WO2017010356A1

WO2017010356A1 - Glass substrate

Info

Publication number: WO2017010356A1
Application number: PCT/JP2016/069915
Authority: WO
Inventors: 朋美安部; 林　英明; 小池　章夫
Original assignee: 旭硝子株式会社
Priority date: 2015-07-14
Filing date: 2016-07-05
Publication date: 2017-01-19
Also published as: CN107835793A; CN107835793B

Abstract

The present invention relates to a glass substrate having a bottom face that is in contact with molten metal during molding using the float process, and a top face that is on the reverse side of the bottom face, wherein X as found in the following formula is more than 0.15 and less than 0.38. X=[(integral value corresponding to sodium concentration in bulk at 50nm)-(integral value of sodium concentration from surface of top face to depth of 50nm)]/(integral value corresponding to sodium concentration in bulk at 50nm)

Description

Glass substrate

The present invention relates to a glass substrate used for a flat panel display (FPD) such as a plasma display and a liquid crystal display, a touch panel, a solar cell and the like.

Various glass plates, such as a glass substrate for flat panel displays (FPD), such as a plasma display and a liquid crystal display, a glass substrate for touch panels, and a glass substrate for thin film solar cells, are manufactured by the float method as an example.

When manufacturing a glass plate using the float process, a transport path having a plurality of rollers is provided on the downstream side of the float bath in which the molten metal is stored, and a glass ribbon formed by the float bath by the rollers. Is gradually cooled while being continuously conveyed. The glass ribbon formed by the float bath is gradually cooled and solidified while being continuously conveyed by a plurality of rollers constituting the conveyance path, and a glass substrate is obtained by being cut into a predetermined length. .

When a film of ITO (tin-added indium oxide), AZO (aluminum-added zinc oxide) or the like is formed on the glass substrate thus obtained by a sputtering method, there is a problem that white turbidity occurs on the back surface of the film.

The white turbidity deposited on the glass surface can be eliminated by washing, but the number of processes increases and the production efficiency is poor. In addition, when films are formed on both surfaces of a glass substrate by a sputtering method, it is desired to develop a technique that cannot be washed if such white turbidity occurs and can prevent the formation of white turbidity.

Therefore, an object of the present invention is to provide a glass substrate that can prevent the formation of white turbidity on the back surface of the film during film formation by sputtering.

The present inventors considered that the above-mentioned cloudiness is precipitation of some components, and conducted various studies. When manufacturing glass by the float method, there is a problem that the glass ribbon is scratched due to the contact between the glass ribbon and a plurality of rollers in the conveyance path. The bottom surface, which is the surface in contact with the surface, is subjected to dealkalization by spraying SO ₂ gas and reacting with glass components to form a sulfate film (hereinafter also referred to as SO ₂ treatment). (For example, Japanese Patent Laid-Open No. 02-14841), the possibility that such SO ₂ treatment is involved in the above-described cloudiness generation was examined.

As a result, the present inventors have determined the sodium concentration in the top surface in a glass substrate having a bottom surface that is in contact with the molten metal during forming by the float method and a top surface that is the surface opposite to the bottom surface. The inventors have found that by setting the specific range, it is possible to suppress the formation of white turbidity on the rear surface of the film when the film is formed by sputtering, and the present invention has been completed.

That is, the present invention is as follows.
1. It has a bottom surface that is a surface in contact with the molten metal at the time of forming by the float method and a top surface that is the surface opposite to the bottom surface, and X obtained by the following formula is more than 0.15 and less than 0.38 Glass substrate. In the following formula, the sodium concentration is measured by an X-ray photoelectron spectrometer.
X = [(integrated value for 50 nm of sodium concentration in bulk) − (integrated value of sodium concentration from top surface to depth of 50 nm)] / (integrated value for 50 nm of sodium concentration in bulk)
2. _2. The glass substrate as described in 1 above, containing 3 to 6% of Al ₂ O ₃ in terms of mass percentage based on oxide.
3. 3. The glass substrate according to

item

1 or 2, which is a glass substrate for forming an ITO film.
4). 4. The glass substrate according to any one of items 1 to 3, including a film formed by a sputtering method.
5). 5. The glass substrate according to item 4 above, wherein the film is an ITO film.
6). 6. A touch panel comprising the glass substrate according to any one of 1 to 5 above.

