JPH04243970A - Production of carbon/carbon composite material - Google Patents

Abstract

PURPOSE:To provide production method for obtaining carbon/carbon composite material free from crack and peeling simple in impregnation process. CONSTITUTION:A pitch based carbon fiber precursor having 1000-1000000 ratio of length/diameter and carbonaceous pitch are packed into a vacuum vessel and heated under reduced pressure to give a impregnate, which is then subjected to carbonization treatment under press or under pressure to produce the objective carbon/carbon composite material.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing carbon/carbon composite materials.

0002

[Prior Art] Carbon/carbon composite materials are materials that have unique properties such as maintaining high strength and high modulus of elasticity even at high temperatures of 1,000°C or higher, and having a small coefficient of thermal expansion. It is expected to be used for equipment parts, brakes, furnace materials, etc.

[0003] In order to composite carbon materials and carbon fibers, generally a unidirectional laminate of carbon fibers, a two-dimensional woven laminate,
A commonly used method is to impregnate reinforcing fibers such as mat-like molded product laminates, felt-like molded product laminates, three-dimensional fabrics, three-dimensional laminates, etc. with carbonaceous pitch or thermosetting resin and then carbonize them. . However, the above composite process is complex and requires a long manufacturing time.

0004

[Problems to be Solved by the Invention] One of the methods for making composites of carbon materials and carbon fibers in a simple process is to mix short carbon fibers and molten carbon pitch, and carbonize the mixture to form carbon/carbon fibers. A method of making carbon composite materials has also been attempted.

However, if carbon fibers and carbonaceous pitch are simply mixed and carbonized, the distribution of carbon fibers and pores will become non-uniform as the content of carbon fibers increases.

[0006] Furthermore, while carbonaceous pitch shrinks significantly during carbonization, carbon fiber hardly shrinks under these conditions, resulting in misalignment and cracks in the carbonized molded product. This is particularly noticeable when the length of the carbon fibers is short.

Furthermore, when carbon fibers and carbonaceous pitch are impregnated, carbonized, and molded directly under press, there is a problem that it is difficult to make the thickness of the molded product uniform.

[0008]

[Means for Solving the Problems] The present inventors have made extensive studies on a method for manufacturing a carbon/carbon composite material that solves the above problems and exhibits excellent performance through a simple manufacturing process, and as a result, the present invention has been developed. has been completed.

That is, the present invention has a length/diameter ratio of 1,
000 to 1,000,000 pitch-based pre-carbonized fibers and 10 to 95 parts by weight of carbonaceous pitch are heated under reduced pressure in a vacuum container to form an impregnated molded product, and then the impregnated molded product is heated under reduced pressure in a vacuum container. The present invention relates to a method for producing a carbon/carbon composite material, which is characterized by carbonizing a material under a press or under pressure, and further carbonizing if necessary.

[0010] The method for producing a carbon/carbon composite material according to the present invention will be described in detail below.

[0011] The pitch-based pre-carbonized fiber as used in the present invention refers to a fiber having a diameter of usually 5 to 100 μm (microns) obtained by melt-spinning carbonaceous pitch as a raw material and subjecting the resulting pitch fiber to infusibility treatment and pre-carbonization treatment. , preferably 7-3
The fiber is 0 μm.

[0012] First, the carbonaceous pitch is usually 100~
Coal-based or petroleum-based pitch having a softening point of 400°C, preferably 150 to 350°C is used. Further, as the carbonaceous pitch, either optically isotropic pitch or anisotropic pitch can be used, but optically anisotropic pitch with an optically anisotropic phase content of 60 to 100 vol% is particularly used. Preferably used.

[0013] The carbonaceous pitch is melt-spun into pitch fibers by a known method, and then subjected to infusibility treatment.

The infusibility treatment is usually carried out under an oxidizing gas atmosphere at a temperature of usually 50 to 400°C, preferably 100 to 350°C, for usually 10 minutes to 20 hours. The oxidizing gas includes air,
Examples include oxygen, nitrogen oxide, sulfur oxide, halogen, and mixtures thereof. Although the pressure of the oxidizing gas is not particularly limited, it is usually carried out at normal pressure.

