Insulation sheets and insulation materials

Abstract

We provide an insulating sheet that exhibits excellent thermal insulation properties. [Solution] A heat insulating sheet comprising carbon fibers and flake graphite, characterized in that the ratio of the thickness of the heat insulating sheet to the average particle diameter of the flake graphite (thickness of the heat insulating sheet / average particle diameter of the flake graphite) is 5 to 20.

Description

Technical Field

[0001] The present invention relates to a heat insulation sheet and a heat insulating material.

Background Art

[0002] A sheet-like heat insulating material (also referred to as a heat insulation sheet) in which carbon fibers are integrated with carbides is widely used as a heat insulating material for high-temperature furnaces such as semiconductor manufacturing furnaces and ceramic sintering furnaces because of its high heat resistance temperature and excellent heat insulation characteristics. Such a heat insulation sheet may be used in the form of a laminate of a plurality of sheets or a wound laminate, that is, it may be used alone as a heat insulation sheet, or may be used in combination with other heat insulating materials by a method such as attaching it to the surface of other heat insulating materials.

[0003]

[0004] For example, Patent Document 1 discloses that by using a heat insulation coating agent composed of a carbonized material having a carbonization rate of 40% or more, flaky graphite (also referred to as scaly graphite), an adhesive, and a solvent, no cracks occur on the surface of the coating layer after firing, and it has surface smoothness and surface glossiness, and almost no peeling of the coated surface is observed, and a coating layer having excellent mechanical strength and oxidation resistance can be formed on the surface of the carbonized molded product.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the coating layer formed using the heat-insulating coating agent described in Patent Document 1 did not possess sufficient heat-insulating properties. The reason for this is thought to be the orientation of the scaly graphite in the coating layer.

[0007] Generally, scaly graphite has greater thermal conductivity in the in-plane direction perpendicular to the thickness direction than in the thickness direction. Therefore, from the viewpoint of improving the thermal insulation of the coating layer in the thickness direction, it is necessary to orient the scaly graphite in a direction perpendicular to the thickness direction of the coating layer (in-plane direction).

[0008] In contrast, in the method described in Patent Document 1, the fluidity of the coating liquid is suppressed by the action of an adhesive in the coating liquid in order to prevent the occurrence of lamination cracks. As a result, the scaly graphite does not orient in the in-plane direction, and it is thought that the heat insulation properties were not sufficiently improved.

[0009] This invention was made to solve the above-mentioned problems, and aims to provide an insulating sheet and insulating material that can exhibit excellent thermal insulation properties. [Means for solving the problem]

[0010] The present invention relates to a heat insulating sheet comprising carbon fibers and flake graphite, characterized in that the ratio of the thickness of the heat insulating sheet to the average particle diameter of the flake graphite (thickness of the heat insulating sheet / average particle diameter of the flake graphite) is 5 to 20.

[0011] The thermal conductivity of the insulating sheet depends on the arrangement of the flake graphite. That is, in insulating sheets containing the same amount of flake graphite, the thermal conductivity in the thickness direction of the insulating sheet is lower when the flake graphite is oriented in an in-plane direction perpendicular to the thickness direction of the insulating sheet than when the flake graphite is oriented in the thickness direction of the insulating sheet.

[0012] Furthermore, the layered surface of the flake graphite easily reflects heat emitted from the heat source. In other words, since the insulating sheet is positioned with its in-plane direction facing the heat source, the more the flake graphite is oriented in the in-plane direction of the insulating sheet, the better it can reflect heat emitted from the heat source, resulting in superior insulating properties.

[0013] For the reasons stated above, it can be said that higher thermal insulation properties can be achieved when the flake-like graphite is oriented in the in-plane direction of the thermal insulation sheet.

[0014] In the heat insulating sheet of the present invention, the ratio of the thickness of the heat insulating sheet to the average particle diameter of the flake graphite is 5 to 20. This suppresses the orientation of the laminated surface of the flake graphite perpendicular to the sheet, making it easier for the flake graphite to orient in the in-plane direction of the heat insulating sheet. Therefore, the heat insulating properties can be improved compared to the case where the flake graphite is oriented in the thickness direction.

[0015] The heat insulating sheet of the present invention preferably has a thickness of 0.5 to 2.0 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 0.5 mm thick, it becomes more prone to damage. If the thickness of the insulation sheet exceeds 2.0 mm, it may become difficult to obtain the orientation of the flaky graphite described above, which can lead to a decrease in insulation properties.

[0016] In the heat insulating sheet of the present invention, the average particle size of the flaky graphite is preferably 15 to 400 μm. When the average particle size of the flake graphite is within the above range, the layering surface of the flake graphite in the insulating sheet is suppressed from being perpendicular to the sheet, and the flake graphite is more likely to be oriented in the direction of the insulating sheet's surface.

