Patent GB-518119-A (GB)
Title: Improvements in and relating to films having optical properties and to methods of manufacturing the same
IPC: B29D7/01
Filed: 1938-06-11
Abstract: 518,119. Screens for cathode-ray tubes. BRITISH THOMSON-HOUSTON CO., Ltd. June 11, 1938, No. 17376. Convention date, June 11, 1937. [Class 39 (i)] [Also in Groups XX and III] A stratified film, formed on a base member as of glass or polished chromium, of the kind in which each stratum comprises a monomolecular layer wherein similar molecules are similarly oriented, has numerous voids of molecular dimentions in each layer, forming a molecular lattice. The film is coated in the manner described by Blodgett in the Journal of the American Chemical Society, Volume 57, pages 1007-1022, in apparatus comprising a trough 10, Fig. 1, resting in a temperature control tank 11, and a lever mechanism 16, 20 whereby the base 14 to be coated may be raised and lowered through the surface of liquid in the trough 10. This liquid may consist of water containing a soluble barium salt, e.g., the acetate, upon which is flowed sufficient stearic acid dissolved in benzene to form a monomolecular surface layer of barium stearate and stearic acid. To prevent disruption of this layer, it is enclosed by a floating waxed silk thread 25, Fig. 2, and a thin layer of oil is floated on the liquid outside the thread. As the base 14 is raised and lowered, successive monomolecular films are deposited on it. If the pH value of the liquid is lower than 8, a layer is deposited each time the base is raised or lowered, the molecular orientation being different in the layers deposited by lifting from that in the layers deposited by lowering ; but if the pH value is higher than 8, deposition occurs only on lowering, and the orientation is the same in all the layers. After a sufficient number of layers have been coated, the stearic acid is removed from the layers as by treatment with benzene, leaving in each layer a monomolecular lattice of barium stearate. According to the thickness of the film, it exhibits various colours produced by interference when viewed at an angle, and such films may be used as colour standards. A film of thickness equal to at least 900 A.U. is mentioned. The resulting refractive index of the film can be adjusted by varying the proportion of stearic acid in the coatings, which is determined by the pH value of the liquid in the tank. The film may be varied by absorption of other substances, e.g., oil, into the voids of the lattices, and if a moderately volatile oil such as tetradecane or kerosine is used, various portions of the film may be heated to cause selective vaporization of the oil, and thereby local colour changes. In this way, if an invisible infra-red light image is projected on such a film, a visible or photographically reducible image may be produced thereon. Other uses of the film mentioned are as standards for minute thickness measurements and as devices for the detection of minute quantities of material substances. Other materials which -may be used in forming the films are barium arachidate, barium palmitate, calcium stearate, lead stearate, chlorophyll, and cholesterol, and composite films may be prepared having differently constituted layers. The Specification as open to inspection under Sect. 91 states that other media such as cathode ray producing means may be used to stimulate the film, which may therefore be used for television ; and that the films may be used as sieves or filters for the segregation of substances of molecular magnitude greater than the dimensions of the voids in the lattice. This subject-matter does not appear in the Specification as accepted.