Method for extending the lifetime of a molten salt composition, method for manufacturing a chemically strengthened glass, glass aid and raw material for glass

Abstract

The present invention relates to a method for extending the life of a molten salt composition, a method for producing a chemically strengthened glass, a glass aid, and a raw material of glass. The present invention relates to a method for extending the life of a molten salt composition, which comprises a step of adding a glass aid to a molten salt composition used in a chemical strengthening treatment of a glass for chemical strengthening, wherein the total of the contents of SiO2 and Al2O3 in the glass aid is 60% or more in mass% on an oxide basis.

Description

[0001] This application is a divisional application of the Chinese patent application No. 202080030666.5, filed on April 20, 2020. TECHNICAL FIELD

[0002] The present application relates to a method for extending the life of a molten salt composition, a method for manufacturing a chemically strengthened glass, a glass aid, and a raw material for glass. BACKGROUND

[0003] As a protective glass for displays of portable terminals such as smartphones, a glass capable of withstanding drop strength is required, and a chemically strengthened glass having a high surface compressive stress value (CS) and a large depth of layer of compressive stress (DOL) is being actively developed.

[0004] In the chemical strengthening treatment, by immersing a glass for chemical strengthening in a molten salt composition, alkali metal ions having a small ionic radius in the glass for chemical strengthening are exchanged with alkali metal ions having a large ionic radius in the molten salt composition, whereby a compressive stress layer is formed on the surface of the glass for chemical strengthening to obtain a chemically strengthened glass. If the molten salt composition after the treatment sufficiently contains alkali metal ions having a large ionic radius, it can be directly used again for the chemical strengthening treatment of a new glass for chemical strengthening. However, due to the chemical strengthening treatment, the amount of ions having a large ionic radius in the molten salt composition decreases, and the amount of ions having a small ionic radius increases, so the number of uses of the molten salt composition is limited.

[0005] In order to increase the number of uses of the molten salt composition, that is, to extend the life of the molten salt composition, a technique of adding an additive (aid) to the molten salt composition is known. For example, in Patent Literature 1, a technique of adding a Li absorbing glass for chemical strengthening to a molten salt composition is disclosed.

[0006] In addition, in Patent Literature 2, a technique of adding a Na salt and a K salt of a heteroanion to a molten salt composition, and by a reaction with them, discharging ions having a small ionic radius in the molten salt composition to the outside of the system in the form of a solid precipitate is disclosed.

[0007] Prior Art Documents

[0008] Patent Literature

[0009] Patent Literature 1: Japanese Patent No. 4410354

[0010] Patent Literature 2: Japanese Patent Application Laid-Open No. 2013-67555

[0011] Non-Patent Literature

[0012] Non-patent literature 1: "New Glasses and Their Properties", First Edition, Business Systems Research Unit, August 20, 1984 SUMMARY

[0013] PROBLEMS TO BE SOLVED BY THE INVENTION

[0014] However, the Li absorbing glass described in Patent Literature 1, the Na salt and K salt of the heteroanion described in Patent Literature 2, and the water in the molten salt composition react, and there is a problem that the pH of the molten salt composition increases. When the pH increases, OH - The glass network is cut, precipitates are generated on the surface of the glass, and the transparency of the glass decreases. In recent years, particularly in applications such as protective glass for displays of portable terminals, it is required that the chemically strengthened glass has a significantly higher strength than conventional glasses, and the ion exchange amount in the chemical strengthening treatment is significantly larger than that in the chemical strengthening treatment of conventional glasses such as the glass for magnetic recording media described in Patent Literature 1. As the ion exchange amount increases, it is also required to shorten the chemical strengthening time, and in order to shorten the strengthening time, it is required to strengthen at a higher temperature. The higher the temperature of the strengthening, the more significant the cutting of the glass network and the accompanying decrease in the transparency of the glass due to the increase in the pH, and therefore, it is required that the pH is less likely to increase than conventional Li absorbing agents.

[0015] In view of the above, an object of the present application is to provide a method for extending the life of a molten salt composition capable of suppressing an increase in the pH of the molten salt composition.

[0016] In addition, an object of the present application is to provide a glass aid for use in the above-mentioned method for extending the life of a molten salt composition.

[0017] In addition, an object of the present application is to provide a method for manufacturing a chemically strengthened glass and a raw material of a glass that suppresses production costs.

[0018] MEANS FOR SOLVING THE PROBLEMS

[0019] That is, a method for extending the life of a molten salt composition according to the present application includes a step of adding a glass aid to a molten salt composition used in a chemical strengthening treatment of a glass for chemical strengthening, wherein the total of the contents of SiO2 and Al2O3 in the glass aid is 60% or more in mass% on an oxide basis.

[0020] In one embodiment of the method for extending the life of a molten salt composition according to the present application, the total of the contents of SiO2, Al2O3, Na2O, P2O5, B2O3, MgO, and K2O in the glass aid can be 95% or more in mass% on an oxide basis.

[0021] In one embodiment of the method for extending the life of a molten salt composition of the present application, the content of Li2O in the glass aid can be 3% or less and the content of Na2O can be 5% or more, in terms of mass% on an oxide basis.

[0022] In one embodiment of the method for extending the life of a molten salt composition of the present application, the content of Li2O in the glass aid can be 3% or less and the content of K2O can be 5% or more, in terms of mass% on an oxide basis.

[0023] In one embodiment of the method for extending the life of a molten salt composition of the present application, the water content of the glass aid can be 5% or less.

[0024] In one embodiment of the method for extending the life of a molten salt composition of the present application, the glass aid can be in a plate shape.

[0025] In one embodiment of the method for extending the life of a molten salt composition of the present application, the glass aid can be in a granular shape.

[0026] In one embodiment of the method for extending the life of a molten salt composition of the present application, the chemically strengthening glass can contain 1% or more of Li2O, in terms of mass% on an oxide basis.

[0027] In one embodiment of the method for extending the life of a molten salt composition of the present application, the chemically strengthening glass can contain 1% or more of Na2O, in terms of mass% on an oxide basis.

[0028] In one embodiment of the method for extending the life of a molten salt composition of the present application, the molten salt composition can contain a nitrate.

[0029] One embodiment of the method for extending the life of a molten salt composition of the present application further has a step of taking out the glass aid that has absorbed Li and / or Na from the molten salt composition, which can be performed within 24 hours from the step of adding the glass aid to the molten salt composition.

[0030] The method for producing a chemically strengthened glass of the present application has: a step of immersing a glass aid in a molten salt composition so that the glass aid absorbs Li and / or Na contained in the molten salt composition, the content of SiO2 and Al2O3 in the glass aid being 60% or more in total, in terms of mass% on an oxide basis; a step of taking out the glass aid that has absorbed Li and / or Na from the molten salt composition; a step of producing a chemically strengthening glass using the taken-out glass aid as a material; and a step of performing a chemical strengthening treatment on the chemically strengthening glass.

[0031] In one embodiment of the method for producing a chemically strengthened glass according to the present application, the total content of SiO2, Al2O3, Na2O, P2O5, B2O3, MgO, and K2O in the glass aid can be 95% or more in mass% on an oxide basis.

