JP7426264B2 - Molded insulation material and its manufacturing method - Google Patents

Description

The present invention relates to a molded heat insulating material using carbon fibers and a method for manufacturing the same, and more particularly to a molded heat insulating material on which a surface layer is formed to improve durability and a method for manufacturing the same.

Carbon fiber-based heat insulating materials are used in a variety of applications because they have excellent thermal stability and heat insulation performance, and are lightweight. Such heat insulating materials include carbon fiber felt made by intertwining carbon fibers, and carbon fiber molded heat insulating material made by impregnating carbon fiber felt with a resin material and carbonizing it. Carbon fiber felt has the advantage of being excellent in flexibility, and carbon fiber molded heat insulating material has the advantage of having excellent shape stability and being capable of fine processing.

Which heat insulating material to use is appropriately selected depending on the purpose and application. The latter carbon fiber molded insulation material has excellent thermal stability, insulation performance, and shape stability, so it is used in single-crystal silicon pulling equipment, polycrystalline silicon casting furnaces, metal and ceramic sintering furnaces, and vacuum deposition furnaces. It is used as a heat insulating material for high-temperature furnaces such as

However, in equipment for manufacturing single crystal or polycrystalline silicon, SiO gas is generated in a high-temperature furnace, and oxygen gas is mixed into the manufacturing atmosphere as an impurity gas. SiO gas and oxygen gas have high activity (reactivity), and when carbon fiber molded insulation material and SiO gas react, SiC is produced, and when carbon fiber molded insulation material and oxygen gas react, carbon oxides (carbon monoxide, carbon dioxide, etc.) are generated. As a result, the carbon fibers in particular deteriorate, the skeletal structure constituted by the carbon fibers collapses, and the heat insulating effect obtained by the skeletal structure forming a large number of spaces is reduced. Further, due to this deterioration, there is a fear that the carbon fibers in particular are pulverized and released into the atmosphere in the furnace, reducing product quality.

Furthermore, in industrial furnaces, the pressure inside the furnace may be higher than atmospheric pressure. In such cases, the pressure difference causes a flow of atmospheric gas (nitrogen gas or argon gas) in the furnace, but if the highly active atmospheric gas penetrates into the internal space of the molded insulation, the internal structure of the molded insulation deteriorates. The insulation performance will deteriorate.

To address this problem, the present inventors have proposed a technique for forming a surface layer by sequentially forming a dense base layer and a surface coating layer on at least one surface of a molded heat insulating material (Patent Document 1 ).

JP2018-158874

According to this technology, it is possible to create a molded insulation material that can suppress gas penetration into the molded insulation material without sacrificing durability.

As a result of intensive research into molded heat insulating materials, the present inventor found that the following problem occurs when the technique of Patent Document 1 is used in a high-frequency induction heating type furnace.

When the surface resistivity of the surface layer is low, an induced current for high frequency induction heating is generated in the surface layer, thereby generating heat. As a result, the surface layer becomes hot, the heat insulating effect is reduced, the surface layer is more likely to deteriorate, and energy costs also increase due to the generation of unnecessary current. In the technique of Patent Document 1, the surface layer is a dense layer made of highly conductive carbon, so the surface resistivity is low, and it is not suitable for use in a high-frequency induction heating type furnace. Note that high-frequency induction heating generates heat by itself in a non-contact manner, so it has advantages such as high heating efficiency and good workability.

If no surface layer is provided, this problem will not occur because the induced current will hardly flow, but when applied to a high-frequency induction heating furnace, functions such as gas permeation blocking function and powder falling prevention function are required. There are many things.

The present invention was made to solve the above problems, and provides a molded insulation material that is suitable for use in a high-frequency induction heating type furnace and that can suppress gas penetration into the molded insulation material. The purpose is to provide.

The method for manufacturing the molded heat insulating material according to the present invention is as follows.
A molded heat insulating material having a carbon fiber felt in which carbon fibers are intertwined and a protective carbon layer made of carbonaceous material that covers the surface of the carbon fibers of the carbon fiber felt has a carbonaceous aggregate and a softening point on at least one surface thereof. an impregnating step in which the thermosetting resin particles are impregnated with a surface coating liquid dispersed in a dispersion medium in which the thermosetting resin particles are not dissolved, and after the impregnation step, heating to a temperature equal to or higher than the softening point. a softening step of softening the thermosetting resin particles and fixing the carbonaceous aggregate to the molded heat insulating material; and after the softening step, firing at 500° C. or higher to soften the thermosetting resin particles. A method for manufacturing a shaped heat insulating material, comprising: a carbonizing firing step.

