WO2011077734A1 - Glass plate manufacturing method and glass plate manufacturing apparatus - Google Patents

Abstract

Disclosed is a glass plate manufacturing method which includes: a melting step wherein a molten glass is obtained by melting a glass raw material; a forming step wherein a glass ribbon is formed of the molten glass by means of a down-draw method; a vaporization promoting step wherein vaporization of vaporization components from the molten glass surface and/or the glass ribbon surface is promoted; a cooling step wherein the glass ribbon is cooled; and a cutting step wherein a glass plate is obtained by cutting the glass ribbon.

Description

Glass plate manufacturing method and glass plate manufacturing apparatus

The present invention relates to a glass plate manufacturing method for manufacturing a glass plate using a downdraw method and a glass plate manufacturing apparatus particularly suitably used for this manufacturing method.

In a flat panel display (hereinafter referred to as “FPD”) such as a liquid crystal display or a plasma display, a thin glass plate having a thickness of, for example, 1.0 mm or less is used as a glass substrate. In recent years, the size of a glass plate for an FPD glass substrate has been increased. For example, the size of a glass plate called an eighth generation is 2200 mm × 2500 mm.

The down draw method is most often used to manufacture such a glass plate for an FPD glass substrate. For example, in the overflow down draw method, a ribbon of glass ribbon is continuously formed by overflowing molten glass from a groove of a forming apparatus. At that time, the glass ribbon is pulled downward, and the thickness is adjusted by the pulling speed. Then, a glass ribbon is cut | disconnected by predetermined length, and a glass plate is manufactured.

For example, Patent Document 1 discloses a molding unit which is a part of a glass plate manufacturing apparatus as shown in FIG. This molding unit includes a molding device 7 and a heat insulating structure 8 surrounding the molding device 7. The heat insulating structure 8 is for maintaining the temperature of the molten glass overflowing from the molding apparatus 7 by maintaining high-temperature air around the molding apparatus 7. Normally, except for the gate 81 through which the glass ribbon passes. It is a sealed structure.

Specifically, in the molding unit disclosed in Patent Document 1, the heat insulating structure 8 includes a container-shaped main body 8A that opens downward and a gate structure 8B that is disposed so as to close the opening of the main body 8A. ing. The inside of the gate structure 8B is hollow, and cooling air is supplied to the inside of the gate structure 8B through the cooling pipe 82. Thereby, in the shaping | molding unit disclosed by patent document 1, the glass ribbon 9 can be cooled immediately after formation.

Further, in the molding unit disclosed in Patent Document 1, the gate structure 8B is provided with a jet outlet 83 that jets cooling air from the cooling pipe 82 into a space covered with the main body 8A. The glass ribbon 9 is also cooled by the cooling air flowing into 81.

Special table 2009-519884

Here, high surface quality is required for glass plates for FPD glass substrates and glass plates for cover glasses. Therefore, it is important to prevent the surface of the glass plate from being damaged.

By the way, from the glass in the molten state (the molten glass and the glass ribbon immediately after the formation), volatile components are volatilized at the boundary surface in contact with air. The inventors of the present invention can form a desired compressive stress layer on both main surfaces of the glass plate by effectively utilizing this phenomenon in the downdraw method, and this can damage the surface of the glass plate. I thought it could be prevented.

However, when the cooling air is introduced into the heat insulating structure 8 as in the molding unit disclosed in Patent Document 1, the molten glass flowing down on the wall surface of the molding apparatus 1 is also cooled. Volatilization of volatile components from the glass surface is suppressed. As a result, it is not possible to form a compressive stress layer having a high stress value, and it is not possible to obtain a glass plate whose surface is hardly damaged (first problem).

Further, even if forced convection is generated in the vicinity of the gate 81 as in the molding unit disclosed in Patent Document 1, the upper air, that is, most of the air in the space covered by the main body 8A remains in that place. Therefore, it remains unchanged that volatilization of volatile components from the molten glass is suppressed (second problem).

In view of such circumstances, an object of the present invention is to provide a glass plate manufacturing method capable of obtaining a glass plate whose surface is hardly damaged. Moreover, this invention aims at providing the glass plate manufacturing apparatus which can accelerate | stimulate volatilization of the volatile component from the molten glass which overflows from a shaping | molding apparatus especially suitably used for this manufacturing method.

In order to solve the first problem, the present invention includes a melting step of melting a glass raw material to obtain a molten glass, a forming step of forming a glass ribbon from the molten glass by a downdraw method, and the molten glass And a volatilization promoting step for promoting volatilization of a volatile component from at least one surface of the glass ribbon, a cooling step for cooling the glass ribbon, and a cutting step for cutting the glass ribbon to obtain a glass plate. A glass plate manufacturing method is provided.

In order to solve the second problem, the present invention is an apparatus for forming a glass ribbon by causing molten glass to overflow from both sides of the groove and guiding and fusing the overflowed molten glass together on the wall surface; A heat insulating structure that surrounds the forming device and has a gate through which the glass ribbon formed by the forming device passes, and the heat insulating structure promotes volatilization of volatile components from the surface of the molten glass. In order to do so, a discharge port is provided for discharging the gas introduced along the molten glass flowing from the outside of the heat insulating structure into the heat insulating structure and flowing down on the wall surface of the molding apparatus, to the outside of the heat insulating structure. A glass plate manufacturing apparatus is provided.

According to the present invention, it is possible to obtain a glass plate in which a compressive stress layer having a high stress value is formed on both main surfaces and the surface is hardly damaged.

It is a schematic block diagram which shows the glass plate manufacturing apparatus which enforces the glass plate manufacturing method which concerns on one Embodiment of this invention. It is sectional drawing of the shaping | molding unit which is a part of glass plate manufacturing apparatus of 1st Embodiment. It is a perspective view of the shaping | molding unit shown in FIG. It is sectional drawing of the shaping | molding unit of a modification. It is sectional drawing of the shaping | molding unit of another modification. It is sectional drawing of another shaping | molding unit. It is sectional drawing of the shaping | molding unit which is a part of glass plate manufacturing apparatus of 2nd Embodiment. It is a graph which shows the relationship between the depth in the glass plate of Example 1, 2 and Si ratio. It is a graph which shows the relationship between the internal stress of the glass plate of Example 1, and depth. It is sectional drawing of the shaping | molding unit which is a part of the conventional glass plate manufacturing apparatus.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description relates to an example of the present invention, and the present invention is not limited to these.