[0032] The glass aid according to the present application is used to extend the life of a molten salt composition by absorbing Li ions and / or Na ions contained in the molten salt composition used in the chemical strengthening treatment of a glass, wherein the total content of SiO2and Al2O3in the glass aid is 60% or more in mass% on an oxide basis.

[0033] In one embodiment of the glass aid according to the present application, the total content of SiO2, Al2O3, Na2O, P2O5, B2O3, MgO, and K2O in the glass aid can be 95% or more in mass% on an oxide basis.

[0034] The raw material of the glass according to the present application is a glass, and the total content of SiO2, Na2O, and Li2O in the glass is 95% or more in mass% on an oxide basis, and the total content of Li2O and Na2O is 15% or more.

[0035] Effects of the Invention

[0036] The method for extending the life of a molten salt composition according to the present application can suppress the increase in the pH of the molten salt composition. DETAILED DESCRIPTION

[0037] Hereinafter, embodiments of the method for extending the life of a molten salt composition, the method for producing a chemically strengthened glass, and the glass aid according to the present application will be described, but the present application is not limited to the following embodiments, and can be arbitrarily modified within the scope of the gist of the present application.

[0038] In the present specification, "%" in the content of the components of a glass means mass% on an oxide basis.

[0039] In the present specification, in the case where "~" is used to indicate a numerical range, a range including the numerical values recited before and after it as lower limit values and upper limit values is indicated.

[0040] In the present specification, "chemically strengthened glass" means a glass after a chemical strengthening treatment, and "glass for chemical strengthening" means a glass before a chemical strengthening treatment.

[0041] GLASS AID

[0042] First, the glass aid of the present embodiment will be described. The glass aid of the present embodiment is a glass aid for reducing the concentration of ions of a small alkali metal contained in a molten salt composition used in chemical strengthening treatment of a chemically strengthened glass, and increasing the concentration of ions of a large alkali metal, and prolonging the life of the molten salt composition. Note that, in the case where the molten salt composition is used for Li-Na exchange and / or Li-K exchange, the small alkali metal is Li, and in the case where the molten salt composition is used for Na-K exchange, the small alkali metal is Na. In addition, in the case where the molten salt composition is used for Li-Na exchange, the large alkali metal is Na, and in the case where the molten salt composition is used for Li-K exchange and / or Na-K exchange, the large alkali metal is K.

[0043] The total (total amount) of the contents of SiO2and Al2O3in the glass aid of the present embodiment is 60% or more in terms of mass% on an oxide basis. In addition, the total of the contents of SiO2, Al2O3, Na2O, P2O5, B2O3, MgO, and K2O in the glass aid of the present embodiment is preferably 95% or more.

[0044] The glass aid of the present embodiment is in a glass state, and the total amount of SiO2and Al2O3is large, being 60% or more, and thus the reaction with water in the molten salt is small, and the increase in the pH of the molten salt composition can be suppressed. The total amount of SiO2and Al2O3in the glass aid of the present embodiment is preferably 65% or more.

[0045] From the viewpoint of suppressing the reduction in the transparency of the glass caused by OH - The pH of the molten salt composition after the addition of the glass aid of the present embodiment is preferably approximately neutral from the viewpoint of suppressing the reduction in the transparency of the glass caused by OH

[0046] In addition, when the total of the contents of SiO2, Al2O3, Na2O, P2O5, B2O3, MgO, and K2O in the glass aid of the present embodiment is 95% or more, the effect of prolonging the life of the molten salt composition is particularly high, and the elution of ions that hinder chemical strengthening is particularly small, as will be described below, and thus this is preferred.

[0047] When the glass aid is added to the molten salt composition containing small alkali metal ions, the large alkali metal ions in the glass aid exchange (ion exchange) with the small alkali metal ions in the molten salt composition, the small alkali metal ions in the molten salt composition are absorbed by the glass aid, and the large alkali metal ions in the glass aid are released into the molten salt composition, thereby prolonging the life of the molten salt composition.

[0048] The present inventors and others have conducted repeated research, and as a result, it has been found that a glass containing, as a main component, an oxide of an element having an atomic number of less than 20, and more specifically a glass containing SiO2, Al2O3, Na2O, P2O5, B2O3, MgO, and K2O as main components has an excellent molten salt life-prolonging effect. That is, it has been found that this glass has an effect of prolonging the life of a molten salt composition by absorbing small alkali metal ions in the molten salt composition and releasing large alkali metal ions. In addition, it has been found that since this glass does not easily dissolve ions that hinder chemical strengthening in a molten salt composition, the compressive stress value resulting from chemical strengthening does not easily decrease. It is believed that in the case where the glass aid contains a large amount of elements having an atomic number of 20 or more, the molten salt composition life-prolonging effect becomes smaller for the following reasons.

[0049] First, trivalent or pentavalent ions function as network modifiers of the glass aid, but large ions having an atomic number of greater than 20 are difficult to move in the Si skeleton, and when such elements are present, the movement of alkali metal ions in the glass aid is hindered, and thus the ion exchange amount decreases.

[0050] In addition, divalent ions such as CaO and SrO do not significantly decrease the ion exchange amount of the glass aid, but when dissolved in a molten salt composition, they remain on the surface of the glass to be chemically strengthened, and hinder the chemical strengthening process. Therefore, even if a glass aid containing a large amount of divalent ions is added to a molten salt composition, the life of the molten salt composition is not prolonged. Note that it is also disclosed in Non-Patent Literature 1 that ions such as CaO and SrO hinder the chemical strengthening process.

[0051] Therefore, in the glass aid of the present embodiment, in order to ensure an excellent molten salt life-prolonging effect, it is preferable to set the total of the contents of SiO2, Al2O3, Na2O, P2O5, B2O3, MgO, and K2O, which are components containing elements having an atomic number of less than 20, to 95% or more. In addition, the total of the contents of SiO2, Al2O3, Na2O, P2O5, B2O3, MgO, and K2O in the glass aid of the present embodiment is more preferably 96% or more, and further preferably 98% or more, and there is no particular limitation on the upper limit, and it can be 100%.

[0052] Next, the preferable ranges of the contents of these components will be described.

[0053] The optimum composition of the glass aid can be roughly classified into two types depending on the method of use. One is a composition that prioritizes chemical durability in comparison with the amount of absorption of small alkali metal ions and the amount of release of large alkali metal ions, that is, the ion exchange amount. Since the chemical durability is excellent, the reaction with water in the molten salt composition is less, and the pH of the molten salt composition is inhibited from rising. Therefore, it is possible to add more aid to the molten salt composition than in the past, and the life extension effect is improved compared with the past. On the other hand, there is also a composition that prioritizes the ion exchange amount compared with the chemical durability. By increasing the ion exchange amount per unit amount of aid, the life extension effect is improved compared with the past. In addition, the above two examples are cited, but a composition intermediate thereto can also be used.

[0054] In addition, depending on whether the small alkali metal ion that is the object of ion exchange is either of Li or Na, the optimum composition of the glass aid also differs. Hereinafter, a detailed explanation will be given.

[0055] (First composition)

[0056] First, the preferable range of the composition of the glass aid that prioritizes chemical durability in the case where the small alkali metal ion is Li (hereinafter also referred to as "first composition") will be explained.

[0057] SiO2is a component that constitutes the skeleton of the glass aid.

