Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Patent
1996-06-17
1999-04-27
Le, Hoa T.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
427189, 427190, 428330, 428469, 428471, 428472, 428697, 428702, B32B 516, B05D 302
Patent
active
058979484
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a resin-based surface-treated steel sheet and a process for its production, and more specifically it relates to a surface-treated steel sheet with a resin-based chemical treatment coating which has excellent corrosion resistance, particularly corrosion resistance at worked sections, and excellent low solubility for hexavalent chromium, as well as a process for its production.
BACKGROUND ART
A common method for improving the corrosion resistance of cold-rolled steel sheets, Zn-plated steel sheets and Zn-based alloy-plated steel sheets used for automobiles, household electronic appliances and building materials involves chromate treatment to form a chromate film. The chromate treatment is accomplished by the electrolyte chromate method or chromate application method. For the electrolyte chromate method, the bath used has been prepared, for example, by adding various anions to a mixture consisting mainly of chromic acid with addition of sulfuric acid, phosphoric acid, boric acid and a halogen, and treating the steel sheet by cathodic electrolysis. The chromate application method is associated with the problem of elution of chromium from the chromate-treated steel sheet, and therefore a method is adopted by which the hexavalent chromium is previously reduced with a reducing agent; for example, there are known sheets coated with an acidic aqueous solution composed mainly of trivalent chromium and containing a water-soluble chromate salt, an inorganic colloid compound and an inorganic anion, and sheets treated with a solution containing an inorganic colloid or inorganic anion with chromic acid of which part of the hexavalent chromium is reduced to trivalent, or chromic acid wherein the hexavalent chromium and trivalent chromium are in a specified ratio. There is also known a method of forming a composite with an organic polymer to immobilize the chromium and a method of further covering the chromate coating with an organic polymer.
Although those chromate coatings which are formed by electrolysis have low elution of chromium, their corrosion resistance cannot be said to be sufficient, while they have also had some problems in terms of scratch resistance of the coating during working and corrosion resistance after working.
Also, when chromate coatings formed by the application method are used in the form as applied, the chromate coating tends to undergo elution. Moreover, the corrosion resistance and coating adhesion have not always been sufficient, while the scratch resistance of the coating during working and corrosion resistance after working are also not always sufficient.
In the case of resin-type chromates, various types of resins are added to the chromic acid bath, at which time such resins gradually undergo reaction by the powerful oxidizing action of the chromic acid, making it difficult to maintain stability in the bath.
Thus, reduction of the hexavalent chromium beforehand in order to minimize chromium elution certainly reduces the corrosion resistance, while it does not completely prevent the chromium elution, and the adhesion is also insufficient. Also, in the chromium reduction method using a reducing organic polymer, the stability of the water-dispersable or water-soluble organic polymer itself becomes poor, while the chromium elution-preventing effect is low. The method of organic polymer coating also involves increased costs brought about by more steps, as well as problems such as chromium elution from damaged sections or cut sections of the coated film and impaired weldability, and for such reasons there have been proposed metal surface-treating compositions such as described in Japanese Unexamined Patent Publication No. 5-230666, which are composed of a mixture of an organic polymer aqueous emulsion of an organic polymer consisting of 0.1-10 wt % of an ethylenic unsaturated carboxylic acid component, 1-30 wt% of a hydroxyl group-containing monomer component and 60-98.9 wt % of another ethylenic unsaturated compound, stably dispersed in an aqu
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Jitsuhara Ikuo
Sakon Tadashi
Sekoguchi Maki
Shoji Hiromasa
Tadokoro Kenichiro
Le Hoa T.
Nippon Steel Corporation
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