Method for molding ceramic material, method for manufacturing ceramic article

Abstract

To provide a method for molding a ceramic material with high shape precision that can suppress cracking and deformation upon demolding and allows demolding by more simple operation and a method for producing a ceramic article having reduced burrs.SOLUTION: A method for molding a ceramic material comprises a raw material mixing step (S1) where ceramic powder, a resin a hardener and a solvent are mixed to obtain a casting liquid to be a ceramic material, a casting liquid injection step (S2) where the casting liquid is injected into a cavity 10 of a water-soluble molding die 1 formed with a water-soluble polymer material, a hardening step (S3) where the resin in the casting liquid injected into the water-soluble molding die 1 is hardened into a hardened body having a desired shape and a demolding step (S4) where the hardened body is demolded from the water-soluble molding die 1.SELECTED DRAWING: Figure 1B

Description

Technical Field

[0001] The present invention relates to a mold, a method for molding a ceramic material, and a method for manufacturing a ceramic article. In particular, the present invention relates to a mold, a method for molding a ceramic material, and a method for manufacturing a ceramic article, which can suppress cracks and deformation of a molded body and a cured body during molding of a ceramic material, and obtain a ceramic molded body and a sintered body having desired dimensions and shapes.

Background Art

[0002] For the molding of ceramic articles, various molding methods such as injection molding, casting molding, extrusion molding, and gel casting can be used, and ceramic articles of various shapes can be produced.

[0003] In the molding of ceramic articles, a mold for obtaining a desired product shape is used. In the case of a hard mold, the cured body obtained by gel curing of the cured body may be easily cracked during handling at the time of demolding. In order to suppress cracking at the time of demolding, a soft mold is also known. In this case, however, the mold may be deformed during casting and a desired shape may not be obtained, or the desired dimensional accuracy may not be achieved.

[0004] On the other hand, a method for manufacturing a ceramic article has been proposed in which a mold having a desired rigidity during casting and non-water-absorbing and meltable or fusible by heating (see, for example, Patent Documents 1 and 2) or a solvent-soluble mold (see, for example, Patent Documents 3 and 4) is used to obtain a cured body.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the case of a mold that can be melted or fused by heating as described above, the relationship between the melting or fusing temperature of the mold and the molding temperature for obtaining a cured body must be adjusted, and there are cases where the materials that can be used are limited under the molding conditions (curing conditions). In addition, when using a solvent-soluble mold, a specific organic solvent must be prepared as the solvent, which is troublesome and costly.

[0007] In view of the above problems, the present invention provides a method for molding a ceramic material and a method for manufacturing a ceramic article obtained by sintering a cured body obtained by the method, which can suppress the occurrence of cracking, deformation, etc. during demolding in the production of ceramic articles, can be demolded by a simpler operation, and can obtain a ceramic cured body with high shape accuracy.

Means for Solving the Problems

[0008] As a result of intensive studies by the present inventors to solve the above problems, it has been found that a highly shape-accurate ceramic cured body can be obtained by a simple operation by casting and filling a slurry-like ceramic material into a water-soluble mold, curing it, and then dissolving the water-soluble mold in water for demolding.

[0009] That is, a water-soluble mold according to one aspect of the present invention is formed of a water-soluble polymer material and has a cavity filled with a ceramic material inside for obtaining a cured body having a desired shape. The method for molding a ceramic material according to one aspect of the present invention comprises mixing a ceramic powder, a resin, a curing agent, and a solvent to prepare a casting liquid that becomes the ceramic material, casting the casting liquid into a water-soluble molding die made of a water-soluble polymer material, curing the resin in the casting liquid cast into the water-soluble molding die to form a cured body having a desired shape, and dissolving the water-soluble molding die in water to demold the cured body.

[0010] Further, the method for manufacturing a ceramic article according to one aspect of the present invention comprises drying the cured 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.

Advantages of the Invention

[0011] According to the water-soluble molding die and the method for molding a ceramic material according to one aspect of the present invention, no extra external force is applied to the cured body during demolding, so a cured body with good shape retention and high shape accuracy can be obtained. Further, according to the method for manufacturing a ceramic article according to one aspect of the present invention, since the above-described cured body is dried, degreased, and fired to manufacture a sintered body, a ceramic article having a desired shape can be obtained.

Brief Description of the Drawings

[0012]

Figure 1A

Figure 1B

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0013] Hereinafter, a water-soluble mold, a method for molding a ceramic material, and a method for manufacturing a ceramic article, which are embodiments of the present invention, will be described in detail.

[0014] [Water-soluble mold] A water-soluble mold according to an embodiment of the present invention is a water-soluble mold formed of a water-soluble polymer material and having a cavity filled with a ceramic material therein to obtain a cured body having a desired shape.

[0015] As the water-soluble mold, for example, as shown in FIGS. 1A and 1B, there is a water-soluble mold 1 having a cavity 10 for obtaining a cured body having a desired shape and formed such that the cavity 10 is covered with a mold made of a water-soluble polymer material. Further, the water-soluble mold 1 has an injection port 1a for injecting a ceramic material into the cavity 10.

[0016] Examples of the water-soluble polymer material used for the water-soluble mold 1 include materials that can maintain their shape until the molding material cures (gels) and dissolve upon contact with water. More specifically, materials having characteristics suitable for the molding method described later, that is, materials that dissolve upon contact with water and do not melt upon heating during curing and demolding are preferred.

