JP3339075B2 - Carbon fiber reinforced carbon composite, method for producing the same, 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 carbon fiber reinforced carbon composite material (hereinafter referred to as "C / C composite material") capable of controlling friction and mechanical properties, a method for producing the same, and a sliding material using the same. It is.

[0002]

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

In general, a C / C composite material is prepared by impregnating or mixing a PAN-based, pitch-based or rayon-based carbon fiber with a thermosetting resin such as phenolic resin or furan resin or a thermoplastic resin such as pitches. It is manufactured by firing in a non-oxidizing atmosphere, followed by densification and graphitization. As a method of controlling the coefficient of friction, for example, as disclosed in Japanese Patent Publication No. 60-54270, a method of impregnating coal tar or coal tar and / or pitch with a furan resin and controlling the friction coefficient is disclosed. As disclosed in JP-A-595959, a method of randomly orienting relatively long fibers (4 to 6 cm) and short fibers (0.015 to 0.3 cm), and further as disclosed in JP-B-3-78498. The carbon fiber reinforced thermosetting resin composite material, in which the carbon fibers are oriented to cross the plane perpendicular to the axis of the cylinder, is cut in the direction perpendicular to the axis of the cylinder, fired, densified, and A method of orienting carbon fibers at an angle is known.

As a method for controlling the mechanical strength, for example, as disclosed in Japanese Patent Application Laid-Open No. Sho 62-266239, a short fiber reinforced C / C composite material having excellent friction characteristics only in the sliding portion on the surface is used. Used, short fiber reinforced C / C in the center
In order to supplement the mechanical strength of the composite material, a method is known in which a two-dimensional fabric, a so-called woven fabric, is used as a C / C composite material using a reinforcing material.
Further, as seen in EP 0 499 916 A1, the sliding layer on the surface has a “fine” structure composed of segments in which short fibrous carbon fibers are randomly distributed and having an average pore diameter of 50 μm or less. It is known to have a "rough" structure composed of a short fiber carbon fiber mesh and having an average pore diameter of 100 μm or more.

[0005]

However, in the method disclosed in Japanese Patent Publication No. 60-54270, the essential carbon fiber orientation is not described by focusing only on the matrix. In the method described in JP-A-59459, two types of different carbon fibers had to be mixed, and no specific effect of the carbon fiber length was 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 plane perpendicular to the axis of the cylinder has to be cut into a ring, and the process is complicated. . Further, in the above-mentioned method, there is no specific description from the viewpoint of controlling the friction coefficient, but merely shows a general tendency. on the other hand,
The method described in Japanese Patent Application Laid-Open No. 62-266239 concerning control of mechanical strength is expensive because the woven fabric is used as a central structural material, and is simply reinforced. Had not been. Further, the method described in EP 0 499 916 A1 mentions only the points of wear and reinforcement of strength. Therefore, there is no mention in these publications regarding control of friction coefficient and strength balance design.

Accordingly, the present invention provides a C / C composite material which is simpler than the above-mentioned known methods and can control the coefficient of friction and mechanical properties, and a method for producing the same.
The purpose is to expand the use of the composite material as a sliding material.

[0007]

Means for Solving the Problems As a result of repetition of studies to solve the above-mentioned problems, the present inventors have laid open a sheet in which short fiber carbon fiber bundles are defibrated and fibers are two-dimensionally randomly oriented. In the production, when the degree of defibration of the carbon fiber bundle is changed, the mechanical properties and the coefficient of friction change. For example, if the coefficient of friction is high, the coefficient of friction of the C / C composite material is low in the case of high fibrillation, and In the case of defibration, on the other hand, it is found that the higher the defibration, the higher the mechanical strength, the higher the defibrillation, and the higher the strength, the higher the tensile strength, bending strength and impact strength. Thus, the present invention has been completed.

