WO2011158774A1 - Optical glass - Google Patents

Abstract

The disclosed optical glass has a low glass transition temperature (Tg) and exhibits high clarity, excellent chemical durability, a low index of refraction, and low dispersion (specifically, an index of refraction (nd) between 1.48 and 1.54 and an Abbe number (νd) between 59 and 67). Said optical glass is characterized by containing essentially no PbO and containing, by mass, 45.5-70% SiO₂, 10-44% B₂O₃, 7.2-20% Al₂O₃, 0-7% TiO₂, 1-20% Na₂O, 0-9% Li₂O, 0-2% ZrO₂, and less than 0.1% Sb₂O₃, with the sum of the amounts of Na₂O, Li₂O, and K₂O being between 3% and 30% and the sum of the amounts of B₂O₃, Na₂O, Li₂O, and K₂O divided by the sum of the amounts of Al₂O₃ and SiO₂ being between 0.16 and 0.80.

Description

Optical glass

The present invention relates to optical glass.

For applications such as optical pickup lenses for CD, MD, DVD and other optical disk systems, imaging lenses for digital cameras, video cameras, camera-equipped mobile phones, and transmission / reception lenses used for optical communication, the refractive index nd is 1. So-called BK type glass having an optical constant of 48 to 1.54 and an Abbe number νd of 59 to 67 is used.

For the glass used in these photographing lenses, first, molten glass is dropped from the tip of a nozzle to produce a glass droplet once, and then a preform glass is produced by grinding, polishing and washing. Alternatively, a molten glass is rapidly cast to produce a glass block, which is similarly ground, polished and washed to produce a preform glass. Next, the so-called mold press molding method is widely used, in which the preform glass is heated to a softened state, pressed with a precision-processed mold, and the surface shape of the mold is transferred to the glass. Yes.

Patent Documents 1 to 5 show BK type glass compositions.

Japanese Unexamined Patent Publication No. 2000-53441 Japanese Unexamined Patent Publication No. 2000-247678 Japanese Unexamined Patent Publication No. 2005-104824 Japanese Laid-Open Patent Publication No. 5-1931979 Japanese Unexamined Patent Publication No. 2002-201037

The glass transition point of the glass disclosed in Patent Document 1 is as high as 550 ° C. or higher, and mass production by a press is difficult.

On the other hand, Patent Documents 2 to 5 disclose glass compositions having a glass transition point of 550 ° C. or less and excellent press mass productivity. The glasses disclosed in Patent Documents 2 and 3 contain TiO ₂ as an essential component in order to increase chemical durability. However, TiO ₂ may cause the glass to be colored and is not suitable for glass used for lens applications. It is. TiO _{2 also} makes the glass highly viscous. For this reason, the clarity of glass deteriorates and a large amount of Sb ₂ O ₃ is often required as a fining agent.

The glass disclosed in Patent Document 4 has a high viscosity at 1250 to 1300 ° C., and there is a possibility that a method of forming droplet glass by spontaneously dropping molten glass from a nozzle may not be adopted. The less Al ₂ O _3, chemical durability such as acid resistance tends to be lower. In the glass composition disclosed in Patent Document 5, the total amount of B ₂ O ₃ and the alkali component is as large as 37% or more, so there is a concern that the chemical durability is low.

In view of the above problems, the object of the present invention is a low refractive index and low dispersion (specifically, a refractive index nd of 1.48 to 1) having a low glass transition point, good clarity and excellent chemical durability. And an optical glass having an Abbe number νd of 59 to 67).

The optical glass of the present invention is, by mass%, SiO ₂ 45.5 to 70%, B ₂ O ₃ 10 to 44%, Al ₂ O ₃ 7.2 to 20%, TiO ₂ 0 to 7%, Na ₂ O. 1-20%, Li ₂ O 0-9%, R ₂ O 3-30% (R ₂ O is the total amount of Na ₂ O, Li ₂ O and K ₂ O), ZrO ₂ 0-2%, Sb ₂ O ₃ 0 to less than 0.1%, (B ₂ O ₃ + R ₂ O) / (Al ₂ O ₃ + SiO ₂ ) is 0.16 to 0.80 and is substantially free of PbO To do. In the present invention, “substantially free of PbO” means that PbO is not intentionally added to the glass, and does not mean that unavoidable impurities are completely eliminated. More objectively, it means that the content of PbO including impurities is 0.01% or less. In addition, regarding the term “containing” in the present invention, a component defined as “0 to” means “0%”, that is, it may not be included at all.

