JP3109928B2 - Method for producing carbon fiber reinforced carbon composite material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon fiber reinforced carbon composite material (abbreviated as C / C) used as a heat-resistant structural material, wherein carbon fiber is used as a reinforcing material and carbon is used as a matrix material.

[0002]

2. Description of the Related Art In recent years, carbon fiber reinforced carbon composite materials using carbon fiber as a reinforcing material and carbon as a matrix material, that is, C
/ C has been spotlighted as a structural material, a friction material, and a conductive material because it has heat resistance, specific strength, and light weight that cannot be achieved with metals and the like. This C / C is basically a method of carbonizing a resin impregnated in carbon fiber or a method of depositing carbon as a matrix material on carbon fiber in a gas phase by a CVD (chemical vapor deposition) method. It is manufactured by.

On the other hand, in a carbon fiber reinforced resin composite material (referred to as CFRP) in which a reinforcing material is carbon fiber and a matrix material is a resin, the stronger the bonding strength between the carbon fiber and the resin as the matrix material, the higher the strength. Since a composite material can be obtained, carbon fibers having been subjected to a surface treatment and having O and N functional groups introduced into the carbon fiber surface are used. Such surface-treated carbon fibers have good wetting properties and high strength. By X-ray photoelectron spectroscopy, the oxygen concentration ratio (O _1S
/ C _1S : hereinafter, abbreviated as O / C ratio) is about 0.2
It is about. Generally, the larger the O / C ratio, the stronger the bond between the carbon fiber and the resin and the higher the mechanical strength of the composite material.

On the other hand, the carbon material itself serving as the C / C matrix material has a small elongation at break and exhibits brittle fracture. In the C / C using such a carbon material as a matrix material, cracks generated in the carbon material cut the carbon fiber when the carbon fiber as the reinforcing material and the carbon material as the matrix material are firmly bonded to each other. Progresses, leading to brittle fracture, resulting in low-strength C / C. On the other hand, when the bond between the carbon fiber and the carbon material is weak, the cracks generated in the carbon material change the direction at the interface with the carbon fiber, and the carbon fiber is pulled out. /
It is known that C can be obtained.

As the form of carbon fiber used for C / C, it is known that high strength C / C can be obtained by using long fibers or continuous fibers rather than short fibers. In the case of manufacturing a two-dimensional reinforcing material such as a plate material, higher strength is obtained when carbon fibers are oriented in a more linear form. For this reason, when a woven material is used as carbon fiber, satin weave is more suitable than plain weave, and it is known that higher strength C / C can be obtained by laminating unidirectional fiber layers in the cross direction. I have.

[0006]

However, in the above-mentioned conventional method for producing a C / C by laminating unidirectional fiber layers, the production steps, ie, the molding and curing step, the post-curing step and the carbonizing step, are not performed. In addition, delamination or deformation of the laminate occurred, and it was very difficult to obtain a good C / C product.

Accordingly, an object of the present invention is to provide a method for easily producing high-strength C / C used as a heat-resistant structural material without delamination or deformation.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a unidirectional prepreg by impregnating a carbon fiber which has not been subjected to a surface treatment with a phenol resin. Are laminated in one direction or laminated in a cross direction, and the obtained laminate is molded and cured by heating and pressing,
The obtained molded body is heated up to 250 ° C. at a heating rate represented by the following formula (1), and a heating rate (° C./hr)<7 (mm × ° C./hr)/thickness (mm) Perform post-curing treatment by heating in air, carbonization treatment, densification treatment,
The present invention provides a method for producing a carbon fiber reinforced carbon composite material, which comprises performing a graphitization treatment as necessary.

