Heat insulation material

Abstract

To provide a heat insulation material that is excellent in thermal insulation performance in a temperature range of 1400°C or higher.SOLUTION: A heat insulation material is a cylindrical heat insulation material including a carbon fiber and a resin carbide. The heat insulation material is an integral molding and has an inner surface of which surface roughness Ra is 50 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermal insulation material. [Background technology]

[0002] Carbon fiber insulation materials have high heat resistance and excellent insulating properties, and are therefore widely used as insulation materials for high-temperature furnaces such as semiconductor manufacturing furnaces and ceramic sintering furnaces.

[0003] The shape of the heat insulating material is appropriately determined depending on the shape of the object to be insulated. For example, a cylindrical heat insulating material is used to insulate a cylindrical object.

[0004] For example, Patent Document 1 discloses a method for directly producing a hollow cylindrical carbon fiber molding from a slurry containing carbon fibers using a suction molding die. The hollow cylindrical insulation material manufactured using a suction molding mold has most of the carbon fibers arranged parallel to the heat source, allowing it to exhibit high insulation performance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 02-208264 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the heat insulating material produced by the method described in Patent Document 1 has insufficient heat insulating performance in the temperature range of 1400°C or higher. The reason for this is thought to be that the heat insulating material manufactured by the method described in Patent Document 1 has a rough inner surface and is unable to sufficiently reflect light radiated from the heat source.

[0007] The present invention has been made to solve the above problems, and an object of the present invention is to provide a heat insulating material that has excellent heat insulating performance in a temperature range of 1400°C or higher. [Means for solving the problem]

[0008] The insulating material of the present invention is a cylindrical insulating material containing carbon fiber and resin carbide, characterized in that the insulating material is an integrally molded body and the surface roughness Ra of the inner surface of the insulating material is 50 μm or less.

[0009] The heat insulating material of the present invention has an inner surface roughness Ra of 50 μm or less, and therefore easily reflects radiant light emitted from a heat source, providing excellent heat insulating performance.

[0010] In the heat insulating material of the present invention, the surface roughness Ra of the inner surface of the heat insulating material may be 10 μm or more. Even if the surface roughness Ra of the inner surface of the heat insulating material is less than 10 μm, the property of sufficiently reflecting light radiated from the heat source is not significantly improved compared to when the surface roughness Ra is 10 μm or more and 50 μm or less. Therefore, from the viewpoint of improving the heat insulating performance by reflecting the light radiated from the heat source, it can be said that a surface roughness Ra of the heat insulating material of 10 μm or more and 50 μm or less is sufficient.

[0011] The heat insulating material of the present invention preferably contains flake graphite. If the heat insulating material contains flake graphite, the heat insulating performance can be further improved. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view schematically showing an example of a heat insulating material of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a perspective view schematically showing an example of an integral molding die. [Figure 4] FIG. 4 is a diagram schematically illustrating an example of a method for producing a carbon fiber molding using the integral molding die shown in FIG. [Figure 5] FIG. 5 is a diagram showing a schematic view of the initial state of papermaking in the method shown in FIG. [Figure 6] FIG. 6 is a partial enlarged view of the area indicated by the dashed line in FIG. [Figure 7] FIG. 7 is a diagram schematically showing a state in which carbon fibers are further deposited on the state shown in FIG. [Figure 8] FIG. 8 is a partial enlarged view of the area indicated by the dashed line in FIG. [Figure 9] FIG. 9 is a perspective view schematically showing another example of an integral molding die. [Figure 10] FIG. 10 is a diagram schematically illustrating an example of a method for producing a carbon fiber molding using the integral molding die shown in FIG. [Figure 11] FIG. 11 is an enlarged cross-sectional view of a carbon fiber molding obtained by the method shown in FIG. [Figure 12] FIG. 12 is an enlarged cross-sectional view of a carbon fiber molding obtained by yet another example of the method for producing a carbon fiber molding using an integral molding die. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention.

[0014] [Insulation material] The insulating material of the present invention is a cylindrical insulating material containing carbon fiber and resin carbide, characterized in that the insulating material is an integrally molded body and the surface roughness Ra of the inner surface of the insulating material is 50 μm or less.

