JP2010083703A - Optical glass, glass gob for press forming, and optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical glass which suppresses defects due to foreign materials and residues in the glass and has a lower content of Sb oxides than conventional optical glass. <P>SOLUTION: The optical glass has a refractive index nd of 1.80-1.88 and an Abbe's number νd of 20-30, contains 18-38 mass% of SiO<SB>2</SB>as a glass component, and externally contains Sn oxides, Ce oxides and Sb oxides in such amounts satisfying the expression (1): 0<A(Sn)+A(Ce)+A(Sb)≤3.6, the expression (2): 0<A(Sn)+A(Ce)≤3.5 and the expression (3): 0≤A(Sb)≤0.1, wherein A(Sn) represents a content (mass%) of the Sn oxides; A(Ce) represents a content (mass%) of the Ce oxides; and A(Sb) represents a content (mass%) of the Sb oxides. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to optical glass, a glass material for press molding, and an optical element.

In recent years, with higher functionality and more compact imaging optical systems, the demand for high refractive index and high dispersion glass optical elements is increasing. Silicate-based glass is known as a high refractive index / high dispersion type glass used in such an optical element (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2004-155639

  In the glass used for such an optical element, the presence of defects such as residual bubbles and foreign matters in the glass becomes a product defect. For this reason, it is necessary to suppress defects in the glass. In particular, in the glass used for an optical element constituting an imaging optical system used for an image sensor such as a CCD or CMOS, further suppression of foreign matter defects is required.

  The above-described foreign matter in the glass is generated when the glass raw material is melted, for example, when the melting container is eroded by the glass melt, and a part of the container is mixed into the glass as fine particles or fragments. Therefore, in order to suppress the occurrence of defects in the glass and foreign matter, it is necessary to shorten the melting time of the glass raw material. However, if the melting time of the glass raw material is shortened, defoaming in the glass melt becomes insufficient and residual bubble defects occur. In order to suppress residual foam defects, Sb oxide is usually added as a defoaming agent (clarifier) in the glass raw material (see, for example, Patent Document 1). However, in recent years, a glass having a lower Sb oxide content in the glass is being demanded as the glass used in the optical element.

  The present invention has been made in view of the above circumstances, and suppresses foreign matter defects and residue defects in the glass, and uses an optical glass having a smaller Sb oxide content than before, and uses the same. It is an object to provide a glass material for press molding and an optical element.

The above-mentioned subject is achieved by the following present invention.
That is, the optical glass of the present invention has a refractive index nd of 1.80 or more and 1.88 or less, an Abbe number νd of 20 or more and 30 or less, and, as a glass component, a proportion of SiO ₂ of 18 mass% or more and 38 mass% or less. In addition, Sn oxide, Ce oxide and Sb oxide are included so as to satisfy the following formulas (1) to (3).
Formula (1) 0 <A (Sn) + A (Ce) + A (Sb) ≦ 3.6
Formula (2) 0 <A (Sn) + A (Ce) ≦ 3.5
Formula (3) 0 ≦ A (Sb) ≦ 0.1
[In the formulas (1) to (3), A (Sn) represents the content (mass%) of the Sn oxide, and A (Ce) represents the content (mass%) of the Ce oxide. , A (Sb) represents the content (% by mass) of the Sb oxide. ]

Further, an embodiment of the optical glass of the present invention is represented by _{mass%, SiO 2: 22.0~35.0%, Na} 2 O: 4.0~17.0%, BaO: 2.0~25 It is preferable to contain each component of 0.0%, TiO ₂ : 18.0 to 27.0%, and Nb ₂ O ₅ : 13.0 to 26.0%.

Another embodiment of the optical glass of the present invention is represented by mass%, _SiO 2: 18% or more but less than 30%, BaO: less than 12% or more _{23%, TiO 2: 22~37%} , Nb 2 O 5 : less than 7% or more _{16%, Na 2 O: 5~20} %, K 2 O: 0~6%, CaO: 0~5%, SrO: 0~5%, ZrO 2: 0~4%, Ta 2 It is preferable that O ₅ : 0 to 3% and P ₂ O ₅ : 0% or more and less than 0.5% and substantially free of PbO, As ₂ O ₃ and F.

