KR101384375B1 - Method of manufacturing glass plate - Google Patents

Abstract

According to this invention, in the manufacturing method of the glass plate which has the process of flowing and shape | molding molten glass G continuously supplied on molten tin M in the bathtub 22 on molten tin M, the glass of a glass plate Is an alkali free glass, and the temperature of the molten glass G by which the viscosity of molten glass G becomes 10 ⁴ dPa * s is 1200 degreeC or more. In each bottom brick 36 of the bathtub 22, the total content of the low melting point elements is 20% by mass or less in terms of oxide. The low melting point element is an element whose eutectic point in the two-component system of the oxide and tin oxide (SnO) of the low melting point element is lower than the maximum temperature of the upper surface 36a of the corresponding bottom brick 36.

Description

Manufacturing method of glass plate {METHOD OF MANUFACTURING GLASS PLATE}

The present invention relates to a method of manufacturing a glass plate.

As a shaping | molding method of a glass plate, the float method is used widely. The float method flows the molten glass continuously supplied on the molten tin in a bathtub, and shape | molds it in strip shape (for example, refer patent document 1).

The atmosphere on the molten tin becomes a reducing atmosphere containing hydrogen gas in order to prevent oxidation of the molten tin.

The bathtub is composed of, for example, a box-shaped metal case open upward, and bottom bricks and side bricks installed in the metal case. As the brick bottom and side brick, typically alumina (Al ₂ O ₃₎ - is used a brick type silica (SiO _2).

Japanese Patent Application Laid-Open No. 50-3414

Since the molten tin in a bathtub is heated from above, it becomes low temperature as it goes below. Therefore, the gas component (for example, oxygen, hydrogen, water, etc.) dissolved in molten tin supersaturates and precipitates on the upper surface of a relatively low temperature bottom brick, and forms bubbles. Moreover, the gas which permeate | transmitted in the bottom brick forms a bubble in the upper surface of a bottom brick.

When these bubbles grow to a certain size, they are spaced apart from the bottom brick upper surface, float to the interface between the molten tin and the molten glass, and form concave defects on the lower surface of the molten glass. As a result, a concave defect (FOBB (Fine Open Bottom Bubble)) is formed on the contact surface (bottom surface) with the molten tin of the glass plate which is the product.

Conventionally, since the place where FOBB generate | occur | produces was dispersed, the yield of the glass plate was low. In particular, the present inventors have found that the glass of the glass plate is remarkable when the glass of the glass plate is an alkali free glass having a high molding temperature as compared with general soda lime glass.

This invention is made | formed in view of the said subject, and an object of this invention is to provide the manufacturing method of the glass plate of the alkali free glass with a favorable yield.

In order to solve the said subject, the manufacturing method of the glass plate by one aspect of this invention,

In the manufacturing method of the glass plate which has a process of flowing and shape | molding the molten glass continuously supplied on the molten tin in a bathtub on the said molten tin,

The glass of the said glass plate is an alkali free glass, the temperature of the said molten glass whose viscosity of the said molten glass turns into 10 ⁴ dPa * s is 1200 degreeC or more,

In each bottom brick of the bath, the content of the total of the low melting point elements is 20% by mass or less in terms of oxides,

The low melting point element is an element whose eutectic point in the two-component system of the oxide of the low melting point element and tin oxide (SnO) is lower than the maximum temperature of the upper surface of the corresponding bottom brick.

According to this invention, the manufacturing method of the glass plate of the alkali free glass with a good yield is provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the float bath used at the shaping | molding process of the alkali free glass plate by one Embodiment of this invention.
It is a figure which shows the relationship between the wettability of the molten tin with respect to a bottom brick by one Embodiment of this invention, and the shape of the bubble formed on a bottom brick.
FIG. 3 is a diagram showing a relationship between wettability of molten tin with respect to a conventional bottom brick and the shape of bubbles formed on the bottom brick.
4 is a SEM photograph of a cut surface of the crucible according to Example 1. FIG.
FIG. 5: is explanatory drawing of the test which examines the number of the defect formed in the glass for evaluation in Example 1. FIG.
6 is a SEM photograph of a cut surface of the crucible according to Comparative Example 1. FIG.
FIG. 7 is an enlarged SEM photograph of part of FIG. 6.
8 is a map of Sn elements obtained by elemental analysis of the same region as the SEM photograph of FIG. 7 by EDS.
9 is a map of Al elements obtained by elemental analysis of the same region as the SEM photograph of FIG. 7 by EDS.
10 is a map of Si elements obtained by elemental analysis of the same region as the SEM photograph of FIG. 7 by EDS.
11 is a SEM photograph of a cut surface of the crucible according to Reference Example 1. FIG.

