JP6075714B2 - Optical glass - Google Patents

Description

  The present invention relates to an optical glass suitable as a lens for an optical device.

  In recent years, higher performance of digital cameras and video cameras, specifically, miniaturization, higher magnification, higher definition, and the like have been promoted. In order to achieve such high performance, optical lens glass used in digital cameras and video cameras is often required to have characteristics such as high refractive index, high dispersion and anomalous dispersion ( For example, see Patent Document 1).

  By the way, depending on the application, characteristics other than the above optical characteristics may be required. For example, in addition to the above required characteristics, a telescope lens and a camera lens used in a high temperature environment are required to have a low coefficient of thermal expansion and good shape stability against temperature changes. Similarly, for a stepper or a lens using a high-power light, a good shape stability against temperature change is strongly demanded.

JP 2009-179538 A

  At present, conventionally proposed optical glass does not have sufficient low thermal expansion characteristics. Although it is possible to reduce the thermal expansion to some extent by improving the composition, there is a problem in that the refractive index tends to decrease. Therefore, it is difficult to achieve both a low thermal expansion characteristic and a high refractive index.

  In view of the above problems, an object of the present invention is to provide an optical glass having excellent shape stability with respect to a temperature change and having high refractive index characteristics.

The optical glass of the present invention is an optical glass formed by precipitating a crystal containing at least two components selected from Li ₂ O, MgO, ZnO, Al ₂ O ₃ and SiO ₂ as a main crystal, and having a mass %, La ₂ O ₃ + Gd ₂ O ₃ + Nb ₂ O ₅ + Ta ₂ O ₅ + WO ₃ 3.8 to 20%, and the coefficient of thermal expansion at 30 to 300 ° C. is −10 to 70 × 10 ⁻⁷ / ° C.

  Here, the “main crystal” refers to a crystal having the largest content among the crystals contained in the glass.

  It is preferable that at least one selected from β-quartz solid solution, β-spodumene solid solution, garnite, enstatite, forsterite and cordierite is precipitated as a main crystal.

By _{mass%, SiO 2 20~65.5%, Al} 2 O 3 14~30%, Li 2 O 0~10%, 0~20% MgO, 0~30% ZnO, TiO 2 0~10%, and preferably contains ZrO ₂ 0%.

Furthermore, by _{mass%, B 2 O 3 0~20%} , P 2 O 5 0~10%, Na 2 O 0~5%, and preferably contains _K 2 O _0~5%.

  It is preferable that the lead component, the arsenic component and the fluorine component are not substantially contained.

  The average particle size of the main crystal is preferably 100 nm or less.

  It is preferable that the refractive index is 1.55 to 1.85 and the Abbe number is 25 to 70.

The coloring degree λ _{70 at a} thickness of 5 mm is preferably 600 nm or less.

Here, “coloring degree λ ₇₀ ” refers to the shortest wavelength at which the transmittance is 70% in the transmittance curve.

  It is preferable for an optical lens.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the optical glass which is excellent in the shape stability with respect to a temperature change, and has a high refractive index characteristic.

The optical glass of the present invention is formed by depositing crystals inside. The coefficient of thermal expansion can be reduced by precipitating low expansion crystals in the glass matrix, and as a result, the glass has excellent shape stability against temperature changes. Specifically, since a crystal containing at least two components selected from Li ₂ O, MgO, ZnO, Al ₂ O ₃ and SiO ₂ is precipitated, an effect of reducing the thermal expansion coefficient can be obtained. Further, in the above crystal, different components are hardly dissolved in the crystal, and fine crystals are likely to precipitate. Therefore, high transmittance can be obtained by precipitating the crystal as a main crystal in glass. In addition, the difference between the liquidus temperature and the molding temperature is large, and a stable glass is easily obtained. Furthermore, it is easy to obtain a glass excellent in Knoop hardness (for example, 550 or higher (6th or higher)).