  Moreover, the glass material for press molding of this invention consists of the optical glass of this invention.

  The optical element of the present invention includes the optical glass of the present invention.

  According to the present invention, an optical glass in which foreign matter defects and residue defects in glass are suppressed and the content of Sb oxide is smaller than that in the past, and a glass material for press molding and an optical element using the optical glass are provided. Can be provided.

<Optical glass>
The optical glass of the present embodiment has a refractive index nd of 1.80 or more and 1.88 or less, an Abbe number νd of 20 or more and 30 or less, and, as a glass component, SiO ₂ in a proportion of 18 mass% or more and 38 mass% or less. And Sn oxide, Ce oxide and Sb oxide are included so as to satisfy the following formulas (1) to (3).
Formula (1) 0 <A (Sn) + A (Ce) + A (Sb) ≦ 3.6
Formula (2) 0 <A (Sn) + A (Ce) ≦ 3.5
Formula (3) 0 ≦ A (Sb) ≦ 0.1
[In the above formulas (1) to (3), A (Sn) represents the content (mass%) of the Sn oxide, and A (Ce) represents the content (mass% of the Ce oxide). A (Sb) represents the content (mass%) of the Sb oxide. ]

-Refractive index nd and Abbe number νd-
The optical glass of the present embodiment has a refractive index nd of 1.80 to 1.88 and an Abbe number νd of 20 to 30. In other words, the optical glass of the present embodiment has a high refractive index and low dispersion characteristics. Here, from the viewpoint of obtaining a higher refractive index, the refractive index nd is preferably 1.84 or more. The larger the refractive index nd, the better. However, it is difficult to select a glass composition that can achieve other characteristics and manufacturability while achieving a high refractive index. It is as follows. Further, from the viewpoint of obtaining low dispersibility, the Abbe number νd is preferably 25 or less.

-Glass component-
The optical glass of the present embodiment includes a SiO ₂ in a proportion of 18 wt% or more 38 wt% or less. If the content of SiO ₂ is less than 18% by mass, the glass structure is unstable and devitrified. On the other hand, if the content exceeds 38.0% by mass, the refractive index cannot be 1.88 or less, and a highly refractive optical glass cannot be obtained.

There are two preferred embodiments of the glass composition of the optical glass of the present embodiment. Hereinafter, in the optical glass of the present embodiment, unless otherwise specified, the content of each component is expressed in mass%. In the first aspect, priority is given to obtaining a glass with little coloration, and expressed in mass%, SiO ₂ : 22.0 to 35.0%, Na ₂ O: 4.0 to 17.0%, _{BaO: 2.0~25.0%, TiO 2:} 18.0~27.0%, Nb 2 O 5: is an optical glass containing 13.0 to 26.0% of each component.

First, SiO ₂ is a main component that forms optical glass. If the content of SiO ₂ is less than 22.0%, the glass tends to be unstable (easy to devitrify), and in addition, it tends to be colored. On the other hand, when the content exceeds 35.0%, it becomes difficult to obtain an optical glass having a high refractive index. Therefore, the content of SiO ₂ is determined to be in the range of 22.0 to 35.0%. A more preferable content is in the range of 25.0 to 32.0%.

Na 2 _O, together with improving melting property of the glass, has the effect of stabilizing the glass. If the Na ₂ O content is less than 4.0%, such an effect may not be obtained. On the other hand, if the content exceeds 17.0%, the desired optical constant may not be obtained. Therefore, the content of Na ₂ O was determined to be in the range of 4.0 to 17.0%. A more preferable content is in the range of 12.0 to 14.0%.

  BaO has the effect of increasing the refractive index and stabilizing the glass. If the BaO content is less than 2.0%, such an effect may not be obtained. On the other hand, if the content exceeds 25.0%, the specific gravity of the glass may become too large. Therefore, the content is determined to be in the range of 2.0 to 25.0%. A more preferable content is in the range of 9.0 to 17.0%.

