JP2013067559A - Optical glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide optical glass containing bismuth oxide having good preform productivity and mold pressability.SOLUTION: The optical glass contains, by mass%, 10% to less than 90% of BiOand has optical constants including a refractive index [nd] of 1.70 or higher and an Abbe number [νd] of 10 or greater, and exhibits viscosity at liquidus temperature of 0.4 Pa s or higher. It is preferred that the yield point of glass [At] be 600 °C or below and that the liquidus temperature be 950 °C or below.

Description

  The present invention relates to an optical glass containing bismuth oxide, and more particularly to an optical glass having good pressability.

  In recent years, with the rapid progress of higher integration and higher functionality of equipment that uses optical systems, there has been an increasing demand for higher precision, lighter weight, and smaller optical systems. Optical designs using aspherical lenses using high refractive index and high dispersion glass are becoming mainstream.

  In particular, it is expensive and low-efficiency to produce an aspheric lens by grinding or polishing methods. Therefore, as a method for manufacturing an aspheric lens, a preform material obtained by cutting and polishing a gob or a glass block is heated and softened. By pressing this with a mold with a high-precision surface, the grinding / polishing process is omitted, and low-cost and mass production is realized.

  In order to achieve the purpose of low-cost and mass production of this aspherical lens, it is impossible to meet the purpose of low-cost and mass production unless the mold used for the mold press can be used repeatedly. For this purpose, it is necessary to set the temperature during mold pressing as low as possible in order to suppress the surface oxidation of the mold as much as possible. Further, the upper limit temperature of the mold press and the transition temperature and the glass yield point are correlated, and the lower these temperatures are, the more the progress of surface oxidation of the mold is suppressed, which is preferable from the viewpoint of the mold life. Furthermore, it is necessary to sufficiently study the cost of manufacturing the preform material, which is a pre-stage of molding.

  As a method for producing a preform, there is a method in which a glass melt is dropped and cooled. This method has a high mass productivity of the preform material itself, and the manufacturing cost is currently the lowest. Furthermore, since the preform obtained by this method is close to a spherical or biconvex lens shape, the shape change amount at the time of mold pressing can be reduced, and the mass productivity of the glass itself can be improved.

  When a preform is produced by dropping a glass melt, the conditions at the time of production and the characteristics of the glass itself must be mutually optimized. In particular, the higher the refractive index and the higher the dispersion, the smaller the amount of glass forming oxide, and the glass tends to have a lower viscosity. In other words, when a preform material is molded by this molding method in a high refractive index and high dispersion glass, it is difficult to obtain a shape close to a spherical or biconvex lens with a smooth and even curved surface when the viscosity is low. Therefore, the viscosity of the glass melt at the time of preform molding must be fully studied.

  Further, the liquidus temperature (devitrification temperature) must be lower than the temperature at the time of glass molding, for example, preform production, that is, the glass should not be devitrified at the time of dropping. Therefore, if the viscosity of the glass melt is low, the temperature of the glass melt must be lowered in order to increase the viscosity of the glass melt. Then, it falls below the liquidus temperature (devitrification temperature), and devitrification occurs in the preform material. Furthermore, the tendency becomes remarkable in the high refractive index and high dispersion glass. On the other hand, since the liquidus temperature is high, the problem of devitrification is solved by increasing the temperature during the manufacture of the preform. However, the glass becomes low-viscosity, and not only preform molding cannot be performed, but also problems such as premature wear due to seizure of the glass to the mold and surface oxidation of the mold occur.

  As described above, the composition of the optical glass for mold press has the desired optical constant, low glass yield point, and low glass transition point. Is necessary.

In recent years, Patent Documents 1 and ₂ disclose glass containing P ₂ O ₅ as a main component as a material for precision pressing, in which a press molding temperature is 700 ° C. or lower and crystals are difficult to precipitate during pressing. These materials can be softened and pressed at a lower temperature than conventional SiO ₂ glass. However, these glasses also have problems such as high yield point temperature of glass and easy coloration of the glass.

