JP2006021969A - Optical glass and optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical glass which contains no lead and arsenic compounds substantially, is low in T<SB>g</SB>and T<SB>L</SB>, has excellent devitrification resistance and is suitable for press molding. <P>SOLUTION: The optical glass for press molding contains each component of 5-20% SiO<SB>2</SB>, 0-5% Al<SB>2</SB>O<SB>3</SB>, 20-40% B<SB>2</SB>O<SB>3</SB>, 8-20% Li<SB>2</SB>O (where, excluding 8%), 0-5% Na<SB>2</SB>O, 0-5% K<SB>2</SB>O, 8-20% Li<SB>2</SB>O+Na<SB>2</SB>O+K<SB>2</SB>O (where excluding 8%), 0-10% MgO, 0-20 CaO, 0-20% BaO, 0-10% SrO, 5-20% MgO+CaO+BaO+SrO, 0-10% ZnO, 0-10% Y<SB>2</SB>O<SB>3</SB>, 5-30% La<SB>2</SB>O<SB>3</SB>, 7-30% Gd<SB>2</SB>O<SB>3</SB>, 0-10% TiO<SB>2</SB>, 0-10% ZrO<SB>2</SB>, 0-10% Nb<SB>2</SB>O<SB>5</SB>, 0-10% Ta<SB>2</SB>O<SB>5</SB>, 0-5% WO<SB>3</SB>, 0-5% Bi<SB>2</SB>O<SB>3</SB>and 0-3% Sb<SB>2</SB>O<SB>3</SB>by weight. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical glass and an optical element made of the optical glass, and more particularly to an optical glass suitable for press molding and an optical element made of the optical glass.

  As a method of manufacturing an optical element such as a glass lens, an optical element is directly molded by pressing glass heated to a temperature higher than the deformation temperature (At) using a heated molding die consisting of a pair of upper and lower molds. The so-called press-molding method, which has a smaller number of manufacturing steps than the conventional molding method for polishing glass, can produce an optical element in a short time and at a low cost. It has come to be used.

This press molding method can be roughly divided into a reheating method and a direct press method. In the reheating method, gob preforms or polishing preforms having almost the final product shape are prepared, then these preforms are heated again above the softening point, and press molded with a pair of heated upper and lower molds to obtain the final product. It is a method of shape. On the other hand, the direct press method is a method in which a molten glass droplet is directly dropped from a glass melting furnace onto a heated mold and press-molded to obtain a final product shape. In any of these types of press molding methods, when molding glass, it is necessary to heat the press mold to a temperature near or above the glass transition temperature (hereinafter sometimes referred to as “Tg”). For this reason, the higher the Tg of the glass, the easier the surface oxidation of the press mold and the change of the metal composition occur, and the mold life is shortened, resulting in an increase in production cost. Mold deterioration can be suppressed by molding in an inert gas atmosphere such as nitrogen, but the molding equipment becomes complicated and the inert gas running cost is required to control the atmosphere. Production costs increase. Accordingly, it is desirable that the glass used in the press molding method has a Tg as low as possible. In order to improve the devitrification resistance, it is desirable that the liquidus temperature (hereinafter sometimes referred to as “T _L ”) is as low as Tg.

However, in recent years, there have been concerns about adverse effects on the human body of lead compounds that have been conventionally used to lower Tg. For this reason, it has become a strong market demand not to use lead compounds. Thus, various techniques for reducing Tg and _{TL of} glass without using a lead compound have been studied and proposed (for example, Patent Documents 1 to 3).
Japanese Patent Laid-Open No. 5-58669 (Claims) JP-A-8-59282 (Claims) JP 2003-176151 A (Claims)

However, the optical glasses of Patent Document 1 and Patent Document 2 are not low enough to satisfy Tg. Further, the optical glass of Patent Document 3 still has a high T _{L and} has a problem in devitrification resistance.

The present invention has been made in view of such conventional problems, and an object, is substantially free of compounds such as lead and arsenic, Tg and T _L is lower, the devitrification resistance It is to provide an optical glass which is excellent in press and suitable for press molding.

  Another object of the present invention is to provide an optical element having a predetermined optical constant and containing substantially no compound such as lead or arsenic and having high productivity.

As a result of intensive studies to achieve the above object, the present inventor, as a result of containing a large amount of Li ₂ O in the SiO ₂ —B ₂ O ₃ glass composition, Tg while maintaining a predetermined optical constant. It has been found that, by containing La ₂ O ₃ and Gd ₂ O ₃ in a large amount, _TL can be lowered and viscosity suitable for molding can be obtained.

