TW201512116A - Chemically strengthened glass and method for producing chemically strengthened glass - Google Patents

Abstract

The present invention is chemically strengthened glass having, at the glass surface, a compression stress layer that has been subjected to ion exchange, wherein the chemically strengthened glass has a low-density layer resulting from the surface of the compression stress layer having a lowered density, the thickness of the low-density layer is 5-200 nm inclusive, and the ratio (D1/D3) of the density (D1) of the low-density layer and the density (D3) of an intermediate layer sandwiched between compressive stress layers and extending at the glass center section is at least 0.5 and less than 0.93.

Description

Method for producing chemically strengthened glass and chemically strengthened glass

The present invention relates to a novel chemically strengthened glass and a method of producing the same.

A glass substrate that covers a glass or a display such as a digital camera, a mobile phone, or a PDA (Personal Digital Assistants) is a glass obtained by chemical strengthening treatment by ion exchange or the like (hereinafter sometimes referred to as " Chemically strengthened glass"). Although the theoretical strength of the glass is high, the strength is greatly reduced due to the damage. Chemically strengthened glass has higher mechanical strength than unreinforced glass and prevents damage to the glass surface, so it is suitable for such applications.

Moreover, in recent years, the example used as the cover glass for solar cells has also increased. By replacing the existing cover glass with chemically strengthened glass, the same degree of mechanical strength can be achieved even if the thickness is reduced. By the weight reduction of the glass, there is an advantage that it is provided in a portion that was previously impossible to be set due to weight limitation, or that the load on the construction is reduced.

Chemical strengthening treatment by ion exchange generates compressive stress on the glass surface by replacing metal ions (such as Na ions) having a small ionic radius in the glass with metal ions (such as K ions) having a larger ionic radius. The layer, which increases the strength of the glass.

Further, in various displays and the like, an anti-reflection function is often required, and in the tempered glass reinforced by chemical treatment by ion exchange, an anti-reflection function is also required. Usually in chemically strengthened glass, after the antireflection film is formed, K ions cannot be diffused. It is difficult to carry out the strengthening treatment to the inside of the glass. Therefore, it is necessary to form an anti-reflection film after the strengthening treatment.

In order to impart low reflectivity to the obtained chemically strengthened glass, an antireflection film is formed as a multilayer film or a single layer film on the surface of the glass. As a method of coating an antireflection film of a multilayer film on a surface of a substrate, a method of sequentially laminating a film having a relatively high refractive index and a film having a relatively low refractive index on a substrate, or alternately laminating a plurality of layers by the above lamination method is known. A technique of obtaining a multilayer film with a film having a relatively high refractive index and a relatively low refractive index (Patent Document 1).

As a method of forming an antireflection film, a sol-gel method of coating a coating liquid containing fine particles and forming a gelled antireflection film by heat treatment is low in production cost and high in production, so currently Is becoming the mainstream. As the antireflection film formed by such a sol-gel method, for example, a hydrolysis condensate containing a ruthenium compound, a metal chelate compound, and a low refractive ruthenium sol are known (Patent Document 2).

On the other hand, in recent years, there has been disclosed a method for producing an antireflection-strengthened glass in which an antireflection film is optimized, a chemical strengthening treatment is performed after forming an antireflection film, and K ions are diffused into the inside of the glass. Strengthening of glass (Patent Document 3).

Further, by having a specific texture structure on the surface, it is possible to impart low reflectivity (Patent Document 4).

Further, the low reflectivity of the glass means that the transmittance is high, and the transmittance is improved by lowering the density of the glass surface, that is, lowering the refractive index.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 4-357134

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2002-221602

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2011-88765

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2013-40091

However, in the prior art which imparts low reflectivity to the chemically strengthened glass, when the antireflection film contains two or more layers of the film as in Patent Document 1, the antireflection effect can be surely exhibited by the optical design. However, there is an incident angle dependency of the reflectance, and since the number of times of coating the film needs to be two or more, it is inevitable that the manufacturing cost is increased. On the other hand, when the antireflection film is formed of a single layer, the heat treatment and the etching treatment are performed after the metal oxide film is temporarily formed, or the chemical reaction treatment with the gas is performed after the metal oxide film is temporarily formed. Therefore, although it is a single-layer anti-reflection film, it is difficult to achieve a reduction in manufacturing cost.

Further, in the method of forming an antireflection film by a sol-gel method before chemical strengthening of glass, as in Patent Document 2, since it is necessary to form an antireflection film one by one for a product subjected to chemical strengthening treatment, productivity is also obtained. Significantly reduced, the advantages of the high productivity inherent in the sol-gel process are lost.

On the other hand, even if the method of forming an antireflection film before the chemical strengthening treatment as described in Patent Document 3, at least the following three steps must be performed before the chemical strengthening treatment step.

(1) A step of preparing a coating liquid from a ruthenium compound, a hollow ruthenium sol, and a metal chelating compound in advance.

(2) A step of applying a coating liquid onto the glass.

(3) The steps of drying and heat treating the glass.

Due to these steps, in addition to the need for previous chemical strengthening treatment equipment, new investment in equipment is also required.

Further, in Patent Document 4, it is necessary to have a processing process different from the chemical strengthening treatment of glass such as a textured structure on the glass surface, and it is necessary to have a high cost in order to manufacture a low-reflection chemically strengthened glass to which low reflectivity is imparted. Moreover, in terms of manufacturing particularity, it is very difficult to perform low-reflection treatment on both sides of the chemically strengthened glass or to perform large-area low-reflection treatment. difficult.

Accordingly, an object of the present invention is to provide a chemically strengthened glass having a low density layer (low refractive index layer) in a surface layer by forming a modified layer called a low density layer by densifying the surface of the chemically strengthened glass. Its manufacturing method.

