JP2022139011A - Strengthened glass and method for manufacturing the same - Google Patents

Abstract

To provide strengthened glass with less warp, while having high compressive stress on both a first principal surface and a second principal surface .SOLUTION: A method for manufacturing strengthened glass includes: a preparation step S1 of preparing glass for strengthening having a first principal surface and a second principal surface, and a heterogeneous layer at a surface layer part of the second principal surface; a heat treatment step S2 of holding the glass for strengthening at a holding temperature of a strain point -15°C or higher for 3 minutes or longer to apply a heat treatment; and a chemical strengthening step S3 of chemically strengthening the glass for strengthening through an ion exchange treatment to obtain strengthened glass.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to tempered glass and a method for producing the same.

In recent years, tempered glass has been widely used as cover glass for various devices such as mobile phones (especially smart phones), digital cameras, PDAs (portable terminals), and touch panel displays. Such tempered glass is generally produced by chemically strengthening glass for strengthening by ion exchange treatment (for example, Patent Document 1).

WO2013/088856

In the manufacturing process of tempered glass, one main surface (hereinafter referred to as the first main surface) of the tempered glass may be removed by mechanical polishing or the like before the tempered glass is chemically tempered. Such removal of the surface layer portion of the first main surface is performed, for example, as a part of processing the end face shape of the tempered glass into a special shape.

However, as a result of intensive research by the present inventors, when the surface layer portion of the first main surface of the glass for strengthening is removed by polishing or the like in this way, the tempered glass obtained by chemical strengthening has a large warp that does not meet product standards. known to occur.

Although the cause of this warpage is not clearly elucidated, it is currently thought to be as follows. That is, the heterogeneous layer formed during the molding process of the tempering glass exists on each of the surface layer portions of the first main surface and the second main surface located on the opposite side of the tempering glass. This heterogeneous layer has the property of promoting ion exchange. Therefore, when the heterogeneous layer is removed by mechanical polishing of the surface layer portion of the first main surface, the degree of progress of ion exchange differs between the first main surface and the second main surface during chemical strengthening, resulting in a difference between the two main surfaces. A stress difference occurs, and due to this stress difference, a large warp occurs in the tempered glass.

In addition, since the first main surface from which the heterogeneous layer that promotes ion exchange has been removed tends to have a lower compressive stress during chemical strengthening, this may cause a decrease in the strength of the tempered glass.

Even if the foreign layer on the first main surface side is not completely removed, the same phenomenon occurs if the thickness of the foreign layer on the first main surface side and the thickness of the foreign layer on the second main surface side are significantly different. is thought to occur.

An object of the present invention is to provide a tempered glass having high compressive stress on both the first main surface and the second main surface and having a small warpage.

(1) The present invention, which has been devised to solve the above problems, comprises a forming step of forming a reinforcing glass having a first main surface and a second main surface located on the opposite side of the first main surface; , a slow cooling step of slowly cooling the tempering glass at a cooling rate of 0.5 ° C./s or more immediately after molding, a removing step of removing the surface layer portion of the first main surface of the tempering glass, and straining the tempering glass. A heat treatment step of holding a temperature of −15° C. or higher for 3 minutes or more for heat treatment, and a chemical strengthening step of chemically strengthening the tempering glass by ion exchange treatment to obtain tempered glass are provided in this order.

In the tempering glass that has undergone the slow cooling step (cooling rate: 0.5° C./s or more), a heterogeneous layer is formed on each surface layer of the first main surface and the second main surface. When the surface layer portion of the first main surface is removed, part or all of the foreign layer on the first main surface side is also removed together. Therefore, if chemical strengthening is performed in this state, the tempered glass may be greatly warped. Therefore, in the present invention, after the removal step and before the chemical strengthening step, a heat treatment step is performed in which the tempering glass is heat-treated by holding it at a strain point of −15° C. or higher for 3 minutes or longer. According to such a heat treatment, the heterogeneous layer can be reproduced (or formed) on the surface layer portion of the first main surface of the tempering glass. Therefore, even if the glass for strengthening is chemically strengthened after that, it is possible to suppress the occurrence of a large warp in the tempered glass. In addition, since chemical strengthening is performed in a state in which the heterogeneous layer is formed on the surface layer portions of each of the first main surface and the second main surface, high compressive stress can be realized on both main surfaces.

(2) In the configuration of (1) above, it is preferable that, of the first main surface and the second main surface, only the surface layer portion of the first main surface is removed in the removing step.

In this way, only the heterogeneous layer on the first main surface side of the tempering glass is removed, so if chemical strengthening is performed in this state, the tempered glass is likely to warp. In other words, the effect of reproducing the heterogeneous layer by the heat treatment process of the present invention is particularly useful.

(3) The present invention, invented to solve the above problems, has a first main surface and a second main surface located opposite to the first main surface, and a surface layer portion of the second main surface. A preparation step of preparing a tempering glass having a heterogeneous layer, a heat treatment step of holding the tempering glass at a holding temperature of -15 ° C. or higher for 3 minutes or more and heat-treating the tempering glass, and chemically strengthening the tempering glass by ion exchange treatment. and a chemical strengthening step of obtaining tempered glass.

In this way, after the preparatory step and before the chemical strengthening step, the heat treatment step of holding the tempering glass at a strain point of −15° C. or higher for 3 minutes or more for heat treatment is performed. According to such a heat treatment, a foreign layer can be formed (regenerated) on the surface layer portion of the first main surface of the tempering glass. Therefore, even if the glass for strengthening is chemically strengthened after that, it is possible to suppress the occurrence of a large warp in the tempered glass. In addition, since chemical strengthening is performed in a state in which the heterogeneous layer is formed on the surface layer portions of each of the first main surface and the second main surface, high compressive stress can be realized on both main surfaces.

(4) In the configuration of (3) above, the heterogeneous layer in the preparatory step may be formed by slowly cooling the tempering glass at a cooling rate of 0.5° C./s or more during the molding process.

(5) In any one of the above configurations (1) to (4), the tempering glass is preferably formed by an overflow downdraw method or a slot downdraw method.

(6) In any one of the above configurations (1) to (5), in the heat treatment step, the holding temperature is +50° C. or less of the strain point, and the holding time at the holding temperature is preferably 10 minutes or more.

In this way, since the heat treatment is performed at a relatively low temperature for a long time, unintended deformation of the tempering glass can be suppressed.

(7) In any one of the configurations (1) to (5) above, the holding temperature in the heat treatment step is preferably the strain point +85° C. or higher.

In this way, the heterogeneous layer can be efficiently formed (regenerated).

(8) In any one of the configurations (1) to (7) above, in the heat treatment step, the holding time at the holding temperature is preferably 60 minutes or less.

In the heat treatment step, the longer the holding time at the holding temperature, the more effective the formation (regeneration) of the heterogeneous layer. )can do. Therefore, in consideration of production efficiency, the retention time at the retention temperature is preferably 60 minutes or less.

