JP2018080096A - Cover glass, display device and manufacturing method of cover glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cover glass hardly generating changes of color tones even when an antireflection film is formed on a glass substrate on which 2-step chemical reinforcement treatment is conducted.SOLUTION: There is provided a cover glass having a glass substrate with a compressive stress layer on a surface and an antireflection film arranged on at least one main surface of the glass substrate, the glass substrate contains phosphorus, a profile of compressive stress of the compressive stress layer has one or more inflection point and difference of avalues, Δaand difference of b, Δbat any 2 points in the glass surface having the antireflection film satisfy the following formula (1). √{(Δa)+(Δb)}≤4 (1).SELECTED DRAWING: None

Description

  The present invention relates to a cover glass, a display device, and a method for manufacturing the cover glass.

  In recent years, there are increasing opportunities for image display devices to be used in various devices such as navigation systems and speedometers mounted on vehicles and the like. As a characteristic of the cover glass of such an image display device, from the viewpoint of safety and appearance improvement, it is required to reduce reflection of external light and prevent an image from becoming difficult to see due to reflection of external light on the screen. It has been.

  As a means for preventing reflection and reflection on the glass surface, an antireflection technique for reducing surface reflection is known. As an antireflection technique, it has been proposed to reduce the reflection of light at the interface between the laminate and the air by laminating several layers having appropriate values of refractive index and optical film thickness as an optical interference layer ( Patent Document 1).

  In addition, although glass has high theoretical strength, its strength is greatly reduced due to scratches. Therefore, a chemically strengthened glass with a compressive stress layer formed on the glass surface by ion exchange or the like is used for the cover glass that requires strength. It has been. Here, it has been proposed to further increase the strength by performing chemical strengthening treatment in two stages (Patent Document 2).

JP 2003-215309 A US Patent Application Publication No. 2015/239775

  However, when a two-stage chemical strengthening treatment is performed using a glass substrate containing phosphorus among the glass substrates, and the antireflection film is provided on the glass substrate after the chemical strengthening treatment, the color tone of the glass substrate changes unevenly, It has been found that a problem of so-called color unevenness occurs.

  An object of the present invention is to provide a cover glass that hardly changes in color tone even when an antireflection film is formed on a glass substrate subjected to a two-step chemical strengthening treatment.

The inventors of the present invention have found out that the density reduction layer formed by performing the two-step chemical strengthening treatment on the glass substrate affects the occurrence of the color tone change, and is a cover glass in which the density reduction layer does not exist. It has been found that the above problems can be solved if there is. That is, the present invention relates to the following cover glass.
[1] A cover glass having a glass substrate having a compressive stress layer on a surface and an antireflection film provided on at least one main surface of the glass substrate,
The glass substrate includes phosphorus;
The compressive stress profile of the compressive stress layer has one or more inflection points;
A cover glass in which an a ^* value difference Δa ^* and an b ^* value difference Δb ^* at any two points in the glass surface having the antireflection film satisfy the following formula (1).
√ {(Δa ^* ) ² + (Δb ^* ) ² } ≦ 4 (1)
[2] An arbitrary 10 cm ² square portion in the glass surface having the antireflection film is selected as a measurement range, the measurement range is divided into 11 × 11, and a at all 100 intersection points of the bisector. ^* from the values and ^{b *} values, determined ^{a *} maximum value ^a _* max of, ^{a *} minimum value ^a _* min of, ^{b *} of the maximum value ^b _* max, ^{b *} the minimum value ^b _{* min,} respectively, the ^{a *} The difference between _max and the a ^* _min (a ^* _max− a ^* _min ) is Δa ^*, and the difference between the b ^* _max and the b ^* _min (b ^* _max− b ^* _min ) is the Δb ^* . The cover glass according to [1].
[3] The cover glass according to [1] or [2], wherein the glass substrate containing phosphorus is a glass substrate containing 4 to 15% of P ₂ O ₅ in a molar percentage based on oxide.
[4] The cover glass according to any one of [1] to [3], wherein the antireflection film is a laminate including at least one layer containing niobium and one layer containing silicon.
[5] The cover glass according to any one of [1] to [4], wherein the reflectance is 2% or less.
[6] The cover glass according to any one of [1] to [5], further including an antifouling film on the antireflection film.
[7] A chemical strengthening process in which a chemical strengthening process for generating a compressive stress layer on the surface of the glass substrate containing phosphorus is performed in two stages
A density reduction layer removing step of removing a surface layer of at least one main surface of the glass substrate by 5 nm or more;
The manufacturing method of a cover glass which has an antireflection film formation process which forms an antireflection film in the main surface which performed the said density reduction layer removal in order.
[8] A display device having a display panel and the cover glass according to any one of [1] to [6] on a display surface side of the display panel.

