JP2007039324A - Manufacturing method of alkali-free glass and alkali-free glass plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of alkali-free glass of a low bubble content suitable for a glass substrate for a flat panel display. <P>SOLUTION: In this manufacturing method of the alkali-free glass, a raw material is prepared by regulating the content of SnO<SB>2</SB>to 0.01-2.0 mass% relative to 100 mass% of the total of the mother composition, which composition being shown below, and after heating and melting the raw material at 1,500-1,650°C, in the state of a melt glass of 1,300-1,500°C, oxygen bubbles generating at the interface of the molten glass and the platinum member are absorbed by oxidation of the SnO to SnO<SB>2</SB>. The composition in mass% of the mother composition is 58.4-66.0% SiO<SB>2</SB>, 15.3-22.0% Al<SB>2</SB>O<SB>3</SB>, 5.0-12.0% B<SB>2</SB>O<SB>3</SB>, 0-6.5% MgO, 0-7.0% CaO, 4-12.5% SrO. and 0-2.0% BaO, wherein (MgO+CaO+SrO+BaO) is 9.0-18.0%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing alkali-free glass with less bubbles, and an alkali-free glass plate suitable for a flat panel display substrate with less bubbles produced by the method.

  Substrate glass for flat panel displays is broadly classified into alkali glass containing alkali metal oxide and alkali-free glass substantially free of alkali metal oxide. Alkali glass substrates are used for plasma displays (PDP), inorganic electroluminescence displays, field emission displays (FED), etc., and alkali-free glass substrates are liquid crystal displays (LCD), organic electronics luminescence displays. (OLED) etc.

Among them, a glass substrate for LCD or the like is required to have the following characteristics because a thin film of metal or metal oxide is formed on the surface.
(1) It is a non-alkali glass that does not substantially contain alkali metal ions (the alkali metal oxide in the glass substrate diffuses into the thin film as alkali metal ions and may deteriorate the film characteristics. To prevent deterioration).
(2) It has a high strain point (in order to minimize deformation and shrinkage of the glass substrate due to the glass substrate being exposed to high temperature in the thin film transistor (TFT) formation process).
(3) Sufficient chemical durability against various chemicals used for TFT formation. In particular, buffered hydrofluoric acid (hydrofluoric acid + ammonium fluoride; BHF) used for etching SiO _X and SiN _X , chemical solution containing hydrochloric acid used for etching ITO (indium oxide doped with tin), metal electrode Durability to various acids (nitric acid, sulfuric acid, etc.) used for etching or alkaline resist stripping solution.
(4) There shall be no defects (bubbles, striae, inclusions, undissolved materials, pits, scratches, etc.) affecting the display on the inside and surface of the glass substrate.

  In recent years, as the area of glass substrates for flat panel displays increases, the number of defects per glass substrate increases even if the glass substrates have the same defect density. I have done it. In particular, the bubble defect is a major defect.

Conventionally, a method has been adopted in which As ₂ O ₃ , Sb ₂ O _3, or the like is added to alkali-free glass as a clarifier for reducing bubbles generated when the raw material is dissolved, thereby reducing the bubbles in the alkali-free glass. . However, As ₂ O ₃ and Sb ₂ O ₃ , especially As ₂ O _3, are very excellent fining agents in terms of removing bubbles from the molten glass. It has been demanded.

Further, in order to reduce bubbles generated when the raw material is dissolved, tin oxide is added to the glass raw material as a clarifier, and the Sn ²⁺ / total Sn ratio (= Sn-redox) in the glass is 0.13 by redox titration. A method of melting a glass raw material under the above conditions has been proposed (Patent Document 1). In this method, oxygen gas generated by the reduction reaction from SnO ₂ to SnO floats on the surface of the molten glass together with fine bubbles in the molten glass to be defoamed.
Further, a method has been proposed in which SnO ₂ is added to a glass raw material, the glass raw material is heated to 1350 ° C. or higher, and degassed under reduced pressure (Patent Document 2). In this method, as in the above method, the oxygen gas generated by the reduction reaction of SnO ₂ becomes a large bubble under reduced pressure together with the fine bubbles in the molten glass and floats on the surface of the molten glass to be defoamed.

