GB1110765A - Improvements in or relating to metallizing surfaces which are electrically non-conductive - Google Patents

Abstract

A method of metallizing an electrically non-conductive surface (e.g. of plastics, paper laminated phenolic boards, glass, other mineral, vegetable or synthetic material) comprises the steps of (a) initially cleaning the surface, (b) rendering the surface porous by removing at least part of the outermost surface layer, (c) washing, or washing and heating the porous surface, or treating the same chemically so as to remove resulting residues and precipitates, (d) providing a priming or keying medium for the nuclei of a catalytic salt solution by the application of a base metal salt solution (e.g. an alcholic or aqueous SnCl2 solution) acting as a priming or keying solution, (e) applying a solution of the catalyst (which may comprise Ag, Au, Pd or Pt), (f) heating the surface, and (g) chemically depositing a metal (e.g. Cu, Ni or Sn) from a solution on the surface after the catalyst has penetrated into the same. After the step (c) and prior to the step (d) a coat of resin may be applied to the surface, the outer surface of the coat being rendered porous. Step (b) for rendering the surface porous may be (i) chemical using an aqueous acid or alkaline etchant or an organic solvent, or (ii) mechanical using grit blasting or honing or (iii) by irradiating the surface with electrons or (iv) by subjecting the surface to electric discharges, e.g. using a corona discharge. The catalyst of step (e) may be derived from a salt solution of Au or Pt in either an aqueous or organic medium, e.g. of alcohol, ketone, ester or aromatic hydrocarbon, and may contain surface active agents and penetrants. Heating step (f) may be carried out in an inert atmosphere or vacuum and after the heating the surface may be cooled or quenched in air or water. In metal-deposition step (g), Cu may be deposited from Fehling's solution using HCHO and NH2NH2 as reducing agents; Ni may be deposited from alkaline or acid nickel chloride solutions using hypophosphite as a reducing agent; or Sn may be deposited from a solution comprising K2SnO3, KCN and KOH. The surface to be plated may be dipped in a concentrated solution of the reducing agent before immersing in a plating bath. The metal may be applied from a plurality of solutions of decreasing concentrations. Successive solutions may comprise different metals, the metal in the preceding solution being catalytic to depostion of metal in a succeeding solution. After plating, the metallized surface may be annealed in an oven, its thickness be increased by electro-plating and then be machined. In metallizing Si plastics or polytetrafluoroethylene plastics, the extra step of applying resin to the cleaned surface is included between steps (c) and (d). The Examples are of (1) making printed circuits on both sides of a polyester film by depositing chemically reduced Cu followed by electro-plated Cu and chemically reduced Sn. Details of masking during plating are given. (2). Making printed circuits on paper laminated phenolic boards by depositing chemically reduced Ni followed by chemically reduced Cu and electroplated Cu. (3). Making acetal resin mechanical components such as wheels, gears, pinions and rollers by depositing electroless Ni, and chemically reduced Cu for the initial deposits followed by electroplated Cu and Ni and finished with hard Cr. (4). Making metallized "Terylene" (Trade Mark) fabric, e.g. for safety belts in motor vehicles, by depositing either chemically reduced Cu or electroless Ni and electro-plating with Cu and/or Ni. Other objects which may be metallized are glass or other mineral fibres, before or after they have been woven, felted or otherwise joined into sheets or mats, and ropes, cords or strings made of mineral, vegetable or synthetic fibres.