JPWO2010071202A1 - Glass and glass processing method - Google Patents

Abstract

The glass of the present invention is composed of three components of La2O3, TiO2 and SiO2, or four components of La2O3, TiO2, SiO2 and ZrO2, and the composition expressed in mol% is 13.5% ≦ La2O3 ≦ 19%, 57.5. % ≦ TiO2 ≦ 77.5%, 4.5% ≦ SiO2 ≦ 9.5%, 0% ≦ ZrO2 ≦ 17.5%. As a method for treating the glass of the present invention, when the glass transition point of the glass of the present invention is expressed as Tg, the glass is held in a temperature region of (Tg-50 ° C.) or more and Tg or less for 10 minutes or more and 120 minutes or less. A method is available. As another method for processing the glass of the present invention, the glass of the present invention held in a flowing gas is irradiated with a laser, and the glass is heated and melted at a temperature equal to or higher than the melting point of the glass for 20 seconds. A method of cooling the glass after holding for 300 seconds or less can also be used.

Description

  The present invention relates to glass and a method for processing the glass.

  A glass material of a certain size is made by rapidly cooling a raw material melted with a crucible. However, in the case of a composition in which crystals are easily formed, crystals are precipitated during cooling, so that a transparent and uniform glass lump cannot be obtained. Such a phenomenon is called “crystallization” or “devitrification”, and a composition that is easily crystallized cannot be a practical glass material. Therefore, in developing a glass composition having novel characteristics (for example, optical characteristics such as high refractive index and low dispersion), how to prevent crystallization is a major constraint.

  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 occurs as a nucleation point.

  Glass crystallization proceeds in the temperature region between the glass transition point and the glass melting point. The glass state in this temperature region is a metastable state that is more unstable than the crystal, and if the crystal nucleus exists and the crystallization rate is high, the glass crystallizes. 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 obtain an optical element by performing processing such as polishing, a certain size (at least the minimum diameter (minimum portion length) of about 0.5 mm or more) is required.

  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 has been proposed (see, for example, Patent Document 1). According to this method, since the glass can be melted and solidified without being brought into 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 -based composition (hereinafter referred to as a three-component system including the case where ZrO ₂ is not included for convenience) are high refractive index components. Therefore, the refractive index of this ternary glass is as high as 2.2 or higher. In addition, La ₂ O ₃ is a component that reduces the wavelength dispersion, so that it becomes a low-dispersion glass among the glasses having a refractive index exceeding 2. 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, although a spherical glass with a diameter of 1 to 2 mm can be obtained depending on the containerless solidification method, crystallization occurs during cooling when trying to make the glass larger than that, so that the use of the obtained glass is limited. was there. For example, a general camera lens requires a lens diameter of about 5 mm at a minimum, but the size cannot be secured with glass produced by a containerless solidification method. Furthermore, in order to manufacture glass industrially by the containerless solidification method, a high-power laser device, an optical device for laser control, a gas floating device, and the like are necessary, which increases the equipment cost. was there. Furthermore, when the containerless solidification method is used, minute spherical glasses must be sequentially produced one by one, which is disadvantageous in terms of productivity and cost.

  In addition, according to the study by the present inventors, even if an attempt is made to vitrify a conventional ternary glass by virtue of a rapid cooling method that can be carried out more easily than a containerless solidification method and can reduce costs, Therefore, it has been very difficult to produce a glass lump that is large enough to be used as a material for an optical element.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a glass that is hardly crystallized to such an extent that it can be vitrified even by a method other than the containerless solidification method.

Further, a glass containing a large amount of TiO ₂ such as the above three-component glass is likely to have a low transmittance in a short wavelength region (purple light or less) or to generate a color that can be visually confirmed. There was also a problem. Therefore, an object of the present invention is to provide a glass processing method for suppressing the decrease in transmittance and the occurrence of coloring in order to solve such problems.

  As a result of intensive studies, the inventors of the present invention have achieved vitrification that can be vitrified by methods other than the containerless solidification method while maintaining optical properties comparable to those of the conventional ternary glass. An easy composition was found.

