JPH0663136B2 - Pitch-based carbon fiber manufacturing method - 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 a point, have been variously 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 layering and orienting planar polymeric aromatic hydrocarbons produced by the thermal polycondensation reaction of a carbonaceous raw material, and is regarded as a precursor of the graphite final 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, a so-called neomesophase pitch is formed, which 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 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.

The present inventors have paid attention to the above-mentioned problems, and have studied intensively,
It was found that the above drawbacks can be overcome by passing the spinning pitch through the shearing material layer before feeding the spinning pitch to the spinning nozzle, and the proposal was made earlier (Japanese Patent Application No. 59-131641). It is thought that if the spinning pitch that has passed through the shear layer is held in the molten state for a long period of time, the fluidized units of the refined spinning pitch will be re-united, and the state before passing through the shear layer will be restored. Therefore, the time required for the spinning pitch to reach the spinning nozzle after passing through the shearing material layer is within 30 minutes, preferably 20
It was proposed that it is preferable to place the shearing material layer so that the time is within a minute, more preferably within 10 minutes and as short as possible.

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

Therefore, in order to obtain carbon fibers with excellent characteristics, it is preferable to provide a shearing material layer, that is, a filling layer directly above the nozzle portion, but in the case of a multi-hole spinneret, the filling material is homogeneous in each hole. If it is difficult to insert it uniformly, and if it is not possible to insert it uniformly, the difference in the composition of each hole filled with the packing layer causes the fluctuation of the flow rate of the spinning pitch discharged from each spinning nozzle, and the unevenness of the fineness (spinning nozzle from each spinning nozzle is caused. There is a drawback that results in a distribution of the diameter of the fibers that are dispensed.

[Means for solving problems]

Therefore, as a result of further studies by the present inventors, as a filler, a metal material or an inorganic material having a coral tree-like structure having a particle diameter within a very limited range of 2 to 3 times the diameter of the spinning nozzle hole is used. When using powder, it was found that the distribution of fiber diameters spun from each hole was extremely small, and the present invention was reached based on this finding.

That is, an object of the present invention is to stably produce a Pitch-based carbon fiber in which the generation of wedge-shaped cracks extending in the fiber axis direction is suppressed without the fiber cross-sectional structure being substantially in a radial orientation. Become.

That is, the purpose is to melt-spin a spinning pitch from a spinning nozzle, perform infusibilization treatment, then carbonize it, and then, if necessary, graphitize it to produce a pitched carbon fiber. A powder having a coral tree-like structure made of a metal material or an inorganic material having a particle diameter of 2 to 3 times the diameter of the spinning nozzle hole is filled as a filling layer immediately above the nozzle, and the spinning pitch is filled with the powder. It is easily achieved by circulating and spinning the layers and the spinning nozzles.

Hereinafter, in order to explain the present invention 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. Various conventional types 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 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,
40% or more obtained by heat treatment under an inert gas atmosphere such as nitrogen or argon, or under blowing,
In particular, a pitch containing 70% or more of optically anisotropic structure can be preferably used as a spinning pitch.

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 with a diameter of about 2 cm according to the usual method, and after polishing the surface, the entire surface is covered all over. It is determined by observing under a polarizing microscope (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 crush layer and then supplied to the spinning nozzle for spinning.

Here, the packed bed is one that is filled in the spinning pitch flow passage and immediately above the spinning nozzle, and the flow of the spinning pitch is subdivided by passing the molten spinning pitch through the layer. And the mesophases of the spinning pitch are disturbed while passing through the layer, resulting in a pitch fiber having a fiber cross-section that is not substantially radially oriented. As the filler constituting the filling layer, specifically, a metal material such as stainless steel, copper, or aluminum, which can sufficiently withstand a temperature of about 350 to 400 ° C., or a ceramic, glass, or an inorganic material such as graphite. It is a powder having a coral tree-like structure, and its particle size is 2-3 times the diameter of the spinning nozzle described later. Regardless of whether the filler particle size is smaller or larger than this range, the diameter distribution of the fibers spun from each hole is not uniform, and yarn breakage frequently occurs during spinning, and the desired fiber cannot be stably obtained. .

Here, it is an enlarged view of the vicinity of the spinning nozzle portion in various forms of the spinning device provided with the filling layer of the present invention in FIGS. 1 to 4. 1 is a spinneret, 2 is a spinning nozzle, 3 is an inlet, and 4 is a packed layer. The thickness of the filling layer 4 is preferably thick from the viewpoint of the effect on the crystal orientation described later, but in order to bring out the effect, it is sufficient if the number of particles is about 5 when it is installed directly above the nozzle portion. However, if it is unnecessarily thick, the distribution resistance of the pitch becomes large and the cost of the equipment becomes high. Therefore, the thickness of the packed bed is at most 20.
mm. Of course, it is desirable to make the thickness of the filling layer filling each hole as uniform as possible. The spinning nozzle used in the present invention has a pore size of 0.05 to 0.5 mm and a length of 0.01.
It is preferable to select from the range of ~ 5 mm, but the shape is not particularly limited, a straight tubular shape, a shape in which the intermediate portion of the spinning nozzle is enlarged, or a shape in which the lower portion of the spinning nozzle is enlarged. Spinning nozzles of any shape, such as those described above, can be used.

