TW201736310A - Method for producing chemically toughened glass - Google Patents

Abstract

The present invention provides a method for producing chemically toughened glass, which is capable of sufficiently eliminating cracks and latent scratches in the glass surface in comparison to conventional methods. The present invention relates to a method for producing chemically toughened glass, which is characterized by comprising: a step for preparing a glass plate containing alkali ions; a step for preparing an inorganic salt that contains other alkali ions having an ionic radius larger than the ionic radius of the above-described alkali ions; a step for performing ion exchange of the alkali ions of the glass plate and the alkali ions of the inorganic salt in an atmosphere having a dew-point temperature of 20 DEG C or more; and a step for removing a part of the surface of the ion-exchanged glass plate.

Description

Method for producing chemically strengthened glass

The present invention relates to a method of producing a chemically strengthened glass.

In recent years, chemically strengthened glass has been used as a cover glass for various display devices, and the industry is seeking further improvement in strength. In order to increase the strength of the chemically strengthened glass, it is revealed that the Na in the glass is ion-exchanged with K in the inorganic salt by contacting the glass containing sodium with a specific inorganic salt containing potassium nitrate, thereby performing chemical strengthening. After the treatment, treatment with an acid and a base is carried out (Patent Document 1). Patent Document 1 describes that although the surface of the glass after the chemical strengthening treatment is not polished or the etching treatment using hydrofluoric acid or the like is used, the surface strength of the glass is drastically improved. Prior Art Document Patent Document Patent Document 1: International Publication No. 2015/008763

[Problems to be Solved by the Invention] However, in recent years, there has been a case where a removal amount larger than the surface removal amount described in Patent Document 1 is desired. The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing a chemically strengthened glass which can increase the amount of surface removal compared to the prior art. [Means for Solving the Problems] As a result of intensive studies, the inventors of the present invention have found that the amount of water vapor at the time of chemical strengthening treatment can be used to drastically increase the amount of surface removal of glass, thereby completing the present invention. That is, the present invention relates to the following <1> to <19>. <1> A method for producing a chemically strengthened glass, comprising the steps of: preparing a glass plate containing an alkali ion; preparing an inorganic salt containing an alkali ion having an ionic radius larger than the alkali ion; and having a dew point temperature of 20 ° C or more In the environment, ion exchange of the alkali ions of the glass plate with the other alkali ions of the inorganic salt is performed; and a portion of the surface of the glass plate subjected to the ion exchange is removed. <2> The method for producing a chemically strengthened glass according to the above <1>, wherein the step of performing ion exchange is performed in an environment having a dew point temperature of 30 ° C or higher. <3> The method for producing a chemically strengthened glass according to the above <1>, wherein the step of performing ion exchange is performed in an environment having a dew point temperature of 40 ° C or higher. The method for producing a chemically strengthened glass according to any one of the above aspects, wherein the step of performing ion exchange is performed in an environment having a dew point temperature of 50 ° C or higher. The method for producing a chemically strengthened glass according to any one of the above aspects, wherein the step of performing ion exchange is performed in an environment in which the dew point temperature is equal to or lower than a temperature of the inorganic salt. get on. The method for producing a chemically strengthened glass according to any one of the above aspects, wherein the environment in the step of performing ion exchange is to include water vapor from the water vapor supply unit. The gas is introduced into the upper space of the inorganic salt, and the introduction amount of the gas containing water vapor is 0.01 mg/min or more per 1 cm ³ of water vapor. The method for producing a chemically strengthened glass according to any one of the above aspects of the present invention, characterized in that, in the step of performing the ion exchange, the gas containing the water vapor is supplied from the venting portion. The introduction into the inorganic salt is carried out, and the introduction amount of the gas containing water vapor is 0.01 mg/min or more per 1 cm ³ of the water vapor supply amount. The method for producing a chemically strengthened glass according to any one of the above aspects, wherein the step of preparing the inorganic salt is prepared to include a component selected from the group consisting of K ₂ CO ₃ and Na ₂ CO ₃ . An inorganic salt of at least one of a group consisting of KHCO ₃ , NaHCO ₃ , Li ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ CO ₃ , MgCO ₃ , CaCO ₃ , and BaCO ₃ and potassium nitrate. The method for producing a chemically strengthened glass according to any one of the above aspects, wherein the step of removing a portion of the surface of the glass sheet comprises: subjecting the ion exchanged glass sheet to The step of acid contact. The method for producing a chemically strengthened glass according to the above <9>, wherein the step of removing a portion of the surface of the glass sheet is followed by the step of contacting the acid, and further comprising contacting the glass sheet with a base. step. <11> The method for producing a chemically strengthened glass according to the above <10>, characterized in that the step of contacting the acid and the step of contacting the alkali further includes a step of washing the glass plate. The method for producing a chemically strengthened glass according to any one of the above aspects, wherein the step of performing the ion exchange and the step of removing a portion of the surface of the glass sheet are Further, the step of washing the glass plate is included. The method for producing a chemically strengthened glass according to any one of the above-mentioned <10>, wherein the step of contacting the alkali further comprises the step of washing the glass plate. The method for producing a chemically strengthened glass according to any one of the above aspects, wherein the step of contacting the acid uses a solution having a pH of less than 7. <15> The method for producing a chemically strengthened glass according to the above <14>, wherein the solution having a pH of less than 7 is a weak acid. <16> The method for producing a chemically strengthened glass according to the above <14>, wherein the solution having a pH of less than 7 is a strong acid. The method for producing a chemically strengthened glass according to any one of the above-mentioned <10>, wherein the step of contacting the alkali is a solution having a pH of more than 7. <18> The method for producing a chemically strengthened glass according to the above <17>, wherein the solution having a pH of more than 7 is a weak base. <19> The method for producing a chemically strengthened glass according to the above <17>, wherein the solution having a pH of more than 7 is a strong base. According to the present invention, it is possible to provide a method for producing a chemically strengthened glass which can increase the amount of surface removal as compared with the prior art.

