Green sheet manufacturing method

Abstract

One embodiment of the present invention relates to a method of manufacturing a green sheet, a method of manufacturing a sintered silicon nitride or a green sheet molding material. This method of manufacturing a green sheet comprises: a step for preparing an aqueous silicon nitride slurry which contains at least silicon nitride, water and a binder and in which the content of water is 10-70 parts by mass per 100 parts by mass of silicon nitride; a decompression treatment step for subjecting the aqueous silicon nitride slurry to a decompression treatment to give a slurry for molding green sheet; and a sheet molding step for molding the slurry for molding green sheet into a molded sheet.

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a method for producing a green sheet, a method for producing a silicon nitride sintered body, or a green sheet molding material. [Background technology]

[0002] Silicon nitride sintered bodies, which are made by sintering silicon nitride powder at high temperatures, are characterized among various ceramic sintered bodies by their light weight, high mechanical strength from room temperature to high temperatures, excellent chemical resistance, thermal conductivity, and electrical insulation, and are used as heat dissipation substrates, wear-resistant components, high-temperature structural components, etc.

[0003] One example of a method for producing sintered silicon nitride is to sinter a sheet-like compact called a green sheet, which is produced by dispersing raw materials such as silicon nitride powder and a binder in a solvent to form a silicon nitride slurry into a sheet using a doctor blade method or the like.

[0004] In the conventional production of green sheets using the doctor blade method, organic solvents such as toluene and alcohol have been used as the solvent for the slurry from the viewpoints of ease of molding and drying (e.g., Patent Documents 1 and 2). For example, in Patent Document 1, a green sheet is produced using a slurry in which a mixed solution of toluene and ethanol is used in total at 70 parts by weight for 100 parts by weight of a mixed powder of silicon nitride and a sintering aid. In Patent Document 2, a green sheet is produced using a slurry with a solids concentration of 60%, and ethyl alcohol is given as an example of the solvent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-052072 [Patent Document 2] Japanese Patent Application Publication No. 2020-093978 Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, organic solvents have traditionally been used as the solvent for the slurry used to produce green sheets. However, in recent years, there has been a demand for production methods with less environmental impact. Therefore, the present inventors attempted to produce green sheets using water as the slurry solvent, which has a lower environmental impact than organic solvents. However, they found that using water as the solvent resulted in the problem of a large number of bubbles forming in the resulting green sheets. Furthermore, they found that firing a green sheet containing a large number of bubbles results in defects such as dents and voids on the surface of the resulting sintered body, resulting in problems such as poor mechanical and electrical properties.

[0007] In one embodiment of the present invention, water is used as a solvent for the slurry to reduce the environmental impact while producing a green sheet in which the generation of bubbles is suppressed. [Means for solving the problem]

[0008] The inventors conducted extensive research and found that when water is used as the slurry solvent, a portion of the silicon nitride in the slurry reacts with water to generate gas, resulting in the formation of numerous bubbles in the green sheet. Further investigation revealed that when water is used as the slurry solvent, the binder forms micelles during mixing of the slurry raw materials, which adversely affects the properties of the resulting sintered body. Therefore, a decompression treatment step is required to break down these micelles, in which the silicon nitride aqueous slurry is treated under reduced pressure. Meanwhile, the inventors also found that the reaction between silicon nitride and water primarily occurs during the decompression treatment step. Based on these findings, the inventors investigated the composition of a silicon nitride water slurry that would enable the production of a green sheet in a short vacuum treatment process in order to suppress the generation of gas during the vacuum treatment process. As a result, they found that by using a silicon nitride water slurry in which the amount of water in the slurry is limited to a specific range, it is possible to effectively suppress the generation of bubbles in the green sheet, and thus completed the present invention. An example of the configuration of the present invention is as follows.

