Claims
- 1. A process for the preparation of photographic direct-positive emulsions which contain silver halide crystals of layered structure and can produce a latent internal image, which comprises causing a shell of silver halide to grow on chemically sensitised silver halide cores and subjecting the surface of the shell first to a sulphur/gold sensitisation and then to a digestion with a solution of an alkali metal iodide which contains 0.1 to 20 mol % of alkali metal iodide, relative to the silver halide, to at least partially convert the surface of the shell to silver iodide in an amount sufficient to avoid the necessity for using a fogging agent or a second exposure to develop a photographic material comprising the direct-positive emulsion.
- 2. In a photographic material containing at least one direct-positive emulsion, the improvement wherein the direct-positive emulsion is as defined in claim 1.
- 3. A process for the production of photographic direct-positive images, which comprises exposing and developing the photographic material of claim 2.
- 4. A process according to claim 1, wherein a silver halide core emulsion is used in which the coefficient of variation of the crystal size of the silver halide cores is less than 20%.
- 5. A process according to claim 1, wherein the chemical sensitisation of the silver halide cores is carried out with sulphur, selenium and/or tellurium compounds or with nobel metal compounds.
- 6. A process according to claim 1, wherein the chemical sensitisation of the silver halide cores is carried out with sulphur, selenium and/or tellurium compounds in combination with noble metal compounds.
- 7. A process according to claim 5, wherein the noble metal compounds are gold or iridium compounds.
- 8. A process according to claim 6, wherein the noble metal compounds are gold or iridium compounds.
- 9. A process according to claim 5, wherein 0 to 50 .mu.mol of sulfphur, selenium and/or tellurium compound and 0 to 25 .mu.mol of noble metal compounds per mol of silver are used for chemical sensitisation.
- 10. A process according to claim 6, wherein 0 to 50 .mu.mol of sulphur, selenium and/or tellurium compound and 0 to 25 .mu.mol of noble metal compounds per mol of silver are used for chemical sensitisation.
- 11. A process according to claim 5, wherein 0.1 to 100 .mu.mol of sulphur, selenium and/or tellurium compound and 0.01 to 200 .mu.mol of noble metal compound per mol of silver are used for the chemical sensitisation.
- 12. A process according to claim 6, wherein 0.1 to 100 .mu.mol of sulphur, selenium and/or tellurium compound and 0.01 to 200 .mu.mol of noble metal compound per mol of silver are used for the chemical sensitisation.
- 13. A process according to claim 1, wherein the chemically sensitised silver halide cores are coated with a shell of silver bromide, silver chloride or silver chlorobromide.
- 14. A process according to claim 13, wherein the silver halide cores are coated with such a quantity of silver halide shell that the ratio of the volume of the silver halide cores and of the volume of the shell is 1:50 to 5:1.
- 15. A process according to claim 1, wherein the shell is chemically sensitised with sodium thiosulphate in combination with gold thiocyanate or chloroauric acid.
- 16. A process according to claim 1, wherein 1 to 50 .mu.mol of sulphur sensitiser and 1 to 100 .mu.mol of noble metal sensitiser are used per mol of silver.
- 17. A process according to claim 16, wherein 4 to 15 .mu.mol of sulphur sensitiser and 3 to 25 .mu.mol of noble metal sensitiser are used per mol of silver.
- 18. A process according to claim 1, wherein the digestion is carried out with a solution which contains 0.5 to 10 mol % of alkali metal iodide, relative to silver halide.
- 19. A process according to claim 1, wherein the pAg value is adjusted to 8-9 after the treatment of the shell with a solution of an alkali metal iodide.
- 20. A process according to claim 1, wherein spectral sensitisation is effected simultaneously with the sulphur/gold sensitisation of the shell.
- 21. A process according to claim 1, wherein the shell treated with iodide ions is spectrally sensitised.
- 22. A direct-positive emulsion obtained by the process according to claim 1.
Priority Claims (1)
Number |
Date |
Country |
Kind |
5268/84 |
Nov 1984 |
CHX |
|
Parent Case Info
This application is a continuation of now abandoned application Ser. No. 790,908, filed Oct. 24, 1985.
US Referenced Citations (4)
Continuations (1)
|
Number |
Date |
Country |
Parent |
790908 |
Oct 1985 |
|