JP3484711B2 - Method for producing carbon fiber reinforced carbon composite - 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 short fiber reinforced carbon composite material which is excellent in strength, friction and sliding characteristics and is particularly suitable as a sliding material for high speed and high energy vehicles.

[0002]

2. Description of the Related Art Generally, carbon fiber reinforced carbon composite materials (hereinafter referred to as "C / C composite materials") are made of PAN-based, pitch-based or rayon-based long-short carbon fibers and phenol resin.
Manufactured by impregnating or mixing a thermosetting resin such as furan resin or a thermoplastic resin such as pitches or the like, and then heat-molding the mixture which is heat-molded, densified and graphitized. There is.

C / C composite materials are used as brakes for aircraft and vehicles because they are excellent in friction characteristics, mechanical characteristics, heat resistance, and lightweight. As a method of reinforcing the carbon fibers used in the C / C composite material, there is a method of using a two-dimensional woven fabric, a so-called woven fabric, or a method of using short fibers as in the present invention, but it is easy to obtain a uniform friction surface. A short fiber reinforced C / C composite material has been generally used as a friction material because it is inexpensive. However, with the recent increase in size and speed of aircraft and vehicles, higher heat capacity, higher thermal conductivity,
High strength has come to be required for C / C composite materials.
In particular, C / C composite materials for aircraft and high-speed vehicles have a large diameter (outer diameter ~
500 mmφ) and high rotation (up to 8000 rpm), high heat capacity and high thermal conductivity are required.

For example, outer diameter 500 mmφ, inner diameter 120 m
mφ, bulk density 1.8 kg / cm ³ and rotation speed 8000 rp
The tensile strength required when used under the condition of m can be obtained by the following formula as the stress (σ _t ) _{MAX in the} circumferential direction.

[0005]

[Equation 1] Where γ: bulk density (1.8 × 10 ⁻³ kg / cm ³ ) r ₂ : outer radius (25 cm) r ₁ : inner radius (6 cm) ω: angular velocity (8000/60) × 2π = 838 rad
/ S ν: Poisson's ratio (0.2) ∴ (σ _t ) _MAX = 654 kg / cm ² = 6.5 kg /
mm ² (σ _t ) _MAX = 806 kg / cm ² = 8.1 kg / mm
² (MAX value when r ₁ = r ₂ )

Therefore, at least 8.5 kg / mm ² or more, preferably 9 kg / mm ² or more, more preferably 10 k.
A tensile strength of g / mm ² or more is required. However, the strength of conventional short fiber reinforced C / C composites is insufficient, so in order to use woven cloth or to maintain friction characteristics, woven cloth is used for the central part and only C / C of the surface is short fiber reinforced type. Composite materials have been proposed as brake materials for large vehicles. However, the C / C composite material using a woven fabric is expensive and inferior in frictional characteristics, so that it does not satisfy the required characteristics as a brake material.

[0007]

Therefore, the present inventors have focused on the short fiber reinforced C / C composite material and have no such problems as described above, and have a C / C useful as a sliding material for high-speed vehicles. We have made an intensive study to provide

[0008]

[Means for Solving the Problems] In order to solve the above problems, the present inventors have diligently studied a C / C composite material using short fibers, and in particular, using pitch-based carbon fibers as carbon fibers, By impregnation with pitch for densification, graphitization at 2200 ° C or higher before further densification, and densification firing temperature of 2100 ° C or less provide high strength, high heat capacity, high thermal conductivity, and friction. C / with excellent characteristics
The present inventors have found that a C composite material can be manufactured and have reached the present invention.

That is, the gist of the present invention is to provide pitch-based short carbon fibers.
The fiber is disentangled and the fibers are oriented in a two-dimensional random manner.
Sheet, and the resin or
After impregnating with pitch and stacking and molding it, 220
Bake at 0 ° C or higher, then impregnate the fired product with pitch
Repeat the densification treatment by firing at 100 ° C or lower several times.
Reached the maximum temperature after the densification process during the final heat treatment
Achieving a tensile strength of 8.5 kg / mm
On ² or more, a bulk density 1.8 g / cm ³ or more, the thermal conductivity of 100W
/ M · K or more and C having a porosity of 10% or less
/ C composite material manufacturing method . The present invention will hereinafter be described in detail, as the carbon fiber used in the present invention, to use a pitch-based carbon fiber is a high capacity and high thermal conductivity. Further, if necessary, inorganic fibers such as SiC, Al ₂ O ₃ and carbon black, and inorganic substances may be added.

