JP2004068231A - Method for producing polyacrylonitrile-based fiber and device for stretching yarn in bath - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a polyacrylonitrile-based fiber having less defects and a good quality by inhibiting the adhesion among single fibers in a hot water stretching process of the polyacrylonitrile-based fiber production and improving stretching property. <P>SOLUTION: This method for producing the polyacrylonitrile-based fiber by stretching the yarn obtained by spinning the polyacrylonitrile-based polymer, in a hot water bath is characterized by setting ≤3,000dTex/mm yarn density M of the yarn progressing into the hot water bath and stretching under ≤2.5mN/dTex tension on the yarn, and a device for stretching the yarn in the bath suitable for being used in the method is provided. <P>COPYRIGHT: (C)2004,JPO

Description

【００３６】
【発明の効果】
本発明によれば、熱水浴中で生じる接着を回避し、ＰＡＮ系繊維の品位、ひいてはこれを焼成して得られる炭素繊維の特性を向上させうる。さらには、熱水浴での接着を抑制させることによりＰＡＮ系繊維製造の際の全延伸倍率を向上させられ安価にＰＡＮ系繊維を製造しうる。
【図面の簡単な説明】
【図１】本発明の浴延伸装置の一例を示す模式的な側面透視図である。
【図２】本発明の浴延伸装置の他の一例を示す模式的な側面透視図である。
【図３】従来の延伸装置の例を示す模式的な側面透視図である。
【符号の説明】
１　　熱水
２ａ、２ｂ　　入り側ローラー
２ｃ、２ｄ　　出側ローラー
３ａ　　熱水浴液面に接するガイド
３ｂ、３ｃ　ガイド
４　　糸条
５　　熱水槽[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a production technique of polyacrylonitrile fibers mainly used for precursor fibers for carbon fibers and the like, and more specifically, to prevent adhesion during drawing in a hot water bath and improve drawability. The present invention relates to a method for producing polyacrylonitrile-based fibers, which can efficiently produce high-quality polyacrylonitrile-based fibers, and a yarn bath stretching apparatus.
[0002]
[Prior art]
BACKGROUND ART Carbon fibers have been widely used in recent years, such as large structural members and sports goods, due to their excellent specific strength and specific elastic modulus. Depending on the difference in the precursor fiber, the carbon fiber is a PAN-based carbon fiber obtained by using a polyacrylonitrile (hereinafter abbreviated as PAN) -based fiber as a precursor, or a pitch obtained by using a fiber obtained from a pitch extracted from petroleum or coal as a precursor. Carbon fibers, and cellulosic carbon fibers using regenerated cellulose fibers as precursors. Among them, PAN-based carbon fibers have particularly excellent properties and are used in a wide range of applications. As a spinning method for fiberizing a PAN-based polymer, a dry spinning method, a wet spinning method, a dry-wet spinning method, and the like are well known. Among them, the dry-wet spinning method in which the surface morphology of the obtained fiber is easy to maintain a smooth and circular shape and the surface layer denseness is easy to increase is widely used because high-performance carbon fiber is easily obtained. . However, since the PAN-based fiber obtained by this dry-wet spinning method has a high surface smoothness, adhesion between single fibers tends to occur when the draw ratio is increased in a hot water bath. When the adhesion between the single fibers occurs in the yarn, that portion remains as a defect after carbonization, which may cause deterioration in the physical properties of the finally obtained carbon fiber. As described above, it is well known that the properties of the PAN-based carbon fiber largely depend on the properties and properties of the precursor PAN-based fiber, and many studies have been made to control the properties and properties. It has been done. In particular, in producing a PAN-based fiber, when the yarn is stretched in a hot water bath, the single fibers constituting the yarn are easily adhered to each other. Therefore, a technique for suppressing adhesion in hot water bath stretching. Many have been proposed.
[0003]
For example, Japanese Patent No. 2853484 provides a technique for regulating the temperature of a roller on the side into which a stretching bath is inserted in order to suppress adhesion in hot water bath stretching. However, this technique cannot control the temperature unevenness of the yarn, and thus has a problem that the adhesion suppressing effect is not sufficient, particularly in the case of a yarn having a large fineness.
