Method for producing unidirectional ceramic fiber prepreg, and unidirectional ceramic fiber prepreg

Abstract

The present disclosure provides a means that can provide a prepreg having a fine and dense matrix structure by improving the impregnability of the matrix between nonwoven fabric fibers.　The present disclosure relates to a method for producing a unidirectional ceramic fiber prepreg, the method comprising: a step for preparing a plurality of unidirectionally oriented ceramic fibers and a ceramic particle-containing composition; a step for obtaining a coating film by coating the ceramic particle-containing composition on a support; a step for obtaining a ceramic particle-containing composition impregnated body by immersing the plurality of unidirectionally oriented ceramic fibers in the coating film; and a step for peeling the support, after the ceramic particle-containing composition impregnated body has been dried, to obtain a unidirectional ceramic fiber prepreg.

Description

Manufacturing method for unidirectional ceramic fiber prepreg and unidirectional ceramic fiber prepreg

[0001] The present disclosure relates to a method for producing a unidirectional ceramic fiber prepreg and to a unidirectional ceramic fiber prepreg.

[0002] Depending on the type, ceramic materials have advantages such as excellent hardness, mechanical strength, heat resistance, impact resistance, wear resistance, oxidation resistance, or corrosion resistance, or a small coefficient of thermal expansion, etc. For these reasons, ceramic materials are expected to be used in a variety of applications, such as electronic components and high-temperature structural members.

[0003] Ceramic materials are sometimes used as composite materials of multiple ceramic materials or composite materials of ceramic and other materials for the purposes of further improving functionality, production efficiency, etc. Examples of such composite materials include those formed using prepregs containing ceramic fibers and ceramic particles.

[0004] For example, Japanese Patent No. 6978896 discloses a method for producing a ceramic-based composite member, which includes a slurry preparation step of preparing a slurry in which an oxide-based ceramic powder is dispersed in a dispersion medium, and an impregnation step of impregnating a sheet made of inorganic fibers with the slurry to form a slurry-impregnated sheet.

[0005] However, the method described in Japanese Patent No. 6978896 has the problem that the matrix does not penetrate well into the spaces between the fibers of the nonwoven fabric, and internal bubbles are formed, making it impossible to obtain a prepreg having a dense matrix structure.

[0006] Therefore, an object of the present disclosure is to provide a means for improving the impregnation of the matrix between the fibers of the nonwoven fabric and obtaining a prepreg having a dense matrix structure.

[0007] In order to solve the above problems, according to one embodiment of the present disclosure, there is provided a method for producing a unidirectional ceramic fiber prepreg, including the steps of: preparing a plurality of unidirectionally oriented ceramic fibers and a ceramic particle-containing composition; applying the ceramic particle-containing composition to a support to obtain a coating film; immersing the plurality of unidirectionally oriented ceramic fibers in the coating film to obtain a ceramic particle-containing composition-impregnated body; and drying the ceramic particle-containing composition-impregnated body and then peeling off the support to obtain a unidirectional ceramic fiber prepreg.

[0008] According to another embodiment of the present disclosure, there is provided a unidirectional ceramic fiber prepreg including a plurality of ceramic fibers oriented in one direction and a ceramic particle-containing composition impregnated into the plurality of ceramic fibers, wherein a coefficient of variation in the number of the ceramic fibers per unit section in a cut surface along the thickness direction of the unidirectional ceramic fiber prepreg is 2.0 or less.

[0009] FIG. 1 is a view showing an SEM photograph of a cross section cut along the thickness direction of a unidirectional ceramic fiber prepreg obtained in an example.

[0010] According to one embodiment of the present disclosure, there is provided a method for producing a unidirectional ceramic fiber prepreg, comprising the steps of: preparing a plurality of unidirectionally oriented ceramic fibers and a ceramic particle-containing composition; applying the ceramic particle-containing composition to a support to obtain a coating film; immersing the unidirectionally oriented ceramic fibers in the coating film to obtain a ceramic particle-containing composition-impregnated body; and drying the ceramic particle-containing composition-impregnated body and then peeling off the support to obtain a unidirectional ceramic fiber prepreg. The production method of the present disclosure having such a configuration improves the impregnation of the matrix between the fibers of the nonwoven fabric, thereby enabling the production of a prepreg having a dense matrix structure.

[0011] According to another embodiment of the present disclosure, there is provided a unidirectional ceramic fiber prepreg including a plurality of ceramic fibers oriented in one direction and a ceramic particle-containing composition impregnated into the plurality of ceramic fibers, wherein a coefficient of variation in the number of the ceramic fibers per unit section in a cut surface along the thickness direction of the unidirectional ceramic fiber prepreg is 2.0 or less.

[0012] In this specification, the term "prepreg" refers to a composite material in a semi-cured state produced by impregnating a plurality of unidirectionally oriented ceramic fibers with a ceramic particle-containing composition.

[0013] The manufacturing method described in the above-mentioned Japanese Patent No. 6978896 includes a step of preparing an immersion bath containing a slurry in which an oxide-based ceramic powder is dispersed in a dispersion medium, and then immersing a sheet made of inorganic fibers in the immersion bath to impregnate the spaces between the fibers of the sheet with the slurry. However, this method has a problem in that the inorganic fibers contained in the sheet have strong adhesion and binding properties to each other, making it difficult for the slurry to penetrate into the interior of the sheet.

[0014] One possible solution to this problem is to place a plurality of ceramic fibers oriented in one direction (hereinafter simply referred to as "unidirectional ceramic fibers") into an immersion bath of slurry and impregnate the interior of the unidirectional ceramic fibers with the slurry. However, the inventors of the present disclosure have found that this method can cause problems such as the formation of fiber bundles and gaps when the fibers are removed from the immersion bath, resulting in the formation of internal bubbles and preventing the production of a prepreg with a dense matrix structure.

[0015] In view of the above-mentioned problems, the inventors of the present disclosure conducted extensive research. As a result, the inventors of the present disclosure discovered that a prepreg with excellent dispersion of unidirectional ceramic fibers can be obtained by a manufacturing method including forming a coating film made of a composition (slurry) containing ceramic particles in advance and then immersing unidirectional ceramic fibers in the coating film. This method makes it possible to obtain a prepreg with improved dispersion of unidirectional ceramic fibers, with a coefficient of variation of the number of ceramic fibers per unit section of 2.0 or less, in a very simple manner. The obtained prepreg has a dense matrix structure. As a result, ceramic matrix composites (CMCs) obtained by sintering the prepreg are expected to have excellent mechanical properties. Therefore, such CMCs are considered suitable for a wide range of applications, such as electronic components and high-temperature structural components.

[0016] Although the present disclosure will be described below by way of example, the present disclosure is not limited to the following examples and can be modified in various ways within the scope of the claims. The embodiments described in this specification can be combined in any manner to form other embodiments.

[0017] In this specification, unless otherwise specified, operations and measurements of physical properties are carried out at room temperature (20° C. or higher and 25° C. or lower) and at a relative humidity of 40% RH or higher and 50% RH or lower.

[0018] [Coefficient of Variation] In a unidirectional ceramic fiber prepreg according to an embodiment of the present disclosure, the coefficient of variation of the number of unidirectional ceramic fibers per unit section in a cross section along the thickness direction is 2.0 or less. A coefficient of variation of 2.0 or less allows a prepreg to be obtained with a dense matrix structure. A smaller coefficient of variation indicates more even dispersion of the unidirectional ceramic fibers in the prepreg, suggesting that a prepreg with a denser matrix structure can be obtained, thereby resulting in a ceramic-based composite material with excellent mechanical properties. On the other hand, a coefficient of variation exceeding 2.0 can result in fiber bundling, gaps, and internal bubbles, preventing the production of a prepreg with a dense matrix structure. The coefficient of variation is preferably 1.7 or less, more preferably 1.5 or less.

