JP5621253B2 - Carbon fiber bundle and method for producing the same - Google Patents

Description

  The present invention relates to an electrolytically oxidized carbon fiber bundle and a method for producing the same.

Composite materials using carbon fiber bundles as reinforcements are lightweight and have excellent strength and elastic modulus, so applications have been developed over a wide range of fields as components for sports and leisure goods or as spacecraft components. It has been put into practical use.
The carbon fiber bundle is usually impregnated into a matrix resin and molded as a composite material. Conventionally, the carbon fiber bundle has not always had sufficient adhesion to the matrix resin.
Therefore, in order to activate the fiber surface of the carbon fiber bundle in order to improve the adhesion between the carbon fiber bundle and the matrix resin, the carbon fiber bundle is subjected to surface treatment such as chemical oxidation treatment, vapor phase oxidation treatment, electrolytic oxidation treatment, etc. Often given. Among these surface treatment methods, the electrolytic oxidation treatment method is a practical surface treatment method that has good operability and easy reaction control.

  In recent years, with the expansion of applications and demand for composite materials, for the purpose of improving the productivity of composite materials, the number of single fibers constituting precursor fibers, which are precursor fibers of carbon fibers, tends to increase. In addition, the number of yarns of carbon fiber bundles to be fired at the same time is increasing, and accordingly, surface treatment uniformity is also required.

However, when carbon fiber bundles having a large number of single fibers are subjected to electrolytic oxidation treatment, single fibers located on the surface (outer peripheral portion) side of the fiber bundle are subjected to electrolytic oxidation treatment more than single fibers located on the inner side of the fiber bundle. Therefore, the carbon fiber bundle is not subjected to electrolytic oxidation treatment on the inside and outside of the carbon fiber bundle, and the adhesiveness and the characteristics (particularly strength) of the composite material tend to decrease. That is, oxidation is difficult to proceed with single fibers located on the inner side of the fiber bundle, and oxidation proceeds too much with single fibers located on the outer peripheral side of the fiber bundle. Therefore, the single fiber located on the inner side of the fiber bundle is insufficient in electrolytic oxidation treatment and has a low adhesive force with the matrix resin. On the other hand, since the single fiber located on the outer peripheral side of the fiber bundle is sufficiently oxidized, the adhesive strength with the matrix resin can be sufficiently obtained, but the fiber strength tends to be lowered due to excessive oxidation.
Thus, the carbon fiber bundle with a large number of single fibers is difficult to be uniformly electrolytically oxidized up to the inside of the fiber bundle, and as a result, when it is a composite material, the adhesion with the matrix resin is insufficient, And it was difficult to demonstrate sufficient strength.

  By the way, as an effect by the electrolytic oxidation treatment, not only the improvement of the adhesion of the carbon fiber bundle to the matrix resin but also the improvement of the impregnation property (wetting property) of the matrix resin to the carbon fiber bundle is important. If the impregnation property of the matrix resin to the carbon fiber bundle is not uniform inside and outside the fiber bundle, the fiber bundle is likely to have a part where there is no interface for transmitting the strength of the carbon fiber, which adversely affects the properties of the composite material. It becomes.

Many methods for surface treatment of carbon fiber bundles by electrolytic oxidation have been reported so far.
For example, in Patent Document 1, the carbon fiber used as the anode is subjected to electrolytic oxidation treatment by intermittently supplying power in an acidic electrolyte solution, specifically, energizing for 5 seconds and repeating 60 seconds for 5 seconds. And the method of surface-treating carbon fiber is disclosed.
According to Patent Document 1, by intermittently supplying power, the amount of bonded oxygen of the carbon fiber can be increased and the bonded state of oxygen can be controlled. As a result, the compatibility with the matrix resin is improved and the strength is increased. A large composite material can be manufactured.

Further, in Patent Document 2, the electrolytic oxidation treatment is performed by setting the applied voltage to 10 V or more, setting the pulse feeding interval so that the feeding time is 0.02 seconds or less, and the feeding stop time is 5 times or more of the feeding time. Thus, a method for surface treatment of carbon fibers is disclosed.
According to Patent Document 2, by intermittently supplying power to the carbon fiber, OH ⁻ ions are replenished (non-energized) and electrolytic oxidation (energized) to the center of the carbon fiber alternately. As a result, since OH ⁻ ions are sufficiently present in the central portion of the carbon fiber, an oxidation reaction occurs and a uniform treatment can be obtained.

In Patent Document 3, the treatment current waveform is a rectangular wave composed of a current value A in which the carbon fiber surface potential is positive with respect to the reference electrode and a current value B in which the carbon fiber surface potential is negative, and the application of the current values A and B A method for surface-treating carbon fibers by setting the time to a predetermined value is disclosed.
According to Patent Document 3, the concentration polarization layer formed on the carbon fiber surface can be thinned by intermittently changing the surface potential of the carbon fiber, and the lines of electric force are uniformly dispersed on the surface of the carbon fiber. Since it becomes easy, it becomes difficult to form a weak layer on the surface. Further, by making the carbon fiber surface potential negative, it is possible to remove the generated minute amount of the fragile layer. In addition, the electrolytic solution easily diffuses into the fiber bundle. The decrease in the adhesive strength between the carbon fiber and the matrix resin is considered to be caused by a fragile layer formed on the surface of the carbon fiber, so that the formation of the fragile layer is suppressed or the generated fragile layer is removed. 3 can improve the adhesive force between the carbon fiber and the matrix resin.