[0058] In order to improve the stability of the glass aid, the content of SiO2of the glass aid of the first composition is preferably 52% or more, more preferably 54% or more, and further preferably 57% or more.

[0059] On the other hand, in order to improve the meltability of the glass aid, the content of SiO2of the glass aid of the first composition is preferably 95% or less, more preferably 92% or less, and further preferably 90% or less.

[0060] Na2O is an essential component for Li-Na ion exchange.

[0061] In order to increase the ion exchange amount, the content of Na2O of the glass aid of the first composition is preferably 5% or more, more preferably 9% or more, and further preferably 11% or more.

[0062] On the other hand, in the case where the content of Na2O is excessive, the chemical durability easily deteriorates. The content of Na2O of the glass aid of the first composition that prioritizes chemical durability is preferably 25% or less, more preferably 22% or less, and further preferably 20% or less.

[0063] Al2O3 is a component that hinders ion exchange of alkali metal ions, but is also a component that improves chemical durability. The content of Al2O3 of the glass aid of the first composition can be 0%, but as long as it is within a range that exerts the effects of the present application, the glass aid of the first composition can also contain Al2O3.

[0064] In the case where the glass aid of the first composition contains Al2O3, the ratio of the content of Al2O3 to the content of Na2O (Al2O3 / Na2O) is preferably small, for example, it is preferably 2.0 or less, more preferably 1.5 or less, and further preferably 1.1 or less. The content of Al2O3 is preferably 40% or less, more preferably 30% or less, and further preferably 20% or less.

[0065] In order to obtain sufficient chemical durability, the total amount of SiO2 and Al2O3 is preferably 65% or more, more preferably 70% or more, and further preferably 75% or more. On the other hand, in order to increase the amount of ion exchange, the total amount of SiO2 and Al2O3 is preferably 95% or less, more preferably 92% or less, and further preferably 90% or less.

[0066] P2O5, B2O3, although not essential components, can be contained in the glass aid of the first composition. When the contents of these components are too much, chemical durability easily becomes poor, and thus the contents of these components are each preferably 10% or less, more preferably 5% or less, and further preferably 2% or less. The lower limit of the contents of these components is not particularly limited, and can be 0%, but in order to improve the melting property of the glass, it is preferably 0.1% or more, more preferably 0.5% or more, and further preferably 1.0% or more.

[0067] MgO, K2O, although not essential components, can be contained in the glass aid of the first composition. When the contents of these components are too much, chemical durability easily becomes poor, and thus the contents of these components are each preferably 15% or less, more preferably 10% or less, and further preferably 7% or less. The lower limit of the contents of these components is not particularly limited, and can be 0%, but in order to improve the melting property of the glass, it is preferably 1% or more, more preferably 3% or more, and further preferably 5% or more.

[0068] In addition, when a large amount of Li2O is contained in the glass aid, ion exchange of Na ions in the glass aid with Li ions in the molten salt is difficult to occur. Therefore, in order to ensure sufficient ion exchange amount in the glass aid of the first composition, it is preferable to set the content of Li2O to 3% or less. The content of Li2O of the glass aid of the first composition is more preferably 2% or less, and further preferably 1% or less.

[0069] In addition, the lower limit of the content of Li2O in the glass aid of the first composition is not particularly limited and can be 0%.

[0070] (Second composition)

[0071] Next, the preferable range of the composition of the glass aid that prioritizes chemical durability when the small alkali metal ion is Na (hereinafter also referred to as "second composition") will be described. Note that the glass aid having the second composition can undergo ion exchange with Na as the small alkali metal ion as well as ion exchange with Li as the small alkali metal ion.

[0072] As for SiO2, P2O5, B2O3, and MgO, the same applies to the first composition, and thus the description is omitted.

[0073] K2O is known to be an essential component for Na-K ion exchange and also contributes to K-Li ion exchange.

[0074] In order to increase the ion exchange amount, the content of K2O in the glass aid of the second composition is preferably 5% or more, more preferably 9% or more, and further preferably 11% or more.

[0075] On the other hand, in the case where the content of K2O is excessive, the chemical durability tends to deteriorate. The content of K2O in the glass aid of the second composition that prioritizes chemical durability is preferably 28% or less, more preferably 20% or less, and further preferably 16% or less.

[0076] Al2O3 is a component that hinders ion exchange of alkali metal ions, but is also a component that improves chemical durability. The content of Al2O3 in the glass aid of the second composition can be 0%, but as long as it is within a range where the effects of the present application are exerted, the glass aid of the second composition can also contain Al2O3.

[0077] In the case where the glass aid of the second composition contains Al2O3, the ratio of the content of Al2O3 to the content of K2O (Al2O3 / K2O) is preferably small, for example, 2.0 or less, more preferably 1.5 or less, and further preferably 1.1 or less. The content of Al2O3 is preferably 40% or less, more preferably 30% or less, and further preferably 20% or less.

[0078] In order to obtain sufficient chemical durability, the total amount of SiO2 and Al2O3 is preferably 65% or more, more preferably 70% or more, and further preferably 75% or more. On the other hand, in order to increase the ion exchange amount, the total amount of SiO2 and Al2O3 is preferably 95% or less, more preferably 92% or less, and further preferably 90% or less.

[0079] Li2O is a component that exchanges with Na ions in the molten salt composition. However, a glass aid with a large amount of Li2O releases Li ions into the molten salt composition when absorbing Na ions in the molten salt composition. Li ions in the molten salt composition have an effect of shortening the life of the molten salt composition, and thus are not preferred components. Therefore, the content of Li2O in the glass aid of the second composition is preferably small, and specifically, the content of Li2O in the glass aid of the second composition is preferably 3% or less, more preferably 1.5% or less, and further preferably 0.5% or less. The glass aid of the second composition can not contain Li2O.

[0080] In addition, when a large amount of Na2O is contained in the glass aid, ion exchange of K ions in the glass aid with Na ions in the molten salt composition is difficult to occur. Therefore, in order to secure a sufficient amount of ion exchange in the glass aid of the second composition, the content of Na2O is preferably set to 30% or less. The content of Na2O in the glass aid of the second composition is more preferably 25% or less, and further preferably 20% or less. On the other hand, when a large amount of Na2O is contained in the glass aid, ion exchange of Na ions in the glass aid with Li ions in the molten salt composition sometimes has an effect of prolonging the life of the molten salt composition. In the case where ion exchange of Li ions in the molten salt composition with Na ions in the glass aid and ion exchange of Na ions in the molten salt composition with K ions in the glass composition are targeted, the content of Na2O in the glass aid of the second composition is preferably 2% or more, more preferably 5% or more, and further preferably 10% or more.

[0081] The lower limit of the content of Na2O in the glass aid of the second composition is not particularly limited, and can be 0%.

[0082] (Third Composition)

[0083] Next, the preferred range of the composition of the glass aid that prioritizes the amount of ion exchange in the case where the small alkali metal ion is Li (hereinafter also referred to as "third composition") is described.

[0084] SiO2is a component that constitutes the skeleton of the glass aid.

[0085] In order to improve the stability of the glass, the content of SiO2in the glass aid of the third composition is preferably 55% or more, more preferably 60% or more, and further preferably 65% or more.

