JP5796905B2 - Tempered glass substrate, glass and method for producing tempered glass substrate - Google Patents

Description

  The present invention relates to a tempered glass substrate, and more particularly to a tempered glass substrate suitable for a mobile phone, a digital camera, a PDA (mobile terminal), a solar cell cover glass, or a touch panel display.

  Devices such as mobile phones, digital cameras, PDAs, or touch panel displays are becoming increasingly popular.

Conventionally, in these applications, a resin such as acrylic has been used as a protective member for protecting the display. However, since the Young's modulus of acrylic resin is low, the acrylic resin substrate may bend when the display is pressed with a finger or the like, and display defects may occur due to contact with the display. In addition, there is a problem in that it is easily scratched and visibility is likely to deteriorate. One method for solving these problems is to use a glass substrate as a protective member. The glass substrate used for these protective members has (1) high mechanical strength, (2) low density, (3) can be supplied in large quantities at low cost, and (4) excellent foam quality. Is required. In order to satisfy the requirement of (1), a glass substrate (so-called tempered glass substrate) reinforced by ion exchange or the like is conventionally used (see Patent Document 1 and Non-Patent Document 1).
JP 2006-83045 A Tetsuro Izumiya et al., “New Glass and its Properties”, first edition, Management System Research Institute, Inc., August 20, 1984, p. 451-498

Non-Patent Document 1 describes that when the Al ₂ O ₃ content in the glass composition is increased, the ion exchange performance of the glass is improved and the mechanical strength of the glass substrate can be improved.

However, if the Al ₂ O ₃ content in the glass composition is increased, the devitrification resistance of the glass is deteriorated, and the glass is easily devitrified during molding, so that the production efficiency and quality of the glass substrate are deteriorated. To do. Moreover, when the devitrification resistance of glass is poor, it can be molded only by a method such as roll molding, and a glass plate with high surface accuracy cannot be obtained. Therefore, a separate polishing step must be added after the glass plate is formed. However, when the glass substrate is polished, minute defects are likely to occur on the surface of the glass substrate, and it becomes difficult to maintain the mechanical strength of the glass substrate.

  Under such circumstances, it has been difficult to achieve both ion exchange performance and devitrification resistance of glass, and it has been difficult to significantly improve the mechanical strength of the glass substrate. In addition, in order to reduce the weight of devices, glass substrates used in devices such as touch panel displays are becoming thinner year by year. Since a thin glass substrate is easily damaged, a technique for improving the mechanical strength of the glass substrate has become increasingly important.

  Then, this invention makes it a technical subject to obtain the tempered glass board | substrate with high mechanical strength and excellent moldability by making ion exchange performance and devitrification resistance of glass compatible.

As a result of various investigations, the inventor of the present invention contains a predetermined amount of B ₂ O ₃ and regulates the content of Na ₂ O and Al ₂ O ₃ to improve the ion exchange performance of the glass, It has been found that the surface compressive stress can be increased and the devitrification of the glass can be suppressed, and the present invention has been proposed.

That is, the tempered glass substrate of the present invention is a tempered glass substrate having a compressive stress layer on the surface, a tempered glass substrate having a compressive stress layer on the surface, as a glass composition, in mass%, SiO ₂ 40 to _{75%, Al 2 O 3 10~20} %, B 2 O 3 0.01~8%, Li 2 O 0~5%, Na 2 O 10~20%, 0~10% MgO, CaO 0~4% , SrO + BaO 0 to 10%, Na ₂ O / Al ₂ O ₃ ratio by mass ratio is 0.7 to ₂ , the compressive stress layer is a chemically strengthened layer having a depth of 27 μm or less, and the end face of the substrate There is no compressive stress layer on the surface of the film. Unless otherwise specified, “%” means mass% in the following description.

Further, the tempered glass substrate of the present invention is a tempered glass substrate having a compressive stress layer on the surface, as a glass composition, in _{mass%, SiO 2 40~75%, Al} 2 O 3 10~17.5%, B _{2 O 3 0.01~8%, Li 2} O 0~4%, Na 2 O 10~20%, 0~6% MgO, CaO 0~4%, SrO + BaO 0~7%, P 2 O 5 0~ _10%, TiO 2 _0~10%, containing _{ZrO 2 0~10%, Na 2 O} / K 2 O ratio in the mass ratio is preferably from 0.8 to 2.

Further, the tempered glass substrate of the present invention is a tempered glass substrate having a compressive stress layer on the surface, as a glass composition, in _{mass%, SiO 2 40~70%, Al} 2 O 3 10~16.5%, B _{2 O 3 0.01~6%, Li 2} O 0~4%, Na 2 O 10~20%, 0~6% MgO, CaO 0~4%, SrO + BaO 0~7%, P 2 O 5 0~ 10%, TiO ₂ 0-10%, ZrO ₂ 0-10%, the mass ratio of Na ₂ O / K ₂ O is 0.8-1.5, and a compressive stress layer is formed on the surface of the substrate end face. Is preferably absent .

The tempered glass substrate of the present invention preferably contains a SnO ₂ 0.01 to 6%.

The tempered glass substrate of the present invention _preferably contains TiO ₂ + ZrO ₂ 0.1~15%.

Moreover, it is preferable that the tempered glass substrate of this invention contains MgO + CaO + SrO + BaO 0.1 to 10%.

Moreover, it is preferable that the tempered glass substrate of this invention is chemically strengthened.

Further, the tempered glass substrate of the present invention, compressive stress of the surface is more than 300 MPa, and a thickness of 10 ~ 27 mu m of the compressive stress layer, it is preferable tensile stress within the glass substrate is less than 200 MPa. Here, “surface compressive stress” and “thickness of compressive stress layer” are the number of interference fringes observed when a sample is observed using a surface stress meter (FSM-6000 manufactured by Toshiba Corporation) and The value calculated from the interval. Moreover, the tensile stress inside a glass substrate represents what is calculated by the following formula | equation.

“Tensile stress inside glass substrate = (compressive stress value × stress depth) / (plate thickness−stress depth × 2)”
The tempered glass substrate of the present invention preferably has an unpolished surface. Here, “unpolished surface” means that the main surface (so-called front surface and back surface) of the glass substrate is not polished. In other words, it means that both surfaces are fired surfaces, and the average surface roughness (Ra) of the surface is measured by a method according to SEMI D7-97 “Measurement method of surface roughness of FPD glass substrate” Further, the average surface roughness (Ra) is 10 Å or less, preferably 5 Å or less, more preferably 2 Å or less. Note that the end surface portion may be subjected to polishing treatment such as chamfering.

