WO1990007594A1

WO1990007594A1 - Process for producing pitch-base carbon fiber

Info

Publication number: WO1990007594A1
Application number: PCT/JP1987/000041
Authority: WO
Inventors: Hiroaki Morita; Kazutoshi Haraguchi; Eiji Tanigawa
Original assignee: Hiroaki Morita; Kazutoshi Haraguchi; Eiji Tanigawa
Priority date: 1986-01-22
Filing date: 1987-01-22
Publication date: 1990-07-12
Also published as: JPH0413450B2; JPS62170527A

Abstract

A process for producing pitch-base carbon fiber by melt-spinning, making infusible, and carbonizing a pitch material, which comprises passing molten pitch through a circular, odd-shaped or slit-type capillary section before a final nozzle to thereby apply a shearing stress of 1/2 or more of that to be applied in the final nozzle, temporarily keeping the molten pitch in a shearing stress-free state, and spinning through the nozzle pore.

Description

Specification

Method for producing pitch-based carbon fiber

'Technical field .

The present invention relates to a method for producing pitch-based carbon fiber.

Background technology

Carbon fibers made from pitch-based materials can produce products with lower manufacturing costs and higher elastic modulus than carbon fibers made from organic synthetic fibers such as polyacrylonitrile as a precursor. It is expected that it can be a cheaper and higher-performance material because it is easier. However, commercially available pitch-based carbon fibers have a tensile strength of about 20 O kg Z mm ² or less, have poor quality stability, and cannot be said to be sufficiently satisfactory.

Generally, in the pitch-based carbon fiber, the molecular aggregation state of the fiber cross section (hereinafter referred to as a higher-order cross-sectional structure) varies depending on the spinning conditions. Basically, molecules form crystals in the concentric direction of the fiber (so-called onion type), or form crystals in the radial direction from the center of the fiber (radial type).

Or, they are distributed in any direction without showing the directionality (random type), but in actual fibers, there are some that mix these. Furthermore, defects such as cracks, cracks, voids, etc. are present in part or all of the fiber. In some cases, including the presence or absence of defects, the morphology of the cross-sectional higher-order structure of pitch-based carbon steel is complex and diverse. The existence of such various defects and the higher-order structure of the cross section is one of the main causes for deteriorating the quality stability of the pitch-based carbon fiber.

The occurrence of the above-mentioned defects and the formation of the higher-order structure of the cross section vary depending on the physical properties of the spinning pitch, but are most affected by the spinning conditions and fluctuate. Therefore, in order to improve the quality stability of carbon fiber, even if the physical properties of the spinning pitch are slightly different, it is possible to produce a carbon fiber with a constant high-order cross-sectional structure with almost no defects. It is necessary to establish spinning technology. In other words, it hardly generates defects such as cracks, cracks, and voids, and stably forms an onion-type structure, a Z-type structure, or a random-type structure, which is a high-order sectional structure effective for expressing high tensile strength. Technology is required.

Disclosure of the invention

The inventor of the present invention has conducted intensive studies in view of the state of the art as described above. When passing through the nozzle, a shear stress of a certain value or more is applied, and then the molten pitch is temporarily kept in a state where substantially no shear stress is applied. In this case, it has been found that the problems of the prior art can be substantially eliminated or greatly reduced. That is, the present invention relates to a method for producing pitch-based carbon fiber in which a pitch-based material is melt-spun, made infusible, and carbonized, and the molten pitch is formed into a circular, irregular or slit-type cavity before reaching a final nozzle hole. After applying a shear stress of not less than 1 to 2 times the shear stress applied to the final nozzle hole by passing a part of the molten pitch, the molten pitch is temporarily held in a state where shear stress is not substantially applied, and then The present invention relates to a method for producing pitch-based carbon fiber, wherein the fiber is spun through a nozzle hole.

According to the present invention, a pitch-based graphite fiber can be produced by graphitization in the carbonization step. Therefore, in the present specification, carbonization includes graphitization, and carbon fiber is used as including graphite fiber.

