesion to paints and chemical conversion agents, so the current practice is to remove the films as described above. be. However, since the coating film allows a certain amount of water and air to pass through and is further deteriorated by ultraviolet rays, it is desirable that the base material has good corrosion resistance. Therefore, in order not to impair the corrosion resistance of the base stainless steel, a passive film or BA
To maintain durability, it is necessary to apply a coating with good adhesion to the surface without removing the film.

The present invention was made in order to solve the problem of applying a good coating to the surface film of stainless steel, which has poor paint adhesion.

(Means for Solving the Problems) The gist of the present invention is to apply an alkyl silicate to a stainless steel surface, dry it, and then conduct silane coupling of an organosilicon monomer having two or more different reactive groups in the molecule. This is a method for surface treatment of stainless steel with excellent paint adhesion, which is characterized by applying an alcohol solution containing a chemical agent and drying it. That is, in the present invention, in order to apply a coating with good adhesion without removing the surface film of stainless steel and making the surface rough, first, an alkyl silicate, which is an organosilicon compound that has an affinity for the surface film, is applied. and dry, coat with silica (
Sin 2) The surface is modified by forming a film, but since a silica film alone has poor adhesion to the paint, the present invention further forms a film that has an affinity for both the silica film and the paint. .

(effect) First, the method for forming the silica film in the first step will be described.

As has long been known, ethyl silicate, a typical alkyl silicate, separates into silica and ethyl alcohol through hydrolysis, forming a highly adhesive silica film with excellent heat resistance and corrosion resistance on metal surfaces. . Ethyl silicate 4O with 40% Si02 is usually used as this agent to improve the yield of silica.In this paper, it is necessary to form it thinly and uniformly, so a hydrolyzed product of alcohol is used. It was diluted (ethyl alcohol or Improvil alcohol) and applied to a bright annealed stainless steel plate using a dropping roll squeegee and dried. Through the above treatment, the surface of the stainless steel is uniformly coated with an extremely thin silica film. Ethyl silicate is generally used as the alkyl silicate treatment solution in the present invention, but other methyl silicate and probyl silicate can also be used. However, since the hydrolytic reactivity decreases as the alkyl group becomes longer, it is better for the treated film to be uniform and thin in the present invention, so the above-mentioned conditions are optimal.

Next, in the second step, a silane coupling agent is used to form a surface with excellent paint adhesion.

Silane cuffling agents have reactive groups (methoxy groups, ethoxy groups, silanol groups, etc.) that chemically bond with inorganic materials.
Organosilicon monomers with two different reactive groups (vinyl group, epoxy group, methacrylic group, amine group, etc.) that chemically bond with organic materials, trimethylmethoxysilane, vinyltriethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, γ-
Aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and the like are commercially available. These have been widely used as processing agents for improving adhesion, and known techniques related to this include Japanese Patent Publication No. 55-41.
711, % Publication No. 55-4 17 1 2, Special Publication No. 55-41713, Special Publication No. 60-22067, etc. The treatment liquid in these inventions is an aqueous solution of a silane coupling agent or an aqueous alcohol solution containing water-soluble Ti,
Compounds such as Zr and Mo are added to improve performance. The objects to be treated include iron, non-ferrous metals, plated steel sheets, and chemically treated steel sheets, but aqueous solutions and aqueous dispersions are not suitable for stainless steel, especially stainless steel copper strips coated with bright annealed BA coating. Since there is a problem with wettability, the present inventors conducted studies to establish the applicable conditions. The results will be described below.

The test material used was a 4 mm thick SUS 430 cold-rolled stainless steel plate with a bright annealing finish. Ethyl silicate was diluted with isopropyl alcohol, applied with a dropping roller, and dried. A silicate film was formed on the surface. A solution of 80 g/l' of N-β (aminoethyl) γ-aminopropyltrimethoxysilane in isopropyl alcohol, which is a silane coupling agent, for both the treated product and the untreated product with bright annealing finish. and its aqueous solution were applied using a dripping roll squeezer,
It was dried at 100-120°C. Regarding the above treated materials,
Both the ethyl silicate-treated specimen and the untreated bright annealed specimen were coated and subjected to a coating film adhesion test. Electrodeposition coating (26°C, 120V, 2min) was performed using an acrylic cationic paint, and baking was performed at 180°C for 25 minutes to obtain a film thickness of 20 to 23μ.

