CN108473368B

CN108473368B - Method for producing chemically strengthened glass

Info

Publication number: CN108473368B
Application number: CN201680076423.9A
Authority: CN
Inventors: 藤原祐辅; 鹿岛出
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 2015-12-28
Filing date: 2016-12-26
Publication date: 2021-10-29
Anticipated expiration: 2036-12-26
Also published as: KR20180098268A; CN108473368A; JPWO2017115765A1; TW201736310A; TWI725921B; TWI710536B; TW202110768A; JP6288392B2; WO2017115765A1

Abstract

The present invention provides a method for producing chemically strengthened glass capable of sufficiently removing cracks and potential scratches on the glass surface as compared with the prior art. The present invention relates to a method for producing chemically strengthened glass, characterized in that the method for producing chemically strengthened glass includes the steps of: preparing a glass plate containing alkali metal ions; The process of inorganic salts of other alkali metal ions; the process of performing ion exchange between the alkali metal ions of the glass plate and the other alkali metal ions of the inorganic salts in an atmosphere with a dew point temperature of 20°C or higher; and a step of removing a part of the surface of the glass plate after the ion exchange.

Description

Method for producing chemically strengthened glass

Technical Field

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

Background

In recent years, chemically strengthened glass has been used as a cover glass for various display devices, and further improvement in strength has been demanded. In order to improve the strength of chemically strengthened glass, it is disclosed that a glass containing sodium is brought into contact with a specific inorganic salt containing potassium nitrate to perform a chemical strengthening treatment by ion-exchanging Na in the glass with K in the inorganic salt, and then a treatment with an acid and an alkali is performed (patent document 1).

Patent document 1 describes: the surface strength of the glass is dramatically improved without polishing the glass surface after the chemical strengthening treatment or etching treatment using hydrofluoric acid or the like.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2015/008763

Disclosure of Invention

Problems to be solved by the invention

However, in recent years, a larger amount of surface removal than that described in patent document 1 may be desired.

In view of the above circumstances, an object of the present invention is to provide a method for producing chemically strengthened glass, which can improve the amount of surface removal compared to conventional methods.

Means for solving the problems

The present inventors have made extensive studies and as a result, have found that the amount of glass removed from the surface can be dramatically increased by controlling the amount of water vapor during the chemical strengthening treatment, and have completed the present invention.

That is, the present invention relates to the following < 1 > - < 19 >.

< 1 > a method for producing a chemically strengthened glass, comprising:

preparing a glass plate containing alkali metal ions;

preparing an inorganic salt containing another alkali metal ion having an ion radius larger than that of the alkali metal ion;

performing ion exchange between the alkali metal ions of the glass plate and the other alkali metal ions of the inorganic salt in an atmosphere having a dew point temperature of 20 ℃ or higher; and

and removing a part of the surface of the glass sheet after the ion exchange.

< 2 > the method for producing a chemically strengthened glass as defined in above < 1 >, wherein the step of performing ion exchange is performed in an atmosphere having the dew point temperature of 30 ℃ or higher.

< 3 > the method for producing a chemically strengthened glass as defined in the above < 1 > or < 2 >, wherein the step of performing ion exchange is performed in an atmosphere having the dew point temperature of 40 ℃ or higher.

< 4 > the method for producing a chemically strengthened glass as defined in any one of the above < 1 > to < 3 >, wherein the step of performing ion exchange is performed in an atmosphere having the dew point temperature of 50 ℃ or higher.

< 5 > the method for producing a chemically strengthened glass as defined in any one of the above < 1 > to < 4 >, wherein the step of performing ion exchange is performed in an atmosphere in which the dew point temperature is equal to or lower than the temperature of the inorganic salt.

< 6 > the method for producing a chemically strengthened glass as defined in any one of the above < 1 > to < 5 >, wherein an atmosphere in the step of performing ion exchange is formed by introducing a gas containing water vapor from a water vapor supply part into an upper space of the inorganic salt, and an introduction amount of the gas containing water vapor is 1cm per 1cm³The amount of steam supplied in (4) is 0.01 mg/min or more.

< 7 > the method for producing a chemically strengthened glass as defined in any one of the above < 1 > to < 5 >, wherein an atmosphere in the step of performing ion exchange is formed by introducing a gas containing water vapor into the inorganic salt from a bubbling portion, and an introduction amount of the gas containing water vapor is 1cm per 1cm³The amount of steam supplied in (4) is 0.01 mg/min or more.

< 8 > the method for producing a chemically strengthened glass as defined in any one of the above < 1 > to < 7 >, wherein in the step of preparing the inorganic salt, a compound containing K selected from the group consisting of₂CO₃、Na₂CO₃、KHCO₃、NaHCO₃、Li₂CO₃、Rb₂CO₃、Cs₂CO₃、MgCO₃、CaCO₃And BaCO₃At least one salt of the group consisting of potassium nitrate and an inorganic salt of potassium nitrate.

< 9 > the method for producing a chemically strengthened glass as defined in any one of the above < 1 > to < 8 >, wherein the step of removing a part of the surface of the glass plate comprises a step of bringing the ion-exchanged glass plate into contact with an acid.

< 10 > the method for producing chemically strengthened glass as defined in above < 9 >, wherein the step of removing a part of the surface of the glass plate further comprises a step of bringing the glass plate into contact with an alkali after the step of bringing the glass plate into contact with an acid.

The method of producing chemically strengthened glass, as described in < 11 > and < 10 > above, further comprising a step of cleaning the glass plate between the step of contacting with an acid and the step of contacting with an alkali.

< 12 > the method for producing a chemically strengthened glass as defined in any one of the above < 1 > to < 11 >, further comprising a step of cleaning the glass plate between the step of performing ion exchange and the step of removing a part of the surface of the glass plate.

< 13 > the method for producing a chemically strengthened glass as defined in any one of the above < 10 > to < 12 >, wherein the step of contacting with an alkali further comprises a step of cleaning the glass plate.

