WO2020059819A1

WO2020059819A1 - Carbon-fiber-molded heat insulator and manufacturing method thereof

Info

Publication number: WO2020059819A1
Application number: PCT/JP2019/036824
Authority: WO
Inventors: 雅和森本; 曽我部　敏明; 寛吉村
Original assignee: 大阪ガスケミカル株式会社
Priority date: 2018-09-21
Filing date: 2019-09-19
Publication date: 2020-03-26
Also published as: CN112424523A; JP7373498B2; JPWO2020059819A1; CN112424523B

Abstract

[Problem] To provide a carbon-fiber-molded heat insulator in which heat insulation performance is high and stress breakage can be prevented. [Solution] A carbon-fiber-molded heat insulator in which a plurality of carbon fiber sheets configured from a carbonaceous substance are stacked, each of the carbon fiber sheets having carbon fiber felt in which carbon fibers are three-dimensionally and randomly interlaced, and a protective carbon layer that covers a carbon fiber surface of the carbon fiber felt. The carbon fibers include isotropic-pitch carbon fibers and polyacrylonitrile carbon fibers. The ratio by mass of the isotropic-pitch carbon fibers relative to the total mass of the carbon fibers is 25% or greater, the ratio by mass of the polyacrylonitrile carbon fibers relative to the total mass of the carbon fibers, is 5% or greater, the ratio of the combined mass of the isotropic-pitch carbon fibers and the polyacrylonitrile carbon fibers relative to the total mass of the carbon fibers is 90% or greater, and the bulk density of the carbon-fiber-molded heat insulator is 0.10 to 0.25 g/cm³.

Description

Carbon fiber molded heat insulating material and method for producing the same

The present invention relates to a molded heat insulating material using carbon fibers.

Since carbon fiber has excellent thermal and chemical stability, carbon fiber felt formed by entanglement of carbon fiber and carbon fiber sheet obtained by impregnating carbon fiber felt with a resin material and carbonizing it are heat insulating materials. Widely used for sound absorbing materials. Carbon fiber felt has an advantage of being excellent in flexibility, and a carbon fiber sheet has an advantage of being excellent in shape stability and capable of fine processing. In addition, when the carbon fiber sheet is used in an environment in which oxygen gas or SiO gas is generated, the carbonized resin material reacts with these gases prior to the carbon fiber, so that the carbon fiber is less likely to deteriorate. .

Which one to use is appropriately selected according to the purpose of use and application. Here, the formed heat insulating material formed by laminating carbon fiber sheets is excellent in thermal stability, heat insulation performance and shape stability. It is used as a heat insulator for high-temperature furnaces such as sintering furnaces and vacuum deposition furnaces.

In recent years, the demand for energy saving and cost reduction has been further increased, and a molded heat insulating material having lower thermal conductivity and a molded heat insulating material having the same heat insulation performance and longer life as the conventional one have been demanded. .

成形 Also, stress may be applied to the molded heat insulating material depending on the use condition, but if the stress is excessively applied, the carbon fiber sheet constituting the formed heat insulating material is cracked. When the crack progresses, the carbon fiber sheet may be broken, and in such a case, the heat insulating function cannot be exhibited. When a carbon fiber felt having excellent flexibility is used, such a problem does not occur, but in some cases, a molded heat insulating material must be used from the viewpoint of shape stability and the like.

Here, the case where external stress is applied to the molded heat insulating material, the case where the molded heat insulating material comes into contact with the surrounding members, and the case where internal stress is applied is the case where the molded heat insulating material is locally rapidly heated. And so on.

技術 By the way, as a technique relating to a heat insulating material using carbon fiber, the following Patent Document 1 is cited.

JP 2008-196552 A

技術 The technique of Patent Document 1 is a technique relating to a carbon fiber heat insulating material obtained by compression-molding and firing a laminate of a resin-impregnated carbon fiber felt impregnated or coated with a resin binder and a carbon fiber felt.

According to this technology, a decrease in heat insulation is suppressed while increasing rigidity, and workability on a wall such as a heating furnace can be facilitated.

However, in this technology, it is essential to include a portion of carbon fiber felt that does not contain a resin, but this portion is poor in workability and difficult to finely process. There is a problem that the strength of the carbon fiber is low and the component of the carbon fiber is not oxidized prior to the carbon fiber.

The present invention has been made to solve the above-described problems, and has as its object to provide a carbon fiber molded heat insulating material having excellent heat insulating performance and capable of suppressing breakage due to stress.

The present invention according to a carbon fiber molded heat insulating material for solving the above problems is configured as follows.
A carbon fiber molded heat insulating material in which a plurality of carbon fiber sheets made of a carbonaceous material are laminated, wherein the carbon fiber sheet comprises a carbon fiber felt in which carbon fibers are randomly entangled three-dimensionally, and the carbon fiber felt. And a protective carbon layer covering the surface of the carbon fiber. The carbon fibers include isotropic pitch-based carbon fibers and polyacrylonitrile-based carbon fibers. The mass ratio of the isotropic pitch-based carbon fiber to the total mass of the carbon fiber is 25% or more, and the mass ratio of the polyacrylonitrile-based carbon fiber to the total mass of the carbon fiber is 5% or more, The ratio of the total mass of the isotropic pitch-based carbon fiber and the polyacrylonitrile-based carbon fiber to the total mass of the carbon fiber is 90% or more, and the bulk density of the carbon fiber molded heat insulating material is 0.10 or more. ０．２0.25 g / cm ³ .

