TWI791431B - chemically strengthened glass - Google Patents

Abstract

The chemically strengthened glass of the present invention is characterized by having a compressive stress layer on the surface, and having an average compressive stress value of 350 MPa or more at a depth of 7 μm to 16 μm from the surface.

Description

chemically strengthened glass

The present invention relates to a chemically strengthened glass, in particular to a chemically strengthened glass suitable for a cover glass of a mobile phone, a digital camera, a personal digital assistant (PDA), and a touch panel display.

Devices such as mobile phones (especially smart phones), digital cameras, PDAs, touch panel displays, and large televisions tend to become more and more popular.

Ion-exchange-treated chemically strengthened glass is used as a cover glass for these uses (see Patent Document 1 and Non-Patent Document 1). In addition, in recent years, chemically strengthened glass has been increasingly used in packaging parts such as digital signage, mice, and smartphones. [Prior Art Documents] [Patent Documents]

[Patent Document 1] Japanese Patent Laid-Open No. 2006-83045 [Patent Document 2] Japanese Patent Laid-Open No. 2011-133800 [Non-Patent Document]

[Non-Patent Document 1] Toruo Izumitani et al., "New Glass and Its Physical Properties", first edition, Management Systems Research Institute Co., Ltd., August 20, 1984, p.451-498

However, as described above, chemically strengthened glass is used for the cover glass of a smartphone, but the cover glass may be broken.

According to the analysis of the present inventors, the breakage of the cover glass is mainly caused by the impact on the end face. As a measure to reduce the damage, it is effective to increase the stress depth of the end surface so that the crack existing on the end surface does not progress. However, if the stress depth of the end surface is enlarged, the internal tensile stress value becomes large, and the chemically strengthened glass tends to self-destruct. In particular, this tendency becomes remarkable when the thickness of the cover glass is reduced.

Therefore, the present invention was made in view of the above circumstances, and its technical problem is to create a chemically strengthened glass that is hard to break even when the end face is impacted.

As a result of diligent research conducted by the present inventors, it was found that there is a strong correlation between the compressive stress value at a specific depth from the surface of the chemically strengthened glass and the end surface strength, and it was found that The compressive stress value at the position is specified to be more than a predetermined value, the above-mentioned technical problem can be solved, and it is proposed as the present invention. That is, the chemically strengthened glass of the present invention is characterized by having a compressive stress layer on the surface and having an average compressive stress value of 350 MPa or more at a depth of 7 μm to 16 μm from the surface. Furthermore, after strictly specifying the glass composition of the glass for chemical strengthening, regarding the final ion exchange treatment (for example, in the case of the first ion exchange treatment, the first ion exchange treatment, in the case of the second ion exchange treatment, The following is the 23rd ion exchange treatment), if the temperature is set to 390°C to 420°C, the time is set to 1.5 hours to 4 hours, and the ion exchange liquid is set to KNO ₃ of 90% by mass or more, then it can be suitably Increase the average compressive stress value at the depth of 7μm~16μm.

Here, the "compressive stress value" and "stress depth" are determined from the number of observed interference fringes and their intervals when using the software FsmV of the surface stress meter (FSM-6000LE manufactured by Orihara Seisakusho Co., Ltd.) to observe and measure the sample. For the calculated value, when measuring, set the measurement setting (strengthening type) to chemical strengthening II, set the measurement mode to exact solution (exact solution) mode, and use the inflection point position for the calculation of the boundary position of the depth measurement. And, as the "stress depth", the value of DOL_zero calculated by FsmV is adopted. In addition, as the "internal tensile stress value", the value of CT_cv obtained by the above measurement was used. Furthermore, as "the depth of the ion exchange layer", the value of DOL_tail obtained by the said measurement was used.

Second, the chemically strengthened glass of the present invention preferably has a compressive stress value at a depth of 12 μm from the surface of 350 MPa or more.

Third, the chemically strengthened glass of the present invention preferably has a compressive stress value of 450 MPa or more at a depth of 7 μm from the surface, and a compressive stress value of 250 MPa or more at a depth of 16 μm from the surface.

Fourth, the chemically strengthened glass of the present invention preferably has a curved compressive stress curve in the depth direction from the surface.

