Thermal insulation material and method for manufacturing thermal insulation material

Abstract

The present invention provides an insulating material containing carbon fibers and flaky graphite, but with an impurity concentration of 20 ppm or less. [Solution] A cylindrical thermal insulation material comprising a spiral-wound laminate of thermal insulation sheets containing carbon fibers and flake graphite, characterized in that the average particle size of the flake graphite is 25 to 400 μm and the impurity concentration is 20 ppm or less.

Description

Technical Field

[0001] The present invention relates to a heat insulating material and a method for manufacturing the same.

Background Art

[0002] Heat insulating materials made of carbon fiber are widely used as heat insulating materials for high-temperature furnaces such as semiconductor manufacturing furnaces and ceramic sintering furnaces because they have a high heat resistance temperature and excellent heat insulating performance.

[0003] Such heat insulating materials are used in the form of a laminate obtained by winding a plurality of heat insulating sheets.

[0004] Although heat insulating materials usually contain impurities of several hundred to several thousand ppm, the impurity concentration of furnace materials for semiconductor manufacturing is required to be 20 ppm or less.

[0005] Patent Document 1 discloses a method of pickling the obtained carbon fiber formed heat insulating material in order to reduce the impurity concentration of the carbon fiber formed heat insulating material obtained by impregnating a carbon fiber base material with a thermosetting resin and then carbonizing it.

Prior Art Documents

Patent Documents

[0006] ​​​​​​​​​​​​​​​​​​However, the process of acid-treating flake graphite and then heating it is a common method for producing expanded graphite. In other words, the acid inserted between the layers of graphite expands, significantly increasing its volume and causing it to lose its flake graphite properties. Therefore, there was a problem in that the method described in Patent Document 1 could not be applied to thermal insulation materials containing flaky graphite.

[0009] In addition to the method described above, another known method for reducing the impurity concentration in thermal insulation materials is to react them with halogen gas at a temperature of around 2000°C. However, when the inventors tried this method, they encountered the problem that some of the flaky graphite detached from the thermal insulation material.

[0010] In other words, a thermal insulation material containing carbon fibers and flake graphite, but with an impurity concentration of 20 ppm or less, and a method for producing it, were previously unknown.

[0011] This invention was made to solve the above problems and aims to provide a thermal insulation material containing carbon fibers and flake graphite, but with an impurity concentration of 20 ppm or less, and a method for producing the same. [Means for solving the problem]

[0012] The present invention provides a cylindrical thermal insulation material in which a thermal insulation sheet containing carbon fibers and flake graphite is wound and laminated in a spiral shape, characterized in that the average particle size of the flake graphite is 25 to 400 μm and the impurity concentration is 20 ppm or less.

[0013] The thermal insulation material of the present invention has an impurity concentration of 20 ppm or less. Therefore, it can also be used as an in-furnace material for semiconductor manufacturing. Furthermore, since the average particle size of the flake graphite is 25-400 μm, it is possible to prevent the flake graphite from falling off the insulation material, thereby improving the insulation properties.

[0014] The heat insulating sheet of the present invention preferably has a thickness of 0.3 to 2 mm. If the thickness of the insulation sheet is within the above range, it is possible to achieve both the strength and insulation properties of the insulation sheet. If the insulation sheet is less than 0.3 mm thick, it becomes more prone to damage. If the thickness of the insulation sheet exceeds 2 mm, the flake-like graphite may not orient itself in the direction within the plane of the insulation sheet, which can lead to a decrease in insulation properties.

[0015] The present invention relates to a method for manufacturing a heat insulating sheet, characterized by firing a precursor sheet laminate, which is obtained by spirally winding and laminating a precursor sheet containing carbon fibers and flaky graphite with an average particle diameter of 25 to 400 μm, and then heating it in a halogen gas atmosphere at a temperature of 1800 to 2500°C to perform a high-purity treatment.

[0016] In the method for producing the thermal insulation material of the present invention, a precursor sheet laminate is formed by spirally winding and laminating precursor sheets containing carbon fibers and flake-like graphite with an average particle size of 25 to 400 μm. After firing, the laminate is heated in a halogen gas atmosphere at a temperature of 1800 to 2500°C. In this case, ordinary flake graphite causes the problem of partial shedding from the insulating material, but when flake graphite with an average particle size of 25 to 400 μm is used, the above problem does not occur. Therefore, it is possible to obtain an insulating material that contains carbon fibers and flake graphite, but with an impurity concentration of 20 ppm or less. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 is a schematic perspective view showing an example of the thermal insulation material of the present invention. [Figure 2] Figure 2 is a magnified view of a top-down view of the insulation material shown in Figure 1. [Figure 3] Figure 3 is a schematic perspective view showing an example of an insulating sheet that constitutes the insulating material of the present invention. [Figure 4] Figure 4 is a schematic cross-sectional view showing an example of an insulating sheet. [Figure 5] Figure 5 is an enlarged cross-sectional view schematically showing another example of an insulating sheet.

