JP4626939B2 - Carbon fiber manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a high-strength carbon fiber.

  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. 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 save energy 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 focusing on new ways of using and researching them.

  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.

  In general, an acrylic fiber is used as a precursor which is a raw material fiber. When producing carbon fiber from this acrylic fiber, after carrying out oxidation treatment (flameproofing treatment) while stretching or shrinking the acrylic fiber in an oxidizing atmosphere of 200 to 300 ° C., 300 or more, or 1000 ° C. or more Carbon fiber is produced by carbonization in an inert gas atmosphere.

  In particular, the fiber treatment method in the carbonization process at around 300 to 900 ° C. greatly affects the strength expression of the carbon fiber, and many studies have been made so far.

  In Patent Document 1, the flame-resistant fiber is carbonized at 300 to 800 ° C. while being stretched in an inert atmosphere in a range of up to 25%, and processed so as not to be negative with respect to the original length of the flame-resistant fiber. It is disclosed to obtain high strength carbon fibers.

  Moreover, in patent document 2 and patent document 3, in order to control the rapid change of the fiber length in 500 degreeC vicinity, 300-500 degreeC, 500-800 degreeC, and a high intensity | strength are divided by dividing a process into two. It is disclosed that carbon fibers can be obtained.

However, it is difficult to control the physical properties of the fiber only with parameters such as temperature range and specific gravity described in these methods. Therefore, a method for obtaining a high-strength carbon fiber while controlling the physical properties of the fiber has been demanded.
JP 54-147222 A (pages 1 to 3) JP 59-150116 A (pages 1 and 2) Japanese Patent Publication No. 3-23651 (pages 1 to 3)

  While the present inventor has been variously studied to solve the above problems, the maximum stretch ratio obtained by TMA measurement, the flameproof fiber having an orientation degree at 26 ° obtained by wide-angle X-ray measurement of a predetermined range, Based on the maximum draw ratio, the carbon fiber obtained by carbonization at a predetermined stretch ratio is known to have high strength, and the present invention has been completed.

  Accordingly, an object of the present invention is to provide a method for producing a high-strength carbon fiber that solves the above problems.

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

  [1] A flame-resistant fiber having a maximum draw ratio [A]% obtained by TMA measurement of 10% or more and an orientation degree at 26 ° of 75% or more obtained by wide-angle X-ray measurement is measured in an inert atmosphere at a temperature. After heat treatment at 300 to 600 ° C. and a stretching ratio [A × 0.35] to [A × 0.55]% indicated by the maximum stretching ratio [A]%, the temperature is 600 to 1600 ° C. in an inert atmosphere. A method for producing carbon fiber, which is heat-treated at a temperature.

  According to the carbon fiber production method of the present invention, the maximum stretch ratio obtained by TMA measurement and the flameproof fiber having a predetermined degree of orientation at 26 ° obtained by wide-angle X-ray measurement are stretched by the maximum stretch ratio. Since the carbonization treatment is performed under conditions including the setting of a predetermined range of the rate, it is possible to reliably control the physical properties of the fiber during the treatment, and stably produce high-strength carbon fibers.

  Hereinafter, the present invention will be described in detail.

  The flame-resistant fiber used as a starting material in the carbon fiber production method of the present invention has a maximum draw ratio [A]% obtained by TMA measurement of 10% or more, and an orientation degree at 26 ° obtained by wide-angle X-ray measurement of 75%. That's all.

The maximum draw ratio (TMA _max ) [A]% with respect to an arbitrary stress (TMA stress) of the flameproof fiber in the TMA measurement can be obtained by the following method.
1. Flame-resistant fibers are collected and fixed to a fiber measuring jig with a measurement effective length of 1 cm.
2. While stretching the flame-resistant fiber with an arbitrary stress per unit cross-sectional area in an N ₂ gas atmosphere, the temperature is increased from 25 ° C. to 400 ° C. at a rate of temperature increase of 20 ° C./min. TMA stretch ratio measurements are measured on the fibers.
3. The maximum TMA measurement stretch ratio among the measured TMA measurement stretch ratios during the stretching heat treatment is defined as the TMA maximum stretch ratio.

