JP2011046543A - Carbon fiber-reinforced carbon composite material and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a C/C composite manufactured through a resin impregnation method, which acquires sufficient strength as a brake material and improved shear strength between layers, even when omitting or reducing the number of cycles of a densification process wherein resin impregnation and baking are repeated in a manufacturing process for the C/C composite by the resin impregnation method, and the method for manufacturing the same. <P>SOLUTION: The carbon fiber-reinforced carbon composite material is manufactured through the resin impregnation method comprising: heating and press-molding a carbon fiber preform prepared by impregnating a carbon fiber with a carbon precursor resin; and baking the same in an inert atmosphere. Here, a carbonized microfibrillated cellulose powder is contained in the carbon fiber precursor resin so as to provide the C/C composite that acquires sufficient strength as a brake material etc. even when omitting or reducing the number of cycles of a densification process wherein resin impregnation and baking are repeated. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a carbon fiber reinforced carbon composite material (hereinafter also referred to as “C / C composite”) and a method for producing the same, and more specifically, a brake material without performing a densification step or reducing the number of times. In particular, the present invention relates to a C / C composite having a sufficient bending strength and a manufacturing method thereof.

  C / C composite is a composite material with carbon fiber as filler and matrix as carbon. Generally, it has higher mechanical properties than carbon material and lighter than metal material. There are many advantages. Further, the C / C composite has advantages such as high heat resistance and good friction and wear characteristics. For this reason, C / C composites are widely used for nozzle cones for spacecrafts, leading edges, brake disks for aircraft and automobiles, artificial tooth roots, and the like.

  As described above, the C / C composite has excellent mechanical properties, but its production requires a lot of labor and time. As a general method for producing a C / C composite, there are a resin impregnation method and a chemical vapor deposition method (CVD method). The resin impregnation method is a simple method that does not require large-scale equipment as compared with the CVD method. In this resin impregnation method, a carbon fiber preform impregnated with a thermosetting resin as a carbon precursor such as furan resin or phenol resin is molded and cured, and then carbonized in an inert atmosphere to obtain a C / C composite. Is the method. However, since the carbonization yield of the resin is usually about 60%, a densification step in which the resin is repeatedly impregnated and fired is required until the required density and mechanical strength of the product are obtained (patent) (Refer to Literature 1, 2 etc.). Further, the C / C composite has a problem that the interlaminar shear strength, particularly the mode II interlaminar toughness value is low.

JP-A-5-345667 Japanese Patent Laid-Open No. 2003-342081

  In view of the problems in the conventional C / C composite as described above, in the production of the C / C composite by the resin impregnation method, even if the densification step of repeating resin impregnation and firing is not performed or the number of times is reduced, It is an object of the present invention to provide a C / C composite having a sufficient strength as a brake material and the like and having improved interlayer shear strength and a method for producing the same.

  As a result of intensive research to achieve the above object, the present inventors, as a result of the resin (the precursor of the matrix impregnated into the carbon fiber as the filler) when producing the C / C composite by the resin impregnation method ( By adding carbon to the base material resin in advance, the mechanical properties of the product are improved, the required mechanical strength is given to the product even if the densification process is not performed or the number of times is reduced, and the interlaminar shear strength In addition, the present inventors have found that an improved C / C composite can be obtained and completed the present invention.

  That is, the carbon fiber reinforced carbon composite material (C / C composite) according to the present invention comprises carbon precursor resin containing carbonized microfibrillated cellulose (hereinafter also referred to as “carbonized MFC”) powder. And

  Further, the method for producing a carbon fiber reinforced carbon composite material according to the present invention is based on a resin impregnation method in which a carbon fiber preform obtained by impregnating a carbon precursor resin into carbon fiber is heated and pressed and then fired in an inert atmosphere. A method for producing a carbon fiber reinforced carbon composite material, wherein the carbon fiber precursor resin contains carbonized MFC powder. In the present invention, the “carbon fiber preform” refers to a sheet-like carbon fiber impregnated with a precursor resin (matrix resin) serving as a matrix, and the resin-impregnated carbon fiber. Can be formed by a filament wiping method, including both those formed into a sheet shape, and those obtained by impregnating a carbon fiber aggregate formed into a predetermined shape such as a sheet shape with a resin.

  The carbonized MFC powder is preferably obtained by carbonizing freeze-dried microfibrillated cellulose (hereinafter also referred to as “MFC”) in an inert atmosphere. Moreover, it is preferable to use a phenol resin as said carbon precursor resin (base material resin).

  The carbon fiber reinforced carbon composite material (C / C composite) according to the present invention as described above can be suitably used as a brake material.

  The C / C composite according to the present invention having the above-described structure is improved in bending strength and interlaminar shear strength by adding carbon powder to the precursor resin in advance, compared with a normal C / C composite. Even if it is not made or the number of times is reduced, it has sufficient bending strength as a brake material.

