JP2011148683A - Glass plate and method for producing glass plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass plate whose surface is strengthened when the glass plate is produced to such an extent that the surface does not adversely affect the efficiency of processing treatment after glass forming and is not easily scratched, and to provide a method for producing the glass plate. <P>SOLUTION: The glass plate is produced by a down-draw method. The glass plate has a tensile stress layer formed in the inner part of the glass plate and compressive stress layers formed on both sides of the tensile stress layer. The compressive stress layers are each formed in a depth range of >10 μm and ≤50 μm from the surface of the glass plate along the thickness direction of the glass plate, and the thickness of the compressive stress layer is less than 1/13 of the thickness of the glass plate. The absolute value of the stress value of the compressive stress layer is 4 MPa or less, and the absolute value of the stress value of the tensile stress layer is 0.4 MPa or less. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a glass plate manufactured by a downdraw method and a method of manufacturing a glass plate by a downdraw 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 FPD glass substrate has been increased in size, and for example, a glass plate called an eighth generation having a size of 2200 mm × 2500 mm is used.

  The down draw method is most often used to manufacture such an FDP glass substrate. In the down draw method, a glass ribbon is continuously formed by overflowing molten glass from a groove of a forming apparatus. At that time, the glass ribbon is pulled down by a roller or the like. At this time, the thickness of the glass ribbon is adjusted by the pulling speed of the glass ribbon. Then, a glass ribbon is cut | disconnected by predetermined length, and a glass plate is manufactured.

  For example, Patent Document 1 discloses a glass plate manufacturing apparatus as shown in FIG. This glass plate manufacturing apparatus includes a forming device 7 and a heat insulating structure 8 surrounding the forming 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 glass plate manufacturing apparatus 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. It is configured. 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 glass plate manufacturing apparatus disclosed by patent document 1, the glass ribbon 9 can be cooled immediately after formation.

On the other hand, there is known a glass substrate for display that can be reduced in thickness and weight, has high mechanical strength and transparency, and can be manufactured in a short time (Patent Document 2). The glass substrate, a SiO ₂ 40 to 70 wt%, the _Al 2 _{O 3} 0.1 to 20 wt%, a Na ₂ O 0 to 20 wt%, 0-15 wt% of Li ₂ O, the ZrO ₂ The glass material contains 0.1 to 9% by weight, and the total content of Li ₂ O and Na ₂ O is 3 to 20% by weight. A compressive stress layer having a depth of 50 μm or more is formed on the surface of the glass substrate by chemical strengthening treatment.

Special table 2009-519884 JP 2002-174810 A

  By the way, a volatile component volatilizes from the molten glass in the interface which contacts air. The inventors of the present invention thought that a desired compressive stress layer could be formed on both the front and back surfaces of the glass plate if this volatilization was effectively utilized by the downdraw method.

  However, when the heat insulating structure 8 has a sealed structure as in the manufacturing apparatus disclosed in Patent Document 1, volatilization of volatile components from the molten glass overflowing from the molding apparatus is suppressed, so that the stress value A high compressive stress layer cannot be formed.

  In Patent Document 1, the gate structure 8B is provided with a jet 83 for jetting cooling air from the cooling pipe 82 into a space covered with the main body 8A, and cooling air is supplied from the jet 83 to the gate 81. It is also disclosed to cool the glass ribbon 9 by flowing it. However, even if forced convection is generated in the vicinity of the gate 81 in this way, the air above it, that is, most of the air in the space covered by the main body 8A remains in that place, so that volatile components from the molten glass Volatilization is still suppressed.

  In the glass substrate disclosed in Patent Document 2, a compressive stress layer is formed on the surface of the glass plate by performing ion exchange and performing chemical strengthening treatment. However, chemically strengthening a glass substrate using alkali ions used for ion exchange affects, for example, TFT (Thin Film Transistor) characteristics formed on the glass substrate of the liquid crystal display device, and further contaminates the liquid crystal material. This is not preferable. For this reason, the tempered glass chemically strengthened by ion exchange is difficult to be used for a liquid crystal display device glass substrate or the like. Even if chemical strengthening treatment by ion exchange is possible, it is inevitable that the surface of the glass plate is damaged in the pre-process of chemical strengthening treatment. On the other hand, if the above chemical strengthening treatment is performed immediately after the formation of the glass plate, the efficiency of the subsequent processing treatment including cutting of the glass surface, grinding / polishing of the glass plate, and shape processing is reduced.

  In view of such circumstances, the present invention provides a glass plate manufacturing apparatus capable of promoting volatilization of volatile components from molten glass overflowing from a molding apparatus, and a glass plate manufacturing method using the glass plate manufacturing apparatus. In addition, a first object is to provide a glass plate obtained by the glass plate manufacturing method.

  Therefore, the present invention provides a glass plate whose glass surface is strengthened to such an extent that it does not adversely affect the efficiency of processing after glass forming and the glass surface is hardly damaged when the glass plate is produced. A second object is to provide a manufacturing method.

(First invention)
In order to achieve the first object, one aspect of the present invention is an apparatus for manufacturing a glass plate by a downdraw method, in which molten glass is overflowed from both sides of a groove, and the overflowed molten glass is walled. And a heat insulating structure having a gate that surrounds the forming device and has a gate through which the glass ribbon formed by the forming device passes. The body is provided with a discharge port that is introduced into the heat insulating structure from outside the heat insulating structure and discharges the gas that has risen along the molten glass flowing down the wall surface of the molding apparatus to the outside of the heat insulating structure. A glass plate manufacturing apparatus is provided.

  One embodiment of the present invention is a method for producing a glass plate by a downdraw method, wherein the heat insulation is made from outside the heat insulation structure while overflowing molten glass from both sides of a groove of a molding apparatus surrounded by the heat insulation structure. There is provided a glass plate manufacturing method including a step of raising a gas introduced into a structure along a molten glass flowing down on a wall surface of the molding apparatus and then discharging the gas outside the heat insulating structure.

  Furthermore, one embodiment of the present invention provides a glass plate obtained by the above glass plate manufacturing method, and having a compressive stress layer on both front and back surfaces.

(Second invention)
In order to achieve the second object, one embodiment of the present invention provides a glass plate formed by a downdraw method. The glass plate
A tensile stress layer formed inside the glass plate; and a compressive stress layer formed on both sides of the tensile stress layer.
The compressive stress layer is formed in a depth range from 10 μm to 50 μm or less along the thickness direction of the glass plate from the surface of the glass plate, and the thickness of the compressive stress layer is equal to the thickness of the glass plate. Less than one-third.
The absolute value of the stress value of the compressive stress layer is 4 MPa or less, and the absolute value of the stress value of the tensile stress layer is 0.4 MPa or less.

Another embodiment of the present invention provides a method for producing a glass plate. The manufacturing method is
Melting glass raw materials,
Using a downdraw method to form a glass ribbon from molten glass;
Cutting the glass ribbon to form a glass plate.
In the step of forming the glass ribbon, a compressive stress layer formed in a range of a depth of 10 μm to 50 μm along the thickness direction of the glass ribbon from the surface of the glass ribbon, the thickness of the glass ribbon Two compressive stress layers having a thickness of less than one-third of the thickness and having an absolute value of compressive stress of 4 MPa or less, and sandwiched between the two compressive stress layers, and an absolute value of tensile stress of 0 The glass ribbon is formed so as to have a tensile stress layer of 4 MPa or less.

  When the glass plate of the present invention is produced, the glass surface is strengthened to such an extent that the glass surface is not easily damaged without adversely affecting the efficiency of processing after glass forming. The glass manufacturing method of this invention can manufacture the said glass plate efficiently.

It is a figure which shows the internal stress distribution of the glass plate of this embodiment. It is a figure which shows the internal stress distribution of the conventional glass plate obtained when glass is strengthened at a slow cooling process. It is a figure explaining an example of the flow of the manufacturing method of the glass plate of this embodiment. It is sectional drawing of the glass plate manufacturing apparatus which manufactures the glass plate of this embodiment. It is a perspective view of the glass plate manufacturing apparatus shown in FIG. It is sectional drawing of the glass plate manufacturing apparatus of a modification. It is sectional drawing of the glass plate manufacturing apparatus of another modification. It is a figure which shows distribution of the internal stress measured about the glass plate of this embodiment. It is a figure which shows distribution of Si atom density | concentration (%) measured about the glass plate of this embodiment. It is sectional drawing of the conventional glass manufacturing apparatus.

  Hereafter, the manufacturing method of the glass plate and glass plate of this invention is demonstrated.

(Outline explanation of glass plate)
FIG. 1 is a diagram showing an internal stress distribution of the glass plate 10 of the present embodiment.
The glass plate 10 is manufactured by a downdraw method, and is suitably used for, for example, an FPD glass substrate. The thickness and size of the glass plate 10 are not particularly limited. Tempered glass obtained by chemically strengthening the glass plate 10 is used, for example, as a cover glass for a display screen of an electronic device.
As shown in FIG. 1, the glass plate 10 includes a tensile stress layer 12 formed inside the glass plate and a compressive stress layer 14 formed on both sides of the tensile stress layer 12.
The compressive stress layer 14 is formed in a depth range of 10 μm to 50 μm or less along the thickness direction of the glass plate 10 from the surface of the glass plate 10, and the thickness of the compressive stress layer 14 is the thickness of the glass plate 10. Less than 1/13. The absolute value of the stress value of the compressive stress layer 14 is 4 MPa or less, and the absolute value of the stress value of the tensile stress layer 12 is 0.4 MPa or less.

