Ceramic items

Abstract

According to the present invention, a ceramic article having good properties is obtained. A method for molding a ceramic material comprises: a step for mixing a ceramic powder, a sintering aid, a resin, a curing agent, and a solvent to prepare a ceramic casting liquid that becomes a ceramic material; a step for injecting the ceramic casting liquid into a mold which can be dissolved in a non-aqueous solvent and inside which a cavity is formed; a step for forming a cured body having a desired shape by curing the resin in the ceramic casting liquid that has been injected into the mold; and a step for dissolving the mold in a non-aqueous solvent to release the cured body. The mold is formed from a soluble resin which can be dissolved in a non-aqueous solvent, and has an elastic modulus of 500 [MPa] to 5,000 [MPa] and a thermal conductivity of 0.05 [W / mK] to 0.40 [W / mK].

Description

[Technical Field]

[0001] The present invention relates to ceramic articles, methods for forming ceramic materials, methods for manufacturing ceramic articles, and forming tools. [Background technology]

[0002] Ceramic articles can be formed using various molding methods such as injection molding, slip casting, extrusion molding, and gel casting, allowing ceramic articles to be produced in a variety of shapes.

[0003] In molding ceramic articles, a mold is used to form the desired product shape. For example, Patent Document 1 describes a mold that melts with heated water when demolding, and Patent Documents 2 and 3 describe molds made of polystyrene foam that are dissolved with a solvent when demolding. By melting or dissolving the mold to demold in this way, it is possible to demold the molded body without applying stress to it, and damage to the molded body when demolding can be suppressed.

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-34572 [Patent Document 2] Patent No. 5146010 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-228424 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a need to obtain ceramic articles with good properties.

[0006] One aspect of the present invention has been made in consideration of the above-mentioned problems, and aims to provide a ceramic article with good properties by appropriately forming a molded body, a method for forming a ceramic material that can obtain a ceramic article with good properties, a method for manufacturing a ceramic article, and a molding die. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the objectives, the ceramic article of the present disclosure is a spherical ceramic article that is a sintered ceramic body, and has a recess on its surface that runs along the circumferential direction, and the recess has a depth of 1% or less of the diameter of the ceramic article.

[0008] In order to solve the above-mentioned problems and achieve the object, the method for molding a ceramic material according to the present disclosure includes the steps of: mixing a ceramic powder, a sintering aid, a resin, a curing agent, and a solvent to prepare a ceramic casting liquid that will become a ceramic material; pouring the ceramic casting liquid into a mold that is soluble in a non-aqueous solvent and has an internal cavity; curing the resin in the ceramic casting liquid poured into the mold to form a hardened body having a desired shape; and dissolving the mold in the non-aqueous solvent to demold the hardened body, wherein the mold is formed from a soluble resin that is soluble in the non-aqueous solvent and has an elastic modulus of 500 [MPa] to 5000 [MPa] and a thermal conductivity of 0.05 [W / mK] to 0.40 [W / mK].

[0009] In order to solve the above-mentioned problems and achieve the objectives, the method for manufacturing a ceramic article according to the present disclosure includes the steps of drying the hardened body obtained by the ceramic material molding method to form a molded body, degreasing the molded body to form a degreased body, and firing the degreased body to form a sintered body.

[0010] In order to solve the above-mentioned problems and achieve the object, the molding die of the present disclosure contains a soluble resin that dissolves in a non-aqueous solvent, has a cavity inside which a ceramic material is filled to obtain a hardened body of a desired shape, and has an elastic modulus of 500 [MPa] to 5000 [MPa] and a thermal conductivity of 0.05 [W / mK] to 0.40 [W / mK]. [Effects of the Invention]

[0011] According to one aspect of the present invention, a ceramic article with good properties can be obtained. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a molding die according to this embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of the molding die according to this embodiment. [Figure 3] FIG. 3 is a partially enlarged view of FIG. [Figure 4] FIG. 4 is a flowchart illustrating the method for molding a ceramic material according to this embodiment. [Figure 5] FIG. 5 is a diagram illustrating the steps for obtaining a hardened body in a desired shape. [Figure 6] FIG. 6 is a flowchart illustrating a method for manufacturing a ceramic article according to this embodiment. [Figure 7] FIG. 7 is a schematic diagram of a ceramic article according to this embodiment. [Figure 8] FIG. 8 is a diagram schematically showing a CT image of the ceramic article according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments, and when there are multiple embodiments, the present invention also includes configurations that are made by combining the respective embodiments. Furthermore, numerical values ​​include the range of rounding.

[0014] (molding mold) Fig. 1 is a schematic diagram of a molding die according to this embodiment. Fig. 2 is a schematic cross-sectional view of the molding die according to this embodiment. As shown in Fig. 2, molding die 10 according to this embodiment is a mold having a cavity (space) C formed therein, into which a ceramic material is filled to obtain a hardened body of a desired shape. Molding die 10 is formed from a soluble resin, and can be said to have a shape in which cavity C is covered with a mold made of the soluble resin.

[0015] (Mold characteristics) The mold 10 is soluble in a non-aqueous solvent. In other words, the soluble resin used in the mold 10 is a resin that dissolves in a non-aqueous solvent. Non-aqueous solvents will be described later. The dissolution rate of the mold 10 in a non-aqueous solvent is preferably 1 μm / min to 80 μm / min, more preferably 5 μm / min to 30 μm / min, and even more preferably 6 μm / min to 15 μm / min. A dissolution rate within this range allows the mold 10 to be appropriately dissolved and demolded. The dissolution rate of the mold 10 refers to the thickness (μm) of the mold 10 that dissolves divided by time. The dissolution rate of the mold 10 can be measured by any method, but may be measured by the following method. A ceramic material is hardened in a mold 10 having a thickness of 1.6 mm, and the mold 10 is immersed in methylene chloride at a temperature of 25°C. The time it takes for casting mold 10 to completely dissolve is measured and taken as the dissolution time, and the value obtained by dividing 1.6 mm by the dissolution time is taken as the dissolution rate. Note that a numerical range expressed with "to" means a numerical range that includes the numbers before and after "to" as the lower and upper limits, and the same meaning will be used hereinafter when "to" is used.

[0016] It is preferable that molding die 10 does not melt when heated during hardening of the ceramic material in cavity C. The melting point of molding die 10 is preferably 70°C or higher, and may be 80°C to 250°C, or 100°C to 230°C. The melting point of molding die 10 may also be 100°C or higher, 120°C to 250°C, or 150°C to 230°C. When the melting point of molding die 10 is within this range, melting of molding die 10 during molding is suppressed, and a hardened body of the desired shape can be appropriately obtained.

[0017] The molding die 10 has a modulus of elasticity of 500 MPa to 5000 MPa, preferably 700 MPa to 4000 MPa, and more preferably 1100 MPa to 2600 MPa. The modulus of elasticity here refers to the tensile modulus of elasticity, i.e., Young's modulus, and may refer to a value under conditions of, for example, 23°C and 0%°C relative humidity. The molding die 10 also has a tensile strength of preferably 500 MPa to 5000 MPa, more preferably 1000 MPa to 3000 MPa. The tensile strength here may refer to a value under conditions of, for example, 23°C and 0%°C relative humidity. By setting the modulus of elasticity and tensile strength of the molding die 10 within these ranges, the molding die 10 is able to stably maintain the shape of the molding material until it hardens (gels) without deforming to the extent that it would allow the molded article to have the desired shape. Tensile strength and tensile modulus can be measured according to ISO 527-1 and ISO 527-2.

[0018] The thermal conductivity of the forming mold 10 is 0.05 [W / mK] to 0.40 [W / mK], preferably 0.08 [W / mK] to 0.30 [W / mK], and more preferably 0.1 [W / mK] to 0.2 [W / mK]. When the thermal conductivity is within this range, heat can be appropriately transferred to the ceramic material in the cavity C during the curing step, allowing the ceramic material to be appropriately cured. The thermal conductivity can be measured, for example, according to JIS A1412-2.

[0019] The soluble resin used in mold 10 is preferably primarily composed of at least one material selected from the group consisting of polystyrene, ABS (Acrylonitrile-Butadiene-Styrene) resin, acrylic resin, polycarbonate, epoxy resin, and polyester. Furthermore, the soluble resin used in mold 10 is more preferably primarily composed of polystyrene. An example of polystyrene is Toyo Styrol's high-impact polystyrene H350. By using such a material as the soluble resin used in mold 10, the above-described properties can be appropriately imparted to mold 10. Here, "primary component" refers to, for example, a material that accounts for 50% or more, preferably 80% or more, and more preferably 95% or more, by mass, of the entire mold 10.