[0015] FIG. 1 is a perspective view schematically showing an example of a heat insulating material of the present invention. The heat insulating material 1 is cylindrical and extends in the longitudinal direction (the direction indicated by the arrow Z in FIG. 1), with an inner diameter R1, an outer diameter R2, a thickness t, and a length h. The dimension h of the heat insulating material 1 in the longitudinal direction is also referred to as the height. The heat insulating material 1 is an integrally molded body containing carbon fiber and resin carbide.

[0016] FIG. 2 is a cross-sectional view taken along line II-II in FIG. As shown in FIG. 2, the thickness t of the heat insulating material 1 is the distance between the inner surface 1a and the outer surface 1b of the heat insulating material 1 in a plane perpendicular to the longitudinal direction Z (XY plane).

[0017] The surface roughness Ra of the inner surface 1a of the heat insulating material 1 is 50 μm or less. If the surface roughness Ra of the inner surface 1a is 50 μm or less, the radiant light emitted from the heat source is easily reflected, and the heat insulating performance is excellent.

[0018] The surface roughness Ra is the arithmetic mean roughness Ra specified in JIS B 0601: 2013. In this specification, the average value of the arithmetic mean roughness Ra measured with a laser microscope at 10 randomly selected points on the inner surface of the thermal insulation material is defined as the surface roughness Ra of the inner surface of the thermal insulation material.

[0019] The surface roughness Ra of the inner surface of the heat insulating material may be 10 μm or more. Even if the surface roughness Ra of the inner surface of the heat insulating material is less than 10 μm, the property of sufficiently reflecting light radiated from the heat source is not significantly improved compared to when the surface roughness Ra is 10 μm or more and 50 μm or less. Therefore, from the viewpoint of improving the heat insulating performance by reflecting the light radiated from the heat source, it can be said that a surface roughness Ra of the heat insulating material of 10 μm or more and 50 μm or less is sufficient.

[0020] The inner diameter of the heat insulating material is preferably 50 to 1000 mm. The outer diameter of the heat insulating material is preferably 60 to 1200 mm.

[0021] The thickness of the heat insulating material is preferably 5 to 100 mm.

[0022] The length (height) of the heat insulating material is preferably 150 to 550 mm.

[0023] (carbon fiber) The insulation material includes carbon fiber.

[0024] The average fiber length of the carbon fibers is preferably 0.4 to 2 mm. By setting the average fiber length of the carbon fibers to 0.4 to 2 mm, the smoothness of the inner surface of the heat insulating material is likely to be improved.

[0025] The average fiber diameter of the carbon fibers is preferably 1 μm to 30 μm. When the average fiber diameter of the carbon fibers is 30 μm or less, the conductive heat transfer effect of the carbon fibers themselves can be suppressed, and when the average fiber diameter of the carbon fibers is 1 μm or more, the light-shielding properties are excellent and radiant heat transfer can be suppressed.

[0026] The carbon fiber may be any of pitch-based carbon fiber, PAN-based carbon fiber, and rayon-based carbon fiber, and may be either graphite or carbonaceous.

[0027] The heat insulating material includes a resin charcoal. The resin carbonized material is a material obtained by carbonizing a resin such as an organic binder by heating it in a non-oxidizing atmosphere. By filling the gaps between the carbon fibers with the resin carbide, the smoothness of the inner surface of the heat insulating material is improved, making it easier to reflect the radiant light emitted from the heat source.

[0028] The content of the resin carbonized material is not particularly limited, but it is preferable that it accounts for 10 to 40% of the weight of the heat insulating material. If the resin char content is less than 10%, the gaps between the carbon fibers on the inner surface of the heat insulating material cannot be filled, and the surface roughness Ra of the inner surface may not be reduced sufficiently. On the other hand, if the content of resin carbonized material exceeds 40%, the proportion of carbon fiber in the heat insulating material becomes too small, and the heat insulating performance may not be fully exhibited.

[0029] The insulating material preferably contains flake graphite. If the heat insulating material contains flake graphite, the heat insulating performance can be further improved.

[0030] Flake graphite is graphite that has a thin, scaly shape. Specifically, flake-shaped graphite is graphite that is in the form of flakes and has a thickness of 100 μm or less.

[0031] As the flake graphite, natural graphite can be used.