TiO ₂ has an effect of increasing the refractive index and dispersion, stabilizing the glass, and further reducing the specific gravity of the glass. If the content of TiO ₂ is less than 18.0%, such an effect may not be obtained. On the other hand, if the content exceeds 27.0%, the glass may be easily colored. Therefore, the content is determined to be in the range of 18.0 to 27.0%. A more preferable content is in the range of 19.0 to 23.0%.

Nb ₂ O ₅ has the effect of increasing the refractive index and dispersion without causing the glass to be colored as much as TiO ₂ . If the content of Nb ₂ O ₅ is less than 13.0%, it is difficult to obtain such an action. On the other hand, when the content exceeds 26.0%, Nb ₂ O ₅ has a large specific gravity, so that the specific gravity of the glass may increase. For this reason, content was defined as the range of 13.0-26.0%. A more preferable content is in the range of 18.0 to 25.0%.

In addition, one or more specific amounts of K ₂ O, SrO, B ₂ O ₃ , Al ₂ O ₃ , MgO, ZnO, Y ₂ O ₃ , Ta ₂ O ₅ , Li ₂ O, and ZrO ₂ are required. May be further contained. The reasons for limiting to these components will be described below.

K ₂ O, like Na ₂ O, has the effect of improving the melting property of the glass and stabilizing the glass. However, if it is contained in a large amount, the desired optical constant may not be obtained. Therefore, the upper limit of the content of K ₂ O is preferably 8.0%, and in addition, the total amount of K ₂ O and Na ₂ O is preferably in the range of 8 to 17%. The more preferable content of K ₂ O is in the range of 3.0 to 5.0%, and the more preferable total amount is in the range of 9.0 to 13.0%.

  SrO, like BaO, has the effect of increasing the refractive index and stabilizing the glass. However, if the content exceeds 10.0%, the glass tends to devitrify, so the content is preferably 10.0% or less. A more preferable content is in the range of 3.0 to 4.0%.

B ₂ O ₃ promotes melting of the glass and stabilizes the glass, but if it is contained in an amount exceeding 1.0%, the glass may be colored. For this reason, the content is preferably 1.0% or less. A more preferable upper limit of the content is 0.5%.

Al ₂ O ₃ improves the chemical durability of the glass, but if its content exceeds 2.0%, the viscosity may increase. Therefore, the content is preferably 2.0% or less. A more preferable upper limit of the content is 1.0%.

MgO, ZnO, Y ₂ O ₃ and Ta ₂ O ₅ are added for the purpose of adjusting the optical constants (refractive index and dispersion) of the optical lens according to the application. If MgO and ZnO are contained in excess of 3.0%, the glass may be devitrified. Therefore, the content of MgO and ZnO is preferably 3.0% or less. A more preferable upper limit of the content is 1.0%.

_The glass when the content exceeds the Y 2 _{O 3} and _Ta 2 _{O 5} 3.0% there is a risk of devitrification. Accordingly, the content of Y ₂ O ₃ and Ta ₂ O ₅ is preferably 3.0% or less. A more preferable upper limit of the content is 2.0%.

Li ₂ O has a role of adjusting the viscosity of the glass. However, if it is contained in an amount exceeding 3.0%, volatilization becomes violent and composition fluctuations occur in the upper and lower portions of the glass, and striae easily occur. Therefore, the content is preferably 3.0% or less. A more preferable upper limit of the content is 1.0%.

ZrO ₂ improves the chemical durability of the glass, but if it exceeds 4.0%, the glass tends to devitrify rapidly. Therefore, the content is preferably 4.0% or less. A more preferable upper limit of the content is 3.0%. If necessary, an appropriate amount of a conventionally known additive may be added as a glass component.

In the second aspect, priority is given to obtaining a glass having good devitrification resistance at the time of reheating. In terms of mass%, SiO ₂ : 18% or more and less than 30%, BaO: 12% or more and 23% _{less, TiO 2: 22~37%, Nb} 2 O 5: less than 7% or more _{16%, Na 2 O: 5~20} %, K 2 O: 0~6%, CaO: 0~5%, SrO: 0 _{~5%, ZrO 2: 0~4%} , Ta 2 O 5: 0~3% and _P 2 _O 5: includes 0% or more and less than 0.5%, and substantially the PbO, _As 2 _{O 3} and F Optical glass not included.