The carbon fiber used in the present invention is mainly a fiber obtained by carbonizing a fiber such as rayon, polyacrylonitrile, pitch or the like by a known method, or a graphitized fiber obtained by heat-treating the fiber at a higher temperature. Can be In the present invention, “the surface treatment is not performed” means that a functional group such as oxygen and / or nitrogen is not actively introduced into the surface of the carbon fiber. Such a carbon fiber is a fiber which has been carbonized (processed into a high-strength fiber) or graphitized (processed into a high-elasticity fiber), and is not subjected to an oxidation process or the like. The reason for using carbon fibers that have not been subjected to surface treatment in the present invention is that, in the surface-treated carbon fibers, the bond between the carbon fibers and the carbon material as a matrix material becomes strong, and cracks in the carbon materials cut the carbon fibers when broken. This results in brittle fracture, resulting in low strength C / C.

On the other hand, most of ordinary carbon fibers are subjected to oxidation treatment after carbonization or graphitization to introduce functional groups such as oxygen and / or nitrogen on the fiber surface in order to be used for the production of CFRP. In such a case, in normal processing, O / C
The ratio is around 0.2. The surface O / C ratio of the carbon fiber not subjected to the surface treatment is usually 0.07 or less, which is extremely lower than the O / C ratio used for the CFRP, which is about 0.2. The surface O / C ratio of the carbon fiber not subjected to the surface treatment varies depending on the fiber treatment, for example, the production conditions such as the temperature such as carbonization and graphitization. The O / C of the untreated carbon fiber used in the present invention is desirably 0.055 or less. The reason is that if the O / C exceeds 0.055 value, high strength C / C cannot be obtained. The grounds for employing these O / C values will be described below.

The ratio of the strength of the used carbon fiber to the strength of C / C, that is, the strength contribution ratio is defined by the following equation (2).

[0012]

(Equation 1)

Here, _Vf is the fiber volume content in C / C. F is the reciprocal of the number of reinforcing directions, which is 1 for a one-way reinforcing material and ２ for a two-way reinforcing material. FIG. 1 shows the relationship between the strength contribution and the oxygen concentration ratio (O / C) of the carbon fiber surface for the C / C densified four times at the pitch. According to FIG. 1 and the formula (2), in order to obtain high strength C / C, carbon fiber having high strength and high strength contribution rate, that is,
It can be seen that fibers having a small O / C ratio are suitable. In the present invention, since the tensile strength of the high-strength C / C 2D material is generally required to be 50 kgf / mm ² or more, such a high-strength C / C material is obtained. For this purpose, the O / C ratio needs to be 0.055 or less. On the other hand, when the O / C ratio exceeds 0.055, the strength contribution ratio becomes low, and the strength of the carbon fiber is not sufficiently reflected in C / C, resulting in low strength C / C.

The reason why the O / C ratio is desirably 0.055 or less will be described below. For example, in FIG.
The C / C strength using a carbon fiber 2D material having a strength of 383 kgf / mm ² with /C=0.027 is expressed by the following equation. C / C strength = 383 × 0.6 (V _f ) × 1/2 (2D) × 0.49 (contribution ratio) = 56.3 kgf / mm ² (equivalent to Example 1) /C=0.05, strength 519kgf /
strength of C / C using 2D material of the carbon fibers of mm ² is represented by the following formula. C / C strength = 519 × 0.6 (V _f ) × １ ／ (2D) × 0.32 (contribution ratio) = 49.8 kgf / mm ² (equivalent to Example 2) /C=0.065, strength 500kgf
The strength of C / C using a 2D material of carbon fiber / mm ² is represented by the following equation. C / C strength = 500 × 0.6 (V _f ) × 1/2 (2D) × 0.17 (contribution ratio) = 25.5 kgf / mm ² (comparative product of Comparative Example 3) It is understood that the O / C ratio is appropriately equal to or less than 0.055.

In the present invention, the O / C ratio is measured by
It can be determined by X-ray photoelectron spectroscopy. In the present invention, the tensile strength of the carbon fiber which has not been surface-treated is at 280 kgf / mm ² or more and a tensile modulus is desirably 30 × 10 ³ kgf / mm ² or more. The reason is that high tensile strength C / C cannot be obtained unless the tensile strength and the tensile modulus are equal to or more than these values.