[0032] The average particle size of the flake graphite is preferably 25 to 400 μm. The average particle size of flake graphite can be measured by sieve analysis in accordance with "Industrial analysis and testing methods for natural graphite" described in JIS M 8511 (2014).

[0033] The orientation direction of the flake graphite is not particularly limited, but it is preferable that the flake graphite be oriented along the longitudinal direction of the heat insulating material.

[0034] The content of flake graphite is not particularly limited, but it is preferable that it accounts for 6 to 30% of the weight of the heat insulating material.

[0035] The heat insulating material of the present invention is an integrally molded body. An integrally molded body is one that is integrally formed to have that shape from the beginning, and does not include a body that is made by rolling a flat carbon fiber sheet into a cylindrical shape or a body that is made by winding and stacking long carbon fiber sheets.

[0036] An integrally molded body containing carbon fiber and resin carbide can be obtained, for example, by a papermaking method using an integral molding die.

[0037] [Insulation material manufacturing method] The heat insulating material of the present invention can be produced, for example, by a process including an integral molding process of integrally molding a cylindrical carbon fiber molding containing carbon fiber and an organic binder, and a firing process of firing the carbon fiber molding in a non-oxidizing atmosphere.

[0038] (Integrated molding process) A cylindrical carbon fiber molding containing carbon fibers and an organic binder can be obtained, for example, by preparing a suspension in which carbon fibers and an organic binder are dispersed in a dispersion medium such as water, and then forming the suspension into a paper using an integral molding die. However, it is preferable to adjust the papermaking conditions so that the irregularities on the surface of the integral molding mold are not reflected on the inner surface of the obtained carbon fiber molding.

[0039] An example of a method for preventing the unevenness of the surface of the integral molding mold from being reflected on the inner surface of the carbon fiber molding is to relatively slow down the suction speed of the suction pump (volume of fluid sucked per unit time) at the beginning of papermaking. An example of this method will be described with reference to FIGS.

[0040] FIG. 3 is a perspective view schematically showing an example of an integral molding die. The integral molding die 50 shown in FIG. 3 is a hollow cylinder having a side surface 51 and a top surface 52, and extends along the longitudinal direction (the direction indicated by the arrow Z in FIG. 3). The side surface 51 is provided with numerous holes 53. The holes 53 are through holes that reach the space inside the integral molding die 50. The top surface 52 does not have any holes 53 . The surface opposite to the top surface 52 is open, and a suction pump or the like is connected to this opening.

[0041] The size of the holes may be such that the carbon fibers contained in the suspension cannot pass through. That is, the maximum length of the holes is preferably smaller than the average fiber length of the carbon fibers. The size of each hole is 0.1 to 3 mm. 2 It is preferable that:

[0042] The holes may all be the same size or may vary in size from place to place. For example, among the holes arranged on the side surface, the size and arrangement of the holes arranged near the top surface and the holes arranged far from the top surface may be different.

[0043] By adjusting the size and arrangement of the holes for each location, it is possible to adjust the rate at which the carbon fibers are deposited on the surface of the integral molding die. If the rate at which the carbon fibers are deposited on the surface of the integral molding die is uniform, it is possible to reduce the density variation rate in the resulting thermal insulation material.

[0044] FIG. 4 is a diagram schematically illustrating an example of a method for producing a carbon fiber molding using the integral molding die shown in FIG. As shown in FIG. 4, the integral molding die 50 is immersed in the slurry 60 while being connected to a suction pump (not shown) via a suction pipe 70 .

[0045] The slurry 60 is a suspension in which carbon fibers and an organic binder are dispersed in a dispersion medium such as water. In this state, when a suction pump (not shown) is operated to suck the fluid from inside the integral molding die 50, the pressure inside 59 of the integral molding die 50 is reduced and the external slurry 60 is sucked into the interior 59 of the integral molding die 50 through the hole 53.

[0046] At this time, the suction speed (volume of fluid sucked per unit time) of the fluid sucked through the suction pipe 70 is slowed down. Specifically, it is preferable to adjust the volume of fluid sucked by the suction pump per unit time immediately after the start of papermaking, divided by the total area of ​​the side surfaces of the integral molding die 50, to 1500 to 2000 mm / min. In FIG. 4, the slow suction speed of the fluid sucked through the suction pipe 70 is indicated by the dashed arrow.

