JPH055218A - Production of carbon fiber having high strand strength - Google Patents

Abstract

PURPOSE:To produce the subject carbon fibers having excellent openability by melt-spinning a pitch, collecting the spun fibers, subjecting the collected pitch fibers to an infusibilization treatment and further to a carbonization treatment, and subsequently subjecting the infusibilized fibers or carbonized fibers to a thermal treatment in a prescribed temperature range under an atmosphere containing steam. CONSTITUTION:A method for producing the objective carbon fibers 1 by melt- spinning a pitch, collecting the spun fibers, subjecting the collected fibers to an infusibilization treatment, subjecting the infusibilized fibers to a carbonization treatment and, if necessary, further subjecting the carbonized fibers to a graphitization treatment is characterized by subjecting the infusibilized fibers or the carbonized fibers to a thermal treatment at 1000-1800 deg.C under a steam- containing atmosphere.

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 pitch-based carbon fiber, and more particularly to a method for producing carbon fiber having high strand strength.

[0002]

2. Description of the Related Art Carbon fiber is a material having a high specific strength and a high specific elastic modulus, and has attracted attention as a filler fiber for high performance composite materials. Currently, PAN-based carbon fibers made from polyacrylonitrile (PAN) and pitch-based carbon fibers made from pitches are manufactured as carbon fibers, but PAN-based carbon fibers are more widely used because they were generally preceded by development. Used as a high-strength, high-elasticity, high-performance carbon fiber, mainly PA
At present, N-based carbon fibers are being used with various modifications.

However, the PAN-based carbon fiber has a limit in further increasing the elasticity, and the PAN as the raw material is expensive, and the yield of the carbon fiber per raw material is low. ing. Therefore, in recent years, various studies have been conducted to improve the characteristics of pitch-based carbon fibers, which have higher elasticity and are expected to be used in a wider range of applications.

In order to improve the characteristics of pitch-based carbon fibers, instead of the isotropic pitch conventionally used as a spinning raw material, the raw material pitch is heat-treated to develop a molecular species that develops anisotropy and is easily oriented. Since the method of using the formed pitch, so-called mesophase pitch (Japanese Patent Publication No. Sho 49-8634), has been proposed, it is mainly carried out by adjusting the properties of the spinning pitch.

For example, in JP-A-49-19127, a raw material pitch is heat-treated in an inert gas atmosphere to form highly oriented mesophases, and a pitch containing 40 to 90% by weight of the mesophases. Has been proposed as a spinning pitch. However, since it takes a long time to mesomorphize the isotropic raw material pitch by such a method,
Japanese Unexamined Patent Publication No. 54-160427 proposes a method in which the raw material pitch is previously treated with a sufficient amount of a solvent to perform mesomorphization in a short time. That is, the raw material pitch is treated with a solvent such as benzene and toluene to obtain the insoluble matter,
7. It is heat-treated at a temperature of 230 to 400 ° C. for a short time of 10 minutes or less, so that it is highly oriented and the optically anisotropic portion is 7.
A method has been proposed in which so-called neo-mesophases having a quinoline-insoluble content of 5% by weight or more and 25% by weight or less are formed, and such neo-mesophases are used as a spinning pitch.

The spinning pitch thus obtained is melt-spun to obtain pitch fibers, which are then infusibilized, carbonized or further graphitized to produce high-strength, high-elasticity and other high-performance carbon fibers. It By the way, the carbon fiber thus obtained is usually impregnated with a matrix resin such as an epoxy resin, a polyamide resin, or a phenol resin to form a so-called prepreg, which is molded by various molding methods, and is used as a fiber-reinforced plastic for leisure / sports or , Used as various industrial materials. Therefore, in order to develop the mechanical properties of the carbon fiber reinforced plastic,
It is important for each carbon fiber to have good mechanical properties such as high strength and high elasticity, and at the same time, the carbon fiber should be well dispersed in the matrix resin and the mechanical properties of the carbon fiber itself should be sufficiently exhibited. It becomes a factor.

In other words, no matter how large the strength or elastic modulus of carbon fiber is, if the dispersion of the carbon fiber in the matrix resin is poor, the mechanical function of the carbon fiber reinforced plastic will be insufficient. That is. Therefore, first, regarding the dispersibility in the matrix resin, it is necessary that the single fibers of the carbon fibers used are not fused to each other, that is, the carbon fibers must be sufficiently defibrated.

