阅读说明：本技术 碳纤维成型隔热材料及其制作方法 (Carbon fiber forming heat insulation material and manufacturing method thereof ) 是由 森本雅和 曾我部敏明 吉村宽 于 2019-09-19 设计创作，主要内容包括：本发明提供一种隔热性能高且能够防止应力破坏的碳纤维成型隔热材料。一种碳纤维成型隔热材料,所述碳纤维成型隔热材料层叠多个由碳质物质构成的碳纤维片材,所述碳纤维片材包括：碳纤维毡,所述碳纤维毡由碳纤维在三维上随机地缠绕；及保护碳层,所述保护碳层被覆所述碳纤维毡的碳纤维表面。所述碳纤维包括各向同性沥青系碳纤维和聚丙烯腈系碳纤维。在所述碳纤维总质量中所述各向同性沥青系碳纤维所占的质量比例为25％以上,在所述碳纤维总质量中所述聚丙烯腈系碳纤维所占的质量比例为5％以上,在所述碳纤维总质量中所述各向同性沥青系碳纤维和所述聚丙烯腈系碳纤维的合计质量所占的比例为90％以上,且所述碳纤维成型隔热材料的堆积密度为0.10～0.25g/cm~3。(The invention provides a carbon fiber molding heat insulating material which has high heat insulating performance and can prevent stress failure. A carbon fiber molded heat insulating material in which a plurality of carbon fiber sheets made of carbonaceous material are stacked, comprising: a carbon fiber felt in which carbon fibers are randomly wound in three dimensions; and the protective carbon layer covers the surface of the carbon fiber felt. The carbon fibers compriseAn isotropic pitch-based carbon fiber and a polyacrylonitrile-based carbon fiber. The mass ratio of the isotropic pitch-based carbon fibers in the total mass of the carbon fibers is 25% or more, the mass ratio of the polyacrylonitrile-based carbon fibers in the total mass of the carbon fibers is 5% or more, the total mass ratio of the isotropic pitch-based carbon fibers and the polyacrylonitrile-based carbon fibers in the total mass of the carbon fibers is 90% or more, and the bulk density of the carbon fiber-forming heat-insulating material is 0.10 to 0.25g/cm 3 。)

1. A carbon fiber molded heat insulating material characterized by comprising a plurality of carbon fiber sheets made of a carbonaceous material stacked together,

the carbon fiber sheet has: a carbon fiber felt in which carbon fibers are randomly wound in three dimensions; and

a protective carbon layer covering the carbon fiber surface of the carbon fiber felt,

the carbon fiber includes isotropic pitch-based carbon fiber and 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 proportion of the polyacrylonitrile-based carbon fiber in the total mass of the carbon fiber is more than 5 percent,

the total mass of the isotropic pitch-based carbon fiber and the polyacrylonitrile-based carbon fiber is 90% or more of the total mass of the carbon fibers, and

the bulk density of the carbon fiber forming heat-insulating material is 0.10g/cm³～0.25g/cm³。

2. The carbon fiber shaped heat insulating material according to claim 1,

the isotropic pitch-based carbon fiber is a curved carbon fiber.

3. The carbon fiber shaped heat insulating material according to claim 1 or 2,

the mass ratio of the carbon fibers to the protective carbon layer in the carbon fiber sheet is 100: 5-100: 50.

4. A method for manufacturing a carbon fiber shaped heat insulating material as defined in claim 1, comprising the steps of:

a felt making step of randomly winding carbon fibers in three dimensions to form a carbon fiber felt;

a prepreg production step of impregnating the carbon fiber mat with a thermosetting resin to produce a prepreg of a carbon fiber sheet;

a laminating step of stacking a plurality of the prepregs to form a prepreg laminate;

a bonding step of heating the prepreg laminate under pressure to bond the prepreg laminate; and

a carbonization step of heat-treating the prepreg laminate after the bonding step in an inert gas atmosphere to carbonize the thermosetting resin,

as the carbon fiber, a carbon fiber satisfying the following conditions is used:

(i) includes isotropic pitch-based carbon fibers and polyacrylonitrile-based carbon fibers;

(ii) the mass ratio of the isotropic pitch-based carbon fibers in the total mass of the carbon fibers is 25% or more;

(iii) the mass proportion of the polyacrylonitrile-based carbon fiber in the total mass of the carbon fiber is more than 5%; and

(iv) the proportion of the total mass of the isotropic pitch-based carbon fiber and the polyacrylonitrile-based carbon fiber in the total mass of the carbon fibers is 90% or more.

Technical Field

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

Background

Since carbon fibers have excellent thermal stability and chemical stability, carbon fiber mats formed by winding carbon fibers and carbon fiber sheets obtained by impregnating a resin material into a carbon fiber mat and carbonizing the carbon fiber mat are widely used for heat insulating materials, sound absorbing materials, and the like. The carbon fiber felt has an advantage of excellent flexibility, and the carbon fiber sheet has an advantage of excellent shape stability and is capable of being finely processed. In addition, in the case where the carbon fiber sheet is used in an environment where oxygen or SiO gas is generated, the carbide of the resin material reacts with these gases before the carbon fiber, and thus there is an advantage that the carbon fiber is hardly deteriorated.

