JPH0788604B2 - Method for manufacturing pitch-based carbon fiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a Pitch-based carbon fiber, and more specifically, to stably produce a Pitch-based carbon fiber exhibiting improved strength. It is about the method.

[Conventional technology]

Carbon fiber is a material with a high specific strength and a high specific elastic modulus, and has received the most attention as a filler fiber for high-performance composite materials. Among them, Pitch-based carbon fiber has abundant raw materials and has a high yield in the carbonization process. It has various advantages over polyacrylonitrile-based carbon fiber, which has a high elastic modulus.

By the way, various spinning pitches, which are raw materials of the pitch-based carbon fiber having such advantages, have been studied.

That is, instead of the isotropic pitch that has been conventionally used as a spinning pitch, a carbonaceous raw material is heat-treated to develop anisotropy, and by using a pitch having a molecular species that is easily oriented, Since it was reported that a high-performance pitch-based carbon fiber could be obtained (Japanese Patent Publication No. Sho 49-8634), various studies have been conducted on the preparation of a spinning pitch having good orientation.

As is well known, carbonaceous raw materials such as heavy oil, tar and pitch are used.
When heated to 350 to 500 ° C., small spheres having a particle size of several microns to several hundreds of microns and exhibiting optical anisotropy under polarized light are formed in the materials. Then, upon further heating, these small spheres grow and coalesce, and finally the whole becomes a state exhibiting optical anisotropy. This anisotropic structure is formed by stacking and orienting planar polymeric aromatic hydrocarbons produced by a thermal polycondensation reaction of a carbonaceous raw material in layers, and is regarded as a precursor of a graphite crystal structure.

A heat-treated product containing such an anisotropic structure is generally called a mesophase pitch.

As a method of using such a mesophase pitch as a spinning pitch, for example, a petroleum-based pitch may be used under a standing condition.
A method has been proposed in which heat treatment is performed at 350 to 450 ° C. to obtain a pitch containing 40 to 90% by weight of mesophase, which is used as a spinning pitch (JP-A-49-19127).

However, since it takes a long time to mesomorphize an isotropic carbonaceous raw material by such a method, the carbonaceous raw material is previously treated with a sufficient amount of a solvent to obtain an insoluble matter thereof, which is heated at 230 to 400 ° C. By heat treatment at a temperature of 10 minutes or less for a short period of time, it is highly oriented, the optically anisotropic portion is 75% by weight or more, and the quinoline insoluble content is 25% by weight or less, so-called neomefaze pitch is formed. A method using this as a spinning pitch has been proposed (Japanese Patent Laid-Open No. 54-160427).

In addition, as a spinning pitch having good orientation for producing high-characteristic carbon fibers, for example, an optical fiber obtained by hydrogenating coal tar pitch in the presence of tetrahydroquinoline, and then heating at about 450 ° C. for a short time is used. Isotropic and has a property of changing anisotropically by being heated to 600 ° C. or more, that is, a so-called premesophase pitch (Japanese Patent Laid-Open No. 58-1842).
No. 1), or a so-called dormant mesophase, which is obtained by hydrogenating a mesophase pitch by the Birch reduction method or the like and shows orientation in that direction when an external force is applied with optical isotropy. (JP-A-57-100186) and the like have been proposed.

Pitch fibers can be obtained by melt spinning such a spinning pitch through a nozzle. Then, the Pitch-type high-performance carbon fiber can be obtained by infusibilizing, carbonizing, and optionally graphitizing the Pitch-type fiber.

[Problems to be solved by the invention]

According to the conventional method, when spinning is performed using a spinning pitch having good orientation as described above, the laminated structure of the planar polymer hydrocarbon in the obtained pitch fiber tends to have radial orientation in the fiber cross section, and as a result, Subsequent infusibilization treatment, since tensile stress due to carbonization shrinkage during carbonization acts in the circumferential direction of the fiber cross section, a wedge-shaped crack extending in the fiber axis direction occurs in the cross section of the obtained carbon fiber, There was a drawback that impaired the commercial value of carbon fiber.

[Means for solving problems]

The present inventors have paid attention to the above-mentioned problems, and as a result of earnest study,
It has been found that the above drawbacks can be overcome by passing a particular layer of shear material before feeding the spinning pitch to the spinning nozzle and based on this finding the present invention has been reached.

