Insulation material

Abstract

To provide insulation material capable of suppressing heating defects and partial deterioration.SOLUTION: In a tubular heat insulator containing carbon fiber, the insulator is divided longitudinally into three sections of upper, middle and lower, and annular insulation pieces having a predetermined length in the lengthwise direction are cut out from the upper portion, the central portion and the lower portion, respectively, the density is determined using a total of 24 sample pieces obtained by dividing each insulation piece into eight equal parts in the circumferential direction, the maximum value is denoted as ρmax, the minimum value is denoted as ρmin, and the average value is denoted as ρave, the average density ρave is 0.10 to 0.25 g / cm3, and the density variation rate, expressed as [(ρmax)-(ρmin)] / (ρave)×100 is 15% 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 manufacturing a cylindrical heat insulating material by winding and laminating carbon fiber felt. Furthermore, Patent Document 2 discloses a method for directly producing a hollow cylindrical carbon fiber molding from a slurry containing carbon fibers using a suction molding die. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-291869 [Patent Document 2] Japanese Patent Application Publication No. 02-208264 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the cylindrical heat insulating materials manufactured by the methods described in Patent Documents 1 and 2 sometimes have variations in density.

[0007] In a method such as that described in Patent Document 1, in which a long sheet containing carbon fiber is wound to form a cylindrical insulating material, it is thought that variations in density of the sheet are amplified by the stacking period during winding, resulting in variations in density.

[0008] In the method of immersing a suction molding mold in a slurry containing carbon fibers, as in Patent Document 2, the carbon fibers in the slurry settle over time, creating a concentration distribution, which is thought to affect the density variation.

[0009] If the density of the insulation material varies as in Patent Documents 1 and 2, the insulation performance will be reduced in some areas, resulting in a large temperature distribution inside the furnace, which will cause insufficient heating of the object to be heated and will lead to partial deterioration of the insulation material, resulting in an increase in the frequency of replacement of the insulation material.

[0010] 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 suppress insufficient heating and partial deterioration. [Means for solving the problem]

[0011] The thermal insulating material of the present invention is a cylindrical thermal insulating material containing carbon fiber, and the thermal insulating material is divided into three parts in the longitudinal direction, namely, an upper part, a central part, and a lower part. Annular pieces of the thermal insulating material having a predetermined length in the longitudinal direction are cut out from each of the upper, central, and lower parts. Each of the thermal insulating material pieces is divided into eight equal parts in the circumferential direction to obtain a total of 24 sample pieces, and the maximum density is calculated using the obtained sample pieces. max , the minimum value is ρ min , the average value is ρ ave When the average density ρ ave is 0.10~0.25g / cm 3 and [(ρ max )-(ρ min )] / (ρ ave )×100 is 15% or less.

[0012] The heat insulating material of the present invention has a density variation rate of 15% or less, which reduces density variation and prevents the temperature distribution in the furnace from becoming too large. As a result, it is possible to prevent insufficient heating of the object to be heated and partial deterioration of the heat insulating material.

[0013] In the heat insulating material of the present invention, the density variation rate may be 3% or more. If the density variation rate is 15% or less and 3% or more, it is possible to sufficiently exert the effect of preventing insufficient heating of the object to be heated and partial deterioration of the heat insulating material. Therefore, the density variation rate may be 3% or more.

[0014] 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 density variations caused by such gaps can be reduced.

[0015] 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]

[0016] [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 perspective view schematically showing an upper portion, a central portion, and a lower portion when the heat insulating material shown in FIG. 1 is divided into three portions in the length direction. [Figure 3] FIG. 3 is a perspective view schematically showing a piece of heat insulating material cut out from the lower part of the heat insulating material shown in FIG. [Figure 4] FIG. 4 is a perspective view schematically showing an example of a sample piece cut out from the piece of heat insulating material shown in FIG. [Figure 5] FIG. 5 is a perspective view schematically showing an example of an integral molding die. [Figure 6] FIG. 6 is a diagram schematically illustrating an example of a method for producing a carbon fiber molding using an integral molding die. [Figure 7] FIG. 7 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

[0017] 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.

[0018] [Insulation material] The thermal insulating material of the present invention is a cylindrical thermal insulating material containing carbon fiber, and the thermal insulating material is divided into three parts in the longitudinal direction, namely, an upper part, a central part, and a lower part. Annular pieces of the thermal insulating material having a predetermined length in the longitudinal direction are cut out from each of the upper, central, and lower parts. Each of the thermal insulating material pieces is divided into eight equal parts in the circumferential direction to obtain a total of 24 sample pieces, and the maximum density is calculated using the obtained sample pieces. max , the minimum value is ρ min , the average value is ρ ave When the average density ρ ave is 0.10~0.25g / cm 3 and [(ρ max )-(ρ min )] / (ρ ave )×100 is 15% or less.

