JPH054322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a viscous silica sol, which is useful as an intermediate raw material for various ceramics, and particularly very useful as a raw material for producing silica fibers. .

[Conventional technology]

Research has been conducted on the production of silicate glass by hydrolyzing metal alkoxides and heating the resulting gel, and it has also been discovered that the solution develops stringiness during the hydrolysis of the alkoxide solution. Research has been conducted on producing silicate-based glass fibers by spinning fibers and heating them. For example, silicon tetraethoxide is hydrolyzed in the presence of a hydrochloric acid catalyst to form a viscous sol. Numerous papers and patents have been published regarding the production of silica glass fibers and silica glass, including a method for synthesizing and obtaining silica fibers [Ceramic Industry Association Journal, Vol. 86, No. 11, pp. 552-559 (1978)]. has been done.

When spinning gel fibers using the preparation method described in the above paper, the gelation rate is relatively fast in the viscosity range where spinning is possible, and gelation progresses before the gel fibers become sufficiently thin, resulting in thin silica gel fibers. It is difficult to stably and continuously spin the fibers.

In order to solve this problem, a method has been proposed in which a Si compound represented by the following general formula () is added to silica sol to reduce the reactivity of silica sol (Japanese Unexamined Patent Publication No. 297237/1982).

General formula () Y ₁ (Y ₂ ) (Y ₃ ) SiX In the formula, Y ₁ , Y ₂ , Y ₃ are alkyl groups, allyl groups, or aryl groups, and X is H, Cl, Br, I, OH group, or OR (R is an alkyl group having 1 to 10 carbon atoms) However, in the method of adding the Si compound to the silica sol, if X is a halogen, the strong acid HX generated by hydrolysis and polycondensation will rather gel. Other Si compounds are also expensive compounds. Furthermore, the Si compound added is monofunctional,
Although it may be effective in reducing the reactivity of the sol, the proportion incorporated into the final glass is small, and the added Si compounds tend to scatter during the firing process.

[Problem to be solved by the invention]

The object of the present invention is to inexpensively and easily produce a silica viscous sol that can stably and continuously spin thin gel fibers.

[Means to solve the problem]

The present invention provides a method for producing a viscous silica sol by hydrolyzing a metal alkoxide whose main component is silicon alkoxide in the presence of an acidic catalyst to form a viscous solution, in which the viscosity of the viscous solution is The above object was achieved by a method for producing a viscous silica sol, which is characterized in that silicon alkoxide and/or silicon alkoxide oligomer are added when the sol reaches 10 poise or more.

Examples of the silicon alkoxide used in the present invention include silicon methoxide, silicon ethoxide, and silicon isopropoxide.

The metal alkoxide containing silicon alkoxide as a main component may contain alkoxides of titanium, aluminum, or zirconium in addition to silicon alkoxide.

As the acidic catalyst used in the hydrolysis of the metal alkoxide, it is preferable to use a strong acid such as hydrochloric acid, hydrofluoric acid, or sulfuric acid, and the amount used is preferably 0.001 to 0.5 in molar ratio to the silicon alkoxide.

It is particularly preferred that the amount of water used for hydrolysis is in a molar ratio of 0.5 to 2.0 relative to silicon alkoxide.

In this hydrolysis, in order to carry out the reaction uniformly, it is preferable to use an organic solvent, dissolve the metal alkoxide in the organic solvent, and react as a solution. As the organic solvent, alcohols, ketones such as acetone and methyl ethyl ketone, water such as tetrahydrofuran, and solvents that dissolve both silicon alkoxide are used. Generally, an alcohol of the same type as the alkoxy group of silicon alkoxide is used.

By reducing pressure from the solution that started this hydrolysis,
Alternatively, the viscosity of the reaction solution gradually increases by proceeding with hydrolysis and polycondensation while evaporating the organic solvent at normal pressure.

The silicon alkoxide and/or silicon alkoxide oligomer added at a stage after the viscosity of the solution increases, that is, at the second stage of the reaction, is also added when the viscosity of the reaction solution reaches 10 poise or more.

If the reaction solution is added at a viscosity of less than 10 poise, the viscosity decreases significantly due to the addition of the silicon alkoxide and/or silicon alkoxide oligomer, which is not preferable since it will not exhibit stringiness.

It is preferable to add silicon alkoxide etc. when the viscosity of the reaction solution reaches 100 poise or more.

The silicon alkoxide added at this time may be different from the silicon alkoxide initially used. In addition, the silicon alkoxide oligomer to be added has an average polymerization degree of 2 to 10.
In this case as well, the type of alkoxy group may be different.

To add silicon alkoxide, etc. to a viscous solution, silicon alkoxide may be added to the viscous solution as is, or the silicon alkoxide, etc. may be diluted with an appropriate organic solvent and added. However, the reaction when these are added is relatively slow, and there is no problem in adding them as they are, which is preferable.

The amount of the silicon alkoxide etc. to be added is 0.01 to 2 mol, more preferably 0.01 to 0.5 mol, per 1 mol of Si in the viscous solution obtained by hydrolysis. The amount added is appropriately set depending on the required degree of stabilization of the sol, but the larger the amount added, the more stable the sol tends to be. When the amount added is less than 0.01 mol, the stabilizing effect is insufficient and it is difficult to stably obtain thin gel fibers. Furthermore, if the amount added exceeds 2 moles, the viscosity of the silica sol decreases extremely, making spinning impossible.
When the amount added is relatively large, the ratio of the added silicon alkoxide introduced into the gel fiber decreases, and loss due to scattering during spinning increases.

