CN111747661A - Manufacturing method of chemically strengthened glass, molten salt composition, and life extension method of molten salt composition - Google Patents

Abstract

The present invention relates to a method for producing chemically strengthened glass, a molten salt composition, and a method for extending the life of a molten salt composition. The method for producing chemically strengthened glass according to the present invention comprises: and a step for chemically strengthening the lithium-containing glass using a molten salt composition that contains at least one of potassium nitrate and sodium nitrate, a different-type anionic compound, and boron as an impurity, wherein the molten salt composition further contains a nitrate of a 2-valent metal.

Description

Manufacturing method of chemically strengthened glass, molten salt composition, and molten salt composition life extension method

technical field

The present invention relates to a method for producing a chemically strengthened glass, a molten salt composition, and a method for extending the life of the molten salt composition.

Background technique

Glass that has been chemically strengthened by ion exchange or the like is used as a cover glass for display devices such as digital cameras, cell phones, and PDAs (Personal Digital Assistants: Portable Information Terminals), etc. for chemically strengthened glass). For chemically strengthened glass used for these applications, high strength is required for both the surface and the end surface in order to satisfy the purpose.

The chemical strengthening treatment by ion exchange is a treatment in which alkali metal ions with a small ionic radius existing near the surface of the glass plate are replaced by alkali metal ions with a larger ionic radius by ion exchange at a temperature below the glass transition temperature. Thereby, compressive stress remains on the surface of the glass, and the strength of the glass is improved.

Li-containing glass (hereinafter, referred to as lithium-containing glass) is a glass that can obtain a deep compressive stress layer depth (hereinafter, referred to as DOL) by high-speed ion exchange (for example, replacement of Li ions with Na ions or K ions) Material. Therefore, in recent years, expectations for developing chemical strengthening treatments for lithium-containing glasses have increased.

The chemical strengthening treatment of the lithium-containing glass differs from the chemical strengthening treatment of the glass not containing Li ions in many points, such as the dissolution of Li ions into the molten salt composition; and the like. In the chemical strengthening treatment of lithium-containing glass, in particular, due to the reduction of the expansion coefficient of the glass before and after the chemical strengthening treatment, the reduction of the stress (CT) of the chemically strengthened glass, and the deterioration of the appearance of the chemically strengthened glass (increase in the haze value) high), the life of the molten salt composition used for chemical strengthening treatment tends to be shortened. This has become a major issue in the management of chemical strengthening treatment of lithium-containing glass.

In chemical strengthening of the lithium-containing glass, as a means for eliminating the influence of Li ions, a method of adding sodium metasilicate or the like as a dissimilar anion compound to the molten salt composition in advance is used. According to this method, by adsorbing Li ions in the molten salt composition by sodium metasilicate, the strengthening performance of the molten salt composition can be recovered, and the CT of the obtained chemically strengthened glass can be improved.

prior art literature

Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 61-178004

SUMMARY OF THE INVENTION

The problem to be solved by the invention

The present inventors have found that when boron is contained as an impurity in a molten salt composition containing a dissimilar anion compound, the appearance of the obtained chemically strengthened glass is deteriorated in the chemical strengthening treatment of the lithium-containing glass, and the molten salt composition The lifespan of things is shortened.

The following mechanism is considered as the reason why the appearance of the chemically strengthened glass is deteriorated by boron. The addition of the dissimilar anion compound increases the pH of the molten salt composition, and boron exists in the form of boric acid at pH 9 or higher. The etching of the glass is accelerated by boric acid, and lithium-containing crystals are formed on the glass surface and the surface layer, the glass surface becomes embrittled, and the crystals fall off, thereby becoming defects and deteriorating the appearance.

Therefore, an object of the present invention is to provide a method for chemically strengthening lithium-containing glass in a molten salt composition containing at least one of potassium nitrate and sodium nitrate, a dissimilar anion compound, and boron as an impurity In the manufacturing method of the chemically strengthened glass of the process, the deterioration of the external appearance of the chemically strengthened glass due to the mixing of boron can be suppressed, and the life of the molten salt composition can be extended.

means to solve the problem

The present inventors have found a method for producing chemically strengthened glass including a step of chemically strengthening lithium-containing glass using a molten salt composition containing at least one of potassium nitrate and sodium nitrate, a dissimilar anion compound, and boron as an impurity Among them, by making the molten salt composition contain a nitrate of a divalent metal, the above-mentioned problems can be solved, and the present invention has been completed.

