JP5267464B2 - Method for producing alkali-free glass - Google Patents

Description

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

  Since the glass for a liquid crystal display substrate is required to be substantially free of alkali metals, alkali-free glass is used as the glass. Further, the alkali-free glass for a liquid crystal display substrate is required to have high chemical resistance and durability, to have few bubbles in the glass, high homogeneity, and high flatness. Therefore, in order to impart chemical resistance and durability to non-alkali glass, it is necessary to include a boron source in the glass raw material, and to reduce bubbles in the non-alkali glass, molten glass when producing alkali-free glass. The bubbles contained in the above are defoamed (hereinafter referred to as “Kyosei”). As the boron source, orthoboric acid that is inexpensive and easily available is used.

As a clarification method, a method is known in which SnO ₂ is used as a clarifier and a clarification gas is generated by a change in the valence of Sn due to temperature rise of the molten glass (Patent Document 1).
However, the alkali-free glass for a liquid crystal display substrate is a glass that has a melting temperature higher than 100 ° C. and hardly melts compared to alkali-containing glass such as plasma display substrate glass, architectural glass, and automotive glass. Therefore, SnO ₂ is consumed when the glass raw material is melted at a high temperature, and there is a problem that a sufficient amount of SnO ₂ does not remain when the clarified gas is generated by raising the temperature of the molten glass.

As an effective clarification method using SnO ₂ , after melting a glass raw material at a high temperature, the glass raw material is held at a low temperature to regenerate SnO ₂ , and then heated to a temperature higher than the melting temperature to generate a clarified gas. A method is known (Patent Document 2).
In the case of this method, effective clarification can be expected, but since the process is complicated and the energy loss is large, it is difficult to stably produce an alkali-free glass with low bubbles and low bubbles. On the other hand, when trying to melt the glass raw material at a low temperature, the silica sand, which is the main component of the glass raw material, is difficult to melt, so unmelted silica is generated in the molten glass, and a homogeneous glass cannot be obtained. To do.

Further, when silica sand having a small particle size is used in order to easily melt silica sand, the silica sand is likely to aggregate. When silica sand agglomerates, the homogeneity and flatness of the alkali-free glass deteriorate.
Japanese Patent Laid-Open No. 2004-075498 International Publication No. 2007/018910 Pamphlet

  This invention provides the manufacturing method which can obtain the alkali free glass with few bubbles in glass, and high uniformity and flatness.

The method for producing alkali-free glass of the present invention is a method for producing alkali-free glass in which a glass raw material containing a fining agent is melted and molded into a glass matrix composition raw material containing silica sand and a boron source. In which the ratio of particles having a particle diameter of 100 μm or more is 2.5% by volume or less, boric anhydride is used as the boron source, and 100% by mass of the boron source (in terms of B ₂ O ₃₎ ) Containing 10 to 100% by mass (converted to B ₂ O ₃ ), using at least SnO ₂ as the fining agent, and melting the glass raw material in at least the following two steps. And
(A) A step of heating the glass raw material at a temperature at which the viscosity of the molten glass becomes more than 10 ^2.4 dPa · s to obtain a molten glass.
(B) After the step (a), the molten glass is at a temperature such that the viscosity of the molten glass is 10 ^2.4 dPa · s or less, and a temperature higher by 30 ° C. than the temperature in the step (a). The process which heats by and defoams the foam in molten glass.
In the method for producing an alkali-free glass of the present invention, it is preferable that a hydroxide of aluminum or an alkaline earth metal is included in the glass matrix composition raw material.

In the method for producing an alkali-free glass of the present invention, a glass matrix composition raw material is prepared so as to be an alkali-free glass having the following glass matrix composition (1) in terms of oxide-based mass percentage. On the other hand, it is preferable to add 0.01 to 2% by mass of tin in terms of SnO ₂ to obtain a 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 mass%, BaO: 0 to 13.5 mass%, MgO + CaO + SrO + BaO: 9 to 29.5 mass% (1).

In the method for producing alkali-free glass of the present invention, 3% by mass or less chloride in terms of Cl, 3% by mass or less sulfate in terms of SO ₃ and 3% by mass in terms of F with respect to the glass matrix composition raw material. It is preferable to add 0.01 to 5% by mass in a total amount of one or more selected from the group consisting of 1% or less of fluoride to make a glass raw material.
In the method for producing an alkali-free glass of the present invention, a nitrate is further added in an amount of 0.01 to 10% by mass in terms of NO ₃ and a cullet made of an alkali-free glass is added in an amount of 15 to 300% by mass with respect to the glass matrix composition raw material. It is preferable to use a glass raw material.

