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

Abstract

A method for producing a ceramic molded body according to an embodiment of the present invention comprises a first preparation step, a second preparation step, a third preparation step, and a molding step. In the first preparation step, a first slurry is prepared by mixing a ceramic powder, a sintering aid powder, and a solvent. In the second preparation step, a second slurry containing a ceramic powder, a sintering aid powder, a binder, and a solvent is prepared. In the third preparation step, the first slurry and the second slurry are mixed to prepare a third slurry having a TI (Thixotropic Index) value smaller than that of the first slurry. In the molding step, the third slurry is used to mold a ceramic molded body.

Description

Method for manufacturing ceramic molded bodies and method for manufacturing ceramic sintered bodies

[0001] The embodiments described later generally relate to methods for manufacturing ceramic molded bodies and methods for manufacturing ceramic sintered bodies.

[0002] Ceramic sintered bodies come in various forms, including silicon nitride sintered bodies, aluminum nitride sintered bodies, aluminum oxide sintered bodies, and zirconium oxide sintered bodies. Their applications are diverse, including substrates for semiconductor devices and wear-resistant components. For example, Japanese Patent Publication No. 7472408 (Patent Document 1) discloses a bearing ball using a silicon nitride sintered body with controlled dissolved oxygen content. The bearing ball described in Patent Document 1 exhibits excellent durability even at high rotational speeds.

[0003] The manufacturing process for ceramic sintered bodies involves preparing a slurry by mixing raw material powders, forming a ceramic molded body, degreasing the ceramic molded body, and then sintering it. A slurry of raw material powders is used in the manufacturing of ceramic sintered bodies. For example, Japanese Patent Application Publication No. 2020-1968 (Patent Document 2) discloses a technology that includes a granulation step in the molding process in which the raw material powder slurry is granulated using a spray drying device. By using granulated powder in the molding process, the moldability of the ceramic molded body is improved. As in Patent Document 1, when manufacturing bearing balls, mold molding is used in the molding process. Mold molding involves filling upper and lower molds with raw material powder and applying pressure to form a ceramic molded body. By using granulated powder when performing mold molding, the moldability of the ceramic molded body is improved.

[0004] Japanese Patent Publication No. 7472408, Japanese Unexamined Patent Publication No. 2020-1968

[0005] In Patent Document 2, ceramic powder suspended in the spray dryer during the granulation process was recovered using a cyclone device. The recovered ceramic powder was then mixed in the granulation process. However, simply using the granulated powder mixed with the recovered ceramic powder sometimes resulted in variations in the moldability of the ceramic molded body. After investigating the cause, it was found that the problem lay in the slurry before it was granulated.

[0006] The embodiment addresses these issues and provides a method for manufacturing ceramic molded articles using a slurry that is good for the moldability of the ceramic molded articles.

[0007] The method for manufacturing a ceramic molded body according to this embodiment comprises a first preparation step, a second preparation step, a third preparation step, and a molding step. The first preparation step involves preparing a first slurry by mixing ceramic powder, sintering aid powder, and a solvent. The second preparation step involves preparing a second slurry containing ceramic powder, sintering aid powder, a binder, and a solvent. The third preparation step involves mixing the first slurry and the second slurry to prepare a third slurry with a Thixotropic Index (TI) value smaller than that of the first slurry. The molding step involves molding a ceramic molded body using the third slurry.

[0008] A flow diagram showing an example of a method for manufacturing a ceramic molded body according to the embodiment. A flow diagram showing an example of a method for manufacturing a ceramic sintered body according to the embodiment. An external view showing a first example of a ceramic molded body. An external view showing a second example of a ceramic molded body. An external view showing a third example of a ceramic molded body. An external view showing a first example of a ceramic sintered body. An external view showing a second example of a ceramic sintered body. An external view showing a third example of a ceramic sintered body. Embodiment

[0009] The following describes in detail embodiments of methods for manufacturing ceramic molded bodies and ceramic sintered bodies, with reference to the drawings.

[0010] The method for manufacturing a ceramic molded body according to this embodiment comprises a first preparation step, a second preparation step, a third preparation step, and a molding step. The first preparation step involves preparing a first slurry by mixing ceramic powder, sintering aid powder, and a solvent. The second preparation step involves preparing a second slurry containing ceramic powder, sintering aid powder, a binder, and a solvent. The third preparation step involves mixing the first slurry and the second slurry to prepare a third slurry with a TI value smaller than that of the first slurry. The molding step involves molding a ceramic molded body using the third slurry.

