Optical glass, precision press-molding preform, process for producing the preform, optical element and process for producing the element

A process for producing an optical element, which comprises heating a precision press-molding preform and precision press-molding the preform with a mold, said precision press-molding preform being formed of an optical glass comprising, by mol %,

• 5 to 25.37% of B2O3, provided that the content of B2O3 is 15.27% by weight or less,
• 3 to 50% of SiO2,
• 10 to 40% of TiO2,
• 10.45 to 40% of ZnO,
• 5 to 20% of La2O3 provided that the content of La2O3 is over 27% by weight,
• 0 to 10% of Gd2O3,
• 0 to 15% of Nb2O5,
• 0 to 10% of ZrO2,
• 0 to 5% of Ta2O5,
• 0 to 10% of Bi2O3,
• 0 to 6% of MgO,
• 0 to 8% of CaO,
• 0 to 10% of SrO,
• 0 to 6% of BaO
• provided that the total content of MgO, CaO, SrO and BaO is 15% or less,
• 0 to 20% of Li2O, and
• 0 to 5% of Na2O,
• containing no PbO or As2O3, optionally containing not more than 1% by weight of Sb2O3 as a refining agent, having a refractive index (nd) of over 1.88 and an Abbe's number (vd) of 35 or less and having a glass transition temperature of 620° C. or lower.

A process for producing an optical element, which comprises heating a precision press-molding preform and precision press-molding the preform with a mold, said precision press-molding preform being formed of an optical glass comprising, by mol %,

• 5 to 25.37% of B2O3, provided that the content of B2O is 15.27% by weight or less,
• 3 to 50% of SiO2,
• 10 to 40% of TiO2,
• 10.45 to 40% of ZnO,
• 5 to 20% of La2O3, provided that the content of La2O3 is over 34.92% by weight,
• 0 to 10% of Gd2O3,
• 0 to 15% of Nb2O5,
• 0 to 10% of ZrO2,
• 0 to 5% of Ta2O5,
• 0 to 10% of Bi2O3,
• 0 to 6% of MgO,
• 0 to 8% of CaO,
• 0 to 10% of SrO,
• 0 to 6% of BaO, the content of BaO being less than 13% by weight,
• provided that the total content of MgO, CaO, SrO and BaO is 15% by weight or less,
• 0 to 20% of Li2O,
• 0 to 5% of Na2O,
• 0 to 1% of Sb2O3,
• provided that the content of Sb2O3 is 1% by weight or less, containing no PbO or As2O3, having a refractive index (nd) of over 1.88 and an Abbe's number (vd) of 35 or less, and having a glass transition temperature of 620° C. or lower.