[0015] Pre-carbonization treatment is carried out using Ar, He, Xe, Rn, N
2 gas, preferably in an inert gas atmosphere such as Ar gas, usually at 400 to 1,000°C, preferably at 500 to 8°C.
00℃, more preferably 550 to 700℃, usually 10
Pre-carbonization treatment is performed for 5 minutes to 5 hours to obtain pre-carbonized fibers. The pressure during the pre-carbonization treatment is not particularly limited and is usually carried out at normal pressure. If the temperature of the pre-carbonization treatment is less than 400℃, the strength as a reinforcing fiber will be insufficient, and if it exceeds 1,000℃, the resulting carbon/carbon composite material will partially deteriorate due to insufficient adhesiveness. Causes peeling.

[0016] The thus obtained pre-carbonized fiber is cut into pieces with a length/diameter ratio of 1,000 to 1,000,000, preferably 5,000 to 50,000, and more preferably It is desirable that the length of the pre-carbonized fibers is shorter than the intended molded body. If the length/diameter ratio is less than the above range, the reinforcing effect is insufficient,
Moreover, it is not preferable because the carbon/carbon composite material tends to crack during carbonization, and if it exceeds the above range, it is not preferable because the distribution of reinforcing fibers in the obtained carbon/carbon composite material is difficult to become uniform.

For example, in the case of pre-carbonized fibers having an average diameter of 10 μm, the length is from 1 to 100 cm, preferably from 1 cm to
It is 50cm. These can be used in the form of single fibers or bundles of 500 to 10,000 single fibers. These precarbonized fibers can be filled into a vacuum container, generally by gravity dropping, mechanical transfer, or other methods.

As the carbon pitch to be impregnated into the pre-carbonized fiber, basically the same pitch as the raw material for the pre-carbonized fiber can be used. In other words, coal-based or oil-based bitches are used. The carbonaceous pitch can be either an optically isotropic pitch or an anisotropic pitch, and the content of the optically anisotropic phase is 60 to 100 vol.
% optically anisotropic pitch is particularly preferably used. Further, the carbonaceous pitch can be used in any shape depending on the convenience of handling, for example, in the form of lumps, pellets, powder, or fibers.

The filling ratio of the pitch-based pre-carbonized fibers and the carbonaceous pitch is 5 to 90 parts by weight, preferably 5 to 50 parts by weight, and 10 to 95 parts by weight of the pitch-based pre-carbonized fibers.
Parts by weight, preferably 50 to 95 parts by weight. If the mixing ratio of pitch-based pre-carbonized fibers is less than the above range,
The addition effect is not sufficient, and, for example, sufficient strength is not expressed in a bending test of composite materials.

[0020] Impregnation is carried out by filling the pitch-based pre-carbonized fibers and carbonaceous pitch into a vacuum container and heating and melting them under reduced pressure. In this case, the reduced pressure is, for example, 1×10
-4 to 750 mmHg, preferably 1 x 10-2 to 30
This can be done at about 0 mmHg. The heating temperature is usually above the softening point of the carbonaceous pitch and below the decomposition start temperature, preferably at least 30°C higher than the softening point and below the decomposition start temperature, more preferably from 180 to 450°C. The carbonaceous pitch thus heated and melted is impregnated into pitch-based pre-carbonized fibers to form an impregnated molded product.

[0021] The above impregnation is usually carried out under reduced pressure,
In order to improve impregnating properties, depressurization and pressurization with an inert gas can be repeated.

[0022] The mixture after impregnation is a molded body with a low bulk density, but in order to improve this bulk density, pressing may be applied at the time of impregnation. The press pressure in this case is, for example, 0.01 to 50 kg/cm2. Note that in order to lower the viscosity of the carbonaceous pitch during impregnation, it can be diluted with a solvent, and aromatic hydrocarbons, pyridine, quinoline, etc. can be used as the solvent.

Furthermore, in the present invention, when filling the pitch-based pre-carbonized fibers and the carbonaceous pitch into a vacuum container, the pitch-based pre-carbonized fibers and the carbonaceous pitch are mixed together in order to completely impregnate them and ensure uniform dispersion of the two. It is desirable to laminate layers of alternating pitches. At this time, the thickness of each layer is selected appropriately,
It is usually desirable to have a thickness of about 1 to 200 mm. In addition, the number of laminated layers is
The number of layers can be determined as appropriate depending on the thickness of each layer and the dimensions of the intended molded product, but it is usually desirable to have 2 to 100 layers. Impregnation in this case can be performed in the same manner as above.