The tempered glass substrate of the present invention preferably has a liquidus temperature of 1200 ° C. or lower. Here, “liquid phase temperature” means that glass is crushed, passed through a standard sieve 30 mesh (500 μm sieve opening), and the glass powder remaining in 50 mesh (300 μm sieve sieve) is placed in a platinum boat, and the temperature gradient The temperature at which crystals are precipitated after being kept in the furnace for 24 hours.

The tempered glass substrate of the present invention preferably has a liquidus viscosity of 10 ^4.0 dPa · s or more. Here, “liquidus viscosity” refers to the viscosity of the glass at the liquidus temperature. In addition, the higher the liquidus viscosity and the lower the liquidus temperature, the better the devitrification resistance of the glass and the moldability of the glass substrate.

The tempered glass substrate of the present invention is preferably used for a touch panel display.

The tempered glass substrate of the present invention is preferably used for a cover glass of a mobile phone.

Moreover, it is preferable to use the tempered glass substrate of this invention for the cover glass of a solar cell.

Moreover, it is preferable that the tempered glass substrate of this invention is used as a protective member of a display.

The glasses according to the invention also, in _{mass%, SiO 2 40~75%, Al} 2 O 3 10~20%, B 2 O 3 0.01~8%, Li 2 O 0~5%, Na 2 O 10-20%, MgO 0-10%, CaO 0-4%, SrO + BaO 0-10% in mass ratio, Na ₂ O / K ₂ O ratio is 0.7-2, It is preferable to use it.

The glass according to the present invention preferably contains a SnO ₂ 0.01 to 6%.

The method of manufacturing a tempered glass substrate of the present invention, in _{mass%, SiO 2 40~75%, Al} 2 O 3 10~20%, B 2 O 3 0.01~8%, Li 2 O 0~5% , Na ₂ O 10-20%, MgO 0-10%, CaO 0-4%, SrO + BaO 0-10%, and Na ₂ O / Al ₂ O ₃ ratio is 0.7-2 by mass ratio It was obtained after melting a glass raw material prepared so as to have a glass composition, forming the glass into a plate shape, and then forming a compressive stress layer having a depth of 27 μm or less on the glass surface by performing an ion exchange treatment. The tempered glass substrate is cut into a predetermined size.

The method of manufacturing a tempered glass substrate of the present invention preferably contains a SnO ₂ 0.01 to 6%.

Moreover, it is preferable that the manufacturing method of the tempered glass board | substrate of this invention shape | molds in plate shape with a down draw method.

Moreover, it is preferable that the manufacturing method of the tempered glass board | substrate of this invention shape | molds in plate shape with the overflow down draw method.

  The tempered glass substrate of the present invention is made of glass having high ion exchange performance. Moreover, since it is made of glass having excellent devitrification resistance, an overflow down draw method or the like can be employed. Therefore, polishing after molding is unnecessary and there are no micro defects caused by polishing. Therefore, there is an effect that the mechanical strength is high.

  Further, since it can be manufactured without performing a polishing step, the manufacturing cost can be reduced, and it can be supplied at low cost.

  Therefore, the tempered glass substrate of the present invention can be suitably used for touch panel displays, mobile phone cover glasses, solar cell cover glasses, display protection members, and the like. The touch panel display is mounted on a mobile phone, a digital camera, a PDA, or the like. In the touch panel display for mobile use, there is a strong demand for weight reduction, thinning, and high strength, and a thin and high mechanical strength glass substrate is required. In that respect, the tempered glass substrate of the present invention is suitable for mobile use because it has sufficient mechanical strength for practical use even if the plate thickness is reduced.

The glass according to the present invention has high ion exchange performance. Moreover, since it is excellent in devitrification resistance, it can be molded by an overflow down draw method or the like.

Therefore, if the glass according to the present invention is used, a tempered glass substrate having high mechanical strength can be produced at low cost.

  Moreover, since the manufacturing method of the tempered glass of this invention uses the glass which has high ion exchange performance and is excellent in devitrification resistance, the tempered glass board | substrate with high mechanical strength can be produced cheaply.

The tempered glass substrate of the present invention has a compressive stress layer on its surface. Methods for forming a compressive stress layer on the surface of a glass substrate include a physical strengthening method and a chemical strengthening method. The tempered glass substrate of the present invention preferably forms a compressive stress layer by a chemical tempering method. The chemical strengthening method is a method of introducing alkali ions having a large ion radius into the surface of a glass substrate by ion exchange at a temperature below the strain point of the glass. If the compressive stress layer is formed by the chemical strengthening method, even if the plate thickness of the glass substrate is thin, the strengthening treatment can be performed satisfactorily and a desired mechanical strength can be obtained. Further, when the glass substrate is cut after forming the compressive stress layer on the glass substrate, it is not easily broken unlike a glass substrate reinforced by a physical strengthening method such as an air cooling strengthening method.

The ion exchange conditions are not particularly limited, and may be determined in consideration of the viscosity characteristics of the glass. In particular, it is preferable to ion-exchange K ions in the KNO ₃ molten salt with a Na component in the glass substrate because a compressive stress layer can be efficiently formed on the surface of the glass substrate.

  The reason for limiting the glass composition to the above range in the tempered glass substrate of the present invention will be described below.

SiO ₂ is a component that forms a network of glass, and its content is 40 to 75%, preferably 50 to 70%, 40 to 70%, 45 to 65%, particularly 49 to 60%. When the content of SiO ₂ is too large, it becomes difficult to melt and mold the glass, or the thermal expansion coefficient becomes too small, and it becomes difficult to match the thermal expansion coefficient with the surrounding materials. On the other hand, if the content of SiO ₂ is too small, it becomes difficult to vitrify. Moreover, the thermal expansion coefficient of glass becomes large, and the thermal shock resistance of glass tends to decrease.

Al ₂ O ₃ is a component that enhances ion exchange performance. It also has the effect of increasing the strain point and Young's modulus of the glass, and its content is 10 to 20%. When the content of Al ₂ O ₃ is too large, forming by an overflow down draw method and the like becomes difficult devitrified crystal glass becomes easily deposited. In addition, the thermal expansion coefficient of the glass becomes too small, making it difficult to match the thermal expansion coefficient with the surrounding material, or the high-temperature viscosity of the glass becomes high, making it difficult to melt. When the content of Al ₂ O ₃ is too small, a possibility arises which can not exhibit a sufficient ion exchange performance. Accordingly, the preferred range of Al ₂ O ₃ is 10 to 17.5%, further 10 to 16.5%, 12 to 16.5%, 12 to 16%, 12 to 15.5%, particularly 13 to 15%. It is.