[0004]
Further, Japanese Patent No. 3039093 provides a technique of stretching a yarn having a specific yarn density index by regulating the yarn width thereof with a guide having a specific shape in order to suppress adhesion in hot water bath stretching. . However, the fact is that even if this technique was used as it was, the effect of suppressing the adhesion was not sufficient.
[0005]
[Problems to be solved by the invention]
The present invention provides a method for efficiently producing a high-quality PAN-based fiber with few defects by suppressing adhesion between single fibers in a hot water drawing step in PAN-based fiber production and improving drawability. The purpose is to:
[0006]
[Means for Solving the Problems]
The PAN fiber of the present invention has the following configuration in order to solve the above-mentioned problems. That is, when a yarn obtained by spinning a polyacrylonitrile polymer is drawn in a hot water bath to produce a polyacrylonitrile fiber, the yarn density M of the yarn entering the hot water bath is set to 3, 000 dTex / mm or less, and a tension applied to the yarn is 2.5 mN / dTex or less, which is a method for producing polyacrylonitrile fiber.
[0007]
Further, the yarn bath stretching apparatus of the present invention has the following configuration in order to solve the above problems. That is, a hot water tank for forming a hot water bath, a guide for introducing the yarn into the hot water bath, and a stretching means for giving stretching to the yarn, and the guide is provided with A yarn bath stretching apparatus, which is arranged on a liquid surface of a hot water bath.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail.
[0009]
The present inventors have conducted extensive studies on places where single fibers are likely to adhere to each other and factors that influence the occurrence of adhesion. As a result, the yarn obtained by spinning the polyacrylonitrile-based polymer was treated with hot water. When introduced into a bath, it was found that by controlling the yarn density and the tension in an appropriate range, a dramatic effect of suppressing adhesion could be obtained.
[0010]
In the present invention, first, a PAN-based polymer is spun to obtain a yarn. Usually, as the PAN-based polymer, one containing 95% by weight or more of acrylonitrile and further copolymerizing a comonomer within 5% by weight as needed can be used. Examples of the comonomer include organic acids such as acrylic acid, methacrylic acid, and itaconic acid, esters thereof such as methyl, ethyl, propyl, and isopropyl, and / or salts thereof such as ammonium, tetramethylammonium, and tetraethylammonium, and acrylylamide and the like. And the like. The PAN-based polymer is usually prepared as a stock solution for spinning dissolved in an organic or inorganic solvent.
[0011]
Next, a so-called spinning is performed, in which the PAN-based polymer is passed through a die to form a fiber. In this case, a wet spinning method of directly spinning in a coagulation bath to obtain a coagulated yarn, A commonly known spinning method such as a dry-wet spinning method in which the spun yarn is introduced into a coagulation bath to form a coagulated yarn can be adopted, but the cross-sectional shape of the resulting fiber is circular and the surface shape is The present invention has a particularly remarkable effect when adopted in a dry-wet spinning method in which adhesion is likely to occur during drawing in a hot water bath due to easy smoothing. Further, the yarn to be drawn has a particularly remarkable effect when the number of filaments per yarn is 3,000 or more and 100,000 or less.
[0012]
The solvent component in the coagulation bath usually remains in the obtained coagulated yarn, and the precursor fiber containing too much solvent component remains in a high-temperature carbonized atmosphere when it is baked into carbon fiber. Since these solvent components and the like are scattered, the resulting carbon fibers form defects serving as starting points of destruction, and thus reduce the physical properties of the obtained carbon fibers. It is common to go through a washing step of washing and removing in hot water. This washing step may be performed before or after the stretching step in a hot water bath described below, and may also serve as the washing step in the stretching step in a hot water bath described later. .
[0013]
In the present invention, a yarn obtained by spinning a PAN-based polymer is drawn in a hot water bath.
