JP2006104604A - Method for producing flameproofed fiber and carbon fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a flameproofed fiber for carbon fibers of high orientation, high strength and high grade by stabilizing operating conditions of an apparatus for production. <P>SOLUTION: A precursor running by forming paths in a plurality of stages while performing drawing or shrinking in an oxidizing atmosphere is heat-treated. Tests for measuring the knot strength are carried out by forming a knot in a precursor single filament in the path in an optional stage, applying tension to the knotted single filament and measuring a change in stress while increasing the strain of the single filament. In the resultant stress-strain curve, the draw ratio corresponding to a point P of stress fall and re-rise at which the stress rises according to an increase in strain, then rapidly falls once, passes through the point P of stress fall and re-rise and further re-rises is taken as the upper limit of the draw ratio of the precursor in the path in the optional stage. The total draw ratio (total draw ratio in the flameproofing step) in the flameproofing step is 1.01-1.08 and the precursor is heat-treated to produce the flameproofed fiber. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing flame-resistant fibers useful for producing highly oriented, high-strength, high-grade carbon fibers, and the like, and a method for producing carbon fibers using the flame-resistant fibers.

  Conventionally, a precursor (precursor fiber) for producing carbon fiber is used to obtain a flame resistant fiber by subjecting it to a flame resistant treatment, and further, a high performance carbon fiber is obtained by subjecting this flame resistant fiber to a carbonization treatment. Is widely known, and this method is also practiced industrially.

In particular, in recent years, the use of carbon fiber has been expanded from sports and leisure goods to the aerospace field, particularly to primary structural materials for aircraft. In addition, various industries have made efforts to reduce energy consumption by reducing the weight of products by taking advantage of the high specific strength and specific elasticity of carbon fibers, thereby contributing to the reduction of CO ₂ emissions. We are paying attention to new usages and are conducting research.

  Under such circumstances, carbon fibers are also required to solve problems such as higher performance, lower manufacturing costs, and higher quality with excellent handling properties.

  On the other hand, when producing carbon fiber, the properties of the precursor, which is the raw fiber, directly affect the performance of the target carbon fiber. Therefore, it is desired to develop a precursor for carbon fiber production that has high performance, low production cost, and good handleability.

  Generally, a polyacrylonitrile (PAN) type fiber is used as a precursor which is a raw material fiber. When producing carbon fiber from this PAN-based fiber, after subjecting the PAN-based fiber to an oxidation treatment (flame-proofing treatment) while stretching or shrinking in an oxidizing atmosphere of 200 to 260 ° C., 260 ° C. or more, usually A method of carbonizing and producing in an inert gas atmosphere at 1000 ° C. or higher is known.

  In particular, the fiber processing method in the flameproofing process greatly affects the development of the strength of the carbon fiber, and many studies have been made so far (for example, Patent Documents 1 to 3).

Patent Document 1 discloses a flameproof treated yarn having a flameproof elongation rate in the range of −10 to 10% (drawing ratio 0.9 to 1.1) and a fiber density of 1.30 to 1.42 g / cm ^3. It is disclosed that a high-strength carbon fiber can be obtained by carbonizing. However, in this flameproofing treatment method, shrinkage or stretching is performed in all the flameproofing treatment steps that require a long time, and no optimum contraction is performed for strength development.

In Patent Document 2, an elongation rate of 3% or more (stretching ratio of 1.03 or more) is given until the fiber density reaches 1.22 g / cm ³ , and the subsequent shrinkage is substantially suppressed and flameproofing treatment is performed. It is disclosed that high strength carbon fibers can be obtained by carrying out and then carbonizing.

In Patent Document 3, after the flameproofing treatment is performed at an elongation rate of 3% or more (stretching ratio of 1.03 or more) until the fiber density reaches 1.22 g / cm ³ , an elongation rate of 1% or more ( It is disclosed that a carbon fiber having a strand strength of 460 kgf / mm ² or more can be obtained by performing a drawing treatment at a draw ratio of 1.01 or more.