Hereinafter, the present invention will be described in detail with reference to the drawings. In addition, in the following drawings, the same or corresponding code | symbol is attached | subjected to the same or corresponding structure, and description is abbreviate | omitted.

The manufacturing method of the glass plate which concerns on this embodiment has a melting process, a shaping | molding process, a slow cooling process, and a cutting process, for example.

A melting process melt | dissolves the glass raw material which mixed and manufactured several types of raw materials, and obtains a molten glass. After inject | pouring into a melting furnace, a glass raw material melt | dissolves by the radiant heat of the flame sprayed from a burner, and turns into molten glass.

The shaping | molding process continuously supplies the molten glass obtained by a melting process on molten tin in a bathtub, flows a molten glass on molten tin, and shape | molds, and obtains a plate-shaped glass (so-called glass ribbon). The plate glass is cooled while flowing in a predetermined direction and is pulled out of the molten tin.

The slow cooling process cools the plate glass obtained by a shaping | molding process in a slow cooling furnace. The plate glass is slowly cooled while being conveyed horizontally in the slow cooling furnace from the inlet of the slow cooling furnace toward the outlet.

The cutting process cuts the plate-shaped glass cooled by the slow cooling process to predetermined dimension with a cutter. In a cutting process, the width direction both edge part (so-called ear | edge part) of plate glass is excised. This is because both edge portions in the width direction of the plate glass become thick under the influence of surface tension and the like.

In this way, the glass plate which is a product is obtained. Glass of the glass sheet is a alkali-free glass that is substantially free of alkali metal oxides _{(Na 2 O, K 2 O} , Li 2 O , etc.). 0.1 mass% or less of the total amount of content of an alkali metal oxide may be sufficient as an alkali free glass, for example, and it is used as a board | substrate for liquid crystal displays.

The alkali free glass is, for example, in terms of mass% based on an oxide basis, SiO ₂ : 50% to 73% (preferably 50 to 66%), Al ₂ O ₃ : 10.5% to 24%, B ₂ O ₃ : 0% to 12%, MgO: 0% to 8%, CaO: 0% to 14.5%, SrO: 0% to 24%, BaO: 0% to 13.5%, ZrO ₂ : 0% to 5%, and MgO + CaO + SrO + BaO: 8% to 29.5% (preferably 9% to 29.5%).

The alkali-free glass, in the case to both high distortion point and a high solubility, as preferably shown in oxide-based mass%, SiO _2: 58% to _{66%, Al 2 O 3:} 15% to 22%, B ₂ O ₃ : 5%-12%, MgO: 0%-8%, CaO: 0%-9%, SrO: 3%-12.5%, BaO: 0%-2%, MgO + CaO + SrO + BaO : 9% to 18%.

The alkali-free glass, in particular, when it is desired to obtain a high strain point, is preferably expressed in terms of mass% on the basis of oxide, SiO ₂ : 54% to 73%, Al ₂ O ₃ : 10.5% to 22.5%, B ₂ O ₃ : 0% to 5.5%, MgO: 0% to 8%, CaO: 0% to 9%, SrO: 0% to 16%, BaO: 0% to 2.5%, MgO + CaO + SrO + BaO: 8% to 26% %to be.

In the case of an alkali free glass, the temperature of the molten glass in which the viscosity of a molten glass turns into 10 ⁴ dPa * s (poise) is 1200 degreeC or more. The place where the viscosity of a molten glass becomes about 10 <^4> dPa * s is normally set in the vicinity of the inlet 12 of the float bath 10 (refer FIG. 1) used at a shaping | molding process. The molten glass supplied on the molten tin M in the inlet 12 of the float bath 10 is shape | molded, flowing in a predetermined direction.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the float bath used at the shaping | molding process of the glass plate by one Embodiment of this invention.

The float bath 10 (hereinafter, simply referred to as the "bath 10") causes the molten glass G continuously supplied on the molten tin M in the bath 22 to flow on the molten tin M. Mold. The molten glass G is supplied on the molten tin M near the inlet 12 of the bath 10, and then cooled while flowing in a predetermined direction, and molten tin near the outlet 14 of the bath 10. It is raised from (M).

