WO2018043361A1 - Method for producing chemically toughened glass - Google Patents

Abstract

The present invention provides a method for producing a chemically toughened glass, which improves the texture to the touch of the glass. The present invention relates to a method for producing a chemically toughened glass, which comprises: a step for preparing a glass containing alkali ions; a step for preparing an inorganic salt which contains other alkali ions that have a larger ionic radius than the alkali ions contained in the glass, and which has a pH of 8 to 14 (inclusive) when formed into a 10 wt% aqueous solution; and a step for performing ion exchange between the alkali ions contained in the glass and the other alkali ions contained in the inorganic salt in an atmosphere having a dew point of 39°C or higher.

Description

Method for producing chemically strengthened glass

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

Chemically strengthened glass is used as a cover glass for various display devices. As one method for improving the strength of chemically strengthened glass, Patent Document 1 discloses that Na in glass and K in the inorganic salt are brought into contact with a specific inorganic salt containing potassium nitrate. A method is disclosed in which a chemical strengthening treatment is performed by ion-exchange of and then an acid and alkali treatment is performed. Patent Document 1 describes that the surface strength of glass is remarkably improved without subjecting the glass surface after chemical strengthening treatment to etching treatment using polishing or hydrofluoric acid.

International Publication No. 2015/008763

In recent years, the function of enlarging / reducing the screen using a finger through the cover glass has become widespread. Therefore, the cover glass is required to have a function of not only a simple strength but also a touch feeling with a finger. However, Patent Document 1 does not disclose a glass manufacturing method for improving the touch feeling with a finger.

Therefore, in view of the above circumstances, an object of the present invention is to provide a method for producing chemically tempered glass for improving the function of touch comfort.

The method for producing chemically strengthened glass according to the first aspect of the present invention includes a step of preparing a glass containing alkali ions, and another alkali ion larger than the ion radius of the alkali ions contained in the glass, and is 10 wt%. A step of preparing an inorganic salt having a pH of 8 or more and 14 or less when an aqueous solution is used, and the alkali ion contained in the glass and the other alkali contained in the inorganic salt in an atmosphere having a dew point temperature of 39 ° C. or more. And a step of ion exchange with ions.

According to the present invention, it is possible to provide a method for producing chemically tempered glass for improving the touch feeling of glass.

Drawing 1 is a mimetic diagram showing a manufacturing process in a manufacturing method of chemically strengthened glass concerning the present invention. FIG. 2 is a schematic diagram of an experimental system for forming an atmosphere in an ion exchange process.

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 without departing from the gist of the present invention. In the present specification, “to” indicating a numerical range is used in the sense of including the numerical values described before and after the numerical value as a lower limit value and an upper limit value.

In the present specification, “wt%”, “mass%”, and “wt%” have the same meaning.

<Method for producing chemically strengthened glass>
The method for producing chemically strengthened glass according to the present invention (hereinafter also abbreviated as the method of the present invention)
(A) preparing a glass containing alkali ions;
(B) preparing an inorganic salt containing other alkali ions larger than the ion radius of the alkali ions contained in the glass and having a pH of 8 or more and 14 or less when a 10 wt% aqueous solution is formed;
(C) ion exchange between the alkali ions contained in the glass and other alkali ions contained in the inorganic salt in an atmosphere having a dew point temperature of 39 ° C. or higher;
It is characterized by including. Each step will be described below.

[(A) Step of preparing glass containing alkali ions]
The glass used in the method of the present invention only needs to contain alkali ions, and various glasses can be used as long as they have a composition that can be strengthened by molding and chemical strengthening treatment. Among them, it is preferable to contain sodium, and specific examples 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 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 ° C., clarified, and then supplied to a molding apparatus. It can be manufactured by forming into a plate shape and slowly cooling.

It should be noted that 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 slot down method and a redraw method), a float method, a roll-out method, and a press method can be employed. Of these, the float method is preferred in that cracks are likely to occur on at least a part of the glass surface, and the effects of the present invention are more prominent.

The thickness of the glass is not particularly limited, but is usually preferably 5 mm or less, more preferably 3 mm or less, and even more preferably 1 mm or less for effective chemical strengthening treatment. Preferably, 0.7 mm or less is particularly preferable.

Further, the shape of the glass used in the method of the present invention is not particularly limited. For example, various shapes of glass such as a flat plate shape having a uniform plate thickness, a shape having a curved surface on at least one of the front surface and the back surface, and a three-dimensional shape having a bent portion can be employed.

