JP2013181264A - Carbon fiber bundle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high quality carbon fiber bundle that has few single fiber interlace in the fiber bundle and is excellent in spreading property, despite a large single fiber fineness and excellent productivity.SOLUTION: The carbon fiber bundle includes a single fiber having a fineness of 0.75 dtex to 2.5 dtex. The shape of a cross section perpendicular to the fiber axis of the single fiber is of a circularity of 0.70-0.90. The CF value calculated from a drop distance of a hook drop is 10-30. The carbon fiber bundle has a total fineness of 25,000-90,000 dtex.

Description

  The present invention relates to a carbon fiber bundle excellent in spreadability.

  Carbon fiber is widely used in various applications, for example, aerospace materials such as aircraft and rockets, tennis rackets, golf shafts, fishing rods, etc. due to its mechanical and chemical properties and light weight. It is also being used in the field of transportation machinery such as ships and automobiles. In recent years, due to the high conductivity and heat dissipation of carbon fibers, there is a strong demand for application to electronic device parts such as mobile phone and personal computer casings and fuel cell electrodes. In this way, the range of application is widened, but for carbon fibers, the demand for increased production and cost reduction is becoming stricter.

Conventionally, the following method can be used to carbonize a polyacrylonitrile-based precursor fiber bundle (hereinafter referred to as a PAN-based precursor fiber bundle). First, several tens to several hundreds of PAN-based precursor fiber bundles are arranged in a sheet shape and subjected to flame resistance treatment in an oxidizing atmosphere at 200 to 300 ° C.
The flameproof fiber bundle obtained by the flameproofing treatment is subsequently introduced into a firing (carbonization treatment) step in an inert atmosphere at 300 ° C. or higher to obtain carbon fibers. Thereafter, by performing electrolytic oxidation treatment in the electrolytic solution, or by performing oxidation treatment in the gas phase or liquid phase, the affinity and adhesion between the carbon fiber and the matrix resin in the composite material are improved, A process of applying a sizing agent is common.

  Here, as a means for increasing the production amount in the field of synthetic fibers, the number of yarns is increased or the thickness of each yarn is increased to increase the thickness of the yarn bundle. A method for increasing the discharge amount is known. Increasing the yarn bundle in this way will increase production while minimizing the increase in equipment costs, and at the same time will lead to cost reductions in major industrial fibers such as polyester and nylon. Is also widely used.

  Patent Document 1 uses a carbon fiber precursor fiber bundle having a high roundness and a large single fiber fineness to suppress burning spots during the flameproofing treatment, and despite the large total fineness, We have proposed a technique for obtaining carbon fiber bundles that are less tangled, have better spreadability, and are more productive.

JP 2008-202207 A

In the technique of Patent Document 1, although the total fineness is large and the productivity is excellent, the single fiber entanglement in the yarn bundle is small and the carbon fiber bundle having excellent spreadability has a cross-sectional shape of 8 μm or more in diameter, true A carbon fiber bundle has been proposed in which 36,000 or more single fibers having a circularity of 0.95 or more and a tensile strength of 3 GPa or more are converged.
However, the spreadability and spreadability were not sufficient.

  As a result of intensive studies, the present invention has less entanglement of single fibers in the fiber bundle, despite having a large single fiber fineness and excellent productivity as compared with the carbon fiber bundle described in Patent Document 1. An object of the present invention is to provide a high-quality carbon fiber bundle excellent in spreadability.

The above-mentioned problems are solved by the present invention comprising the following technical means (1) to (3).
(1) The carbon fiber bundle of the present invention has a single fiber fineness in the range of 0.75 dtex to 2.5 dtex, and a cross-sectional shape perpendicular to the fiber axis of the single fiber has a roundness of 0.70 to 0.00. 90 and the CF value calculated from the drop distance of the hook drop is 10-30.
(2) The carbon fiber bundle of the present invention preferably has a total fineness of 25,000 to 90,000 dtex.
(3) The carbon fiber bundle of the present invention is produced using a PAN-based carbon fiber precursor fiber bundle composed of a polyacrylonitrile-based copolymer having 95 to 99 mol% of acrylonitrile units and 1 to 5 mol% of hydroxyalkyl methacrylate units. It is preferable that the carbon fiber bundle be made.

  According to the present invention, there is provided a high-quality carbon fiber bundle that has a single fiber fineness and high productivity, and has few single fiber entanglement in the fiber bundle and excellent spreadability.

It is the schematic of the apparatus for fiber-opening evaluation.

