JPH08158162A - Carbon fiber manufacturing method - Google Patents

Abstract

(57) [Summary] [Structure] Acrylic fiber yarns that have been steam-stretched and have a water content of 1% or more and 7% or less are flame-resistant and carbonized. Method for producing carbon fiber. [Effect] The surface fluff of the acrylic fiber yarn can be reduced, and when the acrylic fiber yarn is subjected to flame resistance and carbonization treatment, there is little yarn damage, and the strength of the resulting carbon fiber is excellent. Can be one.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon fiber, and in particular, a carbon fiber precursor yarn having less fluff on the surface thereof and having less flame damage and less yarn damage when carbonized. The present invention relates to a manufacturing method.

[0002]

2. Description of the Related Art Carbon fibers are prepared by spinning an organic or inorganic solvent solution of an acrylic polymer in a coagulation bath and then washing it with water and then stretching it in the bath, or stretching it in the bath and washing it with water. In many cases, the acrylic fiber yarn produced by drying and densifying is subjected to flame resistance and carbonization treatment. Here, in the drawing in the bath, since water or an aqueous solution is often used as the bath liquid, there is a limit to increase the drawing temperature, and it is sufficient to make the acrylic fiber yarn highly oriented and high in strength. There is a drawback that it is difficult to obtain a moderately high draw ratio. Therefore,
In order to increase the draw ratio of acrylic fiber yarns, JP
No. 8-214520 discloses that after drawing in a bath, drying and densifying, secondary drawing is performed with a pressure steam drawing machine having a small diameter nozzle while maintaining a yarn tension of 0.3 to 0.7 g / d. Is proposed. However, when such a method is simply applied, the obtained acrylic fiber yarn has a lot of fluffs on its surface, and there are many defects that the yarn is damaged when it is flameproofed and carbonized. . JP-A-58
In JP-A-214521, in order to reduce the occurrence of fluff on the surface of an acrylic fiber yarn, in the process of drawing in a bath, drying and densifying, and then applying pressure steam drawing, the wetness of steam is controlled to immediately after steam drawing. It has been proposed to perform pressure steam drawing so that the water content of the yarn is 7% or more and 20% or less. However, although such a method is certainly effective in reducing the fluff generated on the surface of the acrylic fiber yarn, when the acrylic fiber yarn is flame-proofed and carbonized, yarn damage may occur. In some cases, although the yarn damage was not observed, the strength of the obtained carbon fiber decreased.

[0003]

SUMMARY OF THE INVENTION The object of the present invention is to reduce the number of fluffs on the surface of an acrylic fiber yarn, and to reduce the damage to the yarn when it is subjected to flame resistance and carbonization treatment, and to obtain the strength of the resulting carbon fiber. It is to provide a method for producing an excellent carbon fiber.

[0004]

The present invention has the following structure in order to solve the above problems. That is, a method for producing a carbon fiber, which comprises subjecting a steam-stretched acrylic fiber yarn having a water content of 1% or more and less than 7% to flame resistance and carbonization treatment. is there.

The present invention will be described in detail below.

The acrylic fiber yarn in the present invention is steam-drawn. The yarn before steam drawing can be obtained by a conventionally known method. For example, the acrylic polymer may be a homopolymer of acrylonitrile or a copolymer of acrylonitrile obtained by copolymerizing a small amount of a comonomer, for example, 0.1% of itaconic acid.
To about 1% of the copolymer is dissolved in a known organic or inorganic solvent, and a spinning dope is spun, stretched in a bath, and dried and densified. As the spinning method, a wet spinning method of directly spinning in a coagulating bath may be adopted, or a dry / wet spinning method of spinning a yarn once spun in air to solidify in a bath may be adopted. The drawing in the bath may be carried out directly on the spun yarn, or may be carried out after washing the spun yarn with water to remove the solvent. In-bath stretching is preferably performed in a stretching bath at 35 ° C. to 98 ° C. about 1.5 to 6 times. Dry densification is performed by drying the yarn after drawing in a bath with a hot roller or the like, but the drying temperature, the drying time and the like can be appropriately selected.

The yarn thus obtained is steam-drawn. Steam drawing is usually 1 to 6 kg / cm
^{2 at} a temperature of 120-170 ° C in ² G pressurized steam
It is preferable to stretch the film about 6 times.