Although it does not specifically limit as a composition of the glass used with the method of this invention, For example, the following glass compositions are mentioned.
(1) Composition expressed as mol% based on oxide, SiO ₂ 50-50%, Al ₂ O ₃ 1-25%, Li ₂ O 0-10%, Na ₂ O 0-18% A glass containing 0 to 10% of K ₂ O, 0 to 15% of MgO, 0 to 10% of CaO and 0 to 5% of ZrO ₂ (2) The composition expressed by mol% on the basis of oxide is SiO 2 ₂ to 50 to 74%, Al ₂ O ₃ to 1 to 10%, Na ₂ O to 6 to 14%, K ₂ O to 3 to 11%, MgO to 2 to 15%, CaO to 0 to 6% and ZrO ₂ 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%, the content of MgO and CaO the total is 7-15% glass (3) composition viewed in mole percent on the oxide basis is, SiO ₂ and 68-8 %, The _{Al 2 O 3 4 ~ 10%} , a Na ₂ O 5 ~ 15%, the _{K 2} O 0 to 1%, glass 4-15% and the ZrO ₂ and MgO containing 0 to 1% (4) composition viewed in mole percent on the oxide basis is, the SiO ₂ 67 ~ 75%, the _{Al 2 O 3 0 ~ 4%} , 7 ~ 15% of Na ₂ O, the _{K 2} O 1 ~ 9%, a MgO 6 to 14% and 0 to 1.5% of ZrO ₂ , the total content of SiO ₂ and Al ₂ O ₃ is 71 to 75%, the total content of Na ₂ O and K ₂ O is 12 to When the CaO content is 20%, the glass content is less than 1%. (5) The composition expressed by mass% based on the oxide is 65 to 75% for SiO ₂ and 0.002 for Al ₂ O ₃ . Gala containing 1-5%, MgO 1-6%, CaO 1-15% and Na ₂ O + K ₂ O 10-18% (6) The composition expressed by mass% based on the oxide is SiO ₂ 60-72%, Al ₂ O ₃ 1-10%, MgO 5-12%, CaO 0.1-5%, It contains 13 to 19% Na ₂ O and 0 to 5% K ₂ O, and RO / (RO + R ₂ O) is 0.20 or more and 0.42 or less (wherein RO is an alkaline earth metal oxide) , R ₂ O represents an alkali metal oxide.) (7) The composition expressed in mol% based on the oxide is 55.5 to 80% for SiO ₂ and 12 to 20% for Al ₂ O _3. A composition containing 8 to 25% of Na ₂ O, 2.5% or more of P ₂ O ₅ and glass containing 8% or more of an alkaline earth metal RO (RO is MgO + CaO + SrO + BaO) (8) mol%. the SiO ₂ 57 ~ 76.5%, an _{Al 2 O 3 12 ~ 18%} , a Na ₂ O 8 _25%, P 2 _{O 5} 2.5-10%, the composition was displayed in mole percent of the glass (9) oxide basis, containing 1% or more alkaline earth metals RO, the SiO ₂ 56 ~ 72%, Al ₂ O ₃ 8-20%, B ₂ O ₃ 3-20%, Na ₂ O 8-25%, K ₂ O 0-5%, MgO 0-15%, CaO 0-15 %, the SrO ₂ 0 ~ 15%, a BaO 0 ~ 15% and ZrO ₂ in a composition that displays in mole percent of glass (10) oxide basis contains 0 to 8% of SiO ₂ 50 ~ 80%, Al ₂ O ₃ 1-25%, Li ₂ O 1-15%, Na ₂ O 5-18%, K ₂ O 0-10%, MgO 0-15%, CaO 0-10% And glass containing 0-5% of ZrO ₂

[(B) Step of preparing an inorganic salt containing other alkali ions larger than the ionic radius of the alkali ions contained in the glass and having a pH of 8 or more and 14 or less when a 10 wt% aqueous solution is obtained]
The chemically strengthened glass produced by the method of the present invention has an ion-exchanged compressive stress layer on the glass surface. In the ion exchange method, the surface of glass is ion exchanged to form a surface layer in which compressive stress remains. Specifically, alkali metal ions (Li ions and / or Na ions) having a small ion radius on the glass surface are exchanged with other alkali ions (Na ions and / or larger ions) at a temperature below the glass transition point by ion exchange. (K ion). Thereby, compressive stress remains on the surface of the glass, and the strength of the glass is improved.

In the method of the present invention, chemical strengthening treatment is performed by ion exchange by bringing the glass containing alkali ions into contact with an inorganic salt containing other alkali ions larger than the ion radius of alkali ions contained in the glass. . Therefore, the inorganic salt used in the method of the present invention contains other alkali ions larger than the ionic radius of the alkali ions contained in the glass.

The inorganic salt has a pH of 8 or more, preferably 9 or more, more preferably 10 or more, when a 10 wt% aqueous solution is used. Moreover, pH is 14 or less, Preferably it is 13 or less, More preferably, it is 12 or less. By setting the pH of the inorganic salt within the above range, the cutting of the glass network by hydroxide ions is easily promoted, and the formation of the uneven layer due to the reduction in density described later is facilitated. The pH of the inorganic salt is measured with a pH meter at 25 ° C.

