Insulating material, heat treatment device, and method for manufacturing insulating material

Abstract

Provided are an insulating material having low thermal conductivity, a heat treatment device provided with the insulating material, and a method for manufacturing the insulating material.　The insulating material is formed from a sheet-shaped molded body and provided with a carbon fiber layer A, wherein the carbon fiber layer A is a sheet-shaped layer including a carbon fiber mat, the average diameter of carbon fibers constituting the carbon fiber mat is 10 μm or less, and the carbon fibers constituting the carbon fiber mat are oriented substantially orthogonal to the thickness direction of the carbon fiber layer A.

Description

Thermal insulation material, heat treatment apparatus, and method for manufacturing thermal insulation material

[0001] The present invention relates to a thermal insulation material, a heat treatment apparatus equipped with the thermal insulation material, and a method for manufacturing the thermal insulation material.

[0002] Insulating materials using carbon fibers are widely used as insulating materials for high-temperature furnaces such as single-crystal pulling furnaces, vacuum deposition furnaces, and ceramic incinerators due to their excellent heat insulation properties and low heat capacity (for example, Patent Document 1).

[0003] Recently, there has been an increasing demand for energy conservation and cost reduction, leading to a need for insulation materials with lower thermal conductivity.

[0004] International Publication No. 2020 / 059819

[0005] The present invention has been made in view of the above-mentioned problems, and its object is to provide a thermal insulation material with low thermal conductivity, a heat treatment apparatus equipped with the thermal insulation material, and a method for manufacturing the thermal insulation material.

[0006] The inventors have found that the above problems can be solved by providing a carbon fiber layer A composed of carbon fibers oriented substantially perpendicular to the thickness direction and having an average diameter of 10 μm or less, and have completed the present invention. Specifically, the present invention provides the following.

[0007] (1) A thermal insulation material formed from a sheet-like molded body, comprising a carbon fiber layer A, wherein the carbon fiber layer A is a sheet-like layer including a carbon fiber mat, the average diameter of the carbon fibers constituting the carbon fiber mat is 10 μm or less, and the carbon fibers constituting the carbon fiber mat are oriented substantially perpendicular to the thickness direction of the carbon fiber layer A.

[0008] (2) The thermal insulation material described in (1), wherein the resistivity ratio is 20 or higher.

[0009] (3) The thermal insulation material described in (1), wherein the resistivity ratio is 30 or higher.

[0010] (4) An insulating material described in any one of (1) to (3), wherein the resistivity in the thickness direction of the insulating material is 10 mΩ·m or more.

[0011] (5) The thermal insulation material according to any one of (1) to (4), wherein the proportion of carbon fiber layer A with an orientation angle of 10° or more with respect to the direction perpendicular to the thickness direction of the carbon fibers is less than 2%.

[0012] (6) An insulating material according to any one of (1) to (5), wherein the proportion of the insulating material whose orientation angle with respect to the direction perpendicular to the thickness direction is 10° or more is less than 12%.

[0013] (7) The thermal insulation material according to any one of (1) to (6), wherein the average fiber length of the carbon fibers constituting the carbon fiber layer A is 20 mm or more and less than 50 mm.

[0014] (8) The thermal insulation material according to any one of (1) to (7), further comprising a carbon fiber layer B, wherein the orientation of the carbon fibers constituting the carbon fiber layer B is randomly arranged in three dimensions.

[0015] (9) The thermal insulation material according to (8), wherein the sum of the number of carbon fiber layers A and the number of carbon fiber layers B is three or more.

[0016] (10) The thermal insulation material according to any one of (1) to (9), wherein the carbon fibers constituting the carbon fiber layer A are anisotropic carbon fibers.

[0017] (11) The thermal insulation material according to (8) or (9), wherein the carbon fibers constituting the carbon fiber layer B are isotropic carbon fibers.

[0018] (12) A heat treatment apparatus comprising an insulating material described in any one of (1) to (11), wherein the insulating material is positioned to separate the inside and outside of the furnace, and a carbon fiber layer A is positioned on the side that is exposed to higher temperatures.

[0019] (13) A method for manufacturing an insulating material according to any one of (1) to (11), wherein the carbon fiber mat constituting the carbon fiber layer A is manufactured by a papermaking method.

[0020] A method for manufacturing an insulating material according to any one of (14), (8), (9), and (11), wherein a carbon fiber layer A and a carbon fiber layer B are bonded together with an adhesive-impregnated sheet.

[0021] According to the present invention, it is possible to provide a thermal insulation material with low thermal conductivity in high-temperature ranges, a heat treatment apparatus equipped with the thermal insulation material, and a method for manufacturing the thermal insulation material.

[0022] An image showing the thermal insulation material (a laminate of carbon fiber layer A and carbon fiber layer B) according to this embodiment, analyzed using a non-destructive structural analysis device.

[0023] The present invention will be described in detail below, but the following description is merely one example of an embodiment of the present invention, and the present invention is not limited to the following description as long as it does not exceed the spirit of the invention, and can be modified and implemented as such without departing from the spirit of the invention.

[0024] <<Thermal Insulation Material>> The thermal insulation material of the present invention comprises a carbon fiber layer A. The carbon fiber layer A is a sheet-like layer containing a carbon fiber mat. The average diameter of the carbon fibers constituting the carbon fiber mat is 10 μm or less. The carbon fibers constituting the carbon fiber mat are oriented substantially perpendicular to the thickness direction of the carbon fiber layer A. The carbon fiber layer A is a thermal insulation material formed from a sheet-like molded body. The sheet-like molded body is moldable and includes molded bodies formed into cylindrical shapes, etc., by bending or curving.

[0025] In the heat insulating material of the present invention, the reason for the low thermal conductivity is presumed as follows. Patent Document 1 discloses that the heat insulating property increases as the ratio of the space obtained by binding the contacts between carbon fibers and the volume of the space increase, and also increases as the number of protective carbon layers binding the contacts between carbon fibers increases. However, as a result of investigations by the present inventors, it has been found that when the volume of the space as described above increases, the influence of radiative heat transfer in which heat is transferred in the form of electromagnetic waves through the space becomes greater, and particularly in a high temperature range of 1500°C or higher, the influence becomes remarkable. In the heat insulating material of the present invention, since the carbon fiber mat contained in the carbon fiber layer A is composed of relatively thin carbon fibers having an average diameter of 10 μm or less, compared with the case of being composed of relatively thick carbon fibers, the projected area ratio of the carbon fibers in an arbitrary cross section parallel to the orientation direction of the carbon fibers in the carbon fiber mat is increased (for example, 12 carbon fibers having a diameter of 10 μm and the same fiber length and density have the same total mass as 3 carbon fibers having a diameter of 20 μm, but the total projected area is doubled by simple calculation). As a result, the radiant light is blocked by the carbon fibers and the radiative heat transfer is suppressed. Further, since the carbon fibers constituting the carbon fiber mat are oriented substantially orthogonally to the thickness direction (heat flow direction) of the carbon fiber layer A, the projected area ratio of the carbon fibers in a cross section orthogonal to the thickness direction is increased, and thus the radiative heat transfer is also suppressed.

[0026] Furthermore, the heat insulating material of the present invention is also likely to reduce the thermal conductivity in a low temperature range of less than 1500°C. When the carbon fibers are oriented parallel to the thickness direction (heat flow direction) of the carbon fiber layer A, heat is likely to be conducted along the carbon fibers, but in the heat insulating material of the present invention, since the carbon fibers are oriented substantially orthogonally to the heat flow direction, it is considered that the conductive heat transfer in the heat flow direction is suppressed.

