JP2023125227A - Carbon fiber bundle and method for manufacturing the same - Google Patents

Abstract

To provide a carbon fiber bundle with high strand strength, in which defects in the fibers are controlled without reducing the strand elastic modulus and a method for manufacturing the same.SOLUTION: There is provided a carbon fiber bundle in which N/C, representing the ratio of the number of nitrogen atoms to the number of carbon atoms on the fiber surface of the carbon fiber bundle as determined by X-ray photoelectron spectroscopy, is 0.005 to 0.05. There is also provided a manufacturing method for obtaining a carbon fiber bundle by heating a carbon fiber precursor fiber bundle. The manufacturing method for the carbon fiber bundle comprises: heat treating at 2000°C or higher in an inert atmosphere; immersion in an acidic aqueous solution; immersion in an alkaline aqueous solution; and electrolytic treatment in at least the alkaline aqueous solution.SELECTED DRAWING: None

Description

The present invention relates to a carbon fiber bundle and a method for manufacturing the same.

Carbon fibers have higher specific strength and specific modulus than other fibers. This carbon fiber bundle, which is a collection of single carbon fibers, is used as a reinforcing fiber for composite materials for sports, aviation, and space applications, as well as for general industrial applications such as automobiles, civil engineering, architecture, pressure vessels, and wind turbine blades. It is being widely deployed, and there is a high demand for further performance improvements.

Polyacrylonitrile (PAN) carbon fibers, which are widely used among carbon fibers, are generally manufactured industrially as follows. First, a spinning solution containing an acrylonitrile polymer as a precursor is wet-spun, dry-spun, or dry-wet-spun to obtain an acrylic fiber bundle as a carbon fiber precursor. The obtained carbon fiber precursor acrylic fiber bundle is heated in an oxidizing atmosphere at a temperature of, for example, 180 to 400°C to convert it into a flame-resistant fiber bundle, and then heated in an inert atmosphere at a temperature of, for example, 1000°C or higher to form a carbon fiber bundle. A carbon fiber bundle is obtained by

Carbon fiber is a brittle material, and the slightest defect causes a decrease in strength, so various studies are being conducted to reduce the number of defects that cause breakage. Specifically, a method has been proposed for controlling the size and state of existence of defects in carbon fibers so that they fall within a specific range.
For example, in Patent Document 1, after carrying out a single fiber tensile test with a sample length of 10 mm, the total number N of pairs of fractured surfaces of randomly selected fibers and at least one of the paired fractured surfaces are Carbon fibers in which the ratio (n/N) of the number of pairs in which defects of 50 nm or more are present is 35% or less, the average single fiber diameter is 4.3 μm or more, and the strand strength is 8.0 GPa or more A bundle is disclosed.

International Publication No. 2018/003836

However, in the carbon fiber bundle described in Patent Document 1, although defects that may lead to breakage have been evaluated in a single fiber tensile test, they do not contribute to strength development under conditions consistent with actual usage conditions. Evaluation of such defects is not always possible.

An object of the present invention is to provide a carbon fiber bundle with controlled defects in the fibers and high strand strength without reducing the strand elastic modulus, and a method for producing the same.

