Optical glass for precision press molding, preform for precision 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 B 2 O 3 , SiO 2 , La 2 O 3 , Gd 2 O 3 , ZnO, Li 2 O, ZrO 2 and Ta 2 O 5 as essential components, containing 0 to 1 mol % of Sb 2 O 3 as an optional component, substantially containing none of PbO and Lu 2 O 3 , 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.

What is claimed is:  
     
         1 . An optical glass for precision press molding, comprising B 2 O 3 , SiO 2 , La 2 O 3 , Gd 2 O 3 , ZnO, Li 2 O, ZrO 2  and Ta 2 O 5  as essential components, containing 0 to 1 mol % of Sb 2 O 3  as an optional component, substantially containing none of PbO and Lu 2 O 3 , having a glass transition temperature of 630° C. or lower, and 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 ). 
     
     
         2 . An optical glass for precision press molding, comprising B 2 O 3 , SiO 2 , La 2 O 3 , Gd 2 O 3 , ZnO, Li 2 O, ZrO 2  and Ta 2 O 5  as essential components, containing 0 to 1 mol % of Sb 2 O 3  as an optional component, substantially containing none of PbO and Lu 2 O 3 , having a glass transition temperature of 630° C. or lower, and having a refractive index nd of greater than 1.85 and an Abbe's number νd of greater than 35.  
     
     
         3 . An optical glass comprising, as essential components and by mol %, 15 to 40% of B 2 O 3 , 3 to 25% of SiO 2 , 5 to 20% of La 2 O 3 , 5 to 20% of Gd 2 O 3 , 2 to 35% of ZnO, 0.5 to 15% of Li 2 O, 0.5 to 15% of ZrO 2  and 0.2 to 10% of Ta 2 O 5 , containing 0 to 15% of WO 3 , 0 to 8% of Y 2 O 3 , 0 to 8% of Yb 2 O 3  and 0 to 1% of Sb 2 O 3  as optional components, and further containing Nb 2 O 5 , BaO and GeO 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 2 O 3 , having a glass transition temperature of 630° C. or lower, and 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 ). 
     
     
         4 . An optical glass as recited in  claim 1 ,  2  or  3 , which contains La 2 O 3 , Gd 2 O 3 , Yb 2 O 3 , Y 2 O 3  and Sc 2 O 3 , the total content of La 2 O 3 , Gd 2 O 3 , Yb 2 O 3 , Y 2 O 3  and Sc 2 O 3  being 12 to 32 mol %, the molar ratio of the content of La 2 O 3  to said total content being 0.35 to 0.66.  
     
     
         5 . A preform for precision press molding which is made of the optical glass recited in any one of  claims 1  to  4 .  
     
     
         6 . An optical element which is made of the optical glass recited in any one of  claims 1  to  4 .  
     
     
         7 . A process for the production of a preform for precision press molding, which comprises flowing a molten glass made of the optical glass recited in any one of  claims 1  to  4  from a flow pipe, isolating molten glass having a predetermined weight, and shaping the isolated molten glass having the predetermined weight while the isolated molten glass is in a softened state.  
     
     
         8 . A process for the production of an optical element which comprises heating a preform made of an optical glass to soften the preform and producing the optical element from the softened preform by precision press molding, said preform being the preform recited in  claim 5  or the preform produced by the method recited in  claim 7.