TW201714853A - Method for producing reinforced glass plate - Google Patents

Abstract

This method for producing a reinforced glass plate is characterized by being provided with: a step for preparing a glass plate for reinforcement which includes, as the glass composition, expressed in mass%, 40-75% of SiO2, 0-30% of Al2O3, 5-25% of Na2O, 0-10% of K2O, and substantially no Li2O; a step in which a first ion exchange solution including at least a molten potassium nitrate salt is used to perform first ion exchange treatment on the glass plate for reinforcement, to obtain a reinforced glass plate intermediate, and the reinforced glass plate intermediate is subsequently extracted from the first ion exchange solution; a step in which some or all of the potassium nitrate salt adhered to the surface of the reinforced glass plate intermediate is removed, and heat treatment is subsequently performed; and a step in which a second ion exchange solution is used to perform second ion exchange treatment on the heat-treated reinforced glass plate intermediate to obtain the reinforced glass plate, and the reinforced glass plate is subsequently extracted from the second ion exchange solution.

Description

Method for manufacturing reinforced glass plate

The present invention relates to a method for producing a tempered glass sheet, and more particularly to a method for producing a tempered glass sheet in which a concentration distribution curve of potassium in a depth direction is curved and a warpage amount is small.

For cover glass of mobile phones, ion exchange treated tempered glass sheets have been used. Since the tempered glass sheet has higher mechanical strength than the unreinforced glass sheet, it is suitable for this purpose (see Patent Document 1 and Non-Patent Document 1).

In recent years, it is required to prevent breakage from the start of pressing of stone, sand, etc., when the cover glass is dropped.

In order to prevent such damage, for example, Patent Document 2 discloses that the first ion exchange treatment is performed on the glass plate for reinforcement by the ion exchange solution having a relatively high sodium (Na) ion concentration, and the concentration of Na ions is relatively high. The low ion exchange solution is subjected to a second ion exchange treatment, whereby the distribution curve of the potassium (K) ion concentration in the depth direction of the tempered glass sheet is bent to prevent the destruction. [Prior Art Document] [Patent Literature]

[Patent Document 1] JP-A-2006-83045 [Patent Document 2] Japanese Patent Laid-Open Publication No. 2011-529438 [Non-Patent Document]

[Non-Patent Document 1] Izumi Ryo, et al., "New Glass and Its Physical Properties", First Edition, Business Systems Research Institute Co., Ltd., August 20, 1984, p.451-498

[Problems to be Solved by the Invention] However, in the two-stage ion exchange treatment described in Patent Document 2, two types of ion exchange tanks are required, resulting in an increase in the production cost of the tempered glass sheet. That is, an ion exchange tank containing an ion exchange solution having a relatively high concentration of Na ions and an ion exchange tank containing an ion exchange solution having a relatively low concentration of Na ions are required, resulting in an increase in the manufacturing cost of the tempered glass sheet.

Further, in the two-stage ion exchange treatment described in Patent Document 2, the first ion exchange treatment takes a long time, and the manufacturing cost of the tempered glass sheet increases. Further, when the first ion exchange treatment takes a long time, the amount of warpage of the tempered glass sheet is likely to increase, and it is difficult to apply it to a cover glass of a mobile phone or the like.

Therefore, the present invention has been made in view of the above circumstances, and a technical object thereof is to invent a method for suppressing an increase in manufacturing cost, suppressing a warpage amount of a tempered glass sheet, and bending a distribution curve of a K ion concentration in a depth direction. . [Means to solve the problem]

The present inventors conducted various studies and found that by providing a heat treatment step between the two-stage ion exchange treatment and providing a step of removing the potassium nitrate salt attached to the glass surface before the heat treatment step, the solution can be solved. The technical subject is described as the present invention. That is, the method for producing a tempered glass sheet according to the present invention includes the step of preparing a glass sheet for reinforcement containing 40% to 75% of SiO ₂ and 0% to 30% by mass%. Al ₂ O ₃ , 5% to 25% Na ₂ O, and 0% to 10% K ₂ O as a glass composition, and substantially free of Li ₂ O; for the reinforcing glass plate, use at least potassium nitrate to be melted The first ion exchange solution of the salt is subjected to a first ion exchange treatment, thereby obtaining a step of removing the tempered glass plate intermediate from the first ion exchange solution after obtaining the tempered glass plate intermediate; and attaching the surface to the tempered glass plate intermediate a step of performing heat treatment after removing part or all of the potassium nitrate salt; and performing a second ion exchange treatment on the tempered glass plate intermediate after the heat treatment using the second ion exchange solution, thereby obtaining a tempered glass plate The step of removing the strengthened glass plate from the diion exchange solution. Here, the term "substantially free of Li ₂ O" means that the content of Li ₂ O in the glass composition is 0.1% by mass or less (preferably less than 0.01% by mass).

In the method for producing a tempered glass sheet of the present invention, the glass composition of the glass sheet for reinforcement is restricted as described above, and a heat treatment step is provided between the two-stage ion exchange treatment. If it is set as such, the ion diffusion of the glass surface layer can be promoted, and the stress depth of the compressive stress layer of the tempered glass sheet intermediate body can be increased in a short time.

Further, in the method for producing a tempered glass sheet of the present invention, a step of removing potassium nitrate adhered to the surface of the glass is provided before the heat treatment step. If it is set as such, the tempered glass sheet intermediate body is not easily warped after the heat treatment, and the tempered glass sheet is easily applied to the cover glass of the mobile phone.

Second, in the method for producing a tempered glass sheet of the present invention, it is preferred to limit the Na ion concentration of the second ion exchange solution to within ±12% of the Na ion concentration of the first ion exchange solution. By setting in this manner, it is easy to reuse the first ion exchange solution after the first ion exchange treatment as the second ion exchange solution, and the manufacturing cost of the tempered glass sheet can be reduced.

Third, in the method for producing a tempered glass sheet of the present invention, it is preferred to perform the first ion exchange treatment and the second ion exchange treatment using the same ion exchange tank. By setting it as such, it is possible to perform two-stage ion exchange treatment using one ion exchange tank, and it is possible to reduce the manufacturing cost of the tempered glass sheet.