The present invention has the following aspects.
[1] A carbon fiber bundle obtained by X-ray photoelectron spectroscopy, in which the ratio N/C of the number of nitrogen atoms to the number of carbon atoms on the fiber surface of the carbon fiber bundle is 0.005 to 0.05.
[2] The carbon fiber bundle according to [1], which has a strand strength of 5.2 to 7.0 GPa and a strand elastic modulus of 370 to 430 GPa.
[3] The carbon fiber bundle according to [1] or [2], wherein the value of I _pa calculated by the method described in the specification is 0.01 to 0.25 μA/cm ² .
[4] Any of [1] to [3], wherein the ratio O/C of the number of oxygen atoms to the number of carbon atoms on the fiber surface of the carbon fiber bundle obtained by X-ray photoelectron spectroscopy is 0.01 to 0.25. Carbon fiber bundle described in Crab.
[5] The carbon fiber bundle according to any one of [1] to [4], wherein the N/C in a region etched by 5 nm from the carbon fiber surface is 0.005 to 0.04.
[6] The carbon fiber bundle according to any one of [1] to [5], wherein the N/C in a region etched by 10 nm from the carbon fiber surface is 0.005 to 0.04.
[7] The carbon fiber bundle according to any one of [1] to [6], wherein the N/C in a region etched by 15 nm from the carbon fiber surface is 0.01 to 0.04.
[8] The carbon fiber bundle according to any one of [1] to [7], wherein the N/C in a region etched by 20 nm from the carbon fiber surface is 0.02 to 0.04.
[9] The carbon fiber bundle according to any one of [1] to [8], wherein the carbon fiber bundle has a single fiber diameter of 5.0 to 7.0 μm.
[10] The carbon fiber bundle according to any one of [1] to [8], wherein the carbon fiber bundle has a single fiber diameter of 5.5 to 6.7 μm.
[11] The carbon fiber bundle according to any one of [1] to [8], wherein the carbon fiber bundle has a single fiber diameter of 5.7 to 6.7 μm.
[12] A manufacturing method for obtaining a carbon fiber bundle by heating a carbon fiber precursor fiber bundle, which comprises heat-treating the carbon fiber precursor fiber bundle at 2000°C or higher in an inert atmosphere and then immersing it in an acidic aqueous solution. , followed by immersion in an alkaline aqueous solution and electrolytic treatment in at least the alkaline aqueous solution.
[13] The method for producing a carbon fiber bundle according to [12], wherein electrolytic treatment is performed in the acidic aqueous solution.
[14] The method for producing a carbon fiber bundle according to [13], wherein the amount of electricity in the electrolytic treatment in the acidic aqueous solution is 0 to 30 coulombs per gram of carbon fiber to be treated.
[15] The method for producing a carbon fiber bundle according to any one of [12] to [14], wherein the amount of electricity in the electrolytic treatment in the alkaline aqueous solution is 5 to 200 coulombs per gram of carbon fiber to be treated.
[16] The method for producing a carbon fiber bundle according to any one of [12] to [15], wherein the acidic aqueous solution has a pH of 1 to 4.

According to the present invention, defects contained in the fibers are controlled without reducing the strand elastic modulus, and a carbon fiber bundle with high strand strength and a method for manufacturing the same can be provided.

The present invention will be explained in detail below. The following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention only to these embodiments. The present invention can be implemented in various ways without departing from the spirit thereof.
In addition, unless otherwise specified, a numerical range expressed using "~" in this specification means a range that includes the numerical values written before and after "~" as the lower limit value and upper limit value, and "A ~ "B" means greater than or equal to A and less than or equal to B.

[Carbon fiber bundle]
The carbon fiber bundle of the present invention is composed of a plurality of single carbon fibers bundled together, and may be in the form of continuous fibers or may be in the form of cut into predetermined lengths.
Examples of carbon fibers include polyacrylonitrile (PAN) carbon fibers, rayon carbon fibers, pitch carbon fibers, and the like. Among these, PAN-based carbon fibers are preferred from the viewpoint of excellent productivity and mechanical properties on an industrial scale.

The number of single fibers in the carbon fiber bundle is preferably 8,000 to 20,000, more preferably 10,000 to 18,000, even more preferably 12,000 to 18,000. If the number of filaments is greater than or equal to the above lower limit, it will have excellent workability, and if it is less than or equal to the above upper limit, it will be excellent in handleability.

In the carbon fiber bundle of the present invention, the ratio N/C of the number of nitrogen atoms to the number of carbon atoms on the fiber surface of the carbon fiber bundle obtained by X-ray photoelectron spectroscopy is 0.005 to 0.05.
When the N/C is 0.005 or more, affinity with the resin is easily obtained, and when it is 0.05 or less, there are few defects contained in the fibers, and it is easy to suppress a decrease in strand strength.
From these viewpoints, the N/C is preferably 0.007 to 0.045, more preferably 0.01 to 0.04.
The N/C of the carbon fiber bundle can be controlled by using an electrolyte containing nitrogen atoms in the surface treatment of the carbon fibers and adjusting the amount of electricity during the electrolytic oxidation treatment.

The carbon fiber bundle of the present invention preferably has a strand strength of 5.2 to 7.0 GPa and a strand elastic modulus of 370 to 430 GPa.
If the strand strength of the carbon fiber bundle is 5.2 GPa or more, the strength of the composite can be easily increased, so the degree of design freedom can be easily improved, and if it is 7.0 GPa or less, the firing time during production of the carbon fiber bundle will not be long. , easy to manufacture with good productivity. From these viewpoints, the strand strength is preferably 5.5 to 6.9 GPa, more preferably 5.9 to 6.8 GPa.
Strand strength is measured in accordance with JIS R 7608:2007.

If the strand elastic modulus of the carbon fiber bundle in the present invention is 370 GPa or more, sufficient rigidity can be easily obtained when made into a composite, and if it is 430 GPa or less, the carbon fiber bundle can be efficiently formed without increasing the firing temperature too high. Obtainable.
From these viewpoints, the strand elastic modulus is preferably 375 to 430 GPa, more preferably 380 to 430 GPa.
Strand elastic modulus is measured according to method A of JIS R 7608:2007.