Fifth, the chemically strengthened glass of the present invention preferably contains 40% to 80% of SiO ₂ , 5% to 30% of Al ₂ O ₃ , 0 to 5% of Li ₂ O, 5% to 25% % Na ₂ O as the glass composition.

Sixth, the chemically strengthened glass of the present invention preferably has a liquidus viscosity of 10 ^4.0 dPa·s or higher. Here, the "liquidus temperature" refers to the following value: After the glass is pulverized, it passes through a 30-mesh standard sieve (with a sieve diameter of 500 μm) and remains on a 50-mesh standard sieve (with a sieve diameter of 300 μm) glass powder was added to the platinum boat, and kept in the temperature gradient furnace for 24 hours, and then the value obtained by measuring the temperature of crystallization. In addition, the "liquidus viscosity" refers to the value obtained by measuring the viscosity of the glass in liquidus temperature by the platinum ball pulling method.

Seventh, the chemically strengthened glass of the present invention preferably has a temperature of 1300° C. or lower at a high temperature viscosity of 10 ^4.0 dPa·s. Here, the "temperature at a high temperature viscosity of 10 ^4.0 dPa·s" refers to a value measured by the platinum ball pulling method.

Eighth, the chemically strengthened glass of the present invention preferably has a coefficient of thermal expansion in the temperature range of 30°C to 380°C of 95×10 ^-7 /°C or less. Here, "the thermal expansion coefficient in the temperature range of 30 degreeC - 380 degreeC" means the value measured with the dilatometer.

Ninthly, the chemically strengthened glass of the present invention is preferably in the shape of a flat plate. If so, it will be easy to apply to the cover glass of a smartphone, etc.

Tenth, the chemically strengthened glass of the present invention preferably has a thickness of 0.1 mm to 2.0 mm and a stress depth of 10 μm or more.

Eleventh, the chemically strengthened glass of the present invention is preferably a cover glass for a touch panel display.

The chemically strengthened glass of the present invention has a compressive stress layer on the surface. As a method of forming a compressive stress layer on the surface, there are a physical strengthening method and a chemical strengthening method. The chemically strengthened glass of the present invention forms a compressive stress layer by a chemical strengthening method. The chemical strengthening method is a method of introducing alkali ions with a large ionic radius to the surface of the glass by ion exchange treatment at a temperature below the strain point of the glass. If the compressive stress layer is formed by the chemical strengthening method, even when the thickness of glass is small, a compressive stress layer can be formed suitably.

The composition of the ion exchange liquid may be determined in consideration of the viscosity characteristics of the glass for chemical strengthening, and the like. As the ion exchange liquid, various ion exchange liquids can be used, but KNO ₃ molten salt or mixed molten salt of NaNO ₃ and KNO ₃ is preferable. In this way, a compressive stress layer can be efficiently formed on the surface.

In the chemically strengthened glass of the present invention, the average compressive stress value at a depth of 7 μm to 16 μm from the surface is 350 MPa or more, preferably 400 MPa or more, 450 MPa or more, 500 MPa or more, 520 MPa or more, 550 MPa or more. Above MPa, preferably above 570 MPa. If the average compressive stress value at a depth of 7 μm to 16 μm from the surface is too low, the strength of the end face tends to decrease. On the other hand, if the average compressive stress value at a depth of 7 μm to 16 μm from the surface is too large, the internal tensile stress may become extremely high. Therefore, the average compressive stress value at a depth of 7 μm to 16 μm from the surface is preferably 1000 MPa or less. Furthermore, after strictly specifying the glass composition of the glass for chemical strengthening, regarding the final ion exchange treatment (for example, in the case of the first ion exchange treatment, the first ion exchange treatment, in the case of the second ion exchange treatment, The following is the second ion exchange treatment), if the temperature is set to 390°C to 420°C, the time is set to 1.5 hours to 4 hours, and the ion exchange liquid is set to KNO ₃ of 90% by mass or more, then it can be suitably Increase the average compressive stress value at the depth of 7 μm to 16 μm.

