JP2011225418A - Optical glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical glass in which cloudiness is hard to be generated on the surface of lenses, and which has excellent mass productivity.SOLUTION: The optical glass comprises, by mass, 30 to 70% SiO, 4 to 20% (not including 4%) AlO, 15 to 60% BO; and 0.001 to 0.1% (not including 0.1%) SbO.

Description

  The present invention relates to an optical glass.

Optical lenses for CD, MD, DVD and other various optical disk systems, imaging lenses for digital cameras, video cameras, camera-equipped mobile phones, and transmission / reception lenses used for optical communications include aspherical lenses. Widely used. Various glass has been proposed as a glass material for lenses. For example, SiO ₂ —B ₂ O ₃ as shown in Patent Documents 1 to 6 as an optical glass having a refractive index of 1.45 to 2.2 and an Abbe number of 30 or more. Based glass has been proposed.

  As a method for manufacturing this type of lens, for example, the following method is known.

  First, molten glass is dropped from the tip of a nozzle to produce droplet glass (droplet forming), and necessary processing such as grinding, polishing, and washing is performed to produce preform glass. Alternatively, a molten glass is rapidly cast to produce a glass ingot, which is then ground, polished and washed to produce a preform glass. Subsequently, the preform glass is heated and softened, pressure-molded with a mold having a highly accurate molding surface, and the surface shape of the mold is transferred to the glass to produce a lens.

Such a molding method is generally called a mold press molding method and has been widely adopted in recent years as a method suitable for mass production.
JP 2007-169086 A JP 2006-306635 A JP 2004-292306 A JP 2003-176151 A JP-A-7-149536 JP 2004-137145 A

  When preform glass is molded and press-molded, spiders may be generated on the glass surface. Spiders on the lens surface can be a fatal defect because they block and scatter light transmitted through the lens.

  An object of the present invention is to provide an optical glass which is less likely to generate spider on the lens surface and has excellent mass productivity.

As a result of various tests, the present inventor has found that when a relatively high-viscosity preform glass is pressed, spiders are easily generated. Upon further investigation, it was found that the cause of spiders was caused by Sb ₂ O ₃ contained in the glass as a fining agent. On the other hand, if Sb ₂ O ₃ is completely reduced, there is a concern about deterioration of the clarity of the glass. Therefore, the present inventor has found a composition range in which both spider prevention and clarity can be achieved.

That is, the optical glass of the present invention is, in mass%, SiO ₂ 30 to 70%, Al ₂ O ₃ 4 to 20% (excluding 4%), B ₂ O ₃ 15 to 60%, Sb ₂ O _3. It is characterized by containing 0.001% to 0.1% (excluding 0.1%).

In the present invention, it is preferable to further contain SO ₃ 0.005 to 0.5 wt%.

  According to the said structure, since the clarity of glass is improved, higher foam quality can be achieved.

  In the present invention, the basicity of the glass defined by (total number of moles of oxygen atoms / total field strength of cations) × 100 is preferably 11 or less. In the present invention, “Field Strength” (hereinafter referred to as “FS”) is obtained by the following Equation 1.

Formula 1 F. S. = Z / r ²
Z represents an ionic valence, and r represents an ionic radius. Note that the values of Z and r in the present invention are the values in Table 1 (values described in “Science Manual Basic Bias Revised 2nd Edition (published by Maruzen Co., Ltd., 1975)”).

According to the above arrangement, the smaller the basicity is an index indicating reduction of the glass, it is possible to effectively suppress fogging during the press due to the Sb ₂ O _3.

  In the present invention, it is preferably for mold press molding.

  According to the said structure, the effect of this invention can be enjoyed exactly.

  The optical lens of the present invention is made of the above glass.

  The method for producing optical glass of the present invention is characterized by using sulfate as a fining agent.

  According to the said structure, the clarity of glass improves and the optical glass excellent in the bubble quality can be manufactured.

  In the method of the present invention, the amount of sulfate added is preferably 5% by mass or less with respect to 100% by mass of the glass raw material.

