Optical glass, precision press-molding preform, optical element and processes for production of these

Abstract

Provided are optical glasses having a phosphate-containing composition that can materialize highly useful optical properties including high-refractivity and high-dispersion properties; an optical glass comprising P 2 O 5 , SiO 2 and Li 2 O as essential components, comprising Na 2 O and K 2 O as optional components, having an Li 2 O/(Li 2 O+Na 2 O+K 2 O) molar ratio of from 1/3 to 1 and having an Abbe's number (νd) of 30 or less, and an optical glass comprising P 2 O 5 , SiO 2 and Li 2 O as essential components, having the property of transmittance that when light is caused to vertically enter one of two plane and mutually parallel optically polished surfaces of a sample of the glass having a thickness of 10.0±0.1 mm and caused to exit from the other surface, the wavelength at which the transmittance represented by the ratio of transmitted light intensity to incidence light intensity (transmitted light intensity/incidence light intensity) comes to be 70% is 510 nm or less, having a refractive index (νd) of 1.80 or more and an Abbe's number (νd) of 30 or less and having a liquidus temperature of less than 1,000° C.

1 . An optical glass comprising P 2 O 5 , SiO 2  and Li 2 O as essential components, comprising Na 2 O and K 2 O as optional components, having an Li 2 O/(Li 2 O+Na 2 O+K 2 O) molar ratio of from 1/3 to 1 and having an Abbe's number (νd) of 30 or less.  
   
   
       2 . The optical glass of  claim 1 , which has a refractive index (nd) of 1.80 or more.  
   
   
       3 . An optical glass comprising P 2 O 5 , SiO 2  and Li 2 O as essential components, having the property of transmittance that when light is caused to vertically enter one of two plane and mutually parallel optically polished surfaces of a sample of the glass having a thickness of 10.0±0.1 mm and caused to exit from the other surface, the wavelength at which the transmittance represented by the ratio of transmitted light intensity to incidence light intensity (transmitted light intensity/incidence light intensity) comes to be 70% is 510 nm or less, having a refractive index (nd) of 1.80 or more and an Abbe's number (νd) of 30 or less and having a liquidus temperature of less than 1,000° C.  
   
   
       4 . The optical glass of  claim 1 , which comprises at least one component selected from Nb 2 O 5 , WO 3 , TiO 2  or Bi 2 O 3 .  
   
   
       5 . The optical glass of  claim 1 , which is a glass for precision press-molding.  
   
   
       6 . A process for producing an optical glass comprising P 2 O 5  and SiO 2  as glass components, 
 which comprises either heating and melting a first raw material comprising SiO 2  to make a melt, or preparing a cullet raw material from said melt,    mixing a second raw material comprising a phosphoric acid compound, a melt obtained by heating and melting said second raw material or a cullet raw material obtained from said melt of the second raw material with said melt of the first raw material or the cullet raw material obtained from said melt of the first raw material, melting the mixture and melting said optical glass.    
   
   
       7 . A precision press-molding preform formed of the optical glass of  claim 5 .  
   
   
       8 . A precision press-molding preform that is formed of an optical glass comprising, as essential components, P 2 O 5 , SiO 2  and an alkali metal oxide including Li 2 O, having an SiO 2  content of 0.5 to 4 mol % and having a refractive index (nd) of 1.80 or more and an Abbe's number (νd) of 30 or less, and of which the entire surface is formed by solidification of said glass in a molten state or is a free surface.  
   
   
       9 . A process for producing a precision press-molding preform, which comprises separating a molten glass gob having a predetermined weight from a glass in a molten state and shaping said molten glass gob into that preform of  claim 7  which has a weight equivalent to said weight before said molten glass gob is cooled to solidness.  
   
   
       10 . A process for producing a precision press-molding preform, which comprises separating a molten glass gob having a predetermined weight from an optical glass in a molten state, the optical glass being produced by the process for producing an optical glass as recited in  claim 6 , and shaping said molten glass gob into a preform having a weight equivalent to said weight before said molten glass gob is cooled to solidness,  
   
   
       11 . An optical element formed of the optical glass of  claim 1 .  
   
   
       12 . A process for producing an optical element, which comprises precision press-molding a preform formed of a glass, 
 wherein the precision press-molding preform of  claim 7  is precision press-molded.    
   
   
       13 . A process for producing an optical element, which comprises precision press-molding a preform formed of a glass, 
 wherein a precision press-molding preform produced by the process of  claim 9  is precision press-molded.    
   
   
       14 . The process for producing an optical element as recited in  claim 12 , wherein the precision press-molding preform is introduced into a press mold, and said preform and said press mold are heated together.  
   
   
       15 . The process for producing an optical element as recited in  claim 12 , wherein the precision press-molding preform heated is introduced into the press mold to precision press-mold the preform.