Thermally-insulating layers and direct thermal imaging members containing same
View Patent ↗Multicolor thermal imaging members are described that comprise color-forming layers that are separated by thermally-insulating layers and can be addressed with a thermal printing head in contact with a surface to form an image. The thermally-insulating layers are designed to be as thin as possible consistent with at least partially independent addressing of the color-forming layers, and are formulated so as not to lead to instabilities either before or after printing or to give rise to dimensional changes of a thermal imaging member when it is subjected to changes in temperature or humidity. Coating compositions for manufacturing such thermally-insulating layers are also provided.
1. A thermal imaging member comprising:
(A) a substrate having first and second opposed surfaces;
(B) first and second color-forming layers carried by said first surface of said substrate; said first color-forming layer being closer to said first surface of said substrate than said second color-forming layer; and
(C) a thermally-insulating layer between said first and second color-forming layers, said thermally-insulating layer comprising at least 50% by weight of a polymeric latex material and at least 5% by weight of an organic material that has a glass transition temperature of at least 80° C.
2. The thermal imaging member of claim 1 wherein said organic material is a phenolic compound with molecular weight less than 2000.
3. The thermal imaging member of claim 1 wherein said organic material is chosen from the group consisting of 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl)isocyanurate and 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane.
4. The thermal imaging member of claim 1 , further comprising a third color-forming layer carried by said first surface of said substrate, said third color-forming layer being further from said first surface of said substrate than said second color-forming layer.
5. The thermal imaging member of claim 4 , further comprising a second thermally-insulating layer between said second and said third color-forming layers, said second thermally-insulating layer comprising at least 50% by weight of a polymeric latex material and at least 5% by weight of an organic material that has a glass transition temperature of at least 80° C.
6. The thermal imaging member of claim 5 wherein said organic material is a phenolic compound with molecular weight less than 2000.
7. The thermal imaging member of claim 5 wherein said organic material is chosen from the group consisting of 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl)isocyanurate and 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane.
8. The thermal imaging member of claim 5 wherein the square of the thickness of the thermally-insulating layer separating said first and second color-forming layers divided by its thermal diffusivity is at least four times greater than the square of the thickness of said second thermally-insulating layer divided by its thermal diffusivity.