JP2009114557A - Uniformly surface-treated carbon fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber that has a surface uniformly treated by electrolytic oxidation and excellent surface adhesiveness, and to provide a method for producing the same. <P>SOLUTION: The method for producing a carbon fiber includes applying a voltage between a traveling carbon fiber as a positive terminal and a negative terminal by an electrolytic oxidation apparatus having an electrolytic bath 3 storing an electrolyte 7, a positive terminal roller 11 arranged above the water surface of the electrolyte 7, immersion rollers 13 and 15 for continuously immersing a carbon fiber 9 passed from the positive terminal roller in the electrolyte in the electrolytic bath, a guide roller 17 that pulls up the carbon fiber 9 from the electrolyte 7 and is arranged above the water surface of the electrolyte, the negative terminal 5 that is immersed in the electrolyte 7 in the electrolytic bath 3 and arranged on the rear side of a bath immersion position A to the electrolyte of carbon fiber in the traveling direction of carbon fiber and carrying out electrolytic oxidation of carbon fiber in a surface treatment electric quantity in a range of 3 C/g-8.5 C/g. The carbon fiber obtained by the method is a carbon fiber having a reduced treatment unevenness between the inside and the outside of fiber bundle and having a high impregnation with a matrix resin. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a carbon fiber excellent in interfacial adhesion obtained by an electrolytic oxidation method and a method for producing the same.

  Carbon fiber composites reinforced with carbon fibers of thermosetting resins and thermoplastic resins have excellent features such as high tensile strength and tensile modulus, and excellent heat resistance and fatigue properties. Widely used in fields such as aviation and space.

  Carbon fiber is manufactured by heating raw fiber such as acrylic fiber to 200 to 300 ° C. in the air to make it flame resistant fiber, and then firing at 1000 ° C. or higher in an inert gas atmosphere.

  Mechanical properties such as strength and elastic modulus of the carbon fiber composite material are greatly influenced by the affinity and adhesion between the carbon fiber and the matrix resin. Therefore, after passing through the flameproofing step and the carbonization step, an oxidation treatment for introducing oxygen-containing functional groups into the surface of the carbon fiber is generally performed for the purpose of increasing the affinity with the matrix resin.

  As the oxidation treatment of the carbon fiber surface, it is known to treat by a method such as chemical liquid oxidation / electrolytic oxidation or gas phase oxidation in a liquid phase. Among these surface treatments, electrolytic oxidation treatment in a liquid phase has been widely adopted because of high productivity and uniform treatment. The liquid phase electrolytic oxidation treatment is a treatment method in which carbon fiber is electrolytically oxidized by applying a voltage between a carbon fiber as an anode and a negative electrode in an aqueous electrolyte solution.

  Carbon fibers are manufactured in a bundle shape of about 1,000 to 80,000 in the manufacturing process. Carbon fibers that have been electrolytically oxidized using an electrolytic oxidation treatment device under normal conditions have an insufficient oxidation state of the fibers located inside compared to the oxidation state of the fibers located outside the bundle, and the surface oxidation state varies. There is. When carbon fiber with non-uniform surface oxidation treatment is blended with the matrix resin, the adhesion between the part of the carbon fiber surface with few functional groups and the matrix resin is insufficient, and a composite material with high composite properties can be obtained. Absent.

  In order to solve the non-uniformity of the surface treatment, Japanese Patent Application Laid-Open No. 2002-38368 describes a treatment apparatus that uniformly oxidizes carbon fiber bundles. In this processing apparatus, a cathode tank is disposed between two anode tanks, and after impregnating carbon fiber with an electrolyte in the upstream anode tank, the cathode tank and the downstream anode tank are brought into contact with the liquid surface. The carbon fiber is oxidized by running the carbon fiber. This apparatus requires three electrolytic cells, and a simpler apparatus is required.

  In order to solve the non-uniformity of the surface treatment, methods have been proposed in which a voltage is intermittently applied to the carbon fiber bundle to improve the diffusion efficiency inside the carbon fiber bundle and anodize (Patent Documents 2 to 4). Such). Any of them leads to reduction of processing spots between the carbon fiber bundle inside and the outer periphery. However, in order to perform processing intermittently, the processing spots between the inside and the outer periphery of the carbon fiber bundle are reduced, but the improvement in the spots in the carbon fiber longitudinal direction and the machine width direction has not been achieved.

