JPS586976A - Surface treatment of aluminum hot dipped steel plate - Google Patents

Abstract

PURPOSE:To provide high corrosion resistance even under severe environment without degrading the beautiful silver white gloss that an aluminum hot-dipped steel plate posseses by forming a chromate film on said plate then treating the same with an org. silicone water repelling agent. CONSTITUTION:After a chromate film of 5-40mg/m<2> in terms of a content of Cr is formed on the surfaces of an aluminum hot-dipped steel plate, an org. silicone water repelling agent is applied on the top surface thereof by a spray method or the like. The treated surface is dried without rinsing, whereby the intended surface treatment is executed. Chromating treatments which are practised heretofore with Zn, Al or their metallic plated products are applicable to the chromating treatment in this case. For example, water repelling agents of silicone oil emulsion type are enumerated for the org. silicone water repelling agent. If the dry-treated film of the water repelling agent is 0.01-20mu thick, the purpose of this invention is fulfilled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface treatment of aluminized steel sheets, which provides excellent surface treatment even under harsh environments and in processed parts without impairing the beautiful silvery luster of hot-dip aluminized steel sheets. The present invention relates to a treatment method for the purpose of providing corrosion resistance.

In general, hot-dip aluminized steel sheets are characterized by a beautiful surface with a silvery white luster and excellent corrosion resistance. but,
This corrosion resistance is not necessarily satisfactory in environments where high salt water condenses or at the bottom of automobile muffler materials where No. 3, ions, etc. accumulate.

Therefore, chromate treatment using chromium-based or chromium phosphate-based chromate treatment has been conventionally performed, but these treatment conditions do not provide sufficient corrosion resistance under the harsh environment described above. In particular, there are problems with corrosion resistance in processed parts such as bent parts.

Therefore, chromate skin I obtained under normal processing conditions
! If a larger amount of chromate film is applied than X, the corrosion resistance will be good, but the beauty of the silvery white surface will be lost due to the chromate film, and if it is based on chromic acid, it will be yellowish, and if it is based on chromium sinate, it will be greenish. , and the beautiful silvery white surface is not only spoiled, but also the gloss is reduced.

Further, there are problems in that the chromate treatment takes a very long time.

Therefore, we investigated a surface treatment that would provide excellent corrosion resistance without impairing the beautiful silvery white color, which is one of the characteristics of aluminized steel sheets mentioned above.

As a result, it was found that applying and drying an organic silicon water repellent after chromate treatment would serve the purpose. According to the treatment method of the present invention, by performing the chromate treatment, the subsequent application of the organic silicon water repellent can be performed uniformly and without unevenness. The absence of this chromate film is undesirable because uneven coating of the organosilicon water repellent occurs and corrosion of uncoated areas is accelerated.

Furthermore, since the organosilicon water repellent also has some degree of water permeability and moisture permeability, if there is no chromate film, the aluminum will corrode, causing a problem in terms of corrosion resistance.

Application of an organic silicon water repellent is not only desirable from the viewpoint of corrosion resistance, but also protects the soft aluminum and improves its lubricity, which relieves stress in the processed area and improves the corrosion resistance of the processed area. Chromate film only□/al-)□. 6
．． A2゜Ya0.・□P, since such slipperiness cannot be expected, the chromate film will peel off or fall off in the processed area, exposing the aluminum base and significantly reducing the corrosion resistance of the processed area.

In the present invention, after forming a chromate film with a chromium content of 5 to 40 rlLg/.2 on the surface of a hot-dip aluminized steel sheet, the upper surface is further coated with the sugery method or the dipping method.

This is a surface treatment method characterized by applying organic silicon water repellent treatment using any of the roll coating methods and drying without washing with water.

The chromate treatment that constitutes the present invention is a chromate treatment that has conventionally been widely performed on metal plated products such as zinc, aluminum, or the like, and is not particularly limited.
The amount of chromium in the chromate film is 5 to 40 WLg/
, 2 can be applied as the chromate treatment of the present invention as long as it forms a chromate film containing 2. For example, basically chromic acid.