In the present invention, by mass, SiO ₂ 47 to 60%, B ₂ O ₃ 10 to 35%, Al ₂ O ₃ 7.2 to 20%, TiO ₂ 0 to 2%, Na ₂ O 1 to 20% Li ₂ O 0-9%, R ₂ O 3-30% (R ₂ O is the total amount of Na ₂ O, Li ₂ O and K ₂ O), ZrO ₂ 0-2%, Sb ₂ O ₃ 0- It is preferably less than 0.1%, (B ₂ O ₃ + R ₂ O) / (Al ₂ O ₃ + SiO ₂ ) being 0.16 to 0.80, and substantially not containing PbO.

In the present invention, it is preferable to further contain 0.003 to 0.5% by mass of SO ₃ .

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

In the present invention, the refractive index nd is preferably 1.48 to 1.54 and the Abbe number νd is 59 to 67.

According to the above configuration, it can be used as BK type glass.

In the present invention, the glass transition point is preferably 530 ° C. or lower.

According to the above configuration, excellent press mass productivity can be obtained.

The glass of the present invention is preferably used for mold press molding.

The method for producing an optical glass of the present invention is a method for producing the glass, characterized in that sulfate is used as a fining agent.

According to the above configuration, the clarity of the glass can be improved, and an optical glass with better foam quality can be produced.

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.

The optical glass of the present invention can achieve an optical constant of low refractive index and low dispersion used for an optical lens of an optical pickup lens of various optical disk systems such as a photographing lens of a general digital camera or a video camera. In particular, a refractive index nd of 1.48 to 1.54 and an Abbe number νd of 59 to 67 or more can be easily achieved. From The possible high-temperature viscosity is low, it is possible to clear one less than wt% Sb ₂ O _3. Further, since the glass transition point is low and the press temperature can be lowered, the glass component is hardly volatilized, and the mold accuracy is not lowered, and the mold is not deteriorated or contaminated. Moreover, since the weather resistance is good, the physical properties are not deteriorated and the surface is not deteriorated during the production process or use of the product. Therefore, the optical glass of the present invention is excellent in mass productivity of preform glass.

The optical glass of the present invention, _SiO 2 45.5 _{~ 70%} by _{mass%, B 2 O 3 10 ~} 44%, Al 2 O 3 7.2 ~ 20%, TiO 2 0 ~ 7%, Na 2 O 1 -20%, Li ₂ O 0-9%, R ₂ O 3-30% (R ₂ O is the total amount of Na ₂ O, Li ₂ O and K ₂ O), ZrO ₂ 0-2%, Sb ₂ O ₃ 0 ~ less than _{0.1%, (B 2 O 3} + R 2 O) / (Al 2 O 3 + SiO 2) is _{SiO 2 -B 2 O 3 -Al 2} O having a composition of 0.16 to 0.80 _{It is a 3} series glass. Moreover, since a PbO component is an environmentally unpreferable component, it does not contain substantially.

Of the above components, SiO ₂ and Al ₂ O ₃ function to lower the refractive index and Abbe number of glass. On the other hand, B ₂ O ₃ and Na ₂ O have a function of increasing the Abbe number.

Of the above components, R ₂ O and B ₂ O ₃ have the effect of reducing the viscosity. However, if a large amount of R ₂ O and B ₂ O ₃ is contained, the weather resistance tends to deteriorate and the mass productivity tends to decrease. On the other hand, Al ₂ O ₃ and SiO ₂ have the effect of improving the weather resistance, but deteriorate the clarity because the glass is made highly viscous. Therefore, in the present invention, (a total amount of Al ₂ O ₃ amount and SiO ₂ amount), (B ₂ O ₃ amount and R ₂ O amount) in order to achieve both low viscosity of glass and prevention of deterioration of weather resistance. The ratio of (total amount) (B ₂ O ₃ + R ₂ O) / (Al ₂ O ₃ + SiO ₂ ) is adjusted to 0.16 to 0.80 by mass ratio. When this value is in the range of 0.16 to 0.80, it is possible to obtain weather resistance excellent in mass productivity while keeping the viscosity low. If (B ₂ O ₃ + R ₂ O) / (SiO ₂ + Al ₂ O ₃ ) is in the range of 0.40 to 0.75, it becomes easy to obtain a glass particularly excellent in weather resistance.