In the present invention, the molten pitch-based material is passed through a circular, irregular or slit-type part of the cavities provided in front of the final nozzle hole, so that the shear stress applied to the final nozzle hole is 12 times or more. Preferably, after applying a shear stress of 12 to 10 times, it is necessary to temporarily hold the shear stress in a state where the shear stress is not substantially applied, and then to spin through the final nozzle hole. The shear stress applied to the molten pitch-based material in a part of the cavity is less than 1/2 of the shear stress at the final nozzle. In some cases, the desired effect is not fully exhibited. Also, when a shear stress is applied by a method other than the cavitation method, for example, through a gap between dense fillers, the desired effect cannot be obtained. Furthermore, when shear stress is applied to the molten pitch-based material at a part of the cavities and the spinning is immediately performed from the final nozzle hole without maintaining a state in which shear stress is not substantially applied, the present invention is also applicable. The effect of the invention is not exhibited. The cross section of the part of the cavity used in the present invention may be circular, slit type (or rectangular type), or other irregular type (square, cross, Y-shaped, etc.). Is also good. . Kiyabira Li one cross-sectional area及beauty length also, as long as it is capable of adding the required shear stress is not particularly limited, usually the cross-sectional area 5 X 1 0 - ³ ~

Approximately 5 X 1 ram ² and length of about 0.1 to 3.0 O ram. The cross-sectional area is substantially the total cross-sectional area of the opening of a part of the cab.

The time required to maintain the molten pitch between the part of the cavity and the final nozzle hole without substantially applying shear stress to the molten pitch depends on the type and properties of the pitch used, the spinning temperature, and the pitch discharge per unit time. the amount differs more shapes of some Kiyabirari and nozzle holes, but are not particularly limited, is usually time melting peak Tutsi of 1 0 ³ to 1 0 ⁵ times the time through a portion Kiyabira Li I like it. Part of the cavity and the final nozzle hole In order not to apply shear stress to the molten pitch during the period, the portion (hereinafter referred to as the stress relaxation portion) was hollowed out so that no shear stress works except for the outer wall of the pack and / or the nozzle introduction hole. Shall be.

The spinning pitch used in the present invention can be obtained by subjecting a pitch-like substance to thermal polycondensation in an inert gas flow. The pitch-like substance may be any of petroleum pitch, coal pitch and pyrolysis residue pitch from organic compounds, and has a softening point (measured by a softening point measuring device of METTLER, Switzerland). 8 0 to 3 2 5. C's are preferred. In particular, when coal-based pitch such as coal tar or coal tar pitch is used as a raw material, prior to the thermal polycondensation, the method described in Japanese Patent Application Laid-Open No. 57-88016 is followed. By previously heat-treating the raw material pitch with an aromatic reducing solvent at 350 to 500, the spinnability can be further improved, but the spinning pitch should be spinnable. It is not particularly limited.

The cross-sectional area of the final nozzle hole used in the present invention is not particularly limited, but is usually about 5 × 10 ³ to 10 ¹ ram ² o

In the present invention, the pitch fiber obtained as described above is infusibilized in a conventional manner, for example, in an oxygen atmosphere at a temperature of about 300 to 340, and in the case of carbonization, nitrogen, carbon dioxide, 100 to 2000 in an atmosphere such as argon. C, 200 to 300 in argon for graphitization. By heating at about C, carbon fibers having an elliptical cross section are obtained. BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are schematic diagrams showing the higher-order sectional structure of a carbon fiber obtained by the method of the present invention. FIGS. 3 to 5 show Examples 1 and 2. 6 and 7 are scanning electron micrographs showing the higher-order cross-sectional structure of the carbon fiber obtained in Comparative Examples 4 and 5, and FIGS. 6 and 7 show the higher-order cross-sectional structure of the carbon fiber obtained in Comparative Examples 4 and 5. It is a scanning electron micrograph showing the structure. The cross-section higher-order structure of the carbon fiber obtained by the present invention has an onion-type structure in part or all (see FIGS. 1 and 2). If part of the structure is onion-type, the onion-type structure exists in the inner layer and the random-type structure (Fig. 1 (a)) or the radial-type structure (Fig. 1 (b) )) Exists. The shear stress was measured using the effective shear stress w = dyne / ciff on the wall when the molten pitch passes through the cavity or nozzle.

P r

w 2 δ

Where Ρ is the pressure difference (dyneZ ci) β is the effective cavity or nozzle length (cm) r is the cavity or nozzle radius (cm)

It was done.

The invention's effect

According to the present invention, the following effects can be obtained.

(i) The finally obtained carbon fiber hardly has micro defects such as cracks, voids and the like inside.

(ii) Because of its excellent quality stability, even if the physical properties of the pitch-based material slightly fluctuate, carbon with a stable higher-order structure in which at least a part of the fiber cross-section is of an onion type Fiber is obtained.

(ii) As a result of the above (i) and (ii), the tensile strength of carbon steel fiber is improved to dog width.

(iv) Furthermore, the frequency of yarn breakage during spinning using a multi-hole nozzle is reduced, and stable continuous spinning becomes 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 as an onion structure, resin composites and carbon composites can be obtained while maintaining the stable mechanical properties of carbon fiber. It is possible to select various surface molecular arrangements that have good adhesion to resin and carbon in the body.