  According to the present invention, a cover glass having high strength and small color tone change is provided.

FIG. 1 is a graph showing the CS profile of the cover glass of Example 1. FIG. 2 is a graph showing the CS profile of the cover glass of Reference Example 1.

The cover glass of the present invention has an antireflection film on at least one surface of a glass substrate, and the difference between a ^* values Δa ^* and b ^* values at any two points in the glass surface on the side having the antireflection film. The difference Δb ^* satisfies the following expression (1).
√ {(Δa ^* ) ² + (Δb ^* ) ² } ≦ 4 (1)
Expression (1) is an index of color distribution in the glass surface, and when it is 4 or less, it means that the difference in color distribution in the glass surface is small, that is, the change in color tone is small. Formula (1) is preferably 3 or less, more preferably 2 or less.

Δa ^* in equation (1) can be calculated from the difference between two types of a ^* values measured by selecting two arbitrary points on the glass surface of the cover glass having the antireflection film. Δb ^* can be similarly calculated. a ^* and b ^* are luminous reflectances obtained by measuring the spectral reflectance of the surface of the substrate that has been subjected to antireflection treatment by a spectrocolorimeter (JIS Z 8729 (2004)). Year)).

Specifically, an arbitrary 10 cm ² square portion in the glass substrate is selected as a measurement range, the measurement range is divided into 11 × 11 equal parts, and a ^* value at 100 intersections of the bisector. from and ^{b *} values, determined ^{a *} maximum value ^a _* max of, ^{a *} minimum value ^a _* min of, ^{b *} of the maximum value ^b _* max, ^{b *} the minimum value ^b _{* min,} ^{respectively,} _{a * max} and a It is preferable that a difference between ^* _min (a ^* _max− a ^* _min ) is Δa ^* and a difference between b ^* _max and b ^* _min (b ^* _max− b ^* _min ) is Δb ^* .

The measurement range may be any area 10 cm ^2, the shape is not limited to a square. When the measurement range is not square, 100 measurement points may be selected as appropriate so that the distribution of luminous reflectances a ^* and b ^* within the measurement range can be understood.

  The cover glass of the present invention has a bending point where the compressive stress profile of the compressive stress layer on the surface of the glass substrate is 1 or more. The compressive stress profile is a correlation between the depth (μm) from the outermost surface of the glass and the compressive stress (CS). The inflection point of the compressive stress profile is a feature that appears when a multi-step chemical strengthening process is performed on a glass substrate. A glass substrate subjected to two or more stages of chemical strengthening has two or more regions having different slopes of compressive stress profiles, and therefore has one or more bending points in the CS profile. For example, when a two-step chemical strengthening process is performed, one inflection point is obtained. The compression stress profile has one or more bending points, that is, the glass substrate of the present invention that has been subjected to chemical strengthening in two or more stages has improved crack resistance when applied with a low load and has excellent scratch strength. . A specific method of the two-stage chemical strengthening treatment will be described later in the section of the manufacturing method.

  While the strength of the glass substrate is improved by subjecting the glass substrate to two or more steps of chemical strengthening, a low-density layer is formed on the surface of the glass substrate, although the mechanism is not clear. Since the low-density layer has a refractive index different from that of the glass substrate, if an antireflection film is further formed here, it is as if the low refractive index layer is non-uniformly present between the antireflection film and the glass substrate. It is considered that a change in color tone is likely to occur as a result. In this invention, the cover glass of this invention which satisfy | fills Formula (1) can be manufactured by forming an anti-reflective film, after removing the density reduction layer of the glass substrate surface produced in the chemical strengthening process.

<Glass substrate>
The glass substrate in the present invention contains phosphorus as an essential component. By chemically strengthening a glass substrate containing phosphorus as an essential component in two stages, the strength of the glass can be significantly increased.
The glass substrate containing phosphorus is preferably a glass substrate containing 4 to 15% of P ₂ O ₅ in terms of a molar percentage based on oxide. The content of P ₂ O ₅ is more preferably 4 to 10%. By being in this range, the scratch strength of the glass substrate is improved.