If the molded insulation material has carbon fiber felt and a protective carbon layer made of carbonaceous material that covers the surface of the carbon fibers of the carbon fiber felt, there will be no possibility that the active material mixed in as impurities or generated in the furnace will be mixed around the molded insulation material. When a gas (oxygen gas, SiO gas, etc.) is present, the protective carbon layer covering the carbon fiber surface reacts with the active gas before the carbon fiber. This prevents the carbon fibers from reacting with the active gas and causing deterioration.

Here, when the protective carbon layer reacts with oxygen gas, the carbon forming the protective carbon layer becomes carbon dioxide gas and is removed, and when it reacts with SiO gas, it becomes SiC and remains without being removed. However, in either case, since the skeletal structure made of carbon fibers is maintained, the heat insulating effect obtained by the skeletal structure forming a large number of spaces is maintained.

In the present invention, a surface coating layer is formed on the surface of the molded heat insulating material. This layer is made of carbonaceous aggregate and thermosetting resin particles after the surface coating liquid, in which carbonaceous aggregate and thermosetting resin particles are dispersed in a dispersion medium that does not dissolve the thermosetting resin, penetrates into the molded insulation material. It is made by softening and then carbonizing it. Then, a portion of the voids between the carbon fibers of the molded heat insulating material are filled with the aggregate and the carbonized thermosetting resin, and the diameter of the path through which the gas passes becomes smaller. For this reason, gas intrusion into the inside of the molded heat insulating material is suppressed. Furthermore, the surface coating layer also acts to prevent powder from falling off from the molded heat insulating material.

Further, the surface coating liquid is in a state in which the thermosetting resin particles and the aggregate are dispersed without being dissolved, and the molded heat insulating material is impregnated with the thermosetting resin particles and the solid aggregate in an agglomerated state. Thereafter, when heated at a temperature equal to or higher than the softening point of the thermosetting resin particles, the thermosetting resin particles soften and deform. As a result, the thermosetting resin particles adhere and fix the aggregate to the carbon fibers that constitute the molded heat insulating material. Thereafter, when firing is performed, the softened thermosetting resin particles are carbonized without losing the aggregate fixing function. The surface coating layer formed in this manner becomes non-uniform due to agglomeration of particles, that is, it has many gaps in the surface direction. As a result, the surface resistance of the surface coating layer can be increased (lower conductivity), and when used in a high-frequency induction heating type furnace, induced current and induction heating in the surface coating layer can be reduced.

Note that if the softening step is not performed, the thermosetting resin particles will not have the effect of fixing and adhering the aggregate to the molded insulation material (a surface coating layer cannot be formed), so the softening step of the thermosetting resin particles will not be performed. is an essential step. Furthermore, if a solvent is used instead of a dispersion medium to dissolve the thermosetting resin particles, the thermosetting resin will spread uniformly throughout, reducing the surface resistance of the surface coating layer produced.

In other words, according to the manufacturing method of the present invention, while effectively suppressing the intrusion of gas into the inside of the molded heat insulating material, it is possible to make it difficult for induced current to flow (increase surface resistance). It is possible to realize molded insulation material suitable for

A known method can be used for impregnation with the surface coating liquid, such as a method in which the molded heat insulating material is immersed in a container containing the surface coating liquid, a method in which it is added using a spray or a brush, and the like. In order to facilitate impregnation, application may be performed while applying pressure.

The surface coating layer is formed on at least one surface of the molded heat insulating material, but may be formed on two or more surfaces. As the number of surfaces on which the surface coating layer is formed increases, the cost increases accordingly, so it may be determined as appropriate depending on the application of the molded heat insulating material, the arrangement of the heat source, etc.

The dispersion medium is not particularly limited as long as it does not dissolve the thermosetting resin, but it is preferably inexpensive and has a low boiling point. Among these, water that is inexpensive and has no environmental impact is more preferable, and water whose purity has been increased by ion exchange, distillation, etc. is even more preferable.

(thermosetting resin)
Here, in this specification, the mere "thermosetting resin" means the one before softening, the "after softening" means the one after softening and before thermosetting, and the one after thermosetting and before carbonization. Those that are carbonized are distinguished by adding words such as "after thermosetting" and those that are carbonized are "after carbonization."

Furthermore, the softening point refers to the temperature at which the resin begins to deform when the temperature of the resin is increased. Note that not all thermosetting resins have a softening point, and thermosetting resins that do not have a softening point (such as resins that have been treated to make them infusible) are not used in the present invention. Further, the softening point of the thermosetting resin can be, for example, a catalog value of a commercially available product, or can also be determined according to JIS K 5601-2-2.

Further, the catalog values for the softening points of commercially available thermosetting resins may not be at a single specific temperature, but may vary over a wide range. In this case, a temperature equal to or higher than the softening point means a temperature equal to or higher than its lower limit. The softening step is preferably performed at a temperature above the median value, more preferably above the upper limit.