That is, an object of the present invention is to produce a pitch-based carbon fiber in which the fiber cross-sectional structure is not substantially in the radial orientation and the generation of wedge-shaped cracks extending in the fiber axis direction is suppressed.

That is, the purpose is to melt-spin a spinning pitch containing an optically anisotropic layer of 70% or more from a spinning nozzle, perform infusibilization treatment, then carbonize it, and, if necessary, graphitize it to obtain a pitch-based carbon. In the method for producing fibers, a nonwoven fabric or woven fabric of fine fibers of a metal material, or a shearing material layer composed of a filler composed of fine particles having sharp protrusions is provided in the upstream portion of the spinning nozzle, It can be easily achieved by circulating a spinning pitch in the order of the shearing material layer and the spinning nozzle and spinning.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. As the spinning pitch of the present invention, a molecular species that is easily oriented is formed, and there is no particular limitation as long as it gives an optically anisotropic pitch, and as described above. Various conventional ones can be used.

However, if a high specific strength and a high specific elastic modulus are not required, an amorphous aspitch can be used. Examples of the carbonaceous raw material for obtaining these spinning-type pitches include coal-based coal tar, coal tar pitch, coal liquefaction, petroleum heavy oil, tar, and pitch. These carbonaceous raw materials usually contain impurities such as free carbon, unmelted coal and ash,
It is desirable to remove these impurities in advance by a known method such as filtration, centrifugation, or static sedimentation using a solvent.

Further, the carbonaceous raw material can be pretreated by, for example, a method in which soluble components are extracted with a specific solvent after heat treatment, or a method in which hydrogenation is performed in the presence of a hydrogen donating solvent or hydrogen gas. You can leave it.

In the present invention, the carbonaceous raw material or the pretreated carbonaceous raw material is usually 350 to 500 ° C., preferably 38
At 0 to 450 ° C. for 2 minutes to 50 hours, preferably 5 minutes to 5 hours,
Pitches having an optically anisotropic structure of 70% or more, which are obtained by heat treatment under an atmosphere of an inert gas such as nitrogen or argon or under blowing, can be suitably used as spinning pitches.

The optically anisotropic structure ratio of the spinning pitch in the present invention is a value obtained as the area ratio of the portion showing the optical anisotropy in the spinning pitch sample under a polarization microscope at room temperature.

Specifically, for example, a Pitch sample crushed into a few mm square is embedded with a sample piece on almost the entire surface of the resin having a diameter of about 2 cm according to a conventional method, and after polishing the surface, the entire surface is covered with a polarizing microscope. It is obtained by observing under (100 magnification) and measuring the ratio of the area of the optically anisotropic portion to the total surface area of the sample.

In the present invention, the spinning pitch is passed through the shearing material layer and then supplied to the spinning nozzle for spinning.

Here, the shearing material layer means in the spinning pitch flow passage,
It is disposed upstream of the spinning system nozzle, and the molten spinning pitch passes through this layer to subdivide the flow of the spinning pitch, and shear applied to the spinning pitch while passing through the layer. The force controls the laminated state of the mesophases, and as a result, a pitch fiber having a fiber cross-sectional structure which is not substantially radially oriented is provided. As the filler constituting the shearing material layer, specifically, such that it can sufficiently withstand a temperature of about 350 to 400 ° C., stainless steel, copper, a non-woven fabric or a woven fabric of fine fibers of a metal material such as aluminum,
Alternatively, a fine particle having a plurality of sharp protrusions is used. For example, when a powdery or granular filler is used, fine particles having a sharp protrusion such as a coral tree (see FIG. 5) or a cornpeito shape ( Those shown in FIG. 6) are preferable. In particular, it passes through a 10-mesh sieve, but does not pass through a 325-mesh sieve, preferably it passes through a 50-mesh sieve.
Most preferably, a metal powder having a particle size that does not pass through a 100 mesh sieve is called a coral tree-like metal powder.

Here, FIGS. 1 to 4 are enlarged views of the vicinity of the spinning nozzle portion in various forms of the spinning apparatus provided with the shearing material layer of the present invention. 1 is a spinneret, 2 is a spinning nozzle,
3 is a wire mesh for supporting the shearing material layer, 4 is an introduction hole, 5
Indicates a shear material layer and 6 indicates a space portion.