Note R _{2 O} and B total amount of ₂ O ₃ increases the chemical durability of the glass decreases. In particular, when the total amount of these components exceeds 37%, even when (B ₂ O ₃ + R ₂ O) / (Al ₂ O ₃ + SiO ₂ ) is adjusted to a mass ratio in the range of 0.16 to 0.80, It becomes difficult to obtain good weather resistance. Therefore, the total amount of B ₂ O ₃ and R ₂ O is preferably 37% or less.

Also in terms of clarity, but preferably larger the Sb ₂ O _3, when Sb ₂ O ₃ is too large, the glass surface became cloudy during pressing, also shorten the life of the mold to deteriorate the mold shape End up. Therefore, the upper limit of Sb ₂ O ₃ is limited to less than 0.1%.

Hereinafter, the reason for specifying the content of each component as described above will be described in detail. Unless otherwise specified, the following “%” means “mass%”.

In the present invention, if the content of SiO ₂ is small, it is difficult to lower the refractive index. Therefore, the content of SiO ₂ is set to 45.5% or more, preferably 47% or more, more preferably 50%. Is done. When the content of SiO ₂ is too much, the high temperature viscosity of the glass becomes high, clarity is deteriorated. Further, the glass transition point is increased and the pressability is deteriorated. For these reasons, the content of SiO ₂ should be set to 70% or less, preferably 65% or less, more preferably 60% or less, still more preferably 59% or less, and particularly 58% or less.

B ₂ O ₃ has the effect of increasing the Abbe number, lowering the viscosity of the glass, and further lowering the glass transition point. However, when a large amount of B ₂ O ₃ is contained, chemical durability, particularly acid resistance, is significantly deteriorated. In addition, the volatilization during the press increases and the press die is deteriorated. For this reason, the content of B ₂ O ₃ is limited to 10 to 44%, preferably 12 to 40%, more preferably 15 to 35%, still more preferably 16 to 25%, and particularly preferably 17 to 22%. Should.

Al ₂ O ₃ is an effective component for enhancing chemical durability. In particular, even a highly alkali-containing glass containing 13% or more of R ₂ O can improve acid resistance, water resistance and weather resistance. However, when a large amount of Al ₂ O ₃ is contained, the viscosity of the glass at high temperature increases and the clarity is remarkably deteriorated. Further, the glass transition point is remarkably increased and the pressability is deteriorated. The content of Al ₂ O ₃ is 7.2 to 20%, preferably 7.5 to 18%, more preferably 8 to 15%, and particularly preferably 8.5 to 11%.

Na ₂ O, Li ₂ O, and K ₂ O are components that lower the high-temperature viscosity of glass to improve clarity and lower the glass transition point. Furthermore, there is an effect of lowering the refractive index.

The content of R ₂ O representing the total amount of alkali metal oxides (Na ₂ O, Li ₂ O and K ₂ O) is 3% or more, preferably 5% or more, 8% or more, 10% or more, 13% or more. It is set to 14.5% or more, particularly preferably 15% or more. On the other hand, when the content of R 2 _O is too large increases volatilization from the glass during pressing, deteriorating the press die. Moreover, the volatilization at the time of melting increases, which deteriorates the melting kiln and the melting apparatus, and the mass productivity deteriorates. For this reason, the content of R ₂ O should be set to 30% or less, preferably 25% or less, more preferably less than 18%.

Among the alkali components, Na ₂ O has an effect of lowering the high temperature viscosity, and is an essential component for obtaining excellent clarity. It is also effective for lowering the glass transition point, and the press temperature can be lowered. The content of Na ₂ O is set to 3% or more, preferably 6% or more, particularly preferably 7% or more. Weather resistance is lowered and the content of Na 2 _O is large. Also, it volatilizes during pressing and contaminates the mold. For this reason, the content of Na ₂ O should be set to 20% or less, preferably 15% or less, more preferably 12% or less, and particularly preferably 9.5% or less.

Li ₂ O is not an essential component, but it is desirable to contain 1% or more, particularly 2.5% or more. However Li 2 when the content of _O is too large tends to weather resistance is deteriorated. When the content of Li ₂ O exceeds 9%, even if (B ₂ O ₃ + R ₂ O) / (Al ₂ O ₃ + SiO ₂ ) is adjusted to 0.16 to 0.80 in terms of mass ratio, Durability tends to decrease, and weather resistance deteriorates significantly. Further, in the glass of the present invention, the refractive index is unduly raised. For these reasons, the content of Li ₂ O should be limited to 9% or less, further 7% or less, and particularly 5% or less.

