Method for producing acrylonitrile fiber bundles

Abstract

The present invention addresses the problem of providing a method with which, when manufacturing an acrylonitrile-based fiber bundle by means of a dry-wet spinning method, it is possible to stably manufacture a high-grade, high-quality acrylonitrile-based fiber bundle even if the traveling speed of a coagulated yarn is increased or the number of discharge holes in a cap is maximized in order to increase the production efficiency. As a solution, the present invention provides an acrylonitrile-based fiber bundle manufacturing method in which, after pushing a spinning stock solution out into the air from a plurality of discharge holes in a cap 1, the spinning stock solution is moved downward into a coagulating bath solution 12 retained in a coagulating bath 2 to form a coagulated yarn 3 and, after folding back the coagulated yarn 3 by using a turning guide 4 disposed in the coagulating bath solution 12 below the cap 1, the coagulated yarn 3 is taken out of the coagulating bath solution 12 to the outside thereof. The acrylonitrile-based fiber bundle manufacturing method satisfies the following 1-3: 1) the axial direction of the turning guide 4 is a direction perpendicular to both a traveling direction Da in which the coagulated yarn 3 moves toward the turning guide 4 from a liquid surface 9 of the coagulating bath solution and a take-out direction Db in which the coagulated yarn 3 is taken out of the coagulating bath 2 from the turning guide 4. 2) the region in which the coagulated yarn 3 travels between the liquid surface 9 of the coagulating bath solution and the turning guide 4 has two or more yarn present regions 24 in which the coagulated yarn 3 is continuously present in the traveling direction Da of the coagulated yarn 3 and at least one absent region 23 in which the coagulated yarn 3 is not continuously present in the traveling direction Da of the coagulated yarn 3, and the at least one yarn absent region 23 is flanked by the two yarn present regions 24. 3) in the at least one yarn absent region 23, the width of the turning guide 4 in the axial direction at the liquid surface 9 of the coagulating bath solution is at least four times greater than the shortest distance among the discharge holes in the cap 1.

Description

[Technical field]

[0001] The present invention relates to a method for stably producing a high-quality, high-grade acrylonitrile fiber bundle suitable for producing a carbon fiber bundle. [Background technology]

[0002] In the production of acrylonitrile fiber bundles used for precursor fiber bundles of carbon fiber bundles, it is important to reduce the production cost by increasing the production efficiency. In order to meet this demand, a wide variety of methods have been adopted, such as a method of increasing the number of holes arranged in a spindle per spindle, a method of increasing the number of spindles or the number of yarns, and a method of increasing the running speed of the yarns. Among these methods, increasing the number of holes in a spindle per spindle (multiple holes, high-density arrangement of discharge holes) and increasing the running speed of the yarns (high speed) have a great advantage in that they can meet the above-mentioned demand without requiring a large capital investment.

[0003] In particular, the dry-wet spinning method in which an air gap is provided between the spinneret and the surface of the coagulating bath liquid is an excellent method for increasing the yarn running speed, since the spinning dope discharged from the spinneret surface can be thinned and deformed in the area of ​​the air gap where the air resistance is small. In addition, this spinning method stabilizes the quality and grade of the obtained acrylonitrile fiber bundle by keeping the air gap at a constant distance, and can achieve high productivity.

[0004] In this dry-wet spinning method, generally, after the spinning dope is extruded from the spinneret into the air, the coagulated thread obtained by the contact of the spinning dope with the coagulating bath travels downward in the coagulating bath (to the bottom of the coagulating bath), and after traveling a certain distance, changes direction at a direction changing guide, travels diagonally upward (to the liquid surface of the coagulating bath), and finally escapes from the coagulating bath into the air and is transported to the next process. Since accompanying flows are generated by the traveling of the coagulated thread, the accompanying flows are increased by increasing the traveling speed, increasing the number of holes, and arranging the discharge holes at a high density. The increase in accompanying flows increases the flow rate of the coagulating bath around the coagulated thread, which causes uneven tension and uneven physical properties of the coagulated thread, and the quality and grade of the acrylonitrile fiber bundle are reduced. In addition, the increase in the flow rate of the coagulating bath increases the fluctuation in the liquid level of the coagulating bath, which reduces the spinnability and ultimately leads to a decrease in production efficiency. In other words, controlling the flow of this coagulation bath liquid is extremely important for improving the quality and grade of acrylonitrile fiber bundles as well as production efficiency.

[0005] Thus, as a method for controlling the flow of the coagulation bath liquid around the coagulated yarn, there is a method described in Patent Document 1. In the spinning method of Patent Document 1, a block consisting of a plurality of nozzle holes of a spinneret is formed, and the block is divided into two or more, and the distance between adjacent blocks is set to be at least twice the distance between the spinneret and the liquid surface of the coagulation bath liquid. In addition, it is described that a protrusion is provided on a direction changing guide in the coagulation bath liquid to change the running position of the coagulated yarn, thereby controlling the flow of the coagulation bath liquid and improving the spinnability of the coagulated yarn.

[0006] Furthermore, the spinning method of Patent Document 2 describes that a capillary having two or more openings separates the coagulated yarn from the coagulating bath liquid, and a plurality of direction-changing guides are arranged downstream of the capillary having two or more openings to divide the coagulated yarn into a plurality of parts in the take-up direction, thereby suppressing turbulence in the flow of the coagulating bath liquid at the liquid surface of the coagulating bath liquid and the generation of vortexes, thereby enabling the production of high-quality and consistent coagulated yarn. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. Hei 2-91206 [Patent Document 2] Japanese Patent Application Publication No. 2-112409 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the conventional spinning methods have the following problems.

[0009] In the spinning method of Patent Document 1, the accompanying flow around the coagulated yarn in the coagulation bath liquid cannot be sufficiently alleviated, and there are cases in which the spinnability of the coagulated yarn cannot be improved.

