JP7569007B2 - Method for producing ion-exchanged glass, mixture for ion exchange, and apparatus for producing ion-exchanged glass - Google Patents

Description

The present invention relates to a method for producing ion-exchanged glass, an apparatus for producing ion-exchanged glass, and a mixture for ion exchange.

In recent years, chemically strengthened glass that has been ion-exchanged has been used for the cover glass of display devices. This type of ion-exchange process is generally performed by immersing the glass in a molten salt and exchanging ions in the glass and ions in the molten salt, which have different ionic radii. For example, ion-exchange process is performed by dissolving Li ions in the glass into the molten salt and introducing Na ions or K ions in the molten salt into the glass, or by dissolving Na ions in the glass into the molten salt and introducing K ions in the molten salt into the glass.

In the mass production process of ion-exchanged glass, this type of ion exchange process is repeated for multiple lots of glass using the same molten salt. As a result, ions that dissolve from the glass (hereinafter referred to as "dissolved ions") gradually accumulate in the molten salt, and the concentration of the dissolved ions in the molten salt gradually increases. If the concentration of dissolved ions becomes excessively high, it becomes difficult to carry out the above-mentioned ion exchange process, resulting in a problem of reduced productivity.

In order to solve such problems, a technique for adjusting the concentration of eluted ions by adding a phosphate to a molten salt has been developed (for example, see Patent Document 1). In the technique disclosed in Patent Document 1, an alkali metal phosphate such as Na ₃ PO ₄ or K ₃ PO ₄ is added to the molten salt, and the phosphate absorbs the eluted ions in the molten salt, thereby suppressing an increase in the concentration of eluted ions in the molten salt.

US Patent Application Publication No. 2018/0362399

However, when phosphate is added as in Patent Document 1, the metals constituting the equipment, such as the molten salt tank and the jigs for holding the glass, are corroded by the phosphate, which causes the production equipment to deteriorate easily. In addition, the corroded metal may adhere to the glass, which may cause defects in the ion-exchanged glass products produced.

The present invention aims to provide a method for producing ion-exchanged glass, an ion-exchange mixture, and an ion-exchanged glass production apparatus that can maintain product quality, i.e., achieve high productivity, while preventing deterioration of production equipment.

The method for producing ion-exchange glass according to the present invention is characterized in that it comprises a step of immersing a part or the whole of ion-exchange glass containing an alkali metal component in an ion-exchange mixture to perform an ion-exchange treatment, the ion-exchange mixture containing a molten salt and an alkali metal silicate as an additive, and the alkali metal silicate contains an alkali metal component that is ion-exchangeable with an alkali metal component that dissolves from the ion-exchange glass into the molten salt during ion exchange.

In the method for producing ion-exchanged glass according to the present invention, it is preferable that the alkali metal silicate contains an alkali metal component having a larger ionic radius than an alkali metal component eluted from the ion-exchange glass into the molten salt in the ion exchange treatment, the alkali metal component eluted from the ion-exchange glass into the molten salt in the ion exchange treatment is Li ion, and the alkali metal silicate contains at least one type selected from Na ₂ SiO ₃ , Na ₄ SiO ₄ , Na ₂ Si ₂ O ₅ , and Na ₂ Si ₄ O ₉ .

In the method for producing ion-exchange glass according to the present invention, it is preferable that the glass for ion exchange is an alkali aluminosilicate glass containing 1.0 mol % or more of Li ₂ O as a composition, and the molten salt contains one or more types selected from NaNO ₃ and KNO ₃ .

In the method for producing ion-exchanged glass according to the present invention, it is preferable that the alkali metal component eluted from the ion-exchange glass into the molten salt during the ion exchange treatment is Na ion, and the alkali metal silicate contains at least one selected from K ₂ SiO ₃ , K ₄ SiO ₄ , K ₂ Si ₂ O ₅ , and K ₂ Si ₄ O ₉ .

In the method for producing ion-exchanged glass according to the present invention, it is preferable that the alkali metal component eluted from the ion-exchange glass into the molten salt during the ion exchange treatment is Na ion, and the alkali metal silicate contains at least one selected from Li ₂ SiO ₃ , Li ₄ SiO ₄ , Li ₂ Si ₂ O ₅ , and Li ₂ Si ₄ O ₉ .

In the method for producing ion-exchange glass according to the present invention, it is preferable that the glass for ion exchange is an alkali aluminosilicate glass containing 1.0 mol % or more of Na ₂ O as a composition, and the molten salt contains KNO ₃ .

In the method for producing ion-exchanged glass according to the present invention, it is preferable that the alkali metal silicate is a powdered alkali metal silicate crystal.

In the method for producing ion-exchanged glass according to the present invention, it is preferable that the powdered alkali metal silicate has an average particle size D50 of 10 to 1000 μm.

The method for producing ion-exchanged glass according to the present invention preferably further comprises a step of stirring the molten salt after adding the alkali metal silicate to the molten salt.

In the method for producing ion-exchanged glass according to the present invention, it is preferable that the amount of alkali metal silicate added is 0.1 to 30 parts by mass per 100 parts by mass of the molten salt.