[0027] <Carbon Fiber Layer A> The carbon fiber layer A is a sheet-like layer containing a carbon fiber mat. The carbon fiber mat contains carbon fibers. The carbon fibers constituting the carbon fiber mat are oriented substantially orthogonally to the thickness direction of the carbon fiber layer A. The orientation can be determined, for example, by observing the proportion of fibers arranged in a direction orthogonal to the thickness direction on the cut surface of the heat insulating material cut along the thickness direction. It is sufficient that almost all carbon fibers are oriented substantially orthogonally, and it is not necessary for all carbon fibers to be oriented substantially orthogonally. Also, "substantially orthogonally oriented" includes cases where the orientation is deviated within a range of ±10 degrees from the orthogonal angle in addition to the case of being completely orthogonally oriented. That the carbon fibers are oriented substantially orthogonally to the thickness direction means, for example, when the heat insulating material includes only the carbon fiber layer A, the average diameter of the carbon fibers constituting the heat insulating material is 10 μm or less, the specific resistance ratio is 135 or more, or the specific resistance value in the thickness direction of the heat insulating material is 45 mΩ·m or more, or the proportion of the orientation angle of the carbon fibers constituting the heat insulating material being 10° or more is less than 2%, which can also be confirmed from the examples described later. Also, in the case of a heat insulating material composed of a laminate with the carbon fiber layer A including a carbon fiber layer other than the carbon fiber layer A, there is a layer composed of carbon fibers with an average diameter of 10 μm or less, the specific resistance ratio is 20 or more, or the specific resistance value in the thickness direction of the heat insulating material is 10 mΩ·m or more, or the proportion of the layer where the orientation angle of the carbon fibers constituting the heat insulating material is 10° or more is less than 12%, which can also be confirmed from the examples described later.

[0028] Such a carbon fiber layer A can be obtained, for example, by firing a carbon fiber mat or a laminate thereof in which almost all carbon fibers are oriented in the planar direction. The carbon fiber mat is formed into a mat shape, for example, by continuously scooping up carbon fibers from a slurry liquid in which carbon fibers are dispersed using a long net or the like by a so-called papermaking method, dehydrating, and then adding and curing a binder resin. In this specification, the carbon fiber mat is regarded as a kind of carbon fiber sheet which is a sheet-like molded body containing carbon fibers. The carbon fiber sheet also includes the carbon fiber felt described later.

[0029] The average diameter of the carbon fibers constituting the carbon fiber mat is 10 μm or less, preferably 8 μm or less. This reduces the thermal conductivity in high and low temperature ranges. The lower limit of the average diameter of the carbon fibers is not particularly limited, but may be, for example, 1 μm or more, 3 μm or more, or 5 μm or more. If the average diameter is above the lower limit, the carbon fibers are easier to manufacture and production efficiency is improved. In this specification, the average diameter of the carbon fibers is the average value obtained by measuring the diameter of 5 carbon fibers at 20 different locations on the cross section parallel to the thickness direction of the carbon fiber layer, observed by scanning electron microscope, and averaging the diameters of a total of 100 carbon fibers.

[0030] The average fiber length of the carbon fibers constituting the carbon fiber layer A is preferably 20 mm or more and less than 50 mm, more preferably 25 mm or more and 45 mm or less, and even more preferably 30 mm or more and 40 mm or less. If it is 20 mm or more, the compressive stress of the manufactured carbon fiber layer A can be suppressed, and delamination between layers can be suppressed when laminated. If it is longer than 50 mm, the production efficiency will decrease due to the deterioration of fiber dispersibility and deterioration of slurry liquid filterability, as the carbon fibers tend to entangle with each other when manufacturing the carbon fiber mat used to form the carbon fiber layer A. In this specification, the average fiber length of the carbon fibers is the average value obtained by measuring the length of 10 carbon fibers whose start and end points can be confirmed in a cross section perpendicular to the thickness direction of the carbon fiber layer observed with a digital microscope.

[0031] The carbon fibers constituting the carbon fiber layer A may be anisotropic or isotropic, as long as the carbon fibers are oriented substantially perpendicular to the thickness direction. It is preferable to include anisotropic carbon fibers in order to further suppress conductive heat transfer in the thickness direction of the carbon fiber layer A. The mass percentage of anisotropic carbon fibers is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass, based on the total mass of the carbon fibers constituting the carbon fiber mat.

[0032] Examples of carbon fibers constituting the carbon fiber layer A include pitch-based carbon fibers, polyacrylonitrile-based (PAN-based) carbon fibers, rayon-based carbon fibers, and noboroid carbon fibers. Among these, from the viewpoint of obtaining anisotropic carbon fibers, it is preferable to include pitch-based carbon fibers and PAN-based carbon fibers, and from the viewpoint of facilitating the preparation of carbon fibers with small thread diameters, it is even more preferable to include PAN-based carbon fibers.

[0033] In carbon fiber layer A, it is preferable that needle punching, which causes warp threads to be oriented in the thickness direction, is not performed, as this further suppresses conductive heat transfer in the thickness direction of carbon fiber layer A.

[0034] The bulk density of the carbon fiber layer A is preferably 0.07 g / cm³. ３ 0.25g / cm or more ３ More preferably, 0.07 g / cm³ ３ 0.21g / cm or more ３ The following applies:

[0035] The carbon fiber layer A may contain carbonized resin in addition to carbon fibers. The resin is, for example, applied to the carbon fiber sheet used to form the carbon fiber layer. Examples of resins include those described in the method for manufacturing heat insulating materials described later. The mass of carbon fibers constituting the carbon fiber mat is preferably 70% by mass or more of the total mass of the carbon fiber layer A. In this specification, the mass of carbon fibers constituting the carbon fiber layer can be calculated from the mass of the carbon fiber sheet before application, the carbon residue rate of the carbon fibers, the carbon residue rate of the resin, and the amount of resin applied to the carbon fiber sheet used to form the carbon fiber layer.

[0036] <Carbon Fiber Layer B> The thermal insulation material of the present invention preferably further comprises a carbon fiber layer B. The carbon fiber layer B contains carbon fibers. The carbon fibers constituting the carbon fiber layer B are randomly oriented in three dimensions. Therefore, the random orientation in three dimensions strengthens the entanglement of the fibers in the thickness direction, making it possible to manufacture a thicker single layer, thus reducing the number of layers required and lowering the workload for manufacturing. In addition, in carbon fiber layer A, the carbon fibers are oriented substantially perpendicular to the thickness direction of carbon fiber layer A, making it rigid and prone to brittle fracture when external stress is applied. By including a carbon fiber layer B composed of carbon fibers randomly oriented in three dimensions, when manufacturing thermal insulation material of the same thickness, it is easier to achieve greater flexibility and improve moldability, such as being able to manufacture thermal insulation material with curvature, compared to thermal insulation material consisting only of carbon fiber layer A.

[0037] Such a carbon fiber layer B can be obtained, for example, by firing a carbon fiber felt or a laminate thereof in which carbon fibers are randomly oriented in three dimensions. Carbon fiber felt can be obtained, for example, by depositing carbon fibers and entangling and / or bonding the fibers. Methods for depositing include air lamination and carding, and methods for entangling and / or bonding the fibers include needle punching, air bonding, stitch bonding, and thermal bonding.

[0038] The average diameter of the carbon fibers constituting the carbon fiber layer B is preferably 3 μm or more and 30 μm or less, more preferably 5 μm or more and 20 μm or less.

