JP2019043099A - Carbon fiber sheet laminate and manufacturing method therefor - Google Patents

Abstract

To provide a carbon fiber sheet laminate capable of preventing stress breakage.SOLUTION: There is provided a carbon fiber sheet laminate having a fiber felt by randomly subjecting carbon fibers to crossconnection in three dimension, and a protective carbon layer for coating a carbon fiber surface of the fiber felt, in which a plurality of carbon fiber sheets constituted by carbonaceous are laminated, in which the carbon fiber contains an isotropic pitch-based carbon fiber and a polyacrylonitrile-based carbon fiber, a mass ratio of the isotropic pitch-based carbon fiber in total mass of the carbon fiber is 20% or more, a mass ratio of the polyacrylonitrile-based carbon fiber in total mass of the carbon fiber is 20% or more, a ratio of total mass of the isotropic pitch-based carbon fiber and the polyacrylonitrile-based fiber in total mass of the carbon fiber is 90% or more.SELECTED DRAWING: Figure 1

Description

  BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a carbon fiber sheet laminate, and more particularly to a carbon fiber sheet laminate capable of suppressing breakage due to stress.

  Since carbon fibers are excellent in thermal stability and chemical stability, carbon fiber felts formed by entanglement of carbon fibers, and carbon fiber sheets obtained by impregnating carbon fiber felts with a resin material for carbonization are heat insulators and carbon steel sheets. It is widely used as a sound absorbing material. The carbon fiber felt has an advantage of being excellent in flexibility, and the carbon fiber sheet has an advantage of being excellent in shape stability and capable of being finely processed. In addition, when used in an environment in which oxygen gas or SiO gas is generated, the carbon fiber sheet has an advantage that the carbon fiber is less likely to deteriorate since the carbonized resin material reacts with these gases prior to the carbon fiber. .

  Which one to use is appropriately selected depending on the purpose of use and application. Here, since the molded heat insulating material which is used by laminating the carbon fiber sheets is excellent in thermal stability and heat insulation performance and excellent in shape stability, a single crystal silicon pulling apparatus, a polycrystalline silicon cast furnace, metal and ceramics. It is used as a heat insulating material for high temperature furnaces such as sintering furnaces and vacuum deposition furnaces.

  By the way, although stress may be applied to a shaping | molding heat insulating material depending on a use condition, when stress is applied excessively, a crack arises in the carbon fiber sheet which comprises a shaping | molding heat insulating material. If the crack progresses, the carbon fiber sheet may be broken, and in such a case, the heat insulating function can not be exhibited. When using a carbon fiber felt excellent in flexibility, such a problem does not occur, but there are also cases where it is necessary to use a shaped heat insulating material from the viewpoint of shape stability and the like.

  Here, as the case where external stress is applied to the formed heat insulating material, when the formed heat insulating material and the members around it come in contact, as the case where internal stress is applied, the formed heat insulating material is rapidly heated locally Etc. are assumed.

  By the way, as a technique regarding the heat insulating material using a carbon fiber, the following patent document 1 is mentioned.

JP, 2008-196552, A

  The technology of Patent Document 1 is a technology relating to a carbon fiber insulation material obtained by compression molding of a laminate of a resin-impregnated carbon fiber felt and a carbon fiber felt impregnated or coated with a resin binder and fired.

  According to this technique, the decrease in heat insulation is suppressed while the rigidity is increased, and the application to a wall body such as a heating furnace can be facilitated.

  However, in this technology, although it is essential to include a resin-free carbon fiber felt portion, this portion has poor processability and is difficult to microfabricate, and there is no resin component that contributes to adhesion, so it is mechanical. There is a problem that the strength and adhesive strength are low, and since the carbon fiber does not contain a component to be oxidized prior to the carbon fiber, the skeleton of the carbon fiber is broken due to the oxidative consumption and the heat insulating property is lowered.

  The present invention was made in order to solve the above-mentioned subject, and an object of the present invention is to provide a carbon fiber sheet layered product which was able to control destruction by stress.

