JP3395261B2 - Method for producing carbon fiber reinforced carbon composite material, carbon fiber reinforced composite material, and sliding material using the same - 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 (hereinafter referred to as C / C composite material) having excellent friction characteristics and mechanical characteristics, and a sliding material using the same. is there.

[0002]

2. Description of the Related Art Conventionally, metal disc rotors have been used as sliding materials for brakes for aircraft and vehicles and clutches for vehicles. However, in recent years, C / C composite materials have been used for sliding materials such as disc rotors of brakes for the purpose of reducing the weight of vehicles and improving the characteristics such as heat resistance.

Generally, a C / C composite material is obtained by impregnating or mixing PAN-based, pitch-based or rayon-based long and short carbon fibers with a thermosetting resin such as phenol resin or furan resin or a thermoplastic resin such as pitch. It is manufactured by firing the molded product in a non-oxidizing atmosphere, and further densifying and graphitizing.

[0004]

The friction characteristics desired as a brake material are that the torque waveform is smooth and the friction coefficient is constant at any speed during sliding, that is, the torque waveform is rectangular (see FIG. 1). Is desired. However, in a general C / C composite material, a so-called fade phenomenon occurs in which the friction coefficient decreases when the temperature becomes high. Therefore, under high load conditions such as high energy level and high pressure, the temperature of the brake material increases during sliding, and the friction coefficient increases. However, the torque waveform becomes concave (see FIG. 2) due to the decrease in the friction coefficient, and a stable friction coefficient cannot be obtained. Further, a high level of friction coefficient is desired, but for that reason, there is a drawback that the wear amount increases when the hardness is lowered.

[0005]

Therefore, the inventors of the present invention have repeatedly conducted studies to solve the above-mentioned problems, and as a result, defibrate short fiber-like carbon fiber bundles to form a sheet in which fibers are two-dimensionally randomly oriented. When the degree of defibration of the carbon fiber bundle is changed in producing the, the coefficient of friction changes, and in the case of low defibration, the coefficient of friction of the C / C composite increases, and in the case of high defibration, it decreases to the contrary. I found that. Next, when the sizing agent is attached to the carbon fibers when the resin or pitch is impregnated, the adhesion with the carbon fibers is reduced. Therefore, by using short fibrous carbon fibers to which substantially no sizing agent is attached, and by performing a specific heat treatment, a carbon fiber reinforced carbon composite material having a high friction coefficient and low wear, and a stable torque curve The inventors have found that the sliding material used can be obtained and have reached the present invention. That is, an object of the present invention is to provide a C / C composite material having a high friction coefficient, low wear, and a stable torque curve, and a sliding material using the same, and an object of the present invention is to provide a sizing agent substantially. A short fibrous carbon fiber bundle composed of a plurality of single fibers that are not adhered is defibrated to prepare a sheet in which fibers are two-dimensionally randomly oriented, impregnated with a resin or pitch, laminated and molded, and fired, In a method for producing a carbon fiber-reinforced carbon composite material, which comprises repeating pitch impregnation and firing at a final heat treatment temperature or lower, the carbon fiber bundle remains as a bundle, and the final heat treatment temperature is 2400 ° C. or lower and the final porosity is 10 vol% or lower. It is easily achieved by a certain method for producing a carbon fiber-reinforced carbon composite material, and a carbon fiber-reinforced carbon composite material produced by this method and a sliding material using the same.

The details of the present invention will be described below. Known carbon fibers such as pitch-based, PAN-based or rayon-based carbon fibers can be used as the carbon fibers used in the present invention. However, when the sizing agent adheres to the carbon fiber bundle, the impregnation of the matrix raw material into the fiber deteriorates, and the adhesiveness between the fiber and the matrix decreases. Therefore, in the present invention, the carbon fiber to which the sizing agent is not substantially attached is used. When the sizing agent is attached in such a large amount as to affect the adhesiveness between the fiber and the matrix, the sizing agent is removed in advance by a method such as solvent washing or thermal decomposition treatment. The form of the carbon fiber is usually a tow, a strand, a roving, a yarn or the like, which is composed of a single fiber bundle of 2000 to 8000, and a short fiber form obtained by cutting these is used. In the present invention, usually 3 to 1
A short fiber bundle of about 00 mm, preferably about 5 to 50 mm is used.