The glass of the present invention is composed of three components of La ₂ O ₃ , TiO ₂ and SiO ₂ , or four components of La ₂ O ₃ , TiO ₂ SiO ₂ and ZrO ₂ , and the composition represented by mol% is
13.5% ≦ La ₂ O ₃ ≦ 19%
57.5% ≦ TiO ₂ ≦ 77.5%
4.5% ≦ SiO ₂ ≦ 9.5%
0% ≦ ZrO ₂ ≦ 17.5%
Meet. Further, the preferred composition range in the glass of the present invention consists of four components of La ₂ O ₃ , TiO ₂ , SiO ₂ and ZrO ₂ , expressed in mol%,
16% ≦ La ₂ O ₃ ≦ 18%
63.9% ≦ TiO ₂ ≦ 65.9%
5.5% ≦ SiO ₂ ≦ 7.5%
10.6% ≦ ZrO ₂ ≦ 12.6%
It is.

  Furthermore, the present invention provides, as a first method for treating the glass of the present invention described above, when the glass transition point of the glass is represented by Tg, the glass is placed in a temperature region of (Tg-50 ° C.) or more and Tg or less for 10 minutes. Provided is a method for treating glass, which is maintained for a period of 120 minutes or less.

  Furthermore, the present invention provides a second method for treating the glass of the present invention, wherein the glass held in a flowing gas is irradiated with laser, and the glass is heated at a temperature equal to or higher than the melting point of the glass. A glass processing method is provided in which the glass is cooled after being held for 20 seconds to 300 seconds in a molten state.

  The glass of the present invention has a composition that is harder to crystallize than conventional three-component glasses. Therefore, according to the present invention, vitrification is possible even if a method other than the containerless solidification method is used.

Further, according to the glass processing method of the present invention, even if the glass of the present invention contains a relatively large amount of TiO ₂ , it is possible to suppress a decrease in transmittance in the short wavelength region and the occurrence of coloring.

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. It is a schematic diagram which shows the apparatus used when melting a glass raw material by the containerless solidification method. 4A and 4B are diagrams illustrating a method for measuring the internal transmittance of spherical glass in Examples. It is a graph which shows the relationship between internal transmittance and heat processing time about the glass of Example 3. FIG. It is a graph which shows the relationship between internal transmittance and heat processing time about the glass of Example 4. FIG.

The glass of the present invention is composed of 3 components of La ₂ O ₃ , TiO ₂ and SiO ₂ , or 4 components of La ₂ O ₃ , TiO ₂ , SiO ₂ and ZrO ₂ , and the composition shown in mol% is
13.5% ≦ La ₂ O ₃ ≦ 19%
57.5% ≦ TiO ₂ ≦ 77.5%
4.5% ≦ SiO ₂ ≦ 9.5%
0% ≦ ZrO ₂ ≦ 17.5%
Meet.

Although conventional ternary glass contains TiO ₂ which is an intermediate oxide, the glass network forming ability of TiO ₂ is a typical glass network forming component (SiO ₂ , S, B ₂ O _3, etc.) Therefore, it is difficult to form a network structure and vitrification is difficult. In addition, since the conventional ternary glass has a high melting point, it takes a long time to cool down, and crystal nuclei are generated during cooling and crystal growth occurs, which is a cause of devitrification. For this reason, it is difficult to obtain a practical glass material by devitrifying immediately by a normal melting method.

Therefore, the present inventors have improved the composition based on the conventional three-component system, and are composed of four components in which SiO ₂ is added in the above composition range to the conventional three-component system as a composition that facilitates vitrification. A composition and a three-component system having SiO ₂ as an essential component by removing ZrO ₂ from the conventional three-component system have been found.

Further, the preferred composition range of the glass of the present invention consists of four components of La ₂ O ₃ , TiO ₂ , SiO ₂ and ZrO ₂ , expressed in mol%,
16% ≦ La ₂ O ₃ ≦ 18%
63.9% ≦ TiO ₂ ≦ 65.9%
5.5% ≦ SiO ₂ ≦ 7.5%
10.6% ≦ ZrO ₂ ≦ 12.6%
It is. Among the glasses of the present invention, a glass satisfying this preferred composition range can be easily vitrified, and can also achieve good optical properties comparable to those of conventional three-component glasses.

The glass of the present invention is composed of the above four components or the above three components, but the component inevitably mixed as an impurity is, for example, about 5 mol% as the upper limit (preferably about 2 mol% as the upper limit). ) May be included. Examples of impurities include SnO ₂ , B ₂ O ₃ , Na ₂ O, MgO, P ₂ O ₅ , K ₂ O, ZnO, Nb ₃ O ₅ , MoO ₃ , AgO, Ta ₂ O ₅ , WO ₃ , Nd. ₂ O ₅ , PbO, Al ₂ O _{3 and the} like.

