KR101022682B1 - Process for producing alkali-free glass - Google Patents

Abstract

The manufacturing method which can obtain the alkali free glass with few bubbles in a glass, and high homogeneity and flatness is provided. Melting a glass raw material containing silica sand and a boron source, and a manufacturing method of a non-alkali glass for forming, from the boron source boron source 100% by weight of (B ₂ O ₃ equivalent) in anhydrous boric acid as a 10 to 100% by weight (Converted to B ₂ O ₃ ) It is used.

Description

Production method of alkali-free glass {PROCESS FOR PRODUCING ALKALI-FREE GLASS}

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

Since it is requested | required that an alkali metal is not contained substantially in glass substrates for displays, such as a liquid crystal display device, alkali free glass is used as the glass substrate. In addition, the glass substrate is required to have high chemical resistance, durability, low 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 an alkali free glass, the glass raw material is difficult to melt. Therefore, it is necessary to use the thing with small particle diameter as a silica sand which is a main component of a glass raw material.

Also, in order to impart solubility, chemical resistance, and durability in an alkali-free glass, it is effective to contain the B ₂ O ₃ in the composition. As a source of B ₂ O ₃ is (also referred to as a simple acid.) Orthoboric acid from inexpensive and easy to obtain points are used.

However, when the glass raw material containing orthoboric acid is used, the following problems may arise.

(1) In the presence of orthoboric acid, silica sand having a small particle size tends to aggregate, and the input amount of the glass raw material into the molten kiln tends to be unstable. Therefore, the temperature of the molten glass in a molten kiln becomes unstable, and circulation and residence time of a molten glass become unstable. As a result, melting of a glass raw material becomes nonuniform, and the composition of a molten glass becomes nonuniform.

(2) When a glass raw material contains an alkaline earth metal compound, the orthoboric acid melt | dissolved in the glass raw material inlet of a melting pot, and an alkaline earth metal compound aggregate, and a core is likely to generate | occur | produce. Since the orthoboric acid and the alkaline earth metal compound are also components that promote the melting of the silica sand, when a core is generated, the melting of the glass raw material in the melting kiln becomes uneven, and the composition of the molten glass becomes uneven.

When the problem of (1) or (2) arises, since the homogeneity of molten glass will worsen, the homogeneity and flatness of the molded alkali free glass will become low. Moreover, since circulation and a residence time become unstable, a part of molten glass flows out from a molten kiln before a bubble comes out from the molten glass in a molten kiln by a clarifier. Moreover, since melting of a glass raw material is nonuniform, the effect of the clarifier to the silica sand melted late becomes inadequate, and foam | bubble does not fully fall out from a molten glass.

In order to improve the homogeneity of an alkali free glass, the glass raw material by which the particle diameter of the alkaline-earth metal compound (strontium carbonate and dromite.) Was controlled is proposed (patent document 1). However, the glass raw material does not consider aggregation of the glass raw material by orthoboric acid. Only controlling the particle diameter of the alkaline earth metal compound does not inhibit aggregation of the glass raw material by orthoboric acid, and thus does not have an effect on the reduction of homogeneity due to the aggregation.

Patent Document 1: Japanese Unexamined Patent Publication No. 2003-40641

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

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

Means to solve the problem

Method of producing an alkali-free glass of the present invention provides a method of producing an alkali-free glass melting and forming a glass raw material containing silica sand and a boron source, a boron source 100% by weight of anhydrous boric acid as the boron source (B ₂ O ₃ equivalent) in, characterized by using terms that it contains 10 to 100 mass% (B ₂ O _3).

As said glass raw material, it is preferable to use the glass raw material which has a composition which becomes an alkali free glass which has the following composition (1) as a mass percentage display on an oxide basis, and the alkali free glass which has the following composition (2) or (3) It is especially preferable to use the glass raw material which has a composition to become.

SiO ₂ : 50 to 66 mass%, Al ₂ O ₃ : 10.5 to 22 mass%, B ₂ O ₃ : 5 to 12 mass%, 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%. (One).

SiO ₂ : 58 to 66 mass%, Al ₂ O ₃ : 15 to 22 mass%, B ₂ O ₃ : 5 to 12 mass%, MgO: 0 to 8 mass%, CaO: 0 to 9 mass%, SrO: 3 To 12.5 mass%, BaO: 0 to 2 mass%, MgO + CaO + SrO + BaO: 9 to 18 mass%. (2).

