Cover member

Abstract

A cover member configured from a sintered body containing a stabilizing element, composed of zirconia which includes at least tetragonal zirconia, having an average crystal particle size from 10-250 nm, inclusive, and having a relative density of at least 99.85%.

Description

Technical Field

[0001] The present disclosure relates to a cover member, and more particularly to a cover member for a touch panel of an electronic device.

Background Art

[0002] Touch panels are widely used as display devices / input means for electronic devices such as smartphones, portable game devices, and car navigation systems, and cover members are laminated on the touch panels for the purpose of preventing damage thereto. Currently, glass materials are widely adopted as cover members, but the cover members require a thickness of a certain level or more in order to have practical strength. However, due to the configuration of the electronic device, space saving is required for the cover member. For example, it has been proposed to use transparent ceramics such as sapphire as the cover member (Patent Document 1), and as such transparent ceramics, it has been proposed to use zirconium oxide having a flexural strength of 200 to 400 MPa or aluminum oxide having a flexural strength of about 400 MPa as the cover member (Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] With the recent improvement in performance of touch panels, there is a further demand for thinner cover members. However, since sapphire is difficult to process, thin processing is not practical in terms of cost. On the other hand, the zirconium oxide and aluminum oxide proposed in Patent Document 2 did not have sufficient strength.

[0005] An object of the present disclosure is to provide a cover member that can be made thinner still further.

Means for Solving the Problems

[0006] The present invention is as described in the claims, and the gist of the present disclosure is as follows. [1] A cover member composed of a sintered body containing a stabilizing element, made of zirconia containing at least tetragonal zirconia, having an average crystal grain size of 10 nm or more and 250 nm or less, and having a relative density of 99.85% or more. [2] The cover member according to [1] above, wherein the stabilizing element is one or more selected from the group consisting of scandium, yttrium, and lanthanoid rare earth elements. [3] The cover member according to [1] or [2] above, wherein the stabilizing element is yttrium. [4] The cover member according to [3] above, wherein the content of the stabilizing element is 2.0 mol% or more and 6.0 mol% or less. [5] The cover member according to any one of [1] to [4] above, wherein the sintered body contains one or more selected from the group consisting of germanium, aluminum, and silicon. [6] The cover member according to any one of [1] to [5] above, having a thickness of 0.1 mm or more and 1.0 mm or less. [7] A display device including the cover member according to any one of [1] to [6] above. [8] An electronic device including the display device according to [7] above.