The present invention according to a carbon fiber sheet laminate for solving the above problems is configured as follows.
Carbon felt including a fiber felt in which carbon fibers are randomly entangled three-dimensionally and a protective carbon layer covering the carbon fiber surface of the fiber felt, wherein a plurality of carbon fiber sheets made of carbonaceous material are laminated It is a fiber sheet laminated body, Comprising: The mass of the said isotropic pitch-based carbon fiber which contains the isotropic pitch-based carbon fiber and a polyacrylonitrile-based carbon fiber, and occupies in the total mass of the said carbon fiber The ratio is 20% or more, the mass ratio of the polyacrylonitrile-based carbon fiber in the total mass of the carbon fiber is 20% or more, and the isotropic pitch-based carbon fiber in the total mass of the carbon fiber It is characterized in that the proportion of the total mass of the polyacrylonitrile carbon fiber is 90% or more.

  In the above configuration, the carbon fiber constituting the carbon fiber sheet contains isotropic pitch-based carbon fiber and polyacrylonitrile (PAN) -based carbon fiber, and isotropic pitch-based with respect to the total mass of carbon fiber The carbon fiber is regulated to 20% by mass or more, the PAN-based carbon fiber is 20% by mass or more, and the total of both is regulated to 90% by mass or more.

  The strength of the carbon fiber sheet tends to be higher as the number of protective carbon layers binding the carbon fiber mutual points is larger. Here, the PAN-based carbon fiber has a property that the strength of the PAN-based carbon fiber is high and the fibers are not easily entangled with each other. For this reason, the carbon fiber sheet using only PAN-based carbon fibers has few strength points because there are few contact points between the carbon fibers because the fibers are not easily entangled. However, after the protective carbon layer that bonds the carbon fiber contacts is broken, if one carbon fiber sheet is cracked because the PAN-based carbon fiber maintains the carbon fiber sheet to a certain degree, It is difficult for this crack to progress continuously to other (adjacent) carbon fiber sheets, and the carbon fiber sheet laminate does not break at a stretch.

  On the other hand, isotropic pitch-based carbon fibers have the properties of high flexibility, easy intertwining of the fibers, and lower strength as a single body than PAN-based carbon fibers. For this reason, the carbon fiber sheet using only isotropic pitch carbon fibers has many carbon fiber mutual contacts and high strength as a carbon fiber sheet. However, the strength of the carbon fiber sheet after the destruction of the protective carbon layer that bonds the carbon fiber contact points is insufficient, and the cracks produced by one carbon fiber sheet continue to other carbon fiber sheets. It is easy to progress and the carbon fiber sheet laminate is destroyed at a stretch.

  On the other hand, the isotropic pitch carbon fiber and PAN are controlled by regulating the mass blending ratio of the isotropic pitch carbon fiber and the PAN carbon fiber as described above and randomly entangled three-dimensionally. It is possible to realize a carbon fiber sheet laminate having the advantages of both of the carbon fibers. That is, while maintaining the strength as a carbon fiber sheet by isotropic pitch-based carbon fiber, the strength of the carbon fiber sheet is maintained to a certain extent even after a crack is generated by a stress by the PAN-based carbon fiber, and the crack is propagated Can be realized.

  Here, if the amount of isotropic pitch-based carbon fiber in the entire carbon fiber is too small, the effect of the isotropic pitch-based carbon fiber can not be sufficiently obtained. In addition, when the amount of the PAN-based carbon fiber in the whole carbon fiber is too small, the effect of the PAN-based carbon fiber can not be sufficiently obtained. For this reason, the mass of isotropic pitch carbon fiber occupying in the whole carbon fiber is regulated to 20% or more, more preferably to 25% or more, and most preferably to 30%. In addition, the mass of the PAN-based carbon fiber in the whole carbon fiber is regulated to 20% or more, more preferably 25% or more, and most preferably 30%.

  Carbon fibers may also contain other carbon fibers such as anisotropic pitch carbon fibers and rayon carbon fibers, but in order to sufficiently obtain the effect of isotropic pitch carbon fibers and PAN carbon fibers The total mass of isotropic pitch-based carbon fiber and PAN-based carbon fiber in the entire carbon fiber is regulated to 90% or more, more preferably 95% or more, and most preferably 100% (other carbon Does not contain fiber).