An example of an embodiment of the present invention will be described with reference to FIG.
The bobbin which wound up the carbon fiber bundle to 1 is mounted | worn, and a carbon fiber bundle is made to drive to the winding-up part of 7 using a drive device. In order to make the tension constant, the nip roll 3 and the dancer roll 4 are used. In order to open the carbon fiber bundle, five fixed guides 5 are arranged. The tow width measuring device 6 is arranged between the fixed guides 5 to continuously measure the opened tow width. The material of the fixed guide 5 and the free roll 2 is not particularly defined.

<Acrylonitrile polymer>
Examples of the acrylonitrile-based polymer that can be used as a raw material for the PAN-based precursor fiber bundle, which is a raw material for the carbon fiber bundle of the present invention, include an acrylonitrile homopolymer or copolymer, or a mixture thereof.

  Content of the hydroxyalkyl methacrylate unit in a copolymer is 1-5 mol%. The carboxylic acid ester group of the hydroxyalkyl methacrylate unit is thermally decomposed into a carboxylic acid group at a high temperature of 250 ° C. or higher. If the content of the hydroxyalkyl methacrylate unit in the copolymer is 1 mol% or more, when the carboxylic acid ester group of the hydroxyalkyl methacrylate unit becomes a carboxylic acid group in the flameproofing step, the flameproofing reaction is performed. Sufficient effect to promote is obtained. On the other hand, if it is 5 mol% or less, runaway of the flameproofing reaction can be suppressed. Further, it is possible to suppress a decrease in the carbonization yield accompanying the elimination of the hydroxyalkyl group in the flameproofing step.

  The lower limit of the content of the hydroxyalkyl methacrylate unit is preferably 1.2 mol% or more from the viewpoint of securing the denseness of the carbon fiber precursor fiber bundle (hereinafter referred to as “precursor fiber bundle” as appropriate), and has higher performance. The amount of 1.5 mol% or more is more preferable in that a fiber is obtained. Further, the upper limit of the content of the hydroxyalkyl methacrylate unit is preferably 4.0 mol% or less from the viewpoint of suppressing a runaway reaction in the flameproofing step, and 3.0 from the viewpoint of suppressing a decrease in carbonization yield. The mol% or less is more preferable.

  Examples of the hydroxyalkyl methacrylate used as a raw material for the hydroxyalkyl methacrylate unit include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, monoglyceryl methacrylate, and tetrahydrofurfuryl methacrylate. It is done. Furthermore, these hydroxyalkyl acrylates may be used in combination.

  2-Hydroxyethyl methacrylate has a hydroxyethyl group elimination temperature of 240 ° C. or higher in the flameproofing process, a bulkiness sufficient for improving oxygen permeability, and a hydroxyethyl group elimination. It is suitable as a constituent component of the copolymer of the present invention from the viewpoints of little decrease in mass when obtained and industrial availability.

<Other monomers>
The copolymer of the present invention contains acrylonitrile units and hydroxyalkyl methacrylate units, but may contain other monomer units as necessary.

  As the other monomer, a vinyl monomer copolymerizable with acrylonitrile is preferable. Specifically, (meth) acrylate esters such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, chloride Vinyl halides such as vinyl, vinyl bromide, vinylidene chloride, acids such as (meth) acrylic acid, itaconic acid, crotonic acid and their salts, maleic acid imide, phenylmaleimide, (meth) acrylamide, styrene, α- Examples include methylstyrene and vinyl acetate. These may be used alone or in combination of two or more.

  The content of other monomer units in the copolymer of the present invention is preferably 3.5 mol% or less in consideration of the content of acrylonitrile units and hydroxyalkyl methacrylate units.

  Examples of a polymerization method for obtaining an acrylonitrile-based polymer that can be used as a raw material for a PAN-based precursor fiber bundle that is a raw material for a carbon fiber bundle of the present invention include, for example, redox polymerization in an aqueous solution and suspension polymerization in a heterogeneous system. And emulsion polymerization using a dispersant, but are not limited thereto.

  As a spinning method of the precursor fiber bundle of the carbon fiber bundle obtained in the present invention, a known method can be adopted, and specific examples include a wet spinning method, a dry wet spinning method, a dry spinning method and the like. Among these, the wet spinning method is preferably used from the viewpoint of productivity.

  The spinning solution is discharged and spun into a coagulation bath through a spinneret to obtain a coagulated yarn. The roundness of the single fiber of the precursor fiber bundle can be controlled in the coagulation process in the spinning process. As the coagulation bath conditions, a concentration of 30% by mass to 60% by mass and a temperature of 20 ° C. to 40 ° C. are preferable. If the coagulation bath conditions are within this range, a precursor fiber bundle having a roundness of 0.70 or more and 0.90 or less can be obtained while maintaining an appropriate coagulation rate.