Further, the thermosetting resin particles are not particularly limited as long as they have a softening point, and particles of phenol resin, furan resin, polyimide resin, epoxy resin, etc. can be used, and among them, phenol resin particles are preferable. Further, the average particle diameter of the thermosetting resin particles is preferably 3 to 100 μm, more preferably 5 to 70 μm, and even more preferably 10 to 40 μm. In addition, the average particle diameter can be set to the center particle diameter D50 determined by laser diffraction.

The softening point (if there is a range, its lower limit) of the thermosetting resin particles is preferably 140 to 90°C, more preferably 120 to 90°C, and even more preferably 100 to 90°C. preferable. If the softening point is too high, it is necessary to apply high temperature in the softening step, resulting in high costs. If the softening point is too low, the material will soften even during work at room temperature, reducing workability. Further, it is preferable that the thermosetting resin particles are softened and the dispersion medium is removed by volatilization in the softening step, and it is most preferable to use water as the dispersion medium and simultaneously perform the softening and volatilization of the water by heating at 100°C.

Further, the shape of the thermosetting resin particles is not particularly limited, and may be spherical, ellipsoidal, or other irregular shapes, or may be a mixture thereof.

Further, the residual carbon percentage (mass after firing/mass before firing x 100) of the thermosetting resin particles is preferably 30 to 70%, more preferably 40 to 70%, and 50 to 70%. It is even more preferable that there be.

(aggregate)
The shape of the aggregate used in the surface coating liquid is not particularly limited, and may be in the form of particles, milled (short fibers), or the like. Note that fibers with circular end faces (short fibers), fibers with an aspect ratio of 9 or more, etc. are not particulate.

Here, when the shape of the aggregate is particulate, such as spherical or elliptical, the effect of reducing the diameter of the gas path is greater than when the aggregate has a shape with a high aspect ratio, such as fibrous or acicular shape. . Preferably, the aggregate contains graphite particles and milled carbon fibers.

Moreover, in this specification, carbon means something in a broad sense, and may be amorphous (hardly graphitizable or easily graphitizable) or graphitic.

Further, when the aggregate contains particulate carbon such as graphite particles, the average particle size thereof is preferably 3 to 100 μm, more preferably 5 to 60 μm, and even more preferably 10 to 40 μm.

When milled carbon fibers are included in the aggregate, the average fiber diameter is preferably 5 to 30 μm, more preferably 6 to 20 μm, and still more preferably 7 to 18 μm. In addition, the average fiber length (length average fiber length) is such that the average particle diameter is preferably 0.04 to 0.8 mm, more preferably 0.1 to 0.6 mm, and still more preferably 0.2 to 0. The length shall be 5 mm. The length average fiber length Z _L is calculated as follows, where the individual fiber length is X _n , Z _L = (X ₁ ² +X ₂ ² +X ₃ ² +...+X _n ² )/(X ₁ +X ₂ +X ₃ + ...+X _n ).

(Surface coating liquid)
The mass ratio of carbonaceous aggregate to thermosetting resin particles in the surface coating liquid is preferably 30:70 to 80:20, more preferably 35:65 to 75:25, and 40:70 to 80:20. More preferably, the ratio is 60 to 70:30.

In the fired surface coating layer, the mass ratio of the carbonaceous aggregate to the carbonized material of the thermosetting resin particles is preferably 45:65 to 90:10, and preferably 50:50 to 85. :15 is more preferable, and even more preferably 55:45 to 80:20.

Further, the mass ratio of the solid content (aggregate + thermosetting resin particles) in the surface coating liquid to the total mass (aggregate + thermosetting resin particles + dispersion medium) is preferably 5 to 40% by mass. It is more preferably 10 to 35% by mass, and even more preferably 15 to 30% by mass.

(Softening step)
The softening step is preferably carried out in a temperature range of from the softening point of the thermosetting resin to the softening point +30°C, more preferably in the temperature range of the softening point to the softening point +20°C, and in the temperature range of the softening point to the softening point +10°C. It is more preferable to carry out the reaction within a temperature range. In view of the balance between cost and sufficient softening, it is preferable to carry out the process within the above temperature range.

Further, the heating time of the softening step is preferably 15 to 120 minutes, more preferably 15 to 60 minutes, and even more preferably 15 to 30 minutes. In view of the balance between cost and sufficient softening, it is preferable to carry out the heating within the above time range.

Further, the firing temperature in the surface coating layer forming step is preferably 1000 to 2500°C, more preferably 1500 to 2500°C, and even more preferably 2000 to 2500°C. The firing time is preferably 1 to 9 hours, more preferably 2 to 8 hours, and even more preferably 3 to 7 hours.