Which one is used is appropriately selected depending on the purpose and use. Among them, a molded heat insulating material used by laminating carbon fiber sheets is excellent in thermal stability and heat insulating performance and in shape stability, and therefore is used as a heat insulating material for high temperature furnaces such as a silicon single crystal pulling apparatus, a polysilicon casting furnace, a metal and ceramic sintering furnace, and a vacuum vapor deposition furnace.

In recent years, demands for energy saving and cost reduction have further increased, and there is a demand for a molded heat insulating material having lower thermal conductivity and a molded heat insulating material having heat insulating performance of the same degree as that of conventional materials and having a longer life.

In addition, although stress may be applied to the molded heat insulating material depending on the use situation, if stress is applied excessively, cracks may be generated in the carbon fiber sheet constituting the molded heat insulating material. If cracks develop, the carbon fiber sheet may be damaged, and in this case, the heat insulating function may not be performed. Such a problem does not occur when a carbon fiber felt having excellent flexibility is used, but from the viewpoint of shape stability and the like, it may be necessary to use a molded heat insulator in some cases.

In this case, the molded heat insulating material may be in contact with surrounding members as the case where external stress is applied to the molded heat insulating material, or may be locally and rapidly heated as the case where internal stress is applied.

Incidentally, as a technique related to a heat insulating material using carbon fibers, the following patent document 1 can be cited.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2008-196552

The technique of patent document 1 relates to a carbon fiber heat insulator in which a laminate of a carbon fiber mat and a resin-impregnated carbon fiber mat impregnated or coated with a resin binder is compression-molded and sintered.

According to this technique, it can be said that the rigidity is improved and the reduction of the heat insulating property is suppressed, and the workability of the wall such as the heating furnace can be easily performed.

However, this technique requires the inclusion of a carbon fiber mat partially containing no resin, but this portion has problems such as poor processability and difficulty in fine processing, low mechanical strength and adhesive strength because of the absence of a resin component contributing to adhesion, and reduced heat insulation because of the deformation of the skeleton of the carbon fiber due to oxidation consumption because of the exclusion of a component oxidized before the carbon fiber.

Disclosure of Invention

Problems to be solved

The present invention has been made to solve the above problems, and an object of the present invention is to provide a carbon fiber molded heat insulating material which is excellent in heat insulating performance and can suppress damage due to stress.

Means for solving the problems

In order to solve the above problems, the present invention relating to a carbon fiber molded heat insulating material is configured as follows.

A carbon fiber molded heat insulating material in which a plurality of carbon fiber sheets made of carbonaceous material are stacked, comprising: a carbon fiber felt in which carbon fibers are randomly wound in three dimensions; and the protective carbon layer covers the 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 fibers in the total mass of the carbon fibers is 25% or more, the mass ratio of the polyacrylonitrile-based carbon fibers in the total mass of the carbon fibers is 5% or more, the total mass ratio of the isotropic pitch-based carbon fibers and the polyacrylonitrile-based carbon fibers in the total mass of the carbon fibers is 90% or more, and the bulk density of the carbon fiber-forming heat-insulating material is 0.10 to 0.25g/cm³。

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"), and the mass of the isotropic pitch-based carbon fibers is preferably 25 mass% or more, the mass of the PAN-based carbon fibers is preferably 5 mass% or more, and the total of both is preferably 90 mass% or more, with respect to the total mass of the carbon fibers.

The heat insulating performance of the carbon fiber molded heat insulating material tends to be higher as the ratio of the space obtained by bonding the joints of the carbon fibers and the volume of the space become larger. In addition, the solid conduction in the thickness direction of the molded heat insulating material tends to be higher as it is smaller. The strength of the carbon fiber molded heat insulating material tends to be higher as the number of protective carbon layers binding the joints of the carbon fibers increases.

As a result of intensive studies, the inventors of the present invention have found the following. PAN-based carbon fibers have high strength and high elasticity when used alone, and are characterized in that the fibers are difficult to orient in a direction parallel to the thickness direction of the sheet (easy to randomly orient in two dimensions), and the fibers are difficult to entangle with each other. Therefore, it is difficult to increase the volume of the space between the carbon fibers by using only the PAN-based carbon fiber molded heat insulating material. In addition, since the carbon fiber molded heat insulating material using only PAN-based carbon fibers is difficult to entangle fibers with each other, it is not possible to improve the strength without increasing the amount of the protective carbon layer covering the surface of the carbon fibers. However, since the PAN-based carbon fibers maintain the strength of the carbon fiber sheet to some extent after the protective carbon layer of the contact point to which the carbon fibers are bonded is broken, if a crack is generated in one carbon fiber sheet, the crack is hard to progress to another (adjacent) carbon fiber sheet, and the carbon fiber molded heat insulating material is not immediately broken.

On the other hand, isotropic pitch-based carbon fibers have characteristics that they are highly flexible, they are easily randomly oriented in three dimensions, they are easily entangled with each other, and their strength when used alone is lower than that of PAN-based carbon fibers. Therefore, a carbon fiber molded heat insulating material formed using only isotropic pitch-based carbon fibers tends to increase the volume of the space between the carbon fibers, but solid conduction due to the carbon fibers tends to occur. In addition, a carbon fiber molded heat insulating material formed using only isotropic pitch-based carbon fibers has high strength as a carbon fiber molded heat insulating material even when the number of contacts between carbon fibers is large and the number of protective carbon layers is small. However, since the strength of the carbon fiber sheet is insufficient after the protective carbon layer of the contact point to which the carbon fiber is bonded is broken, cracks generated in one carbon fiber sheet easily progress to the other carbon fiber sheet, and the carbon fiber molded heat insulating material is immediately broken.

