WO2015008760A1 - 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

Chemically tempered glass and method for producing chemically tempered glass

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

Cover glass of display devices such as digital cameras, mobile phones, and PDAs (Personal Digital Assistants), and glass substrates of displays are sometimes referred to simply as “chemically tempered glass” glass that has been chemically strengthened by ion exchange or the like. .) Is used. Although glass has a high theoretical strength, the strength is greatly reduced by scratching. Chemically tempered glass is suitable for these applications because it has higher mechanical strength than unstrengthened glass and prevents damage to the glass surface.

In recent years, the number of cases used as cover glass for solar cells has increased. By replacing the existing cover glass with chemically strengthened glass, the same mechanical strength can be achieved even if it is made thinner. By reducing the weight of the glass, there is an advantage that the installation in a place where the conventional installation could not be performed due to the weight restriction and the load of construction are reduced.

Chemical strengthening treatment by ion exchange compresses the glass surface by substituting metal ions with a small ionic radius (for example, Na ions) and metal ions with a larger ionic radius (for example, K ions) contained in the glass. This is a process for generating a stress layer and improving the strength of the glass.

In addition, various displays and the like often require an antireflection function, and tempered glass strengthened by chemical treatment by ion exchange may also require an antireflection function. Usually, in chemically strengthened glass, K ions cannot be diffused into the glass after the antireflection film is formed, so that it is difficult to perform a strengthening treatment. For this reason, the antireflection film must be formed after the reinforcement treatment.

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

As a method of forming an antireflection film, the sol-gel method in which a coating liquid containing fine particles is applied and an antireflection film that is gelled by heat treatment is formed at a low production cost and high production. Then it has become mainstream. As an antireflection film formed by such a sol-gel method, for example, a film containing a hydrolyzed condensate of a silicon compound, a metal chelate compound, and a low refractive silica sol is known (Patent Document 2).

On the other hand, in recent years, a method for producing an antireflective tempered glass has been disclosed in which an antireflective film is optimized, and after the antireflective film is formed, chemical strengthening treatment is performed to diffuse K ions into the glass to reinforce the glass. (Patent Document 3).
Moreover, low reflectivity can be provided also by giving the surface a peculiar texture structure (patent document 4).

Note that the low reflectivity of the glass means that the transmittance is high, and the transmittance can be improved by reducing the density of the glass surface, that is, reducing the refractive index.

Japanese Laid-Open Patent Publication No. 4-357134 Japanese Unexamined Patent Publication No. 2002-221602 Japanese Unexamined Patent Publication No. 2011-88765 Japanese Unexamined Patent Publication No. 2013-40091

However, in the conventional technique for imparting low reflectivity to chemically strengthened glass, when the antireflection film is composed of two or more multilayer films as in Patent Document 1, the antireflection effect is surely achieved by optical design. However, since the reflectance depends on the incident angle and the number of coatings of the film is required twice or more, the production cost is inevitable. On the other hand, when the antireflection film is composed of a single layer, after forming the metal oxide film, heat treatment and etching treatment are performed, or after forming the metal oxide film, the chemical reaction treatment with the gas. Therefore, it is difficult to reduce the manufacturing cost even though it is a single-layer antireflection film.

Further, in the method of forming an antireflection film by a sol-gel method before chemically strengthening glass as disclosed in Patent Document 2, an antireflection film must be formed for each product subjected to chemical strengthening treatment. However, the productivity is remarkably lowered, and the advantage of high productivity inherent in the sol-gel method is lost.

On the other hand, even if it is a method of forming an antireflection film before chemical strengthening treatment as in Patent Document 3, at least the following three steps are required before the chemical strengthening treatment step.
(1) A step of preparing a coating solution in advance from a silicon compound, a hollow silica sol, and a metal chelate compound.
(2) A step of applying a coating solution to glass.
(3) A step of drying and heat-treating the glass.
For these reasons, it is necessary to newly invest in facilities in addition to the conventional chemical strengthening treatment apparatus.

Also in Patent Document 4, a processing process different from the chemical strengthening process of glass, such as giving a texture structure to the glass surface, is required, and in order to produce a low reflective chemically strengthened glass imparted with low reflectivity. High cost was necessary. In addition, due to manufacturing characteristics, it has been very difficult to perform low reflection treatment on both surfaces of chemically strengthened glass or low reflection treatment on a large area.

Therefore, in the present invention, a chemically tempered glass having a low density layer (low refractive index layer) on the surface layer and a manufacturing method thereof are formed by forming a modified layer called a low density layer by reducing the surface of the chemically tempered glass. The purpose is to provide.

