Thermal insulation material

Abstract

To provide a thermal insulation material capable of simultaneously improving thermal insulation performance and preventing delamination of layers.SOLUTION: A cylindrical thermal insulation material contains carbon fibers. The proportion of the number of carbon fibers having an orientation angle of 0° or more and less than 70° relative to the thickness direction, which is perpendicular to both the longitudinal and circumferential directions of the thermal insulation material, is 20-40%, and the proportion of the number of carbon fibers having an orientation angle of 70° or more and 90° or less is 60-80%.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 thermal insulation performance of the thermal insulation material produced by the method described in Patent Document 1 was lower than expected. This is thought to be due to the fact that the amount of carbon fibers oriented in the thickness direction of the thermal insulation material was greater than expected.

[0007] In order to improve the insulating performance, it is necessary to increase the proportion of carbon fibers oriented in a direction perpendicular to the thickness direction of the insulating material. However, if the proportion of carbon fibers oriented in a direction perpendicular to the thickness direction of the insulating material becomes too high, there will be almost no entanglement between the carbon fibers in the thickness direction, and there is a concern that the insulating material may peel off.

[0008] 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 can achieve both improved heat insulating performance and prevention of layer peeling. [Means for solving the problem]

[0009] The insulating material of the present invention is a tubular insulating material containing carbon fibers, characterized in that the proportion of the number of carbon fibers having an orientation angle of 0° or more and less than 70° with respect to the thickness direction perpendicular to the longitudinal and circumferential directions of the insulating material is 20 to 40%, and the proportion of the number of carbon fibers having an orientation angle of 70° or more and 90° or less is 60 to 80%.

[0010] In the heat insulating material of the present invention, the ratio of the number of carbon fibers having an orientation angle of 0° or more and less than 70° with respect to the thickness direction is 20 to 40%, so that the entanglement of the fibers in the thickness direction is sufficiently maintained and layer peeling is unlikely to occur. Furthermore, the ratio of the carbon fibers having an orientation angle of 70° or more and 90° or less with respect to the thickness direction is 60 to 80%, so that the thermal conductivity in the thickness direction can be reduced and the heat insulating performance can be improved. Therefore, the heat insulating material of the present invention can achieve both improved heat insulating performance and prevention of layer peeling.

[0011] In the heat insulating material of the present invention, the heat insulating material is preferably an integrally molded body. When the insulating material is an integrally molded body, there are no gaps (seams) that occur when one or more non-cylindrical insulating materials are deformed or combined to form a cylindrical shape, so it is possible to prevent a decrease in insulating performance due to such gaps.

[0012] 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]

[0013] [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 an enlarged view schematically showing the portion enclosed by the dashed line in FIG. [Figure 4] FIG. 4 is a perspective view schematically showing an example of an integral molding die. [Figure 5] FIG. 5 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 6] FIG. 6 is a diagram schematically showing a state in which deposition of carbon fibers has been completed in the step shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] [Insulation material] The insulating material of the present invention is a tubular insulating material containing carbon fibers, characterized in that the proportion of the number of carbon fibers having an orientation angle of 0° or more and less than 70° with respect to the thickness direction perpendicular to the longitudinal and circumferential directions of the insulating material is 20 to 40%, and the proportion of the number of carbon fibers having an orientation angle of 70° or more and 90° or less is 60 to 80%.

[0016] 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.

[0017] The inner diameter R1 of the heat insulating material is preferably 50 to 1000 mm. The outer diameter R2 of the heat insulating material is preferably 60 to 1200 mm.

[0018] The thickness of the heat insulating material is preferably 10 to 100 mm.

[0019] The length (height) of the heat insulating material is preferably 150 to 550 mm.

[0020] 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). That is, the thickness direction of the heat insulating material 1 is also a direction perpendicular to the length direction Z of the heat insulating material and the circumferential direction of the heat insulating material.