When spraying the SO ₂ gas to the bottom surface of the glass ribbon to SO ₂ treatment in producing a glass plate using a float process, wraparound SO ₂ gas to the top surface, a sodium ion concentration by the SO ₂ gas And the mobility of sodium ions on the top surface is increased. Therefore, when the film is formed on the bottom surface by the sputtering method after the SO ₂ treatment, the electric field changes in the portion where the sputtered particles are behind the top surface, and sodium ions whose mobility is increased by the SO ₂ treatment are formed on the glass surface. It is thought that it precipitates and NaCO ₃ is formed and white turbidity is formed.

The glass substrate of the present invention can reduce the mobility of sodium ions on the glass surface by setting the sodium concentration on the top surface to a specific range, and NaCO ₃ is deposited during film formation by sputtering. It can suppress cloudiness. Therefore, by using the glass substrate of the present invention as a glass substrate for film formation by sputtering, there is no need for a step of washing the cloudiness, and film formation on the glass substrate by sputtering is low cost and high productivity. A flat panel display, a touch sensor, a thin film solar cell, or the like produced through the process can be provided.

FIGS. 1A to 1C show the concentration distribution of sodium in the surface layer of the glass substrate.

The glass substrate of the present invention has a bottom surface that is in contact with the molten metal at the time of forming by the float process, and a top surface that is the surface opposite to the bottom surface, and X determined by the following formula is 0.15. It is a glass substrate that is ultra-less than 0.38.
X = [(integrated value for 50 nm of sodium concentration in bulk) − (integrated value of sodium concentration from top surface to depth of 50 nm)] / (integrated value for 50 nm of sodium concentration in bulk)

The sodium concentration in the above formula is obtained by measuring the Na atomic weight (atomic%) with an X-ray photoelectron spectrometer. Examples of the X-ray photoelectron spectrometer include ESCA5500 manufactured by ULVAC-PHI.

Specifically, the sodium concentration from the surface of the top surface of the glass substrate to 10 μm is obtained by grinding the glass substrate with cerium oxide water slurry to 8000 nm, and then sputter etching to 10 μm with a C ₆₀ ion beam to obtain X-ray photoelectrons The Na atomic weight (%) is measured by a spectroscopic device.

The integral amount of sodium concentration from the surface of the top surface of the glass substrate to a depth of 50 nm is obtained by sputter etching the glass substrate with a C ₆₀ ion beam, and the amount of Na atoms every 1.5 nm or 3 nm by an X-ray photoelectron spectrometer. (%) Measure and calculate the integral.

In the above formula, “bulk” refers to a portion not affected by surface treatment such as dealkalization, and in the present invention, refers to a portion having a depth of 10 μm or more from the glass surface. The “integrated value for 50 nm of the sodium concentration in the bulk” means a value obtained by calculating the integrated value of the sodium concentration for 50 nm depth from the sodium concentration at a depth of 10 μm from the surface of the top surface of the glass. .

When the value of X is 0.38 or more, when the film is formed on the bottom surface of the glass substrate by the sputtering method, the electric field in the portion where the sputtered particles are turned on the top surface, which is the film forming back surface, changes. Sodium ions, which have been dealkalized by SO ₂ treatment and have a high mobility, are deposited on the glass surface, and NaCO ₃ is formed and becomes cloudy. The X is also preferably less than 0.35, and more preferably less than 0.33.

Further, when the X is 0.15 or less, the surface layer Na concentration is high, and it becomes easy to burn, so that white turbidity tends to be generated. X is preferably more than 0.18, and more preferably more than 0.20.