[0010] In addition, when the filaments in the coagulated filament run in a crowded state, the accompanying flow increases, and the speed of the flow of the coagulating bath liquid toward the coagulated filament increases near the liquid surface of the coagulating bath liquid, causing collisions between the filaments and the generation of local vortices (hereinafter referred to as local vortices) near the liquid surface of the coagulating bath liquid. When this local vortex occurs, the air gap, which is the distance between the spinneret and the liquid surface of the coagulating bath liquid, fluctuates. In addition, the increase in the accompanying flow increases the swaying of the coagulated filament between the spinneret and the direction change guide, and these factors increase the fluctuation of the liquid surface of the coagulating bath liquid, causing filament breakage, and in the worst case, spinning may become impossible.

[0011] Furthermore, in the spinning method of Patent Document 1, a block of a spinneret having a plurality of discharge holes is provided, and the distance between the blocks is increased, so that the width of the spinneret becomes long. In addition, the width of the coagulation bath also becomes long. In a system in which multiple spindles are provided with a coagulation bath, increasing the width of the spinneret and the width of the coagulation bath requires a wide facility, which may increase the facility cost.

[0012] Next, according to the findings of the present inventors, in the spinning method of Patent Document 2, as described in Patent Document 1, the accompanying flow around the coagulated yarn in the coagulation bath cannot be sufficiently alleviated, and the liquid flow of the coagulation bath may be disturbed, local vortexes may be generated, and yarn breakage may occur, which may make spinning impossible. As a result, it may not be possible to produce a high-quality and consistent coagulated yarn. In particular, as described in the examples of Patent Document 2, the winding speed after drawing is low at 400 m / min (the take-up speed in the coagulation bath is 10 m / min or less), and the number of holes in the nozzle of the spinneret is small at 400, so the scale of the accompanying flow is small and does not pose a problem, but the above problem may become apparent at high take-up speeds (take-up speed of 25 m / min or more) and with a large number of holes (several thousand holes).

[0013] In addition, in the spinning method of Patent Document 2, multiple direction change guides are provided to divide the coagulated yarn, and the yarns must be passed through each direction change guide, which may cause a deterioration in operability. In addition, a thin tube is provided below the coagulating bath to allow the coagulating bath liquid to flow outside the coagulating bath, and therefore multiple circulation lines and recovery lines for the coagulating bath liquid are required, which may complicate the equipment and increase the equipment costs.

[0014] As described above, in producing an acrylonitrile fiber bundle, it is extremely important to control the flow of the coagulation bath liquid around the coagulated yarn and the fluctuation of the liquid level of the coagulation bath liquid, but as described above, various problems remain, which have been an obstacle to the production of an acrylonitrile fiber bundle. Therefore, solving these problems is of great industrial significance.

[0015] Therefore, an object of the present invention is to provide a method for stably producing a high-quality acrylonitrile fiber bundle in a dry / wet spinning method, even if the running speed of the coagulated yarn is increased or the number of discharge holes of the spinneret is maximized in order to improve production efficiency. [Means for solving the problem]

[0016] The present inventors have set up the following hypotheses as to why the techniques of Patent Documents 1 and 2 cannot sufficiently improve the spinnability of coagulated yarn.

[0017] In the technology of Patent Document 1, when the running speed of the coagulated yarn is increased, an accompanying flow occurs in the running area of ​​the coagulated yarn, and to compensate for this, a liquid flow of the coagulating bath liquid occurs from the periphery of the coagulated yarn toward the coagulated yarn, and the speed of the liquid flow becomes the highest near the liquid surface of the coagulating bath liquid. As a result, a large drag is applied to the coagulated yarn in a direction perpendicular to the running direction of the coagulated yarn, and it is thought that the yarns in the coagulated yarn become densely packed together.

[0018] In the technology of Patent Document 2, if the direction in which the coagulated yarn is divided is the same as the direction Dc of the flow of the coagulating bath liquid toward the coagulated yarn, collision of the flow of the coagulating bath liquid cannot be avoided, so when the take-up speed of the coagulated yarn is increased, an accompanying flow occurs in the running area of ​​the coagulated yarn, and accordingly, a flow of the coagulating bath liquid occurs from the periphery of the coagulated yarn toward the coagulated yarn, and the speed of the flow is the highest near the liquid surface of the coagulating bath liquid. In particular, the flow of the coagulating bath liquid toward the coagulated yarn from the periphery collides from a direction perpendicular to the running direction of the coagulated yarn, which is thought to cause the yarns in the coagulated yarn to become densely packed together.

[0019] Based on the above hypothesis, the present inventors have conducted extensive research to solve these problems and have arrived at the present invention.

[0020] That is, the method for producing an acrylonitrile fiber bundle includes extruding a spinning dope into the air from a plurality of discharge holes of a spinneret, causing the dope to enter downward into a coagulating bath liquid stored in a coagulating bath to form a coagulated yarn, turning back the coagulated yarn at a direction-changing guide disposed in the coagulating bath liquid below the spinneret, and then drawing the yarn out of the coagulating bath liquid, and is characterized in that the following 1) to 3) are satisfied.

[0021] 1) The direction of the change of direction guide is perpendicular to both the running direction of the coagulated yarn from the liquid surface of the coagulating bath toward the change of direction guide and the take-up direction in which the yarn is pulled out of the coagulating bath from the change of direction guide.

[0022] 2) The running area of ​​the coagulated yarn from the liquid surface of the coagulation bath liquid to the direction changing guide has two or more yarn-present areas where coagulated yarns are continuously present in the running direction of the coagulated yarn, and at least one yarn-non-present area where no coagulated yarns are continuously present in the running direction of the coagulated yarn, and the yarn-non-present area is located between the two yarn-present areas.

