JPH10245234A - Production of refractive index distribution type optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a gel in a constant shape without causing the volume contraction, crack generation and deformation of the gel by placing the washed gel and an inactive liquid having a larger specific gravity than that of the gel and not compatible with a solvent, etc., contained in the gel in a vessel for drying the gel on the production of a refractive index distribution type optical element by a sol-gel method. SOLUTION: This method for producing a refractive index distribution type optical element comprises stirring and mixing a metal alkoxide, etc., as a raw material, an alcohol as a solvent, water for hydrolyzing the metal alkoxide, etc., a catalyst for accelerating the hydrolysis reaction, and a specific metal component for imparting a concentration distribution in the following process, pouring the obtained sol into a gelation vessel such as a cylindrical vessel, heating the sol to form the gel, immersing the gel in a distribution-imparting solution for eluting the fine crystals of the added metal component for a constant time to impart the concentration distribution, and subsequently fixing the metal component. The metal alkoxide is selected from tetramethoxysilane, etc., and the alcohol is selected from methanol, ethanol, etc. The catalyst is selected from hydrochloric acid, acetic acid, etc. The specific metal component is selected from lead acetate, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical element made of a multi-component glass having a refractive index distribution by a sol-gel method.

[0002]

2. Description of the Related Art The synthesis of glass by the sol-gel method involves the steps of mixing a metal alkoxide as a raw material, an alcohol as a solvent, water for a hydrolysis reaction and a catalyst with stirring to prepare a sol, Of the gel, a drying step of removing the solvent in the gel to form a dry gel, and a sintering step of making the dry gel non-porous. In addition, in the production of an optical element made of a multi-component glass to which a refractive index distribution has been imparted, a distribution imparting solution such as an acid capable of selectively eluting a metal component in a gel is provided before the drying step described above. This can be achieved by immersing the gel for a certain period of time and then inserting a step of washing to remove the distribution-imparting liquid.

In the above-mentioned drying step, the gel is transferred to a drying container and dried. However, there is a problem in that the gel shrinks in volume during drying and is broken or distorted. For this reason, various shapes of drying containers or drying methods have been proposed to prevent the gel from being cracked or distorted even when the gel shrinks in volume. For example, a method of drying using a suspension jig that holds the upper part of the gel in a state of free shrinkage, a method of putting the gel in a cylindrical drying container and drying while rotating, a method caused by surface tension A method has been developed in which a drying control additive for preventing cracking of a gel is added to a cleaning solution for removing a distribution-providing solution, followed by washing with the cleaning solution and drying.

Further, Japanese Patent Application Laid-Open No. 62-70236 discloses a method of filling a liquid containing a sol component into the space of a cylindrical container for drying in order to improve the roundness, warpage and yield of a gel. It is shown. Japanese Patent Application Laid-Open No. 57-1065
No. 29 discloses a method in which a sol is poured into a liquid that is not compatible with the sol and has a large specific gravity to cause gelation in order to prevent distortion of the gel.

[0005]

Various types of drying containers or drying methods have been proposed to prevent the gel from being cracked or distorted even if the gel shrinks in volume, but all of them have a small effect. However, there is a problem that much labor is required and the cost of the apparatus is high.

In the method disclosed in Japanese Patent Application Laid-Open No. 62-70236, the liquid filled in the cylindrical container has a buffering action against external fluctuations (impact, temperature, etc.). It is possible to prevent distortion. However, since the filled liquid is a liquid containing a sol component, there is a problem that this liquid permeates into the gel during the drying process and cannot be dried as a result.

In the method disclosed in Japanese Patent Application Laid-Open No. 57-106529, when the sol is gelled in a suspended state with a liquid that is not compatible with the gel and has a large specific gravity, the sol is allowed to stand still even if the sol is left standing. Is deformed by a slight external vibration or a stress at the time of contraction of the sol, so that a gel having a constant shape cannot be produced. Since the refractive index distribution type optical element performs distribution imparting by selectively eluting the metal component in the gel, the gel before imparting the distribution must always have a constant shape, as described above. When a gel having a constant shape cannot be formed, an optical element having a non-uniform refractive index distribution to be applied has a problem.