[0039] The carbon fibers constituting the carbon fiber layer B may be anisotropic or isotropic carbon fibers, but it is preferable to include isotropic carbon fibers in the carbon fiber layer B, where the carbon fibers are also oriented in the thickness direction, as this further suppresses heat conduction in the thickness direction. The mass percentage of isotropic carbon fibers is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass, relative to the total mass of the carbon fibers constituting the carbon fiber layer B.

[0040] As the carbon fibers constituting the carbon fiber layer B, pitch-based carbon fibers, polyacrylonitrile-based (PAN-based) carbon fibers, rayon-based carbon fibers, novoloid carbon fibers, and the like can be mentioned. Among these, it is preferable to include pitch-based carbon fibers from the viewpoint of suppressing conductive heat transfer. The mass ratio of the pitch-based carbon fibers is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass, based on the total mass of the carbon fibers constituting the carbon fiber layer B.

[0041] In the carbon fiber layer B, needle punching is preferably performed. By performing needle punching, the strength and durability of the carbon fiber layer B can be enhanced. The punching density of the needle punching is preferably 4 punches / cm ２ or more and 40 punches / cm ２ or less, more preferably 5 punches / cm ２ or more and 20 punches / cm ２ or less, and still more preferably 6 punches / cm ２ or more and 10 punches / cm ２ or less. A smaller punching density can suppress conductive heat transfer in the thickness direction of the carbon fiber layer B.

[0042] The bulk density of the carbon fiber layer B is preferably 0.10 g / cm ３ or more and 0.25 g / cm ３ or less, more preferably 0.12 g / cm ３ or more and 0.20 g / cm ３ or less.

[0043] Similar to the carbon fiber layer A, the carbon fiber layer B may include, in addition to carbon fibers, those obtained by carbonizing a resin. The mass of the carbon fibers constituting the carbon fiber layer B is preferably 80% by mass or more based on the total mass of the entire carbon fiber layer A.

[0044] <Layer structure of the insulation material> The number of carbon fiber sheets constituting the carbon fiber layer A may be one, two or more to increase the layer thickness, or it may be divided into two or more layers by sandwiching another carbon fiber layer in between. The number of carbon fiber layer A layers in the insulation material varies depending on the thickness of the insulation material and the amount of resin impregnated into the carbon fiber layer, but per 1 cm of insulation material thickness, it is preferably 0.1 layers / insulation material thickness (cm) or more, more preferably 1.0 layer / insulation material thickness (cm) or more, and even more preferably 2.0 layers / insulation material thickness (cm). There is no particular upper limit to the total number of carbon fiber layer A layers, but for example, it may be 10 layers / insulation material thickness (cm) or less, 5 layers / insulation material thickness (cm) or less, or 3 layers / insulation material thickness (cm) or less.

[0045] When the thermal insulation material of the present invention comprises a carbon fiber layer B, the number of carbon fiber sheets constituting the carbon fiber layer B may be one, two or more to increase the thickness of the layer, or it may be divided into two or more layers by sandwiching another carbon fiber layer in between. The number of carbon fiber layers B varies depending on the thickness of the thermal insulation material, but preferably there are 0.1 layers / thickness of thermal insulation material (cm) or more, and more preferably 1.0 layer / thickness of thermal insulation material (cm) or more per 1 cm of thickness of thermal insulation material. There is no particular upper limit to the total number of carbon fiber layers B, but for example, it may be 10 layers / thickness of thermal insulation material (cm) or less, 5 layers / thickness of thermal insulation material (cm) or less, or 2 layers / thickness of thermal insulation material (cm) or less.

[0046] When the thermal insulation material of the present invention includes a carbon fiber layer B, the total number of carbon fiber layers A and carbon fiber layers B is preferably 3 or more, more preferably 10 or more, and even more preferably 15 or more. With 3 or more layers, in addition to flexibility, the shrinkage stresses cancel each other out among the carbon fiber layers, which have different thermal shrinkage characteristics, reducing residual stress and improving durability, such as suppressing delamination. There is no particular upper limit to the total number of carbon fiber layers A and carbon fiber layers B, but for example, it may be 50 or less, 30 or less, or 25 or less. The number of layers may be odd or even, but by making both outermost layers carbon fiber layers A, the stress is distributed, making warping and delamination less likely.

[0047] The total thickness of the carbon fiber layer A is preferably 10% or more, more preferably 25% or more, and even more preferably 40% or more, relative to the total thickness of the insulation material. If it is 10% or more, the thermal conductivity at high temperatures tends to decrease. There is no particular upper limit to the total thickness of the carbon fiber layer A, but it is preferably 90% or less, more preferably 70% or less, and even more preferably less than 50%. If the proportion of the carbon fiber layer A is high, the number of windings (layers) of the constituent carbon fiber sheets increases, which worsens the productivity of the insulation material.

[0048] When the thermal insulation material of the present invention includes a carbon fiber layer B, the total thickness of the carbon fiber layer B is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more, relative to the total thickness of the thermal insulation material. A higher proportion of the carbon fiber layer B increases the flexibility of the thermal insulation material, making it easier to process molded bodies with curvature, such as cylindrical shapes. Furthermore, the total thickness of the carbon fiber layer B is preferably 90% or less, more preferably 75% or less, and even more preferably 60% or less. If it is 90% or less, it tends to reduce the thermal conductivity in the high-temperature range.

[0049] The combined ratio of the thickness of carbon fiber layer A to the thickness of carbon fiber layer B is preferably 60% or more, more preferably 80% or more, and even more preferably 90% or more, and may be 100%, relative to the total thickness of the thermal insulation material. This makes it easier to obtain the effects of the present invention.

[0050] The thickness of the insulation material is determined appropriately according to its intended use and is not particularly limited, but for example, it may be 5 mm to 500 mm or 10 mm to 300 mm.

[0051] <Characteristics of the Thermal Insulation Material> The resistivity ratio of the thermal insulation material is preferably 20 or higher, more preferably 25 or higher. There is no particular upper limit to the resistivity ratio of the thermal insulation material, but for example, it is 200 or less and 120 or less. Furthermore, the resistivity ratio of thermal insulation material composed only of carbon fiber layer A is 80 or higher, and the resistivity ratio of thermal insulation material laminated with carbon fiber layer A and carbon fiber layer B is 30 or higher. In this specification, the resistivity ratio of the thermal insulation material is a value obtained by the measurement method described in the examples below. The resistivity value in the thickness direction of the thermal insulation material is preferably 10 mΩ·m or higher, more preferably 12 mΩ·m or higher, and even more preferably 14 mΩ·m or higher. There is no particular upper limit to the resistivity value of the thermal insulation material, but for example, it is 100 mΩ·m or less and 60 mΩ·m or less. In this specification, the resistivity value of the thermal insulation material is a value obtained by the measurement method described in the examples below. The proportion of carbon fibers constituting carbon fiber layer A in the thermal insulation material that have an orientation angle of 10° or more is preferably less than 2%, more preferably less than 1%, and even more preferably less than 0.5%. The lower limit of the proportion of thermal insulation material with an orientation angle of 10° or more is not particularly limited, but is preferably 0%, more preferably 0.1% or more than 0%. The above proportion of thermal insulation material formed by laminating carbon fiber layer A and carbon fiber layer B is preferably less than 12%, and even more preferably 10% or less. In this specification, the proportion of carbon fibers constituting the thermal insulation material with an orientation angle of 10° or more is a value obtained by the measurement method described in the examples below.

