JP3383993B2 - Method for producing carbon fiber reinforced carbon composite material and sliding material using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a carbon fiber reinforced carbon composite material (hereinafter referred to as C / C composite material) whose friction coefficient can be controlled.
And a sliding member using the same.

[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 a long fiber or short fiber carbon fiber with a resin or pitch, press-molding the mixture, and then subjecting this to 600 to 2500 in an inert atmosphere.
It is manufactured by firing at ℃.

As a method of controlling the coefficient of friction, for example, as disclosed in Japanese Patent Publication No. 60-54270, a method of controlling by impregnating coal tar or coal tar and / or pitch with a furan resin, or a special method. Fairness 1
Relatively long fibers (4-6 cm) and short fibers (0.015-0.3 cm) as seen in -59459.
Method for randomly orienting, and Japanese Patent Publication No. 3-78
No. 498, a carbon fiber reinforced thermosetting resin composite material in which carbon fibers are oriented so as to cross a plane perpendicular to the axis of the cylinder is cut in a direction perpendicular to the axis of the cylinder, and fired.
A method of densifying and orienting carbon fibers at an angle with respect to a sliding surface is known.

[0004]

However, in the method described in Japanese Patent Publication No. 60-54270, only the matrix is focused on and the essential orientation of the carbon fibers is not mentioned, and the Japanese Patent Publication No. In the method described in Japanese Patent Laid-Open No. 1-59459, two different kinds of carbon fibers have to be mixed, and the specific effect of the carbon fiber length has not been shown. Further, in the method described in Japanese Patent Publication No. 3-78498, a disk in which carbon fibers are oriented so as to cross a surface perpendicular to the axis of the cylinder has to be sliced, resulting in a complicated process. Further, in the above method, from the viewpoint of controlling the friction coefficient, there is no specific description, and only a general tendency is shown. Therefore, the present invention provides a method for producing a C / C composite material that can control the friction coefficient more easily than the above-described methods known so far, and expands the use of the C / C composite material as a sliding material. The purpose is to do.

[0005]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the inventors have defibrated short fiber-like carbon fiber bundles to produce a sheet in which the fibers are two-dimensionally randomly oriented. When the defibration degree of the carbon fiber bundle is changed during production, various strengths and friction coefficients change. For example, in the case of a high defibration, the friction coefficient of the C / C composite material is low and low when the defibration coefficient is high. On the contrary, in the case of defibration, it was found that the friction coefficient was high, and the present invention was completed.

That is, in the present invention, a correlation equation between the degree of defibration of the carbon fiber bundle and the mechanical characteristics such as the friction coefficient should be obtained in advance, and the correlation equation should be used in accordance with the desired friction coefficient. A method capable of producing a C / C composite material having a desired friction coefficient and the like by determining the defibration degree of a carbon fiber bundle, and producing, molding and densifying a carbon fiber sheet having a defibration degree according to the defibration degree, and C / C manufactured by the manufacturing method
The present invention relates to a sliding material using a composite material.

The details of the present invention will be described below. The most important thing in the present invention is to previously obtain a correlation equation between the degree of defibration of the carbon fiber bundle and various mechanical strengths. The friction coefficient will be described below as an example. The correlation between the degree of defibration and the coefficient of friction is usually obtained by a linear equation. Specifically, it is expressed as in the following formula-1, and the coefficients A and B of the formula-1 are obtained, and the defibration degree = A−B × friction coefficient ... It also changes depending on the evaluation method of the degree of defibration, and also by changing the type of raw material such as carbon fiber or resin used or manufacturing conditions other than the degree of defibration. Therefore, in determining the coefficients A and B, the above factors are fixed to specific conditions, and a C / C composite material in which only the defibration degree is changed to at least 2 types, preferably 3 or more types is manufactured in advance, The friction coefficient must be measured and the correlation between the defibration degree and the friction coefficient must be investigated.