[0009] One embodiment of the present invention relates to a method for producing a silicon nitride aqueous slurry containing at least silicon nitride, water, and a binder, the water content of which is 10 to 70 parts by mass per 100 parts by mass of silicon nitride; a decompression treatment step of subjecting the silicon nitride aqueous slurry to a decompression treatment to obtain a slurry for forming a green sheet; a sheet forming step of forming the green sheet forming slurry to obtain a sheet formed body; The method for producing a green sheet includes the steps of:

[0010] The silicon nitride aqueous slurry preferably further contains an antifoaming agent, which is preferably a polyether-based antifoaming agent, and the amount of the antifoaming agent blended is preferably 0.25 to 5.0 parts by mass per 100 parts by mass of silicon nitride.

[0011] The reduced pressure treatment is preferably carried out at a temperature of 15°C or higher and 55°C or lower.

[0012] Moreover, one embodiment of the present invention includes a method for producing a silicon nitride sintered body, which includes a step of firing the green sheet obtained by the method for producing a green sheet at a temperature of 1500 to 2000°C.

[0013] Furthermore, one embodiment of the present invention is a green sheet molding material obtained from a silicon nitride water slurry containing silicon nitride, water, and a binder, in which the amount of water is 10 to 70 parts by mass per 100 parts by mass of silicon nitride. The silicon nitride aqueous slurry preferably contains a polyether antifoaming agent, and the amount of the polyether antifoaming agent blended is preferably 0.25 to 5.0 parts by mass per 100 parts by mass of silicon nitride. [Effects of the Invention]

[0014] According to one embodiment of the present invention, it is possible to produce a green sheet with reduced bubble formation in the production of a green sheet using water as the slurry solvent. By using this green sheet, it is possible to produce a silicon nitride sintered body under production conditions that impose a smaller environmental burden than conventional methods for producing a silicon nitride sintered body that use an organic solvent as the slurry solvent, and it is also possible to obtain a silicon nitride sintered body with good physical properties.

[0015] Furthermore, by using water as the solvent for the slurry, there is no risk of explosion or the like due to the evaporation of the remaining solvent in the subsequent firing step, which has the advantage of simplifying the manufacturing equipment for silicon nitride sintered bodies. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Green sheet manufacturing method> One embodiment of the present invention is a method for producing a green sheet, comprising: a step of obtaining a silicon nitride aqueous slurry containing at least silicon nitride, water, and a binder, wherein the amount of water is 10 to 70 parts by mass per 100 parts by mass of silicon nitride; a decompression treatment step of subjecting the silicon nitride aqueous slurry to a decompression treatment to obtain a slurry for green sheet molding; and a sheet molding step of molding the slurry for green sheet molding to obtain a sheet molded body.

[0017] <Step of obtaining silicon nitride aqueous slurry> The step of obtaining a silicon nitride water slurry is a step of obtaining a silicon nitride water slurry containing at least silicon nitride, water, and a binder, with the blending amount of water being 10 to 70 parts by mass per 100 parts by mass of silicon nitride.

[0018] [Silicon nitride] The silicon nitride aqueous slurry contains silicon nitride. For such a silicon nitride aqueous slurry containing silicon nitride, it is preferable to use silicon nitride powder as a raw material. The silicon nitride powder to be added to the silicon nitride aqueous slurry is not particularly limited as long as it is a powdered substance represented by the chemical formula Si3N4, and any known powder can be used. For example, the silicon nitride powder may be a powder containing α-Si3N4 particles, a powder containing β-Si3N4 particles, or a mixture of both. In particular, it is preferable to use a silicon nitride powder containing 80% or more, especially 90% or more, of β-Si3N4 particles. The silicon nitride powder to be mixed in the silicon nitride aqueous slurry may be one type or two or more types.

[0019] The specific surface area of ​​the silicon nitride powder to be mixed into the silicon nitride water slurry is preferably 5 m 2 / g or more, preferably 20m 2 / g or less. The specific surface area of ​​silicon nitride powder is 5m 2 On the other hand, if the specific surface area is less than 20 m / g, the sinterability tends to decrease. 2 If the content exceeds 1 / g, a reaction with water is likely to occur during the preparation of the slurry described below, and air bubbles are likely to be trapped in the resulting slurry, which requires a long time to degas, and as a result, the amount of air bubbles in the resulting green sheet tends to increase. The specific surface area of ​​the silicon nitride powder is more preferably 7 m 2 / g or more, and more preferably 15m 2 The specific surface area in this specification means the BET specific surface area measured by the BET single-point method using nitrogen gas adsorption.

