JP6134606B2 - Method for producing molded heat insulating material and molded heat insulating material - Google Patents

Description

  The present invention relates to a molded heat insulating material used for a high temperature electric furnace and the like, and a manufacturing method thereof.

A molded heat insulating material obtained using carbon fiber as a material has high purity without containing metal, is excellent in thermal stability, is self-supporting, and is lightweight. Therefore, it is used in various high-temperature electric furnaces such as single crystal silicon pulling furnace, polycrystalline silicon growth furnace, sapphire single crystal pulling furnace, silicon carbide single crystal pulling furnace, metal and ceramic sintering furnace, vacuum evaporation furnace, etc. Yes.
In particular, recently, demands for energy saving and cost reduction have further increased, and a molded heat insulating material having lower thermal conductivity and excellent heat insulating performance has been demanded. Using a molded heat insulating material having excellent heat insulating performance can reduce the volume of the molded heat insulating material necessary for obtaining a predetermined heat insulating performance as well as reducing the amount of power used. Therefore, it contributes to cost reduction also from the point that the inside of a furnace can be used widely widely.

  In order to obtain a molded heat insulating material having excellent heat insulating performance, for example, it is conceivable to increase the bulk density of the formed heat insulating material by increasing the amount per unit volume of the carbon fiber responsible for the heat insulating performance. However, increasing the bulk density leads to an increase in the cost of the molded heat insulating material. In addition, since the molded heat insulating material having a large bulk density has a large heat capacity itself, the total heat capacity is increased in the furnace in which the molded heat insulating material having a high bulk density is arranged, and the amount of electric power used increases.

  Patent Document 1 describes a heat insulating material made of carbon fiber felt (needling felt) as a molded heat insulating material having a low bulk density. The carbon fiber felt is generally called a needling felt and is obtained by entanglement of carbon fibers by a needle punch. Patent Document 1 discloses a heat insulating material obtained by laminating a resin-impregnated carbon fiber felt obtained by impregnating or coating a carbon fiber felt with a resin binder and a carbon fiber felt not provided with a resin binder, compression molding, and firing. It is disclosed.

JP 2008-196552 A

  However, according to the study by the present inventors, the heat insulating material obtained by the method disclosed in Patent Document 1 has not had sufficient heat insulating performance.

  An object of the present invention is to provide a molded heat insulating material having a small bulk density and excellent heat insulating performance and a method for producing the same.

The method for producing a molded heat insulating material according to the present invention includes a defibrating step of defibrating a carbon fiber aggregate composed of a large number of carbon fibers, and a fiber obtained by mixing heat-fusible fibers with the defibrated carbon fibers. A web forming process for forming an airlaid web from the mixture, a fiber bonding process for treating the airlaid web with hot air to bond the carbon fibers in the airlaid web with the heat-fusible fibers, and a fiber bonding process. An impregnation step of impregnating 5 to 30 parts by mass of a thermosetting resin with respect to 100 parts by mass of the carbon fiber non-woven fabric for heat insulating material precursor, and a curing step of curing the prepreg to obtain a cured product And a firing step of firing the cured product.
The carbon fiber aggregate is preferably an aggregate of pitch-based isotropic carbon fibers.
The fiber length of the carbon fiber in the fiber mixture is preferably 1 to 10 mm.
The proportion of the heat-fusible fiber in the fiber mixture is preferably 1 to 30% by mass.
The basis weight of the carbon fiber non-woven fabric for heat insulating material precursor is preferably 200-1500 g / m ² .
The molded heat insulating material of the present invention is a carbonized material produced using a carbon fiber nonwoven fabric for a heat insulating material precursor formed from an air laid web containing carbon fibers and a resin, and has a bulk density of 0.10 to 0.15 g. / Cm ³ .

  In this specification, the bulk density is the volume (length × width × thickness) calculated from the measured values of the length, width, and thickness of the molded heat insulating material. Divided by and obtained.

  According to the present invention, it is possible to provide a molded heat insulating material having a small bulk density and excellent heat insulating performance, and a method for producing the same.

It is a schematic perspective view which shows the shaping | molding heat insulating material of Example 1 typically. 2 is a scanning electron micrograph of the molded heat insulating material of Example 1. FIG. It is a graph which shows the heat conductivity of the shaping | molding heat insulating material of Example 1 and Comparative Examples 1 and 2. It is explanatory drawing explaining the method to measure thermal conductivity.

Hereinafter, the present invention will be described in detail.
The method for producing a molded heat insulating material according to the present invention includes a defibrating step of defibrating a carbon fiber aggregate composed of a large number of carbon fibers, and a fiber obtained by mixing heat-fusible fibers with the defibrated carbon fibers. A web forming step for forming an airlaid web from the mixture, a fiber bonding step for bonding the carbon fibers in the airlaid web with fusible fibers by hot air treatment, and a heat insulating material obtained by the fiber bonding step Carbon fiber nonwoven fabric for precursor (hereinafter sometimes simply referred to as carbon fiber nonwoven fabric) 100 parts by mass is impregnated with 5 to 30 parts by mass of a thermosetting resin to form a prepreg, and the prepreg is cured. And a curing step for obtaining a cured product and a firing step for firing the cured product.

