Process for curing acid-curable finishes

A process for curing baking finishes which contain an acid-curable resin and, as a curing catalyst, a blocked sulfonic acid of the formula I ##STR21## in which m is 0 or 1 and n is 1 or 2, R.sup.1 is C.sub.1 -C.sub.12 -alkyl, C.sub.1 -C.sub.4 -halogenoalkyl, C.sub.2 -C.sub.6 -alkenyl, C.sub.5 -C.sub.12 -cycloalkyl, C.sub.6 -C.sub.10 -aryl which is unsubstituted or mono- or poly-substituted by halogen, C.sub.1 -C.sub.16 -alkyl, C.sub.1 -C.sub.4 -alkoxy, phenoxy, phenyl or nitro, furyl, thienyl, C.sub.7 -C.sub.12 -aralkyl, C.sub.1 -C.sub.8 -alkoxy, C.sub.5 -C.sub.8 -cycloalkoxy, phenoxy or H.sub.2 N--CO--NH--, R.sup.2 is as defined for R.sup.1 or is --CN, C.sub.2 -C.sub.5 -alkanoyl, benzoyl, C.sub.2 -C.sub.5 -alkoxycarbonyl, phenoxycarbonyl, --N(R.sup.4)(R.sup.5), morpholino or piperidino, or R.sup.1 and R.sup.2, together with the atoms to which they are linked, form a 5-membered to 8-membered ring to which 1 to 2 benzo radicals can be fused, R.sup.4 being hydrogen, C.sub.1 -C.sub.12 -alkyl, phenyl, C.sub.2 -C.sub.9 -alkanoyl or benzoyl and R.sup.5 being hydrogen, C.sub.1 -C.sub.12 -alkyl or cyclohexyl, and R.sup.3, with n=1, is C.sub.1 -C.sub.18 -alkyl, C.sub.6 -C.sub.10 -aryl which is unsubstituted or mono- or poly-substituted by halogen, C.sub.1 -C.sub.4 -halogenoalkyl, C.sub.1 -C.sub.16 -alkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkyl-CONH-, phenyl-CONH-, benzoyl or nitro, C.sub.5 -C.sub.12 -cycloalkyl, C.sub.7 -C.sub.9 -aralkyl, camphoryl, --CF.sub.3, --CCl.sub.3 or --NH.sub.2, and, with n=2, R.sup.3 is C.sub.2 -C.sub.12 -alkylene, or unsubstituted or C.sub.1 -C.sub.12 -alkyl-substituted phenylene, naphthylene, diphenylene or oxydiphenylene, which comprises irradiating the finish with short-wave light, whereby the free sulfonic acid is formed, and then fully curing it at an elevated temperature.