JPS62170527A - Production of pitch-based carbon fiber - Google Patents

Abstract

PURPOSE:To produce the titled fiber causing little fibrillation and cracking, etc., by applying a shear stress of higher than a specific level to a molten pitch material in a capillary part before final nozzle hole and temporarily maintaining the pitch material in a state free from shear stress. CONSTITUTION:A molten pitch material is passed through a circular, modified or slit capillary part placed before the final nozzle hole. A shearing stress of >=1/2 of the stress imparted in the final nozzle hole is applied to the pitch by this process. The pitch material is temporarily maintained in a state essentially free from shear stress and, thereafter, passed through the final nozzle hole to obtain a carbon fiber having stable higher-order cross-sectional structure. At least a part of the fiber cross-section has an onion-like form.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for producing pitch-based carbon fiber.

Prior art and its problems Carbon fiber made from pitch-based material has 1. Compared to carbon fibers whose precursors are organic synthetic fibers such as polyacrylonitrile, they can be made into cheaper, higher-performance materials mainly because they have lower manufacturing costs and can easily produce products with high elastic modulus. It is expected that However, commercially available pitch-based carbon fibers have a tensile strength of 200
It is about KFl/s2 or less, and the quality stability is poor, so it is difficult to say that it is completely satisfactory.

Generally, in pitch-based carbon fibers, the state of molecular aggregation in the cross section of the fiber (hereinafter referred to as cross-sectional higher-order grooves) varies depending on the spinning conditions. That is, basically, the molecules form crystals in the concentric direction of the fiber (so-called onion type), the crystals form in the radial direction from the center of the fiber (radial type), or the molecules form crystals in the direction of the concentric circles of the fiber (so-called onion type), or the molecules form crystals in the radial direction from the center of the fiber (radial type). It is roughly divided into two types (random type) in which fibers are distributed in the direction of , but in actual fibers, there are also fibers with a mixture of these types. Furthermore, defects such as vertical cracks, cracks, and voids may be present in part or all of the fibers, and if the presence or absence of defects is included, the morphology of the cross-sectional higher-order structure of pitch-based carbon fibers is complex and diverse. The existence of such various defects and cross-sectional higher-order structures is one of the main causes of deteriorating the quality stability of pitch-based carbon fibers.

Although the occurrence of defects and the formation of a cross-sectional higher-order structure as described above vary depending on the physical properties of the spinning pitch, they are most greatly influenced and fluctuated by the spinning conditions. Therefore, in order to improve the quality stability of carbon fibers, it is necessary to develop a spinning technology that can always produce carbon fibers with almost no defects and a constant cross-sectional higher-order structure, even if the physical properties of the spinning pitch vary slightly. need to be established. In other words, onion-type and/or high-order cross-sectional structures that hardly cause defects such as vertical cracks, cranks, and voids, and are effective in developing high tensile strength.
Alternatively, a technique for stably forming a random structure is required.

Means for Solving the Problems As a result of intensive research in view of the current state of the technology as described above, the inventor of the present invention has developed a method for spinning a molten pitch-based material before reaching the final nozzle hole during melt-spinning of the pitch-based material. When the molten pitch is passed through a capillary part of a specific shape to apply a shear stress of a certain value or more, and then after holding the molten pitch in a state where no shear stress is applied, the pitch is passed through a nozzle hole for spinning. discovered that the problems of the prior art can be substantially eliminated or greatly reduced. That is, the present invention provides a method for producing pitch-based carbon fiber in which a pitch-based material is melt-spun, infusible, and carbonized, in which the molten pitch is passed through a circular, irregularly shaped, or slit-shaped capillary section before reaching the final nozzle hole. By applying a shear stress of 1/2 or more of the shear stress received at the final nozzle hole, the molten pitch is temporarily held in a state where no shear stress is applied substantially, and then passed through the nozzle hole for spinning. The present invention relates to a method for producing pitch-based carbon fiber characterized by the following.