In the method for producing ion-exchanged glass according to the present invention, it is preferable to further include a step of performing the ion exchange treatment multiple times by sequentially immersing multiple different lots of ion-exchanged glass in the molten salt, measuring the stress characteristics of the ion-exchanged glass obtained after the ion exchange treatment of a predetermined lot of ion-exchanged glass, and a step of determining whether or not to add an alkali metal silicate to the molten salt depending on the measurement results of the stress characteristics.

In the method for producing ion-exchanged glass according to the present invention, it is preferable to measure the surface compressive stress of the glass as a stress characteristic, add an alkali metal silicate to the molten salt, and then perform ion exchange on the next lot of ion-exchanged glass if the surface compressive stress is less than a predetermined threshold value, and perform ion exchange on the next lot of ion-exchanged glass without adding an alkali metal silicate to the molten salt if the surface compressive stress is equal to or greater than the predetermined threshold value.

The ion exchange mixture according to the present invention is a glass ion exchange mixture containing a molten salt and an additive, and preferably contains one or more molten salts selected from _NaNO3 and _KNO3 , and contains an alkali metal silicate as the additive.

The ion exchange mixture according to the present invention preferably contains 0.1 to 30 parts by mass of an alkali metal silicate as an additive, based on 100 parts by mass of the molten salt.

In the ion exchange mixture according to the present invention, the alkali metal silicate is a powdery crystalline substance, and preferably contains at least one type selected from Na ₂ SiO ₃ , Na ₄ SiO ₄ , Na ₂ Si ₂ O ₅ , and Na ₂ Si ₄ O ₉ .

In the ion exchange mixture according to the present invention, the alkali metal silicate is a powdered crystalline material, and preferably contains at least one type selected from Li ₂ SiO ₃ , Li ₄ SiO ₄ , Li ₂ Si ₂ O ₅ , and Li ₂ Si ₄ O ₉ .

The ion-exchange glass manufacturing apparatus according to the present invention comprises any one of the above-mentioned ion exchange mixtures and a storage tank for storing the ion exchange mixture, and at least a portion of the contact surface of the storage tank with the ion exchange mixture is made of metal.

The ion-exchange glass manufacturing apparatus according to the present invention further includes a jig that holds the ion-exchange glass and is immersed in the ion-exchange mixture, and it is preferable that the contact surface of the jig with the ion-exchange mixture is made of metal.

In the ion-exchange glass manufacturing apparatus of the present invention, the metal is preferably stainless steel.

The method for producing ion-exchanged glass according to the present invention includes a step of immersing a part or the whole of ion-exchange glass containing Na ₂ O as a glass composition in an ion-exchange mixture to perform ion exchange treatment, and is characterized in that the ion-exchange mixture contains a molten salt and a lithium salt as an additive.

Compared to conventional technology, the present invention can suppress deterioration of production equipment and decline in product quality.

1 is a schematic diagram of an apparatus for producing ion-exchanged glass according to a first embodiment of the present invention. 1 is a flowchart outlining a method for producing ion-exchanged glass according to a first embodiment of the present invention.

First Embodiment
Hereinafter, a method for producing ion-exchanged glass, an apparatus for producing ion-exchanged glass, and a mixture for ion exchange according to a first embodiment of the present invention will be described.

Figure 1 is a schematic diagram of an ion-exchanged glass manufacturing apparatus according to a first embodiment of the present invention. The ion-exchanged glass manufacturing apparatus 1 is a processing apparatus for subjecting ion-exchange glass G1 to ion exchange processing to obtain ion-exchanged glass GX. The ion-exchanged glass manufacturing apparatus 1 includes an ion-exchange mixture 10, a storage tank 11, and a jig 12.

The ion exchange mixture 10 is a treatment agent that undergoes ion exchange with the components in the ion exchange glass G1 by coming into contact with the ion exchange glass G1. The ion exchange mixture 10 contains a molten salt 101 and an additive 102.

The molten salt 101 is a salt containing a component in the ion-exchange glass G1 and a component capable of ion exchange, and is typically an alkali nitrate. Examples of the alkali nitrate include NaNO ₃ , KNO ₃ , and LiNO ₃ , and these can be used alone or in combination. In this embodiment, a mixed salt of NaNO ₃ and KNO ₃ is used as an example. The mixing ratio of NaNO ₃ and KNO ₃ may be determined arbitrarily, but may be, for example, 5 to 95% NaNO ₃ and 5 to 95% KNO ₃ by mass %, preferably 30 to 80% NaNO ₃ and 20 to 70% KNO ₃ , and more preferably 50 to 70% NaNO ₃ and 30 to 50% KNO ₃ .

The additive 102 is a substance containing an alkali metal component that is ion-exchangeable with the alkali metal component eluted from the ion exchange glass G1 into the molten salt 101 during the ion exchange process, and is a metal salt containing a monovalent metal component different from the eluted ions. In this embodiment, the additive 102 can be, for example, an alkali metal silicate containing an alkali metal component with a larger ionic radius than the alkali metal component eluted from the ion exchange glass G1 into the molten salt 101 as the alkali metal salt.

