WO2024117030A1

WO2024117030A1 - Heat insulating material, and method for producing heat insulating material

Info

Publication number: WO2024117030A1
Application number: PCT/JP2023/042142
Authority: WO
Inventors: 敏樹伊藤; 祐介太田; 健太野村; 伸藤井
Original assignee: イビデン株式会社
Priority date: 2022-11-29
Filing date: 2023-11-24
Publication date: 2024-06-06

Abstract

This heat insulating material comprises a molded body including a carbon fiber and a scale-like graphite, the heat insulating material being characterized in that the carbon fiber and the scale-like graphite are bonded via a carbonaceous binder, and the scale-like graphite is included in at least a half area in the thickness direction of the molded body.

Description

Insulation material and method for manufacturing the same

The present invention relates to an insulating material and a method for manufacturing an insulating material.

Insulation materials made from carbon fibers have a high heat resistance and excellent insulating properties, so they are widely used as insulation for high-temperature furnaces such as single crystal pulling equipment and ceramic sintering furnaces.

Insulating materials using carbon fibers are widely used in the form of highly porous felt, paper products, etc., to suppress heat transfer through the carbon fibers. Generally, felt is deformable, so it is used as a component that fills empty spaces to fill those spaces, or as an insulating material that surrounds other parts. On the other hand, paper products have high shape retention, so they are processed into a specified shape and used as insulating parts. Felt can also be used as an insulating part with good shape retention by compressing it and then fixing it with a binder.

Insulation materials that use carbon fibers can fall off due to oxidation in the furnace and mechanical friction, resulting in the generation of particles. Such defects can also cause a decrease in the insulation against radiation.

In order to solve these problems, Patent Document 1 discloses a composite carbonaceous insulation material having a carbonaceous insulation member with a bulk density of 0.1 to 0.4 g/cm ³ , a carbonaceous protective layer with a bulk density of 0.3 to 2.0 g/cm ³ , and a pyrolytic carbon coating having a bulk density greater than that of the carbonaceous protective layer, in which the carbonaceous insulation member and the carbonaceous protective layer are joined by a dense carbonaceous intermediate layer containing flake graphite, and the carbonaceous insulation member and the pyrolytic carbon coating are provided via a dense carbonaceous surface layer containing flake graphite, thereby suppressing wear, deterioration, and powdering of the carbon fibers during use and obtaining a composite carbonaceous insulation material with excellent heat insulating properties.

Patent Document 2 discloses that the surface of a carbon fiber molded insulation material is coated with a coating agent containing scaly graphite in order to improve the insulation properties, prevent carbon fiber powder from scattering, and prevent the penetration of gas generated from sintered metal.

JP 2000-327441 A JP 2005-133033 A

In both

Patent Documents

1 and 2, flake graphite is used for the purpose of densifying a part of the heat insulating material, such as the intermediate layer or the surface. However, since the densified part of the flake graphite is only the intermediate layer or only a part of the surface, it is not possible to sufficiently prevent radiative heat transfer. In addition, since it is dense, it is not possible to efficiently prevent conductive heat transfer.
Both

Patent Documents

1 and 2 focus on the densification effect of flake graphite, but do not particularly consider the heat insulating properties of flake graphite itself.

The present invention was made to solve the above problems, and the object of the present invention is to provide an insulating material that can exhibit excellent insulating properties against both radiative and conductive heat transfer.

The insulating material of the present invention is an insulating material consisting of a molded body containing carbon fiber and flake graphite, characterized in that the carbon fiber and the flake graphite are bonded together via a carbonaceous binder, and the flake graphite is contained in at least half of the area of the molded body in the thickness direction.

Flake graphite has a higher reflectance of synchrotron radiation than other carbon-based materials.
In the insulating material of the present invention, flake graphite is contained in an area of at least half of the thickness of the molded body, so that radiant light can be efficiently reflected and heat transfer due to radiation can be suppressed in the temperature range of 1,400°C or higher, thereby improving the insulating performance.
Furthermore, in the insulating material of the present invention, the flake graphite is not concentrated in a certain area, so the insulating material is not densified even in areas that contain flake graphite, thereby suppressing heat transfer by conduction and improving the insulating performance.

