JPWO2008132887A1 - Method for producing alkali-free glass - Google Patents

Abstract

Provided is a production method capable of obtaining an alkali-free glass having few bubbles in glass and high uniformity and flatness. In a method for producing an alkali-free glass in which a glass raw material containing a silicon source, an alkaline earth metal source and a boron source is melted and molded, an alkaline earth metal hydroxide is used as an alkaline earth metal source as the alkaline earth metal source. Non-alkaline glass characterized by using 15 to 100 mol% (MO conversion) of 100 mol% of metal source (MO conversion, where M is an alkaline earth metal element, the same shall apply hereinafter) The manufacturing method is adopted.

Description

  The present invention relates to a method for producing an alkali-free glass.

  Since a glass substrate for a display such as a liquid crystal display device is required to be substantially free of alkali metals, alkali-free glass is used as the glass substrate. Further, the glass substrate is required to have high chemical resistance and durability, few bubbles in the glass, high homogeneity, and high flatness.

By the way, since the alkali metal compound is not substantially contained in the glass raw material of the alkali-free glass, the glass raw material is difficult to melt. Therefore, it is necessary to use a sand having a small particle size as the silica sand which is the main component of the glass raw material.
In order to impart solubility, chemical resistance and durability to the alkali-free glass, it is effective to include B ₂ O _{3 in the} composition. As a raw material for B ₂ O ₃ , orthoboric acid (also simply referred to as boric acid) is used because it is inexpensive and easily available.

However, when a glass raw material containing orthoboric acid is used, the following problems may occur.
(1) In the presence of orthoboric acid, silica sand with a small particle size tends to aggregate, and the amount of glass raw material charged into the melting furnace tends to become unstable. Therefore, the temperature of the molten glass in the melting furnace becomes unstable, and the circulation / retention time of the molten glass becomes unstable. As a result, the melting of the glass raw material becomes non-uniform or the composition of the molten glass becomes non-uniform.
(2) When the glass raw material contains an alkaline earth metal compound, the orthoboric acid melted at the glass raw material inlet of the melting furnace and the alkaline earth metal compound are aggregated, and lumps are likely to occur. Since orthoboric acid and alkaline earth metal compounds are components that promote the melting of silica sand, if lumps occur, the melting of the glass raw material in the melting furnace becomes uneven or the composition of the molten glass becomes uneven. .

  When the problem (1) or (2) occurs, the homogeneity of the molten glass is deteriorated, so that the homogeneity and flatness of the formed alkali-free glass are lowered. Further, since the circulation / retention time becomes unstable, a part of the molten glass flows out of the melting furnace before the bubbles are removed from the molten glass in the melting furnace by the refining agent. Moreover, since the melting of the glass raw material is not uniform, the effect of the clarifying agent on the quartz sand that has been melted late is insufficient, and the bubbles are not sufficiently removed from the molten glass.

In order to improve the homogeneity of the alkali-free glass, a glass raw material in which the particle size of an alkaline earth metal compound (strontium carbonate and dolomite) is controlled has been proposed (Patent Document 1). However, the glass raw material described in Patent Document 1 does not consider any silica sand that melts late. When the melting of the silica sand is delayed, the unmelted silica sand is trapped by the bubbles generated in the glass melt and gathers near the surface layer of the glass melt, whereby the SiO in the surface layer of the glass melt and other parts _There was a difference in the composition ratio of the _two components, and the homogeneity of the glass could be reduced.
Japanese Patent Laid-Open No. 2003-40641

  The present invention provides a production method capable of obtaining an alkali-free glass having few bubbles in glass and excellent in homogeneity and flatness.

