JPH08169720A - Production of glass - Google Patents

Abstract

PURPOSE: To inhibit the progress of cracking due to a discontinuous part of a skeleton at the time of drying and firing, and cracking by shrinkage at the time of firing a refractive index profile-type optical element due to pore volume distribution from the peripheral edge parts of a bulky body to the entire bulky body and to prevent the cracking of the central part of the resultant glass. CONSTITUTION: Cylindrical gel 5 with holes 10 pierced in the peripheral edge parts of both ends from the periphery is formed by a sol-gel method and this gel 5 is dried and fired. At this time, cracking is caused only in the peripheral edge parts of the gel 5 but cracking stops at the positions of the holes 10 and does not propagate to the central part of the resultant glass.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass manufacturing method applicable to optical elements such as cameras and microscopes.

[0002]

2. Description of the Related Art Generally, sol.
The gel method is known. In this method, a sol prepared by hydrolysis reaction / polycondensation reaction using a catalyst such as an acid / base from a silicon alkoxide or the like as a raw material is gelated, dried and then densified to obtain a glass body. Is the way.

Further, a method for producing a gradient index optical element by applying this sol-gel method is disclosed in JP-A-3-29581.
No. 8 publication. This method prepares a sol in which a metal salt is introduced into an alkoxide of silicon, immerses the obtained wet gel in an organic solvent containing another type of metal salt, and replaces both metal salts to obtain a concentration. Is applied, followed by drying and firing to obtain a glass body having a refractive index distribution.

The gradient index optical element is an element in which the refractive index continuously changes in a medium, and controlling the composition distribution is known to be effective for various optical aberration corrections. ing. In particular, a material having a refractive index distribution in the radial direction is highly useful as an optical lens. Here, the refractive index difference (Δ
n). The refractive index distribution type optical element having a large Δn has a high optical effect because the bending of the light ray in the medium is large.

However, in the sol-gel method, the gel often cracks during the gel drying step and the final step of firing, and various measures have been proposed. JP-A-64
JP-A-65034 discloses that a dry gel produced by a sol-gel method is fired after cutting or cutting the outer peripheral portion thereof, thereby removing structural differences, microcracks, and the like generated during drying, and manufacturing a glass body without cracks. The method is described.

Further, in Japanese Patent Laid-Open No. 1-119531, dry gel produced by the sol-gel method or the surface portion of a porous body is polished and ground, and then baked to obtain a structural difference, a microcrack or the like generated during drying. To produce a glass body without cracks.

In Japanese Patent Laid-Open No. 63-95124, a concentration distribution is formed in a metal component of silica gel containing at least one metal component prepared by a sol-gel method, and the concentration distribution is brought into contact with an aqueous solution of silicon alkoxide. There is described a method for producing a gradient index optical element in which a defective portion of gel caused by imparting a concentration distribution is reinforced and bubbles are prevented from being generated during baking and vitrification.

Further, in Japanese Patent Application No. 5-132959,
After producing a porous body in which a metal salt or a metal oxide is distributed with a gradient, by exposing a portion of the porous body having a high non-porous temperature, it is possible to condense the -OH group in the gel. Accordingly, it has been proposed that the H ₂ O gas generated inside the gel is allowed to escape from the non-porous portion to the outside of the gel to prevent cracking.

[0009]

When a glass body is produced by the sol-gel method, the gel, which is a porous body, is accompanied by a significant volume shrinkage due to densification during drying or firing, so that a fired body without cracks should be prepared. It is extremely difficult to obtain. As shown in FIG. 2, the bulk body 1 generated during the firing process
2 (see (A) of FIG. 2) often progresses further in the process of firing, and often extends to the entire bulk body 1 (see (B) of FIG. 2). In such a case, even if an attempt is made to cut out several parts having a desired size from the manufactured glass, for example, a cylindrical glass, a few lenses will be produced, and the yield will be very poor. There was a problem that the cost per part of the above becomes extremely high.

In particular, the gel having a concentration distribution in the composition for the purpose of imparting a distribution to the refractive index has many distributions of shrinkage ratio due to the composition distribution, and therefore, cracks frequently occur during drying or firing. Further, when manufacturing a glass having a large Δn, it is necessary to introduce a metal component with a large concentration difference, and therefore this phenomenon appears remarkably, and it is difficult to manufacture a gradient index optical element having a large Δn. there were.

