JP6621983B2 - Carbon fiber for heat insulating material and heat insulating material using the same - Google Patents

Description

  The present invention relates to a carbon fiber for a heat insulating material and a heat insulating material using the same.

  Carbon fibers obtained using isotropic pitch as a carbon precursor are widely used as felt heat insulating materials or molded heat insulating materials. The molded heat insulating material is a material that is impregnated with a resin having a high carbonization rate and is molded, cured, carbonized, graphitized, etc. into a shape according to the purpose. In addition, isotropic pitch-based carbon fibers are excellent in thermal stability and flexibility and have high shape selectivity. Currently, it is used in industrial furnaces, and specific examples thereof include, for example, a heat insulating material for a silicon single crystal pulling apparatus.

  As for the heat insulating material used in this way, about 90% of the volume is usually space. In particular, radiant heat in a high temperature region (for example, 1300 ° C. or higher) is blocked by this space to cause radiation loss, thereby producing a heat insulation effect. In this case, since space formation is more important, only the space formation method when forming a heat insulating material using carbon fiber has been studied, and almost no consideration is given to the thermal conductivity and heat insulation performance of the carbon fiber itself. Not discussed.

  However, when trying to obtain a sufficient heat insulating performance by reducing the heat insulating material (when using a small heat insulating material), there is less room for forming a large space, and the volume ratio of the carbon fiber is increased. In this case, the thermal conductivity and heat insulation performance of the carbon fiber itself are important.

  On the other hand, it is also known to insulate a U-shaped reactor by filling it with a brand name fiber cast. The fiber cast is composed of a ceramic fiber, an inorganic binder, or the like. However, such a ceramic fiber has a heat resistant temperature of 1000 to 1200 ° C. and cannot be applied to a device having a higher temperature. For this reason, for example, materials other than carbon fibers such as ceramic fibers can be used in a low temperature region of 1300 ° C. or lower, but the chemical resistance of carbon fibers and the low wettability (low reactivity) with molten metal. For example, a carbon fiber-based heat insulating material is useful. At such low temperatures, the proportion of radiant heat decreases, so it is more important that the carbon fiber itself has a low thermal conductivity.

  For example, Patent Document 1 describes that an airgel fiber can be used as a heat insulating material for a jacket heater (mantle heater). In addition to organic fibers, inorganic fibers, etc., carbon fibers are mentioned as the fibrous body. It becomes possible to make it more compact by using the carbon fiber excellent in heat insulation for the heat insulating material of such a heater.

International Publication No. 2012/077648

  The present invention is intended to solve the above problems. Specifically, when a small high-temperature heating device is to be insulated, a small or thin heat insulating material is required. In that case, a carbon fiber having a low thermal conductivity is considered to be a suitable material. The carbon fiber is generally 6 to 20 μm in diameter and very thin, and is suitable for constituting a small heat insulating material. Another object of the present invention is to provide a carbon fiber having a low thermal conductivity and a flexible small structure (heat insulating material) using such a carbon fiber.

  Another object of the present invention is to provide a carbon fiber that can exhibit heat insulation not only in the fiber axis direction but also in the radial direction. Moreover, it aims also at providing the flexible small heat insulating material using such a carbon fiber.

As a result of intensive studies to solve the above problems, the present inventors can obtain carbon fibers that have solved the above problems by setting the thermal conductivity in the fiber axis direction and the amount of open pores to a specific range. I found out. The present invention has been completed through further research based on this finding. That is, the present invention includes the following configurations.
Item 1. A carbon fiber for a heat insulating material having a thermal conductivity in the fiber axis direction of 1 to 10 W / m · K and an open pore volume of 0.1 cm ³ / g or less.
Item 2. Item 2. The carbon fiber for a heat insulating material according to Item 1, wherein the apparent density is less than 2.0 g / cm ³ .
Item 3. Item 3. The carbon fiber for a heat insulating material according to Item 1 or 2, wherein the closed pore radius is 6 nm or more when the closed pore estimated by a Guinier plot by a small angle X-ray scattering method is a sphere.
Item 4. Item 4. The carbon fiber for a heat insulating material according to any one of Items 1 to 3, which is a heat-treated product at 700 to 2400 ° C using isotropic pitch as a carbon precursor.
Item 5. A method for producing a carbon fiber for a heat insulating material having a thermal conductivity in the fiber axis direction of 1 to 10 W / m · K and an open pore volume of 0.1 cm ³ / g or less,
The manufacturing method provided with the process of heat-processing the precursor fiber of the said carbon fiber for heat insulating materials at 700-2400 degreeC.
Item 6. Item 6. The method according to Item 5, wherein the precursor fiber is a precursor fiber composed of an isotropic pitch.
Item 7. The heat insulating material using the carbon fiber for heat insulating materials in any one of claim | item 1-4, or the carbon fiber for heat insulating materials obtained by the manufacturing method of Claim 5 or 6.
Item 8. Item 8. The heat insulating material according to Item 7, wherein the carbon fiber for heat insulating material is bonded by a heat resistant resin or a carbon bond.
Item 9. Item 8. The heat insulating material according to item 7, wherein the heat insulating material is formed into a sheet shape, a test tube shape, a drawstring shape, a bat shape or a crucible shape using a nonwoven fabric made of carbon fiber for heat insulating material.
Item 10. Item 8. The thermal insulation carbon fiber is bonded with a heat-resistant resin or a carbon bond, and is formed into a sheet shape, a test tube shape, a drawstring shape, a bat shape, a crucible shape, or a container shape. Insulation.

