JP2009203083A - Optical glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide optical glass having a high refractive index and having high transmittance in a wider range at an ultraviolet region in ultraviolet to visible light regions. <P>SOLUTION: The optical glass having a refractive index nd of ≥1.80 and an inside transmittance at 420 nm of ≥96.5% is provided, wherein the optical glass includes a composition containing Nb<SB>2</SB>O<SB>5</SB>, WO<SB>3</SB>, TiO<SB>2</SB>, GeO<SB>2</SB>, TeO<SB>2</SB>and Bi<SB>2</SB>O<SB>3</SB>each in <1% by mass. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical glass. In detail, it is produced by mold flow molding optical glass that can produce various high-performance optical lenses by pressure molding with a precision-processed mold, and surface flow by machining or heating. It relates to optical glass such as a glass lens.

  Optical glass is used in various applications such as optical pickup lenses for CD, MD, DVD, and other various optical disc systems, photographing lenses for video cameras and general cameras, and condensing lenses in the field of optical communication. These optical glasses are generally produced by methods such as mold press molding, machining, and surface flow by heating.

  For example, manufacture by a mold press molding method is performed as follows.

  First, molten glass is dropped from the tip of a nozzle to produce droplet glass (droplet molding), and grinding, polishing, and washing are performed to produce a preform glass. Alternatively, the molten glass is rapidly cast, a glass ingot is once produced, and the preform glass is produced by grinding, polishing, and washing. Subsequently, the preform glass is heated and softened, and pressure-molded with a precision-processed mold, and the surface shape of the mold is transferred to the glass to produce a lens.

  When adopting the mold press molding method, glass having a glass transition temperature Tg as low as possible (at least 650 ° C. or less) is required in order to accurately mold press mold the lens while suppressing deterioration of the mold. The glass of this is proposed (for example, refer patent documents 1-3).

  By the way, if a devitrified material is produced when producing a preform glass, the basic performance as a mold press lens cannot be obtained. Therefore, it is important that the glass has excellent devitrification resistance. Moreover, it is desired not to use harmful substances such as lead in the glass component because of increasing awareness of environmental problems.

In recent years, optical lenses such as optical pickup lenses and photographing lenses of various optical disk systems have been studied to reduce the number of lenses or reduce the number of lenses for the purpose of cost reduction. In order to realize this, a glass material having a high refractive index and low dispersion (large Abbe number) or a high refractive index and high dispersion (small Abbe number) is required. Further, a press lens having a large diameter is used for a high-performance imaging lens, and a glass material with high transmittance is required. Also in the field of optical communication and the like, a glass material having a high refractive index is required as a condenser lens.
JP 2003-267748 A JP 2003-248897 A JP 2006-16295 A

In general, in order to produce an optical glass having a high refractive index, it is necessary to contain a large amount of components that contribute to improving the refractive index, such as La ₂ O ₃ , Gd ₂ O ₃ , and Ta ₂ O ₅ . However, when these components are contained in a large amount, the devitrification resistance of the glass tends to deteriorate. Some of these components reduce the transmittance of the glass. The problem due to a decrease in the transmittance of glass is particularly noticeable when used for large-diameter lenses.

  Then, this invention makes it a subject to provide the optical glass which has a high refractive index and has a high transmittance | permeability in a wide range by the ultraviolet region from ultraviolet to visible region.

  As a result of various studies, the present inventors have found that the above-mentioned problems can be solved by suppressing components contributing to a higher refractive index contained in the optical glass to an appropriate ratio or less, and propose the present invention. It is.

That is, the optical glass of the present invention is an optical glass having a refractive index nd of 1.80 or more and an internal transmittance at 420 nm of 96.5% or more, and the composition is Nb ₂ O ₅ , WO ₃ , The contents of TiO ₂ , GeO ₂ , TeO ₂ , and Bi ₂ O ₃ are each less than 1% by mass%.

Nb ₂ O ₅ , WO ₃ , TiO ₂ , GeO ₂ , TeO ₂ , and Bi ₂ O ₃ are components that contribute to increasing the refractive index of the glass, but cause a decrease in the transmittance of the glass. Specifically, there are those in which the components themselves are colored and those that promote the coloring of impurities contained in the glass. If it is contained in a large amount, it becomes difficult to solve the problems of the present invention, and its use must be kept to a minimum. In the present invention, the transmittance of the glass can be improved by limiting the contents of these components to less than 1%. Further, for example, a devitrified substance that hinders transparency during preform molding hardly occurs, and there is no problem in use as a mold press lens.