The proportion of the area of the molded body that contains flake graphite can be measured from a scanning electron microscope (SEM) photograph of the cross section of the molded body. Specifically, by looking at the SEM photograph of the cross section and distinguishing between areas that contain flake graphite and areas that do not contain flake graphite, and then scanning the molded body in the thickness direction, the length occupied by the area that contains flake graphite can be divided by the thickness of the molded body to determine whether it is contained in an area that is equal to or greater than half.

In the heat insulating material of the present invention, it is preferable that the area of the flake graphite occupies 5% or more of at least one surface of the molded body.
When the ratio of the area occupied by the flake graphite to the surface area of the molded body is 5% or more, the reflectance of radiant light can be further increased.
The above ratio can be obtained by specifying the area of the flake graphite from an SEM photograph of the surface of the thermal insulation material by image analysis and dividing it by the total area.

In the heat insulating material of the present invention, it is preferable that a coating layer, which is a layer containing carbon-based particles between the carbon fibers, is provided on the surface of the molded body.
The coating layer can improve the gas barrier properties of the thermal insulation material and can also suppress the generation of particles due to deterioration of the carbon fibers.

In the heat insulating material of the present invention, the carbon-based particles and the carbon fibers of the coating layer are preferably bonded to each other with a carbon-based adhesive.
When the carbon-based particles and carbon fibers constituting the coating layer are bonded to each other with a carbon-based adhesive, the coating layer becomes strong.

In the heat insulating material of the present invention, the carbon-based particles are preferably at least one carbon-based particle selected from the group consisting of graphite other than flake graphite, carbon black, glassy carbon particles, and particles obtained by pulverizing carbon fibers.
At least one carbon-based particle selected from the group consisting of graphite other than flake graphite, carbon black, glassy carbon particles, and particles obtained by pulverizing carbon fibers has a low impurity content and is made of the same carbon-based material as the carbon fibers that constitute the thermal insulation material, and therefore has high durability in high temperature ranges.

In the heat insulating material of the present invention, the carbon-based particles preferably have an average particle size of 10 nm to 500 μm.
When the average particle size of the carbon-based particles is 10 nm to 500 μm, a thin coating layer can be formed in the gaps between the carbon fibers, and the heat insulating material can ensure a high level of bonding with the carbon fibers. Also, the thickness of the coating layer, which tends to have a high thermal conductivity, can be prevented from becoming too thick.

In the heat insulating material of the present invention, the coating layer preferably has a thickness of 10 μm to 1000 μm.
When the thickness of the coating layer is 1000 μm or less, a decrease in the heat insulating performance can be suppressed.

In the heat insulating material of the present invention, the density of the molded body in the region containing the flake graphite is preferably 0.1 to 0.8 g/ ^cm3 .
By setting the density of the region containing flake graphite to 0.1 to 0.8 g/ ^cm3 , the heat insulating material is not densified even in the portion containing the flake graphite, and heat transfer by conduction is suppressed, thereby improving the heat insulating performance.

The first embodiment of the method for manufacturing a thermal insulation material of the present invention is characterized by including a molding step of obtaining a carbon fiber aggregate containing carbon fibers, flake graphite, and an organic binder, the flake graphite being contained in at least 1/2 of the thickness direction, and a joining step of carbonizing the organic binder contained in the carbon fiber aggregate and joining the carbon fibers and the flake graphite with a carbonaceous binder obtained by carbonizing the organic binder.

In the first embodiment of the method for producing a thermal insulation material of the present invention, the method for forming the carbon fiber aggregate in the forming step is preferably a method for making a paper from a solution containing the carbon fibers, the flake graphite, and the organic binder.

The second embodiment of the method for manufacturing a thermal insulation material of the present invention is characterized by including a flake graphite arrangement step of arranging flake graphite on at least one surface of an aggregate of carbon fibers, an organic binder addition step of adding an organic binder to the surface of the aggregate on which the flake graphite is placed, and a joining step of carbonizing the organic binder and joining the carbon fibers and the flake graphite with a carbonaceous binder obtained by carbonizing the organic binder.