The type of alkali metal silicate added as the additive 102 is preferably appropriately selected according to the alkali metal component eluted from the ion-exchange glass G1 into the molten salt 101. In the present first embodiment, a case will be described in which the ion-exchange glass G1 is a lithium aluminosilicate glass, and the alkali metal component eluted into the molten salt 101 is Li ions. In this case, the alkali metal silicate is preferably sodium silicate. The sodium silicate includes at least one selected from Na ₂ SiO ₃ (sodium metasilicate), Na ₄ SiO ₄ , Na ₂ Si ₂ O ₅ , and Na ₂ Si ₄ O _9. The sodium silicate is preferably anhydrous, but may be a hydrate. According to this configuration, Li ions eluted into the molten salt 101 are ion-exchanged with Na ions contained in the alkali metal silicate, and an increase in the concentration of Li ions in the molten salt 101 can be suppressed.

The alkali metal silicate is preferably a crystalline substance. Furthermore, the alkali metal silicate is preferably a powdered alkali metal silicate crystalline substance. The alkali metal salt crystalline substance is preferably in a powdered state when added to the molten salt, but may be in a powdered state by pulverizing in the molten salt after addition to the molten salt. The average particle size D50 of the powder is preferably 10 to 1000 μm. In order to improve the ion exchangeability with the alkali metal component eluted from the ion exchange glass, the average particle size D50 of the powder is more preferably 900 μm or less, 800 μm or less, 700 μm or less, 500 μm or less, or 450 μm or less. In order to prevent dust before addition, the average particle size D50 of the powder is more preferably 20 μm or more, 50 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, or 250 μm or more.

The amount of additive 102 to be added to the molten salt 101, i.e., the amount of alkali metal salt, is preferably measured and added so that the amount of alkali metal salt is 0.1 to 30 parts by mass when the amount of molten salt 101 is 100 parts by mass. The amount of alkali metal salt added is more preferably 1 to 30 parts by mass, 2 to 25 parts by mass, 3 to 20 parts by mass, or 4 to 15 parts by mass. If the amount of additive 102 added is too small, a sufficient ion adjustment effect cannot be obtained, and if the amount added is too large, there is a concern that the cost of the additive will increase.

In the first embodiment, as the alkali metal silicate, potassium silicate can be used in place _{of sodium silicate or in combination with sodium silicate. The potassium silicate includes at least one selected from K2SiO3, K4SiO4, K2Si2O5, and K2Si4O9 . The potassium silicate is preferably an anhydride ,} but may be a hydrate.

The storage tank 11 is a tank that stores the ion exchange mixture 10. At least a portion of the contact surface of the storage tank 11 with the ion exchange mixture 10 is made of metal. In this first embodiment, the inner surface 11S of the storage tank 11 is made of stainless steel. It is preferable that the storage tank 11 further includes an opening for inserting and removing the jig 12 and the ion exchange glass G1, and a lid for covering the opening (not shown).

The jig 12 is a member that holds the ion-exchange glass G1. During the ion exchange process, the jig 12 is immersed in the ion-exchange mixture 10 in the storage tank 11 while holding the ion-exchange glass G1. At least a portion of the contact surface of the jig 12 with the ion-exchange mixture 10 is made of metal. In this first embodiment, the entire jig 12 is made of stainless steel. The jig 12 is carried in and out of the storage tank 11 by a transport device (not shown).

The ion-exchange glass G1 is a glass article before the ion-exchange process, which is to be the target of the ion-exchange process. In the first embodiment, the ion-exchange glass G1 is in the form of a rectangular plate. The plate thickness of the ion-exchange glass G1 is, for example, 2.0 mm or less, more preferably 1.0 mm or less, and even more preferably 0.3 mm to 0.9 mm. The length of the ion-exchange glass G1 is, for example, 5 mm to 5000 mm, 15 mm to 1000 mm, 30 mm to 500 mm, 50 mm to 300 mm, or 70 mm to 200 mm, and the width of the ion-exchange glass G1 is, for example, 1 mm to 4000 mm, 10 mm to 1000 mm, 30 mm to 500 mm, 40 mm to 300 mm, or 50 mm to 150 mm.

As described above, in the first embodiment, the ion exchange glass G1 is an alkali aluminosilicate glass, and for example, the glass composition preferably contains, in mass %, 40% to 70% SiO ₂ , 10% to 30% Al ₂ O ₃ , 0% to 3% B ₂ O ₃ , 5% to 25% Na ₂ O , 0% to 5.5% K ₂ O , 0.1% to 10% Li ₂ O , 0% to 5.5% MgO, and 2% to 10% P ₂ O ₅ .

