Insulation

Abstract

The present invention provides an insulating material composed of a single type of sheet that is less prone to cracking due to thermal expansion of the object being insulated. [Solution] A cylindrical thermal insulation material in which thermal insulation sheets containing carbon fibers are wound and laminated in a spiral shape, wherein there are spaces between the laminated thermal insulation sheets, and the ratio of the total thickness of the spaces to the thickness of the thermal insulation material in a cross-section obtained by cutting the thermal insulation material in a direction perpendicular to the longitudinal direction is 1.0 to 10.0%.

Description

[Technical Field]

[0001] This invention relates to thermal insulation materials. [Background technology]

[0002] Insulation materials made from carbon fiber are widely used as insulation materials for high-temperature furnaces such as semiconductor manufacturing furnaces and ceramic sintering furnaces, due to their high heat resistance and excellent insulation performance.

[0003] The shape of the insulating material used in induction heating furnaces is determined appropriately depending on the shape of the object to be insulated, but for example, cylindrical insulating material is often used to insulate a columnar object (object to be heated).

[0004] However, when heating an object using a cylindrical insulating material, the thermal expansion of the object caused stress to be applied to the inside of the insulating material, sometimes resulting in cracking.

[0005] As a way to solve these problems, for example, Patent Document 1 describes a high-strength carbon fiber sheet in which carbon fibers are randomly oriented and a protective carbon layer is formed, and an insulating material in which carbon fiber layers are alternately laminated in which carbon fibers are oriented perpendicular to the lamination direction and which relieve stress in the thickness direction. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 6916706 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the method of laminating two types of sheets, as described in Patent Document 1, had the problem of being complicated to manufacture.

[0008] This invention was made to solve the above problems, and aims to provide an insulating material composed of a single type of sheet that is less prone to cracking due to thermal expansion of the object being insulated. [Means for solving the problem]

[0009] The present invention provides a cylindrical thermal insulation material in which thermal insulation sheets containing carbon fibers are wound and laminated in a spiral shape, wherein there are spaces between the laminated thermal insulation sheets, and the ratio of the total thickness of the spaces to the thickness of the thermal insulation material in a cross-section obtained by cutting the thermal insulation material in a direction perpendicular to the longitudinal direction is 1.0 to 10.0%.

[0010] The thermal insulation material of the present invention is a cylindrical thermal insulation material in which thermal insulation sheets are wound and laminated in a spiral shape. In other words, the thermal insulation material of the present invention is composed of a single thermal insulation sheet. Therefore, there is no need to prepare two types of sheets as in Patent Document 1, and the manufacturing method is not complicated. Furthermore, the thermal insulation material of the present invention has spaces between the laminated thermal insulation sheets, the thickness of which is 1.0 to 10.0% of the thickness of the thermal insulation material. Having such spaces allows the stress on the thermal insulation material to be relieved even if the object to be insulated inside expands due to heat during heating, thereby preventing cracking of the thermal insulation material.

[0011] In the present invention, when the thermal insulation material is cut in a direction perpendicular to the longitudinal direction and the thermal insulation material is divided into an inner layer and an outer layer by a reference line that divides the thermal insulation material into two equal parts in the thickness direction, the inner layer and the outer layer each have one or more spaces between the thermal insulation sheets, and it is preferable that the total thickness of the outer layer spaces is greater than the total thickness of the inner layer spaces. With the above configuration, the stress caused by the thermal expansion of the object being insulated can be sufficiently relieved. In addition, because the inner layer is relatively dense, radiant heat emitted from the object being insulated is less likely to pass through, thus improving the insulation effect.

[0012] In the thermal insulation material of the present invention, the total thickness of the outer layer space is preferably 1.1 to 10 times the total thickness of the inner layer space. With the above configuration, the stress caused by the thermal expansion of the object being insulated can be further reduced.

[0013] In the thermal insulation material of the present invention, it is preferable that the average thickness of each of the above-mentioned spaces is 0.01 to 1 mm. If the average thickness of each of the above spaces is within the above range, the stress caused by the thermal expansion of the object being insulated can be sufficiently relieved, and the radiant heat emitted from the object being insulated can be less likely to pass through, thereby achieving a high level of insulation.

