JPH1059741A - Non-alkali glass and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate foam as display defect and to improve fining property, heat resistance and chemical resistance by adding SnO2 in a specific glass raw material mixture as a fining agent and forming after fusing. SOLUTION: The glass raw material mixture is obtained by mixing 40-70wt.% (hereafter called %) SiO2 , 6-25% Al2 O3 , 5-20% B2 O3 , 0-10% MgO, 0-15% CaO, 0-30% BaO, 0-10% SrO and 0-10% ZnO. To the mixture, 0.05-2.0% SnO2 is added as the fining agent and after fused, formed into a prescribed shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkali-free glass, particularly to an alkali-free glass used as a transparent glass substrate for a display or the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, non-alkali glass has been used as a transparent glass substrate for a liquid crystal display or the like. Alkali-free glass used for display applications is required to be free from bubbles that cause display defects in addition to properties such as heat resistance and chemical resistance.

[0003] As such an alkali-free glass,
More various glasses have been proposed, and the present applicant has
No. 63-74935, SiO_Two -Al_Two O_Three -B
_Two O _Three -Propose alkali-free glass based on CaO-BaO
ing.

[0004]

An alkali-free glass used as a substrate for a liquid crystal display does not contain an alkali metal component, so that a vitrification reaction does not easily occur, and the viscosity of the melt is high. Therefore, the melting of this type of alkali-free glass must be performed at a higher temperature than in the case of glass containing alkali. As ₂ O ₃ which can sometimes generate a large amount of fining gas is used.

However, As ₂ O ₃ is very toxic, and may pollute the environment during the glass manufacturing process or the treatment of waste glass, and its use is being restricted.

An object of the present invention is to provide As ₂ O ₃ as a fining agent.
It is an object of the present invention to provide a non-alkali glass and a method for producing the same, which do not use any of them, and which do not have bubbles serving as display defects.

[0007]

The present applicant has conducted various experiments and found that Sn was used as a fining agent instead of As ₂ O _3.
The inventors have found that the above object can be achieved by using O _2, and propose the present invention.

That is, the alkali-free glass of the present invention comprises 40 to 70% of SiO _{2 and 6 to 2} of Al ₂ O ₃ by weight percentage.
_{5%, B 2 O 3 5~20} %, 0~10% MgO, C
aO 0 to 15%, BaO 0 to 30%, SrO 0 to 1
0%, ZnO 0-10%, SnO ₂ 0.05-2%
Characterized by being essentially free of alkali metal oxides.

[0009] manufacturing method of alkali-free glass of the present invention, SiO ₂ 40 to 70% by weight percentage, Al ₂ O _{3
6~25%, B 2 O 3 5~20} %, MgO 0~1
0%, CaO 0-15%, BaO 0-30%, Sr
Production of alkali-free glass which has a composition of 0 to 10% of O and 0 to 10% of ZnO and which is formed by melting a glass raw material mixture prepared so as to be essentially free of an alkali metal oxide and then molding. in the method, characterized by adding SnO ₂ 0.05 to 2.0 wt% as a fining agent in a glass raw material formulation.

[0010]

[Function] In order to obtain a bubble-free alkali-free glass, a fining gas that is effective in breaking bubbles at the time of melting at a high temperature is generated, and the diameter of micro bubbles existing in the glass melt is increased, floated and removed. There is a need to. Therefore, a component that decomposes at a high temperature and generates a large amount of fining gas is essential, but SnO ₂ is 1
In a high temperature range of 400 ° C. or higher, a large amount of oxygen gas is generated by a chemical reaction due to a change in the valence of Sn ions.

In the present invention, SnO ₂ is used as a fining agent.
By adding, a fining effect in a high temperature range can be obtained, so that an alkali-free glass free of bubbles that causes display defects can be obtained.

Next, a method for producing an alkali-free glass of the present invention will be described.

First, a glass raw material mixture is prepared so as to obtain a glass having a desired composition. The composition range of the glass and the reason for the limitation are described below.