The pH of the inorganic salt can be adjusted to a desired range by a known method. As a method for adjusting the pH of the inorganic salt, specifically, for example, when the alkali ion contained in the glass is Na ion, the inorganic salt is an inorganic salt containing potassium nitrate (KNO ₃ ), and Examples thereof include a method of adding at least one salt selected from the group consisting of K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ , and NaHCO ₃ .

For example, when potassium nitrate is included 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 glass to be chemically strengthened. Among the above salts, salts excluding potassium nitrate (hereinafter sometimes referred to as “flux”) have a property of cutting a glass network represented by Si—O—Si bonds. Since the temperature at which the chemical strengthening treatment is performed is as high as several hundred degrees Celsius, the covalent bond between Si—O of the glass is appropriately broken at that temperature, and the formation of the uneven layer due to the lowering of density described later tends to proceed.

The degree of breaking the covalent bond varies depending on the chemical composition treatment conditions such as the glass composition, the type of salt (flux) used, the temperature and time for the chemical strengthening treatment, but the four covalent bonds extending from Si. Of these, it is considered preferable to select conditions that are sufficient to break one or two bonds.

In addition to potassium nitrate and flux, the inorganic salt includes, for example, alkali chlorides or alkali borates such as sodium chloride, potassium chloride, sodium borate or potassium borate within a range not inhibiting the effects of the present invention. But you can. These may be added alone or in combination of two or more.

The sum of the carbonate anion concentration and the hydrogen carbonate anion concentration obtained by the following formula in the inorganic salt is preferably 4 mol% or more, more preferably 6 mol% or more. This concentration is preferably 4 mol% or more because the amount of water in the molten salt in the chemical strengthening treatment can be increased and the formation reaction of the uneven layer on the glass surface described later can be promoted.
{(Carbonate anion concentration) + (hydrogen carbonate anion concentration)} (mol%) = {(amount of carbonate anion in inorganic salt) + (amount of hydrogen carbonate anion in inorganic salt)} (mol) / (in inorganic salt) Total anion) (mol) x 100

Since the carbonate anion concentration and the hydrogen carbonate anion concentration in the molten salt cannot be directly measured, a part of the molten salt is taken out, and a commercially available standard solution (NaHCO ₃ ) with pure water using a carbon dioxide meter TiN-9004. After preparing a calibration curve by dilution, a sample solution diluted 130 times with pure water is measured.

At this time, since all the hydrogen carbonate anions are converted into carbonate anions, the value of the carbonate anion concentration detected in the measurement corresponds to the sum of the carbonate anion concentration and the hydrogen carbonate anion concentration. Further, the sum of the carbonate anion concentration and the hydrogen carbonate anion concentration is not more than the sum of the saturated carbonate anion concentration and the saturated bicarbonate anion concentration.

[(C) Step of ion-exchange between the alkali ions contained in the glass and other alkali ions contained in the inorganic salt in an atmosphere having a dew point temperature of 39 ° C. or higher]
Next, in an atmosphere having a dew point temperature of 39 ° C. or higher, the alkali ions contained in the glass prepared in step (a) and the other alkali ions contained in the inorganic salt prepared in step (b) are ion-exchanged. Perform chemical strengthening treatment.

In the chemical strengthening treatment, glass is immersed in a molten salt, and alkali ions (Li ions or Na ions) in the glass are ion-exchanged with other alkali ions (Na ions or K ions) having a large ion radius in the molten salt ( Is performed). By this ion exchange, the composition of the glass surface can be changed to form the compressive stress layer 20 having a high density on the glass surface [FIGS. 1 (a) to 1 (b)]. Since compressive stress is generated by increasing the density of the glass surface, the glass can be strengthened.

Actually, the density of the chemically strengthened glass gradually increases from the outer edge of the intermediate layer 30 (bulk) existing in the center of the glass toward the surface of the compressive stress layer. There is no clear boundary between 20 and 20 where the density changes rapidly. Here, the intermediate layer is a layer present in the center of the glass and sandwiched between the compressive stress layers. Unlike the compressive stress layer, this intermediate layer is a layer that is not ion-exchanged.

In the method of the present invention, an inorganic salt having a pH of 8 or more and 14 or less when a 10 wt% aqueous solution is used, and chemical strengthening is performed in an atmosphere having a dew point temperature (hereinafter sometimes simply referred to as “dew point”) of 39 ° C. or more. By performing the treatment, it is possible to sufficiently increase the amount of water vapor in the molten salt to form the uneven layer 10 on the glass surface [FIGS. 1 (b) to (c)]. Here, since the density of the uneven layer 10 is lower than the density inside the glass, it is also referred to as a low density layer. The thickness of the uneven layer 10 can be increased by increasing the amount of water vapor in the molten salt in the chemical strengthening treatment.