< 14 > the method for producing a chemically strengthened glass as defined in any one of the above < 9 > to < 13 >, wherein a solution having a pH of less than 7 is used in the step of contacting with an acid.

< 15 > the method for producing chemically strengthened glass as defined 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 as defined above < 14 >, wherein the solution having a pH of less than 7 is a strong acid.

The method of producing chemically strengthened glass as defined in any one of the above < 10 > to < 16 >, wherein a solution having a pH of more than 7 is used in the step of contacting with the alkali.

< 18 > the method for producing a chemically strengthened glass as described in 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 as described above < 17 >, wherein the solution having a pH of more than 7 is a strong base.

According to the present invention, a method for producing chemically strengthened glass, which can improve the amount of surface removal compared to conventional methods, can be provided.

Drawings

Fig. 1 is a schematic diagram for explaining a method of a ball and ring test.

FIG. 2 is a schematic view showing a process for producing a chemically strengthened glass of the present invention.

Fig. 3 is a schematic diagram of an experimental system for forming an atmosphere in a step of performing ion exchange.

Detailed Description

The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented within a range not departing from the gist of the present invention. In the present specification, "to" indicating a numerical range is used in a meaning including numerical values described before and after the range as a lower limit value and an upper limit value.

< method for producing chemically strengthened glass >

The method for producing a chemically strengthened glass of the present invention is characterized by comprising:

(a) preparing a glass plate containing alkali metal ions;

(b) preparing an inorganic salt containing another alkali metal ion having an ion radius larger than that of the alkali metal ion;

(c) performing ion exchange between the alkali metal ions of the glass plate and the other alkali metal ions of the inorganic salt in an atmosphere having a dew point temperature of 20 ℃ or higher; and

(d) and removing a part of the surface of the glass sheet after the ion exchange.

(glass composition)

The glass used in the present invention may contain an alkali metal ion, and glasses of various compositions may be used as long as they have a composition that can be shaped 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, alkali barium glass, aluminoborosilicate glass, and the like.

The method for producing the glass is not particularly limited, and the glass can be produced by: a desired glass raw material is charged into a continuous melting furnace, and the glass raw material is heated and melted, preferably at 1500 to 1600 ℃, clarified, supplied to a forming apparatus, formed into a sheet shape, and gradually cooled.

Various methods can be used for forming the glass. For example, various forming methods such as a down-draw method (e.g., an overflow down-draw method, a flow-hole down-draw method, a redraw method, etc.), a float method, a roll method, and a press method can be used. Among them, the float method is preferable because the effect of the present invention is more remarkable since cracks are likely to be generated on at least a part of the glass surface.

The thickness of the glass is not particularly limited, but is usually preferably 5mm or less, more preferably 3mm or less, further preferably 1mm or less, and particularly preferably 0.7mm or less, in order to efficiently perform the chemical strengthening treatment.

In addition, the shape of the glass used in the present invention is not particularly limited. For example, glass having 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 rear surfaces, and a three-dimensional shape having a curved portion or the like can 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 contains 50 to 80% of SiO in mol% based on the oxide ₂2 to 25 percent of Al₂O₃0 to 10% of Li₂O, 0-18% of Na₂O, 0 to 10% of K₂O, 0-15% of MgO, 0-5% of CaO and 0-5% of ZrO₂The glass of (2);

(2) the composition expressed by mol% based on oxide contains 50-74% of SiO₂1 to 10 percent of Al₂O₃6 to 14 percent of Na₂O, 3 to 11 percent of K₂O, 2-15% of MgO, 0-6% of CaO and 0-5% of ZrO₂，SiO₂And Al₂O₃The total content of (A) is 75% or less, Na₂O and K₂Glass with a total content of O of 12-25% and a total content of MgO and CaO of 7-15%;

(3) the composition expressed by mol% based on oxide contains 68-80% of SiO₂4 to 10 percent of Al₂O₃5 to 15 percent of Na₂O, 0 to 1% of K₂O, 4-15% of MgO and 0-1% of ZrO₂The glass of (2);

(4) the composition expressed by mol% based on oxide contains 67-75% of SiO₂0 to 4% of Al₂O₃7 to 15 percent of Na₂O, 1 to 9 percent of K₂O, 6-14% of MgO and 0-1.5% of ZrO₂，SiO₂And Al₂O₃The total content of (a) is 71-75%, and Na₂O and K₂Glass containing 12 to 20% of total O and less than 1% of CaO;

(5) the composition contains 65 to 75% of SiO in terms of mass% based on the oxide₂0.1 to 5 percent of Al₂O₃1 to 6 percent of MgO, 1 to 15 percent of CaO and Na₂O+K₂Glass with O content of 10-18%;

(6) the composition contains 60 to 72% of SiO in terms of mass% based on oxides₂1 to 10 percent of Al₂O₃5 to 12 percent of MgO, 0.1 to 5 percent of CaO and 13 to 19 percent of Na₂O, 0 to 5% of K₂O, and RO/(RO + R)₂O) is 0.20 to 0.42 (wherein RO represents an alkaline earth metal oxide, and R is₂O represents an alkali metal oxide);

(7) the composition expressed by mol% based on oxide contains 55.5-80% of SiO₂12 to 20 percent of Al₂O₃8 to 25 percent of Na₂O, 2.5% or more of P₂O₅Glass containing 1% or more of alkaline earth metal RO (RO is MgO + CaO + SrO + BaO);

(8) the composition expressed by mol% based on oxide contains 57-76.5%SiO₂12 to 18 percent of Al₂O₃8 to 25 percent of Na₂O, 2.5 to 10 percent of P₂O₅Glass containing 1% or more of alkaline earth metal RO;

(9) the composition expressed by mol% based on oxide contains 56-72% of SiO₂8 to 20 percent of Al₂O₃3% -20% of B₂O₃8 to 25 percent of Na₂O, 0 to 5% of K₂O, 0-15% MgO, 0-15% CaO, 0-15% SrO₂0 to 15 percent of BaO and 0 to 8 percent of ZrO₂The glass of (2).

