JP3290714B2 - Method of manufacturing refractive index distribution type optical element - Google Patents

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 a gradient index optical element used as an optical lens of a camera, a microscope or the like by a sol-gel method.

[0002]

2. Description of the Related Art Generally, a method of manufacturing a refractive index distribution type optical element by a sol-gel method is disclosed in Japanese Unexamined Patent Publication No. 3-2698.
No. 18, JP. Non-Cryst. Solids.
99. The method described in (160-167) is known. This is because, in addition to the skeleton-forming metal oxide, a metal component for imparting a refractive index distribution is introduced into the sol and the gel, and the distribution is imparted to the metal component such that the refractive index distribution becomes parabolic in the radial direction. And a method for obtaining a glass body having a desired refractive index distribution. This will be described in detail below.

[0003] First, a sol containing lead as a first metal component to be distributed as lead acetate is prepared and then gelled to produce a wet gel. The gel is then dissolved in various solvents, i.e., isopropanol (hereinafter abbreviated as "IPA"), a solvent having a 8: 2 volume ratio of IPA and acetone, a solvent having a 5: 5 volume ratio of IPA and acetone, and acetone. Soak sequentially. By gradually immersing in a solvent having a low solubility of lead acetate in this way, microcrystals of lead acetate are deposited on the wall surfaces of the pores in the gel and fixed. Next, the gel is immersed in a distribution imparting liquid to impart a distribution of the metal composition to the gel. Ethanol is used for the distribution imparting liquid used here, and potassium as the second metal component is added to the liquid as potassium acetate. Potassium, which is the second metal component, is used to compensate for fluctuations in the coefficient of thermal expansion of glass due to the convex shape of lead, which is the first metal component.

Here, since the solubility of lead acetate in ethanol is relatively high, when ethanol infiltrates into the gel, the fine crystals of lead acetate once precipitated and fixed on the pore walls of the gel are dissolved and eluted. The potassium acetate contained in the distribution-imparting liquid enters the gel via the distribution-imparting solvent. The shape of the distribution formed at this time can be controlled by the immersion time in the distribution imparting liquid and the like. This gel is again IP
By immersing stepwise from A into acetone, the first and second metal components are deposited as microcrystals on the wall surfaces of the gel pores and fixed again. Dry this gel,
By firing the obtained dry gel, a glass body having a refractive index distribution in the radial direction can be obtained. As shown in FIG. 5, the composition distribution in the radial direction of the glass produced in this way has a distribution of convexities in lead and concaves in potassium.
The refractive index distribution had a convex shape as shown in FIG.

Japanese Patent Laid-Open No. 3-80133 discloses that in order to obtain a high refractive index distribution type optical element having a high optical design effect, a composition distribution consisting of a composite distribution of convex and concave portions must be provided. It is disclosed in the gazette.

[0006]

However, the transparent glass body produced by the above-mentioned prior art method often has cracks on the surface, which is insufficient for use as an optical element. The cause of the cracks is due to the distribution of the coefficient of thermal expansion (hereinafter abbreviated as “α”) resulting from having a composition distribution in the radial direction. It is considered that α became a concave distribution due to the introduction of potassium.

In this regard, the composition distribution of the produced glass body was examined, and the radial distribution of α was roughly estimated. As a result, a concave distribution shape was obtained as shown in FIG. That is, it is considered that tensile stress is generated in the circumferential direction of the fired glass due to the distribution of α, and this causes cracks.

Here, paying attention to the composition of potassium in FIG.
If the difference between the central part and the peripheral part is reduced, the distribution of α in FIG. 7 is considered to be constant in the radial direction. At this time, in order not to change the shape of the refractive index distribution in the radial direction,
It is considered that the distribution applying time should be the same as the conventional method, and the concentration of the potassium salt in the distribution applying liquid should be reduced.

However, even in this case, cracking was not avoided. When examining the shape of this composition distribution, as shown by a solid line in FIG. 8, potassium had a desired distribution, but at the same time, the distribution shape of lead also changed and was not the intended composition distribution shape. .

In order to avoid cracks, it is conceivable to shorten the distribution giving time. However, it is not possible to avoid cracks by merely changing the time.
There is a drawback that the uneven shape changes at the same time, and a desired refractive index distribution cannot be obtained. In any case, it is impossible to obtain a desired optical element.

Furthermore, in the conventional method having these disadvantages, as described above, it is impossible to change the concave shape and the convex shape of the metal component, respectively. Although it was possible to manufacture an optical element having a high optical design effect, it was practically impossible.

The present invention has been made in view of such conventional problems, and it is possible to individually control the composition distribution shape of each metal component in a gel, to have no cracks when firing the gel, and to obtain a desired shape. An object of the present invention is to provide a method of manufacturing a gradient index optical element having a refractive index distribution.