Fourth, in the method for producing a tempered glass sheet of the present invention, the first ion exchange treatment is preferably performed so that the reinforcing characteristic index X of the tempered glass sheet intermediate body satisfies the relationship of -0.65 ≦ X ≦ - 0.50. Here, the strengthening characteristic index X is when the compressive stress value of the compressive stress layer on the surface of the tempered glass sheet intermediate is CS (MPa) and the stress depth is DOL (μm), by DOL = (-27065 × X) -13348) × The value calculated by the formula of CS ^X. In addition, the "compression stress value" and the "stress depth" are values calculated based on the number of interference fringes observed using a surface stress meter (for example, FSM-6000 manufactured by Toshiba Corporation) and the interval therebetween.

Fifth, in the method for producing a tempered glass sheet of the present invention, the thickness of the potassium nitrate salt adhering to the surface of the tempered glass sheet intermediate body is preferably 2 mm or less, and the variation in the thickness of the potassium nitrate salt is 1 mm or less. Part or all of the potassium nitrate salt attached to the surface of the tempered glass sheet intermediate is removed. When it is set as described above, the in-plane unevenness of the compressive stress value and the stress depth of the compressive stress layer of the tempered glass sheet intermediate after heat treatment becomes small, and as a result, the amount of warpage of the tempered glass sheet is easily reduced.

Sixth, the method for producing a tempered glass sheet of the present invention preferably limits the heat treatment temperature to 300 ° C to 600 ° C.

Seventh, the method for producing a tempered glass sheet of the present invention preferably limits the heat treatment time to 30 minutes or more and less than 1440 minutes.

Eighth, the method for producing a tempered glass sheet of the present invention is preferably a heat treatment using an electric furnace, and the temperature unevenness in the electric furnace is limited to within ±100 °C.

Ninth, in the method for producing a tempered glass sheet of the present invention, the second ion exchange treatment is preferably performed in such a manner that the distribution curve of the K ion concentration in the depth direction of the tempered glass sheet is curved in a region having a depth of less than 30 μm from the surface layer. . Here, the "distribution curve of the K ion concentration in the depth direction" can be confirmed by analyzing the cross section of the tempered glass sheet by an electron beam microanalyzer (for example, EPMA-1720H manufactured by Shimadzu Corporation).

Tenth, in the method for producing a tempered glass sheet of the present invention, the second ion exchange treatment is preferably performed so that the amount of warpage of the tempered glass sheet is 300 μm or less. Here, the "warpage amount" refers to the maximum thickness of the thickness gauge that can be inserted when a thickness gauge placed on a fixed plate is inserted into a thickness gauge.

Eleventh, in the method of manufacturing the tempered glass sheet of the present invention, the obtained tempered glass sheet is preferably used for a cover glass of a touch panel display.

The method for producing a tempered glass sheet according to the present invention includes the step of preparing a glass sheet for reinforcement containing 40% to 75% of SiO ₂ and 0% to 30% of Al ₂ O ₃ by mass%. 5% to 25% of Na ₂ O and 0% to 10% of K ₂ O are used as a glass composition and are substantially free of Li ₂ O. The reason for limiting the content range of each component as described above with respect to the glass plate for tempering of the present invention is as follows. In the description of the range of the content of each component, % means that the mass % is unless otherwise specified.

SiO ₂ is a component of the network forming the glass. The content of SiO ₂ is 40% to 75%, preferably 44% to 70%, 47% to 68%, 50% to 66%, 53% to 64%, particularly preferably 55% to 62%. When the content of SiO ₂ is too small, it is difficult to form glass, and the coefficient of thermal expansion becomes too high, and the thermal shock resistance is liable to lower. On the other hand, when the content of SiO ₂ is too large, the meltability, moldability, and bending workability are liable to lower, and the coefficient of thermal expansion is too low, so that it is difficult to match the coefficient of thermal expansion of the peripheral material.

Al ₂ O ₃ is a component that improves ion exchange performance, and is a component that increases strain point or Young's modulus. The content of Al ₂ O ₃ is from 0% to 30%. When the content of Al ₂ O ₃ is too small, the ion exchange performance cannot be sufficiently exhibited. In addition, there is a problem that the crack generation rate becomes high. Therefore, the preferred lower limit range of Al ₂ O ₃ is 1% or more, 3% or more, 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, 11% or more, and 12%. Above, 13% or more, 14% or more, 15% or more, especially 16% or more. On the other hand, when the content of Al ₂ O ₃ is too large, devitrified crystals are easily precipitated in the glass during molding, and it is difficult to form the glass sheet by an over-flow down draw method or the like. In particular, when a glass plate is molded by an overflow down-draw method using a molded body of alumina, devitrified crystals of spinel are easily precipitated at the interface with the molded body of alumina. In addition, the coefficient of thermal expansion becomes too low, and it is difficult to match the coefficient of thermal expansion of the peripheral material. In addition, the acid resistance is also lowered, which is difficult to apply to the acid treatment step. Further, the high-temperature viscosity is high, and the meltability or bending workability is liable to lower. Therefore, the preferred upper limit of Al ₂ O ₃ is 29% or less, 28% or less, 27% or less, 26% or less, 25% or less, and particularly preferably 24% or less.

Na ₂ O is an ion exchange component with K ions in the molten salt of potassium nitrate, and is a component which improves the meltability or formability by lowering the high-temperature viscosity. Further, Na ₂ O is also a component for improving resistance to devitrification and reactivity with a molded body refractory. When the content of Na ₂ O is too small, the meltability or formability is lowered, or the coefficient of thermal expansion is lowered, or the ion exchange performance is liable to lower. Therefore, the content of Na ₂ O is 5% or more, and the preferred lower limit range is 7% or more, more than 7.0%, 10% or more, 12% or more, 13% or more, and particularly 14% or more. On the other hand, when the content of Na ₂ O is too large, the thermal expansion coefficient becomes too high, the thermal shock resistance is lowered, or it is difficult to match the thermal expansion coefficient of the peripheral material. In addition, sometimes the strain point is too low, or the composition of the glass composition is broken, and the devitrification resistance is lowered. Therefore, the content of Na ₂ O is 25% or less, and the upper limit is preferably 23% or less, 21% or less, 20% or less, 19% or less, 18% or less, 17.5% or less, and particularly preferably 17% or less.

