JP2015161056A - Acrylonitrile precursor fiber bundle for carbon fiber and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acrylonitrile precursor fiber bundle which has appropriate surface denseness suitable for formation of carbon fiber having higher mechanical characteristics and its production method.SOLUTION: A method of producing an acrylonitrile precursor fiber bundle for carbon fiber includes obtaining a fiber bundle spun under a specified drawing condition through a step of causing the fiber bundle to shrink or stretch 0.95-1.3 times in a water bath at 40°C or higher under a specified coagulation condition in spinning by dry-wet spinning, and applying an oil agent containing a silicone compound to the fiber bundle to a specified coating amount of the silicone compound.

Description

  The present invention relates to an acrylonitrile precursor fiber bundle used for producing carbon fibers and a method for producing the same.

  For the purpose of improving the mechanical properties of a resin-based molded product, it is generally performed to combine a fiber with a resin as a reinforcing material. In particular, molding materials made by combining carbon fibers with excellent specific strength and specific elasticity with high-performance resins exhibit very good mechanical properties, so they can be used as structural materials for aircraft, high-speed moving bodies, etc. It is being actively promoted. In addition, there is a demand for higher strength and higher rigidity for this molding material as well as a request for further improvement in specific strength and specific rigidity. With regard to the performance of carbon fiber, higher strength and higher elastic modulus are also required. Is required.

  In order to produce such a high-performance carbon fiber, it is desired to obtain an acrylonitrile precursor fiber bundle for carbon fiber having excellent strength development. Up to now, technologies for improving the structural density of precursor fibers and eliminating defect points have been studied. However, most of the fractures of carbon fibers have started from the surface, and in particular, the densification and defects of the fiber surface Elimination of points is indispensable for further strengthening the carbon fiber. One of the causes of this defect point formation is an oil agent imparted to the precursor fiber. Adhesion between single fibers due to insufficient heat resistance or excessive excess adhesion of this oil agent, and the oil agent inside the fiber. The effect of microvoids due to penetration is large.

  Patent Document 1 proposes a method for producing an acrylonitrile-based precursor fiber bundle having high density as a whole and extremely high density on the fiber surface. In Patent Document 2, since the oil agent penetrates into the inside of the fiber to inhibit densification, a technique for suppressing the permeation of the oil agent has been proposed by paying attention to micro voids on the fiber surface. Patent Document 3 proposes a technique related to acrylonitrile-swelling fibers for carbon fibers that have a dense internal structure by optimizing the coagulation and drawing conditions of the spun fiber and that can suppress oil penetration in the vicinity of the surface. Has been.

Japanese Patent Publication No. 6-15722 Japanese Patent Laid-Open No. 11-124744 International Publication No. 2010/143680

  However, in the precursor fiber bundle obtained by the techniques described in these patent documents, the oil agent permeation may be excessively suppressed, and the adhesion of the oil agent to the fiber surface or excessive adhesion may be caused. For this reason, in these techniques, the effect of stably controlling the adhesion and penetration state of the oil agent in the precursor fiber bundle may be insufficient, and the carbon fiber strength required by the present inventors cannot be stably expressed. There was a case. Accordingly, an object of the present invention is to provide an acrylonitrile precursor fiber bundle having an appropriate surface density and a method for producing the same in order to obtain carbon fibers having higher mechanical properties.

  The present invention is a method for producing an acrylonitrile precursor fiber bundle for carbon fibers to which a silicone compound is adhered, wherein (1) a polymer having an acrylonitrile unit content of 96.0% by mass or more is dissolved in an organic solvent. A step of producing a coagulated fiber bundle from the raw spinning solution by a dry and wet spinning method, (2) a step of stretching the coagulated fiber bundle in air to 1.0 to 1.2 times, and (3) step The fiber bundle obtained from step 2 is stretched in an aqueous solution containing an organic solvent. At that time, the total draw ratio of step 2 and step 3 with respect to the solidified fiber bundle obtained from step 1 is 2.0 times or more and 4.0 times. (4) the step of removing the organic solvent from the fiber bundle obtained from step 3, and (5) the fiber bundle obtained from step 4 in a water bath at 40 ° C. or higher 0.95 times or more 1 .Shrinking or stretching to 3 times or less (6) including a step of attaching an oil agent containing a silicone compound to the fiber bundle obtained from step 5; and (7) a step of drying the fiber bundle obtained from step 6; The temperature (° C.) of the aqueous solution containing is represented by A, the concentration (mass ratio) of the organic solvent in the aqueous solution containing the organic solvent is represented by B, and applied to the fiber bundle obtained from step 2 in the aqueous solution containing the organic solvent. When the draw ratio (ratio) to be expressed is represented by C and the temperature (° C.) of the water bath is represented by D in Step 5, the relationship represented by the following formula (1) is satisfied. Production of an acrylonitrile precursor fiber bundle for carbon fiber, which gives the fiber bundle an amount of the oil agent such that the content of the silicone compound with respect to the later dried fiber bundle is 0.7% by mass or more and 2.0% by mass or less. Is the method.

  Further, the present invention is an acrylonitrile precursor fiber bundle for carbon fiber to which a silicone compound is adhered, wherein the content of the silicone compound in the fiber bundle is 0.7% by mass or more and 2.0% by mass or less. The fineness of the single fiber is 0.5 dtex or more and 0.95 dtex or less, the ratio of the major axis to the minor axis (major axis / minor axis) of the fiber section of the single fiber is 1.00 or more and 1.01 or less, and the center line average roughness ( Ra) is an acrylonitrile precursor fiber bundle for carbon fibers having a size of 3 nm to 10 nm.

  The present invention is preferably an acrylonitrile precursor fiber bundle for carbon fibers having no surface uneven structure extending in the fiber axis direction of single fibers.

Furthermore, an acrylonitrile precursor fiber bundle for carbon fibers, in which the silicone compound is an amino-modified silicone compound that satisfies the following conditions (1) and (2), is preferable.
(1) Kinematic viscosity at 25 ° C. is 50 cst or more and 5000 cst or less,
(2) An amino equivalent is 1700 g / mol or more and 15000 g / mol or less.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an acrylonitrile precursor fiber bundle having moderate surface density and a method for producing the same in order to obtain carbon fibers having higher mechanical properties.

  As a result of intensive studies on the above problems, the inventors of the present invention obtained an oil agent containing a silicone compound in a fiber bundle obtained by spinning an acrylonitrile precursor fiber bundle for carbon fiber under a specific coagulation condition and a specific drawing condition. It discovered that the said subject could be solved by providing so that the adhesion amount of this silicone compound might become a specific amount.

  Thus, a fiber bundle having a dense fiber structure can be obtained by spinning under specific coagulation conditions and specific drawing conditions. Further, by applying an oil agent to the obtained fiber bundle so that the adhesion amount of the silicone compound falls within a specific range, the carbon fiber having an appropriate surface density can be controlled. An acrylonitrile precursor fiber bundle can be obtained. In the present invention, the “surface” includes the meaning of the surface layer.

  Furthermore, this precursor fiber bundle has a high-quality and high-performance carbon fiber bundle that has excellent mechanical performance by being subjected to flameproofing treatment and carbonization treatment, and can be used for aircraft use, industrial use, etc. Can be obtained. Further, a molding material (fiber reinforced resin) having high mechanical properties can be obtained by the carbon fiber bundle.

  Hereinafter, the present invention will be described in detail.

<Acrylonitrile precursor fiber bundle for carbon fiber>
In the acrylonitrile precursor fiber bundle for carbon fibers of the present invention (hereinafter sometimes referred to as “precursor fiber bundle”), an oil containing a silicone compound adheres to the entire surface, for example. The acrylonitrile precursor fiber bundle for carbon fiber is a fiber bundle that becomes a precursor of carbon fiber, and each fiber constituting the fiber bundle can be made of an acrylonitrile-based polymer described later.

  The acrylonitrile precursor fiber bundle for carbon fiber of the present invention is obtained by, for example, applying a silicone fiber to a fiber bundle (precursor fiber bundle before oil agent adhesion) obtained by spinning a spinning stock solution comprising the following acrylonitrile-based polymer and an organic solvent. After applying and drying the oil containing a compound, it can be obtained by subjecting it to a stretching treatment by hot stretching or steam stretching.

  Further, the content (attachment amount) of the silicone compound in the acrylonitrile precursor fiber bundle for carbon fiber of the present invention is 0.7 mass relative to the precursor fiber bundle at the stage after drying and stretching treatments. % To 2.0% by mass

[Acrylonitrile polymer]
The acrylonitrile-based polymer used as a raw material for the precursor fiber bundle may contain at least an acrylonitrile unit, and may be a homopolymer of acrylonitrile or a copolymer of acrylonitrile and another monomer. . Other monomers may be used alone or in combination of two or more.

