The present invention provides a primer for adhesive tapes with improved adhesion-promoting properties. This is achieved with a primer comprising a mixture G, which is dissolved or dispersed in one or more solvents, consisting of at least one co-polymer obtained by co-polymerization of a monomer mixture, comprising an amount of at least 90 wt% of the following monomers: vinylcaprolactam and/or vinylpyrrolidone; - one or more of the monomers a) and/or b): a) acrylic acid ester of a linear, primary alcohol having 2 to 10 carbon atoms in the alkyl group of the alcohol, b) acrylic acid ester of a branched, non-cyclic alcohol having 3 to 12 carbon atoms in the alkyl group of the alcohol, - at least one chlorinated polyolefin, and at least one metal compound selected from the group consisting of metal acetylacetonates, metal alkoxides and alkoxy-metal acetylacetonates.