  Here, the carbon fiber sheet laminate includes one in which a plurality of plate-like carbon fiber sheets are stacked, and one in which one or a plurality of carbon fiber sheets are spirally wound and stacked. Be

  Further, it is preferable that carbon fiber sheets constituting the carbon fiber sheet laminate have the same bulk density, thickness, mass blending ratio of carbon fibers, and the like.

  In addition, the carbon fiber sheet disposed on the surface (one or both) of the carbon fiber sheet laminate may be impregnated with pyrolytic carbon, or may include carbonaceous particles such as graphite particles and amorphous carbon particles. You may use. Moreover, it is good also as a structure which affixes and uses a surface layer with a bulk density, a volume fraction of carbon fiber, etc. on the surface of a carbon fiber sheet laminated body. By setting it as such a structure, wear and dust generation of a carbon fiber sheet laminated body can further be suppressed. Moreover, when not including these, a manufacturing process can be simplified and cost reduction. In addition, it is preferable not to contain components other than carbon fiber and a protective carbon layer in carbon fiber sheets other than a surface.

  The carbon fiber sheet laminate according to the present invention can be used as a molded heat insulating material for high temperature furnaces such as single crystal silicon pulling apparatus, polycrystalline silicon cast furnaces, sintering furnaces for metals and ceramics, vacuum deposition furnaces, etc. It can also be used as a sound absorbing insulation material, a heat insulation board for ships, etc.

  When a carbon fiber sheet laminate is used as a molded heat insulating material, the protective carbon layer is present if there is active gas (oxygen gas, SiO gas, etc.) mixed as impurities or generated in the furnace around the carbon fiber sheet laminate. React with the active gas ahead of the carbon fiber. Thereby, it is suppressed that carbon fiber and active gas react and deteriorate.

  Here, when the carbonaceous matter reacts with oxygen gas, it is removed as carbon dioxide gas, and when it reacts with SiO gas, it remains as SiC without being removed, but in either case it is made of carbon fiber To maintain the adiabatic action obtained by the skeletal structure forming a large number of spaces.

  The carbon fiber sheet laminate is formed by laminating a plurality of carbon fiber sheets made of carbonaceous matter, and therefore the carbon fiber sheet laminate does not contain components other than carbonaceous matter.

  In the above configuration, the isotropic pitch-based carbon fiber can be a curved carbon fiber. When the carbon fiber is curved, the entanglement of the carbon fibers can be further enhanced.

  Here, the curved carbon fiber means the length L1 when the fiber is drawn in a straight line (ie, the fiber length), and the maximum length of the curved fiber in the natural state (or the maximum point in the natural state) L1 / L2 (ratio of L1 and L2) is 1., where L2 is the length at which this dimension becomes the largest when the dimension, ie, the distance between any two points on a curved fiber, is measured. It is defined (or defined) as a carbon fiber having three or more curved shapes. In addition, when pulling a fiber etc., the curve of a fiber may not be hold | maintained temporarily. Therefore, in order to make the measurement condition more accurate, the length L2 is the maximum in the natural state of the curved fiber after free-falling the fiber of the length L1 from a predetermined height (for example, about 30 to 100 cm) It may be measured as the length. In addition, the maximum length L2 often has variation in each curved carbon fiber, and usually, a plurality of measured values [eg, 5 or more (eg, 5 to 200), preferably 10 or more (eg, For example, it can be determined as an average value (average maximum length) of about 10 to 100), and more preferably 20 or more (for example, about 20 to 50) measurement values.

  In addition, since it is difficult to make a PAN-based carbon fiber into a curved shape in the manufacturing method, it is preferable to use a non-curved (linear) one.