  However, the content of acrylonitrile units in the polymer is preferably 96.0% by mass or more, more preferably 97.0% by mass or more, and further preferably 97.5% by mass or more. Further, the content of acrylonitrile units in this polymer is preferably 99.7% by mass or less, more preferably 99.0% by mass or less, and further preferably 98.5% by mass or less.

  By making the content of the acrylonitrile unit in this polymer 96.0 mass% or more and 99.7 mass% or less, the structural irregularity of the ladder polymer formed by the flameproofing reaction can be further reduced. The decomposition reaction during the temperature treatment can be further suppressed, and a dense carbon fiber with few defects that cause a decrease in strength can be easily obtained.

  In addition, as the other monomer copolymerized with acrylonitrile (first component), a known monomer in the field of carbon fiber can be used as appropriate. In the present invention, any one of a carboxyl group and an ester group is used as the other monomer. It is preferable to use an unsaturated hydrocarbon (unsaturated hydrocarbon compound) (second component) having one or both. By using this unsaturated hydrocarbon, the self-heating accompanying the intramolecular cyclization reaction in flame resistance can be suppressed, and thermal damage can be suppressed. Examples of the unsaturated hydrocarbon having one or both of a carboxyl group and an ester group include acrylic acid, methacrylic acid, itaconic acid, methyl acrylate, methyl methacrylate, and ethyl acrylate. . These unsaturated hydrocarbons may be used alone or in combination of two or more.

  The content of the unsaturated hydrocarbon unit in the acrylonitrile-based polymer is preferably 0.3% by mass or more and 4.0% by mass or less, more preferably 1.0% by mass or more and 3.0% by mass or less. More preferably, the content is 5% by mass or more and 2.5% by mass or less.

  It is known that the unsaturated hydrocarbon component having this specific functional group serves as a starting point for the flameproofing reaction. If the content of the unsaturated hydrocarbon in the polymer is 0.3% by mass or more, an appropriate flameproofing reaction can be easily caused, and the structure formation of the flameproofed fiber can be hindered. It can be easily suppressed. On the other hand, if the content of the unsaturated hydrocarbon is 4.0% by mass or less, a rapid reaction due to the presence of a large number of reaction starting points can be easily suppressed, and as a result, formation of a rough structural form is achieved. Can be easily suppressed, and a carbon fiber having high performance can be easily obtained. That is, when the content of the unsaturated hydrocarbon component in the polymer is 0.3% by mass or more and 4.0% by mass or less, the balance between the start point of the flameproofing reaction and the reaction rate is easily improved. In addition, it is possible to easily suppress the formation of a structural mismatching portion that has a dense structure and becomes a defect point in the carbonization process. Moreover, since it has moderate reactivity, a flameproofing reaction can be caused in a relatively low temperature range, and a flameproofing process excellent in both economic efficiency and safety can be performed. Therefore, it is possible to obtain a flame-resistant fiber suitable for obtaining a carbon fiber having a graphene laminated structure with few structural irregularities and defects in a high yield.

  From the above, the acrylonitrile-based polymer contains 96.0% by mass or more and 99.7% by mass or less of acrylonitrile units, and an unsaturated hydrocarbon compound unit having one or both of a carboxyl group and an ester group. An acrylonitrile-based copolymer containing 0.3% by mass or more and 4.0% by mass or less is preferable.

  Further, the acrylonitrile-based polymer may contain acrylamide derivatives such as acrylamide, methacrylamide, N-methylolacrylamide, N, N-dimethylacrylamide, vinyl acetate and the like as the third component.

  In addition, content of each structural unit in an acrylonitrile-type polymer can be specified by NMR.

  The polymerization method for synthesizing the acrylonitrile-based polymer is not particularly limited. For example, redox polymerization in an aqueous solution, suspension polymerization in a heterogeneous system, emulsion polymerization using a dispersant, radical polymerization in an organic solvent, etc. Such polymerization methods may be used, and the present invention is not limited by the difference in these polymerization methods.

  The mass average molecular weight of the acrylonitrile polymer is preferably 100,000 or more and 700,000 or less, more preferably 200,000 or more and 600,000 or less. Usually, it is desired that the spinning dope used for shaping the acrylonitrile polymer into fibers has an optimum spinnability in order to continue spinning stably. Spinnability is related to the molecular weight of the polymer used and the polymer concentration in the spinning dope. When the molecular weight of the polymer is low, the polymer concentration in the spinning dope is usually set to a high Yarn is obtained. Here, if the mass average molecular weight of the polymer is 100,000 or more, by setting the polymer concentration in the spinning dope high, appropriate spinnability can be easily expressed, Even when the polymer concentration is high, it can be easily and uniformly dissolved. Further, if the polymer has a mass average molecular weight of 700,000 or less, it can be easily dissolved in a solvent used for the spinning dope, and it is not necessary to lower the polymer concentration in the spinning dope. The denseness required for expression can be easily maintained, and the decrease in productivity during spinning can be easily prevented.

[Oil agent containing silicone compound]
The oil used in the present invention contains a silicone compound, and may contain other additives as described later as required. By adhering this oil agent to the precursor fiber bundle (before attaching the oil agent), fusion between the fibers can be suppressed, and the abrasion resistance of the fibers can be further improved.

  In addition, 30 mass% or more and 95 mass% or less are preferable, as for content of the silicone compound in the said oil agent, More preferably, they are 50 mass% or more and 93 mass% or less, More preferably, they are 70 mass% or more and 91 mass% or less. If this content is 30% by mass or more, the effect of suppressing fusion between fibers and the effect of scratch resistance, which are roles of the oil agent, can be easily exerted. Moreover, if this content is 95 mass% or less, stability of an oil agent (emulsion) can be easily made into sufficient level, and manufacture of the stable precursor fiber bundle can be performed easily. In addition, the said oil agent can contain a silicone compound as a main component (component contained most).

[Silicone compound]
The silicone compound only needs to have a siloxane bond in the main chain (main skeleton), for example, and a known silicone compound can be appropriately used. However, from the viewpoint of interaction with the acrylonitrile-based polymer constituting the fiber, as the silicone compound, either one of amino-modified polydimethylsiloxane modified with an amino group and epoxy-modified polydimethylsiloxane modified with an epoxy group or It is preferable to use both. In particular, it is more preferable to use amino-modified polydimethylsiloxane as the silicone compound from the viewpoint of easy coating of the precursor fiber surface before adhesion of the oil agent and difficulty of desorption from the surface.

  Further, in these modified polydimethylsiloxanes, a part of methyl groups of the polydimethylsiloxane skeleton may be substituted with phenyl groups, and in this case, excellent heat resistance can be imparted to the precursor fiber bundle.

  The amino-modified type in the amino-modified polydimethylsiloxane is not particularly limited. However, for example, primary side chain type in which primary amine is introduced, primary side chain type in which primary and secondary amines are introduced, both amino group introduced into both ends of polydimethylsiloxane skeleton. A terminal-modified type can be preferably used. Moreover, these mixed types may be used, and multiple types may be mixed and used.

The most preferred amino-modified polydimethylsiloxane has a kinematic viscosity at 25 ° C. of 5.0 × 10 ⁻⁵ m ² / s (50 cSt) or more and 5.0 × 10 ⁻³ m ² / s (5000 cSt) or less. And an amino equivalent is 1700 g / mol or more and 15000 g / mol or less.

If this kinematic viscosity is 5.0 × 10 ⁻⁵ m ² / s or more, it can easily have a sufficient molecular weight that does not volatilize, and the silicone compound can be scattered from the precursor fiber throughout the flameproofing process. It can be easily suppressed. As a result, the oil agent can easily exhibit its original function, and stable carbon fiber can be easily produced. Moreover, if the said kinematic viscosity is 5.0 * 10 < ^-3 > m < ² > / s or less, generation | occurrence | production of the following phenomena can be suppressed easily. That is, in the flameproofing process, part of the oil agent is transferred from the precursor fiber bundle to a roll or the like, and the transferred oil agent is subjected to a heat treatment for a relatively long time to increase its viscosity and become sticky. A phenomenon in which a part of the fiber bundle is wound around a roll or the like can be easily prevented.

  In addition, by setting the amino equivalent to 1700 g / mol or more, the thermal reactivity of the silicone compound can be easily suppressed, a part of the oil agent is transferred from the fiber bundle to the roll, and a part of the fiber bundle is wound on the roll. Sticking can be easily prevented. By setting the amino equivalent to 15000 g / mol or less, sufficient affinity between the precursor fiber and the silicone compound can be easily obtained, so that the silicone compound can be easily scattered from the precursor fiber throughout the flameproofing process. Can be suppressed.