[0086] On the other hand, in order to improve the meltability of the glass, the content of SiO2in the glass aid of the third composition is preferably 75% or less, more preferably 73% or less, and further preferably 69% or less.

[0087] Na2O is an indispensable component for Li-Na ion exchange.

[0088] In order to increase the ion exchange amount, the content of Na2O in the glass aid of the third composition is preferably 20% or more, more preferably 25% or more, and further preferably 30% or more.

[0089] On the other hand, in the case where the content of Na2O is excessive, the chemical durability tends to be poor. The content of Na2O in the glass aid of the third composition is preferably 45% or less, more preferably 40% or less, and further preferably 35% or less.

[0090] Al2O3is a component that hinders ion exchange of alkali metal ions and is a component that improves chemical durability. The content of Al2O3in the glass aid of the third composition is preferably 0%, but the glass aid of the third composition can contain Al2O3as long as it is within a range in which the effects of the present application are exerted.

[0091] In the case where the glass aid of the third composition contains Al2O3, the ratio of the content of Al2O3to the content of Na2O (Al2O3 / Na2O) is preferably small, for example, 0.3 or less, more preferably 0.2 or less, and further preferably 0.1 or less.

[0092] In order to obtain sufficient chemical durability, the total amount of SiO2and Al2O3is preferably 60% or more, and more preferably 65% or more. On the other hand, in order to increase the ion exchange amount, the total amount of SiO2and Al2O3is preferably 80% or less, more preferably 75% or less, and further preferably 70% or less.

[0093] P2O5and B2O3, although not essential components, can be contained in the glass aid of the third composition. When the contents of these components are excessive, the chemical durability tends to be poor, and thus the content of each of these components is preferably 10% or less, more preferably 5% or less, and further preferably 2% or less. The lower limit of the content of each of these components is not particularly limited and can be 0%, but in order to improve the melting property of the glass, it is preferably 0.1% or more, more preferably 0.5% or more, and further preferably 1.0% or more.

[0094] MgO and K2O, although not essential components, can also be contained in the glass aid of the third composition. When the contents of these components are excessive, the chemical durability tends to be poor, and thus the content of each of these components is preferably 10% or less, more preferably 5% or less, and further preferably 3% or less. The lower limit of the content of each of these components is not particularly limited and can be 0%, but in order to improve the melting property of the glass, it is preferably 0.1% or more, more preferably 0.5% or more, and further preferably 1% or more.

[0095] In addition, when a large amount of Li20 is contained in the glass aid, ion exchange of Na ions in the glass aid with Li ions in the molten salt is difficult to occur. Therefore, in order to ensure a sufficient amount of ion exchange in the glass aid of the third composition, the content of Li20 is preferably set to 3% or less. The content of Li20 in the glass aid of the third composition is more preferably 2% or less, and further preferably 1% or less.

[0096] In addition, the lower limit of the content of Li20 in the glass aid of the third composition is not particularly limited, and can be 0%.

[0097] (Fourth Composition)

[0098] Next, the preferable range of the composition of the glass aid that prioritizes the amount of ion exchange when the small alkali metal ion is Na (hereinafter also referred to as "fourth composition") will be described. Note that the glass aid having the fourth composition can not only undergo ion exchange with Na as the small alkali metal ion, but also ion exchange with Li as the small alkali metal ion.

[0099] As for Si02, P205, B203, and MgO, the same as the third composition, and thus the description is omitted.

[0100] K20 is known to be an indispensable component for Na-K ion exchange, and also contributes to K-Li ion exchange.

[0101] In order to increase the Na absorption amount, the content of K20 in the glass aid of the fourth composition is preferably 20% or more, more preferably 25% or more, and further preferably 30% or more.

[0102] On the other hand, in the case where the content of K20 is excessive, chemical durability is likely to deteriorate. The content of K20 in the glass aid of the fourth composition is preferably 45% or less, more preferably 40% or less, and further preferably 35% or less.

[0103] Al203is a component that hinders ion exchange of alkali metal ions, but is also a component that improves chemical durability. The content of Al203in the glass aid of the fourth composition can be 0%, but as long as it is within a range where the effects of the present application are exerted, the glass aid of the fourth composition can also contain Al203.

[0104] In the case where the glass aid of the fourth composition contains Al203, the ratio of the content of Al203to the content of K20 (Al203 / K20) is preferably small, and for example, is preferably 0.3 or less, more preferably 0.2 or less, and further preferably 0.1 or less.

[0105] To obtain sufficient chemical durability, the total amount of SiO2and Al2O3is preferably 60% or more, more preferably 65% or more. On the other hand, to increase the ion exchange amount, the total amount of SiO2and Al2O3is preferably 80% or less, more preferably 75% or less, further preferably 70% or less.

[0106] Li2O is a component that exchanges with Na ions in the molten salt composition. However, when a glass aid with much Li2O absorbs Na ions in the molten salt composition, Li ions are released into the molten salt composition. Li ions in the molten salt composition have an effect of shortening the life of the molten salt composition, and therefore Li2O is an undesirable component. Therefore, the less the content of Li2O in the glass aid of the fourth composition is, the more preferable it is, and specifically, the content of Li2O is preferably 3% or less, more preferably 1.5% or less, further preferably 0.5% or less. The glass aid of the fourth composition can not contain Li2O.

[0107] In addition, when a large amount of Na2O is contained in the glass aid, ion exchange of K ions in the glass aid with Na ions in the molten salt composition is difficult to occur. Therefore, to ensure sufficient ion exchange amount in the glass aid of the fourth composition, it is preferable to set the content of Na2O to 30% or less. The content of Na2O in the glass aid of the fourth composition is more preferably 25% or less, further preferably 20% or less. On the other hand, when a large amount of Na2O is contained in the glass aid, by ion exchange of Na ions in the glass aid with Li ions in the molten salt composition, sometimes has an effect of extending the life of the molten salt. In the case where ion exchange of Li ions in the molten salt composition with Na ions in the glass aid and ion exchange of Na ions in the molten salt composition with K ions in the glass composition are targeted, the content of Na2O in the glass aid of the fourth composition is preferably 2% or more, more preferably 5% or more, further preferably 10% or more.

[0108] The lower limit of the content of Na2O in the glass aid of the fourth composition is not particularly limited, and can be 0%.

[0109] Next, the other components are described. Note that the description of the other components is the same in the case where chemical durability is prioritized, in the case where ion exchange amount is prioritized, in the case where the small ion is Li ion, and in the case where the small ion is Na ion.

[0110] The glass aid of the present embodiment can contain other components within a range where the effects of the present application are exerted. For example, the glass aid of the present embodiment can contain N, F, S, Cl, and the like.

[0111] In addition, as described above, the content of the sum of the elements having an atomic weight of 20 or more in the glass adjuvant of the present embodiment is preferably small, and is preferably 5% or less, more preferably 3% or less, and further preferably 1% or less. Examples of the elements having an atomic weight of 20 or more include Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, La, Gd, Ca, Sr, Ba, Zr, Ta, W, and the like.

[0112] As a specific composition of the glass adjuvant of the present embodiment, for example, the following compositions (A) and (B) can be given.

