Compositions: coating or plastic – Coating or plastic compositions – Corrosion inhibiting coating composition
Reexamination Certificate
2001-04-12
2002-07-16
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Corrosion inhibiting coating composition
C148S247000, C427S388100, C427S388400, C428S469000
Reexamination Certificate
active
06419731
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the nonchromate rust prevention of aluminum and more particularly to a nonchromate rust preventive agent suited to the treatment of aluminum sheeting in a coil form, a method of rust prevention and a rust-preventive aluminum product.
BACKGROUND OF THE INVENTION
The rust prevention of aluminum or aluminum alloy has heretofore been made by spraying or dipping using a reactive chromate or phosphate-chromate agent or a coating-type chromating agent. In the field of such chromating agents, there have been developed those which are comparatively environment-benign through contrivances such as film weight reduction or replacement of the harmful hexavalent chromium with the low-toxicity trivalent chromium. However, the risk for environmental contamination at waste disposal cannot be said to be nil.
On the other hand, with regard to the nonchromate reactive type treating agent and coating type treating agent, Japanese Kokoku Publication Sho-55-38997, for instance, discloses an acidic cleaning agent comprising polyacrylic resin and zirconium fluoride, among other components. Further, Japanese Kokai Publication Hei-4-232281 discloses an aqueous acidic solution comprising an anionic acrylic acid-acrylamide copolymer, zirconyl ammonium fluoride and nitric acid. Japanese Kokai Publication Hei-11-106954 discloses an acidic treating composition comprising a water-soluble phenolic resin, a zirconium or other metal-containing compound, a silane coupling agent, and hydrofluoric acid, phosphoric acid and/or acetic acid.
However, the corrosion resistance imparted by the nonchromate type treating agents disclosed in the above patent publications is invariably poor as compared with that provided by chromate type treating agents and has not satisfied practical needs. The object of the present invention is to provide a nonchromate rust preventive agent for aluminum which, despite its being of the nonchromate type, is capable of affording sufficient corrosion resistance and, even when applied to the material for heat-exchanger fins, for instance, does not allow development of white rust. A further object is to provide a method of rust prevention and a rust-preventive aluminum product.
SUMMARY OF THE INVENTION
The nonchromate rust preventive agent for aluminum according to the present invention comprises a zirconium compound, a fluoride ion, a water-soluble resin and an aluminum salt,
the concentration of said zirconium compound being 100 to 100000 ppm as zirconium ion,
the concentration of said fluoride ion being 125 to 125000 ppm,
the concentration of said water-soluble resin being 100 to 100000 ppm on a nonvolatile basis,
and the concentration of said aluminum salt being 10 to 10000 ppm as aluminum ion.
The fluoride ion concentration, when a fluorozirconium compound is used as said zirconium compound, represents the sum of the concentration derived from the fluorine compound and the concentration derived from the fluorozirconium compound.
As said zirconium compound, a fluorozirconic acid and/or an ammonium fluorozirconate may be used.
Moreover, said water-soluble resin preferably has a functional group capable of binding to said zirconium compound and/or aluminum in film formation.
The method of nonchromate rust prevention according to the present invention comprises treating an aluminum substrate with said rust preventive agent to form the film in the weight range of 10 to 1000 mg/m
2
in terms of zirconium.
The rust-preventive aluminum product of the present invention is obtainable by a nonchromate rust preventive treatment using said rust preventive agent.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is now described in detail.
As mentioned above, the nonchromate rust preventive agent of the invention comprises a zirconium compound, a fluoride ion, a water-soluble resin and an aluminum salt.
The above zirconium compound is a cardinal component capable of binding to the aluminum (inclusive of aluminum alloy; the same applies hereinafter) surface etched by the fluoride ion to form a rust preventive layer and, at the same time, binding to and curing the water-soluble resin to insure formation of a tough resin film. As examples of such zirconium compound, a there can be mentioned fluorozirconic acid, the lithium, sodium, potassium and ammonium salts of fluorozirconic acid, zirconium sulfate, zirconyl sulfate, zirconiumnitrate, zirconyl nitrate, zirconium fluoride and zirconium carbonate, among others. These zirconium compounds can be used singly or in a combination of two or more species. The preferred concentration of the zirconium compound in the rust preventive agent is 100 to 100000 ppm as zirconium ion, the range of 1000 to 10000 ppm being still more preferred. When the zirconium ion concentration is less than 100 ppm, corrosion resistance and adhesion to the hydrophilic coating film to be used for heat-exchanger fins tend to be decreased. On the other hand, formulating the zirconium compound in excess of 100000 ppm will not be rewarded with any further improvement in performance but rather increases the cost of production.
The fluoride ion mentioned above can be supplied by using, for example, hydrofluoric acid, ammonium fluoride, ammonium hydrogen fluoride, sodium fluoride, sodium hydrogen fluoride or the like. When a fluorine-containing zirconium compound, such as fluorozirconic acid and ammonium fluorozirconate, is used as the zirconium ion donor, the fluoride ion is partly supplied from such a compound. The fluoride ion concentration of the rust preventive agent is preferably 125 to 125000 ppm, more preferably 1250 to 12500 ppm. The fluoride ion concentration referred to above is the concentration of the fluoride ion present in free state in the rust preventive solution and can be measured by using an instrument having a fluoride ion electrode, for instance. When the fluoride ion concentration is lower than 125 ppm, the degree of etching of the aluminum surface is insufficient so that no adequate rust preventive film may be constructed. Exceeding 125000 ppm is not rewarded with any further improvement in performance but rather increases the cost burden. The zirconium-fluorine ratio, Zr/F, is preferably 0.5 to 0.9 by weight, more preferably 0.6 to 0.8 by weight. Above or below this range, no sufficient corrosion resistance is obtained.
The above water-soluble resin preferably has a functional group, such as carboxyl, hydroxyl, sulfo, amino or the like, which is capable of binding to the zirconium compound and/or aluminum substrate in film formation. As examples of such water-soluble resin, the following can be mentioned.
(a) Unsaturation-polymerizable water-soluble polymers having carboxyl and/or hydroxyl groups, such as poly(meth)acrylic acid, (meth)acrylic acid-(meth)acrylate copolymers, styrene-(meth)acrylic copolymers, polyvinyl alcohol obtainable by partial saponification of polyvinyl acetate resin, polyvinylpyrrolidone, and polymers of (meth)acrylamide derivatives such as N-methylolated (meth)acrylamide.
(b) Naturally-occurring macromolecular compounds having carboxyl and/or hydroxyl groups as well as their derivatives, for example cellulose derivatives such as carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), methylcellulose (MC), ethylcellulose (EC), ethylhydroxyethylcellulose (EHEC), etc., ethylcellulose derivatives and their sodium, potassium and ammonium salts, among others.
(c) Water-soluble polyester resins, for example the water-solubilized resin obtainable by half-esterification of the hydroxyl group of a polyester resin with trimellitic anhydride and neutralization of the residual carboxyl group with an amine or the like and the water-soluble resin obtainable by reacting polyethylene glycol with a polybasic acid.
(d) Water-soluble epoxy resins, for example water-soluble epoxy resins such as di- or polyglycidyl ethers of aliphatic polyhydric alcohols, diglycidyl esters of dicarboxylic acids, nitrogen-containing heterocycle-containing epoxy compounds, etc. and water-dis
Inbe Toshio
Takahashi Masashi
Yamasoe Katsuyoshi
Green Anthony J.
Nippon Paint Co. Ltd.
Shanks & Herbert
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