JPH02107565A - Production of high-strength carbon composite material - Google Patents

Abstract

PURPOSE:To obtain the title high-strength carbon composite material with a simple process by specifically carbonizing specified polyacrylonitrile-based carbon fiber and coal tar pitch. CONSTITUTION:The polyacrylonitrile-based carbon fiber having 0.005-0.50 oxygen-contg. functional group amt. (OIS/CIS) and 0.001-0.010 nitrogen-contg. functional group amt. (NIS/CIS) on the surface is two-dimensionally or three- dimensionally oriented, and the product is impregnated with coal tar pitch. The carbon fiber impregnated with the pitch is carbonized, the product is then impregnated with the coal tar pitch essentially free of a quinoline-insoluble component, and the carbonization at 800-1,200 deg.C is repeated until the bulk sp.gr. becomes >=1.5g/cm<3>. The CIS, OIS, and NIS are the peak area obtained by the X-ray photoelectric spectroscopic analysis (ESCA) at the ionization potentials of 280-292eV, 520-540eV, and 395-405eV.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for producing a carbon fiber reinforced carbon composite material.
More specifically, the present invention relates to a method for producing a high-strength carbon composite material using carbon fiber as a filler and coal tar pitch as a matrix.

<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 a C/C composite), and this C/C composite has excellent mechanical properties and heat resistance properties. It has excellent corrosion resistance, friction, and braking properties, and has been put to 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 first wall material for nuclear reactors and fusion reactors, as a medical material for bones and joints, and as a turbine material.

There are various methods for manufacturing C/C composites with such excellent properties, but carbon fiber tow, resin loss, felt, etc. are impregnated with a thermosetting resin such as phenolic resin to create a prepreg, and these are laminated. A common method is to make a molded product by curing it.

Carbon fiber itself has extremely strong anisotropy, and a C/C composite, which is a composite material using carbon fiber as a reinforcing material, has strong anisotropy. A common method to alleviate this anisotropy of carbon fibers is to weave a three-dimensional fabric using tow, then impregnate it with a thermosetting resin such as phenolic resin, and then heat and harden it to obtain a molded article. has been adopted.

The matrix is the phenol shown above.

Thermosetting resins such as epoxy and furan, and thermoplastic resins such as coal-based and petroleum-based pinch resins are generally used.

However, when thermosetting resin is used, although it has the advantage of being easy to shape, it is expensive, and furthermore, after impregnating carbon fiber with this resin, it requires fairly strict temperature control in the heating and curing process. And what about this process itself? It is JtH and requires a lot of effort and time.

Furthermore, the true specific gravity of the carbide of this thermosetting resin is 1.4 to 1.
．． 5 g/cd, which is smaller than the true specific gravity of pitch carbide, which is a thermoplastic resin, of 1.8 to 1.9 g/d;
When a thermosetting resin is used as a matrix, there is a problem that the bulk specific gravity of the C/C composite does not increase much, resulting in poor mechanical properties.

When using a thermoplastic resin, such as pitch, as a matrix, pitch is cheaper than thermosetting resins and has the advantage of having a higher true specific gravity of carbide, but it is difficult to heat pitch under normal pressure. In this case, the carbonization yield is low, and the pitch is carbonized through the molten phase.
Bubbling occurs during the carbonization process, and its own pores remain in the C/C composite. Due to the presence of these pores, the bulk specific gravity of the C/C composite does not increase even if the densification process of re-impregnating pitch is repeated many times (bulk specific gravity: 1.3 to 1.5 g/c+1), N There is a problem that mechanical strength is low (bending strength near to lokg/*4).

<Problems to be Solved by the Invention> The object of the present invention is to use polyacrylonitrile carbon fiber as a filler and coal tar pinch as a matrix in a simple process, and to achieve a bending strength of 30k.
The present invention provides a method for manufacturing a high-strength C/C composite of g/mj or more at low cost.