[0017] Examples of such water-soluble polymer materials include alkylene glycols, polyvinyl alcohols, aliphatic polyamides, cellulose derivatives, polyvinylpyrrolidone, or composites thereof. More specifically, examples of alkylene glycols include polyethylene glycol (PEG), polyethylene oxide (PEO), polypropylene glycol (PPG), polypropylene oxide (PPO), etc. Examples of polyvinyl alcohols include polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH), butenediol vinyl alcohol copolymer (BVOH), etc. Examples of aliphatic polyamides include the "AQ nylon" series (manufactured by Toray Chemical Co., Ltd.), and examples of cellulose derivatives include methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, etc.

[0018] From the above characteristics, the melting point of the water-soluble polymer material is preferably 100°C or higher, more preferably 120 - 250°C, and particularly preferably 150 - 230°C.

[0019] In addition to the above, the water-soluble polymer material may contain water-insoluble components. Examples of the water-insoluble components include known components that are mixed with resin materials such as inorganic fillers. When an inorganic filler is mixed, the rigidity when forming a mold can be improved, and the shape retention can be made good. Since the inorganic filler does not dissolve in water, it will be dispersed or precipitated in water during the mold removal process described later. The inorganic filler may be recovered and reused after the mold removal operation.

[0020] The water-soluble mold 1 is obtained by forming it by a known molding method so as to have a cavity of a desired shape. Examples of the molding method of the water-soluble mold 1 include injection molding, blow molding, etc. Also, the water-soluble mold 1 may be integrally formed or formed in a divided manner (split mold).

[0021] In FIG. 1, a spherical cavity 10 (the obtained cured body, molded body, and sintered body are spherical) is exemplified. The cavity 10 is not limited to a spherical shape and can be of any shape. In this embodiment, since the mold removal is performed by dissolving the mold in water, even when the cavity has a complex shape with many irregularities or entanglements, or a shape that is easily damaged such as a constricted shape or a thin wire shape, a cured body, molded body, and sintered body that retain the desired shape can be stably obtained without damaging the desired shape.

[0022] The water-soluble mold 1 is formed of a material having the property of dissolving in water as described above. The mold removal operation of the water-soluble mold 1 may be performed by contacting with water, preferably by immersion in water, as described later. The time for the water-soluble mold to dissolve at this time varies depending on the type of the water-soluble polymer material used, the wall thickness of the mold, the temperature of the water used, etc., so it can be appropriately adjusted by changing the combination of these conditions.

[0023] For the water-soluble mold 1, the dissolution rate of the water-soluble polymer material used is preferably 0.02 to 0.50 g / min, more preferably 0.04 to 0.20 g / min. The dissolution rate of the water-soluble polymer material is the value when the water temperature of the contacting water is 80 °C and the water-soluble polymer concentration in water is 20% or less.

[0024] As described above, the water-soluble mold 1 preferably has high shape retention. During the filling of the ceramic material and subsequent demolding, it has the rigidity to stably retain the shape of the molded body without deforming the shape of the molded body to the desired shape. As those having such characteristics, the tensile strength (23 °C, relative humidity 0%) of the water-soluble polymer material is 20 to 150 N / mm 2 is preferable, and 40 to 100 N / mm 2 is more preferable. Also, the tensile modulus of elasticity (23 °C, relative humidity 0% °C) is preferably 500 to 5000 N / mm 2 is preferable, and 900 to 4500 N / mm 2 is more preferable. The tensile strength and the tensile modulus of elasticity can be measured according to ISO 527-1 and ISO 527-2.

[0025] The thickness of the water-soluble mold 1 can be adjusted in consideration of the dissolution rate, rigidity, etc. of the water-soluble polymer material as described above. As the thickness of the water-soluble mold, for example, it is preferably about 0.2 to 5.0 mm, more preferably about 0.5 to 2.0 mm. The thickness of the water-soluble mold may be appropriately determined in consideration of the use conditions and the like. By adjusting the thickness of the water-soluble mold, the dissolution time of the water-soluble mold 1 in the demolding process described later can be adjusted.

[0026] For the water-soluble mold 1, it is preferable that there is one inlet for the casting liquid. This is because when the casting (injection) of the casting liquid is completed, it can be easily sealed by simply closing one place of the inlet.

[0027] Note that, in this case, an example of one inlet for the casting liquid is shown, but a plurality of inlets may be provided. When there is one inlet, it is preferable in terms of the small number of processes required to obtain a desired shape in the vicinity of the inlet of the molded body or sintered body. When there are a plurality of inlets, it is preferable in terms of uniform injection of the casting liquid and improvement of productivity, but there may be a case where processing at a plurality of locations in the vicinity of the inlet is required in the molded body or sintered body.

[0028] The water-soluble mold 1 may be provided with a film formed of a water-repellent material on its inner surface. When a film is formed of a water-repellent material, the water-soluble mold 1 and the casting liquid filled therein do not come into direct contact with each other, so that the surface of the molded body can be made smoother. In particular, when water is used as the solvent of the casting liquid, the water-soluble mold 1 and the water of the solvent do not interfere with each other, so that the surface of the molded body can be made smoother. Further, when there are irregularities on the inner surface of the water-soluble mold 1, the film can reduce the influence of the irregularities on the inner surface of the water-soluble mold 1, so that the surface of the molded body can be made smoother.

