Patent GB-746804-A (GB)
Title: Emulsions and elements for colour photography
IPC: G03C7/327
Filed: 1954-05-26
Abstract: 746,804. Colour photographic emulsions. DU PONT DE NEMOURS & CO., E. I. May 26, 1954 [June 23, 1953], No. 15603/54. Class 98 (2). Silver halide is precipitated into an aqueous solution of a benzaldehyde polyvinyl acetal free from colour forming substituents, allowed to ripen, treated if desired to remove water soluble salts, and the resulting dispersion is mixed with a polyvinyl acetal colour former together with any other desired emulsion constituents. Normally the dispersion is divided into three parts to which appropriate sensitizing dyes and colour former acetals are added to produce the three emulsions for true or false colour films or papers. The first mentioned acetal thus acts as protective colloid and the method permits production of three balanced acetal emulsions from a single precipitation instead of three precipitations directly into the polyvinyl acetal colour formers. Preferably precipitation is effected into a water-soluble to hydrophilic polyvinyl acetal of mixed benzaldehyde and an aldehyde containing a carboxylic or sulphonic solubilizing group, such as sodium benzaldehyde o-sulphonate; and such acetals and also the colour-former acetals are further described with reference to Specifications 535,341, 593,088, 598,475, 598,477, 598,479, 627,125, 627,353, 632,835, 635,294, 652,928, 662,793, 671,713, 695,164, 704,558 and 705,950. Example 1 describes precipitation of silver bromide into an aqueous ethanol solution of the mixed polyvinyl acetal referred to above, 75 minutes ripening, coagulation and water washing to remove soluble salts, redispersion in aqueous ethanol, addition of more of the same mixed acetal, division into three parts, additions to the parts to produce a set of sensitized acetal colour former emulsions of conventional sequence; coating on to a cellulose triacetate film base already carrying two nitrocellulose layers and a subbing layer containing a yellow colourforming polymer of the foregoing type, with a sub-layer and anti-halation layer on the reverse side; sensitometric exposure, processing and densitometer comparison to evaluate speed, gamma and colour balance for intended use as motion picture colour-duplicating negative. Example II is directed to production of a somewhat similar but high contrast multilayer film using the sequence of green sensitized yellow colour former emulsion layer directly on the subbing layer, followed by red sensitized cyan colour former and then tartrazine containing magenta colour former layers for exposure with coloured light through colour separation records and processing to colour positive. Alternatively exposure may be effected through an appropriate film of the type described in example I. Examples III to VI indicate halide precipitation into mixed acetals made from varying proportions of benzaldehyde and the o-sodium sulphonate derivative thereof and the production and evaluation of single colour-forming layers coated therefrom on to separate films. Example VII describes production of a high contrast three-emulsion film of conventional sequence for exposure through a colour negative of similar sequence and processing to colour positive. The Specification concludes by quoting numerous halides and silver salts for the precipitation, general emulsion sensitizers, anti-fogging agents, hardeners, additional colloids to modify solution viscosity or vary film thickness or permeability; and then a range of aromatic, aliphatic and heterocyclic aldehydes which may be used in the non-colour forming acetal in replacement of part of the benzaldehyde.