Thermal imaging system
A multicolor imaging system is described wherein at least two, and preferably three, different image-forming layers of a thermal imaging member are addressed at least partially independently by a thermal printhead or printheads from the same surface of the imaging member by controlling the temperature of the thermal printhead(s) and the time thermal energy is applied to the image-forming layers. Each color of the thermal imaging member can be printed alone or in selectable proportion to the other color(s). Novel thermal imaging members are also described.
1. A thermal imaging member comprising:
(a) a substrate having first and second opposed surfaces;
(b) at least first, second and third image-forming layers carried by said first surface of said substrate, said first image-forming layer having a higher activation temperature than said second image-forming layer, and said second image-forming layer having a higher activation temperature than said third image-forming layer;
(c) one or more spacer layers providing a time delay positioned between a first pair of image-forming layers, said first pair of image-forming layers consisting of said first and said second image-forming layers; and
(d) one or more spacer layers providing a different time delay positioned between a second pair of said image-forming layers, said second pair of image-forming layers comprising said third image-forming layer;
wherein the thickness of the one or more spacer layers positioned between said first pair of image-forming layers is less than the thickness of the one or more spacer layers positioned between said second pair of image-forming layers, each of the different time delays being a function of the respective thicknesses and usable for defining printing regions for colors to be formed.
2. The thermal imaging member of claim 1 , in which said spacing between said second pair of image-forming layers is at least twice as great as said spacing between said first pair of image-forming layers.
3. The thermal imaging member of claim 1 , in which said spacing between said second pair of image-forming layers is at least four times as great as said spacing between said first pair of image-forming layers.
4. The thermal imaging member of claim 1 , where the activation temperature of said first image-forming layer is at least 30° C. higher than the activation temperature of said second image-forming layer.
5. The thermal imaging member of claim 1 , wherein the activation temperature of said second image-forming layer is at least 30° C. higher than the activation temperature of said third image-forming layer.
6. The thermal imaging member of claim 1 , in which said first pair of image-forming layers consists of said first and said second image-forming layers, and said second pair of image-forming layers consists of said second and said third image-forming layers.
7. The thermal imaging member of claim 1 , wherein the time delay is a thermal time delay.
8. The thermal imaging member of claim 1 , wherein each of the different one or more spacer layers comprises material having substantially the same heat capacity and substantially the same thermal conductivity.