That is, the present invention provides a method for producing chemically strengthened glass comprising using a molten salt composition containing at least one of potassium nitrate and sodium nitrate, a dissimilar anion compound, and boron as an impurity The process of chemically strengthening the lithium-containing glass, wherein the molten salt composition further contains a nitrate of a divalent metal.

In addition, the present invention provides a molten salt composition that is used for chemical strengthening of lithium-containing glass and contains at least one of potassium nitrate and sodium nitrate, a dissimilar anion compound, and molten boron as an impurity. A salt composition, wherein the molten salt composition further contains a nitrate of a divalent metal.

In addition, the present invention provides a method for prolonging the life of a molten salt composition, which is a method for prolonging the life of a molten salt composition for chemical strengthening of lithium-containing glass, wherein at least one of potassium nitrate and sodium nitrate is included in the method. A divalent metal nitrate is mixed in the molten salt composition of the compound, the dissimilar anion compound, and boron as an impurity.

Invention effect

In the manufacturing method of the chemically strengthened glass of this invention, the divalent metal nitrate is contained in the molten salt composition containing a dissimilar anion compound and containing boron as an impurity. By doing so, the divalent metal ion precipitates boric acid and inhibits the etching of the glass by boric acid, thereby suppressing the deterioration of the appearance of the chemically strengthened glass due to the incorporation of boron, and prolonging the life of the molten salt composition.

Description of drawings

1(A) is a graph showing the relationship between the treated area and DOC1 of the chemically strengthened glass when Ca(NO ₃ ) ₂ ·4H ₂ O is added or not added to the molten salt composition. Fig. 1(B) is a graph showing the relationship between the treated area and the CT of the chemically strengthened glass when Ca(NO ₃ ) ₂ ·4H ₂ O is added or not added to the molten salt composition. Fig. 1(C) is a graph showing the relationship between DOL and CS of chemically strengthened glass when Ca(NO ₃ ) ₂ ·4H ₂ O is added or not added to the molten salt composition.

2 is a graph showing the relationship between the treated area and the CS of the chemically strengthened glass when Ca(NO ₃ ) ₂ ·4H ₂ O is added to the molten salt composition (Example 1).

Detailed ways

Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be implemented with arbitrary modifications without departing from the gist of the present invention.

Hereinafter, although one form of the manufacturing method of the chemically strengthened glass which concerns on this invention is demonstrated, this invention is not limited to this.

The method for producing chemically strengthened glass according to the present invention includes a step of chemically strengthening the lithium-containing glass using a molten salt composition containing at least one of potassium nitrate and sodium nitrate, a dissimilar anion compound, and boron as an impurity, and is characterized by the fact that However, the molten salt composition further contains nitrate of a divalent metal.

(glass composition)

The glass used in the present invention only needs to contain lithium, and any glass of various compositions can be used as long as it has a composition capable of being strengthened by forming and chemical strengthening treatment. Specifically, aluminosilicate glass, soda lime glass, borosilicate glass, lead glass, alkali barium glass, aluminoborosilicate glass, etc. are mentioned, for example.

The method for producing glass is not particularly limited, and it can be produced by throwing a desired glass raw material into a continuous melting furnace, heating and melting the glass raw material at preferably 1500° C. to 1600° C., clarifying it, supplying it to a forming apparatus, and then The molten glass is formed into a plate shape and slowly cooled.

In addition, various methods can be employ|adopted for shaping|molding of glass. For example, various forming methods such as a down-draw method (for example, an overflow down-draw method, an orifice down-draw method, a redraw method, etc.), a float method, a rolling method, and a pressing method can be adopted. Among them, the float method is preferable from the viewpoint that cracks are easily generated in at least a part of the glass surface and the effects of the present invention are more prominently observed.

