JPH01176235A - Production of silica glass - Google Patents

Abstract

PURPOSE:To prevent the generation of crack and craze in a glass, facilitate the production of glass and reduce the cost of a silica glass produced by sol-gel process, by adding an organic monomer and/or oligomer in a sol-forming process and polymerizing the monomer, etc., in the gelling and drying stages. CONSTITUTION:A silicon alkoxide (e.g. silicon tetramethoxide) is added to water which may contain mineral acids, organic acids or bases as a catalyst. The obtained mixture is added and mixed with a solution produced by dissolving an organic monomer and/or oligomer such as vinyl acetate or acrylic acid in a solvent such as methanol. The alkoxide is hydrolyzed by this process to form a sol solution. If necessary, the solution is added with a solution of polymerization initiator, transferred to a closed vessel having a prescribed form and left standing at room temperature - 100 deg.C for several min - several tens days to effect the simultaneous gelatinization and polymerization of the monomer, etc. The obtained polymer is dried by leaving at room temperature - 100 deg.C for several hr - several tens days and then sintered by heating at 1,000-1,300 deg.C at a heating rate of 50-200 deg.C/hr.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing silicate glass used for optical applications, semiconductor industry, electronic industry, physics and chemistry, and the like.

(Prior Art) In recent years, the sol-gel method has been attracting attention as a new method for producing silicate glass.

The method for producing silicate glass by the sol-gel method is as follows.

Silicon alkoxide and/or its polycondensate represented by the general formula Si (OR) * (where R represents an alkyl group), such as (RO)sSi(OSi(OR)), 1O5i(OR)
Water (an acid or alkali may be added as a catalyst in advance) is added to s (n = O~8) to hydrolyze it into silica hydrosil. At this time, a suitable alcohol may be added as a solvent so that the silicon alkoxide and water form a homogeneous system.

This silica hydrosil solution is gelled by standing still, raising the temperature, adding a gelling agent, etc. Thereafter, the gel is dried to obtain silica gel.

Silica glass is obtained by sintering this dried gel in a suitable atmosphere.

This sol-gel method has the following features.

(Since it can be produced at a lower temperature than the conventional vapor phase chemical vapor deposition method in which the soot produced by flame hydrolysis etc. using 115iC1a etc. as a raw material is sintered and vitrified, it can save energy and reduce costs.

(2) Since it can be used as a raw material in a liquid state, it can be easily purified and highly purified.

(3) Since liquid phase mixing is possible at room temperature, homogeneous glass can be produced even when mixed with other components.

(Problems to be Solved by the Invention) There are still unresolved problems in the production of silicate glass by the sol-gel method, which has various advantages as described above.

In particular, there are problems in that the gel tends to crack or crack during the process of drying the gel, and it is difficult to produce a monolithic large-sized dried gel at a low yield.

One of the causes of cracks and cracks is that stress is generated in the gel as water, alcohol, etc. evaporate during gel drying, and if this stress is greater than the strength of the gel, it is thought that the gel will crack or break. There is.

As a countermeasure to this problem, methods have been taken to lower the porosity of the container and control the evaporation rate of water, alcohol, etc., but these methods are insufficient. Cracks and cracks during the gelation and drying shrinkage processes are largely due to the internal structure of the gel and the drying conditions.

The present invention provides a method for producing silicate glass that does not cause cracking or cracking.

(Means for Solving the Problems) The present invention considers that stress generated due to evaporation of solvents such as water and alcohol during gel drying is a cause of cracks and cracks, and the present invention is designed to withstand such large stress. Organic monomers and/or
Alternatively, this method was based on the discovery that gel strength capable of withstanding the stress generated in the drying process could be obtained by adding an oligomer and polymerizing it during the gelling and/or drying process.

The silicon alkoxide used in the present invention is not only a silicon alkoxide monomer (polycondensates may also be used; for example, (CHsO) OSl (OSl(OCIIs)
x), OSl (OCRs)s (n −0 ~ B )
can be mentioned. One or more of these can be used.

To the water added for hydrolysis, a mineral acid such as hydrochloric acid or sulfuric acid, or an organic substance such as formic acid or acetic acid may be added as a catalyst, and not only ammonia but also an organic base such as ethylenediamine may be added as a base.

There is no particular restriction on the monomer or oligomer of the organic substance added in the step of forming a sol solution, but it is preferable that it is compatible with silicon alkoxide and water, but even if it is not compatible with silicon alkoxide, it can be made compatible by adding an appropriate solvent. It may also be made soluble. For example, vinyl acetate,
Acrylic acid, acrylamide, vinylpyrrolidone, etc. can be mentioned.