<Glass plate manufacturing method>
A glass plate manufacturing method according to an embodiment of the present invention is performed by a glass plate manufacturing apparatus 100 as shown in FIG. 1, for example. The glass plate manufacturing apparatus 100 includes a melting tank 51, a fining tank 52, a forming apparatus 1, and a heat insulating structure 2 that surrounds the forming apparatus 1. In the melting tank 51, a melting step for melting the glass raw material to obtain the molten glass 3 is performed, and in the clarification tank 52, a clarification step for clarifying the molten glass 3 is performed. The forming apparatus 1 performs a forming process, and forms a glass ribbon 4 from the molten glass 3 by an overflow down draw method. In the heat insulating structure 2, a volatilization promoting step is performed to promote volatilization of volatile components from the surface of the molten glass 3, and in some cases, from the surface of the molten glass 3 and the glass ribbon 4 immediately after formation. Moreover, the glass plate manufacturing apparatus 100 includes a pulling device including a pair of rollers that pulls the glass ribbon 4 formed by the forming device 1 downward, a cooling device (not shown) that performs a cooling process for cooling the glass ribbon 4, A cutting device (not shown) that performs a cutting step of cutting the glass ribbon 4 at a predetermined length to obtain a glass plate. In addition, although not shown in figure, the stirring apparatus which improves the homogeneity of glass by stirring the molten glass 3 with a stirring blade etc. between the clarification tank 52 and the shaping | molding apparatus 1 may be arrange | positioned.

The glass raw material charged into the molten layer 51 is a glass such as borosilicate glass, aluminosilicate glass, aluminoborosilicate glass, soda lime glass, alkali silicate glass, alkali aluminosilicate glass, or alkali aluminogermanate glass. The prepared one can be used. The glass obtained by the production method of the present invention is not limited to the above, and any glass containing at least SiO ₂ and a volatile component may be used.

Here, the “volatile component” is a component that is more volatile than SiO ₂ , in other words, saturated vapor at the glass melting temperature (the temperature of the glass at which the viscosity of the glass is 1.0 × 10 ⁵ Pa · s or less). A component whose pressure is higher than that of SiO ₂ . Examples of the volatile component include Al ₂ O ₃ , B ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO, BaO, ZrO ₂ , and SnO ₂ . It is not limited to these. Since B ₂ O ₃ , alkali oxides (Li ₂ O, Na ₂ O, K ₂ O) and alkaline earth metal oxides (MgO, CaO, SrO, BaO) are highly volatile, the glass composition is Preferably, at least one of them is contained.

These volatile components, the saturated vapor pressure at the glass melting temperature higher than SiO _2, when or immediately after molding volatilizes earlier than SiO ₂ (glass in a molten state). In other words, in the molding process in which a glass ribbon is formed from molten glass, components other than SiO ₂ volatilize on the surface of the molten glass. As a result, the surface of the glass plate after molding has a content of Si atoms. A silica-rich layer that is larger than the content of Si atoms inside the glass is formed. Further, when the silica-rich layer is formed on the surface of the glass plate, compressive stress layers are formed on both main surfaces of the glass plate due to the difference in thermal expansion coefficient from the inside of the glass plate.

The content of the volatile component in the glass composition at the center position in the thickness direction of the glass plate is preferably 10% or more (or 15% or more), expressed as mass%, and is 30% or more. More preferably, it is 35% or more (or 40% or more). When the content of the volatile component in the glass composition is less than 10%, volatilization of the volatile component is not promoted, and a silica-rich layer or a compressive stress layer is hardly formed on the glass plate surface. On the other hand, when a large amount of volatile components are contained, volatilization increases excessively, making it difficult to homogenize the glass. Therefore, it is preferably 50% or less (or 45% or less, 42% or less), and more preferably 40% or less.

An example of a silicate glass for liquid crystal is aluminoborosilicate glass having substantially the following composition. In the present specification, hereinafter, all contents are expressed by mass%, and more preferable contents are shown in parentheses. In addition, “substantially” means to allow the presence of trace components inevitably mixed from industrial raw materials in a range of less than 0.1% by mass.
SiO ₂ : 50 to 70% (55 to 65%, 57 to 64%, 58 to 62%)
Al ₂ O ₃ : 5 to 20% (10 to 20%, 12 to 18%, 15 to 18%)
B ₂ O ₃ : 0 to 15% (5 to 15%, 6 to 13%, 7 to 12%)
MgO: 0 to 10% (0.01 to 5% or more, 0.5 to 4%, 0.5 to 2%)
CaO: 0-10% (1-9%, 3-8%, 4-7%, 4-6%)
SrO: 0 to 10% (0.5 to 9%, 3 to 8%, 3 to 7%, 3 to 6%)
BaO: 0 to 10% (0 to 8%, 0 to 3%, 0 to 1%, 0 to 0.2%)
ZrO ₂ : 0 to 10% (0 to 5%, 0 to 4%, 0 to 1%, 0 to 0.1%)

Another example of the silicate glass for liquid crystal is aluminoborosilicate glass having substantially the following composition.
SiO ₂ : 50 to 70% (55 to 65%, 58 to 62%)
Al ₂ O ₃ : 10-25% (15-20%, 15-18%)
B ₂ O ₃ : 5 to 18% (8 to 14%, 10 to 13%)
MgO: 0-10% (1-5%, 1-2%)
CaO: 0-20% (1-7%, 4-7%)
SrO: 0-20% (1-10%, 1-3%)
BaO: 0 to 10% (0 to 2%, 0 to 1%)
K ₂ O: 0 to 2% (0.1 to 2%, 0.1 to 0.5%)
SnO ₂ : 0 to 1% (0.01 to 0.5%, 0.01 to 0.3%)
However, the content of SnO ₂ in the above composition is a value converted by treating all Sn components having a plurality of valences as SnO ₂ .

The silicate glass for cover glass contains the following components as an essential component, for example.
SiO ₂ : 50 to 70% (55 to 65%, 57 to 64%, 57 to 62%)
Al ₂ O ₃ : 5 to 20% (9 to 18%, 12 to 17%)
Na ₂ O: 6-30% (7-20%, 8-18%, 10-15%)
Moreover, the following components may be included as arbitrary components.
Li ₂ O: 0 to 8% (0 to 6%, 0 to 2%, 0 to 0.6%, 0 to 0.4%, 0 to 0.2%)
B ₂ O ₃ : 0 to 5% (0 to 2%, 0 to 1%, 0 to 0.8%)
K ₂ O: 0 to 10% (1 to 6%, 2 to 5%, 2 to 4%)
MgO: 0-10% (1-9%, 2-8%, 3-7%, 4-7%)
CaO: 0-20% (0.1-10%, 1-5%, 2-4%, 2-3%)
ZrO ₂ : 0 to 10% (0 to 5%, 0 to 4%, 0 to 1%, 0 to 0.1%)

As an example of the silicate glass for the cover glass, there is an alkali aluminosilicate glass having substantially the following composition.
SiO ₂ : 50 to 70%
Al ₂ O ₃ : 5 to 20%
Na ₂ O: 6 to 20%
K ₂ O: 0 to 10%
MgO: 0-10%
CaO: more than 2% to 20%
ZrO ₂ : 0 to 4.8%
Furthermore, preferably, the following conditions are satisfied.
・ (SiO ₂ content) − (Al ₂ O ₃ content) /2=46.5 to 59%
-The content ratio of CaO / RO (where R is at least one selected from Mg, Ca, Sr and Ba) exceeds 0.3.-The sum of the SrO content and the BaO content is 10%. Less than (ZrO ₂ + TiO ₂ ) / SiO ₂ content ratio 0 to less than 0.07 B ₂ O ₃ / R1 ₂ O (where R1 is at least one selected from Li, Na and K) Content ratio of 0 to less than 0.1)

As another example of the silicate glass for the cover glass, there is an alkali aluminosilicate glass having substantially the following composition.
SiO ₂ : 58 to 68%
Al ₂ O ₃ : 8 to 15%
Na ₂ O: 10 to 20%
Li ₂ O: 0 to 1%
K ₂ O: 1 to 5%
MgO: 2-10%

In addition, the molten glass 3 may also be comprised substantially from said each component.

