JPS61163128A - Preparation of optical glass - Google Patents

Abstract

PURPOSE:To obtain transparent optical glass by drying and sintering gel by the sol-gel method while preventing deformation of the gel obtd. by the hydrolysis of solution comprising silicon alcoholate, water, and an org. solvent by retarding the volume change of the gel. CONSTITUTION:After hydrolyzing a solution consisting essentially of silicon alcoholate, water, and an org. solvent, obtd. gel is dried and sintered to prepare a transparent glass body by the sol-gel method. In this method desired optical glass is obtd. by adding at least one kind of metal alcoholate resulting negative volume change of the gel formed in accompany with hydrolysis to the solution. Said metal alcoholate is pref. at least one selected from a group consisting of alcoholates of Ge, Ti, Zr, and B.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing optical glass, in particular, by hydrolyzing a metal alcoholate mainly composed of silicon alcoholate to obtain a porous gel, and sintering the gel. The present invention relates to an optical glass manufacturing method for obtaining quartz glass having a predetermined shape.

BACKGROUND ART Conventionally, the so-called sol-gel method has been known and used to produce highly pure ceramics by hydrolyzing metal alkoxides, followed by drying and sintering. Until now, the shapes of ceramics produced by this method have been limited to those of fine powder or buried earth, and the fine powder has been compressed and then sintered to obtain molded products.

On the other hand, in recent years, in the above-mentioned sol-gel method, a silicon alcoholate solution is directly hydrolyzed in a container with a predetermined shape, and the resulting gel is dried and sintered in that shape to make it non-porous. A method of obtaining a transparent glass body having the shape of is proposed. This method of directly obtaining a molded product in a predetermined shape from a metal alcoholate solution molds a liquid, so compared to the classical method of compression molding powder and then sintering, there are differences in the uniformity of the product and the simplicity of the process. It has various advantages such as In this method, it is important to obtain a dry gel having a predetermined shape without problems such as deformation or breakage before sintering.

According to the above method, especially when producing an optically flat surface or an uneven surface with a constant radius of curvature using a container shape or mold, the porous gel to which the predetermined surface is transferred is deformed by drying and sintering. A serious drawback was that problems such as surface distortion frequently occurred.

As described above, the authors carefully observed the causes of gel deformation, and found that the causes are (i) the volume of the gel changes as gelation progresses, and (ii)
(iii) There is a possibility of deformation due to gravity; (iv) When the gel dries, there is a certain adhesive force between the inner wall of the substrate and the gel; (iv) When the gel dries, there is a possibility of deformation due to gravity; It was thought that this is due to a sudden change in the solvent composition, which causes a sudden change in the interfacial tension at the interface between the solution containing the gel and the gel.

The above gel deformation factor (ii) can be overcome by making the inner wall of the container smooth and coating it with a material with low wettability, such as Teflon, which has a large contact angle (see JP-A-57-22127). , also (iii
) can be solved by reducing the deformation due to gravity from the container shape and gel shape (Japanese Patent Laid-Open No. 57
For (iv), use a high boiling point organic solvent as the organic solvent in the silicon alcoholate solution, or add the high boiling point organic solvent after gelation and before drying and then dry. This can be solved by (separate application pending by the present inventors).

On the other hand, there is currently no known method for suppressing the factor listed in (i), ie, the deformation due to the volume change of the gel accompanying gelation, and this remains as a future challenge.

Problems to be Solved by the Invention As mentioned above, when using the sol-gel method, especially when producing a product having an optically flat surface or an uneven surface with a constant radius of curvature, it is difficult to transfer a desired surface. There was a serious problem that the porous gel was deformed by drying and sintering.

There are four possible causes for this, and solutions have already been proposed that give somewhat satisfactory results for three of them, but so far no satisfactory solutions have been found for the deformation caused by the change in gel volume accompanying gelation. Laws have not been developed.

Therefore, an object of the present invention is particularly to provide a solution to the deformation factor (i).

Means for Solving the Problems The inventors have conducted various studies to develop solutions to the unresolved deformation factors, and have found that the volume change associated with gelation is a positive volume change due to hydrolysis of silicon alcoholate. The present inventors have discovered that this can be easily overcome by adding a metal alcoholate which exhibits a volume reduction upon hydrolysis, and have completed the present invention.

That is, the method for producing optical glass of the present invention is a sol-gel method in which a transparent glass body is produced by hydrolyzing a solution containing silicon alcoholate, hydraulic power, and an organic solvent as main components, and then drying and sintering the resulting gel. This method is characterized in that a metal alcoholate is added to the raw material solution, and the gel generated upon hydrolysis exhibits a negative volume change.

In the method of the present invention, a silicon alkoxide having a short alkoxy group such as tetramethoxysilane or tetraethoxysilane can be used as the silicon alcoholate.

