JPH04209827A - Production of pitch-based carbon fiber - Google Patents

Abstract

PURPOSE:To surely and readily obtain the subject fiber having a cross section of no radial structure by discharging plural pitch streams from plural small pitch discharge holes, fusing the pitch streams before solidification and forming one fiber. CONSTITUTION:Spinning is carried out as follows. A spinning nozzle equipped with plural small holes 1 on the pitch discharge surface is initially used to discharge pitch from the respective small holes 1 of the above-mentioned nozzle. The discharged pitch streams are then fused to constitute one fiber. The resultant pitch fiber is subsequently infusibilized and then carbonized to afford the objective fiber. Furthermore, the spinning nozzle having 3 small holes having 0.1-0.12mmphi hole diameter at 0.1mm nozzle interval is preferably used in order to carry out spinning so as to fuse the discharged pitch streams and constitute one fiber.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing pitch-based carbon fibers, and particularly to a method for producing pitch-based carbon fibers whose fiber cross section does not have a radial structure when purchased. It is.

[Prior Art] When spinning liquid crystal pitch such as mesophase pitch, when the liquid crystal pitch passes through a part of the capillary of the spinning nozzle, it is subjected to strong shearing force with the wall of the capillary, resulting in a fiber cross section. It is known that the structure tends to be radial. Fibers that have a radial structure during the spinning process tend to have cracks on the fiber surface in the fiber axis direction during the subsequent firing process, making them susceptible to mechanical deformation and resulting in a significant decrease in commercial value. are doing.

The cross-sectional structure is determined during the spinning process. Therefore, various improvements have been made to the spinning process in order to obtain fibers that do not have the above-mentioned radial structure.

For example, there is a method of inserting a filler directly above the capillary of the spinning nozzle, a method of changing the shape of the capillary of the spinning nozzle, and the like. Specifically, as a method of placing a filler directly above a capillary, Conventional Example 1; a method of filling irregularly shaped powder (
JP-A No. 61-258022), Conventional Example 2: Method of adding a static mixer (JP-A No. 63-75119), Conventional Example 3: Method of adding a filter (JP-A No. 63-993)
27), or Conventional Example 4: A method of inserting a special foreign substance called an insert (Japanese Patent Laid-Open No. 64-6123). In addition, as a method for deforming a capillary, conventional example 5; a method of providing a buffer region in the middle of a capillary (Japanese Patent Application Laid-Open No. 61-7
5820). These methods attempt to prevent the pitch flowing out of the nozzle hole from being radially oriented by disturbing the flow of pitch within the nozzle hole, but each method has the following drawbacks. Conventional Example 1: It is difficult to make the filling state uniform in each hole, which tends to cause non-uniform flow. In addition, there is a risk of blockage due to filling in some cases, and maintenance is also difficult. Conventional Example 2 The static mixer itself is very expensive and is not a very practical method. Also, it is difficult to fix and maintain the mixer.

Conventional Example 3: It is necessary to spin the fiber immediately after passing through the filter, but it is very difficult to fix the filter directly above the capillary without any gaps. Conventional Example 4: It is difficult to manufacture and fix the insert and to mount it uniformly, and it is expected that it will be very expensive. Conventional Example 5: Manufacturing the nozzle requires very detailed processing and is expected to be very expensive.

Furthermore, since most of these techniques disturb the pitch flow before the capillary, there is a possibility that reorientation occurs and radialization occurs when the pitch passes through the capillary. The only modification of Conventional Example 4 is to try to suppress reorientation by passing something like a needle through a part of the capillary, but it is unlikely to have the effect of sufficiently disturbing the pitch flow, and it is It is also possible that the flow path becomes narrower and the shear force is strengthened, promoting orientation. Also, the capillary is usually 0.1 to 0.2 ma
+φ, at most about 0.5 mmφ, so it is expected that the above-mentioned work would be extremely difficult in practice.

[Problems to be solved by the invention] As described above, the conventional method does not have a reliable effect of preventing radial formation, and also has various problems in spinning stability, processing accuracy, cost, installation method, maintenance, etc. There is,
This was hardly a practical method. Therefore, the present invention aims to provide a practical method that is excellent in spinnability, processing accuracy, and the like.

[Means for Solving the Problems] The method for producing pitch-based carbon fiber of the present invention involves spinning pitch from a spinning nozzle, making it infusible, and then carbonizing or graphitizing it to produce pitch-based carbon fiber. The gist is to use a spinning nozzle in which a plurality of micropores are provided on the surface, and to perform spinning so that the pitch discharged from each micropore is fused after discharge to form one carbon fiber.