The composition of the glass substrate is not particularly limited as long as it contains phosphorus in the above-described amount and can be strengthened by molding and chemical strengthening treatment. Examples thereof include the following glass compositions.
A glass containing 40 to 70% of SiO ₂ , 11 to 25% of Al ₂ O ₃ , 4 to 15% of P ₂ O ₅ , and 13 to 25% of Na ₂ O in terms of mole percentage based on oxide.
Further, the glass substrate preferably contains 0 to 6% of B ₂ O ₃ , 0 to 5 mol% of K ₂ O, or 0 to 20% of Li ₂ O in terms of an oxide-based mole percentage. Moreover, it is preferable that a glass substrate contains 0-20% of MgO, 0-20% of CaO, 0-20% of SrO, or 0-15% of BaO by the oxide-based molar percentage display. Furthermore, when a glass substrate contains an alkaline-earth metal, it is preferable to contain 0-10 mol% RO (total amount of MgO + CaO + SrO + BaO). Glass _substrate, ZrO 2, TiO _2, and it is preferable that the SnO ₂ containing 0-5 mol% in total.

  The glass substrate in the present invention preferably has a maximum compressive stress (Compressive Stress, hereinafter abbreviated as CS) of the surface compressive stress layer of 300 to 1200 MPa. If CS of a glass substrate is an above-described value, the intensity | strength of glass can fully be made high. CS is more preferably 400 to 1000 MPa, and further preferably 500 to 900 MPa.

  The glass substrate in the present invention preferably has an ion exchange depth (Depth of layer, hereinafter abbreviated as DOL) of 5 to 80 μm. DOL is a depth at which birefringence can be confirmed. DOL is measured using a surface stress meter (FSM). If the DOL of the glass substrate is the value described above, the glass substrate has high durability against scratches, and as a result, the strength of the glass substrate can be sufficiently increased. The DOL is more preferably 7 to 60 μm, further preferably 10 to 30 μm.

The glass substrate in the present invention preferably has a maximum tensile stress inside the glass substrate (hereinafter abbreviated as CT) of 30 to 100 MPa. If CT is the value described above, the glass substrate is difficult to break. CT is more preferably 35 to 70 MPa, and further preferably 40 to 65 MPa. The CT of the glass substrate has the following relationship with the plate thickness (t, unit: μm), CS (unit: MPa), and DOL (unit: μm).
CT = (CS × DOL) / (t−2 × DOL)

The glass substrate in the present invention preferably has a depth of compression stress layer (Depth of Compression, hereinafter abbreviated as DOC) of 30 μm or more. The depth DOC of the compressive stress layer is the glass depth at which the stress value becomes 0 MPa inside the glass. If the DOC of the glass substrate is the above value, CT can be reduced even if CS is increased. The DOC is more preferably 30 to 100 μm, further preferably 35 to 80 μm. The DOC has the following relationship with the plate thickness (t, unit: μm) and DOL (unit: μm).
DOC = DOL × (1-DOL / t)

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

  Various methods can be employed for forming the glass. For example, various forming methods such as a down draw method (for example, an overflow down draw method, a slot down method, a redraw method, etc.), a float method, a roll out method, and a press method can be adopted.

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

  The glass substrate is preferably chemically strengthened in two stages in order to increase the strength of the cover glass. Chemical strengthening is performed before the antireflection film is formed. A specific method will be described later in the section of the manufacturing method.

<Antireflection film>
The cover glass of the present invention has an antireflection film by performing an antireflection film treatment (also referred to as “AR treatment”) on at least one main surface of the chemically strengthened glass substrate.
The material of the antireflection film is not particularly limited, and various materials can be used as long as they can suppress light reflection. For example, the antireflection film may have a structure in which a high refractive index layer and a low refractive index layer are laminated. The high refractive index layer here is a layer having a refractive index of 1.9 or more at a wavelength of 550 nm, and the low refractive index layer is a layer having a refractive index of 1.6 or less at a wavelength of 550 nm.

  The high refractive index layer and the low refractive index layer may each include one layer, but may include two or more layers. When two or more high refractive index layers and low refractive index layers are included, it is preferable that the high refractive index layers and the low refractive index layers are alternately laminated.

  In particular, in order to improve the antireflection performance, the antireflection film is preferably a laminate in which a plurality of layers are laminated. For example, the laminate has a total of 2 or more and 8 or less layers. It is more preferable that two or more layers and four or less layers are laminated. The laminate here is preferably a laminate in which a high refractive index layer and a low refractive index layer are laminated as described above, and the total number of layers of each of the high refractive index layer and the low refractive index layer is It is preferable that it is the said range.