  In particular, the optical glass of the present invention regulates the internal transmittance at 420 nm to 96.5% or more, so that the transmittance near the short wavelength visible region is good, and a large-diameter press lens used for a high-performance imaging lens, etc. It is suitable as a material. The “internal transmittance” refers to the transmittance excluding the surface reflection loss on the incident side and the emission side of the sample. In the present invention, “internal transmittance” refers to internal transmittance at a thickness of 10 mm, and specifically, is calculated from measured values of transmittance including surface reflection losses of thicknesses of 5 mm and 10 mm, respectively.

As another form, the optical glass of the present invention has a refractive index nd of 1.80 or more and a wavelength of the transmittance absorption edge of 300 nm or less, and in composition, Nb ₂ O ₅ , WO ₃ , TiO ₂ , The contents of GeO ₂ , TeO ₂ , and Bi ₂ O ₃ are each less than 1% by mass%.

As described above, Nb ₂ O ₅ , WO ₃ , TiO ₂ , GeO ₂ , TeO ₂ , and Bi ₂ O ₃ are components that contribute to the increase in the refractive index of glass, but the cause of the decrease in the transmittance of glass. Therefore, in the present invention, the transmittance of the glass can be improved by limiting the contents of these components to less than 1% each. Further, for example, a devitrified substance that hinders transparency during preform molding hardly occurs, and there is no problem in use as a mold press lens.

  In particular, since the optical glass of the present invention is regulated to a low wavelength region where the wavelength of the transmittance absorption edge is 300 nm or less, it is possible to increase the transmittance near the short wavelength visible region. Therefore, it is suitable as a material for a large-diameter press lens used for a high-performance imaging lens. The “wavelength at the transmittance absorption edge” refers to a wavelength at which the transmittance is 0.5% in the transmittance curve at a thickness of 10 mm. The reason why the transmittance absorption edge is evaluated at a wavelength at which the transmittance is 0.5% is that the peak is broad in the vicinity of 0%, and thus the variation is large.

As another embodiment, the optical glass of the present invention has a refractive index nd of 1.80 or more and a wavelength λ _{T75 at} which the transmittance of 75% is 387 nm or less, and the composition is Nb ₂ O ₅ , WO ₃ , TiO ₂ , GeO ₂ , TeO ₂ , Bi ₂ O ₃ are each characterized by being less than 1% by mass.

As described above, Nb ₂ O ₅ , WO ₃ , TiO ₂ , GeO ₂ , TeO ₂ , and Bi ₂ O ₃ are components that contribute to the increase in the refractive index of glass, but the cause of the decrease in the transmittance of glass. Therefore, in the present invention, the transmittance of the glass can be improved by limiting the contents of these components to less than 1% each. In addition, for example, a devitrified substance that hinders transparency during preform molding hardly occurs, and there is no problem in use as a mold press lens.

In particular, in the optical glass of the present invention, the wavelength λ _{T75 at} which the transmittance is 75% is 387 nm or less, and the transmittance near the short wavelength visible region can be increased. Therefore, it is suitable as a material for a large-diameter press lens used for a high-performance imaging lens. In the present invention, the wavelength λ _Ta (hereinafter also referred to as “coloring degree λ _Ta ”) at which the transmittance is a% is measured according to the Japan Optical Glass Industry Association Standard (JOGIS). Specifically, it refers to the wavelength at which the transmittance is a% in the transmittance curve at a thickness of 10 mm.

In the optical glass of the present invention, it is preferable that Nb ₂ O ₅ + WO ₃ + TiO ₂ + GeO ₂ + TeO ₂ + Bi ₂ O ₃ is less than 1% by mass. Here, “Nb ₂ O ₅ + WO ₃ + TiO ₂ + GeO ₂ + TeO ₂ + Bi ₂ O ₃ ” means the total amount of Nb ₂ O ₅ , WO ₃ , TiO ₂ , GeO ₂ , TeO ₂ , Bi ₂ O _3. To do.

In the optical glass of the present invention, the wavelength λ _{T70 at} which the transmittance is 70% is preferably 370 nm or less.

In the optical glass of the present invention, the wavelength λ _{T5 at} which the transmittance is 5% is preferably 315 nm or less.

  The optical glass of the present invention preferably has an Abbe number νd of 36 or more.

In the composition of the optical glass of the present invention, the content of Fe ₂ O ₃ is preferably 20 ppm or less.

Fe ₂ O ₃ is a coloring component contained as an impurity in the glass and causes a decrease in the transmittance of the glass. Accordingly, when a large amount of Fe ₂ O ₃ is contained, it is difficult to solve the problems of the present invention. Therefore, the content is preferably kept to a minimum.

The optical glass of the present invention preferably contains Sb ₂ O ₃ in composition.

Sb ₂ O ₃ has an effect of suppressing coloring by Fe ₂ O ₃ . Moreover, the effect as a clarifier is also acquired simultaneously.

