Release film for molding and ceramic molding method using the same

Abstract

To provide a mold release film for molding that can easily release a ceramic molded body without using a conventional alginic acid mold release film and that does not cause a defect such as a crack or a split during firing of the molded body, and a ceramic molding method using the same.SOLUTION: A web-like sheet made of an insoluble nanofiber aggregate is used as a mold release film formed on an inner wall surface of a mold. If necessary, an insoluble powder particle is allowed to coexist with an insoluble nanofiber. At this time, a value obtained by dividing a volume of the insoluble powder particle by a volume of the insoluble nanofiber falls within a range of 0.2 to 20.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a release film for use in a mold when molding a ceramic compact, and a ceramic molding method using the same.

Background Art

[0002] In a method for manufacturing a ceramic fired body, a mold is often used when molding a ceramic material into a predetermined shape. There are various methods for a ceramic molding method of molding a ceramic green body before firing with a mold, for example, a casting molding method, a sheet molding method, a press molding method, and the like.

[0003] For example, taking the casting molding method as an example, a slurry in which a ceramic raw material powder and a binder are dispersed in a dispersion medium (hereinafter referred to as "ceramic slurry") is poured into the inside of a water-absorbing porous mold (hereinafter referred to as "mold") having a predetermined shape. Next, most of the dispersion medium (water) contained in the ceramic slurry is absorbed by the mold, and the dispersion medium is separated from the ceramic raw material powder and the binder. After sufficiently separating the dispersion medium, the ceramic compact composed of the ceramic raw material powder and the binder is removed from the mold. When a part of the ceramic slurry penetrates into the porous mold during this mold release, there is a problem that the adhesion between the mold and the ceramic compact becomes strong and the mold cannot be released. Therefore, it is necessary to form a release film for reducing the adhesion between the mold and the ceramic compact on the casting surface inside the mold.

[0004] In the common ceramic molding method, the slip casting method, gypsum molds (hereinafter referred to as "gypsum molds") are used. When using gypsum molds, an aqueous solution of ammonium alginate, a water-soluble organic substance, is applied to the casting surface. As a result, calcium ions leaching from the gypsum mold react with the ammonium alginate, forming an insoluble alginate release film made of calcium alginate on the casting surface. However, in the slip casting method using gypsum molds, calcium ions and sulfate ions from the gypsum mold contaminate the molded product as impurities, making it difficult to produce high-purity molded products.

[0005] Therefore, to form high-purity molded bodies by the slip casting method, porous molds made of ceramics without eluting components, porous molds made of metal, resin molds, composite molds, etc., are used. However, if gypsum is not used as the raw material for the mold, an alginate release film will not be formed on the casting surface. For this reason, it is necessary to use a mold release film that does not use an alginate release film. As an example of a slip casting method using such a release film, the ceramic slurry slip casting method described in Patent Document 1 below has been proposed. In the slip casting method described in Patent Document 1 below, a layer of a composition consisting of acid-type carboxymethylcellulose and carboxymethylcellulose sodium salt is formed and used as a release film.

[0006] Furthermore, a ceramic casting method is proposed in Patent Document 2 below. In the casting method of Patent Document 2 below, a release agent is applied to form a release film by applying a release agent containing the same ceramic components as the ceramic slurry used as the molding raw material, and a film-forming organic substance which is one of the following: carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, sodium polyacrylate, polyvinyl alcohol, sodium alginate, or ammonium alginate. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 07-025659 [Patent Document 2] Japanese Patent Application Publication No. 63-247002 [Overview of the project] [Problems that the invention aims to solve]

[0008] Incidentally, in the above-mentioned Patent Document 1, a release film is formed using a water-soluble raw material called carboxymethylcellulose sodium salt, resulting in a relatively dense release film that fills the pores (water-absorbing pores) of the mold. As a result, there was a problem that the water absorption of the mold during casting decreased, and the molding time became longer. Furthermore, there was a problem that the release properties decreased because the adhesion between the mold and the release film became stronger. In particular, when used for ceramic molded bodies with complex shapes or thin walls, there was a problem that deformation or breakage of the molded body occurred during release.

[0009] Furthermore, in the above-mentioned Patent Document 2, a mixture of the same ceramic components as the molding raw material and a film-forming organic substance is used. In this case, for example, fine ceramic raw materials used in the production of fine ceramic slurry easily enter the pores of the mold and are fixed to the mold by the film-forming organic substance. As a result, the adhesion between the mold and the release film becomes strong, which has the problem of causing deformation or damage to the ceramic molded body during release. On the other hand, by using a coarse-grained raw material with the same ceramic composition as the molding raw material, the adhesion between the mold and the release film can be reduced. However, in this case, since the coarse-grained raw material adheres to the surface of the ceramic molded body, there is a problem that differences in firing shrinkage occur during firing, resulting in defects such as cracks and fractures.

[0010] Therefore, the present invention aims to address the above-mentioned problems by providing a mold release film that allows for easy release of ceramic molded bodies without using conventional alginate release films, and prevents defects such as cracks and fractures from occurring during firing of the ceramic molded bodies, as well as a ceramic molding method using the same. [Means for solving the problem]

[0011] In solving the above problems, as a result of intensive research, the inventors of the present invention have found that by using a web-like sheet composed of an aggregate of insoluble nanofibers as a release film, and if necessary, using a web-like sheet in which insoluble nanofibers and insoluble powder particles are used in combination as a release film, the above object can be achieved, and thus the present invention has been completed.

[0012] That is, according to claim 1, the release film for molding according to the present invention is When manufacturing fired ceramic bodies, a release film formed on the inner wall surface of a mold used for molding a ceramic molded body, For molding which is characterized by being a web-like sheet composed of an aggregate of insoluble nanofibers. and without the coexistence of insoluble powder particles

[0013] Further, according to claim 2, the present invention is the release film for molding according to claim 1, A mold release film formed on the inner wall surface of a mold used for molding a ceramic molded body before firing, when manufacturing a fired ceramic body, Composed of an aggregate of insoluble nanofibers characterized in that insoluble powder particles coexist in the web-like sheet. death, The value obtained by dividing the volume of the insoluble nanofibers by the volume of the insoluble powder particles is within the range of 0.2 to 20.

