JP6709850B2 - Oriented alumina sintered body and manufacturing method thereof - Google Patents

Description

The present invention relates to an oriented alumina sintered body and a method for producing the same.

As a method for producing an oriented alumina sintered body, for example, the method of Patent Document 1 is known. In this method, a plate-like alumina powder and a fine alumina powder are mixed, a binder and a dispersion medium are added to the mixture to prepare a slurry, and the slurry is tape-formed, and then the tape is laminated to form a molded body, and molded. The body is fired to obtain an oriented alumina sintered body. The oriented alumina sintered body thus obtained has a flat plate shape and a high degree of c-plane orientation.

On the other hand, as a method of manufacturing a ceramic plate having a curved surface portion, for example, the method of Patent Document 2 is known. In this method, first, a ceramics green sheet is heated in an environment where the glass transition point of the binder contained in the sheet is 10° C. or higher and 40° C. or lower, and bending is performed on the heated ceramics green sheet. .. Next, the ceramic green sheet after bending is fired. By doing so, a ceramic plate having a curved surface portion can be obtained. According to this manufacturing method, it is said that it is possible to suppress the occurrence of cracking of the ceramic green sheet during bending.

International Publication No. 2016/084722 Pamphlet JP, 2005-30233, A

However, there is no description or suggestion in any of Patent Documents 1 and 2 regarding an oriented alumina sintered body having a curved surface portion. Moreover, after laminating tapes as in Patent Document 1 to form a flat plate-shaped molded product, the molded product is heated in an environment of 10° C. or higher and 40° C. or lower of the glass transition point of the binder as in Patent Document 2. However, when the bending process is performed, there is a problem that cracks and wrinkles are formed during the bending process. Therefore, it is not possible to obtain an oriented alumina sintered body having a curved surface portion by simply combining Patent Documents 1 and 2.

The present invention has been made to solve such a problem, and its main object is to provide an oriented alumina sintered body having a curved surface portion.

The oriented alumina sintered body of the present invention,
An oriented alumina sintered body having a curved surface portion,
Alumina particles of the curved surface portion, the crystal orientation in the normal direction of the curved surface portion,
It is a thing.

The manufacturing method of the oriented alumina sintered body of the present invention,
(A) A plate-shaped alumina containing 2 to 30 parts by mass of an organic binder with respect to 100 parts by mass of mixed alumina powder in which plate-shaped alumina powder and fine alumina powder having an average particle size smaller than the thickness of the plate-shaped alumina powder are mixed. The molded body is bent at a processing temperature set within a range in which the glass transition point of the organic binder plus 45° C. is a lower limit value, and the decomposition temperature of the organic binder minus 50° C. is an upper limit value. A step of obtaining an alumina molded body,
(B) a step of obtaining an oriented alumina sintered body by firing an alumina formed body having the curved surface portion,
Is included.

According to the method for producing an oriented alumina sintered body of the present invention, it is possible to relatively easily produce an oriented alumina sintered body having a curved surface portion.

The "decomposition temperature of the organic binder" is defined as the temperature at which the weight is reduced by 10% when TG-DTA measurement (temperature rising rate 10°C/min, in air) is performed on the binder alone. Hereinafter, the glass transition point is abbreviated as Tg, and the decomposition temperature is abbreviated as Td.

The perspective view of the curved surface part 10. AA sectional drawing of FIG. The perspective view of the curved surface part 20. Sectional drawing of the oriented alumina sintered compact 30. Sectional drawing of the oriented alumina sintered body 40. 4A and 4B are explanatory views of observation points P1 to P3, where FIG. 7A is a plan view of the curved surface portion 10 and FIGS. It is explanatory drawing of observation point P6-P8, (a) is a back view of the curved surface part 10, (b)-(d) is sectional drawing. Explanatory drawing of the method of measuring the angle which the normal line and the orientation axis at an observation point make. It is a schematic diagram of a plate-like alumina particle, (a) is a top view, (b) is a front view. It is an explanatory view of lower mold 50, (a) is a top view and (b) is a BB sectional view. It is explanatory drawing of the upper mold 60, (a) is a top view, (b) is CC sectional drawing. Explanatory drawing of bending process. The appearance photograph after the surface of the alumina sintered body obtained in Experimental Example 1 was mirror-finished by polishing.