[0047] The initial stage of papermaking refers to the period from immediately after the suction pump starts suction until the carbon fibers accumulate on the surface of the integral molding die to a thickness of about 1 mm.

[0048] By setting the suction pump suction speed relatively slow in the early stages of papermaking, it is possible to prevent the carbon fibers from getting into the holes of the integral molding die. If the suction pump suction speed is too fast (too large), the carbon fibers tend to be oriented in the direction of the slurry flow as they are sucked toward the holes of the integral molding die, making it easier for the carbon fibers to get into the holes of the integral molding die. If carbon fibers get into the holes in the integral molding die at the beginning of papermaking, the carbon fibers that have gotten into the holes in the integral molding die themselves will protrude from the carbon fiber molding, forming convex portions. Since these convex portions are formed only in the portions of the inner surface of the carbon fiber molding where the holes in the integral molding die are formed, the portions of the inner surface of the carbon fiber molding where the convex portions are formed coincide with the portions of the holes in the integral molding die. This results in the formation of irregularities on the inner surface of the carbon fiber molding.

[0049] Furthermore, the carbon fibers that have entered the holes in the integral molding die are continuously pulled toward the inside of the integral molding die during papermaking, and may pull other entangled carbon fibers into the holes in the integral molding die, causing a state in which part of the inner surface of the carbon fiber molding enters the holes in the integral molding die, which may result in the formation of irregularities on the inner surface of the carbon fiber molding.

[0050] On the other hand, if the suction speed of the suction pump is too slow (too small), the carbon fibers in the slurry may segregate or gaps may form between the carbon fibers, which may result in crack-like streaks on the inner surface of the carbon fiber molding. As a result, irregularities may be formed on the inner surface of the carbon fiber molding.

[0051] FIG. 5 is a diagram showing a schematic view of the initial state of papermaking in the method shown in FIG. As shown in Figure 5, by setting the suction speed of the suction pump to a relatively slow speed at the beginning of papermaking in the method shown in Figure 4, a carbon fiber layer 100' is formed in which the carbon fibers in the slurry are thinly deposited on the side surface 51 of the integral molding die 50.

[0052] FIG. 6 is a partial enlarged view of the area indicated by the dashed line in FIG. As shown in FIG. 6, the carbon fibers 5 constituting the carbon fiber layer 100 ′ formed on the side surface 51 of the integral molding die 50 do not penetrate into the holes 53 .

[0053] 5 and 6, suction by the suction pump is continued until a sufficient amount of carbon fibers is deposited on the side surface 51 of the integral molding die 50. At this time, it is preferable to make the suction speed of the suction pump faster (larger) than at the beginning of suction. For example, the volume of fluid sucked by the suction pump per unit time divided by the total area of ​​the side surfaces of the integral molding die 50 (hereinafter also referred to as suction flow rate) may be adjusted to 2000 to 3000 mm / min.

[0054] FIG. 7 is a diagram schematically showing a state in which carbon fibers are further deposited on the state shown in FIG. As shown in FIG. 7, by continuing suction by the suction pump from the state shown in FIG. 5, a sufficient amount of carbon fibers are layered on the side surface 51 of the integral molding die 50, and a carbon fiber molding 100 is formed. At this time, even if the suction flow rate by the suction pump is set to 2000 to 3000 mm / min, the already formed carbon fiber layer 100' prevents the carbon fibers from entering the holes 53, so that no new carbon fibers enter the holes 53.

[0055] FIG. 8 is a partial enlarged view of the area indicated by the dashed line in FIG. As shown in Fig. 8, the carbon fibers 5 that make up the carbon fiber molding 100 do not enter the holes 53. The carbon fiber molding 100 is an integrally molded body, since it is molded integrally to have a cylindrical shape from the beginning.

[0056] It is preferable to rotate the integral molding die 50 about an axis in the longitudinal direction simultaneously with the suction by the suction pump. In Fig. 4, the rotation direction of the integral molding die 50 is indicated by a curved arrow. By performing suction with a suction pump while rotating the integral molding die 50, carbon fibers are deposited uniformly on the side surface 51 of the integral molding die 50. As a result, it is possible to reduce variations in the density of the carbon fibers in the obtained carbon fiber molding. Furthermore, since the carbon fibers are deposited simultaneously on the side surface of the integral molding die 50, no seams are formed in the deposited carbon fibers.

