JP2013044057A - Acrylonitrile-based polymer solution, method for producing the same and method for producing carbon fiber precursor acrylonitrile-based fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acrylonitrile-based polymer solution from which a carbon fiber having high strength is obtained; a method for producing the same; and a method for producing a carbon fiber precursor acrylonitrile-based fiber using the polymer solution.SOLUTION: The acrylonitrile-based polymer solution is a solution in which an acrylonitrile-based polymer that comprises 95.0 mass% or more but 99.0 mass% or less of acrylonitrile monomer units and 1.0 mass% or more but 5.0 mass% or less of vinyl monomer units including carboxylic acid capable of copolymerization with the acrylonitrile monomer units are dissolved in a solvent. A concentration of the acrylonitrile-based polymer in the polymer solution is 18 mass% or more but 26 mass% or less, and the absorbance thereof calculated by a method defined in a description is 40 or more but 50 or less. The method for producing the acrylonitrile-based polymer solution and the method for producing the carbon fiber precursor acrylonitrile-based fiber are also disclosed.

Description

  The present invention relates to an acrylonitrile-based polymer solution that is a raw material for carbon fiber precursor fibers, a method for producing the same, and a method for producing carbon fiber precursor acrylonitrile-based fibers.

  It is known that carbon fibers have a high specific strength and specific elastic modulus compared to other fibers. For this reason, carbon fiber is being widely deployed as a reinforcing fiber for composite materials in general industrial applications such as automobiles, civil engineering, architecture, pressure vessels, windmill blades, in addition to conventional sports and aerospace applications. .

Among carbon fibers, acrylonitrile-based carbon fibers are most widely used, and acrylonitrile-based carbon fibers can be obtained by a production method having the following steps.
A step of preparing an acrylonitrile polymer solution (spinning stock solution) by dissolving an acrylonitrile polymer in a solvent. A step of obtaining a carbon fiber precursor fiber by wet spinning or dry wet spinning of the spinning dope. A flameproofing step in which the precursor fiber is heat-treated (flameproofing) in an oxidizing atmosphere at 200 to 300 ° C. to form a flameproof fiber. A step of heat-treating (carbonizing) the flame-resistant fiber in an inert atmosphere at 300 to 2500 ° C.
However, although the carbon fiber obtained in this way is excellent in physical properties and quality, it is often expensive to manufacture, and therefore, in industrial applications where cost reduction is required, it is sufficient to make it more versatile. Not realized. Further, for aerospace applications, there is a demand for further strengthening of carbon fibers.

  As a method for producing a high-strength carbon fiber, there is a reduction in scratches and defects existing in the carbon fiber. In particular, foreign matter in the carbon fiber and voids called voids having a size of 500 nm or less present inside the carbon fiber are factors that reduce the strength of the carbon fiber. One of these causes is a stock solution thermally deteriorated material having a size of several tens of nm or more (hereinafter referred to as a gel-like material) contained in the spinning dope, especially a gel-like material having a size of several hundred nm or more. May greatly reduce the strength of the carbon fiber. This gel-like product is generated by the progress of a crosslinking reaction and a cyclization reaction within the polymer molecular chain and between the molecular chains. Therefore, it is important for producing high-strength carbon fibers that foreign substances such as gels contained in the spinning dope are not mixed into the precursor fibers. Moreover, reducing the gel-like substance contained in the spinning dope contributes to stabilization of the production process of the precursor fiber and the carbon fiber and improvement of productivity.

  As one of the methods for removing the gel-like material contained in the spinning dope, Patent Document 1 selects only the spinning dope having a light transmittance of wavelength 450 nm of 60% or more and a light transmittance of 550 nm of 90% or more, A method is described in which a spinning stock solution containing a large amount of gel is removed from the process by introducing it into the next process.

  Patent Document 2 describes a method of removing foreign matters such as gels contained in a spinning dope using a filter device.

  Further, in Patent Document 3, by using a dissolution apparatus with a rotating body, the acrylonitrile-based polymer is uniformly dispersed in a solvent by a shearing force by stirring and accompanying heat generation, so that almost no external heating is required. The method for producing an undissolved spinning dope while suppressing the generation of gel-like materials is described.

JP 2006-348422 A JP 2009-235662 A JP 2002-45671 A

  However, in Patent Document 1, the light absorbance (or transmittance) at around 350 nm correlates with a nano-sized gel-like material in which the cross-linking reaction and the cyclization reaction between the polymer molecular chains and the molecular chains are not progressing greatly. Is not mentioned, and furthermore, there is no mention of a method for reducing foreign matters such as gels during the preparation of the spinning dope.

  Further, Patent Document 2 does not mention removal of a gel-like material having a thickness of several hundred nm or less, which is an obstacle to further increasing the strength of carbon fibers.

  Further, in the method of Patent Document 3, the solution may be heated at places such as around the agitation shaft and the agitation blade, and a gel-like substance may be easily generated. It may be difficult to reduce things.

  Therefore, it may be difficult to greatly reduce a small gel-like material having a size of several hundreds of nanometers from the spinning dope by the conventional technique, and a high-strength carbon fiber may not be obtained.

  Therefore, an object of the present invention is to provide an acrylonitrile-based polymer solution capable of obtaining high-strength carbon fibers, a method for producing the acrylonitrile-based polymer solution, and a method for producing a carbon fiber precursor acrylonitrile-based fiber using the polymer solution. It is said.

The method for producing the acrylonitrile-based polymer solution of the present invention includes:
A method for producing an acrylonitrile polymer solution by heating an acrylonitrile polymer dispersion in which an acrylonitrile polymer containing an acrylonitrile monomer unit is dispersed in a dispersion medium, the production method satisfying the following conditions: .
1. The temperature of the dispersion before heating is -20 ° C or higher and 40 ° C or lower,
2. The dispersion temperature Y (° C.) after 1 minute from the start of heating is 60 ° C. or more and 125 ° C. or less.
3. An acrylonitrile-based polymer solution in which the dispersion is dissolved is obtained within 5 minutes to 12 minutes after the start of heating. At this time, the temperature Z (° C.) of the obtained polymer solution is expressed by Formula 1. Fulfill,
4). The temperature of the acrylonitrile polymer solution is controlled to 30 ° C. or more and 90 ° C. or less within 3 minutes from the time of obtaining the acrylonitrile polymer solution,
(Formula 1)
−0.006 × Y ² + 0.47 × Y + 112 (° C.) ≦ Z (° C.) ≦ −0.30 × Y + 145 (° C.).

  In the method for producing an acrylonitrile-based polymer solution of the present invention, the temperature of the dispersion from 1 minute after the start of heating of the acrylonitrile-based polymer dispersion until the acrylonitrile-based polymer solution is obtained is 60 ° C. or higher and 130 ° C. or lower. It is preferable that

  The method for producing an acrylonitrile-based polymer solution of the present invention is such that the acrylonitrile-based polymer is 95.0% by mass to 99.0% by mass of the acrylonitrile monomer unit and can be copolymerized with the acrylonitrile monomer. It is preferably composed of 1.0% by mass to 5.0% by mass of a vinyl monomer unit containing a carboxylic acid.

  In the method for producing an acrylonitrile-based polymer solution of the present invention, the dispersion medium is preferably dimethylformamide, dimethylacetamide, or dimethylsulfoxide.