B ₂ O ₃ is effective in reducing the high temperature viscosity and density of the glass and improving the ion exchange performance of the glass, particularly the compressive stress value. Furthermore, it has the effect of stabilizing the glass, making it difficult to precipitate crystals, and lowering the liquidus temperature of the glass. However, too much B ₂ O ₃ is not preferable because ion exchange causes coloring of the glass surface called burnt, the water resistance of the glass decreases, and the depth of the compressive stress layer decreases. Therefore, the content of B ₂ O ₃ is 0.01 to 8%, preferably 0.01 to 6%, 0.1 to 4%, 0.5 to 4%, particularly 1 to 3%.

Li ₂ O is an ion exchange component and a component that lowers the high temperature viscosity of the glass and improves meltability and moldability. Further, Li ₂ O is a component that has an effect of improving the Young's modulus of glass. Li ₂ O is highly effective in increasing the compressive stress value among alkali metal oxides. However, if the Li ₂ O content is too large, the liquidus viscosity is lowered and the glass tends to devitrify. In addition, the thermal expansion coefficient of the glass becomes too large, and the thermal shock resistance of the glass is lowered, or it is difficult to match the thermal expansion coefficient with the surrounding materials. Furthermore, if the low-temperature viscosity is too low and stress relaxation is likely to occur, the compressive stress value may be lowered. Therefore, the content of Li ₂ O is 0 to 5%, more preferably 0 to 4%, 0 to 2%, 0 to 1%, 0 to 0.5%, and 0 to 0.1%. Most preferably, it is not substantially contained, that is, suppressed to less than 0.01%.

Na ₂ O is an ion exchange component and has the effect of reducing the high temperature viscosity of the glass and improving the meltability and moldability. Na ₂ O is also a component that improves the devitrification resistance of the glass. The content of Na ₂ O is 10-20%, but more preferable content is 10-19%, 12-19%, 12-18%, 12-17%, 13-17%, especially 14- 17%. When the content of Na ₂ O is too large, the thermal expansion coefficient of the glass becomes too large, and the thermal shock resistance of the glass is lowered, or it is difficult to match the thermal expansion coefficient with the surrounding materials. Moreover, there is a tendency that the strain point is excessively lowered or the balance of the glass composition is lost and the devitrification resistance of the glass is deteriorated. On the other hand, when the content of Na 2 _O is less deteriorated the meltability, too coefficient of thermal expansion becomes small, the ion exchange performance deteriorates.

  MgO is a component that lowers the high-temperature viscosity of glass to increase meltability and formability, and increases the strain point and Young's modulus. Among alkaline earth metal oxides, MgO has the effect of improving ion exchange performance. Is expensive. The content of MgO is 0 to 10%. However, when the content of MgO increases, the density and thermal expansion coefficient of the glass tend to increase or the glass tends to devitrify. Therefore, the content is 0 to 6%, 0 to 4%, 0 to 3.5%, 0.01 to 3.5%, 0.5 to 3.5%, and 1 to 3.5%. It is desirable.

  CaO is a component that lowers the high-temperature viscosity of glass to improve meltability and formability, and increases the strain point and Young's modulus. Among alkaline earth metal oxides, CaO has the effect of improving ion exchange performance. Is expensive. The content of CaO is 0 to 4%. However, when the content of CaO increases, the density and thermal expansion coefficient of the glass increase, the glass tends to devitrify, and the ion exchange performance tends to deteriorate. Therefore, the content is preferably 0 to 3%, 0.1 to 3%, 0.5 to 3%, particularly 1 to 3%.

  SrO and BaO are components that lower the high-temperature viscosity of the glass to improve the meltability and formability, and increase the strain point and Young's modulus, but by suppressing the total amount of these to 10% or less, The ion exchange performance can be effectively improved. That is, since SrO and BaO have an action of inhibiting the ion exchange reaction, it is difficult to improve the mechanical strength when these components are contained in a large amount. The preferred range of SrO + BaO is 0-5%, 0-3%, 0-2.5%, 0-2%, 0-1%, especially 0-0.1%.

  The SrO and BaO contents are each preferably 0 to 5%. When the content of SrO or BaO increases, the ion exchange performance deteriorates, the glass density and thermal expansion coefficient increase, and the glass tends to devitrify. The SrO content is desirably 2% or less, 1.5% or less, 1% or less, 0.5% or less, and particularly preferably 0.1% or less. The BaO content is preferably 2.5% or less, 2% or less, 1% or less, 0.8% or less, 0.5% or less, and particularly preferably 0.1% or less.

TiO ₂ is a component that has an effect of improving ion exchange performance. Moreover, although there exists an effect which reduces the high temperature viscosity of glass, when the content increases too much, glass will color or it will become easy to devitrify. Therefore, the content is 0 to 10%, preferably 0 to 8%, 0.5 to 7%, 1 to 6%, 2 to 6%, particularly 3 to 6%.

ZrO ₂ has the effect of remarkably improving the ion exchange performance and increasing the viscosity and strain point in the vicinity of the liquid phase viscosity of the glass. However, if the content is too large, the devitrification resistance is significantly reduced. Therefore, the content is 0 to 10%, preferably 0 to 8%, 0.5 to 7%, 1 to 6%, 2 to 6%, particularly 3 to 6%.

In the present invention, from the viewpoint of improving ion exchange performance, it is desirable to contain 0.1 to 15% (preferably 1 to 12%, more preferably 3 to 10%) of ZrO ₂ and TiO ₂ in total. Further, a reagent may be used as the TiO ₂ source and the ZrO ₂ source, or it may be contained from impurities contained in the raw material.

P ₂ O ₅ is a component that enhances the ion exchange performance of the glass, and has an effect of particularly increasing the compressive stress thickness. However, when the content of P ₂ O ₅ is increased, the glass is phase-separated or the water resistance is lowered. Therefore, the content is 10% or less, 8% or less, 5% or less, 4% or less, particularly 3%. The following is desirable.