In the above configuration, the carbon fibers constituting the carbon fiber sheet include isotropic pitch-based carbon fibers and polyacrylonitrile-based carbon fibers (hereinafter, referred to as “PAN-based carbon fibers”). Preferably, the mass of the isotropic pitch-based carbon fiber is 25% by mass or more, the mass of the PAN-based carbon fiber is 5% by mass or more, and the total of both is 90% by mass or more.

断熱 The heat insulating performance of the carbon fiber molded heat insulating material tends to increase as the ratio of the space obtained by binding the contact points between the carbon fibers and the volume of the space increase. Further, the smaller the solid conduction in the thickness direction of the molded heat insulating material, the higher the tendency. In addition, the strength of the carbon fiber molded heat insulating material tends to increase as the number of protective carbon layers binding the contact points between the carbon fibers increases.

Here, as a result of intensive research, the present inventors have learned the following. PAN-based carbon fibers have high strength and elasticity as a single substance, and are difficult to be oriented in a direction parallel to the thickness direction of the sheet (easy to be randomly oriented two-dimensionally), and are difficult to be entangled with each other. Have. For this reason, the carbon fiber molded heat insulating material using only the PAN-based carbon fiber does not easily increase the volume of the space between the carbon fibers. Further, in the carbon fiber molded heat insulating material using only PAN-based carbon fiber, since the fibers are hardly entangled with each other, the strength cannot be increased unless the amount of the protective carbon layer covering the carbon fiber surface is increased. However, after the protective carbon layer that binds the carbon fiber contacts is broken, the PAN-based carbon fiber maintains the strength of the carbon fiber sheet to a certain extent, so if one carbon fiber sheet cracks, It is difficult for the crack to continuously progress to another (adjacent) carbon fiber sheet, and the carbon fiber molded heat insulating material does not break at once.

On the other hand, the isotropic pitch-based carbon fiber has the property that the flexibility is high, the fibers are easily oriented three-dimensionally at random, the fibers are easily entangled with each other, and the strength of a simple substance is lower than that of the PAN-based carbon fiber. Have. For this reason, the carbon fiber molded heat insulating material using only the isotropic pitch-based carbon fiber easily increases the volume of the space between the carbon fibers, but easily causes solid conduction by the carbon fiber. Further, a carbon fiber molded heat insulating material using only isotropic pitch-based carbon fiber has high strength as a carbon fiber molded heat insulating material even though there are many contacts between carbon fibers and the amount of protective carbon layer is small. However, the strength of the carbon fiber sheet after the protective carbon layer that binds the carbon fiber contacts is broken is insufficient, and the cracks generated in one carbon fiber sheet continue to the other carbon fiber sheet. It is easy to progress, and the carbon fiber molded heat insulating material is destroyed at a stretch.

On the other hand, the isotropic pitch-based carbon fiber and the PAN-based carbon fiber are set at a mass mixing ratio as described above, and are randomly entangled three-dimensionally. By setting the bulk density to 0.10 to 0.25 g / cm ³ , a carbon fiber molded heat insulating material having both advantages of the isotropic pitch-based carbon fiber and the PAN-based carbon fiber can be realized. That is, while the space volume related to heat insulation is increased by the isotropic pitch-based carbon fiber, the solid conduction of the carbon fiber can be reduced by the PAN-based carbon fiber, and thereby the heat insulation performance can be dramatically improved. .

Also, on the strength side, while maintaining the strength of the carbon fiber sheet by the isotropic pitch-based carbon fiber, after the cracks caused by the stress, the strength of the carbon fiber sheet is kept to a certain degree by the PAN-based carbon fiber. It is possible to realize a carbon fiber molded heat insulating material which is maintained and hardly causes crack propagation.

If the bulk density is too low, the strength becomes insufficient, while if the bulk density is too high, solid conduction easily occurs, and the volume and ratio of the space between the carbon fibers become small, so that the heat insulating performance is reduced. Will be insufficient.

Here, if the amount of the isotropic pitch-based carbon fiber in the entire carbon fiber is too small, the effect of the isotropic pitch-based carbon fiber cannot be sufficiently obtained. If the amount of the PAN-based carbon fiber in the entire carbon fiber is too small, the effect of the PAN-based carbon fiber cannot be sufficiently obtained. Therefore, the mass of the isotropic pitch-based carbon fiber in the entire carbon fiber is adjusted to 25% or more, preferably 27% or more, and more preferably 30% or more. The mass of the PAN-based carbon fiber in the entire carbon fiber is adjusted to 5% or more, preferably 9% or more, more preferably 10% or more.

The mass ratio of the isotropic pitch-based carbon fiber to the PAN-based carbon fiber in the carbon fiber is preferably 20:80 to 95: 5, more preferably 27:73 to 91: 9, and 30:70 to 90:90. : 10 is more preferred. From the viewpoint of further improving the heat insulation performance, the mass ratio may be set to 40:60 to 60:40.

The carbon fiber may include other carbon fibers such as anisotropic pitch-based carbon fiber and rayon-based carbon fiber. However, in order to sufficiently obtain the effects of the isotropic pitch-based carbon fiber and the PAN-based carbon fiber, The total mass of the isotropic pitch-based carbon fiber and the PAN-based carbon fiber in the whole fiber is 90% or more. The ratio of the total mass is more preferably 95% or more, and still more preferably 100% (that is, it is most preferable not to include other carbon fibers other than the isotropic pitch-based carbon fiber and the PAN-based carbon fiber). preferable).

