JPH0653930B2 - Method for producing hot dip aluminum coated steel sheet coated with silicone resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is applied to applications such as automobile mufflers that are exposed to condensate during cold start and to hot gas during running. The present invention relates to a method for producing a silicone resin-coated hot dip aluminum plated steel sheet exhibiting heat resistance and corrosion resistance.

(Prior Art) Hot-dip aluminized steel sheet has a beautiful glossy silver-white appearance and is also excellent in heat resistance and corrosion resistance, so it has been used in large quantities in automobile muffler materials by taking advantage of these features. .

However, in recent years, three-way catalysts have been used in automobile mufflers due to exhaust emission regulations, and corrosive ions (chlorine ions, sulfate ions, etc.) have become contained in the condensate in the muffler. Corrosion has become a problem in automobile mufflers. This corrosion occurs because corrosive ions are concentrated and the condensate with a lowered pH acts on the microscopic plating defects that are usually present in hot-dip aluminized steel sheet. Alternatively, the only option was to use stainless steel plates made of completely different materials.

For this reason, a hot-dip aluminum-plated steel sheet or a ferritic stainless steel sheet coated with a silicon-modified polyester coating to which heat resistance is added by adding aluminum metal powder has been conventionally used for an automobile muffler using a three-way catalyst.

(Problems to be solved by the invention) However, since the aluminum metal powder-added silicone resin-modified polyester resin coating and the ferritic stainless steel plate are expensive, the cost of the muffler becomes significantly higher than that of the case where it is manufactured by the hot dip aluminum plated steel plate. there were.

(Means for Solving Problems) Therefore, the present inventors have conducted various studies in order to develop an inexpensive heat-resistant and corrosion-resistant material suitable for an automobile muffler, and as a result,
We have succeeded in firmly forming an inexpensive and heat-resistant silicone resin film on a hot-dip aluminized steel sheet.

Silicone resin is excellent in heat resistance and corrosion resistance, and is cheaper than silicone resin-modified polyester resin with aluminum metal powder added, but since silicone resin does not adhere to anything other than siliceous materials such as glass and asbestos, it can be applied to hot-dip aluminum plated steel sheets. Cannot be applied.

For this reason, the present inventors have used a silicone resin modified with an organic resin that imparts adhesion to the hot dip aluminum plated steel sheet, after applying a coating agent of the organic resin-modified silicone resin to the hot dip aluminum plated steel sheet, A silicone resin film was formed by thermally decomposing the resin component. That is, the present invention comprises forming a chromate film on a hot dip aluminum plated steel sheet, then forming an organic resin-modified silicone resin coating film on the chromate film, and thermally decomposing the organic resin used to modify the silicone resin. The present invention provides a method for producing a silicone resin-coated hot dip aluminum plated steel sheet, which is characterized by forming a silicone resin film.

FIG. 1 shows a cross section of a silicone resin-coated molten aluminum-plated steel sheet according to the present invention, where 1 is a steel sheet, 2 is an aluminum plating layer, 3 is a chromate film, and 4 is a silicone resin film.

In the present invention, the formation of the chromate film is because when the acrylic resin-modified silicone resin coating agent is directly applied to the hot dip aluminum plated steel sheet, coating unevenness is likely to occur and the film adhesion after thermal decomposition and the corrosion resistance are poor. . The chromate film may be formed by a chromate treatment which has been conventionally performed on zinc or a zinc alloy, and is not particularly limited. The chromate coating amount is preferably 5 to 40 mg / m ² in terms of total chromium amount. If it is less than 5 mg / m ² , the corrosion resistance is insufficient, and if it exceeds 40 mg / m ² , the film exhibits a yellow-green interference color and the appearance is impaired when the coating material is varnish, which is preferable. Absent. Corrosion resistance of 40 mg / m ² is sufficient, and increasing the corrosion resistance causes an increase in chromate treatment cost.

A known organic resin-modified silicone resin coating may be used, and for example, MF40 manufactured by Shin-Etsu Chemical Co., Ltd. or SZ7706 manufactured by Toray Silicone Co., Ltd. (both are emulsion type) may be used. Further, the application to the hot dip aluminum plated steel sheet may be carried out by a conventionally known coating method such as a spray method, a dipping method or a roll coating method after forming a chromate film.

The thermal decomposition conditions after coating are determined by the organic resin used for modification. For example, in the case of the above-mentioned MF40, a silicone resin is modified with an acrylic resin, and the heat decomposition range of the acrylic resin of this MF40 is as shown in FIG. Here, A is a range where a uniform silicone resin film is formed, and B is a range where a uniform silicone resin film is not formed due to insufficient heating. When the heat resistance of the silicone resin is taken into consideration, for example, when the acrylic resin is thermally decomposed at 300 ° C., it may be heated for 50 hours or more. The carbon of the acrylic resin remains in the silicone resin film due to this thermal decomposition, but this carbon does not reduce the heat resistance and corrosion resistance of the silicone resin film. It is also possible to add a coloring pigment or a corrosion resistant additive to the silicone resin film.

