JPS6047924B2 - Method for producing carbon fiber precursor yarn - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a carbon fiber precursor yarn, and particularly to a method for producing a high strength and elongation carbon fiber precursor yarn with less fuzz on the surface of the yarn.

The method of producing a fibrous precursor by spinning a solvent solution of an acrylic polymer, washing it with water, stretching it, and drying it and then firing it to obtain carbon fiber or graphite fiber (hereinafter simply referred to as carbon fiber) is widely known. It is being The present invention relates to a method for producing acrylic fibers, ie, carbon fiber precursor threads, before firing to obtain carbon fibers. Conventionally, carbon fiber precursor yarn has been produced by spinning a solution of an acrylic polymer in an organic or inorganic solvent into a coagulating medium, washing it with water, and then drawing it in a drawing process. It was generally manufactured by drying and densifying it.

However, since the liquid composition of bath-liquid drawing is water or an aqueous solution, there is an upper limit to the drawing temperature, and the drawback is that it is not possible to obtain a drawing ratio sufficient to impart high strength to the yarn. Therefore, the yarn after bath drawing and drying and densification is subjected to steam drawing again in pressurized steam. In order to apply pressurized steam to the running yarn, it is necessary to create an atmosphere system with as little steam leakage as possible so that the yarn runs within it, and this type of drawing is usually called a labyrinth nozzle. A pressurized steam drawing machine is used in which several pipes having small diameters of 1 to 1 m are connected at the inlet and outlet. The yarn enters through the entrance labyrinth nozzle, is drawn in the drawing machine, and exits through the exit labyrinth nozzle. One of the reasons why acrylic carbon fiber precursor yarns are drawn in steam is that acrylic fibers do not have a melting point like other polyamide and polyester fibers, so dry drawing is practically impossible. One example is that it is physically impossible.

In other words, drawing of acrylic fibers can only be carried out in a water bath or steam.
By the way, in the conventional manufacturing process of carbon fiber precursor,
The process that caused the most single yarn breakage, ie, yarn fuzz, was the steam drawing process using pressurized steam, which also often occurred frequently at the start of operation.

As a result of repeated studies on the causes of the above-mentioned fluff, the present inventors found that the amount of water in pressurized steam, or in other words, the wetness of the steam, fluctuates, and by controlling this wetness, They discovered that the yarn could be stretched while maintaining a constant moisture content, leading to the present invention.

Therefore, *an object of the invention is to provide a method for producing a carbon fiber precursor thread that has less fuzz and sagging on the thread surface and has straight strength and elongation. The structure of the present invention is that when an acrylic polymer solution is spun, stretched in a bath, dried and densified, and then steam-stretched in pressurized steam to obtain a carbon fiber precursor string, the yarn immediately after steam-stretching contains moisture. It is characterized by controlling the wetness of the steam so that the ratio is 7 to 20.

Hereinafter, a more detailed explanation and preferred embodiments of the present invention will be described.

The acrylic polymer used in the present invention is a homopolymer of acrylonitrile or a copolymer obtained by copolymerizing a small amount of comonomer, for example, 0% itaconic acid.

A copolymer in which about 1 to 1% of the copolymer is copolymerized is preferably used.

As the solvent for the acrylic polymer, known organic and inorganic solvents can be used. In the present invention, this acrylic polymer solution must be subjected to at least spinning, stretching in a bath, and drying and densification. The fiber may be spun directly into a coagulation bath, or may be spun once into air and then coagulated in the bath.
The bath drawing may be carried out directly on the spun yarn, or may be carried out after once washing with water to remove the solvent. The drawing in bath is usually carried out by about 2 to 6 times in a drawing bath at 50 to 98°C, but the present invention is not limited thereto. Drying and densification is carried out by drying the yarn after drawing in a bath with a hot roller or the like, and the drying temperature, time, etc. can be selected as appropriate. The most characteristic feature of the present invention is that the wetness of the steam is controlled so that the moisture content of the yarn immediately after steam drawing is 7 to 20%.

Since the yarn immediately before entering the steam drawing machine has been dried and densified, the moisture content is substantially O.