  The heat insulating carbon fiber of the present invention can exhibit heat insulation not only in the fiber axis direction but also in the radial direction. For this reason, the heat insulating material using the carbon fiber for heat insulating material of the present invention has a small heat conduction by the carbon fiber, and can reduce the heat conduction by the passage of gas or radiant heat. In particular, it is more effective for a small or thin heat insulating material that has little room for forming a lot of space.

  In the carbon fiber for a heat insulating material of the present invention, the size of closed pores can be made relatively large. For this reason, the heat insulating material using the carbon fiber for a heat insulating material of the present invention enables the closed pores in the carbon fiber to block the radiant heat (radiation loss), and the heat insulating performance in the radial direction of the carbon fiber is high. The heat insulating property can be effectively expressed in the radial direction. Again, this is more effective for small or thin insulations that have less room to form a lot of space.

  When such a heat insulating material of the present invention is formed into a desired shape, it is possible to obtain a flexible heat insulating material.

2 is an adsorption / desorption isotherm of carbon fibers of Examples 2 and 6. The left figure shows the results of Example 2, and the right figure shows the results of Example 6. It is a Guinier plot by the small angle X ray scattering method of the carbon fiber of Examples 2-6.

1. Carbon fiber for heat insulating material The carbon fiber for heat insulating material of the present invention has a thermal conductivity in the fiber axis direction of 1 to 10 W / m · K and an open pore volume of 0.1 cm ³ / g or less. The carbon fiber for a heat insulating material of the present invention having such characteristics can reduce heat conduction by the carbon fiber. Moreover, since the carbon fiber for a heat insulating material of the present invention having such characteristics has few open pores, heat conduction due to passage of gas and radiant heat can be reduced.

  The carbon fiber for heat insulating material of the present invention includes pitch-based carbon fiber (coal-based pitch-based carbon fiber and petroleum-based pitch-based carbon fiber), polyacrylonitrile (PAN) -based carbon fiber, rayon-based carbon fiber, phenol-based carbon fiber, and cellulose. Any of the carbon-based carbon fibers can be used. Among these, in the present invention, pitch-based carbon fibers are preferable from the viewpoint that the degree of development of graphite crystals by heat treatment can be controlled by controlling the structure during pitch purification, and graphite by heat treatment is preferable. An isotropic pitch-based carbon fiber with a low degree of crystal growth is more preferable. “Pitch-based carbon fiber” means carbon fiber produced using pitch as a raw material (carbon precursor). An isotropic pitch-based carbon fiber is a carbon fiber when the pitch is isotropic. “Isotropic” is optically isotropic and means that molecules, a group of molecules, and the like are randomly oriented. By “carbon precursor” is meant a series of carbonized intermediates that are in a stage prior to the intended final carbon product. In the present invention, the carbon precursor is preferably isotropic pitch, and the final carbon product is preferably isotropic pitch-based carbon fiber.

  “Pitch”, which is a carbon precursor, is a liquid tar obtained during dry distillation of wood, coal, etc., bitumen obtained from oil sand, etc., oil obtained by dry distillation of oil shale, etc., residual oil by distillation of crude oil, It is a solid material at room temperature obtained by heat treatment and polymerization of tar and the like produced by cracking of petroleum fractions. Specific examples include (a) coal-based pitch, (b) petroleum-based pitch, and (c) synthetic pitch obtained by polymerizing aromatic compounds such as naphthalene. Pitch is a mixture of a myriad of condensed polycyclic aromatic compounds chemically. Examples of the coal-based pitch obtained using coal as a raw material include pitch obtained by heat treatment of coal tar generated from a coke oven.

  In the present invention, the pitch used as a raw material is not particularly limited, but may be a coal-based pitch, particularly a coal-based isotropic pitch.

  The softening point of the pitch (particularly isotropic pitch) is not particularly limited, and can be appropriately set according to the spinning method in the method for producing the carbon fiber for heat insulating material described later.