The optical glass of the present invention contains B ₂ O ₃ and La ₂ O ₃ as essential components in the composition, and is at least selected from the group consisting of ZnO, ZrO ₂ , Gd ₂ O ₃ and Ta ₂ O _5. It is preferable that one type is contained and substantially no lead component, arsenic component, or F component is contained.

  The optical glass of the present invention is an environmentally preferable glass because it does not substantially contain a lead component, an arsenic component, and an F component. In the present invention, “substantially does not contain” means that it is not intentionally added to the glass, and does not mean that unavoidable impurities are completely eliminated. More objectively, it means that the content including impurities is 0.1% by mass or less.

The optical glass of the present invention is composed of, in terms of mass%, SiO ₂ 0-21%, B ₂ O ₃ 4-30%, ZnO 0-40%, ZrO ₂ 0-10%, La ₂ O ₃ 15-50. %, Gd ₂ O ₃ 0 to 40%, and Ta ₂ O ₅ 0 to 30% are preferable. With respect to the term “containing” in the present invention, the component defined as “0” means “0%”, that is, it may not be included at all.

  Moreover, it is preferable that the glass transition point of the optical glass of this invention is 650 degrees C or less.

  For example, optical glass for mold press molding enables press molding at a low temperature when the glass transition temperature is low. Therefore, contamination of the mold due to oxidation of the mold or volatilization of the glass component, and further between the glass and the mold. Fusion can be suppressed.

The optical glass of the present invention has a specific refractive index and transmittance absorption edge wavelength, and the composition includes Nb ₂ O ₅ , WO ₃ , TiO ₂ , GeO ₂ , TeO ₂ , Bi ₂ O _3. It is limited to a specific amount.

  The object of the present invention is to obtain an optical glass having a refractive index nd of 1.80 or more, preferably 1.83 or more, more preferably 1.85 or more.

  The Abbe number νd is 36 or more, preferably 38 or more, more preferably 40 or more, and still more preferably 41 or more.

  The optical glass of the present invention has an internal transmittance at 420 nm of 96.5% or more, preferably 96.7 or more. When the internal transmittance at 420 nm is less than 96.5%, the transmittance in the vicinity of the short wavelength visible region is inferior, and in particular, it is difficult to use as a large-diameter press lens used for a high-performance imaging lens.

  Further, the optical glass of the present invention has an internal transmittance of 95% or more, preferably 95.2 or more at 400 nm. When the internal transmittance at 400 nm is less than 95%, the transmittance in the vicinity of the short wavelength visible region is inferior, and in particular, it becomes difficult to use as a large-diameter press lens used for a high-performance imaging lens.

  In the optical glass of the present invention, the wavelength at the transmittance absorption edge is 300 nm or less, preferably 295 nm or less, more preferably 290 nm or less. When the wavelength of the transmittance absorption edge exceeds 300 nm, the transmittance in the vicinity of the short wavelength visible region is inferior, and in particular, it is difficult to use as a large-diameter press lens used for a high-performance imaging lens.

In the optical glass of the present invention, the wavelength λ _{T75 at} which the transmittance is 75% is 387 nm or less, preferably 385 nm or less, more preferably 380 nm or less. When λ _T75 exceeds 387 nm, the transmittance near the short wavelength visible region is inferior, and in particular, it becomes difficult to use as a large-diameter press lens or the like used for a high-performance imaging lens.

In the optical glass of the present invention, the wavelength λ _{T70 at} which the transmittance is 70% is 370 nm or less, preferably 365 nm or less, more preferably 360 nm or less, and further preferably 355 nm or less. When λ _T70 exceeds 370 nm, the transmittance near the short wavelength visible region is inferior, and in particular, it is difficult to use as a large-diameter press lens used for a high-performance imaging lens.

In the optical glass of the present invention, the wavelength λ _{T5 at} which the transmittance is 5% is 315 nm or less, preferably 315 nm or less, more preferably 305 nm or less, and further preferably 300 nm or less. When λ _T5 exceeds 315 nm, the transmittance near the short wavelength visible region is inferior, and in particular, it becomes difficult to use as a large-diameter press lens used for a high-performance imaging lens.

In the composition of the optical glass of the present invention, the contents of Nb ₂ O ₅ , WO ₃ , TiO ₂ , GeO ₂ , TeO ₂ and Bi ₂ O ₃ are each limited to less than 1% by mass. The reason for this limitation is as follows.