SiO ₂ : 50 to 61.5 mass%, Al ₂ O ₃ : 10.5 to 18 mass%, B ₂ O ₃ : 7 to 10 mass%, MgO: 2 to 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).

Effects of the Invention

According to the manufacturing method of the alkali free glass of this invention, there are few bubbles in glass, and the alkali free glass with high homogeneity and flatness can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the manufacturing method of the alkali free glass in an Example.

It is a figure which shows the measuring point of the composition in a sample.

Explanation of the sign

12: glass raw material

16: alkali free glass

Carrying out the invention  Best form for

An alkali free glass is manufactured by melting and shape | molding the glass raw material containing a silica sand and a boron source. An alkali free glass is manufactured as follows, for example.

(i) Glass raw materials are mixed by mixing the silica sand and boron source, Al ₂ O ₃ , alkaline earth metal oxides (MgO, CaO, SrO, BaO), clarifiers, etc. To prepare.

(Ii) The glass raw material and, if necessary, a cullet having the same composition as that of the target alkali free glass is continuously introduced into the molten kiln from the glass raw material inlet of the molten kiln, and melted at 1500 to 1600 ° C to melt the molten glass. Shall be. A cullet is the glass waste discharged | emitted in the process of manufacture of an alkali free glass, etc.

(Iii) The molten glass is molded to have a predetermined thickness by a known molding method such as float method.

(Iii) After cooling the shape | molded glass ribbon, it cuts to a predetermined magnitude | size and obtains plate-shaped alkali free glass.

(Gross sand)

The average particle diameter (D ₅₀₎ of the silica is, 15 ~ 60㎛ are preferred, and 20 ~ 45㎛ is more preferable, and 20 ~ 40㎛, more preferably, 20 ~ 30㎛ is particularly preferred. Since, by the mean diameter (D ₅₀₎ of silica sand over 15㎛ to further suppress aggregation of the silica sand, the bubble is more small, the homogeneity, the flatness higher alkali-free glass is obtained. By setting the average particle diameter (D ₅₀ ) of the silica sand to 60 µm or less, since the silica sand is easily melted uniformly, an alkali free glass having fewer bubbles and higher homogeneity and flatness is obtained.

(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 ), boric anhydride (B ₂ O ₃ ), and the like. In manufacture of a normal alkali free glass, orthoboric acid is used at the point which is cheap and easy to obtain.

In the present invention, anhydrous boric acid as a boron source in the boron source to 100% by mass (in terms of B ₂ O _3), is used in that it contains (in terms of B ₂ O ₃₎ 10 ~ 100% by weight. By making boric anhydride 10 mass% or more, aggregation of a glass raw material is suppressed, and the effect of reducing foam | bubble, the homogeneity, and the improvement of flatness is acquired. As for boric anhydride, 20-100 mass% is more preferable, and 40-100 mass% is more preferable.

As boron compounds other than boric anhydride, orthoboric acid is preferable at the point of being cheap and easy to obtain.

(Other raw materials)

Other raw materials include Al ₂ O ₃ , alkaline earth metal oxides (MgO, CaO, SrO, BaO), and the like.

Such as the refining agent, to improve the melting property, the refining property, moldability, and may be contained in the ZnO, SO _3, F, Cl, SnO _2.

(frit)

A glass raw material is a powdery mixture which mixed each said raw material.

The composition of a glass raw material is made into the composition which becomes the alkali free glass which has a target composition. As a composition of a glass raw material, the composition used as the alkali free glass which has the composition (1) mentioned later is preferable, and the composition used as the alkali free glass which has the composition (2) or (3) mentioned later is especially preferable.

(Alkali-free glass)

The alkali-free glass is obtained by the production process of the present invention contains the B ₂ O ₃ derived from SiO _2, and a boron source derived from silica sand in the composition. The alkali-free glass is, would that is substantially free of alkali metal oxides such as Na ₂ O, K ₂ 0.

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

Composition (1):

As alkali-free glass, since it has the characteristics as a glass substrate for a display (thermal expansion coefficient ^25x10 <^-7> -60 * 10 <^-7> / degreeC), chemical-resistance, durability, etc., it is suitable for shaping | molding to a plate glass, The alkali free glass which has the following composition (1) as a reference mass percentage display is preferable.

