JP7024565B2 - Manufacturing method of chemically strengthened glass - Google Patents

Description

The present invention relates to a method for producing chemically tempered 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.

Lithium-containing glass (hereinafter, also abbreviated as lithium-containing glass) is useful from the viewpoint of further improving the strength and is widely used. Chemical strengthening of a lithium-containing glass is a step of bringing an inorganic salt (for example, sodium nitrate) composition containing sodium into contact with the lithium-containing glass to ion-exchange Li ions in the glass with Na ions in the inorganic salt composition. including.

The present inventors have found that when a lithium-containing glass is chemically fortified with an inorganic salt composition containing sodium nitrate, white turbidity is generated on the glass surface during the cumulative treatment and the appearance quality is deteriorated. Further, the cause of the white turbidity of the glass is that the Li ion concentration in the molten salt of the inorganic salt composition increases cumulatively as the treated area of the lithium-containing glass by the inorganic salt composition in the chemical strengthening increases. I found that.

When the Li ion concentration in the molten salt increases, Li ions accumulate on the glass surface due to the action of the Li ions in the molten salt and components such as magnesium or phosphorus in the glass exchanging ions, and in an environment where Li ions are present. It is considered that the crystal nucleation formation temperature is lowered and glass components such as magnesium, phosphorus or silicate react with Li ions on the glass surface to crystallize, resulting in white turbidity and deterioration of appearance quality. As described above, cloudiness in the present specification means that the glass component reacts with Li ions on the glass surface to crystallize, and the reaction with the salt precipitated in the molten salt of the inorganic salt composition causes the glass component to crystallize. It does not mean the resulting crystals.

Therefore, an object of the present invention is to provide a method for producing a chemically strengthened glass having excellent appearance quality by suppressing the occurrence of white fogging in the chemically strengthened glass containing lithium.

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

That is, the present invention is as follows.
1. 1. A method for producing chemically strengthened glass, which comprises a step of ion-exchange between Li ions in the glass and Na ions in the inorganic salt composition by contacting a glass containing lithium 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 according to 1 above, wherein the Li ion concentration in the inorganic salt composition is 5500 wt ppm or less.
3. 3. The method for producing chemically strengthened glass according to 2 above, wherein the Li ion concentration in the inorganic salt composition is 4000 wt ppm or less.
4. The method for producing chemically strengthened glass according to any one of 1 to 3 above, wherein the inorganic salt composition contains at least Na ₂ CO ₃ .
5. The method for producing chemically strengthened glass according to 4 above, wherein the inorganic salt composition contains 0.3 wt% or more of Na ₂ CO ₃ .
6. The method for producing chemically strengthened glass according to 4 above, wherein the inorganic salt composition contains 1.0 wt% or more of Na ₂ CO ₃ .
7. The method for producing chemically strengthened glass according to any one of 1 to 3 above, 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 Na HCO ₃ . ..
8. The method for producing chemically strengthened glass according to any one of 1 to 7 above, wherein the ion exchange step is performed in an atmosphere having a dew point temperature of 15 ° C. or lower.
9. The method for producing chemically strengthened glass according to any one of 1 to 8 above, 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 an acid treatment of the glass after the ion exchange step and an alkali treatment of 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, may be referred to as "melting agent") is contained. In addition, the lithium-containing glass is chemically strengthened by the inorganic salt composition containing sodium nitrate. When the melt is added to the molten salt of the inorganic salt composition containing sodium nitrate, it becomes carbonate ion, phosphate ion and hydroxide ion, respectively, and elutes into the molten salt of the inorganic salt composition during the chemical strengthening treatment. By capturing the Li ions that had been formed, the occurrence of white turbidity can be suppressed, and chemically strengthened glass with excellent appearance quality can be manufactured.

FIG. 1 is a schematic diagram of an experimental system for forming an atmosphere in the process of ion exchange.

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 and carried out without departing from the gist of the present invention.
Further, in the present specification, "-" indicating a numerical range is used to mean that the numerical values described before and after the numerical range are included as the lower limit value and the upper limit value.