SiO ₂ is a component that forms a glass skeleton, and has an effect of improving the chemical durability and heat resistance of the glass. If the content is too low, the effect cannot be obtained sufficiently. If the content is too high, the glass tends to be devitrified, making it difficult to form, and increasing the viscosity, making it difficult to homogenize the glass. become.

B ₂ O ₃ is a component that lowers the viscosity of the glass and promotes melting and clarification of the glass. When there is too much content, the acid resistance of glass will fall and it will become difficult to homogenize glass.

Al ₂ O ₃ is a component forming a glass skeleton, and has an effect of improving the chemical durability and heat resistance of the glass. It also has the effect of increasing ion exchange performance and etching rate. If the content is too small, the effect cannot be obtained sufficiently. On the other hand, when there is too much content, the viscosity of glass will rise and it will become difficult to melt | dissolve, and acid resistance will fall.

MgO and CaO are components that lower the viscosity of the glass and promote glass melting and fining. Mg and Ca are advantageous components for improving the solubility while reducing the weight of the resulting glass because the proportion of the alkaline earth metal that increases the density of the glass is small. However, when the content is too large, the chemical durability of the glass is lowered.

SrO and BaO are components that lower the viscosity of the glass and promote the melting and clarification of the glass. Moreover, it is also a component which improves the oxidizability of a glass raw material and improves clarity. However, when the content is too large, the density of the glass is increased, the weight of the glass plate is not reduced, and the chemical durability of the glass is lowered.

Li ₂ O is one of the ion exchange components, and is a component that lowers the viscosity of the glass and improves the meltability and moldability of the glass. Li ₂ O is a component that improves the Young's modulus of glass. Furthermore, Li ₂ O has a high effect of increasing the compressive stress value among alkali metal oxides. However, if the Li ₂ O content is too high, the liquid phase viscosity is lowered and the glass is easily devitrified, making it difficult to mass-produce inexpensive glass using the downdraw method. Moreover, the thermal expansion coefficient of the glass becomes too high, the thermal shock resistance of the glass is lowered, and it becomes difficult to match the thermal expansion coefficient with peripheral materials such as metals and organic adhesives. Furthermore, there is an inconvenience that the ion exchange salt is rapidly deteriorated in the ion exchange process which is a step of strengthening the glass substrate. Moreover, since stress relaxation generate | occur | produces in the heating process after chemical strengthening and a compressive stress value falls because a low-temperature viscosity falls too much, sufficient intensity | strength cannot be obtained.

Na ₂ O is an ion exchange component, and is an essential component that lowers the high temperature viscosity of the glass and improves the meltability and formability of the glass. Moreover, it is a component which improves the devitrification resistance of glass. If the content is less than 6%, the meltability of the glass is lowered, and the cost for melting becomes high. Moreover, since ion exchange performance also falls, sufficient intensity | strength cannot be obtained. In addition, the coefficient of thermal expansion is excessively reduced, and it becomes difficult to match the coefficient of thermal expansion with peripheral materials such as metals and organic adhesives. Furthermore, since the glass tends to be devitrified and the devitrification resistance is lowered, the glass cannot be applied to the overflow downdraw method, so that mass production of inexpensive glass becomes difficult. On the other hand, if the content exceeds 20%, the low-temperature viscosity decreases, the thermal expansion coefficient becomes excessive, the impact resistance decreases, and the thermal expansion coefficient is difficult to match with peripheral materials such as metals and organic adhesives. . Further, since devitrification resistance is lowered due to deterioration of the glass balance, it is difficult to mass-produce inexpensive glass using the downdraw method.

K ₂ O is an ion exchange component and is a component that can improve the ion exchange performance of the glass by containing it. K ₂ O is a component that lowers the high-temperature viscosity of the glass to improve the meltability and moldability of the glass and at the same time improve the devitrification resistance. However, if the content of K ₂ O is too large, the low-temperature viscosity decreases, the thermal expansion coefficient becomes excessive, and the impact resistance decreases, which is not preferable when applied as a cover glass. In addition, it becomes difficult to match the thermal expansion coefficient with peripheral materials such as metals and organic adhesives. Moreover, since the devitrification resistance is lowered due to the deterioration of the glass balance, mass production of inexpensive glass using the downdraw method becomes difficult.

Na ₂ O and K ₂ O, or degrade the TFT characteristic eluted from the glass, since it is a component or to damage the substrate during the heat treatment the coefficient of thermal expansion of the glass is increased to a glass substrate for a display device When applying, it is not preferable to contain a large amount. However, by deliberately containing the above components in the glass, the basicity and meltability of the glass are increased and the valence fluctuates while suppressing deterioration of TFT characteristics and thermal expansion of the glass within a certain range. It is also possible to facilitate the oxidation of the metal and exhibit clarity.

ZrO ₂ is a component that significantly improves the ion exchange performance and increases the viscosity and strain point in the vicinity of the devitrification temperature of the glass. ZrO ₂ is also a component that improves the heat resistance of the glass. However, when the content of ZrO ₂ becomes too large, the devitrification temperature increases and the devitrification resistance decreases.

TiO ₂ is a component that improves ion exchange performance and a component that lowers the high-temperature viscosity of glass. However, when the content of TiO ₂ is too large, the devitrification resistance is lowered. Further, the glass is colored, which is not preferable for a cover glass. Further, since the glass is colored, the ultraviolet transmittance is also lowered, and therefore, when the treatment using the ultraviolet curable resin is performed, the ultraviolet curable resin cannot be sufficiently cured.

A refining agent can be added as a component for defoaming bubbles in the glass. The fining agent is not particularly limited as long as it has a small environmental burden and excellent glass fining properties. For example, it is made of a metal oxide such as tin oxide, iron oxide, cerium oxide, terbium oxide, molybdenum oxide and tungsten oxide. There may be mentioned at least one selected.

As ₂ O ₃ , Sb ₂ O _3, and PbO are substances that cause a reaction with valence fluctuation in molten glass and have the effect of clarifying the glass, but these are substances with a large environmental load. Therefore, in the glass plate of this embodiment, As ₂ O ₃ , Sb ₂ O ₃ and PbO are not substantially contained in the glass. In this specification, “substantially not containing As ₂ O ₃ , Sb ₂ O _3, and PbO” means less than 0.01% and intentionally not containing impurities.