Further, in order to make the carbonization process described later more efficient, pressure may be applied during impregnation in order to improve the bulk density of the compact after impregnation. In this case, the press pressure is usually 0.01 to 50 kg/cm2.

[0025] In this way, an impregnated molded product is obtained.

Next, the impregnated molded product is carbonized under a press or under pressure, and if necessary, carbonized under normal pressure or under pressure.

[0027] Carbonization under the press is usually 5 to 500 kg/cm2, preferably 10 to 10 kg/cm2 by hot pressing.
Uniaxial pressure of 0 kg/cm2 is applied, usually 400 to 2,0
This is carried out by heating to 00°C, preferably 400 to 1,000°C.

Carbonization under pressure can be carried out, for example, by vacuum sealing the impregnated molded product in a closed container, and then applying carbonization to Ar, He, Xe, Rn, etc.
, N2 gas, preferably an inert gas such as Ar gas, to a pressure of usually 50 to 10,000 kg/cm2, preferably 200 to 2,000 kg/cm2, and usually 400 to 2,000°C, preferably 400 to 1 ,000
This is done by heating to ℃.

[0029] Carbonization under normal pressure is carried out under an inert gas atmosphere, usually at 400 to 3,000°C, preferably at 400 to 2,000°C.
This is done by heating to 0°C.

[0030] Carbonization can also be carried out using a HIP (hot isostatic pressing) device.

[0031] Pressure heat treatment in the HIP equipment is usually carried out using an inert gas at a pressure of 50 to 10,000 kg/cm2,
Preferably, the pressure is applied to 200 to 2,000 kg/cm2, and the temperature is usually 400 to 2,000°C, preferably 400 to 1
,000°C.

[0032] Further, after the above carbonization, further carbonization can be carried out if necessary. The conditions at this time can be selected as appropriate, but it is particularly preferable to perform the first carbonization under pressure or a press, and the subsequent carbonization under normal pressure, in order to carry out the carbonization process simply and efficiently.

[0033] In order to improve the mechanical properties of the obtained carbon/carbon composite material, further densification treatment can be performed. The densification treatment method is carried out, for example, by impregnating a carbon/carbon composite material with carbonaceous pitch, furan resin, phenol resin, etc., firing it under normal pressure or under pressure, and repeating this process as necessary.

[0034] The volume content of reinforcing fibers in the carbon/carbon composite material produced by the above method can be arbitrarily determined depending on the purpose, but is usually 5 to 75%, preferably 10 to 60%.
It is.

[0035]

[Effects of the Invention] According to the method of the present invention, a carbon/carbon composite material having high strength and uniformity can be produced by a simple process.

[0036]

[Examples] The present invention will be specifically explained with reference to Examples below, but the present invention is not limited thereto.

Example 1 Petroleum pitch having a softening point of 280° C. and an optically anisotropic phase content of 100 vol % was melt-spun.
Pitch fibers with an average diameter of 13 μm were obtained. After infusible treatment of this pitch fiber, 760 mmHg of N2 gas was added.
By firing at 00°C, pitch-based pre-carbonized fibers with a diameter of 10 microns were obtained. This pitch-based pre-carbonized fiber was made into a fiber bundle of 2,000 fibers, and the length/diameter ratio was 1.
5,000 (average).

Next, 50 parts by weight of the cut pitch-based pre-carbonized fibers and 100 parts by weight of powdered petroleum pitch having a softening point of 280° C. and an optically anisotropic phase content of 100 vol% were filled into a vacuum container. This was then reduced in pressure to 1 x 10-2 mmHg and heated to 350°C to be impregnated for 2 hours to obtain an impregnated molded product.

[0039] Subsequently, the impregnated molded product was uniaxially pressurized to 12.5 kg/cm2 with a hot press, heated to 500°C, and further held at 1,000°C for 1 hour in argon gas at normal pressure. Carbonization treatment was performed to obtain a carbon/carbon composite material.

The obtained carbon/carbon composite material had a uniform thickness, and no cracks or delaminations were observed.