[0014] In the thermal insulation material of the present invention, the thickness of the thermal insulation sheet is preferably 0.3 to 2.0 mm. When the thickness of the insulation sheet is within the above range, the stress caused by the thermal expansion of the object being insulated can be sufficiently relieved. Furthermore, the carbon fibers contained in the insulation sheet tend to orient in a direction perpendicular to the thickness direction of the insulation sheet, thus improving the insulation performance.

[0015] In the thermal insulation material of the present invention, it is preferable that the number of winding layers of the thermal insulation sheet is 15 to 300. When the number of windings and layers of the insulation sheet is within the above range, a sufficient amount of space can be maintained between the insulation sheets, making it easier to relieve the stress caused by the thermal expansion of the object being insulated.

[0016] The thermal insulation material of the present invention preferably has an inner diameter of 50 to 1000 mm. If the inner diameter of the insulation material is within the above range, an object to be insulated that has a thermal expansion amount that the insulation material can tolerate can be inserted into the insulation material.

[0017] In the present invention, it is preferable that, in the cross-section obtained by cutting the thermal insulation material in a direction perpendicular to the longitudinal direction, at least a portion of the above-mentioned spaces overlap in the thickness direction of the thermal insulation material. When the spaces are arranged as described above, the stress applied from the heat insulation target can be dispersed into the plurality of spaces, so that breakage of the heat insulating material is further prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] [Figure 1] Figure 1 is a perspective view schematically showing an example of the heat insulating material of the present invention. [Figure 2] Figure 2 is a partially enlarged view of a cut surface obtained by cutting the heat insulating material shown in Figure 1 in a direction perpendicular to the longitudinal direction. [Figure 3] Figure 3 is a cross-sectional view schematically showing a space between heat insulating sheets. [Figure 4] Figure 4 is an optical microscope image of a cut surface of the heat insulating material according to Example 1. [Figure 5] Figure 5 is a schematic view showing an example of a step of inserting a jack inside a test jig. [Figure 6] Figure 6 is a schematic view showing an example of a step of inserting a test jig and a jack inside the heat insulating material. [Figure 7] Figure 7 is a schematic view showing an example of a step of extending the jack inside the heat insulating material. [Figure 8] Figure 8 is a schematic view showing an example of a case where the jack is extended until a crack occurs in the heat insulating material. DETAILED DESCRIPTION OF EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0019] 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 modified and applied within the scope not changing the gist of the present invention.

[0020] [Heat Insulating Material] The heat insulating material of the present invention is a cylindrical heat insulating material in which heat insulating sheets containing carbon fibers are spirally wound and laminated, has spaces between the laminated heat insulating sheets, and is characterized in that, on a cut surface obtained by cutting the heat insulating material in a direction perpendicular to the longitudinal direction, the ratio of the total thickness of the spaces to the thickness of the heat insulating material is 1.0 to 10.0%.

[0021] Figure 1 is a schematic perspective view showing an example of the thermal insulation material of the present invention. As shown in Figure 1, the thermal insulation material 1 is cylindrical with an outer diameter R1, an inner diameter R2, and a height h, and has a cylindrical cavity 100 inside.

[0022] The thickness t0 of the insulation material 1 is the length of the shortest distance connecting the inner surface 1a and the outer surface 1b of the insulation material 1 in a plane perpendicular to the longitudinal direction (indicated by arrow Z in Figure 1) (a plane parallel to arrows X and Y in Figure 1). This length is measured at eight points at 45-degree intervals along the central angle of the inscribed circle of the inner surface 1a of the insulation material 1, and the average value is used.

[0023] The shape of the insulation material can be cylindrical, but a cylindrical shape is preferable.

[0024] The cross-sectional area of ​​the cylindrical cavity 100 located inside the insulation material, when cut in a direction parallel to a plane perpendicular to its longitudinal direction, is 20 to 8000 cm². 2 It is preferable that this be the case.

