TWI391353B - Molded glass for molding - Google Patents

Description

Optical glass for press molding

The present invention relates to an optical glass for press molding.

Optical glass having a refractive index (nd) of 1.65 to 1.75 and an Abbe number (vd) of 45 or more is used for optical reading lenses of CD, MD, DVD, and other various optical disk systems, and optical lenses such as photographic lenses for cameras or general cameras. In the lens. Previously, as such a glass, lead-containing glass based on SiO ₂ -PbO-R' ₂ O (R' ₂ O is an alkaline metal oxide) has been widely used, but in recent years, environmental problems have been taken into consideration, and instead, Non-lead glass such as B ₂ O ₃ —RO (RO is an alkaline earth metal oxide)-La ₂ O ₃ glass is being used. (For example, refer to Patent Documents 1, 2)

[Patent Document 1] Japanese Patent Laid-Open No. Hei 1-186934

These optical reading lenses or photographic lenses are produced as follows.

First, a molten glass is dropped from the front end of the nozzle to prepare a temporary droplet-shaped glass, which is ground, polished, and washed to obtain a preformed glass. Alternatively, the molten glass is subjected to rapid cold casting to prepare a temporary glass block, and the preformed glass is obtained by grinding, grinding, and washing. Next, in the mold which has been subjected to precision machining, the preformed glass is heated to a softened state, and press forming is performed to transfer the surface shape of the mold to the glass. This forming method is called a press forming method and is widely used. An optical reading lens or a photographic lens is produced in this manner.

However, B ₂ O ₃ —RO (RO is an alkaline earth metal oxide)-La ₂ O ₃ glass contains a large amount of alkaline earth metal oxide (RO) in order to increase the refractive index of the glass, and has the following problem: In the cutting, grinding and washing steps of glass, the glass component is eluted in the grinding washing water or various washing solutions, causing surface deterioration, etc., and the weather resistance is poor, even if it is a final product, if it is exposed to high temperature and humidity for a long time. In the state, the surface of the glass will be deteriorated and damaged.

Moreover, the B ₂ O ₃ -RO-La ₂ O ₃ -based glass has a high softening point (Ts) and also has a softening point (Ts) of more than 650 ° C. In the press molding method, in order to soften the nitrate material, it is heated to near the softening point to be molded, and the press mold is heated to a temperature near the softening point. When the softening point of the nitrate material is high, the mold is also high in temperature, and causes problems such as promoting deterioration of the mold and the like, deterioration of the forming precision, or mold contamination due to volatilization of the glass component, or the glass and the mold become easy. Welding, etc. In order to reduce the softening point of the glass, it is also considered to further add a basic metal oxide (R' ₂ O) to the glass. However, if R' ₂ O is contained, the weather resistance is further deteriorated.

An object of the present invention is to provide a press molding capable of improving the above problems, having a refractive index (nd) of 1.65 to 1.75, an Abbe number (vd) of 45 or more, high weather resistance, and being suitable for compression molding and containing no lead. Use optical glass.

That is, the present invention relates to the contents described in the following (1) to (8).

(1) An optical glass for press molding, which has a refractive index (nd) of 1.65 to 1.75, an Abbe number (vd) of 45 or more, a softening point of 650 ° C or less, and no lead; and ΔT = {forming temperature (10) temperature of ¹⁰ poises) ^-} liquidus temperature of above 20 ℃, according to Japan optical glass industry Association standard JOGIS weight loss of the powder method for water resistance of 0.2% or less, acid by Japan optical glass industry Association standard JOGIS the powder method The weight loss is 1.2% or less and contains B ₂ O ₃ -La ₂ O ₃ -ZnO-Gd ₂ O ₃ -based glass.

(2) The optical glass for press molding according to (1), which contains 24 to 45% of B ₂ O ₃ , 5 to 35% of La ₂ O ₃ , and 10 to 30% of ZnO, by weight %. 0.5 to 20% of Gd ₂ O ₃ .

(3) The optical glass for press molding according to (1), which contains 2 to 15% of R' ₂ O (R' represents at least one of Li, Na, and R).

(4) The optical glass for press molding according to (1), which contains 2 to 10% of Li ₂ O, 0 to 5% of Na ₂ O, and 0 to 5% of K ₂ O by weight %.