The materials of the high refractive index layer and the low refractive index layer are not particularly limited, and can be selected in consideration of the required degree of antireflection, productivity, and the like. As a material constituting the high refractive index layer, for example, a material containing at least one selected from niobium, titanium, zirconium, tantalum, and silicon can be preferably used. Specifically, niobium oxide (Nb ₂ O ₅ ), titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), silicon nitride, and the like can be given. As a material constituting the low refractive index layer, for example, a material containing silicon can be preferably used. Specific examples include silicon oxide (SiO ₂ ), a material containing a mixed oxide of Si and Sn, a material containing a mixed oxide of Si and Zr, a material containing a mixed oxide of Si and Al, and the like. It is done.

  The high refractive index layer is either one selected from a layer containing niobium or a layer containing tantalum from the viewpoint of productivity and refractive index, and the low refractive index layer contains silicon. More preferably, the high refractive index layer is a layer containing niobium. That is, the antireflection film is preferably a laminate including one or more layers each containing niobium and silicon.

In the cover glass of the present invention, the antireflection film may be provided on at least one main surface of the glass substrate, but may be provided on both main surfaces of the glass substrate as necessary.
The method for forming the antireflection film will be described in detail in the section of the production method.

<Anti-fouling film>
From the viewpoint of protecting the glass surface, the cover glass of the present invention may further have an antifouling film (also referred to as “Anti Finger Print (AFP) film”) on the antireflection film. The antifouling film can be composed of, for example, a fluorine-containing organosilicon compound. The fluorine-containing organosilicon compound is not particularly limited as long as it imparts antifouling properties, water repellency, and oil repellency, and includes, for example, a polyfluoropolyether group, a polyfluoroalkylene group, and a polyfluoroalkyl group. And fluorine-containing organosilicon compounds having one or more groups selected from the group. The polyfluoropolyether group is a divalent group having a structure in which polyfluoroalkylene groups and etheric oxygen atoms are alternately bonded.

  Further, as a fluorine-containing organosilicon compound having one or more groups selected from the group consisting of a commercially available polyfluoropolyether group, polyfluoroalkylene group and polyfluoroalkyl group, KP-801 (trade name, Shin-Etsu Chemical Co., Ltd.) KY178 (trade name, manufactured by Shin-Etsu Chemical), KY-185 (trade name, manufactured by Shin-Etsu Chemical), KY-195 (trade name, Shin-Etsu Chemical) Co., Ltd.), OPTOOL (registered trademark) DSX and OPTOOL AES (both trade names, manufactured by Daikin) can be preferably used.

  The antifouling film is laminated on the antireflection film. When anti-reflection coatings are formed on both main surfaces of the glass substrate, anti-staining coatings can be formed on both anti-reflection coatings. It is good. This is because the antifouling film only needs to be provided in a place where a human hand or the like may come into contact, and can be selected according to its use.

  The cover glass of this invention may have a light-shielding part on the surface or the back surface. The light shielding portion is formed in a frame shape so as to surround the display surface of the display panel. A character, a figure, a logo, etc. may be formed in the area | region which has a light-shielding part. Further, the area having the light shielding portion may have a camera window or an area through which infrared rays pass.

<Contact angle>
The cover glass of the present invention preferably has a water contact angle of 90 ° or more. As a result, the cover glass surface has water repellency and oil repellency, and it is possible to obtain a cover glass on which dirt is hardly adhered. In order to set the contact angle to 90 ° or more, for example, having the antifouling film is mentioned.

<Reflectance>
The cover glass of the present invention preferably has a luminous reflectance of 2% or less. If the luminous reflectance is within the range, reflection can be sufficiently prevented. The luminous reflectance is defined based on JIS Z8701. A D65 light source was used as the light source.

<Production method of cover glass>
The cover glass of the present invention can be produced by, for example, the following steps, but is not limited thereto.
Process 1: Chemical strengthening treatment process 2: Densified layer removal process 3: Antireflection film formation process 4: Antifouling film formation

  The antifouling film can be formed as necessary. Furthermore, a printing process for forming a light shielding portion can be performed as necessary.

The printing process is a process of printing a printing pattern according to the purpose and application such as frame-shaped printing or logo printing in a color selected as appropriate when the cover glass needs to be decorated. Although any known printing method can be applied, for example, screen printing is suitable.
The printing process is preferably performed before the formation of the antireflection film and after the removal of the low-density layer. This is to prevent the printing unit from being affected by the process for removing the density-reducing layer.

  Since the antifouling film is formed for protecting the glass surface, it is preferable to form the antifouling film after the final step, that is, after the formation of the antireflection film.

