Thermally developable materials with narrow disperse amorphous silica
View Patent ↗Thermally developable materials including photothermographic and thermographic materials having an outermost backside layer that includes amorphous silica particles having a narrow particle size distribution. The narrower particle size distribution provides reduced haze and increased surface roughness that reduces blocking and machine feeding at comparable weight percent. The materials can also include conductive layers underneath the outermost backside layer.
1. A thermally developable material that comprises a support having on one side thereof, one or more thermally developable imaging layers comprising a binder and in reactive association, a non-photosensitive source of reducible silver ions, and a reducing agent composition for said non-photo-sensitive source reducible silver ions, and
having disposed on the backside of said support an outermost backside layer comprising amorphous silica particles in one or more binder polymers, wherein the standard deviation divided by the mean volume diameter of said silica particles is less than 0.28.
2. The material of claim 1 wherein the mean volume diameter of said amorphous silica particles is at least 3 μm greater than the dry thickness of said outermost backside layer.
3. The material of claim 1 wherein said outermost backside layer has a dry thickness of from about 2.1 to about 2.5 μm and the mean volume diameter of said amorphous silica particles is from 7 and 9.5 μm with a standard deviation of less than 2.2 μm.
4. The material of claim 1 wherein said outermost backside layer has a Bekk Smoothness value of less than 20 seconds.
5. The material of claim 1 wherein said outermost backside layer comprises a polyvinyl acetal or cellulosic polymer as a binder.
6. The material of claim 1 wherein said outermost backside layer has a dry thickness of from about 1 to about 7 μm.
7. The material of claim 1 wherein said silica particles are present in said outermost backside layer in an amount of from about 20 to about 100 mg/m 2 .
8. The material of claim 1 further comprising a backside conductive layer underneath said outermost backside layer.
9. The material of claim 8 wherein said backside conductive layer comprises a metal oxide that is present in said backside conductive layer in an amount of from about 0.05 to about 1 g/m 2 distributed within one or more binder polymers that are present in an amount of from about 15 to about 60 weight %.
10. The material of claim 9 wherein said metal oxide comprises non-acicular zinc antimonate.
11. The material of claim 8 wherein said backside conductive layer has a dry thickness of from about 0.05 to about 1.1 μm.
12. The material of claim 8 wherein said backside conductive layer and said outermost backside layer have been formulated in organic solvents and have been simultaneously coated.
13. The material of claim 8 wherein said outermost backside layer comprises a cellulosic ester polymer and said backside conductive layer comprises a single phase mixture of a polyester and a polyvinyl acetal or a cellulose ester.
14. The material of claim 1 wherein said non-photosensitive source of reducible silver ions is a silver salt of an aliphatic carboxylate or a mixture of silver salts of aliphatic carboxylates, at least one of which is silver behenate.
15. The material of claim 1 that is a non-photosensitive thermographic material.
16. The material of claim 1 that is a photothermographic material further comprising a photosensitive silver halide.
17. The material of claim 8 wherein said outermost backside layer is immediately adjacent said backside conductive layer, and said outermost backside layer further comprises a smectite clay that has been modified with a quaternary ammonium compound.
18. A method of forming a visible image comprising:
(A) imagewise exposing the material of claim 1 that is a photothermographic material to electromagnetic radiation to form a latent image,
(B) simultaneously or sequentially, heating said exposed photothermographic material to develop said latent image into a visible image.
19. The method of claim 18 comprising using said visible image for a medical diagnosis.
20. A method of forming a visible image comprising thermal imaging of the material of claim 1 that is a thermographic material.
21. A black-and-white photothermographic material that comprises a support having on one side thereof, one or more thermally developable imaging layers comprising a binder and in reactive association, a photosensitive silver halide, a non-photosensitive source of reducible silver ions, and a reducing agent composition for said non-photosensitive source reducible silver ions, and
having disposed on the backside of said support, a simultaneously coated outermost backside layer and a non-imaging backside conductive layer:
a) said outermost backside layer comprising a film-forming polymer, amorphous silica particles, and a smectite clay that has been modified with a quaternary ammonium compound,
b) said non-imaging backside conductive layer being interposed between and directly adhering said support to said outermost backside layer, said non-imaging backside conductive layer comprising a mixture of two or more polymers that include a first polymer serving to promote adhesion of said backside conductive layer directly to said support, and a second polymer that is different than and forms a single phase mixture with said first polymer, wherein:
1) said backside conductive layer has a water electrode resistivity measured at 21.1° C. and 50% relative humidity of 1×10 12 ohms/sq or less,
2) the total amount of mixture of two or more polymers in said backside conductive layer is at least 15 weight %,
3) said backside conductive layer comprises a conductive metal oxide,
4) said film-forming polymer of said outermost backside layer is a cellulose acetate butyrate and said second polymer of said backside conductive layer is a cellulose acetate butyrate,
5) said silica particles are present in an amount of from about 30 to about 70 mg/m 2 of said outermost backside layer,
6) said outermost backside layer has a dry thickness of from about 1 to about 5 μm,
7) the mean volume diameter of said amorphous silica particles is about 7 to about 9.5 μm with a standard deviation of less than 2.2 μm,
8) said amorphous silica particles extend at least 5 μm above the surface of said dried outermost backside layer, and
9) said backside conductive layer has a dry thickness of from about 0.10 to about 0.3 μm.
22. The material of claim 21 wherein said photosensitive silver halide is one or more preformed silver halides and said non-photosensitive source of reducible silver ions comprises silver behenate.