WO2022168734A1

WO2022168734A1 - Cover member

Info

Publication number: WO2022168734A1
Application number: PCT/JP2022/003151
Authority: WO
Inventors: 光二松井; 明生池末; 雄一幾原
Original assignee: 国立大学法人東京大学; 株式会社ワールドラボ; 東ソー株式会社
Priority date: 2021-02-03
Filing date: 2022-01-27
Publication date: 2022-08-11
Also published as: JPWO2022168734A1

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

cover material

The present disclosure relates to a cover member, and more particularly 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 such as smartphones, portable game devices, and car navigation systems, and cover materials are laminated to prevent damage to touch panels. At present, a glass material is widely used as the cover member, but the cover member needs to have a certain thickness or more in order to have practical strength. However, space saving is required for the cover member due to the structure of electronic equipment devices. For example, the use of transparent ceramics such as sapphire as the cover member (cover glass) has been proposed (Patent Document 1) As such transparent ceramics, it has been proposed to use zirconium oxide with a bending strength of 200 to 400 MPa or aluminum oxide with a bending strength of about 400 MPa as a cover member (Patent Document 2).

Japanese Patent Publication No. 2016-540257 JP 2012-174053 A

With the recent high performance of touch panels, there is a demand for even thinner cover materials. However, since sapphire is difficult to process, thinning is not practical in terms of cost. On the other hand, zirconium oxide and aluminum oxide proposed in Patent Document 2 do not have sufficient strength.

An object of the present 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 sintered body made of zirconia containing a stabilizing element and 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. cover member.
[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, which has 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.

According to the present disclosure, it is possible to provide a cover member that can be made even thinner than conventional cover members.

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

Hereinafter, the present disclosure will be described by showing an example of an embodiment.
Each term in this embodiment is as follows.
“Bending strength” is a value of three-point bending strength determined by a three-point bending test according to JIS R 1601. The bending strength was measured using a pillar-shaped sintered body sample with a distance between fulcrums of 30 mm, a width of 4 mm, and a thickness of 3 mm. do it.
"Relative density" is the ratio (%) of actual density to theoretical density. The measured density of the sintered body is the ratio (g/cm ³ ) of the volume measured by the Archimedes method to the mass measured by mass measurement. 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)A2C} ] (3)
ρ ₀ =100/[( _YA / _3.987 )+(YG/ _3.637 )+(YS/2.2)
+(100-YA- _YG - _YS ₎ / _ρZ ] (4)
In formulas (1) to (4), ρ ₀ is the theoretical density, ρ _Z is the theoretical density of zirconia, A and C are constants, and X is the sum of yttrium converted to zirconia (ZrO ₂ ) and yttria (Y ₂ O ₃ ). Yttria-equivalent yttrium molar ratio (mol%), and Y _A , Y _G and Y _S are zirconia, yttrium, aluminum, germanium and silicon of the sintered body, respectively, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , GeO ₂ and SiO ₂ are the mass ratios of aluminum converted to Al ₂ O ₃ , germanium converted to GeO ₂ and silicon converted to SiO ₂ (% by mass).
The "crystalline phase" can be identified by powder X-ray diffraction (hereinafter also referred to as "XRD") measurement. Conditions for XRD measurement include the following conditions.
Radiation 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 XRD measurement described above, the XRD peak corresponding to each crystal plane of zirconia is measured as a peak having a peak top at 2θ below.
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°
XRD peaks corresponding to the (111) plane of tetragonal zirconia and cubic zirconia are measured in duplicate, and the peak top 2θ 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 crystal phase of zirconia, and is a value obtained from 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 fraction (%), I _m (111) is the peak height of the XRD peak corresponding to the (111) plane of monoclinic zirconia, and I _m (11-1) is the monoclinic The peak height of the XRD peak corresponding to the (11-1) plane of crystalline zirconia, and I _t (111) is the peak height of the XRD peak corresponding to the (111) plane of tetragonal zirconia.
"Crystallite size" is a value obtained by the following formula (6).
Dx=κλ/(β cos θ) (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 for powder X-ray diffraction measurement (λ = 0.15418 nm), and β is the following ( 7) is the half width (in radians) obtained from the formula, and θ is the black angle (°) of the reflection corresponding to the (111) plane of tetragonal zirconia in XRD measurement.
β=(B ² −b ² ) ^1/2 ×(π/180) (7)
B is the measured value of the half-value width of the (111) plane of tetragonal zirconia, and b is a constant obtained by XRD measurement of a standard sample of quartz sand with a grain size of 60 μm after being treated at 800° C. for 6 hours in the air. is the half width of 2θ of quartz sand corresponding to 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.
In the present embodiment, 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 A cover member comprising:

