Examples of further suitable surface modifiers are mono- and polyamines, particularly those of the general formula R3-n NHn, wherein n=0, 1 or 2 and the radicals R independently are alkyl groups having 1 to 12, particularly 1 to 6 and particularly preferred 1 to 4 carbon atoms (e.g. methyl, ethyl, n-and i-propyl and butyl) and ethylene polyamines (e.g. ethylene diamine, diethylene triamine, etc.);