JPS5848679A - Surface treatment of steel plate coated with aluminum by hot dipping - Google Patents

Abstract

PURPOSE:To enhance the corrosion and slipping resistances of a steel plate coated with Al by hot dipping by forming a chromate film contg. a prescribed amount of Cr on the plate and by carrying out surface treatment with a prescribed organosilicon water repellent. CONSTITUTION:A chromate film having 5-40mg/m<2> total Cr content is formed on a steel plate coated with Al by hot dipping. A treating agent is prepared by adding silica sol to an organosilicon water repellent of silicone oil emulsion type, silicone varnish emulsion type or silicone varnish type so as to adjust the amount of SiO2 to 30-180% of the amount of silicon resin in the repellent. Said chromate film is treated with the treating agent to form an organosilicon film having 0.01-20mum thickness on the surface of the chromate film. Thus, a surface with superior corrosion and slipping resistances is obtd.

Description

[Detailed description of the invention] The present invention relates to surface treatment of aluminized steel sheets,
The purpose is to maintain excellent corrosion resistance even in harsh environments without completely losing the beautiful silvery luster of hot-dip aluminized steel sheets, and to provide a combination of anti-slip properties and a subsequent treatment method.

The features of hot-dip aluminized steel sheets are a beautiful surface with a silver-white luster and excellent corrosion resistance. However, this corrosion resistance is not necessarily satisfactory in environments where high salt water condenses or at the bottom of automobile muffler materials where NOs ions and the like accumulate. Therefore, chromate treatment based on chromium or chromium phosphate has been conventionally performed, but these treatment conditions do not provide sufficient corrosion resistance under the harsh environment described above. Therefore, if a larger amount of chromate film than that obtained under normal treatment conditions is applied, corrosion resistance will be improved, but if a chromate film of more than a certain amount is applied, the corrosion resistance will decrease, and It is difficult to obtain a high degree of corrosion resistance with just a film.

This means that when applying a large amount of chromate film using reactive chromate treatment, there are areas where chemical conversion reactions are more likely to occur and areas where it is less likely to occur due to microscopically non-uniform distribution of elements in the original plate. exists, and the difference in the amount of chromate film deposited at these locations becomes large, creating a potential difference,
This is thought to be because pitting corrosion is more likely to occur.

Well, if you apply a large amount of chromate film, it will be yellowish if it is chromium-based! If it is based on chromium phosphate, it will exhibit a greenish interference color, and the beautiful silver white surface of the aluminum plating surface will be damaged. Moreover, the gloss is significantly 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 sacrificing the beautiful silvery white color, which is one of the features of aluminized steel sheets mentioned above.

As a result, by applying the silichromate treatment nine times after the chromate treatment, the subsequent application of the organosilicon water repellent containing silica sol can be uniformly and evenly, and the adhesion can be completely improved. The absence of this chromate film is undesirable because it causes uneven coating and promotes corrosion in the uncoated areas. The applied film also has a slight water permeability and moisture permeability,
If there is no chromate film, the aluminum will corrode, which is not desirable in terms of corrosion resistance.

The present inventors previously proposed in patent application wA56-103166 that by using an organosilicon water enriching agent, it is possible to improve the lubricity and relieve the stress in the processed part, thereby improving the corrosion resistance of the processed part. However, if the slipperiness is maintained excessively, the load will collapse during transportation, and when used as a building material, especially for roofs, during construction, the material may fall due to co-sliding.
There are problems with workability such as slippage of workers' feet. As a result of various studies, it has been concluded that excessive slippage can be prevented by adding silica sol. Silica sol itself has the advantage of being stable against moisture and other environmental factors and having no adverse effect on corrosion resistance.

The present invention involves forming a chromate film on the surface of a hot-dip aluminized steel sheet with a chromium content of 5 to 40''g/IPLJ, followed by a spray method or a dipping method.

