JPS59168113A - Melt-spinning of multifilaments for carbon fiber - Google Patents

Abstract

PURPOSE:When melt-spinning of pitch is effected with a spinneret with a plurality of holes, a specific pressure is applied to the back side of the holes to enable stable and high-speed producion of multifilaments of pitch carbon fibers with high uniformity of less thickness fluctuation. CONSTITUTION:When pitch is melt-spun by means of a spinneret with 500 or more orifices, a pressure higher than 2.0kg/cm<2>.G is applied to the back side of the spinneret holes. EFFECT:The process according to the present invention permits successful spinning even at a high speed over 1,000m/min without bubbles caused by pyrolysis, and yarn breakage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a melt-spinning method for producing pitch-based fibers, particularly pitch-based carbon fiber multifilaments, with a small variation rate of single filament fineness.

Conventionally, known methods for obtaining carbon fibers by melt-spinning pitch include a method of extruding molten pitch using a stationary spinneret, a method using rotary centrifugal spinning, and the like. However, all of these techniques focus on the pitch, carbonization, and graphitization of the spinning dope, and have not even examined the relationship between the properties of melt-spun yarn and the subsequent carbonized and graphitized fibers. Not yet.

However, the temperature dependence of the melt viscosity of Vidge (3-1) is extremely large, and even a slight change in temperature can greatly change the performance.

(2) Since vidge is a mixture, it tends to have uneven viscosity.
In particular, in bits with a developed optically creditable component, there is a difference in viscosity between them and the optically isotropic part, and there is a strong tendency for viscosity unevenness to occur.

(3) At the temperature at which Big is melt-spun, the viscosity is usually 10
The yarn size is extremely low at ~300 voids, and with ordinary melt spinning methods, the single yarn fineness varies greatly, making it difficult to produce 1 q of uniform yarn.

It is known that there are some problems such as:

Conventionally, when manufacturing carbon fiber from such pitch, melt spinning was usually performed at an extremely low speed of 20 III/min ljj degrees using a single hole spinneret, but this method was developed due to the problems of the above-mentioned bitch 4. It was considered a good thing. However, in such conventional techniques, there is no intention to reduce the variation in single yarn fineness and make it uniform, and therefore, in all cases, the fluctuation rate of single yarn fineness is large. In such fibers, the low-fineness fiber portions of filaments 1 to 1 are likely to break or fluff during the spinning and subsequent processes, and if the fineness is adjusted to prevent yarn breakage, the infusibility will become the infusibility. However, the actual situation is that pitch-based carbon fibers have been manufactured at the expense of such yarn properties ↑1.

Such unevenness in fineness becomes more important as the number of bath-melt spun filaments increases, and pitch-based multifilaments have not been produced on a practical level.

In view of this technical background, the present inventors
As a result of intensive research on the technology for industrially producing multifilamen with small filaments, we found that there is a relationship between the back pressure of the discharge hole and the fluctuation rate of fineness, and that the relationship becomes stronger as the number of multifilaments increases. The present invention was achieved by investigating the following.

That is, in the present invention, when melt-spinning pitch using multi-hole gold, I! The back pressure of the exit hole is 2.0KO/cm2
- A method for melt spinning multifilament for pitch-based carbon fibers, which is characterized by performing melt spinning under conditions exceeding G.

By employing such a configuration, the present invention has been able to produce for the first time the bitty-based carbon fiber 1 with a small variation in fineness in the form of a multifilament 1 in a stable and linear manner. In particular, according to the present invention, it is possible to
Even if a multi-hole metal from 0 to 10 is used, it is possible to stably obtain a uniform pitch type fiber.

In the present invention, [11 outlet back surface 11] refers to a branch part where one flow of melt pip is distributed to each nozzle hole, and a branch part where one flow of melt pip is distributed to each nozzle hole. Defined by difference. Unlike ordinary polymers, Pitch G is a mixture of a very wide variety of compounds, and its viscosity is less uniform than ordinary polymers. Even if the pressure is extremely low and there is a slight variation in pressure, non-uniformity of flow is likely to occur between the discharge holes. Therefore, in pitch melt spinning, it is extremely important to increase the above-mentioned discharge hole back pressure to stabilize and equalize the flow between each Tagawa hole.

