Tempered glass substrate and method for fabricating the same

Strengthened glass substrate and manufacturing method thereof

TEMPERED GLASS SUBSTRATE AND METHOD FOR FABRICATING THE SAME

The present invention relates to a strengthened glass substrate, in particular to a protective glass suitable for mobile phones, digital cameras, PDAs (personal digital assistants), solar cells, or touch panel displays. display) The strengthened glass substrate of the substrate.

Devices such as mobile phones, digital cameras, PDAs, solar batteries, or touch panel displays are widely used and tend to become more and more popular.

Previously, in these applications, a resin substrate such as an acrylic was used as a protective member for protecting a display. However, the acrylic resin substrate has a low Young's Modulus, so when the display surface of the display is pressed with a pen or a human finger, it is easy to bend, and the resin substrate is brought into contact with the internal display, resulting in display bad. In addition, acrylic resin substrates also have problems that the surface is easily damaged and visibility is easily deteriorated. One way to solve these problems is to use glass substrates as protective components. The glass substrate (protective glass) used as a protective component requires: (1) high mechanical strength, (2) low density and light weight, (3) inexpensive and large supply, (4) excellent bubble quality, (5) It has high light transmittance in the visible light range, (6) It has a high Young's modulus as it is not easy to bend when pressing the surface with a pen or finger. Especially when the requirement (1) is less than sufficient, it is not enough to be used as a protective member. Therefore, glass substrates strengthened by ion exchange or the like (so-called strengthened glass substrates) have been used conventionally (refer to Patent Document 1, Non-Patent Document 1 ).

Patent Document 1: Japanese Patent Laid-Open No. 2006-83045

Non-Patent Document 1: "New Glass and Its Physical Properties", First Edition, Management System Research Institute Co., Ltd., August 20, 1984, pages 451-498. In Non-Patent Document 1: If you increase the Al in the glass composition₂O₃The content can improve the ion exchange performance of the glass and increase the mechanical strength of the glass substrate.

However, if the Al in the glass composition is increased₂O₃When the content is contained, the devitrification resistance of the glass deteriorates, and the glass is easily devitrified during molding, which deteriorates the production efficiency, quality, etc. of the glass substrate. In addition, if the devitrification resistance of the glass is poor, it can only be formed using a method such as roll forming, and thus a glass plate with high surface accuracy cannot be obtained. Therefore, it is necessary to add another polishing step after the glass plate is formed. However, if the glass substrate is polished, minute defects are likely to occur on the surface of the glass substrate, making it difficult to maintain the mechanical strength of the glass substrate.

According to the above, it is difficult to achieve the ion exchange performance and devitrification resistance of glass at the same time, and it is 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 thin glass substrates are easily damaged, techniques for improving the mechanical strength of glass substrates have become increasingly important.

Therefore, the technical problem of the present invention is to obtain a glass substrate with high mechanical strength by simultaneously realizing the ion exchange performance and devitrification resistance of glass.

The inventors conducted various studies and found out that by reducing the Al in the glass₂O₃Content or Na₂Setting the O content in an appropriate range can ensure high ion exchange performance and meltability. In addition, it has been found that since it is cut to a predetermined size after the strengthening treatment, the manufacturing cost of the strengthened glass can be reduced, and the present invention is proposed.

That is, the strengthened glass substrate of the present invention is a strengthened glass substrate having a compressive stress layer on the surface, and is characterized in that the composition of the strengthened glass substrate contains 40% to 71% by mass of SiO₂, 3%~21% Al₂O₃, 0%~3.5% Li₂O, 7%~20% Na₂O and 0%~15% K₂At the same time as O, the strengthened glass substrate is cut after strengthening treatment. In addition, as long as there are no special regulations, "%" in the following description means mass percentage.

In addition, the strengthened glass substrate of the present invention is a strengthened glass substrate having a compressive stress layer on the surface, and is characterized in that the composition of the strengthened glass substrate contains 40% to 70% by mass of SiO₂, 12%~21% Al₂O₃, 0%~3.5% Li₂O, 10%~20% Na₂O, 0%~15% K₂At the same time as O, it is preferable that the strengthened glass substrate is cut after strengthening treatment. Here, "internal tensile stress" is calculated according to the following formula.

In addition, the strengthened glass substrate of the present invention is preferably chemically strengthened.

In addition, the internal tensile stress of the strengthened glass substrate of the present invention is preferably 200 MPa or less.

Tensile stress inside the glass substrate = (compressive stress value × stress depth) / (board thickness-stress depth × 2)

Preferably, the compressive stress of the surface of the strengthened glass substrate of the present invention is 300 MPa or more, and the thickness of the compressive stress layer is 10 μm or more. Here, "surface compressive stress" and "thickness of compressive stress layer" are based on the number of interference fringes observed and their Calculate the interval.

Furthermore, the strengthened glass substrate of the present invention preferably has an unpolished surface. Here, the "non-polished surface" means that both surfaces (the so-called front surface and the back surface) of the glass substrate are not polished. In other words, it means that both sides are fire polishing surfaces, which can reduce the average surface roughness (Ra). The average surface roughness (Ra) is measured by the method according to SEMI D7-97 "Method for Measuring the Surface Roughness of FPD Glass Substrates", and should be 10 or less<img file="TWI386397B_D0001.tif" he="57" id="i0001" img-content="character" img-format="tif" inline="no" orientation="portrait" wi="46" />, Preferably less than or equal to 5<img file="TWI386397B_D0002.tif" he="57" id="i0002" img-content="character" img-format="tif" inline="no" orientation="portrait" wi="46" />, Better is less than or equal to 2<img file="TWI386397B_D0003.tif" he="58" id="i0003" img-content="character" img-format="tif" inline="no" orientation="portrait" wi="47" />. In addition, the end surface of the glass substrate may be subjected to polishing treatment such as chamfering or etching treatment.

In addition, the tempered glass substrate of the present invention preferably has a liquidus temperature of 1200°C or less. Here, the "liquid phase temperature" means that the glass is pulverized, passed through a standard sieve of 30 mesh (mesh opening 500 μm), and the remaining glass powder in 50 mesh (mesh opening 300 μm) is put into platinum In a boat, the temperature at which crystals precipitate after being kept in a temperature gradient furnace for 24 hours.

In addition, the strengthened glass substrate of the present invention preferably has a liquid phase viscosity of 10 or more^4.0dPas. Here, the "liquid phase 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 easier the devitrification resistance of the glass is improved and the glass substrate is easier to shape.

