JP5601557B2 - Optical glass - Google Patents

Description

  The present invention relates to an optical glass, and more particularly to an optical glass for mold press molding.

Higher refractive index and lower dispersion are often required as optical characteristics of glass used in optical lenses such as optical pickup lenses for CD, MD, DVD and other various optical disk systems, video cameras and photographing lenses for general cameras. ing. For these applications, B ₂ O ₃ —ZnO—La ₂ O ₃ glass having a refractive index (nd) of 1.78 to 1.88 and an Abbe number (νd) of 35 to 45 is conventionally used. . (For example, Patent Document 1)
JP 2002-362938

  As a method of manufacturing an optical pickup lens or a photographic lens, once a molten glass is formed into an ingot, the glass material cut out to an appropriate size is polished and then mold pressed, and the molten glass is dropped from the tip of the nozzle. Then, a method is known in which a glass material formed by droplet forming, that is, droplet forming, is molded or polished without being polished.

However, B ₂ O ₃ —ZnO—La ₂ O ₃ glass has a problem of low workability because it has high devitrification properties and the liquidus temperature rises. That is, since B ₂ O ₃ —ZnO—La ₂ O ₃ glass has a strong tendency to devitrify, mass production is poor when an ingot is produced by rapidly casting molten glass. Further, in droplet forming, molten glass is dropped from the tip of the nozzle, so that the molding viscosity of glass capable of forming droplets has a lower limit of about 10 ^0.5 poise. However, B ₂ O ₃ —ZnO—La ₂ O ₃ glass is devitrified at a low viscosity of 10 ^0.5 poise or less, and is not suitable for droplet forming. If the liquid is dropped at a viscosity of 10 ^0.5 poises or less, the glass flows out in a continuous flow, so that liquid droplets cannot be formed.

Although a devitrification resistance improving composition using a B ₂ O ₃ —La ₂ O ₃ —Y ₂ O ₃ composition has been studied, the refractive index is lowered in this system.

An object of the present invention is to provide an optical glass having a refractive index (nd) of 1.78 to 1.88 and an Abbe number (νd) of 35 to 42.5 and having excellent devitrification resistance.

As a result of the inventor's investigation, it was found that the main cause of devitrification in the B ₂ O ₃ —ZnO—La ₂ O ₃ glass is that La ₂ O ₃ is contained in a large amount. . La ₂ O ₃ is a component for increasing the refractive index, but if it is contained in a large amount, it tends to increase the devitrification property. If the devitrification property of the glass is increased, crystals precipitate during the production. This leads to product quality degradation. Therefore, the present inventor has found that the above problem can be achieved by substituting part of La ₂ O ₃ of the B ₂ O ₃ —ZnO—La ₂ O ₃ glass with Gd ₂ O _3. It came to propose an invention.

That is, the optical glass of the present invention has a refractive index (nd) of 1.78 to 1.88, an Abbe number (νd) of 35 to 42.5, and a temperature at ΔT = (10 ^0.5 poise-liquidus temperature). ) Is made of B ₂ O ₃ —ZnO—La ₂ O ₃ —Gd ₂ O ₃ glass having a temperature of 20 ° C. or higher, and B ₂ O ₃ 13.7 to 45% and La ₂ O ₃ 5 to 25% by mass%. ZnO 10 to 45%, Gd ₂ O ₃ 0.5 to 21 %, SiO ₂ 0 to 10 %, Li ₂ O 0 to 10%, Ta ₂ O ₅ 0.5 to 20%, ZrO _{2 0 to} 15% Y ₂ O ₃ 0 to 3.8 %, WO _{30 to} 4.5 %, Nb ₂ O ₅ 0.5 to 15%, and Sb ₂ O ₃ 1% or less.

  The refractive index (nd) in the present invention is a measured value for the d-line (587.6 nm) of a helium lamp. Abbe number (νd) is obtained by using the refractive index of d-line and the refractive index of F-line (486.1 nm) of hydrogen lamp, and C-line (656.3 nm) of hydrogen lamp, and Abbe number (νd) = {( nd-1) / (nF-nC)}.