The manufacturing method of the carbon fiber sheet laminated body which concerns on this invention for solving the said subject is comprised as follows.
A fiber felt producing step of intermingling carbon fibers three-dimensionally randomly to form a fiber felt, a prepreg producing step of impregnating the fiber felt with a thermosetting resin to produce a prepreg of a carbon fiber sheet, and the prepreg A plurality of lamination steps to form a prepreg laminate, and a binding step of heating while pressurizing the prepreg laminate to thermally cure the thermosetting resin to bind the prepreg. Heat-treating the obtained prepreg laminate in an inert gas atmosphere to carbonize the thermosetting resin, and the carbon fiber comprises an isotropic pitch carbon fiber and a polyacrylonitrile carbon And the mass ratio of the isotropic pitch carbon fiber to the total mass of the carbon fiber is at least 20%, and the total quality of the carbon fiber The mass ratio of the polyacrylonitrile-based carbon fiber to 20% or more, and the ratio of the total mass of the isotropic pitch-based carbon fiber to the polyacrylonitrile-based carbon fiber to the total mass of the carbon fiber is 90% or more A method of producing a carbon fiber sheet laminate which is

  The carbon fiber sheet laminate according to the present invention can be manufactured by the above manufacturing method.

  As described above, according to the present invention, it is possible to realize a carbon fiber sheet laminate capable of suppressing breakage due to stress.

FIG. 1 is a perspective view schematically showing the structure of a carbon fiber sheet laminate according to the present invention. FIG. 2 is a diagram showing an outline of a three-point bending test. FIG. 3 is a graph showing the results of a three-point bending test. FIG. 4 is a diagram showing an outline of the peeling test. FIG. 5: is a microscope cross-section photograph of the carbon fiber sheet laminated body concerning Example 1, Comprising: Fig.5 (a) shows a thing from a plane direction, FIG.5 (b) from a side direction, respectively.

Embodiment
FIG. 1 is a perspective view schematically showing the structure of a carbon fiber sheet laminate according to the present embodiment. The carbon fiber sheet laminate 100 according to the present embodiment has a fiber felt in which carbon fibers are entangled, and a protective carbon layer made of carbonaceous material covering the carbon fiber surface of the fiber felt, and is made of carbonaceous material. The carbon fiber sheet 1 to be made is laminated (in FIG. 1, eight carbon fiber sheets 1 are laminated). Moreover, in the carbon fiber sheet 1, carbon fibers are three-dimensionally randomly oriented.

  The carbon fiber constituting the carbon fiber sheet 1 contains isotropic pitch-based carbon fiber and polyacrylonitrile (PAN) -based carbon fiber, and the ratio of isotropic pitch-based carbon fiber to the total mass of carbon fiber is 20% or more, the proportion of PAN-based carbon fiber in the total mass of carbon fiber is 20% or more, and the proportion of the total mass of isotropic pitch-based carbon fiber and PAN-based carbon fiber in the total mass of carbon fiber is 90% or more Is regulated.

  Here, the PAN-based carbon fiber has high strength as a single substance, and the fibers are not easily entangled with each other. On the other hand, isotropic pitch carbon fibers are highly flexible and easily intertwined with each other, and the strength of single carbon fibers is lower than that of PAN carbon fibers. By controlling the mass blending ratio of the isotropic pitch carbon fiber and the PAN carbon fiber as described above, the entanglement between the isotropic pitch carbon fiber and the strength of the PAN carbon fiber are achieved. A carbon fiber sheet laminate can be realized.

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

  Here, the isotropic pitch-based carbon fiber is a carbon fiber whose raw material is infusibilized isotropic pitch, and commercially available ones can be used. Pitch is a mixture of innumerable condensed polycyclic aromatic compounds chemically and is liquid tar obtained upon dry distillation of wood, coal etc., bitumen obtained from oil sand, oil obtained by dry distillation of oil shale, There are residual oil obtained by distillation of crude oil, tar produced by cracking of petroleum fractions, and the like which are obtained by heat treatment and polymerization at a normal temperature obtained by polymerization. Specific examples thereof include pitch derived from coal, pitch derived from petroleum, and synthetic pitch obtained by polymerizing an aromatic compound such as naphthalene.