[0019] 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 t1, and a length h. The dimension h of the heat insulating material 1 in the longitudinal direction is also referred to as the height.

[0020] 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.

[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] In order to calculate the average density and density variation rate of the heat insulating material of the present invention, 24 sample pieces are cut out from the heat insulating material. This procedure will be explained with reference to Figs. 2, 3 and 4.

[0024] FIG. 2 is a perspective view schematically showing an upper portion, a central portion, and a lower portion when the heat insulating material shown in FIG. 1 is divided into three portions in the length direction. 2, the heat insulating material 1 can be divided into three parts in the length direction: an upper part 1a, a central part 1b, and a lower part 1c. The lengths of the upper part 1a, the central part 1b, and the lower part 1c are each 1 / 3 of the length h of the heat insulating material 1.

[0025] Next, annular pieces of the heat insulating material having a predetermined length in the longitudinal direction are cut out from each of the upper, central and lower portions. In FIG. 2, the heat insulating material piece 11c cut out from the lower portion 1c is shown in a dark color. The length of the heat insulating material piece 11c is 1 / 10 of the length h of the heat insulating material 1.

[0026] However, if 1 / 10 of the length h of the insulation 1 is 30 mm or less, the length of the insulation piece shall be the smaller of 1 / 3 of the length h of the insulation or 30 mm.

[0027] Fig. 3 is a perspective view showing a typical example of a piece of heat insulating material cut out from the lower part of the heat insulating material shown in Fig. 2. As shown in Fig. 3, the shape of the heat insulating material piece 11c is the same cylindrical (annular) shape as the heat insulating material 1, except that its length is 1 / 10 of that of the heat insulating material 1. Therefore, the shape of the heat insulating material piece 11c when viewed from the longitudinal direction Z is the same as that of the heat insulating material 1.

[0028] In Figures 2 and 3, the lowest part of the lower part 1c of the insulation material 1 is cut out to form the insulation material piece 11c, but the insulation material piece may also be cut out from the top or center of the lower part 1c as long as it has a predetermined length in the longitudinal direction.

[0029] Next, the heat insulating material piece 11c shown in FIG. 3 is divided into eight equal parts in the circumferential direction to obtain eight test pieces 11c1, 11c2, 11c3, 11c4, 11c5, 11c6, 11c7, and 11c8.

[0030] FIG. 4 is a perspective view schematically showing an example of a sample piece cut out from the piece of heat insulating material shown in FIG. The sample piece 11c1 is one of the sample pieces obtained by dividing the heat insulating material piece 11c shown in FIG. 3 into eight equal parts in the circumferential direction. The density of the sample piece is calculated from the volume determined from the outer dimensions of the obtained sample piece and the weight.

[0031] The density of the remaining seven sample pieces cut out from the heat insulating material piece 11c is also determined in the same manner.

[0032] The same procedure is repeated for the pieces of insulating material cut from the upper portion 1a of the insulating material 1 and the pieces of insulating material cut from the central portion 1b of the insulating material 1, and the densities of a total of 24 sample pieces are determined.

[0033] The maximum density obtained from a total of 24 sample pieces (maximum density) was ρ max , the minimum value (minimum density) is ρ min , the average value (average density) is ρ ave is.

[0034] In the heat insulating material of the present invention, the average density ρ ave is 0.10~0.25g / cm 3 and [(ρ max -ρ min ) / ρ ave ] × 100 is 15% or less.

[0035] The heat insulating material of the present invention has a density variation rate of 15% or less, which reduces density variation and prevents the temperature distribution in the furnace from becoming too large. As a result, it is possible to prevent insufficient heating of the object to be heated and partial deterioration of the heat insulating material. If the density variation rate is 15% or less, the density variation is small and the temperature distribution inside the furnace can be prevented from becoming large, which in turn prevents the heating object from being heated poorly and the insulation from being partially deteriorated.

[0036] If the density variation rate is 15% or less and 3% or more, it is possible to fully exert the effect of preventing insufficient heating of the object to be heated and partial deterioration of the heat insulating material. Therefore, the density variation rate may be 3% or more.

[0037] (carbon fiber) The insulation material includes carbon fiber.

[0038] The average fiber length of the carbon fibers is preferably 0.4 to 4 mm.

[0039] 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.

[0040] 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.

[0041] The insulating material preferably contains flake graphite. If the heat insulating material contains flake graphite, the heat insulating performance can be further improved.

[0042] Flake graphite is graphite that has a thin, flaky shape. Specifically, flake-shaped graphite is graphite that is in the form of flakes and has a thickness of 100 μm or less.