[0011] Figure 1 shows an example of a flow chart of a method for manufacturing a ceramic molded body according to an embodiment. Figures 3 to 5 show ceramic molded bodies 1 manufactured by the method for manufacturing ceramic molded bodies according to an embodiment. In the figures, reference numeral 1 indicates a ceramic molded body, reference numeral 11 indicates a ceramic molded body 1 that does not have a strip-shaped portion but has a spherical portion, reference numeral 12 indicates a ceramic molded body 1 that has a spherical portion A1 and a strip-shaped portion B1, and reference numeral 13 indicates a plate-shaped ceramic molded body 1.

[0012] The method for manufacturing the ceramic molded body 1 according to this embodiment includes a first preparation step ST1, a second preparation step ST2, a third preparation step ST3, and a molding step ST4, as shown in Figure 1. First, in the first preparation step ST1, a first slurry is prepared by mixing ceramic powder, sintering aid powder, and solvent.

[0013] In this specification, "ceramic powder" refers to the ceramic powder that serves as the base material (main material). The ceramic powder that serves as the base material refers to the powder corresponding to the component that is most abundant by mass in the ceramic sintered body. Examples of ceramic sintered bodies 2 (illustrated in Figures 6 to 8) include silicon nitride sintered bodies, aluminum nitride sintered bodies, aluminum oxide sintered bodies, and zirconium oxide sintered bodies. The base material of a silicon nitride sintered body is silicon nitride powder. The base material of an aluminum nitride sintered body is aluminum nitride powder. The base material of an aluminum oxide sintered body is aluminum oxide powder. The base material of a zirconium oxide sintered body is zirconium oxide powder.

[0014] Sintering aid powders improve the sinterability of ceramic powders. Examples of sintering aids include one or more compounds selected from rare earth elements, aluminum, calcium, magnesium, iron, zirconium, hafnium, niobium, tungsten, molybdenum, and silicon. Examples of compounds include oxides, carbides, nitrides, and composite compounds.

[0015] Examples of solvents include water, alcohol, and organic solvents. The solvent plays a role in mixing the ceramic powder and sintering aid powder to form a slurry.

[0016] The first slurry is a mixture of at least ceramic powder, sintering aid powder, and a solvent. It is preferable that no binder is added to the first slurry. The first slurry may contain a binder, but it is preferable that it does not contain a binder for adjusting the TI value, as will be described later. Furthermore, if the first slurry contains a binder, it is preferable that the binder content is lower than that of the second slurry.

[0017] Furthermore, it is preferable that no plasticizer is added to the first slurry. However, a dispersant may be added to the first slurry. The dispersant has the effect of preventing the aggregation of powder in the slurry. Examples of dispersants include surfactants, polyacrylates, polyethylene glycol derivatives, and phosphates. Plasticizers are added to give flexibility and elasticity to the ceramic molded body 1. Examples of plasticizers include glycerin and phthalate esters.

[0018] Next, in the second preparation step ST2, a second slurry containing ceramic powder, sintering aid powder, binder, and solvent is prepared. In the second preparation step ST2, it is not necessary to actively add binder when preparing the second slurry, as the binder is already contained in the recycled powder described later. Furthermore, the ceramic powder, sintering aid powder, and solvent contained in the second slurry are the same as those used in the first slurry. It is also preferable that the ceramic powder, sintering aid powder, and solvent used in the first slurry and the second slurry are the same.

[0019] The binder included in the second slurry is intended to provide shape retention for the ceramic molded body 1 and fluidity that allows it to deform under large external forces. Furthermore, the binder is preferably an organic binder. Since the organic binder is burned away in the degreasing process ST5 and the sintering process ST6 described later, it has little adverse effect on the quality of the ceramic sintered body 2. Examples of organic binders include polyvinyl alcohol resin, polyvinyl butyral resin, polyvinyl acetal resin, and acrylic resins.

[0020] A plasticizer may be added to the second slurry as needed. A dispersant may also be added to the second slurry as needed.

[0021] The difference between the first slurry and the second slurry is that the second slurry always contains a binder. Furthermore, the preparation of the first and second slurries shall include a grinding step as needed, and the slurries shall be broken down using a ball mill, bead mill, or the like. By breaking down the slurries, the TI value of each slurry can be controlled. Note that the order of the first preparation step ST1 and the second preparation step ST2 does not matter, and they may be performed simultaneously.

