JPH01145372A - Production of carbon fiber-reinforced carbonaceous composite - Google Patents

Abstract

PURPOSE:To obtain in high efficiency the title lightweight composite outstanding in strength and heat resistance, by coating carbon fiber heat-treated at relatively low temperatures with a tar oil such as anthracene oil, carrying out treatment under press heating followed by impregnation with a thermosetting resin or pitch and then sintering. CONSTITUTION:First, a carbon fiber is produced by infusibilization treatment in air at 280 to 350 deg.C of a fibrous pitch formed by spinning e.g., mesophase pitch or optically isotropic pitch, followed by heat treatment at relatively low temperatures of 500 to 800 deg.C in an inert gas atmosphere. Secondly, this carbon fiber is coated with at least one king of tar oil selected from anthracene oil, coal tar and coal tar pitch. Thirdly, the resultant coated carbon fiber is put into a mold of desired shape, and subjected to press heating treatment at 600 to 800 deg.C pref. in an inert atmosphere under a load of 0.1 to 10kg/cm<2>-G. Finally, the resulting form is impregnated with a thermosetting resin or pitch under pressure to fill the pores therewith followed by sintering while, if needed, preventing the pitch from distilling out, thus obtaining the objective carbonaceous composite.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a novel method for producing carbon fiber-reinforced carbon composite materials. More specifically, the present invention relates to a method for efficiently producing carbon fiber-reinforced carbon composite materials that are useful as new materials, are lightweight, and have high strength and heat resistance.

BACKGROUND OF THE INVENTION In recent years, research and development of new materials has been actively conducted, and among these, carbon fiber reinforced composite materials are attracting attention as materials that are lightweight and have excellent strength and heat resistance.

Many manufacturing methods have been developed for this composite material, but the most common methods are to mold carbon fibers with a thermosetting resin such as 7-enol resin, solidify and then sinter them, or to add hydrocarbons to carbon fibers as a carbon source. A method has been used in which carbon is deposited between the carbon fibers by thermal CVD.

However, in the former method, because the carbon yield from the thermosetting resin is low, only a material with many pores and low strength can be obtained, and it is necessary to repeat impregnation and firing to improve the strength. However, this requires repeated complicated operations and is inevitably expensive.

On the other hand, the latter method has a slow deposition rate and requires a long time for production, so it is not practical.

In addition, a method using self-sintering carbon as a matrix has recently been developed. Because it is a substance, it is difficult to mix it uniformly with the fibers, and in order to attach it to the fibers, electrodeposition must be used, which is a complicated operation.
You cannot avoid being at an economic disadvantage.

All of these methods use carbon fibers fired at a temperature of about 1000°C or higher; however, they also use pitch fibers spun from pitch, which is the raw material for producing pitch-based carbon fibers, or those that are infusible. A method is also known in which carbonized fibers are laminated and carbonized as they are or by applying a slight load (Japanese Unexamined Patent Publications No. 101405/1983,
2-47014).

The products obtained by this method have high porosity and are lightweight but lack strength, so they are further impregnated with pitch and fired (Japanese Patent Laid-Open Publication No. 1983-1999).
-47014).

This method involves the fusion of fibers during carbonization, so when laminating and carbonizing thermoplastic pitch fibers, unless a low heating rate is used, the fusion of fibers will progress excessively. The disadvantage is that the fiber morphology cannot be maintained. Furthermore, pitch fibers and infusible pitch fibers are difficult to handle due to their low strength, and also have drawbacks such as significant shrinkage due to thermal decomposition and polycondensation reactions during carbonization, which may cause the fused portions to separate.

Problems to be Solved by the Invention The present invention overcomes the drawbacks of the conventional method for producing carbon fiber-reinforced carbon composite materials, and produces carbon fiber-reinforced carbon composites that are lightweight and have excellent physical properties such as strength and heat resistance. The purpose was to provide a method for efficiently manufacturing materials.

Means for Solving the Problems The present inventors have conducted various studies on the manufacturing method of carbon fiber-reinforced carbon composite materials. Based on this knowledge, he discovered that the purpose could be achieved by applying a specific tar oil and heat-treating it under prescribed conditions, then impregnating it with thermosetting resin or pitch and firing it at a prescribed temperature. The present invention has now been completed.

That is, in the present invention, in an inert atmosphere, 500 to 800
At least one tar oil selected from anthracene oil, coal tar, and coal tar pitch is applied to carbon fibers that have been heat-treated at a temperature in the range of °C.
600~ under a load of 1~10 kg/cta''-G
Provided is a method for producing a carbon fiber-reinforced carbon composite material, which is characterized in that the material is heat-treated at a temperature in the range of 800°C, impregnated with a thermosetting resin or pitch, and then fired at a temperature of 1000°C or higher. be.

The present invention will be explained in detail below.

In the method of the present invention, pitch-based or P
Any AN type can be used.