The carbon fiber bundle of the present invention preferably has an I _pa value of 0.01 to 0.25, calculated by the method described in the specification.
If the value of I _pa is 0.01 or more, affinity with the resin can be easily obtained, and if it is 0.25 or less, it is easy to suppress a decrease in strand strength.
From these viewpoints, the value of I _pa is more preferably 0.05 to 0.22, and even more preferably 0.07 to 0.20.
The value of I _pa can be controlled by applying an acidic electrolyte as an electrolyte in surface treatment of carbon fibers and adjusting the amount of electricity in electrolytic oxidation treatment.

In the carbon fiber bundle of the present invention, the ratio O/C of the number of oxygen atoms to the number of carbon atoms on the fiber surface of the carbon fiber bundle obtained by X-ray photoelectron spectroscopy is preferably 0.01 to 0.25.
If the O/C is 0.01 or more, affinity with the resin can be easily obtained, and if it is 0.25 or less, a decrease in strand strength can be easily suppressed.
From these viewpoints, the O/C is more preferably 0.02 to 0.22, and even more preferably 0.03 to 0.20.
The surface oxygen concentration O/C of carbon fibers can be controlled by adjusting electrolytic treatment conditions in surface treatment of carbon fibers.

In the carbon fiber bundle of the present invention, the N/C in a region etched by 5 nm from the carbon fiber surface is preferably 0.005 to 0.04.
Furthermore, it is preferable that the N/C in a region etched by 10 nm from the surface of the carbon fiber is 0.005 to 0.04. Furthermore, it is preferable that the N/C in a region etched by 15 nm from the surface of the carbon fiber is 0.01 to 0.04. More preferably, the N/C in a region etched by 20 nm from the carbon fiber surface is 0.02 to 0.04.
If it is more than the said lower limit, affinity with resin will be easily obtained, and if it is less than the said upper limit, it will be easy to suppress a fall in strand strength.
The N/C on the carbon fiber surface can be controlled by adjusting the electrolytic treatment conditions in the surface treatment of the carbon fiber.

The carbon fiber bundle of the present invention preferably has a single fiber diameter of 5.0 to 7.0 μm, more preferably 5.5 to 6.7 μm, and even more preferably 5.7 to 6.7 μm.
If the diameter of the single fiber is 5.0 μm or more, the opening property of the fiber tends to be good, and if it is 8.0 μm or less, the convergence property of the carbon fiber bundle is maintained and it is easy to handle.

<Method for manufacturing carbon fiber bundles>
The carbon fiber bundle is obtained by heat-treating a carbon fiber precursor fiber bundle.
In the heat treatment, carbonization treatment is performed in an inert atmosphere after flameproofing treatment in an oxidizing atmosphere.

(Carbon fiber precursor fiber bundle)
Examples of the carbon fiber precursor fiber bundle include bundles of single fibers such as PAN fibers, rayon fibers, and pitch fibers. Among these, as the carbon fiber precursor fiber bundle, a carbon fiber precursor fiber bundle in which single fibers of PAN fibers are bundled is preferable. Hereinafter, a carbon fiber precursor fiber bundle in which single fibers of PAN fibers are bundled is also referred to as a "carbon fiber precursor acrylic fiber bundle."
The carbon fiber precursor acrylic fiber bundle is produced by spinning a spinning solution containing an acrylonitrile polymer, for example, into a coagulated thread, and subjecting it to conventionally known washing, bath stretching, oiling, drying and densification, stretching, etc., as necessary. It can be obtained with
The acrylonitrile-based polymer only needs to have an acrylonitrile unit in its molecular structure, and may be a homopolymer of acrylonitrile or a copolymer of acrylonitrile and other monomers (for example, methacrylic acid, etc.). There may be. The content ratio of acrylonitrile units and other monomer units in the copolymer can be appropriately set depending on the properties of the carbon fiber bundle to be produced.

The method for spinning a spinning solution containing an acrylonitrile polymer is not particularly limited, but examples include wet spinning in which the spinning solution is directly spun into a coagulation bath, dry spinning in which the spinning solution is coagulated in the air, and spinning methods in which the spinning solution is once placed in the air. Examples include dry-wet spinning, in which the material is spun in a bath and then coagulated in a bath. Among these, carbon fiber precursor acrylic fiber bundles are produced by dry-wet spinning a spinning solution containing an acrylonitrile polymer, from the viewpoint of reducing surface wrinkles on the side surfaces of single fibers and suppressing the generation of defects due to surface shapes. Preferably, it is a fiber bundle manufactured by.
In the spinning method using wet spinning or wet/dry spinning, a spinning solution can be spun into a coagulation bath through a nozzle having a hole with a circular cross section. As the coagulation bath, it is preferable to use an aqueous solution containing the solvent used in the spinning solution from the viewpoint of ease of solvent recovery.

