JP2011105599A - Optical glass, preform for precision press molding, optical element and methods for producing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide optical glass having a refractive index of ≥1.70, an Abbe's number of ≥50 and a low temperature softening property, exhibiting excellent glass stability. <P>SOLUTION: The optical glass having a refractive index of ≥1.70 and an Abbe's number of ≥50, includes 20-80% B<SB>2</SB>O<SB>3</SB>, 0-30% SiO<SB>2</SB>, 1-25% Li<SB>2</SB>O, 0-20% ZnO, 4-30% La<SB>2</SB>O<SB>3</SB>, 1-25% Gd<SB>2</SB>O<SB>3</SB>, 0-20% Y<SB>2</SB>O<SB>3</SB>, 0-5% ZrO<SB>2</SB>, 0-25% MgO, 0-15% CaO and 0-10% SrO by mol%. Here, the total content of the components is ≥97%; the molar ratio: [ZnO/(La<SB>2</SB>O<SB>3</SB>+Gd<SB>2</SB>O<SB>3</SB>+Y<SB>2</SB>O<SB>3</SB>)] is ≤0.8; the molar ratio: [(CaO+SrO+BaO)/(La<SB>2</SB>O<SB>3</SB>+Gd<SB>2</SB>O<SB>3</SB>+Y<SB>2</SB>O<SB>3</SB>)] is ≤0.8; Ta<SB>2</SB>O<SB>5</SB>may be included as an arbitrary component; and the molar ratio: [(ZrO<SB>2</SB>+Ta<SB>2</SB>O<SB>5</SB>)/(La<SB>2</SB>O<SB>3</SB>+Gd<SB>2</SB>O<SB>3</SB>+Y<SB>2</SB>O<SB>3</SB>)] is ≤0.4. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to an optical glass having an optical constant having a refractive index n _d of 1.70 or more and an Abbe number ν _d of 50 or more, a precision press-molding preform made of the glass, and an optical element made of the glass, and It relates to the manufacturing method.

  With the advent of digital cameras and camera-equipped mobile phones, devices that use optical systems are rapidly becoming highly integrated and highly functional. Along with this, there is an increasing demand for higher precision, lighter weight, and smaller size for optical systems.

  In recent years, optical designs using aspherical lenses are becoming mainstream in order to realize the above requirements. For this reason, in order to stably supply a large amount of aspherical lenses using high-performance glass at a low cost, precision press molding technology (mold) that directly forms optical functional surfaces by press molding without grinding and polishing processes. (Also referred to as molding technology), and the demand for optical glass having low-temperature softening properties suitable for precision press molding is increasing year by year. Among such optical glasses, there is a glass having a high refractive index and low dispersion. An example of such glass is described in Patent Document 1.

JP2002-249337

  In order to utilize the merit of the precision press molding technique, it is desirable to directly produce a glass material called a preform used for press molding from molten glass. This method is called a preform hot forming method, in which the molten glass is flowed out and the molten glass ingot corresponding to one preform is separated one after another, and the resulting molten glass ingot is cooled. It is formed into a preform having a smooth surface. Therefore, this method forms a large glass block from molten glass, and has a higher glass utilization rate than the method of cutting, grinding, and polishing this block, so that glass waste generated during processing does not come out, and processing time is reduced. It has an excellent feature that it does not cost.

  On the other hand, in the hot forming method, it is necessary to accurately separate an amount of the molten glass lump corresponding to one preform and form the preform so as to prevent defects such as devitrification and striae. Therefore, glass having excellent glass stability in a high temperature range is required for hot forming.

By the way, when the Abbe number ν _d is maintained at a predetermined value or higher and the refractive index n _d is increased, the tendency of the glass to be easily crystallized increases and finally vitrification becomes difficult. Since the glass for precision press molding further imparts low-temperature softening properties, there is a tendency that a decrease in glass stability is promoted. Accordingly, while maintaining the Abbe number ν _d to be 50 or more, preferably 52 or more, the refractive index n _d is increased to 1.70 or more, and the low temperature softening property suitable for precision press molding is imparted, It has been difficult to achieve a glass stability that can be molded.

The present invention has been made in order to solve the above problems, and has a refractive index n _d of 1.70 or more and an Abbe number ν _d of 50 or more, and has low-temperature softening properties and excellent glass stability. An object of the present invention is to provide an optical glass, a precision press-molding preform made of the glass and a manufacturing method thereof, and an optical element made of the glass and a manufacturing method thereof.

Means for achieving the object is as follows.
[1] Refractive index n _d is 1.70 or more, Abbe number ν _d is 50 or more,
In mol% display,
B ₂ O ₃ 20-80%,
SiO ₂ 0-30%,
Li ₂ O 1-25%,
ZnO 0-20%,
La ₂ O ₃ 4-30%,
Gd ₂ O ₃ 1-25%,
Y ₂ O ₃ 0-20%,
ZrO ₂ 0-5%,
MgO 0-25%,
CaO 0-15%,
SrO 0-10%,
And the total amount of the components is 97% or more,
The molar ratio [ZnO / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] is 0.8 or less, and the molar ratio [(CaO + SrO + BaO) / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] is 0.8 or less,
Optical glass which can contain Ta ₂ O ₅ as an optional component and has a molar ratio [(ZrO ₂ + Ta ₂ O ₅ ) / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] of 0.4 or less .
[2] The optical glass according to [1], wherein the total amount of Li ₂ O and ZnO is 2 to 30%, and the molar ratio (ZnO / Li ₂ O) is 6 or less.
[3] The optical glass according to [1] or [2], in which the refractive index n _d and the Abbe number ν _d satisfy the following formula (1).
n _d ≧ 2.235−0.01 × ν _d (1)
[4] A precision press-molding preform comprising the optical glass according to any one of [1] to [3].
[5] An optical element comprising the optical glass according to any one of [1] to [3].
[6] In a method for producing a precision press-molding preform that separates a molten glass lump from an outflowing molten glass and molds it into a precision press-molding preform in the process of cooling the molten glass lump.
A method for producing a precision press-molding preform, comprising molding a precision press-molding preform made of the optical glass according to any one of [1] to [3].
[7] A method for producing an optical element, wherein the precision press-molding preform according to [4] or the precision press-molding preform produced by the method according to [6] is heated to perform precision press molding.
[8] The method for manufacturing an optical element according to [7], wherein a preform for precision press molding is introduced into a press mold, and the preform and the mold are heated together to perform precision press molding.
[9] The method for manufacturing an optical element according to [7], wherein the preform for precision press molding is heated and then introduced into a preheated press mold and precision press molding is performed.