As a manufacturing method of the glass substrate of this invention, a glass raw material is melt | dissolved and it shape | molds by the float glass process. In the float method, when rolls are transported in the slow cooling process, SO ₂ gas (sulfurous acid gas) is sprayed in the air on a glass ribbon having a high temperature to react with the glass components in order to prevent scratches caused by the rolls. An SO ₂ treatment is performed to deposit sulfate on the glass surface for protection.

SO ₂ treatment is usually one surface of the glass ribbon, in particular, by blowing SO ₂ gas on the surface (bottom surface) of the glass ribbon on the side in contact with the transport roller, forming a protective film by sulfate In order to prevent the surface from being scratched by conveyance. In the float process, SO ₂ treatment can be performed simultaneously in the slow cooling step.

The SO ₂ gas is a mixed gas of SO ₂ and air, N ₂ , Ar, or He. Examples of the sulfate include Na salt, K salt, Ca salt, Sr salt and Ba salt, and are usually precipitated as a composite of these salts.

By controlling the condition of the SO ₂ treatment, the X can be controlled and adjusted to a predetermined range. Specifically, for example, a method of preventing SO ₂ gas sprayed on the bottom surface of the glass ribbon from flowing around the top surface by the following methods (1) to (5) is effective.
(1) When SO ₂ gas is blown onto the bottom surface of the glass ribbon, ventilation is performed to lower the sealing property of the slow cooling furnace so that the SO ₂ gas does not enter the top surface of the glass ribbon. Specifically, in the slow cooling furnace, the SO ₂ gas concentration in the upper space on the top surface of the glass ribbon is preferably 1 to 200 ppm, more preferably 5 to 50 ppm.
(2) By blowing alternative gas such as N ₂ or dry air on the top surface, the SO ₂ gas sprayed on the bottom surface of the glass ribbon is prevented from flowing around the top surface. Specifically, in the slow cooling furnace, the SO ₂ gas concentration in the upper space on the top surface of the glass ribbon is preferably 1 to 200 ppm, more preferably 5 to 50 ppm.
(3) when blowing a SO ₂ gas to the bottom surface of the glass ribbon, spraying SO ₂ gas locally bottom surface. Specifically, the SO ₂ gas is preferably sprayed from a distance close to the bottom surface, and the distance is preferably 1 mm to 200 mm, more preferably 5 mm to 50 mm.
(4) adjusting the temperature of the glass substrate when spraying the SO ₂ gas to the bottom surface of the glass ribbon. Specifically, the temperature of the glass substrate is preferably 400 to 700 ° C., more preferably 450 to 650 ° C., and still more preferably 500 to 600 ° C.
(5) the processing time of blowing SO ₂ gas to the bottom surface of the glass ribbon is adjusted by the speed of the glass ribbon. Specifically, the speed of the glass ribbon is preferably 1 to 30 m / min, more preferably 5 to 20 m / min.

The SO ₂ treatment is preferably carried out in the molding process by the float method when it is slowly cooled to room temperature in a slow cooling furnace after being taken out from the molding furnace (float bath). For example, SO ₂ gas can be sprayed before the glass ribbon enters the annealing furnace. It is also possible by blowing SO ₂ gas continuously even after the glass ribbon enters the annealing furnace. Alternatively, the SO ₂ gas spray may be started after the glass ribbon has entered the slow cooling furnace. After slow cooling, the glass ribbon can be cut into a predetermined size and formed into a glass substrate.

As a composition of the glass substrate of this invention, the range (mass percentage display of an oxide basis) shown below is mentioned, for example.
SiO ₂ : 63 to 75%
Al ₂ O ₃ : 3 to 6%
MgO: 3-10%
CaO: 0.5-10%
SrO: 0 to 3%
BaO: 0 to 3%
Na ₂ O: 10-18%
K ₂ O: 0 to 8%
ZrO ₂ : 0 to 3%
Fe ₂ O ₃ : 0.005 to 0.25%
With such a glass composition, a high-quality glass substrate can be easily obtained, and strengthening (chemical strengthening) by ion exchange can be performed. Hereinafter, this glass composition will be described.

