JPS63249721A - Production of carbon fiber and apparatus for centrifugal spinning used therefor - Google Patents

Abstract

PURPOSE:To rapidly lower the surface temperature of discharged pitch and reduce shots, etc., by controlling the temperature near the nozzle surface to a low value. CONSTITUTION:Coal or petroleum pitch 3 is fed to a heated rotating spinning nozzle 5 and discharged from nozzle holes 7 to the outside air and form a drawn and fiberized pitch 8. Cooling air 12 is fed from cooling gas feeding nozzles 9 and 10 to keep the atmospheric temperature near the nozzle surface at a low value. the temperature of pitch discharged from the nozzle holes is kept at 200-400 deg.C and controlled so that the ratio (l/d) of the distance [l(m)] apart in the radial direction from the nozzle surface to the nozzle hole diameter [d(m)] may be within the range of 10-20 and the atmospheric temperature (t) may satisfy the relation expressed by the formula t<=Sp-K.(l/d).(T-Sp) [Sp is softening point ( deg.C) of the raw material pitch: T is the discharging temperature ( deg.C) of the pitch; K=0.013].

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing carbon fibers using coal-based and petroleum-based pitches as raw materials, and a centrifugal spinning apparatus used in this method.

(Prior Art) Many reports have been made so far regarding centrifugal spinning technology used to produce carbon fibers using coal-based or petroleum-based pitch as a raw material. Conventional centrifugal spinning techniques are disclosed, for example, in Japanese Patent Application No. 60-246085 and Japanese Patent Application Publication No. 57-1544.
As seen in Publication No. 16, etc., both prevent the temperature drop in the atmosphere near the nozzle surface during spinning by processing the surface of the spinning nozzle or supplying hot air, or actively heat it to improve the molten state of the discharge pitch. The aim was to increase the stretching effect by increasing the length of flight in the process to obtain thinner fibers, and to suppress the occurrence of clumps (shot) of pitch that did not turn into fibers.

(Problems with the conventional technology) However, as mentioned above, when the temperature of the nozzle surface atmosphere is increased, the drop in the pitch temperature immediately after discharge is prevented, and the viscosity of the pitch does not increase and the rigidity of the pitch does not increase. As a result of the poor stability of the pitch cone formed at the exit, yarn breakage is more likely to occur, and the number of shots caused by this is increased. At the same time, nozzle surface contamination increases, such as the adhesion of low-viscosity pitch to the nozzle surface and vapor generated from high-temperature pitch adhesion to the nozzle surface. Furthermore, the number of shots caused by nozzle surface contamination also increases.

The shot contained in the spun fibers causes quality deterioration such as a decrease in strength and appearance of the carbon fiber product. In addition, nozzle surface contamination during spinning not only causes the occurrence of shots, but is also the biggest factor that hinders the extension of continuous spinning time.

Therefore, an object of the present invention is to provide a draw-spinning technique that can reduce the occurrence of this shot and reduce the nozzle surface contamination.

(Means for Solving the Problems) In the present invention, the above-mentioned shot generation and nozzle surface staining can be prevented by keeping the ambient temperature near the nozzle surface low, contrary to the common sense of conventional draw-spinning technology. That is.

If a method of lowering the discharge pitch temperature (and increasing the viscosity) is adopted, pitch cone stability increases, yarn breakage decreases, shot occurrence and nozzle surface fouling are also reduced, but spinning temperature (
Lowering the discharge pitch temperature itself lowers the drawing efficiency and makes it difficult to obtain thin fibers, making it difficult to use. However, in reality, lowering the temperature of the surface layer of the discharge pitch is effective in increasing the stability of the pitch cone and preventing nozzle surface contamination caused by low viscosity pitch and steam generation. If is high, the stretching efficiency is hardly affected by the temperature of the nozzle atmosphere. For this reason, the present invention aims to solve the problem by keeping the ambient temperature near the nozzle surface, which was conventionally attempted to be kept as high as possible, at a low temperature and quickly lowering the temperature of the discharge pitch surface. It is something to do.

The present invention aims to quickly lower the discharge pitch surface temperature and reduce shots by controlling the temperature near the nozzle surface to a low temperature, but the temperature in the very vicinity of the nozzle surface is difficult to measure and control. Furthermore, measuring the temperature in the region after the pitch has been completely stretched and made into fibers is ineffective and meaningless. Furthermore, the temperature to be controlled also varies depending on the diameter of the pitch fibers to be discharged.

