Methods for direct thermal recording media based on selective change of state
Direct thermal recording media are designed to operate based on a thermally-induced change of state rather than a thermally-induced chemical reaction between a leuco dye and an acidic developer. The media use two types of solid scattering particles, one of which changes its state from solid to liquid during printing, and the other of which does not. The former particles, upon melting, fill spaces between the latter particles, thus eliminating or substantially reducing light scattering, which makes an underlying colorant visible at selected print locations where heat is locally applied. The media can provide high quality thermally-produced images at print speeds at least as high as 10 inches per second (ips).
1. A method of making a recording medium, comprising:
providing a substrate and a colorant;
forming a thermal insulating layer atop the substrate;
forming a first light-scattering layer atop the thermal insulating layer, the first light-scattering layer being porous and comprising first solid scattering particles having a first melting point; and
as part of forming the first light-scattering layer, or in a separate step of forming a second light-scattering layer, providing a plurality of second solid scattering particles not being chemically reactive, and the second solid scattering particles having a second melting point;
wherein the second melting point is lower than the first melting point such that the recording medium is adapted for dynamic thermal printing wherein the second solid scattering particles, but not the first solid scattering particles, melt at selected print locations, and the second solid scattering particles, when melted, fill spaces between the first solid scattering particles; and
wherein providing the colorant includes providing the colorant in the thermal insulating layer.
2. The method of claim 1 , wherein providing the colorant in the thermal insulating layer includes dispersing the colorant throughout the thermal insulating layer.
3. The method of claim 1 , wherein the substrate comprises a polymeric film.
4. The method of claim 3 , wherein the polymeric film comprises polypropylene.
5. The method of claim 1 , wherein the second particles comprise a non-polymeric crystalline organic material.
6. The method of claim 1 , wherein the recording medium so made provides a print quality characterized by an ANSI value of at least 1.5 when used with a thermal printer energy setting of 11.7 mJ/mm 2 at a print speed of 6, 8, or 10 ips.
7. A method of making a recording medium, comprising:
providing a substrate;
forming a thermal insulating layer atop the substrate;
forming a light-scattering layer atop the thermal insulating layer, the light-scattering layer being porous and comprising first solid scattering particles having a first melting point;
as part of forming the light-scattering layer, providing a plurality of second solid scattering particles proximate the light-scattering layer, the first and second solid scattering particles not being chemically reactive, the second solid scattering particles having a second melting point; and
providing a colorant beneath the light scattering layer;
wherein the second melting point is lower than the first melting point such that the recording medium is adapted for dynamic thermal printing wherein the second solid scattering particles, but not the first solid scattering particles, melt at selected print locations, and the second solid scattering particles, when melted, fill spaces between the first solid scattering particles.
8. The method of claim 7 , wherein providing the colorant includes providing the colorant on the thermal insulating layer.
9. The method of claim 7 , wherein providing the colorant includes providing the colorant in the thermal insulating layer.
10. The method of claim 9 , wherein providing the colorant in the thermal insulating layer includes dispersing the colorant throughout the thermal insulating layer.
11. The method of claim 7 , wherein providing the colorant includes providing the colorant under the thermal insulating layer.
12. The method of claim 11 , wherein forming the thermal insulating layer includes forming the thermal insulating layer atop the colorant.
13. The method of claim 7 , wherein the substrate comprises a polymeric film.
14. The method of claim 13 , wherein the polymeric film comprises polypropylene.
15. The method of claim 7 , wherein the second particles comprise a non-polymeric crystalline organic material.
16. The method of claim 7 , wherein the recording medium so made provides a print quality characterized by an ANSI value of at least 1.5 when used with a thermal printer energy setting of 11.7 mJ/mm 2 at a print speed of 6, 8, or 10 ips.