[0022] Next, in the third preparation step ST3, the first slurry and the second slurry are mixed to prepare the third slurry. The third preparation step ST3 may also include a crushing step using a ball mill or bead mill, if necessary. By performing the crushing step, the TI value of the third slurry can be controlled. In addition, in the third preparation step ST3, there may be cases where the first slurry or the second slurry is deficient in binder, so binder may be added as needed.

[0023] The TI value of the third slurry shall be smaller than the TI value of the first slurry. TI stands for Thixotropic Index. The TI value is an indicator of the variability of the slurry.

[0024] When the shear rate is continuously increased using a rotational viscometer, the viscosity generally decreases in fluids that exhibit cohesiveness. In this case, the ratio of the viscosity η1 at the first shear rate to the viscosity η2 at the second shear rate is the TI value. That is, the TI value is expressed by the following equation (1): TI value = η2 / η1 …(1)

[0025] In this embodiment, the first shear rate is set to 60 min －１ , the second shear rate is set to 6 min －１ This is the TI value at the first shear rate of 60 min. －１This refers to 60 rpm. This is because it is preferable to have a certain difference between the first shear rate and the second shear rate. Also, the second shear rate is 6 min. －１ This refers to 6 rpm. Furthermore, the sample volume should be between 50 ml and 400 ml. The closer the TI value is to 1, the closer it is to the behavior of a Newtonian fluid, meaning it is a highly dispersed slurry with no or very weak aggregation.

[0026] The fact that the TI value of the third slurry is lower than that of the first slurry indicates that the dispersibility has improved by controlling the mixing ratio (mass%) of the first and second slurries.

[0027] Next, in molding step ST4, the ceramic molded body 1 is molded using the third slurry. By using the third slurry, which has good dispersibility, the moldability of the ceramic molded body 1 is improved. Furthermore, when the total of the first slurry and the second slurry is 100% by mass, it is preferable that the second slurry is in the range of 5% by mass or more and 90% by mass or less. If the mixing ratio of the second slurry is less than 5% by mass, it may become difficult to control the TI value of the third slurry to 5 or less. Also, if the proportion of the second slurry exceeds 90% by mass, the effect of adding the first slurry may be insufficient. For this reason, when the total of the first slurry and the second slurry is 100% by mass, it is preferable that the mixing ratio of the second slurry is in the range of 5% by mass or more and 90% by mass or less, and more preferably 10% by mass or more and 85% by mass or less.

[0028] It is preferable that the TI value of the first slurry is 6 or higher, and the TI value of the third slurry is 5 or lower. Furthermore, it is preferable that the TI value of the second slurry is 5 or lower. This method involves mixing slurries with different TI values ​​to obtain a third slurry with good dispersibility. Using a first slurry with a TI value of 6 or higher indicates that some degree of aggregation is occurring.

[0029] The upper limit of the TI value of the first slurry is not particularly limited, but it is preferably 10 or less. If the TI value exceeds 10, the cohesiveness becomes too high, which may make it difficult to control the TI value of the third slurry to 5 or less. Therefore, the TI value of the first slurry is preferably in the range of 6 to 10, and more preferably in the range of 6 to 9. In addition, the viscosity of the first slurry, when measured at 60 rpm, is preferably in the range of 70 cps to 5000 cps, and more preferably in the range of 100 cps to 500 cps.

[0030] The lower limit of the TI value of the third slurry is not particularly limited, but it is preferably 2 or higher. If the TI value is less than 2, the cohesiveness is low, which may increase manufacturing time and costs. For example, if the cohesiveness is too low, the amount of ceramic powder in the slurry may be too small. In this case, the number of times the slurry needs to be filled into the mold will increase. This may lead to an increase in manufacturing time and costs. For this reason, the TI value of the third slurry is preferably in the range of 2 to 5. In addition, the viscosity of the third slurry is preferably in the range of 30 cps to 300 cps when measured at 60 rpm.

[0031] As mentioned above, it is preferable not to add a binder to the first slurry. By not adding a binder to the first slurry, aggregation of ceramic powders becomes easier, making it easier to control the TI value to 6 or higher. Similarly, it is preferable not to add a plasticizer to the first slurry.

[0032] In molding process ST4, a ceramic molded body 1 is manufactured by a combination of mold forming, cold isostatic pressing (CIP), rolling granulation, extrusion molding, doctor blade method, and multiple molding methods.