[0057] The rotation speed of the integral molding die is preferably 10 to 60 rpm.

[0058] The orientation of the integral molding mold when performing suction with the suction pump is not particularly limited, but it is preferable to position the integral molding mold so that its longitudinal direction coincides with the horizontal direction, as shown in Figure 4.

[0059] This is because the carbon fibers settle in the slurry. Because natural settling of carbon fibers occurs in the slurry, the concentration of carbon fibers may be higher in the lower part of the slurry than in the upper part. The magnitude of this slurry concentration may be reflected in the amount of carbon fibers deposited on the surface of the integral molding die. Therefore, when the integral molding die is immersed in the slurry with its longitudinal direction aligned vertically and suction is performed using a suction pump, the magnitude of the concentration of carbon fibers resulting from the natural settling of carbon fibers is reflected in the amount of deposited carbon fibers, which may result in large variations in the density of the resulting thermal insulation along the length.

[0060] The suspension may be stirred while the fluid in the integral mold is being sucked by the suction pump. By stirring the suspension while the fluid in the one-piece molding mold is being sucked in with a suction pump, the natural settling of the carbon fibers described above can be suppressed, and the density variation in the length direction of the insulation material can be suppressed.

[0061] If necessary, flake graphite or the like may be added to the suspension. When flake graphite is contained in the suspension, a carbon fiber molding containing flake graphite can be obtained.

[0062] The carbon fiber molding obtained by the above procedure is fired at about 2000° C. in a non-oxidizing atmosphere to obtain the heat insulating material of the present invention. If the carbon fiber molded body before firing is an integrally molded body, the heat insulating material after firing can also be said to be an integrally molded body.

[0063] The non-oxidizing atmosphere includes an inert atmosphere and a reducing atmosphere.

[0064] The inert atmosphere is an atmosphere whose main component is an inert gas. Examples of the inert gas include nitrogen and argon.

[0065] The reducing atmosphere is an atmosphere in which the atmosphere is a reducing gas. The reducing gas may include hydrogen, carbon monoxide, hydrocarbons, chlorine, and the like.

[0066] The firing time is not particularly limited, but is preferably 1 to 5 hours. Furthermore, cutting may be carried out to adjust the shape of the outer diameter and height of the heat insulating material after firing.

[0067] Another example of a method for preventing the unevenness of the surface of the integral molding mold from being reflected on the inner surface of the carbon fiber molding is to place a mesh on the side surface of the integral molding mold. An example of this method will be described with reference to FIGS.

[0068] FIG. 9 is a perspective view schematically showing another example of an integral molding die. The integral molding die 55 shown in FIG. 9 is a hollow cylinder having a side surface 51 and a top surface 52, and extends along the longitudinal direction (the direction indicated by the arrow Z in FIG. 9). The side surface 51 is provided with numerous holes 53. The holes 53 are through holes that reach the space inside the integral molding die 50. A mesh 54 is provided to cover the surface of the side surface 51. The top surface 52 does not have any holes 53 . The surface opposite to the top surface 52 is open, and a suction pump or the like is connected to this opening. The integral molding die 55 shown in FIG. 9 is similar to the integral molding die 50 shown in FIG.

[0069] The mesh is made of metal, and the size of the openings is preferably smaller than the length of the fibers used, specifically, 12 mesh to 50 mesh is preferably used. When a mesh is provided, the size of the holes in the integral mold may be larger than the average fiber length of the carbon fibers used.

[0070] It is preferable that the non-opening portions of the mesh are arranged so as to block part of the surface of the hole in the integral mold. By arranging the non-opening portions of the mesh so as to block part of the surface of the hole in the integral mold, the carbon fibers are prevented from entering the hole in the integral mold.

[0071] FIG. 10 is a diagram schematically illustrating an example of a method for producing a carbon fiber molding using the integral molding die shown in FIG. In the integral molding die 55 shown in FIG. 9, the surface of the side surface 51 is covered with a mesh 54, and therefore the mesh 54 can prevent the carbon fibers in the slurry from entering the holes 53. Therefore, as shown in FIG. 10, it is possible to prevent the carbon fibers 5 from entering the holes 53 of the integral molding die 50 without slowing down the suction speed of the suction pump at the beginning of papermaking.