In Patent Document 5, the reduction rate, which is a value obtained by dividing the amount of reduced electricity by the sum of the amount of oxidized electricity and the amount of reduced electricity, is set to 0.001 to 0.5, and anodization and cathodic reduction on the carbon fiber surface It is described that a uniform treatment effect can be obtained by repeating periodically. However, the obtained fiber bundle has only a 30% variation in adhesive force indicated by the interfacial shear force, and the uniform treatment is insufficient.
JP 2002-38368 A (FIG. 1) JP 63-264967 A (Claims) JP-A-7-189113 (Claims) JP-A-1-298275 (FIG. 1) JP-A-10-266066 (Claims)

  An object of the present invention is to provide a carbon fiber and a method for producing the carbon fiber in which the surface is uniformly oxidized and carbon fibers exhibiting high composite properties when blended in a matrix resin are obtained.

  As a result of intensive studies, the present inventor has found that there is a certain relationship between the position of the negative electrode relative to the position of the carbon fiber in the electrolytic solution bathed in the electrolytic oxidation treatment apparatus and the oxidation treatment state of the carbon fiber surface. I found it. Furthermore, it was found that carbon fibers that had been subjected to surface treatment using a device in which the negative electrode position was provided at a predetermined position had very little variation in the oxidation state of the surface, and the present invention was completed. It was.

  That is, the present invention that solves the above problems is described below.

  [1] Surface oxygen concentration O / C measured by X-ray photoelectron spectroscopy is 0.05 to 0.15, and surface property Ipa of carbon fiber measured by cyclic voltammetry is 0.16 to 0.16. A carbon fiber having a variation of the carbon fiber surface treatment degree of 0.25, measured by a cyclic voltammetry method, of 6% or less.

  [2] An electrolytic bath in which an electrolytic solution is stored, an anode roller disposed above the electrolytic solution water surface of the electrolytic bath, and a carbon fiber that has passed through the anode roller are continuously fed into the electrolytic solution in the electrolytic bath. An immersion roller immersed in the electrolyte, a guide roller disposed above the surface of the electrolytic solution for pulling up the carbon fiber from the electrolytic solution, and immersed in the electrolytic solution in the electrolytic bath, into the electrolytic solution of the carbon fiber in the running direction of the carbon fiber And a negative electrode disposed on the rear side of the bathing position of the carbon fiber, and applying a voltage between the negative electrode with the traveling carbon fiber as an anode, and having a surface treatment quantity of electricity 3 to The method for producing carbon fiber according to [1], wherein the carbon fiber is electrolytically oxidized in a range of 8.5 C / g.

  [3] The carbon fiber production method according to [2], wherein the carbon fiber electrolytic oxidation treatment device is used, which is disposed below the carbon fiber that travels while the negative electrode is immersed in an electrolytic solution.

  In the electrolytic oxidation treatment apparatus used in the present invention, the negative electrode is disposed in the electrolytic cell on the rear side from the bathing position of the carbon fiber in the electrolytic solution in the running direction of the carbon fiber. As a result, the oxidation treatment of the carbon fiber is performed slowly, and the surface of the carbon fiber is uniformly oxidized. The carbon fiber bundle of the present invention, which is surface-treated with this apparatus, has very few treatment spots between the fibers present inside and the fibers present on the outer periphery. Since the voltage applied between the anode and the cathode of the apparatus is always constant, there are very few processing spots occurring between the fiber directions of the carbon fiber bundle. Furthermore, when a large number of carbon fiber bundles are run in parallel and simultaneously surface-treated, there is little variation in the surface treatment state between the carbon fibers. Since the carbon fiber of the present invention has little variation in the surface treatment state and high affinity with a resin, a carbon fiber composite material having high mechanical strength can be obtained by blending with a thermosetting resin or a thermoplastic resin.

  FIG. 1 shows a schematic configuration diagram of an example of an electrolytic oxidation treatment apparatus used in the present invention.

  In FIG. 1, 1 is an electrolytic oxidation treatment apparatus, and 3 is an electrolytic cell. The electrolytic cell 3 includes immersion rollers 13 and 15 and a negative electrode 5 inside. An electrolytic solution 7 such as sulfuric acid is stored in the electrolytic bath 3, and the lower side of the immersion rollers 13 and 15 and the negative electrode 5 are immersed in the electrolytic solution 7. The immersion rollers 13 and 15 have the same diameter and are attached at the same height.

