JP2020007222A - Method for manufacturing chemically strengthened glass - Google Patents

Abstract

To provide a method for manufacturing a chemically strengthened glass, allowing the glass to be sufficiently chemically strengthened.SOLUTION: A method for manufacturing a chemically strengthened glass including the step of contacting an inorganic salt containing potassium nitrate and glass for ion exchange of Na in the glass with K in the inorganic salt includes the step of adding a salt containing at least one anion selected from the group consisting of SO, CO, HCO, PO, HPOand HPOto the inorganic salt prior to the ion exchange. The inorganic salt contains at least one of Mgand Ca, and satisfies any one of conditions of having a Mgcontent of 5 ppm by mass or more and having a Cacontent of 50 ppm by mass or more, before the addition of salt.SELECTED DRAWING: None

Description

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

  2. Description of the Related Art In a flat panel display device used for a digital camera, a mobile phone, a personal digital assistant (PDA), or the like, in order to protect the display and enhance the aesthetic appearance, a thin plate-shaped device having a larger area than an image display portion is used. It has been practiced to place a cover glass on the front of the display. Although glass has a high theoretical strength, the strength is greatly reduced by scratching.Therefore, for the cover glass that requires strength, chemical strengthening with a compressive stress layer formed on the glass surface by ion exchange using inorganic salts etc. Glass is used.

  Conventionally, when the concentration of alkali metal impurities such as Li and Na is increased in the inorganic salt for strengthening glass, additives such as potassium pyrophosphate, potassium orthophosphate, and potassium pyroantimonate are added to remove them. (Patent Documents 1 and 2 and Non-Patent Document 1).

JP-A-46-38514 International Publication No. WO 2014/045977

Doklady Akademii Nauk SSSR (1975), 225 (6), 1373-6 [Chem. Tech. ].

  However, the present inventor has pointed out that the presence of a very small amount of alkaline earth metal impurities such as Mg and Ca other than alkali metal impurities in the inorganic salt for strengthening glass sometimes makes it impossible to appropriately strengthen the glass. The inventors have found.

  An object of the present invention is to provide a method for producing chemically strengthened glass in which glass is sufficiently chemically strengthened and a chemically strengthened glass in which chemical strengthening is sufficiently performed.

The present inventors have found that the presence of a salt having a specific anion in an inorganic salt for chemical strengthening can suppress the effects of magnesium and calcium, making it possible to appropriately strengthen the glass surface. Was completed.
That is, the present invention is as follows.
A method for producing chemically strengthened glass, comprising a step of ion-exchanging Na in the glass and K in the inorganic salt by contacting the inorganic salt containing potassium nitrate with the glass,
Prior to the ion exchange, at least one selected from the group consisting of SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , PO ₄ ³⁻ , HPO ₄ ²⁻ and H ₂ PO ₄ ^{− in the} inorganic salt. A step of adding a salt having an anion of
Before the addition, the inorganic salt contains at least one of Mg ²⁺ and Ca ²⁺ , and has a Mg ²⁺ content of 5 mass ppm or more and a Ca ²⁺ content of 50 mass ppm or more. Manufacturing method of chemically strengthened glass.

  According to the present invention, a compressive stress layer can be stably applied to a glass surface, and appropriate strengthening can be performed.

  Hereinafter, the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

<Production method of chemically strengthened glass>
The production method according to the present invention includes a step of ion-exchanging Na in the glass with K in the inorganic salt by contacting the inorganic salt containing potassium nitrate with the glass. And adding a salt having a specific anion to the inorganic salt before addition of the salt having the specific anion, wherein the inorganic salt contains at least one of Mg ²⁺ and Ca ²⁺ , and the Mg ²⁺ content is 5 mass ppm or more. And Ca ²⁺ content satisfying any condition of 50 mass ppm or more.

(Glass composition)
The glass used in the present invention only needs to contain sodium, and various compositions can be used as long as the glass has a composition that can be strengthened by molding and chemical strengthening treatment. Specific examples include aluminosilicate glass, soda lime glass, borosilicate glass (borosilicate glass), lead glass, alkali barium glass, and aluminoborosilicate glass (aluminoborosilicate glass). Above all, soda lime glass is preferable from the viewpoint of easily obtaining the effects of the present invention.

  The method for producing glass is not particularly limited, and a desired glass raw material is put into a continuous melting furnace, and the glass raw material is preferably heated and melted at 1500 to 1600 ° C., clarified, and then supplied to a molding apparatus, and then the molten glass is fed. It can be manufactured by forming into a plate shape and slowly cooling.

