TW202413305A - Method for producing strengthened glass, and ion-exchange liquid - Google Patents

Abstract

A method for producing strengthened glass comprising a step in which a glass 1 to be strengthened that contains an alkali metal component is brought into contact with an ion-exchange liquid 2 and is thereby subjected to an ion-exchange treatment. The ion-exchange liquid 2 comprises a molten salt 2a and a boron compound 2b as a pH regulator.

Description

Method for manufacturing strengthened glass and ion exchange fluid

The present invention relates to a method for manufacturing strengthened glass and an ion exchange liquid.

In recent years, tempered glass has been widely used in cover glasses of various electronic terminals, display devices, etc. Tempered glass includes a compressive stress layer formed by ion exchange treatment on the surface layer, and has a high surface strength that can inhibit the formation and development of cracks in the surface.

In the ion exchange treatment, the strengthening glass is immersed in an ion exchange liquid containing a molten salt, and alkali ions with a small ion radius in the strengthening glass are ion exchanged with alkali ions with a large ion radius in the molten salt, thereby forming a compressive stress layer on the surface of the strengthening glass. In this case, as the molten salt, for example, a molten salt containing NaNO ₃ is used.

In addition, in the ion exchange treatment, the strengthening glass is sometimes immersed in an ion exchange liquid containing a molten salt, and the alkali ions with a large ion radius in the strengthening glass are reversely ion exchanged with the alkali ions with a small ion radius in the molten salt, thereby relieving the compressive stress of the compressive stress layer formed on the surface of the strengthening glass (for example, refer to Patent Document 1). The reverse ion exchange is performed separately from the ion exchange or simultaneously with the ion exchange. In this case, as the molten salt, for example, a molten salt containing LiNO ₃ is used.

From the perspective of mass production, it is common to use this ion exchange solution repeatedly for multiple strengthening glasses. However, if the ion exchange solution is used at high temperature for a long time, it may deteriorate as the pH value rises.

Patent document 2 states that when an ion exchange treatment is performed using such a deteriorated ion exchange solution, the precipitate caused by ^OH- in the ion exchange solution causes a white hazy appearance defect in which the transparency of the strengthened glass is reduced. In the same document, in order to suppress the occurrence of such a white hazy appearance defect, silicic acid is added to the ion exchange solution containing a molten salt to reduce the pH value of the ion exchange solution. [Prior art document] [Patent document]

[Patent document 1] International Publication No. 2020/075709 [Patent document 2] Japanese Patent Publication No. 2021-59481

[The problem that the invention wants to solve]

The solubility of silicate in water described in Patent Document 2 is low. Therefore, if silicate added to the ion exchange liquid adheres to the surface of the strengthened glass, it is difficult to remove it by washing. As a result, surface defects caused by silicate may occur in the strengthened glass.

In addition, the inventors of the present application have conducted diligent research and have found that, when an ion exchange treatment is performed using an ion exchange solution that deteriorates as the pH value increases, the surface strength of the strengthened glass may decrease even if the white haze appearance defect does not occur. The reason for this is believed to be that OH ^- in the ion exchange solution partially corrodes the surface of the strengthened glass to produce surface roughness. Therefore, regardless of whether the white haze appearance defect occurs or not, it is necessary to reliably suppress the increase in the pH value of the ion exchange solution.

The subject of the present invention is to manufacture reinforced glass with few surface defects and high surface strength while reliably suppressing the increase in the pH value of the ion exchange liquid. [Means for solving the problem]

(1) The present invention, which was first developed to solve the above-mentioned problem, is a method for producing strengthened glass, which includes the step of bringing an ion exchange liquid into contact with a strengthening glass containing an alkali metal component to perform an ion exchange treatment on the strengthening glass. The method for producing strengthened glass is characterized in that the ion exchange liquid contains a molten salt and a pH adjuster, and the pH adjuster is a boron compound.

In this way, even if the pH value of the ion exchange liquid increases, the pH value of the ion exchange liquid can be reliably lowered by the pH adjuster containing the boron compound. In this way, the reduction in the surface strength of the manufactured strengthened glass can be suppressed. In addition, if the pH adjuster is a boron compound, it has high solubility in water, so even if the pH adjuster adheres to the strengthened glass, it can be easily removed by washing. In other words, it is not easy to cause surface defects in the strengthened glass due to the pH adjuster.

(2) In the structure of (1), the pH adjuster preferably contains at least one of B ₂ O ₃ and B(OH) ₃ as the boron compound.

In this way, the pH adjuster is stable in the ion exchange solution, so that unnecessary reactions are less likely to occur. In addition, the solubility of the pH adjuster in water becomes good.

(3) In the structure of (1) or (2), preferably, the content of the pH adjuster in the ion exchange liquid is 0.1 to 10 parts by mass, based on 100 parts by mass of the molten salt.

When the pH adjuster is a boron compound, even such a small amount can actually lower the pH of the ion exchange fluid.

(4) In the structure of any one of (1) to (3) above, the pH value of a 20 mass % aqueous solution prepared by mixing the ion exchange liquid with water is preferably 8 or less.

If so, it is possible to more reliably suppress a decrease in the surface strength of the strengthened glass.

(5) In the structure of any one of (1) to (4), the content of the pH adjuster in the ion exchange liquid is preferably adjusted so that the surface roughness Sa of the strengthened glass becomes 3.0 nm or less.

If so, it is possible to more reliably suppress a decrease in the surface strength of the strengthened glass.

(6) In the structure of any one of (1) to (5) above, the pH adjuster is preferably contained in the ion exchange liquid in the form of a powder or a powder aggregate.

If so, the handling of the pH adjuster becomes easy.

(7) In the structure of (6), the ion exchange treatment is preferably performed by arranging an ion exchange liquid and a strengthening glass in an ion exchange tank, and the pH adjuster is arranged in the ion exchange tank in a state of being isolated from the strengthening glass by an isolation member that can pass through the ion exchange liquid.

In this way, it is possible to suppress the unreacted pH adjuster from being attached to the strengthening glass (or the strengthening glass) and being carried out of the ion exchange tank.

(8) In the structure of (7), the pH adjuster is preferably disposed at the bottom layer of the ion exchange tank via a separation member.

The boron compound used as a pH adjuster has a low density and floats in the ion exchange solution. However, if an isolation member is used, it can be sunk to the bottom layer of the ion exchange tank in advance. As a result, it is easy to maintain the state of isolation between the boron compound and the strengthening glass. In addition, a part of the boron compound that passes through the isolation member is dispersed in the ion exchange solution during the process of rising in the ion exchange solution due to buoyancy. Therefore, the pH value of the entire ion exchange solution can be efficiently lowered.

(9) In the structure of any one of (1) to (8), the molten salt preferably contains at least one of LiNO ₃ and NaNO ₃ .