FIG. 1 is a cross-sectional view showing a schematic example of a heat insulating material of the present invention. FIG. 2 is a partially enlarged view of the portion indicated by the dashed line in FIG. FIG. 3 is a view of the heat insulating material shown in FIG. 1 as viewed from a first main surface of the molded body. FIG. 4 is a cross-sectional view showing a schematic diagram of another example of the heat insulating material of the present invention.

The following is a detailed description of an embodiment of the present invention. However, the present invention is not limited to the following embodiment, and can be modified as appropriate within the scope of the present invention.

[Thermal insulation]
The insulating material of the present invention is an insulating material consisting of a molded body containing carbon fiber and flake graphite, wherein the carbon fiber and the flake graphite are bonded together via a carbonaceous binder, and the flake graphite is contained in an area of at least half of the molded body in the thickness direction.

The insulation material consists of a molded body containing carbon fiber and flake graphite.

(Carbon fiber)
The average fiber diameter of the carbon fibers constituting the molded body is preferably 1 μm to 20 μm.
When the average fiber diameter of the carbon fibers is 20 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 property is excellent and radiative heat transfer can be suppressed.

The average fiber length of the carbon fibers is preferably 2 mm to 10,000 mm.
The average fiber length of the carbon fibers may be 2 mm to 8 mm, or 10 mm to 10,000 mm.

The carbon fiber can be either pitch-based carbon fiber or PAN-based carbon fiber, and can be either graphitic or carbonaceous carbon fiber.

The molded article is preferably composed of a needle mat of carbon fiber or a paper-made article of carbon fiber.
The carbon fiber needle mat and carbon fiber paper article are composed of randomly arranged carbon fibers, and therefore can exhibit high thermal insulation properties, and are particularly suitable as molded articles that constitute thermal insulation materials.

When the molded body is composed of a needle mat of carbon fibers, the average fiber length of the carbon fibers is preferably 10 mm to 10,000 mm.
When the molded article is made of a carbon fiber paper body, the carbon fibers preferably have an average fiber length of 2 mm to 8 mm.

(flake graphite)
Flake graphite is graphite having a thin, scaly shape.
Specifically, flake-shaped graphite having a thickness of 100 μm or less is defined as flake graphite.
In the heat insulating material of the present invention, flake graphite is contained in a region of at least half of the molded body in the thickness direction.

Flake graphite has a higher reflectance of synchrotron radiation than other carbon-based materials.
The ratio of the region containing flake graphite in the thickness direction of the molded body can be determined by the following method.
First, the cut surface of the molded body cut in the thickness direction is photographed by an SEM.
Next, "flake graphite" is identified from the obtained SEM photograph (image), and regions containing flake graphite are distinguished from regions not containing flake graphite.
Then, assuming that the length of the region containing flake graphite in the thickness direction of the molded body is _T2 and the thickness of the molded body is _T1 , the proportion of the region containing flake graphite in the thickness direction of the molded body can be calculated by _T2 / _T1 .

In the heat insulating material of the present invention, the ratio of the region containing flake graphite in the thickness direction of the molded body is 1/2 or more.
The ratio of the area containing flake graphite in the thickness direction of the molded body is preferably 3/4 or more.

Natural graphite can be used as flake graphite.

The average particle size of the flake graphite is not particularly limited, but is preferably 2 to 500 μm.
When the average particle size of the flake graphite is 2 μm to 500 μm, the reflectance of radiated light is high, and the thermal conduction by the flake graphite can be suppressed.
The average particle size of the flake graphite can be measured by a sieve analysis method in accordance with "Industrial analysis and testing methods for natural graphite" described in JIS M 8511 (2014).

It is preferable that the flake graphite is exposed on at least one surface of the molded body.
The surface of the molded body on which the flake graphite is exposed has high properties of reflecting radiant light, so that the heat insulating performance in the temperature range of 1400° C. or higher can be further improved.

In the heat insulating material of the present invention, it is preferable that the area ratio of the flake graphite on at least one surface of the molded body is 5% or more.
When the area ratio of the flake graphite on at least one surface of the molded body is 5% or more, the reflectance of radiated light on that surface can be further increased.

The area ratio of flake graphite to the surface of the molded body can be determined by determining the area of flake graphite exposed on the surface of the molded body from an SEM photograph of the surface of the molded body using image analysis or the like, and dividing this by the total area.