ΔT is a temperature range obtained as follows. First, a temperature corresponding to 10 ^0.5 poise is obtained by a platinum ball pulling method. The liquid phase temperature is crushed and classified into a powder form of 297 to 500 μm, put into a platinum boat, kept in an electric furnace having a temperature gradient for 24 hours, and then allowed to cool in air. It is the temperature specified by calculating | requiring the deposition position of devitrification with an optical microscope. The difference between the temperature corresponding to 10 ^0.5 poise thus obtained and the liquidus temperature is taken as ΔT.

In the optical glass of the present invention, the contents of La ₂ O ₃ , Gd ₂ O ₃ and ZnO are 0.1 ≦ (La ₂ O ₃ + Gd ₂ O ₃ ) /ZnO≦5.0 on a mass% basis. It is preferable to have a relationship.

  The optical glass is preferably used for mold press molding.

The optical glass of the present invention has a refractive index of 1.78 to 1.88 (used for optical lenses such as optical pickup lenses for various optical disk systems such as CD, MD, DVD, video cameras and general cameras). nd) and an Abbe number (νd) of 35 to 42.5 . In addition, the working temperature range is wide, the preform glass is excellent in mass productivity, and the weather resistance is good, so that the physical properties are not deteriorated and the surface is not deteriorated during the production process or use of the product.

  Further, if a composition having a low basicity is selected, there is no fusion with a mold during pressing, and mass productivity is very good. Furthermore, it is possible to produce a glass with a low softening point. The lower the softening point, the harder the glass component is volatilized, and the lowering of molding accuracy and the deterioration and contamination of the mold do not occur.

  Therefore, it is suitable as an optical glass for mold press molding.

The optical glass of the present invention has a refractive index (nd) of 1.78 to 1.88, an Abbe number (νd) of 35 to 42.5 , and ΔT = (temperature at 10 ^0.5 poise−liquidus temperature) of 20 ° C. has the above described _{B 2 O 3 -ZnO-La 2} O 3 -Gd 2 O 3 based glass. The reason why various characteristics are limited as described above in the present invention will be described.

  First, regarding the refractive index, for example, when glass is used as a lens, the higher the refractive index, the thinner the lens can be, which is advantageous for downsizing the optical device. The refractive index of the optical glass of the present invention is 1.78 or more, preferably 1.785 or more, more preferably 1.79 or more. The upper limit of the refractive index is 1.88 or less, preferably 1.87 or less in consideration of the stability of the glass.

The optical glass of the present invention has an Abbe number of 35 or more, particularly preferably 37 or more, and more preferably 39 or more. However Abbe number is preferred because the wavelength dispersion of the higher refractive index becomes smaller, a point or we 4 2.5 The following stability maintenance and glass with a high refractive index.

If ΔT = (temperature at 10 ^0.5 poise−liquidus temperature) is 20 ° C. or higher, particularly 30 ° C. or higher, and further 40 ° C. or higher, a sufficient working temperature can be secured. Can be manufactured with good yield. ΔT is preferably as large as possible, and the upper limit of the ΔT is not particularly limited, but in practice, it is preferably 300 ° C. or less, particularly 200 ° C. or less. The temperature corresponding to 10 ^0.5 poise corresponds to the forming temperature when the droplet forming method is adopted. Since glass is most easily devitrified when droplet forming is performed, if the difference ΔT between the temperature at 10 ^0.5 poise and the liquidus temperature is 20 ° C. or more, all forming including the droplet forming method is performed. In the method, molding can be performed without causing devitrification.

The composition of the B ₂ O ₃ —ZnO—La ₂ O ₃ —Gd ₂ O ₃ glass is not particularly limited as long as it satisfies all the above characteristics. In order to obtain B ₂ O ₃ —ZnO—La ₂ O ₃ —Gd ₂ O ₃ glass having the above characteristics, an appropriate composition may be selected in consideration of the following points.