[0052] The bulk density of the insulation material is preferably 0.10 g / cm³. ３ 0.25g / cm or more ３ More preferably, 0.12 g / cm³ ３ 0.20g / cm or more ３ The following applies:

[0053] <Molded Thermal Insulation Material> The shape of the thermal insulation material of the present invention is not particularly limited. Examples include plate-shaped thermal insulation materials in which carbon fiber layers are laminated in a plate shape, and cylindrical thermal insulation materials in which carbon fiber layers are wound in a spiral shape and laminated. Among these, thermal insulation materials molded so that the carbon fiber layer A is positioned further upstream with respect to the flow of heat are more preferred.

[0054] <Applications of the Insulating Material> The insulating material of the present invention is not particularly limited, but because it has low thermal conductivity in the high-temperature range, it is suitably used as an insulating material for high-temperature furnaces (heating temperature: 500°C to 3000°C, preferably 1500°C to 3000°C) used for purposes such as sintering of cemented carbide metals and ceramics, and crystal growth of silicon, gallium, silicon carbide, etc.

[0055] ≪Method for Manufacturing Thermal Insulation Material≫ The method for manufacturing thermal insulation material of the present invention includes, for example, the following steps (1) to (4): (1) A step consisting of a carbon fiber mat manufacturing step or a carbon fiber felt manufacturing step for manufacturing a carbon fiber sheet, and an impregnation step for impregnating the carbon fiber sheet (carbon fiber mat or carbon fiber felt) with resin (carbon fiber sheet manufacturing step) (2) A step of laminating carbon fiber sheets impregnated with thermosetting resin (lamination step) (3) A step of curing the obtained laminate by heating (curing step) (4) A step of firing the cured laminate (firing step)

[0056] <Carbon Fiber Sheet Manufacturing Process> In the carbon fiber sheet manufacturing process, carbon fiber sheets, such as carbon fiber mats or carbon fiber felts, are produced, the carbon fiber sheets are impregnated with resin, and then dried.

[0057] (Carbon Fiber Mat Manufacturing Process) The carbon fiber mat manufacturing process consists of the following steps (i) to (iii): (i) A slurry generation step in which carbon fibers are dispersed in a dispersion solution obtained by dispersing adhesive resins such as starch, polyacrylamide, casein, vinyl acetate resin, and polyvinyl alcohol in water or white water to obtain a carbon fiber slurry liquid. (ii) A molding step in which a mat-like molded product is obtained by a so-called papermaking method in which carbon fibers are continuously scooped up from the slurry liquid using a long mesh or the like. (iii) A drying step in which the obtained mat-like molded product is dehydrated and dried.

[0058] Cellulose-based fibers such as plant fibers, regenerated fibers, semi-synthetic fibers, and cellulose nanofibers can be added to the above dispersion solution. Adding cellulose-based fibers can improve the strength of the mat-like molded product. However, the presence or absence of addition and the amount should be adjusted depending on the filtration efficiency during the dewatering process in the drying step. After the dewatering and drying steps, a pre-impregnation step of impregnating with resin can be added as needed. Thermosetting resins and thermoplastic resins can be used as the resin for impregnation, and can be appropriately selected depending on the solvent used in the next step and the required strength. Thermosetting resins are particularly preferred, and epoxy resins are more preferred.

[0059] (Carbon Fiber Felt Manufacturing Process) The carbon fiber felt manufacturing process consists of the following steps (i) and (ii): (i) A step of defibrating carbon fibers using the airlaid method to form a web (ii) A step of felting the web by performing needle punching at regular intervals

[0060] (Impregnation process) In the impregnation process, a carbon fiber molded body is obtained by impregnating a carbon fiber sheet (carbon fiber mat or carbon fiber felt) with a thermosetting resin. The impregnation with the thermosetting resin can be carried out according to known methods, such as the dipping method or the spray coating method.

[0061] (Thermosetting resin) Examples of resins to be impregnated into the carbon fiber sheet include urea resin, melamine resin, phenol resin, epoxy resin, unsaturated polyester resin, alkyd resin, urethane resin, and furan resin. Among these, phenol resin, which has a high carbonization yield, is preferred. These resins are preferably used as a solution dissolved in a solvent. Examples of solvents vary depending on the type of resin, but include alcohols such as methyl alcohol, ethyl alcohol, and denatured alcohol, and water. The non-volatile content concentration of the solution varies depending on the type of resin, but is preferably 15 to 80 parts by mass, and more preferably 25 to 60 parts by mass, per 100 parts by mass of the solution. The amount of the solution impregnated into the carbon fiber sheet varies depending on the type of carbon fiber sheet. In the case of carbon fiber felt, it is preferably 10 to 100 parts by mass, and more preferably 20 to 50 parts by mass, per 100 parts by mass of carbon fiber felt. On the other hand, in the case of carbon fiber mats, the amount of resin is preferably 50 to 150 parts by mass, more preferably 60 to 130 parts by mass, per 100 parts by mass of carbon fiber mat. If the amount of impregnation is too much, the thermal conductivity in the thickness direction of the mat will increase, and if it is too little, the strength will decrease and abnormalities such as peeling may occur. Therefore, the amount of resin impregnation is adjusted as appropriate to obtain the desired heat insulation and strength.

[0062] <Lamination Process> In the lamination process, carbon fiber sheets impregnated with thermosetting resin are laminated.

[0063] (Carbon fiber sheet used to form carbon fiber layer A) An example of a carbon fiber sheet used to form carbon fiber layer A is a carbon fiber mat impregnated with the resin described above.

[0064] It is preferable that the carbon fiber sheet is not needle-punched, as this further suppresses conductive heat transfer in the thickness direction of the carbon fiber layer A.

[0065] (Carbon fiber sheet used to form carbon fiber layer B) An example of a carbon fiber sheet used to form carbon fiber layer B is a carbon fiber felt impregnated with the resin described above.

[0066] (Adhesive-impregnated sheet) In the thermal insulation material of the present invention, when a certain number of carbon fiber mats are stacked to adjust the thickness of carbon fiber layer A, or when a carbon fiber layer B is further provided, it is preferable to bond the carbon fiber mats to each other or carbon fiber layer A and carbon fiber layer B with an adhesive-impregnated sheet. This makes it easier to bond two carbon fiber layers with different properties and suppresses a decrease in peel strength. As a result, even a thermal insulation material consisting of two carbon fiber layers having different expansion and contraction rates with respect to heat can withstand longer-term use. On the other hand, if the number of adhesive-impregnated sheets increases, conductive heat transfer through the sheet layer increases, and in particular, the thermal insulation performance in the thickness direction of carbon fiber layer A decreases.

[0067] The sheets used for adhesive impregnation are not particularly limited, but examples include cellulose screens (e.g., bleached cloth), carbon fiber paper screens, carbon fiber cloth screens, and rayon screens.

[0068] The adhesive may be applied to both the carbon fiber sheet and the sheet for adhesive impregnation, or to either one of them. Applying the adhesive to the sheet for adhesive impregnation can increase the breaking strength. As the adhesive, for example, the resin described in paragraph

[0046] of Japanese Patent Application Publication No. 2015-217669 can be used.

[0069] The process of laminating carbon fiber sheets is not particularly limited. When manufacturing a cylindrical heat insulating material, for example, the winding process described in paragraph

[0048] of Japanese Patent Application Publication No. 2015-217669 can be employed.

[0070] <Curing Process> In the curing process, the laminate of carbon fiber sheets is cured by heating. The heating temperature is not limited as long as it is the temperature at which the resin impregnated in the carbon fiber sheets hardens, but for example, it can be set between 100°C and 200°C. The heating time can also be specified as appropriate, but for example, it can be set between 10 minutes and 20 hours.