By limiting the content of Sb ₂ O _{3 in} the optical glass of the present invention, it is possible to obtain a glass that does not generate spider on the glass surface during pressing. For this reason, high surface accuracy of the lens surface is maintained, and the glass is excellent in mass productivity. Further, by containing a small amount of Sb ₂ O ₃ , even high-viscosity glass can be clarified without unnecessarily high-temperature and long-time glass melting.

  Therefore, the optical glass of the present invention includes optical pickup lenses for CD, MD, DVD and other various optical disc systems, imaging lenses for digital cameras, video cameras, camera-equipped mobile phones, transmission / reception lenses used for optical communication, etc. It is suitable as a glass material for optical lenses obtained by mold press molding.

The glass of the present invention is 30% by mass of SiO ₂ , 15 to 60% of B ₂ O ₃ , 4 to 20% of Al ₂ O ₃ (excluding 4%), Sb ₂ O ₃ 0.001 by mass%. -0.1% (excluding 0.1%).

  If the composition is in the above range, a glass having an optical constant of refractive index nd of 1.45 to 2.2, preferably 1.50 to 1.8, Abbe number of 30 or more, preferably 40 or more is easily designed. can do.

The optical glass such as _{SiO 2 -B 2 O 3 -Al 2} O 3 system glass containing SiO ₂ at least 30 wt%, generally as _Sb 2 _{O 3} is a fining agent 0.1 to 0.4 mass % (For example, Patent Documents 1 to 4). However, when the glass comes into contact with a high-temperature mold during pressing, Sb ₂ O ₃ in the glass is reduced and deposited to contaminate the mold, which adheres to the glass surface and becomes a spider. In the following description, “%” means “% by mass” unless otherwise specified.

Therefore, the present invention prevents spiders generated on the glass surface during pressing by limiting Sb ₂ O ₃ to less than 0.1%. The upper limit of Sb ₂ O ₃ is preferably 0.08% or less, particularly 0.05% or less.

On the other hand, the lower limit of Sb ₂ O ₃ is limited to 0.001% or more from the viewpoint of obtaining a glass that has no bubbles inside and is not colored by the dissolution of platinum. The lower limit of Sb ₂ O ₃ is preferably 0.005% or more and 0.01% or more. If it is less than 0.001%, a sufficient clarification effect cannot be obtained, and bubbles remain in the glass. In addition, when clarifying with less than 0.001% of Sb ₂ O ₃ , it is conceivable to elevate bubbles by increasing the melting time or increasing the melting temperature. The amount of platinum that dissolves in the glass increases and the glass becomes colored. Another possible method is to reduce the depth of the glass melt in the melting container to shorten the bubble floating time, but this is not preferable from the viewpoint of productivity. If the content of Sb ₂ O ₃ is 0.001% or more, a clarified amount of gas is released, and bubbles are included even if the melting time is extremely long or the melting temperature is not extremely high. Moreover, it becomes possible to obtain glass without coloring. Furthermore, since it contains 15% or more of B ₂ O ₃ , it becomes easy to become a glass having a low high temperature viscosity, and it becomes easier to obtain a glass without bubbles. The preferred number of bubbles inside the glass is 20 / g or less. Further, 10 / g is preferable, and 5 / g or less is particularly preferable.

If there is a concern about insufficient clarification by making Sb ₂ O ₃ less than 0.1%, the melting time is lengthened, the melting temperature is increased, the depth of the glass melt at the time of melting is decreased, It can supplement by means, such as using another clarifier together.

As other fining agents, use of sulfates such as sodium sulfate, potassium sulfate, calcium sulfate, barium sulfate, strontium sulfate, and aluminum sulfate is effective. When sulfate is used, clarified bubbles are released at 1200 to 1500 ° C., and the glass can be clarified effectively. However, if the amount of sulfate used is too large, SO ₂ gas is generated during pressing to contaminate the mold, or bubbles remain in the glass due to excessive clarification. The amount of sulfate added is preferably 5% by mass or less, more preferably 1% by mass or less, based on 100% by mass of the glass raw material. The amount of SO ₃ in the obtained glass composition is preferably 0.005 to 0.5% by mass, particularly 0.01 to 0.3% by mass.

