JPS58169516A - Improved production process for carbon fiber - Google Patents

Abstract

PURPOSE:Acrylic yarn is pretreated with a dilute aqueous solution of a water- soluble high-molecular substance, then calcined and carbonized to prevent the yarn from filament-loosening at the preoxidation process, to produce carbon fibers without fluffing, yarn breakage and fusing between filaments. CONSTITUTION:An aqueous solution of a water-soluble high-molecular substance, preferably gua gum, pectin, PVA or polyethyene glycol, preferably with a concentration of 0.01-5%, is applied to an acrylic yarn by spraying, print-rolling or dipping so that the pick-up becomes 50-500% based on the precursor. Then, preferably after drying to increase collecting properties, the resultant yarn is calcined and carbonized. The application of the dilute solution is made, preferably after yarn making, during or after finishing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for producing carbon fibers, and more particularly to a method for producing carbon fibers by firing acrylic fibers that have been subjected to a specific pretreatment.

Conventionally, various methods have been disclosed for producing carbon fibers, but in particular, methods using acrylic fibers as precursors,
A common method is to first perform flameproofing treatment by wetting at 200 to 400°C, and then carbonize at a temperature of 400 to 16,000°C.

However, during the process of making the acrylic fibers flameproof, some of them thermally decompose and turn into tar, contaminating the inside of the furnace, and the resealing of the decomposed products into the fibers deteriorates the physical properties of the carbon fibers used as products. It has the disadvantage of being

It is necessary to improve the convergence of acrylic fibers from the viewpoint of improving the passage characteristics of the precursor through the firing furnace. The fibers adhere to each other and heating causes inter-fiber fusion, exposing the serious drawback of poor fibrillation properties as filamentary carbon fibers.Therefore, during such treatment, substances that suppress exothermic decomposition are added. Although attempts have been made to add it to acrylic fibers, no good additive or method of addition has yet been found.

On the other hand, methods to maintain good splitting properties of heat-treated fibers have been studied, but these methods tend to cause the yarns to spread out and become fluffy. Also, so-called "unraveling" and "thread breakage"
These and other inconvenient phenomena occur frequently, leading to serious problems in the production of carbon fibers, such as poor processability and non-uniform physical properties of the product.

In view of the current situation, the inventors of the present invention aimed to produce a good carbon fiber (the present invention was achieved as a result of extensive research).

The gist of the present invention is to provide improved production of carbon fibers, which is characterized in that prior to the firing process, a dilute aqueous solution of a water-soluble polymer is added to acrylic fibers, and then the fibers are fired and carbonized according to a conventional method. According to the present invention, it is possible to improve the process passability of the precursor and provide carbon fibers of excellent quality.

The first effect of the present invention is that since a dilute aqueous solution of a water-soluble polymer is added to acrylic fibers, the adhesion state is extremely uniform, and there is no possibility of non-adhesion caused by oil release agents (carbon fibers). The second reason is that the acrylic fibers have good yarn convergence properties when subjected to heat history of 200 to 400°C, and even when processed under tension, the precursors do not disintegrate. First, there is no inconvenience such as "unraveling" or "thread breakage" of the yarn due to uneven thermal contraction of each yarn, and thirdly, there is no damage when the precursor comes into contact with rolls, etc. It is possible to make extremely high-quality carbon fibers that are resistant to oxidation.

The fourth reason is that according to the method of the present invention, the yarn bundle that has been subjected to a thermal history of 200 to 400°C loses convergence after passing through the carbonization process, has good splitting properties, and is continuously carried out at 300 to 400°C.
The fourth purpose is to prevent inconveniences such as mutual fusion between fibers in the yarn carbonization process at 700°C, and the fourth purpose is to add a dilute water-soluble polymer aqueous solution to the precursor yarn. Therefore, it is safe because no flammable gas is generated by heating, and the fifth is that the yarn is oxidized without leaving any traces during carbonization.
Power) Karu! The VjK water-soluble polymer leaves almost no ash, so there is no deterioration in carbon fiber properties.Sixth, the carbon fibers produced by the method of the present invention do not impair the strength and elastic modulus originally possessed by carbon fibers. (and exhibits uniform and excellent performance.

The water-soluble polymer substances of the present invention are substances that dissolve in water without decomposition and give a thickening effect, and include polysaccharides, polysaccharide derivatives, and polyols, and the polysaccharides include quar gum, locust bean gum, and quince. Seed gum, tara gum, carrageenan, phaseleran, arabic fuctan.

Gum Arabic, Gum Tragacanth, Gum Karaya.

Pectin, starch, mallow, the/su/gum.

Examples of polysaccharide derivatives include starch, guar gum, locust bean gum, cellulose, oxidized derivatives of alginic acid, carboxymethyl derivatives, hydroxyalkyl derivatives, ester derivatives with alkylene glycol, grafted derivatives, etc. can be given.

Examples of polyols include polyvinyl alcohol and polyethylene glycol.

Any of these water-soluble polymers can be applied to the present invention, but those that can be uniformly adhered to acrylic fibers when their aqueous solutions are added and that do not cause gelation are particularly preferred. It is.

For the above reasons, preferred water-soluble polymers include guar gum, locust bean gum, thickened carrageenan, pectin, xanthan gum, polyvinyl alcohol, polyethylene glycol, hydroxyalkyl derivatives of guar gum, and hydroxyalkylcellulose.

In the present invention, when dissolving a water-soluble polymer in water, “&
It is necessary to dissolve it uniformly so that "Harumi" does not occur.

Moreover, it is pointless to prepare a particularly highly concentrated solution, and in that case, it would actually lead to poor processability such as "gum-up".