The single fiber fineness of the carbon fiber precursor fiber bundle is preferably 0.5 to 2.5 dtex, more preferably 0.7 to 2 dtex. If the single fiber fineness is equal to or greater than the above lower limit value, it becomes easier to obtain a carbon fiber bundle with less yarn breakage, and when it is equal to or less than the above upper limit value, it becomes easier to obtain a carbon fiber bundle with small performance unevenness.
The number of single fibers in the carbon fiber precursor fiber bundle is preferably 8,000 to 20,000, more preferably 10,000 to 18,000, even more preferably 12,000 to 18,000. If the number of single fibers is 8,000 or more, it has excellent processability, and if it has 20,000 or less, it has excellent handleability.

The carbon fiber precursor fiber bundle is transferred to a firing process, where it is sequentially subjected to flameproofing treatment, carbonization treatment, surface oxidation treatment, and sizing treatment to become a carbon fiber bundle.

(Flame resistant treatment)
In the flame resistant treatment process (flame resistant process), the carbon fiber precursor fiber bundle is heated in an oxidizing atmosphere to convert it into a flame resistant fiber bundle.
The flame-retardant treatment is carried out in a hot air circulation type flame-retardant furnace at 180-280°C, with the furnace atmosphere temperature set at 180-280°C, and the density of the flame-retardant fiber after the flame-retardant treatment is 1.28-1.42 g/ A method of heating a carbon fiber precursor fiber bundle until the carbon fiber precursor fiber bundle reaches cm ³ is mentioned. If the density of the flame-resistant fiber is equal to or higher than the above lower limit, it will be easy to prevent adhesion between single fibers during the next step, carbonization treatment. If the density of the flame resistant fiber is below the above upper limit, the flame resistant process will not take too long and will be economical.
Examples of the gas that forms the oxidizing atmosphere include air, oxygen, nitrogen dioxide, and the like. Among these, air is preferable from the economic point of view.
The flameproofing treatment time is preferably 30 to 100 minutes.

In the flameproofing treatment, it is preferable to perform an elongation operation from the viewpoint of easily maintaining the orientation of the fibril structure.
The elongation rate in the flameproofing treatment is preferably 1 to 8%. If the elongation rate in the flame-retardant treatment is equal to or higher than the above lower limit, it will be easy to maintain or improve the orientation of the fibril structure, and a carbon fiber bundle with excellent mechanical properties will be easily obtained. If the elongation rate in the flameproofing treatment is below the above upper limit, the fibril structure itself is less likely to break and the subsequent structure formation of the carbon fibers is less likely to be impaired, making it easier to obtain a high-strength carbon fiber bundle.

(Carbonization treatment)
The flame-resistant fiber bundle is continuously guided to a carbonization process (carbonization process).
In the carbonization step, the flame-resistant fiber bundle is heated in an inert atmosphere to obtain a carbon fiber bundle.
Examples of the gas forming the inert atmosphere include nitrogen, argon, helium, and the like. Among these, nitrogen is preferred from the economic point of view.

The temperature of the carbonization treatment (carbonization treatment temperature) is preferably 300 to 2500°C.
The carbonization temperature is preferably raised during the carbonization treatment. When raising the temperature, for example, install multiple carbonization furnaces and set the temperature of each carbonization furnace so that the temperature increases from the upstream carbonization furnace to the downstream carbonization furnace. This can be achieved by sequentially passing the flame-resistant fiber bundle from the carbonization furnace to the downstream carbonization furnace.
Hereinafter, an example in which the carbonization treatment is performed by increasing the carbonization treatment temperature will be described.

In this embodiment, the first carbonization treatment is performed in a first carbonization furnace with a temperature gradient of 300°C to 800°C in an inert atmosphere, and the second carbonization treatment is performed in an inert atmosphere from 1000°C to 2500°C. Carbonization treatment is performed sequentially to carbonize the flame-resistant fiber bundle. Note that the second carbonization treatment may be performed using a plurality of heat treatment furnaces.

The method for producing a carbon fiber bundle of the present invention is a method for producing a carbon fiber bundle by heating a carbon fiber precursor fiber bundle, in which the carbon fiber bundle is heat-treated at 2000°C or higher in an inert atmosphere, and then heated in an acidic aqueous solution. It is preferable to immerse the substrate in water, then immerse it in an alkaline aqueous solution, and perform electrolytic treatment at least in the alkaline aqueous solution.