(9) In any one of the above configurations (1) to (8), the tempered glass obtained in the chemical strengthening step has a difference ( The absolute value of CS1-CS2) is preferably 40 MPa or less.

If the heat treatment process as described above is performed in advance, tempered glass having an absolute value of CS1-CS2 of 40 MPa or less can be easily and reliably produced in the chemical strengthening process. If the tempered glass has a small absolute value of CS1-CS2, it is possible to reliably suppress the occurrence of large warpage.

(10) In any one of the configurations (1) to (9) above, the tempering glass may be sheet glass having a thickness of 0.3 mm or less.

In other words, the present invention is a technique that is also effective for manufacturing such extremely thin sheet glass.

(11) In any one of the above configurations (1) to (10), the tempering glass has a glass composition of SiO ₂ 50 to 80%, Al ₂ O ₃ 5 to 25%, and B ₂ O in terms of mol %. ₃ 0-15%, Li ₂ O 0-20%, Na ₂ O 1-20%, K ₂ O 0-10%.

If the glass for strengthening has such a glass composition, the problem of warpage associated with the heterogeneous layer during chemical strengthening tends to occur, and the effects of the present invention are particularly useful.

(12) The present invention, invented to solve the above problems, has a first compressive stress layer in the surface layer portion of the first main surface, and the surface layer of the second main surface located opposite to the first main surface. Tempered glass having a second compressive stress layer in the part, wherein the absolute value of the difference (Ra1-Ra2) between the surface roughness Ra1 of the first main surface and the surface roughness Ra2 of the second main surface is 0.1 nm Above, each of the compressive stress CS1 of the first main surface and the compressive stress CS2 of the second main surface is 820 MPa or more, and the compressive stress CS1 of the first main surface and the compressive stress CS2 of the second main surface The absolute value of the difference (CS1-CS2) is 40 MPa or less.

In this way, the surface roughness Ra1 of the first main surface and the second main surface Even when the absolute value of the difference from the surface roughness Ra2 of is large, it is possible to provide tempered glass with small warp while having high compressive stress on both main surfaces.

According to the present invention, it is possible to provide a tempered glass having high compressive stress on both the first main surface and the second main surface and having a small warp.

BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart which shows the manufacturing method of the tempered glass which concerns on 1st embodiment of this invention. FIG. 3 is a cross-sectional view showing the tempering glass in the preparatory step of the first embodiment; 4 is a graph illustrating heat treatment conditions in the heat treatment step of the first embodiment; FIG. 4 is a cross-sectional view showing the tempering glass after the heat treatment step and before the tempering step of the first embodiment; It is a flow figure showing a manufacturing method of tempered glass concerning a second embodiment of the present invention. It is sectional drawing which shows the manufacturing apparatus used by 2nd embodiment. FIG. 5 is a cross-sectional view showing the tempering glass in the cutting step of the second embodiment; FIG. 10 is a cross-sectional view showing the reinforcing glass in the removal step of the second embodiment; FIG. 4 is a cross-sectional view showing the tempering glass in the heat treatment step of the second embodiment; FIG. 5 is a cross-sectional view showing tempered glass according to a third embodiment of the present invention;

EMBODIMENT OF THE INVENTION Hereinafter, it demonstrates, referring drawings for the tempered glass which concerns on embodiment of this invention, and its manufacturing method. Note that redundant description may be omitted by assigning the same reference numerals to corresponding components in each embodiment. When only a part of the configuration is described in each embodiment, the configurations of other embodiments previously described can be applied to other portions of the configuration. Moreover, not only the combinations of the configurations explicitly specified in the description of each embodiment, but also the configurations of a plurality of embodiments can be partially combined even if they are not specified unless there is a particular problem with the combination.

(First embodiment)
As shown in FIG. 1, the first embodiment of the present invention illustrates a method for manufacturing tempered glass.

As shown in the figure, the method for manufacturing tempered glass according to the present embodiment includes a preparation step S1, a heat treatment step S2, and a chemical strengthening step S3 in this order. That is, the heat treatment step S2 is performed after the preparation step S1, and the chemical strengthening step S3 is performed after the heat treatment step S2.

The preparation step S1 is a step of preparing the tempering glass 1 shown in FIG. The tempering glass 1 is untempered sheet glass and has a first major surface 2 and a second major surface 3 opposite the first major surface 2 . That is, the first main surface 2 and the second main surface 3 face each other in the thickness direction.

The tempering glass 1 is sheet glass having a thickness of 2 mm or less. The thickness of the tempering glass 1 is preferably 300 μm or less, 150 μm or less, 20 μm or more and 150 μm or less, 20 μm or more and 120 μm or less, or 25 μm or more and 120 μm or less. A tempered glass obtained from a very thin tempered glass 1 of 300 μm or less can be suitably used as a cover glass of a so-called foldable type device, in which the display surface of the display can be folded. On the other hand, for example, when the tempered glass obtained from the tempered glass 1 is used as a cover glass of a non-bending type (straight type) device, the thickness of the tempered glass 1 is preferably more than 0.3 mm and 2 mm. 0.45 mm or more and 2 mm or less and 0.5 mm or more and 0.85 mm or less. Note that the tempered glass obtained from the tempered glass 1 also has substantially the same thickness as the tempered glass 1 . When removing the surface layer 2a of the first main surface 2 and/or the surface layer 3a of the second main surface 3 of the tempered glass 1 in the tempered glass manufacturing process, the thickness of the tempered glass 1 is removed. later thickness (see symbol D1 in FIG. 8).

A heterogeneous layer 4 is formed on the surface layer portion 2 a of the second main surface 3 of the tempered glass 1 . In the present embodiment, the heterogeneous layer 4 is formed only on the surface layer portion 3a of the second main surface 3 of the first main surface 2 and the second main surface 3 of the tempering glass 1 . The heterogeneous layer 4 is, for example, a layer having a thickness of 5-10 μm. The heterogeneous layer 4 is a layer having properties different from those of the inner layer 5 of the tempering glass 1, and has a property of promoting ion exchange in the chemical strengthening step S3. In the present embodiment, the surface layer portion 2a of the first main surface 2 has no heterogeneous layer formed thereon, so the surface layer portion 2a of the first main surface 2 has properties similar to those of the inner layer 5. FIG. In addition, a foreign layer thinner than the foreign layer 4 on the second main surface 3 side may be formed on the surface layer portion 2 a of the first main surface 2 .

Although the detailed structure of the heterogeneous layer 4 has not yet been elucidated at the present time, (1) a layer whose structure is more relaxed than that of the internal layer 5, (2) a layer having a different moisture content from that of the internal layer 5, and (3) an internal layer. It is presumed to be composed of layers having a composition different from that of 5. However, the heterogeneous layer 4 is formed during slow cooling (slow cooling condition: cooling rate of 0.5 ° C./s or more) immediately after forming the plate-shaped reinforcing glass 1 (strictly speaking, the glass ribbon) from the molten glass. has been found to be formed in Examples of the method for forming the tempering glass 1 that satisfies such slow cooling conditions include a down-draw method such as an overflow down-draw method and a slot down-draw method (for example, cooling conditions of 3 to 10° C./s), and a float method. (for example, a cooling condition of 0.5 to 2° C./s). In order to obtain a smooth surface, it is preferable to use an overflow down-draw method as a molding method. The tempered glass 1 formed by the overflow down-draw method has a forming confluence surface inside.