[0029] Examples of the water-repellent material include fluorine-based resins and silicone-based resins, and fluorine-based resins are preferable. Examples of the fluorine-based resin include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), and the like. Examples of the silicone-based resin include polysiloxane and polydimethylsiloxane. As the water-repellent material, the above-mentioned materials may be used alone or in combination of two or more.

[0030] The film of the water-repellent material can be formed by applying the water-repellent material to the inner surface of the water-soluble mold 1 and drying it. Examples of the coating method of the water-repellent material include coating with a brush and known coating methods such as dip coating and spray coating. When forming a coating of a water-repellent material, the thickness of the coating only needs to be such that the water-soluble mold 1 and the casting liquid do not come into contact. For example, 0.1 to 100 μm is preferable, and 5 to 30 μm is more preferable.

[0031] [Method for molding ceramic material] The method for molding a ceramic material according to an embodiment of the present invention includes a raw material mixing step, a casting liquid injection step, a hardening step, and a demolding step (FIG. 2). Each step will be described separately.

[0032] (Raw material mixing step) The raw material mixing step is a step of mixing a ceramic powder having a desired composition with a resin, a hardening agent, and a solvent to obtain a slurry-like ceramic material (hereinafter referred to as a casting liquid) (S1).

[0033] The ceramic powder is not particularly limited as long as it becomes a ceramic by sintering, and known ceramic powders can be mentioned. Examples of such ceramic powders include aluminum oxide, zirconium oxide, silicon oxide, silicon nitride, silicon carbide, aluminum nitride, sialon, and the like. These may be used alone or in combination of two or more.

[0034] The ceramic powder has a 50% particle size D of the ceramic powder so that a stable sintered body can be obtained in the sintering step described later. 50 is preferably less than 1.0 μm. When the 50% particle size D 50 is 1.0 μm or more, molding defects may be caused by particle sedimentation in the slurry, leading to a decrease in sintering density. The 50% particle size D 50 is more preferably 0.8 μm or less, and even more preferably 0.6 μm or less. Also, the particle size D 50 is preferably 0.1 μm or more because it prevents scattering and clogging during handling and facilitates procurement.

[0035] When silicon nitride (Si3N4) is used as the ceramic powder, the structure obtained by sintering preferably has a form in which the primary phase crystal particles mainly composed of silicon nitride are bonded by a glassy and / or crystalline bonding phase.

[0036] When silicon nitride is used as the ceramic powder, as the ceramic powder, a powder having an α-phase conversion rate of silicon nitride contained in the powder of 70% or more is preferable, 80% or more is more preferable, and 90% or more is even more preferable. In the case of a silicon nitride powder having an α-phase conversion rate of less than 70%, the incorporation effect of the acicular structure during the phase transition from α to β during sintering cannot be sufficiently obtained, and the strength of the sintered body decreases. If the silicon nitride powder has an α-phase conversion rate of 90% or more, a sufficient incorporation effect can be obtained, and a sintered body having high strength, particularly high toughness, can be obtained. The content of silicon nitride having such an α-phase conversion rate in the ceramic powder is preferably 85% by mass or more, and more preferably 92% by mass or more.

[0037] In addition, a sintering aid for improving sintering is blended in the ceramic powder. Examples of the sintering aid include at least one selected from the group of elements of Group 2 (alkaline earth metals), Group 3 (rare earths (scandium group)), Group 4 (titanium group), Group 5 (earth metals (vanadium group)), Group 13 (boron group (earth metals)), and Group 14 (carbon group). The content thereof in the ceramic powder is preferably 1 to 15% by mass in terms of oxide conversion, and more preferably 2 to 8% by mass. In order to obtain a uniform and high-strength sintered body, it is preferable that the content of the sintering aid is small, but if it is less than 1% by mass, sintering may become difficult.

[0038] The resin is a component for shaping the ceramic material into a desired shape in the curing process described later, and examples thereof include known curable resins. As the resin used in the present embodiment, a resin that requires shape retention in the curing process and forms a three-dimensional network structure by a polymerization reaction is used. The resin is preferably liquid in terms of enhancing the fluidity of the casting liquid and having good filling properties into the water-soluble mold described later.

[0039] In addition, the resin must be easily removable from the ceramic compact in the debinding process after the curing process and before sintering. Examples of the resin used in this embodiment include epoxy resins, phenolic resins, melamine resins, acrylic resins, urethane resins, and the like. Among them, epoxy resins are preferably used because they have good shape retention. Examples of epoxy resins include glycidyl ether type epoxy resins of bisphenols such as bisphenol A type and bisphenol F type, phenolic novolak type epoxy resins, cresol novolak type epoxy resins, glycidyl amine type epoxy resins, aliphatic epoxy resins and other glycidyl ether type epoxy resins, glycidyl ester type epoxy resins, methyl glycidyl ether type epoxy resins, cyclohexene oxide type epoxy resins, rubber-modified epoxy resins, and the like.

[0040] The average molecular weight of the epoxy resin is preferably 20 to 30,000. The average molecular weight of the epoxy resin is more preferably 50 to 3,000 and even more preferably 50 to 2,500 in terms of easy mixing of the resin and the powder and obtaining a certain mechanical strength.