On the other hand, in recent years, platinum having excellent heat resistance has come to be used in processing steps such as defoaming, stirring, and transporting (such as transporting molten glass through a channel tube) after melting raw materials. However, there is a problem that oxygen bubbles are newly generated from the interface between the platinum and the molten glass. However, in the conventional method for suppressing the generation of bubbles when melting the glass raw material, SnO ₂ is used in the processing step after the melting step, that is, in the step where the molten glass temperature is lower than the glass temperature in the melting step. Reduction reaction to SnO hardly occurs. In addition, the bubbles generated at the platinum interface are initially attached as fine bubbles on the platinum surface, and it is difficult to float and defoam together with the oxygen gas generated by the conventional reduction reaction from SnO ₂ to SnO. In particular, in recent years, there has been a demand for further reduction of bubbles remaining in the display substrate glass, and suppression of the platinum interface bubbles has become a new important issue.
JP 2004-75498 A JP 2000-239023 A

  The present invention performs the defoaming of bubbles contained in the molten glass when melting the glass raw material, and then melts in a process step of performing degassing, stirring, or transferring under reduced pressure under the condition of contacting with the platinum member. Provide a method for producing alkali-free glass that effectively suppresses the generation of bubbles by defoaming bubbles generated at the interface between glass and a platinum member (hereinafter also referred to as platinum), and a flat panel with few bubbles An object is to provide a non-alkali glass plate suitable for a glass substrate for display.

As a result of various experiments, the present inventor has a predetermined Sn-redox glass, melts a predetermined glass raw material at a predetermined temperature, and converts bubbles contained in the molten glass into SnO ₂ in the molten glass. The oxygen bubbles generated on the surface of the molten glass together with oxygen bubbles generated by the reduction reaction of SnO to SnO, and then, in the treatment step, the molten glass generates oxygen bubbles generated at the interface between the molten glass and platinum at a predetermined temperature. The present invention was completed by finding that it is absorbed by an oxidation reaction to SnO ₂ .

Therefore, the present invention dissolves a glass raw material that is substantially free of alkali metal oxide and has the following composition as a matrix composition, and depressurizes the molten glass under a condition of contacting with a platinum member. A method for producing alkali-free glass including a treatment step of foaming, stirring, or transferring, so that 0.01% to 2.0% of SnO ₂ is contained with respect to 100% of the total amount of the mother composition in terms of mass percentage. After the raw material is prepared and the raw material is heated and melted at 1500 to 1650 ° C., bubbles contained in the molten glass float on the surface of the molten glass together with oxygen bubbles generated by the reduction reaction of the SnO ₂ in the molten glass to SnO. after, in the process, in a state in which the molten glass is in the 1300 to 1500 ° C., the oxygen bubbles generated at the interface between the molten glass and the platinum member, the oxidation reaction to SnO ₂ of the SnO A method for producing an alkali-free glass to be absorbed.
Composition by mass percentage display:
_{SiO 2: 58.4~66.0%, Al 2} O 3: 15.3~22.0%, B 2 O 3
: 5.0 to 12.0%, MgO: 0 to 6.5%, CaO: 0 to 7.0%, SrO
: 4 to 12.5%, BaO: 0 to 2.0%,
(MgO + CaO + SrO + BaO): 9.0 to 18.0%

  In the method for producing an alkali-free glass of the present invention, it is preferable to perform the vacuum degassing under a reduced pressure of 160 to 660 torr.

In the method for producing an alkali-free glass of the present invention, the temperature when the molten glass has a viscosity of 10 ² dPa · s is preferably 1600 ° C. or higher.

  Moreover, this invention is a glass plate manufactured by the method in any one of the above.

The present invention also provides:
It is a non-alkali glass that contains substantially no alkali metal oxide and has the following composition as a parent composition, expressed as a percentage by mass of the oxide standard, and SnO ₂ is 0 with respect to 100% of the total amount of the mother composition. A float glass plate containing 15% or more and less than 1%.
Composition by mass percentage display:
_{SiO 2: 58.4~66.0%, Al 2} O 3: 15.3~22.0%, B 2 O 3: 5.0~12.0%, MgO: 0~6.5%, CaO : 0 to 7.0%, SrO: 4 to 12.5%, BaO: 0 to 2.0%, (MgO + CaO + SrO + BaO): 9.0 to 18.0%

The glass plate of the present invention preferably has a thermal expansion coefficient at 50 to 350 ° C. of 25 × 10 ⁻⁷ to 40 × 10 ⁻⁷ / ° C.

  The method for producing an alkali-free glass of the present invention comprises defoaming bubbles contained in molten glass when melting the glass raw material, and oxygen bubbles generated at the interface between the molten glass and platinum in the subsequent processing step. Can be degassed. In addition, since the produced alkali-free glass has a small coefficient of linear expansion and extremely few bubbles, it is suitable for applications requiring such properties, such as substrates for liquid crystal display panels and photomask substrates.