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

In addition, the shape of the glass used in the present invention is not particularly limited. For example, glass of various shapes such as a flat plate shape having a uniform plate thickness, a shape in which at least one of the front and back surfaces has a curved surface, and a three-dimensional shape having a curved portion or the like can be used. In addition, before the chemical strengthening process, it is preferable to subject glass to shape processing according to the application, for example, mechanical processing such as cutting, end surface processing, and drilling processing.

The content of lithium in the glass used in the present invention is preferably 0.1% to 20% in terms of molar percentage on an oxide basis.

It does not specifically limit as a composition of glass, For example, the composition of the following glass is mentioned.

In terms of molar percentage on oxide basis, it contains 50%-80% SiO ₂ , 2%-25% Al ₂ O ₃ , 0.1%-20% Li ₂ O, 0.1%-18% Na ₂ O, 0%-10% K ₂ O, 0%-15% MgO, 0%-5% CaO, 0%-5% P ₂ O ₅ , 0%-5% B ₂ O ₃ , 0% Composition of -5 _{% Y2O3} and 0-5 _% ZrO2.

The chemically strengthened glass obtained by the production method of the present invention has a compressive stress layer obtained 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 with residual compressive stress. Specifically, at a temperature below the glass transition temperature, alkali metal ions (typically Li ions and Na ions) with a small ionic radius on the surface of the glass plate are replaced by alkali metal ions with a larger ionic radius ( Typically, Na ions or K ions with respect to Li ions, K ions with respect to Na ions). Thereby, compressive stress remains on the surface of the glass, and the strength of the glass is improved.

(molten salt composition)

In the production method of the present invention, chemical strengthening is performed by bringing the lithium-containing glass into contact with the molten salt composition containing at least one of potassium nitrate and sodium nitrate. Thereby, Li ions on the glass surface are ion-exchanged with K ions and Na ions in the molten salt composition, thereby forming a high-density compressive stress layer. As a method of bringing the glass into contact with the molten salt composition, a method of coating a paste-like molten salt composition on the glass, a method of spraying the molten salt composition on the glass, or immersing the glass in a glass heated to a melting point or higher may be used. Among them, the method of immersing glass in the molten salt composition is preferable.

The molten salt composition is preferably a molten salt composition having a melting point below the strain point (usually 500° C. to 600° C.) of the chemically strengthened glass, and in the present invention contains potassium nitrate (melting point: 334° C.) and nitric acid A molten salt composition of at least one of sodium (melting point is 308°C). By containing at least one of potassium nitrate and sodium nitrate, the molten salt is preferably in a molten state below the strain point of the glass and is easy to handle in the operating temperature range (use temperature range). In the molten salt composition, the total content of potassium nitrate and sodium nitrate is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more mass % or more.

The molten salt composition contains a heterogeneous anion compound. The heterogeneous anion compound refers to a compound containing an anion species different from the anion constituting the molten salt. By containing a dissimilar anion compound in a molten salt composition, the dissimilar anion compound in a molten salt composition reacts with Li ion, and Li ion in a molten salt composition can be adsorb|sucked. As a dissimilar anion compound, a dissimilar anion sodium, a dissimilar anion potassium are mentioned, for example. Examples of the dissimilar anion sodium include sodium metasilicate, sodium orthosilicate, sodium sesquisilicate, sodium phosphate, and sodium carbonate. As a dissimilar anion potassium, potassium metasilicate, potassium phosphate, potassium carbonate are mentioned, for example. These dissimilar anion compounds may be used alone or in combination of two or more.

For example, when sodium metasilicate is used as the dissimilar anion compound in the molten salt composition, the reaction formula between the dissimilar anion compound and the Li ion in the molten salt composition is as follows.

Na ₂ SiO ₃ →NaSiO ₃ ^- +Na ⁺

NaSiO ₃ ^- +Li ⁺ →LiNaSiO ₃

SiO ₃ ^2- +2Li ⁺ →Li ₂ SiO ₃

For chemical strengthening treatment of lithium-containing glass, Li ions are present in the glass surface layer due to the dissolution of Li ions into the molten salt composition, and the presence of Li ions in the molten salt composition prevents Li ions in the glass from interacting with each other. Ion exchange of Na ions in molten salt compositions. When the molten salt composition of the present invention contains a dissimilar anion compound, Li ions in the molten salt composition are adsorbed by the dissimilar anion compound to suppress this hindrance, the strengthening performance of the molten salt composition becomes stable, and stress can be increased.