The compressive stress value at a depth of 7 μm from the surface is preferably at least 450 MPa, at least 550 MPa, at least 600 MPa, at least 650 MPa, and at least 680 MPa, particularly preferably at least 700 MPa. If the compressive stress value at a depth of 7 μm from the surface is too low, the end face strength tends to decrease. On the other hand, if the compressive stress value at a depth of 7 μm from the surface is too large, the internal tensile stress may become extremely high. Therefore, the compressive stress value at a depth of 7 μm from the surface is preferably 1000 MPa or less.

The compressive stress value at a depth of 12 μm from the surface is preferably at least 350 MPa, at least 400 MPa, at least 450 MPa, at least 480 MPa, at least 500 MPa, and at least 530 MPa, particularly preferably at least 550 MPa. If the compressive stress value at a depth of 12 μm from the surface is too low, the end surface strength tends to decrease. On the other hand, if the compressive stress value at a depth of 12 μm from the surface is too large, the internal tensile stress may become extremely high. Therefore, the compressive stress value at a depth of 12 μm from the surface is preferably 1000 MPa or less. Furthermore, the compressive stress value at a depth of 12 μm from the surface has a higher correlation with the end surface strength than the compressive stress values at other depths.

The compressive stress value at a depth of 16 μm from the surface is preferably at least 250 MPa, at least 280 MPa, at least 320 MPa, at least 360 MPa, and at least 400 MPa, particularly preferably at least 430 MPa. If the compressive stress value at a depth of 16 μm from the surface is too low, the strength of the end face tends to decrease. On the other hand, if the compressive stress value at a depth of 16 μm from the surface is too large, the internal tensile stress may become extremely high. Therefore, the compressive stress value at a depth of 16 μm from the surface is preferably 800 MPa or less. Furthermore, the compressive stress value at a depth of 16 μm from the surface has a stronger correlation with the end face strength than the compressive stress values at other depths.

The surface compressive stress value is preferably at least 600 MPa, at least 700 MPa, at least 750 MPa, at least 800 MPa, and at least 850 MPa, particularly preferably at least 900 MPa. As the compressive stress value on the surface becomes larger, the mechanical strength of the chemically strengthened glass becomes higher. On the other hand, if an extremely large compressive stress is formed on the surface, microcracks are likely to be formed on the surface, and the mechanical strength of the chemically strengthened glass may conversely decrease. In addition, when an extremely large compressive stress is formed on the surface, there is a possibility that the internal tensile stress becomes extremely high. Therefore, the compressive stress value on the surface is preferably 1400 MPa or less. Furthermore, if the time of ion exchange treatment is shortened or the temperature of ion exchange treatment is lowered, the compressive stress value on the surface tends to increase.

The stress depth is preferably at least 10 μm, at least 20 μm, at least 30 μm, at least 35 μm, at least 40 μm, and at least 45 μm, particularly preferably at least 50 μm and not more than 90 μm. If the stress depth is too small, the end surface strength is likely to decrease. On the other hand, if the stress depth is too large, the internal tensile stress becomes too large, and the chemically strengthened glass tends to self-destruct. Furthermore, when the time of ion exchange treatment is prolonged or the temperature of ion exchange liquid is increased, the depth of stress tends to increase.

In the chemically strengthened glass of the present invention, the compressive stress curve in the depth direction from the surface is preferably curved. If so, the average compressive stress value and stress depth at a depth of 7 μm to 16 μm from the surface can be increased, and internal tensile stress can be reduced. Furthermore, if the ion exchange treatment is performed multiple times, the compressive stress curve in the depth direction can be bent from the surface.

When multiple ion exchange treatments are performed, the temperature of the final ion exchange treatment (for example, the second ion exchange treatment in the case of two ion exchange treatments) is preferably 390°C to 430°C, especially 400°C to 420°C, the time for the final ion exchange treatment is preferably 1.5 hours to 5 hours, especially 2 hours to 4.5 hours. This makes it easy to increase the average compressive stress value at a depth of 7 μm to 16 μm from the surface.

When ion exchange treatment is performed a plurality of times, it is preferable to perform ion exchange treatment twice. In this way, the compressive stress curve in the depth direction can be efficiently bent from the surface.

