JPH0811844B2 - Method for producing 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.

[Prior Art] Carbon fiber is a material with a high specific strength and high inelastic modulus, and has received the most attention as a filler fiber for high-performance composite materials. Above all, pitch-based carbon fibers are abundant in the raw materials, It has various advantages over polyacrylonitrile-based carbon fibers, such as large retention and easy production of fibers with high elastic modulus.

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

That is, instead of the isotropic pitch conventionally used as the spinning pitch, by heating the carbonaceous raw material, anisotropy develops, by using a pitch in which molecular species that are easily oriented are formed, Since it was reported that a high-performance pitch-based carbon fiber can be obtained (Japanese Patent Publication No. Sho 49-8634), various studies have been made on the preparation of a spinning pitch having good orientation.

As is well known, heating carbonaceous raw materials such as heavy oil, tar, and pitch to 350 to 500 ° C causes optical anisotropy under polarized light with particle diameters of several microns to several hundreds of microns in these substances. The globules shown are generated. 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, heat treatment of petroleum pitch at about 350 to 450 ° C. under static conditions to obtain a pitch containing 40 to 90% by weight of mesophase. A method of using this as a spinning pitch has been proposed (JP-A-49-19127).

However, since it takes a long time to mesomorphize an isotropic carbon raw material by such a method, the carbonaceous raw material is previously treated with a sufficient amount of a solvent to obtain its insoluble matter, which is then heated at 230 to 400 ° C.
At a temperature of 10 minutes or less, it is heat-treated for a short time to form a so-called neomefaze pitch that is highly oriented and has an optically anisotropic portion of 75% by weight or more and a quinoline insoluble content of 25% by weight or less. A method of using this as a spinning pitch has been proposed (JP-A-54-160427).

In addition, as a spinning pitch with good orientation for producing high-performance carbon fibers, for example, an optical pitch obtained by hydrogenating coal tar pitch in the presence of tetrahydroquinoline and then heat-treating at about 450 ° C for a short time Pitch which is isotropic and has a property of being anisotropically changed by heating to 600 ° C. or more, that is, a so-called premesophase pitch (Japanese Patent Laid-Open No. 58-18
No. 421), or a pitch obtained by hydrogenating a mesophase pitch by a Birch reduction method or the like and showing orientation in that direction when an external force is applied with optical isotropy, a so-called dormant mesophase. (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-based high-performance carbon fiber can be obtained by infusibilizing, carbonizing, and optionally graphitizing the pitch fiber.

[Problems to be solved by the invention]

By 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 pitch fiber obtained is likely 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 problems, and as a result of diligent studies, they found that the above drawbacks were overcome by passing the spinning pitch through the mesh layer before supplying the spinning pitch, 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 the spinning pitch from a spinning nozzle, subject it to infusibilization treatment, then carbonize it, and, if necessary, graphitize it to produce a pitch-based carbon fiber. As a pitch containing 70% or more of an optically anisotropic structure, a thickness of 2 mm or less at the spinning nozzle side end of the spinning pitch introducing hole in the upstream portion from the inlet of the spinning nozzle through the space. Using a spinneret in which the angle from the space to the inlet of the spinning nozzle is 90 ° or more, the time required to reach the spinning nozzle after passing the spinning pitch is 1
It is easily achieved by circulating the mesh layer and the spinning nozzle in that order within a minute, and spinning.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The spinning pitch of the present invention is not particularly limited as long as a molecular species that is easily oriented is formed and it gives an optically anisotropic pitch, as described above. Various conventional ones can be used.

However, amorphous pitch can be used when a high specific strength and a high specific elastic modulus are not required. Examples of the carbonaceous raw material for obtaining these spinning 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, for example, a method of extracting a soluble component with a specific solvent after heat treatment, or a method of hydrogenation in the presence of a hydrogen-donating solvent or hydrogen gas, a preliminary treatment. You may leave it.

In the present invention, the carbonaceous raw material or the pretreated carbonaceous raw material is usually 350 to 500 ° C., preferably
At 380 to 450 ° C. for 2 minutes to 50 hours, preferably 5 minutes to 5 hours under an atmosphere of an inert gas such as nitrogen or argon, or
A pitch containing 40% or more, particularly 70% or more of an optically anisotropic structure obtained by heat treatment under blowing can be suitably used as a spinning pitch.

The optically anisotropic structure ratio of the spinning pitch in the present invention is,
It is a value obtained as an area ratio of a portion showing optical anisotropy in a 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 a resin having a diameter of about 2 cm according to a conventional method, the surface is polished, and then 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 mesh layer and then supplied to the spinning nozzle for spinning.

