Optical glass, glass material for press molding, optical element, and method of manufacturing same

Abstract

A method of making a press-moldable glass, including melting starting materials, forming a melt, and annealing a formed glass, wherein the melt has a composition such that, (1) when rapidly cooled to room temperature, it becomes glass that has a scattering coefficient of less than 0.005 cm-1 at wavelengths of from 400 to 2,500 nm or comprises crystals with a volumetric ratio of less than 10-6, and (2) when maintained for three hours at a temperature 10° C. higher than the glass transition temperature, maintained for 10 min at a temperature yielding a viscosity of 104.5 to 103.5 dPa·s, and then rapidly cooled to room temperature, (3) the resulting glass has (a) a scattering coefficient of at least one wavelength from 400 to 2,500 nm of greater than 0.01 cm-1 or (b) crystals with a volumetric ratio of greater than 10-5. A temperature for annealing is lower than for glass transition.

What is claimed is: 
     
         1 . An optical glass, which comprises essential components in the form of SiO 2 , BaO, and TiO 2 ; and exhibits a refractive index (nd) greater than or equal to 1.80 and an Abbé number (vd) less than or equal to 30, wherein the number density of the crystal particles precipitating out after being maintained for five hours at a temperature 20° C. higher than the glass transition temperature and then for five minutes at 900° C. is less than or equal to 12/mm 3 . 
     
     
         2 . The optical glass according to  claim 1 , which comprises, expressed as weight percentages, greater than or equal to 24 percent and less than 30 percent of SiO 2 , greater than or equal to 12 percent and less than 23 percent of BaO, and 22 to 37 percent of TiO 2 . 
     
     
         3 . The optical glass according to  claim 1 , wherein the weight ratio SiO 2 /TiO 2  of SiO 2  to TiO 2  exceeds 0.86. 
     
     
         4 . The optical glass according to  claim 1 , which comprises, expressed as weight percentages, 10.50 to 20 percent of Na 2 O. 
     
     
         5 . The optical glass according to  claim 1 , which comprises, expressed as weight percentages, 0 to 4.00 percent of K 2 O. 
     
     
         6 . The optical glass according to  claim 1 , which comprises, expressed as weight percentages, 0 to 1 percent of Sb 2 O 5 . 
     
     
         7 . The optical glass according to  claim 1 , which has a glass transition temperature ranging from 600° C. to 625° C. 
     
     
         8 . The optical glass according to  claim 1 , wherein the wavelength λ70 at which the transmittance reached 70 percent ranges from 405 nm to 442 nm. 
     
     
         9 . The optical glass according to  claim 1 , which comprises, expressed as weight percentages, 0 to 5 percent of CaO, 0 to 5 percent of SrO, 0 to 4 percent of ZrO 2 , 0 to 3 percent of Ta 2 O 5 , greater than or equal to 0 percent and less th10.A glass material for press molding comprised of the optical glass according to  claim 1 . 
     
     
         11 . An optical element comprised of the optical glass according to  claim 1 .
 an 0.5 percent of P 2 O 5 , and essentially not comprising PbO, As 2 O 3 , and F.   
     
     
         10 . A glass material for press molding comprised of the optical glass according to  claim 1 . 
     
     
         11 . An optical element comprised of the optical glass according to  claim 1 .