  The thermal conductivity in the fiber axis direction of the carbon fiber for thermal insulation of the present invention is 1 to 10 W / m · K, preferably 3.5 to 9 W / m · K, more preferably 4.2 to 8 W / m · K. It is. It is difficult to manufacture a material having a thermal conductivity in the fiber axis direction of the carbon fiber for heat insulating material of less than 1 W / m · K. On the other hand, if the thermal conductivity in the fiber axis direction of the carbon fiber for thermal insulation exceeds 10 W / m · K, the thermal conductivity of the carbon fiber itself is too high, and the thermal insulation performance of the obtained thermal insulation becomes poor. In addition, the thermal conductivity in the fiber axis direction of the carbon fiber for thermal insulation is measured by the gas displacement method, the specific heat is measured using a differential scanning calorimeter, and the thermal diffusivity is measured using the optical alternating current method. In addition, the thermal conductivity is determined by (apparent density) × (specific heat) × (thermal diffusivity).

Open pores of the carbon fiber heat insulating material of the present invention, 0.1 cm ³ / g or less, preferably 0.08 cm ³ / g, more preferably at most 0.05 cm ³ / g. When the amount of open pores of the carbon fiber for heat insulation exceeds 0.1 cm ³ / g, heat conduction due to passage of gas and radiant heat becomes easy, and the heat insulation performance of the obtained heat insulation becomes poor. In addition, there is no restriction | limiting in particular in the lower limit of the amount of open pores of the carbon fiber for heat insulating materials, and 0 cm < ³ > / g is the most preferable. Moreover, the open pore volume of the carbon fiber for a heat insulating material is obtained by using the total pore volume measured by the BET method as the open pore volume. In the BET method, only the amount of pores existing on the carbon fiber surface can be determined, and therefore the total pore volume by the BET method corresponds to the amount of open pores.

The apparent density of the insulation material for the carbon fiber of the present invention is preferably less than 2.0 g / cm ^3, more preferably 1.0~1.9g / cm ^3, more preferably 1.3~1.7g / cm ³ . By making the apparent density of the carbon fiber for heat insulating material within this range, while keeping the crystallinity of the carbon fiber for heat insulating material more impaired, the closed pores existing in the carbon fiber are made larger, and the closed pores radiate heat. Further shielding (radiation loss), the heat insulation performance in the radial direction of the carbon fiber can be further increased, and the heat insulation performance of the obtained heat insulating material can be further improved. Thereby, it is also possible to form a thin sheet-like heat insulating material that is thermally insulated in the carbon fiber radial direction. In addition, the apparent density of the carbon fiber for heat insulating materials is measured by a gas substitution method.

  The radius of the closed pores of the carbon fiber for heat insulating material of the present invention is preferably 6 nm or more, more preferably 6.5 to 15 nm, and even more preferably 7 to 13 nm. By making the radius of the closed pores of the carbon fiber for heat insulating material within this range, the closed pores can block the radiant heat (radiation loss), and the heat insulation performance in the radial direction of the carbon fiber can be further improved, and the heat insulation of the obtained heat insulating material The performance can be further improved. Thereby, it is also possible to form a thin sheet-like heat insulating material that is thermally insulated in the carbon fiber radial direction. In addition, the radius of the closed pores of the carbon fiber for heat insulating material is a closed pore radius calculated when the closed pores estimated by the Guinier plot by the small angle X-ray scattering method are assumed to be spheres.

  The carbon fiber for a heat insulating material of the present invention will be described in detail in a method for producing a carbon fiber for a heat insulating material described later, but is a heat treated product of 700 to 2400 ° C. (particularly 700 to 2400 ° C. using an isotropic pitch as a carbon precursor). Heat treatment product of 1100 to 2400 ° C. (especially heat treatment product of 1100 to 2400 ° C. using isotropic pitch as a carbon precursor), more preferably heat treatment of 1300 to 2400 ° C. It is more preferable to be a product (particularly a heat treated product of 1300 to 2400 ° C. using isotropic pitch as a carbon precursor). By setting the heat treatment temperature of the carbon fiber for the heat insulating material within this range, the graphite crystallinity of the carbon fiber is hardly excessively developed and the structure remains non-oriented, so there are fewer open pores and more closed pores. It is easy to obtain carbon fibers that can be developed and have low thermal conductivity and high heat insulation. Further, a more suitable selection can be made according to the application.

  Although the fiber diameter of the carbon fiber for heat insulating materials of this invention is not specifically limited, 6-18 micrometers is preferable on the average, and 11-14 micrometers is more preferable. By setting the fiber diameter of the carbon fiber for a heat insulating material within this range, a suitable heat insulating performance can be exhibited while ensuring the mechanical strength of the fiber. The average fiber diameter of the carbon fiber for heat insulation is measured by observation with a magnifying glass and an image analyzer.

  The fiber length of the carbon fiber for heat insulating material of the present invention is not particularly limited, but the preferable fiber length is different between the felt heat insulating material and the molded heat insulating material. That is, in the felt heat insulating material, since it is necessary to entangle the fibers by, for example, a needle punch, it is necessary to use mat fibers that are aggregates of short fibers having a length of several centimeters to several tens of centimeters. preferable.