That is, the kinematic viscosity at 25 ° C. of the amino-modified polydimethylsiloxane is 5.0 × 10 ⁻⁵ m ² / s or more and 5.0 × 10 ⁻³ m ² / s or less, and the amino equivalent is 1700 g / mol or more and 15000 g / mol or less. If so, there is no wrapping of fibers due to the transfer of the oil agent to a roll or the like, and there is no sudden scattering of the oil agent in the flameproofing process, and it is easy to perform stably continuously from spinning to flameproofing treatment for a long time. I can do it.

  The kinematic viscosity at 25 ° C. can be measured with an Ubbelohde viscometer according to ASTM D 445-46T.

  Examples of the primary side chain type amino-modified polydimethylsiloxane include KF-864, KF-865, KF-868, KF-8003 (all trade names, manufactured by Shin-Etsu Chemical Co., Ltd.) and the like. Examples of the first and second class side chain types include KF-859, KF-860, KF-869, and KF-8005 (all trade names, manufactured by Shin-Etsu Chemical Co., Ltd.). Examples of both-end-modified types include Silaplane FM-3311, FM-3221, FM-3325 (all trade names, manufactured by Chisso Corporation) and KF-8012 (trade names, manufactured by Shin-Etsu Chemical Co., Ltd.). It is done. These siloxanes all satisfy the above kinematic viscosity range and amino equivalent range.

[Other additives]
The oil agent can contain additives such as a surfactant for converting the oil agent into a water-based emulsion and a softener and a smoothing agent for imparting excellent process passability. As this surfactant, a nonionic surfactant is usually used, and in particular, an ethylene oxide (EO) / propylene oxide (PO) adduct of a pluronic type or higher alcohol is used. Examples of this surfactant include Newpol PE-78, PE-108, and PE-128 (all trade names, manufactured by Sanyo Chemical Industries), which are polyoxyethylene / polyoxypropylene block polymers, NIKKOL BL. -9EX (trade name, manufactured by Nikko Chemicals Co., Ltd., emulsifier) is preferable. As the softener and the smoothing agent, an ester compound, a urethane compound, or the like can be used.

[Content of silicone compound in precursor fiber bundle]
The content (attachment amount) of the silicone compound in the acrylonitrile precursor fiber bundle for carbon fiber of the present invention is 0.7% with respect to 100% by mass of the precursor fiber bundle to which the oil agent is attached, dried and stretched. The mass is not less than 2.0% by mass. The content of the silicone compound is preferably 0.9% by mass or more and 1.9% by mass or less, more preferably 1.0% by mass or more and 1.7% by mass or less. When the content is 0.7% by mass or more, it is possible to prevent fusion between fibers and a decrease in scratch resistance due to insufficient coating of the fiber surface with the oil agent. If it is 2.0% by mass or less, excessive penetration of the oil into the fiber is prevented, the formation of defect points is suppressed, and the flame-resistant structure is irregular due to fiber sticking or insufficient oxygen diffusion due to excessive adhesion. Can be reduced.

  As described above, the content of the silicone compound in the precursor fiber bundle is measured with respect to the precursor fiber bundle obtained by attaching an oil agent to the fiber bundle and performing drying and stretching treatment. It can be determined from the amount of oil attached and the content of the silicone compound in the used oil. The oil agent adhesion amount of the precursor fiber bundle can be obtained from this difference by Soxhlet extraction of the precursor fiber bundle to which the oil agent is adhered with methyl ethyl ketone for 8 hours, and the mass of the precursor fiber bundle before and after extraction is precisely weighed.

  This precursor fiber bundle has a single fiber fineness of 0.5 dtex or more and 0.95 dtex or less, and the ratio of the major axis to the minor axis (major axis / minor axis) of the fiber section of the monofilament is 1.00 or more and 1. 01 or less, it is preferable that there is no surface uneven structure extending in the fiber axis direction of the single fiber, and the center line average roughness (Ra) is 3 nm or more and 10 nm or less.

  If the Ra value is 3 nm or more, the smoothness of the precursor fiber filament surface is not excessive. This is because the low stretchability in the spinning process derived from the skin layer formed in the solidification process does not cause small breakage of the surface layer fibrils, and the formation of minute defect points can be avoided. Furthermore, due to excessive convergence as a fiber bundle that is an aggregate of filaments, non-uniform flame resistance treatment due to inhibition of oxygen diffusion into the filament in the flame resistance process can be avoided. On the other hand, by setting the Ra value to 10 nm or less, it is considered that the denseness of the structure in the vicinity of the surface layer can be made to a sufficient level.

  When the surface has a Ra value of 3 nm or more and 10 nm or less, the structure in the vicinity of the surface layer is at a sufficient level and can have a structure having sufficient stretchability. It is possible to reduce the chance of forming defect points in the vicinity of the surface layer. As a result, a high-strength carbon fiber bundle can be obtained. From the above viewpoint, the lower limit of the Ra value is preferably 4 nm or more, and more preferably 5 nm or more. The upper limit of the Ra value is preferably 8 nm or less, and more preferably 7 nm or less.

  Here, the surface concavo-convex structure extending in the fiber axis direction indicates a ridge structure that exists substantially parallel to the fiber axis direction. The acrylonitrile fiber bundle undergoes volume shrinkage due to solidification and subsequent stretching treatment, and a wrinkle structure extending in the fiber axis direction is formed on the surface. In the present invention, this wrinkle structure does not exist in a remarkable form. By suppressing the formation of a strong skin layer in the solidification process and realizing a gradual volume shrinkage, the formation of the ridge structure is suppressed. Further, it is known that the formation of this wrinkle structure is greatly suppressed by dry and wet spinning.

  A fiber having a ratio of a major axis to a minor axis (major axis / minor axis) of a single fiber cross section of 1.00 to 1.01 is a single fiber having a perfect circle or a cross section close to a perfect circle, and a structure near the fiber surface. Excellent uniformity. A more preferable ratio of the major axis to the minor axis (major axis / minor axis) is 1.00 to 1.005.

  Since the fiber having a single fiber fineness range of 0.5 to 0.95 dtex has a small fiber diameter, it can reduce the structural non-uniformity in the cross-sectional direction that occurs in the firing step. A more preferable range is 0.6-0.90 dtex. In addition, dtex represents the mass (g) of the single fiber per length 10,000 m.

[Measurement of surface uneven structure of precursor fiber]
Both ends of the single fiber of the precursor fiber bundle are fixed with a carbon paste on a metal sample holder plate attached to the scanning probe microscope apparatus, and measured with a scanning probe microscope under the following conditions. First, the shape image of a single fiber is measured with a scanning probe microscope. For the measurement image, 10 cross-sectional profiles in the direction perpendicular to the fiber axis are measured by image analysis to determine the centerline average roughness Ra. Measurement is performed on 10 single fibers, and an average value is obtained.

〔Measurement condition〕
Equipment: SII Nano Technologies, Inc. SPI4000 probe station, SPA400 (unit),
Scanning mode: Dynamic force mode (DFM) (shape image measurement),
Probe: SI-DF-20, manufactured by SII Nano Technologies
Rotation: 90 ° (scanned in a direction perpendicular to the fiber axis direction),
Scanning region: fiber axis direction 3.0 μm × circumferential direction 3.0 μm,
Scanning speed: 1.0 Hz
Number of pixels: 512 × 512,
Measurement environment: room temperature, in air.

  For one single fiber, one image is obtained under the above conditions, and the image is subjected to image analysis under the following conditions with image analysis software (SPIWin).

(Image analysis conditions)
The obtained shape image is subjected to flat processing, median 8 processing, and cubic inclination correction to obtain an image obtained by fitting the curved surface to a flat surface. From the surface roughness analysis of the flattened image, the cross-sectional profile in the direction perpendicular to the fiber axis is measured to determine the centerline average roughness Ra.

[Flat processing]
This is a process for removing distortion and waviness in the Z-axis direction that appear in the image data due to lift, vibration, scanner creep, and the like, and is a process for removing distortion of data due to device factors in SPM measurement.

[Median 8 processing]
By performing operations between S and D1 to D8 in a 3 × 3 window (matrix) centered on the data point S to be processed, and replacing the Z data of S, a filter effect such as smoothing or noise removal is obtained. It is. In the median 8 process, the median value of 9 points of Z data of S and D1 to D8 is obtained and S is replaced.

[Third-order tilt correction]
Inclination correction is to correct the inclination by obtaining and fitting a curved surface by least square approximation from all data of the processing target image. (Primary), (Secondary), and (Cubic) indicate the order of the curved surface to be fitted, and in the cubic, the cubic curved surface is fitted. By the cubic inclination correction process, the curvature of the fiber of the data is eliminated and a flat image is obtained.