[0023] 3) In at least one of the yarn-free regions, the axial width of the direction-changing guide at the liquid surface of the coagulation bath liquid is four times or more the shortest distance between the discharge holes in the spinneret. Effect of the Invention

[0024] According to the present invention, in a dry-wet spinning method, it is possible to stably produce a high-grade, high-quality acrylonitrile-based fiber bundle under excellent controllability of the liquid flow of the coagulation bath liquid in the vicinity of the coagulated yarn and high production efficiency (high speed (increased running speed of the yarn), multi-hole (increased number of discharge holes of the spinneret), and high density (increased arrangement density of the discharge holes of the spinneret)). [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic cross-sectional view of a dry / wet spinning apparatus used in a first embodiment of the present invention. [Diagram 2] 1( a ), 1 ( b ), and 1 ( c ) are schematic cross-sectional views showing examples of the shape of a coagulation bath in a dry / wet spinning apparatus used in an embodiment of the present invention. [Diagram 3] FIG. 1 is a diagram showing a liquid flow pattern of a coagulation bath liquid in a conventional dry-wet spinning apparatus. [Figure 4] FIG. 2 is a top view of a dry / wet spinning apparatus used in the method for producing an acrylonitrile fiber bundle of the present invention, showing the state of the liquid flow on the liquid surface of the coagulation bath liquid. [Diagram 5]FIG. 2 is a top view of a dry / wet spinning apparatus used in the method for producing an acrylonitrile fiber bundle of the present invention, showing the state of the liquid flow on the liquid surface of the coagulation bath liquid. [Figure 6] FIG. 2 is a top view of a dry / wet spinning apparatus used in the method for producing an acrylonitrile fiber bundle of the present invention, showing the state of the liquid flow on the liquid surface of the coagulation bath liquid. [Figure 7] FIG. 1 is a schematic cross-sectional view of a conventional dry / wet spinning apparatus. [Figure 8] FIG. 2 is a diagram showing measurement positions of flow velocity in a coagulation bath liquid in a dry / wet spinning apparatus. [Figure 9] FIG. 2 is a diagram showing measurement positions of flow velocity in a coagulation bath liquid in a dry / wet spinning apparatus. [Figure 10] FIG. 2 is a diagram showing measurement positions of flow velocity in a coagulation bath liquid in a dry / wet spinning apparatus. [Figure 11] FIG. 4 is a schematic cross-sectional view of a dry / wet spinning apparatus used in a second embodiment of the present invention. [Figure 12] FIG. 11 is a schematic cross-sectional view of a dry / wet spinning apparatus used in a third embodiment of the present invention. [Figure 13] FIG. 11 is a schematic cross-sectional view of a dry / wet spinning apparatus used in a fourth embodiment of the present invention. [Figure 14] FIG. 11 is a schematic cross-sectional view of a dry / wet spinning apparatus used in a fifth embodiment of the present invention. [Figure 15] FIG. 13 is a schematic cross-sectional view of a dry / wet spinning apparatus used in a sixth embodiment of the present invention. [Figure 16] FIG. 11 is a schematic cross-sectional view of a dry / wet spinning apparatus used in a fifth embodiment of the present invention. [Figure 17] This is a diagram showing the measurement position of the fiber width in the coagulation bath in a dry / wet spinning apparatus. [Figure 18] FIG. 11 is a schematic cross-sectional view of a dry / wet spinning apparatus according to Comparative Example 2. [Figure 19] FIG. 11 is a schematic cross-sectional view of a dry / wet spinning apparatus according to Comparative Example 5. [Figure 20] FIG. 2 is a cross-sectional view in a direction parallel to the liquid surface of the coagulation bath liquid, which diagrammatically shows a yarn ratio presence region and its surrounding region. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The method for producing an acrylonitrile fiber bundle of the present invention will be described in detail below with reference to the drawings.

[0027] FIG. 1 is a schematic cross-sectional view showing a dry-wet spinning apparatus used in a first embodiment of the present invention. As shown in FIG. 1, the present invention is composed of a spinneret 1, a coagulation bath 2, a coagulated yarn 3, and a direction change guide 4, and a coagulation solution 12 is stored in the coagulation bath 2. After the spinning dope is extruded into the air from a plurality of discharge holes of the spinneret 1, it is landed on the liquid surface 9 of the coagulation bath liquid, and the coagulated yarn 3 obtained by contacting the spinning dope with the coagulation bath liquid enters the coagulation bath liquid, is turned back at the direction change guide 4, and then travels through the coagulation bath liquid toward the liquid surface 9 of the coagulation bath liquid, and has a running path in which it is drawn out into the air. Here, the direction in which the coagulated yarn 3 travels from the liquid surface 9 of the coagulation bath liquid toward the direction change guide 4 is defined as a running direction Da, and the direction in which the coagulated yarn 3 travels from the direction change guide 4 toward the liquid surface 9 of the coagulation bath liquid is defined as a take-up direction Db. The direction change guide 4 is arranged in a direction perpendicular to the running direction Da of the coagulated yarn 3 and the take-up direction Db of the coagulated yarn 3. The running region of the coagulated yarn 3 between the liquid level 9 of the coagulating bath liquid and the direction changing guide 4 has two or more yarn-present regions 24 in which the coagulated yarn 3 is continuously present with respect to the running direction Da of the coagulated yarn 3, and at least one yarn-free region 23 in which the coagulated yarn 3 is not continuously present with respect to the running direction Da of the coagulated yarn. The yarn-free region 23 is sandwiched between the two yarn-present regions 24. The width of this yarn-free region 23 in the axial direction of the direction changing guide 4 at the position of the liquid level 9 of the coagulating bath liquid is equal to or greater than a certain width, which will be described later.

[0028] Here, the running region of the coagulated yarn 3 refers to the region inside the outermost running coagulated yarn 3 among the collection of coagulated yarns 3 running from the liquid level 9 of the coagulating bath liquid to the direction changing guide 4. The yarn non-existent region refers to a region 23 represented by a set of positions in a cross section parallel to the liquid level of the coagulating bath liquid shown in Figure 20, where an imaginary circle 26 having a diameter equal to the shortest distance between the discharge holes in the spinneret can exist without overlapping with the cross section of a single yarn 25 in the coagulated yarn. The position where an imaginary circle having a diameter equal to the shortest distance between the discharge holes in the spinneret 1 overlaps with the cross section of a single yarn 25 in the coagulated yarn refers to the position shown in 26' in Figure 20. The present invention is characterized in that, in each cross section of the running area of ​​the coagulated yarn 3 in the running direction Da of the coagulated yarn 3 from the liquid level 9 of the coagulating bath liquid to the direction changing guide 4, the yarn non-existent area 23 exists continuously in the running direction Da of the coagulated yarn 3 (i.e., the coagulated yarn 3 does not exist continuously in the running direction Da of the coagulated yarn 3). In addition, the area of ​​the running area of ​​the coagulated yarn 3 excluding the yarn non-existent area 23 is referred to as a yarn present area 24.