Examples of the method of bringing the glass into contact with the inorganic salt include a method of applying a paste-like inorganic salt, a method of spraying an inorganic salt aqueous solution onto the glass, or a method of immersing the glass in a salt bath of a molten salt heated to a melting point or higher. Among these, the method of immersing in molten salt is preferable.

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, it can be obtained by preparing a potassium nitrate molten salt and then adding the flux to the potassium nitrate molten salt. As another method, it can be obtained by mixing potassium nitrate and a flux and then melting a mixed salt of the potassium nitrate and the flux.

The molten salt used in the method of the present invention preferably has a Na concentration of 500 ppm by weight or more, 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 uneven layer is easily deepened by the acid treatment step described later. There is no restriction | limiting in particular as an upper limit of Na density | concentration, It is permissible until a desired surface compressive stress (CS) is obtained.

Note that the molten salt that has been subjected to the chemical strengthening treatment one or more times contains sodium eluted from the glass. Therefore, if the Na concentration is already within the above range, glass-derived sodium may be used as it is as the Na source, or when the Na concentration is insufficient or when an unused molten salt is used for the chemical strengthening treatment. It can be prepared by adding an inorganic sodium salt such as sodium nitrate.

The chemical strengthening treatment (ion exchange step) in the present invention can be specifically performed by the following procedure. First, the glass is preheated, and the above-described molten salt is adjusted to a temperature at which chemical strengthening is performed. Next, the preheated glass is immersed in the molten salt for a predetermined time, and then the glass is pulled up from the molten salt and allowed to cool. In addition, it is preferable to perform shape processing according to a use, for example, mechanical processing, such as a cutting | disconnection, an end surface processing, and a drilling process, before a chemical strengthening process to glass.

The preheating temperature of glass depends on the temperature immersed in the molten salt, but is generally preferably 100 ° C. or higher. The chemical strengthening temperature is preferably not more than the strain point of the glass to be tempered (usually 500 to 600 ° C.), particularly preferably 350 ° C. or more in order to obtain a higher compressive stress layer depth, shortening the processing time and promoting the formation of the uneven layer Therefore, 400 ° C. or higher is more preferable, and 430 ° C. or higher is more preferable.

The immersion time of the glass in the molten salt is preferably 1 minute to 10 hours, more preferably 5 minutes to 8 hours, and even more preferably 10 minutes to 4 hours. In such a range, a chemically strengthened glass excellent in the balance between strength and depth of the compressive stress layer can be obtained, which is preferable.

The ion exchange process is performed in an atmosphere with a dew point temperature of 39 ° C or higher. The dew point temperature is preferably 50 ° C. or higher, more preferably 60 ° C. or higher, further preferably 70 ° C. or higher, more preferably 80 ° C. or higher, and particularly preferably 90 ° C. or higher. By setting the dew point temperature to 39 ° C. or higher, the amount of water vapor (moisture amount) in the molten salt in the chemical strengthening treatment is sufficiently increased, the formation of the uneven layer 10 on the glass surface is promoted, and the touch feeling of the glass Can be improved. Further, the upper limit of the dew point temperature is preferably set to be equal to or lower than the temperature of the inorganic salt (molten salt) for performing ion exchange.

The following may be considered as the reason why the uneven layer is formed on the chemically strengthened glass obtained by performing chemical strengthening treatment in a molten salt having a large amount of water vapor (water content). When carbonate ions forming the molten salt react with water, hydrogen carbonate ions and hydroxide ions are generated as shown in the following formula.

Here, when the amount of water in the molten salt is large, the equilibrium in the above formula is tilted to the right, and a large amount of hydrogen carbonate ions and hydroxide ions are generated. Since hydroxide ions are ions that promote the cutting of the glass network, it is considered that the formation of an uneven layer on the glass surface is promoted by generating more hydroxide ions.

The dew point temperature may be such that the dew point temperature at least near the interface of the molten salt is within the above range, and the vicinity of the interface means an atmosphere in an area of 200 mm or less from the interface of the molten salt. The dew point can be measured with a Vaisala DRYCAP® DMT346 dew point converter. In addition, the dew point in this specification is a value when it is considered that an equilibrium is established between the molten salt and the atmosphere in the vicinity of the molten salt interface.

The dew point can be achieved by introducing water vapor into the molten salt and / or the atmosphere in the vicinity of the interface of the molten salt before and / or simultaneously with the ion exchange step. That is, water vapor itself or a gas containing water vapor may be bubbled directly into the molten salt, or a gas containing water vapor or water vapor may be introduced into the space above the molten salt. Moreover, it is also possible to send water (liquid) itself directly into the molten salt within a range where no steam explosion occurs.