Mode for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be specifically described. However, the present invention is not limited to the following embodiments, and can be appropriately changed and applied within the scope of not changing the gist of the present invention.

[0019] [Heat insulating material] The heat insulating material of the present invention is a cylindrical heat insulating material in which a heat insulating sheet containing carbon fiber and flaky graphite is wound and laminated in a spiral shape, and the average particle diameter of the flaky graphite is 25 to 400 μm, and the impurity concentration is 20 ppm or less.

[0020] The heat insulating material of the present invention contains carbon fiber and flaky graphite, and contains only 20 ppm or less of elements other than carbon, and has a very low impurity concentration; therefore, it can also be used as a furnace interior material for semiconductor manufacturing.

[0021] The impurities in the heat insulating material refer to the ash remaining when the heat insulating material is burned in air. Therefore, the impurity concentration of the heat insulating material is obtained by dividing the weight of the ash obtained by burning the heat insulating material in air by the weight of the heat insulating material before combustion.

[0022] FIG. 1 is a perspective view schematically showing an example of the heat insulating material of the present invention. As shown in FIG. 1, the heat insulating material 1 is cylindrical with an outer diameter R1, an inner diameter R2, and a height h, and a cylindrical space 100 is provided inside.

[0023] The thickness t0 of the heat insulating material 1 is the length connecting the inner surface 1a and the outer surface 1b of the heat insulating material 1 at the shortest distance in a plane orthogonal to the height direction (the direction indicated by the arrow Z in FIG. 1) (a plane parallel to the arrows X and Y in FIG. 1), and is measured at eight locations every 45 degrees of the central angle of the inscribed circle of the inner surface 1a of the heat insulating material 1, and the average value is taken.

[0024] The shape of the heat insulating material may be cylindrical, and may be cylindrical or square cylindrical, but cylindrical is preferred.

[0025] The cross-sectional area of ​​the space inside the insulation material, when cut in a direction parallel to a plane perpendicular to the height direction, is 20 to 8000 cm². 2 It is preferable that this be the case.

[0026] When the insulation material is cylindrical, the inner diameter is preferably 50 to 1000 mm. The inner diameter R2 of the insulation material 1 is the diameter of the inscribed circle of the inner surface 1a of the insulation material 1 in a plane perpendicular to the height direction, and is the average value of the diameters of the inscribed circles of both end faces and the central face that bisects the insulation material 1.

[0027] When the insulation material is cylindrical, the outer diameter is preferably between 60 and 1200 mm. The outer diameter R1 of the insulation material 1 is the diameter of the inscribed circle of the outer surface 1b of the insulation material 1 in a plane perpendicular to the height direction, and is the average value of the diameters of the inscribed circles of both end faces and the central face that bisects the insulation material 1.

[0028] The height of the insulation material is preferably between 150 and 1000 mm. The height is measured at eight points on the inner surface 1a of insulation material 1, at 45-degree intervals between the central angles of the inscribed circle, and the average value is used.

[0029] The density of the insulation material is 0.10 to 0.30 g / cm³. 3 Preferably, it is 0.15 to 0.25 g / cm³. 3 It is preferable that it be so.

[0030] The density of an insulating material can be determined by calculating its volume from its external and internal dimensions, and then dividing its weight by its volume.

[0031] It is preferable that the value obtained by dividing the difference between the maximum density and the minimum density when the insulation material is divided into 8 sections in the circumferential direction by the average density ((maximum density - minimum density) / average density × 100 (%)) is 5% or less. When the above conditions are met, the variation in density in the circumferential direction of the insulation material is sufficiently reduced, which in turn helps to suppress heating failures and localized deterioration of the insulation material.

[0032] The density of the thermal insulation material when it is divided into eight sections in the circumferential direction can be determined by dividing the thermal insulation material 1 into eight equal parts in a plane perpendicular to the height direction of the thermal insulation material, using a central angle of 45 degrees for the inscribed circle of the inner surface 1a of the thermal insulation material 1. Furthermore, a rectangular parallelepiped with a volume of 35% or more of each of the eight divided sections is cut out, and the volume and weight of each section are measured. If it is not possible to cut out a rectangular parallelepiped with a volume of 35% or more of each section, the volume of each section is measured using a known three-dimensional measuring machine.