  Above the electrolytic cell 3, an anode roller 11 is provided on the front side in the traveling direction of the carbon fiber 9, and a guide roller 17 is provided on the rear side. The anode roller 11 is a metal roller whose surface is positively charged, and an electrolytic current is supplied from a power source (not shown). After passing through the anode roller 11, the carbon fiber 9 is guided to the immersion rollers 13 and 15 and immersed in the electrolytic solution. Since the carbon fiber 9 has high conductivity, it acts as an anode in the electrolytic solution. When a voltage is applied between the anode roller 11 and the negative electrode 5, the surface of the carbon fiber is electrolytically oxidized, and oxygen-containing functional groups such as a carboxyl group and a carbonyl group are introduced to the carbon fiber surface. The carbon fiber 9 whose surface has been subjected to electrolytic oxidation treatment passes through the immersion rollers 13 and 15 and then is pulled up from the electrolytic solution 7 by the guide roller 17, and the electrolytic oxidation treatment is completed.

  In the electrolytic oxidation treatment apparatus 1, the negative electrode 5 is disposed behind the carbon fiber 9 where the carbon fiber 9 is immersed in the electrolytic solution 7 and behind the carbon fiber 9 where the carbon fiber 9 is immersed in the electrolytic solution. Has been. By disposing the negative electrode 5 behind the bathing position A, the oxidation reaction of the bathed carbon fiber becomes slow, and the surface of the carbon fiber is uniformly electrolytically oxidized.

  The position where the negative electrode 5 is disposed is not particularly limited as long as it is located behind the carbon fiber bathing position A in the running direction of the carbon fiber. It is preferable to adjust the position of the negative electrode 5 so that the carbon fiber passes over the negative electrode 5 after 3 to 20 seconds, more preferably after 8 to 20 seconds after entering the bath. The running speed of the carbon fiber is usually about 50 to 600 m / h.

  In the above description, the case where the upper side of the immersion rollers 13 and 15 is higher than the liquid level of the electrolytic solution has been described. However, the entire immersion roller may be completely submerged. From the viewpoint of preventing troubles caused by winding the roller, the upper side of the immersion rollers 13 and 15 is preferably higher than the liquid level. Specifically, the immersion rollers 13 and 15 are mounted such that the diameter thereof is preferably 50 to 80%, more preferably 60 to 70% higher than the liquid level.

  Examples of the electrolytic solution 7 used for the electrolytic oxidation treatment of carbon fiber include inorganic acids such as sulfuric acid, nitric acid and hydrochloric acid, inorganic hydroxides such as sodium hydroxide and potassium hydroxide, inorganic substances such as ammonium sulfate, sodium carbonate and sodium hydrogen carbonate. Examples include aqueous electrolyte solutions such as salts.

  As the carbon fiber to be subjected to electrolytic oxidation treatment in the present invention, any carbon fiber such as petroleum / coal pitch-based, rayon-based, lignin-based, etc. can be used in addition to polyacrylonitrile (PAN) -based carbon fiber.

  The carbon fibers 9 are usually manufactured in a bundle shape in which about 1000 to 80000 filaments having a diameter of 4 to 8 μm are gathered. In the processing apparatus of this invention, it is not limited to the said fiber diameter and the number of filaments, It is possible to process what kind of fiber diameter and number of filaments.

The amount of electricity applied to the carbon fiber 9 may be appropriately determined from the surface oxygen concentration ratio O / C and the Ipa value according to conditions such as the type of electrolyte used in the electrolytic solution 7 and the elastic modulus of the carbon fiber 9. For example, when an electrolytic oxidation treatment of carbon fiber having an elastic modulus of 24 ton / mm ² using an aqueous ammonium sulfate solution as an electrolytic solution, it is preferable that the amount of electricity applied to the carbon fiber is 3 to 8.5 C / g. It is more preferable to set it as 4-7 C / g.

  The electrolytic oxidation treatment temperature of the carbon fiber 9 is in the range of 10 to 80 ° C, but preferably 20 to 50 ° C.

  As an index for the surface treatment of the carbon fiber, it is preferable to manage it by the surface oxygen concentration ratio (O / C) of the carbon fiber that can be measured using X-ray photoelectron spectroscopy (ESCA). When the carbon fiber bundle of the present invention is blended with a thermosetting resin to form a composite material, it is preferable to perform electrolytic oxidation treatment so that O / C is 0.05 to 0.15.

  If the O / C is lower than 0.05, the surface treatment effect is not sufficient, the adhesiveness with the matrix resin is lowered, and the composite material cannot obtain stable mechanical properties. On the other hand, if O / C is higher than 0.15, the surface of the carbon fiber is excessively oxidized and the fiber itself becomes brittle, so that stable mechanical properties cannot be obtained.

  Surface oxygen concentration O / C is 0.05 to 0.15, Ipa measured by the cyclic voltammetry method is 0.16 to 0.25, surface measured by the method described in Examples described later The carbon fiber of the present invention having a treatment degree variation of 6% or less can be obtained by performing a surface treatment using the above-described electrolytic oxidation treatment apparatus with a surface treatment electricity of 3 to 8.5 C / g.