(Defibration process)
In the defibrating process, a carbon fiber aggregate composed of a large number of carbon fibers is defibrated.
Here, the carbon fiber aggregate is an aggregate in which a large number of carbon fibers are physically entangled. For example, a mat (cotton-like material) obtained by capturing (collecting) the fibers after spinning together and firing them. ); A chop obtained by cutting the mat; a needling felt obtained by subjecting the mat to needle punching; and the like. These carbon fiber aggregates may be used alone or in combination of two or more.

As the needling felt, an end material of the needling felt can be preferably used.
The end material of the needling felt is an unnecessary end portion cut off from the needling felt in the trimming process, and is difficult to be reused as the needling felt material. Therefore, the end material of needling felt is generally disposed of as industrial waste. According to the manufacturing method of the present invention, a molded heat insulating material can be manufactured without any problems even if it is an end material of a needling felt that has been conventionally discarded.

Examples of carbon fibers constituting the carbon fiber aggregate include polyacrylonitrile (PAN), pitch (isotropic and anisotropic), phenol resin, rayon, cellulose, and polyvinyl alcohol (PVA). Of carbon fiber. Although the carbon fiber aggregate should just be comprised from 1 or more types of these carbon fibers, the thing containing pitch type isotropic carbon fiber is preferable from points, such as the heat conductivity of carbon fiber itself being small.
The carbon fiber constituting the carbon fiber aggregate may be either a curved line having crimps or a straight line having no crimps. For example, when the carbon fiber aggregate is a needling felt or an end material of a needling felt, the carbon fibers constituting them often have crimps from the viewpoint of easy entanglement.

There is no restriction | limiting in particular in the fiber length of the carbon fiber which comprises a carbon fiber aggregate, The fiber length according to the form of the carbon fiber aggregate may be sufficient. In the case of mat, needling felt, end material of needling felt, etc., the fiber length of carbon fiber is, for example, 10 to 100 mm, and in the case of chop, the fiber length of carbon fiber is, for example, 2 to 10 mm.
Although there is no restriction | limiting in particular also about the fiber diameter of the carbon fiber which comprises a carbon fiber aggregate | assembly, For example, if it is the range of 8-18 micrometers, it will be easy to form an air-laid web and it is preferable at the point of heat insulation performance. When the thickness is less than 8 μm, the mechanical strength of the carbon fiber such as delamination strength is weakened, and it tends to be difficult to form an airlaid web. When it exceeds 18 μm, the heat insulation performance tends to be lowered.

In this specification, the fiber length means a weighted average fiber length of the fiber lengths measured using an image analyzer for 200 fibers.
Moreover, a fiber diameter means the weighted average fiber diameter of the fiber diameter measured about 200 fibers using the magnifier.

  As a method of defibrating the carbon fiber aggregate, any method can be used as long as the carbon fiber aggregate can be defibrated to the extent that an air-laid web can be formed in the web forming process described later, and it is adopted according to the form of the carbon fiber aggregate. it can. Specifically, a defibrating method using a sample roller card machine, a blower or the like can be mentioned. Depending on the defibration method, at least some of the many carbon fibers constituting the carbon fiber aggregate may be broken or cut to shorten the fiber length. There is no problem because the airlaid method is employed, which enables the web to be formed satisfactorily even if the fiber length is relatively short. Further, before the defibrating step or between the defibrating step and the web forming step, a cutting step for cutting the carbon fiber aggregate or the defibrated carbon fiber may be performed as necessary. .

(Web forming process and fiber bonding process)
In the web forming step, an airlaid web is prepared by an airlaid method using a fiber mixture obtained by mixing heat-fusible fibers with defibrated carbon fibers. The airlaid method is a method for forming a web in which fibers are randomly laminated three-dimensionally using an air flow. Therefore, according to the airlaid method, a good web can be formed from fibers having a relatively short fiber length. 1-10 mm is preferable and, as for the fiber length of the carbon fiber in a fiber mixture, 2-6 mm is more preferable. If the fiber length of the carbon fiber in the fiber mixture is in such a range, it is easy to form an airlaid web in the web forming step.