According to the methods of Patent Documents 2 and 3, high-strength carbon fibers can be obtained by the conventional methods. However, in the flame-proofing process of continuous stretching after the fiber density becomes 1.22 g / cm ³ or more, a lot of single yarn breakage, fluff and the like occur, and the production of stable flame-resistant fiber and carbon fiber is impaired. It is.
Japanese Examined Patent Publication No. 63-28132 (pages 2 and 3) Japanese Patent Publication No. 3-23649 (Claims) Japanese Patent Publication No. 3-23650 (Claims)

  While the present inventor has made various studies in order to solve the above problems, the precursor is adjusted while adjusting the draw ratio while measuring the change in stress in the nodule strength measurement test according to the progress of the flame resistance of the precursor. Stretching and flame resistance treatment eliminates single yarn breakage, fluff, etc., and stable production of flame resistant fibers is possible.Carbon fibers obtained by carbonizing the flame resistant fibers are highly oriented, high strength, It was learned that the quality is high, and the present invention has been completed.

  Accordingly, the object of the present invention is to solve the above problems, a method for producing flame-resistant fibers as an intermediate raw material for high-orientation, high-strength, high-grade carbon fibers, and carbon using the flame-resistant fibers. It is in providing the manufacturing method of a fiber.

  The present invention for achieving the above object is described below.

  [1] A method for producing a flame-resistant fiber by heat-treating a precursor that travels by forming a plurality of passes while stretching or shrinking in an oxidizing atmosphere, wherein In the stress-strain curve obtained in the knot strength measurement test in which the change in stress is measured while increasing the strain of the single yarn by applying tension to the single knot yarn, the stress increases as the strain increases. The stretch ratio corresponding to the stress drop re-rise point that rises and then rises again after the stress drop re-rise point that suddenly drops is the upper limit of the stretch ratio of the precursor in the optional pass, and the flameproofing step A method for producing flame-resistant fibers, characterized in that the precursor is heat-treated at a total draw ratio (total stretch ratio of flameproofing step) of 1.01 to 1.08.

  [2] The method for producing flame-resistant fibers according to [1], wherein the obtained flame-resistant fibers have a specific gravity of 1.45 or less.

  [3] A method for producing carbon fiber, comprising heat-treating the flameproof fiber produced by the method according to [1] in an inert gas atmosphere.

  According to the method for producing a flame-resistant fiber of the present invention, the precursor is stretched and flame-proofed while adjusting the stretch ratio while measuring the change in stress in the nodule strength measurement test according to the progress of the flame resistance of the precursor. Therefore, there is no breakage of single yarn, fluff, etc., stable production of flame-resistant fibers can be achieved, and carbon fibers obtained by carbonizing this flame-resistant fiber have high orientation and high strength, and fluff and yarn High quality with few slices.

  Hereinafter, the present invention will be described in detail.

  The precursor, which is a raw material for the flame-resistant fiber of the present invention, is preferably a PAN-based precursor because a flame-resistant fiber suitable as an intermediate raw material for obtaining the highest quality carbon fiber can be obtained. In addition to the PAN-based precursor, a pitch-based, phenol-based, cellulose-based or rayon-based precursor can also be used.

  PAN-based precursors, for example, a spinning solution containing a homopolymer or copolymer obtained by polymerizing a monomer containing 95% by mass or more of acrylonitrile in a wet or dry-wet spinning method such as spinning, washing, drying, stretching, etc. Can be obtained by doing As the monomer to be copolymerized, methyl acrylate, itaconic acid, methyl methacrylate, acrylic acid and the like are preferable.

  The precursor thus obtained is flame-resistant according to the method for producing flame-resistant fibers of the present invention to obtain flame-resistant fibers. By carbonizing this flame resistant fiber, highly oriented and high strength carbon fiber can be obtained.

  In the flameproofing process in the method for producing flameproofed fibers of the present invention, a precursor that travels in a multi-stage path is heat-treated while stretching or shrinking in an oxidizing atmosphere. At this time, the stress change in the knot strength measurement test of the precursor in each pass is measured, and the precursor is stretched and flameproofed while adjusting the stretch ratio based on the obtained data.