<Step 1: Chemical strengthening treatment>
As the chemical strengthening treatment, for example, a metal ion (for example, Na ion) having a small ionic radius and a metal ion (for example, K ion) having a larger ionic radius contained in the glass are replaced with a compressive stress on the glass surface. Chemical strengthening by so-called ion exchange, which improves the strength of the glass by generating a layer, is performed twice or more.
Specifically, a glass substrate is immersed in molten salt to form a compressive stress layer on the glass surface. The molten salt is preferably an inorganic potassium salt that is in a molten state below the strain point (usually 500 to 600 ° C.) of the glass to be chemically strengthened, and preferably contains, for example, potassium nitrate (melting point 330 ° C.). The molten salt may contain other inorganic potassium salts in addition to potassium nitrate, and examples thereof include combinations with one or more selected from alkali sulfates such as potassium sulfate and potassium chloride, alkali chlorides and potassium carbonate, and the like. .

  The chemical strengthening treatment temperature of the glass (temperature of the molten salt bath) is preferably equal to or lower than the strain point (usually 500 to 600 ° C.) of the glass to be strengthened, and 350 ° C. or higher in order to obtain a higher compressive stress depth (DOL). preferable.

  The glass substrate may be preheated before the chemical strengthening treatment. The preheating temperature depends on the temperature of the molten salt bath, but is generally preferably 100 ° C. or higher.

  As conditions for the first-stage chemical strengthening treatment, the glass substrate is immersed in a molten salt heated and dissolved at 350 to 600 ° C. for 10 minutes to 20 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. Thereafter, the glass substrate is pulled up from the molten salt and held at a temperature of glass transition point + 50 ° C. or higher for 30 minutes to 30 hours.

  As conditions for the second-stage chemical strengthening treatment, the glass substrate is immersed in a molten salt heated and dissolved at 350 to 600 ° C. for 10 minutes to 20 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. Thereafter, the glass substrate is pulled up from the molten salt and held at a temperature of glass transition point + 50 ° C. or higher for 30 minutes to 30 hours. The molten salt used in the second stage may have the same composition as the first stage or a different composition.

  For the chemical strengthening tank for performing the chemical strengthening treatment, metals, quartz, ceramics, and the like can be used. Among these, a metal material is preferable from the viewpoint of durability, and a stainless steel (SUS) material is preferable from the viewpoint of corrosion resistance.

<Process 2: Densification layer removal>
The densified layer formed by performing the two-step chemical strengthening is removed. Specifically, a physical method such as polishing with an abrasive may be used.

  Examples of the method of polishing using an abrasive include a method of polishing the surface layer of the main surface of the glass substrate using a polishing liquid containing an abrasive selected from calcium carbonate, cerium oxide, colloidal silica, and the like.

  In removing the densified layer, the surface layer of the glass substrate main surface is removed by 5 nm or more, preferably 10 nm or more, and more preferably 30 nm or more. With such a removal amount, the low-density layer can be sufficiently removed. However, the upper limit of the removal amount is preferably 4 μm, more preferably 3 μm or less, and even more preferably 2 μm or less from the viewpoint of increasing the glass production efficiency.

  The density-reducing layer removal may be performed on at least one main surface of the glass substrate. When the antireflection film is formed on both main surfaces of the glass substrate, the density-reducing layer is also removed on both main surfaces.

<Step 3: Antireflection film formation>
The method for forming the antireflection film is not particularly limited, and various film forming methods can be used. In particular, it is preferable to form a film by a method such as pulse sputtering, AC sputtering, or digital sputtering. According to these methods, a dense antireflection film can be formed and durability can be ensured.

  For example, when film formation is performed by pulse sputtering, a glass substrate is placed in a chamber of a mixed gas atmosphere of inert gas and oxygen gas, and a target is selected so as to obtain a desired composition. I can make a film.

  At this time, the gas type of the inert gas in the chamber is not particularly limited, and various inert gases such as argon and helium can be used.

  The pressure in the chamber by the mixed gas of the inert gas and oxygen gas is not particularly limited, but the surface roughness of the antireflection film is easily preferred by setting the pressure in the range of 0.5 Pa or less. Since it can be set as a range, it is preferable. This is because if the pressure in the chamber by the mixed gas of inert gas and oxygen gas is 0.5 Pa or less, the mean free path of the film forming molecules is secured, and the film forming molecules reach the substrate with more energy. To do. Therefore, it is considered that rearrangement of film forming molecules is promoted, and a film having a relatively dense and smooth surface can be formed. The lower limit value of the pressure in the chamber by the mixed gas of the inert gas and oxygen gas is not particularly limited, but is preferably 0.1 Pa or more, for example.