SiO ₂ is an effective component for maintaining the solubility and flow viscosity of glass as a network-forming oxide, and it is effective for maintaining the glass structure stably and improving the devitrification resistance. Need. However, when it is 30% or more, the refractive index is lowered, and it is difficult to obtain the high refractive index glass of the present invention. Therefore limiting the SiO ₂ to below 18% to 30%, but preferably less than 30% more than 24%.

  BaO is more effective in increasing the durability and thermal stability of the glass by setting its content to 12% or more. However, if it is added in an amount of 23% or more, the Abbe number increases and it may be difficult to obtain a highly dispersed glass. A more preferable content of BaO is 14 to 20%.

TiO ₂ is more effective in imparting high refraction and high dispersion characteristics to glass by setting its content to 22% or more. However, since TiO ₂ is the main component of crystals generated when reheated and softened and is also a nucleating oxide, devitrification resistance is remarkably high when it tries to match the target refractive index exceeding 37%. In addition to the decrease, the transmission absorption edge may shift to the long wavelength side. In addition, the more preferable content of TiO ₂ is 25 to 32.5%.

Nb ₂ O ₅ is effective for imparting high refraction and high dispersion characteristics to glass or stabilizing the glass by setting its content to 7% or more. However, if it exceeds 16%, the devitrification resistance may be deteriorated. The content of Nb ₂ O ₅ is more preferably 10% or more and less than 16%.

Network-modified oxides such as Na ₂ O and K ₂ O are effective components for lowering the glass transition temperature (Tg). Therefore, the Na ₂ O content is preferably 5% or more. However, from the viewpoint of suppressing a decrease in devitrification resistance and a decrease in refractive index, Na ₂ O is preferably 20% or less. The Na ₂ O content is more preferably 9.5 to 13.5%. Further, K ₂ O is preferably 6% or less, and more preferably 5% or less.

  CaO and SrO have the same effect as BaO. When using these components, the content is preferably 0 to 5%. If it exceeds 5%, the devitrification resistance may decrease.

ZrO ₂ and Ta ₂ O ₅ are components that provide a high refractive index, and have an effect of improving devitrification resistance when added in a small amount. However, if the amount of ZrO ₂ exceeds 4% and the amount of Ta ₂ O ₅ exceeds 3%, the devitrification resistance may be lowered. Therefore, the amount of ZrO is preferably 0 to 4%, and the amount of Ta ₂ O ₅ is preferably in the range of 0 to 3%. Of these two components, it is particularly preferable to use ZrO ₂ .

P ₂ O ₅ has a strong effect of forming crystal nuclei. _Therefore, for the P 2 _{O 5,} or not added, it is preferably less than 0.5% even when adding. Furthermore, it is preferable that PbO and As ₂ O ₃ are not substantially contained due to a strong demand for environmental protection. It is preferable to substantially eliminate F, since the homogeneity is greatly lowered due to volatilization during dissolution.

Furthermore, the total content of SiO ₂ , BaO, TiO ₂ , Nb ₂ O ₅ , Na ₂ O, K ₂ O, CaO, SrO, ZrO ₂ , Ta ₂ O ₅ is preferably 95% or more, and 99% More preferably, it is more preferably 100%.

In addition, the total content of SiO ₂ , BaO, TiO ₂ , Nb ₂ O ₅ , Na ₂ O and ZrO ₂ is more preferably 95% or more, still more preferably 99% or more, and 100% It is particularly preferable that

  With the above composition, an optical glass having a refractive index (nd) of 1.80 to 1.88, an Abbe number (νd) of 20 to 30 and excellent devitrification resistance can be obtained. In the silicate glass composition other than the second embodiment, the devitrification resistance is remarkably lowered particularly in the range where the refractive index (nd) is 1.84 or more and the Abbe number (νd) is 25 or less. There is a tendency. However, the glass of the second embodiment can be satisfactorily molded without any problem in terms of devitrification resistance even when the above-described optical constant is satisfied.

