JPH10266024A - Production of carbon fiber and production apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carbon fiber without causing yarn breakage due to unevenness of yarn thickness, ignition, etc., by subjecting a polyacrylonitrile-based precursor fiber bundle having thick fineness to flameproof treatment under specific conditions by passing the fiber bundle through a flameproof furnace in zigzags. SOLUTION: The cross section form of a polyacrylonitrile-based precursor fiber bundle having >=30,000 total denier is kept in a rectangle having 10-50 average flatness ratio defined by a ratio of yarn width to yarn thickness. Apparent average fineness per mm width of fiber bundle is preferably kept to 3,000 to 10,000 denier and the fiber bundle is passed through a flameproof furnace in zigzags and subjected to flameproof treatment at 200-300 deg.C. Then, the treated fiber bundle is subjected to carbonization treatment at 500-1,500 deg.C to provide the objective carbon fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing carbon fibers, and more particularly, to a method and an apparatus for subjecting a large amount of multifilament polyacrylonitrile-based precursor fibers to oxidizing treatment.

[0002]

2. Description of the Related Art As shown in FIG. 1, a method of oxidizing an acrylic precursor fiber is to arrange a guide roll 2 on both sides of an oxidization furnace 1 and to oxidize a precursor fiber bundle 3 in a zigzag manner. The method of passing through a furnace is common.

[0003] In such a flame-proofing step, as a method for preventing entanglement of treated yarns, getting over a guide roll, and unevenness of treatment, for example, Japanese Patent Publication No. 59-28662 discloses a grooved roll having a defined groove shape. A method has been proposed in which a plurality of fibers are used to separate and separate the yarns while guiding the precursor fiber bundles into the grooves of the roll while keeping the cross-sectional shape of the yarns circular.

However, such a method has a problem that when the number of treated yarns increases, the maximum thickness of the yarn increases when the cross-sectional shape is circular, and the yarn tends to break due to heat storage.

[0005] For this reason, there is a problem that the production has to be carried out at a lower temperature of the oxidizing treatment, and it takes a long time to obtain oxidized fibers having sufficiently advanced oxidizing treatment. Also,
Since the oxygen required for the oxidation reaction is difficult to diffuse into the interior of the yarn, the obtained oxidation-resistant fiber has a different degree of oxidation resistance between the interior of the yarn and the surface of the yarn. There was a problem that caused.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the problems in the prior art when a multifilament polyacrylonitrile-based precursor fiber is subjected to a flame-resistant treatment, and to provide a uniform flame-resistant flame retardation. It is an object of the present invention to obtain fibers and to obtain high-quality, high-quality carbon fibers that do not cause fluff, yarn damage, and the like even in the subsequent carbonization step.

[0007]

Means for Solving the Problems To solve the above-mentioned problems, the method for producing carbon fibers of the present invention uses a total denier number of 3
In the method for producing carbon fibers, a polyacrylonitrile-based precursor fiber bundle of not less than 000 is zigzag-passed through an oxidizing furnace at 200 to 300 ° C., and then subjected to oxidizing treatment at 500 to 1500 ° C. The method is characterized in that the cross-sectional shape of the precursor fiber bundle in the flame-proofing treatment is maintained in a substantially rectangular shape having an average flatness defined by a yarn width / yarn thickness ratio in a range of 10 to 50.

[0008] In the flame-proofing treatment, it is preferable that the apparent average fineness per 1 mm width of the precursor fiber bundle having a substantially rectangular cross-sectional shape is maintained at 3,000 to 10,000 denier.

The average flatness and apparent average fineness can be controlled by grooved rolls arranged on both sides of the oxidizing furnace.

Further, in the above-mentioned oxidation treatment, the tension of the precursor fiber bundle in the oxidation treatment furnace is set to 3.8 × 10 ^−2.
It is preferable to control the amount in the range of 〜1.9 × 10 ⁻¹ g / denier.

[0011] The method for producing carbon fibers according to the present invention is characterized in that in the apparatus for producing carbon fibers having an oxidizing furnace for oxidizing a polyacrylonitrile-based precursor fiber bundle having a total denier of 30,000 or more, On both sides of the furnace, rolls having grooves for guiding the precursor fiber bundles are arranged so as to form a yarn path for passing the precursor fiber bundles in a zigzag manner through the oxidizing furnace, and the shape of the grooved roll is as follows ( 1), (2),
It is characterized by satisfying the expression (3). 0.7 ≦ b / a <1 (1) 0.2 × a ≦ h ≦ 0.4 × a (2) 0.2 × (ab) ≦ R ≦ 0.4 × (ab) ( 3)

In the above formula, symbol a indicates the width of the groove top, b indicates the width of the groove bottom, h indicates the depth of the groove, and R indicates at least the radius of the roundness of the groove bottom corner.