[Operation] In the present invention, the plurality of pitches discharged from the pitch discharge hole are fused before solidification, so the orientation state immediately before solidification is disturbed by the fusion, resulting in carbon fibers without a radial structure. That is, as mentioned above, the radialization of the pitch is promoted by the strong shear force when passing through a part of the capillary, so it is necessary to weaken the shear force or disturb the structure after passing through the capillary. However, in the present invention, after passing through the capillary, Since the orientation is disturbed by utilizing the flow tendency when the pitches fuse together, radialization can be effectively prevented.

This will be explained in more detail below.

It is preferable that the micropores of the spinning nozzle satisfy the following requirements.

Shape: Although not particularly limited, a circular shape is preferred for processing purposes.

Dimensions: Since the pitch discharged from multiple micropores is wound up as a single fiber, the diameter of the holes is preferably smaller than normal, and is preferably 0.15a+'mφ or less, more preferably 0.10mφ or less.
It is approximately 0.12m+11φ.

Number: It may be more than one, but three is considered most suitable in order to achieve the purpose with the minimum number. 2
In the case of 3 pieces, the spinning stability is slightly inferior to that of 3 pieces.

Nozzle interval: Since it is necessary to fuse the pitches after discharge before solidifying, it is necessary to make the interval narrower than at least the length after discharge until solidification. From theoretical analysis of melt spinning, when pitch discharge rate: 6 cc/111 inch, nozzle hole 125 holes, nozzle diameter: 0.20 mmφ, and ambient temperature = 25°C, solidification occurs at approximately 1.6 CI1111 L/1 from the discharge surface. It happens.

This calculation result varies depending on the setting conditions, but if these are taken into consideration, it is considered to be approximately between 1co+ and 2ca+. Therefore, unless the maximum is 2CO1 or less, no matter how the pitches are collected after being discharged, they will not become one fiber. Also, due to nozzle processing constraints, the minimum interval is 0. Since la+m is 0 or more, it is desirable that the interval be 0.1+*m to 2C■, more preferably 0.1+++a.

Carbon fibers having no radial structure can be obtained by performing normal spinning using a spinning nozzle having micropores having the above configuration. Figure 341 (a) shows an example of a spinning nozzle.
), (b), and FIG. 2(a).

(b) shows a modified example. A modified example is one in which the rocky part in the figure is carved out, and the pitch can be collected in the carved part for spinning, and can be used in cases such as when the pitch does not form into one fiber because the temperature of the pitch is low. It is considered to be effective.

The present invention will be explained in more detail with reference to examples below, but the following examples do not limit the present invention, and all modifications and implementations within the scope of the spirit of the preceding and later descriptions are included within the technical scope of the present invention. Ru.

[Example] Example Spinning and firing were carried out under the following conditions using a nozzle having three micropores shown in FIG.

Pitch used: Mesophase carbonaceous material 95% or more, softening point 2
60°C Spinning temperature: 355-365°C, (most stable at 360°C) Spinning pressure: 2-5 kg/cm” (pressurized with nitrogen)
Winding speed: 100~500m/+in (250
(most stable at m/min) Firing: After infusibility treatment in air, graphitization was carried out at 2000°C. The obtained carbon fiber showed a random structure and no cracks etc. occurred even after firing.

Comparative Example 1 When two of the three pores of the spinning nozzle used in the example were artificially blocked with a carbon fiber material and treated in the same manner as in the example, the fiber cross section had a completely radial structure.

Comparative Example 2 Spinning and firing were performed under the following conditions using a single-hole nozzle with a capillary diameter of 0.2 amφ.

Pitch used: Same as in the example Spinning temperature: 353 to 370°C (most stable at 362°C) Spinning pressure: 2 to 9 kg/cod' (pressurized with nitrogen) Winding speed: 100 to 900 m/win ( 30
(Most stable at 0 m/win) Firing: Processed in the same manner as in the example The cross section of the fiber thus obtained showed a radial structure and had cracks after firing.

[Effects of the Invention] The present invention is configured as described above, and it has become possible to reliably and easily produce carbon fibers that do not have a radial structure. The shape of a part of the nozzle hole capillary of the present invention can be the same cylindrical shape as the conventional one, so the processing accuracy and maintainability are unchanged from the conventional one, and since no filler is used, there is no variation in pitch flow rate and stable spinning is possible. can be done.

[Brief explanation of the drawing]

341 Figure (a) and '! Figure J2 (a) is a partial sectional view of the spinning nozzle used in the present invention, and Figure 1 (b) is a partial cross-sectional view of the spinning nozzle used in the present invention.
and Fig. 2(b) are respectively Fig. 1(a) and Fig. 2(a).
It is a plan view seen from the A1 or A2 direction inside.

Claims (1)

[Claims] When pitch is spun from a spinning nozzle, made infusible, and then carbonized or graphitized to produce pitch-based carbon fiber, a spinning nozzle with a plurality of micropores provided on the pitch discharge surface is used, and the pitch is spun from each micropore. A method for producing pitch-based carbon fibers, which comprises spinning the discharged pitches so that they are fused to form one carbon fiber after being discharged.