(molded insulation material)
The molded heat insulating material manufactured by the manufacturing method according to the present invention is as follows.
In a molded heat insulating material having a carbon fiber felt in which carbon fibers are intertwined and a protective carbon layer made of carbonaceous material that covers the carbon fiber surface of the carbon fiber felt, at least one surface of the molded heat insulating material has a carbonaceous material. It is characterized by having a surface coating layer in which the aggregate is fixed with a carbonized product of softened thermosetting resin particles.

The bulk density of the surface coating layer is preferably 0.1 to 2.0 g/cm ³ , more preferably 0.15 to 1.5 g/cm ³ , and more preferably 0.2 to 0.8 g/cm 3 More preferably, it is ³ .

In addition, the bulk density of the molded heat insulating material main body portion (the portion on which the surface coating layer is not formed) is preferably 0.07 to 0.3 g/cm ³ , and 0.13 to 0.3 g/cm ³ . It is more preferable that the amount is 0.16 to 0.3 g/cm ³ .

Further, the difference in bulk density between the surface coating layer and the main body of the molded heat insulating material is preferably 0.03 to 1.8 g/cm ³ , more preferably 0.1 to 1.0 g/cm ³ . It is more preferably 0.2 to 0.4 g/cm ³ .

The thickness of the surface coating layer (the thickness of the area impregnated with the surface coating liquid) is preferably 0.1 to 5 mm, more preferably 0.1 to 2 mm, and preferably 0.2 to 1 mm. More preferred.

As described above, according to the present invention, it is possible to realize a carbon fiber molded heat insulating material that can suppress gas penetration at low cost and is suitable for application to a high-frequency induction heating type furnace.

FIG. 1 is a scanning electron micrograph of a surface coating layer of a shaped heat insulating material according to Example 1, in which (a) shows before firing and (b) shows after firing. FIG. 2 is a scanning electron micrograph of the surface coating layer of the shaped heat insulating material according to Example 2, in which (a) shows before firing and (b) shows after firing. FIG. 3 is a scanning electron micrograph of the surface coating layer of the molded heat insulating material according to Comparative Example 1 before firing. FIG. 4 is a scanning electron micrograph of the surface coating layer of the molded heat insulating material according to Comparative Example 2, in which (a) shows before firing and (b) shows after firing. FIG. 5 is a scanning electron micrograph of the surface coating layer of the molded heat insulating material according to Comparative Example 3, in which (a) shows before firing and (b) shows after firing. FIG. 6 is a diagram schematically showing a method for measuring the surface resistivity of a surface coating layer. FIG. 7 is a diagram schematically showing a gas permeation test device.

(Embodiment)
A molded heat insulating material according to the present invention includes a carbon fiber felt in which carbon fibers are intertwined and a protective carbon layer made of carbonaceous material that covers the carbon fiber surface of the carbon fiber felt. One surface has a surface coating layer in which carbonaceous aggregate is fixed by carbonized material of softened thermosetting resin particles.

The carbon fibers constituting the molded heat insulating material are not particularly limited, and include, for example, anisotropic or isotropic pitch derived from coal or petroleum, polyacrylonitrile (PAN), rayon, phenol, and cellulose. A single type of carbon fiber or a mixture of multiple types can be used.

The microscopic structure of carbon fibers is not particularly limited, and only carbon fibers with the same shape (crimped type, straight type, diameter, length, etc.) may be used, or carbon fibers with different structures may be mixed. It's okay. However, the type of carbon fiber and its microscopic structure affect the physical properties of the molded heat insulating material produced, so it is best to select it appropriately depending on the application.

As for the microscopic structure of the molded heat insulating material, it is preferable to use one in which carbon fibers oriented in random directions intersect in a complicated manner.

Moreover, the shape of the molded heat insulating material is not particularly limited, and may be plate-shaped, rectangular parallelepiped, cylindrical, or the like. Further, the surface coating layer may be cut into a desired size after being formed, or the surface coating layer may be formed after being cut into a desired size.

The protective carbon layer is present so as to cover the entire surface of the carbon fiber, or a part of the surface of the carbon fiber, or to fill in the space between the carbon fibers. Further, the protective carbon layer only needs to be carbonaceous, and the compound from which it is derived is not particularly limited. Among these, it is preferable to use a carbonized resin material that can be impregnated into carbon fiber felt. As such resin materials, thermosetting resins such as phenol resins, furan resins, polyimide resins, and epoxy resins are preferred.

Here, only one type of thermosetting resin (material for the protective carbon layer) may be used in manufacturing the molded heat insulating material, or two or more types may be used in combination. Further, the thermosetting resin may be contained in the carbon fiber felt as it is, or may be diluted with a solvent and then contained in the carbon fiber felt. As the solvent, alcohols such as methyl alcohol and ethyl alcohol can be used.

