Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-11-22
2001-03-13
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C106S014140, C106S014210, C148S247000, C148S273000, C148S275000, C428S472000, C428S628000
Reexamination Certificate
active
06200693
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns a novel liquid for the surface treatment of aluminum or aluminum alloy materials for imparting superior corrosion resistance and paint film holding properties to such surfaces. Fields in which the invention can be used with particular effectiveness include the surface treatment of aluminum heat exchanger fins and aluminum alloy coils and sheets.
RELATED ART
The liquids used for the surface treatment of aluminum and aluminum alloy materials can be broadly classified as being of the chromate type or the non-chromate type. Chromic acid chromate forming treatment liquids and phosphoric acid chromate forming treatment liquids can be cited as typical examples of chromate type treatment liquids.
Chromic acid chromate forming treatment liquids have been in practical use since about 1950 and today they are widely used for the surface treatment of heat exchanger fins, aluminum wheels, building materials and aircraft materials. These chromic acid chromate forming treatment liquids contain chromic acid and fluoride as a reaction promotor as essential components, and a formed film which contains some hexavalent chromium is obtained on the metal material surface.
Phosphoric acid chromate forming treatment liquids are an invention disclosed in U.S. Pat. No. 2,438,877; they contain chromic acid, phosphoric acid and hydrofluoric acid as the main components, and a formed film which has hydrated chromium phosphate as the main component is obtained on the metal material surface. No hexavalent chromium is included in this formed film. Therefore these materials are being widely used at the present time as a paint undercoating treatment for the bodies and lids of beverage cans.
Although a formed film which has been obtained with such a surface treatment liquid of the chromate type has excellent corrosion resistance and paint film holding properties, harmful hexavalent chromium is contained in the treatment liquid and so the use of a treatment liquid which does not contain hexavalent chromium at all is desirable in terms of avoiding environmental problems.
The method disclosed in Japanese Unexamined Patent Application (Kokai) 52-131937 can be cited as a typical invention of a non-chromate type surface treatment liquid. This surface treatment liquid is an acidic aqueous coating solution, with a pH from about 1.5 to about 4.0, which contains zirconium or titanium or a mixture of the two, phosphate and fluoride. A formed film which has zirconium or titanium oxide as the main component is obtained on the metal surface when a metal surface is treated with such a surface treatment liquid. The non-chromate type surface treatment liquids do have the advantage of not containing hexavalent chromium, and they are widely used at present for the surface treatment of drawn-and-ironed (hereinafter usually abbreviated as “DI”) aluminum cans, but there is a disadvantage in that the corrosion resistance of the film which is formed is not as good as that of a chromate film.
Furthermore, the method of treatment disclosed in Japanese Unexamined Patent Application (Kokai) 57-41376 involves the surface treatment of the surface of aluminum, magnesium, or an alloy of these metals, using an aqueous solution which contains one type, or two or more types, of titanium salt or zirconium salt and one type, or two or more types, of imidazole derivative.
The corrosion resistance of the film, according to the illustrative examples, is such that there is no rusting in 48 hours when tested in accordance with JIS-Z-2371. However, although this performance was satisfactory 15 years ago, it cannot be said to be truly adequate at the present time. This specification also indicates that oxidizing agents such as nitric acid or hydrogen peroxide or potassium permanganate can be used as well, being added in amounts, calculated as compounds, of from 0.01 to 100 grams per liter (hereinafter usually abbreviated as “g/l”), but there are no illustrative examples of oxidizing agents such as potassium permanganate.
Furthermore, a method of surface treatment whereby a formed film is obtained on the surface of an aluminum material with an aqueous solution which contains potassium permanganate or potassium manganate, or both of these materials, and mineral acid (HNO
3
, H
2
SO
4
, HF), alkali (KOH, NaOH, NH
4
OH), neutral fluoride (KF, NaF), acidic fluoride (NH
4
HF
2
, NaHF
2
, KHF
2
), silicofluoride (MnSiF
6
, MgSiF
6
) and the like has been disclosed in Japanese Unexamined Patent Application (Kokai) H8-144063. However, a corrosion resistance similar to or better than that of a chromate film cannot be anticipated when long term corrosion resistance tests are carried out with formed films which had been obtained with this liquid.
As indicated above, the problems of the corrosion resistance of the film which is formed and the treatment of the waste surface treatment liquid, for example, remain when the aforementioned conventional non-chromate type surface treatment liquids are used. From this viewpoint, the non-chromate type surface treatment liquids are hardly being used at all at the present time on the surface treatment part of manufacturing lines for aluminum based metal coils and sheets and the aluminum fins for heat exchanges, where especially good corrosion resistance is required.
Hence, at the present time the prior art does not provide any surface treatment liquid, for aluminum or aluminum alloy materials, which does not contain hexavalent chromium, which has excellent effluent treatment properties and with which a formed film which has excellent corrosion resistance and paint film adhesion properties is obtained.
PROBLEM TO BE SOLVED BY THE INVENTION
The present invention is intended to resolve the problems described above which are associated with the prior art, and in practical terms it is intended to provide a surface treatment liquid with which a film comprising specified metals can be obtained on an aluminum or aluminum alloy material surface and which can impart excellent corrosion resistance and paint film holding properties.
SUMMARY OF THE INVENTION
It has been discovered that it is possible to obtain a formed film which has excellent corrosion resistance and paint film adhesion properties on an aluminum or aluminum alloy surface by using a surface treatment liquid of pH from 1.0 to 6.0 which contains a prescribed amount of permanganic acid or one or more of its salt(s) and a prescribed amount of at least one type of compound selected from among water soluble titanium compounds and water soluble zirconium compounds, and the invention is based upon this discovery.
More particularly, a surface treatment liquid of this invention is a water-based liquid which contains from 0.01 to 50 g/l of permanganic acid and/or its salts, and from 0.01 to 20 g/l of at least one compound selected from among water soluble titanium compounds and water soluble zirconium compounds, and which has a pH of from 1.0 to 6.0.
DETAILED DESCRIPTION OF THE INVENTION
In this invention it is important that a complex film comprising compounds of two or more metal elements and which includes manganese, such as manganese and titanium, manganese and zirconium or manganese, titanium and zirconium, is formed, and the corrosion resistance of the formed film which is obtained is improved by this means.
Permanganic acid and/or its salts can be used to introduce the acid(s) and/or salt(s) thereof into a surface treatment liquid of this invention, and no narrow limitation is imposed upon the particular type of material used. The total concentration of permanganic acid and salt(s) thereof must be within the range from 0.01 to 50 g/l, and preferably is within the range from 0.05 to 20 g/l. A formed film may be obtained even if the concentration of permanganic acid and/or salt(s) thereof is less than 0.01 g/l, but this is undesirable, because the corrosion resistance and paint film adhesion properties of any such film are poor. A good formed film is obtained with a concentration of more than 50 g/l, but the properties of the film are
Kawaguchi Motoki
Maeda Kazuhiro
Nakada Kazuya
Harper Stephen D.
Henkel Corporation
Jaeschke Wayne C.
Jones Deborah
Koehler Robert R.
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