Prodn. of coated non-conductors esp. plastics - by suitably oxidising the surface to increase its electrical conductivity and then spraying electrostatically with liquid or powder

摘要

Articles made of wholly or partly non-conducting materials, and plastics in particular, are produced with a surface coating by raising the electrical conductivity of the areas concerned and then coating them electrostatically, the increase in conductivity being produced by a controlled oxidation, using one of various methods. The oxidation process e.g. etches the surface areas with highly ionised gas such as a corona discharge or a vacuum plasma discharge. The surface can however be treated with an oxidising flame or oxidising acid. The areas concerned are then electrostatically sprayed with powder or liquid. The oxidation of the areas concerned increases the polar proportions of the molecular groups in the material on the surface. In addition the decomposition products in the surface area also increase the conductivity, so that the area attracts the charged particles of the coating. ADVANTAGE - The method completely avoids altering the surface or other general properties of the material. It consequently greatly widens the fields of application of electrostatic coatin