JP2014163012A - Production method of acrylic precursor fiber for carbon fiber, and production method of carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high quality carbon fiber by which an acryl precursor fiber in which appearance quality is favorable under the high-speed spinning is obtained by a production method in which an oil solution is uniformly imparted to a bundle inside without breaking a fiber in an oil solution process in a production process of the acrylic precursor fiber for the carbon fiber.SOLUTION: A production method of an acrylic precursor fiber for a carbon fiber is characterized in that in a method for producing an acrylic precursor fiber, when a fiber obtained by which an acrylic polymer is performed by spinning twist by a dry wet type spinning or wet type spinning method, is performed by water washing and bath drawing, then imparted by an oil solution by an oil solution process, a fiber swelling degree just before being introduced in the oil solution process is in a range of 90 to 230%, an average fiber density in the oil solution process is 80 to 220 tex/mm, and an average fiber tensile force is in a range of 0.6 to 1.3 g/tex, imparting of the oil solution to the fiber is performed by using a water dispersion liquid in which the oil solution is performed by water dispersion.

Description

  The present invention relates to a method for producing a high-quality acrylic precursor fiber for carbon fiber, which is excellent in quality and operability while maintaining high productivity in the production process (spinning process) of acrylic precursor fiber, and carbon. The present invention relates to a fiber manufacturing method.

  Carbon fiber has been developed for a variety of applications including aerospace applications, taking advantage of its high strength and specific modulus. In particular, carbon fibers using polyacrylonitrile-based precursor fibers as starting materials are widely used because of their high specific strength and excellent processability. In recent years, as demand for carbon fibers has increased, there has been a high demand for cost reduction, and a further increase in production process has been demanded. Generally, polyacrylonitrile-based carbon fibers are heated to 220-300 ° C. in a oxidizing atmosphere (flame-proofing treatment) to convert the precursor fibers into flame-resistant fibers, and then heated to 1000 ° C. or more in an inert atmosphere ( It can be obtained by carbonization treatment, but if adhesion of single fibers occurs in the production process, fluff is generated, the operability is deteriorated and the strength is significantly reduced. In order to solve this problem, in the precursor fiber manufacturing process, a large number of adhesive agents are mainly controlled by applying an oil agent mainly composed of various modified silicones having excellent heat resistance and releasability to the precursor fiber. Proposals have been made. Ideally, the oil agent should be uniformly applied to a single fiber in as little amount as possible to form an oil agent film, and when applying the oil agent, the traveling fiber is widened with a constant tension, and the oil agent is spread into the fiber bundle. It is important to quickly infiltrate, and the synergistic effect of uniform application can be enhanced by applying to the fiber an oil agent selected from an appropriate range of oil viscosity.

  Furthermore, keeping the fiber swelling degree just before introduction into the oil agent process within a specific range is one of the important factors for improving the quality and operability in the yarn production process and the firing process, and the swelling degree is too high ( And the oil agent penetrates into the inside of the single fiber and the amount of the oil agent applied to the surface of the single fiber is reduced. Therefore, adhesion occurs and the operability deteriorates and the quality of the carbon fiber deteriorates. Further, if the degree of swelling is too low (yarn denseness is too high), the fiber converging property is too high to make it difficult for the oil agent to penetrate into the fiber bundle, making it difficult to uniformly apply the oil agent.

  In the conventional techniques described below, there has been no technique approached from the viewpoints of the fiber width, tension, oil viscosity of the oil agent, and fiber swelling degree, which are factors involved in uniformly applying the oil agent to these fibers. Specifically, a method for producing an acrylic fiber tow that prevents damage to single yarn by maintaining a constant width of the tow traveling in the oil bath by using a guide and improving the quality and operability ( Patent Document 1), an oil application method (Patent Document 2) that regulates the width of a traveling tow by a weir when applying an oil to a tow made of a plurality of fibers, or an ultrasonic transmitter provided in an oil bath A method of treating an oil agent while applying vibration to the bath (Patent Document 3), a method of treating an oil agent while applying vibration to the tow and processing liquid using a vibro processor having a perforated basket roller (Patent Document 4), in an oil bath For example, a method of bringing a vibrating guide bar into contact with the yarn when the yarn is immersed in the oil and applying the oil agent (Patent Document 5) has been proposed.