The tempering glass 1 is, for example, an alkali aluminosilicate glass, and has, for example, a glass composition of SiO ₂ 50 to 80%, Al ₂ O ₃ 5 to 25%, B ₂ O ₃ 0 to 35%, Li ₂ O 0-20%, Na ₂ O 1-20%, Li ₂ O+Na ₂ O 1-20%, K ₂ O 0-10%. A representative glass satisfying such a glass composition is T2X-1 manufactured by Nippon Electric Glass Co., Ltd. The tempering glass ₁ may have a glass composition that does not substantially contain Li2O. _The phrase “substantially free of Li ₂ O” means that although Li ₂ O is not actively added as a glass component, it is allowed to be mixed in at an impurity level. It means that the content is less than 500 ppm. The tempered glass obtained by chemically strengthening the tempering glass 1 and the molten glass for molding the tempering glass 1 also have substantially the same glass composition as the tempering glass 1 .

The reasons why the above glass composition is preferable are shown below. In addition, in description of the content range of each component, % display refers to mol% unless otherwise specified.

_SiO2 is a component that forms the network of glass. If the content of SiO ₂ is too small, vitrification becomes difficult, and the coefficient of thermal expansion becomes too high, which tends to lower the thermal shock resistance. Therefore, the preferred lower range of _SiO2 is 50% or more, 55% or more, 57% or more, 59% or more, especially 61% or more. On the other hand, if the content of SiO ₂ is too high, the meltability and moldability tend to deteriorate, and the coefficient of thermal expansion becomes too low, making it difficult to match the coefficient of thermal expansion with that of surrounding materials. Therefore, the preferred upper range of _SiO2 is 80% or less, 70% or less, 68% or less, 66% or less, 65% or less, especially 64.5% or less.

Al ₂ O ₃ is a component that enhances ion exchange performance, and also a component that enhances strain point, Young's modulus, fracture toughness and Vickers hardness. Therefore, the preferable lower limit range of Al ₂ O ₃ is 5% or more, 8% or more, 10% or more, 11% or more, and 11.2% or more. On the other hand, if the content of Al ₂ O ₃ is too high, the high-temperature viscosity increases and meltability and moldability tend to deteriorate. On the other hand, if the content of Al ₂ O ₃ is too high, devitrified crystals are likely to precipitate in the glass, making it difficult to form a plate by an overflow down-draw method or the like. In particular, when an alumina-based refractory is used as a compact refractory and a glass plate is formed by an overflow down-draw method, devitrified crystals of spinel tend to precipitate at the interface with the alumina-based refractory. Furthermore, if the content of Al ₂ O ₃ is too high, the acid resistance is also lowered, making it difficult to apply the acid treatment process. Therefore, the preferred upper limit range of Al ₂ O ₃ is 25% or less, 21% or less, 20.5% or less, 20% or less, 19.9% or less, 19.5% or less, 19.0% or less, especially 18.9% or less.

B ₂ O ₃ is a component that lowers the high-temperature viscosity and density, stabilizes the glass to make crystal precipitation difficult, and lowers the liquidus temperature. B ₂ O ₃ is a component that suppresses Young's modulus and increases bending strength and crack resistance. However, if the content of B ₂ O ₃ is too high, the ion exchange treatment tends to cause discoloration of the surface called discoloration, lower water resistance, and lower compressive stress in the compressive stress layer. be. Therefore, the preferable lower limit range of B ₂ O ₃ is 0% or more, 0.01% or more, 0.02% or more, 0.1% or more, 0.3% or more, and the preferable upper limit range is 35 % or less, 30% or less, 25% or less, 22% or less, 20% or less, particularly 15% or less. From the standpoint of giving priority to increasing the CS, the content of B ₂ O ₃ is more preferably 0.2 to 5%, 0.3 to 1%. On the other hand, from the viewpoint of giving priority to suppressing the Young's modulus, the content of B ₂ O ₃ is more preferably 10 to 25%, 15 to 23%, or 18 to 22%.

Li ₂ O is an ion exchange component, and particularly a component that ion-exchanges Li ions contained in the glass and K ions in the molten salt to obtain high surface compressive stress. In addition, Li ₂ O is a component that lowers high-temperature viscosity and enhances meltability and moldability. Therefore, the preferable lower limit range of Li ₂ O is 0% or more, 3% or more, 4% or more, 4.2% or more, 5% or more, 5.5% or more, 6.5% or more, 7% or more, 7.3% or more, 7.5% or more, 7.8% or more, especially 8% or more. Further, the preferred upper limit range of Li ₂ O is 20% or less, 15% or less, 13% or less, 12% or less, 11.5% or less, 11% or less, 10.5% or less, less than 10%, 9. 9% or less, 9% or less, particularly 8.9% or less.

Na ₂ O is an ion-exchange component and also a component that lowers high-temperature viscosity and enhances meltability and moldability. Na ₂ O is also a component that improves devitrification resistance and reaction devitrification resistance with molded refractories, particularly alumina refractories. If the content of Na ₂ O is too small, the meltability tends to decrease, the coefficient of thermal expansion tends to decrease too much, and the ion exchange rate tends to decrease. Therefore, the preferable lower limit range of Na ₂ O is 1% or more, 5% or more, 7% or more, 8% or more, 8.5% or more, 9% or more, 9.5% or more, 10% or more, 11% 12% or more, particularly 12.5% or more. On the other hand, if the content of Na ₂ O is too high, the phase separation viscosity tends to decrease. On the other hand, if the content of Na ₂ O is too large, the acid resistance may be lowered, or the component balance of the glass composition may be impaired, resulting in a decrease in devitrification resistance. Therefore, the preferred upper limit range of Na ₂ O is 20% or less, 19.5% or less, 19% or less, 18% or less, 17% or less, 16.5% or less, 16% or less, 15.5% or less, In particular, it is 15% or less.

K ₂ O is a component that lowers high-temperature viscosity and improves meltability and moldability. Furthermore, K ₂ O is also a component that improves devitrification resistance and increases Vickers hardness. However, if the K ₂ O content is too high, the phase separation viscosity tends to decrease. On the other hand, if the K ₂ O content is too high, the acid resistance tends to be lowered, or the component balance of the glass composition is lacking, and rather the devitrification resistance tends to be lowered. Therefore, the preferred lower limit range of K ₂ O is 0% or more, 0.01% or more, 0.02% or more, 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, It is 2% or more, 2.5% or more, 3% or more, particularly 3.5% or more, and the preferable upper limit range of K ₂ O is 10% or less, 5.5% or less, 5% or less, especially 4.5% or less. less than 5%.

