JPS6366393B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for pre-painting a stainless steel plate in order to improve the adhesion between the stainless steel plate and the coating film both initially and over time. Recently, stainless steel sheets have been used in a wide variety of fields such as building materials, vehicles, equipment, and kitchen supplies, and are popular as high-grade durable materials due to their inherent high corrosion resistance. When used in an environment containing chlorine gas or sulfur dioxide gas, pitting corrosion is likely to occur, and in areas where dust such as iron powder is exposed, so-called "corrosion rust" may occur, damaging the appearance. are doing. In addition, the appearance of stainless steel has a unique metallic luster, which may give off a sense of strangeness depending on the application, and since it is a single metallic color, it has the disadvantage of lacking a variety of colors or designs with patterns. ing.
Therefore, in order to eliminate the above-mentioned drawbacks, methods of painting stainless steel plates have been conventionally implemented, but at present no suitable surface conditioning method or pretreatment method for stainless steel plates during painting has been found. That is, typical pretreatment methods currently in use include solvent cleaning, alkaline cleaning, and fluoronitric acid treatment, but these pretreatment methods still have the following problems. It's on. Solvent cleaning merely removes oils, fats and dirt, and does not have the effect of fundamentally improving the adhesion of the coating, but only prevents the deterioration of the adhesion of the coating due to oils, fats and dirt. Alkaline cleaning is also effective in removing oil and dirt like the solvent cleaning described above, but the alkali components that adhere to the stainless steel surface after cleaning cannot be sufficiently removed by washing with water, so this reduces the adhesion of the coating film. decreases and deterioration over time is also significant. Fluo-nitric acid treatment is effective in improving the adhesion of paint films, but existing conventional painting equipment cannot be used for painting, so new fluoro-nitric acid treatment and pollution treatment equipment is required. The amount of capital investment is large, which poses an economic problem. Furthermore, with only fluoronitric acid treatment, not only does the adhesion force deteriorate over time, but it also has poor moisture resistance and water resistance, and may be left in a humid environment for a long time.
When immersed, the adhesive strength tends to decrease. As mentioned above, with conventional pretreatment methods for painting, not only is the initial adhesion of coatings such as paint films weak, but they also deteriorate significantly over time, and when used as exterior building materials, the paint film will develop minute blisters within a few years. may occur. Therefore, the present inventors have solved these problems in one go, and provided a painting pretreatment method that can be easily and inexpensively processed using current industrial-scale painting equipment. By applying this method, it has become possible to obtain a coated stainless steel sheet with excellent initial adhesion of the coating film, corrosion resistance, and resistance to deterioration over time. The present invention is a method for pre-painting a stainless steel sheet, which is characterized in that prior to painting, a stainless steel sheet is subjected to a normal phosphate treatment, washed with hot water, squeezed with a roll, and then subjected to a coated chromate treatment. It is related to. The present inventors had previously proposed phosphate treatment of stainless steel plates (Patent Application No. 1983-90550).
It is clear that the initial adhesion between the coating film or organic film and the stainless steel plate, as well as the moisture resistance and water resistance, are significantly improved. Phosphate treatment in the present invention is conventionally widely carried out as a pre-painting treatment for galvanized steel sheets, etc. Phosphate treatment solutions include commonly commercially available zinc phosphate treatment agents for galvanized steel sheets, such as Manufactured by Nippon Paint Co., Ltd., product name "Granodine ZS"
#8100" or iron phosphate treatment agent for cold-rolled steel sheets, such as Nippon Parker Co., Ltd., product name "Bonderite #901", which generally contains SUS 304 and SUS 430 series stainless steels containing fluorine ions, nitrate ions, and phosphate ions. The purpose of the present invention can be achieved in part by using a material that has a moderate etching effect on the roll and treating it under such standard conditions. After squeezing, we proposed applying a coating-type chromate treatment. The coating type chromate treatment liquid according to the present invention has recently been developed.