[0020] It is preferable that the inner surface of the mold 10 is free from a coating of components other than the soluble resin. That is, it is preferable that the soluble resin on the inner surface of the mold 10 is not completely covered by a coating of other components, and that the soluble resin is exposed in at least a portion of the inner surface, and it is preferable that the soluble resin is exposed over the entire inner surface. If a coating of components other than the soluble resin is present on the inner surface of the mold 10, it may remain undissolved when the soluble resin, which is the main component, is dissolved, and the coating may need to be removed in a separate process. Therefore, it is preferable that no coating or only a small amount of coating is present, as this improves productivity. Furthermore, if the coating is a component unnecessary for the final ceramic material, it is preferable that it does not remain.

[0021] (shape of mold) The molding die 10 is made up of two or more divided bodies that are fitted together. As shown in Figures 1 and 2, in this embodiment, the molding die 10 includes a first divided body 12 and a second divided body 14. An injection port 16 is connected to the first divided body 12.

[0022] As shown in Fig. 2, a first cavity (space) C1a is formed inside the first division 12. The portion of the first division 12 that mates with the second division 14 is not covered with a member (soluble resin), so the first cavity C1a is open when the first division 12 and the second division 14 are not mated. A first cavity (space) C1b is formed inside the second division 14. The portion of the second division 14 that mates with the first division 12 is not covered with a member (soluble resin), so the first cavity C1b is open when the first division 12 and the second division 14 are not mated.

[0023] As shown in FIG. 2, a second cavity (space) C2 is formed inside the injection port 16. The injection port 16 has an open end on the side connected to the first division 12, so the second cavity C2 and the first cavity C1a communicate with each other via the connection between the first division 12 and the second cavity C2. Furthermore, the injection port 16 has an open injection port 16a at the end opposite the side connected to the first division 12. Therefore, the second cavity C2 and the first cavity C1a communicate with the outside via the injection port 16a. A constriction 18 is formed on the inner circumferential surface of the connection between the injection port 16 and the first division 12, in other words, between the second cavity C2 and the first cavity C1a. The constriction 18 is a protrusion that protrudes radially inward from the inner circumferential surface of the connection between the injection port 16 and the first division 12. Therefore, when viewed in the axial direction of the injection port portion 16, the opening area of ​​the portion between the second cavity C2 and the first cavity C1a (the portion where the constriction 18 is formed) is smaller than the opening area of ​​the second cavity C2 and the opening area of ​​the first cavity C1a. However, the shape of the injection port portion 16 is not limited to the above description and may be any shape. Furthermore, the constriction 18 is not an essential component and may not be provided.

[0024] As described above, the first cavity C1a is formed inside the first divided body 12, the first cavity C1b is formed inside the second divided body 14, and the second cavity C2 is formed inside the injection port portion 16. When the second divided body 14 of the first divided body 12 is fitted together, the first cavity C1a, the first cavity C1b, and the second cavity C2 are connected to form the cavity C. In other words, the cavity C includes the first cavity C1a, the first cavity C1b, and the second cavity C2.

[0025] The portions of the cavity C formed by the first cavity C1a and the first cavity C1b are shaped to give the hardened body the desired shape. That is, if the portion formed by the first cavity C1a and the first cavity C1b is referred to as the first cavity C1, the first cavity C1 is shaped to give the hardened body the desired shape. In this embodiment, the first cavity C1 is spherical, and the resulting hardened body, green body, and sintered body are also spherical. However, the first cavity C1 is not limited to a spherical shape and can have any shape. In this embodiment, the molding die 10 is demolded by dissolving the molding die 10 with a non-aqueous solvent. Therefore, even if the cavity has a complex shape with many irregularities or intricate shapes, or a shape that is easily damaged, such as a constricted or thin line shape, hardened bodies, green bodies, and sintered bodies that retain the desired shape can be reliably obtained without damaging the desired shape. The first cavity C1 includes the first cavity C1a and the first cavity C1b, and can also be said to be a cavity formed inside the first divided body 12 and the second divided body 14 that are fitted together.

[0026] On the other hand, the second cavity C2 of the cavity C is in communication with the first cavity C1 and is provided with an injection port 16a. The second cavity C2 can be said to be a portion for injecting the ceramic material into the first cavity C1.

[0027] The mold 10 preferably has one injection port for injecting the ceramic material. This is because, when the injection of the ceramic material is completed, the mold can be easily sealed by simply closing one injection port. However, multiple injection ports may be provided. A single injection port is preferable because it reduces the amount of processing required to obtain the desired shape in the vicinity of the injection port of the green body or sintered body. Multiple injection ports are preferable in terms of uniform injection of the ceramic casting liquid and improved productivity, but may require processing in multiple locations in the vicinity of the injection port of the green body or sintered body.

[0028] The thickness of the portion of the molding die 10 that forms the first cavity C1 is referred to as thickness D1. In this case, thickness D1 is preferably 0.5 mm to 3.0 mm, more preferably 0.6 mm to 2.0 mm, and even more preferably 0.8 mm to 1.6 mm. With thickness D1 within this range, the molding die 10 can maintain its strength during molding and dissolve properly when demolded. Note that thickness D1 can also be considered the length from the inner peripheral surface to the outer peripheral surface of the portion that forms the first cavity C1. In other words, thickness D1 can be considered the thickness from the inner peripheral surface 12a to the outer peripheral surface 12b of the first division 12, or the thickness from the inner peripheral surface 14a to the outer peripheral surface 14b of the second division 14.

[0029] Furthermore, the arithmetic mean roughness Ra of the inner surface of the portion of the molding die 10 that forms the first cavity C1 is preferably 0.01 μm or more and 5 μm or less, more preferably 0.05 μm or more and 1 μm or less, and even more preferably 0.1 μm or more and 0.5 μm or less, as specified in JIS B 0601:2001. Having the surface roughness of the inner surface of the first cavity C1 within this range ensures the dimensional accuracy and surface flatness of the cured body and reduces poor appearance. The inner surface of the portion that forms the first cavity C1 can also be referred to as the inner circumferential surface 12a of the first division 12 or the inner circumferential surface 14a of the second division 14.

[0030] Furthermore, the volume of the second cavity C2 is preferably 0.5% to 5% by volume of the first cavity C1, more preferably 0.8% to 4% by volume, and even more preferably 1% to 3% by volume. By keeping the volume of the second cavity C2 within this range, even if the ceramic material shrinks during hardening, the ceramic material filled in the second cavity C2 can be drawn into the first cavity C1, thereby ensuring the dimensional accuracy of the hardened body.

[0031] (Fitting points between the divided parts) FIG. 3 is a partially enlarged view of FIG. 2. FIG. 3 shows the mating portion between the first division 12 and the second division 14. As shown in FIG. 3, the first division 12 includes a main body 12A and a protruding portion 12B. The main body 12A forms the first cavity C1a and, in this embodiment, is a hollow, hemispherical member with an open portion on the side mating with the second division 14. The protruding portion 12B protrudes from an end 12Aa of the main body 12A that mating with the second division 14 toward the side mating with the second division 14. The protruding portion 12B is provided so that the inner circumferential surface of the protruding portion 12B and the inner circumferential surface of the main body 12A are integral with each other. In other words, the inner circumferential surface of the protruding portion 12B and the inner circumferential surface of the main body 12A form the inner circumferential surface 12a of the first division 12. On the other hand, protrusion 12B is provided so that the outer peripheral surface of protrusion 12B is located closer to inner peripheral surface 12a (radially inward) than the outer peripheral surface of main body 12A. That is, the outer peripheral surface of main body 12A forms outer peripheral surface 12b of first segment 12. Note that although Fig. 3 is a cross-sectional view showing only a portion in the circumferential direction, protrusion 12B is formed over the entire circumferential area of ​​main body 12A.

[0032] The second division 14 includes a main body 14A and a protrusion 14B. The main body 14A forms the first cavity C1b, and in this embodiment, is a hollow, hemispherical member with an open portion on the side that fits into the first division 12. The protrusion 14B protrudes from an end 14Aa of the main body 14A that fits into the first division 12 toward the side that fits into the first division 12. The protrusion 14B is provided so that the outer peripheral surface of the protrusion 14B and the outer peripheral surface of the main body 14A are integrated. In other words, the outer peripheral surface of the protrusion 14B and the outer peripheral surface of the main body 14A form the outer peripheral surface 14b of the second division 14. Meanwhile, the protrusion 14B is provided so that the inner peripheral surface of the protrusion 14B is located closer to the outer peripheral surface 14b (radially outward) than the inner peripheral surface of the main body 14A. That is, the inner peripheral surface of main body portion 14A forms inner peripheral surface 14a of second divided body 14. Protrusion 14B is formed over the entire circumferential area of ​​end portion 14Aa. Although Fig. 3 is a cross-sectional view showing only a portion in the circumferential direction, protrusion 14B is formed over the entire circumferential area of ​​main body portion 14A.

[0033] 3, the first division body 12 and the second division body 14 are fitted together by inserting the protruding portion 12B of the first division body 12 into the inside of the protruding portion 14B of the second division body 14. When the first division body 12 and the second division body 14 are fitted together, the tip end 12Ba of the protruding portion 12B of the first division body 12 contacts the end 14Aa of the main body portion 14A of the second division body 14, radially inward of the protruding portion 14B of the second division body 14. Furthermore, the tip end 14Ba of the protruding portion 14B of the second division body 14 contacts the end 12Aa of the main body portion 12A of the first division body 12, radially outward of the protruding portion 12B of the first division body 12.