In the molten salt composition, the content of the dissimilar anion compound is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and further preferably 1% by mass or more with respect to the entire molten salt composition. When the content of the dissimilar anion compound in the molten salt composition is 1 mass % or more, Li ions in the molten salt composition can be effectively adsorbed, and the strengthening performance of the molten salt composition can be stabilized. Moreover, content of the dissimilar anion compound in a molten salt composition becomes like this. Preferably it is 10 mass % or less, More preferably, it is 7.5 mass % or less, More preferably, it is 5 mass % or less.

In the molten salt composition, the content of the dissimilar anion compound is preferably 0.1 mol % to 10 mol % with respect to the total content of potassium nitrate and sodium nitrate. By setting the amount of the dissimilar anion compound relative to the total content of potassium nitrate and sodium nitrate to the above range, Li ions in the molten salt composition can be effectively adsorbed, and the strengthening performance of the molten salt composition can be stabilized.

The content of boron contained as an impurity in the molten salt composition is preferably as small as possible, preferably 100 mass ppm or less, more preferably 50 mass ppm or less, and still more preferably 10 mass ppm or less. In addition, the typical content of boron is 10 mass ppm to 50 mass ppm. In addition, containing boron as an impurity means adding boron unintentionally. For example, when boron is contained in impurities of the raw material of the molten salt composition, etc., it can be mixed into the molten salt.

The molten salt composition contains nitrates of divalent metals. As said divalent metal, Ca, Mg, Ba, Zn, Cu, Fe, Pb, Ni, Mn, Sn are mentioned, for example, Ca, Mg, and Ba are preferable. Nitrate of a divalent metal may be used alone or in combination of two or more.

The boron contained in the molten salt composition as an impurity exists in the form of boric acid under high pH conditions, but by including the nitrate of a divalent metal in the molten salt composition, the divalent metal ion can be reacted with boric acid to The boric acid is allowed to settle. Thereby, the deterioration of the appearance of the chemically strengthened glass due to the incorporation of boron can be suppressed, and the life of the molten salt composition can be extended.

As a specific example, about (1) the case of nitrate containing Mg(NO ₃ ) ₂ as a divalent metal in the molten salt composition; (2) the case of containing Ca(NO ₃ ) ₂ as a divalent metal in the molten salt composition In the case of nitrate, the reaction formula between boric acid and metal ions is shown below.

In the molten salt composition, when the boron content per 1 g of the entire molten salt composition is 3.57×10 ⁻² mass ppm or less, the content of the nitrate of the divalent metal is preferably 0.02 mol % or more. By making the content of the nitrate of the divalent metal within the above-mentioned range, the reaction with boron contained in the molten salt composition as an impurity can be positively and appropriately reacted, the influence of boron can be effectively eliminated, and the contamination of boron can be suppressed. The appearance of the chemically strengthened glass deteriorates, and the life of the molten salt composition can be further extended. On the other hand, when the boron content per 1 g of the entire molten salt composition is 3.57×10 ⁻² mass ppm or less, the content of the nitrate of the divalent metal is preferably 0.5 mol % or less, and more preferably 0.3 mol % Below, it is more preferable that it is 0.25 mol% or less. By making content of the nitrate of a divalent metal in the said range, ion exchange will not be inhibited.

In the molten salt composition, the content of the nitrate of the divalent metal is preferably 0.5 mol or more, more preferably 1 mol or more, and further preferably 2 mol or more with respect to 1 mol of boron. When the addition amount of the divalent metal nitrate with respect to boron is within the above-mentioned range, the influence of boron contained in the molten salt composition as an impurity can be effectively eliminated, and the appearance of chemically strengthened glass due to the incorporation of boron can be suppressed. poor, the life of the molten salt composition can be further extended. On the other hand, the content of the nitrate of the divalent metal is preferably 6.5 mol or less, more preferably 6 mol or less, with respect to 1 mol of boron. When the content of the divalent metal nitrate is within the above range, ion exchange is not hindered.