The molten salt containing at least one of LiNO ₃ and NaNO ₃ is prone to undergo a decomposition reaction of the molten salt, and the pH value of the ion exchange liquid caused by the decomposition reaction is prone to rise. In particular, the temperature at which LiNO ₃ undergoes a decomposition reaction is low, so it is easy to produce an increase in pH. Therefore, for such a molten salt, it is particularly useful to use a pH adjuster containing a boron compound.

(10) In the structure of (9), it is preferred that the molten salt substantially does not contain KNO ₃ .

The molten salt containing KNO ₃ is less likely to undergo a decomposition reaction of the molten salt, and the pH value of the ion exchange solution caused by the decomposition reaction is less likely to increase. Therefore, for a molten salt containing at least one of LiNO ₃ and NaNO ₃ and substantially containing no KNO ₃ , it is particularly useful to use a pH adjuster containing a boron compound.

(11) In the structure of (9) or (10), it is preferred that the method comprises the step of performing a two-stage ion exchange treatment, and the ion exchange solution is used in the first stage of the ion exchange treatment.

In this way, a deep compressive stress layer can be formed on the strengthening glass in the first stage ion exchange treatment while suppressing the increase in the pH value of the ion exchange solution in the first stage, and a high surface compressive stress can be applied in the second stage ion exchange treatment.

(12) In the structure of any one of (1) to (11) above, the strengthening glass is preferably an alkali aluminosilicate glass containing 1 mol % or more of Li ₂ O as a glass composition.

If so, a two-stage ion exchange treatment is performed, and it is easy to achieve a high surface compressive stress while forming a compressive stress layer to a deep position. On the other hand, during the ion exchange treatment, Li ions are dissolved from the strengthening glass, and the Li ion concentration in the ion exchange solution increases. In this way, if the Li ion concentration increases, it is possible to hinder the progress of the ion exchange treatment. If the pH adjuster contains a boron compound, the Li ions in the ion exchange solution can also be adsorbed during the reaction process of lowering the pH value of the ion exchange solution. Therefore, even if a lithium adsorbing material that adsorbs Li ions is added separately from the pH adjuster, there is an effect of reducing the Li ion concentration in the ion exchange solution and maintaining the progress of ion exchange well.

(13) In the structure of (12), the strengthening glass preferably contains, in mol%, 40% to 80% _SiO2 , 1% to 30% _Al2O3 , 0% to _{10% B2O3 ,} 0% to 10% MgO, ₁ % to 28% _Li2O , 1% to 25% _Na2O , 0% to 10% _K2O , 0% to 10% _P2O5 , _and 0% to 10% _ZrO2 as a glass composition.

(14) In the structure of any one of (1) to (13), it is preferred that the method further comprises: a step of measuring the pH value of the ion exchange solution; and a step of adding a pH adjuster to the ion exchange solution based on the pH measurement result.

In this way, after the rise in the pH value in the ion exchange liquid is confirmed, the pH adjuster can be added. In other words, it is easy to always keep the pH value of the ion exchange liquid below a certain value.

(15) The present invention, which was first made to solve the above-mentioned problem, is an ion exchange liquid used for ion exchange treatment of strengthening glass containing an alkaline metal component, wherein the ion exchange liquid comprises: a molten salt and a pH adjuster, and the pH adjuster is a boron compound.

If this ion exchange liquid is used to perform ion exchange treatment on strengthening glass, the same effect as the corresponding structure can be achieved. [Effect of the invention]

According to the present invention, it is possible to produce a strengthened glass having few surface defects and high surface strength while reliably suppressing an increase in the pH value of the ion exchange solution.

Hereinafter, a manufacturing device for tempered glass, a manufacturing method for tempered glass, and an ion exchange liquid of an embodiment of the present invention are described. Furthermore, in each embodiment, repeated descriptions are sometimes omitted by labeling corresponding components with the same symbol. In the case where only a part of the structure is described in each embodiment, the structure of other embodiments described previously can be applied to the other parts of the structure. In addition, not only the combination of structures explicitly described in the description of each embodiment is possible, but also the structures of multiple embodiments can be partially combined with each other even if it is not explicitly stated, especially as long as no obstacles are caused in the combination.

<First embodiment> (Strengthened glass manufacturing device and ion exchange liquid) As shown in FIG1 , the first embodiment of the strengthening glass manufacturing device is a processing device for performing ion exchange treatment on strengthening glass 1 to obtain strengthened glass. The device includes an ion exchange tank 3 storing ion exchange liquid 2 and a fixture 4 holding the strengthening glass 1.

The ion exchange liquid 2 is a treatment agent that performs ion exchange with components in the strengthening glass 1 by contacting with the strengthening glass 1. The ion exchange liquid 2 contains a molten salt 2a and a boron compound 2b. In this embodiment, the boron compound 2b is contained in a container 5 that can pass through the ion exchange liquid 2.

The molten salt 2a is a salt containing a component capable of ion exchange with a component in the strengthening glass 1, and is typically an alkali metal nitrate. The alkali metal nitrate preferably contains at least one of NaNO ₃ , KNO ₃ and LiNO _3. The composition of the molten salt 2a can be appropriately changed according to the glass composition of the strengthening glass 1, the conditions of the ion exchange treatment (for example, the treatment temperature or the treatment time), and the like.

In this embodiment, a case where a mixed salt of LiNO ₃ and NaNO ₃ is used as the molten salt 2a and a one-stage ion exchange treatment is performed on the same strengthening glass 1 is described. In addition, regarding the ion exchange treatment, two or more stages of ion exchange treatment may be performed on the same strengthening glass 1.

The mixing ratio of LiNO ₃ and NaNO ₃ can be arbitrarily specified. For example, the mixing ratio of LiNO ₃ and NaNO ₃ can be set to 30% to 100% NaNO ₃ and 0% to 70% LiNO ₃ in terms of mass %, preferably 70% to 100% NaNO ₃ and 0% to 30% LiNO ₃ , and more preferably 95% to 100% NaNO ₃ and 0% to 5% LiNO ₃ .

Boron compound 2b is a non-glass pH adjuster for lowering the pH of ion exchange solution 2, i.e., molten salt 2a. Boron compound 2b has high solubility in water. In the present embodiment, boron compound 2b contains at least one of _B2O3 and B(OH) ₃ as a main component. Here, the so-called main component refers to a content of 90% by mass or more, preferably 95% by _mass or more, and more preferably 98% by mass or more relative to all components constituting boron compound 2b. Furthermore, boron compound 2b may also contain impurities (e.g., 3% by mass or less).