The chemically strengthened glass of the present invention has a compressive stress layer obtained by ion exchange on the surface of the glass. In the ion exchange method, the surface of the glass is ion-exchanged to form a surface layer in which compressive stress remains. Specifically, at a temperature not higher than the glass transition temperature, alkali metal ions (Li ions and/or Na ions) having a small ion radius on the surface of the glass sheet are replaced with other alkali metal ions (Na ions and/or K ions) having a larger ion radius by ion exchange. This causes a compressive stress to remain on the surface of the glass, thereby improving the strength of the glass.

In the manufacturing method of the present invention, the chemical strengthening treatment is performed as follows: an inorganic salt containing another alkali metal ion having an ionic radius larger than that of the alkali metal ion contained in the glass is brought into contact with the glass containing the alkali metal ion to perform ion exchange. That is, the alkali metal ions contained in the glass are ion-exchanged with other alkali metal ions contained in the inorganic salt.

When the alkali metal ion contained in the glass is Na ion, the inorganic salt is potassium nitrate (KNO)₃) More preferably further comprising an inorganic salt selected from the group consisting of K₂CO₃、Na₂CO₃、KHCO₃、NaHCO₃、Li₂CO₃、Rb₂CO₃、Cs₂CO₃、MgCO₃、CaCO₃And BaCO₃At least one salt of the group consisting of.

For example, when potassium nitrate is contained in the inorganic salt, potassium nitrate has a melting point of 330 ℃ and has a melting point not higher than the strain point (usually 500 to 600 ℃) of the glass to be chemically strengthened. Among the above salts, salts other than potassium nitrate (hereinafter, also referred to as "flux") have a property of cutting a network of glass represented by an Si — O — Si bond. Since the temperature at which the chemical strengthening treatment is performed is as high as several hundred ℃, covalent bonds between Si and O of the glass are appropriately cleaved at this temperature, and the low-density treatment described later is easily performed.

The degree of cleavage of the covalent bond also varies depending on the glass composition, the type of salt (flux) used, and the chemical strengthening treatment conditions such as temperature and time under which the chemical strengthening treatment is performed, and it is considered that the conditions selected to be such that 1 to 2 bonds of 4 covalent bonds protruding from Si are cleaved are preferable.

The Na ions (or Li ions) on the glass surface are ion-exchanged with the K ions (or Na ions) in the inorganic salt, thereby forming a high-density compressive stress layer. As a method of bringing the glass into contact with the inorganic salt, a method of applying a paste-like inorganic salt, a method of spraying an aqueous solution of the inorganic salt to the glass, a method of immersing the glass in a salt bath of a molten salt heated to a melting point or higher, and the like are possible, and among these, a method of immersing in a molten salt is preferable.

The amount of the flux is preferably 0.1 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol% or more, and particularly preferably 2 mol% or more. From the viewpoint of productivity, the saturated solubility of each salt is preferably not more than. If the amount is excessively increased, corrosion of the glass may occur. For example, in₂CO₃When used as a flux, the amount is preferably 24 mol% or less, more preferably 12 mol% or less, and particularly preferably 8 mol% or less.

The inorganic salt contains other chemical species than potassium nitrate and the flux within a range not to impair the effects of the present invention, and examples thereof include: alkali metal chloride salts such as sodium chloride, potassium chloride, sodium borate and potassium borate, alkali metal borate salts, and the like. These may be added alone or in combination of two or more.

(production of molten salt)

The molten salt can be produced by a known process. For example, when the inorganic salt is a molten salt containing potassium nitrate and a flux, the inorganic salt can be obtained by preparing a molten potassium nitrate salt and then adding the flux to the molten potassium nitrate salt. Alternatively, the potassium nitrate may be obtained by mixing potassium nitrate with a flux and then melting a mixed salt of the potassium nitrate and the 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, and more preferably 1000 ppm by weight or more. It is more preferable that the Na concentration in the molten salt is 2000 ppm by weight or more because the low-density layer is easily deepened by the following acid treatment step. The upper limit of the Na concentration is not particularly limited, and the Na concentration up to a level at which a desired surface Compressive Stress (CS) can be obtained can be allowed.

The molten salt subjected to the chemical strengthening treatment at least once contains sodium eluted from the glass. Therefore, if the Na concentration is within the above range, sodium derived from glass can be used as the Na source as it is, and when the Na concentration is insufficient or when a molten salt that is not used for chemical strengthening is used, adjustment can be made by adding an inorganic sodium salt such as sodium nitrate.

(step of performing ion exchange)

Subsequently, the prepared molten salt is used for chemical strengthening treatment. The chemical strengthening treatment is performed as follows: by immersing the glass in the molten salt, the alkali metal ions (Li ions or Na ions) in the glass are ion-exchanged (substituted) with other alkali metal ions (Na ions or K ions) having a large ionic radius in the molten salt. By changing the composition of the glass surface by this ion exchange, a pressure stress layer 20 having a high density on the glass surface can be formed [ fig. 2(a) to (b) ]. Since the densification of the glass surface generates a compressive stress, the glass can be strengthened.

In fact, since the density of the chemically strengthened glass gradually increases from the outer edge of the intermediate layer 30 (bulk) present at the center of the glass to the surface of the compressive stress layer, there is no clear boundary where the density rapidly changes between the intermediate layer 30 and the compressive stress layer 20. Herein, the intermediate layer means a layer existing in the central portion of the glass and sandwiched between the compressive stress layers. The intermediate layer is a layer that is not ion exchanged, unlike the compressive stress layer.

The chemical strengthening treatment (step of performing ion exchange) in the present invention can be specifically performed by the following procedure.

