Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-07-06
2002-07-23
Mayekar, Kishor (Department: 1741)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C204S484000, C204S506000
Reexamination Certificate
active
06423425
ABSTRACT:
BACKGROUND
The present invention is directed to an article, such as an automobile body, that is electrocoated with a chip-resistant coating and a process for electrodepositing a chip-resistant coating on a substrate.
Multi-layered coating composites find use in various industries including the coating and/or painting of motor vehicles. In several of these industries, and in the automotive industry in particular, a substrate can have from two to six or more coating layers. These coating layers protect the substrate and provide a decorative finish.
Multi-layered coating composites for metal substrates often use electrodeposition coatings as an initial resinous coating layer to protect the metal substrate from corrosion. Cationic electrodeposition coatings have become the coatings of choice for corrosion protection. Electrodeposition has become increasingly important in the coatings industry because, by comparison with non-electrophoretic coating means, electrodeposition offers higher paint utilization, outstanding corrosion protection, low environmental contamination, and a highly automated process.
A spray-applied chip resistant coating layer is often present in multi-layered coating composites for motor vehicles. The chip resistant layer protects the surface of the substrates from losing paint through chipping when the vehicle is hit with solid debris, such as gravel and stones. The art for achieving chip resistance from spray applied primer coatings has postulated that reducing the differential in impact energy between the multiple coating layers should improve chip resistance of the coating. This is especially applicable when coating layers have excessive difference of hardness between them. This reduction in the differential would lessen delamination between the coatings, such as between an undercoat and an intermediate coat or between a top coat and an intermediate coat.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a coating system having both good chip resistance and corrosion protection, while additionally providing efficiencies in application and processing through the elimination of a paint layer. These efficiencies include superior paint utilization, lower environmental contamination, and a highly automated process.
The present invention includes a coated article that comprises a corrosion-resistant electrically conductive substrate that is free of an electrodeposited coating and an electrodeposited film-forming composition applied to at least a portion of the surface of the corrosion-resistant electrically conductive substrate. The film forming composition includes a curable electrodepositable elastomeric polymer. The substrate typically is one of aluminum or alloys thereof, zinc or zinc alloy surface treated steel, such as galvanized steel, that is coated with a non-insulating layer of a zinc-rich or iron phosphide-rich organic coating. The present invention also includes a process for electrocoating a corrosion-resistant electrically conductive substrate which is free of an electrodeposited coating, including the step of electrodepositing a coating composition onto a surface of the electrically conductive substrate, the coating composition including a curable elastomeric polymer.
The corrosion-resistant substrate combined with an elastomeric electrodeposited coating performs as well or better than a less corrosion-resistant substrate coated with an electrodeposited corrosion-resistant primer followed by a spray-applied primer-surface layer. The above-described coating aids in 1) bonding the finished layer(s) to the substrate, 2) preventing chipping damage, 3) leveling defects in the substrate and providing a uniform under-layer, 4) protecting repairs and cut edges, and 5) resisting damage due to exposure to ultraviolet light.
DETAILED DESCRIPTION OF THE INVENTION
The use of numerical values in the various ranges specified in this application, unless expressly indicated otherwise, are stated as approximations as though the minimum and maximum values within the stated ranges were both preceded by the word “about.” In this manner slight variations above and below the stated ranges can be used to achieve substantially the same results as values within the ranges. Also, the disclosure of these ranges is intended as a continuous range including every value between the minimum and maximum values.
The present invention is directed to a coated article, typically an automobile body that includes a corrosion-resistant, electrically conductive substrate that has been coated with one or more layers of a film-forming composition. The corrosion-resistant substrate can be inherently corrosion-resistant, such as aluminum, or a substrate, such as a ferrous substrate, that has been rendered corrosion-resistant by application of a suitable pretreatment composition. The film-forming layer(s) include a layer that contains a curable, film-forming elastomeric polymer that is electrodeposited onto the corrosion-resistant, electrically conductive substrate. The elastomeric polymer preferably is a curable polyurethane, polyurea or poly(urethane-urea) that typically is the reaction product of a polyisocyanate and an active hydrogen-containing polymeric material. The active hydrogen-containing polymeric material preferably is a polyoxyalkylene ether polyol, a polyoxyalkylenepolyamine or a mixture thereof. The elastomeric polymer preferably contains a minimum amount of polyurea linkages when cured.
Corrosion-resistant conductive substrates include, without limitation, metal substrates such as stainless steel; zinc or zinc alloy surface treated steel, that is coated with a zinc-rich or iron phosphide-rich organic coating; aluminum; copper; magnesium or alloys thereof. By “surface treated” it is understood that the surface of the steel has a zinc or zinc alloy layer that is introduced by a variety of known processes such as by, without limitation galvanizing or cladding the steel substrate. The substrate can be treated with a phosphating solution such as a zinc phosphating solution as described in U.S. Pat. No. 5,588,989. Combinations or composites of ferrous and/or non-ferrous metals also can be used, such as GALVALUME, GALVANNEAL and GALFAN zinc-aluminum alloys.
The terms “corrosion-resistant,” and the like, refer to the relative resistance of the substrate to corrosion as compared to cold rolled steel. By “non insulating” it is meant that a coating does not interfere in any substantial way with the electrodeposition of the film-forming composition of the present invention (i.e., render the electrodeposited layer commercially unacceptable).
The pre-treatment composition also may be a solution that comprises one or more Group IIIB or IVB element-containing compounds or mixtures thereof solubulized or dispersed in a carrier medium, typically an aqueous medium. The Group IIIB and IVB elements are defined by the CAS Periodic Table of the Elements as shown, for example, in the Handbook of Chemistry and Physics, (60th Ed. 1980). Transition metal compounds and rare earth metal compounds typically are compounds of zirconium, titanium, hafnium, yttrium and cerium and mixtures thereof. Typical zirconium compounds may be selected from hexafluorozirconic acid, alkali metal and ammonium salts thereof, ammonium zirconium carbonate, zirconyl nitrate, zirconium carboxylates and zirconium hydroxy carboxylates such as hydrofluorozirconic acid, zirconium acetate, zirconium oxalate, ammonium zirconium glycolate, ammonium zirconium lactate, ammonium zirconium citrate, and mixtures thereof. Hexafluorozirconic acid is preferred. An example of a yttrium compound is yttrium nitrate. An example of a titanium compound is fluorotitanic acid and its salts. An example of a hafnium compound is hafnium nitrate. An example of a cerium compound is cerous nitrate. Preferably, the Group IIIB or IVB metal compounds are in the form of metal salts or acids which are water soluble. The Group IIIB or IVB metal compound is typically present in the carrier medium in an amount of 10 to 5000 ppm metal, prefer
Corrigan Victor G.
Faucher Philippe
McCollum Gregory J.
Pawlik Michael J.
Van Buskirk Ellor James
Altman Deborah M.
Mayekar Kishor
PPG Industries Ohio Inc.
Uhl William J.
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