Hereinafter, the term “mass percentage reference” may be omitted, and only the quantity (%) may be described.
The present invention substantially does not contain an alkali metal oxide, melts a glass raw material having the following composition as a base composition, and degassed the molten glass under a condition where the molten glass is brought into contact with a platinum member. A method for producing an alkali-free glass including a processing step of stirring or transferring, wherein the raw material contains 0.01 to 2.0% of SnO ₂ with respect to 100% of the total amount of the mother composition in terms of mass percentage. After the raw material was heated and melted at 1500 to 1650 ° C., bubbles contained in the molten glass were floated on the surface of the molten glass together with oxygen bubbles generated by the reduction reaction of the SnO ₂ in the molten glass to SnO. after, in the processing step, the molten glass in the presence of the 1300 to 1500 ° C., the oxygen bubbles generated at the interface between the molten glass and the platinum member, it is absorbed by the oxidation reaction of the SnO ₂ of the SnO It is a method for producing an alkaline glass.
Composition by mass percentage display:
_{SiO 2: 58.4~66.0%, Al 2} O 3: 15.3~22.0%, B 2 O 3
: 5.0 to 12.0%, MgO: 0 to 6.5%, CaO: 0 to 7.0%, SrO
: 4 to 12.5%, BaO: 0 to 2.0%,
(MgO + CaO + SrO + BaO): 9.0 to 18.0%

  In the vacuum degassing, the glass is preferably defoamed under a reduced pressure of 160 to 660 torr, and more preferably 200 to 400 torr.

In the present invention, the raw material is melted at 1500 to 1650 ° C., preferably 1550 to 1650 ° C., so that SnO ₂ is easily reduced to SnO in the molten glass. Therefore, the viscosity is 10 ²
The glass composition is 58.4 to 66.0% for SiO ₂ , 15.3 to 22.0% for Al ₂ O ₃ , and B ₂ O so that the temperature at which dPa · s becomes 1600 ° C. or higher. ₃ is 5.0 to 12.0%, MgO is 0 to 6.5%, CaO is 0 to 7.0%, SrO is 4 to 12.5%, and BaO is 0 to 2.0%. , (MgO + CaO + SrO + BaO) is 9.0 to 18.0%.

The alkali-free glass of the present invention is
It is a non-alkali glass that contains substantially no alkali metal oxide and has the following composition as a parent composition, expressed as a percentage by mass of the oxide standard, and SnO ₂ is 0 with respect to 100% of the total amount of the mother composition. A float glass plate containing 15% or more and less than 1%.
Composition by mass percentage display:
_{SiO 2: 58.4~66.0%, Al 2} O 3: 15.3~22.0%, B 2 O 3: 5.0~12.0%, MgO: 0~6.5%, CaO : 0 to 7.0%, SrO: 4 to 12.5%, BaO: 0 to 2.0%, (MgO + CaO + SrO + BaO): 9.0 to 18.0%

[SiO ₂ ]
In the alkali-free glass of the present invention, SiO ₂ is a network former and is essential. Since SiO ₂ has a large effect of reducing the density of the glass, it is preferable that the content is large. However, if the content of SiO ₂ is too large, the solubility of the glass is lowered and the devitrification temperature is increased. % Or less. On the other hand, if the content of SiO ₂ is too small, the strain point cannot be sufficiently increased, the chemical durability is deteriorated, and the thermal expansion coefficient is increased, so that it is 58.4% or more. Preferably it is 59.0-65.0%, More preferably, it is 60.0-64.0%.

[Al ₂ O ₃ ]
In the alkali-free glass of the present invention, Al ₂ O ₃ is a component that suppresses the phase separation of the glass, lowers the thermal expansion coefficient, and increases the strain point. The content of Al ₂ O ₃ for exhibiting the effect is 15.3% or more. On the other hand, if the content of Al ₂ O ₃ is too large, the solubility of the glass deteriorates, so it is 22.0% or less. Preferably it is 15.8-21.0%, More preferably, it is 16.5% -20.0%.

[B ₂ O ₃ ]
In the alkali-free glass of the present invention, B ₂ O ₃ is a component that prevents the occurrence of white turbidity due to BHF and achieves a reduction in thermal expansion coefficient and density without increasing the viscosity at high temperatures. If the content of B ₂ O ₃ is too small, the BHF resistance deteriorates, so it is 5.0% or more. If the amount is too large, the acid resistance is deteriorated and the strain point is lowered, so that it is 12.0% or less. Preferably 6.0
It is 11.5%, More preferably, it is 7.0-11.0%.

[Alkaline earth metal oxides]
In the alkali-free glass of the present invention, MgO is a preferred component in alkaline earth metal oxides because it lowers the thermal expansion coefficient but does not lower the strain point. If the content of MgO is too large, white turbidity due to BHF and phase separation of the glass are likely to occur, so it is 6.5% or less. Preferably it is 1.0-6.0%, More preferably, it is 2.0-5.0%.