[0020] 〔water〕 The silicon nitride aqueous slurry uses water as a solvent, which reduces the environmental impact compared to when an organic solvent is used. The water is not particularly limited, and tap water or the like may be used, but it is preferable to use pure water or ion-exchanged water.

[0021] The amount of water in the silicon nitride aqueous slurry is 10 parts by mass or more, preferably 30 parts by mass or more, and 70 parts by mass or less, preferably 50 parts by mass or less, per 100 parts by mass of silicon nitride. By limiting the amount of water to 70 parts by mass or less, it is possible to effectively suppress the formation of bubbles remaining in the green sheet.

[0022] As described above, the reason why the amount of water in the silicon nitride water slurry is set to 10 to 70 parts by mass can prevent air bubbles from remaining in the green sheet is not clear, but the inventors believe it to be as follows. In other words, if the amount of water in the binder-containing silicon nitride water slurry is limited to 10 to 70 parts by mass, the concentration of binder present on the silicon nitride surface and between the silicon nitride particles will increase, and it is thought that this will reduce the opportunity for contact between silicon nitride and water. As a result, it is possible to reduce the generation of gases such as ammonia gas that are generated by the reaction between silicon nitride and water, and it is also thought that the generation of bubbles due to the gas generation will also be reduced. Furthermore, in the slurry, the binder molecules dispersed in water tend to form micelles that contain air bubbles, and a decompression treatment step is required to remove these. It is believed that the amount of micelles generated can be suppressed by limiting the amount of water blended. By suppressing the amount of micelles generated, it is possible to complete the decompression treatment step in a shorter time, and as a result, it is believed that the generation of gas during the decompression treatment step can be suppressed.

[0023] 〔binder〕 A binder is blended into the silicon nitride aqueous slurry, which makes it easier to maintain the desired shape of the sheet formed from the silicon nitride aqueous slurry. As the binder, it is preferable to use an organic polymer, and examples thereof include polyvinyl alcohol, polyvinyl butyral, methyl cellulose, alginic acid, polyethylene glycol, carboxymethyl cellulose, ethyl cellulose, and acrylic resin. The binder to be blended in the silicon nitride aqueous slurry may be one type or two or more types.

[0024] The amount of binder to be blended in the silicon nitride water slurry is preferably 1 to 30 parts by mass per 100 parts by mass of silicon nitride, and the blending amount may be determined appropriately depending on molding conditions and the like.

[0025] [Additives] The silicon nitride aqueous slurry may contain known additives within the range that does not impair the effects of the present invention. The silicon nitride aqueous slurry may contain one or more types of additives.

[0026] [Sintering aid] It is preferable to add a sintering aid to the silicon nitride aqueous slurry. There are no particular restrictions on the sintering aid as long as it is one that can be used for sintering silicon nitride powder, but compounds that do not contain oxygen atoms are particularly preferred because they can suppress a decrease in the thermal conductivity of the resulting silicon nitride sintered body.

[0027] Preferred oxygen-free compounds are carbonitride compounds containing rare earth elements or magnesium (hereinafter also referred to as "specific carbonitride compounds") and nitride compounds containing magnesium (hereinafter also referred to as "specific nitride compounds"). By using one or more compounds selected from the group consisting of specific carbonitride compounds and specific nitride compounds as sintering aids, silicon nitride sintered bodies with high thermal conductivity can be more effectively and easily obtained. The specific carbonitride compounds are believed to function as gettering agents that adsorb oxygen that may be contained in the silicon nitride powder blended into the silicon nitride aqueous slurry, and the specific nitride compounds are believed to reduce the total oxygen content of the silicon nitride sintered bodies. As a result, the use of one or more compounds selected from the group consisting of specific carbonitride compounds and specific nitride compounds is believed to result in silicon nitride sintered bodies with higher thermal conductivity. The specific carbonitride-based compound and the specific nitride-based compound may each be used alone or in combination of two or more.