In Patent Document 4, carbon is obtained by periodically repeating anodization and cathodic oxidation so that the reduction rate (= reduction electricity amount / (oxidization electricity amount + reduction electricity amount)) is 0.001 to 0.5. A method for surface treating fibers is disclosed.
According to Patent Document 4, a uniform surface treatment effect can be obtained by periodically repeating anodization and cathodic oxidation at a specific reduction rate.

Patent Document 5 discloses a method for surface-treating a carbon fiber bundle by subjecting a carbon fiber bundle having 24,000 or more single fibers as an anode to electrolytic oxidation treatment for 4 seconds or more with an electric quantity of 7.5 to 45 C / g. Is disclosed.
According to Patent Document 5, it is said that a carbon fiber bundle with little variation can be obtained by electrolytic oxidation treatment with an electric quantity of 7.5 to 45 C / g for 4 seconds or more.

JP-A 63-264967 JP-A-1-298275 JP-A-7-207573 Japanese Patent Laid-Open No. 10-266066 JP 2002-38368 A

  However, in the surface treatment methods described in Patent Documents 1 to 5, it is not always easy to perform the electrolytic oxidation treatment uniformly to the inside of the fiber bundle. In particular, the carbon fiber bundle obtained by the surface treatment method described in Patent Document 4 has a variation in adhesive strength represented by an interfacial shear force of only about 30% or less, and the variation in electrolytic oxidation treatment was significant.

Patent Documents 1 and 2 are methods for surface-treating a carbon fiber bundle having a small number of single fibers (about 4000 to 6000) constituting a single fiber bundle. Accordingly, when the surface treatment is performed on a carbon fiber bundle in which the number of single fibers is further increased, a sufficient effect cannot be obtained, and it is difficult to uniformly perform electrolytic oxidation treatment to the inside of the fiber bundle.
Moreover, in patent document 3, the surface treatment is performed for the carbon fiber bundle whose number of single fibers is 12,000, and compared with patent documents 1 and 2, the number of single fibers is large. However, in recent years, the number of single fibers has been further increased in order to improve the production efficiency of carbon fibers, and so-called large tow carbon fiber bundles made of 24,000 or more single fibers have been produced. When the surface treatment method described in Patent Document 3 is applied to such a large tow type carbon fiber bundle, it is difficult to uniformly perform electrolytic oxidation treatment to the inside of the fiber bundle.

Furthermore, in Patent Document 4, carbon fiber bundles having 18000 single fibers and 24000 single fibers are respectively surface-treated. In any case, the dispersion of the adhesive strength between single fibers is 24%, and the fiber bundles It is not possible to carry out the electrolytic oxidation treatment even to the inside.
Moreover, in patent document 5, although the carbon fiber bundle whose number of single fibers is 48000 is surface-treated, it does not mention about processing the carbon fiber bundle more than that. Further, the amount of electricity at the time of electrolytic oxidation treatment is as high as 7.5 to 45 C / g, and when the amount of electricity is lowered, it is difficult to perform electrolytic oxidation treatment sufficiently and uniformly to the inside of the fiber bundle.

The present invention has been made in view of the above circumstances, and even when the number of single fibers is large and the electrolytic oxidation treatment is performed with a small amount of electricity, when the composite material is used, the adhesiveness with the matrix resin is good and sufficient. It is an object to provide a carbon fiber bundle that can exhibit a sufficient strength.
It is another object of the present invention to provide a method for producing a carbon fiber bundle that can perform electrolytic oxidation treatment uniformly even inside the fiber bundle even when the number of single fibers is large and the treatment is performed with a small amount of electricity.

As a result of intensive studies, the inventors have determined the CV value of the surface oxygen concentration of the carbon fiber bundle subjected to electrolytic oxidation treatment and the CV value of the current value flowing per unit area, thereby increasing the number of single fibers, Further, it has been found that even when the electrolytic oxidation treatment is performed with a small amount of electricity, the adhesiveness with the matrix resin is improved when the composite material is formed, and sufficient strength can be exhibited.
Therefore, the present inventors paid attention to the relationship between each CV value of the carbon fiber bundle and the conditions of the electrolytic oxidation treatment, particularly the conditions such as the power feeding method, the amount of electricity, and the treatment time. And by optimizing the conditions of electrolytic oxidation treatment, the diffusion efficiency of the electrolytic solution is improved. As a result, even when processing with a large number of single fibers and a small amount of electricity, the inside of the fiber bundle can be electrolyzed uniformly. It has been found that it can be subjected to oxidation treatment, and can suppress adhesion and impregnation spots with the matrix resin, and the present invention has been completed.