The heat-fusible fiber functions as a binder for bonding at least a part of the melted carbon fiber and bonding the defibrated carbon fiber by hot air treatment in a fiber bonding step described later.
Such heat-fusible fibers include a core-sheath type heat-fusible composite fiber obtained by combining two types of resins having different melting points and melting only the surface of the fiber. The heat-fusible conjugate fiber having a core-sheath structure has a structure in which a sheath made of a resin having a low melting point is formed on the outer periphery of a core made of a resin having a high melting point. For example, polypropylene fiber (melting point 160 ° C.) There is a PE / PP composite fiber in which a sheath made of polyethylene (melting point: 130 ° C.) is formed on the outer periphery of the core made of.
When using a heat-sealable composite fiber having such a core-sheath structure, hot air treatment is performed in the fiber bonding process at a temperature at which the sheath melts and the core does not melt (for example, 140 ° C.), and only the sheath is melted. Let

Other examples of the heat-fusible conjugate fiber include PET / PET conjugate fiber, PE / PE conjugate fiber, PP / PP conjugate fiber, PE / PET conjugate fiber, PP / PET conjugate fiber, and PE / PP conjugate fiber. is there. Two or more kinds of heat-fusible conjugate fibers may be used in combination.
PET means polyethylene terephthalate, PE means polyethylene, and PP means polypropylene.

The fiber length of the heat-fusible fiber is preferably 1 to 10 mm, and more preferably 2 to 6 mm. With such a fiber length, it is easy to form an airlaid web.
If the fineness of the heat-fusible fiber is, for example, in the range of 1 to 30 dtex, it is preferable in terms of mixing with carbon fibers and binding properties.

The proportion of the heat-fusible fiber in the fiber mixture is preferably 1 to 30% by mass and more preferably 5 to 20% by mass in 100% by mass of the fiber mixture. When it is at least the lower limit of the above range, the carbon fibers can be sufficiently bonded together in the fiber bonding step.
If it is not more than the upper limit of the above range, the bulk density of the molded heat insulating material finally obtained will be within an appropriate range.

  In the web forming process, for example, by using an airlaid web forming machine, the defibrated carbon fiber and the heat-fusible fiber are uniformly mixed in the air to prepare a fiber mixture, and a suction box is provided. The fiber mixture is lowered along with the intake air flow toward the mesh-like endless belt that is mounted on the conveyor and travels. An airlaid web can be formed by dropping and depositing the fiber mixture on the belt. In this case, on the mesh endless belt, first, the first air-permeable carrier sheet is drawn out, and the air-laid web is formed on the first air-permeable carrier sheet as described above. From the viewpoint of stably performing the fiber bonding step described later, it is preferable to laminate the second air-permeable carrier sheet to form a three-layer web laminate.

In the fiber bonding step, hot air treatment is performed on the air-laid web formed in the web forming step, and the carbon fibers in the air-laid web are bonded by heat-fusible fibers. When the air laid web forms a three-layer web laminate having a breathable carrier sheet on both sides as described above, the hot air treatment is performed on the web laminate, What is necessary is just to peel a breathable carrier sheet.
By such a method, the carbon fiber nonwoven fabric for heat insulating material precursors is obtained.

As hot air treatment, the air laid web is passed through a through air dryer having a rotating drum having air permeability on the peripheral surface and heat treated (hot air circulating rotary drum method), or the air laid web is passed through a box type dryer, and the air laid web And a method of heat treatment by passing hot air through (hot air circulation conveyor oven method).
In addition, you may perform a hot press process for the purpose of fine-tuning the density of a carbon fiber nonwoven fabric after a fiber bonding process.

Thus the basis weight of the carbon fiber nonwoven fabric produced by is preferably in the range of 40~3000g / ^{m 2,} the range of 200~1500g / ^{m 2} is more preferable. When the basis weight is in such a range, a carbon fiber nonwoven fabric having an appropriate thickness as a heat insulating material precursor can be obtained. For example, if it is a carbon fiber nonwoven fabric having a basis weight of 200 to 1500 g / m ² , the thickness is preferably 9 to 45 mm. If the thickness is out of the above range, in the impregnation step described later, when the thermosetting resin cannot be uniformly impregnated, or the removal of the solvent from the thermosetting resin after the impregnation becomes uneven, making it difficult to form a prepreg. There is a case.
The basis weight of the carbon fiber non-woven fabric is determined by controlling the feed rate of carbon fiber and heat-fusible fiber and controlling the speed (mechanism speed) of the mesh endless belt when forming the air laid web. It can control by the method of adjusting the supply amount of the surrounding carbon fiber and heat-fusible fiber.

  Such a carbon fiber nonwoven fabric preferably has a tensile strength of 10 N / 50 mm or more and a breaking elongation of 5% or more. If the tensile strength and elongation at break do not satisfy the above ranges, the prepreg tends to break when the prepreg is produced.

  The molded heat insulating material of the present invention is preferably formed by impregnating a carbon fiber nonwoven fabric produced as described above with a thermosetting resin to form a prepreg (impregnation step), and then curing the prepreg to obtain a cured product ( It can be manufactured by firing the cured product) and firing the cured product (firing step).