[0033] Figure 2 is a magnified view of a top-down view of the insulation material shown in Figure 1. In Figure 2, the thickness direction of the insulation sheet 10 is indicated by a double-headed arrow t, the thickness of the insulation material 1 is indicated by a double-headed arrow t0, and the thickness of the insulation sheet 10 is indicated by a double-headed arrow t1. The thickness of the insulation sheet is the average value obtained by measuring the thickness at 10 random locations.

[0034] As shown in Figure 2, the thermal insulation material 1 is made up of 15 layers of thermal insulation sheets 10 wound in a spiral pattern. Although not shown in Figure 2, the thermal insulation sheet 10 that makes up the thermal insulation material 1 is a single long sheet, and there are no seams or joints in the thermal insulation sheet 10. Therefore, the part that makes up the inner surface 1a of the thermal insulation material 1 corresponds to one end of the thermal insulation sheet 10, and the part that makes up the outer surface 1b of the thermal insulation material 1 corresponds to the other end of the same thermal insulation sheet 10.

[0035] If the insulation sheet 10 is rolled and laminated starting from the center, then the beginning portion of the insulation sheet 10 forms the inner surface 1a of the insulation material 1, and the end portion of the insulation sheet 10 forms the outer surface 1b of the insulation material 1.

[0036] The inner surface 1a of the insulation material 1 is the surface exposed to the cylindrical space 100, and the outer surface 1b of the insulation material 1 is the surface not exposed to the cylindrical space 100. The inner surface 1a and the outer surface 1b of the insulation material 1 face each other in a plane perpendicular to the height direction Z of the insulation material 1.

[0037] The thickness t1 of the heat insulating sheet 10 is not particularly limited, but is preferably 0.3 to 2 mm. When the thickness of the insulation sheet is 0.3 to 2 mm, the number of layers of insulation sheet per unit thickness of the insulation material can be increased, and variations in density in the plane of the insulation sheet are less likely to be reflected in variations in density in the circumferential direction of the insulation material. As a result, the insulation material has reduced variations in density in the circumferential direction. When variations in density in the circumferential direction are reduced, it is possible to suppress the occurrence of localized deterioration of insulation performance, which can lead to a larger temperature distribution inside the furnace, and to suppress localized deterioration of the insulation material.

[0038] The thickness t0 of the insulation material 1 is preferably 5 to 100 mm. If the thickness of the insulation material is within the above range, it is possible to achieve sufficient insulation performance while preventing the heating furnace from becoming excessively large.

[0039] The number of layers of the insulation sheet 10 constituting the insulation material 1 is preferably 15 to 300 layers. When the number of layers of insulation sheets is within the above range, variations in the density of the insulation material in the circumferential direction can be particularly suppressed.

[0040] Figure 3 is a schematic perspective view showing an example of an insulating sheet that constitutes the insulating material of the present invention. Since the heat insulating sheet 10 is a flexible sheet, it may be stored in a rolled-up state, for example, as shown in Figure 3.

[0041] (Insulation sheet) The insulation sheet contains carbon fiber.

[0042] The average fiber length of the carbon fibers is preferably 0.4 mm to 4 mm. The average fiber length of carbon fibers is calculated by measuring the longitudinal length of 20 randomly selected carbon fibers using any method and averaging the results.

[0043] The average fiber diameter of the carbon fibers is preferably 1 μm to 30 μm. If the average fiber diameter of the carbon fibers is 30 μm or less, the effect of conductive heat transfer by the carbon fibers themselves can be suppressed. Furthermore, if the average fiber diameter of the carbon fibers is 1 μm or more, excellent light shielding properties are achieved, and radiative heat transfer can be suppressed. The average fiber diameter of carbon fibers is calculated by measuring the fiber diameter of 20 randomly selected carbon fibers using a scanning electron microscope (SEM) and averaging the results.

[0044] Carbon fibers can be pitch-based, PAN-based, or rayon-based, and either graphite-based or carbonaceous carbon fibers can be used.

[0045] The heat insulating sheet is preferably made of a carbon fiber papermaking material. Since carbon fiber papermaking materials are composed of randomly oriented carbon fibers, they can exhibit high thermal insulation properties and are particularly suitable as thermal insulation sheets for thermal insulation materials.