As a result of earnest study, the inventors added a specific salt to the molten salt used for the chemical strengthening treatment, and maintained the Na concentration in the molten salt at a certain value or higher and the glass after the chemical strengthening treatment. By performing at least one of the acid treatments, it was found that a chemically strengthened glass having a surface layer with low reflectivity can be obtained using a single glass as a raw material, and the present invention has been completed. It was.

That is, the present invention relates to the following <1> to <7>.
<1> A chemically strengthened glass having an ion-exchanged compressive stress layer on the glass surface, the surface of the compressive stress layer having a low density layer, and the thickness of the low density layer being 5 nm or more and 200 nm. And the ratio (D1 / D3) of the density (D1) of the low-density layer and the density (D3) of the intermediate layer present in the center of the glass and sandwiched between the compressive stress layers is 0.5 or more and 0.00. A chemically strengthened glass that is less than 93.
<2> The chemistry according to <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 (C1> C3). Tempered glass.
<3> The chemically strengthened glass according to <1> or <2>, wherein the low density layer has a H / (Na + K) molar ratio (C1) of 1.0 or more.
<4> The chemically tempered glass according to any one of <1> to <3>, wherein the glass is aluminosilicate glass or soda lime glass.
<5> A method for producing chemically tempered glass in which Na in the glass and K in the molten salt are ion-exchanged by immersing the glass in a molten salt containing potassium nitrate, wherein K is contained in the molten salt. _At least one salt selected from the group consisting of 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 is added. And a step of washing the glass after the ion exchange, and further, a step of setting the Na concentration in the molten salt to 500 ppm by weight or more and a step of acid-treating the glass after the washing A method for producing chemically strengthened glass, comprising:
<6> The method for producing chemically tempered glass according to <5>, including both a step of setting the Na concentration in the molten salt to 500 ppm by weight or more and a step of acid-treating the glass after the washing.
<7> The method for producing chemically strengthened glass according to <5> or <6>, wherein the step of setting the Na concentration in the molten salt to 500 ppm by weight or more includes the step of adding Na salt to the molten salt.

The chemically strengthened glass according to the present invention is provided with low reflectivity by having a low-density layer in which the surface of the ion-exchanged compressive stress layer is reduced in density, and another device is provided for providing low reflectivity. The processing process used is not required separately. Therefore, when manufacturing low-reflective chemically tempered glass, the cost can be reduced as compared with the conventional case.
Further, according to the method for producing chemically strengthened glass according to the present invention, a low-reflective chemically strengthened glass can be obtained by using a single glass as a raw material and forming a compressive stress layer and a low density layer on the surface thereof. Therefore, low-reflection treatment can be performed on a large area glass or both surfaces of glass, which is very useful.

1 (a) to 1 (c) are schematic views showing a process for producing chemically strengthened glass according to the present invention. FIG. 2 is a diagram showing H and Si profiles in the depth region from the surface of Example 1 to 500 nm obtained by RBS-ERDA analysis.

Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be arbitrarily modified without departing from the gist of the present invention.
Here, in the present specification, “mass%” and “weight%”, “mass ppm” and “weight ppm” have the same meaning.
In this specification, “Na concentration” means a concentration as Na.

<Chemical tempered glass>
The chemically strengthened glass according to the present invention is a chemically strengthened glass having an ion-exchanged compressive stress layer on the glass surface, and has a low density layer in which the surface of the compressive stress layer is further reduced in density.
In this specification, the term “compressive stress layer” refers to the ion exchange between Na ions on the glass surface and K ions in the molten salt by immersing the glass as a raw material in an inorganic potassium molten salt such as potassium nitrate. It is a high density layer to be formed.

(Molten salt)
The molten salt for glass reinforcement used to obtain the chemically strengthened glass according to the present invention (hereinafter sometimes simply referred to as “molten salt”) contains an inorganic potassium salt. As the inorganic potassium salt, those having a melting point below the strain point (usually 500 to 600 ° C.) of the glass to be chemically strengthened are preferable. In the present invention, a molten salt containing potassium nitrate (melting point 330 ° C.) as a main component is preferable. If potassium nitrate is a main component, it is preferable because it is in a molten state below the strain point of glass and is easy to handle in the operating temperature range. Here, the main component means that the content in the molten salt is 50% by mass or more.
Hereinafter, the “potassium nitrate molten salt” containing potassium nitrate as a main component as an inorganic potassium salt of the molten salt will be described as an example.