In addition to sulfates, the use of SnO ₂ and CeO ₂ is also conceivable. However, SnO ₂ may cause spiders during pressing as with Sb ₂ O ₃ , so addition of a large amount should be avoided. The SnO ₂ content is preferably less than 0.1%. Moreover, CeO ₂ may be colored, so it should be avoided to add a large amount. The CeO ₂ content is preferably less than 0.1%. Furthermore, the total amount of Sb ₂ O ₃ , SnO ₂ and CeO ₂ is preferably less than 0.1% and 0.001% or more. Note that As ₂ O _3, which is widely known as a fining agent, is harmful, so it is desirable not to contain it substantially. Here, “substantially not contained” means 0.00001% or less.

  In the optical glass of the present invention, it is preferable that the basicity of the glass defined by (total number of moles of oxygen atoms / total number of cation field strength) × 100 is 11 or less. When the basicity exceeds 11, the reducibility of Sb ions in the glass becomes strong, and Sb easily precipitates during pressing, so that spiders are easily generated.

  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, the cation in the glass is more easily reduced than a glass having a low basicity.

When WC is used for the mold, it is considered that Sb ions are difficult to reduce if the basicity of the glass is 11 or less, preferably 9.5 or less. If the basicity of the glass exceeds 11, Sb in the glass is likely to be reduced, and even if Sb ₂ O ₃ is less than 0.1%, spiders are generated on the glass surface, and mass productivity may deteriorate.

The change in basicity is mainly due to F.A. S. The influence of is great. F. S. When the component having a large value is increased, the basicity tends to decrease. S. When a component having a small value is increased, the basicity tends to increase. For this reason, when it is going to lower the basicity of glass, for example, comparatively F.I. S. Increase the composition ratio of SiO ₂ , B ₂ O _3, WO _3, etc. having a large F. S. Small _Li 2 _O with, Na 2 O, SrO, it is sufficient to reduce BaO or the like.

  When the glass of the present invention is a low softening point glass in which mold press molding can be employed, the effect can be further enjoyed. Specifically, the low softening point glass refers to a glass having a glass transition point Tg of 700 ° C. or lower. When the molding temperature becomes high, the glass component tends to volatilize, causing irregularities on the press molding surface and causing deterioration of the mold. Therefore, a more preferable glass transition point is 650 ° C. or less, and further 600 ° C. or less. Particularly preferred is 580 ° C. or lower.

Below, the reason for limiting to content and the range of each component of glass is shown. Note that Sb ₂ O ₃ and other fining agents are as described above, and are omitted in the following description.

SiO ₂ is a component that constitutes the skeleton of the glass, is a component that has a large effect of increasing the Abbe number after B ₂ O ₃ , and is also a component that improves weather resistance. As the content of SiO ₂ increases, the high-temperature viscosity increases. Further, the refractive index is low and the softening point tends to be high. When the content of SiO ₂ decreases, the acid resistance and weather resistance tend to deteriorate. The content of SiO ₂ is 30 to 70%, preferably 38 to 62%, more preferably 42 to 60%, and still more preferably 48 to 60%.

B ₂ O ₃ has a remarkable effect of lowering the high temperature viscosity of the glass, and makes it easy to obtain a glass having a low high temperature viscosity. When the content of B ₂ O ₃ is too small, the clarity is remarkably deteriorated. In addition, it becomes difficult to set the Abbe number to a value of 30 or more. If the B ₂ O ₃ content is too large water resistance, acid resistance tends to decrease. The content of B ₂ O ₃ is 15 to 60%, preferably 20 to 40%, more preferably 20 to 30%, still more preferably 20 to 25%, and particularly preferably 20 to 23%.