K ₂ O is a component that promotes ion exchange, and is a component which tends to increase the stress depth in the alkali metal oxide. Further, it is a component which improves the meltability or formability by lowering the high-temperature viscosity. Further, it is also a component for improving resistance to devitrification. However, if the content of K ₂ O is too large, the coefficient of thermal expansion becomes too high, the thermal shock resistance is lowered, or it is difficult to match the thermal expansion coefficient of the peripheral material. In addition, there is a tendency that the strain point is excessively lowered, or the composition of the glass composition is broken, and the devitrification resistance is lowered. Therefore, the preferred upper limit of K ₂ O is 10% or less, 9% or less, 8% or less, 7% or less, and particularly 6% or less. Further, in the case of adding K ₂ O, the amount of addition is preferably 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, and particularly preferably 2% or more. Further, when K ₂ O is added as much as possible, it is 0% to 1%, 0% to less than 1.0%, particularly 0% to 0.05%.

Li ₂ O is an ion exchange component with K ions in a molten salt of potassium nitrate, and is a component that improves the meltability, moldability, and workability by lowering the high-temperature viscosity, and is a component that increases the Young's modulus, but is A component which deteriorates an ion exchange solution containing a potassium nitrate molten salt during ion exchange treatment. Further, when the content of Li ₂ O is too large, the liquidus viscosity is lowered, the glass is easily devitrified, and the thermal expansion coefficient is excessively high, the thermal shock resistance is lowered, or it is difficult to match the thermal expansion coefficient of the peripheral material. Therefore, the glass plate for tempering of the present invention contains substantially no Li ₂ O in the glass composition.

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

B ₂ O ₃ is a component which lowers the viscosity or density at a high temperature and stabilizes the glass to make it difficult to precipitate crystals and lower the liquidus temperature. Moreover, it is a component which improves the fracture-resistant rate, and improves the damage resistance. However, when the content of B ₂ O ₃ is too large, coloring of the surface of the glass called brown spots due to ion exchange treatment, or water resistance is lowered, or the stress depth is likely to be small. Therefore, the preferred range of B ₂ O ₃ is 0% to 10%, 0% to 9%, 0% to 8%, 0% to 7%, 0% to 6%, 0% to 5%, and 0% to 4%, 0% to 3%, 0% to 2%, especially 0.1% to 1%.

MgO is a component which improves the meltability or formability by lowering the high-temperature viscosity, or increases the strain point or Young's modulus, and has a large effect of improving ion exchange performance in the alkaline earth metal oxide. Therefore, the preferred lower limit range of MgO is 0% or more, 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, and particularly 2% or more. However, when the content of MgO is too large, the density or the coefficient of thermal expansion tends to be high, and the glass tends to devitrify. In particular, when a glass plate is molded by an overflow down-draw method using a molded body of alumina, devitrified crystals of spinel are easily precipitated at the interface with the molded body of alumina. Therefore, the preferred upper limit of MgO is 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, and particularly 3% or less.

CaO is not accompanied by a decrease in devitrification resistance as compared with other components, and the effect of lowering the high-temperature viscosity to improve the meltability or formability, or increasing the strain point or Young's modulus is large. However, when the content of CaO is too large, there is a tendency that the density or the coefficient of thermal expansion becomes high, and the balance of the composition of the glass composition is broken, and the devitrification resistance is likely to be lowered, or the ion exchange performance is lowered, or the ion exchange solution is easily deteriorated. Therefore, the preferred content of CaO is 0% to 6%, 0% to 5%, 0% to 4%, 0% to 3.5%, 0% to 3%, 0% to 2%, and 0% to 1%. Especially 0% to 0.5%.

SrO and BaO are components which improve the meltability or formability or increase the strain point or Young's modulus when the high-temperature viscosity is lowered. However, if the content is too large, the ion exchange reaction is easily hindered, and the density or thermal expansion coefficient is high, or Glass is easily devitrified. Therefore, the preferable contents of SrO and BaO are 0% to 2%, 0% to 1.5%, 0% to 1%, 0% to 0.5%, 0% to 0.1%, particularly 0% to less than 0.1%, respectively.

ZnO is a component that enhances ion exchange performance, and particularly has a large effect of increasing the compressive stress value. Further, it is a component which does not lower the low-temperature viscosity and lowers the high-temperature viscosity. However, when the content of ZnO is too large, there is a tendency that the glass undergoes phase separation, or the resistance to devitrification decreases, or the density becomes high, or the stress depth becomes small. Therefore, the content of ZnO is preferably 0% to 6%, 0% to 5%, 0% to 3%, particularly preferably 0% to 1%.

TiO ₂ is a component that improves ion exchange performance, and is a component that lowers the high-temperature viscosity. If the content is too large, the glass is colored or devitrified. Therefore, the content of TiO ₂ is preferably from 0% to 4.5%, from 0% to 0.5%, particularly preferably from 0% to 0.3%.

ZrO ₂ is a component that significantly improves the ion exchange performance, and is a component that increases the viscosity or strain point in the vicinity of the liquid phase viscosity. However, if the content is too large, the devitrification resistance is remarkably lowered, and the density becomes Too high. Therefore, the content of ZrO ₂ is preferably 0% to 5%, 0% to 4%, 0% to 3%, particularly preferably 0.001% to 2%.

P ₂ O ₅ is a component that enhances ion exchange performance, particularly a component that increases the stress depth. However, if the content of P ₂ O ₅ is too large, the glass undergoes phase separation or the water resistance is remarkably lowered. Therefore, the content of P ₂ O ₅ is preferably 0% to 10%, 0% to 3%, 0% to 1%, particularly preferably 0% to 0.5%.