In addition, the melted spinning pitch is discharged from the spinning nozzle 2 through the filling layer 4 and spun. When the spinning layer is discharged by providing the filling layer 4, the spinning pitch is at least 2 kg / cm ² · G or more, preferably Is 5 kg / cm ² · G or more,
More preferably, it is necessary to apply a pressure of 10 kg / cm ² · G or more to perform spinning.

[Work]

In the present invention, the melted spinning pitch passes through the packing layer 4 to subdivide the flow of the spinning pitch, and the stacked state of the mesophases is disturbed in the packing layer 4.
It is considered that the Pitch fibers having a substantially non-radial orientation in the fiber cross-sectional structure and further the Pitch-based carbon fibers can be obtained.

Further, in the present invention, by using a packing layer having a particle diameter limited to 2 to 3 times the diameter of the spinning nozzle portion, the pressure loss for each hole is most uniform, and spinning is performed using a multi-hole nozzle. In doing so, the distribution of the diameter of the fibers spun from each hole becomes small, and the spinning is performed stably.

[Effect of the present invention]

Therefore, the fluidity of the spinning pitch is improved by the packed bed 4, and the generation of gas or bubbles generated from the spinning pitch at the spinning temperature is suppressed by the pressurizing operation within the above range during spinning. Furthermore, since the holes with a small outflow amount are reduced, spinning stability is improved, and pitch fibers having improved characteristics can be stably manufactured 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. It is possible to obtain a Pitch-based carbon fiber having a small fineness unevenness.

Here, the onion-like orientation means that the main portion of the fiber cross-sectional area has concentric molecular orientation, and
In particular, the outer peripheral portion includes those having a radial orientation such that cracking does not occur due to the subsequent carbonization or graphitization treatment. 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.

The coefficient of variation in the examples is a value calculated using the following formula.

x = individual measured value = arithmetic average value of individual measured values n = number of samples Example 1 A reactor of 60 was mixed with coal tar pit and an equal amount of hydrogenated aromatic oil at a rate of 50 / hr. And processed. At this time, the temperature of the reactor was 450 ° C. After passing the reaction solution obtained from this reactor, it was distilled under reduced pressure to recover the aromatic oil and obtain a residual pitch. Then, the residual pitch was heat-treated at 430 ° C. for 125 minutes while bubbling nitrogen gas to obtain a mesophase pitch. The anisotropy ratio of the obtained mesophase pitch was 100%.

Next, a spinneret having 120 holes of spinning nozzles (hole diameter 0.1 mm, length 0.1 mm of spinning nozzle 2) as shown in FIG. 1 was used, and a size of 60-65 mesh (0.208
~ 0.246 mm) and a metal powder made of stainless steel in the shape of a coral tree, which had been sieved, was filled to a thickness of about 10 mm.

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 a diameter of 10 μm 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 carbonized fibers. The tensile strength and fineness unevenness of this carbon fiber were measured, and the results are shown in Table 1.

Comparative Example 1 The size of the filling layer is 100 to 150 mesh (0.104 to 0.147).
mm) was spun in exactly the same manner as in Example 1 except that the sieved coral-like metal powder was charged, but the homogeneity of the outflow rate from each hole was inferior, and the nozzle with a small flow rate caused a stable It was difficult to spin.

[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; Introduction hole, 4; Packing layer

Claims (4)

[Claims] 1. A spinning pitch is melt-spun from a spinning nozzle,
In a method for producing a Pitch-based carbon fiber by performing infusibilization treatment, then carbonization treatment, and further graphitization treatment if necessary, in the upstream portion of the spinning nozzle, the diameter is 2 to 3 times the diameter of the spinning nozzle hole. A metal material or an inorganic material having a particle diameter of a packing layer made of a powder having a coral tree-like structure, and the spinning pitch is circulated through the packing layer and the spinning nozzle in this order for spinning. -Based carbon fiber manufacturing method. 2. The method for producing a pitch-based carbon fiber according to claim 1, wherein the spinning pitch is a pitch having an optical anisotropy of 40% or more. 3. The method for producing a pitch-based carbon fiber according to claim 1, wherein the diameter of the spinning nozzle hole is 0.05 to 0.5 mm. 4. The method for producing a pitch-based carbon fiber according to claim 1, wherein the spinning pitch is melt-spun under a pressure of ² kg / cm ² · G or more.