That is, press-molding the optical glass of the present invention, in _{weight%, SiO 2: 5~20%,} Al 2 O 3: 0~5%, B 2 O 3: 20~40%, Li 2 O: 8~ 20% (excluding 8%), Na ₂ O: 0 to 5%, K ₂ O: 0 to 5%, but Li ₂ O + Na ₂ O + K ₂ O: 8 to 20% (however, 8% Not included), MgO: 0-10%, CaO: 0-20%, BaO: 0-20%, SrO: 0-10%, provided that MgO + CaO + BaO + SrO: 5-20%, ZnO: 0-10%, Y ₂ O ₃ : 0 to 10%, La ₂ O ₃ : 5 to 30%, Gd ₂ O ₃ : 7 to 30%, TiO ₂ : 0 to 10%, ZrO ₂ : 0 to 10%, Nb ₂ O ₅ : 0 _{~10%, Ta 2 O 5:} 0~10%, WO 3: 0~5%, Bi 2 O 3: 0~5%, Sb 2 O 3: 0~3% each glass of It characterized by having a minute. Hereinafter, “%” means “% by weight” unless otherwise specified.

  Here, it is preferable that the refractive index (nd) is in the range of 1.60 to 1.70, the Abbe number (νd) is in the range of 50 to 62, and the glass transition temperature (Tg) is 530 ° C. or lower.

From the viewpoint of devitrification resistance and moldability, the liquidus temperature (T _L ) is preferably 950 ° C. or lower, and the viscosity at the liquidus temperature is preferably 0.5 poise or higher.

  Moreover, according to this invention, the optical element which consists of said optical glass is provided. Such an optical element is preferably a lens, a prism, or a mirror.

In the optical glass of the present invention, by containing a specific amount of a predetermined glass component, an optical constant having a high refractive index and a low dispersion can be obtained without using a compound such as lead or arsenic that may cause adverse effects on the human body. In addition, the Tg is low and the press formability is excellent, and the _TL is low and the devitrification resistance is excellent.

  Further, since the optical element of the present invention is produced by press-molding the optical glass, it has the characteristics of the optical glass, has high production efficiency, and can be reduced in cost.

The reason why each component of the optical glass of the present invention is limited as described above will be described below. First, SiO ₂ is a component (glass former) constituting a glass skeleton, and if the content is less than 5%, the durability of the glass deteriorates. On the other hand, when the content of SiO ₂ exceeds 20%, the devitrification resistance deteriorates. Moreover, it becomes difficult to obtain a glass having a high refractive index. Therefore, the content of SiO ₂ is determined to be in the range of 5 to 20%. A more preferable content of SiO ₂ is in the range of 5 to 19%.

Al ₂ O ₃ has the effect of increasing the viscosity while improving the durability of the glass. When the content of Al ₂ O ₃ exceeds 5%, the devitrification resistance of the glass deteriorates and the meltability deteriorates. Therefore, the content of Al ₂ O ₃ is set in the range of 0 to 5%.

B ₂ O ₃ is a component that constitutes a glass skeleton in the same manner as SiO _{2. If} the content of B ₂ O ₃ is less than 20%, the glass tends to devitrify. On the other hand, if the content exceeds 40%, the refractive index is lowered and a desired optical constant cannot be obtained. Therefore, the content of B ₂ O ₃ is set to a range of 20 to 40%. A more preferable content is in the range of 20 to 38%.

Li ₂ O has a great effect on reducing the weight of the glass and lowering the Tg. The effect and the Li ₂ O content is not more than 8% can not be sufficiently obtained. On the other hand, if the content of Li ₂ O exceeds 20%, the durability of the glass is deteriorated and the refractive index is lowered, so that a desired optical constant cannot be obtained. Therefore, the content of Li ₂ O was determined to be in the range of 8 to 20% (excluding 8%). A more preferable content of Li ₂ O is in the range of 8.5 to 19%.

Na ₂ O and K ₂ O are useful as components for lowering Tg. However, when each content exceeds 5%, the devitrification resistance is remarkably deteriorated. Therefore, the contents of Na ₂ O and K ₂ O were set in the range of 0 to 5%, respectively.

When the total amount of R ′ ₂ O (R ′ = Li, Na, K) component is 8% or less, the effect of lowering Tg cannot be obtained sufficiently, while the total amount of R ′ ₂ O component is 20%. When it exceeds, durability will deteriorate and a refractive index will fall, and a desired optical constant will no longer be obtained. Therefore, the total amount of R ′ ₂ O is set to a range of 8 to 20% (excluding 8%). A more preferable total amount of R ′ ₂ O is in the range of 8.5 to 19%.