Both Li ₂ O and Na ₂ O are components that ion-exchange with K ions in the molten salt to obtain high surface compressive stress. Therefore, the preferred lower limit range of Li ₂ O + Na ₂ O is 1% or more, 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, 11% or more, 12% or more, 13% or more, 14% or more, 15% or more, 16% or more, 17% or more, 18% or more, particularly 18.5% or more. On the other hand, if the content of Li ₂ O+Na ₂ O is too large, the coefficient of thermal expansion becomes too high, and the thermal shock resistance tends to decrease. On the other hand, when the content of Li ₂ O+Na ₂ O is too large, the component balance of the glass composition may be lost, and the devitrification resistance may rather deteriorate. Therefore, the preferred upper limit range of Li ₂ O+Na ₂ O is 20% or less, particularly 19% or less. Here, "Li2O _{+ Na2O} " refers to the _total amount of Li2O and _Na2O .

In addition to the above components, the tempering glass 1 may contain, for example, the following components as a glass composition.

MgO is a component that lowers high-temperature viscosity, improves meltability and formability, and raises the strain point and Young's modulus. Among alkaline earth metal oxides, MgO is a component that is highly effective in enhancing ion exchange performance. be. However, if the MgO content is too high, the density and thermal expansion coefficient tend to increase, and the glass tends to devitrify. Therefore, the preferred upper limit range of MgO is 12% or less, 10% or less, 8% or less, 6% or less, and particularly 5% or less. When MgO is introduced into the glass composition, the preferred lower limit range of MgO is 0.1% or more, 0.5% or more, 1% or more, particularly 2% or more.

Compared to other components, CaO has a large effect of lowering high-temperature viscosity, improving meltability and moldability, and raising strain point and Young's modulus without lowering devitrification resistance. The content of CaO is preferably 0 to 10%. However, if the content of CaO is too high, the density and coefficient of thermal expansion will increase, and the composition of the glass will be unbalanced. Therefore, the preferred content of CaO is 0-5%, 0.01-4%, 0.1-3%, especially 1-2.5%.

SrO is a component that lowers high-temperature viscosity, improves meltability and moldability, and raises strain point and Young's modulus without reducing devitrification resistance. However, if the content of SrO is too high, the density and coefficient of thermal expansion are increased, the ion exchange performance is lowered, and the component balance of the glass composition is lost, so that the glass tends to devitrify. A preferred content range of SrO is 0 to 5%, 0 to 3%, 0 to 1%, especially 0 to less than 0.1%.

BaO is a component that lowers high-temperature viscosity, improves meltability and moldability, and raises strain point and Young's modulus without reducing devitrification resistance. However, if the content of BaO is too high, the density and coefficient of thermal expansion are increased, the ion exchange performance is lowered, and the component balance of the glass composition is lost, so that the glass tends to devitrify. A suitable content range of BaO is 0 to 5%, 0 to 3%, 0 to 1%, especially 0 to less than 0.1%.

ZnO is a component that enhances ion exchange performance, and is particularly effective in increasing compressive stress. ZnO is a component that lowers the high-temperature viscosity without lowering the low-temperature viscosity. However, if the ZnO content is too high, the glass tends to undergo phase separation, the devitrification resistance is lowered, the density is increased, and the stress depth of the compressive stress layer is reduced. Therefore, the content of ZnO is preferably 0 to 6%, 0 to 5%, 0 to 1%, 0 to 0.5%, particularly 0 to less than 0.1%.

ZrO ₂ is a component that remarkably enhances the ion exchange performance and also a component that increases the viscosity near the liquidus viscosity and the strain point. Yes, and can be too dense. Therefore, the preferred upper range of ZrO ₂ is 10% or less, 8% or less, 6% or less, especially 5% or less. If it is desired to increase the ion exchange performance, it is preferable to introduce _{ZrO2 into} the glass composition. % or more, especially 1% or more.

P ₂ O ₅ is a component that enhances the ion exchange performance, and particularly a component that increases the stress depth of the compressive stress layer. Also, P ₂ O ₅ is a component that suppresses the Young's modulus. However, if the content of P ₂ O ₅ is too high, the glass tends to undergo phase separation. Therefore, the preferred upper range of P ₂ O ₅ is 10% or less, 8% or less, 6% or less, 4% or less, 2% or less, 1% or less, especially less than 0.1%.

As a clarifier, one or more selected from the group of As ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , F, Cl and SO ₃ (preferably the group of SnO ₂ , Cl and SO ₃ ) 30000 ppm (3%) may be introduced. The content of SnO ₂ +SO ₃ +Cl is preferably 0 to 10000 ppm, 50 to 5000 ppm, 80 to 4000 ppm, 100 to 3000 ppm, particularly 300 to 3000 ppm, from the viewpoint of receiving an appropriate clarification effect. Here, "SnO ₂ +SO ₃ +Cl" refers to the total amount of SnO ₂ , SO ₃ and Cl.

Preferred content ranges for SnO ₂ are 0-10000 ppm, 0-7000 ppm, especially 50-6000 ppm. Preferred content ranges for SO ₃ are 0-1000 ppm, 0-800 ppm, especially 10-500 ppm. Preferred Cl content ranges are 0 to 1500 ppm, 0 to 1200 ppm, 0 to 800 ppm, 0 to 500 ppm, particularly 50 to 300 ppm.

Rare earth oxides such as Nd ₂ O ₃ and La ₂ O ₃ are components that increase the Young's modulus, and are components that can control the tint of the glass by decolorizing when a complementary color is added. However, rare earth oxides are expensive as raw materials, and when introduced in large amounts, the devitrification resistance tends to decrease. Therefore, the content of rare earth oxides is preferably 4% or less, 3% or less, 2% or less, 1% or less, especially 0.5% or less.

In the present invention, it is preferred that substantially no As ₂ O ₃ , F, PbO, and Bi ₂ O ₃ are contained from the viewpoint of environmental considerations. Here, “substantially free of As ₂ O ₃ ” means that although As ₂ O ₃ is not actively added as a glass component, it is allowed to be mixed in at an impurity level. , the content of As ₂ O ₃ is less than 500 ppm. "Substantially free of F" means that F is not actively added as a glass component, but is allowed to be mixed in at an impurity level. Specifically, the F content is less than 500 ppm. pointing to something "Substantially free of PbO" means that PbO is not actively added as a glass component, but is allowed to be mixed in at an impurity level. Specifically, the PbO content is less than 500 ppm. pointing to something "Substantially free of _Bi2O3 " means that although _Bi2O3 is not _actively added as a glass component _, it is allowed to be mixed in at an _impurity level. It means that the content of _O3 is less than 500ppm.

The composition of the tempering glass 1 is an example, and any composition of glass can be used as long as it contains an ion-exchangeable component. The glass for strengthening in the present invention includes glass articles in a broad sense including vitreous, for example, glass ceramics including both crystalline and vitreous (or referred to as crystallized glass). .