Preferred embodiments of the present invention will be shown below. The oriented alumina sintered body of the present embodiment has a curved surface portion, and the alumina particles on the curved surface portion are crystal-oriented in the normal direction of the curved surface portion. The crystal-oriented axis is not particularly limited, and examples thereof include c-axis, a-axis, m-axis, and r-axis, and among these, c-axis is preferable. The curved surface portion refers to a portion that is not a flat surface but is a continuously curved surface.

An example of the curved surface portion is shown in FIGS. 1 is a perspective view of the curved surface portion 10, FIG. 2 is a sectional view taken along the line AA of FIG. 1, and FIG. 3 is a perspective view of the curved surface portion 20. The dotted line in FIG. 1 is drawn for convenience so that it looks three-dimensional. FIG. 2 is a cross-sectional view taken along a plane passing through the apex of the curved surface portion 10 and including a normal line at the apex. The curved surface portion 10 is a part of a spherical surface, and the upper surface thereof is a convex surface area 10a and the lower surface thereof is a concave surface area 10b. Looking at the cross section of the curved surface portion 10, the c-axis of the alumina particles (arrow in FIG. 2) is oriented in the direction normal to the convex surface region 10a. The curved surface portion 20 is a part of a cylindrical surface. In addition, in the curved surface portion, although not shown, a concave curved surface and a convex curved surface may be continuous. In that case, the boundary between the concave curved surface and the convex curved surface becomes the outer edge of each curved surface.

The oriented alumina sintered body of the present embodiment may have only a curved surface portion or may have a curved surface portion and other portions. FIG. 4 is a sectional view of the oriented alumina sintered body 30, and FIG. 5 is a sectional view of the oriented alumina sintered body 40. The oriented alumina sintered body 30 has a curved surface portion 32 and a flat surface portion 34, and the arrow indicates the c-axis of alumina particles. The curved surface portion 32 has an arch shape on both the upper surface and the lower surface. The c-axis of the alumina particles is oriented in the normal direction of the convex region 32a of the curved surface portion 32 and the normal direction of the surface 34a of the flat portion 34. The boundary between the convex surface area 32a of the curved surface portion 32 and the surface 34a of the flat surface portion 34 becomes the outer edge of the convex surface area 32a. The oriented alumina sintered body 40 has a curved surface portion 42 and a flat surface portion 44, and the arrow indicates the c-axis of alumina particles. The curved surface 42 has an arched upper surface and a flat lower surface. The c-axis of the alumina particles is oriented in the normal direction of the convex region 42a of the curved surface portion 42 and the normal direction of the surface 44a of the flat portion 44. The boundary between the convex surface region 42a of the curved surface portion 42 and the surface 44a of the flat surface portion 44 becomes the outer edge of the convex surface region 42a.

In the oriented alumina sintered body of the present embodiment, when a normal line is drawn at each of at least three observation points on the curved surface portion in the cross section of the oriented alumina sintered body, the orientation axis of the alumina particles on each normal line is It is preferable that the ratio of those falling within ±15° with respect to the normal is 60% or more. The angle between the normal line and the orientation axis at each observation point is more preferably within ±12°, further preferably within ±10°, further preferably within ±8°, and particularly preferably within ±5°. Further, the above-mentioned ratio is more preferably 70% or more, further preferably 80% or more, particularly preferably 90% or more. In determining the three observation points, when the curved surface portion is viewed in plan, the extreme point of the convex surface area or concave surface area of the curved surface portion is set as the first observation point, and the convex area of the curved surface portion is passed through the extreme value point. Or, when the length of a line segment drawn so as to intersect with the outer edge of the concave region becomes the longest, the midpoints (2 points) of each end point of the line segment and the extreme point are the two remaining observation points. Preferably. The extreme point is the highest point in the convex area and the lowest point in the concave area.