According to the present invention, pitch-based graphite fibers can also be produced by graphitizing in the carbonization step. Therefore, in this specification, carbonization includes graphitization, and carbon fiber is used to include graphite fiber.

In the present invention, a shear stress of 1/2 or more of the shear stress experienced at the final nozzle hole is applied by passing the molten pitch-based material through a circular, irregularly shaped, or slit-shaped capillary section provided in front of the final nozzle hole. It is essential to hold the fiber in a state in which no shear stress is applied to it, and then pass it through the final nozzle hole for spinning. If the shear stress that the molten pitch-based material receives in the capillary part is necessarily less than 1/2 of the shear stress in the final nozzle part,
The desired effect is not fully exerted. Further, the desired effect cannot be obtained even when shear stress is applied through a gap in a dense filler using a method other than the capillary method, for example. Furthermore, the effects of the present invention are exhibited even when spinning is performed immediately from the final nozzle hole without maintaining a state in which no shear stress is applied after shear stress is applied to the molten pitch-based material in the capillary section. Not done. The cross-sectional shape of the capillary part used in the present invention may be circular, slit-shaped (or rectangular), or other irregular shapes (square, cross-shaped, 7-shaped, etc.).

The cross-sectional area and length of the capillary are not particularly limited as long as they can apply the necessary shear stress, but usually have a cross-sectional area of about 5 x 10 - 5 x 102 #, and a length of about 0.1 -
It is about 3.0 km.

The time required to maintain the molten pitch in a state where no shear stress is applied to it between the capillary section and the final nozzle hole depends on the type and nature of the pitch used, the spinning temperature, the amount of pitch discharged per unit time, and the capillary. Although it is not particularly limited and varies depending on the capillary section and the shape of the nozzle hole, the time taken for the melt pitch to pass through the capillary section is usually 103
~10" is preferable. In order to avoid applying shear stress to the molten pitch between the capillary part and the final nozzle hole, the said part (hereinafter referred to as stress relaxation part) should be connected to the punctured outer wall and/or the nozzle introduction hole. It is assumed that it is hollowed out so that no shear stress is applied except for.

The spinning pitch used in the present invention is obtained by thermally polycondensing a pitch-like substance under an inert gas flow. The pitch-like substance may be any of petroleum-based pitch, coal-based pitch, and pyrolysis residue pitch from organic compounds. In particular, when coal tar or coal-based pitch such as coal tar pitch is used as a raw material, the raw material pitch is subjected to aromatic reducing properties in advance according to the method described in JP-A-57-88016 prior to thermal polycondensation. 350-5 depending on solvent
The spinnability can be further improved by heat treatment at 00'C, but the pitch for spinning is not particularly limited as long as it can be spun.

There is no particular restriction on the cross-sectional area of the final nozzle hole used in the present invention, but it is usually 5 x 10-3 to 10-1 m!
It is about 112.

In the present invention, the pinch fibers obtained as described above are processed in accordance with a conventional method, for example, in an oxygen atmosphere with a length of 300 to 340'.
After infusibility at about C, 1000 ~
It is turned into carbon fiber by heating at about 3000'C.

The cross-sectional higher-order structure of the carbon fiber obtained by the present invention has an onion-type structure in part or in whole (see FIGS. 1 and 2). If a portion has an onion-type structure, the onion-type structure exists in the inner layer and the random-type structure (Figure 1 (a)) or radial type structure (Figure 1 (b)) exists in the outer layer. exist.

Effect of the invention According to the present invention, the following effects are achieved.

(i> The carbon fiber finally obtained has almost no microscopic defects such as vertical cracks, cracks, and voids inside it.

(ii) It has excellent quality stability, so even if the physical properties of the pitch-based material used as the raw material change slightly, carbon fibers with a stable cross-sectional higher-order structure in which at least a portion of the fiber cross section is onion-shaped can be obtained. .

(iii) As a result of (i) and (ii) above, the tensile strength of carbon fibers is greatly improved.