(Impregnation process)
Examples of the thermosetting resin used in the impregnation process include an epoxy resin, a phenol resin, a vinyl ester resin, an unsaturated polyester resin, a thermosetting acrylic resin, a polyurethane resin, and a polyimide resin. Can be used. The use of a thermosetting resin as the resin is preferable in terms of workability and carbonization yield, and phenol resin is particularly preferable. The thermosetting resin is preferably used in the form of a solution dissolved in a solvent. As a solvent, although it changes with kinds of thermosetting resin, alcohol, such as methyl alcohol, ethyl alcohol, and denatured alcohol, water, etc. are mentioned. In that case, the non-volatile content concentration (solid content concentration) of the solution in which the thermosetting resin is dissolved varies depending on the type of the resin, but is preferably 30 to 80% by mass, and more preferably 40 to 70% by mass. If the nonvolatile content concentration is too large, the viscosity becomes too high and impregnation tends to be difficult. If the non-volatile concentration is too small, it takes time to remove the solvent.
The impregnation amount of the thermosetting resin is preferably 5 to 30 parts by mass, more preferably 5 to 15 parts by mass, further preferably 10 to 15 parts by mass, and 12 to 15 parts by mass with respect to 100 parts by mass of the carbon fiber nonwoven fabric. Is particularly preferred. If the amount of impregnation is less than the lower limit of the above range, the mechanical strength of the molded heat insulating material is lowered, which causes a problem in practical use. When the upper limit of the above range is exceeded, the bulk density of the molded heat insulating material becomes too high. When the bulk density is too high, the cost of the molded heat insulating material is increased. In addition, since the molded heat insulating material having a large bulk density has a large heat capacity itself, the total heat capacity is increased in the furnace in which the molded heat insulating material having a high bulk density is arranged, and the amount of electric power used increases. Furthermore, when the amount of impregnation exceeds the upper limit of the above range, the amount of carbon fiber is relatively reduced, and the heat insulating performance of the molded heat insulating material is lowered.

(Curing process and firing process)
In the curing step, a prepreg obtained by impregnating a carbon fiber nonwoven fabric with a thermosetting resin is heated and cured.
When the shape of the molded heat insulating material to be manufactured is a flat plate shape, a plurality of prepregs cut to a predetermined length (for example, 500 to 2000 mm) are prepared, and these are stacked to form a laminate. Next, the obtained laminate is compressed to a predetermined thickness (for example, 10 to 80 mm) using, for example, a press machine provided with two pressing plates, and heated and heated in this state to perform molding and curing. A flat cured product is obtained. The compression conditions, heating temperature, heating time, and the like can be appropriately set according to the thickness, bulk density, type of impregnated thermosetting resin, and the like.

  When the shape of the molded heat insulating material to be manufactured is a cylindrical shape, it is formed into a cylindrical shape by, for example, winding a prepreg while applying a predetermined force to a metal shaft (columnar shape) using a winder. To do. Next, this molded body is held in an electric furnace and heated to perform molding and curing to obtain a cylindrical cured product. The heating temperature, the heating time, and the like can be appropriately set according to the size, bulk density, type of the thermosetting resin impregnated, and the like.

In the firing step, a molded heat insulating material is obtained by heating and firing the cured product obtained in the curing step under an inert gas atmosphere such as helium, nitrogen, or argon or under vacuum conditions. A baking process is a process of carbonizing hardened | cured material. The heating temperature (maximum temperature) in the firing step is, for example, 1500 to 2500 ° C., and the maximum temperature holding time for holding at the maximum temperature is 0.5 to 5 hours.
Here, carbonization includes graphitization. In general, in the case of carbonization, there are cases where it refers to carbonization in a narrow sense that does not include graphitization, and carbonization in a broad sense that also includes graphitization, but carbonization in this specification refers to carbonization in a broad sense. Means.

The molded heat insulating material manufactured in this way consists of a carbonized material manufactured using a carbon fiber nonwoven fabric for heat insulating material precursor formed from an airlaid web containing carbon fibers and a resin, and has a bulk density of 0.10. It is as small as ˜0.15 g / cm ³ and has excellent heat insulation performance. For example, the thermal conductivity measured at a sample average temperature of 1400 ° C. in a nitrogen gas atmosphere with an absolute pressure of 1 atm (101 kPa) by a steady method is about 0.2 to 0.38 [W / m · K].
Molded insulation with excellent heat insulation performance can reduce power consumption when used in high-temperature electric furnaces, etc., as well as the volume of molded insulation necessary to obtain the prescribed heat insulation performance can be reduced. Can be used widely and effectively. In addition, since the bulk density is small, the cost is low and the heat capacity of itself is small, so that the total heat capacity in the furnace in which the molded heat insulating material is arranged can be suppressed to a small amount, and the amount of power used can be reduced from that point. Therefore, the molded heat insulating material of the present invention is extremely useful from the viewpoint of energy saving and cost reduction.
In addition, the measurement of the thermal conductivity by a steady method cuts out a disk-shaped sample from the shaping | molding heat insulating material to be measured, and measures using this sample, as described in the following Example.