[0029] In addition, the coagulating bath 2 is best provided with a coagulating bath bottom surface 6 that is shallow along the take-up direction Db of the coagulated yarn 3 turned back by the direction-changing guide 4. In this case, the volume of the coagulating bath 2 can be reduced, and the volume of the coagulating bath liquid can be reduced. On the other hand, as shown in FIG. 2, the coagulating bath bottom surface 6 may have a bottom shape that is parallel to the liquid level 9 of the coagulating bath liquid (FIG. 2(a)), or may have a bottom shape that is deep along the running direction Da of the coagulated yarn 3 turned back by the direction-changing guide 4 (FIG. 2(b)). In addition, the coagulating bath bottom surface 6 may have a bottom shape that is partially stepped (FIG. 2(c)). In this case, at the bottom surface 6 of the coagulating bath between the position where the coagulated thread 3 is drawn into the air and the rear surface 8 of the coagulating bath, the shape of the bottom is parallel to the liquid level 9 of the coagulating bath liquid, so that a large area can be formed into which the liquid flow caused by the accompanying flow of the coagulated thread 3 flows, thereby reducing the flow rate of this liquid flow, minimizing collisions at the rear surface 8 of the coagulating bath, and suppressing fluctuations in the liquid level 9 of the coagulating bath liquid. The shape of the bottom of the coagulating bath 2 is not particularly limited because it does not affect the main flow of the coagulating bath liquid as described later.

[0030] In order to achieve high productivity, which is the most important point of this invention, A. Increase the running speed of solidified yarn 3 B. Maximize the number of nozzle holes on nozzle 1 C. High density arrangement of discharge holes Hereinafter, the principle by which a high-grade, high-quality acrylonitrile-based fiber bundle can be stably produced even if the coagulation bath is heated to a temperature of 1000° C. or lower is described. In this specification, the flow of the coagulation bath liquid in the coagulation bath is referred to as a liquid flow, and among the liquid flows, the liquid flows that flow in parallel with the coagulated yarn 3 in the running direction Da and the take-up direction Db of the coagulated yarn 3 as the coagulated yarn 3 runs are defined as accompanying flows.

[0031] First, when the above measures (A. to C.) are taken to increase productivity in the conventional acrylonitrile fiber bundle manufacturing method outside the scope of the present invention, the accompanying flow in the coagulation bath increases in all cases. This mechanism is explained with reference to FIG. 3. As the coagulated yarn 3 runs, an accompanying flow occurs in the running direction Da in the running region from the liquid level 9 of the coagulation bath liquid to the direction change guide 4, and an accompanying flow occurs in the take-up direction Db in the running region from the direction change guide 4 to the liquid level 9 of the coagulation bath liquid. Then, with the generation of this accompanying flow, a liquid flow toward the coagulated yarn 3 occurs in the region below the spinneret 1, and the speed of this liquid flow is maximum near the liquid level 9 of the coagulation bath liquid. In particular, since it is necessary to pull out the coagulated yarn 3 toward the outside of the liquid level 9 of the coagulation bath liquid downstream of the direction change guide 9, the speed of the liquid flow flowing into the region below the spinneret 1 becomes very large due to the accompanying flow generated in the take-up direction Db of the coagulated yarn 3. As a result, this liquid flow collides with the coagulated thread 3 between the liquid surface 9 of the coagulating bath and the direction changing guide 4, and the collision energy becomes larger in proportion to the faster flow rate in the vicinity of the liquid surface 9 of the coagulating bath. As a result, the threads in the coagulated thread 3 are pulled from the periphery to the center, causing contact between the threads and local vortexes, resulting in a significant decrease in spinnability, grade, and quality.

[0032] In contrast, the method for producing an acrylonitrile-based fiber bundle of the present invention is characterized in that, even when the measures (A. to C.) for achieving high productivity are taken, it has the effect of slowing down the speed of the liquid flow colliding with the coagulated yarn 3. Specific methods for achieving this include a method of reducing the accompanying flow that is the source of the liquid flow toward the coagulated yarn 3 and reducing the liquid flow itself, and a method of dividing the liquid flow toward the coagulated yarn 3 and forming a yarn-free region 23 that has low resistance to the liquid flow, thereby reducing the ratio of the liquid flow colliding with the coagulated yarn 3. The production method of the present invention can apply these two methods simultaneously.

[0033] A method for reducing the speed of the liquid flow colliding with the coagulated yarn 3 will be described. In the production method of the present invention, as shown in Fig. 1, the running region of the coagulated yarn 3 from the liquid level 9 of the coagulating bath liquid to the direction changing guide 4 has two or more yarn-present regions 24 in which the coagulated yarn 3 is continuously present in the running direction Da of the coagulated yarn 3, and at least one yarn-free region 23 in which the coagulated yarn 3 is not continuously present in the running direction Da of the coagulated yarn 3. The yarn-free region 23 is present between the two yarn-present regions 24. The width of the yarn-free region 23 in the axial direction of the direction changing guide 4 at the liquid level 9 of the coagulating bath liquid is set to be four or more times, preferably eight or more times, the shortest distance between the discharge holes in the spinneret 1.

[0034] As a result, by dividing the coagulated yarns 3 from the liquid level 9 of the coagulating bath liquid to the direction changing guide 4 into multiple yarn groups (two in Fig. 1), the direction in which the accompanying flow is generated is dispersed and the scale of the accompanying flow itself can be reduced compared to a conventional single yarn group. Regarding the width of the yarn-free region 23 in the axial direction of the direction changing guide 4 at the liquid level 9 of the coagulating bath liquid, if there are multiple yarn-free regions, the effects of the present invention can be obtained if at least one of them satisfies the relationship with the shortest distance between the discharge holes in the spinneret 1, but it is preferable that all of the multiple yarn-free regions satisfy the relationship with the shortest distance between the discharge holes in the spinneret 1, because the effects of the present invention become more pronounced.

