JPH0299608A - Production of precursor for producing carbon fiber - Google Patents

Abstract

PURPOSE:To obtain the subject precursor having a high strand strength with hardly any fluffing by spinning a spinning solution of an acrylonitrile-based polymer, drawing the resultant fiber in a bath, drying and densifying the drawn fiber, secondarily drawing the fiber and thermally relaxing the obtained fiber using a wet-heat type far infrared heater relaxing device. CONSTITUTION:An acrylonitrile-based polymer containing at least 90wt.% acrylonitrile (preferably a copolymer containing 0.5-3wt.% copolymerized methacrylic acid) is dissolved in a solvent to provide a spinning solution, which is then spun into a fiber. The resultant tiber is subsequently drawn in a bath, dried and densified, then secondarily drawn so as to afford >=10 times total draw ratio. The drawn tiber is then thermally relaxed, preferably at 100-250 deg.C using a wet-heat type far infrared heater relaxing device (preferably <=2% relaxing shrinkage factor) to provide the objective precursor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a novel method for producing a precursor for producing carbon fibers.

[Conventional technology]

From the company, the precursor for carbon fiber production is made by spinning a solution of acrylonitrile-based polymer in an organic or inorganic solvent into a coagulation bath.
After washing with water, the yarn is generally drawn in a drawing machine, or after stretching in a drawing machine, washing with water, and then drying and densifying the yarn.

However, since the liquid composition of bath drawing is an aqueous solution, there is a limit to the drawing temperature, and there is a drawback 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 secondary drawing again. This secondary stretching method may be any of the following stretching methods: hot water stretching, steam stretching, pressurized saturated steam stretching, decorative steam stretching, dry heat stretching, hot pin stretching, or any of these stretching methods. A method that combines two or more stretching methods is widely known.

However, when the total stretching ratio is increased to 10 times or more by the above-mentioned secondary stretching, the obtained precursor for carbon fiber production tends to generate fuzz during the firing process. Therefore, carbon fibers with high strength could not be obtained, although the stretching ratio in the firing process was lowered to a low value. Furthermore, in order to obtain high-strength carbon fibers, if treatment was carried out without lowering the drawing ratio in the firing process, frequent fluffing and resulting mid-breaks were likely to occur, resulting in extremely poor operational stability.

As for these improved methods, the present applicant previously proposed Japanese Patent Application Laid-Open No. 6S-99.
No. 516 proposed secondary stretching in a steam atmosphere using a far-infrared heater stretching machine. As an improvement method for these, the present invention uses secondary drawing and further heats and relaxes the yarn with a total drawing ratio of 10 times or more, thereby reducing the amount of fuzz even if the drawing ratio in the firing process is not lowered. The present invention proposes a method for producing a precursor for producing carbon fibers, which produces carbon fibers with extremely low occurrence and no mid-cutting, and which yields high-strength carbon fibers.

[Problem to be solved by the invention]

When producing carbon fiber from a carbon fiber production precursor,
It is widely known that stretching is performed by about 1 to 1.15 times in the firing process.

In order to obtain high-strength carbon fibers, a carbon fiber manufacturing precursor with a total stretching ratio of 10 times or more is used in the firing process.
．． It is anticipated that it will be necessary to stretch the film by a factor of two or more. However, precursors for producing carbon fibers manufactured by conventional techniques with a total stretching ratio of 10 times or more have low drawability in the firing process, so carbon fibers obtained by stretching the total stretching ratio of 1.2 times or more in the firing process are low. In terms of quality, there was a lot of fuzz, and there were some mid-cuts due to runaway reactions due to the fuzz during the process, and the operational stability was not good.

Furthermore, in order to reduce fuzz, carbon fibers are produced industrially by lowering the drawing ratio in the firing process, but at present they exhibit low values for both strength and elastic modulus.

An object of the present invention is to provide a method for producing a precursor for producing carbon fibers, which produces highly strong carbon fibers with significantly less fuzz and no mid-cutting.

