JP5393070B2 - Carbon fiber and method for producing the same - Google Patents

Description

  The present invention relates to a carbon fiber excellent in surface / interface characteristics and a method for producing the same, which is used when a composite material is produced by combining a matrix material and carbon fiber.

  As a method for producing carbon fiber, a method of using a precursor fiber such as polyacrylonitrile (PAN) as a raw fiber and obtaining carbon fiber through flameproofing treatment and carbonization treatment is widely known (e.g., patent document). 1). The carbon fibers thus obtained have good characteristics such as high specific strength and specific elastic modulus.

  In recent years, industrial applications of composite materials using carbon fibers [for example, carbon fiber reinforced plastic (CFRP) and the like] have been greatly expanded. Especially in the sports / leisure field, aerospace field, and automobile field, (1) higher performance (higher strength, higher elasticity), (2) lighter (fiber weight reduction and fiber content reduction), ( 3) There is an increasing demand for improvement in the physical properties of higher composite materials when composited (improvement of carbon fiber surface / interface properties).

  In order to pursue high performance in the composite of carbon fiber and matrix material such as resin, the characteristics of the matrix material are also important, but it is necessary to improve the surface characteristics, strength and elastic modulus of the carbon fiber itself. It is essential. In other words, by combining materials with high adhesion between the carbon fiber surface and the matrix material, and dispersing the matrix material and the carbon fiber more uniformly, the composite material with higher performance (high strength, high elasticity) can be obtained. Can be obtained.

  The improvement of the surface properties, strength, and elastic modulus of carbon fibers has been studied conventionally (see, for example, Patent Documents 2 to 4).

  However, conventional carbon fibers are insufficient to satisfy the requirements of the composite material.

Therefore, the present inventor has repeatedly studied in order to solve the above-described problems, and has a surface on which the wrinkles oriented in the fiber axis direction have the resin-impregnated strand strength, the resin-impregnated strand elastic modulus and density in a predetermined range. It has been found that when the carbon fibers possessed are combined with a matrix material to form a composite material, good adhesion to the matrix material is developed, and an application was made earlier (Patent Document 5).
JP 2001-131833 A (Claims) Japanese Patent Publication No. 8-6210 (Claims) JP 2003-73932 A (Claims) JP-A-11-152626 (Claims) JP 2007-177368 A (Claims)

  However, in the production method described in Patent Document 4, the obtained carbon fiber has variations in strength, for example, even if the strand strength is high, the measured length (X) and strength (Y) of a single fiber to be described later It has been found that the slope (a) in the relational expression obtained in (1) and (2) may not be good, and that the compressive strength in the transverse direction of single fibers described later may be low.

  The present inventor has found that the carbon fiber strength (Y) decreases as the measured length (X) of the single fiber increases, while variously examining the above problems. This relationship is obtained by taking the logarithmic value [Ln (X)] of the measured length of the fiber on the horizontal axis and the carbon fiber strength (Y) on the vertical axis. It was found that variation in carbon fiber strength can be evaluated by a), and variation in strength with respect to the single fiber measurement length can be reduced by setting the slope (a) within a predetermined range. Similarly, it has been found that the strength in the measurement direction of a single fiber can be evaluated by the compressive strength in the transverse direction of the single fiber.

  Moreover, the electrical resistance value (A) obtained from the slope obtained from the applied current-applied voltage measurement and the electrical resistance value (B) obtained from the slope obtained from the applied current-applied voltage measurement using the conductive paste. It has been found that carbon fibers having a ratio (A / B) in a predetermined range have good surface / interface characteristics and high strength.

  Furthermore, it has been found that a carbon fiber having an indent surface modulus in a predetermined range measured by a scanning probe microscope (SPM) has a high strength and a high elastic modulus.

  Furthermore, when the acrylic precursor fiber is subjected to flameproofing treatment and carbonization treatment under a predetermined condition to obtain raw material carbon fiber, and then performing a plurality of surface oxidation treatments by electrolytic oxidation in nitric acid, the first step It was found that the carbon fiber having the above-mentioned good physical properties can be produced by performing the surface oxidation treatment with a predetermined amount of electricity, and the present invention has been completed.

  Accordingly, an object of the present invention is to provide a carbon fiber and a method for producing the same, which have solved the above problems.

  The present invention for achieving the above object is as follows.

