JP2010031418A - Method for producing precursor fiber for carbon fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a precursor fiber for carbon fiber having high quality and containing few fluffs while shortening a drying-drawing step as far as possible to improve the productivity. <P>SOLUTION: The method for producing the precursor fiber for a carbon fiber includes the spinning of a spinning dope obtained by dissolving a polyacrylonitrile polymer and the drawing of the obtained swollen yarn in a superheated steam atmosphere at 110-185°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a carbon fiber precursor fiber that can enhance the productivity as a carbon fiber precursor fiber.

  Among the carbon fibers, the most widely used polyacrylonitrile (hereinafter abbreviated as PAN) carbon fibers are usually prepared by spinning a spinning solution comprising a PAN polymer as a precursor thereof into a wet spinning or dry process. A swollen yarn obtained by spinning or dry-wet spinning is stretched after drying to obtain a carbon fiber precursor fiber (hereinafter sometimes abbreviated as precursor fiber), and then the temperature is 200 to 400 ° C. It is manufactured industrially by heating in an oxidizing atmosphere to convert it to flame-resistant fibers, and heating and carbonizing in an inert atmosphere at a temperature of at least 1000 ° C., but further improving productivity The request is high.

  Studies to improve the productivity of PAN-based carbon fibers have been made from the viewpoints of spinning, flame resistance or carbonization of carbon fiber precursor fibers. In particular, the prior art for improving the productivity of precursor fibers has the following problems. That is, in spinning to obtain a precursor fiber, (1) a spinning speed, a coagulation condition and a limiting speed (hereinafter also referred to as spinnability) for taking a coagulated yarn derived from the characteristics of the PAN-based polymer solution and its The ultimate draw ratio derived from the solidified structure, that is, the final spinning speed, in addition to (2) the single fiber fineness of the precursor fiber and (3) the number of yarns and the total fineness with respect to the machine width of the spinning equipment in spinning Productivity is limited by the product (dtex / cm), that is, the yarn density. Since the single fiber fineness of the precursor is directly related to the performance of the carbon fiber, it is difficult to change it. Although it is effective to increase the yarn density in spinning, there is a limit to reducing the interval for avoiding interference with adjacent yarns. If the yarn density is the same, an increase in the size of the equipment can be considered to improve the production volume, but there are problems in equipment design such as enlarging the rollers, which is difficult. In order to increase production without increasing the number of spinning facilities, it is effective to develop technology that increases spinning speed. There are a variety of processes that limit the spinning speed, and even if one process is improved, the other processes limit the spinning speed, and it is necessary to improve them comprehensively. Above all, the drying process and the drawing process are very long. However, if the spinning speed is increased, it is necessary to make the process longer in order to maintain the efficiency in each process, and the equipment productivity is improved. There was a problem that it was difficult to do.

  The production process of a general precursor fiber will be described in more detail. A PAN-based polymer solution is discharged into a coagulation bath through a die to form a yarn, and further, a swollen yarn is passed through a washing step in which the solvent is replaced with water. And densified by drying, and then drawn into precursor fibers. In order to omit the drying step, there was also a method of stretching the swollen yarn in pressurized steam before drying, but the moisture content of the yarn remained almost unchanged after stretching, compared to the yarn speed before stretching. Since the yarn speed after drawing is very high, the drying efficiency is deteriorated, and there is a problem that a longer drying facility is required if sufficient drying is attempted. Also, there was a method of dry-heat stretching while drying the swollen yarn, but the dry heat stretching reduces the stretchability compared to the pressurized steam stretching, that is, the stretch ratio cannot be increased, so the final spinning speed is reduced. When trying to reach the desired speed, it is necessary to increase the spinning speed before drying, and in order to increase the spinning speed before drying, it is necessary to lengthen the coagulation bath and washing process. Thus, it was difficult to improve the final spinning speed.

  On the other hand, it is known that superheated steam has a drying effect. An example in which superheated steam has been studied in the spinning process of acrylic fiber is an example of using relaxation treatment after drying (see Patent Document 1), but it is not used as a heating medium for drying or stretching. In addition, a technique using atmospheric pressure steam in a wet heat stretching process after drying has been proposed (see Patent Document 2), but there is no description of overheating, and it refers to a treatment at about 100 ° C. because it is wet heat, The purpose of the technique is also to obtain an acrylic fiber having a high bulkiness and a high shrinkage rate, and not for obtaining a precursor fiber having a high orientation and a low shrinkage rate. In addition, there are those exemplified that superheated steam is not suitable as a drawn heat medium after drying (see Patent Document 3) and general examples (see Patent Document 4). Furthermore, Patent Document 4 describes that stretching is performed using a far-infrared heater in a steam atmosphere, and although there is a possibility that the atmosphere is a superheated steam atmosphere, the occurrence of yarn damage due to pressurized steam stretching after drying is described. It was not intended to shorten the drying process and improve the productivity of the precursor fiber.

That is, with any conventionally known technique, drying and stretching cannot be completed in an integrated manner in a short time.
Japanese Patent Laid-Open No. 51-133533 JP 2003-313742 A JP-A-8-158162 JP-A-63-99316

  An object of the present invention is to solve the above-mentioned problems and to provide a method for producing a high-quality precursor fiber for carbon fiber with less fuzz while improving productivity by shortening the drying / stretching process as much as possible. To do.

  In order to achieve the above object, the present invention has the following configuration. That is, it is a method for producing a carbon fiber precursor fiber in which a swollen yarn obtained by spinning a spinning solution in which a polyacrylonitrile-based polymer is dissolved is drawn in an atmosphere containing superheated steam at a temperature of 110 to 185 ° C.

  ADVANTAGE OF THE INVENTION According to this invention, the precursor fiber for carbon fibers with few fuzzing can be manufactured, shortening a drying and extending | stretching process and improving productivity.

  In the present invention, the swollen yarn is obtained by spinning a spinning solution in which a PAN polymer is dissolved, and more specifically, usually, a PAN polymer solution in which a PAN polymer is dissolved in a solvent. Fiber yarns containing water through a coagulation step of spinning by spinning from a spinneret by a wet spinning method or a dry-wet spinning method, and a washing step of washing and stretching the fiber yarn obtained in the coagulation step in a water bath Obtained as an article. And in this invention, the superheated steam extending process which extends | stretches this swelling thread | yarn in the atmosphere containing superheated steam is included.

First, the PAN polymer suitably used in the present invention will be described. In the present invention, the weight average molecular weight is Mw, the Z average molecular weight is Mz, the Z + 1 average molecular weight is _{MZ + 1} , and the number average molecular weight is abbreviated as Mn. When referring to all PAN polymers in the spinning solution, the subscript (P )

  In the present invention, a spinning solution in which a PAN-based polymer having a weight average molecular weight Mw (P) of preferably 200,000 to 700,000, more preferably 300,000 to 500,000 is dissolved in a solvent is used. In the case of a low molecular weight PAN-based polymer having an Mw (P) of less than 200,000, the stretchability in the superheated steam stretching process may be lowered. Moreover, in a high molecular weight PAN polymer having Mw (P) exceeding 700,000, the entanglement increases and the stretchability may decrease. Mw (P) can be controlled by changing the amounts of monomers, polymerization initiators, chain transfer agents and the like during polymerization.