As a method for avoiding this, Japanese Patent Laid-Open No. 3-2
According to the method described in Japanese Patent Publication No. 95818, not only is the metal component contained in the gel eluted, but a distribution is formed by exchanging it with a metal component having a different contribution to the refractive index, such as potassium, to form a skeleton of the skeleton formed by the eluted metal component. Although it is also considered to reinforce the density, the exchange of metal differs depending on the concentration and diffusion rate of both metal ions, and the ionic radius is different even when exchanges are equivalent, so the pore volume Is not always completely reinforced,
There were cases where cracks could not be avoided.

The method described in Japanese Patent Application Laid-Open No. 64-65034 and the method described in Japanese Patent Application Laid-Open No. 1-119531 are for cutting the outer peripheral portion and the surface portion of a gel. When used as a lens in an optical system such as a camera, the optical axis exists in the element medium itself,
Normal centering steps cannot be used. Further, even if chamfering is performed with the outer periphery of the gel as an impact, it is not preferable to process the outer peripheral portion because the gel may be damaged by the force applied when the gel is held.

In addition, in the method described in Japanese Patent Laid-Open No. 63-95124, since the gel whose distribution has been once formed is immersed in the solution, the metal component introduced by a salt to form the distribution is re-diffused. The shape of the refractive index distribution is disturbed, or Δn
There was a problem with the reproducibility of the distribution shape, such as a small one.

In the method described in Japanese Patent Application No. Hei 5-132959, cracks caused by making the outer periphery of the gel nonporous are exposed by exposing a portion having a high glass transition point. It was not possible to expect a suppressing effect on cracks that were uniform but occurred. This is because the cracks that occur during firing are not only high and low at the vitrification temperature, but also microcracks that occur during the treatment of the gel before firing, and large differences in shrinkage due to too large a composition concentration distribution. This is because it is considered to be the cause.

The present invention has been made in view of such conventional problems, and cracks caused by discontinuous portions of the skeleton during drying and firing and a refractive index distribution type optical element due to pore volume distribution. An object of the present invention is to provide a method for producing glass, in which cracks due to shrinkage during firing are limited to only the peripheral edge portion and are suppressed from proceeding to the entire bulk body to prevent cracking in the central portion of the glass.

[0016]

In order to solve the above-mentioned problems, the invention according to claim 1 is to manufacture a glass, in which a gel with some holes is prepared by a sol-gel method, and the gel is prepared. Was dried and baked. The invention according to claim 2 is characterized in that, in the invention according to claim 1, the gel has a cylindrical shape, and at least one hole is opened within a length of a radius of the gel from the end face. Claim 3
The invention according to claim 1 is the invention according to claim 1 or 2,
The hole is obliquely opened from the outer peripheral surface of the gel toward the end surface. The invention according to claim 4 is characterized in that, in the invention according to claim 1, 2 or 3, the hole is tapered toward the tip. Claim 5
The invention according to claim 1 is characterized in that, in the invention according to claims 1 to 4, the glass is a gradient index optical element.

[0017]

FUNCTION One of the causes of cracking of the glass produced by the sol-gel method is strain due to stress generated during drying or firing. This remarkably occurs at the discontinuous portion of the gel skeleton, that is, the surface portion of the gel. In particular, due to the structural difference depending on the shape of the gel, as shown in FIG. 3, the stress is apt to occur at the portion (A portion) where the angle between the two adjacent surfaces is small, but this is always the case with the container. This is particularly noticeable at the bottom surface portion that is in contact with and bears the weight of the gel itself. The firing causes the SiOH residues in the skeleton to react and bond with each other, resulting in densification so as to crush the pores. However, as shown in FIG. 3, since the skeleton is discontinuous at the corners, the reaction progresses. A difference occurs in the degree and stress is generated. This often causes cracking. That is, in many cases, cracks are first generated from the end portion such as the bottom portion of the bulk body. Here, by preventing the growth of cracks from the end portion to the central portion of the bulk body, it becomes possible to use the central portion of the glass.