The reaction conditions for hydrolysis and polycondensation after adding silicon alkoxide and/or silicon alkoxide oligomer are the properties of the silica viscous sol in the viscous solution when these are added, and the required final silica sol. Although it can be easily determined experimentally from the properties of the viscous sol, the desired viscous silica sol can be obtained by simply adding the silicon alkoxide and the like and then leaving it at room temperature for about a day. Naturally, it is also possible to advance the reaction by heating the viscous silica sol.

The method for spinning this silica viscous sol is not particularly limited, and conventional spinning methods can be used.

[Effect]

When obtaining gel fibers from a viscous silica sol through a spinning operation, in normal production, gelation progresses relatively quickly due to the reaction of the silanol groups present in the sol, making it difficult to stably obtain thin fibers. .

In the present invention, silicon alkoxide and/or
Furthermore, the mechanism as to why gel fibers can be stably obtained by spinning when silicon alkoxide oligomers are added is still largely unknown theoretically, but it is likely that these silicon alkoxides are present in the above-mentioned sol. It is thought that the gelation rate can be reduced by reacting with the silanol groups.

Furthermore, although the silicon alkoxide added here is a polyfunctional compound having a tetrafunctionality or higher, it is an interesting fact that it does not promote gelation and contributes to stabilizing the sol. This is thought to be due to the low density of silanol groups in the precursor (the sol state before gel formation is called), and the gelation rate of the sol is It seems possible to stably obtain thin gel fibers while reducing the reactivity without losing the reactivity itself.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples. However, the present invention is not limited to these examples.

Example 1 1 mole of silicon ethoxide and 1 mole of ethanol were mixed, a mixture of 1.3 moles of water acidified with 0.5 N hydrochloric acid and 1 mole of ethanol was added, and the mixture was placed in a constant temperature bath at 50°C and 60% humidity. The mixture was left to stand for two days to obtain a silica viscous sol (this will be referred to as the "first stage silica viscous sol"). The clay of this first stage silica viscous sol was 150 poise.

0.1 mol of silicon ethoxide (mole ratio to Si in the viscous sol is 0.1) is added as is,
After thorough stirring and homogenization, the mixture was left at room temperature for one day to produce a viscous silica sol, which was then used for spinning.

Spinning was performed using a nozzle with a diameter of 160 μm. The obtained gel fiber has a fiber diameter of 18.5 μm.
Therefore, stable continuous spinning was possible.

Comparative Example 1 The first stage silica viscous sol in Example 1 was directly spun using the spinning method of Example 1.

The gel fiber obtained thereby has a diameter of
The diameter of the fiber is approximately 35 μm, and when the winder speed is increased to obtain thinner fibers, the fibers break, making it difficult to continuously obtain thinner fibers.

Example 2 0.2 mol of silicon methoxide (molar ratio to Si in the viscous sol: 0.2) was directly added to the first-stage viscous silica sol in Example 1, and the mixture was thoroughly stirred.
After homogenization, the mixture was left at room temperature for 2 days to obtain a viscous silica sol, which was then spun.

The gel fiber obtained had a diameter of 15.3 μm and could be stably and continuously spun.

Example 3 An average of 3.2-mer silicon methoxide oligomer 0.08 was added to the first stage silica viscous sol in Example 1.
mol (molar ratio to Si in the viscous sol: 0.08) was added as it was, thoroughly stirred and homogenized, and then heated to 50°C.
This was left for one day to obtain a viscous silica sol, which was then spun.

The gel fiber obtained had a diameter of 16.5 μm and could be stably and continuously spun.

Example 4 The same formulation as in Example 1 was reacted for 4 days in a constant temperature bath at 50° C. and 50% humidity to obtain a viscous sol with a viscosity of 870 poise. To this viscous sol, 0.15 mol of silicon oxyoligomer having an average of 4.8 mer (molar ratio to Si in the viscous sol: 0.15) was added, stirred thoroughly and homogenized, and then left at 50°C for one day to form a silica viscous sol. This was then spun.

The obtained gel fiber had a diameter of 14.8 μm and could be stably and continuously spun.

Comparative Example 2 The first stage viscous sol in Example 4 was directly spun. The diameter of the gel fiber obtained is 38μm
In order to obtain thinner fibers, if the winder speed was increased, the fibers would break, making it difficult to continuously obtain thinner fibers.

〔Effect of the invention〕

According to the present invention, it is possible to change the gelation rate of a viscous silica sol with an inexpensive additive component that does not have any adverse effect on the final ceramic fiber. Thereby, it is possible to easily obtain a viscous silica sol that can continuously and stably obtain particularly thin silica fibers.

Claims (1)

[Claims] 1. A method for producing a viscous silica sol by hydrolyzing a metal alkoxide whose main component is silicon alkoxide in the presence of an acidic catalyst to form a viscous solution, in which the viscosity of the viscous solution is 10
A method for producing a viscous silica sol, which comprises adding silicon alkoxide and/or silicon alkoxide oligomer when the viscous sol reaches a poise or higher.