Means for Solving the Problems> The present invention provides a surface oxygen-containing functional group amount (0□/CIs) of 0.005 to 0.050. Amount of nitrogen-containing functional groups (Nlff
/Cps) in the range of 0.001 to 0.010, two- or three-dimensionally oriented polyacrylonitrile carbon fibers are impregnated with coal tar pitch, and then carbonized in the impregnated state. Then, the treated material is impregnated with coal tar pitch containing substantially no quinoline insoluble matter, and then carbonized until the bulk specific gravity is 1.
．． This is a method for producing a high-strength carbon composite material, which is characterized by repeating the process until it reaches 5 g/ct1 or more.

However, C13 and 011N Is each have an ionization potential of 280 by X-ray photoelectron spectroscopy (ESCA).
~292eV, 520~540eV, 395~40
This is the peak area determined in the range of 5 eV.

For Kusaku Next, the content of the present invention will be explained in more detail.

The weaving methods of carbon fibers used in the production of C/C composites are distinguished by the orientation direction of the fibers: (1) two-dimensional orientation of the fibers, such as cross-laminated materials and cross-laminated materials; (2) two-dimensional orientation. It can be classified as a three-dimensional orientation in which the vertical system is oriented in the thickness direction of the laminated material. The present invention uses these two-dimensionally and three-dimensionally oriented carbon fibers as fillers.

Types of carbon fiber can be broadly classified based on their raw materials, and include polyacrylonitrile, rayon, and pitch type carbon fibers, but polyacrylonitrile type carbon fibers are inexpensive and have high strength.
In the present invention, a high strength polyacrylonitrile yarn is used.

By the way, a composite material made of carbon fiber and plastic (
In the production of CFRP, carbon fibers are surface-treated in advance to increase the adhesion between carbon fibers and plastic and to increase the strength of CFRP. However, the present inventors have introduced C/C composite (CF).
The amount of oxygen- and nitrogen-containing functional groups on the carbon fiber surface is also important in the production of RC), and from the viewpoint of strength, OSs/C13
The value is 0.005 to 0.050. It has been found that the value of N13/C13 is limited within the range of 0.001 to 0.010.

The amount of oxygen- and nitrogen-containing functional groups can be determined by X-ray photoelectron spectroscopy (E
SCA). 0.0 on the carbon fiber surface determined by X-ray photoelectron spectroscopy. .

/C15, that is, the number of oxygen atoms/the number of carbon atoms, is the oxygen-containing functional group (carboxyl group, hydroxyl group,
Ols is a parameter indicating the amount of carbonyl groups, etc.
/C+ The larger the value of s, the larger the amount of oxygen-containing functional groups. Also, N13/C13 on the carbon fiber surface, that is, the number of nitrogen atoms/
The number of carbon atoms is a parameter indicating the amount of nitrogen-containing functional groups (such as amide groups and amino groups) on the surface of carbon fibers, and N13
The larger the value of /C13, the larger the amount of nitrogen-containing functional groups.

01 of carbon fiber surface layer. The content of N I 3 and N I 3 can be adjusted by surface treatment to bond a functional group to the fiber surface or by controlling the firing temperature during fiber production.

Here, between the polyacrylonitrile carbon fiber having both oxygen-containing functional groups and nitrogen-containing functional groups on the surface and the matrix carbon, carbonization treatment during the production of the C/C base material, and further During the carbonization process in the densification process, chemical and physical adhesive forces are formed. The temperature at which coal cool pitch turns into coke due to heat (8
It is thought that this adhesive force is formed at a temperature of 00 to 1200'C), but the magnitude of this adhesive force depends on the amount of oxygen- and nitrogen-containing functional groups on the carbon fiber surface. That is, ESC
In carbon fibers with O13/C13 of less than 0.005 and N13/C13 of less than 0.001 on the carbon fiber surface according to A, the adhesive force between the carbon fiber and the matrix carbon is weak, and C/
C composite has no strength. O13 on carbon fiber surface
/C13 is 0.050 or more, N's/C+3 is o, oi
.

