JPH02167859A - Production of carbon fiber-reinforced carbon composite material - Google Patents

Abstract

PURPOSE:To obtain a carbon-fiber reinforced carbon composite material, excellent in flexural strength and interlayer shearing strength by coating the surface of carbon fiber with an organic polymer, impregnating the coated carbon fiber with a thermosetting resin, forming the impregnated carbon fiber and carbonizing the polymer and resin. CONSTITUTION:The surface of reinforcing carbon fiber is precoated with an organic polymer and then impregnated with a thermosetting resin which is a matrix precursor. The impregnated carbon fiber is subsequently formed and the polymer and resin are carbonized to afford a carbon-fiber reinforced composite material effectively used as high-temperature furnace materials, disk brakes, electrodes, etc. In this case, an organic polymer capable of forming a thin film and solidifying on the surface of the carbon fiber after the coating without dissolving in impregnating with the thermosetting resin which is the matrix precursor and rapidly destroyed by fire in carbonization without leaving carbonized components is used as the organic polymer and, e.g. polyvinyl alcohol, gelatin or starch, is preferred.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a method for producing a carbon fiber-reinforced carbon composite material, and more specifically relates to a method for producing a carbon fiber-reinforced carbon composite material. The present invention relates to a method for producing a carbon fiber-reinforced carbon composite material having a transverse strength and an interlaminar shear strength of 9.

(Prior art) Carbon fiber-reinforced carbon composite materials (hereinafter referred to as %compo), which are effectively used for high-temperature furnace materials, disc brakes, electrode materials, etc., are composed only of carbon, which is an inherently brittle material. Since it is a carbon material consisting of two types of fibers and a matrix, it has extremely high strength and fracture resistance, and is developing new uses not found in conventional carbon materials.

Various methods have been developed for manufacturing %Combo, but they can be roughly divided into two types: impregnating carbon fiber (hereinafter referred to as C0F) with thermosetting resin such as phenol resin or furan resin, depending on the type of matrix carbon. method that can be molded, molded, and carbonized.

Similarly, impregnate C and F with thermoplastic resin such as pitch,
Molding, carbonization, or hot press method to simultaneously perform molding and carbonization. Furthermore, there are three methods (CVD method) in which hydrocarbon gas such as benzene or propane is brought into contact with COF at high temperature to deposit pyrolytic carbon.

Among these, from the viewpoint of productivity and cost, those using thermosetting resins as matrix precursors are currently mainstream.

However, when a thermosetting resin is used as the matrix precursor of the % combo, the carbonization yield of the thermosetting resin is usually 50%.
~60%, the composite after carbonization has many voids due to the large volumetric shrinkage of the matrix part. At this point, the % component is still insufficient in terms of strength,
High strength achieved by repeating pitch and thermosetting resin re-impregnation and carbonization several times.

We are planning to increase the density.

(Problems to be Solved by the Invention) By the way, when a thermosetting resin is used as a matrix precursor, there is a state of carbon fiber reinforced plastic (C, F, R, P) during the manufacturing process. ,C,F,
The higher the adhesive strength between C, F, R, and P, the higher the strength of C, F, R, and P. This is an important point when manufacturing C, F, R, and P. And commercially available C, F,
Among them, there are various types that have been subjected to surface treatments to improve adhesion with resin.

On the other hand, even in the case of % combo, matrix carbon and c.

F, which is expected to yield a high strength %combo if the adhesive strength is high, but when a thermosetting resin is used as a matrix precursor, a large volumetric shrinkage of the matrix part occurs during carbonization. At this time, the thermoset resin and C and F are firmly adhered.

The matrix part that is about to shrink and the C that is about to stop shrinking
, F, and stress is generated between them.

For this reason, the matrix is fragmented in places and 1%
It leaves voids in the combo structure, and the C6F deteriorates, breaks, or becomes brittle due to stress caused by shrinkage of the matrix.

Furthermore, the thermoset resin part of the solid matrix precursor tends to form large voids starting from one point where stress is concentrated, rather than finely dispersing the voids generated by shrinkage, especially in C and F. On the other hand, in the parallel direction, since there is only a weak matrix, shrinkage of the matrix portion tends to form voids that cause large separation along the carbon fiber interface.

The % combo obtained in this way is that the large void is C
,F, running between the layers, C,F, decreases from its initial strength due to shrinkage stress in the matrix, and furthermore, because the matrix carbon is fixed to C,F, C,F, loses its original flexibility. It becomes brittle. As a result, when external stress is applied to the %combo, a large void in one tissue becomes a defect.
The brittle C and F, which easily become the starting point of fracture, are assimilated into the brittle matrix, unable to widely disperse external stress, and the fracture progresses linearly, making it difficult to develop high strength. The large voids generated between the C and F layers naturally reduce the shear strength of the composite.