[0046] The insulation sheet contains not only carbon fiber but also flaky graphite. Because flake graphite easily reflects heat emitted from a heating element, the presence of flake graphite in an insulating sheet can improve its thermal insulation performance.

[0047] Scaly graphite is graphite that has a thin, scaly shape. Specifically, flaky graphite with a thickness of 100 μm or less is defined as flake graphite.

[0048] Flake graphite reflects heat emitted from heat sources more readily than other carbon-based materials. Therefore, including flake graphite in an insulating sheet can improve its thermal insulation performance.

[0049] Figure 4 is a schematic cross-sectional view showing an example of an insulating sheet. The thermal insulation sheet 10 shown in Figure 4 contains flake graphite 20. However, the carbon fibers that make up the thermal insulation sheet 10 are omitted in Figure 4.

[0050] Natural graphite can be used as the flaky graphite.

[0051] The average particle size of flake graphite is 25–400 μm. If the average particle size of the flake graphite is within the above range, the flake graphite will not fall off the insulating sheet even when heated in a halogen gas atmosphere for high-purity treatment. The average particle size of flake graphite can be measured by sieve analysis in accordance with the "Industrial Analysis and Testing Methods for Natural Graphite" described in JIS M 8511 (2014).

[0052] If flake graphite cannot be separated from the insulation sheet, the average particle size of the flake graphite is measured by the following method. First, a single layer of insulation sheet is cut from the insulation material and then cut into a square with planar dimensions of 9 mm x 9 mm. Next, the insulation sheet is cut in half lengthwise. Then, one of the cut surfaces is photographed with a scanning electron microscope (SEM), and the flaky graphite exposed on the cut surface is identified in a 3 mm x 3 mm area approximately in the center of the cut surface. Based on the outer diameter shape of each flake of graphite, the area is determined, and then the diameter of the circle corresponding to that area is calculated from the obtained area, and this is taken as the particle size of the flake of graphite. Perform the same procedure for all flaky graphite exposed in a 3mm x 3mm area, and calculate the average value.

[0053] The arrangement (orientation) of flake-like graphite in the thermal insulation sheet is not particularly limited, but it is preferable that it be oriented along the in-plane direction of the thermal insulation sheet. The in-plane direction of the thermal insulation sheet is the direction perpendicular to the thickness direction of the thermal insulation sheet. In the heat insulating sheet 10 shown in Figure 4, the flake-like graphite 20 is oriented along a plane perpendicular to the thickness direction of the heat insulating sheet 10 (the direction indicated by the double-headed arrow t). When the flake-like graphite is oriented in the direction of the plane, it becomes easier to reflect the heat emitted from the heating element, thereby improving the thermal insulation performance.

[0054] The content of flake graphite is not particularly limited, but it is preferably 5-30% of the weight of the insulation material.

[0055] In a thermal insulation sheet, it is preferable that the carbon fibers and flake graphite are joined via a carbonaceous binder. In this case, it can be said that the thermal insulation sheet contains a carbonaceous binder in addition to the carbon fibers and flake graphite.

[0056] Figure 5 is a schematic, enlarged cross-sectional view showing another example of an insulating sheet. In the heat insulating sheet 10 shown in Figure 5, the flake-like graphite 20 is oriented in a direction perpendicular to the thickness direction of the heat insulating sheet 10 (indicated by the double-headed arrow t in Figure 5). In addition, in the heat insulating sheet 10, the carbon fibers 30 and the flake-shaped graphite 20 are bonded together via the carbonaceous binder 40 contained in the heat insulating sheet 10. This prevents the flake-shaped graphite 20 from falling off. Furthermore, the carbonaceous binder 40 is formed when the organic binder is carbonized by heating in a non-oxidizing atmosphere. Therefore, it does not constitute an impurity.

[0057] [Method of manufacturing insulation material] The present invention relates to a method for producing a thermal insulation material, characterized by firing a precursor sheet laminate, which is obtained by spirally winding and laminating precursor sheets containing carbon fibers and flaky graphite with an average particle size of 25 to 400 μm, and then heating it in a halogen gas atmosphere at a temperature of 1800 to 2500°C to perform a high-purity treatment.

[0058] (Method for manufacturing precursor sheets) The precursor sheet can be obtained, for example, by preparing a suspension in which carbon fibers and flake-shaped graphite with an average particle size of 25 to 400 μm are dispersed in a dispersion medium such as water, and then forming (papermaking) it into a sheet.

