Method for producing ceramic degreased body and method for producing ceramic sintered body

Abstract

This production method according to an embodiment produces a ceramic degreased body by heating and degreasing a ceramic molded body in a continuous furnace. The continuous furnace includes: a heating unit that heats the ceramic molded body; a maintaining unit that maintains the temperature of the ceramic molded body; and a cooling unit that cools the ceramic molded body. The oxygen concentration in at least part of the heating unit is lower than the oxygen concentration in at least part of the maintaining unit. An exothermic reaction caused by a change in oxygen concentration is caused in the ceramic molded body while the ceramic molded body passes through at least said part of the maintaining part.

Description

Method for manufacturing degreased ceramic body and method for manufacturing sintered ceramic body

[0001] The embodiments described below generally relate to a method for manufacturing a degreased ceramic body and a method for manufacturing a sintered ceramic body.

[0002] Ceramic materials have properties such as high hardness, insulation, and wear resistance. In particular, fine ceramics with high purity and uniform particle size are used in a variety of fields, including capacitors, actuator materials, and refractory materials. In the production of fine ceramics, the raw materials are formed into the product shape, and then the ceramic compact is sintered. This process yields fine ceramics with the shape required for the product.

[0003] In the process of forming raw materials into the product shape, it is difficult to form them simply by processing the raw material powder. For this reason, to facilitate forming, a resin component called a binder is mixed with the raw materials to obtain a ceramic green body. A debinding process is then carried out on the ceramic green body before sintering. In the debinding process, the resin component of the ceramic green body is heated and removed. A debinding ceramic body is obtained through the debinding process. In the debinding process, a batch furnace or belt furnace has been used to efficiently remove the resin component.

[0004] Patent Document 1 describes a method for degreasing inorganic compounds including ceramics. Patent Document 1 describes preventing explosion of flammable gas generated from ceramic molded bodies in degreasing using a continuous furnace. It also describes degreasing while reducing heat loss due to exhaust gas flowing in an exhaust system.

[0005] Patent Document 2 describes the control of the inflow gas during degreasing. According to Patent Document 2, the occurrence of cracks in the degreased body can be prevented by lowering the oxygen gas concentration inside the furnace.

[0006] Patent Document 3 describes degreasing of nitride green sheets using a continuous furnace. According to the technique described in Patent Document 3, ceramic molded bodies can be degreased in a continuous manner in air or an inert atmosphere.

[0007] Patent No. 4523499 International Publication No. 2005 / 047207 Japanese Patent Application Laid-Open No. 2023-70973

[0008] However, when degreasing non-oxide ceramics using the degreasing method described in Patent Document 1, it is difficult to control the combustion reaction, which can lead to a long manufacturing time. In the degreasing method described in Patent Document 2, the amount of heat generated is large when the amount of oxygen is increased. Controlling the heat generation state can lead to a long manufacturing time. In the degreasing method described in Patent Document 3, when air degreasing is performed, the timing of the exothermic reaction is not controlled, which can lead to oxidation of the surface of the degreased body.

[0009] In a manufacturing method according to an embodiment, a ceramic degreased body is manufactured by heating and degreasing a ceramic formed body in a continuous furnace. The continuous furnace includes a heating section for heating the ceramic formed body, a holding section for maintaining the temperature of the ceramic formed body, and a cooling section for cooling the ceramic formed body. The oxygen concentration in at least a portion of the heating section is lower than the oxygen concentration in at least a portion of the holding section. While the ceramic formed body passes through at least a portion of the holding section, an exothermic reaction caused by a change in oxygen concentration occurs in the ceramic formed body.

[0010] FIG. 1 is a top view showing an example of a continuous furnace. FIG. 2 is a cross-sectional view showing an example of a continuous furnace. FIG. 3(a) is a graph showing examples of heat treatment conditions in a manufacturing method according to an embodiment. FIG. 3(b) is a graph showing examples of nitrogen concentrations in various parts of a continuous furnace. FIG. 3(c) is a graph showing examples of oxygen concentrations in various parts of a continuous furnace. FIG. 4 is a schematic diagram showing an example of an exothermic reaction during air degreasing in degreasing using a continuous furnace according to an embodiment. FIG. 5 is a cross-sectional view showing an example of a molded body placed in a setter in degreasing using a continuous furnace according to an embodiment. FIGS. 6(a) and 6(b) are cross-sectional views showing an example of temperature measurement of a molded body in a setter in degreasing using a continuous furnace according to an embodiment. FIG. 7 is a flowchart showing a manufacturing method according to an embodiment. FIG. 8 is a perspective view showing an example of a ceramic substrate. FIG. 9(a) is a side view showing an example of a bearing ball. FIG. 9(b) is a side view showing an example of a bearing.

[0011] Hereinafter, the method for manufacturing a degreased ceramic body and the method for manufacturing a sintered ceramic body according to the embodiments will be described in detail with reference to the drawings.

[0012] In a manufacturing method according to an embodiment, a ceramic degreased body is manufactured by heating and degreasing a ceramic formed body in a continuous furnace. The continuous furnace includes a heating section for heating the ceramic formed body, a holding section for maintaining the temperature of the ceramic formed body, and a cooling section for cooling the ceramic formed body. The oxygen concentration in at least a portion of the heating section is lower than the oxygen concentration in at least a portion of the holding section. While the ceramic formed body passes through at least a portion of the holding section, an exothermic reaction caused by a change in oxygen concentration occurs in the ceramic formed body.

[0013] Fig. 1 is a top view showing an example of a continuous furnace. Fig. 2 is a cross-sectional view showing the X-X' cross section when a ceramic molded body is passing through the continuous furnace of Fig. 1. In Figs. 1 and 2, 1 is the continuous furnace, 2 is a heating / cooling section, 2a is a heater, 3 is a main body section, and 4 is a belt section. In Fig. 2, 5 is a ceramic molded body (hereinafter simply referred to as "molded body"), 6 is a setter, 10 is an inlet section, 11 is a heating section, 12 is a holding section, 13 is a cooling section, and 14 is an outlet section.

[0014] The heating and cooling section 2 is provided on top of the main body section 3 and has a processing space for degreasing the molded body 5. A belt section 4 is provided on the upper surface of the main body section 3. The main body section 3 has a drive section (not shown) for driving the belt section 4. The molded body 5 is placed on the belt section 4 and transported by the belt section 4. The molded body 5 transported into the heating and cooling section 2 is heated and cooled while passing through the heating and cooling section 2. The degreased molded body 5 (degreased body) is then transported out of the heating and cooling section 2.

[0015] In the example shown in Fig. 2, a setter 6 is placed on the belt unit 4 and is transported by the belt unit 4. A plurality of compacts 5 are arranged inside the setter 6. The setter 6 is transported by the belt unit 4 from an entrance portion 10 to an exit portion 14.

[0016] A space for degreasing the molded body 5 is provided inside the heating / cooling section 2, and includes a heating section 11, a holding section 12, and a cooling section 13. The heating section 11, the holding section 12, and the cooling section 13 are continuous spaces. The temperatures in the heating section 11, the holding section 12, and the cooling section 13 are different from one another. The molded body 5 is heated while passing through the heating section 11. The temperature of the heated molded body 5 is maintained while passing through the holding section 12. The molded body 5 is then cooled while passing through the cooling section 13.

