WO2010071144A1 - Glass - Google Patents

Abstract

Disclosed is a glass which comprises WO₃ and at least one component selected from a group consisting of La₂O₃, SrO and BaO, wherein the content (by mol%) of WO₃ meets the requirement represented by the following formula: 25% ≤ WO₃ ≤ 85%, and which meets at least one of the three requirements represented by the following formulae (i) to (iii): (i) 15% ≤ La₂O₃ ≤ 25%; (ii) 15% ≤ SrO ≤ 25%; and (iii) 15% ≤ BaO ≤ 25%.  For example, when the glass meets the requirement represented by formula (i), the glass may additionally comprise at least one component selected from a group consisting of TiO₂ and SiO₂.  In this case, the glass has following contents (by mol%): 25% ≤ WO₃ ≤ 85%, 15% ≤La₂O₃ ≤ 25%, 0% ≤ TiO₂ ≤ 55%, and 0% ≤ SiO₂ ≤ 10%.  It becomes possible to provide a glass having, a refractive index (n_d) and an Abbe’s number (ν_d) respectively represented by the following formulae: 1.90 ≤ n_d ≤ 2.30 and 25 ≤ν_d ≤ 45.

Description

Glass

The present invention relates to glass, particularly glass that is suitably used as an optical material.

Optical systems used in cameras, microscopes, telescopes, endoscopes, etc., correct aberrations by combining lenses made of materials with different optical properties (mainly refractive index and Abbe number representing wavelength dispersion). ing. The wider the combination of the refractive index and the Abbe number, the greater the degree of freedom in optical design, which is advantageous. Particularly, a high refractive index material and a low dispersion material (material having a large Abbe number) are useful. Regarding optical glass, which is a typical lens material, a new composition has been developed in the direction of higher refractive index and lower dispersion, and it continues today.

FIG. 5 shows the refractive index and Abbe number of about 100 types of optical glass commercially available from a certain optical glass manufacturer (Sumita Optical Glass). The area where the points are plotted is a realizable range as the optical glass. This region is almost the same even in the case of products from other optical glass manufacturers.

When expanding the optical properties of optical glass, the biggest obstacle is glass crystallization. Optical glass is produced by cooling and solidifying a raw material melted with a crucible. However, in the case of a glass composition in which crystals are easily formed, crystals are precipitated during cooling, so that a transparent and uniform glass mass cannot be obtained. Such a phenomenon is called “crystallization” or “devitrification”. The biggest reason why the glass outside the region shown in FIG. 5 has not been put into practical use is crystallization.

Crystallization may occur as a result of the growth of small crystals in the glass, but when the glass is in contact with a solid (such as clay or platinum as a crucible material), the interface is It is known that crystallization is very likely to occur as a nucleation point.

The crystallization of the glass proceeds in the intermediate temperature range between the molten state and the solid state. In the molten state, the atoms can move freely to some extent, so the crystal does not precipitate. In the solid state, the atoms do not move, so the crystal does not grow. Therefore, it can be said that crystallization can be prevented if it passes through a temperature range where crystallization occurs due to rapid cooling in a short time. As a specific method of rapid cooling, a method of “placing a molten raw material between metal rollers” or “injecting it into water” is used. However, the glass obtained by such a quenching method has a problem of being difficult to use as an optical element such as a lens because it is in the form of a fine powder or flake. In order to use the lens material, it is necessary to prepare a homogeneous glass body having a certain size (at least the minimum diameter (minimum portion length) is 0.5 mm or more, preferably 1 mm or more). is there.

As a method of producing a glass of a certain size while having a composition that is easy to crystallize, glass is produced by a containerless solidification method in which the raw material is suspended in the air with an upward gas nozzle and irradiated with a laser in that state to vitrify it. A method is disclosed (for example, see Patent Document 1). According to this method, since the glass can be melted and solidified without being in contact with a container such as a crucible, crystallization with the interface as a nucleation point can be prevented. As a result, a glass sphere having a weight of 20 mg composed of barium titanate, which is a ferroelectric substance that is very easily crystallized, is obtained.

