Ceramic sheet and method for producing same

Abstract

Provided is a method for producing a ceramic sheet, said method comprising: a primary sheet molding step for molding, into a sheet shape by pressurization, a composition which contains resin and a ceramic material; a laminate forming step for obtaining a laminate by layering a plurality of primary sheets in the thickness direction or folding or winding a primary sheet; a slicing step for obtaining a secondary sheet by slicing the laminate at an angle of not more than 45° relative to the layering direction; and a firing step for firing the secondary sheet.

Description

Ceramic sheet and manufacturing method thereof

[0001] The present invention relates to a ceramic sheet and a method for manufacturing the same.

[0002] Ceramic sheets have been used for a wide range of applications. It is known that various properties of ceramic sheets can be improved by controlling their structure. For example, Patent Document 1 proposes a method for producing an oriented ceramic sintered body by dispersing a predetermined non-ferromagnetic powder in a solvent, solidifying and molding the resulting slurry in a magnetic field, and then sintering the resulting slurry. Patent Document 1 also proposes an oriented alumina ceramic sintered body in which the (006) diffraction intensity in X-ray diffraction on the C-plane-oriented surface of the alumina crystal is 1.2 times or more the (110) diffraction intensity.

[0003] Japanese Patent Application Laid-Open No. 2002-193672

[0004] In recent years, there has been a demand for ceramic sheets with excellent properties different from those of conventionally provided ceramic sheets. Therefore, an object of the present invention is to provide a ceramic sheet having a novel orientation structure.

[0005] The present inventors have conducted extensive research to achieve the above object, and have discovered that a ceramic sheet having a novel orientation structure can be obtained by forming a composition containing a resin and a ceramic material into a sheet, obtaining a primary sheet, stacking a plurality of these primary sheets in the thickness direction to obtain a laminate, slicing the laminate into secondary sheets, and firing the secondary sheets, thereby completing the present invention.

[0006] The present invention aims to advantageously solve the above-mentioned problems, and provides a ceramic sheet manufacturing method comprising the steps of: a primary sheet forming step of pressurizing a composition containing a resin and a ceramic material into a sheet to obtain a primary sheet; a laminate forming step of stacking a plurality of the primary sheets in the thickness direction or folding or rolling the primary sheets to obtain a laminate; a slicing step of slicing the laminate at an angle of 45° or less to the stacking direction to obtain a secondary sheet; and a firing step of firing the secondary sheet. This manufacturing method can efficiently provide a ceramic sheet having a novel orientation structure.

[0007] In the ceramic sheet manufacturing method of the present invention, it is preferable to carry out a degreasing step prior to the firing step, in which the secondary sheet is heated in an atmosphere of 300°C or higher to degrease it, and to carry out the firing step in an atmosphere of 1000°C or higher. This manufacturing method can more efficiently provide a ceramic sheet having a novel oriented structure. Note that the temperatures in the degreasing step and the firing step are at 1 atm.

[0008] In the method for producing a ceramic sheet of the present invention, it is preferable that the thickness of the primary sheet is 2.5 mm or less. This method makes it possible to more efficiently provide a ceramic sheet having a novel oriented structure.

[0009] In the method for producing a ceramic sheet of the present invention, the volume fraction of the ceramic material in the primary sheet is preferably 50% by volume or more and 75% by volume or less, based on the total volume of the resin and the ceramic material. This production method can improve the quality of the ceramic sheet having a novel orientation structure.

[0010] The present invention aims to advantageously solve the above-mentioned problems. The ceramic sheet of the present invention is a ceramic sheet made of a sintered ceramic body, characterized in that the value of the a-axis of the ceramic sheet when subjected to Lotgering analysis is positive. Such a ceramic sheet has a novel orientation structure. The Lotgering analysis of the ceramic sheet can be performed according to the method described in the Examples.

[0011] Here, the ceramic sheet of the present invention preferably has a negative c-axis value when subjected to Lotgering analysis. When the c-axis value is negative when subjected to Lotgering analysis, the ceramic sheet has a relatively high a-axis orientation, which can result in favorable attributes.

[0012] In the ceramic sheet of the present invention, the ceramic may contain alumina. A ceramic sheet containing alumina as the ceramic has excellent quality.

[0013] Furthermore, in the ceramic sheet of the present invention, the ceramic preferably contains flaky ceramic. When the ceramic sheet contains flaky ceramic, the thermal conductivity is excellent. Furthermore, in the ceramic sheet of the present invention, the proportion of the flaky ceramic in the ceramic is preferably 65% ​​by volume or less. When the proportion of the flaky ceramic is 65% by volume or less of the total ceramic, the strength of the ceramic sheet can be increased.