In addition to potassium nitrate and sodium nitrate, the molten salt composition may contain other chemical substances within a range that does not inhibit the effects of the present invention, and examples thereof include nitrates, sulfates, carbonates, and chlorides. Among them, as nitrate, lithium nitrate, cesium nitrate, silver nitrate, etc. are mentioned, for example. As a sulfate, lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, silver sulfate, etc. are mentioned, for example. As carbonate, lithium carbonate, sodium carbonate, potassium carbonate, etc. are mentioned, for example. As a chloride, lithium chloride, sodium chloride, potassium chloride, cesium chloride, silver chloride, etc. are mentioned, for example. These molten salts may be used alone or in combination of two or more.

As a process for chemically strengthening the lithium-containing glass using a molten salt composition containing at least one of potassium nitrate and sodium nitrate, a dissimilar anion compound, and boron as an impurity in the method for producing a chemically strengthened glass of the present invention, For example, glass is immersed in the molten salt composition of about 350 degreeC - about 500 degreeC for 0.1 hour - 10 hours.

The above-mentioned process may be regarded as the first step of strengthening treatment, and after the above-mentioned step, the second and subsequent strengthening treatments may be performed using a molten salt composition containing K ions (for example, a molten salt composition containing potassium nitrate). Preferably, a cleaning step is provided between the first-step strengthening treatment and the second-step strengthening treatment.

Specifically, for example, as the second-step strengthening treatment, the glass is immersed in a K ion-containing metal salt composition (for example, a potassium nitrate-containing molten salt composition) at about 350° C. to about 500° C. for about 0.1 hours to about 10 hours. When the chemical strengthening treatment of the second step and subsequent steps is performed, the total treatment time is preferably 10 hours or less, more preferably 5 hours or less, and even more preferably 3 hours or less, from the viewpoint of production efficiency.

(Life extension method of molten salt composition)

According to the present invention, by including a divalent metal nitrate in the molten salt composition, even when boron is contained as an impurity in the molten salt composition, it is possible to extend the amount of potassium nitrate used for chemical strengthening of the lithium-containing glass. The service life (lifetime) of the molten salt composition of at least one of and sodium nitrate and a heterogeneous anion compound.

Therefore, as one aspect of the present invention, a method for extending the life of a molten salt composition, which is a method for extending the life of a molten salt composition for chemical strengthening of lithium-containing glass, in which potassium nitrate and Nitrate of a divalent metal is mixed with at least one of sodium nitrate, a dissimilar anion compound, and a molten salt composition of boron as an impurity.

In order to quantitatively evaluate the service life (life) of the molten salt composition, the stress (CT) of the chemically strengthened glass, the expansion ratio of the glass before and after chemical strengthening, and the appearance (haze) of the chemically strengthened glass can be used as indexes.

When the stress of the chemically strengthened glass is used as an index of the life of the molten salt composition, the CT value as an index is set as a value obtained from a molten salt containing at least one of potassium nitrate and sodium nitrate in an initial state. The CT value is set to a CT value equal to or greater than a desired value (%) at 100%. In addition, the Li ion concentration in the molten salt composition when the CT value as an index cannot be obtained in the chemical strengthening treatment, that is, when the value (%) is less than the desired value, is used as the service life of the molten salt composition.

When the stress of the chemically strengthened glass is used as an index of the life of the molten salt composition, specifically, for example, the life of the molten salt composition can be evaluated as follows. First, a Li ion source was intentionally added to the molten salt composition in order to simulate a state in which the chemical strengthening treatment was repeated. Then, the lithium-containing glass is chemically strengthened with the molten salt composition to which the Li ion source is added, and when the CT value of the treated glass is lower than the CT value as an index, the Li ion concentration is calculated from the added amount of the Li ion source. , which can be used as an indicator of the life of the molten salt composition.

The expansion coefficient refers to the expansion coefficient of the glass after the chemical strengthening treatment with respect to the glass before the chemical strengthening treatment. When the expansion ratio is used as an index of the life of the molten salt composition, the expansion ratio as the index is set as the expansion ratio obtained from the molten salt containing at least one of potassium nitrate and sodium nitrate in the initial state as The expansion ratio of the desired value (%) at 100%. Moreover, the Li ion concentration in the molten salt composition when the expansion coefficient as an index cannot be obtained in the chemical strengthening treatment, that is, when it is less than a desired value (%), is used as the service life of the molten salt composition.