The flake graphite in the molded body is preferably oriented in a direction parallel to the thickness direction of the molded body.
When the degree of orientation of the flake graphite in the molded body is within the above range, the effect of reflecting radiant light by the flake graphite becomes particularly strong, thereby further improving the heat insulating performance in the temperature range of 1400°C or higher.

(Carbonaceous binder)
The carbon fibers and the flake graphite are bonded together via a carbonaceous binder.

A carbonaceous binder is an organic binder that is carbonized by heating in a non-oxidizing atmosphere. Details will be given later.

(Molded body)
The shape of the molded body is not particularly limited, but examples thereof include a flat plate shape and a cylindrical shape.
The shape of the molded body may be appropriately determined in accordance with the shape of the object to be insulated.
The thickness of the molded body is not particularly limited, but is preferably 3 to 550 mm.

The bulk density of the molded body in the region containing the flake graphite is preferably 0.1 to 0.8 g/cm ³ .

(Covering layer)
The surface of the molded article may be provided with a coating layer.
The coating layer may cover a part of one surface of the molded body, or may cover the entirety of the one surface.

The coating layer may be provided only on the first main surface of the molded body, only on the second main surface, or on both the first and second main surfaces.

The coating layer is a layer that contains carbon-based particles between the carbon fibers.

The thickness of the coating layer is not particularly limited, but it is preferable that it be between 10 μm and 1000 μm.

The carbon fibers constituting the coating layer can be preferably the same as those constituting the molded body.

In the coating layer, the carbon fibers and the carbon-based particles are preferably bonded to each other with a carbon-based adhesive.
When the carbon fibers and the carbon-based particles are bonded to each other with a carbon-based adhesive, the coating layer becomes strong, and the gas barrier properties of the heat insulating material can be further improved.

Note that carbon-based adhesives are made by carbonizing an organic binder when it is heated in a non-oxidizing atmosphere. Details will be given later.

Note that carbon-based adhesives and carbonaceous binders are both made by carbonizing an organic binder when heated in a non-oxidizing atmosphere, and there is no substantial difference between them. However, they are distinguished for convenience because they are used to bond different objects.

The carbon-based particles are preferably at least one carbon-based particle selected from the group consisting of graphite other than flake graphite, carbon black, glassy carbon particles, and particles obtained by pulverizing carbon fibers.
In the following description, the term "carbon-based particles" does not include flake graphite.

The glassy carbon particles are obtained by pulverizing non-graphitizable carbon such as phenol resin carbide.
The particles obtained by pulverizing carbon fibers are also called milled carbon fibers. The average fiber length of the milled carbon fibers is preferably, for example, 20 μm to 500 μm.

The carbon-based particles preferably have an average particle size of 10 nm to 500 μm.
When the average particle size of the carbon-based particles is 10 nm to 500 μm, the carbon-based particles can easily penetrate into the gaps between the carbon fibers, and a thin coating layer can easily be formed.

Hereinafter, an example of the heat insulating material of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a schematic example of a heat insulating material of the present invention.

As shown in FIG. 1 , the thermal insulation material 1 includes a molded body 10 .
The molded body 10 has a flat plate shape having a first main surface 10a and a second main surface 10b opposed to each other in the thickness direction.
The molded body 10 is made of carbon fibers (not shown in FIG. 1) and flake graphite 20 .
The molded body 10 has regions 12 containing flake graphite 20 and regions 13 not containing flake graphite 20 .
The thickness of the region 12 containing the flake graphite 20 is a length indicated by _T2 in FIG.
The length _T2 of this region is 2/3 of the thickness _T1 of the molded body 10.
Therefore, it can be said that the heat insulating material 1 shown in FIG. 1 contains flake graphite 20 in an area of at least half of the molded body 10 in the thickness direction.

FIG. 2 is a partially enlarged view of the portion indicated by the dashed line in FIG.
As shown in FIG. 2 , in the region 12 containing the flake graphite 20 , the carbon fibers 30 and the flake graphite 20 are bonded to each other by a carbonaceous binder 40 .