[0035] 4, the liquid surface 9 of the coagulation bath liquid has two regions, a yarn-present region 24 where coagulated yarns 3 exist, and a yarn-free region 23 where no coagulated yarns 3 exist, which creates a difference in liquid flow resistance between the yarn-present region 24 and the yarn-free region 23. As a result, the liquid flows more easily in the yarn-free region 23 than in the yarn-present region 24, and the liquid flow is divided, allowing the speed of the liquid flow to the coagulated yarns 3 to be reduced.

[0036] Therefore, in order to obtain the above-mentioned effect, it is important to provide a yarn-free region 23 at the position where the accompanying flow starts to occur and at the position where the liquid flow colliding with the coagulated yarn 3 is at its maximum, that is, to provide a yarn-free region 23 between yarn-existing regions 24 at the liquid level 9 of the coagulation bath. At that time, since the liquid flow caused by the accompanying flow generated in the take-up direction Db flows into the region below the spinneret 1 from a direction perpendicular to the axial direction of the direction-changing guide 4, it is necessary for the direction-changing guide 4 to have a width of at least a certain interval in the axial direction (at least four times the distance between the shortest discharge holes of the spinneret 1).

[0037] On the other hand, in the embodiment shown in FIG. 7, which is outside the scope of the present invention, a plurality of direction change guides 4 (in the take-up direction Db in FIG. 7) are arranged, and the coagulated yarn 3 is split for each direction change guide 4, thereby forming a yarn non-existence region 23. However, as described above, the liquid flow flows into the lower region of the spinneret 1 from a direction perpendicular to the axial direction of the direction change guide 4 (from right to left in FIG. 7), and therefore there is no yarn non-existence region 23 on the side where the liquid flow collides, and therefore the liquid flow deceleration effect is not obtained. In particular, in a form of a coagulation bath in which the accompanying flow generated in the take-up direction Db is the main component, the liquid flow deceleration effect is significantly reduced. In addition, the workload of threading the coagulated yarn 3 through each of the direction change guides 4 is extremely large, and operability is reduced.

[0038] Furthermore, the width of the yarn-free region 23 of the coagulated yarn 3 in the direction of the direction changing guide 4 is preferably at least four times the shortest distance between the discharge holes of the spinneret 1 continuously between the liquid level 9 of the coagulating bath liquid and the direction changing guide 4. This enhances the dispersion effect in the direction in which the accompanying flow is generated, and more significantly reduces the liquid flow that impinges on the coagulated yarn 3. Furthermore, when there are multiple yarn-free regions 23 and yarn-present regions 24, the axial width of the direction changing guide 4 may be constant or variable.

[0039] Furthermore, it is preferable that the maximum width of the coagulated yarn 3 in the axial direction of the direction diverting guide 4 at the direction diverting guide 4 is 1.2S or less, relative to the maximum width S in the axial direction of the direction diverting guide 4 for the coagulated yarn 3 at the liquid level 9 of the coagulating bath liquid (the width of the yarn presence region 23 that is outermost in the direction of the direction diverting guide 4). By setting it in this range, the direction of generation of the accompanying flow is dispersed, and the width of the discharge hole of the spinneret 1 can be narrowed, making it possible to reduce equipment costs.

[0040] As described above, in a system in which multiple coagulating baths are installed in parallel, shortening the width H of the coagulating bath reduces the cost of equipment and the amount of the coagulating bath liquid itself, which leads to a reduction in the recovery load. In order to shorten the width H of the coagulating bath, it is effective to shorten the maximum width S of the coagulated thread 3 at the liquid surface 9 of the coagulating bath liquid and to bring the ratio S / H closer to 1, but it is preferable to keep the ratio in the range of 0.5≦S / H≦0.95. Here, when the ratio S / H is brought closer to 1, the flow velocity of the liquid flow accompanying the accompanying flow increases, but the effect of decelerating the liquid flow by using the manufacturing method of the present invention becomes more significant.

[0041] Furthermore, since the production method of the present invention aims to reduce the liquid flow colliding with the coagulated yarn 3, as shown in Figures 8, 9, and 10, it is preferable that the average flow speed of the coagulating bath liquid toward the coagulated yarn is 14 mm / sec or less at a position 40 mm deep from the liquid surface of the coagulating bath liquid and 20 mm away in the take-up direction Db of the coagulated yarn, parallel to the liquid surface of the coagulating bath liquid, from the position closest to the position where the coagulated yarn is pulled out of the coagulating bath in the running area of ​​the coagulated yarn.

[0042] Next, another embodiment of the present invention will be described in detail. The number of non-yarn regions 23 of the coagulated yarn 3 may be one as shown in FIG. 1, or may be two or more as shown in FIG. 11 (second embodiment of the present invention). By increasing the number of non-yarn regions of the coagulated yarn 3, the effect of decelerating the liquid flow colliding with the coagulated yarn 3 can be obtained. On the other hand, if the number of non-yarn regions 23 increases, the width of the coagulation bath 2 increases, which increases the equipment cost, and the landing angle of the coagulated yarn 3 on the liquid surface 9 of the coagulation bath liquid may become steep, which may cause a decrease in spinnability, so there is a limit to the number of non-yarn regions 23. Therefore, it is preferable that the number of non-yarn regions is four or less.

[0043] In the manufacturing method of the present invention, one method for forming the coagulated yarn 3 into yarn-free regions 23 is to use a fiber splitting guide 13 between the liquid surface 9 of the coagulation bath liquid and the direction changing guide 4, as shown in Fig. 12 (third embodiment of the present invention). Alternatively, protrusions or grooves may be formed in the direction changing guide 4 to split the coagulated yarn 3, or it may be combined with a fiber splitting guide, and the method is not particularly limited.

[0044] As shown in Fig. 13 (fourth embodiment of the present invention), in the manufacturing method of the present invention, the width of the yarn-free region 23 between the liquid level 9 of the coagulation bath liquid and the direction change guide 4 in the direction of the direction change guide 4 may be variable. It may gradually decrease or increase. As shown in Fig. 14 (fifth embodiment of the present invention) and Fig. 15 (sixth embodiment of the present invention), the width of the yarn-free region 23 may be constant. As shown in Fig. 16 (seventh embodiment of the present invention), each yarn-free region 24 may be formed by coagulated yarns discharged from different spinnerets corresponding to each region.