  However, in Patent Documents 1 and 2, it is possible to prevent fiber damage by keeping the fiber density introduced into the oil process relatively constant and preventing mixing with adjacent fibers. Since the oil viscosity and the degree of fiber swelling immediately before application of the oil agent are not considered, the effect of uniformly applying the oil agent to the fiber is small, and the quality of the obtained carbon fiber is insufficient. Further, in Patent Documents 3 and 4, it is preferable from the viewpoint of uniform application because the oil agent easily penetrates into the fiber bundle by mechanically widening the fiber, but it is not preferable to actively vibrate in the oil agent bath. The stability of the oil agent itself decreases and the particle size of the oil agent increases, so the state of oil agent application to the fibers is not uniform, and the location where the oil agent is applied excessively generates surface defects in the firing process, There is a problem that leads to a decrease in strength.

In addition to this, an oil agent application method (Patent Document 6) in which an oil agent is pumped into the oil agent tank using a screw pump and the oil agent is injected over the entire width of the fiber bundle has been proposed. It is difficult to maintain the operability because the fiber is damaged and the fiber is damaged, causing winding and thread breakage troubles.
Further, in Patent Document 7, there is a proposal for uniformly applying the oil agent by defining the time from the contact of the oil agent treatment liquid to the acrylic fiber bundle to the drying, but it is possible to further increase the yarn-making speed. From the viewpoint, securing the time after the application of the oil becomes a problem that is difficult to achieve.

  Furthermore, if the degree of swelling of the fiber immediately before applying the oil agent is too high, the oil agent easily penetrates into the inside of the single fiber and the amount of oil agent applied to the surface decreases, so that the single fibers adhere to each other in the subsequent drying step, and the post-stretching step As a result, the single fiber breakage occurs, leading to a decrease in quality and operability, leading to a decrease in the strength of the resulting carbon fiber. On the other hand, if it is too low, there is a problem that the convergence property of the fiber is too high and the oil agent hardly penetrates into the fiber bundle. For example, in Patent Document 8, there is a proposal to provide a water-soluble silicone oil agent after adjusting the degree of swelling of the stretched yarn to a certain range, but the fiber density, fiber tension, oil viscosity of the oil agent and Is not taken into consideration, so single yarn breakage due to blending with adjacent yarns occurs in the oil agent process, maintaining the quality and operability is difficult, and the quality of the obtained carbon fiber is also The result was insufficient.

Japanese Patent No. 3891025 JP 2009-263817 A JP 59-204914 A Japanese Patent Publication No.55-17132 JP-A-1-266214 JP 2002-249920 A JP 2009-215664 A JP 58-214517 A

  In view of the background of such prior art, the present invention provides an oil agent process in an acrylic precursor fiber manufacturing process that quickly and uniformly imparts an oil agent into a fiber bundle without damaging the fiber while maintaining high productivity. According to this method, acrylic precursor fibers having good quality and operability are obtained, and high-quality carbon fibers are provided.

  That is, an object of the present invention is to provide a method for producing an acrylic precursor fiber that uniformly imparts an oil agent into a fiber bundle while suppressing fiber damage, and to maintain high productivity and operability. Another object of the present invention is to provide a method for producing an excellent acrylic precursor fiber or high-quality carbon fiber.

  In order to solve such problems, the present invention introduces a fiber obtained by spinning an acrylic polymer by dry-wet spinning or wet spinning method into an oil agent process when applying an oil agent in an oil agent process after washing with water and drawing in a bath. The fiber swelling degree immediately before performing is in the range of 90 to 230%, the average fiber density in the oil agent process is in the range of 80 to 220 tex / mm, and the average fiber tension is in the range of 0.6 to 1.3 g / tex, It is a method for producing an acrylic precursor fiber for carbon fiber, characterized in that the oil agent is applied to the fiber using an aqueous dispersion in which the oil agent is dispersed in water.