According to the glass of the second aspect, it is easy to prevent devitrification of the molded product even when the molten glass is press-molded while the glass is in a softened state to produce a glass molded product. However, when forming a glass material for press molding from molten glass, annealing the material, and then making an optical element by heating, softening and re-forming, about the devitrification resistance of the glass Special attention needs to be paid. In the glass of the second embodiment, the crystallization tendency in reheating and softening depends on the amount of SiO _{2 and} the amount of TiO ₂ . Therefore, when re-molding by reheating and softening, in order to improve devitrification resistance, the amount of SiO ₂ with respect to the amount of TiO ₂ expressed by mass% (mass ratio SiO ₂ / TiO ₂ ) Is preferably 0.8 or more, and more preferably 0.86 or more.

In addition to the above-mentioned components, a substance whose content should be restricted for improving devitrification resistance, that is, a rare earth metal oxide such as Al ₂ O ₃ , La ₂ O ₃ , Y ₂ O ₃ , Gd ₂ O ₃ , Platinum will be described.
In view of the above reason, the content of Al ₂ O ₃ is preferably 0.2% or less, and more preferably not added.

The total content of La ₂ O ₃ , Y ₂ O ₃ and Gd ₂ O ₃ is also preferably 1% or less, more preferably 0% in view of the above reasons. In addition, the total content of rare earth metal oxides is preferably 1% or less, and more preferably 0%. For the above reason, platinum Pt is also a substance that needs to be paid sufficient attention so as not to be mixed into the glass, and is preferably set to 10 ppm or less, and it is particularly desirable to completely prevent mixing.

-Sn oxide, Ce oxide and Sb oxide-
Next, the Sn oxide, Ce oxide, and Sb oxide added in the outer ratio will be described. First, in the present specification, Sn oxide, Ce oxide, and Sb oxide mean those existing in the state of oxide in the glass regardless of the valence of the metal elements constituting these oxides. . For example, examples of Sn oxide include SnO and SnO ₂ , examples of Ce oxide include examples of CeO ₂ and Ce ₂ O _3, and examples of Sb oxide include Sb ₂ O ₃ , Examples thereof include Sb ₂ O ₅ . Therefore, the Sn oxide content A (Sn) means the total amount of oxides such as SnO and SnO _2, and the Ce oxide content A (Ce) means CeO ₂ , Ce ₂ O. ₃ means the total amount of oxides such as _3, and the Sb oxide content A (Sb) means the total amount of oxides such as Sb ₂ O ₃ and Sb ₂ O ₅ .

These three types of metal oxides (hereinafter sometimes referred to as “additives”) have an effect of enhancing the clarification effect during glass melting. In addition to this, the optical glass contains components (for example, Nb ₂ O ₅ , TiO ₂ , WO ₃ , Bi ₂ O _3, etc.) that may color the glass by a reduction reaction during melting of the glass. If present, it also has an action of suppressing the coloring. In addition, As oxide is known as a metal oxide having an excellent clarification effect. However, in the optical glass of the present embodiment, it is not necessary to use an As oxide in order to ensure the clarification effect by using the three kinds of additives described above so as to satisfy the formulas (1) to (3). .

  As described above, the contents of these three kinds of additives need to satisfy the relationships shown in the formulas (1) to (3). That is, A (Sn) + A (Ce) + A (Sb) needs to be more than 0% by mass and 3.6% by mass or less. When A (Sn) + A (Ce) + A (Sb) is 0% by mass, clarification at the time of melting the glass cannot be promoted, so that residual bubble defects occur. Further, when the melting time of the glass raw material is lengthened in order to avoid the occurrence of residual bubble defects, foreign matter defects are generated. Furthermore, when a component that may color the glass by a reduction reaction during melting of the glass is contained in the glass, the glass is colored. On the other hand, when A (Sn) + A (Ce) + A (Sb) exceeds 3.6% by mass, the additive remains undissolved in the glass and becomes a foreign matter defect, and this foreign matter becomes a light scattering source. . In addition to this, coloring due to the additive itself occurs. Further, when a large amount of Sn oxide or Ce oxide is used, Sn or Ce easily functions as a crystal nucleus forming agent. For this reason, when the optical glass of this Embodiment is utilized as an optical element through a reheating process like the glass raw material for press molding, it may devitrify.