That is, the infusibilized fiber (hereinafter simply referred to as infusible fiber) and the carbonized or graphitized fiber (hereinafter simply referred to as carbon fiber) in the pitch-based carbon fiber manufacturing step are the same as those in the previous step. Due to the sizing agent, sizing agent, and other oiling agents used in the above, and due to the thermal alteration of the fibers themselves in each process, the single fibers fuse together, resulting in uneven quality, and inconsistent dispersion of the single fibers in the matrix resin. Since it becomes uniform and the homogeneity of the composite material is impaired, it must be defibrated in a supple and non-fusion state at any stage of infusibilization, carbonization or graphitization.

Conventionally, as a method for defibrating infusible fibers or carbon fibers, a method of subjecting the fibers to turbulence, a bending method of passing through a guide such as a bar, a wire or a rotating pin while bending zigzag, a convex shape A method of contacting a curved surface of a roll having a curved surface (JP-A-55-57015),
A method of contacting the inclined surfaces of two or more taper rollers (Japanese Patent Laid-Open No. 61-124645), a method of defibrating in a fluid (Japanese Patent Laid-Open No. 57-89638), and the like have been proposed. In addition, a method of treating the surface of carbon fiber or infusibilized fiber with a gas containing oxygen or the like to defibrate or improve the strength of carbon fiber (Japanese Patent Laid-Open No. 61-215716, Japanese Patent Laid-Open No. 63-215716). Japanese Patent No. 665523, JP-A-63-1
No. 75122) is known. All of these achieve the purpose by treating the carbon fiber in an inert gas containing oxygen and slightly etching the surface.

[0010]

However, the conventional method, for example, the mechanical defibration method is insufficient in the defibration effect in spite of the high equipment cost, and the anodic oxidation is a device for increasing the surface area. In addition to complicated operations and small surface area improvement, there are problems such as waste liquid treatment. In addition, even if carbon fiber or graphite fiber carbonized at high temperature in an inert atmosphere is heat-treated in an atmosphere containing an oxygen-containing inert gas, the surface of the fiber is already stabilized and becomes inactive. The effect of improvement is not large, and in reality, oxygen gas reacts with carbon fiber with a large amount of heat generation, so it is difficult to control the reaction, and the peroxidation reaction progresses in some filaments, making it sufficiently satisfactory. It has been difficult to obtain carbon fibers with high strand strength to be achieved.

[0011]

The inventors of the present invention have made extensive studies as to a method for defibrating pitch-based carbon fibers and improving the strand strength. As a result, surprisingly, the infusible fibers or carbon fibers were steamed. We have found an epoch-making method in which carbon fibers with high strand strength and good defibration property can be produced by heat treatment in an atmosphere containing them.

Further, the carbon fiber thus obtained is subjected to secondary carbonization in an inert atmosphere at a temperature higher than the above-mentioned primary carbonization temperature to freely control the strength and elastic modulus of the fiber according to the purpose of use. The present invention has been completed by finding that the above can be achieved. That is, an object of the present invention is to provide a method for producing a carbon fiber having good defibration property and high strand strength, and yet another object of the present invention is the strength of the fiber,
Another object of the present invention is to provide a method for producing a carbon fiber having a high strand strength, the elastic modulus of which can be freely controlled. Another object of the present invention is to provide strength of the single fiber itself, particularly JIS R-76.
The purpose of the present invention is to provide a method for producing a high-strand-strength carbon fiber that expresses a resin-impregnated strand strength comparable to the strength of the single fiber itself, which is obtained according to 01-1986, 6.6.1. Spinning, infusibilizing the pitch fiber obtained by bundling, to obtain infusibilized fiber, then carbonized, further in the method of producing a carbon fiber by graphitizing treatment, infusible fiber or Carbon fiber in a steam-containing atmosphere at a temperature of over 1,000 ° C.
It is easily solved by a method for producing a high-strand-strength carbon fiber, which is characterized by performing a heat treatment at 800 ° C. or lower.