When introducing water vapor or a gas containing water vapor or water (liquid) (hereinafter, simply referred to as “water vapor”), the molten salt may or may not be stirred. Stirring is preferable in terms of shortening.

The time from the introduction of water vapor, etc. until equilibrium is reached varies depending on the amount of gas or liquid to be introduced, the water vapor concentration, the method of introduction, etc., but it cannot be generally stated, but the dew point of the above atmosphere is stable and constant. Can be judged as having reached equilibrium.

As the gas containing water vapor, a gas that does not affect the chemical strengthening treatment can be used. For example, as shown in FIG. 2, a dry gas A such as air, nitrogen gas, carbon dioxide gas or the like is introduced into heated water 24. By doing it, it can be set as the gas B (gas containing water vapor | steam) B containing the water vapor | steam with high humidity.

As the water 24 used as a water vapor supply source, it is preferable to use pure water such as ion-exchanged water from the viewpoint of suppressing scale accumulation on piping and the like. The water 24 is heated by, for example, a water bath using a water tank 25.

More specifically, as a method of introducing water vapor or the like, (1) introducing gas B containing water vapor into the space above the inorganic salt (molten salt 26) from the water vapor supply unit, and (2) inorganic salt from the bubbling unit. Examples thereof include introducing gas B containing water vapor into (molten salt 26), or (3) introducing water (liquid) directly into inorganic salt (molten salt 26). Among these, it is preferable to form the atmosphere by the above (1) or (2).

In addition, a water vapor supply unit, a bubbling unit, or an introduction unit for introducing water (liquid) may be appropriately provided according to the apparatus, and is not particularly limited.

When a gas containing water vapor is introduced into the space above the molten salt, the amount of water vapor supplied in the gas introduced per 1 cm ³ is preferably 0.04 mg / min or more, and more preferably 0.08 mg / min or more.

When water (liquid) is directly introduced into the molten salt, the flow rate of water introduced per 1 cm ³ is preferably 0.04 mg / min or more, and more preferably 0.08 mg / min or more.

When a gas containing water vapor is directly bubbled in an inorganic salt (in a molten salt), the amount of water vapor supplied in the gas introduced per 1 cm ³ is preferably 0.04 mg / min or more, and 0.08 mg / min or more. Is more preferable.

The thickness of the concavo-convex layer 10 is about 100 to 200 nm in the conventional ion exchange process in which water vapor is not introduced, whereas in the method of the present invention, the pH when the aqueous solution is 10 wt% is 8 or more and 14 or less. The thickness can be increased to 300 nm or more by ion exchange in an atmosphere having a dew point temperature of 39 ° C. or higher using a salt.

The uneven layer 10 can be removed by, for example, an acid treatment step and an alkali treatment step described later. The thickness of the uneven layer 10 is preferably 300 nm or more from the viewpoint of the amount of glass surface removal.

In addition, the average depth of cracks and latent scratches on the glass surface generated in the glass processing process including the glass manufacturing process and the chemical strengthening process is about 500 nm. Therefore, the thickness of the uneven layer 10 is more preferably 500 nm or more, and further preferably 600 nm or more.

The thickness of the concavo-convex layer can be determined from the period (Δθ) measured by the X-ray reflectivity method (X-ray-Reflectometry: XRR).

The density of the uneven layer is preferably lower than the density of the region (bulk) deeper than the ion-exchanged compressive stress layer from the viewpoint of glass surface removability. The density of the uneven layer can be obtained from the critical angle (θc) measured by XRR. In addition, it is also possible to confirm the formation of the concavo-convex layer and the thickness of the layer by simply observing a cross section of the glass with a scanning electron microscope (SEM).

In addition, you may provide the process of removing the uneven | corrugated layer 10 according to the objective. The thickness of the concavo-convex layer 10 is set to be equal to or greater than the average depth of cracks and latent scratches existing on the glass surface. Tempered glass can be obtained.

The formed concavo-convex layer 10 may be removed by a step of contacting with an acid or an acid / alkali described later in the step of removing a part of the surface of the glass. In this case, if all the cracks and latent scratches on the glass surface are shallower than the thickness of the concavo-convex layer, all the cracks and latent scratches can be removed in the step of contacting with alkali.

The surface strength of the chemically strengthened glass can be increased by removing cracks and latent scratches on the glass surface that cause a decrease in strength in the chemically strengthened glass.

[Washing process]
The method of the present invention preferably further includes a step of washing the glass between the step of ion exchange and the step of removing part of the surface of the glass. In the cleaning step, the glass is cleaned using industrial water or ion exchange water. Use the treated water if necessary. Of these, ion-exchanged water is preferred.

