JPS61186520A - Production of pitch carbon yarn - Google Patents

Abstract

PURPOSE:To obtain the titled yarn having high strength stably while suppressing occurrence of wedge-shaped cracks in the fiber axis direction, by setting a packed layer consisting of a spherical filler in the upper stream of spinning nozzle, making spinning pitch flow through the packing layer and the spinning nozzle in this order, and spinning the pitch. CONSTITUTION:In subjecting spinning pitch to melt spinning from a spinning nozzle, the packed layer 5 consisting of a spherical filler (e.g., glass beads) is set through the wire cloth 3, etc on the upper stream part of the spinning nozzle 2 of the spinneret 1, the spinning pitch is made to flow the packed layer 5 and the spinning nozzle 2 in this order,and spun. Then it is made infusible, further carbonized, and, if necessary, graphitized, to give the aimed carbon yarn. The particle diameters of the spherical filler is preferably in a range from a size not to pass 325 meshes sieve to a size to pass 10 meshes sieve.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing pitch-based carbon fiber, and more specifically, a method for stably producing pitch-based carbon fiber that exhibits improved strength. It's about how to do it.

[Conventional technology]

Carbon fiber is a material with high specific strength and specific modulus, and is attracting 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. Equipolyac IJ O with high fiber elastic modulus
It has various advantages compared to Nido-U carbon fiber.

Incidentally, various types of spinning pitch, which is a raw material for pitch-based carbon fibers having such advantages, have been studied.

In other words, instead of the isotropic pitch conventionally used as spinning pitch, by heat-treating the carbonaceous raw material and using pitch in which anisotropy develops and molecular species that are easily oriented are formed, Since it was reported that pitch-based carbon fibers with high properties could be obtained (Tokuko Akihirota ftJl/-),
Various studies have been made regarding the preparation of spinning pitch with good orientation.

As is well known, when carbonaceous raw materials such as heavy oil, tar, pitch, etc. are heated to JIO-100°C, optical anisotropy occurs under polarized light, with particle sizes ranging from several microns to several hundred microns. The spherules shown are produced. When the material is further heated, these small spheres grow and coalesce, and finally the entire material exhibits optical anisotropy. This anisotropic structure is composed of planar polymeric aromatic hydrocarbons produced by thermal polycondensation reactions of carbonaceous raw materials, stacked and oriented in layers, and is considered to be a precursor of graphite crystal structure.

A heat-treated product containing such an anisotropic structure is generally called a meso-7Aze pitch.

As a method of using such meso7Aze pitch as a spinning pitch, for example, petroleum pitch is mixed with about 310-Hiroze pitch under static conditions. A method has been proposed in which a pitch containing mesophase of ≠θ~013% is obtained by heat treatment at 0°C, and this is used as a spinning pitch (Japanese Patent Application Laid-open No.
issue).

However, it takes a long time to mentize an isotropic carbonaceous raw material by such a method, so the carbonaceous raw material is treated in advance with a sufficiently careful solvent to obtain its insoluble content, and the
i at a temperature of 0°C.

After being heat-treated for a short time of less than 1 minute, it is highly oriented, has an optically anisotropic portion of 7j weight f% or more, and has a quinoline soluble content of 2! A method has been proposed in which a so-called neomets needs pitch with a weight i% or less is formed and this is used as a spinning pitch (% Kaisho!
Hiro-/60 Hiro 27).

In addition, as a spinning pitch with good orientation for producing high-performance carbon fibers, for example, coal tar pitch is hydrogenated in the presence of tetrahydroquinoline and then heated at about 4110°C.
It is optically isotropic and too
Pitch that has the property of becoming anisotropic when heated above ℃, so-called pre-mesophase pitch (JP-A-1
1-11172/), or a pitch obtained by hydrogenating men 7A pitch by Birch reduction method etc., which is optically isotropic and shows orientation in that direction when an external force is applied, so-called dormantments. AIDS (Unexamined Japanese Patent Publication No. 7-
/DO/No. 16) etc. have been proposed.

Pitch fibers can be obtained by melt-spinning such spinning pitch through a nozzle. Next, by making the pitch fiber infusible, carbonizing it, and optionally graphitizing it, a pitch-based carbon fiber with high properties can be obtained.