That is, the carbon fiber bundle of the present invention is composed of 49000-175000 single fibers, and satisfies the following conditions (a) and (b).
(A): CV value {(standard deviation of surface oxygen concentration / average value of surface oxygen concentration) × 100} of surface oxygen concentration measured by X-ray photoelectron spectroscopy is 8% or less.
(B): CV value {(standard deviation of ipa value / average value of ipa value) × 100} of the current value (ipa value) flowing per unit area measured by the cyclic voltammetry method is 5% or less.

Moreover, the manufacturing method of the carbon fiber bundle of the present invention uses a carbon fiber having a tow width of 8 mm or more in the form of a bundle of 49000-175000 single fibers as an anode, and the tension per 24,000 single fibers is 4 kg or less. Then, electricity is directly applied to the carbon fiber via a roll-shaped anode by a contact power feeding method , and then the carbon fiber is led to an electrolytic cell filled with an electrolyte and provided with a cathode, It is characterized by carrying out electrolytic oxidation treatment for 5 seconds or more by running while contacting .

Even if the carbon fiber bundle of the present invention has a large number of single fibers and is electrolytically oxidized with a small amount of electricity, when it is made into a composite material, it has good adhesiveness with a matrix resin and can exhibit sufficient strength. .
In addition, according to the method for producing a carbon fiber bundle of the present invention, even when the number of single fibers is large and the treatment is performed with a small amount of electricity, the inside of the fiber bundle can be uniformly electrolytically oxidized. Moreover, when it is set as a composite material, the carbon fiber bundle which has favorable adhesiveness with matrix resin and can exhibit sufficient intensity | strength can be manufactured.

It is the schematic which shows an example of the electrolytic oxidation apparatus used for this invention. It is the schematic which shows an example of the electrolytic oxidation apparatus which employ | adopted the non-contact electric power feeding system.

Hereinafter, the present invention will be described in detail.
The carbon fiber bundle of the present invention consists of single fibers of 49000 to 17500 or less, and can be obtained by subjecting carbon fibers in the form of bundles to surface treatment by electrolytic oxidation treatment.
Hereinafter, the carbon fiber in the form of a bundle of single fibers that is electrolytically oxidized in the present invention is referred to as a “fiber bundle before treatment”.

The pre-treatment fiber bundle is obtained by firing the precursor fiber bundle. As the firing method, a known method can be adopted, and examples thereof include a method in which the precursor fiber bundle is subjected to flame resistance treatment in a flame resistance furnace, and then pre-carbonization treatment and carbonization treatment in a carbonization furnace.
Examples of the precursor fiber bundle include polyacrylonitrile-based, pitch-based, rayon-based, and the like, and polyacrylonitrile-based is preferable from the balance of cost and performance.

The number of single fibers constituting the untreated fiber bundle is 4900 to 175000, preferably 60000 to 175000.
The method for setting the number of single fibers within the above range is not particularly limited. For example, a method using a precursor fiber having a large tow volume as a starting material, a plurality of precursor fibers having a low tow volume, and a yarn in the middle of a firing process. The method of doing is mentioned.

The carbon fiber bundle of the present invention satisfies the following conditions (a) and (b).
<Condition (a)>
The carbon fiber bundle of the present invention has a CV value {(standard deviation of surface oxygen concentration / average value of surface oxygen concentration) × 100} of the surface oxygen concentration (O / C) measured by X-ray photoelectron spectroscopy of 8%. It is as follows.
The CV value of the surface oxygen concentration (O / C) is an index representing the degree of variation in the surface oxygen concentration of the carbon fiber bundle. When the CV value exceeds 8%, oxidation occurs non-uniformly. Therefore, when a carbon fiber bundle treated with a small amount of electricity in the electrolytic oxidation treatment described later is used as a composite material, a matrix resin for the carbon fiber bundle. Adhesiveness to decreases.

The surface oxygen concentration (O / C) of the carbon fiber bundle and its CV value can be determined as follows.
First, the carbon fiber bundle is cut into a predetermined length, fixed to the sample holder of the measuring device using double-sided tape, the photoelectron escape rate is 90 °, and the inside of the measuring chamber of the measuring device is 1 × 10 ⁻⁶ Pa. Keep the vacuum.
As correction of the peak accompanying charging during measurement, first, the binding energy value of the main peak of C _1S (surface carbon concentration) is adjusted to 285.6 eV. Then, the C _1S peak area is obtained by drawing a straight base line in the range of 282 to 296 eV. On the other hand, the peak area of O _1S (surface oxygen concentration) is obtained by drawing a straight base line in the range of 528 to 540 eV.
The surface oxygen concentration (O / C) can be obtained by the atomic ratio calculated by dividing the ratio of the peak area of O _{1S and} the peak area of C _1S obtained previously by the sensitivity correction value unique to the apparatus. .
The same operation is performed on three cut carbon fiber bundles, the surface oxygen concentration (O / C) is determined for each, the average value and the standard deviation are calculated, and the CV value is determined by the following equation (1).
CV value [%] = (standard deviation of surface oxygen concentration / average value of surface oxygen concentration) × 100 (1)

<Condition (b)>
The carbon fiber bundle of the present invention has a CV value {(standard deviation of ipa value / average value of ipa value) × 100} of a current value (ipa value) flowing per unit area, measured by a cyclic voltammetry method. % Or less.
The ipa value is an index of the surface property ipa of the carbon fiber bundle, meaning that the higher the ipa value, the larger the surface area of the carbon fiber bundle, and the anchor strength improves the adhesive strength with the matrix resin. However, when the CV value of the ipa value exceeds 5%, oxidation occurs unevenly. Therefore, when a carbon fiber bundle treated with a small amount of electricity in the electrolytic oxidation treatment described later is used as a composite material, carbon The characteristic (strength) of the fiber bundle is not sufficiently exhibited, and the bending strength of the composite material is lowered.