SnO ₂ has an effect of improving ion exchange performance. Therefore, the content of SnO ₂ is preferably 0% to 3%, 0.01% to 3%, 0.05% to 3%, 0.1% to 3%, particularly preferably 0.2% to 3%.

One or two or more of 0% to 3% of a group selected from the group consisting of Cl, SO ₃ and CeO ₂ may be added as a clearing agent.

The content of Fe ₂ O ₃ is preferably less than 1000 ppm (less than 0.1%), less than 800 ppm, less than 600 ppm, less than 400 ppm, and particularly preferably less than 300 ppm. Further, after the content of Fe ₂ O ₃ is limited to the above range, the molar ratio Fe ₂ O ₃ /(Fe ₂ O ₃ +SnO ₂ ) is preferably limited to 0.8 or more, 0.9 or more, and particularly 0.95 or more. When set in this way, the transmittance (400 nm to 770 nm) having a thickness of 1 mm is easily increased (for example, 90% or more).

The rare earth oxides such as Nd ₂ O ₃ and La ₂ O ₃ are components which increase the Young's modulus. However, the cost of the raw material itself is high, and if it is added in a large amount, the devitrification resistance is liable to lower. Therefore, the content of the rare earth oxide is preferably 3% or less, 2% or less, 1% or less, or 0.5% or less, and particularly preferably 0.1% or less.

In order to reduce the environmental load, the glass plate for tempering of the present invention preferably contains substantially no As ₂ O ₃ , Sb ₂ O ₃ , PbO, F, or Bi ₂ O ₃ as a glass composition. Here, "substantially free of As ₂ O ₃ " means that the content of As ₂ O ₃ is less than 0.05%. The phrase "substantially free of Sb ₂ O ₃ " means that the content of Sb ₂ O ₃ is less than 0.05%. The term "substantially free of PbO" means that the content of PbO is less than 0.05%. The term "substantially free of F" means that the content of F is less than 0.05%. The term "substantially free of Bi ₂ O ₃ " means that the content of Bi ₂ O ₃ is less than 0.05%.

The glass plate for tempering of the present invention preferably has the following characteristics.

The density is preferably 2.6 g/cm ³ or less, 2.55 g/cm ³ or less, 2.50 g/cm ³ or less, 2.48 g/cm ³ or less, 2.46 g/cm ³ or less, and particularly preferably 2.45 g/cm ³ or less. The lower the density, the more lightweight the tempered glass sheet can be. Further, if the content of SiO ₂ , B ₂ O ₃ , or P ₂ O ₅ in the glass composition is increased, or the content of the alkali metal oxide, the alkaline earth metal oxide, ZnO, ZrO ₂ , or TiO ₂ is decreased, the density is liable to lower. .

The slow cooling point is preferably 730 ° C or lower, 700 ° C or lower, 670 ° C or lower, 640 ° C or lower, 620 ° C or lower, 600 ° C or lower, or 580 ° C or lower, and particularly preferably 560 ° C or lower. When the slow cooling point is limited to the above range, the bending workability is improved. In addition, when the content of B ₂ O ₃ or an alkali metal oxide in the glass composition is increased, the slow cooling point is liable to lower, and when the content of SiO ₂ or Al ₂ O ₃ is increased, the slow cooling point is likely to rise.

The softening point is preferably 1020 ° C or lower, 990 ° C or lower, 960 ° C or lower, 930 ° C or lower, 900 ° C or lower, 860 ° C or lower, 840 ° C or lower, or 820 ° C or lower, and particularly preferably 800 ° C or lower. When the slow cooling point is limited to the above range, the bending workability is improved. In addition, when the content of B ₂ O ₃ or an alkali metal oxide in the glass composition is increased, the softening point is liable to lower. On the other hand, when the content of SiO ₂ or Al ₂ O ₃ is increased, the softening point is likely to increase.

The temperature at a high temperature viscosity of 10 ^4.0 dPa·s is preferably 1400 ° C or lower, and particularly preferably 1350 ° C or lower. The lower the temperature at a high-temperature viscosity of 10 ^4.0 dPa·s, the more the burden on the molding equipment is reduced, and the life of the molding equipment is prolonged, and as a result, the manufacturing cost of the tempered glass sheet is easily lowered. The temperature at a high temperature viscosity of 10 ^2.5 dPa·s is preferably 1720 ° C or lower, 1680 ° C or lower, 1650 ° C or lower, 1610 ° C or lower, 1580 ° C or lower, or 1550 ° C or lower, and particularly preferably 1520 ° C or lower. The lower the temperature at a high temperature viscosity of 10 ^2.5 dPa·s, the lower the temperature can be melted, the burden on the glass manufacturing equipment such as the melting kiln is reduced, the bubbles are easily reduced, and the quality is improved. As a result, the manufacturing cost of the tempered glass sheet is easily reduced. Further, when the content of the alkali metal oxide, the alkaline earth metal oxide, ZnO, B ₂ O ₃ , or TiO _{2 is} increased, or the content of SiO ₂ or Al ₂ O ₃ is decreased, the high-temperature viscosity is liable to lower.

The liquidus temperature is preferably 1230 ° C or lower, 1200 ° C or lower, 1170 ° C or lower, 1150 ° C or lower, 1100 ° C or lower, 1050 ° C or lower, 1000 ° C or lower, or 950 ° C or lower, and particularly preferably 900 ° C or lower. The lower the liquidus temperature, the more resistant to devitrification or formability. Further, the liquidus viscosity is preferably 10 ^4.0 dPa·s or more, 10 ^4.4 dPa·s or more, 10 ^4.8 dPa·s or more, 10 ^5.0 dPa·s or more, 10 ^5.3 dPa·s or more, or 10 ^5.5 dPa·s or more. 10 ^5.7 dPa·s or more, 10 ^5.8 dPa·s or more, particularly preferably 10 ^6.0 dPa·s or more. Furthermore, the higher the liquid phase viscosity, the higher the resistance to devitrification or formability. Furthermore, if the content of Na ₂ O, K ₂ O, B ₂ O ₃ in the glass composition is increased, or the content of Al ₂ O ₃ , Li ₂ O, MgO, ZnO, TiO ₂ , ZrO ₂ is decreased, the liquid phase The temperature is easily lowered, and the liquid phase viscosity is liable to become high.