[0045] Next, each member common to the dry / wet spinning apparatus used in the production method of the present invention and the shape of each member will be described in detail.

[0046] The die 1 used in the manufacturing method of the present invention has a rectangular cross section in the best mode, but is not limited thereto, and may have a circular, elliptical, or polygonal cross section. The ejection holes arranged in the die 1 are best arranged in a rectangular region, but are not limited thereto. The number of ejection holes is preferably in the range of 1,000 to 60,000, and more preferably in the range of 6,000 to 24,000, and within this range, the effects of the present invention can be maximized. The arrangement density of the ejection holes arranged on the ejection surface of the die 1 is preferably 1 mm 2 or less per 1 mm 2 of the die 1. 2 Number of holes per unit: 0.06 / mm 2 More than 0.25 pieces / mm is preferable. 2 The above is more preferable.

[0047] In addition, it is preferable to use a single spinneret 1 in the production method of the present invention in order to reduce equipment costs, but two or more spinnerets 1 may be arranged in the width direction of the coagulation bath to discharge coagulated yarn 3.

[0048] Furthermore, as the take-up speed of the coagulated yarn 3 increases, the accompanying flow in the coagulating bath increases, and the speed of the liquid flow toward the coagulated yarn 3 traveling between the spinneret 1 and the direction-changing guide 4 near the liquid surface 9 of the coagulating bath also increases. In the production method of the present invention, the take-up speed at which the coagulated yarn is taken out of the coagulating bath is preferably 50 m / min or less. On the other hand, in order to prevent a decrease in production efficiency, the speed at which the coagulated yarn 3 is taken out of the coagulating bath is preferably 25 m / min or more.

[0049] In the coagulation bath 2 used in the manufacturing method of the present invention, a supply port 10 is preferably provided on the bottom surface 6 of the coagulation bath, and the supply port 10 is preferably connected to a liquid circulation pump (not shown) so that the coagulation solution is supplied from the liquid circulation pump. In this case, the coagulation solution in the coagulation bath 2 is preferably allowed to flow out from the upper edges of the front surface 7 and the rear surface 8 of the coagulation bath.

[0050] In addition, the direction changing guide 4 used in the production method of the present invention is preferably configured in one stage to turn back the coagulated yarn 3, but is not limited to this, and may be configured in two or more stages if the turn back is at a steep angle.

[0051] The spinning dope used in the production method of the present invention may be one in which an acrylonitrile polymer is dissolved in a solvent, but is not particularly limited thereto. Examples of monomers that can be copolymerized with acrylonitrile (AN) include acrylic acid, methacrylic acid, itaconic acid, and their alkali metal salts, ammonium salts, and lower alkyl esters, acrylamide and its derivatives, allylsulfonic acid, methallylsulfonic acid, and their salts or alkyl esters.

[0052] In addition, examples of the solvent that can be used in the spinning dope used in the production method of the present invention include an aqueous zinc chloride solution, dimethylacetamide, dimethylsulfoxide (hereinafter abbreviated as DMSO), and dimethylformamide.

[0053] In addition, it is preferable to perform drawing in a bath after spinning by the manufacturing method of the present invention and drawing the coagulated yarn 3 into the air. The spun coagulated yarn 3 is preferably washed with water after drawing in a bath, or drawn in a bath after washing with water to remove the remaining solvent. After drawing in a bath, an oil is usually applied and dried and densified with a hot roller or the like. If necessary, a secondary drawing such as steam drawing is performed after that. In the present invention, a plurality of acrylonitrile-based fiber bundles obtained through these steps are combined by a group of free roller guides for bundling before being wound up or stored in a can, and are wound up into a package by a winder or stored in a can. In another embodiment, a plurality of wound acrylonitrile-based fiber bundles can be unwound or drawn out from the can and combined by a group of free roller guides for bundling. The number of single yarns constituting such an acrylonitrile-based fiber bundle is preferably 1,000 or more, more preferably 2,000 or more. There is no particular upper limit on the number of single yarns, but it is usually 100,000 or less.

[0054] Next, a method for producing a carbon fiber bundle from the acrylonitrile fiber bundle obtained by the production method of the present invention will be described.

[0055] The acrylonitrile fiber bundle produced by the above-mentioned method for producing an acrylonitrile fiber bundle is subjected to a flame-resistant treatment in an oxidizing atmosphere such as air at 200 to 300 ° C. The treatment temperature is preferably raised from a low temperature to a high temperature in multiple stages in order to obtain a flame-resistant fiber bundle, and further, it is preferable to draw the fiber bundle at a high draw ratio within a range in which fluff does not occur in order to fully express the performance of the carbon fiber bundle. Next, the obtained flame-resistant fiber bundle is heated to 1,000 ° C or more in an inert atmosphere such as nitrogen to produce a carbon fiber bundle. Thereafter, anodization is performed in an electrolyte aqueous solution to impart functional groups to the carbon fiber surface, thereby making it possible to enhance adhesion with the resin. In addition, it is preferable to impart a sizing agent such as an epoxy resin to obtain a carbon fiber bundle with excellent abrasion resistance. EXAMPLES

[0056] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these.

[0057] (1) Average flow velocity of the coagulation bath liquid near the liquid surface In the state where microbubbles were generated in the coagulation bath using a microbubble generator (BT-50-5 manufactured by Nishiyama Pump Co., Ltd.), the flow velocity of the coagulation bath liquid was measured (sampling cycle 25 Hz, measurement time 30 seconds) using an ultrasonic Doppler flow meter (10-MHZ ADV manufactured by SonTek Co., Ltd.). The measurement points for the flow velocity of the coagulation bath liquid were set at three points on the side of the front surface 8 of the coagulation bath with respect to the center of the nozzle 1, as shown in Figures 8, 9, and 10. The vertical positions of the measurement points were 40 mm in the depth direction from the liquid surface 9 of the coagulation bath liquid, and the widthwise positions of the measurement points were 160 mm away on both sides of the center of the nozzle 1 in the width direction of the coagulation bath, and at the center position. Measurement was performed at the three points set in this way. At each measurement position, the time average value (absolute value) of the measured value ((sampling cycle 25 pieces / second) x continuous measurement time 30 seconds = 750 pieces) was calculated.