[0033] Mold molding is a method of forming a ceramic molded body 1 using a mold. For example, it is formed by applying pressure with upper and lower molds. CIP is a method of forming a ceramic molded body 1 by applying isotropic pressure using water pressure. For example, CIP is formed using a rubber mold. Rolling granulation is a method of forming a ceramic molded body 1 by rolling a core material and attaching ceramic powder to its periphery. Extrusion molding is a method of forming a ceramic molded body 1 by pouring a slurry into a mold, applying pressure, and pushing it out from the exit of the mold. The doctor blade method is a type of method of forming into a sheet. In the doctor blade method, the thickness of the slip carried on the carrier can be controlled by adjusting the distance between the knife edge (doctor blade) and the carrier. When producing ceramic sintered bodies 21 and 22 for bearing balls (shown in Figures 6 and 7), mold molding, CIP, or rolling granulation is used to produce ceramic molded bodies 11 and 12 (shown in Figures 3 and 4). When producing a plate-shaped ceramic sintered body 23 (shown in Figure 8) for semiconductor devices, a ceramic molded body 13 (shown in Figure 5) is produced using extrusion molding or a doctor blade method.

[0034] Furthermore, the molding process ST4 preferably includes a granulation process ST41. Granulation refers to the process of forming raw materials such as slurry into granular material. Methods for producing granulated powder include methods using a spray drying apparatus. A spray drying apparatus can produce granular material by spraying slurry into a high-temperature airflow and rapidly drying it. Examples of spraying methods include rotary atomization and spray nozzle. Furthermore, the average particle size of the granulated powder is preferably within the range of 50 μm to less than 150 μm. When the average particle size of the granulated powder is within this range, the manufacturing efficiency and moldability of the ceramic molded body 1 can be improved.

[0035] The molding method using granulated powder is suitable for the above-mentioned mold molding, CIP, or rolling granulation. In mold molding, granulated powder is filled into a mold and pressurized to obtain a molded body. In CIP, granulated powder is filled into a rubber mold and pressurized to obtain a molded body. Rolling granulation can be performed using granulated powder as a core material. In addition, in CIP, a molded body obtained by other methods may be filled into a rubber mold. For example, when producing a ceramic sintered body 21 for bearing balls (shown in Figure 6), a method of CIP treatment may be used for a ceramic molded body 11 (shown in Figure 3) obtained by mold molding.

[0036] Furthermore, the second slurry obtained in the n+1 (where n is an integer greater than or equal to 1) second preparation step ST2 is a slurry obtained from material that was obtained in the molding step ST4 prior to the nth step and is not sent to the next degreasing step ST5. For example, it is preferable that the second slurry be prepared from ceramic powder and sintering aid powder (which may also include a binder and solvent) produced by returning the ceramic molded bodies 1 that were determined to be defective from among the multiple ceramic molded bodies 1 produced in the molding step ST4. Alternatively, the second slurry may be prepared from ceramic powder and sintering aid powder (which may also include a binder and solvent) produced by returning powder that did not become ceramic molded bodies 1 or defective molded bodies in the molding step ST4.

[0037] Furthermore, the second slurry may be prepared again from the powder obtained by drying the slurry that was prepared once. As will be described later, when the third slurry is recovered from the spray-drying apparatus, it is recovered as a powder by drying. For this reason, the second slurry may be prepared from the powder obtained from the recovered third slurry.

[0038] Therefore, in the n-th shaping step ST4 after the n-th second preparation step ST2, a spray dryer is used when producing the granulated powder. In the subsequent (n + 1)-th second preparation step ST2, the second slurry can also be prepared from the ceramic powder and the sintering aid powder produced by returning the powder recovered from the wall surface in the spray dryer in the shaping step ST4 before the n-th time and dried. Note that at least one of the powder obtained by drying the third slurry recovered from the spray dryer (and the cyclone device) and the powder obtained by pulverizing the defective ceramic compact described later is referred to as recycled powder.

[0039] Examples of the recycled powder include the powder after a defective ceramic compact that did not become the ceramic compact 1 is pulverized. The defective ceramic compact 1 is one of the plurality of ceramic compacts 1 formed in the shaping step ST4 in which shape defects such as cracks and chips have occurred. The recycled powder may also be generated in the granulation step ST41. For example, it may be a powder formed by drying the third slurry adhering to the wall surface in the spray dryer when producing the granulated powder using the spray dryer. Since the dried product of the third slurry adhering to the wall surface and the powder obtained by the cyclone device at the subsequent stage of the spray dryer are not put into the shaping step for shaping into a form matching the predetermined sintered body shape, at least one of them corresponds to the powder that did not become the ceramic compact 1. The cyclone device can also obtain the powder by sucking the gas in the spray dryer. Further, the shaping step ST4 can also use the granulated powder obtained in the granulation step ST41.