[0034] The thickness D2 of the protrusion 12B is preferably 0.5 mm to 2.0 mm, more preferably 0.7 mm to 1.5 mm, and even more preferably 0.8 mm to 1 mm. Having the thickness D2 within this range ensures alignment between the tip 12Ba of the protrusion 12B and the end 14Aa of the main body 14A, thereby preventing a gap from forming between the first and second divisions 12 and 14. This prevents outside air from entering the interior of the molding die 10, allowing for the appropriate production of a cured body. Having the thickness D2 of the protrusion 12B within the above numerical range also prevents the protrusion 12B from becoming too thin, ensuring strength. The thickness D2 can also be considered the thickness in the normal direction of the portion where the divisions fit together, or the thickness of the member on the inner circumferential surface of the portion where the divisions fit together.

[0035] The first division 12 and the second division 14 are fitted together as described above, but the fitting structure is not limited to that described above. For example, in the above example, the first division 12 has a protrusion 12B formed on its inner circumferential surface, the second division 14 has a protrusion 14B formed on its outer circumferential surface, and the protrusion 12B is inserted into the protrusion 14B. However, this is not limited to this. For example, conversely, the second division 14 may have a protrusion formed on its inner circumferential surface, and the first division 12 may have a protrusion formed on its outer circumferential surface, and the protrusion on the second division 14 may be inserted into the protrusion on the first division 12.

[0036] The molding die 10 has the above-described configuration. However, the molding die 10 is not limited to the above-described configuration. For example, the molding die 10 may not be configured to include multiple divided bodies, but may be an integrally formed mold.

[0037] The mold 10 can be manufactured by any method so as to have a cavity C of the desired shape. Examples of methods for molding the mold 10 include melt molding. Melt molding is a method in which the material of the mold 10 is melted, molded into the desired shape, and then hardened. Examples of methods for molding the mold 10 include injection molding and blow molding.

[0038] (Method for forming ceramic materials) Next, a method for molding a ceramic material according to this embodiment will be described. In this embodiment, the ceramic material is molded using a molding die 10. Fig. 4 is a flowchart illustrating the method for molding a ceramic material according to this embodiment.

[0039] 4, in this molding method, a raw material mixing step is first performed. In the raw material mixing step, ceramic powder having a desired composition is mixed with a resin, a curing agent, and a solvent to obtain a slurry-like ceramic material (hereinafter referred to as a ceramic casting liquid) (S1).

[0040] The ceramic powder is not particularly limited as long as it can be sintered to form a ceramic, and examples thereof include known ceramic powders. Examples of the ceramic powder include aluminum oxide, zirconium oxide, silicon oxide, silicon nitride, silicon carbide, aluminum nitride, and sialon. These may be used alone or in combination of two or more.

[0041] The ceramic powder is made to have a 50% particle size D of the ceramic powder so that a stable sintered body can be obtained in the sintering process described later. 50 The 50% particle size D is preferably less than 1.0 μm. 50 If the particle size is 1.0 μm or more, the particles may settle in the slurry, causing molding defects and resulting in a decrease in sintered density. 50 is more preferably less than 0.9 μm, and even more preferably less than 0.8 μm. 50 A particle size of 0.1 μm or more is preferable because it prevents scattering and clogging during handling and makes procurement easier.

[0042] Furthermore, when silicon nitride (Si3N4) is used as the ceramic powder, the structure obtained by sintering is preferably one in which main phase crystal grains, mainly composed of silicon nitride, are bonded together by a glassy and / or crystalline binder phase.

[0043] When silicon nitride is used as the ceramic powder, the ceramic powder preferably contains silicon nitride with an alpha phase ratio of 70% or more, more preferably 80% or more, and even more preferably 90% or more. Silicon nitride powder with an alpha phase ratio of less than 70% does not sufficiently incorporate the acicular structure during the alpha-to-beta phase transition during sintering, resulting in reduced strength of the sintered body. Silicon nitride powder with an alpha phase ratio of 90% or more provides a sufficient incorporation effect, resulting in a sintered body with high strength, particularly toughness. The content of silicon nitride with such an alpha phase ratio in the ceramic powder is preferably 85% by mass or more, more preferably 92% by mass or more.

[0044] Furthermore, a sintering aid is blended into the ceramic powder to improve sintering. Examples of sintering aids include those containing at least one element selected from the group consisting of Group 2 (alkaline earth metals), Group 3 (rare earth (scandium group)), Group 4 (titanium group), Group 5 (earth metals (vanadium group)), Group 13 (boron group (earth metal)), and Group 14 (carbon group). The content of this sintering aid in the ceramic powder is preferably 1% to 15% by mass, and more preferably 2% to 8% by mass, calculated as oxide. To obtain a uniform, high-strength sintered body, a lower content of sintering aid is preferable; however, if the content is less than 1% by mass, sintering may become difficult.

[0045] The resin is a component for forming the ceramic material into a desired shape in the curing process described below, and examples thereof include known curable resins. The resin used in this embodiment is required to have shape retention in the curing process and to form a three-dimensional network structure by polymerization reaction. The resin is preferably liquid, as it increases the fluidity of the ceramic casting liquid and provides good filling properties into the molding die 1 described below.

[0046] Furthermore, the resin must be easily removable from the ceramic compact during the degreasing process after the curing process and before sintering. Examples of resins used in this embodiment include epoxy resins, phenolic resins, melamine resins, acrylic resins, and urethane resins. Among these, epoxy resins are preferred due to their excellent shape retention. Examples of epoxy resins include glycidyl ether epoxy resins of bisphenols such as bisphenol A and bisphenol F, phenol novolac epoxy resins, cresol novolac epoxy resins, glycidyl amine epoxy resins, glycidyl ether epoxy resins such as aliphatic epoxy resins, glycidyl ester epoxy resins, methyl glycidyl ether epoxy resins, cyclohexene oxide epoxy resins, and rubber-modified epoxy resins. It is preferable that the resin added to the ceramic casting liquid be a different material from the soluble resin of the casting mold 10.

[0047] When an epoxy resin is used as the resin added to the ceramic casting liquid, the average molecular weight of the epoxy resin is preferably 20 to 30000. The average molecular weight of the epoxy resin is more preferably 50 to 3000, and even more preferably 50 to 2500, in that mixing of the resin with powder is easy and a certain level of mechanical strength is obtained.

[0048] The curing agent is used to harden the resin and is selected depending on the resin to be used. As the curing agent, a water-soluble agent that quickly hardens the resin is preferred, and examples thereof include amine-based curing agents, acid anhydride-based curing agents, polyamide-based curing agents, etc. Amine-based curing agents are preferred because they react quickly, and acid anhydride-based curing agents are preferred because they can produce a cured product with excellent thermal shock resistance.

[0049] Examples of amine-based curing agents include aliphatic amines, alicyclic amines, and aromatic amines, and any of monoamines, diamines, triamines, and polyamines can be used. Examples of acid anhydride-based curing agents include methyltetrahydrophthalic anhydride and dibasic acid polyanhydrides.

[0050] The solvent adjusts the viscosity of the mixture of raw materials used to form a slurry, facilitating the filling of the ceramic casting liquid into the forming die 10 (described later). Examples of solvents that can be used include water (HO), alcohols, and other organic solvents. Of these, aqueous solutions are preferred from the standpoint of production costs and environmental impact.

[0051] The resin and solvent should be selected so that they have good affinity with each other, in order to facilitate the removal of the resin in the degreasing step described below. If the resin and solvent have poor affinity, they may separate and segregate inside the compact, which may cause defects such as pores during sintering.

[0052] The ceramic powder, resin, curing agent, and solvent are mixed to prepare a ceramic casting liquid. A dispersant or the like may be added as needed. Mixing may be performed using a known method, such as a dissolver, homomixer, kneader, roll mill, sand mill, ball mill, bead mill, vibrator mill, high-speed impeller mill, ultrasonic homogenizer, shaker, planetary mill, planetary mixer, in-line mixer, or the like.

[0053] As a dispersant to be added as needed, a pH adjuster, a surfactant, a polymer dispersant, etc. can be appropriately selected and added to dissociate the aggregates of the ceramic powder and further disperse it. It is preferable that the pH adjuster, surfactant, polymer dispersant, etc. do not adversely affect the gelation of the curable resin.

[0054] The basic pH adjuster may be a basic organic substance, for example, ammonia, alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine, choline, guanidines, and quaternary ammonium salts such as tetramethylammonium hydroxide.

[0055] As the acidic pH adjuster, inorganic acids, organic acids and salts thereof can be used, such as phosphoric acid, nitric acid, citric acid, malic acid, acetic acid, lactic acid, oxalic acid, tartaric acid, etc. and salts thereof, and amphoteric salts of amino acids, etc.

