| 摘要 |
1511901 Moulding lenses BAUSCH & LOMB Inc 18 April 1975 [6 May 1974 8 April 1975] 16228/75 Heading B5A In the casting of lenses from material which changes volume on polymerization using a mould having a reservoir connected through a restriction to the moulding cavity, the mould cavity is completely filled and the reservoir at least partly filled with the polymerizable material, and the mould parts are configured to produce axial and/or radial alignment thereof. Preferably polymerization is inhibited in the reservoir during polymerization in the mould cavity so that material may pass to or from the cavity to compensate for any change in volume. In Fig. 3 a male member 13 is brought into contact with projections 131 on a female member 115 containing polymerizable material, thereby forming a mould cavity 133 and displacing excess material into an annular reservoir 135. The spaces between the projections 131 form part annular restrictions through which material can pass. The members 13 and 115 are made of glass to facilitate polymerization by U.V. irradiation through either of them. An annular shield 141 is used initially so that the centre is polymerized first, and finally the flash in the reservoir is polymerized. With certain cross-linking hydrophilic polymers the oxygen in the air inhibits polymerization and a nitrogen atmosphere is necessary during polymerization of the flash. In cases where a thermosetting material is heated to cure it both the initial expansion and the subsequent shrinkage of the material will be accommodated by the reservoir. In Fig. 7 the upper and lower female members 413, 15 are axially aligned with a very small clearance at 49 and 51. The viscosity of the moulding material and the weight of the upper member are chosen so that a thin film remains between the members 413, 15 to form a restricted connection 429 between the cavity 431 and the reservoir 433. The cured lens is machined by mounting the male member, with the lens still attached, on a lathe having a rotating fly cutter for generating the desired curvature. |