The present invention, the ratio of _Na 2 O / _Al 2 _{O 3} in mass ratio, characterized in that it is a 0.7 to 2. That is, when this ratio is smaller than 0.7, the glass is easily devitrified. On the other hand, when it becomes larger than 2, the ion exchange performance of the glass is lowered. Further, the thermal expansion coefficient becomes too large, and the thermal shock resistance of the glass is lowered, and it is difficult to match the thermal expansion coefficient with the surrounding materials. Moreover, there exists a tendency for a strain point to fall or to lack the balance of a glass composition, and for the devitrification resistance of glass to fall. The preferable range of the ratio of Na ₂ O / Al ₂ O ₃ is 0.8-2, more preferably 0.8-1.5, further 0.85-1.5, and further 1-1. 4 and 1.1 to 1.4. Furthermore, it is 0.9-1.4, Furthermore, it is 1-1.4, The range of 1.1-1.4 is especially desirable.

  The tempered glass substrate of the present invention is composed of the above components, but the following components can be added within a range not impairing the properties of the glass.

K ₂ O has an effect of promoting ion exchange, and has a high effect of increasing the depth of the compressive stress layer among alkali metal oxides. It also has the effect of reducing the high temperature viscosity of the glass and improving the meltability and formability. K ₂ O is also a component that improves devitrification resistance. However, when the content of K _{2 O} is too large, the thermal expansion coefficient of the glass is increased, or reduced thermal shock resistance of the glass, the peripheral material and thermal expansion coefficient may become less likely matched. Furthermore, there is a tendency that the strain point is lowered or the balance of the glass composition is lost and the devitrification resistance of the glass is deteriorated. Therefore, the content is 0 to 15%, preferably 0.1 to 12%, 0.5 to 10%, 1 to 8%, particularly 1 to 6%.

Further, when the content of the alkali metal oxide R ₂ O (R is one or more selected from Li, Na, and K) is excessive, the glass tends to be devitrified, and the thermal expansion coefficient of the glass is increased. If it becomes too large, the thermal shock resistance of the glass will decrease, and it will be difficult to match the thermal expansion coefficient with the surrounding materials. In addition, the strain point of the glass is too low, and it may be difficult to obtain a high compressive stress value. Furthermore, the viscosity in the vicinity of the liquidus temperature may decrease, and it may be difficult to ensure a high liquidus viscosity. Accordingly, R ₂ O is desirably contained in an amount of 10 to 25%, preferably 13 to 22%, more preferably 15 to 20%, and particularly 16.5 to 20%.

The range of _{K 2} O / Na 2 O weight ratio of is preferably 0-2. It is possible to change the magnitude of the compressive stress value and the depth of the stress layer by changing the ratio of K ₂ O / Na ₂ O. When it is desired to set the compressive stress value high, it is desirable to set it in the range of 0 to 0.5, preferably 0 to 0.3, more preferably 0 to 0.2. On the other hand, when the thickness of the compressive stress layer is made deeper, it is desired to be 0.5 to 2, more preferably 1 to 2, still more preferably 1.2 to 2, and most preferably 1.5 to 2. When this ratio is greater than 2, the glass composition is not balanced and the glass composition tends to be devitrified, the high-temperature viscosity is increased, the meltability is lowered, and a high compressive stress value is hardly obtained.

  When the alkaline earth metal oxide R′O (R ′ is one or more selected from Mg, Ca, Sr, Ba) increases, the density and thermal expansion coefficient of the glass increase, and the devitrification resistance deteriorates. In addition to this, the ion exchange performance tends to deteriorate. Therefore, the total amount of the alkaline earth metal oxide R′O is 0.1 to 10%, preferably 1 to 8%, more preferably 1.5 to 8%, still more preferably 2 to 6%, most preferably Preferably it is 2 to 5%.

  ZnO is a component that enhances the ion exchange performance of the glass, and is particularly effective in increasing the compressive stress value. Moreover, it is a component which has the effect of reducing a high temperature viscosity, without reducing the low temperature viscosity of glass. However, when the content of ZnO increases, the glass tends to undergo phase separation, devitrification deteriorates, the density increases, and the thickness of the compressive stress layer decreases. Therefore, the content is 0 to 4%, preferably 0 to 2%, more preferably 0 to 1%, and still more preferably 0 to 0.5%.

Also the value of the total amount obtained by dividing the total amount of R _{2 O} of R'O becomes large, it appears a tendency that devitrification resistance of the glass deteriorates. Therefore, it is desirable to regulate the value of R′O / R ₂ O to 0.5 or less, 0.4 or less, or 0.3 or less by mass fraction.

SnO ₂ acts as a glass refining agent and has an effect of further improving the ion exchange performance. However, when the content is increased, devitrification due to SnO ₂ occurs or the glass tends to be colored. There is. Therefore, it is desirable to contain 0.01 to 6%, 0.01 to 3%, especially 0.1 to 1%.

The _As 2 _O 3 as a fining _{agent, Sb 2 O 3, CeO 2} , SnO 2, F, Cl, selected from the group of SO ₃ was one or two or more may be contained 0-3%. However, As ₂ O ₃ and F, especially As ₂ O ₃ should be refrained from use as much as possible from the consideration of the environment, and it is desirable not to contain them substantially. Here, “substantially not containing” means that the material is not actively used as a raw material but is mixed as an impurity, and the content is less than 0.1%. Therefore, the content of the fining agent preferred in the present invention is SnO ₂ + CeO ₂ + Cl 0.001 to 1%, preferably 0.01 to 0.5%, more preferably 0.05 to 0.4%. In addition, as described above, SnO ₂ also has an effect of improving the ion exchange performance, so that SnO ₂ 0.01 to 3%, preferably 0.01 to 1. 5, more preferably 0.1 to 1%. However, if SnO ₂ is used as a fining agent, the glass may be colored. Therefore, when it is necessary to keep the transmittance of the glass high, Sb ₂ O ₃ or SO ₃ may be used as a fining agent. Specifically, Sb ₂ O ₃ 0.01 to 6%, preferably 0.01 to 3%, or SO ₃ 0.001 to 6%, preferably 0.001 to ₃ %. good. Further, from the viewpoint of suppressing the coloring of the glass while improving the ion exchange performance, it is desirable that SnO ₂ + Sb ₂ O ₃ + SO ₃ coexist and 0.01 to 10% in total is contained.

Further, rare earth oxides such as Nb ₂ O ₅ and La ₂ O ₃ are components that increase the Young's modulus of glass. However, the cost of the raw material itself is high, and if it is contained in a large amount, the devitrification resistance deteriorates. Therefore, it is desirable to limit their content to 3% or less, 2% or less, 1% or less, 0.5% or less, and particularly 0.1% or less.