First, the glass is preheated to adjust the temperature of the molten salt to be chemically strengthened. Subsequently, the preheated glass is immersed in the molten salt tank 27 for a predetermined time, and then the glass is pulled out from the molten salt and naturally cooled. Before the chemical strengthening treatment, the glass is preferably subjected to shape processing corresponding to the application, for example, mechanical processing such as cutting, end face processing, and hole forming.

The preheating temperature of the glass depends on the temperature of immersion in the molten salt, and is preferably 100 ℃ or higher.

The chemical strengthening temperature is preferably not higher than the strain point (usually 500 to 600 ℃) of the glass to be strengthened, particularly preferably not lower than 350 ℃ in order to obtain a higher depth of compressive stress layer, more preferably not lower than 400 ℃ and still more preferably not lower than 430 ℃ in order to shorten the treatment time and promote the formation of a low-density layer.

The time for immersing the glass in the molten salt is preferably 1 minute to 10 hours, more preferably 5 minutes to 8 hours, and still more preferably 10 minutes to 4 hours. Within this range, a chemically strengthened glass having an excellent balance between strength and depth of the compressive stress layer can be obtained, and therefore, this range is preferable.

In the production method of the present invention, the low-density layer formed in the step of contacting with an acid, which will be described later, can be thickened by increasing the amount of water vapor in the molten salt at the time of glass impregnation. Since the low-density layer can be removed in the step of contacting with alkali, the low-density layer can be removed together with the crack or the potential scratch (potential ) by setting the thickness of the low-density layer to be equal to or more than the average depth of the crack or the potential scratch existing on the glass surface. Therefore, excellent surface strength of the chemically strengthened glass can be achieved.

The step of performing ion exchange is performed in an atmosphere having a dew point temperature of 20 ℃ or higher. The dew point is preferably 30 ℃ or higher, more preferably 40 ℃ or higher, still more preferably 50 ℃ or higher, and still more preferably 60 ℃ or higher. The upper limit is preferably set to a temperature of the inorganic salt (molten salt) that undergoes ion exchange or lower.

The dew point temperature (hereinafter, may be simply referred to as "dew point") may be at least in the vicinity of the interface of the molten salt within the above range, and the vicinity of the interface is an atmosphere in a region of 200mm or less from the interface of the molten salt. The dew point may be measured by a Vaisala DRYCAP (registered trademark) DMT346 dew point transmitter. The dew point in the present specification is a value considered to be a value at which an equilibrium is established between the molten salt and the atmosphere in the vicinity of the interface between the molten salt and the molten salt.

The dew point can be achieved by introducing water vapor into the molten salt and/or into the atmosphere in the vicinity of the interface of the molten salt before and/or simultaneously with the step of performing ion exchange. For example, by adding a steam supply unit to the molten salt tank, steam can be introduced into the molten salt and/or the atmosphere near the interface of the molten salt.

That is, the water vapor itself supplied from the water vapor supply unit, or the gas containing water vapor and water (liquid) may be directly blown into the molten salt, or the water vapor or the gas containing water vapor may be introduced into the upper space of the molten salt. In addition, water (liquid) itself may be added dropwise to the molten salt in a range where water vapor explosion does not occur.

When water vapor, a gas containing water vapor, or water (liquid) (hereinafter, may be simply referred to as "water vapor or the like") is introduced, the molten salt may be stirred or not stirred, but stirring is preferably performed in view of shortening the time until equilibrium is reached.

The time from the introduction of the water vapor or the like until the equilibrium is reached differs depending on the amount of the gas or liquid to be introduced, the water vapor concentration, the introduction method, and the like, and therefore cannot be considered in a short time.

As the gas containing water vapor, a gas that does not affect the chemical strengthening treatment can be used, and for example, as shown in fig. 3, a dry gas a such as air, nitrogen, or carbon dioxide gas is introduced into heated water 24, whereby a gas B containing water vapor and having a high humidity (gas containing water vapor) can be produced.

The water 24 used as the water vapor supply source is preferably pure water such as ion exchange water, from the viewpoint of suppressing deposition of scale on pipes and the like. The water 24 is heated by, for example, a water bath using a water tank 25. Further, the water 24 itself may be heated by, for example, a boiler or the like to generate steam.

More specifically, examples of the method of introducing the water vapor and the like include (1) introducing the gas B containing the water vapor from the water vapor supply unit into the upper space of the inorganic salt (molten salt 26), (2) introducing the gas B containing the water vapor from the bubbling unit into the inorganic salt (molten salt 26), and (3) directly introducing water (liquid) into the inorganic salt (molten salt 26). Among them, the atmosphere is preferably formed by the above (1) or (2).

As one embodiment of introducing the gas B containing water vapor into the upper space of the inorganic salt (molten salt 26), for example, there are: a method of spraying the water vapor or the like supplied from the water vapor supply unit onto the upper part of the inorganic salt or the vicinity of the interface of the inorganic salt by a sprayer. It is preferable to introduce water vapor or the like by a sprayer because the water vapor concentration in the upper space of the inorganic salt can be easily controlled to be substantially uniform.

The steam supply unit, the bubbling unit, the introduction unit for introducing water (liquid), and the atomizer-matching device may be appropriately provided, and are not particularly limited. Specifically, the number of the sprayers may be single or plural. In particular, when the molten salt tank is a large tank, the water vapor concentration in the upper space of the inorganic salt can be easily controlled to be substantially uniform by spraying water vapor or the like with a plurality of sprayers.

In the presence of water vapourWhen the gas is introduced into the upper space of the molten salt, the gas is introduced per 1cm³The amount of water vapor supplied to the gas introduced in (2) 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, the amount of water per 1cm³The flow rate of water introduced in (2) is preferably 0.01 mg/min or more, more preferably 0.02 mg/min or more.