FIG. 3 is a view of the heat insulating material shown in FIG. 1 as viewed from a first main surface of the molded body.
As shown in FIG. 3 , flake graphite 20 is exposed on the first main surface 10 a of the compact 10 .
The area ratio of the flake graphite 20 to the first main surface 10a can be obtained by dividing the area occupied by the flake graphite 20 shown in FIG. 3 by the area of the first main surface 10a in FIG.
When the area ratio of the flake graphite to the first main surface is 5% or more, the reflectance of radiated light can be further increased.

FIG. 4 is a cross-sectional view showing a schematic diagram of another example of the heat insulating material of the present invention.
The heat insulating material 2 shown in FIG. 4 has a molded body 10 and a coating layer 50 provided on a first main surface 10 a of the molded body 10 .
The coating layer can improve the gas barrier properties of the thermal insulation material and can also suppress the generation of particles due to deterioration of the carbon fibers.

[Method of manufacturing the heat insulating material]
A first embodiment of the method for manufacturing a thermal insulation material of the present invention is characterized by including a molding step of obtaining a carbon fiber aggregate containing carbon fibers, flake graphite, and an organic binder, the carbon fiber aggregate containing the flake graphite in at least half of a region in the thickness direction, and a joining step of carbonizing the organic binder contained in the carbon fiber aggregate and joining the carbon fibers and the flake graphite with a carbonaceous binder obtained by carbonizing the organic binder.

(Molding process)
In the molding step, a carbon fiber aggregate is obtained, which contains carbon fibers, flake graphite, and an organic binder, and in which the flake graphite is contained in at least half of the region in the thickness direction.
Examples of methods for obtaining the carbon fiber aggregate include a method of impregnating an aggregate of carbon fibers in a solution containing flake graphite and an organic binder, and a method of papermaking a solution containing carbon fibers, flake graphite, and an organic binder.

Among these, the method of papermaking from a solution containing carbon fiber, flake graphite, and an organic binder is preferred. That is, in the first embodiment of the method of manufacturing a thermal insulation material of the present invention, the method of forming the carbon fiber aggregate in the molding step is preferably a method of papermaking from a solution containing carbon fiber, flake graphite, and an organic binder.

In the method of papermaking a solution containing carbon fibers, flake graphite, and an organic binder, the solution containing carbon fibers, flake graphite, and an organic binder is poured into a specified mold, and the solvent (dispersion medium) is removed to obtain a carbon fiber aggregate containing carbon fibers, flake graphite, and an organic binder.
In the solution poured into the mold, the flake graphite is dispersed almost uniformly. When the solvent (dispersion medium) is removed from the solution, the flake graphite may move together with the solvent (dispersion medium), but as long as the solvent (dispersion medium) is removed by a normal method, the flake graphite does not move excessively, and the obtained carbon fiber aggregate contains the flake graphite in a region of 1/2 or more in the thickness direction.

(Joining process)
In the bonding step, the organic binder contained in the carbon fiber aggregate is carbonized, and the carbon fibers and the flake graphite are bonded together by the carbonaceous binder obtained by carbonizing the organic binder.

The heating conditions in the bonding step are not particularly limited, but it is preferable to heat at a temperature of 700 to 2100° C. in a non-oxidizing atmosphere for 1 to 12 hours.
The non-oxidizing atmosphere includes an inert atmosphere and a reducing atmosphere.

The inert atmosphere is an atmosphere containing an inert gas as a main component.
The inert gas includes nitrogen, argon, and the like.

The reducing atmosphere is an atmosphere containing a reducing gas as a main component.
The reducing gas includes hydrogen, carbon monoxide, hydrocarbons, chlorine, and the like.

Examples of organic binders include phenolic resin, polyvinyl alcohol (PVA), and pitch.

By going through the above steps, the heat insulating material of the present invention is obtained.
When it is desired to form a coating layer on the first main surface of the molded body, it is preferable to carry out the coating layer forming step described below.