When performing 2 ion exchange treatments, the ratio of small alkali ions (such as Li ions, Na ions, especially Na ions) in the ion exchange liquid for the 2nd ion exchange treatment is preferably higher than that used for the 2nd ion exchange treatment. The ratio of the alkali ions in the ion-exchange solution of the primary ion-exchange treatment is small. This makes it easy to increase the average compressive stress value at a depth of 7 μm to 16 μm from the surface. Furthermore, the size of alkali ions is Li ion<Na ion<K ion.

When the ion exchange treatment is performed twice, the content of _KNO in the ion exchange liquid used for the first ion exchange treatment is preferably less than 75% by mass, 70% by mass or less, especially 60% by mass or less. The content of _KNO3 in the ion exchange liquid used for the second ion exchange treatment is preferably 75% by mass or more, 85% by mass or more, 95% by mass or more, especially 99.5% by mass or more. When the content of KNO ₃ in the ion exchange liquid falls outside the above-mentioned range, it becomes difficult to increase the average compressive stress value at a depth of 7 μm to 16 μm from the surface.

When carrying out ion exchange treatment for 2 times, be used for the NaNO in the ion-exchange liquid of ion _- exchange treatment of the 2nd time Content preferably is than be used for the NaNO in the ion-exchange liquid of ion-exchange treatment of the 1st time ₃ content The content is small, more preferably at least 5% by mass, more preferably at least 10% by mass, particularly preferably at least 15% by mass. In addition, the _NaNO3 content in the ion exchange liquid used for the second ion exchange treatment is preferably 25 mass % or less, 20 mass % or less, 15 mass % or less, 10 mass % or less, 5 mass % or less, especially It is 0.5 mass % or less. If there is too much NaNO ₃ in the ion exchange liquid used for the second ion exchange treatment, it will be difficult to increase the average compressive stress value at a depth of 7 μm to 16 μm from the surface.

The chemically strengthened glass of the present invention preferably contains 40% to 80% of SiO ₂ , 5% to 30% of Al ₂ O ₃ , 0 to 5% of Li ₂ O, and 5% to 25% of Na in mass %. ₂ O as a glass composition. The reason for limiting the content range of each component as mentioned above is shown below. In addition, in description of the content range of each component, the expression form of % means mass %.

SiO ₂ is the constituent that forms the network of the glass. The content of SiO ₂ is preferably 40%-80%, 50%-75%, 56%-70%, 58%-68%, particularly preferably 59%-65%. Furthermore, when it is desired to improve the ion exchange performance as much as possible, the content of SiO ₂ is preferably 40%-65%, 45%-60%, 50%-60%, and particularly preferably 53%-58%. When the content of SiO ₂ is too small, vitrification becomes difficult, and the coefficient of thermal expansion becomes too high, which tends to lower thermal shock resistance. On the other hand, if the content of SiO ₂ is too large, the meltability and formability tend to decrease.

Al ₂ O ₃ is a component that improves ion exchange performance, and is a component that increases the strain point or Young's modulus. The content of Al ₂ O ₃ is preferably 5% to 30%. When the content of Al ₂ O ₃ is too small, the coefficient of thermal expansion becomes too high, thermal shock resistance tends to decrease, and ion exchange performance may not be fully exhibited. Therefore, the suitable lower limit range of Al ₂ O ₃ is 7% or more, 8% or more, 10% or more, 12% or more, 14% or more, 15% or more, especially 16% or more. Furthermore, when it is desired to improve the ion exchange performance as much as possible, the suitable lower limit range of Al ₂ O ₃ is 16% or more, 18% or more, 20% or more, 22% or more, 24% or more, especially 26% or more. On the other hand, if the content of Al ₂ O ₃ is too high, devitrified crystals tend to precipitate in the glass, making it difficult to shape the glass by an overflow down draw method or the like. In addition, the thermal expansion coefficient becomes too low, and it is difficult to match the thermal expansion coefficient of the surrounding materials, and the high-temperature viscosity becomes high, and the meltability tends to decrease. Therefore, the suitable upper limit range of Al ₂ O ₃ is 28% or less, 25% or less, 21.5% or less, especially 19.5% or less.