Example Examples are shown below together with Reference Examples and Comparative Examples to further clarify the features of the present invention.

Reference example 1

Softening point '1 1 0. C, quinoline-insoluble content 0.18%, benzene-insoluble content 35%, a mixed solution of 1 part by weight of coal tar pitch and 2 parts by weight of hydrogenated heavy anthracene oil in an autoclave 4 3 After heating with stirring at 0 ° C for 60 minutes, the mixture was heated with a pressurized filter and then heated under reduced pressure at 300 to remove hydrogenated heavy lanthanum oil to obtain reduced pitch. .

Into a reactor equipped with a gas inlet tube, a thermocouple, a stirrer and a distillate removing tube, put the reduced pitch 5 O kg obtained above into a reactor, and reduce the pressure to 410 to 480 while introducing nitrogen gas under stirring. Removal of molecular weight components and thermal polycondensation were performed. Table 1 shows the properties of the two types of hot polycondensation pitches obtained by selecting the reaction time and temperature as Xo. 1-2. -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 under mixing with hydrogenated heavy vanthracene oil. Table 1 shows the properties of the resulting hot polycondensation pitch as No. 3.

Thermal polycondensation Q I B I Softening point Pitch No. (% by weight) (% by weight) (° C)

1 3 5 9 5 3 1 8

2 2 2 9 3 3 1 3

3 4 0 9 2 3 1 5 Note: The softening point is a softening point measuring device manufactured by METTLER SWITZERLAND.

Was measured by Example:! ~ 3

0.15 ram diameter, 0.4 mm length of thin tubing 100 pieces (total cross-sectional area 1.77 mm ² ) consisting of 100 tubing, stress relief part with a volume of about 15 ctn ³ and diameter 0 2.2 Using a spinning device equipped with a 4 ram length nozzle (100 nozzle holes), the hot polycondensation pitches Nos. 1 to 3 obtained in Reference Examples 1 and 2 were spun. . In the spinning process, the pitch is subjected to a shear stress of about 250% of the shear stress applied to the final nozzle hole in a part of the cavity, and then is subjected to stress relaxation to receive no shear stress. Again gave shear stress.

The pitch fibers thus obtained are in air at 300. C for 30 minutes, then heat up to 1200 in N ₂ gas atmosphere. 0 Heated to obtain carbon fiber.

Table 2 shows the average time (hr) during which a pitch fiber having a diameter of 10 m can be continuously spun without causing yarn breakage, and the higher-order sectional structure and defect content of the carbon fiber obtained above. Table 2

Scanning electron micrographs showing the higher-order cross-sectional structures of the carbon fibers obtained in Examples 1, 2 and 3 are shown in FIG. 3 (approximately 260,000 times) and FIG. Times) and Fig. 5

(Approximately 1700 times).

Examples 4 to 6

The shape, number, total cross-sectional area and shear stress key shown in Table 3 Using a spinning device equipped with a part of a billet, a stress relaxation section with a volume of about 18 and a diameter of 0.2, a length of 0.4 dragon nozzle (100 nozzle holes), obtained in Reference Example 1. The resulting hot polycondensation pitch ι1 was spun, and the obtained pitch fibers were infusibilized and carbonized in the same manner as in Examples 1-3 to obtain carbon fibers.

Third, the sectional higher-order structure and defect content of the obtained carbon fiber are described below.

3 Key villa

Defect-containing shape Number of gross meta 断 ratio of shear stress.

Example (mm ² ) (%, Nozzle part) Ratio (%) Long 咖 .25ram Internal waste onion type

4 Ellipse 50 1.28 Approx. 400% 0 Short chain 0.13mm Outside 朥 random type Inside! ) Onion type

5 Shozo ¾ type (0.2 sides per side) 70 1.21 Approx. 450% 4 Outerwear radial type 0.3mm width inside ^ onion type

6 slit 30 0.9 About 600% 2 r length, 0.1 mm external radiating type

It is clear that even when a spinning device having a part of the cabillary having an irregular cross section is used, a carbon fiber having an inner-layer onion type higher-order cross-sectional structure with few defects can be obtained. Comparative Examples 1 to 3

Nozzle with 0.2 ram diameter and 0.4 mm length

After spinning the thermal polycondensation pitches で 3 3 obtained in Reference Examples 1 and 2 using a spinning apparatus equipped with The treatment was performed to obtain carbon fibers.

Table 4 shows the higher-order cross-sectional structure and defect content of the obtained carbon fiber, and the average time (hr) for continuously spinning a pitch fiber having a diameter of 10 m without causing thread breakage.

