JPH0244019A - Impregnating pitch for producing carbon composite material reinforced with carbon fiber and its production - Google Patents

Abstract

PURPOSE:To obtain the title impregnating pitch being inexpensive and having high stability at high temp. by allowing the pitch to contain a specified proportion of quinoline insolubles constituted of free carbon and spherical mesophase having a specified particle size range, and regulating a softening point of the pitch to be in a specified range. CONSTITUTION:A soft pitch (30-70 deg.C softening point) or a medium pitch (70-110 deg.C softening point) contg. 3-10wt.% free carbon is prepd. as starting material, and spherical mesophase having 10-15mum particle size is generated by heating the pitch at 350-500 deg.C in inert gas atmosphere such as N2. Then, the pitch contg. the generated mesophase is distilled under <=20mmHg reduced pressure in order to improve carbonization yield of the pitch to remove thus a low molecular weight fraction, and the softening point of the pitch is adjusted to 200-250 deg.C. Thus, an aimed impregnating pitch for producing a carbon composite material reinforced with carbon fiber is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an impregnating pitch used to increase the bulk density of a carbon fiber-reinforced carbon composite material and a method for manufacturing the same.

<Prior art> A carbon composite material made of carbon as a matrix and reinforced with carbon fibers is called a carbon fiber-reinforced carbon composite material (hereinafter referred to as C/C-composite), and this C/C-composite has excellent mechanical properties and heat resistance. It has excellent properties, corrosion resistance, and frictional braking properties. Utilizing these properties, it has been put into practical use as aerospace equipment components such as rocket nozzles, space shuttle noses and leading edges, and aircraft brake discs. Recently, it has been put to practical use as a material for the first wall of containers for nuclear reactors and fusion reactors, as a medical material for bones and joints, and as a turbine material.

There are various methods for producing C/C-composites with such excellent properties, including carbon fiber tow, cloth,
A common method is to impregnate felt or the like with a thermosetting resin such as a phenolic resin to make a prepreg, which is then laminated and cured to form a molded body, which is then carbonized in an inert atmosphere.

However, at this stage, the C/C-composite (hereinafter referred to as C/C-
The bulk density of the base material (referred to as the base material) is only about 60% of the theoretical value, which is extremely insufficient in terms of strength.

Therefore, densification treatment (densification treatment) is usually performed, but the most common treatment method is resin impregnation, which uses thermosetting resins such as phenol, epoxy, and furan, and thermoplastic resin pitch as impregnants. It is. This method involves firing the C/C-base material, then impregnating it with the above resin under vacuum and pressure, and repeating the process of carbonizing it again 8 to 15 times to reduce the bulk density to about 80% of the theoretical value. (C/C-composite bulk density 1.6 to 1.88/C11),
C/C-: 7 embosites are made to have a high density. In this way, the densification process usually has to be repeated 8 to 15 times, which requires a lot of effort and time.
-Composites have become very expensive.

When a thermosetting resin is used as the impregnating material, this resin is expensive, and furthermore, it requires very strict temperature control in the process of impregnating the C/C-base material and then heating and curing it. , and what about this process itself?
! It is complicated and requires a lot of effort and time. Furthermore, the true density of the carbide of this thermosetting resin is 1.4 to 1.5 g/
cj, which is smaller than the true density of pitch carbide, which is a thermoplastic resin, 1.8 to 1.9 g/cj, and when a thermosetting resin is impregnated, the bulk density of the C/C-composite is The problem is that it doesn't go up very much.

On the other hand, when impregnated with thermoplastic resin such as pitch,
Although pitch has the advantage of being cheap and easily increasing the bulk density of the C/C-composite, it has a low carbonization yield, and furthermore, carbonization i! After about 3 seconds, the pinch goes through the melt phase and carbonizes, which causes problems such as bubbling and impregnated pitch flowing out from the C/C base material. In order to increase the bulk density, a considerable number of densification treatments are performed. In a pinch, under pressure (10 to 1000 kg/
It is true that carbonization with c+i) increases the carbonization yield and increases the bulk density of the resulting C/C-composite, but this treatment requires special equipment because it is performed under pressure. After all, C/C-
There are problems in manufacturing composites.