An aspect of the method for producing chemically strengthened 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 may contain lithium and may have various compositions as long as it has a composition that can be strengthened by molding or chemical strengthening treatment. Specific examples thereof include aluminosilicate glass, soda-lime glass, borosilicate glass, lead glass, alkaline barium glass, and aluminhosilicate glass.

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

Various methods can be adopted for forming the glass. For example, various molding 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 rollout method, a press method, and the like can be adopted. Above all, the float method is preferable in that cracks are likely to occur on at least a part of the glass surface and the effect of the present invention is more remarkable.

The thickness of the glass is not particularly limited, 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. It is preferably 0.7 mm or less, and particularly preferably 0.7 mm or less.

Further, the shape of the glass used in 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 and the like can be adopted. It is preferable that the glass is subjected to mechanical processing such as cutting, end face processing and drilling, depending on the intended use, before the chemical strengthening treatment.

The composition of the glass is not particularly limited, and examples thereof include the following glass compositions.
In the molar percentage display based on oxides, SiO ₂ is 50 to 80%, Al ₂ O ₃ is 2 to 25%, Li ₂ O is 0.1 to 20%, Na ₂ O is 0.1 to 18%, and K. ₂ O is 0 to 10%, MgO is 0 to 15%, CaO is 0 to 5%, P ₂ O ₅ is 0 to 5%, B ₂ O ₃ is 0 to 5%, and Y ₂ O ₃ is 0 to 5. % And ZrO ₂ containing 0-5%.

[Inorganic salt composition]
The chemically strengthened glass produced by the production method of the present invention has a compressive stress layer formed by ion exchange on the glass surface. In the ion exchange method, the surface of the glass is ion-exchanged to form a surface layer in which compressive stress remains. Specifically, by exchanging ions at a temperature below the glass transition point, alkali metal ions having a small ionic radius on the surface of the glass plate (for example, Li ions and / or Na ions) are exchanged with other alkaline ions having a larger ionic radius. Substitute with (eg, Na ion and / or K ion). As a result, 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, in the chemical strengthening treatment, the glass containing the above-mentioned alkaline ion is brought into contact with the molten salt of the inorganic salt composition containing another alkaline ion having an ionic radius larger than that of the alkaline ion contained in the glass. It is done by exchanging ions. That is, the alkaline ion (Li ion) contained in the glass and another alkaline ion (Na ion) contained in the 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. Further, 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. Further, the salt excluding sodium nitrate and potassium nitrate (hereinafter, also referred to as “flux”) among the above salts has a property of capturing Li ions in the molten salt of the inorganic salt composition. By capturing Li ions during the chemical tempered treatment, it is possible to suppress the occurrence of white fogging and produce chemically tempered glass with excellent appearance quality.

The degree of suppression of white fogging varies depending on the glass composition, the type of salt (melting agent) used, the temperature at which the chemical fortification treatment is performed, the time and other chemical fortification treatment conditions, but 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 the inorganic salt onto the glass, and a method of immersing the glass in a salt bath of a molten salt heated to a temperature higher than the melting point. However, among these, the method of immersing in a molten salt is preferable.

The amount of the flux added is preferably 0.1 wt% (wt% is weight percent) or more, more preferably 0.3 wt% or more, still more preferably 0.5 wt% or more from the viewpoint of controlling white cloudiness. Further, from the viewpoint of impurity precipitation, it is preferably 4.0 wt% or less, more preferably 3.0 wt% or less, still more preferably 2.0 wt% or less. The flux can prevent the lithium on the glass surface from reacting with the glass component to crystallize by capturing Li ions in the inorganic salt composition, and can suppress white turbidity caused by Li in the molten salt. ..

In addition to the above-mentioned inorganic salts containing sodium nitrate, the inorganic salt composition includes, for example, sodium chloride, sodium borate, sodium sulfate, sodium sulfate, sodium chloride, and sodium boric acid, as long as the effects of the present invention are not impaired. It may contain salts such as salt, potassium chloride and potassium borate. These may be added alone or in combination of two or more.