In addition, the strengthened glass substrate of the present invention is preferably used as a cover glass of a display.

In addition, the strengthened glass substrate of the present invention is preferably used as a cover glass for solar cells.

In addition, the method for manufacturing a strengthened glass substrate of the present invention is characterized in that it is blended into a SiO content of 40% to 71% by mass.₂, 3%~21% Al₂O₃, 0%~3.5% Li₂O, 7%~20% Na₂O, 0%~15% K₂The glass raw material composed of O glass is melted and formed into a plate shape, and then subjected to ion exchange treatment to form a compressive stress layer on the glass surface, and is cut after strengthening treatment.

[Effects of the invention]

The strengthened glass substrate of the present invention is produced from glass with high ion exchange performance. In addition, the strengthened glass substrate of the present invention is produced from glass having excellent devitrification resistance, and therefore, a glass substrate with a small surface roughness can be obtained by employing an overflow down-draw method or the like. Therefore, there is no need for grinding after forming, and there are no minute defects due to grinding. Therefore, the mechanical strength is high and the manufacturing cost due to grinding is not increased, so it can be produced at low cost.

The tempered glass substrate of the present invention is suitable as a cover glass for mobile phones, digital cameras, PDAs, solar cells, and touch panel display substrates. In addition, touch panel displays are mounted on mobile phones, digital cameras, PDAs, etc. In touch panel displays for mobile use, there is a strong demand for lightweight, thinner, and high-strength, as well as thin and high mechanical strength. glass substrate. In terms of the above-mentioned points, the strengthened glass substrate of the present invention has sufficient mechanical strength in practical use even if the plate thickness is reduced, and therefore, is suitable for mobile use.

In addition, since the glass of the present invention 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 glass substrate with a small surface roughness and high mechanical strength can be produced inexpensively.

In addition, the method for producing a strengthened glass of the present invention uses a glass having high ion exchange performance and excellent devitrification resistance, and therefore, a strengthened glass substrate with high mechanical strength can be produced inexpensively.

The strengthened glass substrate of the present invention has a compressive stress layer on its surface. As for the method of forming the compressive stress layer on the surface of the glass substrate, there are a physical strengthening method and a chemical strengthening method. The strengthened glass substrate of the present invention preferably has a compressive stress layer formed by a chemical strengthening method. The chemical strengthening method is a method of introducing alkaline ions with a large ion radius to the surface of the glass substrate by ion exchange at a temperature equal to or lower than the strain point of the glass. If the compressive stress layer is formed by the chemical strengthening method, even if the thickness of the glass substrate is thin, the strengthening treatment can be performed well, and the desired mechanical strength can be obtained. Furthermore, even if the glass substrate is cut after forming the compressive stress layer on the glass substrate, it is not easily broken like a glass substrate strengthened by a physical strengthening method such as an air-cooling strengthening method.

The conditions of ion exchange are not particularly limited, and may be determined in consideration of the viscosity characteristics of the glass and the like. Especially if the KNO₃The K ions in the molten salt and the Na component in the glass substrate are ion-exchanged to efficiently form a compressive stress layer on the surface of the glass substrate, which is preferable.

In the strengthened glass substrate of the present invention, the reason why the glass composition is limited to the above range is explained as follows.

SiO₂It is a component that forms a network of glass, and its content is 40% to 71%, preferably 40% to 70%, 40% to 63%, 45% to 63%, 50% to 59%, Especially preferred is 55% to 58.5%. If SiO₂Too much content makes it difficult to melt and shape the glass, or the coefficient of thermal expansion becomes too small, making it difficult to integrate the coefficient of thermal expansion with surrounding materials. On the other hand, if SiO₂If the content is too small, it is difficult to vitrify. In addition, if the coefficient of thermal expansion of the glass increases, the thermal shock resistance of the glass tends to decrease.

Al₂O₃It is a component that improves ion exchange performance. In addition, it also has the effect of increasing the strain point and Young's modulus of the glass, and its content is 3% to 21%. If Al₂O₃If the content of is too much, devitrified crystals are likely to precipitate in the glass, and it is difficult to form by the overflow down-draw method or the like. In addition, if the thermal expansion coefficient of the glass is too small, the thermal expansion coefficient and the surrounding materials are difficult to integrate, or the high-temperature viscosity of the glass becomes high and it is difficult to melt. If Al₂O₃If the content is too small, there is a concern that sufficient ion exchange performance will not be exhibited. According to the above point of view, as for Al₂O₃The upper limit is more preferably 20% or less, 19% or less, 18% or less, 17% or less, and 16.5% or less. In addition, the lower limit is more preferably 7.5% or higher, 8.5% or higher, 9% or higher, 10% or higher, 12% or higher, 13% or higher, and 14% or higher.

Li₂O is an ion exchange component, and at the same time, it is a component that reduces the high-temperature viscosity of the glass and improves the meltability or formability. Moreover, Li₂O is a component that increases the Young's modulus of glass. In addition, Li₂O has a high effect of increasing the compressive stress value in alkali metal oxides. However, if Li₂If the content of O is too large, the viscosity of the liquid phase decreases, and the glass tends to devitrify. In addition, if the thermal expansion coefficient of the glass is too large, the thermal shock resistance of the glass is reduced, or the thermal expansion coefficient is difficult to integrate with the surrounding materials. Moreover, if the low-temperature viscosity is excessively lowered and stress relaxation is likely to occur, the compressive stress value may become lower instead. Therefore, Li₂The content of O is 0%~3.5%, more preferably 0%~2%, 0%~1%, 0%~0.5%, 0%~0.1%, and the best is that it is not contained substantially, that is, it is suppressed in Less than 0.01%.

Na₂O is an ion exchange component, and at the same time, it is a component that reduces the high-temperature viscosity of the glass and improves the meltability or formability. In addition, Na₂O is also a component that improves the devitrification resistance of glass. Na₂The content of O is 7%-20%, more preferably 10%-20%, 10%-19%, 12%-19%, 12%-17%, 13%-17%, especially 14%~ 17%. If Na₂If the content of O is too large, the thermal expansion coefficient of the glass becomes too large, and the thermal shock resistance of the glass decreases, or the thermal expansion coefficient and the surrounding materials are difficult to integrate. In addition, the strain point is excessively lowered, or the glass composition is out of balance, and the devitrification resistance of the glass tends to deteriorate. On the other hand, if Na₂When the content of O is small, the meltability deteriorates, the thermal expansion coefficient becomes too small, or the ion exchange performance deteriorates.