Among the alkali-free glass (100 _{mass%), SiO 2: 50 ~} 66 _{wt%, Al 2 O 3: 10.5} ~ 22 _{mass%, B 2 O 3: 5} ~ 12% by weight, MgO: 0 ~ 8% by weight, CaO : 0-14.5 mass%, SrO: 0-24 mass%, BaO: 0-13.5 mass%, MgO + CaO + SrO + BaO: 9-29.5 mass%. (One).

Composition (2):

As alkali-free glass, a strain point is 640 degreeC or more, a thermal expansion coefficient and a density are small, the turbidity by the buffered fluoric acid (BHF) used for etching is suppressed, and it is excellent also in durability with respect to chemicals, such as hydrochloric acid, and melting The alkali free glass which has the following composition (2) as a mass percentage display on an oxide basis is preferable at the point which is easy to shape | mold and is suitable for float molding.

Among the alkali-free glass (100 _{mass%), SiO 2: 58 ~} 66 _{wt%, Al 2 O 3: 15} ~ 22 _{wt%, B 2 O 3: 5} ~ 12% by weight, MgO: 0 ~ 8% by weight, CaO : 0-9 mass%, SrO: 3-12.5 mass%, BaO: 0-2 mass%, MgO + CaO + SrO + BaO: 9-18 mass%. (2).

By the SiO ₂ more than 58% by weight, up strain point of alkali-free glass, it becomes excellent in the chemical resistance, the thermal expansion coefficient is lowered. By the SiO ₂ to less than 66% by mass, it becomes excellent in the melting property of the glass, it is excellent in devitrification property.

Al ₂ O ₃ suppresses phase separation of the alkali-free glass, lowers the coefficient of thermal expansion, and increases the strain point.

, The above effects are expressed by the Al ₂ O ₃ with at least 15% by weight. By the Al ₂ O ₃ less than 22% by mass, it is excellent in the melting property of the glass.

B ₂ O ₃ is thereby lowering the coefficient of thermal expansion and density of the alkali-free glass suppresses the clouding of the alkali-free glass by BHF, and without increasing the viscosity at high temperature.

By the B ₂ O ₃ less than 5% by mass, it is excellent in BHF resistance of alkali-free glass. B ₂ O ₃ by 12 mass% or less, transformation point goes up with becomes good acid resistance of alkali-free glass.

Mg0 suppresses the increase of the thermal expansion coefficient and density of an alkali free glass, and improves the meltability of a glass raw material.

By making MgO 8 mass% or less, the clouding by BHF is suppressed and the powdery phase of an alkali free glass is suppressed.

CaO improves the meltability of the glass raw material.

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

SrO suppresses powder phase of an alkali free glass and suppresses the cloudiness of the alkali free glass by BHF.

The said effect is expressed by making SrO 3 mass% or more. By making SrO 12.5 mass% or less, the thermal expansion coefficient of an alkali free glass falls.

BaO suppresses powder phase of an alkali free glass, improves meltability, and improves devitrification characteristics.

By making BaO 2 mass% or less, the density of an alkali free glass falls and a thermal expansion coefficient falls.

By making MgO + CaO + SrO + BaO 9 mass% or more, the meltability of glass becomes favorable. By making MgO + CaO + SrO + BaO into 18 mass% or less, the density of an alkali free glass falls.

In the composition (2), the melting property, the refining property, is to improve the moldability, ZnO, SO _3, F, Cl, may be contained in a total amount less than 5% by weight of SnO _2. In addition, it is preferable because the number of airborne required for the processing of cullet, PbO, As ₂ O _3, Sb ₂ O ₃ a, and do not contain, except that the unavoidable incorporation into such an impurity.

Composition (3):

As alkali-free glass, since it is excellent in the characteristic as a glass substrate for a display, excellent in reduction resistance, homogeneity, and bubble suppression, and suitable for shaping | molding by a float method, the following composition (3) is shown as the mass percentage display on an oxide basis. The alkali free glass which has is especially preferable.

Among the alkali-free glass (100 _{mass%), SiO 2: 50 ~} 61.5 _{weight%, Al 2 O 3: 10.5} ~ 18 _{mass%, B 2 O 3: 7} ~ 10% by weight, MgO: 2 ~ 5% by weight, CaO : 0-14.5 mass%, SrO: 0-24 mass%, BaO: 0-13.5 mass%, MgO + CaO + SrO + BaO: 16-29.5 mass%. (3).