Patent Document 3 discloses a glass mainly composed of Bi ₂ O ₃ , but its refractive index and dispersion are not sufficient, and the glass transition point is high. Further, there is a problem that the tendency to devitrification is strong.

JP-A-7-97234 JP 2002-173336 A Japanese Patent Laid-Open No. 9-20530

  The present invention has been made in view of the above problems, and has a low glass yield point and good mold pressability, that is, a smooth curved surface, while imparting high refractive index and high dispersion characteristics. A glass capable of obtaining a uniform preform is provided.

As a result of intensive studies to solve the above-mentioned problems, the present inventor, in a glass containing a Bi ₂ O ₃ component, preferably has a refractive index by combining an alkali metal oxide and / or an alkaline earth metal oxide. [Nd] is 1.70 or more, Abbe number [νd] is 10 to 35 optical constant, glass yield point [At] is 600 ° C. or lower, glass liquidus temperature is 950 ° C. or lower, and The present inventors have found that an optical glass having a preform productivity and a good mold pressability can be obtained when the viscosity of the glass melt at the liquidus temperature of the glass is 0.4 Pa · s or more, and the present invention has been completed. More specifically, the present invention provides the following.

(1) By mass%, Bi ₂ O ₃ is contained in an amount of 10% or more and less than 90%, an optical constant having a refractive index [nd] of 1.70 or more and an Abbe number [νd] of 10 or more, and a liquidus temperature. An optical glass having a viscosity of 0.4 Pa · s or more.

  According to the optical glass of the present invention, since the viscosity at the liquidus temperature is 0.4 Pa · s, the preform surface is smooth and has a uniform shape in the manufacture of the preform by dropping the glass melt. Becomes easy.

  “Liquid phase temperature” means that a glass sample pulverized with a certain particle size is placed on a platinum plate, held in a furnace with a temperature gradient for 30 minutes, taken out, and the presence or absence of softened glass crystals is observed with a microscope. This is the lowest temperature at which no crystal is observed.

  “Viscosity” is the degree of viscosity of the fluid. In the present invention, the viscosity η (Pa · s) is obtained and measured by a ball pulling-up type viscometer (manufactured by Opt Enterprise Co., Ltd.).

(2) 10% or more and less than 75% Bi ₂ O ₃ by mass%, an optical constant having a refractive index [nd] of 1.70 or more, an Abbe number [νd] of 15 or more, and a liquidus temperature The optical glass according to (1), which has a viscosity of 1.0 Pa · s or more.

According to this aspect, since the Bi ₂ O ₃ content is 10% or more and less than 75% and the viscosity at the liquidus temperature is 1.0 Pa · s or more, in the production of the preform by dropping the glass melt, The surface of the preform is smooth and it becomes easier to obtain a uniform shape.

(3) mass% of an optical glass according to _Bi 2 _{O 3} and containing less than 80% than 55% (1).

According to this aspect, the stability of the glass can be improved by adding Bi ₂ O ₃ to 55% or more and less than 80%.

  (4) The optical glass according to any one of (1) to (3), wherein the yield point [At] of the glass in the optical glass is 600 ° C. or lower.

  According to this aspect, since the temperature at the time of mold press molding can be set low, it becomes easy to suppress the surface oxidation of the mold and further suppress the deterioration of the mold as compared with the conventional case.

  The “bending point” is a temperature at which the glass stops stretching and then starts to shrink when the glass is heated. In the present invention, the temperature rise rate is 8 ° C./min. taking measurement.

  (5) The optical glass according to any one of (1) to (4), wherein the liquidus temperature is 950 ° C. or lower.

  According to this aspect, since the temperature of molten glass forming can be set low, devitrification hardly occurs during glass forming.

  (6) The optical glass according to any one of (1) to (4), wherein the liquidus temperature is 800 ° C. or lower.

  According to this aspect, since the temperature of molten glass forming can be set low, devitrification hardly occurs during glass forming.