Na ₂ O is an ion exchange component, and also a component that reduces high-temperature viscosity and improves melting and moldability. Na ₂ O is also a component that improves devitrification resistance and reaction devitrification with a molded refractory, especially an alumina refractory. If the content of Na ₂ O is too small, the melting property decreases, the thermal expansion coefficient decreases too much, and the ion exchange rate tends to decrease. Therefore, the preferred lower limit range of Na ₂ O is 5% or more, 7% or more, 8% or more, 8.5% or more, 9% or more, 9.5% or more, 10% or more, 11% or more, 12% or more, and particularly 12.5% or more by mass. On the other hand, if the content of Na ₂ O is too high, the phase separation generation viscosity tends to decrease. In addition, acid resistance may decrease, or the glass composition may lack a component balance, resulting in a decrease in devitrification resistance. Therefore, a suitable upper limit range of Na ₂ O is 25% or less, 22% or less, 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, particularly 15% or less.

K ₂ O is a component that reduces high-temperature viscosity and improves melting and moldability. It is also a component that improves devitrification resistance and increases Vickers hardness. However, if the content of K ₂ O is too high, the phase separation viscosity is likely to decrease. In addition, acid resistance decreases, and the glass composition is unbalanced, and devitrification resistance tends to decrease. Therefore, the preferred lower limit range of K ₂ O is, in mass%, 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, 2% or more, 2.5% or more, 3% or more, particularly 3.5% or more, and the preferred upper limit range is 5.5% or less, 5% or less, particularly less than 4.5%.

Li ₂ O is an ion exchange component, and also a component that reduces high-temperature viscosity and improves melting and moldability. It is also a component that increases Young's modulus. 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 0.1% or more, 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, particularly 2.5% or more, in mass%, and the preferred upper limit range is 10% or less, 8% or less, 5% or less, 4.5% or less, 4.0% or less, particularly less than 3.5%.

The above-mentioned ion exchange glass G1 can be produced, for example, as follows.

First, glass raw materials prepared to obtain the above glass composition are fed into a continuous melting furnace, heated and melted at 1500°C to 1600°C, clarified, and then fed into a forming device, where they are formed into a plate shape or the like by the overflow downdraw method, and slowly cooled to produce glass G1 for ion exchange. Note that various forming methods can be used in addition to the overflow downdraw method. For example, forming methods such as the float method, the downdraw method (slot down method, redraw method, etc.), the roll-out method, and the press method can be used.

After forming the ion exchange glass G1, or simultaneously with forming, bending may be performed as necessary. In addition, cutting, drilling, surface polishing, chamfering, edge polishing, etching, and other processing may be performed as necessary.

The following describes a method for producing ion-exchanged glass using the above-mentioned ion-exchanged glass production apparatus 1. Figure 2 is a flowchart showing an overview of the method for producing ion-exchanged glass according to the first embodiment of the present invention.

2, a molten salt preparation process is performed (step S1). Specifically, _NaNO3 and _KNO3 are mixed and heated to melt in the container 11 to prepare a molten salt 101.

Next, an ion exchange process is performed (step S2). Specifically, a plurality of sheets of ion exchange glass G1 are held in a jig 12 as one lot and immersed in molten salt 101. Conditions such as the temperature of the molten salt and the immersion time in the ion exchange process may be determined arbitrarily, but the temperature of the molten salt is, for example, 350°C to 500°C, preferably 360°C to 470°C, 360°C to 450°C, 360°C to 430°C, or 360°C to 410°C. The immersion time is, for example, 0.1 to 30 hours, preferably 0.2 to 20 hours, 0.3 to 15 hours, 0.4 to 10 hours, or 0.5 to 5 hours. By subjecting the ion exchange glass G1 to ion exchange processing, ion exchange glass GX is obtained.

When the ion exchange process for one lot is completed, the next lot of ion exchange glass G1 is subjected to the ion exchange process, and the ion exchange process is repeated until the ion exchange process for a predetermined number of lots is completed (NO in step S3).

On the other hand, when ion exchange for a predetermined number of lots is completed (YES in step S3), the stress characteristics of the ion-exchanged glass GX obtained in the final ion-exchange process are measured. Specifically, the surface compressive stress CS of the ion-exchanged glass GX is measured using a stress measuring device.

In the present invention, the stress characteristics can be measured using a known stress measurement method and a known stress measurement device. For example, the stress characteristics can be measured using a surface stress meter FSM-6000LE or SLP-1000 manufactured by Orihara Seisakusho Co., Ltd., either alone or in combination.

After the stress characteristic measurement is completed, it is determined whether the stress characteristic is less than a predetermined threshold value (step S5). The threshold value may be set arbitrarily according to the product specifications and the measuring device, and can be set to any value within the range of, for example, 300 to 1000 MPa. Specifically, in this first embodiment, it is determined whether the value of the surface compressive stress CS is less than 400 MPa, for example. More preferably, if the value of the surface compressive stress CS of the first lot of ion-exchanged glass GX is taken as 100%, it is preferable to set the threshold value to a compressive stress value that is 75 to 85% of that value.

If the stress characteristic is equal to or greater than the predetermined threshold (NO in step S5), the ion exchange process is performed on the next lot, and the above-described steps S2 to S5 are repeated.

On the other hand, if the stress characteristic is less than the predetermined threshold value (YES in step S5), an addition process is performed to add an alkali metal silicate as an additive 102 to the molten salt 101 (step S6). By this addition process, the ion exchange mixture 10 according to the present invention is formed inside the storage tank 11.