[0017] A heater 2a is provided on the outer periphery of the heating / cooling unit 2. The heater 2a heats the heater 2a so that each part of the heating / cooling unit 2 functions as a heating unit 11, a holding unit 12, and a cooling unit 13. In other words, the space inside the heating / cooling unit 2 is divided into the heating unit 11, the holding unit 12, and the cooling unit 13 based on the temperature change of the molded body 5 passing through the space. The arrangement, number, output, etc. of the heater 2a are adjusted so that the molded body 5 is heat-treated according to the temperature profile described below.

[0018] 2, 21 is a first supply unit, 22 is a second supply unit, 23 is a curtain gas supply unit, 24 is an exhaust unit, 25 is a curtain gas supply unit, and 26 is an exhaust unit. These elements are provided to control the atmosphere inside the heating / cooling unit 2. Note that in FIG. 1, the heater 2a, the first supply unit 21, the second supply unit 22, the curtain gas supply unit 23, the exhaust unit 24, the curtain gas supply unit 25, and the exhaust unit 26 are omitted.

[0019] The first supply unit 21 supplies a first gas to the inside of the heating / cooling unit 2. The first gas is an inert gas and does not substantially contain oxygen. For example, the first gas is nitrogen gas. The oxygen concentration in the first gas is preferably 0.1% by volume or less, and more preferably 0.01% by volume or less.

[0020] The second supply unit 22 supplies a second gas to the inside of the heating / cooling unit 2. The second gas contains oxygen. As long as the second gas contains oxygen, it may contain other components. The oxygen concentration in the second gas is preferably 10% by volume or more, more preferably 15% by volume or more, and most preferably 20% by volume or more. For example, air can be used as the second gas.

[0021] The first supply unit 21 is provided in the heating unit 11 or the holding unit 12. The second supply unit 22 is provided in the holding unit 12 or the cooling unit 13. The first supply unit 21 is located between the inlet of the heating / cooling unit 2 and the second supply unit 22. When the second gas is supplied by the second supply unit 22, oxygen spreads from the second supply unit 22 toward the heating unit 11. When the first gas is supplied by the first supply unit 21, the spread of oxygen toward the heating unit 11 is suppressed. The supply of the first gas and the second gas forms an oxygen concentration gradient inside the heating / cooling unit 2.

[0022] The curtain gas supply unit 23 is provided at the inlet of the heating unit 11 and supplies an inert gas. The curtain gas supply unit 25 is provided at the outlet of the cooling unit 13 and supplies an inert gas. The curtain gas supply unit 23 and the curtain gas supply unit 25 increase the pressure inside the heating and cooling unit 2 to be higher than the pressure outside the heating and cooling unit 2. This makes it possible to prevent air outside the heating and cooling unit 2 from flowing into the heating and cooling unit 2. For example, the curtain gas supply unit 23 and the curtain gas supply unit 25 supply nitrogen gas to form a so-called nitrogen curtain.

[0023] The exhaust unit 24 is provided near the curtain gas supply unit 23 and exhausts the interior of the heating and cooling unit 2. The first gas supplied from the first supply unit 21 flows toward the exhaust unit 24. The exhaust unit 26 is provided near the first supply unit 21 and exhausts the interior of the heating and cooling unit 2. The second gas supplied from the second supply unit 22 flows toward the exhaust unit 26. The flow of the first gas from the first supply unit 21 to the exhaust unit 24 and the flow of the second gas from the second supply unit 22 to the exhaust unit 26 can increase the changes in the nitrogen concentration and the oxygen concentration inside the heating and cooling unit 2.

[0024] FIG. 3( a) is a graph illustrating heat treatment conditions in the manufacturing method according to the embodiment. FIG. 3( b) is a graph illustrating the nitrogen concentration in each part of the continuous furnace 1. FIG. 3( c) is a graph illustrating the oxygen concentration in each part of the continuous furnace 1. In FIGS. 3( a) to 3(c), the horizontal axis represents the elapsed time since the compact 5 was carried into the heating and cooling section 2. In the continuous furnace 1, the compact 5 moves over time. Therefore, the horizontal axis corresponds to the position of the compact 5 in the heating and cooling section 2. The vertical axis in FIG. 3( a) represents the temperature of the space in which the compact 5 is located, which is substantially the same as the temperature of the compact 5. The vertical axes in FIGS. 3( b) and 3(c) represent the nitrogen concentration and the oxygen concentration, respectively.

[0025] Here, as shown in FIG. 3( a), the time from the start of temperature increase of the molded body 5 to the start of temperature maintenance of the molded body 5 is referred to as "temperature increase time H1." The molded body 5 is heated by the heating section 11, and the temperature is maintained by the maintenance section 12. Therefore, the temperature increase time H1 is also the time from when the molded body 5 enters the heating section 11 to when it enters the maintenance section 12. The time from the start to the end of temperature maintenance is referred to as "temperature maintenance time H2." The temperature maintenance time H2 is also the time from when the molded body 5 enters the maintenance section 12 to when it enters the cooling section 13. The temperature decrease time from the end of temperature maintenance to the end of temperature decrease is referred to as "temperature decrease time H3." The temperature decrease time H3 is also the time from when the molded body 5 enters the cooling section 13 to when it leaves the cooling section 13.

[0026] In the example shown in FIG. 3( a), the molded body 5 is heated from room temperature to a temperature T1 and maintained at the temperature T1. The molded body 5 is then cooled from the temperature T1 to 100°C or lower (e.g., room temperature). The maintained temperature T1 refers to the range from the maximum temperature to minus 50°C in the temperature profile. In other words, the time during which the temperature is maintained in the range from the maximum temperature to minus 50°C in the temperature profile is the temperature maintenance time H2. The time from the start of the temperature increase of the molded body 5 to the start of the temperature maintenance time H2 is the temperature increase time H1. The time from the end of the temperature maintenance time H2 until the molded body 5 is cooled to 100°C is the temperature decrease time H3.

[0027] 3(b) and 3(c), there are changes in the nitrogen concentration and oxygen concentration inside the heating / cooling unit 2. Specifically, the nitrogen concentration in at least a part of the heating unit 11 is higher than the nitrogen concentration in at least a part of the holding unit 12. The oxygen concentration in at least a part of the holding unit 12 is higher than the oxygen concentration in at least a part of the heating unit 11.

[0028] 2 , the first supply unit 21 and the exhaust unit 26 are provided near the boundary between the heating unit 11 and the holding unit 12. The first supply unit 21 supplies a first gas toward the heating unit 11. The second supply unit 22 is provided in the cooling unit 13 and supplies a second gas toward the holding unit 12. For this reason, the nitrogen concentration and the oxygen concentration change significantly near the boundary between the heating unit 11 and the holding unit 12.

