JPH03197362A - Production of carbon fiber-reinforced carbon composite material - Google Patents

Abstract

PURPOSE:To obtain a carbon fiber-reinforced carbon composite material having high density and excellent flexural strength, etc., by preparing a prepreg by using a carbon fiber with no surface treatment, subjecting to a carbonizing treatment, further impregnating with a carbonizable material applying a hot hydrostatic pressure and carbonizing. CONSTITUTION:A carbon fiber aggregate composed of carbon fiber with no surface treatment and generating functional group such as carboxyl group or hydroxyl group, or carbon fiber having no functional group generated by a surface treatment, is prepared. In the next, said carbon fiber aggregate and a carbonizable material (e.g. phenolic resin) are used to form a prepreg, and the carbonizable material is carbonized. Then, a resultant prepreg is further impregnated with a carbonizable material same as or different from the above- mentioned carbonizable material by a hot hydrostatic pressure treatment and the carbonizable material is carbonized to afford the objective highly densified carbon fiber-reinforced carbon composite material.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention impregnates a prepreg made of carbon fibers and a carbonizable material with a carbonizable material, and then carbonizes the carbonizable material to produce high-density carbon. The present invention relates to a method for manufacturing a fiber-reinforced carbon composite material (hereinafter abbreviated as C/C composite material).

[Prior art] C/C composite materials have high specific strength and excellent heat resistance, and their strength characteristics especially at temperatures above 1500°C are unparalleled. Used as a heat-resistant material in the space field.

C/C composite materials are normally manufactured through the steps shown in FIG. That is, a prepreg is produced by combining a carbon fiber aggregate and a carbonizable substance, such as a thermosetting polymer material or pitch, by a method such as impregnation. Next, the prepregs are laminated to form a multilayer body, which is integrated by pressure molding, and then fired to carbonize the carbonizable material or further graphitize it to produce a C/C composite material. Incidentally, if necessary, the density may be improved by repeating impregnation with a carbonizable substance that is the same as or different from the above carbonizable substance and carbonization or graphitization.

By the way, as the carbon fibers constituting the carbon fiber aggregate, carbon fibers that have been surface-treated to produce functional groups such as carboxyl groups and hydroxyl groups are usually used to improve the adhesion between the carbon fibers and the matrix. There is. However, in this case, the volume shrinks due to thermal decomposition of the carbonizable substance during the heat treatment, so thermal stress is generated at the interface between the carbon fiber and the matrix. As a result, cracks are likely to occur at the interface, and if cracks occur inside, the cracks cannot be filled even with subsequent impregnation treatment, resulting in a decrease in strength.

Therefore, attempts have been made to prevent cracking during heat treatment by using carbon fibers that have not been subjected to surface treatment to generate the above-mentioned functional groups, or from which functional groups once generated by the surface treatment have been removed. However, in this case, the adhesion between the carbon fibers and the matrix is poor, and in the case of C/C composite materials that have not been subjected to densification treatment, when a bending test is performed, fracture occurs due to fiber buckling on the compression side, and the surface This has the disadvantage that the strength is lower than when untreated carbon fiber is used. Therefore, as mentioned above, it has been considered to repeat the impregnation and carbonization treatment to increase the density, but it is currently considered difficult to achieve a sufficient increase in density despite the time it takes.

[Problems to be Solved by the Invention] The present invention provides a method using carbon fibers that are less likely to cause cracks between the carbon fibers and the matrix, that is, carbon fibers that have not been subjected to surface treatment or from which functional groups generated by surface treatment have been removed. The present invention aims to provide a method for effectively densifying a C/C composite material, and furthermore, to provide a method for manufacturing a C/C composite material having excellent strength.

[Means for Solving the Problems] The method for producing a C/C composite material of the present invention comprises carbon fibers that have not been subjected to a surface treatment that generates functional groups, or that are made of carbon fibers from which functional groups generated by the surface treatment have been removed. After making prepreg using carbon fiber aggregate and carbonizable material,
In a method of manufacturing a carbon composite material by carbonizing the carbonizable substance, further impregnating the carbonizable substance with the same or different carbonizable substance, and carbonizing the same, the impregnation with the carbonizable substance is carried out by hot isostatic pressing. The gist lies in what is done through processing.