In the configuration of this embodiment, a surface coating layer is provided on at least one surface of the molded heat insulating material, and the surface coating layer is arranged on the surface on the active gas source (heat source) side. , the permeation of active gas by airflow is suppressed. Furthermore, this layer also suppresses deterioration and powdering of carbon fibers. Therefore, a heat insulating effect can be obtained for a long period of time, and the life of the molded heat insulating material can be extended.

(Method for manufacturing surface coating layer)
The surface coating layer is formed on the shaped insulation material as follows.

(Impregnation step)
A surface coating liquid consisting of carbonaceous aggregate, thermosetting resin particles having a softening point, and a dispersion medium is applied to at least one surface of the molded insulation material, and the surface coating liquid is infiltrated into this area. let At this time, the molded heat insulating material may be applied under pressure. The dispersion medium may be any medium as long as it does not dissolve the thermosetting resin particles, but water is particularly preferred.

(Softening step)
Thereafter, the thermosetting resin particles are softened by heating to a temperature higher than the softening point, and the carbonaceous aggregate is fixed to the molded heat insulating material by the softened thermosetting resin particles. At this time, the dispersion medium may be removed by volatilization at the same time. In this case, a configuration is adopted in which the dispersion medium is heated to a temperature higher than its boiling point.

(Baking step)
After this, the thermosetting resin is carbonized by heat treatment at 500 to 2500°C in an inert atmosphere, and the carbonaceous aggregate is fixed to the molded insulation material during the softening step. The resin particles are carbonized. This forms a surface coating layer.

The surface coating layer formed in this manner suppresses the penetration of active gas, but has a high surface resistivity and does not allow induced current to flow easily. Therefore, it is suitable for insulating furnaces that use high-frequency induction heating.

Here, between the softening step and the firing step, a thermosetting step may be performed in which the thermosetting resin particles are heated to a temperature higher than the thermosetting temperature of the thermosetting resin particles.

Here, carbonization as used herein means a broad meaning including graphitization. For example, especially when heat-treated at a temperature of 2000°C or higher, the graphite structure of the surface coating layer may develop, but in the present invention, the aggregate of the surface coating layer may be either amorphous or graphitic. , or a mixture thereof.

The present invention will be explained in more detail based on examples.

(Example 1)
(Surface coating liquid preparation step)
Phenol resin particles (DIC Phenolite OI-305A, softening point 90-100°C, average particle size 15 μm), natural scaly graphite powder (Shin-etsu Kasei BF-30A/S, average particle size 30 μm), carbon fiber milled ( S-242 manufactured by Osaka Gas Chemicals, average fiber diameter 13 μm, average fiber length 0.36 mm, aspect ratio 28) was mixed at a mass ratio of 30:50:20 to form a mixed powder. This mixed powder and purified water were mixed at a mass ratio of 16:84, and the mixed powder was dispersed in the purified water to prepare a surface coating liquid.

(Impregnation step)
A cylindrical molded insulation material with an outer diameter of 220 mm x an inner diameter of 160 mm and a height of 400 mm, and a disc-shaped molded insulation material that serves as the upper and lower lids (DON-1000-H manufactured by Osaka Gas Chemicals, bulk density 0.16 g/cm) ³ ) The surface coating liquid was impregnated onto all surfaces (all surfaces located on the outside) using a brush so that the impregnation thickness was the same. The surface coating liquid was impregnated to an area of 0.3 mm from the surface of the molded heat insulating material.

(Softening step)
The molded insulation material impregnated with the surface coating solution was placed in an oven and heated in the atmosphere at 100° C. for 30 minutes to soften the phenolic resin particles and evaporate water.

(Baking step)
Thereafter, heat treatment was performed at 2000° C. for 5 hours in an inert atmosphere to carbonize the phenol resin particles, thereby producing a molded heat insulating material according to Example 1. The bulk density of the surface coating layer was 0.28 g/cm ³ .

(Example 2)
A molded heat insulating material according to Example 2 was produced in the same manner as in Example 1 above, except that the surface coating liquid preparation step and the softening step were performed as follows. The surface coating liquid was impregnated up to a region of 0.3 mm from the surface of the molded heat insulating material, and the bulk density of the surface coating layer was 0.31 g/cm ³ .

(Surface coating liquid preparation step)
Phenol resin particles (Bell Pearl S-899 manufactured by Air Water, softening point 110-120°C, average particle size 20 μm), natural scaly graphite powder (BF-30A/S manufactured by Shinetsu Kasei), milled carbon fiber (manufactured by Osaka Gas Chemicals) S-242) at a mass ratio of 55:38:7, and further mix this mixed powder and purified water at a mass ratio of 18:82, disperse the mixed powder in purified water, and coat the surface. A solution was prepared.