One or more of these can be used.

The solvent used at this time can be appropriately selected depending on the silicon alkoxide and the types of monomers and oligomers to be added.

The silicon alkoxide, water, solvent, monomer, or oligomer are thoroughly mixed using a stirrer or the like to make the resulting sol as uniform as possible. In addition, ultrasonic waves may be irradiated, silica fine powder may be added to this sol, and the atmosphere in the process of forming a sol solution is not particularly limited and can be selected as appropriate depending on the type of monomer or oligomer to be added. can.

The generated sol solution is quickly transferred to another container and allowed to gel. During gelation, it is preferable to seal the container in order to prevent rapid evaporation of the solvent such as alcohol from the generated gel.

In this gelling step and then in the drying step, it is necessary to add an operation to polymerize the monomer added to the sol solution. The operations for this polymerization include the following.

(2) adding a polymerization initiator at the same time as adding monomers and oligomers, (2) heating, (2) irradiating with light, (2) irradiating with radiation, etc.

In addition, such operations can be selected as appropriate depending on the type of hexamer and oligomer to be added. The degree of polymerization is adjusted to produce a polymer sufficient to withstand the stress generated during the drying process.

In the drying process, instead of using a lid with holes, the gel is dried and shrunk and solidified in an appropriate atmosphere to form a dry gel. A silicate glass is then produced by sintering using a sol-gel method.

Generally used conditions are used for the gelling step, drying step, and sintering step.

For example, leave for several minutes to several tens of days at room temperature to 100°C, leave for several hours to several tens of days at room temperature to 100°C, and leave at 10qO to
Heat to 1300°C for 50~b.

Example 1 Silicon tetramethoxide (St (OCH3))
100 mj of methanol in 141 m1! ,0.01mol
/j! 72 ml of ammonia water was added and mixed well.

Furthermore, methanol IQ Q m 1 in this solution! [Add a solution in which 14.7 g of vinyl nitrate is dissolved and mix at room temperature until the mixture is sufficiently homogeneous. After thorough mixing, a polymerization initiator solution prepared by dissolving 0.1 g of azobisisobutyronitrile in 10 ml of methanol is added. Immediately thereafter, the solution was transferred to a sealed container and heated to 60°C to perform gelation and polymerization reactions.
After drying at 120° C. for 10 days, dry gel was dried at 120° C. for 1 day to obtain a dry gel without any cracks or cracks. This dried gel was heated at 1200° C. in a firing furnace to obtain silica glass free from crackling and foaming.

This silica glass has no devitrification or bubbles and is of high quality. Further, as a result of analysis, the properties of this silica glass matched those of commercially available silica glass.

Example 2 Silicon tetramethoxide (St (OCRs) *)
160ml of methanol in 141ml, 0.01mol/
j! 72 mJ of aqueous ammonia was added and mixed well. In addition, 60% throat lolidon aqueous solution WL24.5 is added to this dissolution.
g and nitrogen gas was passed through the mixture for 1 hour while stirring. After thorough mixing, the sol solution is transferred to a closed container and heated to 70°C to perform gelation and polymerization reactions. Thereafter, the gel was dried at 70° C. for 7 days and then at 120° C. for 1 day in place of a lid with holes to obtain a dry gel without any cracks or cracks. This dried gel was heated at 1200° C. in a firing furnace to obtain silica glass free from crackling and foaming.

This silica glass has no devitrification or bubbles and is of high quality. Further, as a result of analysis, the properties of this silica glass matched those of commercially available silica glass.

(Effects of the Invention) According to the present invention, it is possible to easily manufacture large silica glass by the sol-gel method without causing cracks or cracks.There is basically no restriction on the size. The shape is not limited to a plate-like shape, but also a rod-like or tubular shape, which can be manufactured at a lower cost than before.

Furthermore, because the present invention allows silica glass to be produced at a lower cost than before, it can be used not only in fields such as photomask substrates for IC manufacturing, which have traditionally been used, but also in fields where it has not been used until now due to its high price. It will also be possible to expand demand for.

Claims (1)

[Claims] 1. In a method for producing silica glass by the sol-gel method, which includes the steps of hydrolyzing silicon alkoxide to obtain a sol solution, gelling the sol, drying the gel, and firing the sol solution. Organic monomers and/or oligomers are added in the process, and then organic monomers and/or oligomers are added in the gelling process and/or drying process.
Or a method for producing silicate glass, characterized by polymerizing oligomers.