The ipa value and the CV value of the carbon fiber bundle can be determined by the cyclic voltammetry method disclosed in JP-A-60-246864.
The cyclic voltammetry method referred to in the present invention is a method of measuring the relationship between the current and the electrode potential (voltage) using a carbon fiber bundle as the working electrode in an analyzer comprising a potentiostat and a function generator. That is.

Specifically, first, a solution in which 5% phosphoric acid aqueous solution is used to adjust the pH to 3 and nitrogen is bubbled to remove the remaining oxygen is prepared.
An Ag / AgCl electrode as a reference electrode, a platinum electrode having a sufficient surface area as a counter electrode, and a carbon fiber bundle as a working electrode are inserted into this solution, and the current and electrode potential of the carbon fiber bundle are measured.
The potential operation range is -0.2 to 0.8 V, the potential operation speed is 2 mV / sec, a potential-current curve is drawn with an XY recorder, swept three or more times, and when the curve becomes stable, Ag / With respect to the AgCl electrode, the current is read with the potential at +0.4 V as a standard, and the ipa value is calculated according to the following formula (2). In the formula (2), “sample length” is the length in the longitudinal direction of the carbon fiber bundle used for the working electrode, and “weight per unit” is the unit length of the carbon fiber bundle used for the working electrode. It is weight.
ipa value [μA / cm ² ] = current value [μA] / sample length [cm] × {4π × weight per unit area [g / m] × number of single fibers / density [g / cm ³ ]} ^1/2. 2)

The same operation is performed on three cut carbon fiber bundles, the ipa value is obtained for each, the average value and the standard deviation are calculated, and the CV value is obtained by the following equation (3).
CV value [%] = (standard deviation of ipa value / average value of ipa value) × 100 (3)

  Carbon fiber bundles that satisfy the conditions (a) and (b) described above are not only in the longitudinal direction of the fiber bundle before treatment but also in the radial direction of the fiber bundle before treatment, that is, the surface treatment (electrolytic oxidation). It is obtained by processing. In order to perform the electrolytic oxidation treatment uniformly to the inside of the single fiber bundle, the pre-treatment fiber bundle is used as an anode, and the tow width of the pre-treatment fiber bundle is 8 mm or more and the treatment time is 5 seconds or more by the contact power feeding method. is important.

By setting the toe width of the untreated fiber bundle to 8 mm or more, even when the number of single fibers is 49000 or more, the electrolytic solution is sufficiently diffused to the inside of the fiber bundle, and the electrolytic oxidation treatment can be performed uniformly. When the toe width of the pre-treatment fiber bundle is less than 8 mm, the electrolytic solution is not easily diffused to the inside of the fiber bundle when the pre-treatment fiber bundle having a single fiber number of 49000 or more is subjected to electrolytic oxidation treatment. It is not uniformly electrolytically oxidized. Therefore, it becomes difficult to obtain a carbon fiber bundle that satisfies the above-described conditions, particularly the condition (b).
The toe width of the pre-treatment fiber bundle at the time of electrolytic oxidation treatment is appropriately determined depending on the number of single fibers of the carbon fiber bundle to be produced, but is preferably 8 mm or more when the number of single fibers is between 49000 and 175000. The upper limit of the tow width is not particularly limited, but is preferably 20 mm or less from the viewpoint of carbon fiber productivity.

Further, by setting the electrolytic oxidation treatment time to 5 seconds or more, even within a small amount of electricity, the inside of the fiber bundle can be uniformly electrolytically oxidized. If the treatment time is less than 5 seconds, it is necessary to increase the amount of electricity in order to ensure a sufficient electrolytic oxidation treatment effect. However, when the amount of electricity increases, even the inside of the fiber bundle is not uniformly subjected to electrolytic oxidation treatment, and treatment spots tend to be generated. Therefore, it becomes difficult to obtain a carbon fiber bundle that satisfies the above-described conditions, particularly the condition (b).
Even if the treatment time for the electrolytic oxidation treatment is set long, the effect reaches its peak. In addition, if the treatment time is lengthened, the production rate of the process is reduced, or the electrolytic oxidation treatment apparatus needs to be enlarged, resulting in an increase in the production cost of the carbon fiber bundle. Accordingly, the processing time is preferably 12 seconds or less.

  When electrolytically oxidizing the pre-treatment fiber bundle, the tension per 24,000 single fibers is preferably 4 kg or less. When the tension per 24,000 single fibers is 4 kg or less, the electrolyte solution is more easily diffused into the fiber bundle, and the electrolyte solution diffusion efficiency can be easily increased. In addition, fluffing of the unprocessed fiber bundle during the electrolytic oxidation treatment can be suppressed, so that a high-quality carbon fiber bundle and a composite material can be easily obtained.