[0017] In the heat insulating sheet of the present invention, it is preferable that the ratio of the volume of flake graphite to the volume of carbon contained in the heat insulating sheet (volume of flake graphite / volume of carbon contained in the heat insulating sheet) is 5 to 25%. When the ratio of the volume of the flaky graphite to the volume of the carbon content in the heat insulating sheet is within the above range, it becomes easier to balance the flexibility and the heat insulating properties of the heat insulating sheet.

[0018] The heat insulating material of the present invention is characterized in that a plurality of the heat insulating sheets of the present invention are laminated. Since the heat insulating material of the present invention is formed by laminating a plurality of the heat insulating sheets of the present invention, it has excellent heat insulating properties.

Brief Description of Drawings

[0019] [Figure 1] FIG. 1 is a perspective view schematically showing an example of the heat insulating sheet. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an example of the heat insulating sheet. [Figure 3] FIG. 3 is an enlarged cross-sectional view schematically showing another example of the heat insulating sheet.

Modes for Carrying Out the Invention

[0020] 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 without changing the gist of the present invention.

[0021] [Heat Insulating Sheet] The heat insulating sheet of the present invention is a heat insulating sheet composed of carbon fiber and flaky graphite, and the ratio of the thickness of the heat insulating sheet to the average particle diameter of the flaky graphite (thickness of the heat insulating sheet / average particle diameter of the flaky graphite) is 5 to 20.

[0022] FIG. 1 is a perspective view schematically showing an example of the heat insulating sheet. As shown in FIG. 1, the heat insulating sheet 10 is a flexible sheet and may be stored in a wound state.

[0023] FIG. 2 is a cross-sectional view schematically showing an example of the heat insulating sheet. The heat insulating sheet 10 shown in Figure 2 contains carbon fibers (not shown) and flaky graphite 20. The ratio of the thickness t0 of the insulating sheet to the average particle size of the flake graphite 20 (thickness t0 of the insulating sheet / average particle size of the flake graphite) is between 5 and 20. When the above conditions are met, the uprighting of the flake-like graphite 20 within the heat insulating sheet 10 is suppressed, and the flake-like graphite is more likely to orient along the in-plane direction of the heat insulating sheet (the direction perpendicular to the double-headed arrow t in Figure 2), as shown in Figure 2. Therefore, the heat insulating properties can be improved compared to the case where the flake-like graphite is oriented in the thickness direction. The thickness of the insulation sheet will be the average of the thickness measured at 10 random locations. 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).

[0024] 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, cut out a thermal insulation sheet to form a 9mm x 9mm square in plan view. Next, cut the thermal insulation sheet in half so that its thickness is divided in half. Then, photograph one of the cut surfaces with a scanning electron microscope (SEM) and identify the flaky graphite exposed on the cut surface in a 3mm x 3mm area approximately in the center of the cut surface. Based on the outer diameter shape of each flake-shaped graphite particle, its area is determined, and then the diameter of the circle corresponding to that area is calculated from the obtained area and defined as the particle size of that flake-shaped graphite particle. Perform the same procedure for all flaky graphite exposed in a 3mm x 3mm area, and calculate the average value.

[0025] The flake-like graphite is preferably oriented along the in-plane direction of the heat insulating sheet. The in-plane direction of the heat insulating sheet is the direction perpendicular to the thickness direction of the heat insulating sheet. In the heat insulating sheet 10 shown in Figure 2, the flake-like graphite 20 is oriented along an in-plane direction 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 in-plane direction, it becomes easier to reflect heat emitted from the heating element, thereby improving the thermal insulation properties.

[0026] The ratio of the thickness of the insulating sheet to the average particle diameter of the flake graphite (thickness of the insulating sheet / average particle diameter of the flake graphite) is preferably 5 to 20, and more preferably 5 to 10.

[0027] The thickness of the insulation sheet is preferably 0.5 to 2.0 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 0.5 mm thick, it becomes more prone to damage. If the thickness of the insulation sheet exceeds 2.0 mm, it may become difficult to obtain the orientation of the flaky graphite described above, which can lead to a decrease in insulation properties.

[0028] The density of the insulation sheet is 0.15-0.28 g / cm³. 3 It is preferable that this be the case. The density of the insulation sheet is determined by cutting out a square from the sheet in the in-plane direction and calculating the apparent volume and weight from the cut-out outer shape (plan view shape and thickness). The same operation is performed at 10 randomly selected locations, and the average value is calculated to determine the density of the insulation sheet.

[0029] (Carbon fiber) The carbon fibers used to construct the insulation sheet can be pitch-based carbon fibers, PAN-based carbon fibers, or rayon-based carbon fibers, and either graphite-based or carbonaceous carbon fibers can be used.

