Method for producing ceramic sintered body

Abstract

To provide a method for producing a ceramic sintered compact by which the surface waviness of the ceramic sintered compact can highly be prevented.SOLUTION: A method for producing a ceramic sintered body, comprising: a coating step of dry-coating at least one surface of a green body containing a ceramic powder with a boron nitride powder to obtain a green body having a boron nitride layer; a laminating step of laminating a plurality of the green bodies having a boron nitride layer; and a firing step of firing the laminate to produce a laminate of a ceramic sintered body, wherein the boron nitride powder is coated while applying a voltage between a boron nitride powder supply unit and the green body.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a ceramic sintered body. [Background technology]

[0002] In recent years, ceramic sintered bodies have been widely used as substrates for semiconductor modules and structural components. For example, substrates for power element modules that mount high-power, high-heat-generating semiconductor elements are required to have high mechanical strength, high thermal conductivity, and high electrical insulation. Ceramic sintered bodies excel in these properties, and in recent years, ceramic sintered bodies have come to be widely used as substrates for power element modules.

[0003] Ceramic sintered bodies are produced by firing green bodies whose main component is ceramic powder. The green bodies are fired using an electric furnace or the like, but to reduce production costs, multiple green bodies are stacked and fired simultaneously. When firing multiple stacked green bodies, it is common to coat the surfaces of the green bodies with a separating material to facilitate separation of the sintered ceramic bodies after firing.

[0004] For example, Patent Document 1 describes a method for producing a ceramic sintered body in which ceramic powder is molded to produce green bodies, a slurry containing a separating material made of boron nitride (BN) is applied to the green bodies, the green bodies coated with the slurry are stacked, and the stacked green bodies are fired, thereby simultaneously firing a plurality of green bodies. Patent Document 2 also describes a method in which a slurry containing boron nitride powder, a dispersion medium, and a dispersant is applied to one side of a green body to form a separating material layer, and then the green bodies are stacked and fired, thereby simultaneously firing a plurality of green bodies. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-216577 [Patent Document 2] Japanese Patent Application Publication No. 2023-173138 Summary of the Invention [Problem to be solved by the invention]

[0006] When applying a separation material to a green body, wet application is generally used, in which a slurry of the separation material is applied to the green body, as described in Patent Document 1 and Patent Document 2. However, according to the investigations conducted by the present inventors, it was thought that wet application was the cause of the surface waviness of the green body.

[0007] When wet coating is performed, the green body absorbs the solvent and swells. When the solvent is then removed by drying, localized differences in drying speed are unavoidable, and it is thought that the difference in drying shrinkage causes surface waviness.

[0008] If the green body has surface waviness, the surface waviness of the resulting ceramic sintered body will increase, causing a decrease in adhesion when a metal layer is formed on the ceramic sintered body by various metallization methods, etc. Therefore, an object of the present invention is to provide a manufacturing method that can highly prevent surface waviness of ceramic sintered bodies. [Means for solving the problem]

[0009] In order to solve the above problems, the inventors conducted extensive research. Specifically, they investigated the use of dry coating without using a solvent in order to prevent surface waviness caused by drying shrinkage. However, it was difficult to apply boron nitride uniformly to the surface of the green body by simply performing dry coating, and surface waviness could not be sufficiently prevented. After further investigation into this point, they found that surface waviness could be suppressed by applying a voltage between the boron nitride powder supply unit and the green body when dry coating boron nitride onto the green body, which led to the completion of the present invention.

[0010] That is, the present invention is a method for producing a ceramic sintered body, comprising the steps of: a coating step of dry-coating boron nitride powder onto at least one surface of a green body containing ceramic powder to obtain a green body having a boron nitride layer; a stacking step of stacking a plurality of green bodies having the boron nitride layer; and a firing step of firing the stack to produce a stack of ceramic sintered bodies, wherein the coating of the boron nitride powder is carried out while applying a voltage between a boron nitride powder supply unit and the green body. 2 ~0.60mg / cm 2 Preferably, the boron nitride powder has an average particle size D50 of 5 to 20 μm. Preferably, the ceramic is silicon nitride. [Effects of the Invention]