As a result of intensive research, the inventors of the present invention found that by adding a specific salt to the molten salt used in the chemical strengthening treatment, the Na concentration in the molten salt is maintained at a constant value or more and after chemical strengthening treatment. The glass is subjected to at least one of acid treatment, and a chemically strengthened glass in which one sheet of glass is used as a raw material and whose surface layer has been imparted with low reflectivity can be obtained, thereby completing the present invention.

That is, the present invention relates to the following <1> to <7>.

<1> A chemically strengthened glass comprising an ion-exchanged compressive stress layer on a surface of a glass, comprising: a low-density layer obtained by lowering a surface of the compressive stress layer, wherein the thickness of the low-density layer is 5 nm or more and 200 nm or less, and the ratio (D1/D3) of the density (D1) of the low-density layer to the density (D3) of the intermediate layer which is present in the center portion of the glass and sandwiched in the compressive stress layer is 0.5 or more and is not Up to 0.93.

<2> The chemically strengthened glass according to the above <1>, wherein the H/(Na+K) molar ratio (C1) of the low-density layer is larger than the H/(Na+K) molar ratio (C3) of the intermediate layer. , ie (C1>C3).

<3> The chemically strengthened glass according to <1> or <2> above, wherein the low density layer has a H/(Na+K) molar ratio (C1) of 1.0 or more.

The chemically strengthened glass according to any one of <1> to <3> wherein the glass is an aluminosilicate glass or a soda lime glass.

<5> A method for producing a chemically strengthened glass by ion-exchange of Na in the glass with K in the molten salt by immersing the glass in a molten salt containing potassium nitrate, and including melting to the above Adding to the salt is selected from the group consisting of K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ , NaHCO ₃ , K ₃ PO ₄ , Na ₃ PO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , KOH and NaOH. a step of at least one salt and a step of washing the glass after the ion exchange, and further comprising the step of causing the Na concentration in the molten salt to be 500 ppm by weight or more and the step of subjecting the glass to acid treatment after the washing At least either step.

<6> The method for producing a chemically strengthened glass according to the above <5>, which comprises the steps of: setting the Na concentration in the molten salt to 500 ppm by weight or more, and subjecting the glass to acid treatment after the washing.

<7> The method for producing a chemically strengthened glass according to the above <5>, wherein the step of causing the Na concentration in the molten salt to be 500 ppm by weight or more includes a step of adding a Na salt to the molten salt.

The chemically strengthened glass of the present invention imparts low reflectivity by including a low-density layer in which the surface of the ion-exchanged compressive stress layer is reduced in density, and further requires no processing steps for using other means for imparting low reflectivity. . Therefore, when manufacturing a chemically strengthened glass of low reflectivity, the cost can be reduced compared with the prior art.

Further, according to the method for producing a chemically strengthened glass of the present invention, a sheet of glass is used as a raw material, and a compressive stress layer and a low-density layer are formed on the surface thereof, whereby a chemically strengthened glass having low reflectivity can be obtained, so that a large area can be obtained. It is very useful to perform low reflection treatment on both sides of the glass or glass.

1‧‧‧Low density layer

2‧‧‧Compressive stress layer

3‧‧‧Intermediate

Fig. 1 (a) to (c) are schematic views showing the steps of producing the chemically strengthened glass of the present invention.

Fig. 2 is a view showing the distribution of H and Si in the region of the depth of 500 nm from the surface of Example 1 by RBS-ERDA analysis.

The present invention will be described in detail below, but the present invention is not limited to the embodiments described below, and may be carried out without departing from the scope of the invention.

Here, in the present specification, the meanings of "% by mass" and "% by weight", "ppm by mass" and "ppm by weight" are respectively the same.

In the present specification, the expression "Na concentration" means the concentration in terms of Na.

<Chemical tempered glass>

The chemically strengthened glass of the present invention has an ion-exchanged compressive stress layer on the surface of the glass, and has a low-density layer in which the surface of the compressive stress layer is further reduced in density.

In the present specification, the "compressive stress layer" is a high-density layer formed by immersing a glass as a raw material in an inorganic potassium molten salt such as potassium nitrate to form a Na ion and a molten salt on the surface of the glass. The K ion in the ion exchange.

(molten salt)

The molten salt for glass reinforcement (hereinafter sometimes simply referred to as "molten salt") for obtaining the chemically strengthened glass of the present invention contains an inorganic potassium salt. The inorganic potassium salt preferably has a melting point below the strain point (usually 500 to 600 ° C) of the glass subjected to chemical strengthening. In the present invention, it is preferred to contain potassium nitrate (melting point 330 ° C) as a main component. salt. When potassium nitrate is a main component, it is preferably in a molten state below the strain point of the glass, and it is easy to handle in the use temperature region. Here, the main component means that the content in the molten salt is 50% by mass or more.

Hereinafter, the inorganic potassium salt of the molten salt will be described by taking "potassium nitrate molten salt" containing potassium nitrate as a main component as an example.

The molten salt preferably further comprises a component selected from the group consisting of K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ , NaHCO ₃ , K ₃ PO ₄ , Na ₃ PO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , KOH and NaOH. At least one salt of the group, more preferably containing at least one salt selected from the group consisting of K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ and NaHCO ₃ .

K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ , NaHCO ₃ , K ₃ PO selected from the properties of a network having a network in which a glass represented by a Si—O—Si bond is cleaved is added to a molten salt of potassium nitrate. _4. At least one salt of a group consisting of Na ₃ PO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , KOH, and NaOH (hereinafter sometimes referred to as "flux"). Since the temperature at which the chemical strengthening treatment is performed is as high as several hundred ° C, the covalent bond between the Si—O of the glass is appropriately cut at this temperature, and the lower density treatment described later is facilitated.