  If the coagulation bath concentration is 60% by mass or less, the exchange rate of the solvent and water on the surface of the spinning dope discharged into the coagulating bath exceeds the diffusion rate of water into the spinning dope, and the precursor fiber bundle The roundness is maintained within the above range, and a dense precursor fiber can be obtained. Furthermore, adhesion between the single yarns of the precursor fiber bundle can be suppressed. In particular, when spinning a precursor fiber bundle having a large single fiber fineness and a total fineness, the concentration is preferably 55% by mass or less from the viewpoint of further suppressing adhesion between single yarns. In addition, if the coagulation bath concentration is 30% by mass or more, it is possible to suppress that the exchange rate of the solvent and water on the surface of the spinning dope discharged into the coagulating bath significantly exceeds the diffusion rate of water into the spinning dope. In addition, the roundness of the precursor fiber bundle can be maintained within the above range within a range where rapid shrinkage of the coagulated yarn does not occur, and a dense precursor fiber bundle can be obtained.

  On the other hand, if the coagulation bath temperature is 40 ° C. or less, the exchange rate of the solvent and water on the surface of the spinning dope discharged into the coagulation bath is significantly higher than the diffusion rate of water into the spinning dope. The circularity of the precursor fiber bundle can be maintained within the above range within a range where the shrinkage of the coagulated yarn does not occur, and a dense precursor fiber can be obtained. Moreover, if it is 20 degreeC or more, the replacement | exchange speed | rate of the solvent and water in the surface of the spinning dope discharged in the coagulation bath, and the diffusion rate of the water in a spinning dope will be maintained appropriately, and precursor fiber will be stabilized. A bundle can be produced. Furthermore, it is not necessary to cool the coagulation bath excessively, capital investment and running costs can be suppressed, and the precursor fiber bundle can be produced at low cost.

<Entanglement process>
Next, the moisture content of the fiber bundle that has been subjected to steam drawing or dry heat drawing is adjusted with a touch roll as necessary, and then subjected to entanglement treatment by blowing air by a known method to obtain precursor fibers. Get a bunch. In the present invention, the entanglement treatment is essential, and by providing entanglement between the filaments of the precursor fiber bundle, it is possible to obtain a fiber bundle that imparts convergence and retains the shape of one tow. Moreover, it is difficult to disperse the fiber bundle, and the passability of the firing process can be improved. When the entanglement treatment is not carried out or when it is insufficient, the fiber bundle width of the carbon fiber precursor fiber bundle is remarkably widened in the firing step, particularly the flameproofing step.

  The entanglement degree in the precursor fiber bundle subjected to the entanglement treatment is preferably in the range of 5 to 20 pieces / m, more preferably in the range of 10 to 14 pieces / m. If the entanglement degree is 5 pieces / m or more, the fiber bundle is difficult to be separated and the passability of the firing process is good. Moreover, if the entanglement degree is 20 pieces / m or less, the resulting carbon fiber bundle has good resin impregnation and spreadability.

  The entanglement degree of the precursor fiber bundle in this specification is a parameter indicating how many times one single fiber in the fiber bundle is entangled with other adjacent single fibers per 1 m of fiber length. The degree of entanglement is measured by the hook drop method.

<Cross-sectional shape of single fiber of carbon fiber precursor fiber bundle>
In the present invention, the roundness is a value obtained by the following formula (1), and S and L are obtained by SEM observation and image analysis of a cross section perpendicular to the fiber axis of the single fiber. Cross-sectional area S and circumference L.
Roundness = (4πS) / L ² (1)

<Cross sectional shape>
The single fiber cross-sectional shape of the precursor fiber bundle of the present invention has a roundness of 0.70 or more and 0.90 or less. Moreover, it is preferable that a cross-sectional shape is an empty bean type. The single fiber cross-sectional shape of the precursor fiber bundle becomes the single fiber cross-sectional shape of the carbon fiber. If the cross-sectional shape is an empty bean type with a roundness of 0.90 or less, the cross-section with a roundness of around 1.00 has a better opening than a carbon fiber bundle close to a perfect circle. It is not clear why the carbon fiber bundle having a roundness of 0.70 or more and 0.90 has better openability than the carbon fiber bundle having a roundness of around 1.00. When the circularity approaches 1.0, the convergence tends to be too high. If the bundling property is too high, it is considered that the single fiber is difficult to spread uniformly and the spreadability is deteriorated. On the other hand, as shown in Japanese Patent Application Laid-Open No. 11-124743, etc., in carbon fiber having a relatively simple cross section such as flat and three leaves, single fibers are engaged with each other, and spreadability is lowered. . In addition, for single fibers with complex irregular cross-sections such as 8-leaf and C-type, single fibers rarely mesh with each other, but conversely, it becomes impossible to pack single fibers closely, and when prepreg is manufactured The fiber content cannot be increased, and the mechanical properties of the composite material are reduced. For the reasons described above, the roundness of the single fiber constituting the carbon fiber precursor fiber bundle is preferably 0.70 or more and 0.90 or less, and more preferably 0.75 or more and 0.85 or less.