[Problem that the invention seeks to solve]

When spinning using a spinning pitch with good orientation as described above by the conventional method, the layered structure of planar polymeric hydrocarbons in the resulting pitch fiber tends to be radially oriented within the fiber cross section, and as a result, During the subsequent infusibility treatment and carbonization treatment, tensile stress caused by carbonization shrinkage acts in the circumferential direction of the fiber cross section, so wedge-shaped cracks extending in the fiber axis direction occur in the cross section of the obtained carbon fiber. There were drawbacks that diminished the commercial value of carbon fiber.

[Means for solving problems]

The inventors of the present invention took note of the above problems and as a result of intensive study,
It has been found that the above drawbacks can be overcome by passing the spinning pitch through a packed bed made of spherical filler before feeding it to the spinning nozzle, and based on this knowledge, the present invention has been achieved.

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 radially oriented and the generation of wedge-shaped cracks extending in the fiber axis direction is suppressed.

That is, this purpose is to produce a pitch-based carbon fiber by melt-spinning spinning pitch from a spinning nozzle, performing an infusibility treatment, followed by a carbonization treatment, and further graphitizing treatment if necessary. This can be easily achieved by providing a packed layer made of spherical filler upstream of the nozzle, allowing the spinning pitch to flow through the packed layer and the spinning nozzle, and spinning.

In the following, the present invention will be described in detail.The spinning pitch of the present invention is not particularly limited as long as it forms a molecular species that is easily oriented and provides an optically anisotropic pitch. A variety of conventional ones can be used, such as.

However, if high specific strength and specific modulus are not required, amorphous pitch can also be used. Examples of carbonaceous raw materials for obtaining these spinning pitches include coal-based coal tar, coal tar pitch, coal liquefaction, petroleum-based heavy oil, tar, and pitch. These carbonaceous feedstocks usually contain impurities such as carbon, undissolved coal, and ash, which can be removed by well-known methods such as filtration, centrifugation, or static sedimentation using solvents. It is desirable to remove it in advance using a method.

Further, the carbonaceous raw material is pre-treated by, for example, heat-treated and then extracted with a specific solvent, or hydrogenated in the presence of a hydrogen-donating solvent or hydrogen gas. In the present invention, the carbonaceous raw material or the pretreated carbonaceous raw material is heated at a temperature of usually 330 to 200°C, preferably 3ro to 200°C for 2 minutes! An optically anisotropic structure of UO% or more, especially 10% or more obtained by heat treatment for θ time, preferably j minutes to j hours, in an inert gas atmosphere such as nitrogen or argon, or while blowing. The pitch containing the above can be suitably used as the spinning pitch.

The optically anisotropic texture ratio of a spinning pitch as used in the present invention is a value determined as the area ratio of a portion exhibiting optical anisotropy in a spinning pitch sample under a polarizing microscope at room temperature.

Specifically, for example, a pitch sample is crushed into several square pieces, and the sample piece is embedded into almost the entire surface of a resin with a diameter of about 2 mm using a conventional method. After polishing the surface, the entire surface is thoroughly inspected using a polarizing microscope ( It is determined by observing under a magnification of 100 times) and measuring the ratio of the area of the optically anisotropic portion to the total surface area of the sample.

In the final stage, the spinning pitch is passed through a packed layer made of spherical fillers and then supplied to a spinning nozzle for spinning.

The packed layer made of spherical filler is disposed in the spinning pitch flow path upstream of the spinning nozzle, and when the molten spinning pitch passes through the layer, the spinning pitch is The flow of pitch is segmented, and the stacked state of the mesophase of the spun pitch is disturbed while passing through the layer, resulting in pitch fibers having a cross-sectional structure of fibers that are not substantially radially oriented.

Although the cause of this is not clearly elucidated, a single spherical filler does not exert a force that disturbs the stacked state of Menphase, but the accumulation of many spherical fillers causes the spherical fillers to It is presumed that the packed bed itself has a large number of intricately curved channels, and as a result, stress that disturbs the stacked state of the menphase is applied to the spinning pitch passing through the layer.