[0014] SiO ₂ is a component that forms a glass network, and its content is 40 to 70%, preferably 45 to 70%.
~ 65%. When the content of SiO ₂ is less than 40%, the chemical resistance is deteriorated, and the strain point is lowered, whereby the heat resistance is deteriorated. When the content is more than 70%, the high-temperature viscosity is increased, the melting property is deteriorated, and the cristobalite is devitrified. It becomes easier for substances to precipitate.

Al ₂ O ₃ is a component for improving the heat resistance and devitrification resistance of the glass, and its content is 6 to 25%, preferably 10 to 20%. If Al ₂ O ₃ is less than 6%, the devitrification temperature rises remarkably and devitrification tends to occur in the glass. If it is more than 25%, the acid resistance, especially the buffered hydrofluoric acid resistance, decreases and the glass substrate surface is deteriorated. Cloudiness is likely to occur.

B ₂ O ₃ is a component that acts as a flux, lowers the viscosity and facilitates melting, and has a content of 5 to 20%.
%, Preferably 6 to 15%. If the content of B ₂ O ₃ is less than 5%, the effect as a flux will be insufficient, and if it is more than 20%, the hydrochloric acid resistance will be reduced, and the strain point will be lowered, thus deteriorating heat resistance.

MgO is a component that lowers the viscosity at high temperature without lowering the strain point and facilitates melting of the glass.
-10%, preferably 0-7%. MgO is 10%
If the amount is larger, the buffered hydrofluoric acid resistance of the glass is remarkably reduced. CaO also functions similarly to MgO, and its content is 0 to 15%, preferably 0 to 10%. When the content of CaO is more than 15%, the buffered hydrofluoric acid resistance of the glass is significantly reduced. BaO is a component that improves the chemical resistance of the glass and also improves the devitrification property.
-30%, preferably 0-20%. BaO is 30
%, The strain point is lowered and the heat resistance is deteriorated. SrO
Has the same effect as BaO, and its content is from 0 to 10
%, Preferably 0 to 7%. If the content of SrO is more than 10%, the devitrification will increase, which is not preferable. ZnO is a component that improves buffered hydrofluoric acid resistance and also improves devitrification, and its content is 0 to 10%, preferably 0 to 7%.
%. On the other hand, if the content of ZnO is more than 10%, the glass is liable to be devitrified, and the strain point is lowered, so that heat resistance cannot be obtained. If the total amount of MgO, CaO, BaO, SrO, and ZnO is less than 5%, the high-temperature viscosity becomes high and the melting property deteriorates, and the glass is easily devitrified. Becomes worse, which is not preferable.

In addition to the above components, ZrO ₂ , TiO
₂ , Fe ₂ O _{3 and the} like can be added up to 5% in total.

Next, SnO ₂ is added to the glass raw material preparation. Amount of SnO ₂ is 0.05 to 2.0 wt% with respect to the glass raw material formulation 100% by weight. The reason is that if it is less than 0.05%, there is no refining effect and 2.0%
If the amount is larger, the amount of volatilization increases and the glass is liable to deteriorate.

Subsequently, the prepared glass raw material is melted.
At this time, a large amount of oxygen gas is generated by a chemical reaction due to a change in the valence of SnO ₂ , and bubbles in the glass are removed.

Thereafter, the molten glass is formed into a desired shape. When used for display applications, it is formed into a thin plate using a method such as a fusion method, a downdraw method, a float method, or a rollout method.

Thus, the weight percentage of SiO _{2
40~70%, Al 2 O 3 6~25} %, B 2 O 3 5
-20%, MgO 0-10%, CaO 0-15%,
BaO 0-30%, SrO 0-10%, ZnO 0
The alkali-free glass of the present invention having a composition of 10% to 10% and SnO2 of 0.05 to ₂ % and containing essentially no alkali metal oxide can be obtained.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

Example 1 Table 1 shows the effect of SnO _2. Sample a was a conventional alkali-free glass to which As ₂ O ₃ was added as a fining agent, and sample b was a sample from sample a to As.
Alkali-free glass prepared except for ₂ O ₃ , sample c is A
₃ shows an alkali-free glass of the present invention to which SnO ₂ is added instead of s ₂ O ₃ .