Advantages of the Invention

[0007] According to the present disclosure, it is possible to provide a cover member that can be made thinner still further than conventional cover members.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0009] Hereinafter, an example of an embodiment will be shown and described for the present disclosure. Each term in this embodiment is as follows. "Bending strength" is the value of the three-point bending strength obtained by a three-point bending test according to JIS R 1601. The measurement of the bending strength may be performed using a columnar sintered body sample with a distance between fulcrums of 30 mm, a width of 4 mm, and a thickness of 3 mm, and the average value of 10 measurements may be taken as the bending strength of the sintered body in this embodiment. "Relative density" is the ratio (%) of the actually measured density to the theoretical density. The actually measured density of the sintered body is the ratio of the volume measured by the Archimedes method to the mass measured by mass measurement (g / cm 3 ). When the stabilizing element is yttrium, the theoretical density is the density (g / cm 3 ) obtained from the following formulas (1) to (4). A = 0.5080 + 0.06980X / (100 + X) (1) C = 0.5195 - 0.06180X / (100 + X) (2) ρ Z = [124.25(100 - X) + 225.81X] / [150.5(100 + X)A 2 C] (3) ρ0 = 100 / [(Y A / 3.987) + (Y G / 3.637) + (Y S / 2.2) + (100 - Y A - Y G - Y S ) / ρ Z (4) In formulas (1) to (4), ρ0 is the theoretical density, ρ Zis the theoretical density of zirconia, A and C are constants, X is the molar ratio (mol%) of yttria-converted yttrium to the total of zirconia (ZrO2) and yttria (Y2O3)-converted yttrium, and Y A , Y G and Y S are the mass ratios (mass%) of alumina-converted aluminum, germania-converted germanium, and silica-converted silicon to the total of sintered body zirconia, yttrium, aluminum, germanium, and silicon, in terms of ZrO2, Y2O3, Al2O3, GeO2, and SiO2, respectively. The "crystalline phase" can be identified by powder X-ray diffraction (hereinafter also referred to as "XRD") measurement. The following conditions can be cited as the conditions for XRD measurement. X-ray source: CuKα ray (λ = 0.15418 nm) Measurement mode: continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ = 26° to 33° In the above XRD measurement, the XRD peak corresponding to each crystal plane of zirconia is measured as a peak having a peak top at the following 2θ. XRD peak corresponding to the (111) plane of monoclinic zirconia: 2θ = 31 ± 0.5° XRD peak corresponding to the (11-1) plane of monoclinic zirconia: 2θ = 28 ± 0.5° The XRD peaks corresponding to the (111) plane of tetragonal zirconia and cubic zirconia are measured overlappingly, and the 2θ of the peak top is 2θ = 30 ± 0.5°. XRD measurement can be performed using a general X-ray diffractometer (for example, MiniFlex, manufactured by RIGAKU). The "monoclinic ratio" is the ratio of monoclinic zirconia in the crystalline phase of zirconia, and is a value obtained by the following formula (5) for the XRD pattern of zirconia. f m = [I m (111) + I m (11-1)] × 100 / [I m (111)+I m (11 - 1)+I t (111)] (5) In the above formula, f m is the monoclinic ratio (%), I m (111) is the peak height of the XRD peak corresponding to the (111) plane of monoclinic zirconia, I m (11 - 1) is the peak height of the XRD peak corresponding to the (11 - 1) plane of monoclinic zirconia, and, I t (111) is the peak height of the XRD peak corresponding to the (111) plane of tetragonal zirconia. The "crystallite size" is a value obtained by the following formula (6). Dx = κλ / (βcosθ) (6) Here, Dx is the crystallite size (nm) of the zirconia crystallite, κ is the Scherrer constant (= 1), λ is the wavelength of the X - ray source for powder X - ray diffraction measurement (λ = 0.15418 nm), β is the full - width at half - maximum (in radians) obtained from the following formula (7), and θ is the Bragg angle (°) of the reflection corresponding to the (111) plane of tetragonal zirconia in the XRD measurement. β=(B 2 -b 2 ) 1 / 2 ×(π / 180) (7) B is the measured value of the full - width at half - maximum of the (111) plane of tetragonal zirconia, b is a constant obtained by performing XRD measurement on quartz sand with a particle size of 60 μm after being treated at 800 °C for 6 hours in the atmosphere as a standard sample, and is the full - width at half - maximum of 2θ of quartz sand corresponding to 2θ of the XRD peak corresponding to the (111) plane of tetragonal zirconia obtained by the said measurement.

[0010] Hereinafter, the cover member of the present embodiment will be described. This embodiment is a cover member composed of a sintered body containing a stabilizing element and made of zirconia containing at least tetragonal zirconia, having an average crystal grain size of 10 nm or more and 250 nm or less, and a relative density of 99.85% or more.

[0011] (Sintered body) The sintered body constituting the cover member of the present embodiment contains a stabilizing element and is a sintered body made of zirconia containing at least tetragonal zirconia, that is, a so-called zirconia sintered body, and more specifically, a partially stabilized zirconia sintered body.