[0071] <Firing Process> The firing process can be carried out at a temperature of 3000°C or lower in a non-oxidizing atmosphere. Examples of non-oxidizing atmospheres include vacuum, nitrogen atmosphere, and argon atmosphere. The temperature is not particularly limited as long as carbonization occurs, but is preferably 650°C to 3000°C, more preferably 1000°C to 3000°C. If further graphitization is required, a temperature of 2000°C to 3000°C is preferable. By firing at a temperature higher than the operating temperature of the insulation material, decomposition gases from the insulation material during use can be suppressed.

[0072] <Grinding Process> The resulting fired body can be used as is as an insulating material, but if it is a fired wound body, it is preferable to grind the inner and outer surfaces. Known grinding methods can be used, such as grinding using a lathe or machining center. By grinding, the dimensional accuracy of the molded body can be improved by processing it to a predetermined dimension and making fine adjustments.

[0073] <Heat Treatment Equipment> The heat treatment equipment of the present invention is equipped with the heat insulating material of the present invention. Examples of heat treatment equipment include high-temperature furnaces (heating temperature: 500°C to 3000°C, preferably 1500°C to 3000°C) used for purposes such as sintering cemented carbide metals and ceramics, and crystal growth of silicon, gallium, silicon carbide, etc.

[0074] In the present invention, the heat insulating material is preferably positioned to separate the inside and outside of the furnace, and the carbon fiber layer A is preferably positioned on the side of the heat insulating material that is exposed to higher temperatures. Since the effect of radiant heat transfer is large in the high-temperature range (1500°C or higher), positioning the carbon fiber layer A on the side of the heat insulating material that is exposed to higher temperatures makes it easier to reduce the thermal conductivity in the high-temperature range.

[0075] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0076] The materials, manufacturing methods, and winding machines used in the examples and comparative examples are shown below. The average diameter and average fiber length of the carbon fibers are shown in Tables 1 to 3. Carbon fiber mats 1 and 2: Carbon fiber sheets obtained by using the method described in

[0057] to obtain carbon fibers (PX35 (manufactured by Zoltek), PAN-based, anisotropic), in which the carbon fibers are oriented substantially perpendicular to the thickness direction (bulk density: 0.06 g / cm³). ３ Thickness: 1.5 mm, Fiber content: 90 g / m ２ ). Carbon fiber mat 3: A carbon fiber sheet (bulk density: 0.06 g / cm³) obtained by using the method described in

[0057] to obtain carbon fibers (KCF-100 (manufactured by Kureha Corporation), pitch-based, isotropic), wherein the carbon fibers are oriented substantially perpendicular to the thickness direction. ３ Thickness: 1.5 mm, Fiber content: 90 g / m ２ ). Carbon fiber felt 1: A carbon fiber sheet (bulk density: 0.06 g / cm³) obtained by using the method described in

[0059] with longer carbon fibers (KCF-100 (manufactured by Kureha Corporation), pitch-based, isotropic), in which the carbon fibers are randomly oriented in three dimensions. ３ Thickness: 10 mm, Fiber content: 600 g / m ２ Punching density: 8 punches / cm ２ ). Carbon fiber felt 2: A carbon fiber sheet (bulk density: 0.06 g / cm³) obtained by using the method described in

[0059] to obtain longer carbon fibers (PX35 (manufactured by Zoltek), PAN-based, anisotropic), in which the carbon fibers are randomly oriented in three dimensions. ３ Thickness: 10 mm, Fiber content: 600 g / m ２ Punching density: 25 punches / cm ２ ). Phenolic resin: Showa Denko's Showol BRS-3897. Phenolic resin impregnation: Method as described in

[0060] . Adhesive: A mixture of IF-3000 and OI-305A manufactured by DIC Corporation. Bleached cloth: Bleached cloth manufactured by Hasegawa Tora Spinning Co., Ltd. (Balance: 105 g / m ２ ). Winding machine: Manufactured by Aiya Kogyo Co., Ltd.

[0077] For carbon fiber mats 1-3 and carbon fiber felts 1 and 2, materials were used that had been impregnated with phenolic resin, then soaked in the impregnation solution, and cured overnight to allow excess solvent to evaporate. For the bleached cloth, adhesive was applied and it was dried at 110°C.

[0078] In the following, the carbon fiber layer formed using carbon fiber felt 1 is referred to as carbon fiber layer b, and the carbon fiber layer formed using other carbon fiber mats or carbon fiber felts is referred to as carbon fiber layer a.

[0079] <Example 1> (Preparation of cylindrical heat insulating material) A bleached cloth coated with adhesive and dried was set on the winding core of a winding machine and wound around once beforehand. Four ends of a carbon fiber mat 1 impregnated with phenolic resin were overlapped, and the ends were inserted between the winding core of the winding machine and the bleached cloth. The carbon fiber mat 1 was wound onto the bleached cloth and the winding machine while applying tensile tension (tensile force) to the bleached cloth. The tension of the bleached cloth was adjusted using the thickness as an indicator in order to make the density of the wound body constant. Winding was stopped when the thickness reached 100 mm, and the winding core and the wound body were removed from the winding machine as a single unit. The obtained wound body was hardened by heat treatment at 140°C for 8 hours. The hardened wound body was removed from the winding core, and a fired wound body was obtained by firing it under vacuum at 2000°C or higher. Finally, the inner surface, outer surface, and both ends of the wound body were ground using a machining center (NC516PU manufactured by SHODA Corporation) to obtain the cylindrical heat insulating material of Example 1.

[0080] (Preparation of plate-shaped insulation material) In addition, to achieve a layer structure similar to that of the cylindrical insulation material, a carbon fiber mat 1 impregnated with phenolic resin and a bleached cloth coated with adhesive and dried were laminated together, and the laminated material was pressed and hardened using a press heated to over 150°C while being compressed. The resulting laminated board was fired under vacuum at over 2000°C to obtain the plate-shaped insulation material of Example 1.

[0081] <Example 2> (Preparation of cylindrical insulation material) A bleached cloth coated with adhesive and dried was set on the winding core of a winding machine and wound once beforehand. Six carbon fiber mats 1 impregnated with phenolic resin were stacked and the ends were inserted between the winding core of the winding machine and the bleached cloth set on the winding core. Then, the carbon fiber mats 1 were wound on the winding machine while applying tensile tension (tensile force) to the bleached cloth set on the winding core. When the rotating body reached a predetermined thickness of 50 mm, two carbon fiber felts 1 impregnated with phenolic resin were inserted instead of the carbon fiber mats 1. The tension of the bleached cloth was adjusted using the thickness as an indicator in order to keep the density of the wound body constant. When the thickness reached 100 mm, winding was stopped and the winding core and the wound body were removed from the winding machine as a single unit. The obtained wound body was cured by heat treatment at 140°C for 8 hours. The hardened winding was removed from the winding core and fired at over 2000°C under vacuum to obtain a fired winding. Finally, the inner surface, outer surface, and both ends of the winding were ground using a machining center (NC516PU manufactured by SHODA Corporation) to obtain the cylindrical heat insulating material of Example 2. The cylindrical heat insulating material of Example 2 had a two-layer structure consisting of carbon fiber layer a and carbon fiber layer b, with carbon fiber layer a positioned on the inside.