The Young's modulus is preferably 65 GPa or more, 67 GPa or more, 69 GPa or more, 70 GPa or more, 71 GPa or more, 73 GPa or more, and particularly preferably 75 GPa or more. The higher the Young's modulus, the less the tempered glass sheet is less likely to be deflected. When used for a touch panel display or the like, even if the surface of the tempered glass sheet is strongly pressed by a pen or the like, the amount of deformation of the tempered glass sheet becomes small. As a result, it is easy to prevent the tempered glass sheet from coming into contact with the liquid crystal element located on the back surface and causing display failure. Further, since the amount of deformation of the stress generated during the strengthening treatment is small, it is easy to reduce the dimensional change of the tempered glass sheet before and after the ion exchange treatment.

The thickness of the glass plate for tempering of the present invention is preferably 1.5 mm or less, 1.0 mm or less, or 0.7 mm or less, and particularly preferably 0.1 mm to 0.5 mm. The smaller the thickness of the glass plate for reinforcement, the more lightweight the cover glass can be.

The method for producing a tempered glass sheet according to the present invention comprises the steps of: taking out a tempered glass from a first ion exchange solution after performing a first ion exchange treatment using a first ion exchange solution containing at least a potassium nitrate molten salt for the tempered glass sheet; Board intermediates. When a first ion exchange solution containing a molten salt of potassium nitrate is used, it is easy to ion-exchange the K ions in the ion exchange solution with the Na ions in the glass plate for reinforcement.

The ratio of the potassium nitrate molten salt in the first ion exchange solution is 95% by mass or more, 97% by mass or more, 98% by mass or more, 99% by mass or more, 99.5% by mass or more, and particularly 99.9% by mass or more. If the proportion of the potassium nitrate molten salt in the first ion exchange solution is too small, it is difficult to ensure the required strengthening characteristics in a short time.

In the method for producing a tempered glass sheet of the present invention, it is preferred that the first ion exchange treatment is performed so that the reinforcing characteristic index X of the tempered glass sheet intermediate satisfies the relationship of -0.65 ≦ X ≦ - 0.50. Further, the preferred lower limit range of the reinforcing characteristic index X is -0.64 or more, -0.63 or more, -0.62 or more, -0.61 or more, particularly -0.60 or more, and the preferred upper limit range is -0.51 or less, -0.52 or less, -0.53 or less. , especially -0.54 or less. When the strengthening characteristic index X is outside the above range, it is difficult to obtain a stress distribution in which the distribution curve of the K ion concentration in the depth direction is curved after the heat treatment and the second ion exchange treatment.

The method for producing a tempered glass sheet according to the present invention includes the step of removing a part or all of the potassium nitrate salt adhering to the surface of the tempered glass sheet intermediate, followed by heat treatment.

If the first ion exchange treatment is performed using the first ion exchange solution containing the molten salt of potassium nitrate, the potassium nitrate salt adheres to the surface of the tempered glass plate intermediate, but the adhered potassium nitrate salt causes the strengthening of the glass plate intermediate. The in-plane non-uniformity of the enhanced features. Therefore, if part or all of the potassium nitrate salt adhered to the surface of the glass is removed, the in-plane unevenness of the reinforcing property of the tempered glass sheet intermediate can be reduced. Regarding the method of removing the potassium nitrate salt adhering to the surface of the glass, various methods are conceivable, and examples thereof include a method of washing the surface of the tempered glass plate intermediate with a cleaning liquid, and removing the potassium nitrate salt; A method of lowering the lifting speed when lifting in an ion exchange tank. According to the former method, the adhered potassium nitrate salt is easily removed, but an additional washing step is required, and the time required for the total manufacturing step becomes long. According to the latter method, the potassium nitrate adhered can be easily removed without adding another device or step, but it is difficult to completely remove potassium nitrate adhering to the glass surface. Further, the adhered potassium nitrate salt may be removed by a method other than the above, for example, a low-temperature heat treatment at 350 ° C or lower.

When lifting the tempered glass plate intermediate body from the ion exchange tank, the lifting speed is preferably 10000 mm/min or less, 5000 mm/min or less, 3000 mm/min or less, 2000 mm/min or less, and particularly preferably 1000 mm/ Min below. The slower the lifting speed, the more the amount of potassium nitrate can be reduced.

The thickness of the potassium nitrate salt adhering to the surface of the tempered glass sheet intermediate before heat treatment is preferably 2 mm or less, 1.5 mm or less, 1.0 mm or less, 0.8 mm or less, 0.5 mm or less, 0.3 mm or less, 0.2 mm or less, or 0.18. Below mm, 0.16 mm or less, 0.14 mm or less, 0.12 mm or less, 0.10 mm or less, 0.08 mm or less, 0.06 mm or less, 0.04 mm or less, 0.02 mm or less, and particularly preferably 0.01 mm or less. The variation in thickness of the potassium nitrate salt in the surface of the tempered glass sheet is preferably 0.8 mm or less, 0.6 mm or less, 0.5 mm or less, 0.4 mm or less, 0.3 mm or less, 0.2 mm or less, 0.1 mm or less, 0.08 mm or less, 0.06 or less. Below mm, 0.04 mm or less, 0.02 mm or less, and particularly preferably 0.01 mm or less. The potassium nitrate salt attached to the surface of the glass undergoes an ion exchange reaction upon heat treatment, resulting in a non-uniform stress distribution. As a result, the warpage of the tempered glass sheet is caused. Therefore, the variation in thickness and thickness of the potassium nitrate salt adhering to the glass surface is appropriate. The ion exchange reaction is less likely to occur during the heat treatment, and the amount of warpage of the strengthened glass plate can be reduced.