By the SiO ₂ at least 50% by mass, the acid resistance of alkali-free glass becomes good, and the density is lowered, up transformation point, and the thermal expansion coefficient decreases, the Young's modulus is raised. By the SiO ₂ to less than 61.5 mass%, it is excellent in devitrification property of the alkali-free glass.

Al ₂ O ₃ suppresses powder phase of the alkali free glass, increases the strain point, and increases the Young's modulus.

, The above effects are expressed by the Al ₂ O ₃ more than 10.5% by weight. By the Al ₂ O ₃ less than 18% by mass, the devitrification property, the acid resistance and the BHF resistance of alkali-free glass becomes fine.

B ₂ O ₃ reduces the density of the alkali free glass, improves the BHF resistance, improves the meltability, improves the devitrification property, and lowers the coefficient of thermal expansion.

, The above effects are expressed by the B ₂ O ₃ less than 7% by mass. By the B ₂ O ₃ less than 10% by weight, up transformation point of the alkali-free glass, and the Young's modulus is increased, it is excellent in acid resistance.

Mg0 lowers the density of the alkali free glass and improves meltability without excessively lowering the strain point without increasing the coefficient of thermal expansion.

The said effect is expressed by making MgO into 2 mass% or more. By making MgO 5 mass% or less, powder phase of an alkali free glass is suppressed and the said devitrification characteristic, acid resistance, and BHF resistance become favorable.

CaO does not raise the density of an alkali free glass, does not raise a thermal expansion coefficient, does not reduce a strain point excessively, and improves meltability.

By making CaO 14.5 mass% or less, the devitrification characteristic of an alkali free glass becomes favorable, a thermal expansion coefficient falls, a density falls, and acid resistance alkali resistance becomes favorable.

SrO does not raise the density of an alkali free glass, does not raise a thermal expansion coefficient, does not reduce a strain point excessively, and improves meltability.

By making SrO 24 mass% or less, the devitrification characteristic of an alkali free glass becomes favorable, a thermal expansion coefficient falls, a density falls, and acid resistance and alkali resistance become favorable.

BaO suppresses powder phase of alkali-free glass, improves devitrification characteristics, and improves chemical resistance.

By making BaO 13.5 mass% or less, the density of an alkali free glass falls, a thermal expansion coefficient falls, a Young's modulus rises, meltability becomes favorable, and BHF resistance becomes favorable.

By making MgO + CaO + SrO + BaO 16 mass% or more, the meltability of glass becomes favorable. By making MgO + CaO + SrO + BaO 29.5 mass% or less, the density and thermal expansion coefficient of an alkali free glass fall.

In the composition 3, meltable, the refining property, is to improve the moldability, ZnO, SO _3, F, Cl, may be contained in a total amount less than 5% by weight of SnO _2. In addition, since a lot of air is required for the processing of the cullet, it is preferable not to contain PbB, As ₂ O ₃ , Sb ₂ O ₃ except that it is unavoidably mixed as impurities or the like.

According to the production process of the alkali-free glass of the present invention, to use in that it contains 10 to 100 mass% (B ₂ O ₃ equivalent) in a boron source boron source 100 mass% (B ₂ O ₃ equivalent) in anhydrous boric acid as described above Therefore, there are few bubbles in glass, and the alkali free glass with high homogeneity and flatness can be obtained.

In the conventional manufacturing method, orthoboric acid is used as the boron source, but in the presence of orthoboric acid, silica sand having a small particle size tends to aggregate, resulting in more bubbles in the alkali-free glass obtained, and homogeneity and flatness. The degree is lowered.

MEANS TO SOLVE THE PROBLEM In order to suppress the aggregation of a silica sand by the moisture contained in a glass raw material, and to suppress aggregation of a silica sand, the present inventors should reduce the moisture contained in a glass raw material, ie, orthoboric acid which contains many water molecules in a molecule | numerator. It was found that the amount of boric anhydride was increased by reducing the amount of.

Moreover, in the conventional manufacturing method, when a glass raw material contains an alkaline earth metal compound, the orthoboric acid melt | dissolved in the glass raw material inlet of a melting kiln and an alkaline earth metal compound tend to aggregate, and as a result, a bubble exists in the alkali free glass obtained More, and homogeneity and flatness are lowered.

