The method relates to a primer comprising a mixture, dissolved or dispersed in one or more solvents, of I) a pressure-sensitive adhesive comprising at least one base polymer component obtainable by free-radical copolymerization of the following monomers: a) at least one acrylic ester of a linear, primary alcohol having 2 to 10 carbon atoms in the alkyl radical of the alcohol, b) at least one acrylic ester of a branched, acyclic alcohol having 4 to 12 carbon atoms in the alkyl radical of the alcohol, c) 8 to 15 per cent by mass of acrylic acid, based on the sum of the monomers, d) optionally up to 10 per cent by mass of further copolymerizable monomers, based on the sum of the monomers, II) at least one thermal crosslinker based on a metal acetylacetonate, a metal alkoxide or an alkoxy metal acetylacetonate, III) at least one chlorinated polyolefin, characterized in that the concentration of the sum of the thermal crosslinkers based on the sum of the base polymer components of the pressure-sensitive adhesive is in the range from 0.05 per cent by mass to 5.0 per cent by mass.