Next, these carbon fiber bundles are defibrated to produce a two-dimensional random sheet. At that time, if necessary, S
Inorganic fibers such as iC, Al ₂ O ₃ and carbon black,
You may add an inorganic substance. The defibration degree of the carbon fiber bundle is set to a low defibration level such that the carbon fiber bundle partially remains as a bundle. As a specific defibration method, for example, there is a method in which a random webber, which is common in the production of nonwoven fabrics, is used, and a carbon fiber bundle is passed through a plurality of opposed cylinders with needle ridges to defibrate it in a dry manner. In this case, the degree of defibration can be changed by changing the rotation speed of the cylinder. Further, a beater used for beating treatment of pulp or the like, a pulper used for defibration treatment, or the like is used to wet-defibrate the carbon fiber bundle dispersed in the solvent, and then papermaking,
There is also a method of drying. In this case, the degree of defibration can be changed by changing the processing time.

Next, the degree of defibration of the carbon fiber bundle in the carbon fiber sheet is evaluated, and it is determined whether or not the expected low defibration sheet is produced. By immediately reflecting this result in the production conditions, the accuracy of the defibration degree can be further improved, so that the evaluation method of the defibration degree is simple and quick, and the carbon fiber sheet can be easily handled. It is desired to be able to evaluate in the state of a so-called prepreg impregnated with a resin or the like.

The method for evaluating the degree of defibration is not particularly limited, but for example, when the degree of defibration increases, the disentangled carbon fibers are more entangled with each other, and the bulkiness of the sheet increases, so that a certain area, A certain number of sheets having a weight W (g) are laminated, and a thickness t (mm) of the entire sheet when a certain load is applied to the sheets is measured to obtain a defibration index (X) defined in Formula-1. There is a way.

[0010]

## EQU1 ## Disentanglement index (X) = t / W ... Equation-1

Since the sheet thickness t increases as the degree of defibration increases, the defibration index (X) also increases. In the case of this method, the evaluation can be performed even after the sheet is impregnated with a resin or the like. However, since the value of the defibration index (X) changes depending on the type of carbon fiber, resin, etc., and the ratio of both, it is necessary to always evaluate under the same conditions. As another example of the evaluation method of the degree of defibration, focusing on the fact that the gap between the fibers decreases as the degree of defibration increases, the light transmittance T (%) is measured using a sheet having a constant weight and a constant area. Is measured
There is a method of obtaining the defibration index (Y) defined in Expression-2.

[0012]

[Equation 2] Disentanglement index (Y) = 100-T ... Formula-2

As the degree of defibration increases, the transmittance T decreases, so that the defibration index (Y) increases. In this method as well, the evaluation can be performed even after the sheet is impregnated with resin, but if the sheet weight (weight per unit area) is too large, light cannot be transmitted regardless of the defibration degree. Therefore, there is a limit to the weight of the sheet that can be evaluated.

The basis weight of the defibrated sheet may be various, but 10-500 g / m ² is optimal in view of handleability, impregnation property and uniformity. Phenol resin, furan resin,
Alternatively, it is impregnated with a matrix such as petroleum-based or coal-based pitch and then dried. At that time, the matrix is used by dissolving it in a solvent such as alcohol, acetone, or anthracene oil and adjusting the viscosity to an appropriate value.

Next, as a method for specifically evaluating that this dried sheet is a desired low-defibration sheet, for example, the basis weight of the sheet is 200 g / m ² , and the amount of impregnated phenol resin is 120 g / m ^2. 95 × 9 impregnation sheet
Twenty sheets cut into 5 mm were stacked, and the thickness t (mm) of the sheet when a load of 2.2 kg was applied was divided by the weight W (g) of the 20 sheets, and the defibration index defined by Equation-1 was obtained. When X is determined, if it is 1 or less, the carbon fiber bundle is the C / C material of the present invention that remains as a bundle, and preferably 0.3 to
The value is preferably 0.9, particularly preferably about 0.5 to 0.85.

The sheets thus obtained are laminated, filled in a mold, and pressure-molded at a temperature of 100 to 500 ° C. to obtain Vf.
(Fiber content) = 5-65%, preferably 10-55%
Obtain a molded body of a certain degree. Thereafter, it is fired in an inert gas atmosphere such as N ₂ gas at a temperature rising rate of 1 to 200 ° C./h at a temperature of 800 ° C. or more and 2800 ° C. or less, preferably a maximum temperature of densification or more and 2500 ° C. or less. , C / C composite material is obtained.

