WO2019142603A1 - Optical glass - Google Patents

Abstract

Provided is an optical glass having desired optical characteristics, favorable devitrification resistance, and excellent mass producibility. This optical glass is characterized by: comprising a SiO₂-Ta₂O₅-R₂O (wherein R is at least one kind selected from Li, Na and K) glass having a refractive index (nd) of 1.59-1.80, an Abbe number (νd) of 25-55, and a partial dispersion ratio (θg, F) of 0.605 or less; and containing, on a mass basis, 0 to less than 25% of Nb₂O₅ and more than 0 to 20% of TiO₂.

Description

Optical glass

The present invention relates to an optical glass particularly suitable as an optical lens of a digital camera or video camera or a lens for optical communication.

BACKGROUND In recent years, digital cameras and video cameras have become increasingly sophisticated, and more specifically, miniaturization, high magnification, high definition, and the like are in progress. In order to achieve such high performance, glass for optical lenses used in digital cameras and video cameras is often required to have characteristics such as high refraction, low dispersion, and anomalous dispersion. _{A 2-} Nb ₂ O ₅ based glass or the like has been proposed (see, for example, Patent Document 1).

By the way, as a manufacturing method of an optical lens used for a digital camera, a video camera, etc., once molding molten glass into an ingot, polishing a glass material cut out from this to a suitable size from this, mold pressing it, melting There is known a method in which glass is dropped from the tip of a nozzle to form droplets, that is, after a glass material formed by so-called droplet forming is polished, or mold pressing is performed without polishing.

International Publication No. 2016/067921

Although the conventional SiO ₂ -Nb ₂ O ₅ -based glass has desired optical properties, it has a problem that the devitrification is strong and the mass productivity is poor.

In view of the above problems, an object of the present invention is to provide an optical glass which has desired optical properties, is excellent in devitrification resistance, and is excellent in mass productivity.

The optical glass of the present invention is SiO ₂ -Ta ₂ having a refractive index (nd) of 1.59 to 1.80, an Abbe number (νd) of 25 to 55, and a partial dispersion ratio (θg, F) of 0.605 or less O ₅ -R ₂ O (R is at least one selected from Li, Na, and K) and contains Nb ₂ O ₅ 0 to less than 25%, TiO ₂ more than 0 to 20% by mass% It is characterized by The SiO ₂ -Ta ₂ O ₅ -R ₂ O-based glass means a glass containing SiO ₂ , Ta ₂ O ₅ and R ₂ O as essential components.

As a result of investigations by the present inventors, the main cause of devitrification in conventional SiO ₂ -Nb ₂ O ₅ glasses is to increase the refractive index and to increase the anomalous dispersion (decrease the partial dispersion ratio). It was found that a large amount of Nb ₂ O ₅ which is a component of is contained. Therefore, a SiO ₂ -Ta ₂ O ₅ -R ₂ O-based glass containing Ta ₂ O ₅ as an essential component, which is also a component that reduces the content of Nb ₂ O ₅ as much as possible and also reduces the refractive index and the partial dispersion ratio It has been found that devitrification can be suppressed while achieving high refractive index and low partial dispersion ratio. In addition, the weather resistance is also improved, and deterioration of physical properties, deterioration of the glass surface, and the like are less likely to occur during the manufacturing process or product use. By including the R 2 _O as an essential component, it is possible to obtain a glass of low dispersion.

The optical glass of the present invention, further, in _{mass%, SiO 2 20 ~ 70%} , Ta 2 O 5 6 ~ 70%, ZrO 2 0 ~ 15%, P 2 O 5 0 ~ 10%, R 2 O (R Preferably contains at least one selected from Li, Na and K) and more than 0 to 40%, and substantially does not contain a lead component, an arsenic component and a fluorine component. “R ₂ O more than 0 to 40%” means that the total content of Li ₂ O, Na ₂ O and K ₂ O is more than 0 to 40%.