If the above carbon fibers are used, the bond between the matrix carbon from the coal tar pitch and the carbon fibers will be too strong, and during the carbonization process, the carbon fibers will be damaged due to the difference in shrinkage rate between the carbon fibers and the matrix carbon. Cracks appear, C
/C composite lacks strength. Furthermore, in bending tests of C/C composites, because strong adhesive force is formed between the matrix carbon and carbon fibers, the matrix carbon and carbon fibers break together and the carbon The high strength properties of the fibers are not reflected in the properties of the C/C composite.
By using carbon fibers whose N's/Cps is in the range of 0.001 or more, o, and oio, an appropriate adhesive force is formed between the carbon fibers and the matrix carbon. Moreover, the C/C composite thus obtained has a high strength with a bending strength of 30 kg/cm or more.

The ESCASC method is generally well known, for example, "Aromatics" Vol. 40, No. 1.2, 30-3.
Although described in detail on page 5 (1988), the measurement conditions of the present invention are shown below.

Equipment 1-V, manufactured by G5Ccientific, ESCA LAB~5 Excited X-ray -AIKg (1486,6eV) X-ray output...100W Measurement degree of vacuum -1,0X10-"mbar Measurement temperature ・
・・20℃ Cl3 peak area is ionization potential 280~29
In the range of 2 eV, 01. Peak area is 520-540
eV range, N 1g peak area is 395-405
It was determined from the eV range. In the present invention, (Ls/Cps is the ratio of the 01. peak area to the cps peak area, and N1
3/C13 is defined as the ratio of NI3 peak area to cps peak area.

Next, the temperature of the recarbonization treatment in the densification treatment is 800 to 1
Limited to a temperature of 200°C.

At temperatures below 800°C, the carbonization reaction has not yet been fully completed, and the coal tar pitch that is the matrix does not turn into coke, and a moderate adhesive force is formed between the carbon fibers and the matrix carbon. The C/C composite has no strength, and furthermore, at a temperature of 1200°C Mi, cracks are likely to occur due to thermal contraction of the matrix carbon, and as a result, the moderate adhesion between the carbon fibers and the matrix carbon once formed is weak. As a result, the C/C composite loses its strength.

Here, the final C/C composite has a bulk specific gravity of 1.
Must be 5g/c+f1 or higher.

A low-density C/C composite with a bulk specific gravity of less than 1.5 g/d has many pores and therefore lacks strength.

That is, impregnation and carbonization (800 to 120
0"C) The process is usually repeated 2 to 6 times until the bulk specific gravity is 1.
A C/C composite having a property of 5 g/cr1 or more has a high strength with a mechanical property of a bending strength of 30 kg/m4 or more.

Next, in the present invention, inexpensive coal tar pitch is used as the raw material for the carbon material serving as the matrix. Pitch from high-temperature carbonized coal tar is rich in aromaticity, has a high carbonization rate and true specific gravity, and has relatively low viscosity, so it is suitable as a raw material matrix for C/C composites. There is.

Here, the coal tar pitch for the C/C composite of the present invention is a binder pitch normally used as a binder in the production of carbon products such as artificial graphite electrodes and impermeable graphite, and an impregnation pitch used in the impregnation process of these carbon products. These coal tar pitches, which can be any pitch, are typical thermoplastic resins, and when the pitch is fluidized at the softening point, when the temperature is raised, the pitch is 0.5po.
When the temperature is further increased, the viscosity increases due to coking (carbonization) at a temperature of 500 to 600°C, and finally solidifies.

In order to produce a strong C/C composite, it is important that coal tar pitch, which is the matrix, sufficiently penetrates between the carbon fiber filaments, but pitch has a sufficiently low viscosity and low surface tension. These properties make it desirable as an impregnating material.

Further, the carbonization treatment after impregnating the carbon fiber with the matrix is performed while the carbon fiber is immersed in the pitch that is the matrix. Coal tar pitch is thermoplastic, so although it melts during the carbonization process, the molten pitch penetrates between the carbon fiber filaments and carbonizes, and the surrounding molten pitch fills the pores created by bubbling, resulting in carbonization. No large cranks or pores are observed in the C/C composite after treatment. Furthermore, with this method, the carbon fibers are carbonized while being immersed in the pitch, so conventional prepregs are made and then laminated. There is no problem of pitch flowing out during molding or carbonization, which was seen in the molding and then carbonizing method.

