JPH0377133B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing borosilicate glass,
More specifically, the present invention relates to a method for producing borosilicate glass, in which a dry gel is prepared from a mixture of silica sol, silicic acid fine powder, and a boron-containing compound, and the dried gel is fired to form glass.

Due to recent technological advances, very strict requirements have been placed on the materials used.

For example, there are demands for high temperature resistant materials and extremely low expansion materials. Quartz glass is famous as a material that satisfies this requirement.

However, this quartz glass has the disadvantage that it is extremely expensive because natural quartz is repeatedly crushed and washed, and then treated at a high temperature of about 2000°C.

As a substitute for quartz glass, Vycor glass is used because it has somewhat lower temperature characteristics but is cheaper.

The method for producing this Vycor glass is as follows.

First, a molded article is made from a low-alkali glass containing three components of Nb ₂ O, B ₂ O ₃ and SiO ₂ . Next, this molded product
Reheat to 600°C to phase separate silicic acid and sodium borate. Next, sodium borate is chemically soluted with concentrated hydrochloric acid, and the molded product made of a silicic acid skeleton is heated without losing its shape, so that it becomes a transparent glass phase.

Although it is somewhat cheaper than quartz glass because it goes through such a somewhat complicated process, it is too expensive to be used as ordinary plate glass.

On the other hand, LCD televisions have been attracting a lot of attention recently.

The display body of this LCD TV is often made of TFT (thin film transistor).

Depending on the semiconductor material used, TFTs are amorphous (a)-Si type, poly(p)-Si type, CdSe type,
InS ¹ is divided into B type, Te type, etc., but among these, the p-Si type has advantages such as high carrier mobility, ability to turn on peripheral circuits, and can be made into a chip, although the manufacturing process is difficult. is the most promising.

However, p-Si type TFT requires alkali-free and highly heat-resistant glass as a base for its manufacture.

Quartz glass is the best heat-resistant glass, but because it is expensive, Vycor glass, which is one step lower, is being considered. However, as can be seen from the manufacturing method, this glass inevitably contains some sodium content, which is a fatal drawback.

The present invention has been made in order to provide a method for manufacturing inexpensive heat-resistant glass that does not have the drawbacks of quartz glass and Vycor glass, has a low sodium content, and is low in sodium content.

Next, an outline of the present invention will be described.

The present invention is basically a method for producing borosilicate glass using silica sol obtained by hydrolyzing an alkyl silicate, fine silicic acid powder, and boron oxide as raw materials.

Up to now, various manufacturing methods using one or two of these raw materials have been announced, but none of them yield large clumps or result in foaming,
There were problems such as crystallization. In addition to the above objects, the object of the present invention is to improve these drawbacks of the conventional methods.

As the raw material alkyl silicate, any compound having an alkyl group can be used, but methyl silicate, ethyl silicate, isopropyl silicate, etc. are suitable from the viewpoint of raw material procurement.

As the fine silicic acid powder, a fine powder with a diameter of about 50 Å to 1000 Å is suitable.
o-Sil (Cabot), Aevosil (Degussa), D,
Products such as C, Silica (Dow-Corning) can be considered.

Possible boron-containing substances include boric acid, boron oxide, trimethoxyboron, triethoxyboron, and tripropoxyboron.

A mixing method using the above raw materials will be described below.

First, a suitable alkyl silicate is added to an aqueous solution (which may contain alcohol or acid, or both) and is stirred and mixed to perform hydrolysis.

After hydrolysis, fine silicic acid powder is added to this solution with stirring and mixed thoroughly. Next, further boric acid (or boron oxide) is added to this mixture and mixed thoroughly. When triethoxyporone or the like is used, it may be added to an aqueous solution together with an alkyl silicate and hydrolyzed, or it may be hydrolyzed separately and the hydrolyzate may be added after mixing with fine silicic acid powder. The concentration of boron is preferably 1 to 4 percent by weight in terms of boron oxide present in the glass of the final product.

In addition, it is even better if stirring is performed using ultrasonic waves during stirring and mixing. Finally, after stirring, a furnace filtration step may be performed to remove unrefined lumps.