This is a surface treatment method characterized by adding silica sol and treating with an organosilicon water repellent using one of the roll coating methods, followed by drying without washing with water.

The chromate treatment that constitutes the present invention is a chromate treatment that has been widely used for zinc and aluminum plated products in the past, and is not particularly limited. 67m,
Any material that forms a chromate film containing t@ is subject to the chromate treatment of the present invention.

For example, basically chromic acid, chromic acid-fluoride.

Examples include reactive chromate treatment solutions having compositions such as chromic acid-mineral acid and chromic acid-organic acid. In addition, commercially available treatment liquids are available under the trade name “Alodin+10004 (Nippon Paint Co., Ltd. I
I), r Allozin 407-47J (manufactured by Nippon Paint Co., Ltd.), and the like.

Furthermore, recently, the so-called "no-rinse chromate treatment" has been popularized as a new non-polluting ``no-rinse chromate treatment'' that can replace the aforementioned reactive chromate treatment or phosphate treatment for all aluminum plates, cold-rolled steel sheets, and galvanized steel sheets. A coating-type chromate treatment solution, that is, an applicator chromate treatment, also constitutes the present invention.69 As a typical example, a commercially available treatment agent has a product name of “
Acomet C" (Kansai Paint Co., Ltd.), r Allozin N
R-3" (manufactured by Nippon Paint Co., Ltd.).The most important thing in the present invention is +Z) in the chromate film.
By specifying the am amount to 5 to 40 g/W, . There is no special rice production for the remainder of the season. On the other hand, 4o9g//r,,
When it exceeds 2, the effect on corrosion resistance is small when the water repellent according to the present invention is applied, but a yellow-green interference color is exhibited and the appearance is impaired. It is also uneconomical as it increases the cost of chromate treatment.

The organic water repellent constituting the present invention is a silicone oil emulsion type, a silicone varnish emulsion type, a silicone varnish water-soluble type, etc. Silicone oil emulsion types include product names FZ315 (manufactured by Nippon Nijika Co., Ltd.) and FZ3.
143 (manufactured by Nihon Nihon Kasha) lFZ 350 (Japan z=
Rikisha m), 5M8701 (10' silicone tl1M), silicone varnish emulsion mold (!: L
Product name: MF 40 (Shin-Etsu Chemical Co., Ltd. 11), S
M 8702 < Tov Season Company d), SZ 7
7ω6 (Toshi Silicone Co., Ltd. JA) + silicone varnish Water-soluble type includes product name Polon C (manufactured by Shin-Etsu Chemical Co., Ltd.).

The silica sol in the present invention is a colloid solution in which ultrafine particles of silicic anhydride are dispersed in water, and the particle size is 7 to 5.
A commercially available product with 0 horse μ is available under the trade name Snowtex (manufactured by Nichiryo Kagaku Kogyo Co., Ltd.). If the proportion of silica sol mixed with the organic water repellent is less than 60%, the effect against slipping will not be exhibited, and if it exceeds 180%, the effect of the water repellent will decrease, which is undesirable, so it should be in the range of 50 to 1801. preferable.

In the present invention, it is necessary to add a silica sol to form a uniform film on the entire organic water repellent, and the dry film thickness is 0.
If it is 01μ to 20μ, the object of the present invention can be achieved.

If it is less than 0.01 μm, the effect will be poor, and it will be difficult to form a uniform film, resulting in a spot-like film, which is not preferable. 20μ
Although it is possible to achieve the objectives of the present invention, such as improving corrosion resistance and maintaining gloss, even if the amount exceeds the required level, the quality is more than necessary, and there is no advantage in terms of cost. 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 skin i thickness is 0.01 to 20μ.

The water repellent film forming method of the present invention includes a roll coating method,
It can be formed by a conventionally known method such as a dipping method or a spray method.

The present invention is a Zn-At alloy plated steel plate and an aluminum plate.

It can also be applied to aluminum products.

Hereinafter, the present invention will be explained in detail with reference to Examples.

