JPH0558669A - Optical glass - Google Patents

Abstract

PURPOSE:To contrive the improvement in the chemical durability and homogeneity of an optical glass by specifying the refractive index, Abbe number and flexure point of the optical glass. CONSTITUTION:15-45wt.% of B2O3, 0-30wt.% of SiO2 (but B2O3+SiO2=35-55 wt.%), 19-35wt.% of La2O3, 0-10wt.% of Gd2O3, 0-10wt.% of ZrO2, 0-10wt.% or Ta2O5 (but ZrO2+Ta2O5=0.5-10wt.%), 0-8 wt.% of Al2O3, 0.5-25wt.% or SrO, 0-10wt.% of MgO, 0-15wt.% of CaO, 0-20wt.% or BaO, 0-10wt.% or ZnO (but MgO+CaO+BaO+ZnO=0-30wt.%, and when the SrO is 15.5-25wt.%, the BaO is 0-5wt.%), 2.5-8wt.% or Li2O, 0-10wt.% of Na2O and 0-10wt.% of K2O (but Li2O+Na2O+K2O=2.5-15wt.%) are mixed with each other, and melted in the glass state to obtain an optical glass having optical constants consisting of a refractive index of approximately 1.63-1.75 and an Abbe number of approximately 45-60, and having a flexure point of 555-640 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a refractive index (Nd) of about 1.
63-1.75, Abbe number (νd) optical constant in the range of about 45-60, and yield point (At) in the range of 555-640 ° C.
B ₂ O ₃ —La ₂ O ₃ − having excellent chemical durability
ZrO ₂ and / or Ta ₂ O ₅ —SrO—Li ₂ O
System optical glass.

[0002]

2. Description of the Related Art Conventionally, a glass having the above optical constant has a typical lanthanum borate composition, for example, JP-B 31-4686, JP-A 48-61517 and JP-A 54-54. Various glasses have been disclosed as disclosed in Japanese Patent No. 3115 and the like. However, since these glasses generally have a high yield point and exceed 650 ° C., they are unsuitable as glasses which have recently been required to have excellent mold pressability for direct molding of optical elements. Therefore, various types of glass have been developed for the purpose of imparting a low softening property while maintaining the optical constant. For example, JP-A-59-146
No. 952, B ₂ O ₃ − containing fluorine (F).
La ₂ O ₃ —BaO—R ′ ₂ O (R ′ is an alkali metal element) type glass is disclosed. However, this glass is liable to volatilize due to the fluorine (F) component in the melting step, and it is difficult to obtain high homogeneity. In addition, JP-A 1-286934
No. In _{Japanese, B 2 O 3 -SiO 2 -La} 2 O 3 -CaO
And / or BaO-Li ₂ O based glass is disclosed, but this glass has poor chemical durability and is difficult to put into practical use.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the conventional glass and has a refractive index (Nd) of about 1.63 to 1.75 and an Abbe number (νd) of about 45 to 60. Deflection point (A
It is an object of the present invention to provide an optical glass having more excellent chemical durability and homogeneity while maintaining t).

[0004]

In order to achieve the above-mentioned object, the present inventors have achieved a low softening property of B ₂ O ₃ -La ₂ O _3-.
Based on Li ₂ O-based glass, various tests and studies were conducted on components to be added to it, and the glass composition was changed to B.
₂ O ₃ —La ₂ O ₃ —ZrO ₂ and / or Ta
_By adopting a ₂ O ₅ —SrO—Li ₂ O system, it is possible to further improve the chemical durability of glass while maintaining a predetermined optical constant and a low softening property suitable for a mold press, that is, a low yield point. As a result, they have completed the present invention.

The characteristics of the optical glass according to the present invention are, in weight%, B ₂ O ₃ 15 to 45%, SiO ₂ 0 to 30%,
However, B ₂ O ₃ + SiO ₂ 35 to 55%, La ₂ O _{3
19~35%, Gd 2 O 3 0~10} %, ZrO 2 0
_{~10%, Ta 2 O 5 0~10} %, provided that ZrO <sub>2
+ Ta 2 O 5 0.5~10%,</sub> Al 2 O 3 0~8%, S
rO 0.5-25%, MgO 0-10%, CaO 0
-15%, BaO 0-20%, ZnO 0-10%,
However, MgO + CaO + BaO + ZnO 0-30
%, And BaO 0 for SrO 15.5 to 25%
Less than _{~5%, Li 2 O2.5~8%,} Na 2 O 0~1
_{0%, K 2 O 0~10%} , provided that _Li 2 O + _Na 2 O
+ K ₂ 0 containing each component in the range of 2.5 to 15%, and having an optical constant in the range of a refractive index (Nd) of about 1.63 to 1.75 and an Abbe number (νd) of about 45 to 60. 555-64
It has a yield point (At) in the range of 0 ° C.

Next, the reason why the content of each component is limited as described above will be described. That is, the B ₂ O ₃ component is a glass-forming component that is advantageous for imparting low softening properties to the glass, but its amount is in the range of 15 to 45% in order to maintain devitrification resistance and chemical durability of the glass. Is appropriate. SiO ₂
In order to improve the chemical durability, the components can be added in the range where the low softening property can be maintained, that is, up to 30%. However, B ₂ O
The total amount of ₃ and the SiO ₂ component should be in the range of 35 to 55% for the devitrification resistance of the glass and the maintenance of the target optical constant.

The La ₂ O ₃ component must be contained in an amount of 19% or more in order to make the refractive index of glass a target value.
If the amount exceeds 35%, the glass tends to devitrify.
The Gd ₂ O ₃ component can be added to adjust the optical constant of the glass, but up to 10% is sufficient.