The strain point of the tempering glass 1 varies depending on the glass composition, so it is not particularly limited, but is, for example, 500 to 650.degree. Here, let the strain point of the glass for reinforcement 1 be the value measured based on ASTM C336.

The heat treatment step S2 is a step of regenerating the heterogeneous layer by subjecting the tempering glass 1 to a heat treatment. As shown in FIG. 3, the heat treatment step S2 includes a temperature raising step S21 for raising the temperature of the tempering glass 1 from around room temperature to a holding temperature P, and heating the tempering glass 1 at the holding temperature P for a predetermined holding time Q. A holding step S22 for holding and a temperature lowering step S23 for lowering the temperature of the tempering glass 1 from the holding temperature to around room temperature are provided in this order. The heat treatment step S2 can be performed using a batch-type or continuous-type heating furnace.

The heating rate in the temperature raising step S21 is, for example, 10 to 1000° C./min. Also, the temperature lowering rate in the temperature lowering step S23 is, for example, 10 to 1000° C./min. The temperature increase rate in the temperature increase step S21 and the temperature decrease rate in the temperature decrease step S23 are not particularly limited as long as the heat treatment conditions in the holding step S22 are satisfied.

The holding temperature P in the holding step S22 is the strain point of −15° C. or higher of the tempering glass 1, and the holding time Q in the holding step S22 is 3 minutes or longer. According to the heat treatment step S2 including the holding step S22, the heterogeneous layer 6 is reproduced on the first main surface 2 of the tempering glass 1, as shown in FIG. That is, the heterogeneous layers 4 and 6 having approximately the same thickness can be formed again on the surface layer portions 2a and 3a of the first main surface 2 and the second main surface 3 of the tempering glass 1, respectively.

In the holding step S22, from the viewpoint of suppressing unintended deformation of the tempering glass 1, it is preferable that the holding temperature P is +50° C. or lower than the strain point and the holding time Q is 10 minutes or longer. In this case, the retention time Q is more preferably 30 minutes or longer. Of course, even in this case, the retention time Q should be 3 minutes or longer.

In the holding step S22, from the viewpoint of efficiently reproducing the heterogeneous layer 6, the holding temperature P is preferably equal to or higher than the strain point +85°C. In this case, the holding time Q is preferably 3 minutes or more, 10 minutes or more, especially 30 minutes or more.

In the holding step S22, the holding time Q is preferably 60 minutes or less from the viewpoint of improving production efficiency.

The chemical strengthening step S3 is a step of chemically strengthening the tempering glass 1 by ion exchange treatment to obtain tempered glass. The tempering glass 1 is treated by being immersed in molten salt for ion exchange treatment, for example.

The molten salt is a salt containing a component ion-exchangeable with the component in the tempering glass 1, and is typically an alkali nitrate. Alkaline nitrates include NaNO ₃ , KNO ₃ , LiNO ₃ and the like, and these can be used alone (at 100% by mass) or in combination. When a plurality of types of _{alkali nitrates are} mixed _, the mixing ratio may be arbitrarily determined. 20-70%, more preferably 50-70% NaNO ₃ and 30-50% KNO ₃ .

Conditions such as the temperature of the molten salt and the immersion time may be set according to the glass composition and the like within the range where desired stress characteristics can be obtained. 355°C to 470°C, 360°C to 450°C, 365°C to 430°C, especially 370°C to 410°C. Also, the immersion time is, for example, 3 to 300 minutes, preferably 5 to 120 minutes, more preferably 7 to 100 minutes.

In addition, the chemical strengthening step S3 may include a preheating step of preheating the tempering glass 1 in order to suppress breakage of the tempering glass 1 due to thermal shock during tempering. In this case, the heat treatment step S2 may be performed as part of the preheating step. In addition, when the production efficiency is rather lowered by changing the existing process, it is preferable to perform the preheating process and the heat treatment process S2 independently as described above. In this case, after the heat treatment step S2 and before the preheating step, the temperature of the tempering glass 1 may be once lowered to room temperature (0 to 50° C.).

After the chemical strengthening step S3, the tempered glass is preferably washed and dried. In addition, the tempered glass is preferably protected by attaching a protective film to its surface. As the protective film, it is preferable to use a self-adhesive film or a slightly adhesive film.

In the tempered glass manufacturing method as described above, the heterogeneous layer 6 is also reproduced on the surface layer portion 2a of the first main surface 2 of the tempered glass 1 by the heat treatment in the heat treatment step S2. That is, the heterogeneous layers 4 and 6 having approximately the same thickness are formed on the surface layer portions 2a and 3a of the first main surface 2 and the second main surface 3 of the tempering glass 1, respectively. Therefore, if the tempering glass 1 is chemically tempered in the subsequent chemical strengthening step S3, it is possible to obtain tempered glass having high compressive stress on both main surfaces and having a small warp.

(Second embodiment)
As shown in FIG. 5, the second embodiment of the present invention illustrates a method for manufacturing tempered glass.

As shown in the figure, the method for manufacturing tempered glass according to the present embodiment includes a forming step T1, a slow cooling step T2, a cooling step T3, a cutting step T4, a removing step T5, a heat treatment step T6, A chemical strengthening step T7 is provided in this order. The forming step T1, the slow cooling step T2, the cooling step T3, the cutting step T4, and the removing step T5 correspond to the preparatory step S1 of the first embodiment. Note that the preparation step S1 of the first embodiment is not limited to these steps T1 to T5. The preparation step S1 may be, for example, a step of performing only some of these steps (for example, the removal step T5).

The forming step T1 is a step of forming the tempering glass 1 (strictly speaking, a glass ribbon) using the overflow down-draw method in this embodiment. The method for forming the tempering glass 1 is not limited to this, and may be another down-draw method such as a slot down-draw method, or a known forming method such as a float method.

The slow cooling step T2 is a step of slowly cooling the tempering glass 1 at a cooling rate of 0.5° C./s or more immediately after molding. Here, "immediately after molding" means a high-temperature state before the molded tempering glass 1 is cooled to around room temperature. In other words, the slow cooling step T2 is different from the heat treatment of reheating the tempering glass 1 once cooled to around room temperature.

The cooling step T3 is a step of cooling the tempering glass 1 to around room temperature.

In this embodiment, the manufacturing apparatus 11 shown in FIG. 6 is used in the forming process T1, the slow cooling process T2, and the cooling process T3. The manufacturing apparatus 11 includes a forming zone 14 for continuously forming the glass ribbon 13 from the molten glass 12, a slow cooling zone 15 for slowly cooling the glass ribbon 13, a cooling zone 16 for cooling the glass ribbon 13 to near room temperature, and a forming zone. 14, the gradual cooling zone 15 and the cooling zone 16 are each provided with roller pairs 17 provided in a plurality of upper and lower stages. In the forming zone 14, the forming process T1 is performed, in the slow cooling zone 15, the slow cooling process T2 is performed, and in the cooling zone 16, the cooling process T3 is performed.