The bath 10 is connected to the tub 22 accommodating the molten tin M, the side walls 24 and the side walls 24 installed along the outer circumferential upper edge of the tub 22, and upwards of the tub 22. And a ceiling 26 to cover. The ceiling 26 is provided with a gas supply path 30 for supplying a reducing gas to the space 28 formed between the tub 22 and the ceiling 26. Moreover, the heater 32 as a heating source penetrates through the gas supply path 30.

The gas supply passage 30 supplies a reducing gas to the space 28 in the bath 10 in order to prevent oxidation of the molten tin M. The reducing gas contains, for example, 1 to 15 vol% of hydrogen gas and 85 to 99 vol% of nitrogen gas. The space 28 in the bath 10 is set to an air pressure higher than atmospheric pressure in order to prevent air from entering into the gap between bricks constituting the side wall 24.

In order to adjust the temperature distribution in the bath 10, the heater 32 is provided in multiple numbers at intervals, for example in the flow direction (X direction) and the width direction (Y direction) of molten glass G. The output of the heater 32 is controlled such that the temperature of the molten glass G is lowered toward the outlet 14 from the inlet 12 of the bath 10. In addition, the output of the heater 32 is controlled so that the thickness of the molten glass G may become uniform in the width direction (Y direction).

The bathtub 22 is comprised of the box-shaped metal case 34 opened upward, and the bottom brick 36 and the side brick 38 installed in the metal case 34. As shown in FIG. The metal case 34 prevents the atmosphere from entering the tub 22 from the side or the bottom. The plurality of bottom bricks 36 are two-dimensionally arranged at a slight interval such that they do not come into contact with each other by thermal expansion. The plurality of bottom bricks 36 are surrounded by a plurality of side bricks 38 arranged in an annular fashion.

Since molten tin M in the bathtub 22 is heated from above by the heater 32, it becomes low temperature as it goes below. Therefore, gas components (for example, oxygen, hydrogen, water, etc.) dissolved in the molten tin M are supersaturated and precipitated on the upper surface 36a of the relatively low temperature bottom brick 36 to form bubbles B. . Moreover, the gas (for example, hydrogen etc.) which permeate | transmitted in the bottom brick 36 forms the bubble B in the upper surface 36a of the bottom brick 36. FIG.

When these bubbles B grow to a certain size, they are spaced apart from the upper surface 36a of the bottom brick 36, float to the interface between the molten tin M and the molten glass G, and the molten glass G A concave defect is formed on the lower surface of the As a result, the concave defect FOBB is formed in the contact surface (bottom surface) with the molten tin M of the glass plate which is the product.

The present inventors have focused on decreasing the number of bubbles B as the size of one bubble B increases, when the total mass of bubbles B generated per unit time is the same. In order for the bubble B to grow large on the bottom brick 36, it is important to lower the wettability of the molten tin M to the bottom brick 36.

It is a figure which shows the relationship between the wettability of the molten tin with respect to a bottom brick by one embodiment of this invention, and the shape of the bubble formed on a bottom brick. 3 is a diagram showing a relationship between wettability of molten tin with respect to a conventional bottom brick and the shape of bubbles formed on the bottom brick. The wettability of the molten tin with respect to the bottom brick of this embodiment of FIG. 2 is lower than the wettability of the molten tin with respect to the conventional bottom brick of FIG. "Low wettability" means that molten tin is hard to get wet with a bottom brick, and "high wettability" means that molten tin is easy to get wet with a bottom brick. For convenience of description, the shape of the bubble at the time of high wettability is demonstrated first.

Conventionally, as shown in FIG. 3, since wettability is high, the contact angle (theta) 100 of the molten tin M with respect to the bottom brick 6 is small, and the contact area of the bottom brick 6 and the bubble B100 is small. . Therefore, since the molten tin (M) is to be drawn in between the bottom brick (6) and the bubble (B100), the bubble (B100) is easily separated from the bottom brick (6) before large growth, and small bubbles (B100) Many are formed.

In general, the wettability of the molten metal to the oxide is low, and therefore, the wettability of the molten tin M to the bottom brick 6 at the start of production of the glass plate is low. However, with the passage of time, the tin oxide slightly contained as an impurity in the molten tin M and the bottom brick 6 react to form a reaction layer (denatured layer) on the surface of the bottom brick 6. It is thought that wettability increases.