Further, the degree of cutting the covalent bond varies depending on the glass composition, the type of the inorganic salt (flux) to be used, and the chemical strengthening treatment conditions such as the temperature and time at which the glass is immersed in the molten salt, and it is considered to be preferable. The condition for cutting off one or two of the four covalent bonds from which Si is extended is selected.

For example, when K ₂ CO _{3 is} used as the flux, if the content of the flux in the molten salt is 0.1% by weight or more and the chemical strengthening treatment temperature is 350 to 500° C., the chemical strengthening treatment time is preferably 1 Minutes to 10 hours, more preferably 5 minutes to 8 hours, and further preferably 10 minutes to 4 hours.

From the viewpoint of productivity, the amount of the flux added is preferably equal to or less than the saturated solubility at the temperature at which the molten salt is used, and if it is excessively added, there is a possibility of causing corrosion of the glass.

In addition to the potassium nitrate and the flux, the molten salt may contain other chemical species within a range that does not inhibit the effects of the present invention, and examples thereof include alkali metal chlorides or alkalis such as sodium chloride, potassium chloride, sodium borate, and potassium borate. Metal borate, etc. These may be added alone or in combination.

(Method 1 of manufacturing molten salt)

The molten salt can be produced by the steps shown below.

Step 1a: Preparation of potassium nitrate molten salt

Step 2a: adding the flux to the potassium nitrate molten salt prepared in the above step 1a

(Step 1a - Preparation of potassium nitrate molten salt -)

In the step 1a, potassium nitrate is introduced into a vessel, heated to a temperature above the melting point, and melted, thereby preparing a molten salt. Since the melting point of potassium nitrate is 330 ° C and the boiling point is 500 ° C, Melting is carried out at a temperature within this range. In terms of the balance between the surface compressive stress (CS) and the compressive stress layer depth (DOL) imparted to the glass and the strengthening time, it is particularly preferable to set the melting temperature to 350 to 470 °C.

A metal, quartz, ceramic, or the like can be used for the container in which potassium nitrate is melted. Among them, from the viewpoint of durability, a metal material is preferable, and a stainless steel (SUS) material is preferable from the viewpoint of corrosion resistance.

(Step 2a - Addition of flux to the potassium nitrate molten salt prepared in step 1a -)

In the step 2a, the above-mentioned flux is added to the potassium nitrate molten salt prepared in the step 1a, and while maintaining the temperature within a certain range, the mixture is mixed by a stirring blade or the like to make the whole uniform. When a plurality of kinds of fluxes are used in combination, the order of addition is not limited and may be added at the same time.

The temperature is preferably not less than the melting point of potassium nitrate, i.e., 330 ° C or higher, more preferably 350 to 500 ° C. Further, the stirring time is preferably from 1 minute to 10 hours, more preferably from 10 minutes to 2 hours.

(Manufacturing method 2 of molten salt)

In the method 1 for producing a molten salt, a method of adding a flux after preparing a molten salt of potassium nitrate has been exemplified, and a molten salt can also be produced by the steps shown below.

Step 1b: Mixing potassium nitrate with flux

Step 2b: melting of the mixed salt obtained in the above step 1b

(Step 1b - Mixing Potassium Nitrate with Flux -)

In the step 1b, potassium nitrate and a flux are put into a container, and mixing is performed by a stirring blade or the like. When a plurality of kinds of fluxes are used in combination, the order of addition is not limited and may be added at the same time. The container can use the same one as the user in the above step 1a.

(Step 2b - Melting of the mixed salt obtained in Step 1b -)

In the step 2b, the mixed salt obtained in the step 1b is heated and melted. Since potassium nitrate has a melting point of 330 ° C and a boiling point of 500 ° C, it is melted at a temperature within this range. The surface compressive stress (CS) and compressive stress layer depth (DOL) that can be imparted to the glass In terms of balance and strengthening time, it is particularly preferable to set the melting temperature to 350 to 470 °C. The stirring time is preferably from 1 minute to 10 hours, more preferably from 10 minutes to 2 hours.

In the molten salt obtained by the above steps 1a and 2a or steps 1b and 2b, when a precipitate is generated by the addition of a flux, it is allowed to stand until the precipitate precipitates before the chemical strengthening treatment of the glass is performed. Until the bottom of the container. A flux containing an amount exceeding the saturated solubility or a salt obtained by exchanging the cation of the flux in the molten salt is contained in the precipitate.

Above, the molten salt can be prepared by the above steps 1a and 2a or steps 1b and 2b. In the following, step 1a or 1b may be simply referred to as "step 1", and step 2a or 2b may be simply referred to as "step 2".

Moreover, after step 2, the following step 2' can also be performed as needed.

Step 2': Adjustment of Na concentration in molten salt

The Na concentration in the molten salt can be adjusted by adding Na salt represented by NaNO ₃ to the molten salt to be produced. The details of step 2' will be described later.

(Chemical strengthening treatment - formation of compressive stress layer -)

Next, the chemical strengthening treatment method will be described.

The chemical strengthening treatment is carried out by immersing the glass in a molten salt to replace metal ions (Na ions) in the glass with metal ions (K ions) having a large ionic radius in the molten salt. By changing the composition of the glass surface by the ion exchange, the compressive stress layer 2 having a high density of the glass surface can be formed. Since the compressive stress is generated due to the high density of the glass surface, the glass can be strengthened [Fig. 1 (a) to (b)].

Furthermore, in practice, the density of the chemically strengthened glass is gradually increased from the outer edge of the intermediate layer 3 existing in the center of the glass toward the surface of the compressive stress layer, so that there is no sharp density between the intermediate layer 3 and the compressive stress layer 2. The clear boundary of change. Here, the intermediate layer means a layer existing in the center portion of the glass and sandwiched in the compressive stress layer. The intermediate layer, unlike the compressive stress layer, is a layer that is not ion exchanged.