[0015] Further, according to Claim 3 claim 3, the present invention is the release film for molding according to claim 2, characterized in that the insoluble powder particles are at least one selected from the group consisting of ceramic particles, carbon particles, resin particles, polysaccharide particles, and protein particles.

[0016] Further, according to Claim 4 claim 4, the present invention is the release film for molding according to claim 2, A mold release film formed on the inner wall surface of a mold used when manufacturing a ceramic fired body having a ceramic composition X, characterized in that the insoluble powder particles are the same ceramic particles as the molding raw material to be molded in the mold, or ceramic The ceramics consist of the aforementioned ceramic composition X. particles having the same ceramics as the molding raw material, although the particle sizes are different. Composition and particle size Ceramics composed of composition X [[ID=SO]]characterized by being particles.

[0017] In addition, the present invention Claim 5 According to the description of Claims 1 to 4 a mold release film for molding according to any one of the insoluble nanofibers are polysaccharide nanofibers or protein nanofibers - characterized in that it is at least one selected from the group consisting of

[0018] In addition, the present invention Claim 6 According to the description of Claim 5 a mold release film for molding according to that described in characterized in that the pore size size of the web-like sheet is within the range of 1 nm to 1000 nm

[0019] In addition, the ceramic molding method according to the present invention Claim 7 According to the description of Claims 1 to 4 a ceramic molding method using a mold release film for molding according to any one of a mold release film forming step of forming the mold release film for molding on the inner wall surface of the mold; a molding step of charging a ceramic molding material into the mold having the mold release film formed on the inner wall surface to obtain a predetermined ceramic molded body, In the mold release film forming step, a dispersion operation of dispersing the insoluble nanofibers or mixing and dispersing the insoluble nanofibers and the insoluble powder particles to obtain a dispersion; characterized by comprising a coating operation of coating the dispersion on the inner wall surface of the mold

[0020] In addition, the present invention Claim 8 According to the description of Claim 7 a ceramic molding method according to that described in characterized in that the content of the insoluble nanofibers in the dispersion is within the range of 0.01% by volume to 2.0% by volume

Advantages of the Invention

[0021] According to the above configuration, the mold release film for molding according to the present invention Used when manufacturing ceramic fired bodies, for shaping ceramic molded bodies before firing. The release film formed on the inner wall surface of a mold is a web-like sheet composed of an aggregate of insoluble nanofibers. Insoluble powder particles may also be present on the web-like sheet. In this case, it is preferable that the value obtained by dividing the volume of insoluble nanofibers by the volume of insoluble powder particles is in the range of 0.2 to 20. As a result, it is possible to easily release ceramic molded bodies without using conventional alginate release films, and a mold release film can be provided that prevents defects such as cracks and fractures from occurring during firing of the molded bodies.

[0022] Furthermore, according to the above configuration, the insoluble powder particles may be at least one of the group consisting of ceramic particles, carbon particles, resin particles, polysaccharide particles, and protein particles. Ceramic particles that have the same composition and particle size as the molding material consisting of ceramic composition X to be molded in a mold, or ceramics that have different particle sizes but consist of the same ceramic composition X as the molding material. It may also be in the form of particles. These factors allow the above-mentioned effects to be exerted more concretely and effectively.

[0023] Furthermore, according to the above configuration, the insoluble nanofibers are polysaccharide nanofibers. or Protein nanofibers - It may also consist of at least one type from the group. This allows the above effects to be exerted more specifically and effectively.

[0024] Furthermore, according to the above configuration, the pore size of the web-like sheet is preferably in the range of 1 nm to 1000 nm. This allows the above effects to be exhibited more concretely and effectively.

[0025] Furthermore, according to the above configuration, the ceramic molding method according to the present invention is Claims 1 to 4 This method uses a mold release film described in any one of the above. This ceramic molding method comprises a mold release film formation step and a molding step. In the mold release film formation step, the mold release film is formed on the inner wall surface of the mold. In the molding step, a ceramic molding material is poured into the mold on which the mold release film has been formed on the inner wall surface to obtain a predetermined ceramic molded body.

[0026] Here, the release film formation process comprises a dispersion operation and a coating operation. In the dispersion operation, insoluble nanofibers are dispersed to obtain a dispersion. Alternatively, insoluble nanofibers and insoluble powder particles are mixed and dispersed to obtain a dispersion. In the coating operation, the dispersion is coated onto the inner wall surface of the mold. As a result, it is possible to easily release ceramic molded bodies without using conventional alginate release films, and a ceramic molding method can be provided that prevents defects such as cracks and fractures from occurring during firing of the molded bodies.

[0027] Furthermore, according to the above configuration, it is preferable that the dispersion used in the ceramic molding method according to the present invention contains insoluble nanofibers in the range of 0.01% to 2.0% by volume. This allows the above effects to be exhibited more concretely and effectively. [Brief explanation of the drawing]

[0028] [Figure 1] This is an operation flow diagram showing an overview of the dispersion operation in the release film formation step of the ceramic molding method according to this embodiment. [Figure 2] This is an operation flow chart showing an overview of the coating operation in the release film formation step of the ceramic molding method according to this embodiment. [Figure 3] This is an operation flowchart showing an overview of the molding process of the ceramic molding method according to this embodiment. [Figure 4] This is an electron microscope image of the surface of release film 1 in Example 1. [Figure 5] This is an electron microscope image of the surface of release film 2 in Example 2. [Figure 6] This is a schematic diagram illustrating a method for evaluating the adhesion strength between a mold and a ceramic molded body. [Modes for carrying out the invention]

[0029] The mold release film according to the present invention and the ceramic molding method using the same will be described in detail below with reference to embodiments. In the following embodiments, the slip molding method will be mainly described as a specific example of the ceramic molding method, but the mold release film according to the present invention can also be used in other ceramic molding methods such as sheet molding and press molding.

[0030] First, the components of the mold release film according to the present invention will be described. The mold release film is a web-like sheet made of an aggregate of insoluble nanofibers. Alternatively, the mold release film may be a web-like sheet in which insoluble powder particles are coexisting with the aggregate of insoluble nanofibers.

