Epoxysilane-based hybrid coating has been widely studied for application of abrasion resistant coatings for various substrates. Especially Al-O containing epoxy-hybrid material shows the highest abrasion resistance. For hard coating on polymer substrate thermally and UV curable coating are available for abrasion resistance, the thermally curable type showing higher abrasion resistance. Hard coating on polymer substrate also needs a low curing temperature, short heat treatment time, good adhesion to substrate and transparency. Epoxysilane-based hybrid material fabricated by sol-gel method was appropriate for hard coating materials because it could be densified and hardened at low temperature (about 120℃).
3-glycidoxypropyltrimethoxy-silane which is used as general epoxysilane and TMOS (Tetramethylorthosilicate) form the epoxy-silica network structure. After aluminum butoxyethoxide incorporated into epoxy-silica network, Al-O containing epoxy-hybrid materials can be obtained. Aluminum butoxyethoxide acts as catalyst for epoxy ring opening reaction and inorganic condensation. The electrophillic attack of Al-OR, Al-OH species accelerates ring opening and inorganic condensation reaction. In general there are three possibilities for the reaction of the epoxy group. First, the ring can be opened by methanol, produced by the hydrolysis of the silicon alkoxide, resulting in a methylether. Instead of methanol water can convert the epoxy group, thereby yielding a diol. The third possibility is the reaction of the oxirane with another epoxy ring, resulting in oligo- or poly(ethyleneoxide) derivatives. The quantitative results of epoxy rings and their derivative was obtained by using $^{13}C$ nuclear magnetic resonance spectroscopy and derivative was obtained by using $^{13}C$ nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy.
That result confirms that aluminum butoxyethoxide act as catalyst for epoxy ring opening reaction and there are mainly oligo(ethyleneoxide) derivative in hybrid materials rather than poly(ethyleneoxide). $^{29}Si$ NMR result shows the increase of condensation degree by catalytic effect of aluminum butoxyethoxide and Si-O-Al hetero-metallic bonding. 10 mol%-aluminum butoxyethoxide has the most efficient catalytic effect for both reactions. The condensation degree and epoxide polymerization was saturated above 10 mol% aluminum butoxyethoxide.
The hardness of coating with different amount of aluinum butoxyethoxide was characterized by nanoindentors. The hardness of coating is increased rapidly by 10 mol%-aluminum butoxyethoxide. More 10 mol%, the hardness was linearly increased. Less 10 mol%, hardness of coating was determined by epoxide polymerization and inorganic condensation and above 10 mol%, by bonding between alumina and silica. Instead of TMOS, TEOS(Tetraethylorthosilicate) and PhTMS(Phenyltrimethoxysilane) was used in order to reduce hardness and increase flexibility of coating. Colloidal silica was used in order to enhance the hardness of coating. In case of colloidal silica, hard coating with larger silica has high hardness than silica made by silicon alkoxide. In TEOS and PhTMS cases, the change of hardness show the similar results in TEOS case.
In order to apply to abrasion resistance coating of polymer substrate, the reduction in haze in the Taber-Abrasive test of coating compared with that of pure polymer substrate. In case of acidic stabilized silica sol has lowest haze valuein taber test, TMO hard coating has highes haze value. ASTM D 3359 test shows hard coating has excellent adhesion on PMMA and pure adhesion on PC (PolyCarbonate). The adhesion on PC was enhanced by inserting layers consisted of 3-APTMS( Aminopropyltrimethoxysilane) between hard coating and PC substrate. The transparent hard coating was confirmed by UV-Vis spectroscopy.