Al ₂ O ₃ is a component constituting a glass skeleton together with SiO ₂ and has an effect of improving weather resistance. Moreover, it has the remarkable effect which suppresses that the alkaline component in glass elutes in water. When the content of Al ₂ O ₃ is too large becomes high temperature viscosity of the glass, clarity is deteriorated. Also, the refractive index tends to be low and the softening point tends to be high. When the content of Al ₂ O ₃ is too small chemical durability is deteriorated. Moreover, the stability of the glass deteriorates. The range of the content of Al ₂ O ₃ is 4 to 20% (however, not including 4%), preferably 5 to 15%, more preferably 8 to 13%.

  Components other than those described above can be appropriately added to the glass according to the present invention.

Li ₂ O, Na ₂ O and K ₂ O have the effect of lowering the melting temperature and softening point and improving workability. The preferable total amount is 0 to 20%, the more preferable total amount is 1 to 18%, and the still more preferable total amount is 8 to 18%. When the total amount of Li ₂ O, Na ₂ O and K ₂ O increases, the surface alteration tends to be easily altered in the cleaning process. In addition, the liquidus temperature rises, the working range is narrowed, and the mass productivity tends to be adversely affected. On the other hand, when the total amount thereof decreases, the softening point increases and the workability tends to be impaired.

Na ₂ O is a component that lowers the high temperature viscosity of the glass and improves the clarity. Moreover, it has the effect of lowering the melting temperature and softening point and improving workability. However, if the amount is too large, the amount of volatile matter formed by B ₂ O ₃ —Na ₂ O at the time of glass melting increases, which tends to promote the generation of striae. The preferable Na ₂ O content is 0 to 12%, particularly 0.1 to 10%.

Li ₂ O is a component that lowers the high temperature viscosity of the glass and increases the clarity. Moreover, since it has the effect of decreasing the softening point and improving workability, it is used as an essential component. A preferable range of the content of Li ₂ O is 0 to 12%, and a more preferable range is 0.1 to 10%. If it exceeds 12%, the phase separation is strong, the liquidus temperature becomes high, and the workability deteriorates. On the other hand, when the amount is small, the melting temperature tends to be high, and the clarity tends to deteriorate.

K ₂ O, like Li ₂ O and Na ₂ O, is a component that lowers the high-temperature viscosity of glass to increase clarity, and has the effect of increasing workability by lowering the melting temperature and softening point. However, if the amount is too large, the amount of volatile matter formed by B ₂ O ₃ —K ₂ O at the time of glass melting increases, which tends to promote the generation of striae. The content of K ₂ O is desirably 12% or less, particularly 10% or less.

  MgO, SrO, BaO, CaO and ZnO are effective in reducing the high temperature viscosity of the glass. It is also a component that increases the refractive index. When the total amount is too large, the weather resistance is lowered, and the lens surface is likely to be spoiled. The preferable total amount is 0 to 20%, more preferably 0 to 10%.

  CaO is a component that can increase the weather resistance and acid resistance by substituting an alkali metal component because it has the effect of lowering the softening point next to the alkali metal oxide. It also has the effect of increasing the refractive index. However, if contained in a large amount, the glass surface is likely to be altered when exposed to a high temperature and humidity environment for a long period of time. A preferable range of the content of CaO is 0 to 15%, and a more preferable range is 0.1 to 10%.

  BaO is a component that improves weather resistance and increases the refractive index, and also improves workability by lowering the liquidus temperature of the glass. However, if contained in a large amount, the glass surface is likely to be altered when exposed to a high temperature and humidity environment for a long period of time. A preferable range of the content of BaO is 0 to 20%, and a more preferable range is 0.1 to 10%.

  SrO, like BaO, is a component that increases weather resistance and increases the refractive index, and also improves workability by lowering the liquidus temperature of the glass. However, if contained in a large amount, the glass surface is likely to be altered when exposed to a high temperature and humidity environment for a long period of time. A preferable range of SrO content is 0 to 20%, and a more preferable range is 0.1 to 10%.