Fibers with a maximum draw ratio (TMA ^max ) [A]% obtained from TMA of less than 10% cannot be improved in the degree of orientation required for high strength in the first carbonization process following the flame resistance process. Therefore, it is difficult to suppress the strength reduction. Furthermore, fluff and single yarn breakage are likely to occur, and stable production cannot be achieved.

  The degree of orientation in wide-angle X-ray measurement (diffraction angle 26 °) can be determined as follows.

About 12,000 single fibers of flame resistant fiber are bundled, and the fibers are aligned in the fiber axis direction using acetone to converge the bundle.
1. About 12,000 single fibers of flame resistant fiber are bundled, and the fibers are aligned in the fiber axis direction using acetone to converge the bundle.
2. 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.
3. 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 in the vicinity of 2θ26 degrees.
4). 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
Calculate the degree of orientation.

  If the degree of orientation at 26 ° obtained from the wide-angle X-ray measurement of the flame-resistant fiber is less than 75%, the degree of orientation must be improved when the flame-resistant fiber is subjected to the first carbonization treatment. Necessary. However, a high draw ratio causes breakage of single yarn, and it becomes difficult to maintain a stable process state. Therefore, the degree of orientation needs to be 75% or more.

  Moreover, you may use the said flameproof fiber manufactured with the following method. Examples of the precursor for producing the flame resistant fiber include polyacrylonitrile (PAN), pitch, phenol, rayon and the like. Among these precursors, the highest strength carbon fiber can be obtained by using a PAN-based one (acrylic fiber).

  This acrylic fiber is prepared by, for example, treating 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 and stretching. Can be obtained by doing As the monomer to be copolymerized, methyl acrylate, itaconic acid, methyl methacrylate, acrylic acid and the like are preferable.

  By adjusting the draw ratio in the drawing treatment after spinning, washing and drying, the maximum draw ratio obtained from TMA measurement of flame-resistant fiber obtained by flame-proofing treatment in the next step and obtained from wide-angle X-ray measurement 26 Physical properties such as the degree of orientation at ° can be within the above range. The draw ratio is preferably adjusted to 3.1 to 6.4 times, and more preferably adjusted to 3.3 to 6.2 times.

  The acrylic fibers thus obtained are flame-resistant according to a known method to obtain flame-resistant fibers. High-strength carbon fibers can be obtained by carbonizing the flame-resistant fibers according to the carbon fiber production method of the present invention.

  In the carbonization step in the carbon fiber production method of the present invention, the flame-resistant fiber is stretched at a temperature of 300 to 600 ° C. in an inert atmosphere and the stretch ratio [A × 0. 35] to [A × 0.55]% to obtain a first carbonized fiber obtained by heat treatment, and the first carbonized fiber in an inert atmosphere at a temperature of 600 to 1600 ° C. A second carbonization step of obtaining a second carbonized fiber by heat treatment.

  If the stretch rate in the first carbonization step is less than [A × 0.35]%, the stretch is poor, and thus high-strength carbon fibers cannot be obtained. On the other hand, when the stretch ratio in the first carbonization step is larger than [A × 0.55]%, fluff and thread breakage are liable to occur due to excessive stretching, and improvement in the degree of orientation cannot be expected, resulting in stable process. There is a possibility of impairing sex.

  The obtained second carbonized fiber, that is, the carbon fiber obtained after completion of the second carbonization step may be subsequently subjected to surface treatment by a known method. Furthermore, it is preferable to perform sizing treatment for the purpose of facilitating the post-processing of the carbon fiber and improving the handleability. 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.

  In addition, it is preferable that the single fiber diameter after a 2nd carbonization process is 4.0-7.5 micrometers.

  The carbon fiber thus obtained has high strength and can be produced by the production method of the present invention.

The strength of the carbon fiber can be indicated by tensile strength or the like. However, the measured value of the tensile strength tends to be higher as the fiber diameter is smaller even if the actual strength is the same. Therefore, in order to evaluate the real strength of the carbon fiber, the strength [C] MPa obtained by correcting the measured strength [B] MPa with the fiber diameter [d] μm is expressed by the following formula: C = B × (d / 10) ^0.65
Calculate using.

  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 acrylic fiber 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.