[0056] Examples of surfactants include alkylamine salts, aliphatic or aromatic quaternary ammonium salts, heterocyclic quaternary ammonium salts such as pyridinium and imidazolium, aliphatic or heterocyclic phosphonium or sulfonium salts, and acetylene glycol.

[0057] Examples of polymer dispersants include polymers having primary to tertiary amines, quaternary ammonium bases, or quaternary phosphonium bases in the polymer main chain or side chain, homopolymers of acrylic acid or salts thereof, water-soluble aminocarboxylic acid polymers, and (co)polymers of acrylic acid esters.

[0058] These pH adjusters, surfactants and polymer dispersants may be used alone or in combination of two or more.

[0059] Furthermore, in the case of room temperature curing types, the reaction begins as soon as the resin and curing agent are mixed. Therefore, a resin-added slurry containing a resin and a curing agent-added slurry containing a curing agent may be prepared separately, and the separately prepared slurries may be mixed at the time of use. When the resin-added slurry and the curing agent-added slurry are prepared separately, the ceramic powder may be mixed into either of the slurries, or may be mixed into both slurries, or a slurry containing ceramic powder may be prepared separately from both slurries. In particular, it is preferable to mix the ceramic powder into both the resin-added slurry and the curing agent-added slurry and prepare them to have similar concentrations, as this reduces concentration fluctuations when mixed and allows for stable operation.

[0060] A ceramic casting liquid is prepared using the raw material slurry, which is the raw material mixture described above. The viscosity of the ceramic casting liquid may be any viscosity that allows easy filling in the casting liquid injection step described below. For example, the viscosity at a shear rate of 10 [1 / s] is preferably 50 Pa·s or less, and more preferably 20 Pa·s or less. Considering ease of handling after filling, the viscosity of the ceramic casting liquid is more preferably in the range of 0.1 Pa·s to 10 Pa·s. The viscosity of the ceramic casting liquid can be easily adjusted by the amount of solvent used and the amount of resin added to the raw materials used.

[0061] In addition, air may be entrained during the mixing of the raw materials in the raw material mixing process, resulting in the inclusion of gas in the resulting ceramic casting liquid. Therefore, if necessary, a degassing process is performed to remove gas from the ceramic casting liquid before the next process, the casting liquid injection process. If gas is contained in the ceramic casting liquid, pores due to air bubbles may form inside the liquid during the hardening process, and these may remain in the ceramic article obtained by firing.

[0062] The degassing step can be performed by degassing the ceramic casting liquid under reduced pressure using a degassing pump (vacuum pump) or a degassing mixer. The degassing can be performed, for example, for 1 to 120 minutes under reduced pressure of 0.6 kPa to 10 kPa. When a degassing mixer is used, the raw material mixing step and the degassing step can be performed simultaneously. Examples of degassing mixers include a planetary mixer and a rotation-revolution mixer equipped with a vacuum pump.

[0063] (Pouring liquid injection process) The casting liquid pouring step is a step of pouring the ceramic casting liquid obtained through the raw material mixing step and, if necessary, the degassing step, into the casting mold 10 (S2). In the casting liquid pouring step, the ceramic casting liquid is poured into the cavity C through the pouring port 16a. In this case, it is preferable to pour the ceramic casting liquid so that the first cavity C1 and the second cavity C2 of the cavity C are filled with the ceramic casting liquid.

[0064] To inject the ceramic casting liquid into the mold 10, any device capable of delivering the ceramic casting liquid and supplying it into the mold 10 can be used. Examples of such devices include a diaphragm pump, a tube pump, and a syringe pump. A rotary positive displacement diaphragm pump equipped with a precision constant velocity cam, which has a structure that does not generate pulsation, is particularly preferred. An in-line mixer, which can mix the raw materials and prepare the ceramic casting liquid while delivering it, can also be used. When using an in-line mixer, the raw material mixing process and the casting liquid injection process can be performed simultaneously. Furthermore, when separately preparing the resin-added slurry and the hardener-added slurry for molding, as described above, an in-line mixer is preferred because it can mix the two slurries and immediately deliver them to the mold 10 to fill it. In addition to the above-mentioned devices, a two-liquid mixing and discharging device may be used. Furthermore, a method of discharging using a fixed-volume cylinder may be used, or a valve switching method using a mono pump with reduced pulsation may be used. A separate mixer may also be used as the slurry mixing device.

[0065] (hardening process) In the curing step (S3), after the ceramic casting liquid is poured into the mold 10, the resin component in the ceramic casting liquid is cured to harden the ceramic material into a desired shape. In the curing step, the ceramic casting liquid is cured under desired hardening conditions according to the properties of the ceramic casting liquid.

[0066] For example, in the case of a ceramic casting liquid that hardens at room temperature, the reaction begins as soon as the resin-added slurry and the hardener-added slurry are mixed, and the mixture is then left to harden for a predetermined period of time. The hardening time is about 1 hour to 3 days, and from the viewpoint of production efficiency, 1 hour to 24 hours is preferred, and 1 hour to 12 hours is more preferred.

[0067] In the case of a thermosetting casting liquid, it is sufficient to heat the liquid to the desired temperature and ensure sufficient curing time. For example, the heating temperature when curing the resin is preferably within the range of 30°C to 85°C, more preferably within the range of 40°C to 70°C, and even more preferably within the range of 50°C to 60°C. The heating time, i.e., the time for which the temperature is maintained, is preferably 5 to 2880 minutes, more preferably 10 to 1440 minutes, and even more preferably 30 to 180 minutes.

[0068] (Demolding process) The demolding step is a step of removing the hardened ceramic material body hardened in the hardening step from the molding die 10 (S4). In the demolding step, the molding die 10 is brought into contact with a non-aqueous solvent to dissolve the molding die 10 in the non-aqueous solvent, and the hardened body is demolded. In order to effectively dissolve the molding die 10, it is preferable to contact the molding die 10 with the non-aqueous solvent by immersion in the non-aqueous solvent. If immersion in a non-aqueous solvent is used to dissolve the molding die 10, the molding die 10 with the hardened ceramic material inside can be easily demolded by simply leaving it in the non-aqueous solvent.

[0069] The non-aqueous solvent is a liquid whose main component is a component other than water, and dissolves the soluble resin in the casting mold 10. Preferably, the non-aqueous solvent dissolves the soluble resin in the casting mold 10 but does not dissolve the resin in the ceramic casting liquid. The non-aqueous solvent preferably contains, as its main component, at least one material selected from the group consisting of methylene chloride, d-limonene, acetone, and toluene. Here, the term "main component" refers to, for example, a material whose proportion relative to the total amount of the non-aqueous solvent is 50% or more.

[0070] In the demolding step, it is preferable to dissolve the forming mold 10 in a non-aqueous solvent and demold the hardened body in a temperature environment lower than the heating temperature used to harden the resin in the ceramic casting liquid in the hardening step. Furthermore, it is preferable to dissolve the forming mold 10 in a non-aqueous solvent and demold the hardened body in an environment ranging from 10°C to 40°C. By demolding at such a relatively low temperature, it is possible to prevent the hardened body from being heated more than necessary, and to produce an appropriate ceramic article. Furthermore, the demolding time, i.e., the time during which the casting mold 10 is in contact with the non-aqueous solvent, is preferably 20 to 1800 minutes, more preferably 30 to 240 minutes, and even more preferably 60 to 180 minutes. By setting the demolding time within this range, the casting mold 10 can be appropriately dissolved and demolded.

[0071] The demolding step may be carried out simultaneously with the hardening step described above. That is, the demolding step may be carried out immediately after the ceramic casting liquid is poured into the molding die 10. In this case, the molding die 10 filled with the ceramic casting liquid is brought into contact with a non-aqueous solvent immediately after the ceramic casting liquid is filled, and the dissolution of the molding die 10 proceeds. At this time, the hardening (gelling) of the ceramic casting liquid proceeds simultaneously with the dissolution of the molding die 10.

[0072] In this case, however, the ceramic casting liquid is allowed to harden sufficiently to dissolve the mold 10, so that it does not come into contact with the non-aqueous solvent used for demolding before it has fully hardened. Specifically, the mold 10 is manufactured so that the exposure dissolution time of the mold 10 is longer than the hardening time of the ceramic casting liquid (hardening time < exposure dissolution time). By adjusting both the hardening time and the exposure dissolution time, the mold 10 dissolves (exposing a portion of the hardened body inside) after the ceramic casting liquid hardens, and a hardened body of the desired shape is obtained. The hardening time refers to the time from immediately after preparation of the ceramic casting liquid until the ceramic casting liquid can maintain the shape of the mold due to gel hardening, and the exposure dissolution time refers to the time from immersion of the mold 10 in the non-aqueous solvent until a portion of the hardened body inside is exposed.