[0011] According to the present invention, a ceramic sintered body having highly suppressed surface waviness can be easily obtained. DETAILED DESCRIPTION OF THE INVENTION

[0012] The method for producing a ceramic sintered body of the present invention includes a coating step of dry-coating boron nitride powder onto at least one surface of a green body containing ceramic powder to obtain a green body having a boron nitride layer, and is characterized in that the boron nitride powder is coated while a voltage is applied between a boron nitride powder supply unit and the green body. It is presumed that coating while applying a voltage between the boron nitride powder supply unit and the green body allows the boron nitride primary particles to reach the green body from the supply unit along the electric field, making it easier to coat the green body uniformly.

[0013] The distance between the supply unit and the green body is not particularly limited, but is preferably 1 mm or more and 500 mm or less, and more preferably 10 mm or more and 300 mm or less, in order to make it easier to apply boron nitride uniformly and efficiently.

[0014] The direction of the voltage between the supply unit and the green body is not particularly limited, and the green body side may be positive or negative. The voltage between the supply unit and the green body is not particularly limited, and can be, for example, 0.1 kV to 40 kV. The attractive force (Coulomb force) acting on the primary particles of boron nitride is proportional to the voltage between the supply unit and the green body and inversely proportional to the square of the distance between the supply unit and the green body. Therefore, the voltage may be adjusted depending on the distance between the supply unit and the green body. Specifically, when the distance between the supply unit and the green body is short, it is preferable to lower the voltage. For example, when the distance is less than 25 mm, the voltage is preferably 0.1 kV to 20 kV, and more preferably 0.4 kV to 10 kV. When the distance between the supply unit and the green body is long, it is preferable to increase the voltage. For example, when the distance is 25 mm or more, the voltage is preferably 2.0 kV to 40 kV, and more preferably 5.0 kV to 30 kV.

[0015] The method for applying the boron nitride powder is not particularly limited, and examples thereof include a method in which the supply unit is used as a sieve to apply the boron nitride powder, and a method in which the powder is adhered to the surface of a rotating roller and then peeled off from the roller and scattered.

[0016] The method of applying the boron nitride powder using a sieve can be carried out, for example, by electrostatic screen printing. In electrostatic screen printing, a voltage is applied between an electrostatic screen plate (sieve) and the green body to generate an electrostatic field, and then the boron nitride powder is released into the electrostatic field through holes in the electrostatic screen plate, thereby applying the boron nitride powder to the green body. Application by such electrostatic screen printing can be carried out using commercially available equipment such as an electrostatic screen printer. An example of such equipment is an electrostatic screen printing device (Berg Industrial Co., Ltd.).

[0017] In the sieve coating method, it is preferable to supply electrically charged boron nitride powder. By charging the boron nitride powder, the agglomeration of boron nitride particles is suppressed due to electrical repulsion, and the powder can be applied to the green body as single particles. Applying the powder as single particles makes it easier to control the size of the boron nitride particles on the green body, making it easier to control surface waviness.

[0018] The method for charging the boron nitride powder is not particularly limited, and can be carried out by a known method. A simple method includes, for example, charging by friction between powders or between a powder and a device. The boron nitride powder can be charged by placing it on a sieve and rubbing it with another object, or by rubbing the boron nitride powder against a stainless steel plate, aluminum plate, or the like after incorporating it into something that can hold the powder, such as a sponge. The powder may also be rubbed against the mesh part of a sieve or the side of the container over the sieve. The rubbing time is not particularly limited, and may be, for example, from 3 to 100 seconds.

[0019] The boron nitride powder may be positively or negatively charged. The absolute value of the charged potential of the boron nitride immediately before application is 0.30 kV or more, preferably 0.50 kV or more. There is no particular upper limit to the absolute value of the charged potential, but if it is too high, handling becomes difficult, so it is preferable to set it to 5.0 kV or less, particularly 3.0 kV or less.

[0020] The amount of charged potential can be measured using a surface electrometer. In the measurement, the charged hexagonal boron nitride powder on the sieve may be measured directly, or if the hexagonal boron nitride powder is charged by rubbing it with a sponge or the like, the hexagonal boron nitride powder adhering to the sponge or the like may be measured.

