Air-drying lacquer binder of a ring-opening product of (I) an epoxidized polyoctenylene or cylco-octene-cycloene copolymer having an average molecular weight of from 600 to 3000 and (II) one or more of (a) an unsaturated carboxylic acid containing from 6 to 22 carbon atoms, (b) an alcohol containing from 2 to 6 hydroxy groups (c) a hydroxyalkylamine containing at least one hydroxyalkyl group, the hydroxy groups of the alcohols (b) and the hydroxyalkylamines (c) being esterified with an unsaturated carboxylic acid containing from 6 to 22 carbon atoms to an OH number of less than 25, and wherein the ring opening product has an average molecular weight of from 1500 to 10,000 and an acid number of from 0.1 to 20. The invention also relates to a process for producing this lacquer binder and to its use in high-solids lacquer systems.