  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 high uniformity and flatness can be obtained.

It is a figure which shows the location which cuts out the glass plate for samples from columnar glass.

<Method for producing alkali-free glass>
The alkali-free glass is produced by melting and molding a glass raw material in which a fining agent is added to a glass mother composition raw material containing silica sand and a boron source. The alkali-free glass is produced, for example, through the following steps in order.
(I) Silica sand and boron source, optionally Al ₂ O ₃ , alkaline earth metal oxides (MgO, CaO, SrO, BaO) and / or aluminum or alkaline earth metal hydroxides are targeted A step of preparing a glass mother composition raw material by mixing at a ratio that results in a glass mother composition of non-alkali glass, and adding a fining agent or the like to the glass mother composition raw material to obtain a glass raw material.
(Ii) A step of continuously charging the glass raw material and, if necessary, the cullet from the glass raw material charging port of the melting furnace into the melting furnace and melting it into a molten glass.
(Iii) A step of forming the molten glass into a glass ribbon having a predetermined thickness by a known forming method such as a float method.
(Iv) A step of slowly cooling the formed glass ribbon and then cutting it into a predetermined size to obtain a plate-like non-alkali glass.

In the present invention, as the silica sand, a medium having a median diameter of 15 to 60 μm and a ratio of particles having a particle diameter of 100 μm or more is 2.5% by volume or less, and boric anhydride as the boron source, Of the boron source 100% by mass (in terms of B ₂ O ₃ ), using 10 to 100% by mass (in terms of B ₂ O ₃ ), using SnO ₂ as the clarifier, the step (ii) It is characterized in that it is divided into at least the following two steps.
(A) A step of heating the glass raw material at a temperature at which the viscosity of the molten glass becomes more than 10 ^2.4 dPa · s to obtain a molten glass.
(B) After the step (a), the molten glass is at a temperature such that the viscosity of the molten glass is 10 ^2.4 dPa · s or less, and a temperature higher by 30 ° C. than the temperature in the step (a). The process which heats by and defoams the foam in molten glass.

Step (i):
(Silica sand)
Median diameter of silica sand, that is, in the particle size distribution of the powder, the volume frequency of particles larger than a certain particle size, particle size accounts for 50% of its Zenkonatai (hereinafter, referred to as D _50.) Is, 15～60Myuemu 20-50 μm is preferable, 20-40 μm is more preferable, and 20-30 μm is more preferable. In particular, D ₅₀ of silica sand is preferably less than 30 μm, more preferably 27 μm or less. By the D ₅₀ of the silica sand or more 15 [mu] m, since the agglomeration of the silica sand is suppressed, the foam is further reduced, homogeneity, the alkali-free glass is high flatness can be obtained.
By the D ₅₀ of the silica sand and 60μm or less, the silica sand is easily uniformly molten, bubbles less, homogeneity, the alkali-free glass is high flatness can be obtained.

The proportion of silica sand having a particle size of 100 μm or more in the particle size distribution is 2.5% by volume or less, and more preferably 0% by volume. By making the proportion of particles having a particle size of 100 μm or more 2.5 vol% or less, the silica sand is easily melted uniformly, so that an alkali-free glass with few bubbles and high homogeneity and flatness can be obtained.
The particle size distribution of silica sand is measured by a laser diffraction / scattering method.

(Boron source)
Examples of the boron compound as the boron source include orthoboric acid (H ₃ BO ₃ ), metaboric acid (HBO ₂ ), tetraboric acid (H ₂ B ₄ O ₇ ), and anhydrous boric acid (B ₂ O ₃ ). In the production of ordinary alkali-free glass, orthoboric 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, and 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 aggregates are likely to be generated. Since orthoboric acid and alkaline earth metal compounds are components that promote the melting of silica sand, when aggregates are generated, the melting of the glass raw material in the melting furnace becomes non-uniform, and the composition of the molten glass is non-uniform. It becomes.

  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.

Regarding the problem (1), the present inventors may reduce the moisture contained in the glass raw material in order that aggregation of the silica sand occurs due to the moisture contained in the glass raw material, and to suppress the aggregation of the silica sand. That is, it has been found that the amount of orthoboric acid containing a large amount of water molecules in the molecule can be reduced and the amount of boric anhydride can be increased.
As for the problem (2), the present inventors have lost one water molecule from orthoboric acid heated at the glass raw material inlet to become metaboric acid, and liquefied metaboric acid and alkali at 150 ° C. or higher. In order to suppress the aggregation of the earth metal compound and the aggregation of the metaboric acid and the alkaline earth metal compound, a boron source containing boric anhydride, in which water molecules are further lost from the metaboric acid, is used. It was found that it should be used.

