THE MECHANISM OF THERMOINDUCED ELECTROSTATIC IMAGE-FORMATION IN POLEDFERROELECTRIC POLYMER-FILMS

Ferroelectric polymer films have been shown to be useful for heat-mode electrostatic image recording. In connection with this novel imaging process, changes of state at heating were investigated on a copolymer of vinylidene fluoride and tetrafluoroethylene. First, an attempt to e stimate the degree of polarization from the analysis of corona chargin g curves of films partially depolarized with heat pulses is described. For films exposed to a flash light (50 mJ/cm2, 10 ms), dipoles were e stimated to be disordered by about 20%. This magnitude seems to be ins ufficient for explaining the observed electrostatic contrast. Another heating effect likely responsible for image formation was found. When poled films were subjected to heat pulse, they were charged up to 40 t o 60 V with a polarity opposite that employed for poling. This can be attributed to a combined effect of pyroelectricity and leakage of surf ace charges.