In the present invention, the ZrO ₂ and / or Ta ₂ O ₅ component is contained in the glass together with the SrO component, which will be described later, to maintain a predetermined yield point and to significantly improve the chemical durability. It is an important ingredient found. The amounts of these components should be limited to 10% each to maintain devitrification resistance. Also,
The total amount of these components is required to be 0.5% or more in order to exert the above-mentioned effects, and is 1 for maintaining devitrification resistance.
The limit should be 0%.

The Al ₂ O ₃ component is the above ZrO ₂ or Ta.
Unlike ₂ O ₅ , it is unexpectedly easy to devitrify the glass, so it is better not to use it positively, but depending on the composition of the glass, it can be added up to 8% for adjusting the optical constant.

The SrO component is most advantageous in view of increasing the optical constant of the glass and chemical durability, devitrification resistance and low softening property in comparison with other divalent metal oxide components. It is an important component, and as described above, it is contained together with the ZrO ₂ and / or Ta ₂ O ₅ components to remarkably improve the chemical durability, but the effective amount is 0.5 to 25%. Other divalent metal oxide components MgO, CaO,
BaO and ZnO components may be added for adjusting optical constants, etc., but the amounts of these components are 10% and 15%, respectively.
%, 20% and 10%, the stability of glass tends to be impaired. However, the total amount of one or more of these other divalent metal oxide components should be in the range of 0 to 30% in order to maintain the target optical constant and devitrification resistance. Further, when the amount of the SrO component is 15.5 to 25%, the amount of the BaO component should be less than 5% in order to maintain the devitrification resistance of the glass.

The Li ₂ O component is an important component because it has a particularly large effect of giving the glass a low softening property, but in order to exert the effect while maintaining the devitrification resistance of the glass, the amount thereof should be set. It should be in the range of 2.5-8%. Na
_{The 2} O and K ₂ O components can be added as necessary,
The amounts should be up to 10% for maintaining devitrification resistance and chemical durability. However, Na ₂ O and K
_For the same reason, the total amount of one or two kinds of ₂ O and the Li ₂ O component is set to 2.5 to 15%.

Components such as Nb ₂ O ₅ , TiO ₂ , WO ₃ and PbO may be added to the optical glass of the present invention within a range that does not impair the desired properties. Further, as a defoaming and clarifying agent, components such as Sb ₂ O ₃ , As ₂ O ₃ and fluorine (F) may be added in appropriate amounts.

[0013]

EXAMPLES Next, with respect to the example compositions (No. 1 to No. 12) of the optical glass of the present invention and the comparative composition examples (No. A and No. B) of the conventional optical glass,
Table 1 shows the refractive index (Nd), Abbe number (νd), yield point (At, ° C), and chemical durability measurement test results of each of the obtained glasses.

[0014]

[Table 1]

In the chemical durability test, each glass sample (about 30 × 30 × 5 mm) having a fractured surface and a polished surface was subjected to 3N-
Immersion in an aqueous nitric acid solution (25 ° C) for 1 hour and observing the degree of erosion on both surfaces, marking the ones with no change in surface condition and maintaining transparency, and marking both surfaces rough The method of displaying a cross mark that caused the occurrence of transparency and whose transparency was clearly impaired was adopted. These glass samples were prepared by weighing and mixing optical raw materials such as oxides, carbonates, nitrates, and hydroxides at a predetermined ratio, and then charging them into a platinum crucible, depending on the difficulty of melting depending on the composition. It was obtained by melting and homogenizing at a temperature of 100 to 1,350 ° C., then casting in a mold and slowly cooling.

As can be seen from Table 1, each of the glasses of the examples of the present invention exhibited the target Nd value, νd value and At value, and the chemical durability was remarkably improved as compared with the glasses of the comparative examples. There is. Further, all of these glasses have excellent devitrification resistance and are easily homogenized. For this reason, the glasses of the above-mentioned examples are easy to manufacture, suitable for mold pressing, and the surface condition is hard to change.

[0017]

As mentioned above, according to the present invention, the optical glass of the present invention _has a specific composition of _{B 2 O 3 -La 2 O 3} -ZrO 2 and / or _{Ta 2 O 5 -SrO-Li 2} O component system Therefore, it has an optical constant in the range of Nd of about 1.63 to 1.75 and νd of about 45 to 60, and a yield point (At) in the range of 555 to 640 ° C., and has chemical durability. Is much better. In addition, it is easy to manufacture, easy to homogenize, and suitable for mold pressing.

Claims (1)

[Claims] 1. By weight% B ₂ O ₃ 15-45%, Si
O ₂ 0 to 30%, but B ₂ O ₃ + SiO ₂ 35
_{~55%, La 2 O 3 19~35} %, Gd 2 O 3
_{0~10%, ZrO 2 0~10%,} Ta 2 O 5 0~
10%, but ZrO ₂ + Ta ₂ O ₅ 0.5-1
0%, Al ₂ O ₃ 0 to 8%, SrO 0.5 to 25%,
MgO 0-10%, CaO 0-15%, BaO 0
~ 20%, ZnO 0-10%, but MgO + Ca
O + BaO + ZnO 0-30%, and SrO 1
In the case of 5.5 to 25%, BaO 0 to less than 5%, Li ₂ O
_{2.5~8%, Na 2 O 0~10%} , K 2 O 0~1
0%, provided that _{Li 2 O + Na 2O + K2} O2.5~
Contains each component in the range of 15% and has a refractive index (Nd)
About 1.63 to 1.75, Abbe number (νd) about 45 to 60
An optical glass having an optical constant in the range of 1 and a yield point (At) in the range of 555 to 640 ° C.