Here, the mesh layer means a layer disposed in the spinning pitch flow passage and upstream of the spinning nozzle, and the spinning pitch in the molten state passes through the layer to subdivide the spinning pitch flow. And the laminated state of the spinning pitch mesophases is disturbed while passing through the layer, and as a result, a pitch fiber having a fiber cross-sectional structure which is not substantially radially oriented is provided. As the net that constitutes the mesh layer, specifically, a metal material such as stainless steel, copper, or aluminum, or a fine particle of an inorganic material such as ceramic, glass, or graphite, which can sufficiently withstand a temperature of about 350 to 400 ° C. It is a plain weave, a twill weave, or a tatami weave of such fibers.

Further, a metal flat plate punched with innumerable small holes, or a so-called expanded metal obtained by putting a slit on a metal plate with a molding tool and pulling it, is also used in the present invention.

If the mesh size is too large, the effect of subdividing the cross-sectional structure of the obtained fiber into a structure not having a radial orientation is reduced, so the mesh size is preferably as small as possible.
Specifically, the mesh size is smaller than 50 mesh, preferably smaller than 100 mesh, more preferably 200.
Those smaller than mesh are used. These nets are 1
Although the number of sheets may be one, it is possible to stack up to five sheets, but the thickness of the mesh layer is configured to be 2 mm or less.

Here, FIGS. 1 to 4 are enlarged views showing the vicinity of the spinning nozzle portion in various forms of the spinning apparatus provided with the mesh layer of the present invention. 1 is a spinneret, 2 is a spinning nozzle, 3
Is a mesh layer, 4 is an introduction hole, and 5 is a space.

As shown in these figures, the mesh layer 3 is installed above the nozzle inlet, but if the spinning pitch that has passed through the mesh layer 3 is held in a molten state for a long time, the flow of the refined spinning pitch is reduced. Since it is considered that the units are united again and return to the state before passing through the mesh layer 3, the time required for the spinning pitch to reach the spinning nozzle after passing through the mesh layer 3 is within 1 minute, preferably within 30 seconds, and further preferably Is preferably installed via the space 5 of the mesh layer 3 so that the time is as short as possible within 10 seconds.

Here, the time required for the spinning pitch to reach the spinning nozzle after passing through the mesh layer 3 is from the lower end of the mesh layer 3 to the upper end of the inlet of the spinning nozzle, that is, the inner volume of the space 5 divided by the discharge amount of the spinning pitch.

The shape of the space portion 5 can be various shapes as shown in FIGS. 1 to 5, but the angle θ of the portion from the space portion 5 to the inlet of the spinning nozzle 2, that is,
When the angle θ formed by the space portion 5 and the joining portion of the inlet of the spinning nozzle 2 is set to 90 ° or more, preferably 120 ° or more, the cross-sectional structure of the obtained fiber is subdivided into a non-radial orientation structure. This is preferable because the effect of doing so is further increased. The joint between the space 5 and the inlet of the spinning nozzle 2 may have a curved portion so that the angle θ does not become less than 90 °.

The shape of the spinning nozzle is not particularly limited, but for example, a spinning nozzle having a hole diameter of 0.05 to 0.5 mm and a length of 0.01 to 5 mm is used.

The spinning nozzle means a fine hole portion that flows immediately before the spinning pitch is spun and defines a yarn diameter, and the hole diameter means a diameter of a fine hole that discharges the spinning pitch. The spinning nozzle used in the present invention has any shape such as a straight tubular shape satisfying the conditions in the above range, a shape in which the middle portion of the spinning nozzle is enlarged, or a shape in which the lower portion of the spinning nozzle is enlarged. The spinning nozzle of can also be used.

The spinning pitch is discharged from the spinning nozzle 2 through the mesh layer 3 and spun. When the spinning pitch is discharged by providing the mesh layer 3, the spinning pitch is usually 0.5 kg / cm ² ·.
The spinning can be performed by applying a pressure of G or more, preferably 2 kg / cm ² · G or more.

[Work]

In the present invention, the molten spinning pitch is the mesh layer 3
By subdividing the flow of the spinning pitch,
Moreover, it is considered that the layered state of the mesophases is disturbed in the mesh layer 3 and pitch fibers and thus pitch-based carbon fibers whose fiber cross-sectional structure is not substantially radially oriented are obtained.

[Effect of the present invention]

Therefore, the network layer 3 improves the fluidity of the spinning pitch, and the pressurizing operation within the above range during spinning suppresses the generation of gas or bubbles generated from the spinning pitch at the spinning temperature. Improved stability,
Pitch fibers having improved properties can be stably manufactured for a long time.