Next, an especially preferable aspect is demonstrated about the silicate glass for liquid crystals. As will be described later, it is preferable that the molten glass 3 contains many volatile components from the viewpoint of increasing the stress value of the compressive stress layer. For silicate glass whose main component is SiO _2, the components other than SiO ₂ is for easily volatilize during relatively melt than SiO _2, a volatile component in a broad sense. Examples of the volatile component having high volatility in the glass composition exemplified above include B ₂ O ₃ , SnO ₂ (volatile as SnO), and K ₂ O. Accordingly, the content of these components is preferably high. However, if volatilization becomes excessive, problems occur during molding. Therefore, the upper limit of the content of B ₂ O ₃ is more preferably 14% by mass, and particularly preferably 13% by mass. Further, when the SnO ₂ content is high, devitrification may occur in the glass. Therefore, from the viewpoint of preventing devitrification of the glass, the upper limit of the SnO ₂ content is more preferably 0.5% by mass, and particularly preferably 0.3% by mass. Furthermore, since K ₂ O used as a glass melting accelerator dissolves from the glass plate and causes problems when added in a large amount, the upper limit of the content of K ₂ O is more preferably 0.5% by mass. .

In the glass plate manufacturing method of the present embodiment, the volatilization promoting step is performed in the heat insulating structure 2. For this reason, a silica-rich layer is formed on the surface of the manufactured glass plate. Hereinafter, this glass plate will be described.

(1) Silica-rich layer “Silica-rich layer” refers to the Si atom content in the center glass composition in the thickness direction of the glass plate as a reference value, and the ratio of the Si atom content in the glass composition to this reference value. The area | region from the position used as 1.05 or more to the main surface of a glass plate is shown.

The glass plate surface, the silica-rich layer is formed the content of SiO ₂ is larger than SiO ₂ content of the center in the thickness direction of the glass plate. The depth of the silica-rich layer is preferably more than 0 to 20 nm, more preferably more than 0 to 15 nm (further, 1 to 12 nm, 2 to 11 nm, 3 to 11 nm). Thereby, a compressive stress layer having a sufficient depth can be obtained. On the other hand, the depth of the silica-rich layer can be increased by promoting volatilization from the surface of the glass ribbon immediately after the formation. Arise. Therefore, the depth of the silica rich layer is preferably 30 nm or less.

In the silica-rich layer, the maximum value of the ratio of the Si atom content in the glass composition with respect to the reference value is preferably 1.06 or more, 1.08 or more (more preferably 1.10 or more, 1.12 or more). , 1.14 or more, 1.15 or more, 1.16 or more, 1.18 or more).

Alternatively, the maximum value of the Si atom content in the glass composition of the silica-rich layer is preferably 1% or more, more preferably 1.5% or more (more (2% or more, 2.5% or more, 3% or more) is more preferable.

Alternatively, the maximum value of the SiO ₂ content of the silica-rich layer is preferably 0.5% or more higher than the center SiO ₂ content in the thickness direction of the glass plate, preferably 1% or more (and 1.5 % Or more, 2% or more, 2.5% or more, 3% or more).

When the silica-rich layer satisfies the above conditions, a sufficient difference in thermal expansion coefficient can be obtained between the glass plate surface and the inside of the glass plate, and a compressive stress layer is formed on both main surfaces of the glass plate. Can do. Moreover, it becomes possible to improve the Vickers hardness and durability of the glass plate surface, and to prevent the glass plate from being broken.

Here, when the Si atom content or the SiO ₂ content of the silica-rich layer formed on the glass plate surface is less than the above range, a sufficient difference in thermal expansion coefficient is obtained between the glass plate surface and the inside of the glass plate. The compressive stress layer having a sufficiently large stress value cannot be formed. Or sufficient Vickers hardness and durability cannot be acquired.

On the other hand, if the Si atom content or SiO ₂ content of the silica-rich layer exceeds the above upper limit, the quality (physical characteristics, thermal characteristics, chemical characteristics) of the glass plate will change, and the conventional application will be changed. It may become unusable. For example, it becomes difficult to cut or etch a glass plate.

Further, in the silica-rich layer formed on the glass plate produced according to the present embodiment, the position where the Si atom content or the SiO ₂ content rate is the largest is not on the glass plate surface but more than 0 from the glass plate surface. May be in the range of 5 nm.

When a silica-rich layer is formed on the glass plate surface, a compressive stress layer is formed on the portions along the two main surfaces of the glass plate due to the difference in thermal expansion coefficient between the glass plate surface and the inside of the glass plate. A tensile stress layer is formed between the stress layers. According to the glass plate manufacturing method of the present embodiment, the stress profile drawn by plotting the compressive stress value and the tensile stress value becomes specific.

It is possible to form a compressive stress layer on both principal surfaces of the glass plate by rapidly cooling the glass ribbon in the cooling process, but the stress profile of the glass plate thus obtained is like a parabola. (The compressive stress layer in this case is caused by a difference in heat transfer between the glass plate surface and the inside of the glass plate due to a constant heat transfer coefficient in the glass). On the other hand, in the glass plate obtained by the glass plate manufacturing method of the present embodiment, the compressive stress layer is formed by the volatilization promoting step, that is, the difference in thermal expansion coefficient due to the silica rich layer is different from that of the compressive stress layer. Contributes to formation. For this reason, a compressive stress layer is formed in a region close to the main surface of the glass plate (that is, the depth of the compressive stress layer is shallow). In addition, the compressive stress layer has a larger stress value than that obtained when the compressive stress layer is formed by rapid cooling (the compressive stress layer and the tensile stress layer are balanced, so that the compressive stress layer becomes thin when the compressive stress layer becomes thin). The stress value becomes higher). That is, since the compressive stress layer having a larger stress value than the case where the compressive stress layer is formed by rapid cooling is formed near the surface of the glass plate obtained by the glass plate manufacturing method of the present embodiment, the surface of the glass plate Is more difficult to scratch. Furthermore, the tensile stress layer has a substantially constant stress value except for both sides in the thickness direction of the glass plate. That is, the stress profile of the glass plate obtained by the glass plate manufacturing method of this embodiment has a flat U shape with a wide bottom.

(2) Compressive stress layer It is preferable that the depth of a compressive stress layer is 50 micrometers or less. The depth of the compressive stress layer can be increased by promoting volatilization from the surface of the glass ribbon immediately after formation, but this causes deviations from the proper forming conditions or lowers productivity. It is. The depth of the compressive stress layer is more preferably 45 μm or less, still more preferably 40 μm or less, and particularly preferably 38 μm or less. In addition, the compression layer stress layer depth in this specification has shown the depth of the compression stress layer formed in the part along one main surface of a glass plate. That is, the compressive stress layer having the above-mentioned depth is formed on each of both main surfaces of the glass plate.