[0029] Due to the change in oxygen concentration shown in FIG. 3(c), the compact 5 is subjected to degreasing with a low oxygen concentration and degreasing with a high oxygen concentration. Here, for ease of explanation, degreasing with a low oxygen concentration is referred to as "nitrogen degreasing." Degreasing with a high oxygen concentration is referred to as "air degreasing." Furthermore, as shown in FIGS. 3(b) and 3(c), the area inside the heating / cooling unit 2 where nitrogen degreasing is performed is referred to as the "first area A1." The area where air degreasing is performed is referred to as the "second area A2." The timing at which nitrogen degreasing is switched to air degreasing is referred to as "timing Ha."

[0030] The first area A1 includes at least a portion of the heating section 11. The second area A2 includes at least a portion of the holding section 12. In the first area A1, the oxygen concentration is less than 5% by volume. In the second area A2, the oxygen concentration is 5% by volume or more. The first area A1 and the second area A2 are distinguished based on the oxygen concentration. Furthermore, degreasing performed in a space where the oxygen concentration is less than 5% by volume is nitrogen degreasing. Degreasing performed in a space where the oxygen concentration is 5% by volume or more is air degreasing.

[0031] When air debinding is performed after nitrogen debinding, an exothermic reaction occurs in the compact 5 due to a change in oxygen concentration. In the manufacturing method according to the embodiment, the timing of the occurrence of this exothermic reaction is within the temperature holding time H2. That is, the exothermic reaction occurs while the compact 5 is passing through the holding section 12.

[0032] If the timing of the exothermic reaction occurs within the temperature holding time H2, the debinding by temperature rise is completed, and the debinding by air proceeds slowly and uniformly. In contrast, if the timing of the exothermic reaction occurs within the temperature rise time H1, the debinding reaction proceeds rapidly, and the debinding state may become uncontrollable. If the debinding state is not properly controlled, resin components may remain in the molded body, and the properties of the debinding body may deteriorate. On the other hand, if the timing of the exothermic reaction occurs within the temperature drop time H3, nitrogen debinding is performed at the maximum temperature. Even if air debinding is performed thereafter, the air debinding may be insufficient, and the resin components that adhered to the surface during nitrogen debinding may remain unburned.

[0033] In the manufacturing method according to the embodiment, it is preferable that the timing Ha at which nitrogen degreasing is switched to air degreasing is after 0.5H1 and before (H1 + 0.5H2). In other words, if the time from when the heating section 11 starts heating the compact 5 to when the compact 5 enters the second area A2 is H, then 0.5H1≦H≦H1 + 0.5H2 is satisfied. For example, in the continuous furnace 1, if the heating time H1 is 3 hours, the temperature holding time H2 is 4 hours, and the temperature dropping time H3 is 5 hours, then 0.5H1 refers to 1.5 hours after the start of the heating. (H1 + 0.5H2) refers to 2 hours after the start of temperature holding (5 hours after the start of the heating). By setting the timing Ha to be after 0.5H1 and before (H1 + 0.5H2), an exothermic reaction due to a change in oxygen concentration can occur within the temperature holding time H2.

[0034] The exothermic reaction caused by switching to air degreasing occurs with a certain time lag after the oxygen concentration in the atmosphere surrounding the compact 5 reaches 5% by volume or more. The exothermic reaction is a reaction in which the temperature of the degreased body becomes about 15°C to 25°C higher than the furnace temperature after switching from nitrogen degreasing to air degreasing.

[0035] Fig. 4 is a graph enlarging portion A of Fig. 3. Fig. 4 schematically shows an example of an exothermic reaction due to air debinding in a manufacturing method according to an embodiment. In Fig. 4, Ha is the timing at which the process is switched to air debinding, Hb is the start timing of the exothermic reaction, Hc is the peak timing of the exothermic reaction, Hd is the end timing of the exothermic reaction, T1 is the average temperature of the molded body 5 during the temperature holding time H2, and T2 is the maximum temperature of the molded body 5 during the exothermic reaction.

[0036] The exothermic reaction occurs between timing Hb and timing Hd. However, since the temperature of the compact 5 fluctuates during the temperature holding time H2, it is difficult to clearly identify the timings Hb and Hd. Therefore, here, timing Hc, at which the temperature peak occurs, is considered to be the timing at which the exothermic reaction occurs.

[0037] During debinding, resin components such as the binder contained in the compact 5 are combusted. When the oxygen concentration in the space where the compact 5 exists increases, the combustion reaction of the resin components is accelerated. An exothermic reaction occurs as a result of this combustion reaction being accelerated. For example, if the organic matter has a hydrocarbon group, carbon dioxide derived from the carbon atoms and water derived from the hydrogen atoms are generated, and the combustion heat generated at this time causes a temperature change.

[0038] By controlling the timing at which the oxygen concentration reaches 5% by volume or more, the timing of the exothermic reaction due to air debinding can be controlled. In this case, the timing Hc at which the exothermic reaction occurs is preferably after 0.2H2 and before the end of the temperature holding time H2. In other words, if HR is the time from when the compact 5 enters the heating section 11 to the timing Hc at which the exothermic reaction occurs, it is preferable that H1 + 0.2H2 ≦ HR ≦ H1 + H2 be satisfied. More preferably, the timing Hc at which the exothermic reaction occurs is after 0.4H2 and before 0.8H2 from the start of temperature holding. In other words, it is more preferable that H1 + 0.4H2 ≦ HR ≦ H1 + 0.8H2 be satisfied.

[0039] As long as the timings Ha and Hc can be controlled within the above-mentioned ranges, the control of the atmosphere in the heating / cooling unit 2 can be changed as appropriate. For example, gas may be continuously supplied from the heating unit 11 and the holding unit 12, or gas may be intermittently supplied from the heating unit 11 or the holding unit 12. The flow rate of the gas supplied from the heating unit 11 or the holding unit 12 may be changed depending on the transport position of the compact 5.

[0040] For example, the entire continuous furnace 1 is composed of a single furnace core tube. The temperature at each position within the furnace core tube is controlled, and a section functioning as a heating section 11, a section functioning as a holding section 12, and a section functioning as a cooling section 13 are provided within the furnace core tube. Furthermore, by controlling the airflow within the furnace core tube, the concentrations of nitrogen and oxygen can be controlled, as shown in Figures 3(b) and 3(c).

[0041] Multiple furnace chambers may be provided by providing one or more shutters inside the furnace core tube. Providing shutters allows for more precise control of the airflow. For example, providing shutters facilitates control of the atmosphere in each furnace chamber. In this case, a furnace chamber for replacing the atmosphere may be provided between the first area A1 and the second area A2. In this furnace chamber, the gas is appropriately replaced by nitrogen gas purging. When the shutter between the nitrogen-atmosphere furnace chamber and the replacement furnace chamber is opened, the oxygen concentration in the replacement furnace chamber is controlled to less than 5% by volume.

[0042] The temperature rise time H1, temperature holding time H2, and temperature drop time H3 are set appropriately depending on the size of the compacts 5, the number of compacts 5, etc. Preferably, the temperature rise time H1 is 1 hour or more and 11 hours or less. The temperature holding time H2 is 3 hours or more and 5 hours or less. The temperature drop time H3 is 2 hours or more and 10 hours or less. By controlling the temperature rise time H1, temperature holding time H2, and temperature drop time H3 within these ranges, the compacts 5 can be degreased with a good yield while maintaining the degreasing efficiency per unit time.