In the case of blowing a gas containing water vapor directly into an inorganic salt (into a molten salt), per 1cm³The amount of water vapor supplied to the gas introduced in (2) is preferably 0.01 mg/min or more, more preferably 0.02 mg/min or more.

The reason why the surface strength of the chemically strengthened glass obtained by performing the ion exchange step in the molten salt having a large amount of water vapor (water content) is higher is considered as follows.

When the carbonate ion forming the molten salt reacts with water, bicarbonate ion and hydroxide ion are generated as shown in the following formula.

Here, when the moisture content in the molten salt is large, the equilibrium in the above formula is inclined rightward, and many bicarbonate ions and hydroxyl ions are generated. Since the hydroxide ions are ions that promote the cutting of the glass network, it is considered that the formation of a low-density layer on the glass surface is promoted by the generation of more hydroxide ions.

The sum of the carbonate anion concentration and the bicarbonate anion concentration in the inorganic salt obtained by the following formula is preferably 4 mol% or more, and more preferably 6 mol% or more. The concentration of 4 mol% or more is preferable because the reaction for forming a low-density layer on the glass surface can be accelerated.

{ (carbonate anion concentration) + (bicarbonate anion concentration) } (mole%) { (carbonate anion amount in inorganic salt) + (bicarbonate anion amount in inorganic salt) } (mol)/(total anion amount in inorganic salt) (mol) × 100

It is to be noted thatSince the carbonate anion concentration and the bicarbonate anion concentration in the molten salt could not be directly measured, a part of the molten salt was taken out, and a commercial standard solution (NaHCO) was diluted with pure water using a carbon dioxide meter TiN-9004₃) A calibration curve was prepared, and then a sample solution diluted 130 times with pure water was measured. In this case, since all of the bicarbonate anions are converted into carbonate anions, the concentration of carbonate anions detected by the measurement corresponds to the sum of the concentration of carbonate anions and the concentration of bicarbonate anions.

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 a step of contacting with an acid in a step of removing a part of the surface of the glass plate, which will be described later, and has a thickness of about 100nm to about 200nm in a conventional ion exchange step in which water vapor is not introduced, whereas the thickness can be adjusted to 300nm or more by performing ion exchange in an atmosphere in which water vapor is introduced and the dew point temperature is 20 ℃ or more.

Since the average depth of cracks or potential scratches on the glass surface generated in the glass production process or the glass processing process including the chemical strengthening treatment process is about 500nm, the thickness of the low-density layer is more preferably 500nm or more, and still more preferably 600nm or more.

The low-density layer formed can be removed by a step of bringing into contact with an alkali, which will be described later, among the steps of removing a part of the surface of the glass plate. Therefore, if the depth of the crack or the potential scratch on the glass surface is shallower than the thickness of the low-density layer, all of the crack and the potential scratch can be removed by the process of contacting with alkali.

The surface strength of the chemically strengthened glass can be made higher by removing cracks or potential scratches on the glass surface that cause a decrease in the strength of the chemically strengthened glass.

(step of cleaning)

In the production method of the present invention, it is preferable that a step of cleaning the glass plate is further included between the step of performing ion exchange and the step of removing a part of the surface of the glass plate. In the cleaning step, the glass is cleaned with industrial water, ion-exchanged water, or the like. The industrial water is treated as required. Among them, ion-exchanged water is preferable.

The cleaning conditions vary depending on the cleaning liquid used, and when ion-exchanged water is used, it is preferable to perform cleaning at 0 to 100 ℃ from the viewpoint of completely removing the attached salts.

In the step of cleaning, various methods can be used, such as a method of immersing the chemically strengthened glass in a water tank containing ion-exchanged water or the like, a method of exposing the glass surface to running water, and a method of spraying a cleaning liquid onto the glass surface with a water sprayer.

(Process for removing part of the surface of the glass plate)

And a step of removing a part of the surface of the ion-exchanged glass sheet. The step of removing a part of the surface of the glass sheet preferably includes a step of bringing the glass sheet into contact with an acid, and more preferably includes a step of bringing the glass sheet into contact with an alkali after the step of bringing the glass sheet into contact with an acid.

(step of contacting with an acid)

In the production method of the present invention, it is preferable to perform a step of bringing the glass into contact with an acid (acid treatment step) as a step of removing a part of the surface of the glass plate after the step of performing the ion exchange or the step of cleaning.

The acid treatment of the glass is performed 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, a low-density layer is formed by modifying, specifically, reducing the density of, a surface layer having a compressive stress layer on the glass surface.

The solution is not particularly limited if it is acidic, and the pH may be less than 7, and the acid used may be either weak or strong. Specifically, acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, oxalic acid, carbonic acid, and citric acid are preferable. These acids may be used alone or in combination of two or more.

The temperature at which the acid treatment is carried out varies depending on the kind, concentration and time of the acid used, but is preferably 100 ℃ or lower.

The time for performing the acid treatment varies depending on the kind, concentration and temperature of the acid used, but is preferably 10 seconds to 5 hours, and more preferably 1 minute to 2 hours, from the viewpoint of productivity.

The concentration of the solution to be subjected to the acid treatment varies depending on the kind of the acid used, the time, and the temperature, but is preferably a concentration at which the corrosion of the container is less likely, and more specifically, is preferably 0.1 to 20 wt%.

Since the low-density layer can be removed by alkali treatment described later, the thicker the low-density layer is, the easier the glass surface is to remove. As described above, the thickness of the low-density layer is preferably 300nm or more, more preferably 500nm or more, and further preferably 600nm or more, from the viewpoint of the removal amount of the glass surface.

From the viewpoint of removability of the glass surface, the density of the low-density layer is preferably lower than the density of a region (bulk) deeper than the compressive stress layer after ion exchange. The thickness of the low-density layer can be determined from the period (. DELTA.theta.) measured by X-ray reflectance (XRR). The density of the low-density layer can be determined from the critical angle (θ c) measured by XRR.