[0012] The stabilizing element is an element having a function of stabilizing zirconia, and examples thereof include one or more selected from the group consisting of scandium, yttrium, and lanthanoid rare earth elements. It is preferably at least one of scandium and yttrium, and more preferably yttrium. In the present embodiment, the content of the stabilizing element may be a content at which zirconia is partially stabilized. For example, when the stabilizing element is yttrium, the content of the stabilizing element (hereinafter, also referred to as the "amount of stabilizing element", and the amount of stabilizing element when the stabilizing element is yttrium or the like is also referred to as the "yttrium content", etc.) is 2.0 mol% or more or 2.5 mol% or more, and 6.0 mol or less, 5.0 mol% or less, or 4.0 mol% or less.

[0013] The amount of the stabilizing element is the molar ratio of the oxide equivalent amount of the stabilizing element to the total of the zirconia (ZrO2) equivalent amount of zirconium (Zr) and the oxide equivalent amount of the stabilizing element in the sintered body. For example, the yttrium content is the molar ratio of the amount of yttrium converted to yttria to the total of the amount of zirconium (Zr) converted to zirconia (ZrO2) and the amount of yttrium (Y) converted to yttria in the sintered body (={Y2O3 / (ZrO2+Y2O3)}×100 [mol%]) and can be determined thereby.

[0014] The sintered body may contain one or more selected from the group consisting of germanium (Ge), aluminum (Al), and silicon (Si), preferably at least one of germanium and aluminum (hereinafter also referred to as "additive element"). When the sintered body contains an additive element, the amount of stabilizing element is at least, and the grain boundary strength between crystal grains tends to be high, and further thinning of the cover member of the present embodiment becomes possible. The additive element is at least aluminum, and preferably aluminum and germanium. The content of the additive element (hereinafter also referred to as "additive element amount", and when the additive element is germanium or the like, the additive element amount is also referred to as "germanium content", etc.) is arbitrary, but is 0% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, and further, 1.5% by mass or less, 1.0% by mass or less, or 0.5% by mass or less. The additive element amount is the mass ratio of the amount of the additive element in terms of oxide to the total amount of the amount of zirconium (Zr) in the sintered body in terms of zirconia (ZrO2), the amount of stabilizing element in terms of oxide, and the amount of additive element in terms of oxide. For example, in a sintered body containing germanium and the balance being yttrium-containing zirconia, the germanium content is obtained as {GeO2 / (ZrO2 + Y2O3 + GeO2)}×100 [mass%], and in a sintered body containing germanium and aluminum and the balance being yttrium-containing zirconia, the additive element amount is obtained as {(Al2O3 + GeO2) / (ZrO2 + Y2O3 + GeO2 + Al2O3)}×100 [mass%].

[0015] Preferably, the sintered body contains nothing other than unavoidable impurities. Hafnia (HfO2) can be exemplified as an unavoidable impurity of zirconia. In calculating values related to the composition such as the composition and relative density in the present embodiment, hafnia contained in the sintered body may be regarded as zirconia and these values may be calculated accordingly.

[0016] The sintered body is made of zirconia containing at least tetragonal zirconia, preferably made of zirconia with tetragonal phase as the main phase, and more preferably made of zirconia consisting only of tetragonal phase. Thereby, even in the case of forming a thin cover member, it is less likely to be damaged during processing. "With tetragonal phase as the main phase" means a state of the crystal phase in which the proportion of tetragonal phase is the highest among monoclinic, cubic, and tetragonal phases contained in the crystal phase of zirconia. The ratio of tetragonal phase in the crystal phase of zirconia can be calculated by the Rietveld method from the X-ray diffraction (XRD) pattern of the sintered body. In zirconia with tetragonal phase as the main phase, the ratio of tetragonal phase calculated above is 50% by mass or more.

[0017] The sintered body has an average crystal grain size of 10 nm or more and 250 nm or less, and a relative density of 99.85% or more. Thereby, a sintered body having translucency applicable as a cover member is obtained. The average crystal grain size of the sintered body is preferably 50 nm or more and 200 nm or less, and more preferably 50 nm or more and 175 nm or less.