Coal tar pitch loses weight through thermal decomposition or volatilization of low-molecular components during carbonization, and becomes pitch coke after carbonization. Taking this into consideration, the ratio of the two-dimensionally and three-dimensionally oriented carbon fibers to the coal tar pitch may be adjusted so that the C/C composite is present in the pitch coke after carbonization.

To explain in more detail, a required number of planar fabrics such as hand-woven, twill-woven, and satin-woven fabrics in which carbon fibers are two-dimensionally oriented are laminated,
A laminate made of carbon fiber.

This laminate is held by plates made of carbon material that are tightened from above and below to form a preform. In the case of three-dimensionally oriented carbon fibers, pitch impregnation treatment may be performed as is. In this way, the laminate consisting of the two-dimensionally oriented planar fabric and the three-dimensionally oriented carbon fiber are impregnated without soaking the molten coal tar pitch. ), and this impregnation temperature is usually 150 to 300°C.

600~10 with the carbon fiber still immersed in the pitch
Carbonization treatment is carried out at 00°C, but this may be done under normal pressure, increased pressure or reduced pressure. This carbonization treatment requires a temperature increase of 30~
It can be carried out at a relatively high rate of 600° C./hr, and C/C composites can be produced easily and efficiently.

The C/C composite obtained in this way does not have sufficient bulk density and strength, and it is necessary to repeat impregnation treatment and carbonization treatment by conventional methods as appropriate to obtain a C/C composite with high density and high strength. (Densification treatment) The impregnating material used in this impregnation treatment is preferably inexpensive coal tar pitch.This coal tar pitch is rich in aromaticity and has a high carbonization rate and true specific gravity, and is preferable from the viewpoint of characteristics.

It is important here that this coal tar pitch does not substantially contain quinoline-insoluble matter. This is because the insoluble quinoline content in the pitch is solid particles, and these particles block the pores in the carbon material, thereby significantly reducing the permeation rate of the impregnating material during the impregnation operation.

As mentioned above, the recarbonization process in this impregnation process is 800~
Perform at 1200°C. This impregnation-recarbonization process can be repeated 2 to 6 times to obtain a C/C composite having a bulk specific gravity of 1.5 g/cm2 or more.

The reason why the bulk specific gravity must be 1.5 g/cm or more is that the bulk specific gravity is 1.5 g/c+! This is because a C/C composite with a low density of less than 10% has a large number of pores and therefore lacks strength.

Although the present invention has been described using coal tar pitch as a matrix, the present invention is not limited to this, and a high strength C/C composite can be produced using the same method using petroleum pitch.

<Example> Example 1 Three-dimensionally oriented carbon fiber with a fiber diameter of 7 IM (polyacrylonitrile yarn used, O on the carbon fiber surface by ESCA)
rs/C13 = 0.038. Nls/C1
3 = o, oos) was charged into an impregnation tank and melted at 220'C. -9.0 wt%, the properties of these pitches were measured in accordance with JIS K-2425. The same applies hereinafter) were injected into an impregnating tank under vacuum in an amount of 5 ml and 11 g to impregnate the carbon fibers with the pitch. Subsequently, the carbon fibers were carbonized to 600° C. while immersed in the pitch in a nitrogen gas atmosphere at a temperature increase rate of 200° C/hr under normal pressure, and further maintained at this temperature for 1 hour. Next, after taking out the molded body from the impregnation tank, the temperature was raised to 1000°C at a rate of 300'C/h in a nitrogen gas atmosphere, and the C/C composite (C/C
C base material) was obtained. This C/C,l material has a bulk specific gravity of 1.15
g/c′llll.

