JP2019026508A - Back cover glass - Google Patents

Abstract

To provide a back cover glass having high hardness and high reflection and preferably having high radio wave permeability.SOLUTION: There is provided a back cover glass in which a light-shielding layer is formed on one principal surface of a glass substrate and a reflection color-adjusting layer is formed on the other principal surface of the glass substrate, wherein the reflection color-adjusting layer is formed by alternately laminating a film made of a high refractive index material and a film made of a low refractive index material a plurality of times and is formed so that the difference in refractive indexes at a wavelength of 550 nm between the film made of a high refractive index material and the film made of a low refractive index material is 0.1 or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a back cover glass of an image display device used for mobile devices such as mobile phones and tablet terminals.

  In recent years, with the spread of mobile devices equipped with image display devices such as mobile phones and tablet terminals, research and development of back cover glasses that protect not only the display surface of the image display device but also the back surface against impact etc. (Patent Document 1).

  In the case of the cover glass disposed on the display surface side of the image display device, the required characteristics other than the mechanical strength are required to have high light transmittance, but the back cover glass disposed on the back surface side of the image display device. In this case, the required characteristics other than mechanical strength are required to be excellent in aesthetics. Therefore, the glass plate used as the back cover glass is subjected to a decorating process on the main surface that becomes the exposed surface when used.

As the decoration processing performed for the above-mentioned purpose, the light from the image display device is shielded and the light-shielding layer for adjusting the color, and the reflection color adjustment for adjusting the color tone of the reflected light from the light-shielding layer Formation of a layer is common (patent documents 2 and 3).
As the light shielding layer, metal materials such as aluminum, copper, silver, etc., metal layers composed of oxides such as indium, tin, zinc, etc., niobium, titanium, zirconium, tantalum, hafnium, aluminum, silicon, copper, iron In general, layers coated with dark ink containing chromium, oxides, nitrides, lower oxides, and lower nitrides are used, but inks using inorganic colorants and organic colorants are applied. May be formed.
The reflection color adjustment layer is generally a laminated film in which a film made of a high refractive index material and a film made of a low refractive index material are alternately laminated a plurality of times.

Republished Patent No. 2006-098181 JP 2014-227309 A JP 2014-197324 A JP-T-2006-524581

  FIG. 2 is a cross-sectional view schematically showing the configuration of a conventional back cover glass. In the back cover glass 100 shown in FIG. 2, the reflective color adjustment layer 130 and the light shielding layer 120 are formed in this order toward the inner side of the back cover glass 100 with respect to the glass substrate 110. The antifouling layer 140 is formed in the direction.

  Conventionally, a back cover glass that protects the back surface of an image display device from an impact or the like peels off, discolors, cracks, or scratches on the reflective color adjustment layer 130 when exposed to an environment such as impact, rubbing, high temperature, and high humidity. As shown in FIG. 2, a film made of a high refractive index material constituting the reflective color adjustment layer 130 and a low refractive index toward the inner side of the back cover glass 100 with respect to the glass substrate 110 as shown in FIG. It was formed by laminating films made of a rate material.

However, when the reflection color adjustment layer 130 is formed in the inner direction of the back cover glass 100 with respect to the glass substrate 110, if an impact is applied to the outer surface of the glass substrate 110 where the reflection color adjustment layer 130 is not formed, the reflection color adjustment layer 130 is reflected. There is a problem that cracks occur on the inner surface of the glass substrate 110 that forms an interface with the adjustment layer 130, and cracks occur in the reflective color adjustment layer 130 starting from this.
Further, when a material having a low resistance value such as a metal is used for the light shielding layer 120, radio wave shielding occurs, so that the structure is unsuitable for wireless power feeding and communication.

Patent Document 4 discloses a highly transmissive cover glass article, but the back cover glass is preferably highly reflective for the following reasons.
The color that can be seen when the back cover glass is viewed from the outside overlaps the color that the light shielding layer 120 has transmitted through the reflection color adjustment layer and the color that light incident from the outside is reflected by the reflection color adjustment layer. , Can make the desired color. That is, when the reflective layer has a certain amount of reflectance, desired color characteristics can be obtained.

  An object of the present invention is to provide a back cover glass having high hardness and high reflection, preferably high radio wave permeability.

  In order to achieve the above object, the present invention provides a back cover glass in which a light-shielding layer is formed on one main surface of a glass substrate and a reflection color adjusting layer is formed on the other main surface of the glass substrate, The adjustment layer is formed by alternately laminating a film made of a high refractive index material and a film made of a low refractive index material several times, and the wavelength of the film made of the high refractive index material and the film made of the low refractive index material Provided is a back cover glass characterized in that the difference in refractive index at 550 nm is 0.1 or more.

  In the back cover glass of the present invention, the film made of the high refractive index material preferably has a refractive index of 1.8 or more at a wavelength of 550 nm.

  In the back cover glass of the present invention, the film made of the low refractive index material preferably has a refractive index of 1.5 or less at a wavelength of 550 nm.

