JP2019182686A - Manufacturing method of chemically reinforced glass - Google Patents

Abstract

To provide a method for manufacturing a chemically reinforced glass excellent in appearance quality by suppressing generation of white cloud by chemical reinforcement of a lithium-containing glass.SOLUTION: The invention relates to a manufacturing method of a chemically reinforced glass, including a process for ion exchange of Li ion in a glass and Na ion in an inorganic salt composition by contacting the glass containing lithium with the inorganic salt composition containing sodium nitride, in which the inorganic salt composition contains at least one kind of ion selected from a group consisting of carbonate ion, phosphate ion and hydroxide ion.SELECTED DRAWING: None

Description

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

  In recent years, chemically strengthened glass having a compressive stress layer formed on the glass surface by ion exchange or the like has been used as a cover glass for various display devices, and further improvement in its strength is required. In chemically strengthened glass, the strength can be improved by increasing the surface compressive stress value (CS) of the compressive stress layer and increasing the depth (DOL) of the compressive stress layer.

  Glass containing lithium (hereinafter also abbreviated as lithium-containing glass) is useful from the viewpoint of further improving the strength and is widely used. The chemical strengthening of a lithium-containing glass is a process in which an inorganic salt (for example, sodium nitrate) composition that normally contains sodium is brought into contact with the lithium-containing glass to exchange Li ions in the glass with Na ions in the inorganic salt composition. including.

  The present inventors have found that when lithium-containing glass is chemically strengthened with an inorganic salt composition containing sodium nitrate, white haze is generated on the glass surface during the cumulative treatment, and the appearance quality is lowered. In addition, as a cause of white cloudiness of the glass, it is because the Li ion concentration in the molten salt of the inorganic salt composition increases cumulatively as the treatment area of the lithium-containing glass by the inorganic salt composition in chemical strengthening increases. I found out.

  When the Li ion concentration in the molten salt increases, Li ions accumulate in the glass surface layer due to the action of ion exchange between the Li ions in the molten salt and the components such as magnesium or phosphorus in the glass. The crystal nucleation temperature is lowered, and glass components such as magnesium, phosphorus, or silicate react with Li ions on the surface of the glass and crystallize, so that it is considered that white haze is generated and appearance quality is deteriorated. In addition, the white cloud in this specification is a thing which a glass component reacts with Li ion of a glass surface layer, and crystallized as mentioned above, and reacts with the salt which precipitated in the molten salt of an inorganic salt composition. It does not mean the resulting crystals.

  Accordingly, an object of the present invention is to provide a method for producing a chemically strengthened glass that suppresses the occurrence of white clouding in chemical strengthening of a lithium-containing glass and is excellent in appearance quality.

  The present inventors have at least one selected from the group consisting of carbonates, phosphates and hydroxides, as white cloudiness generated by chemically strengthening a lithium-containing glass with an inorganic salt composition containing sodium nitrate. It has been found that it can be suppressed by adding a salt to the inorganic salt composition, and the present invention has been completed.

That is, the present invention is as follows.
1. A method for producing chemically strengthened glass comprising a step of ion-exchanging Li ions in the glass and Na ions in the inorganic salt composition by bringing a glass containing lithium into contact with an inorganic salt composition containing sodium nitrate. There,
The inorganic salt composition is a chemically strengthened glass containing at least one salt selected from the group consisting of Na ₂ CO ₃ , K ₂ CO ₃ , KHCO ₃ , NaHCO ₃ , K ₃ PO ₄ , Na ₃ PO ₄ , KOH and NaOH. Manufacturing method.
2. 2. The method for producing chemically strengthened glass as described in 1 above, wherein the Li ion concentration in the inorganic salt composition is 5500 ppm by weight or less.
3. 3. The method for producing chemically strengthened glass as described in 2 above, wherein the Li ion concentration in the inorganic salt composition is 4000 ppm by weight or less.
4). 4. The method for producing chemically tempered glass according to any one of 1 to 3, wherein the inorganic salt composition contains at least Na ₂ CO ₃ .
5. 5. The method for producing chemically strengthened glass as described in 4 above, wherein the inorganic salt composition contains 0.3 wt% or more of Na ₂ CO ₃ .
6). 5. The method for producing chemically tempered glass as described in 4 above, wherein the inorganic salt composition contains 1.0 wt% or more of Na ₂ CO ₃ .
7). The method for producing chemically tempered glass according to any one of 1 to ₃ , wherein the inorganic salt composition contains at least one salt selected from the group consisting of Na ₂ CO ₃ , K ₂ CO ₃ , KHCO ₃ and NaHCO _3. .
8). 8. The method for producing chemically strengthened glass according to any one of 1 to 7, wherein the ion exchange step is performed in an atmosphere having a dew point temperature of 15 ° C. or lower.
9. 9. The method for producing chemically strengthened glass according to any one of 1 to 8, wherein the atmosphere in the ion exchange step is formed by introducing a gas dried by an air dryer.
10. The method for producing chemically strengthened glass according to any one of 1 to 9, further comprising a step of acid-treating the glass after the ion-exchange step and a step of alkali-treating the glass after the acid treatment.

