Crosslinker of the formula I or a mixture of at least two crosslinkers of the formula where R 1 and R 2 are each independently selected from H, -(CH 2) r R 4, with r = 0 to 12, especially r = 1 to 8, -OR 5, -NHR 5, where R 4 and R 5 are each independently selected from the group consisting of H, an alkyl group optionally containing a heteroatom, especially -O-and/or -N-, and having 1 to 18 carbon atoms, a cycloalkyl group optionally containing a heteroatom, especially - O- and/or -N-, and having 3 to 18 carbon atoms, an alkylaryl group optionally containing a heteroatom, especially -O- and/or -N-, and having 6 to 18 carbon atoms, a bivalent alkylene group having 1 to 10 carbon atoms, an alkylene oxide group having at least 4 carbon atoms, especially having 4 to 16 carbon atoms, for example an epoxybutyl, epoxypentyl, epoxyhexyl, epoxyheptyl, epoxyoctyl, epoxynonyl or epoxydecyl group, a polyether group, such as polyalkylene oxide polyether, a polyhydroxy-functional group having 1 to 18 carbon atoms, a heteroaromatic group containing -O-and/or -N- and having 5 to 18 carbon atoms and an -O-or -NH-polyether group containing one or more different polyglycol units (CH 2 CH 2 O) p R", of which preferably at least one is arranged in a terminal position, where p is 4 to 20 and R" is an alkyl radical having 1 to 18 carbon atoms or H, and where each G 1 corresponds to a group of the formula IIa -(C=O)-NH-R-Si(OR') 3 (IIa) where R in the formula IIa in each case independently corresponds to an aliphatic (cyclo)alkylene radical having 1 to 10 carbon atoms, and R' in formula IIa in each case independently represents a linear, branched or cyclic alkyl radical having 1 to 10 carbon atoms. where R 1 and R 2 are each independently selected from H, -(CH 2) r R 4, with r = 0 to 12, especially r = 1 to 8, -OR 5, -NHR 5, where R 4 and R 5 are each independently selected from the group consisting of H, an alkyl group optionally containing a heteroatom, especially -O-and/or -N-, and having 1 to 18 carbon atoms, a cycloalkyl group optionally containing a heteroatom, especially - O- and/or -N-, and having 3 to 18 carbon atoms, an alkylaryl group optionally containing a heteroatom, especially -O- and/or -N-, and having 6 to 18 carbon atoms, a bivalent alkylene group having 1 to 10 carbon atoms, an alkylene oxide group having at least 4 carbon atoms, especially having 4 to 16 carbon atoms, for example an epoxybutyl, epoxypentyl, epoxyhexyl, epoxyheptyl, epoxyoctyl, epoxynonyl or epoxydecyl group, a polyether group, such as polyalkylene oxide polyether, a polyhydroxy-functional group having 1 to 18 carbon atoms, a heteroaromatic group containing -O-and/or -N- and having 5 to 18 carbon atoms and an -O-or -NH-polyether group containing one or more different polyglycol units (CH 2 CH 2 O) p R", of which preferably at least one is arranged in a terminal position, where p is 4 to 20 and R" is an alkyl radical having 1 to 18 carbon atoms or H, and where each G 1 corresponds to a group of the formula IIa -(C=O)-NH-R-Si(OR') 3 (IIa) where R in the formula IIa in each case independently corresponds to an aliphatic (cyclo)alkylene radical having 1 to 10 carbon atoms, and R' in formula IIa in each case independently represents a linear, branched or cyclic alkyl radical having 1 to 10 carbon atoms.