The forming zone 14 and the slow cooling zone 15 are constituted by a furnace in which the conveying path of the glass ribbon 13 is surrounded by walls, and a heating device such as a heater for adjusting the temperature of the glass ribbon 13 is installed at an appropriate place in the furnace. are placed in On the other hand, in the cooling zone 16, the circumference of the conveying path of the glass ribbon 13 is open to the ambient temperature outside atmosphere without being surrounded by walls, and a heating device such as a heater is not arranged. A desired heat history is imparted to the glass ribbon 13 by passing through the slow cooling zone 15 and the cooling zone 16 .

A molded body 18 for molding the glass ribbon 13 from the molten glass 12 by the overflow downdraw method is arranged in the inner space of the molding zone 14 . In the molding step T1, the molten glass 12 supplied to the molded body 18 overflows from a groove (not shown) formed in the top portion 18a of the molded body 18 in the internal space of the molding zone 14. The extruded molten glass 12 travels along both side surfaces 18b of the molded body 18 having a wedge-shaped cross section and merges at the lower end 18c, whereby the plate-like glass ribbon 13 is continuously molded. The molded glass ribbon 13 is conveyed downward while maintaining its vertical posture.

The internal space of the slow cooling zone 15 has a predetermined temperature gradient downward. In the slow cooling step T2, the vertical glass ribbon 13 is moved downward in the internal space of the slow cooling zone 15, so that the glass ribbon 13 is slowly cooled at a cooling rate of 0.5° C./s or more. The cooling rate during slow cooling is preferably 1° C./s or more, 2° C./s or more, 3.5° C./s or more, 4° C./s or more, particularly 5° C./s or more. Also, the cooling rate during slow cooling is preferably 20° C./s or less, 15° C./s or less, particularly 12° C./s or less. Such a slow cooling step T<b>2 suppresses the internal strain of the glass ribbon 13 and forms heterogeneous layers on both main surfaces of the glass ribbon 13 . The temperature gradient in the internal space of the slow cooling zone 15 can be adjusted, for example, by a heating device provided on the inner surface of the wall of the slow cooling zone 15 .

A plurality of roller pairs 17 sandwich both widthwise end portions of the vertically oriented glass ribbon 13 from both the front and back sides. The uppermost roller pair 17 located in the forming zone 14 are chill rollers, sometimes referred to as edge rollers. In addition, in the inner space of the slow cooling zone 15 or the like, the plurality of roller pairs 17 may include those that do not sandwich the width direction end portions of the glass ribbon 13 . That is, the interval between the roller pairs 17 facing each other may be made larger than the thickness of both widthwise end portions of the glass ribbon 13 so that the glass ribbon 13 passes between the roller pairs 17 .

In the present embodiment, both ends in the width direction of the glass ribbon 13 obtained by the manufacturing apparatus 11 have a larger plate thickness than the central portion in the width direction due to the effects of shrinkage during the molding process (hereinafter referred to as "edges"). ”).

The cutting step T4 is a step of cutting the glass ribbon 13 that has undergone the forming step T1, the slow cooling step T2, and the cooling step T3 to obtain the tempering glass 21 shown in FIG. Specifically, in the cutting step T4, for example, (1) after cutting the glass ribbon 13 to obtain a large plate-shaped mother glass, the mother glass is cut to obtain the tempering glass 21; 2) In some cases, the glass ribbon 13 is wound into a roll to obtain a glass roll, and then the glass ribbon 13 unwound from the glass roll is cut to obtain the tempering glass 21 .

As shown in FIG. 7, the surface layers 22a and 23a of the first main surface 22 and the second main surface 23 of the tempering glass 21 obtained through the cutting step T4 have heterogeneity caused by the slow cooling step T2. Layers 24 and 25 are formed.

As shown in FIG. 8, the removing step T5 is a step of removing only the surface layer portion 23a of the first main surface 22 of the first main surface 22 and the second main surface 23 of the tempering glass 21. As shown in FIG. That is, the thickness D1 of the tempering glass 21 after the removing step T5 is thinner than the thickness D0 of the tempering glass 21 before the removing step T5 (cutting step T4) by the removal thickness ΔD. ΔD is preferably 1-50 μm, 2-40 μm, especially 3-30 μm. In addition, if the removed thickness of the second main surface 23 is smaller than the removed thickness of the first main surface 22, the surface layer portions 22a and 23a of the first main surface 22 and the second main surface 23 may be removed. . Part or all of the foreign layer 24 on the side of the first main surface 22 is removed by such a removing step T5, and the thickness of the foreign layer 25 on the side of the second main surface 23 is reduced to the thickness of the foreign layer on the first main surface 22 side. 24 thickness (including zero). The removing step T5 is performed, for example, as part of processing the end surface of the tempering glass 21 into a special shape such as a so-called 2.5D shape in which the end surface is obliquely inclined.

A method for removing the surface layer of the reinforcing glass 21 is not particularly limited, but examples thereof include chemical polishing such as etching, mechanical polishing such as abrasive grain polishing, and chemical mechanical polishing (CMP). In this embodiment, etching is used as a method for removing the surface layer of the tempering glass 21 .

When mechanical polishing is used, for example, water-resistant abrasive paper to which #1000 alumina abrasive grains are adhered is slid on the first main surface 22 of the tempering glass 21 while adding water. After that, chemical mechanical polishing may be performed using cerium oxide powder.

When etching is used, for example, in a state in which a protective film is formed on the second main surface 23 of the tempering glass 21, the entire tempering glass 21 is immersed in a liquid etchant to wet-etch the tempering glass 21. As the protective film, in addition to an anti-etching film that completely prevents the second main surface 23 from being removed by etching, an etching rate that makes the etching rate of the second main surface 23 slower than the etching rate of the first main surface 22 is used. Retardant membranes can be used. The protective film is peeled off from the tempering glass 21 after the etching is completed.

As the etchant, an acidic or alkaline aqueous solution capable of etching glass can be used.

As an acidic etchant, for example, an acidic aqueous solution containing HF can be used. When an aqueous solution containing HF is used, the etching rate for glass is high and the productivity is improved.

The aqueous solution containing HF is, for example, an aqueous solution containing only HF or a combination of HF and HCl, HF and HNO ₃ , HF and H ₂ SO ₄ , or HF and NH ₄ F. The concentration of each compound of HF, HCL, HNO ₃ , H ₂ SO ₄ and NH ₄ F is preferably 0.1-30 mol/L. _In etching using an aqueous solution containing HF _, a fluoride containing a glass component is produced as a by _- product, which may cause a decrease in the etching rate or cause defects. By using a mixed acid with other acids, the by-product can be decomposed to suppress a decrease in productivity. When etching is performed using an acidic aqueous solution, it is preferable that the temperature of the acidic aqueous solution is, for example, 10 to 30.degree.

As an alkaline etching medium, an alkaline aqueous solution containing NaOH or KOH can be used. Since the alkaline aqueous solution has a relatively low etching rate for glass as compared with the above etching medium containing HF, it has the advantage of facilitating precise control of the etching amount.