According to the present invention, it is possible to provide an optical glass having a refractive index n _d of 1.70 or more and an Abbe number ν _d of 50 or more, having low-temperature softening properties and excellent glass stability. Furthermore, according to the present invention, it is possible to provide a precision press-molding preform made of the glass and a manufacturing method thereof, and an optical element made of the glass and a manufacturing method thereof.

It is sectional explanatory drawing of a precision press apparatus.

Hereinafter, the present invention will be described in more detail.
[Optical glass]
The optical glass of the present invention has a refractive index n _d of 1.70 or more and an Abbe number ν _d of 50 or more,
In mol% display,
B ₂ O ₃ 20-80%,
SiO ₂ 0-30%,
Li ₂ O 1-25%,
ZnO 0-20%,
La ₂ O ₃ 4-30%,
Gd ₂ O ₃ 1-25%,
Y ₂ O ₃ 0-20%,
ZrO ₂ 0-5%,
MgO 0-25%,
CaO 0-15%,
SrO 0-10%,
And the total amount of the components is 97% or more,
The molar ratio [ZnO / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] is 0.8 or less, and the molar ratio [(CaO + SrO + BaO) / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] is 0.8 or less,
Ta ₂ O ₅ can be included as an optional component, and the molar ratio [(ZrO ₂ + Ta ₂ O ₅ ) / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] is 0.4 or less.

  Hereinafter, unless otherwise specified, each content and the total amount thereof are mol%, and the ratio between the contents, the ratio between the total amounts, and the ratio between the content and the total amount are expressed in molar ratios.

In the present invention, the molar ratio [(CaO + SrO + BaO) / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] is based on the total content of La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ . The ratio of the total content of CaO, SrO and BaO, and the molar ratio [ZnO / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] are La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ . Ratio of ZnO content to total content, molar ratio [(ZrO ₂ + Ta ₂ O ₅ ) / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] means La ₂ O ₃ , Gd ₂ O ₃ and It means the ratio of the total content of ZrO ₂ and Ta ₂ O _{5 to} the total content of Y ₂ O ₃ .

B ₂ O ₃ is a glass network forming component, is an essential component that imparts low dispersion characteristics and has a function of lowering the glass transition temperature. If the content is less than 20%, the stability of the glass decreases, the liquidus temperature rises, and it becomes difficult to form a preform. On the other hand, the refractive index decreases due to excessive introduction. Therefore, the content of B ₂ O ₃ in the optical glass of the present invention is 20 to 80%. A preferable range is 25 to 75%, and a more preferable range is 25 to 72%.

SiO ₂ is an optional component that improves the stability of the glass by being introduced in an appropriate amount, and also provides a viscosity suitable for molding when a preform is molded from molten glass. However, the refractive index decreases due to excessive introduction, and the meltability of the glass decreases. Therefore, the content is 0 to 30%, preferably 1 to 27%, more preferably 2 to 25%.

Li ₂ O is an essential component that increases the refractive index and significantly lowers the glass transition temperature as compared with other alkali metal oxide components, and also functions to improve the meltability of the glass. It is difficult to obtain the above effect if the amount is too small, and if the amount is too large, the devitrification resistance of the glass is lowered, making it difficult to form a high-quality preform directly from the molten glass that flows out, and weather resistance. The nature is also reduced. Therefore, the content is 1 to 25%, preferably 2 to 20%, more preferably 3 to 18%.

From the viewpoint of glass transition temperature, glass stability, etc., it is preferable to optimize the distribution of network forming components and Li ₂ O, and the molar ratio [Li ₂ O / (B ₂ O ₃ + SiO ₂ )] is 0. The range is preferably 0.02 to 0.25, more preferably 0.04 to 0.20, and still more preferably 0.06 to 0.18.

ZnO is a component that lowers the melting temperature, the liquidus temperature and the glass transition temperature, improves the chemical durability and weather resistance of the glass, and increases the refractive index. However, if it is introduced excessively, it becomes difficult to maintain the Abbe number ν _d at 50 or more, so the content is made 0 to 20%, preferably 0 to 16%, more preferably 1 to 14%.

In the optical glass of the present invention, the total content of Li ₂ O and ZnO (Li ₂ O + ZnO) is preferably 2% or more in order to achieve the required low-temperature softening property. However, when the total amount is excessive, the devitrification resistance of the glass is lowered or the dispersion is increased. Therefore, it is preferable to set Li ₂ O + ZnO to 2 to 30%. More preferably, it is 3 to 25%, and further preferably 4 to 23%.

Furthermore, the molar ratio (ZnO / Li ₂ O) is preferably 6 or less in order to keep the Abbe number ν _d at 50 or more while providing the required low-temperature softening property. The molar ratio is preferably 0 to 5, more preferably 0.2 to 4.