FIG. 6 is an explanatory diagram showing an example of a method of determining three observation points P1 to P3 on the convex surface area 10a of the curved surface portion 10, and FIG. 6A is a plan view of the convex surface area 10a of the curved surface portion 10 in plan view. It is a figure. In FIG. 6(a), a line segment is drawn which has two end points as two intersections that pass through the extreme points (uppermost points) of the convex area 10a and intersect the outer edge of the convex area 10a. Although such line segments can be drawn innumerably, a line segment having the longest length is selected from the line segments, and both end points of the line segment are defined as intersection points P4 and P5. In FIG. 6A, since the plan view of the convex surface area 10a is elliptical, the longest line segment has a long diameter. In this case, one of the three observation points is the highest point (observation point P1) of the convex area 10a of the curved surface portion 10. The remaining two are the midpoint of the line segment connecting the intersection P4 and the observation point P1 (observation point P2) and the midpoint of the line segment connecting the intersection P5 and the observation point P1 (observation point in the plan view). P3). Then, in order to investigate the orientation of the alumina particles on the normal line at the observation point P1, a cross-sectional view of the convex region 10a taken along a plane passing through the observation point P1 and including the normal line NL1 at the observation point P1 (FIG. 6(b)) is used. To examine the orientation of the alumina particles on the normal line of the observation point P2, a cross-sectional view of the convex region 10a taken along a plane passing through the observation point P2 and including the normal line NL2 at the observation point P2 (FIG. 6(c ) Reference) is used. In order to examine the orientation of the alumina particles on the normal line of the observation point P3, a cross-sectional view of the convex region 10a taken along a plane passing through the observation point P3 and including the normal line NL3 at the observation point P3 (see FIG. 6(d ) Reference) is used. When the normal line NL2 at the observation point P2 is on the same plane as the cross section of the observation point P1 shown in FIG. 6B, the cross section of the observation point P2 matches the cross section of the observation point P1. Sometimes, the cross section of the observation point P2 does not match the cross section of the observation point P1. The same applies to the cross section of the observation point P3.

FIG. 7 is an explanatory diagram showing an example of a method of determining three observation points P6 to P8 in the concave surface area 10b of the curved surface portion 10, and FIG. 7A is a plan view of the concave surface area 10b of the curved surface portion 10 in plan view. It is a figure. In FIG. 7A, a line segment having two end points that intersect the outer edge of the concave surface area 10b and pass through the extreme points (bottom points) of the concave surface area 10b is drawn. Although such a line segment can be drawn innumerably, the line segment having the longest length is selected from the line segments, and both end points of the line segment are defined as intersection points P9 and P10. In FIG. 7A, since the plan view of the concave surface region 10b is elliptical, the longest line segment has a long diameter. In this case, one of the three observation points is the lowest point (observation point P6) of the concave area 10b of the curved surface portion 10. The remaining two are the midpoint of the line segment connecting the intersection P9 and the observation point P6 (observation point P7) and the midpoint of the line segment connecting the intersection P10 and the observation point P6 (observation point in the plan view). P8). Then, in order to investigate the orientation of the alumina particles on the normal line of the observation point P6, a cross-sectional view of the concave region 10b taken along a plane passing through the observation point P6 and including the normal line NL6 at the observation point P6 (FIG. (See (b)) is used. In order to examine the orientation of the alumina particles on the normal line of the observation point P7, a cross-sectional view of the concave region 10b taken along a plane passing through the observation point P7 and including the normal line NL7 at the observation point P7 (FIG. 7(c ) Reference) is used. In order to examine the orientation of the alumina particles on the normal line of the observation point P8, a cross-sectional view of the concave region 10b taken along a plane passing through the observation point P8 and including the normal line NL8 at the observation point P8 (see FIG. 7(d ) Reference) is used. When the normal line NL7 at the observation point P7 is on the same plane as the cross section of the observation point P6 shown in FIG. 7B, the cross section of the observation point P7 coincides with the cross section of the observation point P6. Sometimes, the cross section of the observation point P7 does not match the cross section of the observation point P6. The same applies to the cross section of the observation point P8.

The angle formed by the normal line and the orientation axis at each observation point can be measured as shown in FIG. FIG. 8 is an explanatory diagram of a method for measuring the angle formed by the normal line at the observation point and the orientation axis. First, the oriented alumina sintered body of the present embodiment is cut. For example, when the curved surface portion of the oriented alumina sintered body includes the convex area 10a of FIG. 6A, the cross sections of FIGS. 6B to 6D are obtained for each of the three observation points P1 to P3. Disconnect. When the curved surface portion of the oriented alumina sintered body includes the concave region 10b of FIG. 7A, the cross sections of FIGS. 7B to 7D are obtained for each of the three observation points P6 to P8. Disconnect. After the cross section thus cut is polished by ion milling, the polished cross section is subjected to EBSD (Electron Back Scatter Diffraction Patterns) measurement using a scanning electron microscope. Then, a normal line is drawn at each observation point, and among the alumina particles arranged in the thickness direction of the oriented alumina sintered body, the alumina particles (alumina particles shown in gray in FIG. 8) that come into contact with this normal line are determined. Then, the angle between the normal line at the observation point and the c-axis of the alumina particles in contact with this normal line is obtained.