  Moreover, the preferable method for producing an acrylic precursor fiber for carbon fiber of the present invention is such that the oil viscosity at 25 ° C. of the oil agent is in the range of 500 to 10,000 cSt, and the aqueous dispersion contains at least one amino-modified silicone. It is an aqueous dispersion containing.

  Further, the carbon fiber production method of the present invention is such that the acrylic precursor fiber for carbon fiber thus produced is fired at 220 to 300 ° C. in an oxidizing atmosphere, and then 1000 ° C. or more in an inert atmosphere. It is the manufacturing method of carbon fiber obtained by baking with.

  In the present invention, by controlling the degree of fiber swelling immediately before being introduced into the oil agent process in the production process of acrylic precursor fibers, the oil agent penetration into the single fiber is suppressed, and the average fiber density and average fiber tension in the oil agent process are controlled. Is controlled within a certain range, and the oil agent is applied to the fiber using an aqueous dispersion in which the oil agent is dispersed in water, preferably, the oil agent is within a certain oil viscosity range, Since the dispersion contains at least one amino-modified silicone, it is possible to uniformly apply the oil to the fiber bundle without damaging the fiber, and it is excellent in quality and operability while maintaining high productivity. Acrylic precursor fiber can be obtained. Moreover, it becomes possible to obtain a high-quality carbon fiber by baking the acrylic precursor fiber of the present invention.

  The present inventors diligently studied about a method for producing an acrylic precursor fiber for carbon fiber that uniformly imparts an oil agent into the fiber bundle without damaging the fiber while maintaining high productivity, and the following idea It came. In other words, the degree of fiber swelling just before introduction into the oil agent process, the fiber density and fiber tension of the fiber running through the oil agent process, and the oil viscosity of the oil agent are important factors from the viewpoint of imparting the oil agent uniformly to the fiber. It was possible to obtain high-quality acrylic precursor fibers with excellent quality and operability while maintaining production.

  Here, the acrylic polymer used for the production of the acrylic precursor fiber for carbon fiber of the present invention is a polymer mainly composed of acrylonitrile, and acrylonitrile is 90% by mass or more and 99.9% by mass or less, An acrylic copolymer obtained by copolymerizing a monomer copolymerizable with acrylonitrile is preferably used. Preferable monomers that can be copolymerized with acrylonitrile include acrylic acid, methacrylic acid, itaconic acid, allyl sulfonic acid, methallyl sulfonic acid, and alkali salts and ammonium salts thereof, hydroxyethyl acrylonitrile, and the like. Further, a third component such as methyl acrylate may be included. By setting the acrylonitrile copolymerization ratio in the acrylic polymer to 90% by mass or more, it is possible to prevent a decrease in productivity due to an excessive increase in the weight loss rate of the fiber in the firing step or a decrease in heat resistance. I can do it. Moreover, by setting it as 99.9 mass% or less, the fall of the drawability of acrylic type precursor fiber can be prevented, and favorable processability can be ensured.

  Such an acrylic polymer is prepared as a spinning dope in a state dissolved in an organic or inorganic solvent. From the viewpoint of the stability of the spinning solution, an organic solvent such as dimethylacetamide (DMAc) or dimethylsulfoxide (DMSO) is preferably used as the solvent. As a method of spinning using such a spinning dope, in the present invention, a method of introducing a fiber into a coagulation bath by wet or dry wet spinning is used. The fiber drawn from the coagulation bath is washed with the coagulation solvent and then stretched at a desired magnification in warm water or hot water, or is stretched at a desired magnification in warm water or hot water and then washed with water and introduced into the oil agent process. Is done.