[0041] The curing agent cures the resin and is selected according to the resin to be used. As the curing agent, those that are water-soluble and can cure the resin quickly are preferred. Examples include amine-based curing agents, acid anhydride-based curing agents, polyamide-based curing agents, and the like. Amine-based curing agents are preferred in that the reaction is rapid, and acid anhydride-based curing agents are preferred in that cured products with excellent heat shock resistance can be obtained.

[0042] Examples of amine-based curing agents include aliphatic amines, alicyclic amines, aromatic amines, etc., and any of monoamines, diamines, triamines, and polyamines can be used. Examples of acid anhydride-based curing agents include methyltetrahydrophthalic anhydride, dibasic acid polyanhydride, and the like.

[0043] The solvent adjusts the viscosity of the mixture of raw materials to be used to make it slurry-like, facilitating the filling of the casting liquid into the water-soluble mold described later. As the solvent, for example, water, alcohols, and other organic solvents can be used. Among them, an aqueous system is preferable from the viewpoints of manufacturing cost and environmental load.

[0044] Note that the resin and the solvent are selected to have a good affinity for each other in order to facilitate the removal of the resin in the debinding process described later. If the affinity between the resin and the solvent is poor, the resin and the solvent may separate and segregate inside the molded body, possibly causing defects such as pores during sintering.

[0045] The above-mentioned ceramic powder, resin, curing agent, and solvent are mixed to obtain a casting liquid. A dispersant or the like is added as necessary. At this time, the mixing may be performed by a known method. For example, a dissolver, a homomixer, a kneader, a roll mill, a sand mill, a ball mill, a bead mill, a vibrator mill, a high-speed impeller mill, an ultrasonic homogenizer, a shaker, a planetary mill, a self-revolving and revolving mixer, an in-line mixer, etc. can be mentioned.

[0046] As the dispersant to be added as necessary, a pH adjuster, a surfactant, a polymer dispersant, etc. can be appropriately selected and added in order to dissociate and further disperse the aggregation of the ceramic powder. It is preferable that the pH adjuster, the surfactant, the polymer dispersant, etc. do not adversely affect the gelation of the curable resin described above.

[0047] As the basic pH adjuster, basic organic substances can be used. For example, alkanolamines such as ammonia, monoethanolamine, diethanolamine, and triethanolamine, choline, guanidines, quaternary ammonium salts such as tetramethylammonium hydroxide, etc. can be mentioned.

[0048] As the acidic pH adjuster, inorganic acids, organic acids, and their salts can be used. For example, phosphoric acid, nitric acid, citric acid, malic acid, acetic acid, lactic acid, oxalic acid, tartaric acid, etc. and their salts, amphoteric salts such as amino acids, etc. can be mentioned.

[0049] Examples of surfactants include alkylamine salts, aliphatic or aromatic quaternary ammonium salts, heterocyclic quaternary ammonium salts such as pyridinium and imidazolium, phosphonium or sulfonium salts containing aliphatic or heterocyclic rings, acetylene glycols, and the like.

[0050] 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 and its salts, water-soluble aminocarboxylic acid-based polymers, or (co)polymers of acrylic acid esters.

[0051] These pH adjusters, surfactants, and polymer dispersants may be used alone or in combination of two or more.

[0052] In the case of room temperature curing type, since the reaction starts from the time when the resin and the curing agent are mixed, a resin addition slurry containing the resin and a curing agent addition slurry containing the curing agent are separately prepared, and the separately prepared slurries may be mixed at the time of use. When the resin addition slurry and the curing agent addition slurry are separately prepared, the ceramic powder may be mixed in either slurry, may be mixed in both slurries, or a slurry containing the ceramic powder may be separately prepared separately from both slurries. Among them, since there are few concentration fluctuations and the like when mixed and stable operation can be performed, it is preferable to mix the ceramic powder in both the resin addition slurry and the curing agent addition slurry and adjust them to the same concentration.

[0053] Using the raw material slurry which is the above-mentioned raw material mixture, a casting liquid is prepared. The viscosity of the casting liquid only needs to be such that filling can be easily performed in the casting liquid injection process described later. 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 the handling property after filling, the viscosity of the casting liquid is more preferably in the range of 0.1 to 10 Pa·s. The viscosity of the casting liquid can be easily adjusted by the amount of solvent used and the amount of resin added in the raw materials used.

[0054] Note that air or the like may be entrained by mixing in the raw material mixing process, and gas may be contained in the obtained casting liquid. Therefore, if necessary, a defoaming process for removing the gas contained in the casting liquid is performed before the casting liquid injection process, which is the next process. If gas is contained in the casting liquid, pores due to air bubbles may occur inside during the curing process, and may remain in the ceramic article obtained by firing.

[0055] The defoaming process may be carried out by defoaming the casting liquid under reduced pressure, and a defoaming pump (vacuum pump), a defoaming mixer, or the like is used. Defoaming may be performed, for example, for 1 to 5 minutes under a reduced pressure of 0.6 to 10 kPa. When using a defoaming mixer, the raw material mixing process and the defoaming process can be carried out simultaneously. Examples of the defoaming mixer include a rotation-revolution mixer equipped with a vacuum pump, a planetary mixer, and the like.

[0056] (Casting Liquid Injection Process) The casting liquid injection process is a process of injecting the casting liquid obtained through the above raw material mixing process and, if necessary, the defoaming process into a water-soluble mold (S2).