The above-mentioned fired C / C composite material has a large number of pores, and it cannot be practically used practically as it is. Therefore, the densification treatment of impregnating pitch and firing to reduce the pores is repeated a plurality of times. A preferable pitch is a softening point of 70 to 120 ° C., more preferably 8
0 to 90 ° C., toluene insoluble matter 10 to 30%, more preferably 13 to 20%, quinoline insoluble matter 1% or less, fixed carbon 4
It is 0% or more, more preferably 50% or more. In addition, in order to exert the effect of further densification, JP-A-1-
It is also possible to carry out a densification treatment for impregnating and carbonizing by the method described in Japanese Patent No. In order to improve wear resistance and heat capacity, the densification treatment is repeated until the final porosity becomes 10% or less. The porosity is measured by a conventional method, and specifically, a mercury porosimeter is usually used.
If the final maximum firing temperature of the densification treatment exceeds 2400 ° C., the crystallinity of the impregnated matrix develops and the shrinkage associated therewith reduces the adhesion between the fiber and the matrix. On the contrary, when the temperature is low, the oxidation resistance becomes poor. Therefore, the repeating firing temperature during the densification treatment is set to the final heat treatment temperature or lower, and the final heat treatment temperature is 2400 ° C. or lower, preferably the final heat treatment temperature is 1600 to 2200 ° C.
Is more preferably in the range of 1600 to 2000 ° C. 100 times to shorten the densification process
After repeating impregnation-firing at a treatment temperature of about 0 ° C., heat treatment is performed at a temperature near the final heat treatment temperature and below the final heat treatment temperature, and further, after performing a densification treatment that repeats impregnation-firing at a treatment temperature of about 1000 ° C., The final heat treatment can be performed at 2400 ° C or lower.

In this way, a high coefficient of friction and low wear,
Further, a C / C composite material having a stable torque curve can be manufactured. If this is used as a sliding material, C with excellent friction characteristics
/ C Sliding material.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. (Example 1) 40 filaments cut into 30 mm length
Pitch-based carbon fiber bundle of No. 00, which does not use a sizing agent, is defibrated with a random webber, and the basis weight is 200 g / m ² of 2.
A sheet was randomly oriented. Further, the sheet was impregnated with a phenol resin diluted with ethanol and then dried to prepare a sheet impregnated with 120 g / m ² of the phenol resin.

From this state sheet, 20 samples having a size of 95 × 95 mm were taken, and the weight W (g) thereof was measured. Next, these 20 sheets are stacked with their ends aligned to be 2.2k.
Thickness of 20 webs under load of g (mm)
Was measured. The defibration index X defined by the formula-1 was calculated from the W and t, and it was confirmed that a sheet having a defibration index X of 0.80 was obtained as intended. This sheet is
It was confirmed with the naked eye that the carbon fiber bundle remained as a bundle.

The obtained sheet is stacked and filled in a mold, and 25
Pressure molding was performed at 0 ° C. to obtain a molded body having Vf = about 50%.
This molded product was fired in an inert atmosphere at 2000 ° C. in a heating furnace, impregnated with pitch, and then heated in an inert atmosphere in a heating furnace.
It was baked up to 000 ° C. Further, after repeating the same impregnation-firing operation, a treatment at 2000 ° C. was performed, and then a pitch impregnation-firing operation was repeated, and finally, a treatment at 2000 ° C. was performed to obtain C / C of the present invention having a porosity of 8%. A C composite material was obtained.
Using this C / C composite material, the inertial friction test was repeated 100 times under the conditions of a rotation speed of 5000 rpm and a surface pressure of 12 kg / cm ² , and the friction characteristics were measured. These results are shown in Table-1.
Shown in.

(Embodiment 2) Sheets equivalent to those in Embodiment 1 are stacked and filled in a mold and pressure-molded at 250 ° C., Vf = about 5
A 0% compact was obtained. This molded product was fired in an inert atmosphere to 2400 ° C., impregnated with pitch, and fired in an inert atmosphere to 1000 ° C. in a heating furnace. Furthermore, after repeating the same impregnation-firing operation, a treatment at 2000 ° C. is performed, and then the pitch impregnation-firing operation is repeated,
Finally, it was treated at 2000 ° C. to obtain a C / C composite material of the present invention having a porosity of 8%. Using this C / C composite material, the inertial friction test was repeated 100 times under the conditions of a rotation speed of 5000 rpm and a surface pressure of 12 kg / cm ² , and the friction characteristics were measured.
The results are shown in Table-1.