  In the present invention, transition metal elements such as Co and Ni that strongly color the glass are not preferable because they reduce the transmittance of the glass substrate. In particular, when used in touch panel display applications, if the content of transition metal elements is large, the visibility of the touch panel display is impaired. Specifically, it is desirable to adjust the amount of raw material or cullet used so that it is 0.5% or less, 0.1% or less, and particularly 0.05% or less.

Moreover, substances such as PbO and Bi ₂ O ₃ should be refrained from use as much as possible from the consideration of the environment. It is desirable that they are not substantially contained, and the contents in that case are each less than 0.1%.

  The tempered glass substrate of the present invention can have a preferable glass composition range by appropriately selecting a suitable content range of each component. Among them, examples of more suitable glass composition ranges are as follows.

(1) in _{mass%, SiO 2 40~75%, Al} 2 O 3 10~17.5%, B 2 O 3 0.01~8%, Li 2 O 0~4%, Na 2 O 10~20 _{%, 0~6% MgO, CaO 0~4} %, SrO + BaO 0~7%, P 2 O 5 0~10%, TiO 2 0~10%, ZrO 2 0~10%, R'O 1.5~ A glass composition containing 8% and having a Na ₂ O / Al ₂ O ₃ ratio of 0.8 to _{2 in} terms of mass ratio.

(2) in _{mass%, SiO 2 40~75%, Al} 2 O 3 10~17.5%, B 2 O 3 0.01~8%, Li 2 O 0~4%, Na 2 O 10~20 _{%, 0~6% MgO, CaO 0~4} %, SrO + BaO 0~7%, P 2 O 5 0~10%, TiO 2 0~10%, ZrO 2 0~10%, R'O 1.5~ A glass composition containing 8%, SnO ₂ 0.01 to 6%, and having a mass ratio of Na ₂ O / Al ₂ O ₃ ratio of 0.8 to ₂ .

(3) _{mass%, SiO 2 40~70%, Al} 2 O 3 10~16%, B 2 O 3 0.1~4%, Li 2 O 0~2%, Na 2 O 12~18%, MgO 0-3%, CaO 0-3%, SrO + BaO 0-4%, ZnO 0-1%, P ₂ O ₅ 0-10%, TiO ₂ 0-8%, ZrO ₂ 0-8%, glass composition _Na 2 O / _Al 2 _{O 3} ratio of 0.9 to 1.4 in mass ratio.

(4) in _{mass%, SiO 2 50~70%, Al} 2 O 3 12~16%, B 2 O 3 1~3%, Li 2 O 0~2%, Na 2 O 14~18%, K 2 O 1-5%, MgO 0.5-3%, CaO 0.5-3%, SrO + BaO 0-2%, ZnO 0-1%, P ₂ O ₅ 0-5%, TiO ₂ 0-5%, A glass composition containing 0 to 5% of ZrO _{2 and} having a Na ₂ O / Al ₂ O ₃ ratio of 1 to 1.3 by mass ratio.

(5) in _{mass%, SiO 2 40~75%, Al} 2 O 3 10~17.5%, B 2 O 3 0.01~8%, Li 2 O 0~5%, Na 2 O 10~20 _{%, 0~6% MgO, CaO 0~4} %, SrO + BaO 0~7%, P 2 O 5 0~10%, TiO 2 0~10%, ZrO 2 0~10%, Sb 2 O 3 0.01 A glass composition containing ˜6% and having a mass ratio of Na ₂ O / Al ₂ O ₃ ratio of 0.7-2.

(6) _{mass%, SiO 2 40~75%, Al} 2 O 3 10~17.5%, B 2 O 3 0.01~8%, Li 2 O 0~5%, Na 2 O 10~20 _{%, 0~6% MgO, CaO 0~4} %, SrO + BaO 0~7%, P 2 O 5 0~10%, TiO 2 0~10%, ZrO 2 0~10%, SO 3 0.001~6 % containing glass composition _Na 2 O / _Al 2 _{O 3} ratio of 0.7 to 2 at a mass ratio.

(7) in _{mass%, SiO 2 40~75%, Al} 2 O 3 10~17.5%, B 2 O 3 0.01~8%, Li 2 O 0~5%, Na 2 O 10~20 %, MgO 0-6%, CaO 0-4%, SrO + BaO 0-7%, P ₂ O ₅ 0-10%, TiO ₂ 0-10%, ZrO ₂ 0-10%, SnO ₂ + Sb ₂ O ₃ 0 A glass composition containing 0.01 to 10% and having a mass ratio of Na ₂ O / Al ₂ O ₃ ratio of 0.7 to ₂ .

(8) in _{mass%, SiO 2 40~75%, Al} 2 O 3 10~17.5%, B 2 O 3 0.01~8%, Li 2 O 0~5%, Na 2 O 10~20 %, MgO 0-6%, CaO 0-4%, SrO + BaO 0-7%, P ₂ O ₅ 0-10%, TiO ₂ 0-10%, ZrO ₂ 0-10%, SnO ₂ + Sb ₂ O ₃ + SO ₃ A glass composition containing 0.01 to 10% and having a mass ratio of Na ₂ O / Al ₂ O ₃ ratio of 0.7 to ₂ .

  The tempered glass substrate of the present invention preferably satisfies the following characteristics.

The tempered glass substrate of the present invention has the above glass composition and a compressive stress layer on the glass surface. The compressive stress of the compressive stress layer is preferably 600 MPa or more and 800 MPa or more, more preferably 1000 MPa or more, further preferably 1200 MPa or more, and further preferably 1300 MPa or more. As the compressive stress increases, the mechanical strength of the glass substrate increases. On the other hand, when an extremely large compressive stress is formed on the surface of the glass substrate, microcracks are generated on the surface of the substrate, and the strength of the glass may be lowered. Moreover, since there exists a possibility that the tensile stress which exists in a glass substrate may become extremely high, it is preferable to set it as 2500 Mpa or less. In order to increase the compressive stress, the content of Al ₂ O ₃ , TiO ₂ , ZrO ₂ , MgO, ZnO may be increased, or the content of SrO or BaO may be reduced. Further, the time required for ion exchange may be shortened or the temperature of the ion exchange solution may be lowered.