  The carbon fiber bundle of the present invention has a carbon fiber surface property Ipa value of 0.16 to 0.25, preferably 0.16 to 0.22, and more preferably 0.16 to 0.20. When Ipa is lower than 0.16, the surface treatment effect is not sufficient, the adhesiveness with the matrix resin is lowered, and the composite material cannot obtain stable mechanical properties. On the other hand, if Ipa is higher than 0.25, the surface of the carbon fiber is excessively oxidized and the fiber itself becomes brittle, so that stable mechanical properties cannot be obtained.

  The carbon fiber bundle of the present invention has a carbon fiber surface treatment variation of 6% or less measured by a cyclic voltammetry method, preferably 5% or less, more preferably 4% or less. If the dispersion of the carbon fiber surface treatment degree is higher than 6%, the adhesion between the part of the carbon fiber surface with few functional groups and the matrix resin becomes insufficient, the adhesion state with the matrix resin becomes poor, and excellent mechanical properties. Cannot be obtained. The smaller the variation in the degree of carbon fiber surface treatment, the higher the mechanical strength when blended in the matrix resin. Therefore, although the lower limit is not particularly set for the variation in the degree of surface treatment, the carbon fiber bundle obtained by the surface treatment using the above apparatus is about 2% when the variation in the degree of surface treatment is the smallest.

  The surface treatment of the carbon fiber strand was performed by the methods of Examples and Comparative Examples shown below. In each of the examples and comparative examples, the carbon fiber after electrolytic oxidation treatment was subjected to the surface oxygen concentration ratio O / C, the carbon fiber surface property Ipa, the variation in the carbon fiber surface treatment degree, the strand strength and elasticity of the carbon fiber. The rate and IPSS were measured.

[Measurement of surface oxygen concentration ratio O / C]
The measurement was performed using an X-ray photoelectron spectrometer (ESCA JPS-9000MX) manufactured by JEOL Ltd. The carbon fiber strand was put in a measurement chamber whose pressure was reduced to 10 ⁻⁶ Pa, and irradiated with X-rays generated under conditions of an electron beam acceleration voltage of 10 kV and 10 mA using Mg as a counter electrode. The area ratio was calculated from the spectrum of photoelectrons generated from oxygen atoms and carbon atoms, and was defined as the surface oxygen concentration ratio O / C.

[Measurement of carbon fiber surface property Ipa by cyclic voltammetry]
A phosphoric acid aqueous solution having an electric conductivity of 90 mS / cm was prepared using phosphoric acid. An Ag / AgCl electrode was used as the reference electrode, a platinum electrode having a sufficient surface area as the counter electrode, and a carbon fiber bundle as the working electrode.

  The potential operation range was −0.2 V to 0.8 V, and the potential operation speed was 5 mV / sec. A potential-current curve was drawn by sweeping three times or more. When the potential-current curve was stabilized, the current value was read with respect to the Ag / AgCl electrode with the potential at +0.4 V as the standard.

The carbon fiber surface property Ipa was calculated according to the following formula.
Ipa [μA / cm ² ] = current value [μA] / sample length [cm] × {4π, basis weight [g / m], filament number / density [g / cm ³ ]} ^1/2

[Variation in the degree of carbon fiber surface treatment]
In order to obtain the variation Ipa of the carbon fiber surface treatment degree in the present invention, the carbon fiber bundle was divided into two or more, and Ipa was measured for each. From the Ipa measurement value of each split carbon fiber bundle, the ratio of the standard deviation to the average value, that is, the CV value was obtained as Ipa variation.

[Measurement method of strand strength and elastic modulus of carbon fiber]
The resin-impregnated strand strength of the carbon fiber was measured by the method defined in JIS R7601. The density was measured by Archimedes method, and the sample fiber was defoamed in acetone and measured.

[In-plane shear stress (IPSS)]
Moreover, using the carbon fiber bundle after the electrolytic oxidation treatment, the carbon fiber bundle was aligned in one direction to obtain a carbon fiber sheet. The obtained carbon fiber sheet was impregnated with an epoxy resin (manufactured by Toho Tenax Co., Ltd., # 135, curing temperature 180 ° C.) and then heated to 80 to 100 ° C. to prepolymerize the epoxy resin to obtain a unidirectional prepreg. . Subsequently, the obtained eight unidirectional prepregs were laminated so that the fiber direction was [+ 45 / −45 / −45 / + 45 / + 45 / −45 / −45 / + 45] in order, and the content of the carbon fiber bundle Produced a fiber reinforced plastic sheet having a volume content of 60%.