In the alkali-free glass of the present invention, CaO is a component that improves the solubility of the glass. If the content of CaO is too large, the coefficient of thermal expansion is increased and the devitrification temperature is increased, so that it is 7.0% or less. Preferably it is 1.0 to 6.5%, and more preferably 2.0 to 6.0%.
If the CaO content is more than 7.0%, SnO ₂ may be reduced from about 1400 ° C., which is lower than about 1500 ° C. where the raw material melts and glassifies by heating. There is a case where there is a problem that many oxygen bubbles (initial bubbles) are contained in the molten glass at the time of conversion.

In the alkali-free glass of the present invention, SrO controls the phase separation of the glass and is a relatively effective component against white turbidity against BHF. The SrO content is preferably 4.0% or more. If the SrO content is too large, the coefficient of thermal expansion increases, so it is 12.5% or less. Preferably it is 4.5 to 11.0%, more preferably 5.0 to 10.0%.
Further, when the SrO content is less than 4%, SnO ₂ reduction reaction takes place from about 1400 ° C., which is lower than about 1500 ° C., where the raw material melts and vitrifies by heating, and when it is vitrified. There arises a problem that many oxygen bubbles (initial bubbles) are contained in the molten glass.

  In the alkali-free glass of the present invention, BaO is a component that suppresses the phase separation of the glass, improves the solubility of the glass, and suppresses the devitrification temperature. When there is too much content of BaO, the density of glass will become large and the tendency to increase a thermal expansion coefficient will be strong. From the viewpoint of lowering the density and reducing the thermal expansion coefficient, it is preferable that the content of BaO is set to 2.0% or less and the content is inevitably contained. More preferably, it is 1.0% or less.

  In the alkali-free glass of the present invention, if the total content of the alkaline earth metal oxide (RO), that is, (MgO + CaO + SrO + BaO) is too small, it is difficult to dissolve the glass. On the other hand, if the amount is too large, the density of the glass increases, so it is 18.0% or less. Preferably it is 9.5 to 17.0%, more preferably 10.0 to 16.0%.

[SnO ₂ ]
In the present invention, SnO ₂ added to the glass raw material is reduced to SnO when heated and melted at 1500 to 1650 ° C. to generate oxygen bubbles and float on the surface of the molten glass together with the bubbles contained in the molten glass. Then, in the treatment step, in the state where the molten glass is in a state of 1300 to 1500 ° C., the oxygen generated at the interface between the molten glass and platinum is SnO,
SnO + 1/2 · O ₂ → SnO ₂
It absorbs by the oxidation reaction which becomes and defoams so-called platinum interface bubbles.

The defoaming effect of the platinum interfacial bubbles increases as the Sn-redox [Sn ²⁺ / total Sn] in the molten glass increases. Therefore, the Sn-redox of the obtained glass is 0.3 or more, preferably 0.5 or more by oxidation-reduction titration. Moreover, Sn-redox is 0.1 or more by the measuring method of Sn-Mossbauer spectroscopy. On the other hand, if the Sn-redox is too large, there is a risk of causing corrosion / deterioration of the equipment composed of platinum. Moreover, Sn-redox is 0.3 or less by the measuring method of Sn-Mossbauer spectroscopy.

The amount of SnO ₂ added in the present invention depends on the composition of the alkali-free glass, but is 0.01% or more, preferably 0.05% or more, more preferably 0.1% with respect to 100% of the total amount of the matrix composition. % Or more. From the viewpoint that defoaming in the treatment process can be performed more stably, it is more preferably 0.15% or more with respect to the total amount of the mother composition of 100%, and defoaming in the treatment process is performed more stably. In addition to the fact that it is possible to perform the defoaming when the raw material is dissolved by heating, it is particularly preferably 0.2% or more. On the other hand, even if the amount of SnO ₂ added is too large, the defoaming effect is saturated and there is a risk of affecting the properties of the glass. In addition, when forming into a sheet glass by the float process, SnO ₂ is a float forming region. Is less than 1.0%, preferably less than 1.0%, and more preferably 0.6%. It is as follows.

  From the viewpoint that the precipitation of Sn on the glass surface can be stably suppressed, it is more preferably 0.5% or less.

In addition, when vacuum degassing is performed in the treatment process, the SnO ₂ content is 0.25% relative to the total amount of the mother composition of 100% from the viewpoint that glass defects during vacuum vacuum degassing can be suppressed. It is particularly preferred that

For these reasons, in order to obtain a stable glass quality when forming plate glass by the float process, the content of SnO ₂ is 0.15% or more and 1% with respect to 100% of the total amount of the mother composition. It is preferably less than 0.15%, more preferably 0.15 to 0.5%, and still more preferably 0.2 to 0.5%.
Furthermore, in order to obtain a stable glass quality when vacuum degassing is performed in the treatment step and a plate glass is formed by the float process, the SnO ₂ content is set to 0. 0% with respect to the total amount of the mother composition of 100%. It is more preferably 15 to 0.25%, particularly preferably 0.2 to 0.25%.
An essential component added to the glass raw material of the present invention is SnO ₂ , but when SO ₃ , Fe ₂ O ₃ , Cl, F or the like is further added to the raw material, the glass defoaming / clarifying effect is promoted / strengthened. It is valid.