  In the method for producing chemically strengthened glass of the present invention, at least one salt selected from the group consisting of carbonates, phosphates and hydroxide salts (hereinafter sometimes referred to as “flux”) is contained. The lithium-containing glass is chemically strengthened by the inorganic salt composition containing sodium nitrate. When the flux is added to the molten salt of inorganic salt composition containing sodium nitrate, it becomes carbonate ion, phosphate ion and hydroxide ion, respectively, and elutes into molten salt of inorganic salt composition during chemical strengthening treatment By capturing the Li ions, the occurrence of white clouding can be suppressed, and a chemically strengthened glass excellent in appearance quality can be produced.

FIG. 1 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, but 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 and an upper limit.

  One aspect of the method for producing chemically tempered glass according to the present invention (hereinafter also abbreviated as the production method of the present invention) will be described below, but the present invention is not limited thereto.

[Glass]
The glass used in the present invention only needs to contain lithium, and glass having various compositions can be used as long as it has a composition that can be strengthened by molding and chemical strengthening treatment. Specific examples include aluminosilicate glass, soda lime glass, borosilicate glass, lead glass, alkali barium glass, and aluminoborosilicate glass.

  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 preferably heated and melted at 1500 to 1600 ° C., clarified, and then supplied to a molding apparatus. It can be produced by forming into a plate shape and slowly cooling it.

  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, a redraw method, etc.), a float method, a roll out method, and a press method can be adopted. 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 further preferably 1 mm or less in order to effectively perform the chemical strengthening treatment. Preferably, 0.7 mm or less is particularly preferable.

  Moreover, the shape of the glass used by this invention is not specifically 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. 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.

Although it does not specifically limit as a composition of glass, For example, the following glass compositions are mentioned.
Oxide-based molar percentage display, SiO ₂ 50-80%, Al ₂ O ₃ 2-25%, Li ₂ O 0.1-20%, Na ₂ O 0.1-18%, K the ₂ O 0% to MgO 0 to 15% 0 to _5% of _CaO, P 2 _{O 5 0-5%} B 2 _{O 3 0-5%} the Y 2 _{O 3} 0 to 5 % And ZrO ₂ from 0 to 5%.

[Inorganic salt composition]
The chemically strengthened glass produced by the production method of the present invention has a compressive stress layer formed on the glass surface by ion exchange. In the ion exchange method, the surface of glass is ion exchanged to form a surface layer in which compressive stress remains. Specifically, by performing ion exchange at a temperature below the glass transition point, alkali metal ions having a small ionic radius on the glass plate surface (for example, Li ions and / or Na ions) are exchanged with other alkali ions having a larger ionic radius. (For example, Na ions and / or K ions). Thereby, compressive stress remains on the surface of the glass, and the strength of the glass is improved.

In the production method of the present invention, the chemical strengthening treatment is performed by bringing the glass containing alkali ions mentioned above into contact with the molten salt of the inorganic salt composition containing other alkali ions larger than the ion radius of the alkali ions contained in the glass. It is performed by ion exchange. That is, the alkali ion (Li ion) contained in glass and the other alkali ion (Na ion) contained in an inorganic salt composition are ion-exchanged.
In this case, the inorganic salt composition is an inorganic salt containing sodium nitrate and may further contain potassium nitrate. Furthermore, it is more preferable to contain one kind of salt selected from the group consisting of Na ₂ CO ₃ , K ₂ CO ₃ , KHCO ₃ , NaHCO ₃ , K ₃ PO ₄ , Na ₃ PO ₄ , KOH and NaOH. Among these, Na ₂ CO ₃ , K ₂ CO ₃ , KHCO ₃ , and NaHCO ₃ are preferable, and Na ₂ CO ₃ is more preferable.

  Sodium nitrate has a melting point of 308 ° C., and has a melting point below the strain point (usually 500 to 600 ° C.) of the glass to be chemically strengthened. In addition, a salt from which sodium nitrate and potassium nitrate are excluded (hereinafter sometimes referred to as “flux”) has the property of capturing Li ions in the molten salt of the inorganic salt composition. By capturing Li ions during the chemical strengthening treatment, it is possible to suppress the occurrence of white clouding and to produce chemically strengthened glass having excellent appearance quality.

  In addition, although the degree of white cloudiness suppression changes also with chemical strengthening process conditions, such as the kind of glass composition and the salt (flux) to be used, the temperature which performs a chemical strengthening process, and time, in the inorganic salt composition containing sodium nitrate, It is considered preferable to select conditions that can appropriately capture the amount of Li ions.