Therefore, the present inventors conducted spinning using standard pitch as a raw material under various conditions, and found that the distance 1! (m) and the nozzle hole diameter d (m), the ambient temperature t is within the range of 10 to 20 (C1l/d)
is the following formula: % formula %) (1) (In the formula, K = 0.013, Sp is the softening point of the raw material pitch ('C), and T is the pitch discharge temperature (C)). It has been found that when the temperature is satisfied, stains on the shot and nozzle surfaces can be reduced without being particularly affected by temperatures outside the range, and the present invention has been completed.

That is, in a method for producing carbon fiber using coal-based or petroleum-based pitch as a raw material and using a rotating disk-shaped spinning nozzle in a centrifugal spinning process in which the nozzle hole discharge pitch temperature during spinning is 200 to 400°C, f/d. The ambient temperature t within the range of 10 to 20 is expressed by the following formula: %
The present invention relates to a method for manufacturing carbon fiber characterized by controlling the relationship expressed by the formula (%) (1).

In addition, the present invention provides a centrifugal spinning apparatus used for realizing such a method, in which a cooling gas supply nozzle of an atmosphere cooling apparatus that discharges a cooling gas controlled to satisfy the relationship of equation (1) is connected to a spinning nozzle. The present invention relates to a centrifugal spinning device characterized in that it is provided in a pair of upper and lower sides or only on the upper side or the lower side with respect to the hole surface.

Actually, if the temperature at the position where the value of ff/d is 10 and 20 satisfies the relationship (1) 2 above, then jl'/d
It has been confirmed that the conditions necessary for the present invention are satisfied within the range of =10 to 20.

In addition, when using a raw material with physical properties extremely different from ordinary coal and petroleum-based pitch, the value of K in the above formula (1) is 0.0.
13 is expressed by the following formula: % formula %) (2) Here, ω: throughput per nozzle hole (k!/hour).

Cp: Raw material specific heat (Kcal/kg"C) h: Raw material thermal conductivity (Kcal/m.hr."C).

μ: Atmospheric gas viscosity (kg/m・sec) ρ: Raw material density (kg/m3).

■: Nozzle surface flow velocity (m/hour) Just replace it with the value found in .

In order to satisfy the above conditions, it is necessary to remove the hot air supply device, etc., which are normally installed in conventional centrifugal spinning apparatuses to maintain the ambient temperature near the surface of the spinning nozzle. Even so, the ambient temperature near the nozzle surface is usually quite high due to radiant heat on the surface of the spinning nozzle and heat due to the discharge pitch. Therefore, it is generally necessary to install a nozzle for supplying cooling gas or the like effective in lowering the ambient temperature near the nozzle surface near the spinning nozzle, and to constantly supply the cooling gas near the nozzle surface during spinning. The cooling gas supply nozzles of the atmosphere cooling device may be set in pairs on the upper and lower sides of the spinning nozzle hole surface, only on the upper side, or only on the lower side, as long as they can be set to the conditions shown by the above formula (1).

In addition, regarding the temperature and amount of the cooling gas to be supplied (
1) The combination of numerical values is not particularly specified as long as it is within the range that can be set to the conditions shown by the formula.

However, if it is possible to set the temperature near the surface of the spinning nozzle to the condition shown in equation (1) above by keeping the atmosphere around or in the room where the spinning device is installed extremely low, , the cooling gas supply nozzle can be omitted.

(Function) FIG. 1 shows a preferred example of the centrifugal spinning apparatus of the present invention. The heated and melted pitch 3 is supplied by a metering gear pump 1 through a raw material supply pipe 2 to a rotating spinning nozzle 5 heated by a heater 4 . The thus supplied pitch is discharged into the outside air from the nozzle hole 7 by the centrifugal force of the nozzle and the pressure generated by the liquid thickness 6 inside the nozzle 5, and is drawn and turned into fibers 8. At this time, air 12 controlled to room temperature or low temperature is supplied by the atmosphere cooling device 13 from the cooling gas supply nozzles 9 and 10 provided above and below the spinning nozzle 5 to keep the ambient temperature near the nozzle surface low.

As a result, the temperature of the surface layer of the discharged pitch 3 decreases rapidly, and its surface viscosity increases, which increases the rigidity of the pitch cone 11 and the portion 12 following it, and increases the resistance against high relative atmospheric velocity. Furthermore, the shape stability is improved, the occurrence of thread breakage due to breakage of the pitch cone 11, etc. is reduced, and the occurrence of shots caused by this is reduced.

