Photothermographic material and image forming method

1. An image forming method using a photothermographic material comprising, on at least one side of a support, an image forming layer comprising at least a photosensitive silver halide, a non-photosensitive silver salt of a fatty acid, a reducing agent, and a binder, wherein the photothermographic material comprises an acetylene compound represented by the following formula (II) or a salt thereof:

wherein R 2 represents a substituted or unsubstituted alkyl group, aryl group, or heterocyclic group; R 3 represents a hydrogen atom or a substituent substituting for a hydrogen atom on a benzene ring; n1 represents an integer of 1; and n2 represents an integer of from 0 to 4;

wherein the image forming method comprises:

1) imagewise exposing the photothermographic material with lights to record a latent image on the photothermographic material; and

2) thermally developing the photothermographic material at a temperature of 107° C. to 140° C. to convert the latent image into a visible image by thermal development.

2. The image forming method according to claim 1 , wherein the compound represented by formula (II) or a salt thereof is a compound represented by the following formula (III) or a salt thereof:

wherein R 2 has the same meaning as in formula (II).

3. The image forming method according to claim 1 , wherein a mean grain size of the photosensitive silver halide is from 0.01 μm to 0.20 μm.

4. The image forming method according to claim 3 , wherein the binder is formed by a polymer latex.

5. The image forming method according to claim 3 , wherein the photosensitive silver halide is subjected to gold sensitization.

6. The image forming method according to claim 4 , wherein the polymer latex contains 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 the group consisting of a hydrogen atom, an alkyl group having from 1 to 6 carbon atoms, a halogen atom, and a cyano group.

7. The image forming method according to claim 6 , 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.

8. The image forming method according to claim 1 , wherein the photothermographic material further comprises at least one development accelerator represented by the following formulae (A-1) or (A-2):

Q 1 -NHNH-Q 2   Formula (A-1)

wherein Q 1 represents an aromatic group or a heterocyclic group which bonds to —NHNH-Q 2 at a carbon atom; and Q 2 represents one selected from a carbamoyl group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a sulfonyl group, or a sulfamoyl group; and

wherein R 1 represents one selected from an alkyl group, an acyl group, an acylamino group, a sulfonamide group, an alkoxycarbonyl group, or a carbamoyl group; R 2 represents one selected from a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, an acyloxy group, or a carbonic acid ester group; R 3 and R 4 each independently represent a hydrogen atom or a group substituting for a hydrogen atom on a benzene ring; and R 3 and R 4 may bond to each other to form a condensed ring.

9. The image forming method according to claim 1 , wherein the photosensitive silver halide has an average silver iodide content of 40 mol % or higher.

10. The image forming method according to claim 9 , wherein the compound represented by formula (II) or a salt thereof is a compound represented by the following formula (III) or a salt thereof:

wherein R 2 has the same meaning as in formula (II).

11. The image forming method according to claim 9 , wherein 50% or more of a total projected area of the photosensitive silver halide is occupied by tabular grains having an aspect ratio of 2 or more.

12. The image forming method according to claim 11 , wherein a mean equivalent circular diameter of the tabular grains is from 0.3 μm to 5.0 μm.

13. The image forming method according to claim 11 , wherein the aspect ratio of the tabular grains is from 5 to 100.

14. The image forming method according to claim 9 , wherein the average silver iodide content of the photosensitive silver halide is 80 mol % or higher.

15. The image forming method according to claim 9 , wherein the photosensitive silver halide is subjected to gold sensitization.

16. The image forming method according to claim 9 , wherein the photothermographic material further comprises a silver iodide complex-forming agent.

17. The image forming method according to claim 9 , wherein the photothermographic material further comprises at least one development accelerator represented by the following formulae (A-1) or (A-2):

Q 1 -NHNH-Q 2   Formula (A-1)

wherein Q 1 represents an aromatic group or a heterocyclic group which bonds to —NHNH-Q 2 at a carbon atom; and Q 2 represents one selected from a carbamoyl group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a sulfonyl group, or a sulfamoyl group; and

wherein R 1 represents one selected from an alkyl group, an acyl group, an acylamino group, a sulfonamide group, an alkoxycarbonyl group, or a carbamoyl group; R 2 represents one selected from a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, an acyloxy group, or a carbonic acid ester group; R 3 and R 4 each independently represent a hydrogen atom or a group substituting for a hydrogen atom on a benzene ring; and R 3 and R 4 may bond to each other to form a condensed ring.

18. The image forming method according to claim 9 , wherein the photothermographic material comprises the image forming layer on both sides of the support.

19. The image forming method according to claim 1 , wherein the image forming layer is prepared by:

preparing the photosensitive silver halide containing the compound represented by formula (II);

preparing a coating solution for the image forming layer by adding the photosensitive silver halide and at least the non-photosensitive silver salt of a fatty acid, the reducing agent, and the binder;

and coating the coating solution.

20. An image forming method, which is an X-ray image forming method using a photothermographic material comprising, on at least one side of a support, an image forming layer comprising at least a photosensitive silver halide, a non-photosensitive silver salt of a fatty acid, a reducing agent, and a binder, wherein the photosensitive silver halide has an average silver iodide content of 40 mol % or higher, and the photothermographic material comprises an acetylene compound represented by the following formula (II) or a salt thereof:

wherein R 2 represents a substituted or unsubstituted alkyl group, aryl group, or heterocyclic group; R 3 represents a hydrogen atom or a substituent substituting for a hydrogen atom on a benzene ring; n1 represents an integer of 1; and n2 represents an integer of from 0 to 4;

wherein the image forming method comprises:

1) bringing the photothermographic material into contact with a fluorescent intensifying screen;

2) imagewise exposing the photothermographic material with X-rays to record a latent image on the photothermographic material; and

3) thermally developing the photothermographic material at a temperature of 107° C. to 140° C. to convert the latent image into a visible image by thermal development.