(5) The optical glass for press molding according to (1), which contains 6 to 20% of SiO ₂ , 0 to 10% of Al ₂ O ₃ , 0 to 10% of MgO, and 0 to 0% by weight. 10% BaO, 0-15% SrO, 0~5% ZrO ₂ , 0-15% Y ₂ O ₃ , 0-10% Ta ₂ O ₅ , 0~1% Sb ₂ O ₃ .

(6) The optical glass for press molding according to (1), which contains 0 to 25% of RO by weight % (R represents one or more of Mg, Ba, and Sr).

(7) The optical glass for press molding according to (1), which substantially does not contain TiO ₂ , Nb ₂ O ₅ or CaO.

(8) An optical glass for press molding, which comprises 24 to 45% of B ₂ O ₃ , 5 to 35% of La ₂ O ₃ , 10 to 30% of ZnO, and 0 to 10% of Ta by weight %. ₂ O ₅ , 2~10% Li ₂ O, 0~5% Na ₂ O, 0~5% K ₂ O, 0~15% R' ₂ O (R' means Li, Na, K One or more), 6 to 20% SiO ₂ , 0 to 10% Al ₂ O ₃ , 0 to 10% MgO, 0 to 10% BaO, 0 to 15% SrO, 0 to 25% RO (R represents one or more of Mg, Ba, and Sr), 0 to 5% of ZrO ₂ , 0 to 15% of Y ₂ O ₃ , 0.5 to 20% of Gd ₂ O ₃ , and 0 to 1% of Sb ₂ O ₃ , and substantially does not contain TiO ₂ , Nb ₂ O ₅ , CaO.

The optical glass for press molding of the present invention has a refractive index (nd) of 1.65 to 1.75 and an Abbe number (vd) of 45 or more, and can be used for an optical reading lens for CD, MD, DVD, and various other optical disk systems, a camera or In an optical lens such as a photographic lens for a general camera. Further, since the softening point is low and the glass component is less likely to volatilize, the molding accuracy is not deteriorated and the mold is deteriorated or contaminated. Moreover, since the working temperature range is wide, the mass production of the preformed glass is excellent, and the weather resistance is good, the physical properties are not deteriorated or the surface is deteriorated during the manufacturing process or the use of the product. Therefore, it can be suitably used as an optical glass for press molding.

Hereinafter, the present invention will be described in detail.

In addition, the percentages in this specification are based on weight, unless otherwise indicated. Again, all percentages defined by weight are the same as those defined by mass.

In the optical glass for press molding of the present invention, since the refractive index (nd) of the glass is 1.65 to 1.75 and the Abbe number (vd) is 45 or more, it can be used as an optical lens for a small optical element having less dispersion and high function.

Here, the refractive index (nd) in the present specification is represented by a measured value of the d-line (587.6 nm) of the xenon lamp.

Further, the Abbe number (vd) in the present specification means that the refractive index of the d-line, the F-line of the hydrogen lamp (486.1 nm), and the refractive index of the C-line (656.3 nm) of the hydrogen lamp are used. The number of shells (vd) = [(nd-1) / (nF-nC)] is the value calculated by the formula. Here, nF is the refractive index value of the F line (486.1 nm) of the hydrogen lamp, and nC is the refractive index value of the C line (656.3 nm) of the hydrogen lamp.

Further, since the softening point (Ts) of the glass is 650 ° C or lower (preferably 625 ° C or lower, more preferably 615 ° C or lower), the molding can be carried out at a low temperature, and deterioration of the mold can be suppressed. Further, it is possible to suppress mold contamination caused by volatilization of the glass component or fusion of the glass and the mold.

Here, the softening point (Ts) can be measured, for example, based on the fiber elongation method of Japanese Industrial Standard R-3104.

Further, since the operating temperature range (?T) of the glass is 20 ° C or higher (preferably 25 ° C or higher, more preferably 30 ° C or higher), devitrification or pulverization during melting and molding steps can be suppressed. Pre-formed glass can be produced in volume.

Here, the operating temperature range (ΔT) can be obtained as follows. First, a platinum ball pulling method determination molding temperature (T _W), corresponding to a temperature of 10 to obtain ^1.0 poise of. Further, the liquid phase temperature (T _L ) was pulverized into a powder having a maximum particle diameter of 297 to 500 μm, classified, placed in a boat made of platinum, and held in an electric furnace having a temperature gradient for 24 hours. It was cooled in the air and measured by an optical microscope to determine the position of devitrification. The difference between the forming temperature (T _W ) and the liquid phase temperature (T _L ) obtained in this manner was taken as the working temperature range (ΔT).