  In the method for producing an acrylonitrile-based polymer solution of the present invention, the content of the acrylonitrile-based polymer in the acrylonitrile-based polymer dispersion is preferably 18% by mass or more and 26% by mass or less.

  In the method for producing an acrylonitrile-based polymer solution of the present invention, the means for heating the acrylonitrile-based polymer dispersion is preferably a shell-and-tube type single tube or multi-tube heat exchanger.

  In the method for producing an acrylonitrile polymer solution of the present invention, an acrylonitrile polymer dispersion liquid is passed through the tube side of the shell-and-tube type single tube or multi-tube heat exchanger, and a heating medium is passed through the shell side. It is preferable to make it liquid.

In the method for producing an acrylonitrile-based polymer solution of the present invention, the radius A (mm) of an inscribed circle with respect to a tube cross section in a shell-and-tube type single tube or multi-tube heat exchanger satisfies the following formula 2. preferable.
(Formula 2)
4.0 (mm) ≦ A (mm) ≦ 10.0 (mm).

The method for producing an acrylonitrile-based polymer solution of the present invention is such that the average flow rate C (m / min) of the acrylonitrile-based polymer dispersion in the shell-and-tube type single-tube or multi-tube heat exchanger is the following formula 3 It is preferable to satisfy.
(Formula 3)
0.0010 / B (m / min) ≦ C (m / min) ≦ 0.0500 / B (m / min)
(However, B represents the inner peripheral length (m) of the tube cross section in the shell-and-tube type single tube or multi-tube heat exchanger).

  In the method for producing an acrylonitrile-based polymer solution of the present invention, it is preferable to use a plurality of the shell-and-tube type single-tube or multi-tube heat exchangers connected in series.

  The method for producing a carbon fiber precursor acrylonitrile fiber of the present invention comprises spinning the acrylonitrile polymer solution obtained by the above production method by a dry-wet spinning method or a wet spinning method to obtain a carbon fiber precursor acrylonitrile-based fiber. It is characterized by obtaining.

  The method for producing a carbon fiber precursor acrylonitrile fiber of the present invention is the above-described dry-wet spinning method or wet spinning method, wherein the polymer is obtained when the acrylonitrile-based polymer solution obtained by the production method is discharged from a nozzle. It is preferable to keep the temperature of the polymer solution at 30 ° C. or more and 90 ° C. or less until the temperature is controlled to 30 ° C. or more and 90 ° C. or less within 3 minutes from the time when the solution is obtained and then discharged from the nozzle.

The acrylonitrile-based polymer solution of the present invention comprises a vinyl-based monomer unit 1 containing 95.0% by mass or less and 99.0% by mass or less of an acrylonitrile monomer unit and a carboxylic acid copolymerizable with the acrylonitrile monomer. A polymer solution in which an acrylonitrile-based polymer composed of 0.0 mass% to 5.0 mass% is dissolved in a solvent,
The concentration of the acrylonitrile-based polymer is 18% by mass or more and 26% by mass or less, and the absorbance calculated by the following method is 40 or more and 50 or less.
Method for calculating absorbance The acrylonitrile-based polymer solution is diluted 20-fold by mass with the solvent, placed in a cell having a thickness of 1 cm, the absorbance A ₃₅₀ at a wavelength of 350 nm is measured, and the absorbance is calculated using Equation 4 below. calculate.
(Formula 4)
Absorbance = absorbance A ₃₅₀ / (mass of acrylonitrile polymer in 1 g of acrylonitrile polymer solution before dilution (g) × mol amount of carboxylic acid (mol) in 1 mol of acrylonitrile polymer).

  In the acrylonitrile-based polymer solution of the present invention, the solvent is preferably dimethylformamide, dimethylacetamide, or dimethylsulfoxide.

  According to the present invention, it is possible to provide an acrylonitrile-based polymer solution capable of obtaining a high-strength carbon fiber, a method for producing the same, and a method for producing a carbon fiber precursor acrylonitrile-based fiber using the polymer solution.

  So far, a method for removing gels of about 1 μm or more in an acrylonitrile polymer solution (spinning stock solution) has been discussed, but gels of several hundreds of nanometers, which can hinder further strengthening of carbon fibers, have been discussed. There has been little discussion on how to reduce it significantly.

  Therefore, the present inventors have intensively studied a method for reducing a gel-like material having a size of several hundreds of nanometers contained in a spinning dope which can be an obstacle to aiming for further strengthening of carbon fiber, and as a result, achieve the above object. Therefore, the present inventors have found a novel and useful production method of the present invention.

  The method for producing an acrylonitrile-based polymer solution of the present invention is capable of greatly reducing the amount of gel-like material generated during dissolution while efficiently dissolving the acrylonitrile-based polymer in a solvent. It is possible to reduce the gel-like material of several hundred nm or more. For this reason, a high-strength carbon fiber can be obtained using the polymer solution obtained by this manufacturing method.

  In addition, the present inventors have found that by setting the absorbance of the acrylonitrile-based polymer solution calculated by Equation 4 within a specific range, it is possible to minimize the number of undissolved substances and gel-like substances having a size of 100 nm or more. As a result, it was found that high-strength carbon fibers can be easily obtained.

  The acrylonitrile-based polymer solution of the present invention has a very small amount of gel-like material having a thickness of 100 nm or more as compared with the conventional one. Therefore, high-strength carbon fibers can be easily produced using this polymer solution. .

<Method for producing acrylonitrile-based polymer solution>
The acrylonitrile polymer solution of the present invention and the production method thereof will be described below.
In the method for producing an acrylonitrile-based polymer solution of the present invention, an acrylonitrile-based polymer dispersion (sometimes simply referred to as a dispersion) is heated to obtain an acrylonitrile-based polymer solution (also simply referred to as a polymer solution or a spinning stock solution). Is). The dispersion is obtained by dispersing an acrylonitrile-based polymer containing an acrylonitrile monomer unit in a dispersion medium. In the obtained polymer solution, the acrylonitrile-based polymer is dissolved in the solvent (the same as the dispersion medium).

  In addition, it is preferable to use dimethylacetamide, dimethylformamide, or dimethyl sulfoxide as a dispersion medium at the time of dispersion (solvent at the time of dissolution), which has a high coagulation rate and easily improves productivity.

In the method for producing an acrylonitrile-based polymer solution of the present invention, an acrylonitrile-based polymer dispersion having a temperature of −20 ° C. or more and 40 ° C. or less before heating, more specifically, immediately before heating is heated. For this reason, the temperature until the heating operation is performed on the dispersion using a heat exchanger or the like is maintained at −20 ° C. or higher and 40 ° C. or lower. In that case, it heats so that the dispersion liquid temperature Y (degreeC) 1 minute after starting a heating may be 60 degreeC or more and 125 degrees C or less. In addition, an acrylonitrile-based polymer solution in which the dispersion was dissolved within 5 minutes to 12 minutes from the start of heating (the above polymer was dissolved in the solution used as the dispersion medium) was obtained, and the obtained heavy weight was obtained. The temperature Z (° C.) of the combined solution is set so as to satisfy the formula 1.
(Formula 1)
−0.006 × Y ² + 0.47 × Y + 112 (° C.) ≦ Z (° C.) ≦ −0.30 × Y + 145 (° C.).

