Patent GB-580237-A (GB)
Title: Improvements in or relating to photographic developers
IPC: G03C5/30
Filed: 1944-12-07
Abstract: 580,237. Photographic developers. GALLAFENT, V. (Du Pont de Nemours & Co., E. I.). Dec. 7, 1944, No. 24513. [Class 98 (ii)] A latent image in a silver halide emulsion layer is developed by treatment with a developer comprising a ternary addition compound of an o- or p-polyhydroxybenzene, an o- or p-aminophenol, and an o-phenylenediamine which is unsubstituted or substituted in the p-position to one of the amino groups only by a halogen atom or an alkyl group, the three compounds being present in the addition compound in a molecular ratio of small whole numbers, and the addition compound having a sharp melting point. The polyhydroxybenzene may be hydroquinone, 2-hydroxyhydroquinone, pyrogallol, pyrocatechol, bromo- or chloro-hydroquinone, 2 : 3-dichloro- or 2 : 3-dibromo-hydroquinone, or chlorotoluhydroquinone. The aminophenol may be p-aminophenol, 2 : 4-diaminophenol, or 4-chloro-2-methylaminophenol. The o-phenylenediamine may be unsubstituted o-phenylenediamine, or an o-phenylenediamine in which the 4-position is substituted by a halogen, e.g. chloro atom or an alkyl (e.g. methyl or ethyl) group. With a particular selection of three components, only one ratio gives a crystalline product having a sharp melting point. The ternary body may be prepared in aqueous solution, or a relatively water-insoluble component may be dissolved in an organic solvent. Sodium bisulphite may be added. A binary compound may be first formed, and the third component added. In example 1, o-phenylenediamine, pyrocatechol and p-aminophenol are dissolved in water, aqueous sodium bisulphite solution and decolourising carbon, the mixture is heated to boiling, sodium hydrosulphite is added, the hot mixture is filtered under vacuum and the crystals separated out. In example 2, 4 - methyl - o - phenylenediamine, pyrocatechol and p-aminophenol are dissolved in water, and the compound is prepared as in example 1. In example 3, a compound is prepared as in example 1 from 4-chloro-o-phenylenediamine, pyrocatechol and p-aminophenol. In example 4, the same compound is prepared as in example 3, but an etherial solution of 4-chloro-o-phenylenediamine. In example 5, a compound is prepared as in example 1 from o-phenylenediamine, pyrocatechol and o-aminophenol. In example 6, a binary compound is prepared by dissolving o - phenylenediamine and hydro - quinone in water, aqueous sodium bisulphite and decolourising carbon is added, the mixture is brought to boiling temperature, sodium hydrosulphite is added, and the crystalline binary composition is filtered off. An aqueous solution of p-aminophenol is added to the binary compound together with aqueous sodium bisulphite and decolourising carbon, and the ternary compound is crystallised out. In example 7, a compound is prepared as in example 1 from o-phenylenediamine, hydroquinone and o-aminophenol; in example 8 from o-phenylenediamine, pyrogallol and paminophenol; in example 9 from o-phenylenediamine, chlorohydroquinone and p-aminophenol; in example 10 from o-phenylenediamine, bromohydroquinone and p-aminophenol ; and in example 11 from o-phenylenediamine, chlorotoluhydroquinone (4 - chloro - 1- methyl - 2 : 5 - hydroxy benzene) and p - amino - phenol. A developing solution comprises the ternary compound, sodium sulphite, borax and water. With the ternary compound of example 1, the pH is 8.16. Using less sodium sulphite and borax, the pH is 8.8. The sodium sulphite may be omitted and the borax may be replaced by sodium carbonate, potassium carbonate, sodium hydroxide, or trisodium phosphate. Potassium bromide may be added. A colour developer comprises the ternary compound, sodium sulphite, sodium carbonate and water, together with an ethyl alcohol solution of 2 : 4- dichloro-alpha-naphthol.