[0014]
The hot water bath referred to in the present invention is a bath filled with hot water at 30 to 98 ° C., preferably 60 to 95 ° C. The yarn is in contact with the entry side and the exit side of the yarn to regulate the speed. By arranging the driving roller, the yarn can be drawn. If the temperature of the hot water is too low, the film may not be stretched substantially. If the temperature of the hot water is too high, the temperature and humidity around the hot water bath also increase, and the working environment around the bath deteriorates. The drive roller can be placed on the entrance and exit side of a single hot water bath, but it can extend over multiple hot water baths. By controlling the state of the yarn at the time of entry into the range specified in the present invention, it can be suitably achieved. The draw ratio of the yarn can be controlled by the speed difference between the drive rollers on the entrance side and the exit side.
[0015]
When a yarn is stretched in a hot water bath, the yarn is stretched by applying a high tension and temperature to the yarn, and with this, adhesion between the single fibers is induced. In particular, the single fiber located in the outermost layer of the yarn is bonded to a roller arranged in a hot water bath by pressure bonding to cause adhesion. That is, at the very moment when the yarn enters the hot water bath, the inventors have discovered that adhesion between the single fibers has occurred, and control the yarn state at this moment under appropriate conditions. This has led to the present invention.
[0016]
In the present invention, when the yarn is stretched in the hot water bath, the yarn density M when the yarn enters the hot water bath is 3000 dTex / mm or less, preferably 100 to 3,000 dTex / mm, more preferably. Is 400 to 2,500 dTex / mm, more preferably 1,000 to 2,000 dTex / mm, and the tension applied to the yarn is 2.5 mN / dTex or less, preferably 2.0 mN / dTex or less. .
[0017]
In addition, the yarn density M referred to in the present invention refers to a value defined by the following equation (1), which is a measure of the extent of the yarn.
[0018]
M (dTex / mm) = D (dTex) / L (mm) (1)
Here, D is the total fineness when entering the hot water bath, and L is the width of the yarn bundle when entering the hot water bath.
[0019]
If the yarn density is too large, the temperature unevenness and tension unevenness in the yarn become large, and the adhesion suppressing effect is reduced.On the other hand, if the yarn density is too small, the yarn is greatly expanded in order to greatly expand the yarn. As a result, thread pain is likely to occur.
[0020]
In addition, if the tension applied to the yarn here is too large, the adhesion suppressing effect is reduced, while if the tension is too small, the yarn is not substantially stretched.
[0021]
In order to satisfy the above conditions, it is preferable to use a bath stretching apparatus as shown in FIG. In FIG. 1, hot water 6 is stored in a hot water tank 5 to form a hot water bath. A guide 3a for introducing the yarn into the hot water bath is provided so as to be in contact with the liquid surface of the hot water bath. The yarn is drawn by a drawing applying means (not shown) such as a driving roller.
The process speed of the yarn is first regulated by a driving roller (not shown), and then the yarn is widened by a guide 3a via entry rollers 2a and 2b, and introduced into a hot water bath. The yarn introduced into the hot water bath is folded back by the immersion roller 2c and drawn out of the hot water bath, and the process speed is regulated by the driving roller via the outlet roller 2d. The guide 3a may not necessarily be in contact with the liquid surface of the hot water bath or may be in the vicinity of the liquid surface. It can be controlled with precision. FIG. 2 shows an example of a yarn drawing device using guides 3b and 3c instead of the entry-side roller 2b.
[0022]
As described above, when the spun yarn is stretched in hot water, the yarn is brought into contact with the guide immediately before entering the hot water, so that the yarn can be squeezed and widened, and the yarn can be expanded. To promote the entry of hot water into the hot water bath, reduce the temperature unevenness when entering the hot water bath, and suppress the adhesion between single yarns. When the yarn enters the hot water bath in contact with the roller, there is almost no relative movement of the single fiber in the yarn on the roller, and the yarn enters the hot water bath with its position fixed. Therefore, unevenness in temperature and unevenness in tension cannot be reduced, and the adhesion between the single fibers frequently occurs particularly between the single fibers located in the yarn surface layer portion. From such a viewpoint, it is preferable that the guide in contact with the hot water bath has a non-rotating, rod-like shape rather than a free roller. When a curved or V-shaped guide is used, the time for entering the hot water bath is different for each single fiber in the yarn, and accordingly, when stretched, tension unevenness occurs in the yarn, and as a result, In some cases, adhesion may easily occur in a portion having a high tension. Even if a guide used in addition to the guide existing in contact with the liquid surface of the hot water bath has a curved shape or a V-shaped guide, the effect of the present invention is not significantly affected.