Specifically, if the thickness of the compressive stress layer 14 is W ₁ , the thickness W ₁ is greater than 0 μm and 50 μm or less, and less than 1/13 of the thickness W ₀ of the glass plate 10. The maximum value S ₁ of the stress value (absolute value) of the compressive stress increase 14 is 4 MPa or less, and the maximum value S ₂ of the stress value (absolute value) of the tensile stress layer 12 is 0.4 MPa or less.

A thick solid line in FIG. 1 indicates an internal stress distribution along the thickness direction of the glass plate 10, that is, a compression / tensile stress profile. FIG. 2 is a diagram showing an internal stress distribution of a conventional glass plate obtained when glass is rapidly cooled in a slow cooling process.
The compression / tensile stress profile obtained when the glass is rapidly cooled in the slow cooling process is a profile that draws a parabola. The compressive stress layer formed on the glass plate when the glass is rapidly cooled is caused by a difference in thermal expansion between the glass surface and the inside. This difference in coefficient of thermal expansion is caused by the thermal conductivity of the glass. In addition, the thickness W ′ ₁ (see FIG. 2) of the compressive stress layer conventionally obtained in the slow cooling step is 1/10 or more of the thickness W ′ ₀ of the glass plate.

On the other hand, in the glass plate 10, a thin compressive stress layer 14 is formed in the vicinity of the surface of the glass plate 10 due to a difference in thermal expansion caused by the Si high concentration region formed on the glass surface. As described later, the Si high concentration region is formed by promoting volatilization of volatile components or increasing the volatilization amount from the surface of the molten glass or glass ribbon in the glass ribbon forming step. At this time, the tensile stress layer 12 has a substantially constant low stress value in the thickness direction of the glass plate 10 so that the tensile stress value of the conventional tensile stress layer draws a parabola in the thickness direction of the glass plate. It is different from the case where it is distributed.
Further, since the compression by the compressive stress layer 14 and the tensile force by the tensile stress layer 12 are canceled in the entire glass plate 10, the stress value (absolute value) of the compressive stress layer 14 is canceled to cancel the tensile stress when the compressive stress layer 14 becomes thin. ) Will be higher. For this reason, the compressive stress layer 14 has a stress value larger than the stress value of the compressive stress layer obtained only when, for example, the glass is rapidly cooled in the slow cooling step. That is, since the compressive stress layer 14 having a large stress value is formed on the glass surface on the glass plate 10, the glass surface of the glass plate 10 is compared with a conventional glass plate that has been strengthened by only a slow cooling process. Hard to scratch.
Hereinafter, the glass plate 10 will be described in more detail.

(Outline explanation of glass plate)
The thickness W ₁ of the compressive stress layer 14 formed on the glass plate 10 is greater than 0 μm and not greater than 50 μm. The compressive stress layer 14 is formed on the glass surface. That is, the compressive stress layer 14 is formed in a range of a maximum depth of 50 μm from the glass surface. In other words, the depth from the surface of the compressive stress layer 14 is 50 μm or less. The depth of the compressive stress layer can be increased by promoting volatilization from the surface of the molten glass or glass ribbon in the molding process, but if the depth of the compressive stress layer 14 exceeds 50 μm, Deviation of proper molding conditions or decrease in productivity occurs. For this reason, the depth from the surface of the compressive stress layer 14 is 50 μm or less. For this reason, it is preferable that the depth of the compressive-stress layer 14 is 45 micrometers or less, 40 micrometers or less, and 38 micrometers or less. Such a preferred embodiment is realized by adjusting the glass plate manufacturing conditions and the glass plate composition including the conditions for promoting the volatilization of volatile components from the surface of the molten glass or the glass ribbon being formed or increasing the volatilization amount. Can be done.

In addition, the depth of the compressive stress layer 14 in this specification shows the depth from the glass surface of the deepest part of the compressive stress layer formed in one surface among the front and back of the glass plate 10. FIG. That is, the compressive stress layer 14 having the above depth is formed on the front and back surfaces of the glass plate 10 from the glass surface.
The depth of the compressive stress layer 14 is more than 10 μm. By setting the depth of the compressive stress layer 14 to more than 10 μm, it is possible to prevent the glass from being easily broken by fine scratches resulting from handling. The depth of the compressive stress layer 14 is more preferably 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, or 35 μm or more in consideration of the point that the glass plate 10 is not easily damaged even if a deep flaw is applied.
The depth of the compressive stress layer 14 formed on the glass surface is less than 1/13 of the thickness W ₀ of the glass plate 10, but less than 1/15, less than 1/17, less than 1/20, 1/22 Less than 1/24.
Such a preferred embodiment is also realized by adjusting the glass plate manufacturing conditions and the glass plate composition including the conditions for promoting the volatilization of volatile components from the surface of the molten glass or the glass ribbon being molded or increasing the volatilization amount. Can be done.

The stress value (absolute value) of the compressive stress layer 14 formed near the surface of the glass plate 10 is 4 MPa at the maximum. If the maximum value of the stress value (absolute value) exceeds 4 MPa, the sum of the stress values of the compressive stress layer 14 becomes large, and it becomes difficult to process the glass plate 10, for example, shape processing. For this reason, it is preferable that the maximum value of the stress value (absolute value) of the compressive stress layer 14 is 3.7 MPa or less, 3.5 MPa or less, 3.0 MPa or less, or 2.8 MPa or less. Moreover, it is preferable that the maximum value of the stress value (absolute value) of the compressive stress layer 14 is 0.1 MPa or more, 0.5 MPa or more, 1 MPa or more, 1.5 MPa or more, 2 MPa or more. Since the compressive stress layer 14 is a layer having a stress value (absolute value) exceeding 0 MPa, the mechanical strength of the glass plate 10 is improved by forming the compressive stress layer 14 on the glass surface of the glass plate 10.
In addition, the “stress value” in the present specification indicates an average value of 0 to 10 μm from the surface of the sample of the glass substrate 10 cut from the glass surface at every predetermined depth. Therefore, locally, a glass plate in which the compressive stress layer 14 has a stress value exceeding the range of the stress value is also included as the glass plate 10.

As described above, the stress value of the tensile stress layer 12 formed inside the glass plate 10 is substantially constant in the thickness direction of the glass plate 10. The stress value of the tensile stress layer 12 is 0.4 MPa or less as described above. When the maximum value of the stress value (absolute value) of the tensile stress layer 12 exceeds 0.4 MPa, for example, when cutting a glass plate, a scribe line having a predetermined depth inserted for cutting is the thickness of the glass plate. In some cases, the glass plate 10 extends unexpectedly in the vertical direction, making it difficult to divide the glass plate 10 into a desired dimension. For this reason, it is preferable that the maximum value (absolute value) of the stress value of the tensile stress layer 12 is 0.3 MPa or less, 0.2 MPa or less, 0.15 MPa, or 0.10 MPa. In the present embodiment, the maximum value of the stress value (absolute value) of the compressive stress layer 14 on the glass surface / the maximum value of the stress value (absolute value) of the tensile stress layer 12 can be 6 or more.
Further, the tensile stress layer 12 of the glass plate 10 at the central portion 4/5 (hereinafter, simply referred to as “tensile center region”) of the tensile stress layer 12 excluding 1/10 on both sides in the thickness direction of the glass plate 10. It is preferable that the fluctuation of the stress value at, that is, the difference between the maximum value and the minimum value of the stress value (absolute value) is 0.12 MPa or less. Thereby, the cutting property of a glass plate can be improved. More preferably, they are 0.10 Mpa or less, 0.05 Mpa or less, 0.02 Mpa or less. Such a preferred embodiment is also realized by adjusting the glass plate manufacturing conditions and the glass plate composition including the conditions for promoting the volatilization of volatile components from the surface of the molten glass or the glass ribbon being molded or increasing the volatilization amount. Can be done.

Since the stress value of the tensile stress layer 12 formed inside the glass plate 10 is substantially constant in the thickness direction of the glass plate 10, the stress value of the tensile stress layer draws a parabola in the thickness direction of the glass plate 10. The tensile stress layer 12 can be kept thin as compared with the case where the tensile stress layer 12 is formed.
More specifically, the stress value of the tensile stress layer 12 of the glass plate 10 is substantially constant in the thickness direction of the glass plate 10, and only in the slow cooling step compared to the maximum value (absolute value) of the stress value. The maximum value (absolute value) of the tensile stress value of the obtained conventional glass plate is large. That is, in the conventional glass plate, the tensile stress layer is formed with a parabolic profile so as to cancel out the compressive stress of the compressive stress layer formed on the glass surface. For this reason, when the thickness of the glass plate is reduced, the thickness of the tensile stress layer for canceling the compressive stress of the compressive stress layer on the glass surface is also reduced. For example, when a glass plate is cut, a scribe line of a predetermined depth inserted for cutting extends unexpectedly in the thickness direction of the glass plate, and the glass plate 10 has a desired dimension. It may be difficult to divide. However, since the stress value of the tensile stress layer 12 of the glass plate 10 of the present embodiment is substantially constant in the thickness direction of the glass plate 10, the maximum value of the stress value of the tensile stress layer is difficult to increase. Processing can also be performed with high accuracy.