The molten salt is further 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. It is preferable to contain at least one salt, and it is more preferable to contain 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 ₄ , Na ₃ PO ₄ having the property of cutting a glass network typified by Si—O—Si bond into a molten salt of potassium nitrate. At least one salt selected from the group consisting of K ₂ SO ₄ , Na ₂ SO ₄ , KOH and NaOH (hereinafter sometimes referred to as “flux”) is added. Since the temperature at which the chemical strengthening treatment is performed is as high as several hundred degrees Celsius, the covalent bond between Si—O of the glass is appropriately broken at that temperature, and the density reduction treatment described later easily proceeds.
The degree of breaking the covalent bond varies depending on the glass composition, the type of inorganic salt (flux) used, the temperature at which the glass is immersed in the molten salt, the chemical strengthening treatment conditions such as time, etc. Of these covalent bonds, it is considered preferable to select a condition that can break one or two bonds.

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 wt% or more and the chemical strengthening treatment temperature is 350 to 500 ° C., the chemical strengthening treatment time is 1 minute. -10 hours are preferable, 5 minutes to 8 hours are more preferable, and 10 minutes to 4 hours are more preferable.

The addition amount of the flux is preferably equal to or lower than the saturation solubility at the temperature at which the molten salt is used from the viewpoint of productivity, and excessive addition may lead to glass corrosion.

The molten salt may contain other chemical species in addition to potassium nitrate and the flux as long as the effects of the present invention are not impaired. For example, alkali salts such as sodium chloride, potassium chloride, sodium borate, potassium borate, etc. Examples include chlorides and alkali borates. These may be added alone or in combination of two or more.

(Method 1 for producing molten salt)
The molten salt can be produced by the steps shown below.
Step 1a: Preparation of molten potassium nitrate salt Step 2a: Addition of flux to the molten potassium nitrate salt prepared in Step 1a

(Step 1a-Preparation of molten potassium nitrate salt)
In step 1a, potassium nitrate is put into a container and heated to a temperature equal to or higher than the melting point to melt, thereby preparing a molten salt. Since potassium nitrate has a melting point of 330 ° C. and a boiling point of 500 ° C., it melts at a temperature within that range. In particular, the melting temperature is preferably 350 to 470 ° C. from the viewpoint of the balance between the surface compressive stress (CS) and the compressive stress layer depth (DOL) that can be applied to the glass, and the strengthening time.

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

(Step 2a-Addition of flux to molten potassium nitrate prepared in Step 1a)
In Step 2a, the above-mentioned flux is added to the potassium nitrate molten salt prepared in Step 1a, and the whole is mixed uniformly with a stirring blade while keeping the temperature within a certain range. When using a plurality of fluxes in combination, the order of addition is not limited, and they may be added simultaneously.
The temperature is preferably not less than the melting point of potassium nitrate, that is, not less than 330 ° C., more preferably 350 to 500 ° C. The stirring time is preferably 1 minute to 10 hours, more preferably 10 minutes to 2 hours.

(Method 2 for producing molten salt)
In the manufacturing method 1 of the above molten salt, the method of adding a flux after preparation of the molten salt of potassium nitrate is exemplified, but the molten salt can also be manufactured by the steps shown below.
Step 1b: Mixing of potassium nitrate and flux Step 2b: Melting of the mixed salt obtained in Step 1b

(Step 1b-Mixing of potassium nitrate and flux-)
In step 1b, potassium nitrate and a flux are put into a container and mixed with a stirring blade or the like. When using a plurality of fluxes in combination, the order of addition is not limited, and they may be added simultaneously. The same container as that used in the above step 1a can be used.

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

In the molten salt obtained by the above steps 1a and 2a or steps 1b and 2b, when precipitates are generated by the addition of a flux, the precipitates are precipitated at the bottom of the container before chemical strengthening treatment of the glass. Let stand until This precipitate includes a flux exceeding the saturation solubility and a salt in which the cations of the flux are exchanged in the molten salt.
As described above, the molten salt can be prepared by the steps 1a and 2a or the steps 1b and 2b. Hereinafter, 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”.

Further, following step 2, the following step 2 ′ may be performed as necessary.
Step 2 ′: Adjustment of Na Concentration in Molten Salt By adding a Na salt typified by NaNO ₃ to the produced molten salt, the Na concentration in the molten salt can be adjusted. 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 performed by immersing glass in a molten salt and replacing metal ions (Na ions) in the glass with metal ions (K ions) having a large ionic radius in the molten salt. By this ion exchange, the composition of the glass surface can be changed to form the compressive stress layer 2 in which the glass surface has a high density. Since compressive stress is generated by increasing the density of the glass surface, the glass can be strengthened [FIGS. 1 (a) to 1 (b)].
In practice, the density of the chemically strengthened glass gradually increases from the outer edge of the intermediate layer 3 existing in the center of the glass toward the surface of the compressive stress layer. There is no clear boundary between which the density changes rapidly. Here, the intermediate layer is a layer present in the center of the glass and sandwiched between the compressive stress layers. Unlike the compressive stress layer, this intermediate layer is a layer that is not ion-exchanged.
Specifically, the chemical strengthening treatment in the present invention can be performed by the following step 3.
Process 3: Chemical strengthening treatment of glass

(Process 3-Chemical strengthening treatment of glass-)
In step 3, the glass is preheated, and the molten salt prepared in steps 1 and 2 or steps 1, 2, and 2 ′ is adjusted to a temperature at which chemical strengthening is performed. Next, the preheated glass is immersed in the molten salt for a predetermined time, and then the glass is pulled up from the molten salt and allowed to cool. In addition, it is preferable to perform shape processing according to a use, for example, mechanical processing, such as a cutting | disconnection, an end surface processing, and a drilling process, before a chemical strengthening process to glass.