Patent Document 2 lists many glass compositions produced by the containerless solidification method. For example, a plurality of examples of glass having a La ₂ O ₃ —TiO ₂ —ZrO ₂ -based composition (which may not contain ZrO ₂ ) produced using a containerless solidification method are illustrated.

All of the components contained in the La ₂ O ₃ —TiO ₂ —ZrO ₂ composition (hereinafter referred to as a three-component system including the case where ZrO ₂ is not contained for convenience) are high refractive index components. Therefore, the refractive index of this ternary glass is 2.2 or more, which is much higher than general optical glass. Therefore, this ternary glass is very useful as an optical material such as a lens.

JP 2006-248801 A International Publication No. 2008/032789 Pamphlet

However, all of the three-component glass compositions described as specific examples in the above-mentioned patent documents contain a very large amount of TiO ₂ . Specifically, the molar ratio of TiO ₂ is 57% even in the smallest example (Example sample 9-1 of Patent Document 2), and in all other examples it exceeds 80%. From this, it is clear that TiO ₂ is the basis for glass formation. TiO ₂ is a component that makes the refractive index very high, but on the other hand, it also has a great effect of increasing dispersion due to wavelength. Therefore, the glass composition conventionally proposed as a glass containing a large amount of TiO ₂ results in a highly dispersed material having an Abbe number of less than 25.

The present invention has been made to solve the above-described problems, and can be an optical material having a high refractive index and low dispersion, which could not be realized by a general optical glass or a conventional oxide glass based on TiO _2. It is an object to provide glass.

In order to solve the above problems, the present invention includes WO ₃ and at least one selected from the group consisting of La ₂ O ₃ , SrO and BaO, and the composition expressed in mol% is 25% ≦ WO ₃ ≦ 85% is satisfied, and
(I) 15% ≦ La ₂ O ₃ ≦ 25%,
(Ii) 15% ≦ SrO ≦ 25%, and
(Iii) 15% ≦ BaO ≦ 25%,
A glass that satisfies at least one of the three conditions is provided.

The glass of the present invention can realize a high refractive index and low dispersion, which has been difficult to realize with general optical glass or oxide glass having a conventional composition based on TiO ₂ . For this reason, the area | region of the optical characteristic of optical glass can be expanded rather than before by using the glass of this invention as optical glass. In addition, the glass of the present invention has a composition that is easy to crystallize compared to the composition of general optical glass, but can be vitrified at low cost by using a manufacturing method such as a rapid cooling method or a containerless solidification method. It becomes.

It is a figure which shows the optical characteristic of the glass obtained by the Example of this invention, and the range of a preferable optical characteristic. In an Example, it is a figure which shows a mode that the refractive index of spherical glass is measured. In an Example, it is a figure explaining the optical space | interval of a pattern and spherical glass at the time of measuring the refractive index of spherical glass, and the distance from the upper surface of spherical glass to the real image of a pattern. In an Example, it is a schematic diagram which shows the apparatus used when melting a glass raw material by the containerless solidification method. It is a figure which shows the range of the optical characteristic of the optical glass marketed, and the range of a preferable optical characteristic.

The glass of the present invention contains WO ₃ and at least one selected from the group consisting of La ₂ O ₃ , SrO and BaO. The composition of the glass of the present invention, expressed in mol%, satisfies 25% ≦ WO ₃ ≦ 85%, and
(I) 15% ≦ La ₂ O ₃ ≦ 25%,
(Ii) 15% ≦ SrO ≦ 25%, and
(Iii) 15% ≦ BaO ≦ 25%,
At least one of the three conditions is satisfied. In addition, the glass of this invention may contain oxide components other than the said component. In that case, an oxide component other than the above components may be added to improve the optical properties, easiness of vitrification, chemical durability and the like of the glass of the present invention. The glass of the present invention may be substantially composed of the above components (consisting of WO ₃ and at least one selected from the group consisting of La ₂ O ₃ , SrO and BaO). Satisfies the above composition range. Note that “substantially composed of the above components” means that other components than the above components are not included except for components inevitably mixed as impurities. In addition, the component mixed as an impurity is 5 mol% or less, for example, Preferably it is 2 mol% or less.