When the glass plate 10 is viewed from the glass composition, the glass plate 10 has a Si high concentration region (hereinafter referred to as a Si rich layer) in a depth range from 0 to 30 nm along the thickness direction from the glass surface. Is formed. The Si-rich layer is a region where the concentration ratio of the Si atomic concentration (atomic%) to the Si atomic concentration (atomic%) at the center position in the thickness direction of the glass plate 10 is higher by 5% or more. The range in which the Si rich layer is located is preferably more than 0 to 25 nm, 2 to 20 nm, 5 to 16 nm, and 8 to 16 nm. On the other hand, the depth of the Si-rich layer can be increased by promoting volatilization from the surface of the molten glass or glass ribbon in the molding process. Decrease. Alternatively, when the depth of the Si-rich layer exceeds 30 nm, etching becomes difficult when the glass surface of the glass plate 10 is etched. On the other hand, when the depth of the Si-rich layer exceeds 30 nm, the stress value (absolute value) of the compressive stress layer 14 formed on the glass surface increases, resulting in inconvenience that the cutting ability of the glass plate is lowered. Therefore, the depth of the Si rich layer is preferably 30 nm or less.
The Si rich layer has a maximum peak of Si atom concentration, and the Si atom concentration along the thickness direction of the glass plate 10 decreases from the position of the maximum peak toward both sides. By having such a glass composition, the compressive stress layer 14 and the tensile stress layer 12 described above are formed. The Si atom concentration means the atomic percentage of Si with respect to the entire glass component excluding oxygen atoms (all glass components excluding oxygen atoms such as Si, Al, B, Ca, Sr, and Ba).
At this time, a volatile component having a higher vapor pressure (saturated vapor pressure) than SiO ₂ in the molten glass state (for example, the viscosity of the glass is 10 ^4.5 to 10 ⁵ poise or the temperature 1100 to 1300 ° C.) is the thickness of the glass plate. It is preferable that 30% by mass or more is contained in the center position in the vertical direction in terms of forming the Si rich layer.

Here, when the concentration ratio is less than 5%, a sufficient difference in thermal expansion coefficient between the glass surface and the inside cannot be obtained, and the compressive stress layer 14 is not effectively formed. Alternatively, sufficient Vickers hardness and durability cannot be obtained.
On the other hand, when the concentration ratio exceeds 30%, the quality (physical characteristics, thermal characteristics, chemical characteristics) of the glass plate changes, and for example, it becomes difficult to cut or etch the glass plate and use it for desired applications. It may not be possible. From this point, it is preferable that the concentration ratio has an upper limit of 30%.
In the Si-rich layer, the peak position where the Si atom content and the Si atom concentration are highest is located in a range of 0 to 5 nm deep from the glass surface.

By forming the Si-rich layer in the depth range from 0 to 30 nm along the thickness direction from the glass surface, a sufficient difference in coefficient of thermal expansion can be obtained between the glass surface and the inside. The compressive stress layer 14 can be formed. Moreover, it becomes possible to improve the Vickers hardness and durability of the glass surface, and to prevent the glass plate 10 from being broken. That is, since Si is a component that improves the Vickers hardness, the Vickers hardness of the glass surface of the glass plate 10 is increased by the Si-rich layer formed on the glass surface. Moreover, since Si is excellent in chemical resistance, the durability of the glass plate 10 on which the Si-rich layer is formed on the glass surface is also improved. In addition, since the Vickers hardness of the glass surface is improved as compared with a conventional glass plate, the crack generation rate is reduced, and it is possible to obtain an effect that the glass surface is less likely to be damaged and hardly damaged.
The Vickers hardness of the glass surface of the glass plate 10 is, for example, 4 GPa or more, 5 GPa or more, and preferably 5.3 GPa or more. Alternatively, the Vickers hardness of the glass surface is improved by 0.01% or more in comparison with the Vickers hardness inside the glass, and is 0.02% or more, 0.05% or more, 0.10% or more, 1% or more. It is preferable to improve.

Thus, the glass plate 10 has the tensile stress layer 12 and the compressive stress layer 14 in terms of internal stress, and has a Si-rich layer near the glass surface in terms of composition. In the glass ribbon forming step, which will be described later, the glass plate 10 is made of, for example, SiO ₂ from the surface of the molten glass or glass ribbon in a glass molten state having a glass viscosity of 10 ^4.5 to 10 ⁵ poise or a temperature of 1100 to 1300 ° C. It can be obtained by promoting volatilization of a volatile component having a higher saturated vapor pressure.
Each aspect of the preferable numerical range described above also adjusts the glass plate production conditions and the glass plate composition including conditions for promoting volatilization of volatile components from the surface of the molten glass or glass ribbon during molding or increasing the volatilization amount. Can be realized.

Such a glass plate 10 may be further strengthened by performing chemical strengthening treatment by ion exchange. The glass plate 10 may not be subjected to chemical strengthening treatment by ion exchange. Embodiment of this invention also includes the tempered glass by which the glass surface of the glass plate 10 was chemically strengthened by ion exchange. In this case, the above-mentioned Si-rich layer and the ion exchange treatment region by ion exchange are formed side by side on the glass surface. The ion exchange treatment region is a region in which ion exchange components such as Li and Na, which are components in the glass surface, are exchanged with ion exchange components such as K in the treatment liquid for ion exchange. At this time, a large compressive stress layer is formed on the chemically strengthened glass plate 10 by overlapping the compressive stress layer by the chemical strengthening process with the compressive stress layer 14 resulting from the Si-rich layer. The thickness of the compressive stress layer formed from the glass surface toward the inside by ion exchange is 20 to 100 μm.
The maximum stress value (absolute value) of the compressive stress layer expanded by ion exchange is preferably 300 MPa or more, and more preferably 400 MPa or more. By setting the maximum value of the stress value (absolute value) to 300 MPa or more, the chemically strengthened glass plate 10 can obtain sufficient strength to protect a display or the like, for example. In addition, although the intensity | strength of glass improves, so that the said stress value (absolute value) is high, the impact when the tempered glass is damaged also becomes large. In order to prevent an accident due to the impact, the chemically strengthened glass plate 10 preferably has a maximum stress value (absolute value) of the compressive stress layer of 950 MPa or less, more preferably 800 MPa or less, More preferably, it is 700 MPa or less. On the other hand, the stress value (absolute value) of the tensile stress layer is unlikely to increase as compared with a conventional glass plate in which a compression stress layer is formed on the glass surface by rapidly cooling the glass.

  The thickness of the compressive stress layer after the chemical strengthening treatment is 20 μm or more, preferably 30 μm or more and 40 μm or more. As the thickness of the compressive stress layer increases, even when the tempered glass is deeply scratched, the tempered glass is less likely to break, and the variation in mechanical strength is reduced. On the other hand, the thickness of the compressive stress layer is 100 μm or less. The thickness of the compressive stress layer is preferably 90 μm or less and 80 μm or less in consideration of ease of processing of the tempered glass.

  In addition, it is preferable that the thickness of the cover glass to which the tempered glass to which the glass plate 10 and the glass plate 10 were chemically strengthened is applied is 1.5 mm or less. Here, in the glass plate of 1.5 mm or more, the strength of the glass plate itself is increased, and the compressive stress layer 14 formed in the vicinity of the glass surface does not function sufficiently. That is, the thickness of the glass plate 10 or the cover glass formed in the present embodiment is preferably 1.0 mm or less, 0.7 mm or less, 0.5 mm or less, 0.3 mm or less. The thinner the thickness, the more remarkable the effect of the present invention.

  Moreover, the glass plate manufacturing method of this embodiment is suitable for a large glass plate. This is because the larger the glass plate, the larger the amount of bending and the easier the glass plate breaks due to fine scratches resulting from handling, but the occurrence of the above problem can be reduced by forming the compressive stress layer 14 on the glass surface. Because. For this reason, when the width direction of the glass plate 10 is a glass plate of 1000 mm or more and 2000 mm or more, the effect of this invention becomes remarkable.

(Glass type of glass plate)
As the glass used for the glass plate 10, types such as borosilicate glass, aluminosilicate glass, aluminoborosilicate glass, soda lime glass, alkali silicate glass, alkali aluminosilicate glass, and alkali aluminogermanate glass can be used. In addition, the glass applicable to the glass plate of the present invention is not limited to the above type, and at least at SiO ₂ and the glass melting temperature (glass viscosity is 10 ^4.5 to 10 ⁵ poise or temperature 1100 to 1300 ° C.). saturated vapor pressure may be a type of glass including, a high volatile component than SiO _2. Al ₂ O ₃ is a network-forming oxide and is a component having a relatively low saturated vapor pressure among glass components. However, in this embodiment, since the saturated vapor pressure is higher than that of SiO ₂ , Al ₂ O ₃ is included in the volatile component.
In addition, it is more preferable that content of the volatile component in a glass composition is 30 mass% or more, and it is further more preferable that it is 35 mass% or more and 40 mass% or more. Therefore, in the tensile stress layer 12 of the glass plate 10 where the volatile components of the glass plate 10 do not volatilize, the content of the volatile components is 30% by mass or more. When the content of the volatile component in the glass composition is less than 30% by mass, volatilization of the volatile component is not promoted, and it becomes difficult to form a Si-rich layer or a compressive stress layer on the glass surface. Further, when a large amount of volatile components are contained, volatilization increases excessively and it becomes difficult to homogenize the glass. For this reason, it is preferable that content of the volatile component in a glass composition is 60 mass% or less, 50 mass% or less, and it is further more preferable that it is 45 mass% or less.