At least one salt selected from the group consisting of the flux is put into a container and mixed with the inorganic molten salt containing sodium nitrate by a stirring blade or the like. When a plurality of salts are used in combination, the order of addition is not limited and may be added at the same time.

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

The mixture is then heated to melt. Melting is performed at a temperature equal to or higher than the melting point (308 ° C.) of sodium nitrate. In particular, it is more preferable to set the melting temperature to 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, more preferably 10 minutes to 2 hours.

In the molten salt of the inorganic salt composition obtained by the above method, when a precipitate is generated due to the addition of a flux, the precipitate is settled on the bottom of the container before the chemical strengthening treatment of the glass. Stand still.

The molten salt of the inorganic salt composition has a Li ion concentration of preferably 5500 wt ppm or less, more preferably 4000 wt ppm or less, and is at least selected from the group consisting of carbonates, phosphates and hydroxide salts. By including a kind of salt in the inorganic salt composition, the effect of suppressing the occurrence of white cloudiness can be exhibited.

[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. It 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 the inorganic salt composition onto the glass, and a molten salt of the inorganic salt composition heated to a temperature higher than the melting point. Examples thereof include a method of immersing the glass in the salt bath of the above, and among these, a method of immersing the glass in the molten salt of the inorganic salt composition is preferable.

Specifically, for example, the chemical strengthening treatment for immersing the glass in the molten salt of the inorganic salt composition can be carried out 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 out of the molten salt and allowed to cool.

The preheating temperature of the glass depends on the temperature of immersion in the molten salt, but is generally preferably 100 ° C. or higher. After immersing the glass in the molten salt, it is pulled out of the molten salt and allowed to cool.

The chemical tempering temperature is preferably not less than the strain point of the tempered glass (usually 500 to 600 ° C.), and particularly preferably 350 ° C. or higher 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, still more preferably 10 minutes to 4 hours. Within such a range, chemically strengthened glass having an excellent balance between strength and DOL can be obtained.

The chemically strengthened treatment is preferably carried out in an atmosphere having a dew point temperature of 20 ° C. or lower from the viewpoint of improving the appearance quality of the obtained 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. The lower limit of the dew point temperature is not particularly limited, but it is usually preferably −60 ° C. or higher from the viewpoint of dew point control equipment. When the chemical strengthening treatment is performed with the dew point temperature set to 15 ° C. or lower, it is effective to control the dew point temperature as described later. If the dew point temperature is 15 ° C. or higher, for example, around 20 ° C., the chemical strengthening treatment can be performed without controlling the dew point temperature.

The "dew point temperature" (hereinafter, also abbreviated as dew point) in the present specification is a value when it is considered that an equilibrium has been established between the molten salt and the atmosphere near the molten salt interface. The dew point can be measured by the Vaisala DRYCAP® DMT346 dew point transducer. The dew point temperature may be such that 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 a region of 200 mm or less from the interface of the molten salt.

The dew point temperature is preferably controlled within ± 5 ° C., more preferably within ± 4 ° C., and even more preferably within ± 3 ° C. By controlling the dew point temperature within ± 5 ° C, the performance of the chemically strengthened glass can be made uniform.

Specific examples of the method for setting the dew point of the atmosphere 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 fortification tank, and the atmospheric dew point can be lowered. Commercially available air dryers can be used, and examples thereof include IDG5M4-02-S manufactured by SMC Corporation and IDG60SAM4-03 manufactured by SMC Corporation.
(2) A gas such as air or nitrogen can be dehumidified with an adsorbent before being introduced into the chemically strengthened tank to lower the atmospheric dew point. Commercially available adsorbents can be used.
(3) A gas such as air or nitrogen can be dehumidified using a dehumidifier before being introduced into the chemically strengthened tank to lower the atmospheric dew point. A commercially available dehumidifier can be used.

Specifically, as the method (1), as shown in FIG. 1, a gas X such as air, nitrogen gas, and carbon dioxide gas is introduced into the air dryer 31 to obtain a dehumidified gas Y. , A method of introducing a dehumidified gas into the space above the inorganic salt composition (molten salt) 33 in the chemical strengthening tank 32 and the like. The introduction section for introducing the dehumidified gas may be appropriately provided according to the apparatus, and is not particularly limited. Examples of the introduction unit include a compressor, a cylinder, and the like.

