JPH01221521A - Spinning of pitch - Google Patents

Abstract

PURPOSE:To obtain a uniform pitch fiber by delivering molten pitch into a water vapor-contg. high-speed air flow to decrease the content of nonfibrous formed product in the resultant fiber. CONSTITUTION:(A) A molten pitch is delivered through a spinneret around which (B) an air containing water vapor or combustion exhaust gas containing water vapor is allowed to flow pref. under a negative pressure, on a water column basis, of 100-1,000mm at a speed of >=100m/sec, thus obtaining the objective pitch fiber.

Description

Detailed Description of the Invention (a) Field of Industrial Application The present invention relates to a method for melt-spinning pitch.6 The present invention relates to a method for melt-spinning pitch.6 This invention relates to a method for spinning melt-spinning pitch by pulling molten pitch with a high-speed air current to form fibers. Concerning how to reduce the amount of.

(b) Conventional technology As a method that allows extremely high-speed spinning in melt spinning, there is a method called the so-called melt blow method, in which a high-speed airflow flows out from around the spinning hole and is pulled by this airflow to form fibers. Are known.

As one type of melt blowing method, US Patent 3,8
No. 25.380 and No. 3,849.241 use a nine-edge die with a nine-edge cross section, a spinning hole or slit is provided at the tip of the die with a triangular cross section in the center, and a knife spindle is provided on both sides of the center die. A technology has been disclosed in which high-temperature air is jetted out from a shaped air discharge slit to blow away the polymer liquid discharged from the central part, atomize it, form it into a fibrous form, and collect the fibers on a collection surface. ing.

JP-A-58-132079 discloses a method of spinning pitch using such a knife-type spinneret. In this method, high-softening point petroleum pitch with a softening point of 250°C or higher and a mesophase content of practically 0% is used as a raw material and is melt-blown spun. Although a good nonwoven fabric can be obtained with such pitch, the mesophase content is Melt-blown spinning using this method is difficult and expensive because it uses pitch as a raw material, which has a high content of carbon.

There is some ambiguity in the description of this patent, but when pitch with a large amount of mesophase is used as a raw material, polycondensation of the pitch progresses rapidly upon heating, which may result in a decrease in spinnability. It is presumed that this is because different components separate and separate, resulting in a decrease in spinnability.

Another method of melt-blown spinning is U.S. Pat.
In No. 0.570, a tubular spinning hole for extruding the fiber raw material is provided in a nozzle that blows out heated air, and the fiber-forming thermoplastic polymer, which is the fiber raw material, is extruded from the tubular spinning hole, and the fiber-forming thermoplastic polymer is extruded by the heated air. A method is disclosed in which fibers are formed by traction and sent to a collection device to be formed into a nonwoven fabric.

The problem with this method is that the heated air quickly spreads out after exiting the nozzle, resulting in insufficient traction. For this reason, it is necessary to raise the heated air temperature to an extremely high temperature to increase the jetting speed and to lower the viscosity of the fiber-forming thermoplastic polymer. Therefore, the problem is that the cost of heating the air is extremely high.

In particular, when the fiber raw material is a material such as pitch that has extremely low strength during spinning, even if you try to increase the traction force by preventing the traction air from spreading, the spun yarn may break due to the vortex of the air. , it is difficult to increase traction.

When performing melt blow spinning using air that is much hotter than the temperature of the fiber raw material, there is a problem that the temperature below the spinneret becomes high and the coagulation of the spun yarn is slow. When the coagulation of the spun yarn is delayed, the spun yarn tends to become non-uniform, resulting in low carbonization yield and generally low strength of the resulting product.

In the case of pitch fibers, the spun yarn is inherently extremely brittle;
A decrease in the uniformity of the spun yarn results in a significant increase in the weak points of the fibers, which poses a problem that makes the spun yarn extremely difficult to handle.

(C) Problems to be Solved by the Invention The present invention solves the problems that occur frequently when pitch is melt-blown spun, and that the coagulation of the spun yarn is slow and the resulting spun yarn tends to be non-uniform. The purpose is to resolve the points.

(D) Means for Solving the Problems The present invention provides that when molten pitch discharged from a spinning hole is pulled by a high-speed airflow flowing out from around the spinning hole to form fibers, the high-speed airflow contains water vapor as the main component. This is a pitch spinning method characterized by containing.

Steam, especially superheated steam, or combustion waste gas is used as the high-velocity air flow.

The advantage of using an air stream containing water vapor is primarily that the jet velocity from the nozzle is high and the traction force is high. Water vapor has a lower viscosity than air, so it is not suitable for traction due to fluid viscosity, but in the case of pitch, the spun yarn is easily broken, so the traction force due to the negative pressure generated by the ejector effect at the discharge hole is This appears to be the reason why the traction force of water vapor is so large.

Second, it has a large infrared radiation ability and is rapidly cooled by radiation cooling. Since air is almost transparent to infrared rays and has a low thermal conductivity, it acts as an extremely efficient heat insulator for the spun yarn. Air is mainly cooled by forced convection heat transfer that entrains surrounding low-temperature air. For this reason, the spun yarn is cooled relatively slowly, and the resulting spun yarn tends to have poor uniformity, tends to break easily, and tends to have an increased number of shots.

