JP2018084002A - Method for producing polyacrylonitrile precursor fiber and method for producing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polyacrylonitrile precursor fiber that supplies an acrylonitrile copolymer with its gels inhibited from occurring or increasing and thereby is superior in process stability, quality stability, operability and productivity, and also provide a method for producing a carbon fiber.SOLUTION: A method for producing a polyacrylonitrile precursor fiber is provided which comprises spinning a spinning raw material liquid comprising an acrylonitrile copolymer obtained by copolymerizing acrylonitrile with a carboxyl group-having vinyl monomer. In the method, the number of gels in the spinning raw material liquid measured by a method defined in the description is regulated to be 10/g or less.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a high-quality polyacrylonitrile-based precursor fiber and a method for producing a carbon fiber. More specifically, after obtaining a spinning dope that suppresses the generation and increase of foreign substances such as gel, which is a polyacrylonitrile higher-order structure, a polyacrylonitrile-based precursor with good process stability, quality stability, operability, and productivity is obtained. The present invention relates to a method for producing body fibers and a method for producing carbon fibers.

  Carbon fiber has high specific strength and specific elastic modulus compared to other fibers. For this reason, as a reinforcing fiber for composite materials, in addition to conventional sports and aerospace applications, it is also widely deployed in general industrial applications such as automobiles, civil engineering / architecture, pressure vessels and windmill blades. There is a strong demand for quality stabilization.

  Among the carbon fibers, the most widely used polyacrylonitrile-based carbon fiber is obtained by wet-spinning, dry-spinning, or dry-wet spinning of the acrylonitrile-based copolymer as a precursor to obtain a carbon fiber precursor fiber. It is industrially produced by heating it in an oxidizing atmosphere at a temperature of 200-400 ° C. to convert it to flame-resistant fiber and heating it in an inert atmosphere at a temperature of at least 1000 ° C. for carbonization. Yes.

  The quality and quality of polyacrylonitrile-based carbon fibers are improved from the viewpoints of spinning, flame resistance, and carbonization of carbon fiber precursor fibers, and because they are brittle materials, there are few surface defects and inherent defects. Due to the great influence, delicate attention has been paid to the generation of defects.

  However, in general, deterioration of the acrylonitrile-based copolymer spinning solution itself generates foreign substances such as gel, which is a polyacrylonitrile higher-order structure, and in the manufacturing process of precursor fibers for carbon fibers, discharge failure occurs from the spinning nozzle holes. It is known that the thread breaks immediately after discharge.

  As a technique for suppressing gel formation and increase of acrylonitrile copolymer, there are a method of adding a radical polymerization inhibitor as disclosed in Patent Document 1, and an ethylenic double bond as disclosed in Patent Document 2. There has been proposed a method of containing a certain amount of a compound containing. Although these methods can certainly suppress gel formation and increase, they lead to increased production costs, and radical polymerization inhibitors and compounds containing ethylenic double bonds act as foreign substances in the manufacturing process after spinning, thus improving operability. And mechanical properties may be reduced. Further, Patent Document 3 proposes a method for stably producing precursor fibers for carbon fibers by controlling the holding temperature and passage time of the spinning dope to suppress the formation and increase of gels. 4, it is known that the unreacted acrylonitrile residual ratio is one of the factors of gel formation and increase, and is not sufficient as a method for suppressing gel formation and increase.

  The technique for managing the gel of acrylonitrile copolymer is also disclosed in Patent Document 5, but the method for measuring the number of gels disclosed in Patent Document 5 is measurement in the visible light region using an optical microscope. Since it is impossible to accurately grasp the number of gels that affect the spinning operability and the quality stabilization, it is not sufficient to manage the number of gels in the spinning dope by this method.

  For these reasons, there is a demand for a method for producing polyacrylonitrile-based precursor fibers and a method for producing carbon fibers that suppress the gel formation and increase in the spinning dope and improve the quality and quality.

JP-A-1-168750 JP 2002-249924 A Japanese Patent Laying-Open No. 2015-71844 JP 2004-91943 A Korean Published Patent No. 10-2011-0078249

  Accordingly, in view of the background of such conventional technology, a spinning stock solution containing an acrylonitrile-based copolymer that suppresses the formation and increase of gel is supplied, and a polyacrylonitrile-based precursor with good process stability, quality stability, operational efficiency, and productivity is provided. It is an object of the present invention to provide a body fiber manufacturing method and a carbon fiber manufacturing method.