[0014] According to the present invention, it is possible to provide a ceramic sheet having a novel oriented structure.

[0015] Hereinafter, embodiments of the present invention will be described in detail.

[0016] (Ceramic Sheet) The ceramic sheet of the present invention is a ceramic sheet made of a sintered ceramic body and has a novel orientation structure. More specifically, the ceramic sheet of the present invention has a positive a-axis value when subjected to Lotgering analysis, and the a-axis of the crystal axes of the ceramic constituting the ceramic sheet is oriented in the thickness direction of the ceramic sheet (the a-axis is parallel to the thickness direction). Such a ceramic sheet has excellent thermal conductivity in the thickness direction and anisotropic thermal conductivity, in which the thermal conductivity in the thickness direction is higher than that in the direction of the main surface of the ceramic sheet. Here, "main surface of the ceramic sheet" means at least one surface of the ceramic sheet.

[0017] In the ceramic sheet of the present invention, the phrase "the a-axis of the ceramic crystal axes is oriented in the thickness direction of the ceramic sheet" means that the ceramic crystals constituting the ceramic sheet are oriented in the a-axis direction, and further, the a-axis direction substantially coincides with the thickness direction of the ceramic sheet. If the a-axis direction of the ceramic crystals in the ceramic sheet is oriented in the thickness direction of the sheet, the ceramic sheet will have excellent thermal conductivity and will exhibit anisotropic thermal conductivity, in which the thermal conductivity is higher in the thickness direction than in the main surface direction of the sheet.

[0018] In this specification, the fact that the ceramic crystals constituting the ceramic sheet are "oriented in the a-axis direction" can be understood not only by the a-axis value being positive when analyzed by Lotgering analysis, but also by the value (hereinafter sometimes expressed as "a / c") obtained by dividing the scattering intensity in a plane corresponding to the a-axis direction of the crystal obtained by X-ray diffraction (XRD) described in the examples by the scattering intensity in a plane corresponding to the c-axis direction.

[0019] Here, according to the method described in the examples, the value obtained by dividing the value of a / c when the a-axis direction is oriented in the thickness direction of the ceramic sheet by the value of a / c when the a-axis direction is not oriented in the thickness direction of the ceramic sheet (hereinafter, sometimes referred to as the "ceramic vertical orientation parameter") is preferably 1.50 or more, more preferably 1.55 or more, more preferably 3.00 or more, and particularly preferably 3.60 or more. If the value of the vertical orientation parameter is equal to or greater than this lower limit, the a-axis direction of the ceramic crystals is more favorably oriented in the thickness direction of the ceramic sheet, and such a ceramic sheet has even better thermal conductivity.

[0020] The ceramic sheet must have a positive a-axis value (Lotgering factor) when analyzed by Lotgering analysis, preferably 0.010 or more, and even more preferably 0.020 or more. Such a ceramic sheet has excellent thermal conductivity in the thickness direction and high anisotropy of thermal conductivity. The upper limit of the a-axis value when analyzed by Lotgering analysis is not particularly limited and can be, for example, 1.000 or less. According to the principles of Lotgering analysis, in the case of perfect orientation, the Lotgering factor value is 1.000, and in the case of no orientation, the Lotgering factor value is zero. The closer the Lotgering factor value is to 1, the higher the degree of orientation.

[0021] Furthermore, the ceramic sheet preferably has a negative c-axis value (Lotgering factor) when subjected to Lotgering analysis, preferably −0.0001 or less, and more preferably −0.0010 or less. Because the a-axis of such a ceramic sheet is relatively oriented, it has excellent thermal conductivity in the thickness direction and high anisotropy of thermal conductivity. The lower limit of the c-axis value when subjected to Lotgering analysis is not particularly limited and can be, for example, −0.0030 or more. Based on the principles of Lotgering analysis, a negative Lotgering factor means that the proportion of crystal grains oriented along the c-axis is lower than that of a non-oriented sample, i.e., the proportion of crystal grains oriented along axes other than the c-axis is relatively high.

[0022] Furthermore, the ceramic sheet preferably has a thermal conductivity in the thickness direction divided by the thermal conductivity in the principal surface direction (hereinafter also referred to as the "thermal conductivity anisotropy parameter") of 1.01 or more, more preferably 1.05 or more. Such a ceramic sheet has anisotropy in thermal conductivity. The upper limit of the thermal conductivity anisotropy parameter is not particularly limited, but can be, for example, 3.0 or less.