[0025] When the insulation material is cylindrical, the inner diameter is preferably 50 to 1000 mm. If the inner diameter of the insulation material is between 50 and 1000 mm, then an object to be insulated that has a thermal expansion amount that the insulation material can tolerate can be inserted into the insulation material. The inner diameter R2 of the insulation material 1 is the diameter of the contour shape (circle) that constitutes the inner surface 1a of the insulation material 1 in a plane perpendicular to the longitudinal direction. It is the average value of the diameters of the contour shapes that constitute the inner surface 1a at the two end faces located at both ends of the insulation material 1 in the longitudinal direction, and at the cross-section obtained when the height h of the insulation material 1 is bisected.

[0026] 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 contour shape (circle) that constitutes the outer surface 1b of the insulation material 1 in a plane perpendicular to the longitudinal direction. It is the average of the diameters of the contour shapes that constitute the outer surface 1b at the two end faces located at both ends in the longitudinal direction of the insulation material 1, and at the cross-section obtained when the height h of the insulation material 1 is bisected.

[0027] The length (height) of the insulation material in the longitudinal direction is preferably 150 to 1000 mm. The height h of the insulation material 1 is determined by taking measurements at eight points on the inner surface 1a of the insulation material 1, at 45-degree intervals between the central angles of the inscribed circle, and taking the average value of these measurements.

[0028] 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.

[0029] 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.

[0030] 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. In this specification, the density variation of the thermal insulation material is evaluated by dividing the difference between the maximum and minimum densities when the thermal insulation material is divided into eight sections in the circumferential direction by the average density. Therefore, this value is also referred to as the density variation rate. In other words, it is preferable that the thermal insulation material of the present invention has a density variation rate of 5% or less, as shown by the above formula.

[0031] 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 into eight equal parts in a plane perpendicular to the longitudinal 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 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.

[0032] The volume resistivity of the insulation material is 8 × 10―4 It is preferable that it be Ω·m or greater, and 20 × 10 ―4 It is more preferable that the above conditions are met. When the volume resistivity is within the above range, no induced current is generated in the insulating material during induction heating, allowing for efficient heating of the object being insulated. The volume resistivity of the thermal insulation material was measured using the four-probe method, specifically the circumferential volume resistivity at room temperature.

[0033] Figure 2 is a partially enlarged view of a cross-section obtained by cutting the insulation material shown in Figure 1 in a direction perpendicular to its longitudinal direction. 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.

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

[0037] The thickness t1 of the insulation sheet 10 is preferably 0.3 to 2.0 mm. When the thickness of the insulation sheet is 0.3 to 2.0 mm, the number of windings and layers of the insulation sheet per unit thickness of the insulation material can be increased, and variations in density in the in-plane direction 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] If the thickness of the insulation sheet is less than 0.3 mm, defects such as tearing become more likely to occur in the insulation sheet, making the manufacturing process itself difficult. In addition, the mechanical strength of the insulation sheet decreases, increasing the likelihood of damage to the insulation sheet during winding and lamination.

[0039] 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.

[0040] The number of windings and layers of the insulating sheet 10 that constitutes the insulating material 1 is preferably 15 to 300 layers. When the number of windings and layers of the insulation sheet is within the above range, variations in the circumferential density of the insulation material can be particularly suppressed. The number of windings and layers of insulation sheets can be determined by dividing the thickness of the insulation material by the thickness of the insulation sheet. Note that decimal values ​​are truncated to determine the number of windings and layers.

[0041] The insulation material 1 has spaces 20 between the laminated insulation sheets 10.

[0042] The insulation material 1 is divided into an inner layer 110 and an outer layer 120 by a reference line b that divides the insulation material 1 in the thickness direction into two equal parts.

[0043] The space 20 of the inner layer 110 is also called the inner layer space 21, and the space 20 of the outer layer 120 is also called the outer layer space 22.

[0044] The insulation material 1 may have only one of the inner layer space 21 or the outer layer space 22, but it is preferable that it has both the inner layer space 21 and the outer layer space 22.