Since the yarn just before entering the steam drawing machine is usually after dry densification, the moisture content is substantially 0.
%. However, since steam drawing is performed in pressurized steam, the yarn retains water during this period and the acrylic fiber yarn after leaving the steam drawing machine contains water to some extent. In the present invention, an acrylic fiber yarn having a water content after steam drawing of 1% or more and less than 7%, preferably 3% or more and 6% or less is subjected to flame resistance and carbonization treatment.

When the water content of the acrylic fiber yarn is less than the above range, not only the number of fluffs on the surface of the acrylic fiber yarn increases, but also the yarn damages during the subsequent flameproofing and carbonization treatment and the resulting carbon is obtained. Fiber strength is reduced. The reason why such a phenomenon occurs is not clear, but it is presumed as follows. That is, when the water content of the pressurized steam-stretched acrylic fiber yarn is smaller than the above range, the supplied steam is expected to be in the state of superheated steam, and the stretching is performed only in the steam by the heat medium. Since water acts as a plasticizer in the stretching of the acrylic fiber yarn, the plasticizing effect is reduced in the superheated steam, resulting in uneven tension in each yarn. This causes unevenness in the thickness of each single yarn, resulting in not only uneven basis weight of the resulting acrylic fiber yarn, but also the thin portion of the single fiber is cut into fluff, which is high in flame resistance and carbonization. It is thought that the yarn may be damaged because it cannot withstand the tension.

On the other hand, if the water content of the acrylic fiber yarn is higher than the above range, even if the surface fluff of the acrylic fiber yarn can be reduced, the effect is almost saturated and the moisture in the subsequent flameproofing treatment is reduced. Not only does the evaporation load increase, but also a difference in tension caused due to uneven temperature rise of the yarn due to such a local variation in evaporation, and the strength of the resulting carbon fiber decreases.

In order to keep the yarn water content of the acrylic fiber yarn within the above range, it is not possible to evaporate water from the acrylic fiber yarn having an excessive water content after steam drawing before flame resistance. However, since it is necessary to cope with equipment for adding such a preliminary drying step, it is preferable that the acrylic fiber yarn immediately after the pressure steam drawing is subjected to flame resistance and carbonization treatment as it is.

The water content of the acrylic fiber yarn immediately after the steam drawing is somewhat affected by the pressure of the steam in the steam drawing machine or the residence time of the yarn, but the most important factor is the supply to the steam drawing machine. It is the wetness of steam. That is, it is important to control the wetness of the steam so that the water content of the acrylic fiber yarn immediately after the steam drawing falls within the above range. The wetness of such a steam is a relatively high level of wetness, so it is sufficient if the equipment can always supply the steam of high wetness without special control, but the steam supplied industrially. In many cases, the steam boiler is usually manufactured for multiple purposes, and the steam boiler is located at a location remote from the steam drawing machine, and there is a large gap between the steam pressure and the original pressure supplied to the steam drawing. In such a case, the wetness of the steam supplied to the steam drawing is often not so large that the yarn water content can be controlled within the above range. Therefore, before supplying the steam to the steam drawing machine, for example, by installing a plurality of pressure reducing valves in series in the steam line to reduce the pressure in multiple stages, it is possible to maintain the wetness of the steam at a high level. Applied. Further, it is more preferable to employ a control method in which a water cooling jacket is provided on the steam pipe to cool the steam after the multistage depressurization, the relative humidity of the steam is raised, and the steam is supplied to the steam drawing machine.

A schematic diagram of a steam supply line which is preferably used for steam drawing in the present invention is shown in FIG.
The multi-purpose high-pressure steam is decompressed once with the pressure reducing valve 1 and then with the pressure reducing valve 2 through the filter 2 so that the pressure can be used again in the steam drawing machine. It is sent to the cooler 4 provided and cooled by the cooling water, and the relative degree of wetness increases. The steam having increased wetness is drained by the drain separator 5 and then placed in a steam drawing machine. At this time, the degree of wetness of steam can be adjusted more appropriately by changing the flow rate, temperature, etc. of the cooling water supplied to the cooler.

[0014]

EXAMPLES The present invention will be specifically described below with reference to examples.

The water content of the acrylic fiber yarn, the strand strength of the carbon fiber, and the nonuniformity of the weight of the carbon fiber were measured as follows.