The preheating temperature of glass depends on the temperature immersed in the molten salt, but is generally preferably 100 ° C. or higher.

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

The immersion time of the glass in the molten salt is preferably 1 minute to 10 hours, more preferably 5 minutes to 8 hours, and even more preferably 10 minutes to 4 hours. If it exists in this range, the chemically strengthened glass excellent in the balance of an intensity | strength and the depth of a compressive-stress layer can be obtained.

(Low density layer)
The chemically strengthened glass according to the present invention further has a low density layer 1 in which the surface of the compressive stress layer 2 is reduced in density (FIGS. 1B to 1C).
The low density layer is formed by Na (leaching) from the outermost surface of the compressive stress layer (leaching), and H entering (substituting) instead. This can be done by at least one of them. In addition, although the detail of the process 5 is mentioned later, the following process 4 is performed before the process 5.
Process 4: Glass cleaning process 5: Acid treatment of glass after passing through process 4

(Step 4-Glass cleaning-)
In step 4, glass is cleaned using industrial water, ion exchange water, or the like. Of these, ion-exchanged water is preferred. The washing conditions vary depending on the washing solution used, but when ion-exchanged water is used, washing at 0 to 100 ° C. is preferable from the viewpoint of completely removing the attached salt.

However, even if the glass is chemically strengthened in the molten salt to which the above-mentioned flux is added, the permeability of the chemically strengthened glass is slightly higher than that in the case of chemically strengthening the flux in the molten salt to which the flux is not added. can do. This is considered to be because the above-described leaching occurs only in the normal water cleaning step, and the surface of the compressive stress layer is reduced in density. However, the effect of forming the low density layer in that case is weak, and it is considered that the effect is further promoted by the step 5 described later.

As described above, when the surface of the compressive stress layer of the chemically strengthened glass is reduced in density, a low-reflectivity glass having a reduced refractive index and improved glass transmittance can be obtained.
The density of the low-density layer can be obtained from the critical angle (θc) measured by the X-ray reflectivity method (XRR). Further, the thickness of the low density layer can be obtained from the period (Δθ) measured by XRR. In addition, it is also possible to confirm the formation of the low density layer and the thickness of the layer by simply observing a cross section of the glass with a scanning electron microscope (SEM). The density of the intermediate layer can be similarly obtained 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 are determined by X-ray photoelectron spectroscopy (XPS), and the H / Si molar ratio is Rutherford Backscattering Spectrometry (RBS) -elasticity. Each can be confirmed by a recoil detection method (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, because it is related to the maximum wavelength of light that passes through the glass.

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

Further, the magnitude 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.

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

(Step 2 '-Adjustment of Na concentration in molten salt-)
In step 2 ′, the Na concentration in the molten salt used for the chemical strengthening treatment in step 3 is adjusted to 500 ppm by weight or more as necessary.
By setting the Na concentration in the molten salt to 500 ppm by weight or more, the cutting of the network on the outermost surface of the glass and the low-density treatment can proceed easily, and the low-density layer is deepened.

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

(Step 5-Acid treatment of glass after Step 4)
In step 5, the glass cleaned in step 4 is further subjected to acid treatment.
When step 5 is performed after step 4, the density of the outermost surface of the compressive stress layer of the chemically strengthened glass is promoted by acid treatment of the cleaned chemically strengthened glass. In addition, when the step 5 is performed after the chemical strengthening treatment is performed with the molten salt whose Na concentration is adjusted in the step 2 ′, the deeper density layer can be further deepened.

The acid treatment of glass is a treatment in which Na and / or K on the surface of 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 used may be a weak acid or a strong acid, and does not depend on its pH. Specifically, acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, oxalic acid, carbonic acid and citric acid are preferred. These acids may be used alone or in combination.

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

The thickness of the low density layer to be formed can be controlled by the type and concentration of the acid used for the acid treatment, the temperature of the acid treatment, the time, and the like.
Since the maximum transmission wavelength of light transmitted through the glass is determined by the thickness of the low density layer, the acid treatment conditions may be appropriately determined according to the use of the chemically strengthened glass.