A carbon fiber which has not been subjected to a surface treatment is impregnated with a phenol resin as a molding resin to prepare a unidirectional prepreg. The carbon fiber may be sized with a resin of the same system as the molding resin in terms of handleability. Molding and curing step: The method of laminating prepregs in which carbon fibers are impregnated with a phenol resin in the present invention is lamination in one direction or cross lamination. 0 ° / 9 for cross lamination
0 °, 0 ° / 45 ° / 90 ° / -45 °, or 0 ° / 6
There is a method of laminating in a direction of 0 ° / 120 ° or the like.

After laminating the prepreg, a temperature at which the phenol resin is cured using a mold or the like, usually 140 ° C.
It is heated and pressurized to 170 ° C. to form and harden. In this step, it is preferable that the interlayer shear strength of the molded article after the molding and before the post-curing is 3 kgf / mm ² or less. Particularly preferably, it is preferable interlayer shear strength is 2 kgf / mm ² or less. The reason is that strong adhesion between the carbon fibers and the resin With high phenolic resin interlayer shear strength, in the subsequent carbonization step, damage carbon fiber by shrinkage of the resin, the high-strength C / C Is not obtained. On the other hand, when producing a normal CFRP, the interlaminar shear strength of the obtained laminated molded article is generally about 7 kgf / mm ² , and the interlaminar shear strength of the post-cured molded article of the present invention. It is characterized by a low shear strength.

In the present invention, the reason why a phenol resin is used as a raw material for forming a C / C matrix material is the wettability between the resin and the carbon fiber, and the interlayer shear strength after molding.
Is is correlated, the low wettability, because interlaminar shear strength after molding is low. The phenolic resin used should choose the wettability is particularly low resin with carbon fiber, the interlayer shear strength before curing post and after molding 3kgf
/ Mm ² or less is preferable. Also,
In the molding and curing step using a phenolic resin, the molded product is liable to cause delamination. Therefore, it is better to lower the curing temperature, preferably to about 120 to 150 ° C., and to slow down the cooling rate.

Post-curing step: The molded product formed and cured in the above-mentioned molding and curing step is taken out of a mold or the like and transferred to a post-curing step.
In the post-curing step, the temperature is raised to 170 ° C. to 250 ° C. in air, and the heating is performed. The rate of the temperature rise is represented by the following formula (1) according to the thickness of the molded product. , 250 ° C. in air.

Heating rate (° C./hr)<7 (mm × ° C./hr)/thickness (mm) Formula (1) When the temperature rising speed is faster than the value of the above formula (1), peeling occurs in a molded product. Otherwise, deformation occurs, and a good composite material cannot be obtained. The significance of performing the post-curing step is to completely react unreacted components in the molded product and to eliminate residual distortion during curing. Further, it is for preventing the delamination during the carbonization by partially oxidizing the resin. As described above, in order to prevent delamination and deformation of the product, it is necessary to heat the product slowly and for a long time as shown by the above formula (1).

Carbonization step: A step of carbonizing a phenol resin while raising the temperature to about 1000 ° C. in a nitrogen atmosphere. In the present invention, the rate of temperature rise during the carbonization treatment is expressed by the following equation (3), and the rate of temperature rise (° C./hr)<60 (mm)
× ° C./hr)/thickness (mm) It is desirable to be represented by the formula (3). The reason is that if the heating rate is higher than this value, delamination may occur in C / C.
Generally, the larger the product, the slower the temperature needs to be raised. The reason is that if the decomposition gas is not gradually released, a temperature gradient will occur in the product and delamination and / or deformation will occur.

Densification step (re-impregnation and re-carbonization step):
After the completion of the carbonization step, the matrix material in the composite material is carbonized and becomes C / C. However, in one carbonization, the carbon material as the matrix material is porous and has low mechanical properties. Therefore, usually, a liquid pitch or the like is impregnated (or pressurized) into the pores in the carbon material by vacuum, Recarbonize in a nitrogen atmosphere. Usually, the re-impregnation treatment and the re-carbonization treatment are repeated several times to perform the densification treatment.