Specifically, the chemical strengthening treatment of the present invention can be carried out by the following step 3.

Step 3: Chemical strengthening treatment of glass

(Step 3 - Chemical strengthening treatment of glass -)

In step 3, the glass is preheated, and the molten salt prepared in the above steps 1 and 2 or the above steps 1, 2 and 2' is adjusted to a temperature at which chemical strengthening is performed. Next, after the preheated glass is immersed in the molten salt for a certain period of time, the glass is lifted from the molten salt and left to cool. Further, it is preferred to process the glass according to the shape of the application before the chemical strengthening treatment, for example, cutting, end surface processing, and drilling.

The preheating temperature of the glass depends on the temperature immersed in the molten salt, and is usually preferably 100 ° C or more.

The chemical strengthening temperature is preferably below the strain point of the tempered glass (usually 500 to 600 ° C), and is preferably 350 ° C or more in order to obtain a larger compressive stress layer depth.

The immersion time of the glass in the molten salt is preferably from 1 minute to 10 hours, more preferably from 5 minutes to 8 hours, and still more preferably from 10 minutes to 4 hours. When it is in this range, the chemically strengthened glass which is excellent in the balance of the strength and the depth of the compressive stress layer can be obtained.

(low density layer)

The chemically strengthened glass of the present invention further has a low-density layer 1 in which the surface of the compressive stress layer 2 is reduced in density [Fig. 1 (b) to (c)].

The so-called low-density layer is formed by Na (or) escaping (leaching) from the outermost surface of the compressive stress layer, and H is introduced (displaced), and can be formed by at least one of the above step 2' and the following step 5 One is done. Furthermore, the details of step 5 will be described later, and step 4 below is performed before step 5.

Step 4: Washing the glass Step 5: Acid treatment of the glass after step 4

(Step 4 - Washing the glass -)

In step 4, the glass is washed with industrial water, ion exchange water or the like. Among them, ion exchange water is preferred. The conditions for washing vary depending on the cleaning liquid to be used, and in the case of using ion-exchanged water, in terms of completely removing the adhered salt, it is preferably Wash at 0~100 °C.

However, even if the glass is chemically strengthened only in the molten salt to which the flux is added, the permeability of the chemically strengthened glass can be slightly improved as compared with the case where the chemical strengthening treatment is performed in the molten salt to which no flux is added. The reason for this is considered to be that the surface of the compressive stress layer is reduced in density even if the above-described leaching is caused only by the usual washing step using water. However, it is considered that the effect of forming the low-density layer in this case is weak, and the effect is further promoted by the following step 5.

As described above, by lowering the surface of the compressive stress layer of the chemically strengthened glass to lower the refractive index, it is possible to obtain a glass having a low reflectivity in which the transmittance of the glass is improved.

The density of the low density layer can be determined by the critical angle (θc) measured by X-ray-reflection spectroscopy (XRR). Further, the thickness of the low-density layer can be obtained from the period (Δθ) measured by XRR. Further, in simple terms, the formation of the low-density layer and the thickness of the layer can be confirmed by observing the cross section of the glass by a scanning electron microscope (SEM). Further, the density of the intermediate layer can be obtained in the same manner by removing the compressive stress layer by polishing, etching, or the like.

The Na/Si molar ratio and the K/Si molar ratio of the low density layer can be confirmed by X-ray photoelectron spectroscopy (XPS), and the H/Si molar ratio can be reversed by the Raspford It was confirmed by Rutherford Backscattering Spectrometry (RBS)-Elastic Recoil Detection Analysis (ERDA). That is, the H/(Na+K) molar ratio of the low density layer can be determined by XPS and RBS-ERDA. Further, the H/(Na+K) molar ratio of the intermediate layer can be obtained in the same manner by removing the compressive stress layer by polishing, etching, or the like.

The thickness of the low-density layer is preferably 5 nm or more and 200 nm or less, and more preferably 50 nm or more and 200 nm or less, depending on the maximum wavelength of light transmitted through the glass.

The density of the low density layer is from the viewpoint of the low reflectivity of the obtained chemically strengthened glass. The ratio (D1/D3) of the degree (D1) to the density (D3) of the intermediate layer is preferably 0.5 or more and less than 0.93, more preferably 0.7 or more and less than 0.85, still more preferably 0.7 or more and less than 0.8.

Further, the relationship between the H/(Na+K) molar ratio (C1) of the low-density layer and the H/(Na+K) molar ratio (C3) of the intermediate layer is preferably C1>C3.

In terms of imparting low reflectivity, the H/(Na+K) molar ratio (C1) of the low-density layer is preferably 1.0 or more, and more preferably 10.0 or more.

(Step 2'-Adjustment of Na concentration in molten salt -)

In the step 2', the Na concentration in the molten salt used in the chemical strengthening treatment of the above step 3 is adjusted to 500 ppm by weight or more as needed.

By setting the Na concentration in the molten salt to 500 ppm by weight or more, it is easy to cut the network structure on the outermost surface of the glass and to reduce the density, and to deepen the low-density layer.

The Na concentration in the molten salt can be adjusted by adding an inorganic sodium salt represented by sodium nitrate.

(Step 5 - Acid treatment of the glass after step 4 -)

In step 5, the glass washed in step 4 is further subjected to an acid treatment.

When the step 5 is carried out after the step 4, the chemically strengthened glass to be washed is subjected to an acid treatment to promote the lowering of the outermost surface of the compressive stress layer of the chemically strengthened glass. Further, in the case where the step 5 is carried out after performing the chemical strengthening treatment in the molten salt in which the Na concentration is adjusted in the step 2', further deepening of the low-density layer can be achieved.