[0008] The present invention has been made in view of the above problems, and a refractive index distribution type gel that can always obtain a gel having a constant shape without breaking or distorting even if the gel shrinks in volume during the drying step. An object of the present invention is to provide a method for manufacturing an optical element.

[0009]

In order to achieve the above object, the present invention provides a method for gelling a sol prepared using a metal alkoxide as a raw material, immersing the gel in a solution that elutes a metal component, and then washing the gel. In a method of manufacturing a gradient index optical element by a sol-gel method of drying and sintering, a washed gel and an inert liquid having a higher specific gravity than the gel and incompatible with a solvent contained in the gel. And dried in a drying container.

That is, in the present invention, first, a metal alkoxide or the like as a raw material, an alcohol as a solvent, water for hydrolyzing the metal alkoxide or the like, a catalyst for accelerating the hydrolysis reaction, and a concentration in a subsequent step. A sol is prepared by stirring and mixing with a specific metal component for providing a distribution. As the metal alkoxide, tetramethoxysilane, tetraethoxysilane, tetra-n-butoxytitanium, etc. can be selected, as the alcohol, methanol, ethanol, butanol, etc. can be selected, and as the catalyst, hydrochloric acid, acetic acid, ammonia, piperazine, etc. can be selected. The specific metal component can be selected from lead acetate, barium acetate and the like.

Next, the sol is poured into a gelling container having a desired tubular shape such as a cylinder, and heated to room temperature or about 50 ° C. to gel it in a jelly state. The gelling container has a high cylindricity and a smooth inner surface (for example, a cylindricity of 0.05, an inner surface of the inner surface) in order to make the concentration distribution shape of the metal component to be applied in the subsequent step concentrically circular. It is preferred to use a tubular bottomed container (roughness 5 μm). This tubular bottomed shape may be a polygon or the like. The material of the container may be polytetrafluoroethylene, polypropylene, T
PX (polymethylpentene) or PEEK (polyetheretherketone) whose inner surface is treated with silicone can be selected.

After gelation in this way, in order to fix the added metal component in the gel, a solution having a low solubility of the metal component is placed in a container, and the gel is immersed in this solution. Microcrystals of a metal component for providing a concentration distribution are precipitated.

Next, a distribution-providing solution for eluting the microcrystals of the metal component in the gel is stored in a container, and the gel is immersed in the distribution-providing solution for a certain period of time so that the gel moves from the outer surface of the gel to the center. It gives a concentration distribution in which the metal component gradually changes. Examples of the distribution providing solution include acetone and IPA.
(Isopropyl alcohol), methanol, an aqueous solution of sulfuric acid, or the like. Thereafter, the metal component present in the gel is fixed with a distribution fixing solution.

Thereafter, the distribution fixing solution is washed and the gel provided with the concentration distribution of the metal component is dried. This drying is
An inert liquid having a higher specific gravity than the gel and incompatible with the solvent contained in the gel is placed in a drying container having a large internal volume, and the gel is maintained in a state where the gel can freely float. Also,
In drying, the temperature is usually gradually raised from room temperature and finally raised to 15
The mixture is heated to about 0 ° C. to evaporate the solvent and water contained in the gel, and the gel is dried. At this time, the gel releases the solvent and water and contracts in volume due to the polycondensation reaction.

In this drying, for example, a columnar gel is apparently in a state where gravity does not work due to the inert liquid put in the drying container, and the force acting on the lower side of the gel due to the weight of the gel, or the gel. The friction between the outer surface of the gel and the inner wall of the container, as well as the cracking and distortion due to the stress applied by the volume shrinkage of the gel itself can be prevented.