The reason why the heat insulating performance of the molded heat insulating material of the present invention is excellent is considered to be that the molded heat insulating material of the present invention is obtained using a carbon fiber nonwoven fabric formed from an air laid web as a material.
That is, the air laid web is formed by lowering a fiber mixture of defibrated carbon fibers and heat-fusible fibers. Therefore, most of the carbon fibers in the air laid web are selectively arranged almost perpendicularly to the web thickness direction (heat insulation direction), and there are almost no carbon fibers arranged in parallel to the web thickness direction. The carbon fibers arranged in parallel with the web in the thickness direction cause a decrease in heat insulation performance, as will be described in detail in the examples described later. Therefore, the molded heat insulating material of the present invention having almost no carbon fibers arranged in parallel to the heat insulating direction is considered to have excellent heat insulating performance.

  The molded heat insulating material of the present invention can be applied to various high-temperature electric furnaces such as a single crystal silicon pulling furnace, a polycrystalline silicon growth furnace, a sapphire single crystal pulling furnace, a silicon carbide single crystal pulling furnace, a metal and ceramic sintering furnace, and a vacuum deposition furnace. It is preferably used in a furnace.

In the above description, as a method of manufacturing the molded heat insulating material, a method of using a thermosetting resin in the impregnation step and performing the curing step and the firing step after the impregnation step is exemplified. However, as the resin, a thermoplastic resin may be used instead of the thermosetting resin. In that case, after performing the above-described defibrating step, web forming step, and fiber bonding step, in the impregnation step, 5 to 30 parts by mass of a molten thermoplastic resin is impregnated with respect to 100 parts by mass of the carbon fiber nonwoven fabric. And a prepreg is formed. Next, instead of the curing step, a solidification step of cooling and solidifying the thermoplastic resin in a molten state is performed to obtain a molded body composed of the carbon fiber nonwoven fabric and the solidified thermoplastic resin. Next, a firing step for firing the molded body is performed.
Examples of the thermoplastic resin include polyethylene resin, polyvinyl alcohol resin, polypropylene resin, vinyl chloride resin, vinylidene chloride resin, polyamide resin, and the like, and one or more of these can be used.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to these Examples.
[Example 1]
(Defibration process)
Needling felt cut off from a needling felt (made by Osaka Gas Chemical Co., Ltd., Donakabo Felt (carbonaceous grade)) made of 100% pitch-based isotropic carbon fiber (fiber diameter: 13 μm) as a carbon fiber aggregate. The end material was defibrated with a sample roller card machine (manufactured by Intec Co., Ltd.) to obtain a defibrated carbon fiber.

(Web formation process)
A mesh that travels while being mounted on a conveyor equipped with a suction box while uniformly mixing the fibrillated carbon fiber and the core-sheath type heat-fusible conjugate fiber (PE / PP conjugate fiber) into a fiber mixture. The first air-permeable carrier sheet was fed out on the endless belt, and the fiber mixture was lowered onto the first air-permeable carrier sheet together with the intake air flow. Then, an airlaid web was formed by dropping and depositing on the belt, and then a second air-permeable carrier sheet was laminated on the airlaid web to form a three-layer web laminate.
Wherein the amount of carbon fibers per airlaid web unit area 465 g / m ^2, the amount of heat-fusible conjugate fiber was 82 g / m ^2, the ratio of the heat-fusible composite fiber of the fiber mixture is 15 mass %.
In addition, the air laid web in the web laminate was observed, and the fiber length (weighted average fiber length) of only 200 carbon fibers in the web laminate was measured using an image analyzer (manufactured by Nireco Corporation, LUZEX-AP). It was 3 mm when measured. The fiber length measured here is the same as the fiber length of the carbon fiber in the fiber mixture before forming the airlaid web.

(Fiber binding process)
The three-layer web laminate obtained in the web forming process is passed through a box-type dryer and treated with hot air at 140 ° C. (hot air circulating conveyor oven method), and the carbon fibers in the air laid web are bonded by heat-fusible composite fibers. It was. Next, the first and second breathable carrier sheets on both sides were peeled to obtain a carbon fiber nonwoven fabric, which was wound up by a winder.
The basis weight of this carbon fiber nonwoven fabric was 547 g / m ² .
The obtained carbon fiber nonwoven fabric was cut into a length of 150 mm and a width of 50 mm as a sample, and the sample was subjected to a tensile test in an environment of 23 ° C. and 50% RH, and the tensile strength and elongation at break were measured. did.
The length of the carbon fiber nonwoven fabric is a length along the flow direction of the sheet in the web forming step, and the width of the carbon fiber nonwoven fabric is a length orthogonal to the flow direction of the sheet. Moreover, the conditions of the tensile test were a span of 100 mm and a tensile speed of 200 mm / min, and the sample was pulled along the length direction of the sample.
As a result, the tensile strength was 30 N / 50 mm and the elongation at break was 9%.