[0040] In the second slurry, recycled powder can be reused, that is, powder produced by crushing defective ceramic molded bodies 1 that were rejected in the previous process, or powder that did not become ceramic molded bodies 1 (powder obtained by drying the third slurry). In other words, defective ceramic molded bodies and the third slurry that did not become ceramic molded bodies 1 are powdered and returned to the slurry to be used as the second slurry (the (n+1)th second slurry). This reduces waste material. At least the ceramic powder and sintering aid powder (which may also include binders and solvents) can be reused, thus improving the efficiency of material use.

[0041] Furthermore, in the second preparation step ST2, as the (n+1)th second slurry, new ceramic powder, sintering aid powder, binder, solvent, etc., may be added as needed to the reused powder generated before the nth time. In particular, it is effective to adjust the ratio of ceramic powder to sintering aid powder in the second preparation step ST2 to the desired ratio. Also, since the reused powder can be generated before the nth time, it may be used after accumulating several batches. According to the method for manufacturing ceramic molded bodies 1 and ceramic sintered bodies 2 of the embodiment, even if reuse is repeated, it is possible to suppress variations between multiple ceramic molded bodies 1 and multiple ceramic sintered bodies 2.

[0042] Furthermore, it is desirable that the main component of the ceramic powder used in the first slurry and the second slurry be of the same type, and preferably one selected from silicon nitride, aluminum nitride, aluminum oxide, and zirconium oxide. In addition, the average particle size of the ceramic powder is preferably 3 μm or less.

[0043] It is preferable to use two or more types of sintering aids as the first slurry and the second slurry. Examples of the sintering aid include one or more compounds selected from rare earth elements, aluminum, calcium, magnesium, iron, zirconium, hafnium, niobium, tungsten, molybdenum, and silicon. Examples of the compound include oxides, carbides, nitrides, and composite compounds. Further, the average particle size of the sintering aid powder is preferably 3 μm or less. When the total of the ceramic powder and the sintering aid powder is 100% by mass, the sintering aid powder is preferably in the range of 1% by mass to 20% by mass. Further, the sinterability of the ceramic sintered body 2 can be improved by using two or more types of sintering aids. For example, in Patent Document 1, three to four types of sintering aids such as Y ２ O ３ , Al ２ O ３ , TiO ２ are used. By improving the formability of the ceramic molded body 1 using two or more types of sintering aids, the yield can be improved. Further, by using recycled powder, cost advantages and the effect of suppressing waste materials can be obtained.

[0044] Further, the ceramic sintered body 2 can be produced using the obtained ceramic molded body 1. The manufacturing method of the ceramic sintered body 2 shown in FIG. 2 includes a degreasing step ST5 of degreasing the good-quality ceramic molded body 1 (untreated molded body) among the ceramic molded bodies 1 obtained in the molding step ST4 of the manufacturing method of the ceramic molded body 1 shown in FIG. 1 to generate a degreased ceramic molded body 1 (degreased body), and a sintering step ST6 of sintering the degreased body to generate the ceramic sintered body 2.

[0045] In the degreasing step ST5, it is preferable to perform the degreasing treatment of the untreated molded body within the range of 300°C or higher and 700°C or lower. The degreasing by the degreasing step ST5 is carried out in the air or a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include nitrogen and argon. By performing the degreasing step ST5, the binder in the degreased body can be burned out, and the solvent in the degreased body can also be removed. By performing the degreasing step ST5, a degreased body can be obtained.

[0046] Next, in the sintering step ST6, the degreased body is sintered. The sintering in the sintering step ST6 is preferably carried out within the range of 1600°C to 1950°C. The sintering in the sintering step ST6 may be either atmospheric pressure sintering or pressure sintering. Examples of pressure sintering include atmospheric pressurization, hot pressing, and hot isostatic pressing (HIP). The sintering step ST6 is carried out in an environment such as air, a non-oxidizing atmosphere, or a vacuum. Examples of non-oxidizing atmospheres include a nitrogen atmosphere or an argon atmosphere. Furthermore, the sintering step ST6 may be a combination of multiple sintering steps. For example, HIP may be performed after atmospheric pressure sintering.