Nb ₂ O ₅ is a component having a large effect of increasing the refractive index of glass. In the glass containing Ta ₂ O ₅ in a large amount, there is a function of improving the devitrification resistance _{(La 2 O 3, Ta 2} O 5 and B ₂ O ₃ in devitrification suppression formed) . However, the addition of a small amount significantly reduces the Abbe number. In addition, since the absorption in the ultraviolet region is large and the absorption edge in the transmittance curve is shifted to the long wavelength side to reduce the transmittance in the short wavelength region, the transmittance in the 390 to 440 nm is lowered, and as a short wavelength lens May interfere with the use of. Therefore, the content of Nb ₂ O ₅ is limited to less than 1%, preferably 0.5% or less, more preferably 0.3% or less, still more preferably 0.1% or less. When it is desired to make the content as low as possible, it is preferable that it is not substantially contained.

WO ₃ is a component that increases the refractive index of glass. Further, since a glass skeleton is formed as an intermediate oxide, there is also an effect of improving devitrification resistance (suppression of devitrification materials formed of B ₂ O ₃ and La ₂ O ₃ ). However, like Nb ₂ O ₅ , there is a tendency to reduce the transmittance in the short wavelength region by shifting the absorption edge of the transmittance to the longer wavelength side. Therefore, the content of WO ₃ is limited to less than 1%, preferably 0.5% or less, more preferably 0.3% or less, still more preferably 0.1% or less, and substantially no content. Most preferred.

TiO ₂ is a component that increases the refractive index of glass. In addition, although there is an effect of improving devitrification resistance (suppression of devitrified materials formed of B ₂ O ₃ and La ₂ O ₃ ), similarly to Nb ₂ O ₅ , the absorption in the ultraviolet region is large, There is also a tendency to shift the absorption edge to the longer wavelength side. Therefore, the content of TiO ₂ needs to be less than 1%, preferably 0.5% or less, more preferably 0.3% or less, still more preferably 0.1% or less, and does not contain substantially. Most preferred.

GeO ₂ is a component that increases the refractive index of glass. In addition, although there is an effect of improving devitrification resistance (suppression of devitrified materials formed of B ₂ O ₃ and La ₂ O ₃ ), similarly to Nb ₂ O ₅ , the absorption in the ultraviolet region is large, There is also a tendency to shift the absorption edge to the longer wavelength side. Therefore, the content of GeO ₂ needs to be less than 1%, preferably 0.5% or less, more preferably 0.3% or less, still more preferably 0.1% or less, and is not substantially contained. Most preferred.

TeO ₂ is a component that increases the refractive index of glass. Similar to Nb ₂ O ₅ , the absorption in the ultraviolet region is large, and the absorption edge tends to shift to the long wavelength side. Therefore, the content of TeO ₂ needs to be less than 1%, preferably 0.5% or less, more preferably 0.3% or less, still more preferably 0.1% or less, and does not contain substantially. Most preferred.

Bi ₂ O ₃ is a component that increases the refractive index of glass. Similar to Nb ₂ O ₅ , the absorption in the ultraviolet region is large, and the absorption edge tends to shift to the long wavelength side. Therefore, the content of Bi ₂ O ₃ needs to be less than 1%, preferably 0.5% or less, more preferably 0.3% or less, and still more preferably 0.1% or less. Most preferably it is not contained.

In order to suppress the coloring of the glass and improve the transmittance, Nb ₂ O ₅ + WO ₃ + TiO ₂ + GeO ₂ + TeO ₂ + Bi ₂ O ₃ is less than 1%, preferably 0.5% or less, more preferably 0.8%. It may be 3% or less, more preferably 0.1% or less, and it is particularly preferable that these components are not substantially contained.

In the composition of the optical glass of the present invention, the content of Fe ₂ O ₃ is 20 ppm or less, preferably 10 ppm or less, more preferably 5 ppm or less. When the content of Fe ₂ O ₃ exceeds 20 ppm, the transmittance of the glass is reduced. In addition, although it does not specifically limit about a lower limit, Generally, it is 0.1 ppm or more, Furthermore, 0.5 ppm or more, Especially 1 ppm or more.

The optical glass of the present invention preferably contains Sb ₂ O ₃ as an essential component in the composition. As described above, Sb ₂ O ₃ has an effect of suppressing coloring by Fe ₂ O _3, and in order to sufficiently obtain the effect, the content of Sb ₂ O ₃ is 0.01% or more by mass%. It is preferable that it is 0.1% or more. The upper limit is not particularly limited, but when it is contained in a large amount, the devitrification resistance of the glass tends to deteriorate, so its content is 2% or less, preferably 1% or less.

In particular, in order to obtain a high refractive index glass, at least selected from the group consisting of ZnO, ZrO ₂ , Gd ₂ O ₃ and Ta ₂ O ₅ containing B ₂ O ₃ and La ₂ O ₃ as essential components. It is preferable to contain 1 type.