When the expansion ratio is used as an index of the life of the molten salt composition, specifically, for example, the life of the molten salt composition can be evaluated as follows. First, a Li ion source was intentionally added to the molten salt composition in order to simulate a state in which the chemical strengthening treatment was repeated. Then, the lithium-containing glass is chemically strengthened with the molten salt composition to which the Li ion source is added, and when the expansion coefficient of the treated glass is lower than the expansion coefficient as an index, the Li ion concentration is calculated from the addition amount of the Li ion source. , which can be used as an indicator of the life of the molten salt composition.

When the appearance (haze) of the chemically strengthened glass is used as an index of the life of the molten salt composition, for example, the haze value obtained from the molten salt containing at least one of potassium nitrate and sodium nitrate in the initial state is 0.1 % to 0.2%, for example, the Li ion concentration in the molten salt composition when the haze value is increased to more than 1% is used as the service life of the molten salt composition. "Haze" is measured by the method described in JIS K7136:2000 (ISO14782:1999). For the measurement of the haze, a haze meter (model NDH7000) manufactured by Nippon Denshoku Kogyo Co., Ltd. can be used.

When the haze value is used as an index of the life of the molten salt composition, specifically, for example, the life of the molten salt composition can be evaluated as follows. First, a Li ion source was intentionally added to the molten salt composition in order to simulate a state in which the chemical strengthening treatment was repeated. Then, the lithium-containing glass is chemically strengthened with the molten salt composition to which the Li ion source is added, and when the haze value of the glass after the treatment is greater than the haze value as an index, Li ions are calculated from the added amount of the Li ion source. The concentration can be used as an indicator of the life of the molten salt composition.

[Example]

Hereinafter, although the Example of this invention is demonstrated concretely, this invention is not limited to this.

(glass composition)

As the glass to be chemically strengthened, the glass having the following composition represented by the mol % on an oxide basis was used.

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%

(Evaluation method of glass)

(1) Stress

CT is obtained from the surface compressive stress value (CS, unit: MPa) and the depth of the compressive stress layer (DOC1, unit: μm) when CS is 0, as shown in the following formula. The surface compressive stress value (in MPa) of the glass, the compressive stress value at each depth (in MPa), and the depth of the compressive stress layer (DOL, in μm) were measured using a surface stress meter (FSM- 6000) and a scattered light photoelastic stress meter (SLP-1000) manufactured by Orihara, Ltd. Regarding the stress (CT) in Table 1, when σ≦5, the standard deviation σ of CT in the case where nitrate of divalent metal was not added was evaluated as “no abnormality”.

CT=CS[MPa]*DOC1[mm]/(Glass thickness[mm]-2*DOC1[mm])

(2) Appearance

Regarding the appearance, the boundary value (limit value) of the haze value was set to 1.4%, and the evaluation was performed using the treated area when the haze value was reached. Here, the "treatment area" means the cumulative treatment area (m ² /kg) of the glass after chemical strengthening treatment with the molten salt composition per unit mass of the molten salt composition. The haze (Hz) (%) was measured according to the method specified in JIS K7136:2000 using a haze meter (manufacturer: Nippon Denshoku Kogyo Co., Ltd., model: NDH7000).

(3) Expansion rate

Regarding the expansion coefficient of glass, let the length of any side of the main surface of the glass before chemical strengthening be L ₀ , and the length of the above-mentioned side of the glass after chemical strengthening be L, according to the formula |LL ₀ |/L ×100(%) calculation. In addition, when the "expansion coefficient" in Table 1 was not significantly different from the case where the nitrate of the divalent metal was not added, it was evaluated as "no abnormality".

[Test Example 1] Analysis of the influence of cumulative chemical strengthening treatment on glass/molten salt composition

The chemical strengthening treatment was cumulatively performed, and the influence on the molten salt composition and the glass with the addition of the nitrate of the divalent metal was examined.

