JPS61620A - Spinning of carbon fiber - Google Patents

Abstract

PURPOSE:To produce the titled fiber having high strength and quality, by introducing molten precursor pitch into a pressurizing part of a spinning apparatus, keeping under high pressure to dissolve bubbles into the pitch, and extruding and spinning the pitch, thereby removing fine bubbles in high efficiency and enabling stable and continuous spinning of the pitch. CONSTITUTION:In the production of carbon fiber by the melt-spinning, infusibilization, carbonization, or further graphitization of a precursor pitch, the precursor pitch is melted by heating in the melter 1, introduced into the pressurizing part 3 of a spinning apparatus with a gear pump 2, and maintained under a high pressure of >=50kg/cm<2> to dissolve fine bubbles into the pitch. Thereafter, the precursor pitch is transferred to the nozzle header 5 with the gear pump 4 attached to the downstream side of the pressurizing part 3, extruded through the nozzle 6 to effect the melt-spinning, collected with the collector 7, and wound around the bobbin 8. The produced fiber is infusibilized and carbonized to obtain the objective carbon fiber.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention belongs to the field of pitch (petroleum, coal)-based carbon fiber production, and the technical content described in this specification is based on the production of adjusted precursor pitch under high pressure. [Prior art] In carbon fiber production, precursors obtained through a pitch adjustment process are proposed. Pitch is determined by the next melt-spinning process, which gives the fiber shape and also determines its diameter.In general, the smaller the diameter of carbon fiber, the higher its strength, so it is necessary to produce thinner and longer fibers in the spinning process. However, when compared to polyester and polypropylene, which are common raw materials for melt spinning, pitch-based materials have the drawbacks of being difficult to maintain quality stability and being stiff and having poor spinnability. Therefore, it has been difficult to stably spin long fibers with a pitch of about 10 μrn for a long time.

In this sense, when producing pitch-based carbon fibers, it is important (for stable spinning) to completely remove insoluble matter and air bubbles that cause yarn breakage during melt spinning of precursor pitch. Particularly in the case of pitch, since its molecular weight distribution is large, low molecular weight volatile components gasify near the spinning temperature, and residual components of the organic solvent used in the process of preparing precursor pitch gasify and form fine bubbles, causing spinning. This often causes thread breakage inside. Furthermore, even if the fibers do not break, air bubbles remaining in the fibers cause defects in the fiber structure, which has an adverse effect such as significantly lowering the strength of the carbonized or graphitized fibers.

Therefore, in the melt spinning of blender pitch, it is an important technical problem to sufficiently remove the solid content in advance and remove air bubbles mixed in the pitch (defoaming). ) Therefore, when the solid content has been sufficiently removed, what remains is defoaming, and conventionally, the most common defoaming method is a stationary defoaming method. This stationary defoaming method is a method in which precursor pitch is heated to a high temperature to a viscosity of about 1 to 40 poise, held for about 15 to 60 minutes, and air bubbles mixed in the pitch are floated and separated under reduced pressure. It is. Using this method, the coarse air bubbles taken in by the pitch can be removed quite efficiently.However, the defoaming viscosity is still high, so it is difficult to remove the fine air bubbles (about a few μm) that are mixed in the precursor pitch. It requires a holding time of several hours or more, and a vacuum degassing operation of about 15 to 60 minutes is insufficient.Furthermore, in the case of fc, which takes several hours to carry out this treatment, the precursor pitch It has been confirmed that when the pitch is exposed to high temperatures for a long period of time, the quality of the pitch changes and its spinnability is significantly impaired.

In order to overcome this drawback, it is possible to reduce the viscosity by 1 poise or less, but this is not suitable because it not only causes severe foaming of the precursor pitch itself but also promotes coking of the pitch.

In the end, the inventors' research revealed that not only is it not easy to efficiently remove air bubbles of several micrometers using the conventional static degassing method, but also that this method can stably and continuously form pitch fibers of about 10 micrometers without yarn breakage. It has been found that spinning is extremely difficult. The purpose of the present invention is to realize stable continuous spinning by efficiently removing air bubbles mixed in the precursor pitch, especially fine air bubbles of several μm or less. In particular, the gist of the present invention to achieve this objective is as set forth in the claims at the beginning of this specification.