  The polydispersity Mz (P) / Mw (P) of the PAN polymer in the spinning solution is not particularly limited, but excellent spinnability can be obtained by using a PAN polymer having a specific molecular weight distribution. This is preferable because the final spinning speed can be easily increased without the spinnability becoming rate-limiting. That is, the polydispersity Mz (P) / Mw (P) is preferably 2.7 to 6, more preferably 3 to 5.8, and still more preferably 3.2 to 5.5. If Mz (P) / Mw (P) is less than 2.7, the strain hardening is weak and the discharge stability of the PAN-based polymer is insufficient and high-speed spinning becomes difficult, while Mz (P) / Mw (P ) Exceeds 6, the entanglement becomes too large and discharge becomes difficult.

  In the molecular weight distribution, it is preferable to use a PAN-based polymer having a molecular weight component content of 1 to 4% which is 5 times or more of Mw (P). If the content of the molecular weight component 5 times or more of Mw (P) is less than 1%, the strain hardening is weak and the improvement in the discharge stability from the spinneret of the spinning solution containing the PAN polymer may be insufficient. If it exceeds 1, the strain hardening is too strong and the discharge stability improvement degree of the PAN-based polymer may be insufficient. From this point of view, the molecular weight content of 5 times or more of Mw (P) is more preferably 1.2 to 3.8%, and further preferably 1.5 to 3.6%. The content of the molecular weight component of 5 times or more of Mw (P) is a value obtained from the logarithm of the polystyrene equivalent molecular weight measured by the GPC method and the molecular weight distribution curve drawn by the refractive index difference, and is an integral value of the entire molecular weight distribution. The ratio occupied by the integral value of the peak area, which is a molecular weight of 5 times or more the polystyrene equivalent molecular weight with respect to is shown. Since the refractive index difference substantially corresponds to the weight of the molecule eluted per unit time, the integrated value of the peak area substantially corresponds to the weight mixing ratio.

  Further, the smaller Mw (P) / Mn (P) is, the smaller the content of low molecular components that are likely to be structural defects of the carbon fiber. Therefore, the smaller the Mw (P) / Mn (P), the more preferable Mw (P) / Mw (P). ) / Mn (P) is preferably small. That is, even if the molecular weight side is broad and the low molecular weight side is broad, the drop in ejection stability is small, but the low molecular weight side is preferably as sharp as possible, and Mz (P) / Mw (P) is Mw. It is more preferably 1.5 times or more, and further preferably 1.8 times or more with respect to (P) / Mn (P). According to the study by the present inventors, in radical polymerization such as aqueous suspension or solution method, which is usually performed in the polymerization of acrylonitrile (hereinafter abbreviated as AN), the molecular weight distribution has a lower molecular weight side. Therefore, Mw (P) / Mn (P) is larger than Mz (P) / Mw (P). Therefore, when performing polymerization under special conditions such as the type and ratio of the polymerization initiator and sequential addition, or when using general radical polymerization, there is a method of mixing two or more PAN-based polymers. The method of mixing is simple. The smaller the number of types to be mixed, the easier and the two types are often sufficient from the viewpoint of ejection stability.

The Mw of the polymer to be mixed is a PAN-based polymer having a large Mw as the A component, and a PAN-based polymer having a small Mw is the B component. The Mw of the A component is preferably 800,000 to 15 million, more preferably Is 1 million to 5 million, and the Mw of the B component is preferably 150,000 to 700,000. This is a preferred embodiment because the larger the Mw difference between the A component and the B component, the larger the Mz / Mw and M _{Z + 1} / Mw of the mixed polymer tend to be, but when the Mw of the A component is greater than 15 million In some cases, the productivity of the A component may decrease, and when the Mw of the B component is less than 150,000, the strength of the precursor fiber may be insufficient.

  Specifically, the weight average molecular weight ratio between the A component and the B component is preferably 2 to 45, and more preferably 20 to 45.

  The weight ratio of the A component and the B component is preferably 0.003 to 0.3, more preferably 0.005 to 0.2, and 0.01 to 0.1. Further preferred. When the weight ratio of the A component to the B component is less than 0.003, strain hardening may be insufficient, and when it is greater than 0.3, the discharge viscosity of the polymer solution may increase so that the discharge may become difficult. The weight average molecular weight ratio of the A component and the B component and the weight ratio of the A component and the B component are obtained by dividing the peak of the molecular weight distribution measured by GPC into the shoulder and the peak portion, and the Mw of each peak and the peak area ratio. Is measured by calculating.

  When mixing the polymer of component A and component B, a method of mixing both polymers and then diluting with a solvent, a method of mixing each of the polymers diluted in a solvent, and a high molecular weight material that is difficult to dissolve A method in which the B component is mixed and dissolved after diluting the A component in the solvent, and a solution in which the monomer constituting the B component is mixed with a solution obtained by diluting the high molecular weight A component in the solvent. It is possible to employ a mixing method. For mixing, a method of stirring in a mixing tank, a method of quantifying with a gear pump or the like and mixing with a static mixer, a method of using a twin screw extruder, or the like can be preferably employed. From the viewpoint of uniformly dissolving the high molecular weight product, a method of first dissolving the component A which is a high molecular weight product is preferable. In particular, in the case of producing a carbon fiber precursor, the dissolved state of the high molecular weight component A is extremely important, and even if a slight amount of undissolved material exists, it is recognized as a foreign substance. When it is filtered by the filter medium or small enough not to be filtered, a void may be formed inside the carbon fiber.

  Specifically, the polymer concentration of the component A with respect to the solvent, that is, when assuming a solution consisting only of the component A and the solvent, the polymer concentration of the component A in the solution is preferably 0.1 to 5% by weight. Then, the B component is mixed, or the monomers constituting the B component are mixed and polymerized. The polymer concentration of the component A is more preferably 0.3 to 3% by weight, and further preferably 0.5 to 2% by weight. More specifically, the polymer concentration of the component A is preferably a quasi-dilute solution in which the polymers are slightly overlapped as an aggregate state of the polymer, and the component B is mixed or the component B is mixed. When the constituent monomers are mixed and polymerized, the mixed state is likely to be uniform, so that a dilute solution that is in an isolated chain state is a more preferable embodiment. The concentration of the dilute solution is considered to be determined by the intramolecular exclusion volume determined by the polymer molecular weight and the solubility of the polymer in the solvent. It is less likely to aggregate and deposit in the filter media. When the polymer concentration exceeds 5% by weight, an undissolved product of component A may be present. When the polymer concentration is less than 0.1% by weight, it is effective because it is a dilute solution depending on the molecular weight. Is often saturated.

  In the present invention, as described above, the polymer concentration with respect to the solvent of the component A is preferably 0.1 to 5% by weight, and then the method of mixing and dissolving the component B may be used. From the viewpoint, it is preferable to employ a method in which a monomer obtained by diluting a high molecular weight material in a solvent and a monomer constituting the component B are mixed and the monomers are mixed by solution polymerization.