In the manufacturing method of the present invention, it is preferable to perform heat treatment at 2000° C. or higher in an inert atmosphere. The strand elastic modulus can be easily increased by heating at 2000°C or higher.
From this point of view, it is more preferable to perform heat treatment at 2100°C or higher in an inert atmosphere, and even more preferably to perform heat treatment at 2200°C or higher.

(surface treatment)
The method for producing carbon fiber bundles of the present invention includes heat treatment at 2000°C or higher in an inert atmosphere, followed by immersion in an acidic aqueous solution, followed by immersion in an alkaline aqueous solution, and at least electrolytic treatment in the alkaline aqueous solution. It is preferable to do so.
By performing a strong surface treatment in an acidic aqueous solution and then a gentle surface treatment in an alkaline aqueous solution, it is possible to increase the affinity with the resin without reducing the elastic modulus, thereby increasing the strand strength. It becomes easier to raise the price.

The amount of electricity in the electrolytic treatment in the alkaline aqueous solution is preferably 5 to 200 coulombs (C) per gram of carbon fiber to be treated.
When the amount of electricity is 5 coulombs/g or more, it is easy to increase the affinity with the resin, and when it is 200 coulombs/g or less, it is difficult to reduce the strand strength.
From these viewpoints, the amount of electricity is more preferably 6 to 100 coulombs/g, and even more preferably 7 to 20 coulombs/g.

(Surface oxidation treatment)
Examples of methods for surface oxidation treatment include electrolytic oxidation, chemical oxidation, and air oxidation. Among these, electrolytic oxidation, which is widely practiced industrially, is preferred because it allows stable surface oxidation treatment.
In the production method of the present invention, it is preferable to perform electrolytic treatment with an acid.

By using an electrolyte containing nitrogen atoms and adjusting the amount of electricity during electrolytic oxidation treatment, the N/C of the carbon fiber surface obtained by X-ray photoelectron spectroscopy can be controlled to 0.005 to 0.05. .
Therefore, it is preferable that the electrolyte has nitrogen atoms.
In addition, by applying an acidic electrolyte as an electrolyte and adjusting the amount of electricity in electrolytic oxidation treatment, it is possible to control I _Pa , which indicates the surface treatment state, to 0.010 to 0.25 μA/ ^cm2 , and to control X-ray photoelectron The O/C of the carbon fiber surface obtained by spectroscopy can be controlled to 0.01 to 0.25.

Examples of the electrolyte include sulfuric acid, nitric acid, phosphoric acid, ammonium carbonate, ammonium bicarbonate, ammonium sulfate, calcium hydroxide, sodium hydroxide, potassium hydroxide, and the like. Among these, phosphoric acid and ammonium bicarbonate are preferred.
The amount of electricity applied to the electrolytic treatment in an acidic aqueous solution is preferably 0 to 30 coulombs/g. Even if the amount of electricity is 0, there is a surface treatment effect, but it is more preferably 1 coulomb/g or more, and even more preferably 5 coulombs/g or more. Moreover, if it is 30 coulombs/g or less, there is little damage to the fiber surface and it is difficult to reduce the strand strength. From this viewpoint, the upper limit of the amount of electricity is more preferably 25 coulombs/g or less, and even more preferably 20 coulombs/g or less.
The electrolytic treatment may be performed using one type of electrolytic solution, or may be performed multiple times. From the viewpoint of processing in a short time while developing adhesiveness with the matrix resin, it is preferable to perform the processing multiple times.

(Sizing process)
In the sizing process, a sizing agent dissolved in an organic solvent or a sizing agent emulsion liquid dispersed in water using an emulsifier is applied to the carbon fiber bundle by a roller dipping method, a roller contact method, etc., and then dried. It can be carried out.
As the sizing agent, known ones can be used, and examples thereof include sizing agents mainly composed of epoxy resin, polyether resin, epoxy-modified polyurethane resin, and polyester resin.
The amount of the sizing agent attached to the surface of the carbon fiber can be controlled by adjusting the concentration of the sizing agent liquid and adjusting the amount of squeezing. Drying can be performed using hot air, a hot plate, a heated roller, various infrared heaters, and the like.

<Effect>
The carbon fiber bundle of the present invention described above has a carbon fiber surface N/C of 0.005 to 0.05 obtained by X-ray photoelectron spectroscopy.
In such a carbon fiber bundle, defects contained in the fibers are controlled, a decrease in the strand elastic modulus is suppressed, and the strand strength is high.
In addition, with the method for producing a carbon fiber bundle described above, it is possible to easily produce a carbon fiber bundle whose N/C on the carbon fiber surface obtained by X-ray photoelectron spectroscopy is 0.005 to 0.05, and the strand strength is It becomes easier to obtain a carbon fiber bundle having a strand modulus of 5.2 to 7.0 GPa and a strand elastic modulus of 370 to 430 GPa.