The optical glass of the present invention may further contain, by mass%, R′O (R ′ is at least one selected from Mg, Ca, Sr, and Ba) 0 to less than 10%, ZnO 0 to 15% preferable. “R′O 0 to less than 10%” means that the total content of MgO, CaO, SrO and BaO is 0 to less than 10%.

The optical glass of the present invention preferably further contains 0 to 15% of B ₂ O _{3 in} mass%.

The optical glass of the present invention preferably further contains, by mass%, 0 to 10% of La ₂ O ₃ + Gd ₂ O ₃ + Bi ₂ O ₃ + Y ₂ O ₃ + Yb ₂ O ₃ + TeO ₂ + GeO ₂ . La ₂ O ₃ + Gd ₂ O ₃ + Bi ₂ O ₃ + Y ₂ O ₃ + Yb ₂ O ₃ + TeO ₂ + GeO ₂ is La ₂ O ₃ , Gd ₂ O ₃ , Bi ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ Mean the total content of TeO ₂ and GeO ₂ .

The optical glass of the present invention preferably has a weight ratio of SiO ₂ / B ₂ O ₃ of 2 or more. SiO ₂ / B ₂ O ₃ means a value obtained by dividing the content of SiO _{2 by} the content of B ₂ O ₃ .

The optical glass of the present invention preferably has a mass ratio of Nb ₂ O ₅ / Ta ₂ O ₅ of less than 15. Nb ₂ O ₅ / Ta ₂ O ₅ means a value obtained by dividing the content of Nb ₂ O _{5 by} the content of Ta ₂ O ₅ .

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the optical glass which has a desired optical characteristic and is favorable in devitrification resistance and excellent in mass-productivity.

The optical glass of the present invention has a refractive index (nd) of 1.59 to 1.80, an Abbe number (νd) of 25 to 55, and a partial dispersion ratio (θg, F) of 0.605 or less. The reasons why the various characteristics are limited as described above in the present invention will be shown below.

For example, when optical glass is used as a lens, the higher the refractive index, the thinner the lens can be, which is advantageous for miniaturizing an optical device. Therefore, the refractive index of the optical glass of the present invention is 1.59 or more, preferably 1.6 or more, 1.61 or more, 1.62 or more, and particularly preferably 1.63 or more. On the other hand, in order to improve the refractive index of glass, it is necessary to add a large amount of Nb ₂ O ₅ or the like. However, the component that improves the refractive index, such as Nb ₂ O ₅ , is also a component that makes the glass unstable. Therefore, it is necessary to define the upper limit of the refractive index in consideration of the stability of the glass. Specifically, the refractive index of the optical glass of the present invention is 1.80 or less, 1.79 or less, 1.78 or less, 1.77 or less, 1.76 or less, in particular 1.75 or less preferable.

The Abbe number of the optical glass of the present invention is 25 or more, preferably 26 or more, 27 or more, and particularly 28 or more, in order to achieve low dispersion characteristics. On the other hand, in order to improve the Abbe number of glass, it is necessary to add a large amount of R ₂ O or the like. However, the component that improves the Abbe number, such as R ₂ O, is also a component that reduces the refractive index. Therefore, it is necessary to define the upper limit of the Abbe number in consideration of the refractive index. Specifically, the Abbe number of the optical glass of the present invention is 55 or less, preferably 53 or less, 51 or less, 49 or less, 47 or less, particularly 45 or less.

The partial dispersion ratio of the optical glass of the present invention is preferably 0.605 or less, more preferably 0.604 or less, and particularly preferably 0.603 or less, in order to achieve anomalous dispersion characteristics. On the other hand, components such as Nb ₂ O ₅ which lower the partial dispersion ratio of the glass make the glass unstable. Therefore, it is necessary to define the lower limit of the partial dispersion ratio in consideration of the stability of the glass. Specifically, the partial dispersion ratio of the optical glass of the present invention is preferably 0.55 or more, particularly 0.555 or more.

Next, the glass composition of the optical glass of the present invention will be described.