[0023]
The material of the guide is selected to have a low coefficient of friction with the yarn so that the yarn is not excessively rubbed. For example, a material in which hard chrome plating is applied to the surface of an alloy such as stainless steel, ceramics, or the like is used. Use of a mirror-finished or matte-finished guide surface is suitable for preventing the yarn from being excessively abraded.
[0024]
By using the method of the present invention, adhesion within the yarn in a hot water bath can be reduced independently of the temperature of hot water.
[0025]
In the present invention, the stress between the guide and the yarn in contact with the liquid surface of the hot water bath is set to 2.0 mN / dTex or less, preferably 1.5 mN / dTex or less. This stress can be obtained by actually measuring the tension applied to the yarn in the direction of the yarn bundle in the hot water bath with a tensiometer, and dividing this tension into the guide shaft direction by vector. In the examples described later, TENSION METER HS-3000 (manufactured by EIKO Corporation) was used as a tensiometer. If the stress between the guide and the yarn is too large, the effect of suppressing adhesion within the yarn tends to decrease, and if it is too small, the effect of widening the yarn tends to decrease. Although the effect of widening the yarn can be increased by increasing the number of guide steps (number), it is not advisable to use too many guides from the viewpoint of productivity.
[0026]
As a means for adjusting the stress between the guide and the yarn, the contact angle between the guide and the yarn is generally changed, but the draw ratio may be changed. The preferred range of the contact angle is 1 ° or more and 30 ° or less, preferably 2 ° or more and 20 ° or less, and the preferred range of the draw ratio is 2.0 or more and 10.0 or less. It can be set appropriately so as to fall within a predetermined range.
[0027]
By adopting the above guide arrangement in the drawing in the hot water bath, the adhesion between the single fibers in the yarn is remarkably reduced, and the drawing magnification in the hot water bath is 2 times or more and 10 times. It is possible to increase the following. By increasing the draw ratio in a hot water bath in this way, the orientation of the fibers accompanying the drawing can be improved, and the yarn drawn in the hot water bath has little adhesion and high orientation. Therefore, it is suitable for producing a high-performance carbon fiber.
[0028]
In the present invention, the yarn drawn in hot water becomes a PAN-based fiber through an oil agent application step, a dry densification step, a secondary drawing step, and the like, as necessary. As the oil agent used in the oil agent applying step, when the PAN-based fiber is made of carbon fiber, it is preferable to use a modified silicone-based oil agent having a high sticking suppression effect in carbonization. The drying and densification step can be performed using a heating roller or the like, and the temperature and time can be appropriately selected. After the dry densification step, a secondary stretching step may be employed, and as the secondary stretching, dry heat stretching may be employed, but stretching in pressurized steam having good post-stretchability can be preferably employed.
[0029]
In the present invention, the stretching ratio in a hot water bath can be improved by reducing the adhesion, but when the above-described secondary stretching step is employed, there is also a feature that the stretching ratio there can be improved. . The reason why the draw ratio in the secondary drawing step is improved by the present invention is not always clear, but if there is a large amount of adhesion between the single fibers in the yarn to be subjected to the secondary drawing, it may occur during dry heat or pressure steam. When the film is stretched in the above manner, it is considered that the magnification at the time of the second stretching cannot be set high because the bonded portion becomes the starting point of the single fiber break. According to the present invention, the total draw ratio of hot water bath stretching and secondary stretching can be set as high as 10 times or more and 30 times or less, and a PAN-based fiber suitable as a high-performance carbon fiber precursor can be produced. become able to.
[0030]
The PAN-based fiber obtained by the above-described production method has little adhesion between single fibers, has good quality, and is suitable for obtaining high-performance carbon fibers.