[Means to solve the problem]

The gist of the invention is that at least 90 wt4
A spinning solution prepared by dissolving an acrylonitrile polymer containing acrylonitrile of The objective is to produce a precursor for producing carbon fibers by heating and relaxing using a far-infrared heater relaxation device.

The present invention will be specifically explained below.

The acrylonitrile polymer of the present invention is a homopolymer of acrylonitrile or a copolymer obtained by copolymerizing a small amount of a comonomer, and preferably a copolymer obtained by copolymerizing methacrylic acid with α5 to 5 μm. acryloni) IJ
As the solvent for the v-based polymer, known organic and inorganic solvents can be used. In the present invention, this acrylonitrile polymer solution must be subjected to at least spinning, bath stretching, drying and densification, and secondary stretching.

The spinning method may be wet or dry. The bath drawing may be carried out directly on the spun yarn, or may be carried out after washing with water to remove the solvent. Stretching in a bath is preferably carried out by about 2 to 6 times in a stretching bath at 80°C to 98°C.

Drying and densification can be carried out by drying the yarn after drawing in a bath using a heating roll or the like, and the drying temperature, drying time, etc. can be selected as appropriate. In the secondary stretching, the total stretching ratio is 10
The yarn is drawn to be more than double in size, and the methods include hot water drawing method, steam drawing method, pressurized saturated steam drawing method,
One of the stretching methods such as heated steam stretching method, dry heat stretching method, hot bottle stretching method, etc., or a stretching method that combines two or more of these stretching methods; In addition, it is possible to use a moist heat drawing method using a far-infrared heater drawing machine, which uses a heating method sufficient for the drawing necessary to impart high strength to the yarn without passing it through a strong flow of pressurized gas. However, the present invention is limited to these stretching methods, and the most characteristic feature of the present invention is that a moist heat type far-infrared heater relaxation device is used when heating and relaxing the yarn after the secondary drawing. It is to ease the situation. The heating temperature for heating relaxation is 100°C or more and less than 250°C, preferably 11
It is preferable that the heating relaxation be performed at a temperature of 0° C. or more and 200° C. or less, and a relaxation shrinkage rate of 24 or less. When the heating temperature is less than 100° C., the relaxation effect is not exhibited because the relaxation shrinkage rate is small.

If the relaxation shrinkage rate is greater than 2, the stretchability in the firing process will be good, but high strength carbon fiber #i will not be obtained.

FIG. 1 is a schematic diagram showing a wet heat type far infrared heater relaxation device and yarn used in the present invention, and shows a far infrared heater 1,
Thermometer 2, steam 3, supply o-1v4, withdrawal a-A/
5, a pressure gauge 6, and a thread 7 are shown.

〔Example〕

The present invention will be explained below with reference to Examples.

(1) Method for measuring surface gloss i) The precursor for carbon fiber manufacturing is arranged in parallel to form a sample surface.

11) In a plane having an angle of 90° with respect to the fiber axis direction, a beam of constant luminous intensity is applied toward the sample surface from a 45° direction from the sample surface.

l11) Measure the illuminance (L8) of the light beam reflected from the sample surface within the above-mentioned plane at a reflection angle of 456.

By the operations from 1y)i) to 111), L8 measured from a carbon fiber manufacturing precursor that was not secondarily stretched was taken as LO, and the LEI /1100 ratio was determined and used as the contrast gloss.

Contrast gloss = (1-La/Lo)xlo.

The contrast gloss obtained from operations i) to 10 is evaluated as follows.

(2) Measuring method of yarn damage') A carbon fiber manufacturing precursor was continuously supplied by low V drive to a flameproofing furnace in a hot air atmosphere with a temperature gradient in the range of 225 to 260°C, and left to stay for 34 minutes. Perform flameproofing treatment. The tension in the flame-retardant treatment is approximately 120 cape/d,
The fiber length is kept at Habohara length. The density of the flame-resistant fibers is in the range of 1.37 to 1.399/cm''.

