Patent GB-507855-A (GB)
Title: Improvements in or relating to impregnating and sealing media for electrical purposes
IPC: H01B3/18
Filed: 1937-12-21
Abstract: 507,855. Synthetic rubber; impregnating-compositions. SIEMENS & HALSKE AKT.-GES. Dec. 21, 1937, No. 35415. Convention date, Dec. 21, 1936. [Class 2 (iii)] [Also in Group VIII] An impregnating and sealing medium for electrical purposes is manufactured by partially depolymerizing a hydrogenated rubber hydrocarbon having a high degree of polymerization (the term "rubber hydrocarbon" denoting a polymerization product of butadiene and its homologues, e.g. isoprene or dimethylbutadiene, or associated mixed polymerizates), by heating it with exclusion of oxygen from the atmosphere, to such an extent that it is rendered readily soluble, particularly in liquid benzine hydrocarbons or chlorinated hydrocarbons, and readily. fusible without the use of a solvent and without decomposition, and preferably to such an extent that the viscosity of a 10 per cent solution of the product is so low that the solution is filterable through paper without the aid of pressure. The process may be carried out by first forming a hydrogenated rubber hydrocarbon having a high degree of polymerization by hydrogenation of a rubber hydrocarbon under conditions of high hydrogen pressure, e.g. initially '80 atmospheres, and then reducing the hydrogen pressure to about 10 atmospheres while maintaining the temperature at 250-300‹ C. The partially depolymerized rubber hydrocarbon may be dissolved in a solvent which is insoluble in water, has a @@ boiling point and is preferably dielectrically non-polar, e.g: a benzine hydrocarbon liquid, the solution then being filtered with the aid of an absorption medium, e.g. active aluminium oxide, as many times as are necessary for complete purification, the solvent being eliminated with the aid of reduced pressure and increased temperature, e.g. under a pressure of 2 mm. of mercury at about 120‹ C., and there being added, before or after the removal of the solvent, a dielectrically non-polar liquid or liquefied hydrocarbon, e.g. a hydrocarbon of the paraffin series such as liquid paraffin, white oil or the substance known under the Registered Trade Mark "Vaseline," The products may be used in apparatus conveying a plurality of communication currents of very wide or very high frequency bands. In examples: (1) hydrogenated highly polymerized isoprene rubber in solid insoluble form (obtained by heating isoprene with metallic sodium in a closed vessel and treating the product at 180- 200‹ C., with hydrogen under a pressure of 70 atmospheres in the presence of a catalyst consisting of finely divided nickel) is heated, e.g. at 270‹ C., in an autoclave containing hydrogen at a moderate pressure, e.g. 10 atmospheres; the product is dissolved in commercial benzine, the solution is passed over highly active aluminium oxide under reduced pressure, liquid paraffin is added, and the solvent is then removed by distillation under reduced pressure in several steps; (2) instead of adding liquid paraffin to the solution as in (1), the solvent is first removed and there is then added a liquefied paraffin which is solid at room temperature.