[0057] The water-soluble mold is a container made of a water-soluble material and can stably maintain its shape during the processes of injecting and curing the casting liquid. The water-soluble mold dissolves upon contact with water, and examples include the water-soluble mold described as one embodiment of the present invention above.

[0058] To inject the casting liquid into the water-soluble mold, an apparatus capable of feeding the casting liquid and supplying it into the water-soluble mold can be used. For example, pumps such as diaphragm pumps, tube pumps, and syringe pumps are generally mentioned. In particular, a rotary positive displacement diaphragm pump equipped with a precision constant-speed cam having a structure that does not generate pulsation is preferable. Also, an in-line mixer or the like that can feed while mixing the raw materials to prepare the casting liquid can be used. When using an in-line mixer, the above raw material mixing step and the casting liquid injection step can be performed simultaneously. Further, when separately preparing and molding the resin addition slurry and the hardener addition slurry as described above, the in-line mixer can preferably mix both slurries and immediately feed and fill them into the water-soluble mold.

[0059] (Curing step) The curing step is to cure the resin component in the casting liquid after injecting the casting liquid into the water-soluble mold and cure the ceramic material into a desired shape (S3). In the curing step, it is cured under desired curing conditions according to the characteristics of the casting liquid.

[0060] For example, in the case of a room temperature curing type casting liquid, since the reaction starts and curing occurs from the time when the resin addition slurry and the hardener addition slurry are mixed, it may be left for a predetermined time. The curing time is about 1 hour to 3 days, preferably 1 to 24 hours, and more preferably 1 to 12 hours from the viewpoint of production efficiency.

[0061] Also, in the case of a heat curing type casting liquid, it may be heated to a desired temperature and a sufficient curing time may be ensured. For example, it may be heat cured at 30 to 95°C for 5 minutes to 2880 minutes. Considering production conditions and production efficiency, etc., 35 to 95°C for 5 minutes to 1440 minutes is preferable, and 50 to 85°C for 5 minutes to 180 minutes is more preferable.

[0062] (Demolding step) The demolding process is a process of removing the cured body of the ceramic material cured in the curing process from the water-soluble mold (S4). In the demolding process, the water-soluble mold may be brought into contact with water and dissolved. In order to effectively dissolve the water-soluble mold, the contact with water is preferably immersion in water. If immersion in water is used for dissolving the water-soluble mold, it is extremely easy to demold by simply leaving the water-soluble mold with the ceramic material cured inside in water.

[0063] As the water used in the demolding process, water at normal temperature (23°C) may be used, but warm water heated to promote dissolution may also be used. When using warm water, its temperature is preferably, for example, 30 to 80°C, more preferably 40 to 70°C, and particularly preferably 50 to 60°C.

[0064] In addition, if the time until the water-soluble mold 1 is completely dissolved is too long, demolding cannot be performed efficiently. If the time until the water-soluble mold 1 is completely dissolved is too short, the solubility of the mold in water may be too high or the wall thickness of the mold may be too thin, so the shape retention of the cured body may deteriorate. Therefore, the total dissolution time until the water-soluble mold 1 is completely dissolved is preferably 10 to 480 minutes, and more preferably 30 to 300 minutes.

[0065] Also, the demolding process may be carried out simultaneously with the above-described curing process. That is, after injecting the casting liquid into the water-soluble mold 1, the demolding process may be immediately performed. In this case, the water-soluble mold 1 filled with the casting liquid is immediately brought into contact with water after the casting liquid is filled, and the dissolution of the water-soluble mold proceeds. At this time, the curing (gelation) of the casting liquid proceeds simultaneously with the dissolution of the water-soluble mold.

[0066] However, in this case, before the casting liquid is sufficiently cured, the casting liquid is sufficiently cured with respect to the dissolution of the water-soluble mold 1 so as not to come into contact with the water used for demolding. Specifically, the water-soluble mold 1 is manufactured such that the exposure and dissolution time of the water-soluble mold is longer than the curing time of the casting liquid (curing time < exposure and dissolution time). By adjusting both the curing time and the exposure and dissolution time, after the casting liquid is cured, the water-soluble mold is dissolved (a part of the internal molded body is exposed), and a cured body having a desired shape is obtained.

[0067] The curing time means the time from immediately after the casting liquid is prepared until the casting liquid can maintain the shape of the mold by gel curing, and the exposure and dissolution time means the time from when the water-soluble mold 1 is immersed in water until a part of the cured body inside it is exposed.

[0068] Note that the "curing time" in this specification refers to the time until the formation of a three-dimensional network structure proceeds due to the polymerization reaction of the resin and the curing agent in the casting liquid, and the casting liquid becomes a cured body that is a viscoelastic solid and has sufficient hardness to withstand handling. If the demolding process is carried out in a state where the cured body does not have a hardness of a predetermined value or more, or if the cured body after demolding is advanced to the drying process, deformation or cracks will occur in the cured body.

[0069] The hardness sufficient for handling is appropriately determined according to the shape and dimensions, but the "hardness sufficient for handling" in this specification means that the cured body has a flexural modulus value of 2 MPa or more. The method for confirming the "curing time" in this specification is to prepare at least 3 pieces (n = 3) for each predetermined elapsed time (for example, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, 60 minutes, 120 minutes, 180 minutes) of round bar cured bodies for fracture inspection simultaneously with the cured body in one aspect of the present invention, and perform a three-point bending test for each predetermined elapsed time, and take the time when the flexural modulus becomes 2 MPa or more. For example, the measurement conditions are as follows.

