Low charge-voltage frost recording on a photosensitive thermoplastic medium

Claim 1

In a method of recording at a first surface of a single layer of a thermoplastic medium composed of an optically transparent organic resin in the form of a thermoplastic polystyrene having a resistivity at its softening point between substantially 10 12 and substantially 10 18 ohm-centimeters and having dispersed therein particles of photosensitive copper phthalocyanine dye responsive to visible radiation, the steps of: substantially uniformly and directly charging at least a portion of said first surface to a predetermined charge density in a first predetermined period of time substantially lower than the normal thereshold charge density required to produce a frost pattern at said surface in the absence of exposure to visible radiation but in the presence of subsequent exposure to heat, directly exposing said portion, through a second surface opposite said first surface, after said first predetermined period of time, to visible radiation in the form of an image pattern for a second predetermined period of time, and directly subjecting said portion during a third predetermined period of time falling within said second predetermined period of time to thermal radiation from planar radiant heater means disposed in spaced substantially parallel relation with respect to said surface, whereby a frost image is generated upon said portion that is an image substantially replicating said image pattern, said third predetermined period of time falling mainly in the later part of said second predetermined period of time and said second predetermined period of time extending to a time later than the end of said third predetermined period of time.