  MgO can be added up to 10% in order to increase the weather resistance and increase the refractive index. However, if the content is large, the tendency of phase separation is strong, and the liquidus temperature tends to be increased. A preferred range for the content of MgO is 10% or less, a more preferred range is 8% or less, and a further preferred range is 5% or less.

  ZnO is a component added to increase the refractive index and improve the weather resistance, and can be contained up to 5%. However, as the content increases, the Abbe number tends to decrease, the tendency to devitrification also increases, and it becomes difficult to obtain a homogeneous glass. Therefore, the content is desirably 3% or less.

ZrO ₂ is a component added to increase the refractive index and improve the weather resistance. However, when the content increases, the Abbe number tends to decrease, and the tendency to devitrification also increases, so that a homogeneous glass cannot be obtained. Therefore, the content is preferably 3% or less, and more preferably less than 0.1%.

La ₂ O ₃ has the effect of increasing the refractive index without reducing the Abbe number. However, since it tends to devitrify if contained excessively, the content is preferably 2.5% or less, more preferably less than 1%. Further, when performing mold press molding, if the content is large, there is a tendency to fuse with the mold.

Bi ₂ O ₃ can be added to increase the refractive index. However, if the content increases, the glass tends to be colored, so it is preferably 5% or less, and more preferably less than 0.1%.

P ₂ O ₅ is a component added to reduce the liquidus temperature. However, as the content increases, the glass tends to phase-separate and the surface tends to become cloudy in the cleaning step, so the content is preferably 5% or less, and more preferably less than 0.1%. desirable.

TiO ₂ and Nb ₂ O ₅ are effective components for increasing the refractive index, but on the other hand, since the Abbe number is remarkably lowered, the content of each of TiO ₂ and Nb ₂ O _{5 is} 0.3%. The content is preferably set to the following, and more preferably less than 0.1%.

  PbO is an effective component for increasing the refractive index, but it is preferably not substantially contained since it is an environmental load substance.

  Considering the influence on the environment, the F component is preferably not substantially contained.

  Next, a method for manufacturing an optical component such as a lens using the optical glass of the present invention will be described.

  First, a glass material prepared to have a desired composition is melted in a melting container.

From the viewpoint of using Sb ₂ O ₃ or sulfate as a fining agent, the melting temperature of the glass is preferably 1150 ° C. or higher. Furthermore, 1200 degreeC or more is preferable, and it is especially preferable that it is 1250 degreeC or more. From the viewpoint of preventing glass coloring due to Pt melting from platinum metal constituting the melting vessel, the melting temperature is preferably 1450 ° C. or lower, more preferably 1400 ° C. or lower, particularly preferably 1350 ° C. or lower, most preferably 1300 ° C. The following is preferred.

  If the melting time is too short, there is a possibility that it cannot be clarified sufficiently. Therefore, the melting time is preferably 2 hours or more, and more preferably 3 hours or more. However, from the viewpoint of preventing glass coloring due to Pt penetration from the melting vessel, the melting time is preferably within 8 hours, particularly within 5 hours.

  Moreover, since productivity will worsen if the depth of the glass melt in a melting container is too shallow, it is preferable that it is 30 mm or more, especially 50 mm or more. On the other hand, if it is too deep, it takes time for the bubbles to rise, and therefore it is 1 m or less, preferably 0.5 m or less.

  Subsequently, the molten glass is formed into a preform having a size that can be mold-pressed, and the preform is heat-softened and mold-pressed and processed into a desired shape, and then washed and dried to produce an optical component.

  As a method for forming a preform, it may be prepared by cutting out into a predetermined shape from a plate-like or lump-like glass piece and polishing and washing. However, a predetermined amount is dropped continuously before grinding, polishing and washing. It is preferable to use a droplet forming method because it can be easily formed.

  Hereinafter, the optical glass of this invention is demonstrated in detail based on an Example.

  Each sample was produced as follows.