Here, an example of the method for producing a carbon fiber bundle of the present invention will be specifically described with reference to FIG.
FIG. 1 is a schematic diagram illustrating an example of an electrolytic oxidation apparatus that employs a contact power supply method, which is used in the present invention.
Here, the “contact power supply method” is a method of supplying power to the unprocessed fiber bundle by directly applying electricity to the unprocessed fiber bundle via the roll-shaped electrode.

In the electrolytic oxidation apparatus 1 shown in FIG. 1, one electrolytic tank 12 filled with an electrolytic solution is installed along the traveling direction of the untreated fiber bundle 11. The electrolytic cell 12 has a cathode 13 disposed therein and serves as a cathode cell. Rolled anodes 14 and 15 are installed on the upstream side and downstream side of the electrolytic cell 12, and the anodes 14 and 15 and the cathode 13 are connected to a DC power source 16. Further, on the upstream side of the anode 14 and on the downstream side of the anode 15, conveyance rolls 17 and 17 for conveying the unprocessed fiber bundle 11 are installed.
As the transport roll 17, a groove roll having a groove on the surface that can regulate the toe width of the fiber bundle 11 before processing is preferable. If the groove roll is used, it is easy to adjust the tow width of the unprocessed fiber bundle 11 to be electrolytically oxidized to a desired size.
As the electrolytic solution filled in the electrolytic cell 12, an aqueous alkaline electrolyte solution is preferable, and as the alkaline electrolyte, an ammonium hydrogen carbonate salt is preferable. In addition, although acidic electrolyte, especially nitric acid may be used as electrolyte, when using acidic electrolyte, since an anode may corrode, it is good to use alkaline electrolyte.

The untreated fiber bundle 11 is guided by the transport roll 17 in the order of the upstream anode 14, the electrolytic bath 12, and the downstream anode 15 and travels in the electrolytic oxidation apparatus 1.
The untreated fiber bundle 11 is directly charged with electricity when passing through the anode 14. And it guide | induces to the electrolytic vessel 12, and drive | works, contacting the liquid level of electrolyte solution. When traveling in the electrolytic cell, the untreated fiber bundle 11 acts as an anode, and the untreated fiber bundle 11 itself is subjected to electrolytic oxidation treatment. That is, the electrolytic oxidation process is performed in the electrolytic cell 12. Then, the carbon fiber bundle 18 which passed the anode 15 and was subjected to electrolytic oxidation treatment is obtained.

  The electrolytic oxidation apparatus 1 adopting the contact power supply method directly supplies electricity to the unprocessed fiber bundle 11 via the anode 14, and thus can sufficiently supply power. Therefore, the untreated fiber bundle 11 can sufficiently function as an anode in the electrolytic cell 12. As a result, even if the number of single fibers is large or the amount of electricity during the electrolytic oxidation treatment is reduced, the electrolytic oxidation treatment can be performed sufficiently and uniformly to the inside of the fiber bundle, and the above-described condition (a) A carbon fiber bundle satisfying (b) can be easily obtained.

The present invention is characterized in that the pre-treatment fiber bundle is electrolytically oxidized by the contact power feeding method, but when the electrolytic oxidation treatment is performed by the non-contact power feeding method, the inside of the fiber bundle is not uniformly electrolytically oxidized.
Here, an example of the electrolytic oxidation treatment of the unprocessed fiber bundle by the non-contact power feeding method will be described with reference to FIG. The “non-contact power supply method” is a method of supplying electricity to the fiber bundle before treatment by indirectly applying electricity to the fiber bundle before treatment via the electrolytic solution in the electrolytic cell.

  In the electrolytic oxidation apparatus 2 shown in FIG. 2, three electrolytic tanks 22 a, 22 b, and 22 c filled with an electrolytic solution are installed in series along the traveling direction of the untreated fiber bundle 21. Of these three electrolytic cells, the central electrolytic cell 22b has a cathode 23 disposed therein, which is a cathode cell. In addition, anodes 24 and 25 are respectively disposed in the electrolytic tanks 22a and 22c on the upstream side and the downstream side of the electrolytic tank 22b, thereby forming an anode tank. The anodes 24 and 25 and the cathode 23 are connected to a DC power source 26. Furthermore, conveyance rolls 27 and 27 for conveying the unprocessed fiber bundle 21 are installed on the upstream side of the electrolytic cell 22a and the downstream side of the electrolytic cell 22c, respectively.

The untreated fiber bundle 21 is guided in order from the upstream electrolytic tank by the transport roll 27, that is, in the order of the electrolytic tanks 22a, 22b, and 22c, and travels in contact with the liquid level of the electrolytic solution in each electrolytic tank.
When the pre-treatment fiber bundle 21 passes through the electrolytic cell 22a as an anode cell while contacting the liquid surface of the electrolytic solution, electricity is indirectly applied through the electrolytic solution. And it guide | induces to the electrolytic cell 22b which is a cathode cell, and it drive | works, contacting the liquid level of electrolyte solution. When traveling through the electrolytic cell 22b, the untreated fiber bundle 21 acts as an anode, and the untreated fiber bundle 21 itself is subjected to electrolytic oxidation. That is, the electrolytic oxidation process is performed in the electrolytic bath 22b. Thereafter, it passes through the electrolytic cell 22c, which is an anode cell, and the carbon fiber bundle 28 subjected to electrolytic oxidation treatment is obtained.