  What is produced by a well-known method can be used for an isotropic pitch type carbon fiber. For example, pitches of petroleum or coal origin can be spun and deposited on a pedestal to obtain a mat of pitch fibers. The resulting mat is a collection of pitch fibers of varying lengths generally in the range of 5 to 400 mm. Although the method of spinning is not particularly limited, it is generally carried out by melt spinning. As a method of melt spinning, there are a vortex method and a centrifugal method. According to the vortex method, curved fibers are obtained, while non-curved (linear) fibers are obtained by centrifugation. The infusibilization treatment and carbonization treatment of pitch fibers are performed to obtain a carbon fiber mat. The infusibilization step is a step of introducing oxygen to the surface of the pitch fiber for oxidation. The atmosphere of the infusibilization step can be air or NOx. The temperature of the carbonization treatment is not particularly limited, but can be 700 to 1200 ° C. in consideration of economy and the like. In addition, when a bent fiber is used, the fibers are more easily entangled in the fiber felt, and the strength can be easily increased.

  The isotropic pitch carbon fiber preferably has an average fiber diameter (diameter) of 7 to 20 μm, more preferably 9 to 18 μm, and still more preferably 11 to 15 μm. Moreover, it is preferable that it is 5-400 mm, as for the length, it is more preferable that it is 8-350 mm, and it is further more preferable that it is 10-300 mm.

  Polyacrylonitrile (PAN) carbon fibers are obtained by carbonizing polyacrylonitrile fibers, and commercially available products can be used. The PAN-based carbon fiber preferably has a fiber length of 20 to 200 mm, and 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.

  Further, any carbon fiber is not particularly limited as a microscopic structure of carbon fiber, and only one having the same shape (curved shape, linear shape, cross-sectional shape, etc.) may be used, or different structures may be used. Although it may be mixed, it is preferable that the isotropic pitch-based carbon fiber is curved, and the PAN-based carbon fiber is linear (not curved).

  Moreover, it does not specifically limit as a shape of the fiber felt which comprises a carbon fiber sheet, and length and width are not specifically limited, either. As a fiber felt, for example, one having a thickness of about 3 to 15 mm can be used. In addition, as a microscopic structure of carbon fiber felt, one in which carbon fibers oriented in random directions in three dimensions intersect intricately is used.

  In addition, the protective carbon layer covers the entire surface of the carbon fibers constituting the fiber felt or a part of the surface of the carbon fibers. The protective carbon layer may be carbonaceous (amorphous carbon or graphitic carbon), and 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 be impregnated into the fiber felt. Among them, thermosetting resins such as phenol resin, furan resin, polyimide resin and epoxy resin are preferable. When a thermosetting resin is used, the carbon fibers and the laminated carbon fiber sheets can be easily and firmly bonded by heat curing and carbonization.

  Here, only one type of thermosetting resin may be used, or two or more types may be mixed and used. The thermosetting resin may be contained as it is in the fiber felt, or may be diluted with a solvent and contained in the fiber felt. As the solvent, alcohols such as methyl alcohol and ethyl alcohol can be used.

  Moreover, a fiber felt may cut | disconnect after manufacturing a carbon fiber sheet laminated body using a long thing and a long width thing, and you may cut | disconnect beforehand to the size of a carbon fiber sheet laminated body.

Here, the bulk density of the carbon fiber sheet laminate is preferably 0.05~0.30g / cm ^3, more preferably 0.07~0.20g / cm ^3, 0.10~ More preferably, it is 0.18 g / cm ³ .

  Moreover, it is preferable that it is 100: 5-100: 100, and, as for mass ratio of the carbon fiber in a carbon fiber sheet and a protection carbon layer, it is more preferable that it is 100: 10-100: 80, and 100: 15-100. More preferably, it is 60.

  The thickness of each carbon fiber sheet is preferably 3 to 15 mm, more preferably 5 to 12 mm, and still more preferably 6 to 10 mm.

  Next, a method of manufacturing a carbon fiber sheet laminate will be described.