  The present invention for solving this problem has the following configuration. That is, the method for producing a polyacrylonitrile-based precursor fiber according to the present invention comprises spinning a spinning stock solution containing an acrylonitrile-based copolymer obtained by copolymerizing acrylonitrile and a vinyl-based monomer having a carboxyl group, into a polyacrylonitrile-based precursor. A method for producing a polyacrylonitrile-based precursor fiber for obtaining a fiber, characterized in that the number of gels in a spinning dope measured by the method described in the specification is controlled at 10 / g or less.

  In the present invention, the number of gels in the spinning dope is determined by the following measuring method.

<Method for measuring the number of gels in the spinning dope>
After diluting 50 g of the spinning stock solution 20 times with the solvent used in the spinning stock solution, the solution was passed through a PTFE membrane filter JHWP (pore diameter 0.45 μm), the entire membrane filter surface was observed, the number of bright spots was counted, and spinning was performed. The number of gels per gram of stock solution (unit: pieces / g) was determined. The light source can be selected from, for example, a wavelength range of 365 to 405 nm using invisible light, but is not necessarily limited thereto.

  In addition, the carbon fiber production method of the present invention is a flame resistance method in which a polyacrylonitrile-based precursor fiber is obtained by the above-described polyacrylonitrile-based precursor fiber production method and then flame-resistant in air at a temperature of 200 to 300 ° C. A pre-carbonization step of pre-carbonizing the fiber obtained in the step and the flameproofing step in an inert atmosphere at a temperature of 300 to 800 ° C., and a fiber obtained in the pre-carbonization step of 1,000 to 3,000 ° C. The carbon fiber manufacturing method which performs the carbonization process which carbonizes in the inert atmosphere of this temperature.

  According to the present invention, it is possible to provide a method for producing a polyacrylonitrile-based precursor fiber and a method for producing a carbon fiber, which can suppress the outflow of gel to the yarn production process and have good process stability, quality stability, operability, and productivity. be able to.

  Hereinafter, embodiments of the present invention will be described in detail.

[Polymerization method and composition of polymerization raw materials]
In the method for producing an acrylonitrile-based copolymer of the present invention, it can be selected from known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization and the like, and it should be solution polymerization from the viewpoint of productivity and quality stability. preferable. As a solution in the case of solution polymerization, an organic solvent in which an acrylonitrile copolymer such as dimethyl sulfoxide, dimethyl formamide, dimethylacetamide or the like is soluble can be used.

  In the present invention, the acrylonitrile copolymer is a copolymer obtained by copolymerizing acrylonitrile and a vinyl monomer having a carboxyl group copolymerizable therewith. Here, the monomer used as the raw material of the acrylonitrile-based copolymer contains acrylonitrile in an amount of 90% by mass or more, preferably 95% by mass or more, more preferably 98% by mass or more, and a vinyl having a carboxyl group as a flameproofing promoting component. The system monomer is contained in an amount of 0.1 to 10% by mass, preferably 0.1 to 5% by mass, more preferably 0.1 to 2% by mass.

  If the amount of acrylonitrile is less than 90% by mass, the strength and productivity may be lowered due to an increase in the amount of components that are eliminated when producing carbon fibers. When the content of the vinyl monomer having a carboxyl group is less than 0.1 parts by mass, the effect of promoting flame resistance cannot be expected, and when it exceeds 10 parts by mass, the reaction cannot be controlled because the flame resistance is excessively promoted. is there.

  Examples of the vinyl monomer having a carboxyl group include vinyl esters such as vinyl acetate, acrylic acid, methacrylic acid, itaconic acid, and esters and salts thereof such as methyl acrylate, sodium methacrylate, and acrylamide. However, in the present invention, it is preferable to use at least one acid monomer selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid in order to promote flame resistance.

  The spinning dope in the present invention is preferably a solution in which the acrylonitrile copolymer is dissolved in a solvent such that the acrylonitrile copolymer is 15 to 25% by mass, and more preferably 17 to 25% by mass. When the content of the acrylonitrile copolymer is less than 15%, when the polyacrylonitrile precursor fiber is produced by spinning the spinning dope, the solidified structure formed becomes sparse, and the polyacrylonitrile precursor fiber and the carbon fiber The strength of the may decrease. On the other hand, if the acrylonitrile copolymer content exceeds 25% by mass, the viscosity of the spinning dope becomes too high, and it is necessary to increase the pressure resistance of the equipment, which is economically disadvantageous.