Furthermore, since the temperature of the surface of the pitch 11 discharged at high temperature rapidly lowers, the generation of steam is suppressed, and the adhesion to the nozzle surface is reduced, resulting in less contamination on the nozzle surface.

(Example) Next, the present invention will be explained based on Examples and Comparative Examples.

112, 611-3 Using a spinning nozzle with a nozzle hole diameter of 0.5 mm and rotating at a circumferential speed of 27 m/sec, the softening point S, = 230''C
The raw material pitch was spun at a discharge temperature T=310°C. The results obtained are shown in Table 1 below. In Table 1, Comparative Examples 1.2 can be said to be within the range of spinning conditions based on conventional ideas. In addition, the amount of contamination on the nozzle surface refers to the amount of contamination on the nozzle surface after one hour of continuous spinning, as shown in Figure 2. It is the value obtained by dividing the weight of the kimono by the area covered.

・13 4, 6 Using a spinning nozzle with a nozzle hole diameter of 0.3 and rotating at a circumferential speed of 36 m/sec, raw material pitch with a softening point of 5P = 280 °C was spun at a discharge temperature of T = 350 °C. went. The results obtained are shown in Table 2 below. In Table 2, Comparative Examples 4 and 5 can be said to be within the range of spinning conditions based on conventional ideas.

Further, the amount of nozzle surface contamination was determined in the same manner as in Example 1.

(Effects of the Invention) As confirmed in Tables 1 and 2 above, when the ambient temperature near the surface of the spinning nozzle reaches the value specified in the present invention,
It can be seen that the amount of shot contained in the fibers and the amount of nozzle surface contamination are drastically reduced. A reduction in shot ffl directly leads to an improvement in product quality, and a reduction in the amount of surface contamination leads to an extension of the continuous operation time of the spinning device. Usually, when the amount of nozzle surface contamination exceeds 10 mm g, the fiber quality deteriorates, so in the conventional spinning method in Comparative Examples 1, 2.4, and 5, the continuous operation time was extremely short, but in Examples 1 to 4, the continuous operation time was extremely short.
Since it takes quite a long time to reach this value of 10 mm g, it can be seen that it has a great effect on extending the continuous operation time.

Furthermore, from a comparison of the average fiber diameters of each Example and Comparative Example, it was confirmed that even if the temperature of the nozzle surface atmosphere was kept low, the effect of stretching was not significantly reduced.

As explained above, the present invention is sufficiently effective in reducing the occurrence of shots and nozzle surface contamination during carbon fiber production.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an overview of a centrifugal spinning apparatus as an example of the present invention in operation and equipped with a cooling air supply nozzle, and FIG. 2 is a nozzle surface contamination amount as an indicator of the degree of nozzle surface contamination. FIG. 2 is a side view of the centrifugal spinning apparatus main body showing a measurement target range. l... Metering gear pump 2... Raw material supply pipe 3.
...Feed material pitch 4...Nozzle heating heater 5...Centrifugal spinning nozzle 6...Liquid thickness 7...Nozzle hole 8...
- Fiber (chemical pitch) 9... Cooling gas supply nozzle (top) 10... Cooling gas supply nozzle (bottom) 11... Pitch cone 12... Cooling gas 13... Atmosphere cooling device

Claims (1)

[Scope of Claims] 1. Production of carbon fiber using coal-based or petroleum-based pitch as a raw material and having a nozzle hole discharge pitch temperature of 200 to 400°C during spinning in a centrifugal spinning process using a rotating disc-shaped spinning nozzle. In the method, the ratio of the distance l (m) radially away from the spinning nozzle surface and the nozzle hole diameter d (m)
The atmospheric temperature t in the range of l/d) from 10 to 20 is expressed by the following formula: t≦S_p-K・(l/d)・(T-S_p) (1)(
In the formula, K=0.013, S_p is the softening point of the raw material pitch (
A method for producing carbon fibers, characterized in that the method is controlled to satisfy the relationship expressed by: (°C) and T is a pitch discharge temperature (°C). 2. In a centrifugal spinning device equipped with a rotating disc-shaped spinning nozzle, the distance l in the radial direction from the spinning nozzle surface
(m) and the nozzle hole diameter d (m) (l/d) is 10~
The ambient temperature t within the range of
In the formula, K=0.013, S_p is the softening point of the raw material pitch (
The cooling gas supply nozzle of the atmosphere cooling device, which discharges cooling gas controlled to satisfy the relationship expressed by A centrifugal spinning device characterized in that it is provided in a pair or only on the upper side or the lower side.