(Means for Solving the Problems) The present inventors studied precursor pitches containing fine bubbles, and found that the pitch was several tens of ky/cm.
It was found that when held under the above high pressure, most of the microbubbles of 10 μm or less were dissolved into the pitch. However, the viscosity suitable for precursor pitch spinning is 1500 poise or less, which is lower than the spinning viscosity of polyester #17) E1J7-.
It was practically difficult to spin fine fibers while dissolving the air bubbles by applying an extrusion pressure of .

Therefore, in the present invention, a zero-pressure part is provided in the spinning device, especially in front of a part of the nozzle header, and the precursor pitch is pressurized here to dissolve the fine bubbles, and while maintaining that state, the pitch is transferred to the nozzle hole. We adopted a method of discharging more water and winding it up on a pobbin.

As a result, stable spinning with almost no yarn breakage was possible.

The degree of pressurization performed in the method of the present invention depends on the type of precursor pitch, but a pressure of 50 kg/1wr" or more, preferably 80 kg/an or more is applied to the precursor pitch, and If the residence time in the pressurized part is 10 minutes or more, preferably 20 minutes or more, the bubbles will dissolve and almost disappear, and the bubbles will remain dissolved and remain in the precursor state. In order to realize pitch spinning, it is necessary to feed the pitch into a part of the nozzle header within 10 minutes, preferably within 5 minutes after passing through the pressure section, and discharge the pitch from the nozzle hole for spinning and wind it onto a bobbin.Pressure section The fact is that if the precursor pitch that has gone through the process stays for more than 10 minutes in a part of the nozzle header, the dissolved air bubbles will reappear, causing yarn breakage, creating defects in the fiber structure, and reducing the strength of carbonized and graphitized fibers. I found out.

(Function) Next, the limitations of the above numerical limitations will be explained in conjunction with the explanation of the apparatus used to carry out the method of the present invention.

Figure 1 shows the IFi melter in Figure 0, which shows the overall view of the spinning apparatus according to the present invention. Hold and let stand to defoam. 2 in the diagram is a gear pump, which is a precursor that has undergone the above treatment.
The pitch is fed into the next stage pressurizing section 8 and pressurized to a predetermined pressure to dissolve microbubbles in the pitch.The residence time of the precursor pitch in this pressurizing section is 20 minutes, and the downstream Use another gear pump number on the side to set the blender pitch to 4.
At this time, the time required for the pitch to be discharged from the nozzle hole, that is, the residence time of the nozzle header part 5, was set at 6 minutes at a flow rate of CC/min. The nozzle 6 used has a nozzle hole diameter D = 0.8
mmφ, %=8.50 hole, and the discharged precursor pitch is 5 on the winding bobbin 8 via the concentrator 7.
It was wound up continuously at a speed of 0.00 m/min.

FIG. 2 shows a sectional view of the pressure section 8. As shown in FIG. This pressurizing section 8 is composed of a bubble dissolving section 9, a pressure sensor 10, a 10 μm filter 11, a buffer plate 12, and a gear pump number. The buffer plate 12 has four pores of 1 mmφ, and is designed to prevent the inlet pressure to the gear pump 4 from becoming too high by increasing the pressure loss in this part.0 Without this buffer plate, the gear pump will not work. The inlet pressure to 4 becomes too high, and the precursor pitch flows out from the gear clearance, making it extremely difficult to control its flow rate.

Using the above device, we investigated a suitable pressure level in the pressurizing section. The precursor pitch used in this study had a softening point of 251°C and a benzene insoluble content of 5'7.2.
It is an optically isotropic pitch containing a trace amount of quinoline dissolved in %.
50 kg/cmg% 80 kg/lyn", 100
The yarn breakage time in Table 0, which shows the spinning test results when a pressure of 47 cm'' was applied, represents the time from the start of winding until one fiber forms a broken line.

From Table 1, it can be seen that the pressure to be applied by the pressure section is preferably 7 m or more per 50, more preferably 801 v/2 or more.