  The present invention will be specifically described below.

(Glass of the present invention)
The melting point of the glass of the present invention is lower than that of conventional ternary glass. As a result, the glass of the present invention is easily melted and the time required for rapid cooling is shortened, so that the vitrification is much easier than the conventional ternary glass. Furthermore, the glass of the present invention has a large temperature difference between the glass transition point and the crystallization temperature, so that crystallization hardly occurs when it is gradually cooled at a temperature near the glass transition point in order to remove strain.

  Further, among the glasses of the present invention, those satisfying the above preferred composition range have a slightly lower refractive index than conventional ternary glasses, but have a higher Abbe number and improved dispersibility. In addition, good optical characteristics can be realized.

  Next, the manufacturing method of the glass of this invention, especially the cooling method are demonstrated.

  The composition of the glass of the present invention has a higher refractive index and lower dispersion than ordinary optical glass, but it is easier to crystallize than ordinary optical glass. Therefore, it is difficult to vitrify by melting and cooling (solidifying) with a normal crucible. There are cases. In that case, it is good to use the method of quenching and vitrifying by dropping the molten raw material in the air. As another example, as shown in the examples to be described later, the molten raw material is transparent and homogeneous by using a rapid cooling method such as “dropping onto a metal plate” or “dropping into boiling water”. Glass can also be obtained.

  In the “drop on metal plate” method, the molten raw material is rapidly cooled when it collides with the metal surface, and the raw material is finely divided and scattered by the collision. It is cooled and vitrified.

  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.

As also shown in Example 1 to be described later, the glass of the present invention containing SiO ₂ as a composition component can be obtained as a glass having a certain size or a flake-like glass by a rapid cooling method, and thus can be used for various optical elements. it can.

(Glass processing method of the present invention)
According to the experiments by the present inventors, the conventional three-component system containing a large amount of TiO ₂ has a composition that tends to deteriorate the transmission in the short wavelength region (purple light, ultraviolet light), but when SiO ₂ is added thereto, the transmittance is further increased. Tended to get worse. That is, the glass of the present invention has a composition in which the transmittance in the short wavelength region is likely to deteriorate and coloring is likely to occur. For example, when colored glass is used for a camera lens, there arises a problem that the color of the image is deteriorated. In addition, when colored glass is used for an apparatus using a laser such as an optical disk, there arises a problem that the signal intensity is lowered. For these reasons, the use of colored glass is limited.

The cause of coloring is thought to be that Ti ³⁺ is generated inside the glass and this Ti ³⁺ absorbs light of a short wavelength. The reason why Ti ³⁺ is produced may be that Ti ⁴⁺ in the glass is reduced by melting at a high temperature, or that oxygen deficiency of TiO ₂ is generated in the stage before melting. Therefore, in order to suppress the coloring of the glass, it is considered that Ti ³⁺ generated in the glass may be oxidized to Ti ⁴⁺ by some method. The inventors' research has confirmed that the glass of the present invention can be effectively reduced in color by holding the glass of the present invention by heating at a temperature in the vicinity of the glass transition point for a certain period of time. According to this method, the coloration of the glass can be suppressed and the transmittance in the short wavelength region can be improved.

Regarding the oxidation of Ti ³⁺ in glass, it is known that in titanophosphate glass, water present in the glass oxidizes Ti ³⁺ by heating and holding the glass at a temperature near the glass transition point ( (See DS Carson and RD Maurer, J. Non-Cryst. Solids, 11,368 (1973)). Since the glass of the present invention also contains Ti as a component, it is considered that the same reaction occurs. Since the influence of the ambient atmosphere on this reaction is small, the treatment is not limited to the air but may be performed in a gas such as N ₂ , O ₂ , Ar, CO ₂ or the like.

In addition, in the case of metals, the expensive number is more stable at a low temperature than at a high temperature. Compared to the melting temperature of glass, the glass transition point is low. Therefore, it is considered that Ti ³⁺ generated at the time of melting is heated in the vicinity of the glass transition point, whereby the expensive number is stabilized and becomes Ti ⁴⁺ .