[Evaluation of cross-sectional shape of precursor fiber]
The ratio of the major axis to the minor axis (major axis / minor axis) of the fiber cross section of the single fiber constituting the fiber bundle is determined as follows. After passing a fiber bundle for measurement through a tube made of vinyl chloride resin having an inner diameter of 1 mm, the sample is prepared by cutting the fiber bundle with a knife. Next, this sample was bonded to the SEM sample stage with the fiber cross section facing upward, and Au was further sputtered to a thickness of about 10 nm, and then an electron microscope (manufactured by Philips, product name: XL20 scanning type) was used. The cross section of the fiber is observed under conditions of an acceleration voltage of 7.00 kV and a working distance of 31 mm, and the major axis and the minor axis of the fiber section of the single fiber are measured.

<Method for producing acrylonitrile precursor fiber bundle for carbon fiber>
The acrylonitrile precursor fiber bundle for carbon fibers of the present invention can be obtained, for example, by a production method including the following steps.
(I) A step of spinning a spinning solution in which a polymer containing an acrylonitrile unit is dissolved in an organic solvent to produce a coagulated fiber bundle (spinning step).
(Ii) A step of stretching and washing the obtained coagulated fiber bundle (stretching and washing step).
(Iii) A step of attaching an oil containing a silicone compound to the fiber bundle obtained from step ii (oil agent attaching step).

[Step i]
First, a coagulated fiber bundle is prepared by spinning a spinning solution obtained by dissolving a polymer constituting the fibers of the precursor fiber bundle in an organic solvent.

  As the polymer used in step i, the acrylonitrile-based polymer described above can be used as appropriate. For example, the content of acrylonitrile units in the polymer can be 96.0 mass or more. The number of fibers (yarns) constituting the coagulated fiber bundle (yarn bundle) can be 600 to 24,000, for example. The number of fibers constituting the fiber bundle can be the number of fibers constituting the precursor fiber bundle, the flame-resistant fiber bundle, and the carbon fiber bundle without changing in subsequent steps.

  The organic solvent used for the spinning dope is not particularly limited as long as it can dissolve the polymer to be used. However, from the viewpoint of solubility, dimethylformamide, dimethylacetamide, or dimethyl sulfoxide is preferably used. More preferred is dimethylformamide, which has an excellent ability to dissolve acrylonitrile-based polymers.

  The solid concentration of the spinning dope, that is, the concentration of the polymer in the spinning dope is preferably 20% by mass or more and 25% by mass or less, and more preferably 22% by mass or more and 24% by mass or less. If the solid content concentration is 20% by mass or more, the amount of the organic solvent that moves from the inside of the fiber (filament) to the outside of the fiber can be easily reduced in the solidification process, and a solidified fiber bundle having the necessary denseness can be obtained. Can be easily obtained. Moreover, if this solid content concentration is 25 mass% or less, it can have moderate stock solution viscosity easily, and when spinning, the stock solution discharge from a nozzle will be stabilized further, and manufacture will become easy. That is, by setting the solid content concentration in the spinning dope to 20% by mass or more and 25% by mass or less, it is easy to stably produce a coagulated fiber bundle having a high density and a homogeneous structure.

  The temperature of the spinning dope is preferably 50 ° C. or higher and 70 ° C. or lower. If the temperature of the spinning dope is 50 ° C. or higher, the viscosity of the stock solution can be easily adjusted without adjusting the solid concentration low, and if it is 70 ° C. or less, the temperature difference from the coagulating solution is easy. Can be made smaller. That is, when the temperature of the spinning dope is 50 ° C. or higher and 70 ° C. or lower, it is easy to stably produce a coagulated fiber bundle having a high density and a homogeneous structure.

  The spinning method may be, for example, either a wet spinning method or a dry wet spinning method, but is preferably a dry wet spinning method. This is because it is easy to form dense solidified fibers, and in particular, the denseness of the precursor fiber surface can be easily increased. In the dry-wet spinning method, the prepared spinning solution is once spun into the air from a spinneret having a large number of nozzle holes, and then discharged into a conditioned coagulating liquid (coagulating bath) to coagulate the coagulated fiber. Is the method of taking over.

  Note that a mixed solution of an organic solvent and water is usually used for the coagulation liquid. As the organic solvent, an organic solvent that can be used for the spinning dope can be used in the same manner, but the organic solvent used for the spinning dope is usually used for the coagulating solution.

  The concentration of the organic solvent in the coagulation liquid is preferably 78.5% by mass or more and 82.0% by mass or less, more preferably 79.0% by mass or more and 81.7% by mass or less, and still more preferably 79.6% by mass. % Or more and 81.4% by mass or less.

  The fiber structure of the coagulated fiber is also deeply related to the later application of the oil agent. If the concentration of the organic solvent in the coagulated liquid is 78.5% by mass or more, the following can be achieved. That is, it is possible to easily suppress the formation of the skin layer while easily maintaining an appropriate denseness inside the fiber, and it is possible to easily obtain a good oil agent familiarity to the fiber surface when the oil agent is applied. Adhering spots and excessive adhesion to the surface can be easily suppressed. In addition, if the concentration of the organic solvent in the coagulation liquid is 82.0% by mass or less, it is possible to easily suppress the permeation of excess oil into the fiber while easily maintaining an appropriate density on the fiber surface. I can do it. That is, when the concentration of the organic solvent in the coagulation liquid is 78.5% by mass or more and 82.0% by mass or less, both the surface and the inside of the fiber are dense, and the adhesion and penetration state of the oil agent is good in the subsequent oil agent application step. A coagulated fiber bundle can be easily obtained.

  Here, the temperature of the coagulation liquid is preferably −5 ° C. or higher and 20 ° C. or lower, more preferably 0 ° C. or higher and 15 ° C. or lower, and further preferably 5 ° C. or higher and 10 ° C. or lower. When the temperature of the coagulation liquid is −5 ° C. or more and 20 ° C. or less, it is easy to form dense coagulated fibers, and in particular, the denseness of the fiber surface can be improved.

  From the above, for example, step i is a step of producing a coagulated fiber bundle by a wet and wet spinning method from a spinning stock solution in which a polymer having an acrylonitrile unit content of 96.0% by mass or more is dissolved in an organic solvent (step) 1).

[Step ii]
Next, the obtained solidified fiber bundle is subjected to stretching and washing treatment. In that case, there is no restriction | limiting in particular in the order of extending | stretching and a washing process, You may wash after extending | stretching and you may perform extending | stretching and washing | cleaning simultaneously. The cleaning method may be any method as long as the organic solvent can be removed from the fiber bundle.

However, it is preferable that this process ii is a multistage extending | stretching process including the following processes 2-5. In step 5, the fiber bundle may be relaxed and contracted instead of being stretched.
(2) A step of stretching the coagulated fiber bundle to 1.0 times or more and 1.2 times or less in the air (first stretching step).
(3) The fiber bundle obtained from step 2 is stretched in an aqueous solution containing an organic solvent, and the total draw ratio of step 2 and step 3 with respect to the solidified fiber bundle obtained from step 1 is 2.0 times or more. The process of making it 4.0 times or less (2nd extending process).
(4) A step of removing the organic solvent from the fiber bundle obtained from step 3 (cleaning step).
(5) A step of shrinking or stretching the fiber bundle obtained from step 4 to 0.95 times or more and 1.3 times or less in a water bath at 40 ° C. or higher (shrinking or third stretching step).

  In addition, the draw ratio and shrinkage ratio of the fiber bundle in steps 2, 3 and 5 can be measured by the following methods. That is, it is measured from the difference in rotational speed between rolls that are arranged before and after each step and grip the traveling yarn.

  Below, each process of the process 2-the process 5 is demonstrated in detail.

-Step 2 (first stretching step)
First, the coagulated fiber bundle obtained from step i (for example, step 1) is stretched in air to 1.0 to 1.25 times. The coagulated fiber bundle obtained from step i is usually swollen with a large amount of the organic solvent used, and further has a fibril structure. If the stretch ratio in the air of the coagulated fiber bundle is 1.0 times or more, non-uniform shrinkage can be easily suppressed. Furthermore, if this stretch ratio is 1.0 times or more and 1.2 times or less, formation of a sparse fibril structure can be easily avoided. Moreover, it is preferable that the extending | stretching rate in the air is 1.0 times or more and 1.15 times or less from a viewpoint of suppressing the structural destruction of the fiber in a multistage extending | stretching process.

-Step 3 (second stretching step)
Next, the fiber bundle subjected to the first stretching treatment is stretched with an aqueous solution containing an organic solvent. At that time, the total draw ratio of the first drawing step (in the air) and the second drawing step (in the aqueous solution) is 2.0 times or more and 4.0 times or less.

  If the total draw ratio is 2.0 times or more, sufficient stretching can be easily performed on the solidified fiber bundle, and a fibril structure oriented in the fiber axis direction can be easily formed. Moreover, if this total draw ratio is 4.0 times or less, the occurrence of breakage of the fibril structure itself can be easily suppressed, and a precursor fiber bundle having a dense structure can be easily obtained. That is, when the total draw ratio is 2.0 times or more and 4.0 times or less, a dense fibril structure oriented in the axial direction of the fiber can be easily formed. A more preferable total draw ratio is 2.2 times or more and 3.7 times or less, and further preferably 2.4 times or more and 3.4 times or less.

