Lens and process for the production thereof

Abstract

A lens formed of a high-refractivity low-dispersion glass and free of fogging and scorching on its optical-function surface, which is obtained by precision press-molding of an optical glass having a refractive index (nd) of over 1.83, an Abbe's number (νd) of 40 or more and a glass transition temperature (Tg) of 640° C. or lower and containing no Li2O and has one form of a meniscus form, a biconcave form or a plano-concave form.

Description

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing a change in the temperature of a mold and a change in a molding pressure with the passage of time in a process for the production of a lens in the present invention.

FIG. 2 is a schematic drawing of one example of a pressing apparatus for use in a process for the production of a lens in the present invention.

Claims

1. A lens formed of an optical glass having a refractive index (nd) of over 1.83, an Abbe's number (νd) of 40 or more and a glass transition temperature (Tg) of 640° C. or lower and containing no Li2O and obtained by precision press-molding and the lens having one form of a meniscus form, a biconcave form or a plano-concave form.

2. The lens of claim 1, wherein the optical glass contains, as essential components, B2O3, La2O3 and ZnO and has contents of said components determined to give an refractive index (nd) of over 1.83, an Abbe's number (νd) of 40 or more and a glass transition temperature (Tg) of 640° C. or lower.

3. The lens of claim 2, wherein the optical glass contains, by mol %, 20 to 45% of B2O3, 5 to 24% of La2O3 and 22 to 42% of ZnO.

4. The lens of claim 1, which has a concave meniscus form or a biconcave form.

5. A process for the production of a lens by heating and precision press-molding a glass material, which comprises introducing a glass material formed of an optical glass having a refractive index (nd) of over 1.83, an Abbe's number (νd) of 40 or more and a glass transition temperature (Tg) of 640° C. or lower and containing no Li2O into a press mold and precision press-molding the glass material to produce a lens having one form of a meniscus form, a biconcave form or a plano-concave form.

6. The process for the production of a lens as recited in claim 5, which uses, as the glass material, an optical glass containing B2O3, La2O3 and ZnO as essential components and having contents of said components determined to give an refractive index (nd) of over 1.83, an Abbe's number (νd) of 40 or more and a glass transition temperature (Tg) of 640° C. or lower.

7. The process for the production of a lens as recited in claim 6, wherein said glass material is formed of an optical glass containing, by mol %, 20 to 45% of B2O3, 5 to 24% of La2O3 and 22 to 42% of ZnO.

8. The process for the production of a lens as recited in claim 5, wherein a lens having a concave meniscus form or a biconcave form is obtained by the precision press-molding.

9. The process for the production of a lens as recited in claim 5, which comprises the steps of softening the glass material by heating and pressing the glass material with a mold comprising a first mold member whose molding surface for forming an optical-function surface of a lens to be obtained is a concave surface or a flat surface and a second mold member whose molding surface is a convex surface,cooling said mold until said glass material in said mold comes to have a temperature of a glass transition temperature (Tg) or lower, andtaking said glass material cooled out of said mold,the cooling being carried out in said step of cooling the mold in a manner that the temperature of the first mold member reaches the glass transition temperature (Tg) of said glass material before the temperature of the second mold member.

10. The process for the production of a lens as recited in claim 5, which comprises the pressing step of softening the glass material by heating and pressing the glass material with a mold comprising a first mold member whose molding surface for forming an optical-function surface of a lens to be obtained has a relatively large curvature radius or paraxial curvature radius and a second mold member whose molding surface has a relatively small curvature radius or paraxial curvature radius, the cooling step of cooling said mold until said glass material in said mold comes to have a temperature of the glass transition temperature (Tg) or lower, andthe step of taking said glass material cooled out of said mold,the cooling being carried out in said cooling step in a manner that the temperature of the first mold member reaches the glass transition temperature (Tg) of said glass material before the temperature of the second mold member, thereby to produce a biconcave lens.