The flame-resistant fibers are passed through a carbonization furnace with a temperature gradient ranging from 320 to 700°C and a heat treatment furnace at 1350°C in a nitrogen gas atmosphere for residence times of 7 minutes and 4.5 minutes, respectively, to bake them into carbon fibers. .

11) Tension (1f/10
Apply ``d)'' and apply enough air to lift the fluff.

11)) The raised fluff is expressed as the number of strands per 10' of fluff. The number of fluffs obtained is evaluated as follows.

(3) Method for measuring stretchability during firing i) Using an apparatus equipped with an open tube in which hot air was flowed between the row V and the roll, the oven temperature was set to 240°C, and the stretching ratio was determined from the rotation speed ratio of the rolls before and after opening. seek.

ii) The max stretching ratio is the stretching ratio at which fuzz occurs. The obtained maw stretching ratio is evaluated as follows.

Example 1 Acrylonitrile 99wtl and methacrylic acid 1vt%
An acrylonitrile-based polymer copolymerized with is dissolved in dimethyV formamide (hereinafter abbreviated as DMF) 1C, and the solid content is 20
It was used as a wtl spinning stock solution. Add the spinning stock solution to pure water 5 Q v
Temperature 30 with composition of rt96 D M P 70 wtl
It was spun from a nozzle with a hole diameter of 1080 mm in a spinning bath at ℃, stretched in a 95℃ bath and a 100℃ bath, dried and densified, and then subjected to secondary stretching using a steam stretching machine. Ta.

Thereafter, the mixture was heated and relaxed by changing the heating temperature and relaxation shrinkage rate using a wet heat type far-infrared heater relaxation device to create a fiber precursor. The properties of the obtained carbon fiber manufacturing precursor were as shown in Table 1. Further, these precursors for producing carbon fibers are continuously supplied by a low V drive to a flameproofing furnace in a hot air atmosphere having a temperature gradient in the range of 225 to 260 ° C. by a conventional method,
It was left there for 34 minutes to perform flameproofing treatment. The tension in the flameproofing treatment was approximately 120 μ/d. The density of the flame-resistant fibers was in the range of 1.57 to 1.3997 cm.
The carbon fibers were fired by passing through a carbonization furnace having a temperature gradient in the range of 0°C and a heat treatment furnace at 1350°C for residence times of 7 minutes and 45 minutes, respectively. The properties of the obtained carbon fiber are
The results were as shown in the table.

Comparative examples under each condition are also the first. Shown in the table.

As shown in Table 1, excellent stretchability can be achieved in the firing process by heating and relaxing using a moist heat type far infrared heater relaxation device at a heating temperature of 100°C or more and less than 250°C and a relaxation shrinkage rate of 24 or less. It was possible to produce a precursor for producing carbon fibers with extremely low occurrence of fuzz. The strand bending degree of the obtained carbon fiber was also 430 cm.
This indicates high strength.

〔Effect of the invention〕

The precursor for producing carbon fibers obtained according to the present invention has excellent drawability in the firing process, generates extremely little fluff, and in addition, carbon fibers with high strand strength can be obtained.

[Brief explanation of drawings]

FIG. 1 shows a schematic diagram of a wet heat type far-infrared heater relaxation device used in the present invention.

Claims (1)

[Scope of Claims] 1. A spinning dope in which an acrylonitrile polymer containing at least 90 wt% of acrylonitrile is dissolved in a solvent is subjected to spinning, bath stretching, drying and densification, and then secondary stretching to obtain a total stretching ratio. 1. A method for producing a precursor for carbon fiber production, which comprises stretching the precursor by 10 times or more and then heating and relaxing it using a moist heat type far-infrared heater relaxation device. 2. The manufacturing method according to claim 1, wherein the heating temperature for heating relaxation is 100°C or more and less than 250°C. 3. The manufacturing method according to claim 1 or 2, wherein the relaxation shrinkage rate upon heating relaxation is 2% or less.