The depth of the compressive stress layer is preferably more than 10 μm. If the compression stress layer has a certain depth, it is possible to prevent the glass plate from being easily broken by fine scratches resulting from handling. In order to prevent breakage of the glass plate even if deeper scratches are made, the depth of the compressive stress layer is more preferably 15 μm or more, and further preferably 20 μm or more (particularly 25 μm or more, 30 μm or more, 35 μm). Above).

Or it is preferable that the depth of a compressive-stress layer is less than 1/13 of the plate | board thickness of a glass plate, and less than 1/15 (Furthermore, less than 1/17, less than 1/20, less than 1/22, 1 More preferably, it is less than / 24).

The maximum compressive stress value of the compressive stress layer is preferably 4 MPa or less. It is because the workability of a glass plate will worsen if it exceeds 4 MPa. The maximum compressive stress value is more preferably 3.7 MPa or less, still more preferably 3.5 MPa or less (particularly 3.0 MPa or less, 2.8 MPa or less).

In addition, the maximum compressive stress value of the compressive stress layer is preferably 0.4 MPa or more from the viewpoint of improving the mechanical strength of the glass plate, and is 1 MPa or more (more preferably 1.5 MPa or more, 2 MPa or more). More preferably.

In addition, the “stress value” in the present specification is a value when measured every 10 μm range in the thickness direction from the main surface of the glass plate. Therefore, locally, there may be a compressive stress value exceeding the range of the compressive stress value (the same applies to the tensile stress value described later).

(3) Tensile Stress Layer As described above, the tensile stress layer formed inside the glass plate has a substantially constant stress value except for both sides in the thickness direction of the glass plate. Difference between the maximum value and the minimum value of the tensile stress value in the central portion 4/5 of the tensile stress layer excluding 1/10 on both sides in the thickness direction of the glass plate (hereinafter simply referred to as “tensile center region”) (tensile stress The value deviation) is preferably 0.2 MPa or less, more preferably 0.15 MPa or less (more preferably 0.10 MPa or less, 0.05 MPa or less, 0.02 MPa or less).

When the tensile stress value of the tensile stress layer becomes large, when the glass plate is cut, the scribe line having a predetermined depth inserted for cutting extends unexpectedly, and the glass plate is divided into desired dimensions. May be difficult. According to this embodiment, even if the maximum compressive stress of the surface layer is increased, the tensile stress can be maintained at a small value. For example, (absolute value of maximum compressive stress of surface layer) / (absolute value of maximum tensile stress of tensile stress layer) = 6 or more can be set. For example, the maximum tensile stress value of the tensile stress layer is preferably 0.4 MPa or less. If the maximum tensile stress value of the tensile stress layer exceeds 0.4 MPa, when cutting the glass plate, the scribe line of a predetermined depth inserted for cutting will extend unexpectedly, and the desired dimension will be obtained. This is because it may be difficult to divide the glass plate. The maximum tensile stress value of the tensile stress layer is more preferably 0.3 MPa or less, still more preferably 0.2 MPa or less (particularly 0.15 MPa, 0.10 MPa or less).

In addition, since the stress value of the tensile stress layer formed inside the glass plate is substantially constant in the thickness direction of the glass plate, compared with the case where the stress value of the tensile stress layer draws a parabola in the thickness direction of the glass plate And the effect that a glass plate becomes difficult to break is acquired.

More specifically, the tensile stress value of the glass plate obtained by the glass plate manufacturing method of the present embodiment is substantially constant in the thickness direction of the glass plate, and the maximum value of the tensile stress value is the glass in the cooling process. It is smaller than the maximum tensile stress value of the tensile stress layer formed only by quenching the ribbon. If the tensile stress value becomes extremely large, the glass plate may be broken at the time of processing or the like. Therefore, it is preferable that the tensile stress value is small. Note that the depth of the compressive stress layer formed only by rapidly cooling the glass ribbon in the cooling process is usually 1/10 or more of the thickness of the glass plate. The depth of the compressive stress layer formed by the method is, for example, less than 1/13 of the plate thickness. In other words, as the plate thickness decreases, the tensile stress layer thickness that cancels the compressive stress of the compressive stress layer on the surface of the glass plate also decreases, so the tensile stress that is formed only by rapidly cooling the glass ribbon in the cooling process. The stress value of the layer increases, and as a result, the processing accuracy of the glass plate decreases. However, since the stress value of the tensile stress layer of the glass plate obtained by the glass plate manufacturing method of the present embodiment is substantially constant in the thickness direction of the glass plate, the maximum value of the tensile stress value is also reduced, Processing can also be performed with high accuracy.

(4) Vickers hardness The Vickers hardness of the surface of the glass plate obtained by the glass plate manufacturing method of this embodiment is larger than the Vickers hardness inside a glass plate. That is, the glass plate obtained by the glass plate manufacturing method of the present embodiment has an improved surface Vickers hardness, so that the crack generation rate is reduced, the scratch is less likely to be damaged, and it is difficult to break. .

The Vickers hardness of the glass plate surface formed in the present embodiment is preferably 4 GPa or more, more preferably 5 GPa or more, and further preferably 5.35 GPa or more. Alternatively, the ratio of the Vickers hardness of the glass plate surface to the Vickers hardness inside the glass plate is preferably 1.01 or more, more preferably 1.02 or more (more preferably 1.05 or more, 1.10 or more).

(5) Plate thickness It is preferable that the thickness of the glass plate obtained by the glass plate manufacturing method of this embodiment is 1.5 mm or less. When the thickness is 3 mm or more, the strength of the glass plate itself is increased, and the compressive stress layer formed in the vicinity of the surface does not have a sufficient effect. The thickness of the glass plate is more preferably 1.0 mm or less (further 0.7 mm or less, 0.5 mm or less, 0.3 mm or less). The thinner the glass plate is, the more remarkable the effect of the present invention is.

(6) Size of glass plate The glass plate manufacturing method of this embodiment is suitable for a large glass plate. This is because the larger the glass plate, the greater the amount of deflection, and the glass plate tends to break due to fine scratches caused by handling, but the occurrence of the above problem can be reduced by forming a compressive stress layer on the glass plate surface. Because. For this reason, the glass plate manufacturing method of this embodiment is suitable for manufacture of the glass plate whose width direction is 1000 mm or more and 2000 mm or more, for example.

In the present embodiment, a volatilization promoting step for promoting volatilization of volatile components from the surface of the molten glass 3 and, in some cases, from the surface of the molten glass 3 and the glass ribbon 4 immediately after the formation is performed. The volatilization of the volatile component from at least one surface of the molten glass and the glass ribbon may be promoted. To achieve this, the partial pressure of the volatile component in the atmosphere facing the surface of at least one of the molten glass and the glass ribbon (the pressure of the volatile component when the gas other than the volatile component is removed from the atmosphere) and the volatile component What is necessary is just to enlarge the difference with saturated vapor pressure. As an example, the concentration of the volatile component in the atmosphere facing the surface of at least one of the molten glass and the glass ribbon may be reduced. In particular, when the molding step is performed using the molding apparatus 1 in the heat insulating structure 2 as in the present embodiment, the molten glass 3 that flows down the gas introduced from the outside of the heat insulating structure 2 into the heat insulating structure 2. And after making it contact with the surface of the glass ribbon 4 to be pulled down, it may be discharged out of the heat insulating structure 2.

