Thermal indicators
View Patent ↗A thermal indicator using indicia formed by opaque ink applied to a thermal imaging material element is described. The ink is substantially the same color as the imaging element background and remains substantially hidden until the imaging element background changes color when heated. Time-temperature exposure indicating labels can be prepared using a printer with direct thermal type and ink jet type print heads.
1. A method of hiding and revealing an authentication print to indicate whether a sheet media item is authentic, the method comprising:
printing with ink of a first color the authentication print on a first portion of the sheet media item having a thermally sensitive coating of an initial color which substantially matches the first color of the authentication print to render the first color of the authentication print substantially invisible against the initial color of the thermally sensitive coating and thereby to hide the authentication print;
applying heat to a second portion of the sheet media item which is different from the first portion of the sheet media item to provide a message of a second color on the second portion of the sheet media item, wherein the second color of the message on the second portion of the sheet media item is different from the first color of the authentication print on the first portion of the sheet media item; and
at the same time heat is being applied to the second portion of the sheet media item, applying heat to the first portion of the sheet media item to change the thermally sensitive coating from the initial color which substantially matches the first color of the authentication print to a different color to render the first color of the authentication print visible against the different color of the thermally sensitive coating and thereby to reveal the authentication print to indicate that the sheet media item is authentic.
2. A method according to claim 1 , wherein (i) the first color is a color which is substantially white, and (ii) the second color is a color which is other than substantially white.
3. A method according to claim 1 , wherein the second color is a color which is substantially black.
4. A method according to claim 1 , wherein (i) the first color is a color which is substantially white, and (ii) the second color is a color which is substantially black.
5. A method of hiding and revealing an authentication print to indicate whether a sheet media item is authentic, the method comprising:
printing with ink of a substantially light color the authentication print on a first portion of the sheet media item having a thermally sensitive coating of an initial color which substantially matches the substantially light color of the authentication print to render the substantially light color of the authentication print substantially invisible against the initial color of the thermally sensitive coating and thereby to hide the authentication print;
applying heat to a second portion of the sheet media item which is different from the first portion of the sheet media item to provide a message of a color which is a substantially dark color on the second portion of the sheet media item; and
at the same time heat is being applied to the second portion of the sheet media item, applying heat to the first portion of the sheet media item to change the thermally sensitive coating from the initial color which substantially matches the substantially light color of the authentication print to a different color to render the substantially light color of the authentication print visible against the different color of the thermally sensitive coating and thereby to reveal the authentication print to indicate that the sheet media item is authentic.
6. A method according to claim 5 , wherein the different color to which the thermally sensitive coating changes from the initial color is substantially black.
7. A method according to claim 5 , wherein the substantially light color of the ink is a substantially white color.
8. A method according to claim 5 , wherein (i) the different color to which the thermally sensitive coating changes from the initial color is substantially black, and (ii) the substantially light color of the ink is a substantially white color.
9. A method of hiding and revealing an authentication print to indicate whether a sheet media item is authentic, the method comprising:
printing with ink of a substantially white color the authentication print on a first portion of the sheet media item having a thermally sensitive coating of an initial color which substantially matches the substantially white color of the authentication print to render the substantially white color of the authentication print substantially invisible against the initial color of the thermally sensitive coating and thereby to hide the authentication print;
applying heat to a second portion of the sheet media item which is different from the first portion of the sheet media item to provide a message of a substantially black color on the second portion of the sheet media item; and
at the same time heat is being applied to the second portion of the sheet media item, applying heat to the first portion of the sheet media item to change the thermally sensitive coating from the initial color which substantially matches the substantially white color of the authentication print to a different color to render the substantially white color of the authentication print visible against the different color of the thermally sensitive coating and thereby to reveal the authentication print to indicate that the sheet media item is authentic.
10. A method according to claim 9 , wherein the different color to which the thermally sensitive coating changes from the initial color is substantially black.
11. A method according to claim 9 , wherein the substantially white color of authentication print is a substantially opaque white color.
12. A method according to claim 9 , wherein (i) the different color to which the thermally sensitive coating changes from the initial color is substantially black, and (ii) the substantially white color of the ink is a substantially opaque white color.