(Softening step)
The molded insulation material impregnated with the surface coating solution was placed in an oven and heated in the atmosphere at 120° C. for 30 minutes to soften the phenolic resin particles and evaporate water.

(Comparative example 1)
A molded heat insulating material according to Comparative Example 1 was produced in the same manner as in Example 2, except that the temperature in the softening step was 100°C. As a result, the adhesion of the aggregate was insufficient both after the softening step and after the firing step, and powder fell off due to impact etc., making it impossible to form a surface coating layer of sufficient quality.

(Comparative example 2)
A molded heat insulating material according to Comparative Example 2 was produced in the same manner as in Example 2 above, except that the surface coating liquid preparation step and the softening step were performed as follows. The surface coating liquid was impregnated up to a region of 0.6 mm from the surface of the molded heat insulating material, and the bulk density of the surface coating layer was 0.39 g/cm ³ .

(Surface coating liquid preparation step)
Phenol resin particles (Bell Pearl S-899 manufactured by Air Water), natural scaly graphite powder (BF-30A/S manufactured by Shinetsu Kasei), and milled carbon fiber (S-242 manufactured by Osaka Gas Chemicals) were mixed in a mass ratio of 55:38:7. A mixed powder was prepared by mixing at a ratio of . This mixed powder and methanol were mixed at a mass ratio of 18:82, and the phenol resin particles were dissolved in the methanol to prepare a surface coating solution.

(Softening step)
The molded heat insulating material impregnated with the surface coating solution was placed in an oven and dried in the atmosphere at 80° C. for 30 minutes to volatilize methanol contained in the solution.

(Comparative example 3)
A molded heat insulating material according to Comparative Example 3 was produced in the same manner as Comparative Example 2, except that the surface coating liquid production step was performed as follows. The surface coating liquid was impregnated up to a region of 0.4 mm from the surface of the molded heat insulating material, and the bulk density of the surface coating layer was 0.36 g/cm ³ .

(Surface coating liquid preparation step)
Phenol resin particles (PHENOLITE OI-305A manufactured by DIC), natural scaly graphite powder (BF-30A/S manufactured by Shinetsu Kasei), and milled carbon fiber (S-242 manufactured by Osaka Gas Chemicals) were mixed in a mass ratio of 30:50:20. A mixed powder was prepared by mixing at a ratio of . This mixed powder and methanol were mixed at a mass ratio of 16:84, and the phenol resin particles were dissolved in the methanol to prepare a surface coating solution.

(Microscope observation)
1 shows the surface coating layer of the molded insulation material according to Example 1, FIG. 2 shows the surface coating layer of the molded insulation material according to Example 2, FIG. 3 shows the surface coating layer of the molded insulation material according to Comparative Example 1, and FIG. 5 is a scanning electron micrograph of the surface coating layer of the molded heat insulating material according to Comparative Example 2, and FIG. indicates after firing. In addition, in Comparative Example 1, a scanning electron microscope photograph of the surface coating layer after firing was not taken because a lot of powder falling of the solid content of the surface coating layer occurred.

As can be seen from FIGS. 4(a) and 5(a), the thermosetting resin (before firing) 6 impregnated on the surface of the molded heat insulating material 1 in Comparative Examples 2 and 3 was dissolved in methanol and spread. Because it is made of acetate, it has a uniform film-like appearance throughout. Therefore, as shown in FIGS. 4(b) and 5(b), the thermosetting resin 7 maintains its film-like shape even after firing. Further, this film-like thermosetting resin fixes the aggregate 5 to the carbon fibers 4 that constitute the molded heat insulating material.

Further, as shown in FIG. 3, in Comparative Example 1, the thermosetting resin 6 did not soften before firing and maintained the shape of the particles. In Comparative Example 1 in which the thermosetting resin particles were not softened, the added aggregate and the like fell off due to impact before and after firing. That is, in the firing step, it is not possible to obtain the aggregate fixing effect of the thermosetting resin particles, and it is inappropriate to form the surface coating layer under conditions that do not soften the thermosetting resin particles.

On the other hand, in Examples 1 and 2, as shown in FIGS. 1(a) and 2(a), the thermosetting resin 6 and the aggregate 5 are in an aggregated state, and are unevenly distributed rather than uniformly. ing. Then, the thermosetting resin 6 does not maintain the particle shape before impregnation, but is in a softened and deformed state, and this softened and deformed thermosetting resin 6 causes bones in the carbon fibers 4 constituting the molded insulation material. Material 5 is fixed.