  In the back cover glass of the present invention, the film made of the high refractive index material and the film made of the low refractive index material in the reflective color adjustment layer are selected from the group consisting of Si, Al, Zr, and Ti. It is preferably made of an oxide film, a nitride film, and an oxynitride film containing one or more elements.

  In the back cover glass of the present invention, the light shielding layer comprises any one selected from the group consisting of an inorganic colorant ink, an organic colorant ink, and an ink containing an inorganic filler in an organic resin. The average transmittance of the back cover glass from the layer side from a wavelength of 400 nm to a wavelength of 750 nm is preferably 5% or less.

  In the back cover glass of the present invention, the glass substrate is a chemically tempered glass having a compressive stress layer on the surface, and the reflective color adjusting layer is formed on the surface of the chemically tempered glass having the compressive stress layer. Is preferred.

In the back cover glass of the present invention, it is preferable that the Martens hardness measured from the reflective color adjusting layer side satisfies at least one of the following (1) and (2).
(1) The Martens hardness at 50 nm indentation depth of the Vickers indenter is 6000 N / mm ² or more.
(2) The Martens hardness at the indentation depth of 100 nm of the Vickers indenter is 6000 N / mm ² or more.

  In the back cover glass of the present invention, the reflective color adjusting layer is preferably formed by sputtering.

  In the back cover glass of the present invention, it is preferable that the reflective color adjusting layer is located outside the glass substrate when the back cover glass is used.

  In the back cover glass of the present invention, an antifouling film is preferably provided on the reflective color adjusting layer.

According to the back cover glass of the present invention, high hardness and high reflection can be achieved.
According to the preferred embodiment of the back cover glass of the present invention, it is possible to achieve higher radio wave permeability.

FIG. 1 is a cross-sectional view schematically showing one configuration example of the back cover glass of the present invention. FIG. 2 is a cross-sectional view schematically showing a configuration example of a conventional back cover glass. FIG. 3 shows an example of a radical assist sputtering apparatus. FIG. 4 is a schematic diagram for explaining a ball-on-ring test method.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view schematically showing one structural example of the back cover glass of the present invention.
The back cover glass 10 shown in FIG. 1 has the glass substrate 11 which makes a transparent base material. The glass substrate 11 has two main surfaces (an upper main surface and a lower main surface in the figure).
In the back cover glass 10 shown in FIG. 1, a light shielding layer 12 is formed on one main surface (upper main surface in the drawing) of the glass substrate 11, and the other main surface (in the drawing, A reflective color adjusting layer 13 and an antifouling film 14 are formed in this order on the lower main surface.
However, in the back cover glass of the present invention, the glass substrate 11, the light shielding layer 12, and the reflection color adjusting layer are essential components, and the antifouling film 14 is an arbitrary component.

  In the back cover glass 10 shown in FIG. 1, the light shielding layer 12, the reflective color adjusting layer 13, and the antifouling film 14 are formed on different main surfaces of the glass substrate 11 forming a transparent base material. Here, the light shielding layer 12 is formed toward the inner side of the back cover glass 10 with respect to the glass substrate 11, and the reflection color adjusting layer 13 and the antifouling film 14 are formed with respect to the glass substrate 11 in the back cover glass. 10 is formed in the outward direction.

The back cover glass 10 shown in FIG. 1 has the reflective color adjustment layer 13 formed on the glass substrate 11 toward the outer side of the back cover glass 10, so that in the conventional back cover glass 100 shown in FIG. The problem of reduced surface strength is eliminated.
However, in the back cover glass 10 shown in FIG. 1, since the impact is applied to the reflection color adjustment layer 13 formed toward the outer side of the back cover glass 10 with respect to the glass substrate 11, the reflection color adjustment layer 13 is sufficient. It is required to have hardness.
In this specification, in this specification, the Martens hardness measured from the reflective color adjustment layer side (hereinafter referred to as Martens hardness in the present specification) is used as an index.
The back cover glass 10 shown in FIG. 1 preferably satisfies at least one of the following (1) and (2).
(1) The Martens hardness at 50 nm indentation depth of the Vickers indenter is 6000 N / mm ² or more.
(2) The Martens hardness at the indentation depth of 100 nm of the Vickers indenter is 6000 N / mm ² or more.
In addition, the back cover glass 10 shown in FIG. 1 has also solved the problem that the outer surface of the back cover glass is cracked when the reflective color adjusting layer 13 has sufficient hardness.

  Further, the reflection color adjusting layer 13 in the back cover glass 10 shown in FIG. 1 includes a film made of a high refractive index material (hereinafter referred to as a high refractive index film) and a film made of a low refractive index material (hereinafter referred to as a low refractive index film). Is described as a refractive index film), and the “color” when the back cover glass 10 is viewed from the outside direction is optically designed by alternately laminating a plurality of times. In this specification, “color” means “hue”, “saturation”, and “lightness”. The back cover glass 10 shown in FIG. 1 is a back cover glass excellent in design that can express a desired “color” by having the reflective color adjustment layer 13.

