GB615890A - Improvements in cross-linked crystalline films - Google Patents

Abstract

<PICT:0615890/IV(a)/1> A light-polarizing film is obtained by stretching a film of an organic polymer and then treating the film in the stretched microcrystalline state with a halogen compound which intensifies the polarizing effect and with an alkyl silicate so as to render the extended or stretched film substantially non-retractive. The treatment of the stretched film may be carried out as a continuous process on a long length of film. The treatment of polyvinyl acetal films is restricted to this continuous form of the process. The film may be treated simultaneously or separately with the halogen compound and the alkyl silicate. For the stretching step, the film may be brought into a rubbery-elastic state by means of heat or swelling agents. Heat may be supplied by infra-red rays. The organic polymer from which the film is obtained may be a polymethylene, polyvinylidene chloride, polyvinyl alcohol, polyvinyl ether, polyvinyl ester, polyamide, rubber or rubber homologue, amylose, keratin, or silk fibroin. Iodine, bromine, chlorine, fluorine, hydrochloric acid, or hydrofluoric acid may be employed as the intensifying compound, and the alkyl silicate may be ethyl orthosilicate. The treatment appears to form p cross-linkages between the long chains of atoms in the molecules of the film substance. The colour of the film produced may be neutral gray or blue-green according to the intensity of the chemical treatment. As shown, the film 10, which has previously been submitted to a stretching operation, is unwound from a roll and passed through the treatment tanks 4, 5, 6, and drying chamber 19. The film may be of polyvinyl butyral, and tank 4 may contain an aqueous solution of iodine, n-propyl alcohol, hydriodic acid and a sulphonated alcohol wetting agent. The tank 5 may contain a solution of ethyl silicate in n-propyl alcohol. Tank 6 contains a liquid such as isopropyl or butyl ether for removing excess of reagents. The treatment may be effected at 30 DEG C. If desired, the tank 4 may contain a solution of iodine in n-propyl alcohol and ethyl silicate. When the treatment is carried out at 20 DEG C., the polarizing film obtained may be of a neutral gray colour, but when the temperature is 30-40 DEG C., the film obtained may be of a blue-green tint. For making light-polarizers, the films may be treated with plasticisers and laminated. Specification 591,943 is referred to. The Specification as open to inspection under Sect. 91, comprises also the treatment of films of other polymeric substances, e.g. phosphonitrilic chloride or fluoride, polymerized sulphur or selenium, sulphur trioxide polymers, and silicates. It also comprises the use of other cross-linking agents or agents for permeation of the crystal lattice, e.g. oxygen, cyanogen, ethylene, acetylene, iron carbonyl, magnesium ethyl, sulphur chloride, carbon disulphide, sulphuric acid, zinc chloride, ammonia, amines, and caustic alkalis. This subject-matter does not appear in the Specification as accepted.