[0021] FIG. 3 is an enlarged view schematically showing the portion enclosed by the dashed line in FIG. As shown in Figure 3, the carbon fibers 5 constituting the thermal insulating material 1 are loosely intertwined with each other and oriented at a predetermined angle with respect to the thickness direction (the direction indicated by the double-headed arrow t in Figure 3). In this case, the angle formed between the direction in which the carbon fibers extend (orientation direction) and the thickness direction is the orientation angle.

[0022] For example, among the carbon fibers 5 constituting the insulating material 1 shown in Figure 3, the orientation angle of the carbon fibers extending in a direction parallel to the thickness direction t is 0°, and the orientation angle of the carbon fibers extending in a direction parallel to the length direction Z is 90°.

[0023] In the thermal insulating material of the present invention, the carbon fibers constituting the thermal insulating material are classified into two types depending on the orientation angle relative to the thickness direction.

[0024] One type is carbon fibers with an orientation angle of 0° or more and less than 70° with respect to the thickness direction. Carbon fibers having this orientation angle extend along the thickness direction of the heat insulating material, and it can be said that this ensures entanglement of the carbon fibers with each other in the thickness direction. Therefore, by setting the ratio of the number of carbon fibers with such an orientation angle to 20 to 40%, peeling of layers in the heat insulating material is suppressed.

[0025] The other type is carbon fiber with an orientation angle of 70° or more and 90° or less relative to the thickness direction. Carbon fibers having this orientation angle are arranged in a direction substantially perpendicular to the thickness direction of the heat insulating material, and serve to improve the heat insulating properties in the thickness direction. Therefore, when the number of carbon fibers with such an orientation angle is 60 to 80%, the heat insulating material exhibits excellent heat insulating performance.

[0026] In addition, the percentage of carbon fibers in the insulating material whose orientation angle relative to the thickness direction is 0° or more and less than 70°, and the percentage of carbon fibers whose orientation angle relative to the thickness direction is 70° or more and 90° or less, can be determined using micro X-ray CT. Specifically, a cube with sides of 10 mm was cut out from the insulation material, and the orientation direction of all carbon fibers in the area within the central cube with sides of 3 mm was identified using a micro X-ray CT device. The number of carbon fibers with an orientation angle of 0° or more and less than 70° relative to the reference thickness direction was counted, as well as the number of carbon fibers with an orientation angle of 70° or more and 90° or less. The measurement conditions may be, for example, X-ray output: 80 kV, 45 μA, exposure time: 499 ms, and sensitivity: 0.25 pF.

[0027] As the micro X-ray CT device, for example, TOSCANER-32300μFD manufactured by Toshiba IT Control Systems Corporation can be used. For analyzing the micro X-ray CT data, for example, commercially available analysis software (for example, VGStudio MAX3.4 Material Pack manufactured by Volume Graphics, Inc.) can be used.

[0028] The heat insulating material of the present invention preferably has a thermal conductivity in the thickness direction (insulation direction) of 2.0 W / m·K or less at 2000° C. The thermal conductivity is measured by the laser flash method. If the thermal conductivity in the thickness direction (insulation direction) at 2000°C is 2.0 W / m·K or less, it can be said to have excellent thermal insulation performance as an insulating material.

[0029] (carbon fiber) The body and plate are each made of carbon fiber.

[0030] The average fiber length of the carbon fibers is preferably 0.4 to 4 mm.

[0031] The average fiber diameter of the carbon fibers is preferably 1 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 radiative heat transfer can be suppressed.

[0032] 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.

[0033] The insulating material preferably contains flake graphite. If the heat insulating material contains flake graphite, the heat insulating performance can be further improved.

[0034] 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.

[0035] As the flake graphite, natural graphite can be used.

[0036] 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).

[0037] The orientation direction of the flake graphite is not particularly limited, but it is preferable that the flake graphite is oriented along the longitudinal direction.

[0038] 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.