  In the electrolytic oxidation apparatus 2 adopting the non-contact power feeding method, electricity is indirectly applied to the fiber bundle 21 before treatment through the electrolytic solution in the electrolytic tank 22a which is an anode tank. The power supply is insufficient compared to the contact power supply method to be applied. For this reason, in the electrolytic cell 22b which is a cathode cell, the untreated fiber bundle 21 cannot sufficiently function as an anode, and as a result, it is difficult to uniformly perform electrolytic oxidation treatment to the inside of the fiber bundle. In particular, if the amount of electricity during the electrolytic oxidation treatment is small, processing spots are likely to occur, and the adhesion between the carbon fiber bundle and the matrix resin of the composite material using the obtained carbon fiber bundle tends to be lowered.

  As described above, according to the present invention, the fiber bundle before processing having a tow width of 8 mm or more is subjected to electrolytic oxidation treatment for 5 seconds or more by the contact power feeding method, and therefore, the case where the number of single fibers is large and the amount of electricity is treated However, the electrolytic oxidation treatment can be uniformly performed to the inside of the fiber bundle. As a result, a carbon fiber bundle satisfying the conditions (a) and (b), which has been subjected to electrolytic oxidation treatment uniformly to the inside as well as the longitudinal direction of the fiber bundle, is obtained. When the carbon fiber bundle is a composite material, the carbon fiber bundle has good adhesion to the matrix resin and can exhibit sufficient strength.

In the present invention, even when the number of single fibers is as small as less than 49000, it is possible to obtain a carbon fiber bundle that is uniformly electrolytically oxidized to the inside of the fiber bundle. However, when the number of single fibers is small, even the conventional method may be able to uniformly perform electrolytic oxidation treatment to the inside of the fiber bundle.
However, when the number of single fibers is as large as 49000 to 175000, it is difficult to uniformly perform electrolytic oxidation treatment to the inside of the fiber bundle by the conventional method.
The present invention is particularly suitable for the case where a fiber bundle having a large number of single fibers of 49000 to 175000 is subjected to electrolytic oxidation treatment.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these.
The fiber bundle before processing used in this example and various measurement methods are as follows.

<Fiber bundle before treatment>
Polyacrylonitrile-based precursor fiber bundle (single fiber fineness: 1.0 dtex, number of single fibers: 60000) is flame-resistant in air at 220 ° C. to 270 ° C., and further pre-carbonized in an inert atmosphere at 700 ° C. Then, carbonization was performed at a maximum treatment temperature of 1400 ° C. to obtain a fiber bundle before treatment.

<Strand test>
The strand strength and strand modulus of the carbon fiber bundle were measured according to JIS R7601.

<Measurement of surface oxygen concentration (O / C) and its CV value>
The surface oxygen concentration (O / C) of the carbon fiber bundle and its CV value were determined as follows.
First, the carbon fiber bundle is cut into a predetermined length, fixed to the sample holder of the measuring device using double-sided tape, the photoelectron escape rate is 90 °, and the inside of the measuring chamber of the measuring device is 1 × 10 ⁻⁶ Pa. The vacuum was maintained.
As correction of the peak accompanying charging during measurement, first, the binding energy value of the main peak of C _1S (surface carbon concentration) is adjusted to 285.6 eV. Then, the C _1S peak area was determined by drawing a straight base line in the range of 282 to 296 eV. On the other hand, the peak area of O _1S (surface oxygen concentration) was determined by drawing a straight base line in the range of 528 to 540 eV.
The surface oxygen concentration (O / C) was obtained by an atomic ratio calculated by dividing the ratio of the peak area of O _{1S and} the peak area of C _1S obtained previously by the sensitivity correction value unique to the apparatus.
The same operation was performed on three cut carbon fiber bundles, the surface oxygen concentration (O / C) was determined for each, the average value and the standard deviation were calculated, and the CV value was determined by the following equation (1).
CV value [%] = (standard deviation of surface oxygen concentration / average value of surface oxygen concentration) × 100 (1)

<Measurement of ipa value and its CV value>
The ipa value of the carbon fiber bundle and its CV value were determined by the cyclic voltammetry method as follows.
In addition, as a measuring device, an analyzer (“HZ-3000 AUTOMATIC POLARIZATION SYSTEM” manufactured by Hokuto Denko Co., Ltd.) composed of a potentiostat and a function generator was used.