Furthermore, the following effects can also be expected by using a boron source containing boric anhydride.
(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, when Cl is contained in the fining agent, HCl is eliminated 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.

Therefore, in the present invention, as the boron source, boric acid anhydride, of the boron source 100 _{wt% (B} 2 _{O 3} basis), 10 to 100 _{wt% (B} 2 _{O 3} equivalent) is used one containing. 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. The boric anhydride is more preferably 20 to 100% by mass, further preferably 50 to 100% by mass, and particularly preferably 100% by mass.
As the boron compound other than boric anhydride, orthoboric acid is preferable because it is inexpensive and easily available.

(Other ingredients)
Other raw materials include Al ₂ O ₃ , alkaline earth metal oxides (MgO, CaO, SrO, BaO), Al (OH) ₃ , alkaline earth metal hydroxides (Mg (OH) ₂ , Ca (OH) ) ₂ , Ba (OH) ₂ , Sr (OH) ₂ ).
In the present invention, the inclusion of aluminum or an alkaline earth metal hydroxide in the glass matrix composition raw material promotes initial melting in the step of melting the glass raw material (step (a)), and the molten glass at a lower temperature. Is preferable in that it is obtained. Moreover, in this invention, you may make the glass mother composition raw material contain the hydroxide which consists of aluminum and an alkaline-earth metal.
In addition, as described above, when part or all of the boron source in the glass raw material is anhydrous boric acid in order to reduce the amount of water in the molten glass, the amount of water in the molten glass is excessively reduced and the pressure is reduced. In the defoaming step, the bubbles are reduced, the foam floating speed is decreased, and the homogeneity and flatness of the alkali-free glass may be deteriorated. In this case, it is preferable to add a hydroxide of aluminum or an alkaline earth metal in order to supplement the amount of water in the molten glass.
As the hydroxide, it is preferable to use Al (OH) ₃ in terms of promoting the initial melting. Further, as the alkaline earth metal hydroxide, at least one of Mg (OH) _{2 and} Ca (OH) ₂ is preferably used, and Mg (OH) ₂ is particularly preferably used.
When the alkaline earth metal hydroxide is contained in the glass matrix composition raw material, the content is 100 mol% of the alkaline earth metal source (in terms of MO, where M is an alkaline earth metal element). A range of 15 to 100 mol% (in terms of MO) is preferable. When the amount of hydroxide added is 15 mol% or more, the unmelted amount of the SiO ₂ component contained in the silica sand can be reduced in the step (a). Therefore, it is possible to prevent unmelted SiO _{2 from} being taken into the bubbles when the bubbles are generated in the glass melt and collecting near the surface of the glass melt. As a result, it is possible to prevent a difference in the composition ratio of SiO ₂ between the surface layer of the glass melt and the portion other than the surface layer, thereby reducing the homogeneity and flatness of the glass.
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 hydroxide, the better .
For the same reason as in the case of the alkaline earth metal hydroxide, the content when Al (OH) ₃ is contained in the glass matrix composition raw material is 100 mol% of aluminum source (in terms of Al ₂ O ₃ ). of preferably in the range of 15 to 100 mole% _(Al 2 _{O 3} conversion).
Also, as the molar ratio of hydroxide in the aluminum 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 hydroxide, the better.

(Glass mother composition raw material)
The glass mother composition raw material is a powdery mixture in which the respective raw materials are mixed.
The glass matrix composition raw material is prepared so as to be an alkali-free glass having a target glass matrix composition.
As a composition of a glass mother composition raw material, a composition which becomes a non-alkali glass of a glass mother composition (1) described later is preferable, and a non-alkali glass of a glass mother composition (2) or a glass mother composition (3) described later is obtained. Such a composition is particularly preferred.

(Clarifier)
The fining agent is a component that improves the fining property and is added to the glass matrix composition raw material.
In the present invention, at least SnO ₂ is used as a fining agent.
The valence of Sn oxide changes from SnO ₂ (Sn ⁴⁺ ) to SnO (Sn ²⁺ ) at a high temperature of 1400 ° C. or higher. As the valence changes, a clarified gas (oxygen gas) is released. When a valence of SnO _{2 of a} certain ratio or more changes to SnO, sufficient clarification gas is released, and effective clarification becomes possible.

The added amount of tin is preferably 0.01 to 2% by mass, more preferably 0.1 to 0.7% by mass in terms of SnO ₂ with respect to the glass matrix composition raw material. When the amount of tin added is 0.01% by mass or more, fining is sufficiently performed. By setting the amount of tin added to 2% by mass or less, the generation of defects such as unfused tin can be suppressed.