Next, a specific example of a molding unit composed of the molding apparatus 1 and the heat insulating structure 2 will be described in detail.

<First Embodiment>
2 and 3 show a forming unit 10A which is a part of the glass plate manufacturing apparatus of the first embodiment. This molding unit 10 </ b> A is for performing a volatilization promoting step by discharging the gas introduced from the outside of the heat insulating structure 2 into the heat insulating structure 2 to the outside of the heat insulating structure 2. By introducing fresh air into the heat insulating structure 2 in this way, the concentration of vaporized volatile components in the heat insulating structure 2 can be reduced, and thus the volatilization of volatile components from the surface of the molten glass 3 can be achieved. Can be promoted. This is because when the volatile component is saturated in the heat insulating structure 2, the volatilization of the volatile component further does not proceed. In particular, in this embodiment, gas is raised along the surface of the molten glass 3 that flows down.

The forming apparatus 1 has a pentagonal wedge-shaped (narrow home base shape) cross-sectional shape that is pointed downward, and includes an upper surface provided with a linearly extending groove 11 and both ends of the upper surface parallel to the groove 11. And a pair of wall surfaces 12 facing downward. In the present specification, for convenience of explanation, the direction in which the groove 11 extends on the horizontal plane is also referred to as the X direction, the direction orthogonal to the X direction on the horizontal plane is also referred to as the Y direction, and the vertical direction is also referred to as the Z direction (see FIG. 2). ).

The groove 11 gradually decreases in depth from one end to the other end so that the molten glass 3 supplied to one end from a supply pipe (not shown) overflows uniformly over the entire length. Each of the pair of wall surfaces 12 includes a vertical surface that hangs vertically from an end portion of the upper surface in the Y direction, and an inclined surface that is inclined inward so as to approach each other from the lower end portion of the vertical surface. The lower end portions intersect to form a ridge line extending in the X direction.

Then, the forming apparatus 1 continuously forms the strip-shaped glass ribbon 4 by causing the molten glass 3 to overflow from both sides of the groove 11 and guiding and fusing the overflowed molten glass with the wall surface 12.

The heat insulating structure 2 forms a molding chamber in which the molding apparatus 1 is accommodated. Specifically, the heat insulating structure 2 is made of a material having excellent heat insulating properties, and the bottom wall 21 and the ceiling wall 23 that face each other with the molding device 1 interposed therebetween in the vertical direction, and the bottom wall 21 and the ceiling wall 23. And a rectangular cylindrical peripheral wall 22 that connects the peripheral edges of the two. In the center of the bottom wall 21, a gate 25 through which the glass ribbon 4 formed by the molding apparatus 1 passes is provided. Note that the heat insulating structure 2 may have a hollow structure, and air for heating or cooling may be supplied to the inside.

In the present embodiment, a plurality of discharge ports 26 penetrating the peripheral wall 22 are provided at the upper portion of the long wall portion on the Y direction side facing the wall surface 12 of the molding device 1 in the peripheral wall 22, and the Y direction of the peripheral wall 22 is provided. A plurality of inlets 27 penetrating the peripheral wall 22 are provided in the lower part of the long wall portion on the side. For this reason, an air flow as shown by arrows a, b, and c in FIG. 1 is formed by natural convection. That is, air outside the heat insulating structure 2 is introduced into the heat insulating structure 2 through the introduction port 27, and this air rises along the molten glass 3 flowing down on the wall surface 12 of the molding apparatus 1, and then the discharge port 26. Through the heat insulating structure 2. In this way, by raising the fresh air taken from outside in the heat insulating structure 2, the concentration of the volatile component in the atmosphere facing the surface of the molten glass 3 is lowered, and the volatile component becomes saturated. it is possible to prevent, can promote the volatilization of volatile components from the molten glass 3 (e.g. _{B 2 O 3, SnO, K} 2 O). In other words, since the difference between the partial pressure of the volatile component and the saturated vapor pressure of the volatile component in the atmosphere facing the surface of the molten glass 3 can be increased, the volatilization of the volatile component from the surface of the molten glass 3 is promoted. Can be made. The portion where the volatile component has volatilized, that is, the surface of the molten glass 3 in contact with the rising air, becomes a compressive stress layer when the glass ribbon 4 is cooled. In order to increase the stress value of the compressive stress layer, the molten glass 3 preferably contains many volatile components.

In addition, the discharge port 26 and the introduction port 27 may be provided also in the short wall part by the side of the X direction in the surrounding wall 22. FIG. Alternatively, the discharge port 26 and the introduction port 27 can be provided only in the short wall portion on the X direction side of the peripheral wall 22. However, in order to volatilize volatile components uniformly over the entire width of the molten glass 3, it is preferable that the discharge ports 26 and the introduction ports 27 are provided at a constant pitch only on the long wall portion on the Y direction side of the peripheral wall 22. .

Further, the shape and quantity of the discharge port 26 and the introduction port 27 can be appropriately selected as long as the necessary strength is maintained in the peripheral wall 22. For example, the shape of the discharge port 26 and the introduction port 27 may be circular as shown in FIG. 2, or the number may be reduced as a slit shape extending in the X direction. For example, when the discharge port 26 and the introduction port 27 are circular, the diameter is preferably 1 to 20 mm. This is because if the diameter exceeds 20 mm, the strength of the heat insulating structure 2 may be insufficient. In addition, in order to discharge | emit gas from the heat insulation structure 2 uniformly and effectively, it is more effective that the discharge port 26 is a slit extended over the whole width direction of a glass ribbon. However, the larger the opening area, the more the air flow rate increases, resulting in an increase in the surface defects of the glass plate, deterioration of the surface irregularities of the glass plate, and difficulty in securing the molding temperature. However, as shown below, the temperature of air or inert gas introduced into the heat insulating structure 2 from the inlet 27 is set to the target temperature in the heat insulating structure 2 and This can be solved by adjusting the flow rate so that the pressure can be maintained at a predetermined pressure.

Furthermore, the air introduced into the heat insulating structure 2 through the inlet 27 is preferably at a temperature that does not lower the temperature of the molten glass 3 or the glass ribbon 4, for example. Here, if the amount of air to be introduced is small, even if room temperature air is introduced, the temperature of the molten glass 3 and the glass ribbon 4 does not decrease so much, so room temperature air may be introduced. On the other hand, if the amount of air to be introduced is large, the temperature of the molten glass 3 and the glass ribbon 4 is greatly reduced when air at normal temperature is introduced. In this case, it is preferable to provide a heating means for heating the air introduced through the inlet 27 to a predetermined temperature outside or inside the heat insulating structure 2. When using the heating means, the temperature of the air is substantially equal to the temperature of the molten glass 3 outside the heat insulating structure 2 (for example, within a range of ± 10% of the temperature of the molten glass) or higher. It is preferable to heat the air and introduce the heated air into the heat insulating structure 2.