[0013] In such a method and apparatus for producing carbon fiber, the cross-sectional shape of the precursor fiber bundle to be oxidized by a grooved roll having a specific cross-sectional shape is substantially rectangular and has an average oblateness of 10 to 50. Because it can be flat in the range, it is possible to perform flame resistance uniformly and quickly, and even when processing a large amount, high quality that does not generate fluff or yarn damage in the subsequent carbonization process, A high-grade flame-resistant fiber can be obtained, and the carbon fiber obtained therefrom also has high quality and high quality.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the cross-sectional shape of a precursor fiber bundle to be subjected to oxidization treatment is maintained in a substantially rectangular shape, and the average flatness is controlled in the range of 10 to 50.

Here, the substantially rectangular shape refers to a shape surrounded by two sets of substantially parallel straight lines, and the corner may include a curve, that is, R. The average flatness of the substantially rectangular yarn cross section was defined as follows.

The driving of the running yarn is stopped, and five points are measured in the width direction of the yarn using a generally known photoelectric transmittance measuring device, and the measured values are averaged to obtain a yarn thickness A. Was measured at 1-cm intervals in the longitudinal direction using calipers and averaged to obtain a yarn width B, and a value obtained by dividing B by A was defined as an average oblateness.

When the average flatness is less than 10, the yarn thickness increases, and the runaway reaction due to the accumulation of reaction heat in the flame-proofing step easily causes yarn breakage and ignition. If the oxidization temperature is lowered in order to control this, the oxidization time is greatly lengthened and the productivity is reduced.

On the other hand, when the average flatness exceeds 50, the yarn width increases, the number of treated yarns with respect to the width of the oxidizing furnace decreases, and the equipment productivity decreases. Therefore, the average oblateness is 10
The range is preferably 50, and more preferably 15 to 35.

The apparent average fineness per 1 mm of the width of the substantially rectangular precursor fiber bundle maintained at an average oblateness of 10 to 50 is an apparent average fineness that varies according to the total fineness of the yarn to be treated. If it is less than 2,000 denier, the amount of treated yarn is reduced, and the equipment productivity is reduced.

Further, if the apparent average fineness exceeds 10,000 denier, the thickness may increase and runaway due to the oxidization resistance reaction may occur. The production will decrease.

Therefore, it is preferable that the apparent average fineness of the treated yarn in the flame resistance is in the range of 3,000 to 10,000 denier. More preferably 4,000-
It is in the range of 8,000 denier.

In order to achieve the above-mentioned average flatness and apparent average fineness, the precursor fiber bundles are arranged on both sides of the oxidizing furnace, and zigzag the precursor fiber bundle into and out of the oxidizing furnace, for example, reciprocate a plurality of times in the horizontal direction. The guide roll for passing through the zigzag may be a grooved roll having the following shape.

As the guide roll for transporting the yarn into the oxidizing furnace, a flat roll can be considered in addition to the grooved roll. However, if a flat roll is used, it is difficult to regulate the width and thickness of the yarn within a certain range. It is. Further, adjacent yarns may be entangled on the roll, causing fluffing and winding on the roll. In order to prevent these, it is preferable to use a grooved roll as the yarn guide roll for conveying the flame-resistant furnace, but by using a grooved roll having a specific shape as described below, it is possible to specify the aforementioned flame-resistant yarn. Is controlled to the cross-sectional shape.

The shape of the grooved roll is as follows (1):
It is characterized by satisfying the expressions (2) and (3). 0.7 ≦ b / a <1 (1) 0.2 × a ≦ h ≦ 0.4 × a (2) 0.2 × (ab) ≦ R ≦ 0.4 × (ab) ( 3) where a is the width of the groove top, b is the width of the groove bottom,
h indicates the depth of the groove, and R indicates the radius of at least the corner of the groove bottom. Of these, R can also be applied to the top of the wall between the grooves. Each dimension of the groove 4 is shown in FIG. The arrangement of the grooved rolls with respect to the flameproofing furnace is, for example, the same as that shown in FIG. That is, the zigzag precursor fiber bundles 3 in the horizontal direction are provided on both sides of the oxidation furnace 1.
A plurality of grooved rolls 2 that form the yarn path are provided.

In order to keep the cross-sectional shape of the precursor fiber bundle yarn in a flat and substantially rectangular sheet, it is necessary to provide a width at the bottom of the groove, and the ratio b / a of the width a of the groove top and the width b of the groove bottom is required. Is less than 0.7, the groove shape is close to a V-shape and cannot be maintained in a substantially rectangular sheet shape. On the other hand, when b / a exceeds 1, the groove shape becomes a C-shape, and machining of the groove becomes difficult.