[0031] Here, we will explain the term "insoluble" as applied to insoluble nanofibers and insoluble powder particles. In this invention, "insoluble" means that when preparing the dispersion (described later) used to form the release film, the components constituting the release film do not completely dissolve in the water (the dispersion medium does not act as a solvent) when water at room temperature is used as the dispersion medium, and the aqueous dispersion state can be maintained. Therefore, it does not mean that it is completely hydrophobic, but rather that even if the surface is hydrophilic or partially hydrophilic, it does not completely dissolve in water.

[0032] Therefore, conventional release films, such as alginate release films, are made of calcium alginate and are insoluble in water, but the ammonium alginate used to form the release film is water-soluble and does not constitute the insoluble nanofibers of the present invention. However, when acidic alginate is used to form the release film, it can be used as the insoluble nanofibers of the present invention.

[0033] On the other hand, polysaccharides such as carboxymethylcellulose are insoluble in water in their acidic form, but may become water-soluble in their sodium form. However, the degree of water solubility and hydrophilicity changes even in the sodium form depending on the degree of substitution of the carboxyl group. In such cases, it can be determined by whether or not it is in a state where it is "not completely dissolved in water." Furthermore, even highly substituted carboxymethylcellulose can be used as the insoluble nanofiber of the present invention when used in its acidic form.

[0034] Next, we will explain the "nanofibers" of insoluble nanofibers. At this stage, the definition of "nanofibers" is not consistent across books and academic societies. Therefore, in this invention, we define them as follows: "Nanofibers" refer to fibrous materials with a diameter in the range of 1 nm to 1000 nm and an aspect ratio of 10 or more. Furthermore, the materials constituting the nanofibers are not particularly limited, but may include, for example, polysaccharide nanofibers, protein nanofibers, carbon nanofibers, carbon nanotubes, ceramic nanofibers, or mixtures thereof.

[0035] In this invention, examples of polysaccharide nanofibers include cellulose nanofibers, chitosa nanofibers, chitin nanofibers, acid-type alginate nanofibers, and acid-type carboxymethylcellulose nanofibers. Examples of protein nanofibers include silk nanofibers.

[0036] In this invention, it is preferable to use cellulose nanofibers among polysaccharide nanofibers as the insoluble nanofiber. Cellulose nanofibers come in various forms depending on the preparation method and the type of plant used. Preparation methods include homogenization, homogenization and twin-screw extruder, combined physical treatment and enzymatic hydrolysis, water jet defibration, TEMPO(2,2,6,6-tetramethylpiperidine 1-oxyl) oxidation, or bacterial cellulose.

[0037] In this invention, there are no particular limitations as long as the cellulose nanofibers are insoluble, but it is preferable to use cellulose nanofibers produced by water jet defibration, which can maintain a high degree of polymerization of cellulose and produce fine nanofibers. On the other hand, in cellulose nanofibers produced by TEMPO oxidation with a hydrophilic surface, it is possible to produce fine nanofibers down to cellulose microfibrils by introducing uniform carboxyl groups. However, even in this case, they do not dissolve completely and are considered to be an aqueous dispersion and insoluble nanofibers.

[0038] Next, the term "powder particles" in the insoluble powder particles will be explained. In the present invention, "powder particles" are not particularly limited as long as they are insoluble in water, but examples include particles of metals, ceramics such as metal oxides, metal nitrides, and metal carbides, carbon, resins such as thermoplastic resins and thermosetting resins, polysaccharides, and proteins. Among these, ceramic particles, carbon particles, resin particles, polysaccharide particles, and protein particles are preferred, and mixtures thereof may also be used.

[0039] In this invention, it is preferable to use carbon particles or ceramic particles as insoluble powder particles. Furthermore, among ceramic particles, it is preferable to use ceramic particles that are the same as the molding raw material used in the mold, or particles with different particle sizes but containing the same ceramic components as the molding raw material used in the mold. It is even more preferable to use carbon particles, resin particles, polysaccharide particles, protein particles, etc., because they disappear during the firing process in which the molded ceramic body is fired and do not remain in the product after firing.

[0040] Furthermore, the shape of the insoluble powder particles may be plate-shaped particles, rod-shaped particles, spherical particles, porous particles, fibrous particles, etc. The average particle diameter of the insoluble powder particles is preferably in the range of 0.1 μm to 100 μm, more preferably in the range of 0.5 μm to 50 μm, and most preferably in the range of 0.1 μm to 30 μm. If the average particle diameter is larger than 100 μm, coarse irregularities will be formed on the surface of the ceramic molded body, causing damage to the ceramic molded body during demolding. Also, if the average particle diameter is smaller than 0.1 μm, the cohesive force of the powder particles will be strong, and good demolding properties cannot be obtained. The average particle diameter of the insoluble powder particles can be measured by laser diffraction, light scattering, image analysis, etc.

[0041] Next, the ceramic molding method according to the present invention and the method for forming the mold release film used therein will be specifically described. Here again, the slip molding method will be mainly described as a specific example among the ceramic molding methods, but the mold release film according to the present invention can also be used in other ceramic molding methods such as sheet molding and press molding.

[0042] The ceramic molding method according to this embodiment consists of a release film formation step and a molding step. In this embodiment, a mold release film in which insoluble powder particles coexist with an aggregate of insoluble nanofibers will be described as a specific example. Furthermore, in this embodiment, cellulose nanofibers will be used as an example of insoluble nanofibers, and carbon powder particles will be used as an example of insoluble powder particles. However, the present invention is not limited to the embodiments described below.

[0043] 1. Release film formation process First, the release film formation process will be explained. In the release film formation process, a mold release film (hereinafter referred to as "release film") is formed on the inner wall surface of the mold. The release film formation process consists of a dispersion operation and a coating operation.

[0044] 1-1.Distributed operation In the dispersion operation, a dispersion is prepared using cellulose nanofibers and carbon powder particles with water as the dispersion medium. Alternatively, the dispersion may be prepared using only cellulose nanofibers without the carbon powder particles. Figure 1 is a flowchart illustrating the overview of the dispersion operation. In Figure 1, first, in step 11, the cellulose nanofibers and carbon powder particles are prepared as the materials to be dispersed. It is preferable to use cellulose nanofibers that have been pre-dispersed in water. Similarly, it is preferable to use carbon powder particles that have been pre-dispersed in water.