  The test for measuring the knot strength of the precursor is performed according to JIS L 1015. That is, with respect to the precursor single yarn sampled in an arbitrary pass, a knot is formed in the single yarn, and the change in stress is measured while increasing the strain of the single yarn by applying tension to the knotted single yarn.

  In this nodule strength measurement test, as the precursor flame resistance increases in the pass of the arbitrary stage, the stress rises according to the strain, then drops sharply and then rises again. A stress-strain curve (nodule SSC) with an ascending point) is obtained (see FIG. 1). Here, the strain point at which the stress rapidly drops is referred to as a stress drop re-rise point P.

  Note that the specific gravity of the precursor tends to gradually increase as the precursor becomes flame resistant. Therefore, the progress of the precursor in flame resistance can be determined by the specific gravity of the precursor (see FIG. 2).

  For example, when the specific gravity of the precursor in the arbitrary-stage pass is 1.22, the strain (elongation) at the stress drop re-elevation point P is about 0.16 mm with respect to the precursor sample length of 10 mm. The draw ratio corresponding to this strain [1.6%] is [1.016]. If expressed by the general formula, when a strain of [a%] is obtained, [1+ (a / 100)] is set as the draw ratio.

  In addition, when the flameproofing treatment is in an initial state, a clear stress drop re-elevation point P may not be shown. For this reason, the nodule strength measurement test is performed according to an index indicating the progress of flame resistance such as the specific gravity of the precursor. Generally, when the specific gravity of the precursor is 1.19 or more, the stress drop re-rise point P is indicated.

  In the production process of the flame-resistant fiber of the present invention, the precursor is heat-treated with the draw ratio corresponding to the strain at the stress drop re-elevation point P as the upper limit of the draw ratio of the precursor in the optional step. If the draw ratio exceeds this upper limit value, many single yarn breaks occur in the flameproofing step and / or the carbonization step described later, and it is not preferable because stable production cannot be performed. And since the intensity | strength of the carbon fiber obtained becomes low, it is unpreferable.

  On the other hand, the lower limit of the stretch ratio of the precursor in the optional pass is not particularly limited. However, in order to obtain a high-quality, highly-oriented flameproof fiber, the total draw ratio in the flameproofing process (total stretch ratio of the flameproofing process) is 1.01-1.08, preferably 1.02-1. .07.

  When the total draw ratio of the flameproofing process is less than 1.01, the degree of orientation of the resulting flameproof fiber is lowered, which is not preferable. Furthermore, the orientation degree and strength of the carbon fiber obtained by carbonizing this flame resistant fiber as an intermediate raw material is not preferable.

  When the total stretching ratio of the flameproofing step exceeds 1.08, it is not preferable because many single yarn breaks occur in the flameproofing step and / or the carbonization step described later, and stable production cannot be performed. And since the intensity | strength of the carbon fiber obtained becomes low, it is unpreferable.

  In the stress-strain curve (normal SSC) in the normal strength measurement test, not the nodule strength measurement test, the stress gradually increases without decreasing in the middle as the precursor strain increases (see FIG. 1). Therefore, normal SSC is not suitable as a judgment material for adjusting the stretch ratio of the precursor in the arbitrary-stage pass.

  In addition, the stress-strain curve of the precursor before the flameproofing treatment (precursor SSC) and the stress-strain curve of the precursor in the path where flameproofing is not sufficiently advanced are also reduced as the precursor strain increases. It rises gradually without doing (refer to FIG. 1).

  The stretch ratio of the precursor in the pass where the flame resistance is not sufficiently advanced is not particularly limited. However, in order to obtain a high-quality, highly-oriented flame-resistant fiber, as described above, the total stretching ratio of the flame-proofing process is set to 1.01 to 1.08, preferably 1.02 to 1.07.

  The degree of orientation of the precursor can be evaluated by the degree of orientation in wide-angle X-ray measurement (diffraction angle 17 °). The degree of orientation in this wide-angle X-ray measurement (diffraction angle 17 °) can be determined as follows.

  About 12,000 single fibers of the precursor after the drawing treatment are bundled, and the fibers are aligned in the fiber axis direction using acetone to converge the bundle.