K₂O has the effect of promoting ion exchange, and has a high effect of deepening the depth of the compressive stress layer in the alkali metal oxide. In addition, K₂O is a component that has the effect of reducing the high-temperature viscosity of the glass and improving the meltability or formability. In addition, K₂O is also a component that improves resistance to devitrification. K₂The content of O is 0%-15%. If K₂If the content of O is too large, the thermal expansion coefficient of the glass will increase, and the thermal shock resistance of the glass will decrease, or the thermal expansion coefficient will be difficult to integrate with surrounding materials. Moreover, the strain point is excessively lowered or the glass composition is out of balance, and the devitrification resistance of the glass tends to deteriorate. Therefore, it is preferable to set the upper limit to 12% or less, 10% or less, 8% or less, or less than Equal to 6%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%.

If alkali metal oxide R₂If the content of O (R is one or more selected from Li, Na, and K) is too large, the glass is liable to devitrify. In addition, the thermal expansion coefficient of the glass becomes too large, and the thermal shock resistance of the glass decreases, or the thermal expansion coefficient Difficult to integrate with surrounding materials. In addition, if the alkali metal oxide R₂When the content of O is too large, the strain point of the glass may be excessively lowered, and a high compressive stress value may not be obtained. Furthermore, the viscosity near the liquidus temperature may decrease, making it difficult to ensure a high liquidus viscosity. Therefore, R₂The content of O is preferably 22% or less, 20% or less, especially 19% or less. On the other hand, if R₂When the content of O is too small, the ion exchange performance or meltability of the glass may deteriorate. Therefore, R₂The content of O is preferably 8% or more, 10% or more, 13% or more, and particularly 15% or more.

In addition, it is ideal to add (Na₂O+K₂O)/Al₂O₃The value of is set in the range of 0.7 to 2, preferably 0.8 to 1.6, more preferably 0.9 to 1.6, particularly preferably 1 to 1.6, and most preferably 1.2 to 1.6. If this value is greater than 2, the low-temperature viscosity is excessively reduced, thereby reducing the ion exchange performance, or the Young's modulus, or the coefficient of thermal expansion becomes higher, so that the thermal shock resistance is likely to be reduced. In addition, the composition is out of balance and easily causes devitrification. On the other hand, if this value is more than 0.7, the meltability or devitrification is likely to deteriorate.

In addition, K₂O/Na₂The range of the mass ratio of O is preferably 0-2. By making K₂O/Na₂The mass ratio of O changes, so that the magnitude of the compressive stress value and the depth of the stress layer can be changed. When it is desired to set a higher compressive stress value, it is preferable to adjust the above-mentioned mass ratio to 0-0.5, especially 0-0.3, 0-0.2. On the other hand, when it is desired to further deepen the depth of the stress or to form a deep stress in a short time, it is preferable to adjust the above-mentioned mass ratio to 0.3-2, especially 0.5-2, 1-2, 1.2-2, 1.5 ~2. Here, the reason for setting the upper limit of the above-mentioned mass ratio to 2 is that if it is more than 2, the composition of the glass is out of balance and devitrification is likely to occur.

In the strengthened glass substrate of the present invention, the glass composition may consist only of the above-mentioned basic components, or other components may be added within a range that does not greatly impair the characteristics of the glass.

For example, the alkaline earth metal oxide R'O (R' is one or more selected from Mg, Ca, Sr, and Ba) is a component that can be added according to various purposes. However, if there are too many alkaline earth metal oxides R'O, the density or thermal expansion coefficient of the glass tends to increase, devitrification resistance tends to deteriorate, and ion exchange performance tends to deteriorate. Therefore, the content of the alkaline earth metal oxide R'O should preferably be 0% to 9.9%, 0% to 8%, 0% to 6, 0% to 5%.

MgO is a component that lowers the high-temperature viscosity of glass to improve meltability or formability, or increases the strain point or Young's modulus, and has a high effect of improving ion exchange performance in alkaline earth metal oxides. The content of MgO is preferably 0% to 6%. However, if the content of MgO increases, the density and thermal expansion coefficient of the glass increase, or the glass is likely to lose clarity. Therefore, the content of MgO is preferably 4% or less, 3% or less, 2% or less, and 1.5% or less.

CaO is a component that lowers the high-temperature viscosity of the glass to improve the meltability or formability, or improves the strain point or Young's modulus, and has a high effect of improving ion exchange performance in alkaline earth metal oxides. The content of CaO is preferably 0% to 6%. However, if the content of CaO increases, the density and coefficient of thermal expansion of the glass may increase, or the glass may easily devitrify, or the ion exchange performance may be further deteriorated. Therefore, its content is preferably 4% or less and 3% or less.

SrO and BaO are components that reduce the high-temperature viscosity of the glass to increase the meltability or formability, or increase the strain point or Young's modulus, and the content of each is preferably 0% to 3%. If the content of SrO or BaO increases, the ion exchange performance tends to deteriorate. In addition, the density and thermal expansion coefficient of the glass increase, or the glass is likely to lose clarity. The content of SrO is preferably 2% or less, 1.5% or less, 1% or less, 0.5% or less, 0.2% or less, especially 0.1% or less. In addition, the content of BaO is preferably 2.5% or less, 2% or less, 1% or less, 0.8% or less, 0.5% or less, 0.2% or less, especially 0.1% or less.

In addition, ZnO is a component that improves the ion exchange performance of glass, and particularly has a large effect of increasing the value of compressive stress. In addition, it is a component that has the effect of not lowering the low-temperature viscosity of the glass but lowering the high-temperature viscosity, and the content of ZnO can be set to 0% to 8%. However, if the content of ZnO increases, the glass will undergo phase separation, devitrification, or density will increase. Therefore, the content of ZnO is preferably 6% or less, 4% or less, especially 3% or less. .

In the present invention, by controlling the content of SrO+BaO at 0% to 5%, the ion exchange performance can be more effectively improved. That is, SrO and BaO have the effect of inhibiting the ion exchange reaction as described above, and therefore containing a large amount of these components is not conducive to obtaining a strengthened glass with high mechanical strength. The preferable range of SrO+BaO is 0% to 3%, 0% to 2.5%, 0% to 2%, 0% to 1%, 0% to 0.2%, especially 0% to 0.1%.

In addition, if the content of R'O is divided by R₂If the value obtained from the O content increases, the devitrification resistance of the glass tends to deteriorate. Therefore, it is better to calculate the R'O/R₂The value of O is limited to 0.5 or less, 0.4 or less, and 0.3 or less.