[0018] The sintered body of the present embodiment has a relative density of 99.85% or more, and more preferably 99.88% or more. The relative density may be 100% or less.

[0019] Furthermore, the sintered body of the present embodiment may be a sintered body obtained by a known sintering method such as a sintered body in a state obtained by normal pressure sintering (so-called normal pressure sintered body), a sintered body in a state obtained by pressure sintering (so-called pressure sintered body), etc.

[0020] The sintered body preferably has a flexural strength of 500 MPa or more or 800 MPa or more. The upper limit of the flexural strength is arbitrary as long as it has practical workability, but the flexural strength of the sintered body may be 2000 MPa or less or 1800 MPa or less.

[0021] If the linear transmittance at a thickness of 0.1 mm is 45% or more, sufficient transparency is exhibited when used as a cover member. It is more preferable that the linear transmittance is 47% or more or 50% or more. Although it is preferable that the linear transmittance at a thickness of 0.1 mm is high, it may be 75% or less or 70% or less. The linear transmittance at a thickness of 0.1 mm can be calculated from the following formula by measuring the linear transmittance of a sample with a thickness of 1 mm. When measuring the linear transmittance of a sample with a thickness of 1 mm, use a sintered body with a surface roughness (Ra) ≦ 0.02 μm on both sides of the sample, and the measurement can be performed by irradiating the sample with light having a wavelength of 600 nm using a general spectrophotometer (for example, V-650, manufactured by JASCO Corporation). The linear transmittance (t 600 ; %) at a thickness of 1 mm can be calculated by subtracting the diffuse transmittance from the total light transmittance measured by an integrating sphere.

[0022] Furthermore, from the obtained linear transmittance, the linear transmittance (T) at a thickness of 0.1 mm can be obtained by the following formula. T [%] = (1 - R) 2 exp(-0.1μ)×100 R ={(1 - n) / (1 + n)} 2 In the above formula, T is the linear transmittance at a thickness of 0.1 mm, R is a coefficient, and n is the refractive index of zirconia. In this embodiment, n may be 2.14. μ is the absorption coefficient and can be obtained from the following formula. μ = -In{(t 600 / 100)×(1 / 0.753)}

[0023] (Cover member and display device) Examples of the display device include a display device having a touch panel, and more specifically, a display device having a capacitive touch panel. FIG. 2 shows a cross-sectional view of an example of a display device having a touch panel. The display device (200) in FIG. 2 is configured by laminating elements of a cover member (201), a touch panel (202), and a display module (203). Although not shown in FIG. 2, an adhesive member such as an adhesive sheet may be provided between the elements to fix them.

[0024] The cover member (201) may be composed of the above-described sintered body, and the shape may be any desired shape suitable for the display device. For example, cubic, rectangular parallelepiped, polyhedron, plate, disk, columnar, conical, spherical, substantially spherical, and other basic shapes can be exemplified.

[0025] The thickness of the cover member (201) is preferably 0.1 mm or more or 0.2 mm or more, and 1.0 mm or less or 0.5 mm or less.

[0026] Examples of the method of the touch panel (202) include one or more selected from the group consisting of a resistive film method, an optical method, and a capacitive method, and the capacitive method is preferred.

[0027] Examples of the display module (203) include one or more selected from the group consisting of a liquid crystal module, a TFT (Thin Film Transistor), an OLED (Organic Light Emitting Diode), an inorganic EL (Inorganic Electro-Luminescence), an electronic paper, and a transmissive display, and preferably OLED and inorganic EL.

[0028] <Manufacturing Method> The manufacturing method of the cover member of this embodiment is arbitrary. The sintered body may be manufactured by any method so as to have a desired shape, and this may be used as the cover member.

[0029] As a method for manufacturing a sintered body, there is provided a manufacturing method including a step of sintering a green compact made of zirconia powder containing a stabilizing element, having a crystallite size of 5 nm or more and 40 nm or less, and a monoclinic ratio of 5% or more and 50% or less to obtain a pre-sintered body, and a step of subjecting the pre-sintered body to hot isostatic pressing treatment at 1000°C or more and less than 1200°C.