3- That is, in the present invention, when melt-spinning pitch, the discharge hole back pressure exceeds 2.0 Kg/cm2-G, preferably 2.2 Kg/cm2-G or more, particularly 3°0 tl/cm.
2. It is essential to adopt the condition of G or higher.

When pitch is melt-spun at a pressure lower than the back pressure of the discharge hole, the fibrous fineness of the spun fibers has a large fluctuation rate, and especially in the case of multifilament, the inter-fiber fluctuation rate further increases, forming a homogeneous carbon fiber. I can't.

In the present invention, as a means for increasing the discharge hole back pressure,
How to reduce the diameter of the mouthpiece hole, how to lengthen the length of the mouthpiece hole,
A method of increasing the pressure loss in the distribution pipe up to the mouth hole can be preferably applied. - Pitch-based carbon fibers having a fiber diameter of 30μ or less are usually preferable from the viewpoint of yarn properties after carbonization, but if the discharge per single hole is made smaller, the fineness variation rate will become even larger; By applying the present invention, both the intra-fiber and inter-fiber fineness variations -4= can be significantly reduced.

However, when the diameter of the cap hole is extremely small, for example, 0.1 mm or less, the defect of the cap clogging due to infusible foreign matter in the pitch is likely to occur, requiring countermeasures such as strengthening filtration. Particularly in the case of multifilaments, such defects are likely to occur, so it is preferable to select a cap with a hole diameter of more than 0.1 mm.

[1 gold of the present invention, if there are many holes, C
can also be applied, but usually 100 holes or more, preferably 2
00 small balls or more, more preferably 500 balls or more. In such a multi-ball metal, the back pressure of the discharge hole of the present invention forms a uniform 41-pitch flow in each hole, which is an extremely important requirement. The multifilaments 1 to 1 are industrially produced with excellent pitch uniformity.

In addition, according to the present invention, fibers having a random structure or fibers having a radial structure can be formed as necessary by selecting the pitch as a raw material and the spinning conditions.

For example, when melt-spinning an optically anisotropic pitch, the shear velocity γ in the die hole shown by equation (1) is set to 550 sec-1 or less in the die discharge hole portion, and the following (2
) A multifilament with a random structure can be obtained by using a method of melt spinning with an orientation forming parameter f of 90 or more (jf).

γ-32(:)/π[)3・・・・・・・・・・・・(
1) f−γf[・・・・・・・・・・・・・・・・・・
・・・・・・(2) [Q: Pitch flow Mi (Cm3/s
ec) D: Cap hole diameter (c...) 1: Average residence time in the cap hole (sea)] The average residence time in the cap hole (sea) in the above formula is determined from the following equation (3).

−πD2M/4Q・・・・・・・・・(3) “α:1
"Length of the matching hole Cm)] In this method, the shear rate γ is 2505ec-1
By selectively selecting a strip 1 having an orientation formation parameter f of 50 or less for preferably 150 seconds or less, a multifilament having a highly randomly oriented structure can be stably obtained.

Further, if the above-mentioned shear rate γ is set to 550 sec -1 or higher and the orientation formation parameter [ is set to 100 or higher, 11iH with radial orientation can be formed.

In the case of radial orientation, the shear speed γ is further 650 se
c- or more, and the orientation formation parameter f is 140 or more.
By selectively selecting '1', fibers with a roughly high degree of radial orientation are formed.

Such radial silk yarn exhibits excellent performance in terms of elastic modulus, thermal conductivity, electrical conductivity, etc., while random structure yarn exhibits excellent performance in terms of elasticity and elastic modulus. There is.