Here, the shape of the carbon fiber molded heat insulating material is not particularly limited, and one in which a plurality of plate-like carbon fiber sheets are laminated, or one or a plurality of carbon fiber sheets, which are spirally wound and laminated. And the like.

炭素 Further, it is preferable that the carbon fiber sheets constituting the carbon fiber molded heat insulating material have the same bulk density, thickness, mass mixing ratio of carbon fibers, and the like.

In addition, the carbon fiber sheet placed on the surface (one or both) of the carbon fiber molded heat insulating material is impregnated with pyrolytic carbon or contains carbonaceous particles such as graphite particles and amorphous carbon particles. May be used. Further, a configuration may be employed in which a surface layer having a high bulk density, a high volume fraction of carbon fibers, and the like is attached to the surface of the carbon fiber molded heat insulating material. With such a configuration, it is possible to further suppress the wear and dust generation of the carbon fiber molded heat insulating material. If these are not included, the manufacturing process can be simplified and the cost can be reduced. It is preferable that the carbon fiber sheet other than the surface does not contain components other than the carbon fiber and the protective carbon layer.

炭素 The carbon fiber molded heat insulating material according to the present invention can be used as a molded heat insulating material for high temperature furnaces such as a single crystal silicon pulling apparatus, a polycrystalline silicon casting furnace, a sintering furnace for metals and ceramics, and a vacuum evaporation furnace.

活性 If there is an active gas (oxygen gas, SiO gas, etc.) mixed as an impurity or generated in the furnace around the carbon fiber molded heat insulating material, the protective carbon layer reacts with the active gas prior to the carbon fiber. Thereby, it is suppressed that carbon fiber and active gas react and deteriorate.

Here, when the carbonaceous material of the protective carbon layer reacts with oxygen gas, it is removed as carbon dioxide gas. When it reacts with SiO gas, it remains as SiC and remains without being removed. Since the skeletal structure constituted by the fibers is maintained, the heat insulating effect obtained by the skeletal structure forming a large number of spaces is maintained.

(4) The amount of the protective carbon layer is determined in consideration of the required heat insulation performance, strength, atmosphere gas in the use environment, life requirement, installation space, and the like. In general, the smaller the amount of the protective carbon layer, the higher the heat insulation performance, and the larger the amount of the protective carbon layer, the higher the durability and strength against oxidative consumption and the like. The ratio between the mass of the carbon fibers and the mass of the protective carbon layer in the molded heat insulating material is preferably from 100: 5 to 100: 50, more preferably from 100: 5 to 100: 45, and from 100: 8 to 100. : 42 is more preferable.

Note that the molded carbon fiber heat insulating material is formed by laminating a plurality of carbon fiber sheets made of carbonaceous material. Therefore, the carbon fiber molded heat insulating material does not contain any components other than carbonaceous material.

In the above configuration, the isotropic pitch-based carbon fiber may be a curved carbon fiber. When the carbon fibers are curved, the entanglement between the carbon fibers can be further increased. In addition, the length in the natural state can be made smaller than that of a linear shape, thereby making it possible to reduce the influence of a decrease in heat insulation performance due to solid conduction.

Here, the term “curved carbon fiber” refers to a length when the fiber is linearly pulled (ie, fiber length) L1, the maximum length of the curved fiber in the natural state (or the maximum point in the natural state). When the dimension, that is, the distance between any two points on the curved fiber is measured, and the length at which this distance is greatest) is L2, the ratio of L1 to L2 (L1 / L2) is 1.3. It is defined as a carbon fiber having the above curved shape. In some cases, such as when the fiber is pulled, the curved shape of the fiber may not be temporarily maintained. Therefore, the length L2 is set to the maximum value in the natural state of the curved fiber after the fiber having the length L1 is freely dropped from a predetermined height (for example, about 30 to 100 cm) in order to obtain more accurate measurement conditions. It may be measured as length. In addition, the maximum length L2 often varies among the curved carbon fibers, and can usually be obtained as an average value (average maximum length) of a plurality of measured values. In this case, the number of measurement values for obtaining the average value (the number of measurements) is preferably 5 or more, more preferably 10 or more, and still more preferably 20 or more. On the other hand, the upper limit of the number of measurements is not particularly limited, but is about 200, preferably about 100, and more preferably about 50.

The PAN-based carbon fiber is not curved (L1 / L2 is less than 1.3, that is, L1 / L2 is less than 1.3, because it is difficult to make the PAN-based carbon fiber curved (L1 / L2 is 1.3 or more)). It is preferable to use a linear one).

The method for manufacturing a carbon fiber molded heat insulating material according to the present invention for solving the above problems is configured as follows.
A felt preparation step of forming carbon fiber felt by randomly entangled carbon fibers three-dimensionally, a prepreg preparation step of impregnating the carbon fiber felt with a thermosetting resin to prepare a prepreg of a carbon fiber sheet, A laminating step of stacking the prepreg to form a prepreg laminate, heating the prepreg laminate under pressure, a binding step of binding the prepreg laminate, and applying the bound prepreg laminate to an inert gas atmosphere. And a carbonization step of carbonizing the thermosetting resin. The carbon fibers include (i) an isotropic pitch-based carbon fiber and a polyacrylonitrile-based carbon fiber, and (ii) the mass ratio of the isotropic pitch-based carbon fiber to the total mass of the carbon fiber is 25%. (Iii) the mass ratio of the polyacrylonitrile-based carbon fiber in the total mass of the carbon fiber is 5% or more, and (iv) the isotropic pitch-based carbon fiber and the polyacrylonitrile in the total mass of the carbon fiber. The carbon fiber whose total mass ratio is 90% or more is used.