As other fining agents, the glass matrix composition raw material further comprises 3% by mass or less of chloride in terms of Cl, 3% by mass or less of sulfate in terms of SO ₃ and 3% by mass or less of fluoride in terms of F. One or more selected from the group may be added in a total amount of 0.01 to 5% by mass. Since many man-hours needed to cullet processing, _PbO, the _{As 2 O 3, Sb 2 O} 3, preferably does not contain, except those that inevitably mixed as impurities like.

(Caret)
The cullet is glass waste discharged in the process of manufacturing alkali-free glass.
As a cullet, what has the same composition as the glass mother composition of the target non-alkali glass is preferable.

The amount of cullet added is preferably 15 to 300 mass% with respect to the glass matrix composition raw material. By making the addition amount of cullet 15% by mass or more, initial meltability can be secured. The amount of cullet by 300 mass% or less can exhibit a clear effect of SnO _2.

(Other additives)
When using cullet, it is preferable to add nitrate simultaneously.
In the cullet, there is a large proportion of Sn oxide used as a fining agent in the state of SnO (Sn ²⁺ ), and the ability to generate a fining gas is reduced. Therefore, by adding nitrate at the time of remelting the cullet, SnO (Sn ²⁺ ) is oxidized to SnO ₂ (Sn ⁴⁺ ) by the nitrate, so that clarification can be effectively performed without adding SnO ₂ to the cullet again. It can be carried out.

The addition amount of nitrate is preferably 0.01 to 10% by mass in terms of NO ₃ with respect to the glass matrix composition raw material. By making the addition amount of the nitrate 0.01% by mass or more, SnO in the cullet can be efficiently oxidized to SnO ₂ . Even if the amount of nitrate added exceeds 10% by mass, the oxidation to SnO ₂ is saturated and the effect is small.

Step (ii):
(Process (a))
Step (a) is an initial melting step, which is a step of melting the glass raw material to uniformly vitrify it.
The temperature in the step (a) is a temperature at which the viscosity of the molten glass is more than 10 ^2.4 dPa · s, and a temperature at which the viscosity of the molten glass is at least 10 ^2.5 dPa · s, A temperature at which the viscosity of the molten glass is 10 ^2.6 to 10 ^2.9 dPa · s is more preferable. When the viscosity of the molten glass exceeds 10 ^2.9 dPa · s, the initial melting is difficult to be homogeneous. Therefore, a temperature that is 10 ^2.9 dPa · s or less is preferable. Further, the temperature in the step (a) is preferably 1400 ° C. or higher.
Vitrification can be performed while suppressing consumption of SnO ₂ by setting the temperature in the step (a) to such a temperature that the viscosity of the molten glass exceeds 10 ^2.4 dPa · s. Therefore, the clarification in the subsequent step (b) can be performed efficiently, and the bubbles in the glass can be reduced.

Thus, in the present invention, since at least SnO ₂ is used as a fining agent, the glass raw material is heated at a relatively low temperature, that is, at a temperature at which the viscosity of the molten glass exceeds 10 ^2.4 dPa · s. It is necessary to use molten glass.
However, when only orthoboric acid is used as the boron source, silica sand tends to aggregate at that temperature, so unfused silica is likely to be generated in the molten glass.
On the other hand, in the present invention, since the glass mother composition raw material contains boric anhydride as a boron source, the glass raw material is uniformly melted even at this temperature, and the generation of unfused silica is suppressed.

  The time for the step (a) is preferably from 100 to 900 minutes, more preferably from 150 to 500 minutes.

(Process (b))
Step (b) is a clarification step, in which the molten glass is heated to a relatively high temperature, that is, a temperature at which the viscosity of the molten glass is 10 ^2.4 dPa · s or less, and 30 ° C. above the temperature in step (a). This is a step of heating at a higher temperature, generating a clarified gas by changing the valence of Sn, and defoaming bubbles in the molten glass.

The temperature in the step (b) is a temperature at which the viscosity of the molten glass is 10 ^2.4 dPa · s or less, and a temperature at which the viscosity of the molten glass is 10 ^2.3 dPa · s or less is preferable, A temperature at which the viscosity of the molten glass is 10 ^1.8 to 10 ^2.2 dPa · s is more preferable. When the viscosity of the molten glass is less than 10 ^1.8 dPa · s, the furnace material is easily eroded and defects are likely to occur. Therefore, a temperature of 10 ^1.8 dPa · s or higher is preferable.
Moreover, the temperature in the step (b) is 30 ° C. or higher than the temperature in the step (a), preferably 50 ° C. or higher than the temperature in the step (a), and higher than the temperature in the step (a). A temperature higher by 70 ° C. or more is more preferable. The temperature in the step (b) is preferably 1700 ° C. or lower.
By setting the temperature in the step (b) to a temperature at which the viscosity of the molten glass is 10 ^2.4 dPa · s or less and 30 ° C. or more higher than the temperature in the step (a), the clarified gas is made efficient. It can be generated well and clarification can be performed efficiently, and bubbles in the glass can be reduced.