[0043] As the flake graphite, natural graphite can be used.

[0044] 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).

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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 would occur when one or more non-cylindrical insulating materials are deformed or combined to form a cylindrical shape, so density variations caused by such gaps can be reduced.

[0049] 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.

[0050] An integrally molded body containing carbon fibers can be obtained, for example, by a papermaking method using an integral molding die.

[0051] [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.

[0052] 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.

[0053] FIG. 5 is a perspective view schematically showing an example of an integral molding die. The integral molding die 50 shown in FIG. 5 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. 5). 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] FIG. 6 is a diagram schematically illustrating an example of a method for producing a carbon fiber molding using an integral molding die. As shown in Fig. 6, 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. 6, the fluid being sucked through the suction pipe 70 is indicated by a thick straight arrow.

[0058] 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.

[0059] At the same time, the integral molding die 50 is rotated around an axis in the longitudinal direction. In Fig. 6, 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.

[0060] The rotation speed of the integral molding die is preferably 10 to 60 rpm.

[0061] 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. 6. 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] FIG. 7 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 too large for the carbon fibers to pass through, the carbon fibers in the slurry 60 cannot pass through the side surface 51. As a result, as shown in Fig. 7, the carbon fibers are deposited on the side surface 51, and a carbon fiber molding 100 is obtained.

[0066] Such a carbon fiber molding 100 is fired at about 2000°C in a non-oxidizing atmosphere, whereby the average density is reduced to 0.10 to 0.25 g / cm. 3 Thus, the heat insulating material of the present invention can be obtained with a density variation rate suppressed to 15% or less.

[0067] 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.

[0068] The non-oxidizing atmosphere includes an inert atmosphere and a reducing atmosphere.

[0069] The inert atmosphere is an atmosphere whose main component is an inert gas. Examples of the inert gas include nitrogen and argon.

[0070] 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.

[0071] 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.

[0072] Instead of the integral molding die shown in Fig. 5, 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.

[0073] In this case, the body is divided into three parts in the length direction, namely, the upper part, the center part, and the lower part, and annular pieces of insulation material having a predetermined length in the length direction are cut out from each of the upper, center, and lower parts. Each piece of insulation material is divided into eight equal parts in the circumferential direction to obtain a total of 24 sample pieces, and the density is calculated using the obtained sample pieces. The average density ρ ave is 0.10~0.25g / cm 3 and [(ρ max )-(ρ min )] / (ρ ave ) × 100 is 15% or less, the plate part is included in the thermal insulation material of the present invention. ave and [(ρ max )-(ρ min )] / (ρ ave ) × 100. However, the maximum value of the density obtained using the 24 specimens mentioned above plus eight specimens obtained by dividing the plate into eight circumferential sections, for a total of 32 specimens, is d max , the minimum value is d min , the average value is d ave When the average density d ave is 0.10~0.25g / cm 3 and [(d max )-(d min )] / (d ave )×100 is preferably 15% or less.

[0074] The present specification discloses the following:

[0075] The present disclosure (1) provides a cylindrical heat insulating material containing carbon fiber, The heat insulating material was divided into three parts in the length direction, namely, an upper part, a central part, and a lower part, and circular pieces of heat insulating material having a predetermined length in the length direction were cut out from each of the upper, central, and lower parts. Each piece of heat insulating material was divided into eight equal parts in the circumferential direction to obtain a total of 24 sample pieces, and the maximum density was calculated using the obtained sample pieces. max , the minimum value is ρ min , the average value is ρ ave When the average density ρ aveis 0.10~0.25g / cm 3 and [(ρ max )-(ρ min )] / (ρ ave ) × 100 is 15% or less.

[0076] The present disclosure (2) is the heat insulating material according to the present disclosure (1), in which the density variation rate is 3% or more.

[0077] The present disclosure (3) is the heat insulating material according to the present disclosure (1) or (2), in which the heat insulating material is an integrally molded body.

[0078] The present disclosure (4) is an insulating material that is an optional combination with any of the present disclosures (1) to (3), wherein the insulating material contains flake graphite.

[0079] (Example) EXAMPLES Hereinafter, examples will be given that more specifically disclose the present invention, but the present invention is not limited to these examples.

[0080] (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.

[0081] Example 1 An integral molding die as shown in FIG. 5 was 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 (phenolic resin) contained in the carbon fiber molding, and the carbon fibers were bonded by the carbonaceous binder. The molding was then cut to obtain a heat insulating material according to Example 1. The heat insulating material 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.