Furthermore, this C/C base material is coated with coal tar pitch (softening point = 8
7. 0°C, benzene insoluble content = 18.0 wt%, quinoline insoluble content = trace) in 3 mm and 11 g under vacuum 21
After impregnation at 0°C, the molded body was heated at 20°C in a nitrogen atmosphere.
Carbonization treatment was carried out to 1000° C. at a heating rate of /hr. This impregnation and carbonization treatment was repeated a total of 4 times to obtain a bulk specific gravity of 1.688.
/ cd and a bending strength of 33.8 kg/m.

The test piece in this characteristic test is 50 x 10 x 1.5 m.
It is a rectangular parallelepiped with (length x width x thickness), and the bulk specific gravity is determined from the volume determined from the dry weight and dimensions of the test piece.The bending strength is determined using the three-point bending test method, and the distance between the supports is 11 fl and 140 m, and the crosshead speed in the autograph is is 1 rag
/ am. The standard for Naifetsuji is JIS K.
6911, the radius of curvature of the tip of the fulcrum edge is 2 fields, and the radius of curvature of the tip of the pressure wedge is 5IwII. The number of measurement tests was 3.

Example 2 A C/C composite was produced under exactly the same conditions as in Example 1 except that three-dimensional woven carbon fibers with different amounts of oxygen- and nitrogen-containing functional groups on the surface of the carbon fibers were used. A high-strength C/C composite having a bending strength of 30 kg/m4 or more was obtained from any of the carbon fibers.

The results are shown in Table 1.

Example 3 A C/C composite was manufactured under exactly the same conditions as in Example 1, except that the carbonization temperature in the densification treatment was changed to 800°C. Table 1 shows the properties of the obtained C/C composite.

Example 4 A C/C composite was manufactured under exactly the same conditions as in Example 1, except that the carbonization temperature in the densification treatment was changed to 1200°C. Table 1 shows the properties of the obtained C/C composite.

Comparative Example 1 A C/C composite was produced under the same conditions as in Example 1 except that carbon fibers with different amounts of oxygen- and nitrogen-containing functional groups on the carbon fiber surface were used.

These carbon fibers have O1 on the carbon fiber surface by ESCA.
3/CI! , N's/C1s were outside the scope of the present invention, and the C/C composite obtained from this carbon fiber had a bending strength of 10 to 15 kg/mJ.

The results are shown in Table 1.

Comparative Example 2 In Example 1, the carbonization temperature in the densification treatment was set to 7
A C/C composite was produced under exactly the same conditions except that the temperature was 00°C. Table 1 shows the properties of the obtained C/C composite.
Shown below.

Comparative Example 3 In Example 1, the carbonization temperature in the densification treatment was changed to 1
．． A C/C composite was produced under exactly the same conditions except that the temperature was 300"C. The properties of the obtained C/C composite are shown in Table 1.

Example 5 Thirteen hand-woven planar fabrics made of two-dimensionally oriented carbon fibers with a fiber diameter of 7 pm were laminated, and only the outer frame was tightened from above and below with carbon material to form a preform. This carbon fiber is of polyacrylonitrile type, and the carbon fiber surface was determined by ESCA as O13/C13-0,042,N13/
It has a characteristic of C+s=0.007.

This preform was charged into an impregnating tank, and coal tar pitch melted at 200°C (softening point -I (0.5°C, benzene insoluble content = 15.8 wt%, quinoline insoluble content = 3.
5 wt%) was injected into the impregnation tank under a vacuum of 5 mmHH to impregnate the carbon fibers with pitch.

Subsequently, the carbon fibers were heated for 600 minutes while immersed in the pitch in a nitrogen gas atmosphere at a heating rate of 200°C/hr under normal pressure.
The molded body was carbonized to ℃ and further held at this temperature for 1 hour. After taking out the molded body from the zero-order impregnation tank, it was heated in a nitrogen gas atmosphere for 30 minutes.
The temperature was raised to 1000″C at a heating rate of 0°C/hr, and
A C composite (C/C base material) was obtained. This C/C base material had a bulk specific gravity of 1.22 g/c+J. Furthermore, this C/
Coal tar pitch (softening point -87.0°C, benzene insoluble content -18.0 wt%) on C base material.