  The method for adjusting the polymer concentration of the component A to the solvent to 0.1 to 5% by weight may be a method using dilution or a method using polymerization. When diluting, it is important to stir until it can be diluted uniformly, and the dilution temperature is preferably 50 to 120 ° C. The dilution time varies depending on the dilution temperature and the concentration before dilution, and may be appropriately set. When the dilution temperature is less than 50 ° C, it may take time to dilute, and when it exceeds 120 ° C, the component A may be altered. In addition, from the viewpoint of reducing the process of diluting the overlapping of the polymers and mixing them uniformly, from the production of the A component to the start of mixing of the B component, or the polymerization of the monomer constituting the B component. Meanwhile, the polymer concentration with respect to the solvent of the component A is preferably controlled in the range of 0.1 to 5% by weight. Specifically, when the component A is produced by solution polymerization, the polymerization is stopped when the polymer concentration with respect to the solvent is 5% by weight or less, and the component B is mixed therewith, or the monomer constituting the component B is added. It is a method of mixing and polymerizing the monomers. Usually, when the ratio of the charged monomer to the solvent is small, it is often difficult to produce a high molecular weight product by solution polymerization, so the ratio of the charged monomer is increased. However, when the amount is 5% by weight or less, the polymerization rate is low and a large amount of unreacted monomer remains. The B component may be mixed after removing the unreacted monomer by volatilization, but from the viewpoint of omitting the process, it is preferable to solution polymerize the B component using the unreacted monomer.

  The component A preferably used in the present invention desirably has compatibility with PAN, and is preferably a PAN-based polymer from the viewpoint of compatibility. As the composition, AN is preferably 93 to 100 mol%, more preferably 98 to 100 mol%, and the monomer copolymerizable with AN may be copolymerized if it is 7 mol% or less. When the component chain transfer constant is smaller than AN and it is difficult to obtain the required Mw, it is preferable to reduce the amount of the copolymerization component as much as possible.

  Examples of monomers copolymerizable with AN include acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters, acrylamide and its derivatives, allyl sulfonic acid, methallyl sulfonic acid and Those salts or alkyl esters can be used.

  In the present invention, the polymerization method for producing the PAN-based polymer as the component A can be selected from solution polymerization method, suspension polymerization method and emulsion polymerization method. For the purpose of polymerization, it is preferable to use a solution polymerization method. In the case of polymerizing using the solution polymerization method, as the solvent, for example, a solvent in which PAN is soluble, such as an aqueous zinc chloride solution, dimethyl sulfoxide, dimethylformamide, and dimethylacetamide, is preferably used. If it is difficult to obtain the required Mw, a solvent having a large chain transfer constant, that is, a solution polymerization method using a zinc chloride aqueous solution or a suspension polymerization method using water is also preferably used.

  As a composition of the PAN-based polymer that is the component B suitably used in the present invention, AN is preferably 93 to 100 mol%, and more preferably 98 to 100 mol%. A monomer copolymerizable with AN may be copolymerized if it is 7 mol% or less. However, as the amount of the copolymerization component increases, molecular breakage due to thermal decomposition at the copolymerized portion becomes more prominent in the flameproofing step. The tensile strength of the carbon fiber decreases.

  Examples of the monomer copolymerizable with AN include, for example, acrylic acid, methacrylic acid, itaconic acid and alkali metal salts thereof, ammonium salts and lower alkyl esters, acrylamide and derivatives thereof, allyl, from the viewpoint of promoting flame resistance. Sulfonic acid, methallylsulfonic acid and their salts or alkyl esters can be used.

  In the present invention, the polymerization method for producing the PAN-based polymer as the component B can be selected from a solution polymerization method, a suspension polymerization method and an emulsion polymerization method. For the purpose of polymerization, it is preferable to use a solution polymerization method. In the case of polymerizing using the solution polymerization method, as the solvent, for example, a solvent in which PAN is soluble, such as an aqueous zinc chloride solution, dimethyl sulfoxide, dimethylformamide, and dimethylacetamide, is preferably used. Among these, dimethyl sulfoxide is preferably used from the viewpoint of PAN solubility. The raw materials used for these polymerizations are preferably used after passing through a filter medium having a filtration accuracy of 1 μm or less.

  The PAN-based polymer described above is dissolved in an organic solvent such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide in which the PAN-based polymer is soluble, or an inorganic salt solvent which is an aqueous solution of an inorganic salt such as an aqueous zinc chloride solution or an aqueous rhodium soda solution. And spinning solution. When using the solution polymerization, if the solvent used for the polymerization and the spinning solvent are the same, the PAN-based polymer solution obtained after the polymerization can be used as it is or simply by diluting it with the spinning solvent. Therefore, a step of separating the PAN polymer from the PAN polymer solution obtained after polymerization and dissolving the separated PAN polymer in the spinning solvent becomes unnecessary.

  The polymer concentration of the PAN-based polymer in the spinning solution is not unclear because the relationship between the polymer concentration and the viscosity varies greatly depending on the solvent used, but it is preferably in the range of 5 to 30% by weight. . In the case of an organic solvent, it is more preferably 14 to 25% by weight, and most preferably 18 to 23% by weight. In the case of an inorganic salt solvent, it is preferably in the range of 5 to 18% by weight. When the polymer concentration is less than 5% by weight, the amount of solvent used increases, which is not economical, and the coagulation rate in the coagulation bath is decreased, voids are generated inside, and a dense structure may not be obtained. When the coalescence concentration exceeds 30% by weight, the viscosity increases, and spinning tends to be difficult. The polymer concentration of the spinning solution can be adjusted according to the amount of solvent used.

  In the present invention, the polymer concentration is the weight percent of the PAN polymer contained in the PAN polymer solution. Specifically, after weighing the PAN-based polymer solution, the measured PAN-based polymer solution is removed to a solvent that does not dissolve the PAN-based polymer and is compatible with the solvent used for the PAN-based polymer solution. After solvent, the PAN polymer is weighed. The polymer concentration is calculated by dividing the weight of the PAN polymer after desolvation by the weight of the PAN polymer solution before desolvation.

  The spinning solution viscosity at a temperature of 45 ° C is preferably in the range of 15 to 200 Pa · s, more preferably in the range of 20 to 100 Pa · s, and more preferably in the range of 25 to 60 Pa · s. Most preferred. When the solution viscosity is less than 15 Pa · s, capillary breakage tends to occur at the spun yarn, and thus the speed at which the yarn coming out from the die is taken, that is, the spinnability tends to decrease. Moreover, when solution viscosity exceeds 200 Pa * s, it will become easy to gelatinize and the tendency for a filter medium to become obstruct | occluded easily will be shown. The viscosity of the spinning solution can be controlled by Mw (P), polymer concentration, solvent type, and the like.

  In the present invention, the viscosity of a PAN polymer solution such as a spinning solution at a temperature of 45 ° C. can be measured with a B-type viscometer. Specifically, the PAN-based polymer solution placed in a beaker is immersed in a hot water bath adjusted to a temperature of 45 ° C. to adjust the temperature, and as a B-type viscometer, for example, B8L manufactured by Tokyo Keiki Co., Ltd. Using a viscometer, rotor No. 4 is used, and the viscosity of the PAN polymer solution is in the range of 0 to 100 Pa · s. p. m. The viscosity of the spinning solution is in the range of 100 to 1000 Pa · s. p. m. Measure with

  In the present invention, prior to spinning the spinning solution, it is preferable to pass through the filter medium to remove the polymer raw material and impurities mixed in each step. The filtration accuracy of the filter medium is preferably 1 to 10 μm, more preferably 3 to 10 μm, and even more preferably 5 to 10 μm. In the present invention, the filtration accuracy of the filter medium is defined by the particle diameter (diameter) of spherical particles capable of collecting 95% while passing through the filter medium. Therefore, there is a relationship between the filter filtration accuracy and the aperture diameter, and it is common to increase the filtration accuracy by narrowing the aperture diameter. When the filtration accuracy is larger than 10 μm, foreign matter in the obtained spinning solution increases, and fluff may be generated during stretching in the firing and stretching step. On the other hand, if the filtration accuracy is less than 1 μm, not only foreign substances but also ultra-high molecular weight components contained in the spinning solution may be selectively filtered / clogged to lower Mz (F) / Mw (F).