  Further, the temperature of the polymer solution is controlled to 30 ° C. or more and 90 ° C. or less within 3 minutes from the time when the acrylonitrile polymer solution is obtained. Moreover, it is preferable to control the temperature to 50 ° C. or higher and 70 ° C. or lower.

  If these requirements are satisfied, it is not always necessary to continuously heat the dispersion when dissolving the dispersion to obtain a polymer solution. In the present invention, the dispersion is made at −20 ° C. or more and 40 ° C. or less. On the other hand, the heating operation may be performed at least once. Moreover, when obtaining a polymer solution from a dispersion liquid, cooling operation can also be performed as needed.

  Moreover, it is preferable that the temperature of the dispersion liquid from 1 minute after a heating start to obtaining an acrylonitrile-type polymer solution shall be 60 degreeC or more and 130 degrees C or less.

  In addition, for example, when using a shell-and-tube type single-tube or multi-tube heat exchanger, which will be described later, as the dispersion heating means, the time from the start of heating at the point where the dispersion temperature is measured is the heating start point. To the dispersion temperature measurement point can be obtained by dividing the volume inside the pipe by the flow rate. For example, when the dispersion liquid is passed through the tube side of this heat exchanger, the temperature of the dispersion liquid can be measured using a thermocouple inserted in the center of the tube cross section that is the flow path of the dispersion liquid. it can. When there are a plurality of tubes in the heat exchanger, the temperature of the dispersion can be an average value of the temperatures measured in all of the tubes.

  By setting the acrylonitrile polymer dispersion before heating to −20 ° C. or higher, the viscosity of the dispersion increases moderately with the progress of slight dissolution, thereby preventing concentration spots due to sedimentation of the acrylonitrile polymer in the dispersion. Can do. Moreover, the excessive viscosity raise of a dispersion liquid can be suppressed by making the acrylonitrile-type polymer dispersion liquid before a heating into 40 degrees C or less, and process passability improves.

  By setting the dispersion temperature 1 minute after the start of heating to 60 ° C. or higher, the amount of undissolved material can be reduced, and by setting it to 125 ° C. or lower, the generation of gel-like materials can be suppressed. Further, an acrylonitrile-based polymer solution having a temperature Z (° C.) within the range of Formula 1 in which the dispersion is dissolved within 5 minutes to 12 minutes is obtained. When the temperature of the obtained polymer solution is equal to or higher than the lower limit temperature calculated from Equation 1, the amount of undissolved material can be reduced, and when the temperature is equal to or lower than the upper limit temperature, the generation of gel-like material is suppressed. be able to.

It can be visually confirmed that the acrylonitrile-based polymer is dissolved in the solvent used as the dispersion medium. When the polymer solution is produced by a method that satisfies the conditions of the production method of the present invention, the solution can also be confirmed by absorbance. In that case, the absorbance calculated by the following method is 35 to 50. Become.
Absorbance Calculation Method The acrylonitrile-based polymer solution is diluted 20-fold in terms of mass with the solvent used as the dispersion medium, placed in a 1 cm-thick cell, and the absorbance A ₃₅₀ at a wavelength of 350 nm is measured. The absorbance is calculated using.
(Formula 4)
Absorbance = absorbance A ₃₅₀ / (mass of acrylonitrile polymer in 1 g of acrylonitrile polymer solution before dilution (g) × mol amount of carboxylic acid (mol) in 1 mol of acrylonitrile polymer).

  Moreover, it is preferable to raise the temperature of the dispersion for less than 1 minute from the start of heating substantially monotonically so that it becomes 60 ° C. or more and 125 ° C. or less after 1 minute from the start of heating. In addition, it is preferable that the temperature of the dispersion liquid after obtaining the acrylonitrile-based polymer solution 1 minute after the start of heating is 60 ° C. or more from the viewpoint of reducing the remaining undissolved substance, and from the viewpoint of reducing the generated gel-like substance. It is preferable to set it at 130 degrees C or less. The temperature of the dispersion from 1 minute until the polymer solution is obtained is a measured value of temperature while changing the measurement position using a thermocouple inserted in the center of the cross section of the tube that is the flow path of the dispersion. Can be identified by monitoring.

  In the above production method, the dispersion can be dissolved within 5 to 12 minutes from the start of heating, and a polymer solution can be obtained. By setting the time for heating and dissolving the dispersion to 5 minutes or longer, undissolved material can be easily reduced, and by setting it to 12 minutes or shorter, generated gel-like material can be easily reduced.

  Further, by controlling the temperature of the polymer solution to 30 ° C. or more within 3 minutes from the time of obtaining the polymer solution, the fluidity of the acrylonitrile-based polymer solution can be maintained, and carbon fibers are produced. In this case, the permeability in the process after producing the polymer solution is improved. In addition, by controlling the temperature of the polymer solution to 90 ° C. or less within 3 minutes from the time of obtaining the polymer solution, the cross-linking reaction between the molecules of the polymer chain in the acrylonitrile-based polymer solution and between the molecules. , And the progress of the cyclization reaction can be suppressed, and an increase in the amount of gel can be prevented.

  As a means for heating the acrylonitrile-based polymer dispersion, a well-known heating means in the field of carbon fiber can be used, but a heat exchanger is preferably used from the viewpoint of production efficiency. From the viewpoint of heat transfer efficiency and maintenance efficiency, it is preferable to use a shell-and-tube type single tube or multi-tube heat exchanger as the heat exchanger. Hereinafter, description will be made focusing on the shell-and-tube type single tube or multi-tube heat exchanger.

  In this heat exchanger, it is preferable that the dispersion liquid is passed through the tube side and the heating medium is passed through the shell side from the viewpoints of efficiency and reduction of residence space. In addition, as a heating medium, well-known heating media, such as heating steam and oil, can be used, for example.

Moreover, it is preferable that the radius A (mm) of the inscribed circle in contact with the inner periphery of the tube cross section in the heat exchanger satisfies the following formula 2. The tube cross section is a cross section when the tube is cut in a direction perpendicular to the axis, and the inscribed circle is an inscribed circle with respect to the inner circumference of the cross section.
(Formula 2)
4.0 (mm) ≦ A (mm) ≦ 10.0 (mm)
The radius A more preferably satisfies the following formula 5.
(Formula 5)
6.0 (mm) ≦ A (mm) ≦ 8.0 (mm)
When the radius A of the inscribed circle is 4.0 mm or more, the tube is hardly clogged, and an acrylonitrile-based polymer solution can be easily obtained stably and continuously. Moreover, when the radius A is 10.0 mm or less, the temperature difference between the tube wall and the central portion of the tube does not increase, and a uniform polymer solution can be easily obtained.

Further, the inner peripheral length B (m) of the tube in the shell-and-tube type single tube or multi-tube heat exchanger and the average flow rate C (m / min) of the acrylonitrile polymer dispersion in the heat exchanger are as follows: It is preferable to satisfy Equation 6 (a variation of Equation 3 described above). The inner peripheral length is the inner peripheral length of the tube cross section described above.
(Formula 6)
0.0010 (m ² / min) ≦ B × C (m ² /min)≦0.0500 (m ² / min).