(Covering layer forming process)
In the coating layer forming step, for example, a slurry containing at least carbon-based particles is applied onto the first main surface of the compact, and then fired to form the coating layer.
Through the above process, a coating layer made of the carbon fibers constituting the compact and the carbon-based particles contained in the slurry is formed on the first main surface of the compact.
The firing conditions are preferably the same as the heating conditions in the lower bonding step described above.
The slurry may also contain an organic binder.
When the slurry contains an organic binder, the organic binder becomes a carbon-based adhesive that bonds the carbon fibers and the carbon-based particles together upon firing, making the coating layer stronger.

The second embodiment of the method for manufacturing a thermal insulation material of the present invention is characterized by including a flake graphite arrangement step of arranging flake graphite on at least one surface of an aggregate of carbon fibers, an organic binder addition step of adding an organic binder to the surface of the aggregate on which the flake graphite is placed, and a joining step of carbonizing the organic binder and joining the carbon fibers and the flake graphite with the carbonaceous binder obtained by carbonizing the organic binder.

Examples of a method for preparing an aggregate of carbon fibers include a needling method and a papermaking method.
In the case of the needling method, for example, carbon fibers having an average fiber length of 10 mm to 10,000 mm are laminated in a sheet form, and the carbon fibers are entangled by needling to obtain an aggregate of carbon fibers.

In the case of the papermaking method, for example, a suspension is prepared in which carbon fibers with an average fiber length of 2 mm to 8 mm are dispersed in a dispersion medium such as water, and an aggregate made of carbon fibers can be obtained by papermaking using a mold.

In the case of the papermaking method, the suspension may contain an organic binder.
When the suspension contains an organic binder, the carbon fibers are fixed together during papermaking, improving moldability. In addition, the organic binder remains in the carbon fiber molded body and can bind the carbon fibers together, improving the handleability of the molded body at a stage prior to the joining process described below.

The organic binder that may be contained in the suspension may be the same as the organic binder that may be used in the joining process described below.

(Flake graphite arrangement process)
In the flake graphite arranging step, flake graphite is arranged on at least one surface of an aggregate of carbon fibers.
The amount of flake graphite to be arranged is preferably 5 to 60% by weight of the aggregate made of carbon fibers.

(Organic binder addition process)
In the organic binder adding step, an organic binder is added to the surface of the aggregate of carbon fibers having the flake graphite arranged thereon.
At this time, by using the organic binder in a state of dispersion (organic binder dispersion) in which the organic binder is dispersed in a solvent, the organic binder dispersion penetrates into the aggregate made of carbon fibers in the depth direction.
At this time, some of the flake graphite arranged on the surface of the carbon fiber aggregate penetrates into the carbon fiber aggregate in the depth direction together with the organic binder, resulting in a state in which the flake graphite is diffused in the carbon fiber aggregate in the depth direction.

The resulting flake graphite is arranged, and multiple carbon fiber aggregates with added organic binder are stacked together, resulting in a state in which flake graphite is contained in at least half of the area in the thickness direction.

(Joining process)
In the bonding step, the organic binder is carbonized by heating, and the carbon fibers and the flake graphite are bonded together by the carbonaceous binder obtained by carbonizing the organic binder.
By the above-mentioned flake graphite arranging step and organic binder adding step, the resulting molded body contains flake graphite in an area of at least half of the thickness direction.

Through the above steps, the heat insulating material of the present invention is obtained.
When it is desired to form a coating layer on the first main surface of the molded body, it is preferable to further carry out a coating layer forming step.
The coating layer forming step is the same as the coating layer forming step described in the first embodiment of the method for producing a thermal insulating material of the present invention.

The following items are disclosed in this specification:

The present disclosure (1) provides a thermal insulation material comprising a molded body containing carbon fiber and flake graphite,
The carbon fibers and the flake graphite are bonded to each other via a carbonaceous binder,
The heat insulating material is characterized in that the flake graphite is contained in an area of at least half of the molded body in the thickness direction.

The present disclosure (2) is an insulating material according to the present disclosure (1), in which the flake graphite occupies 5% or more of the area of at least one surface of the molded body.

The present disclosure (3) is the insulating material according to the present disclosure (1) or (2), in which a coating layer is provided on the surface of the molded body, the coating layer being a layer containing carbon-based particles between the carbon fibers.

The present disclosure (4) is the insulating material described in the present disclosure (3), in which the carbon-based particles and the carbon fibers of the coating layer are bonded to each other with a carbon-based adhesive.