  In the present invention, carbon fiber precursor fibers can be produced by spinning the spinning solution described above by a dry, wet, or dry-wet spinning method. Among these, the dry and wet spinning method is preferably used because it is easy to increase the spinning speed. Also, wet spinning is preferably used because it is easy to increase the spinning speed under the specific coagulation bath conditions described later.

  The diameter of the die hole used for spinning is preferably 0.04 mm to 0.2 mm, and more preferably 0.1 to 0.15 mm. When the die hole diameter is smaller than 0.04 mm, shear stress is applied when the die is discharged, and high-speed spinning tends to be difficult. On the other hand, when the diameter of the die hole exceeds 0.2 mm, high-speed spinning may be difficult without excessive stretching in order to obtain a fiber having a single fiber fineness of 1.5 dtex or less.

  The spinning draft of the spinning solution is preferably in the range of 2.5-50. The spinning draft rate is more preferably in the range of 5 to 15, and still more preferably in the range of 10 to 15.

Here, the spinning draft rate refers to the surface speed of the roller (the take-up speed of the coagulated yarn) having a driving source with which the spinning yarn first leaves the spinneret and the linear velocity of the spinning solution in the spinneret hole ( The value divided by the discharge linear velocity. The discharge linear velocity is a value obtained by dividing the volume of the spinning solution discharged per unit time by the die hole area. Accordingly, the discharge linear velocity is determined by the relationship between the discharge amount of the spinning solution and the hole diameter of the spinneret. That is, the spinning draft rate is expressed by the following formula.

Spinning draft rate = (coagulated yarn take-up speed) / (discharge line speed) Increasing the spinning draft rate greatly contributes to fiber diameter reduction, and the draw ratio in the subsequent spinning process can be set low. . If stretching in the spinning solution state, the PAN polymer entanglement is weakened by the solvent and is easy to relax. Therefore, it can be stretched with less tension than the stretching in the subsequent spinning process, and the molecular chain is broken. It is preferable because it is difficult. If the spinning draft ratio is less than 2.5, the draw ratio in the subsequent spinning process must be set high, and the spinning draft is 15 from the viewpoint of suppressing the decrease in Mz (F) / Mw (F). The following is sufficient.

  In the present invention, the coagulation bath preferably contains a solvent such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide used as a spinning solvent and a so-called coagulation promoting component. As the coagulation accelerating component, those that do not dissolve the PAN-based polymer and are compatible with the spinning solvent are preferable. Specifically, ethanol, methanol, water, and particularly water is preferably used. In dry and wet spinning, known conditions can be set as conditions for the coagulation bath. In wet spinning, it is preferable to set a concentration condition exceeding the critical concentration. That is, in general, in wet spinning, when the critical spinning draft rate is measured by increasing the concentration of the coagulation bath and fixing other conditions, the critical spinning draft rate decreases, and suddenly stops at a certain critical concentration. It is widely known to increase. The critical concentration varies depending on the type and amount of copolymer component of PAN polymer, additives such as ammonia, temperature of coagulation bath, type of solvent and coagulant, etc. There is a need to. Under such a concentration condition, the critical spinning draft rate is greatly increased, so that high speed spinning is easy to perform.

  From the viewpoint of performing high-speed spinning, the spinning solution is solidified in a coagulation bath to form a yarn, and then taken up by a roller having a drive source. The take-up speed of the swollen yarn is 50 to 500 m / min. preferable. When the take-up speed is less than 50 m / min, productivity is lowered, and a take-up speed of 500 m / min is often sufficient.

  The carbon fiber precursor fiber is subjected to a water washing step of washing and drawing the fiber yarn obtained in the coagulation step in a water bath, and a superheated steam drawing step of drawing the swollen yarn obtained in the water washing step in a superheated steam atmosphere. Is obtained. As long as it does not deviate from the object of the present invention, it may be dried or stretched again after the superheated steam stretching step.

  In the washing step, it is usually preferable not only to perform washing with water to replace the solvent remaining in the coagulated yarn and water, but also to perform stretching in a bath or in the air thereafter. In the washing step, washing and stretching may be reversed, may be integrated, or may not be stretched. The bath liquid temperature in the water washing step is preferably 20 to 95 ° C. Moreover, what is necessary is just to set the draw ratio in a water washing process suitably, but it is preferable that it is 1-5 times. In addition to the properties of the spinning solution, the moisture content of the yarn after the washing step varies depending on the maximum value of the bath liquid temperature and the drawing conditions in the washing step. A lower moisture content is preferable because drying takes a shorter time and lower energy.

  The yarn after the water washing step may be used as a swollen yarn for the hot steam drawing step described later, but for the purpose of preventing fusion of single fibers, the oil agent comprising silicone or the like on the yarn after the water washing step Is preferably given. The step of applying the oil agent is not limited to this step, and it may be performed after superheated steam stretching or both. When using a silicone oil agent, it is preferable to use one containing a modified silicone such as an amino-modified silicone having high heat resistance. Oil is often applied in the form of a water emulsion, and in order to increase the moisture content of the swollen yarn, the yarn from which excess water has been removed with a nip roller after application of the oil is used as a swollen yarn for the superheated steam drawing process. It is preferable. Since the moisture content of the swollen yarn immediately before the superheated steam stretching is controlled to be within the range of 20 to 200% by weight, drying and stretching are performed efficiently in the superheated steam stretching step, and more preferably such moisture. The rate is 60 to 170% by weight. When the moisture content exceeds 200% by weight, the superheated steam drawing process may be long. When the moisture content is less than 20%, fusion occurs between the yarns, and the drawability is deteriorated. In the present invention, the moisture content (% by weight) includes the weight C (g) of the yarn to be measured and the weight D (g) in which the yarn is dried at 120 ° C. for 4 hours and does not contain moisture. To (C / D-1) × 100. The thing which volatilizes by the process of 120 degreeC x 4 hours is included as a water | moisture content other than water in this invention, for example, the solvent which could not be substituted with water at the washing process, and the volatile acidic compound contained in an oil agent are mentioned.