  MgO has the effect of reducing the weight of the glass, improving the refractive index, and lowering the dispersion, but if it exceeds 10%, the glass becomes unstable and devitrification resistance deteriorates. Therefore, the content of MgO is set to a range of 0 to 10%.

  CaO has the effect of reducing the weight of the glass, improving the refractive index, and improving the durability of the glass. However, if it exceeds 20%, the glass becomes unstable and the devitrification resistance deteriorates. Therefore, the CaO content is set to a range of 0 to 20%.

  BaO and SrO have the effect of adjusting the refractive index and improving the stability of the glass. However, when the content exceeds 20% and 10%, the devitrification resistance deteriorates. Therefore, the BaO content is set to a range of 0 to 20%, and the SrO content is set to a range of 0 to 10%.

  When the total amount of RO (R = Mg, Ca, Ba, Sr) components is less than 5%, the refractive index decreases and a desired optical constant cannot be obtained. On the other hand, when the total amount of RO components exceeds 20% Devitrification resistance deteriorates. Therefore, the total amount of RO is set to a range of 5 to 20%. A more preferable total amount of RO is in the range of 5 to 18%.

  ZnO has the effect of increasing the refractive index of the glass, but if the content exceeds 10%, the devitrification resistance deteriorates. Therefore, the ZnO content is set to a range of 0 to 10%.

Y ₂ O ₃ has the effect of increasing the refractive index of the glass. However, if the content exceeds 10%, the devitrification resistance deteriorates and _TL increases. Therefore, the content of Y ₂ O ₃ is set to a range of 0 to 10%.

La ₂ O ₃ has the effect of increasing the refractive index of the glass and maintaining the dispersion, but if the content is less than 5%, the refractive index decreases and the desired optical constant cannot be obtained, while the content is 30. When it exceeds%, the phase separation becomes strong and _TL becomes high. Therefore, the content of La ₂ O ₃ is set to a range of 5 to 30%. A more preferable content of La ₂ O ₃ is in the range of 5 to 27%.

Gd ₂ O ₃ increases the refractive index of the glass, improves the light resistance of the glass, and lowers _TL. However, if the content is less than 7%, the refractive index decreases and the desired optical constant is obtained. On the other hand, when the content exceeds 30%, the devitrification resistance of the glass decreases. Therefore, the content of Gd ₂ O ₃ is set to a range of 7 to 30%. A more preferable content of Gd ₂ O ₃ is in the range of 7 to 27%.

TiO ₂ has the effect of increasing the refractive index, but when the content exceeds 10%, the devitrification resistance is deteriorated and _TL is increased. Therefore, the content of TiO ₂ is set in the range of 0 to 10%.

ZrO ₂ has the effect of increasing the refractive index and increasing the weather resistance of the glass. However, if the content exceeds 10%, the devitrification resistance is deteriorated and the _TL is increased. Therefore, the content of ZrO ₂ is set to a range of 0 to 10%.

Nb ₂ O ₅ has the effect of increasing the refractive index of the glass and improving the meltability of the glass, but if the content exceeds 10%, the predetermined dispersion cannot be maintained. Therefore, the Nb ₂ O ₅ content is set to a range of 0 to 10%.

Ta ₂ O ₅ has the effect of increasing the refractive index of the glass and improving the weather resistance of the glass. However, if the content exceeds 10%, the devitrification resistance is deteriorated and _TL is increased. Therefore, the content of Ta ₂ O ₅ is set to a range of 0 to 10%.

WO ₃ and Bi ₂ O ₃ have the effect of increasing the refractive index of the glass, but if the content exceeds 5%, the degree of coloration of the glass deteriorates. Therefore, the contents of WO ₃ and Bi ₂ O ₃ are determined to be in the range of 0 to 5%, respectively.

Sb ₂ O ₃ has the effect of improving the clarification effect when added in a small amount. Therefore, the Sb ₂ O ₃ content is set to a range of 0 to 3%.

In addition, in the optical glass of the present invention, of course, conventionally known glass components and additives such as CuO and GeO ₂ may be added as long as they do not impair the effects of the present invention.

  The optical element of the present invention is produced by press-molding the optical glass. The press molding method includes a direct press molding method in which molten glass is dropped from a nozzle into a mold heated to a predetermined temperature and press molded, and a preform material is placed on the mold and exceeds the glass softening point. There is a reheating molding method in which heating and press molding are performed. According to such a method, polishing and grinding steps are not required, productivity is improved, and an optical element having a shape difficult to process such as a free curved surface or an aspherical surface can be obtained.