In short, in a composite using a thermosetting resin as a matrix precursor, if the adhesion between the matrix resin and C or F is good, a high-strength composite will not necessarily be obtained. The strength of the % combo decreases because the stress caused by the large volumetric shrinkage creates large voids that serve as starting points for fracture, and the C, F, strength deteriorates and becomes brittle.

(Means for solving the problem) Even if a thermosetting resin is used as the matrix precursor of the composite, C
, F, without deterioration or embrittlement, and to obtain high strength by dispersing external stress over a wide area without concentrating it on one point. As a result of studying methods to improve the strength, the inventors found that if the matrix precursor thermosetting resin and C and F are not firmly bonded, the shrinkage stress of the matrix part during carbonization will be reduced to C and F. Therefore, this invention was developed based on the fact that C0F does not deteriorate or become brittle.

That is, in this invention, as a means of suppressing the adhesion between C, F and the matrix precursor resin, the surfaces of C, F, and the like are coated in advance with an organic polymer having a low (unpreferable) carbonization yield. This is what we are trying to solve.

In other words, in this invention, the surface of reinforcing carbon fibers is coated in advance with an organic polymer with no carbonization yield, then impregnated with a thermosetting resin as a matrix precursor, and then molded and carbonized. This is a method for manufacturing a carbon fiber reinforced carbon composite material.

C and F that can be used in this invention are any carbon or graphite fibers such as PAN (polyacrylonitrile), pitch, and rayon, and may be in the form of chopped fibers, long fibers, woven fabrics, or nonwoven fabrics. Good too.

These C and F are first impregnated with an organic polymer solution. The impregnation method involves immersing C, F in an organic polymer solution, or spraying a spray of organic polymer onto C, F. Any method that can coat the surface may be used. The organic polymer referred to here refers to the C, F, which is coated thinly and uniformly over the entire surface, and serves to prevent direct contact between the C, F and the resin during impregnation with thermosetting resin varnish in the subsequent process. is doing. That is, the cross section of C, F after impregnating the matrix precursor with thermosetting resin is as shown in Figure 1 of the drawing, where there is first a thin organic polymer layer 2 around the surface of the carbon fiber (C, F) 1, and then It is surrounded by a thermosetting resin 3 which is a matrix precursor.

However, in this treatment, it is desirable that the organic polymer forms a clear three-layer structure without being dissolved in C, F, and the matrix precursor thermosetting resin. Therefore, the organic polymer is in a solution state when it is coated on the CoFo surface, but by later heating it at room temperature or around 50°C, it must form a uniform in-phase film on the C, F and surface. Furthermore, in the step of impregnating the matrix precursor thermosetting resin varnish, this organic polymer film must not be torn or dissolved, and must form a solid S-retaining film on the CoFl surface. Examples of organic polymers that meet this condition include those that do not dissolve in the matrix precursor thermosetting resin varnish solvent; 1 Since alcohols are often used as solvents for varnishes, polyvinyl alcohol (PVA), gelatin, starch, etc. Water-soluble, non-alcohol-soluble organic polymers are preferred.

The thermosetting resin-impregnated carbon fiber body (prepreg) prepared in this way is molded into C, F, and R by heat molding or filament wind molding according to conventional methods.

P, and then the matrix part is carbonized in a non-oxidizing atmosphere to obtain a % composite, but C, F, because the surface is coated with an organic polymer.

400 to 600℃, when large shrinkage of the matrix begins
In the vicinity, the organic polymer has already been thermally decomposed and burned away, forming donut-shaped voids 5 around the carbon fibers (C, F,) 1 as shown in FIG. As a result, the matrix carbon portion 4 shrinks.

Even if it deforms, it is not in close contact with C and F.

C and F will not deteriorate or become brittle.

Furthermore, since the matrix part is not constrained by C and F, voids due to matrix shrinkage are caused by stress concentration between shrinkage of the matrix part and C and F, as in the conventional method, and voids are generated at - locations. Since there are no large voids and they are uniformly dispersed in the composite structure, defects that become starting points for destruction are less likely to occur even under external stress, and C and F deteriorate. Because it has not become brittle.

% combo has high strength and high toughness.

In addition, in the direction parallel to C and F, for the above reason, the stress during shrinkage is relaxed, so voids that become the starting point for delamination are less likely to occur, and therefore the interlayer shear strength is lower than that of the conventional method. It improves by comparison. However, in this % combo, matrix carbon and C0F are not strictly adhered.

It is thought that it is difficult to efficiently transmit stress from the outside, but the physical properties of C and F deteriorate due to the fact that there are very few voids between C and F and the matrix carbon, and due to the adhesion of matrix carbon. Since no embrittlement or embrittlement occurs, as a result, the % combo of the present invention can achieve high strength. However, if the void 5 between C, F, 1 and matrix carbon 4 is too large, C, F, and matrix carbon will clearly separate and cannot be said to be in a sufficient composite state, resulting in the physical properties of the resulting % combo. If the value is lower than the % combo of the conventional method, that is, if the thickness of the organic polymer coated on C and F becomes too thick, the effect of the present invention will not be exhibited. It has been found that the effective organic polymer coating thickness in this invention is 0.1 to 3 μm.