[0023] The ceramic constituting the ceramic sheet is not particularly limited, and examples thereof include alumina, barium titanate, boron nitride, silicon nitride, silicon carbide, and hydroxyapatite. The ceramic constituting the ceramic sheet preferably contains alumina. When the ceramic contains alumina, the ceramic sheet has high quality.

[0024] Furthermore, the ceramic constituting the ceramic sheet preferably contains scaly ceramic. Ceramic sheets containing scaly ceramic have excellent thermal conductivity. In this case, the ratio of scaly ceramic to the total volume of the ceramic is preferably 65% ​​by volume or less, more preferably 55% by volume or less, and even more preferably 40% by volume or less. When the ratio of scaly ceramic to the total volume of the ceramic is equal to or less than the upper limit, the quality of the ceramic sheet is high. More specifically, when producing a ceramic sheet according to the manufacturing method of the present invention described below, using a composition in which the ratio of scaly ceramic is equal to or less than the upper limit can suppress flake peeling during the firing process, thereby improving the quality of the resulting ceramic sheet. Furthermore, from the viewpoint of further improving the orientation of the crystal axes of the ceramic, when the ceramic sheet contains scaly ceramic, the ratio of scaly ceramic to the total volume of the ceramic is preferably 15% by volume or more.

[0025] The ceramic constituting the ceramic sheet may include particulate ceramic in addition to or instead of the above-mentioned flaky ceramic. The ceramic sheet is made of a sintered body of such ceramic. Therefore, in the ceramic sheet, the flaky or particulate ceramic does not exist independently, but rather forms a dense structure in which multiple pieces are bonded to each other.

[0026] (Method for Manufacturing Ceramic Sheet) The ceramic sheet of the present invention having these characteristics can be efficiently manufactured according to the method for manufacturing a ceramic sheet of the present invention. The method for manufacturing a ceramic sheet of the present invention is characterized by comprising the following steps: a primary sheet forming step in which a composition containing a resin and a ceramic material is pressed into a sheet to obtain a primary sheet; a laminate forming step in which multiple primary sheets are stacked in the thickness direction or folded or rolled up to obtain a laminate; a slicing step in which the laminate is sliced ​​at an angle of 45° or less relative to the stacking direction to obtain a secondary sheet; and a firing step in which the secondary sheet is fired. Furthermore, the manufacturing method of the present invention preferably includes a degreasing step in which the secondary sheet is heated in an atmosphere of 400° C. or higher to degrease it prior to the firing step. Each step is described below.

[0027] <Primary Sheet Forming Step> In the primary sheet forming step, a composition containing a resin and a ceramic material is pressed into a sheet to obtain a primary sheet.

[0028] [Composition] Here, the composition can be prepared by mixing a resin, a ceramic material, and any other components.

[0029] Ceramic Material: The ceramic material may be any of the various ceramics described above that may be included in the ceramic sheet of the present invention. When the ceramic material is particulate, it may be any particulate ceramic material having a volume average particle diameter D50 of 0.4 μm to 10.0 μm, without any particular limitation. When the ceramic material is flaky, it may be any flaky ceramic material having a volume average particle diameter D50 of 2 μm to 10 μm, without any particular limitation. The term "particulate" refers to a ceramic material having an aspect ratio of 5 or less. The aspect ratio can be determined by observing the ceramic material with a scanning electron microscope (SEM), measuring the maximum diameter (major diameter) and the particle diameter (minor diameter) perpendicular to the maximum diameter for 50 randomly selected ceramic particles, and calculating the average ratio of the major diameter to the minor diameter (major diameter / minor diameter). In the above, for example, when observing a scaly ceramic material with an SEM, the "long diameter" refers to the length in the direction of the long axis of the main surface of the scaly ceramic material, and the "short diameter" refers to the length in the direction perpendicular to the long axis of the main surface on the same plane as the main surface.

[0030] Furthermore, in ceramic materials, it is preferable that the c-axes of the crystal grains tend to be oriented in the thickness direction. Here, the "thickness" direction of a particulate ceramic material refers to determining the longest axis when the particulate ceramic material is approximated as a pseudo-ellipsoid, determining two axes perpendicular to this longest axis (which are also perpendicular to each other), and regarding the direction of the shorter of these two axes as the thickness direction. Furthermore, in scaly ceramic materials, the direction perpendicular to the direction of the principal surface is considered to be the thickness direction. Here, in ceramic materials, "the c-axes of the crystal grains tend to be oriented" means that the crystal grains are regularly arranged in the secondary crystals (i.e., the ceramic material). Furthermore, when such ceramic materials are oriented using the manufacturing method of the present invention, the orientation effect is more easily achieved.

