GB666858A - Improvements in or relating to methods of manufacturing aspherical lenses of plastic material - Google Patents

Abstract

666,858. Moulding aspherical lenses. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. May 14, 1948. [May 20, 1947] No. 13235/48. Class 87(ii). A method of making an aspherical lens of plastic material comprises (a) making a cast from a mother mould, using a gelatinous mass as the casting material, (b) drying the cast, (c) making a daughter mould from the dried cast, and (d) making a lens from the daughter mould. Thus, a gelatinizable liquid, e.g. a solution of gelatine in water, is admitted through a tube 4, Fig. 1, to the space between a mould 2 and a table 1 where it is coagulated into a mass 7. The coagulation is effected by cool liquid flowing through the mould via tubes 5, 6. The mass is removed from the mould and dried, to give the shrunken cast 8, Fig. 4, and any errors present in the mould 2 are reduced by the shrinking. A daughter mould 9, Fig. 6, is then made from the cast 8, this mould being made by electrodeposition of metal on to the cast (in which case the surface of the cast may be rendered conductive by applying a metallic layer thereto by vaporization) or by applying metal by the Schoop method or by the use of wax or of metals melting at low temperature. The mould 9 thus made may be secured to the upper stamp 10 of a press including a lower stamp 11 and a mounting 12, an aspherical lens 13 of transparent artificial resin being made in this press. The lens may be made of thermosetting or thermoplastic substances, e.g. polystyrene or polymethylmethacrylate. Instead of resin, the lens may be made of a gelatinous mass, in which case the mould 9 may be provided with channels for the passage of a cooling liquid. By using different concentrates of gelatinous mass in the first step (Fig. 1) lenses of different shapes may be obtained.