Specifically, in terms of mass%, SiO _{2 0 to} 21%, B ₂ O ₃ 4 to 30%, ZnO 0 to 40%, ZrO ₂ 0 to 10%, La ₂ O ₃ 15 to 50%, Gd ₂ O ₃ 0-40%, preferably contains a composition of Ta ₂ O ₅ 0~30%.

  Below, the reason which specified content of each component in this way is explained in full detail.

SiO ₂ is a component constituting the skeleton of the glass, and has the effect of suppressing devitrification and improving weather resistance. It also has the effect of increasing the Abbe number. The content of SiO ₂ is 0 to 21%, preferably 1 to 20%, more preferably 3 to 16%, and further preferably 3.5 to 10%. If the content of SiO ₂ is too large, the refractive index of the glass tends to decrease or the softening point tends to increase. On the other hand, if the content of SiO ₂ is too small, the glass becomes unstable and the devitrification resistance deteriorates or phase separation is likely to occur, and the weather resistance such as acid resistance and water resistance tends to deteriorate. .

B ₂ O ₃ is a component that constitutes the skeleton of the glass, and is also a component that maximizes the Abbe number. The content is 4 to 30%, preferably 5 to 30%, more preferably 7 to 25%, and still more preferably 7 to 20%. If the B ₂ O ₃ content is too large, a tendency that weather resistance is deteriorated with B ₂ O ₃ and La ₂ O ₃ devitrification is liable to be formed which is formed by at glass forming, also the refractive index decreases There is. On the other hand, if the content of B ₂ O ₃ is too small, it becomes difficult to obtain a glass having a high Abbe number, specifically 40 or more, particularly 41 or more.

  ZnO is a component that increases the refractive index of glass. Moreover, since the glass viscosity is lowered, the glass transition temperature can be lowered, and therefore, it is easy to obtain a glass that is difficult to fuse with the mold. In addition, even if added in a large amount, it is a component that hardly reduces the Abbe number. Furthermore, there is an effect of improving weather resistance. In addition, since the tendency to devitrification is not so strong as compared with alkaline earth metal components (MgO, CaO, SrO, BaO), a homogeneous glass can be easily obtained even if contained in a large amount. The content of ZnO is 0 to 40%, preferably 1 to 35%, more preferably 1 to 30%, and further preferably 2 to 20%. If the ZnO content is too large, the weather resistance tends to deteriorate. On the other hand, when the content of ZnO is too small, it becomes difficult to obtain a glass having a low glass transition temperature. Moreover, it becomes easy to fuse | melt glass with a metal mold | die.

ZrO ₂ is a component that increases the refractive index and is also a component that hardly reduces the Abbe number. Moreover, since a glass skeleton is formed as an intermediate oxide, the devitrification resistance (suppression of devitrification substances formed by B ₂ O ₃ and La ₂ O ₃ ) is improved, and chemical durability is improved. There is also an effect. The content of ZrO ₂ is 0 to 10%, preferably 2 to 10%, more preferably 3 to 8%. If the content of ZrO ₂ is too large, the glass transition temperature rises and the press formability deteriorates, and at the same time, devitrified materials containing ZrO ₂ as a main component tend to precipitate.

La ₂ O ₃ is a component capable of increasing the refractive index without substantially reducing the Abbe number. Its content is 15-50, preferably 20-50%, more preferably 22-48%, and even more preferably 25-46%. When the content of La ₂ O ₃ is too small, a sufficiently high refractive index tends to be difficult to obtain. On the other hand, when the content of La ₂ O ₃ is too large, the devitrification resistance of the glass deteriorates, for example, devitrification formed by B ₂ O ₃ and La ₂ O ₃ is likely generated during glass molding . Further, the glass is easily devitrified during press molding.

Gd ₂ O ₃ is a component that increases the refractive index of glass. In addition, it has an effect of improving devitrification resistance (suppression of devitrified substances formed of B ₂ O ₃ and La ₂ O ₃ ), and is a component capable of expanding the working temperature range. Furthermore, it is easy to obtain glass that is difficult to fuse with the mold. The content of Gd ₂ O ₃ is 0 to 40, preferably 0 to 30%, more preferably 5 to 20%. When the content of Gd ₂ O ₃ is too large, homogeneous glass stronger phase separation tendency of glass is difficult to obtain. Further, in the composition system containing B ₂ O ₃ and La ₂ O ₃ , devitrified substances formed of La ₂ O ₃ , B ₂ O ₃ and Gd ₂ O ₃ are likely to precipitate on the surface (surface devitrification). It tends to increase the liquidus temperature of the glass. Also, the Abbe number tends to decrease. However, Gd ₂ O ₃ has a lower degree of Abbe number lower than other components that lower the Abbe number (eg, Ta ₂ O ₅ , WO ₃ , TiO _2, etc.).