  A high-density compressive stress layer is formed by ion exchange between Li ions on the glass surface and Na ions in the inorganic salt composition. As a method of bringing the glass into contact with the inorganic salt composition, a method of applying a paste-like inorganic salt, a method of spraying an aqueous solution of an inorganic salt onto the glass, a method of immersing the glass in a salt bath of a molten salt heated to a melting point or higher Of these, a method of immersing in molten salt is desirable.

  The amount of the flux added is preferably 0.1 wt% (wt% is weight percent) or more, more preferably 0.3 wt% or more, and still more preferably 0.5 wt% or more, from the viewpoint of white haze control. Moreover, from the point of impurity precipitation, it is preferable that it is 4.0 wt% or less, More preferably, it is 3.0 wt% or less, More preferably, it is 2.0 wt% or less. The flux can capture Li ions in the inorganic salt composition to prevent the glass surface layer from reacting with the glass component and crystallize, and can suppress white clouding caused by Li in the molten salt. .

  In addition to the above-mentioned inorganic salt containing sodium nitrate, the inorganic salt composition is not limited to the effects of the present invention, for example, sodium chloride, sodium borate, sodium sulfate, sodium sulfate, sodium chloride, sodium boric acid. A salt such as a salt, potassium chloride, or potassium borate may be contained. These may be added alone or in combination of two or more.

  To the inorganic molten salt containing sodium nitrate, at least one salt selected from the group consisting of the fluxes is charged into a container and mixed with a stirring blade or the like. When a plurality of salts are used in combination, the order of addition is not limited, and they may be added simultaneously.

  A metal, quartz, ceramics, etc. can be used for the container which melts sodium nitrate. Among these, a metal material is preferable from the viewpoint of durability, and a stainless steel (SUS) material is preferable from the viewpoint of corrosion resistance.

  The mixture is then heated to melt. Melting is performed at a temperature equal to or higher than the melting point of sodium nitrate (308 ° C.). In particular, the melting temperature is preferably 350 to 480 ° C. from the viewpoint of the balance between the surface compressive stress (CS) and the compressive stress layer depth (DOL) that can be applied to the glass, and the strengthening time. The stirring time is preferably 1 minute to 10 hours, and more preferably 10 minutes to 2 hours.

  In the molten salt of the inorganic salt composition obtained by the above-described method, in the case where precipitates are generated by the addition of a flux, before the precipitates are precipitated at the bottom of the container before the chemical strengthening treatment of the glass. Leave still.

  The molten salt of the inorganic salt composition has a Li ion concentration of preferably 5500 ppm by weight or less, more preferably 4000 ppm by weight or less, so that at least selected from the group consisting of carbonates, phosphates and hydroxide salts. The effect of suppressing the occurrence of white cloudiness by incorporating a kind of salt in the inorganic salt composition can be expressed.

[Chemical strengthening treatment]
In the chemical strengthening treatment (ion exchange step) in the production method of the present invention, the glass is brought into contact with the inorganic salt composition, and the metal in the glass has an ionic radius larger than that of the metal ion in the inorganic salt composition. This is done by substituting with metal ions.

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

  Specifically, the chemical strengthening treatment in which the glass is immersed in the molten salt of the inorganic salt composition can be performed, for example, by the following procedure. First, the glass is preheated, and the 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.

  The preheating temperature of the glass depends on the temperature immersed in the molten salt, but is generally preferably 100 ° C. or higher. After dipping the glass in the molten salt, the glass is pulled up from the molten salt and allowed to cool.

  The chemical strengthening temperature is preferably not more than the strain point (usually 500 to 600 ° C.) of the glass to be tempered, and particularly preferably 350 ° C. or more in order to obtain a higher DOL.

  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. If it exists in this range, the chemically strengthened glass excellent in the balance of an intensity | strength and DOL can be obtained.

  The chemical strengthening treatment is preferably performed in an atmosphere having a dew point temperature of 20 ° C. or less from the viewpoint of improving the appearance quality of the resulting chemically strengthened glass. The dew point temperature is preferably 20 ° C or lower, more preferably 10 ° C or lower, further preferably 5 ° C or lower, particularly preferably 0 ° C or lower, and most preferably -5 ° C or lower. Although the minimum of dew point temperature is not specifically limited, From the point of dew point control equipment, it is preferable that it is normally -60 degreeC or more. When the chemical strengthening treatment is performed at a dew point temperature of 15 ° C. or lower, it is effective to manage the dew point temperature as described later. In addition, if a dew point temperature is 15 degreeC or more, for example, 20 degreeC vicinity, a chemical strengthening process can be performed without controlling a dew point temperature.