The present invention will be described in detail below, but the present invention is not limited to the embodiments described below, and may be arbitrarily changed without departing from the spirit and scope of the invention. In addition, in the present specification, the "~" indicating the numerical range is used in the meaning of including the numerical values described before and after the lower limit and the upper limit. <Method for Producing Chemically Strengthened Glass> The method for producing a chemically strengthened glass according to the present invention comprises the steps of: (a) preparing a glass plate containing an alkali ion; (b) preparing another alkali ion having an ion radius larger than the alkali ion; (c) performing ion exchange between the alkali ion of the glass plate and the other alkali ions of the inorganic salt in an environment having a dew point temperature of 20 ° C or higher; and (d) removing the above-mentioned ion exchange One part of the surface of the glass plate. (Glass composition) The glass used in the present invention may contain an alkali ion, and any composition may be used as long as it has a composition which can be formed and strengthened by chemical strengthening treatment. Among them, sodium is preferably contained, and specific examples thereof include aluminosilicate glass, soda lime glass, borosilicate glass, lead glass, basic bismuth glass, and aluminum borosilicate glass. The method for producing the glass is not particularly limited, and the molten glass raw material can be heated by heating the molten glass raw material at 1500 to 1600 ° C, preferably after 1500 to 1600 ° C, and then supplied to the forming apparatus, followed by melting glass. It is formed into a plate shape and is slowly cooled. Further, various methods can be employed for forming the glass. For example, various forming methods such as a down-draw method (for example, an overflow down-draw method, a flow-down method, and a re-drawing method), a floating method, a rolling method, and a press method can be employed. Among them, it is easy to cause cracks in at least a part of the glass surface, and the effect of the present invention is more remarkable. The thickness of the glass is not particularly limited, and is usually preferably 5 mm or less, more preferably 3 mm or less, further preferably 1 mm or less, and particularly preferably 0.7 mm or less, in order to carry out the chemical strengthening treatment efficiently. Further, the shape of the glass used in the present invention is not particularly limited. For example, a glass having a uniform plate thickness, a shape having a curved surface at least one of the front surface and the back surface, and a glass having various shapes such as a curved portion or the like may be used. The composition of the chemically strengthened glass of the present invention is not particularly limited, and examples thereof include the following glass compositions: (1) The composition represented by the mole % of the oxide includes 50 to 80% of SiO. ₂ 2 to 25% Al ₂ O ₃ , 0 to 10% of Li ₂ O, 0 to 18% Na ₂ O, 0 to 10% of K ₂ O, 0 to 15% of MgO, 0 to 5% of CaO, and 0 to 5% of ZrO ₂ The glass (2) has a composition of 50 to 74% of SiO represented by the mole % of the oxide standard. ₂ 1 to 10% Al ₂ O ₃ 6 to 14% Na ₂ O, 3 to 11% of K ₂ O, 2 to 15% of MgO, 0 to 6% of CaO, and 0 to 5% of ZrO ₂ , SiO ₂ And Al ₂ O ₃ The total content is 75% or less, Na ₂ O and K ₂ The total content of O is 12 to 25%, and the total content of MgO and CaO is 7 to 15%, and the composition represented by mole % of oxide is 68 to 80% of SiO. ₂ 4 to 10% Al ₂ O ₃ 5 to 15% Na ₂ O, 0 to 1% of K ₂ O, 4 to 15% of MgO and 0 to 1% of ZrO ₂ The glass (4) has a composition of 67 to 75% of SiO represented by the mole % of the oxide standard. ₂ 0 to 4% Al ₂ O ₃ 7 to 15% Na ₂ O, 1 to 9% of K ₂ O, 6 to 14% of MgO and 0 to 1.5% of ZrO ₂ , SiO ₂ And Al ₂ O ₃ The total content is 71 to 75%, Na ₂ O and K ₂ The total content of O is 12 to 20%, and in the case of containing CaO, the glass (5) having a content of less than 1% contains 65 to 75% of SiO in terms of the mass% of the oxide. ₂ 0.1 to 5% Al ₂ O ₃ , 1 to 6% of MgO, 1 to 15% of CaO, and Na ₂ O+K ₂ The glass represented by O to 10 to 18% (6) contains 60 to 72% of SiO in a composition represented by mass% of oxide. ₂ 1 to 10% Al ₂ O ₃ 5 to 12% of MgO, 0.1 to 5% of CaO, and 13 to 19% of Na ₂ O, 0 to 5% of K ₂ O, and RO / (RO + R ₂ O) is 0.20 or more and 0.42 or less (in the formula, RO represents an alkaline earth metal oxide, R ₂ The composition of the glass (7) in which O represents an alkali metal oxide is represented by the mole % of the oxide, and the composition contains 55.5 to 80% of SiO. ₂ 12 to 20% Al ₂ O ₃ , 8 to 25% Na ₂ O, 2.5% or more of P ₂ O ₅ The composition of the glass (8) of 1% or more of the alkaline earth metal RO (RO is MgO+CaO+SrO+BaO) represented by the mole % of the oxide is 57 to 76.5% of SiO. ₂ 12 to 18% Al ₂ O ₃ , 8 to 25% Na ₂ O, 2.5 to 10% of P ₂ O ₅ The composition of the glass (9) of the alkaline earth metal RO of 1% or more, which is represented by the mole % of the oxide, contains 56 to 72% of SiO. ₂ 8 to 20% Al ₂ O ₃ 3 to 20% of B ₂ O ₃ , 8 to 25% Na ₂ O, 0 to 5% of K ₂ O, 0 to 15% of MgO, 0 to 15% of CaO, and 0 to 15% of SrO ₂ 0 to 15% BaO and 0 to 8% ZrO ₂ Glass The chemically strengthened glass of the present invention has an ion exchange compressive stress layer on the surface of the glass. In the ion exchange method, the surface of the glass is ion-exchanged to form a surface layer of residual compressive stress. Specifically, at the temperature below the glass transition point, the alkali metal ions (Li ions and/or Na ions) having a smaller ionic radius on the surface of the glass plate are replaced by ion exchange to other alkali ions having a larger ionic radius ( Na ion and / or K ion). Thereby, the compressive stress remains on the surface of the glass, and the strength of the glass is improved. In the production method of the present invention, the chemical strengthening treatment is carried out by contacting an inorganic salt containing an alkali ion having an ionic radius larger than an alkali ion contained in the glass with the alkali ion-containing glass and performing ion exchange. That is, the alkali ions contained in the glass are ion-exchanged with other alkali ions contained in the inorganic salt. When the alkali ion contained in the glass is Na ion, the inorganic salt contains potassium nitrate (KNO). ₃ The inorganic salt, and more preferably, contains a selected from K ₂ CO ₃ Na ₂ CO ₃ KHCO ₃ NaHCO ₃ Li ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ CO ₃ MgCO ₃ CaCO ₃ And BaCO ₃ At least one salt of the group consisting of. For example, when potassium nitrate is contained in the inorganic salt, the melting point of potassium nitrate is 330 ° C, and the melting point is below the strain point (usually 500 to 600 ° C) of the chemically strengthened glass. Further, among the above-mentioned salts, a salt other than potassium nitrate (hereinafter also referred to as a "flux") has a property of cutting a network of glass represented by a Si-O-Si bond. Since the temperature at which the chemical strengthening treatment is performed is as high as several hundred ° C, the covalent bond between the Si—O of the glass is appropriately cut at this temperature, and the following