In addition, examples of organic solvents include lower alcohols such as methanol, ethanol, and propatool.
In general, any organic solvent that is compatible with water can be used. In addition, as already mentioned, in order to more effectively prevent gel deformation and breakage due to sudden changes in the gel-containing solution composition when drying the gel, it is necessary to use a high boiling point organic solvent or an organic solvent containing it, e.g. It is desirable to use butanol, pentanol, hexanol, ethylene glycol, glycerin, mixtures thereof, or mixtures thereof with methanol, ethanol, propatool, etc.

Furthermore, as a metal alcoholate which is useful in the method of the present invention and shows a decrease in gel volume upon hydrolysis, Ge1T is used.
Alcoholates of alcohols such as tSZr, B, etc., such as Ge(i-OC3H1) =, Ge(t OC4
89) 4, Ti(i-OC3Ht) 4, Zr (
Examples include i-OC3H7)4, B(OC,H5)3, and the like. Generally, in alcoholates of the same metal, the larger the number of carbon atoms in the alkoxy group, the higher the volume reduction rate.

For reference, the rate of volume change due to gelation of various alcoholates is shown in Table 1 below.

Table 1 According to the method of the present invention, the deformation based on the volume change of the gel is
This problem could be easily solved by using metal alcoholates, which exhibit negative volume changes upon gelation.

Silicon alcoholate, e.g. 1fsi (OCH3)
The hydrolysis of 4 can be expressed by the following formula.

In this formula, the numerical value written below the chemical formula is the volume of each component expressed in cc, and it can be seen that the volume increased by 5.1 cc before and after the reaction. This increase corresponds in relative terms to a positive volume change of 2.8% (see Table 1). The same is true for tetramethoxysilane, which shows an increase of 0.7% as shown in Table 1. It can be seen that such a positive volume change continues even after gelation, giving strain to the gel.

Therefore, according to the method of the present invention, by adding in advance a metal alcoholate whose gel shows a negative volume change upon gelation as described above to the raw material solution (sol) of optical glass, silicon alcoholate can be dissolved. It is possible to compensate for the volume increase accompanying gelation during hydrolysis and effectively prevent deformation of the resulting gel.

EXAMPLES Hereinafter, the method of the present invention will be explained in more detail using examples. However, the scope of the present invention is not limited by the following examples.

Example 1 Tetramethoxysilane, tetrabutoxygermanium,
Water and methanol molar ratio: 0.85:0.15
: The solution was adjusted so that the ratio was 4:4. The solution was gelatinized at 30°C in a petri dish with a flat bottom, and then dried.
A dry gel with a flat bottom was obtained. The dried gel was heated in oxygen for 6 hours.
The temperature was raised to 00°C, and then sintered by heating to 1000°C in vacuum to obtain a transparent glass body. The distortion of the bottom surface of the glass body was 0.2 μm or less within a 5 mm long section.

For comparison, tetramethoxysilane, water, and methanol were added in a molar ratio of l without adding tetrabutoxygermanium.
A dry gel was prepared under the same conditions as above using a solution mixed at a ratio of:4:4. The surface distortion of the dried gel was approximately 2 μm within a 5 mm long section.

The results of tracking the change in volume over time of the gel obtained as described above are shown graphically in FIG. As is clear from this figure, when germanium alcoholate is not added, the volume shows a large change over time, but when germanium alcoholate is added according to the present invention, almost no change in volume over time is observed.

As described in detail, the present invention suppresses gel volume change in the sol-gel method, thereby preventing gel deformation and making it possible to produce transparent optical glass in a desired shape. Particularly when manufacturing glass parts that require flat or curved surface precision, this method has the advantage of reducing distortion of the coughing surface.

[Brief explanation of drawings]

The attached FIG. 1 is a graph showing changes over time in the volume of a gel obtained by hydrolyzing a raw material solution according to the method of the present invention, in comparison with that of a conventional gel. Patent applicant: Nippon Telegraph and Telephone Public Corporation Attorney, Patent attorney: Masahiko Arai Address 1-1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo Name (4
22) Nippon Telegraph and Telephone Corporation 4, Agent 6, Subject of amendment (1) Column for detailed explanation of the invention in the specification (2) "By force..." on page 3, line 20 of the same document The description "deformation due to force" has been corrected to "deformation due to force."

Claims (2)

[Claims] (1) In the sol-gel method, in which a transparent glass body is produced by hydrolyzing a solution containing silicon alcoholate, water, and an organic solvent as main components, and then drying and sintering the resulting gel, the solution is added to the solution along with the hydrolysis. The above-mentioned method for producing transparent glass, characterized in that at least one metal alcoholate is added in which the resulting gel exhibits a negative volume change. (2) The method according to claim 1, wherein the metal alcoholate is at least one selected from the group consisting of Ge, Ti, Zr, and B alcoholates.