Patent GB-472981-A (GB)
Title: Improvements in and relating to sound films
IPC: G11B7/00
Filed: 1936-04-02
Abstract: 472,981. Photographic sound-record films. GASPAR, B. April 2, 1936, Nos. 9765 and 9766. Convention dates, April 2, 1935 and March 24, 1936. [Class 98 (ii)] A sound film contains a plurality of individual sound records of different sources. each of which consists of a coloured record which absorbs a por tion of the spectrum but allows the passage of the rays absorbec by the other differently coloured sound recorc or records. A positive film consists of a layer support a with three picture layers, e.g. a layer b coloured yellow with chrysophenine G and sensitized for green light, disposed over a layer c coloured purple-red with azofuchsine and sensitized for red light, and on the other side of the support a layer d sensitized to green, e.g. with erythrosine. In addition to copying the picture components therein, positive originals of two sound records, e.g. French and English versions, are copied in the outer layers b, d by means of green light, the middle purplered layer restricting the copying to the particular layer concerned. In the layer c a diffuse exposure is effected. The film is developed, fixed and treated with a dye destroying reagent. e.g. 5 per cent solution of carbamide in 2 per cent citric acid, finally yielding sound records in blue. green and yellow. The yellow sound record f is reproduced by blue light employing a light sensitive with a silver-silver oxide layer sensitized with caesium or a platinum surface with an atomic layer of potassium deposited thereon. The blue-green record e is reproduced by red light employing a silversilveroxide-caesium cell. If white light is used in the reproduction, the separation of the sound records is effected by colour selective cells or by colour filters, prisms, oxide, &c. used in front of or behind the film. In order to prevent one sound record influencing the absorption of the coloured light used for the other sound record, a weak yellow negative of the blue-green positive is copied into one of the three layers, thus balancing the variations in the absorption of blue light. When the weak yellow negative is to be copied into the bluegreen layer d, after finishing the dyestuff. the picture blue-green layer is treated with 5 per cent copper chloride solution which converts the silver in the blue-green layer into silver chloride. This is fogged and converted into a dyestuff picture by a solution of alpha-chloracetoacetic ester, diethyl-paraphenylene-diamine, acetone and water, the time being chosen to form the appropriate amount of yellow dyestuff. The silver is bleached in the usual manner. When the weak record is in the middle layer c, the purple red image is made so that its absorption of blue light is complementary to that of the blue-green layer. The compensation may also be obtained by having the positive and negative sound records of different colours either in different layers or in strips on a single film. Reproduction is by light of mixed colours, e.g. blue and red, the light being passed through a slit B, Fig. 9, on to a prism D, and divided and directed on to two cells E<1>, E<2> connected in opposition without phase difference.