Optical glass and process for the production of optical products

Abstract

Disclosed is an optical glass having high-refractivity and low-dispersion optical properties and having a low glass transition point so that a heat-treating furnace can be operated for a long period of time. The present invention provides an optical glass having a refractive index nd of at least 1.875, an Abbe's number vd of at least 39.5 and a glass transition point Tg of 700° C. or lower, an optical glass which is a borosilicate glass comprising at least one selected from La 2 O 3 , Gd 2 O 3 , Y 2 O 3 or Yb 2 O 3 and at least one selected from ZrO 2 , Ta 2 O 5 or Nb 2 O 5 , wherein the ratio (weight ratio) of the total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3 and Yb 2 O 3 to the total content of SiO 2 and B 2 O 3 is from 3.2 to 5 and the ratio (weight ratio) of the total content of ZrO 2 , Ta 2 O 5 and Nb 2 O 5 to the total content of SiO 2 and B 2 O 3 is from 1.1 to 1.5, and which has a refractive index nd of at least 1.875 and an Abbe's number vd of at least 39.5, and the like.

1 . An optical glass having a refractive index nd of at least 1.875, an Abbe's number vd of at least 39.5 and a glass transition point Tg of 700° C. or lower.  
     
     
         2 . The optical glass of  claim 1 , which is a borosilicate glass comprising at least one selected from La 2 O 3 , Gd 2 O 3 , Y 2 O 3  or Yb 2 O 3  and at least one selected from ZrO 2 , Ta 2 O 5  or Nb 2 O 5 , wherein the weight ratio of the total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3  and Yb 2 O 3  to the total content of SiO 2  and B 2 O 3  is from 2 to 4 and the weight ratio of the total content of ZrO 2 , Ta 2 O 5  and Nb 2 O 5  to the total content of SiO 2  and B 2 O 3  is from 1 to 2.  
     
     
         3 . The optical glass of  claim 2 , which further contains ZnO whose weight ratio to the total content of SiO 2  and B 2 O 3  is more than 0 but not more than 2.  
     
     
         4 . The optical glass of  claim 3 , wherein the weight ratio of the total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3  and Yb 2 O 3  to the total content of SiO 2  and B 2 O 3  is from 2 to 4, the weight ratio of the total content of ZrO 2 , Ta 2 O 5  and Nb 2 O 5  to the total content of SiO 2  and B 2 O 3  is from 1 to 2 and the weight ratio of ZnO to the total content of SiO 2  and B 2 O 3  is from 0.1 to 0.5.  
     
     
         5 . The optical glass of  claim 1 , which has a glass composition comprising, by % by weight, 3 to 10% of SiO 2 , 7 to 15% of B 2 O 3 , 0 to 5% of GeO 2 , 0 to 15% of ZnO, 30 to 60% of La 2 O 3 , 0 to 30% of Gd 2 O 3 , 0 to 10% of Y 2 O 3 , 0 to 5% of Yb 2 O 3 , 2 to 8% of ZrO 2  and 13 to 19% of Ta 2 O 5 , wherein the total content of SiO 2 , B 2 O 3  and GeO 2  is 14 to 20% by weight, the total content of B 2 O 3  and ZnO is at least 9% by weight, the total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3  and Yb 2 O 3  is 50 to 60% by weight and the total content of the above components is at least 95% and further wherein the composition contains, by % by weight, 0 to 1% of Li 2 O and 0 to 3% of Nb 2 O 5 .  
     
     
         6 . The optical glass of  claim 5 , which contains, by % by weight, 9 to 12% of B 2 O 3  and 1 to 7% of ZnO and has a B 2 O 3  and ZnO total content of at least 12% by weight.  
     
     
         7 . The optical glass of  claim 5 , which contains, by % by weight, 6 to 9% of SiO 2 , 9 to 12% of B 2 O 3  and 0 to 5% of GeO 2  and has an SiO 2 , B 2 O 3  and GeO 2  total content of 16 to 19% by weight.  
     
     
         8 . The optical glass of  claim 1 , which has a glass composition comprising, by % by weight, 5 to 10% of SiO 2 , 7 to 13% of B 2 O 3 , 0 to 5% of GeO 2 , 0 to 15% of ZnO, 30 to 60% of La 2 O 3 , 0 to 30% of Gd 2 O 3 , 0 to 5% of Y 2 O 3 , 0 to 5% of Yb 2 O 3 , 2 to 8% of ZrO 2  and 13 to 19% of Ta 2 O 5 , wherein the total content of SiO 2 , B 2 O 3  and GeO 2  is 14 to 20% by weight, the total content of B 2 O 3  and ZnO is at least 9% by weight and the total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3  and Yb 2 O 3  is 50 to 60% by weight, and further wherein the total content of the above components exceeds 95% by weight, the composition further contains, by % by weight, 0 to 3% of Nb 2 O 3 , 0 to 3% of WO 3 , 0 to 3% of Al 2 O 3 , 0 to 3% of Bi 2 O 3 , 0 to 3% of Ga 2 O 3  and 0 to 1% of Sb 2 O 3 , the total content of BaO, SrO, K 2 O and MgO is 0 to 3% by weight, and the total content of Na 2 O, K 2 O and Li 2 O is 0 to 1% by weight.  
     