The optical glass of the present invention is composed of SiO ₂ -Ta ₂ O ₅ -R ₂ O (R is at least one selected from Li, Na, and K) based glass, and Nb ₂ O ₅ 0 to 25% by mass% Less than, contains TiO ₂ 0 to more than 20%. Within the above composition range, the characteristics having a refractive index of 1.59 to 1.80, an Abbe number of 25 to 55, and a partial dispersion ratio of 0.605 or less can be easily achieved.

The reasons for limiting the composition range as described above will be described below. In the following description of the glass composition, "%" means "% by mass" unless otherwise noted.

SiO ₂ is a component that forms a glass skeleton. Moreover, it has the effect of improving the weather resistance, and in particular, the effect of suppressing the selective elution of components such as alkali metal oxides in the glass into water is high. Furthermore, it is a component which can lower liquidus temperature and can control devitrification. The content of SiO ₂ is preferably 20 to 70%, 21 to 65%, 22 to 60%, particularly 25 to 55%. When the content of SiO ₂ is too small, it is difficult to obtain the above effect. On the other hand, if the content of SiO ₂ is too large, the meltability may be reduced and cords and bubbles due to unmelted may easily remain in the glass, and the required quality as glass for lens may not be satisfied.

Ta ₂ O ₅ is a component for achieving high refractive index and is a component having a high effect of reducing the partial dispersion ratio. Further, among the components capable of achieving high refractive index, it is a component which is relatively difficult to raise the liquidus temperature (it is difficult to cause devitrification). The content of Ta ₂ O ₅ is preferably 6 to 70%, 10 to 60%, 15 to 50%, and particularly preferably 20 to 45%. When the content of Ta ₂ O ₅ is too small, the above-mentioned effect is hardly obtained. On the other hand, if the content of Ta ₂ O ₅ is too large, the liquidus temperature rises and crystals mainly composed of Ta ₂ O ₅ tend to be precipitated, which tends to make vitrification difficult.

R ₂ O (R is at least one selected from Li, Na and K) is a component to achieve low dispersion, and is a component to reduce the partial dispersion ratio. It also has the effect of lowering the softening point and facilitating vitrification. The content of R ₂ O is preferably more than 0 to 40%, 0.5 to 37.5%, 1 to 35%, 1.5 to 32.5%, particularly 2 to 30%. When the content of R ₂ O is too small, the above-described effect is hardly obtained. On the other hand, when the content of R ₂ O is too large, chemical durability tends to be reduced. In addition, it becomes difficult to obtain high refractive glass.

The content of each component of Li ₂ O, Na ₂ O and K ₂ O is 0 to 40%, 0.1 to 37.5%, 0.5 to 35%, 1 to 32.5%, in particular It is preferably 1.5 to 30%.

Nb ₂ O ₅ is a component for achieving high refractive index, and also has an effect of reducing the partial dispersion ratio. However, if the content is too large, the glass tends to be unstable. That is, the liquidus temperature rises, and crystals mainly composed of Nb ₂ O ₅ are easily precipitated, and vitrification becomes difficult. Accordingly, the content of Nb ₂ O ₅ is 0 to less than 25%, preferably 0.1 to 20%, 0.5 to 15%, and particularly preferably 1 to 10%.

In the optical glass of the present invention, in order to achieve good devitrification resistance, it is preferable to appropriately adjust the total amount of Li ₂ O and Nb ₂ O ₅ (Li ₂ O + Nb ₂ O ₅ ). Specifically, Li ₂ O + Nb ₂ O ₅ is preferably 45% or less, 40% or less, 30% or less, and particularly 25% or less.

TiO ₂ is a component for achieving high refractive index, and also has an effect of reducing the partial dispersion ratio. Moreover, coloring of the glass by ultraviolet light can be suppressed. The content of TiO ₂ is preferably more than 0 to 20%, 0.1 to 17%, 0.5 to 15%, and particularly preferably 1 to 13%. When the content of TiO ₂ is too small, the above-mentioned effect is hardly obtained. On the other hand, when the content of TiO ₂ is too large, the devitrification resistance tends to be reduced and the vitrification tends to be difficult. In addition, the visible light transmittance tends to be reduced.