[0019] In this specification, the coefficient of variation is a value calculated by the following method. Specifically, a unidirectional ceramic fiber prepreg is cut along the thickness direction, and an image of the cut surface is taken using a low-vacuum scanning electron microscope. As an example, the area to be photographed is 192 μm long x 256 μm wide. The resulting image is divided into four sections vertically across the entire thickness of the prepreg, and into four sections with a width of 256 μm. This results in a total of 16 sections, and the number of ceramic fibers per section is measured (a total of 16 sections are measured). The standard deviation and average value of the number of ceramic fibers at the 16 sections are calculated, and the value obtained by dividing the standard deviation by the average value is used as the coefficient of variation. More specifically, the coefficient of variation can be measured by the method described in the Examples.

[0020] The coefficient of variation can be controlled by adjusting the viscosity of the ceramic particle-containing composition to be impregnated into the unidirectional ceramic fibers, the immersion time, the tension of the fibers, etc.

[0021] [Ceramic Fibers] The ceramic fibers according to an embodiment of the present disclosure are oriented in one direction, improving the mechanical properties of the prepreg. The orientation direction of the ceramic fibers may be the same as the longitudinal direction of the prepreg according to the present disclosure. The ceramic fibers are not particularly limited as long as they are fibers essentially composed of ceramic. Here, the ceramic content in the unidirectional ceramic fibers is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass (upper limit 100% by mass) relative to the total mass of the unidirectional ceramic fibers. The ceramic content in the unidirectional ceramic fibers can be evaluated by, for example, weight change by thermogravimetric analysis.

[0022] The ceramic constituting the unidirectional ceramic fiber is not particularly limited, and examples thereof include materials commonly used in known ceramic fibers. Examples include glass, silicon carbide, alumina, silica, mullite, and carbon. Examples include oxides or composite oxides of Si, Ti, Zr, Mg, Hf, Al, and rare earth elements, as described in International Publication No. 2012 / 077787. The ceramic constituting the unidirectional ceramic fiber may be used alone or in combination of two or more. The ceramic fiber is more preferably silicon carbide (SiC) fiber, alumina fiber, mullite fiber, or carbon fiber.

[0023] The unidirectional ceramic fibers may be commercially available or manufactured. The method for obtaining the manufactured products is not particularly limited, and they can be obtained, for example, by opening a ceramic fiber bundle. The opening method can be a known method alone or a combination of several known methods.

[0024] The ceramic fibers may be used singly or in combination of two or more. The average fiber length, average fineness, etc. of the ceramic fibers may be appropriately changed depending on the application.

[0025] The fiber content (Vf) of the unidirectional ceramic fibers in the prepreg according to the present disclosure is preferably 20% by volume or more, more preferably 25% by volume or more, and even more preferably 30% by volume or more. Furthermore, the fiber content (Vf) of the unidirectional ceramic fibers in the prepreg according to the present disclosure is preferably 85% by volume or less, more preferably 80% by volume or less, and even more preferably 75% by volume or less. That is, the fiber content (Vf) of the unidirectional ceramic fibers in the prepreg according to the present disclosure is preferably 20% by volume or more and 85% by volume or less, more preferably 25% by volume or more and 80% by volume or less, and even more preferably 30% by volume or more and 75% by volume or less. A fiber content (Vf) within this range ensures an appropriate number of fibers in the prepreg, eliminating adhesion between fibers and fiber-deficient areas, thereby advantageously preventing localized fracture after the final sintered body is formed. The fiber content (Vf) can be obtained by a calculation method in accordance with ASTM D3171 or JIS K7075: 1991. The fiber content (Vf) can be controlled by adjusting the thickness of the coating film produced from the ceramic particle-containing composition in the production method described below, the basis weight of the fibers used, the solids concentration of the slurry, and the like.

[0026] [Ceramic Particle-Containing Composition] The unidirectional ceramic fiber prepreg according to the present disclosure comprises a ceramic particle-containing composition (hereinafter also simply referred to as "composition") impregnated into a plurality of unidirectional ceramic fibers. The ceramic particle-containing composition generally comprises (A) ceramic particles, (B) a binder, (C) a plasticizer, (D) water, and, as necessary, further comprises (E) an acid, (F) a thickener, (G) other components, etc. These components are described below.

[0027] <(A) Ceramic Particles> A ceramic particle-containing composition according to an embodiment of the present disclosure includes ceramic particles as component (A). In this specification, the term "ceramic particles" refers to particles containing ceramic.

[0028] The ceramic content relative to the total mass of the ceramic particles that can be used as component (A) is not particularly limited, but is preferably 50 mass% or more, more preferably 70 mass% or more, and even more preferably 90 mass% or more (upper limit 100 mass%). The ceramic content can be evaluated by weight change using thermogravimetric analysis.

[0029] The type of ceramic contained in the ceramic particles used as component (A) is not particularly limited. Examples of the ceramic contained in the ceramic particles include compounds composed only of carbon, oxides, hydroxides, carbides, carbonates, nitrides, halides, phosphates, borides, etc. The oxide is not particularly limited, but examples thereof include silicon oxide, aluminum oxide (alumina, Al ２ O ３ ), mullite, copper oxide, iron oxide, nickel oxide, tin oxide, cadmium oxide, zinc oxide, zirconium oxide, etc. The hydroxide is not particularly limited, but examples thereof include aluminum hydroxide (Al(OH) ３ ) and the like. Carbides are not particularly limited, but examples thereof include silicon carbide (SiC) and boron carbide. Nitrides are not particularly limited, but examples thereof include silicon nitride, gallium nitride, titanium nitride, and lithium nitride. Furthermore, examples of the ceramic contained in the ceramic particles include oxides or composite oxides of Si, Ti, Zr, Mg, Hf, Al, and rare earth elements described in International Publication No. 2012 / 077787. The ceramic particles may contain one type of these ceramics alone, or may contain two or more types in combination.

[0030] In a preferred embodiment of the present disclosure, component (A) comprises ceramic particles containing at least one selected from the group consisting of oxides, carbides, nitrides, and borides. The content of the ceramic particles containing at least one selected from the group consisting of oxides, carbides, nitrides, and borides relative to the total mass of component (A) is preferably 50 mass% or more, more preferably 90 mass% or more (up to 100 mass%). The ceramic particles of component (A) are even more preferably ceramic particles containing at least one selected from the group consisting of oxides, carbides, nitrides, and borides.

[0031] In a more preferred embodiment of the present disclosure, component (A) comprises ceramic particles containing at least one selected from the group consisting of oxides and carbides. The content of the ceramic particles containing at least one selected from the group consisting of oxides and carbides relative to the total mass of component (A) is preferably 50 mass% or more, more preferably 90 mass% or more (up to 100 mass%). It is even more preferred that the ceramic particles of component (A) are ceramic particles containing at least one selected from the group consisting of oxides and carbides.

[0032] In a further preferred embodiment of the present disclosure, the carbide-containing ceramic particles include silicon carbide-containing ceramic particles. The content of the silicon carbide-containing ceramic particles relative to the total mass of the carbide-containing ceramic particles is preferably 50 mass% or more, more preferably 90 mass% or more (upper limit 100 mass%). The carbide-containing ceramic particles in component (A) are more preferably silicon carbide-containing ceramic particles.

[0033] In a further preferred embodiment of the present disclosure, the oxide-containing ceramic particles include ceramic particles containing at least one selected from the group consisting of alumina and mullite. The content of the ceramic particles containing at least one selected from the group consisting of alumina and mullite relative to the total mass of the oxide-containing ceramic particles is preferably 50 mass% or more, more preferably 90 mass% or more (up to 100 mass%). It is even more preferred that the oxide-containing ceramic particles in component (A) are ceramic particles containing at least one selected from the group consisting of alumina and mullite.