This so-called coating is popular worldwide as a new, non-polluting, no-rinse chromate treatment for aluminum steel sheets, cold-rolled steel sheets, and sub-sharpened steel sheets, replacing phosphate treatment and reactive chromate treatments using spray or immersion methods. This is a cut-type chromate treatment agent. For example, manufactured by Kansai Paint Co., Ltd., product name "Akomet C"; manufactured by Nippon Paint Co., Ltd., product name "Alodine"
NR-2, NR-3, etc., basically contains hexavalent chromium and trivalent chromium, and contains 10 to 200 g of hexavalent chromium, that is, _CrO3 ,
Trivalent chromium contains 20 to 60% of the total chromium amount, and further contains silica or various organic substances. After coating, any material that evaporates and solidifies the water in the coating solution on the plate surface at a plate temperature of 60 to 120°C to form a chromate-based film is suitable for the coating type chromate treatment solution of the present invention. What is particularly important is that the amount of chromium deposited after applying the coating type chromate treatment solution is 2 to 60 mg/
m ² is desirable. If it is less than 2 mg/m ² , the effect is only the phosphate and acid treatment in the previous step, and the initial adhesion of the coating film is insufficient, especially in terms of scratch resistance, adhesion over time, and corrosion resistance. Even if the amount of chromium exceeds 60 mg/m ² , the adhesion of the paint film does not deteriorate drastically, but there are variations in the adhesion of the paint film, and even if the amount of chromium is increased, the corrosion resistance does not improve and instead deteriorates. There is a tendency to The excellent pretreatment performance of the present invention is due to the synergistic effect of the chromate film formed by the combination of the preceding phosphate treatment and the coated chromate treatment. Regarding the effect of phosphate treatment on stainless steel sheets, the present inventors have previously introduced a patent application filed in 1982.
As detailed in the specification of No. 90550, there are variations in performance such as paint film adhesion depending on the production lot of stainless steel sheets, poor scratch resistance, and poor adhesion over time. I couldn't resolve it. This is basically considered to be due to surface contamination during the manufacturing process of the stainless steel sheet, especially the adhesion of ultra-trace amounts of organic carbon. The surface of stainless steel is covered with a strong and dense oxide film, and if organic carbon such as oil is adsorbed on the surface, it cannot be completely removed with normal degreasing, and it remains on a microscopic scale, making it difficult to resist water. Even if it comes into contact with a phosphate treatment solution that has poor wettability, the entire surface will not be treated uniformly, leaving an unreacted state on a microscopic level. Therefore, it is considered that it is not possible to completely prevent variations and deterioration of adhesion over time. By applying a paint-on type chromate treatment to the phosphate-treated board, chromic acid is further adsorbed on top of it using the phosphate radicals adsorbed on the surface as a medium, forming a chromate film that wets the surface, resulting in the phosphate treatment. The organic matter in the inert carbon-contaminated parts that could not be adsorbed by phosphate radicals is oxidized with chromic acid to completely remove organic components harmful to paint film adhesion and form chromic chromate. It is something. If an attempt is made to directly coat a stainless steel plate with a chromate treatment solution without phosphate treatment, the treatment solution will be repelled and the coating will not be uniform, and the adhesion of the coating will be insufficient. In addition, if only the previous phosphate treatment is used, continuous operation will cause sludge to become entrapped, and if water is not washed thoroughly, moisture resistance may sometimes deteriorate due to a small amount of sludge adhering to the surface. However, in the case of the present invention, even if such sludge adheres, by applying the coated chromate treatment liquid, a trace amount of sludge will become chromium phosphate and dissolve, completely separating the coating film and stainless steel plate. It becomes a harmless substance for adhesion and significantly improves moisture resistance. As is clear from the Examples described later, the present invention shows stable and excellent adhesion, and in particular, the scratch resistance is extremely improved. This shows that the coated steel sheet can withstand extremely severe processing such as roll forming and press forming. In particular, excellent secondary adhesion means excellent moisture resistance. It can be said that it functions satisfactorily as a coated steel sheet even under high temperature, high humidity, or water leakage environments. Furthermore, as is clear from the adhesion properties over time, all of the comparative products showed significant deterioration, indicating that the actual bonding strength between the stainless steel plate surface and the coating film had decreased. Furthermore, as evidenced by the corrosion resistance test, even when exposed to a corrosive environment for a long period of time, unlike comparative products, it can completely prevent "crevice corrosion", which is the most important thing to watch out for when using stainless steel. On the other hand, when painted stainless steel sheets are used as roofing or wall materials, various solvent-containing substances such as adhesives, caulking materials, and backing materials are used simultaneously. In this case, solvent resistance is extremely important, and the product produced by the method of the present invention exhibits extremely excellent performance, completely different from comparative products. As described above, the product of the present invention is a stable and excellent pre-painting treatment method that is not found in conventional products (comparative products). In addition to performance, by implementing the method of the present invention, variations between lots can be completely eliminated, and it is a pretreatment method with extremely low manufacturing cost. This pretreatment process can be easily applied to the current production line for colored galvanized iron plates, etc., and the present invention can also be applied to special steel and various general stainless steel materials, so there are industrial merits. It's huge. Next, the embodiment will be further explained. EXAMPLE A stainless steel plate having a thickness of 0.4 mm, a width of 200 mm, and a length of 300 mm was subjected to pre-painting treatment according to the present invention under the treatment conditions shown in Table 1. 80 pre-treated specimens
After drying with hot air at ℃, it was immediately painted, and a coating accuracy test was conducted and evaluated. The test results obtained are shown in Table 2. At that time, apply epoxy-modified polyester clear paint using a bar coater to a dry coating of 7 μm.