The oriented alumina sintered body of the present embodiment can have transparency by having high density and high purity. That is, from the viewpoint of transparency, high density, high purity, and high orientation are preferable. The transparent oriented alumina sintered body oriented in the normal direction of the curved surface portion is a mirror-polished surface of the surface, and is a cover glass for smartphones, smart watches, wristwatches, etc. having curved surface portions, various window materials, optical members such as lenses. It can be used for The transparent oriented alumina sintered body that is oriented in the normal direction of the curved surface section is more transparent than the sintered body in which a curved transparent oriented alumina sintered body is processed and cut to give the curved surface section. It is characterized by high transparency when viewed.

The manufacturing method of the oriented alumina sintered body of the present embodiment is as follows: (a) 100 parts by mass of mixed alumina powder obtained by mixing plate-like alumina powder and fine alumina powder having an average particle size smaller than the thickness of the plate-like alumina powder. Processing temperature set in a flat alumina molded body containing 2 to 30 parts by mass of an organic binder in a range in which Tg of the organic binder is 45° C. as a lower limit and Td of the organic binder is 50° C. as an upper limit. And a step of obtaining an alumina molded body having a curved surface portion by (1) and (b) obtaining an oriented alumina sintered body by firing the alumina molded body having a curved surface portion.

In the step (a), it is preferable to use a mixed powder obtained by mixing a plate-shaped alumina powder and a fine alumina powder having an average particle size smaller than that of the plate-shaped alumina powder as an alumina raw material for producing the alumina molded body. By doing so, the plate-like alumina powder serves as a seed crystal (template), the fine alumina powder serves as a matrix, and the template undergoes homoepitaxial growth while taking in the matrix. Such a manufacturing method is called a TGG (Templated Grain Growth) method. In the TGG method, the fine structure of the obtained alumina sintered body can be controlled by the particle size and the mixing ratio of the plate-like alumina powder and the fine alumina powder, and the densification can be performed as compared with the case of firing the plate-like alumina powder alone. It is easy to improve the degree of orientation.

The content of the plate-like alumina powder in the mixed powder is not particularly limited and may be 100% by mass, but 0.1 to 50% by mass is preferable. This is because if it is less than 0.1% by mass, the degree of c-plane orientation of the obtained alumina sintered body is unlikely to be high, and if it exceeds 50% by mass, alumina may be difficult to sinter. The content of the plate-shaped alumina powder is more preferably 0.1 to 15% by mass, further preferably 0.5 to 5% by mass, and particularly preferably 1.5 to 5% by mass. In this case, the degree of c-plane orientation obtained is sufficiently high, and the amount of expensive plate-like alumina used is relatively small, which is advantageous in terms of cost. From the viewpoint of increasing the degree of orientation of the obtained alumina sintered body, the thickness of the particles forming the plate-like alumina powder is preferably larger than the average particle diameter of the particles of the fine alumina powder. Further, the particle size of the plate surface of the plate-like particles constituting the plate-like alumina powder is preferably large from the viewpoint of high orientation, preferably 1.5 μm or more, more preferably 5 μm or more, further preferably 10 μm or more, 15 μm or more is particularly preferable. However, from the viewpoint of densification, it is preferable that the grain size of the plate surface is small, and 30 μm or less is preferable. Therefore, in order to achieve both high orientation and densification, it is preferable that the grain size of the plate surface is 1.5 to 20 μm. The plate-like alumina powder is preferably of high purity. The purity of the plate-like alumina powder is preferably 99% by mass or more, more preferably 99.9% by mass or more, and further preferably 99.99% by mass or more. However, an impurity element that volatilizes and disappears during firing may be included, and for example, an element such as F or S may be included.

In the step (a), it is preferable to use a polymer as the organic binder, and it is more preferable to use a butyral-based polymer, an acrylic-based polymer or a methacrylic-based polymer. Examples of the butyral-based polymer include polyvinyl butyral. BM-2 manufactured by Sekisui Chemical Co., Ltd. is a butyral-based polymer and has Tg of 67° C. and Td of 350° C. Examples of acrylic polymers include acrylic acid ester polymers. Kyoeisha Chemical's KC7025T is an acrylic polymer having a Tg of 56°C and a Td of 235°C. Examples of methacrylic polymers include methacrylic acid ester polymers. Negami Kogyo's M6003 is a methacrylic polymer and has Tg of 20°C and Td of 244°C.