La ₂ O ₃ is an essential component that functions to increase the refractive index while maintaining low dispersibility, and to increase chemical durability and weather resistance. However, since the introduction of the excess reduces the stability of the glass and increases the glass transition temperature, the content thereof is 4 to 30%, preferably 4 to 25%, more preferably 5 to 22%, still more preferably. 6 to 20%.

Gd ₂ O ₃ is an essential component that functions in the same manner as La ₂ O ₃ , but when introduced excessively, the stability of the glass is lowered and the glass transition temperature is also raised, so its content is made 1 to 25%. The content is preferably 1 to 20%, more preferably 1 to 18%, still more preferably 2 to 18%, and still more preferably 3 to 16%.

From the viewpoint of improving the stability of the glass, it is preferable to adjust the distribution of the amount of La ₂ O _{3 and the} amount of Gd ₂ O ₃ , and La ₂ O ₃ / Gd ₂ O ₃ is 0.5-5. The range is preferably 0, more preferably 0.8 to 4.8, even more preferably 0.8 to 4.6, and 0.9 to 4.4. Is more preferable, and it is even more preferable to be in the range of 1.0 to 4.2.

Y ₂ O _{3 is} also an optional component that functions in the same manner as La ₂ O ₃ and Gd ₂ O _3, and has the merit of increasing the thermal stability of the glass and lowering the liquidus temperature when introduced in a small amount. However, since the stability of the glass is lowered and the glass transition temperature is also raised by excessive introduction, the content is 0 to 20%, preferably 0.1 to 20%, more preferably 0.2 to 20%. More preferably, it is 0.3 to 20%, more preferably 0.3 to 15%, still more preferably 0.3 to 10%. In particular, in order to obtain a high refractive index and low dispersibility with n _d ≧ 1.7 and ν _d ≧ 52, the content is preferably 0.5 to 20%, more preferably 0.5 to 15%. Is more preferable, and it is still more preferable to set it as 1 to 12%. In order to improve the thermal stability of the glass while maintaining high refractive index and low dispersion characteristics, it is preferable to introduce Y ₂ O ₃ as an essential component.

In the optical glass of the present invention, it is preferable that La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ coexist as glass components. By introducing three or more kinds of rare earth oxide components in this way, the stability of the glass can be further enhanced as compared with the case of containing two or less kinds of rare earth oxide components.

ZrO ₂ is an optional component introduced for improving the weather resistance of the glass and adjusting the optical constant, and works to increase the stability of the glass when introduced in a small amount. The content is decreased and the dispersion is increased, so the content is 0 to 5%, preferably 0 to 4.5%, more preferably 0 to 4%. In particular, in order to obtain a high refractive index and low dispersibility of n _d ≧ 1.7 and ν _d ≧ 52, the content is preferably 0 to 3%, more preferably 0 to 2%. 0 to 1.5% is more preferable, and 0 to 0.5% is particularly preferable.

When MgO is introduced instead of ZnO or Li ₂ O, it can reduce the dispersion of the glass and improve the chemical durability. However, excessive introduction causes a decrease in refractive index and an increase in the glass transition point. The content is 0 to 25%, preferably 0 to 20%, more preferably 0 to 15%.

  CaO lowers the glass transition temperature and adjusts the optical properties. However, the excessive introduction reduces the stability of the glass and raises the liquidus temperature. , Preferably 0.2 to 14%, more preferably 0.5 to 12%.

  SrO increases the chemical durability and functions to adjust the optical properties, but the glass stability decreases due to excessive introduction and increases the liquidus temperature, so the content is 0-10%, Preferably it is 0 to 5%, more preferably 0 to 3%.

The optical glass of the present invention has a molar ratio [ZnO / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] of 0.8 or less from the viewpoint of enhancing the high refractive index and low dispersibility. When the molar ratio exceeds 0.8, it is difficult to obtain a desired optical constant. The molar ratio is preferably 0.75 or less, more preferably 0.7 or less, still more preferably 0.65 or less, and even more preferably 0.6 or less.

Furthermore, it is preferable to introduce a smaller component than the component having a large ionic radius as the alkaline earth component from the viewpoint of achieving both a high refractive index of n _d ≧ 1.7 and the stability of the glass. Therefore, in the optical glass of the present invention, the molar ratio [(CaO + SrO + BaO) / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] is set to 0.8 or less. When the molar ratio exceeds 0.8, it is difficult to achieve both high refractive index and glass stability. The molar ratio is preferably 0.6 or less, more preferably 0.5 or less, and still more preferably 0.4 or less.

  In the optical glass of the present invention, the total content of the above components is 97% or more. When a large amount of components other than the above components are introduced into the optical glass of the present invention, problems such as low dispersion characteristics, high refractive index characteristics, and glass stability are caused. Therefore, it is desirable to increase the total amount of the components. The total content is preferably 98% or more, more preferably 99% or more, and still more preferably 100%.

Other components include Ta ₂ O ₅ , F, Al ₂ O ₃ , Yb ₂ O ₃ , Sc ₂ O ₃ , and Lu ₂ O ₃ .
Ta ₂ O ₅ functions to increase the refractive index, but increases the dispersion, so the amount of introduction should be reduced. In the optical glass of the present invention, La ₂ O ₃ , Gd ₂ O ₃ , Y ₂ O ₃ , ZrO ₂ , and Ta ₂ O ₅ , which are components having a high refractive index, are added to a group (La ₂ O ₃₎ that maintains low dispersion characteristics. , Gd ₂ O ₃ , Y ₂ O ₃ ) and dispersion enhancing groups (ZrO ₂ , Ta ₂ O ₅ ), and optimizing the ratio of the total amount of each group, Ta ₂ O ₅ which is an optional component Limit the amount of introduction. That is, in the optical glass of the present invention, the molar ratio [(ZrO ₂ + Ta ₂ O ₅ ) / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] is 0.4 or less. When the molar ratio exceeds 0.4, it is difficult to maintain low dispersion characteristics. The molar ratio is preferably 0.3 or less, more preferably 0.27 or less, still more preferably 0.255 or less, still more preferably 0.225 or less, even more preferably 0.2 or less, and even more preferably 0. .18 or less, still more preferably 0.1 or less, particularly preferably 0.05 or less, and most preferably 0.