[1] A carbon fiber having a strength of 6100 MPa or more, an elastic modulus of 340 GPa or more, and a specific gravity of 1.76 or more,
Ratio between the electrical resistance value (A) obtained from the slope obtained from the applied current-applied voltage measurement and the electrical resistance value (B) obtained from the slope obtained from the applied current-applied voltage measurement using a conductive paste ( A / B) is A / B ≦ 1.30
The relational expression y = aLn (X) + b obtained from the measured length (X) and strength (Y) of the single fiber
The slope (a) is 0 ≧ a> −650
And an indentation surface modulus measured by a scanning probe microscope (SPM) is in the range of 8 to 11.5 GPa.

  [2] Acrylic precursor fibers obtained by spinning a spinning dope from a spinneret are heat-treated at 200 to 280 ° C. in heated air to obtain flame-resistant fibers, and the resulting flame-resistant fibers are treated with an inert gas atmosphere. After performing carbonization treatment at a temperature of 1600 to 2000 ° C., when performing surface oxidation treatment by electrolytic oxidation in nitric acid in a plurality of stages, the first stage surface oxidation treatment is performed with an electric quantity of 50 to 270 c / g. The method for producing carbon fiber as described in [1], wherein

  The carbon fiber of the present invention has a logarithmic value [Ln (X)] of the measured length of the fiber on the horizontal axis and the slope (a) of the straight line formed by taking the carbon fiber strength (Y) on the vertical axis. Ratio (A / B) of the electrical resistance value (A) obtained from the slope obtained from the applied voltage measurement and the electrical resistance value (B) obtained from the slope obtained from the applied current-applied voltage measurement using a conductive paste ), And the indent surface modulus measured by a scanning probe microscope (SPM) is in a predetermined range, so that there is little variation in carbon fiber strength, and the strength and elasticity are high.

  According to the production method of the present invention, when the acrylic raw material carbon fiber is subjected to a plurality of stages of surface oxidation treatment by electrolytic oxidation in nitric acid, the first stage surface oxidation treatment is performed with a larger amount of electricity than usual. Therefore, the above-described carbon fiber having good physical properties can be easily produced.

  Hereinafter, the present invention will be described in detail.

The carbon fiber of the present invention has a strength of 6100 MPa or more, preferably 6150 MPa or more, an elastic modulus of 340 GPa or more, preferably 340 to 370 GPa, and a specific gravity of 1.76 or more, preferably 1.76 to 1.80. The carbon fiber of the present invention has an electrical resistance value (A) obtained from the slope obtained from the applied current-applied voltage measurement and an electrical resistance value obtained from the slope obtained from the applied current-applied voltage measurement using a conductive paste. Ratio (A / B) to (B) is A / B ≦ 1.30
Range.

  The electrical resistance value (A) is measured by the following method. As shown in FIG. 1 (A), 25 cm of the evaluation carbon fiber strand 2 is sampled, and the applied electrodes 4 and 6 and the detection ends 8 and 10 for measuring the voltage and current are attached to the positions 2 cm on both ends. These electrodes and detection ends are sandwiched between electrode clips and electrically connected to the following measuring device. The applied current I [A] is changed and the applied voltage E [v] is measured for each. Reference numeral 12 denotes a voltage / current measuring device. As the voltage / current measuring device 12, an electrochemical measuring device HSV100 manufactured by Hokuto Denko Co., Ltd. is used.

From this measured value, the electrical resistance value (Ω · g / m ² )
= (E [v] / I [A]) x 100/25 x fineness [tex] / 1000
Thus, the electric resistance value (A) is obtained.

  Next, as shown in FIG. 1 (B), covering the surface and both ends of the strand from the both ends of the same carbon fiber strand 2 for evaluation to the respective electrode and the attachment position of the detection end, a conductive paste (dortite) 14, 16 is applied and the conductive paste is dried, the electrode and the detection end are sandwiched between electrode clips, and the electrical resistance value (B) is obtained in the same manner.

  The electric resistance value (A) is divided by the electric resistance value (B) to obtain the electric resistance value ratio (A / B).

  In the present invention, the defined electrical resistance values (A) and (B) are as described above. It is considered that the electric resistance value (A) mainly measures the current flowing along the surface of the single fiber in the carbon fiber strand. For the electrical resistance value (B), a carbon fiber strand covering the end face of the strand with a conductive paste such as a silver paste is used. For this reason, in the measurement of the electrical resistance value (B), it is considered that the current is a current flowing through the single fiber surface and inside the single fiber.

