Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2001-01-03
2001-12-11
Green, Anthony (Department: 1755)
Stock material or miscellaneous articles
Composite
Of metal
C106S014120, C106S014130, C106S014140, C106S014440, C148S243000, C148S258000, C148S264000, C148S267000, C428S469000, C428S472000, C428S472300
Reexamination Certificate
active
06329067
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
This invention relates to a chromating solution that can form a chromate film from which hexavalent chromium ions may little dissolve out, and a chromated metal sheet obtained using such a chromating solution.
2. Description of related art
In recent years, as chromating solutions for metal sheets such as steel sheets coated with zinc, aluminum or an alloy of these, copper-coated steel sheets and aluminum sheets, coating types are prevailing in which an aqueous solution of a water-soluble chromium compound such as a chromic acid and a chromate is coated on a metal sheet followed by drying without washing with water to form a chromate film. If chromium ions contained in such a chromating solution are all held by hexavalent chromium ions, the chromate film formed tends to be a film from which hexavalent chromium ions may dissolve out when the metal sheet is treated, and also the film may be moisture-absorptive. Accordingly, as disclosed in, e.g., Japanese Patent Applications Laid-open No. 59-31872 (a method of chromating galvanized steel sheets) and No. 3-219087 (a chromating solution for galvanized steel sheets), usually the hexavalent chromium ions are partly reduced with a reducing agent to insoluble, trivalent chromium ions so that the chromate film can be improved in corrosion resistance and moisture resistance.
As the reducing agent, organic compounds such as monohydric or polyhydric alcohols, hydrocarbons and polysaccharides and inorganic compounds such as hydrogen peroxide and hydrazine are conventionally used. When, however, these reducing agents are used to reduce hexavalent chromium ions to trivalent chromium ions at a reduction percentage of more than 50%, the trivalent chromium ions turn into chromium hydroxide because the pH increases with an increase in reduction percentage, to cause gelation and sedimentation of the chromating solution, making it difficult for the solution to be coated on metal sheets. Hence, the reduction percentage of hexavalent chromium ions has been controlled to be not more than 50%. At such a low reduction percentage, however, the hexavalent chromium ions present in the chromate film may dissolve out to produce yellow stains or to adversely affect handlers, bringing about problems.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a chromating solution that may cause no gelation of the solution even when hexavalent chromium ions are reduced to trivalent chromium ions at a reduction percentage of more than 50%.
Another object of the present invention is to provide a chromated metal sheet on which a chromate film has been formed from which chromium ions may hardly dissolve out and which is not moisture-absorptive.
To achieve the above objects, as a first embodiment, the present invention provides a chromating solution comprising a water-soluble chromium compound and a reducing agent and in which hexavalent chromium ions produced by dissolution of the water-soluble chromium compound have been partly reduced with the reducing agent to trivalent chromium ions, wherein;
the reducing agent comprises an oxycarboxylic acid compound.
As a second embodiment, the chromating solution according to the first embodiment may further comprise a water-soluble or water-dispersible organic resin.
As a third embodiment, the chromating solution according to the first embodiment may further comprise phosphoric acid or a phosphoric acid compound.
As a fourth embodiment, the chromating solution according to the first embodiment may further comprise a silica sol.
The present invention also provides a chromated metal sheet comprising a metal sheet and a chromate film formed thereon by coating with a chromating solution containing a water-soluble chromium compound and a reducing agent oxycarboxylic acid compound, followed by drying without washing with water.
As another embodiment of the above chromated metal sheet, the chromating solution used may further contain i) a water-soluble or water-dispersible organic resin, ii) phosphoric acid or a phosphoric acid compound, or iii) a silica sol.
The chromating solution of the present invention may cause neither gelation nor sedimentation even when hexavalent chromium (chromium(VI)) ions are reduced to trivalent chromium (chromium(III)) ions at a reduction percentage of more than 50%, and hence enables the reduction to trivalent chromium ions at a higher percentage, so that the chromating solution can form a chromate film from which hexavalent chromium ions may little dissolve out.
REFERENCES:
patent: 3719534 (1973-03-01), Vessey et al.
patent: 4171231 (1979-10-01), Bishop et al.
patent: 4263059 (1981-04-01), Guhde et al.
patent: 4392922 (1983-07-01), Tomaszewski
patent: 4439285 (1984-03-01), Tomaszewski
patent: 4460438 (1984-07-01), Tardy et al.
patent: 4477315 (1984-10-01), Tomaszewski
patent: 4477318 (1984-10-01), Tomaszewski
patent: 4644029 (1987-02-01), Cable et al.
patent: 4956027 (1990-09-01), Saeki et al.
patent: 4966634 (1990-10-01), Saeki et al.
patent: 5141822 (1992-08-01), Matsuo et al.
patent: 5230750 (1993-07-01), Shindou et al.
patent: 5366567 (1994-11-01), Ogino et al.
patent: 5378291 (1995-01-01), Ara et al.
patent: 5507884 (1996-04-01), Ogino et al.
patent: 2526832 (1976-01-01), None
patent: 53-108041 (1978-09-01), None
patent: 55-31105 (1980-03-01), None
patent: 55-31120 (1980-03-01), None
patent: 59-31872 (1984-02-01), None
patent: 2-66193 (1990-03-01), None
patent: 3-219087 (1991-09-01), None
patent: 10-81976 (1998-03-01), None
patent: 10-81977 (1998-03-01), None
patent: 63-103081 (1998-05-01), None
Furukawa Shinya
Taketsu Hirofumi
Uchida Yukio
Foley & Lardner
Green Anthony
Nisshin Steel Co. Ltd.
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