In addition, SnO₂It has the effect of improving the ion exchange performance, especially the compressive stress value, so its content is preferably 0.01% to 3%, 0.01% to 1.5%, and 0.1% to 1%. If SnO₂When the content of SnO increases, there will be caused by SnO₂This leads to devitrification, or the tendency of the glass to be easily colored.

In addition, ZrO₂It has the effect of significantly improving the ion exchange performance, increasing the Young's modulus or strain point of the glass, and reducing the high-temperature viscosity. In addition, it has the effect of increasing the viscosity near the liquid phase viscosity of the glass, so by containing a certain amount of ZrO₂, Can improve the ion exchange performance and liquid viscosity at the same time. However, if ZrO₂Too much content may extremely deteriorate the devitrification resistance. Therefore, it is preferable to contain 0.001% to 10%, 0.1% to 9%, 0.5% to 7%, 1% to 5%, and 2.5% to 5%.

In addition, B₂O₃It is a component that has the effect of lowering the liquidus temperature, high-temperature viscosity and density of the glass, and at the same time has the effect of improving the ion exchange performance of the glass, especially the effect of increasing the compressive stress value. Therefore, it can be contained together with the above-mentioned components. However, if B₂O₃Too much content may cause weathering on the surface due to ion exchange, deterioration of the water resistance of the glass, or decrease in liquid phase viscosity. In addition, there is a tendency for the depth of stress to decrease. Therefore, B₂O₃It is 0% to 6%, 0% to 4%, and more preferably 0% to 3%.

In addition, TiO₂It is a component that has the effect of improving ion exchange performance. In addition, it has the effect of reducing the high temperature viscosity of the glass. However, if TiO₂If the content of is too much, the glass will be colored, the devitrification will deteriorate, or the density will increase. Especially when used as a protective glass for displays, if TiO₂The higher the content of, the transmittance of the glass is likely to change when the melting environment or raw materials are changed. Therefore, in the step of bonding the glass substrate and the device with light such as an ultraviolet curable resin, the ultraviolet irradiation conditions are easily changed, and stable production is difficult. Therefore, it is better to set it as 10% or less, 8% or less, 6% or less, 5% or less, 4% or less, 2% or less, 0.7% or less, 0.5% or less, and 0.1 or less %, less than or equal to 0.01%.

In the present invention, from the viewpoint of improving ion exchange performance, it is preferable to contain ZrO within the above-mentioned range₂And TiO₂But as TiO₂Source, ZrO₂The source may be a reagent, or it may be included in impurities contained in the raw material.

In addition, from the viewpoint of achieving both devitrification resistance and high ion exchange performance, it is preferable to determine Al as follows₂O₃+ZrO₂Content.

If Al₂O₃+ZrO₂The content of more than 12% (preferably 12.001% or more, 13% or more, 15% or more, 17% or more, 18% or more, and 19% or more), the glass ion can be more effectively increased Exchange performance is therefore better. However, if Al₂O₃+ZrO₂Too much content will extremely deteriorate the devitrification, so it is preferably 28% or less (preferably 25% or less, 23% or less, 22% or less, and 21% or less).

In addition, P₂O₅It is a component that improves the ion exchange performance of glass, especially the effect of increasing the thickness of the compressive stress layer, so P₂O₅The content is set to 0% to 8%. However, if P₂O₅If the content of P is increased, the glass will have phase separation, or the water resistance or devitrification resistance will be easily reduced. Therefore, P₂O₅The content of is preferably less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, especially less than or equal to 2%.

In addition, it can contain 0.001% to 3% selected from As₂O₃, Sb₂O₃, CeO₂, F, SO₃One or two or more of the Cl group is used as a clarifying agent. However, due to environmental considerations, As₂O₃And Sb₂O₃In use, it should be controlled as much as possible, and each content should be controlled to less than 0.1%, and further controlled to less than 0.01%, preferably, it is not substantially contained. In addition, CeO₂It is a component that reduces the transmittance of glass, so it should be controlled to less than 0.1%, preferably less than 0.01%. In addition, F may reduce the low-temperature viscosity of the glass and cause a decrease in the compressive stress value. Therefore, it should be controlled to less than 0.1%, preferably less than 0.01%. Therefore, the better clarifying agent in the present invention is SO₃And Cl, preferably containing 0.001% to 3%, 0.001% to 1%, 0.01% to 0.5%, more preferably 0.05% to 0.4% SO₃And one or both of Cl.

In addition, Nb₂O₅Or La₂O₃Rare earth oxides such as those 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, these Nb₂O₅Or La₂O₃The content of is ideally controlled to be less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, less than or equal to 0.5%, especially less than or equal to 0.1%.

In addition, in the present invention, transition metal elements such as Co, Ni, etc., which strongly color glass, are undesirable because they reduce the transmittance of the glass substrate. Especially when used for touch panel displays, if the content of transition metal elements is high, the visibility of the touch panel display will be impaired. Specifically, it is desirable to adjust the usage amount of raw materials or glass cullets to 0.5% or less, 0.1% or less, especially 0.05% or less.

In addition, due to environmental considerations, substances such as Pb and Bi should be controlled as much as possible, and their content should be controlled to less than 0.1%.

In the strengthened glass substrate of the present invention, a preferable content range of each component can be appropriately selected, and a preferable glass composition range can be set. The specific example is shown below.

(1) Containing 40%~71% SiO by mass percentage₂, 7.5%~21% Al₂O₃, 0%~2% Li₂O, 10%~19% Na₂O, 0%~15% K₂O, 0%~6% MgO, 0%~6% CaO, 0%~3% SrO, 0%~3% BaO, 0%~8% ZnO, 0.01%~3% SnO₂Glass composition.

(2) Containing 40%~71% SiO by mass percentage₂, 7.5%~21% Al₂O₃, 0%~2% Li₂O, 10%~19% Na₂O, 0%~15% K₂O, 0%~6% MgO, 0%~6% CaO, 0%~3% SrO, 0%~3% BaO, 0%~8% ZnO, 0.01%~3% SnO₂, 0.001%~10% ZrO₂Glass composition.

(3) SiO with a mass percentage of 40%~71%₂, 8.5%~21% Al₂O₃, 0%~1% Li₂O, 10%~19% Na₂O, 0%~10% K₂O, 0%~6% MgO, 0%~6% CaO, 0%~3% SrO, 0%~3% BaO, 0%~8% ZnO, 0.01%~3% SnO₂Glass composition.