On the other hand, in this embodiment, in order to suppress reaction of molten tin M and the bottom brick 36, as each bottom brick 36, content of the sum total of a low melting-point element is 20 mass% or less in oxide conversion. Use brick. The "low melting point element" is an element whose eutectic point in the bicomponent system of the oxide of the said low melting point element and tin oxide (SnO) is lower than the maximum temperature of the upper surface 36a of the corresponding bottom brick 36. As shown in FIG. If the temperature is higher than the eutectic point, a liquid phase is generated, so that the reaction between the oxide of the low melting point element and the tin oxide proceeds rapidly. Tin oxide is contained in molten tin M as a trace amount as an impurity, and tin oxide in molten tin M selectively reacts with a portion having a high concentration of low melting point element in the bottom brick 36. The tin oxide contained in the molten tin M is contained in the bath 10 from air introduced into the bath 10 when the side wall 24 is opened to the atmosphere for production reasons, or from a gap between bricks constituting the side wall 24. It is formed by exposing molten tin (M) to the entrained air.

Here, "the content of the sum total of a low melting point element" is content of one low melting point element when the number of low melting point elements is one, and is a content of the sum total of several low melting point elements when there are a plurality of low melting point elements. .

Since the maximum temperature of the upper surface 36a of the bottom brick 36 differs for every bottom brick 36 (it is lower on a downstream side), the kind of low melting point element may differ for every bottom brick 36. As shown in FIG. In the vicinity of the outlet 14 of the bath 10, since the maximum temperature of the upper surface 36a of the bottom brick 36a is low, the low melting point element does not need to exist in the bottom brick 36.

As a low melting point element, silicon (Si) etc. are mentioned, for example. The eutectic point of silicon oxide (SiO ₂ ) and tin oxide is about 850 ° C., which is lower than the maximum temperature of the upper surface 36a of most bottom bricks 36.

In this embodiment, in each bottom brick 36, since content of the sum total of a low melting-point element is 20 mass% or less (preferably 15 mass% or less, More preferably, 10 mass% or less) in oxide conversion, each The bottom brick 36 and the molten tin M hardly react. When the total content of the low melting point element is 20% by mass or less in terms of oxide, most of the low melting point element constitutes an oxide with other elements in the bottom brick 36, and the melting point of the oxide is determined by the top surface of the bottom brick 36 ( This is because it is higher than the maximum temperature of 36a). Since each bottom brick 36 and molten tin M hardly react, even when time passes from the start of production of a glass plate, the wettability of molten tin M with respect to each bottom brick 36 is low.

In addition, in this embodiment, although the content of the sum total of the low melting point elements in each bottom brick 36 is 20 mass% or less in oxide conversion, the content of the sum total of the low melting element in all the bottom bricks 36 is oxide conversion. It may not be 20 mass% or less. The maximum temperature of the upper surface of the bottom brick is below the temperature of the molten glass G such that the viscosity of the molten glass G becomes 10 ⁴ dPa · s, and the eutectic melting point in the two-component system of the oxide and tin oxide of the low melting point element The content of the sum total of the low melting point elements should just be 20 mass% or less in conversion of oxide, and the at least 1 bottom brick which is temperature exceeding may exceed 0 mass%.

Since the wettability of the molten tin M with respect to each bottom brick 36 is low, as shown in FIG. 2, the contact angle (theta) of molten tin M with respect to the bottom brick 36 is large, and a bottom brick ( 36) and the contact area of the bubble B is large. Therefore, molten tin M is hard to pull in between the bottom brick 6 and the bubble B, and the bubble B is not spaced apart from the bottom brick 36 until it grows large.

As described above, according to the present embodiment, since the size of each bubble B is increased, when the total mass of bubbles B generated per unit time is the same, the number of bubbles B generated per unit time is reduced. As a result, the number of FOBBs formed on the bottom surface of the glass plate decreases, and the yield of the glass plate increases. This effect is remarkably obtained when the glass of a glass plate is an alkali free glass for the following (1)-(2) reasons.

(1) Compared with general soda-lime glass, the alkali free glass has the high shaping | molding temperature of molten glass G, and the temperature of the upper surface 36a of the bottom brick 36 is high. Therefore, when the chemical composition of the bottom brick 36 is the same, reaction of the bottom brick 36 and molten tin M will advance easily.

(2) Since alkali-free glass is different from soda-lime glass and does not substantially contain an alkali metal element (for example, Na and K), the nephelin ((Na, K) AlSiO ₄ of the bottom brick 36 is included. Almost no tug-of-war occurs. Nephlinization forms a dense glass layer on the bottom brick 36, and suppresses the permeation of gas from the inside of the bottom brick 36 to the upper surface 36a. In alkali free glass, since nephelinization hardly occurs, the total mass of the bubble B which generate | occur | produces per unit time increases.