In order to increase the refractive index (nd) in the B ₂ O ₃ —ZnO—La ₂ O ₃ —Gd ₂ O ₃ glass, the content of ZnO, La ₂ O _3, or Gd ₂ O ₃ may be increased. In addition to these components, the refractive index (nd) can be increased by adding Ta ₂ O ₅ , ZrO ₂ , Y ₂ O ₃ , WO ₃ , Nb ₂ O ₅ or the like. In order to increase the Abbe number (νd), the B ₂ O ₃ content may be increased. In order to increase the refractive index (nd) without reducing the Abbe number (νd), La ₂ O ₃ or Y ₂ O ₃ may be used as a refractive index increasing component. Increasing ΔT means decreasing the devitrification tendency of the glass. In the B ₂ O ₃ —ZnO—La ₂ O ₃ —Gd ₂ O ₃ glass, B ₂ O ₃ and it may be increasing the content of ZnO and Gd ₂ O _3. Besides these components, ΔT can be increased by adding SiO ₂ , Ta ₂ O ₅ , ZrO ₂ , WO ₃ or the like.

  In the optical glass of the present invention, the basicity of the glass is preferably 11 or less (preferably 9.5 or less). If the basicity is low, it is possible to prevent the glass and the press mold from being fused at the time of molding by the mold press. In the present invention, the basicity is defined as (total number of moles of oxygen atoms / total number of positive field strength) × 100. The field strength (hereinafter referred to as FS) in the equation is obtained by the following equation.

F. S. = Z / r ²
Z represents an ionic valence, and r represents an ionic radius. The coordination number and ionic valence of the elements in the glass change depending on the glass composition, and the numerical value of the ion radius changes accordingly. Therefore, in calculating an accurate basicity, it is desirable to appropriately select the ionic valence and ionic radius of each element for each composition system. The numerical values of Z and r may be determined by referring to “Chemical Handbook Basic Edition 2nd Edition (1975 Maruzen Co., Ltd.)”. In the present invention, it is appropriate to use the values shown in Table 1 determined with reference to this document.

  The basicity of the glass is an index indicating how much oxygen electrons in the glass are attracted to the cations in the glass. In a glass having a high basicity, the attraction of oxygen electrons by cations in the glass is weak. Therefore, when a glass having a high basicity is in contact with a cation (mold component) that has a strong tendency to require electrons, a cation from the mold tends to enter the glass compared to a glass having a low basicity. . When the cation which is a mold component penetrates (diffuses) into the glass, the mold component concentration in the glass phase near the interface increases. Thereby, since the difference in composition between the glass phase and the mold phase is reduced, the affinity between the two is increased, and the glass is easily wetted by the mold. It is considered that the glass and the mold are fused by such a mechanism. Therefore, as the basicity is lowered, the mold components are less likely to enter the glass, and the glass and the mold are not fused.

  Specifically, if the basicity of the glass is 11 or less, preferably 9.5 or less, it is considered that fusion does not occur. If the basicity of the glass exceeds 9.5, a tendency to fuse with the mold appears, and if it exceeds 11, the glass and the mold are fused to deteriorate the surface accuracy of the product, and the mass productivity is remarkably deteriorated. .

The optical glass of the present invention contains, in mass%, B ₂ O ₃ 13.7 to 45%, La ₂ O ₃ 5 to 25%, ZnO 10 to 45%, Gd ₂ O ₃ 0.5 to 21 %. . Within the above composition range, the refractive index (nd) is 1.78 to 1.88, the Abbe number (νd) is 35 to 42.5, and ΔT = (temperature at 10 ^0.5 poise−liquidus temperature) is B ₂ O ₃ —ZnO—La ₂ O ₃ —Gd ₂ O ₃ -based glass having a temperature of 20 ° C. or higher can be easily obtained. It is also possible to produce a glass having a basicity of 11 or less.