As shown in these figures, the shearing material layer 5 is installed in the introduction hole 4 or the space 6 at the upstream portion thereof depending on the shape of the spinning nozzle and the shape of the shearing material filling material. When the passed spinning pitch is held in a molten state for a long time, it is considered that the fluidized units of the miniaturized spinning pitch are united again, and the state before passing through the shearing material layer 5 is restored, so that the spinning pitching of the spinning pitching material is suppressed. It is preferable to install the shearing material layer 5 so that the time required to reach the spinning nozzle after passing through the layer 5 is within 30 minutes, preferably within 20 minutes, and more preferably within 10 minutes.

Here, the time required for the spinning pitch to reach the spinning nozzle after passing through the shearing material layer 5 is the inner volume from the lower end of the shearing material layer 5 to the upper end of the inlet of the spinning nozzle divided by the discharge amount of the spinning pitch.

The thickness of the shearing material layer 5 varies depending on the type and shape of the shearing material, but a thicker one is preferable and a smaller grain size is more preferable. However, if it is too thick, the flow resistance of the spinning pitch becomes large, and if it is too thin, the desired effect cannot be obtained, so it is usually selected from the range of 3 to 300 mm, preferably 5 to 200 mm.

The shape of the spinning nozzle is It is desirable to use one having a value of 400 or less, preferably 300 or less. When it is more than the above range, the shearing force applied to the spinning pitch becomes large, and the cross-sectional structure of the obtained pitch fiber becomes radial orientation, which is not preferable.

The spinning nozzle means a fine pore portion that flows immediately before spinning the spinning pitch and defines the yarn diameter, and the pore diameter means the diameter of the fine pore from which the spinning pitch is discharged. The spinning nozzle used in the present invention is not particularly limited as long as it satisfies the conditions in the above range, and it has a straight tubular shape, a shape in which the intermediate portion of the spinning nozzle is enlarged, or a lower portion of the spinning nozzle is enlarged. Spinning nozzles of any shape, such as curved shapes, can be used.

Further, the melted spinning pitch supplied to the space portion 6 is discharged from the spinning nozzle 2 through the shearing material layer 5 and spun. At the time of discharging the spinning pitch by providing the shearing material layer 5, at least the spinning pitch is discharged to the spinning pitch. 2kg / cm ² · G or more, preferably 5kg / cm ² · G or more, more preferably 10 kg / cm ² ·
It is necessary to apply a pressure of G or more to perform spinning.

[Work]

In the present invention, when the melted spinning pitch passes through the shearing material layer 5, the flow of the spinning pitch is subdivided, and the shearing force in the shearing material layer 5 disturbs the laminated state of the mesophases, resulting in a fiber cross-section structure. It is considered that pitch fibers which are not substantially radially oriented and thus pitch carbon fibers can be obtained.

[Effect of the present invention]

Therefore, the shearing material layer 5 improves the fluidity of the spinning pitch, and the pressurizing operation in the above range during spinning suppresses the generation of gas or bubbles generated from the spinning pitch at the spinning temperature. Spinning stability is improved, and pitch fibers having improved properties can be stably produced for a long time.

Thus, the obtained pitch fibers are made infusible, and carbonized by graphitization if necessary, to have a fiber cross-section structure of random orientation or onion-like orientation, without a wedge-shaped crack extending in the fiber axis direction, and high characteristics. The Pitch-based carbon fiber can be obtained.

Here, the onion-like orientation means that the main portion of the fiber cross-sectional area has a concentric molecular orientation, and a part, especially the outer peripheral portion, has a radial orientation such that cracking does not occur due to subsequent carbonization or graphitization treatment. Including that.
Moreover, these fiber cross-sectional structures were measured with a polarization microscope.

〔Example〕

 The present invention will be specifically described below with reference to examples.

Example 1 5 An autoclave was charged with 2 kg of coal tar pitches and 2 kg of hydrogenated aromatic oil, and heat-treated at 450 ° C. for 1 hour.
This treated product was distilled under reduced pressure to obtain a residual pitch. Then
While bubbling nitrogen gas to 200 g of this residual pitch, 43
Heat treatment was performed at 0 ° C. for 125 minutes. The anisotropy ratio of the obtained mesophase pitch was 100%.

