JP2000239023A - Production of glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove foams by heating a glass raw material, melting the raw material into a glass melt containing a specific amount of SnO2 and then degassing the glass melt in a high-temperature state at a specific temperature or higher than it under a specified pressure so as to decompose SnO2 and to release an O2 gas. SOLUTION: A glass raw material is heated and melted into a glass melt containing 0.01-2 wt.% SnO2 and the glass melt is made into a high-temperature state at a temp. of >=1,350 deg.C and degassed under a pressure of 50-380 Torr. Thereby, the necessity of use of As2O3 having strong toxicity is eliminated. The temperature of the glass melt is preferably <=1,650 deg.C so as to prevent the corrosion of refractory, platinum, etc., constituting a glass melt furnace and the occurrence of defect of product such as foreign matter and striae from the corroded refractory, platinum, etc. Consequently, high-quantity glass can be produced without shortening the life of a glass melting furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing glass for efficiently removing bubbles generated when melting glass raw materials.

[0002]

2. Description of the Related Art Conventionally, when producing glass, a glass raw material is dissolved into a homogeneous glass melt, but bubbles are generated in the glass melt, and these bubbles cause product defects. In order to remove such bubbles in the glass melt, Na ₂ SO ₄ , As ₂ O ₃ , and Sb ₂ O ₃ are added as fining agents to the glass raw material and dissolved in the glass melt, and the glass in a high temperature state is added. Defoaming is performed from the glass melt using the reaction of the fining agent in the melt. In particular, As ₂ O ₃ has a large defoaming effect and is used for producing high-quality glass.

However, As ₂ O ₃ has a strong toxicity of SnO ₂ ,
Its use is being restricted. In recent years, the use of SnO ₂ as a fining agent to replace As ₂ O ₃ has been attempted. This fining agent uses O ₂ gas released by utilizing the reaction of SnO ₂ in the glass melt in a high temperature state for floating defoaming.

[0004]

THE INVENTION Problems to be Solved] When using As ₂ O _3, 1200 ℃ generated oxidation reaction occurs As ₂ O ₅ of As ₂ O ₃ at a temperature below the glass the As ₂ O ₅ is in the normal A reaction is caused within a temperature range of 1300 to 1600 ° C. to release O ₂ gas, and when the O ₂ gas becomes large bubbles and floats in the glass melt, the bubbles in the glass melt are removed. but on the other hand, when using SnO _2, SnO ₂ is not sufficiently O ₂ gas discharge because the decomposition reaction in a temperature range of 1300 to 1600 ° C. at atmospheric pressure not very active,
There is a problem that bubbles remain in the glass melt and the produced glass does not have the required quality.

[0005] An object of the present invention is to provide a method for producing glass which solves the above-mentioned conventional problems.

[0006]

According to the method for producing glass according to the present invention, the glass raw material is heated so that SnO ₂ becomes 0.01 to less.
Dissolved in a glass melt containing 2% by weight, and then brought the glass melt to a high temperature of 1350 ° C.
It is characterized by defoaming under reduced pressure of orr.

[0007]

According to the present invention, a glass melt containing 0.01 to ₂ % by weight of SnO ₂ is brought into a high temperature state of 1350 ° C. or more to obtain a glass melt.
Since the defoaming is performed under a reduced pressure of about 380 Torr, the decomposition reaction of SnO ₂ actively occurs at a temperature of 1350 ° C. or more by maintaining the glass melt in a melting atmosphere in which the O ₂ partial pressure is reduced, thereby increasing the amount of O 2. ₂ gas is released, and bubbles and O ₂ gas in the glass melt expand according to the Boyle-Charles law to become large bubbles and defoaming is promoted.

When the content of SnO ₂ is less than 0.01% by weight, the amount of O ₂ gas released into the glass melt by the reaction is so small that there is almost no defoaming effect, and the content of SnO ₂ is 2%. If the content is more than 10% by weight, the properties of the glass such as the expansion coefficient are out of the intended range.

When the temperature of the glass melt is set to less than 1350 ° C., the decomposition reaction of SnO ₂ does not sufficiently occur, so that a small amount of O ₂ gas is released, and there is almost no defoaming effect. On the other hand, when the temperature of the glass melt is set to a high temperature exceeding 1650 ° C., erosion of the refractory and platinum constituting the glass melting furnace is promoted, and foreign matter, striae and the like from the eroded refractory and platinum are promoted. It is preferable that the temperature of the glass melt is 1650 ° C. or less, since the product defects described above occur and the life of the glass melting furnace is shortened.

[0010] Further, to reduce the pressure in the glass melting furnace to less than 50 Torr, the equipment becomes large and the cost becomes unreasonable. In the state of reduced pressure of 380 Torr or more, the partial pressure of O ₂ in the melting atmosphere is high, and the decomposition reaction of SnO ₂ is reduced. This does not occur sufficiently, and the bubbles in the glass melt do not expand sufficiently, so that the defoaming effect is small.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for producing glass according to the present invention and comparative examples will be described.

As an example, a glass raw material containing 0.6% by weight of SnO ₂ was added, and as a comparative example, 0.6% by weight of As ₂ O ₃ was added.
The added glass raw material and, as another comparative example, glass raw materials to which no fining agent was added were each placed in a platinum crucible, and these platinum crucibles were heated to 1600 ° C. in a heating furnace at a viscosity of 10 ^2.75 poise over 24 hours. The aluminosilicate glass was melted. Thereafter, each glass melt was poured out of a platinum crucible, solidified and pulverized to produce a cullet of 4 mm or less.

