SUMMARY OF THE INVENTION [0007] The above and other objects of the present invention can be achieved by using a pyrogenically prepared silicon dioxide with the following physicochemical properties: [0008] 1) Average particle size (D50 value) D50???150 nm (dynamic light scattering, 30 wt %) [0009] 2) Viscosity (5 rpm, 30 wt %) ?????100 m???Pas; [0010] 3) Thixotropy of Ti:(??(5 rpm))/(??(50 rpm))???