Li ₂ O is an ion exchange component, and is a component that lowers high-temperature viscosity and improves meltability or formability. In addition, it is a component that increases Young's modulus. Furthermore, the effect of increasing the compressive stress value is large among alkali metal oxides. However, if the content of Li ₂ O is too high, the liquid phase viscosity will decrease, and the glass will easily devitrify. In addition, the thermal expansion coefficient becomes too high, and thermal shock resistance decreases, or it becomes difficult to match the thermal expansion coefficient of surrounding materials. Furthermore, when the low-temperature viscosity decreases too much and stress relaxation tends to occur, the compressive stress value may become smaller on the contrary. Therefore, the content of Li ₂ O is preferably 0-5%, 0.01%-3%, 0.01%-2%, 0.01%-1%, 0.01%-0.5%, especially 0.1%-0.2%. Furthermore, when Li ₂ O is introduced at a content of 0.1% by mass or more, Li ions function as ion exchange components, so that the stress depth can be increased in a short time. As a result, the first ion exchange time can be shortened.

Na ₂ O is a main ion-exchange component, and is a component that lowers high-temperature viscosity and improves meltability or formability. Moreover, _Na2O is also a component which improves devitrification resistance. The content of Na ₂ O is preferably 5% to 25%. When the content of Na ₂ O is too small, the meltability decreases, the thermal expansion coefficient decreases, or the ion exchange performance tends to decrease. Therefore, the suitable lower limit range of Na ₂ O is 8% or more, 10% or more, 11% or more, especially 12% or more. On the other hand, if the content of Na ₂ O is too high, the thermal expansion coefficient becomes too high, and thermal shock resistance decreases, or it becomes difficult to match the thermal expansion coefficients of surrounding materials. In addition, the strain point may be excessively lowered, or the component balance of the glass composition may be lacking, and the devitrification resistance may conversely be lowered. Therefore, the appropriate upper limit range of Na ₂ O is 20% or less, 17% or less, especially 16% or less. Furthermore, when the content of Li ₂ O is more than 0.1%, it is preferable to reduce the content of Na ₂ O, and the content is less than 15%, less than 13%, especially less than 11%.

In addition to the above-mentioned components, for example, the following components may also be introduced.

B ₂ O ₃ is a component that lowers the high-temperature viscosity or density, stabilizes the glass, makes it difficult to precipitate crystals, and lowers the liquidus temperature. In addition, it is a component that improves crack resistance. However, if the content of B ₂ O ₃ is too large, there is a tendency that the ion exchange treatment causes coloring of the surface called gossan, or the water resistance decreases, or the compressive stress value of the compressive stress layer decreases. , or the stress depth of the compressive stress layer becomes smaller. Therefore, the content of B ₂ O ₃ is preferably 0-15%, 0-10%, 0.1%-8%, 0.5%-6%, 1%-4%, especially more than 1%-3%.

K ₂ O is a component that promotes ion exchange, and is a component that has a large effect of increasing the stress depth of the compressive stress layer among alkali metal oxides. In addition, it is a component that lowers high-temperature viscosity and improves meltability or formability. Furthermore, it is also a component which improves devitrification resistance. The content of K ₂ O is 0-10%. When the content of K ₂ O is too high, the thermal expansion coefficient becomes too high, and thermal shock resistance decreases, or it becomes difficult to match the thermal expansion coefficients of surrounding materials. In addition, there is a tendency that the strain point decreases too much, or the component balance of the glass composition is lacking, and the devitrification resistance tends to decrease instead. Therefore, the appropriate upper limit range of K ₂ O is 6% or less, 4% or less, less than 2%, especially less than 1%.

MgO is a component that lowers high-temperature viscosity, improves meltability and formability, or increases strain point or Young's modulus, and is a component that has a large effect of improving ion exchange performance among alkaline earth metal oxides. However, when the content of MgO is too large, the density and the thermal expansion coefficient tend to become high, and the glass tends to devitrify. Therefore, the suitable upper limit range of MgO is 12% or less, 10% or less, 8% or less, 5% or less, especially 4% or less. Furthermore, when MgO is introduced into the glass composition, the suitable lower limit range of MgO is 0.1% or more, 0.5% or more, 1% or more, especially 2% or more.

