Patent ID: 8068126

Claim:
A direct thermal printer for generating an image in a thermal imaging medium, wherein the thermal imaging medium comprises at least a first image forming composition having a first activation temperature and a second image forming composition having a second activation temperature, wherein the first image forming composition and the second image forming composition, when activated, produce different colors, the direct thermal printer comprising: a first thermal printing head configured to make contact with a surface of the thermal imaging medium and comprising a row of heating elements, wherein the row is oriented transverse to a direction of transport of the thermal imaging medium, wherein each heating element is configured to apply heat to the surface such that the second image forming composition is heated to the second activation temperature to form an image; a second thermal printing head configured to make contact with the same surface of the thermal imaging medium and comprising a row of heating elements, said row being oriented transverse to the direction of transport of the thermal imaging medium, wherein each heating element is configured to apply heat to the surface such that the first image forming composition is heated to the first activation temperature to form an image; and a heating element configured to heat the thermal imaging medium in a region between the row of heating elements of the first thermal printing head and the row of heating elements of the second thermal printing head such that a first baseline temperature of the thermal imaging medium at the first thermal printing head is different from a second baseline temperature of the thermal imaging medium at the second thermal printing head by at least about 5° C., wherein the first and second baseline temperatures are lower than the first and second activation temperatures by at least about 5° C.