<Process 4: Antifouling film formation>
The method for forming the antifouling film of this embodiment is not particularly limited, but it is preferable to form the film by vacuum deposition using the above-described fluorine-containing organosilicon compound material.

In general, fluorine-containing organosilicon compounds are stored in a mixture with a solvent such as a fluorinated solvent in order to suppress deterioration due to reaction with moisture in the atmosphere. If it is subjected to the film forming process as it is, the durability of the obtained thin film may be adversely affected.
For this reason, in the present embodiment, the fluorine-containing organosilicon compound that has been subjected to the solvent removal treatment before heating in the heating container, or the fluorine-containing organosilicon that has not been diluted with the solvent (no solvent added) It is preferable to use a compound.

  As an example of the method for forming the antifouling film, in the description of the present embodiment, an example using a fluorine-containing organosilicon compound as a solution or stock solution has been described, but the present invention is not limited thereto. As another method, for example, a so-called deposition pellet in which a certain amount of a fluorine-containing organosilicon compound is impregnated with a porous metal (for example, tin or copper) or a fibrous metal (for example, stainless steel) is commercially available. There is a method of using this (for example, Surf Clear manufactured by Canon Optron). In this case, it is possible to easily form an antifouling film by using an amount of pellets corresponding to the capacity of the vapor deposition apparatus and the required film thickness as a vapor deposition source.

  The cover glass of this invention can be manufactured with the said manufacturing method.

<Display device>
The display device of the present invention has a display panel and a cover glass on the display surface side of the display panel, and the cover glass has at least one of a glass substrate having a compressive stress layer on the surface and containing P as an essential component. The main surface has an antireflection film, the compressive stress profile of the compressive stress layer on the surface of the glass substrate has one or more bending points, and at any two points in the glass surface having the antireflection film The a ^* value difference Δa ^* and the b ^* value difference Δb ^* satisfy the following formula (1).
√ {(Δa ^* ) ² + (Δb ^* ) ² } ≦ 4 (1)

  The preferable form of the cover glass included in the display device of the present invention is the same as the cover glass of the present invention described above.

  Examples of the display panel constituting the display device of the present invention include a liquid crystal display panel (LCD panel) and an organic EL display panel (OLED panel). When the display panel is an LCD panel, the display device of the present invention has a backlight unit on the back surface (the surface on which the cover glass is not provided) of the display panel.

  The display device of the present invention may have a touch panel between the display panel and the cover glass. A known touch panel can be used, and examples thereof include a capacitance type, a resistance film type, and an infrared optical type. The touch panel may be incorporated in the display panel. Examples of such a display panel include an in-cell type and an on-cell type.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these.

A cover glass was produced by the following procedure. The glass substrate used is one of the following.
Glass substrate (1): SiO ₂ 61 mol%, the _Al 2 _{O 3} 15.5 _mol%, P 2 _{O 5} to 7 mol%, a Na ₂ O 16.5 mole% (content, on an oxide basis (It is a value calculated as a mole percentage of.)
Glass substrate (2): Dragon Trail (registered trademark) manufactured by Asahi Glass Co., Ltd.

