Photothermographic material

1. A photothermographic material comprising: an image forming layer comprising at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent, and a binder on at least one side of a support; an outermost layer on the same side of the support as the image forming layer; and a non-photosensitive intermediate layer between the outermost layer and the image forming layer,

wherein 50% by weight or more of a binder of the non-photosensitive intermediate layer is formed by a hydrophobic polymer latex; the outermost layer has a mean thickness of from 0.1 μm to 0.45 μm; the non-photosensitive intermediate layer further contains poly(vinyl alcohol) derivative as a viscosity-increasing agent, and a concentration of the poly(vinyl alcohol) derivative added to a coating solution of the non-photosensitive intermediate layer is in the range of from 0.05 % by weight to 20 % by weight in the coating solution so that the non-photosensitive intermediate layer has a variation coefficient of a thickness distribution of 50% or less based on a mean thickness of the non-photosensitive intermediate layer

wherein the mean thickness and the variation coefficient of the thickness distribution of the non-photosensitive intermediate layer are measured by observation of cross sections of the photothermographic material by means of a scanning electron microscope, and the measurement includes:

preparing cross sections perpendicular to a plane of the photothermographic material;

observing the cross sections over a length of 1 mm by a scanning electron microscope to determine a cross section curve C 1 for the lower face of the non-photosensitive intermediate layer and a cross section curve C 2 for the upper face of the non-photosensitive intermediate layer;

determining the mean thickness T 1 of the non-photosensitive intermediate layer by calculating a length from center lines of C 1 and C 2 , provided that, in the case where C 2 is not clear depending on observation conditions, the mean thickness can be calculated from a coating amount of the non-photosensitive intermediate layer;

calculating an average roughness Rz for C 1 expressed by ten point scores; and

calculating the variation coefficient from the following equation, σ(%)=Rz/T 1 ×100.

2. The photothermographic material according to claim 1 , wherein the variation coefficient of a thickness distribution of the non-photosensitive intermediate layer is 30% or less based on the mean thickness of the non-photosensitive intermediate layer.

3. The photothermographic material according to claim 2 , wherein the variation coefficient of a thickness distribution of the non-photosensitive intermediate layer is 10% or less based on the mean thickness of the non-photosensitive intermediate layer.

4. The photothermographic material according to claim 1 , wherein the mean thickness of the non-photosensitive intermediate layer is from 0.1 μm to 10 μm.

5. The photothermographic material according to claim 4 , wherein the mean thickness of the non-photosensitive intermediate layer is from 0.5 μm to 5 μm.

6. The photothermographic material according to claim 1 , wherein the mean thickness of the non-photosensitive intermediate layer is from 0.5 μm to 5 μm and the variation coefficient of a thickness distribution thereof is 10% or less based on the mean thickness of the non-photosensitive intermediate layer.

7. The photothermographic material according to claim 6 , wherein the mean thickness of the outermost layer is from 0.3 μm to 0.45 μm.

8. The photothermographic material according to claim 1 , wherein 50% by weight or more of a binder of the outermost layer is formed by a hydrophilic polymer.

9. The photothermographic material according to claim 8 , wherein the hydrophilic polymer is gelatin.

10. The photothermographic material according to claim 1 , wherein the outermost layer contains a dispersion of a lubricant.

11. The photothermographic material according to claim 1 , wherein 50% by weight or more of the binder of the image forming layer is formed by a hydrophobic polymer latex.

12. The photothermographic material according to claim 1 , wherein the non-photosensitive intermediate layer comprises an aggregation stabilizer.

13. The photothermographic material according to claim 12 , wherein the aggregation stabilizer is at least one compound selected from the group consisting of an amphoteric surfactant, a nonionic surfactant, and modified polyvinyl alcohols.

14. The photothermographic material according to claim 1 , wherein the hydrophobic polymer latex of the non-photosensitive intermediate layer is a copolymerized polymer latex having a monomer component represented by the following formula (M) in a range of from 10% by weight to 70% by weight:

CH 2 ═CR 01 —CR 02 ═CH 2   Formula (M)

wherein R 01 and R 02 each independently represent one selected from a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a halogen atom, or a cyano group.

15. The photothermographic material according to claim 14 , wherein, in formula (M), both of R 01 and R 02 represent a hydrogen atom, or one of R 01 or R 02 represents a hydrogen atom and the other represents a methyl group.

16. The photothermographic material according to claim 1 , wherein at least one of the non-photosensitive intermediate layer or the outermost layer comprises at least one of a non-photosensitive organic silver salt or a non-photosensitive inorganic silver compound.

17. The photothermographic material according to claim 1 , wherein at least one of the non-photosensitive intermediate layer or the outermost layer comprises a non-photosensitive organic silver salt.

18. The photothermographic material according to claim 1 , wherein the concentration of the poly(vinyl alcohol) derivative added to the coating solution of the non-photosensitive intermediate layer is in the range of from 0.1% by weight to 10% by weight in the coating solution.