  In this heat treatment method, a heating means such as an electric furnace is held at a treatment temperature, and colored glass is put therein. After a predetermined time has elapsed, the glass is taken out and cooled to room temperature in the atmosphere. In order to prevent deformation during processing, the processing temperature must be below the glass transition point Tg. Further, the higher the treatment temperature, the easier the reaction to reduce the coloration proceeds, so the temperature is set to 50 ° C. or lower than the glass transition point Tg. When the treatment temperature is lower than this, it takes time for the reaction, which is not preferable. That is, the heat treatment temperature is a temperature range of (Tg−50 ° C.) or more and Tg or less. The processing time is 10 minutes or more and 120 minutes or less. If it is less than 10 minutes, the above reaction does not proceed sufficiently. Further, even if the treatment exceeds 120 minutes, the transmittance is hardly improved further.

  According to the above processing method, a glass having an internal transmittance of 70% or more per 1 mm thickness at a wavelength of 407 nm can be obtained. Since the wavelength of 407 nm is close to the lower limit of the visible light range, if the internal transmittance at this wavelength can be ensured to be 70% or more, it can be used as a normal camera or microscope lens without any problem.

Coloring can also be reduced by a treatment method in which the container and solidification method and method are used to heat and hold at a temperature higher than the melting point of the glass. That is, the glass in a state of being held in a flowing gas is irradiated with a laser, and the glass is heated and melted at a temperature equal to or higher than the melting point of the glass, and the glass is maintained in that state for 20 seconds to 300 seconds. Then, the coloring can be reduced by cooling the glass. For example, when using the below-mentioned apparatus (refer FIG. 3) for performing a containerless coagulation method, it heats by putting the glass of a process target into an ejection nozzle, and irradiating a laser from the top. At this time, the temperature of the glass increases from room temperature to the melting point or higher in about 5 seconds. After holding for a predetermined time, the laser irradiation is stopped and the glass is rapidly cooled. By holding the glass at a temperature equal to or higher than the melting point, the oxidation of Ti ³⁺ by oxygen dissolved in the glass from the atmosphere and the above-described oxidation of Ti ³⁺ by water in the glass are considered as the mechanisms of color reduction. . The holding time above the melting point is 20 to 300 seconds. If the holding time is less than 20 seconds, the effect of improving the transmittance is almost lost. Further, if the holding time exceeds 300 seconds, the improvement in transmittance is in a state close to saturation before that, which is not preferable in view of production efficiency. According to this processing method, a glass having an internal transmittance of 95% or more per 1 mm thickness at a wavelength of 407 nm can be obtained. If the internal transmittance at a wavelength of 407 nm can be ensured to be 95% or more, it can also be used in an optical apparatus using a violet laser, such as a Blu-ray disc compatible recording / reproducing apparatus.

  EXAMPLES Hereinafter, although this invention is demonstrated still in detail using an Example, this invention is not limited to a following example, unless the summary of this invention is exceeded.

Example 1
100 g of a raw material obtained by mixing oxide (La ₂ O ₃ , TiO ₂ , ZrO ₂ , SiO ₂ ) powder (special grade reagent) so as to have composition 1 shown in Table 1 was placed in a platinum crucible, and an electric furnace It melted at 1400 ° C. in the inside. Next, the crucible was taken out from the electric furnace, and the melt in the crucible was dropped onto a stainless steel plate from a height of about 1 m and rapidly cooled. The slow-cooled portion was devitrified, but the other portions were vitrified, and the largest glass with a size of approximately 50 × 20 × 1 mm was obtained. In addition to this glass, flaky glass and spherical glass were also obtained at the same time, which were formed when the molten raw material collided with the stainless steel plate and the raw material was finely divided and scattered. From this experiment, it was confirmed that glass of a certain size can be easily obtained without using the containerless solidification method according to the composition of the glass of the present invention.

About the obtained spherical glass (diameter of about 1 mm), the refractive index n _d , Abbe number ν _d , melting point Tm, crystallization temperature Tc, and glass transition point Tg were measured by the following methods.