In order to achieve the above object, the present invention employs the following configuration.
The method for producing an alkali-free glass of the present invention is a method for producing an alkali-free glass in which a glass raw material containing a silicon source, an alkaline earth metal source and a boron source is melted and molded. The earth metal hydroxide is contained in an amount of 15 to 100 mol% (MO conversion) out of 100 mol% of the alkaline earth metal source (in terms of MO. However, M is an alkaline earth metal element. The same shall apply hereinafter). It is characterized by using a thing.
The alkaline earth metal as the alkaline earth metal source is preferably one or more elements of Mg, Ca, Sr and Ba.
Further, as the boron source, boric acid anhydride, of the boron source 100 _{wt% (B} 2 _{O 3} conversion), it is preferable to use those containing 10 to 100 _{wt% (B} 2 _{O 3} conversion).

Moreover, it is preferable to use the glass raw material used as the alkali free glass which has the following composition (1) by the mass percentage display of an oxide basis as the said glass raw material, The alkali free glass which has the following composition (2) or (3), It is particularly preferable to use a glass material.
SiO _2: 50-66 _{wt%, Al} 2 O 3: _{10.5~22 wt%, B} 2 O 3: _5~12 wt%, MgO: 0 to 8 mass%, CaO: from 0 to 14.5% by weight , SrO: 0 to 24 mass%, BaO: 0 to 13.5 mass%, MgO + CaO + SrO + BaO: 9 to 29.5 mass% (1).
SiO _2: 58 to 66 _{wt%, Al} 2 O 3: _{15~22 wt%, B} 2 O 3: _5~12 wt%, MgO: 0 to 8 mass%, CaO: 0 to 9 wt%, SrO: 3 ˜12.5 mass%, BaO: 0 to 2 mass%, MgO + CaO + SrO + BaO: 9 to 18 mass% (2).
SiO _2: 50 to 61.5 _{wt%, Al} 2 O 3: _{10.5~18 wt%, B} 2 O 3: _7~10 wt%, MgO: 2 to 5 wt%, CaO: 0 to 14.5 Mass%, SrO: 0 to 24 mass%, BaO: 0 to 13.5 mass%, MgO + CaO + SrO + BaO: 16 to 29.5 mass% (3).

  According to the method for producing an alkali-free glass of the present invention, an alkali-free glass having few bubbles in the glass and excellent in homogeneity and flatness can be obtained.

FIG. 1 is a schematic view showing a method for producing alkali-free glass in Examples. FIG. 2 is a schematic diagram showing the measurement points of the composition in the sample. FIG. 3 is a graph showing ΔSiO ₂ (mass%) of Experimental Examples 1 to 6. FIG. 4 is a graph showing the number of bubbles (kg · kg ⁻¹ ) of 5 μm or more in Experimental Examples 1 to 6.

Explanation of symbols

  12 ... Glass raw material, 16 ... Non-alkali glass

The alkali-free glass is produced by melting and forming a glass raw material containing a silicon source, an alkaline earth metal source, and a boron source. The alkali-free glass is manufactured as follows, for example.
(I) A glass obtained by mixing a silicon source, an alkaline earth metal source, a boron source, and, if necessary, Al ₂ O ₃ , a refining agent, etc. at a ratio that makes the composition of the target non-alkali glass. Prepare raw materials.
(Ii) The glass raw material and, if necessary, cullet having the same composition as the target non-alkali glass composition are continuously charged into the melting furnace from the glass raw material inlet of the melting furnace, and 1500-1600 Melt at 0 ° C. to obtain molten glass. The cullet is glass waste discharged in the process of manufacturing alkali-free glass.
(Iii) The molten glass is molded to have a predetermined thickness by a known molding method such as a float method.
(Iv) After the formed glass ribbon is gradually cooled, it is cut into a predetermined size to obtain a plate-like non-alkali glass.

(Silicon source)
Silica sand can be used as the silicon source contained in the glass raw material when producing the alkali-free glass. Silica sand may be anything as long as it is used for glass production.
The average particle diameter D ₅₀ (median particle diameter) of the silica sand is preferably 15 to 60 μm, and more preferably 20 to 45 μm.
If the average particle diameter D ₅₀ of the silica sand or more 15 [mu] m, aggregation of the silica sand is suppressed, the foam is small, homogeneity, the alkali-free glass is high flatness can be obtained. Further, if the average particle diameter D ₅₀ of the silica sand to 60μm or less, quartz sand is easily uniformly molten, it bubbles even less, homogeneity, the alkali-free glass is higher flatness can be obtained. The average particle diameter is measured, for example, by measuring the particle size distribution by a laser diffraction / scattering method.

