Thermochromic ink and document printed therewith

Abstract

A document which may be a security document has a thermochromic coating which may be a thermochromic ink on the substrate of the document. The ink may include several thermochromic materials which transition from various different colors to substantially clear in appearance as the ink is warmed to various temperatures. The combination of the colors of the thermochromic materials can give the document a different color at a number of different temperatures, until the coating is warmed to the highest color change point. When at or above the highest color change temperature, the coating becomes substantially transparent and the printed area assumes the color of the underlying substrate. The coating may also include non-reactive materials of yet another color that mixes with the colors of the thermochromic materials. The document may additionally include printed indicia on the substrate that are masked by the thermochromic materials at certain temperatures, and not masked by the thermochromic materials at other temperatures.

What is claimed is: 
     
         1 . A thermochromic ink, comprising:
 a first thermochromic material that appears as a first color when it is below a first temperature and that appears substantially transparent when it is above said first temperature, and   a second thermochromic material that appears as a second color when it is below a second temperature and that appears substantially transparent when it is above said second temperature, said second temperature being higher than said first temperature,   whereby said ink appears as a third color which is a mixture of said first and second colors when said ink is at a temperature that is less than said first temperature, said ink appears as said second color when said ink is at a temperature that is less than said second temperature and greater than said first temperature, and said ink appears substantially colorless when said ink is at a temperature that is greater than said second temperature.   
     
     
         2 . The thermochromic ink of  claim 1 , in which said first, second, and third colors all differ. 
     
     
         3 . The thermochromic ink of  claim 1 , in which said first and second thermochromic materials each include microencapsulated leuco dyes. 
     
     
         4 . A thermochromic ink, comprising:
 a first thermochromic material that appears as a first color when it is below a first temperature and that appears substantially transparent when it is above said first temperature,   a second thermochromic material that appears as a second color when it is below a second temperature and that appears substantially transparent when it is above said second temperature,   a third thermochromic material that appears as a third color when it is below a third temperature and that appears substantially transparent when it is above said third temperature, said second temperature being higher than said first temperature and said third temperature being higher than said second temperature,   whereby said ink appears as a fourth color which is a mixture of said first, second, and third colors when said ink is at a temperature that is less than said first temperature, said ink appears as said fifth color which is a mixture of said second and third colors when said ink is at a temperature that is less than said second temperature and greater than said first temperature, said ink appears as said third color when said ink is at a temperature that is less than said third temperature and greater than said second temperature, and said ink appears substantially transparent when said ink is at a temperature that is greater than said third temperature.   
     
     
         5 . The thermochromic ink of  claim 4 , in which said first, second, and third colors all differ. 
     
     
         6 . The thermochromic ink of  claim 4 , in which said first, second, and third thermochromic materials each include microencapsulated leuco dyes. 
     
     
         7 . A thermochromic ink, comprising:
 a first thermochromic material that appears as a first color when it is below a first temperature and that appears substantially transparent when it is above said first temperature,   a second thermochromic material that appears as a second color when it is below a second temperature and that appears substantially transparent when it is above said second temperature, said second temperature being higher than said first temperature, and   a non-reactive material of a third color,   whereby said ink appears as a fourth color which is a mixture of said first, second, and third colors when said ink is at a temperature that is less than said first temperature, said ink appears as a fifth color which is a mixture of said second and third colors when said ink is at a temperature that is less than said second temperature and greater than said first temperature, and said ink appears as the third color when said ink is at a temperature that is greater than said second temperature.   
     
     
         8 . The thermochromic ink of  claim 7 , in which said first, second, and third colors all differ. 
     
     
         9 . The thermochromic ink of  claim 7 , in which said first and second thermochromic materials each include microencapsulated leuco dyes.