(sintered body)
The sintered body that constitutes the cover member of the present embodiment is a sintered body that contains a stabilizing element and is made of zirconia containing at least tetragonal zirconia. body.

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

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

The sintered body contains at least one selected from the group of germanium (Ge), aluminum (Al) and silicon (Si), preferably at least one of germanium and aluminum (hereinafter also referred to as "additive element"). You can stay. When the sintered body contains the additive element, the grain boundary strength between crystal grains tends to increase even when the amount of the stabilizing element is at least, and the thickness of the cover member of the present embodiment can be further reduced. The additive element is at least aluminum, preferably aluminum and germanium. The content of the additive element (hereinafter also referred to as "additional 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 1.5% by mass or less, 1.0% by mass or less, or 0.5% by mass or less. The amount of the additive element is the amount of zirconium (Zr) in the sintered body converted to zirconia (ZrO ₂ ), the amount of the stabilizing element converted to oxide, and the amount of the additive element converted to oxide. For example, the germanium content in a sintered body containing germanium and the balance being yttrium-containing zirconia is {GeO ₂ /(ZrO ₂ +Y ₂ O ₃ +GeO ₂ )}×100[ % by mass]), and the amount of additive elements in the sintered body containing germanium and aluminum and the balance being yttrium-containing zirconia is {(Al ₂ O ₃ +GeO ₂ )/(ZrO ₂ +Y ₂ O ₃ +GeO ₂ +Al ₂ O ₃ )}×100 [mass %]).

The sintered body preferably does not contain any impurities other than unavoidable impurities. Hafnia (HfO ₂ ) can be exemplified as an unavoidable impurity of zirconia. In addition, in calculating values related to composition such as 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.

The sintered body is made of zirconia containing at least tetragonal zirconia, preferably made of zirconia containing tetragonal crystals as a main phase, and more preferably made of zirconia made of only tetragonal crystals. As a result, even when a thin cover member is used, it is less likely to be damaged during processing.
The phrase "having a tetragonal crystal as the main phase" means a crystal phase in which the tetragonal crystal accounts for the highest proportion among the monoclinic crystal, cubic crystal, and tetragonal crystal included in the crystal phase of zirconia. The ratio of tetragonal crystals in the crystal phase of zirconia can be calculated by the Rietveld method of the X-ray diffraction (XRD) pattern of the sintered body. In zirconia having a tetragonal crystal as a main phase, the ratio of the tetragonal crystal calculated above is 50% by 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. As a result, a translucent sintered body that can be applied 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, more preferably 50 nm or more and 175 nm or less.

The sintered body of the present embodiment has a relative density of 99.85% or more, preferably 99.88% or more. The relative density should be 100% or less.

Furthermore, the sintered body of the present embodiment includes a sintered body obtained by normal pressure sintering (so-called normal pressure sintered body), a sintered body obtained by pressure sintering (so-called A sintered body obtained by a known sintering method such as a pressure sintered body) may be used.

The sintered body preferably has a bending strength of 500 MPa or more or 800 MPa or more. The upper limit of the bending strength is arbitrary as long as it has practical workability, but the bending strength of the sintered body is 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 exhibits sufficient transparency when used as a cover member. More preferably, the linear transmittance is 47% or more, or 50% or more. Although the linear transmittance at a thickness of 0.1 mm is preferably as high as possible, 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 in-line transmittance at a sample thickness of 1 mm, both sides of the sample are sintered with a surface roughness (Ra) ≤ 0.02 μm, and the measurement is performed with a general spectrophotometer (eg, V- 650, manufactured by JASCO), and irradiating the sample with light having a wavelength of 600 nm. 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 the integrating sphere.