[0031] Resin: The resin is not particularly limited, and various resins can be used. Examples of such resins include polyethylene-based crystalline resins such as linear or branched high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polypropylene-based crystalline resins such as linear or branched high-density polypropylene and low-density polypropylene, polyolefin-based crystalline resins represented by the group consisting of polymethylpentene, polybutene, polymethylbutene, polymethylhexene, polyvinylnaphthalene, and polyxylene, polyester-based crystalline resins represented by the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate, and aromatic polyester, polyamide-based crystalline resins represented by the group consisting of nylon-6, nylon-66, nylon-12, and polyamideimide, and polyvinyl fluoride. Examples of suitable crystalline resins include fluorine-based crystalline resins represented by the group consisting of ethylene, polytetrafluoroethylene, etc., and other crystalline resins such as rosin-based resins, polyvinylidene chloride, polyacrylonitrile, syndiotactic polystyrene, polyoxymethylene, polyphenylene sulfide (PPS), polyether ether ketone (PEEK), cellulose, acetal resins, chlorinated polyethers, ethylene-vinyl acetate copolymers, and liquid crystal polymers (aromatic polycyclic condensation polymers); as well as elastomers such as acrylonitrile butadiene rubber, styrene-butadiene-styrene block copolymers, styrene-ethylene-butylene-styrene copolymers, styrene-isoprene-styrene block copolymers, styrene-ethylene-propylene-styrene copolymers, silicone rubber, and fluororubber. Among these, acrylonitrile butadiene rubber is preferred.

[0032] Other Components—Other components that can be optionally blended into the composition include, as necessary, other components that can be used in molding the primary sheet. Examples of other components that can be blended into the composition include, but are not limited to, crosslinking agents, reaction initiators, flame retardants such as red phosphorus-based flame retardants and phosphate ester-based flame retardants, plasticizers such as fatty acid ester-based plasticizers, toughness improvers such as urethane acrylates, moisture absorbents such as calcium oxide and magnesium oxide, adhesion improvers such as silane coupling agents, titanium coupling agents, and acid anhydrides, wettability improvers such as nonionic surfactants and fluorine-based surfactants, and ion trapping agents such as inorganic ion exchangers.

[0033] The mixing of the above-mentioned components can be carried out using known mixing devices such as kneaders, mixers such as Henschel mixers, Hobart mixers, and high-speed mixers, twin-screw kneaders, and roll mixers. The mixing may also be carried out in the presence of a solvent. The resin may be dissolved or dispersed in a solvent in advance to form a resin solution, which is then mixed with the ceramic material and any other components. The mixing time may be, for example, 5 minutes to 60 minutes. The mixing temperature may be, for example, 5°C to 160°C.

[0034] [Molding of the composition] The composition prepared as described above can be optionally degassed and crushed, and then pressed to form into a sheet. The sheet-like product obtained by pressing the composition in this manner can be used as a primary sheet. If a solvent is used during mixing, it is preferable to remove the solvent before forming into a sheet. For example, if degassing is performed using vacuum degassing, the solvent can be removed simultaneously during degassing.

[0035] Here, the composition can be formed into a sheet using any known forming method, such as press forming, rolling forming, or extrusion forming, without any particular limitation, as long as the forming method involves applying pressure.

[0036] [Primary Sheet] In the primary sheet formed by pressing the composition into a sheet, it is presumed that the ceramic material is primarily aligned in the in-plane direction. The "ceramic material" aligned in the in-plane direction at the primary sheet stage is a polycrystalline body, which is an aggregate of multiple crystal grains. In the primary sheet, the polycrystalline body is aligned in the in-plane direction, but it is presumed that the crystal axes of the multiple crystal grains that make up the polycrystalline body are largely unchanged at this stage from the state of the polycrystalline body as raw material. As a result of going through the laminate formation process and further slicing process described below, the degree of a-axis orientation in the obtained ceramic sheet is increased.

[0037] The thickness of the primary sheet is preferably 2.5 mm or less, more preferably 2.0 mm or less, and even more preferably 1.5 mm or less. If the thickness of the primary sheet is equal to or less than the above upper limit, cracks or breakage of the sheet due to shrinkage in the subsequent firing step can be effectively suppressed, making it possible to efficiently form a ceramic sheet. The lower limit of the thickness of the primary sheet is not particularly limited, but can be, for example, 0.1 mm or more.