<Flame resistance treatment>
Next, the manufacturing method of the carbon fiber of this invention is demonstrated. First, the precursor fiber bundle is subjected to flameproofing treatment at a temperature of 240 ° C. or higher and 300 ° C. or lower in an oxidizing atmosphere to obtain a flame resistant fiber bundle. In the present invention, “under an oxidizing atmosphere” means in the air containing an oxidizing substance such as nitrogen dioxide, sulfur dioxide and oxygen.

<Pre-carbonization treatment>
After the flameproofing treatment and before the carbonization treatment, a precarbonization treatment can be performed in which the obtained flameproofed fiber bundle is treated in an inert gas at a maximum temperature of 550 ° C. or higher and 800 ° C. or lower.

<Carbonization treatment>
A carbon fiber bundle can be produced by subjecting the obtained flame resistant fiber bundle to carbonization treatment in an inert gas at a temperature of 800 ° C. or higher and 2000 ° C. or lower. Furthermore, a graphite fiber can also be manufactured by processing this carbon fiber in inert gas at high temperature about 2500 degreeC-2800 degrees C or less. The carbon fiber bundle obtained by carbonization treatment has a single fiber basis weight in the range of 0.075 mg / m to 0.25 mg / m, or a single fiber fineness of 0.75 dtex to 2.5 dtex, and a single fiber The cross-sectional shape perpendicular to the axis has a roundness of 0.70 or more and 0.90 or less. The cross-sectional shape is preferably an empty bean type. The reason why the roundness is preferably 0.70 or more and 0.90 or less is as described in [0013] above. The roundness of the single fiber constituting the carbon fiber bundle is preferably 0.70 or more, and more preferably 0.75 or more.

<Surface treatment of carbon fiber bundle>
The carbon fiber bundle of the present invention may be subjected to a surface treatment before the sizing treatment step. For example, it is preferable to improve the affinity and adhesion between the carbon fiber and the matrix resin in the composite material by performing an electrolytic oxidation treatment in the electrolytic solution or by performing an oxidation treatment in a gas phase or a liquid phase. .

  The main components of the sizing agent in the sizing treatment liquid are epoxy resin, epoxy-modified polyurethane resin, polyester resin, phenol resin, polyamide resin, polyurethane resin, polycarbonate resin, polyetherimide resin, polyamideimide resin, polyimide resin, bismaleimide Resins, urethane-modified epoxy resins, polyvinyl alcohol resins, polyvinyl pyrrolidone resins, polyether sulfone resins and the like can be mentioned, and are not particularly limited.

  Content of the sizing agent in a sizing process liquid is not specifically limited, 0.2-20 mass% is preferable, More preferably, it is 3-10 mass%. By setting the content of the sizing agent in the sizing treatment liquid to 0.2% by mass or more, a desired function can be sufficiently imparted to the carbon fiber. Further, by adjusting the content of the sizing agent in the sizing treatment liquid to 20% by mass or less, the adhesion amount of the sizing agent becomes appropriate, and the carbon fiber bundle in the production of the composite material which is a subsequent process is added. The impregnation property of the matrix resin is improved.

  Although the solvent or dispersion medium used for the sizing treatment liquid is not particularly limited, it is preferable to use water from the viewpoints of handleability and safety.

  The amount of the sizing agent attached to 100% by mass of the carbon fiber bundle is preferably 0.3 to 5% by mass, and more preferably 0.4 to 3% by mass. By setting the adhesion amount of the sizing agent to 0.3% by mass or more, a desired function can be sufficiently imparted to the carbon fiber bundle. Moreover, by making the adhesion amount of the sizing agent 3% by mass or less, the impregnation property of the matrix resin into the carbon fiber bundle at the time of manufacturing the composite material which is a subsequent process becomes good.