The carbon fiber used may be in the form of tows, strands, rovings, yarns or the like composed of a plurality of single fibers, and it is preferable to use short fibers obtained by cutting these. And, these short fibers are a bundle of a plurality of single fibers, 1000 to 800
It is formed from 0, preferably 2000 to 6000, and in the present invention, a short fiber bundle of 0.3 to 100 mm, preferably about 5 to 50 mm is used. The diameter and elastic modulus of the carbon fiber itself are not particularly limited within the range generally used as a composite material. When making a C / C composite material,
In order to improve the characteristics, it is important to disintegrate and disperse the short fiber bundle to prepare a two-dimensional random sheet, and to fill the matrix substance between them.

Therefore, in the present invention, the short fiber bundle is dry or wet defibrated to produce a two-dimensional random sheet. Dry defibration here, as a method for producing a sheet that is two-dimensionally randomly oriented, for example, mechanically carbon fiber monofilament commonly used in spinning, manufactured using a random webber to produce a sheet, or There is a method of defibrating with air to manufacture a sheet.

As a method for wet-defibration to produce a two-dimensional randomly oriented sheet, for example, a beater usually used for beating of pulp or the like or a pulper used for defibration is used in a solvent. After defibrating the short fibrous carbon fibers with, for example, supply them little by little to a mold having a screen at the bottom, or evenly disperse them by means such as stirring after defibration, make paper with a wire mesh etc., and dry to make There is a way to do it.
As a solvent for uniformly dispersing short fiber carbon fibers,
Preferably, water, acetone, alcohol having 1 to 5 carbon atoms, anthracene oil, or the like is used, but other organic solvent may be used. Further, it is preferable to disperse or dissolve the phenol resin, furan resin, pitch, or the like in the solvent because the carbon fibers are bonded to each other and the handling in the next step is easier. Furthermore, it is preferable to add a thickening agent such as sodium fibrin glycolate, polyvinyl alcohol, or hydroxycellulose to the solvent because the effect is further increased.

Although various weights (weight per 1 m ² ) of the sheet can be taken, 10-500 g / m ² is optimal in view of handleability, impregnation property and uniformity. The two-dimensional randomly oriented sheet thus obtained is impregnated with a phenol resin, furan resin, or a matrix such as petroleum-based or coal-based pitch and then dried. At this time, the matrix used is one that is dissolved in a solvent such as alcohol, acetone, or anthracene oil and adjusted to have an appropriate viscosity.

Then, the dried sheets are laminated, filled in a mold, and pressure-molded at a temperature of 100 to 500 ° C. to obtain Vf.
(Fiber volume content) = 5 to 65%, preferably 10 to 5
After obtaining a molded body of about 5%, 2200 at a temperature rising rate of 1 to 200 ° C./h in an inert gas atmosphere such as N ₂ gas.
℃, preferably to a temperature of 2400 ℃ or more and 2800 ℃ or less, the thermal conductivity is 100 W / mK or more, preferably 11
0 W / mK or higher, and tensile strength of 8.5 kg / m
m ² or more, preferably 9 kg / mm ² or more, more preferably 10 kg / mm ² or more.

Further, the fired C / C composite material is densified. Examples of the method include a method using CVD and / or a resin, but it is preferable to impregnate a pitch with which high heat capacity and high thermal conductivity are obtained. Then 2 more
A bulk density of 1.8 g / c is obtained by repeating the densification treatment of firing at 100 ° C. or lower a plurality of times to obtain a porosity of 10% or lower.
m ³ or more, preferably 1.9 g / cm ³ or more, which is a C / C composite material having a high heat capacity and excellent friction characteristics and oxidation resistance. As the pitch used at this time, various pitches can be used, but the softening point 70 to 1 is preferable.
50 ° C., more preferably 80 to 90 ° C., toluene insoluble matter 10 to 30%, more preferably 13 to 20%, substantially free of quinoline insoluble matter, fixed carbon 40% or more, more preferably 50% or more. The maximum temperature after the densification process is 2100 ° C to improve the friction characteristics.
It is necessary to be the following, but in order to improve the oxidation resistance, it is preferably 1600 ° C. or higher, and the maximum temperature after the densification treatment step needs to be the temperature at the final heat treatment. is there. The final heat treatment may be a densification step or may be separately provided after the densification step.