Ta ₂ O ₅ is a component that increases the refractive index, chemical durability, and devitrification resistance (suppression of devitrified substances formed of B ₂ O ₃ and La ₂ O ₃ ) of glass. Its content is 0-30%, preferably 3-25%, more preferably 5-22%. When the content of Ta ₂ O ₅ is too large, the Abbe number tends to decrease, and it becomes difficult to obtain desired optical characteristics. In addition, the devitrified material formed by La ₂ O ₃ , Ta ₂ O ₅ and B ₂ O ₃ is precipitated and the liquidus temperature is likely to rise. Further, the cost is increased. When a high Abbe number is not required, a refractive index nd of 1.80 or more can be easily obtained by containing a large amount of Ta ₂ O ₅ .

Lead components (eg, PbO), arsenic components (eg, As ₂ O ₃ ), and F components (eg, F ₂ ) should be avoided in substantial glass for environmental reasons. Therefore, in the present invention, it is preferable that these components are not substantially contained.

In the optical glass of the present invention having the above composition, it is preferable to appropriately adjust the total amount of SiO ₂ and B ₂ O _{3 in} order to obtain a low dispersion and high refractive index glass. Specifically, the total amount of these components is 12 to 33%, preferably 12 to 25%, more preferably 14 to 22%. When the total amount of these components is too small, it becomes difficult to maintain low dispersion, and when it is too large, it becomes difficult to obtain a glass having a high refractive index.

In the optical glass of the present invention having the above composition, in order to obtain a low-dispersion (high Abbe number) glass, particularly a glass having an Abbe number νd of 36 or more, Gd ₂ O ₃ , which is a component that lowers the Abbe number, ta ₂ O _5, WO _3, may be limiting the total amount of TiO _2. Specifically, the total amount of these components is 45% or less, preferably 42% or less.

In addition to the above components, various components can be added to the optical glass of the present invention. For example, Al ₂ O ₃ , CaO, BaO, SrO, Li ₂ O, Na ₂ O, K ₂ O, Y ₂ O ₃ , Yb ₂ O ₃ , fining agent, etc., as long as the properties of the glass of the present invention are not impaired. It can be added.

Al ₂ O ₃ is a component constituting a glass skeleton together with SiO ₂ and B ₂ O ₃ . Moreover, there exists an effect which improves a weather resistance, and the effect which suppresses that the component in glass selectively elutes to water especially is remarkable. Its content is 10% or less, preferably 5% or less. When the content of Al ₂ O ₃ is too large, the glass tends to be devitrified. In addition, the meltability deteriorates and striae and bubbles remain in the glass, which may not satisfy the required quality as lens glass.

Alkaline earth metal oxides (RO) such as CaO, BaO, and SrO act as fluxes and are components that increase the refractive index without decreasing the Abbe number. The total amount of CaO, BaO and SrO is 1 to 20%, preferably 5 to 10%. When the RO content is excessively large, devitrified substances containing B ₂ O ₃ and La ₂ O ₃ as main components are likely to precipitate during the melting and forming process of the preform glass. As a result, the liquidus temperature rises, the working range becomes narrow, and there is a tendency that mass production is difficult. Furthermore, the weather resistance tends to deteriorate, and the elution of the glass component in the polishing cleaning water and various cleaning solutions increases, or the glass surface is altered in a hot and humid state (RO component deposition from the glass surface). Tend to be prominent.

  CaO is a component that increases the refractive index without decreasing the Abbe number. The content of CaO is 0 to 10%, preferably 0 to 5%.

  BaO is a component that increases the refractive index. Moreover, compared with CaO, there is little precipitation amount from the glass surface in a hot and humid state. The BaO content is 20% or less, preferably 10% or less, more preferably 5% or less.

  SrO is a component that increases the refractive index. Moreover, compared with CaO, there is little precipitation amount from the glass surface in a hot and humid state. Therefore, a glass excellent in weather resistance can be obtained by positively containing SrO. Its content is 20% or less, preferably 10% or less, more preferably 5% or less.

  In addition to CaO, BaO, and SrO, MgO may be added as an RO component in order to increase the refractive index. The content of MgO is 10% or less, preferably 5% or less. When there is too much content of MgO, it will become easy to devitrify.

Li ₂ O can be contained as a component for lowering the softening point of the glass, for example, 0.1% or more, preferably 0.5% or more, more preferably 1% or more. Li ₂ O has the greatest effect of lowering the softening point of glass among alkali metal oxides (R ′ ₂ O). However, since Li ₂ O has a strong phase separation property, if its content is large, a devitrified material containing B ₂ O ₃ and La ₂ O ₃ as main components is likely to precipitate, and the liquidus temperature becomes high, resulting in workability. Tend to worsen. Further, when the high content of Li ₂ O, volatiles or increase that occurs during press forming, and may become easier to mold and fusing, press-molding becomes difficult. Therefore, the content is limited to 5% or less, preferably 3% or less, more preferably 1.5% or less.