Here, if the ion exchange liquid 2 is used for a long time at a high temperature, the pH value may rise. The reason is that due to the decomposition reaction of the molten salt 2a contained in the ion exchange liquid 2, the OH ^- in the ion exchange liquid 2 becomes excessive. In this way, if the pH value of the ion exchange liquid 2 (molten salt 2a) rises, the OH ^- in the ion exchange liquid 2 causes surface roughness on the glass surface, which may reduce the surface strength of the strengthened glass.

The decomposition reaction of the molten salt 2a is easy to occur in LiNO ₃ and NaNO ₃ , but not easy to occur in KNO _3. The reason is that the temperature at which the decomposition reaction of the molten salt 2a occurs becomes higher in the order of LiNO ₃ , NaNO ₃ , and KNO _3. Therefore, when the molten salt 2a contains LiNO ₃ and/or NaNO ₃ and does not substantially contain KNO ₃ , the pH-lowering effect of the ion-exchange solution 2 brought about by the boron compound 2b is particularly useful. In addition, the so-called "substantially does not contain KNO ₃ " means that KNO ₃ is not intentionally added to the molten salt 2a, and the molten salt 2a is allowed to contain KNO ₃ dissolved from the self-strengthening glass 1. Specifically, "substantially containing no KNO ₃ " means that the content of KNO ₃ in the molten salt 2a is 1 mass % or less.

An example of the reaction formula of LiNO ₃ and NaNO ₃ is shown below. In the following reaction formula, H ₂ O is considered to be water in the atmosphere dissolved in the ion exchange liquid. [Chemistry 1] RNO ₃ +H ₂ O→ROH+OH ^- +NO ₂ ↑ wherein R is Na or Li.

Furthermore, the principle of pH increase is not limited to this, and can also be explained by other principles.

On the other hand, if the boron compound 2b is added to the ion exchange liquid 2, the pH value of the ion exchange liquid 2 decreases. Although the principle is uncertain, it can be inferred as follows as an example. Li ⁺ or Na ⁺ in the ion exchange liquid 2 and H ⁺ contained in the boron compound 2b undergo ion exchange, and the free H ⁺ in the ion exchange liquid 2 neutralizes OH ^- in the ion exchange liquid 2. It is believed that the pH value of the ion exchange liquid 2 decreases by this neutralization reaction (dehydration reaction).

As a specific example, an example of a reaction formula when B(OH) ₃ is added to the ion exchange solution 2 is shown below. [Chemical 2] 4B(OH) ₃ + 2ROH→R ₂ B ₄ O ₇ + 7H ₂ O wherein R is Na or Li.

Here, in the process of the neutralization reaction, the excess Li ions or Na ions in the ion exchange solution 2 are also adsorbed as reaction products derived from B(OH) _3. In addition, B ₂ O ₃ can also react with part of the moisture in the air to contain H ⁺ , so it is considered that when B ₂ O ₃ is added to the ion exchange solution 2, the same neutralization reaction will also occur. Furthermore, the principle of reducing the pH value of the ion exchange solution 2 is not limited to this, and can also be explained by other principles.

The boron compound 2b is preferably added to the ion exchange liquid 2 so that the pH value of the ion exchange liquid 2 becomes 8 or less. In this way, the surface strength of the strengthened glass is improved. The threshold value of the pH value of the ion exchange liquid 2 is preferably 8 or less, 6 to 8.

In this specification, when the "pH value of the ion exchange liquid 2" is referred to, it refers to the pH value when the ion exchange liquid 2 is mixed with water to prepare an aqueous solution with a concentration of 20 mass%. The aqueous solution is prepared by cooling and solidifying the ion exchange liquid 2, pulverizing it, and then dissolving it in water. The measurement temperature (liquid temperature) of the pH value of the ion exchange liquid 2 is, for example, 25°C ± 5°C. The measuring device of the pH value of the ion exchange liquid 2 is, for example, a desktop pH meter "F-71" manufactured by Horiba, Ltd.

The boron compound 2b is preferably added to the ion exchange liquid 2 so that the surface roughness Sa of the strengthened glass becomes 3.0 nm or less. In this way, the surface strength of the strengthened glass is improved. The threshold value of the surface roughness Sa of the strengthened glass is preferably 3.0 nm or less, 1.5 nm or less, 1.0 nm or less, or 1.0 nm to 0.2 nm.

The boron compound 2b is preferably added to the ion exchange liquid 2 so that the BOR strength of the strengthened glass becomes 1000 MPa or more. The threshold value of the BOR strength of the strengthened glass is preferably 1000 MPa or more, 1200 MPa or more, or 1300 MPa or more.

Regarding the boron compound 2b, it is preferred that the content of the boron compound 2b is added in an amount of 0.1 to 10 parts by mass when the content of the molten salt 2a is set to 100 parts by mass. The content of the boron compound 2b is more preferably 0.1 to 10 parts by mass, 0.1 to 7 parts by mass, or 0.1 to 5 parts by mass. If the content of the boron compound 2b is too small, it may not be possible to obtain a sufficient lowering effect on the pH value of the ion exchange solution 2. On the other hand, if the content of the boron compound 2b is too much, the burden on the equipment or the burden of removing the product derived from the boron compound 2b may increase. From the same point of view, the amount of the boron compound 2b added at one time is preferably 1% by mass or less.

The boron compound 2b is preferably added to the ion exchange solution 2 in the form of a powder or a powder agglomerate. The agglomerate includes a pressed powder (e.g., a tablet). In this embodiment, the boron compound 2b is added in the form of an agglomerate. If it is in the form of an agglomerate, the boron compound 2b gradually dissolves into the ion exchange solution 2. Therefore, the duration of the pH-lowering effect of the ion exchange solution 2 brought about by the boron compound 2b becomes longer, and the frequency of the addition treatment of the boron compound 2b can be reduced.

The ion exchange tank 3 is a tank for storing the ion exchange solution 2. At least a portion of the contact surface of the ion exchange tank 3 with the ion exchange solution 2 is made of a metal that is corrosion-resistant to the molten salt 2a. In the present embodiment, the inner surface of the ion exchange tank 3 is made of stainless steel. Furthermore, it is preferred that the ion exchange tank 3 further includes: a clamp 4 for holding the strengthening glass 1, or an opening for taking out and putting in a container 5 containing the boron compound 2b, and a cover (not shown) covering the opening.

The clamp 4 is a member for holding the strengthening glass 1. During the ion exchange treatment, the clamp 4 is immersed in the ion exchange liquid 2 in the ion exchange tank 3 while holding the strengthening glass 1. At least a portion of the contact surface of the clamp 4 with the ion exchange liquid 2 is made of metal. In this embodiment, the clamp 4 is entirely made of stainless steel. The clamp 4 is carried into and out of the ion exchange tank 3 by a conveying device not shown.