[0030] The average fiber length of the carbon fibers is preferably 0.4 mm to 4.0 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.

[0031] 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.

[0032] 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.

[0033] (Scale-like graphite) The insulation sheet contains flaky graphite. Because flake graphite easily reflects heat emitted from a heating element, including flake graphite in an insulating sheet can improve its thermal insulation properties.

[0034] Scaly graphite is graphite that has a thin, scaly appearance. Specifically, flaky graphite with a thickness of 100 μm or less is defined as flake graphite.

[0035] Natural graphite can be used as the flaky graphite.

[0036] The average particle size of the flake graphite is preferably 15 to 400 μm. When the average particle size of the flake graphite is within the above range, the layering surface of the flake graphite in the insulating sheet is suppressed from being perpendicular to the sheet, and the flake graphite is more likely to be oriented in the in-plane direction of the insulating sheet.

[0037] The ratio of the volume of flake graphite to the volume of carbon contained in the heat insulating sheet (volume of flake graphite / volume of carbon) is preferably 5 to 25%. When the ratio of the volume of flake graphite to the volume of carbon contained in the insulation sheet is within the above range, it becomes easier to achieve both flexibility and thermal insulation properties in the insulation sheet.

[0038] The ratio of the volume of flake graphite to the volume of carbon contained in the insulating sheet is determined by embedding the insulating sheet in resin and then using a scanning electron microscope (SEM) to image the polished surface, which is polished in a direction perpendicular to the thickness direction. Subsequently, the area of ​​carbon in a specific field of view is determined from the image processing, and then, within the same field of view, the area occupied by flake graphite can be determined by identifying the area of ​​each flake graphite based on its outer diameter shape. By performing a similar operation at 10 randomly selected locations and calculating the average value, the ratio of the volume of flake graphite to the volume of carbon contained in the insulating sheet can be determined. Furthermore, flaky graphite and other carbon content can be distinguished by differences in their shape in SEM images, etc.

[0039] 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 insulation sheet contains not only carbon fibers and flake graphite, but also a carbonaceous binder.

[0040] Figure 3 is a schematic, enlarged cross-sectional view showing another example of an insulating sheet. In the heat insulating sheet 10 shown in Figure 3, 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 3). 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. The carbonaceous binder 40 is formed when the organic binder is carbonized by heating in a non-oxidizing atmosphere.

[0041] [Insulation material] The thermal insulation material of the present invention is characterized by being formed by laminating multiple thermal insulation sheets of the present invention.

[0042] The thermal insulation material of the present invention is made by laminating multiple thermal insulation sheets of the present invention, and therefore possesses excellent thermal insulation properties.

[0043] The external shape of the thermal insulation material of the present invention is not particularly limited and may be in the form of a plate or a cylinder. For example, if the outer shape of the insulation material is cylindrical, the insulation material may be constructed by winding and laminating insulation sheets. The number of winding layers at this time is not particularly limited, but it is preferably 15 to 300 layers.

[0044] The heat insulating sheet of the present invention may be used in combination with other heat insulating materials. For example, the thermal insulation sheet of the present invention may be placed along the inside of a cylindrical thermal insulation material. In this case, the number of layers of thermal insulation sheets is preferably 2 to 30.

[0045] [Method for manufacturing insulation sheets] The heat insulating sheet can be obtained, for example, by firing a precursor sheet containing carbon fibers and flaky graphite at approximately 2000°C in a non-oxidizing atmosphere.

[0046] The precursor sheet can be obtained, for example, by preparing a suspension in which carbon fibers and flake graphite are dispersed in a dispersion medium such as water, and then forming (papermaking) it into a sheet.

[0047] 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.

[0048] Non-oxidizing atmospheres include inert and reducing atmospheres.

[0049] An inert atmosphere is an atmosphere whose main component is an inert gas. Examples of inert gases include nitrogen and argon.

[0050] A reducing atmosphere is an atmosphere whose main component is a reducing gas. Examples of reducing gases include hydrogen, carbon monoxide, hydrocarbons, and chlorine.

[0051] Examples of organic binders that act as carbonaceous binders include phenolic resins, polyvinyl alcohol (PVA), and pitch.

[0052] 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.

[0053] The thickness of the precursor sheet is preferably 0.5 to 2.5 mm. If the thickness of the precursor sheet is within the above range, an insulating sheet with a thickness of 0.5 to 2.0 mm can be obtained.

[0054] By adjusting the average particle size of the flake graphite used and the thickness of the precursor sheet being manufactured, the ratio of the thickness of the insulating sheet to the average particle size of the flake graphite (thickness of the insulating sheet / average particle size of the flake graphite) is set to 5-20. It is preferable to use flake graphite with an average particle size of 15 to 400 μm.