The glass of the present invention contains WO ₃ as an essential component. Combining WO ₃ with other oxides can greatly reduce its melting point. Therefore, by combining WO ₃ with a component that can realize low dispersion at a high refractive index, such as La ₂ O ₃ , it is possible to easily melt the raw material and vitrify it. Furthermore, according to the composition of the glass of the present invention, a high refractive index and low dispersion can be realized, so that it is possible to further widen the optical property area of the optical glass.

For example, the glass of the present invention can be a glass satisfying a refractive index n _d of 1.90 ≦ n _d ≦ 2.30 and an Abbe number ν _d of 25 ≦ ν _d ≦ 45 as preferable optical characteristics. This region of preferred optical properties is illustrated in FIGS. This preferred optical property region is on the left side (low dispersion side) in FIG. 1 and FIG. 5 than the Abbe number region of optical glass having a refractive index of more than 1.90 among general optical glass. Optical design that was not possible with optical glass can be realized. The lower limit 1.90 of the refractive index n _d, even compared to conventional optical glasses is the highest class, is very useful in the optical design. Further, the lower limit of the preferable refractive index n _d is 2.00.

As a first composition example of the glass of the present invention, there may be mentioned one having a mixture of WO ₃ and SrO as an essential component. Since SrO is a component that lowers the melting point of glass, there is an advantage that it is easily vitrified. Therefore, for example, as shown in Example 1 to be described later, when the composition of WO ₃ is 80 mol% and SrO is 20 mol%, a glass of a certain size can be obtained by a rapid cooling method. From this, a suitable composition range that is easy to vitrify is shown in mol%, and is in the vicinity of the composition 1-1 of Example 1.
75% ≦ WO ₃ ≦ 85%
15% ≦ SrO ≦ 25%
It is.

As a second composition example of the glass of the present invention, there may be mentioned one having a mixture of WO ₃ and La ₂ O ₃ as an essential component. Examples 2 and 3 described later correspond to this second composition example. Since La ₂ O ₃ is a component having a high refractive index and a low dispersion, according to the second composition example, a glass having a high refractive index and a low dispersion can be obtained more effectively. As for the second composition example, or higher refractive index by adding a certain amount of TiO _2, it may be or added SiO _2. SiO ₂ has an effect of facilitating vitrification, and it becomes easy to make glass of a certain size by a rapid cooling method. In this second composition example, from the results of Example 2 and Example 3 to be described later,
25% ≦ WO ₃ ≦ 85%
15% ≦ La ₂ O ₃ ≦ 25%
0% ≦ TiO ₂ ≦ 55%
0% ≦ SiO ₂ ≦ 10%
Is a suitable composition range that is easy to vitrify.

As for the composition system containing all of _{WO 3, La 2 O 3,} TiO 2, from the results of Example 3, shown in mol%,
25% ≦ WO ₃ ≦ 55%
15% ≦ La ₂ O ₃ ≦ 25%
25% ≦ TiO ₂ ≦ 55%
0% ≦ SiO ₂ ≦ 10%
However, it is a suitable composition range which is easy to vitrify.

As a third composition example of the glass of the present invention, a glass having a mixture of WO ₃ and BaO as an essential component can be mentioned. Example 4 described later corresponds to the third composition example. Although BaO is not as high as La ₂ O _3, it is a component having a high refractive index and a low dispersion. Therefore, according to the third composition example, a glass having a high refractive index and a low dispersion can be obtained more effectively. BaO also has the effect of facilitating vitrification. In the case of the third composition example, as shown in Example 4, for example, when the composition of WO ₃ is 80 mol% and BaO is 20 mol%, it becomes easy to form a glass of a certain size by a rapid cooling method. From this, the preferred range that is easy to vitrify is shown in mol%, and in the vicinity of the composition 4-1 of Example 4,
75% ≦ WO ₃ ≦ 85%
15% ≦ BaO ≦ 25%
It is.