The formation of the low-density layer and the thickness of the layer can be confirmed by simply observing the cross section of the glass with a Scanning Electron Microscope (SEM).

(step of contacting with an alkali)

In the production method of the present invention, it is preferable to further perform a step of contacting with an alkali (alkali treatment step) after the step of contacting with an acid. More preferably, the glass plate is washed after the step of contacting with the acid and before the step of contacting with the alkali in the same manner as the above-described washing step.

The alkali treatment is performed by immersing the chemically strengthened glass in an alkaline solution, and thereby a 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 if it is alkaline, and may have a pH of more than 7, and either a weak base or a strong base may be used. Specifically, bases such as sodium hydroxide, potassium carbonate, and sodium carbonate are preferable. These bases may be used alone or in combination of two or more.

The temperature for the alkali treatment varies depending on the kind, concentration and time of the alkali used, but is preferably 0 to 100 ℃, more preferably 10 to 80 ℃, and particularly preferably 20 to 60 ℃. If in this temperature range there is no risk of corrosion of the glass and is therefore preferred.

The time for the alkali treatment varies depending on the kind, concentration and temperature of the alkali to be used, but is preferably 10 seconds to 5 hours, more preferably 1 minute to 2 hours, from the viewpoint of productivity.

The concentration of the solution to be subjected to the alkali treatment varies depending on the kind of the alkali used, the time, and the temperature, but is preferably 0.1 to 20% by weight from the viewpoint of the glass surface removability.

By the alkali treatment, a part or all of the low-density layer after H penetration is removed, whereby a chemically strengthened glass having improved surface strength can be obtained. In particular, in the present invention, the low-density layer can be made thicker than the depth of cracks or potential scratches present on the glass surface. It is therefore considered that the crack or potential scratch existing on the surface of the glass can be removed simultaneously with the low-density layer, thereby contributing more to the improvement of the surface strength of the glass. After the alkali treatment, a washing step is preferably performed by the same method as described above.

< chemically strengthened glass >

According to the method for producing chemically strengthened glass of the present invention, since the low-density layer can be formed deeper than in the conventional chemical strengthening treatment, the surface layer of the chemically strengthened glass obtained after removing the low-density layer has fewer cracks and potential scratches. Therefore, the chemically strengthened glass obtained by the present invention has very high surface strength.

(glass surface Strength)

The surface strength of the chemically strengthened glass can be evaluated by a ball and ring test.

(ball and Ring test)

The chemically strengthened glass was evaluated from a BoR surface strength F (N) measured by a Ball on Ring (BoR) test in which a glass plate was placed on a stainless steel Ring having a diameter of 30mm and a roundness at the contact portion of 2.5mm, and a load was applied to a Ball made of steel having a diameter of 10mm at the center of the Ring under a static load condition in a state where the Ball was in contact with the glass plate.

The strength of the 1 st main surface and the 2 nd main surface of the chemically strengthened glass preferably satisfies F.gtoreq.1500 × t²More preferably F.gtoreq.1800 Xt²More preferably F.gtoreq.2000 Xt²[ wherein F is BoR plane strength (N) measured by a ball and ring test, and t is a plate thickness (mm) of a glass substrate]. When the BoR plane strength f (n) is within this range, excellent plane strength is exhibited even when the sheet is made thin. The BoR test can be performed by the method described in the examples described later.

(compressive stress layer)

The value of the compressive stress and the depth of the compressive stress layer of the chemically strengthened glass can be measured by using an EPMA (electron probe micro analyzer) or a surface stress meter (for example, FSM-6000 manufactured by zeugo corporation).

(amount of glass surface (Low Density layer) removed)

The removal amount (thickness) of the glass surface (low-density layer) after the alkali treatment can be determined as follows: the weight before and after the chemical treatment was measured by an electronic balance for analysis, and the thickness was converted by using the following formula.

(thickness of removal amount per side) [ (weight before treatment) - (weight after treatment) ]/(specific gravity of glass)/area treated/2

At this time, the specific gravity of the glass was set to 2.48 (g/cm)³) And the calculation is performed.

Examples

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

< evaluation method >

Various evaluations in the present example were performed by the following analytical methods.

(evaluation of glass: surface Strength)

Glass face strength was determined by Ball and Ring (Ball on Ring; BoR) testing. Fig. 1 shows a schematic diagram for explaining a ball and ring test used in the present invention. The glass plate 1 was horizontally placed and pressed with a pressing jig 2 (hardened steel, 10mm in diameter, mirror finished) made of SUS304, and the surface strength of the glass plate was measured.

In FIG. 1, a glass plate as a sample was horizontally placed on a receiving jig 3 made of SUS304 (diameter: 30mm, curvature of contact portion: R2.5mm, contact portion: hardened steel, mirror finished). A pressing jig for pressing the glass sheet is provided above the glass sheet.

In the present embodiment, the central region of the glass plate is pressurized from above the obtained glass plate. The test conditions are as follows.

Lowering speed of pressing jig: 1.0 (mm/min)

At this time, the breaking load (unit N) when the glass was broken was defined as BoR plane strength, and the average value of 20 measurements was defined as BoR average plane strength. However, when the breakage start point of the glass plate is deviated from the ball pressing position by 2mm or more, it is excluded from the data for calculating the average value.

(evaluation of glass: surface stress)

The surface compressive stress value (CS in MPa) and the depth of the compressive stress layer (DOL in μm) of the glass were measured by using a surface stress meter (FSM-6000) manufactured by Seikagaku Kogyo Co.

(evaluation of glass: amount of removal)

The thickness of the removed amount of glass was determined as follows: the weight before AND after the chemical treatment was measured by using an electronic balance for analysis (HR-202 i; manufactured by AND), AND the thickness was converted by using the following equation.

(evaluation of glass: crack or potential scratch)

The presence or absence of a crack or a potential scratch on the glass surface was visually checked under a light source with an illuminance of 1500 lux, and if there was no defect that could be visually recognized, it was judged that no crack or potential scratch was present.