In addition, by repeating the densification process of pitch or thermosetting resin impregnation-carbonization for the %compo obtained in the present invention, the physical properties of the %compo can be further improved. This is because the matrix carbon formed during the initial carbonization is bonded to C and F, and the voids are filled with carbon during this densification process. By densification processing, C,
Although F comes into direct contact with the pitch and thermosetting resin, the stress caused by shrinkage of the matrix during recarbonization is extremely small, and the rate of deterioration of C and F is lower than that of conventional products. It is much smaller, and the adhesion between matrix carbon and C and F is improved at this point.
, F, is utilized by the matrix carbon, so a high strength % combo can be obtained.

Moreover, this %composite can be graphitized if necessary.

This invention will be explained below based on examples.

(Example 1) PAN system C, F, (tensile strength 360 kg/m rr
t, tensile modulus of elasticity 24000 kg/m rd, single fiber diameter 7 pm) A plain weave cloth made of 6000 filaments was immersed in a 3 wt% PVA (polyvinyl alcohol, degree of polymerization 500) aqueous solution for 1 hour, and then the excess 1 then 50 minutes passed through a roller to remove the PVA
The PVA coating layer was completely solidified by drying for one day and night in a constant temperature room at .degree. At this time, C, F, the surface has an average of 1
PVAJ5 of μ-san was formed. The PVA-treated C, F, and cloth were impregnated with a phenolic resin varnish having a solid content of 60% to a content of 50% by weight to obtain a prepreg sheet.

Cut the prepreg sheet into 50cm x 100m.

14 sheets were stacked and heated to a molding thickness of 5 m.

Pressure molded. The maximum treatment temperature at this time was 200° C., and the maximum pressing force was 50 kg/d.

The obtained C, F, R, P plates were embedded in carbon powder and carbonized at 1000°C to obtain a % combo.

This %composite was further subjected to pitch impregnation-carbonization treatment five times, and then graphitized at 2300°C to obtain a %composite. The density of this % composite is 1.55 g/d, bending strength 16.6 kg/mrri', shear strength 1.72 kg
/ m durability.

(Example 2) PVA coated PAN used in Example 1
A prepreg sheet with a J resin content of 55% by weight was prepared by impregnating systems C, F, and cloth with a furan resin having a solid content of 60% with 0.2% by weight of sulfuric acid added, and a prepreg sheet with a J resin content of 55% by weight was prepared under the same conditions as Example 1. Got the combo.

The density of the obtained % combo is 1.49 g/cd, bending strength is 5.9 kg/m rd, shear strength is 1.
It was 63 kg/mrrf.

(Comparative example) Same as the example, PANMC, F, Ri Cm Suni P V
A phenol resin was impregnated in the same manner as in Example 1 without coating A, and the material was converted into C, F, R, P under the same conditions, and further carbonized, densified, and graphitized to obtain a %composite. The density of the obtained %combo is 1.52 g/m.

Bending strength 11-3kg/m rrt, shear strength 1.0
It was 2 kg/mrri'.

(Effects of the Invention) In short, this invention provides that if the matrix front heel body thermosetting resin and C and F are not firmly adhered, the shrinkage stress of the matrix portion during carbonization does not reach C0F, and therefore C , F, which does not deteriorate or become brittle, can be skillfully used to easily obtain a carbon fiber-reinforced carbon composite material that has excellent bending strength and glabella shear strength that have not been previously available. This is a great invention.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the carbon fiber after the matrix front heel body thermosetting resin has been immersed in the present invention, and Figure 2 shows the organic polymer coated on the surface thermally decomposed and disappeared, forming donut-shaped voids around it. FIG. 1... Carbon fiber, 2... Organic polymer layer, 3...
Matrix precursor thermosetting resin, 4...Matrix carbon, 5...Void, jI 1 Even Figure 2 10. Carbon fiber co. , tangible polymer layer

Claims (1)

[Claims] 1. The surface of reinforcing carbon fibers is coated in advance with an organic polymer with no carbonization yield, then impregnated with a thermosetting resin as a matrix precursor, and then molded and carbonized. A method for manufacturing a carbon fiber reinforced carbon composite material obtained by this method. 2 The organic polymer can be coated on the carbon fiber surface in a solution state, and then solidified as a thin film on the carbon fiber surface at room temperature or by heating. 2. The method for producing a carbon fiber-reinforced carbon composite material according to claim 1, wherein the organic polymer layer does not dissolve or break during impregnation, but quickly burns out during carbonization, leaving no carbonized component. 3. The method for producing a carbon fiber reinforced carbon composite material according to claim 1, wherein the organic polymer is polyvinyl alcohol, gelatin, starch or the like. 4. The method for producing a carbon fiber-reinforced carbon composite material according to claim 1, wherein the layer thickness of the organic polymer coated on the carbon fibers is 0.1 to 3 μm.