On the other hand, the isotropic pitch-based carbon fiber and PAN-based carbon fiber are randomly wound in three dimensions by setting the mass mixing ratio of the isotropic pitch-based carbon fiber and PAN-based carbon fiber as described above, and the bulk density of the entire carbon fiber-molded heat insulating material is set to 0.10 to 0.25g/cm³Thus, a carbon fiber-molded heat insulating material having the advantages of both isotropic pitch-based carbon fibers and PAN-based carbon fibers can be realized. That is, the isotropic pitch-based carbon fiber increases the volume of the space involved in heat insulation, and the PAN-based carbon fiber can reduce the solid conduction of the carbon fiber, thereby significantly improving the heat insulation performance.

In addition, in terms of strength, the strength of the carbon fiber sheet is maintained by the isotropic pitch-based carbon fibers, and after cracks caused by stress are generated, the strength of the carbon fiber sheet is maintained to some extent by the PAN carbon fibers, whereby a carbon fiber molded heat insulating material in which crack propagation is difficult to occur can be realized.

On the other hand, if the bulk density is too small, the strength is insufficient, while if the bulk density is too large, solid conduction is likely to occur and the volume and ratio of the spaces between the carbon fibers are small, so that the heat insulating performance becomes insufficient.

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

In addition, the mass ratio of the isotropic pitch-based carbon fiber to the PAN-based carbon fiber in the carbon fibers is preferably 20:80 to 95:5, more preferably 27:73 to 91:9, and further preferably 30:70 to 90: 10. From the viewpoint of further improving the heat insulating 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, but in order to sufficiently obtain the effects of isotropic pitch-based carbon fiber and PAN-based carbon fiber, the total mass of isotropic pitch-based carbon fiber and PAN-based carbon fiber should be 90% or more of the total mass of the carbon fiber. The total mass ratio is more preferably 95% or more, and still more preferably 100% (that is, it is most preferably not containing carbon fibers other than isotropic pitch-based carbon fibers and PAN-based carbon fibers).

The shape of the carbon fiber molded heat insulating material is not particularly limited, and a plurality of plate-like carbon fiber sheets may be stacked, one or a plurality of carbon fiber sheets may be spirally wound and stacked, or the like.

The carbon fiber sheets constituting the carbon fiber molded heat insulating material preferably have the same bulk density and thickness, mass mixing ratio of the carbon fibers, and the like.

The carbon fiber sheet disposed on the surface (one surface or both surfaces) of the carbon fiber molded heat insulator may be impregnated with pyrolytic carbon and used as it is, or may be used as it includes graphite particles, amorphous carbon particles, and the like. Further, a surface layer having a high bulk density, a high volume fraction of carbon fibers, or the like may be applied to the surface of the carbon fiber molded heat insulator. With such a configuration, abrasion and dust generation of the carbon fiber molded heat insulating material can be further suppressed. In addition, when these are not included, the manufacturing steps can be simplified and the cost can be reduced. The carbon fiber sheet other than the surface preferably does not contain components other than carbon fibers and a protective carbon layer.

The carbon fiber molded heat insulating material of the present invention can be used as a molded heat insulating material for a high-temperature furnace such as a silicon single crystal pulling apparatus, a polysilicon casting furnace, a metal and ceramic sintering furnace, a vacuum vapor deposition furnace, or the like.

In addition, when an active gas (oxygen, SiO gas, or the like) mixed as impurities or generated in the furnace exists around the carbon fiber molding material, the protective carbon layer reacts with the active gas before the carbon fibers. Accordingly, the carbon fibers are prevented from being deteriorated by reaction with the active gas.

The carbonaceous material of the protective carbon layer is removed as carbon dioxide gas when reacting with oxygen gas, and is SiC when reacting with SiO gas, and remains without being removed. In either case, however, the skeleton structure made of carbon fibers is maintained, and therefore the heat insulating effect obtained by forming a plurality of spaces by the skeleton structure is maintained.

The amount of the protective carbon layer is determined by taking into consideration the required heat insulating performance, strength, atmospheric gas in the use environment, requirement for life, installation space, and the like. Generally, the less the amount of the protective carbon layer, the higher the heat insulating performance, the more the amount of the protective carbon layer, the higher the durability and strength against oxidation consumption and the like. The ratio of the mass of the carbon fibers to the mass of the protective carbon layer in the molded heat insulating material is preferably 100:5 to 100:50, more preferably 100:5 to 100:45, and still more preferably 100:8 to 100: 42.

Further, since the carbon fiber molded heat insulating material is formed by stacking a plurality of carbon fiber sheets made of a carbonaceous material, the carbon fiber molded heat insulating material does not contain components other than the 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 of the carbon fibers with each other can be further improved. Further, since the length in the natural state can be made smaller than the linear length, the influence of the decrease in the heat insulating performance due to solid conduction can be reduced.