  The time for the step (b) is preferably 60 to 800 minutes, more preferably 120 to 300 minutes.

  The viscosity of the molten glass is measured using a high temperature rotational viscometer.

Step (iii), step (iv):
In step (iii) and step (iv), molding, gradual cooling, and cutting are performed in the same manner as in known methods for producing alkali-free glass.

<Non-alkali glass>
The alkali-free glass obtained by the production method of the present invention contains SiO ₂ derived from silica sand and B ₂ O ₃ derived from a boron source in the glass mother composition. The alkali-free glass is one that does not substantially contain an alkali metal oxide such as Na ₂ O or K ₂ O. Here, substantially not containing an alkali metal oxide means that it contains no alkali metal oxide other than unavoidable impurities mixed from raw materials. That is, it means what does not intentionally contain an alkali metal oxide.

  Hereinafter, the preferable glass mother composition of an alkali free glass is demonstrated.

Glass mother composition (1):
As alkali-free glass, characteristics (thermal expansion coefficient 25 × 10 ^{−7 to} 60 × 10 ⁻⁷ / ° C.), chemical resistance, durability, etc. as liquid crystal display substrate glass. ) And is suitable for molding into a plate glass, an alkali-free glass having the following glass matrix composition (1) is preferred in terms of oxide-based mass percentage.
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).

Glass mother composition (2):
Alkali-free glass has a strain point of 640 ° C or higher, a low coefficient of thermal expansion, a low density, reduced white turbidity due to buffered hydrofluoric acid (BHF) used for etching, and excellent durability to chemicals such as hydrochloric acid From the viewpoint of easy melting and molding and suitable for float molding, an alkali-free glass having the following glass matrix composition (2) is more preferable in terms of oxide-based mass percentage.
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).

Each composition of this composition system will be described.
By making SiO ₂ 58% by mass or more, the strain point of the alkali-free glass increases, the chemical resistance becomes good, and the thermal expansion coefficient decreases. With the SiO ₂ 66 wt% or less, the melting property of the glass is improved, devitrification characteristic becomes good.

Al ₂ O ₃ suppresses the phase separation of alkali-free glass, lowers the thermal expansion coefficient, and increases the strain point.
The al ₂ O ₃ by 15 mass% or more, the effect is expressed. By 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. By setting B ₂ O ₃ to 12% by mass or less, the acid resistance of the alkali-free glass is improved and the strain point is increased.

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.

SrO suppresses the phase separation of the alkali-free glass and suppresses the cloudiness of the alkali-free glass due to BHF.
By making SrO 3% by mass or more, the above effect is exhibited. By making SrO 12.5 mass% or less, the thermal expansion coefficient of an alkali free glass falls.

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. In consideration of the environmental load, it is preferable that it is not substantially contained.

  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.

Glass mother composition (3):
As alkali-free glass, it has excellent properties as glass for liquid crystal display substrates, excellent resistance to reduction, homogeneity, foam suppression, and suitable for molding by float method. An alkali-free glass having a glass matrix composition (3) is particularly preferred.
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).

Each composition of this composition system will be described.
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.

Al ₂ O ₃ suppresses the phase separation of the alkali-free glass, increases the strain point, and increases the Young's modulus.
The al ₂ O ₃ by a 10.5 mass% or more, the effect is expressed. By the al ₂ O ₃ and 18 wt% or less, the devitrification property of the alkali-free glass, acid resistance and the BHF resistance will be good.

B ₂ O ₃ reduces the density of alkali-free glass, improves BHF resistance, improves meltability, improves devitrification characteristics, and decreases the thermal expansion coefficient.
With B ₂ O ₃ to 7% by mass or more, the effect is expressed. 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.

MgO decreases the density of the alkali-free glass, increases the thermal expansion coefficient, does not excessively decrease the strain point, and improves the meltability.
The said effect is expressed by making MgO 2 mass% or more. 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.
In consideration of the environmental load, it is preferable that it is not substantially contained.

  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.