As a crystal containing at least two components selected from Li ₂ O, MgO, ZnO, Al ₂ O ₃ and SiO ₂ (hereinafter also referred to as “main crystal”), β-quartz solid solution (Li ₂ O. Al ₂ O ₃ · nSiO ₂ ; 2 ≦ n <4) β-spodumene solid solution (Li ₂ O · Al ₂ O ₃ · nSiO ₂ ; 4 ≦ n ≦ 8), garnite (ZnO · Al ₂ O ₃ ), enstatite (MgO.SiO ₂ ), forsterite (MgO.2SiO ₂ ), cordierite (MgO.Al ₂ O ₃ .SiO ₂ ) and the like.

  In the optical glass, the content of the main crystal is mass%, preferably 1 to 99%, more preferably 5 to 95%, still more preferably 10 to 90%, and particularly preferably 20 to 80%. If the content of the main crystal is too small, it is difficult to obtain a desired refractive index, Abbe number, or thermal expansion coefficient. In addition, dense crystals are less likely to precipitate and the transmittance tends to decrease. On the other hand, when there is too much content of a main crystal, the transmittance | permeability will fall easily.

  The average grain size of the main crystal is preferably 100 nm or less, more preferably 50 nm or less, and particularly preferably 30 nm or less. If the average grain size of the main crystal is too large, the transmittance tends to decrease due to light scattering. The lower limit of the average grain size of the main crystal is not particularly limited, but if it is too small, it is difficult to obtain a sufficient amount of crystals, and it is preferably 1 nm or more.

The thermal expansion coefficient of the optical glass of the present invention at 30 to 300 ° C. is −10 to 70 × 10 ⁻⁷ / ° C., preferably 0 to 65 × 10 ⁻⁷ / ° C., more preferably 10 to 60 × 10 ^−7. / ° C., more preferably 30 to 55 × 10 ⁻⁷ / ° C. If the thermal expansion coefficient is too large, the dimensional stability against temperature changes tends to be poor. Therefore, when used as a lens, the focal length and the optical path length are likely to change. On the other hand, when the thermal expansion coefficient is too small, the crystal precipitation amount is large, and microcracks tend to be generated in the crystal structure, so that the transmittance tends to decrease.

  The refractive index (nd) of the optical glass of the present invention is preferably 1.55 to 1.85, more preferably 1.56 to 1.83, still more preferably 1.57 to 1.81, and particularly preferably 1. 58 to 1.80, most preferably 1.59 to 1.75.

  The Abbe number (νd) of the optical glass of the present invention is preferably 40 to 70, more preferably 41 to 65, still more preferably 42 to 60, and particularly preferably 43 to 55.

  A higher Abbe number is advantageous in terms of optical design for reducing chromatic aberration in combination with other lenses, but on the other hand, the refractive index tends to decrease and the glass tends to become unstable. In view of such circumstances, it is preferable to adjust the refractive index and the Abbe number to an appropriate range. Specifically, it is preferable that the Abbe number and the refractive index of the optical glass of the present invention have a relationship of −0.0077 × νd + 1.922 ≦ nd ≦ −0.0077 × νd + 1.822.

  In order to correct chromatic aberration in an optical device, it is common to use a combination of a low dispersion glass and a high dispersion glass. Here, it is known that chromatic aberration can be corrected effectively by using a glass having a large partial dispersion ratio as the low dispersion glass. Therefore, the partial dispersion ratio (θg, F) of the optical glass of the present invention is preferably 0.552 or more, and more preferably 0.56 or more.

The optical glass of the present invention contains La ₂ O ₃ , Gd ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ or WO ₃ as an essential component. These components are components that remain in the matrix glass after crystal precipitation and contribute to the improvement of the refractive index. The content of La ₂ O ₃ + Gd ₂ O ₃ + Nb ₂ O ₅ + Ta ₂ O ₅ + WO ₃ is preferably 3.8 to 20%, preferably 4 to 17.5%, more preferably 4.5 to 15 %, More preferably 5 to 12.5%, particularly preferably 5.5 to 10%. When the content of _{La 2 O 3 + Gd 2 O} 3 + Nb 2 O 5 + Ta 2 O 5 + WO 3 is too small, the effect is difficult to obtain. On the other _hand, when the content of _{La 2 O 3 + Gd 2 O} 3 + Nb 2 O 5 + Ta 2 O 5 + WO 3 is too large, tends to be devitrified. Moreover, the amount of precipitation of the main crystal tends to decrease.