The curved carbon fiber is defined as a carbon fiber having a curved shape in which the ratio of L1 to L2 (L1/L2) is 1.3 or more when the length of the fiber when stretched linearly (i.e., the fiber length) is L1 and the maximum length of the curved fiber in the natural state (or the maximum point size in the natural state, that is, the length when the distance between any two points on the curved fiber is measured) is L2. In addition, in the case of drawing a fiber or the like, the curved shape of the fiber may not be maintained temporarily. Therefore, for more accurate measurement conditions, the maximum length of the bent fiber in a natural state after the fiber having a length of L1 freely falls from a predetermined height (e.g., about 30 to 100cm) may be measured as L2. The maximum length L2 often varies among the curved carbon fibers, and can be generally determined as an average value (average maximum length) of a plurality of measured values. In this case, the number of measurement values (number of measurements) used for obtaining the average value is preferably 5 or more, more preferably 10 or more, and further preferably 20 or more. On the other hand, the upper limit of the number of measurements is not particularly limited, but is preferably about 200, more preferably about 100, and further preferably about 50.

In addition, in terms of the production method, it is difficult for the PAN-based carbon fiber to be curved (the L1/L2 is 1.3 or more), and therefore, it is preferable to use a non-curved (L1/L2 is less than 1.3, that is, linear).

The method for producing the carbon fiber molded heat insulating material according to the present invention for solving the above problems is configured as follows.

The method comprises the following steps: a felt making step of randomly winding carbon fibers in three dimensions to form a carbon fiber felt; a prepreg production step of impregnating the carbon fiber mat with a thermosetting resin to produce a prepreg of a carbon fiber sheet; a laminating step of stacking a plurality of the prepregs to form a prepreg laminate; a bonding step of heating the prepreg laminate under pressure to bond the prepreg laminate; a carbonization step of heat-treating the bonded prepreg laminate in an inert gas atmosphere to carbonize the thermosetting resin. As the carbon fiber, a carbon fiber satisfying the following conditions is used: (i) includes isotropic pitch-based carbon fibers and polyacrylonitrile-based carbon fibers; (ii) the mass ratio of the isotropic pitch-based carbon fibers in the total mass of the carbon fibers is 25% or more; (iii) the mass proportion of the polyacrylonitrile-based carbon fiber in the total mass of the carbon fiber is more than 5%; and (iv) the total mass of the isotropic pitch-based carbon fiber and the polyacrylonitrile-based carbon fiber accounts for 90% or more of the total mass of the carbon fibers.

By the above-described production method, the carbon fiber molded heat insulating material according to the present invention can be produced.

ADVANTAGEOUS EFFECTS OF INVENTION

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 damage due to stress.

Drawings

FIG. 1 is a perspective view schematically showing the structure of a carbon fiber molded heat insulating material according to the present invention.

Fig. 2 is a schematic diagram showing a three-point bending test.

Fig. 3 is a microscopic sectional photograph of the carbon fiber molded heat insulating material according to example 1, in which fig. 3(a) shows a top view and fig. 3(b) shows a side view.

Detailed Description

(embodiment mode)

Fig. 1 is a perspective view schematically showing the structure of a carbon fiber molded heat insulating material according to the present embodiment. The carbon fiber molded heat insulating material 100 according to the present embodiment includes: a carbon fiber felt that randomly winds carbon fibers in three dimensions; and a protective carbon layer made of a carbonaceous material covering the carbon fiber surface of the carbon fiber felt, and on which the carbon fiber sheet 1 made of a carbonaceous material is laminated. In one embodiment shown in fig. 1, eight carbon fiber sheets 1 in total are stacked. In addition, in the carbon fiber sheet 1, the carbon fibers are randomly oriented in three dimensions.

The carbon fibers constituting the carbon fiber sheet 1 include isotropic pitch-based carbon fibers and PAN-based carbon fibers, and the mass ratio of the isotropic pitch-based carbon fibers to the total mass of the carbon fibers is 25% or more, the mass ratio of the PAN-based carbon fibers to the total mass of the carbon fibers is 5% or more, and the total mass ratio of the isotropic pitch-based carbon fibers and the PAN-based carbon fibers to the total mass of the carbon fibers is 90% or more. In addition, the bulk density of the carbon fiber molded heat insulating material 100 is 0.10 to 0.25g/cm³。

Among these, the high strength and high elasticity of the PAN-based carbon fiber alone make it difficult to orient the fibers in a direction parallel to the thickness direction of the sheet (easy to randomly orient the fibers in two dimensions), and make it difficult to entangle the fibers with each other. On the other hand, isotropic pitch-based carbon fibers are highly flexible, easily oriented randomly in three dimensions, easily entangled with each other, and lower in strength and elasticity than PAN-based carbon fibers when used alone. By adjusting the mass mixing ratio of the isotropic pitch-based carbon fiber and the PAN-based carbon fiber as described above, a carbon fiber molded heat insulating material in which mainly the isotropic pitch-based carbon fiber is randomly oriented in three dimensions and the PAN-based carbon fiber is randomly oriented in two dimensions is obtained. The molded heat insulating material can combine the advantages of isotropic pitch-based carbon fibers and PAN-based carbon fibers.