(7) The optical glass according to any one of (1) to (6), containing, by mass%, SiO ₂ amount <B ₂ O ₃ amount and a total amount of SiO ₂ + B ₂ O ₃ of 3% to 60%. Or (8) Further, the optical glass according to (7), wherein the ratio of SiO ₂ / B ₂ O ₃ is 0.3 to 0.8. (9) The optical glass according to (4), wherein the total amount of the SiO ₂ + B ₂ O ₃ is 10% or more and 60% or less.

By producing the optical glass with this composition range, it becomes easy to obtain the glass targeted by the present invention having a high viscosity at the liquidus temperature and a low liquidus temperature. Further, by containing a large amount of B ₂ O ₃ than SiO _2, it becomes easy to stabilize the glass.

(10) The optical glass according to any one of (1) to (9) containing 0.1% or more of RO and Rn ₂ O by mass% (where R is Zn, Ba, Sr, Ca, Mg) 1 or more selected from R, and Rn represents 1 or more selected from Li, Na, K, and Cs.), Or (11) The RO component is contained in excess of 0% in (10) The optical glass described. (However, R represents one or more selected from Zn, Ba, Sr, Ca, and Mg, and Rn represents one or more selected from Li, Na, K, and Cs.) And (12) The optical glass according to (10), which contains at least BaO in an amount exceeding 0%. (13) The optical glass according to (10), which contains the RO component in excess of 10% (where R represents at least one selected from Zn, Ba, Sr, Ca, and Mg, and Rn represents Li , One or more selected from Na, K, and Cs.)

  According to this aspect, the alkaline earth metal component and the alkali metal component can easily obtain the effect of improving the stability of the glass and lowering the devitrification temperature. In particular, when the alkaline earth metal is BaO, it is easy to obtain a glass stability improving effect.

(14) The optical glass according to any one of (1) to (13), which contains 0.5% or more of Li ₂ O by mass%.

According to this aspect, the stability of the optical glass is drastically improved by containing 0.5% or more of Li ₂ O.

(15) The total amount of Al ₂ O ₃ + Ga ₂ O ₃ + TiO ₂ + ZrO ₂ + Y ₂ O ₃ + Nb ₂ O ₅ + Gd ₂ O ₃ + Ta ₂ O ₃ + SnO ₂ + WO ₃ by mass% is 1% or less (1) To (14) Any one of the optical glasses.

  According to this aspect, the stability of the optical glass can be improved by including the component specified in (15).

  (16) The optical glass according to any one of (1) to (15), wherein the content of the alkaline earth metal component (BaO, CaO, MgO and SrO) is 10% or more by mass.

  According to this aspect, the stability of the optical glass can be improved by setting the content of the alkaline earth metal component to 10% or more.

(17) the lambda ₇₀ transmittance of wavelength at which 70% of the optical glass is 550nm or less (1) to (16) The optical glass according to any one.

According to this aspect, since λ _{70 of} the optical glass is 550 nm or less, the optical glass has high transparency in the visible region. Therefore, it becomes easy to use effectively as optical glass.

  (18) An optical element obtained by precision press-molding the optical glass according to any one of (1) to (17).

  According to the present invention, since the viscosity at the liquidus temperature is 0.4 Pa · s or more, it becomes easy to provide an optical element by precision press molding.

  (19) A precision press-molding preform made of the optical glass according to any one of (1) to (17), or an optical element obtained by precision press-molding the precision press-molding preform according to (20) (19) .

  According to the present invention, since the viscosity at the liquidus temperature is 0.4 Pa · s or more, it is effective as a precision press molding preform, and an optical element obtained by precision press molding the precision press molding preform is provided. It is easy to manufacture.

  The optical glass of the present invention, by adopting the above-mentioned constituent requirements, can obtain an optical glass with good preform productivity and properties of the preform itself and mold pressability, and does not contain environmentally undesirable substances, It is possible to provide an optical glass having excellent overall properties such as extremely good mold pressability.