First, the cullet of each of the above prepared glasses
Was used to examine the relationship between the fining agent and the reduced pressure. Example
SnO as 1_Two0.6% by weight of glass
50 g again in a platinum crucible and 1600 under atmospheric pressure.
℃, 30 minutes after re-melting, the temperature of 1600 ℃
50, 100, 200, 380 Torr while maintaining
Degassing for 30 minutes under atmospheric pressure (760 Torr)
The number of bubbles per 10 g of glass was measured, and the result was expressed as A
s_TwoO_ThreeComparative Example 1 containing 0.6% by weight of
The results are shown in Table 1 together with Comparative Example 2 in which no additive was added. Also implemented
Example 2 is SnO _TwoMelt containing 0.6% by weight of
Was applied to 10 g of glass when defoamed in the same environment for 60 minutes.
The number of bubbles_TwoO_ThreeComparison with 0.6% by weight
Table with Example 3 and Comparative Example 4 with no fining agent added.
It is shown in FIG.

[0014]

[Table 1]

[0015]

[Table 2]

As is clear from the number of bubbles in Example 1 and Comparative Example 2 in Table 1, the defoaming effect of the fining agent was remarkable. In Example 1, SnO ₂ was compared with As ₂ O ₃ using As ₂ O _3. Although it is inferior to the defoaming effect under the atmospheric pressure as compared with Example 1, 200 Torr
Under a reduced pressure of r or less, a defoaming effect equivalent to that of As ₂ O ₃ is shown. In addition, when the glass melt was held at 1600 ° C. for 60 minutes, as can be seen from the number of bubbles in Table 2, in Example 2, SnO ₂ was obtained under the reduced pressure of 200 Torr to 380 Torr under the reduced pressure of As ₂ O of Comparative Example 3. Overtake the defoaming effect of ₃ , 2
Under a reduced pressure of 00 Torr or less, a remarkable defoaming effect is exhibited.

Next, the relationship between the fining agent and the depressurized state assuming the fining chamber of an actual glass melting furnace mass-produced was examined.
In an actual glass melting furnace, glass raw materials are stored in a melting chamber for about 1 hour.
The glass melt was heated to 500 ° C. and dissolved in the glass melt.
Defoaming is performed by maintaining the temperature at a temperature of ° C. for a predetermined time. In consideration of such melting conditions, the above three types of glass raw materials are melted under atmospheric pressure at 1500 ° C. for 24 hours, and crushed to 4 mm or less to produce each glass cullet.
Using these glass cullets, the defoaming effect of the fining agent was examined.

In Example 3, 50 g of glass cullet containing 0.6% by weight of SnO ₂ was again put into a platinum crucible.
After re-melting at 1600 ° C for 30 minutes under atmospheric pressure,
While maintaining the temperature of 1600 ° C., the glass melt is
It was kept under reduced pressure of orr for 30 minutes, and the number of bubbles per 10 g of glass was measured. The results are shown in Comparative Example 5 in which the same glass was held at atmospheric pressure for 30 minutes, Comparative Example 6 in which 0.6% by weight of As ₂ O ₃ was added, and Comparative Example 7 in which no fining agent was added.
Are shown in Table 3. In Example 4, a glass melt at 1600 ° C. to which 0.6% by weight of SnO ₂ was added was used.
10 g of glass when degassed for 60 minutes under reduced pressure of Torr
The number of bubbles per unit was measured, and the results were compared. Comparative Example 8 in which the same glass was held at atmospheric pressure for 60 minutes, Comparative Example 9 in which 0.6% by weight of As ₂ O ₃ was added, and no fining agent was added. The results are shown in Table 4 together with Comparative Example 10.

[0019]

[Table 3]

[0020]

[Table 4]

As can be seen from the number of bubbles in Table 3, in Comparative Example 5 in which the temperature of the glass melt was increased from 1500 ° C. to 1600 ° C. under atmospheric pressure, SnO ₂ was a defoaming effect at a temperature rise of 100 ° C. Is inferior to Comparative Example 6 using As ₂ O ₃ in comparison with Comparative Example 5 and Comparative Example 8 in which the retention time in Table 4 was set to 60 minutes, indicating that a longer retention time was required for defoaming. However, in Examples 3 and 4 in which the glass melt was held under a reduced pressure of 100 Torr, the defoaming effect of SnO ₂ became remarkable, and even if the holding time was as short as 30 minutes, the same degassing as when holding for 60 minutes was performed. Shows the bubble effect.

[0022]

According to the method for producing glass of the present invention, A
This is a practically excellent effect that high-quality glass can be manufactured without using s ₂ O ₃ and without shortening the life of the glass melting furnace.

Claims (1)

[Claims] 1. A glass raw material is heated so that SnO ₂ becomes 0.0
The glass melt is dissolved in a glass melt containing 1 to 2% by weight, and then the glass melt is brought into a high temperature state of 1350 ° C. or higher to obtain a glass melt of 50 to 38%
A method for producing glass, comprising defoaming under a reduced pressure of 0 Torr.