  In the present specification, “dew point temperature” (hereinafter also abbreviated as “dew point”) 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 measured with a Vaisala DRYCAP® DMT346 dew point converter. The dew point temperature is sufficient if the dew point temperature at least in the vicinity of the interface of the molten salt is less than 20 ° C., 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 temperature is preferably controlled within a range of ± 5 ° C., more preferably ± 4 ° C., and even more preferably ± 3 ° C. By controlling the dew point temperature within a range of ± 5 ° C., the performance of the chemically strengthened glass can be made uniform.

Specific examples of the method for setting the atmospheric dew point to 20 ° C. or lower include the methods shown in the following (1) to (3).
(1) A gas such as air or nitrogen can be dehumidified by passing it through an air dryer before being introduced into the chemical strengthening tank, and the atmospheric dew point can be lowered. A commercially available air dryer can be used, and examples thereof include IDG5M4-02-S manufactured by SMC, IDG60SAM4-03 manufactured by SMC, and the like.
(2) A gas such as air or nitrogen can be dehumidified using an adsorbent before being introduced into the chemical strengthening tank, thereby reducing the atmospheric dew point. A commercially available adsorbent can be used.
(3) A gas such as air or nitrogen can be dehumidified using a dehumidifier before being introduced into the chemical strengthening tank to lower the atmospheric dew point. A commercially available dehumidifier can be used.

  Specifically, as the method of (1), for example, as shown in FIG. 1, the dehumidified gas Y is obtained by introducing a gas X such as air, nitrogen gas, carbon dioxide gas into the air dryer 31. And a method of introducing dehumidified gas into the space above the inorganic salt composition (molten salt) 33 in the chemical strengthening tank 32. In addition, the introduction part which introduces dehumidified gas should just be provided suitably according to an apparatus, and is not restrict | limited in particular. Examples of the introduction unit include a compressor and a cylinder.

  Before the ion exchange step and / or at the same time as the ion exchange step, the molten salt and / or a gas such as nitrogen or the like (hereinafter also simply referred to as a dehumidified gas) dehumidified in the atmosphere in the vicinity of the molten salt interface. By introducing it, the above atmospheric dew point can be achieved. The dehumidified gas can be used as a gas that does not affect the chemical strengthening treatment.

  When the dehumidified gas is introduced, the molten salt may or may not be stirred, but stirring is preferable in terms of shortening the time to reach equilibrium. Although the time from the introduction of the dehumidified gas to reaching the equilibrium varies depending on the amount of gas or liquid to be introduced, the water vapor concentration or the introduction method, etc., it cannot be generally stated, but the atmospheric dew point is stable and constant. If so, it can be determined that equilibrium has been reached.

  The following two points can be considered as reasons for improving the appearance quality by performing the ion exchange step in an atmosphere having a dew point temperature of 20 ° C. or lower.

  The first point is that hydroxide present in the atmosphere reacts with at least one ion selected from the group consisting of carbonate ion, phosphate ion and hydroxide ion contained in the molten salt to form hydroxide ion. . When the hydroxide ions penetrate into the glass surface layer through the molten salt during the chemical strengthening treatment, the density of the glass surface is reduced by cutting (hydrolyzing) the network bonds of the glass, thereby reducing the density of the glass surface. The appearance quality deteriorates due to roughening. By setting the dew point temperature to 20 ° C. or less and reducing the amount of moisture in the atmosphere that is the cause of the reduction in density, the reduction in appearance quality can be suppressed by suppressing the reduction in density.

  The second point is to reduce the amount of water present in the molten salt by reducing the dew point (water vapor amount) of the atmosphere near the interface between the molten salt and / or the molten salt, and between the tempered glass and the molten salt. The ion exchange property between lithium and sodium can be improved, and the strength can be improved by increasing CS and DOL.

  In the production method of the present invention, it is preferable to perform multi-stage chemical strengthening treatment of two or more stages. For example, the step of bringing the lithium-containing glass into contact with the inorganic salt containing sodium nitrate as described above and performing ion exchange is the first-stage chemical strengthening. Subsequently, a compressive stress layer is formed by performing a second-stage chemical strengthening in which an inorganic salt containing potassium (for example, potassium nitrate) is brought into contact with the glass and Na ions in the glass are exchanged with K ions in the inorganic salt. A chemically strengthened glass having a deep depth and a high surface compressive stress value is obtained. The chemical strengthening after the second stage is not particularly limited, and can be chemically strengthened by a conventionally known method.

[Chemical treatment]
The strength of the glass plate ion-exchanged by chemical strengthening treatment can be improved by removing a part of the surface of the glass plate by chemical treatment. The chemical treatment preferably includes an acid treatment step in which the glass is brought into contact with an acid after the above-described ion exchange step, and more preferably includes an alkali treatment step in which the glass plate is brought into contact with an alkali after the acid treatment step. .