(Impregnation process)
The obtained carbon fiber non-woven fabric was impregnated with a phenol resin (resole-based, methyl alcohol solution, nonvolatile content concentration 60 mass%) to obtain a prepreg. The impregnation amount of the phenol resin (resole type) was 14 parts by mass with respect to 100 parts by mass of the obtained carbon fiber nonwoven fabric.
(Curing process)
13 sheets of the obtained prepregs were stacked and placed in a hot press machine, and held at 200 ° C. for 1 hour while being pressurized. The phenol resin was thermally cured to bind the prepregs together to obtain a molded body. At this time, pressure was applied so that the thickness of the molded body was 45 mm.
(Baking process)
Subsequently, the obtained molded body was fired in an inert atmosphere at a maximum temperature of 2000 ° C. for 5 hours.
Thereby, a flat molded heat insulating material having a length L of 1200 mm, a width W of 600 mm, and a thickness D of 43 mm as schematically shown in FIG. 1 was obtained. The bulk density of this molded heat insulating material was 0.14 g / cm ³ .
The length of the molded heat insulating material is a length along the flow direction of the sheet similarly to the length of the above-mentioned carbon fiber non-woven fabric, and the width of the formed heat insulating material is the flow of the sheet similarly to the width of the above-mentioned carbon fiber non-woven fabric. The length is perpendicular to the direction. The thickness of the molded heat insulating material is a length in a direction orthogonal to the length and the width.
FIG. 2 shows a scanning electron microscope (SEM) photograph of the obtained molded heat insulating material in the direction of arrow A (side surface) in FIG.
Moreover, about the obtained shaping | molding heat insulating material, the measurement of the heat conductivity, the linear thermal expansion coefficient, and the delamination strength was performed by the below-mentioned method. The results are shown in Table 1. In addition, about the measurement result of heat conductivity, while plotting the value with respect to sample average temperature in FIG. 3, the value in sample average temperature 600 degreeC, 1000 degreeC, and 1400 degreeC is extracted and shown in Table 1. It was.

(1) Measurement of thermal conductivity A disk-shaped sample having a diameter of 350 mm and a thickness (prepreg lamination direction) of 30 mm was cut out from the molded heat insulating material. Using this sample, in a nitrogen gas atmosphere with an absolute pressure of 1 atm (101 kPa), heat conduction is performed by a standard plate method (Osaka Gas Chemical Co., Ltd. “DONACARBO” catalog), which is a stationary method, at various sample average temperatures. The rate was measured.
The sample average temperature means an arithmetic average value of the temperature on the high temperature side (heating side) and the temperature on the low temperature side of the sample.

The method for measuring thermal conductivity by the standard plate method will be described more specifically with reference to FIG.
A disc-shaped standard plate (diameter: 350 mm, thickness ds: 100 mm) 10 made of a carbon material and having a known thermal conductivity λs at each temperature, and a measurement plate superimposed on one surface 10 b of the standard plate 10 (Diameter D: 100 mm) 11 is used. A flow path 12 is formed inside the measurement plate 11 so that cooling water can be circulated inside the measurement plate 11.

The above-mentioned disk-shaped sample (diameter: 350 mm, thickness d: 30 mm) 20 cut out from the molded heat insulating material is superimposed on the other surface 10a of the standard plate 10 of this apparatus. Then, the surface 20a of the sample 20 that is not in contact with the standard plate 10 is heated from the outside by a heating means such as a heater, and cooling water is allowed to flow through the flow path 12 at a flow rate Fw (for example, 0.04 m ³ / h). . After the steady state is reached, the following (a) to (c) are measured.
(A) Center temperature Ts on the surface 20a of the sample 20
(B) The central temperature To of the surface 10b of the standard plate 10 on the side in contact with the measurement plate 11
Temperature difference between the temperature _{T out} at the temperature _{T in} and an outlet 12b at the inlet 12a of the flow path 12 of (c) the coolant (absolute value) .DELTA.Tw

Next, the value of (Q / S) in the measurement plate 11 is obtained. Q is the heat flow rate and S is the heat flux area.
Specifically, from the value of the temperature difference ΔTw measured in the above (c), the value of the flow rate Fw (known) of the cooling water, and the product C (known) of the specific heat and density of the cooling water, the following formula ( 1), the heat flow rate Q in the measurement plate 11 is obtained. Further, from the diameter D (known) of the measurement plate 11, the heat flow area S is obtained by the following formula (2). Therefore, the value of (Q / S) is determined from the obtained values of Q and S.
Q = Fw × C × ΔTw (1)
S = π (D / 2) ² (2)