<Application>
The carbon fiber bundle of the present invention is combined with, for example, a matrix resin, molded into a composite material, and used for various purposes.
Matrix resins are not particularly limited, but include thermosetting resins such as epoxy resins and phenol resins, radical polymerization resins such as acrylic resins, vinyl ester resins, and unsaturated polyester resins, thermoplastic acrylic resins, polyamide resins, and polyimide resins. , thermoplastic resins such as polycarbonate resin, polypropylene resin, and polyethylene resin. Moreover, modified products of these resins can also be used. Furthermore, a commercially available product may be used as the matrix resin.
Applications of composite materials using carbon fiber bundles are not particularly limited, but include industrial materials such as automobile parts, aerospace materials, civil engineering and construction materials, sports and leisure materials, pressure vessels, and wind turbine blades. It can be used for a wide range of purposes.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited by the following description unless it exceeds the gist thereof.
The various measurement methods performed in this example are as follows.

[Method for measuring single fiber diameter of carbon fiber]
The cross-sectional area of each single carbon fiber was calculated from the density (g/cm ³ ) of the carbon fiber bundle, the mass per 1 m of the carbon fiber bundle, and the number of single fibers in the carbon fiber bundle. The diameter of a perfect circle having an area equal to the cross-sectional area was calculated and used as the diameter of a single carbon fiber.

[Method for measuring density of carbon fiber bundle]
The density of the carbon fiber bundle was measured according to method C (density tube method) described in JIS R 7063:1999.

[Measurement method of O/C and N/C on carbon fiber surface using X-ray photoelectron spectroscopy]
After fixing the cut carbon fiber bundle to a sample holder using double-sided tape, the photoelectron escape velocity was set to 90°, and the measurement chamber of the apparatus was maintained at a vacuum of 1×10 ⁻⁶ Pa to perform measurements. The oxygen concentration O _1S /C _1S was integrated over the range from 538 to 524 eV, and each was evaluated as a percentage of the C _1s peak area.

[Method for measuring N/C etched from carbon fiber surface]
The measurement conditions were as follows.
Equipment: Quantera II (manufactured by ULVAC-PHI)
X-ray source: Al Kα (monochrome) 200μmφ 50W
scan: 0.1eV/step
The carbon fiber bundles used as samples were aligned so that each fiber was oriented in the same direction, so that the vicinity of the measurement point was as smooth as possible. The photoelectron escape angle during measurement was 45°, and the measurement was taken from a direction perpendicular to the fiber axis.
Note that if the measurement is not performed in a direction perpendicular to the fiber axis, the analysis depth will be shallower, and therefore the same results as in the measurement according to the present invention cannot be obtained.

The ion etching was performed using Ar ions. Ions were irradiated at an accelerating voltage of 500 V in an area of 2 mm x 2 mm, and the center position was taken as the measurement point.
During ion etching, the Zalar mode of the apparatus was used, and ion beam irradiation was performed while horizontally rotating the sample at a speed of 360°/min.
The ion etching rate with Quantera II under the above conditions is 1 nm/min in terms of cutting the silicon dioxide film, and in the present invention, 1 minute etching under these conditions is defined as cutting to a depth of 1 nm.
Note that the ion beam irradiation direction and the photoelectron escape direction when measuring photoelectrons do not match. For this reason, if the sample is horizontally rotated and the ion beam is not irradiated, the portion that is a blind spot for the ion beam irradiation will also be measured, making it impossible to obtain the same results as in the measurement according to the present invention.
From the obtained measurement data, the peak area ratio was calculated using the instrument standard analysis software MutiPak, and the atomic number ratio was determined using the sensitivity factor as it was installed in MutiPak.

[Method for measuring I _pa of carbon fiber bundle]
_Ipa was measured by the following method.
The electrolytic solution used was adjusted to pH 3 with a 5% phosphoric acid aqueous solution, and nitrogen was bubbled to remove the influence of dissolved oxygen. A carbon fiber sample was immersed in an electrolytic solution as one electrode, a platinum electrode with sufficient surface area was used as a counter electrode, and an Ag/AgCl electrode was used as a reference electrode. The sample form was a 12000 filament tow with a length of 50 mm. The scanning range of the potential applied between the carbon fiber electrode and the platinum electrode was from −0.2 V to +0.8 V, and the scanning speed was 2.0 mV/sec. Draw a current-voltage curve with an X-Y recorder, sweep it three times or more, and when the curve becomes stable, read the current value i using the potential at +0.4 V with respect to the Ag/AgCl standard electrode as a reference potential, and then I _pa was calculated according to the formula.
I _pa = 1 (μA)/sample length (cm) x (4π x area weight (g/cm) x number of single fibers/density (g/cm ³ )) ^1/2
The apparent surface area was calculated from the sample length and the density and basis weight of the carbon fiber bundle measured by the method described above, and was divided by the current value i to obtain I _pa . This measurement was performed using a cyclic voltametry analyzer (manufactured by Yanagimoto Seisakusho, product name: P-1100 model).