K ₂ O has the effect of lowering the high temperature viscosity of the glass and improving the clarity, like Na ₂ O and Li ₂ O. Further lowering the viscosity without changing the refractive index as compared to Na 2 _O and Li 2 _O, has the effect of lowering the glass transition point. A preferable content of K ₂ O is 0 to 10%, more preferably 1 to 8%, still more preferably 2 to 7%, and particularly preferably 3 to 5.5%.

The content of ZrO ₂ is 2% or less. When the content of ZrO ₂ exceeds 2%, the refractive index becomes too high to obtain a desired refractive index, and the value of (B ₂ O ₃ + R ₂ O) / (Al ₂ O ₃ + SiO ₂ ) Even if it is 0.16 or more, it becomes difficult to sufficiently reduce the viscosity of the glass and the clarity is deteriorated, and it is difficult to make the glass transition point 530 ° C. or less. The content of ZrO ₂ is less than 1%. In addition, it is better not to contain ZrO ₂ unless there is a special circumstance in which ZrO ₂ should be used.

The content of Sb ₂ O ₃ is 0 to less than 0.1%. Sb ₂ O ₃ has an effect of defoaming, and also has an effect of suppressing coloring due to Pt ions (mixed in the glass as impurities by several ppm). However, if the content of Sb ₂ O ₃ is large, the glass surface becomes clouded during pressing. Moreover, Sb ₂ O ₃ has a strong oxidizing power, so if its amount is too large, it will oxidize metals such as Pt and Rh used in the melting vessel, resulting in a decrease in mass productivity. The preferred content of Sb ₂ O ₃ is 0 to 0.09%, in particular 0 to 0.08%.

In the present invention, various components other than the above components can be added. Adding for example _{TiO 2, ZnO, MgO, CaO} , BaO, SrO, and _{La 2 O 3, Gd 2 O} 3, Y 2 O 3, Nb 2 O 5, Ta 2 O 5, GeO 2, P 2 O 5 , etc. be able to.
The content of TiO ₂ is preferably 7% or less. When the content of TiO ₂ is too large, the glass is remarkably colored, or the refractive index becomes too high, making it difficult to obtain a desired refractive index. Moreover, it becomes difficult to make a glass transition point 530 degrees C or less. Further, when the content of TiO ₂ exceeds 7%, the viscosity of the glass is sufficiently lowered even if the value of (B ₂ O ₃ + R ₂ O) / (Al ₂ O ₃ + SiO ₂ ) is 0.16 or more. It becomes difficult to clarify. When the content of TiO ₂ is 0.1% or more, the acid resistance of the glass can be improved. However, since the above disadvantages are likely to occur, the content of TiO ₂ is 2% or less, particularly less than 1%. It is preferable. Note Without special circumstances should use TiO _2, it is better not contain in order to reliably avoid coloration and clarity problems.

ZnO, MgO, CaO, BaO and SrO are components that increase the refractive index and can be used as adjustment of optical constants. However, if the content of each component exceeds 5%, the weather resistance decreases. The preferred range of each component is 0 to 3%, especially 0 to 1%.

La ₂ O ₃ , Gd ₂ O ₃ , and Y ₂ O ₃ are components that increase the refractive index while maintaining the Abbe number, and can be used as adjustment of optical constants. When the content of each component exceeds 5%, it becomes difficult to make the refractive index nd 1.54 or less. The preferred range for each component is less than 1% each.

Nb ₂ O ₅ and Ta ₂ O ₅ are components that remarkably increase the refractive index, and can be used for adjusting the optical constant. If the content of each component exceeds 2%, it is difficult to make the refractive index nd 1.54 or less. The preferred range for each component is less than 1% each.

GeO ₂ can be added for the purpose of increasing the stability and refractive index of the glass. However, since GeO ₂ is a rare raw material, if the amount used is increased, the raw material cost increases. Therefore, even if GeO ₂ is used, its content is preferably small, specifically 0 to 3%, more preferably 0 to 1%, particularly preferably 0 to 0.001%.

P ₂ O ₅ can be added for the purpose of adjusting the glass transition point and viscosity characteristics. However, since the weather resistance of glass falls or devitrification resistance deteriorates, it is not preferable to contain a large amount. Therefore, even if P ₂ O ₅ is used, its content is preferably small, specifically 0 to 10%, more preferably 0 to 1%. Note it is preferable not contain Without special circumstances should be used P ₂ O _5.

In addition to the above, other components may be added as long as the properties of the glass are not impaired.

For example, a clarifying agent can be added to improve clarity. Of these, the 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.