(Example composition of each glass)
For example, the aluminoborosilicate glass includes the following components. In addition, the% display of the composition described below is a mass% display. Aluminoborosilicate glass is used for a flat panel display glass substrate, for example. The indication in the following parentheses is the preferred content of each component.
_{SiO 2: 50~70% (55~65%} , 57~64%, 58~62%),
_{Al 2 O 3: 5~20% (} 10~20%, 12~18%, 15~18%),
B ₂ O ₃ : 0 to 15% (5 to 15%, 6 to 13%, 7 to 12%),
At this time, the following composition may be included as an optional component.
MgO: 0 to 10% (lower limit is 0.01%, lower limit is 0.5%, upper limit is 5%, upper limit is 4%, upper limit is 2%),
CaO: 0 to 10% (lower limit is 1%, lower limit is 3%, lower limit is 4%, upper limit is 9%, upper limit is 8%, upper limit is 7%, upper limit is 6%),
SrO: 0 to 10% (lower limit is 0.5%, lower limit is 3%, upper limit is 9%, upper limit is 8%, upper limit is 7%, upper limit is 6%),
BaO: 0 to 10% (upper limit is 8%, upper limit is 3%, upper limit is 1%, upper limit is 0.2%),
ZrO ₂ : 0 to 10% (0 to 5%, 0 to 4%, 0 to 1%, 0 to 0.1%).

Furthermore, the following composition is illustrated as alumino borosilicate glass. The indication in the following parentheses is the preferred content of each component.
_{SiO 2: 50~70% (55~65%} , 58~62%),
Al ₂ O ₃ : 10 to 25% (15 to 20%, 15 to 18%),
_{B 2 O 3: 5~18% (} 8~14%, 10~13%),
MgO: 0 to 10% (1 to 5%, 1 to 2%),
CaO: 0 to 20% (1 to 7%, 4 to 7%),
SrO: 0 to 20% (1 to 10%, 1 to 3%),
BaO: 0 to 10% (0 to 2%, 0 to 1%),
_{K 2 O: 0~2% (0.1~2} %, 0.1~0.5%),
_{SnO 2: 0~1% (0.01~0.5%} , 0.01~0.3%).

Examples of the alkali aluminosilicate glass include the following components. Alkali aluminosilicate glass is used, for example, as a cover glass for display screens of electronic devices. The indication in the following parentheses is the preferred content of each component.
_{SiO 2: 50~70% (55~65%} , 57~64%, 57~62%),
_{Al 2 O 3: 5~20% (} 9~18%, 12~17%),
_{Na 2 O: 6~30% (7~20} %, 8~18%, 10~15%),
At this time, the following composition may be included as an optional component.
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% (lower limit is 1%, lower limit is 2%, upper limit is 6%, upper limit is 5%, upper limit is 4%),
MgO: 0 to 10% (lower limit is 1%, lower limit is 2%, lower limit is 3%, lower limit is 4%, upper limit is 9%, upper limit is 8%, upper limit is 7%),
CaO: 0 to 20% (lower limit is 0.1%, lower limit is 1%, lower limit is 2%, upper limit is 10%, upper limit is 5%, upper limit is 4%, upper limit is 3%),
_{ZrO 2: 0~10% (0~5%} , 0~4%, 0~1%, 0~0.1%).

Furthermore, the following composition is illustrated as alkali-aluminosilicate glass.
SiO _2: 50~70%,
Al ₂ O _3: 5~20%,
Na ₂ O: 6~20%,
K ₂ O: 0~10%,
MgO: 0 to 10%,
CaO: more than 2% to 20%
ZrO ₂ : 0 to 4.8%,
Furthermore, preferably,
SiO ₂ content -1 / 2 · Al ₂ O ₃ content: 46.5 to 59%,
CaO / RO (wherein R is at least one selected from Mg, Ca, Sr and Ba) content ratio exceeds 0.3%,
SrO content + BaO content is less than 10%,
(ZrO ₂ + TiO ₂ ) / SiO ₂ content ratio is from 0 to less than 0.07,
B ₂ O ₃ / R1 ₂ O (wherein R1 is at least one selected from Li, Na and K) The content ratio is less than 0 to less than 0.1.

Furthermore, the following composition is illustrated as another alkali aluminosilicate glass.
SiO _2: 58~68%,
Al ₂ O _3: 8~15%,
Na ₂ O: 10~20%,
Li ₂ O: 0 to 1%
K ₂ O: 1~5%,
MgO: 2-10%.

(Each component)
SiO ₂ is a component constituting the glass skeleton of the glass plate 10 and has an effect of improving the chemical durability and heat resistance of the glass. When the SiO ₂ content is too low, the effects of chemical durability and heat resistance are not sufficiently obtained, and when the SiO ₂ content is too high, the glass tends to be devitrified, making molding difficult, The viscosity increases and it becomes difficult to homogenize the glass.

Al ₂ O ₃ is a component that forms a glass skeleton, and has an effect of increasing the chemical durability and heat resistance of the glass. It also has the effect of increasing ion exchange performance and etching rate. If the Al ₂ O ₃ content is too low, the effects of chemical durability and heat resistance of the glass cannot be obtained sufficiently. On the other hand, when the Al ₂ O ₃ content is too high, the viscosity of the glass is increased and dissolution becomes difficult, and the acid resistance is lowered.

B ₂ O ₃ is a component that lowers the viscosity of the glass and promotes melting and clarification of the glass. If the B ₂ O ₃ content is too low, the viscosity of the glass becomes high and it becomes difficult to homogenize the glass.

  MgO and CaO are components that lower the viscosity of the glass and promote glass melting and fining. Further, Mg and Ca are advantageous components for improving the meltability while reducing the weight of the obtained glass because the ratio of increasing the density of the glass is small in the alkaline earth metal. However, if the MgO and CaO content is too high, the chemical durability of the glass is lowered.

  SrO and BaO are components that lower the viscosity of the glass and promote glass melting and fining. Moreover, it is also a component which improves the oxidizability of a glass raw material and improves clarity. However, if the SrO and BaO content is too high, the density of the glass increases, the weight of the glass plate cannot be reduced, and the chemical durability of the glass decreases.

Li ₂ O 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 is one of the ion exchange components, and the effect of increasing the depth of the compressive stress layer 14 is high among alkali metal oxides. However, if the Li ₂ O content is too high, the liquidus viscosity is lowered and the glass is easily devitrified, making it difficult to stably mass-produce 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, when performing an ion exchange process for strengthening a glass substrate, there is an inconvenience that the ion exchange salt is rapidly deteriorated in the ion exchange process. Further, if the Li ₂ O content is too high, the low-temperature viscosity of the glass is excessively reduced, stress relaxation occurs in the heating step after chemical strengthening, and the compressive stress value is decreased. Can not get a good strength.

Na ₂ O is an essential component that lowers the high-temperature viscosity of the glass and improves the meltability and moldability of the glass. Moreover, it is a component which improves the devitrification resistance of glass. When the Na ₂ O content is less than 6% by mass, the melting property of the glass is lowered, and the cost for melting is increased. Further, Na ₂ O is an ion exchange component, and when the chemical strengthening treatment is performed, if the Na ₂ O content is less than 6% by mass, the ion exchange performance is also deteriorated, so that sufficient 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 also lowered, it is impossible to apply the downdraw method for overflowing the glass, so that stable mass production of glass becomes difficult. On the other hand, if the Na ₂ O content is too high, the low-temperature viscosity decreases, the thermal expansion coefficient becomes excessive, the impact resistance decreases, and the thermal expansion coefficient matches with peripheral materials such as metals and organic adhesives. It becomes difficult. In addition, since the devitrification resistance is lowered due to the deterioration of the glass balance, it is difficult to stably mass-produce glass using the downdraw method.

K ₂ O is a component that lowers the high-temperature viscosity of the glass and improves the meltability and moldability of the glass and at the same time improves the devitrification resistance. Further, K 2 _O is an ion exchange component, a component capable of improving the ion exchange performance of a glass by containing K 2 _O. However, if the content of K ₂ O becomes too high, 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. Further, when the K 2 _O content is too high, the peripheral material and thermal expansion coefficient such as metal or organic adhesive is hardly matched. Further, since the devitrification resistance is lowered due to the deterioration of the glass balance, it is difficult to stably mass-produce glass using the downdraw method.