[0021] When the charged boron nitride powder is positively charged, the direction of the voltage between the supply unit and the green body is preferably negative on the green body side and positive on the supply unit side.When the charged boron nitride powder is negatively charged, the direction of the voltage between the supply unit and the green body is preferably positive on the green body side and negative on the supply unit side.

[0022] A method for depositing powder on the surface of a rotating roller and then peeling the powder off the roller and scattering it can be achieved, for example, by using an apparatus equipped with a roller at the bottom opening of a powder box containing the powder. In this apparatus, boron nitride powder is loaded into the powder box, and the roller is rotated to deposit the boron nitride powder on the roller surface. The boron nitride powder is then peeled off from the roller surface facing the green body placed below the roller, thereby applying the boron nitride powder to the green body. Since boron nitride powder is constantly being applied from the roller, this method allows for continuous application of boron nitride powder while the green body is continuously transported by a Belcoton Bear. This method is preferred in terms of facilitating efficient production through automation. The method for peeling the boron nitride powder from the roller surface is not particularly limited, and known methods can be used, such as physical action or corona discharge. With this method, boron nitride powder is applied by peeling it off from the roller surface, which makes it less likely to form agglomerates during application and allows it to be applied in a state close to single particles. This makes it easier to control the size of the boron nitride particles on the green body and therefore the surface roughness. Examples of devices for applying boron nitride powder in this way include the Nikka K-VII Spray (Nikka Co., Ltd.), which uses a brush roller to physically peel the powder, and the Nikka K-III Spray (Nikka Co., Ltd.), which peels the powder using corona discharge. Of these, the method of peeling the powder using corona discharge (corona spraying method) is particularly preferred. In a method in which powder is adhered to the surface of a rotating roller and then peeled off from the roller and scattered, an electric field can be formed between the boron nitride powder supply unit (roller) and the green body by, for example, providing a charging device below the green body.

[0023] In the manufacturing method of the present invention, the application of boron nitride powder is carried out by dry application. The application of a separating material (boron nitride powder) to a green body is generally carried out by wet application using a slurry in which boron nitride powder is dispersed in a solvent, but in dry application, the boron nitride powder is used without being dispersed in a solvent. Because dry application does not require a large amount of solvent, it is advantageous in terms of environmental impact and working environment.

[0024] Although cubic boron nitride powder is also available as boron nitride powder, it is preferable to use hexagonal boron nitride powder in the present invention.

[0025] The physical properties of the boron nitride powder used are not particularly limited, and known boron nitride powders can be used. The average particle size D50 of the boron nitride powder is preferably 0.5 to 50 μm, more preferably 3 to 25 μm, and particularly preferably 4 to 20 μm. Setting the particle size within the above range improves handleability and helps prevent surface waviness. The average particle size D50 of the boron nitride powder can be measured by a wet laser diffraction / scattering method. It is preferable to use a suspension in which boron nitride powder is added to water and thoroughly dispersed using a homogenizer as a pretreatment. The average aspect ratio of the boron nitride powder is preferably 5 or more, more preferably 7 or more. The upper limit of the average aspect ratio of the boron nitride powder is not particularly limited, but it can be, for example, 30 or less, particularly 20 or less. The average aspect ratio of boron nitride powder can be determined by randomly selecting 100 different primary particles of boron nitride from a scanning electron microscope image observed at 1000x magnification, measuring the length and thickness of the major axis of the primary particles of boron nitride, calculating the aspect ratio of each (major axis length / thickness length), and taking the average value.

[0026] In the manufacturing method of the present invention, the amount of boron nitride powder to be applied to the green body is not particularly limited, but the amount of boron nitride in the boron nitride layer is preferably 0.01 mg / cm. 2 ~1.0mg / cm 2 It is preferable to set the density to 0.05 mg / cm 2 ~0.7mg / cm 2It is preferable to set the concentration to 0.1 mg / cm 2 ~0.6mg / cm 2 It is more preferable that the boron nitride layer has a too small amount of boron nitride, which limits its effectiveness as a separator. If the boron nitride layer has a too large amount of boron nitride, a large amount of boron nitride powder will remain on the sintered body obtained by firing the green body. If a large amount of boron nitride powder remains, it may adversely affect the bondability with copper and the heat cycle characteristics when the sintered body is used as a heat dissipation substrate or the like.