(4) SiO with a mass percentage of 40%~71%₂, 8.5%~21% Al₂O₃, 0%~1% Li₂O, 10%~19% Na₂O, 0%~10% K₂O, 0%~6% MgO, 0%~6% CaO, 0%~3% SrO, 0%~3% BaO, 0%~8% ZnO, 0.01%~3% SnO₂, 0.001%~10% ZrO₂Glass composition.

(5) SiO whose mass percentage is 40%~71%₂, 9%~19% Al₂O₃, 0%~6% B₂O₃, 0%~2% Li₂O, 10%~19% Na₂O, 0%~15% K₂O, 0%~6% MgO, 0%~6% CaO, 0%~3% SrO, 0%~3% BaO, 0%~6% ZnO, 0.001%~10% ZrO₂, 0.1%~1% SnO₂, Does not contain As substantially₂O₃, Sb₂O₃Glass composition.

(6) SiO whose mass percentage is 40%~71%₂, 9%~18% Al₂O₃, 0%~4% of B₂O₃, 0%~2% Li₂O, 11%~17% Na₂O, 0%~6% K₂O, 0%~6% MgO, 0%~6% CaO, 0%~3% SrO, 0%~3% BaO, 0%~6% ZnO, 0.1%~1% SnO₂, 0.001%~10% ZrO₂, Does not contain As substantially₂O₃, Sb₂O₃Glass composition.

(7) SiO whose mass percentage is 40%~63%₂, 9%~17.5% Al₂O₃, 0%~3% of B₂O₃, 0%~0.1% Li₂O, 10%~17% Na₂O, 0%~7% K₂O, 0%~5% MgO, 0%~4% CaO, 0%~3% SrO+BaO, 0.01%~2% SnO₂, Does not contain As substantially₂O₃, Sb₂O₃, In terms of mass fraction (Na₂O+K₂O)/Al₂O₃The value is 0.9~1.6, K₂O/Na₂O is a glass composition of 0 to 0.4.

(8) SiO with a mass percentage of 40%~71%₂, 3%~21% Al₂O₃, 0%~2% Li₂O, 10%~20% Na₂O, 0%~9% K₂O, 0%~5% MgO, 0%~0.5% TiO₂, 0.01%~3% SnO₂Glass composition.

(9) It is characterized in that it contains 40%~71% SiO by mass percentage₂, 8%~21% Al₂O₃, 0%~2% Li₂O, 10%~20% Na₂O, 0%~9% K₂O, 0%~5% MgO, 0%~0.5% TiO₂, 0.01%~3% SnO₂, Does not contain As substantially₂O₃And Sb₂O₃Glass composition.

(10) It is characterized by containing 40%~65% SiO by mass percentage₂, 8.5%~21% Al₂O₃, 0%~1% Li₂O, 10%~20% Na₂O, 0%~9% K₂O, 0%~5% MgO, 0%~0.5% TiO₂, 0.01%~3% SnO₂, In terms of mass fraction (Na₂O+K₂O)/Al₂O₃The value of is 0.7~2, which does not contain As substantially₂O₃, Sb₂O₃And the glass composition of F.

(11) It is characterized in that it contains 40%~65% SiO by mass percentage₂, 8.5%~21% Al₂O₃, 0%~1% Li₂O, 10%~20% Na₂O, 0%~9% K₂O, 0%~5% MgO, 0%~0.5% TiO₂, 0.01%~3% SnO₂, 0%~8% MgO+CaO+SrO+BaO, calculated by mass fraction (Na₂O+K₂O)/Al₂O₃The value of is 0.9~1.7, which does not contain As substantially₂O₃, Sb₂O₃And the glass composition of F.

(12) It is characterized by containing 40%~63% SiO by mass percentage₂, 9%~19% Al₂O₃, 0%~3% of B₂O₃, 0%~1% Li₂O, 10%~20% Na₂O, 0%~9% K₂O, 0%~5% MgO, 0%~0.1% TiO₂, 0.01%~3% SnO₂, 0.001%~10% ZrO₂, 0%~8% MgO+CaO+SrO+BaO, calculated by mass fraction (Na₂O+K₂O)/Al₂O₃The value is 1.2~1.6, which does not contain As substantially₂O₃, Sb₂O₃And the glass composition of F.

(13) It is characterized by containing 40%~63% SiO by mass percentage₂, 9%~17.5% Al₂O₃, 0%~3% of B₂O₃, 0%~1% Li₂O, 10%~20% Na₂O, 0%~9% K₂O, 0%~5% MgO, 0%~0.1% TiO₂, 0.01%~3% SnO₂, 0.1%~8% ZrO₂, 0%~8% MgO+CaO+SrO+BaO, calculated by mass fraction (Na₂O+K₂O)/Al₂O₃The value is 1.2~1.6, which does not contain As substantially₂O₃, Sb₂O₃And the glass composition of F.

(14) It is characterized in that it contains 40%~59% SiO by mass percentage₂, 10%~15% Al₂O₃, 0%~3% of B₂O₃, 0%~0.1% Li₂O, 10%~20% Na₂O, 0%~7% K₂O, 0%~5% MgO, 0%~0.1% TiO₂, 0.01%~3% SnO₂, 1%~8% ZrO₂, 0%~8% MgO+CaO+SrO+BaO, calculated by mass fraction (Na₂O+K₂O)/Al₂O₃The value is 1.2~1.6, which does not contain As substantially₂O₃, Sb₂O₃And the glass composition of F.

The strengthened glass substrate of the present invention has the above-mentioned glass composition and has a compressive stress layer on the surface of the glass substrate. The compressive stress of the compressive stress layer on the surface is preferably 300 MPa or more, more preferably 600 MPa or more, more preferably 800 MPa or more, more preferably 1000 MPa or more, particularly preferably 1200 MPa or more , It is particularly preferable to be greater than or equal to 1300 MPa. As the compressive stress becomes larger, the mechanical strength of the glass substrate becomes higher. On the other hand, if an extremely large compressive stress is formed on the surface of the glass substrate, microcracks may occur on the surface of the substrate, and the strength of the glass may decrease instead. In addition, since the inherent tensile stress of the glass substrate may become extremely high, it is preferably 2500 MPa or less. In addition, in order to increase the compressive stress, increase Al₂O₃, TiO₂, ZrO₂, MgO, ZnO, SnO₂Or reduce the content of SrO and BaO. In addition, shorten the time required for ion exchange or lower the temperature of the ion exchange solution.