[0013]

In order to achieve the above object, the present invention provides a method for producing a gradient index optical element by a sol-gel method, comprising the steps of: preparing a silica sol;
A step of introducing a first metal component selected from metal species other than silicon as a metal salt into the silica sol and then gelling the gel, and forming the wet gel with a second metal component and a proton different from the first metal component. Immersing in a solution containing a compound for supplying

[0014]

In the following, the disadvantages of the conventional method will be clarified from the viewpoint of its operation, and thereafter, the operation of the present invention for solving the aforementioned disadvantages will be described.

According to the conventional method, when a distribution-providing liquid having a certain degree of solubility is used for the M ₁ salt of the first metal component M ₁ which contributes to the provision of the refractive index distribution present in the gel, The formation of the distribution is such that the distribution imparting liquid enters the gel,
It was thought that the M ₁ salt of the _first metal component M ₁ precipitated on the pore walls was dissolved and eluted out of the gel as a molecule M ₁ salt. On the other hand, the M ₂ salt was present in the distribution-imparting liquid as the second metal component M ₂ , but the formation of this distribution was accompanied by the diffusion of the distribution-imparting liquid into the gel and the infiltration as a molecular M ₂ salt, the second metal component M ₂ was considered to precipitate with the first metal component M ₁ by subsequent processing as microcrystals pore walls within the gel.

However, only the conventional assumption, that is, the assumption that the molecule dissolves as a whole,
The present inventors have newly considered the following assumption since a result having the above-described disadvantage cannot be generated.

That is, when a solvent having a high degree of solubility is used for imparting a distribution to the M ₁ salt of the first metal component M ₁ precipitated on the pore wall of the gel, the first metal component M ₁ becomes a metal salt. That is, in addition to eluting into the distribution-imparting solution as molecules of the M ₁ salt, the actual distribution is determined by the M 1 of the first metal component.
It was assumed ion exchange which occurs through solvent between ₁ ⁺ ion and M ₂ ⁺ ions of the second metal component in the distribution imparting solution is also not negligible. Under this assumption, the first metal component M ₁ inside the gel is outside the gel as M ₁ ⁺ ions, and the second metal component M ₂ in the distribution applying liquid is inside the gel as M ₂ ⁺ ions. It spreads. Considering the charge balance during this ion exchange, the M
_{Even if} the concentration of the disalt is simply reduced, the second metal component M ₂
It is impossible to control only one of the distribution shapes, the concentration of the _first metal component M ₁ also changes, and the distribution of a desired composition, that is, each of the composition distributions cannot be controlled. Becomes

Here, the second metal component M in the distribution imparting liquid is used.
_It was considered that the concentration of the M ₂ salt of _{No. 2} was reduced, and that a substance X other than M ₁ and M ₂ that dissociated in the distribution applying liquid was added to the distribution applying liquid. As a result, M ₂ ⁺ ions of the metal and X ⁺ ions generated from the dissociated substance are mixed in the distribution imparting liquid. At this time, the ion exchange between the M ₁ ⁺ ion in the gel and the M ₂ ⁺ ion outside the gel is performed in the same manner as described above, and the ion exchange between the M ₁ ⁺ ion in the gel and the X ⁺ ion outside the gel is also performed. At the same time occurs, the distribution shape of the M ₁ and M ₂ of the first and second metal component is desired shape. That is, the substance X as the third component
Is added to the distribution-imparting liquid, whereby the second metal component M
Reduction of the first elution amount of the metal component M ₁ due to reduced ₂ concentration, i.e. the shortage of M ₂ ⁺ ions will form such as X ⁺ ions complement, the first metal component M ₁ without reducing the elution amount, it is possible to reduce the concentration gradient of a gel inside the second metal component M _2.

If it is possible to control the convex shape distribution of the _first metal component M _{1 and} the concave shape distribution of the second metal component M ₂ , respectively, the contribution of the refractive index of M _{1 and} the refraction of M ₂ are possible. The refractive index distribution from the index contribution to a desired convex shape, and M
The α distribution from the α contribution of _{1 and} the α contribution of M ₂ can be made constant in a desired radial direction. This is not limited to the relationship between the refractive index distribution and the coefficient of thermal expansion. In general, when attention is paid to two characteristics of glass that depend on a change in composition, each of them can be individually controlled. Here, the refractive index contribution is generally referred to as atomic refraction and the like, and the α contribution is a coefficient of linear thermal expansion when each component is added.