  In the first and second stretching steps, it is particularly preferable that the stretching in air is 1.0 to 1.15 and the stretching ratio in the aqueous solution is 2.2 or more. Since the stretching in this aqueous solution is performed at a relatively high temperature and can be stretched without causing structural destruction, the stretching distribution in the air and in the aqueous solution is preferably set higher in the aqueous solution. .

  Thus, by performing a two-stage drawing process, a swollen fiber bundle with a dense fiber surface can be obtained. In addition, by using a coagulated fiber bundle containing an organic solvent having a degree of swelling of 160% by mass or less, the density of the internal structure of the coagulated fiber is improved, and thereby a swollen fiber bundle having excellent surface density can be obtained. .

  The degree of swelling is determined by treating the collected sample with a tabletop centrifugal dehydrator at 3000 rpm for 10 minutes and weighing it, and setting this value as the wet mass. The sample was washed with water and treated in a dryer at 105 ° C. for 3 hours, then stored in a desiccator for 30 minutes and then weighed to obtain this value as the dry mass. The degree of swelling is calculated by the following formula (2).

  The organic solvent used in the aqueous solution containing the organic solvent can be the same organic solvent that can be used in the spinning dope, but the same organic solvent as that used in the spinning dope is usually used. Further, in the present invention, stretching (step 3) is performed in an aqueous solution (stretching tank) having a higher temperature and a lower organic solvent concentration than the coagulation liquid used in step i, and then a cleaning treatment (step 4 described later). It is particularly preferable to carry out. Thereby, a uniform fibril structure can be easily formed in the coagulated fiber.

  Specifically, the organic solvent concentration in the aqueous solution containing the organic solvent is preferably 20% by mass or more and 70% by mass or less. Within this range, stable stretching treatment can be easily performed on the obtained coagulated fiber, and a dense and uniform fibril structure can be formed inside and on the body fiber. The concentration of the organic solvent in the coagulation liquid is more preferably 30% by mass to 65% by mass, and still more preferably 40% by mass to 60% by mass.

  The temperature of the aqueous solution containing the organic solvent is preferably 40 ° C. or higher and 80 ° C. or lower, more preferably 50 ° C. or higher and 78 ° C. or lower, and further preferably 55 ° C. or higher and 70 ° C. or lower. By setting the temperature to 40 ° C. or higher, good stretchability can be easily ensured, and formation of a uniform fibril structure is facilitated. If it is 80 degrees C or less, generation | occurrence | production of an excessive plasticization effect | action can be suppressed easily, moderate solvent removal on the fiber surface will advance easily, and uniform extending | stretching can be performed easily. As a result, the quality of the obtained fiber bundle can be easily improved.

・ Process 4
Subsequently, the fiber bundle (yarn bundle) obtained by the two-stage drawing treatment is washed, and the organic solvent contained in this fiber bundle (for example, the spinning stock solution and coagulation bath in step 1 and the aqueous solution containing the organic solvent in step 3) Remove the organic solvent used). The washing treatment is preferably performed in a water washing tank at 50 ° C. or higher and 97 ° C. or lower. A more preferable temperature of the water washing tank is 55 ° C. or higher and 75 ° C. or lower. If it is 50 degreeC or more, sufficient removal of an organic solvent can be performed easily, and if it is 97 degreeC or less, destruction of the fibril structure by rapid volume contraction can be avoided easily. The organic solvent concentration in the fiber bundle after passing through the washing tank is preferably 0.2% or less.

-Step 5 (shrinkage or third stretching step)
The fiber bundle obtained from the washing step is contracted or stretched 0.95 times or more and 1.3 times or less in a water bath at 40 ° C. or higher. That is, the fiber bundle in the swollen state free from the organic solvent after the washing step is contracted at a specific shrinkage rate or stretched at a specific draw rate in a water bath at a specific temperature, thereby further adjusting the fiber orientation. Can be increased.

  In addition, the fiber structure of the swelling fiber obtained from the step 5 is closely related to the oil agent application immediately after. By setting the temperature of the water bath to 40 ° C. or higher, the swelling of the fibers can be suppressed. Moreover, it is preferable that the temperature of a water bath shall be 50 to 98 degreeC, More preferably, it is 55 to 85 degreeC, More preferably, it is 60 to 80 degreeC. If the temperature of a water bath is 50 degreeC or more, the swelling of a fiber can be suppressed easily and the penetration | infiltration of the excess oil agent to the inside of a fiber can be suppressed easily. Further, if the temperature of the water bath is 98 ° C. or less, the fiber bundle can be easily swollen appropriately, and good oil agent familiarity to the fiber surface when the oil agent is applied can be easily obtained. Adhering spots and excessive adhesion to the surface can be easily suppressed. That is, by setting the temperature of the water bath to 50 ° C. or more and 98 ° C. or less, it is possible to easily obtain a swollen fiber in which the oil agent adhesion and penetration state is favorable in the immediately subsequent oil agent application step.

  The shrinkage or stretching ratio in step 5 is 0.95 times or more and 1.3 times or less. If the magnification (shrinkage ratio) in step 5 is 0.95 times or more and less than 1.0 times, the fiber bundle obtained in step 4 can be slightly relaxed, and the first and second stretching steps. It is possible to easily remove the stretching distortion caused by the above. By taking the stretching strain of the fiber bundle stretched at a high stretching ratio in the first and second stretching steps in this step 5, stable stretching is performed during the subsequent stretching (for example, stretching in step iii described later). Can be easily performed. If the magnification (stretching magnification) in step 5 is 1.0 to 1.3, the degree of orientation of the fibril structure and the denseness of the fiber surface can be easily improved. In step 5, it is more preferable to contract or stretch the fiber bundle obtained in step 4 at a magnification of 0.97 times to 1.2 times.

  Furthermore, in the manufacturing method of this invention, it is preferable to satisfy | fill following numerical formula (1).

In addition, in said numerical formula (1), each code | symbol represents the following.
A: Temperature (° C.) of an aqueous solution containing an organic solvent in Step 3
B: The concentration (mass ratio) of the organic solvent in the aqueous solution containing the organic solvent in Step 3,
C: Stretch ratio (ratio) to be applied to the fiber bundle obtained in Step 2 in the aqueous solution in Step 3, and D: Temperature of the water bath in Step 5 (° C.).

  By setting the above A to D so as to satisfy this mathematical formula (1), it is possible to easily obtain appropriate oil penetration into the precursor fiber bundle, and when the oil is applied, the oil agent is familiar to the fiber surface. It is very good, and it is possible to easily suppress adhesion spots of oil agent and excessive adhesion to the surface.

  Here, the details of Equation (1) will be described. As described above, in manufacturing the precursor fiber bundle of the present invention, the penetration state of the oil containing the silicone compound is important. It is considered that the structure formed between the step 3 and the step 5 is a state of the fiber bundle when the oil agent treatment is performed, which greatly affects the permeation state of the oil agent. In Step 3 to Step 5, the production conditions governing the structure formation of the fiber bundle include the draw ratio of Step 3 and the organic solvent concentration and temperature of the draw bath water, the draw ratio of Step 5 and the temperature of the draw bath. . In particular, in the formation of the structure of the precursor fiber bundle, the production conditions of step 3 which is a drawing step in an aqueous solution containing an organic solvent are very important, and the draw ratio in this step is considered to be the most important production condition.

  Here, the fiber bundle drawn in this step 3 contains a large amount of an organic solvent, and also contains an organic solvent in the aqueous solution in the drawn layer. Therefore, the fiber bundle stretching treatment here can be said to be a step of stretching a fiber bundle made of a swollen polymer in the presence of an organic solvent. Therefore, the magnitude of the effect of the stretching treatment on the fiber bundle is greatly affected by the concentration of the organic solvent in the stretching tank. Therefore, the substantial effect of the draw ratio needs to consider the effective draw ratio in consideration of the organic solvent concentration in the draw tank, not the actually applied draw ratio. It has been found that the effective draw ratio can be estimated by performing correction according to the following mathematical formula (3) from the actually applied draw ratio C.