[Operations and Examples] Carbon fibers used in the present invention include PAN-based or pitch-based carbon that has not been subjected to surface treatment to generate functional groups, or that has had functional groups generated by the surface treatment removed. Fibers are used. As a method for removing the generated functional groups, there is, for example, a method of heating to 1000° C. or higher in an inert gas atmosphere.

The carbonizable substance is not particularly limited, and thermosetting polymer resins such as phenol resins, epoxy resins, and furan resins, or pitches are used as appropriate, and thermoplastic polymer resins may be used in combination if necessary.

The methods employed in the manufacturing process of the present invention, ie, prepreg manufacturing method, lamination method, carbonization treatment conditions, graphitization treatment conditions, etc., are not particularly limited and may be carried out by conventional methods.

The main point of the present invention is to specify the conditions for impregnation treatment in the impregnation/carbonization (including the case where it progresses to graphitization) process that is repeatedly performed for densification. Therefore, the preferred conditions and effects of the hot isostatic pressing treatment in the impregnation treatment will be described below based on Examples.

Example 1 and Comparative Example 1.2 A C/C composite material was prepared by repeatedly performing pitch impregnation treatment and carbonization treatment under the conditions of 3 f1 shown in Table 1.
The density and bending strength at that time were measured.

1st Table Carbonizable material In Example 1, it was possible to achieve a considerably higher density than in Comparative Example 1, in which the impregnation treatment was carried out at atmospheric pressure. Also, even though it is impregnated under the same high pressure, carbon without surface treatment! In Example 1 using am, higher density was possible than in Comparative Example 2 in which surface treatment was performed.

The reason for this is that in Example 1, the adhesion between the carbon fiber and the matrix was poor, and when the matrix contracted during the carbonization process, fine voids were uniformly formed at the interface between the two, and the voids were impregnated with pitch under high pressure. On the other hand, in Comparative Example 2, the adhesion between the carbon fiber and the matrix is good, so cracks occur locally at the interface during the carbonization process, and even if impregnation treatment is performed under high pressure, the cracks that occur inside are not caused by pitch. This is thought to be because they were unable to penetrate.

FIG. 3 shows the relationship between bending strength and density. When the density is low, the surface-treated material has higher strength, but as the density increases, the surface-treated material has higher strength. This is because when the density is low, the adhesive force between the carbon fibers and the matrix is weak in the case of non-surface-treated carbon fibers, which causes buckling, but as the density increases, the strength increases due to physical reinforcement, whereas the surface-treated Since the adhesive strength is strong, buckling does not occur much even when the density is low, but even when the density becomes high, the physical reinforcement effect is small and the bending strength does not increase much, so the density becomes higher than a certain point. It is thought that the bending strength of the specimen without surface treatment was higher than that of the specimen without surface treatment.

From the above, it can be seen that when carbon fibers without surface treatment are used, it is necessary to increase the density, and hydrostatic pressure treatment is very effective for increasing the density.

Examples 2.3 and 4 C/C composite materials were produced by changing only the impregnation pressure in Example 1. The impregnation pressure was 10 atm (Example 2), 100 atm (Example 3), and 2000 atm (Example 4), respectively. Figure 4 shows the relationship between density and number of impregnations in Example K and Comparative Example. shows. From FIG. 4, it can be seen that while the impregnation pressure is quite effective even at 100 atm, the effect is small above 1000 atm even if the impregnation pressure is increased. Also, even at 10 atmospheres, it is considerably improved compared to atmospheric pressure.

[Effects of the invention] Hot isostatic pressing makes it possible to increase the density of the C/C composite material, and by combining it with carbon fibers that have not been subjected to surface treatment, C/C has excellent bending strength.
/C composite material can now be provided.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the manufacturing process of C/C composite material.
Figure 2 is a graph showing the relationship between the number of impregnations and density when the manufacturing conditions are different, Figure 3 is a graph showing the relationship between density and bending strength, and Figure 4 is the relationship between the number of impregnations and density when the impregnation pressure is different. This is a graph showing.

Claims (1)

[Claims] After making a prepreg using a carbonizable material and a carbon fiber aggregate made of carbon fibers that have not been subjected to surface treatment to generate functional groups or from which functional groups generated by the surface treatment have been removed, the carbonizable material is In the method of producing a carbon composite material by carbonizing the material, and further impregnating it with a carbonizing substance that is the same as or different from the carbonizing substance, and carbonizing the same, the impregnation with the carbonizing substance is carried out by hot isostatic pressure treatment. A method for producing a carbon fiber-reinforced carbon composite material.