In step S6, it is preferable to add the additive 102 to the molten salt 101 and then stir the molten salt 101. Stirring can be performed by inserting a stick, paddle, or the like into the storage tank 11 and operating it manually or automatically by machine. After stirring, the additive may be dispersed in the molten salt 101 before the next process, or the process may wait until the additive 101 settles to the inner bottom of the storage tank 11.

After completing the addition process of step S6, the process of step S2 is carried out on the next lot of ion exchange glass G1, and the above process is repeated. After the process of step S6, a waiting period may be set to wait for a predetermined time until the adjustment of the ion concentration by the additive 102 progresses to a certain extent, and then the process of step S2 may be started. The waiting time after the process of step S6 until the start of step S2 may be set arbitrarily, but may be, for example, 1 minute or more, 5 minutes or more, 10 minutes or more, 30 minutes or more, 1 hour to 24 hours, or 1 hour to 12 hours.

According to the method for producing ion-exchange glass according to the first embodiment described above, the ion balance of the molten salt 101 can be adjusted to an appropriate state by adding an alkali metal silicate as an additive 102 to the molten salt 101 to form the ion exchange mixture 10. Furthermore, by adding an alkali metal silicate as the additive 102, corrosion of the storage tank 11 and the jig 12 can be suppressed. Therefore, the stress characteristics of the obtained ion-exchange glass GX can be stabilized.

In addition, according to the method for producing ion-exchanged glass according to the first embodiment, by adding the additive 102 at an appropriate timing, it is possible to prevent excessive addition of the additive 102 and more appropriately adjust the ion balance of the molten salt 101.

In the above-described first embodiment of the ion-exchange glass manufacturing method, the surface compressive stress CS is measured as a stress characteristic, and the necessity of performing the addition treatment is determined based on the magnitude of the value of the surface compressive stress CS. However, the above-described treatment may be performed based on other stress characteristics. For example, the depth DOC of the compressive stress layer may be measured in step S4, and it may be determined in step S5 whether the depth of the compressive stress layer is less than a predetermined threshold value. In this case, the threshold value of the depth DOC of the compressive stress layer may be set to any value within the range of, for example, 50 to 150 μm. In addition, the threshold value of the depth DOC of the compressive stress layer may be set based on a ratio according to the thickness of the ion-exchange glass G1. In this case, the threshold value of the depth DOC of the compressive stress layer may be set to any value within the range of, for example, 10% to 25% of the thickness of the ion-exchange glass G1.

In the above-described first embodiment of the ion-exchanged glass manufacturing method, a so-called sampling inspection is performed for each predetermined number of lots. However, a measurement process may be performed each time each lot of ion-exchanged glass G1 is subjected to ion exchange processing. In this case, the judgment process of step S3 may be omitted. By performing such processing, the addition process of step S6 can be performed at an appropriate timing, and the outflow of defective products can be more effectively suppressed.

In addition, in the ion-exchanged glass manufacturing method of the first embodiment, the processes of steps S4 and S5 may be omitted. That is, when the ion exchange process for a predetermined number of lots is completed (YES in step S3), the addition process of step S6 may be performed. For example, in cases where the degree of deterioration of the molten salt 101 or the degree of deterioration in the properties of the ion-exchanged glass GX can be predicted based on the number of lots, the number of steps S4 and S5 can be reduced by adopting such a process, thereby making production more efficient.

In addition, in the ion-exchanged glass manufacturing method of the first embodiment described above, after the molten salt preparation process of step S1 and before the ion exchange process of step S2, the addition process of step S6 may be performed, and production may be started in a state in which the additive 102 has been added to the molten salt 101 in advance.

Second Embodiment
In the above-mentioned first embodiment, the case where the increase in the Li ion concentration eluted in the molten salt is suppressed has been described as an example, but the present invention can also be applied to the adjustment of other ion concentrations. For example, the case where the increase in the Na ion concentration eluted in the molten salt is suppressed can be applied as in the following second embodiment. Note that, in the following, differences from the first embodiment will be described, and the description of the other configurations will be omitted as they are the same as those of the first embodiment.

The ion exchange glass G2 according to the second embodiment of the present invention is an alkali aluminosilicate glass containing Na ₂ O as a glass composition and not containing Li ₂ O. More specifically, the ion exchange glass G2 is a glass containing, for example, in mass %, SiO ₂ 40% to 70%, Al ₂ O ₃ 10% to 30%, B ₂ O ₃ 0% to 3%, Na ₂ O 5% to 25%, K ₂ O 0% to 5.5%, MgO 0% to 5.5%, and P ₂ O ₅ 2% to 10% as a glass composition, and not containing Li ₂ O. In the present invention, not containing Li ₂ O means that the content of Li ₂ is less than 0.1 mass %.