Spherical fillers include metals such as stainless steel, steel, and aluminum, or inorganic materials such as ceramics, glass, sand, and graphite, which can sufficiently withstand temperatures of about 310°C to μOO°C, and glass is particularly preferred. Although a small amount of distortion is of course allowed for its shape, it is usually a substantially spherical microsphere, and its size is such that it can pass through a 10-mesh sieve, but it can pass through a 3-mesh sieve. ! The particle size is such that it does not pass through a mesh sieve, preferably within a range that allows it to pass through a JO mesh sieve but does not pass through a 200 mesh sieve. The reason for this is that particles with a particle size larger than 10 meshes are not effective in dividing the flow of the spinning pitch into smaller pieces and disturbing the layered state of the menphase;
If it is smaller than a mesh, the pressure loss in this packed bed during spinning will be too large, resulting in various difficulties in manufacturing the spinning cap.

Here, FIGS. 1 to 3 show enlarged views of the vicinity of the spinning nozzle portion in various forms of the spinning apparatus provided with the filled layer made of the spherical filler of the present invention. 1 is a spinneret, C is a yarn prevention nozzle, 3 is a wire mesh for supporting the packed layer, G is an introduction hole, Y is a packed layer, and O is a space, respectively.

As shown in these figures, depending on the shape of the spinning nozzle, the packed bed guard is installed in the introduction hole or in the space upstream of it. It is thought that if the spinning pitch that has passed through is kept in a molten state for a long time, the flow units of the refined spinning pitch will coalesce again and return to the state before passing through the packed bed. j Filled bed so that the time required to reach the spinning nozzle after passing through the spinning nozzle is as short as possible within 10 minutes, preferably within 1 minute, and more preferably within 1 second! It is preferable to install

Here, the time required for the spinning pitch to reach the spinning nozzle after passing through the filling 717 is the filling layer! It is calculated by dividing the internal volume from the lower end to the upper end of the spinning nozzle inlet by the discharge amount of the spinning pitch.

The thickness of the filled layer j is preferably thicker, and the particle size is also preferably finer. However, if it is too thick, the flow resistance of the spinning pitch will be large, and if it is too thin, the desired effect cannot be obtained, so it is usually 3~JOOwm.
,Preferably·! Selected from the range of ~00tax.

is ≠00 or less, preferably 300 or less. If it exceeds the above range, the shearing force applied to the spinning pitch becomes large and the cross-sectional structure of the resulting pitch fibers becomes radially oriented, which is not preferable.

Note that the term "spinning nozzle" refers to a pore portion through which the spinning pitch flows just before spinning and that defines the yarn diameter, and the pore diameter refers to the diameter of the pore through 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 may be a straight tube, a spinning nozzle with an enlarged middle part, or a spinning nozzle with an enlarged lower part. Any shape of spinning nozzle can be used.

Moreover, the spinning pitch in the molten state supplied to the space WJ is a packed layer! After that, it is discharged from the spinning nozzle λ and spun.
Filled layer! By providing this, when discharging the spinning pitch,
Add a little amount to the spinning pitch of at least 2~G or more, preferably j%
It is necessary to perform spinning by applying a pressure of -G or more, more preferably 10%.G or more.

[For production]

In the present invention, the spinning pitch in the molten state is a filled layer made of a spherical filler! It is thought that by passing through the spinning pitch, the flow of the spinning pitch is segmented and the laminated state of the mesophase is disturbed, resulting in pitch fibers and pitch-based carbon fibers whose fiber cross-sectional structure is not substantially radially oriented.

[Effects of the present invention]

Therefore, a packed layer consisting of spherical fillers! K improves the fluidity of the spinning pitch.

Pressure operation in the above range during spinning suppresses the generation of gas or bubbles generated from the spinning pitch at the spinning temperature, improving spinning stability and making pitch fibers with improved properties stable for a long time. It can be manufactured by Further, the packed bed of the present invention is different from the spinning solution filter often used in various melt spinning methods and is provided separately from it, but it is used to filter the spinning solution again and the final time just before the spinning pitch enters the spinning nozzle hole. It has the effect that some temporary functions can be expected.

By making the pitch fibers thus obtained infusible, carbonizing them, and graphitizing them if necessary, they have a fiber cross-sectional structure with random orientation or onion-like orientation, and high properties without wedge-shaped cracks extending in the fiber axis direction. pitch-based carbon fiber can be obtained.