The concentration of the alkaline component in the aqueous solution containing NaOH or KOH is preferably 1-20 mol/L. When etching is performed using an alkaline aqueous solution, it is preferable that the temperature of the alkaline aqueous solution is, for example, 10 to 130.degree. In addition, when increasing the etching rate to improve the productivity, it is preferable to heat the temperature of the alkaline aqueous solution to 80° C. or higher. Conversely, if it is desired to control the etching amount with higher accuracy, it is preferable to limit the temperature of the alkaline aqueous solution to 70° C. or lower. Further, when the magnitude of the etching rate is more important, it is preferable to use an aqueous solution of NaOH.

The etching may be performed by applying or spraying an etchant onto the first main surface 22 of the tempering glass 21 .

The heat treatment step T6 is a step of regenerating the heterogeneous layer by subjecting the tempering glass 21 to a heat treatment. Specifically, this is a step of heat-treating the tempering glass 21 by holding it at a strain point of −15° C. or higher for 3 minutes or longer, and the details are the same as the heat-treating step S2 of the first embodiment. According to the heat treatment step T6, the foreign layer 24 is reproduced on the first main surface 22 of the tempering glass 21, as shown in FIG. That is, the heterogeneous layers 24 and 25 having approximately the same thickness can be formed again on the surface layer portions 22a and 23a of the first main surface 22 and the second main surface 23 of the tempering glass 21, respectively.

The chemical strengthening step T7 is a step of chemically strengthening the tempering glass 21 by ion exchange treatment to obtain tempered glass, and the details are the same as the chemical strengthening step S3 of the first embodiment. If the chemical strengthening step T7 is performed after the heat treatment step T6, it is possible to obtain a tempered glass having a small warp while achieving high compressive stress on both main surfaces.

(Third embodiment)
As shown in FIG. 10, in the third embodiment of the present invention, tempered glass manufactured by the tempered glass manufacturing method described in the first embodiment or the second embodiment is exemplified.

As shown in the figure, the tempered glass 31 has a first compressive stress layer 33 on the surface layer 32a of the first main surface 32 and a second compressive stress layer 35 on the surface layer 34a of the second main surface 34. . The tempered glass 31 also has a tensile stress layer 37 in the inner layer 36 between the compressive stress layers 33 , 35 . The tempered glass 31 may have a compressive stress layer on the surface layer portion of the end surface connecting the first main surface 32 and the second main surface 34 .

The first major surface 32 comprises a polished surface and the second major surface 34 comprises an unpolished surface. The second major surface 34 is the as-fired surface formed by the overflow downdraw method. That is, the surface roughness Ra1 of the first main surface 32 composed of the polished surface is larger than the surface roughness Ra2 of the second main surface 34 composed of the unpolished surface. The surface roughness Ra1 of the first main surface 32 is 0.1 nm to 2.0 nm, preferably 0.1 nm to 1.0 nm, especially 0.1 nm to 0.5 nm. The surface roughness Ra2 of the second main surface 34 is 0.1 nm to 1.0 nm, preferably 0.1 nm to 0.5 nm, especially 0.1 nm to 0.2 nm. The absolute value of the difference between the surface roughness Ra1 of the first main surface 32 and the surface roughness Ra2 of the second main surface 34 is 0.1 nm or more, preferably 0.1 nm to 1.0 nm, particularly 0.1 nm. ~0.5 nm. Here, "surface roughness Ra (Ra1 and Ra2)" refers to a value measured by a method conforming to JIS B0601:2001. In addition, both the first main surface 32 and the second main surface 34 may be composed of polished surfaces.

The compressive stress CS1 of the first compressive stress layer 33 and the compressive stress CS2 of the second compressive stress layer 35 are respectively 820 MPa or more, preferably 830 MPa, 840 MPa, particularly 850 MPa. However, the compressive stress CS1 of the first compressive stress layer 33 on the side of the first main surface 32, which is the polished surface, is smaller than the compressive stress CS2 of the second compressive stress layer 35 on the side of the second main surface 34, which is the unpolished surface. Tend. The absolute value of the difference (CS1-CS2) between the compressive stress CS1 of the first compressive stress layer 33 and the second compressive stress CS2 of the second compressive stress layer 35 is 40 MPa or less, preferably 30 MPa or less, 20 MPa or less, especially 10 MPa or less. CS1/CS2 is preferably 95% or more and 105% or less. Moreover, each of the stress depth DOL1 of the first compressive stress layer 33 and the stress depth DOL2 of the second compressive stress layer 35 is 1 to 100 μm, preferably 10 to 90 μm, 20 to 80 μm, particularly 30 μm. ˜70 μm. The absolute value of the difference (DOL1−DOL2) between the stress depth DOL1 of the first compressive stress layer 33 and the stress depth DOL2 of the second compressive stress layer 35 is 10 μm or less, preferably 5 μm or less, 3 μm or less, especially It is 1 μm or less. Here, "compressive stress CS (CS1 and CS2)" and "stress depth DOL (DOL1 and DOL2)" are measured using a surface stress meter (eg, FSM-6000 manufactured by Orihara Seisakusho Co., Ltd.), the number of interference fringes and the interval between them.

The tempered glass 31 has a flat plate shape. The warp of the tempered glass 31 is preferably 250 μm or less, more preferably 200 μm or less, and particularly preferably 10 to 150 μm or less.

Although the tempered glass and the manufacturing method thereof according to the embodiment of the present invention have been described, the embodiment of the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention. is possible.

In the above-described embodiment, the case where the tempered glass has a rectangular shape (rectangular or square) in plan view is exemplified, but the shape of the tempered glass is not particularly limited. It can be of any shape, such as a shape.

In the above embodiment, the case of producing tempered glass by one ion exchange treatment was exemplified, but tempered glass may be produced by two or three or more ion exchange treatments.

The tempered glass according to the above embodiments can be used as a laminate by laminating an arbitrary plate-shaped or sheet-shaped resin material, or a transparent material such as a metal material or glass with an adhesive or the like.

EXAMPLES Examples according to the present invention will be described below, but the present invention is not limited to these examples.

As a tempering glass, SiO ₂ 66.4%, Al ₂ O ₃ 11.5%, B ₂ O ₃ 0.5%, K ₂ O 1.4%, Na ₂ O 15.0%, as a glass composition in terms of mol %. A glass plate containing 2% Li ₂ O, 0.02% Li 2 O, 4.8% MgO, 0.1% CaO, and 0.1% SnO ₂ (strain point: 564° C.) was prepared. The tempering glass of this example is a glass plate molded by the overflow down-draw method, and the cooling rate during slow cooling immediately after molding is 5° C./s. The size of the tempered glass is 50 mm in length and width, and 0.7 mm in thickness.