< example 1 >

(step of performing ion exchange)

A molten salt containing potassium carbonate (10 mol%) and sodium (6000 ppm) was prepared by charging 8454g of potassium nitrate, 1324g of potassium carbonate, and 222g of sodium nitrate into a stainless steel (SUS) pot and heating the mixture to 490 ℃ by a mantle heater. The molten salt contains water vapor by introducing air, which has been introduced into water heated to 55 ℃, into the atmosphere in the vicinity of 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 humidified by passing it through water 24 heated to 55 ℃ by a water tank 25, thereby obtaining a humidified gas (air) B containing water vapor.

The gas B containing water vapor is introduced into the upper space of the inorganic salt (molten salt) 26 in the tank where the chemical strengthening treatment is performed through a path heated by the electric heating belt, and thereby the dew point in the step of performing ion exchange is controlled. At this time, each 1cm³The amount of steam supplied in (3) was 0.02 mg/min, and the dew point in the vicinity of the interface of the molten salt was 38 ℃.

A glass plate A having a thickness of 50mm by 0.7mm was prepared, preheated to 350 ℃ to 400 ℃, immersed in a molten salt at 490 ℃ for 1 hour, subjected to an ion exchange treatment, and then cooled to a temperature near room temperature, thereby being subjected to a chemical strengthening treatment. The obtained chemically strengthened glass was washed with water, and the subsequent steps were performed.

Glass composition of glass plate a (expressed in mol% on an oxide basis): SiO 2₂ 64.2％、Al₂O₃ 8.0％、Na₂O 12.5％、K₂O 4.0％、MgO 10.5％、CaO 0.1％、SrO 0.1％、BaO 0.1％、ZrO₂ 0.5％

(step 1 of removing part of the surface: step of contacting with an acid)

In a beaker, 6.0 wt% nitric acid (nitric acid 1.38 (manufactured by kanto chemical corporation) was prepared by diluting with ion-exchanged water), and the temperature was adjusted to 40 ℃ using a water bath. The glass obtained in the chemical strengthening step was immersed in the prepared nitric acid for 120 seconds, and subjected to acid treatment. Then, the glass was washed with water and subjected to the subsequent steps.

(step 2 of removing part of the surface: step of contacting with an alkali)

A 4.0 wt% aqueous solution of sodium hydroxide (48% sodium hydroxide solution (manufactured by kanto chemical corporation) was diluted with ion-exchanged water) was prepared in a beaker, and the temperature was adjusted to 40 ℃. The glass washed after the step of contacting with an acid was immersed in the prepared sodium hydroxide aqueous solution for 120 seconds, and subjected to alkali treatment. Then, the glass was washed with water to wash the alkali on the glass surface. Then, drying was performed by air blowing.

The chemically strengthened glass of example 1 was obtained in the above manner.

The presence of cracks and potential scratches was not confirmed in the resulting chemically strengthened glass.

< example 2 >

A chemically strengthened glass was produced in the same manner as in example 1, except that the potassium carbonate concentration of the molten salt in the ion exchange step was set to 8 mol%, the dew point in the vicinity of the interface of the molten salt was set to 71 ℃, and the chemical strengthening treatment conditions were set to 450 ℃ for 2 hours. The dew point is controlled by introducing a gas containing water vapor per 1cm³The amount of steam supplied in (1) was 0.08 mg/min. In the obtained chemically strengthened glassThe presence of cracks and potential scratches in the glass was 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 ℃. The introduction of a gas containing water vapor for controlling the dew point was not performed.

< comparative example 2 >

A chemically strengthened glass was produced in the same manner as in comparative example 1, except that potassium carbonate was not added to the molten salt in the step of performing ion exchange, sodium was set to 2000 ppm by weight, and acid treatment and alkali treatment were not performed. The presence of cracks and potential scratches was not confirmed in the resulting glass.

< example 3 >

A chemically strengthened glass was produced under the same conditions as in example 1, except that the glass plate B was used. The presence of cracks and potential scratches was not confirmed in the resulting chemically strengthened glass.

Glass composition of glass plate B (expressed in mol% based on oxides): SiO 2₂ 68.0％、Al₂O₃ 12.0％、Na₂O 18.6％、MgO 8.0％

< example 4 >

A chemically strengthened glass was produced under the same conditions as in example 2, except that the same glass as in example 3 was used. The presence of cracks and potential scratches was not confirmed in the resulting chemically strengthened glass.

< comparative example 3 >

A 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. The presence of cracks and potential scratches was not confirmed in the resulting chemically strengthened glass.

< comparative example 4 >

A 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. The presence of cracks and potential scratches was not confirmed in the resulting glass.

< example 5 >

(step of performing ion exchange)

A chemically strengthened glass was produced under the same conditions as in example 2, except that a glass plate C having a thickness of 0.55mmt was used and the dew point in the vicinity of the interface of the molten salt was set to 66 ℃. The presence of cracks and potential scratches was not confirmed in the resulting chemically strengthened glass.

Glass composition of glass plate C (expressed in mol% based on oxides): SiO 2₂ 67％、B₂O₃ 4％、Al₂O₃13％、Na₂O 14％、K₂O＜1％、MgO 2％、CaO＜1％

< comparative example 5 >

A 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. The presence of cracks and potential scratches was not confirmed in the resulting chemically strengthened glass.

The chemically strengthened glass obtained in the above manner was subjected to various evaluations. The glass treatment conditions and evaluation results are shown in table 1. Note that, as the BoR plane strength, BoR average plane strength was shown.

As described above, in examples 1 to 5 and comparative examples 1 to 5, the presence of cracks and potential scratches was not observed in the visual inspection under the light source having the illuminance of 1500 lux. However, as shown in Table 1, examples 1 to 5 exhibited higher BoR plane strength F (N) than comparative examples 1 to 5.