  Moreover, as shown in Formula (2), A (Sn) + A (Ce) needs to exceed 0 mass% and to be 3.5 mass% or less. When A (Sn) + A (Ce) is 0% by mass, A (Sb) needs to be more than 0% by mass and 0.1% by mass or less. When A (Sn) + A (Ce) exceeds 3.5% by mass, the additive remains undissolved in the glass and becomes a foreign matter defect, and the foreign matter becomes a light scattering source. In addition, coloring due to the additive itself occurs. Furthermore, Sn and Ce can easily function as a crystal nucleation agent. For this reason, when the optical glass of this Embodiment is utilized as an optical element through a reheating process like the glass raw material for press molding, it may devitrify.

  Further, when both A (Sn) and A (Ce) exceed 0% by mass (that is, when both Sn oxide and Ce oxide are used in combination), by allowing Sn oxide and Ce oxide to coexist, This is because the glass refining effect can be enhanced over a wide temperature range from a high temperature range to a low temperature range. As a result, as compared with the case where As oxide is used, or the content of Sb oxide is not suppressed to 0.1% by mass or less as shown in Formula (3), more than this is used However, in the optical glass according to the present embodiment, it is possible to ensure an excellent clarification effect.

  Although details of the reason why such an effect is obtained are unknown, the present inventors presume as follows. First, Sn oxide is excellent in the function of promoting clarification by releasing oxygen gas at a high temperature and taking in the fine bubbles contained in the glass to make them large bubbles so that they can float easily. On the other hand, Ce oxide is excellent in the function of extinguishing bubbles by incorporating oxygen present as a gas in glass at a low temperature as a glass component. Thus, Sn oxide and Ce oxide are in a relationship of mutually complementing the fining effect on the temperature range. In addition to this, Sn oxide works to remove both relatively large bubbles and extremely small bubbles when the size of bubbles (the maximum diameter of bubbles (cavities) remaining in the solidified glass) is 0.3 mm or less. strong. For this reason, when Ce oxide is used together with Sn oxide, the density of large bubbles having a maximum diameter of 50 μm or more and 0.3 mm or less can be drastically reduced to several tenths. From the above, it is estimated that the above-described effects can be obtained.

  In addition, A (Sn) and A (Ce) are not particularly limited as long as the formula (2) is satisfied, and can be arbitrarily selected within a range of more than 0% by mass and 3.5% by mass or less. . However, when Sn oxide and Ce oxide are used at the same time for the purpose of exhibiting the above-described effects, A (Sn) and A (Ce) are each in the range of more than 0% by mass and less than 3.5% by mass. Is preferred. In addition, when A (Sn) exceeds 3.5 mass%, Sn oxide will remain undissolved in glass and will become a light-scattering source as a foreign material. Therefore, A (Sn) is preferably 2.5% by mass or less, more preferably 1.5% or less, and further preferably 1.0% by mass or less. Moreover, when A (Ce) exceeds 3.5 mass%, reaction with the refractory and platinum which comprise a melting container will occur, and the impurity concentration in optical glass will increase. In addition, such an increase in impurities adversely affects the surface state of the obtained optical glass. For this reason, when optical glass is molded using a mold, the reaction between the optical glass and the mold is also increased. Therefore, A (Ce) is preferably 2.5% by mass or less, more preferably 1.5% or less, and further preferably 1.0% by mass or less.