  The carbon fiber before the electrolytic oxidation treatment after the carbonization step is finished is covered with a carbon layer having irregular and defective surfaces. Since the carbon layer has a high electric resistance value and a defect, the carbon fiber is likely to be cut from the defect as a starting point, and the strength is weak.

  However, when the first-stage electrolytic oxidation treatment is performed with a larger amount of electricity than usual, such as 50 c / g or more as in the present invention, this defective carbon layer is removed, and as a result, high-strength carbon fibers are removed. Can be obtained.

  The carbon layer having defects removed by the electrolytic oxidation treatment is considered to be on the order of nm or less and cannot be confirmed by ordinary microscope observation. However, a change in the surface structure clearly occurs, and the change is observed as an electric resistance value (A), (B) and an electric resistance value ratio (A / B).

  In the present invention, by performing electrolytic oxidation treatment until A / B ≦ 1.30, the carbon layer having defects is removed from the carbon fibers having invisible defects to obtain high-strength carbon fibers. Is. In the case of A / B> 1.3, many surface layers with many defects remain, resulting in low-strength carbon fibers.

  In addition, in the electrolytic oxidation treatment, when the first stage treatment electricity and / or total electricity is excessive, the obtained carbon fiber has a small indent surface modulus by SPM measurement, or the measurement length of the single fiber. This is not preferable because the absolute value of the slope (a) in the relational expression obtained by the length (X) and the strength (Y) becomes a large numerical value or the strand strength decreases.

The carbon fiber of the present invention has a relational expression y = aLn (X) + b obtained from the measured length (X) and strength (Y) of a single fiber.
The slope (a) is 0 ≧ a> −650
And the indent surface modulus measured by scanning probe microscope (SPM) is in the range of 8 to 11.5 GPa, and preferably has wrinkles oriented in the fiber axis direction on the surface.

  A small absolute value of the slope (a) indicates that the number of defects in the unit length is small.

  A carbon fiber having an indent surface modulus smaller than 8 as measured by a scanning probe microscope (SPM) is a carbon fiber obtained when the electrolytic oxidation treatment is excessive, when the treatment temperature is low and a predetermined elastic modulus cannot be obtained, It is not preferable as a carbon fiber for composite materials. On the other hand, a carbon fiber having an indentation surface modulus exceeding 11.5 GPa is a carbon fiber obtained when the electrolytic oxidation treatment is insufficient, and is not preferable as a carbon fiber for a composite material.

  With the above configuration, as described above, the carbon fiber of the present invention functions as a reinforcing material having good adhesion to the matrix material when combined with the matrix material to form a composite material. Moreover, this carbon fiber is a fiber with less fuzz and yarn breakage.

  The carbon fiber of the present invention can be produced, for example, by the following method.

<Precursor fiber>
As the precursor fiber used in the carbon fiber manufacturing method of this example, an acrylic precursor fiber obtained by spinning a spinning dope from a spinneret is used. Specifically, 90% by mass or more, preferably 95% by mass or more of acrylonitrile, and produced by spinning a spinning solution obtained by homopolymerizing or copolymerizing a monomer containing 10% by mass or less of other monomers, Acrylic precursor fibers are preferred. Examples of other monomers include itaconic acid and (meth) acrylic acid esters.

  As the spinning method, either a wet or dry wet spinning method can be used. However, since the finally obtained carbon fiber forms wrinkles on the surface and adhesiveness with the resin can be expected, the wet spinning method is used. More preferred. In addition, as a spinning solvent, inorganic salt aqueous solution, such as zinc chloride, organic solvents, such as DMF, etc. can be used, It does not specifically limit. Control of the shape of the fiber surface wrinkles can be adjusted by changing the spinning conditions (such as the viscosity of the spinning solution and the spinning speed).

  Precursor fibers are obtained by subjecting the raw fiber after spinning to water washing, drying, stretching, and oiling treatment.

<Flame resistance treatment>
The obtained precursor fiber is subsequently flameproofed at 200 to 280 ° C. in heated air. The treatment at this time is generally carried out in the range of a draw ratio of 0.85 to 1.30, but 0.95 or more is more preferable in order to obtain a carbon fiber with high strength and high elastic modulus. This flameproofing treatment is to obtain flameproofed fibers having a fiber density of 1.3 to 1.5 g / cm ³ , and the tension (stretch distribution) at the time of flameproofing is not particularly limited.

<First carbonization treatment>
The flame-resistant fiber can be carbonized by employing a conventionally known method. For example, the temperature is gradually raised in a first carbonization furnace at 300 to 800 ° C. in a nitrogen atmosphere, and the first carbonization in the first stage is performed under tension by controlling the tension of the flameproof fiber.