The acid treatment of glass is a treatment in which Na and/or K on the surface of the chemically strengthened glass is replaced with H by immersing the chemically strengthened glass in an acidic solution.

The solution is not particularly limited as long as it is acidic, and the acid to be used may be a weak acid or a strong acid, and is not affected by the pH. Specifically, an acid such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, oxalic acid, carbonic acid or citric acid is preferred. These acids may be used singly or in combination of plural kinds.

The temperature at which the acid is treated is also dependent on the type or concentration of the acid used, and the time. The difference is preferably 100 ° C or less.

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

The concentration of the acid-treated solution varies depending on the kind, time, and temperature of the acid to be used, but it is preferably a concentration at which the container is less corroded.

The thickness of the formed low density layer can be controlled by the type of acid used, the concentration of the acid, the temperature of the acid treatment, the time, and the like.

The maximum transmission wavelength of the light transmitted through the glass is determined by the thickness of the low-density layer. Therefore, the acid treatment conditions may be appropriately determined depending on the use of the chemically strengthened glass.

As described above, the thickness of the low density layer is preferably from 5 to 200 nm, more preferably from 50 to 200 nm. There is a tendency that the acid treatment conditions are prolonged, such as the acid treatment time is prolonged, and the increase in the transmittance is increased.

Based on these contents, the acid treatment conditions are appropriately determined depending on the circumstances.

Further, in the case where the low-densification treatment is carried out by the acid treatment in the step 5, it is preferable that the Na concentration and the K concentration in the low-density layer are both lower than the H concentration because a chemically strengthened glass having lower reflectivity can be obtained.

<glass>

The glass to be used in the present invention may be any one 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, alkali bismuth glass, and aluminum borosilicate glass.

The method for producing the glass is not particularly limited, and it can be produced by introducing a desired glass raw material into a continuous melting furnace, heating and melting the glass raw material at 1,500 to 1600 ° C, clarifying, and then supplying it to a forming apparatus. Thereafter, the molten glass is formed into a plate shape and slowly cooled.

Further, 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 flow-down method, and a re-drawing method), a floating method, a rolling method, and a pressing method can be employed.

The thickness of the glass is not particularly limited, and is usually preferably 5 mm or less, more preferably 3 mm or less, in order to carry out the chemical strengthening treatment efficiently.

The composition of the glass for chemical strengthening of the present invention is not particularly limited, and examples thereof include the following glass compositions. (i) containing 50 to 80% of SiO ₂ , 2 to 25% of Al ₂ O ₃ , 0 to 10% of Li ₂ O, and 0 to 18% of Na ₂ O, in terms of composition represented by % by mole. 0 to 10% of K ₂ O, 0 to 15% of MgO, 0 to 5% of CaO, and 0 to 5% of ZrO ₂ glass

(ii) The composition expressed by mole % is 50 to 74% SiO ₂ , 1 to 10% Al ₂ O ₃ , 6 to 14% Na ₂ O, 3 to 11% K ₂ O, 2 ~15% of MgO, 0 to 6% of CaO, and 0 to 5% of ZrO ₂ , the total content of SiO ₂ and Al ₂ O ₃ is 75% or less, and the total content of Na ₂ O and K ₂ O is 12 ~25%, the total content of MgO and CaO is 7~15% glass

(iii) The composition expressed by mol% is 68 to 80% SiO ₂ , 4 to 10% Al ₂ O ₃ , 5 to 15% Na ₂ O, 0 to 1% K ₂ O, 4 ~15% of MgO and 0~1% of ZrO ₂ glass

(iv) The composition expressed by mol% is 67 to 75% SiO ₂ , 0 to 4% Al ₂ O ₃ , 7 to 15% Na ₂ O, 1 to 9% K ₂ O, 6 ~14% of MgO and 0~1.5% of ZrO ₂ , the total content of SiO ₂ and Al ₂ O ₃ is 71~75%, and the total content of Na ₂ O and K ₂ O is 12-20%, and Glass containing less than 1% in the case of CaO

In the case of polishing the glass before the chemical strengthening treatment, for example, a method of polishing the polishing slurry while polishing the polishing slurry may be used, and the polishing slurry may contain an abrasive material and water. As the abrasive, cerium oxide (ceria) and cerium oxide are preferred.

When the glass is ground, the polished glass is washed with a cleaning liquid. net. As the cleaning liquid, a neutral lotion and water are preferred, and it is more preferably washed with water after washing with a neutral detergent. As a neutral lotion, a commercially available person can be used.

The glass substrate washed by the above-described washing step is finally washed with a cleaning liquid. Examples of the cleaning liquid include water, ethanol, and isopropyl alcohol. Among them, water is preferred.

After the final washing described above, the glass was dried. The drying conditions may be selected in consideration of the conditions of the cleaning liquid used in the washing step, the characteristics of the glass, and the like.

The above-mentioned washed glass is applied to the above step 3 of the chemical strengthening treatment.

The chemically strengthened glass of the present invention has been described above, and the chemically strengthened glass of the present invention can be produced by including at least one of the following steps 1 to 4 and steps 2' and 5. Wherein, by including step 2', the low-density layer can be deepened, and by including step 5, the low-density layer can be further deepened, and more preferably, steps 2' and 5 are included. Furthermore, the details of each step are as described above.

Step 1: Preparation of potassium nitrate molten salt (1a) or mixing of potassium nitrate with flux (1b)

Step 2: melting of the molten salt in the potassium nitrate molten salt prepared in the above step 1a (2a) or the mixed salt obtained in the above step 1b (2b)

Step 2': Adjustment of Na concentration in molten salt

Step 3: Chemical strengthening treatment of glass

Step 4: Washing the glass Step 5: Acid treatment of the glass after the above step 4

[Examples]

The present invention will be specifically described below by way of examples, but the present invention is not limited thereto.