Next, the composition of the optical glass other than La ₂ O ₃ , Gd ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and WO ₃ will be described in the present invention. The optical glass of the present invention is not particularly limited as long as crystals containing at least two components selected from Li ₂ O, MgO, ZnO, Al ₂ O ₃ and SiO ₂ can be precipitated as main crystals. Specific examples of the composition of the optical glass of the present invention include, by mass, SiO _{2 20 to} 65.5%, Al ₂ O ₃ 14 to 30%, Li ₂ O 0 to 10%, MgO 0 to 20%, ZnO. _0~30%, TiO 2 _0~10%, and those containing _ZrO 2 0%. The reason why the content of each component is limited as described above will be described below. Unless otherwise specified, “%” in the following description means “% by mass”.

SiO ₂ and Al ₂ O ₃ are components of the glass skeleton or the main crystal. Moreover, there exists an effect which reduces liquidus temperature and suppresses devitrification, and an effect which improves chemical durability. The content of SiO ₂ is preferably 20 to 65.5%, more preferably 22.5 to 62.5%, still more preferably 25 to 60%, and particularly preferably 27.5 to 59%. The content of Al ₂ O ₃ is preferably 14 to 30%, more preferably 15 to 28%, still more preferably 16 to 26%, and particularly preferably 17 to 25%. When the content of SiO ₂ or _Al 2 _{O 3} is too small, the effect is difficult to obtain. On the other hand, if the content of SiO ₂ or Al ₂ O ₃ is too large, the meltability is lowered and the undissolved striae and bubbles are likely to remain in the glass, the refractive index is lowered, the Abbe number Tends to be large, and there is a possibility that the required characteristics as glass for optical lenses may not be satisfied.

Li ₂ O is a constituent component of the main crystal, or a component that lowers the softening point or facilitates vitrification. Further, it is a component for adjusting the partial dispersion ratio. The content of Li ₂ O is preferably 0 to 10%, more preferably 0.1 to 9%, further preferably 0.5 to 8%, and particularly preferably 1 to 7%. On the other hand, when the content of Li ₂ O is too large, it becomes difficult to obtain dense crystals, and it tends to be difficult to achieve high transmittance characteristics. Moreover, it becomes difficult to obtain a high refractive index characteristic.

  MgO and ZnO are constituents of the main crystal or components that form a glass skeleton as an intermediate oxide. Moreover, there exists an effect which makes a softening point fall or vitrification becomes easy. The content of MgO is preferably 0 to 20%, more preferably 0.5 to 10%, and further preferably 1 to 8%. The content of ZnO is preferably 0 to 30%, more preferably 0.5 to 27.5%, still more preferably 1 to 25%, and particularly preferably 2 to 20%. If the content of MgO or ZnO is too small, it is difficult to obtain the above effect. On the other hand, when there is too much content of MgO or ZnO, it will become difficult to obtain a precise | minute crystal | crystallization, and there exists a tendency for achievement of a high transmittance | permeability characteristic to become difficult. Moreover, it becomes difficult to obtain a high refractive index characteristic.

TiO ₂ is a component that acts as a nucleating agent. Moreover, it is a component for achieving high refractive index, and also has an effect of adjusting the Abbe number and the partial dispersion ratio. Furthermore, it has the effect of improving chemical durability and suppressing coloring by ultraviolet light. However, when there is too much the content, there exists a tendency for devitrification resistance to fall and vitrification to become difficult. In addition, the visible region transmittance is likely to decrease. Therefore, the content of TiO ₂ is preferably 0 to 10%, more preferably 0.1 to 8%, still more preferably 0.5 to 7%, and particularly preferably 1 to 6%.