<Second carbonization treatment>
In order to promote further carbonization and graphitization (high crystallization of carbon), the temperature is gradually increased in a second carbonization furnace at 800 to 1500 ° C. in an inert gas atmosphere such as nitrogen, and the first carbonization is performed. Firing is performed by controlling the tension of the fiber.

<Third carbonization treatment>
Also in the third carbonization step, the temperature is gradually raised in an inert gas atmosphere such as nitrogen and the tension of the second carbonized fiber is controlled and fired.

  The firing temperature is preferably kept at 1600 ° C. to 2000 ° C., more preferably 1800 ° C. to 2000 ° C. in the maximum temperature range.

  In each carbonization furnace, it is not preferable to introduce fibers rapidly from the vicinity of the furnace entrance, for example, abruptly at the maximum temperature, because many surface defects and internal defects are generated. Further, if the residence time becomes longer than necessary at a high temperature portion in the furnace, graphitization proceeds excessively, and brittle carbon fibers are obtained, which is not preferable.

<Surface oxidation treatment>
In order to remove the carbon layer having defects from the carbon fibers having invisible defects as described above, the third carbonized fiber is subsequently subjected to a plurality of stages of surface oxidation treatment by electrolytic oxidation in nitric acid, Preferably it is performed in 2 to 5 stages. Of the plurality of stages, the surface oxidation treatment of the first stage is performed at an electric quantity of 50 to 270 c / g, preferably 50 to 120 c / g. The amount of electricity throughout the plurality of stages, that is, the total amount of electricity is preferably 130 to 320 c / g.

  For the surface oxidation treatment at each stage, an electrolytic treatment apparatus is used in which two tanks each having an anode and a cathode arranged in opposite directions are set as one set. The concentration of nitric acid is preferably in the range of 0.1 to 2.0N, and more preferably in the range of 0.5 to 1.5N.

  In the surface oxidation treatment, if the amount of electricity processed and / or the total amount of electricity in the first stage is too small, the electric resistance ratio (A / B) of the obtained carbon fiber becomes a large value, and the measured length of the single fiber This is not preferable because the absolute value of the slope (a) in the relational expression obtained by the length (X) and the strength (Y) becomes a large numerical value and / or the strand strength decreases.

  On the other hand, in the surface oxidation treatment, when the amount of electricity processed and / or the total electricity in the first stage is excessive, the indent surface modulus of the obtained carbon fiber by SPM measurement is a small value, and the measured length of the single fiber Since the absolute value of the slope (a) in the relational expression obtained by (X) and strength (Y) is a large numerical value and / or the strand strength is lowered, it is not preferable.

<Sizing process>
The third carbonized fiber is subsequently subjected to a sizing process. 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 adhesion amount is preferably 0.3 to 2.6% by mass. The sizing agent is generally exemplified by an epoxy resin and a urethane resin, but is not particularly limited.

  The carbon fiber obtained in this manner has wrinkles oriented in the fiber axis direction on the surface, so when combined with a matrix material to form a composite material, it functions as a reinforcing material with good adhesion to the matrix material. To do. Moreover, this carbon fiber is a fiber with less fuzz and yarn breakage in addition to high resin-impregnated strand strength, resin-impregnated strand elastic modulus, and high density.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. Moreover, the processing method in each Example and a comparative example and the evaluation method about the physical property of carbon fiber were implemented with the following method.

<Specific gravity>
Measured by Archimedes method. The sample fiber was degassed in acetone and measured.

<Strand strength, strand elastic modulus>
About the carbon fiber strand for evaluation, strength and elastic modulus were measured by the method prescribed in JIS R7601.

<Indented surface modulus by SPM>
The indentation surface modulus by SPM was measured by the following method.

  The evaluation carbon fiber strand was cut into several mm. This was dispersed in ethanol and dropped onto a mica plate. The carbon fiber was fixed on a mica plate by air drying, and the surface indent was measured with a scanning probe microscope Nano Scope IIIa (SPM manufactured by DI). The modulus of the obtained data was calculated using the attached software.

  The probe used was # 9.

<Inclination (a) in the relational expression obtained from measured length (X) and strength (Y) of single fiber>
A single fiber was taken out from the carbon fiber strand for evaluation, and the strength was measured in accordance with JIS7606. Strength measurement was performed with the measured length (X) of the single fiber being 3, 5, 10, 50 mm, and the average value of n = 20 was defined as the single fiber strength (Y). The slope (a) was determined for a straight line obtained by taking the logarithmic value [Ln (X)] of the measured length of the fiber on the horizontal axis and the carbon fiber strength (Y) on the vertical axis.