Since Li ₂ O, Na ₂ O and K ₂ O are components that are eluted from the glass to deteriorate TFT characteristics, and increase the thermal expansion coefficient of the glass to damage the substrate during heat treatment, flat panel displays When applied as a glass substrate, it is not preferable to contain a large amount. However, by deliberately containing a specific amount of the above components in the glass, while suppressing deterioration of TFT characteristics and thermal expansion of the glass within a certain range, the melting property of the glass is increased, and the basicity of the glass is increased, It is possible to easily oxidize a metal whose valence varies and to exhibit clarity.

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

TiO ₂ is a component that lowers the high temperature viscosity of the glass. TiO ₂ is a component that improves ion exchange performance. However, when the content of TiO ₂ becomes too high, the devitrification resistance is lowered. Furthermore, since the glass is colored, application to a glass substrate for FPD or a cover glass of a display screen of an electronic device is not preferable. Further, since the glass is colored, the ultraviolet transmittance is reduced, and therefore, when the treatment using the ultraviolet curable resin is performed, there is a disadvantage that the ultraviolet curable resin cannot be sufficiently cured.

In the glass of the glass plate 10, a clarifier 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.
In addition, As ₂ O ₃ and Sb ₂ O ₃ are substances having an effect of refining the glass by causing a reaction with valence fluctuation in the molten glass, but As ₂ O ₃ and Sb ₂ O ₃ are environmental loads. Therefore, in the glass plate 10 of this embodiment, As ₂ O ₃ and Sb ₂ O ₃ are not substantially contained in the glass. In the present specification, “substantially not containing As ₂ O ₃ and Sb ₂ O _3” means less than 0.01% by mass and intentionally not containing impurities.

(Glass plate manufacturing method)
Such a glass plate 10 is manufactured using a downdraw method. Drawing 3 is a figure explaining an example of the flow of the manufacturing method of the glass plate of this embodiment. The glass plate manufacturing method includes a melting step (step S10), a refining step (step S20), a stirring step (step S30), a forming step (step S40), a slow cooling step (step S50), and a cutting plate. It mainly includes a process (step S60) and a shape processing process (step S70). Furthermore, a chemical strengthening process by ion exchange may be performed after the shape processing step (step S70).

In the melting step (step S10), in a melting furnace (not shown), the glass raw material is heated by indirect heating by combustion of fossil fuel and direct heating by electric conduction to produce molten glass. The melting of the glass may be performed by other methods.
Next, a clarification process is performed (step S20). In the clarification step, bubbles in the molten glass are removed using the above-described clarifier while the molten glass is stored in a liquid tank (not shown). Specifically, it is performed by a redox reaction of a metal oxide whose valence fluctuates in molten glass. In the molten glass at a high temperature, the metal oxide releases oxygen by a reduction reaction, and this oxygen becomes a gas, and bubbles in the molten glass grow and float on the liquid surface. Thereby, bubbles in the molten glass are defoamed. Or the bubble of oxygen gas takes in the gas in the other bubble in a molten glass, grows, and floats on the liquid level of a molten glass. Thereby, bubbles in the molten glass are defoamed. Further, when the temperature of the glass decreases after defoaming, the metal oxide undergoes an oxidation reaction and absorbs oxygen contained in the small bubbles remaining in the glass without rising. As oxygen is absorbed, the bubbles become smaller and reabsorbed into the glass.
Next, a stirring process is performed (step S30). In the stirring step, the molten glass is passed through a vertically-shown stirring tank (not shown) in order to maintain the chemical and thermal uniformity of the glass. While the molten glass is being stirred by the stirrer provided in the stirring tank, the molten glass moves to the bottom in the vertical downward direction and is guided to the subsequent process. Thereby, nonuniformity of the glass such as striae can be suppressed.

  Next, a molding process is performed (step S40). In the molding process, a downdraw method is used. The down-draw method including overflow down-draw and slot down-draw is a known method using, for example, Japanese Patent Application Laid-Open No. 2010-189220, Japanese Patent No. 3586142 and the apparatus shown in FIG. The molding process in the downdraw method will be described later. Thereby, a sheet-like glass ribbon having a predetermined thickness and width is formed. As a molding method, an overflow downdraw is most preferable among the downdraw methods, but a slot downdraw may be used. However, in order to increase the stress value (absolute value) of the compressive stress layer 14 by promoting the volatilization of volatile components or increasing the volatilization amount, an overflow downdraw with a large volatilization amount is preferable.

Next, a slow cooling process is performed (step S50). Specifically, the glass ribbon formed into a sheet shape is cooled below the annealing point in a slow cooling furnace (not shown) by controlling the cooling rate so that distortion does not occur. Thereby, the glass ribbon has the compressive stress layer 14 and the tensile stress layer 12 in terms of stress, and the Si-rich layer in terms of composition, like the glass plate 10 as the final product.
Next, a cutting board process is performed (step S60). Specifically, the continuously generated glass ribbon is cut every certain length to obtain a glass plate.
Thereafter, a shape processing step is performed (step S70). In the shape processing step, the glass surface and end faces are ground and polished in addition to cutting out to a predetermined glass plate size and shape. For the shape processing, physical means using sandblast, cutter or laser may be used, or chemical means such as etching may be used.

An example of the shape processing of the glass plate 10 is an etching process in which holes are formed in the glass plate 10 and processed into an outer shape including curves and straight lines. The glass plate 10 processed into such an outer shape is used, for example, as a cover glass for a display screen of an electronic device.
In this case, first, a resist material is coated on both main surfaces of the glass plate. Next, the resist material is exposed through a photomask having a pattern having a desired outer shape. Although the outer shape is not particularly limited, for example, an outer shape including a portion having a negative curvature (a portion that turns to the right as it travels while proceeding to the left while looking inside the region of the outer shape along the edge of the outer shape) is there. Next, the resist material after exposure is developed, a resist pattern is formed in a region other than the etched region of the glass substrate, and the etched region of the glass substrate is etched. At this time, when a wet etchant is used as the etchant, the glass substrate is isotropically etched. As a result, the end surface of the glass plate is formed so that the central portion protrudes most outward and the inclined surface is gently curved from the central portion toward both main surface sides. The boundary between the inclined surface and the main surface and the boundary of the same surface of the inclined surface are preferably rounded.

The resist material used in the etching step is not particularly limited, and a material having resistance to an etchant used when etching glass with a resist pattern as a mask can be used. For example, since glass is generally corroded by wet etching of an aqueous solution containing hydrofluoric acid or by dry etching of a fluorine-based gas, a resist material having excellent resistance to hydrofluoric acid is suitable. The etchant includes hydrofluoric acid, sulfuric acid,
A mixed acid containing at least one of nitric acid, hydrochloric acid, and silicic acid can be used.
By using hydrofluoric acid or the above mixed acid aqueous solution as an etchant, a cover glass having a desired shape can be obtained.

Further, when performing shape processing using etching, a complicated outer shape can be easily realized only by adjusting the mask pattern. Furthermore, by performing shape processing by etching, productivity can be further improved and processing costs can be reduced. Note that an alkaline solution such as KOH or NaOH can be used as a stripping solution for stripping the resist material from the glass substrate. The types of the resist material, etchant, and stripping solution can be appropriately selected according to the material of the glass plate.
As an etching method, not only a method of immersing in an etching solution but also a spray etching method in which an etching solution is sprayed can be used. By processing the glass substrate using such etching, it is possible to obtain a cover glass having an end surface with a highly smooth surface roughness. That is, it is possible to prevent the occurrence of microcracks that are inevitably generated when the shape is processed by machining, and the mechanical strength of the cover glass can be further improved.

  In some cases, chemical strengthening treatment by ion exchange is performed after the shape processing step. For example, a glass plate such as aluminoborosilicate glass used for a flat panel display is not subjected to chemical strengthening treatment. On the other hand, a chemical strengthening treatment is performed on a glass plate suitably used for a cover glass of a display screen of an electronic device such as alkali aluminosilicate glass.

By further chemically strengthening the glass plate 10 in which the Si-rich layer and the compressive stress layer 14 are formed in the vicinity of the glass surface, the strength of the glass plate 10 can be further improved. Moreover, compared with the conventional glass plate which forms a compressive-stress layer on the surface by quenching glass, the stress value (absolute value) of the tensile-stress layer of the glass plate of this embodiment does not become large easily.
In order to carry out the ion exchange process, the glass component, it preferably contains Na 2 _O and Li 2 _O is an ion exchange component. The chemically strengthened tempered glass of the present embodiment includes, in addition to a cover glass for a display screen of an electronic device, a casing for a mobile terminal device, a cover glass for a solar cell, a glass substrate for display, a cover glass for a touch panel display, and a touch panel. It can be applied to a glass substrate of a display.
For example, the chemical strengthening treatment can be performed using the following method.

In the chemical strengthening treatment, the glass plate 10 is immersed in a KNO ₃ 100% treatment bath maintained at, for example, about 350 to 550 ° C. for about 1 to 25 hours. At this time, the glass plate is chemically strengthened by ion exchange of Na ⁺ ions or Li ⁺ ions on the surface of the glass with K ⁺ ions or Li ⁺ ions in the treatment bath. Note that the temperature, time, ion exchange solution, and the like during the ion exchange treatment can be changed as appropriate. For example, the ion exchange solution may be a mixed solution of two or more types.