In the optical glass of the present invention, in order to achieve a low partial dispersion ratio, it is preferable to appropriately adjust the total amount (TiO ₂ + Ta ₂ O ₅ ) of TiO ₂ and Ta ₂ O ₅ . Specifically, TiO ₂ + Ta ₂ O ₅ is preferably 18% or more, 20% or more, 30% or more, and particularly preferably 40% or more.

_{Incidentally, Nb 2 O 5, Ta 2} O 5, the effect of lowering the partial dispersion ratio in the TiO ₂ is the largest amount is _Ta 2 _{O 5,} then TiO _2, then a _Nb 2 _{O 5.}

In the optical glass of the present invention, in order to achieve a low partial dispersion ratio, Nb ₂ O ₅ and Ta ₂ O ₅ , TiO ₂ and Ta ₂ O ₅ , SiO ₂ and Ta ₂ O ₅ , and further Nb ₂ O ₅ and TiO ₂ It is preferable to appropriately adjust the ratio of each content of + Ta ₂ O ₅ . Specifically, it is preferable that Nb ₂ O ₅ / Ta ₂ O ₅ is less than 15, 10 or less, and particularly 3 or less in mass ratio. In terms of mass ratio, TiO ₂ / Ta ₂ O ₅ is preferably 5 or less, 4 or less, and particularly 1 or less. It is preferable that SiO ₂ / Ta ₂ O ₅ is 5 or less, 3 or less, and particularly 2 or less in mass ratio. Furthermore, it is preferable that Nb ₂ O ₅ / (TiO ₂ + Ta ₂ O ₅ ) be 10 or less, 5 or less, particularly 2 or less in mass ratio. When any of Nb ₂ O ₅ / Ta ₂ O ₅ , TiO ₂ / Ta ₂ O ₅ , SiO ₂ / Ta ₂ O ₅ and Nb ₂ O ₅ / (TiO ₂ + Ta ₂ O ₅ ) is larger than the above range, It becomes difficult to obtain a low partial dispersion ratio.

The optical glass of the present invention can contain the following components in addition to the components described above.

ZrO ₂ is a component that can increase the refractive index. In addition, since the glass skeleton is formed as an intermediate oxide, there is also an effect of improving the devitrification resistance and improving the chemical durability. However, in order to increase the partial dispersion ratio, it is difficult to obtain desired optical properties if the content is too large. Therefore, the content of ZrO ₂ is 0 to 15%, 0 to 12.5%, 0 to 10%, 0 to 8%, 0.1 to 7.5%, and in particular 0.5 to 6.5%. Is preferred.

P ₂ O ₅ is a component for forming a glass skeleton, and has an effect of suppressing the devitrification and improving the weather resistance. It also has the effect of increasing the Abbe number. However, when the content of P ₂ O ₅ is too large, the weather resistance tends to decrease. In addition, the refractive index is lowered, and the softening point is increased, which tends to make mold press molding at low temperature difficult. Furthermore, the partial dispersion ratio tends to increase unreasonably. Accordingly, the content of P ₂ O ₅ is preferably 0 to 10%, particularly 0 to 5%.

R'O (R 'is at least one selected from Mg, Ca, Sr, and Ba) is a component capable of increasing the refractive index. In addition, since the glass skeleton is formed as an intermediate oxide, there is also an effect of improving the devitrification resistance and improving the chemical durability. However, since these components increase the partial dispersion ratio, it is difficult to obtain desired optical properties if the content is too large. Accordingly, the content of R′O is preferably 0 to less than 10%, 0 to 8%, 0.1 to 7.5%, and particularly 0.5 to 6.5%.

The content of each component of MgO, CaO, SrO and BaO is preferably 0 to 8%, 0 to 5%, particularly 0.1 to 3%.