SiO ₂ is known as a component that forms a network structure in the glass microstructure, and is a main component constituting the glass. The content of SiO ₂ is preferably 63% or more, more preferably 64% or more, still more preferably 65% or more, and particularly preferably 67% or more. Further, the content of SiO ₂ is preferably 75% or less, more preferably 73% or less, still more preferably 71% or less, and particularly preferably 70% or less. When the content of SiO ₂ is 63% or more, it is advantageous in terms of stability and weather resistance as glass. Moreover, an increase in expansion can be suppressed by forming a network structure. On the other hand, when the content of SiO ₂ is 75% or less, it is advantageous in terms of solubility and moldability.

Al ₂ O ₃ is known as a component that improves the weather resistance of glass. Moreover, there exists an effect | action which suppresses the penetration | invasion of the tin from a bottom surface at the time of shaping | molding by a float glass process. Furthermore, there is an effect of promoting dealkalization when the SO ₂ treatment is performed.

The content of Al ₂ O ₃ is preferably 3% or more, more preferably 4% or more, and further preferably 4.5% or more. Further, the content of _Al 2 _{O 3} is preferably at most 6%, more preferably 5.5% or less, more preferably not more than 5%.

If the Al ₂ O ₃ content is 3% or more, stability of the glass is obtained. On the other hand, if the content of Al ₂ O ₃ is 6% or less, the devitrification temperature does not increase greatly even when the viscosity of the glass is high, so melting and forming points in a general soda lime glass production line Is an advantage.

MgO is a component that can stabilize glass and improve solubility.

The content of MgO is preferably 3% or more, more preferably 3.5% or more, still more preferably 4% or more, and particularly preferably 4.5% or more. Further, the content of MgO is preferably 10% or less, more preferably 9% or less, further preferably 8% or less, more preferably 6% or less, still more preferably 5.5% or less, particularly Preferably it is 5% or less.

When the content of MgO is 10% or less, it is difficult to cause devitrification, or a sufficient ion exchange rate can be obtained when chemical strengthening treatment is performed.

CaO is a component that stabilizes the glass, and has the effect of preventing devitrification due to the presence of MgO and improving the solubility. The CaO content is preferably 0.5% or more, more preferably 1% or more, further preferably 3% or more, further preferably 4% or more, particularly preferably 5% or more, and most preferably 6%. That's it. Further, the CaO content is preferably 10% or less, more preferably 9% or less, and still more preferably 8% or less.

When the content of CaO is 0.5% or more, the solubility at high temperature becomes good and devitrification hardly occurs. On the other hand, it can suppress that the thermal expansion coefficient of glass increases that content of CaO is 10% or less.

SrO is an effective component for lowering the viscosity and devitrification temperature of glass. The SrO content is preferably 3% or less, more preferably 2% or less, and still more preferably 1% or less.

BaO is an effective component for lowering the viscosity and devitrification temperature of glass. The BaO content is preferably 3% or less, more preferably 2% or less, and still more preferably 1% or less.

Na ₂ O is a component that lowers the melting temperature and devitrification temperature of glass and improves the solubility and formability of glass. Moreover, when chemically strengthening, it is a component which forms a surface compressive-stress layer by ion exchange.

The content of Na ₂ O is preferably 10% or more, more preferably 11% or more, and further preferably 13% or more. Further, the content of Na ₂ O is preferably 18% or less, more preferably 17% or less, more preferably 16% or less.

When the content of Na ₂ O is 10% or more, fluctuation due to moisture content change is suppressed. On the other hand, when the content of Na ₂ O is 18% or less, sufficient weather resistance is obtained, and the amount of tin entering from the bottom surface can be suppressed during molding by the float process.

Since K ₂ O has an effect of lowering the melting temperature of the glass, it may be contained in a range of 8% or less. When it is 8% or less, the melting temperature can be lowered while suppressing the thermal expansion coefficient of the glass. Preferably 5% or less when they contain K 2 _O, more preferably 4% or less, more preferably 2% or less.