ZrO ₂ is a component that acts as a nucleating agent. Moreover, it is a component for achieving high refractive index, and also has an effect of adjusting the Abbe number and the partial dispersion ratio. Furthermore, it has the effect of improving chemical durability. However, when there is too much the content, there exists a tendency for devitrification resistance to fall and vitrification to become difficult. Therefore, the content of ZrO ₂ is preferably 0 to 10%, more preferably 0.1 to 9%, further preferably 0.5 to 8%, and particularly preferably 1 to 7.5%.

In order to precipitate a dense crystal and achieve high transmittance, it is preferable to appropriately adjust the total amount of TiO ₂ and ZrO ₂ . Specifically, the content of TiO ₂ + ZrO ₂ is preferably 0 to 20%, more preferably 0.1 to 15%, still more preferably 0.5 to 10%, and particularly preferably 1 to 5%. . When the content of TiO ₂ + ZrO ₂ is too large, resistance to devitrification is less likely to vitrify reduced.

  In addition to the above components, the optical glass of the present invention can contain the following components.

B ₂ O ₃ is a component that forms a glass skeleton together with SiO ₂ . Moreover, there exists an effect which improves a weather resistance, and especially the effect which suppresses that the component in glass selectively elutes to water is high. The content of B ₂ O ₃ is preferably 0 to 20%, more preferably 0.1 to 15%. If the B ₂ O ₃ content is too large, it is difficult to obtain a high refractive index characteristic. Also, the partial dispersion ratio tends to be unduly high.

P ₂ O ₅ is a component that forms a glass skeleton, and has an effect of suppressing devitrification and improving weather resistance. It also has the effect of increasing the Abbe number. However, when the content of P ₂ O ₅ is too large, rather weather resistance tends to decrease. In addition, the refractive index tends to decrease. Therefore, the content of P ₂ O ₅ is preferably 0 to 10%, more preferably 0 to 5%.

Na ₂ O and K ₂ O have an effect of lowering the softening point and facilitating vitrification. There is also an effect of adjusting the partial dispersion ratio. However, when the content of Na 2 _O or K _{2 O} is too large, or the weather resistance is lowered, and dimensional stability becomes high thermal expansion coefficient tends to lowered. Furthermore, the refractive index tends to decrease. Therefore, the contents of Na ₂ O and K ₂ O are each preferably 0 to 10%, more preferably 0 to 5%.

In order to achieve a low thermal expansion coefficient and high transmittance due to the precipitation of dense crystals, it is preferable to appropriately adjust the total amount of Na ₂ O and K ₂ O. Specifically, the content of Na ₂ O + K ₂ O is preferably 0 to 10%, more preferably 0.1 to 7.5%, still more preferably 0.5 to 5%, and particularly preferably 1 to 2. .5%.

Bi ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , TeO ₂ and GeO ₂ are components that increase the refractive index. However, when there is too much the content, it will become easy to devitrify at the time of shaping | molding. Therefore, the content of Bi ₂ O ₃ + Y ₂ O ₃ + Yb ₂ O ₃ + TeO ₂ + GeO ₂ is preferably 0 to 10%, more preferably 0 to 9%, still more preferably 0 to 8%, and particularly preferably 0. ~ 5%.

  CaO, SrO, and BaO are components that increase the refractive index. Moreover, since a glass skeleton is formed as an intermediate oxide, there is an effect of improving devitrification resistance and improving chemical durability. However, if the content is too large, the partial dispersion ratio tends to be unduly high. Therefore, the content of CaO + SrO + BaO is preferably 0 to 10%, more preferably 0 to 8%, still more preferably 0.1 to 7, 5%, and particularly preferably 0.5 to 6.5%.

As a fining agent, for example, Sb ₂ O ₃ , SnO ₂ , CeO ₂ , NO ₃ or SO ₃ can be contained. If Sb ₂ O ₃ and CeO ₂ are in a small amount, they also have an effect of improving the visible region transmittance. SnO ₂ acts as a nucleating agent in small amounts. When there is too much content of the said fining agent, it will become easy to color. Accordingly, the content of these components is preferably 1% or less.