More preferably, the inner peripheral length B (m) of the tube and the average flow rate C (m / min) of the acrylonitrile-based polymer dispersion in the heat exchanger satisfy the following formula 7.
(Formula 7)
0.015 (m ² / min) ≦ B × C (m ² /min)≦0.040 (m ² / min).

B × C is the volume of the acrylonitrile polymer dispersion that passes through the tube in the heat exchanger per unit time. When this value is 0.0010 m ² / min or more, the acrylonitrile system only on the tube wall It is possible to easily suppress the temperature rise of the polymer dispersion, it is possible to easily suppress the generation amount of the gel-like material, and the tube is hardly clogged due to the generation of the gel-like material. Moreover, if B × C is 0.0500 m ² / min or less, it is possible to easily prevent the difference in flow rate between the tube center and the tube wall from increasing, and heat can be efficiently transferred to the inside. , Can be dissolved efficiently.

  In order to further increase the production efficiency, it is preferable to use a plurality of shell-and-tube type single pipe or multiple pipe heat exchangers connected in series.

  The acrylonitrile-based polymer used in the method for producing the acrylonitrile-based polymer solution of the present invention may be a homopolymer (homopolymer) obtained by polymerizing only acrylonitrile, including an acrylonitrile monomer unit, A copolymer obtained by copolymerizing acrylonitrile and another monomer may also be used.

  The acrylonitrile-based polymer can contain an acrylonitrile monomer unit as a main component. The blending amount of acrylonitrile in the acrylonitrile-based polymer can be determined in consideration of the quality required for the obtained carbon fiber, but is preferably 95.0% by mass or more and 99.0% by mass or less. If the blending amount of acrylonitrile is 95.0% by mass or more, it is possible to easily prevent fusion between fibers in the firing step for converting the precursor fiber into carbon fiber, and the excellent carbon fiber. Quality and performance can be easily maintained. In addition, it is possible to easily prevent the heat resistance of the acrylonitrile-based polymer from being lowered, and it is possible to easily suppress drying when the precursor fiber is spun. Furthermore, adhesion between single fibers can be easily avoided in processing such as stretching with a heating roller or pressurized steam. If the blending amount of acrylonitrile is 99.0% by mass or less, it is possible to easily prevent the solubility in the solvent from being lowered, to easily prevent the precipitation and coagulation of the acrylonitrile polymer, and to stabilize the spinning stock solution. Therefore, the precursor fiber can be manufactured stably and easily.

  The content of the acrylonitrile monomer unit in the acrylonitrile-based polymer can be specified by the integral ratio of the chemical shift obtained from the 1H-NMR method.

  The monomer other than acrylonitrile in the acrylonitrile polymer can be appropriately selected from vinyl monomers copolymerizable with acrylonitrile, and can be selected from vinyl monomers that improve the hydrophilicity of the acrylonitrile polymer. It is preferable to use a vinyl monomer having an effect of promoting flame resistance.

Examples of the vinyl monomer that improves the hydrophilicity of the acrylonitrile polymer include a vinyl compound having a hydrophilic functional group such as a carboxyl group, a sulfo group, an amino group, an amide group, and a hydroxyl group. The vinyl monomers and vinyl compounds copolymerizable with acrylonitrile are vinyl groups (CH ₂ ═CH—), vinylidene groups (CH ₂ ═C <), vinylene groups (—CH═CH—) and allyl. Any monomer and compound having a carbon-carbon double bond copolymerizable with acrylonitrile such as a group (CH ₂ ═CHCH ₂ ) may be used.

Examples of vinyl monomers having a carboxyl group (carboxylic acids copolymerizable with acrylonitrile monomers) include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, and mesaconic acid. Can be mentioned.
Examples of the vinyl monomer having a sulfo group include allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, vinyl sulfonic acid, and sulfopropyl methacrylate.
Examples of vinyl monomers having an amino group include dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, tertiary butylaminoethyl methacrylate, allylamine, o-aminostyrene, and p-aminostyrene. Can be mentioned.
Examples of the vinyl monomer having an amide group include acrylamide, methacrylamide, dimethylacrylamide, and crotonamide.
Examples of the vinyl monomer having a hydroxyl group include hydroxymethyl methacrylate, hydroxymethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 3-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, Examples include 2-hydroxypropyl acrylate.

  In addition to the acrylonitrile monomer, the hydrophilicity of the acrylonitrile polymer can be easily improved by adding such a vinyl monomer to the polymer. When the hydrophilicity is improved, the density of the obtained precursor fiber is improved, and generation of microvoids in the surface layer portion can be suppressed. The above-mentioned vinyl monomers that improve hydrophilicity can be used singly or in appropriate combination of two or more. The blending amount of the vinyl monomer that improves the hydrophilicity of such an acrylonitrile polymer is preferably 1.0% by mass or more and 5.0% by mass or less in the acrylonitrile polymer.

  Examples of vinyl monomers having an effect of promoting flame resistance include acrylic acid, methacrylic acid, ethacrylic acid, itaconic acid, crotonic acid, citraconic acid, maleic acid, mesaconic acid or their lower alkyl esters, alkali metal salts, ammonium salts Or acrylamide, methacrylamide, etc. are mentioned. Among these, from the viewpoint of obtaining a higher flame resistance promoting effect with a small amount, a vinyl monomer having a carboxyl group is preferred, and vinyl monomers such as acrylic acid, methacrylic acid and itaconic acid are particularly preferred. By blending such a vinyl monomer, it is possible to easily shorten the time for the flameproofing step described later, and to easily reduce the manufacturing cost. The above-mentioned vinyl monomers that promote flame resistance can be used singly or in appropriate combination of two or more. The blending amount of the vinyl monomer having such an effect of promoting flame resistance is preferably 1.0% by mass or more and 5.0% by mass or less in the acrylonitrile polymer.

  Further, in the production method of the present invention, the acrylonitrile-based polymer contains a total of 1 vinyl-based monomer units containing a carboxylic acid copolymerizable with an acrylonitrile monomer (for example, acrylic acid, methacrylic acid, and itaconic acid). It is preferable to contain 0.0 mass% or more and 5.0 mass% or less. As a result, the amount of acrylonitrile in the acrylonitrile-based polymer can be adjusted to 95.0% by mass or more and 99.0% by mass or less, further improving the hydrophilicity of the acrylonitrile-based polymer and introducing a flame resistance promoting component. be able to. In addition, content of the said vinyl-type monomer unit in an acrylonitrile-type polymer can be specified by the integral ratio of the chemical shift obtained from 1H-NMR method.

  The concentration of the acrylonitrile polymer in the acrylonitrile polymer solution is preferably 18% by mass or more and 26% by mass or less, and more preferably 20% by mass or more and 24% by mass or less. This is because if it is 18% by mass or more, a dense coagulated yarn can be easily obtained, and if it is 26% by mass or less, an appropriate viscosity and fluidity can be easily obtained as a spinning dope.

  Further, in the method for producing an acrylonitrile-based polymer solution of the present invention, it is preferable to use a high-boiling point dispersion medium such as dimethylformamide as described above. When these high-boiling point dispersion mediums are used, the dispersion liquid before heating is used. The polymer concentration (content) in the solution and the polymer concentration in the solution after heating do not change. For this reason, the content of the polymer in the dispersion is preferably 18% by mass or more and 26% by mass or less, and more preferably 20% by mass or more and 24% by mass or less for the same reason.