  Similarly, when considering the stretching treatment in step 5, the temperature of water in the stretching tank is important because it has been subjected to solvent washing, and stretching at a temperature below Tg of the acrylonitrile-based polymer Therefore, a large draw ratio as in step 3 cannot be set, and the range is 0.95 or more and 1.3 or less. Accordingly, the stretch ratio in step 5 is less affected than the stretch ratio in step 3 in a situation where the treatment is performed in the range of 0.95 to 1.3 times. However, the temperature of the water in the drawing tank in step 5 greatly affects the structure of the fiber bundle. This is due to the fact that it is positioned as a heat treatment step for a fiber bundle made of a polymer not containing an organic solvent, that is, not in a swollen state. Therefore, the structure of the fiber bundle stretched in step 3 is obtained by stretching the polymer in a swollen state containing an organic solvent, while step 5 is a heat treatment on the fiber bundle formed in step 3. Is considered to cause structural relaxation. In particular, this relaxation is contraction in the fiber cross-sectional direction, which is a direction perpendicular to the fiber axis. As an estimate of this relaxation effect, it is appropriate to express the difference between the Tg of the swollen polymer in step 3 and the Tg of the polymer in step 5 not containing an organic solvent as a scale parameter, and the difference in the processing temperature between step 3 and step 5. Can be considered. Moreover, since it is a relaxation effect, if the temperature of the step 5 is high, the degree of relaxation increases, and as a result, it acts in the direction of reducing the amount of action of the stretching treatment performed in the step 3. Therefore, this relaxation action can be positioned as a correction term for the effective stretch ratio in Step 3 described above.

  Several reports have been made on the Tg of polyacrylonitrile polymers. For example, in the RB Beevers report “Dependence of the glass transition temperature of polyacrylonitrile on molecular weight” (Journal of Polymer Science Part A: General Papers Volume 2, Issue 12, pages 5257, 1964), Tg of polyacrylonitrile polymer containing solvent Can be estimated by the following formula (4).

w2: polymer amount (% by mass) contained in the polymer containing the organic solvent,
Effective range: 90% by mass <w2 <100% by mass.

  Accordingly, the Tg of a polymer containing about 10% by mass of an organic solvent is estimated to be 55 ° C. Actually, the Tg of the fiber bundle in Step 3 was about 55 to 60 ° C. On the other hand, the Tg of polyacrylonitrile polymer not containing an organic solvent is about 100 ° C. As described above, the effect of the substantial stretching treatment can be expressed by the following mathematical formula (5) as the substantial stretching ratio through the steps 3 to 5.

Tgp: Tg of a polymer not containing an organic solvent (100 ° C.)
Tgs: Tg of a polymer containing an organic solvent (60 ° C.)
Here, “Tgp-Tgs” is a polyacrylonitrile-based polymer containing 96.0% by mass or more of acrylonitrile, regardless of the organic solvent, and if the content of the organic solvent is 10 to 15% by mass, Since it is considered that it does not change, it can be normally set as “Tgp−Tgs = 40 ° C.”. Therefore, the substantial stretching ratio can be expressed by the following mathematical formula (6).

  The stretching process in step 3 is performed in the range of 2.0 times to 4.0 times in order to prevent the fibril structure itself from being broken. Based on that range, the optimum range of the substantial draw ratio of the present invention is 2.25 times or more and 3.25 times or less. More preferably, it is 2.00 times or more and 3.10 times or less.

[Step iii]
Next, an oil agent containing a silicone compound is attached to the swollen yarn bundle obtained from step ii (for example, steps 2 to 5 above). In addition, in this invention, content of the silicone compound in the fiber bundle to which this oil agent was made to adhere in process 6 shall be 0.7 mass% or more and 2.0 mass% or less. As this oil agent, the oil agent containing the silicone compound mentioned above can be used suitably. As a method for attaching the oil agent, for example, a dip nip method can be used.

  Subsequently, dry densification treatment is usually performed on the fiber bundle (yarn bundle) to which the oil agent is adhered. The drying densification treatment may be performed by drying and densifying the fiber bundle to which the oil agent is adhered by a known drying method, and is not particularly limited. For example, a method of passing the fiber bundle in contact with a plurality of heating rolls. Is preferably used.

  The fiber bundle after drying and densification is, for example, in pressurized steam of 130 ° C. or higher and 200 ° C. or lower, in a dry heat medium of 100 ° C. or higher and 200 ° C. or lower, or between heated rolls of 150 ° C. or higher and 220 ° C. or lower. Further, the film can be stretched on a heating plate to further improve the orientation and densification. In that case, a preferable draw ratio is 1.8 times or more and 6.0 times or less, more preferably 2.4 times or more and 6.0 times or less, and still more preferably 2.6 times or more and 6.0 times or less.

  From the above, the obtained fiber bundle can be appropriately wound to obtain an acrylonitrile precursor fiber bundle for carbon fibers.

<Method for producing flame-resistant fiber bundle>
A flame-resistant fiber bundle can be obtained by heat-treating the precursor fiber bundle obtained from the present invention in an oxidizing atmosphere (for example, in air) (flame-proofing treatment). At this time, the precursor fiber bundle is passed through a hot air circulation type flameproofing furnace of, for example, 220 ° C. or more and 280 ° C. or less for 30 minutes or more and 100 minutes or less, and the elongation rate is 0% or more and 10% or less. 335 g / cm ³ or more 1.3
A flame resistant fiber bundle of 60 g / cm ³ or less can be obtained. In addition, a precursor fiber bundle arrange | positions so that several bundles may form equal intervals and the same plane, and uses for a flame-proofing process and the carbonization process mentioned later as a sheet-like precursor fiber bundle (precursor sheet). be able to.

  The flameproofing reaction includes a cyclization reaction by heat and an oxidation reaction by oxygen, and it is important to perform these two reactions in a well-balanced manner. In order to perform these two reactions in a well-balanced manner, the flameproofing treatment time is preferably from 30 minutes to 100 minutes. When the treatment time is 30 minutes or more, it can be easily suppressed that the portion where the oxidation reaction has not sufficiently occurred is present inside the single fiber, and the occurrence of large structural spots in the radial direction of the single fiber can be easily suppressed. . As a result, carbon fibers having a uniform structure can be easily produced, and high mechanical performance can be easily expressed. When the treatment time is 100 minutes or less, it is possible to easily suppress the presence of more oxygen in the portion close to the surface of the single fiber, and it is easy to cause a reaction in which excess oxygen disappears by heat treatment at a high temperature thereafter. It is possible to easily obtain a high-strength carbon fiber having no defects. A more preferable flameproofing treatment time is 40 minutes or more and 80 minutes or less.

  When the flameproofing treatment temperature is 220 ° C. or higher, it is possible to easily suppress the presence of more oxygen in the portion near the surface of the single fiber. When the temperature is 260 ° C. or lower, the portion where the oxidation reaction is not sufficiently generated Can be easily suppressed from existing inside the single fiber. A more preferable flameproofing treatment temperature is 225 ° C. or higher and 255 ° C. or lower.

If the density of the fiber bundle obtained from the flame-resistant treatment of 1.335 g / cm ³ or more, it is possible to easily perform sufficient oxidization reaction easily suppress the decomposition reaction caused by the heat treatment in the subsequent high temperature It is possible to easily obtain a high-strength carbon fiber having no defects. When the density of the flame-resistant fiber bundle is 1.360 g / cm ³ or less, the oxygen content of the fiber can be easily adjusted to an appropriate amount, and a reaction in which excess oxygen disappears due to subsequent heat treatment at a high temperature occurs. This can be easily suppressed, and a high-strength carbon fiber free from defects can be easily obtained. The density of the flame-resistant fiber bundle is more preferably 1.340 g / cm ³ or more and 1.350 g / cm ³ or less.

  Proper elongation in the flameproofing furnace is important for maintaining and improving the orientation of the fibril structure forming the fiber. When the elongation rate is 0% or more, the orientation of the fibril structure can be easily maintained, sufficient orientation at the fiber axis in the formation of the carbon fiber structure can be easily obtained, and excellent mechanical performance can be easily expressed. Can do. On the other hand, when the elongation rate is 10% or less, the fibril structure itself can be easily broken, and the high-strength carbon fiber can be formed without damaging the subsequent formation of the carbon fiber structure or causing the break point to be a defect point. Can be easily obtained. A more preferable elongation rate is 3% or more and 8% or less.

Furthermore, in the step of heat-treating the precursor fiber bundle in an oxidizing atmosphere (flame-proofing step), it is preferable to extend the precursor fiber bundle in multiple stages. For example, the extension treatment conditions are divided into at least three blocks. It is preferable to set flameproofing conditions. Specifically, the flameproofing process which has the following processes (1)-(3) is mentioned.
(1) the precursor fiber bundle is the elongation at an elongation of 3.0% or more and 8.0% or less, the fiber density of 1.200 g / cm ³ or more 1.260 g / cm ³ to obtain the following fiber bundle.
(2) A step of stretching the obtained fiber bundle at an elongation rate of 0.0% or more and 3.0% or less to obtain a fiber bundle having a fiber density of 1.240 g / cm ³ or more and 1.310 g / cm ³ or less.
(3) The obtained fiber bundle is contracted or elongated at −1.0% or more and 2.0% or less to obtain a flame-resistant fiber bundle having a fiber density of 1.300 g / cm ³ or more and 1.360 g / cm ³ or less. Process.
In addition, the elongation rate or shrinkage rate of the fiber bundle in each process can be specified by the difference in the rotation speed of the roll that holds the traveling yarn arranged before and after each process.