[0045] The ratio of the total thickness of the space 20 to the thickness t0 of the insulation material 1 is 1.0 to 10.0%. The ratio of the total thickness of the space to the thickness of the insulation material is measured at eight points every 45 degrees of the central angle of the inscribed circle of the inner surface 1a of insulation material 1, and the average value is used. Specifically, the cross-section of the insulation material 1, cut perpendicular to its longitudinal direction Z, is observed with an optical microscope. Eight dividing lines are drawn to divide the cross-section into 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315° sections. The value obtained is the average of the sum of the thicknesses of the spaces located along each dividing line and the thickness of the insulation material 1.

[0046] If the ratio of the total thickness of the space to the thickness of the insulation material is 1.0 to 10.0%, even if the object being insulated inside expands due to heat during heating, the stress on the insulation material can be reduced, preventing cracking of the insulation material.

[0047] It is preferable that the total thickness of the outer layer space 22 is greater than the total thickness of the inner layer space 21. When the total thickness of the outer layer space is greater than the total thickness of the inner layer space, the stress caused by the thermal expansion of the object being insulated can be sufficiently relieved. In addition, because the inner layer becomes relatively denser, radiant heat emitted from the object being insulated is less likely to pass through, thus improving the insulation effect.

[0048] The total thickness of the outer layer space 22 is preferably 1.1 to 10 times, and more preferably 2 to 6 times, the total thickness of the inner layer space 21. When the total thickness of the outer layer space is 1.1 to 10 times the total thickness of the inner layer space, the stress caused by the thermal expansion of the insulated object can be further reduced.

[0049] The total thickness of the inner layer space 21 and the total thickness of the outer layer space 22 are measured at eight locations at 45-degree intervals along the central angle of the inscribed circle of the inner surface 1a of the insulation material 1, and the average value is used.

[0050] In the insulation material 1, at least a portion of the multiple spaces 20 overlap with respect to the thickness direction t. In this case, the inner layer spaces 21 may overlap with each other, the outer layer spaces 22 may overlap with each other, or the inner layer space 21 and the outer layer space 22 may overlap. When at least a portion of multiple spaces overlap in the thickness direction, the stress applied from the object being insulated can be distributed across the multiple spaces, thus better preventing damage to the insulation material.

[0051] Furthermore, if a single space spans both an inner and outer layer, the portion of that space located in the inner layer is treated as the inner layer space, and the portion located in the outer layer is treated as the outer layer space.

[0052] Figure 3 is a schematic cross-sectional view showing the space between the insulation sheets. As shown in Figure 3, the thickness of the space 20 between the insulation sheets 10 is represented by p1.

[0053] The average thickness p1 of space 20 is preferably 0.01 to 1 mm. When the average thickness of each space is 0.01 to 1 mm, the stress caused by the thermal expansion of the object being insulated can be sufficiently relieved, and the radiant heat emitted from the object being insulated is less likely to pass through, resulting in a high level of insulation effect. The average thickness of space 20 is calculated by observing the cross-section of the insulation material 1, cut perpendicular to its longitudinal direction Z, with an optical microscope (5x magnification), drawing dividing lines at 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°, and then taking the average thickness of all spaces observed along each dividing line.

[0054] Furthermore, the spaces between the insulating sheets in this specification are spaces that can be observed and confirmed using an optical microscope (5x magnification).

[0055] (Insulation sheet) The insulation sheet contains carbon fiber.

[0056] The average fiber length of the carbon fibers is preferably between 0.4 mm and 10,000 mm. Furthermore, the average fiber length of the carbon fibers may be between 0.4 mm and 4 mm, or between 10 mm and 10,000 mm. The average fiber length of the carbon fibers is calculated by measuring the longitudinal length of 20 randomly selected carbon fibers using any method and averaging the results.

[0057] 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.

[0058] Carbon fibers can be pitch-based, PAN-based, or rayon-based, and either graphite-based or carbonaceous carbon fibers can be used.

[0059] The heat insulating sheet is preferably made of a carbon fiber needle mat or a carbon fiber papermaking body. Because carbon fiber needle mats and 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.