First, a solution was prepared by adjusting the pH to 3 using a 5% phosphoric acid aqueous solution and removing nitrogen by bubbling nitrogen.
An Ag / AgCl electrode as a reference electrode, a platinum electrode having a sufficient surface area as a counter electrode, and a carbon fiber bundle as a working electrode are inserted into this solution, and the current and electrode potential of the carbon fiber bundle are measured with the above analyzer. It was measured.
The potential operation range was −0.2 to 0.8 V, and the potential operation speed was 2 mV / sec. Draw a potential-current curve with an XY recorder and sweep it three or more times. When the curve is stable, read the current with respect to the Ag / AgCl electrode with the potential at +0.4 V as the standard. ) To calculate the ipa value. In the formula (2), “sample length” is the length in the longitudinal direction of the carbon fiber bundle used for the working electrode, and “weight per unit” is the unit length of the carbon fiber bundle used for the working electrode. It is weight.
ipa value [μA / cm ² ] = current value [μA] / sample length [cm] × {4π × weight per unit area [g / m] × number of single fibers / density [g / cm ³ ]} ^1/2. 2)
The same operation was performed on three cut carbon fiber bundles, the ipa value was determined for each, the average value and the standard deviation were calculated, and the CV value was determined by the following equation (3).
CV value [%] = (standard deviation of ipa value / average value of ipa value) × 100 (3)

<Measurement of interfacial shear strength>
The bond strength between the carbon fiber bundle and the matrix resin was evaluated by measuring the interfacial shear strength by a single fiber embedding (fragmentation) method. As a single fiber embedding method, for example, the method described in “Development and evaluation method of carbon fiber” (Realize), pages 157 to 160 can be used, and specifically, the procedure shown below is used. evaluated.

First, one single fiber was extracted from the carbon fiber bundle and embedded in a matrix resin to prepare a test piece. The test piece was given an elongation greater than the breaking elongation of the fiber (execution of a tensile test). The length of each broken fiber broken in the matrix resin was measured, and the interfacial shear strength was calculated from the following formulas (4) and (5).
Critical fiber length [mm] = 4 × average fiber length [mm] / 3 (4)
Interfacial shear strength [MPa] = fiber strength [MPa] × fiber diameter [mm] / 2 × critical fiber length [mm] (5)
As a matrix resin, 100 parts by mass of “Araldide CY230” manufactured by CIBA-GEIGY Co., Ltd. and 35 parts by mass of “Hardener HY2967” are mixed, poured into a mold, and cured at 20 ° C. for 24 hours. And subsequently cured at 60 ° C. for 6 hours.
In addition, the tensile test is performed in an environment of a temperature of 22 ° C. and a humidity of 50%. After the test piece is stretched within a range where it does not break (elongation: 7%), the length of the broken fiber broken in the resin is polarized. The average fiber length was calculated by reading with a microscope.

<Measurement of bending strength>
The bending strength of the composite material was measured as follows.
First, using a carbon fiber bundle and a matrix resin (“# 350 epoxy resin” manufactured by Mitsubishi Rayon Co., Ltd.), the matrix resin is impregnated so that the content of the carbon fiber bundle is 60% by volume, A fiber-reinforced plastic plate (composite material) having a plate thickness of 2 mm was produced.
With respect to the obtained composite material, the bending strength (FS 90 °) in the direction perpendicular to the fiber direction was measured by a three-point bending short beam method in accordance with ASTM D790.

[Example 1]
<Example 1-1>
Using an aqueous solution of ammonium hydrogen carbonate (5% by mass) as an electrolytic solution for electrolytic oxidation treatment, using the electrolytic oxidation apparatus 1 shown in FIG. 1, a tow width of 10 mm, a treatment time of 12 seconds, and an electric charge of 1.4 C / g Then, the fiber bundle before treatment was electrolytically oxidized to obtain a carbon fiber bundle. The tension during the electrolytic oxidation treatment was 3.2 kg per 24,000 single fibers. Further, the toe width of the fiber bundle before treatment was regulated by using a groove roll having a groove with a width of 10 mm on the surface as the transport roll 17.
Various measurements were performed on the obtained carbon fiber bundle. The results are shown in Tables 1 and 2.

<Examples 1-2 and 1-3>
Except that the amount of electricity was changed to the value shown in Table 1, the fiber bundle before treatment was electrolytically oxidized in the same manner as in Example 1-1 to obtain a carbon fiber bundle.
Various measurements were performed on the obtained carbon fiber bundle. The results are shown in Tables 1 and 2.

[Examples 2 to 4]
Except for changing the tow width, the treatment time, and the amount of electricity to the values shown in Table 1, the fiber bundle before treatment was subjected to electrolytic oxidation treatment in the same manner as in Example 1-1 to obtain a carbon fiber bundle. In Example 4, the conveying roll 17 was changed to a groove roll having a groove having a width of 8 mm on the surface, and the toe width of the fiber bundle before processing was regulated.
Various measurements were performed on the obtained carbon fiber bundle. The results are shown in Tables 1 and 2.

[Comparative Examples 1 and 2]
Except for changing the tow width, the treatment time, and the amount of electricity to the values shown in Table 1, the fiber bundle before treatment was subjected to electrolytic oxidation treatment in the same manner as in Example 1-1 to obtain a carbon fiber bundle. In Comparative Example 1, the tow width of the unprocessed fiber bundle was regulated by changing the conveying roll 17 to a groove roll having a groove with a width of 3 mm on the surface.
Various measurements were performed on the obtained carbon fiber bundle. The results are shown in Tables 1 and 2.