  In this specification, in order to achieve this function, the reflection color adjusting layer 13 is formed so that the difference in refractive index between the high refractive index film and the low refractive index film at a wavelength of 550 nm is 0.1 or more. Yes. If the refractive index difference between the two is less than 0.1, it is difficult to obtain reflection characteristics having a constant value in a wide wavelength range. As a result, when the angle of the back cover is changed, the change in the color of the back cover becomes large, the color changes depending on the viewing angle, and stable colors cannot be obtained.

  The high refractive index film and the low refractive index film used for the reflective color adjustment layer 13 are not particularly limited as long as the difference in refractive index between the two satisfies the above range, but the high refractive index film and the low refractive index film used for the reflective color adjustment layer 13 are not limited. Preferred examples of are as follows.

(High refractive index film)
The high refractive index film preferably has a refractive index of 1.8 or more at a wavelength of 550) nm, more preferably 1.9 or more from the viewpoint of optical adjustment.

(Low refractive index film)
The low refractive index film has a refractive index at a wavelength of 550) nm which is smaller than that of the high refractive index film, and is less than 1.80. The refractive index is preferably 1.5 or less from the viewpoint of adjusting optical characteristics. 1.48 or less is more preferable.

The constituent material of the high refractive index film and the low refractive index film used for the reflective color adjustment layer 13 is an oxide containing one or more elements selected from the group consisting of Si, Al, Ti, Ta, Nb and Zr, Nitride as well as oxynitride can be used.
Examples of the oxide containing the above element include SiO ₂ , Al ₂ O ₃ , TiO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , and ZrO ₂ .
Examples of the nitride containing the above element include Si ₃ N ₄ , AlN, and TiN.
Examples of the oxynitride containing the above element include SiON, AlON, and TiON.

  In the reflective color adjustment layer 13, the constituent materials of the high refractive index film and the low refractive index film may be appropriately selected from these materials so that the refractive index difference between the two satisfies the above-described conditions.

As a constituent material of the high refractive index film, Si ₃ N ₄ , AlON, and TiZrO are more preferable, and AlON is particularly preferable because of high hardness and improved scratch resistance of the obtained back cover glass. The refractive index of Si ₃ N _{4 at} a wavelength of 550 nm is 1.95. In addition, AlON can change a refractive index by changing the content rate of oxygen and nitrogen. The ratio of oxygen and nitrogen is selected so that the selected AlON has a refractive index of 1.85 or more at a wavelength of 550 nm. For example, the refractive index at a wavelength of 550 nm is 1.95. In the present invention, the refractive index can be measured by ellipsometry.

As the constituent material of the low refractive index film, Al ₂ O ₃ , AlON, and SiO ₂ are more preferable because the refractive index is lower than that of the high refractive index constituent material and the reflectance can be easily adjusted by interference. The refractive index of SiO ₂ at 550 nm is 1.47. AlON can change the refractive index by changing the content ratio of oxygen and nitrogen. The ratio of oxygen and nitrogen is selected so that the selected AlON has a refractive index of 1.68 or less at a wavelength of 550 nm. The refractive index at a wavelength of 550 nm is 1.65.

The reflection color adjustment film 13 can be formed by alternately forming a high refractive index film and a low refractive index film constituting the reflection color adjustment film 13 on one main surface of the glass substrate 11. The film formation can be performed by a vapor phase film formation method. Examples of vapor deposition methods include chemical vapor deposition (CVD) and physical vapor deposition (PVD). Examples of chemical vapor deposition (CVD) include thermal CVD, plasma CVD, laser CVD, and atomic layer deposition (ALD). Examples of physical vapor deposition (PVD) include vacuum vapor deposition, ion-assisted vapor deposition, ion plating, and sputtering.
Among these, sputtering is preferable in that a film having high hardness can be obtained under a low film formation temperature. In addition, when the temperature of the glass substrate 11 from after film formation to after film formation exceeds 200 ° C., when chemically strengthened glass is used as the glass substrate, the strength of the glass substrate 11 is reduced and the antifouling film 14 is formed. Since it becomes difficult to adhere, it is necessary to cool the glass substrate 11.

  As the film forming apparatus, for example, a radical assist sputtering apparatus is preferably used. In the radical assist sputtering apparatus, a film formation region and a reaction region are separately provided in a single vacuum vessel, and film formation processing and reaction processing can be performed independently. Hereinafter, the radical assist sputtering apparatus will be specifically described.

FIG. 3 shows an example of a radical assist sputtering apparatus.
A radical-assisted sputtering apparatus 200 shown in FIG. 3 includes an apparatus main body 210 and a drum 220 provided therein. The drum 220 holds the glass substrate, and rotates while holding the glass substrate. The space around the drum 220 is divided into a plurality of regions by the wall portion 230.

  The first region (right side in the figure) is a film formation region, and the target 240 is arranged. A power source 250 is connected to the target 240. In addition, an argon gas supply unit 260 that supplies argon gas is connected to the first region.

  The second region (lower side in the figure) is a reaction region, and a radical source 270 is disposed. A matching machine and an RF source 280 are connected to the radical source 270. In addition, an argon gas supply unit 310 that supplies argon gas, a nitrogen gas supply unit 320 that supplies nitrogen gas, and an oxygen gas supply unit 330 that supplies oxygen gas are connected to the second region.