That is, in the present invention, a correlation equation between the degree of defibration of the carbon fiber bundle and the friction coefficient and the mechanical properties is obtained in advance, and the carbon fiber bundle should be produced using the correlation equation according to the desired friction coefficient and the mechanical properties. The degree of defibration of the carbon fiber bundle is determined, and a carbon fiber sheet having a degree of defibration in accordance therewith is produced. Further, by laminating, forming and densifying so as to obtain desired friction coefficient and mechanical properties, C having desired friction coefficient and mechanical properties is obtained.
The present invention relates to a method for producing a C / C composite material and a sliding material using the C / C composite material produced by the production method.

Hereinafter, the present invention will be described in detail. The most important thing in the present invention is to obtain in advance a correlation equation between the degree of defibration of the carbon fiber bundle and various mechanical strengths. Usually, the correlation between the degree of defibration, the coefficient of friction, and various mechanical strengths is determined by a linear equation. Hereinafter, the friction coefficient will be described as an example. Specifically, the correlation between the degree of defibration and the coefficient of friction is expressed by the following formula-1.

[0010]

## EQU1 ## Degree of defibration = A−B × Friction coefficient Expression-1 At this time, the coefficients A and B in Expression-1 are obtained.
The values of the coefficients A and B change depending on the method of evaluating the degree of defibration, and also change by changing the type of raw material such as carbon fiber or resin to be used or manufacturing conditions other than the degree of defibration. Therefore, when obtaining the coefficients A and B,
The above factors are fixed to specific conditions, and only the degree of defibration is at least 2
A C / C composite material having various kinds, preferably three or more kinds, must be manufactured in advance, and its friction coefficient must be measured to examine the correlation between the degree of defibration and the friction coefficient.

As the carbon fibers used in the present invention, any of pitch-based, PAN-based or rayon-based carbon fibers can be used. When the sizing agent is attached to the carbon fiber bundle, the fiber bundle is difficult to be defibrated. Therefore, it is preferable to reduce the defibration degree, but it is not preferable to increase the defibration degree. The form of carbon fiber is usually 2000
Tow, strand, consisting of a bundle of ~ 8000 short fibers,
Roving, yarn, and the like, and short-fibers obtained by cutting these are used. In the present invention, it is usually 0.3 to 100 mm, preferably 5 to 100 mm.
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
inorganic fibers such as iC, Al ₂ O ₃ , carbon black,
An inorganic substance or the like may be added. The degree of defibration of the carbon fiber bundle is calculated from the target friction coefficient using the formula -1 obtained in advance.
Is determined using Therefore, as a method of defibrating the carbon fiber bundle, a method capable of controlling the degree of defibration in a wide range is desirable.

As a specific defibration method, for example, a method of using a random webber, which is common in the production of nonwoven fabrics, and passing the carbon fiber bundle through a plurality of cylinders having needle ridges to defibrate in a dry manner. There is. In this case, the degree of defibration can be changed by changing the rotation speed or the like of the cylinder. In addition, using beater used for beating processing of pulp and the like, pulper used for defibration processing,
After fibrillating the carbon fiber bundle dispersed in the solvent by wet method,
There are also methods of papermaking and 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 a sheet having the expected degree of defibration is produced. By immediately reflecting this result in the manufacturing conditions, the accuracy of the degree of defibration can be further improved.Therefore, the method for evaluating the degree of defibration is simple and quick, and furthermore, the carbon fiber sheet is used for easy handling. It is desired that evaluation can be performed in a so-called prepreg state impregnated with a resin or the like.

The method for evaluating the degree of defibration is not particularly limited. For example, paying attention to the fact that as the degree of defibration increases, the defibrated carbon fibers become more entangled and the bulk of the sheet increases. A constant number of sheets having a weight of W (g) are stacked, and the thickness t (mm) of the entire sheet when a constant load is applied thereto is measured, and the defibration index (X) defined in Expression-2 is obtained. There is a way.

