JPH03112828A - Production of silica fiber - Google Patents

Abstract

PURPOSE:To obtain an inexpensive and high strength silica fiber reduced in alkali content by adding a specific alkylene carbonate when a silica fiber is produced by using a water glass as the starting raw material. CONSTITUTION:A water glass is added and blended with propylene carbonate and/or butylenecarbonate and the resultant viscous liquid is spun and subjected to dealkalization by an acid treatment and then burned. As the water glass, a water glass rich in content of SiO2 component and having a ratio of Na2 O:SiO2 of 1:3-3.3 is preferably adapted, since dealkalization can be readily carried out and the amount of alkylene carbonate used is reduced. Amount of carbonate used is preferably 1.0-1.6 pts.wt. based on 100 pts.wt. water glass from aspect of spinning properties. As the acid for acid treatment, especially HNO3 and HCI are preferably used. Burning temperature is preferably 800-1000 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing silica fibers, particularly a method for obtaining high-strength silica fibers with low alkali content using inexpensive water glass as a main raw material. .

[Prior Art] Conventionally, as a method for producing silica fiber, for example, 02000
A method in which a silica rod is melt-molded at a high temperature above ℃ and then softened and stretched in a flame and then threaded.■ Using an alkoxide such as tetraethoxysilane as a starting material, adding the acid or alkali necessary for hydrolysis to an alcohol solution of the silica rod. The resulting viscous solution is then gelled, and the resulting viscous solution is then threaded, and then 400 to 120
The so-called sol-gel method, which involves firing at 0°C, uses inexpensive water glass as a starting material, adds an alkali such as caustic soda to it, and evaporates the water to concentrate the resulting viscous liquid. How to
(see Publication No. 2003), etc. are known.

[Problems to be Solved by the Invention] However, the method (2) above has the disadvantages that the melting temperature is quite high, energy costs are high, and it is difficult to control the conditions of the melted string, resulting in low productivity. ing.

In addition, in method (2), the time required to exhibit spinnability is generally relatively short (in addition to the disadvantage of poor workability, the disadvantage is that the cost of the alkoxide used as the starting material is high, so the cost of the silica fiber obtained is also high). have.

Furthermore, in method (2), there is a large amount of alkaline component in the spinning solution (silica crystallizes during firing after spinning, some of the yarn cannot maintain its fiber state, becomes crumbly, or is exposed to high temperatures). It has drawbacks such as a significant decrease in strength.

[Means for Solving the Problems] The present inventor aims to eliminate the various drawbacks of the above-mentioned conventional methods, eliminate troubles caused by alkali while using inexpensive water glass, and obtain inexpensive and high-strength silica fibers. As a result of various studies and examinations aimed at this purpose, it has been found that the above object can be achieved by using a specific alkylene carbonate in combination.

Thus, the present invention provides a method for producing silica fibers, which comprises adding and mixing propylene carbonate and/or butylene carbonate to water glass, spinning the resulting viscous liquid, dealkalizing it by acid treatment, and then firing it. It is on offer.

In the present invention, the water glass used is Na2O
:5iOz=1:1.9 to 3.3 can be used, but it is preferable to have a large SiO□ component because dealkalization is easy and the amount of propylene or butylene carbonate used is small, and Na2O: It is preferable to adopt a composition of SiO□=l: 3 to 3.3.

Next, in the present invention, propylene carbonate and butylene carbonate are used. If an alkylene carbonate lower than these, such as ethylene carbonate, is used, gelation will proceed instantaneously and threading will not be possible.On the other hand, if a carbonate higher than these, such as pentene carbonate, is used, the viscosity will be high enough to be threadable. Both are unsuitable because it takes a long time to form a thick liquid.

Both propylene carbonate and butylene carbonate can be used in substantially the same way, and both can also be used together in any ratio.

The amount of these carbonates to be used is appropriately determined depending on the silica ratio of the water glass used and the spinning conditions, but there is a tendency for the SiO□ component to be large (as it is true, the amount of carbonate used is small).

Generally, when NatO:SiO*=l:3 to 3.3, carbonate is added to 1.0 to 100 parts by weight of water glass.
It is optimal to use it at a ratio of 1.6 parts by weight from the viewpoint of stringability.

When these suitable compositions are employed, after the liquid becomes a viscous liquid that exhibits stringiness, it can continue to maintain its stringiness at room temperature for a long period of 10 to 14 days as at the initial stage.

The viscous liquid thus obtained is threaded according to a conventional method.

The obtained thread exhibits alkalinity, and if it is fired as it is, crystallization progresses, causing the thread to become crumbly and significantly reduced in strength. Therefore, in the present invention, dealkalization, that is, neutralization with an acid is performed.

Examples of acids that can be used include HNO3 and HCI.

Mineral acids such as H, SO, etc. and organic acids such as HCOOH, CH, COOH can be used as appropriate, but especially HNO3, HC
The use of I is particularly preferred since no undesirable impurities remain in the silica fibers finally obtained.

Thus, the fiber after dealkalization is then 400-1200
It is preferable to use a temperature in the range of 800 to 1000 degrees Celsius because it is expected that the denseness and strength of the silica fibers will be improved.

When the method of the present invention is adopted, the spinning period is longer than 10 days (it is superior in terms of workability and effective use of raw materials, and is made from high-purity silica fibers made from inexpensive water glass and with low alkali content. [Example] Example I JIS No. 3 water glass (NazO:SxO, = 1:3)
．． 2 molar ratio) long butylene carbonate 1.
4 g was added and stirred at room temperature for about 1 hour to obtain a uniform viscous liquid. The solution was allowed to stand for about 1 hour to defoam, and then continuously threaded according to a conventional method to obtain gel-like fibers with a diameter of 15 to 20 μm. After drying this fiber at 100°C for 12 hours,
It was immersed for 1 minute to dealkalize it, immersed in ion-exchanged water for 30 minutes, washed, and then dried at 100° C. for 1 hour. The obtained fibers were then heated in an electric furnace at a rate of 10°C/min.
The temperature was raised to 1000°C, held at 1000°C for 1 hour, and then allowed to cool to room temperature to obtain silica fibers.

This fiber has a fiber diameter of lO~15μ and a specific gravity of 2. ONa content 15 ppm, tensile strength 55-60 kg/
It was mm2.

In addition, after storing the above-mentioned viscous I11 liquid in a sealed container at room temperature for 10 days, its spinnability was tested, and silica fibers with the same properties and physical properties were obtained under the same conditions as before storage. .

Example 2 Silica fibers were obtained in the same manner as in Example 1, except that a viscous liquid obtained by adding 1.5 g of propylene carbonate to 100 g of the same water glass as in Example 1 was used.

The fiber diameter of this fiber is 10~15μ, specific gravity 2.1, Na content 18ppm, tensile strength 5'j~64kg/mm.
It was 2.

The viscous liquid was stored in a sealed container at room temperature for 12 days, and then its spinnability was tested, and silica fibers with the same properties and physical properties were obtained under the same conditions as before storage. .

Claims (1)

[Claims] 1. A method for producing silica fibers, which comprises adding and mixing propylene carbonate and/or butylene carbonate to water glass, spinning the resulting viscous liquid, dealkalizing it by acid treatment, and then firing it.