  In such radical assist sputtering apparatus 200, first, a glass substrate is held on drum 220. Thereafter, when the drum 220 rotates, the glass substrate is conveyed to the first region (right side in the drawing). Argon gas is supplied from the argon gas supply unit 260 to the first region. Then, by sputtering the target 240, a film made of the constituent material of the target 240 is formed on the surface of the glass substrate. An example of such a film is a metal film that has not been oxidized or nitrided. By not oxidizing or nitriding, the film forming speed is improved and the film quality is improved because the film formation is performed stably.

  Thereafter, the drum 220 holding the glass substrate rotates, so that the glass substrate is conveyed to the second region (lower side in the figure). Nitrogen gas, argon gas, and oxygen gas are supplied to the second region from the argon gas supply unit 310, the nitrogen gas supply unit 320, and the oxygen gas supply unit 330 as necessary. Oxidation or nitridation is performed when the plasma contacts the film provided on the glass substrate. By using plasma, oxidation and nitridation can be performed uniformly and a dense film can be obtained.

As described above, the reflective color adjustment layer 13 is formed by alternately stacking a high refractive index film and a low refractive index film a plurality of times. Thereby, the progress of scratches is easily stopped at the laminated interface, and the scratch resistance is improved.
In the reflective color adjustment layer 13, the order in which the high refractive index film and the low refractive index film are laminated is not particularly limited, but the low refractive index film is formed on the main surface of the glass substrate 11, and the high refractive index film is formed thereon. It is preferable to stack the layers because the adhesion of the film becomes good.
On the other hand, the outermost layer of the reflective color adjusting layer is preferably a high refractive index film in order to increase the reflectance, because a back cover glass with higher transmittance can be obtained. However, when the antifouling film 14 is provided, it is not necessary to stick to the refractive index.
When the antifouling film 14 is formed on the reflection color adjustment layer 13 as in the cover glass 10 shown in FIG. 1, the outermost layer of the reflection color adjustment layer 13 also from the viewpoint of adhesion to the antifouling film 14. Is preferably a low refractive index film.
That is, it is more preferable that a low refractive index film is formed on the main surface of the glass substrate 11, a high refractive index film is laminated thereon, and the outermost layer of the reflective color adjustment layer 13 is a low refractive index film. . In this case, the total number of layers of the low refractive index film and the high refractive index film in the reflective color adjustment layer 13 is an odd number.

  The film thickness of the single film of the high refractive index film and the low refractive index film constituting the reflective color adjusting layer 13 is not particularly limited, but the film thickness of the single film is preferably 250 nm or less. This is because if the film thickness of the single film exceeds 250 nm, the compressive stress or tensile stress per single film increases, and the back cover glass 10 tends to warp. When the film thickness of the single film is 250 nm or less, the compressive stress or tensile stress per single film is small, and even when the single films are laminated a plurality of times, the back cover glass 10 is unlikely to warp.

The number of stacked high refractive index films and low refractive index films constituting the reflective color adjusting layer 13 is not particularly limited, but it is preferable to stack six or more of these films, and the total film thickness is 850 to 6000 nm. Is preferred. By setting the number of films and the film thickness, excellent scratch resistance can be obtained.
The total number of layers of these films is preferably 20 layers or more, more preferably 40 layers or more, from the viewpoint of the effect of suppressing the progress of scratches due to the interface. The upper limit is usually 100 layers or less.

  The total thickness of the reflective color adjusting layer 13 may be 850 nm or more, but 1000 nm or more is preferable from the viewpoint of securing the strength, and 1500 nm or more is more preferable. The upper limit is preferably 6000 nm or less from the viewpoint of optical properties, more preferably 3000 nm or less, and even more preferably 2500 nm or less. For example, the total film thickness is more preferably 850 to 3000 nm. The total film thickness of the reflective color adjustment layer 13 is the sum of the single film thicknesses of the high refractive index film and the low refractive index film.

The film thickness of the single film of the high refractive index film and the single film of the low refractive index film may be 5 to 250 nm, respectively, but the total thickness of the single film of the high refractive index film is more than the total thickness of the single film of the low refractive index film. It is also preferable that the thickness is thick.
For example, when the total film thickness of the reflective color adjusting layer 13 is 2000 nm, the total thickness of the high refractive index film is preferably 1200 nm or more, and more preferably 1500 nm or more. Moreover, when the total film thickness of the reflective color adjustment layer 13 is 3000 nm, the total thickness of the high refractive index film is preferably 1800 nm or more, and more preferably 2000 nm or more.

  In the high refractive index film and the low refractive index film, the thickness of each single film may be the same or different. Moreover, the high refractive index material and the low refractive index material constituting each single film may be the same or different.

  The low refractive index film is preferably formed by laminating three or more films having a single film thickness of 5 to 250 nm. The low refractive index film is preferably thinner than the thickness of the single film of the high refractive index film because warpage can be further reduced. The thickness of the single film of the low refractive index film can be measured by a contact-type film thickness meter or cross-sectional SEM observation if it is only a single film, and can be measured by ellipsometry in the case of lamination.