<Method for producing carbon fiber bundle>
Next, a carbon fiber bundle can be manufactured by heat-treating the obtained flame-resistant fiber bundle in an inert atmosphere such as nitrogen (carbonization treatment). This carbonization treatment can be carried out in a plurality of stages. For example, by performing the following first and second (optionally third) carbonization steps on the flameproof fiber bundle, A carbon fiber bundle can be obtained.
(1) The flame-resistant fiber bundle is added in the first carbonization furnace having a temperature gradient in an inert atmosphere at a temperature of 300 ° C. or higher and 800 ° C. or lower while adding 2% or more and 7% or less for 1.0 minute or longer 3 A first carbonization step in which heat treatment is performed for 0 minute or less.
(2) A second bundle in which the fiber bundle obtained from the first carbonization step is heat-treated under tension in a second carbonization furnace capable of setting a temperature gradient in an inert atmosphere under tension of 1000 ° C. to 1600 ° C. Carbonization process.
(3) A third carbonization step in which the fiber bundle obtained from the second carbonization step is heat-treated under tension in an inert atmosphere in a third carbonization furnace having a desired temperature gradient.

[First carbonization process]
When the flameproofing treatment temperature is set to 220 to 260 ° C, the starting treatment temperature in the first carbonization step is preferably set to 300 ° C or higher from the viewpoint of allowing the reaction to proceed efficiently. When the treatment temperature (maximum treatment temperature) in the first carbonization step is 800 ° C. or less, it can be easily suppressed that the fiber becomes very brittle, and the transition to the next step is easy. A more preferable treatment temperature range in the first carbonization step is 300 ° C. or higher and 750 ° C. or lower, and more preferably 300 ° C. or higher and 700 ° C. or lower.

  Although there is no restriction | limiting in particular about the temperature gradient which a 1st carbonization furnace has, From the viewpoint of mechanical strength expression, setting a linear gradient at process temperature 300 degreeC or more and 800 degrees C or less suppresses rapid decomposition | disassembly. preferable.

  When the elongation ratio is 2% or more, the orientation of the fibril structure can be easily maintained, and sufficient orientation at the fiber axis in the formation of the carbon fiber structure can be easily obtained, and excellent mechanical performance can be expressed. When the elongation rate is 7% or less, the fibril structure itself can be easily prevented from breaking, and the subsequent formation of the carbon fiber structure is not impaired, and the high-strength carbon fiber does not become a defect point. Can be easily obtained. A more preferable elongation rate is 3% or more and 5% or less.

  A suitable treatment time in the first carbonization step is 1.0 minute or more and 3.0 minutes or less. In the treatment for 1.0 minute or longer, it is possible to easily suppress the occurrence of a violent decomposition reaction accompanying a rapid temperature rise, and it is possible to easily obtain a high-strength carbon fiber. If it is 3.0 minutes or less, it is possible to easily suppress the effect of plasticization and decrease the degree of crystal orientation, and as a result, it is possible to easily obtain carbon fibers having excellent mechanical performance. A more preferable treatment time is 1.2 minutes or more and 2.5 minutes or less.

[Second carbonization process]
Next, heat treatment is performed under tension in a second carbonization furnace in which a temperature gradient can be set in a range of 1000 ° C. to 1600 ° C. in an inert atmosphere such as nitrogen.

  The second carbonization furnace may be 1000 ° C. or higher although it depends on the temperature setting of the first carbonization furnace. Preferably it is 1050 degreeC or more. The temperature gradient is not particularly limited, but it is preferable to set a linear gradient. The treatment time is preferably from 1.0 minute to 5.0 minutes, more preferably from 1.5 minutes to 4.2 minutes. Since the fiber bundle is greatly contracted by the heat treatment in the second carbonization step, it is important to perform the heat treatment under tension. At that time, it is preferable to impart shrinkage (relaxation) or elongation of −6.0% to 2.0% to the fiber bundle. If it is −6.0% or more, good orientation in the fiber axis direction of crystals can be easily obtained, and sufficient performance can be easily obtained. In the case of 2.0% or less, it is possible to easily suppress the destruction of the fiber structure itself, to easily suppress the formation of defect points, and to easily suppress a significant decrease in strength. In the second carbonization step, it is more preferable to impart shrinkage or elongation of −5.0% to 0.5% to the fiber bundle.

[Third carbonization process]
Further, if necessary, heat treatment is performed under tension in an inert atmosphere in a third carbonization furnace having an additional desired temperature gradient. The setting of the treatment temperature in the third carbonization step can be appropriately set according to the desired elastic modulus of the carbon fiber. The temperature gradient of the third carbonization furnace is not particularly limited, but it is preferable to set a linear gradient. In order to obtain carbon fibers having high mechanical performance, the lower the maximum treatment temperature for carbonization treatment, the better. Further, since the elastic modulus can be increased by increasing the treatment time, the maximum treatment temperature of the carbonization treatment can be lowered by increasing the treatment time. Furthermore, by increasing the processing time, the temperature gradient can be set gently, which is effective in suppressing defect point formation.

[Surface treatment process]
The carbon fiber bundle obtained in this way is subjected to surface treatment as necessary. Examples of the surface treatment method include a known method, that is, an oxidation treatment such as electrolytic oxidation, chemical oxidation, and air oxidation. The electrolytic oxidation treatment widely practiced industrially is the most suitable method from the viewpoint that stable surface oxidation treatment is possible and that the surface treatment state can be controlled by changing the amount of electricity. Here, even if the amount of electricity is the same, the surface state varies greatly depending on the electrolyte used and its concentration. However, in an alkaline aqueous solution having a pH higher than 7, the carbon fiber is used as an anode and the coercivity is 10 coulomb / g or more and 200 coulomb / g or less. It is preferable to carry out the oxidation treatment by flowing a quantity of electricity. As the electrolyte, it is preferable to use ammonium carbonate, ammonium bicarbonate, calcium hydroxide, sodium hydroxide, potassium hydroxide, or the like.

[Sizing process]
Next, the obtained carbon fiber bundle is subjected to a sizing treatment as necessary. The sizing agent is performed by applying a sizing solution dissolved in an organic solvent or an emulsion solution dispersed in water with an emulsifier to the carbon fiber bundle by a roller dipping method, a roller contact method, etc., and drying it. Can do. The amount of the sizing agent attached to the surface of the carbon fiber can be adjusted by adjusting the concentration of the sizing agent solution or adjusting the amount of drawing. Drying can be performed using hot air, a hot plate, a heating roller, various infrared heaters, and the like. Subsequently, a sizing agent is attached and dried, and then wound around a bobbin to obtain a carbon fiber bundle to which the sizing agent is attached.

  By applying the above-described firing method (flame-proofing treatment and carbonization treatment) to the precursor fiber bundle of the present invention, a carbon fiber bundle excellent in mechanical performance can be obtained.

[Physical properties of carbon fiber bundles]
The carbon fiber bundle obtained from the precursor fiber bundle of the present invention preferably has a resin-impregnated strand strength of 6500 MPa or more, and preferably has a strand elastic modulus of 260 GPa or more and 380 GPa or less measured by the ASTM method.

  Preparation of the strand test body of the resin-impregnated carbon fiber bundle and measurement of the strength can be performed according to JIS R7608. However, the elastic modulus is calculated using a strain range according to the ASTM method.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1
[1. Preparation of precursor fiber bundle)
Acrylonitrile and methacrylic acid were polymerized by aqueous suspension polymerization to obtain an acrylonitrile copolymer having an acrylonitrile unit / methacrylic acid unit = 98/2 (mass%) and having a mass average molecular weight of 415,000. The obtained polymer was dissolved in dimethylformamide to prepare a spinning dope having a concentration of this polymer of 23.5% by mass.

  Here, the mass average molecular weight of the prepared polyacrylonitrile-based copolymer was measured as follows. GPC system HLC-8120 (trade name) manufactured by Tosoh Corporation was used, and two TOSOH TSK-GEL and SuperHZM-H (trade name) manufactured by Tosoh Corporation were used in series for the column. A dimethylformamide solution of 0.01 mol / l lithium chloride was used as an eluent, the column flow rate was 0.6 ml / min, the polymer concentration was 0.001 g / ml, and the injection amount was 20 μl. Using polystyrene as a standard substance, the mass average molecular weight of the polyacrylonitrile copolymer was determined.

