Aqueous wet coatings for transparent plastic glazing

Abstract

Electrostatically stabilized particulate sols, e.g. aqueous silica or alumina sols, have been surface-modified to reduce the particle/particle interaction and to obtain electrosterically stabilized sols. Epoxy functionalized alkoxysilanes were used as surface modifiers for alumina, silica or zirconia particles to achieve water dispersible nanoparticulate coating materials. After evaporating the organic solvent (produced by hydrolysis and condensation) aqueous sol-gel coatings have been prepared with organic solvent contents below 5%. The storage stability of these materials has been investigated by Si-29-NMR. An amino functionalized alkoxysilane was used as condensation catalyst and the nanocomposite material was thermally cured at 130 degrees C after flow or spray coating on pretreated polycarbonate substrates. The coatings show excellent adhesion which was shown by cross cut and tape test. After 1000 cycles Taber abrasion test (CS-10F, 500 g, DIN 52347) losses of transmittance due to scattering of 2-6% were achieved with a coating thickness of about 5 mu m.