Compared with other components, CaO is not accompanied by a decrease in devitrification resistance, and has a large effect of decreasing high-temperature viscosity, improving meltability or formability, or increasing strain point or Young's modulus. The content of CaO is preferably from 0 to 10%. However, if the content of CaO is too high, the density and thermal expansion coefficient will increase, and the component balance of the glass composition will be lacking, and the glass will be easily devitrified or the ion exchange performance will be easily reduced. Therefore, the suitable content of CaO is 0 to 5%, especially 0 to less than 1%.

ZrO ₂ is a component that improves the ion exchange performance, and is a component that increases the viscosity or strain point near the liquidus viscosity, but if the content is too large, there is a possibility that the devitrification resistance will be significantly reduced, and the density may become too high. High risk. Therefore, the suitable upper limit range of ZrO ₂ is 10% or less, 8% or less or 6% or less, especially 5% or less. Furthermore, when it is desired to improve the ion exchange performance, it is preferable to introduce ZrO ₂ into the glass composition. In this case, the suitable lower limit range of ZrO ₂ is 0.01% or more, 0.5% or more, especially 1% or more.

P ₂ O ₅ is a component that increases the depth of stress, and is a component that shortens the first ion exchange time especially when ion exchange treatment is performed a plurality of times. On the other hand, if the content of P ₂ O ₅ is too high, the glass will easily undergo phase separation during molding. Therefore, the content of P ₂ O ₅ is preferably 0-10%, 0-8%, 0.1%-6%, especially 3%-6%.

ZnO is a component that increases the compressive stress value, and is a component that shortens the second ion exchange time especially when ion exchange treatment is performed multiple times. On the other hand, if the content of ZnO is too large, the glass will easily undergo phase separation during molding. Therefore, the content of ZnO is preferably 0-10%, 0-5%, 0-3%, especially 0.1%-2%.

SnO ₂ is a component that functions as a clarifier and increases the compressive stress value, and its suitable content range is preferably 0ppm~10000ppm (1%), 500ppm~7000ppm, especially 1000ppm~5000ppm. Furthermore, if the content of SnO ₂ is too high, the visible light transmittance tends to decrease.

As other clarifying agents, one or two or more selected from the group of As ₂ O ₃ , Sb ₂ O ₃ , F, Cl, and SO ₃ may be introduced at 0 ppm to 30,000 ppm (3%).

The chemically strengthened glass of the present invention preferably has the following glass properties.

The liquidus temperature is preferably below 1200°C, below 1100°C, below 1050°C, below 1000°C, below 930°C, below 900°C, especially below 880°C. The lower the liquidus temperature is, the more difficult it is for the glass to devitrify when formed into a flat plate shape by the overflow down-draw method or the like.

The liquid phase viscosity is preferably ^104.0 dPa・s or higher, ^104.3 dPa・s or higher, ^104.5 dPa・s or higher, ^105.0 dPa・s or higher, ^105.5 dPa・s or higher, ^105.7 dPa・s or higher, ^105.9 dPa・s or above, especially 10 ^6.0 dPa・s or above. The higher the viscosity of the liquid phase, the harder it is for the glass to devitrify when it is formed into a flat plate shape by the overflow down-draw method or the like.

The temperature at the high temperature viscosity of ^104.0 dPa·s is preferably below 1400°C, below 1350°C, below 1300°C, below 1260°C, below 1230°C, especially below 1200°C. The lower the temperature at the high-temperature viscosity of 10 ^4.0 dPa·s, the less the burden on the shaped refractory and the longer the life of the shaped refractory. As a result, it is easier to reduce the production cost of chemically strengthened glass.

The coefficient of thermal expansion in the temperature range of 30°C to 380°C is preferably at most 95×10 ^-7 /°C, especially at most 92×10 ^-7 /°C. If the thermal expansion coefficient in the temperature range of 30°C to 380°C is too high, the thermal shock resistance is likely to decrease, so it is necessary to prolong the preheating time before immersion in the ion exchange liquid or the slow cooling time after immersion in the ion exchange liquid. In addition, the glass for chemical strengthening is easily broken during bending.