However, since steam drawing is performed in pressurized steam, the yarn retains moisture during this time, and the yarn immediately after leaving the steam drawing machine contains a certain amount of moisture. Steam stretching is usually carried out in pressurized steam of 1 to 6 k9/CltG at a temperature of about 120 to 170° C. and stretched 2 to 6 times. Therefore, the moisture content of the yarn is influenced to some extent by the temperature in the drawing machine, the steam pressure, or the stretching time, but the most important factor that influences the moisture content of the yarn is the moisture of the supplied steam. degree. In other words, if steam with high humidity is supplied, the yarn can retain a large amount of moisture, but if steam with low humidity is supplied, the moisture content of the yarn becomes low. If the moisture content of the yarn after steam drawing is less than 7%, yarn breakage occurs frequently during drawing, and fuzz is generated on the surface of the yarn. When the moisture content of the yarn is 77% or more, the fuzz generation rate decreases rapidly, and when it is 20% or more, this tendency is saturated and the water evaporation load only increases. Therefore,
In the present invention, it is essential to control the wetness of the supplied steam so as to maintain the moisture content of the yarn immediately after steam drawing at 7% or more, preferably 10% or more. However, even if it exceeds 20%, the effect will no longer increase, so it should be controlled to 7 to 20%, preferably 10 to 20%. The yarn moisture content immediately after steam drawing is 7-20%.
Of course, in order to control the temperature, it is sufficient to supply steam with a humidity level of 9 that corresponds to this, but the steam supplied industrially is usually steam manufactured for multiple purposes. In particular, when the steam boiler is located in a completely different location and the steam boiler is transported over a considerable distance using a vibrator, the steam becomes a drain during that time and the humidity level decreases significantly. However, if the operation is stopped and restarted, there will be a big change in the wetness of the steam.In such cases, it is necessary to install a water cooling jacket on the steam vibrator before supplying it to the steam drawing machine. A control method can be used in which the steam is cooled down and the relative humidity of the steam is increased, and then the pressure is reduced to a predetermined level and then supplied to the steam drawing machine. Figure 1 shows a steam humidifying device. showed that.
In Figure 1, 1 is a steam introduction pipe, steam is a cooler,
3 is a pressure reducing valve, ) is a drain separator, and ■ is a steam outlet pipe. Pressurized steam with low humidity is sent from the steam introduction pipe ± to the cooler, where it is cooled by cooling water and its relative humidity increases. The steam with increased humidity is reduced in pressure by a pressure reducing valve u, and then drained by a drain separator 1, and sent to a steam drawing machine (not shown) from a steam outlet pipe u. At this time, the wetness of the steam can be adjusted as appropriate by changing the flow rate, temperature, etc. of the cooling water. Of course, the method of keeping the wetness of the steam constant at a high level is not limited to the method described above, and should be selected appropriately depending on the steam supply conditions. The goal is to install a device that can constantly supply steam with an appropriate humidity level without requiring extensive control. In any case, the moisture content of the yarn immediately after steam drawing is 7 to 20%.
By setting the conditions so that the fuzziness of the thread 5 is significantly reduced, it is possible to produce a precursor thread for obtaining carbon fibers with high strength and elongation. The effects of the present invention will be specifically explained below with reference to Examples.

1 Example 1 Copolymerization of acrylonitrile (AN) and itaconic acid (IA) A dimethyl sulfoxide (DMSO) solution of an acrylic copolymer with a molar ratio of AN/IA=99.7/0.3 (
Polymer concentration 19.5% by weight, viscosity 650, poise/45
(molten C and temperature 65℃) with a diameter of 0.06? φ, number of holes 1
The concentration was 55% through a 000 spinneret at a bath temperature of 65°C (
17) After discharging it into a DMSQ aqueous solution and washing with water, it was stretched to about 3.6 times in a hot water bath, and after giving about 2% of process elongation.
Dry under 5% relaxation at 5°C, then 4.5k9/DG.
The fibers were steam-stretched approximately 3 times in pressurized steam, heat-set at 180° C., and then approximately 2% of finishing oil was added to produce an acrylic precursor fiber yarn.

At this time, prepare pressurized steam with low humidity, and use the steam humidifier shown in Figure 1 to flow 20°C water into the jacket of the cooler, allowing various
A pressurized steam with wetness was created and used.

Table 1 summarizes the yarn moisture content immediately after steam drawing using pressurized steam having various wetness levels and the number of fuzz and sag generated when the yarn was wound up.

The number of fuzz and sagging was measured in g as follows. The thread is placed on a paper bobbin with an outer diameter of 6 cm with zero tension.
．． 1g/d speed? A cheese-wrapped 1f pin with a winding amount of 9k9 was created by winding at 2001T1/Min.

The end face of this cheese-wound bobbin is visually observed, and the number of fuzz and sag generated on the end face is counted and determined as the number of fuzz and sag. From the results in Table 1, it can be seen that when the yarn moisture content is about 7% or more, the number of fuzz and sag generation is small.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a steam humidifier. 1...Steam introduction pipe, 2...Cooler, 3...
Cooling water inlet, 4... Cooling water outlet, 5... Drain separator, 6... Baffle plate, 7... Valve, 8...
Steam outlet pipe, 9...pressure reducing valve.

Claims (1)

[Claims] 1. When the acrylic polymer solution is spun, stretched in a bath, dried and densified, and then steam stretched with pressurized steam to obtain a carbon fiber precursor yarn, the moisture content of the yarn immediately after steam stretching is 7 to 7.
A method for producing a carbon fiber precursor yarn, the method comprising controlling the wetness of steam to 20%.