  In the production method of the present invention, at least one ion selected from the group consisting of carbonate ion, phosphate ion and hydroxide ion contained in the inorganic salt composition has a property of cutting the glass network and is chemically strengthened. Since the treatment temperature is as high as several hundred degrees Celsius, the covalent bond between Si-O of the glass is broken at that temperature, and the surface layer of the compressive stress layer is altered on the surface of the glass after the ion exchange step. It will have a densified low density layer.

  By performing the acid treatment step after the ion exchange step, the density reduction can be further advanced, and a part or all of the low density layer can be removed by the alkali treatment step after the acid treatment step. Cracks and latent scratches existing on the glass surface are removed together with the low-density layer, and a chemically strengthened glass in which deterioration in appearance quality is suppressed can be obtained.

  The thickness of the low density layer is selected from the group consisting of carbonate ion, phosphate ion and hydroxide ion in the inorganic salt composition in the ion exchange step, and the concentration of at least one ion, the lithium concentration in the molten salt, the chemical It can be controlled by the strengthening temperature, chemical strengthening time, etc. The thickness of the low density layer can be calculated from the period (Δθ) measured by the X-ray reflectivity method (X-ray-Reflectometry: XRR).

  The density of the low density 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 low density layer can be determined from the critical angle (θc) measured by XRR. In addition, it is also possible to confirm the formation of the low density layer and the thickness of the layer by simply observing a cross section of the glass with a scanning electron microscope (SEM).

  The timing of the chemical treatment is not particularly limited, but when performing a multi-stage chemical strengthening treatment, the chemical treatment may be performed during the chemical strengthening treatment. For example, when two-stage chemical strengthening is performed, a chemical treatment may be performed between the first-stage chemical strengthening process and the second-stage chemical strengthening process.

  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.

  The solution is not particularly limited as long as it is acidic. For example, it may be less than pH 7, and 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 and 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. Although the time for performing the acid treatment varies depending on the type, concentration and temperature of the acid used, 10 seconds to 5 hours is preferable from the viewpoint of productivity, and 1 minute to 2 hours is more preferable.

  The concentration of the solution for acid treatment varies depending on the type, time, and temperature of the acid used, but is preferably a concentration at which there is little concern about container corrosion, specifically 1 wt% to 20 wt%.

  The alkali treatment of the glass is performed by immersing the chemically strengthened glass in a basic solution, whereby a part or all of the low density layer can be removed. The solution to be subjected to 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.

  Although the temperature which performs an alkali treatment changes also with the kind of base used, a density | concentration, and time, 0-100 degreeC is preferable, 10-80 degreeC is more preferable, and 20-60 degreeC is especially preferable. If it is this temperature range, there is no possibility that glass will corrode and it is preferable.

  Although the time for performing the alkali treatment 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 1 wt% to 20 wt% from the viewpoint of glass surface removability.

  By the alkali treatment, part or all of the low-density layer into which H has penetrated is removed, and a chemically strengthened glass having improved appearance quality can be obtained. Furthermore, since the scratches existing on the glass surface are removed at the same time by removing the low density layer, it is considered that it contributes to the improvement of strength.

  Note that the amount of the low density layer to be removed depends on the conditions of the alkali treatment. From the viewpoint of improving the strength, the strength can be improved even if the entire low density layer is not removed. It is preferable to remove the entire low-density layer from the viewpoint of stably securing the transmittance of the glass.

  In the manufacturing method of this invention, it is preferable to further include the washing | cleaning process which wash | cleans a glass plate between each process, such as an ion exchange process, an acid treatment process, and an alkali treatment process. In the cleaning step, the glass is cleaned using industrial water, ion exchange water, or the like. Of these, it is preferable to use ion-exchanged water. Moreover, it is preferable to use what was processed as needed.

  The washing conditions vary depending on the washing solution, but when ion-exchanged water is used, washing at 0 to 100 ° C. is preferable from the viewpoint of completely removing the attached salt. In the cleaning process, various methods can be used, such as a method of immersing glass in a water bath 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. is there.

  The chemically strengthened glass obtained by the production method of the present invention preferably has no white haze. In this specification, “no cloudiness” means a state where the distance between the glass and the eye of the judge is 50 cm under illumination with an illuminance of 5000 lux, and there is no visible appearance abnormality on the glass surface. Say. The brightness of the inspection environment used an illuminometer FT3424 manufactured by HIOKI. In addition, the inspection was conducted in a clean room of class 1000 or less in order to exclude other causes of appearance hindrance.

  The present invention will be specifically described below with reference examples, examples and comparative examples, but the present invention is not limited thereto.