[0028] The rare earth elements are preferably Y (yttrium), La (lanthanum), Sm (samarium), Ce (cerium), Yb (ytterbium), and the like.

[0029] Examples of carbonitride compounds containing rare earth elements include Y2Si4N6C, Yb2Si4N6C, and Ce2Si4N6C. Of these, Y2Si4N6C and Yb2Si4N6C are preferred because they allow for the easy production of silicon nitride sintered bodies with high thermal conductivity.

[0030] An example of a carbonitride-based compound containing magnesium element is MgSi4N6C. Furthermore, examples of nitride compounds containing magnesium include MgSiN2.

[0031] Among the specific carbonitride compounds and specific nitride compounds, particularly preferred compounds are Y2Si4N6C, MgSi4N6C, and MgSiN2.

[0032] In addition, it is preferable to use a metal oxide as the sintering aid together with the oxygen-free compound. By using a metal oxide as the sintering aid, the sintering of silicon nitride progresses more easily, and a denser and stronger sintered body can be easily obtained.

[0033] Examples of metal oxides include yttria (Y2O3), magnesia (MgO), and ceria (CeO2). Among these, yttria is preferred. One type of metal oxide may be used, or two or more types may be used.

[0034] When a compound not containing oxygen atoms and a metal oxide are used in combination as a sintering aid, the mass ratio of the compound not containing oxygen atoms to the metal oxide (compound not containing oxygen atoms / metal oxide) is preferably 0.2 or more, more preferably 0.4 or more, even more preferably 0.6 or more, and is preferably 4 or less, more preferably 2 or less. When the mass ratio is within this range, a dense silicon nitride sintered body with high thermal conductivity can be easily obtained.

[0035] When a sintering aid is added to the silicon nitride water slurry, the amount of sintering aid added to the silicon nitride water slurry is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and preferably 20 parts by mass or less, more preferably 10 parts by mass or less, per 100 parts by mass of silicon nitride.

[0036] [Antifoaming agent] The silicon nitride aqueous slurry may contain an antifoaming agent. The incorporation of an antifoaming agent makes it easier to destroy bubbles resulting from the gas generated by the reaction between silicon nitride and water, and thus makes it possible to more effectively prevent bubbles from forming in the green sheet. In addition, the antifoaming agent can also destroy bubbles that are generated by taking in external air during the manufacturing operations of the green sheet, such as stirring and molding, making it easier to more effectively prevent bubbles from forming in the green sheet. As the defoaming agent, known defoaming agents can be used, but polyether-based defoaming agents are preferably used.

[0037] Examples of polyether-based defoaming agents include polyoxyalkylenes such as (poly)oxyethylene and (poly)oxypropylene; (poly)oxyalkylene alkyl ethers such as diethylene glycol heptyl ether, polyoxyethylene oleyl ether, polyoxypropylene butyl ether, and polyoxyethylene polyoxypropylene 2-ethylhexyl ether; (poly)oxyalkylene (alkyl)aryl ethers such as polyoxypropylene phenyl ether and polyoxyethylene nonylphenyl ether; acetylene ethers such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5-dimethyl-3-hexyne-2,5-diol, and 3-methyl-1-butyn-3-ol; diethylene glycol oleyl ether; (poly)oxyalkylene fatty acid esters such as polyoxyethylene sorbitan monolaurate and polyoxyethylene sorbitan trioleate; (poly)oxyalkylene alkyl (aryl) ether sulfate salts such as polyoxypropylene methyl ether sodium sulfate and polyoxyethylene dodecylphenol ether sodium sulfate; (poly)oxyalkylene alkyl phosphates such as (poly)oxyethylene stearyl phosphate; and (poly)oxyalkylene alkylamines such as polyoxyethylene laurylamine.

[0038] When an antifoaming agent is added to the silicon nitride water slurry, the amount of antifoaming agent added is not particularly limited, but is preferably 0.25 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 2.0 parts by mass or less, per 100 parts by mass of silicon nitride.

[0039] [Organic solvents] The silicon nitride water slurry can also contain organic solvents other than water, such as alcohol, as a solvent. However, from the viewpoint of environmental impact, it is preferable that the amount of organic solvent used be as small as possible, preferably 50% or less of the amount of the solvent used, more preferably 20% or less, and even more preferably 1% or less.