[0055] [Method of manufacturing insulation material] The thermal insulation material of the present invention can be obtained by stacking multiple thermal insulation sheets obtained by the procedure described above. In this case, multiple insulation sheets may be prepared and laminated, or a single long insulation sheet may be rolled and laminated.

[0056] The layers of insulation sheets may be joined via an organic binder applied to the surface of the insulation sheets, or they may be joined by impregnating the insulation 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 insulation sheet.

[0057] Furthermore, the thermal insulation material of the present invention can be manufactured by firing a laminate obtained by stacking multiple precursor sheets, or a wound laminate, at approximately 2000°C in a non-oxidizing atmosphere. At this time, the layers of precursor sheets may be joined via an organic binder applied to the surface of the precursor sheets, similar to the thermal insulation material, or they may be joined by impregnating the precursor sheets with an organic binder.

[0058] This specification discloses the following:

[0059] This disclosure (1) is a thermal insulation sheet made of carbon fibers and flake graphite, The heat insulating sheet is characterized in that the ratio of the thickness of the heat insulating sheet to the average particle diameter of the flake-like graphite (thickness of the heat insulating sheet / average particle diameter of the flake-like graphite) is 5 to 20.

[0060] Disclosure (2) is the thermal insulation sheet described in Disclosure (1), having a thickness of 0.5 to 2.0 mm.

[0061] Disclosure (3) is the thermal insulation sheet according to Disclosure (1) or (2), wherein the average particle size of the flake graphite is 15 to 400 μm.

[0062] Disclosure (4) is an insulating sheet in any combination of Disclosure (1) to (3) wherein the ratio of the volume of flake graphite to the volume of carbon contained in the insulating sheet (volume of flake graphite / volume of carbon) is 5 to 25%.

[0063] Disclosure (5) is a thermal insulation material characterized by being made by laminating multiple thermal insulation sheets in any combination of any of Disclosures (1) to (4).

[0064] (Examples) The following are examples that more specifically disclose the present invention. However, the present invention is not limited to these examples.

[0065] (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.

[0066] Next, the obtained precursor sheet was heated to 2000°C under an inert atmosphere to carbonize the organic binder (phenol resin) contained in the precursor sheet, thereby obtaining the heat insulating sheet (thickness 0.9 mm) according to Example 1, in which carbon fibers and flake graphite were bonded together by a carbonaceous binder.

[0067] (Examples 2-3, Comparative Examples 1-2) Except for changing the average particle size of the flake graphite and / or the thickness of the insulation sheet as shown in Table 1, the insulation sheets for Examples 2-3 and Comparative Examples 1-2 were obtained using the same procedure as in Example 1. However, the thermal conductivity of the insulation sheet for Comparative Example 1 was not measured because tears were observed in the insulation sheet.

[0068] (Measurement of thermal conductivity) The thermal conductivity in the thickness direction at 2000°C was measured for each example and comparative example of the heat-insulating sheet using the laser flash method. The results are shown in Table 1.

[0069] [Table 1]

[0070] The results in Table 1 confirm that the thermal insulation properties are excellent when the ratio of the thickness of the thermal insulation sheet to the average particle diameter of flake graphite (thickness of thermal insulation sheet / average particle diameter of flake graphite) is between 5 and 20. On the other hand, as in Comparative Example 1, when flake graphite was added to a 0.3 mm thick insulation sheet with a thickness of 1.3 mm such that the ratio of the thickness of the insulation sheet to the average particle diameter of the flake graphite (thickness of the insulation sheet / average particle diameter of the flake graphite) was less than 5, the strength of the insulation sheet decreased, and it was not possible to manufacture the insulation material. [Explanation of Symbols]

[0071] 10 Insulation Sheets 20. Scaly graphite 30 carbon fiber 40 Carbonaceous binders Thickness of t0 insulation sheet

Claims

1. A heat insulating sheet made of carbon fiber and flake graphite, An insulating sheet characterized in that the ratio of the thickness of the insulating sheet to the average particle diameter of the flake-like graphite (thickness of the insulating sheet / average particle diameter of the flake-like graphite) is 5 to 20.

2. The heat insulating sheet according to claim 1, having a thickness of 0.5 to 2.0 mm.

3. The heat insulating sheet according to claim 1 or 2, wherein the average particle size of the flake-like graphite is 15 to 400 μm.

4. The heat insulating sheet according to claim 1 or 2, wherein the ratio of the volume of flake graphite to the volume of carbon contained in the heat insulating sheet (volume of flake graphite / volume of carbon) is 5 to 25%.

5. An insulating material characterized by being made by laminating a plurality of insulating sheets according to claim 1 or 2.

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