  In the drying process after the sizing process, the solvent or dispersion medium of the sizing process liquid is removed by drying. The conditions in this case are preferably a temperature of 120 to 300 ° C. and a range of 10 seconds to 10 minutes, and more preferably a temperature of 150 to 250 ° C. and a range of 30 seconds to 4 minutes. By setting the drying temperature to 120 ° C. or higher, the solvent can be sufficiently removed. Moreover, the quality of the carbon fiber bundle by which the sizing process was carried out can be maintained by making drying temperature into 300 degrees C or less.

  The drying method is not particularly limited, and examples thereof include a method in which the carbon fiber bundle is brought into contact with a hot roll using steam as a heat source and a method in which the carbon fiber bundle is dried in an apparatus in which hot air is circulated. be able to.

<Cross-sectional shape of single fiber of carbon fiber bundle>
In the present invention, the roundness is a value obtained by the above equation (1).

<Cross-sectional shape of single fiber of carbon fiber bundle>
The single fiber cross-sectional shape of the carbon fiber bundle of the present invention has a roundness of 0.70 or more and 0.90 or less. Moreover, it is preferable that a cross-sectional shape is an empty bean type. If the cross-sectional shape is an empty bean type with a roundness of 0.90 or less, the cross-section with a roundness of around 1.00 has a better opening than a carbon fiber bundle close to a perfect circle. It is not clear why the carbon fiber bundle having a roundness of 0.70 or more and 0.90 has better openability than the carbon fiber bundle having a roundness of around 1.00. When the circularity approaches 1.0, the convergence tends to be too high. If the bundling property is too high, it is considered that the single fiber is difficult to spread uniformly and the spreadability is deteriorated. On the other hand, as shown in Japanese Patent Application Laid-Open No. 11-124743, etc., in carbon fibers having a relatively simple irregular cross section such as flat or three leaves, single fibers are engaged with each other, and the spreadability is reduced. To do. In addition, for single fibers with complex irregular cross-sections such as 8-leaf and C-type, single fibers rarely mesh with each other, but conversely, it becomes impossible to pack single fibers closely, and when prepreg is manufactured The fiber content cannot be increased, and the mechanical properties of the composite material are reduced. For the reasons described above, the roundness of the single fiber constituting the carbon fiber precursor fiber bundle is preferably 0.70 or more and 0.90 or less, and more preferably 0.75 or more and 0.85 or less.

<Fineness of single fiber of carbon fiber bundle>
Furthermore, in the carbon fiber bundle of the present invention, the basis weight of the single fiber is in the range of 0.075 to 0.25 mg / m, or the fineness of the single fiber is a 0.75 dtex to 2.5 dtex carbon fiber bundle. preferable.

  When the basis weight of the single fiber is 0.075 mg / m or more, or the fineness of the single fiber bundle is 0.75 dtex or more, it is easy to suppress the decrease in the spreadability due to the small cross section of the single fiber. On the other hand, when the basis weight of the single fiber is 0.25 mg / m or less or the fineness of the single fiber is 2.5 dtex or less, the cross section of the single fiber does not become too large, and the carbon fiber bundle can be efficiently made from an economic viewpoint. It is preferable because it is easy to manufacture. A more preferable range of the basis weight of the single fiber is 0.12 to 0.24 mg / m, and a preferable range of the fineness of the single fiber is a range of 1.2 to 2.4 dtex.

  The carbon fiber bundle of the present invention preferably has a total fineness of 25,000 to 90,000 dtex. A carbon fiber bundle having a total fineness in this range is suitable for the production of large composite materials and molded products. When a plurality of thin fiber bundles are combined and the total fineness is adjusted, the fiber bundles are displaced from each other, and it is difficult to produce a large-sized composite material / molded article with good quality. A total fineness of 25,000 dtex or more is preferable because productivity can be increased and costs can be easily reduced. If the total fineness is 90,000 dtex or less, handling is easy, and from that point, 60,000 dtex or less is more preferable, and 40,000 dtex or less is more preferable.

In the present invention, the converging value of the carbon fiber bundle focused on the fiber bundle is defined by the confounding value in the hook drop method. The confounding value of the carbon fiber bundle by the hook drop method is measured by the following method. The carbon fiber bundle is suspended in the vertical direction, and a weight of 150 g is attached to the lower part of the carbon fiber bundle. The average value x of the carbon fiber bundle bundle with a weight (15 g) inserted into the key needle, and after dropping 50 times, measuring 10 times from the largest to the largest and excluding 10 from the smallest to the smallest Using (cm), the CF value is obtained from the following equation (2).
CF value = 100 / x (1 / m) (2)

If the CF value of the carbon fiber measured in this way is 10 or more, it is easy to prevent the passage of the firing process from deteriorating because the fiber bundle width becomes extremely wide especially in the flameproofing process during carbon fiber production. Therefore, it is not preferable.
On the other hand, if the CF value is 30 or less, the interference between single yarns does not become too large, and this is advantageous in high-order processing applications where spreadability such as filament winding is required. Thus, the CF value for obtaining a carbon fiber excellent in high-order workability is in the range of 15 to 25 (1 / m). More desirably, it is in the range of 17-22 (1 / m).