Quinoline insoluble matter = trace) under a vacuum of Hg at 3 corners 2
After impregnating at 10°C, the molded body was soaked at 10°C in a nitrogen atmosphere.
Carbonization treatment was carried out to 1000°C at a temperature increase rate of 100°C/hr.

This impregnation and carbonization treatment was repeated a total of 5 times, and the bulk specific gravity was 1.7.
A C/C composite having properties of 3 g/c+il and bending strength of 34.8 kg/mJ was obtained.

Comparative Example 4 A C/C composite was obtained in the method for producing a C/C composite in Example 5 under exactly the same conditions except that the impregnation-carbonization treatment in the densification treatment was repeated a total of two times. After a total of two densification treatments. The properties of the product (processed at 1000°C) were a bulk specific gravity of 1.42 g/cd and a bending strength of 16.3 kg/-.

Comparative Example 5 In the manufacturing method of the C/C composite in Example 1, pitch-based carbon fiber with a fiber diameter of 11n was used as the three-dimensionally oriented carbon fiber (01s/
C13=0.048. N I3/C13=0.00
C/C composites were manufactured under the same conditions except that 8) was used.

This item has a bulk specific gravity of 1.75g/c+a and a bending strength of 13.
．． It was a characteristic of 2 kg/soshi.

Example 6 Three-dimensionally oriented carbon fiber with a fiber diameter of 7 μm (polyacrylonitrile yarn used, carbon fiber surface O by ESCA)
13/ CIff= 00O11,N 13/ CIs
= 0.005) was charged into an impregnation tank and melted at 230°C. Petroleum-based pinch (softening point = 108.
0℃.

Benzene insoluble matter = 13. Owt%, quinoline insoluble content -t
race) was injected into the impregnation tank under vacuum at 5awl1g to impregnate the carbon fibers with pitch. Subsequently, the carbon fibers were carbonized at 600° C. while immersed in the pitch in a nitrogen gas atmosphere at a heating rate of 200° C./hr under normal pressure, and further held at this temperature for 1 hour. Next, after taking out the molded body from the impregnating tank, it was heated at 30'C/h in a nitrogen gas atmosphere.
The temperature was raised to 1000° C. at a heating rate of r to obtain a C/C composite (C/C base material). This C/C base material had a bulk specific gravity of 1°18 g/c+A. Furthermore, this C/C base material was impregnated with the above petroleum pitch at 230°C under a vacuum of 3 mmHg, and then this molded body was heated at a heating rate of 20°C/hr for 10 minutes.
Carbonization treatment was carried out to 00°C. This impregnation carbonization treatment was repeated a total of 4 times, and the bulk specific gravity was 1.68 g/c, and the bending strength was 30.2.
A C/C composite weighing 1 kg/kg was obtained.

Since the above high strength C/C composite can be easily obtained,
Is the ripple effect on industry very large? <Effects of invention>

Claims (1)

[Claims] The amount of oxygen-containing functional groups (O_1_3/C_1_3) on the surface is 0.005 or more and less than 0.050, and the amount of nitrogen-containing functional groups (N
Two- or three-dimensionally oriented polyacrylonitrile carbon fibers with a ratio of _1_3/C_1_3) in the range of 0.001 or more and less than 0.010 are impregnated with coal tar pitch, and then carbonized in the impregnated state. Then, this treated material is impregnated with coal tar pitch containing substantially no quinoline-insoluble matter, and then
The bulk specific gravity is 1.5g through the carbonization process at a temperature of ℃.
A method for producing a high-strength carbon composite material, characterized in that the process is repeated until the carbon composite material reaches /cm^2 or more. However, C_1_3, O_1_3, and N_1_3 have ionization potentials of 280 to 292 eV, 520 to 540 eV, and 395 eV, respectively, by X-ray photoelectron spectroscopy (ESCA).
This is the peak area determined in the range of ~405 eV.