Currently, most of the impregnating pitches used are coal tar soft pitch or coal tar medium pitch. However, in the pitch, there is a few percent of an insoluble substance (hereinafter referred to as free carbon) that is quinoline insoluble with a particle size of 1 Pa or less, and this prevents the pitch from penetrating into the pores of the C/C base material. hindering. For this reason, in the case of large C/C-base materials, it actually takes a long time to impregnate the inside of the C/C-base uniformly with pitch, and This is one of the reasons for the occurrence of defective products.

Removing the free carbon present in this coal tar pitch to the trace level on an industrial scale requires a great deal of equipment and labor.Also, even if the amount of free carbon is reduced to 11% or less, the amount of free carbon will still be reduced. The penetration rate does not necessarily increase in proportion to , but on the contrary, it decreases significantly 1
It often indicates the current direction.

Normally, free carbon in the pitch is removed by C during the impregnation operation.
/C- is filtered on the surface of the substrate to form a free carbon filter bed. If there is a lot of free carbon in the pitch for impregnation (
(1-1% or more), the resistance of this filter bed increases and reduces the permeation rate. On the other hand, those with less free carbon (1w
t% or less), the resistance of free carbon passing through the C/C-base material becomes the dominant factor that reduces the permeation rate. In other words, pitches with low free carbon content,
It is thought that it does not form a sufficient free carbon filter bed and blocks the internal pores of the C/C-substrate, thus significantly reducing the permeation rate in the impregnation operation despite the low free carbon content. It will be done. That is, when the content of free carbon is small, it is necessary to avoid clogging of pores in order to increase permeability.

<Invention tries to solve! ! Problem> As mentioned above, C/C-
The bulk density of the composite does not increase, which is why C/C-
The present invention aims to solve the problem that composites have become very expensive and that when coal tar pitch is impregnated, it is not uniformly and sufficiently impregnated into the inside of the C/C base material. The present invention proposes lupitch suitable for impregnation and a method for producing the same.

<Means for Solving the Problems> The present invention provides quinoline insoluble matter composed of free carbon and a nearly spherical mesophase with a diameter of 10 to 15 μm.
For carbon fiber-reinforced carbon composite materials containing ~2511 t% and having a softening point of 200-250°C, pitch for impregnation and pitch containing 3-10 wt'% of free carbon are prepared in an inert gas atmosphere. Heat treatment in a temperature range of 350 to 500°C to generate spherical mesophase with a particle size of 10 to 15n, then heat treatment at a temperature of 300°C or less under reduced pressure of 20 to 11 g or less to adjust the softening point. A method for producing impregnated pitch for carbon fiber-reinforced carbon composite materials characterized by the following.

<For production> Next, the content of the present invention will be explained in more detail.

The present invention uses inexpensive coal cool pitch or petroleum-based cool pitch as a raw material for impregnating C/C-based materials.The present invention uses coal cool pitch obtained by high-temperature carbonization (1000 to 1300 degrees Celsius) to distill coal. Coal tar pitch, which is the residue obtained from the above, is rich in aromatic properties, has a large true specific gravity, and has relatively low viscosity, and is suitable as an impregnating material for C/C-based materials.

By the way, this high-temperature carbonized coal tar contains 0.5 to 10 wt% of quinoline-insoluble matter called free carbon, and this content depends on the structure and operating conditions of the coke oven, and the size of this free carbon is diameter 1 pm
The following fine particles are known.

This free carbon prevents the pitch from penetrating into the pores of the C/C-base material, so the presence of free carbon in the pitch is unfavorable in terms of permeability. On the occasion of
It is said that it becomes the nucleus for the generation of mesophase (spherulites), but during the generation process of mesophase, free carbon does not get sucked into the mesophase, but instead sticks around the mesophase and prevents the coalescence of the mesophase. known to inhibit This mesophase is also quinoline-insoluble and is spherical in the early stages of development.