[0082] (Preparation of plate-shaped insulation material) In addition, to achieve a layer structure similar to that of the cylindrical insulation material, multiple carbon fiber mats 1 impregnated with phenolic resin were laminated to a thickness of 40 mm, and multiple carbon fiber felts 1 impregnated with phenolic resin were laminated to a thickness of 40 mm, and bleached cloth coated with adhesive and dried was laminated so that the bleached cloth was between the mats and felts, and the laminate was pressed and hardened in a press heated to over 150°C while being compressed. The resulting laminate was fired under vacuum at over 2000°C to obtain the plate-shaped insulation material of Example 2. The plate-shaped insulation material of Example 2 had a layer structure comprising one carbon fiber layer a and one carbon fiber layer b.

[0083] <Example 3> Instead of the carbon fiber mat 1 impregnated with phenolic resin, a carbon fiber mat 2 impregnated with phenolic resin was used, and six of the carbon fiber mats 2 were stacked together. The ends were then inserted between the winding core of the winding machine and the bleached cloth. Except for these differences, the cylindrical and plate-shaped insulating materials of Example 3 were obtained in the same manner as in Example 1.

[0084] <Example 4> (Preparation of cylindrical heat insulating material) A bleached cloth coated with adhesive and dried was set on the winding core of a winding machine and wound around once beforehand. A carbon fiber mat 1 impregnated with phenolic resin, a bleached cloth, and a carbon fiber felt 1 impregnated with phenolic resin were laminated so that the bleached cloth was between the carbon fiber mat 1 and the carbon fiber felt 1, and the ends of the laminated material were inserted between the winding core of the winding machine and the bleached cloth set on the winding core. Then, while applying tensile tension (tensile force) to the bleached cloth set on the winding core, the carbon fiber mat 1, carbon fiber felt 1, and bleached cloth were wound on the winding machine. In order to make the density of the wound material constant, the tension of the bleached cloth was adjusted using the thickness as an indicator. When the thickness reached 100 mm, winding was stopped, and the winding core and the wound material were removed from the winding machine as a single unit. The obtained wound material was cured by heat treatment at 140°C for 8 hours. The hardened winding was removed from the winding core and fired at over 2000°C under vacuum to obtain a fired winding. Finally, the inner surface, outer surface, and both ends of the winding were ground using a machining center (NC516PU manufactured by SHODA Corporation) to obtain the cylindrical thermal insulation material of Example 4. The cylindrical thermal insulation material of Example 4 had a structure in which carbon fiber layer a and carbon fiber layer b were alternately repeated one layer at a time, with 15 layers of each layer totaling 30 layers in a thickness of 70 mm. Furthermore, carbon fiber layer a was placed on the innermost side.

[0085] (Preparation of plate-shaped insulation material) In addition, to achieve a layer structure similar to that of the cylindrical insulation material, a carbon fiber mat 1 impregnated with phenolic resin, a carbon fiber felt 1 impregnated with phenolic resin, and a bleached cloth coated with adhesive and dried were laminated together and pressed in a press heated to over 150°C while being compressed, and then hardened. The resulting laminated board was fired under vacuum at over 2000°C to obtain the plate-shaped insulation material of Example 4. The plate-shaped insulation material of Example 4 had a structure in which carbon fiber layer a and carbon fiber layer b were alternately repeated one layer at a time, with 15 layers of each, for a total of 30 layers, within a thickness of 70 mm.

[0086] <Example 5> The cylindrical and plate-shaped insulating materials of Example 5 were obtained in the same manner as in Example 4, except that the number of carbon fiber mats 1 impregnated with phenolic resin was changed from 1 to 3, and a mat made of three layers of carbon fiber mats 1 impregnated with phenolic resin, a bleached cloth, and carbon fiber felt 1 impregnated with phenolic resin were laminated. The cylindrical and plate-shaped insulating materials of Example 5 had a structure in which carbon fiber layer a and carbon fiber layer b were alternately repeated one layer at a time, with 11 layers of each, for a total of 22 layers laminated in a thickness of 70 mm. In addition, the innermost carbon fiber layer a was placed in the cylindrical insulating material of Example 5.

[0087] <Example 6> The cylindrical and plate-shaped insulating materials of Example 6 were obtained in the same manner as in Example 4, except that the number of carbon fiber mats 1 impregnated with phenolic resin was changed from 1 to 6, and a mat made of 6 layers of carbon fiber mats 1 impregnated with phenolic resin, a bleached cloth, and carbon fiber felt 1 impregnated with phenolic resin were laminated together. The cylindrical and plate-shaped insulating materials of Example 6 had a structure in which carbon fiber layer a and carbon fiber layer b were alternately repeated one layer at a time, with 10 layers of each in a thickness of 70 mm, for a total of 20 layers. In addition, the innermost carbon fiber layer a was placed in the cylindrical insulating material of Example 6.

[0088] <Comparative Example 1> (Preparation of Cylindrical Insulation Material) A bleached cloth coated with adhesive and dried was set on the winding core of a winding machine and wound around once beforehand. Two layers of carbon fiber felt 1 impregnated with phenolic resin were stacked, and the ends were inserted between the winding core of the winding machine and the bleached cloth. The carbon fiber felt 1 was wound onto the bleached cloth and the winding machine while applying tensile tension (tensile force) to the bleached cloth. The tension of the bleached cloth was adjusted using the thickness as an indicator in order to keep the density of the wound body constant. Winding was stopped when the thickness reached 100 mm, and the winding core and the wound body were removed from the winding machine as a single unit. The obtained wound body was hardened by heat treatment at 140°C for 8 hours. The hardened wound body was removed from the winding core, and a fired wound body was obtained by firing it under vacuum at 2000°C or higher. Finally, the inner surface, outer surface, and both ends of the wound body were ground using a machining center (NC516PU manufactured by SHODA Corporation) to obtain the cylindrical heat insulating material of Comparative Example 1.

[0089] (Preparation of plate-shaped insulation material) In addition, to achieve a layer structure similar to that of the cylindrical insulation material, carbon fiber felt 1 impregnated with phenolic resin and bleached cloth coated with adhesive and dried were laminated together, and then pressed and hardened using a press heated to over 150°C while being compressed. The resulting laminated board was fired under vacuum at over 2000°C to obtain the plate-shaped insulation material of Comparative Example 1.

[0090] <Comparative Example 2> A cylindrical thermal insulation material and a plate-shaped thermal insulation material of Comparative Example 2 were obtained in the same manner as in Comparative Example 1, except that a carbon fiber felt 2 impregnated with phenol resin was used instead of carbon fiber felt 1 impregnated with phenol resin.

[0091] <Comparative Example 3> A cylindrical thermal insulation material and a plate-shaped thermal insulation material of Comparative Example 3 were obtained in the same manner as in Comparative Example 1, except that a carbon fiber mat 3 impregnated with phenol resin was used instead of the carbon fiber felt 1 impregnated with phenol resin, and six layers of the carbon fiber mat 3 were stacked.

[0092] [Measurement of Average Diameter of Carbon Fibers] The average diameter of carbon fibers in a carbon fiber layer was measured using a cross-section cut perpendicular to the fiber orientation in the carbon fiber layer. The obtained cross-section was observed using a scanning electron microscope (JSM-5510_5510LV, manufactured by JEOL Ltd.) under the analysis conditions of 1000x magnification, 5kV incident voltage, 4mm working distance, and 20 spot size, and the diameters of five carbon fibers within the same field of view were measured. This was also performed in separate, independent fields of view, for a total of 20 fields of view. The diameters of a total of 100 carbon fibers were measured, and the average value was calculated to determine the average diameter of the carbon fibers.

[0093] [Measurement of Average Fiber Length of Carbon Fibers] The average fiber length of carbon fibers was measured from a cross-section perpendicular to the thickness direction of the carbon fiber layer, observed using a digital microscope (VHX-X1, Keyence Corporation). Images were acquired with a magnification of 100x, a field of view of 50mm x 50mm (image stitching), and depth correction enabled. For the carbon fibers to be measured, the length of each carbon fiber was measured for 10 fibers from which the start and end points could be identified, and the average value was calculated to determine the average fiber length of the carbon fibers.