The pitch-based carbon fiber used in the present invention is produced by spinning mesophase pitch containing memphase, which is an optically anisotropic phase, or optically isotropic pitch as a spinning pitch, and then spinning this fibrous pitch (pitch fiber) into a spinning pitch. ) in the air at a temperature usually in the range of 280 to 350°C, and then
It is obtained by heat treatment in an inert gas at a temperature in the range of 500 to 800°C. This heat treatment temperature is 5
If the temperature is lower than 00°C, the strength is low and it is inconvenient to handle, and if the fibers are molded after being coated with tar oil such as anthracene oil, the fibers will fuse together to a large extent, resulting in only a composite material with low strength. Furthermore, if the temperature exceeds 800°C, the fibers will not fuse with each other, making it difficult to obtain a desired molded article.

On the other hand, regarding PAN-based carbon fiber, in an inert atmosphere,
It is used after being heat-treated at a temperature in the range of 500 to 800°C. Products with a heat treatment temperature of less than 500°C have relatively high strength and are not difficult to handle, but as in the case of pitch-based carbon fibers, the degree of fusion between fibers is large, resulting in a composite material with low strength. Moreover, if the temperature exceeds 800° C., the desired molded article cannot be obtained because the fibers do not fuse together like pitch-based fibers.

In the method of the present invention, these carbon fibers are coated with at least one type of tar oil selected from anthracene oil, coal tar, and coal tar pitch oil, and then heat treated. The tar oil used in this case preferably contains a large amount of condensed polycyclic aromatic compounds, has a low viscosity, and has a low carbonization yield. Those containing a large amount of aliphatic hydrocarbons have a weak effect of fusing fibers together; high viscosity and softening points make it difficult to coat the fibers uniformly; and high carbonization yields cause fibers to fuse together. This is not preferable because it inhibits the fusion of Regarding coal tar pitch, if it is soft pitch, it can be used as it is, but since medium and high pitch pitches have high softening points and high carbonization yields, it is preferable to use them after diluting them with anthracene oil or the like. When using tar oil such as creosote oil or absorption oil, which contains more fractions with a lower boiling point than anthracene oil, most of it evaporates at a low temperature during pressure molding, which prevents the fusion of fibers. Not progressing enough.

In the method of the present invention, there is no particular restriction on the method of applying the tar to the carbon fibers, and any suitable method may be used, such as dipping the fibers in tar oil or applying it with a brush.

At this time, even if you try to mold the fibers as they are without applying tar oil, you will not be able to obtain a molded product.

In the method of the present invention, carbon fibers coated with tar oil in this way are put into a mold of a desired shape, and
600-80 under a load in the range of kg/cra”-G
Heat treatment at a temperature in the range of 0°C. This heat treatment is preferably carried out in an inert atmosphere.

When the load is 0. If it is less than Ikg/cra"-G, the fusion between the fibers will not be sufficient, and 10 J!9/CI+"-G
If the pressure exceeds , no effect can be expected despite the high pressure.
There is no particular difference in the bulk density of the molded product from that of 10 ky/cm"-G. The optimum magnitude of this load is appropriately selected depending on the heat treatment temperature of the carbon fiber used, but in general, it is determined by the heat treatment temperature. For low-temperature fibers, it is preferable to reduce the load; excessive load will cause breakage.Furthermore, this treatment temperature must be in the range of 600 to 800°C.If this temperature is less than 600°C, the fibers will not fully fuse together. In addition, in terms of fusion between fibers, so
A temperature higher than 'c' is not necessary, and if it exceeds 800° C., it is not preferable because it causes heat resistance problems in devices such as molds.

The molded product thus obtained has a bulk density of approximately 0.7
~1.0 g/crx" and has many pores.

Therefore, in order to fill these pores, it is necessary to impregnate the material with a thermosetting resin or pitch and perform a firing process. There are no particular restrictions on the impregnation method, and any known method may be used; however, a pressure impregnation method is generally advantageous.

In this pressure impregnation method, a thermosetting resin or pitch for impregnation is placed in a pressurized container, the pressure is reduced, the molded body is placed in the thermosetting resin or pitch, and then 10 kg/cr
Either hold the molded object under pressure of about a2g-G until the resin or pitch sufficiently penetrates into the molded object, or place the molded object in heated and melted pitch and heat-treat it at a temperature of about 400°C to impregnate it. carried out by.

In this way, when a molded body is impregnated with a thermosetting resin or pitch, it may be cured and then fired at a temperature of 1000°C or higher. When impregnated with pitch, since the pitch is thermoplastic, if it is fired as it is, the impregnated pitch will distill out in the process, so the weight will be approximately 30 kg/ctm.
The molded body is treated at a temperature of 600°C or higher under a gas pressure of -G or higher, or the impregnated molded body is placed in a mold for approximately 1 k
g/crI! The process is carried out under a load of −G or more at a temperature of 600° C. or more, and then fired at a temperature of 1000° C. or more, thereby preventing pitch from distilling out.

In this way, a composite material is obtained, which, if necessary, can be further subjected to graphitization treatment at a temperature of 2000° C. or higher.

Effects of the Invention In the method of the present invention, carbon fibers treated at a relatively low temperature of 500 to 800°C cannot be molded as they are because the fibers themselves lack caking properties. It can be easily molded by applying oil.