low-densification treatment can be easily performed. Further, the degree of cutting the covalent bond varies depending on the glass composition, the type of the salt (flux) used, the temperature at which the chemical strengthening treatment is performed, and the chemical strengthening treatment conditions, but it is considered to be preferably selected from Si. The condition that the one or two of the four covalent bonds that are extended are cut off. A high-density compressive stress layer is formed by ion exchange of Na ions (or Li ions) on the surface of the glass with K ions (or Na ions) in the inorganic salt. The method of bringing the glass into contact with the inorganic salt may be a method of applying a paste-like inorganic salt, a method of spraying an aqueous solution of an inorganic salt to glass, or a method of immersing glass in a salt bath of a molten salt heated to a melting point or higher. Etc. Among these, a method of immersing in a molten salt is preferred. The amount of the flux added is preferably 0.1 mol% or more, more preferably 0.5 mol% or more, further preferably 1 mol% or more, and particularly preferably 2 mol% or more. Further, from the viewpoint of productivity, it is preferred that the salt has a saturation solubility or lower. If it is added in excess, there is a tendency to cause corrosion of the glass. For example, in the case of K ₂ CO ₃ When it is used as a flux, it is preferably 24 mol% or less, more preferably 12 mol% or less, and particularly preferably 8 mol% or less. In addition to potassium nitrate and a flux, the inorganic salt may contain other chemical species within a range that does not impair the effects of the present invention, and examples thereof include alkali metal chlorides such as sodium chloride, potassium chloride, sodium borate, and potassium borate or Alkali metal borate, etc. These may be added separately or in combination of plural kinds. (Production of molten salt) The molten salt can be produced by a known procedure. For example, when the inorganic salt is a molten salt containing potassium nitrate and a flux, it can be obtained by preparing a potassium nitrate molten salt and then adding a flux to the potassium nitrate molten salt. Further, as another method, it can be obtained by mixing potassium nitrate with a flux and then melting the mixed salt of potassium nitrate and a flux. The Na concentration of the molten salt used in the production method of the present invention is preferably 500 ppm by weight or more, more preferably 1,000 ppm by weight or more. By setting the Na concentration in the molten salt to 2000 ppm by weight or more, the low-density layer is easily deepened by the acid treatment step described below, which is further preferable. The upper limit of the Na concentration is not particularly limited and can be tolerated within a range in which a desired surface compressive stress (CS) can be obtained. Further, the molten salt which has been subjected to the chemical strengthening treatment once or more includes sodium which is eluted from the glass. Therefore, if the Na concentration is within the above range, sodium derived from glass can be directly used as a source of Na, and when the concentration of Na is insufficient, or when a molten salt which is not used in chemical strengthening is used, It is adjusted by adding an inorganic sodium salt such as sodium nitrate. (Step of performing ion exchange) Next, chemical strengthening treatment is carried out using the prepared molten salt. The chemical strengthening treatment ion-exchanges the alkali ions (Li ions or Na ions) in the glass with other alkali ions (Na ions or K ions) having a larger ionic radius in the molten salt by immersing the glass in the molten salt. (Replacement) implementation. By this ion exchange, the composition of the surface of the glass can be changed to form a compressive stress layer 20 having a high density on the surface of the glass [Fig. 2 (a) to (b)]. The compressive stress is generated by the high density of the glass surface, so that the glass can be strengthened. Furthermore, in practice, since the density of the chemically strengthened glass is gradually increased from the outer edge of the intermediate layer 30 (main body) existing in the center of the glass toward the surface of the compressive stress layer, the intermediate layer 30 and the compressive stress layer 20 are There is no clear boundary between the rapid changes in density. Here, the intermediate layer means a layer which is present in the center of the glass and is sandwiched by the compressive stress layer. The intermediate layer, unlike the compressive stress layer, is a layer that is not ion exchanged. The chemical strengthening treatment (step of performing ion exchange) in the present invention can be specifically carried out in accordance with the following procedure. First, the glass is preheated, and the above molten salt is adjusted to a temperature at which chemical strengthening is performed. Next, after immersing the preheated glass in the molten salt of the molten salt bath 27 for a specific period of time, the glass is taken out from the molten salt and left to cool. Further, it is preferable to process the glass according to the shape of the application before the chemical strengthening treatment, for example, machining such as cutting, end surface processing, and drilling. The preheating temperature of the glass depends on the temperature of the molten salt, and is usually preferably 100 ° C or more. The chemical strengthening temperature is preferably a strain point of the tempered glass (usually 500 to 600 ° C) or less, and in order to obtain a higher compressive stress layer depth, particularly preferably 350 ° C or more, in order to shorten the treatment time and promote the formation of a low density layer. More preferably, it is 400 ° C or more, and further preferably 430 ° C or more. The time during which the glass is immersed in the molten salt is preferably from 1 minute to 10 hours, more preferably from 5 minutes to 8 hours, still more preferably from 10 minutes to 4 hours. Within the above range, a chemically strengthened glass excellent in balance between the strength and the depth of the compressive stress layer can be obtained. In the production method of the present invention, by increasing the amount of water vapor in the molten salt when the glass is immersed, the low-density layer formed in the step of contacting with the acid described below can be thickened. In the step of contacting with the alkali, the low-density layer can be removed, and therefore, the low-density layer can be removed by setting the thickness of the low-density layer to be greater than the average depth of cracks or potential damage existing on the surface of the glass. And remove the crack or potential damage. Therefore, the excellent surface strength of the chemically strengthened glass can be achieved. The step of performing ion exchange is carried out in an environment having a dew point temperature of 20 ° C or higher. The dew point is preferably 30 ° C or more, more preferably 40 ° C or more, further preferably 50 ° C or more, and still more preferably 60 ° C or more. Further, the upper limit is preferably equal to or lower than the temperature of the inorganic salt (molten salt) to be ion-exchanged. Regarding the dew point temperature (hereinafter, abbreviated as "dew point"), the dew point temperature near the interface of at least the molten salt may be within the above range, and the vicinity of the interface means an environment of an area of 200 mm or less from the interface of the molten salt. . The dew point can be measured by a Vaisala DRYCAP (registered trademark) DMT346 dew point converter. Further, the term "dew point" as used herein means a value considered to be a balance between the molten salt and the environment in the vicinity of the molten salt interface. The above dew point can be achieved by introducing water vapor into the environment near the interface of the molten salt and/or molten salt prior to the step of performing ion exchange and/or simultaneously with the step of performing ion exchange. For example, by adding a water vapor supply unit to the molten salt bath, water vapor can be introduced into the environment near the interface between the molten salt and/or the molten salt. In other words, water vapor supplied by the steam supply unit, gas containing water vapor, and water (liquid) can be directly introduced into the molten salt, and steam or a gas containing water vapor can be introduced into the molten salt. The upper space. Further, the water (liquid) itself may be dropped onto the molten salt and introduced without causing a steam explosion. When water vapor or a gas containing water vapor or water (liquid) (hereinafter, abbreviated as "water vapor, etc.") is introduced, the molten salt may be stirred or not stirred, but the time until the equilibrium is shortened is achieved. In terms of aspect, stirring is preferred. Since the time from the introduction of the water vapor or the like to the equilibrium is different depending on the amount of the introduced gas or liquid, the concentration of the water vapor, the introduction method, etc., it cannot be generalized that if the dew point of the environment is stable and fixed, it can be judged that balance. The gas containing water vapor may be a gas which does not affect the chemical strengthening treatment, and for example, a dry gas A such as air, nitrogen gas or carbon dioxide gas may be introduced into the heated water 24 as shown in FIG. A gas containing a relatively high humidity of water vapor (a gas containing water vapor) B. The water 24 used as the water vapor supply source is preferably pure water such as ion-exchanged water in terms of suppressing scale deposition of piping or the like. Further, the water 24 is heated by, for example, a water bath or the like using the water tank 25. Further, water vapor may be generated by, for example, heating the water 24 itself by a boiler or the like. More specifically, (1) a space in which a gas B containing water vapor is introduced into the upper portion of the inorganic salt (molten salt 26) from the steam supply unit, and (2) a self-venting portion The gas B containing water vapor is introduced into the inorganic salt (molten salt 26), or (3) the water (liquid) is directly introduced into the inorganic salt (molten salt 26) or the like. Among them, it is preferred to form the environment by the above (1) or (2). In the form of a space in which the gas B containing water vapor is introduced into the upper portion of the inorganic salt (molten salt 26), for example, water vapor or the like supplied from the steam supply unit is sprayed onto the upper portion of the inorganic salt by a spray or A method near the interface of an inorganic salt. By introducing water vapor or the like by means of a sprayer, it is easy to control the water vapor concentration in the space above the inorganic salt to be substantially uniform, which is preferable. In addition, the water vapor supply unit, the ventilating portion, the introduction unit for introducing the water (liquid), or the atomizer fitting device may be appropriately provided, and is not particularly limited. Specifically, the sprayers may be single or plural. In particular, when the molten salt bath is large, it is easy to control the water vapor concentration in the space above the inorganic salt to be substantially uniform by spraying water vapor or the like with a plurality of atomizers. When introducing a gas containing water vapor into the space above the molten salt, it is introduced to every 1 cm. ³ The amount of water vapor supplied in the gas is preferably 0.01 mg/min or more, more preferably 0.02 mg/min or more. When water (liquid) is directly introduced into the molten salt, it is introduced to every 1 cm. ³ The flow rate of water is preferably 0.01 mg/min or more, more preferably 0.02 mg/min or more. When the gas containing water vapor is directly introduced into the inorganic salt (in the molten salt), it is introduced to every 1 cm. ³ The amount of water vapor supplied in the gas is preferably 0.01 mg/min or more, more preferably 0.02 mg/min or more. The reason why the surface strength of the obtained chemically strengthened glass becomes higher by performing the step of performing ion exchange in the molten salt having a large amount of water vapor (water content) is considered as follows. When the carbonate ion forming the molten salt reacts with water, bicarbonate ions and hydroxide ions are generated as shown in the following formula. [Chemical 1] Here, when the amount of water in the molten salt is large, the equilibrium in the above formula is inclined to the right, and a large amount of bicarbonate ions and hydroxide ions are generated. Since hydroxide ions promote the cleavage of ions in the glass network, it is considered that the formation of a low-density layer on the surface of the glass is promoted by generating more hydroxide ions. The sum of the carbonate anion concentration and the hydrogencarbonate anion concentration obtained by the following formula in the inorganic salt is preferably 4 mol% or more, more preferably 6 mol% or more. By setting the concentration to 4 mol% or more, a low-density layer formation reaction on the glass surface can be promoted, which is preferable. {(carbonate anion concentration) + (bicarbonate anion concentration)} (mol%) = {(the amount of carbonate anion in the inorganic salt) + (the amount of the bicarbonate anion in the inorganic salt)} (mol) / ( The total amount of anions in the inorganic salt) (mol) × 100 Further, since the concentration of the carbonate anion and the concentration of the anion of the bicarbonate in the molten salt cannot be directly measured, a part of the molten salt is taken out, and the carbon dioxide meter TiN-9004 is used. Dilute commercially available standard solution (NaHCO) ₃ After preparing a calibration curve, a sample solution diluted to 130 times with pure water was measured. At this time, since all of the bicarbonate anions are converted into carbonate anions, the value of the carbonate anion concentration detected by the measurement corresponds to the sum of the carbonate anion concentration and the bicarbonate anion concentration. Further, the sum of the carbonate anion concentration and the bicarbonate anion concentration is equal to or less than the sum of the saturated carbonate anion concentration and the saturated bicarbonate anion concentration. The low-density layer is formed by the step of contacting the acid in the step of removing a portion of the surface of the glass plate, and the thickness is 100 to 200 nm in the previous ion exchange step without introducing