  Each configuration of the back cover glass 10 shown in FIG. 1 will be further described.

(Glass substrate 11)
The glass substrate 11 in the back cover glass 10 shown in FIG. 1 preferably has a thickness of 1 mm or less, and more preferably 0.8 mm or less.
The lower limit of the thickness is preferably 0.2 mm or more, and more preferably 0.3 mm or more.

The glass substrate 11 should just be transparent with respect to visible light and near-infrared light, The composition is not specifically limited, Any of inorganic glass and organic glass may be sufficient.
The glass substrate 11 is composed of, for example, soda lime glass, alkali-free glass, borosilicate glass, aluminosilicate glass, sapphire glass, aluminosilicate glass, lithium-containing aluminosilicate glass, and tempered with physical or chemical strengthening. Glass is preferred, and chemically tempered glass made by ion exchange is more preferred.

An example of a suitable composition of the glass substrate 11 is shown below.
SiO _2: 40 to 80 wt%, Al ₂ O _3: 0~35 wt%, B ₂ O _3: 0~15 wt%, MgO: 0 to 20 wt%, CaO: 0 to 20 wt%, SrO: 0 20 wt%, BaO: 0 to 20 wt%, Li ₂ O: 0~20 wt%, Na ₂ O: 0~25 _wt%, K 2 O: _0~20 wt%, TiO _2: 0~10 mass %, And ZrO ₂ : 0 to 10% by mass. However, the above composition accounts for 95% by mass or more of the entire glass.

An example of a more suitable composition of the glass substrate 11 is shown below.
SiO _2: 55 to 75 wt%, Al ₂ O _3: 0~25 wt%, B ₂ O _3: 0~12 wt%, MgO: 0 to 20 wt%, CaO: 0 to 20 wt%, SrO: 0 20 wt%, BaO: 0 to 20 wt%, Li ₂ O: 0~20 wt%, Na ₂ O: 0~25 wt%, K ₂ O: 0~15 wt%, TiO _2: 0~5 by weight %, And ZrO ₂ : 0 to 5% by mass. However, the above composition accounts for 95% by mass or more of the entire glass.

In chemical strengthening, alkali metal ions (typically Li ions and Na ions) having a small ionic radius on the surface of the glass are exchanged with ions having a larger ionic radius (typically K) by ion exchange at a temperature below the glass transition point. Ion). By such ion exchange, a compressive stress layer is formed on the surface of the glass and the strength is improved. Chemical strengthening is usually performed by immersing glass in a molten salt containing an alkali metal.
In addition, when using chemically strengthened glass, it is preferable to form a reflective color adjusting layer on the surface having the compressive stress layer.

(Light shielding layer 12)
The light shielding layer 12 shields the transmitted light transmitted from the inner side of the back cover glass 10, thereby keeping the reflected color of the interference film constant without depending on the object disposed inside the back cover glass 10. To obtain the reflection color characteristics. Therefore, a high light shielding rate is required as a characteristic of the light shielding layer 12. The average transmittance of the back cover glass 10 from the wavelength 400 nm to the wavelength 750 nm from the light shielding layer 12 side is preferably 5% or less, more preferably 1% or less.

The light shielding layer 12 is defined as a film coated on the inner surface of the back cover glass 10 and may be composed of an inorganic colorant ink, an organic colorant ink, and an ink containing an inorganic filler in an organic resin. Preferably, it may be a single layer and may be composed of two or more different materials to adjust the color. In the case of being constituted by a plurality of layers, a transparent layer may be included in the layer, but the transmittance of the light shielding film 12 including the back cover glass 10 is preferably 5% or less, and preferably 1% or less. It is preferable. When the light shielding layer 12 is composed of two or more layers, it may include a scattering layer that scatters light. Moreover, a desired uneven | corrugated shape may be formed in the interface of the back cover glass 10 and the light shielding layer 12, and light may be scattered.
The inorganic material used for the inorganic colorant ink and the inorganic filler material contained in the organic resin are not particularly limited, but highly conductive materials such as iron oxide, copper oxide, chromium, copper, and iron are used. When used, it is preferable to lower the overall conductivity by simultaneously mixing a low conductivity pigment such as silicon oxide or titanium oxide. The sheet resistance of the light shielding layer 12 is preferably 100Ω or more, and more preferably 1000Ω or more.

  The thickness of the light shielding layer 12 is preferably 50 nm or more, and more preferably 300 nm or more.

  The film forming method of the light shielding layer 12 is not particularly limited, but it is preferable to use physical vapor deposition (PVD). Specific examples of physical vapor deposition (PVD) include ion-assisted vapor deposition, ion plating, and sputtering. However, the light shielding film 12 may be formed by a die coating method.

If further insulation is required, a layer made of a highly insulating material such as SiO ₂ may be separately provided on the light shielding layer 12.