  Moreover, it is preferable that the acrylonitrile-type polymer solution of this invention has the light absorbency computed from Formula 4 40-50. A polymer solution having an absorbance within the above range has not only a very small gel-like content, but also a very small amount of foreign matter such as undissolved material, and a high-strength carbon fiber can be easily obtained. When producing a polymer, an improvement in stability in the step after producing the polymer solution can be expected.

Measurement of absorbance In the same solvent as used for dissolving the polymer, the acrylonitrile polymer solution is diluted 20 times with respect to its mass and placed in a 1 cm thick cell, and the absorbance A ₃₅₀ at a wavelength of 350 nm is measured. . Absorbance is calculated by using absorbance A ₃₅₀ and the following formula 4. Note that a Hitachi spectrophotometer (U-3300) can be used to measure the absorbance A _{350, and} the measurement can be performed at 30 ° C.

(Formula 4)
Absorbance = absorbance A ₃₅₀ / (polymer mass (g) in 1 g of acrylonitrile-based polymer solution before dilution × mol amount of carboxylic acid (mol) in 1 mol of acrylonitrile-based polymer).

  In addition, the solvent used for 20 times dilution uses the solvent similar to the solvent at the time of melt | dissolution.

  For example, by performing the method for producing an acrylonitrile-based polymer solution of the present invention under the following conditions (i and ii), a polymer solution having an absorbance shown in Formula 4 within the above range can be obtained.

i) A vinyl monomer unit including acrylonitrile monomer units of 95.0% by mass or more and 99.0% by mass or less and a carboxylic acid copolymerizable with the acrylonitrile monomer of 1.0% by mass or more and 5.0%. Use an acrylonitrile-based polymer composed of mass% or less.
ii) The concentration of the acrylonitrile polymer in the dispersion is set to 18% by mass or more and 26% by mass or less.

<Method for producing carbon fiber precursor acrylonitrile fiber>
Hereinafter, an example of a method for obtaining a carbon fiber precursor acrylonitrile fiber (hereinafter sometimes simply referred to as a carbon fiber precursor fiber) from an acrylonitrile polymer solution will be described in detail.

  The method for producing a carbon fiber precursor acrylonitrile fiber of the present invention is a method for producing a carbon fiber precursor acrylonitrile fiber by spinning the acrylonitrile polymer solution by a dry-wet spinning method or a wet spinning method.

  In the dry-wet spinning method or the wet spinning method, when spinning the acrylonitrile-based polymer solution from a nozzle, the temperature is controlled to 30 ° C. or more and 90 ° C. or less within 3 minutes from the point of obtaining the polymer solution. After that, it is preferable to keep the temperature of the polymer solution at 30 ° C. or higher and 90 ° C. or lower until it is discharged from the nozzle. Further, the temperature of the polymer solution is controlled to 50 ° C. or more and 70 ° C. or less within 3 minutes from the time of obtaining the polymer solution, and then the temperature of the polymer solution is set to 50 ° C. or more and 70 ° C. or less until the polymer solution is discharged from the nozzle. It is more preferable to keep holding. By maintaining the temperature at 30 ° C. or higher, the fluidity of the acrylonitrile-based polymer solution can be easily maintained, and when the carbon fiber is produced, the permeability in the process after producing the polymer solution is particularly good. . In addition, by maintaining the temperature at 90 ° C. or less, it is possible to easily suppress the progress of the cross-linking reaction and the cyclization reaction between the molecules of the polymer chain in the acrylonitrile-based polymer solution and between the molecules. An increase can be easily prevented.

The method for producing a carbon fiber precursor acrylonitrile fiber of the present invention can include, for example, the following steps.
Step 1. A filtration step of filtering the polymer solution before dry-wet or wet-spinning the polymer solution.
Step 2. A coagulation step of spinning the filtered polymer solution into a coagulation bath to obtain coagulated yarn.
Step 3. A wet heat drawing step of wet heat drawing the coagulated yarn to obtain a wet heat drawn yarn;
Step 4. An oil agent composition attaching step of attaching an oil agent composition to the wet heat drawn yarn.
Step 5. A dry densification step of drying and densifying the wet heat stretched yarn to which the oil composition is adhered to obtain a dry dense yarn.
Step 6. A dry heat drawing step in which the dry dense yarn is dry heat drawn to obtain a carbon fiber precursor fiber;

-Filtration process Before spinning a polymer solution, it is the process of filtering foreign substances, such as a dust which may cause process abnormality and a carbon fiber performance fall from a polymer solution with a filter device. Further, when the polymer solution is filtered with a filter device, the polymer solution may be filtered in advance with a pre-filter having a coarse opening.

・ Coagulation process Examples of methods for obtaining carbon fiber precursor fibers include a wet spinning method in which the carbon fiber precursor fiber is spun directly into a coagulation bath, a dry spinning method in which the carbon fiber is coagulated in air, and a coagulation after spinning in the air once. Known spinning methods such as a dry and wet spinning method for solidifying in a bath may be used. Among these, from the viewpoint of further improving the strength and elastic modulus of the carbon fiber, the wet spinning method and the dry wet spinning method are preferable.

  Examples of the spinning shaping by the dry-wet spinning method or the wet spinning method include a method in which an acrylonitrile-based polymer solution is spun into a coagulation bath from a nozzle having a discharge hole having a substantially circular cross section. As the coagulation bath, an aqueous solution containing a solvent (solvent) used for the acrylonitrile-based polymer solution is preferably used from the viewpoint of easy solvent recovery.

  When using the aqueous solution containing the solvent of a polymer solution as a coagulation bath, it is preferable that the solvent concentration in this aqueous solution is 60 mass% or more and 85 mass% or less. Within this range, the carbon fiber precursor fiber can be easily made into a dense structure free from voids, and a carbon fiber having high strength and high elastic modulus can be easily obtained. In addition, stretchability can be secured and productivity is excellent.

  Although the temperature of a coagulation bath is not specifically limited, -10 degreeC or more and 60 degrees C or less are preferable. Within this range, the precursor fiber can be easily made into a dense structure free from voids, and a carbon fiber having high strength and high elastic modulus can be easily obtained. In addition, stretchability can be secured and the productivity is excellent.

-Wet heat drawing process The obtained coagulated yarn is wet-heat drawn in a coagulation bath or a drawing bath to obtain a wet heat drawn yarn. Further, after the coagulated yarn is drawn in the air, the wet heat drawn yarn can be obtained by drawing again in a bath. Furthermore, the wet heat stretched yarn can be brought into a water-swollen state before and after stretching or during stretching. Examples of the stretching bath include water and an aqueous solution containing a solvent used for an acrylonitrile-based polymer solution.

  The solvent concentration of the stretching bath is preferably 0% by mass to 85% by mass. Within this range, the carbon fiber precursor fiber can be easily made into a dense structure free from voids, and a carbon fiber having high strength and high elastic modulus can be easily obtained. In addition, stretchability can be secured and the productivity is excellent.

  The temperature of the stretching bath is not particularly limited, but is preferably 50 to 98 ° C. Within this range, the precursor fiber can be easily made into a dense structure free from voids, and a carbon fiber having high strength and high elastic modulus can be easily obtained. In addition, stretchability can be secured and the productivity is excellent.