In the step (a), 2 to 30 parts by mass of an organic binder is added to 100 parts by mass of the alumina raw material. The addition amount of the organic binder is more preferably 4 to 15 parts by mass. The plasticizer is preferably added in an amount of 0.5 to 25 parts by mass, more preferably 2 to 8 parts by mass, based on 100 parts by mass of the alumina raw material.

In the step (a), a method for producing a flat-plate-shaped alumina molded body includes tape-shaped, extrusion-molded, cast-molded, gel-cast molding, injection-molded, uniaxial press-molded, and combinations thereof with plate-shaped alumina. Any method may be used as long as the powder is oriented. Of these, tape molding is preferable.

In the step (a), the flat plate-shaped alumina molded body is bent by placing the flat-plate-shaped alumina molded body in a bending mold and heating it, followed by uniaxial pressing or cold isostatic pressing (CIP) treatment. It is preferable to carry out. The heating temperature is preferably set within a range in which Tg plus 45° C. of the organic binder is a lower limit value and Td minus 50° C. is an upper limit value. If the heating temperature is lower than the lower limit, the flat alumina molded body may be insufficiently softened, or cracks, wrinkles, and the like may occur during bending, which is not preferable.

In the step (b), the oriented alumina sintered body is obtained by degreasing the alumina molded body having a curved surface portion and then firing it. Further, in order to maintain the shape of the fired body, it is preferable that the density of the alumina formed body is high. Therefore, from the viewpoint of increasing the density of the molded body, it is preferable to uniaxially press or CIP the alumina molded body or degreased body to increase the density.

It is needless to say that the present invention is not limited to the above-described embodiment and can be implemented in various modes within the technical scope of the present invention.

[Experimental Example 1]
1. Preparation of Alumina Sintered Body (1) Preparation of Plate Alumina Powder 96 parts by mass of high-purity γ-alumina powder (TM-300D, manufactured by Daimei Kagaku) and 4 parts by mass of high-purity AlF ₃ powder (manufactured by Kanto Chemical, deer special grade). Parts and 0.17 parts by mass of high-purity α-alumina powder (TM-DAR, manufactured by Daimei Kagaku Co., D50=1 μm) as seed crystals, using an alumina ball of φ2 mm as a solvent for IPA (isopropyl alcohol) for 5 hours. Mixed in pot mill. After mixing with a pot mill, IPA was dried with an evaporator to obtain a mixed powder. 300 g of the obtained mixed powder is put into a sheath (volume 750 cm ³ ) made of high-purity alumina having a purity of 99.5% by mass, a lid made of high-purity alumina having a purity of 99.5% by mass is put, and air flow is performed in an electric furnace. Heat treatment was performed at 900° C. for 3 hours. The flow rate of air was 25,000 cc/min. The heat-treated powder is annealed in air at 1150° C. for 42.5 hours, and then pulverized for 4 hours using alumina balls of φ2 mm to obtain a plate-like alumina having an average particle diameter of 2 μm, a thickness of 0.3 μm, and an aspect ratio of about 7. A powder was obtained. The average particle diameter, average thickness, and aspect ratio of the particles were determined by observing 100 arbitrary particles in the plate-like alumina powder with a scanning electron microscope (SEM). The average particle diameter is the average value of the major axis length of the particle plate surface, the average thickness is the average value of the minor axis length (thickness) of the particles, and the aspect ratio is the average particle diameter/average thickness. FIG. 9 is a schematic view of plate-like alumina particles, (a) is a plan view and (b) is a front view. The plate-like alumina particles have a substantially hexagonal shape when viewed in a plan view, the particle size thereof is as shown in FIG. 9(a), and the thickness is as shown in FIG. 9(b).

(2) Tape forming and bending process 2.0 parts by mass of the plate-like alumina powder prepared in (1) above and fine alumina powder having an average particle size smaller than the thickness of the plate-like alumina powder (AKP-20, manufactured by Sumitomo Chemical Co., Ltd. ) 98.0 parts by mass were mixed. With respect to 100 parts by mass of this mixed alumina powder, 0.025 parts by mass of magnesium oxide (500A, manufactured by Ube Materials), 8 parts by mass of polyvinyl butyral (product number BM-2, manufactured by Sekisui Chemical Co., Ltd.) as a binder, and a plasticizer 4 parts by mass of di(2-ethylhexyl) phthalate (manufactured by Kurogane Kasei), 0.5 part by mass of sorbitan trioleate (Reodol SP-O30, manufactured by Kao) as a dispersant, and xylene and butanol as a dispersion medium 1: 1 mixed solution was added and mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity would be 20000 cP. The slurry thus prepared was molded into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 40 μm to obtain a tape molded body.