In particular, when manufacturing a gradient index optical element, cracks occur due to the difference in contraction rate due to the nonuniform pore volume in addition to the action of this stress. For example, a case will be described in which lead acetate, which is a substance having a function of increasing the refractive index, is introduced into a cylindrical gel having silica as a skeleton with a concentration distribution. As shown in FIG. 4, the porous gel having a distribution in composition has a pore structure having silica as a skeleton, and the lead component 4 has a concentration distribution in the pores of the silica skeleton 3. It has a structure that existed. The pores composed of the silica skeleton 3 are uniform, and the pores are present with a distribution in which the lead component 4 is blocked. As a result, a distribution is formed in the pore volume, resulting in coarse and dense. Since the distribution of the pore volume appears as a difference in shrinkage ratio between parts when forming glass by densification by firing, cracks or cracks often occur.

In the case of forming a distribution in a cylindrical gel containing a metal component, when the concentration distribution is provided by utilizing the step of eluting the metal component, the elution of the metal component is performed only from the side surface of the cylinder. Instead, it is done simultaneously from the top or bottom surface of the cylinder. Therefore, as shown in FIG. 5, the distribution of the metal component in the cross section passing through the axis of the columnar gel 5 has the smallest content in the peripheral portion 6 which is the hatched portion. The obtained gel is shrunk and densified by firing to form a glass body. At this time, the degree of shrinkage of the peripheral edge portion 6 in FIG. 5, which has the largest pore volume, is large. As shown in, the gel 5 was often cracked or cracked from this portion. In FIG. 6, reference numeral 7 indicates a large broken piece.

Therefore, as shown in FIG. 6 (A), a plurality of holes (pinholes) 8 are preliminarily formed in the peripheral edge portion 6 of the columnar dried gel 5 from the outer peripheral surface toward the center, and When the gel 5 was fired using a tubular furnace,
As shown in (B), only the peripheral portion 6 of the gel 5 was cracked, but the crack stopped at the hole 8 and did not proceed to the center of the glass. That is, the cracks generated in the largest shrinkage area could be limited to the peripheral edge portion 6. This is because the stress generated in the peripheral portion 6 is released when the hole 8 has been opened in advance, so that the progress of cracking can be stopped. That is, by guiding the escape route of the stress generated during the gel firing to the hole 8 formed in the peripheral portion 6, it is possible to exhibit the effect of diffusing the stress and suppressing the progress of cracking. In FIG. 6 (B), 9 indicates a broken piece on the peripheral edge portion 6.

The holes to be formed in the gel are the size of the hole, the shape of the tip of the hole, the cross-sectional shape of the hole (circular, elliptical, quadrangular, etc.), the number, the place, and the positional relationship among the plurality of holes (the interval between the holes). , Angle, whether or not holes are connected, etc.), whether it is a hole that penetrates the gel or a hole that does not penetrate the gel, but there are various parameters such as the purpose, gel composition, strength, size, etc. May be selected as appropriate. Since it is difficult to determine the size and number of holes in a general manner, the action will be described below by giving a particularly effective number sequence for some parameters.

As for how to make a hole, as shown in FIG. 7, a non-penetrating hole 8 may be made in a part of the gel 5, but as shown in FIG. 1, it is a hole 10 penetrating the gel 5. Is most effective. This is because the through holes 10 can stop cracks occurring anywhere in the gel 5 in the radial direction. When making a non-penetrating hole in the gel, the shape of the tip of the hole may be rounded. This is because if the shape of the hole is square or it is tapered toward the tip,
This is because a crack may be generated from the hole itself and a crack may be generated in the center part of the gel. As for the direction of the hole, as shown in FIG. 8, the effect is great when the gel 5 is opened obliquely from the outer peripheral surface toward the end surface direction. This is because cracks generated at the peripheral edge of the gel are trapped in the holes that are opened diagonally, but at this time, since the cracks often extend in the direction of the holes, the cracks reach the center of the gel. This is because it can be prevented from stretching.

The above has described the action of trapping the cracks generated at the peripheral edge of the gel by the holes provided in the gel and preventing the growth of the cracks in the necessary central portion of the gel. It is also possible to release the stress by positively causing cracks toward the peripheral portion from the holes provided. An example thereof will be described below.