  In a molded heat insulating material, the case where felt is used for the production differs from the case where milled fiber or chop fiber is used. Here, a molded heat insulating material using felt is referred to as a felt-based molded heat insulating material, and a molded heat insulating material using milled fiber or chopped fiber is referred to as a short fiber-based molded heat insulating material.

  In the case of a felt-based molded heat insulating material, it is preferable to use the mat fiber.

  In the short fiber type heat insulating material, the average fiber length is preferably about 0.04 to 3 mm for milled fibers, and the average fiber length is preferably about 3 to 10 mm for chopped fibers. In addition, the average fiber length of the carbon fiber for heat insulating materials is measured by observation with a magnifier and an image analyzer.

  The aspect ratio (fiber length / fiber diameter) of the carbon fiber for short fiber-based molded heat insulating material of the present invention is not particularly limited, but is preferably 2 to 500 on average when milled fiber is used. When chopped fibers are used, 170 to 1670 is preferable on average. By setting the aspect ratio of the carbon fiber for short fiber-based molded heat insulating material within this range, a suitable heat insulating material can be obtained.

2. Manufacturing method of carbon fiber for heat insulating material Carbon fiber for heat insulating material of the present invention is
It can obtain by the manufacturing method provided with the process of heat-processing the precursor fiber of the carbon fiber for heat insulating materials of this invention at 700-2400 degreeC.

(1) Carbon fiber precursor fiber for heat insulating material In the method for producing the carbon fiber for heat insulating material of the present invention, a carbon fiber precursor for heat insulating material is used as a raw material (hereinafter referred to as carbon fiber precursor for heat insulating material). Simply referred to as “precursor fibers”).

  The precursor fiber is preferably a carbon fiber obtained using pitch (particularly isotropic pitch) as a raw material. That is, the precursor fiber is the same as the carbon fiber for heat insulating material, pitch-based carbon fiber (coal-based pitch-based carbon fiber and petroleum-based pitch-based carbon fiber), polyacrylonitrile (PAN) -based carbon fiber, rayon-based carbon fiber, Any of phenol-based carbon fibers, cellulose-based carbon fibers, and the like can be employed, but pitch-based carbon fibers (particularly isotropic pitch-based carbon fibers) are preferable. Further, the size of the precursor fiber (fiber diameter, fiber length, and aspect ratio) is not particularly limited, but the size of the precursor fiber is for the heat insulating material of the present invention because the size of the fiber is hardly changed by the heat treatment described later. It is preferable to make it the size equivalent to carbon fiber.

  The pitch (particularly the isotropic pitch) is the same as that described above for the pitch and the isotropic pitch. Preferred pitches and isotropic pitches are also the same as described above for pitches and isotropic pitches, and coal-based isotropic pitches are preferred. The softening points of the pitch and the isotropic pitch are not particularly limited, and can be appropriately set depending on the spinning method.

As such precursor fiber, you may synthesize | combine and can also use a commercial item. When using a commercial product, as a specific example,
-Dona Carbo Chop manufactured by Osaka Gas Chemical Co., Ltd. (Part No .: S-231, S-232, S-234, S-331, S-332, etc.)
-Osaka Gas Chemical Co., Ltd. DonaCarbo Mildo (Part No .: S-2404N, S-249, S-241, S-242, S-243, S-244, S-246, S-247, S-343, S-344, SG-244A, SG-249, SG-241, etc.)
・ Carbon fiber mat manufactured by Osaka Gas Chemical Co., Ltd. (Part No .: S-210 etc.)
Etc.

In the present invention, when the precursor fiber is synthesized, the method for producing the precursor fiber is not particularly limited. For example, when obtaining a pitch-based precursor fiber, the following steps:
(I) Step 1 of spinning pitch (particularly isotropic pitch) as a carbon precursor,
(Ii) Step 2 for infusibilizing the spinning (pitch fiber) obtained in Step 1 and (iii) Step 3 for carbonizing the infusible fiber (infusible pitch fiber) obtained in Step 2
It is preferable to produce the precursor fiber by a production method including: Hereinafter, each step will be described.

Step 1: In the spinning step 1, for example, pitch (particularly isotropic pitch) is spun as the carbon precursor. By this step 1, spinning (pitch fiber) is obtained.

  The spinning method is not particularly limited, and examples thereof include melt spinning. Specific melt spinning methods include vortex spinning, spunbond spinning, and centrifugal spinning. Further, the temperature at the time of melt spinning is not particularly limited as long as the pitch (particularly isotropic pitch) is melted. Also, other spinning conditions such as the shape of the nozzle and the spinning speed are not particularly limited, and can be set as appropriate according to the intended use. Note that the vortex spinning is a method in which a hot gas jet stream is blown onto a molten pitch yarn discharged from a nozzle to efficiently draw. In this spinning method, irregularly curved spinning (pitch fibers) can be obtained.

  In Step 1, when pitch fibers are obtained by melt spinning, the pitch fibers are not continuous fibers, and for example, short fibers having a length of several cm to several tens of cm and a certain width are often obtained.