[0016]

## EQU2 ## The degree of defibration (X) = t / W (Equation 2) Since the sheet thickness t increases as the degree of defibration increases, the degree of defibration (X) also increases. In this case,
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 the carbon fiber, the resin and the like, and the ratio between the two, the evaluation must always be performed under the same condition.

As another example of a method for evaluating the degree of defibration, attention is paid to the fact that as the degree of defibration increases, the gap between the fibers decreases, and the light transmittance T using a sheet having a constant weight and a constant area is used. (%) Is measured to determine the defibration index (Y) defined in Expression-3.

[0018]

(3) Fibrillation index (Y) = 100−T (Equation 3) Since the transmittance T decreases as the degree of fibrillation increases, the fibrillation index (Y) 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, if the basis weight (weight per unit area) of the sheet is too large, light cannot be transmitted regardless of the degree of defibration. Therefore, there is a limit on the basis weight of the sheet that can be evaluated.

The basis weight of the defibrated sheet can be various, but considering the handling, impregnation and uniformity, the optimal weight is 10 to 500 g / m ² . The thus obtained sheet having a desired degree of defibration is impregnated with a phenolic resin, a furan resin, or a matrix such as a petroleum-based or coal-based pitch and then dried. At that time, the matrix used is dissolved in a solvent such as alcohol, acetone, anthracene oil or the like and adjusted to an appropriate viscosity.

Next, the dried sheet is subjected to a desired friction.
It is designed and laminated so that characteristics and mechanical characteristics can be obtained. An example
For example, try to lower the coefficient of friction and increase the impact strength
In such a case, first, a desired friction coefficient can be obtained by sliding the surface sliding portion.
The degree of defibration is determined according to the correlation equation. In this case, low
A relatively high degree of defibration is required to obtain a high coefficient of friction. An example
For example, the basis weight of the sheet is 200 g / m^Two, Phenolic resin
120g / m impregnation amount ^Two95 × 95mm
20 pieces are cut into pieces and a 2.2kg load is applied.
The thickness t (mm) of the sheet at the time of the
(G) to determine the defibration index X defined by the formula-2.
In this case, a value of about 0.9 to 1.2 is preferable. Next
The thickness of each of the surface and inner layers, which are the moving parts
The correlation equation so that the required impact strength is obtained.
To determine the degree of defibration of the inner layer. In this case, defibration of the inner layer
The degree is relatively low to obtain high impact strength.
Become. For example, as the defibration index X obtained by the above method,
Is preferably set to a value of about 0.5 to 0.85.

Further, in order to increase the compressive strength by increasing the friction coefficient, first, the degree of defibration is determined according to a correlation equation so that a desired friction coefficient can be obtained for the sliding portion of the surface layer. In this case, the degree of defibration is relatively low to obtain a high coefficient of friction. For example, the defibration index X obtained by the above method is preferably set to a value of about 0.5 to 0.85. Next, the degree of defibration of the inner layer is determined according to a correlation equation so as to obtain a required compressive strength, taking into account the thickness of the sliding portion of the surface layer and the thickness of the inner layer. In this case, the degree of defibration of the inner layer is relatively high to obtain high compressive strength. For example, the defibration degree index X obtained by the above method is preferably a value of about 0.9 to 1.2.

The sheets designed in this manner are laminated, filled in a mold, pressed at a temperature of 100 to 500 ° C., and Vf
(Fiber content) = 5-65%, preferably 10-55%
To obtain a molded product of the order. Thereafter N ₂ heating rate of 1 to 200 ° C. / h in an inert gas atmosphere such as gas 800-25
The temperature is raised to 00 ° C. and calcined to obtain a C / C composite material. The fired C / C composite material is preferably subjected to a densification treatment by using, for example, the following three types of matrices 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 tank heated to a predetermined temperature,
After the inside of the tank is evacuated, a resin or a molten pitch is supplied, and the voids generated by firing are impregnated with the matrix. Thereafter, firing is performed again at a temperature of 800 to 2500 ° C. By repeating the above steps, the desired C / C composite is densified.