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

The molten salt may or may not be agitated when introducing the dehumidified gas, but agitation is preferable in terms of shortening the time until equilibrium is reached. The time from the introduction of the dehumidified gas to reaching equilibrium varies depending on the amount of gas or liquid to be introduced, the water vapor concentration, the introduction method, etc. If so, it can be judged that the equilibrium has been reached.

The following two points can be considered as the reasons why the appearance quality is improved by performing the ion exchange step in an atmosphere where the dew point temperature is 20 ° C. or lower.

The first point is that the water present in the atmosphere reacts with at least one ion selected from the group consisting of carbonate ions, phosphate ions and hydroxide ions contained in the molten salt to form hydroxide ions. .. When the hydroxide ion invades the glass surface layer via the molten salt during the chemical strengthening treatment, the network bond of the glass is broken (hydrolyzed) and the density decreases, and the glass surface becomes low. As it becomes rough, the appearance quality deteriorates. By setting the dew point temperature to 20 ° C. or lower and reducing the amount of water in the atmosphere that is the cause of the low density, the low density can be suppressed and the deterioration of the appearance quality can be suppressed.

The second point is to reduce the amount of water present in the molten salt by lowering the dew point (amount of water vapor) in 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 between lithium and sodium can be improved, and CS and DOL can be enhanced to improve the strength.

In the production method of the present invention, it is preferable to carry out a multi-step chemical strengthening treatment of two or more steps. For example, the step of contacting the lithium-containing glass with the above-mentioned inorganic salt containing sodium nitrate to exchange ions is referred to as the first step of chemical strengthening. Subsequently, the compressive stress layer is subjected to the second step of chemical strengthening in which an inorganic salt containing potassium (for example, potassium nitrate) is brought into contact with the glass to exchange ions between Na ions in the glass and K ions in the inorganic salt. Chemically strengthened glass with a deep depth and a high surface compressive stress value can be obtained. The chemical strengthening in the second and subsequent stages is not particularly limited, and the chemical strengthening can be performed by a conventionally known method.

[Chemical treatment]
The strength of the glass plate ion-exchanged by the chemical strengthening treatment can be improved by removing a part of the surface of the glass plate by the chemical solution treatment. The chemical treatment preferably includes an acid treatment step of bringing the glass into contact with an acid after the above-mentioned ion exchange step, and more preferably includes an alkali treatment step of bringing the glass plate 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 network of glass and is chemically strengthened. Since the temperature at which the treatment is performed is as high as several hundred degrees Celsius, the covalent bond between Si and O of the glass is broken under 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 low density 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 chemically strengthened glass with suppressed deterioration of appearance quality can be obtained.

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

The density of the low-density layer is preferably lower than that of the deeper region (bulk) than the ion-exchanged compressive stress layer from the viewpoint of glass surface removability. The density of the low density layer can be determined by the critical angle (θc) measured by XRR. It is also possible to simply observe the cross section of the glass with a scanning electron microscope (SEM) to confirm the formation of the low density layer and the thickness of the layer.

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

The acid treatment of the glass is carried out by immersing the chemically strengthened glass in an acidic solution, whereby Na and / or K on the surface of the chemically strengthened glass can be replaced with H.

The solution is not particularly limited as long as it is acidic. For example, the pH may be less than 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 preferable. These acids may be used alone or in combination of two or more.

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 lower. The time for performing 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 to be treated with the acid varies depending on the type of acid used, the time and the temperature, but it is preferably a concentration at which there is little concern about container corrosion, and specifically, 1 wt% to 20 wt% is preferable.

Alkaline treatment of glass is performed by immersing chemically strengthened glass in a basic solution, whereby 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, as long as it exceeds pH 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 preferable. These bases may be used alone or in combination of two or more.

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. Within such a temperature range, there is no risk of the glass corroding, which is preferable.