Process 2: Infusibilization process In process 2, spinning (pitch fiber) is infusibilized. By this step 2, an infusible fiber is obtained. The infusibilization treatment is generally performed by oxidative dehydrocyclization, condensation, or the like so that the fiber shape can be maintained by carbonization (carbonization) described later after giving the fiber shape to the carbon precursor. This is a treatment for making it curable. In this step, it is preferable that the infusibilization treatment is performed to introduce oxygen into the pitch fiber and stabilize it by cross-linking with oxygen.

  The method for infusibilization is not particularly limited. For example, hot air is applied to the pitch fibers.

  The atmosphere during the infusibilization treatment is preferably an oxygen-containing atmosphere. As the introduction of oxygen, in addition to air, a gaseous oxidant such as nitrogen oxide or sulfur oxide may be used.

  The temperature during the infusibilization process is not particularly limited. For example, it can be heated to around the spinning temperature.

  Other conditions for the infusibilization treatment (for example, the rate of temperature rise, the retention time for the infusibilization treatment, etc.) are not particularly limited, and can be set as appropriate according to the intended use.

Step 3: In the carbonization treatment step 3, the infusible fiber is carbonized. By this step 3, a precursor fiber is obtained. Carbonization treatment (carbonization treatment) refers to a treatment that releases elements other than carbon to produce a solid with a high carbon content.

  The temperature during the carbonization treatment is not particularly limited. For example, heat treatment is preferably performed at about 700 to 1000 ° C.

  The atmosphere during the carbonization treatment is preferably an inert gas atmosphere (non-oxidizing gas atmosphere), and more preferably a nitrogen gas atmosphere.

  Other carbonization treatment conditions (for example, the rate of temperature rise, the retention time of the carbonization treatment, etc.) are not particularly limited, and can be appropriately set according to the intended use.

After performing the other process carbonization treatment, the precursor fiber is obtained. In general, the precursor fiber is often in the form of a mat. After the precursor fiber is obtained, if necessary, the precursor fiber may be subjected to a cutting process, a pulverizing process, or the like within a range not impairing the effects of the present invention to obtain a milled fiber or a chop fiber. In the cutting process and the pulverizing process, the shape of the precursor fiber can be appropriately changed.

  The pulverization method is not particularly limited. For example, the precursor fiber can be pulverized using a jet mill, a hammer mill, a pin mill, or the like.

  The cutting method is not particularly limited. For example, the precursor fibers can be cut using a roving cutter, a guillotine cutter, a cross cutter, a low-speed shear type screen grinder, or the like.

(2) Heat treatment process with respect to precursor fiber In the manufacturing method of the carbon fiber for heat insulating materials, the carbon fiber for heat insulating material of the present invention is suitably obtained by heat-treating the precursor fiber at 700 to 2400 ° C. By setting the heat treatment temperature of the precursor fiber within this range, the graphite crystallinity of the carbon fiber is not easily developed excessively, and the structure remains non-oriented, resulting in fewer open pores and more closed pores. Therefore, it is easy to obtain carbon fibers having low thermal conductivity and high heat insulation. Further, a more suitable selection can be made according to the application. In addition, 1100-2400 degreeC is preferable from the said viewpoint, and the heat processing temperature of a precursor fiber has more preferable 1300-2400 degreeC. In addition, in the said process 3, when heat processing of 700-1000 degreeC was performed, the heat insulating material of this invention which is the heat processing thing of 700-1000 degreeC, without performing this heat processing process, the carbon fiber obtained at process 3 is used. Carbon fiber may be used.

  The heating method in the heat treatment step is not particularly limited. For example, it can heat-process according to each usage method using well-known various heat processing furnaces.

  The atmosphere of the precursor fiber in the heat treatment step is preferably a non-oxidizing gas atmosphere, and more preferably an inert gas atmosphere such as nitrogen gas or argon gas.

  Other heat treatment conditions (for example, pressure, temperature increase rate, heat treatment holding time, etc.) are not particularly limited, and can be set as appropriate according to the intended use.

3. Heat insulating material The heat insulating material of the present invention is obtained using the carbon fiber for heat insulating material of the present invention described above.

  In a preferred embodiment of the present invention, it is preferable that the carbon fiber for a heat insulating material of the present invention is bonded by a heat resistant resin or a carbon bond.

  In this case, it is preferable that the heat insulating material of the present invention is mainly composed of a carbon fiber felt using the carbon fiber for heat insulating material of the present invention and a carbon matrix.

  Specifically, there are felt-based molded heat insulating materials and short fiber-based molded heat insulating materials. In the case of a felt-based molded heat insulating material, the carbon fiber felt entangles the carbon fiber for the heat insulating material of the present invention or the fiber (the precursor fiber) that becomes the carbon fiber for the heat insulating material of the present invention by heat treatment, for example, the needle punch. To obtain. The thickness of the carbon fiber felt is not particularly limited and is preferably 3 to 15 mm, although the preferred thickness varies depending on the intended use.