The glass of the present invention may be composed of only the respective components shown in the first to third composition examples, or may contain other components. For example, B ₂ O ₃ , Na ₂ O, MgO, P ₂ O ₅ , K ₂ O, ZrO ₂ , ZnO, Nb ₃ O ₅ , MoO ₃ , AgO, SnO ₂ , Ta ₂ O ₅ , Nd ₂ O ₅ , PbO or the like may be added in the range of 10 mol% or less to improve the optical properties, easiness of vitrification, chemical durability, etc. for the glass of the present invention.

The glass of the present invention can be applied as a material for an optical element such as a lens because the minimum portion can have a relatively large size of 0.5 mm or more.

Next, a method for producing the glass of the present invention, particularly a cooling method will be described.

Although the composition of the glass of the present invention is smaller in dispersion than general optical glass, it is easier to crystallize than general optical glass, so vitrification may be difficult by melting and cooling (solidification) with a normal crucible. . Even in that case, for example, as shown in the examples described later, by using a rapid cooling method such as "dropping on a metal plate", "dropping into boiling water", or a containerless solidification method, A transparent and homogeneous glass having a certain size can also be obtained.

In the method of “dropping into boiling water”, water in the vicinity of the melt is immediately vaporized by pouring the melt into boiling water. Done at the same time. Accordingly, both vitrification of the melt by rapid cooling and suppression of crack generation by excessive cooling can be realized. Immediately after throwing the melt into the water, the viscosity is low because the high temperature is maintained for a short time due to the heat insulating action of water vapor. At this time, a part of the melt is divided by the generation of water vapor and becomes spherical due to the surface tension. Thereafter, the melt is cooled by water vapor, and quickly passes through the crystallization temperature range to be vitrified. In this way, spherical glass is obtained from the melt. In this method, it is of course possible to use another liquid maintained at a boiling point or a temperature near the boiling point, instead of boiling water.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In the following examples, the contents of the respective components are all shown in mol%.

Example 1
In Example 1, an attempt was made to vitrify the first composition example (composition 1-1 shown in Table 1) by a rapid cooling method. That is, powders of strontium oxide and tungsten oxide (special grade reagent) were mixed so that the composition of the obtained glass was SrO: 20% and WO ₃ : 80% to obtain a batch of 25 g. This batch was put in an alumina crucible and melted at 1300 ° C. for 30 minutes in an electric furnace. Separately, about 1 liter of pure water was placed in a stainless steel container and boiled with a gas burner. The alumina crucible was taken out from the electric furnace, and the molten glass was sequentially poured into boiling pure water in a stainless steel container. After pouring, the gas burner was stopped and the glass body in pure water was collected. This was dried to obtain a total of 3.5 g of a plurality of transparent and crack-free spherical glasses having a diameter of about 0.7 to 1.9 mm.

About the obtained spherical glass, refractive index _nd and Abbe number (nu) _d were measured by the following method. Note that the refractive index and Abbe number were measured by arbitrarily selecting one from the obtained spherical glasses. The results are shown in Table 1 and FIG. As can be seen from FIG. 1, the composition 1-1 has a small dispersion (in other words, a large Abbe number) and falls within the range of preferable optical characteristics.

<Measurement method of refractive index>
The refractive index was calculated from the focal position of the spherical glass. As shown in FIG. 2, a glass plate 3 having a pattern 3a formed on one side is placed on a stage 2 of a microscope 1, and a spherical glass 4 to be measured is placed thereon. The surface 5 on which the pattern 3a of the glass plate 3 is formed is irradiated with light 5 from which illumination light 8 is made substantially monochromatic by a narrow-band interference filter 9 from below. There are three types of wavelengths corresponding to F-line (486 nm), d-line (588 nm, and C-line (656 nm), because a real image 6 of the pattern is formed near the upper surface of the spherical glass 4 by the lens action of the spherical glass 4. The position (distance z ′ from the upper surface to the real image 6 (see FIG. 3)) was measured using the microscope 1 and the linear gauge 7. As the pattern 3a, a line-and-space lattice of 40 lines / mm was used. The optical distance between the pattern 3a and the spherical glass 4 (−z (z takes a negative value)) is separately determined by measuring the difference in focus position with the microscope 1 for the above three wavelengths. From the values of the diameter (2r) of the spherical glass 4, the distance (z ′) from the upper surface of the spherical glass 4 to the real image 6, and the optical distance (−z) between the pattern 3a and the spherical glass 4, The refractive index n of the glass 4, calculated for each wavelength by the following equation (1) to determine the value of n _C, n _d, n _F. Note that this equation (1), the imaging of paraxial ray It is derived from the relational expression.
(Rz′−rz−2zz ′) n = 2r ² + 2rz′−2rz−2zz ′ (1)

