Varnishes with high hardness, resistant to abrasion, process for their preparation, and application of these varnishes to coating of solid substrates

A process for preparing a varnish comprising (1) polysiloxanes, (2) colloidal silica, (3) a soluble aminoblast resin and (4) solvent, comprising the steps of:

• a. forming component (1) by:
• (i) hydrolyzing and partially condensing a nonepoxidized trialkoxysilane having the formula:
• R--Si--(OR').sub.3
• wherein R is a radical selected from the group consisting of alkyl radicals having from 1 to 4 carbon atoms, chloro-3-propyl, trifluoro-3,3,3-propyl, mercapto-3-propyl, methacryloxy-3-propyl, vinyl, and phenyl;
• and R' is an alkoxyalkyl radical having from 2 to 4 carbon atoms, in the presence of 4 to 90%, by weight of the total of constituents (1) and (2), of component (2);
• (ii) hydrolyzing and partially condensing an epoxidized trialkoxysilane having the formula:
• R"--Si--(OR').sub.3
• wherein R' represents a radical containing an epoxide group, in the presence of the products of a(i);
• and
• (b) mixing 9 to 95%, by weight of the total of constituents (1) and (2), of the product of step a(ii) with:
• (i) 0.5 to 9%, based on the weight of the total of constituents (1) and (2), of component (3), and
• (ii) component (4).

A process for coating a solid substrate with a varnish, said varnish comprising a solvent containing:

• a. 4 to 90% by weight of the total of constituents (a), (b), and (c), of a colloidal silica;
• b. 9 to 95% by weight of the total of constituents (a), (b), and (c), of the product of hydrolysis and partial condensation, in the presence of (a), of at least one nonepoxidized trialkoxysilane having the formula
• R--Si--(OR').sub.3
• wherein R is a radical selected form the group consisting of alkyl radicals having from 1 to 4 carbon atoms, chloro-3-propyl, trifluoro-3,3,3-propyl, mercapto-3-propyl, methacryloxy-3-propyl, vinyl, and phenyl;
• and R' is an alkoxyalkyl radical having from 2 to 4 carbon atoms;
• c. 1 to 87% by weight of the total of constituents (a), (b), and (c) of the product of hydrolysis and partial condensation, in the presence of (a) and (b), of at least one epoxidized trialkyloxysilane of the formula
• R"--Si--(OR').sub.3
• wherein R" represents a radical containing an epoxide group;
• d. 0.5 to 9% by weight of the total of constituents (a), (b), and (c), of a soluble aminoplast resin (d), selected from the group consisting of melamine-formaldehyde and ureaformaldehyde resins, said process comprising the steps of contacting the substrate with the varnish and heating the substrate and varnish to a temperature of 120.degree. C. for a period of up to two hours.