  In addition to this, the method for producing a glass plate includes a cleaning step and an inspection step, but description of these steps is omitted.

In the production of the glass plate 10 of the present embodiment, in the molding process, the volatilization of volatile components is promoted from the glass ribbon or the volatilization amount is increased, thereby forming a Si rich layer. After the slow cooling, the compressive stress layer 14 and the tensile stress layer 12 are formed before the cutting step. The volatile component is a component that is more volatile than SiO ₂ , in other words, in molten glass (for example, the viscosity of the glass is 10 ^4.5 to 10 ⁵ poise, or the temperature is 1100 to 1300 ° C.), and the saturated vapor pressure is higher than that of SiO _2. Indicates a high component. 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 this. B ₂ O ₃ , alkali oxides (Li ₂ O, Na ₂ O, K ₂ O), and alkaline earth metal oxides (MgO, CaO, SrO, BaO) have high volatility, and thus are used as glass components. It is preferable to contain at least one kind. SnO ₂ is volatilized as SnO.
If volatilization is excessive, the glass plate cannot be molded properly. For example, 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. Further, K ₂ O used as a glass melting accelerator is eluted from the glass plate when added in a large amount. Therefore, when used in flat panel display glass substrates such as liquid crystal display device glass substrates, the upper limit of the content of K 2 _O is more preferably 0.5% by mass.

Since these volatile components have a saturated vapor pressure higher than that of SiO ₂ in the molten glass, they are volatilized from the molten glass or glass ribbon at the time of molding (in a molten state of the glass). That is, in a molding process in which a glass ribbon is formed from molten glass, components other than SiO ₂ are volatilized on the glass ribbon surface. As a result, the Si atom concentration in the glass surface after molding has Si atoms inside the glass. A Si-rich layer that is higher than the concentration is formed. Further, when the Si-rich layer is formed on the glass surface of the glass plate, the compressive stress layer 14 is formed on the glass surface due to the difference in thermal expansion coefficient from the inside of the glass.

(Molding equipment)
FIG. 4 is a diagram illustrating an example of a molding apparatus that performs a molding method using a downdraw method.
The forming device 101 has a pentagonal wedge shape (a narrow baseball home base shape) that is pointed downward. The forming apparatus 101 has an upper surface provided with a linearly extending groove 111, a groove 111 provided on the upper surface, and a pair of wall surfaces 112 facing downward from both parallel end portions. In the present specification, for convenience of explanation, the direction in which the groove 111 extends on the horizontal plane (the vertical direction in FIG. 4) is the X direction, the direction perpendicular to the X direction on the horizontal plane is the Y direction, and the vertical direction is the vertical direction. It is also called the Z direction (see Fig. 5).

  The groove 111 gradually decreases in depth from one end to the other end so as to uniformly overflow the molten glass 103 supplied to one end from a supply pipe (not shown) over the entire length. Each of the pair of wall surfaces 112 has 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 ends of these inclined surfaces intersect to form a ridge line extending in the X direction.

  The forming apparatus 101 continuously melts the molten glass 103 from both sides of the groove 111, guides the overflowed molten glasses on the wall surface 112, and fuses them at the lower end of the inclined surface, thereby continuously forming the belt-like glass ribbon 104. Form.

  The heat insulating structure 102 forms a molding space (chamber) in which the molding apparatus 101 is accommodated. Specifically, the heat insulating structure 102 is made of a material having excellent heat insulating properties, and includes a bottom wall 121 and a ceiling wall 123 that face each other with the molding apparatus 101 in the vertical direction, and a bottom wall 121 and a ceiling wall 123. The peripheral wall 122 of the rectangular cylinder which connects the periphery of each. In the center of the bottom wall 121, a gate 125 that allows the glass ribbon 104 formed by the molding apparatus 101 to pass therethrough is provided. The heat insulating structure 102 may have a hollow structure, and air for heating or cooling may be supplied to the inside.

In the present embodiment, as shown in FIG. 4, a plurality of discharge ports 126 penetrating the peripheral wall 122 are provided on the upper portion of the long wall portion of the peripheral wall 122 facing the wall surface 112 of the molding apparatus 101 and facing the Y direction. . Further, a plurality of inlets 127 penetrating the peripheral wall 122 are provided in the lower portion of the long wall portion facing the Y direction of the peripheral wall 122. For this reason, an air flow as shown by arrows a, b, and c in FIG. 4 is formed by natural convection. That is, the air outside the heat insulating structure 102 is introduced into the heat insulating structure 102 through the inlet 127. The introduced air rises along the molten glass 103 flowing down on the wall surface 112 of the molding apparatus 101 and is then discharged out of the heat insulating structure 102 through the discharge port 126. In this way, by raising fresh air taken from outside in the heat insulating structure 102, volatile components from the molten glass 103 (for example, Al ₂ O ₃ , B ₂ O ₃ , Li ₂ O, Na ₂ O). , K ₂ O, MgO, CaO, SrO, BaO, ZrO ₂ , SnO _2, etc.) can be promoted. When the glass ribbon 104 is cooled, a Si-rich layer is formed on the portion where the volatile components are volatilized, that is, on the surface of the molten glass 103 in contact with the rising air. The compression stress layer 14 is formed by the generation of the Si rich layer. In order to increase the stress value (absolute value) of the compressive stress layer 14, it is preferable that the molten glass 103 contains many volatile components.

  In addition, the discharge port 126 and the introduction port 127 may be provided also in the short wall part which faces the X direction in the surrounding wall 122. FIG. Alternatively, the discharge port 126 and the introduction port 127 can be provided only in the short wall portion of the peripheral wall 122 facing the X direction. However, in order to volatilize the volatile components uniformly over the entire width of the molten glass 103, the discharge ports 126 and the introduction ports 127 should be provided at a constant pitch only in the long wall portion facing the Y direction of the peripheral wall 122. preferable.

  Further, the shape and quantity of the discharge port 126 and the introduction port 127 can be appropriately selected as long as the necessary strength is maintained in the peripheral wall 122. For example, the shapes of the discharge port 126 and the introduction port 127 may be circular as shown in FIG. 5, or the number may be reduced as slits extending in the X direction. In order to exhaust gas uniformly and efficiently from the heat insulating structure 102, it is more effective to use a slit extending over the entire width direction of the glass ribbon. However, the wider the opening area of the slit, the more the gas flow rate increases, resulting in problems such as an increase in the surface defects of the glass plate, deterioration of the surface irregularities of the glass, and difficulty in securing the molding temperature. However, as shown below, the problem is that the temperature of air or inert gas introduced into the heat insulating structure 102 from the inlet 127 is set to the target temperature in the heat insulating structure 102 and the heat insulating structure 102 This can be solved by adjusting the gas flow rate so that the pressure can be maintained at a predetermined pressure.

  Furthermore, the air introduced into the heat insulating structure 102 through the inlet 127 is preferably a temperature that does not lower the temperature of the molten glass 103 or the glass ribbon 104, for example. Here, if the amount of air to be introduced is small, the temperature of the molten glass 103 and the glass ribbon 104 does not decrease so much even if air at normal temperature is introduced. For this reason, normal temperature air may be introduced. On the other hand, if the amount of air introduced into the heat insulating structure 102 is large, the temperature of the molten glass 103 and the glass ribbon 104 is greatly lowered when air at normal temperature is introduced. In this case, it is preferable that a heating device (not shown) for heating the air introduced through the inlet 127 to a predetermined temperature is provided outside or inside the heat insulating structure 102.

  In the molding apparatus 101 described above, while the molten glass 103 overflows from both sides of the groove 111 of the molding apparatus 101 surrounded by the heat insulating structure 102, air flows along the molten glass 103 flowing down on the wall surface 112 of the molding apparatus 101. After rising, the heat insulation structure 102 is discharged. Here, the air is introduced from outside the heat insulating structure 102 into the heat insulating structure 102. Thus, volatilization of the volatile components from the molten glass 103 is promoted by the air in the heat insulating structure 102 flowing along the molten glass flowing down on the wall surface 112 of the molding apparatus 101. Thereby, the glass plate 10 in which the compressive-stress layer 14 with a high stress value was formed in the front and back both surfaces of the glass of the glass plate 10 can be obtained.

  In the present embodiment, the discharge port 126 is provided on the upper portion of the peripheral wall 122, but the position of the discharge port 126 is not particularly limited. For example, as shown in FIG. 6, the discharge port 126 may be provided in a portion of the ceiling wall 123 directly above the molding apparatus 101. Even in this case, the air introduced into the heat insulating structure 102 from the outside of the heat insulating structure 102 is raised along the molten glass 103 flowing down on the wall surface 112 of the molding apparatus 101 by natural convection, and then the discharge port 126. Through the heat insulating structure 102. In this case, since the molten glass 103 is in contact with the air passing through the heat insulating structure 102 even at the upper part of the molding apparatus 101, the volatilization of the volatile components is less than when the discharge port 126 is provided at the upper part of the peripheral wall 122. Further promote.

  However, when the discharge port 126 is provided in the ceiling wall 123, falling objects such as dust from above the heat insulating structure 102 may fall into the molten glass 103 through the discharge port 126. From this point of view, it is preferable to provide the discharge port 126 at the upper portion of the peripheral wall 122 as in the embodiment shown in FIGS.

