Demand and timed renewing imaging media

Claim 1

A self-supporting sheet material which is substantially insensitive to marking by the localized application of heat or pressure but which is receptive to ink, pencil, crayon or similar markings and which is adapted to being temporarily or permanently provided with markings by the application of a colorless liquid, comprising in combination: a. a self-supporting base sheet and, b. bonded over at least one side of said base sheet, a reflective opaque white to pastel layer having an image force value of at least 500 grams-force and a cohesion value of at least 200 grams-force, said layer consisting essentially of particles which have a diameter in the range of 0.01 to 750 micrometers and a refractive index in the range of about 1.3 to 2.2, said particles being held in pseudo-sintered juxtaposition by a thermoset binder having a refractive index in the range of about 1.3 to 2.2 so that interconnected microvoids are present throughout said layer, the binder:particle volume ratio being in the range of about 1:20 to 2:3 and the void volume of said layer being in the range of 15-70%, whereby when liquid having a refractive index approximating that of the particles is applied to the exposed surface of said layer, said liquid penetrates the microvoids, thereby reducing the reflectivity of the layer in the vicinity of the liquid-penetrated microvoids to impart transparency.