  In this case, it is preferable to first add a resin component capable of forming a carbon matrix by heat treatment to the carbon fiber felt to produce a so-called prepreg. In producing the prepreg, the carbon fiber felt to which the resin component is added may be dried as necessary.

  As the resin component, a synthetic resin such as a phenol resin, a furan resin, a polyimide resin, or an epoxy resin can be used. These resins may be used alone or in combination of two or more resins. The synthetic resin may be appropriately diluted with an organic solvent such as methyl alcohol or ethyl alcohol.

  In this case, the mixing ratio of the carbon fiber for heat insulating material of the present invention and the resin component is not particularly limited, but the moldability and heat insulating performance of the obtained heat insulating material with respect to 100 parts by mass of the carbon fiber for heat insulating material of the present invention. From the viewpoint, the resin component is preferably 5 to 120 parts by mass.

  In the case of the short fiber type heat insulating material, as one form, there is a method in which milled fibers and / or chop fibers are produced by a dry method or a wet method to produce a sheet in which fibers are randomly oriented in two dimensions. In the case of the dry method, for example, a method of preparing a dry sheet by air raid method while mixing heat-fusible fibers such as polyethylene, polyethylene terephthalate, polypropylene, etc. with the above milled fibers and / or chop fibers as appropriate. The length of the heat-fusible fiber may be 1 to 10 mm, and the mixing amount may be 1 to 30 parts by mass with respect to 100 parts by mass of the carbon fiber.

  In the case of a wet method, for example, the above milled fiber and / or chop fiber dispersed in a solvent such as water, acetone, alcohols, etc. are supplied to a mold having a screen at the bottom, paper-made, and dried to produce a wet sheet. The method of doing is mentioned. At this time, it can be set as the sheet | seat with which the milled fiber and / or the chop fiber were more bound by adding resin components, such as a phenol resin and a furan resin, in a solvent.

The sheet preferably has a basis weight of about 10 to 500 g / m ² , for example. A so-called prepreg is preferably prepared by adding a resin component that can be converted into a carbon matrix by heat treatment in the same manner as in the case of the carbon fiber felt described above.

  When mixing the carbon fiber for heat insulating materials of this invention and a resin component, you may mix various additives as needed. Examples of the additive include a lubricant, a reinforcing material, a filler, and a metal powder.

  Examples of the lubricant include artificial graphite, natural graphite, and molybdenum disulfide. Examples of the reinforcing material include glass fiber and aramid fiber. Examples of the filler include talc and glass beads. Examples of the metal powder include copper powder, brass powder and bronze powder. The content of these additives is not particularly limited, and can be within a range that does not impair the effects of the present invention.

  The heat insulating material thus obtained may be subjected to a heat treatment at a temperature of about 1000 to 2400 ° C. in an inert gas atmosphere as necessary, and the resin component may be carbonized to form a carbon bond.

  On the other hand, as another preferred embodiment of the present invention, there is a felt heat insulating material, and the carbon fiber felt can be used as a heat insulating material as it is as a nonwoven fabric made of carbon fiber for heat insulating material.

  When obtaining a laminated flat plate-shaped heat insulating material, it can be produced by stacking the prepregs. It is preferable that the flat plate-shaped heat insulating material is cured by press molding while heating, after the necessary number of prepregs are stacked according to the thickness of the final product. The heating temperature can be a temperature necessary for the resin component to cure.

  Moreover, not only a flat plate shape but also a cylindrical heat insulating material can be obtained by incorporating a step of winding a prepreg spirally around a cylindrical mandrel.

  On the other hand, by adopting the same method, it may be formed into a sheet shape, a test tube shape, a drawstring shape, a bat shape, a crucible shape, a container shape or the like.

  When the heat insulating material of the present invention is formed into a sheet shape, an external material can be insulated by wrapping around a side surface of a substantially cylindrical metal, a heater or the like. Moreover, you may wind around the inlets, such as a gas chromatography, and you may install in the predetermined location in oven oven.

  When the heat insulating material of the present invention is molded into a test tube shape, it is molded according to the external shape of a test tube, a beaker or other laboratory instrument, an experimental device, etc. Can be insulated from.

  When the heat insulating material of the present invention is formed into a drawstring shape, it is possible to insulate from the high temperature material with the outside inserted inside.

  When the heat insulating material of the present invention is formed into a bat shape, a high-temperature heat-fired body, a high-temperature container after heat treatment, and the like are put into the heat-resistant material of the bat shape, and the outside is the high-temperature heat-fired body, high-temperature container after heat treatment It can be insulated from etc.

  When shape | molding the heat insulating material of this invention in a crucible shape, the said crucible-shaped heat insulating material can be installed in the exterior of a crucible, and the exterior can be thermally insulated from a crucible.

