JPH0829987B2 - Method for producing carbon fiber reinforced carbon composite material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention uses a carbon fiber having a coating layer of a thermosetting thermosetting resin on its surface as a reinforcing fiber, and is reinforced with a carbon fiber having excellent performance. The present invention relates to a method for manufacturing a carbon composite material.

[Conventional technology]

Carbon fiber reinforced carbon composite material (hereinafter abbreviated as c / c composite material) is lightweight, has high strength, and is excellent in heat resistance and touch resistance, and is used for rocket nozzles, nose cones, aircraft disc brakes, etc. It is used in aerospace materials, heating elements, hot plate molds, other mechanical parts, reactor components, etc.

Conventional c / c composite materials are heat-molded by previously impregnating or mixing carbon fibers with a thermosetting resin such as phenol resin or furan resin, or a matrix precursor such as a thermoplastic resin such as pitch. It is manufactured by carbonizing at 600 to 1000 ° C in a non-oxidizing atmosphere, and graphitizing at 1800 to 2500 ° C if necessary.

By the way, it is said that in the composite material, the reinforcing fibers mainly bear the stress applied thereto, and the matrix plays a role of transmission in which the stress is evenly shared by the individual fibers. Therefore, in order to obtain sufficient performance as a composite material, the fibers are evenly distributed in the matrix, the fibers are evenly surrounded by the matrix, and the fibers and matrix are sufficiently adhered. Therefore, it is important that the stress is transmitted smoothly.

[Problems to be solved by the invention]

However, when the c / c composite material is manufactured by the conventional technique, the wettability between the carbon fiber and the matrix precursor is not always good, so when the carbon fiber is impregnated with or mixed with the matrix precursor, the matrix precursor is not mixed between the fibers. It was difficult to make it uniformly penetrate into. In addition, since the shrinkage due to carbonization of the matrix precursor is generally large, if the adhesion between the carbon fiber and the matrix precursor is not sufficient, the interface between the carbon fiber and the matrix carbon changed from the matrix precursor at the end of the carbonization Often created voids. For these reasons, it was difficult to obtain a c / c composite material with sufficient performance because the stress transfer between the carbon fiber and the matrix carbon was impeded.

In the conventional technique, as a method for solving such a problem, generally, the carbonized c / c composite material is again impregnated with resins to cause the end-permeation part of the matrix precursor or the carbonization shrinkage of the matrix precursor. The method of filling the voids at the carbon fiber-matrix carbon interface and carbonizing again is adopted, but in order to completely fill the voids at the end-permeating part and the interface, the steps of impregnation of resins and re-carbonization are repeated many times. Without it, there was a problem that it would not be possible to develop sufficient performance.

[Means for solving problems]

Therefore, the present inventors have improved the wettability of the carbon fiber and the matrix precursor, and as a result of diligent study on a method of increasing the adhesiveness, the carbon fiber for reinforcement was previously prepared, and the matrix precursor during the production of the c / c composite material. It is treated with a dilute solution of a thermosetting resin such as that used as a substance, and then heat treated to form a thin coating layer of the thermosetting resin on the surface of the fiber. The inventors have found that the wettability and adhesiveness with the matrix precursor are improved, and as a result, a c / c composite material having excellent performance can be obtained, and have completed the present invention.

That is, the gist of the present invention is to apply a thermosetting resin solution to carbon fibers and heat-treat the thermosetting resin by heating at a temperature of 50 to 300 ° C. to coat the surface with the thermosetting resin. A carbon fiber-reinforced carbon composite material, characterized in that a carbon fiber having a layer is formed, the obtained thermosetting resin-coated carbon fiber is impregnated with or mixed with a matrix precursor, and then molded and then fired. It depends on the manufacturing method.

 The present invention will be described in detail below.

The carbon fiber used in the present invention may be any kind of known PAN-based, Pitch-based carbon fiber or vapor grown carbon fiber, and its form may be long fiber, short fiber or woven fabric, non-woven fabric and the like. However, the effect of the present invention is particularly large when the single fibers are in a state of being aggregated at a high density, such as long fiber roving or woven cloth.

In the present invention, a dilute solution of the thermosetting resin is applied to the surface of the carbon fiber by a method such as dipping. Examples of the thermosetting resin include a phenol resin, a furan resin, an epoxy resin, and an unsaturated polyester resin.
A phenol resin, particularly a resol type phenol resin, can be preferably used. These thermosetting resins are dissolved and diluted with an alcohol such as ethanol, a hydrocarbon such as hexane or acetone and a solvent to form a solution, which is applied to carbon fibers.