To explain fibers with such radial and random structures using micrographs, a-C in FIGS. 1 and 2 show the respective states 7 of the eight fibers immediately after spinning, after infusibility, and after graphitization, respectively. Figure 1 shows an example of a fiber with a radial structure, and a typical Maltese cross pattern is li! be noticed. Note that C in the figure shows such a fiber graphitized, and it can be clearly seen that some of the fibers are cleaved and damaged. 2. Figures a to C are examples of carbon-41 miscellaneous materials that have a random structure, but in any case, it has been found that this structure dominates the fiber at all stages from spinning to graphitization. Zuru. All such phenomena are observed in color under a polarizing microscope. For example, when observing the fiber immediately after spinning as shown in Figure 1a with a polarizing microscope, if we use the Eimura test plate with the direction in which light is captured where the speed of the test plate is smaller as quadrant 1.3, then Section 1.3
The quadrant is observed as blue and the 2.4th quadrant as yellow.

In the case of FIG. 1a, it is also clear that the internal optical orientation components are radially oriented because the observed positional relationship of the ridges does not change even when the sample is rotated.

In addition, in the case where a non-circular mouthpiece discharge hole is employed in the present invention, the diameter of the mouthpiece hole diameter indicated by -F is applied when it is converted to a circular shape having the same cross-sectional area. In addition, according to the present invention, the shear velocity γ is the flow path diameter of the smallest cross-sectional area of the flow path in the nozzle discharge hole portion, and the average residence time 1 is the average residence time in the flow path in the discharge hole portion. It is measured in time.In other words, the flow path means the flow path portion beyond the minimum cross-sectional area that opens to the outside through which pitch is discharged, and does not include the introduction portion that is inserted into a normal mouthpiece.

According to this method, carbon fiber multifilaments having a random structure or a radial structure can be produced economically on an industrial level.

The term "optically gastrotropic pitch" refers to a pitch containing an optically anisotropic component of 60% or more, preferably 75% or more, more preferably 90% or more.

Vidge can also be extruded under pressure using a metering pump or an inert gas, but extrusion using a metering pump is preferably applied. This is particularly effective when forming a uniform multifilament 1 using a large number of discharge holes or when passing through a filtration process.

The single fiber diameter of the spun fiber obtained by the method of the present invention is 30
A diameter of less than μ is appropriate, and preferably a diameter of 5 to 30 μm, more preferably a range of 7 to 20 μm, from the viewpoint of thread breakage and strength, but diameters other than this range are also effective.

According to the method of the present invention, it is possible to spin a uniform multifilament 1 with small fluctuations in single filament fineness at a high speed that could not be achieved conventionally.

For example, 160m/n+in or more, or even 200my
Osin or higher, 300 m/min or higher
I/j yarn is possible, depending on conditions 1000m/m
It is also possible to perform spinning at ultra-high speeds such as in or more. Furthermore, even in such high-speed spinning, continuous multifilaments 1 to 1 having a uniform diameter can be easily produced.

The present invention also has the effect of eliminating foaming and thread breakage defects caused by pyrolysis gas. When pitch is heated to high temperatures, it generates pyrolysis gas, which can form voids in the pitch fibers and reduce its strength, or foam during spinning and cause yarn breakage.
It has its drawbacks. The inventors of the present invention have found that this drawback tends to disappear as the back pressure of the discharge hole exceeds 2.0 kg/cm2.G. This is particularly effective when it is necessary to perform melt spinning at a higher temperature, such as when optically placed 1/1 pitch.

The thus-formed multifilament is then treated to be infusible, carbonized, and graphitized by a conventional method. As the infusibility treatment, for example, a method of oxidizing in the presence of M complex in normal air at 250 to 420°C can be applied.

It is also preferable from the viewpoint of the efficiency of the infusibility treatment to use an oxidizing gas such as A-syn or No2 instead of oxygen. The fibers subjected to such infusibility treatment are then carbonized and graphitized, and any commonly used method can be applied to this method. Such carbonization treatment includes heating to 800-1700°C in vacuum or inert gas atmosphere, and graphitization treatment includes heating to 1700°C or higher in vacuum or inert gas atmosphere. There are ways to handle it.