  When the heat insulating material of the present invention is molded into a container shape, a high temperature material can be introduced into the inside and the outside can be insulated from the high temperature material inside.

  The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the embodiments.

Production Example 1
The isotropic pitch-based carbon fiber (mat fiber) of Example 1 was obtained as follows.

  First, coal-based isotropic pitch (carbon precursor) was used as a starting material, and the isotropic pitch was spun (spun) by the vortex method. Next, the pitch fiber obtained by the above-described treatment was subjected to an infusibilization treatment in an air (atmosphere) atmosphere. Next, the infusible fiber (infusible pitch fiber) obtained by the above-described treatment was subjected to a heat treatment at a predetermined temperature of 700 to 1000 ° C. in an inert gas atmosphere to perform a carbonization treatment. The spinning treatment, infusibilization treatment, and carbonization treatment were performed continuously. As a result, the isotropic pitch-based carbon fiber mat of Production Example 1 was obtained. This technique is also shown in Reinforced Plastics (1998) Vol. 34, No. 3, p.89-93.

Example 1: 800 ° C
In Production Example 1, the heat treatment under the inert gas atmosphere was performed at less than 800 ° C. to obtain an isotropic pitch-based carbon fiber mat. The carbon fiber mat was put into a resistance furnace, heated to 800 ° C. in an argon gas atmosphere, and the holding time at the maximum temperature was set to 2 hours, whereby the carbon fiber of Example 1 was obtained.

Example 2: 1000 ° C
In Production Example 1, the heat treatment under the inert gas atmosphere was performed at less than 1000 ° C. to obtain an isotropic pitch-based carbon fiber mat. The carbon fiber mat was put into a resistance furnace, heated to 1000 ° C. in an argon gas atmosphere, and the holding time at the maximum temperature was set to 2 hours, whereby the carbon fiber of Example 2 was obtained.

Example 3: 1200 ° C
The isotropic pitch-based carbon fiber mat obtained in Example 2 was put into a resistance furnace, heated to 1200 ° C. in an argon gas atmosphere, and the holding time at the maximum temperature was set to 2 hours. 3 carbon fibers were obtained.

Example 4: 1400 ° C
The isotropic pitch-based carbon fiber mat obtained in Example 2 was put into a resistance furnace, heated to 1400 ° C. in an argon gas atmosphere, and the holding time at the maximum temperature was set to 2 hours. 4 carbon fibers were obtained.

Example 5: 2000 ° C
The isotropic pitch-based carbon fiber mat obtained in Example 2 was put into a resistance furnace, heated to 2000 ° C. under an argon gas atmosphere, and the holding time at the maximum temperature was set to 2 hours. 5 carbon fibers were obtained.

Example 6: 2400 ° C
The isotropic pitch-based carbon fiber mat obtained in Example 2 was put in a resistance furnace, heated to 2400 ° C. in an argon gas atmosphere, and the holding time at the maximum temperature was set to 2 hours. 6 carbon fibers were obtained.

Average fiber diameter The carbon fibers obtained in Examples 1 to 6 were magnified 1000 times using a magnifying glass and an image analyzer manufactured by Hirox. At this time, 10 points of each pitch-based carbon fiber were arbitrarily selected, and the fiber diameters of the 10 points were measured. As a result, the fiber diameter of the carbon fibers of Example 1 was about 14 μm on average, and the fiber diameter of the carbon fibers of Examples 2 to 6 was about 13 μm on average.

Apparent density Apparent density was measured for each carbon fiber of Examples 1-6. Specifically, the apparent density of each carbon fiber was measured by a gas substitution method. As a measuring apparatus, a dry automatic densimeter Accupic 1330-03 manufactured by Micromeritics was used. The gas used for the measurement was helium gas, and the temperature was 25 ° C.

  The apparent density is a value obtained by dividing the mass of the sample by the volume obtained by removing the open pores (pores) from the external volume of the sample. In this case, the open pores (pores) are considered to be pores (pores) through which helium gas penetrates. It can be evaluated that the apparent density indicates the size of closed pores. Specifically, since there is no change in fiber diameter, that is, volume, it is considered that the smaller the apparent density, the larger the closed pores. This result is consistent with the result of the closed pore size estimated from the following Guinier plot of carbon fiber by the small angle X-ray scattering method.

  The results are shown in Table 1.

Thermal conductivity The thermal conductivity in the fiber axis direction of the carbon fibers of Examples 1 to 3 and 5 to 6 is expressed by the following formula from specific heat, thermal diffusivity and apparent density:
Thermal conductivity = (apparent density) x (specific heat) x (thermal diffusivity)
Calculated by

The specific heat of the carbon fibers of Examples 1 to 3 and 5 to 6 was performed at a heating rate of 10 ° C./min using a differential scanning calorimeter manufactured by Perkin-Elmer. At this time, the standard sample was α-Al ₂ O ₃ , the atmosphere was dry nitrogen, and the measurement temperature was 25 ° C.