  Note that various methods can be employed for forming the glass. For example, various forming methods such as a down draw method (eg, an overflow down draw method, a slot down method, a redraw method, etc.), a float method, a roll out method, and a press method can be employed.

  Although the thickness of the glass is not particularly limited, it is usually preferably 5 mm or less, more preferably 3 mm or less, for effectively performing the chemical strengthening treatment.

The composition of the glass in the present invention is not particularly limited, and examples thereof include the following compositions.
(I) 50 to 80% of SiO ₂ , ₂ to 25% of Al ₂ O ₃ , 0 to 10% of Li ₂ O, and 0 to 18% of Na ₂ O in a composition represented by mol% based on oxide. , A composition containing 0 to 10% of K ₂ O, 0 to 15% of MgO, 0 to 5% of CaO, and 0 to 5% of ZrO ₂ , expressed in terms of mol% based on glass (ii) oxide; ₂ 50 to 74%, the _{Al 2 O 3 1~10%, 6~14} % of Na ₂ O, the _{K 2} O 3 to 11% of MgO 2 to 15% Less than six% and ZrO of CaO ₂ , 0 to 5%, the total content of SiO ₂ and Al ₂ O ₃ is 75% or less, the total content of Na ₂ O and K ₂ O is 12 to 25%, and the content of MgO and CaO in the composition the sum of is displayed in mole% of the glass (iii) oxide basis is 7 to 15%, SiO ₂ 68 80%, the _{Al 2 O 3 4~10%, Na} 2 O 5-15% of _{K 2} O 0 to 1% MgO 4-15% and glass containing ZrO ₂ 0~1% (iv ) the composition viewed in mole percent on the oxide basis, of SiO ₂ 67 to 75%, the _{Al 2 O 3 0~4%, 7~15} % of Na ₂ O, 1 to 9% of _{K 2} O, MgO 6 to 14% and ZrO ₂ from 0 to 1.5%, the total content of SiO ₂ and Al ₂ O ₃ is 71 to 75%, and the total content of Na ₂ O and K ₂ O is 12 was 20%, a composition in which the content is in wt% of the glass (v) oxide basis is less than 1% when containing CaO, the SiO ₂ 65 to 75%, the _Al 2 _{O 3} 0 1-5%, MgO 1-6%, CaO 1-15%, the total content of Na ₂ O and K ₂ O Is 10 to 18% and is expressed in terms of mass% based on glass (vi) oxide. SiO ₂ is 65 to 72%, Al ₂ O ₃ is 3.4 to 8.6%, and MgO is 3.3. 6%, the CaO 6.5 to 9%, Na ₂ O of from 13 to 16%, 0 to 1% of _{K 2} O, the TiO ₂ 0 to 0.2%, 0.01 to the _Fe 2 _{O 3} 0.15%, the SO ₃ containing _{0.02~0.4%, (Na 2 O +} K 2 O) / Al 2 O 3 is a glass (vii) oxide basis is 1.8 to 5.0 mass % By composition, SiO ₂ is 60 to 72%, Al ₂ O ₃ is 1 to 10%, MgO is 5 to 12%, CaO is 0.1 to 5%, Na ₂ O is 13 to 19%, the K ₂ O containing _{0~5%, RO / (RO +} R 2 O) of 0.20 or more, 0.42 or less (wherein, alkaline earth metal oxides and RO, _{R 2} O is Shows the alkali metal oxide. ), Which is expressed in terms of mol% based on glass (viii) oxide, containing 67 to 75% of SiO ₂ , 0 to 5% of Al ₂ O ₃ , 1 to 15% of CaO, Na ₂ O and Glass having a total content of K ₂ O of 10 to 18%

(Chemical strengthening)
In the method for producing a chemically strengthened glass according to the present invention, the surface of the glass is strengthened by performing an ion exchange treatment on the surface of the glass to form a surface layer (compressive stress layer) in which compressive stress remains. Generally, ion exchange means that at a temperature lower than the glass transition point, an alkali metal ion (typically, Li ion or Na ion) having a small ionic radius on the glass surface is converted to an alkali ion (typically, Li ion or Na ion) having a larger ionic radius by ion exchange. Typically, it is replaced with Na ion or K ion for Li ion and K ion for Na ion). Thereby, 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, chemical strengthening is performed by bringing glass into contact with an inorganic salt containing potassium nitrate (KNO ₃ ). As a result, a high-density compressive stress layer is formed by ion exchange between Na ions on the glass surface and K ions in the inorganic salt. As a method of contacting the glass with the inorganic salt, a method of applying a paste-like inorganic salt, a method of spraying an aqueous solution of the inorganic salt on the glass, and immersing the glass in a salt bath of a molten salt in which the inorganic salt is heated to a melting point or higher. Although a method and the like are possible, a method of immersing in a molten salt is preferable among these methods.