The molding conditions vary depending on the glass component and the shape of the molded product, but generally the mold temperature is preferably in the range of 350 to 600 ° C., and the temperature range close to the glass transition temperature is particularly preferable. The pressing time is preferably in the range of several seconds to several tens of seconds. The pressing pressure is preferably in the range of 200kgf / cm ² ~600kgf / cm ² by the shape and size of the lens can be molded as high-precision pressing at high pressure.

  The optical element of the present invention can be used as, for example, a digital camera lens, a collimator lens such as a laser beam printer, a prism, or a mirror.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples.

Examples 1-10, Comparative Examples 1-3
Using general glass raw materials such as oxide raw materials, carbonates, and nitrates, glass raw materials were prepared so as to have the target composition shown in Table 1, and thoroughly mixed with powders to prepare mixed raw materials. This is put into a melting furnace heated to 1,000 to 1,300 ° C, melted and refined, homogenized with stirring, cast into a preheated iron or carbon mold, and gradually cooled to produce each sample. did. The refractive index (nd) and Abbe number (νd), glass transition temperature (Tg), liquid phase temperature (T _L ), and viscosity at the liquid phase temperature for each of these samples were measured. The measurement results are shown in Table 1.

  Comparative Example 1 is Example 11 of Patent Document 1 (JP-A-5-58669) described above, Comparative Example 2 is Example 3 of Patent Document 2 (JP-A-8-59282), and Comparative Example 3 is Example 10 of Patent Document 3 (Japanese Patent Application Laid-Open No. 2003-176151) was retested.

The above physical properties were measured according to the test method of Japan Optical Glass Industry Association Standard (JOGIS). That is, the refractive index (n _d ) and the Abbe number (ν _d ) are values when cooled slowly at −30 ° C./hour. The measurement was performed using “KPR-200” manufactured by Kalnew Optical Industry Co., Ltd. The glass transition temperature (Tg) was measured using a thermomechanical analyzer “TMA / SS6000” manufactured by Seiko Instruments Inc. under a temperature rising condition of 10 ° C./min. The liquid phase temperature (T _L ) is measured by using a melting furnace to lower the glass melted at 1,200 ° C. to a predetermined temperature at −100 ° C./hour and holding it at the predetermined temperature for 12 hours. Was poured into a mold and cooled to room temperature to a temperature at which devitrification (crystals) was not confirmed inside the glass. The inside of the glass was observed using an Olympus optical microscope “BX50” at a magnification of 100 times. The viscosity was measured using a high temperature viscosity measuring device “TVB-20H viscometer” manufactured by Advantest Corporation.

As is apparent from Table 1, the optical glasses of Examples 1 to 10 have a high refractive index and low dispersion, and have a glass transition temperature (Tg) of 530 ° C. or lower and a liquidus temperature (T _L ) of 950 ° C. It was as low as below and was excellent in press formability. On the other hand, in all the optical glasses of Comparative Examples 1 to 3, Li ₂ O was as low as 8% or less, so Tg was as high as 530 ° C., and Gd ₂ O ₃ was less than 7%, so that T _L was from 950 ° C. It was highly unsuitable for press formability.

Claims (4)

% By weight
SiO ₂ : 5 to 20%,
Al ₂ O ₃ : 0 to 5%,
B ₂ O ₃ : 20 to 40%,
Li ₂ O: 8 to 20% (excluding 8%),
Na ₂ O: 0 to 5%,
K ₂ O: 0 to 5%,
_{However, Li 2 O + Na 2 O} + K 2 O: 8~20% ( but not including 8%),
MgO: 0 to 10%,
CaO: 0 to 20%,
BaO: 0 to 20%,
SrO: 0 to 10%,
However, MgO + CaO + BaO + SrO: 5-20%,
ZnO: 0 to 10%,
Y ₂ O ₃ : 0 to 10%,
La ₂ O _3: 5~30%,
Gd ₂ O ₃ : 7 to 30%,
TiO _2: 0~10%,
ZrO ₂ : 0 to 10%,
Nb ₂ O ₅ : 0 to 10%,
Ta ₂ O ₅ : 0 to 10%,
WO _3: 0~5%,
Bi ₂ O ₃ : 0 to 5%
Sb ₂ O ₃ : 0 to 3%,
An optical glass for press molding characterized by having each glass component.   The optical glass for press molding according to claim 1, wherein the refractive index (nd) is in the range of 1.60 to 1.70, the Abbe number (νd) is in the range of 50 to 62, and the glass transition temperature (Tg) is 530 ° C or lower. . The optical glass for press molding according to claim 1 or 2, wherein the liquid phase temperature (T _L ) is 950 ° C or lower and the viscosity at the liquid phase temperature is 0.5 poise or more.   An optical element comprising the press-molding optical glass according to claim 1.