[0058] (2) Number of vortexes A water tank made of a transparent acrylic plate was installed on the front side of the coagulation bath 8, and the liquid surface position of the coagulation bath liquid was photographed using a video camera. The liquid surface position of the coagulation bath liquid was photographed for one minute, and the obtained video was cut into 60 frames per second, the number of local vortices generated in each image was counted, and the average number of vortices counted per frame was calculated.

[0059] (3) Quality of acrylonitrile fiber bundle The number of fuzz on a 1,000 m acrylonitrile fiber bundle was counted just before it was wound up, and the quality was evaluated. The evaluation criteria were as follows: A: (Number of fluffs / 1 fiber bundle 1,000m)≦1 B:1<(number of fluffs / 1 fiber bundle·1,000m)≦5 C:5<(number of fluffs / 1 fiber bundle·1,000m)<60 D: (Number of fibers / 1 fiber bundle·1,000 m)≧60.

[0060] (4) Yarn division The yarn is divided in the axial direction of the direction-changing guide or from the rear surface of the coagulating bath to the front surface (hereinafter sometimes referred to as the front-rear direction). The division width associated with yarn division is measured at three locations as shown in Figure 17, and the division at the height of the coagulating bath liquid level, the height at the center between the liquid level of the coagulating bath liquid and the direction-changing guide, and the height of the direction-changing guide are referred to as upper division 20, central division 21, and lower division 22, respectively. The division width changes monotonically decreasing or increasing between each position. When the yarn is divided in the axial direction of the direction-changing guide, the division width is the width of the yarn-free region.

[0061] [Example 1] As shown in Fig. 13, a dry-wet spinning apparatus was used in which the number of divisions of the yarn was 2 in the axial direction of the direction-changing guide, the division widths of the upper division were 10 mm, the center division was 5 mm, and the lower division was 5 mm, and the shortest distance between the discharge holes in the spinneret was 2 mm. The spinning dope was once pushed out of the spinneret into the air, and then entered downward into the DMSO aqueous solution coagulation bath, turned back at an angle of 65° by the direction-changing guide 4, and drawn out of the coagulation bath at 34 m / min, and then carried to the water-washing process. Then, an oil agent mainly composed of amino silicone was applied while drawing in the bath drawing process, and further passed through the drying and post-drawing processes to obtain an acrylonitrile fiber bundle. The average flow velocity V of the coagulation bath near the liquid surface of the coagulation bath was 8 mm / sec, vortices were generated at 0.3 pieces / sec, and the quality of the obtained acrylonitrile fiber bundle was good.

[0062] [Example 2] Example 2 will be described as a pattern in which the division widths of the yarn at the center and lower parts of Example 1 are increased. An acrylonitrile-based fiber bundle was obtained using the same device and conditions as in Example 1, except that the division width of the yarn at the center part was 10 mm and the division width at the lower part was 10 mm, as shown in Fig. 14. The average flow velocity V of the coagulating bath liquid near the liquid surface of the coagulating bath liquid was 4 mm / sec, vortexes were generated at 0.1 pieces / sec, and the quality of the obtained acrylonitrile-based fiber bundle was even better than that of Example 1.

[0063] [Example 3] Example 3 will be described as a pattern in which the number of divisions of the yarn in Example 2 is increased. As shown in Fig. 15, the number of divisions of the yarn was set to 4 in the axial direction of the direction-changing guide, and the division width of the upper division of each yarn was set to 10 mm, the division width of the central division was set to 10 mm, and the division width of the lower division was set to 10 mm. An acrylonitrile-based fiber bundle was obtained using the same device and conditions as in Example 2. The average flow velocity V of the coagulating bath liquid near the liquid surface of the coagulating bath liquid was 3 mm / sec, vortices were generated at 0.1 pieces / sec, and the quality of the obtained acrylonitrile-based fiber bundle was better than that of Example 1, similar to Example 2.

[0064] [Example 4] Example 4 will be described as a pattern using two spinnerets in Example 1. An acrylonitrile-based fiber bundle was obtained using the same device and conditions as in Example 1, except that the number of spinnerets was two as shown in Fig. 16. The average flow velocity V of the coagulating bath liquid near the liquid surface of the coagulating bath liquid was 8 mm / sec, vortexes were generated at a rate of 0.3 pieces / sec, and the quality of the obtained acrylonitrile-based fiber bundle was good.

[0065] [Comparative Example 1] Comparative Example 1 will be described as a pattern in which the thread was not divided. Except for not dividing the thread, an acrylonitrile-based fiber bundle was obtained using the same device and conditions as in Example 1. The average flow velocity V of the coagulating bath near the liquid surface of the coagulating bath was 30 mm / sec, vortexes were generated at a rate of 1.8 pieces / sec, and the quality of the obtained acrylonitrile-based fiber bundle was poor.

[0066] [Comparative Example 2] Comparative Example 2 will be described as a pattern in which the yarn is not divided at the upper division position. An acrylonitrile-based fiber bundle was obtained using the same device and conditions as in Example 1, except that the yarn was not divided at the upper division position as shown in Fig. 18. The average flow velocity V of the coagulating bath liquid near the liquid surface of the coagulating bath liquid was 25 mm / sec, vortexes were generated at 1.6 pieces / sec, and the quality of the obtained acrylonitrile-based fiber bundle was poor.

[0067] [Comparative Example 3] Comparative Example 3 will be described as a pattern in which the yarn is divided in the front-rear direction. As shown in Fig. 7, the yarn was not divided in the axial direction of the direction-changing guide, but was divided into two in the front-rear direction, and an acrylonitrile-based fiber bundle was obtained using the same device and conditions as in Example 1. The average flow velocity V of the coagulating bath liquid near the liquid surface of the coagulating bath liquid was 29 mm / sec, vortices were generated at a rate of 1.8 vortices / sec, and the quality of the obtained acrylonitrile-based fiber bundle was poor.