However, in this case, since the desired properties cannot be obtained if the substance X affects the glass properties, it is necessary that the substance X does not affect the glass properties. Considering this, the substance X is generally preferably an acid such as acetic acid, nitric acid, sulfuric acid, carbonic acid, phosphoric acid, boric acid, lactic acid, citric acid, or water that supplies protons as X ⁺ ions, and other substances. The condition can be satisfied as long as it supplies cations other than protons that do not affect the two glass properties of interest. As glass properties, when considering a combination of thermal expansion coefficient and refractive index, the addition protons, such as an ammonium ion (including alkylammonium ions), decomposes during gel firing NO _X, SO _X, becomes CO _X eliminator A cation of an element that can be formed or an aluminum ion satisfies the condition.

Further, as a condition required for the substance X,
It is considered that it is possible to control only the movement of the desired metal species as long as it forms an anion of the same kind as the anion of the metal species to which the distribution is imparted, without problems such as the size of the anion and the movement of the anion. It is desired that the anion is the same as the anion of the metal species.

For example, if the metal species is acetate, the substance X
Acetic acid, ammonium acetate, aluminum acetate and the like are preferable, and when the metal species is a nitrate, nitric acid, ammonium nitrate, aluminum nitrate and the like are preferable.

The two glass properties that can be controlled are not limited to the above-mentioned relationship between the refractive index and the coefficient of thermal expansion.
It is also possible to control other characteristics such as the refractive index and the glass transition point, and the refractive index and the Abbe number. Furthermore, the state of distribution in the glass is not limited to the combination of the above convex shape and a fixed shape, but a combination of a convex shape and a concave shape,
It is possible to control various combinations such as a combination of a concave shape and a fixed shape, and it is also possible to control various degrees of the change of the unevenness.

[0024]

Example 1 30 ml of tetramethyl silicate, 30 ml of tetraethyl silicate, triethyl borate
4 ml, and 1 / 100N hydrochloric acid aqueous solution 2
5 ml was added and the mixture was stirred at room temperature for 1 hour to perform a partial hydrolysis reaction. Here, 1.25 mol / l lead acetate aqueous solution 1
A mixture of 07.63 ml and 15.35 ml of acetic acid was added. This was further stirred vigorously at room temperature for 3 minutes,
The mixture was allowed to stand for 2 minutes, dispensed into a φ35 polypropylene container, and gelled at room temperature. The obtained gel was aged at 30 ° C. for 5 days, and further immersed in a 0.61 mol / l solution of lead acetate at 60 ° C. using a mixed solvent of IPA: water = 8: 2 to remove acetic acid. And aging of the gel. This gel was immersed in the order of IPA, IPA: acetone = 8: 2, 5: 5, and acetone for 2 days each to precipitate and fix microcrystals of lead acetate in the gel pores.

The obtained homogeneous gel was treated with 0.305 mol / l
A solution of potassium acetate in ethanol and 0.15
After immersing in 150 ml of a solution adjusted to be a 3 mol / l acetic acid ethanol solution for 16 hours to give a distribution, IPA: acetone = 5: 5, acetone, and acetone are immersed in this order for 2 days each to obtain acetic acid. Microcrystals of lead and potassium acetate were precipitated in the gel pores and fixed. This is 3
After drying at 0 ° C. for 5 days, the mixture was heated to 570 ° C. and sintered to obtain a colorless and transparent glass body without cracks.

When the composition distribution of this glass body was examined,
As shown in FIG. 1, the refractive index distribution type optical element had a convex distribution of a lead component and a concave distribution of a potassium component in the radial direction, and had a refractive index distribution as shown in FIG.

Comparative Example 1 A gel similar to that in Example 1 was prepared, immersed in an ethanol solution of 0.305 mol / l potassium acetate, and subjected to a distribution providing operation for 16 hours. Cracks occurred in the glass body obtained by sintering the obtained gel at 565 ° C. That is, cracks could not be avoided only by changing the concentration of potassium acetate. The composition distribution in the radial direction of the glass body was as shown in FIG.

[0028]

Example 2 A sol was prepared in the same manner as in Example 1, and the subsequent treatment and the like were performed in the same manner. The distribution applying time was changed from 16 hours to 8 hours, and the distribution applying liquid was 0.305 mol / l.
Ethanol solution of potassium acetate, and 0.1
The solution was changed to a 20 mol / l acetic acid ethanol solution. In this case also, a glass body free of cracks was obtained. The refractive index distribution at this time was as shown in FIG.
In FIG. 4, the solid line indicates the one provided with the 8-hour distribution in this embodiment, and the broken line indicates the one provided with the 16-hour distribution. Thus, by changing the distribution giving time from 16 hours to 8 hours, the convex shape of lead can be controlled, and if the concave shape of potassium is also controlled, the refractive index type optical element free from cracks can be formed. Was found to be possible (however, the distribution of the refractive index is slightly different due to the different distribution giving time).