により By the above manufacturing method, the carbon fiber molded heat insulating material according to the present invention can be manufactured.

As described above, according to the present invention, it is possible to realize a carbon fiber molded heat insulating material having high heat insulating performance and capable of suppressing destruction due to stress.

FIG. 1 is a perspective view schematically showing a structure of a carbon fiber molded heat insulating material according to the present invention. FIG. 2 is a diagram showing an outline of the three-point bending test. FIGS. 3A and 3B are microscopic cross-sectional photographs of the carbon fiber-molded heat insulating material according to Example 1, in which FIG. 3A shows a plan view and FIG. 3B shows a side view.

(Embodiment)
FIG. 1 is a perspective view schematically showing a structure of the carbon fiber molded heat insulating material according to the present embodiment. The carbon fiber molded heat insulating material 100 according to the present embodiment, a carbon fiber felt in which carbon fibers are randomly entangled three-dimensionally, and a protective carbon layer made of carbonaceous material covering the carbon fiber surface of the carbon fiber felt, And the carbon fiber sheet 1 made of carbonaceous material is laminated. In one embodiment shown in FIG. 1, a total of eight carbon fiber sheets 1 are laminated. In the carbon fiber sheet 1, carbon fibers are randomly oriented three-dimensionally.

The carbon fibers constituting the carbon fiber sheet 1 include isotropic pitch-based carbon fibers and PAN-based carbon fibers, and the proportion of the isotropic pitch-based carbon fibers in the total mass of the carbon fibers is 25% or more; The ratio of the PAN-based carbon fiber to the total mass of the carbon fiber is regulated to 5% or more, and the ratio of the total mass of the isotropic pitch-based carbon fiber and the PAN-based carbon fiber to the total mass of the carbon fiber is regulated to 90% or more. I have. The bulk density of the carbon fiber molded heat insulating material 100 is set to 0.10 to 0.25 g / cm ³ .

Here, the PAN-based carbon fiber has high strength and elasticity as a single substance, the fiber is hardly oriented in a direction parallel to the thickness direction of the sheet (it is easy to be randomly oriented two-dimensionally), and the fibers are hardly entangled with each other. . On the other hand, isotropic pitch-based carbon fibers have high flexibility, fibers are easily oriented three-dimensionally at random, fibers are easily entangled, and the strength and elasticity of a single substance are lower than PAN-based carbon fibers. By controlling the mass mixing ratio of the isotropic pitch-based carbon fiber and the PAN-based carbon fiber as described above, mainly the isotropic pitch-based carbon fiber is three-dimensionally and randomly, and the PAN-based carbon fiber is A two-dimensionally randomly oriented carbon fiber molded heat insulating material is obtained. Such a molded heat insulating material may have both advantages of the isotropic pitch-based carbon fiber and the PAN-based carbon fiber.

In other words, on the heat insulating surface, the PAN-based carbon fibers reduce the solid conduction of the carbon fibers while increasing the space between the PAN-based carbon fibers by expanding the voids between the PAN-based carbon fibers with isotropic pitch-based carbon fibers. And the heat insulation performance can be improved. Also, on the strength side, while maintaining the strength of the carbon fiber sheet by the isotropic pitch-based carbon fiber, after the cracks caused by the stress, the strength of the carbon fiber sheet is kept to a certain degree by the PAN-based carbon fiber. It is possible to realize a carbon fiber molded heat insulating material which is maintained and hardly causes crack propagation.

Here, when the amount of the isotropic pitch-based carbon fiber in the total mass of the carbon fiber is too small, the amount of the PAN-based carbon fiber is too small, or the total mass of both is too small, these effects are obtained. Is not obtained enough.

Here, the isotropic pitch-based carbon fiber is a carbon fiber obtained from an infusible-treated isotropic pitch as a raw material, and a commercially available one can be used. Pitch is chemically a mixture of innumerable condensed polycyclic aromatic compounds, wood, liquid tar obtained at the time of dry distillation of coal, bitumen obtained from oil sand, oil obtained by dry distillation of oil shale, There are solids at room temperature obtained by heat-treating and polymerizing residual oil obtained by distillation of crude oil, tar produced by cracking of petroleum fraction, and the like. Specific examples include pitch derived from coal, pitch derived from petroleum, and synthetic pitch obtained by polymerizing aromatic compounds such as naphthalene.

As the isotropic pitch-based carbon fiber, a fiber produced by a known method can be used. For example, pitch from petroleum or coal is spun and deposited on a table to obtain a mat of pitch fibers. The obtained mat is an aggregate of pitch fibers having different lengths in a range of approximately 5 to 400 mm. In addition, the spinning method is not particularly limited, and spinning by a melt spinning method or a vortex method can be employed. According to the vortex method, a curved fiber is obtained, and according to the melt spinning method, a non-curved (linear) fiber is obtained. Pitch fibers are subjected to infusibilization treatment and carbonization treatment to form a carbon fiber mat. In addition, the infusibilizing step is a step in which oxygen is introduced into the surface of the pitch fiber to oxidize it. The atmosphere in the infusibilization step can be air or NOx. The temperature of the carbonization treatment is not particularly limited, but may be 700 to 1200 ° C. in consideration of economy and the like. When curved fibers are used, the fibers are more likely to be entangled in the carbon fiber felt, and the strength is easily increased.

