JPS62123040A - Optical glass - Google Patents

Abstract

PURPOSE:To obtain the aimed optical glass for lenses precisely pressable at a relatively low temperature, by specifying a composition, consisting essentially of SiO2, B2O3, Li2O, BaO and La2O3 and further containing Na2O, K2O, SrO, ZnO, Gd2O3 and Yb2O3. CONSTITUTION:An optical glass for lenses consisting of 20-40wt% SiO2, 10-20wt% B2O3, 3-9wt% Li2O, 0-10wt% Na2O, 0-7wt% K2O, provided that the total of Li2O, Na2O and K2O is 9-18wt%, 0-11wt% SrO, 13-45wt% BaO, 0-5wt% ZnO, 5-18wt% La2O3, 0-5wt% Gd2O3 and 0-5wt% Yb2O3 and having <=550 deg.C yield temperature (At), 1.595-1.635 refractive index (nd) and >=50 Abbe's number (nud) and relatively low softening point and further characteristic of medium refractive index and low dispersion. The optical glass is stable to devitrification and can be precisely pressed at a relatively low temperature without requiring grinding or polishing after press forming.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical glass for press lenses that can be press-molded at relatively low temperatures and does not require grinding or polishing r'K after press-molding.

BACKGROUND OF THE INVENTION Optical glasses of the SK type and the V S S +< type exist as those having optical constants similar to those of the prior art.

In addition, as a glass for press molding, phosphate-based glass is used in JP-A-5!5-154343 and JP-A-58-79839.
, JP-A No. 60-122749 No. 3), fluorophosphate glass (JP-A No. 56-59 (341, JP-A No. 1135)
G-149343, JP-A-58-217451),
Fluoroborate-based Karasu (18 1988-146952 reference HHg) Potassium 11 has been used.

Problems to be Solved by the Invention The conventional S K type and S S K type optical glasses only have a yield temperature (At) of 630°C or higher, and the pressing temperature is 700°C. It could not be molded unless the temperature was higher than that. Table 1 shows examples of SK type and SSK type (refractive index (n d ), Atsbe number (νd), yield temperature (At)
, and specific gravity).

Table 1 Patents have been published regarding precision Ares I+U machining mold materials that do not require grinding or polishing after press molding, but when the press molding temperature becomes high, problems such as oxidation of the mold material occur, resulting in poor surface accuracy. It is difficult to maintain and is not suitable for mass production. Therefore, it is desirable that the glass to be pressed be formed at the lowest possible temperature. The above patent therefore advances phosphoric acid and boric acid as glass-forming oxides. However, although phosphoric acid and boric acid are advantageous in lowering the temperature, they tend to cause problems in the chemical durability and weather resistance of glass. Furthermore, although the introduction of fluorine is advantageous in lowering the temperature and reducing dispersion, it tends to cause problems in stability during glass melting, mold material, environment, etc. due to volatilization of fluorine at pressing temperature. Glass containing lead is also seen in the above patent, but if it contains lead, volatiles of lead will adhere to the mold material, similar to fluorine, and problems will likely occur in maintaining surface accuracy.

OBJECTS OF THE INVENTION Accordingly, the first object of the present invention is to provide an optical glass for press lenses that can be precision pressed at a relatively low temperature and does not require grinding or polishing after press molding.

The second object of the present invention is that the refraction m(nd) is 1.59.
5-1.635 and an Abbe number (vd) of 50 or more, which is a medium refractive index and low dispersion optical glass.

Means for Solving the Problems The inventors of the present invention took into consideration the various drawbacks of conventional optical glasses and optical glasses for press molding as described above, and as a result of various studies and studies, 5i02, B2O3, Li2O, Bad,
Optical glass with a glass composition that requires La2O3 is
It has almost the same optical constant as the S K type and the S S K type optical glass, can be press-formed at a lower temperature, and has almost no effect on the mold material, and furthermore, the press-forming of the above patent It has better stability, chemical durability, i-10ft property, and meltability than optical glass.
Can be handled in the same way as conventional optical glass, and has a low yield temperature (At)
The present invention was achieved by discovering a glass composition that is optimal as an optical glass for press lenses that does not require grinding or polishing after press molding because of its low resistance.

That is, if the present invention is expressed in Kt1%, 5i02 20-40% B2O3 10-20% Li203-9% Na2O0-10% 200-7% and two Tffli of Li2O, Na2O, K2O or more 9-1
It has a composition of 8% SrOO-11% BaO13-45% Zn00-5% La2O35-18% Gd2O30-5% Yb2O30-5%.