Coal tar pitch is the residue obtained by distilling coal tar and separating and removing light components.In the present invention, we use soft pitch with a free carbon content of 3 to 10-t% (softening point of 30 to 70°C). Or medium pitch (softening point 70-110℃)
) is used as the starting material. This ranopitch is heated to 350 to 500 in an inert gas atmosphere such as nitrogen or argon.
C. to produce spherical mesophase with a particle size of 10-15.

In order to increase the carbonization yield of the pitch containing this mesophase, low molecular components are removed by distillation under reduced pressure of 20 to 11 g or less, and the softening point of the pitch is adjusted to 200 to 250 °C.
and this pitch is used as an impregnation material.

The free carbon in the pitch is a solid particle with a particle size of 1- or less that impedes the permeability of the pitch into the C/C-substrate.
Mesophase is attached around the mesophase generated by heat treatment.Mesophase, on the other hand, has a large particle size of 10 to 1 strm, so it does not form a dense filter bed as in the case of free carbon alone, and it has no permeability. There will be no resistance.

Here, it is necessary to generate a spherical mesophase with a particle size of lθ to 15n. If the particle size is less than lOn, C/C-
A dense filter bed is formed on the surface of the base material, the resistance of this filter bed increases, and the permeation rate decreases.

On the other hand, if the particle size exceeds 15fa, a thick i
This is undesirable because it forms an It bed, which increases the filter bed resistance and ultimately reduces the permeation rate.In other words, the mesophase whose surface is covered with free carbon and whose particle size is 10 to 15 nm is not preferable during impregnation. Appropriate thickness (
In order to form a filter bed of 0.5 to 1.0 I1 m+), the permeability is significantly improved compared to pitch containing only free carbon.

Here, in order to generate mesophase with a particle size of 10 to 15p+*, it is necessary to heat-treat pitch containing 3 to 10-t% of free carbon. This free carbon becomes the core of mesophase generation during the heat treatment of pitch, but it also adheres to the surface of the mesophase and has the function of inhibiting the coalescence of mesophases. If the free carbon content in the pitch is less than 3wt%, mesophases tend to coalesce during heat treatment, and mesophases with a particle size of more than 15μ+* are likely to be generated.On the other hand, if the free carbon content exceeds IO++t%, mesophases tend to coalesce together during heat treatment, and mesophases with a particle size of more than 15μ+* tend to form. If coalescence is inhibited and mesophase with a particle size of less than 10 nm is easily generated, which is not desirable, if pitch containing 3 to 10 wt% of free carbon is heat-treated at 350 to 500°C, the particle size range will be 10 to 15 nm. A mesophase with a value of is generated. At temperatures lower than this temperature range, mesophase is difficult to occur, and at higher temperatures, decomposition and monopolymerization occur.

This is undesirable as it causes coking, etc.

In the pitch for impregnation of the present invention, the quinoline insoluble content is 10
If it is less than 25 wt%, free carbon cannot be sufficiently fixed around the mesophase, and if it exceeds 25 wt%, the filter bed becomes thick and the permeation rate becomes slow. Therefore, the quinoline insoluble content is limited to 10 to 25 wt%.

The presence of mesophase and further the size of the particles can be confirmed by observation using a polarized light microscope. The mesophase surrounded by free carbon is quinoline insoluble matter, and in the liquid pitch, this quinoline insoluble matter exists as solid particles. This quinoline-insoluble content composed of free carbon and mesophase forms a filter bed on the surface of the C/C-base material during impregnation, but what is impregnated inside the C/C-base material is the quinoline-soluble content in the pitch. , the quinoline-soluble component must have high aromaticity and a high carbonization rate.