water vapor. On the other hand, the thickness can be 300 nm or more by performing ion exchange in an environment in which water vapor is introduced and the dew point temperature is 20 ° C or higher. Since the average depth of the crack or potential damage of the glass surface generated in the glass manufacturing step or the glass processing step including the chemical strengthening treatment step is about 500 nm, the thickness of the low density layer is more preferably 500 nm or more, and thus Good for more than 600 nm. The formed low density layer can be removed by the step of contacting the base in the step of removing a portion of the surface of the glass sheet. Therefore, if the depth of the crack or the potential damage of the glass surface is shallow, the thickness of the lower density layer can be completely removed by the step of contacting with the alkali. The surface strength of the chemically strengthened glass can be made higher by removing the crack or potential damage of the glass surface which is the cause of the decrease in the strength of the chemically strengthened glass. (Step of Washing) In the production method of the present invention, it is preferred to further include a step of washing the glass sheet between the step of performing ion exchange and the step of removing a portion of the surface of the glass sheet. In the step of washing, the glass is washed with industrial water, ion-exchanged water or the like. Industrial water is used as needed. In particular, ion exchange water is preferred. The conditions for washing differ depending on the washing liquid to be used, and in the case of using ion-exchanged water, washing at 0 to 100 ° C is preferable in terms of completely removing the adhered salt. In the step of performing the washing, the method of immersing the chemically strengthened glass in a water tank in which ion-exchanged water or the like is placed, or exposing the surface of the glass to the running water, and directing the cleaning liquid to the glass by a water sprayer Various methods such as a method of surface spraying. (Step of removing a portion of the surface of the glass plate) A step of supplying the ion-exchanged glass plate to a portion of the surface of the glass plate. The step of removing a portion of the surface of the glass sheet preferably comprises the step of contacting the glass sheet with an acid, more preferably after the step of contacting the acid, and further comprising the step of contacting the glass sheet with a base. (Step of contacting with acid) In the production method of the present invention, as a step of removing a part of the surface of the glass plate after the step of performing ion exchange or the step of performing the above-described washing, it is preferred to carry out the contact of the glass with the acid. Step (acid treatment step). The acid treatment of the glass is carried out by immersing the chemically strengthened glass in an acidic solution, whereby Na and/or K on the surface of the chemically strengthened glass can be replaced with H. That is, the surface layer having a compressive stress layer on the surface of the glass is further reduced in density, specifically, a low-density layer. The solution is not particularly limited as long as it is acidic, and the pH is less than 7, and the acid used may be a weak acid or a strong acid. Specifically, an acid such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, oxalic acid, carbonic acid or citric acid is preferred. These acids may be used singly or in combination of plural kinds. The temperature at which the acid treatment is carried out also varies depending on the kind, concentration, and time of the acid to be used, and is preferably carried out at 100 ° C or lower. The time for the acid treatment varies depending on the type, concentration, and temperature of the acid to be used, and is preferably from 10 seconds to 5 hours, more preferably from 1 minute to 2 hours, from the viewpoint of productivity. The concentration of the acid-treated solution varies depending on the kind, time, and temperature of the acid to be used, and is preferably a concentration at which the corrosion of the container is less likely to be used, and specifically, it is preferably 0.1% by weight to 20% by weight. Since the low-density layer is removed by the following alkali treatment, the thicker the low-density layer, the easier the glass surface is removed. The thickness of the low-density layer is preferably 300 nm or more, more preferably 500 nm or more, and still more preferably 600 nm or more from the viewpoint of the amount of removal of the glass surface as described above. The density of the low density layer is preferably lower than the density (region) of the region deeper than the ion exchanged compressive stress layer from the viewpoint of glass surface removability. The thickness of the low-density layer can be determined from the period (Δθ) measured by X-ray-reflection spectroscopy (XRR). The density of the low density layer can be determined by using the critical angle (θc) measured by XRR. Further, in simple terms, the formation of the low-density layer and the thickness of the layer can be confirmed by observing the cross section of the glass by a scanning electron microscope (SEM, Scanning Electron Microscope). (Step of Contacting with Alkali) In the production method of the present invention, it is preferred to carry out a step of contacting with a base (alkali treatment step) after the step of contacting with an acid. More preferably, the step of washing the glass plate is carried out in the same manner as the above-described step of washing after the step of contacting with the acid and before the step of contacting with the alkali. The alkali treatment is carried out by immersing the chemically strengthened glass in an alkaline solution, whereby part or all of the low density layer formed in the step of contacting with the acid can be removed. The solution is not particularly limited as long as it is alkaline, and the pH may be more than 7, and a weak base or a strong base may be used. Specifically, a base such as sodium hydroxide, potassium hydroxide, potassium carbonate or sodium carbonate is preferred. These bases may be used singly or in combination of plural kinds. The temperature at which the alkali treatment is carried out varies depending on the kind, concentration and time of the base to be used, and is preferably 0 to 100 ° C, more preferably 10 to 80 ° C, still more preferably 20 to 60 ° C. If it is the above temperature range, it is preferable that no glass is corroded. The time for the alkali treatment varies depending on the kind, concentration, and temperature of the base to be used, and is preferably from 10 seconds to 5 hours, more preferably from 1 minute to 2 hours, from the viewpoint of productivity. The concentration of the alkali-treated solution varies depending on the kind, time, and temperature of the base to be used, and is preferably from 0.1% by weight to 20% by weight from the viewpoint of glass surface removability. By the alkali treatment, part or all of the low-density layer in which H is intruded is removed, whereby chemically strengthened glass having improved surface strength can be obtained. Particularly in the present invention, the thickness of the low density layer can be made deeper than the depth of cracking or potential