Process for preparing chrome surface for coating

#This invention relates to a process for preparing a chrome substrate for application of a polymer coating, and more particularly to a process for preparing a chrome substrate to achieve a durable bond between the chrome substrate and a subsequently applied polymer film.

#Traditional chrome plating creates a smooth, bright chrome finish. It has long been desired to have tinted lustrous metallic finishes, such as black chrome, gold-tinted chrome, and other tinted or colored metallic finishes for decorative purposes. More specifically, there has been a desire for clear polymeric decorative coatings that allow the brightness and luster of chrome plating to be seen, while modifying the appearance by imparting a color or tint to the chrome plating.

#Several methods have been used in an attempt to achieve colored metallic finishes. One method involves electroplating, wherein black chrome and bronze finishes can be created. A problem with the electroplating methods is that it is very difficult to consistently obtain a desired colored metallic finish. Another disadvantage with the electroplating techniques is that they are generally limited to black and bronze colors or combinations thereof.

#The expression “polymer” and derivatives thereof are meant to encompass homopolymers, copolymers, terpolymers, and polymers comprised of four or more monomers. Similarly, the expression “copolymer” and derivatives thereof is meant to encompass polymers that are the reaction product of two or more monomers, including terpolymers and polymers that are the reaction product of four or more monomers. The words “comprising”, “including”, “containing” and derivatives of these words are not meant to exclude other polymers, ingredients and/or components. Similarly, the articles “a” and “an” are generally meant to mean at least one, and should not be construed to mean only one.

#The process of this invention may be used for forming a polymer film coating on generally any metal surface. However, the invention is particularly useful for providing a tenacious, durable adhesive bond between a polymer film coating and a chromium surface. Chrome surfaces have been particularly difficult to coat with a polymeric film that adheres to the surface tenaciously and durably, and in particular it has been difficult to provide a polymeric film coating on chrome surfaces which can withstand extended use in exterior automotive applications, and other hostile or extreme environments. Accordingly, preferred applications for the invention relate to the provision of functional or decorative polymer film coatings on bright chrome surfaces, especially electroplated chrome surfaces.

#In each of the embodiments of this invention, a chrome surface, such as an electrodeposited chrome plating or a chrome coating formed by physical vapor deposition, is treated with an acid solution under conditions and for a period of time sufficient to promote excellent adhesion and adhesive durability between the treated chrome surface and a subsequently applied polymer coating. Chromic acid solutions used in the surface treatments of this invention typically contain from about 1 to about 50 ounces of H2CrO4 per gallon of solution. Other acid solutions that may be used include sulfuric acid solutions.