  As the inorganic salt, those having a melting point below the strain point (normally 500 to 600 ° C.) of the glass to be chemically strengthened are preferably used, and potassium nitrate (melting point 330 ° C.) is contained in the present invention. By containing potassium nitrate, the glass is in a molten state below the strain point of the glass, and handling becomes easy in a use temperature range. The content of potassium nitrate in the inorganic salt is preferably at least 50% by mass.

In the production method of the present invention, SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , PO ₄ ³⁻ , HPO ₄ ²⁻ and H ₂ PO ₄ ⁻ are added to the inorganic salt before the glass is subjected to ion exchange. A salt having at least one anion selected from the group consisting of (hereinafter, also collectively referred to as “specific anion”) is added. In performing ion exchange using an inorganic salt, the inorganic salt is converted into a liquid phase liquid salt. In the present invention, the presence of Mg ²⁺ or Ca ²⁺ in the liquid phase salt causes a compressive stress layer on the glass surface. It was found difficult to form. In the production method of the present invention is therefore, Mg 2+ inorganic salt containing at least one of ^(magnesium ions) and Ca 2+ ^(calcium ion) to, by adding a salt having the specific anion, Mg ²⁺ in an inorganic salt And Ca ²⁺ are trapped and precipitated as a solid of a magnesium salt or a calcium salt with the specific anion, so that Mg ²⁺ or Ca ²⁺ in the liquid phase salt is reduced.

The inorganic salt (liquid phase salt) before the addition of the salt having the specific anion satisfies one of the conditions of an Mg ²⁺ content of 5 mass ppm or more and a Ca ²⁺ content of 50 mass ppm or more. Amount of salt having a specific anion is not well particularly limited as long as the amount of Mg ²⁺ and Ca ²⁺ is sufficiently reduced in the liquid phase salt, of after the addition of inorganic salts, Mg ²⁺ concentration in the liquid phase salt It is preferable to add so that the content is less than 5 ppm by mass and the Ca ²⁺ concentration of the liquid phase salt is less than 50 ppm by mass.

As the specific anion, SO ₄ ^2- or CO ₃ ^2- is preferable from the viewpoint of easy capture (trap) of Mg ²⁺ and Ca ²⁺ .

Examples of the counter cation in the salt having a specific anion include K ⁺ , Na ^+, and Li ⁺ , and K ⁺ or Na ⁺ is preferable.

As the salt having a specific anion, at least one kind of salt selected from the group consisting of K ₂ SO ₄ , KNaSO ₄ , Na ₂ SO ₄ , K ₂ CO ₃ , KNaCO ₃ and Na ₂ CO ₃ is preferable. K ₂ SO ₄ or K ₂ CO ₃ is preferable from the viewpoint of not inhibiting S. In addition, the content of K ₂ SO ₄ in the inorganic salt after the addition of the salt having the specific anion is preferably 0.5% by mass or more. The content of K ₂ CO ₃ in the inorganic salt after the addition of the salt having the specific anion is preferably 0.5% by mass or more.
The salt having a specific anion may be added alone or in combination of two or more.

  The inorganic salt may contain, in addition to potassium nitrate and a salt having a specific anion, other chemical species as long as the effect of the present invention is not impaired. For example, sodium chloride, potassium chloride, sodium borate and potassium borate And the like. These may be contained alone or in combination of two or more.

The inorganic salt for glass strengthening prepared as described above contains a salt having a specific anion, so that the temperature is equal to or higher than the melting point of potassium nitrate and equal to or lower than 600 ° C., the liquid phase salt in a liquid state, and the solid phase salt in a solid state , And the Mg ²⁺ concentration in the liquid phase salt is less than 5 ppm by mass, and the Ca ²⁺ concentration in the liquid phase salt is preferably less than 50 ppm by mass. The solid phase salt preferably contains at least one of a magnesium salt with a specific anion and a calcium salt with a specific anion. That is, the solid phase salt is magnesium sulfate, calcium sulfate, magnesium carbonate, calcium carbonate, magnesium hydrogen carbonate, calcium hydrogen carbonate, magnesium hydrogen phosphate, calcium hydrogen phosphate, magnesium dihydrogen phosphate, calcium dihydrogen phosphate, magnesium phosphate And at least one salt selected from the group consisting of calcium phosphate.
The solid salt preferably has a Mg ²⁺ content of 100 ppm by mass or more, or a Ca ²⁺ content of 100 ppm by mass or more.