Next, using a spinneret as shown in FIG. 1 (hole diameter of spinning nozzle 2 is 0.3 mm, length is 0.6 mm), a stainless mesh 3 of 300 mesh is provided in the introduction hole 4, and shearing is performed above the mesh 3. About 50 ~ 100 mesh size sieve layer 5 is made of stainless steel metal powder in the shape of coral tree.
Filled to a thickness of 10 mm. The installation position of the wire net 3 was such that the time required for the spinning pitch to reach the spinning nozzle 2 after passing through the shearing material layer 5 was the value shown in Table 1.

Next, using the spinneret, the mesophase pitch was melt-spun in the temperature range of 325 to 360 ° C. In either case, it was possible to stably obtain pitch fibers up to 7 μm in diameter for a long time by changing the winding speed of the yarn at the optimum temperature.

Pitch fibers obtained by melt spinning at 336 ° C were infusibilized in air at 310 ° C, and carbonized at 1400 ° C in an argon atmosphere to obtain carbon fibers. The tensile strength and cross-sectional structure of this carbon fiber were measured, and the results are shown in Table 1.

Comparative Example 1 Pitch fibers having a yarn diameter of 9 μm or less could not be stably obtained by spinning in exactly the same manner as in Example 1 except that the shearing material layer was not used. Table 1 shows the physical property values of the carbon fibers obtained in the same manner as in Example 1.

Example 2 Spinneret as shown in FIG. 2 (pore diameter of spinning nozzle 2 is 0.3 m
m, length 0.6 mm), the space 6 formed above the spinneret 1 when the spinneret 1 is set in the spinning device,
Perforation diameter of the shearing material layer 5 is 40 μm and air permeability is 6.4 / cm ^2.
The non-woven fabric of stainless fine fibers of min was filled to a thickness of 10 mm, and the same mesophase pitch as in Example 1 was melt-spun at 336 ° C. By changing the winding speed of the thread, the thread diameter becomes 7
Pitch fibers up to μm could be stably obtained over a long period of time.

The obtained pitch fibers having a yarn diameter of 9 μm were treated in the same manner as in Example 1 to obtain carbon fibers. The tensile strength of the obtained fiber is
The cross-sectional structure was 280 kg / mm ² , and all were random structures.

[Brief description of drawings]

1 to 4 are schematic enlarged cross-sectional views of the vicinity of the spinneret in various aspects of the spinning device used in the present invention. 5 and 6 are enlarged schematic views of an example of the shearing material used in the present invention. 1; Spinneret, 2; Spinning nozzle 3; Wire mesh, 4; Introduction hole 5; Shear material layer, 6; Space part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuyoshi Takakura 1 2447 Fujita, Hachimansai-ku, Kitakyushu, Fukuoka Prefecture Mitsubishi Kasei Kogyo Co., Ltd. Kurosaki Plant (56) Reference JP-A-59-88909 (JP, A) JP-A-59-168113 (JP, A)

Claims (5)

[Claims] 1. A pitch-based carbon obtained by melt-spinning a spinning pitch containing 70% or more of an optically anisotropic phase from a spinning nozzle, infusibilizing treatment, then carbonizing treatment, and if necessary, graphitizing treatment. In the method for producing fibers, a nonwoven fabric or woven fabric of fine fibers of a metal material, or a shearing material layer composed of a filler made of fine particles having sharp protrusions is provided in the upstream portion of the spinning nozzle, A method for producing a pitch-based carbon fiber, characterized in that a spinning pitch is circulated in the shearing material layer and the spinning nozzle in this order for spinning. 2. The method for producing a pitch-based carbon fiber according to claim 1, wherein the filler is a metal powder having a coral tree-like structure. 3. The method for producing a pitch-based carbon fiber according to claim 1, wherein the time required for the spinning pitch to reach the spinning nozzle after passing through the shearing material layer is within 30 minutes. . 4. The method for producing a pitch-based carbon fiber according to claim 1, wherein the spinning nozzle has (spinning nozzle length) / (spinning nozzle hole diameter) ⁴ ≤400. 5. The method for producing a pitch-based carbon fiber according to claim 1, wherein melt spinning is performed under a pressure of ² kg / cm ² · G or more.