[0045] Next, in step 12, the cellulose nanofibers and carbon powder particles dispersed in the prepared water are added to a predetermined amount of water (in this case, pure water). The cellulose nanofiber content in the dispersion to be prepared is preferably in the range of 0.01% to 2.0% by volume, more preferably in the range of 0.05% to 1.0% by volume, and most preferably in the range of 0.1% to 0.5% by volume. If the cellulose nanofiber content is greater than 2.0% by volume, the viscosity of the dispersion will be high, resulting in insufficient water absorption by the mold during release film formation, making it difficult to obtain a uniform release film. Also, if the cellulose nanofiber content is less than 0.01% by volume, it is not possible to form a release film at all.

[0046] Furthermore, the content of carbon powder particles in the dispersion to be prepared is adjusted in relation to the content of cellulose nanofibers. Specifically, the mixing ratio of cellulose nanofibers to carbon powder particles is preferably within the range of 0.2 to 20 when the volume of cellulose nanofibers is divided by the volume of carbon powder particles. The volume of each component, cellulose nanofibers and carbon powder particles, was obtained by dividing their respective weights by their specific gravity. If the value obtained by dividing the volume of cellulose nanofibers by the volume of carbon powder particles is less than 0.2, the carbon powder particles cannot be sufficiently fixed by the cellulose nanofibers, and some of the carbon powder particles will flow into the ceramic molded body during the molding process to obtain the ceramic molded body, contaminating it. Also, if the value obtained by dividing the volume of cellulose nanofibers by the volume of carbon powder particles is greater than 20, the effect of the carbon powder particles will not be significantly apparent. The reason for expressing this as a volume ratio is that the adjustment can be made similarly even if the material and composition of the insoluble nanofibers and insoluble powder particles change and the relationship between their specific gravities changes.

[0047] Next, in step 13, a surfactant is added as a dispersant to the mixture of cellulose nanofibers, carbon powder particles, and pure water. The type and amount of surfactant added are not particularly limited and should be adjusted as appropriate within the range that a stable dispersion can be obtained. Note that the surfactant added here is an organic substance and will disappear during the firing process in which the ceramic molded body is fired, and will not remain in the product after firing.

[0048] Next, in step 14, a stable dispersion is prepared using a dispersion means. The dispersion means is not particularly limited and includes, for example, a homogenizer, a rotary-orbit mixer, a disperser mixer, a ball mill mixer, an intensive mixer, and an ultrasonic disperser. Next, in step 15, the prepared dispersion is passed through a sieve to obtain the stable dispersion of step 16.

[0049] 1-2. Application Procedure In the coating operation, a dispersion of cellulose nanofibers and carbon powder particles is applied to the inner wall surface of the mold. Figure 2 is a flowchart showing an overview of the coating operation. In Figure 2, first, the dispersion obtained in step 21 is prepared. Next, the dispersion is applied to the inside of the mold. The method of applying the dispersion is not particularly limited, but examples include the cast coating method, the spray coating method, and the wash coating method.

[0050] Here, the molding die will be described. The type of molding die is not particularly limited, but it is preferable to use a water-absorbing porous die made of porous metal, porous ceramics, porous carbon, porous resin, porous metal-ceramic composite, porous metal-resin composite, porous metal-carbon composite, porous ceramic-metal composite, porous ceramic-carbon composite, porous ceramic-resin composite, porous carbon-resin composite, or porous carbon-resin composite. Note that the dispersion of this embodiment may also be used in a conventional gypsum mold.

[0051] Furthermore, the raw material particles that make up the mold include metals, ceramics such as metal oxides, metal nitrides, and metal carbides, carbon, and resins such as thermoplastic resins and thermosetting resins. In addition, the particle shapes of the raw materials include plate-like particles, rod-like particles, spherical particles, porous particles, and fibrous particles. Furthermore, in order to improve the water absorption of the mold, the mold may be subjected to hydrophilic coating treatment, ultraviolet irradiation treatment, heat treatment, plasma treatment, etc.

[0052] In this embodiment, the in-slip coating method will be described. In step 22, the dispersion is injected into the mold. Next, in step 23, the mold is left for a predetermined time with the dispersion injected inside. During this time, the cellulose nanofibers and carbon powder particles contained in the dispersion form a film on the molding surface inside the mold. Next, in step 24, the excess dispersion is discharged from inside the mold. Next, in step 25, the mold is left for a predetermined time with the dispersion discharged to increase the strength of the release film formed on the molding surface.

[0053] In this way, the release film of step 26 is obtained. The release film obtained in this way has a single-layer structure. In contrast, by repeating the operations of steps 22 to 25 multiple times, a multilayer and tough release film can also be obtained.

[0054] Here, we will describe the release film formed on the molding surface inside the mold. The release film according to this embodiment is a web-like sheet in which carbon powder particles coexist with an aggregate of cellulose nanofibers. Here, "web" is defined as a sheet composed solely of fibers, and is a thin, film-like material (New Comprehensive Dictionary of Textiles; Senken Shimbunsha). Here, since it may also contain carbon powder particles in addition to fibers, the release film is understood as a sheet-like film similar to a web. For example, it is like a nonwoven fabric and differs from a film, with numerous fibers (cellulose nanofibers) constituting the web being laminated and having pores. Furthermore, the carbon powder particles coexisting with the cellulose nanofibers are sufficiently fixed by the cellulose nanofibers.

[0055] In this embodiment, the thickness of the release film is not particularly limited, but is preferably in the range of 1 μm to 1000 μm, more preferably in the range of 5 μm to 500 μm, and most preferably in the range of 10 μm to 100 μm. If the thickness of the release film is less than 1 μm, the release film will easily break, and a portion of the ceramic molding material (ceramic slurry in the casting method) will pass through the release film and flow into the mold. Also, if the thickness of the release film is greater than 1000 μm, the dispersion medium of the ceramic slurry will not be able to pass through the release film sufficiently, the water absorption will decrease significantly, and it will be difficult to obtain a ceramic molded body. The thickness of the release film can be measured by measuring the thickness using a micrometer, calipers, or microscope observation.