In the chemically strengthened glass of the present invention, the thickness (thickness in the case of a flat plate) is preferably 0.1 mm to 2.0 mm, 0.2 mm to 1.0 mm, 0.3 mm to 0.8 mm, particularly 0.4 mm to 0.7 mm. In this way, it is easy to maintain the mechanical strength and reduce the weight of the display device.

The glass for chemical strengthening of this invention can be produced as follows.

First, glass raw materials prepared so as to have a desired glass composition are put into a continuous melting furnace, heated and melted at 1500°C to 1600°C, clarified, supplied to a forming device, and formed into a flat plate shape Etc., and slow cooling can be used to produce chemically strengthened glass.

As a method of shaping the glass for chemical strengthening, an overflow down-draw method is preferably used. The overflow down-draw method is a method that can form a large-sized glass for chemical strengthening with high surface smoothness, and it is a method that can reduce surface damage of the glass for chemical strengthening as much as possible.

In addition to the overflow down-draw method, various forming methods can also be used. For example, forming methods such as a floating method, a down-draw method (slot down method, redraw method, etc.), a roll out method, and a pressing method can be used.

After shaping|molding the glass for chemical strengthening, bending processing can be performed as needed. In addition, chamfering can also be performed if necessary.

The period of cutting to a desired size is preferably before ion exchange treatment. In this way, a compressive stress layer can also be formed on the end surface. [Example]

Hereinafter, the present invention will be described in detail based on examples. In addition, the following embodiment is only an illustration. The present invention is not limited by the following examples.

Each chemically strengthened glass (sample No. 1 to No. 10) was produced as follows. First, mix glass raw materials to make glass batch. Next, the glass batch is charged into a continuous melting furnace, and the obtained molten glass is clarified and stirred, and then supplied to a molding device. Next, using an alumina-based molded body as a molded body, it was formed into a flat plate shape with a thickness of 0.7 mm by the overflow downdraw method, and then cut into a predetermined size to obtain each glass for chemical strengthening. Thereafter, the end face of each chemically strengthened glass was C-chamfered and ground using a #800 metal bonded grinding wheel. In addition, _the obtained glass for chemical strengthening contained 61.4% of _SiO2 , 18% of _Al2O3 , 0.5% of _B2O3 , 0.1% of _Li2O , and 14.5% of _Na2O by mass _% , 2% K ₂ O, 3% MgO, 0.1% BaO, 0.4% SnO ₂ as the glass composition, the liquidus viscosity is 10 ^6.3 dPa s, and the temperature at high temperature is 10 ^4.0 dPa s is 1255 ℃ , the thermal expansion coefficient in the temperature range of 30°C to 380°C is 91×10 ^-7 /°C.

Furthermore, the ion exchange treatment described in Table 1 was performed using the ion exchange liquid described in Table 1 about each glass for chemical strengthening. In Table 1, DOL_zero represents the stress depth, DOL_tail represents the depth of the ion exchange layer, and CT_cv represents the internal tensile stress value. "CS" and "DOL" in the table are calculated from the number of observed interference fringes and their intervals when using the software FsmV of a surface stress meter (FSM-6000LE manufactured by Orihara Seisakusho Co., Ltd.) to observe and measure samples. When measuring, set the measurement setting (enhancement type) to chemical strengthening II, set the measurement mode to exact solution mode, and use the bending point position for the calculation of the boundary position of the depth measurement. In addition, at the time of measurement, the refractive index of each sample was set to 1.50, and the optical elastic constant was set to 29.5 [(nm/cm)/MPa].

For each of the obtained chemically strengthened glasses, an end face strength test was performed using the pendulum end face tester shown in FIG. 1( a ) and FIG. 1( b ). FIG. 1( a ) is a conceptual perspective view showing a metal jig and a test head for holding a test piece. The test piece 11 was fixed to a metal jig 13 in a state sandwiched between a pair of resin plates 12 made of bakelite. The size of the test piece 11 was 22 mm×30 mm×0.7 mm thick, and a portion of 2 mm×30 mm in the test piece 11 was exposed from the metal jig 13 . The end surface of the exposed portion collides with the test head 14 . The test head 14 is made of SUS, and the radius of curvature R=2.5mm. Fig. 1(b) is a conceptual cross-sectional view showing a collision method in an end face strength test. As shown in Figure 1(b), firstly, the pendulum 15 (arm length 500 mm) installed with the test head 14 is driven down from a height of 10 mm, and the test piece 11 clamped by the metal fixture 13 end-face collision. Thereafter, while raising the height of the pendulum 15 by 10 mm, this operation was continued until the test piece 11 was broken, and the height at which the test piece 11 was broken was defined as the broken height. The end surface strength test was performed 10 times for each chemically strengthened glass, and the arithmetic mean value of the damage height was calculated as the average damage height.