[0073] In this specification, the "curing time" refers to the time it takes for the formation of a three-dimensional network structure to progress through the polymerization reaction between the resin and the curing agent in the ceramic casting liquid, turning the ceramic casting liquid into a hardened body that is a viscoelastic solid and hard enough to withstand handling. If the hardened body is not hard enough to be subjected to the demolding process or if the demolded hardened body is subjected to the drying process, deformation or cracks may occur in the hardened body.

[0074] While the hardness sufficient for handling is determined as appropriate depending on the shape and dimensions, "hardness sufficient for handling" in this specification means that the cured product has a flexural modulus of 2 MPa or more. The method for determining the "curing time" in this specification involves simultaneously preparing round hardened rods for destructive testing at predetermined elapsed times (e.g., 5, 10, 15, 20, 30, 60, 120, and 180 minutes) in a number sufficient for measurement (e.g., 24 pieces), with at least three pieces (n=3) each. A three-point bending test is then performed at each predetermined time interval. The time at which the flexural modulus reaches 2 MPa or more is defined as the time. For example, the measurement conditions are as follows:

[0075] Temperature Room temperature (25±5℃) Distance between fulcrums 30mm Test piece size: φ9mm x 35mm Equipment: Shimadzu Corporation universal testing machine Tensilon AGS-J10kN

[0076] The flexural modulus in a three-point bending test is calculated from the load-elongation graph using the tangent method, which takes any two points from the initial gradient of the straight line. Here, two points, 0.3N and 0.6N, are taken, and calculations are performed using formulas (1) and (2). The number of measurements, n=3, is the average of these, and the flexural modulus of the hardened material can be calculated.

[0077]

number

[0078]

number

[0079] In the above formula, L is the distance between supports (mm), D is the sample diameter (mm), Fmax is the maximum load d (N), ΔF is the change in bending load (N), and ΔS is the change in elongation (N).

[0080] The curing time and exposure dissolution time can be adjusted by the temperature of the non-aqueous solvent used for demolding, the type of forming mold 10 (type and amount of resin and curing agent added, etc.), thickness, etc.

[0081] Furthermore, in this embodiment, a step of removing a portion of the hardened body to obtain a hardened body of a desired shape after the hardened body is demolded in the demolding step may be included. FIG. 5 is a diagram illustrating the step of obtaining a hardened body of a desired shape. As shown in FIG. 5, in the hardening step (step S3), the ceramic casting liquid is hardened in the molding die 10 to form a hardened body P in the molding die 10. Because the ceramic casting liquid is injected into the first cavity C1 and the second cavity C2 in the molding die 10, the hardened body P includes a hardened body P1 that is a portion injected into the first cavity C1 and hardened, and a hardened body P2 that is a portion injected into the second cavity C1 and hardened. Thereafter, in the demolding step (step S4), the molding die 10 is dissolved to obtain the hardened body P that is demolded from the molding die 10.

[0082] Here, a constriction 18 is formed between the first cavity C1 and the second cavity C2. Therefore, the portion between the hardened body P1 and the hardened body P2 corresponding to the constriction 18 is a constriction portion with a smaller diameter than the hardened body P2. In the process of obtaining a hardened body of a desired shape, the hardened body P2 is removed from the hardened body P starting from the constriction portion between the hardened body P1 and the hardened body P2, and the hardened body P1 is obtained as a hardened body of a desired shape.

[0083] (Method for manufacturing ceramic articles) Next, a method for manufacturing a ceramic article according to this embodiment will be described. The method for manufacturing a ceramic article includes a drying step of drying the hardened body obtained by the above-described method for molding a ceramic material to form a molded body, a degreasing step of degreasing the molded body to form a degreased body, and a sintering step of sintering the degreased body to form a sintered body.

[0084] Fig. 6 is a flowchart illustrating a method for manufacturing a ceramic article according to this embodiment. As shown in Fig. 6, the method for manufacturing a ceramic article according to this embodiment includes a raw material mixing step (step S1), a casting liquid injection step (step S2), a hardening step (step S3), a demolding step (step S4), a drying step (step S5), a degreasing step (step S6), and a firing step (step S7). However, the steps from the raw material mixing step to the demolding step (steps S1 to S4) are the same as those in the above-mentioned ceramic material molding method, and therefore, description thereof will be omitted.

[0085] (drying process) The drying step is a step of removing moisture, volatile solvents, etc. from the hardened body obtained in the demolding step and drying to form a molded body (Step S5). In the drying step, the hardened body is dried gently so as not to cause cracks, etc. In other words, the hardened body is dried while preventing the occurrence of cracks, etc. due to shrinkage stress caused by the difference in drying speed between the surface and the interior of the hardened body.

[0086] The drying step is carried out under relatively mild conditions, such as 25°C to 50°C, 50% to 95% relative humidity, and over a long period of time, to remove moisture and other substances contained in the hardened body. The drying step is preferably carried out until the moisture content of the hardened body is 20% or less of its bone-dry mass.

[0087] (Degreasing process) The debinding step is a step in which resin, non-volatile solvent, etc. are removed from the green body obtained in the drying step to obtain a debound body (Step S6). In the debinding step, most of the components that inhibit sintering in the subsequent sintering step are removed. If a large amount of components that inhibit sintering remain, pores may form in the sintered body during sintering, or carbides may be generated as by-products, which may result in the final product not achieving the desired characteristics.

[0088] The degreasing step is carried out under conditions such as slowly raising the temperature to 250°C to 800°C and maintaining the temperature there, for a relatively long period of time, such as 3 to 14 days, to remove resin components and the like contained in the compact. The degreasing step, particularly for silicon nitride, is preferably carried out until the residual carbon content in the compact is 900 ppm or less. However, this does not apply to carbides such as silicon carbide (SiC).

[0089] (Firing process) The firing step is a step of firing the degreased body that has been subjected to the degreasing step to sinter the ceramic material and form a sintered body (ceramic article) (Step S7). The firing in the firing step is to sinter the ceramic material to form a sintered body, i.e., a ceramic article, and a known firing method may be applied.

[0090] The firing conditions are not particularly limited as long as the firing can produce a sintered body, but for example, when firing a molded body containing silicon nitride, firing is preferably performed in a nitrogen atmosphere with an oxygen concentration of 50 ppm or less. The maximum firing temperature in the firing step is set to 1800°C or less, at which point silicon nitride begins to thermally decompose, and this maximum temperature is preferably in the range of 1650°C to 1750°C. The firing time is preferably in the range of 240 minutes to 15 hours, and may be in the range of 240 minutes to 12 hours.

[0091] (Second firing process) The sintered body obtained in the firing step may be subjected to a secondary firing step in order to further improve the sintered body to have desired properties. This secondary firing step is a step in which the sintered body obtained in the firing step (primary firing) is further subjected to high-pressure treatment to densify the structure of the sintered body.

[0092] The high-pressure treatment in this secondary firing step can be hot isostatic pressing (HIP), gas pressure firing, hot pressing, etc. Generally, the sintered body obtained by sintering has high strength, and is preferably treated by HIP at 1500°C to 1750°C and a pressure range of 50 MPa to 200 MPa.

[0093] (ceramic items) 7 is a schematic diagram of a ceramic article according to this embodiment. The ceramic article (sintered body) manufactured by the method for manufacturing a ceramic article according to this embodiment will be referred to as ceramic article 100 below, and the properties of ceramic article 100 will be described.

[0094] The ceramic article 100 is a sintered body of ceramic. The ceramic article 100 is preferably a sintered body of at least one ceramic material selected from the group consisting of aluminum oxide, zirconium oxide, silicon oxide, silicon nitride, silicon carbide, aluminum nitride, and sialon, and more preferably a sintered body of silicon nitride.

[0095] The ceramic article 100 is a sintered body after the firing process but before polishing. That is, although the surface of the sintered body may be polished after the firing process (sintering process), the ceramic article 100 of this embodiment refers to a sintered body in an unpolished state (pre-polished state). However, the ceramic article 100 is not limited thereto, and may refer to a sintered body in a polished state after sintering. Ceramic article 100 may be used for any purpose, but may be used, for example, as a base sphere for a bearing ball. The base sphere here refers to an intermediate product when the final product is a bearing ball, and for example, the final product, a bearing ball, is formed by polishing the surface of ceramic article 100.

[0096] The ceramic article 100 is spherical. Here, "spherical" is not limited to being a perfect sphere. For example, the ceramic article 100 may have a sphericity of preferably within 3%, more preferably within 2.5%, and even more preferably within 2% of the diameter D. For example, for a sintered body having a diameter of 50 mm, the sphericity is preferably 1.5 mm or less, more preferably 1.25 mm or less, and even more preferably 1.0 mm or less. For example, for a sintered body having a diameter of 10 mm, the sphericity is preferably 0.3 mm or less, more preferably 0.25 mm or less, and even more preferably 0.2 mm or less. Here, the diameter D may refer to the average diameter (the arithmetic mean value of the maximum and minimum diameters). Note that ceramic article 100 is a sintered body of hardened body P1 from which hardened body P2 corresponding to the constricted portion of forming mold 10 has been removed, and protrusions may remain in the areas where hardened body P2 was removed. In this case, diameter D of ceramic article 100 refers to the diameter measured at a location on surface 100a of ceramic article 100 other than the protrusions. Therefore, the arithmetic mean value of the maximum and minimum diameters refers to the arithmetic mean value of the maximum diameter of ceramic article 100 measured at a location other than the protrusions and the minimum diameter of ceramic article 100 measured at a location other than the protrusions.