Pinch 350-50 to generate mesophase
The heat treatment is carried out at 0°C, and as a result of this heat treatment, the quinoline-soluble content in the pinch becomes more aromatic and the carbonization yield increases, so that it has desirable characteristics as an impregnated material.

In order to increase the carbonization rate of the heat-treated pitch, low molecular components in the pitch are removed by vacuum distillation, and the softening point is lowered to 200~200.
The temperature is set at 250° C., and this pitch is used as an impregnated pitch. The softening point of the pitch is preferably 200 to 250°C, and the softening point is 20
If the temperature is below 0°C, there will be a considerable amount of low molecular weight components in the pitch (
The carbonization yield will be low. Furthermore, the softening point is 2
If the temperature exceeds 50°C, the viscosity is high and sufficient permeability cannot be obtained at the pitch impregnation temperature.The purpose of vacuum distillation is to remove only the low molecular components in the heat-treated pitch.
At a temperature of 300°C or less, a degree of vacuum of 20 to 11 g or less is desirable. If it exceeds 300°C, thermal deterioration of the pitch will occur, which is undesirable, and if the degree of vacuum is less than 20ml11g, the vacuum will be insufficient and low molecular components will not be removed sufficiently.

The pitch for impregnation obtained in this way has a softening point of 200
~250℃, and the quinoline insoluble content was reduced to 10~25-(%).
Furthermore, when observed under a polarizing microscope, a nearly spherical mesophase (optical anisotropy structure) with a size of 10~15-
is recognized.

Impregnation of pitch into the C/C-base material requires that the pitch has a sufficiently low viscosity (0.5 poise) to uniformly impregnate the inside.
It is necessary to select a temperature that exhibits the following (as measured by a flow tester), and usually this impregnation temperature is 100
The temperature is above -150°C. That is, if the pitch according to the present invention is used, the impregnation temperature will be 300 to 400°C, but at this temperature, the pitch of the present invention is thermally stable and its properties do not change due to heat. The highly thermally reactive components that exist in
At an impregnation temperature of 400°C, the properties do not change.

Although the present invention is a description of coal tar pinch,
It is not limited to this, but coal is carbonized at low temperature (700 to 1
By the method of the present invention, impregnated pitch with excellent permeability and high carbonization yield can be produced using coal tar pitch obtained from coal tar obtained by heating at 0.000° C. and petroleum pitch containing free carbon as starting materials.

<Example> Example-1 Softening point: 55.0°C, free carbon content: 3 Jwt% (
Measurements of these properties were carried out according to JXS-2425.
Coal tar pitch (same below) was heat-treated at 480'C in a nitrogen gas atmosphere for 30 minutes, resulting in a softening point of 175'C.

A heat-treated pitch with a quinoline insoluble content of 9.8 wL% was obtained.

This pitch was distilled at 300°C in a vacuum of 20ml and 11g to remove low molecular components, and the quinoline insoluble content was 10.7w.
%, an approximately spherical impregnated pitch with a diameter of 10 to 15 p+* and a softening point of 205° C. was obtained when observed under a polarizing microscope.

Using this impregnated pitch, a C/C-base material (2-dimensionally oriented r'AN-based high-strength system as reinforcing fibers and phenolic resin as a matrix and fired at 1000°C, size: 300 m x 300IIIlx
6.5mm (length x width x thickness) bulk density 1.30g/
After impregnation at 330°C, recarbonization treatment was performed at 1000°C in an inert gas atmosphere. This pitch impregnation and recarbonization treatment was repeated a total of four times to obtain a high-density C/C-composite with a bulk density of 1.70 g/ctl.

Example-2 Coal cool pitch with a softening point of 90.0°C and 7.5 wt% free carbon was heat-treated at 350'C in a nitrogen gas atmosphere for 8 hours, resulting in a softening point of 185°C and a quinoline insoluble content of 22.0.
After obtaining the heat-treated pitch of wt%, this pitch was distilled at 280'C with a vacuum degree of 20W11g to remove low molecular components, and the softening point was 245"C, and the quinoline insoluble content was 24.3W.
t%, an impregnated pitch containing approximately spherical mesophases with a diameter of 10 to 15 nm was obtained when observed under a polarizing microscope.