[0043] The holding temperature T1 during the temperature holding time H2 is preferably within the range of 350°C or higher and 650°C or lower. If the holding temperature T1 is lower than 350°C, the time required for degreasing may be too long or degreasing may not be sufficient. On the other hand, if the holding temperature T1 exceeds 650°C, the high temperature may cause oxidation of non-oxide raw materials. For this reason, the holding temperature T1 is preferably within the range of 350°C or higher and 650°C or lower, and more preferably within the range of 400°C or higher and 600°C or lower.

[0044] In the manufacturing method according to the embodiment, the difference between the first mass of the compact 5 before it enters the continuous furnace 1 and the second mass of the degreased body after it has been heated in the continuous furnace 1 is preferably 1% or more and 35% or less of the first mass. Here, the value obtained by dividing the difference between the first mass and the second mass by the first mass is referred to as the "mass reduction rate."

[0045] The shape of the compacts 5 can be various, such as cylindrical, spherical, plate-like, or sheet-like. The degreasing efficiency varies depending on the shape of the compacts 5 and the number of compacts 5 being degreased at the same time. For example, if the compacts 5 are spherical, the center of the sphere is more difficult to degrease than the periphery. If the compacts 5 are sheet-like, each compact 5 is easily degreased, but if multiple compacts 5 are stacked, each compact 5 is more difficult to degrease. The mass reduction rate can be used as an indicator of the state of degreasing. A small mass reduction rate indicates insufficient degreasing. A large mass reduction rate may indicate excessive degreasing.

[0046] The preferred mass reduction rate varies depending on the shape of the molded body 5. For example, when the molded body 5 is cylindrical or spherical, the mass reduction rate is preferably in the range of 1% to 10%. When the molded body 5 is cylindrical or spherical, it is difficult to degrease the resin component at the center of the molded body 5 in a short period of time. When the molded body 5 is degreased so that the mass reduction rate exceeds 10%, the degreasing may take a long time. On the other hand, when the mass reduction rate is less than 1%, the degreasing may not be sufficient. Here, "spherical" also includes a shape in which an annular band is provided around the periphery of a sphere. For example, when the molded body 5 is molded by press molding, a band is formed around the sphere.

[0047] When the molded body 5 is in a plate or sheet shape, molding is difficult, and therefore the amount of binder contained in the molded body 5 is large. The thickness of the sheet-like molded body 5 is, for example, 0.1 mm or more and 1 mm or less. In this case, the mass reduction rate is preferably in the range of 10% or more and 20% or less. If the mass reduction rate exceeds 20%, debinding may take a long time and defects such as warping or cracking may occur in the molded body 5. On the other hand, if the mass reduction rate is less than 10%, debinding may not be performed sufficiently, and the performance of the sintered debound body (sintered body) may not be sufficient.

[0048] When the molded body 5 has another complex shape, a larger amount of binder may be contained in the molded body 5 to facilitate molding. Examples of complex shapes include a shape with an uneven surface, a shape with an uneven thickness, a shape with holes, etc. In this case, the mass reduction rate is preferably in the range of more than 20% to 35%.

[0049] For example, the temperature profile shown in Figure 3(a) is obtained when the molded body 5 passes through the continuous furnace 1 (heating and cooling section 2). The horizontal axis of the temperature profile represents time (h) and the vertical axis represents temperature (°C). In this case, the integral value of time with respect to temperature is preferably 2500 or more and 6500 or less. This integral value corresponds to the area of ​​the region enclosed by the horizontal axis and the line segment showing the temperature change with respect to time in the graph showing the temperature profile.

[0050] The product of temperature and time has a significant effect on the state of debinding of the compact 5. For example, when the temperature of the compact 5 is 200°C or higher, the binder contained in the compact 5 reacts, and debinding of the compact 5 progresses. The specific temperature and time for debinding can be set appropriately as long as the temperature is equal to or higher than the temperature at which the binder reacts. For example, similar debinding effects can be obtained when heat treatment is performed at a high temperature for a short time and when heat treatment is performed at a low temperature for a long time.

[0051] If the integral value is less than 2500, the compact 5 may not be sufficiently degreased. On the other hand, if the integral value exceeds 6500, the effect obtained is small and production efficiency is reduced. Therefore, the integral value is preferably in the range of 2500 to 6500, and more preferably in the range of 2800 to 5000.

[0052] The average value of the heating rate is preferably in the range of 100°C / hour or more and 250°C / hour or less. If the heating rate is faster than 250°C / hour, rapid debinding may occur, which may cause cracks in the molded body 5. If the heating rate is slower than 100°C / hour, the temperature change may be more moderate than necessary, which may result in a decrease in production efficiency. Therefore, the average value of the heating rate is preferably in the range of 100°C / hour or more and 250°C / hour or less, and more preferably in the range of 130°C / hour or more and 230°C / hour or less.

[0053] The average temperature drop rate is preferably in the range of 60°C / hour or more and 250°C / hour or less. If the temperature drop rate is faster than 250°C / hour, cracks may occur in the molded body 5 due to a sudden temperature change. On the other hand, if the temperature drop rate is slower than 60°C / hour, the temperature change may be more moderate than necessary, which may result in a decrease in production efficiency. Therefore, the average temperature drop rate is preferably in the range of 60°C / hour or more and 250°C / hour or less, and more preferably in the range of 120°C / hour or more and 180°C / hour or less. The average temperature drop rate is calculated based on the temperature change when the molded body 5 is cooled from the holding temperature to 100°C.

[0054] During debinding, the compacts 5 may be stored in a setter. The continuous furnace 1 has a moving means for continuously moving the compacts 5. The moving means may be a belt type or a roller type. In the belt type, the compacts 5 are moved by a belt conveyor made of metal or the like. In the roller type, the compacts 5 are moved on rollers. The moving means is made of a material with excellent heat resistance such as metal or ceramic. It is preferable that the setter is placed on the moving means.

[0055] FIG. 5 is a perspective view illustrating a setter and a compact. In FIG. 5, 6 is the setter. The setter 6 includes a frame setter 61 surrounding the outer periphery and a bottom plate setter 62 located at the bottom. The setter 6 may be composed of the frame setter 61 and the bottom plate setter 62. A plurality of sheet-shaped compacts 5 are stacked inside the setter 6. Storing the compacts 5 inside the setter 6 can prevent small compacts 5 from falling during degreasing. Furthermore, using the setter 6 can avoid contact between the compacts 5 and the moving means, thereby preventing deterioration of the surface condition of the compacts 5 due to contact.

[0056] The configuration of the setter 6 is not limited to the example shown in Fig. 5. For example, the setter 6 may not include the frame setter 61 and may be composed of only the bottom plate setter 62. The frame setter 61 and the bottom plate setter 62 may be configured as a single unit. The frame setter 61 may also be configured by stacking multiple frame-shaped members.

[0057] The shape of the bottom plate setter 62 is preferably approximately rectangular. For example, when multiple setters 6 are placed on the belt section 4 as shown in FIG. 2 , if the setters 6 are approximately rectangular in plan view, more setters 6 can be arranged adjacent to each other on the belt section 4. This increases the amount of compacts 5 that can be degreased compared to when the bottom plate setter 62 is circular. Furthermore, when the bottom plate setter 62 is approximately rectangular, it is preferable that the corners are chamfered with an R or C. Chamfering the corners can prevent the bottom plate setter 62 from chipping or other problems.