In addition, the weight loss of the water resistance of the powder method according to the Japanese Optical Glass Industry Association JOGIS is 0.2% or less (preferably less than 0.1%, more preferably 0.05% or less), and the weight loss of the acid resistance of the same powder method is 1.2. % or less (preferably 1.1% or less, more preferably 1% or less), and therefore has high weather resistance.

Here, the water resistance and the acid resistance in the present specification mean that the glass sample is crushed to a particle size of 420 to 590 μm according to the Japanese Optical Glass Industry Council Standard 06-1975, and the specific gravity is weighed and placed in a platinum basket. This was placed in a flask containing the reagent and treated in a boiling water bath for 60 minutes to calculate the weight loss (% by weight) of the treated powder glass. Further, the pH of the reagent used in the evaluation of the water resistance was adjusted to 6.5 to 7.5 of pure water, and the reagent used in the acid resistance evaluation was adjusted to a 0.01 N aqueous solution of nitric acid.

Further, the optical glass for press molding of the present invention contains B ₂ O ₃ -La ₂ O ₃ -ZnO-Gd ₂ O ₃ -based glass as a basic component and does not contain lead glass. More specifically, it is calculated by weight %, having 24 to 45% B ₂ O ₃ , 5 to 35% La ₂ O ₃ , 10 to 30% ZnO, and 0.5 to 20% Gd ₂ O ₃ The basic composition of the glass. In general, in the B ₂ O ₃ -RO-La ₂ O ₃ -based glass, in order to obtain a high refractive index, a large amount of an alkaline earth metal oxide, that is, RO, is contained, which is a cause of deterioration in weather resistance of the glass. . Therefore, since the glass of the present invention contains Gd ₂ O ₃ which is a component which can increase the refractive index and suppresses the content of RO, it is possible to maintain a high refractive index and to improve the weather resistance of the glass. Further, by improving the weather resistance of the glass, R' ₂ O (alkaline metal oxide) which is a component which lowers the softening point of the glass can be added in an amount necessary.

Hereinafter, the reason for limiting the range of each component as described above will be described.

The skeleton component of B ₂ O ₃ -based glass has an effect of improving resistance to devitrification. Further, it is a component which increases the Abbe number or lowers the softening point. Further, it has an effect of preventing the glass from being welded to the mold during press molding. The content is 24 to 45%, preferably 24.5 to 35%, more preferably 26.5 to 30%. By setting the content of B ₂ O ₃ to 45% or less, the chemical durability of the glass is not lowered, and weather resistance can be maintained. On the other hand, by setting it as 24 % or more, the devitrification resistance will not be reduced, and a sufficient operating temperature range can be ensured.

La ₂ O ₃ is used to ensure a sufficient operating temperature range and has an effect of not lowering the Abbe number and increasing the refractive index. Further, it also has an effect of suppressing an increase in softening point and improving weather resistance. However, if La ₂ O ₃ is added in a large amount in order to obtain a high refractive index, devitrification increases, and it is necessary to replace a part thereof by Y ₂ O ₃ or the like. The content is 5 to 35%, preferably 7 to 27%, more preferably 9 to 21%. By setting the content of La ₂ O ₃ to 35% or less, the devitrification property is not increased, and the liquidus temperature is not increased. Thus, a sufficient operating temperature range can be secured, and sufficient workability can be maintained. . On the other hand, when it is 5% or more, the refractive index does not fall, and deterioration of weather resistance can be prevented.

ZnO has an effect of increasing the refractive index and suppressing devitrification of the glass. The content is 10 to 30%, preferably 10 to 27%, more preferably 11 to 25%. When the content of ZnO is 30% or less, the phase separation property of the glass is not enhanced, and a homogeneous glass can be obtained. On the other hand, when it is 10% or more, the refractive index does not decrease, devitrification can be suppressed, and the liquidus temperature does not rise, and the operating temperature range can be sufficiently ensured.

Since the Gd ₂ O ₃ system can increase the refractive index component, it has the effect of not requiring a large amount of RO and improving weather resistance. Further, Gd ₂ O ₃ also has an effect of improving weather resistance. Further, it has an effect of suppressing devitrification of the glass, and can expand the operating temperature range. The content is 0.5 to 20%, preferably 1 to 15%, more preferably 6 to 11%. By setting the content of Gd ₂ O ₃ to 20% or less, the phase separation property of the glass is not enhanced, and a homogeneous glass can be obtained. On the other hand, the above effects can also be obtained by setting the content of Gd ₂ O ₃ to 0.5% or more.