[0034] The ceramic particles that can be used as component (A) may be uncoated particles, particles coated with a coating layer (coated particles), or a combination thereof. Here, "coated" means that at least a portion of the particles is coated with a coating layer. The coating layer is not particularly limited, but a coating layer containing aluminum hydroxide is preferred. The coating method is not particularly limited, and known methods can be used. Silicon carbide particles coated with a coating layer containing aluminum hydroxide are not particularly limited, but can be produced by appropriately adopting the methods and conditions described in, for example, WO 2019 / 065956, etc. The composition and structure of the coated particles can be analyzed by, for example, SEM (Scanning Electron Microscope)-EDX (Energy Dispersive X-ray Spectroscopy) observation, TEM (Transmission Electron Microscope)-EDX (Energy Dispersive X-ray Spectroscopy) observation, EELS (Electron Energy Loss Spectroscopy) analysis, or the like, or by combining a plurality of measurements as necessary.

[0035] The ceramic particles that can be used as component (A) may be surface-treated. The type and method of surface treatment are not particularly limited, and known types and methods of surface treatment can be appropriately adopted.

[0036] Preferred examples of component (A) include oxide particles, carbide particles, oxide particles coated with a coating layer, and carbide particles coated with a coating layer. Specific examples include, but are not limited to, silicon oxide particles, mullite particles, alumina particles, copper oxide particles, iron oxide particles, nickel oxide particles, tin oxide particles, cadmium oxide particles, zinc oxide particles, zirconium oxide particles, silicon carbide particles, boron carbide particles, and particles thereof coated with a coating layer. Among these, mullite particles, alumina particles, silicon carbide particles, and silicon carbide particles coated with a coating layer containing aluminum hydroxide (aluminum hydroxide-coated SiC particles) are more preferred. Furthermore, at least one selected from the group consisting of alumina particles, silicon carbide particles, and silicon carbide particles coated with a coating layer containing aluminum hydroxide (aluminum hydroxide-coated SiC particles) is more preferred, with aluminum hydroxide-coated SiC particles being particularly preferred.

[0037] The shape of the ceramic particles that can be used as component (A) is not particularly limited and may be spherical or non-spherical. Specific examples of non-spherical shapes include polygonal prisms such as triangular prisms and quadrangular prisms, cylinders, bale-shaped cylinders in which the center is bulging more than the ends, donut-shaped disks with a central hole, plate-shaped, cocoon-shaped shapes with a central constriction, associative spheres in which multiple particles are integrated, beads-shaped shapes in which multiple particles are connected in a nearly straight line, confetti-shaped shapes with multiple protrusions on the surface, rugby ball-shaped shapes, and needle-shaped shapes that are even thinner than rugby ball-shaped shapes, and are not particularly limited.

[0038] The average primary particle size of the ceramic particles that can be used as component (A) is not particularly limited, but is preferably 0.001 μm or more, more preferably 0.005 μm or more, and even more preferably 0.01 μm or more. Within these ranges, aggregation of the ceramic particles is further suppressed, resulting in a composition with higher dispersibility. The average primary particle size of the ceramic particles that can be used as component (A) is not particularly limited, but is preferably 2.0 μm or less, more preferably 1.5 μm or less, even more preferably 1.0 μm or less, and particularly preferably 0.5 μm or less. Within these ranges, sedimentation of the ceramic particles is further suppressed, resulting in a composition with higher dispersibility. The average primary particle size of the ceramic particles can be calculated based on the average specific surface area (SA) of the ceramic particles calculated from three consecutive measurements using the BET method, using the true density of the ceramic particles, and assuming that the ceramic particles are spherical. The specific surface area of ​​the ceramic particles can be measured, for example, using a Flow Sorb II 2300 manufactured by Micromeritics. In view of the above, examples of the range of the average primary particle size of the ceramic particles that can be used as component (A) include, but are not limited to, 0.001 μm or more and 2.0 μm or less, 0.005 μm or more and 1.5 μm or less, 0.01 μm or more and 1.0 μm or less, and 0.01 μm or more and 0.5 μm or less.

[0039] The average secondary particle diameter of the ceramic particles used as component (A) is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.03 μm or more, even more preferably 0.05 μm or more, and particularly preferably 0.1 μm or more. Within these ranges, the possibility of excessive thickening of the composition is further reduced, resulting in a composition more suitable for coating. The average secondary particle diameter of the ceramic particles that can be used as component (A) is not particularly limited, but is preferably 3 μm or less, more preferably 2 μm or less, even more preferably 1.5 μm or less, and particularly preferably 1 μm or less. Within these ranges, sedimentation of the ceramic particles is further suppressed, resulting in a composition with higher dispersibility. The average secondary particle diameter of the ceramic particles can be measured using a scattering particle size distribution analyzer LA-950 manufactured by Horiba, Ltd. In view of the above, examples of the range of the average secondary particle size of the ceramic particles that can be used as component (A) include, but are not limited to, 0.01 μm or more and 3 μm or less, 0.03 μm or more and 2 μm or less, 0.05 μm or more and 1.5 μm or less, and 0.1 μm or more and 1 μm or less.

[0040] The component (A) may be a commercially available product or a synthetic product. When the ceramic particles are coated particles, the pre-coated particles that are the raw material for the coated particles may also be commercially available products or synthetic products. Examples of commercially available pre-coated particles include, but are not limited to, products manufactured by Fujimi Incorporated under the product names WA#30000 and GC#40000.

[0041] As the component (A), one type of ceramic particles may be used alone, or two or more types of ceramic particles may be used in combination.

[0042] The content of component (A) in the ceramic particle-containing composition is not particularly limited, but is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 10% by mass or more, relative to the total mass of the solids in the composition. Within this range, the amount of other components removed during drying, degreasing, etc. is reduced, resulting in a composition that is superior in terms of production costs. Furthermore, the content of component (A) in the composition is not particularly limited, but is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less, relative to the total mass of the solids in the composition. Within this range, the possibility of excessive thickening of the composition is further reduced, resulting in a composition that is more suitable for coating. For these reasons, examples of the content range of component (A) in the ceramic particle-containing composition include, but are not limited to, 0.1% by mass or more to 90% by mass or less, 1% by mass or more to 80% by mass or less, and 10% by mass or more to 75% by mass or less, relative to the total mass of the solids in the composition. When the composition contains two or more types of component (A), the content of component (A) refers to the total amount of these.

[0043] The ceramic particle-containing composition may contain particles containing boron nitride (BN), but may be substantially free of particles containing BN, or may be completely free of particles containing BN. As used herein, "substantially free of particles containing BN" means that the content of particles containing BN in the ceramic particle-containing composition is less than 0.1 mass% relative to the total mass of the composition. The ceramic particle-containing composition may contain particles containing silicon carbide (SiC), but may be substantially free of particles containing SiC, or may be completely free of particles containing SiC. As used herein, "substantially free of particles containing SiC" means that the content of particles containing SiC in the ceramic particle-containing composition is less than 0.1 mass% relative to the total mass of the composition.

[0044] <Component (B): Binder> The ceramic particle-containing composition according to one embodiment of the present disclosure includes a binder (binder resin) as component (B). Component (B) can improve the moldability and handleability of the prepreg.

[0045] The component (B) is not particularly limited, and known resins can be used. Among these, from the viewpoint of obtaining excellent dispersibility and high stability over time, a resin having a hydroxyl group (hereinafter also referred to as component (B1)) is preferred. Preferred examples of component (B1) include polyvinyl alcohol (PVA); modified polyvinyl alcohol (modified PVA) such as polyvinyl butyral (PVB), polyvinyl propylal, polyvinyl acetal, and polyvinyl formal; hydroxyl-containing glyoxal resin, hydroxyl-containing acrylic resin, phenolic resin, hydroxyl-containing polyvinyl pyrrolidone (PVP), hydroxyl-containing polyester, hydroxyl-containing silicone, and hydroxyl-containing polycarboxylic acid, but are not limited thereto. Among these, from the viewpoint of ease of handling and ease of viscosity adjustment, polyvinyl alcohol and modified polyvinyl alcohol are more preferred, polyvinyl alcohol, polyvinyl butyral, and polyvinyl acetal are even more preferred, and polyvinyl acetal is particularly preferred.