  In the present invention, the degree of fiber swelling immediately before introduction into the oil agent process is in the range of 90 to 230%, which is necessary for uniformly applying the oil agent into the fiber bundle and obtaining high-quality carbon fibers. There is a more preferable range of 120 to 200%. By making the fiber swelling degree 230% or less, when the oil agent is applied, the oil agent penetrates into the single fiber and prevents the single agent adhesion in the drying process derived from less oil agent applied to the surface of the single fiber, Effective in stabilizing quality, quality, and operation. Moreover, by setting the degree of swelling to 90% or more, the compatibility with the applied oil agent is ensured, and the inter-single fiber adhesion in the bath stretching step that occurs when the degree of fiber swelling is excessively reduced is suppressed. I can do it. These can be set by adjusting the stretching temperature and the magnification by setting the copolymer composition of the polymer, the molecular weight, the solvent type, the polymer viscosity, and the single fiber fineness when the oil is applied. Here, the degree of fiber swelling immediately before being introduced into the oil agent process is in the range of 90 to 230%, and as the fiber swelling degree is once increased as it is stretched immediately after spinning, it may be at a time corresponding to the decrease. preferable. By increasing the fiber swelling degree to 230% or less once it is increased due to the progress of drawing, the water and oil agent contained in the fiber bundle can be replaced smoothly, ensuring a good uniform application of oil agent. I can do it. In other words, even when the oil agent is applied when the fiber swelling degree once reaches 230% before the fiber swelling degree increases, the quality and operability of the precursor fiber obtained due to problems such as adhesion between single fibers tend to be slightly lowered. . In addition, the fiber swelling degree in this invention is calculated | required with the following measuring methods.

  About 10 g of fibers immediately before being introduced into the oil agent process are sampled and washed with water for 12 to 16 hours. Next, the fiber weight after dehydration is determined by dewatering at 3000 rpm for 3 minutes using a centrifugal dehydrator (for example, H-110A manufactured by Kokusan Co., Ltd.). Thereafter, the dehydrated sample is dried for 2.5 hours with a dryer controlled at 105 ° C., the fiber weight after drying is determined, and the fiber swelling degree is calculated by the following formula.

  Formula: degree of fiber swelling (%) = ((fiber weight after dehydration−fiber weight after drying) / fiber weight after drying)) × 100.

  Further, in the present invention, the fiber introduced into the oil agent process is in a swollen state containing a certain amount of water in the previous bath stretching process or water washing process, and the water contained in the fiber bundle when the oil agent is applied. If the oil is not smoothly replaced with the oil, it is difficult to uniformly apply the oil, and if the speed is further increased and the speed is further increased, the processing time in the oil process is reduced, and the oil is more into the fiber bundle. Penetration becomes difficult. In order to solve this problem, if the fiber density is lowered, that is, the yarn width is increased as much as possible, the oil agent can easily penetrate into the fiber bundle, but the fiber stretch ratio in the oil agent process is simply lowered to the loose side to reduce the yarn width. When trying to spread, there is a problem that the traveling fiber meanders or the fiber tension becomes too low, the focusing property is impaired, fluff is likely to occur, and the quality is lowered. In order to prevent these, there is a method of inserting a guide or the like between adjacent fibers. However, there are cases where the machine width becomes long and the size of the apparatus cannot be avoided. On the other hand, if the tension is set too high so as to enhance the rubbing effect, the rubbing force with the guide or the like becomes excessive, and there is a problem that the quality is lowered due to fluffing.

  Therefore, in the present invention, it is necessary to set the average fiber density of the fibers traveling in the oil agent process in the range of 80 to 220 tex / mm and the average fiber tension of the traveling fibers to be 0.6 to 1.3 g / tex. It is. A more preferable range is an average fiber density of 90 to 210 tex / mm and an average fiber tension of 0.8 to 1.1 g / tex. By setting the average fiber density to 80 tex / mm or more, high-density fibers can be processed at the same time in a small space, and by setting the average fiber density to 220 tex / mm or less, oil agent permeability into the fiber bundle is ensured. I can do it. Also, by setting the average fiber tension to 0.6 g / tex or more, it is possible to stabilize the yarn path of the fiber running through the oil agent process and prevent blending with adjacent fibers, thereby maintaining the quality and operability. It becomes possible, and by setting it as 1.3 g / tex or less, while being able to ensure the permeability to the bundle of fibers, it becomes possible to prevent the fiber from being scratched or fluffed.