The glass of the present invention may contain R' ₂ O (R' is one or more of Li, Na, and K) in order to lower the softening point. In the present invention, by introducing Gd ₂ O ₃ , the content of RO can be suppressed and the weather resistance can be improved. Therefore, even if R' ₂ O is contained, the weather resistance which can be used in actual use can be maintained.

R' ₂ O is a component for lowering the softening point, and the total amount thereof is 2 to 15%, preferably 2.5 to 10%, more preferably 3 to 8%. By setting the content of R' ₂ O to 15% or less, weather resistance can be maintained, and R' ₂ O is not volatilized from the glass during press molding, thereby preventing welding of the glass and the mold. Further, the liquidus temperature does not rise, and a sufficient working temperature range can be secured, and good mass productivity can be obtained. Further, by setting it to 2% or more, the effect of lowering the softening point of the glass can be obtained.

Among the R' ₂ O, Li ₂ O has the effect of lowering the softening point. The content is 2 to 10%, preferably 2.5 to 8%, more preferably 3 to 6%. However, Li ₂ O has a high devitrification property and a high liquidus temperature, which tends to deteriorate workability. Further, since it has a component which is likely to cause fusion with a mold when it is pressed, the content thereof is limited to 10% or less.

Na ₂ O and K ₂ O have an effect of lowering the softening point. However, when a large amount of these substances are contained, the volatile matter formed by B ₂ O ₃ -R' ₂ O is increased at the time of melting, which contributes to the generation of pulverization. Moreover, vulcanization is generated during the molding of the mold to contaminate the mold, and the life of the mold is greatly shortened. Therefore, the content of Na ₂ O is limited to 0 to 5%, preferably to 0 to 4%. Similarly, the content of K ₂ O is limited to 0 to 5%, preferably to 0 to 4%.

SiO ₂ is a component constituting the skeleton of the glass, and has an effect of suppressing devitrification of the glass and expanding the operating temperature range. Moreover, it also has the effect of improving weather resistance. The content is 6 to 20%, preferably 7 to 18%, more preferably 8 to 15%. When the content of SiO ₂ is 20% or less, the refractive index does not decrease and the softening point does not increase. On the other hand, the above effect can also be obtained by setting it as 6% or more.

Further, the glass of the present invention may contain Al ₂ O ₃ , MgO, BaO, SrO, ZrO ₂ , Y ₂ O ₃ , Ta ₂ O ₅ , Sb ₂ O ₃ or the like.

Hereinafter, the above components will be described in detail.

The Al ₂ O ₃ system constitutes a component of the skeleton and has an effect of improving weather resistance. The content is 0 to 10%, preferably 0 to 5%, more preferably 0 to 4%. Al ₂ O ₃ tends to increase the devitrification tendency. However, if it is 10% or less, it is difficult to devitrify, and since the meltability does not deteriorate, the pores or bubbles do not remain in the glass, and the lens glass can be satisfied. The quality of the requirements.

RO (R represents one or more of Mg, Ba, and Sr) functions as a solvent, and does not lower the Abbe number in B ₂ O ₃ -La ₂ O ₃ -ZnO-Gd ₂ O ₃ -based glass. It can increase the effect of the refractive index. The total amount of the content is 0 to 25%, preferably 0.01 to 23%, 3 to 20% is better, and 7 to 18% is better. When the total content of RO is 25% or less, the pre-molded glass is melted, the devitrified substance is not precipitated in the molding step, and the operating temperature range is not narrowed due to an increase in the liquidus temperature, so that the mass production can be easily performed. Further, it is possible to suppress the glass from being dissolved in the polishing washing water or various washing solutions, and to suppress deterioration of the glass surface in a high-temperature and high-humidity state, and to obtain sufficient weather resistance.

The MgO is a component which increases the refractive index, but it is preferable to enhance the phase separation tendency of the glass, and it is preferable to limit the content to 10% or less, and more preferably to 5% or less.

BaO is a component that increases the refractive index, and also has an effect of lowering the softening point in the glass system. However, since it is sometimes deposited on the surface of the glass in a high-temperature and high-humidity state, if a large amount of BaO is contained, the weather resistance of the final product is remarkably deteriorated. Therefore, the content is preferably 0 to 10%, preferably 1 to 9%, and more preferably 2 to 8%.