The container 5 is an isolation member for isolating the boron compound 2b from the strengthening glass 1. The container 5 is immersed in the ion exchange solution 2 in the ion exchange tank 3 while the boron compound 2b is contained therein. In the present embodiment, the boron compound 2b contained in the container 5 is arranged at the bottom layer of the ion exchange tank 3 storing the ion exchange solution 2. Here, the so-called "bottom layer" refers to, for example, the lower part of the strengthening glass 1 immersed in the ion exchange solution 2.

The density of the aggregate of the boron compound 2b is small and it floats in the ion exchange solution 2, but if it is contained in the container 5, it can sink to the bottom layer of the ion exchange tank 3 in advance. Therefore, it is easy to maintain the state in which the boron compound 2b is isolated from the strengthening glass 1. Therefore, it is possible to suppress the unreacted boron compound 2b from being attached to the strengthening glass 1 (or strengthening glass) or the jig 4 and being taken out of the ion exchange tank 3.

In addition, the aggregates of the boron compound 2b are dissolved into the ion exchange solution 2 and gradually pass through the container 5. A portion of the boron compound 2b that passes through the container 5 is fully dispersed in the ion exchange solution 2 while rising in the ion exchange solution 2 due to buoyancy. Therefore, the pH value of the entire ion exchange solution 2 can be efficiently lowered.

The container 5 is made of a net, a mesh, or a porous member so that the ion exchange liquid 2 can pass through. In addition, in the present embodiment, the container 5 is entirely made of stainless steel. The container 5 is carried into and out of the ion exchange tank 3 by a transport device (not shown).

The strengthening glass 1 is a glass article before the ion exchange treatment that is the object of the ion exchange treatment. In the present embodiment, the strengthening glass 1 is exemplified as a rectangular plate. The plate thickness of the strengthening glass 1 is, for example, 2.0 mm or less, more preferably 1.0 mm or less, and further preferably 0.3 mm to 0.9 mm. The length of the strengthening glass 1 is, for example, 5 mm to 5000 mm, 15 mm to 1000 mm, 30 mm to 500 mm, 50 mm to 300 mm, 70 mm to 200 mm, and the width of the strengthening glass 1 is 1 mm to 4000 mm, 10 mm to 1000 mm, 30 mm to 500 mm, 40 mm to 300 mm, 50 mm to 150 mm.

The strengthening glass 1 is preferably alkali aluminosilicate glass. The strengthening glass 1 may not contain Li ₂ O, but in this embodiment, the strengthening glass 1 contains 1 mol % or more of Li ₂ O. The strengthening glass 1 has substantially the same glass composition as the manufactured strengthening glass.

The alkali aluminosilicate glass preferably contains, in mol%, 40% to 80% SiO ₂ , 1% to 30% Al ₂ O ₃ , 0% to 10% B ₂ O ₃ , 0% to 10% MgO, 1% to 28% Li ₂ O, 1% to 25% Na ₂ O, 0% to 10% K ₂ O, 0% to 10% P ₂ O ₅ , and 0% to 10% ZrO ₂ as a glass composition. In particular, the alkali metal oxide (alkali metal component) is preferably contained in the following range.

Li ₂ O is an ion exchange component. Li ₂ O is a component that reduces high temperature viscosity and improves solubility or formability. Li ₂ O is a component that increases Young's modulus. On the other hand, Li ₂ O is also a component that dissolves during ion exchange treatment and deteriorates the ion exchange solution. Therefore, the preferred lower limit range of Li ₂ O is 1% or more, 1.5% or more, 2% or more, 3% or more, 4% or more, 5% or more, 5.5% or more, 6.5% or more, and especially 7% or more in mole %, and the preferred upper limit range is 28% or less, 20% or less, 15% or less, 13% or less, 12% or less, 11% or less, 10% or less, and especially less than 9%.

Na ₂ O is an ion exchange component. Na ₂ O is a component that reduces high temperature viscosity and improves solubility or formability. Na ₂ O is a component that improves devitrification resistance, and is particularly a component that suppresses devitrification caused by reaction with alumina formed body refractory. If the content of Na ₂ O is too little, the solubility is reduced, or the thermal expansion coefficient is too low, or the ion exchange rate is easily reduced. Therefore, the preferred lower limit range of Na ₂ O is 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, and particularly 7.5% or more in mole %. On the other hand, if the content of Na ₂ O is too much, the viscosity is easily reduced due to phase separation. In addition, sometimes the acid resistance is reduced, or the component balance of the glass composition is lacking, and the devitrification resistance is reduced instead. Therefore, the preferred upper limit range of _Na2O is 25% or less, 22% or less, 20% or less, 19% or less, 18% or less, 17% or less, 16% or less, 15% or less, 14% or less, 13% or less, 12% or less, 11% or less, 10% or less, and particularly 9% or less.

K ₂ O is a component that reduces high temperature viscosity and improves solubility or formability. It is also a component that improves devitrification resistance or increases Vickers hardness. However, if the content of K ₂ O is too high, phase separation occurs and the viscosity is easily reduced. In addition, there is a tendency that acid resistance is reduced or the component balance of the glass composition is lacking, and devitrification resistance is reduced instead. 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, 0.2% or more, 0.3% or more, and particularly 0.35% or more in terms of mole %. The preferred upper limit range of K ₂ O is 10% or less, 5% or less, 3% or less, 2% or less, 1% or less, 0.8% or less, 0.7% or less, 0.6% or less, and particularly less than 0.5%.

The strengthening glass 1 can be produced, for example, in the following manner.

First, glass raw materials prepared in a manner to form the glass composition are put into a continuous melting furnace, heated and melted at 1500°C to 1600°C to form molten glass. Next, the molten glass formed in the melting furnace is clarified and supplied to a forming device, and then formed into a plate shape or the like by an overflow downdraw method, and then slowly cooled. In this way, strengthening glass 1 can be produced. Furthermore, in addition to the overflow downdraw method, various forming methods can be used. For example, forming methods such as float method, downdraw method (slot down method, redraw method, etc.), rollout method, and pressing method can be used.

The strengthening glass 1 may be bent after or during forming. In addition, the strengthening glass 1 may be cut, drilled, surface polished, chamfered, end polished, etched, and the like.

(Manufacturing method of tempered glass) Next, the manufacturing method of tempered glass of the first embodiment is described. In this method, the manufacturing device of tempered glass is used.

In this method, first, as shown in Fig. 2, molten salt is prepared (step S1). Specifically, first, _NaNO3 and _LiNO3 are mixed and heated to melt inside the ion exchange tank 3 to prepare molten salt 2a.