The time for performing the alkaline treatment varies depending on the type, concentration and temperature of the base 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 to be subjected to the alkali treatment varies depending on the type of base used, time and temperature, but is preferably 1 wt% to 20 wt% from the viewpoint of glass surface removability.

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

The amount of the low-density layer to be removed depends on the conditions of the alkaline treatment. From the point of view of improving the strength, the strength can be improved even if the entire low density layer is not removed. It is preferable to remove all of the low density layer from the viewpoint of stably ensuring the transmittance of the glass.

The production method of the present invention preferably further includes a cleaning step of cleaning the glass plate between steps such as an ion exchange step, an acid treatment step, and an alkali treatment step. In the washing step, the glass is washed with working water, ion-exchanged water, or the like. Above all, it is preferable to use ion-exchanged water. In addition, it is preferable to use treated water as needed.

The cleaning conditions differ depending on the cleaning liquid, but when ion-exchanged water is used, cleaning at 0 to 100 ° C. is preferable from the viewpoint of completely removing the attached salt. In the cleaning process, various methods such as immersing the glass in a water tank containing ion-exchanged water, exposing the glass surface to running water, and spraying the cleaning liquid toward the glass surface by a shower can be used. be.

The chemically strengthened glass obtained by the production method of the present invention preferably does not have white fogging. In the present specification, "no white cloudiness" means that the distance between the glass and the eyes of the judge is 50 cm under illumination of 5000 lux, and there is no visible abnormality in the appearance of the glass surface. say. For the brightness of the inspection environment, an illuminometer FT3424 manufactured by HIOKI was used. In addition, the inspection was carried out in a clean room of class 1000 or less in order to exclude other factors of appearance inhibition.

Hereinafter, the present invention will be specifically described with reference to 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 analysis method shown below.

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

(Compressive stress value)
The surface compressive stress value of glass (unit: MPa), the compressive stress value at each depth (unit: MPa), and the depth of the compressive stress layer (DOL, unit: μm) are determined by Orihara Seisakusho's surface stress meter (FSM-). 6000) and a scattered photoelastic stress meter (SLP-1000) manufactured by Orihara Seisakusho Co., Ltd. were used for measurement.

<Manufacturing of chemically strengthened glass>
[Glass plate]
A glass plate having the composition A shown in Table 1 was prepared.
The glass of composition A had the following composition in terms of molar% based on oxides.
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)]
The molten salt material was added to a cup made of SUS and heated to 450 ° C. with a mantle heater to prepare a molten salt having the composition shown in Table 1. A glass of composition A cut into a size of 50 mm × 50 mm was prepared, the molten salt was preheated to 350 to 400 ° C., immersed under the conditions shown in Table 1, chemically strengthened, and then cooled to near room temperature. Obtained chemically tempered glass.

In Reference Example 1, a glass having a composition A having a plate thickness of 0.7 mm was immersed in a molten salt of an inorganic salt composition under the condition of a Li ion concentration of 1230 wt ppm for 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 above-mentioned corresponding concentrations 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, glass having a composition A having a plate thickness of 0.7 mm was chemically strengthened by immersing it in a molten salt of an inorganic salt composition under the condition of a Li ion concentration of 2520 wt ppm. As a result of measuring the atmospheric dew point, it was 20 ° C. in Reference Example 2.

In Reference Examples 3 and 4, a glass having a 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 wt ppm and 2520 wt ppm, respectively. , Chemically strengthened. Sodium carbonate was used as the flux, and the flux was added at a concentration of 0.3 wt%. As a result of measuring the atmospheric dew point, it was 20 ° C. in Reference Example 3 and 19 ° C. in Reference Example 4 .

In Comparative Example 1, glass having a composition A having a plate thickness of 0.7 mm was chemically strengthened by immersing it in a molten salt of an inorganic salt composition containing a flux under the condition of a Li ion concentration of 3900 wt ppm. Sodium carbonate was used as the flux, and the flux was 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.