The present inventors have lost one water molecule from orthoboric acid heated in a glass raw material inlet to metabolic acid, and agglomeration of metabolic acid and alkaline earth metal compound liquefied at 150 ° C or higher, and metabolic acid and alkaline earth metal compound In order to suppress aggregation, it was found that boric anhydride, which is a state in which more water molecules are lost from metaboric acid, may be used.

Moreover, according to the manufacturing method of the alkali free glass of this invention, the following effects can be expected.

(i) Since the amount of water in the glass raw material is suppressed, the heat of vaporization of water when melting the glass raw material is reduced. Therefore, the amount of energy consumed in the melting kiln is reduced by the less heat of vaporization, the energy can be reduced, and the productivity is improved.

(Ii) Since the water (β-OH) in the molten glass is reduced, Cl contained in the clarifier becomes HCl and the volatilization is suppressed by the following reaction. Therefore, the quantity of the clarifier can be reduced, and the processing burden of the exhaust gas containing HCl is reduced.

^{OH - + Cl - → HCl ↑} + O 2 -.

(Iii) Boric acid produced by the loss of one water molecule from orthoboric acid is well volatilized, but boric anhydride is not volatilized well, so that the amount of the boron source can be reduced, and the burden of treating the exhaust gas containing boric acid is reduced. Is reduced.

Although an Example is given to the following and this invention is concretely demonstrated to it, this invention is limited to these Examples and is not interpreted.

[Example 1]

In terms of mass percentage based on oxide, SiO ₂ : 60 mass%, Al ₂ O ₃ : 17 mass%, B ₂ O ₃ : 8 mass%, MgO: 3 mass%, CaO: 4 mass%, SrO: 8 mass% such that the composition is an alkali-free glass having, silica (average particle size (D _50): 40㎛), and as a boron source to adjust the boron compound and the other starting material of a glass base (母) composition material as well as a refining agent that with respect to the glass base material composition 100% by mass, a mixture of 0.3% by mass in terms of a Cl concentration of 0.7% by weight and SO ₃ in a concentration equivalent to prepare a glass raw material. A boron source was mixed in a ratio that represents the ortho-boric acid and anhydrous boric acid in Table 1 in terms of B ₂ O _3.

As shown to Fig.1 (a), the glass raw material 12 of the quantity after the vitrification becomes 250 g was put in the cylindrical rhodium crucible 14 with a bottom of 90 mm in height and 70 mm in outer diameter. The crucible 14 was put into a heating furnace, and 1550 ° C (glass viscosity (η) was equivalent to logη = 2.5 while blowing air at a dew point of 80 ° C from the side of the heating furnace without forcibly stirring the inside of the crucible 14). Temperature), and the glass raw material 12 was melted. After cooling the molten glass to the crucible 14th, as shown to FIG. 1 (b), the sample of 24 mm in length, 35 mm in width, and 1 mm in thickness from the center part of the alkali free glass 16 in the crucible 14 ( 18) cut out.

As shown in Fig. 2, the diameter of the vertical 18 mm and the vertical 15 mm regions (the upper margin 1.5 mm, the left and right margins 10 mm.) Of the central portion of the sample 18 having a length of 24 mm and a width of 35 mm is shown. A beam of 3 mm fluorescent X-rays was irradiated to 30 points in total of 6 vertical spots x 5 horizontal spots, and the composition of the alkali free glass was measured at each point.

Among the composition of the 30 point, by subtracting the minimum value of SiO ₂ (mass%) from the maximum value of SiO ₂ (% by mass), the composition was determined difference (ΔSi0 _2). The results are shown in Table 1.

Smaller ΔSi0 ₂ indicates that the variation in composition is smaller, that is, the homogeneity of the alkali free glass is good. From the results of Table 1, by using a 10 mass% (B ₂ O ₃ basis) or more boron-containing source to the anhydrous acid in a boron source 100 mass% (B ₂ O ₃ basis), which improves the homogeneity of the non-alkali glass It can be seen that.

[Example 2]

In terms of mass percentage based on oxide, SiO ₂ : 57 mass%, Al ₂ O ₃ : 12 mass%, B ₂ O ₃ : 9 mass%, MgO: 4 mass%, CaO: 6 mass%, SrO: 12 mass% of a composition such that the non-alkali glass, silica having (average particle size (D _50): 40㎛), as a boron source to adjust the boron compound, and other materials and to the parent composition of the raw glass, and the glass base composition as the refining agent with respect to the raw material 100% by weight, a mixture of 0.7% by mass in terms of a Cl to a concentration of 0.3% by mass in terms of the SO ₃ concentration, a 0.2% by weight SnO, and the glass raw material. A boron source was mixed in a ratio that represents the ortho-boric acid and anhydrous boric acid shown in Table 2 in terms of B ₂ O _3.