Na ₂ O is an ion exchange component, and also a component that reduces high-temperature viscosity and improves melting and moldability. Na ₂ O is also a component that improves devitrification resistance and reaction devitrification with a molded refractory, especially an alumina refractory. If the content of Na ₂ O is too small, the melting property decreases, the thermal expansion coefficient decreases too much, and the ion exchange rate tends to decrease. Therefore, the preferred lower limit range of Na ₂ O is 5% or more, 7% or more, 8% or more, 8.5% or more, 9% or more, 9.5% or more, 10% or more, 11% or more, 12% or more, and particularly 12.5% or more by mass. On the other hand, if the content of Na ₂ O is too high, the phase separation generation viscosity tends to decrease. In addition, acid resistance may decrease, or the glass composition may lack a component balance, resulting in a decrease in devitrification resistance. Therefore, a suitable upper limit range of Na ₂ O is 25% or less, 22% or less, 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, particularly 15% or less.

K ₂ O is a component that reduces high-temperature viscosity and improves melting and moldability. It is also a component that improves devitrification resistance and increases Vickers hardness. However, if the content of K ₂ O is too high, the phase separation viscosity is likely to decrease. In addition, acid resistance decreases, and the glass composition is unbalanced, and devitrification resistance tends to decrease. Therefore, the preferred lower limit range of K ₂ O is, in mass%, 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, 2% or more, 2.5% or more, 3% or more, particularly 3.5% or more, and the preferred upper limit range is 5.5% or less, 5% or less, particularly less than 4.5%.

In the second embodiment, the alkali metal silicate as an additive contained in the mixture for ion exchange is preferably potassium silicate. _The potassium silicate includes at least one selected from _{K2SiO3 , K4SiO4 , K2Si2O5} , and _{K2Si4O9 .} With this configuration, Na ions dissolved in the molten salt are ion-exchanged with _K ions contained in the alkali metal _silicate , thereby suppressing an increase in the concentration of Na ions in the molten salt.

It is particularly effective to add potassium silicate to a molten salt mainly composed of KNO _3. The molten salt 101 mainly composed of KNO ₃ contains, for example, 80 to 100% KNO ₃ and 0 to 20% NaNO ₃ + LiNO 3 by mass %, preferably 90 to 99.9% KNO ₃ and 0.1 to 10% NaNO ₃ + LiNO ₃ , and more preferably 98.5 to 99.8% KNO ₃ and 0.2 to 1.5% NaNO ₃ + LiNO _3. In such a molten _salt mainly composed of KNO ₃ , Na ions are easily eluted from the glass and the Na ion concentration in the molten salt increases, so the increase in concentration can be effectively suppressed by adding the above-mentioned potassium silicate.

Third Embodiment
In the second embodiment, the case where potassium silicate is used as the additive contained in the ion exchange mixture has been described, but in order to suppress an increase in the Na ion concentration of the molten salt, a lithium salt may be used as the additive. That is, a metal salt containing a metal component with an ionic radius smaller than that of the eluted ions may be used as the additive.

The lithium salt is, for example, a lithium silicate, and includes at least one selected from Li ₂ SiO ₃ (lithium metasilicate), Li ₄ SiO ₄ , Li ₂ Si ₂ O ₅ , and Li ₂ Si ₄ O ₉ .

The lithium salt may be a lithium phosphate, which includes at least one selected from the group consisting of Li ₃ PO ₄ (trilithium phosphate), Li ₂ HPO ₄ and LiH ₂ PO _4. The lithium silicate and the lithium phosphate may be used alone or in combination.

In the third embodiment, the same ion exchange glass and molten salt as those described in the first and second embodiments can be used under similar conditions.

Fourth Embodiment
The ion-exchanged glass GX obtained as 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 preferable to separately prepare and use a molten salt (referred to as the second molten salt) having a higher KNO ₃ mixing ratio than the molten salt 101 (referred to as the first molten salt) used in the first-stage ion-exchange treatment, more preferably the KNO ₃ mixing ratio is 90 mass% or more, and more preferably the molten salt composition described in the second embodiment can be used. According to such a treatment, a deep compressive stress layer is formed in the first-stage ion-exchange treatment for the ion-exchanged glass GX, and a high surface compressive stress CS can be imparted in the second-stage ion-exchange treatment. In addition, it is preferable to adjust the composition of the molten salt, the treatment temperature, the treatment time, etc., so that the surface compressive stress CS of the ion-exchanged glass GX is 700 MPa or more in the second-stage ion-exchange treatment.

In addition, potassium silicate or lithium salt may be added to the second molten salt used in the second stage ion exchange process described above, as in the methods shown in the second and third embodiments. With this configuration, an excessive increase in the Na ion concentration in the second molten salt can be suppressed.

Sodium silicate may also be added to the second molten salt in the same manner as in the first embodiment. If the first ion exchange process results in lithium salt adhering to the glass surface, and the glass is then immersed in the second molten salt in this state to perform the second ion exchange process, the Li ion concentration may increase in the second molten salt, hindering the ion exchange. However, by adding sodium silicate to the second molten salt as described above, the increase in the Li ion concentration in the second molten salt can be suppressed.

In the above embodiments, the ion-exchange glass G1 and the ion-exchange glass GX are exemplified as rectangular plates, but they are not limited to rectangular plates and can be any shape, such as curved plates, disks, tubes, containers, or spheres.