In addition, in this embodiment, since each bottom brick 36 and molten tin M hardly react as mentioned above, deterioration of the upper surface 36a of the bottom brick 36 is suppressed, and the Desorption is suppressed. Since the desorbed particles rise to the interface between the molten tin M and the molten glass G to become a defect of the molten glass G, the quality of the glass plate can be improved by suppressing the detachment of the particles.

A bottom brick 36 as, for example, alumina (Al ₂ O ₃₎ - calcia (CaO) based brick, or alumina (Al ₂ O ₃₎ - zirconia (ZrO ₂₎ based viscosity be fired bricks are used, such as a brick do. In viscous calcined bricks, SiO ₂ or the like is used as a sintering aid, and there is a portion having a high SiO ₂ concentration.

The alumina-calcia-based brick contains, for example, Al ₂ O ₃ : 40% to 85%, CaO: 10% to 40%, and SiO ₂ : 0.5% to 20% in terms of mass% on an oxide basis. SiO ₂ content is preferably from 15 to% by mass or less, more preferably, more preferably 10% by mass is 7% or less, particularly preferably 3 mass% or less, and particularly preferably at most 1% by weight .

The alumina-zirconia-based brick contains, for example, an Al ₂ O ₃ : 40% to 55%, a ZrO ₂ : 30% to 45%, and an SiO ₂ : 0.5% to 20% in terms of mass% on an oxide basis. SiO ₂ The content is preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 7% by mass or less, particularly preferably 3% by mass or less, and particularly preferably 1% by mass or less.

Similar to the bottom brick 36, the side brick 38 may have a content of a total of the low melting point elements in terms of oxide of 20% by mass or less, or may exceed 20% by mass. The molten glass G is inside the side brick 38 at the time of shaping | molding, and the bubble formed in the inner wall surface of the side brick 38 does not cause FOBB.

In addition, although the glass plate of the said embodiment can be used as a board | substrate of a liquid crystal display, a use may be various. For example, a glass plate may be used as a substrate of an organic EL display and a cover glass of a touch panel.

[Example]

Hereinafter, the present invention will be specifically described by way of examples.

[Example 1]

First, bricks are processed to prepare a crucible, metal tin is placed in the prepared crucible, placed in an electric furnace, and the atmosphere in the electric furnace is replaced, and then the metal tin is melted at 1000 ° C. for 60 minutes to melt molten crucible The reactivity of was investigated.

As the brick, alumina (Al ₂ O ₃₎ - were prepared calcia (CaO) based masonry brick A. The brick A is expressed in terms of mass% based on the oxide, and SiO ₂ : 5.7%, Al ₂ O ₃ : 66.0%, CaO: 26.0%, MgO: 1.5%, Na ₂ O: 0.3%, Fe ₂ O ₃ : 0.1% And other components are less than 0.1%, respectively. The chemical composition of the brick A was measured by the fluorescent X-ray analyzer (Rigaku Denki Kogyo Co., Ltd., ZSX100e).

The crucible was processed into a bottomed cylindrical shape (inner diameter 6 mm, inner dimension height 6 mm, bottom wall thickness 3 mm, side wall thickness 2 mm).

As the metal tin, one having a purity of 99.95 mass% (manufactured by Kanto Chemical Co., Ltd., Limited Express) was used. The metal tin was weighed so that the thickness of the molten tin was 5 mm and placed in the crucible.

The atmosphere in the electric furnace was evacuated to 1 kPa by vacuum pump, and then gas was supplied into the electric furnace through the gas supply pipe to be replaced. As the gas, nitrogen gas having an oxygen concentration of 1000 vol ppm was used. Nitrogen gas is used because nitrogen gas has low reactivity with oxygen gas and does not affect the oxygen concentration.

The reactivity of the molten tin with the crucible was cut after solidifying the crucible cooled to room temperature with a resin, and the cut surface was observed by observing with a SEM (Scanning Electron Microscope, manufactured by Keyence, Inc., VE-9800).

4 shows an SEM photograph of the cut surface of the crucible according to Example 1. FIG. As apparent from FIG. 4, no reaction layer with the molten tin 44 was observed on the inner bottom surface of the crucible 41. In addition, it is understood that the gap 45 is partially formed between the crucible 41 and the molten tin 44, so that the wettability of the molten tin 44 with respect to the crucible 41 is low.