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

[Glass component]
The composition range of each component constituting the optical glass of the present invention is described below. Each component is expressed in mass%. In addition, all the glass compositions represented by the mass% in this-application specification are represented by the mass% on the oxide basis. Here, the “oxide standard” means that the oxide, nitrate, etc. used as a raw material of the glass component of the present invention are all decomposed and changed into oxides when melted, and the mass of the generated oxide Is a composition in which each component contained in the glass is described with the total of 100% by mass.

<About essential and optional components>
Bi ₂ O ₃ is a component indispensable for achieving the object of the present invention in order to improve the stability of the glass, to increase the high refractive index and to increase the glass transition point [Tg]. However, if Bi ₂ O ₃ is contained excessively, the glass stability is impaired, and if it is too small, the object of the present invention cannot be satisfied. Therefore, the amount of Bi ₂ O ₃ is 10%, more preferably 20%, most preferably 30%, and the most preferable range is 55% as a lower limit, preferably less than 90%, more preferably less than 80%, most preferably The upper limit is less than 75%.

B ₂ O ₃ or SiO ₂ is an indispensable component as a glass-forming oxide, and is very effective in increasing the devitrification property of the glass and the viscosity with respect to the liquidus temperature. It is a component to improve. The lower limit of the total content of one or two of these components is preferably 3% or more, preferably 5% or more, or preferably 7% or more, and more preferably 10% That's it. However, in order to obtain the target refractive index of the present invention, the upper limit of the content is preferably 60%, more preferably 50%, and most preferably 40%. In this case, it is preferable that the content of B ₂ O ₃ is larger than the content of SiO ₂ . By making the content of B ₂ O ₃ greater than the content of SiO ₂ , the devitrification property of the glass and the viscosity with respect to the liquidus temperature can be improved efficiently.

Although the above two components can achieve the object of the present invention even when introduced into the glass alone, the liquidus temperature of the glass is remarkably lowered by the coexistence of B ₂ O ₃ and SiO _2. Can do. Further, when the ratio of SiO ₂ / B ₂ O ₃ is less than 1.2, the unmelted residue at the time of glass melting tends to be reduced. The ratio is preferably less than 1.1, more preferably less than 1.0, and the most preferable range is 0.3 to 0.8 to obtain a glass having a low liquidus temperature. it can.

In addition, when it is desired to more effectively obtain the target glass yield point of the present invention, the upper limit value of B ₂ O ₃ is preferably 30% or less, more preferably 25% or less, and 20%. The following is most preferable. Further, the upper limit of SiO ₂ is preferably less than 20%, more preferably 15% or less, and most preferably 10% or less. Note SiO ₂ is preferably contained more than 0%.

Al ₂ O ₃ is an effective component for improving chemical durability, but if its amount is too large, the meltability of the glass deteriorates and devitrification increases, and the glass yield point tends to increase. It is in. Therefore, the upper limit is preferably 4%, more preferably 3%, and most preferably 1%.

TiO ₂ is an effective component for increasing the refractive index of glass, contributing to high dispersion, and lowering the liquidus temperature. However, if the amount is too large, the devitrification of the glass tends to increase. is there. Therefore, it is preferably 20% or less, preferably 10% or less, and most preferably 5% or less.

Nb ₂ O ₅ is an effective component for increasing the refractive index of glass, contributing to high dispersion, and improving the devitrification property of glass, but if the amount is too large, the meltability of glass deteriorates. Tend to. Therefore, it is preferably 20% or less, preferably 15% or less, and most preferably 8% or less.

WO ₃ is an effective component for increasing the refractive index of glass, contributing to high dispersion, and lowering the yield point of glass. However, if the amount is too large, the phase separation of the glass tends to increase. Therefore, it is preferably 15% or less, preferably 10% or less, and most preferably 5% or less.

In particular, when it is desired to obtain the high refractive index and high dispersion glass targeted by the present invention, the total amount of TiO ₂ , Nb ₂ O ₅ and WO ₃ is preferably 0.1% or more, and 0.5%. It is preferable to set it to 1% or more.