<Measurement method of refractive index>
The refractive index was calculated from the focal position of the spherical glass. As shown in FIG. 1, 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 were three types of wavelengths corresponding to F-line (486 nm), d-line (588 nm), and C-line (656 nm). Since the lens action of the spherical glass 4 makes a real image 6 of the pattern near the upper surface of the spherical glass 4, the position (distance z ′ from the upper surface to the real image 6 (see FIG. 2)) is linear with the microscope 1. Measurement was performed using a gauge 7. As the pattern 3a, a line / 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)) was obtained separately by measuring the difference in focus position with the microscope 1 for the 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 refraction of the spherical glass 4 The rate n was calculated for each wavelength by the following formula (1) to determine the values of n _C , n _d , and n _F. This equation (1) is derived from the paraxial ray imaging 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)

<Measuring method of melting point, crystallization temperature and glass transition point>
Melting | fusing point Tm, crystallization temperature Tc, and glass transition point Tg were calculated | required by DTA (differential thermal analysis) measurement.

The refractive index n _d , Abbe number ν _d , melting point Tm, crystallization temperature Tc, and glass transition point Tg of the glass of Example 1 obtained by the above method were as follows.
Refractive index n _d = 2.258
Abbe number ν _d = 26
Melting point Tm = 1364 ° C.
Crystallization temperature Tc = 964 ° C.
Glass transition point Tg = 823 ° C.

(Comparative Example 1)
An attempt was made to vitrify the conventional ternary composition composed of La ₂ O ₃ , TiO ₂ and ZrO ₂ containing no SiO ₂ by a rapid cooling method. The composition was Comparative Composition 1 in Table 1, and the experimental method was the same as in Example 1. However, since this three-component composition has a high melting point, the melting temperature was set to 1550 ° C.

  The quenched glass was almost entirely devitrified, and there were a few transparent vitrified portions, but the size was 0.1 mm or less at the maximum, which was not practical. From this, it was confirmed that it is inappropriate to produce a conventional ternary glass by a rapid cooling method.

  Therefore, spherical glass (diameter: about 1.2 mm) having a comparative composition 1 shown in Table 1 was produced by a containerless solidification method. First, the containerless solidification method used in this comparative example will be described.

  FIG. 3 is a schematic view showing the entire apparatus used in this comparative example in order to melt the glass raw material by the 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 procedure for manufacturing the glass of this comparative example using the apparatus shown in FIG. 3 will be described. First, a raw material pellet was separately prepared. The raw material pellets are prepared by mixing a glass material (metal oxide, etc.) powder (special grade reagent) at a predetermined molar ratio so that the composition of the obtained glass is the comparative composition 1 shown in Table 1. It is a raw material. 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 of FIG. 3 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 Universal Laser Systems Inc. of the United States. 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 comparative example, the raw material pellets were placed in the ejection nozzle 41 of the apparatus of FIG. 3, and dry air was flowed at a flow rate of 0.3 to 0.6 L / min to float 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.

The obtained spherical glass was measured for refractive index n _d , Abbe number ν _d , melting point Tm, crystallization temperature Tc, and glass transition point Tg in the same manner as in Example 1, and the following results were obtained. It was.
Refractive index n _d = 2.3205
Abbe number ν _d = 23.0
Melting point Tm = 1421 ° C.
Crystallization temperature Tc = 919 ° C
Glass transition point Tg = 842 ° C.

The refractive index n _d was an extremely high value of 2.3205, and the Abbe number ν _d was 23.0.

When Example 1 is compared with Comparative Example 1 in which no SiO ₂ is added, the glass of Example 1 has a slightly lower refractive index than the glass of Comparative Example 1, but the Abbe number is higher. . In addition, the melting point and glass transition point are significantly lower, and the crystallization temperature is significantly increased. Therefore, it can be seen that the addition of SiO ₂ makes the vitrification very easy. By adding SiO ₂ , spherical glass can be obtained by the containerless solidification method, and as shown in Example 1, glass having a certain size or flaky glass can also be obtained by the rapid cooling method. It is done. For this reason, it can be said that the glass of the present invention is industrially more valuable than the three-component system to which no SiO ₂ is added.

(Example 2)
About the compositions 2-5 shown in Table 1, the vitrification by the rapid cooling method different from the composition 1 of Example 1 was tried.