Na ₂ O has the effect of lowering the softening point of glass, like Li ₂ O. However, if the content is large, volatiles formed by B ₂ O ₃ and Na ₂ O at the time of melting increase, which promotes the generation of striae. Further, B ₂ O ₃ and La ₂ O ₃ devitrification is liable to deposit mainly comprising tend liquidus temperature rises. Furthermore, there is a tendency that the volatile matter generated during press molding increases or it becomes easy to fuse with the mold. From such a viewpoint, the content of Na ₂ O is 10% or less, preferably 5% or less.

K ₂ O also has the effect of lowering the softening point of glass, like Li ₂ O. Its content is 0-10%, preferably 0-5%. When the content of K ₂ O increases, the weather resistance tends to deteriorate. Further, B ₂ O ₃ and La ₂ O ₃ and devitrification precipitates composed mainly of the liquidus temperature tends to increase. Furthermore, there is a tendency that volatile matter generated during press molding increases or that it is easily fused to the mold.

Y ₂ O ₃ and Yb ₂ O ₃ are components that increase the refractive index without decreasing the Abbe number. Therefore, devitrification resistance can be improved by substitution with La ₂ O ₃ . Moreover, by adding an appropriate amount, there is an effect of suppressing phase separation that is likely to occur in B ₂ O ₃ —ZnO—La ₂ O ₃ glass. The contents of Y ₂ O ₃ and Yb ₂ O ₃ are each 15% or less, preferably each 8% or less, more preferably each 2% or less. Y ₂ O ₃ and the Yb ₂ O ₃ is too large devitrification resistance is deteriorated, there is a tendency that the working temperature range is narrow. In addition, striae are likely to occur in the glass. In order to obtain a sufficient effect, Y ₂ O ₃ and Yb ₂ O ₃ are preferably contained in a total amount of 1% or more.

In the above composition range, as a more preferable composition range, by mass%, SiO ₂ 3-20%, B ₂ O ₃ 7-25%, ZnO 1-30%, ZrO ₂ 2-10%, La ₂ O ₃ 22-48%, Gd ₂ O ₃ 0-30%, Ta ₂ O ₅ 3-25%, Sb ₂ O ₃ 0.01-2%, Nb ₂ O ₅ + WO ₃ + TiO ₂ + GeO ₂ + TeO ₂ + Bi ₂ O ₃ contains 0 to 0.5% and, lead component, arsenic component, F component include those substantially free of Nb ₂ O _5.

In the above composition range, as a more preferable composition range, by mass%, SiO ₂ 3.5 to 10%, B ₂ O ₃ 7 to 20%, ZnO 2 to 20%, ZrO ₂ 3 to 8%, La ₂ O ₃ 25-46%, Gd ₂ O ₃ 5-20%, Ta ₂ O ₅ 3-25%, Sb ₂ O ₃ 0.01-2%, Nb ₂ O ₅ + WO ₃ + TiO ₂ + GeO ₂ + TeO ₂ + Bi Examples thereof include those containing 0 to 0.5% of ₂ O ₃ and substantially free of lead component, arsenic component, F component and Nb ₂ O ₅ .

  The optical glass of the present invention has a glass transition temperature of 650 ° C. or lower, preferably 640 ° C. or lower, more preferably 630 ° C. or lower. When the glass transition temperature exceeds 650 ° C., the mold is likely to deteriorate due to oxidation of the mold or contamination of the mold due to volatilization of the glass component, and the glass is likely to be fused with the mold.

  Next, an example of the manufacturing method of the optical glass of this invention is described.

  First, after preparing a glass raw material so that it may become a desired composition, it fuse | melts in a glass melting furnace. Next, the optical glass of the present invention can be obtained by dropping molten glass from the tip of the nozzle to produce droplet glass. Alternatively, the optical glass of the present invention can be obtained by rapidly casting a molten glass, once producing a glass block, grinding, polishing and washing.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these Examples.

  Tables 1 to 5 show examples of the present invention (sample Nos. 1 to 30), and Table 6 shows comparative examples (samples Nos. 31 to 34), respectively.

  Each sample was prepared as follows.

First, glass raw materials were prepared so as to have the composition shown in the table, and were melted at 1300 ° C. to 1450 ° C. for 3 hours using a platinum crucible. After melting, the melt was poured onto a carbon plate, and after annealing, a glass sample suitable for each measurement was obtained. Here, the Fe ₂ O ₃ content in each glass sample was _{2 to 4} ppm.

