JP5862952B2 - Method for producing borosilicate glass - Google Patents

Description

  The present invention relates to a method for producing borosilicate glass, and more specifically to a method for producing borosilicate glass using chlorine as a fining agent.

  In general, borosilicate glass is produced, for example, by forming a glass melt obtained by dissolving a batch or glass cullet, which is a glass raw material powder, into a desired shape and then cooling. In the manufacturing method of borosilicate glass, how to perform a clarification process for removing bubbles caused by, for example, cracked gas generated from a batch from the glass melt has become a major issue.

  Conventionally, as the most common clarification method, there is a method in which a clarification agent that generates gas in a high temperature region is added to a glass raw material and clarification is performed by generating gas from the clarification agent in a clarification step. Examples of the clarifier include a redox clarifier that generates gas by an oxidation-reduction reaction, a decomposer clarifier that generates gas by decomposition, and an evaporative clarifier that generates gas by evaporation. Specific examples of the redox clarifier include arsenic oxide and antimony oxide. Specific examples of the degradable fining agent include sodium sulfate. Specific examples of the evaporating fining agent include sodium chloride.

JP-A-10-114529

  However, antimony oxide and arsenic oxide, which are redox clarifiers, are chemical substances that have a high environmental load, and thus have become difficult to use.

  Sodium sulfate, which is a degradable fining agent, is effective for clarification of soda lime glass. However, when used for melting borosilicate glass having a low solubility of sulfuric acid gas, a reboiling phenomenon of bubbles called reboyl tends to occur. For this reason, sulfates such as sodium sulfate are not suitable for clarifying borosilicate glass.

  Sodium chloride, which is an evaporative fining agent, has a relatively small environmental load and is preferably used for fining borosilicate glass. However, when sodium chloride is used as a fining agent, there is a problem that hydrogen chloride is generated in the melting stage and the equipment is corroded. It is therefore desirable to reduce the amount of sodium chloride used. However, when the amount of sodium chloride used is reduced, it may be difficult to produce a borosilicate glass excellent in foam quality.

  The objective of this invention is providing the manufacturing method of the borosilicate glass which can manufacture the borosilicate glass excellent in foam quality, even if there is little usage-amount of a chlorine compound.

  As a result of experiments by the present inventors, it has been clarified that the temperature at which bubbles start to expand is determined by the gas partial pressure and the water vapor partial pressure of chloride in the glass. And the conclusion that the clarification process should be carried out above this temperature, assuming that the temperature condition where the sum of the gas partial pressure and the water vapor partial pressure of the chlorine compound in the glass melt is 0.50 atm is the bubble expansion start temperature. It came to. As a method for reducing the amount of fining agent used, Patent Document 1 proposes a method using dissolved water in glass. However, this document is directed to soda-lime glass, and does not specifically describe the refining conditions when a chlorine compound and dissolved water are used in combination.

That is, the method for producing a borosilicate glass of the present invention comprises a batch preparation step of preparing a glass raw material batch containing a chlorine compound as a fining agent, a melting step of melting the prepared batch, and bubbles contained in the glass melt. A method for producing a borosilicate glass comprising a refining step for removing and a forming step for forming a glass melt into a predetermined shape, wherein the temperature of the glass melt in the refining step is determined by the gas of a chlorine compound in the glass melt. The temperature is adjusted to a temperature at which the sum of partial pressure and water vapor partial pressure is 0.50 atm or more. “Borosilicate glass” in the present invention refers to glass mainly composed of SiO ₂ and B ₂ O ₃ , and specifically contains SiO ₂ 60 to 85% and B ₂ O _{3 8 to} 20% by mass%. Refers to the glass to be used. “The gas partial pressure of the chlorine compound in the glass melt” means the gas partial pressure P1 obtained by the following formula 1. The “water vapor partial pressure” means a gas partial pressure P2 obtained by the following formula 2.

P1 = Vapor pressure of chlorine compound × Amount of chlorine in glass / chlorine solubility: Formula 1
P2 = (H ₂ O amount in glass / H ₂ O solubility) ² Formula 2
In the present invention, clarification is preferably performed at a temperature at which the gas partial pressure of the chlorine compound in the glass melt is 0.45 atm to 1.5 atm and the water vapor partial pressure is 0.04 atm to 0.3 atm.

  In the present invention, the chlorine compound is preferably an alkali metal chloride, and particularly preferably sodium chloride.

  In this invention, it is preferable to adjust so that the temperature of the glass melt in a clarification process may be set to 1450 to 1700 degreeC.

  According to the method of the present invention, since clarification is performed at a temperature at which the chlorine compound and moisture act efficiently, a borosilicate glass excellent in foam quality can be easily produced. Therefore, borosilicate glass can be produced with a smaller amount of chlorine compound than in the past.

