JPH059036A - Method for producing quartz glass having a refractive index distribution - Google Patents

Abstract

(57) [Summary] [Objective] When silica glass having a refractive index distribution is produced by the sol-gel reaction, cracks are generated during drying and sintering of the gel, and fine particles are present in the glass after sintering. Prevent the formation of bubbles. [Structure] 1 mol% to 10 mol% of silica particles having a particle diameter of 1 μm or less is added to a silica sol dispersion liquid, the silica sol dispersion liquid is put into a glass tube, sealed and left at room temperature to obtain a gel body. After that, the gel body is taken out from the glass tube and immersed in a hydrochloric acid aqueous solution to elute the metal component other than Si from the incomplete network structure composed of the Si component and the metal other than Si by diffusion, and A concentration gradient is given to a metal component other than Si, and then the gel body obtained in the above step is dried and then sintered to obtain quartz glass having a refractive index distribution.

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 silica glass having a refractive index distribution used as a rod lens or the like.

[0002]

2. Description of the Related Art Light transmitted through a transparent material has a property of traveling toward a high refractive index. Therefore, a rod lens made of quartz glass is manufactured in which all the incident light is made to intersect the optical axis by gradually increasing the refractive index from the surface toward the center.

The sol-gel method is known as one of the methods for manufacturing this rod lens. This sol-gel method is shown in FIG.
As shown in, water is added to an alcohol solution of silicon alkoxide as a main component and an alcohol solution of metal alkoxide for forming a refractive index distribution to form a silica sol, and the silica sol is kept at a temperature of several tens of degrees Celsius for several hours. To wet the wet gel, and then immerse this wet gel in acidic water to elute the metal that constitutes the metal alkoxide, give a concentration gradient of the metal in the wet gel body, and then sinter it after drying. By doing so, quartz glass having a refractive index distribution is obtained.

In the above-mentioned method, cracks are likely to occur during the drying and sintering of the wet gel, and since the glass after sintering contains fine bubbles, it is used as an optical transmission component requiring severe properties. There are challenges. Therefore, JP-A-3-28132 proposes to add silica powder to silica sol.

[0005]

Although the generation of cracks and bubbles can be suppressed by adding silica powder to silica sol, the addition of a silica component makes it impossible to raise the refractive index and provides a good refractive index distribution. Will not be obtained.

[0006]

Means for Solving the Problems The present inventor has found that by setting the ratio and particle diameter of the silica component to be added within an appropriate range, a good refractive index distribution can be maintained without lowering the refractive index. The present invention is based on the above. Specifically, monodisperse silica particles having a diameter of 1 μm or less are added to silica sol at a ratio of 1 mol% or more and 10 mol% or less with respect to all alkoxides.

[0007]

By adding silica particles having a small particle size, the lack of strength of the skeleton structure of the gel is compensated for, and cracks do not occur during drying or sintering. Also, fine bubbles in the glass after sintering are eliminated.

[0008]

EXAMPLES Examples of the present invention will be specifically described below.
First, tetramethoxysilane silicon alkoxide; Si (OCH _{3) 4,} titanium -n- butoxide as a metal alkoxide other than silicon; Ti (O-n-C 4 H
⁹ ) ₄ , butanol as alcohol; n-C ₃ H ₄ OH was prepared, and the ratio of tetramethoxysilane: titanium-n-butoxide: H ₂ O: butanol was 0.8: 0.
A silica sol dispersion liquid is prepared by mixing so as to be 2: 4: 4.

Next, silica particles are added to the above-mentioned silica sol dispersion liquid. The particle size of silica particles added here is 1μ
m or less, and the addition ratio is 1 mol% to 10 mol%.
The particle size is set to 1 μm or less because if the particle size exceeds 1 μm, the skeleton structure of the gel formed by the sol-gel reaction (hydrolysis / dehydration condensation) will be non-uniform and the insufficient strength of the gel cannot be compensated. Also, the addition ratio of 1 mol% to 10 mol% means that the effect of addition does not appear if it is less than 1 mol% and that the numerical aperture becomes small and the refractive index distribution is smooth if it exceeds 10 mol%. Because you cannot get it.

The above silica sol dispersion is put in a glass tube having an inner diameter of 15 mm, sealed and left at room temperature for 3 days to obtain a gel body. The gel body is Si (OCH _{3) 4} and Ti (O-n-C ₄
It is an incomplete structure of glass network formed by insufficient hydrolysis of H ₉ ) ₄ and condensation reaction involving hydroxyl groups on the surface of silica particles, and contains water and butanol.

After that, the above gel body was taken out from the glass tube and immersed in a 5% hydrochloric acid aqueous solution for 20 hours to obtain the Si component and Ti.
The metal component other than Si, that is, a part of the Ti component is eluted by diffusion from the incomplete network structure of
A concentration gradient (higher concentration toward the inside) is given to the components. And
The gel is washed with water to remove the hydrochloric acid component.

Next, the gel body obtained in the above process was dried and then sintered at 1200 ° C. or higher to prepare a transparent glass body having a diameter of 5 mm and a length of 800 mm. Here, the drying is slowly performed from room temperature to 150 ° C. over 1 to 2 weeks, and the sintering is performed while replacing the atmosphere with a helium atmosphere.

In order to compare the quartz glass according to the present invention obtained by the above-mentioned steps with the conventional quartz glass, 10 transparent glass bodies are produced with and without addition of monodisperse silica particles. However, the generation of cracks and bubbles was compared.

As a result, in the case of the present invention in which the monodisperse silica particles were added, no cracks were generated, and only one bubble was recognized. On the other hand, when the monodisperse silica particles were not added, there were 3 cracks, 8 bubbles were generated, and only 1 crack or bubble was not generated.

Further, the refractive index distribution in the radial direction of the transparent glass body was examined, but as shown in FIG. 2, the effect of the addition of the monodisperse silica particles was not recognized, and a smooth parabolic refractive index distribution was shown. It was

Although tetramethoxysilane was used as the silicon alkoxide in the examples, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, etc. may be used, and titanium is shown as a metal other than silicon. However, a metal alkoxide such as germanium (Ge), zirconium (Zr) or tantalum (Tl) may be used, and sulfuric acid, nitric acid or hydrofluoric acid other than hydrochloric acid may be used as an acid for eluting the metal. You can

[0017]

As described above, according to the present invention,
Since monodispersed silica particles having a diameter of 1 μm or less were added to the silica sol as a starting material at a ratio of 1 mol% to 10 mol% with respect to the total alkoxide, the lack of strength of the skeletal structure of the gel was compensated for, and during drying. It also prevents cracks from forming during sintering, and also prevents generation of fine bubbles in the glass after sintering. Further, the numerical aperture of the glass after firing is in a practical range, a parabola with a smooth refractive index distribution is drawn, and quartz glass excellent in optical characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a procedure for manufacturing a quartz glass body by a sol-gel method.

FIG. 2 is a graph showing a refractive index distribution

Claims (1)

Claim: What is claimed is: 1. A silica sol containing a silicon alkoxide and a metal alkoxide other than silicon is gelled, and then acid-treated to elute the metal constituting the metal alkoxide from the gel so that the metal Create a concentration gradient,
In the method for producing silica glass having a refractive index distribution, in which the gel is then dried and then sintered, monodispersed silica particles having a diameter of 1 μm or less are added to the silica sol in an amount of 1 mol% or more and 10 mol% based on all alkoxides. A method for producing quartz glass having a refractive index distribution, characterized in that it is added in the following proportions.