[0094] [Bulk Density] The length of each side was measured with calipers and the volume was calculated (for cylindrical insulation materials, the inner and outer diameters were measured at four points (90° apart) with calipers, and the area of ​​the base was calculated from the average value. The height was also measured with calipers and the volume was calculated). The weight was measured using a platform scale (HW-10KC, A&D Company, Limited), and the bulk density (g / cm³) was calculated from the volume and weight. ３ ) was sought.

[0095] [Measurement of Resistivity Ratio of Thermal Insulation Material] For each example, a plate-shaped thermal insulation material was cut to have a 40 mm square bottom surface, and copper plates were attached to both ends facing the measurement direction. The copper plates were attached using a conductive adhesive resin (Dotite D-500, manufactured by Fujikura Chemical Co., Ltd.), with the same amount applied to both sides of the thermal insulation material, and then the copper plates were bonded on top. The resistance value in the measurement direction was measured using a Wheatstone bridge 275597 (manufactured by Yokogawa Electric Corporation). Measurements were taken in both the thickness direction and the surface direction, and five samples were measured for each sample with different cut positions. The resistivity values ​​in the thickness direction and surface direction for each sample were calculated using the following formula: Resistivity (mΩ・m) = (Measured electrical resistance value (mΩ) - Offset resistance value (mΩ)) × Measurement area (m ２ ) / Length in the direction of measurement (m)

[0096] The resistivity in the thickness direction is determined by the bulk density (g / cm³) of each sample. ３ An approximate straight line was determined using the least squares method, with the x-axis (horizontal axis) representing the thickness and the y-axis (vertical axis) representing the resistivity (mΩ・m). The resistivity at a bulk density of 0.16 was calculated using this approximate formula and defined as the resistivity in the thickness direction. The resistivity in the surface direction was taken as the average of five samples. The resistivity ratio was calculated using the following formula: Resistivity ratio = Resistivity in the thickness direction / Resistivity in the surface direction

[0097] [Calculation of the proportion of fibers with an orientation angle of 10° or more] For each example, the plate-shaped insulation material was cut into a rectangular parallelepiped measuring 10 mm × 150 mm × 150 mm, with the thickness direction of the insulation material set to 10 mm. In the case of laminated materials, each layer was included in the cut. The cross-section of the cut rectangular parallelepiped was photographed using a non-destructive structural analysis device (TOSCANER-31302μC3, Toshiba IT Control Systems Co., Ltd.). The shooting conditions were: tube voltage 60 kV, tube current 120 μA, slice pitch 0.010 mm, number of slices 300, matrix size 1024 × 1024, number of views 900, number of integrated layers 20, and pixel size 0.0057 mm. The above captured images were analyzed using image analysis software (simpleware Synopsys Co., Ltd.) to calculate the proportion of fibers whose orientation angle is tilted at 10° or more with respect to the direction perpendicular to the thickness direction of the carbon fibers. The analysis using Simpleware was performed in the following order: image loading, application of filters (smoothing filters), mask creation (Threshold), fiber analysis, and vector display (Vectors). The filter used was a Gaussian filter, with Gaussian Sigma set to 2. For the mask, the Lower value was set to the peak on the left side of the histogram (background), and the Upper value was set to the maximum value displayed in the histogram. Fiber analysis was performed in Orientation Only mode, with sampling size (voxel) set to 2, and Region of interest set to 700 x 700 x 250 pixels based on the center of the image. The Vectors setting was set to the default settings of the instrument. Export was performed in that state to output the fiber tensor and eigenvectors at each location in the image. From the output major eigenvectors, the angle of the fibers relative to the lamination direction at each location in the image was determined. The total number of angles was tallied, and the proportion of angles of 10° or more was calculated. Considering the variability depending on the measurement location, the average value of three or more points (field of view) was used as the representative value for that insulation material. For the measurement of each layer in the laminate, the area of ​​the adhesive layer corresponding to the adhesive-impregnated sheet was identified in the image, and the fiber angle of a single layer was measured by using that area as the boundary.The region corresponding to the adhesive layer was identified by referring to Figure 1.

[0098] [Measurement of Average Thermal Conductivity] A cylindrical insulation material sample for each example was placed in a small hearth-lift type carbon furnace (SPS2020M-10 manufactured by Marusho Electric Co., Ltd.), heated to a predetermined furnace temperature (800°C, 1600°C, or 2200°C) under a nitrogen / reduced pressure (approximately 1.3 Pa) atmosphere, and held for 1 hour. The amount of heat transmitted was then determined from the temperature difference between the inlet and outlet of the heat exchange water. The cooling water was circulated to completely cover the outer circumference of the measurement sample. The thermal conductivity was determined using the following equations (1) and (2).

[0099] λ = (Q × ln(r² / r¹)) / (2 × π × L × (TH - TL)) (2) λ: Thermal conductivity [W / m / K] Q: Heat transmission [W] r¹: Sample inner diameter [m] r²: Sample outer diameter [m] L: Sample height [m] TH: High surface temperature [K] TL: Low surface temperature [K]

[0100] Q = mcΔTw (1) Q: Heat transmission [J / s = W] m: Weight of cooling water per unit time [g / s] c: Specific heat of water [J / (g·K)] ΔTw: Cooling water temperature difference [K]

[0101] [Productivity] Productivity was assessed using the number of layers (winds) as an indicator, with a low load indicated by ○, and the degree of the load on manufacturing was defined as follows. The number of layers (winds) refers to the number of carbon fiber sheets that are layered or the number of windings of carbon fiber sheets that are wound when manufacturing the insulation material. The total number of layers (winds) of the laminate described below is the sum of the number of layers (winds) in carbon fiber layer a and the number of layers (winds) in carbon fiber layer b. ○: When manufacturing the laminate described in the Examples and Comparative Examples, the total number of layers (winds) of the laminate / thickness of the insulation material [sheets / cm] is less than 8 [sheets / cm]. △: When manufacturing the laminate described in the Examples and Comparative Examples, the total number of layers (winds) of the laminate / thickness of the insulation material [sheets / cm] is 8 [sheets / cm] or more and less than 16 [sheets / cm]. ×: When manufacturing the laminate described in the Examples and Comparative Examples, the total number of layers (turns) of the laminate / the thickness of the insulation material [layers / cm] is 16 [layers / cm] or more.

[0102] [Flexibility] Regarding flexibility, the thickness to which cylindrical insulation material can be mass-produced is used as an indicator, and flexibility is defined as follows, with ○ indicating no restrictions on the thickness of the insulation material: ○: Cylindrical insulation material can be mass-produced without any problems. △: Cylindrical insulation material can be mass-produced, but there are restrictions on the thickness of the insulation material. ×: Cylindrical insulation material cannot be mass-produced.

[0103] [Durability] Oxidation resistance tests were conducted on each insulation material in an air atmosphere, and the condition of the insulation material after the test was evaluated. Each example of plate-shaped insulation material was cut into a 40 mm cube, placed in a 200 mm x 200 mm x 150 mm quartz case (2 mm thick), and heated in an electric furnace (KDF-P90, Denken Co., Ltd.). The temperature was raised from room temperature to 600°C over 3 hours in a nitrogen atmosphere (flow rate 1 L / min), then switched to an air atmosphere (flow rate 1 L / min) and maintained for 25 hours. After that, heating was stopped, the temperature was lowered by switching to a nitrogen atmosphere (flow rate 1 L / min), and the furnace was left to cool until it reached room temperature. The quartz case was removed from the electric furnace, and the insulation material was evaluated according to the following evaluation criteria. The evaluation criteria are as follows. ○: The insulation material maintains its shape and there is no delamination between layers. △: The insulation material maintains its shape, but delamination is observed between layers. ×: The insulation material is either missing or in powder form, or does not maintain its original shape.