Next, an ion exchange treatment is performed (step S2). Specifically, a plurality of sheets of strengthening glass 1 are held as a batch in a fixture 4 and immersed in an ion exchange solution 2 containing a molten salt 2a. The conditions such as the temperature and immersion time of the ion exchange solution 2 in the ion exchange treatment can be arbitrarily specified. The temperature of the ion exchange solution 2 is, for example, 350°C to 500°C, preferably 360°C to 470°C, 360°C to 450°C, 360°C to 430°C, and 360°C to 410°C. In addition, the immersion time is, for example, 0.1 hour to 30 hours, preferably 0.2 hour to 20 hours, 0.3 hour to 15 hours, 0.4 hour to 10 hours, and 0.5 hour to 5 hours. By subjecting the strengthening glass 1 to ion exchange treatment, a strengthened glass can be obtained.

When the ion exchange treatment of one batch is completed, the ion exchange treatment is performed on the next batch of strengthening glass 1, and the ion exchange treatment is repeated until the ion exchange of a predetermined number of batches is completed (NO in step S3).

On the other hand, when the ion exchange of the predetermined number of batches is completed (YES in step S3), the pH value of the ion exchange solution 2 is measured (step S4).

After the pH value of the ion exchange liquid 2 is measured, it is determined whether the pH value exceeds a predetermined threshold value (step S5). Specifically, in this embodiment, it is determined whether the pH value of the ion exchange liquid 2 exceeds 8, for example.

When the pH value of the ion exchange solution 2 is below a predetermined threshold value (e.g., pH value 8) (No in step S5), the next batch of ion exchange treatment is performed, and the treatment from step S2 to step S5 is repeated.

On the other hand, when the pH value of the ion exchange solution 2 exceeds a predetermined threshold value (for example, pH 8) (Yes in step S5), a boron compound 2b is added to the molten salt 2a as a pH adjuster (step S6).

Furthermore, in step S6, the container 5 containing the boron compound 2b is immersed in the ion exchange solution 2. The container 5 containing the boron compound 2b can also be swung in the ion exchange solution 2. If so, the diffusion rate of the boron compound 2b into the ion exchange solution 2 increases, and the speed at which the pH value of the ion exchange solution 2 decreases can be accelerated.

After the addition treatment of step S6 is completed, the treatment of step S2 is performed on the next batch of strengthening glass 1, and the treatment is repeated. Furthermore, after the treatment of step S6 and before the adjustment of the pH value of the ion exchange solution 2 based on the boron compound 2b progresses to a certain extent, the treatment of step S2 can be started after setting a waiting period for a predetermined time to pass. The waiting time after the treatment of step S6 and before starting step S2 can be arbitrarily specified, for example, more than 1 minute, more than 5 minutes, more than 10 minutes, more than 30 minutes, 1 hour to 24 hours, or 1 hour to 12 hours.

As described above, according to this method, even if the pH of the ion exchange solution 2 increases, the pH of the ion exchange solution 2 can be reliably lowered by the boron compound 2b. This can suppress a decrease in the surface strength of the strengthened glass produced by this method.

In addition, since the boron compound 2b has high solubility in water, even if the boron compound 2b adheres to the strengthened glass, it can be easily removed by washing. In other words, it is not easy to cause surface defects caused by the boron compound 2b in the strengthened glass produced by this method.

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

<Second embodiment> The tempered glass obtained in the first embodiment may be subjected to an additional ion exchange treatment. That is, the ion exchange treatment (step S2) shown in FIG. 2 may be used as the first stage ion exchange treatment, and a second stage ion exchange treatment (not shown) may be further performed.

In the second stage ion exchange treatment, it is preferred to separately prepare a molten salt (referred to as the second molten salt) having a higher mixing ratio of KNO ₃ than the molten salt 2a (referred to as the first molten salt) used in the first stage ion exchange treatment, and it is more preferred that the mixing ratio of KNO ₃ is 90 mass % or more. According to such treatment, a deep compressive stress layer can be formed on the strengthening glass in the first stage ion exchange treatment, and a high surface compressive stress can be given in the second stage ion exchange treatment. Furthermore, in the second stage ion exchange treatment, it is preferred to adjust the composition of the molten salt, the treatment temperature, the treatment time, etc. in such a way that the surface compressive stress of the strengthened glass becomes 700 MPa or more.

Thus, in the case of a two-stage ion exchange treatment, the boron compound 2b must be added to the ion exchange solution of the first stage and can be added to the ion exchange solution 2 of the second stage at will.

Furthermore, although the embodiments of the present invention have been described, the embodiments of the present invention are not limited thereto, and various modifications can be made within the scope of the gist of the present invention.

In the above embodiment, the pH value of the ion exchange liquid 2 is measured and the case where the addition treatment is required is determined based on the pH value, but the treatment may be performed based on other characteristics. For example, in step S4, the surface roughness Sa of the strengthened glass may be measured together with or instead of the pH value. Then, in step S5, it may be determined whether the surface roughness Sa of the strengthened glass is less than a predetermined threshold value. In this case, the threshold value of the surface roughness Sa of the strengthened glass may be set to any value within a range of 3.0 nm or less, for example.

In the above embodiment, the pH value measurement step is performed for each predetermined number of batches, but the pH value measurement step may be performed each time each batch of the strengthening glass 1 is subjected to the ion exchange treatment. In this case, the determination process of step S3 may be omitted. If such a process is adopted, the addition process of step S6 may be performed at an appropriate time, and the outflow of defective products may be more appropriately suppressed.

In the above-mentioned embodiment, the processing of step S4 and step S5 can also be omitted. That is, at the time point when the ion exchange processing of the specified batch number is completed (yes in step S3), the addition processing of step S6 can be performed. For example, when the increase in the pH value of the ion exchange solution 2 can be predicted according to the batch number, by adopting such processing, the man-hours of step S4 and step S5 can be reduced, and the production efficiency can be improved.

In the embodiment described above, the addition treatment of step S6 may be performed after the molten salt preparation step of step S1 and before the ion exchange treatment of step S2, and production may be started in a state where the boron compound 2b is previously added to the molten salt 2a.

In the above-mentioned embodiment, the addition treatment of step S6 may be performed during the ion exchange treatment of step S2. That is, the boron compound 2b may be added in a state where the strengthening glass 1 is immersed in the ion exchange solution 2 of the ion exchange tank 3. However, from the viewpoint of suppressing the adhesion of the boron compound 2b to the strengthening glass 1, it is preferable to add the boron compound 2b in a state where the strengthening glass 1 is not immersed in the ion exchange solution 2 of the ion exchange tank 3.

In the above-described embodiment, the case where the boron compound 2b is contained in the container 5 and added to the ion exchange solution 2 in step S6 is described, but the method of adding the boron compound 2b is not limited thereto. As shown in FIG3 , the auxiliary tank 8 may be connected to the ion exchange tank 3 via the connecting passage 6 and the connecting passage 7 through which the ion exchange solution 2 can pass, and the boron compound 2b may be added to the auxiliary tank 8, thereby supplying the ion exchange solution 2 to which the boron compound 2b in the auxiliary tank 8 is added to the ion exchange tank 3. In this case, the auxiliary tank 8 functions as an isolation member for isolating the boron compound 2b from the strengthening glass 1. In addition, the boron compound 2 b may be added directly to the ion exchange solution 2 stored in the ion exchange tank 3 or the auxiliary tank 8 instead of being contained in the container 5 .

