ABSTRACT
The demand for transparent plastics has been on the increase in many industrial sectors. Hybrid coatings can be prepared over a continuous compositional range from almost organic to almost inorganic. Plastic substrates are thermo-sensitive, and hence, the curing of coatings has to be done at temperature lower than their glass transition temperature. The scratch hardness of hybrid sol–gel coatings is usually reported in terms of its pencil scratch resistance; the pencil test uses constant pressure and variable hardness of the test tool as its fundamental principal. The scratch hardness of coatings is also measured using a scratch tester, which normally uses a diamond indenter tip. The hardness and elastic modulus are measured using the continuous stiffness measurement techniques in the displacement-control mode. Nanocomposite hybrid sol–gel coatings, where the nanoparticles are generated in situ, improve the mechanical properties better than the dispersion of nanoparticles in the hybrid sol–gel matrix.
