Patent Publication Number: US-4929315-A

Title: Method for electroplating a conducting surface

Description:
BACKGROUND OF THE INVENTION 
     The invention described herein relates to a process for galvanic coating (electroplating) of at least one selected area on a conducting surface, in particular a surface of plastic moldings. 
     Electroplating processes are known from, for example, DE-OS 2,648,274 which relates to applying galvanic patterns of metal onto metal or other substrates. In order to obtain the desired pattern or to confine the galvanizing electrolyte to specific areas of the substrate, the substrate is masked. The individual steps of such a masking process have repeatedly been a cause of problems to the present state of the art and have significantly increased process costs. While prior art relates to the production of integrated circuits and is particularly concerned with holding losses of noble metals to a minimum, the process in the automotive industry has been to use black masking paints which are applied to the areas not to be galvanized and are then coated with a metallic finish. In the conventional procedure, for example for partially chrome plated hub caps with a silver metal finish, the black masking paint is first applied to the areas not to be chrome plated. This was then followed by the customary galvanization. The chrome plated areas were subsequently covered (by adhesive or masking tape) and then finally the black areas coated by the first masking paint were painted with a metallic finish. 
     The prior art procedures described are, however, time consuming and costly, particularly with respect to operations and materials. 
     It is thus the object of the present invention to improve the process described at the outset to such an extent that the shortcomings described are reliably avoided and the operations are as economical in materials and time as possible 
     The invention that overcomes these problems includes use of an electrolytic current, in which masking is carried out in order to apply selectively galvanic coating to at least this one area of the conducting surface. An electrically conducting metallic primer is first applied to the whole of the surface of the molding. The area(s) to be galvanically coated are then masked, while a clear coat such as a clear varnish is applied to the area not to be galvanically coated. Following mask removal, the areas of the metallic primer are galvanically coated directly. 
     The process according to the invention makes use of the fact that the metallic finish consists of two layers, viz. the electrically conducting metallic primer or base varnish and the non-conducting clear coat or clear varnish. After the metallic primer and the clear coat have been applied with appropriate masking, the area of the electrically conducting metallic primer can, after removal of the maskings, be galvanically coated directly, thus making the use of a black masking paint which must yet again be recoated, superfluous. This economizes not only in masking and painting operations, but also in materials which would otherwise have to be used for the black masking paint. 
     The above has been a brief description of the prior art and the advantages of the invention. A preferred procedural example is explained in greater detail in the diagrams below and other advantages may be perceived by those skilled in the art. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-section through an assembly of layers during the process according to the invention; 
     FIG. 2 is a further cross-section of the assembly of layers at a different point in time of the process according to the invention; 
     FIG. 3 is a cross-section through an assembly of layers after mask removal; and 
     FIG. 4 is a cross-section through an assembly of layers after completion of the process according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, the molding serving as a substrate is generally designated as 12. The process according to the invention is not confined to any particular moldings. On the contrary, they can be freely chosen in respect of type, shape and size. However, the use of the process according to the invention is especially targeted to the automotive industry, preferably to provide hub caps with a silver metallic finish, the said hub caps being subsequently selectively chrome plated. 
     The whole of the surface 26 of the substrate or molding 12 first receives the metallic primer 14. The edge areas 22, for example, are then masked. It is understood that the format and the number of the maskings may be freely chosen. The area (18) not to be galvanically coated then receives the clear varnish 20, with the result that the assembly of layers shown in FIG. 2 is formed The maskings from the edge area are then removed with the result that the areas to be galvanically coated 16, shown in FIG. 3, are set free or exposed. Finally, conventional galvanizing is effected in such a way that the assembly of layers shown in FIG. 4 having galvanized edge areas 24 are formed. 
     In another embodiment of the process, it is also conceivable that organic or inorganic particles, for example metallic flakes such as bronze flakes, are removed from the primer by means of an etchant prior to the final galvanization.