GB819039A - Preparation of photographic emulsions - Google Patents

Abstract

819,039. Photographic emulsions. GEVAERT PHOTO-PRODUCTEN N.V. June 19, 1957 [June 19, 1956], No. 18914/56. Class 98(2) A photographic gelatino-silver halide emulsion is prepared by forming the silver halide in an aqueous medium in the presence of 2 to 25 parts by weight of gelatin per 100 parts of silver nitrate, the quantity of gelatin not exceeding 3 per cent by weight of the total water present, coagulating to give a powdery precipitate by pouring into an organic liquid miscible with water, washing the precipitate, redispersing it in water and adding the required amount of binding agent. The organic liquid may be methyl acetate, ethyl acetate, methanol, ethanol, acetone or mixtures of these. Alkaline emulsions may be made neutral or acid before precipitation. Chemical sensitizers may be added at the formation stage of the silver halide or during the Ostwald ripening period. It is especially advantageous to add compounds of gold, ruthenium, rhodium, osmium, palladium, iridium or platinum to the redispersed, washed emulsion, before the final gelatine binder is added. In Example 1, aqueous AgNO3 is added to aqueous gelatine containing KBr and KI. After digestion at 45‹C. the emulsion is precipitated by pouring it into acetone. In Example 2, ammoniacal AgNO3 is added to aqueous gelatine containing KBr and KI, and then more aqueous KBr is added followed by ammoniacal AgNO3. Precipitation is with a mixture of acetone and ethanol. In Example 3, aqueous AgNO3 and aqueous NaCl are run simultaneously into aqueous gelatine, followed by ripening and precipitation with acetone. After washing and redispersing in water, aqueous gold chloride is added followed by inert gelatine. In Example 4, aqueous AgNO3 and NH4OH are run simultaneously into aqueous gelatine containing KBr. More aqueous KBr is added followed by ammoniacal AgNO3. Precipitation is with acetone, and the precipitate is washed by twice redispersing it in distilled water and reprecipitating it with acetone. In Examples 1-3, washing is with a mixture of acetone and water, followed by decantation. In all cases the washed precipitate is redispersed in water and gelatine added. In Example 4, aqueous polyethylene glycol mono-stearate is added to the finished gelatine emulsion. In Example 2 of the Provisional Specification, precipitation is effected by pouring into concentrated sodium sulphate solution instead of into an organic liquid. Specification 789,823 is referred to.