ZnO is a component that can increase the refractive index. In addition, since the glass skeleton is formed as an intermediate oxide, there is also an effect of improving the devitrification resistance and improving the chemical durability. However, since ZnO increases the partial dispersion ratio, it is difficult to obtain desired optical characteristics if the content is too large. Therefore, the content of ZnO is preferably 0 to 15%, 0 to 8%, particularly 0.1 to 7%.

In the optical glass of the present invention, in order to achieve a low partial dispersion ratio, the ratio of the content of MgO, CaO, SrO, BaO, ZnO and ZrO ₂ (MgO + CaO + SrO + BaO + ZnO + ZrO ₂ ) to the content of Ta ₂ O ₅ is appropriately adjusted. Is preferred. Specifically, (MgO + CaO + SrO + BaO + ZnO + ZrO ₂ ) / Ta ₂ O ₅ is preferably 0.5 or less, 0.4 or less, and particularly 0.3 or less.

B ₂ O ₃ is a component capable of forming a glass skeleton. Moreover, it has the effect of improving the weather resistance, and in particular, the effect of suppressing the selective elution of the components in the glass into water is high. The content of B ₂ O ₃ is preferably 0 to 15%, less than 0 to 15%, 0 to 10%, and particularly 0.1 to 5%. When the content of B ₂ O ₃ is too large, the partial dispersion ratio tends to increase. In addition, it becomes difficult to obtain high refractive properties.

In the optical glass of the present invention, in order to achieve a low partial dispersion ratio, it is preferable to appropriately adjust the ratio of the content of SiO _{2 to} the content of B ₂ O ₃ . Specifically, it is preferable that SiO ₂ / B ₂ O ₃ be 2 or more, 2.5 or more, and particularly 3 or more.

La ₂ O ₃ , Gd ₂ O ₃ , Bi ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , TeO ₂ and GeO ₂ are components for increasing the refractive index. However, since these components increase the partial dispersion ratio, it is difficult to obtain desired optical properties if the content is too large. Therefore, 0 to 10%, 0 to 9%, 0.1 to 8%, particularly 0.5 to 5 of La ₂ O ₃ + Gd ₂ O ₃ + Bi ₂ O ₃ + Y ₂ O ₃ + Yb ₂ O ₃ + TeO ₂ + GeO ₂ % Is preferred.

WO ₃ is a component for achieving high refractive index, and also has an effect of reducing the partial dispersion ratio. Moreover, coloring of the glass by ultraviolet light can be suppressed. However, when the content is too large, the devitrification resistance tends to be reduced to make vitrification difficult, or the ultraviolet region transmittance tends to be reduced. In addition, affinity with the press die is increased, and the glass tends to be easily fused to the die at the time of mold press molding. Accordingly, the content of WO ₃ is preferably 0 to 10%, 0 to 5%, particularly 0 to 1%.

Al ₂ O ₃ is a component capable of forming a glass skeleton. Moreover, it has the effect of improving the weather resistance, and in particular, the effect of suppressing the selective elution of the components in the glass into water is high. The content of Al ₂ O ₃ is preferably 0 to 10%, particularly 0 to 1%. When the content of Al ₂ O ₃ is too large, devitrification tends to occur. In addition, the meltability may be lowered and cords and air bubbles may remain in the glass, and the required quality as a lens glass may not be satisfied.

For example, Sb ₂ O ₃ , SnO ₂ , CeO ₂ , NO ₃ or SO ₃ can be included as a fining agent. A small amount of Sb ₂ O ₃ also has the effect of improving the visible region transmittance. However, if the content of the above-mentioned fining agent is too large, there is a possibility that unwanted coloration may occur, so the content of each of these components is preferably 5% or less.

Lead components (for example, PbO), arsenic components (for example, As ₂ O ₃ ) and fluorine components (for example, F ₂ ) do not contain substantially because they have a large impact on the environment and there is concern over coloring of glass ( Specifically, it is preferable that each be less than 0.1%.

Next, the method of producing the optical lens used for a digital camera, a video camera, etc. using the optical glass of this invention is demonstrated.