Glass raw materials (carbonates and oxides) prepared so as to have the compositions shown in Tables 2 to 9 were placed in a platinum crucible so that the glass melt had a depth of 50 mm and melted at 1400 ° C. for 3 hours. In this example, soda ash was used as the Na ₂ O raw material. Next, the molten glass was poured out on the carbon plate, cooled and solidified, and then annealed to prepare a sample. The samples thus obtained were evaluated for glass transition point Tg, glass viscosity at 1300 ° C., JOGIS water resistance test, bubble count, spider occurrence probability, and Sb precipitation level. The basicity was calculated. The results are shown in Tables 2-9.

  As is apparent from the table, No. 1 as an example of the present invention. Samples 2, 3, 7, 8, 12, 16, 17, 20, 21, 24, 27, 28, 30 and 32 have 0 to 10 bubbles / g of bubbles inside the glass sample, and spider generation The probability was 0-7%.

  The glass transition point Tg was determined from the intersection of the low temperature line and the high temperature line in the thermal expansion curve.

  The viscosity of the glass at 1300 ° C. was measured by a platinum pulling method.

  The number of bubbles was mirror-polished on the surface of the sample (30 × 30 × 10 mm) remelted at 1300 ° C., and the bubbles in the sample were counted. The number of bubbles per gram was calculated from the counted bubbles and the weight of the sample.

The probability of spider occurrence was evaluated as follows. First, a glass sample was placed on a WC plate coated with Pt—Ir, and heat treatment was performed 100 times in a N ₂ atmosphere at Tg + 25 ° C. for 100 times. Thereafter, the presence or absence of spiders on the glass surface was observed with a microscope. Thus, 100 samples were evaluated and the spider occurrence probability was determined.

The Sb precipitation level was determined by placing a glass sample of φ5 × 5 mm on a WC plate and performing a heat treatment for 15 minutes in an N ₂ atmosphere at 800 ° C. 8900M) WDX. Further, an average value obtained by dividing the total signal amount obtained by the WDX surface analysis by the measurement area was obtained. The surface analysis of WDX was performed at a current of 3 × 10 ⁻⁸ A.

Next, in order to confirm the clarification effect of sulfate, a sample in which a part of the Na ₂ O raw material was replaced with sulfate was prepared, and the number of bubbles was evaluated using the same method as described above. Specifically, no. 8 and no. A sample was prepared using 0.05% and 0.1% sodium sulfate (Na ₂ SO ₄ ) as the 32 Na ₂ O raw material and the remainder as soda ash, and was used for evaluation.

As a result, as shown in Table 10, the number of bubbles in the sample using sulfate was 0 / g. Further, SO ₃ in the glass was 0.005% or more.

The amount of SO ₃ in the glass was measured by ion chromatography after alkali melting of the glass and ion exchange of the liquid.

  The optical glass of the present invention is excellent in mass productivity because it is difficult to generate spider on the surface even when it is mold-pressed and there is no bubble inside. Therefore, it can be suitably used for optical pickup lenses such as CD and DVD, and optical lenses such as video cameras and digital cameras.

Claims (7)

By _mass%, SiO 2 _30~70%, (not including but _{4%) Al 2 O 3 4~20} %, B 2 O 3 15~60%, Sb 2 O 3 0.001~0.1% ( However, an optical glass characterized by containing 0.1%). Further optical glass according to claim 1, characterized in that it contains SO ₃ 0.005 to 0.5 wt%.   3. The optical glass according to claim 1, wherein the basicity of the glass defined by (total number of moles of oxygen atoms / total number of positive field strength) × 100 is 11 or less.   The optical glass according to claim 1, wherein the optical glass is for mold press molding.   An optical lens comprising the optical glass according to claim 1.   It is a method of manufacturing the optical glass of Claims 1-4, Comprising: A sulfate is used as a clarifier, The manufacturing method of the optical glass characterized by the above-mentioned.   The method for producing an optical glass according to claim 6, wherein the addition amount of the sulfate is 5% by mass or less with respect to 100% by mass of the glass raw material.