Further, 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) x 100
R = {(1−n)/(1+n)} ²
In the above equation, T is the in-line transmittance at a thickness of 0.1 mm, R is the modulus, and n is the refractive index of zirconia. In this embodiment, n may be 2.14. μ is an absorption coefficient, which can be obtained from the following formula.
μ=−In{(t ₆₀₀ /100)×(1/0.753)}

(Cover member and display device)
Examples of the display device include a display device with a touch panel and a display device with 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) of FIG. 2 is constructed by laminating elements of a cover member (201), a touch panel (202) and a display module (203). In addition, although not shown in FIG. 2, an adhesive member such as an adhesive sheet may be interposed to fix each element.

The cover member (201) may be composed of the sintered body described above, and may have any desired shape suitable for the display device, such as a cubic shape, a rectangular parallelepiped shape, a polygonal shape, or a plate shape. , discoidal, columnar, conical, spherical, substantially spherical and other basic shapes can be exemplified.

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.

The method of the touch panel (202) includes one or more selected from the group of resistive film method, optical method and capacitance method, preferably the capacitance method.

The display module (203) is, for example, one or more selected from the group of a liquid crystal module, TFT (Thin Film Transistor), OLED (Organic Light Emitting Diode), inorganic EL (Inorganic Electro-Luminescence), electronic paper, and transmissive display. , preferably OLED and inorganic EL can be exemplified.

<Manufacturing method>
The method of manufacturing the cover member of the present embodiment is arbitrary, and a sintered body may be manufactured by an arbitrary method so as to have a desired shape and used as the cover member.

As a method for producing a sintered body, a molded body made of zirconia powder containing a stabilizing element and having a crystallite diameter of 5 nm or more and 40 nm or less and a monoclinic ratio of 5% or more and 50% or less is sintered. and a step of subjecting the presintered body to a hot isostatic press treatment at 1000°C or higher and lower than 1200°C.

A step of sintering a molded body made of zirconia powder containing a stabilizing element, having a crystallite diameter of 5 nm or more and 40 nm or less and a monoclinic fraction of 5% or more and 50% or less, to obtain a pre-sintered body. (Hereinafter, also referred to as a “pre-sintering step”.) The compact to be subjected to the “pre-sintering step” contains a stabilizing element, has a crystallite diameter of 5 nm or more and 40 nm or less, and a monoclinic fraction of 5% or more and 50% or less. It is a molded body made of zirconia. By pre-sintering and hot isostatic pressing such a molded body, a sintered body having mechanical properties and optical properties suitable for a cover member can be obtained.

The compact is a so-called green compact in which zirconia powder particles containing a stabilizing element and having a crystallite diameter 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. is.

The stabilizing element contained in zirconia is an element having a function of stabilizing zirconia, and includes one or more selected from the group of scandium, yttrium and lanthanide rare earth elements, and at least one of scandium and yttrium. Yttrium is preferred, and yttrium is more preferred. The content of the stabilizing element contained in zirconia may be any content that partially stabilizes zirconia. 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.

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

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

The compact may contain at least one selected from the group of germanium, aluminum and silicon, preferably at least one of germanium and aluminum (additional element). The amount of additive element is arbitrary, but it is 0% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, and is 1.5% by mass or less, 1.0% by mass or less, or 0.5% by mass. % by mass or less. The amount of additive element is the amount of zirconium (Zr) in the molded body converted to zirconia (ZrO ₂ ), the amount of stabilizing element converted to oxide, and the amount of additive element converted to oxide, with respect to the sum of the amount of additive element converted to oxide. It is the mass ratio of the converted amount.

The shape of the molded body should be similar to the shape of the intended cover member, taking into account shrinkage due to sintering. Further, the shape of the molded body can be exemplified by at least one selected from the group of cubic, rectangular parallelepiped, polyhedral, columnar, columnar, disk-like and substantially spherical.

The molded body is produced by molding a powder made of zirconia containing a stabilizing element by, for example, at least one molding method selected from the group consisting of uniaxial pressing, cold isostatic pressing, slip casting and injection molding. Just do it. When molding is made using a resin such as a compound, the resin may be removed by heat-treating the resulting molded body (green compact), if necessary. As heat treatment conditions, 400° C. or more and less than 800° C. can be exemplified in the air.