[0056] Furthermore, in this embodiment, the pore size of the release film is not particularly limited, but is preferably in the range of 1 nm to 1000 nm, more preferably in the range of 5 nm to 500 nm, and most preferably in the range of 10 nm to 100 nm. If the pore size of the release film is greater than 1000 nm, the ceramic molding material (ceramic slurry in the casting method) easily permeates the release film and enters the mold, greatly reducing the release properties. Also, if the pore size of the release film is smaller than 1 nm, it inhibits water in the ceramic slurry from permeating the release film, making it difficult to obtain a ceramic molded body. The pore size of the release film can be directly observed and measured using an electron microscope.

[0057] 2. Molding process Next, the molding process will be explained. In the molding process, a ceramic molding material (ceramic slurry in the casting method) is poured into a mold on which a release film has been formed on the inner wall surface (molding surface) to obtain a predetermined ceramic molded body. Figure 3 is an operation flow chart showing an overview of the molding process. In Figure 3, first, in step 31, the ceramic slurry is poured into the mold on which a release film has been formed on the inner wall surface. Next, in step 32, the mold is left for a predetermined time with the ceramic slurry inside. During this time, ceramic particles adhere to the molding surface of the release film.

[0058] Next, in step 33, excess ceramic slurry is discharged from inside the mold. In this way, the molding of the ceramic body is completed in step 34. Next, in step 35, the ceramic body, which has adhered to the mold, is left for a predetermined time. During this time, the moisture in the ceramic body is absorbed by the mold, increasing the strength of the ceramic body. Next, in step 36, the ceramic body is released from the mold.

[0059] In this way, the ceramic molded body of step 37 is obtained. The ceramic molded body obtained in this way is subjected to a drying process and then put into a firing process. In the firing process, if necessary, a degreasing operation is performed and the product is produced by the final firing. [Examples]

[0060] Next, this embodiment will be described in detail based on each example. While the following examples primarily describe the casting method, some descriptions will also cover the press molding and sheet molding methods. In the molding process of each example, alumina will be primarily used as the ceramic molding material. However, in this invention, the ceramic molding material is not limited to alumina, but refers to all commonly used ceramics. Furthermore, this invention is not limited to the following examples.

[0061] Example 1 In this embodiment 1, a single-layer release film consisting of an aggregate of cellulose nanofibers (without the presence of insoluble powder particles) was formed, and a ceramic molded body was obtained by a casting method.

[0062] 1. Release film formation process 1-1.Distributed operation Cellulose nanofibers produced by water jet defibration (manufactured by Sugino Machine Co., Ltd.; aqueous dispersion: solid content concentration 2% by weight, average fiber diameter 10-50 nm, specific surface area 120 m²) 2 A cellulose nanofiber (650 / g) was mixed with deionized water, and a dispersion 1 with a solid content of 0.13% by volume of cellulose nanofiber was obtained by homogenizing.

[0063] 1-2. Application Procedure The obtained dispersion 1 was poured into a porous ceramic mold (composition: alumina, porosity 40%), allowed to stand for 1 minute, and then the dispersion was discharged to obtain a release film 1 on the molded surface of the mold. The thickness of the obtained release film 1 was 44 μm. Figure 4 is an electron microscope image of the surface of the release film 1 in Example 1. From Figure 4, it can be seen that the pore size of the release film 1 was approximately 50 nm. Also from Figure 4, it can be seen that the aspect ratio of the cellulose nanofibers was 10 or more.

[0064] 2. Molding process Next, an alumina slurry (solid content concentration 50% by volume, dispersion medium: water, average particle size 0.3 μm) was poured into a porous ceramic mold on which a release film 1 had been formed. The pouring time was adjusted so that the water content of the resulting ceramic molded body was within the range of 13-14% by weight, and the molding process was carried out. The water content of the obtained ceramic molded body was measured by thermogravimetric analysis.

[0065] Example 2 In this second example, a single-layer release film consisting of a cellulose nanofiber aggregate with carbon powder particles was used, and a ceramic molded body was obtained by a casting method. The same cellulose nanofibers and carbon powder particles (manufactured by Kojun Chemical Laboratory; average particle size 20 μm) as in Example 1 were used, and the dispersion 2 was prepared so that the solid content concentration of the cellulose nanofibers was 0.13 vol% and the volume ratio of cellulose nanofibers to carbon powder particles was 0.6. The casting method was the same as in Example 1. The thickness of the obtained release film 2 was 44 μm. Figure 5 is an electron microscope image of the surface of the release film 2 in Example 2. From Figure 5, it can be seen that the pore size of the release film 2 was approximately 50 nm. Also from Figure 5, it can be seen that the aspect ratio of the cellulose nanofibers was 10 or more.

[0066] Example 3 In this third example, a single-layer release film consisting of a cellulose nanofiber aggregate with carbon powder particles was used, and a ceramic molded body was obtained by a casting method. A release film 3 with the same composition as in the second example was formed in the same porous ceramic mold as in the second example (thickness 50 μm), and casting was performed in the same manner as in the second example, except that a silicon nitride slurry (solid content concentration 25 vol%, dispersion medium: water, average particle size 0.2 μm) was cast into it.

[0067] Example 4 In this Example 4, a single-layer release film in which carbon powder particles coexisted with an aggregate of cellulose nanofibers was used, and a ceramic molded body was obtained by a casting method. The casting method was the same as in Example 2, except that the dispersion 4 was prepared so that the solid content concentration of cellulose nanofibers was 0.27% by volume and the volume ratio of cellulose nanofibers to carbon powder particles was 1.2. The thickness of the obtained release film 4 was 50 μm.

[0068] Example 5 In this Example 5, a single-layer release film in which carbon powder particles coexisted with an aggregate of cellulose nanofibers was used, and a ceramic molded body was obtained by a casting method. The casting method was the same as in Example 2, except that the dispersion 5 was prepared so that the solid content concentration of cellulose nanofibers was 0.40 volume% and the volume ratio of cellulose nanofibers to carbon powder particles was 1.8. The thickness of the obtained release film 5 was 110 μm.

[0069] Example 6 In this Example 6, a single-layer release film in which carbon powder particles coexisted with an aggregate of cellulose nanofibers was used, and a ceramic molded body was obtained by a casting method. The casting method was the same as in Example 2, except that the dispersion 6 was prepared so that the solid content concentration of cellulose nanofibers was 0.27% by volume and the volume ratio of cellulose nanofibers to carbon powder particles was 0.3. The thickness of the obtained release film 6 was 44 μm.