In the embodiment, the strengthened glass may also be a crystallized glass. Crystallized glass is formed by heat-treating (crystallizing) amorphous glass and precipitating inorganic crystals, and the glass contains inorganic crystals. Here, the so-called amorphous glass refers to glass in which no diffraction peak indicating crystallization is confirmed by powder X-ray diffraction method. In the case where the strengthened glass is a crystallized glass, a heat treatment (crystallization) is further performed before the ion exchange treatment (step S2). In the heat treatment, for example, the strengthening glass of the amorphous glass is heated at 700°C to 840°C for 0.1 hours to 15 hours. Thereby, at least one selected from β-lithium nepheline solid solution, β-lithium pyroxene solid solution and zirconia as precipitated crystals is precipitated in the glass.

In the above-mentioned embodiment, the strengthening glass 1 and the strengthened glass are exemplified as rectangular plates, but they are not limited to rectangular plates, and can be applied in any shape such as a curved plate, a disk, a tube, a container, a sphere, etc. Example 1

Hereinafter, the glass article of the present invention will be described based on the embodiments. It should be noted that the following embodiments are merely illustrative, and the present invention is not limited to the following embodiments in any way.

Table 1 shows the solubility of B(OH) ₃ , B ₂ O ₃ and SiO ₂ in water.

[Table 1] Solubility [g/100 g] Temperature [℃] B(OH) ₃ 5.6 20 _{B2O3 ​} 2.8 20 SiO ₂ 0.012 20

It can also be seen from Table 1 that the solubility of B(OH) ₃ and B ₂ O ₃ as boron compounds is much higher than the solubility of SiO _2. Therefore, if it is a boron compound, it can be easily removed by washing even if it adheres to the strengthened glass. Example 2

Next, a single salt of NaNO ₃ and a mixed salt of NaNO ₃ and LiNO ₃ were prepared as molten salts. The ion exchange solution containing these molten salts was kept at a high temperature for a long time to confirm whether the pH value of the ion exchange solution increased. The results are shown in Table 2.

[Table 2] No. Molten salt Liquid temperature[℃] Time until pH value＞8.5 [h] 1 NaNO ₃ 100 wt% 450 20 2 NaNO ₃ 95 wt% / LiNO ₃ 5 wt% 450 3 3 NaNO ₃ 70 wt% / LiNO ₃ 30 wt% 380 89

The pH value in the table refers to the pH value when the ion exchange liquid is mixed with water to prepare an aqueous solution with a concentration of 20 mass%. The aqueous solution is prepared by cooling the ion exchange liquid to solidify, crushing it, and then dissolving it in water. The measurement temperature (liquid temperature) of the pH value of the ion exchange liquid is 25℃±5℃. As a measuring device for the pH value of the ion exchange liquid, a desktop pH meter "F-71" manufactured by Horiba, Ltd. is used.

It can also be confirmed from Table 2 that if the ion exchange solution is kept at a high temperature for a long time, the pH value of the ion exchange solution increases. In addition, it can be confirmed that the pH value of the ion exchange solution increases faster due to the increase in the temperature of the ion exchange solution and/or the increase in the content of _LiNO3 .

As strengthening glass, a glass having a thickness of 0.65 mm and containing, by mol%, 60.5% SiO ₂ , 18.8% Al ₂ O ₃ , 0.1% B ₂ O ₃ , 0.4% K ₂ O, 8.1% Na ₂ O, 7.2% Li ₂ O, 0.5% MgO, 4.3% P ₂ O ₅ , and 0.05% SnO ₂ (by mass%, 51.6% SiO ₂ , 27.9% Al ₂ O ₃ , 0.3% B ₂ O ₃ , 0.6% K ₂ O, 7.5% Na ₂ O, 3.3% Li ₂ O, 0.3% MgO, 8.4% P ₂ O ₅ , and 0.1% SnO ₂ ) was prepared. ) as the glass composition of alkali aluminum silicate glass.

KOH was added to the molten salt of NaNO ₃ and LiNO ₃ to simulate the deterioration of the ion exchange solution and to increase the pH of the ion exchange solution. Next, B ₂ O ₃ was added to the deteriorated ion exchange solution to attempt to lower the pH of the ion exchange solution. Then, the first stage ion exchange treatment was performed on the strengthening glass having the above glass composition using the ion exchange solution in which the pH was attempted to be lowered, and then the second stage ion exchange treatment was performed using the ion exchange solution containing other molten salts. Then, the BOR strength (surface strength) and the like of the strengthened glass obtained by the two-stage ion exchange treatment were measured. The results are shown in Tables 3 and 4. Furthermore, regarding the ion exchange fluid used in the first stage of the ion exchange treatment, as the number of days in the table increases, it means that the usage period is getting longer.

[table 3] No. The first stage of ion exchange treatment Second stage ion exchange treatment Elapsed days Processing conditions KOH _{B2O3 ​} pH CS DOC CT Processing conditions CS DOL BOR Strength (Standard Deviation) White [wt%] [wt%] [MPa] [μm] [MPa] [MPa] [μm] [MPa] 4-1 1 NaNO ₃ 100 wt% 380℃/180min 0.00 0.0 5.9 258.4 124.3 82.5 KNO ₃ 97.5 wt%/ NaNO ₃ 2.5 wt% 380℃/45min 843.6 5.7 2010.4 (163.2) - 4-2 2 0.07 0.0 10.1 60.3 156.6 32.9 849.5 5.4 1792.1 (200.9) - 4-3 3 0.07 0.2 9.6 251.7 123.8 80.5 842.5 5.8 1620.2 (59.9) - 4-4 4 0.07 0.4 7.5 250.6 125.6 81.0 844.2 5.7 1937.8 (102.3) -

[Table 4] No. The first stage of ion exchange treatment Second stage ion exchange treatment Elapsed days Processing conditions KOH _{B2O3 ​} pH CS DOC CT Processing conditions CS DOL BOR Strength (Standard Deviation) White [wt%] [wt%] [MPa] [μm] [MPa] [MPa] [μm] [MPa] 5-1 1 NaNO ₃ 95 wt%/ LiNO ₃ 5 wt% 380℃/180min 0.00 0.0 8.5 141.3 133.2 57.9 KNO ₃ 97.5 wt%/ NaNO ₃ 2.5 wt% 380℃/45min 845.0 5.5 2026.6 (126.4) - 5-2 2 0.07 0.0 10.6 - - - 865.4 5.9 1354.4 (108.5) have 5-3 3 0.07 0.2 9.3 - - - - - 1560.8 (73.8) have 5-4 4 0.07 0.4 6.9 135.2 136.1 57.6 826.9 5.6 1790.7 (116.1) -

In the table, CS refers to the compressive stress on the surface, DOC refers to the depth of the compressive stress layer, DOL refers to the diffusion depth of potassium ions, CT refers to the tensile stress at the center of the plate thickness, BOR strength refers to the surface strength of the ball-on-ring test, and white turbidity refers to the appearance defect that looks whitish and blurry.

