JP7696935B2 - Cover material - Google Patents

Description

The present disclosure relates to a cover member, in particular to a cover member for a touch panel of an electronic device.

Touch panels are widely used as display devices/input means for electronic devices, including smartphones, portable game devices, and car navigation systems, and cover materials are laminated on the touch panels to prevent damage to the touch panels. Currently, glass materials are widely used as cover materials, but the cover materials must be thicker than a certain thickness to provide practical strength. However, due to the configuration of electronic device devices, the cover materials are required to be space-saving. For example, it has been proposed to use transparent ceramics such as sapphire as cover materials (cover glass) (Patent Document 1), and it has also been proposed to use zirconium oxide with a bending strength of 200 to 400 MPa and aluminum oxide with a bending strength of about 400 MPa as cover materials for such transparent ceramics (Patent Document 2).

Special table 2016-540257 publication JP 2012-174053 A

As touch panels have become more sophisticated in recent years, there is a demand for thinner cover materials. However, sapphire is difficult to process, so thinning it is not practical from a cost perspective. On the other hand, the zirconium oxide and aluminum oxide proposed in Patent Document 2 did not have sufficient strength.

The objective of this disclosure is to provide a cover member that can be made even thinner.

The present invention is as described in the claims, and the gist of the present disclosure is as follows.
[1] A cover member made of a sintered body containing a stabilizing element, made of zirconia including 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 the above [1], wherein the stabilizing element is at least one selected from the group consisting of scandium, yttrium and lanthanoid rare earth elements.
[3] The cover member according to the above [1] or [2], wherein the stabilizing element is yttrium.
[4] The cover member according to the above [3], 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 the above [1] to [4], wherein the sintered body contains one or more elements selected from the group consisting of germanium, aluminum and silicon.
[6] The cover member according to any one of the above [1] to [5], having a thickness of 0.1 mm or more and 1.0 mm or less.
[7] A display device comprising the cover member according to any one of [1] to [6] above.
[8] An electronic device comprising the display device according to [7] above.

This disclosure makes it possible to provide a cover member that can be made even thinner than conventional cover members.

FIG. 1 is a SEM image of the sintered body obtained in Example 1 (scale in the figure is 300 nm). FIG. 1 is a schematic diagram showing a cross section of an example of a display device.

Hereinafter, the present disclosure will be described with reference to an example of an embodiment.
The terms used in this embodiment are as follows:
The "bending strength" refers to a three-point bending strength value determined by a three-point bending test in accordance with JIS R 1601. The bending strength is measured using a columnar sintered body sample having a support distance of 30 mm, a width of 4 mm, and a thickness of 3 mm, and the bending strength of the sintered body of this embodiment may be determined by averaging the values measured 10 times.
"Relative density" refers to the ratio (%) of the measured density to the theoretical density. The measured density of a sintered body is the ratio (g/cm ³ ) of the volume measured by Archimedes' method to the mass measured by mass measurement. When the stabilizing element is yttrium, the theoretical density is the density (g/cm ³ ) calculated 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)
ρ ₀ =100/[(Y _A /3.987)+(Y _G /3.637)+(Y _S /2.2)
+(100- _YA - _YG - _YS )/ _ρZ ] (4)
In formulas (1) to (4), _ρ0 is the theoretical density, _ρZ is the theoretical density of zirconia, A and C are constants, X is the molar ratio (mol%) of yttrium converted into yttria relative to the _total of yttrium converted into zirconia ( _ZrO2 ) and yttria ( _Y2O3 ), and _YA , _YG , and _YS are the mass ratios (mass%) of aluminum converted into _Al2O3 , _{germanium converted} into _GeO2 , and silicon converted into _SiO2 relative to the total of zirconia, _yttrium , _aluminum , germanium, and silicon of the sintered body converted into _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 conditions for the XRD measurement are as follows.
Radiation source: CuKα radiation (λ=0.15418nm)
Measurement mode: Continuous scan
Scan speed: 4°/min
Step width: 0.02°
Measurement range: 2θ=26° to 33°
In the above-mentioned XRD measurement, the XRD peaks corresponding to the respective crystal planes of zirconia are measured as peaks having peak tops 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) planes of tetragonal zirconia and cubic zirconia were measured in duplicate, and the 2θ angle of the peak top was 2θ=30±0.5°.
The XRD measurement can be carried out using a general X-ray diffraction device (for example, MiniFlex, manufactured by RIGAKU Corporation).
The "monoclinic ratio" is the ratio of monoclinic zirconia to the zirconia crystal phase, and is a value calculated from the XRD pattern of zirconia using the following formula (5).
f _m = [I _m (111) + I _m (11-1)] x 100
/[I _m (111)+I _m (11-1)+I _t (111)] (5)
In the above formula, f _m is the monoclinic rate (%), 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 calculated by the following formula (6).
Dx=κλ/(βcosθ) (6)
Here, Dx is the crystallite diameter (nm) of the zirconia crystallite, κ is the Scherrer constant (=1), λ is the wavelength of the radiation source in the powder X-ray diffraction measurement (λ=0.15418 nm), β is the half-width (radian) calculated 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 half-width at half maximum of the (111) plane of tetragonal zirconia, and b is a constant obtained by XRD measurement of a standard sample of quartz sand having a particle size of 60 μm after treatment in air at 800° C. for 6 hours, and is the half-width at 2θ of the quartz sand corresponding to the 2θ of the XRD peak corresponding to the (111) plane of tetragonal zirconia obtained by the measurement.

