JPH0826766A - Optical glass - Google Patents

Abstract

PURPOSE:To obtain optical glass having desired optical constants, excellent in chemical durability and stability to devitrification and useful for molding with no environmental pollution by imparting a compsn. contg. prescribed amts. of B2O3, Li2O, ZnO and La2O3 as essential components. CONSTITUTION:A mixture is prepd. by mixing, by weight, 22-35% B2O3, 0.1-2.5% Li2O, 20-35% ZnO and 12-42% La2O3 as essential components with 0-5% SiO2, 0-5% Al2O3, 0-5% Na2O, 0-5% K2O, 0-5% MgO, 0-5% ZrO2, 0-10% CaO 0-10% SrO 0-10% BaO, 0-10% Y2O3, 0--10% Yb2O3 0-10% Nb2O5 0-20% Gd2O3, 0-14% Ta2O5, 0-1% As2O3 and 0-1% Sb2O3 as optional components. The mixture is melted to obtain the objective optical glass having a refractive index (nd) of 1.66-1.77, an Abbe number (nud) of 43-55 and <=620 deg.C deformation temp. (At).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to B ₂ O ₃ --Li ₂ O--Z.
It consists of a basic composition system of nO-La ₂ O ₃ and has a refractive index (nd)
Is about 1.66 to 1.77 and the Abbe number (νd) is about 43 to
55 is optical glass. Further, the optical glass according to the present invention can be molded at a low temperature, and particularly relates to an optical glass useful for molding.

[0002]

2. Description of the Related Art In recent years, as devices using an optical system have been highly integrated and highly functionalized, there has been a strong demand for higher precision, lighter weight and smaller size of the optical system. Optical designs using aspherical lenses are becoming mainstream. For this reason, it is necessary to stably supply a large amount of aspherical lenses at a low cost. Molding technology for obtaining a lens having a predetermined performance without performing the final grinding / polishing process has been actively studied. Further, not only aspherical lenses, but also molding lenses have been studied for lenses having complicated shapes. Along with this, demands for developing optical glass suitable for molding have been increasing year by year.

As the optical glass having the above optical constant, various glasses containing B ₂ O ₃ and La ₂ O ₃ as essential components have been known for a long time. However, the conventional B ₂ O ₃ -La ₂
All optical glasses containing O ₃ as an essential component are focused on improving their chemical durability and devitrification resistance, and their hot formability has not been fully considered. It is hard to say that it is suitable for. Further, since these optical glasses generally have a high yield point, the molding temperature during heat molding is 650 ° C. or higher, which easily causes deterioration of a highly accurate mold, and it is also difficult to realize a highly accurate lens surface. Becomes Therefore, various optical glasses containing B ₂ O ₃ , Li ₂ O, and La ₂ O ₃ as main components have been developed and disclosed as optical glasses for molding having a low yield point. For example,
Japanese Patent Laid-Open No. 4-92834 discloses nd = 1.622 to 1.7.
No. 01, νd = 45.3 to 55.1, and optical glass having At = 504 to 549 ° C. in Examples, Japanese Patent Laid-Open No. 4-92835 discloses nd = 1.740 to 1.78.
5, νd = 38.0 to 47.0, At is 570 ° C. or less (Example At = 500 to 569 ° C.), an optical glass, Japanese Patent Laid-Open No. 5-58669, nd = about 1.63 to.
1.75, vd = about 45-60, At = 555-640
The optical glass characterized by ℃, JP-A-5-201743, nd = 1.65 to 1.75, vd is 50 or more, At
= 560 ° C. or less, such as optical glass.

Japanese Unexamined Patent Publication No. 62-874432 does not disclose the Abbe number, but nd = 1.690 to 1.725,
It is an optical glass containing PbO at At = 570 ° C. or lower and capable of precision pressing at a relatively low temperature.

[0005]

However, the above-mentioned conventional optical glass, particularly the optical glass for molding, has a high precision because the specific element in the glass composition volatilizes and adheres to the mold during heat molding. There is a problem that molding is difficult. Further, from the results of analysis and the like, it is known that the element attached to the mold is mainly a relatively large amount of alkali metal oxide or lead oxide contained for realizing a low yield point.