In addition, in each of the above embodiments, the ion exchange process is intended mainly to improve the strength of the glass, and the ion exchange glass GX is chemically strengthened glass. However, the present invention may also be applied to ion exchange processes for other purposes, such as ion exchange processes for adjusting the refractive index of optical components such as lenses, or for surface treatment of glass for medical use.

Alkali metal silicate used as additive 102 may be a mixture of potassium silicate, sodium silicate, and lithium silicate. For example, when multiple types of alkali metal ions are eluted from ion exchange glass G1, the concentration of each alkali metal ion in molten salt 101 can be suitably adjusted by mixing multiple types of alkali metal silicate depending on the number of types of eluted alkali metal ions.

In addition, in each of the above embodiments, the case where stainless steel is used for the storage tank 11 and the jig 12 is exemplified, but any known type of stainless steel, such as austenitic stainless steel or ferritic stainless steel, can be used as the stainless steel. In addition, the storage tank 11 and the jig 12 may be made of any metal other than stainless steel that is corrosion-resistant to the molten salt 101.

The manufacturing method of ion-exchange glass and the mixture for ion exchange according to the present invention will be described below based on examples. Note that the following examples are merely illustrative, and the present invention is not limited to the following examples in any way.

The samples were prepared as follows: First, ion-exchange glass G1 was prepared, which had a glass composition, in mass %, of 51.6 _% SiO2, 27.9 _{% Al2O3} , _0.3 % _B2O3 , 0.6% _K2O , 7.5% _Na2O , 3.3% _Li2O , 0.3% MgO, _8.4 % _P2O5 , and 0.1% _SnO2 .

Specifically, glass raw materials were mixed to obtain the above composition and melted in a platinum pot at 1600°C for 21 hours. The resulting molten glass was then formed into a plate with a thickness of 0.7 mm by flowing down from a refractory molded body using the overflow downdraw method.

Next, the ion exchange glass was immersed in the ion exchange mixtures having the compositions shown in Table 1, No. 1 to 6, under the temperature and time conditions shown in Table 1, to perform ion exchange treatment. In Table 1, No. 1 to 3 are examples of the present invention, and No. 4 to 6 are comparative examples.

The ion exchange mixtures Nos. 1, 2, and 4 were prepared by mixing LiNO3 into the molten salt to simulate a molten salt with an increased Li ion concentration after repeated ion exchange treatment. On the other hand, the ion exchange mixtures Nos. 3, 5, and ₆ were fresh molten salts that did not contain Li ions.

Na ₂ SiO ₃ was added as an additive to the ion exchange mixtures according to Nos. 1 to 3. On the other hand, no additive was added to the ion exchange mixtures according to Nos. 4 and 6 for comparison. Moreover, Na ₃ PO ₄ was added as an additive to the ion exchange mixture according to No. 5 for comparison. In Table 1, the amount of additive added is expressed in parts by mass when the molten salt is taken as 100 parts by mass.

To evaluate metal corrosivity, plate-shaped metal samples made of SUS304, SUS316, and SUS430, each measuring 1.0 mm thick, 20 mm wide, and 50 mm long, were immersed in the ion exchange mixtures No. 3 and 5.

The properties of the ion exchange mixture and ion exchange glass obtained in this manner are shown in Table 1.

The surface compressive stress CS in Table 1 was measured using a surface stress meter FSM-6000LE manufactured by Orihara Seisakusho Co., Ltd.

The amount of metal corrosion in Table 1 indicates the change in weight of each metal sample piece after immersion in the ion exchange mixture relative to the weight before immersion.

Comparative example No. 4, which has a high Li ion concentration in the molten salt and does not contain any additives, showed a significantly lower surface compressive stress value CS of the ion-exchanged glass than comparative example No. 6, which does not contain Li ions in the molten salt.

On the other hand, it was confirmed that in both Examples 1 and 2 containing Na ₂ SiO ₃ as an additive, the decrease in the surface compressive stress value CS of the ion-exchanged glass was suppressed compared to Comparative Example 4 containing no additive.

In addition, in Comparative Example No. 5, in which Na ₃ PO ₄ was added as an additive, a weight loss was observed for each metal sample immersed, and the occurrence of metal corrosion was confirmed. On the other hand, in the metal samples of Example No. 3, in which Na ₂ SiO ₃ was added as an additive, no weight loss was observed, and it was confirmed that metal corrosion was suppressed.

In the following examples, the effect of adding a lithium salt in suppressing an increase in the Na ion concentration in the molten salt was examined. In Table 2, No. 7 is an example of the present invention, No. 8 is a reference example, and No. 9 is a comparative example.

First, the molten salts having the compositions shown in No. 7 to No. 9 in Table 2 were adjusted to the temperatures shown in Table 1. The molten salts according to No. 7 to No. 9 were adjusted by mixing _NaNO3 into the molten salt in order to simulate a molten salt in which the Na ion concentration has increased after repeated ion exchange treatment.