[0027] In the manufacturing method of the present invention, the boron nitride powder may be applied to only one side of the green body or to both sides of the green body. When the boron nitride powder is applied to both sides of the green body, only one side may satisfy the above-mentioned parameters and application method, but it is preferable that both sides satisfy the above-mentioned parameters and application method.

[0028] The ceramic powder used in the green body of the present invention is not particularly limited as long as it is a ceramic powder used as a raw material for a ceramic sintered body, and examples thereof include silicon nitride, aluminum nitride, titanium nitride, aluminum oxide, titanium oxide, and zirconium oxide. These ceramic powders can be used alone or in combination of two or more. From the viewpoint of obtaining a ceramic sintered body having excellent insulating properties and high thermal conductivity and being used in applications where it is particularly important to suppress surface waviness, the ceramic powder is preferably silicon nitride powder, aluminum nitride powder, aluminum oxide powder, or a mixed powder of aluminum oxide and zirconium oxide, and more preferably silicon nitride powder.

[0029] From the viewpoint of sinterability, the specific surface area of ​​the ceramic powder is preferably 1 m 2 / g or more, especially 2m 2 / g or more, especially 5m 2 / g or more, especially 7m 2 / g or more, and the upper limit is preferably 20m 2 / g or less, especially 15m 2 The specific surface area of ​​the ceramic powder is the BET specific surface area measured by the BET single-point method using nitrogen gas adsorption.

[0030] The green body may contain, in addition to the ceramic powder, a sintering aid, a binder resin, and the like.

[0031] The sintering aid can be any sintering aid commonly used for sintering ceramic powders, and examples include yttria, magnesia, ceria, silica, and calcia. In particular, when the ceramic powder contains silicon nitride powder, carbonitride compounds such as Y2Si4N6C, Yb2Si4N6C, Ce2Si4N6C, and MgSi4N6C, and nitride compounds such as MgSiN2 may be used as sintering aids. The amount of sintering aid in the green body is preferably 1 to 20 parts by mass, and more preferably 3 to 10 parts by mass, per 100 parts by mass of the ceramic powder.

[0032] The binder resin is not particularly limited, but examples thereof include polyvinyl alcohol, polyvinyl butyral, methyl cellulose, alginic acid, polyethylene glycol, carboxymethyl cellulose, ethyl cellulose, acrylic resin, etc. The content of the binder resin in the green body is preferably 1 to 40 parts by mass, more preferably 5 to 30 parts by mass, per 100 parts by mass of the ceramic powder.

[0033] The method for producing the green body is not particularly limited, and the green body may be produced by press molding using a powder obtained by dry mixing the constituent components of the green body, or by wet mixing the constituent components of the green body to produce a slurry for granule production, which is then dried using a spray dryer or the like to produce granules.

[0034] Alternatively, the green body may be produced by wet-mixing the constituent components to prepare a green body molding slurry, and then molding the green body molding slurry into a sheet. The green body molding slurry may be prepared, for example, by weighing out the components in predetermined amounts and stirring and mixing them so that the ceramic powder is dispersed in the dispersion medium. Examples of dispersion devices used for stirring and mixing include ultrasonic dispersion devices, bead mills, ball mills, roll mills, homomixers, ultramixers, disperser mixers, homomixers, through-type high-pressure dispersion devices, collision-type high-pressure dispersion devices, porous high-pressure dispersion devices, clump-removal type high-pressure dispersion devices, (collision + through-type) high-pressure dispersion devices, and ultra-high-pressure homogenizers. After stirring and mixing, the green body slurry may be filtered, if necessary, to remove clumps.