(Alkaline earth metal source)
An alkaline earth metal compound can be used as the alkaline earth metal source. Here, examples of the alkaline earth metal include any one element or two or more elements of Mg, Ca, Sr, and Ba. Specific examples of the alkaline earth metal compound include carbonates such as MgCO ₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , (Mg, Ca) CO ₃ (dolomite), MgO, CaO, BaO, SrO and the like. Oxides and hydroxides such as Mg (OH) ₂ , Ca (OH) ₂ , Ba (OH) ₂ , Sr (OH) ₂ can be exemplified, but in the present invention, some or all of the alkaline earth metal source It is preferable to contain an alkaline earth metal hydroxide.

The content of the alkaline earth metal hydroxide is preferably 15 to 100 mol% (MO conversion) among 100 mol% of the alkaline earth metal source (MO conversion, where M is an alkaline earth metal element). ), More preferably 30 to 100 mol% (in terms of MO), and even more preferably 60 to 100 mol% (in terms of MO). When the content of the hydroxide is less than 15 mol%, when the glass raw material is melted, the unmelted amount of the SiO ₂ component contained in the silica sand increases, and this unmelted SiO ₂ is contained in the glass melt. When bubbles are generated, they are taken into the bubbles and gather near the surface of the glass melt. As a result, a difference in the composition ratio of SiO ₂ occurs between the surface layer of the glass melt and the portion other than the surface layer, which is not preferable because the uniformity of the glass decreases and the flatness also decreases.
Also, as the molar ratio of hydroxide in the alkaline earth metal source increases, the unmelted amount of the SiO ₂ component at the time of melting the glass raw material decreases, so the higher the molar ratio of the hydroxide is, the higher Good.

Specifically, as the alkaline earth metal source, a mixture of an alkaline earth metal hydroxide and a carbonate, an alkaline earth metal hydroxide alone, or the like can be used. As the carbonate, it is preferable to use one or more of MgCO ₃ , CaCO ₃ and (Mg, Ca) CO ₃ (dolomite). As the alkaline earth metal hydroxide, it is preferable to use at least one of Mg (OH) _{2 and} Ca (OH) ₂ , and it is particularly preferable to use Mg (OH) ₂ .

(Boron source)
Next, boron compounds as a boron source include orthoboric acid (H ₃ BO ₃ ), metaboric acid (HBO ₂ ), tetraboric acid (H ₂ B ₄ O ₇ ), anhydrous boric acid (anhydrous B ₂ O ₃ ), and the like. Is mentioned.
In the production of ordinary alkali-free glass, orthoboric acid is used because it is inexpensive and easily available.

In the present invention, in the case of using anhydrous boric acid as a boron source, among the boron source 100 _{wt% (B} 2 _{O 3} basis) preferably contains 10 to 100 _{wt% (B} 2 _{O 3} conversion). By setting the boric anhydride to 10% by mass or more, aggregation of the glass raw material is suppressed, and an effect of reducing bubbles, homogeneity, and improving flatness can be obtained. A more preferable range of boric anhydride is in the range of 20 to 100% by mass. As a boron compound other than boric anhydride, orthoboric acid is preferable because it is inexpensive and easily available.

(Other ingredients)
Examples of other raw materials include Al ₂ O ₃ . Further, ZnO, SO ₃ , F, Cl, SnO ₂ may be contained as a fining agent or the like in order to improve the meltability, the fining property, and the moldability.

(Glass raw material)
The glass raw material is a powdery mixture in which the respective raw materials are mixed.

  The composition of the glass raw material is such that it becomes an alkali-free glass having a target composition. The composition of the glass raw material is preferably a composition that becomes an alkali-free glass having the composition (1) described later, and a composition that becomes an alkali-free glass having the composition (2) or (3) described later is particularly preferable.