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

(White cloudy evaluation)
Under illumination with an illuminance of 5000 lux, the distance between the glass and the eye of the judge was 50 cm, and the case where there was no abnormality in the appearance on the glass surface was marked as ◯, and the case where there was an abnormality in the appearance was marked as x.

(Compressive stress value)
The surface compressive stress value (unit: MPa) of glass, the compressive stress value (unit: MPa) at each depth, and the depth (DOL, unit: μm) of the compressive stress layer are the surface stress meter (FSM- 6000) and a scattered light photoelastic stress meter (SLP-1000) manufactured by Orihara Seisakusho.

<Manufacture of chemically strengthened glass>
[Glass plate]
A glass plate of composition A shown in Table 1 was prepared.
The glass of composition A had the following composition in terms of mol% based on oxide.
Glass A: SiO ₂ 70%, Al ₂ O ₃ 7.5%, Li ₂ O 8.0% Na ₂ O 5.3%, K ₂ O 1.0%, MgO 7.0%, CaO 0.2%, ZrO ₂ 1.0%

[Chemical strengthening process (ion exchange process)]
A molten salt material was added to a SUS cup and heated to 450 ° C. with a mantle heater to prepare molten salts having the compositions shown in Table 1. After preparing a glass of composition A cut to a size of 50 mm × 50 mm, preheating the molten salt at 350 to 400 ° C., immersing it under the conditions shown in Table 1 and performing chemical strengthening treatment, then cooling it to around room temperature, A chemically strengthened glass was obtained.

  In Reference Example 1, glass of composition A having a plate thickness of 0.7 mm was immersed in a molten salt of an inorganic salt composition under the condition that the Li ion concentration was 1230 ppm by weight to perform chemical strengthening. Specifically, lithium nitrate was added to the molten salt of the inorganic salt composition, and the molten salt was prepared so that Li ions had the corresponding concentrations as described above as trace impurities in the molten salt. As a result of measuring the atmospheric dew point, it was 20 ° C. in Reference Example 1.

  In Reference Example 2, chemical strengthening was performed by immersing a glass of composition A having a plate thickness of 0.7 mm in a molten salt of an inorganic salt composition under the condition that the Li ion concentration was 2520 ppm by weight. As a result of measuring the atmospheric dew point, it was 20 ° C. in Reference Example 2.

  In Examples 1 and 2, glass of composition A having a plate thickness of 0.7 mm was immersed in a molten salt of an inorganic salt composition containing a flux under the conditions of Li ion concentrations of 1230 ppm by weight and 2520 ppm by weight, respectively. , Chemical strengthening was performed. As the flux, sodium carbonate was used and added at a concentration of 0.3 wt%. As a result of measuring the atmospheric dew point, it was 20 ° C. in Example 1 and 19 ° C. in Example 2.

  In Comparative Example 1, glass of composition A having a plate thickness of 0.7 mm was immersed in a molten salt of an inorganic salt composition containing a flux under the condition that the Li ion concentration was 3900 ppm by weight to perform chemical strengthening. As the flux, sodium carbonate was used and added at a concentration of 0.3 wt%. As a result of measuring the atmospheric dew point, it was 19 ° C. in Comparative Example 1.

  Examples 3, 4 and 5 are inorganic salt compositions containing a flux of glass having composition A having a thickness of 0.7 mm under the conditions of Li ion concentrations of 1230 ppm, 2520 ppm and 3900 ppm, respectively. It was immersed in a molten salt of the product to perform chemical strengthening. As the flux, sodium carbonate was used and added at a concentration of 1.0 wt%. As a result of measuring the atmospheric dew point, it was 20 ° C. in Example 3, 19 ° C. in Example 4, and 20 ° C. in Example 5.

  In Comparative Example 2, the glass of composition A having a plate thickness of 0.7 mm was immersed in a molten salt of an inorganic salt composition containing a flux under the condition that the Li ion concentration was 5400 ppm by weight to perform chemical strengthening. As the flux, sodium carbonate was used and added at a concentration of 1.0 wt%. As a result of measuring the atmospheric dew point, it was 19 ° C. in Comparative Example 2.

  Examples 6, 7, 8, and 9 are inorganic salts containing a flux with a glass composition of 0.7 mm having a thickness of 0.7 mm and a Li ion concentration of 1230 ppm by weight, 3900 ppm by weight, and 5400 ppm by weight, respectively. It was immersed in a molten salt of the composition and controlled to have an atmospheric dew point in the chemical strengthening treatment of 15 ° C. or lower to perform chemical strengthening. As the flux, sodium carbonate was used and added at a concentration of 1.0 wt%.

  In Comparative Examples 3 and 4, glass of composition A having a plate thickness of 0.7 mm was immersed in a molten salt of an inorganic salt composition containing a flux under the condition that the Li ion concentration was 7020 ppm by weight, and in chemical strengthening treatment Chemical strengthening was performed by controlling the atmospheric dew point to be 15 ° C or lower.