[0070] Temperature Room temperature (25 ± 5°C) Span distance 30 mm Specimen size φ9 mm × 35 mm Device: Universal testing machine Tensilon AGS-J 10kN, manufactured by Shimadzu Corporation

[0071] In the three-point bending test, the flexural modulus is calculated from the load-elongation graph using the tangent method of taking any two points from the initial slope of the linear part. Here, two points of load 0.3 N and 0.6 N are taken, and the calculation is performed according to formulas (1) and (2). With the number of measurements n = 3, the average value can be used as the flexural modulus of the hardened body.

[0072] [Number]

[0073] [Number]

[0074] In the above formula, L is the distance between the fulcrums (mm), D is the sample diameter (mm), Fmax is the maximum load d (N), ΔF is the change in the bending load (N), and ΔS is the change in elongation (N).

[0075] Note that the curing time and the exposure dissolution time can be adjusted according to the temperature of the water used for demolding, the type of the water-soluble mold (the types and addition amounts of the resin and the curing agent, etc.), and the thickness, etc.

[0076] As described above, in this embodiment, it also includes the case where water is used as the solvent of the casting liquid for the water-soluble mold 1. Even when water is actually used as the solvent, most of it is ceramic powder or the like, so good shape retention can be maintained (Examples, etc.), and the feasibility has been confirmed.

[0077] [Method for manufacturing a ceramic article] Next, a method for manufacturing a ceramic article according to an embodiment of the present invention will be described. The method for manufacturing a ceramic article includes a drying step of drying the hardened body obtained by the above-described forming method of the ceramic material to obtain a formed body, a debinding step of debinding the formed body to obtain a debound body, and a sintering step of sintering the debound body to obtain a sintered body.

[0078] That is, the method for manufacturing a ceramic article includes a raw material mixing step, a casting liquid injection step, a hardening step, a demolding step, a drying step, a debinding step, and a firing step (Figure 3). However, since the steps from the raw material mixing step to the demolding step (S1 to S4) are the same as the molding method of the above ceramic material, the description thereof is omitted.

[0079] (Drying step) The drying step is a step of removing moisture, volatile solvents, etc. from the hardened body obtained in the demolding step and drying it to form a molded body (S5). In the drying step, drying is performed gently so as not to cause cracks or the like in the hardened body. That is, drying is performed while preventing the occurrence of cracks or the like due to shrinkage stress caused by the difference in drying rate between the surface and the inside of the hardened body.

[0080] As the conditions of the drying step, for example, at 25 to 30 °C and a relative humidity of 60 to 95%, moisture and the like contained in the hardened body are removed over a relatively long time such as 48 hours to 7 days. The drying step is preferably performed until the moisture content of the hardened body becomes 20% or less with respect to the mass at absolute dryness.

[0081] (Debinding step) The debinding step is a step of removing resin, non-volatile solvents, etc. from the molded body obtained in the drying step to form a debound body (S6). In the debinding step, most of the components that inhibit sintering in the next sintering step are removed. If a large amount of components that inhibit sintering remains, there is a risk that pores will be generated in the sintered body during sintering, or carbides will be generated as by-products, and the characteristics required for the final product cannot be obtained.

[0082] As the conditions of the debinding step, for example, the temperature is raised slowly to 400 to 800 °C and held, and the resin components and the like contained in the molded body are removed over a relatively long time such as 5 days to 14 days as the total processing time. Here, in particular, the debinding step for silicon nitride is preferably performed until the residual carbon amount in the molded body becomes 200 ppm or less. Note that this does not apply to carbides such as silicon carbide (SiC) regarding the residual carbon amount.

[0083] (Firing Process) The firing process is a process of firing the degreased body that has undergone the degreasing process to sinter the ceramic material and obtain a sintered body (ceramic article) (S7). The firing in the firing process is to sinter the ceramic material into ceramics, and a known firing method may be applied.

[0084] As long as the firing process can produce a sintered body by firing, the conditions of the firing process are not particularly limited. For example, when firing a molded body containing silicon nitride, the firing is preferably carried out in a nitrogen atmosphere with an oxygen concentration of 50 ppm or less. Also, the maximum temperature of the firing temperature in the firing process is set to 1800 °C or less at which silicon nitride begins to thermally decompose, and this maximum temperature is preferably in the range of 1650 - 1750 °C. Also, the firing time is preferably in the range of 240 minutes to 12 hours.

[0085] (Secondary Firing Process) In order to further obtain a sintered body having desired properties, the sintered body obtained in the firing process may be subjected to a secondary firing process. This secondary firing process is a process of further performing high-pressure treatment on the sintered body obtained in the above-described firing process (primary firing) to densify the structure of the sintered body.

[0086] As the high-pressure treatment in this secondary firing process, hot isostatic pressing (HIP), gas pressure firing, hot pressing, etc. can be used. Generally, the sintered body obtained by sintering has high strength, and preferably, it is treated by HIP in the range of 1500 - 1700 °C and 50 - 200 MPa.

[0087] The ceramic article manufactured by the manufacturing method of the ceramic article which is one embodiment of the present invention may be, for example, a bearing ball (such as a bearing ball), but is not particularly limited and may be any ceramic article.

Examples

[0088] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not construed as being limited to these examples. Note that Examples 1 to 3 are examples.