[0058] The main component of the setter 6 is preferably any one of aluminum oxide, zirconium oxide, mullite, boron nitride, silicon nitride, aluminum nitride, and silicon carbide. The term "main component" refers to a component contained in an amount of 50 mass% or more. The material of the setter 6 is preferably the same as that of the compact 5. This is to prevent contamination of the compact 5 by the setter 6 when the compact 5 comes into contact with the setter 6.

[0059] When a ceramic setter 6 is used, it is preferable that the setter 6 be separable into a frame setter 61 and a bottom plate setter 62, as shown in Figure 5. If the setter 6 is separable, deformation of the setter 6 due to contraction during cooling can be suppressed. In addition, the degreased body can be easily removed from the setter 6. Even if part of the setter 6 is damaged, the necessary costs can be reduced by replacing only the damaged part.

[0060] For example, when the compact 5 contains oxide ceramics, the setter 6 may be made of aluminum oxide (alumina). ２ O ３ ), zirconium oxide (zirconia: ZrO ２ ), or mullite (Al ６ O １３ Si ２ When the molded body 5 contains nitride ceramics, the setter 6 preferably contains boron nitride (BN), silicon nitride (Si ３ N ４ When the compact 5 includes a carbide ceramic, the setter 6 preferably includes silicon carbide (SiC).

[0061] In the degreasing, the setter 6 can be heated to about 650° C. The above-mentioned material of the setter 6 has a thermal expansion coefficient of 10 ―４ If the thermal expansion coefficient is small, cracking or deformation when the setter 6 is used for degreasing can be suppressed, and the setter 6 can be used repeatedly.

[0062] If the setter 6 is made of metal, there is a possibility that metal will adhere to the surface of the compact 5 when the compact 5 comes into contact with and rubs against the setter 6. Metal adhesion to the surface of the compact 5 can cause defects such as foreign matter. If sintering is performed with foreign matter attached to the degreased body, a sintered body with foreign matter attached will be produced. Foreign matter attached to the sintered body is likely to become the starting point for fracture. For this reason, when using a metallic setter, it is preferable to apply a ceramic coating or other processing to the setter 6 to prevent metal from adhering to the degreased body.

[0063] When multiple molded bodies 5 are stored in the setter 6, it is preferable that the temperature difference between the multiple molded bodies 5 is small. For example, in the manufacturing method according to the embodiment, when the setter 6 passes through the holding section 12, the maximum difference in temperature between the molded bodies 5 stored in the upper part of the setter 6 and the molded bodies 5 stored in the lower part of the setter 6 is 80°C or less. In other words, in the manufacturing method according to the embodiment, the maximum temperature difference between the multiple molded bodies 5 stored in the setter 6 is 80°C.

[0064] A temperature difference may occur between the multiple molded bodies 5 stored in the setter 6. The temperature difference may be caused by gas convection inside the heating / cooling unit 2, the inflow of the first gas, the inflow of the second gas, the position of each molded body 5 in the setter 6, the number of molded bodies 5 stored, thermal conduction of the setter 6, and the like. It is preferable to adjust these factors to reduce the maximum value of the temperature difference. For example, by reducing the difference in the total mass of the molded bodies 5 stored in each setter 6, the maximum value of the temperature difference can be suppressed to 80°C or less.

[0065] By reducing the temperature difference within the setter 6, it is possible to reduce the variation in the debinding state of each compact 5. As a result, it is possible to suppress the variation in the properties of the produced sintered bodies. The maximum value of the temperature difference is more preferably 70°C or less, and most preferably 60°C or less.

[0066] 6(a) and 6(b) are cross-sectional views showing an example of temperature measurement in the manufacturing method according to the embodiment. In Fig. 6(a) and Fig. 6(b), reference numeral 7 denotes a thermocouple. The temperature difference is measured using the thermocouple 7.

[0067] In the example shown in FIG. 6( a), three setters 6 are stacked, and each setter 6 is composed of a bottom plate setter 62 and a frame setter 61. Each setter 6 stores a plurality of molded bodies 5. In this case, one thermocouple 7 is located in a range LU and measures the temperature of one of the molded bodies 5 arranged at the top. Another thermocouple 7 is located in a range LB and measures the temperature of one of the molded bodies 5 arranged at the bottom. When the distance between the topmost molded body 5 and the bottommost molded body 5 is L, the range LU is from the top to 10% of the distance L. The range LB is from the bottom to 10% of the distance L.

[0068] In the example shown in Fig. 6(b), a large setter 6 consisting of a bottom plate setter 62 and a frame setter 61 stores a plurality of molded bodies 5. As in the example shown in Fig. 6(a), one thermocouple 7 is located in range LU and measures the temperature of one of the molded bodies 5 arranged at the top. Another thermocouple 7 is located in range LB and measures the temperature of one of the molded bodies 5 arranged at the bottom.

[0069] As described above, storing a plurality of compacts 5 in the setter 6 can suppress temperature variations among the compacts 5. Furthermore, stacking a plurality of setters 6 and storing a plurality of compacts 5 in each setter 6 can further suppress temperature variations and enable efficient debinding.

[0070] For example, if there is temperature variation within one compact 5, there will be a difference in the debinding state between the periphery and the center of the compact 5. In this case, the interior of the compact 5 will not be sintered sufficiently, and the strength of the sintered body may decrease. If there is temperature variation within multiple compacts 5, there is a possibility that some compacts 5 will not be sufficiently debound. If compacts 5 with insufficient debinding are sintered, a sintered body with low density or discoloration may be produced. In contrast, the manufacturing method according to the embodiment described above makes it possible to obtain a good ceramic debound body.

[0071] According to the manufacturing method of the embodiment, the brightness of the surface hue of the manufactured degreased body is controlled. For example, the brightness of the surface hue of the degreased body is 7 or more and 10 or less in terms of Munsell color system standard brightness V.

[0072] According to the embodiment, the exothermic reaction occurs during the temperature holding time, thereby more uniformly degreasing the molded body 5. As a result, the brightness of the surface color of the degreased body becomes more uniform, and the brightness V is 7 or more and 10 or less. It is more preferable that the brightness V is in the range of 8 or more and 10 or less.

[0073] If an exothermic reaction occurs during the temperature rise period, the degreasing will proceed unevenly due to a rapid degreasing reaction. As a result, some resin components will remain on the degreased body, and part of the surface of the degreased body will turn black. If an exothermic reaction occurs during the temperature drop period, air degreasing will proceed in a state of incomplete combustion. As a result, resin components will remain on the surface of the degreased body, and the entire surface or part of it will turn black. In a degreased body that has been degreased unevenly, the lightness V will fall outside the range of 7 to 10 due to the influence of the black parts.

[0074] The Munsell color system is measured in accordance with JIS Z 8721. For example, in the measurement, the surface of the degreased body is illuminated with a halogen lamp of 12 V voltage and 50 W power, and the brightness of an arbitrary area of ​​5 mm diameter on the surface is measured.