According to the method for producing alkali-free glass of the present invention described above, the silica sand having a D50 of ₁₅ to 60 μm and a ratio of particles having a particle diameter of 100 μm or more is 2.5% by volume or less is used. as boron source, boric acid anhydride, of the boron source 100 _{wt% (B} 2 _{O 3} basis), 10 to 100 _{wt% (B} 2 _{O 3} equivalent) with those containing, as a refining agent, at least SnO ₂ In order to melt the glass raw material in at least two steps (a) and (b), it is possible to obtain an alkali-free glass with few bubbles in the glass and high uniformity and flatness. it can.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention should not be construed as being limited to these examples.
Examples 1 and 2 are experimental examples showing low-temperature meltability, Examples 3 to 5, 7 and 8 are examples, and Example 6 is a comparative example.

[Example 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 silica sand (D ₅₀ : 27 μm, the proportion of particles having a particle size of 100 μm or more: 0% by volume, D ₉₉ (particles in which the volume frequency in the particle size distribution occupies 99%). Diameter): 69 μm), boric anhydride (100% by mass) as a boron source, Al ₂ O ₃ as an aluminum source, and other raw materials to prepare a glass mother composition raw material, and further as a fining agent, the glass mother composition SnO ₂ was added to the raw material by 0.5 mass%, SrCl ₄ was added by 0.5 mass%, and CaSO ₄ .2H ₂ O was added by 0.3 mass% to obtain a glass raw material.

A glass raw material having an amount of 250 g after vitrification was placed in a bottomed cylindrical platinum rhodium crucible having a height of 90 mm and an outer diameter of 70 mm. The crucible is put into a heating furnace, heated at 1525 ° C. (temperature at which the viscosity of the molten glass becomes 10 ^2.6 dPa · s) for 30 minutes while blowing air having a dew point of 60 ° C. from the side of the heating furnace, and then forced by a stirrer. Specifically, the inside of the crucible was stirred for 30 minutes to melt the glass raw material. Thereafter, stirring was stopped and the mixture was allowed to stand for 60 minutes. The molten glass in the crucible was poured onto a carbon plate and cooled in a slow cooling furnace. After cooling, the sample was taken out from the slow cooling furnace, and the number of unfused silica was counted with a stereomicroscope while applying light from the edge of the sample. The results are shown in Table 1.
Further, the same evaluation was carried out by setting the melting temperature of the glass raw material to 1550 ° C. (temperature at which the viscosity of the molten glass becomes 10 ^2.5 dPa · s). The results are shown in Table 1.

[Example 2]
Instead of silica sand 1, silica sand 2 (D ₅₀ : 39 μm, ratio of particles having a particle size of 100 μm or more: 4.2 vol%, D ₉₉ : 153 μm) is used, and orthoboric acid (100 mass%) is used as a boron source. The evaluation was the same as in Example 1 except that. The results are shown in Table 1.

The combination of silica sand 1 and boric anhydride, which is the configuration of the present invention (D ₅₀ : 15 to 60 μm, the ratio of particles having a particle size of 100 μm or more: 2.5% by volume or less), is different from the configuration of the present invention. In comparison with the combination of silica sand 2 and orthoboric acid, it can be seen that the amount of unfused silica is small and the initial dissolution is possible at a lower temperature. Further, since the amount of unfused silica is small, the glass has high homogeneity. Moreover, when it shape | molds to plate glass, glass with high flatness is obtained.

[Example 3]
The same glass mother composition raw material as in Example 1 was added, and 0.5% by mass of SnO ₂ was added as a refining agent to the glass mother composition raw material to obtain a glass raw material.

Step (a):
Half of the glass raw material (corresponding to 125 g in terms of glass) was placed in a 300 cc platinum crucible and allowed to stand for 30 minutes in an electric furnace at 1500 ° C. (temperature at which the molten glass had a viscosity of 10 ^2.7 dPa · s). Once the platinum crucible is taken out from the electric furnace, the remaining half (corresponding to 125 g in terms of glass) is added, and again in an electric furnace at 1500 ° C. (temperature at which the viscosity of the molten glass is 10 ^2.7 dPa · s) for 30 minutes. The glass raw material was melted by standing.

Step (b):
Thereafter, it was quickly transferred to an electric furnace at 1590 ° C. (the temperature at which the viscosity of the molten glass was 10 ^2.3 dPa · s), and allowed to stand for 30 minutes. Thereafter, the glass was transferred to an electric furnace at 730 ° C., and the glass was gradually cooled to 610 ° C. over 2 hours, and further cooled to room temperature over about 10 hours. Then, the glass in the upper center of the crucible is cut into a cylindrical glass having a diameter of 38 mm and a height of 35 mm with a core drill. As shown in FIG. 1, the glass having a thickness of 2 to 5 mm including the central axis 12 of the cylindrical glass 10. Cut into a plate 14. Both surfaces of the cut-out surface were subjected to optical polishing (mirror polishing finish) to prepare an evaluation sample. 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 having 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 remaining bubbles was used. The results are shown in Table 2.