The above-mentioned tape molded body having a thickness of 40 μm was cut into φ47 mm, and 30 pieces were laminated to form a laminated body, and the laminated body was bent. The bending process was performed using the lower mold 50 and the upper mold 60. 10A and 10B are explanatory views of the lower mold 50, FIG. 10A is a plan view, and FIG. 10B is a sectional view taken along line BB. 11A and 11B are explanatory views of the upper mold 60. FIG. 11A is a plan view and FIG. 11B is a cross-sectional view taken along line CC. The lower die 50 is a die having a circular recess 52 on the upper surface. The bottom surface of the circular recess 52 is a concave curved surface 52a. The upper die 60 is a die having a circular convex portion 62 on the lower surface. The surface of the circular convex portion 62 is a convex curved surface 62a. In this experimental example, the circular concave portion 52 and the circular convex portion 62 were φ47 mm, and the radius of curvature of the concave curved surface 52a and the convex curved surface 62a was 160 mm. FIG. 12 is an explanatory diagram of bending work. The above-mentioned laminated body was placed in the circular recess 52 of the lower mold 50, sandwiched by the upper mold 60 from above, and set in a uniaxial press molding machine (having a heating mechanism on the upper and lower surfaces of the press part). Then, while applying a pressure of 20 kgf/cm ² with a uniaxial press molding machine, the mixture was heated at 120° C. for 10 minutes, and then uniaxially pressed at a pressure of 166 kgf/cm ² for 1 minute to obtain a curved shaped article.

Polyvinyl butyral (product number BM-2, manufactured by Sekisui Chemical Co., Ltd.) used as a binder has Tg of 67° C. and Td of 350° C. Therefore, the temperature during bending may be set in the range of (Tg+45)° C. or higher and (Td-50)° C. or lower, that is, in the range of 112° C. or higher and 300° C. or lower, and is set to 120° C. here.

(3) Firing The obtained curved surface-shaped molded body was placed in a degreasing furnace and degreased at 600° C. for 10 hours. The obtained degreased body was put in an alumina sheath, and calcined under atmospheric pressure at 1550° C. for 4 hours under atmospheric pressure to prepare a calcined body. The fired body thus prepared was put in an alumina sheath, and hot isostatic pressing (HIP) treatment was performed under the conditions of Ar gas, pressure of 185 MPa, and 1900° C. for 2 hours.

2. Characteristics of Alumina Sintered Body (1) EBSD Measurement The obtained alumina sintered body was cut so as to include a normal line at each of three observation points P1 to P3 on the convex side curved surface, and the cross section was diamond abrasive grain. After being preliminarily polished by using, a cross section polisher (CP) (manufactured by JEOL Ltd., IB-09010CP) was used for polishing. CP belongs to the category of ion milling. The observation points P1 to P3 were determined by the method described above (see FIG. 6). Carbon was vapor-deposited on the obtained cross section, and EBSD measurement was performed using a scanning electron microscope (SU-5000 manufactured by Hitachi High-Technologies Corporation) in combination with EBSD (Nordlys Nano manufactured by Oxford Instruments). .. The various conditions for the EBSD measurement are as follows.

<EBSD measurement conditions>
Measurement program: AZtec (version 3.3)
・Acceleration voltage: 15 kV
・Spot size: 70
・Work distance: 20mm
・Step width: 5 μm
・Sample tilt angle: 70°
・EBSD camera pinning mode: 1×1
・Frame average: 5 frames ・Static background correction: ON ・Automatic background correction: ON ・Z-axis specification: Z is the normal direction to the sample pedestal surface <Crystal orientation map creation>
Analysis program: OXFORD HKL CHANNEL5 (version 5.12.57.0)
-Use the application "Tango" in the software to create a Texture component map (Crystal orientation map). Mapping in the range 0-90°