  Hereinafter, the present invention will be specifically described with reference to examples. Each measuring method in an Example is as follows.

<Circularity of carbon fiber bundle>
(1) Preparation of sample A carbon fiber bundle cut to a length of 5 cm is embedded in an epoxy resin (Epomount main agent: Epomount curing agent = 100: 9 (mass ratio)), cut to 2 cm, and the cross section is exposed. And mirror-finished.
(2) Etching treatment of observation surface Further, in order to clarify the outer shape of the fiber, the cross section of the sample was etched by the following method.
-Equipment used: JEOL Ltd. JP-170 plasma etching equipment,
Processing conditions: (atmosphere gas: Ar / O ₂ = 75/25, plasma output: 50 W, degree of vacuum: about 120 Pa, processing time: 5 min).
(3) SEM observation The cross section of the sample obtained by said (1) is observed using SEM (PHILIPS FEI-XL20), and the photograph in which five or more fiber cross sections are reflected on the screen is arbitrarily 5 A photo was taken.
(4) Measurement of roundness of single fiber of carbon fiber bundle The outer shape of the fiber cross-section is traced using image analysis software (manufactured by Nippon Roper, product name: Image-Pro PLUS), and the circumference L and area S Was measured. For each sample, 20 pieces were arbitrarily selected from five photographs, but three or more fiber cross sections were selected from one photograph, measured, average values of L and S were obtained, and roundness was calculated by the following equation. .
Roundness = (4πS) / L ²

<Method of measuring tow width for evaluation of spreadability>
As shown in FIG. 1, the carbon fiber bundle is unwound while adjusting the tension by passing the driving roll 2 at a speed of 2 m / min in a state where a tension of 2.0 kgf is applied from above the carbon fiber bobbin package 1. Then, it was wound up by the winding unit 5. The tow width for 50 m was read with a digital dimension measuring device 3 (OMRON Z4LC-28) every 0.1 second and recorded with a data logger, and the average value was calculated.

<Confounding value and CF value with carbon fiber bundle hook drop>
The confounding value by the hook drop method was measured by the following method. The carbon fiber bundle is suspended in the vertical direction, and a weight of 150 g is attached to the lower part of the carbon fiber bundle. After piercing a key with a weight (15 g) into a carbon fiber bundle and measuring the falling distance 50 times, the average value x (10) from the largest to the largest and 10 from the smallest to the smallest is removed x ( cm) was used to obtain the CF value from the following formula.
CF = 100 / x (1 / m)

(7) Amount of carbon fiber sizing agent attached The amount of carbon fiber sizing agent attached after sizing was measured by a Soxhlet extraction method using methyl ethyl ketone. The extraction time was 1 hour.

<Example 1>
Copolymerization was carried out by aqueous suspension polymerization in the presence of acrylonitrile, 2-hydroxyethyl methacrylate, ammonium persulfate-ammonium hydrogen sulfite and iron sulfate, and acrylonitrile units / 2-hydroxyethyl methacrylate units = 98.5 / 1.5 ( An acrylonitrile copolymer comprising (mass ratio) was obtained. This acrylonitrile copolymer was dissolved in dimethylacetamide to prepare a 21% by mass spinning dope. It is discharged through a spinneret (spinning nozzle) having a pore number of 24,000 and a hole diameter of 60 μm into a coagulation bath made of a dimethylacetamide aqueous solution having a concentration of 60% by mass and a temperature of 35 ° C. A fiber bundle (swelling yarn) was obtained by taking up at a speed of 32 times. Next, this fiber bundle was stretched 5.4 times simultaneously with washing with water, and an oil-modified composition of amino-modified silicon / polyoxyethylene (6) lauryl ether = 91/9 (mass ratio) was 1.5% by mass. A second oil bath having the same composition and concentration as the first oil tub after being guided to the fiber bundle, guided to the first oil bath made of the oil treatment liquid dispersed in water at a concentration, once squeezed with a guide The oil agent treatment liquid was again applied to the fiber bundle.