The cover member of this embodiment will be described below.
The present embodiment relates to a cover member constituted by a sintered body that contains a stabilizing element, is made of zirconia including at least tetragonal zirconia, has an average crystal grain size of 10 nm or more and 250 nm or less, and has a relative density of 99.85% or more.

(Sintered body)
The sintered body constituting the cover member of this embodiment is a sintered body made of zirconia containing a stabilizing element and including at least tetragonal zirconia, and is a so-called zirconia sintered body, or further a partially stabilized zirconia sintered body.

The stabilizing element is an element having a function of stabilizing zirconia, and may be one or more selected from the group consisting of scandium, yttrium, and lanthanoid rare earth elements. At least one of scandium and yttrium is preferable, and yttrium is more preferable. In this embodiment, the content of the stabilizing element may be a content that partially stabilizes zirconia. For example, when the stabilizing element is yttrium, the content of the stabilizing element (hereinafter also referred to as the "stabilizing element amount", and when the stabilizing element is yttrium, etc., the stabilizing element amount is also referred to as the "yttrium content") is 2.0 mol% or more or 2.5 mol% or more, and may be 6.0 mol% or less, 5.0 mol% or less, or 4.0 mol% or less.

The amount of the stabilizing element is the molar ratio of the amount of the stabilizing element converted into oxide to the sum of the amount of zirconium (Zr) in the sintered body converted into zirconia (ZrO ₂ ) and the amount of the stabilizing element converted into oxide. For example, the yttrium content can be calculated by the molar ratio of the amount of yttrium converted into yttria to the sum of the amount of zirconium (Zr) in the sintered body converted into zirconia ( _{ZrO 2} ) and the amount of yttrium (Y) converted into yttria (Y 2 O ₃ ) (= {Y ₂ O ₃ / (ZrO ₂ + Y ₂ O ₃ )} × 100 [mol %]).