The content of Ta ₂ O ₅ is preferably suppressed to the range of 0 to 3% from the above reason, more preferably 0 to 2%, still more preferably 0 to 1%, and still more preferably 0 to 0.5%. 0 to 0.2% is even more preferable, 0 to 0.1% is still more preferable, and it is particularly preferable not to introduce.

In order to improve the thermal stability of the glass while maintaining high refractive index and low dispersion characteristics, Y ₂ O ₃ is introduced as an essential component as described above, or [(ZrO ₂ + Ta ₂ O ₅ ) / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] is preferably kept low, the content of Ta ₂ O ₅ is reduced, or Ta ₂ O ₅ is not introduced.

In the B ₂ O ₃ —La ₂ O ₃ -based composition, F functions to expand the vitrifiable range in terms of optical characteristics and to lower the glass transition temperature. However, coexistence with B ₂ O ₃ exhibits remarkable volatility at high temperatures and volatilizes during glass melting and molding, making it difficult to mass-produce glass having a constant refractive index. Further, volatile substances from the glass adhere to the press mold at the time of precision press molding, and there arises a problem that the surface accuracy of the lens is lowered by repeatedly using such a mold. Therefore, the content of F is preferably suppressed to 10% or less, and more preferably 5% or less. In the method of directly forming a preform from molten glass, striations due to volatilization occur and it becomes difficult to obtain an optically homogeneous preform. Therefore, it is preferable to suppress the F content to 3% or less, and do not introduce it. It is more preferable.

Al ₂ O ₃ has a function of improving chemical durability. However, when it is introduced excessively, the refractive index is lowered and the glass transition temperature is also raised. Therefore, the content is preferably 0 to 10%, more preferably 0 to 8%, and still more preferably 0 to 5%.

Sc ₂ O ₃ works in the same way as La ₂ O ₃ , Gd ₂ O ₃ , and Y ₂ O _3, and has the merit of increasing the thermal stability of the glass and lowering the liquidus temperature by introducing a small amount. However, the above-mentioned merit is lost, the stability of the glass is lowered, and the refractive index is also lowered. Sc ₂ O ₃ is an expensive component, and it is desirable not to use it from the viewpoint of cost reduction depending on industrial applications. From the above points, the content is preferably 0 to 20%, more preferably 0 to 18%, still more preferably 0 to 13%, still more preferably 0.1 to 10%, and particularly preferably 0. 0.1 to 5%.

Yb ₂ O ₃ and Lu ₂ O ₃ can also be introduced, respectively, but since the thermal stability of the glass is lowered and the liquidus temperature is remarkably increased, the content of Yb ₂ O ₃ is 0 to 5%. , Preferably 0 to 2%, more preferably 0 to 1%, still more preferably 0 to 0.5%. Further, the content of Lu ₂ O ₃ should be kept in the range of 0 to 5%, preferably 0 to 2%, more preferably 0 to 1%, and still more preferably 0 to 0.5%. Yb ₂ O ₃ and Lu ₂ O ₃ are expensive components, and the optical glass of the present invention does not necessarily require these components. Therefore, neither Yb ₂ O ₃ nor Lu ₂ O _{3 is} introduced from the viewpoint of cost reduction. It is more preferable.

GeO ₂ can also be introduced in the range of, for example, 0 to 10%. However, since it is an expensive component, the amount of introduction is preferably suppressed to 5% or less, and more preferably not introduced.

  Since the stability of the glass is significantly lowered by introducing a small amount of BaO, the content is preferably limited to 2% or less, and more preferably not introduced.

Nb ₂ O ₅ and TiO ₂ also have a strong effect of increasing dispersion, and the Abbe number ν _d increases greatly even when introduced in a small amount. Therefore, in order to maintain the Abbe number ν _d 50 or more, the amount of Nb ₂ O ₅ Is preferably 2% or less, more preferably 1% or less, and most preferably not introduced. In order to maintain an Abbe number ν _{d of} 50 or more, the amount of TiO ₂ is preferably 2% or less, preferably 1% or less, and most preferably not introduced.

Since WO ₃ and Bi ₂ O ₃ also exhibit the same behavior as Nb ₂ O ₅ and TiO ₂ , the respective amounts are preferably 2% or less, more preferably 1% or less. More preferably not introduced.

Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ not only increase the dispersion, but also increase the color of the glass. Since the optical glass of the present invention has an excellent light transmittance even when viewed as a general optical glass, Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ are introduced from the viewpoint of utilizing such characteristics. Preferably not.

Considering that it does not adversely affect the environment, the introduction of Pb, Cr, Cd, As, Th, Te, U should also be avoided. Conventionally, Pb has been used as a major component of optical glass to increase the refractive index. In addition to the above problems, Pb is easily reduced by precision press molding in a non-oxidizing gas atmosphere, and the precipitated metallic lead is pressed. It adheres to the molding surface of the mold and causes problems such as reducing the surface accuracy of the press-molded product. As ₂ O ₃ has also been conventionally added as a fining agent, but in addition to the above problems, it also causes a problem of oxidizing the molding surface of the press mold and shortening the mold life, so it should not be introduced.

