Effect of chromium coating thickness on surface adhesion of polyethylene terephthalate optical film

Abstract

Surface accuracy and shape accuracy are the two key factors that determine the reflective performance of electroforming replication mold. However, the adhesion between the master mold and the replica mold sometimes causes the deformation, fracture and stretching of the microstructure of the mold surface. The reflective performance of the mold surface is reduced. For this reason, this paper proposed a method for reducing the adhesion force by means of a metal Cr transition layer, which was deposited on polyethylene terephthalate (PET) optical film using direct current (DC) magnetron sputtering. The effect of the Cr coating thickness on adhesion force was investigated. The surface of the film was analyzed by the measurement of contact angle, surface energy, surface chemical composition and micro-morphology. The measurements indicate that the surface energy of the PTE films is reduced after being deposited with a thin Cr coating. The reduced surface energy could be due to the fact PET′s polar functional groups were covered by the Cr coating, which must have lower surface energy than the PTE′s surface. In addition, the reduction of surface roughness also helps to reduce the adhesion of PET film surface. The study showed that Cr coating can effectively reduce the surface adhesion of PET optical mold and improve the surface quality of duplicated mold. The work provides a new method to reduce the surface adhesion of PET optical molds for application in electroforming demoulding technology and interfacial adhesion can be adjusted by the thickness of the Cr coating.