The sintered body may contain at least one 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 grain boundary strength between crystal grains tends to be high at least in the amount of stabilizing element, and the cover member of this embodiment can be made even thinner. 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 the amount of the additive element when the additive element is germanium or the like is also referred to as "germanium content") is arbitrary, but may be 0 mass% or more, 0.05 mass% or more, or 0.1 mass% or more, and 1.5 mass% or less, 1.0 mass% or less, or 0.5 mass% or less. The amount of an added element is the mass ratio of the amount of the added element converted into an oxide to the total amount of zirconium (Zr) in the sintered body converted into zirconia (ZrO ₂ ), the amount of the stabilizing element converted into an oxide, and the amount of the added element converted into an oxide. For example, the germanium content in a sintered body containing germanium and the balance consisting of yttrium-containing zirconia is calculated as {GeO ₂ /(ZrO ₂ +Y ₂ O ₃ +GeO ₂ )}×100[mass%], and the amount of the added element in a sintered body containing germanium and aluminum and the balance consisting of yttrium-containing zirconia is calculated as {(Al ₂ O ₃ +GeO ₂ )/(ZrO ₂ +Y ₂ O ₃ +GeO ₂ +Al ₂ O ₃ )}×100[mass%].

It is preferable that the sintered body does not contain anything other than inevitable impurities. An example of an inevitable impurity in zirconia is hafnia (HfO ₂ ). In addition, in the calculation of values related to the composition such as the composition and relative density in this embodiment, the hafnia contained in the sintered body may be regarded as zirconia to calculate these values.

The sintered body is made of zirconia containing at least tetragonal zirconia, preferably made of zirconia having tetragonal crystals as the main phase, and more preferably made of zirconia consisting of tetragonal crystals only, which makes the sintered body less susceptible to breakage during processing even when a thin-walled cover member is used.
"Tetragonal as the main phase" refers to a state in which the proportion of tetragonal crystals is the highest among the monoclinic, cubic and tetragonal crystals contained in the zirconia crystal phase. The proportion of tetragonal crystals in the zirconia crystal phase can be calculated by the Rietveld method of the X-ray diffraction (XRD) pattern of the sintered body. In zirconia with tetragonal crystals as the main phase, the proportion of tetragonal crystals calculated above is 50 mass% or more.

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. This results in a sintered body with translucency that can be used as a cover member. 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.

The sintered body of this embodiment has a relative density of 99.85% or more, and preferably 99.88% or more. The relative density may be 100% or less.

Furthermore, the sintered body of this embodiment may be a sintered body obtained by a known sintering method, such as a sintered body obtained by atmospheric pressure sintering (so-called atmospheric pressure sintered body) or a sintered body obtained by pressure sintering (so-called pressure sintered body).

The bending strength of the sintered body is preferably 500 MPa or more or 800 MPa or more. The upper limit of the bending strength can be any value as long as it has practical processability, but the bending strength of the sintered body is preferably 2000 MPa or less or 1800 MPa or less.

If the sintered body has a linear transmittance of 45% or more at a thickness of 0.1 mm, it will exhibit sufficient transparency when used as a cover member. The linear transmittance is preferably 47% or more or 50% or more. The linear transmittance at a thickness of 0.1 mm is preferably high, but 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 at a thickness of 1 mm of the sample.
To measure the linear transmittance of a sample at a thickness of 1 mm, both sides of the sample are sintered bodies with a surface roughness (Ra) of ≦0.02 μm, and the measurement is performed by irradiating the sample with light at 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 using an integrating sphere.

Furthermore, from the obtained linear transmittance, the linear transmittance (T) at a thickness of 0.1 mm can be calculated using the following formula.
T [%] = (1-R) ² exp (-0.1μ) x 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 set to 2.14. μ is the absorption coefficient, which can be calculated from the following formula.
μ=-In{(t ₆₀₀ /100)×(1/0.753)}

(Cover member and display device)
The display device may be, for example, a display device equipped with a touch panel, or even a display device equipped with a capacitive touch panel. Fig. 2 shows a cross-sectional view of an example of a display device equipped with a touch panel. The display device (200) in Fig. 2 is configured by stacking 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 used to fix the elements together.

The cover member (201) may be made of the above-mentioned sintered body and may have any desired shape suitable for the display device, such as a cube, rectangular prism, polygonal, plate-like, disk-like, columnar, cone-like, spherical, approximately spherical, or other basic shape.

It is preferable that the thickness of the cover member (201) is 0.1 mm or more or 0.2 mm or more, and 1.0 mm or less or 0.5 mm or less.