The washing conditions vary depending on the washing solution used, but when ion-exchanged water is used, washing at 0 to 100 ° C. is preferable from the viewpoint of completely removing the attached salt. Various cleaning methods include, for example, a method of immersing chemically tempered glass in a water tank containing ion-exchanged water, a method of exposing the glass surface to running water, and a method of spraying a cleaning liquid toward the glass surface by a shower. The method is mentioned.

[Step of removing part of the glass surface]
The method of the present invention may further include a step of removing a part of the surface of the glass ion-exchanged by the ion-exchange step. The method of the present invention preferably includes a step of contacting the glass with an acid (acid treatment step) as a step of removing a part of the surface of the glass, and a step of contacting the glass with an alkali after the acid treatment step ( An alkali treatment step) may be further included.

In the method of the present invention, it is preferable to perform a step of contacting the glass with an acid as a step of removing a part of the surface of the glass after the ion exchange step or the washing step.

(Acid treatment process)
The acid treatment 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. In other words, the surface of the glass further has a concavo-convex layer in which the surface layer of the compressive stress layer is altered, specifically, the density is reduced.

The solution used for the acid treatment is not particularly limited as long as it is acidic, and may be less than pH 7. The acid used may be a weak acid or a strong acid. Specifically, acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, oxalic acid, carbonic acid or citric acid are preferred. These acids may be used alone or in combination.

The temperature at which the acid treatment is performed varies depending on the type, concentration, and time of the acid used, but is preferably 100 ° C. or less. The time for the acid treatment varies depending on the type, concentration and temperature of the acid used, but is preferably 10 seconds to 5 hours from the viewpoint of productivity, and more preferably 1 minute to 2 hours.

The concentration of the solution used for the acid treatment varies depending on the type of acid used, the time, and the temperature, but is preferably a concentration at which there is little concern about container corrosion, and specifically 0.1 to 20% by weight.

(Alkali treatment process)
In the production method of the present invention, an alkali treatment step may be included after the acid treatment step. More preferably, after the acid treatment step, before the alkali treatment step, a step of washing the same glass as the step of washing described above is performed.

Alkali treatment is performed by immersing chemically strengthened glass in a basic solution, whereby a part of the uneven layer formed in the acid treatment step can be removed. Thereby, while improving the intensity | strength of glass, desired touch feeling can be obtained.

The solution used for the alkali treatment is not particularly limited as long as it is basic, and may have a pH exceeding 7, and a weak base or a strong base may be used. Specifically, bases such as sodium hydroxide, potassium hydroxide, potassium carbonate and sodium carbonate are preferred. These bases may be used alone or in combination.

The temperature at which the alkali treatment is performed varies depending on the type, concentration and time of the base used, but is preferably 0 to 100 ° C, more preferably 10 to 80 ° C, and particularly preferably 20 to 60 ° C. If it is this temperature range, there is no possibility that glass will corrode and it is preferable.

Although the alkali treatment time varies depending on the type, concentration and temperature of the base used, it is preferably 10 seconds to 5 hours from the viewpoint of productivity, and more preferably 1 minute to 2 hours.

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

A part of the concavo-convex layer 10 may be removed by the alkali treatment. In this case, the thicker the uneven layer, the easier the glass surface is removed. By the alkali treatment, a part of the concavo-convex layer into which H has penetrated is removed, whereby a chemically strengthened glass with improved surface strength can be obtained.

In particular, in the method of the present invention, it is present on the glass surface by chemical strengthening treatment in an atmosphere having a dew point of 39 ° C. or higher using an inorganic salt having a pH of 8 or more and 14 or less when a 10 wt% aqueous solution is used. The thickness of the concavo-convex layer 10 can be made deeper than the depth of cracks and latent scratches. Therefore, it is considered that cracks and latent scratches existing on the glass surface can be removed together with the concavo-convex layer, which contributes further by improving the surface strength of the glass. In addition, it is preferable to pass through the process wash | cleaned by the method similar to the previous after alkali treatment.

<Chemical tempered glass>
According to the method of the present invention, since the uneven layer can be formed deeper than the conventional chemical strengthening treatment, the surface layer of the chemically strengthened glass obtained after removing the uneven layer has fewer cracks and latent scratches. Therefore, the chemically strengthened glass obtained by the method of the present invention has a very high surface strength.

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

[Removal amount of glass surface (uneven layer)]
The removal amount (thickness) of the glass surface (concave layer) after the step of removing a part of the glass surface is to measure the weight before and after the chemical treatment with an analytical electronic balance and convert the thickness using the following formula: It can ask for.
(Removed thickness per side) = [(weight before removing part of glass surface) − (weight after removing part of glass surface)] / (glass specific gravity) / treated area / 2
At this time, the glass specific gravity is calculated as 2.50 (g / cm ³ ).