[0060] When the insulation sheet is made of a carbon fiber needle mat, the average fiber length of the carbon fibers is preferably between 10 mm and 10,000 mm. When the heat insulating sheet is made of carbon fiber paper, the average fiber length of the carbon fibers is preferably 0.4 mm to 4 mm.

[0061] The heat insulating sheet preferably contains 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.

[0062] 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.

[0063] Flake graphite has a higher reflectivity of synchrotron radiation compared to other carbon-based materials. Therefore, including flake graphite in an insulating sheet can improve its thermal insulation performance.

[0064] 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.

[0065] Natural graphite can be used as the flaky graphite.

[0066] 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 the "Industrial Analysis and Testing Methods for Natural Graphite" described in JIS M 8511 (2014).

[0067] 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. When the flake-like graphite is oriented in the direction of the plane, it reflects light emitted from the heating element more easily, thereby improving the thermal insulation performance.

[0068] The content of flake graphite is not particularly limited, but it is preferably 5-30% of the weight of the insulation material.

[0069] 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.

[0070] [Method of manufacturing insulation material] The thermal insulation material of the present invention can be obtained, for example, by winding and laminating precursor sheets containing carbon fibers to obtain a precursor sheet laminate, and then firing it at approximately 2000°C in a non-oxidizing atmosphere under conditions that do not suppress thermal shrinkage toward the inner diameter of the precursor sheet laminate.

[0071] (Manufacturing of precursor sheets) Precursor sheets can be obtained, for example, by preparing a suspension in which carbon fibers are dispersed in a dispersion medium such as water and forming it into a sheet (papermaking), or by performing a needle punching treatment on an aggregate of carbon fibers.

[0072] 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 carbonizes during subsequent heat treatment (firing in a non-oxidizing atmosphere) to become a carbonaceous binder, thus continuing to bind the carbon fibers together even after heat treatment.

[0073] Examples of organic binders that act as carbonaceous binders include phenolic resins, polyvinyl alcohol (PVA), and pitch.

[0074] If the papermaking method does not include an organic binder in the suspension, or if the carbon fiber aggregate is subjected to needle punching, the precursor sheet may be made to contain the organic binder by applying a slurry containing the organic binder to the resulting precursor sheet.

[0075] 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 2.0 mm can be obtained.

[0076] (Manufacturing of precursor sheet laminates) A precursor sheet laminate can be obtained by winding and laminating precursor sheets containing carbon fibers, with a thickness of 0.3 to 3.0 mm, manufactured using the method described above.

[0077] The precursor sheet may be laminated by winding it around a core material, for example.

[0078] The number of winding layers of the precursor sheet is preferably 15 to 300 layers.

[0079] The layers of the stacked precursor sheets may be joined via an organic binder coated on 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.

[0080] (Firing of the precursor sheet laminate) The thermal insulation material of the present invention can be manufactured by firing the above-described precursor sheet laminate at approximately 2000°C under conditions that do not suppress thermal shrinkage toward the inner diameter side of the precursor sheet laminate, and in a non-oxidizing atmosphere.

[0081] The precursor sheets that make up the precursor sheet laminate undergo thermal shrinkage when fired at 2000°C in a non-oxidizing atmosphere. Therefore, when firing under conditions that do not suppress the thermal shrinkage of the precursor sheet laminate toward the inner diameter during this thermal shrinkage, the thermal shrinkage of the precursor sheets causes thermal shrinkage toward the inner diameter of the precursor sheet laminate, and the spaces between the precursor sheets are pulled. As a result, spaces are easily formed between the insulating sheets after firing. On the other hand, by firing the precursor sheet laminate under conditions that suppress thermal shrinkage toward the inner diameter during this thermal shrinkage, the thermal shrinkage of the precursor sheets suppresses thermal shrinkage toward the inner diameter of the precursor sheet laminate, preventing the precursor sheets from being pulled apart. As a result, it becomes less likely for gaps to form between the insulating sheets after firing.