Lead component (for example PbO), arsenic component (for example As ₂ O ₃ ) and fluorine component (for example F ₂ ) have a large environmental load, and there is concern about coloring to glass. Are preferred (specifically less than 0.1% each).

The coloring degree λ ₇₀ of the optical glass of the present invention is preferably 600 nm or less, more preferably 580 nm or less, further preferably 540 nm or less, particularly preferably 520 nm or less, and most preferably 500 nm or less. When the coloring degree λ ₇₀ is too large, there is a risk of hindering use as an optical lens application.

  The yield point of the optical glass of the present invention is preferably 800 ° C. or higher, more preferably 900 ° C. or higher. If the yield point is too low, it may cause dimensional changes when used in a high temperature environment.

  Next, a method for producing the optical glass of the present invention and an optical lens using the optical glass will be described.

  First, raw material powder is prepared so as to have a desired composition, and is melted in a melting container. Here, after producing a cullet by primary melting, secondary melting is performed using the cullet, whereby the refractive index can be adjusted and the composition can be homogenized. By homogenizing the composition, a glass with high transmittance can be obtained. In the secondary melting, the refractive index can be precisely controlled by using a cullet having a high refractive index and a cullet having a low refractive index.

  Next, molten glass is dropped from the tip of the nozzle and shaped into droplets (droplet shaping) to obtain a glass material. Or glass material is obtained by shape | molding molten glass in an ingot shape and cutting out to a suitable magnitude | size. By subjecting the obtained glass material to crystallization treatment under predetermined heat treatment conditions, an optical lens made of the optical glass of the present invention can be obtained. Note that the partial dispersion ratio tends to increase due to crystallization. For example, it is preferable that the partial dispersion ratio of the glass after crystallization is 0.01 or more higher than the partial glass dispersion ratio before crystallization.

  In order to obtain an optical lens having a predetermined shape, it is preferable to perform a polishing process before or after the crystallization process. In addition, since the glass after the crystallization treatment has a high hardness and tends to be difficult to polish, the polishing treatment is preferably performed before the crystallization treatment. Since the crystallization treatment usually involves shrinkage, the polishing treatment is performed in consideration of the shrinkage rate.

  If necessary, the refractive index can be appropriately adjusted by setting the atmosphere during the crystallization treatment to a pressurized atmosphere or a reduced-pressure atmosphere. Specifically, the refractive index can be increased by performing crystallization treatment in a pressurized atmosphere. On the other hand, the refractive index can be lowered by performing the crystallization treatment in a reduced-pressure atmosphere.

  Moreover, it is also possible to crystallize locally by heat treatment using a laser or the like. This makes it possible to form a waveguide in the glass and to produce a microlens array.

  The optical lens made of the optical glass of the present invention can also be used as a lens cap assembled with a metal part.

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

  Tables 1 and 2 show Examples (Sample Nos. 1 to 13) and Comparative Examples (Sample Nos. 14 and 15) of the present invention.

  Each sample was prepared as follows. First, raw material powders were prepared so as to have the respective compositions shown in the table, and melted at 1400 to 1550 ° C. for 3 hours using a platinum crucible. The obtained molten glass was poured out on a carbon plate and annealed to obtain a crystalline glass. The obtained crystalline glass was measured for refractive index (nd), Abbe number (νd), and partial dispersion ratio (θg, F).

  Thereafter, the crystallized glass was obtained by subjecting the crystalline glass to crystallization treatment under the respective heat treatment conditions described in the table.

  The obtained crystallized glass was measured for refractive index, Abbe number, partial dispersion ratio, coloring degree, crystal content, crystal grain size, thermal expansion coefficient, yield point, and Knoop hardness. The results are shown in Tables 1 and 2.

  The refractive index is indicated by a measured value with respect to d-line (587.6 nm) of a helium lamp.

  The Abbe number uses the values of the refractive index of the d-line of the helium lamp and the refractive indices of the F-line (486.1 nm) and C-line (656.3 nm) of the hydrogen lamp, and the Abbe number (νd) = {(nd− 1) / (nF-nC)}.