  It is desirable not to introduce a glass coloring substance, such as Fe, Cu, or Co, except for the purpose of imparting the required spectral characteristics to the glass.

Sb ₂ O ₃ is an optional additive used as a fining agent, and when added in a small amount, absorption due to reduction of impurities such as Fe can be reduced, and coloring of the glass can also be suppressed. However, if added excessively, the above effect is lost, and at the same time, the molding surface of the press mold is oxidized at the time of precision press molding, which adversely affects the life of the press mold. . Therefore, the addition amount is preferably 0 to 0.5% by mass, more preferably 0 to 0.2% by mass.

The optical glass of the present invention is a glass having a refractive index n _d of 1.70 or more and an Abbe number ν _d of 50 or more. For glass having an optical constant in this range, higher refractive index and lower dispersion (higher Abbe number) are desired as the material of the optical element. On the other hand, if the refractive index is increased or the dispersion is lowered while lowering the glass transition temperature, the stability of the glass is significantly lowered. Conventionally, in this region, further higher refractive index and lower dispersion have been achieved. It was difficult to plan. On the other hand, since the optical glass of the present invention is optimized as a glass for precision press molding, a refractive index n _d and an Abbe number ν _d satisfying the following formula (1) can be realized.
n _d ≧ 2.235−0.01 × ν _d (1)
Optical glass satisfying the above formula (1) has higher value as an optical element material.

In addition, in the case where the precision press-molding preform is directly molded from the molten glass lump, excessively high refractive index and low dispersion are not preferable for maintaining the stability of the glass in a good state. It is preferable to set the optical characteristics in a range satisfying the following formula (2), and it is more preferable to set the optical characteristics in a range satisfying the following formula (3). However, even in these cases, it is more preferable to set the optical characteristics in a range satisfying the formula (1).
n _d ≦ 2.285−0.01 × ν _d (2)
n _d ≦ 2.275−0.01 × ν _d (3)

The optical glass of the present invention is a low dispersion glass having an Abbe number ν _d of 50 or more. From the viewpoint of the low dispersibility of the glass, the Abbe number ν _d is preferably 51 or more, more preferably 52 or more, still more preferably 52.5 or more, and even more preferably 53 or more. Preferably, it is 54 or more.

  Furthermore, according to the optical glass of the present invention, a low glass transition temperature suitable for precision press molding can be realized. The preferable range of the glass transition temperature is 635 ° C. or lower, more preferably 620 ° C. or lower. On the other hand, if the glass transition temperature is excessively decreased, it is difficult to achieve higher refractive index and lower dispersion and / or the stability and chemical durability of the glass tend to decrease. Is 535 ° C. or higher, preferably 555 ° C. or higher, more preferably 565 ° C. or higher.

  The optical glass of the present invention has excellent glass stability. For example, a glass having a liquidus temperature of 1090 ° C. or lower can be realized as a measure of stability in a high temperature range required when glass is formed from molten glass. As described above, the optical glass of the present invention can maintain the liquidus temperature below a predetermined temperature while being a high refractive index and low dispersion glass, so that a precision press molding preform can be molded directly from molten glass. it can. The range of a preferable liquidus temperature is 1060 ° C. or lower, more preferably 1050 ° C. or lower, and further preferably 1040 ° C. or lower.

As described above, the optical glass of the present invention can exhibit excellent light transmittance. Quantitatively, λ ₈₀ (nm) is, for example, 410 nm or less, preferably 400 nm or less, more preferably 390 nm or less, further preferably 380 nm or less, more preferably 370 nm or less, even more preferably 360 nm or less, and particularly preferably 350 nm or less. Low coloring can be achieved. The λ ₈₀ (nm) is obtained as follows. A glass sample having a plane parallel to each other and optically polished with a thickness of 10.0 ± 0.1 mm is used, light of intensity Iin is perpendicularly incident on one of the planes, and intensity Iout of light emitted from the other plane Is measured, and the external transmittance (Iout / Iin) is calculated. The external transmittance is obtained in the wavelength range of 280 nm to 700 nm, and the wavelength at which the external transmittance is 80% is defined as λ ₈₀ (nm). In the general optical glass to which no colorant is added like the optical glass of the present invention, almost no absorption is observed on the long wavelength side from the absorption edge from the ultraviolet region to the visible region, so that from λ ₈₀ (nm) to 1550 nm. In the wavelength region up to 80%, an internal transmittance exceeding 80% is obtained in a glass sample having parallel planes optically polished with a thickness of 10.0 ± 0.1 mm, from λ ₈₀ +20 (nm) to 1550 nm In the long wavelength region, a glass sample having planes parallel to each other and optically polished with a thickness of 10.0 ± 0.1 mm can obtain a high internal transmittance exceeding 90%. Further, λ ₇₀ (nm) and λ ₅ (nm) shown in Table 1 described later are wavelengths at which the external transmittance is 70% and 5%, respectively, and the calculation method is based on λ ₈₀ .

  The optical glass of the present invention is suitable not only as a material for a lens constituting an imaging optical system but also for a lens constituting an optical system used for recording / reproducing on an optical disc such as a DVD or CD. As an example, it is suitable as an optical element for recording / reproducing data using blue-violet light (for example, semiconductor laser light having a wavelength of 405 nm) utilizing its excellent light transmittance. More specifically, for example, it is suitable for an objective lens for DVD having a high recording density of 23 GB. This objective lens is mainly an aspherical lens having a numerical aperture of 0.85. Such a lens has a large ratio of the center thickness to the effective diameter, but the optical glass of the present invention has a low refractive index and a high refractive index, so that the ratio can be reduced. Thereby, since the thickness of the lens that transmits blue-violet light can be reduced, the loss of blue-violet light can be reduced in combination with the excellent light transmittance of glass. In addition, it is preferable to reduce the ratio of the center wall thickness / effective diameter from the viewpoint of precision press molding. That is, the volume of the precision press-molding preform is determined by the volume of the lens. Since the objective lens is small, a preform used for molding is suitably spherical or spheroidal. When a spherical preform is used, if the curvature of the lens convex surface is large (the radius of curvature is small), atmospheric gas is trapped between the press mold and the glass, causing a problem called a gas trap where the glass does not reach the area. Cheap. Decreasing the ratio of center wall thickness / effective diameter leads to an increase in the curvature of the convex surface of the lens, which is preferable from the viewpoint of producing a lens with high surface accuracy by precision press molding.