[0075] The main component of the degreased body according to the embodiment is preferably silicon nitride. Silicon nitride has excellent properties such as electrical insulation, mechanical strength, and heat dissipation. For this reason, in recent years, the market has expanded for two types of applications. One of these applications is silicon nitride substrates. Semiconductor elements requiring large currents, such as power electronics and next-generation power semiconductors, are being developed. Accordingly, demand for silicon nitride substrates that combine heat dissipation and electrical insulation is increasing year by year. In particular, heat generation from semiconductor elements is increasing as they become smaller and more powerful. To efficiently dissipate heat, ceramic substrates tend to become thinner. Meanwhile, larger ceramic substrates are being manufactured to reduce manufacturing costs. To efficiently manufacture thin and large silicon nitride substrates, it is necessary to stack multiple thin and large degreased bodies and efficiently degrease them.

[0076] Another application is balls, which take advantage of the mechanical strength properties of silicon nitride. Ball applications include bearings, jigs, tools, gauges, solenoid valves, check valves, and various valves. Among these, silicon nitride balls with large outer diameters are being used in bearing applications, such as wind power generation. There is a demand for efficient degreasing of the degreased silicon nitride balls with large outer diameters.

[0077] The manufacturing method according to the embodiment is suitable for degreasing a molded body 5 containing silicon nitride. For example, the manufacturing method can be applied when stacking and degreasing thin, large, substrate-like molded bodies 5, or when degreasing large, ball-like molded bodies 5. According to the embodiment, a degreased body containing silicon nitride as a main component can be efficiently manufactured.

[0078] By sintering the produced degreased body, a sintered body exhibiting the properties of ceramics can be obtained. By using a degreased body produced by the production method according to the embodiment, a sintered body having good properties can be obtained. For example, if a degreased body that has been insufficiently or unevenly degreased is sintered, the sintering will be uneven. In areas that are not sintered sufficiently, the properties of ceramics will not be exhibited. For example, variations in the density of the sintered body will reduce the thermal conductivity or strength of the sintered body.

[0079] 7 is a flowchart showing a manufacturing method according to an embodiment. First, raw material powders (ceramic powder and sintering aid) are prepared, and a solvent, binder, etc. are added to and mixed with the raw material powders (Step S1). The resulting mixture is molded to produce a compact (Step S2). The compact is debound using a continuous furnace (Step S3). As described above, debinding is performed so that an exothermic reaction occurs during the temperature holding time due to air debinding. The debound body is then sintered to produce a sintered body (Step S4).

[0080] Fig. 8 is a perspective view showing an example of a ceramic substrate. In Fig. 7, reference numeral 30 denotes a ceramic substrate. The ceramic substrate 30 shown in Fig. 7 is obtained by degreasing the sheet-like compact. The ceramic substrate 30 is preferably a silicon nitride substrate.

[0081] Fig. 9(a) is a side view showing an example of a bearing ball. Fig. 9(b) is a side view showing an example of a bearing. The ceramic sintered body can be used as a wear-resistant member. In Fig. 9(a) and Fig. 9(b), 31 is a bearing ball. In Fig. 9(b), 32 is a bearing, 33 is an inner ring, and 34 is an outer ring.

[0082] The bearing ball 31 shown in Fig. 9(a) is a ball-shaped member made of sintered silicon nitride. In the bearing 32 shown in Fig. 9(b), a plurality of bearing balls 31 are arranged between an inner ring 33 and an outer ring 34.

[0083] As an example, a degreased body obtained using the manufacturing method according to the embodiment is sintered to produce a silicon nitride sintered body for substrate use. In this case, the three-point bending strength of the silicon nitride substrate can be increased to 600 MPa or more, or even 700 MPa or more. The thermal conductivity can be increased to 50 W / m·K or more, or even 80 W / m·K or more. According to the embodiment, it is possible to obtain a silicon nitride substrate that has both high strength and high thermal conductivity.

[0084] In another example, a degreased body obtained by the manufacturing method according to the embodiment is sintered to produce a silicon nitride sintered body for use in a ball. In this case, the silicon nitride sintered body has a high Vickers hardness of about 1400 or more and 1800 or less. In addition, the silicon nitride sintered body has a Vickers hardness of 5 MPa m １／２ 10MPa・m or more １／２ According to the embodiment, a silicon nitride sintered body having both a high toughness value and a high Vickers hardness can be obtained. The silicon nitride sintered body according to the embodiment has excellent wear resistance in terms of both a high toughness value and a high Vickers hardness.

[0085] As long as the manufacturing method according to the embodiment has the above-mentioned characteristics, the specific conditions can be set as appropriate. Here, an example of a method for manufacturing ball-shaped silicon nitride sintered bodies with a high yield (number of good products / number of manufactured products) will be described.

[0086] First, sintering aids, additives, solvents, binders, etc. are added to the silicon nitride powder as raw material and mixed. The mixture is then crushed and granulated using a spray dryer. These processes produce a granulated powder from the raw powder. The silicon nitride powder preferably accounts for 85% by mass or more of the silicon nitride powder and sintering aid powder, assuming a total of 100% by mass. The additives include plasticizers, etc. The solvent is water or an organic solvent. The solvent is an organic solvent such as alcohol, ketone, or benzene. The binder is a resin component such as paraffin or polyvinyl alcohol (PVA). The amount of binder added is preferably 3% by mass or more and 20% by mass or less, assuming a total of 100% by mass of the silicon nitride powder and sintering aid powder. Adjusting the amount of binder allows for adjustment of the shape retention and density uniformity of the compact. Furthermore, by forming the mixture into a granulated powder, the silicon nitride powder and sintering aid powder can be uniformly mixed.

[0087] Next, a molding step is performed to obtain a green body using the granulated powder. In the molding step, a die molding method, a rolling granulation method, or the like is used. Subsequently, a step of cold isostatic pressing (CIP) is performed on the green body. In the CIP treatment, isostatic pressure is applied to the green body to crush the granulated powder, thereby reducing density variation.

[0088] Next, a degreasing process is performed to degrease the compact after CIP. In this process, the compact is heated above the decomposition temperature of resin components such as binders to reduce the amount of resin components contained in the compact. For example, the CIP compact obtained in the CIP process is stored in a silicon nitride setter consisting of a bottom plate setter and a frame setter. The CIP compact placed in the setter is heated in a continuous furnace to obtain a degreased compact. For example, the degreasing conditions are set as follows: a heating rate of 100°C / hour, a holding temperature of 500°C, a holding time of 4.0 hours, and a cooling rate of 100°C / hour. In the continuous furnace 1, a nitrogen atmosphere is present near the entrance of the heating / cooling section 2. The atmosphere inside the heating / cooling section 2 is controlled so that the nitrogen degreasing is switched to air degreasing 1.2 hours after the compact enters the heating / cooling section 2.

[0089] Next, a sintering process is performed to sinter the degreased body. The sintering process is preferably performed in a nitrogen atmosphere at a temperature of 1700°C to 2000°C. The pressure during sintering is preferably set within a range of atmospheric pressure to 300 MPa. The atmospheric pressure is 0.10133 MPa (=1 atm). The sintered body obtained by the sintering process may be subjected to a hot isostatic pressing (HIP) process. When producing a ball-shaped silicon nitride sintered body, a ceramic sintered body with a theoretical density of 98% or more is produced.