(2) Ratio of c-axis orientation Crystal orientation mapping was performed in a visual field such that 20 to 50 alumina particles were obtained when a normal line was drawn from the observation point P1 on the cut surface at the observation point P1. At this time, measurement was performed in a plurality of continuous visual fields so that the crystal orientations of all particles in the thickness direction in contact with the normal line could be evaluated. Next, the crystal orientations of all the alumina particles in contact with the normal line drawn from the observation point P1 on the convex side curved surface were examined. The same measurement was carried out at the observation points P2 and P3 to examine the crystal orientation. From the obtained results, the ratio R of particles having c-axis orientation within ±15° with respect to the normal line was calculated for each of the observation points P1 to P3 using the following formula. The results are shown in Table 1.
R=(No/Nt)×100[%]
Nt: Number of all particles existing on the normal line at the observation point (thickness direction of the alumina sintered body) No: On the normal line where the c-axis is oriented within ±15° with respect to the normal line at the observation point Number of particles

[Experimental Example 2]
In producing the alumina sintered body, the above 1. An alumina sintered body was prepared in the same manner as in Experimental Example 1 except that alumina powder (AKP-50, manufactured by Sumitomo Chemical Co., Ltd.) was used as the fine alumina powder in the tape molding of (2), and observation points P1 to P3. The ratio R in was calculated. The results are shown in Table 1.

[Experimental Example 3]
In producing the alumina sintered body, the above 1. In the bending process of (2), an alumina sintered body was produced in the same manner as in Experimental Example 2 except that the heating temperature at the time of uniaxial press forming was 115° C., and the ratio R at the observation points P1 to P3 was obtained. The results are shown in Table 1.

[Experimental Example 4]
In producing the alumina sintered body, the above 1. In the bending process of (2), an alumina sintered body was prepared in the same manner as in Experimental Example 2 except that the heating temperature during uniaxial press molding was 290° C., and the ratio R at the observation points P1 to P3 was obtained. The results are shown in Table 1.

[Experimental Example 5]
In producing the alumina sintered body, the above 1. An alumina sintered body was produced in the same manner as in Experimental Example 2 except that 5 parts by mass of the binder was used in the tape molding of (2), and the ratio R at the observation points P1 to P3 was obtained. The results are shown in Table 1.

[Experimental Example 6]
In producing the alumina sintered body, the above 1. An alumina sintered body was prepared in the same manner as in Experimental Example 2 except that 14 parts by mass of the binder was used in the tape molding of (2), and the ratio R at the observation points P1 to P3 was obtained. The results are shown in Table 1.

[Experiment 7]
In producing the alumina sintered body, the above 1. An alumina sintered body was produced in the same manner as in Experimental Example 2 except that 3 parts by mass of the binder was used in the tape molding of (2), and the ratio R at the observation points P1 to P3 was obtained. The results are shown in Table 1.

[Experimental Example 8]
In producing the alumina sintered body, the above 1. An alumina sintered body was produced in the same manner as in Experimental Example 2 except that 25 parts by mass of the binder was used in the tape molding of (2), and the ratio R at the observation points P1 to P3 was obtained. The results are shown in Table 1.

[Experimental Example 9]
In producing the alumina sintered body, the above 1. An alumina sintered body was produced in the same manner as in Experimental Example 2 except that an acrylic polymer (KC7025T, manufactured by Kyoeisha Chemical Co., Ltd.) was used as a binder in the tape molding of (2), and the ratio R at the observation points P1 to P3. I asked. The results are shown in Table 1.

[Experimental Example 10]
In producing the alumina sintered body, the above 1. An alumina sintered body was prepared in the same manner as in Experimental Example 2 except that a methacrylic polymer (M6003, manufactured by Negami Kogyo Co., Ltd.) was used as a binder in the tape molding of (2), and the ratio R at the observation points P1 to P3. I asked. The results are shown in Table 1.

[Experimental Example 11]
In producing the alumina sintered body, the above 1. An attempt was made to produce an alumina sintered body in the same manner as in Experimental Example 2 except that the heating temperature at the time of uniaxial press molding was set to 100° C. in the bending process of (2), but a curved surface shaped molded body could be obtained. There wasn't.

[Experimental Example 12]
In producing the alumina sintered body, the above 1. An attempt was made to produce an alumina sintered body in the same manner as in Experimental Example 2 except that the heating temperature at the time of uniaxial press molding was set to 310° C. in the bending process of (2), but it was possible to obtain a curved shape molded body. There wasn't.

[Experimental Example 13]
In producing the alumina sintered body, the above 1. An attempt was made to produce an alumina sintered body in the same manner as in Experimental Example 2 except that 1 part by mass of the binder was used in the tape molding of (2), but the tape molded body could not be obtained.