  The swollen yarn thus obtained is subjected to a superheated steam drawing step and drawn in an atmosphere containing superheated steam (hereinafter also referred to as a superheated steam atmosphere) to obtain a precursor fiber. That is, in a drawing machine having a space through which the yarn passes, the space is filled with a superheated steam atmosphere, and the swollen yarn is drawn in such a drawing machine. In the present invention, the superheated steam atmosphere may be an atmosphere of superheated steam alone or a mixed atmosphere of superheated steam and another gas. Any type of gas can be mixed with the superheated steam, but air or nitrogen is preferably used in view of safety and handleability. While the yarn passes through the superheated steam atmosphere, other gases such as air contained between the single fibers of the yarn and water vapor generated from the yarn may be mixed in the atmosphere. "" Refers to the atmosphere of the superheated steam stretching process. As the superheated steam atmosphere, superheated steam alone is most preferable from the balance between stretchability and drying efficiency. In the present invention, superheated steam means that the pressure is lower than the relationship between temperature and pressure of saturated steam. The pressure of the superheated steam atmosphere is preferably 0.09 to 0.15 MPa, and most preferably normal pressure. When the pressure is 0.09 MPa or more, there is little air leakage into the superheated steam stretching process, and when the pressure is 0.15 MPa or less, the drying efficiency is high, and gas leakage from the superheated steam stretching process. There is little outage and it is economical. Any method may be used for generating superheated steam, but it can be obtained by further heating the pressurized saturated steam generated by a boiler or the like to a higher temperature with a burner, an electric heater, induction heating or the like.

  Although the swollen yarn is stretched in such an atmosphere, the temperature of the atmosphere needs to be 110 to 185 ° C., preferably 140 to 180 ° C., more preferably 150 to 170 ° C. at the maximum temperature. When the maximum temperature is less than 130 ° C., drying takes time, and higher temperatures are preferable. However, when the temperature exceeds 180 ° C., the melting point of the PAN-based polymer becomes close to the melting point under wet heat and melts and breaks. In order to perform stretching in stages, a plurality of stretching machines in which the temperature of the superheated steam atmosphere is changed in stages may be used, or a single stretching is performed so that stretching can be performed after preheating to keep the stretching point constant. The machine may be controlled for each block, or a single drawing machine may be used at a constant temperature for convenience.

  A preferable residence time in the superheated steam atmosphere is 5 to 60 seconds. If the residence time is less than 5 seconds, drying may be insufficient, but it is preferable that the residence time is short, and 60 seconds is sufficient. Superheated steam has a high temperature-elevating capability up to 100 ° C. due to high condensation latent heat, and the drying effect is higher than air at 160 ° C. or higher, so that drying is completed in a short time.

  Further, the draw ratio in the superheated steam atmosphere is preferably 2 to 8 times, more preferably 5 to 8 times from the viewpoint of increasing the orientation of the precursor fiber and increasing the spinning speed. In order to obtain a superheated steam atmosphere, superheated steam may be generated outside the stretching machine, and the superheated steam may be introduced into the stretching machine, or the stretching machine into which heated steam has been introduced is heated to a predetermined temperature. A superheated steam atmosphere may be used. In addition, all of the multiple yarns may be simultaneously drawn into one drawing machine and drawn, or the multiple yarns may be divided into several yarns and one drawing for each of the plurality of yarns. It may be introduced into a machine and drawn, or may be introduced into one drawing machine for each yarn and drawn. It is also preferable to use a slit or a seal member at the yarn entrance / exit of the drawing machine so that the superheated steam atmosphere does not leak out. Also, in order to avoid fluctuations in the composition of the superheated steam atmosphere due to water vapor generated from the swollen yarn, an atmosphere gas exhaust port may be provided in the drawing machine and circulated, or from the yarn outlet / outlet of the drawing machine. The atmosphere gas may be positively discharged. When the superheated steam atmosphere is introduced into the drawing machine, the introduction direction may be a direction intersecting or parallel to the yarn traveling direction, but is a parallel direction from the viewpoint of suppressing fuzz of the yarn. Is more preferable.

  After the superheated steam stretching step, it may include a re-stretching step regardless of oiling, drying, and heat medium within the range not impairing the object of the present invention, but these steps are included in order to shorten the process. Preferably not.

  The precursor fiber thus obtained preferably has a moisture content of 0 to 5% by weight. In the present invention, the moisture content can be obtained without further drying after the superheated steam stretching step. Further, if the limit amount of the precursor fiber to be wound is the same, it is possible to increase the precursor fiber to be wound as the moisture content is smaller, and accordingly, the conveyance and the yarn joining interval are widened. In addition, if the moisture content is within 5% by weight, the precursor fiber has high bundling properties, and the lower the moisture content, the poorer the drying efficiency. Therefore, the moisture content can be dried in the flameproofing process without completely drying. It is also preferable to contain moisture within 5% by weight. Also in the prior art, since the yarn that has undergone the drying and densification step contains water again through the pressurized steam drawing step, the precursor fiber having a moisture content comparable to that of the prior art is used to superheat the swollen yarn. If the present invention, which can be obtained only by steam stretching, is adopted, the process can naturally be shortened.

  Moreover, the precursor fiber obtained has a single fiber fineness of preferably 0.7 to 1.5 dtex, more preferably 0.9 to 1.4 dtex. If the single fiber fineness of the precursor fiber is too small, the productivity is reduced. On the other hand, if the single fiber fineness is too large, the difference in internal and external structures of each single fiber after flame resistance becomes large, and the process in the subsequent carbonization process The tensile strength and tensile elastic modulus of the resulting carbon fiber may decrease. The single fiber fineness (dtex) in the present invention is a weight (g) per 10,000 m of single fibers.

  In the present invention, the degree of crystal orientation of the obtained precursor fiber is preferably 88 to 95%. In order to increase the degree of crystal orientation of the carbon fiber, the orientation of the flameproof structure is preferably high, and it is necessary to increase the degree of crystal orientation of the precursor fiber or increase the stretch ratio in the flameproofing step. In any case, it may be controlled within the above range. However, when the crystal orientation degree of the precursor fiber is increased and the drawing ratio of the flameproofing process is lowered, the crystal orientation degree of the precursor fiber is 91 to 95%. Is preferred.

  The resulting precursor fiber is usually in the form of a continuous fiber (filament). In addition, the number of filaments per one yarn (multifilament) is preferably 1,000 to 100,000, more preferably 12,000 to 80,000, still more preferably 24,000 to 50,000. It is. The number of filaments per yarn is preferably larger for the purpose of improving productivity. However, if the number of filaments is too large, it may not be possible to uniformly treat the inside of the bundle.

  Although the precursor fiber obtained in the present invention has high productivity, it has no fuzz and is excellent in quality. Therefore, the carbon fiber manufacturing method also has excellent process passability, and high quality carbon. It can be a fiber. The precursor fiber obtained by the present invention can be converted into carbon fiber as follows, for example. Flame resistance while stretching the precursor fiber produced by the above-described method in an oxidizing atmosphere at a temperature of 200 to 300 ° C., preferably under tension or stretching conditions, more preferably at a stretch ratio of 0.8 to 1.5. After carbonization treatment, pre-carbonization treatment is performed in an inert atmosphere at a temperature of 300 to 800 ° C., preferably with a draw ratio of 0.9 to 1.3, and then a maximum temperature of 1,000 to 3,000 ° C. In an inert atmosphere, carbon fiber is produced by carbonization while preferably stretching at a stretch ratio of 0.9 to 1.0.