Next, each additive shown in Table 2 was added to each molten salt to prepare an ion exchange mixture. _Li2SiO3 was added as an additive to the ion exchange mixture related to _No. 7. _Li3PO4 was added as an additive to the ion exchange mixture related to No. _8. On the other hand, no additive was added to the ion exchange mixture related to No. 9 for comparison. In Table 2, the amount of additive added is expressed in parts by mass when the molten salt is taken as 100 parts by mass.

Next, the Li ion concentration and Na ion concentration of the ion exchange mixture were measured after the time shown in Table 2 had elapsed from the time the additive was added. More specifically, about 10 g of precipitate-free supernatant was collected from each molten salt, and the Li ion and Na ion concentrations were quantitatively analyzed using atomic absorption spectrometry.

According to the above measurement results, the ion exchange mixture of Example No. 7 had a lower Na ion concentration than Comparative Example No. 9, which did not contain any additives, and the effect of suppressing the increase in Na ion concentration was confirmed.

The ion-exchange glass manufacturing method, ion-exchange glass manufacturing apparatus, and ion-exchange mixture of the present invention can be used to manufacture ion-exchange glass used in, for example, smartphones, mobile phones, tablet computers, personal computers, digital cameras, touch panel displays, cover glass for other display devices, in-vehicle panels, magnetic disks, etc.

Reference Signs List 1: Ion-exchange glass manufacturing apparatus 10: Ion-exchange mixture 11: Storage tank 12: Jig 101: Molten salt 102: Additive G1, G2: Ion-exchange glass GX: Ion-exchange glass

Claims (13)

A method for producing ion-exchanged glass, comprising a step of immersing a part or whole of ion-exchangeable glass containing an alkali metal component in a mixture for ion exchange to perform ion exchange treatment,
The ion exchange mixture includes a molten salt and an alkali metal silicate,
the alkali metal silicate contains an alkali metal component that is ion-exchangeable with an alkali metal component eluted from the ion-exchange glass into the molten salt during the ion exchange treatment,
an alkali metal component eluted from the ion-exchange glass into the molten salt during the ion exchange treatment is a Na ion;
_A method for producing _ion - exchanged glass _, wherein the alkali _metal silicate contains at _least one selected from the group consisting of _{Li2SiO3 ,} Li4SiO4 _, Li2Si2O5 _, and Li2Si4O9 _. The ion exchange glass is an alkali aluminosilicate glass containing 1.0 mol % or more of Na ₂ O as a composition,
The method for producing ion-exchanged glass according to claim 1 , wherein the molten salt comprises KNO ₃ . 3. The method for producing ion-exchanged glass according to claim 1, wherein the alkali metal silicate is a powdered alkali metal silicate crystal. 4. The method for producing ion-exchanged glass according to claim 3 , wherein the powdered alkali metal silicate has an average particle size D50 of 10 to 1000 μm. The method for producing ion-exchanged glass according to claim 3 , further comprising the step of stirring the molten salt after adding the alkali metal silicate to the molten salt. 6. The method for producing ion-exchanged glass according to claim 1, wherein the amount of the alkali metal silicate added is 0.1 to 30 parts by mass relative to 100 parts by mass of the molten salt. performing the ion exchange treatment a plurality of times by sequentially immersing a plurality of different lots of the glass for ion exchange in the mixture for ion exchange;
a step of measuring stress characteristics of the ion-exchanged glass obtained in the final ion-exchange treatment after the ion-exchange treatment of a predetermined number of lots of the glass for ion-exchange;
7. The method for producing ion- exchanged glass according to claim 1, further comprising the step of determining whether or not to add the alkali metal silicate to the molten salt depending on a result of the measurement of the stress characteristics. As the stress characteristic, a surface compressive stress of the ion-exchanged glass is measured;
if the surface compressive stress is less than a predetermined threshold value, adding the alkali metal silicate to the molten salt and then performing ion exchange of a next lot of the glass for ion exchange;
when the surface compressive stress is equal to or greater than a predetermined threshold value, the alkali metal silicate is not added to the molten salt, and a next lot of the glass for ion exchange is subjected to ion exchange.
The method for producing the ion-exchanged glass according to claim 7 . A mixture for ion exchange comprising a molten salt and an additive,
The molten salt contains one or more selected from _NaNO3 and _KNO3 ,
The additive includes an alkali metal silicate,
The alkali metal silicate is a powdered alkali metal silicate crystal,
_The alkali metal silicate is at _least one selected _{from the group} consisting _{of Li2SiO3} , Li4SiO4 _, Li2Si2O5 , and _{Li2Si4O9 .} 10. The ion exchange mixture according to claim 9 , comprising 0.1 to 30 parts by mass of an alkali metal silicate as the additive, based on 100 parts by mass of the molten salt. A mixture for ion exchange according to claim 9 or 10 ,
a storage tank for storing the ion exchange mixture;
At least a part of the surface of the container that comes into contact with the mixture for ion exchange is made of metal. Further comprising a jig that holds glass for ion exchange and is immersed in the mixture for ion exchange;
The apparatus for producing ion-exchanged glass according to claim 11 , wherein a surface of the jig in contact with the mixture for ion exchange is made of metal. The ion-exchanged glass manufacturing apparatus according to claim 11 or 12 , wherein the metal is stainless steel.