Adhesion of polymeric materials to metal surfaces

A process for treating a metal substrate to improve adhesion of polymeric materials thereto, comprising the steps of

• intergranular etching a surface of the metal substrate;
• and
• applying an immersion plated metal to the intergranular etched surface by immersing the surface in an immersion plating composition comprising one or more plating metals selected from tin, silver, bismuth, copper, nickel, lead, zinc indium, palladium, platinum, gold, cadmium, ruthenium, cobalt, gallium and germanium,
• wherein the step of intergranular etching is carried out with an intergranular etching composition comprising
• (a) hydrogen peroxide;
• (b) at least one acid, wherein the at least one acid comprises sulfuric acid or a sulfonic acid;
• (c) at least one nitrogen-containing, five-membered heterocyclic compound which does not contain any sulphur, selenium or tellurium atom in the heterocycle;
• and
• (d) at least one adhesive compound selected from sulfinic acids, seleninic acids, tellurinic acids, heterocyclic compounds containing at least one sulfur, selenium and/or tellurium atom in the heterocycle, and sulfonium, selenonium and telluronium salts having the general formula (A),
• in which
• A stands for S, Se or Te;
• R1, R2 and R3 stand for alkyl, substituted alkyl, alkenyl, phenyl, substituted phenyl, benzyl, cycloalkyl, substituted cycloalkyl, R1, R2 and R3 being the same or different;
• and
• X− stands for an anion of an inorganic or organic acid or hydroxide, provided that the acid selected to constitute component (b) is not identical to the sulfinic, seleninic or tellurinic acids selected as component (d).