[0006] These elements not only make it difficult to mold with high precision, but a large amount of alkali metal oxide reduces chemical durability, and lead oxide leads to environmental pollution in the manufacturing process. . Therefore, the present invention has been made in view of the above-mentioned problems of the conventional optical glass, particularly the optical glass for molding.

An object of the present invention is to have a refractive index (nd) of 1.6.
It has an optical constant of 6 to 1.77, an Abbe number (νd) of 43 to 55, a yield point of 620 ° C. or lower suitable for molding, and further, glass composition components do not volatilize during molding. Another object of the present invention is to provide a novel optical glass which is excellent in chemical durability and stability against devitrification and has no environmental pollution.

[0008]

Means for Solving the Problems The present inventor has achieved the above object.
As a result of earnest research to achieve, B₂O₃, Li ₂
O, ZnO, La₂O₃Optical glass composition containing as an essential component
Is the desired optical constant and molding within the prescribed composition range.
It has a yield point suitable for molding, and during molding
Excellent chemical resistance without volatilizing glass composition components
Found that stability and stability against devitrification can be achieved
Then, the present invention was accomplished. That is, the present invention is
Ratio (wt%), SiO₂ 0-5 wt% B₂O₃ 22-35 wt% Al₂O₃ 0-5 wt% Li₂O 0.1-2.5 wt% Na₂O 0-5 wt% K₂O0-5 wt% MgO0-5 wt% CaO0-10 wt% SrO0-10 wt% BaO0-10 wt% ZnO20-35 wt% ZrO₂ 0-5 wt% La₂O₃ 12 to 42 wt% Gd₂O₃ 0 to 20 wt% Y₂O₃ 0-10 wt% Yb₂O₃ 0-10 wt% Nb₂O_Five 0-10 wt% Ta₂O_Five 0-14 wt% As₂O₃ 0 to 1 wt% Sb₂O₃ It has a composition of 0 to 1 wt% and a refractive index (nd) of 1.66 to 1.
77, Abbe number (νd) 43 to 55, yield point (At)
For molding, characterized in that
Provide optical glass.

[0009]

The above composition range has been experimentally found and the reason for limiting the composition range is as follows. Si
O ₂ is a glass-forming oxide that improves the stability against devitrification, but if it exceeds 5 wt%, undissolved substances tend to be generated, and the melting temperature and the yield point rise.

Like SiO ₂ , B ₂ O ₃ is a glass-forming oxide and is an essential component in the present invention. 22 wt%
If it is less than 3, sufficient stability against devitrification cannot be obtained, but 3
If it exceeds 5 wt%, the refractive index is lowered and the chemical durability is lowered. Al ₂ O ₃ improves stability against devitrification and chemical durability, but if it exceeds 5 wt%, the yield point rises.

Li ₂ O is an essential component that lowers the melting temperature and the yield point without significantly lowering the refractive index and lowering the chemical durability as compared with other alkali metal oxides. If it is less than%, a sufficient effect cannot be obtained, and 2.
If it exceeds 5 wt%, the chemical durability and the stability against devitrification decrease. Furthermore, Li ₂ O volatilizes during molding and easily adheres to the mold, making it difficult to mold with high precision.

Na₂O, K₂O has a low melting temperature and yield point
However, if it exceeds 5 wt%, the refractive index will decrease and
Durability and stability against devitrification are also reduced. further,
Na ₂O, K₂O volatilizes during molding and easily adheres to the mold
Therefore, it becomes difficult to mold with high precision. However, Li₂
O, Na₂O, K₂The total amount of O exceeds 5.5 wt%.
If so, the refractive index will decrease, and chemical resistance and devitrification will be reduced.
Stability is also reduced. In addition, these alkali metal acids
The compound is volatilized at the time of molding and easily adheres to the mold, resulting in high accuracy.
Molding becomes difficult. .

Although MgO lowers the melting temperature, it is 5 wt.
When it exceeds%, the stability against devitrification decreases and the tendency of phase separation increases. CaO, SrO, and BaO are useful for adjusting the refractive index and improving the stability against devitrification, but if they exceed 10 wt%, the devitrification tendency increases, and the chemical durability decreases.