  The fiber is affixed to a mount having a hole with a diameter of 1.0 cm in a tensioned state so that the center of the fiber bundle comes to the center of the hole. Thereafter, the mount is fixed to the sample adjusting jig so that the fiber axis and the axis of the jig are parallel to each other.

  Furthermore, this jig is fixed to a wide-angle X-ray diffraction measurement sample stage by a transmission method. When Cu Kα rays are used as the X-ray source and the sample is irradiated, a diffraction pattern (having two peaks) appears at around 2θ17 degrees.

The peak angle of this diffraction pattern is obtained, and measurement is performed for a range of 360 degrees including these angles. Next, a base line is drawn on the graph of the obtained X-ray diffraction chart to determine peak half-value widths H _1/2 and H ′ _1/2 (degrees), and the following degree of orientation = [360− (H _1/2 + H'1 / ₂ )] / 360 (1)
The degree of orientation is calculated by

  The progress of flameproofing in the above flameproofing step, that is, the specific gravity of the obtained flameproofed fiber is preferably 1.45 or less, and more preferably 1.42 or less. When the specific gravity of the flame resistant fiber exceeds 1.45, the stretchability of the fiber is lowered, yarn breakage occurs in the carbonization step, and high strength carbon fiber cannot be obtained, which is not preferable.

  Next, the flame-resistant fiber is baked and carbonized in an inert gas atmosphere such as a nitrogen atmosphere to obtain a carbon fiber. Further, for the purpose of facilitating the post-processing of the carbon fiber and improving the handleability, it is preferable to perform a sizing treatment of the carbon fiber. The sizing method can be carried out by a conventionally known method, and the sizing agent is preferably used after changing its composition as appropriate according to the application, and after uniformly adhering.

  The carbon fiber thus obtained is a carbon fiber having high orientation and high strength, and having less fuzz and yarn breakage.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. Moreover, the evaluation method about the various physical properties of the precursor in each Example and a comparative example, a flame-resistant fiber, and carbon fiber was implemented by the above-mentioned method or the following methods.

<Orientation degree in wide angle X-ray measurement (diffraction angle 17 °)>
X-ray diffractometer: RINT2050 manufactured by Rigaku Corporation was used, and the degree of orientation at a diffraction angle of 17 ° was determined from the half-value widths H _1/2 and H ′ _1/2 by the above formula (1).

<Degree of orientation in wide-angle X-ray measurement (diffraction angle 26 °)>
It was determined in the same manner as the degree of orientation in the wide-angle X-ray measurement (diffraction angle 17 °) except that the diffraction angle was 26 °.

<Tensile strength>
It was measured by the method defined in JIS R7601.

<Fiber specific gravity>
Measured by Archimedes method. Precursor or flameproof fiber sample fibers were degassed in acetone and measured.

Example 1
A spinning stock solution containing acrylic fiber copolymerized with 95% by mass of acrylonitrile, 4% by mass of methyl acrylate, and 1% by mass of itaconic acid was wet-spun, washed with water, dried, drawn, and oiled to obtain a fiber diameter of 12.0 μm. A precursor having 24,000 filaments and a specific gravity of 1.16 was obtained. Further, the degree of orientation of this precursor in wide-angle X-ray measurement (diffraction angle 17 °) was 88.5%.

  The precursor was flameproofed in a hot air circulation flameproofing furnace having a furnace temperature distribution of 230 to 260 ° C.

  The precursor introduced into the flameproofing furnace formed a number of paths [1 pass] lined up in a horizontal plane and traveled horizontally in the flameproofing furnace, then moved out of the flameproofing furnace and provided outside the flameproofing furnace. It is folded back by the folding roller and returned to the flameproofing furnace.

  The precursor that has returned to the flameproofing furnace forms a plurality of paths [2 passes] arranged in a horizontal plane below the one pass, and travels horizontally in the flameproofing furnace. Thereafter, the inside and outside of the flameproofing furnace was repeated up to 7 passes, and the precursor was flameproofed.