Using the glass raw material, an alkali free glass was produced in the same manner as in Example 1 except that the melting temperature was changed to 1420 ° C. (the temperature at which the glass viscosity (η) corresponds to logη = 2.5), and the sample was cut out. , by measuring the composition of the alkali-free glass, it was determined ΔSiO _2. The results are shown in Table 2.

From the result of Table 2, it turns out that the homogeneity of an alkali free glass improves by using boric anhydride as a boron source.

[Example 3]

In terms of mass percentage based on oxide, SiO ₂ : 60 mass%, Al ₂ O ₃ : 19 mass%, B ₂ O ₃ : 9 mass%, MgO: 4 mass%, CaO: 5 mass%, SrO: 3 mass% of a composition such that the non-alkali glass, silica having (average particle size (D _50): 40㎛), as a boron source to adjust the boron compound, and other materials and to the parent composition of the raw glass, and the glass base composition as the refining agent with respect to the raw material 100% by weight, a mixture of 0.7% by mass in terms of a Cl to a concentration of 0.3% by mass in terms of the SO ₃ concentration was then used as a glass material. A boron source was mixed in a ratio that represents the ortho-boric acid and anhydrous boric acid shown in Table 2 in terms of B ₂ O _3.

Using the glass raw material, except that the melting temperature was changed to 1570 ° C. (temperature at which the glass viscosity (η) corresponds to logη = 2.5), an alkali-free glass was produced in the same manner as in Example 1, and the sample was cut out. , by measuring the composition of the alkali-free glass, it was determined ΔSiO _2. The results are shown in Table 3.

From the result of Table 3, it turns out that the homogeneity of an alkali free glass improves by using boric anhydride as a boron source.

[Example 4]

In terms of mass percentage based on oxide, SiO ₂ : 60 mass%, Al ₂ O ₃ : 17 mass%, B ₂ O ₃ : 8 mass%, MgO: 5 mass%, CaO: 6 mass%, SrO: 4 mass% of a composition such that the non-alkali glass, silica having (average particle size (D _50): 40㎛), as a boron source to adjust the boron compound, and other materials and to the parent composition of the raw glass, and the glass base composition as the refining agent with respect to the raw material 100% by weight, a mixture of 0.7% by mass in terms of a Cl to a concentration of 0.3% by mass in terms of the SO ₃ concentration was then used as a glass material. A boron source was mixed in a ratio that represents the ortho-boric acid and anhydrous boric acid shown in Table 4 in terms of B ₂ O _3.

Using the glass raw material, an alkali free glass was produced in the same manner as in Example 1 except that the melting temperature was changed to 1500 ° C. (the temperature at which the glass viscosity (η) corresponds to logη = 2.5), and the sample was cut out. , by measuring the composition of the alkali-free glass, it was determined ΔSiO _2. The results are shown in Table 4.

From the result of Table 4, it turns out that the homogeneity of an alkali free glass improves by using boric anhydride as a boron source.

[Example 5]

In terms of mass percentage based on oxide, SiO ₂ : 60 mass%, Al ₂ O ₃ : 17 mass%, B ₂ O ₃ : 8 mass%, MgO: 3.2 mass%, CaO: 4.0 mass%, SrO: 7.6 mass% of a composition such that the non-alkali glass, silica having (average particle size (D _50): 40㎛), as a boron source to adjust the boron compound, and other materials and to the parent composition of the raw glass, and the glass base composition as the refining agent With respect to 100 mass% of raw materials, 0.7 mass% of Cl was converted in concentration conversion, and 0.3 mass% of SO ₃ in concentration conversion, and it was set as the glass raw material. A boron source is boric acid and anhydrous boric acid were mixed in o to B ₂ O ₃ in terms of the ratio shown in Table 5.

Using the glass raw material, 1550 ° C. (glass viscosity (η) was logη) in the same manner as in Example 1 except that the glass raw material and the cullet having the same composition as that of the target alkali free glass were mixed at a mass ratio of 1: 1. producing the alkali-free glass in temperature) equal to 2.5, and the cut sample, by measuring the composition of the alkali-free glass, was determined ΔSiO _2. The results are shown in Table 5.