  Wet heat drawing can be performed by putting a coagulated yarn in a coagulation bath or a drawing bath and applying tension to the coagulated yarn. In the wet heat stretching, for example, a desired magnification may be achieved once, or a desired magnification may be achieved by stretching in multiple stages in two or more times. In addition, it is preferable to wet-heat-stretch 5 to 15 times in total, combining the stretching in the air and the stretching in the stretching bath. By stretching in this way, the carbon fiber can be easily increased in strength and elastic modulus.

・ Oil agent composition adhesion step The application of the oil agent composition to the wet heat drawn yarn is performed by applying a dispersion (oil solution dispersion) of the oil composition to the wet heat drawn yarn in the water-swollen state after drawing in the bath. It can be carried out. When washing is carried out after drawing in the bath, the oil dispersion can also be applied to the wet-heat drawn yarn in a water-swollen state obtained after drawing and washing in the bath.

  The oil composition can be determined in consideration of the functions required for the carbon fiber precursor fiber, and from the viewpoint of heat resistance, a silicone-based oil composition is preferable, and amino-modified silicone is particularly preferable. If necessary, additives such as an antioxidant, an antistatic agent, an antifoaming agent, an antiseptic, an antibacterial agent, and a penetrating agent can be blended in the oil composition.

  When preparing the oil dispersion, mixing of each component and dispersion in water can be performed using a propeller stirring, a homomixer, a homogenizer, or the like. As another adjustment method, use a phase inversion temperature method to form a water-in-oil type oil dispersion with a homomixer or the like while heating, and then lower the temperature to invert the phase to obtain an oil-in-water oil dispersion. You can also.

  As a method of impregnating the carbon fiber precursor fiber with the oil agent composition, a known method such as a roller method, a guide method, a spray method, or a dip method can be used.

  In attaching the oil composition to the wet heat drawn yarn, impregnation of the wet heat drawn yarn into the oil dispersion may be performed once or may be a multi-stage treatment repeated twice or more. From the viewpoint of more uniformly attaching the oil agent composition to the coagulated yarn, it is preferable to use a multistage treatment.

  The adhesion amount of the oil agent composition in the carbon fiber precursor fiber is preferably 0.1% by mass or more and 2% by mass or less, and 0.5% by mass or more and 1.5% by mass or less with respect to the dry mass of the carbon fiber precursor fiber. More preferably, it is at most mass%. When the adhesion amount of the oil composition is 0.1% by mass or more, the function of the oil composition can be easily expressed sufficiently. When the adhesion amount of the oil composition is 2% by mass or less, it is possible to easily prevent the excessively adhered oil composition from being polymerized in the firing step and inducing adhesion between single fibers.

-Dry densification process Subsequently, the wet heat drawn yarn with the oil composition adhered thereto is dried and densified to obtain a dry densified yarn. For drying densification, a conventionally known method can be used in the field of carbon fibers.

  The drying temperature in the drying and densification of the wet heat drawn yarn to which the oil agent composition is applied is preferably a temperature exceeding the glass transition temperature of the precursor fiber. By processing at such a drying temperature, drying and densification of the wet heat drawn yarn provided with the oil composition can be easily achieved. The drying temperature varies depending on the moisture content of the wet heat drawn yarn to which the oil composition is applied, but is preferably determined in the range of 100 to 200 ° C.

-Dry heat drawing process Subsequently, in order to improve the denseness and the degree of orientation, the dry dense yarn is dry heat drawn to obtain a carbon fiber precursor fiber. Examples of the heat stretching method include a method of stretching while being conveyed by a heating roller and a method of stretching in a pressurized water vapor pressure atmosphere.

  The carbon fiber precursor fiber obtained as described above can be cooled to a room temperature state by passing it through a roll at room temperature. The cooled carbon fiber precursor fiber is wound around a bobbin by a winder, or transferred into a can and stored, and used for the subsequent production of carbon fiber.

<Method for producing carbon fiber>
Below, an example of the method of obtaining carbon fiber from a carbon fiber precursor acrylonitrile-type fiber is demonstrated.

  The carbon fiber can be obtained by firing the carbon fiber precursor fiber (hereinafter referred to as a firing step). The firing process can consist of a flameproofing process and a carbonization process. The conditions for each treatment in the firing step are not particularly limited, but it is preferable to set conditions under which structural defects such as voids are unlikely to occur inside the fiber.

  In the flameproofing treatment step, the precursor fiber is heated for an arbitrary time under tension or stretching conditions in an oxidizing atmosphere to form a flameproof fiber. Examples of the flameproofing method include a hot air circulation method and a fixed hot plate method having a porous plate surface.

  A carbonization process process obtains carbon fiber by heating the flame-proof fiber obtained by the flame-proof process in inert gas atmosphere. A carbonization process can consist of a pre-carbonization process and a carbonization process performed at a temperature higher than a pre-carbonization process.

  The pre-carbonization step can be performed, for example, by heating the flame-resistant fiber under tension in an inert gas atmosphere having a maximum temperature of 550 to 800 ° C.

  The carbonization step can be performed, for example, by heating the pre-carbonized fiber obtained from the pre-carbonization step in an inert atmosphere at 1200 to 3000 ° C.

  By further subjecting the carbon fibers obtained as described above to surface treatment, it is possible to easily improve the adhesiveness of the composite material to the matrix resin. As the surface treatment method, for example, a gas phase or a liquid phase treatment can be employed, and electrolytic treatment is preferable from the viewpoints of productivity and prevention of variation. Examples of the electrolytic solution used for the electrolytic treatment include an aqueous acid solution such as sulfuric acid, nitric acid, and hydrochloric acid, an aqueous alkaline solution such as sodium hydroxide, potassium hydroxide, and tetraethylammonium hydroxide, or an aqueous solution of these salts. Among them, an aqueous solution containing ammonium ions is preferable, and examples thereof include an aqueous solution of ammonium nitrate, ammonium sulfate, ammonium persulfate, ammonium chloride, ammonium bromide, or a mixture thereof.

  The amount of electricity in the electrolytic treatment can be determined according to the carbon fiber. For example, the higher the degree of carbonization, the higher the amount of electricity supplied.

  The obtained carbon fiber can be further subjected to sizing treatment as necessary. The sizing agent used for the sizing treatment can be determined according to the type of the matrix, and those having good compatibility with the matrix are preferable.

  By applying these surface treatments to the carbon fiber, the adhesion between the carbon fiber and the matrix can be facilitated to an appropriate level, and mechanical properties balanced in the vertical and horizontal directions can be easily expressed. it can.

  The carbon fiber precursor fiber obtained from the production method of the acrylonitrile polymer solution of the present invention or obtained by the above-described method using the acrylonitrile polymer solution of the present invention has a size of 100 nm or more. The polymer chain contains almost no gel-like product in which the polymer chain is intramolecularly, intermolecularly crosslinked or intramolecularly cyclized.

  In addition, the carbon fiber obtained by firing the carbon fiber precursor acrylic fiber is very excellent in strength, and is particularly suitable as a reinforcing fiber used for a fiber-reinforced resin composite material for aircraft and space industries.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these. In addition, the following evaluation was performed about the polymer solution and carbon fiber which were obtained from each example.