  In this example, the precursor sample for each pass is collected when the precursor sample goes out of the flameproofing furnace. That is, the n-pass precursor is a precursor sample collected when the n-th pass goes out of the flameproofing furnace. The 7-pass precursor is a so-called flame-resistant fiber after the flame resistance treatment.

  Flame proofing treatment was performed by adjusting the specific gravity and stretch ratio of the precursor in each pass to the conditions shown in Table 1. The stress drop re-elevation point P obtained by sampling the precursor of each pass and performing the nodule strength measurement test was observed for the precursor of 1 pass to 7 passes. That is, it was recognized that the flame resistance was advanced to the extent that at least the stress drop re-elevation point P was exhibited even in one pass. Table 1 shows strain stretch ratios (measurement test stretch ratios) at the stress drop re-elevation point P.

  The draw ratio (actual operation draw ratio) actually applied to the 1-pass to 7-pass precursor is adjusted to be equal to or less than the stretch ratio of the strain at the stress drop re-elevation point P (the above-described upper limit value).

  The total actual operation stretching ratio in 1 pass to 7 passes (total stretching ratio of flameproofing process) is preferably not only 1.030 and the above-mentioned range of 1.01 to 1.08 of the present invention as shown in Table 1. It is adjusted within the range of 1.02 to 1.07. In addition, as shown in Table 1, the specific gravity of the precursor through the first to seventh passes is adjusted to 1.36 at the maximum, which is less than the above-described preferable range of 1.45.

  The obtained flame-resistant fiber was a good fiber having a high degree of orientation of 75.3% in wide-angle X-ray measurement (diffraction angle 26 °) and less occurrence of fluff and yarn breakage.

  Next, this flame resistant fiber was carbonized to produce carbon fiber. The production conditions and production equipment were normal.

  In this example, in the flameproofing treatment and carbonization treatment, the occurrence of fluff and yarn breakage was small, and the operating state of the production apparatus could be stabilized.

  As shown in Table 2, the tensile strength of the carbon fiber obtained through the flameproof fiber of this example was as high as 5200 MPa. Further, the degree of orientation of this carbon fiber in wide-angle X-ray measurement (diffraction angle 26 °) was as high as 80.1%.

Examples 2-5 and Comparative Examples 1-6
The precursor obtained in Example 1 was subjected to flameproofing treatment in the same manner as in Example 1 except that the conditions of the actual operation stretching ratio and the flameproofing process total stretching ratio in each pass shown in Table 1 were adjusted. A flame-resistant fiber having an orientation degree in the fiber quality and wide-angle X-ray measurement (diffraction angle 26 °) shown in 2 was obtained.

  Note that the specific gravity of the precursor through the first pass to the seventh pass was subjected to the same heat treatment as that of Example 1, and as shown in Table 1, it was adjusted to 1.36 at the maximum and the above-mentioned preferable range of 1.45 or less. Yes.

  In each of Examples 2 to 5, the draw ratio actually applied to the 1-pass to 7-pass precursor (actual operation draw ratio) is the strain draw ratio at the stress drop re-elevation point P as shown in Table 1 ( The above upper limit value) has been adjusted.

  Further, in all of Examples 2 to 5, the total actual operation stretching ratio in 1 pass to 7 passes (flame-proofing process total stretching ratio) is within the range of 1.01 to 1 of the present invention described above as shown in Table 1. Adjusted within 0.08.

  As a result, all of the flame-resistant fibers obtained in Examples 2 to 5 have a high degree of orientation in wide-angle X-ray measurement (diffraction angle 26 °) as shown in Table 2, and good generation of fluff and yarn breakage is low. Fiber.

  Next, each flame-resistant fiber of Examples 2 to 5 was subjected to carbonization treatment in the same manner as in Example 1. The fiber quality shown in Table-2, the degree of orientation in wide-angle X-ray measurement (diffraction angle 26 °), Tensile strength carbon fibers were obtained.

  In each of Examples 2 to 5, in the flameproofing treatment and carbonization treatment, the occurrence of fluff and yarn breakage was small, and the operating state of the production apparatus could be stabilized.

