Process for plating plastic part after overmolding

Abstract

A plastic part is provided with decorative metallized surfaces as well as overmolded thermoplasticelastomer grip portions. The plastic part is overmolded with the TPE prior to metallizing the remaining exposed surfaces of the part. A TPE compound with saturated midblocks is used which is stable in the acid environment and elevated temperatures of the plating.

1 . Process for forming a molded plastic part that is at least partly metal plated and which is overmolded with a thermoplastic elastomer to form grip portions, comprising
 molding a substrate of a rigid polymer;   overmolding portions of the molded substrate with a thermoplastic elastomer leaving exposed portions of said molded substrate; and thereafter   forming a decorative metal plating on said exposed portions but not on the thermoplastic overmolded grip portions;   wherein said thermoplastic elastomer is a compound having saturated elastomer midblocks and which is adapted to withstand exposure to an acid environment and elevated temperature of a plating bath; and   wherein said forming of the decorative metal plating is carried out by
 preparing the exposed portions of the molded and overmolded substrate in a bath of chromic acid to etch the surface of said exposed portions; 
 electrolessly palladiumizing said substrate in a bath of stannous chloride and palladium chloride to produce a palladium tin layer on the surface of said exposed portions; 
 removing any plastic residue from the palladium tin layer on said exposed portions; and 
 electroplating the palladium tin on the exposed portions of the substrate in successive plating baths of copper, nickel, and chrome. 
   
     
     
         2 . The process according to  claim 1  wherein said thermoplastic elastomer is a material having a shore hardness between 40 and 90, and a tensile strength of substantially 60 Kg/cm 2 . 
     
     
         3 . The process according to  claim 2  wherein said thermoplastic elastomer is an SEBS polymer, with styrene end blocks and polybutadiene and butylene mid blocks. 
     
     
         4 . The process according to  claim 3 , wherein said thermoplatic elastomer includes is Empilon, PHA 61B. 
     
     
         5 . The process according to  claim 1  wherein said step of palladiumizing is preceded by neutralizing in a bath to remove hexavalent chrome from the surface of the exposed portions of the substrate. 
     
     
         6 . The process according to  claim 1  wherein said steps of palladiumizing and removing plastic residue are followed by dipping the substrate in a bath containing nickel sulphate, ammonium chloride, sodium hypophosphite and sodium citrate.