[0072] FIG. 11 is an enlarged cross-sectional view of a carbon fiber molding obtained by the method shown in FIG. As shown in FIG. 11, all of the carbon fibers 5 constituting the carbon fiber molding 100 are deposited on the mesh 54 , and no carbon fibers 5 enter the holes 53 of the integral molding die 50 . Therefore, it is possible to prevent the formation of irregularities on the inner surface of the carbon fiber molding. The obtained carbon fiber molding 100 is an integrally molded body, since it is molded integrally to have a cylindrical shape from the beginning.

[0073] FIG. 12 is an enlarged cross-sectional view of a carbon fiber molding obtained by yet another example of the method for producing a carbon fiber molding using an integral molding die. FIG. 12 is also an example of a carbon fiber molding obtained using the integral molding die shown in FIG. 3 when the suction speed of the suction pump is not set to a relatively slow condition at the beginning of suction. 12, the carbon fibers 5 enter holes 53 in the side surface 51 of the integral molding die 50. Therefore, it can be said that the inner surface of the carbon fiber molding 101 has irregularities.

[0074] When the carbon fiber molding 101 shown in Figure 12 is fired at approximately 2000°C in a non-oxidizing atmosphere, the inner surface of the resulting heat insulating material has the same irregularities as the carbon fiber molding 101, so it is not possible to obtain a heat insulating material with an inner surface roughness Ra of 50 μm or less.

[0075] When the inner surface of the heat insulating material is polished, polishing marks remain on the surface of the carbon fiber. Therefore, whether the surface roughness Ra of the inner surface has been adjusted by post-manufacturing processing can be confirmed by observing the inner surface of the heat insulating material using an SEM or the like.

[0076] 3 and 9, an integral molding mold having holes on the top surface may be used. By using such an integral molding mold, carbon fibers can be deposited on the top surface of the integral molding mold as well. In this case, the carbon fiber molding obtained will have the carbon fibers deposited on the side surface and the carbon fibers deposited on the top surface integrated (seamless). When an integral molding mold having holes on the top surface is used instead of the integral molding mold shown in FIG. 9, a mesh may be disposed so as to cover the surface of the top surface. By firing such a carbon fiber molding, an insulating material can be obtained that consists of a cylindrical body portion extending in the longitudinal direction and a plate portion disposed at either end of the body portion in the longitudinal direction.

[0077] In this case, if the surface roughness Ra of the inner surface of the body is 50 μm or less, it is included in the heat insulating material of the present invention. In other words, the plate portion is not taken into consideration when calculating the surface roughness Ra of the inner surface. However, the surface roughness Ra of the inner surface of the plate portion is preferably 50 μm or less. The surface roughness Ra of the inner surface of the plate part is the average value of the arithmetic mean roughness Ra measured with a laser microscope at five randomly selected points on the inner surface of the plate part.

[0078] The present specification discloses the following:

[0079] The present disclosure (1) provides a cylindrical heat insulating material containing carbon fiber and resin carbide, The heat insulating material is an integrally molded body, The heat insulating material is characterized in that the surface roughness Ra of the inner surface of the heat insulating material is 50 μm or less.

[0080] The present disclosure (2) is the heat insulating material according to the present disclosure (1), wherein the surface roughness Ra of the inner surface of the heat insulating material is 10 μm or more.

[0081] The present disclosure (3) is the heat insulating material according to the present disclosure (1) or (2), wherein the heat insulating material contains flake graphite.

[0082] (Example) EXAMPLES Hereinafter, examples will be given that more specifically disclose the present invention, but the present invention is not limited to these examples.

[0083] (Preparation of slurry) A slurry (suspension) containing carbon fibers (average fiber diameter: 13 μm, average fiber length: 0.7 mm) and an organic binder (phenolic resin) at a ratio of 100:35 (weight ratio, organic binder is calculated as solid content) was prepared.