[0031]
【Example】
Next, the present invention will be described more specifically with reference to examples. In this example, the bonding state between the single fibers of the yarn, the strand strength and the elastic modulus of the carbon fiber were measured by the following procedure.
(Adhesion between yarn and single fiber)
The oil-free yarn is cut to a length of about 5 mm and dispersed in a 0.1% by weight aqueous solution of a nonionic surfactant Neugen SS (registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). After stirring at 60 rpm with a stirrer, the mixture was filtered through black filter paper and the adhesion was visually determined. Judgment was performed in five stages, and the state where almost no adhesion was made was class 1, and the state where almost all single fibers were adhered was class 5 and the intervals were distributed at equal intervals to make a classification judgment.
(Strand strength and elastic modulus of carbon fiber)
A carbon fiber was prepared by mixing a resin composition obtained by mixing alicyclic epoxy resin “Bakelite” (registered trademark) ERL-4221 (manufactured by Union Carbide Co., Ltd.) with 1000 g, boron trifluoride monoethylamine 30 g and acetone 40 g. It was applied and impregnated by running on a plurality of rollers. This was heated at 130 ° C. for 35 minutes to cure the resin, thereby obtaining a resin-impregnated strand. The obtained resin-impregnated strand was measured for strand strength and elastic modulus according to the method specified in JIS R7601.
(Example 1)
A 20% by weight dimethyl sulfoxide solution of a PAN-based polymer obtained by copolymerizing 99% by weight of acrylonitrile and 1% by weight of acrylic acid was used as a spinning solution. This spinning stock solution is discharged from a spinneret having a diameter of 0.10 mmφ and a discharge hole of 4,000 holes, and once passed through an inert atmosphere into a coagulation bath filled with a 30% by weight aqueous solution of dimethyl sulfoxide at 10 ° C. The coagulated yarn was obtained by intruding and solidifying. The obtained coagulated yarn was washed in a warm water bath at 30 ° C. The washed yarn was drawn by arranging a yarn drawing device as shown in FIG. 1 in two stages. In both the first-stage yarn stretching device and the second-stage yarn stretching device, the entrance-side rollers 2a and 2b, the immersion roller 2c, and the exit-side roller 2d are all made of stainless steel having a surface hard chrome plating. As the guide 3a in contact with the liquid surface of the hot water bath using a roller, a mirror-finished stainless steel 2 mmφ cylindrical rod was used, and the temperature of the hot water 1a was 90 ° C. The angle between the guide 3a and the thread was 2 °. Here, the yarn density of the yarn entering the hot water bath is 1,800 dTex / mm, a tension of 1.5 mN / dTex is applied to the yarn, and the draw ratio in the drawing in the hot water bath is 3.0. Doubled. The drawn yarn drawn out of the second-stage hot water bath out of the bath had an extremely good adhesion of 1.0 class.
[0032]
A modified silicone oil agent was applied to the obtained drawn yarn so as to have an adhesion amount of 1.0% by weight, and dried with a drying roller at 180 ° C. until the moisture content in the fiber became substantially 0%. . The dried yarn was stretched in a saturated pressurized steam at 160 ° C. so that the total draw ratio became 16 times, to obtain a PAN-based fiber bundle having a single fiber fineness of 1.11 dTex and a number of filaments of 4000. The obtained PAN fiber bundle had no fluff and good quality.
[0033]
The obtained PAN-based fiber bundle is subjected to oxidizing treatment in a hot air circulating furnace at 260 ° C. at a draw ratio of 0.90, and then in a heat treatment furnace at a maximum temperature of 700 ° C. in nitrogen at a draw ratio of 0.98. The carbon fiber bundle was carbonized at a draw ratio of 0.95 times in an inert atmosphere at a high temperature of 1,300 ° C. in a high-temperature heat treatment furnace. Using the carbon fiber bundle as an anode, anodic oxidation using an aqueous solution of sulfuric acid as an electrolytic solution is performed, and an aqueous hydrate of bisphenol-A-diglycidyl ether is applied to the carbon fiber in an amount of 1.0% by weight, dried and wound up. Was.