  Furthermore, in the present invention, carbonized MFC powder obtained by carbonizing freeze-dried MFC in an inert atmosphere is used as the carbon powder added to the precursor resin. Normally, MFC can maintain a three-dimensional network structure only when it contains moisture. If carbonized as it is, the moisture contained in MFC will dry and evaporate, and entanglement will occur due to self-condensation and network structure. End up. Therefore, as a pretreatment for carbonization, by removing the water adsorbed on the MFC by lyophilization and then carbonizing, the water harmful to the resin contained in the MFC is removed, and the microfibrillated cellulose Carbonization can be performed while maintaining the three-dimensional microstructure, dispersibility with respect to the precursor resin is improved, and an increase in resin viscosity can be suppressed.

  Further, by using a phenol resin as the precursor resin (matrix resin), a C / C composite can be produced at a low cost and with a high carbonization yield.

A photomicrograph of carbonized microfibrillated cellulose obtained by carbonizing freeze-dried microfibrillated cellulose in an inert atmosphere. The schematic diagram of a bending strength test. The schematic diagram of the ENF test (End Notched Flexure test) which measures a mode II interlaminar fracture toughness value. Explanatory drawing which shows the test piece dimension of an ENF test. The graph which shows the measurement result of a bending elastic modulus. The graph which shows the measurement result of the maximum bending stress. The graph which shows the mode II interlaminar fracture toughness value _GIIC calculated _| required from the ENF test.

  In the present invention, when a C / C composite is produced by a resin impregnation method, carbonized microfibrillated cellulose powder is added to a carbon precursor resin (matrix resin) impregnated in carbon fibers. Other than that, it is the same as the method for producing a C / C composite by a known resin impregnation method.

  For example, any carbon fiber such as pitch-based, PAN-based, or rayon-based may be used as the carbon fiber serving as a filler material. Further, the diameter and elastic modulus of the carbon fiber may be in a range generally used as a composite material and are not particularly limited. Further, the form of the carbon fiber preform is not particularly limited, and a one-dimensional oriented preform formed by a filament wiping method, a two-dimensional oriented preform such as a plain weave, satin weave, a woven fabric, and a non-woven fabric, and a three-dimensional oriented preform. Either of these may be used.

  There is no particular limitation on the precursor resin (matrix resin) which is impregnated into the carbon fiber and becomes the matrix of the C / C composite, and a known matrix resin such as phenol resin, furan resin, and petroleum-based or coal-based pitch is used. Either can be used. Among these resins, a phenol resin is preferable because it is inexpensive and has a high carbonization yield.

  In the present invention, when a C / C composite is produced by a resin impregnation method, carbon powder is added to a precursor resin (matrix resin) as a matrix to be impregnated into the carbon fiber preform. In the present invention, carbonized MFC powder obtained by carbonizing MFC in an inert atmosphere is used as the carbon powder, thereby improving the carbonization yield and improving the interface characteristics of the C / C composite due to the three-dimensional microstructure of the carbonized MFC powder. Improvement is expected, and it is considered that mechanical strength such as shear strength between layers such as bending strength is improved. On the other hand, even if the same carbon powder is used, for example, if graphite is added to the precursor resin (matrix resin), the effect of improving the bending strength and interlaminar shear strength of the C / C composite of the present invention is obtained. (See Examples, Reference Examples and Comparative Examples below). In particular, carbon powder that maintains the three-dimensional structure of MFC can be obtained by carbonizing freeze-dried MFC in an inert atmosphere (see FIG. 1). When carbonized without being lyophilized, the three-dimensional structure is not maintained, and there are cases where the intended effect of improving the bending strength or the like is not sufficiently exhibited.

  Carbonization of MFC is performed by freeze-drying MFC containing moisture using a freeze dryer, and firing the freeze-dried MFC in an inert atmosphere at a high temperature, for example, 800 ° C. for about 3 to 5 hours. Carbonized MFC powder is obtained.

  The method of impregnating the precursor resin into the carbon fiber used as the filler, the resin adhesion amount, and the like may be known. The carbon fiber preform is prepared by forming a carbon fiber pre-impregnated one-dimensionally oriented preform, plain weave, satin weave, woven fabric, non-woven fabric, etc. Alternatively, resin impregnation may be performed after carbon fibers are formed into a carbon fiber composite having a predetermined shape as described above.

  The amount of carbonized MFC powder added to the precursor resin is not particularly limited, but if the added amount is small, the effect may not be exhibited, but the addition of 1% by weight has the effect of improving the desired bending strength. Has been obtained.