The thickness of the compressive stress layer on the surface is preferably 10 μm or more, 15 μm or more, 20 μm or more, and 30 μm or more. The greater the thickness of the compressive stress layer on the surface is, the glass substrate is less likely to be broken even if the glass substrate is deeply damaged. On the other hand, as the thickness increases, the glass substrate may become difficult to cut, or the internal tensile stress may become extremely high and may be damaged. Therefore, the thickness of the compressive stress layer on the surface is preferably 500 μm or less and less than or equal to 500 μm. 100 μm, less than or equal to 80 μm, and less than or equal to 60 μm. In addition, in order to increase the thickness of the compressive stress layer, increase K₂O, P₂O₅, TiO₂, ZrO₂Or reduce the content of SrO and BaO. In addition, the time required for ion exchange can be extended, or the temperature of the ion exchange solution can be increased.

In addition, the tensile stress inside the glass substrate is 200 MPa or less (preferably 150 MPa or less, more preferably 100 MPa or less, and particularly preferably 50 MPa or less). The smaller this value is, the less there is concern about glass breakage due to defects inside the glass substrate. However, if it becomes extremely small, the compressive stress value or stress depth on the surface of the glass substrate will decrease. Therefore, it is preferably greater than Equal to 1 MPa, greater than or equal to 10 MPa, and greater than or equal to 15 MPa.

The tempered glass substrate of the present invention preferably has a plate thickness of 3.0 mm or less, 1.5 mm, 0.7 mm or less, 0.5 mm or less, particularly 0.3 mm or less. The thinner the thickness of the glass substrate, the lighter the weight of the glass substrate can be achieved. In addition, the strengthened glass substrate of the present invention has an advantage that even if the plate thickness is reduced, the glass substrate is not easily broken. In addition, when the glass is formed by the overflow down-draw method, the glass can be thinned or smoothed without grinding, which is advantageous.

The tempered glass substrate of the present invention preferably has an unpolished surface, and the average surface roughness (Ra) of the unpolished surface is preferably 10 or less.<img file="TWI386397B_D0004.tif" he="67" id="i0004" img-content="character" img-format="tif" inline="no" orientation="portrait" wi="45" />, Better is less than or equal to 5<img file="TWI386397B_D0005.tif" he="68" id="i0005" img-content="character" img-format="tif" inline="no" orientation="portrait" wi="44" />, Better is less than or equal to 4<img file="TWI386397B_D0006.tif" he="68" id="i0006" img-content="character" img-format="tif" inline="no" orientation="portrait" wi="46" />, Especially good is 3<img file="TWI386397B_D0007.tif" he="68" id="i0007" img-content="character" img-format="tif" inline="no" orientation="portrait" wi="45" />, The best is less than or equal to 2<img file="TWI386397B_D0008.tif" he="68" id="i0008" img-content="character" img-format="tif" inline="no" orientation="portrait" wi="44" />. In addition, the average surface roughness (Ra) of the surface may be measured by the method according to SEMI D7-97 "Method for Measuring the Surface Roughness of FPD Glass Substrate". The theoretical strength of glass is originally very high, but the use of stress much lower than the theoretical strength also causes damage in many cases. The reason is that in a step after the glass is formed, for example, a polishing step, etc., small defects called Griffith flaws are generated on the surface of the glass substrate. Therefore, if the surface of the strengthened glass substrate is not polished, the original mechanical strength of the glass substrate is not impaired, and therefore the glass substrate is hardly broken. In addition, if the surface of the glass substrate is not polished, the polishing step can be omitted in the manufacturing step of the glass substrate, so the manufacturing cost of the glass substrate can be reduced. In the strengthened glass substrate of the present invention, if both entire surfaces of the glass substrate are not polished, the glass substrate is more difficult to break. In addition, in the strengthened glass substrate of the present invention, in order to prevent damage from the cut surface of the glass substrate, the cut surface of the glass substrate may be chamfered or etched. In addition, in order to obtain an unpolished surface, the glass may be formed by the overflow down-draw method.

The strengthened glass substrate of the present invention preferably has a liquidus temperature of 1200°C or less, 1050°C or less, 1030°C or less, 1010°C or less, 1000°C or less, 950°C or less, and 900°C or less, Especially preferably, it is 870°C or less. In order to lower the liquidus temperature, increase Na₂O, K₂O, B₂O₃Content, or reduce Al₂O₃, Li₂O, MgO, ZnO, TiO₂, ZrO₂The content can be.

The liquid phase viscosity of the glass of the strengthened glass substrate of the present invention is preferably 10 or more^4.0dPas, greater than or equal to 10^4.3dPas, greater than or equal to 10^4.5dPas, greater than or equal to 10^5.0dPas, greater than or equal to 10^5.4dPas, greater than or equal to 10^5.8dPa.s, greater than or equal to 10^6.0dPas, greater than or equal to 10^6.2dPas. To increase the viscosity of the liquid phase, increase Na₂O, K₂O content, or reduce Al₂O₃, Li₂O, MgO, ZnO, TiO₂, ZrO₂The content can be.

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 formability of the glass substrate. And, if the liquidus temperature of the glass is 1200°C or less, and the liquidus viscosity of the glass is 10 or more^4.0dPas, it can be formed by the overflow down-draw method.

The strengthened glass substrate of the present invention preferably has a glass density of 2.8 g/cm or less³, Better is less than or equal to 2.7 g/cm³, Especially preferably less than or equal to 2.6 g/cm³. The lower the density of the glass, the more lightweight the glass substrate can be achieved. Here, the "density" refers to a value measured by the well-known Archimedes method. In addition, in order to reduce the density of the glass, increase SiO₂, P₂O₅, B₂O₃Or reduce the content of alkali metal oxides, alkaline earth metal oxides, ZnO, ZrO₂, TiO₂The content can be.

The thermal expansion coefficient of the glass in the temperature range of 30°C to 380°C of the strengthened glass substrate of the present invention is preferably 70×10^-7 /℃～110×10^-7/°C, better 75×10^-7 /℃～110×10^-7/°C, especially preferably 80×10^-7 /℃～110×10^-7/°C, particularly good is 85×10^-7 /℃～110×10^-7/°C. If the coefficient of thermal expansion of glass is in the above range, the coefficient of thermal expansion is easily integrated with parts such as metal and organic adhesives, and thus the peeling of parts such as metal and organic adhesives can be prevented. Here, the "coefficient of thermal expansion" refers to a value obtained by measuring the average coefficient of thermal expansion in the temperature range of 30°C to 380°C using a dilatometer. In addition, in order to increase the coefficient of thermal expansion, the content of alkali metal oxides and alkaline earth metal oxides may be increased. On the contrary, in order to decrease the coefficient of thermal expansion, the content of alkali metal oxides and alkaline earth metal oxides may be decreased.