  Hereinafter, the production method of the present invention will be described by taking, as an example, an embodiment in which chemical strengthening is performed by a method of immersing glass in a molten salt.

(1-1) Production of molten salt 1
The molten salt can be produced by the following steps.
Step 1a: Preparation of Potassium Nitrate Molten Salt Step 2a: Addition of Salt Having Specific Anion to Potassium Nitrate Molten Salt

(Step 1a-Preparation of Potassium Nitrate Molten Salt-)
In step 1a, a molten salt is prepared by charging potassium nitrate into a container and heating it to a temperature equal to or higher than its melting point and melting it. Melting is performed at a temperature within the range of the melting point (330 ° C.) and boiling point (500 ° C.) of potassium nitrate. In particular, it is more preferable to set the melting temperature to 350 to 470 ° C. from the viewpoint of the balance between the surface compressive stress (CS) and the compressive stress layer depth (DOL) that can be given to glass and the strengthening time.

  Metal, quartz, ceramics, or the like can be used as a container for melting potassium nitrate. Among them, a metal material is preferable from the viewpoint of durability, and a stainless steel (SUS) material is preferable from the viewpoint of corrosion resistance.

(Step 2a-Addition of Salt Having Specific Anion to Potassium Nitrate Molten Salt-)
In step 2a, the above-mentioned salt having a specific anion is added to the potassium nitrate molten salt prepared in step 1a, and the mixture is uniformly mixed with a stirring blade or the like while keeping the temperature within a certain range. When a plurality of salts having a specific anion are used in combination, the order of addition is not limited, and they may be added simultaneously.
The temperature is preferably equal to or higher than the melting point of potassium nitrate, that is, 330 ° C. or higher, and more preferably 350 to 500 ° C. The stirring time is preferably 1 minute to 10 hours, more preferably 10 minutes to 2 hours.

(1-2) Production of molten salt 2
In the production 1 of the molten salt described above, the method of adding the salt having the specific anion after the melting of the potassium nitrate is exemplified. However, the molten salt can also be produced by the following steps.
Step 1b: Mixing of potassium nitrate and a salt having a specific anion Step 2b: Melting of the mixed salt

(Step 1b—mixing of potassium nitrate and a salt having a specific anion—)
In step 1b, potassium nitrate and a salt having a specific anion are charged into a container and mixed with a stirring blade or the like to form a mixed salt. When a plurality of salts are used in combination, the order of addition is not limited, and they may be added simultaneously. The same container as that used in the above step 1a can be used.

(Step 2b-melting of mixed salt-)
In step 2b, the mixed salt obtained in step 1b is heated and melted. The melting temperature is the same as in the above step 1a. Further, it is preferable to melt while stirring with a stirring blade or the like so that the whole becomes uniform, and the stirring time is preferably 1 minute to 10 hours, more preferably 10 minutes to 2 hours.

  In the molten salt obtained by Production 1 or Production 2 of the molten salt, a precipitate is generated by the addition of a salt having a specific anion. Therefore, before the chemical strengthening treatment of the glass, the precipitate is deposited on the bottom of the container. It is preferable to allow the sample to stand still. The precipitate contains a magnesium salt and a calcium salt of a specific anion.

(2) Ion exchange Next, glass is chemically strengthened using the prepared molten salt. Chemical strengthening is performed by immersing glass in a molten salt and replacing metal ions (Na ions) in the glass with metal ions (K ions) having a large ionic radius in the molten salt. By changing the composition of the glass surface by ion exchange, it is possible to form a compressive stress layer with a high-density glass surface, and compressive stress is generated by the high-density glass surface. it can.
The chemical strengthening treatment in the present invention can be specifically performed in the following step 3.

(Step 3-Chemical strengthening treatment of glass-)
First, the glass is preheated, and the molten salt produced as described above is adjusted to a temperature at which chemical strengthening is performed. Next, after immersing the preheated glass in the molten salt for a predetermined time, the glass is pulled out of the molten salt and allowed to cool.
It is preferable that the glass is subjected to mechanical processing such as cutting, end face processing, and drilling before the chemical strengthening treatment. Further, the glass may be polished before chemical strengthening, if necessary.