[0038] The volume fraction of the ceramic material in the primary sheet is preferably 50% by volume or more, more preferably 55% by volume or more, and even more preferably 60% by volume or more, and preferably 75% by volume or less, and more preferably 70% by volume or less, based on the total volume of the resin and ceramic material. If the volume fraction of the ceramic material in the primary sheet is equal to or greater than the above-mentioned lower limit, the occurrence of cracks or breaks in the ceramic sheet during the firing step described below can be effectively suppressed, or firing shrinkage can be reduced, thereby improving the quality of the resulting ceramic sheet. If the volume fraction of the ceramic material in the primary sheet is equal to or less than the above-mentioned upper limit, cracks in the primary sheet itself before firing can be prevented, thereby improving the quality of the resulting ceramic sheet.

[0039] <Laminate Forming Step> In the laminate forming step, a laminate is obtained by stacking multiple primary sheets in the thickness direction, or by folding or winding the primary sheets. Here, the formation of the laminate by folding the primary sheets is not particularly limited and can be performed by folding the primary sheets at a constant width using a folding machine. Furthermore, the formation of the laminate by winding the primary sheets is not particularly limited and can be performed by winding the primary sheets around an axis parallel to the short or long direction of the primary sheets. Furthermore, the formation of the laminate by stacking the primary sheets can be performed using a lamination device without particular limitations. For example, using a sheet lamination device (manufactured by Nikkiso Co., Ltd., product name "Hi-Stacker") can prevent air from entering between the layers, thereby efficiently obtaining a good laminate.

[0040] In the lamination step, the obtained laminate is preferably pressurized in the lamination direction while being heated (secondary pressurization). By performing secondary pressurization in which the laminate is pressurized in the lamination direction while being heated, it is possible to promote fusion bonding between the laminated primary sheets.

[0041] The pressure applied to the laminate in the stacking direction can be 0.05 MPa or more and 0.50 MPa or less. The heating temperature of the laminate is not particularly limited, but is preferably 50° C. or more and 170° C. or less. The heating time of the laminate can be, for example, 10 seconds or more and 30 minutes or less.

[0042] In a laminate obtained by stacking, folding, or rolling the primary sheets, the ceramic material (polycrystalline body) is presumably oriented in a direction substantially perpendicular to the stacking direction. For example, when the ceramic material contains flaky ceramic, the direction of the long axis of the main surface of the flaky ceramic is presumably substantially perpendicular to the stacking direction.

[0043] <(iii) Slicing Step> In the slicing step, the laminate obtained in the above step is sliced ​​at an angle of 45° or less relative to the lamination direction to obtain a secondary sheet. The method for slicing the laminate is not particularly limited, and examples thereof include a multi-blade method, a laser processing method, a water jet method, and a knife processing method. Among these, the knife processing method is preferred because it is easy to make the thickness of the secondary sheet uniform. The cutting tool used to slice the laminate is not particularly limited, and a slicing member having a smooth plate surface with a slit and a blade portion protruding from the slit portion (for example, a plane or slicer with a sharp blade) can be used.

[0044] From the viewpoint of increasing the thermal conductivity in the thickness direction of the resulting ceramic sheet, the angle at which the laminate is sliced ​​is preferably 30° or less relative to the stacking direction, more preferably 15° or less relative to the stacking direction, and preferably approximately 0° relative to the stacking direction (i.e., in the direction along the stacking direction).

[0045] In the secondary sheet obtained in this manner, the ceramic material (polycrystalline body) is well oriented in the thickness direction, and the thermal conductivity in the thickness direction is excellent.

[0046] <Degreasing step> In the degreasing step, which can be optionally performed, the secondary sheet is degreased by heating in an atmosphere of 300°C or higher. The temperature of the atmosphere in the degreasing step is more preferably 350°C or higher, and even more preferably 400°C or higher. The upper limit of the heating temperature in the degreasing step must be lower than the temperature of the atmosphere in the firing step, and can be, for example, 600°C or lower. If the temperature of the atmosphere in the degreasing step is equal to or higher than the above lower limit, the degreasing step can be performed without leaving any resin contained in the primary sheet. Furthermore, if the temperature of the atmosphere in the degreasing step is equal to or lower than the above upper limit, the degreasing step can be performed without carbonizing the resin contained in the primary sheet.

[0047] Here, the degreasing step is preferably carried out under an atmosphere of an inert gas (for example, nitrogen gas or argon gas) at normal pressure (1 atm).

[0048] <Firing Step> In the firing step, the secondary sheet is fired. The atmosphere in the firing step is preferably 1000° C. or higher, more preferably 1500° C. or higher, and preferably 2000° C. or lower. If the temperature of the atmosphere in the firing step is equal to or higher than the lower limit, the ceramic can be sintered more densely.