(Non-alkali glass)
The alkali-free glass obtained by the production method of the present invention contains SiO ₂ derived from a silicon source and B ₂ O ₃ derived from a boron source in its composition. Alkali-free glass refers to glass that does not substantially contain alkali metal oxides such as Na ₂ O and K ₂ O.

  Hereinafter, a preferable composition of the alkali-free glass will be described.

As alkali-free glass, it has characteristics as a glass substrate for display (thermal expansion coefficient: 25 × 10 ^{−7 to} 60 × 10 ⁻⁷ / ° C., chemical resistance, durability, etc.), and can be used for molding into plate glass. From the point of being suitable, the alkali free glass which has the following composition (1) by the mass percentage display of an oxide basis is preferable.
Among the alkali-free glass (100 _mass%), SiO 2: 50~66 _{wt%, Al} 2 O 3: _{10.5~22 wt%, B} 2 O 3: _5~12 wt%, MgO: 0 to 8 mass %, CaO: 0 to 14.5 mass%, SrO: 0 to 24 mass%, BaO: 0 to 13.5 mass%, MgO + CaO + SrO + BaO: 9 to 29.5 mass% (1).

In addition, alkali-free glass has a strain point of 640 ° C. or higher, a low coefficient of thermal expansion and a low density, suppresses white turbidity due to buffered hydrofluoric acid (BHF) used for etching, and is resistant to chemicals such as hydrochloric acid. In particular, alkali-free glass having the following composition (2) in terms of oxide-based mass percentage is particularly preferable because it is excellent in melting, forming and suitable for float forming.
Among alkali-free glass (100% by mass), SiO ₂ : 58 to 66% by mass, Al ₂ O ₃ : 15 to 22% by mass, B ₂ O ₃ : 5 to 12% by mass, MgO: 0 to 8% by mass, CaO: 0 to 9% by mass, SrO: 3 to 12.5% by mass, BaO: 0 to 2% by mass, MgO + CaO + SrO + BaO: 9 to 18% by mass (2).

By setting SiO ₂ to 58 mass% or more, the strain point of the alkali-free glass is increased, the chemical resistance is improved, and the thermal expansion coefficient is decreased. With the SiO ₂ 66 wt% or less, the melting property of the glass is improved, devitrification characteristic becomes good.

By the al ₂ O ₃ and 15 mass% or more, phase separation of the alkali-free glass is suppressed, the thermal expansion coefficient is reduced, the strain point increases.
Further, by making the _Al 2 _{O 3} and 22 wt% or less, the melting property of glass will be good.

B ₂ O ₃ suppresses white turbidity of the alkali-free glass due to BHF, and reduces the thermal expansion coefficient and density of the alkali-free glass without increasing the viscosity at high temperature.
By the B ₂ O ₃ and 5 wt% or more, BHF resistance of the alkali-free glass will be good. Further, the B ₂ O ₃ by 12 mass% or less, the strain point increases with acid resistance of the alkali-free glass will be good.

MgO suppresses an increase in the thermal expansion coefficient and density of the alkali-free glass and improves the meltability of the glass raw material.
By making MgO 8 mass% or less, white turbidity due to BHF is suppressed and phase separation of alkali-free glass is suppressed.

CaO improves the meltability of the glass raw material.
By making CaO into 9 mass% or less, the thermal expansion coefficient of an alkali free glass falls and a devitrification characteristic becomes favorable.

By making SrO 3 mass% or more, the phase separation of an alkali free glass can be suppressed and the cloudiness of the alkali free glass by BHF can be suppressed.
Moreover, the thermal expansion coefficient of an alkali free glass falls by making SrO into 12.5 mass% or less.

BaO suppresses the phase separation of alkali-free glass, improves the meltability, and improves the devitrification characteristics.
By making BaO 2 mass% or less, the density of the alkali-free glass is lowered and the thermal expansion coefficient is lowered.