In the pre-sintering step, the compact may be sintered so as to have a structure in which pores can be sufficiently eliminated by hot isostatic pressing (hereinafter also referred to as "HIP") which is subsequently performed. . 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
150°C/hour or less or 120°C/hour or less Temperature drop 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, "normal pressure sintering" is a method of sintering by heating the object to be sintered (such as a compact or calcined body) during sintering without applying an external force. . The holding time at the pre-sintering temperature may be appropriately changed according to the pre-sintering temperature, and the higher the pre-sintering temperature, the shorter the holding time. The holding time at the pre-sintering temperature can be exemplified from 1 hour to 3 hours. Moreover, it is preferable that the rate of temperature decrease is faster than the rate of temperature increase.

In the manufacturing method of the present embodiment, the pre-sintered body is subjected to a hot isostatic press treatment (hereinafter also referred to as “HIP treatment”) at 1000° C. or more and less than 1200° C. (hereinafter also referred to as “HIP process”). ). 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 higher or 1130° C. or higher, and preferably 1180° C. or lower. Furthermore, the relationship between the HIP treatment temperature and the pre-sintering temperature may be adjusted according to the sinterability of the compact (pre-sintered compact). For example, the HIP treatment temperature should be higher than the pre-sintering temperature. The HIP treatment temperature is higher than the pre-sintering temperature by 5° C. or more and 15° C. or less. As a holding time at the HIP treatment temperature, 0.5 hours or more and 2 hours or less can be exemplified.

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

The manufacturing method of the present embodiment may include a step of heat-treating the cover member after the HIP treatment in an oxidizing atmosphere. Transparency can be adjusted by subjecting the HIP-treated cover member (HIP-treated body) to such steps. 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 or more and 1100°C or less Heat treatment time: 0.5 hours or more and 5 hours or less

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

(Identification of crystal phase)
A general X-ray diffractometer (trade name: Ultima IIV, manufactured by Rigaku) was used to obtain an XRD pattern of the powder sample. Conditions for the XRD measurement are as follows.
Radiation 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°

(Monoclinic phase rate)
An XRD pattern was obtained in the same manner as for identifying the crystal phase, and the monoclinic crystal fraction was determined from the above equation (5).

(Crystallite diameter)
An XRD pattern was obtained in the same manner as for identifying the crystal phase, and the crystallite size was determined from the above formulas (6) and (7).

(relative density)
The actual density of the sintered body sample was measured by the Archimedes method. Prior to the measurement, after measuring the mass of the dried sintered body, the sintered body was placed in water and boiled for 1 hour as a pretreatment. The theoretical density was obtained from formulas (1) to (4), and the relative density (%) was obtained from the value of the actually measured density (ρ) with respect to the theoretical density (ρ ₀ ).

(Average grain size)
The average crystal grain size was obtained by the planimetric method using the SEM observation diagram of the sintered body sample obtained by field emission scanning electron microscope observation. That is, a circle having a known area was drawn on the SEM observation diagram, and the number of crystal grains (Nc) in the circle and the number of crystal grains (Ni) on the circumference of the circle were measured.
After setting the total number of crystal grains (Nc+Ni) to 250±50, the average crystal grain size was obtained using the following formula.
Average grain size = (Nc + (1/2) x Ni)/(A/M ² )
In the above formula, Nc is the number of crystal grains in the 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 scanning electron microscope magnification (5000x). When the number of crystal grains (Nc+Ni) in one SEM observation diagram is less than 200, (Nc+Ni) was set to 250±50 using a plurality of SEM observation diagrams.
Prior to the measurement, the sintered sample was mirror-polished and then thermally etched for pretreatment. Mirror polishing was carried out by scraping the surface of the sintered body with a surface grinder and then polishing it with a mirror polishing apparatus using diamond abrasive grains having an average particle size of 9 μm, 6 μm and 1 μm in that order.

(bending strength)
The bending strength of the sintered body sample was measured by a three-point bending test according to JIS R1601. The bending strength was measured using a pillar-shaped sintered body sample having 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 was taken as the bending strength.