[0047] A ceramic sintered body 2 can be obtained by performing sintering in the sintering process ST6. Figures 6 to 8 show examples of ceramic sintered bodies 2. In the figures, reference numeral 2 denotes a ceramic sintered body, reference numeral 21 denotes a ceramic sintered body 2 that does not have a strip-shaped portion but has a spherical portion, reference numeral 22 denotes a ceramic sintered body 2 that has a spherical portion A2 and a strip-shaped portion B2, and reference numeral 23 denotes a plate-shaped ceramic sintered body 2. Ceramic sintered body 21 is obtained by sintering the ceramic molded body 11 in Figure 3, ceramic sintered body 22 is obtained by sintering the ceramic molded body 12 in Figure 4, and ceramic sintered body 23 is obtained by sintering the ceramic molded body 13 in Figure 5.

[0048] Figure 6 shows a ceramic sintered body 21 having a spherical portion but no strip-shaped portion. The ceramic sintered body 21 is used for bearing balls and the like. Figure 7 shows a ceramic sintered body 22 having a spherical portion A2 and a strip-shaped portion B2 on the circumference of the spherical portion A2. The ceramic sintered body 22 is sometimes called a bearing ball prototype. A bearing ball prototype is a ceramic sintered body before it is polished to form a spherical shape. Figure 8 shows a plate-shaped ceramic sintered body 23. The ceramic sintered body 23 is sometimes called a ceramic substrate. A circuit portion can be formed on the ceramic substrate to create a ceramic circuit board.

[0049] The ceramic sintered body 2 is not limited to bearing balls as ceramic sintered body 21, bearing ball spheres as ceramic sintered body 22, or ceramic substrates as ceramic sintered body 23. The ceramic sintered body 2 can be applied to a variety of things such as rollers, friction stir welding tool members, check balls, and engine parts. Furthermore, polishing or other processing may be applied to the ceramic sintered body 2 as needed.

[0050] The method for manufacturing the ceramic molded body 1 according to this embodiment improves the moldability of the ceramic molded body 1. This suppresses the occurrence of defects such as cracks and chips in the ceramic molded body 1. Furthermore, the uniformity of the dispersion state of the ceramic powder and sintering aid powder is also good. Therefore, weight variation when producing multiple ceramic molded bodies 1 can be suppressed. For example, when 100 ceramic molded bodies 1 are produced, the average weight AW of the ceramic molded bodies 1 and the weight AD, which is furthest from the average weight AW, can be used to calculate the weight variation V (%) from the following formula (2): V (%) = (|AW - AD| / AW) × 100 … (2)

[0051] With the manufacturing method of the ceramic molded body 1 according to this embodiment, the weight variation V can be reduced to 5% or less. Furthermore, good moldability is achieved even when recycled powder is used. This makes it possible to suppress the generation of waste materials.

[0052] (Examples) (Examples 1-3, Comparative Examples 1-2) The ceramic powder and sintering aid powder shown in Table 1 were prepared. Both the ceramic powder and sintering aid powder had an average particle size of 3 μm or less. The mass percentages in Table 1 represent the total of the ceramic powder and sintering aid powder as 100% by mass.

[0053]

[0054] Next, a first slurry was prepared in the first preparation step ST1, and a second slurry was prepared in the second preparation step ST2. The first slurry was a mixture of ceramic powder, sintering aid powder, and solvent. The second slurry was a mixture of ceramic powder, sintering aid powder, binder, and solvent.

[0055] Next, in the third preparation step ST3, the first slurry and the second slurry were mixed to prepare a third slurry. The mixing ratio (mass%) of the first slurry and the second slurry relative to the total, and the TI values ​​of each slurry are shown in Table 2. The method for measuring the TI values ​​is as described above.

[0056]

[0057] In Examples 1 to 3, the TI value of the first slurry was 6 to 8, and the TI value of the second slurry was 2 to 5. Furthermore, the viscosity of the first slurry at 60 rpm was in the range of 70 cps to 400 cps. Also, when the sum of the first and second slurries was 100% by mass, the mixing ratio of the second slurry was in the range of 10% by mass to 80% by mass. In Examples 1 to 3, the TI value of the third slurry was 5 or less. Also, in Examples 1 to 3, the TI value of the third slurry was in the range of 2 to 5.

[0058] Comparative Example 1 was obtained without mixing the first slurry. In other words, in Comparative Example 1, the second slurry became the third slurry. In Comparative Example 2, the TI value of the third slurry was greater than the TI of the first slurry.

[0059] Next, granulated powder was prepared using the third slurry. The granulated powder was prepared using a spray-drying apparatus. The average particle size of the granulated powder was set to be between 50 μm and less than 150 μm. Mold molding was performed using the obtained granulated powder. The ceramic molded body 1 is a ceramic molded body 12 for producing a ceramic sintered body 22 for bearing balls having a band-shaped portion B2 on the circumference of a spherical portion A2 as shown in Figure 7. The ceramic molded body 12 was also used for producing preliminary balls to obtain bearing balls with diameters of 9.5250 mm (3 / 8 inch) and 28.5750 mm (1 1 / 8 inch).