The thickness of the compressive stress layer is preferably 10 μm or more, and most preferably 15 μm or more. The greater the thickness of the compressive stress layer, the more difficult it is to break even if the glass substrate is deeply scratched. Meanwhile, since the glass substrate is less likely to cut, the thickness of the compressive stress layer shall be the 2 7 [mu] m or less. In order to increase the thickness of the compressive stress layer, the contents of K ₂ O and P ₂ O ₅ may be increased or the contents of SrO and BaO may be reduced. Moreover, what is necessary is just to lengthen the time which ion exchange requires, or to raise the temperature of an ion exchange solution.

Further, the tensile stress inside the glass calculated by “tensile stress inside glass substrate = (compressive stress value × stress depth) / (plate thickness−stress depth × 2)” is 200 MPa or less (preferably 150 MPa or less, more preferably Is 100 MPa or less, more preferably 59 MPa or less, and still more preferably 50 MPa or less. The smaller this value, the less likely the glass will break due to defects inside the glass substrate, but if it is too small, it means a decrease in the compressive stress value on the glass surface and a decrease in stress depth. It is preferably 1 MPa or more, 10 MPa or more, or 15 MPa or more.

  The tempered glass substrate of the present invention preferably has a plate thickness of 3.0 mm, 1.5 mm or less, 0.7 mm or less, 0.5 mm or less, particularly 0.3 mm or less. The thinner the glass substrate, the lighter the glass substrate. Further, the tempered glass substrate of the present invention has an advantage that the glass substrate is not easily broken even if the plate thickness is reduced. When glass is formed by the overflow downdraw method, it is advantageous because the glass can be thinned without polishing or the like.

  The tempered glass substrate of the present invention preferably has an unpolished surface, and the average surface roughness (Ra) of the unpolished surface is 10 mm or less, preferably 5 mm or less, more preferably 2 mm or less. The average surface roughness (Ra) of the surface may be measured by a method based on SEMI D7-97 “Measurement method of surface roughness of FPD glass substrate”. The theoretical strength of glass is inherently very high, but breakage often occurs even at a stress much lower than the theoretical strength. This is because a small defect called Griffith flow is generated on the surface of the glass substrate in a step after glass molding, for example, a polishing step. Therefore, if the surface of the tempered glass substrate is unpolished, the mechanical strength of the original glass substrate is hardly impaired, and the glass substrate is hardly broken. Further, if the surface of the glass substrate is unpolished, the polishing process can be omitted in the glass substrate manufacturing process, so that the manufacturing cost of the glass substrate can be reduced. In the tempered glass substrate of the present invention, if both surfaces of the glass substrate are unpolished, the glass substrate becomes more difficult to break. Moreover, in the tempered glass substrate of this invention, in order to prevent the situation which breaks from the cut surface of a glass substrate, you may give a chamfering process etc. to the cut surface of a glass substrate. In order to obtain an unpolished surface, glass may be formed by an overflow down draw method.

In the tempered glass substrate of the present invention, the liquidus temperature of the glass is preferably 1200 ° C or lower, 1050 ° C or lower, 1030 ° C or lower, 1010 ° C or lower, 1000 ° C or lower, and particularly preferably 950 ° C or lower. Here, “liquid phase temperature” means that glass is crushed, passed through a standard sieve 30 mesh (500 μm sieve opening), and the glass powder remaining in 50 mesh (300 μm sieve sieve) is placed in a platinum boat, and the temperature gradient The temperature at which crystals are precipitated after being kept in the furnace for 24 hours. In order to lower the liquidus temperature, the content of Na ₂ O, K ₂ O, B ₂ O ₃ is increased or the content of Al ₂ O ₃ , Li ₂ O, MgO, ZnO, TiO ₂ , ZrO ₂ is increased. The amount may be reduced.

The tempered glass substrate of the present invention, the liquidus viscosity of the glass is ^preferably at least ¹⁰ 4.0 dPa · ^s, more preferably at least ¹⁰ 4.3 dPa · ^s, more preferably not less than ¹⁰ 4.5 dPa · s, 10 ^5.0 dPa · s or more is particularly preferable, and 10 ^5.4 dPa · s or more is most preferable. Here, “liquidus viscosity” refers to the viscosity of the glass at the liquidus temperature. In order to increase the liquid phase viscosity, the content of Na ₂ O, K ₂ O is increased, or the content of Al ₂ O ₃ , Li ₂ O, MgO, ZnO, TiO ₂ , ZrO ₂ is decreased. do it.

In addition, the higher the liquidus viscosity and the lower the liquidus temperature, the better the devitrification resistance of the glass and the better the moldability of the glass substrate. The liquidus temperature of the glass at 1200 ° C. or less, the liquidus viscosity of the glass, if 10 4.0 ^{dPa · s} or more, it can be molded by an overflow down draw method.

The tempered glass substrate of the present invention preferably has a glass density of 2.8 g / cm ³ or less, more preferably 2.7 g / cm ³ or less, and even more preferably 2.6 g / cm ³ or less. As the glass density is smaller, the glass substrate can be made lighter. Here, “density” refers to a value measured by the well-known Archimedes method. In order to reduce the density of the glass, the content of SiO ₂ , P ₂ O ₅ , B ₂ O ₃ is increased, alkali metal oxide, alkaline earth metal oxide, ZnO, ZrO ₂ , TiO ₂ What is necessary is just to reduce content.

The tempered glass substrate of the present invention preferably has a glass thermal expansion coefficient of 70 to 110 × 10 ⁻⁷ / ° C. in a temperature range of 30 to 380 ° C., and preferably 75 to 100 × 10 ⁻⁷ / ° C. More preferably, it is 80-100 * 10 < ^-7 > / degreeC, It is still more preferable that it is 85-96 * 10 < ^-7 > / degreeC. If the thermal expansion coefficient of the glass is in the above range, it becomes easy to match the thermal expansion coefficient with a member such as a metal or an organic adhesive, and peeling of the member such as a metal or an organic adhesive can be prevented. Here, the “thermal expansion coefficient” refers to a value obtained by measuring an average thermal expansion coefficient in a temperature range of 30 to 380 ° C. using a dilatometer. In order to increase the coefficient of thermal expansion, the content of alkali metal oxides and alkaline earth metal oxides may be increased. To decrease the coefficient of thermal expansion, the content of alkali metal oxides and alkaline earth metal oxides is included. The amount may be reduced.