  By making MgO + CaO + SrO + BaO 9 mass% or more, the meltability of the glass becomes good. By making MgO + CaO + SrO + BaO 18% by mass or less, the density of the alkali-free glass is lowered.

In composition (2), ZnO, SO ₃ , F, Cl, SnO ₂ are contained in a total amount of 5% by mass or less of non-alkali glass (100% by mass) in order to improve meltability, clarity, and moldability. May be. Moreover, since a lot of man-hours are required for the treatment of cullet, it is preferable that PbO, As ₂ O ₃ , and Sb ₂ O ₃ are not contained except those that are inevitably mixed as impurities.

In addition, the alkali-free glass in the present invention is excellent in properties as a glass substrate for display, excellent in reduction resistance, homogeneity, foam suppression, and suitable for molding by the float process. Alkali-free glass having the following composition (3) in display is particularly preferred.
Among the alkali-free glass (100 _mass%), SiO 2: 50~61.5 _{wt%, Al} 2 O 3: _{10.5~18 wt%, B} 2 O 3: _7~10 wt%, MgO: 2~ 5 mass%, CaO: 0 to 14.5 mass%, SrO: 0 to 24 mass%, BaO: 0 to 13.5 mass%, MgO + CaO + SrO + BaO: 16 to 29.5 mass% (3).

By making SiO ₂ 50 mass% or more, the acid resistance of the alkali-free glass is improved, the density is lowered, the strain point is raised, the thermal expansion coefficient is lowered, and the Young's modulus is raised. By the SiO ₂ and 61.5 wt% or less, the devitrification property of the alkali-free glass will be good.

By making Al ₂ O ₃ 10.5% by mass or more, the phase separation of the alkali-free glass is suppressed, the strain point is increased, and the Young's modulus is increased. Moreover, by making Al ₂ O ₃ 18% by mass or less, the devitrification characteristics, acid resistance and BHF resistance of the alkali-free glass are improved.

By setting B ₂ O ₃ to 7% by mass or more, the density of the alkali-free glass is reduced, the BHF resistance is improved, the meltability is improved, the devitrification characteristics are improved, and the thermal expansion coefficient is reduced.
The above effects are manifested. By setting B ₂ O ₃ to 10% by mass or less, the strain point of the alkali-free glass is increased, the Young's modulus is increased, and the acid resistance is improved.

By making MgO 2 mass% or more, the density of the alkali-free glass is lowered, the thermal expansion coefficient is not increased, the strain point is not excessively lowered, and the meltability is improved.
By making MgO 5 mass% or less, the phase separation of an alkali-free glass is suppressed, and devitrification characteristics, acid resistance, and BHF resistance are improved.

CaO improves the meltability without increasing the density of the alkali-free glass, without increasing the thermal expansion coefficient, without excessively reducing the strain point.
By making CaO 14.5 mass% or less, the devitrification property of an alkali free glass becomes favorable, a thermal expansion coefficient falls, a density falls, and acid resistance and alkali resistance become favorable.

SrO improves the meltability without increasing the density of the alkali-free glass, without increasing the thermal expansion coefficient, without excessively reducing the strain point.
By setting SrO to 24% by mass or less, the devitrification characteristics of the alkali-free glass are improved, the thermal expansion coefficient is decreased, the density is decreased, and the acid resistance and alkali resistance are improved.

BaO suppresses phase separation of alkali-free glass, improves devitrification characteristics, and improves chemical resistance.
By adjusting BaO to 13.5% by mass or less, the density of the alkali-free glass is lowered, the thermal expansion coefficient is lowered, the Young's modulus is increased, the meltability is improved, and the BHF resistance is improved.

  By making MgO + CaO + SrO + BaO 16 mass% or more, the meltability of the glass becomes good. By setting MgO + CaO + SrO + BaO to 29.5% by mass or less, the density and thermal expansion coefficient of the alkali-free glass are lowered.