In the case of water vapor, if you surround it with a material that is low temperature and has a high ability to absorb infrared rays, it will absorb a large amount of infrared rays emitted by the water vapor, and the water vapor will be rapidly cooled. When the water vapor temperature is below 200°C, cooling becomes very slow, but in this temperature range the pitch is solidified and stress relaxation does not proceed, so there is little effect on yarn quality and shot appearance.

When using combustion waste gas as an air stream, it is preferable to use hydrocarbons as the fuel, and to adjust the temperature of the combustion waste gas, it is preferable to blow water into it to increase the water vapor concentration. The water vapor concentration is preferably 10 to 50 VoI%. It is preferable that the waste gas does not have a high concentration of carbon dioxide. Carbon dioxide has a high infrared emissivity, but as the concentration of carbon dioxide increases, the speed of ejection from the nozzle decreases, which reduces the ability to pull the spun yarn. This is not preferable because it reduces the

The speed of the airflow that pulls the spun yarn is 100 m/s or more at the point where it is ejected from the nozzle, preferably 60 to 2 times the sound speed of the airflow.
00%, most preferably 70-100% of the speed of sound.

If the airflow velocity is too low, there will be insufficient traction force.
The fiber diameter becomes larger, the fiber length becomes longer and non-uniform, and
It is undesirable because it produces a large amount of non-fibrous molded products such as shot, and if the airflow velocity is too high, it generates shock waves and the noise makes the working environment poor, and it consumes a large amount of gas, which increases costs. This is undesirable because it increases the cost and the product quality does not improve accordingly.

The gas that pulls the spun yarn is 0.3
It is preferable to have a pressure of ~4.0 kg/cm2G. If the gas pressure and flow rate are too small, the pulling force will be insufficient, the fiber diameter will increase, the fiber length will become long and uneven, and shot etc. This is undesirable because it produces a large amount of non-fibrous molded material, and if it is too large, it consumes a large amount of gas, which increases the cost, and the quality of the product does not improve accordingly, which is undesirable.

The temperature of the gas that pulls the spun yarn is 80° below the softening point of pitch.
The temperature is higher than 100°C, preferably 100 to 180°C.

If the temperature is too high, the exchange cycle of the spinneret becomes extremely short, which is undesirable; if the temperature is too low,
This is undesirable because the traction force is insufficient, the fiber diameter becomes large, the fiber length becomes long and non-uniform, and a large amount of non-fibrous molded products such as shots are produced.

It is preferable that the spinneret generates negative pressure in the pitch flow path when the spinneret is operated without flowing pitch and only flowing gas at the temperature and pressure of the spinning conditions.

The magnitude of the negative pressure is preferably from 10 to 5,000 −1 water columns, particularly preferably from 100 to 1,000 n++e water columns.

Example 1 Petroleum pitch having a softening point of 285° C. and an optical anisotropy fraction of 100% was subjected to melt blow spinning under the following conditions.

Pitch discharge type 12g 1 minute pitch temperature
320℃ Heating gas (steam) flow rate 0.27 kg/min Heating gas (steam) temperature 420℃ Heating gas (steam) pressure 1.5 kg/am” G spinning hole (pitch discharge hole) 0.3φX 74hole gas discharge hole 1.0φ Spinneret surface temperature 420°C After continuous spinning for 6 hours, 10 locations were randomly sampled from the obtained pitch nonwoven fabric to examine the shape of the fibers.95% of the fiber lengths were 5 to 30 m. It fits between
85% of the fiber diameters fell between 4 and 71 m. The shots were 7 per 10g.

This nonwoven fabric was made infusible by a conventional method, and then carbonized by a conventional method. The strength of the obtained carbon fiber is 154 kg/m
n'' and elongation of 1.0%.

Example 2 When exhaust gas from propane gas combustion was used in place of the steam heated gas in Example 1, a pitch nonwoven fabric with fewer shots similar to that of Habo was obtained.

Example 3 Instead of the optically anisotropic pitch which is the raw material of Example 1,
Using a high softening point isotropic pitch with a softening point of 245°C, spinning was performed using the same device with the pitch temperature, heating gas temperature, and spindle temperature each lowered by 40°C. As in Example 1, the results were uniform. A carbon fiber nonwoven fabric with less shot was obtained.

(E) Functions and Effects of the Invention The present invention relates to a method for reducing the amount of shot contained in fibers in a spinning method in which molten pitch is pulled by a high-speed air current to form fibers.

that's all

Claims (3)

[Claims] (1) A pitch characterized in that when the molten pitch discharged from the spinning hole is pulled by a high-speed airflow flowing out from around the spinning hole and turned into fibers, the high-speed airflow contains water vapor as a main component. spinning method. (2) The pitch spinning method described in the preceding item, characterized in that the high-speed airflow is water vapor. (3) A pitch spinning method in item 1, characterized in that the high-speed airflow is combustion waste gas.