Low cost, blush-resistant silane/silica sol copolymer hardcoat for optical clear plastics

A silane/silica sol copolymer liquid thermosetting hardcoating composition for imparting scratch resistance to transparent plastic substrates, said composition comprising a reaction product of:

• a. an acidified aqueous dispersion of colloidal silica sol having average particle size <100 millimicrons in diameter, with said acidified aqueous dispersion of colloidal silica sol being comprised partly by colloidal silica sol dissolved in water-miscible solvent;
• b. a monomethyl trialkoxy silane mix consisting essentially of 67-100% monomethyltriethoxysilane and 33-0% monomethyltrimethoxysilane, wherein said reactants a and b are copolymerized in a ratio of not less than 30:70 and not more than 70:30,
• wherein said acidified aqueous dispersion of colloidal silica sol being comprised partly by colloidal silica sol dissolved in water-miscible solvent is added along with the additional monomethyl trialkoxy silane mix b into a batch of partly-reacted acidified aqueous dispersion of colloidal silica sol previously silanized with the monomethyl trialkoxy silane mix b,
• and said reaction product along with
• c. a latent condensation catalyst, and
• d. at least one tail solvent;
• such that said silane/silica sol copolymer liquid thermosetting hardcoating composition, when standing at ambient temperature does not gel within 30 days.