[0046] In a preferred embodiment of the present disclosure, the component (B) includes a component (B1): a resin having a hydroxyl group. The content of the component (B1) relative to the total mass of the component (B) is preferably 50 mass% or more, and more preferably 90 mass% or more (upper limit: 100 mass%). The binder of the component (B) is more preferably the component (B1).

[0047] In a further preferred embodiment of the present disclosure, the component (B1): a resin having hydroxyl groups comprises at least one resin (hereinafter also referred to as component (B2)) selected from the group consisting of polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl propylal, polyvinyl acetal, polyvinyl formal, hydroxyl-containing glyoxal resin, hydroxyl-containing acrylic resin, phenolic resin, hydroxyl-containing polyvinylpyrrolidone (PVP), hydroxyl-containing polyester, hydroxyl-containing silicone, and hydroxyl-containing polycarboxylic acid. The content of component (B2) relative to the total mass of component (B1) is preferably 50% by mass or more, more preferably 90% by mass or more (up to 100% by mass). It is more preferable that the component (B1): a resin having hydroxyl groups in component (B) is component (B2). It is particularly preferable that the resin that is component (B) is component (B2).

[0048] The weight-average molecular weight of the binder that can be used as component (B) is not particularly limited, but is preferably 1,000 or more, more preferably 2,000 or more, and even more preferably 5,000 or more. Within these ranges, a composition that can further improve the moldability of the prepreg can be obtained. The weight-average molecular weight of the binder that can be used as component (B) is not particularly limited, but is preferably 500,000 or less, more preferably 100,000 or less, and even more preferably 50,000 or less. Within these ranges, the possibility of excessive thickening of the composition is further reduced, resulting in a composition that is more suitable for coating. The weight-average molecular weight of the binder can be measured by gel permeation chromatography (GPC), specifically, by the method described in the examples. For these reasons, examples of the range of the weight average molecular weight of the resin that can be used as component (B) include, but are not limited to, 1,000 or more and 500,000 or less, 2,000 or more and 100,000 or less, and 5,000 or more and 50,000 or less.

[0049] The component (B) may be a commercially available product or a synthetic product. The commercially available product is not particularly limited, but an example thereof is S-LEC (registered trademark) KW-3 manufactured by Sekisui Chemical Co., Ltd.

[0050] As the component (B), one type of resin may be used alone, or two or more types of resins may be used in combination.

[0051] The content of component (B) in the ceramic particle-containing composition is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more, relative to the total mass of the composition. This range results in a composition that can further improve the moldability of the prepreg. The content of component (B) in the ceramic particle-containing composition is not particularly limited, but is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, relative to the total mass of the composition. This range reduces the amount of other components removed during drying, degreasing, etc., resulting in a composition that is superior in terms of production costs. For these reasons, examples of the content range of component (B) in the ceramic particle-containing composition include, but are not limited to, 0.01% by mass or more to 50% by mass or less, 0.1% by mass or more to 30% by mass or less, and 1% by mass or more to 25% by mass or less, relative to the total mass of the composition. Note that when a composition contains two or more types of component (B), the content of component (B) refers to the total amount of these components.

[0052] The content ratio of the (A) component to the (B) component is not particularly limited. The content of the (B) component is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2.5 parts by mass or more, and particularly preferably 5 parts by mass or more, per 100 parts by mass of the (A) component. Within this range, a composition with better prepreg moldability can be obtained. The content of the (B) component is preferably 1,000 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 50 parts by mass or less, per 100 parts by mass of the (A) component. Within this range, the amount of resin component removed during degreasing is reduced, resulting in a composition with better production costs. For these reasons, the content of the (B) component, relative to 100 parts by mass of the (A) component, may be, but is not limited to, 0.1 parts by mass to 1,000 parts by mass, 1 part by mass to 100 parts by mass, 2.5 parts by mass to 50 parts by mass, or 5 parts by mass to 50 parts by mass.

[0053] <Component (C): Plasticizer> The ceramic particle-containing composition according to an embodiment of the present disclosure preferably includes a plasticizer as component (C). Component (C) can increase the flexibility of the prepreg. In this specification, a plasticizer refers to a compound that has the function of increasing the flexibility of the prepreg according to the present disclosure.

[0054] The component (C) is not particularly limited, and known plasticizers can be used. Among such plasticizers, from the viewpoint of dispersibility in the composition, preferred examples include water-soluble plasticizers such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, and triethanolamine, and plasticizers that are insoluble in water and transfer to emulsions, such as phthalate ester plasticizers such as dibutyl phthalate, but are not limited to these. From the same viewpoint, the component (C) is more preferably a water-soluble plasticizer, even more preferably a water-soluble plasticizer that is a polymer, even more preferably diethylene glycol, triethylene glycol, and polyethylene glycol, and particularly preferably polyethylene glycol. Diethylene glycol, triethylene glycol, and polyethylene glycol are polymers of two, three, and four or more ethylene glycols, respectively.

[0055] In a preferred embodiment of the present disclosure, component (C) includes at least one compound selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, triethanolamine, and dibutyl phthalate (hereinafter also referred to as component (C1)). The content of component (C1) relative to the total mass of component (C) is preferably 50 mass% or more, more preferably 90 mass% or more (upper limit 100 mass%). It is even more preferable that the plasticizer serving as component (C) is component (C1).

[0056] In a more preferred embodiment of the present disclosure, component (C) contains at least one compound selected from the group consisting of diethylene glycol, triethylene glycol, and polyethylene glycol. The content of at least one compound selected from the group consisting of diethylene glycol, triethylene glycol, and polyethylene glycol relative to the total mass of component (C) is preferably 50% by mass or more, more preferably 90% by mass or more (up to 100% by mass). The plasticizer of component (C) is even more preferably at least one compound selected from the group consisting of diethylene glycol, triethylene glycol, and polyethylene glycol.

[0057] The molecular weight of the plasticizer that can be used as component (C) is not particularly limited, but is preferably smaller than the molecular weight of the binder, which is component (B). The molecular weight of the plasticizer calculated from the sum of atomic weights is preferably less than 1,000. Furthermore, for example, when the hydroxyl value of the plasticizer can be measured by neutralization titration, the average molecular weight calculated from the results of the hydroxyl value measurement by neutralization titration is preferably less than 1,000. The average molecular weight calculated from the results of the hydroxyl value measurement by neutralization titration can be calculated based on JIS K 0070:1992. Within these ranges, the effect of the plasticizer is further improved.

[0058] In a preferred embodiment of the present disclosure, the binder as component (B) is a resin having a weight-average molecular weight of 1,000 or more, and the plasticizer as component (C) is a plasticizer having an average molecular weight of less than 1,000 calculated from the results of hydroxyl value measurement by neutralization titration method.

[0059] The plasticizer that can be used as component (C) may be a commercially available product or a synthetic product. Examples of commercially available products include, but are not limited to, polyethylene glycol 200 manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0060] As the component (C), one type of plasticizer may be used alone, or two or more types of plasticizers may be used in combination.

[0061] The content of component (C) in the ceramic particle-containing composition is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more, relative to the total mass of the composition. Within this range, a composition capable of imparting excellent flexibility to the prepreg can be obtained. The content of component (C) in the ceramic particle-containing composition is not particularly limited, but is preferably 50% by mass or less, more preferably 25% by mass or less, and even more preferably 10% by mass or less, relative to the total mass of the composition. Within this range, the amount of plasticizer component removed during degreasing is reduced, resulting in a composition that is superior in terms of production costs. For these reasons, the content of component (C) in the ceramic particle-containing composition may be, but is not limited to, 0.01% by mass or more to 50% by mass or less, 0.1% by mass or more to 25% by mass or less, or 1% by mass or more to 10% by mass or less, relative to the total mass of the composition. Note that when a composition contains two or more types of component (C), the content of component (C) refers to the total amount of these components.