In the method for producing a tempered glass sheet according to the present invention, the heat treatment temperature is preferably from 300 ° C to 600 ° C, and further preferably, the lower limit range is 325 ° C or higher, 350 ° C or higher, 375 ° C or higher, 400 ° C or higher, and 425 ° C or higher. Especially above 450 °C. When the heat treatment temperature is too low, the heat treatment time is prolonged in order to increase the stress depth, and the production cost of the tempered glass sheet is likely to increase. On the other hand, if the heat treatment temperature is too high, the unevenness of the in-plane heat treatment temperature becomes too large, resulting in warpage of the strengthened glass sheet, or when immersed in the second ion exchange solution, due to the second ion exchange solution The temperature difference is poor and the glass sheet is easily damaged. Therefore, the preferred upper limit of the heat treatment temperature is 575 ° C or lower, 550 ° C or lower, 525 ° C or lower, particularly 500 ° C or lower.

The heat treatment time is preferably 30 minutes or longer and less than 1440 minutes, and further preferably, the lower limit range is 45 minutes or longer, 60 minutes or longer, 75 minutes or longer, 90 minutes or longer, and particularly 120 minutes or longer. When the heat treatment time is short, it is difficult to obtain a stress distribution in which the distribution curve of the K ion concentration in the depth direction is curved after the second ion exchange treatment. On the other hand, if the heat treatment time is too long, warpage of the tempered glass sheet intermediate body during heat treatment may occur, or the production efficiency of the tempered glass sheet may be easily lowered. Therefore, the preferred upper limit of the heat treatment time is 1200 minutes or less, 960 minutes or less, 900 minutes or less, 840 minutes or less, 780 minutes or less, 720 minutes or less, 660 minutes or less, 600 minutes or less, 540 minutes or less, or 480 minutes or less. 420 minutes or less, 360 minutes or less, especially 300 minutes or less.

In the case of heat treatment using an electric furnace, the temperature in the electric furnace is not uniform, that is, the heat treatment temperature is not uniform within ±100 ° C, within ±90 ° C, within ±80 ° C, within ±70 ° C, within ±60 ° C Within ±50°C, within ±40°C, within ±30°C, within ±25°C, within ±20°C, within ±15°C, especially within ±10°C. When the temperature in the electric furnace is not excessively large, the in-plane reinforcing property of the tempered glass sheet intermediate after the heat treatment tends to fluctuate, and after the second ion exchange treatment, the tempered glass sheet is easily warped.

In the method for producing a tempered glass sheet of the present invention, it is preferable that the compressive stress value of the compressive stress layer of the tempered glass sheet intermediate body is 700 MPa or less (more preferably 500 MPa or less, 400 MPa or less, particularly preferably 300 MPa or less). In the heat treatment, the heat treatment is preferably performed so that the stress thickness is 40 μm or more (preferably 50 μm or more, 60 μm or more, and particularly preferably 70 μm or more). When it is set as such, after performing the second ion exchange treatment, it is easy to obtain a stress distribution in which the distribution curve of the K ion concentration in the depth direction is curved.

The method for producing a tempered glass sheet of the present invention comprises the steps of: after performing a second ion exchange treatment on the tempered glass sheet intermediate after the heat treatment using the second ion exchange solution, removing the tempered glass sheet from the second ion exchange solution.

In the method for producing a tempered glass sheet of the present invention, it is preferred to limit the Na ion concentration of the second ion exchange solution to within ±12% of the Na ion concentration of the first ion exchange solution. Further, the Na ion concentration of the second ion exchange solution is preferably -11% or more, -10% or more, -9% or more, -8% or more, -7% as compared with the Na ion concentration of the first ion exchange solution. Above, -6% or more, -5% or more, -4% or more, -3% or more, -2% or more, -1% or more, -0.5% or more, particularly preferably -0.3% or more, and preferably + 11% or less, +10% or less, +9% or less, +8% or less, +7% or less, +6% or less, +5% or less, +4% or less, +3% or less, +2% or less, + 1% or less, +0.5% or less, and particularly preferably +0.3% or less. When it is set as such, it is easy to reuse the first ion exchange solution after the first ion exchange treatment as the second ion exchange solution, and as a result, the first ion exchange treatment and the second ion exchange treatment can be performed by the same ion exchange tank. It can reduce the manufacturing cost of the tempered glass sheet.

In the method for producing a tempered glass sheet according to the present invention, it is preferred that the first ion exchange treatment and the second ion exchange treatment are performed by the same ion exchange tank. If it is set as such, it is easy to simplify the manufacturing equipment, and the manufacturing cost of the tempered glass sheet can be reduced.

In the method for producing a tempered glass sheet of the present invention, it is preferable that the compressive stress value of the compressive stress layer of the tempered glass sheet is 300 MPa or more (preferably 400 MPa or more, 500 MPa or more, and particularly preferably 600 MPa or more). In the second ion exchange treatment, the second ion exchange treatment is preferably performed so that the stress thickness is 30 μm or more (preferably 40 μm or more, 50 μm or more, and particularly preferably 60 μm or more). When it is set as such, the tempered glass sheet is not easily broken by the press-in of stone, sand, etc. as a starting point.

Further, it is preferable to carry out the second ion in such a manner that the distribution curve of the K ion concentration in the depth direction of the tempered glass plate is curved in a region having a depth of less than 30 μm from the surface layer (preferably, a region having a depth of 5 μm to 20 μm). Exchange processing. When it is set as such, the tempered glass sheet is not easily broken by the press-in of stone, sand, etc. as a starting point.

Furthermore, it is preferable to perform the second ion exchange treatment so that the amount of warpage of the tempered glass sheet is 300 μm or less (preferably 200 μm or less, 150 μm or less, particularly preferably 110 μm or less). If it is set as such, it is easy to apply a tempered glass plate to the cover glass of a mobile phone. [Example 1]

Hereinafter, the present invention will be described in detail based on examples. However, the following examples are merely illustrative. The invention is not limited by the following examples.

Sample Nos. 1 to 15 are shown in Table 1.