[0089] [Example 1] (Preparation of Slurry ab) 75.73 parts by mass of silicon nitride powder (manufactured by Denka Co., Ltd., trade 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 Seikem) as a dispersant were mixed by a bead mill to prepare a silicon nitride slurry (Slurry ab) serving as the base of the casting liquid. In the above bead mill, silicon nitride balls (manufactured by Nikkato Corporation, diameter 1 mm) were used as the grinding media.

[0090] (Preparation and Defoaming of Slurry a1) 94.56 parts by mass of the above Slurry ab and 5.44 parts by mass of a water-soluble epoxy resin (manufactured by Nagase ChemteX Corporation) were mixed by a vacuum pump-equipped planetary mixer to prepare an epoxy resin-containing silicon nitride slurry (Slurry a1). Note that by performing a decompression treatment (0.6 kPa), Slurry a1 was made to contain no bubbles of 10 μm or more.

[0091] (Preparation and Defoaming 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 by a vacuum pump-equipped planetary mixer to prepare a curing agent-containing silicon nitride slurry (Slurry a2). Note that by performing a decompression treatment (0.6 kPa), Slurry a2 was made to contain no bubbles of 10 μm or more.

[0092] (Injection of Casting Liquid) Slurry a1 was filled into slurry tank 1 and slurry a2 was filled into slurry tank 2 so that they had the same volume. Subsequently, without generating pulsation and without generating air entrainment, two rotary positive displacement diaphragm pumps manufactured by Takumina Co., Ltd. equipped with precision constant-speed cams were used to suck and discharge slurry a1 and slurry a2 from slurry tank 1 and slurry tank 2 respectively, and they were sent to an in-line mixer (product name: Static Mixer) manufactured by Noritake Company through a pipe that merges slurry a1 and slurry a2.

[0093] In the in-line mixer, they were mixed to obtain casting liquid A containing an epoxy resin and a curing agent, and casting liquid A was supplied to and filled in a water-soluble mold connected to the outlet side of the in-line mixer.

[0094] The water-soluble mold used here has the shape shown in FIGS. 1A and 1B and is a mold having a spherical cavity inside. The water-soluble mold is made of butanediol vinyl alcohol copolymer (product name: Nichigo G-Polymer BVE8049, manufactured by Mitsubishi Chemical) with a wall thickness of 0.8 mm, and the diameter of the cavity it has is 64 mm. As the injection port, it is a two-part mold provided with one opening with a diameter of 6.0 mm. The dissolution rate of the butanediol vinyl alcohol copolymer constituting the water-soluble mold is 0.14 g / min at 80°C and with a water-soluble polymer concentration of 0% in water, the tensile strength is 88 N / mm 2 (23°C, relative humidity 0%), and the tensile modulus of elasticity is 3990 N / mm 2 (23°C, relative humidity 0%). The two-part mold becomes the shape of FIG. 1B by previously wetting the opening with ion-exchanged water and pressing and joining them.

[0095] (Curing) In the water-soluble mold 1 filled with casting liquid A, the epoxy resin and the curing agent were reacted and cured.

[0096] (Demolding) The water-soluble mold 1 was immersed in water at room temperature, and then the water was heated to 50 °C to dissolve the water-soluble mold 1 in the water for demolding, and the spherical silicon nitride cured body A was taken out.

[0097] (Drying) In order to suppress the generation of cracks due to rapid drying (cracks caused by shrinkage stress due to the difference in drying rate between the surface and the inside of the sphere) of the demolded silicon nitride cured body (1), it was left standing in a thermostatic and humidistatic chamber controlled at a temperature of 25 °C and a relative humidity of 90% for 1 week for drying.

[0098] (Debinding) The silicon nitride formed body (1) obtained by drying was heated from room temperature to 600 °C over 1 week in an air atmosphere and held at 600 °C for 3 hours to burn out the cured resin component contained in the silicon nitride formed body (1) for debinding treatment.

[0099] (Sintering) The debound silicon nitride formed body (1) was sintered at 1700 °C for 7 hours in a nitrogen atmosphere. After this sintering, a spherical silicon nitride sintered body (1) was obtained.

[0100] (HIP) Furthermore, the silicon nitride sintered body (1) was subjected to HIP (hot isostatic pressing) at a pressure of 100 MPa at 1700 °C for 5 hours using nitrogen gas as a pressure medium. After HIP, a dense spherical silicon nitride sintered body (1) with a density of 3.2 g / cm 3 was obtained.

[0101] [Example 2] After injecting the casting liquid A into the water-soluble mold, the water-soluble mold was immediately immersed in water heated to 50 °C, and a dense spherical silicon nitride sintered body (2) was obtained by the same operation as in Example 1 except that the curing of the casting liquid A and the demolding by the dissolution of the water-soluble mold were allowed to proceed simultaneously. In Example 2, when the curing time, exposure dissolution time, and total dissolution time were examined, the curing time was about 20 minutes, the exposure dissolution time was about 30 minutes, and the total dissolution time was about 3 hours. In this example, it was confirmed that the exposure dissolution time was longer than the curing time, and there was no problem even if curing and demolding proceeded simultaneously.