The short fiber reinforced type C / thus obtained
The C composite material has a tensile strength of 8.5 kg / mm ² or more, a bulk density of 1.8 or more, a thermal conductivity of 100 W / m · K or more, and a porosity of 1
It will be 0% or less, and it will fully satisfy the required characteristics as a brake for aircraft and high-speed vehicles. In measuring the characteristic values, a mercury porosimeter was used for porosity, a laser flash method was used for measuring thermal conductivity, and tensile strength was measured according to JIS K-6911.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist.

[0018]

The present invention will be described in more detail with reference to the following examples. Example Pitch-based carbon fiber having 4000 filaments is 30 mm
The long cut pieces were defibrated with a random webber to obtain a sheet having a basis weight of 200 g / m ² which was two-dimensionally randomly oriented. The sheet was impregnated with a phenol resin diluted with ethanol and then dried to prepare a sheet in which 200 g / m ² of carbon fiber was impregnated with 130 g / m ² of the phenol resin. This sheet was laminated in a mold and pressure-molded at 250 ° C. to obtain a molded body having Vf≈50%. After firing this molded body up to 2400 ° C, it is impregnated with pitch to 1000 ° C.
Bake until. Further, the same impregnation-firing operation was repeated a plurality of times, and then the final heat treatment was performed at 2000 ° C. to obtain a C / C composite material having a porosity of 8%. This C / C
The properties of the composite material are shown in Table 1.

Comparative Example 1 After being molded in the same manner as in Example 1 and baked at 2000 ° C., the same densification treatment as in Example 1 was carried out, and the porosity was 8%.
C / C composite material was obtained. The characteristics of this C / C composite material are shown in Table 1.
Shown in.

[0020]

[Table 1]

Comparative Example 2 100 parts by weight of pitch-based carbon fiber having 4000 filaments was impregnated with 65 parts by weight of a phenol resin and dried, and then 30
A so-called tow prepreg cut to a length of mm was produced. This is filled in a mold and pressure-molded at 250 ° C., and Vf
A molded body of ≈50% was obtained. The compact was densified in the same manner as in Example 1 to obtain a C / C composite material having a porosity of 8%. The characteristics of this C / C composite material are shown in Table 1.

[0022]

According to the present invention, it is possible to easily obtain a short fiber reinforced C / C composite material brake having excellent frictional properties, mechanical properties, thermal properties and oxidation resistance for aircraft and high speed vehicles.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-2-18357 (JP, A) JP-A-2-133373 (JP, A) JP-A-3-8769 (JP, A) JP-A-63- 265863 (JP, A) JP 61-53104 (JP, A) JP 3-140211 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C04B 35/83

Claims (3)

(57) [Claims] 1. A sheet in which fibers of a pitch-based short carbon fiber bundle are defibrated to produce fibers in a two-dimensional random orientation is prepared, and the sheet is impregnated with a resin or pitch serving as a matrix,
This is laminated and molded, then fired at 2200 ° C or higher,
Then, the fired product is impregnated with pitch and fired at 2100 ° C. or lower, and the densification treatment is repeated a plurality of times, and the maximum temperature after the densification treatment step is reached during the final heat treatment. / Mm ² or more, bulk density 1.
A method for producing a carbon fiber-reinforced carbon composite material having characteristics of 8 g / cm ³ or more, thermal conductivity of 100 W / m · K or more, and porosity of 10% or less. 2. The method according to claim 1, wherein a pitch having a softening point of 70 to 150 ° C., a toluene insoluble content of 10 to 30%, and a fixed carbon of 40% or more is used as the pitch to be impregnated in the fired product. 3. The method according to claim 1, wherein the densification treatment is performed at 1600 to 2100 ° C.