(Preparation of fiber felt)
As the fiber felt, one produced by a known method can be used, and a method is adopted in which carbon fibers are easily oriented randomly in three dimensions. As a method of forming the fiber felt, for example, a method in which a fiber in which isotropic pitch-based carbon fiber and PAN-based carbon fiber are mixed is opened by a fiber opening machine and raised and loaded by air pressure, and then a needle punch is used. A method of stirring and mixing in a solution and depositing on a papermaking net, a method of using a needle punch after spinning a fiber felt by a carding means such as a curd machine, and the like can be exemplified. The fiber felt preferably has a thickness of 3 to 20 mm, more preferably 5 to 15 mm. Basis weight of the fiber felt, for example, is preferably from 100 to 2000 g / m ^2, and more preferably 300 to 1500 g / m ^2.

(Preparation of prepreg)
After that, the thermosetting resin solution is sprayed onto the fiber felt and dipped in the thermosetting resin solution, or the 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 of the carbon fiber to the protective carbon layer becomes 100: 5 to 100: 100 after firing.

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

(Cohesion, carbonization)
The laminate produced as described above is heated while being pressurized to thermally cure the thermosetting resin to bind the prepreg. Thereafter, the thermosetting resin is carbonized by heating in an inert gas atmosphere at 1500 to 2500 ° C. for a predetermined time (for example, 1 to 20 hours) to obtain a carbon fiber sheet laminate.

  Here, carbonization referred to in the present specification means in a broad sense including graphitization. For example, when heat treatment is performed particularly at a temperature of 2000 ° C. or higher, it is considered that the graphite structure develops, but in the present invention, the carbonaceous material constituting the carbon fiber sheet laminate is either amorphous carbon or graphitic carbon May be.

  The invention will be described in more detail on the basis of examples.

Example 1
(Production of carbon fiber)
The isotropic pitch derived from coal was melt-spun by a vortex method to obtain a mat composed of bent pitch fibers. The pitch fibers were approximately 10 to 300 mm in length, and the fibers aggregated to form a mat. The mat was heat-treated in an air atmosphere from normal temperature to about 250 to 300 ° C. for a total of 30 minutes to infuse the pitch fibers to obtain a fiber mat. The fiber mat was carbonized at about 1000 ° C. in an inert gas atmosphere to obtain a mat of isotropic pitch carbon fibers (average diameter 13 μm). The linear length of this carbon fiber (ie, the fiber length) is L1, the maximum natural length 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 was measured, L1 / L2 (the ratio of L1 to L2) was 2.1, where L2 is the length at which this distance becomes the largest.

(Preparation of fiber felt)
The above isotropic pitch carbon fibers and polyacrylonitrile (PAN) carbon fibers (manufactured by Toray Industries, Inc., average fiber diameter 7 μm, length 40 mm) are mixed and opened at a mass ratio of 50: 50. A fiber felt (300 × 300 × 10 (thickness) mm, basis weight 560 g / m ² ) was produced by entanglement by a needle punch method.

(Preparation of prepreg)
The fiber felt was dipped in a resol type phenolic resin thermosetting resin solution to prepare a prepreg. At this time, the phenolic resin-based thermosetting resin solution was added such that the carbon mass formed by carbonization of the thermosetting resin in the case of heat treatment at 2000 ° C. is 40 parts by mass with respect to 100 parts by mass of carbon fiber .

(Lamination step)
Eight layers of the above prepreg were laminated to prepare a prepreg laminate.

(Attachment / carbonization step)
The prepreg laminate was placed in a spacer with a thickness of about 40 mm, compressed and pressurized at 200 ° C. for 90 minutes to thermally cure the phenol resin to bind the prepreg laminate. The obtained prepreg laminate was heat-treated at 2000 ° C. in an inert atmosphere to obtain a flat carbon fiber sheet laminate. The bulk density of the obtained carbon fiber sheet laminate was 0.15 g / cm ³ .

(Example 2)
A fiber felt (300 × 300 × 8 (thickness) mm, basis weight 420 g / m ² ) was prepared by setting the mass ratio of isotropic pitch carbon fiber to PAN carbon fiber in preparation of fiber felt at 30:70. A carbon fiber sheet laminate according to Example 2 was obtained in the same manner as Example 1 except for the above. The bulk density of the obtained carbon fiber sheet laminate was 0.14 g / cm ³ .