  Using the obtained test piece, in-plane shear stress (IPSS) was measured according to a ± 45 ° direction tensile method described in JIS K 7079.

Example 1
The electrolytic treatment of the carbon fiber strand (400 tex, the number of filaments: 6K) was performed using the electrolytic oxidation treatment apparatus shown in FIG. The electrolytic cell having a length of 3400 mm, a width of 3600 mm, and a depth of 250 mm was used, and the distance between the immersion rollers 13 and 15 was 2800 mm. A negative electrode 5 of 100 cm × 3600 cm was disposed 2 cm below the dipping rollers 13 and 15 so that the longitudinal direction was perpendicular to the fiber axis direction of the carbon fiber strand. The electrolyte used was 10% ammonium sulfate. A plurality of carbon fiber strands arranged in parallel were supplied to the treatment apparatus, and the surface treatment electricity was 4.75 C / g, and electrolytic oxidation was performed under the conditions shown in Table 1. The immersion time of the carbon fiber in the electrolytic solution was 22 seconds. The time required for the carbon fiber strand to reach the upper side of the negative electrode 5 after entering the bath was 18 seconds.

Example 2
The carbon fiber strand was subjected to electrolytic oxidation treatment in the same manner as in Example 1 except that the surface treatment electricity was 3 C / g and electrolytic oxidation was performed.

Example 3
The carbon fiber strand was subjected to electrolytic oxidation treatment in the same manner as in Example 1 except that the surface treatment electricity was 6 C / g and electrolytic oxidation was performed.

Example 4
The carbon fiber strand was subjected to electrolytic oxidation treatment in the same manner as in Example 1 except that the surface treatment electricity was 8 C / g and electrolytic oxidation was performed.

Comparative Example 1
The carbon fiber strand was subjected to electrolytic oxidation treatment in the same manner as in Example 1 except that the surface treatment electricity was 9 C / g and electrolytic oxidation was performed.

Comparative Example 2
The surface treatment electricity amount was 4.75 C / g, and the carbon fiber strand was subjected to electrolytic oxidation treatment using the apparatus shown in FIG. The negative electrode 5 was disposed in front of the bathing position A in the running direction of the carbon fiber so that the horizontal distance from the bathing position A was 100 mm.

Comparative Example 3
The carbon fiber strand was subjected to electrolytic oxidation treatment in the same manner as in Comparative Example 2 except that the surface treatment electricity was 9 C / g and electrolytic oxidation was performed.

Comparative Example 4
The carbon fiber strand was subjected to electrolytic oxidation treatment in the same manner as in Comparative Example 2 except that the surface treatment electricity was 3 C / g and electrolytic oxidation was performed.

It is a schematic block diagram which shows an example of the electrolytic oxidation processing apparatus used by this invention. It is a schematic block diagram which shows the electrolytic oxidation treatment apparatus used in Comparative Examples 2-4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolytic oxidation processing apparatus 3 Electrolytic tank 5 Negative electrode 7 Electrolytic solution 9 Carbon fiber 11 Anode roller 13, 15 Immersion roller 17 Guide roller A Bathing position

Claims (3)

The surface oxygen concentration O / C measured by X-ray photoelectron spectroscopy is 0.05 to 0.15, and the surface property Ipa of the carbon fiber measured by cyclic voltammetry is 0.16 to 0.25. The carbon fiber has a variation in the degree of carbon fiber surface treatment measured by a cyclic voltammetry method of 6% or less. An electrolytic bath in which the electrolytic solution is stored, an anode roller disposed above the electrolytic solution water surface of the electrolytic bath, and carbon fibers that have passed through the anode roller are continuously immersed in the electrolytic solution in the electrolytic bath. An immersion roller, a guide roller disposed above the electrolytic solution water surface for pulling up the carbon fiber from the electrolytic solution, and immersed in the electrolytic solution in the electrolytic bath and bathed in the electrolytic solution of the carbon fiber in the running direction of the carbon fiber A carbon fiber electrolytic oxidation treatment apparatus having a negative electrode disposed on the rear side of the position, applying a voltage between the negative electrode with the traveling carbon fiber as an anode, and a surface treatment amount of electricity of 3 to 8.5 C / The carbon fiber production method according to claim 1, wherein the carbon fiber is subjected to electrolytic oxidation treatment in a range of g. The manufacturing method of the carbon fiber of Claim 2 using the electrolytic oxidation treatment apparatus for carbon fibers arrange | positioned under the carbon fiber which a negative electrode is immersed in electrolyte solution and drive | works.

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