damage existing on the surface of the glass. Therefore, it is considered that cracks or potential damage existing on the surface of the glass can be removed together with the low-density layer, which contributes to an increase in the strength of the glass surface. Further, it is preferred to carry out the step of washing after the alkali treatment, by the same method as described above. <Chemical tempered glass> According to the method for producing a chemically strengthened glass of the present invention, the low-density layer can be formed deeper than the previous chemical strengthening treatment, and thus the surface of the chemically strengthened glass obtained after removing the low-density layer, Less cracking or potential damage. Therefore, the chemically strengthened glass obtained by the present invention has a very high surface strength. (Glass Strength) The surface strength of the chemically strengthened glass can be evaluated by a ball ring test. (Ball Ring Test) The chemically strengthened glass was evaluated by the BoR face strength F(N) measured by a Ball on Ring (BoR) test in which the glass plate was placed at a diameter of 30 mm. The contact portion has a ring of stainless steel having a curvature radius of 2.5 mm so that the ball containing steel having a diameter of 10 mm is in contact with the glass plate to make the ball centered on the ring under static load conditions. Apply a load. Preferably, the chemically strengthened glass has a strength of the first main surface and the second main surface which satisfy F≧1500×t ² More preferably F≧1800×t ² And further preferably F≧2000×t ² [In the formula, F is the BoR face strength (N) measured by the ball ring test, and t is the plate thickness (mm) of the glass substrate]. By setting the BoR surface strength F(N) to the above range, excellent surface strength is exhibited even in the case of thinning. Further, the BoR test can be carried out by the method described in the following examples. (Compressive Stress Layer) The compressive stress value of the compressive stress layer of the chemically strengthened glass and the depth of the compressive stress layer may be an EPMA (electron probe micro analyzer) or a surface stress meter (for example, FSM manufactured by F. -6000), etc. were measured. (Removal amount of glass surface (low density layer)) The removal amount (thickness) of the glass surface (low density layer) after alkali treatment can be measured by using an analytical electronic balance to measure the weight before and after the chemical treatment and using the following formula Calculated by conversion. (Removal thickness per one side) = [(pre-treatment weight) - (weight after treatment)] / (glass specific gravity) / treatment area / 2 At this time, the specific gravity of the glass was set to 2.48 (g/cm) ³ )Calculation. EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto. <Evaluation Method> Various evaluations in the examples were carried out by the analysis methods shown below. (Evaluation of glass: surface strength) The glass surface strength was measured by a ball on ring (BoR) test. In Fig. 1, a schematic view for explaining the ball ring test used in the present invention is shown. The glass plate was pressed in a state where the glass plate 1 was horizontally placed, and the glass plate was pressed using a press fixture 2 (hardened steel, diameter 10 mm, mirror polished) made of SUS (Steel Use Stainless) 304, and the surface of the glass plate was measured. strength. In Fig. 1, a glass plate serving as a sample was horizontally placed on a SUS304-bearing jig 3 (diameter 30 mm, contact portion curvature R2.5 mm, contact portion quenched steel, mirror polished). Above the glass plate, a pressurizing tool for pressurizing the glass plate is provided. In the embodiment of the present embodiment, the central portion of the glass sheet is pressurized from above the obtained glass sheet. Furthermore, the test conditions are as follows. The descending speed of the press jig: 1.0 (mm/min) At this time, the breaking load (unit N) when the glass was broken was set as the BoR surface strength, and the average value of the 20 measurements was taken as the BoR average surface strength. However, when the breaking point of the glass sheet is 2 mm or more from the ball pressing position, it is excluded from the data used to calculate the average value. (Evaluation of glass: surface stress) The surface compressive stress value (CS, unit MPa) of the glass and the depth (DOL, unit of μm) of the compressive stress layer were obtained using a surface stress meter (FSM-6000) manufactured by Ohara. Determination. (Evaluation of glass: amount of removal) The thickness of the glass was measured by measuring the weight before and after the chemical treatment using an analytical electronic balance (HR-202i, manufactured by AND), and calculating the thickness by the following formula. (Removal thickness per one side) = [(pre-treatment weight) - (weight after treatment)] / (glass specific gravity) / treatment area / 2 At this time, the specific gravity of the glass was set to 2.48 (g/cm) ³ )Calculation. (Evaluation of glass: cracking or potential damage) The presence or absence of cracks or potential damage on the surface of the glass is visually inspected under a light source of 1500 Lux. If there is no visible defect, no crack or potential damage is judged. . <Example 1> (Step of performing ion exchange) To a crucible made of stainless steel (SUS), 8454 g of potassium nitrate, 1324 g of potassium carbonate, and 222 g of sodium nitrate were added, and heated to 490 ° C by a heating mantle to prepare potassium carbonate 10 mol. %, sodium 6000 ppm by weight of molten salt. The molten salt is contained in the molten salt by introducing air which has been introduced into the water heated to 55 ° C into the environment near the interface of the molten salt. The experimental system is shown in Fig. 3, and air is used as the dry gas A, and the air is introduced into the water 24 heated to 55 ° C by the water tank 25 to be humidified to obtain a humidified water vapor. Gas (air) B. The dew point in the step of performing ion exchange is controlled by introducing the gas B containing water vapor into the upper space of the inorganic salt (molten salt) 26 of the tank subjected to the chemical strengthening treatment via a path heated by the electric heating belt. Every 1 cm at this time ³ The water vapor supply amount was 0.02 mg/min, and the dew point near the interface of the molten salt was 38 °C. Prepare a glass plate A of 50 mm × 50 mm × 0.7 mm, preheat it to 350-400 ° C, immerse in molten salt of 490 ° C for 1 hour, perform ion exchange treatment, and then cool to room temperature, thereby performing chemistry Strengthen processing. The obtained chemically strengthened glass was washed with water and supplied to the next step. The glass composition of the glass plate A (indicated by the mole % of the oxide standard): SiO ₂ 64.2%, Al ₂ O ₃ 8.0%, Na ₂ O is 12.5%, K ₂ O is 4.0%, MgO is 10.5%, CaO is 0.1%, SrO is 0.1%, BaO is 0.1%, ZrO ₂ 0.5% (Step of removing one part of the surface: Step of contacting with acid) Prepare 6.0% by weight of nitric acid in a beaker (diluted nitric acid 1.38 (manufactured by Kanto Chemical Co., Ltd.) by ion-exchanged water), and adjust the temperature to a temperature using a water bath 40 ° C. The glass obtained