CS, DOC, DOL, and CT can be derived based on values measured using a surface strain gauge (e.g., FSM-6000LE manufactured by Orihara Seisakusho), or values obtained by synthesizing values measured using a surface strain gauge and a scattered light photoelastic strain gauge (e.g., SLP-1000 manufactured by Orihara Seisakusho).

The BOR strength is measured by the ball-on-ring test shown in Figure 4. Specifically, the test sample (tempered glass) 9 is placed on a ring fixture 10 with an inner diameter of 25 mm, and the tip spherical fixture 11 with a diameter of 12.5 mm is brought into contact with the test sample 9. The tip spherical fixture 11 is lowered to the center of the ring fixture 10 at a speed of 0.5 mm/min and a load is applied. The breaking load (unit: MPa) when the test sample 9 is broken is set as the BOR strength. The BOR strength is the average value of 9 measurements.

White turbidity is a visual measurement of the appearance of the sample (tempered glass), and is determined by whether a whitish and hazy appearance defect is observed.

As shown in Tables 3 and 4, the pH of _the ion exchange solution can be reduced by adding _B2O3 to the molten salt (Samples No. 4-3, No. 4-4, No. 5-3, and No. 5-4). In addition, after the ion exchange solution deteriorates, the BOR strength of the strengthened glass decreases. However, if the pH of the ion exchange solution is restored to below ₈ by adding _B2O3 , the BOR strength of the strengthened glass improves (Samples No. 4-4 and No. 5-4). Example 4

As strengthening glass, a glass having a thickness of 0.70 mm and containing, by mol%, 59.5% SiO ₂ , 19.0% Al ₂ O ₃ , 0.3% B ₂ O ₃ , 0.4% K ₂ O, 8.4% Na ₂ O, 7.7% Li ₂ O, 0.5% MgO, 4.1% P ₂ O ₅ , and 0.1% SnO ₂ (by mass%, 51.6% SiO ₂ , 27.9% Al ₂ O ₃ , 0.3% B ₂ O ₃ , 0.6% K ₂ O, 7.5% Na ₂ O, 3.3% Li ₂ O, 0.3% MgO, 8.4% P ₂ O ₅ , and 0.1% SnO ₂ was prepared. ) as the glass composition of alkali aluminum silicate glass.

KOH was added to the molten salt of NaNO ₃ and LiNO ₃ to simulate the deterioration of the ion exchange solution. Next, B(OH) ₃ was added to the deteriorated ion exchange solution to try to lower the pH of the ion exchange solution. In order to simulate the continuous deterioration of the ion exchange solution, KOH and B(OH) ₃ were continuously added to the ion exchange solution. The results are shown in Figure 5.

As shown in Figure 5, the pH of the ion exchange solution can be continuously reduced by adding B(OH) ₃ .

In addition, the first stage of ion exchange treatment was performed on the strengthening glass having the above glass composition using the ion exchange solution in which the pH value was lowered by adding B(OH) ₃ , and then the second stage of ion exchange treatment was performed using the ion exchange solution containing other molten salts. Then, the surface roughness Sa and BOR strength (surface strength) of the strengthened glass obtained by the two-stage ion exchange treatment were measured. The results are shown in Table 5. In addition, the relationship between the measured surface roughness Sa and BOR strength is shown in Figure 6. Furthermore, with respect to the ion exchange solution used in the first stage of ion exchange treatment, as the number of days in the table increases, it means that the use period is getting longer.

[table 5] No. The first stage of ion exchange treatment Second stage ion exchange treatment Elapsed days Processing conditions KOH B(OH) ₃ pH CS DOC CT Processing conditions CS DOL Surface roughness Sa BOR Strength (Standard Deviation) [wt%] [wt%] [MPa] [μm] [MPa] [MPa] [μm] [nm] [MPa] 6-1 1 NaNO ₃ 95 wt%/ LiNO ₃ 5 wt% 380℃/180min 0.00 0.0 6.2 171 132 57 KNO ₃ 97.5 wt%/ NaNO ₃ 2.5 wt% 380℃/45min 919 5.8 0.87 1514 (72) 6-2 2 0.02 0.0 8.7 154 139 57 923 5.7 1.05 1378 (65) 6-3 3 0.02 0.0 - - - - - - - - 6-4 4 0.02 0.0 - - - - - - - - 6-5 5 0.07 0.0 9.5 159 138 56 914 5.9 1.04 1375 (96) 6-6 6 0.07 0.2 7.1 - - - - - - - 6-7 7 0.07 0.2 - 143 140 56 880 5.7 - - 6-8 8 0.07 0.2 5.7 - - - - - - - 6-9 9 0.07 0.2 7.5 147 138 55 893 5.7 - 1395 (79) 6-10 10 0.07 0.2 - - - - - - - - 6-11 11 0.07 0.2 - - - - - - - - 6-12 12 0.13 0.2 8.7 - - - 905 5.8 1.01 1288 (35) 6-13 13 0.13 0.4 6.7 143 139 54 878 5.7 0.92 - 6-14 14 0.13 0.4 7.8 - - - - - - - 6-15 15 0.20 0.4 9.0 141 139 54 - - 1.10 1130 (188) 6-16 16 0.20 0.6 - - - - - - - - 6-17 17 0.20 0.6 - - - - - - - - 6-18 18 0.20 0.6 - - - - - - - - 6-19 19 0.20 0.6 6.5 142 138 54 867 5.5 - 1432 (94) 6-20 20 0.20 0.6 7.3 147 134 54 869 5.7 0.97 - 6-21 twenty one 0.20 1.0 - - - - - - - - 6-22 twenty two 0.20 1.0 7.2 - - - - - 0.95 1475 (58) 6-23 twenty three 0.20 1.0 6.3 - - - - - - -

The surface roughness Sa is a value measured using a white interferometer VertScan manufactured by Ryoka Systems Co., Ltd. The surface roughness Sa is an average value of three measurements.

As shown in Table 5, in the sample No. 6-1 using the ion exchange solution before deterioration in the first stage of the ion exchange treatment, the BOR strength was 1517 MPa (referred to as the standard BOR strength). In contrast, in the samples using the ion exchange solution deteriorated to a pH value exceeding 8 in the first stage of the ion exchange treatment, the BOR strength decreased by about 10% to 25% relative to the standard BOR strength (for example, samples No. 6-12 and No. 6-15). On the other hand, in the samples using the ion exchange solution restored to a pH value of less than 8 in the first stage of the ion exchange treatment by adding B(OH) ₃ , the BOR strength decreased the most and recovered to within 3% relative to the standard BOR strength (for example, sample No. 6-22).