[0062] The content ratio of the (C) component to the (A) component is not particularly limited. The content of the (C) component is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2.5 parts by mass or more, per 100 parts by mass of the (A) component. Within this range, a composition capable of imparting excellent flexibility to the prepreg is obtained. Furthermore, the content of the (C) component is preferably 1,000 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 50 parts by mass or less, per 100 parts by mass of the (A) component. Within this range, the amount of plasticizer component removed during degreasing is reduced, resulting in a composition that is superior in terms of production costs. For these reasons, the content of the (C) component may be, per 100 parts by mass of the (A) component, 0.1 parts by mass or more to 1,000 parts by mass or less, 1 part by mass or more to 100 parts by mass or less, or 2.5 parts by mass or more to 50 parts by mass, but is not limited thereto.

[0063] The ratio of the content of the (B) component to the (C) component is not particularly limited, but the content of the (B) component is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, and even more preferably 150 parts by mass or more, per 100 parts by mass of the (C) component. The content of the (B) component is preferably 600 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 400 parts by mass or less, per 100 parts by mass of the (C) component. Within these ranges, the hardening of the green sheet by the binder and the flexibility imparted to the green sheet by the plasticizer are properly maintained, preventing cracks and breaks in the finished product and facilitating handling. For these reasons, the content of the (B) component may be, but is not limited to, 50 parts by mass or more to 600 parts by mass or less, 100 parts by mass or more to 500 parts by mass or less, or 150 parts by mass or more to 400 parts by mass, per 100 parts by mass of the (C) component.

[0064] <Component (D): Water> The ceramic particle-containing composition according to one embodiment of the present disclosure preferably contains water as component (D). Component (D) is preferably water containing as few impurities as possible, more preferably water having a total transition metal ion content of 100 ppb or less. The purity of water that can be used as component (D) can be increased by, for example, removing impurity ions using an ion exchange resin, removing foreign matter using a filter, or by distillation. Specifically, it is preferable to use, for example, deionized water (ion-exchanged water), pure water, ultrapure water, distilled water, or the like as component (D).

[0065] <Component (E): Acid> The ceramic particle-containing composition according to an embodiment of the present disclosure may further include an acid as component (E). The component (E) is used as a pH adjuster and can further lower the pH of the composition.

[0066] The component (E) is not particularly limited, and any known acid can be used. The component (E) may be either an organic acid or an inorganic acid. The acid is preferably a non-polymeric acid. The non-polymeric acid is preferably a compound having a total atomic weight of less than 1,000.

[0067] The organic acid is not particularly limited, and examples thereof include carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid, lactic acid, diglycolic acid, 2-furancarboxylic acid, 2,5-furandicarboxylic acid, 3-furancarboxylic acid, 2-tetrahydrofurancarboxylic acid, methoxyacetic acid, methoxyphenylacetic acid, and phenoxyacetic acid; and sulfur-containing organic acids such as methanesulfonic acid, ethanesulfonic acid, and isethionic acid. The inorganic acid is not particularly limited, and examples thereof include carbonic acid, hydrochloric acid, nitric acid, phosphoric acid, hypophosphorous acid, phosphorous acid, phosphonic acid, sulfuric acid, boric acid, hydrofluoric acid, orthophosphoric acid, pyrophosphoric acid, polyphosphoric acid, metaphosphoric acid, hexametaphosphoric acid, etc. Among these, inorganic acids are preferred, nitric acid, sulfuric acid, and hydrochloric acid are more preferred, nitric acid and hydrochloric acid are even more preferred, and hydrochloric acid is particularly preferred.

[0068] In a preferred embodiment of the present disclosure, the acid that can be used as component (E) includes an inorganic acid. The content of the inorganic acid relative to the total mass of component (E) is preferably 50 mass% or more, and more preferably 90 mass% or more (upper limit 100 mass%). The acid that is component (E) is even more preferably an inorganic acid.

[0069] In a further preferred embodiment of the present disclosure, component (E) contains at least one acid selected from the group consisting of carbonic acid, hydrochloric acid, nitric acid, phosphoric acid, hypophosphorous acid, phosphorous acid, phosphonic acid, sulfuric acid, boric acid, hydrofluoric acid, orthophosphoric acid, pyrophosphoric acid, polyphosphoric acid, metaphosphoric acid, and hexametaphosphoric acid (hereinafter also referred to as component (E1)). The content of component (E1) relative to the total mass of component (E) is preferably 50 mass% or more, more preferably 90 mass% or more (upper limit 100 mass%). It is even more preferable that the acid of component (E) is component (E1).

[0070] The component (E) may be a commercially available product or a synthetic product. Furthermore, the component (E) may be a single acid or a combination of two or more acids.

[0071] The content of component (E) in the ceramic particle-containing composition is not particularly limited, but it is preferably an amount that causes the pH of the composition at 25° C. to fall within the preferred range described below.

[0072] <Component (F): Thickener> The ceramic particle-containing composition according to the present disclosure may further include a thickener as component (F). Component (F) can adjust the viscosity of the ceramic particle-containing composition. In this specification, the thickener refers to a compound that has the function of increasing the viscosity of the ceramic particle-containing composition.

[0073] The thickener is preferably a compound capable of achieving a viscosity of 1 Pa·s or more at 25°C in a thickening effect test. Furthermore, a compound capable of achieving a viscosity of 5 Pa·s or more at 25°C in a thickening effect test is more preferred, and a compound capable of achieving a viscosity of 10 Pa·s or more at 25°C is even more preferred. Component (F) preferably contains the compounds listed above. The compounds that become component (B) and component (C) are preferably compounds that have a viscosity of less than 1 Pa·s at 25°C in a thickening effect test. However, the compounds that become component (B) and component (C) are not limited to such compounds.

[0074] The thickening effect test is performed as follows. First, an aqueous dispersion (a dispersion consisting of alumina particles and water) of alumina particles (product name: WA#30000, manufactured by Fujimi Incorporated, average secondary particle diameter: 0.3 μm) with an alumina particle concentration of 25% by mass is prepared. 100 g of this aqueous dispersion with an alumina particle concentration of 25% by mass is added to 5 g of a 2.5% by mass aqueous hydrochloric acid solution while stirring. Next, a test compound is added to the obtained aqueous dispersion (aqueous dispersion containing alumina particles and hydrochloric acid) in an amount of 4 parts by mass or less per 100 parts by mass of the alumina particles. The viscosity of the aqueous dispersion of alumina particles after the addition of the test compound is then measured at 25°C. In the thickening effect test, the maximum viscosity at 25°C when the test compound is added in an amount of 4 parts by mass or less per 100 parts by mass of the alumina particles is used as the standard. The viscosity of the aqueous dispersion of alumina particles can be measured in the same manner as the viscosity of the ceramic particle-containing composition at 25°C.

[0075] Component (F) is not particularly limited, and known thickeners can be used. Thickeners that can be used as component (F) may be ionic or nonionic thickeners. Ionic thickeners may be anionic or cationic thickeners. The thickener is preferably an ionic thickener, more preferably a cationic thickener, and even more preferably a cationic thickener containing a polymer having a (meth)acryloyl group. It is even more preferable that the thickener is a W / O emulsion containing a poly(meth)acrylic acid ester-based cationic polymer (e.g., a cationic polymer containing a (meth)acrylic acid ester structural unit), and particularly preferably a W / O emulsion containing a polymethacrylic acid ester-based cationic polymer (e.g., a cationic polymer containing a methacrylic acid ester structural unit). Component (F) preferably contains a thickener as described above. Here, the term "(meth)acryloyl group" refers collectively to an acryloyl group and a methacryloyl group. The (meth)acrylic acid ester is a general term for acrylic acid ester and methacrylic acid ester.

[0076] The component (F) may be a commercially available product or a synthetic product. Examples of commercially available products include, but are not limited to, Senka Act Gel AP200, Senka Act Gel NS100, Senka Act Gel CM100, and Senka Act Gel CD100, all manufactured by Senka Corporation.