  Next, the manufacturing method of the optical glass of this invention is demonstrated. The optical glass of the present invention can be produced by heating and melting a glass raw material. As the glass raw material, carbonates, nitrates, oxides and the like can be appropriately used. These raw materials are weighed at a predetermined ratio and mixed to prepare a mixed raw material, which is put into a melting furnace heated to, for example, 1200 to 1300 ° C., melted, clarified, stirred, and homogenized, In addition, it is possible to obtain a homogeneous molten glass containing no unmelted material. By forming and gradually cooling the molten glass, the optical glass of the present invention can be obtained.

[Precision Press Molding Preform and Manufacturing Method of Precision Press Molding Preform]
Next, the precision press-molding preform of the present invention and the method for producing the preform will be described. The preform is a glass molded body having a mass equal to that of a precision press-molded product. The preform is molded into an appropriate shape according to the shape of the precision press-molded product, and examples of the shape include a spherical shape and a spheroid shape. The preform is heated and subjected to precision press molding so as to have a viscosity capable of precision press molding.

  The precision press-molding preform of the present invention is made of the optical glass of the present invention described above. The preform of the present invention may have a thin film such as a release film on the surface as necessary. The preform is capable of precision press molding of an optical element having a desired optical constant. Furthermore, the stability of the glass in the high temperature range is high, and the viscosity when the molten glass flows out can be increased, so that the glass lump obtained by separating the molten glass flowing out of the pipe is formed into a preform during the cooling process. This method has the advantage that a high-quality preform can be produced with high productivity.

  The method for producing a precision press-molding preform according to the present invention comprises separating a molten glass lump from the molten glass flowing out, and forming the precision press-molding preform into a precision press-molding preform in the process of cooling the molten glass lump. In this manufacturing method, a precision press-molding preform made of the optical glass of the present invention is molded, which is one of the methods for manufacturing the preform of the present invention. As a specific example, a method of producing a preform by molding a preform with a predetermined weight in the process of separating a glass melt with a predetermined weight from a molten glass flow flowing out from a pipe or the like and cooling the glass mass. it can. This method has an advantage that machining such as cutting, grinding, and polishing is unnecessary. In preforms that have been machined, the distortion of the glass must be reduced to such an extent that it is not damaged by annealing prior to machining. However, according to the above method, the annealing for preventing damage is unnecessary. A preform having a smooth surface can also be formed. In this method, from the viewpoint of providing a smooth and clean surface, it is preferable to mold the preform in a floating state to which wind pressure is applied. A preform whose surface is a free surface is preferred. Furthermore, what does not have the cutting trace called a shear mark is desirable. The shear mark is generated when the molten glass flowing out is cut with a cutting blade. If the shear mark remains even at the stage where it is formed into a precision press-molded product, that portion becomes a defect. Therefore, it is preferable to exclude the sheer mark from the preform stage. As a method for separating molten glass without using a cutting blade and generating a shear mark, a method of dropping molten glass from an outflow pipe, or a molten glass lump of a predetermined weight that supports the tip of the molten glass flow flowing out of the outflow pipe There is a method of removing the above-mentioned support at a timing that can be separated (referred to as a descending cutting method). In the descending cutting method, the glass is separated at the constricted portion formed between the front end side and the outflow pipe side of the molten glass flow, and a molten glass lump having a predetermined weight can be obtained. Then, while the obtained molten glass lump is in a softened state, it is molded into a shape suitable for use in press molding.

  As a method for producing the preform of the present invention, a method in which a glass molded body is made from molten glass, the molded body is cut or cut, ground and polished can be used. In this method, molten glass is poured into a mold to form a glass molded body made of the optical glass, and the glass molded body is machined to make a preform with a desired weight. It is preferable to sufficiently remove the strain by annealing the glass so that the glass is not damaged before machining.

[Optical element and optical element manufacturing method]
The optical element of the present invention is composed of the above-described optical glass of the present invention. The optical element of the present invention is characterized by high refractive index and low dispersion, like the optical glass of the present invention constituting the optical element.

  Examples of the optical element of the present invention include various lenses such as a spherical lens, an aspherical lens, and a microlens, a diffraction grating, a lens with a diffraction grating, a lens array, and a prism. From the application side, digital still cameras, digital video cameras, single-lens reflex cameras, mobile phone cameras, optical lenses for reading and writing data to optical disks such as DVDs and CDs, lenses constituting imaging optical systems The lens (for example, the above-mentioned objective lens) etc. which comprise can be illustrated.

The optical element is preferably obtained by heating, softening and precision press molding the preform of the present invention.
The optical element may be provided with an optical thin film such as an antireflection film, a total reflection film, a partial reflection film, or a film having spectral characteristics, if necessary.

Next, a method for manufacturing an optical element will be described.
The optical element manufacturing method of the present invention is a method for manufacturing an optical element by heating a precision press molding preform produced by the preform of the present invention or the preform manufacturing method of the present invention and precision press molding. .