[0030] The green compact used in the step of sintering a green compact made of zirconia powder containing a stabilizing element, having a crystallite size of 5 nm or more and 40 nm or less, and a monoclinic ratio of 5% or more and 50% or less to obtain a pre-sintered body (hereinafter, also referred to as "pre-sintering step") is a green compact made of zirconia containing a stabilizing element, having a crystallite size of 5 nm or more and 40 nm or less, and a monoclinic ratio of 5% or more and 50% or less. By pre-sintering and hot isostatic pressing such a green compact, a sintered body having mechanical properties and optical properties suitable as a cover member can be obtained.

[0031] The green compact is a so-called compacted powder in which zirconia powder particles containing a stabilizing element, having a crystallite size of 5 nm or more and 40 nm or less, and a monoclinic ratio of 5% or more and 50% or less are physically aggregated.

[0032] The stabilizing element contained in zirconia is an element having a function of stabilizing zirconia, and examples thereof include one or more selected from the group consisting of scandium, yttrium, and lanthanoid rare earth elements, and it is preferably at least one of scandium and yttrium, and more preferably yttrium. The content of the stabilizing element contained in zirconia may be a content at which zirconia is partially stabilized. For example, the yttrium content is 2.0 mol% or more or 2.5 mol% or more, and 6.0 mol% or less, 5.0 mol% or less, or 4.0 mol% or less.

[0033] Since there is a tendency to be easily densified at a relatively low HIP treatment temperature, the crystallite size of zirconia is 10 nm or more or 15 nm or more, and preferably 35 nm or less or 32 nm or less.

[0034] The monoclinic ratio of zirconia is 10% or more, or 15% or more, and preferably 45% or less, or 40% or less.

[0035] The molded body may contain at least one selected from the group consisting of germanium, aluminum, and silicon, preferably at least one of germanium and aluminum (additive element). The amount of the additive element is arbitrary, but may be 0 mass% or more, 0.05 mass% or more, or 0.1 mass% or more, and further may be 1.5 mass% or less, 1.0 mass% or less, or 0.5 mass% or less. The amount of the additive element is the mass ratio of the amount of the additive element in terms of oxide to the total amount of the amount of zirconium (Zr) in the molded body in terms of zirconia (ZrO2), the amount of the stabilizing element in terms of oxide, and the amount of the additive element in terms of oxide.

[0036] The shape of the molded body may be the same as the shape of the target cover member in consideration of shrinkage due to sintering. As the shape of the molded body, at least one selected from the group consisting of cubic, rectangular parallelepiped, polyhedral, columnar, circular columnar, disk-shaped, and substantially spherical can be exemplified.

[0037] The molded body may be produced by molding a powder composed of zirconia containing a stabilizing element by at least one molding method selected from the group consisting of uniaxial pressing, cold isostatic pressing, slip casting, and injection molding. When molding is produced using a resin such as a compound, if necessary, the obtained molded body (compressed powder) may be heat-treated to remove the resin. As the heat treatment conditions, 400°C or more and less than 800°C in the atmosphere can be exemplified.

[0038] In the pre-sintering step, the molded body may be sintered so that the pores can be sufficiently removed by the subsequent hot isostatic pressing (hereinafter also referred to as "HIP"). The following conditions can be mentioned as preferable pre-sintering conditions. Pre-sintering method: Normal pressure sintering Pre-sintering atmosphere: Oxidizing atmosphere, preferably air atmosphere Preliminary sintering temperature: 1000 °C or higher, or 1100 °C or higher, and 1250 °C or lower, 1200 °C or lower, or 1150 °C or lower Heating rate: 50 °C / hour or higher, or 80 °C / hour or higher, and 150 °C / hour or lower, or 120 °C / hour or lower Cooling rate: 100 °C / hour or higher, or 150 °C / hour or higher, and 250 °C / hour or lower, or 200 °C / hour or lower

