Low-cost, user-friendly hardcoating solution, process and coating

Abstract

An improved, user-friendly silane / silica sol copolymer hardcoating composition for protecting optical plastic and other substrates (including wood, metals, glass, plastics and most coated articles) from scratching is able to be manufactured at lower costs and to provide much-improved ease of use in transportation, storage, dipbath (or other coating tank) stability, and blush resistance in ordinary cleanroom atmospheres. The silane / silica sol copolymer is formed as a direct reaction product of an acidic silica sol and monomethyltrialkoxysilane, preferably substantially monomethyltriethoxysilane, in ratios of 30:70 to 70:30, most preferably about 40:60. A tail solvent aids blush resistance, reduces internal stress and permits adhesion to unprimed polycarbonate. Optionally, colloidal silica sol dissolved in water-miscible solvent may be reacted in a second stage with acidic aqueous colloidal silica sol earlier silanized with monomethyltrialkoxysilane.

Description

[0001] This is a divisional of Ser. No. 09 / 328,725, a continuation-in-part application of Ser. No. 08 / 771,866, filed Dec. 12, 1996, now abandoned, which is a divisional of Ser. No. 08 / 430,251, filed May 4, 1995, now U.S. Pat. No. 5,665,814.[0002] The chemical family of silane / silica sol copolymer compositions finds commercial use in heat-curing scratch-resistant hardcoats applied mainly to clear plastic sheets and molded parts. The present invention makes improvements in lowering costs and improving ease of use and performance of specific chemical compositions of monomethyltrialkoxysilan-e copolymerized with acidic aqueous silica sol. These compositions are to be coated onto molded or cast optical lenses (including auto headlamp lenses and spectacle lenses and sports eyewear), plastic extruded or cast sheet (used for windows, protective covers, etc.), and other substrates needing a scratch-and scuff-protective surface finish.II. BACKGROUND OF THE INVENTION[0003] Clark (U.S. Ser. No....

AI Technical Summary

Problems solved by technology

Variations from these conditions may result in blushing of the coating or a poor film formation".

Supplemental dehumidification is needed, calling for expensive regenerative-desiccant-bed air-handling equipment which can easily exceed $100,000 capital, just to handle the volume of clean air recirculating within a fully-enclosed room or machine used for applying such coatings.

Early versions of low-solids, high-water-content Clark coatings when applied, dried, and cured in ordinary, ambient conditions had very poor "blush" resistance; 30 grains of moisture or less was then specified as necessary in the air of the coating drydown area.

However, this stripping operation adds substantially to manufacturing costs.

However, the economic impact of replacing the aqueous silica sols with solvent-based silica sols is extremely negative, by at least a five-fold to ten-fold price factor.

However, coarser wools will produce marks--fine, medium, or coarse scratches.

Another method of testing the hardness of coatings, unfortunately only applicable to flat substrates, is the Taber abrasion test.