[0068] [Comparative Example 4] Comparative Example 4 will be described as a pattern in which the division width of the yarn does not satisfy the division width specified in the present invention. An acrylonitrile-based fiber bundle was obtained using the same device and conditions as in Example 1, except that the division width of the upper division of the yarn was 5 mm, the division width of the central division was 5 mm, and the division width of the lower division was 5 mm. The average flow velocity V of the coagulation bath near the liquid surface of the coagulation bath was 22 mm / sec, vortexes were generated at 1.2 pieces / sec, and the quality of the obtained acrylonitrile-based fiber bundle was poor.

[0069] [Comparative Example 5] Comparative Example 5 will be described as a pattern in which the center of the yarn is not divided and the yarn non-existing region is discontinuous. As shown in Fig. 19, an acrylonitrile fiber bundle was obtained using the same device and conditions as in Example 2, except that the center of the yarn is not divided and the yarn non-existing region is discontinuous. The average flow velocity V of the coagulating bath liquid near the liquid surface of the coagulating bath liquid was 20 mm / sec, vortexes were generated at 1.0 vortex / sec, and the quality of the obtained acrylonitrile fiber bundle was poor.

[0070] [Table 1] [Explanation of symbols]

[0071] 1 Base 2 Coagulation bath 3 Coagulated thread 4. Turning Guide 5 Collection Guide 6 Bottom of coagulation bath 7 Front of coagulation bath 8 Rear side of coagulation bath 9. Coagulation bath liquid level 10 Supply inlet 11 Circulation pump 12 Coagulation bath liquid 13 Fiber separation guide 20 Upper division 21 Center division 22 Lower division 23 Thread-free area 24 Thread presence region 25 Single yarn in solidified yarn 26 An imaginary circle with the shortest distance between the nozzle holes in the nozzle as its diameter 26' An imaginary circle with the diameter of the shortest distance between the nozzles in the die, the inside of which overlaps with the cross section of a single yarn in the solidified yarn S: Maximum width of the coagulated thread at the surface of the coagulation bath T Maximum width of solidified thread at turning guide H Width of coagulation bath M Flow velocity measurement point W: Width of yarn-free region Da Travel direction Db Take-off direction Dc Flow direction

Claims

1. A method for producing an acrylonitrile-based fiber bundle, comprising extruding a spinning dope into the air from a plurality of discharge holes of a spinneret, causing the dope to enter downward into a coagulating bath liquid stored in a coagulating bath to form a coagulated yarn, folding back the coagulated yarn at a direction-changing guide disposed in the coagulating bath liquid below the spinneret, and then drawing the yarn out of the coagulating bath liquid, the method satisfying the following 1) to 3). 1) The direction-changing guide has an axial direction perpendicular to both the running direction of the coagulated yarn from the liquid surface of the coagulating bath toward the direction-changing guide and the take-up direction in which the coagulated yarn is drawn out of the coagulating bath from the direction-changing guide. 2) The running region of the coagulated yarn from the liquid surface of the coagulation bath liquid to the direction changing guide has two or more yarn-present regions in which coagulated yarns are continuously present in the running direction of the coagulated yarn, and at least one yarn-non-present region in which coagulated yarns are not continuously present in the running direction of the coagulated yarn, and the yarn-non-present region is located between the two yarn-present regions. 3) In at least one of the yarn-free regions, the axial width of the direction-changing guide at the liquid level of the coagulation bath liquid is four times or more the shortest distance between the discharge holes in the spinneret.

2. 2. The method for producing an acrylonitrile fiber bundle according to claim 1, wherein the axial width of the direction-changing guide at the liquid level of the coagulating bath liquid in all yarn-free regions is at least four times the distance between the shortest discharge holes in the spinneret.

3. 1mm at the base ２ Number of nozzles per mm: 0.06 ２ The method for producing an acrylonitrile fiber bundle according to claim 1 or 2.

4. 4. The method for producing an acrylonitrile fiber bundle according to any one of claims 1 to 3, wherein the average flow velocity of the coagulating bath liquid toward the coagulated yarn is 14 mm / sec or less at a position that is 40 mm deep from the liquid surface of the coagulating bath liquid and that is 20 mm away in a take-up direction of the coagulated yarn parallel to the liquid surface of the coagulating bath liquid from a position that is closest to a position where the coagulated yarn is pulled out of the coagulating bath liquid in the running region of the coagulated yarn.

5. The method for producing an acrylonitrile fiber bundle according to any one of claims 1 to 4, wherein the spinning dope is extruded from a single spinneret.

6. The method for producing an acrylonitrile fiber bundle according to any one of claims 1 to 5, wherein the number of discharge holes in the spinneret is 1,000 to 60,000.

7. The method for producing an acrylonitrile fiber bundle according to any one of claims 1 to 6, wherein the take-up speed for drawing out the coagulated yarn from the coagulation bath is 25 to 50 m / min.

8. A method for producing an acrylonitrile-based fiber bundle, in which a spinning dope is extruded into the air from a plurality of discharge holes in a spinneret, and then the dope is caused to enter downward into a coagulating bath liquid stored in a coagulating bath to form a coagulated thread, and the coagulated thread is turned back by a direction-changing guide disposed in the coagulating bath liquid below the spinneret, and then drawn out of the coagulating bath liquid, wherein an acrylonitrile-based fiber bundle is produced by a method for producing an acrylonitrile-based fiber bundle that satisfies the following 1) to 3): The acrylonitrile fiber bundle is then flame-resistant treated in an oxidizing atmosphere at 200 to 300°C, and then heated in an inert atmosphere at 1,000°C or higher. 1) The direction-changing guide has an axial direction perpendicular to both the running direction of the coagulated yarn from the liquid surface of the coagulating bath toward the direction-changing guide and the take-up direction in which the coagulated yarn is drawn out of the coagulating bath from the direction-changing guide. 2) The running region of the coagulated yarn from the liquid surface of the coagulation bath liquid to the direction changing guide has two or more yarn-present regions in which coagulated yarns are continuously present in the running direction of the coagulated yarn, and at least one yarn-non-present region in which coagulated yarns are not continuously present in the running direction of the coagulated yarn, and the yarn-non-present region is located between the two yarn-present regions. 3) In at least one of the yarn-free regions, the axial width of the direction-changing guide at the liquid level of the coagulation bath liquid is four times or more the shortest distance between the discharge holes in the spinneret.

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