[0049] Here, the firing step is preferably carried out in an atmosphere of an inert gas (such as nitrogen gas or argon gas) at normal pressure (1 atm), similarly to the degreasing step.

[0050] According to the manufacturing method of the present invention including the steps described above, it is possible to efficiently manufacture the ceramic sheet of the present invention, i.e., a ceramic sheet made of a sintered ceramic body, in which the a-axis of the crystal axes of the ceramic constituting the ceramic sheet is oriented in the thickness direction of the ceramic sheet.

[0051] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified.

[0052] In each of the examples and comparative examples, various attributes and evaluations were measured or evaluated according to the following methods.

[0053] <Thermal Conductivity> The thermal diffusivity α (m ２ / s), specific heat at constant pressure Cp (J / g K) and specific gravity ρ (g / m ３ ) was measured by the following method. ２ / s)] Thermal diffusivity in the X, Y, and Z directions was measured using a thermal property measuring device (manufactured by Bethel Corporation, product name "Thermowave Analyzer TA35"). [Constant pressure specific heat Cp (J / g K)] Specific heat was measured under a temperature rise condition of 10°C / min using a differential scanning calorimeter (manufactured by Rigaku, product name "DSC8230"). [Specific gravity ρ (g / m ３ ) )] The specific gravity (density) (g / m ３The obtained measured values ​​were then substituted into the following formula (I): λ=α×Cp×ρ (I) to determine the thermal conductivity λ (W / m·K) of the ceramic sheet in the X, Y, and Z directions.

[0054] <Anisotropy of thermal conductivity> The anisotropy of thermal conductivity was calculated by using the thermal conductivities λ in the X, Y, and Z directions of the ceramic sheet obtained above and dividing the thermal conductivity in the Z direction by the larger value of the thermal conductivity in the X direction or the thermal conductivity in the Y direction.

[0055] <XRD Profile Measurement> For the ceramic sheets obtained in the Examples and Comparative Examples (excluding Comparative Example 2) and the ceramic particles as non-oriented samples, XRD profiles were measured in the range of 2θ = 20 to 90° when irradiated with X-rays using an XRD device (manufactured by Rigaku, product name "RINT2200"). The ceramic particles as non-oriented samples were prepared by grinding the ceramic sheets obtained in each Example and Comparative Example into powder in a mortar. Specifically, measurements were performed using CuKα radiation at a voltage of 40 kV and a current of 400 mA. For the ceramic sheets, the XRD profile was measured on the sheet surface. <<Lotgering Analysis>> Then, the a-axis orientation degree and c-axis orientation degree were calculated from the obtained XRD profile according to the Lotgering method. Specifically, the Lotgering factor f related to the orientation degree of each axis was calculated according to the following procedure. The Lotgering factor f was calculated using the peak intensity of X-rays diffracted from the target crystal plane according to the following equation (1). f = (ρ - ρ ０ ) / (1-ρ ０ ) (1) where ρ ０ is the X-ray diffraction intensity of the non-oriented sample (I ０ ) and in the case of c-axis orientation, the sum of all diffraction intensities (ΣI ０ The ratio of the total diffraction intensity of all planes perpendicular to the c-axis (planes perpendicular to the c-axis) to the total diffraction intensity of all planes perpendicular to the c-axis (planes perpendicular to the c-axis) was calculated using the following formula (2): ρ0 = ΣI ０ (C-axis vertical plane) / ΣI ０(hkl) (2) ρ was calculated using the X-ray diffraction intensity (I) of the oriented sample. In the case of c-axis orientation, ρ was calculated as the ratio of the sum of the diffraction intensities in the plane perpendicular to the C-axis to the sum of all diffraction intensities (ΣI(hkl)), using the following formula (3) in the same manner as the above formula (2). ρ = ΣI(plane perpendicular to the C-axis) / ΣI(hkl) (3) In the case of a-axis orientation, the Lotgering factor f was calculated in the same manner as above. <<Calculation of Scattering Intensity Ratio>> For Examples 1 to 7 and Comparative Examples 1 and 2, which used alumina as the ceramic material, the scattering intensity in the (300) plane in the XRD profile (2θ = 68°; scattering intensity in the plane corresponding to the a-axis direction) was divided by the scattering intensity in the (006) plane (2θ = 37°; scattering intensity in the plane corresponding to the c-axis direction) to evaluate the degree of orientation in the a-axis direction (a / c). For Example 8 and Comparative Example 3, which used barium titanate as the ceramic material, the degree of orientation in the a-axis direction (a / c) was evaluated by dividing the scattering intensity in the (200) plane (2θ = 44.8°; scattering intensity in the plane corresponding to the a-axis direction) in the XRD profile by the scattering intensity in the (002) plane (2θ = 45.4°; scattering intensity in the plane corresponding to the c-axis direction).