Ta ₂ O ₅ is an effective component for increasing the refractive index of glass and improving chemical durability. However, if the amount of Ta ₂ O ₅ is too large, the phase separation of the glass tends to increase. It can be a component. The upper limit is preferably 15%, more preferably 10%, and most preferably 5%. More preferably not.

ZrO ₂ is an effective component for improving chemical durability. However, if the amount of ZrO ₂ is too large, the tendency of devitrification of the glass increases. Therefore, ZrO ₂ is an optional component. The upper limit is preferably 10%, more preferably 5%, and most preferably 2%. More preferably not.

The components Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , and Yb ₂ O ₃ are effective in improving the chemical durability of the glass and can be optionally added, but the amount is large. The dispersion tends to be low and the devitrification resistance tends to increase. Accordingly, the upper limit of each of these components is 10%, and the upper limit of the total amount of the above components is preferably 10%, preferably 7%, and most preferably 0.1%. . More preferably not.

In addition to Al ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , WO ₃ , TiO ₂ , Nb ₂ O ₅ , Ga ₂ O ₃ , Y ₂ O ₃ and Gd ₂ O _{3 described above} , SnO ₂ and Ga ₂ O ₃ The total amount of is preferably 1% or less for improving the stability of the glass.

  RO (R = Zn, Ba, Ca, Mg, Sr) component is effective in improving the melting property, devitrification resistance and chemical durability of glass, and any of these components is indispensable. . Also, the viscosity at the liquidus temperature is good. The total amount of these ROs (R = Zn, Ba, Ca, Mg, Sr) needs to exceed 0%, preferably 0.1% or more, more preferably 1% or more, further preferably 5% or more. The most preferable content is 10% or more.

  Of the RO components, RO components (alkaline earth metal components) excluding the case where R is Zn are particularly effective in improving the stability of the glass. Therefore, the alkaline earth metal component is particularly preferably 10% or more.

  ZnO is an effective component for improving chemical durability, but if the amount is too large, devitrification is likely to occur. Therefore, the upper limit is preferably 15%, more preferably 10%, and most preferably 5%.

  CaO is an effective component for improving the meltability of glass, but if the amount is too large, devitrification tends to occur. Therefore, the upper limit is preferably 15%, and preferably 10%.

  BaO is an effective component for improving the devitrification and coloring of the glass. However, if the amount is too large, it becomes difficult to obtain the refractive index intended by the present invention. Therefore, the upper limit is preferably 50%, more preferably 40%, and most preferably 35%. The lower limit may be 0%, but preferably exceeds 0%, more preferably 1% or more, and most preferably 3% or more.

  MgO is an effective component for highly dispersing glass, but if the amount is too large, devitrification tends to occur. Therefore, the upper limit is preferably 10%, more preferably 7%, and most preferably 5%.

  SrO is an effective component for improving the devitrification of the glass, but if the amount is too large, devitrification is likely to occur in the reheating test. Therefore, the upper limit is preferably 50%, more preferably 40%, and most preferably 30%.

The Rn ₂ O (Rn = K, Na, Li) component has the effect of lowering the meltability of the glass and the glass yield point. Therefore, the lower limit of the total amount of Rn ₂ O is preferably 0.1% or more, and more preferably 0.5% or more.

Li ₂ O is an effective component for improving the meltability of glass and preventing devitrification in the reheating test. However, if the amount is too large, it is difficult to obtain the target refractive index of the present invention. . Therefore, the upper limit value is preferably 15%, more preferably 10%, and most preferably 5%. Note that by containing Li 2 _O 0.5% or more, it is possible to remarkably improve the stability of the optical glass.

Na ₂ O improves the devitrification property of the glass and is an effective component for preventing the occurrence of devitrification in the reheating test. However, when the amount is too large, the refractive index is lowered. Therefore, the upper limit is preferably 15%, more preferably 10%, and most preferably 5%.

K ₂ O is an effective component for improving the devitrification property of the glass. However, if the amount is too large, the refractive index decreases, making it difficult to obtain the target refractive index of the present invention. Therefore, the upper limit is preferably 20%, more preferably 15%, and most preferably 10%.

