Paper and ink for repeated printing and erasing - uses arrangement which can be changed from visible to invisible state such as a layer of photochromic material

摘要

Paper is made of materials (112) which can be reversibly changed from a visible to an invisible state so that a printed pattern can be erased and the paper reused. The material can have a refractive index or reflectance which changes with heat die to a phase change, or an opto-magnetic layer whose polarisation plane can be changed magnetically, or it can be photochromic and respond to light of different wavelengths. The system has equipment for printing and erasing and can use an ink which has visible/invisible properties. USE/ADVANTAGE - The reusable paper is partic. useful in office automation applications.