[SO ₃ ]
SO ₃ is a component that decomposes to generate a large amount of bubbles and increases the bubbles when the glass raw material is heated. The SO ₃ source may be any salt as long as it is alkali-free, but is usually added as an alkaline earth metal sulfate. The defoaming effect by SO ₃ can be obtained by adding 0.01% or more of SO ₃ to 100% of the total amount of the mother composition. A preferable addition amount is 0.1% or more, and a more preferable addition amount is 0.3% or more. On the other hand, if the amount of SO ₃ added is too large, the generation of oxygen bubbles due to decomposition of SO ₃ becomes excessive, so it is 5.0% or less, preferably 2.0% or less, more preferably 1.0% or less. is there.

[Fe ₂ O ₃ ]
When Fe ₂ O ₃ dissolves the glass raw material,
Fe ₂ O ₃ → 2FeO + 1/2 · O ₂
Oxygen bubbles are generated by the reductive reaction shown by the following, and floats and defoams on the surface of the molten glass together with bubbles in the glass. A defoaming effect is obtained by adding 0.01% or more of Fe ₂ O ₃ to 100% of the total amount of the mother composition, but a preferable addition amount is 0.02% or more. Considering that saturation of the defoaming effect by Fe ₂ O ₃ and coloring of the glass become remarkable, it is 2.0% or less, preferably 1.0% or less, more preferably 0.1% or less.

[F, Cl]
F and Cl are components that generate a large amount of bubbles and increase the bubbles when the glass raw material is melted. However, when used in combination with SO ₃ or Fe ₂ O ₃ , the defoaming effect is dramatic. To increase. F or Cl is usually added as an alkaline earth metal fluoride or chloride. Each addition amount is 0.01% or more, preferably 0.05% or more, more preferably 0.1% or more, with respect to 100% of the total amount of the mother composition. On the other hand, since there is a possibility of affecting the saturation of the fining effect by F or Cl and the characteristics of the glass, it is 5.0% or less, preferably 2.0% or less, more preferably 1.0% or less.

In the present invention, SO ₃ and / or Fe ₂ O ₃ and Cl and / or F are preferably added. The amount of the component added is preferably SO ₃ and / or Fe ₂ O ₃ and Cl and / or F in a total amount of 0.01% or more with respect to 100% of the total amount of the matrix composition, It is particularly preferable that the total amount of SO ₃ and / or Fe ₂ O ₃ is 0.01% or more and the total amount of Cl and / or F is 0.01% or more.

[Glass manufacturing method]
The alkali-free glass of the present invention is produced, for example, by the following method. A glass raw material was prepared with the composition described above. The obtained glass raw material is continuously charged into a glass melting tank and melted by heating at 1500 to 1650 ° C., preferably 1550 to 1650 ° C., and bubbles contained in the molten glass are converted into SnO ₂ in the molten glass. The process of performing degassing, stirring, or transferring under reduced pressure conditions under which the molten glass is brought into contact with the platinum member after being floated and defoamed with the oxygen bubbles generated by the reduction reaction of SnO to SnO , Oxygen bubbles generated at the interface between the molten glass and platinum are absorbed and defoamed by an oxidation reaction of SnO to SnO ₂ in a state where the molten glass is at 1300 to 1500 ° C. Thereafter, in the forming step, the glass plate is formed into a predetermined plate thickness by a plate glass forming method such as a float method, and after slow cooling, it is cut to produce a glass plate having a desired size. In addition, Sn-redox by oxidation-reduction titration of the obtained glass is 0.3 to 0.8, preferably 0.5 to 0.7. Moreover, Sn-redox by the measuring method of Sn-Mossbauer spectroscopy will be 0.1-0.3.

[pressure]
In the production of the alkali-free glass of the present invention, when the absolute pressure at which the molten glass is placed decreases, bubbles contained in the molten glass and bubbles adhering to the platinum interface swell and easily float on the surface of the molten glass. Therefore, it is preferable to carry out vacuum degassing in the production of the glass of the present invention. In particular, when applying to highly viscous glass, that is, glass having a viscosity of 10 ² dPa · s and a temperature of 1600 ° C. or higher, it is preferable to perform degassing under reduced pressure. Specifically, the absolute pressure is 160 to 660 torr, more preferably 200 to 400 torr. Even under reduced pressure, oxygen bubbles generated at the interface between the molten glass of the present invention and platinum are not absorbed by the oxidation reaction of SnO to SnO ₂ and the effect of defoaming is not reduced. This was confirmed at 160 to 760 torr.