Next, using the same spinning device and precursor pitch, we investigated the residence time in the pressurizing section.◇This is an example of conducting a spinning test with varying residence times.1. At this time, the pitch pressure (76, 79° 80) /elN'' in the pressurizing section was changed by changing the internal volume of the bubble dissolving section during pressurization.Other spinning conditions is the same as the above example.The results are shown in Table 2.Table 2 shows that in order to perform stable spinning, the residence time in the pressurizing section is required to be at least 10 minutes. Furthermore, using the same spinning device and precursor pitch, the influence of the residence time of some nozzle headers of the precursor pitch on the effect of the present invention was investigated.As a specific method, a conical shape was This is a spinning test in which the internal volume of the nozzle header was changed by incorporating a container, and the residence time there was changed.The bit pressure at the pressure section at this time was 80 kg/2, and the residence time there was 20 minutes. The results are shown in Table 8, which shows that the residence time of the precursor pitch in a part of the nozzle header needs to be within 10 minutes at most in order to perform stable continuous spinning. Table 8 In addition, when a spinning test was conducted by removing the pressurizing part in the above-mentioned spinning device and directly connecting a part of the nozzle header of the melter, yarn breakage occurred once every 8 to 6 minutes. , it was not possible to perform good spinning.

(Example) Precursor pitch, which is an optically isotropic pitch with a softening point of 251°C, a benzene insoluble content of 57.2%, and a trace amount of quinoline solution, was used, and the apparatus shown in Figures 1 and 2 was used. ,
80.50 on the pitch. 8 to 5 show how the diameter of bubbles mixed in the pitch changes over time when a pressure of 9/cx is applied to the pitch. In this example, the precursor pitch that had been subjected to pressure treatment for a certain period of time was rapidly cooled and sampled, and the diameters of the mixed bubbles were measured to obtain a bubble diameter distribution curve. This was compared with the bubble diameter distribution curve of precursor pitch that was not subjected to pressure treatment, and the change in bubble diameter over time was tracked. Then, 1 (1
It was confirmed that the diameter of bubbles of about 1 μm was reduced to 1 μm or less, or they disappeared completely.

For this reason, when spinning the precursor pitch treated as described above, it was possible to perform stable spinning for a long time without yarn breakage caused by air bubbles. When we removed the pressurizing part and directly connected the melter and a part of the nozzle header and performed a spinning test under the same spinning conditions and precursor pitch, thread breakage occurred once every 8 to 6 minutes. However, it was not possible to perform good spinning. (Effect of the invention) According to the spinning method of the present invention described above, air bubbles mixed in the pitch can be completely defoamed or dissolved and disappeared.
Enables stable continuous spinning without yarn breakage,
Moreover, it is possible to obtain carbon fiber with high strength.

[Brief explanation of the drawing]

Figure i1 is a route diagram of the spinning apparatus used to carry out the method of the present invention; Figures 2 (a) and (1)) are cross-sectional views illustrating the structure of the pressurizing section employed in the present invention; and Figure 8. Figures 4 and 5 are graphs showing the change in bubble diameter over time when the pressurizing pressure is changed.0 1...Melter 2...Gear pump 8...
・Pressure part number... Gear pump 5... Nozzle header 6... Nozzle grating 7... Concentrator 8... Winding bobbin 9... Bubble melting part 10... Pressure sensor 11...・10μ filter 12... Buffer plate O 3rd diagram A Tlf fal (mirri 4th diagram Shudan time (min)

Claims (1)

[Scope of Claims] 1. In the melt spinning of the precursor pitch in the process of manufacturing carbon fiber by melt spinning, infusibility treatment, carbonization treatment, or further graphitization of the precursor pitch, for the precursor pitch after melting, 1. A method for spinning carbon fibers, which comprises introducing the carbon fiber into a pressure section provided in a spinning device and maintaining it at a high pressure to dissolve bubbles, and then performing discharge spinning. 2. The pressure for maintaining high pressure in the pressurizing part of the precursor pitch is 5.
The spinning method according to claim 1, wherein the spinning method is 0 kg/cm^2 or more. 3. The time period for which the precursor pitch is allowed to stay in a high-pressure pressurizing section is 10 minutes or more, and the precursor pitch after passing through the pressurizing section is spun by being discharged from a nozzle hole within 10 minutes. The spinning method according to scope 1.