Patent ID: 7645719

Claim:
A thermal paper comprising: a base sheet with an optional base coating; a thermosensitive coating positioned over the base sheet, said thermosensitive coating comprising color forming compounds, an optional protective top coating positioned over said thermosensitive coating and an optional backcoating positioned over the base sheet on the side opposite the thermosensitive coating; said thermal paper having a solution, dispersion or emulsion for providing a fluorescent security mark printed on said thermosensitive coating or on said optional protective top coating without pre-acting the color forming compounds or disrupting the color forming reaction by said color forming compounds, wherein said solution, dispersion or emulsion comprises a fluorescent compound which responds to ultraviolet light at wavelengths in the range of 200 nm to 400 nm by producing light at wavelengths in the range of 500-600 nanometers, the fluorescent compound in an aqueous carrier comprising an ammonium compound which solution, dispersion or emulsion does not pre-react the color forming compounds or disrupt the color forming reaction by said color forming compounds, the ammonium compound is in an amount of less than 5 percent by weight based on a total weight of the aqueous carrier; and the density of the fluorescent compound within the fluorescent security mark is sufficient such that the response to ultraviolet light at wavelengths in the range of 200 nm to 400 nm can be sensed by a photon detector, without premature coloration of the thermosensitive coating or blocking of the color forming reaction within the thermosensitive coating, the fluorescent security mark is to be printed over thermosensitive coating and the optional backcoating by a printing process which does not require temperatures above 50 to 60 degrees Celsius.