  For Examples 10, 11, and 12, the glass of composition A having a plate thickness of 0.7 mm was used as a molten salt of an inorganic salt composition under the conditions of Li ion concentrations of 1230 ppm, 3900 ppm, and 5400 ppm, respectively. It was immersed in and subjected to chemical strengthening. And after the above-described chemical strengthening step, the following acid treatment step and alkali treatment step were performed to obtain chemically strengthened glass. As a result of measuring the atmospheric dew point, it was 20 ° C. in Example 10, 20 ° C. in Example 11, and 19 ° C. in Example 12.

  For Comparative Example 5, glass of composition A having a thickness of 0.7 mm was immersed in a molten salt of an inorganic salt composition under the condition that the Li ion concentration was 7020 ppm by weight, and chemical strengthening was performed. And after the above-described chemical strengthening step, the following acid treatment step and alkali treatment step were performed to obtain chemically strengthened glass. As a result of measuring the atmospheric dew point, it was 20 ° C. in Comparative Example 5.

  In addition, the control of the atmospheric dew point in the chemical strengthening treatment described in Table 1 is performed by passing an air dryer through the atmosphere near the interface of the molten salt as described above under the condition where the dew point temperature is 15 ° C. or lower. Control by flowing dry air. Although the experimental system is shown in FIG. 1, dehumidified gas Y was obtained by introducing gas X into the air dryer 31. By introducing this dehumidified gas Y into the space above the inorganic salt (molten salt) 33 in the chemical strengthening tank 32, the atmospheric dew point in the chemical strengthening process was controlled. An air dryer (IDG5M4-02-S manufactured by SMC) was used to control each atmospheric dew point.

[Acid treatment process]
13.4 wt% hydrochloric acid (HCl; manufactured by Kanto Chemical Co., Inc.) was prepared in a beaker, and the temperature was adjusted to 41 ° C. using a water bath. The glass obtained in the chemical strengthening step was immersed in adjusted hydrochloric acid for 180 seconds, subjected to acid treatment, then washed several times with pure water, and then dried by air blowing. The glass thus obtained was subjected to the next step.

[Alkali treatment process]
A 4.0 wt% aqueous sodium hydroxide solution was prepared in a beaker, and the temperature was adjusted to 40 ° C. using a water bath. The glass obtained in the acid treatment step was immersed in the prepared potassium hydroxide aqueous solution for 120 seconds, subjected to alkali treatment, then washed several times with pure water, and then dried by air blowing.

  Various evaluation was performed about the chemically strengthened glass obtained above. Table 1 shows the processing conditions and evaluation results of the glass.

  As shown in Table 1, the chemically tempered glass of Reference Example 1 was excellent in appearance quality, but the chemically tempered glass of Reference Example 2 was cloudy. The difference between Reference Example 1 and Reference Example 2 is that the Li ion concentration of Reference Example 2 is 1220 ppm by weight, whereas the Li ion concentration of Reference Example 2 is 2520 ppm by weight.

  Next, by the production method of the present invention, sodium carbonate was added to the molten salt of the inorganic salt composition at a concentration of 0.3 wt% to obtain chemically tempered glasses of Example 1 and Example 2. In particular, in Example 2, the addition of sodium carbonate to the chemical strengthening conditions prevented the occurrence of white haze, and a chemically strengthened glass excellent in appearance quality was obtained. However, the chemically tempered glass of Comparative Example 1 in which sodium carbonate was similarly added at a concentration of 0.3 wt% produced white cloudiness. That is, it is considered that the Li ion concentration in the molten salt was as high as 3900 ppm by weight.

  Furthermore, the chemically tempered glass of Examples 3-5 was obtained by adding sodium carbonate at a concentration of 1.0 wt% to the molten salt of the inorganic salt composition by the production method of the present invention. When the Li ion concentration was in the range of 1230 ppm by weight to 3900 ppm by weight, the occurrence of white clouding was suppressed and the appearance quality was excellent. However, the chemically tempered glass of Comparative Example 2 to which sodium carbonate was added at a concentration of 1.0 wt% produced white cloudiness. It is considered that the Li ion concentration was as high as 5400 ppm by weight.

  Therefore, when sodium carbonate is added at a concentration of 1.0 wt%, by adjusting the Li ion concentration in the molten salt of the inorganic salt composition to be 4000 ppm by weight or less, the occurrence of white haze is suppressed, It was found that chemically strengthened glass having excellent appearance quality can be obtained.