Reference Examples 5 to 7 are inorganic salt compositions containing a melt in the glass of composition A having a plate thickness of 0.7 mm under the conditions of Li ion concentrations of 1230 wt ppm, 2520 wt ppm and 3900 wt ppm, respectively. It was soaked in molten salt and chemically fortified. Sodium carbonate was used as the flux and was added at a concentration of 1.0 wt%. As a result of measuring the atmospheric dew point, it was 20 ° C. in Reference Example 5 , 19 ° C. in Reference Example 6 , and 20 ° C. in Reference Example 7 .

In Comparative Example 2, glass having a composition A having a plate thickness of 0.7 mm was chemically strengthened by immersing it in a molten salt of an inorganic salt composition containing a flux under the condition of a Li ion concentration of 5400 wt ppm. Sodium carbonate was used as the flux and was 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.

In Reference Examples 8 to 11 , the glass of composition A having a plate thickness of 0.7 mm is melted with an inorganic salt composition containing a melt under the conditions of Li ion concentration of 1230 wt ppm, 3900 wt ppm, and 5400 wt ppm, respectively. By immersing in salt, the atmospheric dew point in the chemical strengthening treatment was controlled to be 15 ° C. or lower, and the chemical strengthening was performed. Sodium carbonate was used as the flux and was added at a concentration of 1.0 wt%.

In Comparative Examples 3 and 4, glass having a 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 of a Li ion concentration of 7020 wt ppm, and was subjected to a chemical strengthening treatment. The atmospheric dew point was controlled to be 15 ° C. or lower, and chemical strengthening was performed.

In Examples 1 to 3 , a glass having a composition A having a plate thickness of 0.7 mm was immersed in a molten salt of an inorganic salt composition under the conditions of Li ion concentration of 1230 wt ppm, 3900 wt ppm, and 5400 wt ppm, respectively. And chemical strengthening was done. Then, after the above-mentioned chemically strengthened step, the following acid treatment step and alkali treatment step were carried out to obtain chemically strengthened glass. As a result of measuring the dew point of the atmosphere, it was 20 ° C. in Example 1 , 20 ° C. in Example 2 , and 19 ° C. in Example 3 .

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

In the control of the atmospheric dew point in the chemical strengthening treatment shown in Table 1, under the condition that the dew point temperature is 15 ° C. or lower, the air dryer is passed through the atmosphere near the interface of the molten salt as described above. , Controlled by flowing dry air. Although the experimental system is shown in FIG. 1, the dehumidified gas Y was obtained by introducing the 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 fortification tank 32, the atmosphere dew point in the chemical fortification step was controlled. An air dryer (IDG5M4-02-S manufactured by SMC Corporation) was used to control each atmospheric dew point.

[Acid treatment process]
13.4% by weight 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 the adjusted hydrochloric acid for 180 seconds, subjected to acid treatment, then washed with pure water several times, and then dried by air blowing. The glass thus obtained was subjected to the next step.

[Alkaline treatment process]
A 4.0% by weight 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 a prepared potassium hydroxide aqueous solution for 120 seconds, subjected to alkali treatment, washed with pure water several times, and then dried by air blowing.

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

As shown in Table 1, the chemically strengthened glass of Reference Example 1 was excellent in appearance quality, but the chemically strengthened glass of Reference Example 2 was clouded. The difference between Reference Example 1 and Reference Example 2 is that the Li ion concentration of Reference Example 1 is 1230 wt ppm, whereas the Li ion concentration of Reference Example 2 is 2520 wt ppm.

Next, according to 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 strengthened glass of Reference Examples 3 and 4. In particular, in Reference Example 4 , the occurrence of white cloudiness was suppressed by adding sodium carbonate to the chemically strengthened conditions, and chemically strengthened glass having excellent appearance quality was obtained. However, the chemically strengthened glass of Comparative Example 1 to which sodium carbonate was also added at a concentration of 0.3 wt% had white cloudiness. That is, it is considered that the Li ion concentration in the molten salt was as high as 3900 ppm by weight.