As described above, the thickness of the low density layer is preferably 5 to 200 nm, more preferably 50 to 200 nm. Increasing the acid treatment conditions such as increasing the acid treatment time tends to increase the transmittance increase.
Based on these, acid treatment conditions are appropriately determined according to the situation.

In addition, when the density reduction treatment is performed by the acid treatment in step 5, it is possible to obtain a chemically tempered glass having lower reflectivity because both the Na concentration and the K concentration in the low density layer are lower than the H concentration. To preferred.

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

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

It should be noted that various methods can be employed for forming the glass. For example, various forming methods such as a down draw method (for example, an overflow down draw method, a slot down method and a redraw method), a float method, a roll-out method, and a press method can be employed.

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

Although it does not specifically limit as a composition of the glass for chemical strengthening of this invention, For example, the following glass compositions are mentioned. (I) a composition that is displayed in mol%, the SiO ₂ 50 ~ 80%, the _{Al 2 O 3 2 ~ 25%} , the Li ₂ O 0 ~ 10%, a _{Na 2 O 0 ~ 18%,} K 2 O Is represented by a glass (ii) mol% containing 0-10%, MgO 0-15%, CaO 0-5% and ZrO ₂ 0-5%, SiO ₂ 50-74%, Al ₂ O ₃ 1-10%, Na ₂ O 6-14%, K ₂ O 3-11%, MgO 2-15%, CaO 0-6% and ZrO ₂ 0-5% The total content of SiO ₂ and Al ₂ O ₃ is 75% or less, the total content of Na ₂ O and K ₂ O is 12 to 25%, and the total content of MgO and CaO is 7 to 15%. a composition which is displayed at a certain glass (iii) mol%, a SiO ₂ 68 ~ 80%, the _{Al 2 O 3 4 ~ 10%} , The a ₂ O 5 ~ 15%, the _{K 2} O 0 to 1%, the MgO 4 ~ 15% and ZrO ₂ is composition displaying a glass (iv) mole% containing 0 to 1%, a SiO ₂ 67 -75%, Al ₂ O ₃ 0-4%, Na ₂ O 7-15%, K ₂ O 1-9%, MgO 6-14% and ZrO ₂ 0-1.5% The total content of SiO ₂ and Al ₂ O ₃ is 71 to 75%, the total content of Na ₂ O and K ₂ O is 12 to 20%, and when CaO is contained, the content is 1% Glass that is less than

When the glass is polished before the chemical strengthening treatment, a polishing method includes, for example, a method of polishing with a polishing pad while supplying the polishing slurry, and a polishing slurry containing an abrasive and water can be used as the polishing slurry. As the abrasive, cerium oxide (ceria) and silica are preferable.

If the glass is polished, the polished glass is cleaned with a cleaning solution. The washing liquid is preferably a neutral detergent and water, and more preferably washed with water after washing with a neutral detergent. A commercially available neutral detergent can be used.

The glass substrate cleaned by the cleaning process is finally cleaned with a cleaning solution. Examples of the cleaning liquid include water, ethanol, and isopropanol. Of these, water is preferred.

After the final cleaning, the glass is dried. The drying conditions may be selected in consideration of the cleaning solution used in the cleaning process, the characteristics of the glass, and the like.
The glass after the washing is applied to the step 3 of the chemical strengthening treatment.

Although the chemically strengthened glass according to the present invention has been described above, the chemically strengthened glass according to the present invention can be manufactured by including at least one of the following steps 1 to 4 and steps 2 ′ and 5. it can. In particular, the low density layer can be deepened by including Step 2 ′, and the low density layer can be further deepened by including Step 5, and it is more preferable that both Steps 2 ′ and 5 are included. The details in each step are as described above.
Step 1: Preparation of molten potassium nitrate salt (1a) or mixing of potassium nitrate and flux (1b)
Step 2: Addition of flux to the potassium nitrate molten salt prepared in Step 1a (2a) or melting of the mixed salt obtained in Step 1b (2b)
Step 2 ′: Adjustment of Na concentration in molten salt Step 3: Glass chemical strengthening treatment step 4: Glass washing step 5: Acid treatment of glass after the step 4

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these.
<Evaluation method>
In this example, the structure of the synthesized compound was determined by the analysis method shown below.
(Evaluation of glass: transmittance)
For the transmittance of glass, a transmission spectrum in a wavelength region of 300 nm to 1000 nm is measured using a spectrophotometer (U-4100 manufactured by Hitachi High-Technologies Corporation), and a maximum value T _max of the transmittance in the wavelength range is calculated. did.