by the above chemical strengthening step was immersed in the prepared nitric acid for 120 seconds to carry out an acid treatment. Thereafter, the glass was washed with water and supplied to the next step. (Step 2 of removing a part of the surface: a step of contacting with a base) Preparing a 4.0% by weight aqueous sodium hydroxide solution (diluting 48% sodium hydroxide solution (manufactured by Kanto Chemical Co., Ltd.) by ion-exchanged water) in a beaker, using a water bath The temperature was adjusted to 40 °C. The washed glass was immersed in the prepared aqueous sodium hydroxide solution for 120 seconds after the step of contacting with the acid to carry out alkali treatment. Thereafter, the glass was washed with water to wash the alkali on the surface of the glass. After that, it is dried by air blowing. From the above, the chemically strengthened glass of Example 1 was obtained. Cracks and potential damage to the obtained chemically strengthened glass were not confirmed. <Example 2> The potassium carbonate concentration of the molten salt in the step of performing ion exchange was set to 8 mol%, the dew point in the vicinity of the interface of the molten salt was set to 71 ° C, and the chemical strengthening treatment conditions were set to 450 ° C. Chemically strengthened glass was produced in the same manner as in Example 1 except for the above. Furthermore, every 1 cm is introduced when introducing a gas containing water vapor in order to control the dew point. ³ The water vapor supply was 0.08 mg/min. Cracks and potential damage to the obtained chemically strengthened glass were not confirmed. <Comparative Example 1> A chemically strengthened glass was produced in the same manner as in Example 2 except that the dew point in the vicinity of the interface of the molten salt in the step of performing ion exchange was set to 9 °C. Furthermore, the gas containing water vapor was not introduced to control the dew point. Cracks and potential damage to the obtained chemically strengthened glass were not confirmed. <Comparative Example 2> A chemically strengthened glass was produced in the same manner as in Comparative Example 1, except that potassium carbonate was added to the molten salt in the step of performing the ion exchange, and the sodium was used in an amount of 2000 ppm by weight, and the acid treatment and the alkali treatment were not carried out. It was not confirmed that there was cracking and potential damage to the obtained glass. <Example 3> Chemically strengthened glass was produced under the same conditions as in Example 1 except that the glass plate B was used. Cracks and potential damage to the obtained chemically strengthened glass were not confirmed. Glass composition of glass plate B (molar % of oxide reference): SiO ₂ 68.0%, Al ₂ O ₃ 12.0%, Na ₂ O is 18.6% and MgO is 8.0%. <Example 4> Chemically strengthened glass was produced under the same conditions as in Example 2, except that the same glass as in Example 3 was used. Cracks and potential damage to the obtained chemically strengthened glass were not confirmed. <Comparative Example 3> Chemically strengthened glass was produced under the same conditions as in Comparative Example 1, except that the same glass as in Example 3 was used. Cracks and potential damage to the obtained chemically strengthened glass were not confirmed. <Comparative Example 4> Chemically strengthened glass was produced under the same conditions as in Comparative Example 2, except that the same glass as in Example 3 was used. It was not confirmed that there was cracking and potential damage to the obtained glass. <Example 5> (Step of performing ion exchange) Chemically strengthened glass was produced under the same conditions as in Example 2, except that the glass plate C having a thickness of 0.55 mm was used, and the dew point in the vicinity of the interface of the molten salt was changed to 66 °C. Cracks and potential damage to the obtained chemically strengthened glass were not confirmed. Glass composition of glass plate C (% of moles of oxide reference): SiO ₂ 67%, B ₂ O ₃ 4%, Al ₂ O ₃ 13%, Na ₂ O is 14%, K ₂ O<1%, MgO was 2%, and CaO<1% <Comparative Example 5> Chemically strengthened glass was produced under the same conditions as in Comparative Example 2, except that the same glass as in Example 5 was used. Cracks and potential damage to the obtained chemically strengthened glass were not confirmed. Various evaluations were made on the chemically strengthened glass obtained above. The treatment conditions and evaluation results of the glass are shown in Table 1. Furthermore, the BoR average surface intensity is shown as the BoR surface intensity. [Table 1] As described above, in Examples 1 to 5 and Comparative Examples 1 to 5, when visual inspection was performed under a light source of 1500 lux, no cracks or potential damage were observed. However, as shown in Table 1, Examples 1 to 5 showed higher BoR surface strength F(N) than Comparative Examples 1 to 5. The reason why Examples 1 to 5 showed a higher BoR surface strength F(N) than Comparative Examples 1 to 5 was as follows. In the production method of the present invention, by performing the step of ion-exchange of the alkali ion of the glass plate with the other alkali ions of the inorganic salt in an environment having a dew point temperature of 20 ° C or higher, the chemical strengthening of the glass can be increased. The amount of water vapor in the molten salt forms a low density layer having a depth above the average depth of the crack or potential damage of the glass surface. By removing a portion of the surface of the glass plate subjected to the above ion exchange, the low density layer can be removed, and the crack or potential damage can be sufficiently removed, or the number thereof can be sufficiently reduced, and a high BoR surface strength F can be achieved. (N). The present invention has been described in detail with reference to the specific embodiments thereof, and it is understood that various changes and modifications may be made without departing from the spirit and scope of the invention. In addition, the present application is based on Japanese Patent Application No. 2015-256894 filed on Dec. Again, all of the reference frames cited herein are incorporated herein in their entirety. [Industrial Applicability] According to the method for producing a chemically strengthened glass of the present invention, chemically strengthened glass having a very high surface strength can be obtained without chemical polishing or etching treatment using hydrofluoric acid or the like. That is, it is possible to obtain a chemically strengthened glass which does not have an appearance defect caused by an increase in potential damage caused by an etching treatment by hydrofluoric acid or the like, or an abrasive damage caused by polishing, and is excellent in surface strength. Therefore, regardless of the surface damage of the glass before the chemical strengthening treatment, the presence or absence of the potential damage, or the extent, it can be applied to all the glasses, and the versatility is high. Further, since it can be treated by being immersed in a solution, it is effective in terms of being easy to cope with various glass shapes or large-area glass. Further, compared with the etching treatment using hydrofluoric acid or the like, the safety is high and the cost is low.