  Here, the average fiber density is measured by a simple average value obtained by dividing the yarn width at the entry and exit of the oil process by the fineness, and the average fiber tension is the simple tension at the entry and exit of the oil process. It is measured by an average value.

  In the oil agent process of the present invention, a water-soluble emulsion in which an oil agent component is dispersed in water, an emulsion using an emulsifier, an emulsion in which a silicone oil agent and a non-silicone oil agent are mixed, and the like are applied to a traveling fiber. The method for applying the oil agent is not particularly limited. For example, in the oil bath, the oil agent is treated while vibrating the tow and the treatment liquid using a vibro processor having a perforated basket roller described in the above-mentioned patent document. And a method of immersing the yarn in the oil agent. Among these, since there is an effect that the oil agent is quickly and uniformly distributed inside the fiber bundle, a method (dip method) in which the yarn is immersed in an oil bath to apply the oil agent is preferable. As a dip method, by applying the fibers while running through the guide bar arranged in a zigzag in the oil tank, it prevents the generation of fuzz due to the mixing of fibers with a stable yarn path, up to the inside of the fibers It is more preferable because the oil agent can be permeated. At this time, the number of the guide bars is not particularly limited, but it is more preferable that there are 3 or more, more preferably 5 to 7 odd numbers at regular intervals. The material is not particularly limited, but a stainless steel chrome-plated finish on a mirror surface or satin finish, a smooth finish ceramic, or a coating with "Teflon (registered trademark)" to prevent the fibers from being damaged. Can be used. Alternatively, the fiber may be vibrated using a vibro processor having a perforated basket roller or the like, and the oil agent may be mechanically penetrated into the bundle.

  The oil used in the present invention is not particularly limited as long as the single fibers are bonded to each other by the heat treatment in the carbon fiber production process, and the effect of suppressing the occurrence of surface defects that become the controlling factor of strength reduction can be achieved. Examples of the oil agent used in the oil agent process of the present invention include silicone oil agents such as alkyl-modified silicone, polyether-modified silicone, alcohol-modified silicone, amino-modified silicone, and epoxy-modified silicone, and fatty acid esters such as methyl stearate and methyl oleate. In addition, higher alcohols such as lauryl alcohol and cetyl alcohol, higher fatty acids such as palmitic acid and stearic acid, sulfate esters such as higher alcohol sulfates and polyoxyethylene alkyl sulfates, such as sulfonated hydrocarbons and alkylbenzene sulfonic acids. Sulfonic acids such as alkyl phosphate esters, polyoxyethylene alkyl phosphate esters such as polyoxyethylene alkyl ether Ether derivatives such as polyethylene glycol alkyl esters, sorbitan alkyl esters, ester derivatives such as glycerin alkyl esters, tertiary cations such as alkylamine acid neutralized products, alkyl acidamine acid neutralized products, and the like. A class cationic surfactant, paraffin, mineral oil or the like can be used, and these can be used alone or in combination.

  Among these, more preferably, a silicone-based oil agent having a siloxane bond (—SiO—) in the basic skeleton is preferable, and the group bonded to the silicon atom is a hydrogen atom and / or an alkyl group having 1 to 3 carbon atoms or a phenyl group, Or these alkoxy groups etc. are mentioned. Of these, dimethylsiloxane is particularly preferred as the basic skeleton. In addition, from the viewpoint of uniform application to the fiber, it is preferable to apply the oil agent to the fiber with an aqueous dispersion in which the oil agent is dispersed in water. Among these, from the viewpoint of long-term stability as an aqueous dispersion, An aqueous emulsion using an emulsifier such as polyoxyethylene alkyl ether is more preferable.