The touch panel (202) may be of one or more types selected from the group consisting of a resistive film type, an optical type, and a capacitive type, and is preferably of a capacitive type.

The display module (203) may be, for example, 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), electronic paper, and a transmissive display, and preferably an OLED and an inorganic EL.

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

A method for producing a sintered body includes a process for sintering a 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 rate of 5% or more and 50% or less, to obtain a pre-sintered body, and a process for subjecting the pre-sintered body to hot isostatic pressing at a temperature of 1000°C or more and less than 1200°C.

The molded body used in the process of sintering a molded body made of zirconia powder containing a stabilizing element, having a crystallite diameter of 5 nm to 40 nm, and a monoclinic ratio of 5% to 50% to prepare a pre-sintered body (hereinafter also referred to as the "pre-sintering process") is a molded body made of zirconia containing a stabilizing element, having a crystallite diameter of 5 nm to 40 nm, and a monoclinic ratio of 5% to 50%. By pre-sintering and hot isostatically pressing such a molded body, a sintered body having mechanical and optical properties suitable for a cover member is obtained.

The molded body is a so-called compact, which is a physical aggregation of zirconia powder particles containing a stabilizing element, having a crystallite diameter of 5 nm or more and 40 nm or less, and a monoclinic rate of 5% or more and 50% or less.

The stabilizing element contained in zirconia is an element having a function of stabilizing zirconia, and includes at least one selected from the group consisting of scandium, yttrium, and lanthanoid rare earth elements, and 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 that partially stabilizes zirconia. For example, the yttrium content may be 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.

Since zirconia tends to become densified at relatively low HIP processing temperatures, it is preferable that the crystallite diameter of the zirconia is 10 nm or more or 15 nm or more, and 35 nm or less or 32 nm or less.

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

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 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 converted into an oxide to the total amount of the zirconium (Zr) in the molded body converted into zirconia (ZrO ₂ ), the amount of the stabilizing element converted into an oxide, and the amount of the additive element converted into an oxide.

The shape of the molded body may be the same as the shape of the intended cover member, taking into consideration shrinkage due to sintering. Examples of the shape of the molded body include at least one selected from the group consisting of a cube, a rectangular parallelepiped, a polyhedron, a columnar shape, a cylindrical shape, a disk shape, and a substantially spherical shape.

The molded body may be produced by molding a powder of zirconia containing a stabilizing element using at least one molding method selected from the group consisting of uniaxial pressing, cold isostatic pressing, slip casting, and injection molding. When a resin such as a compound is used to produce the molded body, the resulting molded body (compressed powder body) may be heat-treated to remove the resin, if necessary. Examples of heat treatment conditions include air at 400°C or higher and lower than 800°C.

In the pre-sintering step, the molded body is sintered so as to have a structure that allows pores to be sufficiently eliminated in the subsequent hot isostatic pressing (hereinafter also referred to as "HIP"). Preferred pre-sintering conditions include the following conditions.
Pre-sintering method: normal pressure sintering Pre-sintering atmosphere: oxidizing atmosphere, preferably air atmosphere Pre-sintering temperature: 1000°C or higher or 1100°C or higher, and
1250°C or less, 1200°C or less, or 1150°C or less Heating rate: 50°C/hour or more, or 80°C/hour or more, and
Temperature decreasing rate: 100° C./hour or more or 150° C./hour or more, and
250° C./hour or less or 200° C./hour or less

In this embodiment, "atmospheric sintering" refers to a method of sintering by heating the material to be sintered (such as a compact or calcined body) without applying an external force during sintering. The holding time at the pre-sintering temperature can be changed appropriately depending on the pre-sintering temperature, and the higher the pre-sintering temperature, the shorter the holding time can be. An example of the holding time at the pre-sintering temperature is 1 hour or more and 3 hours or less. It is also preferable that the temperature drop rate is faster than the temperature rise rate.