The strain point of the strengthened glass substrate of the present invention is preferably 500°C or higher, more preferably 510°C or higher, 520°C or higher, 540°C or higher, 550°C or higher, and most preferably 560°C or higher . The higher the strain point of the glass, the better the heat resistance of the glass, and even if heat treatment is performed on the strengthened glass substrate, the strengthened layer is less likely to disappear. In addition, if the strain point of the glass is high, stress relaxation is not likely to occur during the ion exchange process, so a high compressive stress value can be obtained. In order to increase the strain point of the glass, reduce the content of alkali metal oxides, or increase alkaline earth metal oxides, Al₂O₃, ZrO₂, P₂O₅The content can be.

The tempered glass substrate of the present invention preferably has a high temperature viscosity of 10^2.5The equivalent temperature of dPas is less than or equal to 1650°C, less than or equal to 1500°C, less than or equal to 1450°C, less than or equal to 1430°C, less than or equal to 1420°C, and less than or equal to 1400°C. High temperature viscosity with glass 10^2.5The equivalent temperature of dPas is equivalent to the melting temperature of glass, and the high temperature viscosity of glass is 10^2.5The lower the temperature equivalent to dPas, the more the glass can be melted at low temperatures. Therefore, the high temperature viscosity of glass is 10^2.5The lower the temperature equivalent to dPas, the smaller the burden on glass manufacturing equipment such as melting furnaces, and the more the bubble quality of the glass substrate can be improved. Therefore, the high temperature viscosity of glass is 10^2.5The lower the temperature equivalent to dPas, the cheaper the glass substrate can be manufactured. In addition, in order to reduce the high temperature viscosity with glass 10^2.5dPas equivalent temperature, increase alkali metal oxides, alkaline earth metal oxides, ZnO, B₂O₃, TiO₂Content, or reduce SiO₂, Al₂O₃The content can be.

The Young's modulus of the strengthened glass substrate of the present invention is 70 GPa or more, preferably 73 GPa or more, and more desirably 75 GPa or more. Therefore, when used as a cover glass of a display, the higher the Young's modulus, the smaller the amount of deformation when pressing the surface of the cover glass with a pen or finger, thereby reducing damage to the internal display.

In addition, the glass of the present invention is characterized in that it contains 40% to 71% SiO by mass.₂, 3%~21% Al₂O₃, 0%~3.5% Li₂O, 7%~20% Na₂O, 0%~15% K₂O; Preferably, it is characterized in that it contains 40%~71% SiO by mass percentage₂, 7.5%~21% Al₂O₃, 0%~2% Li₂O, 10%~19% Na₂O, 0%~15% K₂O, 0%~6% MgO, 0%~6% CaO, 0%~3% SrO, 0%~3% BaO, 0%~8% ZnO, 0.01%~3% SnO₂; Better is characterized in that: the mass percentage is 40% ~ 71% SiO₂, 8.5%~21% Al₂O₃, 0%~1% Li₂O, 10%~19% Na₂O, 0%~10% K₂O, 0%~6% MgO, 0%~6% CaO, 0%~3% SrO, 0%~3% BaO, 0%~8% ZnO, 0.01%~3% SnO₂, 0.001%~10% ZrO₂. In the glass related to the present invention, the reason for limiting the glass composition to the above-mentioned range and the preferred range are the same as the strengthened glass substrates already explained, and therefore, this description is omitted here. Furthermore, of course, the glass related to the present invention may incorporate the characteristics and effects of the strengthened glass substrate described above.

The glass of the present invention limits each constituent component to the above range, and therefore has good ion exchange performance, and can easily make the surface compressive stress 600 MPa or more and the compressive stress layer thickness 10 μm or more.

The glass of the present invention can be produced by continuously feeding glass raw materials blended to a glass composition within the above composition range into a melting furnace, heating and melting the glass raw materials at 1500°C to 1600°C, and clarifying, and then supplying To the forming device, the molten glass is then formed into a plate shape and slowly cooled.

In order to shape the glass into a plate shape, the overflow down-draw method is preferably used. If the glass substrate is shaped by the overflow down-draw method, it is possible to manufacture a glass substrate that is not polished and has good surface quality. The reason is that when the overflow down-draw method is used, the surface of the glass substrate should not be in contact with the barrel-shaped refractory, but is formed in the state of a free surface, thereby forming unpolished glass with good surface quality. Substrate. Here, the overflow down-draw method is to make molten glass overflow from both sides of a heat-resistant barrel structure, make the overflowing molten glass converge at the lower end of the barrel structure, and stretch it downward to produce glass Substrate method. The structure or material of the barrel structure is not particularly limited as long as the size or surface accuracy of the glass substrate can be achieved as desired, and the quality that can be used for the glass substrate can be achieved. In addition, in order to perform downward stretch molding, any method can be used to apply force to the glass substrate. For example, it is possible to use a method in which a heat-resistant roller having a sufficiently large width is brought into contact with the glass substrate to rotate and extend, or a heat-resistant roller forming a plurality of pairs is only in contact with the vicinity of the end surface of the glass substrate. Extension method. Since the glass of the present invention is excellent in devitrification resistance and has viscosity characteristics suitable for molding, it can be molded with high precision by the overflow down-draw method. In addition, if the liquid phase temperature is less than or equal to 1200°C, and the liquid phase viscosity is greater than or equal to 10^4.0dPas, the glass substrate can be manufactured by the overflow down-draw method.

In addition, in the present invention, when high surface quality is not required, methods other than the overflow down-draw method can be used. For example, various forming methods such as the down-draw method (slot down draw, redraw, etc.), float method, roll out method, and press method can be used. . If the glass is formed by, for example, a pressing method, a small glass substrate can be efficiently manufactured.

In order to manufacture the strengthened glass substrate of this invention, the said glass is prepared first. Then implement strengthening treatment. Cutting the glass substrate into a predetermined size is performed after the strengthening treatment. In this way, the manufacturing cost can be reduced. The strengthening treatment is preferably carried out by ion exchange treatment. The ion exchange treatment can be performed by immersing the glass plate in a potassium nitrate solution at 400°C to 550°C for 1 hour to 8 hours, for example. In consideration of the viscosity characteristics of the glass, the application, the thickness of the sheet, the tensile stress inside the glass, etc., the ion exchange conditions may be selected to be the most appropriate.