(iv) Furthermore, the frequency of yarn breakage during spinning using a multi-hole nozzle is reduced, making stable continuous spinning possible.

(vi) Since the surface of the carbon fiber can be changed to onion, random, or radial while keeping the inside of the carbon fiber in an onion structure, the resin and carbon Various surface molecular arrangements can be selected that provide good adhesion.

EXAMPLES Below, Examples will be shown together with Reference Examples and Comparative Examples to further clarify the characteristics of the present invention.

Reference Example 1 A mixed solution of 1 part of coal tar pitch with a softening point of 110'C, 0.18% of quinoline soluble content, and 35% of benzene insoluble content and 2 parts of hydrogenated anthracene oil was placed in an autoclave. After heating at 430'C for 60 minutes with stirring, the mixture was filtered while hot using a pressure filter, and the hydrogenated andranthene oil was removed at 300'C under reduced pressure to obtain reduced pitch.

50 kg of the reduced pitch obtained above was placed in a reactor equipped with a gas introduction tube, a thermocouple, a stirrer, and a distillate removal tube, and 1
Removal of low molecular weight components and thermal polycondensation were carried out at 410 to 480'C while introducing nitrogen gas under careful stirring. The properties of two types of thermally polycondensed pitches obtained by selecting reaction times and temperatures are shown in Table 1 as Nos. 1 and 2.

Reference Example 2 The same coal tar pitch as in Reference Example 1 was subjected to a thermal polycondensation reaction in the same manner as in Reference Example 1 without undergoing heat treatment while mixing with hydrogenated anthracene oil. The properties of the obtained thermal polycondensation pitch are N.

3 in Table 1.

Table 1 Note: Softening points were measured using a softening point measuring device manufactured by Swiss Mettler.

Examples 1 to 3 A capillary part consisting of 100 thin tubes with a diameter of 0.15 m and a length of 0.4 M, a stress relaxation part with a volume of 150 m3, and a nozzle with a diameter of 0.2# and a length of 0.4 M (number of nozzle holes: 100).
Thermal polycondensation pitch Nos. 1 to 3 obtained in Reference Examples 1 and 2 were spun using a spinning device equipped with a spinning device. In this spinning process, the pitch is subjected to a shear stress of approximately 250% of the shear stress applied to the final nozzle hole in the capillary section, then left in a state where it is not subjected to shear stress by stress relaxation, and then subjected to shear stress again at the final nozzle hole. Added.

The pitch fiber thus obtained was infusible at 300'C in air for 30 minutes, and then heated at 1200'C in N2 gas atmosphere.
Carbon fibers were obtained by heating to .

Table 2 shows the average time (hr) in which pitch fibers with a diameter of 10 μm can be continuously spun without yarn breakage, the cross-sectional higher-order structure of the carbon fibers obtained above, and the defect content.

Table 2■ Also, scanning electron micrographs showing the cross-sectional higher-order structures of the carbon fibers obtained in Examples 1.2 and 3 are shown in Figure 3 (approximately 2600 times) and Figure 4 (approximately 8000 times), respectively. and FIG. 5 (approximately 1700 times magnification).

Examples 4 to 6 Capillary parts having the shape and number shown in Table 3, volumetric 1
Stress relief section of 80m3, diameter 0.2mtn, length 0.
Thermal polycondensation pinch N obtained as a reference example using a spinning device equipped with a 4IIIn nozzle (100 nozzle holes)
o, 1 was spun, and the resulting pitch fibers were used in Examples 1 to 3.
Carbon fibers were obtained by infusibility and carbonization treatment in the same manner as above.

The cross-sectional higher-order structure and defect content of the obtained carbon fiber were
Shown in the table.

Table 3 It is clear that even when a spinning device having a capillary portion with an irregular cross section is used, carbon fibers with almost no defects and an inner layer having an onion-type cross-sectional higher-order structure can be obtained.

Comparative Examples 1 to 3 A nozzle with a diameter of 0.2 and a length of 0.4# (number of nozzle holes: 10)
After spinning the thermal polycondensation pitch Nos. 1 to 3 obtained in Reference Examples 1 and 2 using a spinning device equipped with Carbon fibers were obtained.