[Measurement method of strand physical properties]
The strand strength and strand elastic modulus of the carbon fiber bundle were measured in accordance with JIS R 7608:2007. Note that the strand elastic modulus was calculated using method A of the same method.

[Example 1]
<Preparation of carbon fiber precursor fiber bundle>
An acrylonitrile polymer containing 98% by mass of acrylonitrile units and 2% by mass of methacrylic acid units was dissolved in dimethylformamide to prepare a 23.5% by mass spinning solution.
This spinning solution was spun out from a spinneret having a diameter of 150 μm and 12,000 discharge holes arranged therein for dry-wet spinning. That is, after spinning in the air and passing through a space of approximately 5 mm, it is coagulated in a coagulation solution filled with an aqueous solution containing 79.0% by mass of dimethylformamide, the temperature of which is adjusted to 10°C, to form a coagulated thread. I took over. Next, the film was stretched 1.1 times in air, and then stretched 2.5 times in a stretching tank filled with an aqueous solution containing 35% by mass of dimethylformamide, the temperature of which was adjusted to 60°C. After stretching, the processed fiber bundle containing the solvent was washed with clean water, and then stretched 1.4 times in hot water at 95°C. Subsequently, an oil agent containing amino-modified silicone as a main component was applied to the fiber bundle in an amount of 1.1% by mass, and the fiber bundle was dried and densified. The fiber bundle after drying and densification is stretched 2.6 times between heated rolls to further improve orientation and densification, and then wound to form a carbon fiber precursor fiber bundle (carbon fiber precursor acrylic fiber). bundle). The single fiber fineness of the obtained carbon fiber precursor fiber bundle was 0.8 dtex.

<Preparation of carbon fiber bundle>
A plurality of carbon fiber precursor fiber bundles are arranged in parallel and introduced into a flameproofing furnace, and air heated to 220 to 280° C. is blown onto the carbon fiber precursor fiber bundles to form carbon fiber precursor fiber bundles. A flame resistant fiber bundle having a density of 1.35 g/cm ³ was obtained by flame resistant treatment. The elongation rate was 6%, and the flame resistance treatment time was 70 minutes.

Next, the flame-resistant fiber bundle was passed through a first carbonization furnace having a temperature gradient of 300 to 700° C. in nitrogen while being stretched by 4.5% to perform a first carbonization treatment. The temperature gradient was set to be linear. The processing time was 2.0 minutes.
Further, a second carbonization treatment was performed using a second carbonization furnace in which a temperature gradient of 1000 to 2300° C. was set in a nitrogen atmosphere to obtain a carbon fiber bundle. At that time, the elongation rate in the second carbonization treatment was -4.0%, and the treatment time was 3.5 minutes.

<Surface treatment and sizing treatment of carbon fiber bundles>
Subsequently, the carbon fiber bundle was made to run in a 5% by mass aqueous solution of phosphoric acid, and then in a 5% by mass aqueous solution of ammonium bicarbonate, and at the same time, an electricity amount of 140 coulombs per gram of carbon fiber to be treated was generated using the carbon fiber bundle as an anode. Electricity was applied between the electrode and the opposite electrode so that the result was as follows. No current treatment was performed in the phosphoric acid aqueous solution. Next, after washing with hot water at 90° C., a surface-treated carbon fiber bundle was obtained by drying.
Next, 0.5% by mass of a sizing agent ("Hydran N320" manufactured by DIC Corporation) was attached (sizing treatment) and wound around a bobbin to obtain a carbon fiber bundle.
Regarding the carbon fiber bundle after sizing treatment, single fiber diameter and number, basis weight and density of the carbon fiber bundle, O/C, N/C on the fiber surface of the carbon fiber bundle, N/C after etching, I _pa , strand strength and the strand elastic modulus was measured. These results are shown in Table 1.

[Example 2]
Carbon fiber bundles were produced in the same manner as in Example 1, except that the surface treatment conditions were changed as shown in Table 1, and various measurements were performed. The results are shown in Table 1.