[0034]
The quality of the obtained carbon fiber bundle was good without fuzz. Table 1 summarizes the production conditions and the characteristics of the obtained carbon fiber bundle.
(Example 2)
A PAN-based fiber bundle and a carbon fiber bundle were obtained in the same manner as in Example 1, except that the draw ratio in a hot water bath was changed to 4 times and the total draw ratio was changed to 20 times. The yarn density of the yarn entering the hot water bath and the tension applied to the yarn were as shown in Table 1. The obtained PAN-based fiber bundle and carbon fiber bundle had no fluff and were of good quality. Table 1 summarizes the production conditions and the characteristics of the obtained carbon fiber bundle.
(Example 3)
A PAN-based fiber bundle and a carbon fiber bundle were obtained in the same manner as in Example 1 except that the apparatus shown in FIG. 2 was used as a yarn stretching apparatus, and was changed to be arranged in two stages. The angle between the guide 3a and the thread was 2 °. The yarn density of the yarn entering the hot water bath was 1,800 dTex / mm, and the tension applied to the yarn was as shown in Table 1. The obtained PAN-based fiber bundle and carbon fiber bundle had no fluff and were of good quality. Table 1 summarizes the production conditions and the characteristics of the obtained carbon fiber bundle.
(Comparative Example 1)
A PAN-based fiber bundle and a carbon fiber bundle were obtained in the same manner as in Example 1 except that the apparatus shown in FIG. 3 was used as a yarn stretching apparatus, and was changed to be arranged in two stages. The yarn density of the yarn entering the hot water bath and the tension applied to the yarn were as shown in Table 1. The obtained PAN-based fiber bundle was low in quality with much adhesion between single fibers. Further, the obtained carbon fiber bundle had low physical properties, reflecting the large amount of adhesion between single fibers in the PAN-based fiber bundle as the raw material. Table 1 summarizes the production conditions and the characteristics of the obtained carbon fiber bundle.
(Comparative Example 2)
A PAN-based fiber bundle and a carbon fiber bundle were obtained in the same manner as in Example 2 except that the apparatus shown in FIG. 3 was used as the yarn stretching apparatus, and was changed to be arranged in two stages. The yarn density of the yarn entering the hot water bath and the tension applied to the yarn were as shown in Table 1. The obtained PAN-based fiber bundle was poor in quality because of a large amount of adhesion between single fibers. Table 1 summarizes the production conditions and the characteristics of the obtained carbon fiber bundle.
(Comparative Example 3)
A PAN-based fiber bundle was obtained in the same manner as in Example 3, except that the yarn density when entering the hot water bath was 4,000 dTex / mm. The draw ratio in a hot water bath and the tension applied to the yarn were as shown in Table 1. The resulting PAN-based fiber had poor adhesion due to a large amount of adhesion between single fibers. Table 1 summarizes the production conditions and the characteristics of the obtained carbon fiber bundle.
(Example 4)
A PAN-based fiber bundle and a carbon fiber bundle were prepared in the same manner as in Example 1 except that three fiber bundles of 4,000 filaments pulled out of the coagulation bath were combined into three to form 12,000 yarns. Obtained. The yarn density of the yarn entering the hot water bath and the tension applied to the yarn were as shown in Table 1. The obtained PAN-based fiber bundle and carbon fiber bundle had no fluff and were of good quality. Table 1 summarizes the production conditions and the characteristics of the obtained carbon fiber bundle.
(Example 5)
A PAN-based fiber bundle and a carbon fiber bundle were prepared in the same manner as in Example 2 except that three 4,000 filament fiber bundles pulled up from the coagulation bath were combined into three yarns to make 12,000 yarns. Obtained. The yarn density of the yarn entering the hot water bath and the tension applied to the yarn were as shown in Table 1. The obtained PAN-based fiber bundle and carbon fiber bundle had no fluff and were of good quality. Table 1 summarizes the production conditions and the characteristics of the obtained carbon fiber bundle.
