JPS6134213A - Manufacture of pitch fiber - Google Patents

Abstract

PURPOSE:To produce a pitch fiber useful as a base of high-tenacity carbon fiber, from meso-phase pitch, preventing the end breakage and minimizing the generation of gas, by keeping the pressure at the upper part of the spinneret to a level higher than a specific pressure. CONSTITUTION:The objective fiber can be produced by spinning a pitch (preferably meso-phase pitch) through a spinneret keeping the temperature of the pitch at a melting range, i.e. 300-400 deg.C e.g. in a zone down to the nozzle of the spinneret, and keeping the pressure at the upper part of the spinneret to >=10kg/ cm<2>G, preferably >=20kg/cm<2>G. The rate of extrusion is <=0.2g/min per each nozzle of the spinneret, and the extruded filament is drawn at a take-up speed of <=2,000m/min.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing pitch fibers using pitches, particularly mesoface pitch, which is a base for high-strength carbon fibers.

Carbon fiber is made by infusibleizing pitch fiber in an oxidizing atmosphere.
Obtained by carbonization and graphitization if necessary in an inert atmosphere.

In the high-strength carbon fiber market, yarn diameters of less than 10 μm are common, and therefore it is essential to spin pitch fibers with a yarn diameter of nearly 10 μm. However, when spinning pinch type fibers, it is not possible to perform a stretching operation after spinning unlike polymeric fibers due to the brittle nature of the pitch, so it is necessary to directly stretch the fibers to a thickness of about 10 μm during the spinning operation.

One of the important conditions when spinning pitches is that the pitches have the ability to be drawn to a yarn diameter of about 10 μm, but even if this condition is met, the characteristics of the pitches may cause yarn breakage. Highly stable spinning is difficult. That is, 300
When pitches are melt-spun at a temperature of ~400° C., thermal polycondensation tends to proceed gradually due to the thermal instability of the pitch, and gases mainly composed of hydrogen and lower alkanes tend to be generated. Although this gas is often generated from the optically anisotropic layer interposed in the mesoface pinch (including the mesoface precursor), which has optical anisotropy as a continuous phase,
It also occurs from the optically anisotropic layer, often causing yarn breakage during spinning.

The present inventors have discovered that gas generation can be minimized by spinning at a melt pitch of 300 to 400°C and a pressure of 10/aJG or more in the spinning pack section, and have developed the present invention. It's arrived.

In the present invention, up to the pitch melting heating section and introduction section, and the top of the fiber filling section of the spinning pack, for example, the former is controlled by the sealing pressure with inert gas, the rotation speed of the molten pitch feeding screw, and the tube. In the latter case, by increasing the thickness of the mineral material by adjusting the diameter, etc., it is possible to easily increase the pressure to 10/aJG or more.

Further, in the present invention, a pressure of 10 kg/cjG or more is also required at the portion after passing through the filter material filling section and reaching the spinneret. That is, by setting the pressure loss at the spinneret to 10 kg/cm+JG or more, preferably 20 kg/cm2G or more, the influence of generated gas can be minimized.

The pitch to be spun in the present invention is preferably mesoface pitch. Mesoface pitch is prepared by various treatments, and its spinnability differs depending on the processing conditions, but it has good spinnability at a viscosity of several hundred voids, and is preferably 2,000 or less, preferably 100 to 1,500 voids. Without spinning, it tends to be difficult to obtain a pitch if of nearly 10 μm in diameter.

In the present invention, when spinning pinch yarn, the discharge amount is preferably 0.3 g/min or less, preferably 0.2 g/min or less per discharge hole of the spinneret, and the winding speed is preferably 3000 m/min or less. It is necessary to stretch at 2000 m/min or less. Compared to spinning organic polymers such as organic synthetic resins, the spinning active part,
The strength of the produced fibers differs greatly and is also different from glass fiber for the same reason, so when pinch spinning, it is necessary to take into account the viscosity, discharge amount, winding speed, etc. as mentioned above. The diameter of the discharge hole is also 0.5 or less,
Preferably, better results can be obtained by setting the value to 0.3n or less.

Pinch ta Am? In the case of spinning with a diameter of about 20 μm, for example, if a good mesoface pitch that has been hydrogenated is used, there is no particular problem with a spinneret pressure of 10 kg/cJG, and multi-hole spinning is also possible. Spinning pitch fibers with a diameter of about 10 μm using a small experimental device such as a monohole is possible even at a pressure of about 1 to 2 kg/cm2G, but in industrial production, it is necessary to continuously supply a large amount of pitch Continuous spinning requires continuous and stable ejection from a nozzle with a nozzle hole of 100 holes or more, and the pressure on the nozzle is maintained at 10 kg/cm2G or more to reduce pitch deterioration. It becomes possible to do this.

Mesoface pitch (including mesoface precursor) is
Observation under a polarized light microscope at room temperature shows that the optically anisotropic layer as a continuous phase has good spinnability and, when made into carbon fiber, has a good strength of 150 kg/++j, which is preferable.

When mesoface pitch is heated to 300° C. or higher without pressurization in an inert gas atmosphere, gas generation is visible and tends to become more intense as the temperature rises. In this state, when observing while applying pressure with inert gas,
At 380° C., a slight amount of generated gas is observed under a pressure of 10 kg/c+JG, and at 20 kt/ciG, most of the generated gas is suppressed. In addition, even at 400℃, 20kt/
It is possible to suppress the amount of gas generated under ciG pressure.

Applying this result to multifilament spinning, it is possible to maintain the pinch at a melting temperature of 300 to 400°C up to the discharge port of the spinneret and apply a pressure of 10 kg/JG or higher, preferably 20 kR/cm2G or higher. For example, yarn breakage due to the influence of generated gas can be reduced.

The pitch fibers thus obtained were subjected to infusibility treatment by gradually raising the temperature to 300°C in an oxidizing atmosphere, and then carbonized or graphitized at 1000°C to 3000°C in an inert atmosphere. , carbon fiber or graphite fiber is obtained.

Examples will be specifically described below, but the invention is not limited thereto.

Examples 1 to 4', Comparative Example 1 Mesoface pinch was spun using a spinning machine consisting of a melting tank, a gear pump, and a spinning bag and having 18 outlet holes in the spinneret, and then stretched and taken up by a winding machine. Ta. The mesoface pinch used was the pitch shown in Table 1 prepared by hydrogenation treatment, and the spinning conditions were as shown in Table 1. During spinning, the melting tank was maintained at 350°C and 20°C.
A nitrogen pressure of kt/ciG was applied, and the spinning pack used glass beads with a diameter of 30 μm at a length of 10t4 as a filter medium.
A wire mesh of 0 mesh was laid, a dispersion plate was placed under it, and the distance between the mouthpiece and the dispersion plate was set to 4fi. Adjust the temperature of the upper part of the filter medium in the pack part to 350°C to 390°C, and then reduce the pressure to 1.
It was set to 50-40 kg/c+aG.

Each of the obtained pitch fibers was heated to 300°C at a heating rate of 5°C/min.
℃ in air and held for 15 minutes, then further heated to 800℃ in a nitrogen atmosphere at 50℃/min, and then heated to 1500℃.
Carbon fibers were obtained by holding the carbon fibers in a nitrogen atmosphere furnace for 15 minutes.

For comparison, the pressure at the top of the spinneret was set to 5 kg/c+
ac, & strain. The results are shown in Table 1.

Claims (1)

[Claims] A method for producing pitch fibers, which comprises controlling the pressure above the spinneret to at least 10 kg/cm^2G or more when spinning pitch.