In the equation (2) for defining the depth of the grooved roll, the groove depth h may not be dependent on the equation (2), but the groove depth is not more than 0,0 of the width a of the groove top. If it is less than twice, a part of the running yarn may get over the groove, and the adjacent yarn may get entangled and fluff. Also, the groove depth h
Is greater than 0.4 times the width a of the upper part of the groove, the ratio of the cross-sectional area of the substantially rectangular sheet-shaped yarn to the groove cross-sectional area becomes large,
Processing cost increases and is not economical. Therefore, the groove depth h
Is preferably in the range of 0.2 to 0.4 times the width a of the groove top.

Further, the radius R of the roundness of the groove corner is not particularly limited, but if it is not round, a single thread break may occur at the groove protrusion (the top of the wall between grooves), or the groove recess (groove bottom corner). At the corners of the yarn section), uneven thickness tends to occur at the yarn end. When the groove recesses are rounded, the single yarns are appropriately rearranged, and the thickness unevenness at the yarn end is reduced. When the width of the groove convex portion is increased so as to increase the roundness more than necessary, the roll width is increased, and the width of the flameproofing machine is increased. Therefore, the radius R of the roundness of the groove corner is
0.2 × (a−
b) The range of ≦ R ≦ 0.4 × (ab) is preferable.

The tension applied to the yarn conveyed into the oxidation furnace may be out of the range of 3.8 × 10 ^{-2 to} 1.9 × 10 ^-1 g / denier. If the density is less than 8 × 10 ^-2 g / denier, the yarn is suspended and rubs and fluffs are generated at the bottom of the oxidizing furnace, which lowers the quality and tensile strength of the carbon fiber obtained in the subsequent carbonization step. If the tension is higher than 1.9 × 10 ⁻¹ g / denier, fluffing due to breakage of a single yarn in the flame-proofing step increases, which may cause winding on the roll. In order to obtain the desired oxidized fiber in the stable oxidization process, the tension applied to the yarn should be 3.8 × 10 ^{-2 to} 1.9 per filament of the precursor fiber.
X 10 ^-1 g is preferred, and more preferably 5.
The density is preferably 3 × 10 ^{-2 to} 1.4 × 10 ^-1 g / denier.

[0029]

The present invention will be described below in detail with reference to examples. Example 1 Single yarn denier 1.5d, number of filaments 70,000,
A polyacrylonitrile-based fiber bundle having a total denier of 105,000 was prepared using a grooved roll having a shape of a = 25 mm and b = 20.
mm, h = 5 mm, average flatness 23, yarn width 1 mm
The apparent average fineness of the yarn was regulated to 4,200 denier, and the tension applied to the yarn was set to 5.7 × 10 ^-2 g / denier. When the flameproofing treatment was continuously performed at 250 ° C. for 20 minutes for 20 minutes, the flameproofing was able to be stably performed without breakage of the thread or fluff due to a runaway reaction. The obtained oxidized fiber was subjected to a pre-carbonization treatment at a maximum temperature of 720 ° C. in an inert atmosphere and then to a carbonization treatment at a maximum temperature of 1350 ° C.
It was excellent at 0 kgf / mm ² and elastic modulus 24 t / mm ² .

Example 2 The same polyacrylonitrile fiber as in Example 1 was applied to the yarn with a tension of 1 using the same grooved roll as in Example 1.
When the density was 2 × 10 ^-2 g / denier, the average flatness was 4
0, apparent average fineness per 1 mm of yarn width is 4,20
It became 0 denier. In this state, when flame resistance was obtained in the same manner as in Example 1, the running yarn had many single yarn breaks, and the obtained flame resistant yarn was slightly fuzzed. Further, the tensile strength of the obtained carbon fiber slightly decreased to 280 to 300 kgf / mm ² .

Example 3 The same polyacrylonitrile fiber as in Example 1 was used with the same grooved roll as in Example 1 and the tension applied to the yarn was 4.3 × 10 ^-2 g / denier. Flatness 13; apparent average fineness per 1 mm of yarn width: 4,2
It became 00 denier. In this state, when flame resistance was obtained in the same manner as in Example 1, the yarn was suspended and rubbed and fluffed at the bottom of the flame-resistant furnace, and the quality of the flame-resistant yarn became slightly poor. The tensile strength of the carbon fiber obtained from this is 250-290 kgf
/ Mm ² . However, practically usable low-grade carbon fibers were obtained.