1‧‧‧glass plate
2‧‧‧ Pressing fixture
3‧‧‧Resistance
10‧‧‧Low density layer
20‧‧‧Compressive stress layer
21‧‧‧Regulator
22‧‧‧ Flowmeter
23‧‧‧ check valve
24‧‧‧ water
25‧‧‧Sink
26‧‧‧ molten salt
27‧‧‧ molten salt tank
30‧‧‧Intermediate
A‧‧‧Dry gas
B‧‧‧Gas containing water vapor

Fig. 1 is a schematic view for explaining a method of a ball ring test. 2(a) to 2(d) are schematic views showing the steps of manufacturing the chemically strengthened glass of the present invention. Figure 3 is a schematic diagram of an experimental system for forming an environment in the step of performing ion exchange.

21‧‧‧Regulator

22‧‧‧ Flowmeter

23‧‧‧ check valve

24‧‧‧ water

25‧‧‧Sink

26‧‧‧ molten salt

27‧‧‧ molten salt tank

A‧‧‧Dry gas

B‧‧‧Gas containing water vapor

Claims (19)

A method for producing a chemically strengthened glass, comprising the steps of: preparing a glass plate containing an alkali ion; preparing an inorganic salt containing an alkali ion having an ionic radius larger than the alkali ion; and in an environment having a dew point temperature of 20 ° C or higher, Performing ion exchange between the alkali ion of the glass plate and the other alkali ions of the inorganic salt; and removing a portion of the surface of the glass plate subjected to the ion exchange. The method for producing a chemically strengthened glass according to claim 1, wherein the step of performing ion exchange is carried out in an environment having a dew point temperature of 30 ° C or higher. The method for producing a chemically strengthened glass according to claim 1 or 2, wherein the step of performing the ion exchange is carried out in an environment having a dew point temperature of 40 ° C or higher. The method for producing a chemically strengthened glass according to any one of claims 1 to 3, wherein the step of performing ion exchange is carried out in an environment having a dew point temperature of 50 ° C or higher. The method for producing a chemically strengthened glass according to any one of claims 1 to 4, wherein the step of performing the ion exchange is carried out in an environment in which the dew point temperature is equal to or lower than the temperature of the inorganic salt. The method for producing a chemically strengthened glass according to any one of claims 1 to 5, wherein the environment in the step of performing the ion exchange is carried out by introducing a gas containing water vapor from the water vapor supply portion into the upper space of the inorganic salt. Further, the amount of introduction of the gas containing water vapor is 0.01 mg/min or more per 1 cm ³ of water vapor. The method for producing a chemically strengthened glass according to any one of claims 1 to 5, wherein the environment in the step of performing ion exchange is formed by introducing a gas containing water vapor into the inorganic salt from a venting portion, The introduction amount of the gas containing water vapor is 0.01 mg/min or more per 1 cm ³ of water vapor. The method for producing a chemically strengthened glass according to any one of claims 1 to 7, wherein the step of preparing the inorganic salt is prepared to comprise a component selected from the group consisting of K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ , NaHCO _{3 ,} Li ₂ CO ₃ An inorganic salt of at least one of a group consisting of Rb ₂ CO ₃ , Cs ₂ CO ₃ , MgCO ₃ , CaCO ₃ and BaCO ₃ and potassium nitrate. The method of producing a chemically strengthened glass according to any one of claims 1 to 8, wherein the step of removing a portion of the surface of the glass sheet comprises the step of contacting the glass plate subjected to the ion exchange with an acid. The method of producing a chemically strengthened glass according to claim 9, wherein the step of removing a portion of the surface of the glass sheet is followed by the step of contacting the glass with the alkali. The method for producing a chemically strengthened glass according to claim 10, wherein the step of contacting the acid with the step of contacting the alkali further comprises the step of washing the glass plate. The method for producing a chemically strengthened glass according to any one of claims 1 to 11, wherein the step of performing the ion exchange step and the step of removing a portion of the surface of the glass sheet further comprises the step of washing the glass sheet. The method for producing a chemically strengthened glass according to any one of claims 10 to 12, further comprising the step of washing the glass plate after the step of contacting the alkali. The method for producing a chemically strengthened glass according to any one of claims 9 to 13, wherein the step of contacting the acid uses a solution having a pH of less than 7. The method for producing a chemically strengthened glass according to claim 14, wherein the solution having a pH of less than 7 is a weak acid. The method for producing a chemically strengthened glass according to claim 14, wherein the solution having a pH of less than 7 is a strong acid. The method for producing a chemically strengthened glass according to any one of claims 10 to 16, wherein the step of contacting the alkali uses a solution having a pH of more than 7. The method for producing a chemically strengthened glass according to claim 17, wherein the solution having a pH of more than 7 is a weak base. The method for producing a chemically strengthened glass according to claim 17, wherein the solution having a pH of more than 7 is a strong base.