(Evaluation of glass: density D1 of low density layer, thickness T1 of low density layer)
An X-ray diffractometer (manufactured by Rigaku Corporation: ATX-G, X-ray source: Cu-Kα) is used to measure the density and thickness of the modified layer formed on the glass surface, and the X-ray reflectivity method (XRR) ). The density was calculated from the critical angle (θc) of the X-ray reflectivity pattern, and the layer thickness was calculated from the interference period (Δθ). For analysis, GlobalFit Ver. It calculated using 1.3.3 (Rigaku).

(Measurement of density D3 of the intermediate layer)
A substrate from which the compressive stress layer was removed by polishing, etching, or the like was prepared, and the density D3 of the intermediate layer was calculated by the X-ray reflectivity method.

(Measurement of H / (Na + K) molar ratio C1 of low density layer)
X-ray photoelectron spectroscopy (XPS) was used to measure the Na / Si and K / Si molar ratio of the modified layer formed on the glass surface. XPS analysis after removal of the surface contamination of the sample by using a C ₆₀ ion sputtering gun attached to the apparatus was performed.
Rutherford Backscattering Spectrometry (RBS) -Elastic Recoil Detection Analysis (ERDA) was used for the measurement of the H / Si molar ratio. When determining the H / Si molar ratio by RBS-ERDA analysis, it is necessary to consider the influence of surface contamination by organic substances. Here, it was assumed that the amount of the surface contamination organic substance was 3 × 10 ¹⁵ atoms / cm ² and the density of the surface contamination organic substance was 10 × 10 ²² atoms / cm ³ .
If a phenomenon in which the H count decreases with time during ERDA analysis is observed, correction in consideration of this phenomenon is necessary. From the Na / Si molar ratio and K / Si molar ratio obtained by XPS analysis and the H / Si molar ratio obtained by RBS-ERDA analysis, the H / (Na + K) molar ratio was determined. The analysis conditions for XPS and RBS-ERDA analysis are as follows.

(XPS analysis)
Equipment: ESCA5500 manufactured by PHYSICAL ELECTRONICS
X-ray source: Al Kα
Pass energy: 93.9eV
Energy step: 0.8eV / step
Detection angle: 15 ° with respect to the normal of the sample surface
Ion species sputter gun used in surface _{decontamination: C 60} ion analysis software: MultiPak Ver. 9.3.0.3

(RBS-ERDA analysis)
Equipment: Pelletron 3SDH manufactured by National Electrostatics Corporation
Incident ion: He ⁺⁺
Incident ion energy: 2.3 MeV
RBS scattering angle: 160 degrees ERDA scattering angle: 30 degrees Incident angle: 75 degrees with respect to the normal of the sample surface Sample current: 2 nA
Irradiation amount: 10μC

(Measurement of H / (Na + K) molar ratio C3 of the intermediate layer)
Prepare a substrate from which the compressive stress layer has been removed by polishing, etching, etc., and perform XPS analysis and RBS-ERDA analysis in the same manner as the measurement of the H / (Na + K) molar ratio C1 of the low-density layer described above. A method of calculating the / (Na + K) molar ratio C3 is desirable. However, C3 was calculated | required here using the method calculated from a glass composition mentioned later. If it is confirmed that the glass composition is known and the H concentration in the region deeper than the low density layer is below the detection limit of ERDA analysis (1 mol% or less), the substrate from which the compressive stress layer has been removed by polishing, etching or the like Even without preparing the above, the value of C3 can be easily estimated.

<Glass>
Two types of glass, soda lime glass and aluminosilicate glass, having the following composition were used as the chemically strengthened glass.
Soda lime glass (composition expressed in mol%): 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 in mol%): 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 glass used was polished before the chemical strengthening treatment. Polishing conditions were LP-66 for the foamed polyurethane pad, and Luminox for glass abrasives (cerium oxide having an average particle size of 0.75 to 1.25 μm and a specific gravity of 1.05 to 1.15 g / cm ³ ) for the contained abrasive particles. The polishing rate was 0.07 to 0.10 μm / min, the processing pressure was about 0.15 kg / cm ^2, and 50 μm or more on one side and a total of 150 μm on both sides were removed.

<Example 1>
To a stainless steel (SUS) cup, 2568 g of potassium nitrate, 321 g of potassium carbonate, and 111 g of sodium nitrate were added and heated to 450 ° C. with a mantle heater to prepare a molten salt having a potassium carbonate concentration of 8 mol% and a Na concentration of 10,000 ppm by weight. The prepared molten salt was stirred for 2 hours using a stirring motor and four propeller blades, and the whole was uniformly mixed.
A 50 mm × 50 mm × 0.7 mm aluminosilicate glass was preheated to 200 ° C. to 400 ° C. and then immersed in a molten salt at 450 ° C. for 2 hours for chemical strengthening treatment. After the tempering treatment, the glass was washed twice with ion exchange water at 50 ° C. to 90 ° C., washed with running ion exchange water at room temperature, and dried at 60 ° C. for 2 hours.
Various physical properties of the obtained glass were measured, and D1 / D3 and C1 were calculated. Table 2 shows the measurement results and the calculation results.