[0056] <Vertical Orientation Parameter> For Examples 1 to 7 in which alumina was used as the ceramic material, the values ​​of a / c calculated in these examples were used as "the value of a / c in a state in which the a-axis direction is oriented in the thickness direction of the ceramic sheet," and the value of a / c in Comparative Example 1 obtained above was used as "the value of a / c in a state in which the a-axis direction is not oriented in the thickness direction of the ceramic sheet," and the former was divided by the latter to calculate the vertical orientation parameter of the ceramic. For Example 8 in which barium titanate was used as the ceramic material, the value of a / c calculated in Example 8 was divided by the value of a / c calculated in Comparative Example 3 to calculate the vertical orientation parameter of the ceramic.

[0057] <Quality of ceramic sheet> The quality of the obtained ceramic sheet was evaluated visually. It was confirmed that when the secondary sheet had a large shrinkage during firing, the strips would separate from each other during the firing process. A: The strips were not peeled off and the sheet was able to be fired as a single sheet. B: Strips peeled off in 1 to 4 places, and the sheet separated into 2 to 5 pieces (parts) after firing. C: Strips peeled off in 5 or more places within a single sheet, and the sheet separated into 6 or more pieces after firing.

[0058] Example 1 Primary Sheet Molding Step Preparation of Composition As a resin, 62 parts of nitrile rubber (NBR) that is liquid at room temperature and normal pressure (manufactured by Nippon Zeon Co., Ltd., trade name "Nipol 1312", decomposition onset temperature: 336°C) and 62 parts of nitrile rubber (NBR) that is solid at room temperature and normal pressure (manufactured by Nippon Zeon Co., Ltd., trade name "Nipol 3350", decomposition onset temperature: 375°C) were mixed with 700 parts of a particulate alumina material (manufactured by Nippon Light Metal Co., Ltd., trade name "LS-711C", volume average particle diameter: 0.5 μm, aspect ratio: 1.2) as a ceramic material, using a pressure kneader (manufactured by Nippon Spindle Co., Ltd.) under stirring at a temperature of 150°C for 20 minutes. <<Molding of Primary Sheet>> Next, 50 g of the obtained composition was sandwiched between sandblasted PET films (protective films) having a thickness of 50 μm, and roll-molded (primary pressing) under conditions of a roll gap of 1000 μm, a roll temperature of 50° C., a roll linear pressure of 50 kg / cm, and a roll speed of 1 m / min, to obtain a primary sheet having a thickness of 1.0 mm.

[0059] <Laminate Forming Step> Subsequently, the primary sheet obtained above was cut into a size of 150 mm length × 150 mm width × 0.8 mm thickness, and 188 sheets were laminated in the thickness direction of the primary sheet. Further, the laminate was pressed (secondary pressurization) in the lamination direction at a temperature of 120°C and a pressure of 0.1 MPa for 3 minutes, thereby obtaining a laminate having a height of approximately 150 mm.

[0060] <Slicing step> Then, while pressing the laminated side surface of the secondarily pressed laminate with a pressure of 0.3 MPa, a woodworking slicer (manufactured by Marunaka Iron Works, product name "Super Finishing Planer Super Mecha S") was used to slice at an angle of 0 degrees to the lamination direction (in other words, in the normal direction to the main surface of the laminated primary sheet), thereby obtaining a secondary sheet having a length of 150 mm, a width of 150 mm, and a thickness of 0.30 mm.

[0061] <Degreasing process to firing process> The obtained secondary sheet was then heated at 400°C for 3 days in a nitrogen atmosphere at normal pressure to perform a degreasing process and burn off the resin components (degreasing process), and then the temperature was raised to 1600°C at a rate of 10°C / min in the same atmosphere and fired for 1 day (firing process). Various measurements and evaluations were performed using the obtained ceramic sheet. The results are shown in Table 1.

[0062] Example 2 A ceramic sheet was obtained in the same manner as in Example 1, except that when preparing the composition in the primary sheet molding step, the particulate alumina material used as the ceramic material was changed to a particulate alumina material with a larger diameter (manufactured by Nippon Light Metal Co., Ltd., product name "LS-130F", volume average particle diameter: 3 μm, aspect ratio: 1.2), and various measurements and evaluations were carried out. The results are shown in Table 1.