  In the present invention, the oil agent to be applied to the fiber preferably has an oil viscosity at 25 ° C. in the range of 500 to 10,000 cSt, and the aqueous dispersion used contains at least one amino-modified silicone. It is preferable. More preferably, an epoxy-modified silicone or a polyether-modified silicone may be mixed with the oil agent, and in that case, the oil viscosity when mixed is preferably within the above range. In the present invention, by setting the oil viscosity to 10000 cSt or less, the oil agent can easily enter the fiber bundle, which is preferable from the viewpoint of forming a uniform oil agent film. Furthermore, by setting the viscosity to 500 cSt or more, the oil agent penetrates into the inside of the single fiber, and the adhesion between the single fibers in the drying process derived from the decrease in the oil agent applied to the fiber surface is suppressed. It is possible to suppress the decrease. A more preferable range is 1000 to 7000 cSt.

  The oil viscosity at 25 ° C. of the oil used in the present invention is the viscosity of a single oil component or a mixture of single components. A sample with an oil temperature of 25 ° C. is placed in a Canon Fenske viscometer. The viscosity is calculated from the falling speed in the tube.

Moreover, it is preferable that the fiber running speed in an oil agent process is 30 m or more. The fiber running speed defined here is an average speed in the step of applying the oil agent in the process of producing the acrylic precursor fiber, and is not directly related to the final winding speed. When the draw ratio is determined in order to set the fineness and orientation of the yarn within a desired range, the fiber running speed in the oil agent process is directly related to the productivity of the entire fiber in that range. For example, the productivity when the fiber traveling speed is 49 m / min has a productivity of about 1.9 times proportional to the speed ratio compared to the productivity when the fiber traveling speed is 25 m / min. By setting the fiber running speed to 30 m / min or more, it is possible to obtain a precursor fiber with good quality and high strength potential while ensuring high productivity, and producing high-quality carbon fiber by firing it. can do. A more preferable range is 40 m / min or more.
The fiber to which the oil agent is applied by the above production method is preferably dried quickly in the subsequent drying step. The drying method is not particularly limited, but a method of directly contacting a plurality of suction drum dryers or heating rollers is preferably used. The drying temperature can be set high as long as the single fibers do not adhere to each other. Specifically, 130-200 degreeC is preferable, More preferably, it is 160-200 degreeC. By suppressing the drying temperature to 200 ° C. or less, adhesion between single fibers can be suppressed, and single fiber breakage and roller winding in the subsequent post-drawing step can be reduced. In addition, by performing the drying temperature at 130 ° C. or higher, it is possible to reduce the number of suction drum dryers and heating rollers, which is preferable in terms of cost.

  Moreover, it is good to make a fiber contact a roller in the state expanded as much as possible so that the heating state to a fiber may become uniform. The dried fiber is preferably adjusted to a draw ratio of the drive roll to such an extent that no fuzz is generated in the subsequent post-drawing step, and is stretched twice or more in pressurized steam to obtain an acrylic precursor fiber.

  The acrylic precursor fiber produced in the present invention preferably has 1000 to 100,000 single fibers, and more preferably 500 to 60,000 in the oil agent process. If necessary, the final acrylic precursor fiber is obtained by applying yarn during winding after applying the oil. The fineness of the single fiber of the acrylic precursor fiber is preferably 0.4 to 1.5 dtex, and more preferably 0.6 to 1.3 dtex.

  Carbon fibers can be produced by firing the acrylic precursor fibers thus obtained. Specifically, the precursor fiber is heated to 220 to 300 ° C. in an oxidizing atmosphere such as air to perform a flame resistance treatment. The treatment temperature is preferably increased in multiple stages from low temperature to high temperature in order to obtain flame-resistant fibers, and further, the fibers are stretched at a high stretch ratio within a range not accompanied by fluff generation. It is preferable for sufficiently exhibiting the performance. Next, the obtained flame-resistant fiber is heated to 1000 ° C. or higher in an inert atmosphere such as nitrogen to produce a carbon fiber. Thereafter, by anodizing in an aqueous electrolyte solution, it is possible to impart a functional group to the surface of the carbon fiber and enhance the adhesion to the resin. Moreover, it is preferable to obtain a carbon fiber excellent in scratch resistance by applying a sizing agent such as an epoxy resin.

  Hereinafter, the present invention will be described in more detail with reference to examples.