  Furthermore, as shown in Formula (3), A (Sb) needs to be 0% by mass or more and 0.1% by mass or less. In the present embodiment, Sn oxide or Ce oxide can be used as a fining agent, so that the amount of Sb oxide used can be reduced or zero. The content A (Sb) of the Sb oxide needs to be 0.1% by mass or less, preferably 0.05% by mass or less, more preferably 0.01% by mass or less, The content is more preferably 0.001% by mass or less, and most preferably 0% by mass. When A (Sb) exceeds 0.1% by mass, the amount of Sb oxide used cannot be reduced. In addition, when the value of A (Sn) + A (Ce) is small, Sb oxide may be used to supplement the clarification effect by Sn oxide or Ce oxide.

-Manufacturing method of optical glass-
The optical glass of the present embodiment includes a melting step for melting glass raw materials (such as a vitrification raw material called a batch raw material and a cullet raw material), a clarification step for refining the molten glass obtained by melting, and a clarified molten glass. It is made through a homogenization process for homogenizing and a molding process for outflowing and molding the homogenized molten glass. Among these, the clarification process is performed at a higher temperature than the homogenization process. In the clarification process, bubbles are actively generated in the glass, and fine bubbles contained in the glass are taken in to form large bubbles, thereby facilitating clarification. On the other hand, in the state where the temperature of the glass is lowered toward the outflow, a technique of eliminating bubbles by incorporating oxygen present as a gas in the glass as a glass component is effective.

Note that SnO ₂ is preferably used as the Sn oxide used as the glass raw material. This is because SnO ₂ effectively releases oxygen gas at a high temperature, so that the clarification effect can be improved.

<Glass material for press molding>
Next, the glass material for press molding according to the present embodiment will be described.
The press-molding glass material of the present embodiment is made of the optical glass of the present embodiment described above. The glass material for press molding is molded by pouring a clarified homogeneous molten glass into a mold, annealing the obtained glass molded body, then cutting or cleaving into glass pieces, and barrel-polishing the glass pieces for the purpose It is obtained by setting it as the glass lump of the mass for one press-molded product. Desired optical elements such as spherical lenses and prisms can be made by heating, softening, press molding, annealing, grinding and polishing the glass material thus obtained. Further, the glass piece can be ground and polished to smoothly finish the surface, and a glass material for precision press molding can be obtained.

<Optical element>
Next, the optical element of the present embodiment will be described. The optical element of the present embodiment is obtained by processing the optical glass of the present embodiment described above by grinding, polishing, molding or the like. Specific examples of such an optical element include a convex meniscus lens, a plano-convex lens, a biconvex lens, a concave meniscus lens, a plano-concave lens, a biconcave lens, a microlens, various lenses such as a lens array, a prism, and the like. . The various lenses can be classified into spherical lenses and aspherical lenses. The surface of these optical elements may be coated with an antireflection film or the like as necessary.

  These optical elements can be obtained by heating and softening the aforementioned press-molding glass material, press-molding, annealing the resulting molded product, grinding and polishing, and precision press-molding glass material. Can be obtained by precision press-molding and grinding the non-optical functional surface (for example, centering of the lens) as necessary. Alternatively, it can be obtained by press-molding a clarified and homogenized molten glass, annealing the obtained molded product, and then grinding and polishing.

  Since these optical elements are made of optical glass that does not contain foreign matter such as residual bubbles or unmelted residue when dissolved, and is reduced in coloration, high-definition imaging optical systems such as digital still cameras and digital video It is suitable as an optical element constituting a projection optical system such as a camera, a surveillance camera, an in-vehicle camera, or a projector.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, this invention is not limited to the aspect shown in the Example.

<Production of glass>
Glasses using carbonates, nitrates, oxides, etc. so that each of the glass compositions shown in Table 1 and Table 2 has a composition in which the additives shown in Tables 3 to 11 are added in an external ratio are obtained. The raw materials were prepared. The glass composition shown in Table 1 corresponds to the first aspect, and the glass composition shown in Table 2 corresponds to the second aspect.

  Subsequently, this glass raw material was put into a melting vessel (platinum crucible or silica crucible), melted in the atmosphere at 900 to 1300 ° C. for a predetermined time, clarified and stirred to homogenize. Thereafter, the molten glass was poured into a mold and slowly cooled at a temperature lowering rate of 30 ° C./hr to obtain a glass lump. In addition, about 7,596 types of glass produced here, it was confirmed that neither glass lump has devitrified.