[0070] Example 7 In this Example 7, a single-layer release film in which carbon powder particles coexist with an aggregate of cellulose nanofibers was used, and a ceramic molded body was obtained by a casting method. In the composition of Example 2 above, cellulose nanofibers with different degrees of polymerization were used (manufactured by Sugino Machine Co., Ltd.; aqueous dispersion: solid content concentration 2% by weight, average fiber diameter 10-50 nm, specific surface area 150 m²). 2 Except for changing the composition ( / g, degree of polymerization 200) and adjusting the dispersion 7 so that the solid content concentration of cellulose nanofibers was 0.27% by volume and the volume ratio of cellulose nanofibers to carbon powder particles was 1.2, the casting process was carried out in the same manner as in Example 2 above. The thickness of the resulting release film 7 was 44 μm.

[0071] Example 8 In this Example 8, a single-layer release film in which carbon powder particles coexist with an aggregate of cellulose nanofibers was used, and a ceramic molded body was obtained by a casting method. In the composition of Example 2 above, cellulose nanofibers with different degrees of polymerization were used (manufactured by Sugino Machine Co., Ltd.; aqueous dispersion: solid content concentration 2% by weight, average fiber diameter 10-50 nm, specific surface area 120 m²). 2 Except for changing the cellulose nanofiber ( / g, degree of polymerization 800) and adjusting the dispersion 8 so that the solid content concentration of cellulose nanofiber was 0.27 vol% and the volume ratio of cellulose nanofiber / carbon powder particles was 1.2, the casting process was carried out in the same manner as in Example 2 above. The thickness of the resulting release film 8 was 44 μm.

[0072] Example 9 In this embodiment 9, a single-layer release film in which ceramic / resin composite particles coexist on an aggregate of silk nanofibers was used, and a ceramic molded body was obtained by a casting method.

[0073] 1. Release film formation process 1-1.Distributed operation Silk nanofiber produced by water jet defibration (manufactured by Sugino Machine Co., Ltd.; aqueous dispersion: solid content concentration 5% by weight, average fiber diameter 100 nm, specific surface area 200 m²) 2 A composite powder particle was prepared by adjusting the volume ratio of alumina particles (manufactured by Sumitomo Chemical Co., Ltd.; average particle size 0.7 μm) and acrylic particles (manufactured by SOKEN Co., Ltd.; average particle size 3 μm) to 50:50. This composite powder particle was prepared by adjusting the volume ratio of the average particle size (3 μm) to 50:50. This composite powder particle was then mixed with deionized water, and a dispersion 9 was obtained by homogenizing the mixture so that the solid content concentration of silk nanofibers was 0.3 volume% and the volume ratio of silk nanofibers to composite powder particles was 1.6.

[0074] 1-2. Application Procedure The obtained dispersion 9 was applied to a ceramic / resin composite mold (composition: alumina / acrylic resin, porosity 38%) to obtain a release film 9 on the molding surface of the mold. The thickness of the obtained release film 9 was 205 μm.

[0075] 2. Molding process Next, in the same manner as in Example 2 above, an alumina slurry (solid content concentration 50% by volume, dispersion medium: water, average particle size 0.3 μm) was cast into a ceramic / resin composite mold on which a release film 9 was formed, and the water content of the ceramic molded body was adjusted and cast molding was performed.

[0076] Example 10 In this Example 10, a ceramic molded body was obtained by a casting method using a multilayer release film. On top of the release film of Example 2, chitosan nanofibers (manufactured by Sugino Machine Co., Ltd.; aqueous dispersion: solid content concentration 5% by weight, average fiber diameter 20-50 nm, specific surface area 80 m²) were placed. 2 A multilayer release film 10 (thickness 91 μm) was formed by laminating release films (without the presence of insoluble powder particles) of 1 / g / m² and a degree of polymerization of 480. The multilayer release film 10 was then formed on the molding surface of a porous resin mold (composition: porous phenolic resin, porosity 41%). In addition, casting was performed in the same manner as in Example 2 above. The thickness of the obtained release film 10 was 91 μm.

[0077] Example 11 In this Example 11, a mixed nanofiber was prepared by mixing the same cellulose nanofiber as in Example 1 with carbon nanofiber (manufactured by Almedio Co., Ltd., milled fiber with a fiber diameter of 200-800 nm and a length of 1-15 μm) in a volume ratio of 50:50. This mixed nanofiber was then combined with alumina powder particles (manufactured by Sumitomo Chemical Co., Ltd.; average particle diameter of 0.3 μm) in deionized water, and a dispersion 11 was obtained by homogenizing the mixture so that the solid content concentration of the nanofiber was 0.3 volume% and the volume ratio of the mixed nanofiber / alumina powder particles was 18.0. The coating and molding processes were carried out by casting in the same manner as in Example 1. The thickness of the resulting release film 10 was 112 μm.

[0078] Example 12 In this embodiment 12, a single-layer release film in which carbon powder particles coexist with an aggregate of cellulose nanofibers was used, and a ceramic molded body was obtained by press molding.

[0079] 1. Release film formation process 1-1.Distributed operation Using the same cellulose nanofibers and carbon powder particles as in Example 2 above, dispersion 12 was prepared so that the solid content concentration of cellulose nanofibers was 0.13% by volume and the volume ratio of cellulose nanofibers to carbon powder particles was 1.2.

[0080] 1-2. Application Procedure The obtained dispersion 12 was spray-coated onto the surface of a φ30 mold and then dried to obtain a release film 12 on the molded surface. The thickness of the obtained release film 12 was 34 μm.

[0081] 2. Molding process Next, alumina mixed powder (solid content concentration 80% by volume, average particle size 11 μm) was poured into a mold on which a release film 11 had been formed, and press molding was performed at a press molding pressure of 60 kN.

[0082] Example 13 In this embodiment 13, a single-layer release film in which carbon powder particles coexist with an aggregate of cellulose nanofibers was used, and a ceramic molded body was obtained by sheet molding.

[0083] 1. Release film formation process 1-1.Distributed operation Using the same cellulose nanofibers and carbon powder particles as in Example 2 above, dispersion 13 was prepared so that the solid content concentration of cellulose nanofibers was 0.13% by volume and the volume ratio of cellulose nanofibers to carbon powder particles was 1.2.