Graphitization step (heat treatment step): This step may be carried out as needed. In order to improve physical properties, heat treatment is usually performed in an inert gas atmosphere at a temperature of 2000 ° C. or more. ADVANTAGE OF THE INVENTION According to the manufacturing method of this invention, C / C of high strength, especially high tensile strength can be easily manufactured, and the obtained C / C is used as a heat-resistant structural material for high temperature industrial use, aerospace use, etc. Can be widely applied to.

[0024]

EXAMPLES Example 1 A tensile strength of 383 kgf / mm ² and a tensile elasticity of 42.
0 × 10 ³ kgf / mm ² , surface O / C ratio is 0.02
7 carbon fiber bundles (4.7 μm ×
12,000 vesphite (registered trademark, manufactured by Toho Rayon Co., Ltd.) was impregnated with a resole phenolic resin to prepare a unidirectional prepreg. After the unidirectional prepregs were cross- laminated at 0 ° / 90 °, 50 kgf /
It was pressed and heated at ² mm to obtain a laminated molded plate having a thickness of 1.5 mm. Interlaminar shear strength of this laminated molded plate is 1.4k.
gf / mm ² . Further, the laminated molded plate is subjected to post-curing by heating to 250 ° C. at a heating rate of 3 ° C./hr in air, and then 1000 ° C. at 15 ° C./hr in nitrogen.
Until carbonization. 4 using the pitch
C / C was obtained by performing the densification treatment twice. This C / C has no peeling and deformation, and has a tensile strength of 56.5 kgf / mm.
^{In 2} , a good high strength was obtained. The results are shown in Table 1 below.
Shown in

[Example 2] Tensile strength is 519 kgf / m
m^Two, Tensile modulus is 44.2 × 10^Threekgf / mm^Two,
No oxidation treatment with O / C ratio of 0.05 on the surface
Carbon fiber bundle (4.7 μm x 12000, Vesfi
G: registered trademark, manufactured by Toho Rayon Co., Ltd.)
In the production method of Example 1, the heating rate during carbonization was 6 ° C.
/ Hr by the same manufacturing method as in Example 1 above.
C / C was produced. In the manufacturing process of the second embodiment,
Interlaminar shear strength of the layered sheet is 1.4 kgf / mm^TwoIn
The finally obtained C / C has no peeling or deformation, and
Tensile strength is 50.2kgf / mm ^TwoWith good high strength
Obtained. The results are shown in Table 1 below.

Example 3 The tensile strength was 519 kgf / mm ² and the tensile modulus was 44.
2 × 10 ³ kgf / mm ² , surface O / C ratio is 0.05
Carbon fiber bundle (4.7 μm ×
This carbon fiber bundle was impregnated with a resol-based phenolic resin using 12,000 vesphite (registered trademark, manufactured by Toho Rayon Co., Ltd.) to produce a unidirectional prepreg. After the unidirectional prepregs are cross- laminated at 0 ° / 90 °,
Pressurized and heated at 50 kgf / mm ² at a temperature of 3 ° C.
mm was obtained. The interlayer shear strength of this laminated molded plate was 1.4 kgf / mm ² . Further, the laminated molded plate is subjected to post-curing by heating in air at a heating rate of 0.8 ° C./hr to 250 ° C., and then 6 ° C./h in nitrogen.
The mixture was heated to 1000 ° C. for carbonization. Further, densification treatment was performed four times using the pitch to obtain C / C. This C / C has no peeling or deformation and has a tensile strength of 47.7.
At kgf / mm ² , good high strength was obtained. The results are shown in Table 1 below.

