that can be cross linked by both radiation energy and thermal energy if this kind of hard coating is used to coat the optical film radiation energy such as uv can be used to quickly precure the coating to a tack free state and the final cure will be accomplished by thermal energy u s pat no 6 514 574 discloses such a coating composition which comprises epoxy silanes silicate silica thermal catalyst and effective amount of cationic photoinitiator it is incorporated herein by reference in the case where it is difficult to obtain adequate coating adhesion a primer layer may be applied onto the surface of the optical film before the application of the hard coating composition the primer layer enhances the adhesion between the film substrate and the coating layer a polyurethane or acrylic type of primer is preferred u s pat no 5 310 577 discloses a primer consisting of a thermosetting polyurethane in at least one organic solvent with the polyurethane being formed from a blocked isocyanate which requires the application of heat to disassociate the blocking agent from the polyurethane so that the isocyanate group can then react with the active hydrogen of the polyol to further polymerize and crosslink the primer coating another polyurethane primer is described in u s pat no 5 316 791 in which the primer consists of an aqueous polyurethane dispersion and is dried in air at ambient or elevated temperatures the disclosures of the above u s patents are incorporated by reference herein the optical film.