The present invention will be described in detail below. The spinning pitch for obtaining the carbon fiber used in the present invention is not particularly limited as long as the molecular species that are easily oriented are formed and it gives an optically anisotropic carbon fiber. Various conventional types can be used. Examples of the carbonaceous raw material for obtaining these spinning pitches include, for example, coal-based coal tar, coal tar pitch, coal liquefaction, petroleum-based heavy oil, tar, pitch, or polymerization reaction produced by catalytic reaction of naphthalene or anthracene. Things etc. are mentioned.
Free carbon, unmelted coal,
Impurities such as ash and catalyst are contained, but it is desirable to remove these impurities in advance by a known method such as filtration, centrifugation, or stationary sedimentation separation using a solvent.

Further, the carbonaceous raw material is pretreated by, for example, a method of subjecting the carbonaceous material to heat treatment and then extracting a soluble component with a specific solvent, or a method of hydrogenating in the presence of a hydrogen-donating solvent and hydrogen gas. You may have done. In the present invention, a carbonaceous raw material having an optically anisotropic structure of 40% or more, preferably 70% or more, more preferably 90% or more is suitable. If necessary, the carbonaceous raw material is usually 350 to 500 ° C., preferably 380 to 450 ° C.
2 minutes to 50 hours, preferably 5 minutes to 5 hours, nitrogen,
The heat treatment may be performed in an atmosphere of an inert gas such as argon or water vapor, or while blowing.

The ratio of the optically anisotropic structure of the pitch in the present invention is a value obtained as the area ratio of the portion showing the optical anisotropy in the pitch sample under a polarization microscope at room temperature. Specifically, for example, a pitch sample crushed into several mm square is embedded with a sample piece on almost the entire surface of a resin having a diameter of 2 cm according to a conventional method, and after polishing the surface, the entire surface is covered with a polarizing microscope (100 magnification). ), And the ratio of the area of the optically anisotropic portion to the total surface area of the sample is measured.

Carbon fibers are obtained by melt spinning, bundling, infusibilizing and carbonizing in the usual manner using the above spinning pitch. The carbonization treatment is usually performed for 10 seconds or longer and 6 hours or shorter, preferably 1 second or longer in a temperature range of 400 ° C. or higher and 1,800 ° C. or lower, preferably 400 ° C. or higher and 1,400 ° C. or lower in an atmosphere of an inert gas such as nitrogen or argon. It is carried out in the range of minutes to 2 hours.

Further, the absolute value of the strength of carbon fiber may be insufficient depending on the application. Therefore, when it is desired to obtain a carbon fiber having higher mechanical properties such as strength and elastic modulus than the carbon fiber obtained by the above-mentioned method, after the heat treatment described above, the carbonization is further performed in an inert atmosphere. The object can be achieved by subjecting the fibers to secondary carbonization treatment or graphitization treatment at a temperature higher than the temperature.

The temperature of the secondary carbonization treatment or graphitization treatment may be determined depending on the required mechanical properties such as strength and elastic modulus, but it is important that the temperature is higher than that of the primary carbonization treatment. That is, when the temperature of the secondary carbonization treatment or the graphitization treatment is equal to or lower than the temperature of the primary carbonization treatment, the secondary carbonization treatment or the graphitization treatment hardly contributes to the improvement of the mechanical properties of the carbon fiber.

The secondary carbonization treatment or graphitization treatment temperature is 80
0-3,000 degreeC is preferable. If the temperature is less than 800 ° C, the mechanical properties of the fiber are not improved so much, and if the temperature exceeds 3,000 ° C, the effect of improving the mechanical properties due to the temperature becomes considerably gradual in spite of the large heat source cost, which is industrially advantageous. It cannot be said that. In the present invention, such infusible fiber or carbon fiber, then under a steam atmosphere or nitrogen gas,
In an atmosphere of a mixed gas of an inert gas such as argon gas and water vapor, it is usually 0.1 seconds in a temperature range of more than 1,000 ° C and less than 1,800 ° C, preferably more than 1,050 ° C and less than 1,400 ° C. The heat treatment is performed for 24 hours or less and preferably for 1 second to 6 hours. The water vapor concentration is usually 100 ppm to 100 vol%, preferably 1,000 ppm to 100 vol%.

The water vapor concentration in the present invention largely depends on the treatment temperature and the treatment time. For example, when the treatment is carried out for a long time or at a high temperature, it is preferable to carry out the treatment with a low water vapor concentration, and the treatment at a short time or at a low temperature. In that case, it is preferable to increase the water vapor concentration. Considering the effect of the present invention that the defibration property is good and the fiber exhibits high strength both as a fiber alone and as a resin-impregnated strand, the industrially most preferable treatment condition is 1,050 ° C. or higher and 1,400.
C. or lower, 5 seconds or longer and 90 minutes or shorter, and concentration is 3000 ppm or higher and 60 vol% or lower.