[0082] For example, the amount of thermal shrinkage towards the inner diameter of the precursor sheet laminate can be adjusted by the size of the outer diameter of the core placed in the inner cavity of the cylindrical precursor sheet laminate during firing. Specifically, if the ratio of the outer diameter of the core to the inner diameter of the precursor sheet laminate is 99% or less, thermal shrinkage toward the inner diameter of the precursor sheet laminate is not suppressed. On the other hand, if the ratio of the outer diameter of the core to the inner diameter of the precursor sheet laminate is greater than 99%, thermal shrinkage toward the inner diameter of the precursor sheet laminate is suppressed.

[0083] To adjust the ratio of the outer diameter of the core to the inner diameter of the precursor sheet laminate, the size of the core material used when manufacturing the precursor sheet laminate may be adjusted, or the size of the core used during firing may be adjusted. Furthermore, the inner surface of the precursor sheet laminate may be machined to adjust the ratio of the outer diameter of the core to the inner diameter of the precursor sheet laminate.

[0084] Non-oxidizing atmospheres include inert and reducing atmospheres.

[0085] An inert atmosphere is an atmosphere whose main component is an inert gas. Examples of inert gases include nitrogen and argon.

[0086] A reducing atmosphere is an atmosphere whose main component is a reducing gas. Examples of reducing gases include hydrogen, carbon monoxide, hydrocarbons, and chlorine.

[0087] The inner diameter, outer diameter, and height of the resulting insulation material may be adjusted by machining.

[0088] This specification discloses the following:

[0089] This disclosure (1) is a cylindrical thermal insulation material in which a thermal insulation sheet containing carbon fiber is wound and laminated in a spiral shape, There is a space between the laminated heat insulating sheets, The thermal insulation material is characterized in that, in a cross-section obtained by cutting the thermal insulation material in a direction perpendicular to the longitudinal direction, the ratio of the total thickness of the space to the thickness of the thermal insulation material is 1.0 to 10.0%.

[0090] This disclosure (2) shows that when the insulation material is cut in a direction perpendicular to the longitudinal direction and the insulation material is divided into an inner layer and an outer layer by a reference line that divides the insulation material into two equal parts in the thickness direction, The inner layer and the outer layer each have one or more spaces between the heat insulating sheets, which are the inner layer space and the outer layer space, respectively. The thermal insulation material according to disclosure (1), wherein the total thickness of the outer layer space is greater than the total thickness of the inner layer space.

[0091] Disclosure (3) is the thermal insulation material described in Disclosure (2), wherein the total thickness of the outer layer space is 1.1 to 10 times the total thickness of the inner layer space.

[0092] Disclosure (4) is an insulating material in any combination with any of Disclosures (1) to (3), wherein the average thickness per space is 0.01 to 1 mm.

[0093] Disclosure (5) is an insulating material in any combination of any of Disclosures (1) to (4), wherein the thickness of the insulating sheet is 0.3 to 2.0 mm.

[0094] Disclosure (6) is an insulating material in any combination of Disclosure (1) to (5), wherein the number of winding layers of the insulating sheet is 15 to 300 layers.

[0095] Disclosure (7) is an insulating material having an inner diameter of 50 to 1000 mm, in any combination with any of Disclosures (1) to (6).

[0096] Disclosure (8) is an insulating material in any combination of any of Disclosures (1) to (7), wherein, in a cross-section obtained by cutting the insulating material in a direction perpendicular to the longitudinal direction, at least a portion of the plurality of spaces overlap in the thickness direction of the insulating material.

[0097] (Examples) The following are examples that more specifically disclose the present invention. However, the present invention is not limited to these examples.

[0098] (Example 1) A suspension containing carbon fibers (average fiber diameter: 13 μm, average fiber length: 0.7 mm) and an organic binder (phenol resin) in a ratio of 100:10 (by weight, organic binder is calculated on a solid content basis) was molded by a continuous papermaking method to obtain a precursor sheet (thickness 1.05 mm) made of carbon fibers.

[0099] Next, the obtained precursor sheets were wound around a core material with a diameter of 155 mm to create a cylindrical precursor sheet laminate. The precursor sheet laminate had an inner diameter of 155 mm, an outer diameter of 199 mm, and a height of 50 mm, with 20 layers. 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.