ZnO lowers the melting temperature and the yield point,
It is an essential component effective for adjusting the refractive index, but 20 wt%
If it is less than 35% by weight, a sufficient effect cannot be obtained, and if it exceeds 35% by weight, dispersion becomes large, stability against devitrification decreases, and chemical durability also decreases. ZrO ₂ is stability against devitrification,
Although the chemical durability is improved, if it exceeds 5 wt%, the devitrification tendency is increased and the yield point is increased.

La ₂ O ₃ is an essential component for increasing the refractive index and improving the chemical durability without relatively lowering the stability against devitrification, but if it is less than 12 wt%, a sufficient effect is obtained. If it exceeds 42 wt%, the stability against devitrification decreases and the yield point rises. Gd ₂ O ₃ increases the refractive index and improves the chemical durability without relatively lowering the stability against devitrification, but when it exceeds 20 wt%, the stability against devitrification decreases and the yield point Also rises.

Y ₂ O ₃ and Yb ₂ O ₃ increase the refractive index and improve the chemical durability, but if it exceeds 10 wt%, the stability against devitrification decreases and the yield point rises. Nb ₂ O ₅ ,
Ta ₂ O ₅ raises the refractive index and improves the chemical durability, but when it exceeds 10 wt% and 14 wt%, respectively, the dispersion becomes large and the stability against devitrification decreases.

Although As ₂ O ₃ and Sb ₂ O ₃ are used as defoaming agents, a sufficient effect can be obtained at 1 wt% or less. Further, if Sb ₂ O ₃ exceeds 1 wt%, coloring of the glass is recognized.

[0018]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Example compositions (numerical values are wt%) according to the present invention are shown in Tables 1, 2, and 3 together with optical constants (nd, νd) and yield points (At, numerical values are ° C).

The optical glass according to the present invention is prepared as a compounding raw material by using corresponding oxides, carbonates, nitrates, etc. as raw materials for the respective components, weighing them at a desired ratio, and thoroughly mixing with powder. It can be produced by, for example, charging it into a platinum crucible in an electric furnace heated to 1050 to 1300 ° C., clarifying the melt, homogenizing with stirring, casting in a preheated iron mold, and gradually cooling.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

As described above, according to the present invention, the refractive index (nd) is 1.66 to 1.77 and the Abbe number (νd) is 4.
3 to 55, the yield point (At) is 620 ° C. or less, excellent in chemical durability and stability against devitrification,
An optical glass without environmental pollution is provided.

In addition, since the optical glass according to the present invention has a low yield point, the surface of a highly accurate mold is pressure-transferred onto a glass material so as to have a predetermined performance without requiring a final grinding / polishing step. It is extremely useful for molding to obtain a lens having

Claims (1)

[Claims] 1. A weight ratio (hereinafter referred to as wt%) of SiO ₂ 0 to 5 wt% B ₂ O ₃ 22 to 35 wt% Al ₂ O ₃ 0 to 5 wt% Li ₂ O 0.1 to 2.5 wt% _{Na 2 O 0 ~ 5 wt%} K 2 O 0 ~ 5 wt% , _{however, Li 2 O + Na 2 O} + K 2 O 0.1~ 5.5wt% MgO 0 ~ 5 wt% CaO 0 ~ 10 wt% SrO 0 ~ 10 wt % BaO 0 to 10 wt% ZnO 20 to 35 wt% ZrO ₂ 0 to 5 wt% La ₂ O ₃ 12 to 42 wt% Gd ₂ O ₃ 0 to 20 wt% Y ₂ O ₃ 0 to 10 wt% Yb ₂ O _It has a composition of ₃₀ to 10 wt% Nb ₂ O ₅ 0 to 10 wt% Ta ₂ O ₅ 0 to 14 wt% As ₂ O ₃ 0 to 1 wt% Sb ₂ O ₃ 0 to 1 wt% and a refractive index. (Nd) is 1.66 to 1.77,
Abbe number (νd) is 43-55, yield point (At) is 62
An optical glass having a temperature of 0 ° C. or lower.