The reason why examples 1 to 5 exhibited higher BoR plane strength F (N) than comparative examples 1 to 5 is considered as follows. In the production method of the present invention, the step of ion-exchanging the alkali metal ions of the glass plate with the other alkali metal ions of the inorganic salt in an atmosphere having a dew point temperature of 20 ℃ or higher can increase the amount of water vapor in the molten salt at the time of chemically strengthening the glass, thereby forming a low-density layer having a depth of not less than the average depth of cracks or potential scratches existing on the surface of the glass. By the step of removing a portion of the surface of the glass sheet after the ion exchange, the low-density layer can be removed and the number of cracks or potential scratches can be sufficiently removed or reduced, and a high BoR plane strength f (n) can be achieved.

The present invention has been described in detail with reference to the specific embodiments, but it is apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. It should be noted that the present application is based on japanese patent application (japanese application 2015-256894) filed on 12/28/2015, which is incorporated by reference in its entirety. In addition, all references cited are incorporated herein by reference in their entirety.

Industrial applicability

According to the method for producing chemically strengthened glass of the present invention, chemically strengthened glass having very high surface strength can be obtained without performing polishing or etching treatment using hydrofluoric acid or the like after chemical strengthening. That is, there can be obtained chemically strengthened glass which is free from appearance defects due to expansion of potential scratches caused by etching treatment with hydrofluoric acid or the like and polishing scratches caused by polishing, and which has excellent surface strength.

Therefore, the glass can be applied to all glasses regardless of the presence or absence or degree of surface damage or potential scratches of the glass before the chemical strengthening treatment, and the versatility is high. Further, since the treatment can be performed by immersion in a solution, it is effective in easily coping with various glass shapes, large-area glass, and the like. Further, the etching treatment using hydrofluoric acid or the like is highly safe and low in cost.

Reference numerals

1 glass plate

2 pressing jig

3 bearing clamp

10 low density layer

20 layer of compressive stress

30 middle layer

21 regulator

22 flow meter

23 check valve

24 water

25 water tank

26 molten salt

27 molten salt tank

Claims

1. A method for producing a chemically strengthened glass, comprising:

preparing a glass plate containing alkali metal ions;

a step of removing a part of the surface of the glass sheet after the ion exchange,

wherein,

the step of removing a part of the surface of the glass sheet includes a step of bringing the ion-exchanged glass sheet into contact with an acid.

2. The method for producing a chemically strengthened glass according to claim 1, wherein the step of performing ion exchange is performed in an atmosphere having a dew point temperature of 30 ℃ or higher.

3. The method for producing a chemically strengthened glass according to claim 1, wherein the step of performing ion exchange is performed in an atmosphere having the dew point temperature of 40 ℃ or higher.

4. The method for producing a chemically strengthened glass according to claim 1, wherein the step of performing ion exchange is performed in an atmosphere having a dew point temperature of 50 ℃ or higher.

5. The method for producing a chemically strengthened glass according to any one of claims 1 to 4, wherein the step of performing ion exchange is performed in an atmosphere in which the dew point temperature is equal to or lower than the temperature of the inorganic salt.

6. The method for producing chemically strengthened glass according to any one of claims 1 to 4, wherein the atmosphere in the step of performing ion exchange is formed by introducing a gas containing water vapor from a water vapor supply unit into the upper space of the inorganic salt, and the amount of the gas containing water vapor introduced is 1cm per 1cm³The amount of steam supplied in (4) is 0.01 mg/min or more.

7. The method for producing a chemically strengthened glass according to any one of claims 1 to 4, wherein an atmosphere in the step of performing ion exchange is formed by introducing a gas containing water vapor from a bubbling portion into the inorganic salt, and an introduction amount of the gas containing water vapor is 1cm per 1cm³The amount of steam supplied in (4) is 0.01 mg/min or more.

8. The method for producing a chemically strengthened glass according to any one of claims 1 to 4, wherein in the step of preparing the inorganic salt, a compound selected from the group consisting of K, and K is prepared₂CO₃、Na₂CO₃、KHCO₃、NaHCO₃、Li₂CO₃、Rb₂CO₃、Cs₂CO₃、MgCO₃、CaCO₃And BaCO₃At least one salt of the group consisting of potassium nitrate and an inorganic salt of potassium nitrate.

9. The method for producing a chemically strengthened glass according to claim 1, wherein the step of removing a part of the surface of the glass plate further comprises a step of bringing the glass plate into contact with an alkali after the step of bringing the glass plate into contact with an acid.

10. The method for producing a chemically strengthened glass according to claim 9, further comprising a step of cleaning the glass sheet between the step of contacting with an acid and the step of contacting with an alkali.

11. The method for producing a chemically strengthened glass according to any one of claims 1 to 4, 9 and 10, further comprising a step of cleaning the glass sheet between the step of performing ion exchange and the step of removing a part of the surface of the glass sheet.

12. The method for producing chemically strengthened glass according to claim 9 or 10, further comprising a step of cleaning the glass plate after the step of contacting with alkali.

13. The method for producing a chemically strengthened glass according to claim 1, 9 or 10, wherein a solution having a pH of less than 7 is used in the step of contacting with the acid.

14. The method of manufacturing chemically strengthened glass according to claim 13, wherein the solution having a pH of less than 7 is a weak acid.

15. The method of manufacturing chemically strengthened glass according to claim 13, wherein the solution having a pH of less than 7 is a strong acid.

16. The method for producing a chemically strengthened glass according to claim 9, 10, 14 or 15, wherein a solution having a pH of more than 7 is used in the step of contacting with the alkali.

17. The method of manufacturing chemically strengthened glass according to claim 16, wherein the solution having a pH of greater than 7 is a weak base.

18. The method of manufacturing chemically strengthened glass according to claim 16, wherein the solution having a pH greater than 7 is a strong base.