(Anti-fouling film 14)
As described above, the antifouling film 14 has an arbitrary configuration in the back cover glass 10 shown in FIG. However, by forming an antifouling film on the outermost surface of the back cover glass, it has functions such as suppressing the adhesion of various dirt such as fingerprint marks, sweat, and dust, making it easier to wipe off dirt, and making dirt less noticeable. And the display surface can be kept clean.
The antifouling film 14 may be a film having at least one characteristic selected from the group consisting of antifouling properties, water repellency, oil repellency and lipophilicity, and examples thereof include fluorine-containing organic compounds. More specifically, fluorine-containing organic silicon compounds, hydrolyzable fluorine-containing organic compounds, and the like can be given.
The film thickness of the antifouling film is not particularly limited, but is preferably 2 to 20 nm, more preferably 2 to 15 nm, and further preferably 3 to 10 nm.
By setting the film thickness to 2 nm or more, the outermost surface of the back cover glass is uniformly covered with good adhesion by the antifouling film, which is preferable because it can withstand practical use with high scratch resistance. Moreover, when the film thickness is 20 nm or less, the optical characteristics in a state where the antifouling film is laminated are very good.

Specific examples will be described below, but the present invention is not limited to these examples. Of Examples 1 to 6 shown below, Examples 1 to 3 are comparative examples, and Examples 4 to 6 are examples. In Examples 1 to 6, chemically tempered glass produced by the following procedure was used as the glass substrate.
Glass substrate Potassium nitrate 9700g, Potassium carbonate 890g, Sodium nitrate 400g was put in a stainless steel (SUS) cup, heated to 450 ° C with a mantle heater, molten salt with potassium carbonate concentration 6mol% and sodium concentration 10000ppm by weight Was prepared.

  An aluminosilicate glass (specific gravity 2.48) of 100 mm × 100 mm × 0.56 mm was preheated to 200 to 400 ° C. and then immersed in the molten salt for 2 hours for ion exchange treatment. Then, it cooled to near room temperature and washed with water.

The aluminosilicate glass is composed of SiO ₂ 64.4 mol%, Al ₂ O ₃ 8.0 mol%, Na ₂ O 12.5 mol%, K ₂ O 4.0 mol%, MgO 10.5 mol%, CaO 0.1 mol. %, SrO 0.1 mol%, BaO 0.1 mol%, ZrO ₂ 0.5 mol%.

(Example 1)
On one main surface of the chemically strengthened glass produced by the above procedure, as a reflective color adjusting layer, a high refractive index film, a 10 nm thick Nb ₂ O ₅ film, and a low refractive index film, a 35 nm thick SiO ₂ film As a high refractive index film, an Nb ₂ O ₅ film having a film thickness of 29 nm was formed by a sputtering method.
The film forming conditions are shown below.
Nb ₂ O ₅ film formation during <br/> target: NbO
DC power output (W): 300
Deposition pressure (Pa): 0.3
Process gas flow rate (sccm): Ar / O ₂ = 28/2
SiO ₂ film formation during <br/> target: Si
DC power output (W): 300
Deposition pressure (Pa): 0.3
Process gas flow rate (sccm): Ar / O ₂ = 22/8

Next, a niobium low-order oxide (NbO _a ) film having _a thickness of 1000 nm was formed as a light-shielding layer on the reflective color adjustment layer formed by the above procedure by a sputtering method.
The film forming conditions are shown below.
Target: NbO
DC power output (W): 300
Deposition pressure (Pa): 0.3
Process gas flow rate (sccm): Ar / O ₂ = 30/0

Next, a fluorine-based organic film was formed as the antifouling film on the other main surface of the chemically tempered glass by the following procedure to prepare a back cover glass. The film was formed by a heating vapor deposition apparatus attached to RAS1100BII manufactured by SYNCHRON. The fluorine-based organic film is impregnated with Shin-Etsu Chemical Co., Ltd. KY195 in vapor deposition pellets, and vapor deposition is performed by resistance heating under vacuum with a chamber internal pressure of 1 × 10E- ⁴ or less, and a film thickness of 2 nm or more is formed on the reflective layer did.

The following evaluation was implemented about the back cover glass produced in the above procedure.
(Area strength)
The surface strength of the back cover glass is such that the back cover glass is placed on a ring made of stainless steel with a diameter of 30 mm and the contact portion has a radius of curvature of 2.5 mm, and a sphere made of steel with a diameter of 10 mm is in contact with the back cover glass. In this state, the sphere was evaluated by BOR strength F (N) measured by a ball on ring (BOR) test in which the sphere was loaded at the center of the ring under a static load condition. [F is the BOR strength (N) measured by the ball-on-ring test, and t is the plate thickness (mm) of the back cover glass. ]. FIG. 4 shows a schematic diagram for explaining the ball-on-ring test used in the examples. In the ball-on-ring (BOR) test, the back cover glass 1 was placed horizontally and the back cover glass 1 was pressed using a pressing jig 2 (hardened steel, diameter 10 mm, mirror finish) made of SUS304. 1 is pressurized and the surface strength of the back cover glass 1 is measured.
In FIG. 4, a back cover glass 1 serving as a sample is horizontally installed on a receiving jig 3 made of SUS304 (diameter 30 mm, contact portion curvature R2.5 mm, contact portion is hardened steel, mirror finish). . Above the back cover glass 1, a pressurizing jig 2 for pressurizing the back cover glass 1 is installed.
From the upper side of the back cover glass 1, the central region of the main surface is pressurized. The test conditions are as follows.
Lowering speed of the pressure jig 2: 1.0 (mm / min)
At this time, the breaking load (unit N) when the glass is broken is defined as BOR strength, and the average value of 10 measurements is defined as BOR average strength. However, if the break start point of the back cover glass is 2 mm or more away from the ball pressing position, it is excluded from the data for calculating the average value.
Using chemically tempered glass having a plate thickness of 0.55 mm, the case where the value of the surface strength is 300 N or more was evaluated as ○, and the value less than 300 N was evaluated as ×. For example, the surface strength of the unstrengthened chemically strengthened glass was 515N.