The isotropic pitch-based carbon fiber preferably has an average fiber diameter (diameter) of 7 to 20 μm, more preferably 9 to 18 μm, and further preferably 11 to 15 μm. Further, the length is preferably from 5 to 400 mm, more preferably from 8 to 350 mm, and preferably from 10 to 300 mm.

The PAN-based carbon fiber is obtained by carbonizing a polyacrylonitrile fiber, and a commercially available product can be used. The PAN-based carbon fiber preferably has a fiber length of 20 to 200 mm, more preferably 30 to 80 mm. Further, the average fiber diameter (diameter) is preferably 5 to 13 μm, more preferably 5 to 9 μm, and further preferably 5 to 7 μm.

In addition, any carbon fiber is not particularly limited as a microscopic structure of the carbon fiber, and only those having the same shape (curved, linear, cross-sectional shape, etc.) may be used, or different structures may be used. However, it is preferable that the isotropic pitch-based carbon fiber has a curved shape, and the PAN-based carbon fiber has a small degree of curvature (linear shape).

In addition, the shape of the carbon fiber felt constituting the carbon fiber sheet is not particularly limited, and the length and width are not particularly limited. For example, a carbon fiber felt having a thickness of about 3 to 20 mm can be used. Further, as the microscopic structure of the carbon fiber felt, a carbon fiber felt in which carbon fibers oriented in random directions three-dimensionally intersect is used.

(4) The protective carbon layer covers the entire surface of the carbon fiber constituting the carbon fiber felt or a part of the surface of the carbon fiber. The protective carbon layer may be carbonaceous (amorphous carbon or graphitic carbon), and the amorphous carbon may be either non-graphitizable or graphitizable. The compound from which the protective carbon layer is derived is not particularly limited, but it is preferable to use a resin material that can impregnate the carbon fiber felt. Among them, a thermosetting resin such as a phenol resin, a furan resin, a polyimide resin, and an epoxy resin is preferable. When a thermosetting resin is used, the carbon fibers and the laminated carbon fiber sheets can be easily and firmly bonded to each other by thermosetting and carbonizing.

Here, only one thermosetting resin may be used, or two or more thermosetting resins may be used in combination. Further, the thermosetting resin may be included in the carbon fiber felt as it is, or may be diluted with a solvent and included in the carbon fiber felt. As the solvent, alcohol such as methyl alcohol and ethyl alcohol can be used.

炭素 In addition, the carbon fiber felt may be cut or the like after producing a carbon fiber molded heat insulating material using a long or long material, or may be cut in advance to the size of the carbon fiber molded heat insulating material.

Here, the bulk density of the carbon fiber molded heat insulating material is more preferably 0.10 ~ 0.23g / cm ^3, more preferably from 0.10 ~ 0.20g / cm ^3.

Further, the mass ratio between the carbon fiber and the protective carbon layer in the carbon fiber sheet is preferably 100: 5 to 100: 50, more preferably 100: 5 to 100: 45, and 100: 8 to 100: 45. : 42 is more preferable.

The thickness of each carbon fiber sheet is preferably 3 to 20 mm, more preferably 5 to 15 mm, and further preferably 6 to 12 mm.

Next, a method for manufacturing the carbon fiber molded heat insulating material will be described.

(Preparation of carbon fiber felt)
As the carbon fiber felt, a carbon fiber felt produced by a known method can be used, and a method in which carbon fibers are easily three-dimensionally orientated randomly is adopted. As a method for forming a carbon fiber felt, for example, (1) a carbon fiber in which isotropic pitch-based carbon fiber and PAN-based carbon fiber are mixed (hereinafter, referred to as “carbon fiber mixture” in this section) is used. (2) stirring and mixing the carbon fiber mixture in a solution and depositing it on a papermaking net to form a felt. And (3) a method in which a carbon fiber mixture is spun into a felt shape by carding means such as a card machine, and then the degree of entanglement between the carbon fibers is adjusted using a needle punch. This carbon fiber felt preferably has a thickness of 3 to 20 mm, more preferably 5 to 15 mm. The basis weight of the carbon fiber felt is, for example, preferably 100 to 2000 g / m ² , and more preferably 300 to 1500 g / m ² .

(Prepreg manufacturing process)
After that, a thermosetting resin solution is sprayed on the carbon fiber felt and dipped in the thermosetting resin solution, or a thermosetting resin solution is applied to prepare a prepreg. At this time, the amount of the synthetic resin is adjusted so that the mass ratio between the carbon fiber and the protective carbon layer after firing is 100: 5 to 100: 100.

(Lamination process)
A plurality of the prepregs produced as described above are sequentially laminated so as to have a desired thickness. Alternatively, one or more prepregs may be spirally wound around a cylindrical or cylindrical mandrel and laminated.

(Binding process and carbonization process)
The laminated body produced as described above is heated while being pressurized to thermally cure the thermosetting resin. Thereafter, the mixture is heated in an inert gas atmosphere at 1500 to 2500 ° C. for a predetermined time (for example, 1 to 20 hours) to carbonize the thermosetting resin to obtain a carbon fiber molded heat insulating material.

Here, the bulk density of the carbon fiber molded heat insulating material can be determined by changing the basis weight of the carbon fiber felt, or changing the thickness of the laminate (the thickness of the spacer to be used) after pressing in the binding step. Can be adjusted. When the basis weight is increased or the thickness of the spacer is reduced, the bulk density tends to increase. The bulk density after firing can be inferred from the apparent volume of the laminate after pressurization, and the sum of the mass of carbon fibers and the mass of the residual carbon content of the thermosetting resin.