[0039] The insulating material may include a carbonaceous binder. When the heat insulating material contains a carbonaceous binder, it is possible to bond the carbon fibers together or the carbon fibers to other components (for example, flake graphite). The carbonaceous binder is an organic binder that is carbonized by heating in a non-oxidizing atmosphere.

[0040] The heat insulating material is preferably a one-piece molding. When the insulating material is an integrally molded body, there are no gaps (seams) that occur when one or more non-cylindrical insulating materials are deformed or combined to form a cylindrical shape, so it is possible to prevent a decrease in insulating performance due to such gaps.

[0041] It should be noted that 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.

[0042] An integrally molded body containing carbon fibers can be obtained, for example, by a papermaking method using an integral molding die.

[0043] [Insulation material manufacturing method] The heat insulating material of the present invention can be obtained by firing a cylindrical carbon fiber molding at about 2000° C. in a non-oxidizing atmosphere.

[0044] A cylindrical carbon fiber molding can be obtained, for example, by preparing a suspension in which carbon fibers are dispersed in a dispersion medium such as water, and then forming the suspension into a paper using an integral molding die.

[0045] FIG. 4 is a perspective view schematically showing an example of an integral molding die. The integral molding die 50 shown in FIG. 4 is a hollow cylinder having a side surface 51 and a top surface 52, and extends in the longitudinal direction (the direction indicated by the arrow Z in FIG. 4). 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.

[0046] For example, a mesh may be disposed over the entire side surface 51 of this integral molding die 50 . The size of the holes in the integral molding die 50 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. When a mesh is used, the size of the openings is preferably smaller than the length of the carbon fibers used, and specifically, it is preferable to use 6 to 50 meshes.

[0047] The size of the holes in the integral molding die 50 may all be the same or may vary 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.

[0048] 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.

[0049] FIG. 5 is a diagram schematically illustrating an example of a method for producing a carbon fiber molding using the integral molding die shown in FIG. 5, 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. In Fig. 5, the fluid being sucked through the suction pipe 70 is indicated by a thick straight arrow.

[0050] The slurry 60 is a suspension in which carbon fibers 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 mold 50, the pressure inside 59 of the integral molding mold 50 is reduced, and the external slurry 60 is sucked into the interior 59 of the integral molding mold 50 through the holes 53 of the integral molding mold, and, if a mesh (not shown) is placed, through the mesh and the holes 53 of the integral molding mold.

[0051] At this time, the degree of orientation of the carbon fibers in the resulting insulating material can be adjusted by adjusting the amount of suction (volume of fluid sucked per unit time) of fluid sucked from inside the integral molding mold 50 by the suction pump. For example, by increasing the amount of suction by the suction pump, the proportion of carbon fibers with an orientation angle of 0° or more and less than 70° can be increased, and by decreasing the amount of suction by the suction pump, the proportion of carbon fibers with an orientation angle of 70° or more and 90° or less can be increased.

[0052] It is preferable to adjust 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 to 1500 to 3000 mm / min. In particular, when the suction rate is 2500 mm / min or less, the proportion of carbon fibers having an orientation angle of 70° or more and 90° or less can be increased.

[0053] At this time, the integral molding die 50 may be rotated around an axis in the longitudinal direction. In Fig. 5, 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. In addition, by forming the sheet while rotating the integrally molded body, the proportion of carbon fibers with an orientation angle of 70° or more and 90° or less can be increased.

[0054] The rotation speed of the integral molding die is preferably 10 to 60 rpm.

[0055] The orientation of the integral molding mold when suction is performed by the suction pump is not particularly limited, but it is preferable to orient the integral molding mold so that the longitudinal direction of the integral molding mold coincides with the horizontal direction, as shown in Fig. 5. The reason for this is that 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. This slurry concentration may be reflected in the amount of carbon fibers deposited on the surface of the integral molding die. Therefore, if the integral molding die is immersed in the slurry with its longitudinal direction aligned vertically and suction is performed using a suction pump, the concentration of carbon fibers resulting from natural settling of the carbon fibers may be reflected in the amount of deposited carbon fibers, which may result in large variations in the density of the resulting insulation along the length.