Here, onion-like orientation means that the main part of the fiber cross-sectional area has concentric molecular orientation, and a part of it has a concentric molecular orientation.
In particular, it includes those in which the outer peripheral portion is radially oriented to such an extent that no cracks will occur during subsequent carbonization or graphitization treatment. Moreover, these fiber cross-sectional structures were measured using a polarizing microscope.

〔Example〕

The present invention will be specifically explained below with reference to Examples.

Example 1! The coal tar pitch 2 cod and the hydrogenated aromatic oil misaki were placed in an autoclave and heat-treated at ≠10° C. for 1 hour. This treated product was distilled under reduced pressure to obtain pitch residue. Next, the residue pitch 2009! Heat treatment was performed at 30° C. for 2 minutes while bubbling Ic nitrogen gas. The anisotropy ratio of the obtained mesophase pitch was 100%.

Next, use a spinneret (spinning nozzle hole diameter: 0.J, length: o, 4 mm) as shown in Figure 1, and place the inlet hole ≠!
A stainless steel wire mesh 3 of OO mesh is provided, and a filling layer of spherical filler is provided above the wire mesh 3 with a density of 100~/jO.
Approximately 10 m of grass peas sieved to the size of mesh
Filled with a thickness of The installation position of the wire mesh 3 is the spinning pitch is a packed layer! After passing through, the time until reaching the spinning nozzle 2 is set to be about 00 seconds.

Next, using this spinneret, the mesophase pitch was melt-spun in a temperature range of 32J to 340°C. By changing the yarn winding speed at the optimum temperature, pitch fibers with a yarn diameter of up to 7 μm could be stably spun over a long period of time. I was able to get the target.

The pitch fiber obtained by melt spinning under the conditions of 3 Jt'C was made infusible at 310°C in air, and further spun in an argon atmosphere for 1
Carbon fibers were obtained by carbonization at 1100°C. The tensile strength and cross-sectional structure of this carbon fiber were measured and the results are shown in Table 1.

Comparative Example: Spinning was carried out in exactly the same manner as in Example except that the packed bed consisting of glass beads was not used, but pitch fibers having a yarn diameter of less than μ could not be stably obtained. Table 1 shows the physical properties of the carbon fibers obtained in the same manner as in Example 1.

Table 1

[Brief explanation of the drawing]

1 to 3 are enlarged cross-sectional schematic views of the vicinity of the spinneret in various embodiments of the spinning apparatus used in the present invention. l; Spinneret λ; Spinning nozzle 3; Wire mesh Hiroshi; Introduction hole t; Packed layer t made of spherical filler; Space part Fig. 2 Fig. 3 Fig. 41 One bar

Claims (8)

[Claims] (1) In a method for producing pitch-based carbon fiber by melt-spinning spinning pitch from a spinning nozzle, performing an infusibility treatment, then carbonizing treatment, and further graphitizing treatment as necessary, the method includes: 1. A method for producing pitch-based carbon fiber, comprising: providing a filled layer made of a spherical filler in a section, and spinning the spinning pitch by flowing the spinning pitch through the filled layer and the spinning nozzle in this order. (2) The method for producing a pitch-based carbon fiber according to claim 1, wherein the spinning pitch is a pitch exhibiting optical anisotropy of 40% or more. (3) The method for producing pitch-based carbon fibers according to claim 1 or 2, wherein the spherical filler is made of an inorganic substance or metal. (4) Claims 1 to 3, characterized in that the particle size of the spherical filler is within the range of a size that does not pass through a 325-mesh sieve to a size that allows it to pass through a 10-mesh sieve.
A method for producing a pitch-based carbon fiber according to any one of Items 1 to 3. (5) The method for producing pitch-based carbon fibers according to any one of claims 1 to 4, wherein the spherical filler is glass beads. (6) The pitch-based carbon according to any one of claims 1 to 4, wherein the time required for the spinning pitch to reach the spinning nozzle after passing through the packed bed is within 10 minutes. Fiber manufacturing method. (7) The method for producing pitch-based carbon fiber according to any one of claims 1 to 5, characterized in that the spinning nozzle satisfies (spinning nozzle length)/(spinning nozzle hole diameter)^4≦400. . (8) Claims 1 to 1, characterized in that melt spinning is performed at a spinning pitch of 2 kg/cm^2·G or more.
The method for producing pitch-based carbon fiber according to any one of Item 6.