  As shown in Table 2, the tensile strength of the carbon fibers obtained via the flameproof fibers of Examples 2 to 5 was high. In addition, the degree of orientation of each of the carbon fibers of Examples 2 to 5 in the wide-angle X-ray measurement (diffraction angle 26 °) was high.

  As shown in Table 1, in Comparative Examples 1 to 4, the actual operation draw ratio of at least one pass among the actual operation draw ratios of 1 pass to 7 passes is the strain draw ratio at the stress drop re-elevation point P (described above). The value has been adjusted to exceed the upper limit value.

  Specifically, in Comparative Example 1, 1 pass, in Comparative Example 2 in 2 passes, in Comparative Example 3 in 3 passes, and in Comparative Example 4 in 5 passes, the actual operation stretching ratio is the strain stretching at the stress drop re-elevation point P. It is adjusted to a value that exceeds the magnification (the upper limit mentioned above).

  As shown in Table 1, the comparative example 5 has a total actual operation stretching ratio (total stretching ratio of the flameproofing process) in 1 pass to 7 passes of less than 1.01, which deviates from the scope of the present invention described above. It is adjusted to 000.

  As shown in Table 1, in Comparative Example 6, the total actual operation stretching ratio (total stretching ratio of the flameproofing process) in 1 to 7 passes exceeded 1.08, which deviated from the scope of the present invention described above. .083 is adjusted.

  As a result, as shown in Table 2, all of the flame-resistant fibers obtained in Comparative Examples 1, 2, and 6 have a high degree of orientation in wide-angle X-ray measurement (diffraction angle 26 °), and generation of fluff and yarn breakage occurs. The flame-resistant fibers obtained in Comparative Examples 3 and 4 were all low-quality fibers with many occurrences of fluff and yarn breakage. The flame-resistant fiber obtained in Comparative Example 5 was a low-orientation fiber having an orientation degree of 74.8% in wide-angle X-ray measurement (diffraction angle 26 °).

  Next, each flame-resistant fiber of Comparative Examples 1 to 6 was subjected to carbonization treatment in the same manner as in Example 1, and the fiber quality shown in Table-2, the degree of orientation in wide-angle X-ray measurement (diffraction angle 26 °), Tensile strength carbon fibers were obtained.

  In Comparative Example 5, in the carbonization treatment, there was little occurrence of fluff and yarn breakage, and the operation state of the production apparatus could be stabilized. In Comparative Examples 1-4 and 6, all of the carbonization treatment However, there were many occurrences of fluff and yarn breakage, and the operation state of the production apparatus could not be stabilized.

  As shown in Table 2, the tensile strength of the carbon fibers obtained via the flameproof fibers of Comparative Examples 1 to 6 was low. Further, the degree of orientation of the carbon fiber of Comparative Example 5 in the wide-angle X-ray measurement (diffraction angle 26 °) was as low as 79.8%.

It is a graph which shows the change of the stress with respect to the distortion in a nodule strength measurement test or a normal strength measurement test about the precursor before a flameproofing process or the precursor in a flameproofing process. It is a graph which shows the change of specific gravity with respect to progress of a flameproofing process about the precursor in a flameproofing process.

Claims (3)

A method of manufacturing a flame-resistant fiber that heat-treats a precursor that travels by forming a multi-stage pass while stretching or shrinking in an oxidizing atmosphere. In the stress-strain curve obtained by the knot strength test that measures the change in stress while increasing the strain of the single yarn by applying tension to this single knot yarn, the stress increases as the strain increases, Next, the draw ratio corresponding to the stress drop re-rise point that rises again after passing the stress drop re-rise point that suddenly drops is taken as the upper limit of the stretch ratio of the precursor in the optional step, and the total in the flame resistance process A method for producing flame-resistant fibers, characterized in that the precursor is heat-treated at a draw ratio (total draw ratio of flameproofing step) of 1.01-1.08. The method for producing flame-resistant fibers according to claim 1, wherein the specific gravity of the obtained flame-resistant fibers is 1.45 or less. A method for producing carbon fiber, comprising heat-treating the flame-resistant fiber produced by the method according to claim 1 in an inert gas atmosphere.

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