  The partial dispersion ratio uses the refractive index values of the F-line and C-line of the hydrogen lamp and the g-line (435.8 nm) of the mercury lamp, and the partial dispersion ratio (θg, F) = {(ng−nF) / (nF -NC)}.

The coloring degree λ ₇₀ is obtained by measuring the transmittance in a wavelength range of 200 to 800 nm at an interval of 0.5 nm using a spectrophotometer for an optically polished sample having a thickness of 5 mm ± 0.05 mm. It produced and evaluated by the shortest wavelength which shows the transmittance | permeability 70% in the said transmittance | permeability curve.

  The crystal content was calculated by the halo method based on the chart obtained by X-ray diffraction measurement. The crystal species were also identified at the same time. The crystal grain size was measured based on an image obtained by observing the sample surface with a transmission electron microscope (TEM). Specifically, the average value of the major axis and the minor axis of each crystal in the transmission electron microscope observation image was defined as the crystal size, and the average value of the crystal sizes of any ten crystals was defined as the crystal grain size.

  The thermal expansion coefficient and yield point were measured using a thermal expansion measuring device (dilatometer).

  Knoop hardness was measured using MXT50 (manufactured by Matsuzawa Seiki) in a room maintained at a temperature of 25 ° C. and a humidity of 50%. Specifically, an indenter with a load of 100 g was pressed on the surface of the plate-like sample for 15 seconds, and Knoop hardness was calculated based on the length of the diagonal line of the indentation.

As is apparent from Table 1, No. 1 as an example of the present invention. Each of the samples 1 to 13 (crystallized glass) has a refractive index of 1.5501 to 1.6260, an Abbe number of 44.9 to 55.3, and a partial dispersion ratio of 0.5523 to 0.5842. It had optical properties. Further, the thermal expansion coefficient was 3 to 63 × 10 ⁻⁷ / ° C., and the Knoop hardness was 570 to 700, which satisfied the desired range.

  On the other hand, No. which is a comparative example. Samples 14 and 15 (crystallized glass) had a refractive index as low as 1.5445 or less.

  The optical glass of the present invention is used for optical pickup lenses, video cameras, digital cameras, other general cameras and portable photographing lenses, optical communication lenses, and steppers for CD, MD, DVD, and other various optical disk systems. Suitable for lenses, other optical members such as prisms and optical filters.

Claims (8)

An optical glass obtained by precipitating a crystal containing at least two components selected from Li ₂ O, MgO, ZnO, Al ₂ O ₃ and SiO ₂ as a main crystal, and in terms of mass%, La ₂ O ₃ + Gd ₂ O ₃ + Nb ₂ O ₅ + Ta ₂ O ₅ + WO ₃ 4.5 to 20%, coefficient of thermal expansion at −30 to 300 ° C. is −10 to 70 × 10 ⁻⁷ / ° C. , refractive index 1 .55 to 1.85, and an optical glass characterized by being for an optical lens .   2. The optical glass according to claim 1, wherein at least one selected from a β-quartz solid solution, a β-spodumene solid solution, garnite, enstatite, forsterite and cordierite is precipitated as a main crystal. By _{mass%, SiO 2 20~65.5%, Al} 2 O 3 14~30%, Li 2 O 0~10%, 0~20% MgO, 0~30% ZnO, TiO 2 0~10%, and The optical glass according to claim 1, comprising 0 to 10% of ZrO ₂ . Moreover, the claims in _{mass%, B 2 O 3 0~20%} , P 2 O 5 0~10%, characterized by containing Na 2 O 0 to 5%, and _K 2 O 0 to 5% 3. The optical glass according to 3.   The optical glass according to any one of claims 1 to 4, which does not substantially contain a lead component, an arsenic component, and a fluorine component.   The optical glass according to any one of claims 1 to 5, wherein the main crystal has an average particle size of 100 nm or less. A Tsu optical glass according to any one of claims 1 to 6, characterized in that base number is 40 to 70. The optical glass according to claim 1, wherein a coloring degree λ _{70 at a} thickness of 5 mm is 600 nm or less.