[0113] Composition (A)

[0114] A glass adjuvant containing, in mass% on an oxide basis:

[0115] 52% to 90% of Si02,

[0116] 0 to 40% of Al203,

[0117] 15% or less of MgO,

[0118] 15% or less of K20,

[0119] 3% or less of Li20,

[0120] 5% to 25% of Na20,

[0121] 10% or less of B203, and

[0122] 10% or less of P205,

[0123] the content of the above oxides is 95% or more in total, and the content of Si02and Al203is 65% to 95% in total.

[0124] Composition (B)

[0125] A glass adjuvant containing, in mass% on an oxide basis:

[0126] 55% to 75% of Si02,

[0127] 20% to 45% of Na20,

[0128] 0.3 or less of Al203 / Na20,

[0129] 10% or less of MgO,

[0130] 10% or less of K20,

[0131] 3% or less of Li20,

[0132] 10% or less of B2O3, and

[0133] 10% or less of P2O5,

[0134] The total content of SiO2and Na2O is 95% or more, and the total content of SiO2and Al2O3is 60% to 80%.

[0135] Further, in order to further suppress the increase in the pH of the molten salt composition, the water content of the glass aid of the present embodiment is preferably low, and is preferably 5% or less, more preferably 1% or less, and further preferably 0.1% or less.

[0136] The shape of the glass aid of the present embodiment is not particularly limited, and can be, for example, a plate shape, a sheet shape, or a granular shape (powder shape), and can also be other shapes. When the glass aid is a plate shape, it is easy to take out from the molten salt composition, and is therefore preferred. In the case where the glass aid is a plate shape, the thickness is preferably 0.3 mm or more, more preferably 0.5 mm or more, and further preferably 1.0 mm or more. When the plate thickness is too thick, the alkali metal ion absorption amount decreases, and therefore the plate thickness is preferably 5.0 mm or less. The plate thickness is more preferably 3.0 mm or less, and further preferably 2.0 mm or less.

[0137] On the other hand, when the glass aid is a granular shape, the handleability is excellent, and is therefore preferred. In the case where the glass aid is a granular shape, the particle diameter is preferably 0.3 mm or more, more preferably 0.5 mm or more, and further preferably 1.0 mm or more. On the other hand, in the case where the particle diameter is too large, the alkali metal ion absorption amount decreases, and therefore the particle diameter is preferably 5.0 mm or less. The particle diameter is more preferably 3.0 mm or less, and further preferably 2.0 mm or less. Note that the particle diameter in the present specification indicates the average diameter of the particles.

[0138] <Method for extending the life of a molten salt composition>

[0139] Next, the method for extending the life of a molten salt composition of the present embodiment (hereinafter also simply referred to as "the method for extending the life of the present embodiment" or "the method of the present embodiment") will be described. The method for extending the life of a molten salt composition of the present embodiment includes a step of adding the above-described glass aid of the present embodiment to a molten salt composition used in the chemical strengthening treatment of a glass.

[0140] According to the method for extending the life of a molten salt composition of the present embodiment, the increase in the pH of the molten salt composition can be suppressed, and thus the life of the molten salt composition can be sufficiently extended. The method for extending the life of a molten salt composition of the present embodiment uses the glass aid of the present embodiment, and the glass aid of the present embodiment can suppress the increase in the pH of the molten salt composition due to the reaction with water.

[0141] The life extension method of the present embodiment can be implemented during the chemical strengthening treatment, or can be implemented during a period in which the chemical strengthening treatment is not performed. That is, the glass aid can be added to the molten salt composition in which the glass for chemical strengthening is immersed, or can be added to the molten salt composition in which the glass for chemical strengthening is not immersed.

[0142] At the time of adding the glass aid, it can be spread in the strengthening furnace, or can be put in and taken out of a box, or can be poured into a cassette for strengthened glass as a part of the glass. In the case of using a box, a box having a net structure is preferably used so as to make the molten salt contact with the aid. In addition, when the box is fixed in the cassette, the aid can be easily replaced at the time of taking out and putting in the cassette for chemical strengthening, and thus is preferable.

[0143] In addition, the ion exchange amount of the glass aid added to the molten salt composition gradually decreases, and the life extension effect of the molten salt composition decreases, and thus in this case, it is preferable to take out from the molten salt composition. That is, the life extension method of the present embodiment preferably has a step of taking out the glass aid having absorbed small alkali metals (Li and / or Na) from the molten salt composition.

[0144] In order to improve the productivity of the chemically strengthened glass, the life extension method of the present embodiment is preferably performed in a short time. Thus, in the method of the present embodiment, the step of taking out the glass aid having absorbed small alkali metals from the molten salt composition is preferably performed within 24 hours from the step of adding the glass aid to the molten salt composition, more preferably within 10 hours, and further preferably within 5 hours. In order to also sufficiently extend the life of the molten salt composition in a short time as described above, a glass aid having a total content of Si02, Al203, Na20, P205, B203, MgO, and K20 of 95% or more is preferably used.

[0145] In the life extension method of the present embodiment, the amount of the glass aid added to the molten salt composition is not particularly limited, and can be appropriately adjusted depending on the total amount of the molten salt composition, the content of small alkali metal ions, the desired treatment time, and the like.

[0146] The temperature of the molten salt composition in the life extension method of the present embodiment can be a temperature at which the exchange of small alkali metal ions in the molten salt composition with large alkali metal ions in the glass aid is performed, and from the viewpoint of promoting the ion exchange, is preferably 350°C or higher, more preferably 400°C or higher, and further preferably 420°C or higher. In view of the decomposition of the molten salt, the temperature of the molten salt composition is preferably 500°C or lower, more preferably 475°C or lower, and further preferably 460°C or lower.

[0147] The molten salt composition whose life is extended by the method of the present embodiment can contain large alkali metal ions (Na ions and / or K ions) without particular limitation on the kind thereof, and generally contains a nitrate (sodium nitrate and / or potassium nitrate).

[0148] A glass for chemical strengthening, which chemically strengthens the molten salt composition whose life is extended by the method of the present embodiment, is described.

[0149] The glass for chemical strengthening can contain Li2O and / or Na2O, and various glasses can be used as long as they are glasses having a composition that can be strengthened by a forming and chemical strengthening treatment. As the glass for chemical strengthening, for example, aluminosilicate glass, soda-lime glass, borosilicate glass, lead glass, alkali barium glass, aluminoborosilicate glass, and the like can be listed. Specifically, for example, a glass containing 50 to 80% of SiO2, 2 to 25% of Al2O3, 0.1 to 20% of Li2O, 0.1 to 18% of Na2O, 0 to 10% of K2O, 0 to 15% of MgO, 0 to 5% of CaO, 0 to 5% of P2O5, 0 to 5% of B2O3, 0 to 5% of Y2O3, and 0 to 5% of ZrO2, in terms of molar percentage on an oxide basis, can be used as the glass for chemical strengthening.

[0150] In order to obtain a chemically strengthened glass having a high CS, a large DOL, and particularly high strength by a chemical strengthening treatment, it is preferable to use a glass for chemical strengthening containing a large amount of small alkali metal to increase the ion exchange amount at the time of chemical strengthening. The content of small alkali metal (Li2O and / or Na2O) of the glass for chemical strengthening, which is chemically strengthened using the molten salt composition whose life is extended by the method of the present embodiment, can be, for example, 1% or more, 3% or more, or 5% or more.