  The fiber bundle to which the oil agent treatment liquid was applied again was dried using a heating roll, and dry heat drawing was performed 1.34 times between the heating rolls whose rotation speed was adjusted to a predetermined condition. The total draw ratio from the swollen yarn at this time was 7.4 times. Thereafter, water content was adjusted by applying water to the fiber bundle with a touch roll, and tangential treatment was performed to obtain a PAN-based precursor fiber bundle having a single fiber fineness of 2.5 dtex.

The above-mentioned PAN-based precursor fiber bundle was subjected to a flameproofing treatment at a stretch rate of −1.5% under a temperature distribution of 220 to 260 ° C. for 70 minutes to obtain a flameproofed fiber bundle. The obtained flame-resistant fiber bundle was further pre-carbonized for 1.4 minutes at 700 ° C. and + 3% elongation in a nitrogen atmosphere, followed by 1,300 ° C. and −4.0% elongation in a nitrogen atmosphere. Carbon fiber treatment was performed at a rate of 1.0 minute to obtain a carbon fiber bundle. Thereafter, 80 parts by mass of “Epicoat 828” manufactured by Japan Epoxy Resin Co., Ltd. and 20 parts by mass of “Pluronic F88” manufactured by Asahi Denka Co., Ltd. as an emulsifier are mixed as the main agent in the surface treatment and then sizing treatment, and phase inversion is performed. 0.4% by mass of a sizing agent prepared in an aqueous dispersion by emulsification was adhered, and after a drying treatment, a carbon fiber bundle was obtained. The weight of the single fiber of the obtained carbon fiber bundle was 0.12 mg / m, the fineness of the single fiber was 1.24 dtex, and the roundness was 0.75. The resulting carbon fiber bundle was used to evaluate the fiber opening using the apparatus shown in FIG. The tow width of the carbon fiber bundle at that time was 18.2 mm. The tow width per 1 g of carbon fiber bundles was 11.1 mm. When the hook drop value of this carbon fiber bundle was measured, the CF value was 18. The results are shown in Table 1.
<Example 2>

  It is discharged through a spinneret (spinning nozzle) having a pore number of 12,000 and a hole diameter of 60 μm into a coagulation bath composed of an aqueous dimethylacetamide solution having a concentration of 60% by mass and a temperature of 35 ° C. A fiber bundle (swelling yarn) was obtained by taking up at a speed of 18 times. Next, this fiber bundle was stretched 5.4 times simultaneously with washing with water, and an oil-modified composition of amino-modified silicon / polyoxyethylene (6) lauryl ether = 91/9 (mass ratio) was 1.5% by mass. A second oil bath having the same composition and concentration as the first oil tub after being guided to the fiber bundle, guided to the first oil bath made of the oil treatment liquid dispersed in water at a concentration, once squeezed with a guide The oil agent treatment liquid was again applied to the fiber bundle.

  The fiber bundle to which the oil agent treatment liquid was applied again was dried using a heating roll, and dry heat drawing was performed 1.34 times between the heating rolls whose rotation speed was adjusted to a predetermined condition. The total draw ratio from the swollen yarn at this time was 7.4 times. Thereafter, water content was adjusted by applying water to the fiber bundle with a touch roll, and tangential treatment was performed to obtain a PAN-based precursor fiber bundle having a single fiber fineness of 4.5 dtex.

The above PAN-based precursor fiber bundle was subjected to a flameproofing treatment at a stretching rate of −5.9% for 300 minutes under a temperature distribution of 220 to 260 ° C. to obtain a flameproofed fiber bundle. The obtained flame-resistant fiber bundle was further pre-carbonized in a nitrogen atmosphere at 700 ° C. and a stretch rate of + 3% for 3.2 minutes, and then stretched in a nitrogen atmosphere at 1,300 ° C. and −4.0%. Carbon fiber treatment was performed at a rate of 3.2 minutes to obtain a carbon fiber bundle. The weight of the single fiber of the obtained carbon fiber bundle was 0.23 mg / m, the fineness of the single fiber was 2.31 dtex, and the roundness was 0.83. The resulting carbon fiber bundle was used to evaluate the fiber opening using the apparatus shown in FIG. The tow width of the carbon fiber bundle at that time was 22.6 mm. The tow width per 1 g of carbon fiber bundles was 8.2 mm. When the hook drop value of this carbon fiber bundle was measured, the CF value was 21. The results are shown in Table 1.
<Comparative Example 1>