(Comparative example 1)
A carbon fiber according to Comparative Example 1 was produced in the same manner as in Example 1 except that a fiber felt (300 × 300 × 5 (thickness) mm) was produced using only PAN-based carbon fibers in producing a fiber felt. A sheet laminate was prepared, and the bulk density of the obtained carbon fiber sheet laminate was 0.15 g / cm ³ .

(Comparative example 2)
A fiber felt was prepared in the same manner as in Example 1 except that a fiber felt (300 × 300 × 10 (thickness) mm, fabric weight 500 g / m ² ) was produced using only isotropic pitch carbon fibers. Then, a carbon fiber sheet laminate according to Comparative Example 2 was produced. The bulk density of the obtained carbon fiber sheet laminate was 0.15 g / cm ³ .

(3 point bending test)
The carbon fiber sheet laminates according to Examples 1 and 2 and Comparative Examples 1 and 2 were cut into a length of 250 mm, a width of 40 mm, and a height of 40 mm, respectively, to obtain a test piece 200. The test piece 200 was placed on a table 10 with a distance between supporting points set to 200 mm. A pressure was applied to the test piece 200 by the indenter 20, and the relationship between the pressure and the displacement was measured. The results are shown in FIG. 3 and Table 1.

(Peeling test)
The carbon fiber sheet laminates according to Examples 1 and 2 and Comparative Examples 1 and 2 were cut into a length of 40 mm, a width of 40 mm, and a height of 40 mm, respectively, to obtain a test piece 300. As shown in FIG. 4, the carbon fiber sheet is to be the height direction of the test piece, and the carbon fiber sheet to be the both end faces of the test piece 300 and the jig 30 are made of epoxy adhesive. It fixed using. The test piece 300 was pulled in the height direction using the jig 30, and the peel strength (stress) was measured when the laminated interface of the test piece peeled. The results are shown in Table 1.

  In Comparative Example 1, the maximum stress was as small as 0.38 MPa in the three-point bending test. Further, in Comparative Example 2, although the maximum stress was as large as 0.81 MPa, when the maximum load was reached, the carbon fiber sheet laminate was immediately broken. On the other hand, in Examples 1 and 2, it can be seen that the maximum stress is as large as 0.74 MPa and 0.84 MPa, and no breakage occurs at once even after reaching the maximum load.

  In Comparative Example 1, the peel strength was as small as 10 kPa in the peel test. Moreover, in Comparative Example 2, the peel strength was as large as 55 kPa. On the other hand, in Examples 1 and 2, it can be seen that the peeling strength is 26 kPa and 14 kPa, which is higher than Comparative Example 1. These things are considered as follows.

  In Comparative Example 1, only PAN-based carbon fibers which are high in strength as a single substance but hardly intertwined with each other are used. For this reason, there are few contact points between carbon fibers, and the strength as a carbon fiber sheet is low. However, the crack generated in one carbon fiber sheet is unlikely to progress continuously to the other carbon fiber sheets and does not break at once. This can also be confirmed from the fact that, in the test results of FIG. 3, in the region where the amount of mutation is 13% or more, the displacement proceeds without a large change in stress.

  Further, in Comparative Example 2, only isotropic pitch carbon fibers in which the fibers are easily intertwined are used. For this reason, there are many contact points between carbon fibers, and the strength as a carbon fiber sheet is high. However, cracks generated in one carbon fiber sheet tend to progress continuously to other carbon fiber sheets, and the carbon fiber sheet laminate is broken at once. This can also be confirmed from the test results in FIG. 3 that the stress changes from 0.81 MPa to 0 MPa at a displacement of about 25%.

  On the other hand, in Examples 1 and 2, the isotropic pitch carbon fiber and the PAN carbon fiber are mixed and used. Therefore, the isotropic pitch carbon fiber and the PAN carbon fiber are entangled in the carbon fiber sheet, and the fibers are entwined well by the action of the isotropic pitch carbon fiber. Therefore, while the three-point bending strength and peel strength are maintained high, it is difficult to progress continuously to the other carbon fiber sheets when the generated cracks are generated by the action of the PAN-based carbon fiber, and the bending test Displacement amount of the This can also be confirmed from the fact that in the test result of FIG. 3, in the region where the displacement amount is 20% or more, the displacement progresses without a large change in stress.