[0059] The suspension may contain an organic binder. The presence of an organic binder in the suspension improves moldability by fixing the carbon fibers together during papermaking. The organic binder then carbonizes during subsequent heat treatment (in a non-oxidizing atmosphere) to become a carbonaceous binder, thus continuing to bind the carbon fibers together even after heat treatment.

[0060] Examples of organic binders that act as carbonaceous binders include phenolic resins, polyvinyl alcohol (PVA), and pitch.

[0061] If the papermaking method does not include an organic binder in the suspension, the precursor sheet may be made to contain an organic binder by applying a slurry containing an organic binder to the resulting precursor sheet.

[0062] The thickness of the precursor sheet is preferably 0.3 to 3.0 mm. If the thickness of the precursor sheet is within the above range, an insulating sheet with a thickness of 0.3 to 2 mm can be obtained.

[0063] By following the above procedure, a precursor sheet containing carbon fibers and flaky graphite with an average particle size of 25 to 400 μm is obtained.

[0064] (Manufacturing method for thermal insulation material (before high-purity treatment)) Next, the obtained precursor sheets are wound and stacked in a spiral shape to produce a precursor sheet laminate. The method for producing a precursor sheet laminate by spirally winding and laminating precursor sheets is not particularly limited; for example, the precursor sheets may be wound around a core material for winding and lamination.

[0065] In this case, the number of winding layers is preferably 15 to 300 layers.

[0066] The layers of precursor sheets may be joined via an organic binder applied to the surface of the precursor sheets, or they may be joined by impregnating the precursor sheets with an organic binder. Examples of organic binders include phenolic resin, polyvinyl alcohol (PVA), and pitch. The amount of organic binder can be 5-25% of the weight of the precursor sheet.

[0067] Next, the resulting precursor sheet laminate is fired. This firing process involves carbonizing the organic binder and other components that make up the precursor sheet laminate. Therefore, this process is also called the first firing process.

[0068] The heating temperature in the first firing process is preferably about 2000°C. The heating time in the first firing process is preferably 1 to 5 hours. The first firing process is preferably carried out in a non-oxidizing atmosphere.

[0069] Non-oxidizing atmospheres include inert and reducing atmospheres.

[0070] An inert atmosphere is an atmosphere whose main component is an inert gas. Examples of inert gases include nitrogen and argon.

[0071] A reducing atmosphere is an atmosphere whose main component is a reducing gas. Examples of reducing gases include hydrogen, carbon monoxide, hydrocarbons, and chlorine.

[0072] In the first firing process, the precursor sheet laminate becomes an insulating material. However, since the insulating material obtained at this stage contains impurities exceeding 20 ppm, in this specification, in order to distinguish it from the insulating material that is ultimately produced with an impurity concentration of 20 ppm or less, it is also referred to as insulating material (before high-purity treatment) or insulating material before high-purity treatment.

[0073] Through the above process, an insulating material (before high-purity treatment) is obtained.

[0074] (High-purity treatment) Next, the insulation material (before high-purity treatment) is heated in a halogen gas atmosphere at a temperature of 1800-2500°C to perform a high-purity treatment in which impurities contained in the insulation material (before high-purity treatment) are removed by reacting with the halogen gas.

[0075] Examples of halogen gases used in the high-purity treatment include chlorine, chlorine compounds, fluorine, and fluorine compounds, as well as compounds containing chlorine and fluorine in the same molecule (monochlorotriolmethane, trichloromonofluormethane, dichlorofluorethane, trichloromonofluorethane, etc.). The heating time in the high-purity treatment is preferably 1 to 10 hours.

[0076] The inner diameter, outer diameter, and height of the resulting insulation material may be adjusted by machining. Machining may be performed before or after the high-purity treatment.

[0077] By following the above procedure, the thermal insulation material of the present invention with an impurity concentration of 20 ppm or less can be obtained.

[0078] This specification discloses the following:

[0079] (1) This disclosure provides a cylindrical thermal insulation material in which thermal insulation sheets containing carbon fibers and flake graphite are wound and laminated in a spiral shape, The average particle size of the aforementioned flake-like graphite is 25 to 400 μm. This is an insulating material characterized by having an impurity concentration of 20 ppm or less.

[0080] Disclosure (2) is the thermal insulation material described in Disclosure (1), wherein the thickness of the thermal insulation sheet is 0.3 to 2 mm.