Plate thickness 0.8. ,, Aluminum plating coverage 12067m, 2
After forming a chromate film on a hot-dip aluminized steel sheet under the conditions shown in Table 1, in the case of chromium sulfate, it is washed with water, but in other cases, it is air-dried or force-dried with hot air without washing with water. After that, silica sol was completely added and treated with an organic water repellent to completely form a film. After drying with air or hot air, corrosion resistance was evaluated by visual observation, gloss measurement, salt spray test, and static friction coefficient. Measurements were made.

Furthermore, in order to clarify the effects of the present invention, treatments other than those of the present invention were carried out as comparative examples under the conditions shown in Table 1.

All 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 significant changes or poor casing or gloss were judged to be defective.

○゛;; Good ×: Bad Note 2) Corrosion resistance is determined by salt spray test JIS Z-2371
After 500 hours, test specimens according to the standards in the table below. Note 6: Slip resistance was measured using a static friction coefficient measuring device (manufactured by Shinto Kagakusha).
A static friction coefficient of 0.15μ or less was determined to be defective.

Looking at the finished appearance of the Examples, all of the Examples of the present invention are good, whereas Comparative Example N (11').

If the amount of chromium deposited is large as in i40.9', the appearance will be poor. Further, when a large amount of silica sol is added as in N13', the gloss decreases and the appearance becomes poor.

For reference, the relationship between the amount of silica sol added and gloss is shown in the figure. A gloss of 40 or less due to 45° reflection is considered defective. When silica sol is not added as in comparative examples Nα4′ and Nα6′, and when Nα5′, NIL 8′, N(L
9'], if the amount added is small, the friction coefficient will be less than 0.15μ, and the object of the present invention cannot be achieved.

All examples of the present invention have good slip resistance.

In terms of corrosion resistance, all of the present invention is good, but when the organosilicon water repellent containing silica sol is not applied as in Comparative Examples Na1' and Na7', even if it is applied again, Comparative Examples Nα2' and Nα8 ' When the amount of chromate film is small, as in Comparative Example Nα3, the dry film thickness is 0.01μ.
If it is less than that, it cannot be said that it has sufficient corrosion resistance, and the synergistic effect is not significant.

This is true, and if the amount of chromate film is small, there will be areas where the chromate film is not applied, and even if the entire 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 a very small amount of it passes through and finally reaches the underlying aluminum surface, causing corrosion in areas where there is no chromate film.

The lower limit amount of chromate film in No. 7 is 5'''g as total Or.
/rL'' from the examples. For practical reasons, the upper limit is preferably less than 40 m, g/, 2 for Tota I Cr.

[Brief explanation of the drawing]

The figure shows the relationship between the amount of silica sol added (Si02 min) and the change in gloss.

Claims (1)

[Scope of Claims] 1. A surface treatment for a hot-dip aluminized steel sheet, which comprises forming a chromate film on the hot-dip aluminized steel sheet, and then adding silica sol to the surface and treating the surface with a silicon water repellent. Method. 2. The surface treatment method according to claim 1, wherein the total amount of chromium in the chromate film formed by the chromate treatment is 5 to 40'' g/rnz. 6. The organosilicon water repellent is a silicone oil emulsion type. The surface treatment method according to claim 1 or 2. 4. The surface treatment method according to claim 1 or 2, wherein the organosilicon water repellent is a silicone varnish emulsion type. 5 The surface treatment method according to claim 1 or 2, wherein the organosilicon water repellent is a water-soluble silicone varnish bottle.6 The amount of silica sol added is 8102 to the amount of 81 resin of the organosilicon water repellent. The surface treatment method according to any one of claims 1 to 5, wherein the amount is 60 to 180%. 7. A silicon film formed by organosilicon water repellent treatment by adding silica sol. The surface treatment method according to any one of claims 1 to 6, wherein the thickness is 0.01 to 20μ.