First, a glass raw material prepared to have a desired composition is melted. Next, molten glass is dropped from the tip of the nozzle and formed into droplets (droplet formation) to obtain a glass material. After polishing the obtained glass material, or without polishing, mold pressing is performed to obtain an optical lens having a predetermined shape. It is also possible to adopt a method of forming a molten glass into an ingot shape, polishing the glass material cut into an appropriate size, and performing mold press forming instead of performing the droplet formation.

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

EXAMPLES Hereinafter, the present invention will be described based on examples, but the present invention is not limited to these examples.

Tables 1 and 2 show examples of the present invention (samples Nos. 1 to 21) and comparative examples (sample No. 22).

Each sample was prepared as follows. First, a glass material was prepared so as to have each composition shown in the table, and was melted at 1500 ° C. for 2 hours using a platinum crucible. The obtained molten glass was poured out onto a carbon plate, and after annealing, a sample suitable for each measurement was produced.

The refractive index (nd), the Abbe's number (νd), and the partial dispersion ratio (θg, F) of the obtained sample were measured. The results are shown in the table.

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

The Abbe number (用 い d) = {(nd−) using the refractive index of the d line of the helium lamp and the refractive index of the F line (486.1 nm) and the C line (656.3 nm) of the hydrogen lamp. 1) / (nF-nC)}.

The partial dispersion ratio is the refractive index value of the F line, C line and g line (435.8 nm) of the hydrogen lamp, and the partial dispersion ratio (θg, F) = {(ng-nF) / (nF-nC) Calculated from the equation of}.

As is apparent from the table, the Nos. 1 and 2 which are examples of the present invention. The samples 1 to 21 are vitrified without devitrification, and the refractive index is 1.6394 to 1.7980, the Abbe number is 28.6 to 38.6, and the partial dispersion ratio is 0.5698 to 0.5938 And had the desired optical properties.

On the other hand, No. 1 as a comparative example. Twenty-two samples were not vitrified.

The optical glass of the present invention is a glass material for mold press molding and a glass material for polishing, such as an optical pickup lens for CD, MD, DVD, and other various optical disk systems, a photographing lens for a video camera, a digital camera and other general cameras, It is suitable as glass for communication lenses and the like.

Claims (7)

1. SiO ₂ -Ta ₂ O ₅ -R ₂ O (refractive index (nd) is 1.59 to 1.80, Abbe's number (νd) is 25 to 55, partial dispersion ratio (θg, F) is 0.605 or less R is at least one selected from Li, Na, and K) Optical glass characterized by containing, by mass%, Nb ₂ O ₅ 0 to less than 25%, TiO ₂ more than 0 to 20% by mass .
2. Furthermore, by _mass%, contains _{SiO 2 20 ~ 70%, Ta} 2 O 5 6 ~ 70%, ZrO 2 0 ~ 15%, P 2 O 5 0 ~ 10%, the super ~ 40% _R 2 O 0, The optical glass according to claim 1, which is substantially free of a lead component, an arsenic component and a fluorine component.
3. Furthermore, it is characterized in that, on a percent by mass basis, R′O (R ′ is at least one selected from Mg, Ca, Sr, and Ba) 0 to less than 10%, and ZnO 0 to 15%. Optical glass as described in 2.
4. The optical glass according to any one of claims 1 to 3, further comprising 0 to 15% of B ₂ O ₃ in mass%.
5. Furthermore, La ₂ O ₃ + Gd ₂ O ₃ + Bi ₂ O ₃ + Y ₂ O ₃ + Yb ₂ O ₃ + TeO ₂ + GeO ₂ 0 to 10% is contained by mass%. Optical glass as described in.
6. The optical glass according to any one of claims 1 to 5, wherein SiO ₂ / B ₂ O ₃ is 2 or more in mass ratio.
7. The optical glass according to any one of claims 1 to 6, wherein Nb ₂ O ₅ / Ta ₂ O ₅ is less than 15 in mass ratio.