Here, the term “carbonization” as used in the present specification means a broad meaning including graphitization. For example, when heat treatment is performed at a temperature of 2000 ° C. or more, the graphite structure may be developed. In the present invention, the carbonaceous material constituting the carbon fiber molded heat insulating material is either amorphous carbon or graphitic carbon. May be.

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

(Example 1)
(Preparation of carbon fiber)
Coal-derived isotropic pitch was melt-spun by a vortex method to obtain a mat composed of curved pitch fibers. This mat was an aggregate of pitch fibers, and the length of the pitch fibers was approximately 10 to 300 mm. This mat was heat-treated in an air atmosphere from room temperature to about 250 to 300 ° C. for a total of 30 minutes to infusify the pitch fibers to obtain a fiber mat. This fiber mat was carbonized at about 1000 ° C. in an inert gas atmosphere to obtain a mat of isotropic pitch-based carbon fibers (average diameter 13 μm). The length when the carbon fiber is pulled straight (ie, the fiber length) is L1, the maximum length in the natural state of the curved fiber (or the maximum point size in the natural state, ie, on the curved fiber). When the distance between any two points is measured and the length at which this distance is greatest) is L2, L1 / L2 (the ratio of L1 to L2) is 2.1 (the arithmetic mean of 25 samples). Met.

(Preparation of carbon fiber felt)
The above-mentioned isotropic pitch-based carbon fiber and PAN-based carbon fiber (manufactured by Toray Industries, Inc., average fiber diameter 7 μm, length 60 mm) are mixed and spread at a mass ratio of 50:50, and needle punching is performed. It was entangled to produce a carbon fiber felt (length 45 m, width 1000 mm, thickness 9.5 mm, basis weight 470 g / m ² ).

(Prepreg manufacturing process)
The carbon fiber felt was cut into a length of 1500 mm and a width of 1000 mm. A prepreg was prepared by immersing a resol type phenolic resin-based thermosetting resin solution in the cut carbon fiber felt. At this time, the addition amount of the phenol resin-based thermosetting resin in the prepreg is determined by the amount of carbonaceous material obtained by carbonizing the phenol resin-based thermosetting resin when the prepreg is heat-treated at 2000 ° C. (that is, the amount of the protective carbon layer). ) Was adjusted to 8 parts by mass with respect to 100 parts by mass of carbon fiber.

(Lamination process)
Thirteen layers of the prepreg were laminated to prepare a prepreg laminate.

(Binding process and carbonization process)
The prepreg laminate thus obtained was pressurized at 200 ° C. for 90 minutes to thermally cure the phenol resin while compressing the prepreg laminate obtained so as to have a thickness of about 50 mm, thereby binding the prepreg laminate (binding). Process). Next, the prepreg laminate after the binding step was heat-treated at 2,000 ° C. in an inert atmosphere to obtain a plate-shaped carbon fiber molded heat insulating material (carbonization step). The bulk density of the obtained carbon fiber molded heat insulating material was 0.12 g / cm ³ .

(Example 2)
As the carbon fiber felt, one obtained by mixing and opening isotropic pitch-based carbon fibers and PAN-based carbon fibers at a mass ratio of 30:70 and entangled by a needle punch method was used. This carbon fiber felt had a length of 20 m, a width of 1000 mm, a thickness of 9.5 mm, and a basis weight of 508 g / m ² . Next, a molded heat insulating material according to Example 2 was produced in the same manner as in Example 1 except that this carbon fiber felt was used. The bulk density of the obtained molded heat insulating material was 0.13 g / cm ³ .

(Example 3)
As the carbon fiber felt, one obtained by mixing and opening isotropic pitch-based carbon fibers and PAN-based carbon fibers at a mass ratio of 90:10 and entangled by a needle punch method was used. This carbon fiber felt had a length of 20 m, a width of 1000 mm, a thickness of 9.5 mm, and a basis weight of 470 g / m ² . Next, a molded heat insulating material according to Example 3 was produced in the same manner as in Example 1 except that this carbon fiber felt was used. The bulk density of the obtained molded heat insulating material was 0.12 g / cm ³ .

(Example 4)
In the prepreg production step, the same as in Example 1, except that the amount of the phenolic resin-based thermosetting resin in the prepreg was changed so that the amount of the protective carbon layer was 42 parts by mass with respect to 100 parts by mass of the carbon fiber. Thus, a molded heat insulating material according to Example 4 was produced. The bulk density of the obtained molded heat insulating material was 0.17 g / cm ³ .

(Comparative Example 1)
As the carbon fiber felt, one prepared using only PAN-based carbon fiber (length 40 m, width 1000 mm, thickness 5 mm, weight per unit area: 520 g / m ² ) was used, and the prepreg laminate was made up of 10 prepregs. Was used. Further, in the binding and carbonizing steps, a molded heat insulating material according to Comparative Example 1 was produced in the same manner as in Example 1, except that the prepreg laminate was compressed with a spacer so that the thickness became about 40 mm. . The bulk density of the obtained molded heat insulating material was 0.12 g / cm ³ .

(Comparative Example 2)
As in Example 1, except that a carbon fiber felt prepared using only isotropic pitch-based carbon fiber (length 35 m, width 1000 mm, thickness 10 mm, basis weight 500 g / m ² ) was used. A molded heat insulating material according to Comparative Example 2 was produced. The bulk density of the obtained molded heat insulating material was 0.13 g / cm ³ .