The total content of RO and Rn ₂ O described above is 0.1%, more preferably 5%, most preferably in order to keep the stability at the time of glass forming, that is, the liquid phase temperature and the viscosity at the liquid phase temperature within a predetermined range. Is preferably 10% as the lower limit.

P ₂ O ₅ is a component that is effective in improving the coloring of the glass and can be optionally added. However, if the amount is too large, the phase separation tendency of the glass becomes strong. Therefore, the upper limit is preferably 10%, more preferably 5%, and most preferably 1%. More preferably not.

Sb ₂ O ₃ can be optionally added for defoaming the glass melt, but its amount is sufficiently effective at 3% or less.

GeO ₂ is a component that is effective in improving the coloring of glass and improving the high refractive index and high dispersion, but is a component that can be arbitrarily added because it is expensive. Therefore, the upper limit is preferably 20%, more preferably 10%, and most preferably 5%. More preferably not.

  F has an effect of increasing the meltability of the glass, but is a component that can be optionally added to rapidly reduce the refractive index. Therefore, the upper limit is preferably 5%, more preferably 3%, and most preferably 1%. More preferably not.

<About ingredients that should not be included>
Other components can be added as necessary within the range not impairing the properties of the glass of the present invention. However, even if each transition metal component such as V, Cr, Mn, Fe, Co, Ni, Cu, Ag and Mo excluding Ti is contained alone or in combination with a small amount, the glass is colored and visible. Causes absorption at specific wavelengths in the region. Therefore, it is preferable that the optical glass using a wavelength in the visible region does not contain substantially.

  The Th component can be included for the purpose of increasing the refractive index or improving the stability as glass, and the Cd and Tl components can be included for the purpose of reducing the glass transition point [Tg]. However, each component of Pb, Th, Cd, Tl, and Os tends to be refrained from being used as a harmful chemical material in recent years, so that not only the glass manufacturing process but also the processing process and the disposal after commercialization. Environmental measures are required. Therefore, it is preferable not to include substantially when the influence on the environment is emphasized.

  Since the lead component needs to take measures for environmental measures when manufacturing, processing, and disposing of the glass, the cost becomes high and the glass of the present invention should not contain the lead component.

As ₂ O ₃ is a component that is used to improve bubble breakage (defoaming property) when melting glass. However, when glass is manufactured, processed, and disposed of, environmental measures are taken. Since it is necessary to take it, it is not preferable to include As ₂ O ₃ in the glass of the present invention.

In the present invention, each component is preferably contained in the following range in terms of mass%.
Bi ₂ O ₃ : less than 10 to 90%, and / or SiO ₂ : more than 0% and less than 20%, and / or BaO: 0 to 50%, and / or B ₂ O ₃ : 0 to 30%, and / or or Al ₂ O _3: 0~4%, and / or TiO _2: 0~20%, and / or Nb ₂ O _{5: 0~20%,} and / or WO _3: 0~15%, and / or Ta ₂ O _5: 0~15%, and / or ZrO _2: 0~10%, and / or ZnO: 0 to 15%, and / or MgO: 0%, and / or CaO: 0 to 15%, and / or SrO: 0 to 50%, and / or Li ₂ O: 0~15%, and / or Na ₂ O: 0~15%, and / or K ₂ O: 0~20%, and / or Y ₂ O ₃ : 0-10%, and / or La ₂ O _3: 0 to 10%, and / or Gd ₂ O _3: 0 to 10%, and / or Yb ₂ O _3: 0 to 10%, and / or P ₂ O _5: 0 to 10%, and / or Sb ₂ O _3: 0 to 3%, and / or GeO _2: 0 to 20% and / or F: 0 to 5%

  The optical glass of the present invention has a high refractive index and high dispersion, and can easily obtain a yield point [At] of 600 ° C. or lower. A more preferable range of At is 530 ° C. or lower, and further preferably 500 ° C. or lower.