[0084] Example 1 As shown in Figure 3, the molded part (area per hole: 0.2 mm 2The carbon fiber molding was immersed in the suspension using a suction pump and subjected to papermaking to obtain a cylindrical carbon fiber molding. At this time, the suction flow rate by the suction pump was set to 1500 mm / min for 20 seconds from the start of suction. Thereafter, the suction flow rate was changed to 2000 mm / min, and suction by the suction pump was continued for a total of 70 seconds. The obtained carbon fiber molding was heated to 2000°C in an inert atmosphere to carbonize the organic binder (phenolic resin) contained in the carbon fiber molding, and the carbon fibers and flake graphite were bonded together by the carbonaceous binder. The molding was then cut to adjust the outer diameter and length, yielding a thermal insulator according to Example 1 (the inner surface was not cut or polished). The thermal insulator had a cylindrical shape with inner diameter, outer diameter, thickness, and length (height) of 96.2 mm, 130 mm, 16.9 mm, and 210 mm, respectively.

[0085] Example 2 An integral molding die having a mesh (#30 mesh) as shown in Fig. 9 was immersed in the suspension and papermaking was performed to obtain a cylindrical carbon fiber molding. At this time, the suction flow rate by the suction pump was set to 2000 mm / min from start to finish. Suction by the suction pump was continued for a total of 60 seconds. The obtained carbon fiber molding was heated and cut under the same conditions as in Example 1 to obtain a heat insulating material according to Example 2. The shape of the heat insulating material according to Example 2 was the same as that of the heat insulating material according to Example 1.

[0086] (Comparative Example 1) A heat insulating material according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the suction flow rate was kept constant at 2000 mm / min from the start to the end of suction.

[0087] (Measurement of inner surface roughness) The surface roughness Ra of the inner surface of the insulating materials of Examples 1 and 2 and Comparative Example 1 was measured using a laser microscope (LEXT-OLS4100) manufactured by Olympus Corporation, and the surface roughness Ra of the inner surface was 45 μm in Example 1, 38 μm in Example 2, and 63 μm in Comparative Example 1.

[0088] The heat insulating properties of the heat insulating materials according to Examples 1 and 2 and Comparative Example 1 were measured by the following method. The thermal insulation materials according to Examples 1 and 2 and Comparative Example 1 were placed inside an induction heating furnace, and a cylindrical graphite crucible with a bottom and an outer diameter of 96.2 mm and a height of 140 mm was placed inside. The crucible was induction heated to 2080°C, and then the furnace was evacuated and held in this state for 30 minutes. At this time, the temperatures at the centers of the top and bottom of the crucible were measured, and the temperature difference between the two points was 95°C when the thermal insulation material according to Example 1 was used, 90°C when the thermal insulation material according to Example 2 was used, and 130°C when the thermal insulation material according to Comparative Example 1 was used.

[0089] From the above results, it was confirmed that in Example 1, in which the suction speed was slowed at the beginning of suction, and in Example 2, in which a mesh was provided on the surface of the integral molding mold, the surface roughness Ra of the inner surface of the obtained insulating material was smaller. On the other hand, in Comparative Example 1, in which an integral molding mold without a mesh was used and the suction speed was not changed from the start to the end of suction, it was confirmed that the surface roughness Ra of the inner surface of the obtained insulation material was large.

[0090] Furthermore, from the above results, in Examples 1 and 2, where the inner surface roughness Ra is 50 μm or less, the temperature difference inside the furnace at high temperatures is kept small, which is thought to be due to the improved reflectance of the emitted light. [Explanation of symbols]

[0091] 1. Insulation 1a Inner surface of insulation 1b Outer surface of insulation 5. Carbon Fiber 50, 55 integral molding 51 Side 52 Top 53 holes 54 mesh 59 Inside 60 Slurry (suspension) 70 Suction Pipe 100, 101 Carbon fiber molding 100' carbon fiber layer R1 Insulation Inner Diameter R2 outer diameter of insulation t Thickness of insulation h Length (height) of the insulation

Claims

1. A cylindrical heat insulating material containing carbon fiber and resin carbide, The heat insulating material is an integrally molded body, A heat insulating material characterized in that the surface roughness Ra of the inner surface of the heat insulating material is 50 μm or less.

2. The heat insulating material according to claim 1 , wherein the surface roughness Ra of the inner surface of the heat insulating material is 10 μm or more.

3. The heat insulating material according to claim 1 or 2, wherein the heat insulating material contains flake graphite.

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