[0060] To evaluate the moldability of the ceramic molded body 12, the defect rate D (%) and weight variation V (%) of the ceramic molded body 12 were measured. The defect rate D (%) was measured as the percentage of defects when 1000 ceramic molded bodies 12 were produced. A defect was defined as a crack or chip that could be visually confirmed in appearance. The weight variation V (%) was calculated using formula (2) above, by selecting 100 good ceramic molded bodies and using the average weight AW and the weight AD that was furthest from the average weight AW. The measurement results of the weight variation V (%) are shown in Table 3.

[0061]

[0062] As can be seen from Table 3, in Examples 1 to 3, the defect rate D (%) and weight variation V (%) of the ceramic molded body 1 were low, indicating improvement. Furthermore, in Examples 1 to 3, it was found that the effect could be obtained even when the size of the ceramic molded body 12 was changed.

[0063] In contrast, in both Comparative Examples 1 and 2, the effects of the defect rate D (%) and weight variation V (%) decreased. It was found that the method of not mixing the first slurry and the second slurry, as in Comparative Example 1, resulted in insufficient slurry uniformity. It was also found that the slurry uniformity was insufficient when the TI value of the first slurry was not greater than the TI value of the third slurry, as in Comparative Example 2. In particular, it was found that weight variation was more likely to occur in slurries made of materials with low TI values.

[0064] (Examples 4-6, Comparative Examples 3-4) Next, in Examples 4-6 and Comparative Examples 3 and 4, the recycled powder was reused and used in the second slurry. The recycled powder consisted of powder produced by crushing defective ceramic molded bodies and powder produced by drying the third slurry that adhered to the walls inside the spray dryer (in the examples, powder recovered by the cyclone device was not added). In other words, the second slurry was prepared using recycled powder. In each case, the n+1th second slurry was prepared using the nth recycled powder. The conditions are shown in Table 4. In the third preparation step ST3, a binder was added to the third slurry as needed to adjust the TI value.

[0065]

[0066] In Examples 4 to 6, the TI value of the first slurry was set to 6 to 8, and the TI value of the (n+1)th second slurry was set to 2 to 5. The viscosity of the first slurry at 60 rpm was in the range of 70 cps to 400 cps. When the sum of the first and second slurries was 100% by mass, the mixing ratio of the (n+1)th second slurry was in the range of 10% by mass to 90% by mass. In Examples 4 to 6, the TI value of the (n+1)th second slurry was 5 or less. In Examples 4 to 6, the TI value of the third slurry was in the range of 2 to 5.

[0067] Next, granulated powder was prepared using a third slurry. The granulated powder was prepared using a spray-drying apparatus. Mold molding was performed using the obtained granulated powder. The ceramic molded body 1 is a ceramic molded body 12 for producing a ceramic sintered body 22 for bearing balls having a band-shaped portion B2 on the circumference of a spherical portion A2 as shown in Figure 7. The ceramic molded body 12 was also used for producing preliminary balls to obtain bearing balls with diameters of 9.5250 mm (3 / 8 inch) and 28.5750 mm (1 1 / 8 inch). Similar to Example 1, the defect rate (%) and weight variation (%) of the ceramic molded body 12 were measured. The results are shown in Table 5.

[0068]

[0069] As can be seen from Table 5, in Examples 4 to 6, even when recycled powder was used, the defect rate (%) and weight variation (%) of the ceramic molded body 12 were reduced. Therefore, it was found that the manufacturing methods for the ceramic molded body 12 in Examples 4 to 6 can be used with recycled powder. In contrast, in Comparative Examples 3 and 4, no improvement was observed even when recycled powder was used.

[0070] Furthermore, the ceramic molded bodies 12 that were good products in Examples 1 to 6 were subjected to a degreasing process and a sintering process to obtain ceramic sintered bodies 22. In the sintering process ST6, atmospheric pressure sintering was performed, followed by HIP (High-Intensity Plating). The obtained ceramic sintered bodies 22 are ceramic sintered bodies 22 for bearing balls having a band-shaped portion B2 on the circumference of a spherical portion A2. These ceramic sintered bodies 22 were polished to obtain bearing balls. The wear resistance of the obtained bearing balls was good.

[0071] According to at least one embodiment described above, a slurry with good moldability for ceramic molded articles can be provided.