The secondary carbonization treatment or graphitization treatment is carried out if necessary for the purpose of improving the mechanical properties of the carbon fiber. Does not inhibit the effect of fibrillation and strand strength improvement of the carbon fiber obtained by the heat treatment of the water vapor-containing atmosphere, after the heat treatment of the water vapor-containing atmosphere, the above-mentioned secondary carbonization treatment or graphitization treatment, the surface It is also possible to perform processing and the like. As described above, by heat-treating the infusible fiber or the carbon fiber at a temperature of more than 1,000 ° C. and not more than 1,8,000 ° C. in a steam-containing atmosphere, defibration of the fiber and a significant improvement in strand strength are achieved. .. Further, according to the method of the present invention, the fibers are defibrated, the dispersibility of each single fiber in the matrix resin is improved, and not only the strand strength is improved, but also the single fiber strength seen in each single fiber unit is improved. This also includes the effect that the steam gas removes the surface defects caused by fusion between the single fibers by etching.

Even in the prior art, attempts to remove surface defects and the like by etching have been made as described above, but all of them were methods involving a large amount of heat generation such as oxygen gas. The steam gas used in the present invention shows a particularly great effect when the reaction between carbon atoms on the surface of the carbon fiber and steam is an endothermic reaction or a slight exothermic reaction at a temperature of more than 1,000 ° C. and not more than 18,000 ° C. Therefore, it is considered that the treatment can be performed without causing the strength deterioration due to the peroxidation or the like.

[0023]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples as long as the gist of the present invention is not exceeded.

Example 1 A spinning pitch having a softening point of 300 ° C. and an optical anisotropy ratio of 95% observed under a polarizing microscope was prepared from coal tar pitch. This has a nozzle diameter of 0.1 mm and a hole count of 4,000.
Using a spinneret of 0, melt spinning at a spinneret temperature of 330 ° C.,
A silicon-based oil agent was attached to the obtained pitch fibers having a thread diameter of 12 μm and bundled. This pitch fiber is 30 at 310 ℃
The infusible fiber was obtained by heat-treating in air for 1 minute. Further, this infusible fiber was carbonized in nitrogen gas at 545 ° C. to obtain a carbon fiber. This carbon fiber is steamed with 8,40
Heat treatment was performed in a continuous heating furnace maintained in a nitrogen gas atmosphere containing 0 ppm under conditions of 1,200 ° C. and a residence time of 20 minutes.

The carbon fiber thus obtained is impregnated into the epoxy resin of the matrix without fusion of the fibers,
When the cross section of the carbon fiber with respect to the longitudinal direction is dried and cured at 130 ° C. for 30 minutes and observed with a microscope, the single fiber 1 is uniformly dispersed in the epoxy resin matrix 2 as shown in FIG. showed that.

The physical properties of single fiber and resin-impregnated strand of the obtained fiber were measured by the method of JIS R-7601. The results were as follows. Single fiber physical properties Tensile strength 330 kgf / mm ² Tensile elastic modulus 19 tonf / mm ² Resin impregnated strand physical properties Tensile strength 300 kgf / mm ² Tensile elastic modulus 21 tonf / mm ²

Example 2 Example 1 was repeated except that the residence time at 1,200 ° C. in a nitrogen gas atmosphere containing 8,400 ppm of water vapor was 30 minutes. Various properties of the obtained fiber are shown in Example 1.
The results measured in the same manner as in Table 1 are shown in Table 1.

Example 3 Approximately 50 m of carbon fiber carbonized at 545 ° C. was charged into a batch type heating furnace and heat treated in nitrogen gas containing 8,000 ppm of steam at 1,200 ° C. for a residence time of 60 minutes. It carried out like Example 1. Various properties of the obtained fiber were measured in the same manner as in Example 1 and the results are shown in Table 1.

Example 4 The water vapor concentration in nitrogen was set to 12 vol% and 1,200
The same procedure as in Example 1 was carried out except that the temperature was 30 ° C. and the residence time was 30 seconds. Various properties of the obtained fiber were measured in the same manner as in Example 1 and the results are shown in Table 1.