<Evaluation method>

In the present embodiment, the structure of the synthesized compound was carried out by the analysis method shown below.

(Evaluation of glass: transmittance)

The transmittance of the glass is measured by using a spectrophotometer (U-4100 manufactured by Hitachi High-Technologies Co., Ltd.) to measure the transmission spectrum in the wavelength range of 300 nm to 1000 nm, and the maximum value of the transmittance in the wavelength range is calculated. _Max .

(Evaluation of glass: density D1 of low density layer, thickness T1 of low density layer)

The density and film thickness of the modified layer formed on the surface of the glass were measured by an X-ray diffraction apparatus (manufactured by Rigaku: ATX-G, X-ray source: Cu-Kα) by X-ray reflectance method (XRR). And find it. The density was calculated from the critical angle (θc) of the X-ray reflectance pattern, and the thickness of the layer was calculated from the interference period (Δθ). The analysis was calculated using GlobalFit Ver. 1.3.3 (Rigaku Co., Ltd.).

(Measurement of density D3 of the intermediate layer)

The substrate on which the compressive stress layer is removed by polishing, etching, or the like is prepared, and the density D3 of the intermediate layer is calculated by the X-ray reflectance method.

(Measurement of H/(Na+K) Mo Er ratio C1 in low density layer)

The Na/Si and K/Si molar ratios of the modified layer formed on the surface of the glass were measured by X-ray photoelectron spectroscopy (XPS). The XPS analysis was carried out after removing the surface contamination of the sample using a C ₆₀ ion sputtering gun mounted on the same device.

The H/Si molar ratio was determined using Rutherford Backscattering Spectrometry (RBS)-Elastic Recoil Detection Analysis (ERDA). When the H/Si molar ratio is obtained by RBS-ERDA analysis, the influence of surface contamination caused by organic matter must be considered. Here, it is assumed that the amount of surface-contaminated organic matter is 3 × 10 ¹⁵ atoms/cm ² , and the density of the surface-contaminated organic substance is assumed to be 10 × 10 ²² atoms/cm ³ .

Furthermore, in the case where the phenomenon that the H count decreases with time is confirmed in the ERDA analysis, corrections to be taken into consideration are required. According to the Na/Si molar ratio and the K/Si molar ratio obtained by XPS analysis, the H/Si molar ratio obtained by RBS-ERDA analysis finds H/(Na +K) Moerby. The analysis conditions for XPS and RBS-ERDA analysis are as follows.

(XPS analysis)

Device: ESCA5500 manufactured by PHYSICAL ELECTRONICS

X-ray source: Al Kα

Tongneng: 93.9eV

Energy level: 0.8eV/step

Detection angle: 15° with respect to the normal of the sample surface

Ion species for sputter guns used to remove surface contamination: C ₆₀ ions

Analysis software: MultiPak Ver.9.3.0.3

(RBS-ERDA analysis)

Device: Pelletron 3SDH manufactured by National Electrostatics Corporation

Incident ion: He ⁺⁺

Energy of incident ions: 2.3 MeV

RBS scattering angle: 160 degrees

ERDA scattering angle: 30 degrees

Incidence angle: 75 degrees from the normal to the sample surface

Sample current: 2nA

Irradiation: 10μC

(Measurement of H/(Na+K) Mo Er ratio C3 in the middle layer)

It is preferable to prepare a substrate in which the compressive stress layer is removed by grinding, etching, or the like, and perform XPS analysis and RBS- in the same manner as the measurement of the H/(Na+K) molar ratio C1 of the low-density layer. The ERDA analysis calculates the H/(Na+K) molar ratio C3 of the intermediate layer. However, here, C3 is obtained by a method calculated based on the glass composition described later. When the glass composition is known and the H concentration in the region where the lower density layer is deeper is below the detection limit of the ERDA analysis (1 mol% or less), the substrate having the compressive stress layer removed by polishing, etching, or the like is not prepared. It is also easy to calculate the value of C3.

<glass>

As the glass to be chemically strengthened, two types of glass of soda lime glass and aluminosilicate glass of the following composition are used.

Soda lime glass (composition expressed as % by mole): SiO ₂ 72.0%, Al ₂ O ₃ 1.1%, Na ₂ O 12.6%, K ₂ O 0.2%, MgO 5.5%, CaO 8.6%

Aluminosilicate glass (composition expressed as % by mole): SiO ₂ 64.4%, Al ₂ O ₃ 8.0%, Na ₂ O 12.5%, K ₂ O 4.0%, MgO 10.5%, CaO 0.1%, SrO 0.1 %, BaO 0.1%, ZrO ₂ 0.5%

The above glass is used for being polished before being subjected to chemical strengthening treatment. For the polishing conditions, LP-66 is used for the foamed polyurethane pad, and Luminox (having an average particle diameter of 0.75 to 1.25 μm and a specific gravity of 1.05 to 1.15 g/cm ³ ) is used as the abrasive particles. The polishing rate was set to 0.07 to 0.10 μm/min, the processing pressure was set to be about 0.15 kg/cm ² , the single side was removed by 50 μm or more, and the total of both surfaces was removed by 150 μm.

<Example 1>

2568 g of potassium nitrate, 321 g of potassium carbonate, and 111 g of sodium nitrate were placed in a cup made of stainless steel (SUS), and heated to 450 ° C in a heating mantle to prepare a molten salt of 8 mol% of potassium carbonate and a concentration of Na of 10,000 ppm by weight. The prepared molten salt was stirred for 2 hours using a stirring motor and 4 blades to uniformly mix the whole.