If the molding unit 10A of the present embodiment described above is used, the molten glass 3 overflows from both sides of the groove 11 of the molding apparatus 1 surrounded by the heat insulating structure 2, and the inside of the heat insulating structure 2 from the outside of the heat insulating structure 2. The step of discharging the air introduced to the outside of the heat insulating structure 2 after the air is raised along the molten glass 3 flowing down on the wall surface 12 of the molding apparatus 1 is performed. Thus, the volatilization of the volatile components from the molten glass 3 can be effectively promoted by raising the gas passing through the heat insulating structure 2 along the molten glass flowing down on the wall surface 12 of the molding apparatus 1. . Thereby, the glass plate in which the compressive-stress layer with a high stress value was formed in both main surfaces can be obtained.

In addition, in the said embodiment, although the discharge port 26 is provided in the upper part of the surrounding wall 22, the position of the discharge port 26 is not restrict | limited in particular. For example, the discharge port 26 may be provided in a portion of the ceiling wall 23 directly above the molding apparatus 1 as in a modification of the molding unit 10C shown in FIG. Even if it does in this way, after making the air introduced into the heat insulation structure 2 from the heat insulation structure 2 outside by the natural convection rise along the molten glass 3 which flows down on the wall surface 12 of the shaping | molding apparatus 1, it is the discharge port 26. It can discharge | emit out of the heat insulation structure 2 through. Further, in this case, since the molten glass 3 is in contact with the air passing through the heat insulating structure 2 even above the molding device 1, the volatilization of the volatile components is further increased than when the discharge port 26 is provided on the upper portion of the peripheral wall 22. Can be promoted.

However, when the discharge port 26 is provided in the ceiling wall 23 of the peripheral wall 22, there is a possibility that fallen objects from above the heat insulating structure 2 may fall into the molten glass 3 through the discharge port 26. From this viewpoint, it is preferable to provide the discharge port 26 on the upper portion of the peripheral wall 22 as in the above-described embodiment.

In the above embodiment, the introduction port 27 is provided in the lower part of the peripheral wall 22, but the position of the introduction port 27 is not particularly limited. For example, you may provide the inlet 27 in the bottom wall 21 like the shaping | molding unit 10B of the modification shown in FIG. In this case, if the introduction port 27 is in the region R immediately below the molding apparatus 1, the flow of air from the introduction port 27 may affect the shape stability of the glass ribbon 4. It is preferable to provide the outer side of R.

Further, as shown in FIG. 5, the introduction port 27 can be omitted. Even in this case, the air outside the heat insulating structure 2 is introduced into the heat insulating structure 2 through the gate 25. Thereby, volatilization of a volatile component can be promoted also from the surface of the glass ribbon 4 immediately after formation. However, in this case, gas passes through the gate 25 in the opposite direction to the glass ribbon 4, and the shape stability of the glass ribbon 4 may be impaired. Therefore, an inlet 27 is provided separately from the gate 25. Is preferred.

In the above embodiment, air is introduced into the heat insulating structure 2 and discharged out of the heat insulating structure 2 by natural convection, but they can also be performed by forced convection. It is. For example, the supply pipe may be passed through the lower part of the heat insulating structure 2 and the discharge pipe may be passed through the upper part of the heat insulating structure 2, and a fan may be connected to one of them. In this case, the end portions of the supply pipe and the discharge pipe that open to the space in the heat insulating structure 2 constitute the introduction port and the discharge port, respectively.

By the way, when forced convection is used and the temperature of the air introduced into the heat insulating structure 2 is substantially equal to or higher than the temperature of the molten glass 3, for example, a modification shown in FIG. As in the molding unit 10D, the inlet 27 is provided in the upper part of the heat insulating structure 2, and the air introduced into the heat insulating structure 2 descends along the molten glass 3, and the heat insulating structure from the gate 25. 2 may be discharged outside. However, if the gas is raised along the molten glass 3 flowing down, volatilization of the volatile components can be promoted more remarkably by the counter flow formed by them.

Further, the gas introduced into the heat insulating structure 2 through the inlet 27 or the gate 25 is not necessarily air, and may be an inert gas. As the inert gas, nitrogen is particularly preferably used from the viewpoint of preventing corrosion of the molding apparatus 1 and the heat insulating structure 2. Alternatively, the gas introduced into the heat insulating structure 2 may be a mixture of air and inert gas.

Second Embodiment
Next, with reference to FIG. 7, the shaping | molding unit 10E which is a part of the glass plate manufacturing apparatus of 2nd Embodiment is demonstrated. In addition, the same code | symbol is attached | subjected to the same component as 1st Embodiment, and the description is abbreviate | omitted.

The molding unit 10E of the present embodiment is for performing a volatilization promoting step during the forming step by reducing the pressure inside the heat insulating structure 2. Specifically, the heat insulating structure 2 is provided with a suction port 28, and the vacuum pump 6 is connected to the suction port 28. The numbers of the suction ports 28 and the vacuum pumps 6 are not particularly limited, and may be one or more.

If the pressure inside the heat insulating structure 2 is excessively reduced, a large amount of gas having a lower temperature than that in the heat insulating structure 2 is introduced from the gate 25, the glass is not uniformized, the glass thickness varies, and further distortion occurs. May occur. Therefore, it is preferable to depressurize the heat insulating structure 2 within a range of 1/10 or less of the pressure around the heat insulating structure 2. That is, when the atmospheric pressure in the heat insulating structure 2 is 1 atm, it is preferable to reduce the pressure to 0.9 atm. According to this embodiment, the density | concentration of the volatile component in the atmosphere which faces the surface of the molten glass 3 and the glass ribbon 4 can be reduced. In other words, the difference between the partial pressure of the volatile component and the saturated vapor pressure of the volatile component in the atmosphere facing the surfaces of the molten glass 3 and the glass ribbon 4 can be increased. Moreover, since the energy required in order that a volatile component volatilizes will fall because the inside of the heat insulation structure 2 is pressure-reduced, volatilization of a volatile component is further accelerated | stimulated.

<Other embodiments>
The present invention is applicable not only to the overflow downdraw method but also to, for example, the slot downdraw method. In this case, a volatilization promoting step for promoting volatilization of volatile components from the surface of the glass ribbon 4 immediately after the formation is performed.

Further, the method for realizing the present invention is not limited to the above embodiment, and for example, the volatilization promoting step can be performed after the forming step by lengthening the time for keeping the glass ribbon 4 at a high temperature.

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to these examples.

As shown in FIGS. 2 and 3, five glass plates having a size of 1100 mm × 1300 mm and a thickness of 0.7 mm are manufactured using the molding unit 10A including the heat insulating structure 2 provided with the discharge port 26 and the introduction port 27. (Examples 1 to 5).