The concentration of the thermosetting resin solution is usually 0.2 to 5 wt%, preferably 0.5 to 2 wt%, which is desirable for uniform application on the surface of the fiber. Further, for those requiring a curing agent such as furan resin and epoxy resin, the curing agent is also added to the solution, and the amount thereof is an amount suitable for each resin.

As a method of applying the thermosetting resin solution to the carbon fiber, it is possible to simply immerse the carbon fiber in the solution, but if it is long fiber roving or continuous woven cloth, the solution is filled. From the viewpoint of treatment efficiency, the method of continuously traveling in the tank is preferable. Further, at this time, it is preferable to apply an ultrasonic wave of about 10 to 50 KHz to the tank filled with the solution because it is possible to prevent the influence of processing unevenness due to bubbles or the like between each single fiber and between weaves.

The carbon fiber coated with the thermosetting resin solution is passed through a roller, for example, to remove the excess solution, and then subjected to heat treatment.

By the heat treatment, the thermosetting resin is thermoset, and a thin thermosetting resin layer is formed on the surface of the carbon fiber. The conditions for heat treatment differ depending on the type of thermosetting resin used, but usually 50 to 300 ° C, preferably 80 to 200.
It is heat-treated at a temperature of ° C for 0.2 to 5 hours, preferably 0.2 to 2 hours. At this time, it is desirable that the temperature be gradually raised to a predetermined temperature in order to avoid the rapid desorption of the solvent from the thermosetting resin solution applied to the carbon fibers. Further, the heat treatment is preferably carried out by a method in which carbon fibers are continuously run in a heating furnace from the viewpoint of treatment efficiency.

The carbon fiber obtained as described above has a thin coating layer of thermosetting thermosetting resin formed on its surface,
If the coating layer is too thin, the effect of improving the wettability and adhesiveness with the matrix precursor used for c / c composite material production is not sufficient. The adhesion between the fibers occurs and the subsequent handling of the carbon fibers becomes extremely difficult. Therefore, it is desirable that the thickness of the coating layer is in the range of 0.2 to 3 µ, preferably 0.5 to 1.5 µ as an average thickness.

The thickness of the thermosetting resin coating layer depends almost on the concentration of the thermosetting resin solution applied to the carbon fiber, and it is possible to obtain the desired coating layer thickness by adjusting the concentration of the solution. However, when a high-concentration solution is used, the formation of the coating layer may become uneven. In order to obtain a desired coating layer thickness and achieve uniform coating layer formation, application of a thermosetting resin solution and thermosetting of the thermosetting resin by heat treatment may be repeated. In this case, it is preferable to reduce the concentration of the solution at the beginning and gradually increase the concentration with each repetition in order to form a uniform coating layer, and in terms of handleability of the treated carbon fiber.

The obtained carbon fiber having a coating layer of thermosetting resin on the surface is then impregnated with or mixed with a matrix precursor, and then arranged in a mold and molded under constant heating and pressure conditions. To be done.

As the matrix precursor, a thermosetting resin such as a phenol resin or a furan resin, or a thermoplastic resin such as a pitch can be used, but it is more preferable to use the thermosetting resin in order to exert the effect of the present invention. .

The impregnation or mixing can be appropriately selected depending on the purpose and the like, but when the carbon fibers are long fibers, impregnation or mixing is usually adopted when the carbon fibers are short fibers. The amount of carbon fiber used varies depending on the use of the c / c composite material and cannot be specified unconditionally, but is usually selected from the range of 30 to 70% relative to the volume of the molded body.

The obtained molded body is then fired. For example, a c / c composite material is obtained by performing a carbonization treatment by embedding it in packing coke, and further performing a graphitization treatment if necessary. Also, by repeating the densification treatment of pitch impregnation or resin impregnation-recarbonization after carbonization, if necessary, a c / c composite material with much better performance can be obtained.

〔Example〕

Example 1 Pitch-based carbon fiber roving carbonized at 1000 ° C. (3000
Filament, fiber diameter 12μ, tensile strength 170kg / mm ² ) 45K
A tank filled with 0.5 wt% phenol resin solution (Resol type phenol resin "Resitop PL-2211" manufactured by Gunei Chemical Co., Ltd., 55% resin dissolved and diluted with ethanol), which is operated by ultrasonic waves of Hz and 100 W. It was run inside and then passed through a plurality of rollers before being wound on a drum. The running speed of the carbon fiber roving in this treatment was 10 m / Hr, and the residence time in the tank filled with the phenol resin solution was 1 min.