Then, as shown in FIGS. 1(b) and 2(b), the material is fired while maintaining almost the same state as before firing. That is, in the surface coating layer after firing, the thermosetting resin 7 after carbonization and the aggregate 5 are aggregated and unevenly distributed. Further, the thermosetting resin 7 is carbonized in a softened and deformed state, and this thermosetting resin 7 fixes the aggregate 5 to the carbon fibers 4 constituting the molded heat insulating material. The surface coating layer formed in this manner does not cause powder to fall off due to impact, and has many fine voids formed in areas where particles do not aggregate.

(Measurement of surface resistivity)
Regarding the molded heat insulating materials according to Example 1 and Comparative Example 2, as shown in FIG. ) was used to measure eight points each using the four-probe method, and the arithmetic mean value was determined.

As a result, the surface resistivity of the surface coating layer of Example 1 was 0.264Ω/□, which was 2.05 times higher than the surface resistivity of the surface coating layer of Comparative Example 2, which was 0.129Ω/□. In other words, it is considered that the voids in the surface coating layer of Example 1, which were considered through microscopic observation, increase the surface resistance value of the surface coating layer (lower the conductivity in the surface direction of the surface coating layer).

(power consumption)
Regarding the molded heat insulating materials according to Example 1 and Comparative Example 2, the power consumption when used in a high frequency induction heating furnace was measured.

The molded heat insulating material of Example 1 or Comparative Example 2 was installed in a high-frequency induction heating furnace manufactured by Takeuchi Electric Co., Ltd. After the atmosphere inside the furnace was replaced with argon, the oscillator output was set to 32% and operated. I let it happen. The temperature inside the furnace stabilized after about 30 minutes, and the power consumption at that time was recorded. Subsequently, power consumption at 50% and 65% oscillator output was measured using the same procedure.

As a result, as shown in Table 1 below, the power consumption when using the molded heat insulating material of Example 1 was 8 on average (arithmetic mean of 32%, 50%, and 65%) compared to Comparative Example 2. It had decreased by .5%.

These matters can be considered as follows. As mentioned above, in Comparative Example 2, the phenol resin was added to the molded heat insulating material in a state dissolved in methanol, so a surface coating layer of the carbonized phenol resin was obtained in the form of a film with few voids, as shown in Figure 4. It will be done. This film-like surface coating layer has particularly high conductivity (low surface resistance) in the in-plane direction.

On the other hand, in Example 1, the phenolic resin particles are not dissolved but are added to the molded heat insulating material in a dispersed state. Therefore, the phenol resin does not spread thinly over the entire area impregnated with the surface coating liquid, but is unevenly impregnated in a state where it aggregates with other particles. Through subsequent softening and firing, the phenol resin is carbonized while maintaining its softened shape. Therefore, as shown in FIG. 2, the aggregate aggregates locally, resulting in a surface coating layer that has an appearance with many voids. The surface coating layer with many voids has lower conductivity in the in-plane direction (higher surface resistance) than Comparative Example 2. Therefore, in Example 1, the amount of induced current flowing through the molded heat insulating material is smaller than in Comparative Example 2, resulting in lower power consumption.

Next, the gas permeability of the molded heat insulating materials according to Example 1 and Comparative Example 2 was measured under the following conditions.

(Gas permeation test)
As shown in FIG. 7, the gas permeation test apparatus 100 includes a cap-shaped container 41 placed on a flat plate-shaped table 42, thereby forming a primary space 20. A transmission cell 21 is provided in the primary space 20 . Further, a through hole is provided in the center of the stand 42, and the pipe 35 is connected to the through hole. The space below this table 42 is the secondary space 30. The gas permeation test device 100 also includes a pressure gauge 31 that measures the pressure in the primary space 20 and the secondary space 30.

In addition, an intake pipe 23 is provided to supply gas into the primary space 20, and exhaust pipes 25, 33 are connected to a rotary vacuum pump 34 and exhaust gas from the primary space 20 or the secondary space. is provided. Each of these tubes is provided with a valve 22, 24, 32.

The above molded heat insulating material was cut into a size of 6 cm in length, 6 cm in width, and about 2 cm in thickness to obtain a test piece 10, which was placed in the permeation cell 21 of the gas permeation test device 100. The circumference of this test piece 10 is sealed with silicone rubber 11 to prevent gas leakage, and O-rings 12 made of silicone rubber are installed on the upper and lower surfaces. Thereby, the gas inside the primary side space 20 cannot move to the secondary side space 30 unless it passes through the test piece 10 inside the permeation cell 21.

The measurements were carried out as follows. First, the valves 24 and 32 are opened, and the vacuum pump 34 reduces the pressure in the primary space 20 and the secondary space 30 until they reach a constant vacuum value. Then, the valves 24 and 32 are closed, and the operation of the vacuum pump 34 is stopped. Then, the valve 22 is opened to supply nitrogen gas to the primary space 20 at a constant gas pressure. The nitrogen gas passes through the test piece 10 from the primary space 20 and moves to the secondary space 30, and as a result, the pressure in the secondary space 30 begins to rise. The rate of pressure increase was measured using a pressure gauge 31. From this pressure increase rate, the gas permeability (K) was calculated using the following equations (3) and (4).