Example 5 The carbon fiber tow obtained in Example 3 was further graphitized in argon gas at 2,150 ° C. for a residence time of 0.5 minutes. Various properties of the obtained fiber were measured in the same manner as in Example 1 and the results are shown in Table 1.

Example 6 Water vapor concentration in nitrogen was set to 49 vol% and 1,200
The same procedure as in Example 1 was carried out except that the temperature was 10 ° C. and the residence time was 10 seconds. Various properties of the obtained fiber were measured in the same manner as in Example 1 and the results are shown in Table 1.

Example 7 The carbon fiber tow obtained in Example 5 was further graphitized in argon gas at 2,500 ° C. for a residence time of 1 minute. Various properties of the obtained fiber were measured in the same manner as in Example 1 and the results are shown in Table 1.

Example 8 The infusible fiber used in Example 1 was steamed at 8,400 pp.
m, nitrogen gas atmosphere, 1,200 ℃ residence time 30
Heat treatment was performed under the condition of minutes. Various properties of the obtained fiber were measured in the same manner as in Example 1 and the results are shown in Table 1.

Comparative Example 1 A carbon fiber tow obtained in the same manner as in Example 1 except that the heat treatment temperature was 850 ° C. in a nitrogen gas atmosphere containing 8,400 ppm of steam was further subjected to a nitrogen gas atmosphere. The heat treatment was performed under the conditions of medium temperature of 1,200 ° C. and residence time of 20 minutes. Various properties of the obtained fiber were measured in the same manner as in Example 1, and the results are shown in Table 1 and FIG.

Comparative Example 2 A carbon fiber tow obtained in the same manner as in Example 1 except that the water vapor concentration in nitrogen gas was 49 vol%, the heat treatment temperature was 850 ° C., and the residence time was 3 minutes. Further, heat treatment was performed in a nitrogen gas atmosphere at 1,200 ° C. for a residence time of 20 minutes. Various properties of the obtained fiber were measured in the same manner as in Example 1 and the results are shown in Table 1.

Comparative Example 3 The procedure of Example 1 was repeated, except that nitrogen gas was used as the atmosphere gas for the heat treatment at 1,200 ° C. Various characteristics of the obtained fiber were measured in the same manner as in Example 1, and the results are
The results are shown in the table and FIG. As is clear from Table 1 and FIG. 2, this carbon fiber was poorly dispersed in the epoxy resin matrix and had low strand strength.

Comparative Example 4 The same procedure as in Example 1 was carried out except that the atmosphere for the heat treatment at 1,200 ° C. was nitrogen gas containing 400 ppm of oxygen gas. Various properties of the obtained fiber were measured in the same manner as in Example 1 and the results are shown in Table 1.

[0038]

[Table 1]

[0039]

Industrial Applicability According to the present invention, it is possible to provide a method for producing a high-strand-strength carbon fiber having good defibration property and high-strand strength, and exhibiting resin-impregnated strand strength comparable to that of the single fiber itself.

[Brief description of drawings]

FIG. 1 is a schematic view of a field of view of a cross section of carbon fiber observed by an optical microscope.

FIG. 2 is a schematic view of a field of view of a cross section of carbon fiber observed by an optical microscope.

FIG. 3 is a schematic view of a field of view of a cross section of carbon fiber observed by an optical microscope.

[Explanation of symbols]

 1 carbon monofilament 2 matrix resin

Claims (1)

Claim: What is claimed is: 1. Pitch fibers obtained by melt-spinning pitch and bundling the fibers are infusibilized to obtain infusibilized fibers, then carbonized, and optionally graphitized. In the method for producing a carbon fiber according to the above method, the infusible fiber or the carbon fiber is heated to more than 1,000 ° C. in an atmosphere containing water vapor to exceed 1,80
A method for producing a high-strand-strength carbon fiber, which comprises performing heat treatment at 0 ° C. or lower. 2. The method for producing carbon fiber according to claim 1, wherein the temperature of the heat treatment in the atmosphere containing water vapor is 1,050 ° C. or higher and 1,400 ° C. or lower. 3. The method for producing carbon fiber according to claim 2, wherein the heat treatment time in the atmosphere containing water vapor is 0.1 seconds or more and 24 hours or less. 4. The method for producing carbon fiber according to claim 1, further comprising carbonizing or graphitizing the infusible fiber or the carbon fiber heat-treated in a steam atmosphere.