As the carbon fiber used in the present invention, any of pitch type, PAN type and rayon type carbon fibers can be used. When the sizing agent is attached to the carbon fiber bundle, the fiber bundle becomes difficult to be defibrated. Therefore, it is preferable to reduce the defibration degree, but not to increase the defibration degree. The form of carbon fiber is usually 2000
Tow, strand consisting of ~ 8000 single fiber bundle,
A roving, a yarn, or the like, which is a short fiber obtained by cutting these is used. In the present invention, it is usually 0.3 to 100 mm, preferably 5
A short fiber bundle of about 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, and inorganic substances may be added. The degree of defibration of the carbon fiber bundle is
Formula calculated in advance from the target friction coefficient −
Determine using 1. Therefore, the method for defibrating the carbon fiber bundle is preferably a method capable of controlling the defibration degree in a wide range.

As a specific defibration method, for example, a random webber, which is commonly used in the manufacture of nonwoven fabrics, is used, and a carbon fiber bundle is defibrated by a dry method by passing through a plurality of opposed cylinders having needle threads. There is a way. In this case, the degree of defibration can be increased by increasing the rotation speed of the cylinder. There is also a method in which a beater used for beating of pulp or the like, a pulper used for defibration treatment, and the like are used to wet-defibrate the carbon fiber bundle dispersed in the solvent, and then papermaking and drying. In this case, the degree of defibration can be increased by increasing the treatment time.

Next, the degree of defibration of the carbon fiber bundle in the carbon fiber sheet is evaluated to determine whether or not a sheet having the expected degree of defibration has been produced. Since the accuracy of the defibration degree can be further improved by immediately reflecting this result on the production conditions, it is important that the evaluation method of the defibration degree is simple and quick. The method for evaluating the degree of defibration is not particularly limited, but for example, focusing on the fact that the bulkiness of the sheet increases as the degree of defibration increases, a sheet having a certain area, a certain number of sheets, and a weight W (g) And the total thickness t (m
There is a method of measuring m) and obtaining the defibration index x defined in Formula-2. Disentanglement index x = t / W ... Formula-2

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 types of carbon fiber and resin and the ratio of both, it is necessary to always evaluate under the same conditions. As another example of the defibration degree evaluation, focusing on the fact that the gap between fibers decreases as the defibration degree increases, the light transmittance T (%) is measured using a sheet having a constant weight and a constant area, There is a method of obtaining the defibration index y defined in Expression-3. Disentanglement index y = 100-T ... Formula-3

Since the transmittance T decreases as the degree of defibration increases, the defibration index y increases. This method can be evaluated even after impregnating the sheet with resin, etc., but if the sheet weight (weight per unit area) is too large, light can be transmitted regardless of the defibration degree. There is a limit to the basis weight of the sheet that can be evaluated.

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 thus-obtained sheet having a desired defibration degree is impregnated with a phenol resin, a 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 V.
_f (fiber content) = 5 to 65%, preferably 10 to 55
% Molding is obtained. Then, at a temperature rising rate of 1 to 200 ° C./h in an inert gas atmosphere such as N ₂ gas, 800 to
The temperature is raised to 2500 ° C. and the mixture is fired to obtain a C / C composite agent.
It is preferable that the calcined C / C composite agent is appropriately subjected to a densification treatment by using, for example, the following three types of matrix alone or in combination to further improve the strength.

1) Densification treatment with resin or pitch The above C / C composite material is placed in a bath heated to a predetermined temperature,
After the inside of the tank is evacuated, resin or molten pitch is supplied, and the voids formed by firing are impregnated with the matrix. After that, firing is performed again at a temperature of 800 to 2500 ° C. By repeating the above steps, the target C / C composite material is densified. 2) Densification treatment by CVD The above C / C placed in the reactor by an induction heating coil or the like
The composite material is heated, steams of hydrocarbons or halogenated hydrocarbons are supplied into the reactor together with H ₂ gas, Ar gas or N ₂ gas, and voids are impregnated with the generated pyrolytic carbon,
Densify. Further, if necessary, graphitization treatment is performed to finally produce a C / C composite material having a desired friction coefficient.

Further, for other mechanical properties such as compressive strength, tensile strength, bending strength and impact strength, the correlation with the defibration degree is similarly obtained, and the defibration degree is controlled based on the correlation. It is possible to obtain a C / C composite material having desired properties. In general, the higher the defibration index of compressive strength, the higher the strength, and the lower the defibration index of tensile strength, bending strength, and impact strength, the higher the strength.