The reason why the range of each component of the optical glass according to the present invention is limited as described above is as follows.

5102 is the main component that makes up the crow's mesh, but 4
If it exceeds 0%, the viscosity during melting increases and the yield temperature (
If it is less than 20%, the tendency to devitrify increases.

Like 5i02, B2O3 constitutes a glass network and is an effective component for stabilizing the glass.

It is also effective in homogenizing the crow, and furthermore, by containing it in an appropriate amount, the yielding temperature (At) is lowered. But 10%
If it is less than 20%, the above effect will be less, and if it is more than 20%, chemical durability will deteriorate.

L120 is an important component in the present invention, and by adding an appropriate amount of L120 as an essential component, it has the effect of significantly lowering the temperature during press molding without impairing the stability of the glass. If L, 120 is less than 3%, the above effect will be small, and if it is more than 9%, the devitrification will increase.

Na20 and L20 each contribute to the temperature drop during press molding, but if Na2O is more than 10% and L20 is more than 7%, not only will devitrification increase, but the chemical durability will also deteriorate.

Li2O, Na2O and! < If the content of two or more of 20 is less than 9%, the temperature will rise during press molding, and 1
When it is more than 8%, chemical durability deteriorates and the tendency for devitrification increases.

SrO is an optional compounding component, and by combining it with BaO, the yield temperature (At
), but if the SrO content exceeds 11%, the devitrification will increase and the desired optical performance will not be obtained, so it should be lower than this.

BaO is an essential blending component and is effective in increasing the refractive index Σ6, but if it is less than 13%, the effect is small, and 45
If it's more than 96, you'll lose! ! The trend increases.

ZnO is an optional ingredient and increases chemical durability, but if it exceeds 5%, it will be lost! ! The trend increases.

La2O3 is an essential compounding component, and like BaO, it increases the refractive index and improves chemical durability. When it is less than 5%, the above effect is small, and when it is more than 18%, the yield temperature (At)
This results in an increase in the devitrification tendency.

Yb2O3 and Gd2O3 are optional components, and are used together with La2O3 to adjust optical performance.
It is sufficient for the amount to be 5% or less, and exceeding this amount results in an increase in the yielding temperature (At).

In addition to the above-mentioned components, the optical glass of the present invention may contain GeO2, ZrO2, T, etc., in order to adjust the optical performance, improve meltability, expand the range of glass formation, etc., as long as it does not depart from the purpose of the present invention.
i 02, Nb2O5, Ta205, Y2O3, I
n203, Ga2O3, Al2O3, WO3, MgO,
Cab, PbO, etc. can be contained.

Example Next, the &Il composition of the example according to the present invention (the numerical values are %, refractive index (d), number (νd), yielding temperature (At),
and specific gravity) are shown in Table 2.

The optical glass of the present invention uses corresponding oxides, hydroxides, carbonates, nitrates, etc. as raw materials for each component, weighs them in a predetermined ratio, mixes them thoroughly, and produces a platinum glass as a glass preparation raw material. ;Put it in the electric furnace for 1000-1200 yen.
Melt it at ℃, stir it with a platinum stirring rod to homogenize it, and then pour it into a mold preheated to an appropriate temperature.
Make by cooling slowly. Note that adding a small amount of As2O3 to prevent glass coloring and defoaming, or adding a small amount of an industrially well-known defoaming component does not affect the effects of the present invention.

@Table 2 Effects of the invention According to the invention, when the yielding temperature (At) is 550°C or less,
It has a refraction 'ts (nd) of 1.595-1.635, an Atsbe number (νd) of 50 or more, is stable against devitrification, can be precision pressed at relatively low temperatures, An optical glass for press lenses that does not require grinding or polishing after press molding can be obtained.

Claims (1)

[Claims] SiO2 20-40% by weight B2O3 10-20% by weight Li2O 3-9% by weight Na2O 0-10% by weight K2O 0-7% by weight However, two or more of Li2O, Na2O, K2O 9-18% by weight % SrO 0-11% by weight BaO 13-45% by weight ZnO 0-5% by weight La2O3 5-18% by weight Gd2O3 0-5% by weight Yb2O3 0-5% by weight When the yield temperature (At) is 550°C or less , an optical glass for pressed lenses having a relatively low softening point with a refractive index (nd) of 1.595 to 1.635 and an Abbe number (νd) of 50 or more, and a medium refractive index and low dispersion properties.