[0077] As the component (F), one type of thickener may be used alone, or two or more types of thickeners may be used in combination.

[0078] When component (F) is used, the content of component (F) in the ceramic particle-containing composition is not particularly limited, but it is preferably an amount such that the viscosity of the ceramic particle-containing composition at 25°C falls within the preferred range described below.

[0079] <Component (G): Component Other than Components (A) to (F)> The ceramic particle-containing composition according to an embodiment of the present disclosure may further include a component (G) other than the components (A) to (F) described above, as long as the effect of the present disclosure is not impaired. Component (G) is not particularly limited, and examples thereof include a base (basic compound, alkali), a salt, a chelating agent, an antifoaming agent, an organic solvent, etc.

[0080] The content of component (G) is not particularly limited as long as it is within a range in which the effects of the present disclosure can be obtained, but it is preferably less than 10 mass %, more preferably less than 5 mass %, and even more preferably less than 3 mass %, relative to the total mass of the ceramic particle-containing composition.

[0081] <Total Solids Concentration of Composition> The total solids concentration of the ceramic particle-containing composition according to one embodiment of the present disclosure is not particularly limited, but is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. Furthermore, the total solids concentration of the ceramic particle-containing composition is not particularly limited, but is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. Within these ranges, the viscosity is appropriate for coating, and a high-quality green sheet without cracks or bubbles can be produced. For these reasons, the total solids concentration of the ceramic particle-containing composition may be, but is not limited to, 20% by mass or more to 60% by mass or less, 25% by mass or more to 50% by mass or less, or 30% by mass or more to 45% by mass or less.

[0082] <pH> The pH of the ceramic particle-containing composition according to one embodiment of the present disclosure at 25°C is preferably 3.0 or higher. The pH of the ceramic particle-containing composition at 25°C is more preferably greater than 3.0, and even more preferably 3.1 or higher. Within these ranges, the occurrence of bleed-out of some components during the formation of a ceramic sintered body can be further suppressed. The pH of the ceramic particle-containing composition at 25°C is preferably 12.0 or lower, more preferably 9.0 or lower, even more preferably 7.0 or lower, and particularly preferably 5.5 or lower. Within these ranges, thickening due to dehydration condensation of the resin used as a binder can be further suppressed, further reducing the possibility of excessive thickening of the composition, making the composition more suitable for coating.

[0083] The pH of the ceramic particle-containing composition at 25° C. can be measured using a pH meter, specifically, by the method described in the Examples. From these, the pH of the ceramic particle-containing composition at 25° C. can be, but is not limited to, 3.0 to 12.0, 3.0 to 9.0, more than 3.0 to 7.0, or 3.1 to 5.5.

[0084] <Viscosity> The viscosity of the ceramic particle-containing composition at 25°C is not particularly limited, but is preferably 0.01 Pa·s or more, more preferably 0.03 Pa·s or more, and even more preferably 0.05 Pa·s or more. The viscosity of the ceramic particle-containing composition at 25°C is also not particularly limited, but is preferably 5 Pa·s or less, more preferably 3 Pa·s or less, and even more preferably 2 Pa·s or less. When the viscosity is within this range, a prepreg can be obtained that has excellent dispersion of unidirectional ceramic fibers, with a coefficient of variation of 2.0 or less. Furthermore, the coatability of the ceramic particle-containing composition is further improved, making it easier to impregnate the ceramic fibers with the composition. The viscosity of the ceramic particle-containing composition at 25°C can be measured using a B-type viscometer, specifically, by the method described in the examples. For these reasons, examples of the viscosity range of the ceramic particle-containing composition at 25° C. include, but are not limited to, 0.01 Pa·s or more and 5 Pa·s or less, 0.03 Pa·s or more and 3 Pa·s or less, and 0.05 Pa·s or more and 2 Pa·s or less. The viscosity can be controlled by the type and content of each component in the ceramic particle-containing composition, the total solids concentration, etc.

[0085] <Method for Producing Composition> The method for producing the ceramic particle-containing composition is not particularly limited and may, for example, include mixing component (A): ceramic particles, component (B): binder, component (C): plasticizer, and component (D): water. The method for producing the ceramic particle-containing composition may also include further mixing other components (e.g., the above-mentioned components (E), (F), and (G)) as necessary.

[0086] The component (A) is preferably added as a dispersion containing the component (A) and the component (D). The component (B) is preferably added as a dispersion containing the component (B) and the component (D). Therefore, the method for producing the composition preferably includes mixing a dispersion containing the component (A) and the component (D), a dispersion containing the component (B) and the component (D), and at least one selected from the group consisting of the component (C), a solution containing the component (C), and a dispersion containing the component (C).

[0087] [Method for Manufacturing Prepreg] The method for manufacturing a unidirectional ceramic fiber prepreg according to an embodiment of the present disclosure is not particularly limited, but preferably includes the steps of: (1) preparing a plurality of unidirectionally oriented ceramic fibers and a ceramic particle-containing composition; (2) applying the ceramic particle-containing composition to a support to form a coating film; (3) immersing the unidirectionally oriented ceramic fibers in the coating film to form a ceramic particle-containing composition-impregnated body; and (4) drying the ceramic particle-containing composition-impregnated body and then peeling off the support to form a unidirectional ceramic fiber prepreg. Each step is described below.

[0088] <(1) Step of preparing a plurality of unidirectionally oriented ceramic fibers and a ceramic particle-containing composition> In this step, unidirectional ceramic fibers are prepared. The method for preparing the unidirectional ceramic fibers is not particularly limited, but a method of opening a bundle of ceramic fibers is preferred. Opening is an operation of separating bundles of converged ceramic fibers, which is expected to have the effect of further improving the impregnation ability of the ceramic particle-containing composition.

[0089] When the ceramic fiber bundle is spread, it is preferable to use a fiber spreading device. The spreading method is not particularly limited, and known methods such as a method of alternately passing the fiber bundle through concave and convex rolls, a method of using a drum-shaped roll, a method of applying tension fluctuation to axial vibration, a method of varying the tension of the fiber bundle using multiple friction bodies that reciprocate vertically, a method of blowing air onto the fiber bundle, a method of air-suctioning the fiber bundle, a method of using a spring spreading element, and a method of using an expander roll can be used alone or in appropriate combination.

[0090] In this step, a ceramic particle-containing composition is prepared. The method for preparing the ceramic particle-containing composition is as described above, and therefore, a description thereof will be omitted here.

[0091] <(2) Step of applying the ceramic particle-containing composition onto a support to obtain a coating film> In this step, the ceramic particle-containing composition prepared in the above step (1) is applied onto a support to obtain a coating film.

[0092] As the support, a film made of a resin material is preferably used. Examples of the resin material include polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polycarbonate (PC) resin, acrylic resins such as polymethyl methacrylate (PMMA), cyclic olefin polymer (COP), triacetyl cellulose (TAC) resin, polyethersulfone (PES) resin, polyether ketone (PEK) resin, and polyimide (PI) resin. Among these, polyethylene terephthalate (PET) is preferred. The film made of a resin material may be subjected to a surface treatment such as corona treatment, atmospheric pressure plasma treatment, vacuum plasma treatment, or primer coating treatment.

[0093] The ceramic particle-containing composition can be applied by known methods such as a bar coater method, an applicator method, a curtain flow coater method, a roll coater method, a spray method, a gravure coater method, a comma coater method, a reverse roll coater method, a lip coater method, a die coater method, a slot die coater method, an air knife coater method, a dip coater method, etc. Among these, the applicator method is preferred.

[0094] The thickness of the coating film is preferably from 10 μm to 2000 μm, more preferably from 50 μm to 1800 μm, and even more preferably from 100 μm to 1500 μm. By adjusting the thickness of the coating film, the fiber content (Vf) of the unidirectional ceramic fibers in the prepreg can be controlled to a desired value.

[0095] After forming the coating film, the coating film may be dried if necessary, but it is preferable to immerse the unidirectional ceramic fibers in the coating film without drying.