[0039] In this embodiment, "atmospheric pressure sintering" is a method of sintering by heating the object to be sintered (such as a green compact or a pre-sintered body) without applying an external force during sintering. The holding time at the preliminary sintering temperature may be appropriately changed according to the preliminary sintering temperature, and the higher the preliminary sintering temperature, the shorter the holding time may be. Examples of the holding time at the preliminary sintering temperature can be 1 hour or more and 3 hours or less. Also, it is preferable that the cooling rate is faster than the heating rate.

[0040] The manufacturing method of this embodiment has a step of subjecting the pre-sintered body to hot isostatic pressing treatment (hereinafter, also referred to as "HIP treatment") at 1000 °C or higher and less than 1200 °C (hereinafter, also referred to as the "HIP step"). Through the HIP step, the cover member of this embodiment is obtained.

[0041] In the HIP treatment, the pre-sintered body is treated at a HIP treatment temperature of 1000 °C or higher and less than 1200 °C. The HIP treatment temperature is preferably 1100 °C or higher, or 1130 °C or higher, and is preferably 1180 °C or lower. Furthermore, the relationship between the HIP treatment temperature and the preliminary sintering temperature may be adjusted according to the sinterability of the green compact (pre-sintered body). For example, the HIP treatment temperature is higher than the preliminary sintering temperature, and further, the HIP treatment temperature is 5 °C or more and 15 °C or less higher than the preliminary sintering temperature. Examples of the holding time at the HIP treatment temperature can be 0.5 hour or more and 2 hours or less.

[0042] The atmosphere for HIP treatment may be at least one of an inert atmosphere and a reducing atmosphere, and an argon atmosphere is preferred. The HIP pressure may be 100 MPa or more and 200 MPa or less.

[0043] The manufacturing method of this embodiment may include a step of heat-treating the cover member after HIP treatment in an oxidizing atmosphere. By subjecting the cover member (HIP-treated body) after HIP treatment to such a step, the transparency can be adjusted. The heat treatment conditions are arbitrary, but it is preferable to perform the treatment at a temperature lower than the HIP treatment temperature, and the following conditions can be exemplified. Heat treatment method: Normal pressure firing Heat treatment atmosphere: Oxidizing atmosphere, preferably air atmosphere Heat treatment temperature: 900 °C or more and 1100 °C or less Heat treatment time: 0.5 hours or more and 5 hours or less

Examples

[0044] Hereinafter, the present disclosure will be described using examples. However, the present disclosure is not limited to these examples.

[0045] (Identification of crystal phase) A general X-ray diffractometer (trade name: UltimaIIV, manufactured by Rigaku Corporation) was used to obtain the XRD pattern of the powder sample. The conditions for XRD measurement are as follows. X-ray source: CuKα ray (λ = 0.15418 nm) Measurement mode: Continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ = 26° to 33°

[0046] (Monoclinic phase ratio) An XRD pattern obtained by the same method as the identification of the crystal phase was obtained, and the monoclinic ratio was determined from the above formula (5).

[0047] (Crystallite size) An XRD pattern was obtained in the same manner as the identification of the crystal phase, and the crystallite size was determined from the above equations (6) and (7).

[0048] (Relative density) The actual density of the sintered body sample was measured by the Archimedes method. Prior to the measurement, the mass of the sintered body after drying was measured. Then, the sintered body was placed in water and boiled for 1 hour as a pretreatment. The theoretical density was determined from equations (1) to (4), and the relative density (%) was determined from the value of the actual density (ρ) with respect to the theoretical density (ρ0).