Furthermore, in addition to the above composition, by mass%, SiO ₂ 0 to 10 %, Li ₂ O 0 to 10%, Ta ₂ O ₅ 0.5 to 20%, ZrO ₂ 0 to 15%, Y ₂ O ₃ 0 to 3 _{.8%, WO 3 0~ 4.5%} , Nb 2 O 5 containing 0.5 to 15%. By introducing these components, a glass having a desired refractive index (nd), Abbe number (νd), ΔT, and basicity can be easily produced. Moreover, among the above compositions, Li ₂ O tends to increase devitrification and is a component that is difficult to add to B ₂ O ₃ —ZnO—La ₂ O ₃ -based glass, but the glass of the present invention is La ₂ O _3. Therefore, a relatively large amount of Li ₂ O can be contained, and a glass having a low softening point can be designed.

  The reason for limiting the composition range as described above will be described below.

B ₂ O ₃ is a skeletal component of glass and is effective in improving devitrification resistance. Moreover, it is a component that increases the Abbe number and can lower the softening point. B ₂ O ₃ also has an effect of lowering the basicity of the glass, and is effective in preventing fusion between the glass and the mold in mold press molding. The content thereof is 13.7 to 45%, preferably 13.7 to 29%, more preferably 13.7 to 24%, and further preferably 13.7 to 21%. If B ₂ O ₃ exceeds 45%, the chemical durability of the glass is lowered and the weather resistance is remarkably deteriorated. If it is less than 13.7 %, the Abbe number among the optical constants cannot be sufficiently secured, the devitrification resistance is lowered, and it becomes difficult to obtain glass stably.

La ₂ O ₃ is a component for ensuring a sufficient working temperature range, and has an effect of increasing the refractive index without reducing the Abbe number. Furthermore, there is an effect of suppressing an increase in softening point and improving weather resistance. However, if a large amount is added in order to obtain a high refractive index, devitrification increases, so that it is necessary to partially replace it with Gd ₂ O ₃ or the like. The content of La ₂ O ₃ is 5 to 25%, preferably 7 to 24.5%, more preferably 9 to 24.2%. When La ₂ O ₃ exceeds 25%, devitrification is increased and the liquidus temperature is increased, so that workability is greatly reduced. If it is less than 5%, the refractive index decreases and the weather resistance deteriorates.

ZnO is a component that can increase the refractive index and chemical durability and lower the softening point. Further, glass containing a large amount of B ₂ O ₃ and La ₂ O ₃ tends to devitrify, but ZnO has an effect of suppressing this. The content is 10 to 45%, preferably 15.5 to 30%, more preferably 16 to 21%, and still more preferably 16 to 20%. If ZnO exceeds 45%, the phase separation tendency of the glass becomes strong, and it becomes difficult to obtain a homogeneous glass. If it is less than 10%, the refractive index is lowered, the devitrification suppressing effect cannot be obtained, the liquidus temperature rises, and the working temperature range cannot be sufficiently secured.

Since Gd ₂ O ₃ is a component that increases the refractive index, it is not necessary to contain a large amount of La ₂ O _3, which is effective in improving devitrification resistance. Gd ₂ O ₃ also has an effect of improving devitrification resistance, and is a component that can expand the working temperature range. However, if it is contained in a large amount, the phase separation tendency of the glass becomes strong, and a homogeneous glass is obtained. It becomes difficult, that is, the working temperature range is reduced. The content of Gd ₂ O ₃ is 0.5 to 21 %, preferably 1 to 21 %, 1 to 20%, 1 to 15%, 2 to 10%, more preferably 3 to 9.5%.

