PLATING ON PLASTICS

To plate successfully on A.B.S. (Acrylonitrile Butadiene Styrene) the particles of Butadiene were dispersed and aligned as uniformly as possible on the surface. Inspection by a scanning electron microscope of surfaces that were successfully plated showed that the particles were spherical and regularly arranged. The surface layer after being etched clear of Butadiene was left with numerous well-undercut symmetrical cavities that provided secure mechanical keys for the metal plating. In a specimen with surface stress (that did not plate well) the etched cavities, shallow and seldom undercut, provided only a poor mechanical key. In addition, the stresses tended to relax during subsequent temperature changes when the surface layer deformed thereby loosening the plating.

Compoments were designed with the plating in mind. Good flow during moulding was ensured with a minimum of residual stress. Holes and grooves were provided to facilitate circulation of the plating solution. In the manufacturing process, the time and temperature in moulding was strictly controlled, the use of silicones as mould-release agents was avoided and the feed mechanism was very carefully cleaned after shut-downs.

Meticulous cleaning prior to etching and plating was essential. All traces of mould-release agents and of greases were removed. Slow etching was maintained to avoid too violent action near the undercut cavities in the surface and to improve the accuracy of timing rinsing was thorough and finally the temperature of the plating solution and the time of the process was strictly controlled. The chemical composition of the solution was frequently monitored and adjusted and components were arranged in the plating vat to allow free circulation of the solution on all sides.



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