The present disclosure (5) is the insulating material according to the present disclosure (3) or (4), in which the carbon-based particles are at least one carbon-based particle selected from the group consisting of graphite other than flake graphite, carbon black, glassy carbon particles, and particles of crushed carbon fibers.

The present disclosure (6) is an insulating material according to any one of the present disclosures (3) to (5), in which the carbon-based particles have an average particle size of 10 nm to 500 μm.

The present disclosure (7) is an insulating material according to any one of the present disclosures (3) to (6), in which the coating layer has a thickness of 10 μm to 1000 μm.

The present disclosure (8) is the insulating material according to any one of the present disclosures (1) to (7), wherein the density of the molded body in the region containing the flake graphite is 0.1 to 0.8 g/ ^cm3 .

The present disclosure (9) provides a molding process for obtaining a carbon fiber aggregate including carbon fibers, flake graphite, and an organic binder, the carbon fiber aggregate including the flake graphite in at least half of a region in a thickness direction;
and a bonding step of carbonizing the organic binder contained in the carbon fiber aggregate and bonding the carbon fibers and the flake graphite with a carbonaceous binder obtained by carbonizing the organic binder.

The present disclosure (10) is a method for producing a heat insulating material according to the present disclosure (9), in which the method for forming the carbon fiber aggregate in the forming step is a method for papermaking a solution containing the carbon fibers, the flake graphite, and the organic binder.

The present disclosure (11) provides a flake graphite arranging step of arranging flake graphite on at least one surface of an aggregate of carbon fibers;
an organic binder adding step of adding an organic binder to the surface of the assembly on which the flake graphite is placed;
and a bonding step of carbonizing the organic binder and bonding the carbon fibers and the flake graphite with a carbonaceous binder obtained by carbonizing the organic binder.

(Example)
EXAMPLES Hereinafter, examples that more specifically disclose the present invention will be described, however, the present invention is not limited to these examples.

Example 1
[Molding process]
A dispersion containing carbon fibers (average fiber diameter: 13 μm, average fiber length: 3.3 mm), flake graphite (average particle diameter: 100 μm), and an organic binder (phenolic resin) in a ratio of 100:40:20 (weight ratio, the organic binder is calculated as solid content) was molded by a papermaking method to obtain a sheet-like aggregate (thickness 3 mm) made of carbon fibers.

[Joining process]
This assembly was heated to 2000°C under an inert atmosphere to carbonize the organic binder (phenolic resin) contained in the molded body, thereby obtaining a carbon fiber molded body in which the carbon fibers and flake graphite were bonded together with a carbonaceous binder.

The obtained molded body was cut in the thickness direction, and the proportion of the area containing flake graphite was examined, which was found to be 100%.
The area ratio of the flake graphite to the surface of the molded body was determined to be 10.3% on one main surface (first main surface) and 9.4% on the other main surface (second main surface).

Example 2
A heat insulating material according to Example 2 was obtained in the same manner as in Example 1, except that the average particle size of the flake graphite was set to 400 μm and the dispersion was allowed to stand for 1 hour before being made into a sheet.
The obtained molded body was cut in the thickness direction, and the proportion of the area containing flake graphite was examined, which was 60%.
The area ratio of the flake graphite to the surface of the molded body was determined to be 16.8% on one main surface (first main surface) and 0% on the other main surface (second main surface).

(Comparative Example 1)
A thermal insulating material according to Comparative Example 1 was obtained in the same manner as in Example 1, except that flake graphite was not mixed in. The thermal insulating material according to Comparative Example 1 does not contain flake graphite.

(Comparative Example 2)
A dispersion containing carbon fibers (average fiber diameter: 13 μm, average fiber length: 3.3 mm) and an organic binder (phenol resin) in a ratio of 100:20 (weight ratio, the organic binder is calculated as solid content) was molded by a papermaking method to obtain a sheet-like aggregate (thickness 1 mm) made of carbon fibers.

[Flake graphite arrangement process]
Flake graphite (average particle size: 100 μm) was placed on one main surface of the sheet-like aggregate made of carbon fibers, with the weight of the placed flake graphite being 33% by weight of the sheet-like aggregate made of carbon fibers.