[Comparative Examples 3-1 to 3-3]
The apparatus shown in FIG. 2 was used as the electrolytic oxidation apparatus, and the fiber bundle before treatment was subjected to electrolytic oxidation treatment in the same manner as in Example 1-1 except that the tow width and the amount of electricity were changed to the values shown in Table 1. Carbon A fiber bundle was obtained. The tow width of the fiber bundle before treatment was regulated by using a groove roll having a groove with a width of 8 mm on the surface as the transport roll 27. Moreover, all the electrolytic tanks were filled with ammonium hydrogencarbonate aqueous solution (5 mass%) as electrolyte solution.
Various measurements were performed on the obtained carbon fiber bundle. The results are shown in Tables 1 and 2.

[Comparative Examples 4 and 5]
2 except that the apparatus shown in FIG. 2 is used as the electrolytic oxidation apparatus, an aqueous nitric acid solution (5% by mass) is used as the electrolytic solution filled in all the electrolytic cells, and the tow width and the amount of electricity are changed to the values shown in Table 1. In the same manner as in Example 1-1, the fiber bundle before treatment was electrolytically oxidized to obtain a carbon fiber bundle. The tow width of the fiber bundle before treatment was regulated by using a groove roll having a groove with a width of 8 mm on the surface as the transport roll 27.
Various measurements were performed on the obtained carbon fiber bundle. The results are shown in Tables 1 and 2.

As is clear from Table 2, the carbon fiber bundles obtained in each example having a surface oxygen concentration CV value of 8% or less and an ipa value CV value of 5% or less have interfacial shear strength and bending strength. When the composite material was used, the adhesiveness with the matrix resin was good and sufficient strength was exhibited.
In particular, when Examples 1-1 to 1-3 were compared, it was found that even if the amount of electricity was reduced, the change in interfacial shear strength (strength fluctuation) was small. That is, it was suggested that a carbon fiber bundle excellent in adhesiveness with a matrix resin can be stably produced even if the amount of electricity changes.
Thus, in each Example, even if the number of single fibers was large and the treatment was performed with a small amount of electricity, even the inside of the fiber bundle could be uniformly electrolytically oxidized. And when the obtained carbon fiber bundle was made into the composite material, adhesiveness with a matrix resin was favorable and was able to exhibit sufficient intensity | strength.

On the other hand, the carbon fiber bundles obtained in Comparative Examples 1 and 2 in which the CV value of the ipa value exceeded 5% had a lower bending strength value than the carbon fiber bundles of each Example, and exhibited sufficient strength. could not.
In the case of Comparative Examples 3-1 to 3-3 in which the electrolytic oxidation treatment was performed by the non-contact power feeding method, the obtained carbon fiber bundle had a CV value of surface oxygen concentration exceeding 8%. In particular, in Comparative Examples 3-2 and 3-3 in which the amount of electricity was 2.7 C / g or more, the CV value of the ipa value also exceeded 5%. In Comparative Examples 3-1 to 3-3, when the amount of electricity was changed, the interfacial shear strength was also greatly changed. In particular, when the amount of electricity was reduced, the interfacial shear strength was extremely reduced. That is, it was suggested that when the amount of electricity changes, it is difficult to stably produce a carbon fiber bundle excellent in adhesiveness with a matrix resin.
In the case of Comparative Examples 4 and 5 in which electrolytic oxidation treatment was performed by a non-contact power feeding method and an aqueous nitric acid solution was used as the electrolytic solution, the CV value of the obtained carbon fiber bundle exceeded 5%. In particular, in Comparative Example 4 in which the amount of electricity was 9 C / g, the CV value of the surface oxygen concentration exceeded 8%. These carbon fiber bundles had lower bending strength values than the carbon fiber bundles of the respective examples, and could not exhibit sufficient strength.
As described above, in each comparative example, the electrolytic oxidation treatment could not be performed uniformly up to the inside of the fiber bundle.

1, 2: Electrolytic oxidation apparatus 11, 21: Fiber bundle before treatment 12, 22a, 22b, 22c: Electrolyzer 13, 23: Cathode 14, 15, 24, 25: Anode 16, 26: DC power supply 17, 27: Transport Roll 18, 28: Carbon fiber bundle

Claims (2)

A carbon fiber bundle comprising 49000 to 175000 single fibers and satisfying the following conditions (a) and (b).
(A): CV value {(standard deviation of surface oxygen concentration / average value of surface oxygen concentration) × 100} of surface oxygen concentration measured by X-ray photoelectron spectroscopy is 8% or less.
(B): CV value {(standard deviation of ipa value / average value of ipa value) × 100} of the current value (ipa value) flowing per unit area measured by the cyclic voltammetry method is 5% or less. Using a carbon fiber having a tow width of 8 mm or more in the form of a bundle of 49000-175000 single fibers as an anode,
The tension per 24,000 single fibers is 4 kg or less,
Applying electricity directly to the carbon fiber via a roll-shaped anode by a contact power supply method ,
Next, the carbon fiber bundle is characterized in that the carbon fiber is guided to an electrolytic cell filled with an electrolytic solution and provided with a cathode, and is run while being in contact with the liquid surface of the electrolytic solution and subjected to electrolytic oxidation treatment for 5 seconds or more. Production method.

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