Comparative Example 1 The pitch-based pre-carbonized fibers obtained in Example 1 were made into a fiber bundle of 2,000 pieces, and the length/diameter ratio was 900 (average).
It was cut so that

Next, 50 parts by weight of the cut pitch-based pre-carbonized fibers and 100 parts by weight of powdered petroleum pitch having a softening point of 280° C. and an optically anisotropic phase content of 100 vol% were filled into a vacuum container. This was then reduced in pressure to 1 x 10-2 mmHg and heated to 350°C to be impregnated for 2 hours to obtain an impregnated molded product.

[0043] Subsequently, the impregnated molded product was uniaxially pressurized to 12.5 kg/cm2 with a hot press, heated to 500°C, and further held at 1,000°C for 1 hour in argon gas at normal pressure. Carbonization treatment was performed to obtain a carbon/carbon composite material.

[0044] Several cracks with a length of about 1 to 5 cm were observed on the surface of the obtained carbon/carbon composite material.

Comparative Example 2 Softening point: 280°C, optically anisotropic phase content: 100 vol
% petroleum pitch was melt-spun to obtain pitch fibers with an average diameter of 13 μm. The pitch fibers were treated to be infusible and then fired at 2,000° C. in argon gas at a pressure of 760 mmHg to obtain pitch-based carbon fibers with a diameter of 10 microns. This pitch-based carbon fiber was made into a fiber bundle of 2,000 fibers, and the length/diameter ratio was 15,000 (
Average).

Next, 50 parts by weight of cut pitch-based carbonized fibers and a fiber having a softening point of 280° C. and an optically anisotropic phase content of 1
100 parts by weight of powdered petroleum pitch of 00 vol% was filled into a vacuum container, and the pressure was reduced to 1 x 10-2 mmHg, and the mixture was heated to 350°C to be impregnated for 2 hours to obtain an impregnated molded product.

[0047] Subsequently, the impregnated molded product was uniaxially pressurized to 12.5 kg/cm2 with a hot press, heated to 500°C, and further held at 1,000°C for 1 hour in argon gas at normal pressure. Carbonization treatment was performed to obtain a carbon/carbon composite material.

When the cross section of the obtained carbon/carbon composite material was observed, delamination was observed in several places.

Comparative Example 3 The pitch-based precarbonized fibers obtained in Example 1 were made into a fiber bundle of 2,000 pieces, and the length/diameter ratio was 15,000 (
Average).

Next, 50 parts by weight of the cut pitch-based pre-carbonized fibers and 100 parts by weight of powdered petroleum pitch having a softening point of 280° C. and an optically anisotropic phase content of 100 vol% were placed in a hot press container. Filled and hot pressed 12.5k
A carbon/carbon composite material was obtained by applying uniaxial pressure to g/cm2, heating to 500°C, and then holding at 1,000°C for 1 hour in argon gas at normal pressure for carbonization.

The obtained carbon/carbon composite material had a mixture of high and low fiber content areas, and when the thickness was measured, unevenness of approximately ±10% was observed overall.

Example 2 Softening point: 280°C, optically anisotropic phase content: 100 vol
% petroleum pitch was melt-spun to obtain pitch fibers with an average diameter of 13 μm. This pitch fiber was treated to be infusible and then fired at 800° C. in N2 gas at a pressure of 760 mmHg to obtain a pitch-based pre-carbonized fiber having a diameter of 10 microns. This pitch-based pre-carbonized fiber is made into a fiber bundle of 2,000 fibers, and the length/diameter ratio is 15,000 (average).
It was cut into pieces, and 50 parts by weight was filled in a vacuum container in a layered manner. On top of this pitch-based pre-carbonized fiber layer, a softening point of 28
120 parts by weight of powdered petroleum pitch having an optically anisotropic phase content of 100 vol % at 0° C. was filled in a layered manner. Thereafter, in the same manner, layers of pitch-based pre-carbonized fibers and layers of pelleted petroleum-based pitch were alternately filled to a total of 8 layers.

Next, the pressure in the vacuum container was reduced to 1×10 −2 mmHg, and the mixture was heated to 350° C. and impregnated for 3 hours.
It was made into an impregnated molded product.

[0054] Subsequently, the impregnated molded product was uniaxially pressurized to 15.0 kg/cm2 with a hot press, heated to 450°C, and further held at 1,000°C for 1 hour in argon gas at normal pressure. Carbonization treatment was performed to obtain a carbon/carbon composite material.