  In the embodiment shown in FIGS. 4 and 5, the introduction port 127 is provided in the lower part of the peripheral wall 122, but the position of the introduction port 127 is not particularly limited. For example, as shown in FIG. 7, the inlet 127 may be provided in the bottom wall 121. In this case, if the inlet 127 is in the region R immediately below the molding apparatus 101, the air flow from the inlet 127 may affect the shape stability of the glass ribbon 104. For this reason, the introduction port 127 is preferably provided outside the region R.

  Further, as shown in FIG. 6, the introduction port 127 may not be provided. Even in this case, air outside the heat insulating structure 102 is introduced into the heat insulating structure 102 through the gate 125. However, in this case, air passes through the gate 125 in the opposite direction to the glass ribbon 104, and the shape stability of the glass ribbon 104 may be impaired. It is preferable to provide it.

  4-7, air is introduced into the heat insulating structure 102 and discharged outside the heat insulating structure 102 by natural convection, but air is introduced and discharged by forced convection. It is also possible to do this. For example, a supply pipe may penetrate through the lower part of the heat insulating structure 102, a discharge pipe may penetrate through the upper part of the heat insulating structure 102, and a fan may be connected to the supply pipe or the discharge pipe. In this case, the end portions of the supply pipe and the discharge pipe that open to the space in the heat insulating structure 102 constitute the introduction port and the discharge port, respectively. Other methods for introducing air include, for example, a method in which compression air is introduced under reduced pressure through a filter. The air introduction method is not limited to the above, and other air introduction methods may be used.

  Further, the gas introduced into the heat insulating structure 102 through the inlet 127 or the gate 125 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 101 and the heat insulating structure 102.

In the embodiment shown in FIGS. 4 to 7, gas is introduced into the heat insulating structure 102, and the vaporized volatilization in the heat insulating structure 102 is caused by flowing the gas along the flowing direction of the molten glass 103 or the glass ribbon 104. The concentration of the component (a volatile component having a higher saturated vapor pressure than that of SiO ₂ ) can be reduced. When the gas is not flowed, the volatile component is saturated in the heat insulating structure 102, so that the volatilization of the volatile component cannot be further promoted. That is, the gas introduced into the heat insulating structure 102 functions to reduce the concentration of vaporized volatile components in the heat insulating structure 102. Therefore, the flow of the gas introduced from the outside is not limited to ascending but may be descending.

Further, as another method for promoting the volatilization of the volatile components of the molten glass 103 or the glass ribbon 104, the inside of the molding space in the heat insulating structure 102 can be made a reduced pressure atmosphere. If the molding space in the heat insulating structure 102 is depressurized, volatilization of volatile components is promoted.
For example, the inside of the heat insulating structure 102 can be depressurized by providing a suction device at the discharge port 126 shown in FIG. Note that the number of discharge ports 126 provided in the heat insulating structure 102 and the number of suction devices provided are not particularly limited, and one or more may be provided.
Note that if the molding space in the heat insulating structure 102 is excessively depressurized, a gas having a lower temperature than that in the heat insulating structure 102 is introduced from the gate 125, the glass ribbon 104 is not uniformized, and the thickness of the glass plate 10 varies. And further distortion may occur.
Therefore, it is preferable to depressurize the molding space in the heat insulating structure 102 within a range of 1/10 or less compared to that in the heat insulating structure 102 before pressure reduction. That is, when the pressure in the molding space in the heat insulating structure 102 is 1 atm, it is preferable to reduce the pressure to 0.9 atm.
Thus, the glass ribbon 104 is formed by adjusting the atmosphere of the molding space in the heat insulating structure 102.

Furthermore, as another method for promoting the volatilization of the volatile components of the molten glass 103 or the glass ribbon 104, the atmosphere temperature of the molding space in the heat insulating structure 102 can be increased. If the atmospheric temperature of the molding space in the heat insulating structure 102 rises, the saturated vapor pressure of the volatile component also rises, so that the volatilization of the volatile component is promoted.
In addition, when the atmospheric temperature of the molding space in the heat insulation structure 102 rises too much, it will become difficult to shape | mold the glass ribbon 104, and also energy consumption will increase. For this reason, the range of the increase in the atmospheric temperature of the molding space in the heat insulating structure 102 to be raised is preferably more than 0 to 100 ° C, more preferably more than 0 to 50 ° C, more than 0 to 10 ° C. More preferably it is.
In this way, the atmosphere of the molding space in the heat insulating structure 102 is adjusted, and the partial pressure of the volatile component and the saturated vapor of the volatile component in the atmosphere facing the surface of the molten glass 103 or the glass ribbon 104 in the heat insulating structure 102. Increase the pressure difference. Thereby, the glass ribbon 104 is formed while promoting the volatilization of the volatile components. Such a method of promoting volatilization of volatile components from the surface of the molten glass and glass ribbon can be applied to only one surface in addition to both surfaces of the molten glass and glass ribbon.

Furthermore, as a method of increasing the volatilization amount of the volatile component of the molten glass 103 or the glass ribbon 104, the distance from the lower end portion of the molding apparatus 101 to the upper end portion of the gate 125 in the molding process can be increased. By increasing this distance, the passage time for the glass ribbon 104 to pass through the molding space can be increased. As a result, the time during which the glass ribbon 104 is exposed to a high temperature in the space in the heat insulating structure 102 becomes longer, and the volatilization time increases. For this reason, the volatilization amount of the volatile component of the glass ribbon 104 increases.
If the distance is too long, the thickness of the glass ribbon 104 to be formed changes. For this reason, it is more preferable that the increment of the distance is greater than 0 to 20 mm, greater than 0 to 10 mm, greater than 0 to 5 mm, greater than 0 to 1 mm, and greater than 0 to 0.1 mm.

  Alternatively, the size of the molded body device 101 itself may be increased to increase the length of flow of the wall surface 112 through which the molten glass 103 flows. As a result, the time during which the molten glass 103 is exposed to a high temperature in the space in the heat insulating structure 102 becomes longer, and the volatilization time increases. For this reason, the volatilization amount of the volatile component of the molten glass 103 increases.

  Although various methods for promoting volatilization of volatile components from the molten glass passing through the heat insulating structure 102 or increasing the volatilization amount have been described, these methods can be used alone or in combination.

In the glass plate 10 thus manufactured, the compressive stress layer 14 is thinly formed on the glass surface, so that the glass surface can be prevented from being scratched while maintaining the workability of the glass substrate.
In particular, when the glass plate 10 is used for an FDP glass substrate such as a glass substrate for a liquid crystal display device, it cannot contain a large amount of alkali metal ions that are ion exchange components. Therefore, the glass plate 10 is effective in that the compressive stress layer 14 can be obtained without performing ion exchange. Furthermore, since the compressive stress layer 14 which is thinner and has a larger stress value (absolute value) than the compressive stress layer of the conventional glass plate obtained by rapidly cooling the glass in the slow cooling step, the glass plate 10 is shaped. It can be used effectively as the previous thin glass plate.
A conventional glass plate may be scratched on the surface during conveyance between processes or during cutting or shape processing. However, when the glass plate 10 is chemically strengthened for use as a cover glass, it is possible to prevent the glass surface from being scratched before chemical strengthening, thus preventing damage to the cover glass surface, Surface quality can be improved.

(Example)
FIG. 8 is a diagram showing the distribution of the atomic concentration (%) of Si actually measured for the glass plate 10 of aluminoborosilicate glass. For the atomic concentration (%) of Si, the Si atomic concentration near the surface was measured using an X-ray photoelectron spectrometer (Quantera SXM manufactured 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 the measurement element, Al, B, Ca, Sr, and Ba, which are volatile components having a relatively high content, were specified together with Si, and the ratio of Si in the measurement element was determined. These components are volatile components that volatilize from the surface of the glass ribbon in the glass ribbon forming step. 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 Si atom concentration, these are not included in the measurement elements. The glass plate A and the glass plate B shown in FIG. 9 are glass plates produced by changing the conditions of flowing air using the apparatus shown in FIG.
As shown in FIG. 8, in both the glass plate A and the glass plate B, the region where the Si atom concentration is higher by 5% or more than the glass center position has a depth of more than 0 and 30 nm or less along the thickness direction from the glass surface. It is formed in the range. This is considered to be due to the fact that in the glass plate A and the glass plate B, the amount of volatile components is smaller in the vicinity of the glass surface than in the interior.

In addition, the content rate (mass%) of each composition of the said glass plate A and the glass plate B 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%

FIG. 9 is a diagram showing the distribution of internal stress measured for the glass plate 10 of the glass plate A. As shown in FIG. The internal stress was measured using a micro-area birefringence meter (KOBRA-CCD / X manufactured by Oji Scientific Instruments Co., Ltd.), and the optical path difference rate per cm for each predetermined depth from the surface of the cross section of the glass plate 10 cut in the thickness direction. It is calculated by measuring (optical path difference / optical path length) and dividing this by the photoelastic constant. In addition, "internal stress" has shown the average value of the thickness of 0-10 micrometers along the thickness direction of a glass plate. Therefore, locally, a stress value exceeding the result shown in FIG. 9 may be formed.
As shown in FIG. 9, it can be seen that the compressive stress layer 14 is formed on both the front and back surfaces of the glass plate 10, and the tensile stress layer 14 having a substantially constant tensile stress value is formed therein. It can also be seen that the stress value of the tensile stress layer 14 formed inside the glass plate is substantially constant in the glass plate thickness direction. This is due to the fact that volatile components are reduced in the vicinity of the front and back surfaces of the glass plate 10.