  The optical glass of the present invention can have a high refractive index and high dispersion, and a viscosity at a liquidus temperature of 0.4 Pa · s or more. Furthermore, the preferable range of the viscosity at the liquidus temperature is 0.5 Pa · s or more, more preferably 0.6 Pa · s or more, and most preferably 1.0 Pa · s or more.

  The optical glass of the present invention can be obtained with a liquidus temperature of 950 ° C. or lower. The preferable range of the liquidus temperature is 900 ° C. or lower, more preferably 800 ° C. or lower.

  The optical glass of the present invention can have an Abbe number [νd] of 10 or more. The preferable range of the Abbe number is 10 or more, more preferably 15 or more.

The optical glass of the present invention can be obtained with a glass transmittance λ ₇₀ of 550 nm or less. Furthermore, the preferable range of the transmittance λ ₇₀ of the glass is 500 nm or less, more preferably 485 nm or less.

[Production method]
The optical glass of the present invention is not particularly limited as long as it is a method for producing a normal optical glass. For example, it can be produced by the following method. A predetermined amount of each starting material (oxide, carbonate, nitrate, phosphate, sulfate, fluoride salt, etc.) is weighed and mixed uniformly. The mixed raw material is put into a quartz crucible or an alumina crucible, and after coarse melting, it is put into a gold crucible, platinum crucible, platinum alloy crucible or iridium crucible and melted at 850 to 1250 ° C. for 1 to 10 hours. Then, after stirring and homogenizing, it is lowered to an appropriate temperature and cast into a mold or the like to produce glass.

  The optical glass of the present invention is typically used for lens, prism and mirror applications. Further, in the optical element manufacturing method of the present invention, a molten glass is dropped from an outlet of an outflow pipe such as platinum to produce a typically spherical preform. In the preform, an optical element having a desired shape is manufactured by a precision press molding method.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example and a comparative example, this invention is not limited to a following example.

  The raw materials were weighed so as to have a total amount of 400 g with the compositions shown in Tables 1 to 6 and mixed uniformly. After melting at 950 to 1050 ° C. for 2 to 3 hours using quartz and platinum, the temperature was lowered to 800 to 900 ° C., and further kept for about 1 hour, and then cast into a mold to produce glass. The obtained glass and properties are shown in Tables 1 to 6. Further, Comparative Examples 1 to 7 having the compositions shown in Table 7 were also produced in the same manner as in the above Examples.

  For the optical glasses of Examples 1 to 63 and Comparative Examples 1 to 7, the refractive index [nd], the Abbe number [νd], the liquidus temperature, the viscosity at the liquidus temperature, the glass yield point [At], and the transmittance are measured. went.

  The refractive index [nd] and the Abbe number [νd] were measured for the glass obtained at a slow cooling rate of −25 ° C./Hr.

  The glass yield point [At] was measured with a thermal expansion measuring device at a heating rate of 8 ° C./min.

  About the transmittance | permeability measurement, it carried out according to Japan Optical Glass Industry Association standard JOGIS02. In the present invention, the transmittance is shown not the coloring degree. Specifically, a face-to-face parallel polished product having a thickness of 10 ± 0.1 mm was measured for a spectral transmittance of 200 to 800 nm in accordance with JISZ8722. The wavelength when the transmittance is 70% is shown, and the first decimal place is rounded off.

  About liquid phase temperature, it hold | maintained for 30 minutes in the devitrification test furnace with the temperature gradient of 400 to 1100 degreeC, the presence or absence of the crystal | crystallization was observed with the microscope of 80 times magnification, and liquid phase temperature was measured.

  About viscosity, viscosity (eta) (Pa * s) was calculated | required with the ball pulling-up type viscometer (Model number BVM-13LH by a limited company Opt company company), and the viscosity in liquidus temperature was measured.

  As can be seen from Tables 1 to 6, all of the optical glasses of Examples 1 to 63 of the present invention have an optical constant having a refractive index [nd] of 1.70 or more and an Abbe number [νd] of 10 or more. In addition, since the viscosity at the liquidus temperature is 0.4 Pa · s, the preform productivity is good and suitable for mold press molding.