Hereinafter, the present invention will be specifically described 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) of glass and the depth (DOL, unit: μm) of the compressive stress layer were measured using a surface stress meter (FSM-6000) manufactured by Orihara Seisakusho.

(Fingering comfort)
The glass substrate after washing was palpated by three people. All three were touched and felt good, and the others were marked X.

(Removal amount)
The glass removal amount thickness was determined by measuring the weight before and after chemical treatment (acid treatment and alkali treatment) with an analytical electronic balance (HR-202i, manufactured by AND) and converting the thickness using the following formula. .
(Removed thickness per side) = [(weight before treatment) − (weight after treatment)] / (glass specific gravity) / treated area / 2
At this time, the glass specific gravity was calculated as 2.50 (g / cm ³ ).

<Examples 1 to 5>
(Ion-exchange process)
Potassium nitrate, potassium carbonate and sodium nitrate were added to a stainless steel (SUS) pot and heated to 450 ° C. with a mantle heater to prepare a molten salt having the composition shown in Table 1. Table 1 shows the pH of the inorganic salt (pH of the 10 wt% aqueous solution) when the 10 wt% aqueous solution was used. Water vapor was included in the molten salt by flowing air introduced into water heated to 95 ° C. in an atmosphere near the interface of the molten salt.

The experimental system is shown in FIG. Air was used as the dried gas A, and the air was humidified by passing the air through water 24 heated to 95 ° C. by a water tank 25 to obtain humidified gas (air) B containing water vapor. By introducing this gas B containing water vapor into the space above the inorganic salt (molten salt) 26 of the tank that performs the chemical strengthening treatment through the route heated by the ribbon heater, the dew point was controlled in the ion exchange process. . The amount of water vapor supplied per cm ³ and the dew points near the interface of the molten salt are as shown in Table 1.

After preparing a glass plate of 50 mm × 50 mm × 0.7 mm having the composition shown below, preheating to 350 to 400 ° C., and then immersing in molten salt under the conditions shown in Table 1 and performing ion exchange treatment (chemical strengthening treatment) The chemical strengthening treatment was performed by cooling to near room temperature. The obtained chemically strengthened glass was washed with water, and Examples 1 and 2 were dried by air blow to obtain chemically strengthened glass. In Examples 3 to 5, the chemically strengthened glass obtained was washed with water and then subjected to the following acid treatment step and alkali treatment step.
Glass A composition (expressed as mol% based on oxide): SiO ₂ 68.74%, Al ₂ O ₃ 2.96%, Na ₂ O 14.20%, K ₂ O 0.15%, MgO 6.16% , CaO 7.75%
Glass B composition (expressed as mol% based on oxide): SiO ₂ 64.4%, Al ₂ O ₃ 10.5%, Na ₂ O 16.0%, K ₂ O 0.6%, MgO 8.3% , ZrO ₂ 0.2%
Glass C composition (mole% based on oxide): SiO ₂ 67.0%, Al ₂ O ₃ 13.0%, Na ₂ O 14.0%, B ₂ O ₃ 4.0%, K ₂ O < 1.0%, MgO 2.0%, CaO <1.0%

(Acid treatment process)
6.0% by weight of nitric acid [nitric acid 1.38 (manufactured by Kanto Chemical Co., Ltd.) diluted with ion-exchanged water] was prepared in a beaker, and the temperature was adjusted to the temperature shown in Table 1 using a water bath. Under the conditions shown in Table 1, acid treatment was performed by immersing the glass obtained in the ion exchange treatment step in prepared nitric acid. Thereafter, the glass was washed with water and subjected to an alkali treatment step.

(Alkali treatment process)
A 4.0% by weight sodium hydroxide aqueous solution [48% sodium hydroxide solution (manufactured by Kanto Chemical Co., Ltd.) diluted with ion-exchanged water] was prepared in a beaker, and the temperature was adjusted to the temperature shown in Table 1 using a water bath. . The glass washed after the acid treatment step was immersed in the prepared aqueous sodium hydroxide solution and subjected to alkali treatment. Then, the glass was washed with water to wash the alkali on the glass surface. Thereafter, it was dried by air blow.

<Comparative Examples 1, 3, and 5>
Except that the dew point at the upper part of the chemical tempering furnace was not controlled, a step of ion exchange treatment was performed in the same manner as in Examples 1, 4 and 5, respectively, to obtain chemically tempered glass. At this time, the pH of the 10 wt% aqueous solution, the amount of water vapor supplied per cm ³ and the dew points near the interface of the molten salt were as shown in Table 1. After the ion exchange treatment step, in Comparative Example 5, the obtained chemically strengthened glass was washed with water, and then the acid treatment step and the alkali treatment step were performed in the same manner as in Example 5.