[0100] The inner surface of the obtained precursor sheet laminate was machined to achieve an inner diameter of 155.8 mm. Furthermore, a core (made of graphite, with an outer diameter of 144.7 mm and a height of 60 mm) was inserted into the cavity inside the precursor sheet laminate. The ratio of the outer diameter of the core to the inner diameter of the precursor sheet laminate was 92.9%.

[0101] The precursor sheet laminate, including the core, was heated at 2000°C in a non-oxidizing atmosphere to carbonize the organic binder (phenol resin) contained in the precursor sheet laminate, thereby obtaining the thermal insulation material according to Example 1, in which a thermal insulation sheet made of carbon fiber was wound and laminated. The thermal insulation material in Example 1 was cylindrical with an inner diameter of 151 mm, an outer diameter of 195 mm, a height of 50 mm, and a thickness of 22 mm, and the thickness of the thermal insulation sheet was 0.95 mm.

[0102] (Comparative Example 1) The diameter of the core material around which the precursor sheet is wound was changed to 145 mm, and a precursor sheet laminate with an inner diameter of 145 mm, an outer diameter of 192 mm, and 22 winding layers was obtained. Then, the inner diameter was adjusted to 145.8 mm by machining, changing the ratio of the outer diameter of the core to the inner diameter of the precursor sheet laminate to 99.2%. Except for these changes, the precursor sheet laminate was fired in the same procedure as in Example 1 to obtain the thermal insulation material according to Comparative Example 1. The thermal insulation material in Comparative Example 1 was cylindrical with an inner diameter of 146 mm, an outer diameter of 187 mm, a height of 50 mm, and a thickness of 20.5 mm, and the thickness of the thermal insulation sheet was 0.95 mm.

[0103] (Measurement of the ratio of the total thickness of the space to the thickness of the insulation material) The cross-sections of the thermal insulation materials according to Example 1 and Comparative Example 1, cut perpendicular to the longitudinal direction, were observed with an optical microscope (5x magnification). Eight dividing lines were drawn to separate the material at 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°. The shape and distribution of the spaces located along each dividing line, as well as the thickness of the thermal insulation material, were then confirmed.

[0104] In the thermal insulation material according to Example 1, the ratio of the total thickness of the space to the thickness of the thermal insulation material was 4.8%, and the inner layer and outer layer each had an inner layer space and an outer layer space, with a total thickness of 1,000 mm for the outer layer space and a total thickness of 0.180 mm for the inner layer space. The total thickness of the outer layer space was 5.6 times the total thickness of the inner layer space, and the average thickness per space was 0.17 mm. Figure 4 is an optical microscope image of a cross-section of the thermal insulation material according to Example 1. Figure 4 shows that a space 20 is formed between the insulation sheets 10.

[0105] In Comparative Example 1, the total thickness of the space relative to the thickness of the insulation material was 0.75%, and the inner layer and outer layer each had their own space. The total thickness of the outer layer space was 0.056 mm, the total thickness of the inner layer space was 0.079 mm, and the total thickness of the outer layer space was 0.71 times the total thickness of the inner layer space. The average thickness per space was 0.20 mm.

[0106] (Measurement of maximum deformation) The maximum deformation of the thermal insulation material in Example 1 and Comparative Example 1 was measured using the method shown in Figures 5 to 8. Figure 5 is a schematic diagram showing an example of the process of inserting a jack inside the test fixture. Figure 6 is a schematic diagram showing an example of the process of inserting the test fixture and jack inside the insulation material. Figure 7 is a schematic diagram showing an example of the process of extending the jack inside the insulation material. Figure 8 is a schematic diagram showing an example of the case where the jack is extended until cracks appear in the insulation material.