Comparative Example 1 In the same manner as in Example 1, a polyacrylonitrile fiber having a total denier of 105,000 was replaced with a grooved roll as shown in FIG.
When the tension was 5.7 × 10 ⁻² g / filament as in Example 1, the precursor fiber bundle 12 had an average flatness of 80 and an apparent average fineness of 2,600. It became denier. When oxidized at 216 ° C. in this state, a part of the yarn spread on the flat roll, the adjacent yarns became entangled, and wrapping occurred on the roll, and no oxidized fiber was obtained.

Comparative Example 2 Under the same conditions as in Example 1, the shape of the groove roll was changed as shown in FIG. 4 using a V-groove roll 21 a = 6.5 mm and b = 3 mm which did not satisfy the expression (1). As a result, the cross-sectional shape of the precursor fiber bundle yarn 22 was circular, and the apparent average fineness was 16,000 denier. In order to prevent breakage of the yarn due to heat storage of the yarn and ignition, the initial temperature of oxidization is set to 210.
When the flame resistance was obtained at ℃, it took a long time of 300 minutes to obtain a flame resistant yarn.

The above Examples 1, 2, 3 and Comparative Example 1,
The results of No. 2 are summarized in Tables 1 and 2.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

As described above, according to the method and apparatus for producing carbon fibers of the present invention, in particular, when a multifilament polyacrylonitrile-based precursor fiber bundle having a total denier number of 30,000 or more is flame-proofed, The yarn is kept in the shape of a flat, substantially rectangular sheet, and the average flatness is controlled to a specific range. Therefore, yarn breakage, suppression of fire in the flame-proofing process due to unevenness of the yarn thickness, and fluffing due to interference of adjacent yarns. Thus, it is possible to obtain a stable process without oxidization, obtain an oxidized fiber having an even progress in oxidization resistance, and improve the quality and quality of the carbon fiber obtained therefrom. In addition, equipment productivity can be increased by increasing the apparent average fineness of the precursor fiber. Further, since the multifilament precursor fiber bundle can be uniformly, smoothly and rapidly subjected to the flame-proofing treatment, efficient mass production becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an arrangement of an oxidation furnace and a grooved roll.

FIG. 2 is a sectional view of a groove portion of the grooved roll according to the present invention.

FIG. 3 is a partial sectional view of a flat roll used in Comparative Example 1.

FIG. 4 is a partial sectional view of a V-groove roll used in Comparative Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxidation furnace 2 Roll with groove 3 Precursor fiber bundle 4 Groove

Claims (6)

[Claims] 1. A bundle of polyacrylonitrile-based precursor fibers having a total denier of 30,000 or more is passed through an oxidizing furnace in a zigzag manner at 200 to 300 ° C., followed by oxidizing treatment.
In the method for producing carbon fibers to be carbonized at 00 to 1500 ° C., the cross-sectional shape of the precursor fiber bundle in the oxidization treatment is adjusted such that the average flatness defined by the yarn width / yarn thickness ratio is 10 to 10.
A method for producing carbon fibers, wherein the carbon fibers are maintained in a substantially rectangular shape within a range of 50. 2. The flameproofing treatment according to claim 1, wherein an apparent average fineness per 1 mm width of the precursor fiber bundle whose cross-sectional shape is kept substantially rectangular is kept at 3,000 to 10,000 denier. Method for producing carbon fiber. 3. The method for producing carbon fibers according to claim 1, wherein the average flattening rate is controlled by grooved rolls arranged on both sides of the oxidizing furnace. 4. The method for producing carbon fibers according to claim 2, wherein the apparent average fineness is controlled by grooved rolls arranged on both sides of the oxidizing furnace. 5. The method according to claim 1, wherein the tension of the precursor fiber bundle in the oxidizing furnace is controlled in a range of 3.8 × 10 ^{-2 to} 1.9 × 10 ^-1 g / denier. 3. The method for producing a carbon fiber according to item 1. 6. A carbon fiber manufacturing apparatus having an oxidizing furnace for oxidizing a polyacrylonitrile-based precursor fiber bundle having a total denier of 30,000 or more, wherein the precursor fiber bundle is provided on both sides of the oxidizing furnace. Are arranged so as to form a yarn path through which the precursor fiber bundle passes in a zigzag manner through an oxidizing furnace, and the shape of the grooved roll is as described in (1), (2), and (3) below. An apparatus for producing carbon fiber, which satisfies the formula: 0.7 ≦ b / a <1 (1) 0.2 × a ≦ h ≦ 0.4 × a (2) 0.2 × (ab) ≦ R ≦ 0.4 × (ab) ( 3) (where a is the width of the groove top, b is the width of the groove bottom, h is the depth of the groove, and R is the radius of at least the corner of the groove bottom).