<TMA maximum stretch ratio>
Measurement was performed by the above-described method using a thermomechanical property tester (TMA) 4000S manufactured by Mac Science.

<Degree of orientation in wide-angle X-ray measurement (diffraction angle 26 °)>
X-ray diffractometer: RINT2050 manufactured by Rigaku Corporation was used, and measurement was performed by the method described above.

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

Production Example 1
A spinning stock solution containing a copolymer of 95% by mass of acrylonitrile, 4% by mass of methyl acrylate, and 1% by mass of itaconic acid is wet-spun, washed with water, dried, stretched (stretching ratio: 3.5 times), and oiled. An acrylic fiber having a diameter of 11.4 μm was obtained.

Production Example 2
Acrylic fibers were produced under the same conditions as in Production Example 1 except that the draw ratio during the drawing operation after spinning, washing and drying was 3.0 times to obtain acrylic fibers having a fiber diameter of 12.3 μm.

Production Example 3
Acrylic fibers were produced under the same conditions as in Production Example 1 except that the draw ratio during the drawing operation after spinning, washing and drying was 6.0 times, and acrylic fibers having a fiber diameter of 8.7 μm were obtained.

Production Example 4
An acrylic fiber was produced under the same conditions as in Production Example 1 except that the draw ratio during the drawing operation after spinning, washing and drying was 6.5 times, and an acrylic fiber having a fiber diameter of 8.3 μm was obtained.

Examples 1-4 and Comparative Examples 1-6
The acrylic fibers of Production Examples 1 to 4 were subjected to flameproofing treatment at a draw ratio of 1.06 times in a hot air circulation type flameproofing furnace having a temperature distribution in the furnace of 25 to 250 ° C. in heated air. A flame-resistant fiber having a degree of orientation and an orientation degree in wide-angle X-ray measurement (diffraction angle 26 °) was obtained.

  Next, the obtained flame-resistant fiber was heat-treated at a drawing rate shown in Table 1 in a first carbonization furnace having an in-furnace temperature distribution of 300 to 600 ° C. in an inert atmosphere to obtain a first carbonized fiber. .

  Thereafter, the obtained first carbonized fiber was heat-treated at a draw ratio of 0.94 times in a second carbonization furnace having an in-furnace temperature distribution of 600 to 1400 ° C. in an inert atmosphere, and subsequently by a known method. Surface treatment, sizing, and drying were performed to obtain carbon fibers having fiber diameters, strand strengths, and correction strengths based on fiber diameters as shown in Table 1.

As shown in Table 1, in all of Examples 1 to 4, the flame-resistant fiber as an intermediate raw material has a TMA maximum draw ratio of 10% or more, and the degree of orientation in wide-angle X-ray measurement (diffraction angle 26 °). Was 75% or more. Further, in all of Examples 1 to 4, the stretch ratio during the first carbonization treatment was in the range of 0.35 to 0.55 in terms of the ratio of TMA _max .

  All of the carbon fibers obtained under the conditions of Examples 1 to 4 had high correction strength based on the fiber diameter.

On the other hand, for Comparative Examples 1 to 6, the TMA maximum draw ratio, the degree of orientation in the wide-angle X-ray measurement (diffraction angle 26 °), and the TMA at the time of the first carbonization treatment of the flame-resistant fiber of the intermediate material _At least one of the conditions of the stretch ratio indicated by the _max ratio deviates from the configuration of the present invention. All of the carbon fibers obtained under the conditions of Comparative Examples 1 to 6 had low correction strength due to the fiber diameter and / or fluffed in the first carbonization step.

Claims (1)

A flame-resistant fiber obtained by flame-treating an acrylic fiber having a draw ratio of 3.1 to 3.5 times in a drawing process after spinning, washing and drying, and a maximum draw ratio obtained by TMA measurement [ A] 10% or more of a flame-resistant fiber having a degree of orientation at 26 ° of 75 to 77.5% obtained by wide-angle X-ray measurement in an inert atmosphere at a temperature of 300 to 600 ° C. and the maximum stretch A method for producing carbon fiber, which is heat-treated at a temperature of 600 to 1600 ° C. in an inert atmosphere after heat treatment at a draw ratio [A × 0.35] to [A × 0.50]% indicated by a rate [A]%.