The manufacturing method of this embodiment includes a process (hereinafter also referred to as the "HIP process") in which the pre-sintered body is subjected to hot isostatic pressing (hereinafter also referred to as the "HIP process") at a temperature of 1000°C or higher but lower than 1200°C. The cover member of this embodiment is obtained by the HIP process.

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

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

The manufacturing method of this embodiment may include a step of heat-treating the cover member after the HIP treatment in an oxidizing atmosphere. By subjecting the cover member after the HIP treatment (HIP-treated body) to such a step, the transparency can be adjusted. The heat treatment conditions are arbitrary, but it is preferable to treat 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 to 1100°C Heat treatment time: 0.5 hours to 5 hours

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

(Identification of Crystalline Phases)
An XRD pattern of the powder sample was obtained using a general X-ray diffraction device (product name: Ultima II V, manufactured by Rigaku Corporation). The conditions for the XRD measurement were as follows:
Radiation source: CuKα radiation (λ=0.15418nm)
Measurement mode: Continuous scan
Scan speed: 4°/min
Step width: 0.02°
Measurement range: 2θ=26° to 33°

(Monoclinic fraction)
An XRD pattern was obtained in the same manner as in the identification of the crystal phase, and the monoclinic ratio was calculated from the above formula (5).

(Crystallite size)
An XRD pattern was obtained in the same manner as in the identification of the crystalline phase, and the crystallite size was calculated from the above formulas (6) and (7).

(Relative Density)
The actual density of the sintered body samples was measured by the Archimedes method. Prior to the measurement, the mass of the dried sintered body was measured, and then the sintered body was placed in water and boiled for 1 hour as a pretreatment. The theoretical density was calculated from the formulas (1) to (4), and the relative density (%) was calculated from the value of the actual density (ρ) relative to the theoretical density (ρ ₀ ).

(Average grain size)
The average crystal grain size was determined by a planimetric method using an SEM image of a sintered body sample obtained by field emission scanning electron microscope observation. That is, a circle with a known area was drawn on the SEM image, and the number of crystal grains within the circle (Nc) and the number of crystal grains on the circumference of the circle (Ni) were counted.
The total number of crystal grains (Nc+Ni) was set to 250±50, and the average crystal grain size was calculated using the following formula.
Average grain size=(Nc+(1/2)×Ni)/(A/M ² )
In the above formula, Nc is the number of crystal grains in a circle, Ni is the number of crystal grains 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 grains (Nc + Ni) in one SEM observation image is less than 200, (Nc + Ni) was set to 250 ± 50 using multiple SEM observation images.
Prior to the measurement, the sintered body samples were pretreated by mirror polishing and then thermal etching. The mirror polishing was performed by grinding the surface of the sintered body with a surface grinder, and then polishing with diamond abrasive grains having average grain sizes of 9 μm, 6 μm, and 1 μm in a mirror polishing machine in that order.

(Bending strength)
The bending strength of the sintered body samples was measured by a three-point bending test in accordance with JIS R 1601. The bending strength was measured using a columnar sintered body sample with a support distance of 30 mm, a width of 4 mm, and a thickness of 3 mm, and the bending strength was calculated by averaging the values measured 10 times.

(Linear transmittance)
To measure the linear transmittance of a sample at a thickness of 1 mm, both sides of the sample were sintered bodies with a surface roughness (Ra) of ≦0.02 μm, and 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 using an integrating sphere.
The linear transmittance (T) at a thickness of 0.1 mm was calculated using the following formula.
T [%] = (1-R) ² exp (-0.1μ) x 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 was set to 2.14. μ is the absorption coefficient, which can be calculated from the following formula.
μ=-In{(t ₆₀₀ /100)×(1/0.753)}