Since a small amount of K ₂ O has an effect of suppressing intrusion of tin from the bottom surface at the time of molding by the float method, it is preferably contained when molding by the float method. In this case, the content of K ₂ O is preferably 0.01% or more, more preferably 0.1% or more.

ZrO ₂ is not essential, but may be contained in a range of up to 3% in order to reduce the viscosity at high temperature or improve the acid resistance. If the inclusion of ZrO _2, ZrO ₂ content is preferably at least 0.005%, more preferably at least 0.01%. If ZrO ₂ is added excessively, the melting temperature is increased conversely, but by setting it to 3% or less, increase in viscosity and generation of devitrification can be suppressed. Preferably it is 2% or less, More preferably, it is 1% or less.

Fe ₂ O ₃ is a component that absorbs heat and improves solubility when glass is melted. The content of Fe ₂ O ₃ is preferably 0.005% or more, more preferably 0.008% or more, and still more preferably 0.01% or more. The content of _Fe 2 _{O 3} is preferably at most 0.25%, more preferably 0.2% or less, more preferably not more than 0.15%. In order to prevent the kiln floor temperature from rising, the content of Fe ₂ O ₃ is preferably 0.06% or more. On the other hand, when the content of _Fe 2 _{O 3} is not more than 0.25%, it is possible to suppress the coloring.

In addition, chloride or fluoride may be appropriately contained as a glass refining agent. The glass of this embodiment consists essentially of the components described above, but may contain other components as long as the object of the present invention is not impaired. When such components are contained, the total content of these components is preferably 5% or less, more preferably 3% or less, and typically 1% or less. Hereinafter, the other components will be described as an example.

TiO ₂ is not essential, but is abundant in natural raw materials and is known to be a yellow coloring source. When containing TiO ₂ is preferably 0.2% or less.

SO ₃ is not essential, but is known as a glass fining refiner. When containing SO ₃ is preferably 0.3% or less.

ZnO may be contained up to 2%, for example, in order to improve the melting property of the glass at a high temperature. However, when it is produced by the float process, it is preferably contained substantially because it is reduced by a float bath and becomes a product defect.

B ₂ O ₃ may be contained in a range of 4% or less in order to improve the melting property at high temperature or the glass strength. Preferably it is 3% or less, More preferably, it is 2% or less, More preferably, it is 1% or less. In general, when an alkali component of Na ₂ O or K ₂ O and B ₂ O ₃ are contained at the same time, volatilization becomes intense and the brick is remarkably eroded. Therefore, it is preferable that B ₂ O ₃ is not substantially contained.

Li ₂ O is a component that lowers the strain point to facilitate stress relaxation, and as a result makes it impossible to obtain a stable surface compressive stress layer, so it is preferably not contained, and even if it is contained, its content Is preferably less than 1%, more preferably 0.05% or less, and particularly preferably less than 0.01%.

The glass substrate of the present invention has dimensions that can be formed by the float process, and is finally cut into a size suitable for the intended use. The glass substrate of the present invention is generally cut into a rectangle, but other shapes such as a circle or a polygon can be used without any problem, and includes a glass subjected to drilling.

Examples of the film formed on the glass substrate of the present invention include, for example, SiO ₂ film, ITO film, ZnO film, Al-doped ZnO film, Ga-doped ZnO film, B-doped ZnO film, In-doped ZnO film, and F-doped ZnO. Examples thereof include a film, Ti-doped NbxO ₂ , IZO film (Zn-added In film), SrTiO ₃ film, SnO ₂ film, F-doped SnO ₂ film, Sb-doped SnO ₂ film, TiO ₂ film, and ZrO ₂ film. The material of the film is not particularly limited, and can be selected in consideration of required functions and productivity. In particular, the present invention is more effective when a conductive film such as an ITO film is formed on an insulating film such as a SiO ₂ film.