[0151] The thickness and shape of the glass for chemical strengthening are not particularly limited. The glass for chemical strengthening can be, for example, various shapes such as a flat plate shape having a uniform plate thickness, a shape having a curved surface on at least one of the front and back surfaces, and a three-dimensional shape having a curved portion, and can also be subjected to shape processing according to the use, such as mechanical processing such as cutting, end face processing, and hole processing. As a specific shape of the glass for chemical strengthening, for example, a plate shape having a thickness of 0.3 to 2.0 mm can be listed.

[0152] <Method for manufacturing chemically strengthened glass>

[0153] Next, a method for producing a chemically strengthened glass according to the present embodiment (hereinafter also referred to as "the production method according to the present embodiment") will be described. The method for producing a chemically strengthened glass according to the present embodiment is a method for producing a chemically strengthened glass using a glass aid that has been recovered in the life extension method of the molten salt composition described above as a material.

[0154] That is, the method for producing a chemically strengthened glass according to the present embodiment includes a step of immersing a glass aid in a molten salt composition so that the glass aid absorbs small alkali metals (Li and / or Na) contained in the molten salt composition, the content of SiO2 and Al2O3 in the glass aid being 60% or more in mass% on an oxide basis; a step of taking out the glass aid that has absorbed the small alkali metals (Li and / or Na) from the molten salt composition; a step of producing a glass for chemical strengthening using the taken-out glass aid as a material; and a step of subjecting the glass for chemical strengthening to a chemical strengthening treatment. In the production method described above, the total content of SiO2, Al2O3, Na2O, P2O5, B2O3, MgO, and K2O in the glass aid is preferably 95% or more in mass% on an oxide basis.

[0155] In the life extension method of the molten salt composition according to the present embodiment described above, the small alkali metal ions moved from the glass for chemical strengthening to the molten salt composition are absorbed by the glass aid, and large alkali metal ions are released from the glass aid to the molten salt composition. Therefore, the glass aid used after the life extension method of the molten salt composition according to the present embodiment (hereinafter also referred to as "the used glass aid") contains a large amount of small alkali metals. By using the used glass aid as a material for the glass for chemical strengthening, the use amount of expensive Li materials and Na materials can be reduced, and thus the glass for chemical strengthening, and further the chemically strengthened glass, can be obtained at low cost.

[0156] In the step of causing the glass aid to absorb the small alkali metals (Li and / or Na) contained in the molten salt composition, the glass aid is added to the molten salt composition so that the glass aid absorbs the small alkali metals contained in the molten salt composition. Detailed description is repeated with the description of the life extension method according to the present embodiment described above, and thus is omitted.

[0157] The step of taking out the glass aid that has absorbed the small alkali metals (Li and / or Na) from the molten salt composition in the production method according to the present embodiment is the same as the step of taking out the glass aid that has absorbed the small alkali metals (Li and / or Na) from the molten salt composition in the life extension method according to the present embodiment described above.

[0158] The method of manufacturing the chemically strengthened glass in the process of manufacturing the chemically strengthened glass using the extracted glass aid (used glass aid) as a material is not particularly limited, and for example, the following method can be cited: according to the desired composition, other glass materials are appropriately mixed into the used glass aid and melted, cast into a continuous melting furnace, heated and melted and clarified, and then supplied to a forming device, and then the molten glass is formed into a plate shape and slowly cooled. As the method of forming the molten glass into a plate shape, for example, a float method can be cited.

[0159] The used glass aid is preferably composed of components contained in the chemically strengthened glass, such as SiO2, Al2O3, MgO, Na2O, K2O, Li2O, ZrO2, TiO2, ZnO, B2O3, P2O5, and the like. When the used glass aid contains components not contained in the chemically strengthened glass, it is difficult to use the used glass aid as a raw material for the chemically strengthened glass. In addition, when the used glass aid is used as a raw material for the chemically strengthened glass, it is preferable that the used glass aid contain a small number of types of components. When the number of components increases, the process of mixing with other glass materials as a raw material becomes complicated, and a burden is placed on the process. For example, as the composition of the used glass aid as a raw material for the chemically strengthened glass, a glass in which the total of SiO2, Na2O, and Li2O is 95% or more is preferable. The total of the contents of Na2O and Li2O is preferably 15% or more, more preferably 20% or more, and further preferably 25% or more.

[0160] The method of chemical strengthening treatment in the process of performing chemical strengthening treatment on the chemically strengthened glass is also not particularly limited, and the type, temperature, and treatment time of the molten salt composition used can be appropriately adjusted according to the desired compressive stress distribution.

[0161] Example

[0162] Hereinafter, examples of the present application will be specifically described, but the present application is not limited thereto. In the examples, "ppm" means "mass ppm".

[0163] Manufacture of Glass Aid

[0164] (Glasses 1 and 2)

[0165] Glass plates having the compositions shown in the columns of glasses 1 and 2 in Table 1 were manufactured by a float method. The obtained glass plates were crushed and fractionated, and particles passing through a 2 mm sieve but not passing through a 1 mm sieve were collected, to obtain granular glasses 1 and 2.

[0166] (Glasses 3 to 8)

[0167] The raw materials were prepared in accordance with the composition of the glasses 3 to 8 shown in Table 1, and were melted at 1600°C to 1700°C for 30 minutes, and then the glass obtained by quenching with a rollout machine was pulverized, and was classified in the same manner as in the glass 1, to obtain the granular glasses 3 to 8.

[0168] Note that, in the present specification, the shape of the glass obtained by quenching with a rollout machine is referred to as "sheet shape", and the shape of the glass after classification is referred to as "granular shape".

[0169] (Glasses 9 to 13)

[0170] The raw materials were prepared in accordance with the composition of the glasses 9 to 13 shown in Table 2, and the sheet-shaped and granular glasses 9 to 13 were obtained by the same production method as in the glasses 3 to 8.

[0171] The water content of the obtained glass aids was measured using a heated-dry moisture meter (manufactured by A&D Co., Ltd., MS-70).

[0172] Table 1

[0173]

[0174] Table 2

[0175]

[0176] In Experimental Examples 1 to 14, the Li absorption effect was investigated. Note that Experimental Examples 1, 4 to 9, and 12 to 14 are examples, and Experimental Examples 2, 3, 10, and 11 are comparative examples.

[0177] <Experimental Example 1>

[0178] (First chemical strengthening treatment step)

[0179] 600 g of NaNO3, to which LiNO3 was added in a small amount so as to have a Li concentration (3000 ppm) in an amount shown in the column of "Li amount before addition" of Table 3, was heated to 380°C and was melted.

[0180] Using this molten salt composition, a plate of "Glass A" described later, having a thickness of 0.6 mm, was immersed at 380°C for 1 hour, whereby a chemically strengthened glass was obtained.

[0181] The stress distribution of the obtained chemically strengthened glass was measured using a measuring machine SLP1000 manufactured by Oji Scientific Instruments Co., Ltd., which applies scattered light photoelasticity manufactured by Oji Scientific Instruments Co., Ltd. CS and DOL were read from the obtained stress distribution. The results are shown in the column of "CS before addition" and the column of "DOL before addition" of Table 3.