(Outer surface hardness)
The surface hardness was measured using PICODERTOR HM500 manufactured by Fisher Instruments Co., Ltd. The measurement indenter is a Vickers indenter, the maximum load arrival time is 10 seconds, the creep time is 5 seconds, the indentation load is gradually changed between 0.05 mN and 500 mN, and measurement is performed 5 times under each condition. The average value was taken as the measurement result of the obtained measurement value. At this time, the load is adjusted so that the maximum indentation depth is between 50 nm and 100 nm, the case where the maximum value of Martens hardness with the maximum indentation depth is 50 nm to 100 nm is 6 GPa or more, and less than 6 GPa is x. did.

(Outside scratch strength)
Using a thin film scratch tester CSR-2000 manufactured by Resuka Co., Ltd. under the conditions of a stylus radius of 5 μm, a spring constant of 100 g / mm, a scratch speed of 10 μm, a measurement time of 120 seconds, a measurement end load of 200 mN, a vibration level of 100 μm, and a sampling frequency of 3600 Hz. The critical load on the outer surface was measured. In the case where the obtained load was 150 mN or more, “good” and “less than 150 mN” were marked “x”.

(Radio wave transmission)
Measurement was carried out using a non-contact eddy current method resistance measuring instrument 717 Conductance Monitor manufactured by DELCOM. The inner side surface of the back cover glass was used as a measurement surface, and the resistance value at the center of the colored portion of the back cover glass was measured.

The evaluation results for each item are as follows.
Surface strength: ×
Outside surface hardness: ×
Outer scratch strength: ×
Radio wave permeability: ○

(Example 2)
In the same procedure as in Example 1, as a reflection color adjusting layer on one main surface of chemically strengthened glass, as a high refractive index film, a 12 nm thick AlON film, as a low refractive index film, a 36 nm thick SiO ₂ film, As a high refractive index film, an AlON film having a film thickness of 32 nm was formed by sputtering, and then a niobium low-order oxide (NbO _a ) film having _a film thickness of 1000 nm was formed as a light shielding layer on the reflectance adjustment layer. .
Targets for AlON film deposition conditions shown below: Al
DC power output (W): 300
Deposition pressure (Pa): 0.3
Process gas flow rate (sccm): Ar / O ₂ / N ₂ 19/10
Next, in the same procedure as in Example 1, a fluorine-based organic film was formed as an antifouling film on the other main surface of the chemically strengthened glass to prepare a back cover glass, and various evaluations were performed.
The evaluation results for each item are as follows.
Surface strength: ×
Outside surface hardness: ×
Outer scratch strength: ×
Radio wave permeability: ○

(Example 3)
In the same procedure as in Example 1, as a reflection color adjusting layer on one main surface of the chemically strengthened glass, as a high refractive index film, a 10 nm thick Nb ₂ O ₅ film, and as a low refractive index film, a 35 nm thick SiO ₂ film. After forming an Nb ₂ O ₅ film having a film thickness of 29 nm as a film and a high refractive index film by a sputtering method, a resin-based pigment ink containing a copper oxide filler is used as a light shielding layer on the reflectance adjustment layer by a die coating method Thus, a film thickness of 5 μm was formed. The film forming conditions when the reflectance adjusting layer is formed are the same as in Example 1.
Next, in the same procedure as in Example 1, a fluorine-based organic film was formed as an antifouling film on the reflective color adjustment layer to create a back cover glass, and various evaluations were performed.
The evaluation results for each item are as follows.
Surface strength: ×
Outside surface hardness: ×
Outer scratch strength: ×
Radio wave permeability: ○

(Example 4)
A chromium film having a thickness of 300 nm was formed as a light shielding layer on one main surface of the chemically strengthened glass produced by the procedure of Example 1.
Next, an AlON film as a high refractive index film and an Al ₂ O ₃ film as a low refractive index film are used as the reflection color adjustment layer on the other main surface of the chemically strengthened glass, and a film having a total film thickness of 1500 nm is sputtered. Formed by.
The film forming conditions are the same as in Example 2.
Next, in the same procedure as in Example 1, a fluorine-based organic film was formed as an antifouling film on the reflective color adjustment layer to create a back cover glass, and various evaluations were performed.
The evaluation results for each item are as follows.
Surface strength: ×
Outer surface hardness: ○
Outer scratch strength: ○
Radio wave permeability: ×