  The preheating temperature of the glass depends on the temperature at which it is immersed in the molten salt, but is generally preferably 100 ° C. or higher.

  The chemical strengthening temperature is preferably equal to or lower than the strain point (normally 500 to 600 ° C.) of the glass to be strengthened, and particularly preferably 350 ° C. or higher to obtain a deeper compressive stress layer.

  The immersion time of the glass in the molten salt is preferably 1 minute to 10 hours, more preferably 5 minutes to 8 hours, even more preferably 10 minutes to 4 hours. Within such a range, a chemically strengthened glass having an excellent balance between the surface compressive stress (CS) and the compressive stress layer depth (DOL) can be obtained.

(Step 4-Cleaning of Glass-)
Subsequently, in step 4, the glass after ion exchange is washed. Industrial water, ion-exchanged water and the like can be used for washing, and ion-exchanged water is particularly preferable. Washing conditions vary depending on the washing solution used, but when using ion-exchanged water, washing at 0 to 100 ° C. is preferred from the viewpoint of completely removing attached salts.

<Chemically tempered glass>
The chemically strengthened glass obtained by the production method of the present invention will be described.

(Compressive Stress Value (CS))
In the chemically strengthened glass obtained by the production method of the present invention, the compressive stress value of the surface compressive stress layer is preferably at least 500 MPa, more preferably at least 550 MPa, particularly preferably at least 600 MPa. According to the production method of the present invention, a glass having a desired surface compressive stress can be obtained by performing chemical strengthening using an inorganic salt in which impurities such as Mg ²⁺ and Ca ²⁺ are reduced.

(Compression Stress Layer Depth (DOL))
In the chemically strengthened glass of the present invention, the compressive stress layer depth of the surface compressive stress layer is preferably 3 μm or more, more preferably 5 μm or more.

  The compression stress value and the compression stress layer depth of the compression stress layer can be measured using a surface stress meter (for example, FSM-6000 manufactured by Orihara Seisakusho). Further, the depth of the compressive stress layer can be substituted by the ion exchange depth measured using an EPMA (electron probe micro analyzer) or the like.

  Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

<Evaluation method>
Various evaluations in this example were performed by the following analysis methods.

(Evaluation of glass: surface stress)
The surface compressive stress value (CS, unit: MPa) and the compressive stress layer depth (DOL, unit: μm) were measured using a surface stress meter (FSM-6000) manufactured by Orihara Seisakusho Co., Ltd.

  Of the following test examples, Examples 1 to 5 and 9 to 12 are Examples, and Examples 6 to 8 and 13 to 15 are Comparative Examples.

(Example 1)
9,800 g of potassium nitrate containing Mg ²⁺ and Ca ²⁺ in the amounts shown in Table 1 was charged into a SUS cup, and heated to 450 ° C. with a mantle heater to prepare a molten salt of potassium nitrate. 200 g of potassium sulfate was added thereto to prepare a potassium nitrate molten salt of 2% by mass of potassium sulfate. Table 1 shows the amounts of Mg ²⁺ and Ca ²⁺ after the addition. The amounts of Mg ²⁺ and Ca ²⁺ were measured by ICP emission spectroscopy. SPS3100 manufactured by SII Nanotechnology Co., Ltd. was used as an ICP emission spectrometer.
After preheating glass A (soda lime glass) (50 mm × 50 mm × 0.95 mm) having the following composition to 200 to 400 ° C., immersing it in a molten salt at 450 ° C. for 2 hours, performing ion exchange treatment, and cooling to around room temperature By doing so, a chemical strengthening treatment was performed. The obtained chemically strengthened glass was washed with pure water.
Glass A composition (mol% display based on oxide): 71.1% of SiO ₂ , 1.1% of Al ₂ O ₃ , 12.4% of Na ₂ O, 0.2% of K ₂ O, 6.9% of MgO , CaO 8.3%

(Example 2)
A chemically strengthened glass was obtained in the same manner as in Example 1, except that potassium nitrate containing the amounts of Mg ²⁺ and Ca ²⁺ shown in Table 1 was used.

(Example 3)
A chemically strengthened glass was obtained in the same manner as in Example 1, except that 200 g of potassium carbonate was added instead of potassium sulfate, and a potassium nitrate molten salt of 2% by mass of potassium carbonate was prepared.

(Example 4)
A chemically strengthened glass was obtained in the same manner as in Example 3, except that potassium nitrate containing the amounts of Mg ²⁺ and Ca ²⁺ shown in Table 1 was used.

