Coating processes – With post-treatment of coating or coating material – Heating or drying
Patent
1992-12-18
1994-12-06
Pal, Asok
Coating processes
With post-treatment of coating or coating material
Heating or drying
427421, 427435, 252135, 25217423, 2523892, 252390, 252394, B05D 102, C23F 1100
Patent
active
053709098
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a novel liquid composition for treating the surface of tin-plated steel and/or aluminum and alloys that are predominantly aluminum (both the pure metal and alloys being denoted hereinafter by the word "aluminum" unless the context requires otherwise), particularly the surfaces of drawn-and-ironed (hereinafter "DI") cans made from these materials. The composition imparts an excellent corrosion resistance and paint adhesiveness to the surface of such a can after its formation by the drawing and ironing of metal sheet but before its painting or printing. This novel liquid composition also imparts the excellent mobility or slideability, i.e., low frictional resistance, which is required for the smooth conveyor transport of such a can. The composition also is relatively low in pollution potential, because it contains no deliberately introduced chromate or fluorine. The invention also relates to processes for using the composition according to the invention.
BACKGROUND ART
In the field of liquid compositions for treating the surface of tin-plated DI can of the aforementioned type, one example is the invention disclosed in (1) Japanese Patent Application Laid Open [Kokai or Unexamined] Number 01-100,281 [100,281/89]. This particular invention comprises a film-forming liquid composition for the treatment of metal surfaces in which the liquid composition has a pH of 2 to 6 and contains 1 to 50 g/L of phosphate ions, 0.2 to 20.0 g/L of oxyacid ions, 0.01 to 5.0 g/L of tin ions, and 0.01 to 5.0 g/L of condensed phosphate ion. Treatment with this conversion treatment liquid composition lays down a strongly corrosion-resistant phosphate film on the surface of a tin-plated DI can.
The inventions disclosed in (2) Japanese Patent Application Laid Open Number 01-172,406 [172,406,/89] and U. S. Pat. No. 4,457,790 are examples of a treatment method intended to develop corrosion resistance and adhesiveness through the use of water soluble resin. These inventions teach methods for treating metal surfaces with a solution which contains a derivative of a suitable polyhydric phenol compound and an aminomethylene substituted phenolic polymer or oligomer respectively.
The treatment baths previously employed to treat the surface of aluminum and aluminum alloy of the aforementioned type can be generally classified into chromate types and non-chromate types. The chromate types typically take the form of chromic acid chromate conversion treatments and phosphoric acid chromate conversion treatments. Chromic acid chromate conversion treatments entered into practical application in about 1950, and these are still widely used for heat exchanger fin material and the like. This type of conversion treatment bath is based on chromic acid (CrO.sub.3) and hydrofluoric acid (HF) and also contains an accelerator. It lays down a film which contains modest quantities of hexavalent chromium.
The phosphoric acid chromate conversion treatment derives from the invention in U.S. Pat. Number 2,438,877 (1945), and this type of conversion treatment bath is based on chromic acid (CrO.sub.3), phosphoric acid (H.sub.3 PO.sub.4), and hydrofluoric acid (HF). It forms a film whose principal component is hydrated chromium phosphate (CrPO.sub.4.4H.sub.2 O). As this film does not contain hexavalent chromium, it is currently widely employed as a paint undercoating treatment for the body and lid of beverage cans.
The invention disclosed in Japanese Patent Application Laid Open [Kokai or Unexamined] Number 52-131937 [131,937/77] is a typical prior art example within the realm of non-chromate types of treatments for aluminum. The disclosed treatment bath comprises an acidic aqueous coating solution (pH=approximately 1.0 to 4.0) which contains zirconium or titanium or a mixture thereof, as well as phosphate and fluoride. The application of this conversion treatment bath exemplary of the prior art to the surface of aluminum generates a conversion film whose principal component is zirconium oxide or titanium oxide. While
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Aoki Tomoyuki
Asai Shinichiro
Iino Yasuo
Tanaka Shigeo
Yoshida Masayuki
Achutamurthy P.
Henkel Corporation
Jaeschke Wayne C.
Pal Asok
Szoke Ernest G.
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