After drying at 210℃ for 40 seconds and cooling to room temperature, apply silicone polyester enamel topcoat to a film thickness of 15μ and dry at 230℃ for 60 seconds. I did it.

【table】 #
Note 1) As the iron phosphate, the trade name Bonderite 901 (manufactured by Nippon Parker Co., Ltd.) was used.
#
Note 2) As zinc phosphate, the product name Granozin 8100 (manufactured by Nippon Paint Co., Ltd.) was used.
#
Note 3) The product name Ridrin 75 is a degreasing agent manufactured by Nippon Paint Co., Ltd.

[Table] In Table 2, the primary adhesion test is JIS G
A normal bending test was conducted in accordance with the test method for colored galvanized iron sheets of 3312. The bending test was conducted with 0 and 2 bending inner spacer plates, and after the test, whitening was observed due to minute gaps between the paint film and the stainless steel plate, so the state of whitening was observed with the naked eye. evaluated. ◎ indicates no abnormality, 〇 indicates the initial state of slight whitening, and ○△ indicates slight whitening. △ indicates whitening and slightly poor adhesion. Those marked with an x mark have severe whitening and cracks, and will peel off when treated with cellophane tape. In the secondary adhesion test, the sample was immersed in boiling water at 100°C for 2 hours, left in a room at 20°C and 65RH for 24 hours, and then tested for accuracy in the same way as the primary adhesion test. In the temporal adhesion test, the same accuracy test as the primary adhesion test was conducted on the specimens after 6 months of the outdoor exposure test. In addition, the salt water mound test was conducted for 1000 hours in accordance with JIS Z 2371 on the specimens that had been bent in advance for the primary adhesion test (bending test) between the two inner bends. It was left in a humid state at 50°C and 98% RH for 1000 hours, and evaluated according to the following criteria. ◎: No abnormality observed. ○: Whitening occurs, but no peeling of the paint film is observed. ○△: Whitening occurred and approximately 10% peeling occurred in a part of the paint film. △: 10% or more of the whitened paint film has peeled off. ×: The paint film peeled off and red rust was observed. In the solvent resistance test, the sample was immersed in trichlorene for 1000 hours, and the state of blisters on the flat surface was evaluated with the naked eye according to the following criteria. ◎ indicates no abnormality 〇 indicates 1 blister within 1 mm of direct meridian within 10 x 10 cm
~2 items are acceptable. ○△ mark means there is considerable blistering. △ indicates a mixture of peeling and blistering. The × mark means that the entire surface has been completely peeled off.

Claims (1)

[Claims] 1. A stainless steel plate characterized in that the stainless steel plate is subjected to phosphate treatment, then rolled and squeezed, and then coated with a coated chromate treatment solution in an amount of 2 to 60 mg/m ² of chromium. Pre-painting treatment method. 2. The method for pre-painting a stainless steel sheet according to claim 1, wherein the phosphate treatment is a zinc phosphate treatment. 3. The method for pre-painting a stainless steel sheet according to claim 1, wherein the phosphate treatment is an iron phosphate treatment.