Thus, the obtained pitch fiber is made infusible, carbonized by graphitizing as necessary, has a randomly oriented fiber cross-sectional structure, does not have a wedge-shaped crack extending in the fiber axis direction, high-performance pitch-based carbon Fibers can be obtained.

These fiber cross-sectional structures were measured by a polarization microscope.

〔Example〕

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

Examples 1 to 5 2 kg of coal tar pitch and 2 kg of hydrogenated aromatic oil were placed in an autoclave and heat-treated at 450 ° C. for 1 hour. This treated product was distilled under reduced pressure to obtain a residual pitch. Next, 200 g of this residual pitch was heat-treated at 430 ° C. for 125 minutes while bubbling nitrogen gas. The anisotropic ratio of the obtained mesophase pitch was 100%.

Next, using a spinneret as shown in FIG. 1, the size shown in Table 1 in the introduction hole 4 (500 mesh (thickness 0.06 mm) in Examples 1 and 2 and 200 mesh (thickness in Example 3 0.1
mm)) stainless steel wire mesh (mesh layer) 3 was provided.

The installation position of the wire net is the time until the spinning pitch reaches the spinning nozzle 2 after passing through the mesh layer 3, that is, the residence time in the space is the first.
The values shown in the table were used.

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

Pitch fiber obtained by melt spinning at 336 ℃ is made infusible at 310 ℃ in air, and further 1400 ℃ under argon atmosphere.
Was carbonized to obtain carbon fiber. The tensile strength and cross-sectional structure of this carbon fiber were measured, and the results are shown in Table 1.

Example 4 A spinneret as shown in FIG.
2 mm, flow 0.1 mm), and a stainless mesh of 200 mesh (thickness 0.1 mm) as a mesh layer 3 is installed in the introduction hole 4 at a position where the residence time of the pitch in the space 5 is 3.8 seconds. Spinning and carbonization were carried out in the same manner as in Example 1 except for the above. In spinning, pitch fibers having a yarn diameter of up to 7 μm could be stably obtained for a long time. The results obtained are shown in Table 1.

Example 5 A spinneret as shown in FIG.
1 mm, length 0.1 mm), and a stainless steel wire mesh of 635 mesh (thickness 0.05 mm) as a mesh layer 3 in the introduction hole 4 at a position where the residence time of the pitch in the space 5 is 0.2 seconds. Spinning and carbonization were performed in the same manner as in Example 1 except that the installation was performed. In spinning, pitch fibers having a yarn diameter of up to 7 μm could be stably obtained for a long time. The results obtained are shown in Table 1.

Comparative Example 1 Spinning was performed in the same manner as in Example 1 except that the mesh layer was not used, but pitch fibers having a yarn diameter of 7 μ or less could not be stably obtained. Table 1 shows the physical property values of the carbon fibers obtained in the same manner as in Example 1.

[Brief description of drawings]

1 to 5 are schematic enlarged sectional views of the vicinity of the spinneret in various aspects of the spinning apparatus used in the present invention. 1; Spinneret, 2; Spinning nozzle 3; Mesh layer, 4; Introduction hole 5; Space

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeki Tomano 1000 Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa Sanryo Kasei Co., Ltd. (56) Kai 59-168113 (JP, A) JP 61-12919 (JP, A)

Claims (4)

[Claims] 1. A spinning pitch is melt-spun from a spinning nozzle.
A pitch containing 70% or more of optically anisotropic structure is used as a spinning pitch in a method of producing a pitch-based carbon fiber by performing infusibilization treatment, then carbonization treatment, and further graphitization treatment if necessary. A mesh layer having a thickness of 2 mm or less is provided at an end of the spinning nozzle from the inlet of the spinning nozzle through a space and at the end of the spinning pitch introducing hole on the side of the spinning nozzle, and from the space to the inlet of the spinning nozzle. Using a spinneret having an angle of 90 ° or more, the mesh layer and the spinning nozzle are arranged in this order so that the time required for the spinning pitch to reach the spinning nozzle after passing through the mesh layer is within 1 minute. A method for producing a pitch-based carbon fiber, which comprises circulating and spinning. 2. The method for producing a pitch-based carbon fiber according to claim 1, wherein the mesh layer has a mesh size smaller than 100 mesh. 3. The method for producing a pitch-based carbon fiber according to claim 1, wherein the mesh layer is a metal material or an inorganic material. 4. The method for producing a pitch-based carbon fiber according to claim 1, wherein the mesh is a plain weave, a twill weave, or a tatami weave.