Example 1
The aluminum content as added elements was 0.25 mass%, the germanium content was 0.25 mass%, and the remainder was obtained by a hydrolysis method to obtain 3 mol % yttrium-containing zirconia. Alumina sol, germania powder, and 3 mol % yttrium-containing zirconia powder having a crystallite diameter of 31 nm and a monoclinic rate of 29% were wet-pulverized, mixed, and dried.
The dried mixed powder was uniaxially pressed and then subjected to CIP (Cold Isostatic Pressing) to form a compact (green compact), which was then heated to 1142°C at a heating 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 primary sintered body was subjected to HIP treatment in an argon atmosphere at 150 MPa and 1150°C for 1 hour to obtain a sintered body of this example having an aluminum content of 0.25 mass% and a germanium content of 0.25 mass% as additive elements, and the remainder being zirconia containing 3 mol% yttrium. The sintered body of this example was visually confirmed to have translucency, and the average crystal grain size was 100 nm.
The sintered body of this embodiment has a relative density of 99.91% (actual measured density: 6.074 g/cm ³ ), a bending strength of 1710 MPa, and a linear transmittance of 1.4% at a wavelength of 600 nm when the sample thickness is 1 mm. It is also found that μ=4.0 mm ⁻¹ and the linear transmittance (T) at a thickness of 0.1 mm is 50%. This confirms that the sintered body of this example has the strength and translucency required for use as a cover member.

Example 2
Alumina sol and germania powder were mixed so that the aluminum content as the additive element amount was 0.25 mass% and the germanium content was 0.75 mass%, and the sintered body of this example was obtained by the same method as in Example 1, in which the aluminum content as the additive element amount was 0.25 mass% and the germanium content was 0.75 mass%, with the remainder being zirconia containing 3 mol% yttrium. The sintered body of this example was visually confirmed to have translucency, and the average crystal grain size was 110 nm.
The sintered body of this embodiment has a relative density of 99.90% (actual measured density: 6.053 g/cm ³ ), a bending strength of 1630 MPa, and a linear transmittance of 1.5% at a wavelength of 600 nm when the sample thickness is 1 mm. It is also found that μ=3.9 mm ⁻¹ and the linear transmittance (T) at a thickness of 0.1 mm is 51%. This confirms that the sintered body of this example has the strength and translucency required for use as a cover member.

Example 3
A powder was obtained in the same manner as in Example 1, except that the alumina sol and the germanium powder were mixed so that the aluminum content as the added element amount was 0.15 mass% and the germanium content was 0.25 mass%, with the remainder being 3 mol% yttrium-containing zirconia.
A sintered body of this example was obtained by the same method as in Example 1, except that the obtained powder was used and the pre-sintering temperature was set to 1200° C. The aluminum content as the amount of added elements was 0.15 mass %, the germanium content was 0.25 mass %, and the balance was 3 mol % yttrium-containing zirconia. The sintered body of this example was confirmed to have translucency by visual inspection, and the average crystal grain size was 130 nm.
The sintered body of this embodiment has a relative density of 99.90% (actual density: 6.087 g/cm ³ ), a bending strength of 1700 MPa, and a linear transmittance of 2.2% at a wavelength of 600 nm when the sample thickness is 1 mm. It can also be seen that μ=3.5 mm ⁻¹ and 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 to be used as a cover member.

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

Claims (8)

A cover member for a touch panel, comprising a sintered body which contains 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 , and which is made of zirconia including at least tetragonal zirconia, the content of the stabilizing elements being 2.0 mol% or more and 6.0 mol% or less, the content of the additive elements being 0.05 mass% or more and 1.5 mass% or less, the average crystal grain size being 10 nm or more and 250 nm or less , the relative density being 99.85% or more, and the three-point bending strength measured by a three-point bending test in accordance with JIS R 1601 being 1630 MPa or more . 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. The cover member according to claim 1 or 2, wherein the stabilizing element is yttrium. 4. The touch panel cover member according to claim 1, wherein the zirconia is composed only of tetragonal crystals. 5. The touch panel cover member according to claim 1, which has an in-line transmittance of 45% or more at a thickness of 0.1 mm. The touch panel cover member according to claim 1 , having a thickness of 0.1 mm or more and 1.0 mm or less. A display device comprising the touch panel cover member according to claim 1 . An electronic device equipped with the display device according to claim 7.

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