Thermosetting polyisiloxanic composition for protective coatings and process for coating polycarbonate sheets

Thermosetting organosiloxanic composition constituted by the product of reaction of four components, each one being selected from one of the following classes:

• (a) amino-alkoxy-silanes, to be defined by the general formula (I):
• H.sub.2 N--[(CH.sub.2).sub.m --NH].sub.n --(CH.sub.2).sub.m --Si(OR).sub.3
• wherein:
• R is a C.sub.1 -C.sub.5 linear or branched alkyl group;
• m is an integer of from 1 to 5;
• n is 0 or 1;
• (b) formaldehyde, tiroxane or paraformaldehyde formaldehyde;
• (c) acyloxy-silanes, to be defined by the general formula (II):
• ##STR2## wherein:
• R.sup.1 is a C.sub.1 -C.sub.5 linear or branched alkyl group;
• R.sup.2 is a C.sub.1 -C.sub.5 linear or branched alkyl group, or a C.sub.2 -C.sub.5 alkenyl group;
• (d) water;
• which is obtained by reacting (a) component with (b) component, in the absence of solvents or diluents, in such proportions that the ratio of moles of formaldehyde of (b) component to the amino groups of (a) component of directly from 1.2/1 to 4.0/1, by operating at a temperature of from 22.degree. to 70.degree. C., until a clear solution is obtained;
• by furthermore separately making (c) component interreact with (d) component in an alcoholic solvent, with a ratio of water moles of (d) component to the number of acyloxy groups of (c) component within the range of from 0.1/1 to 0.66/1, by operatiang at least one hour at a temperature of from 5.degree. to 30.degree. C., and finally mixing the product of reaction of (a) and (b) components with the product of reaction of (c) and (d) components in such a way that the molar ratio between initially charged (c) and (a) components is comprised within the range of from 0.1/1 to 2.5/1, by operating at a temperature of from 15.degree. to 30.degree. C.