[0035] The method for producing a green body from the green body molding slurry is not particularly limited, and known molding methods can be used, but molding by a doctor blade method is preferred from the viewpoint of good sheet thickness uniformity, etc. The obtained green body can be processed into an appropriate size and any shape. For example, it is generally processed into a roughly rectangular parallelepiped shape with a side length of 100 mm to 2000 mm and a thickness of 0.3 mm to 1.2 mm. Note that after molding into a size larger than that used for firing, cutting can be performed to obtain the desired shape. Cutting can be performed before or after drying, which will be described later.

[0036] When obtaining a green body from the green body molding slurry, it is preferable to carry out a drying step as necessary. The drying step is a step of further removing the dispersion medium from the green body, which makes it easier to subsequently sinter the green body. For example, when the dispersion medium is water, the drying step can be carried out by leaving the green body at a temperature of about 30°C to 150°C, and it is preferable to dry the green body so that the water content is 10% or less.

[0037] When preparing the green body molding slurry, it is preferable to use water as a dispersion medium. Organic solvents are often used as solvents when wet-mixing ceramics (particularly silicon nitride). However, in recent years, there has been a demand for reducing environmental impact, and the use of water, which has a lower environmental impact, is becoming more common. However, according to the inventors' investigations, using water as a dispersion medium during wet mixing has a greater adverse effect on waviness during wet application than using an organic solvent. Therefore, in the present invention, the use of a green body obtained by sheet-molding using a green body molding slurry containing water as a solvent is particularly effective and is a preferred embodiment.

[0038] In the lamination process, multiple green bodies are stacked to form a laminate with a boron nitride layer between adjacent green bodies. The number of stacked green bodies can be any number, ranging from several to several tens of green bodies.

[0039] When the green bodies contain organic components such as binders, it is preferable to degrease the green body laminate prior to firing. The degreasing temperature for degreasing the green body laminate is preferably 300°C to 1200°C, more preferably 400°C to 1000°C. The degreasing of the green body laminate is typically carried out in an atmosphere of an oxidizing gas such as oxygen or air, a reducing gas such as hydrogen, an inert gas such as argon or nitrogen, carbon dioxide, or a mixture of these, or in a humidified gas atmosphere containing a mixture of these gases and water vapor. The degreasing time at the above degreasing temperature can be appropriately selected depending on the type and amount of organic components such as binders used in the green bodies, and the degreasing atmosphere, but is typically 30 minutes to 12 hours, preferably 2 hours to 10 hours.

[0040] In the firing step, the laminate is fired to produce a laminate of sintered ceramic bodies. The firing conditions are not particularly limited, and the firing may be carried out under known firing conditions for obtaining sintered ceramic bodies.

[0041] For example, when the ceramic of the ceramic powder is silicon nitride or aluminum nitride, firing is preferably carried out in an inert gas atmosphere. An inert gas atmosphere refers to, for example, a nitrogen atmosphere or an argon atmosphere. The firing pressure is not particularly limited, but because high pressures increase the cost of equipment, for example, firing is carried out at a pressure of 10 MPa·G or less, more preferably 3 MPa·G or less, and even more preferably 1 MPa·G or less. Furthermore, when the ceramic of the ceramic powder is silicon nitride, low pressures may cause silicon nitride to decompose during firing, so a firing pressure of 0 MPa·G or more is preferred. The firing temperature is not particularly limited as long as the desired sintering reaction proceeds. For example, when the ceramic of the ceramic powder is silicon nitride, it can be, for example, 1200°C to 2000°C, more preferably 1500°C to 1900°C. The firing time is not particularly limited as long as the desired sintering reaction proceeds, but for example, when the ceramic of the ceramic powder is silicon nitride, it is generally about 3 to 20 hours.

[0042] After the firing step, the ceramic sintered body is separated from the stack of ceramic sintered bodies to obtain a ceramic sintered body. In the stack of ceramic sintered bodies, a boron nitride layer is provided between adjacent ceramic sintered bodies, so that the ceramic sintered body can be easily separated from the stack of ceramic sintered bodies.