  A carbon fiber preform as a base material is obtained by impregnating carbon fiber with a precursor resin to which the carbonized MFC powder is added. The carbon fiber preform is heat-pressed and then carbonized in an inert atmosphere. An improvement in the carbonization yield of the carbon precursor resin can be expected by molding the carbon fiber preform as a base material under high temperature and high pressure conditions of about 150 ° C. and about 15 MPa, for example.

  The carbon fiber preform formed as described above is heated to a maximum temperature, for example, 1000 ° C. in about 10 hours from room temperature in an inert atmosphere, and held for about 1 hour, whereby the precursor resin is carbonized. The intended C / C composite is obtained.

  The C / C composite according to the present invention as described above can be used as a brake material for aircraft, automobiles, other sliding materials, etc. even if the densification process of repeating resin impregnation and firing is not performed or the number of times is reduced. Since it can be suitably used for the same application as the C composite, it is possible to reduce manufacturing effort and cost.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

<Material>
Precursor resin (base material): novolak type phenol resin (manufactured by Sumitomo Bakelite: industrial phenol resin “Sumilite” (registered trademark) PR-51697).
Filler (reinforcing material): unidirectional carbon fiber (manufactured by Mitsubishi Rayon: “Pyrofil” (registered trademark) TR30S12LAB).
Carbon powder:
(A) Carbonized MFC (MFC manufactured by Daicel Chemical Industries, Ltd .: “Serisch” (registered trademark) is used).
(B) Graphite powder: made of Japanese graphite; graphite powder AUP (particle size [6-9 μm]).

<Example 1>
(1) Production of carbonized MFC powder MFC containing 90% by weight of water was freeze-dried using a freeze dryer (FDU-1100, manufactured by Tokyo Science Equipment Co., Ltd.), and the MFC after freeze-drying was placed in an inert atmosphere. Then, heat treatment was performed at 800 ° C. for 3 hours to obtain carbonized MFC powder. This is observed using a scanning electron microscope FE-SEM JSEM7001FD, and a photograph taken is shown in FIG.

(2) Production of C / C composite 1% by weight of carbonized MFC powder was added to the phenol resin, and the carbonized MFC powder was dispersed in the resin by treatment with a process homogenizer for 1 hour. Filament winding was used for laminating the resin and carbon fiber. The winding was hoop wound, and three layers were wound around a square bobbin having a fiber pitch of 2 mm and a side of 250 mm. This was kept at 65 ° C. for 10 hours in an electric furnace together with the bobbin, and the ethanol in the resin was evaporated and dried to be precured. This was pressed by a hotter press at a pressure of 15 MPa and a temperature of 150 ° C. for 2 hours to obtain a carbon fiber reinforced plastic (CFRP). The obtained CFRP was cut into a suitable size using a diamond cutter and then raised from room temperature to a maximum temperature (1000 ° C.) at a temperature rising rate of 3.33 ° C./min in an inert atmosphere in a tubular furnace. Warm and hold for 1 hour to obtain a C / C composite.

<Reference Example 1>
A C / C composite was obtained in the same manner as in Example 1 except that 1% by weight of graphite powder was added to the phenol resin instead of the carbonized MFC powder.

<Comparative Example 1>
A C / C composite was obtained in the same manner as in Example 1 except that no carbon powder (carbonized MFC) was added to the phenol resin.

<Evaluation test method>
(1) Bending test A three-point bending test was conducted to determine the flexural modulus and the maximum bending stress. The test piece dimensions and test conditions followed the three-point bending test method of JISK7074. A schematic diagram of the three-point bending test is shown in FIG. The test measure was 1 mm / min, and the fulcrum distance was 80 mm. The testing machine used was a universal testing machine Autograph AG-A manufactured by Shimadzu Corporation. The equations for obtaining the bending stress and bending elastic modulus are shown below.

  Moreover, the fracture behavior of the test piece during the bending test was observed.

(2) ENF test An EFN test (End Notched Frexxure test) was performed, and a mode II fracture toughness value (Interlaminar Fracture Toughness) was measured. The testing machine used Shimadzu Corporation universal testing machine Autograph AG-A. The test method was based on JISK7086. A schematic diagram of the test is shown in FIG. The test measure was 1 mm / min. The specimen preparation procedure and the method for deriving the mode II fracture toughness value are described below.

(A) Test piece preparation 1) At the time of lamination | stacking of CFRP used as a base material, a copper plate (thickness 0.1mm) is inserted in a lamination | stacking center surface for the introduction of an initial crack. The side of the copper plate was perpendicular to the fiber direction.
2) The test piece was cut out using a diamond cutter so that the longitudinal direction of the test piece coincided with the fiber arrangement direction. At this time, excessive cooling heat was not generated by water cooling during cutting.
3) The test piece dimensions are shown in FIG.