  Acrylonitrile, acrylamide, and methacrylic acid are copolymerized by aqueous suspension polymerization in the presence of ammonium persulfate-ammonium hydrogen sulfite and iron sulfate, and acrylonitrile unit / acrylamide unit / methacrylic acid unit = 96/3/1 (mass ratio). An acrylonitrile copolymer comprising: This acrylonitrile copolymer was dissolved in dimethylacetamide to prepare a 21% by mass spinning dope. It is discharged through a spinneret (spinning nozzle) having a hole number of 60,000 and a hole diameter of 45 μm into a coagulation bath composed of an aqueous solution of dimethylacetamide having a concentration of 60% by mass and a temperature of 35 ° C. A fiber bundle (swelling yarn) was obtained by pulling at a speed. Next, the fiber bundle is stretched 5.3 times at the same time as washing with water, the fiber bundle is dried using a heating roll, and the heating speed is adjusted to 1.7 times between heating rolls adjusted to a predetermined condition. Dry-heat stretching was performed. A PAN-based precursor fiber bundle having a single fiber fineness of 1.0 dtex was obtained in the same manner as in Example 1 except that the total draw ratio from the swollen yarn was 9.0 times.

A carbon fiber bundle was produced from the PAN-based precursor fiber bundle in the same manner as in Example 1. The basis weight of the single fiber of the obtained carbon fiber bundle was 0.05 mg / m, the single fiber fineness was 0.50 dtex, and the roundness was 0.75. The resulting carbon fiber bundle was used to evaluate the fiber opening using the apparatus shown in FIG. The tow width of the carbon fiber bundle at that time was 23.4 mm. The tow width per 1 g of the carbon fiber bundle per unit area was 7.2 mm. When the hook drop value of this carbon fiber bundle was measured, the CF value was 16. The results are shown in Table 1.
<Comparative example 2>

A PAN-based precursor fiber bundle having a single fiber fineness of 2.5 dtex was obtained in the same manner as in Example 1 except that it was discharged into a coagulation bath composed of a dimethylacetamide aqueous solution having a concentration of 67% by mass and a temperature of 38 ° C. .
A carbon fiber bundle was produced from the PAN-based precursor fiber bundle in the same manner as in Example 1. The weight of the single fiber of the obtained carbon fiber bundle was 0.13 mg / m, the fineness of the single fiber was 1.25 dtex, and the roundness was 0.95. The resulting carbon fiber bundle was used to evaluate the fiber opening using the apparatus shown in FIG. The tow width of the carbon fiber bundle at that time was 30.0 mm. The tow width per 1 g of carbon fiber bundles was 6.0 mm. When the hook drop value of this carbon fiber bundle was measured, the CF value was 17. The results are shown in Table 1.
<Comparative Example 3>

A PAN-based precursor fiber bundle having a single fiber fineness of 4.5 dtex was obtained in the same manner as in Example 2 except that it was discharged into a coagulation bath consisting of an aqueous dimethylacetamide solution having a concentration of 67% by mass and a temperature of 38 ° C. .
A carbon fiber bundle was produced from the above PAN-based precursor fiber bundle in the same manner as in Example 2. The carbon fiber bundle obtained had a single fiber basis weight of 0.24 mg / m, a single fiber fineness of 2.43 dtex, and a roundness of 0.95. The resulting carbon fiber bundle was used to evaluate the fiber opening using the apparatus shown in FIG. The tow width of the carbon fiber bundle at that time was 22.0 mm. The tow width per 1 g of the carbon fiber bundle was 7.5 mm. When the hook drop value of this carbon fiber bundle was measured, the CF value was 23. The results are shown in Table 1.
<Comparative example 4>

  Attempted to produce carbon fiber precursor fiber bundle without producing entanglement process in spinning process and tried to produce carbon fiber, but the tow width of carbon fiber precursor fiber bundle was too wide in the flameproofing process, so it passed the process The target carbon fiber bundle could not be produced due to poor properties. The results are shown in Table 1.

1: Carbon fiber bobbin 2: Free roll 3: Nip roll 4: Dancer roll 5: Fixed guide 6: Tow width measuring unit 7: Winding unit 8: Direction of travel of the carbon fiber bundle

Claims (3)

  The fineness of the single fiber is in the range of 0.75 dtex to 2.5 dtex, the cross-sectional shape perpendicular to the fiber axis of the single fiber is 0.70 to 0.90, and the distance from which the hook drop falls A carbon fiber bundle having a calculated CF value of 10 to 30.   The carbon fiber bundle according to claim 1, wherein the total fineness is 25,000 to 90,000 dtex.   The carbon according to claim 1 or 2, which is produced using a PAN-based carbon fiber precursor fiber bundle composed of a polyacrylonitrile-based copolymer having 95 to 99 mol% of acrylonitrile units and 1 to 5 mol% of hydroxyalkyl methacrylate units. Fiber bundle.