[Table 1]

Each sample was prepared as follows. First, the glass raw material was blended so as to have a glass composition in the table, and melted at 1,580 ° C for 8 hours using platinum crucible. Thereafter, the molten glass was discharged to a carbon plate to be formed into a flat plate shape. The obtained tempered glass sheets were evaluated for various characteristics.

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

The strain point Ps and the slow cooling point Ta are values measured according to the method of the American Society for Testing and Materials (ASTM) C336.

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

The temperature at a high temperature viscosity of 10 ^4.0 dPa·s, 10 ^3.0 dPa·s, and 10 ^2.5 dPa·s is a value measured by a platinum ball pulling method.

The coefficient of thermal expansion α is a value obtained by measuring a mean thermal expansion coefficient in a temperature range of 25 ° C to 380 ° C using a dilatometer.

The liquidus temperature TL is a glass powder which has passed through a standard sieve of 30 mesh (mesh aperture of 500 μm) and remains on a 50 mesh (mesh aperture of 300 μm), and is placed in a platinum boat for 24 hours in a temperature gradient furnace. The temperature at which the crystallization was precipitated was measured.

The liquid phase viscosity log η TL is a value obtained by measuring the viscosity of the glass at a liquidus temperature by a platinum ball pulling method.

The Young's modulus E is a value measured by a well-known resonance method.

Then, both surfaces of each sample were subjected to optical polishing, and then immersed in a KNO ₃ molten salt (new KNO ₃ molten salt) at 430 ° C for 4 hours to carry out ion exchange treatment. The surface of each sample was washed after the ion exchange treatment, and the compression of the surface compressive stress layer was calculated according to the number of interference fringes observed by the surface stress meter (FSM-6000 manufactured by Toshiba Corporation) and the interval thereof. Stress value CS and stress depth DOL. In the calculation, the refractive index of each sample was 1.50, and the optical elastic constant was 30 [(nm/cm)/MPa]. [Embodiment 2]

First, the sample No. 2 described in Table 1 was formed into a flat plate shape having a thickness of 0.4 mm by an overflow down-draw method, and then cut into an outer shape of 65 mm × 130 mm to obtain a plurality of reinforcing glass sheets. Further, the glass plate for reinforcement has an average surface roughness Ra of 2 Å or less.

Then, the obtained glass plate for tempering was subjected to ion exchange treatment at 422 ° C for 272 minutes using a potassium nitrate molten salt containing 0.35% by mass of Na ions (corresponding to the first ion exchange solution) (corresponding to the first Ion exchange treatment). Further, the obtained tempered glass sheet intermediate body was lifted from the ion exchange tank at a lifting speed of 3000 mm/min, whereby the potassium nitrate salt adhering to the surface of the tempered glass sheet intermediate was removed. Thereby, the thickness of the potassium nitrate salt attached to the tempered glass sheet intermediate is reduced to 0.1 mm. Moreover, the thickness deviation of the potassium nitrate salt was 0.06 mm. In addition, for the tempered glass sheet intermediate after lifting, the compressive stress of the surface compressive stress layer was calculated according to the number of interference fringes observed using a surface stress meter (FSM-6000 manufactured by Toshiba Corporation) and the interval thereof. The value CS and the stress depth DOL result in a compressive stress value CS of 790 MPa and a stress depth of 45 μm. Then, the tempered glass sheet intermediate was heat-treated at 450 ° C for 240 minutes in an electric furnace. For the tempered glass sheet intermediate after the heat treatment, the compressive stress value CS of the surface compressive stress layer was calculated according to the number of interference fringes observed using a surface stress meter (FSM-6000 manufactured by Toshiba Corporation) and the interval thereof. And the stress depth DOL, the resulting compressive stress value CS is 160 MPa, and the stress depth is 89 μm.

Then, the heat-treated tempered glass sheet intermediate is again immersed in the potassium nitrate molten salt (corresponding to the second ion exchange solution, and the Na ion concentration is substantially equal to that of the first ion exchange solution) at 422 ° C for 26 minutes. The conditions are subjected to ion exchange treatment (corresponding to the second ion exchange treatment). For the obtained tempered glass sheet, the compressive stress value CS and the stress depth of the surface compressive stress layer were calculated according to the number of interference fringes observed using a surface stress meter (FSM-6000 manufactured by Toshiba Corporation) and the interval thereof. DOL, the resulting compressive stress CS is 690 MPa and the stress depth is 67 μm. Further, when the thickness gauge was inserted into the tempered glass sheet placed on the fixing plate, the maximum thickness of the insertable thickness gauge was measured, and as a result, the maximum thickness (warpage amount) was 103 μm. Furthermore, the cross section of the tempered glass sheet was analyzed by an electron beam microanalyzer (EPMA-1720H manufactured by Shimadzu Corporation), and the distribution curve of the K ion concentration in the depth direction of the tempered glass sheet was confirmed, and the result was 15 μm from the surface layer. The curve of the K-concentration of the curved K-zone in the region. Further, the time required to obtain the tempered glass sheet from the tempered glass sheet was 8 hours and 58 minutes.

In the above experiment, Sample No. 2 described in Table 1 was used for the sake of convenience, but Sample No. 1 and No. 3 to No. 15 described in Table 1 were also obtained. The same tendency. [Example 3]

First, the sample No. 2 described in Table 1 was formed into a flat plate shape having a thickness of 0.4 mm by an overflow down-draw method, and then cut into an outer shape of 65 mm × 130 mm to obtain a plurality of reinforcing glass sheets. Further, the glass plate for reinforcement has an average surface roughness Ra of 2 Å or less.