(B) Derivation of Mode II Interlaminar Fracture Toughness Value The mode II interlaminar fracture toughness value immediately after the initiation of crack development is obtained by the following equation.

<Test results>
(1) Bending test results The results of the three-point bending test are shown in FIGS. Regarding the flexural modulus, although there was much variation in the value for Example 1 (indicated as “MFC (1.0 wt%)” in FIG. 5) to which carbonized MFC was added, the average value was improved. As for the maximum bending stress, Example 1 (indicated as “MFC (1.0 wt%)” in FIG. 6) is 230 MPa, and Comparative Example 1 in which nothing is added (in FIGS. 5 and 6, “Normal” ”).) Was improved by about 53% compared to 150 MPa. However, in Reference Example 1 (indicated as “Graphite (1.0 wt%)” in FIGS. 5 and 6) in which graphite powder is added to the base resin, both the flexural modulus and the maximum bending stress are larger than those in Comparative Example 1. There was no difference.

  Furthermore, in the observation of the fracture mode during the three-point bending test, the fracture due to delamination occurred in Comparative Example 1 (Normal) and Reference Example 1 (Graphite), whereas in Example 1 (MFC), the fiber Tensile fracture occurred. Therefore, the C / C composite produced by adding the carbonized MFC powder to the base resin is less likely to cause delamination compared to Comparative Example 1 in which no carbon powder is added and Reference Example 1 in which graphite is added as a carbon powder. It can be seen that it has properties.

  From the above, it can be seen that when a carbonized MFC powder is added to a base resin to produce a C / C composite, the bending strength is improved.

(2) EMF test result The mode II interlaminar fracture toughness value G _IIC obtained from the ENF test is shown in FIG. As is clear from FIG. 7, the C / C composite of Example 1 (shown as “MFC (1 wt%)” in FIG. 7) manufactured by adding carbonized MFC to the base resin does not add anything. Compared to the C / C composite of Comparative Example 1 (indicated as “Normal” in FIG. 7), G _IIC is improved by 30% from 47 j / m ² to 61 j / m ² . From this, it is estimated that the cause of the improvement in the maximum bending strength in the bending test is due to the improvement in G _IIC .

The reason why the G _IIC of the C / C composite of Example 1 manufactured by adding carbonized MFC to the base resin is improved is that a crack bridging mechanism in the three-dimensional direction by adding carbonized MFC to the base resin. It is considered that the interlaminar fracture toughness value was improved. The crack bridging mechanism is a mechanism found in composite materials reinforced mainly with fibers having a high aspect ratio (ratio of fiber length to diameter). The fibers can be broken even if cracks develop in the matrix. In addition, since a mechanism for bridging cracks is obtained, toughening can be achieved. As can be seen from FIG. 1, the carbonized MFC is in the form of fibers, and further maintains a three-dimensional structure with entangled fibers. From this, it is considered that the carbonized MFC acts as a reinforcing fiber in the three-dimensional direction. On the other hand, graphite powder has fine particles and a low aspect ratio. Further, unlike the carbonized MFC, the graphite powder does not have a three-dimensional structure, so the bridge effect cannot be obtained and the performance is not improved.

  The C / C composite according to the present invention can obtain high mechanical strength such as bending strength even if the densification process is not performed or the number of times is reduced, and it can be used for brake materials such as aircraft and vehicles, and other conventionally known applications. Therefore, it can be provided as a cheaper C / C composite.

Claims (8)

  A carbon fiber reinforced carbon composite material comprising carbon precursor resin containing carbonized microfibrillated cellulose powder.   The carbon fiber reinforced carbon composite material according to claim 1, wherein the carbonized microfibrillated cellulose powder is obtained by carbonizing freeze-dried microfibrillated cellulose in an inert atmosphere.   The carbon fiber reinforced carbon composite material according to claim 1 or 2, wherein the carbon precursor resin is a phenol resin.   The brake material which consists of a carbon fiber reinforced carbon composite material in any one of Claims 1-3.   A method for producing a carbon fiber reinforced carbon composite material by a resin impregnation method in which a carbon fiber preform impregnated with a carbon precursor resin is heat-pressed and then fired in an inert atmosphere. A method for producing a carbon fiber-reinforced carbon composite material, comprising carbonized microfibrillated cellulose powder in a body resin.   The method for producing a carbon fiber reinforced carbon composite material according to claim 5, wherein the carbon fiber preform is formed by a filament wiping method.   The method for producing a carbon fiber-reinforced carbon composite material according to claim 5 or 6, wherein the carbonized microfibrillated cellulose powder is obtained by carbonizing freeze-dried microfibrillated cellulose in an inert atmosphere.   The said carbon precursor resin is a phenol resin, The manufacturing method of the carbon fiber reinforced carbon composite material in any one of Claims 5-7.