[0056] 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.

[0057] If necessary, flake graphite, an organic binder, or the like may be added to the suspension. If the suspension contains an organic binder, it bonds the carbon fibers together during papermaking, improving moldability. The organic binder is carbonized during subsequent heat treatment (in a non-oxidizing atmosphere) to become a carbonaceous binder, which continues to bind the carbon fibers together or the carbon fibers and flake graphite together after heat treatment. The amount of the organic binder added to the suspension is preferably 10 to 50% of the weight of the carbon fibers.

[0058] When an organic binder is added to the suspension, it is preferable to stir the suspension after adding the organic binder. The stirring time after the addition of the organic binder is preferably 2 minutes or more, and more preferably 3 minutes or more. If the stirring time after adding the organic binder is less than 2 minutes, the organic binder may not be sufficiently dispersed in the suspension. If the organic binder is not sufficiently dispersed in the suspension, the carbon fibers may undergo unintended partial aggregation or orientation. If a suspension containing carbon fibers that have undergone unintended partial aggregation or orientation is used, it may not be possible to adjust the degree of orientation of the carbon fibers in the resulting insulation material by adjusting the suction volume of the suction pump (the volume of fluid sucked per unit time).

[0059] Additives such as a flocculant and a paper strength agent may be added to the suspension as needed.

[0060] FIG. 6 is a diagram schematically showing a state in which deposition of carbon fibers has been completed in the step shown in FIG. If the size of the holes 53 arranged on the side surface 51 of the integral molding die 50, or the size of the mesh (not shown), is such that the carbon fibers cannot pass through, the carbon fibers in the slurry 60 will accumulate on the side surface 51, and a carbon fiber molding 100 will be obtained. The carbon fiber molding 100 is an integrally molded body, since it is molded integrally into a cylindrical shape from the beginning.

[0061] The heat insulating material of the present invention can be obtained by firing such a carbon fiber molding 100 at about 2000° C. in a non-oxidizing atmosphere.

[0062] In addition, when the carbon fiber molded body before firing is an integral molded body, the heat insulating material after firing is also an integral 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. In addition, cutting may be carried out to adjust the shape of the heat insulating material after firing.

[0067] Instead of the integral molding die shown in Fig. 4, an integral molding die having holes on the top surface may be used. By using such an integral molding die, carbon fibers can be deposited on the top surface of the integral molding die as well. In this case, the carbon fiber molding obtained will be in a state where the carbon fibers deposited on the side surface and the carbon fibers deposited on the top surface are integrated (seamless). 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.

[0068] In this case, the orientation direction of the carbon fibers in the plate portion is not taken into consideration. However, in the plate portion, it is preferable that the proportion of carbon fibers having an orientation angle of 0° or more and less than 70° relative to the length direction of the insulating material (thickness direction of the plate portion) is 20 to 40%, and the proportion of carbon fibers having the above orientation angle of 70° or more and 90° or less is 60 to 80%. Whether the above conditions are met can be confirmed by cutting a cube with sides of 10 mm from the plate, using micro X-ray CT to identify the orientation direction of all carbon fibers in the area within the central cube with sides of 3 mm, and counting the number of carbon fibers with orientation angles of 0° or more and less than 70° relative to the reference length direction, and the number of carbon fibers with orientation angles of 70° or more and 90° or less. The measurement conditions of the micro X-ray CT device are preferably the same as those of the method for determining the proportion of carbon fibers having an orientation angle of 0° or more and less than 70° relative to the thickness direction of the insulation material, and the proportion of carbon fibers having an orientation angle of 70° or more and 90° or less.

[0069] The present specification discloses the following:

[0070] The present disclosure (1) provides a cylindrical heat insulating material containing carbon fiber, The insulating material is characterized in that the proportion of the number of carbon fibers having an orientation angle of 0° or more and less than 70° with respect to the thickness direction perpendicular to the longitudinal direction and circumferential direction of the insulating material is 20 to 40%, and the proportion of the number of carbon fibers having an orientation angle of 70° or more and 90° or less is 60 to 80%.