The present invention also aims to maintain high devitrification resistance and to limit the contents of La ₂ O ₃ and Gd ₂ O ₃ for the purpose of ensuring a wide working temperature range, while ensuring a high refractive index. And contains a large amount of ZnO. In order to achieve both high devitrification resistance and a high refractive index, it is important to keep the contents of La ₂ O ₃ , Gd ₂ O ₃ and ZnO in an appropriate balance. From this point of view, the value of (La ₂ O ₃ + Gd ₂ O ₃ ) / ZnO on a mass% basis is 0.1 to 5.0, particularly 0.2 to 4.0, more preferably 0.3 to 3.0, It is preferable to adjust so that it may exist in the range of 0.5-2.5. By setting this value to 0.1 to 5.0, high devitrification resistance can be maintained without lowering the refractive index. When this ratio increases, the devitrification resistance decreases, and when it decreases, the refractive index tends to decrease.

SiO ₂ is a component constituting the skeleton of glass, and has the effect of improving devitrification resistance and expanding the working range. It also has the effect of improving weather resistance. Its content is 0 to 10 %, preferably 1 to 10 %, more preferably 2 to 10 %. If SiO ₂ exceeds 10 %, the refractive index may be remarkably lowered or the softening point may exceed 650 ° C.

Li ₂ O is a component for lowering the softening point, and the total amount thereof is 0 to 10%, preferably 0.1 to 5%, more preferably 0.5 to 4%. If Li ₂ O exceeds 10%, the liquidus temperature is remarkably increased, the working temperature range is narrowed, and the mass productivity is adversely affected. In addition, the weather resistance is significantly deteriorated.

Ta ₂ O ₅ has the effect of increasing the refractive index, chemical durability and devitrification resistance, and its content is 0.5 to 20%, particularly 0.5 to 15%, and further 1 to 10%. It is preferable. If Ta ₂ O ₅ exceeds 20%, the Abbe number decreases, making it difficult to obtain desired optical characteristics and increasing the cost.

ZrO ₂ is a component that increases the refractive index. Moreover, since glass is formed as an intermediate oxide, there is an effect of improving devitrification resistance and chemical durability. However, when the content of ZrO ₂ increases, the softening point increases and the press formability deteriorates. The content of ZrO ₂ is 0 to 15%, preferably 0.5 to 10%, more preferably 1 to 8%.

Y ₂ O ₃ is a component that increases the refractive index without decreasing the Abbe number. For this reason, 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 content is preferably 0 to 3.8 %, particularly 1 to 3.8 %, and more preferably 2 to 3.8 %. When Y ₂ O ₃ exceeds 3.8 %, devitrification becomes high and the working temperature range becomes narrow.

WO ₃ has the effect of increasing the refractive index. Further, since glass is formed as an intermediate oxide, there is an effect of improving devitrification resistance. Further, the coloring in the ultraviolet region is smaller than that of TiO ₂ . The content of WO ₃ is 0 to 4.5 %, preferably 0.5 to 4%, more preferably 1 to 3.5%. If WO ₃ exceeds 5%, the Abbe number decreases, making it difficult to obtain desired optical characteristics. Excessive addition causes a decrease in ultraviolet transmittance, increases the affinity with a press die, and causes fusion with the die during pressing.

The Nb ₂ O ₅ content, which is a component that increases the refractive index, is 0.5 to 15%, preferably 0.5 to 10%, and more preferably 1 to 8%. If Nb ₂ O ₅ exceeds 15%, the Abbe number decreases, making it difficult to obtain desired optical characteristics.

In addition to the above, various components can be added. For example, Sb ₂ O ₃ can be added as a fining agent. Note To avoid excessive coloring to the glass, the content of Sb ₂ O ₃ is preferably 1% or less.

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

  First, a glass raw material prepared to have a desired composition is melted to obtain a molten glass. Next, molten glass is dropped from the nozzle tip and formed into droplets (droplet forming) to obtain a glass material. Further, after the molded glass material is polished or molded without being polished, a lens having a predetermined shape is obtained.

  Instead of performing droplet forming, it is also possible to adopt a method in which molten glass is formed into an ingot, the glass material cut out to an appropriate size is polished, and then mold pressing is performed.