Air is preferably employed as the oxidizing atmosphere in the flameproofing treatment. The density of the flameproof fiber obtained in this flameproofing step is preferably 1.3 to 1.4 g / cm ³ . That is, when the density of the oxidized fiber is insufficient oxidization is less than 1.3 g / cm ³ is liable to generate single yarns adhesion upon carbonization, with more generation amount of the decomposition gas Therefore, it is difficult to obtain high-performance carbon fibers, the crystal size Lc tends to be coarsened, and the compressive strength is not improved. On the other hand, if the flame resistance is excessively advanced, the main chain of the polymer is broken, and the tensile strength of the finally obtained carbon fiber is lowered. Therefore, the flame resistance density should not exceed 1.4 g / cm ^3. Is preferred.

  In the present invention, the preliminary carbonization treatment and the carbonization treatment are performed in an inert atmosphere. Examples of the gas used in the inert atmosphere include nitrogen, argon, and xenon. From an economical viewpoint, nitrogen is used. Is preferably used. In the preliminary carbonization treatment, it is preferable to set the heating rate in the temperature range to 500 ° C./min or less. Further, the maximum temperature in the carbonization treatment can be appropriately set according to the desired mechanical properties of the carbon fiber. In general, the higher the maximum temperature for carbonization, the higher the tensile modulus of the carbon fiber obtained, but the tensile strength becomes maximum at around 1500 ° C. Therefore, for the purpose of increasing both the tensile strength and the tensile elastic modulus, the maximum temperature of the carbonization treatment is preferably 1,200 to 1,700 ° C, more preferably 1,300 to 1,600 ° C. . On the other hand, when the maximum temperature of the carbonization treatment exceeds 1,500 ° C., the amount of voids generated along with the disappearance of nitrogen atoms increases, so from the viewpoint of obtaining dense carbon fibers, it is preferable to set the temperature to 1,500 ° C. or less. .

  The obtained carbon fiber can be subjected to electrolytic treatment for surface modification. The electrolytic solution used for the electrolytic treatment includes an acidic solution such as sulfuric acid, nitric acid and hydrochloric acid, an alkali solution such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate and ammonium bicarbonate, or a salt thereof as an aqueous solution. Can be used as Here, the amount of electricity required for the electrolytic treatment can be appropriately selected according to the carbonization degree of the carbon fiber to be applied.

  The electrolytic treatment can optimize the adhesion with the carbon fiber matrix in the resulting composite material, the brittle fracture of the composite material due to too strong adhesion, the problem of lowering the tensile strength in the fiber direction, Although the tensile strength in the fiber direction is high, the adhesive property with the matrix resin is inferior, and the problem that the strength characteristics in the non-fiber direction are not expressed is solved, and the resulting composite material has a balance in both the fiber direction and the non-fiber direction. Excellent strength characteristics are developed.

  After the electrolytic treatment, a sizing treatment can also be applied to give the carbon fiber a bundling property. As the sizing agent, a sizing agent having good compatibility with the matrix resin or the like can be appropriately selected according to the type of the matrix resin to be used.

  The carbon fiber obtained by the present invention can be produced by various molding methods such as autoclave molding as a prepreg, resin transfer molding as a preform of a woven fabric, and filament winding. It can be suitably used as a sports member such as a golf shaft.

Hereinafter, the present invention will be described more specifically with reference to examples. Next, a method for measuring various characteristics used in this example will be described.
<Various molecular weights: Mz, Mw, Mn>
A sample solution is prepared in which the polymer to be measured is dissolved in dimethylformamide (added with 0.01 N lithium bromide) at a concentration of 0.1% by weight. About the obtained sample solution, a molecular weight distribution curve is calculated | required from the GPC curve measured on the following conditions using GPC apparatus, and Mz, Mw, and Mn are calculated.
・ Column: Column for polar organic solvent GPC ・ Flow rate: 0.5 ml / min
・ Temperature: 75 ℃
・ Sample filtration: Membrane filter (0.45μm cut)
・ Injection volume: 200 μl
・ Detector: Differential refractive index detector Mw uses at least six types of monodispersed polystyrenes with different molecular weights and known molecular weights to create an elution time-molecular weight calibration curve, and corresponds to the corresponding elution time on the calibration curve. It is obtained by reading the molecular weight in terms of polystyrene.

In this example, CLASS-LC2010 manufactured by Shimadzu Corporation as a GPC device, and TSK-GEL-α-M (× 2) manufactured by Tosoh Corporation as a column and TSK-guard Column α manufactured by Tosoh Corporation, Calibration curves were manufactured by Wako Pure Chemical Industries, Ltd. as dimethylformamide and lithium bromide, 0.45 μm-FHLP FILTER manufactured by Millipore Corporation as a membrane filter, and RID-10AV manufactured by Shimadzu Corporation as a differential refractive index detector. Monodispersed polystyrenes for preparation were those having molecular weights of 184,000, 427,000, 791,000, and 1,300,000, 1,810,000, and 4210,000.
<Viscosity of spinning solution>
A B8L type viscometer manufactured by Tokyo Keiki Co., Ltd. is used as the B type viscometer, rotor No. 4 is used, and the spinning solution viscosity ranges from 0 to 100 Pa · s. p. m. In the range where the viscosity is 100 to 1000 Pa · s, the rotational speed of the rotor is 0.6 r. p. m. In each case, the viscosity of the spinning solution at a temperature of 45 ° C. was measured.
<Crystal orientation degree of precursor fiber>
The degree of orientation in the fiber axis direction was measured as follows. The fiber bundle is cut to a length of 40 mm, and 20 mg is precisely weighed and sampled so that the sample fiber axes are exactly parallel, and then a thickness of 1 mm is uniform using a sample adjusting jig. Sample fiber bundles were arranged. After impregnating with a thin collodion solution and fixing it so as not to lose its shape, it was fixed to a sample table for wide-angle X-ray diffraction measurement. From the half width (H °) of the spread of the profile in the meridian direction including the highest intensity of diffraction observed near 2θ = 17 °, using Cu Kα ray monochromated with a Ni filter as the X-ray source. The degree of crystal orientation (%) was determined using the following formula.

Crystal orientation degree (%) = [(180−H) / 180] × 100
<Single fiber fineness of precursor fiber>
A fiber having a filament number of 6,000 was wound 10 times on a 1 m metal frame, and then the weight was measured to calculate the weight per 10,000 m.
<Water content of swollen yarn or precursor fiber>
The moisture content of the swollen yarn was measured by collecting the swollen yarn immediately after entering the drawing step such as the superheated steam drawing step after the water washing step. The moisture content of the precursor fiber was measured by collecting a precursor fiber wound up by a winder or a precursor fiber stored in a cancel as a specimen. Each specimen is immediately collected in a weighing bottle and weighed, and its weight is defined as C (g). Measure using approximately 10 g. Since swollen yarns and precursor fibers change with time such as storage, it is necessary to measure immediately after each step. After weighing, the sample was dried in an atmosphere of 120 ° C. for 4 hours until there was no decrease in weight, weighed to obtain D (g), and the moisture content was calculated according to the following formula.

Moisture content = (C / D-1) x 100
<Running yarn fluff>
The number of fluffs per minute was measured for the running yarn immediately before winding with a winder.
[Example 1]
100 parts by weight of AN, 1 part by weight of itaconic acid, 0.4 part by weight of AIBN as a radical initiator, and 0.1 part by weight of octyl mercaptan as a chain transfer agent are uniformly dissolved in 370 parts by weight of dimethyl sulfoxide, which is stirred with a reflux tube. Placed in a reaction vessel with wings. After the space in the reaction vessel was purged with nitrogen to an oxygen concentration of 1000 ppm, heat treatment was performed under the following polymerization condition A while stirring, and polymerization was performed by a solution polymerization method to obtain a PAN polymer solution.

