Optical glass for precision press molding, preform for precission press molding, and process for the production thereof

Abstract

A high-refractivity high-dispersion optical glass for producing an optical element, which requires no machining, such as polishing or lapping, of an optical-function surface after precision press molding, containing B2O3, SiO2, La2O3, Gd2O3, ZnO, Li2O, ZrO2 and Ta2O5 as essential components, containing 0 to 1 mol % of Sb2O3 as an optional component, substantially containing none of PbO and Lu2O3, having a glass transition temperature of 630° C. or lower, and (1) having a refractive index nd and an Abbe's number νd which satisfy all of the following relational expressions, 1.80<nd≦1.90, 35≦νd≦50, and nd≧2.025−(0.005×νd) or (2) having an nd of greater than 1.85 and a νd of greater than 35.

Description

TECHNICAL BACKGROUND [0001] 1. Field of the Invention [0002] The present invention relates to an optical glass for precision press molding, a preform for precision press molding, an optical element, and processes for the production of the preform and the optical element. More specifically, the present invention relates to a high-refractivity low-dispersion optical glass which does not require machining of an optical-function surface such as polishing or lapping after precision press molding thereof and which is used for producing an optical element such as an ultra-precision aspherical lens, a precision press molding preform made of the optical glass, an optical element made of the same, and processes for the production of the above preform and optical element. [0003] 2. Prior Art [0004] In recent years, digital cameras have appeared, and as the integration and function of machines and devices using an optical system are rapidly enhanced, it is increasingly demanded to enhance the p...

AI Technical Summary

Benefits of technology

[0010] Under the circumstances, it is an object of the present invention to provide a high-refractivity low-dispersion optical glass which does not require machining of an optical-function surface, such as polishing or lapping, after precision press molding thereof and which is used for producing an optical element, a precision press molding preform made of the above optical glass, an optical element made of the above glass, and processes for the production of the above preform and the above optical element.

Problems solved by technology

However, the above optical glasses aim at an improvement in devitrification resistance, and there is therefore involved a problem that expensive components such as Lu2O3, etc., are essential, or that a large amount of Sb2O3 that is a harmful component is essentially incorporated, for improving such optical glasses in stability.

Further, of glass compositions disclosed in the above Publications, compositions that can attain a refractive index nd>1.8 and an Abbe's number νd>35 very useful for optical designing contain almost no ZnO or Li2O that is said to be effective for decreasing the glass transition temperature, so that they have poor suitability to press molding.

Generally, a glass having such optical constants has a large content of rare earth metal oxide component and has a low degree of stabilization against devitrification, so that it has been difficult to develop a composition that makes it possible to decrease the glass transition temperature to a region in which the glass can be press molded economically.

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