<Compressive strength of single fiber in transverse direction>
A single fiber was taken out from the carbon fiber strand for evaluation, and a sample in which the single fiber was fixed on a slide glass was produced. About this sample, using a micro compression tester “MCTM-200” manufactured by Shimadzu Corporation, using a flat 50 μm indenter, the compression strength is measured at a load speed of 0.071 mN / sec (7.25 mgf / sec), The average value of n = 5 was defined as the compressive strength in the transverse direction of the single fiber.

  The compressive strength in the transverse direction of the single fiber means the compressive strength in the direction perpendicular to the fiber axis direction of the single fiber. This compressive strength is reflected in the post-impact compressive strength (CAI) and compressive properties of the composite material when a composite material is produced using the evaluation carbon fiber.

Example 1
A copolymer spinning stock solution of 95% by mass of acrylonitrile / 4% by mass of methyl acrylate / 1% by mass of itaconic acid is wet-spun, washed with water, dried, drawn and oiled to obtain an acrylic precursor fiber having a fiber diameter of 9.1 μm. Obtained. This precursor fiber was subjected to flame resistance treatment in heated air in which the maximum temperature range of the hot-air circulation type flame resistance furnace was set to 250 ° C. to obtain flame resistant fibers.

  This flame-resistant fiber was subjected to a first carbonization treatment by passing through a temperature range of 300 to 800 ° C. in an inert atmosphere of the first carbonization furnace.

  The first carbonized fiber was subjected to a second carbonization treatment by passing through a temperature range of 800 to 1500 ° C. in an inert atmosphere of a second carbonization furnace.

  Further, the second carbonized fiber was subjected to a third carbonization treatment by passing it through a temperature range of a maximum temperature of 1850 ° C. in an inert atmosphere of a third carbonization furnace.

  Next, in this third carbonization-treated fiber, in the surface oxidation treatment using a nitric acid aqueous solution of 30 ° C. and a concentration of 1.0 N as an electrolytic solution (treatment agent), the total number of treatment steps is two steps. The surface oxidation treatment was performed at 70 c / g and a total processing electricity of 150 c / g.

  Subsequently, a sizing agent is applied and dried by a known method, and the strand strength, strand elastic modulus, specific gravity, electrical resistance value (A), (B), electrical resistance value ratio (A / B), monofilament shown in Table 1 A carbon fiber having a slope (a) in the relational expression obtained from the measured length (X) and strength (Y) was obtained. As a result, good physical properties were obtained as carbon fibers for composite materials.

Examples 2-5 and Comparative Examples 1-4
Except that the third carbonized fiber obtained in Example 1 was treated under the conditions shown in Table 1, the surface oxidation treatment and sizing treatment were performed in the same manner as in Example 1, and the carbon fibers having physical properties shown in Table 1 were obtained. Obtained.

  As a result, as shown in Table 1, the carbon fibers obtained in Examples 2 to 5 had good physical properties as carbon fibers for composite materials as in Example 1. Moreover, the carbon fiber obtained in Example 2 has a high compressive strength of the single fiber in the transverse direction of 1280 MPa. From this compressive strength, it can be seen that good physical properties were obtained as a carbon fiber for a composite material.

  On the other hand, the total number of processing stages and the total amount of processing electricity in Comparative Examples 1 to 3 are the same as those in Examples 1, 3, and 5, respectively, but the amount of processing electricity in the first stage is as small as 30 c / g or 40 c / g. Met. As a result, all of the obtained carbon fibers have a large electrical resistance ratio (A / B), a slope (a) in the relational expression obtained from the measured length (X) and strength (Y) of the single fiber. The absolute value of was a large value, the strand strength was lowered, and the carbon fiber for the composite material was not a good physical property.

  In Comparative Example 4, an aqueous solution of ammonium sulfate was used as the electrolytic solution (treatment agent). As a result, the obtained carbon fiber has a large absolute value of the slope (a) in the relational expression obtained by the numerical value having a large indent surface modulus by SPM measurement and the measured length (X) and strength (Y) of the single fiber. It became a numerical value, the strength decreased, and it was not a good physical property as a carbon fiber for a composite material.