The β-OH of the alkali-free glass of the present invention is 0.25 to 0.6 mm ⁻¹ , preferably 0.3 to 0.5 mm ⁻¹ . If β-OH exceeds 0.6 mm ⁻¹ , bubbles are likely to be generated at the platinum interface. beta-OH measures the infrared transmittance of the non-alkali glass plate, an infrared transmittance at 4000 cm ^-1 and _{(I 0)} and 3570cm ^-1 near minimum infrared transmittance (I) and the glass thickness (d) From this, it is a value obtained by the following formula and is an index of the water content in the glass.
β-OH = (1 / d) log (I ₀ ) / (I)
The alkali-free glass of the present invention preferably has a thermal expansion coefficient at 50 to 350 ° C. of 25 × 10 ⁻⁷ to 40 × 10 ⁻⁷ / ° C.

Table 1 shows the components prepared as industrial glass materials, and Table 2 shows the total amount of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO and BaO for the obtained glass. The content ratio of each component with respect to 100% is expressed in mass percentage.
Examples 1 to 4 and Example 6 are examples of the present invention, and Example 5 is a comparative example.
The raw materials having the composition shown in Table 1 were placed in a platinum crucible and heated at 1500 to 1650 ° C. to dissolve. Thereafter, the molten glass was poured onto a carbon plate to form a plate shape. Next, 20 g of each plate-like glass was placed in a platinum crucible, melted at 1420 ° C. at atmospheric pressure (760 torr) for 4 hours, and then cooled to obtain the glasses shown in Table 2.

About the obtained glass plate, foam volume, Sn-redox, and each component residual amount were measured and analyzed by the following method. The results are shown in Table 2 together with β-OH, the coefficient of thermal expansion, and the temperature when the viscosity is 10 ² dPa · s.
Sn-redox is a value calculated by [Sn ²⁺ amount / total Sn] by measuring Sn ²⁺ amount in molten glass by oxidation-reduction titration.
The bubble volume is a value obtained by measuring the generated bubble volume (cm ³ / m ² ) per unit area of bubbles newly generated and grown on the bottom of the platinum crucible. The bubble volume was determined by assuming a hemisphere from the bubble radius photographed directly with a camera. The small bubble volume indicates that the effect of absorbing oxygen bubbles at the platinum interface due to the oxidation reaction of SnO to SnO ₂ is large.
The glass residual amount of SnO ₂ , SO ₃ , Fe ₂ O ₃ , F and Cl was measured using a fluorescent X-ray analyzer.

When Examples 1-4 are compared with Example 5, it is clear that the defoaming effect increases as the SnO ₂ addition amount of the glass raw material increases.
Note that the defoaming effect is further increased under a reduced pressure of 160 to 660 torr, particularly 200 to 400 torr.
Further, when Examples 1 to 4 and Example 6 and Example 5 are compared, the defoaming effect is increased when the amount of SnO ₂ added to the glass raw material is 0.15% or more, and when the amount is 0.25% or more, The foam effect becomes more prominent.
Further, according to Tables 1 and ₂ , the addition ratio of SnO _{2 in} the raw material and the content ratio of SnO _{2 in} the obtained glass were substantially the same.

Next, evaluation of the number of bubbles contained in the molten glass will be described below.
Table 3 shows the components prepared as industrial glass raw materials, and Table 4 shows the total amount of the matrix composition of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO and BaO for the obtained glass. The content ratio of each component with respect to 100% is expressed in mass percentage.
Examples 8 and 10 are examples of the present invention, and examples 7 and 9 are comparative examples.
The raw materials (Examples 7 to 10) having the compositions shown in Table 3 were placed in separate 300 cc platinum crucibles, allowed to stand for 30 minutes in an electric furnace at 1500 ° C. and dissolved, and then transferred to an electric furnace having the temperature shown in Table 4. The mixture was allowed to stand for the time shown in Table 4. Thereafter, the glass was transferred to an electric furnace at 760 ° C., and the glass was gradually cooled to 560 ° C. over 2 hours, and further cooled to room temperature over about 10 hours. The glass in the upper center of the crucible was cut into a cylindrical glass having a diameter of 38 mm and a height of 35 mm with a core drill, and cut into a glass plate having a thickness of 2 to 5 mm including the central axis of the cylindrical glass. Both sides of the cut surface were optically polished (mirror polished). For the portion corresponding to 1 to 10 mm from the upper surface of the glass of the crucible, the optical polishing surface is observed with a stereomicroscope, the number of bubbles with a diameter of 50 μm or more in the glass plate is measured, and the value is divided by the volume of the glass plate. The number of bubbles. The results are shown in Table 4.