The use of SnO ₂ or CeO ₂ as a clarifier other than sulfate is also conceivable. However, SnO ₂ may cause whitening of the glass surface at the time of pressing in the same manner as 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. Further, it is preferable that the F component is not substantially contained because it may adversely affect the environment. The Cl component is apt to volatilize from the glass during pressing, and it is not preferable to contain it substantially because it significantly accelerates the deterioration of the press mold. Here, “substantially free of As ₂ O ₃ ”, “free of F” and “substantially free of Cl” means that these components are not intentionally added to the glass. It does not mean that unavoidable impurities are completely eliminated. More objectively, it means that the content of these components including impurities is 0.00001% or less for As ₂ O ₃ , 0.01% or less for F, and 0.01% or less for Cl. To do.

Further, since Cu and Ag are components for coloring the glass, it is preferable not to contain them.

The optical glass having the above composition can easily achieve optical constants having a refractive index nd of 1.48 to 1.54 and an Abbe number νd of 59 to 67. In particular, a glass having an optical constant in the range of refractive index nd of 1.50 to 1.52 and Abbe number νd of 60 to 63 can be obtained.

The optical glass having the above composition can easily achieve a glass transition point of 530 ° C. or lower. Furthermore, a glass transition point of 520 ° C. or lower, particularly 510 ° C. or lower can be easily achieved.

Further, the viscosity of the glass corresponding to 1300 ° C. is preferably 10 ^2.0 dPa · s or less, more preferably 10 ^1.9 dPa · s or less. If the viscosity at 1300 ° C. is in the above range, the bubbles contained in the glass are likely to rise, so that clarification becomes easy.

Further, the internal transmittance (λ _{330 nm} ) at 330 nm with a thickness of 10 mm is 85% or more, more preferably 88% or more. If the internal transmittance is in the above range, high transmittance can be maintained even with a large-diameter lens. In order to obtain the internal transmittance, it can be achieved by selecting an oxide with a small amount of Fe ₂ O ₃ mixed in the raw material manufacturing process. For example, MgO and CaO raw materials often contain Fe ₂ O ₃ as impurities. In such cases, it is preferable to avoid using MgO or CaO. Fe ₂ O ₃ is preferably 40 ppm or less.

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

First, glass raw materials are prepared so as to have a desired composition and then melted in a glass melting furnace.

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.

Further, 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.

Also, the depth of the glass melt in the melting vessel is preferably 30 mm or more, particularly 50 mm or more, because the productivity becomes worse if it is too shallow. 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.

Next, molten glass is dropped from the tip of the nozzle to once produce droplet glass to obtain preform glass. Alternatively, a molten glass is rapidly cast to produce a glass block, which is then ground, polished and washed to obtain a preform glass.

Subsequently, it is put into a preform glass in a precision-processed mold and pressure-molded while being heated until it becomes softened, and the surface shape of the mold is transferred to the glass. This molding method is called a mold press molding method and is widely used. In this way, an optical pickup lens and a photographing lens can be obtained.

Hereinafter, the optical glass of the present invention will be described in detail based on examples.

Tables 1 to 3 show examples of the present invention (sample Nos. 1 to 11), and Table 4 shows comparative examples (samples No. 12 to 16).

 

 

 

 

Each sample was prepared as follows.

First, glass raw materials (carbonates and oxides) prepared to have the compositions shown in Tables 1 to 4 were put in a platinum crucible and melted at 1300 ° C. for 2 hours, respectively. 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. Various characteristics of the sample thus obtained were evaluated. The results are shown in each table.

In order to confirm the amount of Fe ₂ O ₃ in the glass, when the glass was dissolved with an acid solution and measured by ICP, No. 6 was 30 ppm and No. 7 was 20 ppm. On the other hand, since No. 10 contained a large amount of MgO, the amount of Fe ₂ O ₃ was as high as 50 ppm.

The refractive index nd is indicated by a measured value at the d-line (wavelength: 587.6 nm) of a helium lamp using a refractometer (Karnew Kashiwa KPR-200).

Abbe's number νd was measured using the refractometer (Karnew KPR-200), d line, hydrogen lamp F line (wavelength: 486.1 nm), and hydrogen lamp C line (wavelength: 656.3 nm). Refractive indexes were respectively measured, and the values thereof were defined as {(nd-1) / (nF-nC)} when nd, nF, and nC were used.

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.

Water resistance was evaluated according to the measuring method (powder method) of JOGIS chemical durability.