  On the other hand, Comparative Example 1 has a low refractive index, does not have an optical constant within the specific range, and has a relatively high yield point.

Comparative Examples 2 to 5 are compositions containing a large amount of ZrO ₂ , Ta ₂ O ₅ , WO ₃ , and Al ₂ O ₃ , but all have a high tendency to devitrification and low viscosity at the liquidus temperature. Therefore, it is not possible to obtain a glass suitable for the mold press molding intended by the present invention.

  In Comparative Example 6, the viscosity with respect to the liquidus temperature is low, and a glass suitable for mold press molding intended by the present invention cannot be obtained.

  Moreover, the comparative example 7 does not vitrify, and the glass suitable for the mold press molding which this invention aims at cannot be obtained.

Claims (20)

Containing 10% or more and less than 90% Bi ₂ O ₃ by mass%,
An optical constant having a refractive index [nd] of 1.70 or more and an Abbe number [νd] of 10 or more;
An optical glass having a viscosity at a liquidus temperature of 0.4 Pa · s or more. Containing 10% or more and less than 75% Bi ₂ O ₃ by mass%,
Abbe number [νd] has an optical constant of 15 or more,
The optical glass according to claim 1, which has a viscosity at a liquidus temperature of 1.0 Pa · s or more. The optical glass of claim 1, wherein the _Bi 2 _{O 3} containing 80% or more and less than 55% by mass%.   The optical glass according to any one of claims 1 to 3, wherein a yield point [At] of the glass in the optical glass is 600 ° C or lower.   The optical glass according to any one of claims 1 to 4, wherein the liquidus temperature is 950 ° C or lower.   The optical glass according to any one of claims 1 to 4, wherein the liquidus temperature is 800 ° C or lower. By mass%, SiO ₂ content _<B 2 _{O 3} amount, _and, SiO _{2 +} B _{2 O 3} of the total amount of 3% to 60% or less containing claims 1 to 6 the optical glass according to any one. The optical glass according to claim 7, wherein the ratio of SiO ₂ / B ₂ O ₃ is 0.3 to 0.8. The optical glass according to claim 7, comprising a total amount of SiO ₂ + B ₂ O ₃ of 5% to 60%. The optical glass according to any one of claims 1 to 9, wherein the optical glass contains 0.1% or more of RO and Rn ₂ O by mass%.
(However, R represents one or more selected from Zn, Ba, Sr, Ca, and Mg, and Rn represents one or more selected from Li, Na, K, and Cs.) The optical glass of Claim 10 which contains the said RO component exceeding 0%.
(However, R represents one or more selected from Zn, Ba, Sr, Ca, and Mg, and Rn represents one or more selected from Li, Na, K, and Cs.)   The optical glass according to claim 10 containing at least BaO in an amount of more than 0%. The optical glass according to claim 10, containing more than 10% of the RO component.
(However, R represents one or more selected from Zn, Ba, Sr, Ca, and Mg, and Rn represents one or more selected from Li, Na, K, and Cs.) The optical glass according to claim 1, which contains 0.5% or more of Li ₂ O by mass%. The total amount of Al ₂ O ₃ + Ga ₂ O ₃ + TiO ₂ + ZrO ₂ + Y ₂ O ₃ + Nb ₂ O ₅ + Gd ₂ O ₃ + Ta ₂ O ₃ + SnO ₂ + WO ₃ by mass% is 1% or less, any one of claims 1 to 14 Or an optical glass.   The optical glass according to any one of claims 1 to 15, wherein the content of the alkaline earth metal component (BaO, CaO, MgO and SrO) is 10% or more by mass. The optical glass according to any one of claims 1 to 16, wherein λ ₇₀ which is a wavelength at which the transmittance of the optical glass is 70% is 550 nm or less.   An optical element formed by precision press-molding the optical glass according to claim 1.   A precision press-molding preform comprising the optical glass according to claim 1.   An optical element obtained by precision press-molding the precision press-molding preform according to claim 19.