| 摘要 |
PURPOSE:To provide a glass composition for a high refractive index segment, having a specific PbO/alkali metal oxide ratio, and capable of forming a multi- focus eyeglass lens by welding to the principal part composed of a light-weight eyeglass material having medium refractive index. CONSTITUTION:The objective glass for multi-focus eyeglass lens has a composition of formula (wt%) wherein the weight ratio of alkali metal oxide/PbO is 0.1-0.3, an nd of 1.67-1.73, nud of >=33, a thermal expansion coefficient of (82- 95)X10<-7> and a sofetning point of 560-640 deg.C. The above glass can be produced by mixing silica powder, sodium carbonate, potassium nitrate, litharge, barium carbonate, zinc white, zirconium oxide, etc. at specific ratios, roughly melting the mixture in a refractory crucible at about 1,250-1,300 deg.C, remelting at about 1,300-1,350 deg.C in a platinum crucible, subjecting to the treatment such as homogenization, etc., and slowly cooling the product.
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