  The method for reducing the unreacted acrylonitrile residual ratio in the spinning dope is not particularly limited, and a known technique can be used. However, a method of supplying and removing a thin film on the inner wall of the degassed tank is common. is there. In order to further reduce the residual ratio of unreacted acrylonitrile, the acrylonitrile copolymer solution is supplied from the upper part of the packed tower that has been decompressed, and the solvent vapor of the acrylonitrile copolymer solution is supplied from the lower part of the packed tower to the acrylonitrile copolymer. For example, a counter current contact with the polymer solution may be mentioned. In the present invention, the unreacted acrylonitrile residual ratio in the spinning dope is preferably 0.001 to 3% by mass, and more preferably 0.001 to 1.5% by mass. If an unreacted acrylonitrile residual ratio is to be made less than 0.001% by mass, the equipment cost of the apparatus becomes high, which is economically disadvantageous. On the other hand, when the unreacted acrylonitrile remaining ratio exceeds 3% by mass, the yield of the spinning dope is lowered, which is economically disadvantageous.

  In the present invention, in order to ionize the carboxyl group portion in the acrylonitrile-based copolymer, a base may be added in an amount of 0.2 molar equivalent or more with respect to the carboxyl group of the vinyl monomer having a carboxyl group used for the copolymerization. preferable. That is, when there is one carboxyl group in one molecule as in acrylic acid, 0.2 mole equivalent or more per mole of acrylic acid, and when there are two carboxyl groups in one molecule as itaconic acid Is preferably added in an amount of 0.4 mole equivalent or more per mole of itaconic acid. Preferred examples of the base include ammonia, amine compounds, and ammonium salts. Ammonia is particularly preferred because it is inexpensive and versatile. As a result, the hydrophilicity of the acrylonitrile copolymer can be improved, and the generation of voids during coagulation in a coagulation bath when producing polyacrylonitrile precursor fibers by wet spinning or dry wet spinning can be suppressed. .

  When the molar equivalent of the base added to the carboxyl group of the vinyl monomer having a carboxyl group is less than 0.2, the hydrophilicity-improving effect of the acrylonitrile copolymer does not appear, and the operation is caused by yarn breakage in the yarn making process. Sex worsens. When the ratio exceeds 1.2, the base is excessive in the spinning dope, contaminates the spinning process, and gelation of the spinning dope tends to be promoted more easily. Is preferable, and the range of 0.3 to 0.8 is more preferable.

  In the present invention, it is essential to manage the number of gels in the spinning dope measured by the above method at 10 pieces / g or less. Further, it is preferably 4 pieces / g or less.

  The number of gels tends to increase when the apparatus for producing the spinning dope is operated for a long time. If the number of gels exceeds 10 / g, the frequency of outflow into the spinning process will increase, and process stability and quality will be stable. Although the performance, operability and productivity are lowered, the gel can be washed and removed by partially or entirely washing the apparatus for producing the spinning dope, and the number of gels in the spinning dope is 10 / g or less can be managed.

  The apparatus for producing the spinning dope in the present invention means that the spinning dope is discharged from the spinning nozzle in the process and the spinning process from the raw material input line for obtaining the acrylonitrile copolymer, the tank for the polymerization reaction, the deaeration tank, and the like. It means the process equipment until it is done.

  The method of washing and removing the gel of the apparatus for producing the spinning dope is physically stripped off, and acrylonitrile copolymers such as dimethylsulfoxide, dimethylformamide, and dimethylacetamide used as solvents for acrylonitrile copolymers are soluble. Washing with an organic solvent, acid washing with a small amount of hydrochloric acid or sulfuric acid mixed with an organic solvent in which acrylonitrile copolymer is soluble, alkali washing with sodium hydroxide or potassium hydroxide, washing with a neutral detergent, etc. Although it is mentioned, it is not limited to these methods. Moreover, an independent method may be sufficient and multiple may be combined. Cleaning by combination is effective.

[Production method of polyacrylonitrile-based precursor fiber]
Next, a preferred example of a method for producing a polyacrylonitrile precursor fiber using the acrylonitrile copolymer obtained by the production method of the present invention will be described.