<Fiber swelling>
About 10 g of fibers immediately before being introduced into the oil agent process are sampled and washed with water for 12 to 16 hours. Next, the fiber weight after dehydration is determined by dewatering at 3000 rpm for 3 minutes using a centrifugal dehydrator (for example, H-110A manufactured by Kokusan Co., Ltd.). Thereafter, the dehydrated sample is dried for 2.5 hours with a dryer controlled at 105 ° C., the fiber weight after drying is determined, and the fiber swelling degree is calculated by the following formula.

Formula: Fiber swelling degree (%) = ((fiber weight after dehydration−fiber weight after drying) / fiber weight after drying)) × 100
<Quality judgment>
Visual determination of the appearance of the product package in which the acrylic precursor fiber is wound up (the total number of fluff and fluff converted to a product end face of 5 cm thickness and product surface converted to 20 cm width). Judgment criteria are as follows.
◎ Judgment = 0 to 1 fluff or fluff number ○ Judgment = 2 to 5 fluff or △ judgment = 6 to 10 fluff or fluff x Judgment = 11 fluff or fluff number that's all.

<Carbon fiber strand strength>
The strand strength of the carbon fiber is determined by subjecting the strand obtained by impregnating a resin of the following composition to the carbon fiber and curing for 35 minutes in a hot air circulating oven adjusted to 130 ° C., and performing a tensile test according to JIS R 7601: 1986. Determined by
CELLOXIDE 2012P: 100 parts by mass Daicel Corp. Boron trifluoride monoethylamine (BF3 / MEA): 3 parts by mass Acetone: 4 parts by mass.

<Quality judgment>
The criteria for the relative index evaluation with the maximum value of the strand tensile strength obtained by the above measuring method as 100 are as follows.
Judgment = over 90. Judgment = over 80, 90 or less.DELTA.determination = 70 over, 80 or less × determination = 70 or less.

<Comprehensive judgment>
The overall judgment results for quality and CF physical properties are as follows.
◎ Judgment = Pass (level that satisfies both quality and CF physical properties)
○ Judgment = Pass (level that satisfies the quality or CF physical properties)
△ Judgment = Fail (Level that either quality or CF physical properties are unsatisfactory)
X Judgment = Fail (level in which both quality and CF physical properties are unsatisfactory).

(Examples 1-8)
A polyacrylonitrile composed of 99.5% by mass of acrylonitrile and 0.5% by mass of itaconic acid was obtained by a solution polymerization method using dimethyl sulfoxide as a solvent, and then a coagulation bath comprising a 40% by mass dimethyl sulfoxide aqueous solution by a dry-wet spinning method. The fiber was spun in, and the fiber was washed in the subsequent washing step, followed by drawing in the bath drawing step. At this time, the degree of fiber swelling temporarily increased and then decreased as it was drawn, and the degree of fiber swelling just before introduction into the oil agent process was 130%. In the subsequent oil agent process, adjustment was made by diluting an amino-modified silicone oil agent having an oil viscosity of 5000 cSt at 25 ° C. with pure water to a concentration of 3.0% by mass. The fiber running speed to be introduced into the oil agent process was set to 49 m / min, and the average fiber density and average fiber tension to run were set as shown in Table 1, and the fibers were immersed in the oil agent bath. Thereafter, excess oil moisture was introduced into the drying process by squeezing the fiber from the oil bath with a nip roll. In the subsequent drying process, a drying process was performed using a heating roller adjusted to 160 ° C. In the subsequent post-drawing step, the polymer was stretched twice in pressurized steam to obtain acrylic precursor fibers having a single fiber fineness of 0.1 tex and a single fiber count of 3000. Thereafter, the acrylic precursor fiber was baked while being conveyed in a flame resistant furnace at 240 to 280 ° C. in the air with a driving roll in the baking process, and converted into flame resistant fiber. Furthermore, after carrying out preliminary carbonization in a pre-carbonization furnace at 300 to 800 ° C. in an inert atmosphere with a driving roll, firing is carried out while conveying in a carbonization furnace in an inert atmosphere at a maximum temperature of 1500 ° C. with a driving roll. Fiber was obtained. The quality of the precursor fiber obtained in Example 1 was good, and the strand strength of the carbon fiber was excellent. Also, in Examples 2 to 8, by applying the conditions shown in Table 1, high-quality precursor fibers can be obtained, and high-quality carbon fibers excellent in strand strength were obtained.