Examples include reactive chromate treatment solutions of compositions such as chromic acid-fluoride, chromic acid-mineral acid, and chromic acid-organic acid. In addition, a commercially available treatment liquid with the trade name [Alodine Φ100OJ
(manufactured by Nippon Paint Co., Ltd.), product name "Alojin 407-4"
7 (manufactured by Nippon Paint Co., Ltd.)". Furthermore, recently, a so-called coating system has become popular as a new pollution-free "no-rinse chromate treatment" that can replace the aforementioned reactive chromate treatment or phosphate treatment for aluminum sheets, cold-rolled sheets, and galvanized steel sheets. Cutting-type adhesive amate treatment, that is, coating-type chromate treatment, also constitutes the present invention, and a typical example of the commercially available treatment agent is H4 (trade name: Acomet C4 (manufactured by Kansai Paint Co., Ltd.)).

Product name: “AlojiyNR-3J” (manufactured by Nippon Paint Co., Ltd.)
You can mention a lot of money. The most important thing in the present invention is to limit the amount of chromium in the chromate film to 5 to 40 M/"; if it is less than 5 gm, the corrosion resistance will be insufficient, especially if the chromium content is The synergistic effect is not particularly noticeable in the left phase.

On the other hand, if it exceeds 40"g/-, there is no big problem in terms of corrosion resistance, but it becomes yellowish-green in color, impairs the silvery white appearance unique to aluminum, and increases the chromate treatment quality, making it uneconomical. .

The organic water repellent that constitutes the present invention is preferably silicone oil emulsion type, silicone varnish emulsion type, water-soluble silicone face type, and organic solvent-soluble type silicone face.
315 (Nihon Uniriki Co., Ltd. ff), product name FZ545
(M), trade name yZ 350 (same).

Product name SM 8702 (manufactured by Toshi Silicone Co., Ltd.)
.

Product name: MF 40 as a silicone varnish emulsion mold
(manufactured by Shin-Etsu Chemical Co., Ltd.), 5M8701 (J[
(manufactured by Silicone Co., Ltd.), water-soluble silicone varnish type, product name Pol on C (same); organic solvent-soluble silicone varnish x, product name FO1on, xc
88, xy 99 (all manufactured by Shin-Etsu Chemical Co., Ltd.)
, product name FZ 9Q5.

yz 904 (all manufactured by Nihon Uniriki Co., Ltd.).

The organic water repellent used in the present invention needs to form a uniform film1, and the actual thickness of the treated dry film is 0.01 to 2.
If it is 0 μ, the object of the present invention can be achieved. 0
．． If it is less than 0.01μ, the effect will be poor9, and it will be difficult to form a uniform film, resulting in a spot-like film, which is not preferable. 2
Even if it exceeds 0μ, it is possible to achieve all of the objectives of the present invention, such as improvement in corrosion resistance, gloss retention, and workability, but if the quality exceeds what is necessary, there will be no cost advantage.

The post-treatment of hot-dip aluminized steel sheets, which is the object of the present invention, is most effective on an industrial scale when the thickness of the organosilicon film is within the range of 0.01 to 20 microns. Roll coating is a method of forming an organic film using organic water repellent.
It can be formed by a conventionally known method such as a dipping method or a spray method.

The present invention can also be applied to Zn-At alloy plated steel sheets, aluminum die-cast products, aluminum plates, and aluminum products.

The present invention will be explained in detail below with reference to Examples.

After forming a chromate film on a hot-dip aluminized steel plate with a thickness of 8 mm and a coating weight of 120 g/W under the conditions shown in Table 1, in the case of chromium phosphate, it is washed with water, but in other cases The material was air-dried or forced-dried with hot air without washing with water, then treated with an organic water repellent to form a film, and air-dried.In order to evaluate corrosion resistance, external appearance was observed with the naked eye, gloss was measured, and A salt spray test (based on J Engineering sz-2371) and a hat bending test were conducted. The main conditions of this test are as follows.

Hat bending conditions die diameter 42.21. Die shoulder 6R punch diameter
42.016, Punch shoulder 6R wrinkle pressing force 300K
g Lubricating oil None Shape Below Margin The test results of the examples of the present invention are summarized in Table 2. .

E 2 Table Note 1) Appearance was determined by the deviation in color tone from the silvery white of the original plate, and those with a significant change were judged to be defective.

Note 2) Judgment of salt water spray test results is based on the table below.

Looking at the appearance of the finishing examples of Examples 9 and 9, the present invention was good in all cases, but when the amount of chromium deposited was large as in Comparative Examples Nα6' and 5', the appearance was poor. An example of the change in color tone due to a chromate film is shown in FIG. 1, but in the case of a chromium/chromate film, it is inevitable that the change in color tone will increase as the thickness of the film increases.

