The invention relates to the use of special mixtures of at least two polycarboxylic acids as crosslinker components for thermally curing powder-lacquer binding agents having groups that are capable of reacting with carboxyl groups. The mixtures include at least two polycarboxylic acids each melting above 95° C. and having up to 20 carbon atoms and consist of at least 5 wt. %, of the polycarboxylic acid with the lowest melting point and at least 10 wt. %, of the polycarboxylic acid with the highest melting point of all polycarboxylic acids present in the mixture to at least 5 wt. %. Additionally, the polycarboxylic acid mixture is a solid below 40° C. and a liquid above 160° C.