The concentration of the dilute aqueous solution of the water-based polymer should preferably be so dilute that it does not impair the mutual adhesion of the acrylic fibers when added to the acrylic fibers and dried. It is recommended that water wW with a molecular concentration of 0.01 to 5% be attached to the precursor at a ratio of 50 to 500% (・0Also, acrylic water in dilute bath solution for water-based polymeric substances) The addition method to the fibers may be any method such as a spray method, a print roll method, or a dipping method.

In some cases, it may also be used as a squeeze roll.

It is preferable to add the dilute water bathing solution of the water bathable polymer substance to the acrylic fibers after the production of the acrylic yarn, during the finishing process, or after the finishing process.

In addition, it is preferable that the acrylic fiber to which a dilute solution of a water-soluble polymer substance is added is once dried to improve convergence before being subjected to flame-retardant treatment.

By using the improved carbon fiber production method of the present invention, it is possible to prevent the fiber bundle from becoming loose in the flame-retardant process, prevent fuzz and yarn breakage, and promote uniform flame-resistance. Furthermore, in the carbonization process, the fiber bundle is divided into fibers to prevent the jit fibers from adhering to each other, and after firing, the water-soluble polymeric substance as an additive is completely acidified. It also has the effect of not leaving any traces, making it possible to obtain carbon fibers with excellent process passability and product physical properties.

Hereinafter, embodiments of the present invention will be explained in more detail with reference to Examples.

Example 1 An acrylic precursor was manufactured by a conventional method, and at the final finishing stage, the acrylic precursor was washed with water and then coated with 0.02% guar gum via a dip roll.
The acrylic precursor was brought into contact with an aqueous solution, drained with a nip roll, and then dried to produce an acrylic precursor.After draining with a nip roll, the moisture content of the acrylic precursor was 150%.

This acrylic precursor was flame-proofed at 200 to 250°C, and then carbonized by raising the temperature to 1200°C in a nitrogen atmosphere. In such cases, no ``bulk'', ``thread breakage'' or ``fuzz'' phenomena were observed during the process. Furthermore, the carbonized fibers had already been completely separated into single fibers, and no mutual adhesion was observed.

The carbon fiber thus obtained had a strength of 400 Ky/- and an elastic modulus of 24 t/-.

Example 2 In the final finishing stage of the acrylic precursor produced in Example 1, the acrylic precursor was once washed with water, and then brought into contact with a 0.2% aqueous solution of hydroxyethyl cellulose via a print roll and squeeze roll, and once squeezed with a squeeze roll. After draining, it was directly subjected to flame-retardant treatment.

The moisture content of the acrylic precursor before flame-retardant treatment was 150%. Flameproofing treatment was performed at a temperature of 200°C to 250°C, and then the temperature was raised to 1200°C in a nitrogen atmosphere to lead to a carbonization step.

In such cases, "barak" and "thread breakage" occur during the process.
No "fluff" phenomenon was observed. Furthermore, the carbonized fibers had already been completely separated into single fibers, and no mutual adhesion between the fibers was observed. The carbon fiber thus obtained had a strength of 380 kg/- and an elasticity number of 23 t/-.

Example 3 An acrylic precursor was manufactured, and in the final finishing step, the acrylic precursor was once washed with water, and then brought into contact with a 0.1% aqueous solution of hydroxyglobyl ether of guar gum via a dip roll nip roll, and once drained. After that, it was immediately subjected to flame-retardant treatment.

The moisture content of the acrylic precursor before flame-retardant treatment is 15.
It was 0%.

Flameproofing treatment was performed at a temperature of 200°C to 250°C, and the temperature was subsequently raised to 1200°C in a nitrogen atmosphere to lead to a carbonization step.

In such cases, "barak", "thread breakage", "
No "fluffing" phenomenon was observed. Furthermore, the carbonized fibers had already been completely separated into single fibers, and no mutual adhesion between fibers was observed. The performance of the carbon fiber thus obtained was uniform and had a strength of 420 Kg/- and an elastic modulus of 24 t/mA.

Example 4 An acrylic precursor was manufactured, and in the final finishing step, the acrylic precursor was once washed with water, and then brought into contact with a 0.02% xanthan gum aqueous solution via a dip roll, and drained using a nip roll. It was later dried to produce an acrylic precursor. The moisture content of the acrylic precursor after draining with a nip roll was 150%.

This acrylic precursor was subjected to flameproofing treatment at a temperature of 200 to 250°C, and then heated to 1200°C under an outdoor atmosphere.
The temperature was raised to 100% to lead to the carbonization process.

In such cases, "barak" and "thread breakage" occur during the process.
No "fuzz" phenomenon was observed. Furthermore, the carbonized fibers had already been completely separated into single fibers, and no mutual adhesion between fibers was observed. The performance of the carbon fiber thus obtained was uniform, and had a strength of 415 Kg/- and an elastic modulus of 24.8 V and 1.

Comparative Example An acrylic precursor was produced by a known method,
In the final finishing step, the acrylic precursor is washed with water, then brought into contact with water via a dip roll, and then drained with a nip roll to achieve a moisture content of 150.
% of acrylic precursor was produced.

When this acrylic precursor was flame-resistant treated at 200 to 250°C, the treated fibers became separated from each other, and when treated with a certain length, they became ``walnut'', ``fluffy'', and ``thread breakage''.
etc., and the processability was extremely poor.

Claims (3)

[Claims] (1) An improved method for producing carbon fibers, which comprises adding a dilute aqueous solution of a water-soluble polymeric substance to acrylic fibers, and then carbonizing the fibers by firing according to a conventional method. (2) The improved method for producing carbon fibers according to claim 1, wherein the water-soluble polymer is a natural sugar or a derivative thereof. (3) The improved method for producing carbon fibers according to claim 1, wherein the water-soluble polymer is a polyol.