[Experimental Example 14]
In producing the alumina sintered body, the above 1. An attempt was made to produce an alumina sintered body in the same manner as in Experimental Example 2 except that 35 parts by mass of the binder was used in the tape molding of (2), but the tape molded body could not be obtained.

[Evaluation]
In the alumina sintered bodies of Experimental Examples 1 to 10, the alumina particles on the curved surface portion were c-axis oriented in the normal direction of the curved surface portion. Further, the proportions R at the three observation points P1 to P3 in Experimental Examples 1 to 10 are all 60% or more, and the proportion R at the three observation points P1 to P3 in Experimental Examples 1 to 6, 9, and 10 is any of them. Was 80% or more. On the other hand, in Experimental Examples 11 and 12, since the temperature during bending was not appropriate, the softening of the alumina molded body was insufficient, cracks and wrinkles were generated during bending, and the shape as designed was accurately obtained. It could not be molded well. In addition, in Experimental Examples 13 and 14, the amount of the binder used was not appropriate, and thus tape molding was difficult and molding could not be performed.

Here, FIG. 13 shows a photograph of the appearance after the surface of the alumina sintered body obtained in Experimental Example 1 was mirror-finished by polishing. From this appearance photograph, it can be seen that the oriented alumina sintered body after mirror-finishing has high transparency.

Experimental Examples 1 to 10 described above correspond to Examples of the present invention, and Experimental Examples 11 to 14 correspond to Comparative Examples. Needless to say, the present invention is not limited to the above-described embodiments and can be carried out in various modes within the technical scope of the present invention.

This application is based on Japanese Patent Application No. 2016-135852 filed on Jul. 8, 2016, and the entire contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY The present invention can be applied to, for example, cover glasses for smart phones, smart watches, wristwatches, various window materials, optical members such as lenses, and the like.

10 curved surface portion, 10a convex surface area, 10b concave surface area, 20 curved surface portion, 30 oriented alumina sintered body, 32 curved surface portion, 32a convex surface area, 34 flat surface portion, 34a surface, 40 oriented alumina sintered body, 42 curved surface portion, 42a Convex area, 44 Plane part, 44a Surface, 50 Lower mold, 52 Circular concave part, 52a Concave curved surface, 60 Upper mold, 62 Circular convex part, 62a Convex curved surface, P1 to P3, P6 to P8 Observation points, P4, P5, P9 , P10 intersections, NL1 to NL3, NL6 to NL8 normals.

Claims (5)

An oriented alumina sintered body having a curved surface portion,
Alumina particles of the curved surface portion, the crystal orientation in the normal direction of the curved surface portion ,
In the cross section of the oriented alumina sintered body, when a normal line is drawn at each of at least three observation points of the curved surface portion, the orientation axis of the alumina particles on each normal line is within ±15° with respect to the normal line. The percentage of items that fit in is 60% or more,
In determining the three observation points, when the curved surface portion is viewed in plan, the extreme point of the convex surface area or the concave surface area of the curved surface portion is set as the first observation point, and the curved surface portion passes through the extreme value point. When the length of a line segment drawn so as to intersect the outer edge of the convex region or the concave region of is the longest, the midpoints of both end points of the line segment and the extreme point are the remaining two observation points. To do
Oriented alumina sintered body. The ratio is 80% or more,
The oriented alumina sintered body according to claim 1 . The alumina particles of the curved surface portion are c-axis oriented in the normal direction of the curved surface portion,
Oriented alumina sintered body according to claim 1 or 2. (A) A plate-shaped alumina containing 2 to 30 parts by mass of an organic binder with respect to 100 parts by mass of mixed alumina powder in which plate-shaped alumina powder and fine alumina powder having an average particle size smaller than the thickness of the plate-shaped alumina powder are mixed. The molded body is bent at a processing temperature set within a range in which the glass transition point of the organic binder plus 45° C. is a lower limit value, and the decomposition temperature of the organic binder minus 50° C. is an upper limit value. A step of obtaining an alumina molded body,
(B) a step of obtaining an oriented alumina sintered body by firing an alumina formed body having the curved surface portion,
A method for producing an oriented alumina sintered body containing: The organic binder is a butyral polymer, an acrylic polymer or a methacrylic polymer,
The method for producing the oriented alumina sintered body according to claim 4 .