It is a graph which shows the expansion behavior of the bubble at the time of glass temperature rising. It is a graph which shows the expansion behavior of the bubble at the time of glass temperature rising. It is a graph which shows the expansion behavior of the bubble at the time of glass temperature rising. It is a graph which shows the relationship between the sum of the gas partial pressure P1 and the water vapor pressure P2 of the chlorine compound in a glass melt, and bubble number density.

The method of the present invention will be described below.
[Raw material preparation process]
Glass raw materials are weighed and mixed to prepare a batch. Specifically, _SiO 2 60 to _85% by mass%, _B 2 O 3 8~20% glass containing, _SiO 2 60 to _85%, especially by _{mass%, B 2 O 3 8~20%} , Al 2 O ₃₁ to 10%, CaO 0 to 5%, BaO 0 to 5%, Na ₂ O 0.1 to 10%, K ₂ O 0.1 to 10%, and further SiO ₂ 65 to 85% by mass%, B ₂ O ₃ 8-20%, Al ₂ O ₃ 1-10%, CaO 0.1-5%, BaO 0.1-5%, Na ₂ O 0.1-10%, K ₂ O 0.1 It is preferable to prepare the glass raw material so as to obtain 5% glass. In addition, although a batch may be comprised only with a raw material, you may use glass cullet together as needed.

Chlorine compounds are used as part of the glass raw material. The amount of chlorine remaining in the glass does not depend on the type of chlorine compound added to the batch, so it can be added in any form, but because of its low toxicity and irritation, alkali metals such as sodium chloride Chloride can be used preferably. The content of the chlorine compound is preferably added so that the Cl content after vitrification is 0.02 to 0.30 mass%, particularly 0.05 to 0.20 mass%.
[Melting process]
The prepared glass material is put into a melting furnace and melted. The melting temperature is preferably about 1350 to 1550 ° C.
[Clarification process]
Clarification is performed at a temperature at which the sum (P1 + P2) of the gas partial pressure P1 and the water vapor pressure P2 of the chlorine compound in the glass melt is 0.5 atm or higher, preferably P1 + P2 is 0.8 atm or higher. Further, it is preferable to clarify at a temperature at which the gas partial pressure P1 of the chlorine compound is 0.45 atm to 1.5 atm, particularly 0.5 atm to 1.0 atm, and further 0.55 atm to 0.8 atm, and the water vapor partial pressure P2 is 0. It is preferable to clarify at a temperature of 0.04 atm to 0.3 atm, particularly 0.06 atm to 0.25 atm, and further 0.08 atm to 0.2 atm.

In general, there are a plurality of gas species such as SO ₂ , O ₂ , CO ₂ and N _{2 in the} glass melt, and if the total pressure (total pressure in the glass melt) exceeds 1 atm, bubbles are generated. Expansion occurs. When a fining agent is added to the glass, the fining gas raises the total pressure in the glass melt.

  In the present invention, this role is played by chlorine compounds and moisture. Although it varies somewhat depending on the melting conditions, at a temperature at which the sum of the gas partial pressure P1 and the water vapor pressure P2 of the chlorine compound is 0.5 atm or more, the amount of diffusion of the chlorine compound and water into the bubbles increases and the bubbles start to expand. . On the other hand, when the temperature is such that P1 + P2 is less than 0.5 atm, the diffusion amount of chlorine compound and moisture into the foam is not sufficient. In other words, since the bubbles are in a temperature range in which expansion is difficult, a sufficient clarification effect cannot be expected at such temperatures.

  P1 and P2 are obtained by the following formulas 1 and 2.

P1 = Vapor pressure of chlorine compound × Amount of chlorine in glass / chlorine solubility: Formula 1
P2 = (H ₂ O amount in glass / H ₂ O solubility) ² Formula 2
Here, the vapor pressure of the chlorine compound (pure substance) is obtained by using the following Antoine equation.

log ₁₀ P = A−B / (T + C) Equation 3
A, B, and C shown in Formula 3 are numerical values specific to the substance called Antoine constants. For example, the vapor pressure P _NaCl of sodium chloride at an absolute temperature T can be obtained from Vapor Pressure of Pure Substitutes Organic Compounds, Ind. By Stull. Eng. Chem. , 39, 517-540 (1947), it is expressed by the following equation.

