GB540464A - Improvements relating to photographic emulsions - Google Patents

Abstract

540,464. Photographic light-sensitive material. KODAK, Ltd., and KNOTT, E. B. June 6, 1940, No. 9902. [Class 98 (ii)] The tendency for a sensitizing dye present in a dye-sensitized silver salt emulsion to wander to a neighbouring second sensitive silver halide emulsion is reduced by dispersing through the first emulsion while it is in the liquid state an oxide or hydroxide of a metal of the 2nd or 3rd Group of the Periodic Table, excluding zinc, the oxide or hydroxide being substantially waterinsoluble or only slightly water-soluble. The dispersion is preferably effected before bringing the emulsions into such a relative position that dye-wandering can occur. The emulsions may be mixed or super-imposed in layers. Colour photographic material may be prepared by applying successively to a support and drying, three emulsions adapted to record the blue, green, and red image-components respectively, each emulsion having had dispersed in it prior to coating an oxide or hydroxide of the type defined above. Mixed emulsion material may be similarly prepared. Multi-contrast material may be similarly prepared using a mixture of or separate layers of emulsions of different contrast and sensitive to different ranges of the spectrum. A substantially water-insoluble organic binder, such as soft lac resin or " Glyptal " (Registered Trade Mark) resin, may be incorporated in any of the emulsions. The oxide or hydroxide may be aluminium oxide, lanthanum oxide, yttrium oxide, barium oxide, strontium oxide, or the corresponding hydroxide. In two-emulsion material, the emulsions may be (a) both silver chloride; (b) both silver bromide; (c) silver chloride and silver bromide; (d) silver chlorobromide and silver chloride; and (e) silver chlorobromide and silver bromide. In some cases the oxide or hydroxide increases the speed, particularly over the spectral range to which the emulsion is optically sensitized. The blue-speed and the speed of non- optically sensitized emulsions may also be increased. The speed-increase becomes greater if the emulsion containing the oxide or hydroxide is kept for some time, e.g. 2 or 3 hours, before coating. The oxide or hydroxide may be added as a finely divided powder or precipitate, but is preferably dispersed or precipitated in a 5 per cent gelatine solution, and this is added to the emulsion before, simultaneously with, or after addition of the dye, but preferably simultaneously or after. Multi-contrast printing paper may be prepared by applying to a paper support a mixture of a non-optically sensitized soft silver bromide emulsion and a yellow-sensitized highcontrast silver chloride emulsion. A table is given of the effect of various oxides and hydroxides on a silver chloride emulsion which, after sensitization with 5-[(1-ethyl-1-(2)-benzoxazolylidene)-ethylidene]-3-ethyl- 1-phenyl - 2 - thiohydantoin is kept at 35 ‹C for 30 minutes and has then added thereto a suspension of the oxide or hydroxide in a 5 per cent aqueous gelatine solution and then the unsensitized bromide emulsion. Metal oxides and hydroxides are more suitable for use with unwashed silver chloride emulsions. Mixtures of the oxides or hydroxides may be employed. Other sensitizing dyes specified are 3- ethyl-5-[(3-ethyl-2(2) - benzothiazylidene) - isopropylidene]-2-thio-2:4(3 : 5)-oxazoledione; 4<SP>1</SP>-methyl- 3:3<SP>1</SP>-diethyloxathiazolo-carbocyanine iodide; 2- [4-(1-piperidyl)-# 1 :3-butadienyl]-benzthiazole ethiodide; 3: 3<SP>1</SP>-diethyl-4: 5-benzoxathiazolinocarbocyanine iodide; and 4'methyl-3:31-diethyloxathiazolocarbocyanine .iodide. An oxide or hydroxide may also be incorporated in a non- optically sensitized emulsion to prevent wandering of dye thereto. In an example, a hard chloride emulsion containing silver equivalent to 200 grams of silver nitrate and having a pH of 7 is sensitized with 5-[(2-ethyl-1(2)-benzoxazolylidene)-ethylidene]-3-ethyl-1-phenyl-2-thiohydantoin and allowed to stand for 30 minutes at 35 ‹C. A suspension containing 20 grams of magnesium oxide is added, followed by a 5 per cent alcoholic solution of 30 grams of soft lac resin. The product is kept at 35‹C until the emulsion speed reaches the desired figure (e.g. 90 minutes). The same quantities of magnesium oxide and resin are added to a soft bromide emulsion also containing silver equivalent to 200 grams of silver nitrate and having a pH value of 7. The two emulsions are mixed, and coated immediately or after one hour. In a second example the procedure is similar, the emulsions being a kinematograph positive bromide emulsion and a hard chloride emulsion, each adjusted to a pH of 7. Specifications 450,958, 494,088 and 540,451 are referred to.