Photothermographic material and method for preparing photosensitive silver halide emulsion

1. A photothermographic material comprising, on at least one surface of a support, at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent and a binder, wherein the material contains a silver iodide complex-forming agent, and wherein

1) the photosensitive silver halide has an average silver iodide content of 40 mol % or higher,

2) 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, and

3) a mean equivalent spherical diameter of the photosensitive silver halide grains is from 0.2 μm to 5 μm and a variation coefficient of an equivalent spherical diameter distribution of the photosensitive silver halide grains is 30% or less.

2. The photothermographic material according to claim 1 , wherein a mean equivalent circular diameter of the photosensitive silver halide grains is from 0.2 μm to 5 μm and a variation coefficient of an equivalent circular diameter distribution of the photosensitive silver halide grains is 30% or less.

3. The photothermographic material according to claim 1 , wherein the average silver iodide content is 80 mol % or higher.

4. The photothermographic material according to claim 1 , wherein the average silver iodide content is 90 mol % or higher.

5. The photothermographic material according to claim 1 , wherein the aspect ratio is from 5 to 200.

6. A method for preparing a photosensitive silver halide for use in a photothermographic material according to claim 1 , wherein grains are formed in the presence of at least one substance selected from an amino group-modified gelatin in which 20% or more of all of the amino groups are modified and a silver halide solvent.

7. The method for preparing a photosensitive silver halide according to claim 6 , wherein the grains are formed in the presence of the silver halide solvent.

8. The method for preparing a photosensitive silver halide according to claim 6 , wherein the grains are formed in the presence of the amino group-modified gelatin in which 20% or more of all of the amino groups are modified.

9. The method for preparing a photosensitive silver halide according to claim 6 , wherein the grains are formed in the presence of the amino group-modified gelatin in which 20% or more of all of the amino groups are modified and the silver halide solvent.

10. The method for preparing a photosensitive silver halide according to claim 7 , wherein an amount of the silver halide solvent being added is increased while the grains are formed.

11. The method for preparing a photosensitive silver halide according to claim 7 , wherein the silver halide solvent is present from the beginning of nucleation.

12. The method for preparing a photosensitive silver halide according to claim 7 , wherein the silver halide solvent is a compound containing at least one atom selected from a sulfur atom, a selenium atom, and a tellurium atom.

13. The method for preparing a photosensitive silver halide according to claim 12 , wherein the silver halide solvent is a compound represented by formula (I):

L a1 -(A a1 -L a2 ) r -A a2 -L a3   Formula (I)

wherein L a1 and L a3 each independently represent one selected from an aliphatic group, an aromatic hydrocarbon group, and a heterocyclic group, and L a2 represents one selected from a divalent aliphatic group, a divalent aromatic hydrocarbon group, a divalent substituted or unsubstituted heterocyclic linking group, and a linking group made up of a combination thereof; A a1 and A a2 each independently represent one selected from —S—, —Se—, —Te—, —O—, —NR a20 —, —CO—, —SO 2 —, and a group made up of a combination thereof; r represents an integer from 0 to 10; L a1 and L a3 may be substituted by one selected from —SO 3 M a1 , —PO 3 M a2 M a3 , —NR a1 (R a2 ), —N + R a3 (R a4 )(R a5 ).X a1 − , —SO 2 NR a6 (R a7 ), —NR a8 SO 2 R a9 , —CONR a10 (R a11 ), —NR a12 COR a13 , —SO 2 R a14 , —PO(—NR a15 (R a16 )) 2 , —NR a17 CONR a18 (R a19 ), —COOM a4 , and a heterocyclic group; M a1 , M a2 , M a3 , and M a4 each independently represent one selected from a hydrogen atom and a counter cation; R a1 to R a20 each independently represent one selected from a hydrogen atom, an aliphatic group, and an aromatic hydrocarbon group; and X a1 − represents an anion; provided that at least one of A a1 and A a2 represents one selected from —S—, —Se—, and —Te—.

14. The method for preparing a photosensitive silver halide according to claim 12 , wherein the silver halide solvent is a compound represented by formula (II):

wherein X b and Y b each independently represent one selected from an aliphatic group, an aromatic hydrocarbon group, a heterocyclic group, —N(R b1 )R b2 , —N(R b3 )N(R b4 )R b5 , —OR b6 , and —SR b7 ; X b and Y b may form a ring; X b and Y b each may be substituted by one selected from the group consisting of a carboxylic acid, a salt thereof, a sulfonic acid, a salt thereof, an amino group, an ammonium group, and a hydroxy group; R b1 , R b2 , R b3 , R b4 , and R b5 independently represent one of a hydrogen atom, an aliphatic group, an aromatic hydrocarbon group, and a heterocyclic group; and R b6 and R b7 each independently represent one of a hydrogen atom, a cation, an aliphatic group, an aromatic hydrocarbon group, and a heterocyclic group.

15. The method for preparing a photosensitive silver halide according to claim 8 , wherein the amino group-modified gelatin is a gelatin having at least one carboxyl group newly introduced when the amino groups are chemically modified.

16. The method for preparing a photosensitive silver halide according to claim 15 , wherein the gelatin is a gelatin having amino groups modified by phthalation.

17. The method for preparing a photosensitive silver halide according to claim 15 , wherein the gelatin is a gelatin having amino groups modified by trimellitation.

18. The method for preparing a photosensitive silver halide according to claim 15 , wherein the gelatin is a gelatin having amino groups modified by pyromellitation.

19. The method for preparing a photosensitive silver halide according to claim 15 , wherein the gelatin is a gelatin having amino groups modified by succination.

20. The photothermographic material according to claim 1 , wherein the silver iodide complex-forming agent is a compound represented by formula (C3):

wherein R 31 to R 35 each independently represent a hydrogen atom or a substituent.

21. The photothermographic material according to claim 20 , wherein the substituent in R 31 to R 35 is a halogen atom, an alkyl group, an aryl group, a carbamoyl group, a hydroxy group, an alkoxy group, an aryloxy group, a carbamoyloxy group, an amino group, an acylamino group, an ureido group, an alkoxycarbonylamino group, or an aryloxycarbonylamino group.

22. The photothermographic material according to claim 1 , wherein the silver iodide complex-forming agent is a compound represented by formula (C4):

wherein R 41 to R 44 each independently represent a hydrogen atom or a substituent.

23. The photothermographic material according to claim 22 , wherein the substituent in R 41 to R 44 is an alkyl group, an alkenyl group, an alkynyl group, an aryl group, a hydroxy group, an alkoxy group, an aryloxy group, or a hetecyclic oxy group.

24. The photothermographic material according to claim 1 , wherein the silver iodide complex-forming agent is a compound represented by formula (C5):

wherein R 51 to R 56 each independently represent a hydrogen atom or a substituent.

25. The photothermographic material according to claim 24 , wherein the substituent in R 51 to R 56 is an alkyl group, an alkenyl group, an alkynyl group, an aryl group, a hydroxy group, an alkoxy group, or an aryloxy group.