Examples of the film material include metal oxides such as silicon nitride, indium oxide, tin oxide, niobium oxide, titanium oxide, zirconium oxide, cerium oxide, tantalum oxide, aluminum oxide, and zinc oxide. Selected from the following: materials, silicon oxide (SiO ₂ ), materials containing mixed oxides of Si and Sn, materials containing mixed oxides of Si and Zr, materials containing mixed oxides of Si and Al The above can be preferably utilized.

The thickness of the film formed on the glass substrate of the present invention is not particularly limited, but is preferably 5 nm or more when the film is an insulating film such as a SiO ₂ film. Preferably it is 8 nm or more. Moreover, it is preferable that it is 50 nm or less, More preferably, it is 40 nm or less, Most preferably, it is 25 nm or less. On the other hand, when the film is a conductive film such as an ITO film, the thickness is preferably 50 nm or more, more preferably 100 nm or more, and further preferably 300 nm. Moreover, it is preferable that it is 600 nm or less, More preferably, it is 500 nm or less. By setting the thickness to 300 nm or more, the resistance value can be suppressed to be sufficiently small, and by setting the thickness to 500 nm or less, the decrease in transmittance can be sufficiently suppressed.

In the glass substrate of the present invention, since X is in the predetermined range, it is possible to suppress the precipitation of NaCO ₃ after the film is formed by the sputtering method. Examples of the sputtering method include a high frequency magnetron sputtering method, a direct current magnetron sputtering method, a pulse sputtering method, an AC sputtering method, and a digital sputtering method. In particular, when an insulating film such as a SiO ₂ film is formed by a high frequency magnetron sputtering method, and a conductive film such as an ITO film is formed thereon by a direct current magnetron sputtering method, the present invention is more effective. Demonstrate the effect.

The thickness of the glass substrate of the present invention is not particularly limited, but is preferably 0.1 mm or more, more preferably 0.3 mm or more. Moreover, it is preferable that it is 4 mm or less, More preferably, it is 2 mm or less, More preferably, it is 1.3 mm or less.

The use of the glass substrate of the present invention is not particularly limited, and examples thereof include flat panel displays (FPD) such as plasma displays, liquid crystal displays and organic EL displays, touch panels, and solar cells.

When forming ITO on both surfaces, for example, in a touch panel equipped with a DITO touch sensor, the white turbidity on the back surface of the film cannot be removed by washing, so the glass substrate of the present invention is particularly effective.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following examples.

The raw material powder having the composition shown in Table 1 by mass percentage display based on oxide is melted at a predetermined temperature, and the thickness is 0.7 mm (Example 1, Example 3, Comparative Example 1 and Comparative Example 2) or 1 by the float process. After forming into a plate shape of 1 mm (Example 2), it was cooled in a continuous slow cooling furnace. In a slow cooling furnace, in order to prevent scratches on the glass surface, SO ₂ gas was sprayed on the bottom surface of the glass ribbon at a glass transition point of + 100 ° C. to a glass transition point of −100 ° C. for dealkalization.

The integrated amount of the sodium concentration at a depth of 10 μm from the surface of the obtained glass substrate and the sodium concentration from the surface of the top surface or the bottom surface of the glass substrate to a depth of 50 nm was measured with a linear photoelectron spectrometer (ESCA5500, manufactured by ULVAC-PHI). It measured using.

The sodium concentration from the surface of the top surface of the glass substrate to 10 μm is that the glass substrate is ground to 8000 nm with an aqueous slurry of cerium oxide, then sputter etched to 10 μm with a C ₆₀ ion beam, and the Na atomic weight is measured by an X-ray photoelectron spectrometer (%) Was measured.

In addition, the integral amount of sodium concentration from the top surface or the bottom surface of the glass substrate to a depth of 50 nm is obtained by sputter etching the glass substrate with a C ₆₀ ion beam and every 1.5 nm or 3 nm by an X-ray photoelectron spectrometer. The amount of Na atom (%) was measured and the integral amount was calculated.