Example 4 The carbon fiber reinforced carbon obtained in Example 3 was further treated at 2200 ° C. for 30 minutes. The obtained C / C is free from peeling and deformation, and has a tensile strength of 63.9 k.
At gf / mm ² , good high strength was obtained. The results are shown in Table 1 below. The tensile strength of Example 3 was 47.7 k.
The tensile strength significantly increased as compared with gf / mm ² .

Comparative Example 1 A tensile strength was 519 kgf / mm ² and a tensile modulus was 44.
2 × 10 ³ kgf / mm ² , surface O / C ratio is 0.05
Carbon fiber bundle (4.7 μm × 1
One-way prepreg was prepared by impregnating 2,000 vesphite (registered trademark, manufactured by Toho Rayon Co., Ltd.) with a resole phenol resin. After the unidirectional prepregs are cross- laminated at 0 ° / 90 °, 50 kgf /
It was pressed and heated at ² mm to obtain a laminated molded plate having a thickness of 1.5 mm. Interlaminar shear strength of this laminated molded plate is 1.4k.
gf / mm ² . After the laminated molded plate was post-cured in air at a heating rate of 6 ° C./hr to 250 ° C., it was heated to 1000 ° C. at 30 ° C./hr in nitrogen to carbonize. Further, densification treatment was performed by repeating pitch impregnation-carbonization four times. In Comparative Example 1,
Since the condition of equation (1) is not satisfied, the obtained C / C
Can not measure tensile strength due to delamination
Was. The results are shown in Table 2 below.

Comparative Example 2 The same carbon fiber bundle as that of Comparative Example 1 (4.7 μm × 120
00, Vesfight: registered trademark, Toho Rayon Co., Ltd.
Using the same method as in Comparative Example 1 except that the thickness of the laminated plate is 3 mm and the rate of temperature rise during post-curing is 3 ° C. C / C was produced in the same manner as in Example 1. In Comparative Example 2,
Was not obtained because the condition of the above formula (1) was not satisfied.
For C / C, peeling occurs and the tensile strength can be measured.
Did not. The results are shown in Table 2 below.

Comparative Example 3 The tensile strength was 500 kgf / mm ² and the tensile modulus was 24.
0 × 10 ³ kgf / mm ² , surface O / C ratio is 0.06
Carbon fiber bundles (4.7 μm ×
12,000 vesphite (registered trademark, manufactured by Toho Rayon Co., Ltd.) was impregnated with a resole phenolic resin to prepare a unidirectional prepreg. This unidirectional prepreg is cross- laminated at 0 ° / 90 ° and then at 140 ° C., 50 kgf /
and pressure thermoforming at mm ^2, to obtain a molded plate having a thickness of 1.5 mm. The shear strength between layers of this molded plate is 3.0 kgf / m.
It was m ^2. Further, the formed plate is heated in air at a heating rate of 3 ° C.
After post-curing at 250 ° C./hr to 250 ° C., carbonization was performed by heating to 1000 ° C. at 6 ° C./hr in nitrogen.
Further, pitch impregnation-carbonization was repeated four times to perform a densification treatment. In Comparative Example 3, the oxygen concentration ratio (O /
C) is larger than 0.055 and 0.065.
In addition, the appearance of the obtained C / C is good, but the tensile strength is
24.8 kgf / mm ² , with extremely low strength
I could only get it. The results are shown in Table 2 below.

Comparative Example 4 A tensile strength was 593 kgf / mm ² and a tensile modulus was 29.
4 × 10 ³ kgf / mm ² , surface O / C ratio is 0.20
Carbon fiber bundle (4.7 μm × 1
One-way prepreg was prepared by impregnating 2,000 vesphite (registered trademark, manufactured by Toho Rayon Co., Ltd.) with a resole phenol resin. This unidirectional prepreg is cross- laminated at 0 ° / 90 ° and then at 140 ° C., 50 kgf /
and pressure thermoforming at mm ^2, to obtain a molded plate having a thickness of 1.5 mm. The interlayer shear strength of this molded plate is 6.2 kgf / m.
It was m ^2. Further, the formed plate is heated in air at a heating rate of 3 ° C.
After post-curing at 250 ° C./hr to 250 ° C., carbonization was performed by heating to 1000 ° C. at 6 ° C./hr in nitrogen.
Further, pitch impregnation-carbonization was repeated four times to perform a densification treatment.