[0072] Although several embodiments of the present invention have been illustrated above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Modifications of these embodiments are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. Furthermore, the embodiments described above can be implemented in combination with each other.

Claims

1. A method for manufacturing a ceramic molded body, comprising: a first preparation step of preparing a first slurry by mixing ceramic powder, sintering aid powder, and a solvent; a second preparation step of preparing a second slurry containing ceramic powder, sintering aid powder, a binder, and a solvent; a third preparation step of mixing the first slurry and the second slurry to prepare a third slurry with a Thixotropic Index (TI) value smaller than that of the first slurry; and a molding step of molding a ceramic molded body using the third slurry.

2. The method for manufacturing a ceramic molded article according to claim 1, characterized in that the TI value of the first slurry is 6 or more, and the TI value of the third slurry is 5 or less.

3. The method for manufacturing a ceramic molded article according to claim 1 or 2, characterized in that the second preparation step does not involve the active addition of the binder during the preparation of the second slurry.

4. The method for manufacturing a ceramic molded body according to claim 1 or 2, characterized in that the molding step includes a granulation step of granulating powder using the third slurry, and the ceramic molded body is molded using the granulated powder obtained in the granulation step.

5. The method for manufacturing a ceramic molded body according to claim 3, wherein the molding step includes a granulation step of granulating powder using the third slurry, and the ceramic molded body is molded using the granulated powder obtained in the granulation step.

6. The method for producing a ceramic molded body according to claim 1 or 2, characterized in that the n (where n is an integer of 1 or more) + 1th second preparation step is to prepare the second slurry from ceramic powder and sintering aid powder produced by returning a plurality of ceramic molded bodies that were determined to be defective from among the molded bodies produced in the molding steps prior to the nth step.

7. The method for producing a ceramic molded body according to claim 5, characterized in that the (n+1)th second preparation step is to prepare the second slurry from ceramic powder and sintering aid powder produced by returning a ceramic molded body that was determined to be defective from among a plurality of ceramic molded bodies produced in the molding steps prior to the nth step.

8. The method for manufacturing a ceramic molded body according to claim 1 or 2, characterized in that the first preparation step and the second preparation step prepare a slurry using two or more types of sintering aid powders.

9. The method for producing a ceramic molded article according to claim 7, characterized in that the first preparation step and the second preparation step prepare a slurry using two or more types of sintering aid powders.

10. The method for producing a ceramic molded article according to claim 1 or 2, characterized in that the ceramic powder is one selected from silicon nitride, aluminum nitride, aluminum oxide, and zirconium oxide.

11. The method for producing a ceramic molded article according to claim 9, characterized in that the ceramic powder is one selected from silicon nitride, aluminum nitride, aluminum oxide, and zirconium oxide.

12. The method for manufacturing a ceramic molded body according to claim 5, characterized in that the molding step uses a spray drying device when producing the granulated powder, and the (n+1)th second preparation step prepares the second slurry from ceramic powder and sintering aid powder generated by returning the powder recovered from the wall surface inside the spray drying device in the molding steps prior to the nth step.

13. The method for manufacturing a ceramic molded body according to 11, characterized in that the molding step uses a spray drying device when producing the granulated powder, and the (n+1)th second preparation step prepares the second slurry from ceramic powder and sintering aid powder generated by returning the powder recovered from the wall surface inside the spray drying device in the molding steps prior to the nth step.

14. The method for producing a ceramic molded article according to claim 1 or 2, characterized in that the third preparation step involves mixing the first slurry with the second slurry, and the mixing ratio of the second slurry is within the range of 5% by mass or more and 90% by mass or less.

15. The method for manufacturing a ceramic molded article according to claim 1 or 2, characterized in that the first preparation step and the second preparation step each include a grinding step, and the slurry is disintegrated using a ball mill or a bead mill.

16. The method for producing a ceramic molded article according to claim 1 or 2, characterized in that the third preparation step involves mixing the first slurry with the second slurry whose TI value is smaller than that of the first slurry.

17. A method for manufacturing a ceramic sintered body, comprising: a degreasing step of degreasing the ceramic molded body obtained by the method for manufacturing a ceramic molded body according to claim 1 or claim 2; and a sintering step of sintering the ceramic molded body after degreasing in the degreasing step.

18. A method for manufacturing a ceramic sintered body, comprising: a degreasing step of degreasing the ceramic molded body obtained by the method for manufacturing a ceramic molded body described in claim 13; and a sintering step of sintering the ceramic molded body after degreasing in the degreasing step.

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