[0096] <(3) Step of immersing a plurality of unidirectionally oriented ceramic fibers into the coating film to obtain a ceramic particle-containing composition-impregnated body> In this step, unidirectional ceramic fibers are immersed into the coating film obtained in step (2) above to obtain a ceramic particle-containing composition-impregnated body.

[0097] When the unidirectional ceramic fibers are immersed, they may or may not be fixed using a frame made of resin or metal.

[0098] The temperature of the coating film during immersion (immersion temperature) is not particularly limited and is usually in the range of 10° C. to 40° C. The immersion time is also not particularly limited and is usually 0.5 minutes to 10 minutes. After immersion, the ceramic particle-containing composition is impregnated into the unidirectional ceramic fibers, and a ceramic particle-containing composition-impregnated body is obtained with the support still attached.

[0099] <(4) Step of drying the ceramic particle-containing composition-impregnated body to obtain a prepreg> In this step, the ceramic particle-containing composition-impregnated body obtained in step (3) above is dried, and then the support is peeled off to obtain a unidirectional ceramic fiber prepreg.

[0100] The drying method is not particularly limited, and examples thereof include heat drying, hot air drying, etc. In the case of heat drying, the drying temperature is preferably in the range of 70° C. or more and 140° C. or less, and the drying time is preferably in the range of 10 minutes or more and 60 minutes or less.

[0101] After drying, the support is peeled off to obtain a unidirectional ceramic fiber prepreg. The thickness of the obtained unidirectional ceramic fiber prepreg is not particularly limited, but is preferably 10 μm to 500 μm, more preferably 20 μm to 300 μm, and even more preferably 50 μm to 200 μm. The width and length of the unidirectional ceramic fiber prepreg can be appropriately set depending on the application.

[0102] By using a manufacturing method including a sintering step of the unidirectional ceramic fiber prepreg thus obtained, it is possible to obtain a ceramic matrix composite (CMC) that uses ceramic fibers as a reinforcing material and whose matrix is ​​also made of a ceramic material. Such a ceramic matrix composite is believed to have excellent mechanical properties.

[0103] Although the embodiments of the present disclosure have been described in detail, it is clear that this is for illustrative and exemplary purposes only and not for limitation, and that the scope of the present disclosure should be interpreted by the appended claims.

[0104] The present disclosure encompasses the following aspects and forms: 1. A method for producing a unidirectional ceramic fiber prepreg, comprising the steps of preparing a plurality of unidirectionally oriented ceramic fibers and a ceramic particle-containing composition, applying the ceramic particle-containing composition to a support to obtain a coating film, immersing the plurality of unidirectionally oriented ceramic fibers in the coating film to obtain a ceramic particle-containing composition-impregnated body, and drying the ceramic particle-containing composition-impregnated body and then peeling off the support to obtain a unidirectional ceramic fiber prepreg; 2. A method for producing a unidirectional ceramic fiber prepreg as set forth in 1. above, wherein the viscosity of the ceramic particle-containing composition at 25°C is 0.01 Pa·s or more and 5 Pa·s or less; 3. A method for producing a unidirectional ceramic fiber prepreg as set forth in 1. or 2. above, wherein the thickness of the coating film is 10 μm or more and 2000 μm or less; 4. 4. A unidirectional ceramic fiber prepreg comprising a plurality of ceramic fibers oriented in one direction and a ceramic particle-containing composition impregnated into the plurality of ceramic fibers, wherein the coefficient of variation of the number of ceramic fibers per unit section in a cut surface along the thickness direction of the unidirectional ceramic fiber prepreg is 2.0 or less: 5. The unidirectional ceramic fiber prepreg according to 4. above, wherein the coefficient of variation is 1.7 or less: 6. The unidirectional ceramic fiber prepreg according to 4. or 5. above, wherein the ceramic fibers are silicon carbide fibers, alumina fibers, mullite fibers, or carbon fibers: 7. The unidirectional ceramic fiber prepreg according to any of 4. to 6. above, wherein the ceramic particles contained in the ceramic particle-containing composition are at least one type selected from the group consisting of alumina particles, silicon carbide particles, and silicon carbide particles coated with a coating layer containing aluminum hydroxide: 8. The unidirectional ceramic fiber prepreg according to 4. above, wherein the fiber content of the ceramic fibers in the unidirectional ceramic fiber prepreg is 20% by volume or more and 85% by volume or less. 7. The unidirectional ceramic fiber prepreg according to any one of items 1 to 7.

[0105] The technology of the present disclosure will be described in more detail using the following examples and comparative examples. However, the technical scope of the present disclosure is not limited to the following examples. Unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass," respectively. In the following examples, unless otherwise specified, the operations were carried out under the conditions of room temperature (25°C) and a relative humidity of 40% RH or more and 50% RH or less.

[0106] Each physical property was measured by the following method.

[0107] (Average Secondary Particle Diameter of Ceramic Particles) The average secondary particle diameter of the ceramic particles was measured as a volume average particle diameter by a dynamic light scattering method using a particle size distribution measuring device (UPA-UT151, manufactured by Nikkiso Co., Ltd.).

[0108] (pH Measurement) The pH of the ceramic particle-containing composition was measured at 25° C. using a pH meter (model number: F-71) manufactured by Horiba, Ltd.

[0109] (Measurement of Viscosity) The viscosity of the ceramic particle-containing composition was measured at 25° C. using a B-type viscometer manufactured by Toki Sangyo Co., Ltd. (model number: TVB-10, rotor No. 27, rotor rotation speed: 60 rpm).

[0110] (Measurement of Weight-Average Molecular Weight of Binder) The weight-average molecular weight (Mw) of the binder contained in the ceramic particle-containing composition was measured as a polyethylene oxide-equivalent value by gel permeation chromatography (GPC) under the following measurement conditions: <GPC Measurement Conditions> Sample concentration: 0.1 mass % Column: "TSKgel (registered trademark) GMPWXL" manufactured by Tosoh Corporation Detector: Differential refractometer Eluent: 100 mM aqueous sodium nitrate solution Flow rate: 1 mL / min Measurement temperature: 40°C Sample injection amount: 200 μL Measurement device: "HLC-8320GPC" manufactured by Tosoh Corporation.

[0111] (Measurement of Molecular Weight of Plasticizer) The average molecular weight of the plasticizer was calculated from the results of measuring the hydroxyl value by neutralization titration based on JIS K 0070: 1992. More specifically, the calculation was performed by the following procedure: (1) Procedure: The hydroxyl value of 0.6 g of plasticizer was determined by JIS K 0070: 1992 "Test methods for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiable matter of chemicals 7.1 Neutralization titration method"; (2) Calculation: The average molecular weight was calculated by the following formula: A = (56106 / B) x 2 A: average molecular weight B: hydroxyl value (unit: mgKOH / g) determined in (1) above 56106: coefficient based on the molecular weight of potassium hydroxide.

[0112] [Production of Prepreg] <Preparation of Unidirectionally Oriented Carbon Fibers> A carbon fiber bundle was opened using a fiber opening device to prepare a plurality of unidirectionally oriented carbon fibers.

[0113] <Aluminum hydroxide-coated silicon carbide (SiC) particles> A 20 mass% aqueous dispersion of silicon carbide (SiC) particles (GC # 40000, average secondary particle diameter 0.36 μm, manufactured by Fujimi Incorporated, powder) was prepared, and 1 M NaOH aqueous solution was added to adjust the pH to 10.0. Next, a 30 mass% aqueous dispersion of sodium aluminate was prepared, and an aqueous dispersion of sodium aluminate in an amount of 50 parts by mass per 100 parts by mass of silicon carbide particles and 9.9 mass% nitric acid were added over 45 minutes while stirring to maintain a pH of 9.0 to 11.0. After further stirring for 45 minutes, 9.9 mass% nitric acid was added so that the pH of the dispersion was 10.5, and an aqueous dispersion containing silicon carbide (SiC) particles coated with aluminum hydroxide was prepared. Thereafter, 9.9% by mass of nitric acid was added to adjust the pH to 3.0, and the mixture was concentrated by suction filtration to obtain an aqueous dispersion of aluminum hydroxide-coated SiC particles with a concentration of 40% by mass.