[0071] The present disclosure (2) is the heat insulating material according to the present disclosure (1), wherein the heat insulating material is an integrally molded body.

[0072] 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.

[0073] (Example) EXAMPLES Hereinafter, examples will be given that more specifically disclose the present invention, but the present invention is not limited to these examples.

[0074] Example 1 50 L of water was placed in a 90 L plastic bucket, and 1.1 kg of carbon fiber (average fiber diameter: 13 μm, average fiber length: 0.7 mm) was added and stirred with a hand mixer (W screw with ring, diameter 150 mm) until the carbon fiber was dispersed. 385 g of organic binder (phenolic resin) was then added and stirred at 1000 rpm for 3 minutes using the hand mixer. A flocculant and paper strength agent were then added and stirred for 30 seconds to prepare a slurry (suspension). An integral molding die and a plain woven wire mesh (30 mesh) as shown in FIG. 3 were immersed in the suspension and subjected to papermaking, to obtain a cylindrical carbon fiber molding. The obtained carbon fiber molding was heated to 2000° C. in an inert atmosphere to carbonize the organic binder (phenol resin) contained in the carbon fiber molding, thereby obtaining a heat insulating material according to Example 1. The shape of the insulation material was cylindrical with inner diameter, outer diameter, thickness, and length (height) of 96.2 mm, 130 mm, 16.9 mm, and 210 mm, respectively.

[0075] (Comparative Example 1) A heat insulating material was produced in the same manner as in Example 1, except that in preparing the slurry, the stirring time after adding the organic binder was set to 1 minute.

[0076] (Angular distribution measurement of carbon fiber) The proportions of the number of carbon fibers having each orientation angle in the heat insulating materials according to Example 1 and Comparative Example 1 were measured using a micro X-ray CT device (TOSCANER-32300μFD manufactured by Toshiba IT Control Systems Corporation). In the heat insulating material of Example 1, the proportion of carbon fibers with an orientation angle of 0° or more and less than 70° was 37.5%, and the proportion of carbon fibers with an orientation angle of 70° or more and 90° or less was 62.5%. In the heat insulating material of Comparative Example 1, the proportion of carbon fibers with an orientation angle of 0° or more and less than 70° was 45.1%, and the proportion of carbon fibers with an orientation angle of 70° or more and 90° or less was 54.9%.

[0077] (thermal conductivity measurement) The thermal conductivity at 2000°C in the thickness direction of the thermal insulating materials of Example 1 and Comparative Example 1 was measured. The thermal conductivity of the thermal insulating material of Example 1 was 1.8 W / m K, while the thermal insulating material of Comparative Example 1 was 2.4 W / m K.

[0078] From the above results, it was confirmed that when the proportion of carbon fibers with an orientation angle of 70° or more and 90° or less is 60% or more, the thermal conductivity in the thickness direction (insulating direction) becomes small. [Explanation of symbols]

[0079] 1. Insulation 1a Inner surface of insulation 1b Outer surface of insulation 5. Carbon Fiber 50 one-piece mold 51 Side 52 Top 53 holes 59 Inside 60 Slurry (suspension) 70 Suction Pipe 100 Carbon fiber molding R1 Insulation Inner Diameter R2 outer diameter of insulation t Thickness of insulation h Length (height) of the insulation

Claims

1. A cylindrical thermal insulation material containing carbon fiber, A heat insulating material, characterized in that the ratio of the number of carbon fibers having an orientation angle of 0° or more and less than 70° with respect to a thickness direction perpendicular to the length direction and circumferential direction of the heat insulating material is 20 to 40%, and the ratio of the number of carbon fibers having an orientation angle of 70° or more and 90° or less is 60 to 80%.

2. The insulation material of claim 1 , wherein the insulation material is a monolithic molding.

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

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