The precision press molding method is also called a mold optics molding method, which is already well known in the technical field to which the present invention belongs.
A surface that transmits, refracts, diffracts, or reflects light rays of the optical element is called an optical functional surface. For example, taking a lens as an example, a lens surface such as an aspherical surface of an aspherical lens or a spherical surface of a spherical lens corresponds to an optical function surface. The precision press molding method is a method of forming an optical functional surface by press molding by precisely transferring a molding surface of a press mold to glass. That is, it is not necessary to add machining such as grinding or polishing to finish the optical functional surface.
Therefore, the optical element manufacturing method of the present invention is suitable for manufacturing optical elements such as lenses, lens arrays, diffraction gratings, and prisms, and is particularly suitable for manufacturing aspherical lenses with high productivity. is there.

  According to the method for producing an optical element of the present invention, an optical element having the above optical characteristics can be produced, and a preform made of optical glass having a low temperature softening property is used. Therefore, the burden on the molding surface of the press mold can be reduced, and the life of the mold (or the release film when a mold release film is provided on the molding surface) can be extended. Further, since the glass constituting the preform has high stability, devitrification of the glass can be effectively prevented even in the reheating and pressing steps. Furthermore, a series of steps for obtaining a final product from glass melting can be performed with high productivity.

  As a press mold used for the precision press molding method, a known mold, for example, a mold having a release film on a molding surface of a mold material such as silicon carbide, cemented carbide, or stainless steel can be used. As the release film, a carbon-containing film, a noble metal alloy film, or the like can be used. The press mold includes an upper mold and a lower mold, and a barrel mold as necessary. Among them, in order to effectively reduce or prevent breakage of a glass molded product during press molding, a press mold made of silicon carbide and a press mold made of cemented carbide (particularly made of cemented carbide not containing a binder, for example, It is more preferable to use a WC press mold, and it is more preferable to provide a carbon-containing film as a release film on the molding surface of the mold.

  In the precision press molding method, it is desirable that the molding atmosphere be a non-oxidizing gas in order to keep the molding surface of the press mold in a good state. The non-oxidizing gas is preferably nitrogen or a mixed gas of nitrogen and hydrogen. In particular, when using a press mold having a carbon-containing film as a release film and having a molding surface, or when using a press mold made of silicon carbide, precision press molding should be performed in the non-oxidizing atmosphere. It is.

Next, a precision press molding method particularly suitable for the method for producing an optical element of the present invention will be described.
(Precision press molding method 1)
In this method, a preform is introduced into a press mold, and the press mold and the preform are heated together to perform precision press molding (referred to as precision press molding method 1).
In precision press molding method 1, precision press molding may be performed by heating the temperature of the press mold and the preform to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁶ to 10 ¹² dPa · s. preferable.
Further, the glass is cooled to a temperature at which the glass exhibits a viscosity of 10 ¹² dPa · s or more, more preferably 10 ¹⁴ dPa · s or more, more preferably 10 ¹⁶ dPa · s or more, and then the precision press-molded product is removed from the press mold. It is desirable to take it out.
Under the above conditions, the shape of the molding surface of the press mold can be accurately transferred with glass, and the precision press molded product can be taken out without being deformed.

(Precision press molding method 2)
This method is characterized in that a precision press-molding preform is heated and then introduced into a preheated press mold and precision press-molded (referred to as precision press molding method 2). According to this method, since the preform is preliminarily heated before being introduced into the press mold, it is possible to manufacture an optical element with good surface accuracy free from surface defects while shortening the cycle time.

  The preheating temperature of the press mold is preferably lower than the preheating temperature of the preform. Since the heating temperature of the press mold can be kept low by such preheating, the consumption of the press mold can be reduced.

In the precision press molding method 2, it is preferable to preheat the preform to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁹ dPa · s or less, more preferably 10 ⁹ dPa · s.
The preform is preferably preheated while floating, and the glass constituting the preform has a viscosity of 10 ^5.5 to 10 ⁹ dPa · s, more preferably 10 ^5.5 dPa · s to 10 ⁹ dPa · s. It is more preferable to preheat to a temperature indicating
Moreover, it is preferable to start cooling the glass simultaneously with the start of the press or during the press.
The temperature of the press mold is preferably adjusted to a temperature lower than the preheating temperature of the preform, and the temperature at which the glass exhibits a viscosity of 10 ⁹ to 10 ¹² dPa · s may be used as a guide.
In this method, it is preferable that after the press molding, the glass is cooled to a viscosity of 10 ¹² dPa · s or more and then released.

  The precision press-molded optical element is taken out from the press mold and gradually cooled as necessary. When the molded product is an optical element such as a lens, an optical thin film may be coated on the surface as necessary.

  The present invention will be further described below with reference to examples. However, this invention is not limited to the aspect shown in the Example.

Production of optical glass Table 1 shows the compositions of the glasses of Examples 1 to 30. In any glass, the corresponding oxides, hydroxides, carbonates, and nitrates are used as raw materials for each component, and after vitrification, the raw materials are weighed so as to have the composition shown in Table 1, and mixed sufficiently. After that, it was put into a platinum crucible and melted in a temperature range of 1200 to 1300 ° C. in an electric furnace, stirred and homogenized, clarified and cast into a mold preheated to an appropriate temperature. The cast glass was cooled to the transition temperature and immediately placed in an annealing furnace, and gradually cooled to room temperature to obtain each optical glass.