[0090] Ceramic balls are manufactured by polishing ball-shaped silicon nitride sintered bodies. A typical example of ball polishing is surface plate processing. For example, a silicon nitride sintered ball is inserted between parallel surface plates. The movement of the polishing surface plate processes the sintered body for the ceramic ball into a perfect sphere. The surface roughness of bearing balls is specified in ASTM F2094. Depending on the application, a grade conforming to ASTM F2094, ISO 26602, or JIS R1669 is adopted for bearing balls. Bearing balls are polished to a surface roughness Ra conforming to that grade. Depending on the grade, mirror finishing may be performed to achieve a surface roughness Ra of 0.01 μm or less.

[0091] (Examples 1 to 11, Comparative Examples 1 to 8) As shown in Table 1, in Examples 1 to 9 and Comparative Examples 1 to 6, silicon nitride powder was prepared as the ceramic material. In Example 10 and Comparative Example 7, mullite was prepared as the ceramic material. In Example 11 and Comparative Example 8, aluminum nitride powder was prepared. In Table 1, silicon nitride powder is represented as SiN, and aluminum nitride powder is represented as AlN. The silicon nitride powder contains 85 mass% or more of silicon nitride, and the aluminum nitride powder contains 85 mass% or more of aluminum nitride.

[0092] In Examples 1 to 6 and Comparative Examples 1 to 4, ball-shaped ceramics were produced. First, sintering aids, additives, solvents, binders, etc. were added to the raw ceramic powder and mixed. The mixture was dried using a spray dryer to obtain granulated powder. The amount of binder added was set within the range of 3 to 15 mass%, assuming the total of the main components and sintering aids to be 100 mass%. The obtained granulated powder was press-molded into a ball shape with a band and an outer diameter of 8 to 20 mm, to obtain a pressed compact. Next, the pressed compact was subjected to CIP treatment.

[0093] In Examples 7 to 11 and Comparative Examples 5 to 8, sheet-shaped ceramics were produced. First, sintering aids, additives, solvents, binders, etc. were added to the raw ceramic powder and mixed. The mixture was formed into a sheet using a sheet forming machine. The sheet was punched using a die to obtain a sheet compact measuring 80 x 80 x 0.7 mm. The amount of binder added was set within the range of 10 to 25% by mass, assuming the total of the main components and sintering aids to be 100% by mass.

[0094] A setter made of silicon nitride, mullite, or aluminum nitride was prepared. The setter had a bottom plate setter and a frame setter. The bottom plate setter measured 100 x 100 x 5 mm. The frame setter was a rectangular tube with outer dimensions of 100 x 100 mm, inner dimensions of 90 x 90 mm, and a height of 50 mm.

[0095] In Examples 1 to 6 and Comparative Examples 1 to 4, ball-shaped press-molded bodies were stored inside a setter. Multiple press-molded bodies were stored up to about 90% of the setter's volume. Three setters were stacked during degreasing.

[0096] In Examples 7 to 13 and Comparative Examples 5 to 8, a sheet-like compact was stored inside a setter. Multiple compacts were stacked to fill approximately 90% of the setter's volume. During degreasing, two setters were stacked.

[0097] A belt-type continuous furnace was used for debinding. The setter was placed on the belt of the continuous furnace and passed through the furnace to debind the compact. The width of the belt was 25 cm. The heating rate, holding temperature, holding time, and cooling rate for debinding are shown in Table 1.

[0098]

[0099] In Table 1, the temperature conditions were measured using thermocouples. One thermocouple was inserted into the top of the upper setter. The other thermocouple was inserted into the bottom of the lower setter. The average value of the temperatures measured by the two thermocouples was used as the temperature of the molded body 5 to create a temperature profile. Based on the temperature profile, the heating rate, holding temperature, holding time, and cooling rate were measured.

[0100] The timing at which degreasing was switched from nitrogen degreasing to air degreasing is shown in Table 2. The exothermic reaction was identified from the temperature profile. The timing at which the temperature difference with respect to the holding temperature was maximum (timing Hc shown in Figure 4) was identified as the timing at which the exothermic reaction due to air degreasing occurred, and is listed in Table 2 as the "exothermic reaction timing." In addition, the maximum temperature difference among the temperatures measured by the two thermocouples was measured. The temperature integral value was calculated from the temperature profile. The results are listed in Table 2.

[0101]

[0102] In each example and comparative example, one degreased body was randomly selected, and the change in mass before and after degreasing (mass before degreasing - mass after degreasing) was calculated. The mass was measured using a precision balance. The mass loss rate (%) was calculated by dividing the change by the mass before degreasing and multiplying by 100, and the result is shown in Table 3.

[0103] In each example and comparative example, ten degreased bodies were randomly selected from the obtained plurality of degreased bodies. The surface brightness of each degreased body was measured based on the Munsell color system. The lowest brightness of the ten degreased bodies is shown in Table 3.

[0104] In each example and comparative example, 100 degreased bodies were randomly selected from the obtained plurality of degreased bodies. The degreased body yield in Table 3 was calculated by randomly selecting 100 degreased bodies under each condition, visually inspecting their appearance, and counting those with black discoloration as defective degreasing, thereby forming the defective rate.

[0105]

[0106] As can be seen from Table 3, in Examples 1 to 11, the surface brightness was within the preferred range and the defective rate of the degreased bodies was low. This is thought to be because the exothermic reaction due to air degreasing occurred during the temperature holding time H2, and the compacts were degreased well. By uniformly degreasing the compacts, the surface brightness was within the preferred range and the occurrence of defects could be suppressed.

[0107] In contrast, in Comparative Examples 1 to 8, the surface brightness of the degreased bodies was outside the preferred range, and the defective rate of the degreased bodies was high. This is thought to be because the timing of the exothermic reaction due to air degreasing occurred outside the temperature holding time H2, and degreasing by air degreasing was insufficient. In the Comparative Examples, it is thought that the resin components that adhered to the surface during nitrogen degreasing remained unburned, causing the surface to discolor.

[0108] The obtained degreased bodies were then subjected to a sintering treatment. The silicon nitride degreased body was sintered in a nitrogen gas atmosphere at 1750°C for 4 hours. The aluminum nitride degreased body was sintered in a nitrogen gas atmosphere at 1780°C for 3 hours. In the comparative example, the sintering of the insufficiently degreased molded body resulted in discoloration remaining on the surface, and a discolored sintered body was obtained.

[0109] As described above, under the conditions of the example, proper degreasing was performed using a continuous furnace, and a good yield was obtained. In contrast, under the conditions of the comparative example, proper degreasing was not performed, resulting in a low yield.