As shown in FIG. 9 (A), a hole 8 is formed in the peripheral edge portion 6 of the gel 5 so as to narrow toward the tip. As described above, when the shape of the hole 8 is narrowed toward the tip, the cracks that have occurred proceed in the direction of the hole 8, so that
As in (B), cracking can be suppressed only in the unnecessary peripheral portion 6.

As described above, according to the present invention, it is possible to suppress only the cracks occurring in the portion where the difference in shrinkage due to the pore volume distribution of the gel skeleton is the largest. Since the only necessary processing is to make a hole, it is easy to process, the number of processed parts is small, and the possibility of new microcracks is greatly reduced compared to the case where the entire outer peripheral part is deleted. It is possible to In addition to this, when various treatments are applied to the gel, cracks that grow from microcracks generated when the peripheral edge of the gel is gripped with tweezers can be reduced.

Further, since only a hole is formed in the peripheral portion, it is possible to form a spherical surface or the like on the gradient index optical element with the outer peripheral portion of the cylinder as a boundary. Further, unlike the case where the skeleton is reinforced with silicon alkoxide or the like, the refractive index distribution once formed is not broken, and the one formed by the distribution giving step can be reproduced with high accuracy. Further, it becomes possible to manufacture a gradient index optical element having a large Δn with a high yield. It has been stated that it is effective to form the holes in this case on the portion where the dopant is most likely to be eluted due to diffusion during distribution.
Specifically, the column-shaped gel has a distribution on the upper and lower edges, and the square-shaped gel has a distribution on the apex (corner) and the periphery of each side. Equivalent to.

Since the diffusion of the metal component complies with the diffusion law, in the case of a cylinder, a large amount of stress is accumulated from the end to within the radius, so at least one hole, preferably about four holes, can be formed in this range. It is particularly effective because of the effect of preventing cracks and the large amount of glass material used. Further, it is preferable that the holes are opened in the radial direction of the gel so that the center portion of the fired glass can be effectively used, but the holes may be deviated from the radial direction.

The present invention can also be applied to a corner formed when a gel charged in a container having a desired shape is broken or damaged during a processing step. Further, here, only the case where the dopant distribution having a convex shape in the radial direction is described, but even if a dopant is introduced from the opposite outside to give a concave distribution, such a corner portion is not diffused. It can be applied to this part because it is fast and the concentration of the dopant is the highest, and the shrinkage ratio is different, which causes the generation of cracks.

As described above, by using the present invention, it is possible to significantly reduce large cracks generated in the glass body manufactured by the sol-gel method. In particular, Δ
It is possible to obtain the central part of a gradient index optical element having a large n without cracking. Although the gradient index optical element has been described here, the present invention is not limited to the described examples as long as the porous body has different shrinkage rates depending on the portion of the porous body. For example, it can be applied to a material in which the refractive index is uniform but the dispersion is distributed due to the distribution of the composition inside the porous body. In addition, even in the case of gels with a uniform composition, it is recommended to use gels with skeletal densities due to differences in reaction speed due to temperature distribution of the sol and container during sol preparation, and differences in drying speed between parts during gel drying. The invention can be applied.

Here, the method of making holes (pinholes) in the dry gel has been shown, but a site for making holes is provided in advance in the container for gelation, and the sol is dispensed into this to make holes. Method for obtaining wet gel, wet gel before and after imparting distribution to the composition, or after drying, after calcination to a stage before densification, mechanical processing is performed by a drill or the like, or hydrofluoric acid is used. Even if the present invention is applied by forming a hole by chemically processing it by means such as the above, it effectively acts to avoid cracking. Similarly, even in a glass body having no compositional distribution, the present invention can be applied to a gel calcined up to the stage of wetting and the stage before densification in the drying and firing steps.

[0031]

【Example】

[Example 1] 110 ml of silicon methoxide and DMF7
8 ml was mixed and stirred. 60 ml of methanol here
And 135 ml of water and 3.6 ml of 1N NH ₄ OH were added. After stirring for several minutes, the mixture was dispensed into a Teflon container having an inner diameter of 30 mm and a flat bottom, to obtain eight cylindrical gels. After gelation, it was dried in a dryer at 60 ° C. to obtain a dry gel.