That is, in terms of heat insulation, the voids between the PAN-based carbon fibers are increased by the isotropic pitch-based carbon fibers to increase the volume of the space associated with heat insulation, and the PAN-based carbon fibers can reduce solid conduction of the carbon fibers, thereby improving the heat insulation performance. In addition, in terms of strength, the strength of the carbon fiber sheet is maintained by the isotropic pitch-based carbon fibers, and after cracks caused by stress are generated, the strength of the carbon fiber sheet is maintained to some extent by the PAN carbon fibers, whereby a carbon fiber molded heat insulating material in which crack propagation is difficult to occur can be realized.

However, if the amount of isotropic pitch-based carbon fibers is too small, the amount of PAN-based carbon fibers is too small, or the total mass of both fibers is too small, these effects cannot be sufficiently obtained.

Among them, the isotropic pitch-based carbon fiber is a carbon fiber that is produced from isotropic pitch that has been subjected to non-melt processing, and commercially available products can be used. Chemically, bitumen is a mixture of numerous condensed polycyclic aromatic compounds, and is a solid at room temperature obtained by heat-treating and polymerizing liquid tar obtained during the dry distillation of wood, coal, and the like, bitumen obtained from oil sands, oil components obtained by the dry distillation of oil shale, residual oil obtained by the distillation of crude oil, tar produced by the cracking of oil fractions, and the like. Specifically, coal-derived asphalt, petroleum-derived asphalt, synthetic asphalt obtained by polymerizing an aromatic compound such as naphthalene, and the like can be cited.

As the isotropic pitch-based carbon fiber, a fiber produced by a known method can be used. For example, pitch derived from petroleum or coal is spun and deposited on a table to obtain a pitch fiber mat. The mat obtained is an aggregate of pitch fibers having different lengths in the range of approximately 5 to 400 mm. The method of spinning is not particularly limited, and a method of spinning by a melt spinning method or a vortex method can be used. A swirl method can be used to obtain a curved fiber, and a melt spinning method can be used to obtain a non-curved (linear) fiber. The infusible treatment and the carbonizing treatment of the pitch fiber are performed to form a carbon fiber mat. The infusible step is a step of introducing oxygen to the surface of the pitch fiber to oxidize the pitch fiber. The atmosphere of the infusible step can be air or NOx. The temperature of the carbonization treatment is not particularly limited, but may be 700 to 1200 ℃ in view of economy and the like. In addition, when curved fibers are used, entanglement between fibers is easier in the carbon fiber mat, and strength is easily increased.

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

The PAN-based carbon fiber is a carbonized polyacrylonitrile fiber, and commercially available ones can be used. The PAN-based carbon fiber preferably has a fiber length of 20 to 200mm, more preferably 30 to 80 mm. The average fiber diameter (diameter) is preferably 5 to 13 μm, more preferably 5 to 9 μm, and still more preferably 5 to 7 μm.

In addition, although any carbon fiber is not particularly limited as to the microstructure of the carbon fiber, only carbon fibers having the same shape (curved shape, linear shape, cross-sectional shape, etc.) may be used, or carbon fibers having different structures may be mixed, the isotropic pitch-based carbon fiber is preferably curved, and the PAN-based carbon fiber is preferably curved to a small extent (linear).

The shape of the carbon fiber mat constituting the carbon fiber sheet is not particularly limited, and the length and width thereof are not particularly limited. As the carbon fiber felt, for example, a carbon fiber felt having a thickness of about 3 to 20mm can be used. In addition, as the microstructure of the carbon fiber felt, a structure in which carbon fibers oriented in three-dimensional random directions intersect complicatedly is used.

In addition, the protective carbon layer covers the entire surface of the carbon fibers constituting the carbon fiber felt or a part of the surface of the carbon fibers. In addition, the protective carbon layer may be a carbonaceous material (amorphous carbon or graphitic carbon), and the amorphous carbon may be either hard or easy to graphitize. The compound from which the carbon layer is derived is not particularly limited, but a resin material that can impregnate the carbon fiber mat is preferably used. Among them, thermosetting resins such as phenol resins, furan resins, polyimide resins, and epoxy resins are 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 carbonization.

Among them, only one kind of thermosetting resin may be used, or two or more kinds of thermosetting resins may be used in combination. In addition, the thermosetting resin may be included in the carbon fiber mat as it is, or may be diluted with a solvent and included in the carbon fiber mat. As the solvent, alcohols such as methanol, ethanol, and the like can be used.

The carbon fiber mat may be cut or the like after the carbon fiber molded heat insulator is produced from a long or wide material, or may be cut in advance to the size of the carbon fiber molded heat insulator.

Among them, the bulk density of the carbon fiber molded heat insulating material is more preferably 0.10 to 0.23g/cm³More preferably 0.10 to 0.20g/cm³。

The mass ratio of the carbon fibers to the protective carbon layer in the carbon fiber sheet is preferably 100:5 to 100:50, more preferably 100:5 to 100:45, and still more preferably 100:8 to 100: 42.

In addition, the thickness of each carbon fiber sheet is preferably 3-20 mm, more preferably 5-15 mm, and further preferably 6-12 mm.

Next, a method for producing the carbon fiber molded heat insulator will be described.