FIG. 2 is a graph showing the relationship between the average compressive stress value at a depth of 7 μm to 16 μm from the surface and the average failure height in an end face strength test. As can be seen from Fig. 2, the average compressive stress value at a depth of 7 μm to 16 μm from the surface and the average damage height in the end face strength test can be considered to have a strong correlation because the correlation coefficient R ² is 0.8847.

As can be seen from Table 1, samples No. 1 to No. 4 had a large average compressive stress value at a depth of 7 μm to 16 μm from the surface, so the evaluation of the end face strength test was good. On the other hand, since samples No. 5 to No. 10 had a small average compressive stress value at a depth of 7 μm to 16 μm from the surface, the evaluation of the end face strength test was poor. [Industrial availability]

The chemically strengthened glass of the present invention is suitable for cover glass of mobile phones, digital cameras, PDAs, and touch panel displays. In addition to these applications, the chemically strengthened glass of the present invention is also expected to be applied to applications requiring high mechanical strength, such as window glass, substrates for magnetic disks, solar cells, substrates for flat panel displays, and cover glasses for solid-state imaging devices. , tableware, etc.

11‧‧‧Test piece 12‧‧‧Resin board 13‧‧‧Metal Fixtures 14‧‧‧Test head 15‧‧‧Pendulum

FIG. 1( a ) is a conceptual perspective view showing the shapes of a test jig and a test head that hold a test piece. FIG. 1( b ) is a conceptual sectional view showing a collision state in an end face strength test. FIG. 2 is a graph showing the relationship between the average compressive stress value at a depth of 7 μm to 16 μm from the surface and the average failure height in an end face strength test.

Claims (11)

A chemically strengthened glass, characterized in that it has a compressive stress layer on the surface, the average compressive stress value at a depth of 7 μm to 16 μm from the surface is 350 MPa or more, and the compressive stress value at a depth of 7 μm from the surface is 652 MPa or more, The compressive stress value at a depth of 16 μm from the surface is 441 MPa or less, and the stress depth is 90 μm or less. The chemically strengthened glass according to claim 1, wherein the compressive stress value at a depth of 12 μm from the surface is 350 MPa or more. The chemically strengthened glass according to claim 1 or 2, wherein the compressive stress value at a depth of 16 μm from the surface is 250 MPa or more. The chemically strengthened glass according to claim 1 or 2, wherein the compressive stress curve in the depth direction from the surface is curved. The chemically strengthened glass as described in item 1 or item 2 of the scope of the patent application, which contains 40%~80% SiO ₂ , 5%~30% Al ₂ O ₃ , and 0~5% Li in mass % ₂ O, and 5%~25% Na ₂ O as the glass composition. The chemically strengthened glass as described in item 1 or item 2 of the patent application has a liquidus viscosity of 10 ^4.0 dPa‧s or more. For the chemically strengthened glass described in item 1 or item 2 of the scope of the patent application, the temperature at a high temperature viscosity of 10 ^4.0 dPa‧s is below 1300°C. The chemically strengthened glass described in claim 1 or claim 2 has a coefficient of thermal expansion in the temperature range of 30°C to 380°C of 95×10 ^-7 /°C or less. Chemically strengthened glass as described in item 1 or item 2 of the patent application, It is in the shape of a flat plate. The chemically strengthened glass described in item 1 or item 2 of the scope of the patent application has a thickness of 0.1 mm to 2.0 mm and a stress depth of 10 μm to 90 μm. The chemically strengthened glass described in item 1 or item 2 of the patent application is used for a cover glass of a touch panel display.

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