(2) Densification treatment by CVD The C / C composite material placed in the reactor is heated by an induction heating coil or the like, and the vapor of hydrocarbons or halogenated hydrocarbons is converted into H ₂ gas and Ar gas. Alternatively, the gas is supplied into the reactor together with a carrier gas such as N ₂ gas, and the generated pyrolytic carbon impregnates and densifies the voids. Further, if necessary, a graphitization treatment is performed to finally produce a C / C composite material having a desired coefficient of friction and mechanical properties.

In this manner, a C / C composite having desired friction coefficient and mechanical properties can be easily produced.

[0026]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the invention. (Example 1) In the production of a sample having a thickness of 10 mm, the thickness of the sliding portion of the surface layer was set to 2.5 mm. The thickness of the inner layer, which is a reinforcing part against impact or the like, was 5 mm.
The characteristics of this sample were designed as follows. Friction coefficient = 0.16 Impact strength = 4 (kg · cm / cm) Then, the correlation between the defibration degree index X in Equation-2 representing the degree of defibration of the carbon fiber bundle and the friction coefficient is represented by A in Equation-1. = 1.81 and B = 4.67, and the correlation between the defibration index X and the impact strength is represented by A = 1.35 in Expression-1.
Under the following production conditions where B = 0.127, first, a defibration index X for producing a C / C composite material having a friction coefficient of the sliding portion = 0.16 is calculated from Expression-4, and the target defibration degree is calculated. An index = 1.06 was obtained.

[0027]

## EQU4 ## Target defibration index (X) = 1.81-4.67 ×
Target friction coefficient ... Equation-4 Next, the impact strength at the time of manufacturing with the target defibration index = 1.06 was determined from Equation-5, and the expected impact strength = 2.3 was obtained.

[0028]

## EQU5 ## Target defibration index (X) = 1.35-0.127
× target impact strength formula-5 So, impact strength of the sample = 4 (kgcm / cm)
When the required impact strength (Z) of the inner layer to obtain the following formula is obtained from Expression-6, Z = 5.7.

[0029]

## EQU6 ## Impact strength of sample: 4 = 2.3 × (2.5 ×
2/10) + Z × 5/10 Expression -6 Therefore, the impact strength of the inner layer = 5.7 (kg · cm / cm)
The defibrillation index X for calculating -5 was calculated by Expression-5, and the target defibration index was obtained as 0.63.

Next, a pitch-based carbon fiber bundle cut into a length of 30 mm and not using a sizing agent of 4000 filaments is defibrated with a random webber, and the defibration degree of the carbon fiber bundle is determined to be 0. Weight per unit at 63 and 1.06 = 20
A two-dimensional randomly oriented sheet of 0 g / m ² was prepared. Further, 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.

[0031] Twenty samples of 95 x 95 mm in size were taken from the state sheet, and the weight W (g) was measured. Next, these 20 sheets were stacked with their edges aligned, and 2.2 k
thickness of 20 webs with a load of g applied (t (mm))
Was measured. From this W and t, the defibration index X defined by the formula-2 is calculated, and the defibration index X is 0.63 as desired,
And 1.06 were obtained.

Next, the degree of defibration degree serving as a sliding portion = 1.06
Are laminated in such a manner that a sheet having a final shape and a thickness of 2.5 mm can be obtained, and a fibrillation index = 0.
63 sheets are laminated in such a manner that a 5 mm thickness can be obtained in the final shape, and a fibrillation degree index serving as a sliding portion is further formed thereon =
1.06 sheets were laminated to obtain a final shape having a thickness of 2.5 mm. The laminated sheet is filled in a mold, and 2
Pressure molding was performed at 50 ° C. to obtain a molded body with Vf = 〜50%. After firing this molded body in an inert atmosphere to 2000 ° C. in a heating furnace, it is heated to 550 ° C. by a high-frequency heating device, dichloroethylene vapor is introduced into the reactor as a nitrogen gas carrier gas, and pores are formed by pyrolytic carbon. Densification treatment for filling was performed.

