Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1999-04-05
2001-09-25
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C428S702000, C148S267000, C148S253000, C148S258000, C148S259000, C148S255000, C148S254000, C106S014140, C106S014440, C252S389500, C252S389240, C252S389300, C252S389530
Reexamination Certificate
active
06294262
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention provides a composition suitable for primary anticorrosive treatment of the surface of a non-ferrous metal, a process for producing said composition, a process for treating the surface of non-ferrous metal with said composition, and non-ferrous metal of which surface is treated with said composition.
2. Related Arts
The surface of a non-ferrous metal substrate, especially a non-ferrous metal plated steel substrate has a very beautiful appearance and shows a relatively good corrosion-resistance. Therefore, materials having non-ferrous metal surface are widely used for manufacturing, such as, auto mobile parts, electronic appliances, heat exchanger part roof, and the like. Although they show relatively good resistance against corrosion, they still suffered from corrosion problem depending on storage condition. Especially, aluminum containing non-ferrous metal materials tend to be suffered from corrosion problem such as blackening or white rust. In order to avoid such problems, the surface of a non-ferrous metal substrate is generally treated with an anticorrosive composition before being processed into a product. Such treatment has known as anticorrosive primary treatment. A method of typical anticorrosive primary treatment is known as chromate treatment, which comprises a step of coating the surface with a chromate film by applying a chromate anticorrosive treatment composition consisting mainly of chromic acid and water.
A conventional chromate primary treatment may be practiced using an aqueous chromate solution comprising partially reduced chromic acid, that is, an aqueous solution containing both Cr
3+
and Cr
6+
. Such the conventional chromate anticorrosive treatment composition can be obtained by reducing a part of hexavalent chromium to trivalent chromium with a reducing agent. Preferred reduction ratio may be determined based on other ingredients of the chromate anticorrosive treatment composition, treatment condition, type of the non-ferrous metal substrate to be treated, and the like. Generally, the chromate anticorrosive treatment composition of which reduction ratio, or a degree of Cr
6+
reduced to Cr
3+
, is from about 30% to about 70% has been used for primary treatment. That is, the typical chromate anticorrosive treatment composition has the Cr
6+
/Cr
3+
weight ratio of between 3/7 and 7/3.
The art knows a variety of reducing agents may be employed in reducing hexavalent chromium to trivalent partially, including organic compounds such as starch, saccharides and alcohols, and inorganic compounds such as hydrazine and hypochlorous acid.
Although this type of primary treatment is popular in the art, it is still difficult to control the reduction rate within the preferred range and to keep the ratio for a long time because of the reducing agent remained in the composition. When a chromate anticorrosive treatment composition of which reduction ratio is low, or the weight ratio of Cr
3+
/Cr
6+
is low, is used for primary treatment, the obtained chromate coating film will appear yellow. In order to avoid this yellowing problem, the thickness of the chromate film must be very thin and highly uniform. Further, since Cr
6+
is soluble in water, the obtained chromate coating film easily loses its adhesivity to a secondary paint under a corrosion inducing condition, and therefore, the corrosion resistance ability of the obtained product of which the primary treated surface being coated with the secondary paint becomes poor.
To the contrary, when the reduction ratio of hexavalent chromium in the treatment composition is high, for example, more than 70%, the composition may set to gel with time, and its corrosion resistance becomes poor. Further, the chromate coating film obtained by the conventional method usually appears an interference pattern. That is, the arts in the field acknowledged that if a chromate anticorrosive treatment composition of which reduction ratio of hexavalent chromium is 100% were used, there would be no possibility to obtain a good result.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a process for anticorrosive primary treatment of the surface of a non-ferrous metal substrate which can form a transparent chromate coating film on the surface having a beautiful appearance and an excellent corrosion resistance without problems of yellowing or blackening. Especially, an anticorrosive primary treatment process which allows to provide a chromate coating film with a wide range of thickness. Another object of the present invention is to provide a composition suitable for the anticorrosive primary treatment of the present invention, and a non-ferrous metal substrate, especially a non-ferrous metal plated steel substrate treated by the process of the present invention.
Accordingly, the present invention provides a process for anticorrosive primary treatment of the surface of a non-ferrous metal substrate comprising the steps of: obtaining a chromate anticorrosive treatment composition by a process comprising the steps of;
providing an aqueous solution comprising hexavalent chromium and an inorganic anion; and adding an excess amount of phosphorus acid to the aqueous solution to reduce substantially 100% of the hexavalent chromium contained in the aqueous solution to trivalent; and,
treating the surface with the chromate anticorrosive treatment composition to form a chromate coating film on the surface.
According to the present invention, transparent chromate coating film can be formed over the surface of the non-ferrous metal substrate without problems such as interference pattern, blackening and yellowing.
In the present invention, a preferable source of the hexavalent chromium is CrO
3
. The CrO
3
may be contained in the starting aqueous solution in an amount of 7.5-100 g/l calculated as CrO
3
. The preferred inorganic anion contained in the starting aqueous solution is phosphoric acid. The aqueous solution preferably contains about 10 to 50 parts by weight of phosphate ion calculated as H
3
PO
4
in relation to 100 parts by weight of hexavalent chromium calculated as CrO
3
.
According to the present invention, the hexavalent chromium in the starting aqueous solution should be reduced in the presence of inorganic anion by means of phosphorous acid to trivalent chromium. The amount of phosphorous acid used in the present process may be about 150-300 parts by weight per 100 parts by weight of chromium calculated as CrO
3
.
The reduction of the hexavalent chromium may be carried out according to any conventional manner. For example, the reducing agent, phosphorous acid, may be added to the aqueous solution containing hexavalent chromium and inorganic anion with stirring at ambient temperature. Thus, such treated aqueous solution may be used as a chromate anticorrosive treatment composition of the present invention.
Thus obtained composition may be applied to the surface of the non-ferrous metal substrate, then the substrate may be dried to form a chromate coating film on the surface. By employing the present process, a coating film having a thickness of about 20-200 mg/m
2
of chromium can be formed on the surface. Thus, the non-ferrous metal substrate treated according to the present process of which surface is coated with a chromate film having a thickness of about 20-200 mg/m
2
of chromium is also within the range of tile present invention.
The chromate anticorrosive treatment composition of the present invention may further comprise a transition metal. The (transition metal)/CrO
3
weight ratio in the composition is preferably from about 0.002 to 1.0.
In addition, the chromate anticorrosive treatment composition of the present invention may further comprise a water dispersible organic polymer. The organic polymer may be preferably contained in the composition in an amount of from about 1 to 30 g/l.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the present invention, an aqueous solution
Jones Deborah
McNeil Jennifer
Nippon Paint Co. Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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