In addition, unlike the conventional method, the sol before gelation is not put into a container together with an inert liquid and then gelled, but the present invention uses another dedicated gelling container to gelate the sol into a predetermined outer shape. Is suspended in the inert liquid in a state in which the gel is held, so that a gel having a constant shape of roundness, smoothness, plane parallelism and the like can be always obtained. The inert liquid used in the present invention is contained in the gel by using the solvent contained in the gel, the product liquid produced during gelation and contained in the gel, and further by using the metal component to fix it in the gel. Incompatible with the fixed distribution solution (hereinafter referred to as solvent etc.)
The solvent and the like are not hindered from being dried, and the vaporized solvent and the like are released from the gel without being taken into the inert liquid, and can be dried well.

Examples of the inert liquid used in the present invention include fluorocarbons such as perfluorocarbon, perfluoropolyether and perfluoroamine, silicones such as polyorganosiloxane, and decane;
Hydrocarbons such as isododecane can be used. Among these inert liquids, those having a boiling point in the range of 100 ° C. to 200 ° C. and having a high vapor pressure for ease of drying are preferred.

The gel dried as described above is taken out of the drying vessel and sintered. In this case, the sintering schedule varies depending on the type and amount of the metal alkoxide present in the gel, the type of the added metal component or the type of the catalyst, etc., but the temperature is usually raised to about 600 ° C. to 1300 ° C. A solvent and the like and water in the gel are vaporized, and a condensation polymerization reaction proceeds to make the gel nonporous, thereby obtaining a gradient index optical element.

[0019]

DETAILED DESCRIPTION OF THE INVENTION Tetramethyl silicate 30 m
1, 30 ml of tetraethyl silicate was used as a metal alkoxide, and the metal alkoxide was mixed with 12.4 ml of triethyl borate as a solvent. Further, 25 ml of 0.01 N hydrochloric acid was added as a catalyst, and the mixture was stirred at room temperature for 1 hour. 1.25 mol / l as metal component
107.63 ml of aqueous lead acetate solution and 15.35 m of acetic acid
1 was added. After this addition, the mixture was further stirred at room temperature for 30 minutes to prepare a sol.

Next, the sol was dispensed into a 35 mm diameter polypropylene container and gelled at room temperature. The obtained gel was left at 30 ° C. for 5 days to ripen the gel. During gelation, methanol, ethanol and water were produced as product liquids. Further, a mixed solvent of IPA (isopropyl alcohol): water = 8: 2 has a concentration of 0.61 mol.
A lead acetate solution having a liquid temperature of 60 ° C. adjusted to 1 / l was prepared, and the aged gel was immersed in a container containing the solution to remove acetic acid from the gel.

Then, a container containing IPA → IPA:
The gel was immersed for 2 days in the order of a container containing a solution of acetone = 8: 2 → a container containing a solution of IPA: acetone = 5: 5 → a container containing acetone.
Lead acetate crystals were precipitated in the gel and fixed.

After this treatment, a potassium acetate concentration of 0.3
05 mol / l and acetic acid concentration of 0.15 mol / l
The ethanol solution adjusted to 150 ml is stored in a container,
The gel was immersed in the ethanol solution in this container for 16 hours to elute lead acetate, and a concentration distribution of lead acetate and potassium acetate was given so as to gradually change from the outer surface of the gel toward the center. Then, IPA: acetone: a container containing 5: 5, a container containing acetone, and a container containing acetone were immersed in each of the distribution fixatives for 2 days, so that lead acetate and potassium acetate were contained in the gel. Was precipitated to fix the concentration distribution shape.