<Examples 2 and 12>
To a SUS cup, 402 g of potassium nitrate and 47.9 g of potassium carbonate were added, and heated to 450 ° C. with a mantle heater 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 four propeller blades, and the whole was uniformly mixed.
After aluminosilicate glass (Example 2) or soda lime glass (Example 12) was tempered, washed and dried in the same manner as in Example 1, acid treatment was performed according to the following procedure.
1 mol / L (1M) hydrochloric acid was prepared in a beaker, and the temperature was adjusted to 40 ° C. using a water bath. The acid treatment was performed by immersing the chemically strengthened glass in the prepared hydrochloric acid for 5 minutes, and then washed with ion-exchanged water three times, followed by drying at 60 ° C. for 2 hours.
Various physical properties of the obtained glass were measured to calculate D1 / D3. Table 2 shows the measurement results and the calculation results.

<Example 3>
The aluminosilicate glass was tempered, washed and dried in the same manner as in Example 1, and then acid-treated in the same manner as in Example 2.
Various physical properties of the obtained glass were measured, and D1 / D3 and C1 were calculated. Table 2 shows the measurement results and the calculation results.

<Examples 4 and 5>
To a SUS cup, 2568 g of potassium nitrate, 321 g of potassium carbonate and 111 g of sodium nitrate were added and heated to 450 ° C. with a mantle heater to prepare a molten salt having 8 mol% potassium carbonate and a Na concentration of 10,000 ppm by weight. The prepared molten salt was stirred for 2 hours using a stirring motor and four propeller blades, and the whole was uniformly mixed.
The aluminosilicate glass was tempered, washed and dried in the same manner as in Example 1 except that the chemical tempering time was 0.5 hour (Example 4) and 1.0 hour (Example 5).
Various physical properties of the obtained glass were measured to calculate D1 / D3. Table 2 shows the measurement results and the calculation results.

<Examples 6 and 7>
To a SUS cup, 385 g of potassium nitrate, 48 g of potassium carbonate and 17 g of sodium nitrate were added and heated to 450 ° C. with a mantle heater to prepare a molten salt having 8 mol% potassium carbonate and a Na concentration of 10,000 ppm by weight. The prepared molten salt was stirred for 2 hours using a stirring motor and four propeller blades, and the whole was uniformly mixed.
The aluminosilicate glass was tempered, washed and dried in the same manner as in Example 1 except that the chemical tempering temperature was 430 ° C. (Example 6) and 470 ° C. (Example 7).
Various physical properties of the obtained glass were measured to calculate D1 / D3. Table 2 shows the measurement results and the calculation results.

<Examples 8 and 9>
394 g of potassium nitrate, 48 g of potassium carbonate and 8 g of sodium nitrate (Example 8) and 33 g of sodium nitrate (Example 9) are added to a SUS cup, heated to 450 ° C. with a mantle heater, 8 mol% of potassium carbonate, and Na concentration Prepared molten salts of 5000 ppm by weight (Example 8) and 20000 ppm by weight (Example 9), respectively. Otherwise, the aluminosilicate glass was tempered, washed and dried in the same manner as in Example 1.
Various physical properties of the obtained glass were measured to calculate D1 / D3. Table 2 shows the measurement results and the calculation results.

<Examples 10 and 11>
In the same manner as in Example 1, the aluminosilicate glass was tempered, washed and dried, and then acid-treated by the following procedure.
1 mol / L (1M) 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 acid treatment was performed by immersing the chemically strengthened glass in the prepared hydrochloric acid for 5 minutes, and then washed with ion-exchanged water three times, followed by drying at 60 ° C. for 2 hours.
Various physical properties of the obtained glass were measured to calculate D1 / D3. Table 2 shows the measurement results and the calculation results.

<Comparative Examples 1 and 5>
Various physical properties of the aluminosilicate glass after polishing (Comparative Example 1) and unpolished soda lime glass (Comparative Example 5) without chemical strengthening were measured, and D1 / D3 was calculated. Table 2 shows the measurement and calculation results of the glass substrate. 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 / the center of the glass (ion-exchanged). No) intermediate layer] density.

<Comparative Examples 2 and 6>
450 g of potassium nitrate was added to a SUS cup and heated to 450 ° C. with a mantle heater to prepare a molten salt having both potassium carbonate and Na concentrations of 0. Except that, aluminosilicate glass (Comparative Example 2) or soda lime glass (Comparative Example 6) was tempered, washed and dried in the same manner as Example 1.
Various physical properties of the obtained glass were measured to calculate D1 / D3. For Comparative Example 2, C1 was also calculated. Table 2 shows the measurement results and the calculation results.