SrO is a component that increases the refractive index, and has an effect of lowering the liquidus temperature compared to other RO components, so that the operating temperature range can be expanded. However, SrO is the same as other RO components, and if it is contained in a large amount, the weather resistance is lowered, and the quality of the product is significantly impaired. The content of SrO is preferably 0 to 15%, preferably 1 to 10%, and more preferably 5 to 9%.

ZrO ₂ is a component that increases the refractive index and improves weather resistance. Further, since glass is formed as an intermediate oxide, it also has an effect of improving resistance to devitrification. However, when the content of ZrO ₂ is increased, the softening point is increased and the moldability is deteriorated. The content of ZrO ₂ is 0 to 5%, preferably 0.5 to 4%, more preferably 1 to 3%.

The Y ₂ O ₃ system does not lower the Abbe number and increases the refractive index component. Therefore, the devitrification resistance can be improved by substitution with La ₂ O ₃ . Further, the addition of Y ₂ O _{3 in an} appropriate amount has an inhibitory effect on the phase separation which is likely to occur in the B ₂ O ₃ -La ₂ O ₃ -ZnO-based glass. The content is preferably 0 to 15%, preferably 1 to 10%, and more preferably 2 to 8%. By setting the content of Y ₂ O ₃ to 15% or less, devitrification of the glass can be suppressed, and a sufficient operating temperature range can be secured.

Ta ₂ O ₅ has an effect of increasing the refractive index, and the content thereof is preferably 0 to 10%, more preferably 0.5 to 5%, and still more preferably 1 to 3%. When the content of Ta ₂ O ₅ is 10% or less, the Abbe number does not decrease, and desired optical characteristics can be obtained.

As the clarifying agent, Sb ₂ O ₃ may also be added. Further, in order to avoid excessive coloring of the glass, the content of Sb ₂ O ₃ is required to be 1% or less.

Further, although TiO ₂ and Nb ₂ O ₅ are components for increasing the refractive index of the glass, the Abbe number is lowered, the absorption in the ultraviolet region is increased, and the transmittance at 390 to 440 nm is decreased, which is used for short. When the wavelength is used in a lens, it may cause an obstacle, so it should be avoided in the glass.

Further, CaO is a component which raises the refractive index. However, since carbonate is formed in a high-temperature and high-humidity environment, the surface of the product is blurred, and the like, and the use in the glass should be avoided.

Further, PbO and As ₂ O _{3 are} environmentally considered, and since Ag and halogens become photoreversible color-changing carriers, substantial use in glass should be avoided.

Further, "avoiding substantial use in glass" in the present invention means that the content is 0.1% or less.

Further, in the optical glass for press molding of the present invention, in order to further prevent welding of the glass and the mold during press molding, it is preferable to set the alkalinity of the glass to 11 or less in addition to the above characteristics (preferably 9.5 or less).

Further, in the present invention, the basicity is defined as (the sum of the molar number of oxygen atoms / the sum of the field strength of the cation) × 100, and the Field Strength (hereinafter referred to as FS) can be obtained by [number 1] Got it.

[Number 1] FS=Z/r ²

Z represents the ion valence and r represents the ionic radius. In addition, the numerical values of Z and r in the present invention use the values in Table 1 (the values described in "Science Handbook Basics Revision 2 (issued by Maruzen Co., Ltd., 1975)"). According to the findings of the inventors, the lower the alkalinity, the more difficult it is to weld to the mold. The mechanism for controlling the degree of welding of the alkalinity of glass will be described below.

Here, SiO _{2 is taken} as an example to describe the calculation method of the alkalinity of the glass.

First, the number of moles of oxygen atoms is determined. 1 mol of SiO ₂ contains 2 mol of oxygen atoms. Thus, by the number of oxygen atoms in 2 mol multiplying the mole% of SiO ₂ in the glass composition, the glass can be obtained in the number of moles of SiO ₂ having an oxygen atom in the. Similarly, the number of moles of oxygen atoms of each component is determined, and the total amount thereof is referred to as "the sum of the molar numbers of oxygen atoms".

Next, find FS. Since the cation Si ^{4 +} is Z=4 and r=0.4, FS=25. Since Si ^{4 +} contains 1 mol in SiO ₂ , FS in the glass is obtained from 25 × 1 (mol) × (% by mole of SiO _{2 in} the composition).