Here, the value of (Q / S), the thermal conductivity λm of the sample 20, the thickness d of the sample 20, the center temperature Ts, and the center temperature Tu of the surface 20b of the sample 20 on the side where the standard plate 10 is in contact are: It has the relationship of following formula (3).
Further, the value of (Q / S), the thermal conductivity λs of the standard plate 10 in contact with the sample 20, the thickness ds of the standard plate 10, and the center temperature of the surface 20b of the sample 20 on the side in contact with the standard plate 10 Tu (that is, the same temperature as the center temperature of the surface 10a on the side of the standard plate 10 that is in contact with the sample 20) and the center temperature To of the surface 10b of the standard plate 10 on the side that is in contact with the measurement plate 11 are as follows. There is a relationship of Formula (4).
Q / S = (λm / d) × (Ts−Tu) (3)
Q / S = (λs / ds) × (Tu−To) (4)

Next, the center temperature Tu is obtained as follows.
First, the center temperature Tu is assumed. Here, since the thermal conductivity λs at each temperature of the standard plate 10 is known as described above, the standard plate 10 at the average temperature ((Tu + To) / 2) of the standard plate 10 using the assumed center temperature Tu. The thermal conductivity λs is also known. Then, among the parameters in the above equation (4), the thermal conductivity λs, the thickness ds of the standard plate 10, the center temperature To, and (Q / S) calculated from the above equations (1) and (2) are all Since it is known, the center temperature Tu can be obtained from the above equation (4).
Then, the assumption of the center temperature Tu and the center temperature from the above equation (4) until the value of the center temperature Tu obtained from the above equation (4) coincides with the initially assumed center temperature Tu. The center temperature Tu is obtained by trial and error that repeats the calculation of Tu.

  When the center temperature Tu is determined in this way, in the above formula (3), parameters other than the thermal conductivity λm of the sample 20 are known, and therefore the thermal conductivity λm can be obtained from the above formula (3). .

(2) Measurement of linear thermal expansion coefficient The linear thermal expansion coefficient was measured in a temperature range from room temperature to 1000 ° C. using a high-temperature thermomechanical analyzer manufactured by Rigaku Corporation, model TMA8310 / H. Table 1 shows the average values from room temperature to 1000 ° C.

(3) Measurement of delamination strength When tensile stress is applied in the thickness direction of the molded heat insulating material, the maximum stress until delamination is delamination is the delamination strength. First, a rectangular parallelepiped sample having a thickness of 43 mm, a length of 40 mm, and a width of 40 mm was cut out from the molded heat insulating material. A metal jig to be attached to the tensile tester is bonded to both sides in the thickness direction of the sample with an adhesive, and the sample is pulled in a direction parallel to the thickness direction with a tensile tester until the layers are separated. Maximum load was measured. The maximum load was divided by the area (sample length 40 mm × width 40 mm) to obtain delamination strength.

[Comparative Example 1]
In the same manner as in Example 1, a carbon fiber nonwoven fabric was obtained. However, the amount of carbon fiber per unit area of the air laid web was 425 g / m ² , the amount of heat-fusible conjugate fiber was 75 g / m ^2, and the basis weight of the carbon fiber nonwoven fabric was 500 g / m ² .
Next, a prepreg was obtained in the same manner as in Example 1 except that the amount of the phenol resin (resole type) impregnated with respect to 100 parts by mass of the obtained carbon fiber nonwoven fabric was changed to 60 parts by mass.
Next, a molded body was obtained in the same manner as in Example 1 except that the number of the prepregs stacked was 15 and the thickness of the molded body was 43 mm.
And the baking process similar to Example 1 was performed, and the shaping | molding heat insulating material of length: 1200mm, width: 600mm, and thickness: 40mm was obtained. When the bulk density of this molded heat insulating material was measured by the same method as in Example 1, it was 0.21 g / cm ³ .
Moreover, about the obtained molded heat insulating material, it carried out similarly to Example 1, and measured thermal conductivity, a linear thermal expansion coefficient, and delamination strength. The results are shown in Table 1. The thermal conductivity is also shown in FIG.

[Comparative Example 2]
Needling felt made of 100% pitch-based isotropic carbon fiber (average diameter 13 μm) as a material for the molded heat insulating material (Donnabo felt made by Osaka Gas Chemical Co., Ltd. (carbonaceous grade, thickness 10 mm, basis weight (basis weight) 500 g) / m ²⁾ was used. then, with respect to the needling felt 100 parts by weight, the same phenolic resin (resol type as that used in example 1) 14 parts by weight was impregnated with and prepregs.
Ten prepregs were stacked and placed in a hot press machine, and held at 200 ° C. for 1 hour while being pressurized, the phenol resin was thermoset to bond the prepregs together, and a molded body was obtained. At this time, pressure was applied so that the thickness of the molded body was 43 mm.
And the baking process similar to Example 1 was performed, and the shaping | molding heat insulating material of length: 1500mm, width: 1000mm, and thickness: 40mm was obtained. When the bulk density of this molded heat insulating material was measured by the same method as in Example 1, it was 0.14 g / cm ³ .
Moreover, about the obtained molded heat insulating material, it carried out similarly to Example 1, and measured thermal conductivity, a linear thermal expansion coefficient, and delamination strength. The results are shown in Table 1. The thermal conductivity is also shown in FIG.