Next, a trade name "Garden D0" having a specific gravity of 1.72, which is incompatible with triethyl borate as a solvent in the gel, a product solution in the gel and each distribution fixing solution, and is an inert liquid.
1 "(Montecatini) with TPX diameter 37
20 ml in a drying container of 20 mm, and the gel to which the concentration distribution was given in the previous step was washed with acetone.
It was transferred into a drying container. The drying container is kept at 30 ° C for 1
The gel was dried by warming to 50 ° C. over 5 days. During drying, the gel contracted in volume from 35 mm in diameter to 18 mm in diameter, but was freely floating in Galden D01 and could be dried without cracking or distortion.
Finally, the gel was taken out of the drying container, heated to 570 ° C. and sintered to obtain a gradient index optical element.

(Embodiment 2) Metal alkoxide in tetramethyl silicate (25.8 ml) and solvent as I
248.4 ml of PA and 15 m of 2N acetic acid as a catalyst
and stirred at room temperature for 30 minutes. Next, 42.6 g of isopropyloxytitanate was added as a metal component, and the mixture was further stirred for 30 minutes. Then, 50 ml of water, IPA3
A mixed solution consisting of 5 ml and 7.5 ml of 1N hydrochloric acid was added dropwise and stirred at room temperature for 30 minutes to prepare a sol. This sol was dispensed into a polytetrafluoroethylene container having a diameter of 40 mm, gelled at room temperature, and this gel was kept at 60 ° C. for 4 days for aging.

Next, a container containing IPA → a container containing IPA: acetone = 8: 2 → IPA: acetone =
The gel was immersed for 2 days each in the order of the container containing 5: 5 and the container containing acetone to precipitate and fix titanium crystals in the gel.

Next, the citric acid concentration is 1 mol / l 3
A prescribed sulfuric acid solution is used as a distribution providing solution, and the gel is immersed in a container containing the sulfuric acid solution for 24 hours to give a concentration distribution in which the concentration of titanium gradually changes from the outer surface of the gel toward the center. Was. Thereafter, it was further immersed in a container containing ethanol as a distribution fixing liquid for one day to precipitate and fix titanium microcrystals.

Then, "Perflod IL-27" having a specific gravity of 1.89, which is incompatible with IPA as a solvent, a product solution at the time of gelation and a distribution fixing solution, and is an inert liquid.
0 ”(product of Tokuyama Soda Co., Ltd.), TPX 42m diameter
30 ml was placed in a drying container of m, and the above-mentioned gel was transferred into the drying container. The drying container is heated from 30 ° C. to 80
The gel was dried by warming to 7 ° C over 7 days. During the drying, the gel contracted in volume, but was in a state of freely floating in the liquid perfluded IL-270 in the drying container,
Drying was possible without cracking or distortion. Finally, the gel was taken out of the drying container, heated to 1150 ° C. and sintered to obtain a gradient index optical element.

(Comparative Example) A gel which had been subjected to the steps from gelation to concentration distribution provision in the same manner as in Embodiment 1 at the same sol composition ratio as in Embodiment 1 was washed with acetone. The sample was transferred to the same TPX drying container having a diameter of 37 mm as in Example 1. At this time, Galden D01, which is an inert liquid, was not charged. The gel was held in an inclined state in contact with the inner surface of the bottom of the drying container. In this state, heating was performed under the same conditions as in the first embodiment. As a result, when the temperature exceeded 130 ° C., cracks appeared in the gel. When the heating was further continued to 150 ° C., even the gel which did not crack was in a bow-shaped state.

[0029]

According to the present invention, an inert liquid having a higher specific gravity than a gel and incompatible with a solvent contained in the gel is placed in a drying container and dried while keeping the gel in a free floating state. Therefore, the gel is not broken or distorted during drying.

Claims (1)

[Claims] 1. A sol gel prepared from a metal alkoxide as a raw material is gelled, the gel is immersed in a solution eluted with a metal component, and then washed, dried, and sintered. The method according to claim 1, wherein the washed gel and an inert liquid having a higher specific gravity than the gel and incompatible with the solvent contained in the gel are placed in a drying container and dried. Manufacturing method of rate distribution type optical element.