<Comparative Examples 2, 4 and 6>
Table 1 shows the sodium content without adding potassium carbonate to the molten salt in the ion exchange step. The pH of the 10 wt% aqueous solution was as shown in Table 1 in terms of the amount of water vapor supplied per cm ³ and the dew points near the molten salt interface. Prepare 50mm x 50mm x 0.7mm glass composition A, B, and C plates, preheat them to 350-400 ° C, then immerse them in molten salt under the conditions shown in Table 1 to perform ion exchange treatment (chemical strengthening treatment) Then, chemical strengthening treatment was performed by cooling to near room temperature. The obtained chemically tempered glass was washed with water and then dried by air blow to obtain chemically tempered glasses of Comparative Examples 2, 4, and 6.

Various evaluations were performed on the chemically strengthened glass obtained above. Table 1 shows the processing conditions and evaluation results of the glass.

As shown in Table 1, it was found that the chemically tempered glasses of Examples 1 to 5 had good finger touch comfort. On the other hand, the chemically tempered glasses of Comparative Examples 1, 3, and 5 in which the dew point in the ion exchange process was not controlled to 39 ° C. or higher were uncomfortable to touch. In addition, regarding the inorganic salt used in the ion exchange step, the chemically tempered glasses of Comparative Examples 2, 4 and 6 having a pH of less than 8 when made into a 10 wt% aqueous solution were uncomfortable to touch.

From these results, the pH when the 10 wt% aqueous solution of the inorganic salt used in the ion exchange step is 8 or more and 14 or less, and the dew point in the ion exchange step is controlled to 39 ° C. or more, so that it is comfortable to touch. It was found that chemically strengthened glass was obtained.

Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application filed on September 2, 2016 (Japanese Patent Application No. 2016-172069), which is incorporated by reference in its entirety. Also, all references cited herein are incorporated as a whole.

According to the method for producing chemically tempered glass of the present invention, chemically tempered glass having a very good touch feeling can be obtained without chemical etching and etching treatment using polishing or hydrofluoric acid. That is, it is possible to obtain a chemically strengthened glass excellent in touch feeling without appearance defects due to expansion of latent scratches accompanying etching treatment with hydrofluoric acid or the like, and polishing scratches accompanying polishing.

The method for producing chemically strengthened glass of the present invention can be applied to any glass and has high versatility. And since a process can be advanced by immersion in a solution, it is efficient at the point of being easy to respond | correspond to various glass shapes and large area glass. Further, the safety is high and the cost is low as compared with the etching process using hydrofluoric acid or the like.

10 Concavity and convexity layer 20 Compressive stress layer 30 Intermediate layer 24 Water 25 Water tank 26 Molten salt

Claims (9)

Preparing a glass containing alkali ions;
Preparing an inorganic salt containing other alkali ions larger than the ion radius of the alkali ions contained in the glass and having a pH of 8 or more and 14 or less when a 10 wt% aqueous solution is formed;
A method for producing chemically tempered glass, comprising a step of ion-exchanging the alkali ions contained in the glass and the other alkali ions contained in the inorganic salt in an atmosphere having a dew point temperature of 39 ° C. or higher. The atmosphere in the ion exchange step is formed by introducing a gas containing water vapor from the water vapor supply unit into the space above the inorganic salt, and the amount of the gas containing water vapor is the water vapor supply per 1 cm ^3. The method for producing chemically strengthened glass according to claim 1, wherein the amount is 0.04 mg / min or more. The atmosphere in the ion exchange step is formed by introducing a gas containing water vapor into the inorganic salt from a bubbling part, and the amount of the gas containing water vapor is 0 for the water supply rate per 1 cm ^3. The method for producing chemically tempered glass according to claim 1, which is 0.04 mg / min or more. The method for producing chemically strengthened glass according to any one of claims 1 to 3, further comprising a step of removing a part of the surface of the glass subjected to the ion exchange. The method for producing chemically tempered glass according to any one of claims 1 to 4, wherein the step of removing a part of the surface of the glass includes a step of bringing the glass into contact with an acid. 6. The method for producing chemically strengthened glass according to claim 5, wherein the step of removing a part of the surface of the glass further includes a step of bringing the glass into contact with an alkali after the step of bringing into contact with the acid. The method for producing chemically tempered glass according to claim 6, further comprising a step of washing the glass between the step of contacting with the acid and the step of contacting with the alkali. The production of chemically strengthened glass according to any one of claims 1 to 7, further comprising a step of washing the glass between the step of ion exchange and the step of removing a part of the surface of the glass. Method. The method for producing chemically tempered glass according to any one of claims 6 to 8, further comprising a step of washing the glass after the step of contacting with the alkali.

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