X and Y were calculated from the obtained measured values according to the following formula. The results are shown in Table 2.
X = [(integrated value of 50 nm of sodium concentration in bulk) − (integrated value of sodium concentration from top surface to depth of 50 nm)] / (integrated value of 50 nm of sodium concentration in bulk) Y = [ (Integral value of 50 nm of sodium concentration in bulk)-(Integrated value of sodium concentration from bottom surface to depth of 50 nm)] / (Integrated value of 50 nm of sodium concentration in bulk)

A glass substrate is set in a sputtering apparatus, and a SiO ₂ layer is formed to a thickness of 30 nm at 300 ° C. on the bottom surface of the glass substrate by a high-frequency magnetron sputtering method. Subsequently, with respect to the total amount of ITO (In ₂ O ₃ and SnO ₂ An ITO layer having a thickness of 450 nm was formed at 350 ° C. by a direct current magnetron sputtering method using a SnO _{2 (} containing 10% by mass) target to obtain a glass substrate with an ITO layer (also simply referred to as a substrate).

After forming the ITO film on the glass substrate, it was left in the air for 24 hours, and the presence or absence of white turbidity on the back surface (top surface) was observed. The presence or absence of white turbidity on the back of the film was evaluated as white turbidity when white turbidity was confirmed visually under a fluorescent lamp in a dark room, and no white turbidity when white turbidity could not be confirmed. The results are shown in Table 2.

Next, the results of determining the sodium concentration distribution in the surface layer of the obtained glass substrate are shown in FIGS. 1 (a) to 1 (c). FIG. 1A shows Example 1 and FIG. 1B shows a sample obtained by mirror polishing the glass of Example 1, and FIG. 1C shows the result of Comparative Example 1. FIG.

Moreover, about the glass substrate of Example 1 and Example 3, a weather resistance is hold | maintained for 14 days in the constant temperature and humidity chamber of temperature 60 degreeC and relative humidity 95%, and the C light source haze rate of the board | substrate before washing | cleaning is a haze meter (Suga test). Evaluation was performed according to HZ-2).

As shown in Table 2, in Comparative Example 1 in which X is 0.38 or more, white turbidity was formed on the back surface of the film by film formation by sputtering, but Examples 1 to 3 in which X was less than 0.38. No cloudiness 3 occurred on the film forming back surface. On the other hand, in Comparative Example 2 where X is 0.15, white turbidity due to burns occurred in the air atmosphere. From this result, it was found that by setting X to be greater than 0.15 and less than 0.38, it is possible to suppress the precipitation of NaCO ₃ on the back surface of the film during the film formation by the sputtering method and the cloudiness.

Moreover, as a result of evaluating weather resistance, the glass of Example 1 had a haze ratio of 0.1% before the test and a haze ratio of 14% after 14 days. The glass of Example 3 had a haze ratio of 0.1% before the test, and a haze ratio of 14 days later was 3.9%. From this result, it was found that the weather resistance was improved by setting the content of Al ₂ O ₃ in the glass substrate to 3 to 6 mass%.

Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. The present application is based on a Japanese patent application (Japanese Patent Application No. 2015-140555) filed on July 14, 2015, and is incorporated by reference in its entirety. Also, all references cited herein are incorporated as a whole.

Claims

It has a bottom surface that is a surface in contact with the molten metal at the time of forming by the float method and a top surface that is the surface opposite to the bottom surface, and X obtained by the following formula is more than 0.15 and less than 0.38 Glass substrate. In the following formula, the sodium concentration is measured by an X-ray photoelectron spectrometer.
X = [(integrated value for 50 nm of sodium concentration in bulk) − (integrated value of sodium concentration from top surface to depth of 50 nm)] / (integrated value for 50 nm of sodium concentration in bulk)
The glass substrate according to claim 1, comprising 3 to 6% of Al 2 O 3 in terms of mass percentage based on oxide.
The glass substrate according to claim 1, which is a glass substrate for forming an ITO film.
The glass substrate according to any one of claims 1 to 3, comprising a film formed by a sputtering method.
The glass substrate according to claim 4, wherein the film is an ITO film.
A touch panel including the glass substrate according to any one of claims 1 to 5.