[0049] (Average crystal grain size) The average crystal grain size was determined by the planimetric method using the SEM observation image of the sintered body sample obtained by field emission scanning electron microscope observation. That is, a circle with a known area was drawn on the SEM observation image, and the number of crystal particles (Nc) inside the circle and the number of crystal particles (Ni) on the circumference of the circle were measured. Assuming that the total number of crystal particles (Nc + Ni) was 250 ± 50, the average crystal grain size was determined using the following equation. Average crystal grain size = (Nc + (1 / 2) × Ni) / (A / M 2 ) In the above equation, Nc is the number of crystal particles inside the circle, Ni is the number of crystal particles on the circumference of the circle, A is the area of the circle, and M is the magnification of the scanning electron microscope observation (5000 times). When the number of crystal particles (Nc + Ni) in one SEM observation image is less than 200, (Nc + Ni) was set to 250 ± 50 using a plurality of SEM observation images. Prior to the measurement, the sintered body sample was mirror polished and then subjected to thermal etching treatment as a pretreatment. The mirror polishing was performed by shaving the surface of the sintered body with a surface grinder and then polishing it in order using diamond abrasive grains with average particle sizes of 9 μm, 6 μm, and 1 μm with a mirror polishing device.

[0050] (Bending strength) The bending strength of the sintered body sample was measured by a three-point bending test according to JIS R1601. The measurement of the bending strength was performed using a column-shaped sintered body sample with a span between supports of 30 mm, a width of 4 mm, and a thickness of 3 mm, and the average value of 10 measurements was taken as the bending strength.

[0051] (Linear transmittance) When measuring the linear transmittance at a sample thickness of 1 mm, the two surfaces of the sample were sintered compacts with a surface roughness (Ra) ≤ 0.02 μm. The measurement was performed by irradiating the sample with light at a wavelength of 600 nm using a general spectrophotometer (e.g., V-650, manufactured by JASCO Corporation). The linear transmittance (t 600 ; %) at a thickness of 1 mm was calculated by subtracting the diffuse transmittance from the total light transmittance measured by an integrating sphere. The linear transmittance (T) at a thickness of 0.1 mm was determined by the following formula. T [%] = (1 - R) 2 exp(-0.1μ) × 100 R = {(1 - n) / (1 + n)} 2 In the above formula, T is the linear transmittance at a thickness of 0.1 mm, R is a coefficient, and n is the refractive index of zirconia. In this example, n was set to 2.14. μ is the absorption coefficient and can be obtained from the following formula. μ = -In{(t 600 / 100) × (1 / 0.753)}

[0052] Example 1 The aluminum content as the additive element amount was 0.25 mass%, the germanium content was 0.25 mass%, and the balance was obtained by a hydrolysis method. An alumina sol, germanium powder, and 3 mol% yttrium-containing zirconia powder with a crystallite diameter of 31 nm and a monoclinic ratio of 29% were wet-milled, mixed, and dried so as to obtain 3 mol% yttrium-containing zirconia. After uniaxially pressing the dried mixed powder, it was subjected to CIP (Cold Isostatic Pressing) treatment to form a compact (compressed powder body). Then, the temperature was raised to 1142 °C at a rate of 100 °C / hour and held for 2 hours for pre-sintering. After pre-sintering, the temperature was lowered to 200 °C at a rate of 200 °C / hour to obtain a primary sintered body. The obtained green compact was subjected to HIP treatment at 150 MPa, 1150 °C for 1 hour in an argon atmosphere, thereby obtaining a sintered body of this example in which the aluminum content as the amount of additive element was 0.25% by mass and the germanium content was 0.25% by mass, and the balance was 3 mol% yttrium-containing zirconia. The sintered body of this example was confirmed to have translucency by visual observation, and the average crystal grain size was 100 nm. The sintered body of this embodiment had a relative density of 99.91% (measured density: 6.074 g / cm 3 ), a flexural strength of 1710 MPa, and a linear transmittance at a wavelength of 600 nm with a sample thickness of 1 mm of 1.4%. Also, μ = 4.0 mm -1 and it was found that the linear transmittance (T) at a thickness of 0.1 mm was 50%. From this, it was confirmed that the sintered body of this example had the strength and translucency that could be used as a cover member.