  In Example 1 in which the ratio of isotropic pitch-based carbon fibers is higher, the strength in the bending test is lower than in Example 2, and the peel strength is higher. Therefore, what is necessary is just to determine the ratio of the isotropic pitch type carbon fiber which occupies for all the carbon fibers, or PAN type carbon fiber from bending strength and peeling strength calculated | required by the intended use. Here, 20% by mass or more of isotropic pitch-based carbon fibers in total carbon fibers, 20% by mass of PAN-based carbon fibers, and the ratio of the total mass of isotropic pitch-based carbon fibers and PAN-based carbon fibers 90% by mass or more.

  The cross-sectional microscope picture of the surface layer vicinity of the carbon fiber sheet laminated body concerning Example 1 is shown in FIG. FIG. 5: is a microscope cross-section photograph of the carbon fiber sheet laminated body concerning Example 1, Comprising: Fig.5 (a) shows a thing from a plane direction, FIG.5 (b) from a side direction, respectively. As shown in FIGS. 5 (a) and 5 (b), the carbon fiber sheet laminate has a relatively large diameter (having an average diameter of 13 μm) and a curved isotropic pitch carbon fiber 3 and a relatively large diameter. It can be seen that the narrow (with an average diameter of 7 μm) PAN-based carbon fiber 4 is randomly entangled three-dimensionally.

  The carbon fiber sheet laminate according to the present invention is excellent in strength, self-supporting ability and processability, and has a high stress relaxation effect. A carbon fiber sheet laminate having such properties is particularly suitable for use in an environment susceptible to stress failure, and its industrial significance is great.

Reference Signs List 1 carbon fiber sheet 3 isotropic pitch carbon fiber 4 polyacrylonitrile carbon fiber 10 base 20 indenter 30 jig 100 carbon fiber sheet laminate 200 test piece 300 test piece

Claims (3)

Carbon felt including a fiber felt in which carbon fibers are randomly entangled three-dimensionally and a protective carbon layer covering the carbon fiber surface of the fiber felt, wherein a plurality of carbon fiber sheets made of carbonaceous material are laminated A fiber sheet laminate,
The carbon fibers include isotropic pitch carbon fibers and polyacrylonitrile carbon fibers,
The mass ratio of the isotropic pitch carbon fiber to the total mass of the carbon fiber is 20% or more,
The mass ratio of the polyacrylonitrile-based carbon fiber to the total mass of the carbon fiber is 20% or more,
The ratio of the total mass of the isotropic pitch carbon fiber and the polyacrylonitrile carbon fiber in the total mass of the carbon fiber is 90% or more.
A carbon fiber sheet laminate characterized in that. The isotropic pitch carbon fiber is a bent carbon fiber,
The carbon fiber sheet laminate according to claim 1, wherein the carbon fiber sheet laminate. A fiber felt producing step of randomly intermingling carbon fibers three-dimensionally to form a fiber felt,
A prepreg production step of impregnating the fiber felt with a thermosetting resin to produce a prepreg of a carbon fiber sheet;
Laminating a plurality of the prepregs to form a prepreg laminate;
A binding step of pressing the prepreg laminate while heating to thermally cure the thermosetting resin to bind the prepreg;
Heat treating the bonded prepreg laminate in an inert gas atmosphere to carbonize the thermosetting resin;
The carbon fibers include isotropic pitch carbon fibers and polyacrylonitrile carbon fibers,
The mass ratio of the isotropic pitch carbon fiber to the total mass of the carbon fiber is 20% or more,
The mass ratio of the polyacrylonitrile-based carbon fiber to the total mass of the carbon fiber is 20% or more,
The manufacturing method of the carbon fiber sheet laminated body whose ratio of the total mass of the said isotropic pitch type carbon fiber and the said polyacrylonitrile type carbon fiber to the total mass of the said carbon fiber is 90% or more.