  The molded heat insulating material obtained in Example 1 had a low bulk density, and had a low thermal conductivity and excellent heat insulating performance at any sample average temperature. The delamination strength was 16 kPa, and it had sufficient machinability, which is one of the main functions of the molded heat insulating material. If the delamination strength is about 5 kPa, the self-supporting property of the molded heat insulating material can be ensured, but in order to ensure sufficient machinability, it is preferably 10 kPa or more.

  On the other hand, although the molded heat insulating material of Comparative Example 1 was excellent in delamination strength, the bulk density was slightly large and the heat insulating performance was inferior to that of Example 1. This is probably because the molded heat insulating material of Comparative Example 1 has a large amount of phenol resin impregnated in the impregnation step and a relatively small amount of carbon fiber.

The molded heat insulating material of Comparative Example 2 had a bulk density equivalent to that of the molded heat insulating material of Example 1, but the heat conductivity was high and the heat insulating performance was not sufficient. This is thought to be due to the following reasons.
The molded heat insulating material of Example 1 was obtained by using a carbon fiber nonwoven fabric formed from an air laid web as a material. Therefore, as can be understood from the scanning electron micrograph of FIG. 2, many carbon fibers are selectively arranged almost perpendicularly to the heat insulation direction, and most of the carbon fibers arranged parallel to the heat insulation direction are unacceptable. It can be understood that a large number of spaces formed by carbon fibers arranged substantially perpendicular to the heat insulation direction generate heat radiation loss and contribute to the heat insulation effect. On the other hand, the molded heat insulating material of Comparative Example 2 was obtained by using a needling felt subjected to a carbon fiber entanglement process by a needle punch as a material. For this reason, the carbon fiber along the traveling direction of the needle punch, that is, a large number of carbon fibers attached in the direction parallel to the heat insulating direction is obtained by the entanglement process by the needle punch. Thus, the carbon fiber parallel to the heat insulation direction conducts heat from the high temperature side to the low temperature side. Therefore, the molded heat insulating material of Comparative Example 2 is considered to be inferior in heat insulating performance as compared with the molded heat insulating material of Example 1.

  In addition, although the molded heat insulating material of Example 1 is provided with delamination strength sufficient for practical use, this is because some of the carbon fibers arranged perpendicular to the heat insulating direction are entangled with each other, and partially. This is thought to be due to the bonding effect of the carbonized product of the phenolic resin present in the resin.

  According to the present invention, a molded heat insulating material having a small bulk density and excellent heat insulating performance can be provided. Since the molded heat insulating material is excellent in heat insulating performance, in addition to being able to reduce the amount of power used when used in a high-temperature electric furnace, etc., the volume of the molded heat insulating material required to obtain the predetermined heat insulating performance can be reduced. The furnace can be used widely and effectively. In addition, since the bulk density is small, the cost is low and the heat capacity of itself is small, so that the total heat capacity in the furnace in which the molded heat insulating material is arranged can be suppressed to a small amount, and the amount of power used can be reduced from that point. Therefore, the present invention is extremely useful in terms of energy saving and cost reduction.

Claims (5)

A defibrating process for defibrating a carbon fiber aggregate composed of a large number of carbon fibers;
A web forming step of mixing heat-fusible fibers with defibrated carbon fibers and forming an airlaid web from the obtained fiber mixture;
A fiber bonding step of treating the airlaid web with hot air to bond the carbon fibers in the airlaid web with the heat-fusible fibers;
An impregnation step of impregnating 5 to 30 parts by mass of a thermosetting resin with respect to 100 parts by mass of the carbon fiber nonwoven fabric for a heat insulating material precursor obtained by the fiber bonding step; and
A curing step for curing the prepreg to obtain a cured product;
And a firing step of firing the cured product.   The method for producing a molded heat insulating material according to claim 1, wherein the carbon fiber aggregate is an aggregate of pitch-based isotropic carbon fibers.   The fiber length of the carbon fiber in the said fiber mixture is 1-10 mm, The manufacturing method of the shaping | molding heat insulating material of Claim 1 or 2 characterized by the above-mentioned.   The ratio of the said heat-fusible fiber in the said fiber mixture is 1-30 mass%, The manufacturing method of the shaping | molding heat insulating material as described in any one of Claims 1-3 characterized by the above-mentioned. The basis weight of the carbon fiber nonwoven fabric for a heat insulating material precursor is 200-1500 g / m ² , The method for producing a molded heat insulating material according to any one of claims 1 to 4.