In composition (3), ZnO, SO ₃ , F, Cl, SnO ₂ is contained in a total amount of 5% by mass or less of non-alkali glass (100% by mass) in order to improve meltability, clarity, and moldability. May be. Moreover, since a lot of man-hours are required for the treatment of cullet, it is preferable that PbO, As ₂ O ₃ , and Sb ₂ O ₃ are not contained except those that are inevitably mixed as impurities.

As described above, according to the method for producing an alkali-free glass of the present invention, an alkaline earth metal hydroxide is used as an alkaline earth metal source at an alkaline earth metal source of 100 mol% (in terms of MO. However, M Is an alkaline earth metal element), and the content of 15 to 100 mol% (in terms of MO) is used, so that the unmelted amount of SiO ₂ in the glass melt is greatly reduced and the amount of bubbles generated As a result, the segregation of SiO ₂ is improved, and an alkali-free glass having high homogeneity and flatness can be obtained.

In the present invention, alkaline earth metal hydroxides (the hydroxides release H ₂ O before glass liquid phase formation (about 400 ° C.), and thus hardly affect liquid phase generation. ) In an alkaline earth metal carbonate (the carbonate releases CO ₂ during the liquid phase formation of glass (600 to 800 ° C.)) compared to the prior art in a glass melt. It is considered that the amount of bubbles generated is reduced and the bubbles in the glass are reduced.
Further, by adding a hydroxide of an alkaline earth metal, which liquid glass melt is tilt to an alkaline side from acidic, thereby the reactivity of the SiO ₂ is increased, unmelted amount of SiO ₂ is reduced it is conceivable that.
As described above, in the present invention, it is possible to synergistically reduce the amount of unmelted SiO _{2 and the} amount of bubbles generated, and obtain an alkali-free glass excellent in homogeneity and flatness. it can.

Further, if the present invention, as the boron source, boric acid anhydride, of the boron source 100 _{wt% (B} 2 _{O 3} equivalent), the use of those containing 10 to 100 _{wt% (B} 2 _{O 3} basis), Glass It is possible to obtain an alkali-free glass with fewer bubbles and higher homogeneity and flatness.

  In particular, when orthoboric acid is used as the boron source, silica sand having a small particle size is likely to aggregate in the presence of orthoboric acid. Aggregation of silica sand is considered to occur due to moisture contained in the glass raw material, and in order to suppress the aggregation of silica sand, the moisture contained in the glass raw material may be reduced. That is, by reducing the amount of orthoboric acid containing many water molecules in the molecule and increasing the amount of boric anhydride, an alkali-free glass with few bubbles, high homogeneity and flatness can be obtained.

  When the glass raw material contains an alkaline earth metal compound, orthoboric acid melted at the glass raw material inlet of the melting furnace and the alkaline earth metal compound may aggregate. Aggregation of orthoboric acid and alkaline earth metal compound is caused by the loss of one water molecule from orthoboric acid heated at the glass raw material inlet to metaboric acid. This metaboric acid is liquefied at 150 ° C or higher and becomes alkaline. Occurs in contact with earth metal compounds. Therefore, by using boric anhydride in which water molecules are further lost from metaboric acid, aggregation of metaboric acid and alkaline earth metal compound can be suppressed, there are few bubbles, and no alkali is high in homogeneity and flatness. Glass can be obtained.