The content of each composition of the molten glass was as follows.
SiO ₂ : 60.9%
Al ₂ O ₃ : 16.9%
B ₂ O ₃ : 11.6%
MgO: 1.7%
CaO: 5.1%
SrO: 2.6%
BaO: 0.7%
K ₂ O: 0.25%
SnO ₂ : 0.13%

Further, the discharge ports 26 were circular with a diameter of 10 mm, and two discharge ports 26 were provided at the upper part of each short wall portion on the X direction side of the peripheral wall 22. The introduction ports 27 were circular with a diameter of 10 mm, and two introduction ports 27 were provided below each short wall portion on the X direction side of the peripheral wall 22.

(test)
About the glass plate of the Example, the atomic concentration of the surface vicinity was measured using the X-ray photoelectron spectrometer (Quantera SXM by ULVAC-PHI). Specifically, the surface of the glass plate was dug down to various depths by sputtering, and the atomic concentration at each depth was measured. As measurement elements, Si, Al, B, Ca, Sr, and Ba, which are volatile components having a relatively high content, were specified, and the ratio of Si in the measurement elements was determined. Among them, the results of Examples 1 and 2 were as shown in FIG. In addition, since the content rate of K and Sn is small among volatile components, and it is considered that the amount thereof has little influence on the ratio of Si, these were not included in the measurement elements.

As can be seen from FIG. 8, in the example, the Si ratio is higher in the region very close to the surface than in the glass plate. This indicates that the volatile components near the surface are reduced, and if a heat insulating structure through which gas passes from the bottom to the top is used, more volatile components are volatilized and a compressive stress layer with a high stress value is formed. It can be seen that it can be formed.

Also, the internal stress was measured for the glass plate of the example. The internal stress was determined by using a micro-area birefringence meter (KOBRA-CCD / X manufactured by Oji Scientific Instruments), and the optical path difference rate per 1 cm per predetermined depth from the surface for a cross section of the glass plate cut in the thickness direction ( (Optical path difference / optical path length) was measured and calculated by dividing by the photoelastic constant. Among them, the result of Example 1 was as shown in FIG.

9 that a compressive stress layer having a high stress value is formed on both main surfaces of the glass plate. Moreover, the stress value of the tensile stress formed on the glass plate was substantially constant in the glass plate thickness direction. This is due to the fact that volatile components are reduced near both main surfaces of the glass plate.

なお、表中の「基準値」とは、上述したとおり、「ガラス板の厚さ方向の中心のガラス組成中におけるＳｉ原子含有量」である。 Table 1 shows the values for the glass plates of Examples 1 to 5.

The “reference value” in the table is “the Si atom content in the glass composition at the center in the thickness direction of the glass plate” as described above.

Next, a scratch test was performed on the glass plates of Examples 1 to 5. Specifically, a scratch hardness tester model 318S manufactured by Eriklin Co., Ltd. having a carbide ball tip having a diameter of 0.75 mm at the tip was used, and a scratch test was performed with a scratch load of 2 N and a scratch length of 30 mm. As a result of observing the surface of the glass plate with a laser microscope, in Examples 1 to 5, no crack was generated on the surface of the glass plate. On the other hand, when the same scratch test was performed after the surface of the glass plate of Example 1 was polished, cracks were generated on the polished surface.

The present invention is particularly suitable for the production of plate glass for FPD glass substrates. Further, the tempered glass obtained by chemically strengthening the glass plate obtained by the present invention is suitably used for a cover glass of a mobile phone, a digital camera, a PDA (portable terminal), a solar cell, and an FPD. For example, application to a substrate for a touch panel display, a window glass, a substrate for a magnetic disk, a cover glass for a solid-state imaging device, tableware and the like can be expected.

Claims (11)

A melting step of melting a glass raw material to obtain a molten glass;
A molding step of forming a glass ribbon from the molten glass by a downdraw method,
A volatilization promoting step for promoting volatilization of volatile components from at least one surface of the molten glass and the glass ribbon;
A cooling process for cooling the glass ribbon;
A cutting step of cutting the glass ribbon to obtain a glass plate;
A glass plate manufacturing method comprising: In the volatilization promoting step, by increasing a difference between a partial pressure of the volatile component and a saturated vapor pressure of the volatile component in an atmosphere facing at least one surface of the molten glass and the glass ribbon, the molten glass and the The glass plate manufacturing method of Claim 1 which promotes volatilization of the volatile component from the surface of at least one of a glass ribbon. In the volatilization promoting step, by reducing the concentration of the volatile component in the atmosphere facing the surface of at least one of the molten glass and the glass ribbon, the volatile component from at least one surface of the molten glass and the glass ribbon The glass plate manufacturing method of Claim 2 which promotes volatilization of. The molding step is performed using a molding device in the heat insulating structure,
In the volatilization promoting step, the gas introduced from outside the heat insulating structure into the heat insulating structure is brought into contact with the surface of the molten glass flowing down and / or the glass ribbon to be lowered, and then discharged out of the heat insulating structure. The method for producing a glass plate according to any one of claims 1 to 3, wherein volatilization of a volatile component from at least one surface of the molten glass and the glass ribbon is promoted. The method for producing a glass sheet according to claim 4, wherein the gas is raised along the surface of the molten glass flowing down and / or the glass ribbon to be pulled down. The glass plate manufacturing apparatus according to claim 4, wherein the gas is air and / or an inert gas. The molding step is performed using a molding device in the heat insulating structure,
The volatilization promoting step promotes volatilization of volatile components from the surface of at least one of the molten glass and the glass ribbon by reducing the pressure inside the heat insulating structure. Glass plate manufacturing method. A molding apparatus that overflows molten glass from both sides of the groove and forms a glass ribbon by inducing and fusing the overflowed molten glass with each other on the wall surface;
A heat insulating structure that includes a gate that surrounds the molding apparatus and allows the glass ribbon formed by the molding apparatus to pass therethrough, and
In order to promote volatilization of volatile components from the surface of the molten glass, the heat insulating structure is introduced into the heat insulating structure from outside the heat insulating structure and flows along the molten glass flowing down on the wall surface of the molding apparatus. A discharge port for discharging the gas that has risen to the outside of the heat insulation structure is provided,
Glass plate manufacturing equipment. The heat insulating structure has a bottom wall provided with the gate, a ceiling wall facing the bottom wall with the molding apparatus interposed therebetween, and a peripheral wall connecting the peripheral edges of the bottom wall and the ceiling wall,
The said discharge port is a glass plate manufacturing apparatus of Claim 8 provided in the upper part of the said surrounding wall. The glass plate manufacturing apparatus according to claim 9, wherein an inlet for introducing the gas into the heat insulating structure is provided at a lower portion of the peripheral wall. The glass plate manufacturing apparatus according to any one of claims 8 to 10, wherein the gas is air and / or an inert gas.

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