Moreover, about the area | region of 24 mm in length and 5 mm in width in the center part of a sample, the number of bubbles which remain in glass was counted, and the number of bubbles per glass 1g was calculated | required. The results are shown in Table 5.

From the result of Table 5, even if a cullet is mixed, it turns out that the homogeneity of an alkali free glass improves and the number of bubbles is reduced by using boric anhydride as a boron source.

[Example 6]

The glass raw material of Example 5 and the cullet which has the composition similar to the composition of the target alkali free glass are mixed by mass ratio 1: 1, and this mixture is continuously thrown into the melting kiln of an actual production line, and it is 1550 degreeC (glass viscosity ( (eta) melt | dissolved at the temperature corresponded to log (eta) = 2.5), and it was set as the molten glass, and the molten glass was shape | molded so that thickness might be 0.7 mm by the float method. The molded glass was annealed to obtain a strip-shaped alkali free glass.

The surface roughness of the center part (about 6.6 m <2>) of the width direction in the lower surface of this alkali free glass was measured with the surface roughness shape measuring instrument (The Tokyo Precision Co., Surfcom 1400D). A lower surface is a surface which was in contact with molten Sn in a float bath, when shape | molding molten glass by the float method, and a width direction is a direction orthogonal to the advancing direction of a strip | plate-shaped alkali free glass. Measurement conditions were based on JIS B0601-1982, cutoff type: 2RC (phase compensation), cutting wavelength: 0.8-8.0 mm, minimum square linear correction.

In the chart of the surface roughness, the difference between the heights of the hills and the valleys adjacent to the peaks was determined, and the maximum height among the height differences was set as the maximum height. The results are shown in Table 6.

The lower the maximum height, the higher the flatness of the alkali free glass is. From the results of Table 6, the flatness is improved in by in anhydrous boric boron source 100 mass% (B ₂ O ₃ equivalent), using a boron source, which contains not less than 10 mass% (B ₂ O ₃ conversion), the alkali-free glass It can be seen that.

The alkali free glass obtained by the manufacturing method of this invention has few bubbles in glass, and is high in homogeneity and flatness. In addition, the chemical resistance because it contains B ₂ O _3, and the durability is also excellent. The alkali free glass is useful as glass substrates for displays, such as a liquid crystal display device.

In addition, all the content of the JP Patent application 2006-133690, a claim, drawing, and the abstract for which it applied on May 12, 2006 is referred here, and it introduces as an indication of the specification of this invention.

Claims (4)

In the manufacturing method of the alkali free glass which melts and shapes the glass raw material containing a silica sand and a boron source, The average particle diameter (D ₅₀₎ of the silica is, 15 ~ 60㎛ and, as the boron source, 100% by weight of anhydrous boric acid boron source (in terms of B ₂ O ₃₎ of 20 to 100 mass% (in terms of B ₂ O ₃₎ I use it to contain As a glass raw material, the glass raw material which has a composition used as an alkali free glass which has the following composition (1) as a mass percentage display on an oxide basis is used. The manufacturing method of the alkali free glass characterized by the above-mentioned. SiO ₂ : 50 to 66 mass%, Al ₂ O ₃ : 10.5 to 22 mass%, B ₂ O ₃ : 5 to 12 mass%, 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%. (One). The method of claim 1, The manufacturing method of the alkali free glass using the glass raw material which has a composition which becomes an alkali free glass which has the following composition (2) as a mass percentage display of an oxide reference | standard as the said glass raw material. SiO ₂ : 58 to 66 mass%, Al ₂ O ₃ : 15 to 22 mass%, B ₂ O ₃ : 5 to 12 mass%, MgO: 0 to 8 mass%, CaO: 0 to 9 mass%, SrO: 3 To 12.5 mass%, BaO: 0 to 2 mass%, MgO + CaO + SrO + BaO: 9 to 18 mass%. (2). The method of claim 1, The manufacturing method of the alkali free glass using the glass raw material which has a composition which becomes an alkali free glass which has the following composition (3) by the mass percentage display of an oxide reference | standard as the said glass raw material. SiO ₂ : 50 to 61.5 mass%, Al ₂ O ₃ : 10.5 to 18 mass%, B ₂ O ₃ : 7 to 10 mass%, MgO: 2 to 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). The method for producing an alkali-free glass according to any one of claims 1 to 3, wherein the composition of the alkali-free glass does not substantially contain BaO.

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