Image forming method for the photothermographic material

1. An image forming method comprising: imagewise exposing and thermal developing a sheet of photothermographic material using an image recording apparatus,

wherein the image recording apparatus has at least the following portions (A) to (D):

(A) a laser irradiation portion that scans the photothermographic material with a laser beam based on image data to expose the photothermographic material;

(B) a transport portion that transports the photothermographic material in the laser irradiation portion;

(C) a thermal developing portion, disposed on the side downstream from the transport portion, and in which a part of one sheet of the photothermographic material is imagewise exposed by the laser irradiation portion and simultaneously a part of the sheet having been already imagewise exposed is developed by heating; and

(D) a guide portion, provided between the transport portion and the thermal developing portion, and allowing a flexion of the photothermographic material generated by a difference between a transport speed in the transport portion and a transport speed in the thermal developing portion:

wherein the photothermographic material comprises at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent represented by following formula (R) and a binder on at least one surface of a support;

wherein R 11 and R 11′ each independently represents an alkyl group having 1 to 20 carbon atoms, R 12 and R 12′ each independently represents a hydrogen atom or a group capable of substituting for a hydrogen atom on a benzene ring, L represents a —S— group or a —CHR 13 — group, R 13 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and X and X 1 each independently represents a hydrogen atom or a group capable of substituting for a hydrogen atom on a benzene ring; and

wherein the photosensitive silver halide contains at least two preformed photosensitive silver halides having respective sensitivities different from each other for a light with the same exposure wavelength and a silver iodide content of the photosensitive silver halide is 40% by mole or more.

2. The image forming method according to claim 1 , wherein the thermal development is started on the sheet within 60 sec after the imagewise exposure.

3. The image forming method according to claim 1 , wherein the thermal development is started on the sheet within 15 sec after the imagewise exposure.

4. The image forming method according to claim 1 , wherein V 1 is a transport speed in the transport portion and V 2 is a transport speed in the thermal developing portion, and V 1 and V 2 satisfy the following relationship: 0.7<V 2 /V 1 ≦1.0.

5. The image forming method according to claim 1 , wherein a difference in sensitivity between the at least two preformed photosensitive silver halides is 0.3 to 1.0 in terms of log E.

6. The image forming method according to claim 1 , wherein the maximum density of a photographic characteristic curve obtained by imagewise exposure and thermal development of the photothermographic material is 3.0 or more, and a y value at a density of 0.5 is 0.8 to 1.8 and a γ value at a density of 1.0 is 2.2 to 3.8.

7. The image forming method according to claim 1 , wherein the at least two preformed photosensitive silver halides have respective average grain sizes, which are different from each other.

8. The image forming method according to claim 7 , wherein the average grain sizes of the preformed photosensitivesilver halides are 5 nm to 100 nm.

9. The image forming method according to claim 7 , wherein a difference in average grain size between the at least two preformed photosensitive silver halides is 20 nm to 95 nm.

10. The image forming method according to claim 1 , wherein the photothermographic material further comprises a compound that can be one-electron-oxidized to provide a one-electron oxidation product, which releases one or more electrons.

11. The image forming method according to claim 1 , wherein at least one of the preformed photosensitive silver halide is chemically sensitized.

12. The image forming method according to claim 1 , wherein the photothermographic material further comprises a compound expressed by the following formula (PO):

Q—(Y) n —C(Z 1 )(Z 2 )X  formula (PO)

wherein Q represents a heterocyclic group, Y represents a divalent linkage group, n represents 0 or 1, Z 1 and Z 2 each independently represents a halogen atom, and X represents a hydrogen atom or an electron-withdrawing group.

13. The image forming method according to claim 1 , wherein the binder is a polymer latex.

14. The image forming method according to claim 1 , wherein the photothermographic material further comprises a developing accelerator.

15. The image forming method according to claim 1 , wherein the photothermographic material further comprises a hydrogen bonding compound.