[0182] (Procedure of adding glass aid)

[0183] An amount of 5 mass% of the particulate glass 4 was added to the molten salt composition, and the mixture was held at 410°C for 3 hours. Then, the molten salt composition was allowed to cool and solidify.

[0184] The content of Li contained in the solidified salt was measured by wet analysis. The measurement results are shown in the column of "Li amount after addition" in Table 2. In addition, the amount of Li trapped was calculated by subtracting the Li amount after addition from the Li amount before addition. The results are shown in the column of "Li trapped amount" in Table 3.

[0185] In addition, 2 g of the solidified salt was added to 20 mL of pure water, and the pH was measured. The measurement results are shown in the column of "pH of the strengthened salt" in Table 3.

[0186] (Second chemical strengthening treatment procedure)

[0187] The solidified salt was heated again to 380°C, and a plate of "Glass A" having a thickness of 0.6 mm was immersed for 1 hour, whereby a chemically strengthened glass was obtained.

[0188] The stress distribution of the obtained chemically strengthened glass was measured using the above-mentioned SLP1000. From the obtained stress distribution, CS and DOL were read. The results are shown in the column of "CS after addition" and the column of "DOL after addition" in Table 3.

[0189] (Glass for chemical strengthening)

[0190] As the glass for chemical strengthening, a glass having the following composition in terms of mol% on an oxide basis was used.

[0191] Glass A: Si02 66.2%, Al203 11.2%, Li20 10.4%, Na20 5.6%, K20 1.5%, MgO 3.1%, CaO 0.2%, Zr02 1.3%, Y203 0.5%

[0192] Glass B: Si02 64.4%, Al203 8.0%, Na20 12.5%, K20 4.0%, MgO 10.5%, CaO 0.1%, SrO 0.1%, BaO 0.1%, Zr02 0.5%

[0193] <Experiment Examples 2 and 3>

[0194] The same treatment and measurement as in Experiment Example 1 were performed using Glass 7 and Glass 8. The results are shown in Table 3.

[0195] Table 3

[0196] Table 3

[0197] <Experiment Examples 4 to 11>

[0198] According to the same procedure as in Experiment Examples 1 to 3, the properties of glasses 1 to 8 as Li absorbents were investigated, and the results are shown in Table 4. The addition amount of the glass aid was set to 17 mass% with respect to the molten salt. In addition, the impregnation temperature and time of the glass aid were set to 450°C and 48 hours, respectively. The other test conditions were the same as in Experiment Examples 1 to 3.

[0199] Table 4

[0200]

[0201] <Experiment Example 12>

[0202] According to the same procedure as in Experiment Example 1, the properties of the granular and flaky glass 4 as Li absorbents were investigated, and the results are shown in Table 5. The addition amount of the glass aid was set to 5 mass% with respect to the molten salt, and the impregnation time of the Li absorbent was varied in the range from 12 hours to 96 hours. The impregnation temperature was set to 450°C for the granular glass aid, and to 410°C for the flaky glass aid. The Li trapping amount and the pH of the molten salt after the addition of the glass aid are shown in Table 5.

[0203] Table 5

[0204]

[0205] <Experiment Example 13>

[0206] According to the same procedure as in Experiment Example 12, the properties of the granular and flaky glass 4 as Li absorbents were investigated, and the results are shown in Table 6. The impregnation temperature of the glass aid was fixed at 410°C, and the impregnation time was fixed at 48 hours, and the addition amount of the glass aid was varied in the range from 1.15 mass% to 5 mass%. The Li trapping amount and the pH of the molten salt after the addition of the glass aid are shown in Table 6. In addition, the moisture amount of the flaky glass 4 was measured, and the result was 0.16 in the water content.

[0207] Table 6

[0208]

[0209] <Experiment Example 14>

[0210] The CS and DOL before and after the addition of the glass aid at the time of the strengthening of "Glass A" and the addition of the glass aid were summarized in Table 7 according to the same procedure as in Experimental Example 1. 600 g of NaNO3 in which LiNO3 was incorporated in a small amount so as to be Li concentration (3000 ppm) was melted at 380°C, and the obtained melt was used as a molten salt, and the thickness of "Glass A" was 0.55 mm. In addition, in the first chemical strengthening treatment step and the second chemical strengthening treatment step, the strengthening of "Glass A" was performed by immersion in the molten salt at 410°C for 4 hours. The granular glass 11 was used as the glass aid, and the glass aid was immersed in the molten salt composition at 410°C for 24 hours. Note that the conditions other than this were the same as in Experimental Example 1.

[0211] Table 7

[0212] Experimental Example 14 Glass aid composition Glass 11 Glass aid shape Granular Glass aid content (%) 0.65 CS before addition (MPa) 187 DOL before addition (μm) 106 CS after addition (MPa) 226 DOL after addition (μm) 104 pH of the strengthening salt 6.0 Li amount before addition (ppm) 3000 Li amount after addition (ppm) 2001 Li trapping amount (ppm) 999

[0213] According to Table 3, in Experimental Examples 2 and 3, the pH after the addition of the glass aid increased. On the other hand, in Experimental Example 1, even after the addition of the glass aid, the pH was in the preferable range of less than 7.9, and was substantially neutral. In addition, in Experimental Examples 2 and 3, although the effect of the decrease in Li in the molten salt due to the addition of the glass aid was observed, the CS after the addition of the glass aid was slightly lower than that before the addition of the glass aid. It is considered that the multivalent ions eluted from the glass aid function as ions that hinder chemical strengthening. The DOL did not greatly change before and after the addition of the glass aid.

[0214] In Table 4 in which the amount of the addition of the glass aid was further increased and the immersion time of the glass aid was further extended, in Experimental Examples 10 and 11, the pH after the addition of the glass aid further increased. On the other hand, in Experimental Examples 4 to 9, although the amount of the addition of the glass aid was large, in all of the glass aids, the pH after the addition was in the preferable range of less than 7.9, and was neutral. In all of the examples, the Li absorption effect could be confirmed, and in Experimental Examples 4, 7, 8, and 9, the CS was confirmed to significantly increase due to the addition of the glass aid.

[0215] In Tables 5 and 6, the granular glass aid (Li absorber) and the sheet-shaped glass aid (Li absorber) were compared using Glass 4, Table 5 in which the amount of the addition was fixed and the immersion time was changed, and Table 6 in which the strengthening time was fixed and the amount of the addition was changed. In either table, there was no great difference in the amount of the capture of Li between the granular glass and the sheet-shaped glass. In addition, in all of the experiments, the pH after the addition was substantially neutral.

[0216] In addition, according to Table 7, in Experimental Example 14, by the addition of Glass 11, Li in the NaNO3 molten salt decreased, and the CS after the addition increased. In addition, the pH of the molten salt after the addition was neutral.

[0217] <Experiment Examples 15 to 18>

[0218] In Experiment Examples 15 to 18, the Na absorption effect was investigated. Note that Experiment Examples 15 to 17 are examples, and Experiment Example 18 is a comparative example.

[0219] (First chemical strengthening treatment step)

[0220] 600 g of KNO3 in which NaNO3 was added in an amount so that the Na concentration (5400 ppm) shown in the column of "Na amount before addition" of Table 8 was heated to 380°C to be molten.