The aluminum silicate glass of 50 mm × 50 mm × 0.7 mm was preheated to 200 ° C to 400 ° C, and then immersed in a molten salt of 450 ° C for 2 hours to carry out chemical strengthening treatment. After the strengthening treatment, the glass was washed twice with ion-exchanged water at 50 ° C to 90 ° C, washed with running water at room temperature with ion-exchanged water, and dried at 60 ° C for 2 hours.

The physical properties of the obtained glass were measured, and D1/D3 and C1 were calculated. The measurement results and the calculation results are shown in Table 2.

<Examples 2, 12>

Add 402g of potassium nitrate and 47.9g of potassium carbonate to the cup made of SUS. A molten salt of 8 mol% of potassium carbonate was prepared by heating to 450 °C. The prepared molten salt was stirred for 2 hours using a stirring motor and 4 blades to uniformly mix the whole.

After the aluminosilicate glass (Example 2) or the soda lime glass (Example 12) was reinforced, washed, and dried in the same manner as in Example 1, the acid treatment was carried out in the following order.

1 mol/L (1 M) of hydrochloric acid was prepared in a beaker, and the temperature was adjusted to 40 ° C using a water bath. The chemically strengthened glass was subjected to an acid treatment by immersing it in the prepared hydrochloric acid for 5 minutes, and then washed with ion-exchanged water for 3 times, and then dried at 60 ° C for 2 hours.

The physical properties of the obtained glass were measured, and D1/D3 was calculated. The measurement results and the calculation results are shown in Table 2.

<Example 3>

The aluminosilicate glass was reinforced, washed, and dried in the same manner as in Example 1, and then subjected to an acid treatment in the same manner as in Example 2.

The physical properties of the obtained glass were measured, and D1/D3 and C1 were calculated. The measurement results and the calculation results are shown in Table 2.

<Examples 4 and 5>

To the cup made of SUS, 2568 g of potassium nitrate, 321 g of potassium carbonate, and 111 g of sodium nitrate were added, and the mixture was heated to 450 ° C by a heating mantle to prepare a molten salt of 8 mol% of potassium carbonate and a concentration of Na of 10,000 ppm by weight. The prepared molten salt was stirred for 2 hours using a stirring motor and 4 blades to uniformly mix the whole.

The aluminosilicate glass was reinforced, washed, and dried in the same manner as in Example 1 except that the chemical strengthening treatment time was 0.5 hours (Example 4) and 1.0 hour (Example 5).

The physical properties of the obtained glass were measured, and D1/D3 was calculated. The measurement results and the calculation results are shown in Table 2.

<Examples 6, 7>

385 g of potassium nitrate, 48 g of potassium carbonate, and 17 g of sodium nitrate were placed in a cup made of SUS, and heated to 450 ° C in a heating mantle to prepare a molten salt of 8 mol% of potassium carbonate and a concentration of Na of 10,000 ppm by weight. The prepared molten salt was stirred for 2 hours using a stirring motor and 4 blades to uniformly mix the whole.

The aluminosilicate glass was reinforced, washed, and dried in the same manner as in Example 1 except that the chemical strengthening treatment temperature was 430 ° C (Example 6) and 470 ° C (Example 7).

The physical properties of the obtained glass were measured, and D1/D3 was calculated. The measurement results and the calculation results are shown in Table 2.

<Examples 8, 9>

394 g of potassium nitrate, 48 g of potassium carbonate, 8 g of sodium nitrate (Example 8), and 33 g of sodium nitrate (Example 9) were placed in a cup made of SUS, and heated to 450 ° C in a heating mantle to prepare potassium carbonate 8 mol% and Na concentration. The molten salt was 5000 ppm by weight (Example 8) and 20000 ppm by weight (Example 9), respectively. Otherwise, the aluminosilicate glass was reinforced, washed, and dried in the same manner as in Example 1.

The physical properties of the obtained glass were measured, and D1/D3 was calculated. The measurement results and the calculation results are shown in Table 2.

<Examples 10 and 11>

After the aluminosilicate glass was reinforced, washed, and dried in the same manner as in Example 1, the acid treatment was carried out in the following order.

1 mol/L (1 M) of HNO ₃ (Example 10) and citric acid (Example 11) were prepared in a beaker, and the temperature was adjusted to 40 ° C using a water bath. The chemically strengthened glass was subjected to an acid treatment by immersing it in the prepared hydrochloric acid for 5 minutes, and then washed with ion-exchanged water for 3 times, and then dried at 60 ° C for 2 hours.

The physical properties of the obtained glass were measured, and D1/D3 was calculated. The measurement results and the calculation results are shown in Table 2.

<Comparative Examples 1, 5>

The physical properties of the aluminosilicate glass (Comparative Example 1) and the unpolished soda lime glass (Comparative Example 5) after the chemical strengthening treatment were measured, and D1/D3 was calculated. The measurement and calculation results of the glass substrate are shown in Table 2. Here, the density D1 of the low-density layer is the density of the outermost surface of the aluminosilicate glass, and the density D3 of the intermediate layer is [the intermediate layer sandwiched between the compressive stress layers/present in the center of the glass (not ion exchanged) The density of the middle layer].

<Comparative Examples 2, 6>

450 g of potassium nitrate was added to a cup made of SUS, and the mixture was heated to 450 ° C by a heating mantle to prepare a molten salt of potassium carbonate and Na having a concentration of 0. Otherwise, the aluminosilicate glass (Comparative Example 2) or the soda lime glass (Comparative Example 6) was reinforced, washed, and dried in the same manner as in Example 1.

The physical properties of the obtained glass were measured, and D1/D3 was calculated. Further, C1 of Comparative Example 2 was also calculated. The measurement results and the calculation results are shown in Table 2.

<Comparative Example 3>

After the aluminosilicate glass was reinforced, washed, and dried in the same manner as in Comparative Example 2, the acid treatment was carried out in the following order.