FIG. 5 shows a test for examining the number of defects formed in the glass for evaluation in Example 1. FIG. In this test, the crucible 51 which processed the brick A was prepared, the metal tin was put into the prepared crucible 51, and the glass 53 for evaluation was put on the carbon jig 52. Subsequently, after installing the crucible 51 in the electric furnace of a glove box, replacing the atmosphere in an electric furnace, the temperature in an electric furnace is raised, the glass 53 for evaluation is thermally deformed, and the molten tin 54 is carried out. On top. Subsequently, after maintaining the temperature in an electric furnace at 1100 degreeC for 10 minutes, the temperature in the electric furnace was lowered to 800 degreeC, and the solidified glass 53 for evaluation was pulled out from the molten tin 54 manually. Then, the glass 53 for evaluation was slow-cooled in the electric furnace, and the number of FOBBs formed in the part which contacted the molten tin 54 of the glass 53 for evaluation was investigated.

The crucible 51 was processed into a bottomed cylindrical shape (inner diameter 60 mm, inner dimension height 40 mm, bottom wall thickness 10 mm, side wall thickness 10 mm).

As the metal tin, one having a purity of 99.95 mass% (manufactured by Kanto Chemical Co., Ltd., Limited Express) was used. The metal tin was weighed so that the thickness of the molten tin was 20 mm and placed in the crucible.

As the glass 53 for evaluation, an alkali free glass plate (40 mm length, 40 mm width, 0.7 mm thickness) was prepared. As a non-alkali glass plate, the display of the oxide-based _{mass%, SiO 2: 60.0%,} Al 2 O 3: 17.0%, B 2 O 3: 8.0%, MgO: 3.0%, CaO: 4.5%, SrO: 7.5% It contained. The chemical composition of the glass plate was measured by the fluorescence X-ray analyzer (The Rigaku Denki Kogyo Co., Ltd. make, ZSX100e).

The atmosphere in the electric furnace was evacuated to 1 kPa by vacuum pump, and then gas was supplied into the electric furnace through the gas supply pipe to be replaced. As the gas, nitrogen gas having a hydrogen concentration of 10% by volume was used.

The number of defects FOBB formed on the glass 53 for evaluation is the part (5 mm x 5) which contacted with the molten tin 54 of the glass 53 for evaluation after cooling the glass 53 for evaluation to room temperature. mm) was examined by observing with an optical microscope. The number of large defects (greater than 300 micrometers in diameter) was 0, and the number of small defects (10-300 micrometers in diameter) was two. In addition, the total number of the number of small defects and the number of big defects was 10% or less compared with the case of the comparative example 1 mentioned later.

The reason why the number of defects is small is that the brick A which is the material of the crucible 51 has a small content of Si which is a low melting point element. Since the content of Si is small, as shown in FIG. 4, the crucible 41 and the molten tin 44 hardly react, and the wettability of the molten tin 44 with respect to the crucible 41 is low. Since the wettability is low, bubbles formed on the inner bottom of the crucible, as shown in FIG. 3, are less likely to float, grow large with bubbles maintained, and as a result, the number of small defects is small.

[Example 2]

In the second embodiment, alumina (Al ₂ O ₃₎ - calcia (CaO) based in the same manner as in the preparation of a brick masonry B, and Example 1, was examined the number of defects formed on the glass for evaluation. Brick B is expressed in terms of mass% based on oxide, SiO ₂ : 5.8%, Al ₂ O ₃ : 82.4%, CaO: 10.2%, MgO: 1.2%, Na ₂ O: 0.2%, Fe ₂ O ₃ : 0.2% And other components are less than 0.1%, respectively.

The number of large defects (greater than 300 micrometers in diameter) is zero, and the number of small defects (10-300 micrometers in diameter) is ten or less.

[Example 3]

In the third embodiment, alumina (Al ₂ O ₃₎ - zirconia (ZrO ₂₎ based in the brick masonry C in the same manner as in Example 1 except that the prepared was examined for the number of defects formed on the glass for evaluation. Brick C contains SiO ₂ : 13.5%, ZrO ₂ : 33.0%, Al ₂ O ₃ : 52.0%, Na ₂ O: 1.3% in terms of mass% of the oxide basis, and 0.1% of the other components, respectively. Is less than.

The number of large defects (greater than 300 micrometers in diameter) is zero, and the number of small defects (10 to 300 micrometers in diameter) is 15.