Further, when boric anhydride is used as described above in the method for producing alkali-free glass of the present invention, the following effects can be expected.
(I) Since the amount of water in the glass material is suppressed, the heat of vaporization of water when the glass material is melted is reduced. Therefore, the amount of energy consumed in the melting furnace is reduced by the amount of heat of vaporization that is reduced, energy saving can be achieved, and productivity is improved.
(Ii) Since moisture (β-OH) in the molten glass is reduced, chlorine (Cl) contained in the refining agent is converted to HCl by the following reaction, and volatilization is suppressed. Therefore, the amount of the refining agent can be reduced, and the treatment burden of the exhaust gas containing HCl is reduced.
OH ⁻ + Cl ⁻ → HCl ↑ + O ²⁻ .
(Iii) Metaboric acid produced by losing one water molecule from orthoboric acid is easy to volatilize, but boric anhydride is difficult to volatilize, so the amount of boron source can be reduced, and treatment of exhaust gas containing metaboric acid The burden is reduced.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[Experiment 1]
In terms of mass percentage based on oxide, SiO ₂ : 60% by mass, Al ₂ O ₃ : 17% by mass, B ₂ O ₃ : 8% by mass, MgO: 3% by mass, CaO: 4% by mass, SrO: 8% by mass. % Of the glass mother composition as a refining agent by preparing a silicon source, an alkaline earth metal source, a boron source and other raw materials so as to be a non-alkali glass having a% composition. With respect to the subsequent 100% by mass, 1.0% by mass of Cl was mixed to obtain a glass raw material.

As the silicon source, the average particle diameter _{D 50} of 26 .mu.m, the minimum diameter to a maximum diameter with quartz sand is 5 to 100 [mu] m. The average particle diameter D ₅₀ was determined by measuring the particle size distribution by a laser diffraction / scattering method (HORIBA LA950WET).
As alkaline earth metal sources, compounds of Mg (OH) ₂ , Ca (OH) ₂ , dolomite ((Mg, Ca) CO ₃ ), MgCO ₃ , CaCO ₃ , and strontium carbonate are shown in Table 1. Table 1 shows the amount of hydroxide in the alkaline earth metal compound in terms of MO.
Furthermore, as shown in Table 1, boric anhydride (anhydrous B ₂ O ₃ ) or orthoboric acid (H ₃ BO ₃ ) was used as the boron source.

  Next, as shown in FIG. 1 (a), a glass raw material 12 having an amount of 250 g after vitrification is placed in a bottomed cylindrical crucible 14 made of platinum rhodium having a height of 90 mm and an outer diameter of 70 mm. I put it in. The crucible 14 was put into a heating furnace, and the inside of the crucible 14 was not forcedly stirred, but air at a dew point of 80 ° C. was blown from the side of the heating furnace at 1550 ° C. (temperature corresponding to a glass viscosity η of log η = 2.5). ) For 1 hour to melt the glass raw material 12. After the molten glass was cooled together with the crucible 14, a plate-like sample 18 having a length of 24 mm, a width of 35 mm, and a thickness of 1 mm was cut out from the center of the alkali-free glass 16 in the crucible 14 as shown in FIG.

As shown in FIG. 2, a fluorescent X-ray beam with a diameter of 3 mm is applied to an area of 18 mm length and 15 mm width (upper margin 1.5 mm, left and right margins 10 mm) of a sample 18 having a length of 24 mm and a width of 35 mm. A total of 30 locations of 6 vertical locations × 5 horizontal locations were irradiated, and the composition of the alkali-free glass at each location was measured.
Of the composition of 30 points, the maximum value of SiO ₂ (wt%) by subtracting the minimum value of SiO ₂ (wt%), was determined composition difference (ΔSiO _2).
Further, the number of bubbles having a maximum length of bubbles of 5 μm or more remaining in the glass was counted in an area of 24 mm in length and 10 mm in the center of the sample 18 to obtain the number of bubbles per kg of glass.
Moreover, when dissolving the glass raw material, to determine the percentage of silica sand remaining without being melted (unmelted SiO _2). Unmelted SiO ₂ is obtained by adding 250 g of raw material to a 4000 mm long × 20 mm wide platinum boat and heating it in a furnace with a temperature gradient of 800-1500 ° C. for 1 hour, and then on the glass surface in the temperature range of 1400-1500 ° C. It was measured by the area occupied by the remaining silica sand. These results are also shown in Table 2, FIG. 3 and FIG.

