Photothermographic material

1. A black-and-white silver image-forming photothermographic material comprising, on one side of a support, an image forming layer containing at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent and a binder, and, on the other side of the support, a non-photosensitive back side layer, wherein the non-photosensitive back side layer contains at least gelatin as a binder, and a total quantity of magnesium and/or calcium element contained in the non-photosensitive back side layer is 1×10 −5 mol/m 2 to 1×10 −3 mol/m 2 .

2. The black-and-white silver image-forming photothermographic material of claim 1 , wherein a coating quantity of gelatin contained in a binder of the non-photosensitive back side layer is 1.0 g/m 2 to 3.0 g/m 2 .

3. The black-and-white silver image-forming photothermographic material of claim 1 , wherein a binder of the non-photosensitive back side layer contains gelatin in an amount of 50% by mass to 100% by mass based on the mass of the binder of the non-photosensitive back side layer.

4. The black-and-white silver image-forming photothermographic material of claim 1 , wherein the non-photosensitive back side layer is formed by coating two or more layers at the same time and subsequently drying the layers.

5. The black-and-white silver image-forming photothermographic material of claim 1 , wherein in the non-photosensitive back side layer, a coating liquid for forming an outermost layer, which is a most distant layer from the support, contains gelatin in an amount of 3.0% by mass to 10.0% by mass based on the mass of the coating liquid for forming the outermost layer.

6. The black-and-white silver image-forming photothermographic material of claim 5 , wherein a surface tension of the coating liquid for forming the outermost layer is at least 2 mN/m less than a surface tension of a coating liquid for forming a layer adjacent to the outermost layer.

7. The black-and-white silver image-forming photothermographic material of claim 5 , wherein a viscosity of a coating liquid for forming the outermost layer is 20 cP to 60 cP at a coating temperature.

8. The black-and-white silver image-forming photothermographic material of claim 6 , wherein a viscosity of the coating liquid for forming the layer adjacent to the outermost layer is 20 cP to 60 cP at a coating temperature.

9. A photothermographic material comprising, on one side of a support, an image forming layer containing at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent and a binder, and, on the other side of the support, an optically functional back layer containing at least one dye that can be discolored by thermal development processing, wherein at least one of the optically functional back layer and a layer adjacent thereto contains at least one polymer having a glass transition temperature of −10° C. to 120° C., the at least one polymer having a glass transition temperature of −10° C. to 120° C. is a latex of a styrene-butadiene copolymer, and the polymer in the back layer is in a range of 10% to 50% by mass based on gelatin in the back layer.

10. The photothermographic material of claim 9 , wherein the optically functional layer contains the at least one polymer having a glass transition temperature of −10° C. to 120° C.

11. The photothermographic material of claim 9 , wherein the optically functional layer contains a base precursor.

12. The photothermographic material of claim 9 , wherein at least one of the optically functional layer and the layer adjacent thereto contains gelatin.