[0084] 1-2. Application Procedure The obtained dispersion 13 was spray-coated onto the surface of a φ30 mold and then dried to obtain a release film 13 on the molded surface. The thickness of the obtained release film 13 was 34 μm.

[0085] 2. Molding process Next, an alumina slurry (solid content concentration 50% by volume, dispersion medium: water, average particle size: 0.3 μm) was formed into a sheet in a mold on which a release film 13 had been formed, and the sheet was formed by natural drying.

[0086] Comparative Example 1 Comparative Example 1 corresponds to Example 1 described above. In this comparative example, no release film was formed on the molding surface of the mold. An alumina slurry (solid content concentration 50% by volume, dispersion medium: water, average particle size: 0.1 μm) was cast into a porous ceramic mold (composition: alumina, porosity 40%), and the casting time was adjusted so that the water content of the ceramic molded body was within the range of 13-14% by weight.

[0087] Comparative Example 2 Comparative Example 2 is a follow-up experiment of a conventional casting method using a plaster mold.

[0088] 1. Release film formation process 1-1.Dissolution operation Ammonium alginate was dissolved in deionized water to a concentration of 1% by weight to obtain an aqueous solution.

[0089] 1-2. Application Procedure The obtained aqueous solution was poured into a plaster mold, allowed to stand for 1 minute, and then drained to obtain an alginate release film on the molded surface of the plaster mold. The thickness of the obtained release film was 50 μm.

[0090] 2. Molding process Next, an alumina slurry (solid content concentration 50% by volume, dispersion medium: water, average particle size 0.3 μm) was poured into a plaster mold on which a release film had been formed, and the pouring time was adjusted so that the water content of the ceramic molded body was within the range of 13-14% by weight, and the molding process was carried out.

[0091] Comparative Example 3 Comparative Example 3 is a replication of the method described in Patent Document 1.

[0092] 1. Release film formation process 1-1.Distributed operation We used sodium carboxymethylcellulose salt (manufactured by Wako Pure Chemical Industries, Ltd.; hereinafter referred to as "CMC-Na") and acid-type carboxymethylcellulose (hereinafter referred to as "CMC-H") obtained by substituting CMC-Na with a 10% nitrate-methanol solution. We mixed 6 parts by weight of CMC-Na, 4 parts by weight of CMC-H, and 250 parts by weight of deionized water, and obtained a dispersion in which CMC-Na was dissolved and CMC-H was dispersed using a homogenizer.

[0093] 1-2. Application Procedure The obtained dispersion was poured into a porous ceramic mold (composition: alumina, porosity 40%), allowed to stand for 1 minute, then the dispersion was discharged and dried in a dryer set to 50°C. Next, the porous ceramic mold was immersed in a 10% nitric acid methanol solution for 5 minutes to perform an immobilization treatment. Then, the excess acid and salt remaining after the immobilization treatment was washed with an 80% methanol solution (methanol:pure water = 80:20), and dried to obtain a release film on the molding surface of the mold. The thickness of the obtained release film was 50 μm.

[0094] 2. Molding process Next, an alumina slurry (solid content concentration 50% by volume, dispersion medium: water, average particle size 0.3 μm) was poured into a porous ceramic mold on which a release film had been formed, and the pouring time was adjusted so that the water content of the ceramic molded body was within the range of 13-14% by weight, and the molding process was carried out.

[0095] Comparative Example 4 Comparative Example 4 is a follow-up experiment of the method described in Patent Document 2.

[0096] 1. Release film formation process 1-1.Distributed operation Alumina powder (average particle size 0.3 μm) was heat-treated to 800°C in an atmospheric furnace, and then mixed with a 2% by weight aqueous solution of polyvinyl alcohol in a 50% by weight:50% by weight ratio. A dispersion was obtained by homogenizing.

[0097] 1-2. Application Procedure The obtained dispersion was poured into a porous ceramic mold (composition: alumina, porosity 40%), allowed to stand for 1 minute, and then the dispersion was discharged to obtain a release film on the mold surface. The thickness of the obtained release film was 190 μm.

[0098] 2. Molding process Next, an alumina slurry (solid content concentration 50% by volume, dispersion medium: water, average particle size 0.3 μm) was poured into a porous ceramic mold on which a release film had been formed, and the pouring time was adjusted so that the water content of the ceramic molded body was within the range of 13-14% by weight, and the molding process was carried out.

[0099] Comparative Example 5 Comparative Example 5 corresponds to Example 2, and was cast in the same manner as in Example 2, except that the volume ratio of cellulose nanofibers to carbon powder particles in the dispersion was adjusted to 0.1. The thickness of the resulting release film was 50 μm.

[0100] Performance evaluation Next, the ceramic molded bodies of each of the above examples and comparative examples were evaluated for the following three items (1) to (3). In addition, the fired ceramic bodies obtained by firing some of the ceramic molded bodies were evaluated for the following item (4). (1) Contamination of ceramic molded products by insoluble powder particles constituting the release film We visually inspected, used an optical microscope, and used an electron microscope to check whether there were any insoluble powder particles floating on the surface of the ceramic molded body that were not sufficiently fixed by insoluble nanofibers. (2) Damage to the ceramic molded body when it is removed from the mold. When the ceramic molded body was removed from the mold, it was visually inspected to check for any defects such as damage. (3) Adhesion between the mold and the ceramic molded body As a value related to the evaluation item in (2) above, the adhesion strength between the mold and the ceramic molded body was evaluated. The method for evaluating the adhesion strength will be described later. (4) Impurities contained in the fired ceramic body The ceramic molded bodies obtained in Examples 1 and 2, and Comparative Example 2, were degreased in an air atmosphere at 800°C, and then fired in an air atmosphere at 1600°C to obtain fired ceramic bodies. The impurities in the obtained fired ceramic bodies were evaluated using an X-ray fluorescence analyzer.