(production 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 randomly oriented in three dimensions is employed. Examples of the method for forming the carbon fiber felt include (1) a method in which carbon fibers (hereinafter, referred to as "carbon fiber mixture" in this section) mixed with isotropic pitch-based carbon fibers and PAN-based carbon fibers are opened by an opener, pneumatically raised, lowered, and stacked, and then molded into a felt shape by needle punching; (2) a method of stirring and mixing the carbon fiber mixture in the solution, depositing on a paper-making net to shape felt by plastic; (3) by cardingA method in which a carding device such as a machine spins a carbon fiber mixture into a felt shape, and then adjusts the degree of entanglement of carbon fibers by needling. The thickness of the carbon fiber felt is preferably 3-20 mm, and more preferably 5-15 mm. The weight per unit area of the carbon fiber felt is preferably 100 to 2000g/m²More preferably 300 to 1500g/m²。

(prepreg production step)

Then, for the carbon fiber mat, a thermosetting resin solution is sprayed and immersed in the thermosetting resin solution, or a thermosetting resin solution is coated to make a prepreg. In this case, the amount of the synthetic resin is adjusted so that the mass ratio of the carbon fiber to the protective carbon layer after sintering is 100:5 to 100: 100.

(laminating step)

A plurality of prepregs fabricated as described above are sequentially stacked to have a predetermined thickness. One or more prepregs may be spirally wound and laminated on a cylindrical or cylindrical mandrel.

(bonding step and carbonization step)

The laminate produced as described above is pressed and heated to thermally cure the thermosetting resin. Then, the thermosetting resin is carbonized by heating at 1500 to 2500 ℃ for a predetermined time (for example, 1 to 20 hours) in an inert gas atmosphere, thereby obtaining a carbon fiber molded heat insulating material.

The bulk density of the carbon fiber molded heat insulating material can be adjusted by changing the weight per unit area of the carbon fiber mat, the thickness of the laminate after pressing in the bonding step (the thickness of the spacer used), or the like. When the weight per unit area is increased or the thickness of the spacer is decreased, the packing density tends to increase. The bulk density after sintering can be estimated from the apparent volume of the laminate after pressing and the sum of the mass of the carbon fibers and the mass of the residual carbon of the thermosetting resin.

Herein, carbonization as used in this specification is intended to define the broad definition of including graphitization. For example, in the case of heat treatment at a temperature of 2000 ℃ or higher, in particular, development of a graphite structure can be considered, but in the present invention, the carbonaceous material constituting the carbon fiber molded heat insulator may be amorphous carbon or graphitic carbon.

Examples

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

(example 1)

(production of carbon fiber)

Isotropic pitch derived from coal was melt spun according to a vortex method to obtain a mat consisting of curved pitch fibers. The mat is an aggregate of pitch fibers, and the pitch fibers have a length of approximately 10 to 300 mm. The mat is heat-treated in an air atmosphere at a temperature of from room temperature to about 250 to 300 ℃ for a total of 30 minutes to prevent the pitch fibers from melting, thereby obtaining a fiber mat. The fiber mat was carbonized at about 1000 ℃ in an inert gas atmosphere to obtain an isotropic pitch-based carbon fiber (average diameter 13 μm) mat. When the length of the fiber stretched in a straight line (i.e., the fiber length) was L1, and the maximum length of the fiber bent in a natural state (or the maximum point size in a natural state, that is, the length at which the distance between any two points on the bent fiber is measured was the maximum) was L2, the ratio (L1/L2) of L1 to L2 was 2.1 (arithmetic average of 25 samples).

(production of carbon fiber felt)

The isotropic pitch-based carbon fibers and PAN-based carbon fibers (made by Toray Industries, Inc., having an average fiber diameter of 7 μm and a length of 60mm) were mixed at a mass ratio of 50:50, split, and entangled by a needle punching method to prepare a carbon fiber felt (having a length of 45m, a width of 1000mm, a thickness of 9.5mm, and a weight per unit area of 470 g/m)²)。

(prepreg production step)

The carbon fiber felt was cut at a length of 1500mm and a width of 1000 mm. A cut carbon fiber mat was impregnated with a resol-type phenolic resin-based thermosetting resin solution to make a prepreg. At this time, the addition amount of the phenol resin-based thermosetting resin in the prepreg was adjusted so that the amount of the carbonaceous material formed by carbonizing the phenol resin-based thermosetting resin (i.e., the amount of the protective carbon layer) was 8 parts by mass with respect to 100 parts by mass of the carbon fiber when the prepreg was heat-treated at 2000 ℃.

(laminating step)

Thirteen layers of the prepregs were stacked to produce a prepreg stacked body.