Na ₂ SiO ₃ , B, and Ca(NO ₃ ) ₂ ·4H ₂ O, which are materials of the molten salt composition, were added to the cups made of SUS so as to have the contents shown in Table 1, respectively. In addition, sodium nitrate was added, and it heated to 450 degreeC with the mantle type resistance heater, and prepared the molten salt composition.

Prepare glass of the above composition cut into a size of 0.65 mm thick and 50 mm × 50 mm, preheat the glass to 350°C to 400°C, and then as a chemical strengthening treatment, immerse the glass in the molten salt composition, and heat it at 410°C. After being treated at ℃ for 4 hours, it was cooled to around room temperature, and the first chemical strengthening treatment was performed, and then the adhering salt was washed with water.

Next, the glass is preheated to 350°C to 400°C, then the glass is immersed in a molten salt of 100 wt% _KNO3 and treated at 440°C for 1 hour, then cooled to room temperature, and subjected to a second chemical strengthening treatment, then The adhering salt is washed with water. After that, the combination of the first chemical strengthening treatment and the second chemical strengthening treatment is repeatedly performed cumulatively.

The stress, appearance, and expansion coefficient were evaluated for the chemically strengthened glass obtained by the second chemical strengthening treatment, and Table 1 shows the results and the influence by the addition of the salt.

In addition, the influence on the stress in the glass deep part by carrying out the cumulative chemical strengthening treatment is shown in FIGS. 1(A) to (C). Fig. 1(A) shows the case of adding Ca(NO ₃ ) ₂ .4H ₂ O (Example 1) or not adding Ca(NO ₃ ) ₂ .4H ₂ O (Comparative Example 2) to the molten salt composition A graph showing the relationship between the treated area and DOC1 of chemically strengthened glass. Fig. 1(B) shows the case of adding Ca(NO ₃ ) ₂ .4H ₂ O (Example 1) or not adding Ca(NO ₃ ) ₂ .4H ₂ O (Comparative Example 2) to the molten salt composition A graph showing the relationship between the treatment area and the CT of the chemically strengthened glass. Fig. 1(C) shows the case of adding Ca(NO ₃ ) ₂ .4H ₂ O (Example 1) or not adding Ca(NO ₃ ) ₂ .4H ₂ O (Comparative Example 2) to the molten salt composition Graph of the CS relationship between DOL and chemically strengthened glass.

The relationship between the treated area and CS of the chemically strengthened glass when Ca(NO ₃ ) ₂ ·4H ₂ O (Example 1) is added to the molten salt composition as an influence on the stress in the glass surface layer portion is shown in Figure 2.

As shown in Table 1, the lithium-containing glass was chemically strengthened using a composition obtained by adding Ca(NO ₃ ) ₂ .4H ₂ O to a molten salt composition containing sodium nitrate, sodium metasilicate, and boron as an impurity. The following Example 1 showed the same appearance and stress as compared with Comparative Example 1 in which boron was not contained in the molten salt composition. In addition, as compared with Comparative Example 2 after chemical strengthening using a molten salt composition containing boron as an impurity and without adding Ca(NO ₃ ) ₂ .4H ₂ O, Example 1 showed the same stress and expansion ratio, And showed excellent appearance.

As shown in FIGS. 1(A) to (C) , it was found that by using the molten salt composition containing sodium nitrate, sodium metasilicate, and boron as impurities and adding Ca(NO ₃ ) ₂ .4H ₂ O, the The lithium glass was chemically strengthened, and showed the same stress as the comparative example in which Ca(NO ₃ ) ₂ ·4H ₂ O was not added, and the chemical strengthening properties were not hindered. In addition, as shown in FIG. 2 , the lithium-containing glass was subjected to chemical strengthening treatment using a molten salt composition containing sodium nitrate, sodium metasilicate, and boron as impurities and added with Ca(NO ₃ ) ₂ .4H ₂ O. The stress value is the same as that in the case where Ca(NO ₃ ) ₂ ·4H ₂ O is not added, and the chemical strengthening properties are not hindered.