[0102] The curing time was measured as follows. While injecting casting liquid A into the water-soluble mold of this example to produce a cured body, 24 round bar cured bodies (size: cylindrical with a diameter (φ) of 9 mm × 35 mm) were produced using the same casting liquid as casting liquid A. The round bar cured bodies were obtained by injecting the same casting liquid as casting liquid A into a polypropylene mold and immersing it in water heated to 50°C. Three out of the 24 round bar cured bodies immersed in water were pulled out of the water every predetermined elapsed time (5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, 60 minutes, 120 minutes, 180 minutes), removed from the mold, and a three-point bending test was performed to calculate the bending strength and bending modulus of elasticity. The bending strength and bending modulus of elasticity at each elapsed time were taken as the average values of three (n = 3). The curing time is the time when the bending modulus of elasticity obtained from the test results becomes 2 MPa or more. The three-point bending test was performed using a universal testing machine Tensilon AGS-J10kN manufactured by Shimadzu Corporation at a temperature of 25°C ± 5°C with a support span of 30 mm. The bending strength and bending modulus of elasticity were calculated using the above-mentioned formulas (1) and (2) described in the detailed description. The bending strength and bending modulus of elasticity at each elapsed time at this time are shown in Table 1.

[0103]

Table 1

[0104] The exposure dissolution time was measured as the time from when the water-soluble mold was immersed in water until the water-soluble mold dissolved and a part of the cured body inside was exposed. The total dissolution time was measured as the time from when the water-soluble mold was immersed in water until the entire water-soluble mold dissolved.

[0105] [Example 3] As a water-soluble mold, the inner surface thereof was fluororesin-coated by spray coating, dried overnight, and a water-soluble mold having a fluorine coating with a thickness of 5 to 20 μm was obtained. A dense spherical silicon nitride sintered body (3) was obtained by the same operation as in Example 1 except that this fluorine-coated water-soluble mold was used.

[0106] Regarding each of the silicon nitride sintered bodies (1) to (3) obtained in the above Examples 1 to 3, the diameters of the molded body after drying and the sintered body after sintering were measured at seven locations. The average value of the diameters, and the difference (max - min) between the maximum value and the minimum value at this time are shown in Tables 2 and 3.

[0107] [Table 2]

[0108] [Table 3]

[0109] From the results of Tables 2 and 3, it was found that a ceramic sintered body having a small diameter variation, high accuracy, and a desired shape (a desired spherical shape in this example) was obtained.

[0110] From the above, according to the method for molding a ceramic material and the method for manufacturing a ceramic article of the present embodiment, a cured body and a sintered body having good shape retention and high shape accuracy were obtained.

Industrial Applicability

[0111] By the mold of the present invention, the method for molding a ceramic material, and the method for manufacturing a ceramic article, the occurrence of cracks, deformation, etc. during demolding can be suppressed, and a ceramic cured body and a ceramic article having high shape accuracy can be manufactured. The ceramic articles manufactured here can be manufactured in complex shapes other than spherical shapes, etc., and similarly, the occurrence of cracks, deformation, etc. during demolding can be suppressed.

Explanation of Reference Numerals

[0112] 1... water-soluble molding type, 1a... injection port, 10... cavity

Claims

1. Mix a ceramic powder, a sintering aid, a resin, a curing agent, and a solvent containing water to prepare a casting liquid that becomes a ceramic material. Cast the casting liquid into a water-soluble mold made of a water-soluble polymer material. Cure the resin in the casting liquid cast in the water-soluble mold to form a cured body having a desired shape. Dissolve the water-soluble mold in water to demold the cured body. The dissolution rate of the water-soluble polymer material is 0.02 to 0.50 g / min under the conditions that the water temperature of the contacting water is 80°C and the concentration of the water-soluble polymer in the water is 20% or less. A method for forming a ceramic material, characterized by the above.

2. The method for forming a ceramic material according to claim 1, wherein the water-soluble polymer material constituting the water-soluble mold is alkylene glycols or polyvinyl alcohols.

3. The method for forming a ceramic material according to claim 1 or 2, wherein a water-soluble mold having a film formed of a water-repellent material on the inner surface is used as the water-soluble mold.

4. The method for forming a ceramic material according to any one of claims 1 to 3, wherein the curing and the demolding are performed simultaneously.

5. The method for forming a ceramic material according to claim 4, wherein in the demolding, the exposure dissolution time of the water-soluble mold where a part of the cured body is exposed is longer than the curing time of the casting liquid.

6. The method for forming a ceramic material according to any one of claims 1 to 5, wherein the demolding is performed by immersing the water-soluble mold in water at 30 to 80°C.

7. The method for forming a ceramic material according to any one of claims 1 to 6, wherein the cured body obtained by the curing is spherical.

8. The method for forming a ceramic material according to any one of claims 1 to 7, wherein the ceramic powder contains one or more selected from aluminum oxide, zirconium oxide, silicon oxide, silicon nitride, silicon carbide, aluminum nitride, and sialon.

9. A method for manufacturing a ceramic article, comprising the method for forming a ceramic material according to any one of claims 1 to 8.

10. The cured body obtained by the method for forming a ceramic material according to any one of claims 1 to 8 is dried to form a formed body, The formed body is degreased to form a degreased body, The degreased body is fired to form a sintered body, A method for manufacturing a ceramic article, characterized by the above.

11. The method for manufacturing a ceramic article according to claim 10, wherein a secondary firing for densifying the sintered body obtained by the firing is performed by hot isostatic pressing (HIP).

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