[0107] First, as shown in Figure 5, two arc-shaped test fixtures 300 were prepared, and a jack 200 was inserted inside them. Next, as shown in Figure 6, the two test fixtures 300 and the jack 200 were inserted into the cavity 100 of the insulation material 1. The jack 200 has a lever 210 and a pressing portion 220, and the pressing portion 220 extends outward when the lever 210 is rotated. During insertion, the test fixture 300 is interposed between the inner surface 1a of the heat insulating material 1 and the pressing portion 220 of the jack 200, and is adjusted so that the pressing portion 220 is in contact with the inner circumferential surface 300a approximately in the center of the test fixture 300, and the outer circumferential surface 300b of the test fixture 300 is brought into close contact with the inner surface 1a of the heat insulating material 1. At this time, a part of the inner surface 1a of the heat insulating material 1 in a direction perpendicular to the direction in which the pressing portion 220 extends (the extension direction of the jack 200) is not covered by the test fixture 300 and is exposed. Subsequently, as shown in Figure 7, the lever 210 of the jack 200 is rotated to press the pressing portion 220 against the inner surface 1a of the heat insulating material 1 via the test jig 300. As shown in Figure 8, the lever 210 is rotated until a crack 50 occurs in the inner surface 1a of the heat insulating material 1, and the distance between the inner surfaces of the heat insulating material in the stretching direction of the jack 200 when the crack 50 occurs (hereinafter also referred to as the inner surface distance) is determined. Inner surface distance R of the heat insulating material 1 when crack 50 occurs 2B from the inner diameter R of the heat insulating material 1 before insertion of the jack 200 2A subtracted by the value (R 2B -R 2A ) is the maximum deformation amount R of the heat insulating material 1 2C . Therefore, it can be said that the larger the maximum deformation amount R 2C , the less likely cracking due to thermal expansion of the object to be insulated occurs.

[0108] The maximum deformation amount R of the heat insulating material according to Example 1 obtained by the above procedure 2C was 9.19 mm, and the maximum deformation amount R of the heat insulating material according to Comparative Example 1 2C was 6.96 mm. From this, it was confirmed that the heat insulating material according to Example 1 is less prone to cracking due to thermal expansion of the object to be insulated.

Description of Reference Numerals

[0109] 1 Heat insulating material 1a Inner surface of heat insulating material 1b Outer surface of heat insulating material 10 Heat insulating sheet 20 Space between heat insulating sheets 21 Inner layer portion space 22 Outer layer portion space 50 Crack 100 Cavity 110 Inner layer portion 120 Outer layer portion 200 Jack 210 Lever 220 Pressing portion 300 Test jig 300a Inner peripheral surface of test jig 300b Outer peripheral surface of test jig b Reference line 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 insulating material in which a carbon fiber insulating sheet is wound and laminated in a spiral shape, There is a space between the laminated heat insulating sheets, The thermal insulation material is characterized in that, in a cross-section obtained by cutting the thermal insulation material in a direction perpendicular to the longitudinal direction, the ratio of the total thickness of the space to the thickness of the thermal insulation material is 1.0 to 10.0%.

2. When the aforementioned insulation material is cut in a direction perpendicular to the longitudinal direction, and the insulation material is divided into an inner layer and an outer layer by a reference line that divides it into two equal parts in the thickness direction, The inner layer and the outer layer each have one or more spaces between the heat insulating sheets, which are the inner layer space and the outer layer space, respectively. The thermal insulation material according to claim 1, wherein the total thickness of the outer layer space is greater than the total thickness of the inner layer space.

3. The thermal insulation material according to claim 2, wherein the total thickness of the outer layer space is 1.1 to 10 times the total thickness of the inner layer space.

4. The thermal insulation material according to claim 1 or 2, wherein the average thickness of each of the aforementioned spaces is 0.01 to 1 mm.

5. The thermal insulation material according to claim 1 or 2, wherein the thickness of the thermal insulation sheet is 0.3 to 2.0 mm.

6. The thermal insulation material according to claim 1 or 2, wherein the number of winding layers of the thermal insulation sheet is 15 to 300 layers.

7. The thermal insulation material according to claim 1 or 2, wherein the inner diameter is 50 to 1000 mm.

8. The thermal insulation material according to claim 1 or 2, wherein in a cross-section obtained by cutting the thermal insulation material in a direction perpendicular to the longitudinal direction, at least a portion of the plurality of spaces overlap in the thickness direction of the thermal insulation material.

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