[0053] Example 2 Except that alumina sol and germanium oxide powder were mixed so that the aluminum content as the amount of additive element was 0.25% by mass and the germanium content was 0.75% by mass, in the same manner as in Example 1, a sintered body of this example in which the aluminum content as the amount of additive element was 0.25% by mass and the germanium content was 0.75% by mass, and the balance was 3 mol% yttrium-containing zirconia was obtained. The sintered body of this example was confirmed to have translucency by visual observation, and the average crystal grain size was 110 nm. The sintered body of this embodiment had a relative density of 99.90% (measured density: 6.053 g / cm 3 ), a flexural strength of 1630 MPa, and a linear transmittance at a wavelength of 600 nm with a sample thickness of 1 mm of 1.5%. Also, μ = 3.9 mm -1 and it was found that the linear transmittance (T) at a thickness of 0.1 mm was 51%. From this, it was confirmed that the sintered body of this example had the strength and translucency that could be used as a cover member.

[0054] Example 3 The alumina sol and the germanium oxide powder were mixed in the same manner as in Example 1, except that the aluminum content as the added element amount was 0.15% by mass and the germanium content was 0.25% by mass, to obtain a powder in which the aluminum content as the added element amount was 0.15% by mass and the germanium content was 0.25% by mass, and the balance was 3 mol% yttrium-containing zirconia. The obtained powder was used, and the sintered body of this example was obtained in the same manner as in Example 1, except that the pre-sintering temperature was 1200°C, in which the aluminum content as the added element amount was 0.15% by mass and the germanium content was 0.25% by mass, and the balance was 3 mol% yttrium-containing zirconia. The sintered body of this example was confirmed to have translucency visually, and the average crystal grain size was 130 nm. The sintered body of this embodiment had a relative density of 99.90% (measured density: 6.087 g / cm 3 ), a flexural strength of 1700 MPa, and a linear transmittance at a wavelength of 600 nm with a sample thickness of 1 mm of 2.2%. Also, μ = 3.5 mm -1 It can be seen that the linear transmittance (T) at a thickness of 0.1 mm is 53%. From this, it can be confirmed that the sintered body of this example has the strength and translucency that can be used as a cover member.

Explanation of Signs

[0055] 200: Display device 201: Cover member 202: Touch panel 203: Display module

Claims

Claim 1: A touch panel cover member comprising a sintered body made of zirconia containing at least tetragonal zirconia and containing one or more stabilizing elements selected from the group consisting of scandium, yttrium, and lanthanoid rare earth elements, and additive elements consisting of germanium and aluminum, wherein the content of the stabilizing element is 2.0 mol% or more and 6.0 mol% or less, the content of the additive element is 0.05% by mass or more and 1.5% by mass or less, the average crystal grain size is 10 nm or more and 250 nm or less, the relative density is 99.85% or more, and the three-point bending strength determined by a three-point bending test according to JIS R 1601 is 1630 MPa or more. Claim 2: The touch panel cover member according to Claim 1, wherein the content of the stabilizing element is 3 mol% or more and 6.0 mol% or less. Claim 3 The cover member according to Claim 1 or 2, wherein the stabilizing element is yttrium. Claim 4: The touch panel cover member according to any one of Claims 1 to 3, wherein the zirconia consists only of tetragonal crystals. Claim 5: The touch panel cover member according to any one of Claims 1 to 4, wherein the linear transmittance at a thickness of 0.1 mm is 45% or more. Claim 6 The touch panel cover member according to any one of Claims 1 to 5, wherein the thickness is 0.1 mm or more and 1.0 mm or less. Claim 7 A display device including the touch panel cover member according to any one of Claims 1 to 6. Claim 8 An electronic device including the display device according to Claim 7.

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