As shown in FIG. 1, a hole 10 having a diameter of 0.2 mm was drilled from the outer peripheral surface of the dry gel 5 at the peripheral edge portions at both ends by drilling two holes 2 in the diameter direction at a total of 4 points. When this gel 5 was fired up to 1200 ° C., small cracks were generated at all peripheral edges and chips were generated, but cracks did not progress to the central portion, and a glass body having a central portion without cracks could be obtained. .

Comparative Example 1 Eight gels were prepared in the same manner as in Example 1. When these gels were burned to 1200 ° C. as they were, 2 pieces were not cracked, but 6 pieces were cracked in the vertical direction from the bottom part to the top surface, and a glass body having a center part without cracks was formed. I couldn't get it.

[Example 2] Tetramethoxysilane Si was used as a raw material for silicon, titanium, barium and potassium.
(OCH ₃ ) ₄ , titanium butoxide monomer Ti (O ⁿ
C ₄ H _{9) 4,} barium acetate Ba (OCOCH _{3) 2,}
Potassium acetate KOCOCH ₃ was used. Si (OCH
₃ ) _{4 To} 20.9 g, 35 ml of ethanol and 4.8 ml of 2N hydrochloric acid were added and stirred at room temperature for 1 hour.
A solution in which 7.7 g of i (O ⁿ C ₄ H ₉ ) ₄ and 35 ml of ethanol were mixed was added and stirred for 1 hour. To this solution, 40 ml of 1M-barium acetate aqueous solution and 16 ml of 17N acetic acid were added and stirred for 1 hour to obtain a sol. This sol was cast into 10 polypropylene containers having a diameter of 18 mm, left to stand in a constant temperature bath at 50 ° C. for gelation, and then further aged. The obtained gel was taken out of the container, and 10 gels were immersed in a solution obtained by mixing 400 ml of ethanol and 7.2 g of lactic acid for 2 days to fix barium acetate microcrystals in the gel.

4.7 g of potassium acetate and 700 of methanol
A solution was prepared by mixing and dissolving with ml, and 10 gels were immersed in this solution for 8 hours to give a convex distribution to the barium component and a concave distribution to the potassium component in the gel. Then, the gel was immersed in 400 ml of acetone for 2 days to fix microcrystals of barium acetate and potassium acetate and dried to obtain a dry gel. As shown in FIG. 7, pinholes having a diameter of 0.3 mm and a depth of 2 mm were formed at the peripheral edges of both ends of the dry gel 5 by hydrofluoric acid, four points in each of the diameter direction and the direction orthogonal thereto, for a total of eight points. When this gel was baked to 700 ° C,
Although a small crack was generated in all of the peripheral edge portions and chipped, the crack did not progress to the central portion, and a glass body having a central portion without cracks could be obtained. When this glass was polished and the optical characteristics were measured, Δn = 0.03.

[Comparative Example 2] A gel was prepared in the same manner as in Example 2.
This was made. When these gels were fired as they were up to 700 ° C., two had no cracks, but eight had cracks in the vertical direction from the bottom to the top during firing and slow cooling. As described above, the yield that can obtain a glass portion without breakage is poor.

[Example 3] Tetramethoxysilane Si was used as a raw material for silicon, titanium, barium and potassium.
(OCH ₃ ) ₄ , titanium butoxide monomer Ti (O ⁿ
C ₄ H _{9) 4,} barium acetate Ba (OCOCH _{3) 2,}
Potassium acetate KOCOCH ₃ was used. Si (OCH
₃ ) _{4 To} 20.9 g, 35 ml of ethanol and 4.8 ml of 2N hydrochloric acid were added and stirred at room temperature for 1 hour.
A solution in which 7.7 g of i (O ⁿ C ₄ H ₉ ) ₄ and 35 ml of ethanol were mixed was added and stirred for 1 hour. To this solution, 60 ml of 1M-barium acetate aqueous solution and 24 ml of 17N acetic acid were added and stirred for 1 hour to obtain a sol. This gel was treated in the same manner as in Example 2 to perform distribution and distribution fixing treatment.