  The thermal diffusivities of the carbon fibers of Examples 1 to 3 and 5 to 6 were obtained by an optical alternating current method using a thermal diffusivity measuring device manufactured by ULVAC-RIKO. The irradiation light was a semiconductor laser. The atmosphere was in a vacuum and the measurement temperature was about 25 ° C.

  The results are shown in Table 2.

Adsorption / desorption isotherm (open pore volume)
The adsorption and desorption isotherms of the carbon fibers of Examples 2 and 6 were determined. Specifically, the adsorption / desorption isotherm by N ₂ (77K) adsorption was determined using BELSORP-max manufactured by Microtrack Bell Co., Ltd.

  Next, based on the obtained adsorption / desorption isotherm, the specific surface area and the total pore volume of each carbon fiber were determined by the BET method. In the BET method, only the pores existing on the carbon fiber surface can be determined, and therefore the total pore volume corresponds to the amount of open pores.

  The results are shown in Table 3 and FIG. In FIG. 1, the left figure shows the results of Example 2, and the right figure shows the results of Example 6. In any of the carbon fibers, the adsorption curve and the desorption curve are almost traced, and it is shown that there are almost no pores on the surface (the amount of open pores is not present or very small even if it exists).

Size of closed pores The carbon fibers of Examples 2 to 6 were measured by a small angle X-ray scattering method. Specifically, a fully automatic horizontal multipurpose X-ray diffractometer SmartLab manufactured by Rigaku Corporation was used, the incident X-ray wavelength was 0.154 nm (CuKα), and the measurement time was 1800 seconds. The sample was dried at 100 ° C. for 2 hours or more in a vacuum dryer before measurement.

  In the small-angle X-ray scattering method, open pores cannot be distinguished from closed pores. However, in the carbon fibers of Examples 2 to 6, the open pores do not exist or the amount of open pores is very small, if any, so the pores are closed. It can be a pore.

The Guinier plot by the small angle X ray scattering method of the carbon fiber of Examples 2-6 is shown in FIG. The Guinier plot is a plot of the natural logarithm ln (I (s)) of the scattering intensity against the square of the scattering parameter s (= 4π sin θ / λ). Here, λ is the X-ray wavelength. By approximating the Guinier region with a straight line, the radius of inertia can be obtained from the inclination. Here, the Guinier region ^{s 2} is the 0.0002A ^-2 following areas. The slope of the line = - a (inertia ^radius) 2/3.

  From the relationship between the radius of inertia and the shape parameter, when the closed pore is assumed to be a sphere, the radius of the sphere is as follows.

When the closed pore is assumed to be a sphere, the radius of the sphere = (5/3) ^1/2 × (inertia radius)
Table 4 shows the results of the calculated radius of inertia and the radius of the closed pore when the closed pore is assumed to be a sphere.

Claims (9)

When the thermal conductivity in the fiber axis direction is 1 to 10 W / m · K, the amount of open pores is 0.1 cm ³ / g or less , and the closed pores estimated by the Guinier plot by the small angle X-ray scattering method are assumed to be spheres A carbon fiber for a heat insulating material, in which the radius of closed pores is 7 nm or more and is not mechanically joined using only an isotropic pitch as a carbon precursor. The carbon fiber for heat insulating materials according to claim 1, wherein the apparent density is less than 2.0 g / cm ³ . The carbon fiber for heat insulating materials according to claim 1 or 2 , which is a heat-treated product at 1300 to 2400 ° C. When the thermal conductivity in the fiber axis direction is 1 to 10 W / m · K, the amount of open pores is 0.1 cm ³ / g or less , and the closed pores estimated by the Guinier plot by the small angle X-ray scattering method are assumed to be spheres A method for producing carbon fibers for a heat insulating material, wherein the radius of closed pores is 7 nm or more , and is not mechanically bonded using only an isotropic pitch as a carbon precursor,
A step of heat-treating an infusible fiber having only an isotropic pitch as a carbon precursor at 700 to 1000 ° C., and
The precursor fiber carbonization process is performed by the process, as engineering heat treatment at 1300 2400 ° C.
A manufacturing method comprising: The manufacturing method of Claim 4 which does not perform mechanical joining. The heat insulating material using the carbon fiber for heat insulating materials in any one of Claims 1-3 , or the carbon fiber for heat insulating materials obtained by the manufacturing method of Claim 4 or 5 . The heat insulating material according to claim 6 , wherein the carbon fiber for heat insulating material is bonded by a heat resistant resin or a carbon bond. The heat insulating material according to claim 6 , wherein the heat insulating material is formed into a sheet shape, a test tube shape, a drawstring shape, a bat shape or a crucible shape using a non-woven fabric made of the carbon fiber for heat insulating material. The carbon fiber heat insulating material is bonded by heat-resistant resin or carbon bond thereof, and a sheet-like, tube-shaped, drawstring shape, bat shape is molded crucible shape, or shape of a container, according to claim 6 Insulation material.

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