(bonding step and carbonization step)

The prepreg laminate obtained as above, a spacer was placed and compressed so that the thickness thereof was approximately 50mm, and pressurized at 200 ℃ for 90 minutes to thermally cure the phenol resin, thereby bonding the prepreg laminate (bonding step). Then, the prepreg laminate after the bonding step was heat-treated at 2000 ℃ under an inert atmosphere, thereby obtaining a carbon fiber molded heat insulating material in a flat plate shape (carbonization step). The bulk density of the obtained carbon fiber molded heat insulating material was 0.12g/cm³。

(example 2)

As the carbon fiber felt, a carbon fiber felt obtained by mixing isotropic pitch-based carbon fibers and PAN-based carbon fibers at a mass ratio of 30:70, opening the fibers, and winding the fibers by a needle punching method was used. The carbon fiber felt has a length of 20m, a width of 1000mm, a thickness of 9.5mm and a unit area weight of 508g/m². Then, a shaped heat insulating material according to example 2 was produced in the same manner as in example 1, except that this carbon fiber mat was used. The bulk density of the resulting shaped thermal insulation material was 0.13g/cm³。

(example 3)

As the carbon fiber felt, a carbon fiber felt obtained by mixing isotropic pitch-based carbon fibers and PAN-based carbon fibers at a mass ratio of 90:10, opening the fibers, and winding the fibers by a needle punching method was used. The carbon fiber felt has a length of 20m, a width of 1000mm, a thickness of 9.5mm and a unit area weight of 470g/m². Then, a shaped heat insulating material according to example 3 was produced in the same manner as in example 1, except that this carbon fiber mat was used. The bulk density of the resulting shaped thermal insulation material was 0.12g/cm³。

(example 4)

In the prepreg manufacturing step, a prepreg was manufactured in the same manner as in example 1, except that the addition amount of the phenolic resin-based thermosetting resin in the prepreg was adjusted so that the amount of the protective carbon layer was 42 parts by mass with respect to 100 parts by mass of the carbon fiberThe shaped heat insulating material according to example 4 was used. The bulk density of the resulting shaped thermal insulation material was 0.17g/cm³。

Comparative example 1

As the carbon fiber felt, only PAN-based carbon fiber (length: 40m, width: 1000mm, thickness: 5mm, basis weight: 520 g/m) was used²) As the prepreg laminate, a prepreg laminate having 10 layers of prepreg stacked layers was used for the carbon fiber felt produced. In addition, in the bonding and carbonizing step, 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 thereof was about 40 mm. The bulk density of the resulting shaped thermal insulation material was 0.12g/cm³。

Comparative example 2

As the carbon fiber felt, except for using only isotropic pitch-based carbon fibers (length 35m, width 1000mm, thickness 10mm, basis weight 500 g/m)²) Except for the production, the molded heat insulating material according to comparative example 2 was produced in the same manner as in example 1. The bulk density of the resulting shaped thermal insulation material was 0.13g/cm³。

Comparative example 3

In the prepreg production step, a molded heat insulating material according to comparative example 3 was produced in the same manner as in comparative example 1, except that the amount of the phenolic resin-based thermosetting resin added to the prepreg was adjusted 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. The bulk density of the resulting shaped thermal insulation material was 0.17g/cm³。

Comparative example 4

In the prepreg manufacturing step, a molded heat insulating material according to comparative example 4 was produced in the same manner as in comparative example 2, except that the addition amount of the phenolic resin-based thermosetting resin in the prepreg was adjusted such that the amount of the protective carbon layer was 42 parts by mass with respect to 100 parts by mass of the carbon fiber. The bulk density of the resulting shaped thermal insulation material was 0.17g/cm³。

(measurement of thermal conductivity)

The molded heat insulating materials according to examples 1 to 4 and comparative examples 1 to 4 were measured for thermal conductivity by the following method.

A disk-shaped sample (test sheet) having a diameter of 350mm and a thickness (stacking direction of prepreg) of 30mm was cut out from the molded heat insulating material. The thermal conductivity was measured using three samples shown in table 1 below at an average temperature in a nitrogen atmosphere having an absolute pressure of 1 atm (101kPa) according to a standard flat plate method (JIS a 1412-2 thermal flow meter method) as a steady state method. The sample average temperature is an arithmetic average of the surface temperature on the high temperature side (heating side) and the surface temperature on the low temperature side of the sample.

(three-point bending test)

The carbon fiber molded heat insulating materials according to examples 1 to 4 and comparative examples 1 to 4 were cut into pieces having a length of 250mm, a width of 40mm, and a height of 40mm to obtain test sheets 200. The test sheet 200 was placed on a stage 10 having an inter-fulcrum distance set to 200 mm. Pressure is applied to the test sheet 200 by the indenter 20, and the relationship between the pressure and the amount of displacement is measured. The results are shown in Table 1. In the portion where the displacement exceeds 40%, it is determined that the test sheet slips and cannot show an accurate displacement if the displacement exceeds 40%, and the displacement is described as 40% or more.

[ TABLE 1 ]

From table 1 above, it is understood that the thermal conductivities of examples 1 to 3 are lower than those of comparative examples 1 and 2 at all temperatures when the protective carbon layers are compared to each other at a thermal conductivity of 8 mass%. In particular, the thermal conductivity of example 1 is 0.05 to 0.13W/mK lower than that of comparative examples 1 and 2 at all temperatures. In addition, when the comparative protective carbon layer has a thermal conductivity of 42 mass%, the thermal conductivity of example 4 is lower by 0.03 to 0.13W/m.K compared with comparative examples 3 and 4. In particular, the difference in thermal conductivity between the examples and the comparative examples becomes large at 1600 ℃.

In addition, although the ratio of the protective carbon layer of example 4 is larger than that of comparative examples 1 and 2, the thermal conductivity of example 4 at 1000 ℃ and 1400 ℃ is almost the same as that of comparative examples 1 and 2, and the thermal conductivity of example 4 at 1600 ℃ which is the sample average temperature is a value smaller than that of comparative examples 1 and 2.