Comparative Examples 5-10
Except that the second carbonized fiber obtained in Example 1 was treated under the conditions shown in Table 1, the third carbonization treatment, the surface oxidation treatment, and the sizing treatment were performed in the same manner as in Example 1, and Table 1 Carbon fibers having the physical properties shown were obtained.

  In Comparative Example 5, the third carbonization treatment temperature was low. As a result, the obtained carbon fiber had a small indent surface modulus by SPM measurement, the elastic modulus was lowered, and the carbon fiber for the composite material was not a good physical property.

  In Comparative Examples 6 to 7, the third carbonization treatment temperature is high, and the total number of processing stages and the total amount of electricity processed are the same as those in Examples 1 to 5, but the amount of electricity processed in the first stage is 20 c / g. It was. As a result, all of the obtained carbon fibers had high strand strength, but had a large electrical resistance value ratio (A / B). In addition, the carbon fiber obtained in Comparative Example 6 has a large absolute value of the slope (a) in the relational expression obtained from the measured length (X) and strength (Y) of the single fiber, and is for composite materials. It was not a good physical property as a carbon fiber. The carbon fiber obtained in Comparative Example 7 had a low compressive strength in the transverse direction of a single fiber of 1100 MPa, and was not a good physical property as a carbon fiber for a composite material.

  In Comparative Example 8, the third carbonization temperature was high and the total number of processing stages and the total amount of electricity processed were the same as those in Examples 1 to 5, but the amount of electricity processed in the first stage was 280 c / g. As a result, although the obtained carbon fiber had high strand strength, the indent surface modulus by SPM measurement was a small numerical value, and it was obtained with the measured length (X) and strength (Y) of the single fiber. The absolute value of the slope (a) in the relational expression was a large numerical value, and the physical properties were not good as a carbon fiber for composite materials.

  In Comparative Example 9, the third carbonization treatment temperature, the total number of treatment stages, and the amount of electricity processed in the first stage were the same as those in Comparative Examples 6 to 7, but the amount of electricity treated was 100 c / g. As a result, the obtained carbon fiber has a large electrical resistance value ratio (A / B), the absolute value of the slope (a) in the relational expression obtained from the measured length (X) and strength (Y) of the single fiber. The value was a large value, the strand strength was lowered, and the physical properties were not good as a carbon fiber for a composite material.

  In Comparative Example 10, the third carbonization treatment temperature, the total number of treatment stages, and the amount of electricity processed in the first stage were the same as those in Comparative Example 8, but the amount of electricity treated in total was 350 c / g. As a result, the obtained carbon fiber has a reduced strand strength, a small indent surface modulus by SPM measurement, and a slope in the relational expression obtained from the measured length (X) and strength (Y) of the single fiber. The absolute value of (a) was a large value, and it was not a good physical property as a carbon fiber for composite materials.

It is a conceptual diagram which shows an example of the electrical resistance value measuring apparatus of a carbon fiber strand, (A) is a conceptual diagram in the case of measuring an electrical resistance value (A) without using an electrically conductive paste, (B) is conductive It is a conceptual diagram in the case of measuring an electrical resistance value (B) using a conductive paste.

Explanation of symbols

2 Carbon fiber strand for evaluation 4, 6 Electrode for applied voltage 8, 10 Voltage, detection end for current measurement 12 Voltage, current measurement device 14, 16 Conductive paste

Claims (2)

A carbon fiber having a strength of 6100 MPa or more, an elastic modulus of 340 GPa or more, and a specific gravity of 1.76 or more,
Ratio between the electrical resistance value (A) obtained from the slope obtained from the applied current-applied voltage measurement and the electrical resistance value (B) obtained from the slope obtained from the applied current-applied voltage measurement using a conductive paste ( A / B) is A / B ≦ 1.30
The relational expression y = aLn (X) + b obtained from the measured length (X) and strength (Y) of the single fiber
The slope (a) is 0 ≧ a> −650
And an indentation surface modulus measured by a scanning probe microscope (SPM) is in the range of 8 to 11.5 GPa. Acrylic precursor fibers obtained by spinning a spinning dope from a spinneret are heat-treated in heated air at 200 to 280 ° C. to obtain flame-resistant fibers. The obtained flame-resistant fibers are heated in an inert gas atmosphere at a temperature. After performing carbonization treatment at 1600 to 2000 ° C., when performing surface oxidation treatment by electrolytic oxidation in nitric acid in a plurality of stages, the first stage surface oxidation treatment is performed with an electric quantity of 50 to 120 c / g. The method for producing a carbon fiber according to claim 1.

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