(Comparative Example 3)
In the prepreg preparation step, the same as Comparative Example 1 except that the amount of the phenolic resin-based thermosetting resin in the prepreg was changed so that the amount of the protective carbon layer was 42 parts by mass with respect to 100 parts by mass of the carbon fiber. Thus, a molded heat insulating material according to Comparative Example 3 was produced. The bulk density of the obtained molded heat insulating material was 0.17 g / cm ³ .

(Comparative Example 4)
In the prepreg production step, the same as Comparative Example 2 except that the amount of the phenolic resin-based thermosetting resin in the prepreg was changed so that the amount of the protective carbon layer was 42 parts by mass with respect to 100 parts by mass of the carbon fiber. Thus, a molded heat insulating material according to Comparative Example 4 was produced. The bulk density of the obtained molded heat insulating material was 0.17 g / cm ³ .

(Measurement of thermal conductivity)
The thermal conductivity of the molded heat insulating materials according to Examples 1 to 4 and Comparative Examples 1 to 4 was measured by the following method.
From the molded heat insulating material, a disk-shaped sample (test piece) having a diameter of 350 mm and a thickness (the direction of prepreg lamination) of 30 mm was cut out. Using this sample, in a nitrogen gas atmosphere at an absolute pressure of 1 atm (101 kPa), at the average temperature of the three samples shown in Table 1 below, a standard plate method (JIS A 1412-2 heat flow meter method), which is a stationary method, was used. The thermal conductivity was measured. The sample average temperature means an arithmetic average value of the temperature of the surface on the high temperature side (heating side) and the temperature of the surface on the low temperature side of the sample.

(Three-point bending test)
Test pieces 200 were obtained by cutting the carbon fiber-molded heat insulating materials according to Examples 1 to 4 and Comparative Examples 1 to 4 to a length of 250 mm, a width of 40 mm, and a height of 40 mm. The test piece 200 was placed on the table 10 in which the distance between supporting points was set to 200 mm. Pressure was applied to the test piece 200 by the indenter 20, and the relationship between the pressure and the displacement was measured. Table 1 shows the results. When the displacement exceeds 40%, it is determined that if the displacement exceeds 40%, the test piece slips and accurate displacement is not exhibited, and the displacement is described as 40% or more.

From Table 1 above, comparing the thermal conductivities when the protective carbon layer is 8% by mass, Examples 1 to 3 have lower thermal conductivities at all temperatures than Comparative Examples 1 and 2. You can see that it is. In particular, the thermal conductivity of Example 1 is lower than that of Comparative Examples 1 and 2 at all temperatures by 0.05 to 0.13 W / m · K. When the thermal conductivity of the protective carbon layer of 42% by mass is compared, the thermal conductivity of Example 4 is 0.03 to 0.13 W at all temperatures as compared with Comparative Examples 3 and 4. / M · K lower. In particular, at 1600 ° C., the difference in thermal conductivity between the example and the comparative example is large.

In Example 4, although the ratio of the protective carbon layer was larger than that of Comparative Examples 1 and 2, the thermal conductivity at 1000 ° C. and 1400 ° C. was almost the same as that of Comparative Examples 1 and 2, and the average sample temperature was 1600 ° C. Is smaller than Comparative Examples 1 and 2.

It should be noted that PAN-based carbon fiber was compared with Comparative Examples 1 and 3 in which the PAN-based carbon fiber was 100% and Comparative Examples 2 and 4 in which the pitch-based carbon fiber was 100% with the same ratio of the protective carbon layer. Of Comparative Examples 1 and 3 in which the thermal conductivity was 100%, respectively, showed lower thermal conductivity.

変位 Further, in the three-point bending test, in Examples 1 to 4, the displacement was 40% or more, and even after reaching the maximum load, there was no sudden breakage. When the maximum stresses are compared for the same ratio of the protective carbon layer, the PAN-based carbon fibers in Examples 1 to 3 and Example 4 are larger than those in Comparative Examples 1 and 3 in which 100% is used. .

These are considered as follows. PAN-based carbon fibers have high strength and elasticity as a single substance, have the property that the fibers are unlikely to be oriented in the direction parallel to the thickness direction of the sheet (easy to be randomly oriented two-dimensionally), and that the fibers are not easily entangled with each other. Have. For this reason, in Comparative Examples 1 and 3 using only the PAN-based carbon fiber, it is difficult to increase the volume of the space between the carbon fibers, and it is difficult to further enhance the heat insulating performance. Further, in the carbon fiber molded heat insulating material using only PAN-based carbon fiber, since the fibers are hardly entangled with each other, the strength cannot be increased unless the amount of the protective carbon layer covering the carbon fiber surface is increased. However, after the protective carbon layer that binds the carbon fiber contacts is broken, the PAN-based carbon fiber maintains the strength of the carbon fiber sheet to a certain extent. It is difficult for the crack to continuously progress to another (adjacent) carbon fiber sheet, and the carbon fiber molded heat insulating material does not break at once.

On the other hand, the isotropic pitch-based carbon fiber has the property that the flexibility is high, the fibers are easily oriented three-dimensionally at random, the fibers are easily entangled with each other, and the strength of a simple substance is lower than that of the PAN-based carbon fiber. Have. Therefore, in Comparative Examples 2 and 4 using only the isotropic pitch-based carbon fiber, although the volume of the space between the carbon fibers is easily increased, solid conduction by the carbon fiber is likely to occur. In addition, a carbon fiber molded heat insulating material using only isotropic pitch-based carbon fibers has many contacts between carbon fibers and has high strength as a carbon fiber molded heat insulating material. However, the strength of the carbon fiber sheet after the protective carbon layer that binds the carbon fiber contacts is broken is insufficient, and the cracks generated in one carbon fiber sheet continue to the other carbon fiber sheet. It is easy to progress, and the carbon fiber molded heat insulating material is destroyed at a stretch.