In addition, when 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% were compared with each other at the same ratio of the protective carbon layer, comparative examples 1 and 3 in which the PAN-based carbon fiber was 100% showed low thermal conductivities, respectively.

In the three-point bending tests, in examples 1 to 4, the displacement was 40% or more and the steel sheet was not broken immediately even after the maximum load was reached. In addition, when the maximum stresses are compared at the same ratio of the protective carbon layers, the maximum stresses of examples 1 to 3 and example 4 are larger than those of comparative examples 1 and 3 in which the PAN-based carbon fiber is 100%, respectively.

These can be considered as follows. PAN-based carbon fibers have high strength and high elasticity when used alone, and are characterized in that the fibers are difficult to orient in a direction parallel to the thickness direction of the sheet (easy to randomly orient in two dimensions), and the fibers are difficult to entangle with each other. Therefore, in comparative examples 1 and 3 using only PAN-based carbon fibers, it is difficult to increase the volume of the space between the carbon fibers and further improve the heat insulating performance. In addition, since the fibers of the carbon fiber molded heat insulating material using only PAN-based carbon fibers are difficult to entangle with each other, it is not possible to improve the strength without increasing the amount of the protective carbon layer covering the surface of the carbon fibers. However, since the PAN-based carbon fibers maintain the strength of the carbon fiber sheet to some extent after the protective carbon layer of the contact point to which the carbon fibers are bonded is broken, if a crack is generated in one carbon fiber sheet, the crack is hard to progress to another (adjacent) carbon fiber sheet, and the carbon fiber molded heat insulating material is not immediately broken.

On the other hand, isotropic pitch-based carbon fibers have characteristics that they are highly flexible, they are easily randomly oriented in three dimensions, they are easily entangled with each other, and their strength when used alone is lower than that of PAN-based carbon fibers. Therefore, in comparative examples 2 and 4 using only isotropic pitch-based carbon fibers, the volume of the space between the carbon fibers is easily increased, but solid conduction due to the carbon fibers is easily generated. Further, a carbon fiber molded heat insulating material formed using only isotropic pitch-based carbon fibers has a large number of carbon fiber-to-carbon joints and has high strength as a carbon fiber molded heat insulating material. However, since the strength of the carbon fiber sheet is insufficient after the protective carbon layer of the contact to which the carbon fiber is bonded is broken, cracks generated in one carbon fiber sheet tend to progress to the other carbon fiber sheet, and the carbon fiber molded heat insulating material is immediately broken.

In contrast, in examples 1 to 4 in which the carbon fibers used satisfy all of the following (i) to (iv), a carbon fiber molded heat insulator having both the advantages of the isotropic pitch-based carbon fiber and the PAN-based carbon fiber can be realized. That is, the isotropic pitch-based carbon fiber increases the volume of the space involved in heat insulation, and the PAN-based carbon fiber can reduce solid conduction of the carbon fiber, thereby improving the heat insulation performance.

(i) Including isotropic pitch-based carbon fibers and polyacrylonitrile-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 polyacrylonitrile-based carbon fiber in the total mass of the carbon fiber is 5% or more.

(iv) The proportion of the total mass of the isotropic pitch-based carbon fibers and the polyacrylonitrile-based carbon fibers in the total mass of the carbon fibers is 90% or more.

In addition, in terms of strength, the strength of the carbon fiber sheet is maintained by the isotropic pitch-based carbon fibers, and after cracks caused by stress are generated, the strength of the carbon fiber sheet is maintained to some extent by the PAN carbon fibers, whereby a carbon fiber molded heat insulating material in which crack propagation is difficult to occur can be realized.

In example 1 in which the ratio of the protective carbon layer was small, the strength in the bending test was low and the heat insulating performance was increased as compared with example 4. In addition, when the amount of the protective carbon layer is increased, durability against active gas is increased and the life can be extended. Thus, the ratio of the protective carbon layers may be determined based on the strength and lifetime required for the intended purpose.

Fig. 3 shows a cross-sectional photomicrograph of the vicinity of the surface layer of the carbon fiber molded heat insulating material according to example 1. Fig. 3 is a microscopic sectional photograph of the carbon fiber molded heat insulating material according to example 1, in which fig. 3(a) shows a top view and fig. 3(b) shows a side view. As shown in fig. 3(a) and (b), in the carbon fiber molded heat insulating material, the PAN-based carbon fibers 4 having a relatively small diameter (average diameter of 7 μm) are oriented in a direction perpendicular to the thickness direction, and the curved isotropic pitch-based carbon fibers 3 having a relatively large diameter (average diameter of 13 μm) are randomly oriented and wound in three dimensions.

[ possibility of Industrial utilization ]

The carbon fiber molded heat insulating material according to the present invention has excellent heat insulating performance and a high stress relaxation effect. The carbon fiber molded heat insulating material having such properties is particularly suitable for environments in which stress failure is likely to occur, environments in which more heat insulating properties are required, and the like, and is of great industrial significance.

(description of reference numerals)

1 carbon fiber sheet

3 Isotropic pitch-based carbon fiber

4 PAN-based carbon fiber

10 tables

20 pressure head

100 carbon fiber formed heat insulating material

200 test sheet