Acid resistance was evaluated according to the measuring method (powder method) of JOGIS chemical durability.

The weather resistance is obtained by observing the surface after being kept at 60 ° C.-90% RH for 24 hours. “O” indicates that the surface is not cloudy, and “X” indicates that the cloudiness is observed. did.

The clarity was evaluated as follows. First, the once formed glass was pulverized and classified into a pulverized glass of 2 mm or less. Subsequently, crushed glass was put into a 300 cc platinum crucible, and the glass amount was adjusted so that the glass height was 30 mm. Next, after holding at 1300 ° C. for 1 hour in an electric furnace, a sample molded into a plate shape having a thickness of 10 mm was mirror-polished, and parallel light was incident from the side of the sample to count bubbles.

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

As is apparent from the table, No. 1 as an example of the present invention. Each of the samples 1 to 11 had a refractive index nd of 1.485 to 1.530 and an Abbe number νd of 57.8 to 64.1. The glass transition point was 490 to 530 ° C. The viscosity at 1300 ° C. was 10 ^1.2 to 10 ^2.0 dPa · s, and the number of bubbles in the glass was 0 to 4 per 1 cm ³ . The JOGIS water resistance (powder method) was 1 to 3 and the weather resistance evaluation was good.

On the other hand, No. which is a comparative example. Nos. 12, 13, and 15 had a viscosity at 1300 ° C. of 10 ^2.2 to 10 ^3.2 dPa · s, and 5 to 20 bubbles / cm ³ remained, so the clarity was low. No. No. 15 has a glass transition point as high as 560 ° C., and mold press molding is expected to be difficult. No. No. 14 had a JOGIS water resistance (powder method) of grade 5, and the weather resistance was poor. No. No. 16 had little Al ₂ O ₃ , JOGIS acid resistance (powder method) was grade 4, and mass productivity was poor.

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. As Na ₂ O raw materials of Nos. 3, 6, 8, and No. 11, sodium sulfate (Na ₂ SO ₄ ) was 0.1 to 0.02% and the remainder was soda ash, and samples were prepared for evaluation.

 

 

As a result, as shown in Tables 5 and 6, the number of bubbles in the sample using sulfate was 0 / g.

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.

Although the invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
The present application is based on a Japanese patent application filed on June 15, 2010 (Japanese Patent Application No. 2010-135760) and a Japanese patent application filed on December 14, 2010 (Japanese Patent Application No. 2010-277730). Which is incorporated by reference in its entirety. Also, all references cited herein are incorporated as a whole.

Claims (8)

1. By mass%, SiO ₂ 45.5 to 70%, B ₂ O ₃ 10 to 44%, Al ₂ O ₃ 7.2 to 20%, TiO ₂ 0 to 7%, Na ₂ O 1 to 20%, Li ₂ O 0-9%, R ₂ O 3-30% (R ₂ O is the total amount of Na ₂ O, Li ₂ O and K ₂ O), ZrO ₂ 0-2%, Sb ₂ O ₃ 0-0.1 %, (B ₂ O ₃ + R ₂ O) / (Al ₂ O ₃ + SiO ₂ ) is 0.16 to 0.80, and contains substantially no PbO.
2. By mass%, SiO ₂ 47-60%, B ₂ O ₃ 10-35%, Al ₂ O ₃ 7.2-20%, TiO ₂ 0-2%, Na ₂ O 1-20%, Li ₂ O 0 9%, R ₂ O 3-30% (R ₂ O is the total amount of Na ₂ O, Li ₂ O and K ₂ O), ZrO ₂ 0-2%, Sb ₂ O ₃ 0-0.1% _2. The optical glass according to claim 1, wherein (B ₂ O ₃ + R ₂ O) / (Al ₂ O ₃ + SiO ₂ ) is 0.16 to 0.80 and substantially does not contain PbO. .
3. The optical glass according to claim 1 or 2, further comprising 0.005 to 0.5% by mass of SO ₃ .
4. 3. The optical glass according to claim 1, wherein the refractive index nd is 1.48 to 1.54 and the Abbe number νd is 59 to 67.
5. The optical glass according to claim 1 or 2, wherein the glass transition point is 530 ° C or lower.
6. The optical glass according to claim 1 or 2, wherein the optical glass is used for mold press molding.
7. A method for producing an optical glass according to claim 1 or 2, wherein sulfate is used as a fining agent.
8. The method for producing an optical glass according to claim 7, wherein the addition amount of the sulfate is 5% by mass or less with respect to 100% by mass of the glass raw material.