As is clear from the results shown in Table 4, from Example 7 and Example 8, the effect of reducing the number of bubbles by SnO ₂ is somewhat observed at 1500 ° C., whereas from Example 9 and Example 10, it is 1590 ° C. Then, the effect of reducing the number of bubbles by SnO ₂ was noticeable.
In the process of increasing the molten glass temperature from 1500 ° C to 1590 ° C, bubbles contained in the molten glass float and defoam on the surface of the molten glass together with oxygen bubbles generated by the reduction reaction of SnO ₂ to SnO. This indicates that the reduction in the number of bubbles became significant.

Next, the relationship between the melting temperature when melting the raw material and the Sn-redox of the glass obtained will be described below.
Table 5 shows the components prepared as industrial glass raw materials, and Table 6 shows the total amount of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO and BaO for the obtained glass. The content ratio of each component with respect to 100% is expressed in mass percentage. Example 11 shows an example of the present invention, and Example 12 shows a comparative example.
The raw materials having the composition shown in Table 5 were allowed to stand in a platinum crucible for 30 minutes in an electric furnace at 1500 ° C to form molten glass, and then transferred to an electric furnace at a predetermined temperature (1500, 1550, 1590, 1630, 1710 ° C). For 30 minutes. Thereafter, the glass was transferred to an electric furnace at 760 ° C., and the glass was gradually cooled to 560 ° C. over 2 hours, and further cooled to room temperature over about 10 hours.
The addition ratio of SnO _{2 in} the raw material and the content ratio of SnO ₂ in the obtained glass were almost the same.

  Moreover, about these glass, the value of Sn-redox was measured with the measuring method of Sn-Mossbauer spectroscopy. The graph which shows the value of Sn-redox with respect to predetermined | prescribed melting temperature about each glass is shown in FIG.

Here, a measurement method of Sn-Mossbauer spectroscopy will be described.
^119m gamma rays generated due to the energy transition from Sn to ¹¹⁹ Sn a (23.8KeV) in the probe, by a transmission method (measuring the gamma-rays transmitted through the glass sample), with a divalent Sn in the sample 4 The abundance ratio (Sn-redox) was measured. Specifically, it is as follows.
The γ-ray exit of the radiation source, a glass sample, a Pd filter, and a light receiving portion of a gas amplification proportional counter (manufactured by LND, model number 45431) were arranged on a straight line having a length of 300 to 800 mm.
As the radiation source, 119m Sn of ^10mCi was used, and the radiation source was moved with respect to the axial direction of the optical system to cause the energy change of γ rays due to the Doppler effect. The speed of the radiation source was adjusted by using a transducer (manufactured by Toyo Research Co., Ltd.) so as to vibrate at a speed of −10 to +10 mm / sec in the axial direction of the optical system.
As a glass sample, a glass flat plate having a thickness of 3 to 7 mm was used.
The Pd filter is for improving the measurement accuracy of γ rays by a gas amplification proportional counter, and has a thickness of 50 μm for removing characteristic X-rays generated from the glass sample when the γ ray is irradiated on the glass sample. Pd foil.
The gas amplification proportional counter detects the received γ-rays. An electric signal indicating the γ dose from the gas amplification proportional counter was amplified by an amplifying device (manufactured by Kansai Electronics Co., Ltd.) to detect a light reception signal. The multi-channel analyzer (Wissel CMCA550) was linked to the above speed information.
The spectrum is obtained by expressing the detection signal from the gas amplification proportional counter on the vertical axis and the velocity of the moving radiation source on the horizontal axis (Mossbauer spectroscopy basics and applications, pages 45-64, Hirotoshi Sato)・ Motomi Katada co-authored by the Society). The integration time required 2 to 16 days before an evaluable signal / noise ratio was obtained.
A peak appearing near 0 mm / sec indicates the presence of tetravalent Sn, and a split peak appearing near 2.5 mm / sec and 4.5 mm / sec indicates the presence of bivalent. Correction factor for each peak area (Journal of Non-Crystaline Solids 337 (2004) pp. 232-240 “The effect of alumina on the Sn2 + / Sn4 + redox equilibrium and the incorporation of tin in Na ₂ O / Al ₂ O ₃ / “SiO ₂ melts” by Darja Benner, et al. (Sn tetravalent: 0.22, Sn divalent: 0.49), and the ratio of the divalent Sn was defined as the Sn-redox value. .