[0097] The diameter D of the ceramic article 100 is preferably 0.5 mm to 80 mm, more preferably 30 mm to 55 mm, even more preferably 45 mm to 55 mm, and even more preferably 49 mm to 51 mm. A diameter within this range makes the ceramic article suitable for use as, for example, a bearing ball.

[0098] The ceramic article 100 has recesses 102 formed on the surface 100a along the circumferential direction R. The recesses 102 are formed when the ceramic article 100 is manufactured by the manufacturing method of this embodiment using a split mold 10. The circumferential direction R refers to the circumferential direction when the direction along the axis passing through the center of the ceramic article 100 is defined as the axial direction, and the adjacent circumferential direction when the direction along the axis passing through the center of the ceramic article 100 is defined as the axial direction. The adjacent circumferential direction refers to a circumferential direction that is shifted within 5% of the diameter from the circumferential position when the direction along the axis passing through the center of the ceramic article 100 is defined as the axial direction. The recesses 102 refer to recessed portions of the surface 100a. The ceramic article 100 does not necessarily need to be recessed throughout the entire circumferential direction R along the portion where the recesses 102 are formed; some sections of the entire circumference of the circumferential direction R along the portion where the recesses 102 are formed may be unrecessed or may protrude. For example, the recesses 102 may be formed in the circumferential direction R of the surface 100a over the entire circumference in the circumferential direction R, and are preferably formed in a section that is 50% or less of the entire circumference in the circumferential direction R, and more preferably formed in a section that is 25% or less of the entire circumference in the circumferential direction R. For example, the recesses 102 may be formed in the circumferential direction R of the surface 100a over a section that is 5% or more of the entire circumference in the circumferential direction R, or may be formed in a section that is 10% or more, or may be formed in a section that is 15% or more. That is, the recesses 102 may be formed in the circumferential direction R of the surface 100a over a range of 5% to 50% of the entire circumference of the circumferential direction R, or may be formed in a range of 15% to 25% of the entire circumference of the circumferential direction R. Here, the recesses 102 being formed in a section that is 50% or less of the entire circumference in the circumferential direction R does not necessarily mean that the recesses 102 are formed continuously in a section that is 50% or less of the entire circumference in the circumferential direction R. The recesses 102 may be formed intermittently along the circumferential direction R, and the total length of the recesses 102 may be 50% or less of the entire circumference in the circumferential direction R. The same may be true when the recesses 102 are formed in a section that is 25% or less of the entire circumference in the circumferential direction R, or when the recesses 102 are formed in a section that is 5% or more of the entire circumference in the circumferential direction R. In this embodiment, the recesses 102 are preferably formed along one circumferential direction R of the ceramic article 100. In other words, it is preferable that the ceramic article 100 does not have multiple recesses 102 extending along different circumferential directions R. In this case, however, it is acceptable for multiple recesses 102 to be formed in series along the same circumferential direction R. The recesses 102 are formed on the surface 100a at locations facing or near the boundary position (see FIG. 3 ) between the inner circumferential surface 12a of the first division 12 and the inner circumferential surface 14a of the second division 14. In other words, the circumferential direction R in which the recesses 102 are formed is located on the surface 100a at locations facing or near the boundary position (see FIG. 3 ) between the inner circumferential surface 12a of the first division 12 and the inner circumferential surface 14a of the second division 14. Because the ceramic article 100 may shrink during the firing process, the circumferential direction R in which the recess 102 is formed may shift to near the point opposite the boundary position between the inner surface 12a of the first division 12 and the inner surface 14a of the second division 14.

[0099] 8 is a diagram schematically showing a CT image of the ceramic article according to this embodiment. Here, the depth A1 and width A2 of the recess 102 are defined as shown in FIG. Depth A1 refers to the distance between a line L connecting one end point 102A and the other end point 102B of recess 102 and a bottom 102C of recess 102 in a CT (computed tomography) image of ceramic article 100. End point 102A refers to the boundary position on one side of recess 102 and a portion of surface 100a other than recess 102 in a direction along surface 100a in the CT image of ceramic article 100. Similarly, end point 102B refers to the boundary position on the other side of recess 102 and a portion of surface 100a other than recess 102 in a direction along surface 100a in the CT image of ceramic article 100. Furthermore, bottom 102C refers to the deepest portion of recess 102 (the portion located most radially inward) in the CT image of ceramic article 100. Width A2 refers to the distance between end points 102A and 102B of recess 102 in the CT image of ceramic article 100. The CT image of the ceramic article 100 refers to an image of the ceramic article 100 captured using an InspecXioSMX-225CT manufactured by Shimadzu Corporation under conditions of an acceleration voltage of 150 kV, an acceleration current of 70 μm, and a voxel size of 0.045 mm to 0.070 mm for magnification.

[0100] The depth A1 of the recess 102 is 1% or less of the diameter D of the ceramic article 100, and is preferably 0.1% to 1%, more preferably 0.1% to 0.6%, and even more preferably 0.1% to 0.4%. That is, the recess 102 may have a depth A1 of 1% or less of the diameter D, preferably 0.1% to 1%, more preferably 0.1% to 0.6%, and even more preferably 0.1% to 0.4%. The recess 102 may be formed over a section of 5% to 10% of the entire circumference in the circumferential direction R of the ceramic article 100, or over a section of 10% to 50% of the entire circumference in the circumferential direction R of the ceramic article 100, or over a section of 15% to 25% of the entire circumference in the circumferential direction R of the ceramic article 100. By forming recesses 102 with such a depth A1, when polishing ceramic article 100, for example, the polishing allowance can be reduced compared to when protrusions with a width visible to the naked eye are formed along the entire circumferential direction, simplifying the polishing process and extending the life of the grinding stone. This is because, in the case of a spherical sintered body with protrusions with a width visible to the naked eye, polishing requires first grinding the protrusions, then removing the burnt surface and polishing to make the diameter uniform. In the case of protrusions, a polishing allowance is required for the protrusions, but in the case of recesses, the polishing allowance for the recesses can overlap with the polishing allowance for removing the burnt surface and for making the diameter uniform. As a result, the polishing allowance for recesses can be smaller than that for protrusions. The depth A1 of the recess 102 is preferably 0.5 mm or less, more preferably 0.05 mm or more and 0.3 mm or less, and even more preferably 0.05 mm or more and 0.2 mm or less.

[0101] The width A2 of recess 102 is preferably 1% or less, more preferably 0.1% to 1%, even more preferably 0.1% to 0.6%, and even more preferably 0.1% to 0.4% of the diameter D of ceramic article 100. That is, the section in which the width A2 of recess 102 is preferably 1% or less, more preferably 0.1% to 1%, even more preferably 0.1% to 0.6%, and even more preferably 0.1% to 0.4% of the diameter D may extend over a section of 5% to 50% of the entire circumference in the circumferential direction R of ceramic article 100, a section of 10% to 50% of the entire circumference in the circumferential direction R of ceramic article 100, or a section of 15% to 25% of the entire circumference in the circumferential direction R of ceramic article 100. By forming recesses 102 of such width A2, when polishing a ceramic article 100, the polishing allowance can be reduced compared to when protrusions are formed over the entire circumferential length, simplifying the polishing process and extending the life of the grinding wheel. The width A2 of the recess 102 is preferably 0.5 mm or less, more preferably 0.05 mm or more and 0.3 mm or less, and even more preferably 0.05 mm or more and 0.2 mm or less.

[0102] The ceramic article 100 has an arithmetic mean roughness Ra of the surface 100a, excluding the recesses 102 and protrusions, as specified in JIS B 0601:2001, of preferably 0.1 μm to 50 μm, more preferably 0.5 μm to 20 μm, and even more preferably 1 μm to 10 μm. The arithmetic mean roughness Ra1 is calculated by sampling a reference length from the roughness curve of the surface 100a. The reference length is, for example, 0.8 mm.

[0103] (effect) As described above, the molding method according to this embodiment includes the steps of: preparing a ceramic casting liquid as a ceramic material by mixing ceramic powder, a sintering aid, a resin, a curing agent, and a solvent; pouring the ceramic casting liquid into a molding die 10 that is soluble in a non-aqueous solvent and has a cavity C formed therein; curing the resin in the ceramic casting liquid poured into the molding die 10 to form a hardened body having a desired shape; and dissolving the molding die 10 in a non-aqueous solvent to demold the hardened body. The molding die 10 is made of a soluble resin that is soluble in a non-aqueous solvent. The molding die 10 has an elastic modulus of 500 MPa to 5000 MPa and a thermal conductivity of 0.05 W / mK to 0.40 W / mK.