Furthermore, the glass plate 10 produced using the apparatus shown in FIG. Further, a glass plate having a compression / tensile stress profile shape different from those of Examples 1 to 5 by removing the compressive stress layer 14 of the glass plate produced by the same method as in Example 1 by surface polishing was used as Comparative Example 1. . During the production of the glass plate, the glass raw material of aluminoborosilicate glass is melted at 1580 ° C. using a continuous melting device equipped with a refractory brick melting tank and a platinum border frame tank, and clarified at 1650 ° C. Then, after stirring at 1500 ° C., a thin glass plate having a thickness of 0.7 mm was formed by the down-draw method using the apparatus shown in FIG. The actual measurement of the Si atom concentration and the internal stress of the glass plates of Examples 1 to 5 and Comparative Example 1 were performed in the same manner as the glass plates A and B.
In addition, a ball tip having a diameter of 0.7 mm (Bosch standard) is provided at the tip of an Erichsen model 318 (manufactured by Eriksen) scratch hardness meter under the conditions of a scratch load of 2 N and a scratch length of 30 mm. The glass plate of Example 1 was scratched. Thereafter, the glass surfaces of the glass plates of Examples 1 to 5 and Comparative Example 1 were observed with a laser microscope, and the glass plate in which cracks due to scratches progressed was defective, and the glass plate in which cracks had not progressed was evaluated as good. .
Table 1 below shows actual measurement results and evaluation results.

From Table 1 above, in each of Examples 1 to 5, the compressive stress layer 14 having a thickness of 50 μm or less is formed. For this reason, it is hard to adversely affect the efficiency of processing after glass forming. Moreover, all of Examples 1-5 were evaluated as good in the evaluation of scratches. From this, it can be seen that the glass surface of the glass plate 10 is strengthened to such an extent that the glass surface is not easily scratched without adversely affecting the efficiency of processing after glass forming.
Moreover, the fluctuation | variation of the stress value in the "tensile center area | region" of the tensile stress layer 12 of Examples 1-5, ie, the difference of the maximum value of stress value (absolute value), and all is 0.12 Mpa or less.

Furthermore, the glass plates of Examples 6 to 8 and Comparative Example 2 having the compositions shown in Table 2 below were chemically strengthened under the following conditions. Comparative Example 2 is a tempered glass obtained by polishing a portion of the compressive stress layer 14 formed on the surface of a glass plate produced by the same method as in Examples 6 to 8, and then chemically strengthening the portion.
The glass plates of Examples 6 to 8 and Comparative Example 2 were prepared by continuously dissolving glass raw materials prepared so as to have the composition shown in Table 2 below, including a refractory brick melting tank and a platinum border frame tank. Using a device, melt at 1520 ° C., clarify at 1550 ° C., stir at 1350 ° C., and then form a thin glass plate with a thickness of 0.7 mm by the down-draw method using the device shown in FIG. A glass plate was obtained. The glass plate of Comparative Example 2 was removed by polishing the surface of the compressive stress layer 14 of the glass plate 10 as in Comparative Example 1.
Next, the glass plates of Examples 6 to 8 and Comparative Example 2 were scratched on the glass surface by the method described above.
The cleaned glass plate is immersed in a 100% KNO ₃ treatment bath maintained at 400 ° C. for about 2.5 hours to exchange Na ⁺ ions existing on the glass surface layer with K ⁺ ions in the treatment bath. The glass plate was chemically strengthened. The glass plate after chemical strengthening was sequentially crushed and washed in a washing tank to obtain dried tempered glass.

The glass surfaces of Examples 6 to 8 and Comparative Example 2 thus obtained were observed with a laser microscope. At this time, the glass plate in which cracks due to scratches progressed was defective, and the glass plate in which cracks did not progress was considered good.
Table 2 below shows the composition and evaluation results.

  From the said Table 2, although evaluation of the damage | wound of Examples 6-8 was favorable, evaluation of the comparative example 2 was unsatisfactory. That is, it was found that Comparative Example 2 cannot prevent the occurrence of scratches. From this, it can be seen that it is preferable that the glass plate has the compressive stress layer 14 and the tensile stress layer 12 from the viewpoint of preventing the occurrence of scratches even when chemical strengthening is performed.

  As mentioned above, although the manufacturing method of the glass plate and glass plate of this invention was demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, even if various improvement and a change are carried out. Of course it is good.

DESCRIPTION OF SYMBOLS 10 Glass plate 12 Tensile stress layer 14 Compressive stress layer 101 Molding apparatus 102 Thermal insulation structure 103 Molten glass 104 Glass ribbon 111 Groove 112 Wall surface 121 Bottom wall 122 Perimeter wall 123 Ceiling wall 125 Gate 126 Outlet 127 Inlet

Claims (13)

A glass plate formed by the downdraw method,
A tensile stress layer formed inside the glass plate, and a compressive stress layer formed on both sides of the tensile stress layer,
The compressive stress layer is formed in a depth range from 10 μm to 50 μm or less along the thickness direction of the glass plate from the surface of the glass plate, and the thickness of the compressive stress layer is equal to the thickness of the glass plate. Less than one-third,
The absolute value of the stress value of the compressive stress layer is 4 MPa or less, and the absolute value of the stress value of the tensile stress layer is 0.4 MPa or less.   2. The difference between the maximum value and the minimum value of the stress value is 0.12 MPa or less in the tensile center region excluding the 1/10 portions on both sides in the thickness direction of the glass plate in the tensile stress layer. The glass plate as described in. The glass plate according to claim 1, wherein the tensile stress layer of the glass plate contains 30% by mass or more of a volatile component having a saturated vapor pressure higher than that of SiO ₂ in the molten state of the glass plate.   The glass plate of any one of Claims 1-3 used for the glass substrate for flat panel displays. A Si high concentration region in which the ratio of the Si atom concentration (atomic%) to the Si atomic concentration (atomic%) at the central position in the thickness direction of the glass plate is 5% or more is higher than 0 along the thickness direction from the glass surface. Formed in a large depth range of 30 nm or less,
The Si high concentration region has a maximum peak of Si atom concentration, and the Si atom concentration along the thickness direction of the glass plate is measured from the position of the maximum peak to the surface of the glass plate and the center of the glass plate. The glass plate according to claim 1, which continuously decreases to a position. Melting glass raw materials,
Using a downdraw method to form a glass ribbon from molten glass;
Cutting the glass ribbon to form a glass plate, and
A compressive stress layer formed in a depth range from 10 μm to 50 μm or less along the thickness direction of the glass ribbon from the surface of the glass ribbon, the compression stress layer being less than one-third of the thickness of the glass ribbon Two compressive stress layers having a thickness and an absolute value of the compressive stress value of 4 MPa or less, and a tensile stress layer sandwiched between the two compressive stress layers and having an absolute value of the tensile stress value of 0.4 MPa or less The glass ribbon is molded so as to have the following. A method for producing a glass plate.   When forming the glass ribbon from the molten glass, the difference between the partial pressure of the volatile component and the saturated vapor pressure of the volatile component in an atmosphere facing at least one surface of the molten glass and the glass ribbon is increased. The manufacturing method of the glass plate of Claim 6 which promotes volatilization of the volatile component from the surface of at least one of the said molten glass and the said glass ribbon, and shape | molds the said glass ribbon. When forming the glass ribbon, the glass ribbon is formed in a space for forming the glass ribbon in order to reduce the concentration of volatile components having a higher saturated vapor pressure than SiO ₂ in the molten glass in the space for forming the glass ribbon. The method for producing a glass plate according to claim 7, wherein a gas flow is formed along the glass ribbon. 8. When molding the glass ribbon, at least one of the pressure and temperature in the space is adjusted so as to promote volatilization of a volatile component having a higher saturated vapor pressure than SiO ₂ in the molten glass. The manufacturing method of the glass plate of description. When forming the glass ribbon, the passage time of the glass ribbon in the space for forming the glass ribbon is adjusted so as to increase the volatilization amount of the volatile component having a higher saturated vapor pressure than the SiO ₂ in the molten glass. The manufacturing method of the glass plate of Claim 6. An apparatus for producing a glass plate by a downdraw 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
The heat insulating structure is provided with a discharge port 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 the wall surface of the molding apparatus to the outside of the heat insulating structure. ing,
Glass plate manufacturing equipment. A method for producing a glass plate by a downdraw method,
While the molten glass overflows from both sides of the groove of the molding apparatus surrounded by the heat insulating structure, the gas introduced into the heat insulating structure from outside the heat insulating structure is raised along the molten glass flowing down on the wall surface of the molding apparatus. And a step of discharging outside the heat insulating structure after
Glass plate manufacturing method. A glass plate obtained by the glass plate manufacturing method according to claim 12,
A glass plate having compressive stress layers on both front and back surfaces.

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