  Hereinafter, the present invention will be described based on examples.

Tables 2 to 6 show examples of the present invention (sample Nos . 3 , 5 to 16 , 18 to 28 , 30 to 34, 37 ) , reference examples (samples No. 1, 2 , 4, 17, 29, 35, 36, 38-42 ) and a comparative example (sample No. 43), 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. for 2 hours using a platinum crucible. After melting, the melt was poured onto a carbon plate, and after annealing, a sample suitable for each measurement was produced.

The obtained sample was measured for refractive index (nd), Abbe number (νd), softening point T _S , droplet forming temperature T _W , liquidus temperature T _L , and working temperature range ΔT. The basicity was calculated. The results are shown in each table.

As is apparent from the table, the examples and reference examples of the present invention are No. Each sample of 1-42 has a refractive index (nd) of 1.7806 to 1.8794, an Abbe number (νd) of 36.8 to 44.7, and a softening point Ts of 675 ° C. or lower. Further, the working temperature range ΔT is 24 ° C. or more, and the workability is excellent. Further, the basicity is 10.99 or less, and it is considered that fusion with the mold hardly occurs. On the other hand, No. which is a comparative example. No. 43 has a working temperature range ΔT of 13 ° C. of 20 ° C. or less, and is inferior in workability.

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

  The Abbe number (νd) is the refractive index 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 the Abbe number (νd) = It was calculated from the {(nd-1) / (nF-nC)} formula.

The softening point T _S was measured by a fiber elongation method based on Japanese Industrial Standard R-3104.

The working temperature range ΔT was determined as follows. The molding temperature T _W is measured by a platinum ball pulling method First, determine the temperature corresponding to 10 ^0.5 poise, it was forming temperature Tw. The sample is pulverized and classified so that the liquid phase temperature T _L is in a powder form of 297 to 500 μm, then placed in a platinum boat, held in an electric furnace having a temperature gradient for 24 hours, and then allowed to cool in air. The measurement was performed by determining the deposition position of devitrification with an optical microscope. The difference between the thus obtained molding temperature T _W and the liquidus temperature T _L and the working temperature range △ T.

  The basicity is calculated based on the formula: (total number of moles of oxygen atoms / total number of cation field strength) × 100. The field strength (hereinafter referred to as FS) in the formula is obtained by the following formula.

F. S. = Z / r ²
Z represents an ionic valence, and r represents an ionic radius. Table 1 was referred to for the values of Z and r in this example.

  The optical glass of the present invention can be suitably used as an optical glass for mold press molding, but is not limited to this. For example, as a lens cap assembled with a spherical lens, a polished lens, or a metal part. It can be used for applications such as optical communication.

Claims (3)

B ₂ O having a refractive index (nd) of 1.78 to 1.88, an Abbe number (νd) of 35 to 42.5, and ΔT = (temperature at 10 ^0.5 poise−liquidus temperature) of 20 ° C. or more. ₃ consists _{-ZnO-La 2 O 3 -Gd 2} O 3 based glass, in terms of _{mass%, B 2 O 3 13.7~45%} , La 2 O 3 5~25%, ZnO 10~45%, Gd 2 _{O 3 0.5~ 21%, SiO 2} 0~ 10%, Li 2 O 0~10%, Ta 2 O 5 0.5 ~20%, ZrO 2 0~15%, Y 2 O 3 0~ 3. An optical glass containing 8 %, WO _{30 to} 4.5 %, Nb ₂ O ₅ 0.5 to 15%, and Sb ₂ O ₃ 1% or less. The contents of La ₂ O ₃ , Gd ₂ O ₃ and ZnO are in a relationship of 0.1 ≦ (La ₂ O ₃ + Gd ₂ O ₃ ) /ZnO≦5.0 on a mass% basis. The optical glass according to claim 1.   The optical glass according to claim 1, wherein the optical glass is used for mold press molding.