[0114] <Analysis of Composition and Structure of Particles in Aqueous Dispersion> The fact that the particles in the dispersion obtained above were aluminum hydroxide-coated SiC particles was confirmed by the following analysis.

[0115] Approximately 2 mL of the aqueous dispersion obtained above was collected and dropped onto a filter (Nuclepore 5 μm) (manufactured by WHATMAN). Subsequently, suction filtration was performed, and then the powder was washed on the filter using 10 mL of pure water, and the particles were dried. The dried particles were then collected on a Si wafer and observed using a scanning electron microscope SU-8000 manufactured by Hitachi High-Technologies Corporation, using SEM (Scanning Electron Microscope)-EDX (Energy Dispersive X-ray Spectroscopy).

[0116] Furthermore, the dried particles were collected on a carbon tape and subjected to EELS (Electron Energy Loss Spectroscopy) analysis using TITAN 80-300 manufactured by FEI.

[0117] In SEM-EDX observation of the particles, C, Al, and O were selected as the elements to be observed, and the EDX spectrum of Al was observed. It was also confirmed that the positions where the EDX spectra of C, Al, and O were observed clearly corresponded to the positions where the particles were observed in the SEM observation image. Therefore, it was determined that the SiC particles were coated with a component containing Al and O.

[0118] In addition, in the EELS analysis of the particles, the observed EELS spectrum was found to be aluminum hydroxide (Al(OH) ３ ) has a spectral shape specific to the EELS standard spectrum (a shape different from that of Al and other compounds containing Al and O). Therefore, it was confirmed that the component containing Al and O is Al(OH). ３ It was determined that it included

[0119] <Preparation of Ceramic Particle-Containing Composition> The aluminum hydroxide-coated silicon carbide particles obtained above, a 20 mass% aqueous dispersion of polyvinyl acetal (water-soluble polymer, product name: S-LEC (registered trademark) KW-3, manufactured by Sekisui Chemical Co., Ltd., degree of polymerization approximately 600, weight-average molecular weight 1,000 or more) as a binder resin, polyethylene glycol (PEG200, number-average molecular weight: 200, weight-average molecular weight less than 1,000, manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.) as a plasticizer, and Olfine (registered trademark) E1004 (manufactured by Nissin Chemical Industry Co., Ltd.) as an antifoaming agent were added to a container in amounts such that the solid content ratio shown in Table 1 below was achieved. The mixture was then stirred for 2 minutes at 1,400 rpm using a planetary centrifugal mixer (Awatori Rentaro, ARE-310, manufactured by Thinky Corporation) to obtain a ceramic particle-containing composition having a total solids concentration of 35.5 mass%.

[0120] The resulting ceramic particle-containing composition had a pH of 3.86 and a viscosity at 25°C of 85 mPa·s.

[0121]

[0122] Example A polyethylene terephthalate (PET) film (Lumirror (registered trademark) S10, film thickness 100 μm, manufactured by Toray Industries, Inc.) was prepared as a support. This PET film was set in a coating machine (IMC-7373, manufactured by Imoto Machinery Co., Ltd.), and the ceramic particle-containing composition obtained above was applied onto the PET film using an applicator to obtain a coating film with a thickness of 450 μm.

[0123] The above-prepared multiple unidirectionally oriented carbon fibers were immersed in the resulting coating film at an immersion temperature of 25°C for 1 minute to obtain a ceramic particle-containing composition impregnated body.

[0124] The obtained ceramic particle-containing composition-impregnated body was placed in a Lightspec thermo-hygrostat (model number: LU-114, manufactured by Espec Corporation) set at 90°C and dried for 20 minutes. After drying was completed, the PET film support was peeled off to obtain a unidirectional ceramic fiber prepreg with a thickness of 137 μm. The fiber content (Vf) of carbon fiber in the obtained unidirectional ceramic fiber prepreg was 45.8 vol%.

[0125] [Calculation of coefficient of variation] The unidirectional ceramic fiber prepreg obtained above was cut in the thickness direction using a vertical slicer (model number: HS-1-S, manufactured by Jusco Engineering Co., Ltd.) to obtain pieces measuring approximately 10 mm x 10 mm. The cut surface of the prepreg was photographed using a low-vacuum scanning electron microscope (model number: JSM-IT100, manufactured by JEOL Ltd., magnification: 500x). The photographed area measured 192 μm long x 256 μm wide.

[0126] The photographs were imported into Jw-cad software, and the photographed area was divided into four sections vertically across the entire thickness of the prepreg and into four sections horizontally with a width of 256 μm. This resulted in a total of 16 sections, and the number of carbon fibers per section was counted for each section. The standard deviation and average value were calculated for the number of carbon fibers counted at the 16 sections. The coefficient of variation of the unidirectional ceramic fibers was calculated by dividing the standard deviation value by the average value, which was 1.247.

[0127] Fig. 1 shows an SEM photograph of a cross section cut along the thickness direction of the unidirectional ceramic fiber prepreg obtained in this example. As is clear from Fig. 1, the prepreg obtained in this example showed good dispersion of unidirectional carbon fibers. This suggests that a ceramic matrix composite material produced using the prepreg obtained in this example may have excellent mechanical properties.

[0128] Comparative Example: A ceramic particle-containing composition was prepared in the same manner as in the above Example, and an immersion bath for the resulting ceramic particle-containing composition was prepared. A plurality of unidirectionally oriented carbon fibers prepared in the same manner as above were immersed in the prepared immersion bath at a temperature of 25°C for 2 minutes. The carbon fibers removed after immersion showed signs of fiber bundling and gap formation, and were therefore very poorly dispersible, making them unusable as prepregs.

[0129] This application is based on Japanese Patent Application No. 2023-169589, filed on September 29, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A method for producing a unidirectional ceramic fiber prepreg, comprising the steps of: preparing a plurality of ceramic fibers oriented in one direction and a ceramic particle-containing composition; applying the ceramic particle-containing composition onto a support to obtain a coating film; immersing the plurality of ceramic fibers oriented in one direction into the coating film to obtain a body impregnated with the ceramic particle-containing composition; and drying the body impregnated with the ceramic particle-containing composition and then peeling off the support to obtain a unidirectional ceramic fiber prepreg.

2. The method for producing a unidirectional ceramic fiber prepreg according to claim 1, wherein the viscosity of the ceramic particle-containing composition at 25°C is 0.01 Pa·s or more and 5 Pa·s or less.

3. A method for producing a unidirectional ceramic fiber prepreg according to claim 1 or 2, wherein the thickness of the coating film is from 10 μm to 2000 μm.

4. A unidirectional ceramic fiber prepreg comprising: a plurality of ceramic fibers oriented in one direction; and a ceramic particle-containing composition impregnated into the plurality of ceramic fibers, wherein the coefficient of variation of the number of the ceramic fibers per unit section in a cut surface along the thickness direction of the unidirectional ceramic fiber prepreg is 2.0 or less.

5. The unidirectional ceramic fiber prepreg according to claim 4, wherein said coefficient of variation is 1.7 or less.

6. The unidirectional ceramic fiber prepreg according to claim 4 or 5, wherein the ceramic fibers are silicon carbide fibers, alumina fibers, mullite fibers, or carbon fibers.

7. The unidirectional ceramic fiber prepreg according to claim 4 or 5, wherein the ceramic particles contained in the ceramic particle-containing composition are at least one type selected from the group consisting of alumina particles, silicon carbide particles, and silicon carbide particles coated with a coating layer containing aluminum hydroxide.

8. A unidirectional ceramic fiber prepreg according to claim 4 or 5, wherein the fiber content of the ceramic fibers in the unidirectional ceramic fiber prepreg is 20 volume % or more and 85 volume % or less.

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