<Abbe number measurement method>
The Abbe number ν _d was calculated by the following equation (2).
ν _d = (n _d −1) / (n _F −n _C ) (2)

(Example 2)
In Example 2, an attempt was made to vitrify the second composition example (composition 2-1 shown in Table 1) containing WO ₃ and La ₂ O ₃ as essential components by a rapid cooling method. That is, lanthanum oxide and tungsten oxide powder (special grade reagent) were mixed so that the composition of the obtained glass was La ₂ O ₃ : 20% and WO ₃ : 80% to obtain a 25 g batch. This batch was put in an alumina crucible and melted at 1300 ° C. for 30 minutes in an electric furnace. Separately, about 1 liter of pure water was placed in a stainless steel container and boiled with a gas burner. The alumina crucible was taken out from the electric furnace, and the molten glass was sequentially poured into boiling pure water in a stainless steel container. After pouring, the gas burner was stopped and the glass body in pure water was collected. This was dried to obtain a total of 0.25 g of a plurality of transparent and crack-free spherical glasses having a diameter of about 0.2 to 1.7 mm.

With respect to the obtained spherical glass, the refractive index n _d and Abbe number ν _d were measured in the same manner as in Example 1. The results are shown in Table 1 and FIG. From FIG. 1, it can be seen that the composition 2-1 is in the range of preferable optical characteristics with small dispersion.

(Example 3)
In Example 3, among the second composition examples, WO ₃ and La ₂ O ₃ are essential components, and further TiO ₂ and / or SiO ₂ are contained as other components (compositions 3-1 to 3 shown in Table 1). 3-4) was melted by a containerless solidification method.

First, the containerless coagulation method used in this example will be described. FIG. 4 is a schematic diagram showing the entire apparatus used in this example in order to melt a glass raw material by a containerless solidification method. This apparatus is provided with an ejection nozzle 41 that allows gas to flow out in order to float the glass raw material (melt). The ejection nozzle 41 is fixed to a column 42 and is connected to a tube 43 for supplying gas. The tube 43 is connected to a high-pressure gas cylinder (not shown) through a regulator 44 and a flow meter 45 for adjusting the flow rate. This apparatus further includes a laser oscillator 46 for irradiating the glass material with laser light. The laser oscillator 46 is fixed to the lateral branch 47 of the support column 42 to which the ejection nozzle 41 is fixed. The traveling direction of the laser beam 48 emitted from the laser oscillator 46 is changed by the mirror 49 fixed to the lateral branch 47, and is focused on the floating body 51 (glass raw material) by the convex lens 50. In the horizontal branch 47, a CCD camera 52 for observing the state of the floating body 51 is installed on the side opposite to the fixed side of the laser oscillator 46.

Hereinafter, the glass manufacturing procedure of the present embodiment using the apparatus shown in FIG. 4 will be described. First, a raw material pellet was separately prepared. The raw material pellets are made of glass material (metal oxide, etc.) powder (special grade chemicals) each having a predetermined molarity so that the resulting glass has the compositions 3-1 to 3-4 shown in Table 1. A glass raw material is prepared by mixing at a ratio. The prepared glass material was ground in a mortar, ethanol was added and mixed well, then placed in a ceramic crucible, and fired at 1000 ° C. for 12 hours (first time) in an electric furnace. The glass raw material after firing is ground again in a mortar, and the viscosity is adjusted by adding ethanol. Then, using a pressing die, a pressure of about 1.6 × 10 ⁸ Pa is applied and the diameter is 2 mm and the thickness is about 1 mm. It was molded into a disk shape. The material molded into a disk shape was baked (second time) at 1100 ° C. for 12 hours in an electric furnace, and sufficiently cooled to obtain raw material pellets.