Next, after the pitch was impregnated, it was baked in an inert atmosphere to 1000 ° C. in a heating furnace. After repeating the same operation of impregnation and firing, a treatment at 2000 ° C. was performed to obtain a C / C composite material of the present invention having a porosity of 12%. Using this C / C composite material, an 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 to measure a friction coefficient.

Further, the impact strength of the C / C composite was measured. Table 1 shows these results. (Comparative Example 1) The defibration index X produced in Example 1 was 1.0.
6 using only the sheet No. 6 in the same manner as in Example 1.
/ C composite material was obtained. Table 1 shows the measurement results of the friction coefficient and the impact strength.

(Comparative Example 2) A C / C composite material was obtained in the same manner as in Example 1 using only the sheet having a defibration index X of 0.63 produced in Example 1. Table 1 shows the measurement results of the impact strength.

[0036]

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

[0037]

[Table 1]

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-224327 (JP, A) JP-A-3-140211 (JP, A) JP-A-63-210065 (JP, A) JP-A-5-205 345671 (JP, A) JP-A-5-345667 (JP, A) JP-A-63-293051 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29B 15/08 C04B 35 / 83

Claims (6)

(57) [Claims] 1. A number of defibrating carbon fiber bundles of short fibers and fibers made of single fibers to prepare a plurality of oriented sheet in a two-dimensional random, this then impregnated with resin or pitch <br / > Laminating and molding , firing and densifying the carbon fiber reinforced carbon composite material to produce a carbon fiber reinforced carbon composite material, the carbon fiber bundle of the sheet forming the inner layer portion and the sheet forming the surface layer portion of the composite material method of producing a carbon fiber-reinforced carbon composite material which is characterized that you vary the fineness case. 2. A short fibrous carbon fiber comprising a large number of single fibers.
A sheet in which fibers are oriented randomly and two-dimensionally after fibrillation
After making several sheets, impregnating them with resin or pitch,
Laminated and molded, fired and densified to produce carbon fiber
Forming the inner layer when producing reinforced carbon composites
Sheet with a lower degree of defibration of the carbon fiber bundle than the sheet
Carbon fiber reinforced carbon characterized by forming a surface layer
Manufacturing method of composite material. 3. A short-fiber carbon fiber comprising a large number of single fibers.
A sheet in which fibers are oriented randomly and two-dimensionally after fibrillation
After making several sheets, impregnating them with resin or pitch,
Laminated and molded, fired and densified to produce carbon fiber
In producing a reinforced carbon composite, the production of the composite
The degree of defibration of carbon fiber used for molding and this carbon fiber
Determine the relationship with the coefficient of friction of the composite
Defibrated to meet the coefficient of friction required for the composite material
Carbon fiber sheet and higher degree of defibration
Sheet made of carbon fiber, and the former
In addition, it is characterized by laminating so that the latter is located in the inner layer part.
Of producing a carbon fiber reinforced carbon composite material. 4. A fibrillation index of a sheet forming an inner layer portion.
Is 0.9 to 1.2, and of the sheet forming the surface layer portion is
Characterized by a defibration index of 0.5 to 0.85
A method for producing the carbon fiber reinforced carbon composite material according to claim 2 or 3.
Law. However, the fibrillation index is calculated as follows. Fibrillation index = t / w (Where t is a defibrated carbon fiber having a basis weight of 200 g / m
^Two Sheet of phenolic resin
120g / m ^Two 9 impregnated so that 5x9
Cut to 5mm and stack 20 sheets, load 2.2kg on this
Is the thickness (mm) of the sheet when multiplied by
(The weight (g) of the 20 stacked sheets at that time) 5. A carbon fiber reinforced carbon composite produced by the production method according to claim 1. 6. A sliding material using the carbon fiber reinforced carbon composite according to claim 5 .