[0081] The present disclosure (3) is a method for producing a thermal insulation material, characterized by firing a precursor sheet laminate, which is obtained by spirally winding and laminating precursor sheets containing carbon fibers and flake-like graphite with an average particle diameter of 25 to 400 μm, and then heating it in a halogen gas atmosphere at a temperature of 1800 to 2500°C to perform a high-purity treatment.

[0082] (Examples) The following are examples that more specifically disclose the present invention. However, the present invention is not limited to these examples.

[0083] (Example 1) A suspension containing carbon fibers (average fiber diameter: 13 μm, average fiber length: 0.7 mm), flaky graphite (average particle size: 100 μm), and an organic binder (phenol resin) in a ratio of 100:17:25 (by weight, organic binder is calculated on a solid content basis) was molded by a continuous papermaking method to obtain a precursor sheet (thickness 1.0 mm) made of carbon fibers.

[0084] Next, the obtained precursor sheets were wound around a core material with a diameter of 80 mm and laminated to obtain a cylindrical precursor sheet laminate. The inner diameter of the precursor sheet laminate was 80 mm, the outer diameter was 140 mm, and the number of winding layers was 30. At this time, the precursor sheets were impregnated with an organic binder (phenol resin) at a rate of 10 parts by weight per 100 parts by weight of the precursor sheet before lamination. The precursor sheet laminate was heated to 2000°C in an inert atmosphere to carbonize the organic binder (phenol resin) contained in the precursor sheet, and a thermal insulation material (thermal insulation sheet thickness 0.9 mm) was obtained before high-purity treatment, in which carbon fibers and flake graphite were bonded together with a carbonaceous binder. Subsequently, the material was heated to 2300°C in a halogen gas atmosphere for 1 hour to perform a high-purity treatment, thereby obtaining the thermal insulation material according to Example 1.

[0085] The inner and outer surfaces of the obtained insulation material were machined. The obtained insulation material had an inner diameter of 96.2 mm, an outer diameter of 130 mm, a height of 210 mm, 19 layers of windings, and a thickness of 16.9 mm.

[0086] (Visual inspection) The appearance of the insulation material obtained in Example 1 was examined to check for any flaky graphite fallout, and the results were judged according to the following criteria. The results are shown in Table 1. ○: No flaky graphite detachment is observed. ×: Scaffold-like graphite detachment is observed.

[0087] (Measurement of impurity concentration) A sample piece was prepared by cutting out a portion of the insulating material according to Example 1. After measuring its weight, the sample piece was burned in air. The impurity concentration was determined from the weight of the test piece before heating and the weight of the obtained ash, and was found to be 2.33 ppm.

[0088] (Examples 2-5, Comparative Examples 1-2) Except for changing the average particle size of the flake graphite to that shown in Table 1, the thermal insulation materials for Examples 2-5 and Comparative Examples 1-2 were obtained using the same procedure as in Example 1. Visual inspection and measurement of impurity concentration were performed on each thermal insulation material. The results are shown in Table 1.

[0089] [Table 1]

[0090] As shown in Table 1, when using flake graphite with an average particle size of 25-400 μm, the high-purity treatment could be performed without the flake graphite falling off. However, in Comparative Example 1, where the average particle size of the flake graphite was less than 25 μm, and in Comparative Example 2, where it exceeded 400 μm, it was confirmed that the flake graphite fell off after the high-purity treatment. [Explanation of Symbols]

[0091] 1. Insulation 1a Inner surface of the insulation material 1b Outer surface of the insulation material 10 Insulation Sheets 20. Scaly graphite 30 carbon fiber 40 Carbonaceous binders 100 cylindrical space R1 insulation material outer diameter Inner diameter of R2 insulation material t0 Thickness of insulation material Thickness of t1 insulation sheet h Height of insulation

Claims

1. A cylindrical thermal insulation material in which thermal insulation sheets containing carbon fibers and flake graphite are wound and laminated in a spiral shape, The average particle size of the aforementioned flake-like graphite is 25 to 400 μm. An insulating material characterized by having an impurity concentration of 20 ppm or less.

2. The thermal insulation material according to claim 1, wherein the thickness of the thermal insulation sheet is 0.3 to 2 mm.

3. A method for producing a thermal insulation material, characterized by firing a precursor sheet laminate, which is obtained by spirally winding and laminating precursor sheets containing carbon fibers and flaky graphite with an average particle size of 25 to 400 μm, and then heating it in a halogen gas atmosphere at a temperature of 1800 to 2500°C to perform a high-purity treatment.

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