The present invention will be described in more detail below with reference to Examples.

11- In addition, the measurement method in the examples is based on the method shown below.

[Optical Anisotropy] After embedding the sample in Evogishi resin, it was polished by a conventional method. The polished surface was observed by reverse polarization using an 0RTHOPLAN microscope manufactured by LeitZ.

The presence of an optically anisotropic component was determined from the isotropic portion and anisotropic portion when observed under polarized light as described above.

[Quinoline solution] This was carried out by a method combining the centrifugation method and the transient method specified in JIS-2425.

[Glass transition temperature] Perkin-E 1mer? The measurement was carried out in a nitrogen atmosphere using 08G-2 manufactured by Ishikawa. After heating the sample to 290° C., the sample was cooled to room temperature, heated again, and measured to remove factors that disturb the baseline, such as dehydration peaks.

[Elemental analysis] Using CHN coder MT-3 model manufactured by Yanagimoto Seisakusho, sample decomposition furnace 900-950°C and oxidation furnace 850°C
, reduction furnace 550℃, helium flow rate 180mQ/n+in
Measured under the following measurement conditions.

[Strong elongation measurement] According to the method specified in J.I.5-R-7601.

The fiber diameter was measured using a scanning electron microscope at a portion adjacent to the strength/elongation measuring section. Further, the area of the cleaved fibers was determined from a microscopic photograph of the cross section.

[Single yarn I! Variation rate of i degrees] Take out 30 single filaments from 1 to 30 single filaments after spinning, measure the diameter of each single filament using a scanning electron microscope, and calculate the variation rate (CV%) using a conventional method. did.

Example 1 Commercially available petroleum pitch was pressure-filtered at 300°C using a 200 mesh glass tube, and then at 310°C and 1011°C.
1111H (L) for 30 minutes to remove low boiling point components. When the obtained pitch was observed with a polarizing microscope, it was found to be substantially optically isotropic. Using 5300-hole eyelets with various hole diameters, the spinning temperature was 280°C and the spinning speed was changed to obtain a -C average diameter of 1.
Pitch fibers of 0-13μ were obtained. The results are shown in Table 1.

Table 1 0 Gold No., hole diameter hole length back pressure speed fluctuation rate 1
0.20 +, 20 6,30 600
312 0.30 0,4 (10,41783
0,303,10'2,20 324
0.30 3.10 0.37 100 8
35 0.50 8,50 2.20 1000
In Table 36, Pore diameter: [:1 Gold hole diameter (mm) Hole length: Gold hole length (mm) Speed: Spinning speed (lIl, /l1lin) Back pressure: Discharge hole back pressure (Kg/cm2・G) Variation rate :Single yarn fineness variation rate (%) In the present invention examples of NO, 1, 3, and 5, the discharge hole back pressure is 2.2f
ll/cm2・G twin yarn with a small fluctuation rate was obtained. On the other hand, in Comparative Examples Nos. 12 and 4, the back pressure of the discharge hole was too small and uniform threads could not be obtained.

Example 2 Coal tar bidge with a softening point of 80°C was heated in a nitrogen atmosphere for about 1 hour to raise the temperature to 410°C and melt it. Heat treatment was performed at 410° C. for 12 hours while stirring. Then, nitrogen was pressurized at 380°C for 20
Insoluble matter was removed by filtration using a glass door of 0.0 ml, followed by vacuum treatment at 420° C. and 5 mm Hgr to remove low-boiling components.

After embedding the obtained pitch in an epoxy resin and polishing it, observation using a reflective polarizing microscope revealed that about 90% or more of the pitch was an optically anisotropic component. The optically anisotropic structure showed a large flow shape. The characteristics of the heat-treated pitch are that the gynoline insoluble content is 63W [
%, a softening point of 340°C, a glass transition temperature of 195°C,
The elemental analysis results were: carbon 93W[%, hydrogen 3.7wt%,
Nitrogen'i, owt%-1! , 1-.