Next, to the additives shown in Table 3 to Table 11, 0.03% by mass (outer percent) Sb ₂ O ₃ added glass, 0.06% by mass (outer percent) Sb ₂ O ₃ was added. A glass lump was also produced for the prepared glass and a glass to which 0.10% by mass (outer percent) of Sb ₂ O ₃ was added, and it was confirmed that devitrification was not observed.

<Evaluation>
The obtained 30,384 kinds of evaluation samples were evaluated for residual bubble defects, foreign matter defects and coloring. As a result, no residual bubble defect or foreign matter defect was observed for the sample to which at least one of Sn oxide and Ce oxide was added, and for the sample to which Sb oxide was further added. It was confirmed that there was no problem as a device. On the other hand, in the sample to which any of Sn oxide, Ce oxide and Sb oxide was not added, residual foam defects and foreign matter defects were observed, and coloring at a level causing problems as an optical element was confirmed. It was.

<Evaluation method and evaluation criteria>
The evaluation methods and evaluation criteria for residual bubble defects, foreign object defects, and coloring are as follows.

-Residual bubble defect-
The obtained glass lump was polished so that the surface was flat and smooth to obtain a sample for evaluation. Next, the presence or absence of residual bubble defects was observed by focusing on an arbitrary position (inside the glass) in the depth direction of the evaluation sample with an optical microscope from the polished surface side of the evaluation sample. The observation magnification at this time was 100 times.

-Foreign object defect-
The obtained glass lump was polished so that the surface was flat and smooth to obtain a sample for evaluation. Next, the presence or absence of foreign matter defects was observed by focusing on an arbitrary position (inside the glass) in the depth direction of the evaluation sample with an optical microscope from the polished surface side of the evaluation sample. The observation magnification at this time was 100 times.

-Coloring-
The obtained glass lump was mirror-polished to a plate shape with a thickness of 5 mm to prepare a sample for evaluation. The difference in the degree of coloring was visually compared with a limit sample (a sample having a problem when used as an optical element) prepared separately, and a case where the same degree of coloring was observed was judged as problematic.

Claims (5)

Refractive index nd is 1.80 or more and 1.88 or less, Abbe number νd is 20 or more and 30 or less,
As a glass component, SiO ₂ is contained in a proportion of 18% by mass or more and 38% by mass or less,
An optical glass characterized by containing Sn oxide, Ce oxide and Sb oxide so as to satisfy the following formulas (1) to (3).
Formula (1) 0 <A (Sn) + A (Ce) + A (Sb) ≦ 3.6
Formula (2) 0 <A (Sn) + A (Ce) ≦ 3.5
Formula (3) 0 ≦ A (Sb) ≦ 0.1
[In the above formulas (1) to (3), A (Sn) represents the content (mass%) of the Sn oxide, and A (Ce) represents the content (mass% of the Ce oxide). A (Sb) represents the content (mass%) of the Sb oxide. ] In terms of mass%, SiO ₂ : 22.0 to 35.0%, Na ₂ O: 4.0 to 17.0%, BaO: 2.0 to 25.0%, TiO ₂ : 18.0 to 27. The optical glass according to claim 1, comprising 0% and Nb ₂ O ₅ : 13.0 to 26.0%. In terms of mass%, SiO ₂ : 18% or more and less than 30%, BaO: 12% or more and less than 23%, TiO ₂ : 22 to 37%, Nb ₂ O ₅ : 7% or more and less than 16%, Na ₂ O: 5 to 5% _{20%, K 2 O: 0~6} %, CaO: 0~5%, SrO: 0~5%, ZrO 2: 0~4%, Ta 2 O 5: 0~3% and _P 2 _O 5: 0 The optical glass according to claim 1, wherein the optical glass contains at least 0.5% and less than 0.5% and substantially does not contain PbO, As ₂ O ₃ and F.   It consists of the optical glass of any one of Claims 1-3, The glass raw material for press molding characterized by the above-mentioned.   An optical element comprising the optical glass according to claim 1.