Polymerization condition A
(1) Temperature increase from 30 ° C to 60 ° C (temperature increase rate 10 ° C / hour)
(2) Hold for 4 hours at a temperature of 60 ° C. (3) Increase the temperature from 60 ° C. to 80 ° C. (temperature increase rate 10 ° C./hour)
(4) Hold for 6 hours at a temperature of 80 ° C. After preparing the obtained PAN-based polymer solution so that the polymer concentration becomes 20% by weight, ammonia gas is blown until the pH becomes 8.5. While neutralizing itaconic acid, an ammonium group was introduced into the polymer to obtain a spinning solution. The obtained PAN-based polymer had Mw of 400,000, Mz / Mw of 1.8, and the spinning solution had a viscosity of 50 Pa · s. After passing the obtained spinning solution through a filter with a filtration accuracy of 10 μm, using a spinneret having a pore number of 12,000 and a nozzle diameter of 0.12 mm at a temperature of 40 ° C., it is once discharged into the air to form a space of about 2 mm. After passing, the mixture was spun at a spinning draft rate of 3 by a dry and wet spinning method introduced into a coagulation bath consisting of an aqueous solution of 75% by weight dimethyl sulfoxide controlled at a temperature of 3 ° C., and taken up at a take-up speed of 50 m / min. The yarn was introduced into the washing process. In the water washing step, the film was washed with water and then stretched at a draw ratio of 2 in warm water having a bath temperature of 65 ° C. A diameter obtained by applying an amino-modified silicone-based silicone oil to a thread that has undergone a water washing step, and squeezing a swollen yarn obtained by squeezing with a nip roller at a pressure of 0.1 MPa, which is a drawing step, with an entrance and exit sealed with a 1 cm square slit This was introduced into a 2 cm cylindrical drawing machine, drawn at a draw ratio of 5 times, and wound up with a winder to obtain a precursor fiber. At this time, the moisture content of the swollen yarn was 90% by weight. In the drawing process, the heating temperature of the drawing machine is set to 140 ° C., and 250 ° C. and 1 atm superheated steam generated by induction heating using 140 ° C. saturated steam as a raw material at a wind speed of 3 m / min. The inside of the drawing machine was filled with a superheated steam atmosphere at 140 ° C. and 1 atm. The running yarn fluffs at this time were 12 pieces per minute, and the obtained precursor fiber had a fineness of 1.0 dtex, a crystal orientation of 93%, and a moisture content of 1% by weight.
[Example 2]
In the stretching step, precursor fibers were obtained in the same manner as in Example 1 except that both the heating temperature of the stretching machine and the temperature of the superheated steam atmosphere in the stretching machine were changed to 150 ° C. The running yarn fluffs at this time were two per minute, and the obtained precursor fiber had a fineness of 1.0 dtex, a crystal orientation of 93%, and a moisture content of 0% by weight.
[Example 3]
A precursor fiber was obtained in the same manner as in Example 1 except that in the stretching step, both the heating temperature of the stretching machine and the temperature of the superheated steam atmosphere in the stretching machine were changed to 160 ° C. The running yarn fluff at this time was 0 per minute, and the obtained precursor fiber had a fineness of 1.0 dtex, a crystal orientation of 93%, and a moisture content of 0% by weight.
[Example 4]
A precursor fiber was obtained in the same manner as in Example 1 except that the heating temperature of the drawing machine and the temperature of the superheated steam atmosphere in the drawing machine were both changed to 170 ° C. in the drawing process. The running yarn fluff at this time was 0 per minute, and the obtained precursor fiber had a fineness of 1.0 dtex, a crystal orientation of 93%, and a moisture content of 0% by weight.
[Example 5]
A precursor fiber was obtained in the same manner as in Example 1 except that the heating temperature of the drawing machine and the temperature of the superheated steam atmosphere in the drawing machine were both changed to 180 ° C. in the drawing process. The running yarn fluffs at this time were three per minute, and the obtained precursor fiber had a fineness of 1.0 dtex, a crystal orientation of 93%, and a moisture content of 0% by weight.
[Comparative Example 1]
In the stretching process, the precursor fiber was obtained in the same manner as in Example 1 except that both the heating temperature of the stretching machine and the temperature of the superheated steam atmosphere in the stretching machine were changed to 190 ° C. I couldn't. The fractured portion was markedly fused.
[Comparative Example 2]
In the drawing step, precursor fibers were obtained in the same manner as in Example 3 except that the superheated steam was not charged into the drawing machine, that is, the inside of the drawing machine was changed to be filled with an air atmosphere at 140 ° C. and 1 atm. The running yarn fluffs at this time were innumerable and poor in quality, but the obtained precursor fiber had a fineness of 1.0 dtex, a crystal orientation of 93%, and a moisture content of 0% by weight. .
[Comparative Example 3]
In the drawing process, the saturated steam to be charged into the drawing machine is reduced to 0.2 MPa, and the saturated water vapor is supplied to the drawing machine in a direction parallel to the yarn traveling direction at a wind speed of 3 m / min without performing induction heating. Thus, a precursor fiber was obtained in the same manner as in Example 3 except that the inside of the drawing machine was changed to be filled with a 0.2 MPa saturated steam atmosphere. At this time, the number of running yarn fluffs was 0 per minute, and the obtained precursor fiber had a fineness of 1.0 dtex, a crystal orientation of 93%, and a moisture content of 80% by weight. Therefore, the weight of the precursor fiber excluding moisture that can be wound with a winder is reduced to almost half, and the productivity is lowered. Next, the obtained precursor fiber was dried in a heat treatment furnace at 180 ° C. for 20 seconds, and further subjected to a flame resistance treatment at a stretch ratio of 1.0 in air having a temperature distribution of 240 to 260 ° C. for 100 minutes. A modified fiber was obtained. Subsequently, the obtained flame-resistant fiber was subjected to a preliminary carbonization treatment while being drawn at a draw ratio of 1.0 in a nitrogen atmosphere having a temperature distribution of 300 to 700 ° C., and further nitrogen having a maximum temperature of 1,300 ° C. In the atmosphere, carbonization was performed with the draw ratio set to 0.96 to obtain a continuous carbon fiber bundle. The strand physical property (tensile strength) of the obtained carbon fiber bundle was 5.4 GPa.
[Example 6]
100 parts by weight of AN, 1 part by weight of itaconic acid, and 130 parts by weight of dimethyl sulfoxide were mixed and placed in a reaction vessel equipped with a reflux tube and a stirring blade. After replacing the space in the reaction vessel with nitrogen to an oxygen concentration of 100 ppm, as a radical initiator, 0.002 part by weight of 2,2′-azobisisobutyronitrile (AIBN) was added and the following polymerization was conducted with stirring. Condition B heat treatment was performed.

Polymerization condition B
-Hold at 65 ° C for 2 hours-Decrease in temperature from 65 ° C to 30 ° C (Temperature drop rate: 120 ° C / hour)
Next, 240 parts by weight of dimethyl sulfoxide, 0.4 part by weight of AIBN as a radical initiator, and 0.1 part by weight of octyl mercaptan as a chain transfer agent were weighed and introduced into the reaction vessel, and the polymerization conditions were further stirred. A heat treatment of A was performed, and the remaining unreacted monomer was polymerized by a solution polymerization method to obtain a PAN polymer solution.