[0104] Tables 1 and 2 below show the layer structure, measurement results of average thermal conductivity, and evaluation results for the examples and comparative examples. The thickness of the insulation material in each example was 70 mm. Note that "two-dimensional" orientation indicates that the carbon fibers are oriented substantially perpendicular to the thickness direction of the carbon fiber layer, while "three-dimensional" orientation indicates that the orientation of the carbon fibers is random in three dimensions.

[0105]

[0106]

[0107] Tables 1 and 2 show that the thermal insulation material of the example, which includes a carbon fiber layer A composed of carbon fibers oriented substantially orthogonal to the thickness direction and having an average diameter of 10 μm or less, exhibits lower thermal conductivity in all temperature ranges from 800°C to 2200°C compared to a typical thermal insulation material consisting of carbon fiber felt using pitch-based carbon fibers (Comparative Example 1). In particular, comparing Comparative Examples 1 and 3 with Example 6, the carbon fiber layer A of Example 6 does not significantly affect the thermal conductivity in the 800°C range, but in the higher temperature ranges of 1600°C and 2200°C, the thermal conductivity of Example 6 is lower, demonstrating an improvement in thermal insulation performance in high-temperature ranges due to the carbon fiber layer A. Furthermore, even if the average diameter of the carbon fibers is 10 μm or less, as in Comparative Example 2, if the carbon fibers are randomly arranged in three dimensions in a felt, the thermal conductivity in higher temperature ranges is suppressed, but the thermal conductivity in relatively low temperature ranges increases. Furthermore, even in the case of a mat where the carbon fibers are substantially perpendicular to the thickness direction, as in Comparative Example 3, if the average diameter of the carbon fibers is greater than 10 μm, the thermal conductivity in the higher temperature range increases. As a result, by incorporating carbon fiber layer A, it becomes possible to realize an insulating material that achieves both thermal insulation from 800°C to 2200°C. Also, compared to Example 4, Comparative Example 1 has a high resistivity in the thickness direction, and Comparative Example 3 has a high resistivity ratio, but the thermal conductivity of Example 4 is kept low. This is thought to be because the resistivity and resistivity ratio mainly reflect conductive heat transfer through the carbon fibers and do not reflect radiative heat transfer. Therefore, the reason why the thermal conductivity is low in Example 6 is thought to be that the average diameter of the carbon fibers constituting the layer corresponding to carbon fiber layer A is smaller than that of Comparative Examples 1 and 3, so the projected area ratio of the carbon fiber layer is higher and radiative heat transfer is suppressed. In addition, as in Examples 2 and Examples 4 to 6, the flexibility of the insulating material is improved by laminating carbon fiber layer B. Furthermore, productivity improved as the proportion of carbon fiber layer B increased, and durability improved when there were three or more layers of carbon fiber layers A and B combined, as in Examples 4 to 6.

[0108] [Compressive Strength] A sample was prepared by cutting carbon fiber mat 1 to 50 mm x 50 mm and stacking three pieces. The weight of each sample was measured using an electronic balance (ML204 Mettler Toledo Co., Ltd.), and the bulk density of each sample was calculated. Then, using an autograph (AGS-H Shimadzu Corporation), the above samples were compressed to a thickness at which the bulk density reached a predetermined value, and the compressive strength [kPa] at which the bulk density reached the predetermined value was measured. Here, the predetermined value is a bulk density of 0.10 to 0.20 g / cm³. ３ Up to 0.01 g / cm³ ３ These are 11 values ​​divided into increments. Each sample was measured at least five times, and the average compressive strength [kPa] at each bulk density was determined. For carbon fiber mats 2 and 3, the average compressive strength [kPa] at each bulk density was determined in the same manner as for carbon fiber mat 1. For carbon fiber mats 1 to 3, the bulk density was 0.13 g / cm³. ３ 0.16 g / cm³ ３ , or 0.20 g / cm³ ３ Table 3 shows the average compressive strength [kPa] in this case.

[0109]

[0110] Table 3 shows that the compressive strength increases as the average fiber length decreases, and this effect becomes more pronounced as the bulk density increases. High compressive strength necessitates higher tension on the bleached cloth set on the winding core during the production of cylindrical insulation materials, increasing the likelihood of the cloth breaking and limiting mass production. Carbon fiber mat 1 and carbon fiber mat 3 have a bulk density of 0.20 g / cm³. ３ However, its compressive strength is about 80 kPa, which is within a range that does not pose a problem for mass production. On the other hand, carbon fiber mat 2 has a bulk density of 0.20 g / cm³. ３ Since the compressive strength exceeds 100 kPa, when mass-producing, it is necessary to limit the size of the cylinder and keep the tension low.

Claims

1. A thermal insulation material formed from a sheet-like molded body, comprising a carbon fiber layer A, wherein the carbon fiber layer A is a sheet-like layer including a carbon fiber mat, the average diameter of the carbon fibers constituting the carbon fiber mat is 10 μm or less, and the carbon fibers constituting the carbon fiber mat are oriented substantially perpendicular to the thickness direction of the carbon fiber layer A.

2. The thermal insulation material according to claim 1, wherein the resistivity ratio is 20 or more.

3. The thermal insulation material according to claim 1, wherein the resistivity ratio is 30 or more.

4. The thermal insulation material according to claim 1, wherein the resistivity in the thickness direction of the thermal insulation material is 10 mΩ·m or more.

5. The thermal insulation material according to claim 1, wherein the proportion of carbon fiber layer A with an orientation angle of 10° or more relative to the direction perpendicular to the thickness direction of the carbon fibers is less than 2%.

6. The thermal insulation material according to claim 1, wherein the proportion of the thermal insulation material having an orientation angle of 10° or more with respect to a direction perpendicular to the thickness direction of the thermal insulation material is less than 12%.

7. The thermal insulation material according to claim 1, wherein the average fiber length of the carbon fibers constituting the carbon fiber layer A is 20 mm or more and less than 50 mm.

8. The thermal insulation material according to claim 1, further comprising a carbon fiber layer B, wherein the orientation of the carbon fibers constituting the carbon fiber layer B is randomly arranged in three dimensions.

9. The thermal insulation material according to claim 8, wherein the sum of the number of carbon fiber layers A and the number of carbon fiber layers B is three or more.

10. The thermal insulation material according to any one of claims 1 to 7, wherein the carbon fibers constituting the carbon fiber layer A are anisotropic carbon fibers.

11. The thermal insulation material according to claim 8 or 9, wherein the carbon fibers constituting the carbon fiber layer B are isotropic carbon fibers.

12. A heat treatment apparatus comprising an insulating material according to any one of claims 1 to 9, wherein the insulating material is positioned to separate the inside and outside of the furnace, and a carbon fiber layer A is positioned on the side exposed to higher temperatures.

13. A method for manufacturing an insulating material according to any one of claims 1 to 7, wherein the carbon fiber mat constituting the carbon fiber layer A is manufactured by a papermaking method.

14. A method for manufacturing an insulating material according to claim 8 or 9, wherein the carbon fiber layer A and the carbon fiber layer B are bonded together with an adhesive-impregnated sheet.

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