Most of the tar oil escapes from the system by evaporation during the molding process, but it is thought that it slightly melts the surfaces of the fibers, which have poor caking properties, and that this fuses and bonds the fibers that come into contact with each other. Furthermore, the thermosetting resin or pitch impregnated into the molded body heated in this manner has the role of reinforcing the molded body made only of fibers.

The carbon fiber-reinforced carbon composite material obtained by the present invention is lightweight and has excellent strength and heat resistance, and is extremely useful as a new material.

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way.

Example 1 After melt-spinning mesoface pitch to obtain pitch fibers of 12 to 15 mesh, they were spun in air at a heating rate of 2°C/min.
It was heated to 20° C. and held for 10 minutes to perform infusibility treatment.

Next, this was heated to SOO℃, 600℃ or SOO℃ in a nitrogen gas stream.
It was heated to OO°C and held for 30 minutes to obtain carbon fibers.

After soaking 1 g of such carbon fiber in anthracene oil and removing excess anthracene oil, a width of 10 mRs was obtained.
It was placed in a mold with a length of 100 mm with both ends open, and then placed in a stainless steel container and placed in a nitrogen gas stream.
Under a load of 0.1 to 7.5 kg 1c, the sample was heated to a predetermined temperature in the range of 600 to 800°C at a heating rate of 5°C/min and held for 60 minutes.

Next, the molded body thus obtained was heated to 300°C, put into melted coal tar pitch with a softening point of 76°C, heated to 430°C, and held for 2 hours to impregnate the pitch. After removing the pitch attached to the surface of the molded product, the above was placed on the frame again, and under a load of 5 kg/cta"-G,
It was heated to 600'0 at a heating rate of °C/min and held for 60 minutes. Next, this was heated to 1000°C at a rate of 10°C/min while flowing nitrogen gas in a tube furnace, held for 60 minutes and fired, and then heated to 2600°C in a Tammann furnace in an argon gas stream. A composite material was obtained by graphitization treatment for 30 minutes.

The carbon fiber-reinforced carbon composite material obtained in this way was
It was cut into a length of 0 mrtr, and the 4-point bending strength was measured under the conditions of a span of 40 mm, an interval of upper push rods of 1 OIII, 1, and a pressurization rate of 0.5 mta. The number of test pieces was four, and the bulk density was determined from the volume and weight. The results are summarized in Table 1.

The fractured surface of the carbon fiber-reinforced carbon composite material graphitized at 2600°C was observed using a scanning electron microscope (SEM). The results are shown in the figure. As is clear from this figure, it can be seen that where the fibers are in contact with each other, they are fused together.

Example 2 Flame-retardant treated fibers of PAN-based carbon fibers were heated at 600°C or 80°C.
Approximately 1 g of the material heat-treated at 0° C. was dipped in anthracene oil and applied, and treated in the same manner as in Example 1. 2
Table 2 summarizes the bending strength of the composite materials obtained by graphitizing at 600°C.

Table 2 SEM of the structure of the composite material graphitized at 2600'O
When observed, the same results as in Example 1 were obtained.

Comparative Example Used in Example 1, 500°C, 600°C1 or 800°C
The fiber structure 19 heat-treated at a temperature of °C was put into a mold as it was, and the HO
Heat treatment was performed at ℃ for 60 minutes. The obtained fibers that were treated at 500°C or 600°C retained their shape, but
When I pressed it with my hands, the fibers came loose.

In addition, the fibers treated at 800° C. had already lost their shape when taken out from the mold, and even if they retained their shape, they could not be obtained.

Example 3 Anthracene oil was added to coal tar pitch with a softening point of 76°C at a weight ratio of 50:50.
Heat to ℃ and mix. This material was slightly soft at room temperature, so it was heated to 100°C to reduce the viscosity. In addition, the pitch system similar to Example 1 and Example 2
Heat-treated the same PAN-based carbon fiber at 800°C and soaked it for about 19 minutes, then put it into a mold similar to Example 1 that had been preheated to about 100°C, and 7.
A load of 5 kg/ctm2-G was applied, heated to goo'c, and held for 60 minutes. Next, this molded body was impregnated with pitch in the same manner as in Example 1, treated at 1000°C, and then treated with graphite at 2600°C to obtain a composite material.

The bulk density and bending strength of these composites are 1.52 g/c+m” and 54&9” for pitch-based carbon fiber, respectively.
/am'', and for PAN-based carbon fiber, it was 1.54 g/cm3 and 112 scraps per 58 kg.

[Brief explanation of the drawing]

The figure is a scanning electron micrograph showing the fiber structure of an example of a carbon fiber-reinforced carbon composite material obtained by the method of the present invention.

Claims (1)

[Claims] 1 At least one tar oil selected from anthracene oil, coal tar, and coal tar pitch is applied to carbon fibers that have been heat-treated at a temperature in the range of 500 to 800 °C in an inert atmosphere, and this is coated with 0.1 ~10kg/cm^
After heat treatment at a temperature in the range of 600 to 800°C under a load of 2-G, impregnating with thermosetting resin or pitch,
A method for producing a carbon fiber-reinforced carbon composite material, which comprises then firing at a temperature of 1000°C or higher.