[Filter replacement frequency]
Leaf disk type using a stainless steel fiber sintered filter (Model No .: NF2M-05C, manufactured by Meisei Shokai Co., Ltd.) with an acrylonitrile polymer solution kept at 65 ° C. at a flow rate of 0.20 L / m ² per minute. A carbon fiber precursor fiber was continuously produced for a long period of time while filtering with a filter device. At this time, the number of times that the filter was replaced between the start date of spinning and the end date (converted per year) was examined. The critical pressure, which is a guide for replacement, was 2.5 MPa.

[Absorbance]
The stock solution for evaluation (polymer solution) was diluted 20-fold on a mass basis with the same solvent as the solvent of the polymer solution into a 1 cm-thick cell, and Hitachi spectrophotometer (model number: U-3300) Was used to measure the absorbance A ₃₅₀ at a wavelength of 350 nm. Absorbance X value was obtained by using absorbance A ₃₅₀ and the following formula.
Absorbance = absorbance A ₃₅₀ / (polymer mass (g) in 1 g of acrylonitrile-based polymer solution before dilution × mol amount of carboxylic acid (mol) in 1 mol of acrylonitrile-based polymer).

[Number of gels of 100 nm or more]
Dilute 20 g of the evaluation stock solution 50-fold by mass with the same solvent as the evaluation stock solution with a PTFE membrane filter (model number: DMT11T1-A0.1 μ, manufactured by Central Filter Industry Co., Ltd.) having a mesh size of 0.1 μm. While maintaining the stock solution temperature at 50 ° C., filtration was performed while maintaining the flow rate at 4 g / min / cm ² . The surface of the membrane filter after solution filtration was observed with a fluorescence microscope, and the number of yellow bright spots per field of view was measured. The measurement was performed 10 times while changing the observed location, and the average number of yellow bright spots measured was multiplied by 50 to obtain a gel-like number of 100 nm or more.

[Carbon fiber strand strength]
The carbon fiber strand strength was measured according to an epoxy resin-impregnated carbon fiber strand method according to JIS-R-7601. The number of measurements was 10 times, and the average value was used as an evaluation target.

Example 1
[Production of acrylonitrile polymer]
Acrylonitrile polymer is produced by supplying each raw material to an overflow type polymerization vessel as follows and stirring while maintaining the temperature in the polymerization vessel at 50 ° C., washing and drying the overflowed polymer slurry. did. In the polymerization vessel, 82.75% by mass of deionized water and 17% by mass of monomer (composition ratio: acrylonitrile (AN) monomer unit: methacrylic acid (MAA) monomer unit (mass ratio)) = 98 : 2), 0.1% by mass of ammonium persulfate, 0.15% by mass of ammonium bisulfite, and 2 ppm by mass of ferrous sulfate heptahydrate, respectively, and continuously with pH 3.0 An appropriate amount of sulfuric acid was added so that The composition of the obtained acrylonitrile-based polymer was AN monomer unit: MAA monomer unit (mass ratio) = 98: 2.

[Production of acrylonitrile polymer solution (spinning stock solution)]
An acrylonitrile polymer dispersion was prepared by stirring and mixing 23% by mass of the acrylonitrile polymer obtained above and 77% by mass of -10 ° C. dimethylformamide (DMF) with a biaxial mixer. During the preparation of the dispersion, the dispersion was not allowed to rise to 0 ° C. or higher. Immediately after dispersing the obtained acrylonitrile-based polymer dispersion, it is passed through the tube side of a three-series shell-and-tube type multi-tube heat exchanger, and pressurized steam is passed through the shell side as a heating medium. The dispersion was dissolved by heating, and an acrylonitrile polymer solution was obtained 10 minutes after the start of heating. The temperature of the dispersion just before passing through (just before heating) was 10 ° C. The dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 10 minutes after the start of heating are as shown in Table 1, Y = 125 (° C.), Z = 95 (° C.) Met. Further, the temperature of the dispersion liquid from 95 ° C. to 130 ° C. from 1 minute after the start of heating until obtaining a polymer solution 10 minutes after the start of heating was 95 ° C.

  Further, the radius A (mm) of the inscribed circle with respect to the tube cross section in the shell-and-tube type multi-tube heat exchanger, the inner peripheral length B (m) of the tube cross section, the average flow velocity C (m / m Min) was controlled as shown in Table 1, A = 6.5 (mm), B = 0.040 (m), and C = 0.60 (m / min).

  The temperature of the polymer solution was changed to 65 ° C. within 3 minutes from the time when the polymer solution was obtained (after 10 minutes from the start of heating), and immediately before the production of the carbon fiber precursor fiber, that is, spinning described later. The temperature of the polymer solution was kept at 65 ° C. until it was discharged from the nozzle.

  Further, Table 1 shows the absorbance X value of the polymer solution obtained 10 minutes after the start of heating and the number (number) of gel-like substances having a size of 100 nm or more as measured by the method described above.

[Production of carbon fiber precursor fiber]
The obtained acrylonitrile-based polymer solution was filtered with a leaf disk type filter device using a stainless steel fiber sintered filter (model number: NF2M-05C, manufactured by Meisei Shokai Co., Ltd.).

  Next, the filtered polymer solution was once discharged into the air from a spinning nozzle having a pore diameter of 150 μm and a pore number of 2000 and passed through a space of about 4 mm, and then from a dimethylformamide aqueous solution having a concentration of 80 mass% and a temperature of 10 ° C. Spinning was performed by introducing into a coagulation bath to obtain a coagulated yarn. The obtained coagulated yarn was stretched 1.1 times in air, then stretched 3.0 times in a dimethylformamide aqueous solution having a concentration of 50% by mass and a temperature of 60 ° C., and 1.1 times in hot water. Washing and solvent removal were performed while stretching. The solvent-removed coagulated yarn was immersed in an amino-modified silicone oil dispersion and densely dried with a heating roller at 140 ° C. The amino-modified silicone oil dispersion used at this time was 90 parts by mass of amino-modified silicone (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KF-8002), and an emulsifier (trade name: Emulgen 108, manufactured by Kao Corporation). 10 parts by mass of the mixture was emulsified with a Gorin mixer (manufactured by SMT Co., Ltd., trade name: pressure homogenizer gorin type) and then added with water, and the composition of the resulting oil dispersion was water. : Amino-modified silicone: Emulsifier (mass ratio) = 98.65: 1.2: 0.15. Subsequently, it was stretched 3.0 times with a hot roll having a surface temperature of 190 ° C., and a carbon fiber precursor fiber having a single fiber fineness of 0.7 dtex was produced at a winding speed of 250 m / min. The filter replacement frequency at this time was as shown in Table 1.

[Manufacture of carbon fiber]
The precursor fiber was passed through a flame-proofing furnace having a temperature gradient of 200 to 280 ° C. in air (flame-proofing treatment) and fired in a carbonization furnace having a temperature gradient of 350 to 2000 ° C. in a nitrogen atmosphere (carbonization). processing). Thereafter, electrolytic oxidation treatment and sizing treatment were performed to obtain carbon fibers.
As shown in Table 1, the strand strength of the obtained carbon fiber was 7.0 GPa.

(Example 2)
Table 1 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 80 (° C.) and Z = 120 (° C.) as shown. Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 120 ° C. after exceeding 1 minute from the start of heating. The others were the same as in Example 1.
The filter replacement frequency and the number of gels (number) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.9 GPa.