Table 4 shows the cross-sectional higher-order structure and defect content of the obtained carbon fibers, as well as the average time (hr) in which pitch fibers with a diameter of 10 μm can be continuously spun without yarn breakage.

Comparative Example 4 The size of the capillary part is 0.3 # in diameter, and the width is 0.6 m.
Thermal polycondensation pitch No. 1 obtained in Reference Example 1 using the same spinning device as in Example 1 except that m (number of threads: 100)
was spun. During this spinning process, the pitch was subjected to a shear stress in the capillary section that was about 30% of the shear stress experienced at the final nozzle hole.

The obtained pitch fibers were subjected to infusibility and carbonization treatment under the same conditions as in Example 1 to obtain 1 q of carbon fibers.

Table 4 shows the cross-sectional higher-order structure and defect content of the carbon fibers.

FIG. 6 shows a scanning electron micrograph (approximately 2800 times magnification) showing the cross-sectional higher-order structure of the carbon fiber obtained in this comparative example.

Comparative Example 5 A capillary section consisting of 100 thin tubes with a diameter of 0.15 m and a length of 0.4% is substantially directly connected to a nozzle section (100 nozzle holes) with a diameter of 0.2 and a length of 0.48. Thermal polycondensation pitch N obtained in Reference Example 1 using the spinning device
o, 1 was spun. In this spinning process, the pitch was subjected to a shear stress of about 250% of the shear stress experienced at the final nozzle hole in the capillary section, and then immediately sheared at the final nozzle hole.

1 q of pinched fibers were subjected to infusibility and carbonization treatment under the same conditions as in Examples 1 to 3 to obtain carbon fibers.

Table 4 shows the cross-sectional higher-order structure and defect content of the carbon fibers.

Further, FIG. 7 shows a scanning electron micrograph (approximately 4000 times magnification) showing the cross-sectional higher-order structure of the carbon fiber obtained in this comparative example.

Table 4 □□□; As is clear from the comparison between the results of Examples 1 to 3 shown in Table 2 and the results of Comparative Examples 1 to 3 shown in Table 4, there is no capillary part and stress relaxation part. When using spinning equipment, even if the raw material pinch is the same, continuous spinning performance is inferior,
The cross-sectional higher order structure is radial type and has a high defect content.

Results of Example 1 shown in Table 2 and Comparative Example 4 shown in Table 4
As is clear from the comparison with the results, when a shear stress of 1/2 or less of that at the final nozzle hole is applied to the capillary part, the content of defects such as vertical cracks and cracks is high.

Furthermore, the results of Example 1 shown in Table 2 and Comparative Example 5 shown in Table 4
As is clear from the comparison with the results, even when using a spinning device that does not have a stress relaxation section between the capillary section and the final nozzle section, the cross-sectional higher-order structure is radial, and the defect content is high. .

[Brief explanation of drawings]

FIGS. 1 and 2 are schematic diagrams showing the cross-sectional higher-order structure of carbon fibers obtained by the method of the present invention, and FIGS. 3 to 5 are
FIGS. 6 and 7 are scanning electron micrographs showing cross-sectional higher-order structures of carbon fibers obtained in Examples 1.2 and 3, and FIGS. 6 and 7 show cross-sections of carbon fibers obtained in Comparative Examples 4 and 5. This is a scanning electron micrograph showing a higher-order structure. (Above) Figure 1 (a) (b) Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] [1] In a method for producing pitch-based carbon fiber in which pitch-based material is melt-spun, infusible, and carbonized, by passing the molten pitch through a circular, irregularly shaped, or slit-shaped capillary part before reaching the final nozzle hole. After applying a shear stress of 1/2 or more of the shear stress received at the final nozzle hole, the molten pitch is temporarily held in a state where no shear stress is applied substantially, and then passed through the nozzle hole to be spun. A method for producing pitch-based carbon fiber.