[0040] [Method for producing silicon nitride aqueous slurry] The method for producing the silicon nitride aqueous slurry is not particularly limited, and may involve, for example, weighing out the components in predetermined amounts and stirring and mixing them so that the silicon nitride powder is dispersed in the solvent. Examples of dispersing devices used for stirring and mixing include ultrasonic dispersers, bead mills, roll mills, homomixers, ultramixers, disperser mixers, penetrating-type high-pressure dispersers, collision-type high-pressure dispersers, porous high-pressure dispersers, trapping-type high-pressure dispersers, (collision + penetrating) type high-pressure dispersers, and ultra-high-pressure homogenizers. After stirring and mixing, if necessary, a process such as filtering may be performed to remove coarse particles from the slurry.

[0041] <Decompression treatment process> In the vacuum treatment step, the silicon nitride aqueous slurry is subjected to vacuum treatment to obtain a slurry for forming a green sheet. The vacuum treatment step is carried out by placing the silicon nitride aqueous slurry under reduced pressure conditions lower than atmospheric pressure (for example, −0.20 MPa·G or higher, for example, −0.08 MPa·G or lower). The reduced pressure treatment process can destroy the micelles of the micellized binder, thereby suppressing the occurrence of defects on the surface of the sintered body obtained by firing the green sheet. Furthermore, by setting the amount of water blended into the silicon nitride water slurry to 10 to 70 parts by mass, as described above, the silicon nitride and water come into contact less frequently, and the amount of micelles generated in the slurry is reduced. This presumably makes it possible to complete the reduced pressure treatment process in a short time and suppress the generation of gas due to the reaction between silicon nitride and water, which causes bubbles in the green sheet.

[0042] The pressure in the decompression treatment step is preferably −0.15 MPa·G or more, and preferably −0.09 MPa·G or less. If the pressure is too low, new bubbles may be generated due to bumping, etc. If the pressure is too high, it tends to be difficult to destroy the micelles sufficiently in a short time.

[0043] The temperature in the reduced pressure treatment step is not particularly limited as long as the silicon nitride water slurry maintains its fluidity, but is preferably 15°C or higher, more preferably 20°C or higher, and even more preferably 25°C or higher, and is preferably 55°C or lower, and more preferably 45°C or lower. If the temperature in the decompression treatment step is low, the efficiency of micelle destruction will be poor, so the decompression treatment step will need to be carried out for a long time, but the reactivity between silicon nitride and water will also be low, allowing for a smaller amount of gas generated per unit time. On the other hand, if the temperature in the decompression treatment step is high, the reactivity between silicon nitride and water will be high, allowing for a larger amount of gas generated per unit time, but the decompression treatment time can be shortened. By balancing these factors, carrying out the decompression treatment step within the above temperature range makes it easy to efficiently suppress the generation of bubbles in the green sheet.

[0044] The preferred time for the reduced pressure treatment step varies depending on the temperature of the reduced pressure treatment, but from the viewpoint of sufficiently destroying micelles and suppressing the generation of gas due to the reaction between silicon nitride and water, it is preferably 1 hour or more and preferably 5 hours or less. When the temperature during the reduced pressure treatment is 25°C or higher, the time for the reduced pressure treatment step is particularly preferably 3 hours or less.

[0045] In the decompression treatment step, depending on the conditions, water as a solvent may be removed, and the viscosity of the slurry (green sheet molding slurry) after the decompression treatment step may differ from that of the silicon nitride water slurry. In this case, the decompression treatment step may be performed to break down the micelles and adjust the viscosity of the green sheet molding slurry to a value suitable for molding. From the viewpoint of formability, the viscosity of the green sheet forming slurry at 23° C. is preferably 1000 mPa·s or more, more preferably 3000 mPa·s or more, and preferably 10000 mPa·s or less, more preferably 7000 mPa·s or less. The viscosity is a value measured by a rotational viscometer.