Example 1

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

Tables 1 to 4 show the glass composition and characteristics of the examples (Sample Nos. 1 to 26) of the present invention. In addition, the appearance of "not" in the table indicates that it has not been determined.

<tables><img file="twi386397b_d0009.tif" he="2640" id="i0009" img-content="drawing" img-format="tif" inline="yes" orientation="portrait" wi="2009" /></tables>

<tables><img file="twi386397b_d0010.tif" he="2419" id="i0010" img-content="drawing" img-format="tif" inline="yes" orientation="portrait" wi="2062" /></tables>

<tables><img file="twi386397b_d0011.tif" he="2652" id="i0011" img-content="drawing" img-format="tif" inline="yes" orientation="portrait" wi="2009" /></tables>

<tables><img file="twi386397b_d0012.tif" he="2297" id="i0012" img-content="drawing" img-format="tif" inline="yes" orientation="portrait" wi="1510" /></tables>

Each sample in Tables 1 to 4 was prepared as follows. First, the glass raw materials were adjusted to the glass composition in the table, and a platinum wafer boat was used to fuse at 1580°C for 8 hours. Then, the molten glass was flowed out onto the carbon plate to form a plate shape. Various characteristics were evaluated with respect to the obtained glass substrate.

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

The strain point Ps and the slow cooling point Ta are measured according to the method of ASTM C336.

The softening point Ts is measured according to the ASTM C338 method.

Viscosity with glass 10^4.0dPas,10^3.0dPas,10^2.5The temperature equivalent to dPas is measured by the Labosphere method.

Young's modulus is measured by bending resonance method.

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

The liquidus temperature TL is to pulverize the glass, pass through a standard sieve of 30 mesh (mesh diameter of 500 μm), put the remaining glass powder of 50 mesh (mesh diameter of 300 μm) into a platinum wafer boat, and keep it in a temperature gradient furnace It is obtained by measuring the temperature of crystal precipitation for 24 hours.

The liquidus viscosity logηTL represents the viscosity of each glass at the liquidus temperature.

The result is: the density of the obtained glass substrate is less than or equal to 2.59 g/cm³, The coefficient of thermal expansion is 83×10^-7 /℃～100×10^-7/°C, so it is suitable for use as a tempered glass material. In addition, the viscosity of the liquid phase is higher than 10^5.1dPas, so overflow down-draw forming can be performed, but 10^2.5The temperature of dPas is low at 1612°C or less, so it can be considered that the productivity is high and a large amount of glass substrates can be supplied inexpensively. In addition, although the glass composition of the unstrengthened glass substrate and the strengthened glass substrate in the surface layer of the glass substrate is different in the microscopic view, there is substantially no difference in the glass composition that forms the entire glass substrate. Therefore, with regard to characteristic values such as density and viscosity, there is substantially no difference between the above-mentioned characteristics of the unstrengthened glass substrate and the strengthened glass substrate. Next, optical polishing was performed on both surfaces of each glass substrate of sample Nos. 1 to 26, and then ion exchange treatment was performed. For sample Nos. 1-8, 13-15, 24 and 25, it is KNO at 430°C₃Each sample was immersed in molten salt for 4 hours. For sample Nos. 9-12, 16-23, and 26, KNO at 460°C₃Each sample was immersed in molten salt for 4 hours to perform ion exchange treatment. After cleaning the surface of each sample after the treatment, a surface stress meter (manufactured by Toshiba Corporation, FSM-6000) was used to calculate the compressive stress value of the surface and the compressive stress layer based on the number of observed interference fringes and their intervals. thickness. After calculation, the refractive index of the sample was 1.53, and the optical elastic constant was 28 [(nm/cm)/MPa].

As a result, each of the glass substrates of sample Nos. 1 to 26 of the example of the present invention has a compressive stress of 500 MPa or more on the surface, and the thickness is 14 μm or more. In addition, the internal tensile stress of the substrate with a thickness of 1 mm is as low as 43 MPa or less.

In addition, using the glass sample of sample No. 15 of the example of the present invention, the thickness of the glass substrate or ion exchange conditions were changed to produce glass test pieces with different internal stresses, and the state of damage due to the internal stress was evaluated.

The evaluation method is as follows.

Using the glass of sample No.15, glass plates with a plate thickness of 0.5 mm and a plate thickness of 0.7 mm were respectively produced, and each glass plate was cut into a size of 35 mm × 35 mm. The respective glass substrates thus obtained were subjected to ion exchange under each condition of 460° C. for 6 hours, 460° C. for 8 hours, and 490° C. for 6 hours, and then compressive stress was measured. The results are shown in Table 5. In addition, the compressive stress is measured by the same method as described above, and the internal stress (tensile stress in the glass substrate) is calculated according to the above-mentioned formula based on the above-mentioned compressive stress value.

<tables><img file="twi386397b_d0013.tif" he="616" id="i0013" img-content="drawing" img-format="tif" inline="yes" orientation="portrait" wi="1673" /></tables>

For each glass substrate in Table 5, scratches were formed on the surface, and when the scratches reached the internal stress layer, in order to investigate whether the glass substrate was damaged, a scribe machine with a wheel chip made of diamond was used. The air pressure is set to 0.3 MPa, the wheel blade angle is 125°, and the wheel grinding grade (grade) is D521, which damages the surface of the glass substrate by hitting the wheel.

Table 6 shows the number of fragments after breaking the glass substrate. In addition, for reference, the number of fragments of the glass substrate for which ion exchange is not performed and the internal stress is 0 is also shown. It can be clearly understood from Table 6 that if the internal stress is 50 MPa to 94 MPa, the number of fragments equal to that of a glass substrate with an internal stress of 0 will be formed.

<tables><img file="twi386397b_d0014.tif" he="922" id="i0014" img-content="drawing" img-format="tif" inline="yes" orientation="portrait" wi="1388" /></tables>

In addition, in the above-mentioned embodiment, for the convenience of description of the present invention, the glass is melted, formed by flowing out, and then optically polished before the ion exchange treatment. When producing on an industrial scale, it is more desirable to produce a glass substrate by an overflow down-draw method or the like, and to perform ion exchange treatment on both surfaces of the glass substrate in an unpolished state.

[Industrial availability]

The tempered glass substrate of the present invention is suitable as a cover glass for mobile phones, digital cameras, PDAs, solar batteries, etc., or a touch panel display substrate. In addition, the strengthened glass substrate of the present invention can be expected to be used in applications requiring high mechanical strength in addition to these applications, such as window glass, substrates for magnetic disks, substrates for flat panel displays, and solid-state imaging. Protective glass, tableware, etc. for components.