(Comparative Example 1) Sheets equivalent to those of Example 1 were stacked and filled in a mold and pressure-molded at 250 ° C., Vf = about 5
A 0% compact was obtained. After firing this formed body in an inert atmosphere to 2000 ° C. in a heating furnace, it is heated to 550 ° C. by a high-frequency heating device, and dichloroethylene vapor is introduced into the reactor by using nitrogen gas as a carrier gas to produce pyrolytic carbon. A densification treatment was performed to fill the pores. Then
It was impregnated with pitch and baked in an inert atmosphere to 1000 ° C. in a heating furnace. Further, after repeating the same impregnation-firing operation, a treatment at 2000 ° C. was performed, and then the pitch impregnation-firing operation was repeated, and finally, a treatment at 2000 ° C. was performed to obtain a C / C composite material having a porosity of 9%. Got Using this C / C composite material, the rotation speed is 5000 rpm and the surface pressure is 12 kg / cm ^2.
The inertial friction test was repeated 100 times under the conditions of, and the friction characteristics were measured. The results are shown in Table-1.

(Comparative Example 2) A pitch-based carbon fiber bundle having a filament number of 4000 and cut into a length of 30 mm, which does not use a sizing agent, is disentangled with a random webber, and a basis weight = 200.
A two-dimensional randomly oriented sheet of g / m ² was produced. Further, the sheet was impregnated with a phenol resin diluted with ethanol and then dried to prepare a sheet impregnated with 120 g / m ² of the phenol resin.

From this state sheet, 20 samples having a size of 95 × 95 mm were taken, and the weight W (g) thereof was measured. Next, these 20 sheets are stacked with their ends aligned to be 2.2k.
Thickness of 20 webs under load of g (mm)
Was measured. The defibration index X defined by the formula-1 was calculated from the W and t, and it was confirmed that a sheet having a defibration index X of 1.1 was obtained. No carbon fiber bundle remained as a bundle was found in this sheet.

The obtained sheet was molded, fired and densified in the same manner as in Example 1 to obtain a C / C composite material having a porosity of 8%. With this C / C composite material, the rotation speed is 5000
The inertial friction test was repeated 100 times under the conditions of rpm and surface pressure of 12 kg / cm ² to measure the friction characteristics. The results are shown in Table-1.

(Comparative Example 3) A pitch-based carbon fiber bundle having 4000 filaments cut to a length of 30 mm and having a 1% polyvinyl alcohol sizing agent attached thereto was defibrated with a random webber to give a two-dimensional random weight of 200 g / m ^2. A sheet oriented to was prepared. Further, the sheet was impregnated with a phenol resin diluted with ethanol and then dried to 120 g / m 2.
A sheet impregnated with the phenol resin of ² was prepared.

From this state sheet, 20 samples having a size of 95 × 95 mm were taken, and the weight W (g) thereof was measured. Next, these 20 sheets are stacked with their ends aligned to be 2.2k.
Thickness of 20 webs under load of g (mm)
Was measured. The defibration index X defined by the formula-1 was calculated from the W and t, and it was confirmed that a sheet having a defibration index X of 0.80 was obtained.

The obtained sheet was molded, fired and densified in the same manner as in Example 1 to obtain a C / C composite material having a porosity of 8%. With this C / C composite material, the rotation speed is 5000
The inertial friction test was repeated 100 times under the conditions of rpm and surface pressure of 12 kg / cm ² to measure the friction characteristics. The results are shown in Table-1.

[0030]

[Table 1]

[0031]

According to the present invention, a high coefficient of friction and low wear,
Further, a C / C composite material having a stable torque curve can be easily obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view of a torque waveform preferable as a sliding material.

FIG. 2 is an explanatory diagram of a torque waveform that is not preferable as a sliding material.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-114835 (JP, A) JP-A-5-345671 (JP, A) JP-A-5-345668 (JP, A) JP-A-3- 140211 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C04B 35/83

Claims (3)

(57) [Claims] 1. A sheet of carbon fibers in the form of short fibers, which is composed of a plurality of single fibers to which a sizing agent is not substantially attached, is defibrated to prepare a sheet in which the fibers are two-dimensionally randomly oriented, and a resin or a pitch is formed. After impregnation, lamination and molding, firing, pitch impregnation, and a method for producing a carbon fiber-reinforced carbon composite material that repeats firing at a final heat treatment temperature or less, at least a part of the carbon fiber bundle remains as a bundle. And the final heat treatment temperature is 24
A method for producing a carbon fiber-reinforced carbon composite material, which has a temperature of 00 ° C. or less and a final porosity of the obtained composite material of 10 vol% or less. 2. A carbon fiber reinforced carbon composite material produced by the production method according to claim 1. 3. A sliding material using the carbon fiber reinforced carbon composite material according to claim 2.