[0221] Using this molten salt composition, a plate of "Glass B" having a thickness of 2.0 mm was immersed at 435°C for 1 hour, whereby a chemically strengthened glass was obtained.

[0222] The stress distribution of the obtained chemically strengthened glass was measured using a measuring machine FSM6000LE manufactured by Kabushiki Kaisha Orikata Seizo. From the obtained stress distribution, CS and DOL were read. The results are shown in the column of "CS before addition" and the column of "DOL before addition" of Table 8.

[0223] (Step of adding glass aid)

[0224] To the above molten salt composition, glass 9 to 12 in an amount of 5 mass% relative to the molten salt composition was added, and the mixture was kept at 435°C for 24 hours. The composition, shape, and water content of the glass aid used are shown in Table 8.

[0225] Then, the molten salt composition was cooled and solidified, and the content of Na contained in the solidified salt was measured by wet analysis. The measurement results are shown in the column of "Na amount after addition" of Table 8. In addition, the Na trapping amount was calculated by subtracting the Na amount after addition from the Na amount before addition. The results are shown in the column of "Na trapping amount" of Table 8.

[0226] In addition, 2 g of the solidified salt was added to 20 mL of pure water, and the pH was measured. The measurement results are shown in the column of "pH of the strengthening salt" of Table 8.

[0227] (Second chemical strengthening treatment step)

[0228] The solidified salt was heated again to 435°C, and a plate of "Glass B" having a thickness of 2.0 mm was immersed for 1 hour, whereby a chemically strengthened glass was obtained.

[0229] The stress distribution of the chemically strengthened glass was measured using the FSM6000LE described above. The stress distribution (CS) and stress concentration (DOL) were read. The results are shown in the "CS after addition" and "DOL after addition" columns of Table 8.

[0230] Table 8

[0231] Experimental Example 15 Experimental Example 16 Experimental Example 17 Experimental Example 18 Glass aid composition Glass 9 Glass 10 Glass 11 Glass 12 Glass aid shape Sheet Sheet Granular Sheet Glass aid content (%) 1.75 1.46 0.65 - CS before addition (MPa) 761 - - - DOL before addition (μm) 26 - - - CS after addition (MPa) 765 763 778 790 DOL after addition (μm) 25 26 25 25 pH of the strengthening salt 6.2 5.4 6.0 8.7 Na amount before addition (ppm) 5400 - - - Na amount after addition (ppm) 4653 5310 4550 3528 Na trapping amount (ppm) 747 90 850 1872

[0232] According to Table 8, the Na absorption effect can be confirmed by adding glass additives 9-12. However, in Experimental Example 18, the pH increased after adding the glass additive. On the other hand, in Experimental Examples 15-17, the pH was essentially neutral and within the preferred range of less than 7.9 after adding the glass additive.

[0233] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2019-086234, filed on April 26, 2019, the contents of which are incorporated herein by reference.

Claims

1. A method for extending the lifespan of a molten salt composition, comprising the step of adding a glass additive to a molten salt composition used in the chemical strengthening treatment of chemically strengthened glass, wherein, Based on oxide mass%, the glass additive contains at least 60% SiO2 and Al2O3, and at least 95% SiO2, Al2O3, Na2O, P2O5, B2O3, MgO, and K2O. The glass additive is in granular form with a particle size of 0.3 mm or more.

2. The method for extending the lifetime of the molten salt composition as described in claim 1, wherein, The glass additive contains less than 3% Li2O and more than 5% Na2O, based on oxide mass percentage.

3. The method for extending the lifespan of the molten salt composition as described in claim 1, wherein, The glass additive contains less than 3% Li2O and more than 5% K2O, based on oxide mass percentage.

4. The method for extending the lifetime of the molten salt composition as described in claim 1, wherein, The water content of the glass additive is less than 5%.

5. A method for extending the lifespan of a molten salt composition, comprising the step of adding a glass additive to a molten salt composition used in the chemical strengthening treatment of chemically strengthened glass, wherein, Based on oxide-based mass percentages, the combined content of SiO2 and Al2O3 in the glass additive is 60% or more. Based on oxides, the total content of SiO2, Al2O3, Na2O, P2O5, B2O3, MgO, and K2O in the glass additive is 95% or more. The chemically strengthened glass contains more than 1% Na2O, based on the mass percentage of oxides.

6. The method for extending the lifetime of the molten salt composition as described in claim 5, wherein, The glass additive contains less than 3% Li2O and more than 5% Na2O, based on oxide mass percentage.

7. The method for extending the lifetime of the molten salt composition as described in claim 5, wherein, The glass additive contains less than 3% Li2O and more than 5% K2O, based on oxide mass percentage.

8. The method for extending the lifespan of the molten salt composition as described in claim 5, wherein, The water content of the glass additive is less than 5%.

9. The method for extending the lifespan of the molten salt composition as described in claim 1 or 5, wherein, The molten salt composition contains nitrates.

10. The method for extending the lifetime of the molten salt composition as described in claim 1 or 5, wherein, The method for extending the life of the molten salt composition further includes a step of removing the glass additive that has absorbed Li and / or Na from the molten salt composition, the step being carried out within 24 hours from the step of adding the glass additive to the molten salt composition.

11. A method for manufacturing chemically strengthened glass, comprising: The process of impregnating a glass additive in a molten salt composition to allow the glass additive to absorb the Li and / or Na contained in the molten salt composition; The process of removing the glass additive that has absorbed Li and / or Na from the molten salt composition; The process of manufacturing chemically strengthened glass using the extracted glass additives as materials; and The process of performing chemical strengthening treatment on the chemically strengthened glass, wherein, Based on oxide mass%, the total content of SiO2 and Al2O3 in the glass additive is 60% or more, and the total content of SiO2, Al2O3, Na2O, P2O5, B2O3, MgO and K2O is 95% or more. The glass additive is in granular form with a particle size of 0.3 mm or larger.

12. The method for manufacturing chemically strengthened glass as described in claim 11, wherein, The pH of the molten salt composition after adding glass additives is less than 7.

9.

13. A glass additive for extending the lifetime of a molten salt composition by absorbing Li ions and / or Na ions contained in the molten salt composition used in the chemical strengthening treatment of glass, wherein, Based on oxide-based mass percentages, the combined content of SiO2 and Al2O3 in the glass additive is 60% or more. The glass additive is in granular form with a particle size of 0.3 mm or larger.

14. The glass additive as described in claim 13, wherein, The total content of SiO2, Al2O3, Na2O, P2O5, B2O3, MgO and K2O in the glass additive is more than 95% based on the mass percentage of oxides.

15. A glass additive, which is the glass additive of claim 13, wherein, The glass additive contains Al2O3 and Na2O. The ratio of Al2O3 content to Na2O content (Al2O3 / Na2O) is less than 2.

0.

16. A glass additive, which is the glass additive of claim 13, wherein, The glass additive contains Al2O3 and K2O. The ratio of Al2O3 content to K2O content (Al2O3 / K2O) is less than 2.

0.

17. A raw material for glass, wherein, The raw material for the glass is used glass additive, which is the glass additive as described in claim 13, and the total content of SiO2, Na2O and Li2O in the used glass additive is more than 95% based on the mass percentage of oxides.

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