JPH06305769A - Optical glass - Google Patents

Abstract

PURPOSE:To produce optical glass having such optical constants as about 1.75-1.85 refractive idnex (Nd) and about 35-50 Abbe's number (nud) and having excellent chemical durability while improving press moldability. CONSTITUTION:This optical glass contains, by weight, 6-15% SiO2, 15-24% B2O3, 25-50% La2O3, 0.1-10% Ta2O, 6-25% ZnO and 0.5-5% Li2O as principal components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention basically relates to SiO ₂ -B ₂
It is made of O ₃ —La ₂ O ₃ —Ta ₂ O ₅ —ZnO—Li ₂ O system and has a refractive index (Nd) of about 1.75 to 1.85 and an Abbe's number (νd) of about 35 to 50. The present invention relates to a novel optical glass having an optical constant and imparting a low transition temperature characteristic to improve mold press moldability and having excellent chemical durability.

[0002]

2. Description of the Related Art Conventionally, a glass having the above optical constant has a typical lanthanum borate composition, and is found in, for example, JP-A-50-14712 and JP-A-55-116641. Thus, various glasses are disclosed. However, these glasses generally have a transition temperature (Tg
Is high and exceeds 600 ° C., so that it is not suitable as a glass which is required in recent years and has excellent mold pressability for direct molding of optical elements. Generally, the value of Tg is a major factor that affects the difficulty of hot forming of glass, but when press-molding softened glass, the press die is exposed near the Tg of the glass, so the Tg of glass is The higher the value is, the more easily the mold surface is oxidized and the metal structure is changed to deteriorate rapidly to shorten the mold life. Therefore, various glasses have been developed for the purpose of providing low Tg characteristics while maintaining the optical constant. For example, JP-A-60-2
The 21338 _{JP, B 2 O 3 -La 2 O} 3 -Y 2 O 3 -L
An i ₂ O—R ″ O (R ″ is a divalent alkaline earth oxide and / or divalent metal oxide) based glass is disclosed, but this glass has improved devitrification resistance. However, the chemical durability is insufficient.

[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 1.75 to 1.85 and an Abbe number (νd) of about 35 to 50. It is an object of the present invention to provide an optical glass having a further excellent chemical durability while maintaining an optical constant in a range and a low Tg characteristic suitable for a mold press.

[0004]

In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive studies and studies, and as a result, have found that SiO ₂ -B _{2 having a} specific composition range not specifically disclosed in the past.
In the O ₃ -La ₂ O ₃ -Ta ₂ O ₅ -ZnO-Li ₂ O based glass, the chemical durability of the glass is further improved while maintaining the predetermined optical constant and the low Tg characteristic suitable for mold pressing. It was found that an improved desired glass was obtained, and the present invention was completed.

The characteristics of the optical glass according to the present invention are:
%, SiO₂ 6-15%, B₂O ₃ 15-24%,
However, SiO₂+ B₂O₃ 21-35%, La₂O₃ Two
5-50%, Gd₂O₃ 0-30%, but La₂O₃+
Gd₂O₃ 27-60%, Ta₂O_Five 0.1-10%,
ZnO 6-25%, ZrO₂ 0-10%, Nb₂O_Five
0-15%, WO₃ 0-5%, Li₂O 0.5-5
%, Al₂O₃ 0-10%, TiO₂ 0-3% range
Containing each component of, and a refractive index (Nd) of about 1.75 to
Optics in the range of 1.85 and Abbe number (νd) of about 35 to 50
It has a constant number and a Tg of 580 ° C. or lower.

Next, the reason why the content of each component is limited as described above will be described. That is, the SiO ₂ component is
If the amount is less than 6%, the chemical durability of the glass decreases, and if the amount exceeds 15%, the low Tg characteristics cannot be maintained. The B ₂ O ₃ component is a glass-forming component advantageous for giving a glass a low Tg, but its amount should be 15 to 24% in order to maintain the devitrification resistance and the chemical durability of the glass. . However, the total amount of SiO ₂ and B ₂ O ₃ components is 21 to 35 in order to maintain the devitrification resistance of the glass and the target optical constant.
%, Preferably 21 to 30%.

The La ₂ O ₃ component must be contained in an amount of 25% or more in order to bring the refractive index of the glass to a target value, but if the amount exceeds 50%, the glass tends to devitrify. Gd ₂
The O ₃ component gives the glass the same optical characteristics as the La ₂ O ₃ component, and thus can be added, but if the amount exceeds 30%, the glass tends to devitrify. However, the total amount of La ₂ O ₃ and Gd ₂ O ₃ components should be 2 in order to maintain the target optical constant and devitrification resistance.
The range is 7 to 60%, preferably 32 to 60%.

In the present invention, the Ta ₂ O ₅ component is Z as described below.
It is an important component that has been found to have the effect of significantly improving the chemical durability while maintaining a predetermined Tg by including it in the glass together with the nO component. The amount is 0.1
If less than 10%, the effect is not sufficient, and the amount is 10%
If it exceeds, the devitrification resistance of the glass deteriorates. In order to obtain the above effect, it is preferable to contain 0.5% or more.

The ZnO component is an important component advantageous in terms of improving devitrification resistance and melting property of glass, and as described above, T
Although it is contained together with the a ₂ O ₅ component to remarkably improve the chemical durability, it is effective that the amount is in the range of 6 to 25%. However, it is preferable to limit the ratio of Ta ₂ O ₅ / ZnO to the range of 0.1 to 0.7 because a glass having more excellent chemical durability can be obtained.