Using this impregnated pitch, C/C-
The base material was impregnated at 350°C and then recarbonized at 1000°C in an inert gas atmosphere. This pitch impregnation and recarbonization treatment was repeated a total of three times to obtain a high-density C/C-composite with a bulk density of 1.69 g/cd.

Example-3 Coal tar pitch with a softening point of 102.5°C and 9.8 wt% free carbon was heated to 430°C in a nitrogen gas atmosphere.
Heat treated for 00 minutes to obtain a heat treated pinch with a softening point of 200°C and a quinoline insoluble content of 18.9wt%. Distillation with Ig at 280°C to remove low molecular components resulted in a product with a softening point of 230°C, a quinoline insoluble content of 21.0 wt%, and a diameter of 10% when observed under a polarizing microscope.
An impregnated pitch containing ~151M approximately spherical mesophase was obtained.

This impregnated pitch was used to create a C/C-base material (2-dimensionally oriented PAN-based high-elastic yarn as reinforcing fibers and fired at 1000°C using coal tar pitch as the raw material for the matrix. Size: 30 (1wX 300IaX)
6.5m (length x width x thickness) bulk density 1.34 g /
C+4) was impregnated at 360'C, and then recarbonized at 100'C in an inert gas atmosphere. This pitch impregnation recarbonization treatment was repeated a total of 4 times, and the bulk density was 115B.
A high-density C/C-combinant of /cd was obtained.

Example-4 Coal tar pitch with a softening point of 75.0'C and 6.2 wt% of free carbon was heat-treated at 500°C for 30 minutes in an argon gas atmosphere, resulting in a softening point of 185°C and a quinoline insoluble content of 18.0 wt%. A heat-treated pitch was obtained. This pitch was distilled at 250°C with a degree of vacuum of 5ml and 11g to remove low molecular components, resulting in a softening point of 248°C and a quinoline insoluble content of 23.7wt%.
, the diameter is 10-15ttts when observed under a polarizing microscope.
An impregnated pitch containing approximately spherical mesophase was obtained.

Using this impregnated pitch, C/C-
After impregnating the base material at 370°C, it was recarbonized at 1ooo''C in an inert gas atmosphere. This pitch impregnation and recarbonization process was repeated a total of 4 times to form a high density C with a bulk density of 1.15g/cd. /C-composite was obtained.

Example-5 Softening point = 108.0'C, free carbon 3.0wt
% of petroleum-based pitch was heat-treated at 480° C. for 60 minutes in a nitrogen gas atmosphere to obtain heat-treated pitch with a softening point of 200° C. and a quinoline insoluble content of 8.9 wt %. This pitch was distilled at 280°C in a vacuum of 8nml 1g to remove low molecular components, resulting in a softening point of 2.110°C and a quinoline insoluble content of 10.3w.
t%, an impregnated pinch was obtained containing approximately spherical mesophases with a diameter of lO~15 μs when observed under a polarizing microscope.

Using this impregnated pitch, C/C-
After impregnating the base material at 330°C, it was soaked for 10 minutes in a nitrogen gas atmosphere.
Recarbonization treatment was carried out at 00'C. This pitch impregnation recarbonization treatment was repeated a total of four times to obtain a high-density C/C-composite with a bulk density of 1.68 g/cd.

Comparative Example-1 Coal tar pitch with a softening point of 90.0°C and free carbon of 7.5 wt% used in Example-2 was heated to a vacuum degree of 5II11.
11 g was distilled at 300'C to remove low molecular weight components to obtain pitch with a softening point of 205°C and a quinoline insoluble content of 12.5 wt%. When this pitch is observed under a polarizing microscope,
No mesophase formation was observed.