[0043] Boron nitride powder may remain on the surface of the ceramic sintered body separated from the laminate. Therefore, it is preferable to remove the boron nitride powder remaining on the surface of the ceramic sintered body after separating the ceramic sintered body from the laminate. For example, it is preferable to subject the ceramic sintered body separated from the laminate to honing using free abrasive grains. In this case, it is preferable to use alumina abrasive grains with an average particle size of 10 to 100 μm as the free abrasive grains. Furthermore, after honing, the ceramic sintered body may be ultrasonically cleaned or washed with a spray of water to remove the alumina abrasive grains and boron nitride powder. It is preferable that the alumina abrasive grains and boron nitride powder are not detected when observing the surface at 1000x magnification using a scanning electron microscope. Polishing may or may not be performed after honing.

[0044] The ceramic sintered body separated from the laminate is cut mechanically or by laser, as required, to obtain a ceramic sintered body of a desired size and shape.

[0045] The manufacturing method of the present invention makes it possible to obtain a ceramic sintered body with highly suppressed surface waviness. Specifically, it is possible to obtain a silicon nitride sintered body with an arithmetic mean waviness Wa of 0.20 μm or less.

[0046] The ceramic sintered body obtained by the manufacturing method of the present invention can be used for any purpose, including, but not limited to, substrates that require a high degree of suppression of surface waviness. Specific examples include various heat dissipation substrates, power module substrates (for automobiles, electric railways, and high-power semiconductors), high-frequency circuit boards, LED packages, and optical pickup submounts (for DVDs and CDs). [Example]

[0047] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to the following examples. The measurements of the various items in the examples and comparative examples were performed by the following methods.

[0048] (1) Evaluation of waviness of silicon nitride substrate The surface waviness of the ceramic sintered body was measured using a surface roughness meter to measure the filtered centerline waviness, and the arithmetic mean waviness Wa, i.e., the arithmetic mean of the absolute values ​​of deviations from the average surface height, was calculated. The measurement conditions were an evaluation length of 4 mm, a measurement speed of 0.3 mm / s, and a cutoff value of 0.8 mm.

[0049] (2) Average particle size of boron nitride powder Boron nitride powder was dispersed in pure water and dispersed for 30 seconds using an ultrasonic homogenizer (Nippon Seiki Seisakusho: US-600T) at 300 W. The suspension was then subjected to wet measurement using a particle size distribution analyzer (Microtrac: MT3300EXII) equipped with a standard sample circulator (Microtrac: SDC).

[0050] The silicon nitride substrate was manufactured using the following raw materials containing silicon nitride powder and a sintering aid. <Silicon nitride powder> ·Betaization rate: 99% ·Average particle size D50: 0.9μm <Sintering aid> Yttria (manufactured by Shin-Etsu Chemical Co., Ltd.) Magnesia (manufactured by Ube Materials Co., Ltd.) <Binders and dispersants> Binder resin: Acrylic resin (manufactured by Fujikura Kasei Co., Ltd.) Dispersant: Cerna D735 (manufactured by Chukyo Yushi Co., Ltd.)