The tempered glass substrate of the present invention preferably has a strain point of 500 ° C or higher, more preferably 540 ° C or higher, more preferably 550 ° C or higher, and further preferably 560 ° C or higher. The higher the strain point of the glass, the better the heat resistance of the glass, and even if the tempered glass substrate is subjected to heat treatment, the tempered layer hardly disappears. Also, if the strain point of the glass is high, stress relaxation is less likely to occur during ion exchange, so a high compressive stress value can be obtained. In order to increase the strain point of glass, the content of alkali metal oxides may be reduced, or the content of alkaline earth metal oxides, Al ₂ O ₃ , ZrO ₂ , P ₂ O ₅ may be increased. .

In the tempered glass substrate of the present invention, the temperature corresponding to a glass high temperature viscosity of 10 ^2.5 dPa · s is preferably 1500 ° C. or less, more preferably 1450 ° C. or less, more preferably 1430 ° C. or less, and more preferably 1420 ° C. or less. 1400 degrees C or less is still more preferable. The lower the temperature corresponding to the high-temperature viscosity of 10 ^2.5 dPa · s of the glass, the smaller the burden on the glass production equipment such as the melting furnace, and the higher the bubble quality of the glass substrate. That is, the lower the temperature corresponding to the glass high temperature viscosity of 10 ^2.5 dPa · s, the cheaper the glass substrate can be produced. The temperature corresponding to the glass high temperature viscosity of 10 ^2.5 dPa · s corresponds to the melting temperature of the glass. The lower the temperature corresponding to the glass high temperature viscosity of 10 ^2.5 dPa · s, the lower the temperature. Glass can be melted. In order to reduce the temperature corresponding to 10 ^2.5 dPa · s, the content of alkali metal oxide, alkaline earth metal oxide, ZnO, B ₂ O ₃ , TiO ₂ is increased, or SiO ₂ , the content of al ₂ O ₃ may be reduced.

The glasses according to the invention also, in _{mass%, SiO 2 40~75%, Al} 2 O 3 10~20%, B 2 O 3 0.01~8%, Li 2 O 0~5%, Na 2 O 10 to 20%, MgO 0 to 10%, CaO 0 to 4%, SrO + BaO 0 to 10%, characterized in that the Na ₂ O / K ₂ O ratio by weight ratio is 0.7 to ₂ , preferably, in _{mass%, SiO 2 40~75%, Al} 2 O 3 10~17.5%, B 2 O 3 0.01~8%, Li 2 O 0~4%, Na 2 O 10~20 %, MgO 0-6%, CaO 0-4%, SrO + BaO 0-7%, P ₂ O ₅ 0-10%, TiO ₂ 0-10%, ZrO ₂ 0-10%, and Na by mass ratio ₂ O / K ₂ O ratio is 0.8-2, more preferably, by mass%, SiO _{2 40~70%, Al 2 O 3 10~16.5} %, B 2 O 3 0.01~6%, Li 2 O 0~4%, Na 2 O 10~20%, 0~6% MgO, CaO _{0~4%, SrO + BaO 0~7%} , P 2 O 5 0~10%, TiO 2 0~10%, containing ZrO 2 0%, the _Na 2 O / _{K 2} O ratio in the mass ratio 0 .8 to 1.5.

In the glass according to the present invention , the reason why the glass composition is limited to the above range and the preferable range are the same as those of the tempered glass substrate described above, and thus the description thereof is omitted here. Furthermore, the glass according to the present invention naturally has the characteristics and effects of the tempered glass substrate described above.

The glasses according to the invention, when 4 hours ion exchange in a KNO ₃ molten salt at 430 ° C., the compressive stress of the surface is more than 600 MPa, and the thickness of the compression stress layer is preferably formed of a 10 ~ 27 mu m. Glass according to the present invention, since the glass composition is regulated within the above range, the ion exchange performance is good, easily the compressive stress of the surface 600MPa or more and a thickness of the compressive stress layer and 10 ~ 27 mu m can do.

  In the glass according to the present invention, a glass raw material prepared so as to have a glass composition within the above composition range is put into a continuous melting furnace, the glass raw material is heated and melted at 1500 to 1600 ° C., clarified, and then supplied to a molding apparatus Then, the molten glass can be formed into a plate shape and slowly cooled.

For the molding, it is preferable to employ an overflow downdraw method. If the glass substrate is formed by the overflow down draw method, a glass substrate that is unpolished and has good surface quality can be produced. The reason for this is that, in the case of the overflow down draw method, the surface to be the surface of the glass substrate does not come into contact with the bowl-like refractory, and is molded in a free surface state. This is because it can be molded. Here, the overflow down draw method is to melt the molten glass from both sides of the heat-resistant bowl-like structure and draw the overflowed molten glass downward while joining at the lower end of the bowl-like structure. This is a method for producing a glass substrate. The structure and material of the bowl-shaped structure are not particularly limited as long as the dimensions and surface accuracy of the glass substrate can be set to a desired state and the quality usable for the glass substrate can be realized. Moreover, in order to perform the downward extending | stretching shaping | molding, you may apply force with what kind of method with respect to a glass substrate. For example, a method may be employed in which a heat-resistant roll having a sufficiently large width is rotated and stretched in contact with the glass substrate, or a plurality of pairs of heat-resistant rolls are only near the end face of the glass substrate. You may employ | adopt the method of making it contact and extending | stretching. Since the glass according to the present invention is excellent in devitrification resistance and has a viscosity characteristic suitable for molding, it is possible to accurately perform molding by the overflow down draw method. If the liquid phase temperature is 1200 ° C. or lower and the liquid phase viscosity is 10 ^4.0 dPa · s or higher, the glass substrate can be produced by the overflow down draw method.

  In addition to the overflow downdraw method, various methods can be employed. For example, various molding methods such as a downdraw method (slot down method, redraw method, etc.), a float method, a rollout method, a press method, and the like can be employed. For example, if glass is formed by a pressing method, a small glass substrate can be efficiently produced.

In order to produce the tempered glass substrate of the present invention, first, the glass is prepared. Next, a strengthening process is performed. For cutting the glass substrate into a predetermined size it is carried out after the strengthening process. In this way, Ru can be reduced and the manufacturing cost of the tempered glass substrate. The strengthening process is desirably performed by an ion exchange process. The ion exchange treatment can be performed, for example, by immersing the glass plate in a potassium nitrate solution at 400 to 550 ° C. for 1 to 8 hours. As ion exchange conditions, optimum conditions may be selected in consideration of the viscosity characteristics of glass, application, plate thickness, tensile stress inside the glass, and the like.