Using this heat-treated pitch, various spindles with different hole diameters and hole lengths were used, and the spinning temperature was 380°C and the spinneret surface temperature was 35°C.
Melt-spun at 5℃, taken off at various yarn speeds, with an average diameter of 1
Various threads of 2μ were obtained.

The molten pitch was distributed at the back of the die into flows corresponding to each discharge hole. The resulting spun yarn has a hardness of 1°3 (1/cm3).
The density of the molten pitch was 1.1 g/'Cll13.

This yarn was placed in a hot air circulation oven and subjected to infusibility treatment in air. The conditions for the infusibility treatment were as follows: First, the temperature was raised from room temperature to 150°C for about 5 minutes, and the temperature was maintained at 150°C for 15 minutes from the start of the temperature rise. Then, the temperature was increased at a rate of 1°C/mi from 150 to 310°C.
The temperature was raised at 310° C. for 30 minutes to complete infusibility. This infusible thread was heated from room temperature to 1200℃ for 5℃ and 7m.
The temperature was raised to 1n to carbonize, and the mixture was further graphitized at 2500°C.

Table 2 summarizes the cross-sectional optical anisotropic structure, strength characteristics, etc. of the graphitized yarn obtained.

In the case of N006.9 according to the present invention, the discharge hole back pressure is 2° 16
-2K(]/Cm2 ・0 or more C was obtained, and a uniform yarn with a small fluctuation rate of medium yarn fineness was obtained, but on the other hand, comparative example No. 7
, E3.101.11 has 11 holes and has a low uniform thread (14 was not formed).

Example 3 The optical internal orientation pitch used in Example 2 was changed to 300 with an aluminum distribution plate 1 upstream of the mouthpiece discharge hole 2 shown in FIG.
A graphitized yarn was obtained in the same manner as in Example 2, except that Whole Rokin 3 was used, the spinning temperature was 370°C, the spinneret surface temperature was 345°C, and the spinning speed was 600 m/min. The density of the yarn after melt spinning was 1.3 g/'Cm3, and the density of the melt pitch was 1.19/cn+3.

The nozzle used had a discharge hole diameter of 0.50 mm and a hole length of 4.5 Qll.
1 m, the shear speed T is 110 sec-+, the average residence time t is 0.66 sec, and the orientation formation parameter f is 8.
It was 9. The shape of the flow path 4 from the distribution plate on the upstream side of the mouthpiece to the discharge hole has a diameter of 1. On+n+, the quality was 117n+m, and the back pressure of the discharge hole was 2.1K or 7cm2-G.

The obtained pitch fiber has a fineness variation rate of 38%, and the graphitized yarn calcined at 2500°C has a strong [&2
2OK (1/mm2, elastic modulus 45 ton/m11
12, and the cross section is Ili! under polarized light. The observed result was that the anisotropic phases were arranged randomly.

For comparison, when spinning was performed in the same manner using only 1 gold without using the distributor 1, the back pressure of the discharge hole was 0° 8 kg/cm.
・G was low, and the fineness fluctuation rate was 60%, which was highly variable.

[Brief explanation of drawings]

Figures 1 and 2 are polarized light micrographs of cross-sections of each fiber having a radial 4 structure and a random structure, tracing the structural changes from spinning to graphitization. Third
The figure shows an example of installing a distribution plate, which is an example of the present invention. In the figure, a shows a cross-sectional view of a fiber called green fiber immediately after melt spinning, b shows a cross-sectional view of the fiber after infusibility, and C shows a cross-sectional view of the fiber after graphitization. Further, 1 is a distribution plate, 2 is a nozzle discharge hole, and 3 is a nozzle portion. Patent applicant Toshi Co., Ltd. 2
1- Figure 1

Claims (1)

[Claims] A method for melt-spinning multifilaments for carbon fibers, characterized in that when pitch is melt-spun using a multi-hole metal, the melt-spinning is performed under conditions where the back pressure of the discharge hole exceeds 2.0, OKCl/cm2.G.