Each component is obtained, and the total amount is referred to as "the sum of the cations of F.S.".

Then, the value obtained by dividing the sum of the molar numbers of the oxygen atoms by the sum of the "F.S. of the cations" is multiplied by 100 as the "alkalinity of the glass".

Next, the mechanism for controlling the degree of alkalinity of the glass will be described.

The alkalinity of the glass is an indicator of how much oxygen electrons in the glass are attracted by the cations in the glass. In glass with a higher alkalinity, the cations in the glass are less attracted to oxygen electrons. Therefore, when the glass having a higher basicity is in contact with a cation (mold component) having a higher electron propensity, it is easier to invade the glass from the cation of the mold than the glass having a lower alkalinity. When the cation as a mold component intrudes (diffusion) into the glass, the concentration of the mold component in the glass phase near the interface increases. Thereby, the difference in composition between the glass phase and the mold phase is reduced, so that the affinity between the two is increased, so that the glass will be easily wetted in the mold. With such a mechanism, the glass is welded to the mold. Therefore, as the alkalinity becomes lower, the mold component becomes less likely to intrude into the glass, and the glass and the mold are not welded.

Specifically, it is considered that if the alkalinity of the glass is 11 or less, preferably 9.5 or less, welding is not caused. When the alkalinity of the glass exceeds 9.5, the mold tends to be welded, and if it exceeds 11, the glass and the mold are welded to each other, and the surface accuracy and mass productivity of the product are remarkably deteriorated.

Next, a method of manufacturing an optical reading lens, a photographic lens, or the like using the glass of the present invention will be described.

First, after the glass raw materials are blended into a desired composition, they are melted in a glass melting furnace.

Next, molten glass was dropped from the front end of the nozzle to prepare a temporary droplet-shaped glass to obtain a preformed glass. Alternatively, the molten glass is subjected to rapid cooling casting to prepare a temporary glass block, which is ground, polished, and washed to obtain a preformed glass.

Then, the preformed glass is placed in a mold which has been subjected to precision machining, and is subjected to press molding while being heated to a softened state, and the surface shape of the mold is transferred onto the glass. This forming method is called a press forming method and is widely used. In this way, an optical reading lens or a photographic lens can be obtained.

[Examples]

Hereinafter, the optical glass for press molding of the present invention will be described in detail based on examples, but the present invention is not limited to the following examples.

Tables 2 and 3 show examples of the present invention (samples Nos. 1 to 11).

Each sample was prepared in the following manner. First, the glass raw material was blended into a composition as shown in the table, and melted at 1250 ° C for 2 hours using a white gold crucible. After the melting, the melt was poured onto a carbon plate, and after annealing, a sample suitable for each measurement was prepared.

For the obtained samples, the refractive index (nd), the Abbe number (vd), the softening point (Ts), the forming temperature (T _W ), the liquidus temperature (T _L ), the operating temperature range (ΔT), and the water resistance were measured. Sex and acid resistance. Also, the alkalinity was calculated. The results of these are as shown in the tables.

As can be seen from the table, in each of the samples Nos. 1 to 11 of the examples of the present invention, the refractive index was 1.6500 to 1.7359, the Abbe number was 48.3 or more, and the softening point was 625 ° C or lower. Moreover, the working temperature range is 24 ° C or more, and workability is excellent. Further, the weight loss of water resistance is 0.10% or less, and the weight loss of acid resistance is 1.10% or less, and weather resistance is good. Further, the alkalinity is 8.07 or less, and it is considered that it is difficult to cause fusion between the mold and the mold.

Further, the refractive index (nd) is represented by a measured value of a xenon lamp with respect to a d line (587.6 nm).

The Abbe number (vd) is a value obtained by using the refractive index of the above d line and the F line of the hydrogen lamp (486.1 nm) and the C line of the hydrogen lamp (656.3 nm), and the Abbe number (vd) = [ (nd-1)/(nF-nC)] was calculated.

The softening point (Ts) was measured using a fiber elongation method based on Japanese Industrial Standard R-3104.