Using this pitch, the impregnation-recarbonization process was repeated four times on the same C/C base material as in Example 1 to obtain a C/C composite. This material has a bulk density of 1.41 g/c4,
It is a low-density pore, and when this C/C-combodift is cut and the cut surface is observed, the surface (1 to 21111i) is as follows.
Although there were no pores, many pores were observed in the center, indicating that the entire C/C-composite was not uniformly impregnated.

Comparative Example-2 The coal tar pitch used in Example 1 with a softening point of 55.0°C and 3.2 wt% free carbon was heat-treated at 300°C in a nitrogen gas atmosphere for 30 hours, and the softening point was 150°C.
A heat-treated pitch with a quinoline insoluble content of 7.5 wt% was obtained. Next, this pitch was distilled at 290°C with a vacuum degree of 8w11g,
After distilling off the low molecular weight components, the softening point was 200°C, and the quinoline insoluble content was 6.8 wt%, and when observed under a polarizing microscope, the particle size was 1 to 1.
A pitch containing a minute mesophase of 3 Ina was obtained.

Using this pitch, the same impregnation-recarbonization treatment as in Example 1 was repeated four times to obtain a C/C7 composite. This material had low density pores with a bulk density of 1.42 g/c+4.

Comparative Example-3 The bitge used in Example-1 was heat-treated at 510'C for 15 minutes, resulting in a softening point of 260°C and a quinoline insoluble content of 30.6wt.
% heat treated pitch was obtained. When this pitch was observed under a polarizing microscope, a spherical mesophase with a particle size of 20 to 45 μl and an amorphous mesophase with a size of about 50 μm were observed.

Using this pitch, the same impregnation-carbonization treatment as in Example 1 was repeated four times to obtain a C/C-composite. This material had low density pores with a bulk density of 1.42 g/c.

Comparative Example-4 Softening point 175°C shown in Example-1, quinoline insoluble content 9
．． Heat-treated pitch of 8wt% at a vacuum level of 201m11g,
By distilling at 340℃ to remove low molecular components, the softening point is 26.
A pitch with a quinoline insoluble content of 15.2 wt% was obtained at 5°C.

Using this pitch, the same impregnation-carbonization treatment as in Example 1 was repeated four times to obtain a C/C-combodift. This had low density pores with a bulk density of 1.52 g/C.

Comparative Example-5 Softening point 175°C shown in Example-1, quinoline insoluble content 9
．． Heat treated pitch of 8wt% at vacuum degree of 50mm and 11g,
Although low molecular components were removed by distillation at 300'C, the softening point was 181°C and quinoline insoluble content was 10.3wt%.
I got the pitch. Using this pitch, the same C/C base material as in Example 1 was subjected to impregnation and carbonization treatment four times.
/C-composite was obtained. This one has a bulk density of 1.5
It had a low density pore of 8 g/c+d.

<Effects of the Invention> As described above, the present invention uses inexpensive coal tar or petroleum-based pitch as an impregnant, and there is no need to separate and remove free carbon present in the pitch. It is stable even at high temperatures, has good permeability into the C/C-substrate, and has a high carbonization yield, so the number of densification treatments required in the production of high-density C/C-composites is only 2 to 4 times, making it easier than conventional This has the effect that a high-density C/C-composite can be obtained at low cost.

Claims (2)

[Claims] 1. Contains 10 to 25 wt% of quinoline insoluble matter, and this quinoline insoluble consists of an approximately spherical mesophase with a diameter of 10 to 15 μm and free carbon, and has a softening point of 200 to 2.
A pitch for impregnation for carbon fiber-reinforced carbon composite materials, characterized by a temperature of 50°C. 2. Pitch containing 3 to 10 wt% of free carbon is heat-treated in an inert gas atmosphere at a temperature range of 350 to 500°C to generate mesophase, and then heat-treated at a temperature of 300°C or less under reduced pressure of 20 mmHg or less to soften the softening point. A method for producing pitch for impregnation for carbon fiber-reinforced carbon composite materials, characterized by adjusting the pitch.