<Example 1>
Step 1: Chemical strengthening treatment Using a glass substrate (1), a glass substrate from which a protective film has been removed is immersed in potassium nitrate heated and dissolved at 450 ° C. for 60 minutes, and then the glass substrate is pulled up from the molten salt to 400 ° C. At 470 minutes. Then, after immersing the glass substrate again in potassium nitrate heated / dissolved at 450 ° C. for 2 minutes, holding at 400 ° C. for 10 minutes and gradually cooling to room temperature in 60 minutes, the profile of the compressive stress has a bending point. A glass substrate was obtained. Subsequently, this glass substrate was immersed in a 40 ° C. warm bath to remove potassium nitrate adhering to the substrate surface.
Step 2: Removal of Densified Layer Next, the glass substrate obtained in Step 1 was immersed in a nitric acid solution (6 wt.%, 40 ° C.) for 3 minutes.
Next, this substrate was used with an aqueous solution (slurry) containing a cerium oxide abrasive having an average particle size of 1.2 to 1.8 μm at a concentration of 4 Be, and a suede pad. One side of the glass substrate after chemical strengthening was polished 20 times. The removal amount of the glass substrate by polishing was about 2 μm.
Step 3: Antireflection Film Formation Next, an antireflection film was formed on one surface by the following procedure.
First, using a niobium oxide target (trade name: NBO target manufactured by AGC Ceramics Co., Ltd.) while introducing a mixed gas obtained by mixing 10% by volume of oxygen gas with argon gas in a vacuum chamber, a pressure of 0.3 Pa, Pulse sputtering is performed under the conditions of a frequency of 20 kHz, a power density of 3.8 W / cm ² , and an inversion pulse width of 5 μsec, and a high refractive index layer made of niobium oxide (niobium) having a thickness of 13 nm is formed on one surface of the glass substrate. did.
Next, while introducing a mixed gas obtained by mixing 40% by volume of oxygen gas into argon gas, using a silicon target, conditions of pressure 0.3 Pa, frequency 20 kHz, power density 3.8 W / cm ² , and inversion pulse width 5 μsec Then, pulse sputtering was performed under the condition of a pulse width of 5 μsec to form a low refractive index layer made of silicon oxide (silica) having a thickness of 35 nm on the high refractive index layer.
Next, in the same manner as in the first layer, a high refractive index layer made of niobium oxide (niobium) having a thickness of 115 nm was formed on the low refractive index layer.
Next, in the same manner as the second layer, a low refractive index layer made of silicon oxide (silica) having a thickness of 90 nm was formed.
In this way, an antireflection film was formed in which a total of four layers of niobium oxide (niobia) and silicon oxide (silica) were laminated.
Step 4: Antifouling film formation An antifouling film material (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KY-185) was introduced into a heating container. Thereafter, the inside of the heating container was deaerated with a vacuum pump for 10 hours or more to remove the solvent in the solution, thereby obtaining a composition for forming a fluorine-containing organosilicon compound film.
Subsequently, the heating container containing the composition for forming the fluorine-containing organosilicon compound film was heated to 270 ° C. After reaching 270 ° C., that state was maintained for 10 minutes until the temperature stabilized. And from the nozzle connected to the heating container containing the composition for forming the fluorine-containing organosilicon compound film with respect to the antireflection film of the transparent substrate on which the antireflection film is placed in the vacuum chamber. Then, a composition for forming a fluorine-containing organosilicon compound film was supplied to form a film. During film formation, the film thickness is measured with a quartz crystal monitor installed in a vacuum chamber, and film formation is performed until the film thickness of the fluorine-containing organosilicon compound film formed on the transparent substrate reaches 4 nm. It was. When the fluorine-containing organosilicon compound film reached 4 nm, the supply of the raw material from the nozzle was stopped, and then the manufactured optical component was taken out from the vacuum chamber. The extracted optical component was placed on a hot plate with the film surface facing upward, and heat-treated in the atmosphere at 150 ° C. for 60 minutes.

<Examples 2 to 4>
A cover glass was produced in the same manner as in Example 1 except that the base material and each processing condition were changed to the conditions shown in Table 1.

<Comparative Example 1>
A cover glass was produced in the same manner as in Example 1 except that Step 2 was not performed.

<Comparative example 2>
A cover glass was produced in the same manner as in Example 1 except that the step 2 was changed to a step of immersing in a 40 ° C. citric acid solution (20 mass%) for 3 minutes. The removal amount of the glass substrate was about 0.1 nm.

<Reference Examples 1 and 2>
A cover glass was prepared in the same manner as in Example 1 except that the step 2 was not performed and the base material and other processing conditions were changed to the conditions shown in Table 2.

  About each cover glass produced by the above, it evaluated by measuring the following item. The results are shown in Tables 1 and 2.

(Luminous reflectance)
Using a spectrocolorimeter (manufactured by Konica Minolta, model: CM-2600d), the spectral reflectance of the surface of the glass substrate that has been subjected to the antireflection treatment is measured in the SCI mode. (Stimulus value Y of reflection defined in JIS Z8701) was determined. At that time, in order to cancel the reflection from the back surface not subjected to the antireflection treatment, the back surface was painted black and measured. The light source was calculated as a D65 light source.