The carbon fiber roving coated with the phenolic resin solution was air-dried at room temperature for 25 hours while still wound on the drum, and then the total length was 0.3.
Heat treatment was carried out by running at a speed of 0.3 m / Hr in a furnace with a central temperature of 200 ° C.

The carbon fiber roving obtained as a result of the above treatment was supple and had a weight increase of 2.6% compared to before treatment. On the other hand, when observing with a scanning electron microscope,
A 0.3 μ thick coating layer was observed.

Then, this carbon fiber roving was cut into pieces each having a length of 27 cm, impregnated with a phenol resin (“Resitop PL-2211” manufactured by Gunei Chemical Co., resin content 55%) as a matrix precursor, air-dried into a preform, and then thickened. 2mm, width 10m
A mold having a length of 230 mm and a length of 230 mm was aligned in one direction and arranged in an amount of Vf = 55%, and molded at a maximum temperature of 250 ° C. and a maximum pressure of 80 kg / cm ² to obtain a molded body.

The compact is embedded in packing coke and carbonized at 1000 ° C to make a c / c composite material, then impregnated with pitch and re-carbonized at 1000 ° C. This densification process is repeated 4 times and then treated at 2000 ° C in an argon atmosphere. Then, a graphitized c / c composite material having a bulk density of 1.67 g / cm ⁸ was obtained.

From this c / c composite material, three test pieces each having a length of 45 mm and a length of 20 mm were cut out and subjected to a three-point bending test with a span distance of 40 mm and 10 mm and a strain rate of 2 mm / min to obtain bending strength and interlaminar shear strength. result, each of 48.9 kg / mm ² as an average value of the triangular test piece, to obtain a value of 2.53kg / mm ^2.

Example 2 A phenol resin solution was applied under the same conditions as in Example 1,
The carbon fiber roving obtained by the heat treatment was applied again with the phenol resin solution and heat treated under the same conditions as in Example 1 except that the concentration of the phenol resin solution was 1.5 wt%. The resulting carbon fiber roving remained pliable, with a 7.8% weight gain over the initially prepared untreated carbon fiber roving. In addition, observation with a scanning electron microscope revealed a coating layer having an average thickness of about 0.7 μm on the surface.

This carbon fiber roving was impregnated with a phenol resin, molded, carbonized, densified and graphitized under the same conditions as in Example 1 to obtain a c / c composite material having a bulk density of 1.69 g / cm ² . The c / c flexural strength in the same manner as in Example 1 per composite result of obtaining an interlayer shear strength, respectively 56.4 kg / mm ^2, to obtain a value of 2.59 kg / mm ^2.

Comparative Example 1 Using the same carbon fiber roving as that used in Example 1 without applying the phenolic resin solution,
Under the same conditions as in Example 1, the resin was impregnated, molded, carbonized, and densified to obtain a c / c composite material having a bulk density of 1.69 g / cm ³ .

The bending strength and the interlaminar shear strength of the c / c composite material were determined in the same manner as in Example 1, and the result was 37.3 kg / mm ² , respectively.
A value of 1.99 kg / mm ² was set.

Comparative Example 2 The phenol resin solution was applied under the same conditions as in Example 1 except that the concentration of the phenol resin solution was 5 wt%, followed by heat treatment. The obtained carbon fiber roving was a solid rod shape. . When this carbon fiber roving was observed with a scanning electron microscope, a large number of portions in which each single fiber was filled with a phenol resin were observed. Of the observed part,
The average thickness of the coating layer calculated from the number and diameter of carbon fibers and the area occupied by the phenol resin was 4.6 μ. Then, this carbon fiber roving was impregnated with a phenol resin under the same conditions as in Example 1, molded, and carbonized.
The c-composite material was twisted in the longitudinal direction, and cracks were observed in the matrix carbon portion between the carbon fiber rovings.

〔The invention's effect〕

According to the method of the present invention, the wettability and adhesiveness of the carbon fiber and the matrix precursor can be improved, and a c / c composite material having excellent performance can be obtained.

Claims (3)

[Claims] 1. A thermosetting resin solution is applied to carbon fibers to form 50
The thermosetting resin is heat-cured by heat treatment at a temperature of ˜300 ° C. to form a carbon fiber having a coating layer of the thermosetting resin having an average thickness of 0.2˜3 μ on the surface thereof. A method for producing a carbon fiber-reinforced carbon composite material, which comprises impregnating or mixing a curable resin-coated carbon fiber with a matrix precursor, followed by molding and then firing treatment. 2. The method according to claim 1, wherein the thermosetting resin is a phenol resin. 3. The method according to claim 1, wherein the concentration of the thermosetting resin solution is 5% by weight or less.