  This spinning stock solution was once spun into air from a spinneret having a diameter of 0.13 mm and a discharge hole with 2000 holes, and then passed through a space of about 4 mm and adjusted to 8 ° C. and 80.1% by mass dimethyl. It was discharged and coagulated in a coagulation liquid filled with an aqueous solution containing formamide, and a coagulated fiber bundle was taken up (step 1).

  Next, the obtained coagulated fiber bundle was stretched 1.1 times in the air (step 2), and then in a pre-stretching tank filled with an aqueous solution containing 55% by mass dimethylformamide adjusted to 60 ° C. Stretched 0 times (step 3). That is, the total draw ratio of steps 2 and 3 with respect to the coagulated fiber bundle obtained from step 1 was 3.3 times. Subsequently, the obtained fiber bundle containing the organic solvent was washed with clean warm water (step 4), and stretched 1.01 times in water at 55 ° C. (step 5).

  Then, the oil agent which has an amino modified silicone compound as a main component was provided to the fiber bundle obtained from the process 5 (process 6), and the dry densification process was performed after that.

Here, as the oil agent mainly composed of the amino-modified silicone, an oil agent comprising 85% by mass of the following amino-modified silicone and 15% by mass of an emulsifier was used. In addition, content of the silicone compound in the fiber bundle which the oil agent obtained from the process 6 adhered was 1.04 mass%.
Amino-modified silicone: KF-865 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd., primary side chain type, viscosity 110 cSt (25 ° C.), amino equivalent 5,000 g / mol).
Emulsifier: NIKKOL BL-9EX (trade name, manufactured by Nikko Chemicals, POE (9) lauryl ether).

  Further, the fiber bundle after drying and densification was stretched 3.1 times between heating rolls at 180 ° C., and after further improving the orientation and densification, it was wound up to obtain a precursor fiber bundle. The single fiber fineness of the precursor fiber was 0.77 dtex.

[2. (Flame resistance treatment)
Next, a plurality of the obtained precursor fiber bundles are introduced into a flameproofing furnace in a state of being aligned in parallel (sheet form), and air heated to 220 ° C. or more and 280 ° C. or less is blown onto the precursor fiber bundles, The precursor fiber bundle was made flame resistant to obtain a flame resistant fiber bundle having a density of 1.342 g / cm ³ . Specifically, in a state where the plurality of precursor fiber bundles are stretched at an elongation rate of 5.0%, a flameproofing treatment is performed to a density of 1.200 g / cm ³ or more and 1.250 g / cm ³ or less. In a state of being stretched at 1.5%, a flame resistance treatment is applied to a density of 1.250 g / cm ³ or more and 1.300 g / cm ³ or less, and further, a state of relaxation at a shrinkage rate of −0.5% is performed. .300 g / cm ³ or more 1.350
Flame-resistant treatment was performed up to g / cm ³ or less to obtain a flame-resistant fiber bundle. The total elongation rate in this flameproofing treatment was 6%, and the total flameproofing treatment time was 40 minutes.

[3. Carbonization treatment)
Next, the obtained flame-resistant fiber bundle was passed through nitrogen in a first carbonization furnace at 300 ° C. or more and 700 ° C. or less while adding 4.5% elongation (first carbonization step). The first carbonization furnace had a linear temperature gradient in which the carbonization treatment start temperature was 300 ° C. and the end temperature was 700 ° C. The carbonization time was 1.9 minutes.

  Subsequently, the obtained fiber bundle was subjected to heat treatment in a state where the fiber bundle was relaxed at a shrinkage rate of −3.8% using a second carbonization furnace having a temperature of 1000 ° C. to 1250 ° C. in a nitrogen atmosphere (second). Carbonization process). The second carbonization furnace had a linear temperature gradient in which the carbonization treatment start temperature was 1000 ° C. and the end temperature was 1250 ° C.

  Subsequently, the obtained fiber bundle was subjected to heat treatment in a state of being relaxed at a shrinkage of −0.1% using a third carbonization furnace having a temperature of 1250 ° C. or more and 1500 ° C. or less in a nitrogen atmosphere (third carbonization). Step), a carbon fiber bundle was obtained. This third carbonization furnace had a linear temperature gradient in which the carbonization treatment start temperature was 1250 ° C. and the end temperature was 1500 ° C. The total shrinkage in the second and third carbonization steps was −3.9%, and the total carbonization treatment time was 3.7 minutes.

[4. (Surface treatment of carbon fiber bundle)
Subsequently, the obtained carbon fiber bundle is run in an aqueous solution containing 10% by mass of ammonium bicarbonate, and this carbon fiber bundle is used as an anode so that the amount of electricity is 40 coulomb per 1 g of the carbon fiber to be treated. The electrode was subjected to an energization treatment with the counter electrode, washed with warm water at 90 ° C., and then dried. Next, 0.5 mass% of Hydran N320 (trade name, manufactured by DIC Corporation) was attached to the obtained fiber bundle, wound around a bobbin, and a surface-treated carbon fiber bundle was obtained.

(Examples 2 to 24 and Comparative Examples 1 to 10)
As shown in Table 1, a precursor fiber bundle was obtained in the same manner as in Example 1 except that the spinning conditions and the amount of the silicone compound adhered to the precursor fiber bundle were changed. Furthermore, a surface-treated carbon fiber bundle was produced from this precursor fiber bundle in the same manner as in Example 1.

  Table 1 summarizes the spinning conditions, the content (giving) of the silicone compound in the precursor fiber bundle, the resin-impregnated strand strength and the strand elastic modulus of the surface-treated carbon fiber bundle.

  As shown in Table 1, the resin-impregnated strand strength and strand elastic modulus of the carbon fiber bundle obtained by firing the precursor fiber bundle to which the oil agent obtained by the production method of Examples 1 to 24 of the present invention was adhered were both high. And sufficient strength to obtain a fiber reinforced resin having high mechanical properties.

Claims (5)

A method for producing an acrylonitrile precursor fiber bundle for carbon fibers to which a silicone compound is attached,
(1) A step of producing a coagulated fiber bundle by a dry-wet spinning method from a spinning stock solution in which a polymer having an acrylonitrile unit content of 96.0% by mass or more is dissolved in an organic solvent;
(2) stretching the coagulated fiber bundle in air to 1.0 to 1.2 times;
(3) The fiber bundle obtained from step 2 is stretched in an aqueous solution containing an organic solvent, and the total draw ratio of step 2 and step 3 with respect to the solidified fiber bundle obtained from step 1 is 2.0 times or more. A step of 4.0 times or less;
(4) removing the organic solvent from the fiber bundle obtained from step 3,
(5) The step of shrinking or stretching the fiber bundle obtained from step 4 to 0.95 times or more and 1.3 times or less in a water bath at 40 ° C. or higher;
(6) a step of attaching an oil agent containing a silicone compound to the fiber bundle obtained from step 5, and (7) a step of drying the fiber bundle obtained from step 6.
In step 3, the temperature (° C.) of the aqueous solution containing the organic solvent is represented by A, the concentration (mass ratio) of the organic solvent in the aqueous solution containing the organic solvent is represented by B, and the step in the aqueous solution containing the organic solvent When the draw ratio (ratio) imparted to the fiber bundle obtained from 2 is represented by C, and the temperature (° C.) of the water bath is represented by D in Step 5, the relationship represented by the following mathematical formula (1) is obtained. Carbon, which gives the fiber bundle an amount of the oil agent in which the content of the silicone compound with respect to the dried fiber bundle after Step 7 is 0.7% by mass or more and 2.0% by mass or less in Step 6 Method for producing acrylonitrile precursor fiber bundle for fiber:
The method according to claim 1, wherein an amino-modified silicone compound satisfying the following conditions (1) and (2) is used as the silicone compound:
(1) Kinematic viscosity at 25 ° C. is 50 cst or more and 5000 cst or less,
(2) An amino equivalent is 1700 g / mol or more and 15000 g / mol or less.   An acrylonitrile precursor fiber bundle for carbon fibers to which a silicone compound is adhered, wherein the content of the silicone compound in the fiber bundle is 0.7% by mass or more and 2.0% by mass or less, and the fineness of a single fiber is 0.5 dtex or more and 0.95 dtex or less, the ratio of the major axis to the minor axis (major axis / minor axis) of the fiber cross section of the single fiber is 1.00 or more and 1.01 or less, and the center line average roughness (Ra) is 3 nm or more and 10 nm. The following are acrylonitrile precursor fiber bundles for carbon fibers.   The acrylonitrile precursor fiber bundle for carbon fibers according to claim 3, which has no surface uneven structure extending in the fiber axis direction of single fibers. The acrylonitrile precursor fiber bundle for carbon fibers according to claim 3 or 4, wherein the silicone compound is an amino-modified silicone compound that satisfies the following conditions (1) and (2):
(1) Kinematic viscosity at 25 ° C. is 50 cst or more and 5000 cst or less,
(2) An amino equivalent is 1700 g / mol or more and 15000 g / mol or less.