[0110] Embodiments of the present invention include the following features. (Feature 1) A method for producing a ceramic degreased body by heating and degreasing a ceramic formed body in a continuous furnace, wherein the continuous furnace includes: a heating section that heats the ceramic formed body; a holding section that maintains the temperature of the ceramic formed body; and a cooling section that cools the ceramic formed body, wherein the oxygen concentration in at least a portion of the heating section is lower than the oxygen concentration in at least a portion of the holding section, and an exothermic reaction caused by a change in oxygen concentration occurs in the ceramic formed body while the ceramic formed body passes through at least a portion of the holding section. (Feature 2) The method for producing a ceramic degreased body according to Feature 1, wherein the continuous furnace includes: a first area including at least a portion of the heating section and having an oxygen concentration of less than 5% by volume; and a second area including at least a portion of the holding section and having an oxygen concentration of 5% by volume or more. (Feature 3) The method for producing a ceramic degreased body according to Feature 2, wherein a first gas containing nitrogen is supplied to the first area, and a second gas containing oxygen is supplied to the second area. (Feature 4) The method for producing a ceramic degreased body according to Feature 2 or 3, wherein 0.5H1≦H≦H1+0.5H2 is satisfied, where H1 is a time from when the heating unit starts to heat the ceramic formed body to when the holding unit starts to maintain the temperature of the ceramic formed body, H2 is a time from when the holding unit starts to maintain the temperature of the ceramic formed body, and H is a time from when the heating unit starts to heat the ceramic formed body to when the ceramic formed body enters the second area. (Feature 5) The method for producing a ceramic degreased body according to any one of Features 1 to 4, wherein a difference between a first mass of the ceramic formed body before it enters the continuous furnace and a second mass of the ceramic degreased body after it has been heated in the continuous furnace is 1% or more and 35% or less of the first mass.(Feature 6) The method for producing a ceramic degreased body according to any one of Features 1 to 5, wherein a temperature profile is acquired while the ceramic molded body is passing through the continuous furnace, and when the horizontal axis represents time (h) and the vertical axis represents temperature (°C), the integrated value of time over temperature is 2500 to 6500. (Feature 7) The method for producing a ceramic degreased body according to any one of Features 1 to 6, wherein the ceramic molded body is stored in a setter and passes through the continuous furnace. (Feature 8) The method for producing a ceramic degreased body according to Feature 7, wherein the setter is primarily composed of any one of aluminum oxide, zirconium oxide, mullite, boron nitride, silicon nitride, aluminum nitride, and silicon carbide. (Feature 9) The method for producing a ceramic degreased body according to Feature 7 or 8, wherein a plurality of the ceramic molded bodies are stored in the setter. (Feature 10) The method for producing a ceramic degreased body according to Feature 9, wherein the maximum difference between the temperature of one or more of the ceramic formed bodies stored above the setter and the temperature of one or more of the ceramic formed bodies stored below the setter in the holding section is 80°C or less. (Feature 11) The method for producing a ceramic degreased body according to any one of Features 1 to 10, wherein, when the lightness of the surface hue of the produced ceramic degreased body is measured, it is V7 or more and V10 or less according to the Munsell color system standards. (Feature 12) The method for producing a ceramic degreased body according to any one of Features 1 to 11, wherein the main component of the produced ceramic degreased body is silicon nitride. (Feature 13) A method for producing a ceramic sintered body, comprising carrying out the method for producing a ceramic degreased body according to any one of Features 1 to 12, and sintering the ceramic degreased body to produce a ceramic sintered body.

[0111] Although several embodiments of the present invention have been illustrated, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. Modifications of these embodiments are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

[0112] DESCRIPTION OF SYMBOLS 1...Continuous furnace 2...Heating / cooling section 2a...Heater 3...Main body section 4...Belt section 5...Degreased body 6...Setter 61...Frame setter 62...Bottom plate setter 7...Thermocouple 10...Inlet section 11...Heating section 12...Holding section 13...Cooling section 14...Outlet section 21...First supply section 22...Second supply section 23...Curtain gas supply section 24...Exhaust section 25...Curtain gas supply section 26...Exhaust section 30...Ceramic substrate 31...Bearing ball 32...Bearing 33...Inner ring 34...Outer ring

Claims

1. A manufacturing method for producing a ceramic degreased body by heating and degreasing a ceramic green body in a continuous furnace, wherein the continuous furnace includes a heating part for heating the ceramic green body, a holding part for maintaining the temperature of the ceramic green body, and a cooling part for cooling the ceramic green body, and the oxygen concentration in at least a part of the heating part is lower than the oxygen concentration in at least a part of the holding part, and a heat generation reaction caused by a change in oxygen concentration is generated in the ceramic green body while the ceramic green body passes through at least a part of the holding part. A manufacturing method for a ceramic degreased body.

2. The continuous furnace includes a first area including at least a part of the heating part and having an oxygen concentration of less than 5% by volume, and a second area including at least a part of the holding part and having an oxygen concentration of 5% by volume or more. The manufacturing method for a ceramic degreased body according to claim 1.

3. A first gas containing nitrogen is supplied to the first area, and a second gas containing oxygen is supplied to the second area. The manufacturing method for a ceramic degreased body according to claim 2.

4. When the time from the start of the temperature rise of the ceramic green body by the heating part to the start of the temperature holding of the ceramic green body by the holding part is H1, the time from the start to the end of the temperature holding of the ceramic green body by the holding part is H2, and the time from the start of the temperature rise of the ceramic green body by the heating part to the time when the ceramic green body enters the second area is H, then 0.5H1 ≦ H ≦ H1 + 0.5H2 is satisfied. The manufacturing method for a ceramic degreased body according to claim 2 or 3.

5. The difference between the first mass of the ceramic green body before entering the continuous furnace and the second mass of the ceramic degreased body after being heated in the continuous furnace is 1% or more and 35% or less of the first mass. The manufacturing method for a ceramic degreased body according to claim 1 or 2.

6. When the temperature profile when the ceramic green body passes through the continuous furnace is obtained, with the horizontal axis being time (h) and the vertical axis being temperature (°C), the integral value of time with respect to temperature is 2500 or more and 6500 or less. The manufacturing method for a ceramic degreased body according to claim 1 or 2.

7. The method for manufacturing a ceramic degreased body according to claim 1 or 2, wherein the ceramic green body is stored in a setter and passes through the continuous furnace.

8. The method for manufacturing a ceramic degreased body according to claim 7, wherein the setter is mainly composed of any one of aluminum oxide, zirconium oxide, mullite, boron nitride, silicon nitride, aluminum nitride, or silicon carbide.

9. The method for manufacturing a ceramic degreased body according to claim 7, wherein a plurality of the ceramic green bodies are stored in the setter.

10. The method for manufacturing a ceramic degreased body according to claim 9, wherein in the holding part, the maximum value of the difference between the temperature of one or more of the ceramic green bodies stored in the upper part of the setter and the temperature of one or more of the ceramic green bodies stored in the lower part of the setter is 80°C or less.

11. The method for manufacturing a ceramic degreased body according to claim 1 or 2, wherein when the lightness of the surface hue of the manufactured ceramic degreased body is measured, it is V7 or more and V10 or less according to the Munsell color system standard.

12. The method for manufacturing a ceramic degreased body according to claim 1 or 2, wherein the main component of the ceramic degreased body to be manufactured is silicon nitride.

13. A method for manufacturing a ceramic sintered body, which executes the method for manufacturing a ceramic degreased body according to claim 1 or 2, and sinters the ceramic degreased body to manufacture a ceramic sintered body.

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