  About the obtained sample, refractive index nd, Abbe number νd, glass transition temperature Tg, and liquidus temperature were measured.

  As is apparent from the table, No. 1 as an example of the present invention. Each of the samples 1 to 30 had a refractive index nd of 1.80 or more and an Abbe number νd of 36 or more.

  The refractive index nd is indicated by the measured value for the d-line (587.6 nm) of the helium lamp.

  The Abbe number νd uses the refractive index value of the d-line and the refractive index of the F-line (486.1 nm) of the hydrogen lamp, and the C-line (656.3 nm) of the hydrogen lamp, and νd = [(nd−1 ) / (NF-nC)].

  The glass transition temperature Tg was evaluated based on a value measured with a thermal expansion measuring device (dilatometer).

The liquidus temperature is obtained by melting glass in an electric furnace at 1350 ° C. for 18 hours, holding it in an electric furnace having a temperature gradient for 5 minutes, then allowing it to cool in the air, and depositing devitrified substances using an optical microscope. It was measured by seeking. If the liquidus temperature is 1200 ° C. or lower, it is easy to achieve a liquidus viscosity of 10 ^0.5 or more, and devitrification hardly occurs even when droplet forming is performed.

  The internal transmittance was first measured using a spectrophotometer (UV-3100 manufactured by Shimadzu Corporation) for each of the polished samples having a thickness of 5 mm ± 0.1 mm and 10 mm ± 0.1 mm in a wavelength range of 800 to 200 nm. The transmittance including the surface reflection loss was measured, and the internal transmittance at wavelengths of 420 nm and 400 nm was calculated from the obtained measured values.

  The degree of coloring was measured using a spectrophotometer on a polished glass having a thickness of 10 mm ± 0.1 mm, and the transmittance in the wavelength range of 200 to 800 nm was measured at 0.5 nm intervals. %, And 5%.

  Further, the wavelength at the transmittance absorption edge was measured in the same manner as the degree of coloration, and was evaluated based on the wavelength at which the transmittance was 0.5%.

  The optical glass of the present invention is suitable for CD, MD, DVD, and other optical pickup lenses for various optical disk systems, video cameras, and photographing lenses for general cameras.

Claims (12)

An optical glass having a refractive index nd of 1.80 or more and an internal transmittance of 420 nm or more of 96.5% or more, wherein the composition is Nb ₂ O ₅ , WO ₃ , TiO ₂ , GeO ₂ , TeO ₂ , An optical glass characterized in that the content of Bi ₂ O ₃ is less than 1% in terms of mass%. An optical glass having a refractive index nd of 1.80 or more and a transmittance absorption edge wavelength of 300 nm or less, and the composition is Nb ₂ O ₅ , WO ₃ , TiO ₂ , GeO ₂ , TeO ₂ , Bi _2. An optical glass characterized in that the content of O ₃ is less than 1% by mass. An optical glass having a refractive index nd of 1.80 or more and a wavelength λ _T75 with a transmittance of 75% of 387 nm or less, and having a composition of Nb ₂ O ₅ , WO ₃ , TiO ₂ , GeO ₂ , TeO ₂ An optical glass characterized in that the content of Bi ₂ O ₃ is less than 1% by mass. The optical glass according to claim 1, wherein Nb ₂ O ₅ + WO ₃ + TiO ₂ + GeO ₂ + TeO ₂ + Bi ₂ O ₃ is less than 1% by mass. The optical glass according to any one of claims 1 to 4, wherein a wavelength λ _{T70 at} which the transmittance is 70% is 370 nm or less. The optical glass according to claim 1, wherein a wavelength λ _{T5 at} which the transmittance is 5% is 315 nm or less.   The optical glass according to claim 1, wherein the Abbe number νd is 36 or more. The optical glass according to any one of claims 1 to 7, wherein in the composition, the content of Fe ₂ O ₃ is 20 ppm or less. The optical glass according to claim 1, wherein Sb ₂ O ₃ is contained as an essential component in the composition. In the composition, B ₂ O ₃ and La ₂ O ₃ are contained as essential components, and at least one selected from the group consisting of ZnO, ZrO ₂ , Gd ₂ O ₃ and Ta ₂ O ₅ is contained, and lead The optical glass according to any one of claims 1 to 9, which contains substantially no component, arsenic component, or F component. In the composition, by _{mass%, SiO 2 0~21%, B} 2 O 3 4~30%, 0~40% ZnO, ZrO 2 0~10%, La 2 O 3 15~50%, Gd 2 O 3 0 40%, the optical glass according to any one of claims 1 to 10, characterized by containing Ta ₂ O ₅ 0~30%.   12. The optical glass according to claim 1, wherein the glass transition point is 650 ° C. or lower.