[0063] Example 3 When preparing the composition in the primary sheet molding step, the blending amounts of various resins and particulate alumina material were changed as shown in Table 1, and 158 parts of flaky alumina material (manufactured by Kinseimatic Co., Ltd., trade name "Seraph", volume average particle diameter: 10 μm, aspect ratio: 1.8) was added as the ceramic material. Except for this, a ceramic sheet was obtained in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0064] (Examples 4 and 5) Ceramic sheets were obtained in the same manner as in Example 3, except that when preparing the composition in the primary sheet molding step, the blending amounts of various resins and various ceramic materials were changed as shown in Table 1, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0065] (Example 6) When preparing the composition in the primary sheet molding step, the blending amounts of various resins and the blending amounts of ceramic materials were changed as shown in Table 1, and ceramic sheets were obtained in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0066] Example 7 A ceramic sheet was obtained in the same manner as in Example 1, except that the thickness of the primary sheet was changed to 2.0 mm in the primary sheet molding step, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0067] (Example 8) When preparing the composition in the primary sheet molding step, the blending amounts of various resins were changed as shown in Table 1, and 900 parts of barium titanate (manufactured by Nippon Chemical Industry Co., Ltd., trade name "Paraceram", volume average particle size: 10 μm, aspect ratio: 1.1, specific gravity: 6.02) was added as the ceramic material. Except for this, a ceramic sheet was obtained in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0068] (Comparative Example 1) The primary sheet obtained in the primary sheet forming step was cut into a size of 50 mm x 50 mm (thickness: 1.0 mm), and was directly subjected to the degreasing step and firing step without being subjected to the slicing step, to obtain a ceramic sheet in the same manner as in Example 1. The obtained ceramic sheet was subjected to various measurements and evaluations in the same manner as in Example 1. The results are shown in Table 1.

[0069] Comparative Example 2: A secondary sheet that had undergone the same primary sheet forming process, laminate forming process, and slicing process as in Example 1 was not subjected to the degreasing process to the firing process. The thermal conductivity of the obtained sheet was measured in the same manner as in Example 1, and the anisotropic parameter of thermal conductivity was calculated.

[0070] (Comparative Example 3) The primary sheet obtained in the primary sheet forming step was cut into a size of 50 mm x 50 mm (thickness: 1.0 mm), and was directly subjected to the degreasing step and firing step without being subjected to the slicing step, to obtain a ceramic sheet in the same manner as in Example 8. The obtained ceramic sheet was subjected to various measurements and evaluations in the same manner as in Example 8. The results are shown in Table 1.

[0071]

[0072] From Table 1, it can be seen that the ceramic sheets made of the sintered ceramic bodies obtained in Examples 1 to 8 have a novel orientation structure in which the a-axis value is positive when analyzed by Lotgering analysis, and the a-axis orientation direction of the ceramic material in the ceramic sheet is vertical (thickness direction of the ceramic sheet).

[0073] According to the present invention, it is possible to provide a ceramic sheet having a novel oriented structure.

Claims

1. a primary sheet forming step of pressing a composition containing a resin and a ceramic material into a sheet shape to obtain a primary sheet; a laminate forming step of laminating a plurality of the primary sheets in a thickness direction or folding or rolling the primary sheet to obtain a laminate; a slicing step of slicing the laminate at an angle of 45° or less with respect to the lamination direction to obtain a secondary sheet; and a firing step of firing the secondary sheet.

2. Prior to the firing step, a degreasing step is carried out in which the secondary sheet is heated in an atmosphere of 300° C. or higher to degrease the secondary sheet; The method according to claim 1 , wherein the firing step is carried out in an atmosphere of 1000° C. or higher.

3. The method according to claim 1 , wherein the primary sheet has a thickness of 2.5 mm or less.

4. The manufacturing method according to any one of claims 1 to 3, wherein a volume fraction of the ceramic material in the primary sheet is 50 volume% or more and 75 volume% or less based on a total volume of the resin and the ceramic material.

5. A ceramic sheet made of a sintered ceramic body, The ceramic sheet has a positive a-axis value when subjected to Lotgering analysis.

6. The ceramic sheet according to claim 5 , wherein the ceramic sheet has a negative c-axis value when subjected to Lotgering analysis.

7. The ceramic sheet of claim 5 , wherein the ceramic comprises alumina.

8. The ceramic sheet according to any one of claims 5 to 7, wherein the ceramic comprises a flaky ceramic.

9. 9. The ceramic sheet according to claim 8, wherein the ratio of the scaly ceramic to the ceramic is 65 volume % or less.