(Example 5)
A resin pigment ink containing a copper oxide filler was formed as a light shielding layer on one main surface of the chemically strengthened glass by a die coating method to a thickness of 5 μm.
Next, a film having a total thickness of 3000 nm is formed by sputtering on the other main surface of the chemically strengthened glass, using a Nb ₂ O ₅ film as a high refractive index film and a SiO ₂ film as a low refractive index film as a reflective color adjusting layer. Formed.
The film forming conditions are the same as in Example 2.
Next, in the same procedure as in Example 1, a fluorine-based organic film was formed as an antifouling film on the reflective color adjustment layer to create a back cover glass, and various evaluations were performed.
The evaluation results for each item are as follows.
Surface strength: ○
Outside surface hardness: ×
Outer scratch strength: ×
Radio wave permeability: ○

(Example 6)
A resin pigment ink containing a copper oxide filler was formed as a light shielding layer on one main surface of the chemically strengthened glass by a die coating method to form a film thickness of 5 μm.
Next, a total film using a Si ₃ N ₄ film as a high refractive index film, an Al ₂ O ₃ film and a SiO ₂ film as a low refractive index film as a reflective color adjusting layer on the other main surface of the chemically strengthened glass A film having a thickness of 3000 nm was formed by a sputtering method.
The film forming conditions are the same as in Example 2.
Next, in the same procedure as in Example 1, a fluorine-based organic film was formed as an antifouling film on the reflective color adjustment layer to create a back cover glass, and various evaluations were performed.
The evaluation results for each item are as follows.
Surface strength: ○
Outer surface hardness: ○
Outer scratch strength: ○
Radio wave permeability: ○

  Table 1 shows the evaluation results (surface strength, outer surface hardness, outer scratch strength, radio wave permeability) of the samples of Examples 1 to 6.

  From the evaluation results in Table 1, as described in Examples 4 to 6, the light-shielding layer is formed on one main surface of the glass substrate, and the reflective color adjustment layer is formed on the other main surface of the glass substrate, thereby increasing the glass strength, A back cover glass having a high value of at least one of the outer surface hardness and the outer scratch strength and having resistance to cracks generated on the inner surface of the glass substrate 10 can be obtained.

10,100 Back cover glass 11,110 Glass substrate 12,120 Light shielding film 13,130 Reflection color adjustment layer
14,140 Antifouling film 200 Radical assist sputtering device 210 Main body 220 Drum 230 Wall 240 Target 250 Power supply 260 Argon gas supply unit 270 Radical source 280 Matching machine and RF source 310 Argon gas supply unit 320 Nitrogen gas supply unit 330 Oxygen gas Supply section

Claims (10)

  A back cover glass in which a light-shielding layer is formed on one main surface of a glass substrate forming a transparent base, and a reflection color adjustment layer is formed on the other main surface of the glass substrate, wherein the reflection color adjustment layer has a high refractive index. A film made of a material and a film made of a low refractive index material are alternately laminated a plurality of times, and there is a difference in refractive index at a wavelength of 550 nm between the film made of the high refractive index material and the film made of the low refractive index material. A back cover glass formed so as to be 0.1 or more.   The back cover glass according to claim 1, wherein the film made of the high refractive index material has a refractive index of 1.8 or more at a wavelength of 550 nm.   The back cover glass according to claim 1 or 2, wherein the film made of the low refractive index material has a refractive index of 1.5 or less at a wavelength of 550 nm.   The film made of the high refractive index material and the film made of the low refractive index material in the reflective color adjustment layer contain one or more elements selected from the group consisting of Si, Al, Zr, and Ti. The back cover glass according to claim 1, comprising an oxide film, a nitride film, and an oxynitride film.   The light shielding layer is any one selected from the group consisting of an inorganic colorant ink, an organic colorant ink, and an ink containing an inorganic filler in an organic resin, from the light shielding layer side. The back cover glass according to any one of claims 1 to 4, wherein the back cover glass has an average transmittance of 5% or less from a wavelength of 400 nm to a wavelength of 750 nm.   The glass substrate is a chemically strengthened glass having a compressive stress layer on the surface, and the reflective color adjusting layer is formed on the surface of the chemically strengthened glass on the side having the compressive stress layer. The back cover glass described in 1. The back cover glass in any one of Claims 1-6 in which the Martens hardness measured from the said reflective color adjustment layer side satisfy | fills at least one among following (1) and (2).
(1) The Martens hardness at 50 nm indentation depth of the Vickers indenter is 6000 N / mm ² or more.
(2) The Martens hardness at the indentation depth of 100 nm of the Vickers indenter is 6000 N / mm ² or more.   The back cover glass according to claim 1, wherein the reflection color adjustment layer is formed by sputtering.   The back cover glass of this invention WHEREIN: The said reflection color adjustment layer is a back cover glass in any one of Claims 1-8 located outside with respect to the said glass substrate at the time of use of a back cover glass.   The back cover glass in any one of Claims 1-9 in which the antifouling film | membrane is provided on the said reflective color adjustment layer.