[0046] The solid content of the slurry for forming the green sheet is preferably 65 to 75% from the viewpoints of formability and ease of carrying out the drying step described below.

[0047] <Green sheet molding material> The green sheet molding material according to one embodiment of the present invention is not particularly limited as long as it is a material obtainable from the silicon nitride aqueous slurry. A specific example of a suitable green sheet molding material is the silicon nitride aqueous slurry or the green sheet molding slurry.

[0048] <Sheet forming process> The sheet forming process for forming the green sheet slurry to obtain a sheet body is not particularly limited, and any known forming method can be used. However, it is preferable to form the green sheet by the doctor blade method, from the viewpoint of obtaining a sheet body with good thickness uniformity.

[0049] The sheet molded body thus formed may be used as a green sheet, but it is preferable to dry the sheet molded body thus formed to form a green sheet.

[0050] The drying step is a step of removing water from the sheet molded body molded as described above, and by carrying out this drying step, the degreasing step and the firing step, which will be described later, can be carried out more easily. The drying step can be carried out by leaving the sheet molded body at a temperature of, for example, about 30 to 150°C. In the drying step, it is preferable to dry the sheet so that the moisture content of the resulting green sheet becomes 10% or less.

[0051] The obtained green sheet may be processed into an appropriate size, any shape, etc., as needed. For example, the size and shape are generally processed into a roughly rectangular parallelepiped shape with a side length of 100 to 2000 mm and a thickness of 0.3 to 1.2 mm.

[0052] Furthermore, the obtained green sheet is preferably subjected to a degreasing step, if necessary, prior to the firing step described below. An example of the degreasing step is a step of heating the sheet compact for the purpose of removing organic substances such as binders from the green sheet.

[0053] The heating temperature during the degreasing step is usually 300°C or higher, preferably 400°C or higher, and usually 1200°C or lower, preferably 1000°C or lower. The heating time for the green sheet in the degreasing step can be appropriately selected depending on the type of binder and the degreasing atmosphere, but is usually 30 minutes or more, preferably 2 hours or more, and usually 140 hours or less, preferably 120 hours or less.

[0054] The degreasing process is usually 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 mixed gas of these, or in an atmosphere of a humidified gas in which these gases are mixed with water vapor.

[0055] <Silicon nitride sintered body> A silicon nitride sintered body according to one embodiment of the present invention can be obtained by firing the green sheet obtained by the above-described method for producing a green sheet (firing step). The firing conditions are not particularly limited, and the firing may be carried out under known firing conditions for obtaining a silicon nitride sintered body.

[0056] The firing is usually carried out in an inert gas atmosphere, such as a nitrogen atmosphere or an argon atmosphere.

[0057] The firing is preferably carried out in a pressure-controlled atmosphere. The pressure at this time is not particularly limited, but low pressure may cause silicon nitride to decompose during firing, and high pressure increases the cost of equipment, etc., so the pressure is, for example, 0 MPa·G or more, and for example, 10 MPa·G or less, preferably 3 MPa·G or less, and more preferably 0.1 MPa·G or less.

[0058] The firing temperature is not particularly limited as long as the desired sintering reaction proceeds, but is usually 1200°C or higher, preferably 1500°C or higher, and usually 2000°C or lower, preferably 1800°C or lower.

[0059] The firing time is not particularly limited as long as the desired sintering reaction proceeds, but is generally set to about 3 to 20 hours.

[0060] The silicon nitride sintered body produced as described above is a sintered body obtained by using water as the solvent for the slurry used in producing the green sheet, and the occurrence of defects such as surface depressions and internal voids due to bubbles generated during the production of the green sheet is suppressed. Furthermore, silicon nitride sintered bodies in which defects such as surface depressions and voids are suppressed in this way have good physical properties such as mechanical properties and electrical properties.

[0061] The three-point bending strength (measured in accordance with JIS R 1601), which is an index of the mechanical strength of the silicon nitride sintered body, is preferably 500 MPa or more, more preferably 550 MPa or more. A silicon nitride sintered body in which defects such as surface depressions and internal voids are suppressed tends to have a three-point bending strength within the above range, and therefore has excellent reliability as a product.

