Coating processes – With post-treatment of coating or coating material – Chemical agent applied to treat coating
Patent
1996-05-09
1997-11-18
Dudash, Diana
Coating processes
With post-treatment of coating or coating material
Chemical agent applied to treat coating
427354, 4273884, B05D 310, B05D 300
Patent
active
056885601
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a process for coating metal surfaces. More specifically, the invention relates to a process that produces highly corrosion-resistant and strongly adherent resin coatings on metal surfaces. This process is applied to the uncured resin coatings that are formed on metal surfaces when the surface of a metal is brought into contact with an autodepositing coating composition that contains acid, oxidizing agent, and water-dispersible or water-soluble organic film-forming resin. The process consists of contacting an uncured resin coating of this type with an aqueous solution that has a pH adjusted to 7 to 11 and that contains at least 1 selection from the following inorganic acids and salts thereof: molybdic acid, tungstic acid, polyphosphoric acid, and polysilicic acid.
BACKGROUND ART
Autodepositing coating compositions as referred to in this invention are acidic coating compositions that contain an organic film-forming resin and that produce a resin coating on the surface of metal brought into contact with the composition. Compositions of this type are disclosed in Japanese
A characteristic feature of these known coating compositions is that immersion of a clean metal surface in the coating composition produces a resin coating whose thickness or weight increases with increasing immersion time. In addition, part of the metal ion eluted from the metal surface by the chemical etching of the coating composition is taken into the coating; this makes possible the efficient formation of a resin coating on the metal surface without utilizing externally supplied electricity as is used in the electrodeposition of coatings.
The conventional coating compositions, however, do not themselves always exhibit a satisfactory adherence or corrosion resistance, and as a result various treatment processes have been examined for the purpose of improving the adherence and corrosion resistance of autodeposited coatings on metal surfaces. For example, Japanese Patent Application Laid Open autodepositing coating processes that consist of application of a waterborne coating composition to a metal substrate followed by baking. This rinse is applied to the uncured autodeposited film between the deposition step and baking step and consists of an aqueous solution or waterborne dispersion whose main component is at least one selection from the group comprising the silicofluorides, borofluorides, titanofluorides, aluminofluorides, and nitrites. The application of this process makes possible the production, without the use of rust-preventing pigments, of autodeposited films that have a good corrosion resistance. teaches a rinse that, as in Japanese Patent Application Laid Open Number Sho 52-56142, is applied to the uncured autodeposited coating between the deposition step and the baking step. In this case, however, the rinse consists of an aqueous solution or waterborne dispersion whose main component is at least one selection from the group comprising amines, the amine salts of carboxylic acids, amino salts, melamine, and amides. The practice of this process is again reported to make possible the production of good corrosion-resistant autodeposited films without the use of rust-preventing pigments. Japanese Patent Application Laid Open Number Sho 60-58474 teaches a process that improves the water resistance of the coatings. In this process, an aqueous alkali metal or ammonium hydroxide solution is applied to the uncured autodeposited film on the metal surface prior to drying. This makes the dried film impermeable to water and thereby improves the water resistance.
U.S. Pat. Nos. 3,647,567 and 4,030,945 and Japanese Patent Application Laid Open Number Sho 61-168673 teach the preparation of good corrosion-resistant autodeposited films by a pre-drying rinse of the uncured autodeposited film on the metal surface with a chromium compound-containing aqueous solution.
In recent years, higher added value has been sought from the painting of metal surfaces, and in particular a higher corrosion resistance and
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Hirota Mutsumi
Honda Takumi
Naito Kazuhisa
Dudash Diana
Henkel Corporation
Jaeschke Wayne C.
Robbins Beatrice N.
Wisdom, Jr. Norvell E.
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