300 g of a raw material mixed with oxide (La ₂ O ₃ , TiO ₂ , ZrO ₂ , SiO ₂ ) powder (special grade reagent) so as to have composition 2 shown in Table 1 is placed in a platinum crucible and placed in an electric furnace. And melted at 1550 ° C. for 30 minutes. Separately, about 1 liter of pure water was placed in a stainless steel container and boiled with a gas burner. The platinum 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 was finished, the gas burner was stopped, and the glass body in pure water was collected and dried. In the case of the composition of composition 2, 1.2 g of spherical glass having a diameter of about 0.5 to 3.0 mm was obtained. However, since the obtained glass has a large absorption at a short wavelength so that it looks almost black, the refractive index and transmittance could not be measured.

Similarly, when glass was prepared for compositions 3 to 5, the following spherical glass was obtained.
Composition 3: spherical glass with a diameter of about 0.5 to 3.0 mm, total 0.6 g Composition 4: spherical glass with a diameter of about 0.7 to 2.2 mm, total 0.4 g Composition 5: diameter of a total 0.6 g However, the refractive index and the transmittance could not be measured because the short wavelength absorption was so large that it looked almost black in the spherical glass of about 0.4 to 2.2 mm.

About the composition 1 of Example 1 and the compositions 2-5 of Example 2, all are shown by mol%,
13.5% ≦ La ₂ O ₃ ≦ 19%
57.5% ≦ TiO ₂ ≦ 77.5%
4.5% ≦ SiO ₂ ≦ 9.5%
0% ≦ ZrO ₂ ≦ 17.5%
It was possible to vitrify even by the rapid cooling method. Furthermore, within this composition range, it is a composition in the vicinity of composition 1 (± 1% width) from which a glass transparent to visible light was obtained.
16% ≦ La ₂ O ₃ ≦ 18%
63.9% ≦ TiO ₂ ≦ 65.9%
5.5% ≦ SiO ₂ ≦ 7.5%
10.6% ≦ ZrO ₂ ≦ 12.6%
Is considered to be a preferred composition range of the glass of the present invention.

  Note that strongly colored glass is inappropriate for light in the visible light range, but in the infrared region where the absorption is small (for example, a wavelength of 1 to 3 μm), since the refractive index is large, for example, a ball with small spherical aberration. Can be used as a lens.

(Reference example)
For reference, a composition in which SiO ₂ was added to a conventional three-component system was melted using a containerless solidification method. The compositions are reference compositions 1 to 18 shown in Table 2. The glass manufacturing method by the containerless solidification method here is the same as that in Comparative Example 1.

  Transparent spherical glass (diameter: about 1.2 mm) was obtained for the reference compositions 1 to 14 shown in Table 2 by the containerless solidification method. Moreover, about reference compositions 15-18, crystallization occurred and it was not able to be set as a transparent glass sphere. Reference composition 7 is the same as the composition of Example 1 of the present invention (Composition 1 in Table 1).

From the results of Table 2, in the composition in which SiO ₂ is added to the conventional three-component system, the composition range in which a transparent spherical glass can be obtained by the containerless solidification method is as follows:
13 ≦ La ₂ O ₃ ≦ 20
55 ≦ TiO ₂ ≦ 80
0.2 ≦ SiO ₂ ≦ 20
0 ≦ ZrO ₂ ≦ 22
It is judged that.

Example 3
In Example 3, with respect to the spherical glass (reference composition 7 (composition 1), glass transition point Tg = 823 ° C.) produced by the containerless solidification method in the above reference example, the transmittance in the short wavelength region is reduced. A treatment for suppressing the occurrence of coloring was performed, and the change in internal transmittance before and after the treatment was confirmed. The internal transmittance (per 1 mm thickness) of the five spherical glasses (samples 6-1 to 6-5) having a diameter of about 1.2 mm obtained in the above reference example was 64 to 83% at a wavelength of 407 nm. It was within the range.

  First, spherical glass was put in an electric furnace maintained at 780 ° C., held for 1 hour or 2 hours, and then cooled to room temperature over about 1 hour. This heat treatment was repeated several times for the same sample, and the change in internal transmittance at the time when the accumulated heat treatment time reached 1, 2, 3, 4 hours was examined. The result is shown in FIG. The internal transmittance increased until the heat treatment time was up to 2 hours, and the internal transmittance hardly changed at the longer heat treatment time. In addition, this heat treatment improved the internal transmittance of all the samples, and even the sample 6-3 having the lowest internal transmittance could achieve 70% or more. The method for measuring the internal transmittance is as follows.