When Δb exceeds 8.0 as shown in FIG. 1, the surface exhibits a yellow-green interference color rather than a silvery white color, and the surface cannot be described as beautiful. Furthermore, even if a coating of approximately 20% is applied, it cannot be said that the corrosion resistance of the processed portion is necessarily improved, as can be seen from Comparative Example 6'.

Among the comparative examples, those in which the organosilicon water repellent of Nα4/, 2/, 3/, etc. were not saved and applied had poor corrosion resistance in the processed parts. In particular, the higher the processing rate, the more remarkable the degree of change becomes.

Furthermore, as mentioned earlier, even if a romate film is applied in such a large amount that the color tone changes significantly, its contribution to the corrosion resistance of the processed part will not be the same. On the other hand, comparative example N
When an organosilicon water repellent is applied to a test material provided with a chromate film similar to c1', the corrosion resistance of the processed portion is significantly improved. This means that the organosilicon water repellent is not only more resistant to processing than the chromate film, but also easier to process, so there is no localized large load on the surface.
It is judged that this is because the surface stretches uniformly and no local defects are created.

An example of how small the forming load can be during processing is shown in FIG. 2 for reference. In Fig. 2, the horizontal axis represents the stroke, and the vertical axis represents the forming load required at that time.For example, when performing hat bending to a height of 6 degrees, the forming load required for the sample of Example N11. may be 270 Kti, but in the case of the sample of Comparative Example Ni11' which is not coated with an organic silicon water repellent, it requires 900 Kg, which means that a deformable load of appreciable amount is applied to the surface. This suggests that when the organosilicon water repellent is fully coated, there is no local concentration of stress, there are few local defects in the film, and good corrosion resistance is achieved.

Looking at Comparative Example No. 114', even if the same organosilicon water repellent is applied, the synergistic effect will not be significant if the underlying cloide film is small. This means that if the amount of extra cyclomate film is small, there will be areas where no chromate film is applied, and even if an organic film is applied on top of it, the film will be thin and have some moisture permeability, so it will not absorb moisture. It is thought that the chromate film permeates through the aluminum surface little by little and finally reaches the underlying aluminum surface, causing corrosion in areas where there is no chromate film. It is determined from the examples that the lower limit of the chromate film is 5zg/- in terms of the total chromium content. From a practical standpoint, it can be said that it is preferable that the upper limit is less than 50 V- in terms of the total chromium content, but as mentioned above, in consideration of the appearance, it is best to keep it less than 40''g/2.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the amount of chromate film and the color tone difference Tl, and FIG. 2 is a diagram showing the effect of applying an organic silicon water shaker on the molding load. In the figure, Curve 1 Color tone difference (Δb) curve 2 for Example Nα6 Color tone difference (Δb) curve 6 for Example Nα7 Curve 4 for Example N14 (all coated with organic silicon water repellent) Curve 4 for Example Nα1 (organic silicon water repellent) Figure 1 Figure 2 Stroke (m skin)

Claims (1)

[Scope of Claims] 1. A method for surface treatment of a hot-dip aluminized steel sheet, which comprises forming a chromate film on the hot-dip aluminized steel sheet and then treating the chromate film with an organic silicon water repellent. 2. The method for surface treatment of a hot-dip aluminized steel sheet according to claim 1, wherein the amount of chromium in the chromate film formed by the chromate treatment is 5 to 40" gm2. 6. The organosilicon water repellent is silicon. 4. A method for surface treatment of a hot-dip aluminized steel sheet according to claim 1 or 2, which is an oil emulsion type.4 Claim 4, wherein the organosilicon water repellent is a 7-lean varnish emulsion type. The method for surface treatment of a hot-dip aluminized steel sheet according to claim 1 or 2. 5. The hot-dip aluminized steel sheet according to claim 1 or 2, wherein the organosilicon water repellent is a water-soluble silicon face type. 6. A surface treatment method for a hot-dip aluminized steel sheet according to claim 1 or 2, wherein the organosilicon water repellent is an organic solvent-soluble silicon-face. 7. An organosilicon water repellent The method for surface treatment of a hot-dip aluminized steel sheet according to any one of claims 1 to 6, wherein the organosilicon film formed by the treatment has a thickness of 0.01 to 20 μm.