[0062] The breakdown voltage of the silicon nitride sintered body is preferably 11 kV or more, and more preferably 13 kV or more. A silicon nitride sintered body having such a breakdown voltage is less likely to suffer from breakdown and is highly reliable as a product.

[0063] The thermal conductivity of the silicon nitride sintered body is preferably 60 W / m·K or more, and more preferably 75 W / m·K or more. The thermal conductivity can be measured by a laser flash method.

[0064] The uses of the silicon nitride sintered body are not particularly limited, and examples thereof include various heat dissipation substrates, power module substrates (for automotive use, electric railway use, and high-power semiconductor use), high-frequency circuit boards, LED packages, optical pickup submounts (for DVDs and CDs), engine or gas turbine materials, turbocharger rotors, diesel engine glow plugs, hot plugs, heater tubes, low-pressure casting stalks, couple protection tubes, degassing blowing pipes, heat-resistant and / or impact-resistant members, abrasive cloth dressing plates, induction hardening jigs, jigs for vehicle body assembly and / or engine manufacturing, jigs for press processes, insulating parts, insulating medical and / or surgical instruments, and rollers for plastic processing. [Example]

[0065] Hereinafter, one embodiment of the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples. Each test method is as follows.

[0066] <Evaluation of bubbles in green sheets> The surfaces of 10 green sheets (300mm x 2000mm x 0.4mm) manufactured under the same conditions and with the same shape were visually observed, and the number of dents per sheet (average number of dents) was calculated and evaluated according to the following evaluation criteria. (Evaluation criteria) A: The number of dents per green sheet is less than 10 B: The number of dents per green sheet is 10 or more but less than 20 C: The number of dents per green sheet is 20 or more but less than 30 D: The number of dents per green sheet is 30 or more but less than 40 E: The number of dents per green sheet is 40 or more.

[0067] <Evaluation of sintered body surface properties> The surfaces of 10 sintered bodies (300 mm x 2000 mm x 0.4 mm) manufactured under the same conditions and with the same shape were visually observed, and the number of dents per body (average number of dents) was calculated and evaluated according to the following evaluation criteria. (Evaluation criteria) A: The number of dents per sintered body is less than 10 B: The number of dents per sintered body is 10 or more but less than 20 C: The number of dents per sintered body is 20 or more but less than 30 D: The number of dents per sintered body is 30 or more but less than 40 E: The number of dents per sintered body is 40 or more

[0068] The raw materials used in the test and their abbreviations are as follows: <Silicon nitride powder> ·C1: Specific surface area 12m 2 / g β-Si3N4 powder <Sintering aid> S1: Yttrium oxide (specific surface area 20 m 2 / g) S2: Magnesium silicon nitride (specific surface area 12 m 2 / g) <Binder> B1: Acrylic resin emulsion (Fujikura Kasei Co., Ltd.: Acrybase EMK-02) <Antifoaming agent> (Polyether-based defoaming agent) D1: Polyoxyalkylene (San Nopco Co., Ltd.: SN Deformer 485)

[0069] Example 1 100 g of silicon nitride powder C1, 5.6 g of sintering aid S1, 3.4 g of sintering aid S2, 24 g of binder B1, 0.5 g of antifoaming agent D1, and 47 g of water were mixed and stirred for 48 hours to obtain a silicon nitride aqueous slurry. The resulting silicon nitride aqueous slurry was placed in a container, and the container was reduced in pressure to -0.1 MPa·G. The container was then left to stand at 30°C for 2.5 hours to obtain a slurry for green sheet molding. The resulting slurry for green sheet molding was then passed through a polyethylene mesh (229 μm mesh size) to remove coarse particles. The resulting slurry was then used to fabricate a sheet compact measuring 300 mm x 2000 mm x 0.4 mm using a doctor blade method. The resulting sheet compact was placed on a plate heater set at 50°C and left to dry for 3 hours to obtain a green sheet. The resulting green sheet was evaluated for bubbles, then degreased at 500°C for 60 hours and fired in a nitrogen atmosphere at 1800°C and 0.1 MPa·G for 16 hours to obtain a silicon nitride sintered body. The surface properties of the resulting silicon nitride sintered body were then evaluated. The composition of the silicon nitride aqueous slurry and the conditions for the reduced pressure treatment process are shown in Table 1, and the evaluation results of the resulting green sheet and silicon nitride sintered body are shown in Table 2.