P _NaCl (atm) = 0.987 × 10 ^{(5.07-8390 / (T-82.6))}
The amount of chlorine in the glass is measured with a fluorescent X-ray analyzer. Chlorine solubility can be determined by the following method. Usually, a part of raw materials added to the batch as an oxide raw material, carbonate raw material, and nitrate raw material is replaced with a chloride raw material, and a batch in which an excessive amount of chloride raw material is added is prepared. This glass raw material is melted at various temperatures in a sealed platinum container, and the amount of chlorine remaining in the glass after melting is measured by a fluorescent X-ray analyzer. In this way, the chlorine solubility at each temperature can be obtained. For example, the chlorine solubility at the absolute temperature T of the glass having the composition shown in Table 1 described later is represented by the following formula.

Chlorine solubility (mass%) = exp (3.34 × 1000 / T−3.06) Equation 4
The amount of H ₂ O in the glass can be substituted by the β-OH value in the glass measured by IR spectroscopy. The β-OH value is measured as follows.

First, an absorption spectrum of 2.7 to 2.9 μm of glass is measured. Then the minimum value of the transmittance of this range as T _1, and also the transmittance at 2.5μm and T _0. By substituting T ₁ and T ₀ thus obtained and the thickness d (mm) of the glass sample into the following formula 5, the β-OH value in the glass can be calculated.

β-OH value = 1 / d × log ₁₀ (T ₀ / T ₁ ) Equation 5
H ₂ O solubility can be determined by the following method. First, the glass is heat-treated for a long time (for example, 48 hours) in an atmosphere of a predetermined H ₂ O partial pressure (P3), and the moisture content (C) after the heat treatment is obtained by the above method and Equation 5. Next, H ₂ O solubility (S) is calculated using Equation 6.

S = C / √P3 Equation 6
For example, the H ₂ O solubility at the absolute temperature T of the glass having the composition shown in Table 1 described later is represented by the following formula.

H ₂ O solubility (mm ⁻¹ ) = exp (0.959 × 1000 / T−0.244)
When clarification is performed at a temperature less than the above range, bubbles are difficult to expand and a sufficient clarification effect is difficult to obtain. On the other hand, if clarification is performed at a temperature exceeding the above range, there is a risk of placing an excessive burden on the melting furnace.

Here, a method for adjusting the fining temperature so that P1 + P2 becomes a temperature of 0.5 atm or more will be introduced. The clarification process is usually performed at a maximum temperature point called a hot spot. In order to obtain the target gas partial pressure, glass dough is collected from this point, the chlorine content and the H ₂ O content are measured, and the gas partial pressure P1 and the water vapor partial pressure P2 of the chlorine compound are obtained. In this way, P1 + P2 is confirmed, and the fining temperature is changed according to this value. By repeating this operation, the clarification temperature corresponding to the target gas partial pressure can be adjusted.

In the present invention in which a chlorine compound is used as a clarifier, clarification is preferably performed at 1450 ° C. or higher. This is because the vapor pressure of the chlorine compound (for example, sodium chloride) exceeds 1 atm, the diffusion from the glass melt into the bubbles becomes remarkable, and the expansion of the bubbles becomes easy. In consideration of the viscosity of general borosilicate glass, it is more preferable to heat the glass melt to 1500 ° C. or higher. However, if the glass melt is heated too much, the glass melting furnace may be severely damaged or the glass quality may deteriorate, and the temperature at which the glass melt is heated is preferably 1700 ° C. or lower.
[Molding process]
A glass melt is formed into a predetermined shape and slowly cooled to obtain a bubble-free glass article made of borosilicate glass. The molding method is not particularly limited. For example, when molding into a tubular shape, a Dunner method, a downdraw method, an updraw method, or the like can be employed.

  Moreover, post-processing, such as an end surface process, can be given to the obtained glass article as needed.

(Experiment 1)
The clarification mechanism of chlorinated compounds is described by Solefity and Vaporization of Halogenides, Glatech. Ber. Glass Sci. Technol. , 73 C2, p43-50 (2000). In this report, Equation 1 described above is shown as a model equation.

  In this model equation, the gas partial pressure of the chlorine compound in the glass at a certain temperature is determined by the vapor pressure of the added chlorine compound (pure substance), the amount of chlorine in the glass and the ratio of its solubility, and the chlorine compound When the partial pressure exceeds 1 atm, gas is diffused from the glass melt into the bubbles, the bubbles expand, and the bubbles are lifted and defoamed so that the bubbles can be removed from the glass melt.

  Therefore, the validity of this model formula was verified. In the experiment, glass cullet having the base composition shown in Table 1 and containing 0.08% by mass and 0.14% by mass of Cl was used. The amount of chlorine in the glass cullet was confirmed by a fluorescent X-ray analyzer.