For each optical glass obtained by the above method, the following method, the refractive index (n _d), Abbe's number ([nu _d), measured specific gravity, glass transition temperature, the liquid phase temperature. The results are shown in Table 1. In addition, Table 1 shows the results of measuring λ ₈₀ , λ _70, and λ ₅ for each optical glass of Examples 1 to 17 by the method described above.
(1) Refractive index (n _d ) and Abbe number (ν _d )
It measured about the optical glass obtained by making slow cooling temperature-fall rate -30 degreeC / hour.
(2) Glass transition temperature (T _g )
The temperature was increased at a rate of 4 ° C./min with a thermomechanical analyzer from Rigaku Corporation.
(3) Specific gravity It calculated using the Archimedes method.
(4) Liquidus temperature (LT)
About 50 g of a glass sample is put in a platinum crucible, and melted at about 1200 ° C. to 1300 ° C. for about 15 to 60 minutes. Then, 980 ° C., 990 ° C., 1000 ° C., 1010 ° C., 1020 ° C., 1030 ° C., 1040 ° C., and 1050 ° C., respectively. Cooling what was kept at 1060 ° C., 1070 ° C., 1080 ° C., 1090 ° C., 1100 ° C. for 2 hours and observing the presence or absence of crystal precipitation with a microscope, the minimum temperature at which no crystals were observed was the liquid phase temperature (L.P. T.).

Manufacture of precision press-molding preforms Next, clarified and homogenized molten glass corresponding to Examples 1 to 30, made of a platinum alloy whose temperature is adjusted to a temperature range in which stable outflow is possible without devitrification of the glass The molten glass lump of the desired preform mass is separated by a dropping or descending cutting method, and the molten glass lump is received by a receiving mold having a gas outlet at the bottom, and the gas outlet A preform for precision press molding was formed while gas was ejected from the glass to float the glass lump. A spherical preform and a flat spherical preform were obtained by adjusting and setting the separation interval of the molten glass.

Production of Optical Element (Aspherical Lens) The preform obtained by the above method was precision press-molded using a press apparatus shown in FIG. 1 to obtain an aspherical lens. More specifically, after the preform is placed between the lower mold 2 and the upper mold 1 constituting the press mold, the quartz tube 11 is energized through a heater (not shown) with a nitrogen atmosphere inside the quartz tube 11. Was heated. The temperature inside the press mold is set to a temperature at which the glass to be molded exhibits a viscosity of 10 ⁸ to 10 ¹⁰ dPa · s, and while maintaining the same temperature, the push bar 13 is lowered and the upper mold 1 is pressed to form the mold. The preform set inside was pressed. The press pressure was 8 MPa, and the press time was 30 seconds. After pressing, the pressure of the press is released, and the glass molded product that has been press-molded is kept in contact with the lower mold 2 and the upper mold 1 until the viscosity of the glass reaches 10 ¹² dPa · s or more. It was cooled and then rapidly cooled to room temperature, and the glass molded product was taken out of the mold and an aspherical lens was obtained. In FIG. 1, the holding member 10 holds the lower die 2 and the barrel die 3, and the support rod 9 supports the upper die 1, the lower die 2, the barrel die 3, and the holding member 10, and is pressed by the push rod 13. Take the pressure of. A thermocouple 14 is inserted into the lower mold 2 to monitor the temperature inside the press mold.
The above lens was suitable as a lens constituting the imaging optical system. Further, the press mold and the preform were changed to appropriate ones, and an objective lens for DVD having a numerical aperture of 0.85 was produced.

  ADVANTAGE OF THE INVENTION According to this invention, the high refractive index low dispersion optical glass suitable for precision press molding can be provided. A precision press-molding preform can be produced from the optical glass of the present invention. Furthermore, according to the present invention, an optical element made of a high refractive index and low dispersion glass can be provided.

1: Upper mold 2: Lower mold 3: Body mold 4: Preform for precision press molding 9: Support bar 10: Holding member 11: Quartz tube 13: Push bar 14: Thermocouple

Claims (9)

The refractive index n _d is 1.70 or more, the Abbe number ν _d is 50 or more,
In mol% display,
B ₂ O ₃ 20-80%,
SiO ₂ 0-30%,
Li ₂ O 1-25%,
ZnO 0-20%,
La ₂ O ₃ 4-30%,
Gd ₂ O ₃ 1-25%,
Y ₂ O ₃ 0-20%,
ZrO ₂ 0-5%,
MgO 0-25%,
CaO 0-15%,
SrO 0-10%,
And the total amount of the components is 97% or more,
The molar ratio [ZnO / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] is 0.8 or less, and the molar ratio [(CaO + SrO + BaO) / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] is 0.8 or less,
Optical glass which can contain Ta ₂ O ₅ as an optional component and has a molar ratio [(ZrO ₂ + Ta ₂ O ₅ ) / (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ )] of 0.4 or less . The optical glass according to claim 1, wherein the total amount of Li ₂ O and ZnO is 2 to 30%, and the molar ratio (ZnO / Li ₂ O) is 6 or less. The optical glass according to claim 1 or 2, wherein the refractive index n _d and the Abbe number ν _d satisfy the following formula (1).
n _d ≧ 2.235−0.01 × ν _d (1) A precision press-molding preform comprising the optical glass according to any one of claims 1 to 3. The optical element which consists of optical glass of any one of Claims 1-3. In the method of manufacturing a precision press-molding preform that separates a molten glass lump from the flowing molten glass and forms the precision press-molding preform in the process of cooling the molten glass lump,
A method for producing a precision press-molding preform comprising molding the precision press-molding preform comprising the optical glass according to claim 1. A method for producing an optical element, wherein the precision press molding preform according to claim 4 or the precision press molding preform produced by the method according to claim 6 is heated to perform precision press molding. The optical element manufacturing method according to claim 7, wherein a precision press molding preform is introduced into a press mold, and the preform and the mold are heated together to perform precision press molding. The method for producing an optical element according to claim 7, wherein the preform for precision press molding is heated and then introduced into a preheated press mold to perform precision press molding.

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