[Example 3]
The same as in Example 2 except that while running in a phosphoric acid aqueous solution, the carbon fiber bundle was used as an anode and energized with a counter electrode so that the amount of electricity was 7 coulombs per gram of carbon fiber to be treated. A carbon fiber bundle was obtained.

[Examples 4 to 6, Comparative Example 1]
A carbon fiber bundle was obtained in the same manner as in Example 3, except that the amount of electricity in the electrolytic treatment in an aqueous phosphoric acid solution was changed as shown in Table 1.

[Comparative example 2]
A carbon fiber bundle was obtained in the same manner as in Example 3, except that the amounts of electricity in the electrolytic treatment in the phosphoric acid aqueous solution and the electrolytic treatment in the ammonium bicarbonate aqueous solution were changed as shown in Table 1.

[Example 7, 8]
A carbon fiber bundle was produced in the same manner as in Example 1, except that the single fiber fineness of the carbon fiber precursor fiber bundle was changed to 1.2 dtex and the surface treatment conditions were changed as shown in Table 1, and various measurements were carried out. went. The results are shown in Table 1.

[Examples 9 to 12, Comparative Examples 3 to 4]
A carbon fiber bundle was produced in the same manner as in Example 3, except that the single fiber fineness of the carbon fiber precursor fiber bundle was changed to 1.2 dtex and the surface treatment conditions were changed as shown in Table 1, and various measurements were carried out. went. The results are shown in Table 1.

Since the carbon fiber bundle of the present invention has high strand strength, it can be used in applications that require high strength, such as automobile parts, aerospace materials, civil engineering and construction materials, sports and leisure materials, pressure vessels, and wind turbine blades. It is useful in a wide range of applications, including industrial materials such as.

Claims (16)

A carbon fiber bundle in which the ratio N/C of the number of nitrogen atoms to the number of carbon atoms on the fiber surface of the carbon fiber bundle obtained by X-ray photoelectron spectroscopy is 0.005 to 0.05. The carbon fiber bundle according to claim 1, having a strand strength of 5.2 to 7.0 GPa and a strand elastic modulus of 370 to 430 GPa. The carbon fiber bundle according to claim 1 or 2, wherein the value of I _pa calculated by the method described in the specification is 0.01 to 0.25 μA/cm ² . According to any one of claims 1 to 3, the ratio O/C of the number of oxygen atoms to the number of carbon atoms on the fiber surface of the carbon fiber bundle obtained by X-ray photoelectron spectroscopy is 0.01 to 0.25. carbon fiber bundle. The carbon fiber bundle according to any one of claims 1 to 4, wherein the N/C in a region etched by 5 nm from the carbon fiber surface is 0.005 to 0.04. The carbon fiber bundle according to any one of claims 1 to 5, wherein the N/C in a region etched by 10 nm from the carbon fiber surface is 0.005 to 0.04. The carbon fiber bundle according to any one of claims 1 to 6, wherein the N/C in a region etched by 15 nm from the carbon fiber surface is 0.01 to 0.04. The carbon fiber bundle according to any one of claims 1 to 7, wherein the N/C in a region etched by 20 nm from the carbon fiber surface is 0.02 to 0.04. The carbon fiber bundle according to any one of claims 1 to 8, wherein the carbon fiber bundle has a single fiber diameter of 5.0 to 7.0 μm. The carbon fiber bundle according to any one of claims 1 to 8, wherein the carbon fiber bundle has a single fiber diameter of 5.5 to 6.7 μm. The carbon fiber bundle according to any one of claims 1 to 8, wherein the carbon fiber bundle has a single fiber diameter of 5.7 to 6.7 μm. A manufacturing method for obtaining a carbon fiber bundle by heating a carbon fiber precursor fiber bundle, the carbon fiber precursor fiber bundle being heat-treated at 2000°C or higher in an inert atmosphere, then immersed in an acidic aqueous solution, and then A method for producing a carbon fiber bundle, which comprises immersing the carbon fiber bundle in an alkaline aqueous solution and performing electrolytic treatment at least in the alkaline aqueous solution. The method for manufacturing a carbon fiber bundle according to claim 12, wherein electrolytic treatment is performed in the acidic aqueous solution. The method for producing a carbon fiber bundle according to claim 12 or 13, wherein the amount of electricity in the electrolytic treatment in the alkaline aqueous solution is 5 to 200 coulombs per gram of carbon fiber to be treated. The method for producing a carbon fiber bundle according to any one of claims 12 to 14, wherein the acidic aqueous solution has a pH of 1 to 4. The method for producing a carbon fiber bundle according to claim 13, wherein the amount of electricity in the electrolytic treatment in the acidic aqueous solution is 0 to 30 coulombs per gram of carbon fiber to be treated.