<Measurement method of internal transmittance>
An outline of an apparatus for measuring the internal transmittance of the spherical glass is shown in FIGS. 4A and 4B. As shown in FIG. 4A, the light emitted from the semiconductor laser 31 having a wavelength of 407 nm is collimated by a collimator 32 and a diaphragm 33 and is condensed by a convex lens 34 having a focal length of 7 mm. After returning to the parallel light flux, the intensity is measured by the optical power meter 36. This intensity is referred to as light intensity A. Next, as shown in FIG. 4B, a spherical glass (diameter D, refractive index n at a wavelength of 407 nm) 37 to be measured is placed on the focal point between the two convex lenses 34 and 35, and the light intensity is set. taking measurement. This intensity is referred to as light intensity B. The transmittance t at the interface between the spherical glass surface and air can be calculated from the well-known Fresnel reflection equation using the following equations (3) and (4).
r = (n−1) ² / (n + 1) ² (3)
t = 1-r (4)
In addition, r is a reflectance. If zero optical loss inside the spherical glass, the transmittance is t ^2. Furthermore, when the intensity of light reciprocating several times by reflection inside the spherical glass is added, the final transmittance is as follows.
t ² + t ² r ² + t ² r ⁴ +... = t ² / (1-r ² )

From this, the internal transmittance τ (per thickness D) of the spherical glass is obtained by the following equation (5).
τ = B / {At ² / (1-r ² )} (5)
Further, the internal transmittance τ ₀ at a specific thickness D ₀ can be calculated by the following equation (6).
τ ₀ = τ ^{(Do / D)} (6)
Here, the internal transmittance is expressed as a percentage (τ ₀ × 100 (%)).

Example 4
In Example 4, the spherical glass (reference composition 7 (composition 1)) produced by the containerless solidification method in the above reference example was subjected to a treatment for improving the transmittance by melting. The internal transmittance (per 1 mm thickness) of the spherical glass before the treatment was in the range of 62 to 83% at a wavelength of 407 nm.

  Using the containerless solidification apparatus and method described in Comparative Example 1, the spherical glass was heated until the temperature of the spherical glass reached the melting point (melting point: 1364 ° C.) or more and the spherical glass was completely melted. This heat treatment was repeated several times for the same sample, and the change in internal transmittance was examined when the accumulated heat treatment time reached 0, 30, 60, 90, 120, 150 and 180 seconds. The internal transmittance was measured by the same method as in Example 3. The result is shown in FIG. From this result, the internal transmittance was improved to 95% or more in all samples by the treatment for 120 seconds.

  The glass obtained by the present invention is low in cost and 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 (7)

It consists of three components of La ₂ O ₃ , TiO ₂ and SiO ₂ , or four components of La ₂ O ₃ , TiO ₂ , SiO ₂ and ZrO ₂ , and the composition expressed in mol% is
13.5% ≦ La ₂ O ₃ ≦ 19%
57.5% ≦ TiO ₂ ≦ 77.5%
4.5% ≦ SiO ₂ ≦ 9.5%
0% ≦ ZrO ₂ ≦ 17.5%
Meet the glass. It consists of four components of La ₂ O ₃ , TiO ₂ , SiO ₂ and ZrO ₂ , and the composition expressed in mol% is
16% ≦ La ₂ O ₃ ≦ 18%
63.9% ≦ TiO ₂ ≦ 65.9%
5.5% ≦ SiO ₂ ≦ 7.5%
10.6% ≦ ZrO ₂ ≦ 12.6%
The glass of Claim 1 satisfy | filling.   The glass according to claim 1, wherein the internal transmittance per 1 mm thickness at a wavelength of 407 nm is 70% or more.   The glass according to claim 3, wherein the internal transmittance per 1 mm thickness at a wavelength of 407 nm is 95% or more.   The glass according to claim 1, wherein the length of the minimum portion is 0.5 mm or more. A method of processing a glass according to claim 1, comprising:
When the glass transition point of the glass is expressed as Tg, the glass is treated in a temperature range of (Tg−50 ° C.) to Tg and below for 10 minutes to 120 minutes. A method of processing a glass according to claim 1, comprising:
The glass in a state of being held in a flowing gas is irradiated with a laser, and the glass is heated and melted at a temperature equal to or higher than the melting point of the glass for 20 seconds to 300 seconds. Cooling, glass processing method.

Images