The pellet produced in this manner is placed on the ejection nozzle 41 in FIG. 4 and suspended with a regulator 44 and a flow meter 45 at an appropriate gas flow rate, and then the laser oscillator 46 is activated to irradiate the pellet with laser light. The pellet was heated. The pellet melted in a few seconds and floated in the nozzle 41 in a spherical state due to its surface tension. When the laser beam irradiation was stopped when the melt became uniform, the melt was quenched and turned into a spherical glass. Since the temperature of the spherical glass dropped to room temperature in a few seconds, it could be taken out from the ejection nozzle 41 with tweezers.

The laser oscillator 46 includes a Universal Laser System Inc., USA. A carbon dioxide laser device “ULC-100-OEM” manufactured by the company was used. The oscillation wavelength was 10.6 μm, and the maximum output was nominally 100 W.

In this example, the raw material pellets were placed in the ejection nozzle 41 of the apparatus shown in FIG. 4, and dry air was flowed at a flow rate of 0.3 to 0.6 L / min to suspend the raw material pellets. In this state, the laser beam was irradiated to melt the raw material pellets, and then cooled by stopping the laser beam irradiation. As a result, a colorless and transparent spherical glass having a diameter of about 1.2 mm was obtained, and devitrification and striae were not observed.

With respect to the obtained spherical glass, the refractive index n _d and Abbe number ν _d were measured in the same manner as in Example 1. The results are shown in Table 1 and FIG. As can be seen from FIG. 1, the compositions 3-1 to 3-4 are in the range of preferable optical characteristics with small dispersion.

Example 4
In Example 4, for the third composition example (composition 4-1 shown in Table 1) containing WO ₃ and BaO as essential components, vitrification was attempted using the same containerless solidification method as in Example 3. As a result, a colorless and transparent spherical glass having a diameter of about 1.2 mm was obtained, and devitrification and striae were not observed. With respect to the obtained spherical glass, the refractive index n _d and Abbe number ν _d were measured in the same manner as in Example 1. The results are shown in Table 1 and FIG. From FIG. 1, it can be seen that the composition 4-1 is in the range of preferable optical characteristics with small dispersion. With composition 4-1, a transparent spherical glass could be produced by the same rapid cooling method as in Example 1.

The glass obtained by the present invention is excellent in optical properties, and can be realized even if it is a certain size. Therefore, it can be suitably used for an optical element such as a lens.

Claims (6)

1. WO ₃ and at least one selected from the group consisting of La ₂ O ₃ , SrO and BaO, the composition represented by mol% satisfies 25% ≦ WO ₃ ≦ 85%, and
   (I) 15% ≦ La ₂ O ₃ ≦ 25%
   (Ii) 15% ≦ SrO ≦ 25%
   (Iii) 15% ≦ BaO ≦ 25%
   Glass satisfying at least one of the three conditions.
2. The values of the refractive index n _d and the Abbe number ν _d are
   1.90 ≦ n _d ≦ 2.30
   25 ≦ ν _d ≦ 45
   The glass of Claim 1 satisfy | filling.
3. The glass according to claim 1, wherein the length of the minimum portion is 0.5 mm or more.
4. A composition comprising La ₂ O ₃ as at least one selected from the group consisting of La ₂ O ₃ , SrO and BaO, and further including at least one selected from the group consisting of TiO ₂ and SiO _2, and expressed in mol% But,
   25% ≦ WO ₃ ≦ 85%
   15% ≦ La ₂ O ₃ ≦ 25%
   0% ≦ TiO ₂ ≦ 55%
   0% ≦ SiO ₂ ≦ 10%
   The glass of Claim 1 satisfy | filling.
5. A composition containing SrO as at least one selected from the group consisting of La ₂ O ₃ , SrO and BaO, and represented by mol%,
   75% ≦ WO ₃ ≦ 85%
   15% ≦ SrO ≦ 25%
   The glass of Claim 1 satisfy | filling.
6. The composition represented by mol% containing BaO as at least one selected from the group consisting of La ₂ O ₃ , SrO and BaO,
   75% ≦ WO ₃ ≦ 85%
   15% ≦ BaO ≦ 25%
   The glass of Claim 1 satisfy | filling.

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