[0025]

[Table 1]

Each sample was prepared as follows.

Glass raw materials were prepared so as to obtain a glass having the composition shown in the table, melted in an electric furnace at 1550 ° C. for 1 hour, and clarification was evaluated. Table 1 shows the results.

As is evident from Table 1, the clarity of the glass of sample b, to which no fining agent was added, was remarkably poor. On the other hand, the glass of sample c to which SnO ₂ was added was As ₂ O ₃
The clarity was good as in the case of sample a using

The clarity of the glass raw material mixture was 155.
The molten glass melted at 0 ° C. for 1 hour was poured out onto a carbon table and, after slow cooling, the number of bubbles remaining in the glass was counted. 1000 pieces were evaluated as Δ, and 100 pieces or less were evaluated as ○.

Example 2 Table 2 shows examples of alkali-free glass obtained by the method of the present invention (samples No. 1 to No. 1).
5) is shown.

[0031]

[Table 2]

Each sample was prepared as follows.

Glass raw materials were prepared so as to obtain a glass having the composition shown in the table, and the clarity was evaluated in the same manner as in Example 1. In addition, these glass raw materials were mixed in an electric furnace for 15 minutes.
The sample was melted at 00 to 1600 ° C. for 16 to 24 hours and molded to obtain a sample.

For each sample thus obtained,
Heat resistance and chemical resistance were evaluated. Table 2 shows the results.

As is clear from Table 2, each sample was excellent in clarity, and also excellent in heat resistance and chemical resistance.

As for heat resistance, the strain point was determined according to ASTM C336.
It measured based on the method of -71. Chemical resistance was evaluated by observing the surface condition of the glass substrate after immersing each sample in a 10% by weight aqueous hydrochloric acid solution maintained at 80 ° C. for 24 hours. X, those without any discoloration were indicated by o. The buffered hydrofluoric acid resistance was determined by immersing each sample in buffered hydrofluoric acid composed of 38.7% by weight ammonium fluoride and 1.6% by weight hydrofluoric acid kept at 20 ° C. for 30 minutes.
Evaluated by observing the surface condition of the glass substrate,
When the surface of the glass substrate became cloudy, the result was x, and when the surface did not change, the result was o.

[0037]

As described above, according to the method of the present invention, the use of SnO ₂ as a fining agent makes it possible to produce an alkali-free glass having excellent fining properties and having no bubbles that cause display defects. It is possible.

Further, the alkali-free glass of the present invention comprises As
It is environmentally preferable because it does not contain ₂ O ₃ .
Moreover, it has no bubbles that cause display defects, and has excellent heat resistance and chemical resistance, and is particularly suitable as a transparent glass substrate for displays.

Claims (2)

[Claims] 1. 40% to 70% by weight of SiO ₂ ,
_{Al 2 O 3 6~25%, B} 2 O 3 5~20%, Mg
O 0-10%, CaO 0-15%, BaO 0-3
0%, SrO 0-10%, ZnO 0-10%, Sn
An alkali-free glass having a composition of O2 0.05 to ₂ % and containing essentially no alkali metal oxide. 2. SiO ₂ 40 to 70% by weight,
_{Al 2 O 3 6~25%, B} 2 O 3 5~20%, Mg
O 0-10%, CaO 0-15%, BaO 0-3
After melting a glass raw material mixture having a composition of 0%, SrO 0-10%, and ZnO 0-10% and containing essentially no alkali metal oxide, the mixture is melted and then molded. In a method for producing glass, 0.05 to SnO ₂ as a fining agent is added to a glass raw material composition.
A method for producing alkali-free glass, comprising adding 2.0% by weight.