(Examples 9 and 10)
Fibers were introduced into the oil agent process by the same production method as in Example 1 except that the fiber swelling degree immediately before introduction into the oil agent process was adjusted according to the bath temperature and draw ratio in the bath drawing process and as shown in Table 1. As a result, as shown in Table 1, high-quality precursor fibers can be obtained, and high-quality carbon fibers excellent in strand strength were obtained.

(Examples 11 and 12)
Except having changed the oil viscosity at 25 degreeC of an oil agent as Table 1, the fiber was introduce | transduced into the oil agent process with the manufacturing method similar to Example 1. FIG. As a result, as shown in Table 1, high-quality precursor fibers can be obtained, and high-quality carbon fibers excellent in strand strength were obtained.

(Examples 13 to 15)
The fibers were introduced into the oil agent process by the same production method as in Example 1 except that the fiber running speed in the oil agent process was changed and introduced into the oil agent bath. As a result, as shown in Table 1, high-quality precursor fibers can be obtained, and high-quality carbon fibers excellent in strand strength were obtained.

(Comparative Examples 1-6)
Precursor fibers and carbon fibers were obtained by the same production method as in Examples 1 to 8, except for the average fiber density and average fiber tension when passing through the oil agent process. As a result, as shown in Table 1, the quality of the precursor fibers deteriorated. The strand strength of the obtained carbon fiber was also unsatisfactory.

(Comparative Examples 7 and 8)
Except having changed the oil viscosity at 25 degreeC of an oil agent as Table 1, the fiber was introduce | transduced into the oil agent process with the manufacturing method similar to Example 1. FIG. As a result, as shown in Table 1, the quality of the precursor fiber deteriorated, and the strand strength of the obtained carbon fiber was also unsatisfactory.

(Comparative Examples 9 and 10)
Fibers were introduced into the oil agent process by the same production method as in Example 1 except that the fiber swelling degree immediately before introduction into the oil agent process was adjusted according to the bath drawing temperature and draw ratio as shown in Table 1. As a result, as shown in Table 1, the quality of the precursor fiber deteriorated, and the strand strength of the obtained carbon fiber was also unsatisfactory.

(Comparative Example 11)
The fibers were introduced into the oil agent process by the same production method as in Comparative Example 4 except that the fiber running speed in the oil agent process was changed and introduced into the oil agent bath. As a result, as shown in Table 1, the quality of the precursor fiber deteriorated, and the strand strength of the obtained carbon fiber was also unsatisfactory.

Claims (3)

In the method of producing an acrylic precursor fiber, when the oil obtained by spinning the acrylic polymer by dry-wet spinning or wet spinning method is applied to the oil agent process after washing with water and drawing with a bath, the oil agent process is performed. The fiber swelling degree immediately before introduction is in the range of 90 to 230%, the average fiber density in the oil agent process is in the range of 80 to 220 tex / mm, and the average fiber tension is in the range of 0.6 to 1.3 g / tex, A method for producing an acrylic precursor fiber for carbon fiber, wherein the oil agent is imparted to the fiber using an aqueous dispersion in which the oil agent is dispersed in water.
The fiber swelling degree is calculated by the following formula.
Formula: Fiber swelling degree (%) = ((fiber weight after dehydration−fiber weight after drying) / fiber weight after drying)) × 100 The acrylic precursor for carbon fiber according to claim 1, wherein the oil agent has an oil viscosity at 25 ° C in a range of 500 to 10,000 cSt, and the aqueous dispersion is an aqueous dispersion containing at least one amino-modified silicone. A method for producing fibers. It is obtained by firing the acrylic precursor fiber for carbon fiber obtained by the production method according to claim 1 or 2 at 220 to 300 ° C. in an oxidizing atmosphere and then firing at 1000 ° C. or more in an inert atmosphere. And carbon fiber manufacturing method.