Fundamentally suitable are ammonium salts with the general formula [NR1 R2 R3 R4 ]+ X-, in which R1, R2, R3 and R4, independently of one another, stand for hydrogen or C1 -C24 alkyl radicals, provided that at least one of the radicals R1, R2, R3 and R4 is a C1 -C24 alkyl radical and X- is a suitable anion readilly chosen by the artisan.