The working temperature range (?T) was obtained as follows. First, a platinum ball pulling method determination molding temperature (T _W), corresponding to a temperature of 10 to obtain ^1.0 poise of. Further, the liquid phase temperature (T _L ) was pulverized to a powder having a maximum particle diameter of 297 to 500 μm, classified, placed in a platinum boat, and maintained in an electric furnace having a temperature gradient for 24 hours. The measurement was carried out by cooling in the air and determining the position of devitrification by an optical microscope. The difference between the forming temperature (T _W ) and the liquid phase temperature (T _L ) obtained in this manner was taken as the working temperature range (ΔT).

Water resistance and acid resistance, according to the Japanese Optical Glass Industry Council specification 06-1975, the particle size of the glass sample is broken to 420~590 μm, the weight of the specific gravity is weighed, placed in a white gold basket, and put into the test. The drug flask was treated in a boiling water bath for 60 minutes to calculate the weight loss (% by weight) of the treated powder glass. Further, the reagent used in the water resistance evaluation was pure water having a pH adjusted to 6.5 to 7.5, and the reagent used in the acid resistance evaluation was an aqueous solution of nitric acid adjusted to 0.01 N.

The alkalinity is calculated based on the formula (sum of the molar number of oxygen atoms/the total field strength of the cation) × 100. Furthermore, the Field Strength (hereinafter referred to as F.S.) in the formula is obtained by the above [1].

Further, Z represents the ion valence, r represents the ionic radius, and the values of Z and r use the values in Table 1.

Claims (9)

An optical glass for press molding, which has a refractive index (nd) of 1.65 to 1.75, an Abbe number (νd) of 45 or more, a softening point of 650 ° C or less, and no lead; and ΔT = {forming temperature (10 ^1.0 poise) The temperature) - liquid phase temperature is 20 ° C or more, and the weight loss in the water resistance of the powder method of JOGIS according to the Japanese Optical Glass Industry Association specification is 0.2% or less, and is in accordance with the powder method of the Japan Optical Glass Industry Association JOGIS. The weight loss is 1.2% or less, and includes B ₂ O ₃ -La ₂ O ₃ -ZnO-Gd ₂ O ₃ glass containing 2.5 to 10% of Li ₂ O and 11 to 30% of ZnO by weight %. The optical glass for press molding of claim 1, wherein the alkalinity of the glass is 11 or less. The optical glass for press molding according to claim 1, wherein 24 to 45% of B ₂ O ₃ , 5 to 35% of La ₂ O ₃ , 11 to 30% of ZnO, and 0.5 to 20% by weight % are calculated. Gd ₂ O ₃ . The optical glass for press molding of claim 1, which contains 2.5 to 15% of R' ₂ O (R' represents one or more of Li, Na, and K). The optical glass for press molding according to claim 1, wherein the weight % is 2.5 to 10% of Li ₂ O, 0 to 5% of Na ₂ O, and 0 to 5% of K ₂ O. The optical glass for press molding according to claim 1, wherein 6 to 20% of SiO ₂ , 0 to 10% of Al ₂ O ₃ , 0 to 10% of MgO, and 0 to 10% of BaO are contained in terms of % by weight. 0 to 15% of SrO, 0 to 5% of ZrO ₂ , 0 to 15% of Y ₂ O ₃ , 0 to 10% of Ta ₂ O ₅ , and 0 to 1% of Sb ₂ O ₃ . The optical glass for press molding according to claim 1, wherein the RO contains 0 to 25% of RO (R represents one or more of Mg, Ba, and Sr). The optical glass for press molding according to claim 1, wherein substantially no TiO ₂ , Nb ₂ O ₅ or CaO is contained. An optical glass for press molding, which comprises 24 to 45% of B ₂ O ₃ , 5 to 35% of La ₂ O ₃ , 11 to 30% of ZnO, and 0 to 10% of Ta ₂ O _{5 by} weight %. 2.5 to 10% of Li ₂ O, 0 to 5% of Na ₂ O, 0 to 5% of K ₂ O, and 2.5 to 15% of R' ₂ O (R' represents one or more of Li, Na, and K ), 6 to 20% of SiO ₂ , 0 to 10% of Al ₂ O ₃ , 0 to 10% of MgO, 0 to 10% of BaO, 0 to 15% of SrO, and 0 to 25% of RO (R means One or more of Mg, Ba, and Sr), 0 to 5% of ZrO ₂ , 0 to 15% of Y ₂ O ₃ , 0.5 to 20% of Gd ₂ O ₃ , and 0 to 1% of Sb ₂ O ₃ , and It does not substantially contain TiO ₂ , Nb ₂ O ₅ or CaO.