1 mol/L (1 M) of hydrochloric acid was prepared in a beaker, and the temperature was adjusted to 40 ° C using a water bath. The chemically strengthened glass was subjected to an acid treatment by immersing it in the prepared hydrochloric acid for 5 minutes, and then washed with ion-exchanged water several times, and then dried at 60 ° C for 2 hours.

The transmittance of the obtained glass and the density D1 of the low-density layer were measured, and D1/D3 was calculated.

<Comparative Example 4>

To the cup made of SUS, 402 g of potassium nitrate and 47.9 g of potassium carbonate were added, and the mixture was heated to 450 ° C by a heating mantle to prepare a molten salt of 8 mol% of potassium carbonate. The prepared molten salt was stirred for 2 hours using a stirring motor and 4 blades to uniformly mix the whole.

The aluminosilicate glass was tempered, washed and dried in the same manner as in Example 1.

The physical properties of the obtained glass were measured, and D1/D3 and C1 were calculated. The measurement results and the calculation results are shown in Table 2.

The processing conditions of the glass substrate or the chemically strengthened glass of Examples 1 to 12 and Comparative Examples 1 to 6 are shown in Table 1, and various evaluation results are shown in Table 2.

Further, the values of C3 of Examples 1 and 3 and Comparative Examples 2 and 4 shown in Table 2 were not obtained by XPS and RBS-ERDA analysis, but were obtained by the method described below.

As described in the <glass> section of the examples, the composition of the aluminosilicate glass used in the examples and the comparative examples represented by mol% is SiO ₂ 64.4%, and Al ₂ O ₃ 8.0%. Na ₂ O 12.5%, K ₂ O 4.0%, MgO 10.5%, CaO 0.1%, SrO 0.1%, BaO 0.1%, and ZrO ₂ 0.5%. That is, Si 21.1%, Al 5.2%, Na 8.2%, K 2.6%, Mg 3.4%, Ca 0.03%, Sr 0.03%, Ba 0.03%, Zr 0.2%, and O 59.2%.

From this, it can be inferred that the (Na+K)/Si molar ratio of the intermediate layer is 0.51.

Further, as an example, FIG. 2 discloses the distribution of H and Si in the region of the depth of 500 nm from the surface of Example 1 by RBS-ERDA analysis. In order to record the horizontal axis of the distribution obtained by RBS-ERDA analysis in depth, the density or film thickness must be assumed. Here, the density is assumed to be 7.97 × 10 ²² atoms/cm ³ . H in the deeper region of the lower density layer is below the detection limit (1 mol% or less).

As shown in the literature (S. Ilievski et al., Glastech. Ber. Glass Sci. Technol., 73 (2000) 39.), the H concentration in a typical glass block is 1 mol% or less. Therefore, it is considered that the H concentration of the intermediate layer is also 1 mol% or less. As described above, Si in the glass is 21.1 mol%, so that the H/Si molar ratio can be estimated to be 0.05 or less.

From the above, it is considered that the H/(Na+K) molar ratio of the intermediate layers of Examples 1 and 3 and Comparative Examples 2 and 4 is 0.1 or less.

According to the results shown in Tables 1 and 2, since the density ratio of the examples was less than 1.0, the low-density layer having a low density of the surface of the chemically strengthened glass was obtained.

The present invention has been described in detail with reference to the specific embodiments thereof, and it is obvious that various changes or modifications may be made without departing from the spirit and scope of the invention. The present application is based on Japanese Patent Application No. 2013-151115, filed on Jan.

[Industrial availability]

According to the present invention, the chemically strengthened glass can be subjected to a low reflection treatment without other processing steps. Further, it is possible to obtain a low-reflection chemically strengthened glass on both sides which has been subjected to the low-reflection treatment over a large area. As a result, the production of low-reflection chemically strengthened glass can be performed at a lower cost, and high productivity can be achieved.

1‧‧‧Low density layer

2‧‧‧Compressive stress layer

3‧‧‧Intermediate

Claims (7)

A chemically strengthened glass comprising an ion-exchanged compressive stress layer on a surface of a glass, comprising: a low-density layer obtained by densifying a surface of the compressive stress layer, wherein the low-density layer has a thickness of 5 nm or more and The ratio (D1/D3) of the density (D1) of the low-density layer to the density (D3) of the intermediate layer sandwiched in the central portion of the glass and the intermediate layer in the compressive stress layer is 0.5 or less and less than 0.93. The chemically strengthened glass of claim 1, wherein the H/(Na+K) molar ratio (C1) of the low density layer is greater than the H/(Na+K) molar ratio (C3) of the intermediate layer, that is, (C1) >C3). The chemically strengthened glass according to claim 1 or 2, wherein the low density layer has a H/(Na+K) molar ratio (C1) of 1.0 or more. The chemically strengthened glass according to any one of claims 1 to 3, wherein the glass is an aluminosilicate glass or a soda lime glass. A method for producing a chemically strengthened glass by ion-exchange of Na in the glass with K in the molten salt by immersing the glass in a molten salt containing potassium nitrate, and including adding the molten salt to the molten salt At least one selected from the group consisting of K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ , NaHCO ₃ , K ₃ PO ₄ , Na ₃ PO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , KOH, and NaOH The step of salt and the step of washing the glass after the ion exchange, and further comprising at least one of a step of increasing the Na concentration in the molten salt to 500 ppm by weight or more, and a step of subjecting the glass to acid treatment after the washing. step. The method for producing a chemically strengthened glass according to claim 5, which comprises simultaneously making the above molten salt The step of neutralizing the Na concentration to 500 ppm by weight or more and subjecting the glass to acid treatment after the above washing. The method for producing a chemically strengthened glass according to claim 5 or 6, wherein the step of causing the Na concentration in the molten salt to be 500 ppm by weight or more comprises the step of adding a Na salt to the molten salt.