After immersing this in 40℃ hot water for 240 hours, the thickness of 2 mm
The adhesion of the coating film was evaluated using a goblin test. In this case, the test results are shown in Table 1, with 0 indicating no peeling of the coating film and 0 indicating poor coating peeling.

Table 1 As shown in Table 1, paints that are brightly annealed or treated only with ethyl silicate have poor adhesion to the paint.
It can be seen that when treating with a silane coupling agent, it is difficult to adhere with an aqueous solution, and an alcohol solution is most suitable. The reactive group that binds to the inorganic material of the silane coupling agent is a stainless steel surface film (BA film or passive film).
Instead, it bonds with the silica film, and as a result, reactive groups that bond with organic materials are formed on the outermost surface and bond with the paint.

All of the above-mentioned solvents can be used as the silane coupling agent treatment liquid in the present invention, and various alcohols, acetone, toluene, ether, etc. can be used as dilutable solvents for each, but they are not suitable for workability, safety, economy, etc. Ethyl alcohol or isopropyl alcohol is most suitable from the viewpoint of stability. The concentration of silane coupling agent is 0.5-2
0 0 g/no is suitable. In other words, 0.5 g/l or more is effective for paint adhesion, but if the formed film becomes thick, the color tone of the paint film will become uneven when applied, so the upper limit should be set at 200 g/l. /4.

In the present invention, the surface treatment liquid may be applied by any conventional method, but it is best to use a roll squeegee to finish the coating, as it is better to make it as thin and uniform as possible as a base for coating. Drying after coating may also be carried out by a normal method, and may be carried out at 60 to 300°C. Next, the effects of the present invention will be specifically illustrated by examples.

(Example) 0. An ethyl silicate agent diluted with Inglobil alcohol was applied to a bright annealed SOS 430 cold rolled stainless steel plate with a thickness of 4 mm using a dropping roll and dried to form a silica film on the surface. . Next, in the silane coupling agent treatment solution, isopropyl alcohol i solution o. t, 0.8, 0.5, 1,
10, 50, 100, 200g/1 concentration, and ethyl alcohol solution of γ-aminoprobyltriethoxysilane 0.1, 0.3, 0.5, 1,
Prepare treatment liquids with concentrations of 10, 50, 100, and 200 g/no, and apply each treatment liquid using a dripping roll squeezer.
◎These were dried at 100-120°C and then electrodeposited using acrylic cationic paint (26°C, 120V, 2
min) and baked at 180°C for 25 minutes. This is 4
After immersion in 0° C. hot water for 240 hr, the adhesion of the coating film was evaluated by a two-way cross test. The test results are shown in Table 2.

In addition, in evaluating paint adhesion, no peeling of the paint film is rated as ○.
, If even a slight amount of peeling occurred, it was rated as ×. The above results show that the concentration of the silane coupling agent that is effective in improving the adhesion of the paint is 0.5 g/λ or more.

Table 2 (Effects of the Invention) By applying the treatment of the present invention to bright annealed stainless steel materials that have poor paint adhesion, it is possible to produce colored stainless steel products with further improved corrosion resistance. Furthermore, the fields of use of stainless steel will be expanded. Furthermore, since the treatment liquid of the present invention is a silicon compound, it is different from chromic acid and is non-polluting, which is advantageous in terms of workability.

Claims (1)

[Claims] It is characterized by applying an alkyl silicate to the stainless steel surface and drying it, then applying an alcohol solution containing a silane coupling agent of an organosilicon monomer having two or more different reactive groups in the molecule and drying it. A method of surface treatment of stainless steel with excellent paint adhesion.