If the thickness of the silicone resin film is less than 0.4μ, the film will not be uniform and heat and corrosion resistance problems will occur.
It is preferably 4 μm or more. However, if it is attempted to make it thicker than 5μ, it takes time for the thermal decomposition of the organic resin, the amount of the coating material used increases, and the cost increases, so the upper limit is preferably 5μ or less. The film thickness after thermal decomposition
To make it 0.4μ or more, apply 0.8% of coating in a dried state.
In order to make the thickness more than or equal to μ and less than or equal to 5 μ, it may be less than or equal to 10 μ. This silicone resin film can be welded if the film thickness is 2 μm or less.

Next, the present invention will be described with reference to examples.

(Example) A chromate film is formed by subjecting a molten aluminum-plated steel sheet having a plate thickness of 0.6 mm and a coating adhesion amount of 40 g / m ² to a chromate treatment, washing it with water, and then spraying it with air or hot air to forcibly dry it. did. After that, an acrylic resin-modified silicone resin coating agent is applied on the chromate film and dried at 150 ° C for 3 minutes, and then at 300 ° C for 5 minutes.
By heating for 0 hour, the acrylic resin in the coating agent was decomposed to obtain a silicone resin-coated hot dip aluminum plated steel sheet.

On the other hand, as comparative materials, a bare hot-dip aluminum plated steel sheet, a chromate-treated hot-dip aluminum-plated steel sheet and a silicone resin-coated hot-dip aluminum-plated steel sheet with insufficient thermal decomposition are prepared, and these are tested together with the silicone resin-coated hot-dip aluminum plated steel sheet in a muffler corrosion simulation test. I went to

In the muffler corrosion simulation test, as shown in FIG. 3 (A), the test piece 5 was put in an air circulation type gear oven 6 and heated at 250 ° C. for 200 hours, and then shown in (B). Like ammonium ion 2500ppm, chlorine ion 5
The test piece 5 was placed in a beaker 8 containing a test solution 7 of 000 ppm, pH 6, and a temperature of 80 ° C. so that the test piece 5 was half immersed.
As shown in (C), dip it in the constant temperature water bath 9 and
It was carried out by a method of holding at 80 ° C. for an hour.

Table 1 shows the chromate treatment method, application of acrylic resin-modified silicone resin and thermal decomposition method, and silicone resin film thickness, and Table 2 shows muffler corrosion simulation test results.

Tables 1 and 2 show that the steel sheet according to the present invention is inferior in corrosion resistance when the coating thickness is thin, but exhibits excellent corrosion resistance when the coating thickness is increased to some extent. If the thermal decomposition of the acrylic resin-modified silicone resin coating is insufficient, the corrosion resistance is poor even if the film thickness is large.

(Effect) As described above, the silicone resin-coated hot-dip aluminum-coated steel sheet according to the present invention exhibits excellent corrosion resistance to the condensate of an automobile muffler using a three-way catalyst. The durability can be remarkably enhanced. Further, the steel sheet price according to the present invention is cheaper than the stainless steel sheet, and the organic resin-modified silicone resin coating material is cheaper than the aluminum metal powder-added silicone-modified polyester resin coating material, so that it is cheaper than the conventional coated hot-dip aluminum plated steel sheet.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a silicone resin-coated hot dip aluminum coated steel sheet according to the present invention, and FIG. 2 is a graph showing the relationship between the temperature and the time when the acrylic resin of the acrylic resin-modified silicone resin coating material is decomposed by heat. Disassemble,
The range in which a uniform silicone resin film is formed and the range in B are ranges in which thermal decomposition is insufficient and a non-uniform silicone resin film is formed. FIG. 3 shows a muffler corrosion simulation test method. (A) shows a state where the test piece is heated, (B) shows a state where the test piece after the heating test is immersed in the test solution in the beaker, (C) shows a state in which the test piece placed in the beaker is immersed and held in a constant temperature bath. 1 ... Steel plate, 2 ... Aluminum plating layer, 3 ... Chromate film, 4 ... Silicone resin film, 5 ... Test piece, 6 ... Gear oven, 7 ... Test solution, 8 ... Beaker, 9 ... … Constant temperature water tank,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenichi Masuhara No. 1 at 7 Takatani Shinmachi, Ichikawa City, Chiba Nisshin Steel Co., Ltd. Ichikawa Research Institute (72) Inventor Kiichiro Katayama 1 at 7 Takatani Shinmachi, Ichikawa City, Chiba Prefecture Nisshin Steel Co., Ltd. Ichikawa Laboratory

Claims (2)

[Claims] 1. A method of forming a chromate film on a hot dip aluminum plated steel sheet, forming an organic resin-modified silicone resin coating film on the chromate film, and thermally decomposing the organic resin used for modifying the silicone resin. A method for producing a hot-dip aluminum-coated steel sheet coated with silicone resin, comprising: 2. The method for producing a silicone resin-coated hot-dip aluminum-coated steel sheet according to claim 1, wherein the coating thickness after thermal decomposition is 0.4 to 5 μm.