(Comparative Example 4)
A PAN-based fiber bundle and a carbon fiber bundle were produced in the same manner as in Comparative Example 1 except that three 4,000 filament fiber bundles pulled out of the coagulation bath were combined into three yarns to obtain 12,000 yarns. Obtained. The yarn density of the yarn entering the hot water bath and the tension applied to the yarn were as shown in Table 1. The obtained PAN-based fiber bundle was low in quality with much adhesion between single fibers. Further, the obtained carbon fiber bundle had low physical properties, reflecting the large amount of adhesion between single fibers in the PAN-based fiber bundle as the raw material. Table 1 summarizes the production conditions and the characteristics of the obtained carbon fiber bundle.
(Comparative Example 5)
A PAN-based fiber bundle and a carbon fiber bundle were prepared in the same manner as in Comparative Example 2 except that three 4,000 filament fiber bundles pulled out of the coagulation bath were combined into 32,000 yarns. Obtained. The yarn density of the yarn entering the hot water bath and the tension applied to the yarn were as shown in Table 1. The drawn yarn drawn out of the second-stage hot water bath out of the bath had an adhesion state of 4.5 class and a large amount of adhesion between single fibers. Table 1 summarizes the production conditions and the characteristics of the obtained carbon fiber bundle.
[0035]
[Table 1]

[0036]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, adhesion which arises in a hot water bath can be avoided, and the quality of PAN type fiber, and the characteristic of the carbon fiber obtained by baking this can be improved. Further, by suppressing the adhesion in a hot water bath, the total draw ratio in producing the PAN-based fiber can be improved, and the PAN-based fiber can be produced at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic side perspective view showing an example of a bath stretching apparatus of the present invention.
FIG. 2 is a schematic side perspective view showing another example of the bath stretching apparatus of the present invention.
FIG. 3 is a schematic side perspective view showing an example of a conventional stretching apparatus.
[Explanation of symbols]
1 Hot water 2a, 2b Inlet rollers 2c, 2d Outlet rollers 3a Guides 3b, 3c in contact with the surface of hot water bath Guide 4 Thread 5 Hot water tank

Claims (11)

In a method for producing a polyacrylonitrile-based fiber by drawing a yarn obtained by spinning a polyacrylonitrile-based polymer in a hot water bath, the yarn density M of the yarn entering the hot water bath is 3,000 dTex. / Mm or less, and a tension applied to the yarn is 2.5 mN / dTex or less, a method for producing polyacrylonitrile-based fibers. The method for producing a polyacrylonitrile fiber according to claim 1, wherein the number of filaments per yarn is 3,000 to 100,000. The method for producing a polyacrylonitrile-based fiber according to claim 1, wherein the yarn is brought into contact with at least one guide to control the yarn density within the range before the yarn enters the hot water bath. 4. The method for producing polyacrylonitrile fiber according to claim 3, wherein the guide closest to the hot water bath liquid surface is in contact with the hot water bath liquid surface. The method for producing a polyacrylonitrile-based fiber according to claim 4, wherein the guide in contact with the liquid surface of the hot water bath has a rod shape. The method for producing a polyacrylonitrile-based fiber according to claim 4 or 5, wherein the stress between the guide and the thread in contact with the liquid surface of the hot water bath is 2.0 mN / dTex or less. The method for producing a polyacrylonitrile-based fiber according to any one of claims 4 to 6, wherein a contact angle between the guide and the thread in contact with the liquid surface of the hot water bath is 1 ° to 30 °. The method for producing a polyacrylonitrile-based fiber according to any one of claims 1 to 7, wherein a draw ratio of the yarn in a hot water bath is 2 or more, and a total draw ratio is 10 or more. The method for producing a polyacrylonitrile-based fiber according to any one of claims 1 to 8, wherein the spinning method is a dry-wet spinning method. A hot water tank for forming a hot water bath, a guide for introducing the yarn into the hot water bath, and a stretching means for giving stretching to the yarn, and the guide is provided with hot water A yarn bath stretching apparatus, which is arranged on a liquid surface of a bath. The yarn drawing apparatus according to claim 10, wherein the guide is disposed in contact with a liquid surface of the hot water bath.

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