On the other hand, in Examples 1 to 4 in which the carbon fibers used were regulated so as to satisfy all of the following (i) to (iv), the advantages of both isotropic pitch-based carbon fibers and PAN-based carbon fibers were obtained. It is possible to realize a carbon fiber molded heat insulating material having the same function. That is, while the space volume related to heat insulation is increased by the isotropic pitch-based carbon fiber, the solid conduction of the carbon fiber can be reduced by the PAN-based carbon fiber, and the heat insulation performance can be enhanced.

(I) It includes isotropic pitch-based carbon fibers and PAN-based carbon fibers.
(Ii) The mass ratio of the isotropic pitch-based carbon fiber to the total mass of the carbon fiber is 25% or more.
(Iii) The mass ratio of the PAN-based carbon fiber to the total mass of the carbon fiber is 5% or more.
(Iv) The ratio of the total mass of the isotropic pitch-based carbon fiber and the PAN-based carbon fiber to the total mass of the carbon fiber is 90% or more.

In addition, in Example 1, in which the ratio of the protective carbon layer was small, the strength in the bending test was lower than in Example 4, and the heat insulation performance was higher. In addition, when the amount of the protective carbon layer increases, the durability against the active gas increases, and the life can be extended. Therefore, the ratio of the protective carbon layer may be determined based on the strength and life required for the intended use.

FIG. 3 shows a cross-sectional micrograph of the vicinity of the surface layer of the carbon fiber molded heat insulating material according to Example 1. FIGS. 3A and 3B are microscopic cross-sectional photographs of the carbon fiber-molded heat insulating material according to Example 1, in which FIG. 3A shows a plan view and FIG. 3B shows a side view. As shown in FIGS. 3A and 3B, in the carbon fiber molded heat insulating material, the PAN-based carbon fiber 4 having a relatively small diameter (average diameter is 7 μm) is oriented in a direction perpendicular to the thickness direction. It can be seen that the isotropic pitch-based carbon fibers 3 having a large target diameter (having an average diameter of 13 μm) are randomly oriented three-dimensionally and entangled.

炭素 The carbon fiber molded heat insulating material according to the present invention is excellent in heat insulating performance and has a high stress relaxation effect. The carbon fiber molded heat insulating material having such properties is particularly suitable for use in an environment in which stress breakdown easily occurs, an environment in which more heat insulating performance is required, and the like, and its industrial significance is great.

REFERENCE SIGNS LIST 1 carbon fiber sheet 3 isotropic pitch-based carbon fiber 4 PAN-based carbon fiber 10 units 20 indenter 100 carbon fiber molded heat insulating material 200 test piece

Claims

A carbon fiber molded heat insulating material in which a plurality of carbon fiber sheets made of a carbonaceous material are laminated,
The carbon fiber sheet has a carbon fiber felt in which carbon fibers are randomly entangled three-dimensionally, and a protective carbon layer that covers the carbon fiber surface of the carbon fiber felt,
The carbon fiber includes an isotropic pitch-based carbon fiber and a polyacrylonitrile-based carbon fiber,
The mass ratio of the isotropic pitch-based carbon fiber to the total mass of the carbon fiber is 25% or more,
The mass ratio of the polyacrylonitrile-based carbon fiber to the total mass of the carbon fiber is 5% or more,
The ratio of the total mass of the isotropic pitch-based carbon fibers and the polyacrylonitrile-based carbon fibers to the total mass of the carbon fibers is 90% or more, and
The bulk density of the carbon fiber molded heat insulating material is 0.10 to 0.25 g / cm 3 ;
A carbon fiber molded heat insulating material, characterized in that:
The isotropic pitch-based carbon fiber is a curved carbon fiber,
The carbon fiber molded heat insulating material according to claim 1, wherein:
A mass ratio of the carbon fiber to the protective carbon layer in the carbon fiber sheet is from 100: 5 to 100: 50;
The carbon fiber molded heat insulating material according to claim 1 or 2, wherein:
Felt making process of forming carbon fiber felt by randomly entangled carbon fibers three-dimensionally,
A prepreg producing step of producing a prepreg of a carbon fiber sheet by impregnating the carbon fiber felt with a thermosetting resin,
A stacking step of stacking a plurality of the prepregs to form a prepreg laminate,
Heating the prepreg laminate under pressure, a binding step of binding the prepreg laminate,
Heat treating the prepreg laminate after the binding step in an inert gas atmosphere, and carbonizing the thermosetting resin,
The carbon fibers include (i) an isotropic pitch-based carbon fiber and a polyacrylonitrile-based carbon fiber, and (ii) the mass ratio of the isotropic pitch-based carbon fiber to the total mass of the carbon fiber is 25%. (Iii) the mass ratio of the polyacrylonitrile-based carbon fiber in the total mass of the carbon fiber is 5% or more, and (iv) the isotropic pitch-based carbon fiber and the polyacrylonitrile in the total mass of the carbon fiber. Using a carbon fiber whose total mass ratio is 90% or more,
A method for producing the carbon fiber molded heat insulating material according to claim 1.