In FIG. 1, as the melting temperature rises, Sn ²⁺ in the glass increases, and this indicates that the reduction reaction of SnO _{2 in} the molten glass to SnO becomes active as the melting temperature rises. Show.

In Example 12 shown in FIG. 1, the raw material was heated, and the reduction reaction of SnO ₂ to SnO started to occur from about 1400 ° C., and about 1450 ° C. (Sn-redox about 10% by Sn-Messbauer spectroscopy measurement method). Since the reduction reaction of SnO ₂ to SnO is activated, oxygen bubbles (initial bubbles) due to the reduction reaction are already generated in the molten glass at around 1500 ° C. where the raw material is vitrified.
Then, around 1500 ° C. when the raw material is vitrified, bubbles in the molten glass and initial bubbles coexist in the system to form coexisting bubbles. For this reason, the molten glass is melted for a long time in order to remove the coexisting bubbles from the molten glass. The present inventor has found a problem that productivity must be lowered due to staying in the tank.
On the other hand, in Example 11 shown in FIG. 1, since the reduction reaction of SnO ₂ to SnO starts to occur from around 1450 ° C., many initial bubbles are not generated at 1450-1500 ° C. Thereafter, the reduction reaction of SnO ₂ to SnO from about 1500 ° C. where the raw material vitrifies (Sn-redox about 10% by Sn-Messbauer spectroscopy measurement method) is activated. Can be lifted. Furthermore, from Table 6, since Example 11 has a lower temperature at which the viscosity becomes 10 ² dPa · s than Example 12, Example 11 is likely to cause bubbles to rise.
Therefore, the method for producing alkali-free glass of the present invention and the alkali-free glass of the present invention have a short time for allowing the molten glass to exist in the melting tank, and are excellent in productivity.
Since the alkali-free glass production method of the present invention and the alkali-free glass of the present invention contain almost no bubbles, they are suitable for glass substrates for flat panel displays.
In particular, the non-alkali glass float glass plate of the present invention formed by the float method has a large area and a thin plate (for example, 0.3 to 1.1 mm) because there are few bubbles and there is no Sn precipitation on the glass surface. Suitable for glass substrates for flat panel displays.

FIG. 1 is a graph showing the relationship between the melting temperature when melting the raw material and the Sn-redox of the glass obtained (according to the measuring method of Sn-Mossbauer spectroscopy).

Claims (6)

A glass raw material substantially free of alkali metal oxides and having the following composition as a parent composition is melted, and the molten glass is degassed under vacuum, stirred, or transferred under the condition of contact with a platinum member. A raw material is prepared so as to contain 0.01 to 2.0% of SnO ₂ with respect to 100% of the total amount of the mother composition in terms of mass percentage. After the raw material is heated and melted at 1500 to 1650 ° C., the bubbles contained in the molten glass are floated on the surface of the molten glass together with oxygen bubbles generated by the reduction reaction of the SnO ₂ in the molten glass to SnO, and then the treatment in step, in a state in which the molten glass is in the 1300 to 1500 ° C., the oxygen bubbles generated at the interface between the molten glass and the platinum member, alkali-free to be absorbed by an oxidation reaction of the SnO ₂ of the SnO Method of manufacturing the class.
Composition by mass percentage display:
_{SiO 2: 58.4~66.0%, Al 2} O 3: 15.3~22.0%, B 2 O 3
: 5.0 to 12.0%, MgO: 0 to 6.5%, CaO: 0 to 7.0%, SrO
: 4 to 12.5%, BaO: 0 to 2.0%,
(MgO + CaO + SrO + BaO): 9.0 to 18.0%.   The method for producing an alkali-free glass according to claim 1, wherein the vacuum degassing is performed under a reduced pressure of 160 to 660 torr. The method for producing alkali-free glass according to claim 1 or 2, wherein the temperature when the molten glass has a viscosity of 10 ² dPa · s is 1600 ° C or higher.   The glass plate manufactured by the method in any one of Claims 1-3. It is a non-alkali glass that contains substantially no alkali metal oxide and has the following composition as a parent composition, expressed as a percentage by mass of the oxide standard, and SnO ₂ is 0 with respect to 100% of the total amount of the mother composition. .Float glass plate containing 15% or more and less than 1%.
Composition by mass percentage display:
_{SiO 2: 58.4~66.0%, Al 2} O 3: 15.3~22.0%, B 2 O 3: 5.0~12.0%, MgO: 0~6.5%, CaO : 0 to 7.0%, SrO: 4 to 12.5%, BaO: 0 to 2.0%, (MgO + CaO + SrO + BaO): 9.0 to 18.0%. The glass plate according to claim 4 or 5, wherein a thermal expansion coefficient of the glass plate at 50 to 350 ° C is 25 × 10 ^-7 to 40 × 10 ^-7 / ° C.

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