[0104] When molding ceramic materials, it is necessary to properly mold the molded body and obtain a good molded body. According to this molding method, gel-cast molding using a mold 10 results in high shape accuracy, favorable surface properties, and a short curing time, thereby increasing productivity. This enables proper molding and the production of a good molded body. Specifically, the mold 10 is made of a material that is soluble in a non-aqueous solvent, allowing it to be dissolved in a non-aqueous solvent and demolded without stress, thereby reducing damage to the hardened body. Furthermore, the mold 10 has a high elastic modulus, which reduces deformation during injection and curing, maintaining the dimensional accuracy and surface flatness of the hardened body and reducing appearance defects. Furthermore, the mold 10 has a relatively high thermal conductivity, which prevents external heat from being transmitted to the ceramic casting liquid, enabling short curing times.

[0105] In the molding method according to this embodiment, it is preferable to use water as a solvent for the ceramic casting liquid, since the use of water allows the hardened body to be appropriately molded.

[0106] The soluble resin of the molding die 10 preferably contains as its main component at least one material selected from the group consisting of polystyrene, ABS resin, acrylic resin, polycarbonate, epoxy resin, and polyester. By using such a material, it becomes possible to appropriately mold the cured body while appropriately suppressing damage to the cured body when it is removed from the mold.

[0107] It is also preferable to use a non-aqueous solvent that can dissolve the soluble resin but does not dissolve the resin in the ceramic casting liquid. By using such a non-aqueous solvent, it is possible to appropriately mold the hardened body while appropriately suppressing damage to the hardened body when it is demolded.

[0108] Furthermore, the heating temperature when hardening the resin in the ceramic casting liquid is preferably within a range of 30° C. to 85° C. When the heating temperature is within this range, the ceramic casting liquid can be properly hardened.

[0109] Furthermore, in this molding method, it is preferable to dissolve the forming mold 10 in a non-aqueous solvent and demold the hardened body in an environment within the range of 10° C. to 40° C. By keeping the temperature during demolding within this range, it is possible to prevent the hardened body from being heated more than necessary, and to produce an appropriate ceramic article.

[0110] Furthermore, forming mold 10 preferably has, as cavity C, a first cavity C1 shaped to give the hardened body a desired shape, and a second cavity C2 that communicates with first cavity C1 and includes an inlet 16a for filling the ceramic casting liquid, and a constriction 18 formed between first cavity C1 and second cavity C2. In this case, the present molding method further includes the step of fracturing the hardened body, starting from the portion corresponding to constriction 18, into a portion that was injected into first cavity C1 and hardened (hardened body P1) and a portion that was injected into second cavity C2 and hardened (hardened body P2), thereby obtaining hardened body P1 of the desired shape, which is the portion that was injected into first cavity C1 and hardened. In this molding method, by filling the second cavity C2 with the ceramic casting liquid, even if the ceramic material hardens and shrinks, the ceramic material filled in the second cavity C2 can be drawn into the first cavity C1, ensuring the dimensional accuracy of the hardened body. Furthermore, the portion corresponding to the constriction 18 has a smaller diameter than the other portions and is therefore more susceptible to fracture. Therefore, by removing the hardened body P2 filled in the second cavity C2 from the portion corresponding to the constriction 18, a hardened body P1 with the desired shape can be easily obtained.

[0111] Furthermore, the method for manufacturing a ceramic article according to this embodiment includes the steps of drying the hardened body obtained by the above-described method for molding a ceramic material to form a molded body, degreasing the molded body to form a degreased body, and firing the degreased body to form a sintered body. Because this manufacturing method uses the above-described method for molding a ceramic material, it is possible to appropriately manufacture a ceramic article as a sintered body.

[0112] The molding die 10 according to this embodiment is formed of a soluble resin that can be dissolved in a non-aqueous solvent, forming a cavity C therein for filling with a ceramic material to obtain a hardened body of a desired shape. The molding die 10 has an elastic modulus of 500 MPa to 5000 MPa and a thermal conductivity of 0.05 W / mK to 0.40 W / mK. Use of this molding die 10 enables proper molding of a hardened body while suppressing damage to the hardened body during demolding. Specifically, since the molding die 10 is made of a material that is soluble in a non-aqueous solvent, it can be dissolved in a non-aqueous solvent and demolded without applying stress, suppressing damage to the hardened body. Furthermore, the use of a molding die 10 with a high elastic modulus suppresses deformation during injection and hardening, maintaining the dimensional accuracy and surface flatness of the hardened body and suppressing defects in appearance. Furthermore, the use of a molding die 10 with a relatively high thermal conductivity suppresses the transfer of external heat to the ceramic casting liquid, enabling short-term hardening.

[0113] The soluble resin of the molding die 10 preferably contains as its main component at least one material selected from the group consisting of polystyrene, ABS (Acrylonitrile-Butadiene-Styrene) resin, acrylic resin, polycarbonate, epoxy resin, and polyester. By using such a material, it becomes possible to appropriately mold the cured body while appropriately suppressing damage to the cured body when it is removed from the mold.

[0114] The non-aqueous solvent preferably contains at least one material selected from the group consisting of methylene chloride, d-limonene, acetone, and toluene as a main component, and by using such a non-aqueous solvent, the casting mold 10 can be appropriately dissolved and demolded.

[0115] Preferably, the mold 10 is made up of two or more segments, which are fitted together to form the mold 10. The thickness D2 of the mold 10 in the normal direction at the portion where the segments fit together is preferably 0.5 mm to 2.0 mm. By keeping the thickness D2 within this range, it is possible to prevent outside air from entering the interior of the mold 10 and to properly produce a cured body. Furthermore, by keeping the thickness D2 within this range, it is possible to prevent the mold from becoming too thin and ensure strength.

[0116] Furthermore, cavity C of mold 10 preferably includes a first cavity C1 shaped to give the hardened body the desired shape, and a second cavity C2 that communicates with first cavity C1 and includes injection port 16a for filling the ceramic material. By including first cavity C1 and second cavity C2, mold 10 can appropriately mold the hardened body.

[0117] Furthermore, the volume of the second cavity C2 is preferably 1% to 5% by volume of the volume of the first cavity C1. By keeping the volume of the second cavity C2 within this range, even if the ceramic material hardens and shrinks, the ceramic material filled in the second cavity C2 can be drawn into the first cavity C1, thereby ensuring the dimensional accuracy of the hardened body.

[0118] Furthermore, it is preferable that the thickness D1 of the portion of molding die 10 that forms first cavity C1 is 0.5 mm to 3.0 mm. By having thickness D1 in this range, strength can be maintained during molding, and the mold can be properly dissolved when removed from the mold.

[0119] The arithmetic mean roughness Ra of the inner surface of the mold 10 that forms the first cavity C1 is preferably 0.01 μm or more and 5 μm or less, as specified in JIS B 0601:2001. Having the surface roughness of the inner surface of the first cavity C1 within this range ensures the dimensional accuracy and surface flatness of the cured body, and also reduces poor appearance.

[0120] Furthermore, it is preferable that the mold 10 is melt-moldable. By allowing the mold 10 to be molded by melt molding, the mold 10 can be easily manufactured.

[0121] The ceramic article 100 according to this embodiment is a spherical ceramic sintered body, and has recesses 102 formed on the surface 100a along the circumferential direction R. The recesses 102 have a depth of 1% or less of the diameter D of the ceramic article 100. Due to the formation of the recesses 102, when polishing the ceramic article 100 according to this embodiment, the polishing stock removal can be reduced compared to when, for example, convex portions are formed along the entire circumferential length, which simplifies the polishing process, extends the life of the grinding stone, and provides favorable properties.

[0122] The width A2 of the recess 102 is preferably 1% or less of the diameter D of the ceramic article 100. By forming the recess 102 with such a width in the ceramic article 100 according to this embodiment, when polishing the ceramic article 100, the polishing stock removal can be reduced compared to when, for example, a case in which convex portions are formed over the entire circumferential length, which simplifies the polishing process, extends the life of the grinding stone, and provides favorable properties.

[0123] Preferably, recesses 102 have a depth A1 of 0.1% to 1% of the diameter of ceramic article 100, and a section having a width A2 of 0.1% to 1% of the diameter of ceramic article 100, the section extending over a length of 5% to the entire circumference in the circumferential direction R of ceramic article 100. By forming recesses 102 of such widths, ceramic article 100 according to this embodiment can reduce the stock removal required when polishing ceramic article 100, simplifying the polishing process and extending the life of the grinding stone, resulting in favorable properties.

[0124] The diameter D of the ceramic article 100 is preferably 0.5 mm or more and 80 mm or less. With the diameter D in this range, the ceramic article 100 can be suitably used as, for example, a bearing ball.

[0125] (Example) Hereinafter, one embodiment of the present invention will be described in more detail based on examples, but the present invention should not be construed as being limited to these examples.