(Linear transmittance)
When measuring the in-line transmittance at a sample thickness of 1 mm, both sides of the sample are sintered with a surface roughness (Ra) ≤ 0.02 μm, and the measurement is performed with a general spectrophotometer (eg, V- 650, manufactured by JASCO Corporation), the sample was irradiated with light having a wavelength of 600 nm. The linear transmittance (t ₆₀₀ ; %) at a thickness of 1 mm was calculated by subtracting the diffuse transmittance from the total light transmittance measured with 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) x 100
R = {(1−n)/(1+n)} ²
In the above equation, T is the in-line transmittance at a thickness of 0.1 mm, R is the modulus, and n is the refractive index of zirconia. In this example, n was set to 2.14. μ is an absorption coefficient, which can be obtained from the following formula.
μ=−In{(t ₆₀₀ /100)×(1/0.753)}

Example 1
Alumina sol and germania powder were added so that the aluminum content was 0.25% by mass, the germanium content was 0.25% by mass, and the balance was obtained by a hydrolysis method, and 3 mol% yttrium-containing zirconia was obtained. and 3 mol % yttrium-containing zirconia powder having a crystallite size of 31 nm and a monoclinic fraction of 29% were wet pulverized, mixed and dried.
The dried mixed powder was uniaxially pressed and then CIP (Cold Isostatic Pressed) processed to form a compact (green compact). Pre-sintered. After the preliminary sintering, the temperature was lowered to 200°C at a rate of 200°C/hour to obtain a primary sintered body.
The resulting primary sintered body was HIP-treated in an argon atmosphere at 150 MPa and 1150° C. for 1 hour, so that the aluminum content and the germanium content of the additive element amount were 0.25% by mass and 0.25% by mass, respectively. and the balance was 3 mol % yttrium-containing zirconia to obtain a sintered body of this example. 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% (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 at a sample thickness of 1 mm. %Met. Also, it can be seen that μ=4.0 mm ⁻¹ and the in-line transmittance (T) at a thickness of 0.1 mm is 50%. From this, it can be confirmed that the sintered body of this example has sufficient strength and translucency to be used as a cover member.

Example 2
Additive elements were added in the same manner as in Example 1 except that the alumina sol and the germania powder were mixed so that the aluminum content as the additive element amount was 0.25% by mass and the germanium content was 0.75% by mass. A sintered body of this example was obtained, which had an aluminum content of 0.25% by mass, a germanium content of 0.75% by mass, and a balance of 3 mol% yttrium-containing zirconia. 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 the present embodiment has a relative density of 99.90% (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 at a sample thickness of 1 mm. %Met. Also, it can be seen that μ=3.9 mm ⁻¹ and the in-line transmittance (T) at a thickness of 0.1 mm is 51%. From this, it can be confirmed that the sintered body of this example has sufficient strength and translucency to be used as a cover member.

Example 3
Additive elements were added in the same manner as in Example 1, except that the alumina sol and the germania powder were mixed so that the aluminum content as the additive element amount was 0.15% by mass and the germanium content was 0.25% by mass. A powder was obtained having an aluminum content of 0.15 wt.
In the same manner 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 additive elements was 0.15% by mass and germanium was added. A sintered body of this example was obtained which was composed of zirconia containing 0.25% by mass of yttrium and the balance being 3 mol% yttrium. The sintered body of this example was visually confirmed to have translucency, and the average crystal grain size was 130 nm.
The sintered body of this embodiment has a relative density of 99.90% (measured 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 at a sample thickness of 1 mm. %Met. Also, it can be seen that μ=3.5 mm ⁻¹ and the in-line 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 sufficient strength and translucency to be used as a cover member.

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

Claims

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. .
The cover member according to claim 1, wherein the stabilizing element is one or more selected from the group consisting of scandium, yttrium and lanthanide rare earth elements.
The cover member according to claim 1 or 2, wherein the stabilizing element is yttrium.
The cover member according to claim 3, wherein the content of the stabilizing element is 2.0 mol% or more and 6.0 mol% or less.
The cover member according to any one of claims 1 to 4, wherein the sintered body contains one or more selected from the group of germanium, aluminum and silicon.
The cover member according to any one of claims 1 to 5, having a thickness of 0.1 mm or more and 1.0 mm or less.
A display device comprising the cover member according to any one of claims 1 to 6.
An electronic device comprising the display device according to claim 7 .