The mixture containing fine silicic acid powder prepared in this way is placed in a container made of Teflon, propylene, etc., and a lid with a hole that allows the amount of solvent evaporation to be adjusted appropriately is placed.
Place in a dryer and dry to form a dry gel.

Next, this dried gel is fired at an appropriate temperature increase rate to obtain borosilicate glass.

This is an outline of the method for producing borosilicate glass of the present invention, and embodiments of the present invention will be further explained in detail with reference to Examples.

Example 1 A mixed solution of 44 ml of ethyl silicate and 5.4 ml of ethanol was added to 36 ml of 0.1N hydrochloric acid and mixed with stirring for 30 minutes. After mixing, add Cab-o while stirring the solution.
- Slowly added 8 g of Sil. After the addition, the mixture was further stirred for a while. While stirring, 0.5 g of boric acid was further added and mixed thoroughly. After thorough mixing, the mixture was placed in a Teflon shear dish with a diameter of 10 cm, covered with a lid capable of controlling the amount of solvent evaporation, and placed in a dryer to dry.
The drying conditions were that the temperature was raised from room temperature to 60°C in 2 days, left at this temperature for 1 day, then raised to 90°C in 1 day, and left at 90°C for 2 days. When the dried gel was fired and sintered at a heating rate of 180°C to 1200°C, clear and clean borosilicate glass was obtained. The resulting glass had a diameter of 4.5 cm, and its properties were almost the same as conventional Vycor glass.

Example 2 Similar results were obtained in the same manner as in Example 1, using 0.56 g of boron oxide instead of boric acid.

Example 3 A mixed solution of 44 ml of ethyl silicate and 5.4 ml of ethanol was added to 36 ml of 0.1N hydrochloric acid and mixed with stirring for 30 minutes. After mixing, 1.2 g of triethoxyboron was further added and stirred. After stirring for a while and becoming a homogeneous solution, 8 g of Cab-o-Sil was added and further stirred. Finally, the mixture was stirred and mixed using ultrasonic waves for 1 hour.

The liquid mixture thus obtained was placed in a propylene plastic container and dried in a dryer while controlling the amount of evaporation. Drying was carried out under the conditions that the temperature was raised to 90°C at a heating rate of 1°C for 1 hour and maintained at 90°C for 2 days.

The dried gel thus obtained was heated at a heating rate of 30°C.
Borosilicate glass was obtained by firing and sintering to 1200°C for hours.

The embodiments of the present invention have been described in the examples above, and in this example, silica sol, silica sol,
Uses fine silicic acid powder and boron-containing ingredients. All of these components play important roles.

The silicic acid fine powder leaves pores even at very high temperatures during firing and sintering, and serves to prevent cracking and foaming during firing and sintering. The silica sol acts as a binder for the fine silicic acid powder and prevents cracking during the production of the dry gel. Boron-containing components ultimately become boron oxide, and since glasses that do not contain these components tend to crystallize, they are thought to play a role in preventing crystallization.

From the above, the present invention is not limited to the above-mentioned embodiments, and when using other fine silicic acid powders, other dry gel preparations, other firing and sintering programs, and other methods may be used. When using an alkyl silicate, it can also be applied when using other boron-containing compounds.

As described above, the present invention is an excellent method for easily obtaining borosilicate glass having properties comparable to quartz glass at a very low temperature. In addition, compared to conventional glasses such as Vycor glass, it is an excellent method that can eliminate alkaline content in principle.

Demand for such an excellent glass manufacturing method is expected in the future. This method will demonstrate its great potential as a manufacturing method for ultra-heat-resistant, alkali-free glass, especially for manufacturing TFT substrate glass for LCD television displays, which is expected to develop in the future.

Claims (1)

[Claims] 1. A method for producing glass in which a silica sol obtained by hydrolyzing an alkyl silicate and a fine silicic acid powder are mixed, dried to form a dry gel, and the dried gel is vitrified by firing. A method for producing borosilicate glass, which comprises further adding a boron-containing substance to the mixture and drying the mixture to form a dry gel.