[Comparative Example 1]

In Comparative Example 1, except that brick D, which is an alumina (Al ₂ O ₃ ) -silica (SiO ₂ ) -based brick, was prepared, the reactivity of the brick and molten tin was examined in the same manner as in Example 1. Brick D is a mass% display based on oxide, and SiO ₂ : 58.0%, Al ₂ O ₃ : 37.0%, CaO: 0.4%, MgO: 0.1%, P ₂ O ₅ : 0.4%, Na ₂ O: 0.1% , K ₂ O: 0.9%, Fe ₂ O ₃ : 1.2%, TiO ₂ : 0.9%, ZrO ₂ : 0.1%, and the other components are less than 0.1%, respectively.

6 shows an SEM photograph of the cut surface of the crucible according to Comparative Example 1. FIG. FIG. 7 shows an enlarged SEM photograph of a portion of FIG. 6. As apparent from FIGS. 6 and 7, the reaction layer 66 with the molten tin 64 was observed at the inner bottom of the crucible 61. Moreover, since the crucible 61 and the molten tin 64 are in close contact, it turns out that the wettability of the molten tin 64 with respect to the crucible 61 is high.

8 is a map of Sn elements obtained by elemental analysis of the same region as the SEM image of FIG. 7 by EDS, FIG. 9 is a map of Al elements elementally analyzed by the same region as the SEM image of FIG. 7, and FIG. 10 is shown in FIG. The map of the Si element which elementally analyzed the same area | region as an SEM photograph by EDS is shown. 8 to 10, the higher the portion, the higher the element concentration. As EDS (Energy Dispersive X-ray Spectrometry), the one attached to the SEM was used.

As is apparent from Figs. 8 to 10, it can be seen that Sn is increased in the portion 67 having less Al and more Si in the inner bottom portion of the crucible 61. This indicates that the molten tin 64 selectively reacts with the portion of the high Si concentration in the crucible 61.

In addition, in the comparative example 1, except having used the said brick D as a brick, it carried out similarly to Example 1, and investigated the number of the defect formed in the glass for evaluation. As a result, the number of large defects (greater than 300 micrometers in diameter) was 0, and the number of small defects (diameter of 10-300 micrometers) was 60.

The reason for the large number of defects is that the brick D, which is a material of the crucible, has a large content of Si, which is a low melting point element. Since the Si content is large, as shown in FIGS. 6 and 7, the reaction layer 66 with the molten tin 64 is formed in the crucible 61 to form the molten tin 64 with respect to the crucible 61. Wetability is high. Since wettability is high, as shown in FIG. 2, the bubble formed on the inner bottom surface of a crucible floats in the small state, As a result, the number of small defects is large.

[Comparative Example 2]

In Comparative Example 2, brick E, which is an alumina (Al ₂ O ₃ ) -silica (SiO ₂ ) -based brick, was prepared, and the number of defects formed in the glass for evaluation was examined in the same manner as in Comparative Example 1. Brick E is in terms of mass% based on the oxide, SiO ₂ : 58.0%, Al ₂ O ₃ : 37.0%, CaO: 0.2%, MgO: 0.3%, Na ₂ O: 0.8%, K ₂ O: 0.9%, Fe ₂ O ₃ : 1.1%, TiO ₂ : 1.6%, and other components are less than 0.1%, respectively.

As a result, the number of large defects (greater than 300 micrometers in diameter) was 0, and the number of small defects (diameter of 10-300 micrometers) was 70.

[Referential Example 1]

In the reference example 1, it was carried out similarly to the comparative example 1 except having used the reducing gas which consists of 10 volume% hydrogen gas and 90 volume% nitrogen gas as gas supplied into the electric furnace after vacuuming. The reactivity of the molten tin was investigated.

The SEM photograph of the cut surface of the crucible by the reference example 1 is shown in FIG. As is apparent from FIG. 11, no reaction layer with molten tin 74 was seen in the crucible 71. In addition, it is understood that a gap 75 is partially formed between the crucible 71 and the molten tin 74, so that the wettability of the molten tin 74 with respect to the crucible 71 is low.

From the result of the reference example 1 and the result of the comparative example 1, it turns out that the trace amount oxygen gas contained in the atmosphere on the molten tin 74 affects the wettability of brick and molten tin. When the oxygen gas is dissolved in the molten tin and the SnO component in the molten tin reacts with the SiO ₂ component of the crucible 71 to form a reaction layer, the wettability is increased.