The ZrO ₂ component is used to adjust the optical constant of glass,
It may be added if necessary to improve the chemical durability, but up to 10% is sufficient. The Nb ₂ O ₅ component is effective in increasing the refractive index of glass and improving chemical durability,
If it exceeds 15%, the glass tends to devitrify. In order to obtain the above effect, it is preferable to contain 0.5% or more. The WO ₃ component has the effect of increasing the refractive index of the glass, suppressing the devitrification tendency, and decreasing the viscosity of the molten glass, but 5%
When it exceeds, the coloring tendency of the glass increases. In order to obtain the above effect, it is preferable to contain 0.5% or more.

The Li ₂ O component is an important component because it has a particularly large effect of imparting a low Tg characteristic to the glass, but in order to maintain the devitrification resistance of the glass and exert its effect,
The amount should be in the range 0.5-5%. Al ₂ O ₃
Since the component is effective for improving chemical durability, 10
% Can be contained. However, if the amount is too large, the viscosity of the molten glass becomes too large, so 5% or less is preferable.

The TiO ₂ component is effective in improving the chemical durability of glass and can be contained up to 3%. In addition, components such as Yb ₂ O _{3 up to} 10% and F _{2 up to} 5% can be added to the optical glass of the present invention as long as desired characteristics are not impaired. Further, as a defoaming and clarifying agent, Sb ₂ O ₃ ,
A proper amount of components such as As ₂ O ₃ may be added.

[0013]

EXAMPLES Next, examples of composition (No. 1 to No. 10) of the optical glass of the present invention and examples of comparative composition (No. A and No. B) of the conventional optical glass will be described. Optical constants (Nd, νd) and acid resistance (S
R) Shown in Table 1 together with numerical values. The SR value is
The results obtained by the measurement are shown in accordance with the measuring method of International Standardization Organization ISO 8424; 1987 (E).
Here, the SR value is graded by the time (h) required for a glass sample in a predetermined acid treatment solution to be corroded by 0.1 μm. In the case of SR value = 4 and 5, a nitric acid solution of PH 0.3 is used, and each is 0.1 to 1.
It shows that h and 0.1 h or less were required. Also, SR
If value = 5, 51, 52 and 53, PH
Using the acetate buffer solution of 4.6, each for 10 hours or more, 1 to
It shows that it took 10 h, 0.1 to 1 h and 0.1 h or less.

[0014]

[Table 1]

[Table 1]

[Table 1]

As can be seen in Table 1, the glass of the example composition of the present invention, No. 8 and No. No. 5 is a glass of a comparative composition example, which has almost the same optical constants, No. 5 A
And No. Compared to B, the SR value improved in both cases,
Shows much better chemical durability. The glasses of other composition examples of the present invention also show excellent SR values. Moreover, all of these glasses have excellent devitrification resistance,
It is also easy to homogenize. Therefore, the glasses of the above-mentioned examples are easy to manufacture, suitable for mold pressing, and have excellent chemical durability. The glasses of the above-mentioned composition examples of the present invention are all weighed and mixed using ordinary optical glass raw materials such as nitrates, carbonates, and oxides, and this is mixed with a platinum crucible at about 1100 to 1350 ° C., About 2-5
It can be obtained by melting and degassing for a period of time, homogenizing by stirring, and then casting in a mold and gradually cooling.

[0016]

As described above, the optical glass of the present invention is made of SiO ₂ —B ₂ O ₃ —La ₂ O ₃ —Ta ₂ O ₅ —ZnO.
Since it has a specific composition of —Li ₂ O-based component system, it has a refractive index (Nd) of about 1.75 to 1.85, an optical constant in the range of Abbe number of about 35 to 50, and a Tg of 580 ° C. or less. It also has excellent chemical durability. Also, it is easy to manufacture and easy to homogenize, and is suitable for mold pressing.

Claims (2)

[Claims] 1. By weight% SiO ₂ 6-15%, B ₂ O
₃ 15 to 24%, but SiO ₂ + B ₂ O ₃ 21 to 35
%, La ₂ O ₃ 25 to 50%, Gd ₂ O ₃ 0 to 30%, provided that La ₂ O ₃ + Gd ₂ O ₃ 27 to 60%, Ta ₂ O ₅
0.1~10%, ZnO 6~25%, ZrO 2 0~
_{10%, Nb 2 O 5 0~15} %, WO 3 0~5%, L
i ₂ O 0.5-5%, Al ₂ O ₃ 0-10%, TiO ₂
It contains each component in the range of 0 to 3% and has a refractive index (N
d) about 1.75 to 1.85, Abbe number (νd) about 35
Optical constant in the range of 50 and transition temperature (T
An optical glass having g). 2. By weight% SiO ₂ 6-15%, B ₂ O
₃ 15-24%, provided that SiO ₂ + B ₂ O ₃ 21-30
%, La ₂ O ₃ 25 to 50%, Gd ₂ O ₃ 0 to 30%, but La ₂ O ₃ + Gd ₂ O ₃ 32 to 60%, Ta ₂ O ₅
0.5~10%, ZnO 6~25%, ZrO 2 0~
10%, Nb ₂ O ₅ 0.5 to 15%, WO ₃ 0.5 to
_{5%, Li 2 O 0.5~5%} , Al 2 O 3 0~5%,
TiO ₂ contains each component in the range of 0 to 3%, and has an optical constant in the range of refractive index (Nd) of about 1.75 to 1.85 and Abbe number (νd) of about 35 to 50 and 580 ° C. or less. The optical glass according to claim 1, having a transition temperature (Tg) of.