(Example 5)
A chemically strengthened glass was obtained in the same manner as in Example 1 except that glass B (aluminosilicate glass) having the following composition (50 mm × 50 mm × 0.95 mm) was used instead of glass A.
Glass B composition (expressed in terms of mol% based on oxide): 64.4% of SiO ₂ , 8.0% of Al ₂ O ₃ , 12.5% of Na ₂ O, 4.0% of K ₂ O, 10.5% of MgO , CaO 0.1%, SrO 0.1%, BaO 0.1%, ZrO ₂ 0.5%

(Example 9)
A chemically strengthened glass was obtained in the same manner as in Example 1, except that glass C (soda lime glass) (50 mm × 50 mm × 0.7 mm) having the following composition was used instead of glass A.
Glass C composition (mol% display based on oxide): 68.74% of SiO ₂ , 2.96% of Al ₂ O ₃ , 14.20% of Na ₂ O, 0.15% of K ₂ O, 6.16% of MgO , CaO 7.75%, SrO 0.00%, BaO 0.00%, ZrO ₂ 0.00%, TiO ₂ 0.02%

(Example 10)
A chemically strengthened glass was obtained in the same manner as in Example 9, except that potassium nitrate containing the amounts of Mg ²⁺ and Ca ²⁺ shown in Table 1 was used.

(Example 11)
A chemically strengthened glass was obtained in the same manner as in Example 9, except that 200 g of potassium carbonate was added instead of potassium sulfate, and a potassium nitrate molten salt of 2% by mass of potassium carbonate was prepared.

(Example 12)
A chemically strengthened glass was obtained in the same manner as in Example 11, except that potassium nitrate containing the amounts of Mg ²⁺ and Ca ²⁺ shown in Table 1 was used.

(Example 6)
A chemically strengthened glass was obtained in the same manner as in Example 1, except that potassium sulfate was not added.

(Example 7)
A chemically strengthened glass was obtained in the same manner as in Example 2 except that potassium sulfate was not added.

(Example 8)
Chemically strengthened glass was obtained in the same manner as in Example 1, except that potassium nitrate containing the amounts of Mg ²⁺ and Ca ²⁺ shown in Table 1 was used, and potassium sulfate was not added.

(Example 13)
A chemically strengthened glass was obtained in the same manner as in Example 9, except that potassium sulfate was not added.

(Example 14, Example 15)
A chemically strengthened glass was obtained in the same manner as in Example 13 except that potassium nitrate containing the amounts of Mg ²⁺ and Ca ²⁺ shown in Table 1 was used.

  Table 1 shows the evaluation results of the obtained chemically strengthened glass.

From the results shown in Table 1, in Examples 1, 3, 5, 9 and 11, even when an inorganic salt having a Mg ²⁺ content of 5 mass ppm or more was used, a glass having a CS of 500 MPa or more was obtained. Further, in Examples 2, 4, 10 and 12, even when an inorganic salt having a Ca ²⁺ content of 50 mass ppm or more was used, a glass having a CS of 500 MPa or more was obtained.

Claims (5)

A method for producing chemically strengthened glass, comprising a step of ion-exchanging Na in the glass and K in the inorganic salt by contacting the inorganic salt containing potassium nitrate with the glass,
Prior to the ion exchange, at least one selected from the group consisting of SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , PO ₄ ³⁻ , HPO ₄ ²⁻ and H ₂ PO ₄ ^{− in the} inorganic salt. A step of adding a salt having an anion of
Before the addition, the inorganic salt contains at least one of Mg ²⁺ and Ca ²⁺ , and has a Mg ²⁺ content of 5 mass ppm or more and a Ca ²⁺ content of 50 mass ppm or more. Manufacturing method of chemically strengthened glass. The liquid phase salt in a liquid state among the inorganic salts after the addition has a Mg ²⁺ concentration of less than 5 ppm by mass, and a Ca ²⁺ concentration of the liquid phase salt is less than 50 ppm by mass. A method for producing the chemically strengthened glass according to the above. The glass is a composition which is displayed in mole percent on the oxide basis, of SiO ₂ 67 to 75%, the _Al 2 _{O 3} 0 to 5%, a CaO containing 1 to 15%, Na ₂ O and _K 2 O The method for producing a chemically strengthened glass according to claim 1 or 2, wherein the glass is a glass having a total content of 10 to 18%. Salt the additive method of producing a chemically strengthened glass according to claim 1, a salt with an SO ₄ ^2-. Salt the additive method of producing a chemically strengthened glass according to claim 1, a salt having a CO ₃ ^2-.