[Example 4]
The same evaluation as in Example 3 was performed, except that the temperature of the step (a) was changed to 1550 ° C. (temperature at which the viscosity of the molten glass was 10 ^2.5 dPa · s). The results are shown in Table 2.

[Example 5]
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: 5% by mass, CaO: 6% by mass, SrO: 4% by mass. Glass mother composition raw material by preparing silica sand 1, boric anhydride (100% by mass) as a boron source, Al ₂ O ₃ as an aluminum source, and other raw materials so as to be an alkali-free glass having a glass mother composition of 5% Further, as a fining agent, 0.5% by mass of SnO ₂ was added to the glass mother composition raw material to obtain a glass raw material.

Step (a):
Half of the glass raw material (corresponding to 125 g in terms of glass) was placed in a 300 cc platinum crucible and allowed to stand for 30 minutes in an electric furnace at 1500 ° C. (temperature at which the molten glass had a viscosity of 10 ^2.5 dPa · s). Once the platinum crucible is taken out from the electric furnace, the remaining half (corresponding to 125 g in terms of glass) is added, and again in an electric furnace at 1500 ° C. (temperature at which the viscosity of the molten glass becomes 10 ^2.5 dPa · s) for 30 minutes. The glass raw material was melted by standing.

Step (b):
Thereafter, it was quickly transferred to an electric furnace at 1590 ° C. (temperature at which the viscosity of the molten glass becomes 10 ^2.1 dPa · s), and left still for 30 minutes. Thereafter, the glass was transferred to an electric furnace at 730 ° C., and the glass was gradually cooled to 610 ° C. over 2 hours, and further cooled to room temperature over about 10 hours. And the evaluation sample was produced like Example 3 and the number of residual bubbles was calculated | required. The results are shown in Table 2.

[Example 6]
The same glass raw material as in Example 2 was prepared.

Step (a):
Half of the glass raw material (corresponding to 125 g in terms of glass) was placed in a 300 cc platinum crucible and allowed to stand for 30 minutes in an electric furnace at 1590 ° C. (temperature at which the molten glass had a viscosity of 10 ^2.3 dPa · s). Once the platinum crucible is taken out from the electric furnace, the remaining half amount (corresponding to 125 g in terms of glass) is added, and again in an electric furnace at 1590 ° C. (temperature at which the viscosity of the molten glass becomes 10 ^2.3 dPa · s) for 30 minutes. It was left to dissolve.

Step (b):
Thereafter, it was quickly transferred to an electric furnace at 1590 ° C. (the temperature at which the viscosity of the molten glass was 10 ^2.3 dPa · s), and allowed to stand for 30 minutes. Thereafter, the glass was transferred to an electric furnace at 730 ° C., and the glass was gradually cooled to 610 ° C. over 2 hours, and further cooled to room temperature over about 10 hours. And the evaluation sample was produced like Example 3 and the number of residual bubbles was calculated | required. The results are shown in Table 2.

[Example 7]
Except that Al (OH) ₃ was used as an aluminum source, it was used as a glass matrix composition raw material in the same manner as in Example 1, and as a refining agent, 0.5% by mass of SnO ₂ and SrCl ₂ with respect to the glass matrix composition raw material. ₄ was added by 0.5% by mass, CaSO ₄ .2H ₂ O was added by 0.3% by mass and CaF ₂ was added by 0.1% by mass to obtain a glass raw material.
An evaluation sample was prepared and the number of remaining bubbles was determined in the same manner as in Example 3 except that the glass raw material obtained above was used. The results are shown in Table 3.
[Example 8]
Temperature 1450 ° C. in step (a) was changed to (a temperature at which the viscosity of the molten glass becomes ¹⁰ 2.8 dPa · s) was evaluated in the same manner as in Example 7. The results are shown in Table 3.