[0018]

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) The correlation between the defibration index x and the friction coefficient of the equation-2, which represents the defibration degree of the carbon fiber bundle, is A
= 1.77, B = 4.33 under the following manufacturing conditions, in order to manufacture a C / C composite material having a target friction coefficient of 0.26, the defibration index x is calculated from Formula-4, The target defibration index x = 0.64 was obtained. Target defibration index x = 1.77-4.33 × target friction coefficient ... Equation-4

Next, a pitch-based carbon fiber bundle, which is cut into 30 mm length and has 4000 filaments and which does not use a sizing agent, is defibrated with a random webber, and the defibration index x of the defibration index x of the carbon fiber bundle is 0. .64, basis weight is 200 g / m ²
A two-dimensional randomly oriented sheet of was obtained. Next, the sheet was impregnated with a phenol resin diluted with ethanol and then dried to prepare a sheet impregnated with 110 g / m ² of the phenol resin per unit area.

Twenty samples having a size of 95 × 95 mm were taken from the sheet in this state, and the weight W (g) thereof was measured. Next, these 20 sheets are stacked with their ends aligned,
The thickness t (mm) of 20 webs was measured with a load of 2.2 kg applied. Then, from W and t, the expression-2 is obtained.
The defibration index x defined in the above was calculated, and it was confirmed that a sheet having a defibration index x of 0.64 was obtained as intended.

This sheet was laminated in a mold and pressure-molded at 250 ° C. to obtain a molded body having V _f -50%. After firing this molded body to 2000 ° C. in a heating furnace, it is heated to 550 ° C. by a high frequency heating device, and dichloroethylene vapor is
Introducing nitrogen gas into the reactor as a carrier gas,
Densification treatment was performed to fill the pores with pyrolytic carbon.

Then, after impregnating the pitch, 1 in a heating furnace
It was baked at 000 ° C. Further, the same impregnation-calcination operation was repeated again. Thereafter, a treatment at 2000 ° C. was performed to obtain a C / C composite material of the present invention. Using this C / C composite material, the inertia 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 coefficient was measured. The friction coefficient of this C / C composite material is shown in Table-1.

(Example 2) In order to manufacture a C / C composite material having a target friction coefficient of 0.22, a target defibration index of 0.82 was obtained from the equation-4. Then, in the same manner as in Example 1, C
A / C composite material was obtained. Table of friction coefficient of this C / C composite
Shown in 1.

(Example 3) In order to manufacture a C / C composite material having a target friction coefficient of 0.165, a target defibration index of 1.06 was obtained from the equation-4. Then, a C / C composite material was obtained in the same manner as in Example 1. The friction coefficient of this C / C composite material is shown in Table-1.

[0025]

According to the present invention, it is possible to easily obtain a C / C composite material having mechanical properties, especially a friction coefficient, according to various uses and requirements.

[0026]

[Table 1]

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

Claims (4)

(57) [Claims] 1. A short fiber-shaped carbon fiber bundle composed of a plurality of single fibers is defibrated to prepare a sheet in which fibers are two-dimensionally randomly oriented, impregnated with a resin or pitch, and then laminated and molded, use fired, in manufacturing the carbon fiber reinforced carbon composite material is treated densified fineness case and this solution of the carbon fiber bundle
With the friction coefficient of carbon fiber reinforced carbon composites obtained by
Seki, and based on this correlation, calculate the desired coefficient of friction.
Used to obtain a carbon fiber-reinforced carbon composite material having the following features: <br /> A method characterized by controlling the degree of defibration of a carbon fiber bundle
Law. 2. The degree of defibration of carbon fiber bundles
Characterized by measuring the bulk height of the produced sheet
The method of claim 1, wherein 3. The degree of defibration of carbon fiber bundles
The method according to claim 1, wherein the light transmittance of the produced sheet is measured. 4. A method according to any one of claims 1 to 3.
Sliding member using granulated carbon fiber-reinforced carbon composite material.