Therefore, it was found that the lithium-containing glass was chemically strengthened by using a composition obtained by adding a divalent metal nitrate to a molten salt composition containing at least one of potassium nitrate and sodium nitrate, a dissimilar anion compound, and boron as an impurity. The treatment can suppress the deterioration of the appearance due to the incorporation of boron, and can prolong the life of the molten salt composition.

[Test Example 2] Liquid phase observation and elemental analysis of molten salt composition

Using a molten salt composition obtained by adding Ca(NO ₃ ) ₂ ·4H ₂ O to sodium nitrate at 450° C. containing 50 mass ppm of boron and 1.15 mass ppm of Na ₂ SiO ₃ The lithium glass is chemically strengthened cumulatively. Table 2 shows the results obtained by measuring the element concentration (mass ppm) in the molten salt composition. Determination of elemental concentrations was carried out by ICP PS3520 UVDIII.

Table 2

As shown in Table 2, it was found that by adding a nitrate of a divalent metal to a molten salt composition containing at least one of potassium nitrate and sodium nitrate, a dissimilar anion compound, and boron as an impurity, the amount of the divalent metal in the molten salt composition can be reduced. boron concentration.

In addition, Ca(NO ₃ ) ₂ ·4H ₂ O was added to the molten salt composition of the treatment area (0 m ² /kg), and the state of the liquid phase was observed after 2 hours, 6 hours, and 25 hours. As a result, it was found that the liquid phase became cloudy immediately after the addition, and the liquid phase of the molten salt composition remained cloudy 2 hours after the addition, but the cloudiness was improved 6 hours after the addition, and 25 hours later, the liquid phase became cloudy. The turbidity of the phase disappeared.

Although this invention was demonstrated in detail with reference to the specific embodiment, it is clear for those skilled in the art that various corrections and changes can be added without deviating from the mind and range of this invention.

This application is based on Japanese Patent Application No. 2019-059039 filed on March 26, 2019, the contents of which are incorporated herein by reference.

Claims (11)

1. A method for producing a chemically strengthened glass, comprising: a step of chemically strengthening a lithium-containing glass using a molten salt composition containing at least one of potassium nitrate and sodium nitrate, a different-type anionic compound, and boron as an impurity,

the molten salt composition also contains a nitrate of a 2-valent metal.

2. The method for producing a chemically strengthened glass according to claim 1, wherein the 2-valent metal is at least one selected from the group consisting of Ca, Mg, and Ba.

3. The method for producing chemically strengthened glass according to claim 1, wherein the 2-valent metal is Ca.

4. The method for producing a chemically strengthened glass according to any one of claims 1 to 3, wherein the content of boron in the molten salt composition is greater than 0 ppm by mass and not greater than 100 ppm by mass.

5. The method for producing a chemically strengthened glass according to any one of claims 1 to 3, wherein a content of the nitrate of the 2-valent metal in the molten salt composition is 0.5 mol or more based on 1 mol of the boron.

6. The method for producing chemically strengthened glass according to any one of claims 1 to 3, wherein the molten salt composition contains the heterogeneous anionic compound in an amount of 0.1 to 10 mol% based on the total amount of potassium nitrate and sodium nitrate.

7. The method for producing a chemically strengthened glass according to any one of claims 1 to 3, wherein the anionic hetero compound is sodium metasilicate or sodium phosphate.

8. The method for producing a chemically strengthened glass according to any one of claims 1 to 3, wherein the method for producing a chemically strengthened glass further comprises: and a step of performing a second stage of chemical strengthening using a molten salt composition containing potassium nitrate.

9. The method for producing a chemically strengthened glass according to any one of claims 1 to 3, wherein a content of the nitrate of the 2-valent metal in the molten salt composition is 6.5 mol or less based on 1 mol of the boron.

10. A molten salt composition for chemical strengthening of lithium-containing glass, the molten salt composition containing at least one of potassium nitrate and sodium nitrate, a different anion compound, and boron as an impurity, wherein the molten salt composition further contains a nitrate salt of a 2-valent metal.

11. A method for prolonging the life of a molten salt composition for use in chemical strengthening of lithium-containing glass, wherein,

a nitrate salt of a 2-valent metal is mixed with a molten salt composition containing at least one of potassium nitrate and sodium nitrate, a different-type anionic compound, and boron as an impurity.

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