  The acrylonitrile-based copolymer solution obtained by the production method of the present invention is spun, introduced into a coagulation bath and solidified to form a coagulated yarn, followed by a water washing step, a drawing step in the bath, an oil agent application step, and a drying step. Through this, a polyacrylonitrile-based precursor fiber is obtained. Moreover, you may add a dry heat extending process and a steam extending process to said process. The solidified yarn may be directly stretched in the bath without the water washing step, or may be stretched in the bath after removing the solvent by the water washing step. Usually, the stretching in the bath is preferably performed in a single or a plurality of stretching baths adjusted to a temperature of 30 to 98 ° C. The draw ratio at that time is preferably 1 to 5 times, and more preferably 1 to 3 times.

  After the stretching step in the bath, it is preferable to apply an oil agent made of silicone or the like to the stretched fiber yarn for the purpose of preventing adhesion between single fibers. As the silicone oil, it is preferable to use a silicone oil containing a modified silicone such as amino-modified silicone having high heat resistance.

  As the drying step, for example, a drying condition in which a drying temperature is 70 to 200 ° C. and a drying time is 10 seconds to 200 seconds gives preferable results. As an improvement in productivity and an improvement in the degree of crystal orientation, it is preferable to stretch in a heating heat medium after the drying step. As the heating heat medium, for example, pressurized steam or superheated steam is suitably used in terms of operational stability and cost, and the draw ratio is usually 1.5 to 10 times.

[Method for producing carbon fiber]
Next, a preferred example of the carbon fiber production method of the present invention will be described.

  In the present invention, the polyacrylonitrile-based precursor fiber obtained as described above is flameproofed in the air at a temperature of 200 to 300 ° C., and the fiber obtained in the flameproofing process is 300 to 800. Carbon through a pre-carbonization step of pre-carbonizing in an inert atmosphere at a temperature of ° C and a carbonization step of carbonizing the fiber obtained in the pre-carbonization step in an inert atmosphere at a temperature of 1,000-3,000 ° C. Fiber can be obtained.

  The carbon fiber obtained by the present invention is a carbon fiber reinforced composite material excellent in various mechanical properties such as post-impact compressive strength by various molding methods such as autoclave molding as a prepreg and molding by resin transfer molding as a preform such as a woven fabric. Therefore, it can be suitably used as a carbon fiber reinforced composite material having excellent post-impact compressive strength for aircraft structural materials, automotive applications, marine applications, sports applications and other general industrial applications.

  Hereinafter, the present invention will be described more specifically with reference to examples. The measurement method used in this example will be described next.

<Remaining ratio of unreacted acrylonitrile>
4.0 g of methanol was added to 1.0 g of the spinning dope to extract monomer components in the spinning dope. The acrylonitrile concentration was measured from the obtained methanol solution by gas chromatography analysis.

(Gas chromatography conditions)
Device: GC-2014 (manufactured by Shimadzu Corporation)
Column: Capillary column DB-1 (manufactured by Shimadzu GLC)
Sample injection volume: 0.4 μL.

<Method for measuring the number of gels in the spinning dope>
After diluting 50 g of the spinning stock solution 20 times with the solvent used in the spinning stock solution, the solution was passed through a PTFE membrane filter JHWP (pore diameter 0.45 μm), the entire membrane filter surface was observed, the number of bright spots was counted, and spinning was performed. The number of gels per gram of stock solution (unit: pieces / g) was determined. The light source was selected from a wavelength range of 365 to 405 nm using invisible light.

<Standard of grade of polyacrylonitrile precursor fiber grade>
The inspection items were evaluated in three stages by visually counting the number of fluff and fluff of 1 cm or more while running the polyacrylonitrile-based precursor fiber at a speed of 1 m / min. The evaluation criteria are as follows.
-Grade 1: within 1 fiber 300m-Grade 2: 2-15 in 300m fiber-Grade 3: 16 or more in 300m fiber