After preparing the polymer concentration to be 20% by weight using the obtained PAN-based polymer solution, the ammonia group was neutralized while itaconic acid was neutralized by blowing ammonia gas until the pH reached 8.5. Was introduced into a PAN-based polymer to obtain a spinning solution. The obtained PAN-based polymer had Mw of 480,000, Mz / Mw of 5.7, M _{Z + 1} / Mw of 14, and the spinning solution had a viscosity of 45 Pa · s. Example except that the spinning solution was changed to the spinning solution obtained as described above, the take-up speed was changed to 70 m / min, and the subsequent draw ratio was made the same as in Example 1 to increase the overall speed. In the same manner as in No. 3, precursor fibers were obtained. At this time, the moisture content of the swollen yarn was 90% by weight. Despite increasing the spinning speed, the quality of the obtained precursor fiber is excellent, and the running yarn fluff at this time is 0 per minute, and the obtained precursor fiber has a fineness. 1.0 dtex, the degree of crystal orientation was 93%, and the moisture content was 0% by weight. Next, the obtained precursor fiber was flameproofed for 100 minutes at a draw ratio of 1.0 in air having a temperature distribution of 240 to 260 ° C. to obtain a flameproof fiber. Subsequently, the obtained flame-resistant fiber was subjected to a preliminary carbonization treatment while being drawn at a draw ratio of 1.0 in a nitrogen atmosphere having a temperature distribution of 300 to 700 ° C., and further nitrogen having a maximum temperature of 1,300 ° C. In the atmosphere, carbonization was performed with the draw ratio set to 0.96 to obtain a continuous carbon fiber bundle. The strand physical property (tensile strength) of the obtained carbon fiber bundle was 5.6 GPa.
[Example 7]
Except that the first AIBN charge was changed to 0.001 part by weight, the space in the reaction vessel was replaced with nitrogen to an oxygen concentration of 1000 ppm, and the polymerization condition A was changed to the following polymerization condition C A spinning solution was obtained in the same manner as in Example 1.

Polymerization condition C
(1) Hold for 4 hours at a temperature of 70 ° C. (2) Decrease in temperature from 70 ° C. to 30 ° C. (Cooling rate 120 ° C./hour)
The obtained PAN-based polymer had Mw of 340,000, Mz / Mw of 2.7, M _{Z + 1} / Mw of 7.2, and the spinning solution had a viscosity of 40 Pa · s. Precursor fibers were obtained in the same manner as in Example 6 except that the spinning solution was changed to the spinning solution obtained as described above. At this time, the moisture content of the swollen yarn is 90% by weight, the running yarn fluff is 0 per minute, and the obtained precursor fiber has a fineness of 1.0 dtex and a crystal orientation of 93%. The moisture content was 0% by weight.
[Example 8]
A spinning solution was obtained in the same manner as in Example 4 except that the first AIBN charge was changed to 0.002 parts by weight and that the holding time was 1.5 hours under the polymerization condition C. The obtained PAN-based polymer had Mw of 320,000, Mz / Mw of 3.4, and M _{Z + 1} / Mw of 12, and the spinning solution had a viscosity of 35 Pa · s. Precursor fibers were obtained in the same manner as in Example 6 except that the spinning solution was changed to the spinning solution obtained as described above. At this time, the moisture content of the swollen yarn is 90% by weight, the running yarn fluff is 0 per minute, and the obtained precursor fiber has a fineness of 1.0 dtex and a crystal orientation of 93%. The moisture content was 0% by weight.
[Example 9]
100 parts by weight of AN, 1 part by weight of itaconic acid, and 360 parts by weight of dimethyl sulfoxide were mixed and placed in a reaction vessel equipped with a reflux tube and a stirring blade. After replacing the space in the reaction vessel with nitrogen to an oxygen concentration of 100 ppm, 0.003 part by weight of AIBN was added as a polymerization initiator, and heat treatment was performed under the following conditions while stirring.
(1) Hold at a temperature of 60 ° C. for 3.5 hours Next, in the reaction vessel, 10 parts by weight of dimethyl sulfoxide, 0.4 part by weight of AIBN as a polymerization initiator, and 0.1 part by weight of octyl mercaptan as a chain transfer agent After the part was metered in, the mixture was further heat-treated under the following conditions while stirring, and the remaining unreacted monomer was polymerized by a solution polymerization method to obtain a PAN polymer solution.
(2) Hold for 4 hours at a temperature of 60 ° C. (3) Increase the temperature from 60 ° C. to 80 ° C. (Temperature increase rate: 10 ° C./hour)
(4) Hold for 6 hours at a temperature of 80 ° C. Use the obtained PAN-based polymer solution to prepare a polymer concentration of 20% by weight, and then blow ammonia gas until the pH reaches 8.5. Thus, an ammonium group was introduced into the PAN polymer while neutralizing itaconic acid to obtain a spinning solution. The obtained PAN-based polymer had a polymer Mw of 400,000, Mz / Mw of 5.2, M _{Z + 1} / Mw of 10, and a spinning solution viscosity of 55 Pa · s. Precursor fibers were obtained in the same manner as in Example 6 except that the spinning solution was changed to the spinning solution obtained as described above. At this time, the moisture content of the swollen yarn is 90% by weight, the running yarn fluff is 0 per minute, and the obtained precursor fiber has a fineness of 1.0 dtex and a crystal orientation of 93%. The moisture content was 0% by weight.
[Example 10]
The spinneret is changed to a spinneret having a hole number of 12,000 and a nozzle hole diameter of 0.06 mm, the temperature of the coagulation bath is changed to 40 ° C., and the spinneret is directly spun into the coagulation bath instead of the dry and wet spinning method. A precursor fiber was obtained in the same manner as in Example 9 except that the wet spinning method was adopted. At this time, the moisture content of the swollen yarn is 140% by weight, the running yarn fluff is 0 per minute, and the obtained precursor fiber has a fineness of 1.0 dtex and a crystal orientation of 93%. The moisture content was 0% by weight.

Claims (5)

A method for producing a carbon fiber precursor fiber in which a swollen yarn obtained by spinning a spinning solution in which a polyacrylonitrile-based polymer is dissolved is drawn in an atmosphere containing superheated steam at a temperature of 110 to 185 ° C. The method for producing a carbon fiber precursor fiber according to claim 1, wherein the swelling yarn has a moisture content of 20 to 200% by weight. The carbon fiber production method according to claim 1 or 2, wherein the pressure of the atmosphere containing superheated steam is 0.09 to 0.15 MPa. The polyacrylonitrile-based polymer has a weight average molecular weight Mw (P) of 200,000 to 700,000, and the polydispersity Mz (P) / Mw (P) (Mz (P) is the Z of the polymer in the spinning solution. The method for producing a carbon fiber precursor fiber according to any one of claims 1 to 3, wherein the average molecular weight is 2.7 to 6. The method for producing a carbon fiber precursor fiber according to any one of claims 1 to 4, wherein the obtained carbon fiber precursor fiber has a moisture content of 0 to 5% by weight and an orientation degree of 88 to 95%.