| 摘要 |
1,200,393. Direct positive photographic elements. E.I. DU PONT DE NEMOURS & CO. Sept.11, 1968 [Sept.12, 1967], No.43272/68. Heading G2C. Unfogged photographic elements which after exposure to actinic radiation can be developed to give positive images directly, comprise a supported internal latent image type halide emulsion layer containing a water-permeable organic colloid binding agent and a metal compound reducing agent for the silver halide, the metal in the compound capable of exhibiting different valencies and the compound employed being one in which the metal does not exhibit its highest valency; the emulsion has a pH less than 7 and sufficiently low to prevent oxidation of the reducing agent. Preferably the reducing agent is Sn Cl 2 , Ti Cl 3 or ferrocent, the pH is lowered by H Cl, optionally together with borax, and the emulsion also contains a protective agent to prevent premature oxidation of the reducing agent (e.g. I 2 , a metal iodide, a spectral sensitizing dye or 2-mercapto - 4-phenylthiazole), Au ions (e.g. in the form of Au Cl 3 ), Pb(NO 3 ) 2 and/or Sn Cl 4 . |