(Water Content of Acrylic Fiber Yarn) The acrylic fiber yarn was treated for 1.5 hours in an oven dryer at 105 ° C., and the weight of the yarn was measured.

(Strand Strength of Carbon Fiber) JIS-R
According to -7601, the strength of the epoxy resin-impregnated strand was determined as an average value of 10 times of measurement.

(Nonuniform Mottling of Carbon Fiber) The weight per 1 m of carbon fiber was evaluated by the relative standard deviation when it was measured 50 times. (Examples 1 to 5, Comparative Examples 2 to 4) Acrylonitrile 99
A 20% dimethylsulfoxide (hereinafter abbreviated as DMSO) solution of an acrylic polymer consisting of 1 mol% of itaconic acid and 1 mol% of itaconic acid was passed through a mouth hole of 0.15 mmφ to form DMSO3.
Discharge into a coagulation bath consisting of 5% / 65% water, then
It was washed with water, drawn in a bath, dried and densified, and drawn about 5 times with a pressure steam drawing machine to produce an acrylic fiber yarn. At this time, as steam supplied to the pressurized steam drawing machine, the pressure was reduced to source pressure 15 kg / cm ² G to 8 kg / cm ² G, the pressure was reduced again to 5.2 kg / cm ² G, and cooled in the cooler cooling By adjusting the amount and temperature of water, steam was adjusted to various degrees of wetness.

Table 1 shows the results of visually observing the number of fluffs generated in the acrylic fiber yarn immediately after the pressure steam drawing and the water content of the yarn. The yarn water content was measured by taking a yarn immediately after steam drawing. In addition, the obtained acrylic fiber yarn is continuously treated at a flameproofing temperature of 260 ° C for 40
After the flameproofing treatment for 1 minute, carbonization was performed by setting the maximum temperature in the furnace to 1800 ° C. to obtain carbon fiber. Occurrence of yarn damage during flame resistance and carbonization treatment Table 2 shows the strand strength and non-uniform weight of the obtained carbon fibers.

(Comparative Example 1) The steam supplied to the pressurized steam drawing machine was obtained by depressurizing the steam having an original pressure of 15 kg / cm ² G to 5.2 kg / cm ² G by one step and then stopping the cooler cooling. An acrylic fiber yarn was produced in the same manner as in Example 1 except for the above.

Table 1 shows the results of visually observing the number of fluff generated on the acrylic fiber yarn immediately after the pressure steam drawing and the water content of the yarn. The yarn water content was measured by taking a yarn immediately after steam drawing. Further, the obtained acrylic fiber yarn was subsequently subjected to flameproofing and carbonization treatment to obtain a carbon fiber. Occurrence of yarn damage during flame resistance and carbonization Table 2 shows the strand strength and non-uniform weight of the obtained carbon fibers.
Shown in

[0022]

[Table 1] In Table 1, the meanings of the quality judgment symbols of the precursors are as follows: ◯: 1 or less when the number of yarn running fluffs generated is 5 minutes;
The number x is 4 or more in 5 minutes.

[0023]

[Table 2] In Table 2, the flame damage resistance and carbonization process yarn damage judgment symbols, ◯, hardly occurred, Δ means slightly generated, and x means frequently generated.

[0024]

According to the present invention, since the water content of the steam-stretched acrylic fiber yarn is within a specific range, it is possible to reduce the surface fluff of the acrylic fiber yarn. When the acrylic fiber yarn is flame-proofed and carbonized, the yarn damage is small, and the strength of the resulting carbon fiber can be made excellent. Furthermore, in a preferred embodiment in which multistage depressurized steam is used for the steam drawing, such an acrylic fiber yarn can be easily and stably obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a steam supply line used in an embodiment of the present invention.

[Explanation of symbols]

 1: First stage pressure reducing valve 2: Filter 3: Second stage pressure reducing valve 4: Cooler 5: Drain separator 6: Source pressure supply steam 7: Steam drawing machine

Claims (2)

[Claims] 1. A steam-drawn acrylic fiber yarn having a water content of 1% or more and less than 7%, which is flame-resistant and carbonized. Production method. 2. The method for producing a carbon fiber according to claim 1, wherein steam drawing is performed using steam that has been subjected to multistage depressurization.