(Color distribution)
First, an arbitrary 10 cm ² square portion of a glass substrate is selected as a measurement range, and the color is measured at 100 points of intersections in the substrate of a grid obtained by equally dividing the measurement range by 11 × 11 as follows. did.
A spectral colorimeter (manufactured by Konica Minolta, model: CM-2600d) is used to measure the spectral reflectance of the surface of the substrate that has undergone antireflection treatment in the SCI mode. From the reflectance, the luminous reflectance ( Color indexes a ^* and b ^* ) defined in JIS Z 8729 were obtained. At that time, in order to cancel the reflection from the back surface not subjected to the antireflection treatment, the back surface was painted black and measured.
The color distribution E is calculated from the maximum and minimum values (a ^* _max , a ^* _min , b ^* _max , b ^* _min ) of a ^* and b ^* out of 100 points. Sought by.
E = √ {(a ^* _max− a ^* _min ) ² + (b ^* _max− b ^* _min ) ² } (1-1)
Subsequently, the measurement range was changed, and the same measurement as described above was repeated a total of 3 times, and E was obtained.

(CS profile, DOC)
The stress profile was measured for the glass substrate using a surface stress measuring machine (manufactured by Orihara Seisakusho, model: FSM-6000LE).
The stress value (unit: MPa) when the glass depth from the outermost surface was 0 μm was defined as the compressive stress (CS) of the outermost layer on one main surface of the chemically strengthened glass. And the presence or absence of a bending point and the inclination of CS before and after the bending point were calculated from the stress profile obtained from the correlation between the glass depth and CS. Further, the glass depth (unit: μm) at which the stress value becomes 0 MPa in the glass was defined as the depth (DOC) of the compressive stress layer.

  In Reference Example 1 and Reference Example 2 in which the chemical strengthening is performed in one stage, the value of the color distribution E is small and the problem that the color tone changes hardly occurs. On the other hand, when chemical strengthening is performed in two stages, as shown in Comparative Example 1, it can be seen that the value of the color distribution E is large and the change in color tone is large when the density-reducing layer is not removed. In addition, it can be seen from the results of Comparative Example 2 that when the removal amount of the low-density layer is insufficient, the value of the color distribution E is large and the color tone change is large.

  On the other hand, the cover glass of each example shows that the change in color tone is reduced because the value of the color distribution E is lowered, and it can be seen that the effect is that the reach-out layer is removed. . Furthermore, since all satisfy | filling E <= 4 in three measurements of the color distribution of each Example, it turns out that the uniformity in a glass surface is also high.

  Further, FIG. 1 shows the CS profile of the cover glass of Example 1 and FIG. 2 of the reference example 1, respectively. Since the glass substrate subjected to chemical strengthening in two stages has two regions having different inclinations of the CS, it can be understood that the glass substrate has one bending point in the CS profile.

Claims (8)

A cover glass having a glass substrate having a compressive stress layer on the surface and an antireflection film provided on at least one main surface of the glass substrate,
The glass substrate includes phosphorus;
The compressive stress profile of the compressive stress layer has one or more inflection points;
A cover glass in which an a ^* value difference Δa ^* and an b ^* value difference Δb ^* at any two points in the glass surface having the antireflection film satisfy the following formula (1).
√ {(Δa ^* ) ² + (Δb ^* ) ² } ≦ 4 (1) An arbitrary 10 cm ² square portion in the glass surface having the antireflection film is selected as a measurement range, the measurement range is divided into 11 × 11, and the a ^* value at all 100 intersections of the bisectors and wherein the b ^* value, ^{a *} maximum value ^a _* max of, ^{a *} minimum value ^a _* min, the ^{b *} maximum value ^b _* max, the calculated ^{b *} the minimum value ^b _{* min,} respectively, and the ^a _{* max} The difference between a ^* _min (a ^* _max− a ^* _min ) is defined as Δa ^*, and the difference between b ^* _max and b ^* _min (b ^* _max− b ^* _min ) is defined as Δb ^*. Cover glass as described in. 3. The cover glass according to claim 1, wherein the glass substrate containing phosphorus is a glass substrate containing 4 to 15% of P ₂ O ₅ in terms of a molar percentage based on an oxide.   The cover glass according to any one of claims 1 to 3, wherein the antireflection film is a laminate including one or more layers containing niobium and a layer containing silicon.   The cover glass according to any one of claims 1 to 4, wherein the reflectance is 2% or less.   The cover glass according to claim 1, further comprising an antifouling film on the antireflection film. A chemical strengthening process in which a chemical strengthening treatment for generating a compressive stress layer on the surface of the glass substrate containing phosphorus is performed in two stages;
A density reduction layer removing step of removing a surface layer of at least one main surface of the glass substrate by 5 nm or more;
The manufacturing method of a cover glass which has an antireflection film formation process which forms an antireflection film in the main surface which performed the said density reduction layer removal in order.   The display apparatus which has a display panel and the cover glass of any one of Claims 1-6 in the display surface side of a display panel.

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