The obtained carbon/carbon composite material had a uniform thickness, and no cracks or delaminations were observed.

Example 3 Softening point: 280°C, optically anisotropic phase content: 100 vol
% petroleum pitch was melt-spun to obtain pitch fibers with an average diameter of 13 μm. After infusible treatment of this pitch fiber,
A pitch-based pre-carbonized fiber with a diameter of 10 microns was obtained by firing at 500° C. in N2 gas at a pressure of 760 mmHg. This pitch-based pre-carbonized fiber is made into a fiber bundle of 4,000 fibers, and the length/diameter ratio is 2,000 (average).
It was cut into pieces, and 50 parts by weight was filled in a vacuum container in a layered manner. On top of this pitch-based pre-carbonized fiber layer, a softening point of 28
150 parts by weight of powdered petroleum pitch having an optically anisotropic phase content of 100 vol % at 0° C. was filled in a layered manner. Thereafter, in the same manner, layers of pitch-based pre-carbonized fibers and layers of pelleted petroleum-based pitch were alternately filled to a total of 8 layers.

Next, the pressure in the vacuum container was reduced to 1 x 10-2 mmHg, and the mixture was heated to 350°C and impregnated for 3 hours.
It was made into an impregnated molded product.

[0058] Subsequently, the impregnated molded product was uniaxially pressurized to 15.0 kg/cm2 with a hot press, heated to 500°C, and further held at 2,000°C for 1 hour in argon gas at normal pressure. Carbonization treatment was performed to obtain a carbon/carbon composite material.

The obtained carbon/carbon composite material had a uniform thickness, and no cracks or delaminations were observed.

Example 4 Softening point: 280°C, optically anisotropic phase content: 100 vol
% petroleum pitch was melt-spun to obtain pitch fibers with an average diameter of 13 μm. After infusible treatment of this pitch fiber,
A pitch-based pre-carbonized fiber with a diameter of 10 microns was obtained by firing at 650° C. in N2 gas at a pressure of 760 mmHg. This pitch-based pre-carbonized fiber was made into 2,000 fiber bundles, which were further cut to have a length/diameter ratio of 30,000 (average), and filled in a vacuum container in a layered manner at 50 parts by weight. Softening point 2 on top of this pitch-based pre-carbonized fiber layer
120 parts by weight of powdered petroleum pitch having an optically anisotropic phase content of 100 vol % at 80° C. was filled in a layered manner. Thereafter, in the same manner, layers of pitch-based pre-carbonized fibers and layers of pelleted petroleum-based pitch were alternately filled to a total of 8 layers.

[0061] The pressure in the vacuum container was reduced to 1 x 10-2 mmHg, and the mixture was heated to 350°C and impregnated for 3 hours to obtain an impregnated molded product.

[0062] Subsequently, the impregnated molded product was uniaxially pressurized to 15.0 kg/cm2 with a hot press, heated to 500°C, and further held at 2,300°C for 1 hour in argon gas at normal pressure. Carbonization treatment was performed to obtain a carbon/carbon composite material.

The obtained carbon/carbon composite material had a uniform thickness and was completely free of cracks and delamination.

Claims (3)

[Claims] [Claim 1] The length/diameter ratio is 1,000 to 1,0.
00,000 pitch-based pre-carbonized fiber and 10 to 95 parts by weight of carbonaceous pitch are heated under reduced pressure in a vacuum container to form an impregnated molded product, and then the impregnated molded product is pressed. Alternatively, a method for producing a carbon/carbon composite material characterized by carbonization under pressure. [Claim 2] The length/diameter ratio is 1,000 to 1,0.
00,000 pitch-based pre-carbonized fibers and 10-95 parts by weight of carbonaceous pitch are alternately laminated in layers in a vacuum container, and heated under reduced pressure to convert the carbonaceous pitch into pitch-based carbonized fibers. A method for producing a carbon/carbon composite material, which comprises impregnating pre-carbonized fibers to form an impregnated molded product, and then carbonizing the impregnated molded product under a press or under pressure. 3. A method for producing a carbon/carbon composite material, which comprises further carbonizing the carbon/carbon composite material obtained by the production method according to claim 1 or 2.