工程（ａ）にてガラス原料を、溶融ガラスの粘度が１０^２．４ｄＰａ・ｓ超となるような温度で加熱し、工程（ｂ）にて溶融ガラスを、溶融ガラスの粘度が１０^２．４ｄＰａ・ｓ以下となるような温度で、かつ前記工程（ａ）における温度より３０℃以上高い温度で加熱した例３〜５は、工程（ａ）においても、ガラス原料を、溶融ガラスの粘度が１０^２．４ｄＰａ・ｓ以下となるような温度で加熱し、工程（ａ）と工程（ｂ）の溶融ガラスの粘度に差のない例６に比較して、残存泡数が少なく、清澄効果が大きいことがわかる。
さらに、ガラス母組成原料中にＡｌ（ＯＨ）_３を含む例７および８では、特に例８は、工程（ａ）にてガラス原料を低い温度で溶解し、溶融ガラスの粘度が高くなっているにもかかわらず、良好な溶融特性が得られ、例７、８では残存泡数が少なく、清澄効果が大きいことがわかる。

In step (a), the glass raw material is heated at a temperature such that the viscosity of the molten glass exceeds 10 ^2.4 dPa · s. In step (b), the molten glass is heated and the viscosity of the molten glass is 10 ^2. Examples 3 to 5 heated at a temperature of ⁴ dPa · s or less and at a temperature 30 ° C. or more higher than the temperature in the step (a) are the viscosity of the molten glass in the step (a). Is heated to a temperature of 10 ^2.4 dPa · s or less, and the number of residual bubbles is small compared to Example 6 where there is no difference in the viscosity of the molten glass in step (a) and step (b). It turns out that the effect is great.
Further, in Examples 7 and 8 in which Al (OH) ₃ is contained in the glass matrix composition raw material, especially in Example 8, the glass raw material is melted at a low temperature in the step (a), and the viscosity of the molten glass is high. Nevertheless, good melting characteristics are obtained, and in Examples 7 and 8, it can be seen that the number of residual bubbles is small and the clarification effect is large.

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 for a liquid crystal display substrate.

The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2007-277802 filed on Oct. 25, 2007 are cited herein as disclosure of the specification of the present invention. Incorporated.

Claims (7)

In a method for producing alkali-free glass, in which a glass raw material containing a fining agent is melted and molded into a glass mother composition raw material containing silica sand and a boron source,
The silica sand having a median diameter of 15 to 60 μm and a ratio of particles having a particle diameter of 100 μm or more is 2.5% by volume or less,
As the boron source, boric acid anhydride, of the boron source 100 _{wt% (B} 2 _{O 3} basis), with those containing 10 to 100 _{wt% (B} 2 _{O 3} basis),
As the clarifier, at least SnO ₂ is used,
A method for producing an alkali-free glass, wherein the glass raw material is melted in at least the following two steps.
(A) A step of heating the glass raw material at a temperature at which the viscosity of the molten glass becomes more than 10 ^2.4 dPa · s to obtain a molten glass.
(B) After the step (a), the molten glass is at a temperature such that the viscosity of the molten glass is 10 ^2.4 dPa · s or less, and a temperature higher by 30 ° C. than the temperature in the step (a). The process which heats by and defoams the foam in molten glass.   The method for producing alkali-free glass according to claim 1, wherein the glass matrix composition raw material contains aluminum or an alkaline earth metal hydroxide. A glass matrix composition raw material is prepared so as to be an alkali-free glass having the following glass matrix composition (1) in terms of oxide-based mass percentage, and tin is 0.01 to _{2 in} terms of SnO ₂ with respect to the glass matrix composition raw material. The manufacturing method of the alkali free glass in any one of Claim 1 or 2 made into glass raw material by adding the 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: 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). A glass mother composition raw material is prepared so as to be an alkali-free glass having the following glass mother composition (2) in terms of oxide-based mass percentage, and tin is 0.01 to _{2 in} terms of SnO ₂ with respect to the glass mother composition raw material. The manufacturing method of the alkali free glass in any one of Claims 1-3 which adds the mass% and makes it a 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 to 2 mass%, MgO + CaO + SrO + BaO: 9 to 18 mass% (2). A glass mother composition raw material is prepared so as to be an alkali-free glass having the following glass mother composition (3) in terms of oxide-based mass percentage, and tin is 0.01 to _{2 in} terms of SnO ₂ with respect to the glass mother composition raw material. The manufacturing method of the alkali free glass in any one of Claims 1-4 which makes a glass raw material by adding mass%.
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). 1 selected from the group consisting of 3% by mass or less of chloride in terms of Cl, 3% by mass or less of sulfate in terms of SO ₃ and 3% by mass or less of fluoride in terms of F with respect to the glass matrix composition raw material. The manufacturing method of the alkali free glass in any one of Claims 1-5 which adds 0.01-5 mass% in a total amount with a seed | species or more to make a glass raw material. The glass matrix composition raw material, further, nitrate is added to 0.01 to 10% by mass in terms of NO ₃ and cullet made of alkali-free glass is added to 15 to 300% by mass to obtain a glass raw material. The manufacturing method of the alkali free glass in any one.

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