Table 1 shows the results of the evaluation of Examples 1 to 3 and Comparative Examples 1 and 2. In Table 1, the composition of the brick shows only SiO ₂ , Al ₂ O ₃ , CaO, MgO, and ZrO ₂ .

As mentioned above, although the manufacturing method of a glass plate was demonstrated by embodiment, an Example, etc., this invention is not limited to the said embodiment, Example, etc. Various modifications and improvements are possible within the scope of the present invention described in the claims.

This application claims the priority based on Japanese Patent Application No. 2012-072495 for which it applied to Japan Patent Office on March 27, 2012, and uses the whole content of Japanese Patent Application No. 2012-072495 for this international application. .

10: Float bath
12: Entrance of float bath
14: Exit of float bath
22: Bathtub
24: sidewall
26: ceiling
28: Space
30: gas supply furnace
32: heater
34: metal case
36: bottom brick
38: side brick
M: molten tin
G: molten glass

Claims (7)

In the manufacturing method of the glass plate which has a process of flowing and shape | molding the molten glass continuously supplied on the molten tin in a bathtub on the said molten tin,
The glass of the said glass plate is an alkali free glass, the temperature of the said molten glass whose viscosity of the said molten glass turns into 10 ⁴ dPa * s is 1200 degreeC or more,
In each bottom brick of the bath, the content of the total of the low melting point elements is 20% by mass or less in terms of oxides,
The low melting point element is an element whose eutectic point in the two-component system of the oxide and tin oxide (SnO) of the low melting point element is lower than the maximum temperature of the upper surface of the corresponding bottom brick,
The bottom brick is an alumina (Al ₂ O ₃ ) -Calcia (CaO) -based brick or alumina (Al ₂ O ₃ ) -zirconia (ZrO ₂ ) -based brick production method. In the manufacturing method of the glass plate which has a process of flowing and shape | molding the molten glass continuously supplied on the molten tin in a bathtub on the said molten tin,
The glass of the said glass plate is an alkali free glass, the temperature of the said molten glass whose viscosity of the said molten glass turns into 10 ⁴ dPa * s is 1200 degreeC or more,
The bathtub comprises a bottom brick,
The maximum temperature of the upper surface of the bottom brick is equal to or lower than the temperature of the molten glass such that the viscosity of the molten glass becomes 10 ⁴ dPa · s, and the eutectic point in the two-component system of the oxide and tin oxide (SnO) of the low melting point element is determined. The content of the sum total of the low melting point element is 20 mass% or less in oxide conversion, in the at least 1 bottom brick which is exceeding temperature,
The low melting point element is an element whose eutectic point in the two-component system of the oxide and tin oxide (SnO) of the low melting point element is lower than the maximum temperature of the upper surface of the corresponding bottom brick,
The bottom brick is an alumina (Al ₂ O ₃ ) -Calcia (CaO) -based brick or alumina (Al ₂ O ₃ ) -zirconia (ZrO ₂ ) -based brick production method. 3. The method according to claim 1 or 2,
The low melting point element is silicon (Si) manufacturing method of a glass plate. 3. The method according to claim 1 or 2,
The alkali-free glass is in oxide-based, in mass% shown, SiO _2: 50% to _{73%, Al 2 O 3:} 10.5% to _{24%, B 2 O 3:} 0% to 12%, MgO: 0% to 8%, CaO: 0% to 14.5%, SrO: 0% to 24%, BaO: 0% to 13.5%, ZrO ₂ : 0% to 5%, MgO + CaO + SrO + BaO: 8% to The manufacturing method of the glass plate which is 29.5%. 5. The method of claim 4,
The alkali-free glass is in oxide-based, in mass% shown, SiO _2: 58% to _{66%, Al 2 O 3:} 15% to _{22%, B 2 O 3:} 5% to 12%, MgO: 0% to 8%, CaO: 0% to 9%, SrO: 3% to 12.5%, BaO: 0% to 2%, MgO + CaO + SrO + BaO: 9% to 18%. 5. The method of claim 4,
The alkali-free glass is in oxide-based, in mass% shown, SiO _2: 54% to _{73%, Al 2 O 3:} 10.5% to _{22.5%, B 2 O 3:} 0% to 5.5%, MgO: 0% to 8%, CaO: 0% to 9%, SrO: 0% to 16%, BaO: 0% to 2.5%, MgO + CaO + SrO + BaO: 8% to 26%. delete

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