[0082] (Comparative Example 1) The same slurry as in Example 1 was used to form a sheet-like carbon fiber molding with a thickness of 3 mm by papermaking and drying. The obtained sheet-like carbon fiber molding was wound around a core material with a diameter of 80 mm to produce a cylindrical sheet wound body. The sheet wound body had an inner diameter of 80 mm, an outer diameter of 170 mm, and 15 wound layers. At this time, the sheet was impregnated with an organic binder (phenolic resin) in an amount of 25 parts by weight per 100 parts by weight of the sheet and laminated. The obtained laminate was heated to 2000°C in an inert atmosphere to carbonize the organic binder (phenolic resin) contained in the carbon fiber molding, and a pre-processed thermal insulation material in which the carbon fibers were bonded with a carbonaceous binder was obtained. The obtained unprocessed heat insulating material was cut into the same shape as the heat insulating material according to Example 1, and the heat insulating material according to Comparative Example 1 was obtained.

[0083] (Measurement of average density and density variation rate) The heat insulating materials according to Example 1 and Comparative Example 1 were divided into three parts in the length direction, namely, the upper part, the center part, and the lower part, and then, from each of the upper part, the center part, and the lower part, annular pieces of heat insulating material having a length that is 1 / 10 of the length of the heat insulating material were cut out. Next, the cut out pieces of heat insulating material were divided into eight equal parts in the circumferential direction to prepare a total of 24 sample pieces. The external dimensions and weight of each of the obtained 24 sample pieces were measured, and the density was calculated. The maximum density ρ calculated from the 24 sample pieces was max , minimum value ρ min and the average value ρ ave are shown in Table 1.

[0084] (Comparative test_simulation) The heat insulating properties (temperature distribution inside the furnace) of the heat insulating materials according to Example 1 and Comparative Example 1 were simulated by the following method. The thermal conductivity corresponding to the density at 24 locations was input for the same size as the thermal insulation materials according to Example 1 and Comparative Example 1, and the specific heat capacity of the thermal insulation material was set as fixed conditions in 50°C increments, such as 922.2 J / kg·K at 100°C, 1580.2 J / kg·K at 500°C, 1934.6 J / kg·K at 1000°C, 2066.4 J / kg·K at 1500°C, and 2135.0 J / kg·K at 2000°C. The emissivity was set to 0.39, and the temperature distribution in an induction heating furnace was simulated. A cylindrical graphite crucible with a bottom, an outer diameter of 96.2 mm and a height of 140 mm, was placed inside the thermal insulation materials according to Example 1 and Comparative Example 1, and the crucible was heated to 2250°C, simulating a state in which the furnace was maintained in a vacuum. The temperature distribution on the inner top surface of the graphite crucible was observed, and the difference between the maximum and minimum values ​​was calculated as the temperature difference. The results are shown in Table 1. The density (X) (g / cm 3 The relationship between the temperature and thermal conductivity (Y) (W / m K) is as follows: Y=3.3X The simulation was carried out using the 3D steady-state calculation software STAR-CCM.

[0085] [Table 1]

[0086] From the results in Table 1, it is considered that the insulating material of Example 1, which was obtained by firing a carbon fiber molding obtained by papermaking while rotating an integral molding mold, has a density variation rate of 15% or less, and that since the temperature difference within the crucible is small, poor heating and partial deterioration can be suppressed. On the other hand, the heat insulating material of Comparative Example 1 had a density variation rate of more than 15%, which is thought to be a factor in preventing insufficient heating and partial deterioration due to the large temperature difference inside the crucible. [Explanation of symbols]

[0087] 1. Insulation 1a Top of insulation 1b Center of the insulation 1c Bottom of insulation 11c Insulation piece 11c1, 11c2, 11c3, 11c4, 11c5, 11c6, 11c7, 11c8 sample pieces 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 t1 insulation thickness h Length (height) of the insulation

Claims

1. A cylindrical thermal insulation material containing carbon fiber, The heat insulating material was divided into three parts in the length direction, namely, an upper part, a central part, and a lower part, and annular pieces of heat insulating material having a predetermined length in the length direction were cut out from each of the upper part, the central part, and the lower part. Each heat insulating material piece was divided into eight equal parts in the circumferential direction to obtain a total of 24 sample pieces, and the density was calculated using the obtained sample pieces. The maximum value was ρ ｍａｘ , the minimum value is ρ ｍｉｎ , the average value is ρ ａｖｅ When the average density ρ ａｖｅ is 0.10 to 0.25 g / cm ３ and [(ρ ｍａｘ )-(ρ ｍｉｎ ) ] / (ρ ａｖｅ ) × 100) is 15% or less.

2. The heat insulating material according to claim 1 , wherein the density variation rate is 3% or more.

3. The heat insulating material according to claim 1 or 2, wherein the heat insulating material is an integrally molded body.

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

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