  First, the glass cullet was put in an electric furnace maintained at 1450 ° C., held for 5 minutes, and then heated to 1650 ° C. to melt and clarify the glass. In this melting and refining process, bubbles contained in the glass were observed, and the relationship between the bubble diameter and temperature was evaluated.

The relationship between the bubble diameter and temperature is shown in FIG. As a result, it was found from FIG. 1 that the larger the amount of chlorine, the greater the speed at which bubbles expand.
(Experiment 2)
In the same manner as in Experiment 1, the same evaluation was performed using glass cullet containing 0.12% by mass and 0.13% by mass of Cl.

The relationship between the bubble diameter and temperature is shown in FIG. In this experiment, it was found that unlike the experiment 1, the speed at which the bubbles expand may be small in spite of the large amount of chlorine.
(Experiment 3)
As a result of considering Experiments 1 and 2, the present inventors speculated that not only the amount of chlorine but also the moisture in the glass had a great influence on the start of expansion of bubbles. Therefore, as shown in Table 2, an experiment similar to Experiment 1 was performed using glass cullet having the same chlorine content and different moisture content. The results are shown in FIG.

From FIG. 3, it was found that the larger the amount of moisture in the glass, the larger the rate of expansion of bubbles, and it became clear that the amount of moisture in the glass contributes to clarification.
(Experiment 4)
The gas partial pressure P1 and water vapor partial pressure P2 of the chlorine compound were adjusted to various values, and the relationship between these partial pressures and the clarification effect was investigated.

  First, glass raw materials were weighed and mixed so as to have the composition shown in Table 3 to prepare raw material batches (A to D). In each raw material batch, sodium chloride was added as a chlorine compound. The amount of water was adjusted by changing the proportion of aluminum hydroxide and alumina used as the alumina raw material.

  The raw material batch thus prepared was placed in an electric furnace maintained at 1500 ° C., heated at 1500 ° C. for 2 hours, heated to 1550 ° C. within 10 minutes, and maintained at this temperature for 2 hours. Thereafter, the obtained glass melt was cooled to obtain glass samples A to D.

  The glass moisture content (β-OH value) was determined for each glass sample thus obtained. Further, the gas partial pressure P1 and the water vapor partial pressure P2 of the chlorine compound at 1550 ° C. were calculated using Equations 1 and 2.

  Furthermore, the center part of glass sample AD was cut out, and the bubble number density was measured. The results are shown in Table 4. FIG. 4 shows the relationship between the sum of the gas partial pressure P1 and water vapor pressure P2 of the chlorine compound in the glass melt and the bubble number density.

  As is apparent from Table 4 and FIG. 4, glass samples C and D having P1 + P2 of 0.5 atm or more had a remarkably low bubble number density. From this result, it can be seen that bubbles can be effectively removed if clarification is performed at a temperature at which P1 + P2 is 0.5 atm or more.

The β-OH value is obtained by processing a glass sample to a plate thickness of 1.0 mm, and obtaining the minimum transmittance T ₁ in an absorption spectrum of 2.7 to 2.9 μm and the transmittance T ₀ at 2.5 μm. After that, the calculation was performed using Equation 5.

  The bubble number density was evaluated by a method of measuring bubbles contained in the central part of the glass lump with a microscope.

  The method of the present invention is suitable as a method for producing a borosilicate glass used for medical purposes, physics and chemistry, and any other applications.

Claims (5)

Batch preparation process for preparing glass raw material batch containing chlorine compound as clarifier, melting process for melting the prepared batch, clarification process for removing bubbles contained in glass melt, and glass melt in a predetermined shape A method for producing a borosilicate glass comprising a forming step of forming a glass, and measuring a chlorine content and a H ₂ O content of a collected glass dough to determine a gas partial pressure and a water vapor partial pressure of a chlorine compound in the glass melt. characterized in that calculates the sum, the temperature of the glass melt in the fining step, the sum of the gas partial pressure and water vapor partial pressure of the chlorine compounds in the glass melt is adjusted to a temperature equal to or greater than the 0.50atm according to the value A method for producing borosilicate glass. 2. The boron according to claim 1, wherein the gas is clarified at a temperature at which a gas partial pressure of a chlorine compound in the glass melt is 0.45 atm to 1.5 atm and a water vapor partial pressure is 0.04 atm to 0.3 atm. Manufacturing method of silicate glass. The method for producing a borosilicate glass according to claim 1 or 2, wherein the chlorine compound is an alkali metal chloride. The method for producing a borosilicate glass according to claim 3, wherein the alkali metal chloride is sodium chloride. The temperature of the glass melt in a clarification process is adjusted so that it may become 1450 to 1700 degreeC, The manufacturing method of the borosilicate glass in any one of Claims 1-4 characterized by the above-mentioned.