[Organic binder addition process]
Next, an organic binder dispersion liquid in which an organic binder (phenol resin) was dispersed in a solvent was added to the surface of the sheet-like aggregate made of carbon fibers having the flake graphite arranged thereon.

[Joining process]
Finally, three sheet-like aggregates made of carbon fibers were stacked and heated to 2000°C under an inert atmosphere to carbonize the organic binder (phenolic resin) contained in the molded body, thereby obtaining a carbon fiber molded body (thermal insulation material according to Comparative Example 2) in which the carbon fibers and flake graphite were bonded together with a carbonaceous binder.

The obtained molded body was cut in the thickness direction, and the proportion of the area containing flake graphite was examined, which was found to be 3%.
Furthermore, the area ratio of the flake graphite to the surface of the molded body was determined to be 30.8% on one main surface (first main surface) and 0% on the other main surface (second main surface).

[Insulation property evaluation]
The heat insulating properties of the heat insulating materials according to Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated in the following manner. The results are shown in Table 1.
Each heat insulating material was placed in an inert atmosphere at 2000° C., and the heat insulating properties were evaluated by the laser flash method. The heat insulating material of Comparative Example 1 was evaluated as having a thermal conductivity reduced by 20% or more, as a circle, as a reduction of 10% or more, and as a cross, as a reduction of less than 10%.

The results in Table 1 confirm that the insulating properties of the insulating materials of Examples 1 and 2 are superior to those of the insulating materials of Comparative Examples 1 and 2.

Reference Signs List 1, 2: Insulating material 10: Molded body 10a: First main surface 10b of molded body: Second main surface 12: Region containing flake graphite 13: Region not containing flake graphite 20: Flake graphite 30: Carbon fiber 40: Carbonaceous binder 50: Coating layer T _1: Thickness of molded body T _2: Length of region containing flake graphite

Claims

A thermal insulation material comprising a molded body containing carbon fiber and flake graphite,
The carbon fibers and the flake graphite are bonded to each other via a carbonaceous binder,
A heat insulating material, characterized in that the flake graphite is contained in an area of at least half of the molded body in the thickness direction.
The heat insulating material according to claim 1, wherein the flake graphite occupies 5% or more of the area of at least one surface of the molded body.
The heat insulating material according to claim 1 or 2, wherein a coating layer is provided on the surface of the molded body, the coating layer being a layer containing carbon-based particles between the carbon fibers.
The heat insulating material according to claim 3, wherein the carbon-based particles and the carbon fibers of the coating layer are bonded to each other with a carbon-based adhesive.
The heat insulating material according to claim 3 or 4, wherein the carbon-based particles are at least one carbon-based particle selected from the group consisting of graphite other than flake graphite, carbon black, glassy carbon particles, and particles of crushed carbon fibers.
The heat insulating material according to any one of claims 3 to 5, wherein the carbon-based particles have an average particle size of 10 nm to 500 μm.
The insulating material according to any one of claims 3 to 6, wherein the coating layer has a thickness of 10 μm to 1000 μm.
The heat insulating material according to any one of claims 1 to 7, wherein the density of the molded body in the region containing the flake graphite is 0.1 to 0.8 g/ cm3 .
a molding step of obtaining a carbon fiber aggregate containing carbon fibers, flake graphite, and an organic binder, the carbon fiber aggregate containing the flake graphite in at least half of a region in a thickness direction;
a bonding step of carbonizing the organic binder contained in the carbon fiber aggregate and bonding the carbon fibers and the flake graphite with a carbonaceous binder obtained by carbonizing the organic binder.
The method for producing a heat insulating material according to claim 9, wherein the method for forming the carbon fiber aggregate in the forming step is a method for producing a paper from a solution containing the carbon fibers, the flake graphite, and the organic binder.
a flake graphite arranging step of arranging flake graphite on at least one surface of an aggregate of carbon fibers;
an organic binder adding step of adding an organic binder to the surface of the assembly on which the flake graphite is placed;
a bonding step of carbonizing the organic binder and bonding the carbon fibers and the flake graphite with a carbonaceous binder obtained by carbonizing the organic binder.