  Further, as shown in Examples 6, 7, 8, and 9, when the Li ion concentration in the molten salt of the inorganic salt composition is in the range of 1230 ppm to 5400 ppm, the dew point temperature is 15 ° C. or lower. It was found that the occurrence of white cloudiness can be suppressed. On the other hand, in Comparative Examples 3 and 4, when the Li ion concentration in the molten salt of the inorganic salt composition exceeded 7000 ppm by weight, white cloudiness was generated even when the dew point temperature was 15 ° C. or lower and further −10 ° C. or lower. Was found to be unable to be suppressed.

  Furthermore, as shown in Examples 10, 11, and 12, when the Li ion concentration in the molten salt of the inorganic salt composition is in the range of 1230 ppm by weight to 5400 ppm by weight, the occurrence of white cloudiness is caused by chemical treatment. It turned out that it can suppress. On the other hand, as shown in Comparative Example 5, it was found that when the Li concentration in the molten salt of the inorganic salt composition exceeds 7000 ppm by weight, the occurrence of white cloudiness cannot be suppressed even if chemical treatment is performed.

  Therefore, when sodium carbonate is added at a concentration of 1.0 wt%, by adjusting the Li ion concentration in the molten salt of the inorganic salt composition to be 5500 ppm by weight or less, the occurrence of white cloudiness is suppressed, It was found that chemically strengthened glass having excellent appearance quality can be obtained.

  From these results, when a lithium-containing glass is chemically strengthened with a molten salt of an inorganic salt composition containing sodium nitrate, Li ions in the glass and Na ions in the molten salt undergo ion exchange, and Li ions in the molten salt It is thought that white fogging occurs due to crystallization of magnesium, phosphorus, silicate, etc. in the glass and Li ions in the molten salt on the glass surface, resulting in a decrease in appearance quality.

  In Table 1, carbonates are used as examples satisfying the chemical strengthening conditions, but even phosphates and hydroxide salts are similarly effective from the viewpoint of Li ion capture.

  In Table 1, sodium carbonate is used as an example satisfying the chemical strengthening conditions. However, when sodium carbonate is added at a concentration of 1.0 wt% or more, for example, 1.5 wt%, the added sodium carbonate may be precipitated. It is necessary to add an inorganic salt as long as sodium carbonate does not precipitate.

  According to the production method of the present invention, at least one salt selected from the group consisting of carbonate, phosphate and hydroxide salt contained in the inorganic salt composition captures Li ions in the molten salt. It is considered that the appearance quality of the resulting chemically strengthened glass can be improved by suppressing the crystallization to suppress the occurrence of white cloudiness.

  According to the method for producing chemically tempered glass of the present invention, it is possible to produce chemically tempered glass excellent in appearance quality by suppressing generation of white cloudiness in chemical strengthening of lithium-containing glass. The chemically strengthened glass obtained by the production method of the present invention can be used for a cover glass for a display such as a mobile phone, a digital camera or a touch panel display.

31 Air dryer 32 Chemical strengthening tank 33 Molten salt

Claims (10)

A method for producing chemically strengthened glass comprising a step of ion-exchanging Li ions in the glass and Na ions in the inorganic salt composition by bringing a glass containing lithium into contact with an inorganic salt composition containing sodium nitrate. There,
The inorganic salt composition is a chemically strengthened glass containing at least one salt selected from the group consisting of Na ₂ CO ₃ , K ₂ CO ₃ , KHCO ₃ , NaHCO ₃ , K ₃ PO ₄ , Na ₃ PO ₄ , KOH and NaOH. Manufacturing method.   The method for producing chemically strengthened glass according to claim 1, wherein the Li ion concentration in the inorganic salt composition is 5500 ppm by weight or less.   The method for producing chemically strengthened glass according to claim 2, wherein the Li ion concentration in the inorganic salt composition is 4000 ppm by weight or less. The method for producing chemically strengthened glass according to claim 1, wherein the inorganic salt composition contains at least Na ₂ CO ₃ . The method for producing chemically strengthened glass according to claim 4, wherein the inorganic salt composition contains 0.3 wt% or more of Na ₂ CO ₃ . The method for producing chemically strengthened glass according to claim 4, wherein the inorganic salt composition contains 1.0 wt% or more of Na ₂ CO ₃ . 4. The chemically strengthened glass according to claim 1, wherein the inorganic salt composition contains at least one salt selected from the group consisting of Na ₂ CO ₃ , K ₂ CO ₃ , KHCO _3, and NaHCO ₃ . Production method.   The method for producing chemically tempered glass according to claim 1, wherein the ion exchange step is performed in an atmosphere having a dew point temperature of 15 ° C. or lower.   The method for producing chemically strengthened glass according to any one of claims 1 to 8, wherein the atmosphere in the ion exchange step is formed by introducing a gas dried by an air dryer.   The method for producing chemically strengthened glass according to any one of claims 1 to 9, further comprising a step of acid-treating the glass after the ion-exchange step and a step of alkali-treating the glass after the acid treatment.

Images