<Comparative Example 3>
The aluminosilicate glass was tempered, washed and dried in the same manner as in Comparative Example 2 and then acid-treated by the following procedure.
1 mol / L (1M) hydrochloric acid was prepared in a beaker, and the temperature was adjusted to 40 ° C. using a water bath. The chemically treated glass was immersed in the prepared hydrochloric acid for 5 minutes for acid treatment, then washed several times with ion-exchanged water, 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 a SUS cup, 402 g of potassium nitrate and 47.9 g of potassium carbonate were added, and heated to 450 ° C. with a mantle heater 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 four propeller blades, and the whole was uniformly mixed.
In the same manner as in Example 1, the aluminosilicate glass was tempered, washed and dried.
Various physical properties of the obtained glass were measured, and D1 / D3 and C1 were calculated. Table 2 shows the measurement results and the calculation results.

Table 1 shows the processing conditions for the glass substrates or chemically tempered glasses of Examples 1 to 12 and Comparative Examples 1 to 6, and Table 2 shows the results of various evaluations.
The values of C3 in Examples 1 and 3 and Comparative Examples 2 and 4 shown in Table 2 were not measured values obtained by XPS and RBS-ERDA analysis, but were determined by the method described below.

As described in the section of <Glass> in the Examples, the composition expressed in mol% of the aluminosilicate glass used in this Example and Comparative Example was 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%. 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%, O 59.2%.
From this, the (Na + K) / Si molar ratio of the intermediate layer can be estimated to be 0.51.
As an example, FIG. 2 shows the H and Si profiles in the depth region from the surface of Example 1 to 500 nm obtained by RBS-ERDA analysis. In order to express the horizontal axis of the profile obtained by RBS-ERDA analysis in terms of depth, it is necessary to assume density or film thickness. Here, the density was assumed to be 7.97 × 10 ²² atoms / cm ³ . H in the region deeper than the low density layer is below the lower limit of detection (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 the bulk of a general glass is 1 mol% or less. Therefore, the H concentration in the intermediate layer is also considered to be 1 mol% or less. As described above, since Si in the glass is 21.1 mol%, the H / Si molar ratio can be estimated to be 0.05 or less.
From the above, it can be said that the H / (Na + K) molar ratio of the intermediate layer in Examples 1 and 3 and Comparative Examples 2 and 4 is 0.1 or less.

From the results shown in Tables 1 and 2, it was found that the density ratio of the examples was less than 1.0, and thus the chemically strengthened glass surface had a low density layer.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application filed on July 19, 2013 (Japanese Patent Application No. 2013-151115), the contents of which are incorporated herein by reference.

According to the present invention, the chemically tempered glass can be subjected to a low reflection treatment without requiring a separate processing step. Furthermore, the low reflection chemically strengthened glass in which the low reflection treatment is applied to both sides can be obtained in a large area. As a result, low-reflective chemically strengthened glass can be produced at low cost, and high productivity can be realized.

1 Low density layer 2 Compressive stress layer 3 Intermediate layer

Claims (7)

1. A chemically tempered glass having a compression stress layer ion-exchanged on the glass surface,
   A low-density layer having a reduced density on the surface of the compressive stress layer;
   The thickness of the low-density layer is 5 nm or more and 200 nm or less, and the ratio (D1) between the density (D1) of the low-density layer and the density (D3) of the intermediate layer that exists in the center of the glass and is sandwiched between the compressive stress layers / D3) is a chemically strengthened glass having a value of 0.5 or more and less than 0.93.
2. The chemically strengthened glass according to claim 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 (C1> C3).
3. The chemically strengthened glass according to claim 1 or 2, wherein an H / (Na + K) molar ratio (C1) of the low-density layer is 1.0 or more.
4. 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.
5. A method for producing chemically strengthened glass, wherein the glass is immersed in a molten salt containing potassium nitrate to ion-exchange Na in the glass and K in the molten salt,
   The molten 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. Adding at least one salt and washing the glass after the ion exchange,
   Furthermore, the manufacturing method of chemically strengthened glass including the process of making Na density | concentration in the said molten salt into 500 weight ppm or more, and the process of acid-treating glass after the said washing | cleaning.
6. The method for producing chemically tempered glass according to claim 5, comprising a step of setting the Na concentration in the molten salt to 500 ppm by weight or more and a step of acid-treating the glass after the washing.
7. The method for producing chemically strengthened glass according to claim 5 or 6, wherein the step of setting the Na concentration in the molten salt to 500 ppm by weight or more includes the step of adding Na salt to the molten salt.

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