[0051] Example 1 (Preparation of green bodies) 100 parts by weight of silicon nitride powder, 5 parts by weight of yttria, 3 parts by weight of magnesia, 0.5 parts by weight of dispersant, and 22 parts by weight of binder were weighed and mixed in a ball mill using water as a solvent and a resin pot and silicon nitride balls for 48 hours. Next, a vacuum defoamer (manufactured by Sayama Riken Co., Ltd.) was used to defoam and adjust the viscosity to produce a raw material slurry. The raw material slurry was then molded into a sheet with a width of 750 mm and a thickness of 420 μm using a doctor blade method. The resulting molded body was dried in air at 40°C to evaporate the solvent, and then cut to a size of 200 mm x 268 mm on the main surface to obtain a green body (green sheet). (Coating process) Boron nitride powder was applied using a Nikka K-VII sprayer (manufactured by Nikka Co., Ltd.) by corona spraying. Specifically, a charging device was installed under the belt conveyor attached to the device, and the device was operated at a voltage of 25 kV and a distance of 50 mm between the powder supply section and the belt conveyor. Hexagonal boron nitride powder (average particle size 1 μm: manufactured by Sanwa Materials) was added to the powder filling section of the device, with voltage applied between the roller and the belt conveyor section, and the test run was continued until the powder application stabilized. The green body was then conveyed by the belt conveyor and passed through the spray section, where boron nitride powder was applied to the green body while voltage was applied between the boron nitride powder supply section and the green body, resulting in a green body with a boron nitride layer. The boron nitride powder application rate was 0.2 mg / cm. 2 The boron nitride discharge speed and the belt conveyor speed were adjusted so that the boron nitride powder was applied to one side of a total of 10 green bodies in the same manner. (Lamination process) Ten green bodies having the boron nitride layer were stacked together so that the surface of one green body having the boron nitride layer was in contact with the surface of another green body not having the boron nitride layer, to produce a stack with a separator layer provided between adjacent green bodies. (Firing process) The laminate was degreased by holding it in an air atmosphere at 400°C for 5 hours. It was then fired in a nitrogen atmosphere at 1830°C for 9 hours under a pressure of 0.8 MPa·G. After firing, the laminate was removed and 10 silicon nitride sintered bodies were separated from the laminate. The silicon nitride sintered bodies were easily separated. (evaluation) All 10 of the resulting silicon nitride sintered bodies were evaluated for waviness. The evaluation results for the ceramic sintered body with the largest Wa value are shown in Table 1. Note that the separability in Table 1 indicates whether or not the 10 silicon nitride sintered bodies could be easily separated from the laminate after the firing process.

[0052] <Examples 2 to 8> Silicon nitride sintered bodies were obtained in the same manner as in Example 1, except that the average particle size and coating amount of the boron nitride powder were changed as shown in Table 1, and evaluations were carried out.

[0053] Example 9 A silicon nitride sintered body was obtained and evaluated in the same manner as in Example 1, except that the coating step was carried out by the electrostatic screen printing method described below. (Coating process) Boron nitride powder was loaded onto the electrostatic screen plate of a T-1 type tabletop electrostatic screen printing machine (manufactured by Berg Kogyo Co., Ltd.), the distance between the electrostatic screen plate and the green body was set at 15 mm, and a voltage of 3 kV was applied to generate an electrostatic field. The boron nitride powder was charged and released into the electrostatic field, and then coated onto the green body to obtain a green body with a boron nitride layer. The amount of charged hexagonal boron nitride powder applied was 0.2 mg / cm. 2 In the same manner, boron nitride powder was applied to one side of a total of 10 green bodies.

[0054] <Comparative Example 1> A silicon nitride sintered body was obtained and evaluated in the same manner as in Example 1, except that the charging device below the belt conveyor was not used in the coating step.

[0055] <Comparative Example 2> A silicon nitride sintered body was obtained and evaluated in the same manner as in Example 3, except that the coating step was carried out in a wet manner as described below. (Coating process) 100 g of boron nitride powder, 100 g of binder (acrylamide polymer solution), 10 g of dispersant (glycerol monostearate), and 2000 g of water were mixed and stirred for 48 hours to obtain a slurry of boron nitride powder. The boron nitride powder slurry was applied to one side of the green body using a spray coater, and then dried at 120°C for 180 minutes to remove the dispersant from the applied boron nitride powder slurry, yielding a green body having a boron nitride layer.

[0056] [Table 1]

Claims

1. a coating step of dry-coating boron nitride powder on at least one surface of a green body containing ceramic powder to obtain a green body having a boron nitride layer; a lamination step of laminating a plurality of green bodies each having a boron nitride layer; a firing step of firing the laminate to produce a laminate of ceramic sintered bodies; Including, The boron nitride powder is applied while applying a voltage between a boron nitride powder supply portion and the green body. A method for manufacturing a ceramic sintered body.

2. In the green body having the boron nitride layer, the amount of boron nitride in the boron nitride layer is 0.01 mg / cm ２ ~0.60mg / cm ２ 2. The method for producing a ceramic powder according to claim 1, wherein

3. 3. The method for producing a ceramic powder according to claim 1, wherein the boron nitride powder has an average particle size of 3 to 25 μm.

4. 3. The method for producing a ceramic sintered body according to claim 1, wherein the ceramic is silicon nitride.

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