K=(Qh)/(ΔPA)...(3)
Q={(p ₂ -p ₁ )V ₀ }/t...(4)
Here, K is the nitrogen gas permeability, Q is the air flow rate, ΔP is the pressure difference between the primary side and the secondary side, A is the permeation area, h is the thickness of the test piece, _p1 is the initial pressure on the secondary side, p ₂ is the final pressure on the secondary side, V ₀ is the volume on the secondary side, and t is the measurement time.

At this time, the average pressure P _{m is approximately 50 to 110 kPa because the measurement is performed within the range of the average pressure P m (} average value of the pressure in the primary space and the secondary space) such that the following equation (5) holds true. Measurements were made within the following range. The gas permeability shown in Table 2 is the value when P _m =100 kPa on the approximate straight line by the least squares method when the gas permeability K is plotted at three or more points against the average pressure P _m .

K=aP _m +b...(5)
Here, a and b are constants.

As a result, it was found that in Example 1, the gas permeability was 800 cm ² /s (approximately 1.42 times) higher than in Comparative Example 2 (gas permeated easily). This is considered to be due to the fact that Comparative Example 2 has a larger bulk density of 0.11 g/cm ³ (approximately 1.39 times) and is twice as thick. However, the difference in gas permeability is about 1.42 times, which is not an order of magnitude difference, and it can be said that there is no big difference in gas permeation blocking performance if the difference in numerical values is of this order. Further, even with the same manufacturing method as in the example, gas permeability comparable to Comparative Example 2 can be obtained if the bulk density, thickness, etc. of the surface coating layer are appropriately set.

In addition, although the bulk density of the molded heat insulating material (main body portion) was set to 0.16 g/cm ³ in the above example, it is not limited to this value. However, since the bulk density affects the heat insulating performance of the molded heat insulating material to be manufactured, the bulk density etc. may be selected depending on the desired heat insulating performance.

As explained above, according to the present invention, it is possible to realize a molded heat insulating material that can suppress the deterioration of heat insulating performance due to gas and is suitable for application to high frequency induction heating type furnaces, so that it can be used in industrial applications. The possibilities are great.

1 Molded insulation material 3 Surface coating layer 4 Carbon fiber 5 Aggregate 6 Thermosetting resin before carbonization 7 Carbonized thermosetting resin 10 Test piece 11 Silicone rubber 12 O-ring 20 Primary space 21 Transmission cell 22 Valve 23 Intake pipe 24 Valve 25 Exhaust pipe 30 Secondary space 31 Pressure gauge 32 Valve 33 Exhaust pipe 34 Vacuum pump 35 Piping 41 Container 42 Unit 100 Gas permeation test device

Claims (5)

A molded heat insulating material having a carbon fiber felt in which carbon fibers are intertwined and a protective carbon layer made of carbonaceous material that covers the surface of the carbon fibers of the carbon fiber felt has a carbonaceous aggregate and a softening point on at least one surface thereof. an impregnation step of impregnating the thermosetting resin particles with a surface coating liquid dispersed in a dispersion medium in which the thermosetting resin particles are not dissolved;
After the impregnation step, heating is performed at a temperature above the softening point of the thermosetting resin particles and below the softening point +30° C. for 15 minutes or more to soften the thermosetting resin particles and form the carbonaceous aggregate. a softening step of securing the molded insulation to the molded insulation;
A method for manufacturing a shaped heat insulating material, comprising, after the softening step, a firing step of carbonizing the thermosetting resin particles by firing at 500° C. or higher. the dispersion medium is water,
The method for manufacturing a molded heat insulating material according to claim 1. The thermosetting resin particles are phenolic resin particles having an average particle diameter of 3 to 100 μm.
The method for manufacturing a shaped heat insulating material according to claim 1 or 2. The mass ratio of the carbonaceous aggregate and the thermosetting resin particles in the surface coating liquid is 30:70 to 80:20.
The method for producing a molded heat insulating material according to any one of claims 1 to 3. A molded heat insulating material comprising a carbon fiber felt in which carbon fibers are intertwined and a protective carbon layer made of carbonaceous material that covers the carbon fiber surface of the carbon fiber felt,
At least one surface of the molded heat insulating material has a surface having a bulk density of 0.1 to 2.0/cm ³ and is made of a carbonaceous aggregate fixed to a carbonized product of softened thermosetting resin particles. having a coating layer;
A molded insulation material characterized by:

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