[0070] <Examples 2 to 5, Comparative Examples 1 to 3> Evaluation was carried out in the same manner as in Example 1, except that the composition of the silicon nitride water slurry and the conditions for the reduced pressure treatment step were changed as shown in Table 1. In Comparative Example 3, the reduced pressure treatment step was not carried out on the silicon nitride water slurry. The composition of the silicon nitride aqueous slurry and the conditions for the reduced pressure treatment process are shown in Table 1, and the evaluation results of the obtained green sheet and silicon nitride sintered body are shown in Table 2.

[0071] [Table 1]

[0072] [Table 2]

[0073] In the above examples, the slurries for forming green sheets obtained by the manufacturing methods of Examples 1 to 5 had solid content concentrations of 65 to 75% and viscosities of 4000 to 6000 mPa·s at 23° C. The viscosities were measured using a rotational viscometer.

[0074] In Examples 1 to 5 according to one embodiment of the present invention, green sheets with fewer bubbles were obtained than in Comparative Examples 1 and 2, which contained a larger amount of water, and as a result, a good sintered body was obtained. In Comparative Example 3, which contained a smaller amount of water, the green sheet itself could not be molded.

Claims

1. obtaining a silicon nitride water slurry containing at least silicon nitride powder, water, and a binder, the amount of water being 10 to 70 parts by mass per 100 parts by mass of the silicon nitride powder; a decompression treatment step of subjecting the silicon nitride aqueous slurry to a decompression treatment to obtain a slurry for forming a green sheet; a sheet forming step of forming the green sheet slurry to obtain a sheet body; Including, the silicon nitride powder has a BET specific surface area of ​​5 m 2 / g or more and 20 m 2 / g or less, as measured by a BET single-point method using nitrogen gas adsorption; the binder is at least one selected from methyl cellulose, alginic acid, polyethylene glycol, carboxymethyl cellulose, ethyl cellulose, and an acrylic resin; The viscosity of the green sheet molding slurry at 23°C is 3000 mPa·s or more and 10000 mPa·s or less. A method for manufacturing a green sheet.

2. The method for producing a green sheet according to claim 1 , wherein the silicon nitride aqueous slurry further contains an antifoaming agent.

3. The method for producing a green sheet according to claim 2, wherein the antifoaming agent is a polyether-based antifoaming agent.

4. 4. The method for producing a green sheet according to claim 2, wherein the amount of the antifoaming agent is 0.25 to 5.0 parts by mass per 100 parts by mass of the silicon nitride powder.

5. The method for producing a green sheet according to any one of claims 1 to 4, wherein the reduced pressure treatment is carried out at a temperature of 15°C or higher and 55°C or lower.

6. A method for producing a silicon nitride sintered body, comprising a step of firing the green sheet obtained by the method for producing a green sheet according to any one of claims 1 to 5 at 1500 to 2000°C.

7. The composition comprises silicon nitride powder, water, and a binder, and the amount of water is 10 to 70 parts by mass per 100 parts by mass of the silicon nitride powder; the silicon nitride powder has a BET specific surface area of ​​5 m 2 / g or more and 20 m 2 / g or less, as measured by a BET single-point method using nitrogen gas adsorption; The binder is obtained from a silicon nitride water slurry, which is at least one selected from methyl cellulose, alginic acid, polyethylene glycol, carboxymethyl cellulose, ethyl cellulose, and acrylic resin. A green sheet molding material which is a slurry for green sheet molding having a viscosity at 23°C of 3000 mPa·s or more and 10000 mPa·s or less.

8. the silicon nitride aqueous slurry contains a polyether-based defoaming agent, The amount of the polyether antifoaming agent blended is 0.25 to 5.0 parts by mass per 100 parts by mass of the silicon nitride powder. The green sheet molding material according to claim 7.

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