Example 1
The apparatus for producing the spinning dope is washed and the gel is removed. Then, 99.5% by mass of acrylonitrile and 0.5% by mass of itaconic acid are added in dimethyl sulfoxide and polymerized by adding azobisisobutyronitrile as a polymerization initiator. An acrylonitrile copolymer solution was obtained. Next, the obtained acrylonitrile copolymer solution is supplied from the upper part of the packed tower whose pressure has been reduced, and dimethyl sulfoxide vapor is supplied from the lower part of the packed tower so as to be in countercurrent contact with the acrylonitrile copolymer solution. The residual ratio of residual acrylonitrile was decreased, and the residual ratio of unreacted acrylonitrile was 0.001% by mass. Next, ammonia gas was neutralized by blowing at 0.5 molar equivalents relative to the total carboxyl groups of itaconic acid used in the copolymerization to obtain a spinning dope having an acrylonitrile copolymer concentration of 20% by mass. . This spinning dope was discharged from a spinning nozzle into a coagulation bath to obtain a coagulated yarn. The coagulated yarn was washed with water and then stretched in warm water, and further an amino-modified silicone silicone oil was applied. The drawn yarn in the bath is subjected to a drying heat treatment using a roller heated to a temperature of 170 ° C., and then drawn in a pressurized steam at a temperature of 150 to 190 ° C. to obtain a single fiber fineness of 1.1 dtex and a filament count of 12 1,000 polyacrylonitrile-based precursor fibers were obtained. There was no discharge failure from the spinning nozzle or yarn breakage immediately after discharge, and the resulting polyacrylonitrile-based precursor fiber had a grade of 1, and the number of gels in the spinning dope collected from the spinning nozzle was 4 / g. there were. During continuous operation, the number of gels in the spinning dope is periodically measured, and when the number of spinning dope gels collected from the spinning nozzle increases to 10 / g, a part of the apparatus for producing the spinning dope is washed. did. The number of gels in the spinning dope collected from the spinning nozzle after washing was 5 / g.

  The obtained polyacrylonitrile-based precursor fiber was baked while being conveyed in a flame-resistant furnace at 240 to 280 ° C. in air with a driving roll, and converted into flame-resistant fibers. Furthermore, after carrying out preliminary carbonization by conveying the inside of a pre-carbonization furnace at 300 to 800 ° C. in an inert atmosphere with a driving roll, firing is performed while conveying the inside of a carbonizing furnace in an inert atmosphere at 1500 ° C. with a driving roll to obtain carbon fibers. It was. The operability of the carbon fiber production process at this time was stable, and continuous operation was possible.

Comparative Example 1
Even after the number of gels in the spinning dope increased to 10 / g, the polyacrylonitrile-based precursor fiber was processed in the same manner as in Example 1 except that the continuous operation was continued without washing the apparatus for producing the spinning dope. Tried to manufacture. However, yarn breakage frequently occurred in the yarn making process, the operability was not stable, continuous operation became difficult, and polyacrylonitrile-based precursor fibers could not be obtained. At this time, the number of gels in the spinning dope collected from the spinning nozzle was 12 / g.

Claims (5)

A method for producing a polyacrylonitrile-based precursor fiber, in which a spinning solution containing an acrylonitrile-based copolymer obtained by copolymerizing acrylonitrile and a vinyl-based monomer having a carboxyl group is spun to obtain a polyacrylonitrile-based precursor fiber, A method for producing a polyacrylonitrile-based precursor fiber, characterized in that the number of gels in a spinning dope measured by the method described in the specification is controlled at 10 pieces / g or less. Furthermore, the unreacted acrylonitrile residual ratio in a spinning undiluted | stock solution is managed by 0.001-3 mass%, The manufacturing method of the polyacrylonitrile-type precursor fiber of Claim 1 characterized by the above-mentioned. The acrylonitrile-based copolymer is obtained by copolymerizing 90% by mass or more of acrylonitrile and a vinyl monomer having 0.1 to 10% by mass of a carboxyl group. A method for producing a polyacrylonitrile-based precursor fiber. The polyacrylonitrile according to any one of claims 1 to 3, wherein 0.2 to 1.2 molar equivalent of a base is added to the spinning stock solution with respect to the carboxyl group of the vinyl monomer having a carboxyl group. Manufacturing method of system precursor fiber. After obtaining a polyacrylonitrile-based precursor fiber by the method for producing a polyacrylonitrile-based precursor fiber according to any one of claims 1 to 4, a flameproofing step of flameproofing in air at a temperature of 200 to 300 ° C, A preliminary carbonization step of precarbonizing the fiber obtained in the flameproofing step in an inert atmosphere at a temperature of 300 to 800 ° C, and a fiber obtained in the preliminary carbonization step at a temperature of 1,000 to 3,000 ° C. A method for producing carbon fiber, which performs a carbonization step of carbonizing in an inert atmosphere.