Image forming method using photothermographic material

1. An image forming method for a photothermographic material comprising, on at least one side of the support, at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent and a binder, wherein the photothermographic material is a sheet material and has a gamma value of 2.0 to 4.0 at an optical density of 1.2 in a photographic characteristic curve, comprising:

imagewise exposing the photothermographic material to laser radiation: and developing the photothermographic material in a thermal developing device configured such that a distance between an exposing section and a developing section is not more than 50 cm and the photothermographic material begins to be developed at an exposed portion thereof while another portion is still being exposed.

2. The method of claim 1 , wherein the photothermographic material is thermally developed while conveyed at a speed of not less than 23 mm/sec.

3. The method of claim 1 , wherein the photosensitive silver halide includes at least two silver halide emulsions having different grain sizes.

4. The method of claim 1 , wherein the non-photosensitive organic silver salt is prepared in the presence of the photosensitive silver halide.

5. The method of claim 1 , wherein:

the photothermographic material has a maximum photosensitive wavelength of from 600 nm to less than 700 nm;

the exposing section of the thermal developing device has a laser irradiation means; and

a distance between a scanning line of the laser irradiation means and an inserting portion of the thermal developing section is not more than 50 cm.

6. An image forming method for a photothermographic material comprising an image forming layer formed on at least one side of the support, the image forming layer comprising at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent and a binder, wherein:

the non-photosensitive organic silver salt includes a silver salt of fatty acid; the photothermographic material has the silver salt of fatty acid at an application amount of 5 mmol/m 2 to 18 mmol/m 2 , comprising:

imagewise exposing the photothermoaranhic material to laser radiation: and developing the photothermographic material in a thermal developing device configured such that a distance between an exposing section and a developing section is not more than 50 cm and the photothermographic material begins to be developed at an exposed portion thereof while another portion is still being exposed.

7. The method of claim 6 , wherein:

the photothermographic material has a protective layer formed at the side of the support at which the image forming layer is formed and at a position farther away from the support than the image forming layer; and

the protective layer includes a compound which chemically reacts with materials vaporized at the time of thermal development to form non-volatile materials as a trapping agent.

8. The method of claim 7 , wherein the trapping agent of the vaporized materials is a compound having a —NH— bond.

9. The method of claim 6 , wherein the photothermographic material has a barrier layer formed at the side of the support at which the image forming layer is formed and at a position farther away from the support than the image forming layer, the barrier layer preventing transmission of the material vaporized at the time of thermal development.

10. The method of claim 9 , wherein the barrier layer includes at least one polymer selected from a group consisting of polyvinyl alcohol, polystyrene and a copolymer thereof, polyvinyl chloride, polyvinyl acetate and a copolymer thereof, water soluble polyester, water insoluble polyester, gelatin and a derivative thereof, and polyvinyl pyrrolidone.

11. The method of claim 9 , wherein the barrier layer includes water insoluble polyester having a glass transition temperature of not less than 150° C. and a number average molecular weight of not less than 10,000.

12. The method of claim 9 , wherein the barrier layer includes polyvinyl alcohol having a saponification rate of not less than 88%.

13. The method of claim 9 , wherein the barrier layer includes polystyrene having at least two epoxy groups in a molecule thereof.

14. The method of claim 9 , wherein the barrier layer includes one of polyacrylate and polymethacrylate.

15. The method of claim 9 , wherein the barrier layer includes one of polyacrylate and polymethacrylate having at least two epoxy groups in a molecule thereof.

16. The method of claim 7 , wherein the protective layer of the photothermographic material has a thickness of 1 μm to 5 μm.

17. The method of claim 9 , wherein the barrier layer of the photothermographic material has a thickness of 1 μm to 5 μm.

18. The method of claim 6 , wherein the silver salt of fatty acid contains silver behenate not less than 50 mol %.