[0126] [Example 1] (Preparation of Slurry ab) A silicon nitride slurry (slurry ab), which would serve as the base for the casting liquid, was prepared by mixing 75.73 parts by mass of silicon nitride powder (manufactured by Denka Co., Ltd., product name SN-9FWS), 3.22 parts by mass of spinel powder as a sintering aid, 19.36 parts by mass of water as a solvent, and 1.69 parts by mass of a 35% aqueous solution of quaternary ammonium salt (manufactured by Seichem) as a dispersant in a bead mill. In the bead mill, silicon nitride balls (manufactured by Nikkato Corporation, diameter 1 mm) were used as grinding media.

[0127] (Preparation and degassing of slurry a1) 94.56 parts by mass of the above slurry ab and 5.44 parts by mass of water-soluble epoxy resin (manufactured by Nagase ChemteX Corporation) were mixed using a planetary mixer equipped with a vacuum pump to prepare an epoxy resin-containing silicon nitride slurry (slurry a1). The slurry a1 was subjected to a reduced pressure treatment (0.6 kPa) to prevent it from containing bubbles of 10 μm or larger.

[0128] (Preparation and degassing of slurry a2) 99.19 parts by mass of the above slurry ab and 0.81 parts by mass of a curing agent (a mixture of triethylenetetramine and 2,4,6-tris(dimethylaminomethyl)phenol in a mass ratio of 2:1) were mixed using a planetary mixer equipped with a vacuum pump to prepare a curing agent-containing silicon nitride slurry (slurry a2). The slurry a2 was subjected to a reduced pressure treatment (0.6 kPa) to prevent it from containing bubbles of 10 μm or larger.

[0129] (casting) Slurry a1 was filled into slurry tank 1, and slurry a2 was filled into slurry tank 2 so that they were the same volume. Subsequently, two rotary positive displacement diaphragm pumps manufactured by TACMINA Corporation, equipped with precision constant velocity cams that do not generate pulsation or air entrainment, were used to suck and discharge slurry a1 and slurry a2 from slurry tank 1 and slurry tank 2, respectively, and the slurry a1 and slurry a2 were sent to an in-line mixer (product name: static mixer) manufactured by Noritake Company through a pipe that joined the slurry a1 and slurry a2.

[0130] The components were mixed in an in-line mixer to prepare casting liquid A containing an epoxy resin and a curing agent, and casting liquid A was supplied to a polystyrene mold connected to the outlet side of the in-line mixer and filled in. The polystyrene mold of Example 1 had an elastic modulus of 2500 MPa and a thermal conductivity of 0.12 [W / mK].

[0131] The polystyrene mold used here has the shape shown in Figures 1 and 2 and is a mold with a spherical cavity inside. The polystyrene mold is made of impact-resistant polystyrene, has a wall thickness of 1.6 mm, and the diameter of the cavity is 62.4 mm. It is a two-piece mold with one opening with a diameter of 6.0 mm as an injection port. The impact-resistant polystyrene that makes up the polystyrene mold has a flexural modulus of 2500 MPa. The two-piece mold was formed into the shape shown in Figure 2 by combining the openings in advance and applying tape from the outside while pressing them together. In the polystyrene mold of Example 1, the volume of the second cavity C2 was 0.3% of the volume of the first cavity C1.

[0132] (hardening) In the polystyrene mold 1 filled with the casting liquid A, the epoxy resin and the curing agent were reacted and cured in a thermostatic chamber maintained at 50° C. for 3.5 hours.

[0133] (Demolding) The polystyrene mold 1 was immersed in methylene chloride at room temperature (25°C), and the polystyrene mold 1 was dissolved in the methylene chloride and demolded, and a spherical hardened silicon nitride body A was taken out.

[0134] (Dry) The demolded hardened silicon nitride body (1) was left to dry for three days in a thermostatic chamber controlled to a temperature of 50°C and a relative humidity that was gradually decreased from 90% to 10%, in order to prevent cracks from occurring due to rapid drying (cracks caused by shrinkage stress resulting from the difference in drying speed between the surface and the interior of the sphere).

[0135] (Degreasing) The dried silicon nitride molded body (1) was heated from room temperature to 600°C in an air atmosphere over a period of 3 days, and then held at 600°C for 3 hours to burn off the cured resin component contained in the silicon nitride molded body (1), thereby carrying out a degreasing treatment.

[0136] (Firing) The degreased silicon nitride molded body (1) was sintered in a nitrogen atmosphere at 1700°C for 7 hours, to obtain a spherical silicon nitride sintered body (1).

[0137] (HIP) Furthermore, the silicon nitride sintered body (1) was subjected to HIP (hot isostatic pressing) at 1700°C under a pressure of 100 MPa using nitrogen gas as a pressure medium for a holding time of 5 hours. After HIP, the density was 3.2 g / cm 3 A dense spherical silicon nitride sintered body (1) was obtained. The diameter of the dense spherical silicon nitride sintered body was 50 mm.

[0138] [Example 2] A two-piece, carved polystyrene foam mold was used. The outer shape was a 102.4 mm sphere, with an internal cavity that was also spherical and 62.4 mm in diameter. The thickness was 20 mm to prevent deformation due to the weight of the slurry. The upper and lower molds were combined and joined by attaching tape to the outside of the joint. Since curing requires time for the slurry temperature to rise, the mold was left to stand in a constant temperature bath at 50°C for 48 hours. Other than that, the procedure was the same as in Example 1. The polystyrene foam mold in Example 2 had an elastic modulus of 7.5 MPa and a thermal conductivity of 0.03 W / mK.

[0139] [Example 3] Casting, curing, and demolding were carried out in the same manner as in Example 1, except that the volume of the second cavity C2 was 2.5% by volume of the volume of the first cavity C1.

[0140] [evaluation] An evaluation was carried out for each example. The surface quality of the five molded bodies was checked for evaluation. It was judged by visual inspection whether the surface was flat without any irregularities or whether any irregularities could be observed. Note that the surface quality (irregularities) visually evaluated in this evaluation did not include any recesses formed in the circumferential direction. As a second evaluation, the curing time was also evaluated. The curing time was measured when molding five molded bodies. It was judged whether the curing time was within 4 hours or longer. Additionally, the five compacts were checked for dents at the connection between the first cavity C1 and the second cavity C2. Those that were visually detected as having a dent extending from the spherical extension of the compact were deemed to have a dent. The denominator in Table 1 is the total number of compacts, and the numerator is the number of compacts with a dent.

[0141] [Table 1]

[0142] [Evaluation results] Table 1 shows the evaluation results for each example. In Examples 1 to 3, which are working examples, recesses were formed along the circumferential direction. Examples 1 and 3 have a flat surface and a curing time of 4 hours or less. Example 2 does not satisfy at least one of the requirements of a flat surface and a curing time of 4 hours or less. Therefore, Examples 1 and 3 are more preferable. For example, Example 3 had good surface quality and could be cured in a short time. Furthermore, no depression occurred between the first cavity C1 and the second cavity C2 used as the injection port. Example 2 had uneven surface quality and required a long time to cure. Example 1 had good surface quality and a long curing time.

[0143] The difference in diameter of the sintered bodies obtained in Example 3 was 0.3 mm. In other words, the difference in diameter between the largest and smallest of the five compacts was 0.3 mm, which was found to be favorable.

[0144] [Check for recesses] CT images of the spherical silicon nitride sintered body obtained in Example 1 were taken and observed. As a result, it was confirmed that recesses were formed along the circumferential direction with a depth A1 (see FIG. 8) of 0.5 mm (1% of the diameter) or less. Note that the recesses in Example 1, whose depth A1 was 1% of the diameter or less, could not be visually confirmed as recesses (irregularities).

[0145] As described above, when a molded body is produced using the mold and method of this embodiment, it is clear that the molded body has good shape accuracy, good surface properties, and a short curing time, resulting in high productivity.

[0146] Although the embodiments and examples of the present invention have been described above, the embodiments are not limited to the contents of these embodiments and examples. Furthermore, the above-described components include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-described embodiments. [Explanation of symbols]

[0147] 10 mold 12 1st division body 14 Second division body 16 Inlet section 100 Ceramic items 100a surface 102 recess C cavity C1 First cavity C2 Second cavity

Claims

1. A spherical ceramic article that is a sintered ceramic body, The surface has a recess along the circumferential direction, the recess has a depth of 1% or less of the diameter of the ceramic article; The ceramic article is a base sphere for a bearing ball, and is a sintered body of at least one of silicon nitride and sialon. Ceramic items.

2. The ceramic article of claim 1 , wherein the width of the recess is 1% or less of the diameter of the ceramic article.

3. A ceramic article as described in claim 1 or claim 2, wherein the recess has a depth of 0.1% to 1% of the diameter of the ceramic article, and a section having a width of 0.1% to 1% of the diameter of the ceramic article, the section having a length of 5% to the entire circumference of the ceramic article.

4. 4. The ceramic article according to claim 1, having a diameter of 0.5 mm or more and 80 mm or less.

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