Of the first main surface and the second main surface of this tempered glass, only the first main surface was removed by 50 μm by mechanical polishing and chemical mechanical polishing, and heat treatment was performed while changing the holding temperature and holding time to obtain each sample ( Examples 1 to 6 and Comparative Examples 1 to 4) were prepared. Note that the sample according to Comparative Example 4 was not subjected to heat treatment after single-sided polishing. The surface roughness Ra1 of the first main surface composed of the polished surface is 0.40 nm, and the surface roughness Ra2 of the second main surface composed of the unpolished surface is 0.17 nm. Here, "Ra1" and "Ra2" refer to values measured by a method conforming to JIS B0601:2001.

Each sample prepared is chemically strengthened (molten salt: KNO ₃ , treatment temperature: 430° C., treatment time: 4 hours) to form a first compressive stress layer on the first main surface of each sample, and the second main surface A second compressive stress layer was formed on the Then, for each sample, the compressive stress CS1 and stress depth DOL1 of the first compressive stress layer were measured, and the compressive stress CS2 and stress depth DOL2 of the second compressive stress layer were measured. Also, from these measurements, CS2-CS1 and CS1/CS2 were calculated for each sample. Table 1 shows the results. Here, "CS1", "CS2", "DOL1" and "DOL2" refer to values measured using FSM-6000 manufactured by Orihara Seisakusho Co., Ltd.

In Comparative Examples 1 to 3 in which the holding temperature is less than −15° C. (450° C.) at the strain point, and in Comparative Example 4 in which no heat treatment is performed, the CS1 of the first main surface, which is the polished surface, is less than 820 MPa, and both main surfaces. It was not possible to produce a tempered glass with a high CS. From this, it can be confirmed that in Comparative Examples 1 to 4, there is no heterogeneous layer on the first main surface of the tempered glass, or the regenerated glass is not sufficiently regenerated.

On the other hand, in Examples 1 to 6, in which the holding temperature is -15 ° C. or higher (550 ° C.) and the holding time is 3 minutes or longer, the CS is 820 MPa or more even on the first main surface, which is the polished surface, and both A tempered glass having a high CS on the main surface could be produced. From this, it can be confirmed that in Examples 1 to 6, the heterogeneous layer was sufficiently reproduced on the first main surface of the tempered glass. In particular, Examples 1 to 3 in which the holding temperature is +85 ° C. (650 ° C.) or more and the holding time is 3 minutes or more, and Examples in which the holding temperature is +50 ° C. or less (550 ° C.) and the holding time is 10 minutes or more. In 5 to 6, the CS1/CS2 (front and back CS ratio) was 96% or more, and a good result was obtained that a tempered glass with a particularly small CS2-CS1 (front and back CS difference) could be produced.

In Comparative Example 4, the warp was about 100 μm before strengthening, but increased to about 300 μm after strengthening. In contrast, in any of Examples 1 to 6, the warpage after strengthening could be suppressed to 250 μm or less. Here, "warp" refers to a value measured using a laser displacement gauge type warp measuring device manufactured by Apollo.

The tempered glass of the present invention can be used, for example, for mobile phones (especially smartphones), tablet computers, personal computers, digital cameras, touch panel displays, cover glasses for other display devices, vehicle-mounted display devices, vehicle-mounted panels, and the like.

1 tempering glass 2 first major surface 3 second major surfaces 4, 6 foreign layer 21 tempering glass 22 first major surface 23 second major surfaces 24, 25 foreign layer 31 tempered glass 32 first major surface 33 first compression Stress layer 34 Second main surface 35 Second compressive stress layer 37 Tensile stress layer S1 Preparation step S2 Heat treatment step S3 Chemical strengthening step T1 Forming step T2 Slow cooling step T3 Cooling step T4 Cutting step T5 Removal step T6 Heat treatment step T7 Chemical strengthening step

Claims (12)

a forming step of forming a tempered glass having a first major surface and a second major surface opposite to the first major surface;
a slow cooling step of slowly cooling the tempering glass at a cooling rate of 0.5° C./s or more immediately after molding;
a removing step of removing a surface layer portion of the first main surface of the tempering glass;
A heat treatment step of heat-treating the tempering glass by holding it at a holding temperature of −15° C. or higher at the strain point for 3 minutes or more;
and a chemical strengthening step of chemically strengthening the tempering glass by ion exchange treatment to obtain tempered glass. The method for producing tempered glass according to claim 1, wherein in the removing step, only the surface layer portion of the first main surface is removed from the first main surface and the second main surface. a preparing step of preparing a tempering glass having a first main surface and a second main surface located opposite to the first main surface, and having a heterogeneous layer on a surface layer portion of the second main surface;
A heat treatment step of heat-treating the tempering glass by holding it at a holding temperature of −15° C. or higher at the strain point for 3 minutes or more;
and a chemical strengthening step of chemically strengthening the tempering glass by ion exchange treatment to obtain tempered glass. 4. The method for producing tempered glass according to claim 3, wherein the heterogeneous layer in the preparation step is formed by slowly cooling the tempering glass at a cooling rate of 0.5[deg.] C./s or more during the molding process. The method for producing tempered glass according to any one of claims 1 to 4, wherein the tempered glass is formed by an overflow down-draw method or a slot down-draw method. The method for producing tempered glass according to any one of claims 1 to 5, wherein in the heat treatment step, the holding temperature is +50 ° C. or less at the strain point, and the holding time at the holding temperature is 10 minutes or more. The method for producing tempered glass according to any one of claims 1 to 5, wherein in the heat treatment step, the holding temperature is a strain point +85°C or higher. The method for producing tempered glass according to any one of claims 1 to 7, wherein in the heat treatment step, the holding time at the holding temperature is 60 minutes or less. 9. The method of claims 1 to 8, wherein the tempered glass obtained in the chemical strengthening step has an absolute value of a difference between the compressive stress CS1 on the first main surface and the compressive stress CS2 on the second main surface of 40 MPa or less. A method for producing a tempered glass according to any one of items 1 to 3. The method for producing tempered glass according to any one of claims 1 to 9, wherein the tempered glass is sheet glass having a thickness of 0.3 mm or less. The tempering glass has a glass composition of SiO ₂ 50 to 80%, Al ₂ O ₃ 5 to 25%, B ₂ O ₃ 0 to 35%, Li ₂ O 0 to 20%, and Na ₂ O in mol%. The method for producing tempered glass according to any one of claims 1 to 10, containing 1 to 20%, Li ₂ O + Na ₂ O 1 to 20%, and K ₂ O 0 to 10%. A tempered glass having a first compressive stress layer on the surface layer portion of the first main surface and a second compressive stress layer on the surface layer portion of the second main surface opposite to the first main surface,
The absolute value of the difference between the surface roughness Ra1 of the first main surface and the surface roughness Ra2 of the second main surface is 0.1 nm or more,
Each of the compressive stress CS1 of the first compressive stress layer and the compressive stress CS2 of the second compressive stress layer is 820 MPa or more, and the compressive stress CS1 of the first compressive stress layer and the compressive stress CS2 of the second compressive stress layer Tempered glass having an absolute value of difference from compressive stress CS2 of 40 MPa or less.

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