In Comparative Example 4, since the oxygen concentration ratio (O / C) on the surface of the carbon fiber was larger than 0.055 and 0.20, the appearance of the obtained C / C was good. The tensile strength was 3.6 kgf / mm ² , and only a material having extremely low strength was obtained. The results are shown in Table 2 below.

[0033]

[Table 1]

[0034]

[Table 2]

According to Tables 1 and 2, the heating conditions in the post-curing step of the present invention are based on the data of Examples 3 and 4 and Comparative Examples 1 and 2 using the same carbon fiber. It is understood that the relationship of the heating rate in the above equation (1) must be satisfied. In addition, from the data of Examples 1 to 4 and Comparative Examples 3 and 4, the interlaminar shear strength after molding and before post-curing (interlaminar shearing of post-cured molded articles after post-curing and before carbonization) (Strength) is not more than 3 kgf / mm ² , the tensile strength of C / C is low.

[0036]

According to the present invention, a unidirectional prepreg is manufactured by impregnating a carbon fiber that has not been subjected to surface treatment with a phenol resin, and the unidirectional prepreg is laminated in one direction or laminated in a cross direction. Then, the obtained laminate is heated and pressurized to form and harden, and the obtained molded product is subjected to the following equation, and the temperature rising rate (° C./h)
r) <7 (mm × ° C./hr)/thickness (mm), post-curing treatment by heating in air to 250 ° C. at a heating rate, followed by carbonization treatment and densification treatment Therefore, high strength C / C used as a heat-resistant structural material can be manufactured by a simple method without delamination or deformation.

[Brief description of the drawings]

FIG. 1 shows the relationship between the strength contribution ratio of carbon fiber reinforced carbon (C / C) subjected to four densification treatments after carbonization and the O / C ratio of carbon fibers.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-161144 (JP, A) JP-A-5-33263 (JP, A) JP-A-5-17259 (JP, A) JP-A-6-161259 48829 (JP, A) JP-A-5-51257 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/52

Claims (5)

(57) [Claims] 1. A one-way prepreg is produced by impregnating a carbon fiber that has not been subjected to a surface treatment with a phenol resin. (2) The one-way prepreg is laminated in one direction or laminated in a cross direction. (3) The obtained laminate is molded and cured by heating and pressurizing. (4) The obtained molded product is obtained by the following equation: Temperature rising rate (° C./hr)<7 (mm × ° C./hr)/ A post-curing treatment is performed by heating in air to a temperature of 250 ° C. at a heating rate indicated by the following formula: (5) Next, carbonization treatment, densification treatment and, if necessary, graphitization treatment are performed. A method for producing a carbon fiber reinforced carbon composite material. 2. An oxygen concentration ratio O _1S / C _{1S on the} surface of the carbon fiber, which is determined by X-ray photoelectron spectroscopy of the carbon fiber not subjected to the surface treatment, is 0.055 or less.
A method for producing the carbon fiber-reinforced carbon composite material according to the above. Wherein the tensile strength of the carbon fiber in which the surface treatment has not been is at 280 kgf / mm ² or more, and carbon fiber reinforced tensile claim 1, wherein the elastic modulus is 30 × 10 ³ kgf / mm ² or more Manufacturing method of carbon composite material. 4. The heating rate during the carbonization treatment is represented by the following equation: heating rate (° C./hr)<60 (mm × ° C./hr)/thickness (mm). 2. The method for producing a carbon fiber reinforced carbon composite material according to claim 1, wherein the carbonization treatment is performed by heating. 5. The method for producing a carbon fiber reinforced carbon composite material according to claim 1, wherein the interlayer shear strength of the molded article after the molding and before the post-curing is 3 kgf / mm ² or less.