  Hereinafter, the present invention will be described based on examples.

  Table 1 shows the glass composition and characteristics of Examples (Sample Nos. 1 to 9) of the present invention. In addition, the display of “not yet” in the table means not measured.

  Each sample of Table 1 was produced as follows. First, the glass raw material was prepared so that it might become the glass composition in a table | surface, and it melted at 1580 degreeC for 8 hours using the platinum pot. Thereafter, the molten glass was poured onto a carbon plate and formed into a plate shape. Various characteristics were evaluated about the obtained glass substrate.

  The density was measured by the well-known Archimedes method.

  The strain point Ps and the annealing point Ta were measured based on the method of ASTM C336.

  The softening point Ts was measured based on the method of ASTM C338.

Temperature corresponding to a viscosity ^{10 4.0 dPa · s, 10 3.0} dPa · s, 10 2.5 dPa · s of the glass was measured by a platinum ball pulling method.

  The thermal expansion coefficient α is obtained by measuring an average thermal expansion coefficient in a temperature range of 30 to 380 ° C. using a dilatometer.

  The liquid phase temperature is obtained by crushing glass, passing through a standard sieve 30 mesh (a sieve opening of 500 μm), putting the glass powder remaining in 50 mesh (a sieve opening of 300 μm) into a platinum boat, and keeping it in a temperature gradient furnace for 24 hours. Then, the temperature at which the crystals are deposited is measured.

  The liquidus viscosity indicates the viscosity of each glass at the liquidus temperature.

As a result, the obtained glass substrate was suitable as a tempered glass material having a density of 2.59 g / cm ³ or less and a thermal expansion coefficient of 92 to 98 × 10 ⁻⁷ / ° C. In addition, the liquid phase viscosity is as high as 10 ^4.9 dPa · s or higher, and overflow downdraw molding is possible, and the temperature at 10 ^2.5 dPa · s is as low as 1482 ° C. It is considered that a glass substrate can be supplied. In addition, although the glass composition differs microscopically in the surface layer of a glass substrate, the glass composition is not substantially different as the whole glass substrate. Therefore, the characteristic values such as density and viscosity are not substantially different between the untempered glass substrate and the tempered glass substrate. Subsequently, sample no. After subjecting both surfaces of each of the glass substrates 1 to 9 to optical polishing, ion exchange treatment was performed. After finishing the surface of each sample after the treatment, the surface compressive stress value and the thickness of the compressive stress layer are determined from the number of interference fringes observed using a surface stress meter (FSM-6000 manufactured by Toshiba Corporation) and the interval therebetween. Was calculated. In the calculation, the refractive index of the sample was 1.53, and the optical elastic constant was 28 [(nm / cm) / MPa].

As a result, sample No. Each of the glass substrates 1 to 9 had a compressive stress of 802 MPa or more on the surface thereof, and had a thickness of 15 to 27 μm . Further, the internal tensile stress was as low as 59 MPa or less in the substrate having a thickness of 0.5 mm.

  In the above examples, for convenience of explanation of the present invention, glass was melted and cast by casting, followed by optical polishing before ion exchange treatment. When implemented on an industrial scale, it is desirable to form a glass substrate by an overflow down draw method or the like, and to perform ion exchange treatment in a state where both surfaces of the glass substrate are unpolished.

  The tempered glass substrate of the present invention is suitable as a glass substrate for a mobile phone, a digital camera, a cover glass such as a PDA, or a touch panel display. In addition to these uses, the tempered glass substrate of the present invention is used for applications requiring high mechanical strength, such as window glass, magnetic disk substrates, flat panel display substrates, solar cell cover glasses, solid-state imaging. Application to cover glass for elements and tableware can be expected.

Claims (13)

A tempered glass substrate having a compressive stress layer on the surface, as a glass composition, in _{mass%, SiO 2 40~75%, Al} 2 O 3 10~20%, B 2 O 3 0.01~8%, Li ₂ O 0 to 5%, Na ₂ O 10 to 20%, MgO 0 to 10%, CaO 0 to 4%, SrO + BaO 0 to 10%, and the ratio of Na ₂ O / Al ₂ O ₃ is 0 A tempered glass substrate, wherein the compressive stress layer is a chemically strengthened layer having a depth of 27 μm or less, and no compressive stress layer is present on the surface of the substrate end face .   The tempered glass substrate according to claim 1, wherein an internal tensile stress is 59 MPa or less. The tempered glass substrate according to claim 1 or 2, characterized in that it contains SnO ₂ 0.01 to 6%. The tempered glass substrate according to any one of claims 1 to 3 , comprising 0.1 to 15% of TiO ₂ + ZrO ₂ . MgO + CaO + SrO + BaO 0.1 to 10% is contained, The tempered glass substrate in any one of Claims 1-4 characterized by the above-mentioned. Compressive stress of the surface at least 300 MPa, and a thickness of 10 ~ 27 mu m of the compressive stress layer, to any one of claims 1 to 5, characterized in that the tensile stress within the glass substrate is less than 59 MPa The tempered glass substrate as described. The tempered glass substrate according to any one of claims 1 to 6, characterized in that has an unpolished surface. The tempered glass substrate according to any one of claims 1 to 7, liquidus temperature, comprising the 1200 ° C. or less of the glass. The tempered glass substrate according to any one of claims 1 to 8, liquidus viscosity, characterized in that it consists ^of 10 ^{4.0 dPa} · s or more of the glass. The tempered glass substrate according to any one of claims 1 to 9, characterized in that used in the touch panel display. By _{mass%, SiO 2 40~75%, Al} 2 O 3 10~20%, B 2 O 3 0.01~8%, Li 2 O 0~5%, Na 2 O 10~20%, MgO 0~ Melting glass raw material containing 10%, CaO 0-4%, SrO + BaO 0-10%, and having a glass composition in which Na ₂ O / Al ₂ O ₃ ratio is 0.7-2 by mass ratio Then, after forming the glass into a plate shape, an ion exchange treatment is performed to form a compressive stress layer having a depth of 27 μm or less on the glass surface, and then the obtained tempered glass substrate is cut into a predetermined size. A method for producing a tempered glass substrate. The method for producing a tempered glass substrate according to claim 12, comprising 0.01 to 6% of SnO ₂ . The method for producing a tempered glass substrate according to claim 12 or 13 , wherein the glass is formed into a plate shape by an overflow down draw method.