Then, with a drill, as shown in FIG. 8, a depth of 3 mm, a diameter of 2 mm on the outer peripheral surface of the gel 5 and a diameter of 0.1 mm at the tip of the hole were set at 4 mm from the lower end of the gel 5, respectively. Four holes (pinholes) 8 were formed obliquely from the outer peripheral surface of the gel 5 toward the lower end surface in the diametrical direction and the direction orthogonal thereto. When this gel was fired up to 700 ° C., cracks all occurred from the peripheral portion to the holes 8, but the cracks did not progress to the central portion, and a glass body having a central portion without cracks could be obtained. When this glass was polished and the optical characteristics were measured, it was a glass having a large refractive index difference of Δn = 0.07.

[Embodiment 4] A dry gel produced in the same manner as in Embodiment 2 is directed to the peripheral edge of the gel 5 from both end surfaces of the gel 5 in an oblique direction toward the outer peripheral surface toward the tip, as shown in FIG. 10 (A). I made a thin hole 8. When this gel was fired, cracks occurred from the holes 8 at around 280 ° C.
The crack remained only in the peripheral portion, and the glass body 11 as shown in FIG. 10B could be obtained. 7 is a broken piece.

Example 5 The sol prepared in the same manner as in Example 1 was dispensed into a square column Teflon container having a height of 50 mm and a side of 100 mm and a flat bottom, and as shown in FIG.
A Teflon-made quadrangular prism 13 having a length of 7 mm was stood up near the four corners of the container 12 and gelled. After aging for 2 weeks, a Teflon stick was taken out from the gel to obtain a dry gel having holes at four corners. When this gel was fired up to 1200 ° C., small cracks were generated at the four corners and the chips were chipped, but the cracks did not progress to the central portion, and a glass body having a central portion without cracks could be obtained.

[0041]

As described above, according to the method for producing glass of the present invention, when the glass body is produced by the sol-gel method, it is possible to reduce the occurrence of cracks in the central portion of the glass, Further, it is possible to manufacture glass without cracks in the central portion of the gradient index optical element having a large Δn.

[Brief description of drawings]

FIG. 1 is a perspective view showing a state in which a through hole is formed in a peripheral edge portion of a cylindrical gel in Example 1.

FIG. 2 is a conceptual diagram when the gel is fired, (A) is a perspective view showing small cracks generated at the peripheral edge of the gel during firing,
(B) is a perspective view showing the crack of the finally obtained glass.

FIG. 3 is an enlarged view showing a corner portion of a gel which is a discontinuous portion of a silica skeleton.

FIG. 4 is an enlarged view showing a state where a metal component is contained in a pore structure having silica as a skeleton with a composition distribution.

FIG. 5 is a conceptual diagram showing the density of composition distribution in a cross section including the axis of a cylindrical gel.

6A and 6B are diagrams showing a columnar gel or glass having a coarse and dense composition distribution in a cross section including an axis. FIG. 6A is a diagram showing pinholes in the gel, and FIG. 6B is a diagram showing the gel shown in FIG. FIG. 6 is a diagram showing cracks generated at the end portion when fired, and (C) is a diagram showing cracks caused by conventional firing in which no pinhole was formed in the gel.

FIG. 7 is a perspective view showing a state in which a gel is perforated in Example 2.

FIG. 8 is a perspective view showing a state in which holes are made in the gel in Example 3.

FIG. 9 is a view showing a state in which a hole having a tapered tip is formed in the peripheral edge portion of the gel from the outer peripheral surface of the gel toward the end face direction.

10 (A) is a perspective view showing a gel with holes formed therein, and FIG. 10 (B) is a perspective view showing a glass body obtained by firing in Example 4. FIG.

11 is a perspective view showing a sol dispensing container used in Example 5. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bulk body 2 Crack 5 Gel 6 Peripheral part 8 Hole 10 Through hole 11 Glass body

Claims (5)

[Claims] 1. A method for producing glass, characterized in that a gel having a part of holes is produced by a sol-gel method, and the gel is dried and fired. 2. The method for producing glass according to claim 1, wherein the gel has a cylindrical shape, and at least one hole is formed within the length of the radius of the gel from the end face. 3. The glass manufacturing method according to claim 1, wherein the holes are formed obliquely from the outer peripheral surface of the gel toward the end surface direction or from the end surface toward the outer peripheral surface direction. 4. The glass manufacturing method according to claim 1, 2 or 3, wherein the hole is tapered toward the tip. 5. The method for producing glass according to claim 1, wherein the glass is a gradient index optical element.