Then, the obtained glass plate for reinforcement was subjected to ion exchange treatment at 430 ° C for 240 minutes using a potassium nitrate molten salt containing 0.27 mass % of Na ions (corresponding to the first ion exchange solution) (corresponding to the first Ion exchange treatment). Further, the obtained tempered glass sheet intermediate body was lifted from the ion exchange tank at a lifting speed of 5000 mm/min, whereby the potassium nitrate salt adhering to the surface of the tempered glass sheet intermediate was removed. The thickness of the potassium nitrate salt attached to the tempered glass sheet intermediate after lifting was 0.2 mm, and the thickness deviation was 0.06 mm. For the tempered glass sheet intermediate, the compressive stress value CS and stress of the surface compressive stress layer were calculated based on the number of interference fringes observed using a surface stress meter (FSM-6000 manufactured by Toshiba Corporation) and the interval thereof. The depth DOL results in a compressive stress CS of 840 MPa and a stress depth of 45 μm. Then, the tempered glass sheet intermediate was heat-treated at 450 ° C for 240 minutes in an electric furnace. For the tempered glass sheet intermediate after the heat treatment, the compressive stress value CS of the surface compressive stress layer was calculated according to the number of interference fringes observed using a surface stress meter (FSM-6000 manufactured by Toshiba Corporation) and the interval thereof. And the stress depth DOL, the resulting compressive stress value CS is 300 MPa, and the stress depth is 84 μm.

Then, the heat-treated tempered glass sheet intermediate is again immersed in the potassium nitrate molten salt (corresponding to the second ion exchange solution, and the Na ion concentration is substantially the same as that of the first ion exchange solution) at 450 ° C for 10 minutes. The ion exchange treatment (corresponding to the second ion exchange treatment) is performed. For the obtained tempered glass sheet, the compressive stress value CS and the stress depth of the surface compressive stress layer were calculated according to the number of interference fringes observed using a surface stress meter (FSM-6000 manufactured by Toshiba Corporation) and the interval thereof. DOL, the resulting compressive stress value CS is 740 MPa and the stress depth is 65 μm. Further, when the thickness gauge was placed on the tempered glass sheet placed on the fixing plate, the maximum thickness of the insertable thickness gauge was measured, and as a result, the maximum thickness (warpage amount) was more than 200 μm. Further, the cross section of the tempered glass sheet was analyzed by an electron beam microanalyzer (EPMA-1720H manufactured by Shimadzu Corporation), and the distribution curve of the K ion concentration in the depth direction of the tempered glass sheet was confirmed, and the result was 15 μm from the surface layer. A curved compressive stress distribution within the area. Further, the time required to obtain the tempered glass sheet from the tempered glass sheet was 8 hours and 10 minutes.

In addition, in the above-mentioned experiment, the sample No. 2 described in Table 1 was used for the sake of convenience, but it is considered that the sample No. 1 and No. 3 to No. 15 described in Table 1 can also be obtained. Propensity. [Industrial availability]

The method for producing a tempered glass sheet of the present invention is suitable as a method for producing a glass substrate such as a cover glass or a touch panel display such as a mobile phone, a digital camera, or a personal digital assistant (PDA). In addition to the above-mentioned applications, the method for producing a tempered glass sheet of the present invention is suitable, for example, as a method for producing a window glass, a flat panel display, a cover glass for a solar cell, a cover glass for a solid-state image sensor, and a tableware.

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Claims (11)

A method for producing a tempered glass sheet, comprising: a step of preparing a glass sheet for reinforcement containing 40% to 75% of SiO ₂ and 0% to 30% of Al ₂ by mass% O ₃ , 5% to 25% of Na ₂ O, and 0% to 10% of K ₂ O are used as a glass composition, and substantially do not contain Li ₂ O; for the glass plate for reinforcement, at least a potassium nitrate molten salt is used. The first ion exchange solution is subjected to a first ion exchange treatment, whereby a step of removing the tempered glass sheet intermediate from the first ion exchange solution after obtaining the tempered glass sheet intermediate; and attaching to the tempered glass a step of performing heat treatment after removing a part or all of the potassium nitrate salt on the surface of the plate intermediate; and performing a second ion exchange treatment on the tempered glass plate intermediate after the heat treatment using the second ion exchange solution, thereby obtaining After strengthening the glass sheet, the step of removing the strengthened glass sheet from the second ion exchange solution. The method for producing a tempered glass sheet according to claim 1, wherein the concentration of Na ions in the second ion exchange solution is limited to within ±12% of the Na ion concentration of the first ion exchange solution. The method for producing a tempered glass sheet according to the first or second aspect of the invention, wherein the first ion exchange treatment and the second ion exchange treatment are performed by the same ion exchange tank. The method for producing a tempered glass sheet according to any one of the preceding claims, wherein the reinforced characteristic index X of the tempered glass sheet intermediate satisfies a relationship of -0.65 ≦ X ≦ - 0.50. In the method, the first ion exchange treatment is performed. Here, the reinforcement characteristic index X is such that the compressive stress value of the compressive stress layer on the surface of the tempered glass sheet intermediate is set to CS (MPa), and the stress depth is set to In the case of DOL (μm), the value calculated by the formula of DOL=(-27065×X-13348)×CS ^X . The method for producing a tempered glass sheet according to any one of the first to fourth aspect, wherein the thickness of the potassium nitrate salt adhered to the surface of the tempered glass sheet intermediate is 2 mm or less, and A part or all of the potassium nitrate salt adhering to the surface of the tempered glass sheet intermediate is removed so that the variation in the thickness of the potassium nitrate salt is 1 mm or less. The method for producing a tempered glass sheet according to any one of claims 1 to 5, wherein the heat treatment temperature is limited to 300 ° C to 600 ° C. The method for producing a tempered glass sheet according to any one of claims 1 to 6, wherein the heat treatment time is limited to 30 minutes or more and less than 1440 minutes. The method for producing a tempered glass sheet according to any one of claims 1 to 7, wherein the heat treatment in the electric furnace is performed, and the temperature unevenness in the electric furnace is limited to within ±100 °C. The method for producing a tempered glass sheet according to any one of the preceding claims, wherein the distribution of the K ion concentration in the depth direction of the tempered glass sheet is less than 30 μm from the surface layer. The second ion exchange process is performed in a manner of bending in the region. The method for producing a tempered glass sheet according to any one of the preceding claims, wherein the second ion exchange treatment is performed such that the amount of warpage of the tempered glass sheet is 300 μm or less. . The method for producing a tempered glass sheet according to any one of claims 1 to 10, wherein the obtained tempered glass sheet is used for a cover glass of a touch panel display.