Further, sodium carbonate was added to the molten salt of the inorganic salt composition at a concentration of 1.0 wt% by the production method of the present invention to obtain chemically strengthened glass of Reference Examples 5 to 7 . When the Li ion concentration was in the range of 1230 wt ppm to 3900 wt ppm, the occurrence of white cloudiness was suppressed and the appearance quality was excellent. However, the chemically strengthened glass of Comparative Example 2 to which sodium carbonate was added at a concentration of 1.0 wt% was clouded. It is considered that this is because 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%, the occurrence of white turbidity is suppressed by adjusting the Li ion concentration in the molten salt of the inorganic salt composition to be 4000 wt ppm or less. It was found that chemically strengthened glass with excellent appearance quality can be obtained.

Further, as shown in Reference Examples 8 to 11 , when the Li ion concentration in the molten salt of the inorganic salt composition is in the range of 1230 wt ppm to 5400 wt ppm, the dew point temperature is set to 15 ° C. or lower to obtain white. It was found that the occurrence of cloudiness can be suppressed. On the other hand, in Comparative Examples 3 and 4, since the Li ion concentration in the molten salt of the inorganic salt composition exceeded 7,000 ppm by weight, white cloudiness occurred even when the dew point temperature was 15 ° C. or lower and further -10 ° C. or lower. Was found to be uncontrollable.

Further, as shown in Examples 1 to 3 , if the Li ion concentration in the molten salt of the inorganic salt composition is in the range of 1230 wt ppm to 5400 wt ppm, the occurrence of white cloudiness can be suppressed by performing the chemical solution treatment. I found out. 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 7,000 wt ppm, the occurrence of white cloudiness cannot be suppressed even if the chemical solution treatment is performed.

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

From these results, when the lithium-containing glass is chemically fortified with the molten salt of the inorganic salt composition containing sodium nitrate, the Li ions in the glass and the Na ions in the molten salt are ion-exchanged, and the Li ions in the molten salt are exchanged. It is considered that white turbidity occurs due to the crystallization of magnesium, phosphorus, silicate, etc. in the glass and Li ions in the molten salt on the glass surface, and the appearance quality deteriorates.

Further, in Table 1, carbonates were used as examples of satisfying the chemical strengthening conditions, but phosphates and hydroxide salts also have the same effect from the viewpoint of Li ion capture.

In Table 1, sodium carbonate was used as an example of satisfying the chemical strengthening condition, but if sodium carbonate is added at a concentration of 1.0 wt% or more, for example, 1.5 wt%, the added sodium carbonate may precipitate. It is necessary to add an inorganic salt within the range where sodium carbonate precipitation does not occur.

According to the production method of the present invention, at least one salt selected from the group consisting of carbonates, phosphates and hydroxide salts contained in the inorganic salt composition captures Li ions in the molten salt. It is considered that the crystallization can be suppressed, the occurrence of white turbidity can be suppressed, and the appearance quality of the obtained chemically strengthened glass can be improved.

According to the method for producing chemically tempered glass of the present invention, it is possible to suppress the occurrence of white fogging in the chemical tempering of lithium-containing glass and to produce chemically tempered glass having excellent appearance quality. The chemically strengthened glass obtained by the production method of the present invention can be used as a cover glass for displays such as mobile phones, digital cameras and touch panel displays.

31 Air dryer 32 Chemical strengthening tank 33 Molten salt

Claims (8)

A method for producing chemically strengthened glass, which comprises a step of ion-exchange between Li ions in the glass and Na ions in the inorganic salt composition by contacting a glass containing lithium with an inorganic salt composition containing sodium nitrate. There,
The ion exchange step is performed in an atmosphere where the dew point temperature is 20 ° C. or lower.
After the ion exchange step, the glass is acid-treated and then further alkaline-treated.
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 wt ppm 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 wt ppm or less. The method for producing chemically strengthened glass according to any one of claims 1 to 3, 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 . The chemically strengthened glass according to any one of claims 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 Na HCO ₃ . Production method. The method for producing chemically strengthened glass according to any one of claims 1 to 7 , wherein the atmosphere in the ion exchange step is formed by introducing a gas dried by an air dryer.

Images