In Table 1, the smaller the ΔSiO ₂ , the smaller the variation in composition, that is, the better the homogeneity of the alkali-free glass. As shown in Table 1, FIG. 3 and FIG. 4, in Examples 1 to 6 in which hydroxide was used as a part of the alkaline earth metal source, ΔSiO ₂ was 0.5 to 2.0% by mass, The amount of melted SiO ₂ is 3 to 18%, and the number of bubbles is 5 × 10 ⁴ to 30 × 10 ⁴ , and ΔSiO ₂ , the amount of unmelted SiO ₂ and the number of bubbles are significantly larger than those of Comparative Example 1. It can be seen that it is reduced. This is because by using hydroxide as the alkaline earth metal source, the liquidity of the glass melt is inclined from the acidic side to the alkaline side, thereby improving the reactivity of SiO _{2 in} the silica sand. It is considered that the amount of molten SiO ₂ has decreased.
In addition, it can be seen that the use of boric anhydride (B ₂ O ₃ ) as the boron source reduces the amount of unmelted SiO ₂ and the number of bubbles and improves the homogeneity. If hydroxide is used for all of the alkaline earth metal source, any of ΔSiO ₂ , the amount of unmelted SiO ₂ and the number of bubbles can be further reduced.
From the above, by using the glass manufacturing method of the present invention, the homogeneity of the glass can be greatly improved, the number of bubbles can be reduced, and an alkali-free glass having excellent flatness can be obtained.

The alkali-free glass obtained by the production method of the present invention has few bubbles in the glass and high homogeneity and flatness. Also, excellent chemical resistance and durability because it contains B ₂ O _3.
The alkali-free glass is useful as a glass substrate for a display such as a liquid crystal display device.

The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2007-108086 filed on April 17, 2007 are incorporated herein by reference as the disclosure of the specification of the present invention. It is.

Claims (5)

In a method for producing alkali-free glass, in which a glass raw material containing a silicon source, an alkaline earth metal source and a boron source is melted and molded,
As the alkaline earth metal source, 15 to 15 mol of an alkaline earth metal hydroxide is used in 100 mol% of the alkaline earth metal source (in terms of MO, where M is an alkaline earth metal element, the same shall apply hereinafter). A method for producing alkali-free glass, comprising using 100 mol% (in terms of MO). As the boron source, boric acid anhydride, of the boron source 100 _{wt% (B} 2 _{O 3} basis), use those containing 10 to 100 _{wt% (B} 2 _{O 3} equivalent), free of claim 1 A method for producing alkali glass. The manufacturing method of the alkali free glass of Claim 1 or 2 which uses the glass raw material used as the alkali free glass which has the following composition (1) by the mass percentage display of an oxide basis as the said glass raw material.
SiO _2: 50-66 _{wt%, Al} 2 O 3: _{10.5~22 wt%, B} 2 O 3: _5~12 wt%, MgO: 0 to 8 mass%, CaO: from 0 to 14.5% by weight , SrO: 0 to 24% by mass, BaO: 0 to 13.5% by mass, MgO + CaO + SrO + BaO: 9 to 29.5% by mass (1) The manufacturing method of the alkali free glass of Claim 1 or 2 using the glass raw material used as the alkali free glass which has the following composition (2) by the mass percentage display of an oxide basis as the said glass raw material.
SiO _2: 58 to 66 _{wt%, Al} 2 O 3: _{15~22 wt%, B} 2 O 3: _5~12 wt%, MgO: 0 to 8 mass%, CaO: 0 to 9 wt%, SrO: 3 -12.5 mass%, BaO: 0-2 mass%, MgO + CaO + SrO + BaO: 9-18 mass% (2) The manufacturing method of the alkali free glass of Claim 1 or 2 using the glass raw material used as the alkali free glass which has the following composition (3) by the mass percentage display of an oxide as the said glass raw material.
SiO _2: 50 to 61.5 _{wt%, Al} 2 O 3: _{10.5~18 wt%, B} 2 O 3: _7~10 wt%, MgO: 2 to 5 wt%, CaO: 0 to 14.5 % By mass, SrO: 0 to 24% by mass, BaO: 0 to 13.5% by mass, MgO + CaO + SrO + BaO: 16 to 29.5% by mass (3)

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