[0029]

Example 3 15 ml of tetramethyl silicate, 15 ml of tetraethyl silicate, 6.2 of triethyl borate
Then, 12.5 ml of a 1/100 N hydrochloric acid aqueous solution was added thereto, and the mixture was stirred at room temperature for 1 hour to perform a partial hydrolysis reaction. To this, a mixture of 53.82 ml of a 1.25 mol / l barium acetate aqueous solution and 15.35 ml of acetic acid was added, and the mixture was vigorously stirred for 3 minutes, then allowed to stand for 2 minutes, and transferred to a φ12 polypropylene container. Pour and gel at room temperature. After aging at 30 ° C. for 7 days, further aging in a 0.65 mol / l barium acetate solution at 60 ° C. to remove acetic acid, followed by successive immersion in methanol, ethanol and acetone to fix barium acetate. Was done.

The obtained homogeneous gel was treated with 0.305 mol / l
Ethanol solution of potassium acetate, and 0.30
The distribution was given for 2 hours in 20 ml of a solution adjusted to be a 5 mol / l acetic acid ethanol solution, and the distribution shape was fixed by successive immersion in methanol, ethanol and acetone. Next, when this was dried at 30 ° C., a gel having a convex shape distribution of barium and a concave shape distribution of potassium in the radial direction was obtained. 650 ° C
By sintering, a transparent glass body without cracks was obtained.

Examination of the optical properties of this glass body reveals that a refractive index distribution type optical element having a composition distribution of high refractive index and low dispersion in the center and low refractive index and high dispersion in the peripheral portion and having a high optical design effect and high optical design effect. Met.

[0032]

Example 4 15 ml of tetramethyl silicate, 15 ml of tetraethyl silicate, 6.2 of triethyl borate
Then, 12.5 ml of a 1 / 100N aqueous hydrochloric acid solution was added thereto, and the mixture was stirred at room temperature for 1 hour to perform a partial hydrolysis reaction. 53.82 ml of a 1.25 mol / l aqueous solution of lead nitrate was added thereto, and the mixture was vigorously stirred for 3 minutes.
The mixture was allowed to stand for 2 minutes, dispensed into a polypropylene container of φ12, and gelled at room temperature. Thereafter, the gel was aged at 30 ° C. for 7 days, further aged in a 0.65 mol / l lead nitrate solution at 60 ° C., and immersed sequentially in methanol, ethanol and acetone to fix lead nitrate.

The obtained homogeneous gel was treated with 0.305 mol / l
0.15 ethanol solution of potassium nitrate and 0.15
The distribution was given for 2 hours in 20 ml of a solution prepared to be a 3 mol / l nitric acid ethanol solution, and the distribution shape was fixed by successive immersion in methanol, ethanol and acetone. Next, when this was dried at 30 ° C., a gel having a convex shape distribution of lead and a concave shape distribution of potassium in the radial direction was obtained. By sintering this gel, a transparent glass body without cracks was obtained.

[0034]

As described above, according to the method of manufacturing the gradient index optical element of the present invention, the composition distribution shape of each metal component in the gel can be individually controlled, and there is no crack and the desired A gradient index optical element having various optical characteristics with a refractive index distribution can be manufactured.

[Brief description of the drawings]

FIG. 1 is a graph showing a composition distribution of a metal component in a glass body obtained in Example 1 of the present invention.

FIG. 2 is a graph showing a refractive index distribution of the glass body of Example 1.

FIG. 3 is a graph showing a composition distribution of a metal component of a glass body obtained in Comparative Example 1.

FIG. 4 is a graph showing a refractive index distribution of a glass body of Example 2 of the present invention.

FIG. 5 shows a metal in a glass body produced by a conventional method.
It is a graph which shows the composition distribution of a component .

FIG. 6 is a graph showing a refractive index distribution of a glass body manufactured by a conventional method.

FIG. 7 is a graph showing a radial distribution of a thermal expansion coefficient estimated from a composition distribution of a glass body produced by a conventional method.

FIG. 8 is a graph showing a composition distribution of a metal component when the concentration of potassium is changed in a conventional method.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-277525 (JP, A) JP-A-61-183136 (JP, A) JP-A-63-64928 (JP, A) 42239 (JP, A) JP-A-4-260609 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03B 8/00-8/04 C03C 21/00 C03B 20/00 C03B 37/00 C03B 37/14

Claims (1)

(57) [Claims] A step of preparing a silica sol; a step of introducing a first metal component selected from metal species other than silicon as a metal salt into the silica sol; and then gelling the wet gel. Dipping in a solution containing a second metal component different from the metal component and a compound that supplies protons.