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  Optical glass for precision press molding, preform for precission press molding, and process for the production thereofUSPTO Application #: 20060234850Title: 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. (end of abstract) Agent: Nixon & Vanderhye, PC - Arlington, VA, US Inventors: Kazutaka Hayashi, Xuelu Zou USPTO Applicaton #: 20060234850 - Class: 501078000 (USPTO) Related Patent Categories: Compositions: Ceramic, Ceramic Compositions, Glass Compositions, Compositions Containing Glass Other Than Those Wherein Glass Is A Bonding Agent, Or Glass Batch Forming Compositions, Silica Containing, Less Than 40 Percent By Weight Silica, And Boron, And Rare Earth (i.e., Elements With Atomic Number 39 Or 57-71) The Patent Description & Claims data below is from USPTO Patent Application 20060234850. Brief Patent Description - Full Patent Description - Patent Application Claims
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 precision of the optical system and to decrease the optical system in weight and size. For materializing the above demands, optical designing using an aspherical lens is coming to be a mainstream. For stably supplying a large volume of aspherical lenses made of a high-functional glass at a low cost, therefore, attention is actively paid to a mold shaping technique of directly forming an optical surface by press molding without polishing and lapping, and demands for an optical glass having high functionality (e.g., high refractivity and low-dispersion/high refractivity and high-dispersion) and being suitable for mold-shaping are increasing year after year. [0005] Precision press molding of glass is a technique of shaping a glass preform under pressure at a high temperature into a glass shaped article having a form and a surface accuracy of an end article or a form and a surface accuracy very close to those of an end article. The above precision press molding enables the highly productive production of shaped articles (molded articles) having a desired form. At present, therefore, the precision press molding is employed to produce optical parts such as spherical lenses, aspherical lenses and diffraction gratings, and the like. For producing an optical glass part by precision press-molding, naturally, it is required to shape a glass preform under pressure at a high temperature as described above, so that a mold used for the pressing is exposed to a high temperature and that a high pressure is applied thereto. It is therefore suppressing the damage that is may be caused on the mold itself and a release film provided on an inner surface of the mold by the high-temperature environment of the press molding, it is desired to decrease the glass transition temperature Tg and sag temperature Ts of a gob preform for glass molding such that they are as low as possible. [0006] As an optical glass having high-refractivity low-dispersion (refractive index nd>1.8 and Abbe's number .nu.d>35) optical constants, various glasses containing B.sub.2O.sub.3 and La.sub.2O.sub.3 are conventionally known. For example, such glasses are disclosed in JP-A-8-217484, JP-A-54-90218 and JP-A-62-100449. [0007] However, the above optical glasses aim at an improvement in devitrification resistance, and there is therefore involved a problem that expensive components such as Lu.sub.2O.sub.3, etc., are essential, or that a large amount of Sb.sub.2O.sub.3 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 .nu.d>35 very useful for optical designing contain almost no ZnO or Li.sub.2O that is said to be effective for decreasing the glass transition temperature, so that they have poor suitability to press molding. [0008] As described above, there has not been proposed any optical glass which attains a refractive index nd>1.8 and an Abbe's number .nu.d>35 (provided that a range surrounded by three points (nd, .nu.d)=(1.85, 35), (1.8, 45) and (1.8, 35) is excluded), or particularly, there has not yet been proposed any optical glass for precision press molding which has optical constants, a refractive index nd>1.85 and an Abbe's number .nu.d>35. [0009] The reason therefor is presumably as follows. 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. SUMMARY OF THE INVENTION [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. [0011] For achieving the above object, the present inventors have made diligent studies and as a result, it has been found that the above object can be achieved by an optical glass containing specific components as essential components and having a glass transition temperature of a specific value or smaller and specific optical constants. On the basis of the finding, the present invention has been completed. [0012] That is, the present invention provides [0013] (1) an optical glass for precision press molding (to be referred to as "optical glass I" hereinafter) comprising B.sub.2O.sub.3, SiO.sub.2, La.sub.2O.sub.3, Gd.sub.2O.sub.3, ZnO, Li.sub.2O, ZrO.sub.2 and Ta.sub.2O.sub.5 as essential components, containing 0 to 1 mol % of Sb.sub.2O.sub.3 as an optional component, substantially containing none of PbO and Lu.sub.2O.sub.3, having a glass transition temperature of 630.degree. C. or lower, and having a refractive index nd and an Abbe's number .nu.d which satisfy all of the following relational expressions, [0014] 1.80<nd.ltoreq.1.90 [0015] 35<.nu.d.ltoreq.50, and [0016] nd.gtoreq.2.025-(0.005.times..nu.d), [0017] (2) an optical glass for precision press molding (to be referred to as "optical glass II" hereinafter) comprising B.sub.2O.sub.3, SiO.sub.2, La.sub.2O.sub.3, Gd.sub.2O.sub.3, ZnO, Li.sub.2O, ZrO.sub.2 and Ta.sub.2O.sub.5 as essential components, containing 0 to 1 mol % of Sb.sub.2O.sub.3 as an optional component, substantially containing none of PbO and Lu.sub.2O.sub.3, having a glass transition temperature of 630.degree. C. or lower, and having a refractive index nd of greater than 1.85 and an Abbe's number .nu.d of greater than 35, [0018] (3) an optical glass (to be referred to as "optical glass III" hereinafter) comprising, as essential components and by mol %, 15 to 40% of B.sub.2O.sub.3, 3 to 25% of SiO.sub.2, 5 to 20% of La.sub.2O.sub.3, 5 to 20% of Gd.sub.2O.sub.3, 2 to 35% of ZnO, 0.5 to 15% of Li.sub.2O, 0.5 to 15% of ZrO.sub.2 and 0.2 to 10% of Ta.sub.2O.sub.5, containing 0 to 15% of WO.sub.3, 0 to 8% of Y.sub.2O.sub.3, 0 to 8% of Yb.sub.2O.sub.3 and 0 to 1% of Sb.sub.2O.sub.3 as optional components, and further containing Nb.sub.2O.sub.5, BaO and GeO.sub.2 as optional components, the total content of the above components being at least 95%, the optical glass substantially containing none of PbO and Lu.sub.2O.sub.3, having a glass transition temperature of 630.degree. C. or lower, and having a refractive index nd and an Abbe's number .nu.d which satisfy all of the following relational expressions, [0019] 1.80<nd.ltoreq.1.90 [0020] 35<.nu.d.ltoreq.50, and [0021] nd.gtoreq.2.025-(0.005.times..nu.d), [0022] (4) an optical glass as recited in the above (1), (2) or (3), which contains La.sub.2O.sub.3, Gd.sub.2O.sub.3, Yb.sub.2O.sub.3, Y.sub.2O.sub.3 and Sc.sub.2O.sub.3, the total content of La.sub.2O.sub.3, Gd.sub.2O.sub.3, Yb.sub.2O.sub.3, Y.sub.2O.sub.3 and Sc.sub.2O.sub.3 being 12 to 32 mol %, the molar ratio of the content of La.sub.2O.sub.3 to said total content being 0.35 to 0.66, Continue reading... 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