Comparative Example 4

Using the same spinning device as in Example 1 except that the size of the capillaries was 0.3 in diameter and 0.6 ram in length (100 pieces), the thermal weight obtained in Reference Example 1 was used. Condensed pitch No. 1 was spun. In this spinning process, the pitch was subjected to a shear stress of about 30% of the shear stress applied to the final nozzle hole in a part of the cavity. The obtained pitch fibers were infusibilized and carbonized under the same conditions as in Example 1 to obtain carbon fibers.

Table 4 shows the sectional higher-order structure and defect content of the carbon fiber. The cross section of the carbon fiber obtained in this comparative example shows the higher-order structure. Fig. 6 shows a 查 -type electron micrograph (approximately 2800 times) of Comparative Example 5

Part of a cabillary consisting of 100 tubules with a diameter of 0.15 11101 and a length of 0.4 ram, and a nozzle section with a diameter of 0.2 mm and a length of 0.4 (number of nozzle holes: 100) Using the spinning apparatus in which the heat polycondensation pitch was substantially directly connected, the hot polycondensation pitch Να1 obtained in Reference Example 1 was spun. During this spinning process, the pitch was subjected to a shear stress of about 250 in the portion of the cavity, which was the shear stress received at the final nozzle hole, and then immediately applied the shear stress at the final nozzle hole.

The obtained pitch fiber was subjected to infusibilization and carbonization under the same conditions as in Examples 1 to 3 to obtain a carbon fiber.

Table 4 shows the sectional higher-order structure and the defect content of the carbon fiber, and a scanning electron micrograph (approximately 400 × magnification) showing the sectional higher-order structure of the carbon fiber obtained in this comparative example. ) Is shown in Fig. 7.

the 4th

As is evident 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, a spinning layer having no part of the capillaries and the stress relaxation portion was used. In this case, even if the raw material pitch is the same, the continuous spinnability is inferior, and the sectional high-order structure is radial and has a high defect content.

As is evident from the comparison between the results of Example 1 shown in Table 2 and the results of Comparative Example 4 shown in Table 4, the shear stress of 1 Z 2 or less received by the final nozzle hole is partially When added, the content of defects such as cracks and cracks is high.

Further, the results of Example 1 shown in Table 2 and Comparative Example 5 are shown in Table 4. As is evident from the comparison with the results of the above, even when using a spinning device that does not have a stress relaxation part between the part of the capillary and the final nozzle, the higher-order cross-sectional structure is a radial type and contains defects. The rate is also high.

Claims

The scope of the claims

1. In the method of manufacturing pitch-based carbon fiber, which melts, spins, infuses, and carbonizes pitch-based material, the molten pitch is circular, irregular, or 'slit-type' capillary before reaching the final nozzle hole. After applying a shear stress of 1 to 2 times or more of the shear stress received in the final nozzle hole by passing through the portion, the molten pitch is once kept in a state where shear stress is not substantially applied. A method for producing pitch-based carbon fiber, comprising:

2. The manufacturing method according to claim 1, wherein the length of a part of the capillaries is 0.1 to 3.0.

3. sectional area of Kiyabira Li part 5 X 1 0 - ³ ~

5. The production method according to claim ^{1, wherein} 5 X 10-1 腳² .

4. The production method according to claim 1, wherein the shear stress at a part of the cavity is 1Z2 to 10 times the shear stress at the final nozzle hole.

5. The production method according to claim 1, wherein the softening point of the molten pitch is 280 to 325.

6. In the method of manufacturing pitch-based carbon fiber, which melts and spins pitch-based material, renders it infusible, and graphitizes, melts the pitch before making it to the final nozzle hole. After applying a shear stress of 1 Z 2 times or more of the shear stress received in the final nozzle hole by passing a part of the billet, the molten pitch is once held in a state where shear stress is not substantially applied, and then A method for producing pitch-based graphite fiber, comprising spinning through a nozzle hole.

7. The production method according to claim 6, wherein a part of the length of the capillaries is 0.1 to 3. Oimn.

8. The cross-sectional area of a part of the capillaries is 5 X 10 _ ³ ~

7. The method according to claim 6, wherein the size is 5 × 10 ⁻¹ mm ² .

9. The production method according to claim 6, wherein the shear stress at a part of the capillaries is 1Z2 to 10 times the shear stress at the final nozzle hole.

10. Melting pitch softening point is 280-325. 7. The production method according to claim 6, wherein the production method is C.

11. A carbon fiber produced by the method according to claim 1.

12. Graphite steel produced by the method according to claim 6.