It can also be confirmed from Figure 6 that the BOR strength is negatively correlated with the surface roughness Sa. In addition, it is known that in samples No. 6-1 to No. 6-23, no turbidity is generated on the glass surface, but even if the deterioration of the surface roughness does not generate turbidity, it will strongly affect the BOR strength. Moreover, in all samples that used an ion exchange solution with a pH value exceeding 8 in the first stage of the ion exchange treatment, the surface roughness Sa exceeded 1.0. Therefore, it can be said that the pH value of the ion exchange solution (molten salt containing LiNO ₃ and/or NaNO ₃ and substantially free of KNO ₃ ) used in the first stage of the ion exchange treatment is preferably set to 8 or less by adding a boron compound. Example 5

When a boron compound is added to an ion exchange solution containing Li ions, it is confirmed whether the boron compound adsorbs Li ions. Specifically, the additive precipitated to the bottom of the ion exchange solution tank of Sample No. 6-23 of Example 4 is collected and recovered, and after the recovered additive is dried, the X-ray diffraction (XRD) pattern of the surface is measured.

The ion exchange solution of sample No. 6-23 is the 23rd day from the start of use and the 17th day from the initial addition of B(OH) ₃ as the boron compound.

The measurement conditions of the X-ray diffraction pattern are as follows. (1) Measurement device: Aeris manufactured by Spectris Inc. (2) Light source: Cu tube (wavelength λ: 1.54 Å) (3) Measurement range (2θ): 5° to 60° (4) Step width: 0.01°

The measurement results of the X-ray diffraction pattern are shown in FIG7. As shown in the figure, in the X-ray diffraction pattern, there are no peaks derived from boric acid and boron oxide, and only peaks of lithium borate or sodium borate are confirmed. Based on this, it can be confirmed that even Li ions contained in LiNO ₃ , which is a small amount of 5 mass%, can be reliably adsorbed by B(OH) ₃ , which is a boron compound. Furthermore, the X-ray diffraction pattern also contains a peak of NaNO ₃ , but it is obtained by measuring the components of the ion exchange solution contained in the additive to be measured as contamination.

1: Strengthening glass 2: Ion exchange liquid 2a: Molten salt 2b: Boron compound 3: Ion exchange tank 4: Clamp 5: Container 6, 7: Connecting channel 8: Auxiliary tank 9: Measurement sample 10: Ring clamp 11: Front ball clamp S1, S2, S3, S4, S5, S6: Steps

FIG. 1 is a schematic diagram of a manufacturing apparatus for tempered glass according to a first embodiment of the present invention. FIG. 2 is a flow chart of a manufacturing method for tempered glass according to a first embodiment of the present invention. FIG. 3 is a schematic diagram of a modified example of the manufacturing apparatus for tempered glass according to the first embodiment of the present invention. FIG. 4 is a perspective view of a test method for a ball-on-ring test. FIG. 5 is a graph showing the change in pH value with the addition of KOH and B(OH) ₃ in Example 4 of the present invention. FIG. 6 is a graph showing the relationship between BOR strength and surface roughness Sa in Example 4 of the present invention. FIG. 7 is a graph showing an X-ray diffraction pattern in Example 5 of the present invention.

1: Strengthening glass

2: Ion exchange fluid

2a: Molten salt

2b: Boron compounds

3: Ion exchange tank

4: Clamp

5:Container

Claims (15)

A method for manufacturing strengthened glass includes the step of bringing an ion exchange liquid into contact with a strengthening glass containing an alkali metal component to perform an ion exchange treatment on the strengthening glass. The method for manufacturing strengthened glass is characterized in that: The ion exchange liquid contains a molten salt and a pH adjuster, and the pH adjuster is a boron compound. The method for producing strengthened glass as described in claim 1, wherein the pH adjuster includes at least one of B ₂ O ₃ and B(OH) ₃ as the boron compound. The method for producing a strengthened glass according to claim 1 or 2, wherein in the ion exchange liquid, when the content of the molten salt is set to 100 parts by mass, the content of the pH adjuster is 0.1 parts by mass to 10 parts by mass. The method for producing a strengthened glass according to claim 1 or 2, wherein the pH value of the aqueous solution having a concentration of 20 mass % when the ion exchange liquid is mixed with water is 8 or less. The method for producing a strengthened glass according to claim 1 or 2, wherein the content of the pH adjuster in the ion exchange solution is adjusted so that the surface roughness Sa of the strengthened glass becomes 3.0 nm or less. The method for producing strengthened glass according to claim 1 or 2, wherein the pH adjuster is contained in the ion exchange liquid in the form of powder or powder aggregate. The method for manufacturing a strengthened glass as described in claim 6, wherein the ion exchange treatment is performed by placing the ion exchange liquid and the strengthening glass in an ion exchange tank, and the pH adjuster is placed in the ion exchange tank in a state of being isolated from the strengthening glass by an isolation member capable of passing through the ion exchange liquid. The method for manufacturing strengthened glass as described in claim 7, wherein the pH adjuster is disposed at the bottom layer of the ion exchange tank via the isolation member. A method for producing strengthened glass as described in claim 1 or 2, wherein the molten salt comprises at least one of LiNO ₃ and NaNO ₃ . The method for producing strengthened glass as described in claim 9, wherein the molten salt does not substantially contain KNO ₃ . The method for manufacturing strengthened glass as described in claim 9 includes the steps of performing a two-stage ion exchange treatment, and using the ion exchange liquid in the first stage of the ion exchange treatment. The method for producing a strengthened glass according to claim 1 or 2, wherein the strengthening glass is an alkali aluminum silicate glass containing 1 mol % or more of Li ₂ O as a glass composition. The method for producing strengthened glass according to claim 12, wherein the strengthening glass contains, in mol%, 40% to 80% _SiO2 , 1% to 30% _Al2O3 , 0% to _{10% B2O3 ,} 0% to 10% MgO, ₁ % to 28% _Li2O , 1% to 25% _Na2O , 0% to 10% _K2O , 0% to 10% _P2O5 , _and 0% to 10% _ZrO2 as a glass composition. The method for manufacturing strengthened glass as described in claim 1 or 2 further comprises: a step of measuring the pH value of the ion exchange solution, and a step of adding the pH adjuster to the ion exchange solution based on the pH value measurement result. An ion exchange liquid is used for ion exchange treatment of strengthening glass containing alkaline metal components, wherein the ion exchange liquid is characterized in that it contains: molten salt and pH adjuster, and the pH adjuster is a boron compound.

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