     
         9 . An optical glass which is a borosilicate glass comprising at least one selected from La 2 O 3 , Gd 2 O 3 , Y 2 O 3  or Yb 2 O 3  and at least one selected from ZrO 2 , Ta 2 O 5  or Nb 2 O 5 , wherein the weight ratio of the total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3  and Yb 2 O 3  to the total content of SiO 2  and B 2 O 3  is from 3.2 to 5 and the weight ratio of the total content of ZrO 2 , Ta 2 O 5  and Nb 2 O 5  to the total content of SiO 2  and B 2 O 3  is from 1.1 to 1.5, and which has a refractive index nd of at least 1.875 and an Abbe's number vd of at least 39.5.  
     
     
         10 . An optical glass which is a borosilicate glass comprising at least one selected from La 2 O 3 , Gd 2 O 3 , Y 2 O 3  or Yb 2 O 3 , at least one selected from ZrO 2 , Ta 2 O 5  or Nb 2 O 5  and ZnO, wherein the weight ratio of the total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3  and Yb 2 O 3  to the total content of SiO 2  and B 2 O 3  is from 2 to 5, the weight ratio of the total content of ZrO 2 , Ta 2 O 5  and Nb 2 O 5  to the total content of SiO 2  and B 2 O 3  is from 0.5 to 3 and the weight ratio of ZnO to the total content of SiO 2  and B 2 O 3  is at least 0.14, and which has a refractive index nd of at least 1.875 and an Abbe's number vd of at least 39.5.  
     
     
         11 . The optical glass of  claim 9 , which has a glass composition comprising, by % by weight, 3 to 10% of SiO 2 , 7 to 15% of B 2 O 3 , 0 to 5% of GeO 2 , 0 to 15% of ZnO, 30 to 60% of La 2 O 3 , 0 to 30% of Gd 2 O 3 , 0 to 10% of Y 2 O 3 , 0 to 5% of Yb 2 O 3 , 2 to 8% of ZrO 2  and 13 to 19% of Ta 2 O 5 , wherein the total content of SiO 2 , B 2 O 3  and GeO 2  is 14 to 20% by weight, the total content of B 2 O 3  and ZnO is at least 9% by weight and the total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3  and Yb 2 O 3  is 50 to 60% by weight, and further wherein the total content of the above components exceeds 95% by weight and the glass composition contains 0 to 1% by weight of Li 2 O and 0 to 3% by weight of Nb 2 O 5 .  
     
     
         12 . The optical glass of  claim 11 , which contains, by % by weight, 9 to 12% of B 2 O 3  and 1 to 7% of ZnO and has a total content of B 2 O 3  and ZnO of at least 12% by weight.  
     
     
         13 . The optical glass of  claim 11  or  12 , which contains, by % by weight, 6 to 9% of SiO 2 , 9 to 12% of B 2 O 3  and 0 to 5% of GeO 2  and has an SiO 2 , B 2 O 3  and GeO 2  total content of 16 to 19% by weight.  
     
     
         14 . An optical glass comprising, by % by weight, 3 to 10% of SiO 2 , 7 to 15% of B 2 O 3 , 30 to 60% of La 2 O 3 , 2 to 8% of ZrO 2  and 13 to 19% of Ta 2 O 5 , wherein the total content of SiO 2  and B 2 O 3  is 14 to 20% by weight, and the total content of the above components is at least 95% by weight.  
     
     
         15 . The optical glass of  claim 14 , wherein part of La 2 O 3  is replaced with Gd 2 O 3  and/or Y 2 O 3 , the content of Gd 2 O 3  is 0 to 30% by weight, the content of Y 2 O 3  is 0 to 10% by weight, the optical glass containing 0 to 15% by weight of ZnO, and further wherein the total content of ZnO and B 2 O 3  is at least 9% by weight, the optical glass having a glass transition point Tg of 700° C. or lower.  
     
     
         16 . The optical glass of  claim 14 , wherein part of La 2 O 3  is replaced with Gd 2 O 3  and/or Y 2 O 3 , the content of Gd 2 O 3  is 0 to 30% by weight, the content of Y 2 O 3  is 0 to 10% by weight, the content of ZnO is 0 to 15% by weight, the content of Nb 2 O 5  is 0 to 3% by weight and the content of Li 2 O is 0 to 1% by weight, the optical glass having a glass transition point Tg of 700° C. or lower.  
     
     
         17 . A glass preform made of the optical glass recited in  claim 1 .  
     
     
         18 . An optical product made of the optical glass recited in  claim 1 .  
     
     
         19 . A process for the production of the optical product recited in  claim 18 , which comprises the steps of melting raw materials for a glass and directly press-molding a molten glass.  
     
     
         20 . The process of  claim 19 , which further comprises the step of annealing a glass molded material obtained by the press-molding, after the step of directly press-molding a molten glass.  
     
     
         21 . A process for the production of an optical product, which comprises the steps of softening the glass preform recited in  claim 17  under heat and press-molding the glass preform softened under heat.  
     
     
         22 . The process of  claim 21 , which further comprises the step of annealing a glass molded material obtained by the press-molding, after the step of press-molding the glass preform.