[0101] Method for evaluating adhesion strength Figure 6 is a schematic diagram showing the method for evaluating the adhesion force between a mold and a ceramic molded body. In Figure 6, the measurement was performed as follows. First, the mold was fixed to the lower fixture of the tensile testing machine, and the dispersion obtained in each example or comparative example was applied to the upper surface of the mold to obtain a release film. Next, the mold was surrounded by a resin sheet, and ceramic slurry was poured into the interior. Then, the measuring fixture (a metal mesh fixed to the tip of a metal rod) connected to the load cell of the tensile testing machine was quickly immersed in the ceramic slurry to perform ceramic molding. The dispersion medium (water) contained in the ceramic slurry was separated by the mold, and a molded body incorporating the measuring fixture was obtained. Next, the measuring fixture incorporated into this molded body was moved in the tensile direction, and the tensile load was measured by the load cell. The tensile stress obtained by dividing the measured tensile load by the area of ​​the molded surface of the mold (area of ​​the release film) was evaluated as the adhesion force.

[0102] Table 1 shows the evaluation results for evaluation items (1) to (4) for each ceramic molded body of Examples 1 to 13 and Comparative Examples 1 to 5. In Table 1, a "-" next to the volume ratio indicates that there is no volume ratio for a single component, and the volume ratio for Comparative Example 4 was not measured. Similarly, a "-" next to the measured value of impurities indicates that it was not measured.

[0103] [Table 1]

[0104] As can be seen from Table 1, the ceramic molding methods of Example 1, which had a release film made only of insoluble nanofibers, and Examples 2 to 13, which had release films made of insoluble nanofibers and insoluble powder particles, obtained good evaluation results in evaluation items (1) and (2). In contrast, in Comparative Examples 1 and 3, damage was observed in the ceramic molded body when released from the mold in evaluation item (2). The reason for the damage observed in Comparative Examples 1 and 3 can be understood from the fact that the adhesion force value in evaluation item (3) was larger than that of Examples 1 to 13. On the other hand, in Comparative Example 4, good evaluation results were obtained in evaluation items (1) and (2). However, since the adhesion force value in evaluation item (3) of Comparative Example 4 was larger than that of Examples 1 to 13, it is considered that there is a high possibility of damage occurring in the ceramic molded body.

[0105] Furthermore, in Comparative Example 5, contamination of the ceramic molded body was observed in evaluation item (1). This is thought to be due to the small volume ratio of cellulose nanofibers to carbon powder particles, which was 0.1. In other words, because the amount of cellulose nanofibers was extremely small compared to the amount of carbon powder particles, the carbon powder particles could not be sufficiently fixed by the cellulose nanofibers, and the carbon powder particles contaminated the ceramic molded body. Also, as mentioned above, evaluation item (4) was confirmed only in some examples and comparative examples. As a result, in the conventional casting method using a gypsum mold in Comparative Example 2, extreme calcium contamination was observed in the fired ceramic body, which is thought to be contamination from the gypsum mold. In contrast, Examples 1 and 2 showed no such contamination and yielded good results. Although analysis was not performed, it is thought that similar results would be obtained in other Examples 3 to 13.

[0106] Thus, in Examples 1 to 13, favorable results were obtained in all evaluation items (1) to (4). In particular, the adhesion force between the ceramic molded body and the mold was reduced to up to 1 / 20th compared to the conventional method. This means that the release properties are greatly improved by using a release film consisting of insoluble nanofibers and insoluble powder particles. As a result, it is possible to produce complex shapes and thin-walled ceramic molded bodies even in ceramic molding methods that do not use alginate films. Furthermore, it can be seen that even better results can be obtained when the volume ratio of cellulose nanofibers / carbon powder particles is within the range of 0.2 to 20.

[0107] As described above, according to the above embodiment, it is possible to easily release ceramic molded bodies without using conventional alginate release films, and a mold release film for molding and a ceramic molding method using the same can be provided that prevents defects such as cracks and fractures from occurring during firing of the molded bodies. [Industrial applicability]

[0108] This invention relates to a mold release film and a ceramic molding method using the same, which enable the production of high-purity, complex-shaped, and thin-walled molded bodies by ceramic molding. By using the mold release film according to the present invention, it is possible to produce high-purity, high-value-added component products more efficiently, which was difficult to achieve with ceramic molding methods using gypsum molds, thereby making a significant contribution to the industrial field.

Claims

1. A mold release film formed on the inner wall surface of a mold used for molding a ceramic molded body before firing, when manufacturing a fired ceramic body, A mold release film characterized by being a web-like sheet composed of an aggregate of insoluble nanofibers, without the coexistence of insoluble powder particles.

2. A mold release film formed on the inner wall surface of a mold used for molding a ceramic molded body before firing, when manufacturing a ceramic fired body, Insoluble powder particles coexist on a web-like sheet composed of aggregates of insoluble nanofibers. A mold release film characterized in that the value obtained by dividing the volume of the insoluble nanofibers by the volume of the insoluble powder particles is in the range of 0.2 to 20.

3. The mold release film according to claim 2, characterized in that the insoluble powder particles consist of at least one of the group consisting of ceramic particles, carbon particles, resin particles, polysaccharide particles, and protein particles.

4. A mold release film formed on the inner wall surface of a mold used when manufacturing a ceramic fired body having a ceramic composition X, The mold release film according to claim 2, characterized in that the insoluble powder particles are ceramic particles having the same composition and particle size as the molding raw material consisting of the ceramic composition X formed by the mold, or ceramic particles having a different particle size but consisting of the same ceramic composition X as the molding raw material.

5. The mold release film according to any one of claims 1 to 4, characterized in that the insoluble nanofiber is at least one of the group consisting of polysaccharide nanofibers or protein nanofibers.

6. The mold release film according to claim 5, characterized in that the pore size of the web-like sheet is in the range of 1 nm to 1000 nm.

7. A ceramic molding method using a mold release film according to any one of Claims 1 to 4, A release film forming step in which the mold release film is formed on the inner wall surface of the mold, The process includes a molding step of pouring a ceramic molding material into a mold on which the mold release film is formed on the inner wall surface to obtain a predetermined ceramic molded body, In the mold release film formation step, A dispersion operation to obtain a dispersion by dispersing the insoluble nanofibers, or by mixing and dispersing the insoluble nanofibers and the insoluble powder particles, A ceramic molding method characterized by comprising a coating operation of applying the dispersion to the inner wall surface of the molding die.

8. The ceramic molding method according to claim 7, characterized in that the content of the insoluble nanofibers in the dispersion is in the range of 0.01% by volume to 2.0% by volume.

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