(Example 3)
Table 1 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 90 (° C.) and Z = 115 (° C.) as shown. Further, the temperature of the dispersion liquid from 90 ° C. to 115 ° C. after 1 minute from the start of heating until 10 minutes after the start of heating until a polymer solution was obtained was changed. The others were the same as in Example 1.
The filter replacement frequency and the number of gels (number) of 100 nm or more were as shown in Table 1, and the obtained carbon fiber had a strand strength of 7.2 GPa.

Example 4
An acrylonitrile-based polymer dispersion was prepared by stirring and mixing 22% by mass of an acrylonitrile-based polymer and 78% by mass of -10 ° C. dimethylformamide with a biaxial mixer. In addition, when the obtained dispersion is dissolved to obtain an acrylonitrile polymer solution, the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 10 minutes after the start of heating are displayed. 1 was changed to Y = 100 (° C.) and Z = 105 (° C.). Moreover, the temperature of the dispersion liquid obtained after exceeding 1 minute from the start of heating until obtaining a polymer solution 10 minutes after the start of heating was changed to 100 ° C. or higher and 105 ° C. or lower. Furthermore, the temperature of the polymer solution is changed to 60 ° C. within 3 minutes from the time when the polymer solution is obtained (after 10 minutes from the start of heating), and then immediately before the production of the carbon fiber precursor fiber. The temperature was kept at 60 ° C. The others were the same as in Example 1.
The filter replacement frequency and the number of gels (numbers) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.8 GPa.

(Example 5)
Table 1 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 105 (° C.) and Z = 105 (° C.) as shown. Further, the temperature of the dispersion liquid from 105 ° C. to 110 ° C. was changed from the time when it exceeded 1 minute after the start of heating to the time when the polymer solution was obtained 10 minutes after the start of heating. The others were the same as in Example 1.
The filter replacement frequency and the number (number) of gels of 100 nm or more were also as shown in Table 1, and the obtained carbon fiber had a strand strength of 7.1 GPa.

(Example 6)
Table 1 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 80 (° C.) and Z = 110 (° C.) as shown. Moreover, the temperature of the dispersion liquid obtained after exceeding 1 minute from the start of heating until obtaining a polymer solution 10 minutes after the start of heating was changed to 80 ° C. or higher and 110 ° C. or lower. The others were the same as in Example 1.
The filter replacement frequency and the number of gels (number) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.7 GPa.

(Example 7)
Table 1 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 105 (° C.) and Z = 105 (° C.) as shown. Further, the temperature of the dispersion liquid from 105 ° C. to 110 ° C. was changed from the time when it exceeded 1 minute after the start of heating to the time when the polymer solution was obtained 10 minutes after the start of heating. Further, the average flow rate C (m / min) of the liquid passing through the tube was changed to C = 1.00 (m / min) as shown in Table 1. The others were the same as in Example 1.
The filter replacement frequency and the number of gels (number) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.9 GPa.

(Example 8)
Table 1 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 105 (° C.) and Z = 105 (° C.) as shown. Further, the temperature of the dispersion liquid from 105 ° C. to 110 ° C. was changed from the time when it exceeded 1 minute after the start of heating to the time when the polymer solution was obtained 10 minutes after the start of heating. Furthermore, as shown in Table 1, the radius A (mm) of the inscribed circle with respect to the tube cross section, the inner peripheral length B (m) of the tube cross section, and the average flow velocity C (m / min), A = 5.0 (mm), B = 0.030 (m) and C = 0.80 (m / min). The others were the same as in Example 1.
The filter replacement frequency and the number (number) of gels of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 7.0 GPa.

Example 9
Table 1 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 105 (° C.) and Z = 105 (° C.) as shown. Further, the temperature of the dispersion liquid from 105 ° C. to 110 ° C. was changed from the time when it exceeded 1 minute after the start of heating to the time when the polymer solution was obtained 10 minutes after the start of heating. Furthermore, as shown in Table 1, the radius A (mm) of the inscribed circle with respect to the tube cross section, the inner peripheral length B (m) of the tube cross section, and the average flow velocity C (m / min), A = 8.0 (mm), B = 0.050 (m), C = 0.50 (m / min). The others were the same as in Example 1.
The filter replacement frequency and the number of gels (numbers) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.8 GPa.

(Example 10)
Table 1 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 105 (° C.) and Z = 105 (° C.) as shown. Further, the temperature of the dispersion liquid from 105 ° C. to 110 ° C. was changed from the time when it exceeded 1 minute after the start of heating to the time when the polymer solution was obtained 10 minutes after the start of heating. Furthermore, the average flow velocity C (m / min) was changed to C = 0.07 (m / min) as shown in Table 1. The others were the same as in Example 1.
The filter replacement frequency and the number of gels (numbers) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.8 GPa.

(Example 11)
Table 1 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 105 (° C.) and Z = 105 (° C.) as shown. Further, the temperature of the dispersion liquid from 105 ° C. to 110 ° C. was changed from the time when it exceeded 1 minute after the start of heating to the time when the polymer solution was obtained 10 minutes after the start of heating. Furthermore, the average flow velocity C (m / min) was changed to C = 1.00 (m / min) as shown in Table 1. The others were the same as in Example 1.
The filter replacement frequency and the number of gels (number) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.9 GPa.

(Example 12)
Six minutes after heating the acrylonitrile polymer dispersion, an acrylonitrile polymer solution was obtained. At that time, the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 6 minutes after the start of heating were Y = 105 (° C.) and Z = 105 (° C. as shown in Table 1. )Met. Further, the temperature of the dispersion liquid from 105 ° C. to 110 ° C. from 1 minute after the start of heating until 6 minutes after the start of heating until a polymer solution was obtained. Further, the temperature of the polymer solution is changed to 65 ° C. within 3 minutes from the time when the polymer solution is obtained (6 minutes after the start of heating), and then until immediately before the production of the carbon fiber precursor fiber, The temperature was kept at 65 ° C. The others were the same as in Example 1. The filter replacement frequency and the number of gels (numbers) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.8 GPa.

(Example 13)
Seven minutes after heating the acrylonitrile polymer dispersion, an acrylonitrile polymer solution was obtained. At that time, the dispersion temperature Y (° C.) one minute after the start of heating and the solution temperature Z (° C.) seven minutes after the start of heating were Y = 115 (° C.) and Z = 100 (° C. as shown in Table 1. )Met. Further, the temperature of the dispersion liquid from 100 ° C. to 120 ° C. after 1 minute from the start of heating until obtaining the polymer solution 7 minutes after the start of heating was 100 ° C. or more. Further, the temperature of the polymer solution is changed to 65 ° C. within 3 minutes from the time when the polymer solution is obtained (7 minutes after the start of heating), and then until immediately before the production of the carbon fiber precursor fiber, The temperature was kept at 65 ° C. The others were the same as in Example 1.
The filter replacement frequency and the number of gels (number) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.7 GPa.

(Example 14)
8 minutes after heating the acrylonitrile polymer dispersion, an acrylonitrile polymer solution was obtained. At that time, the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 8 minutes after the start of heating were Y = 125 (° C.) and Z = 100 (° C. as shown in Table 1. )Met. Further, the temperature of the dispersion liquid from 100 ° C. to 125 ° C. after 1 minute from the start of heating until the polymer solution was obtained 8 minutes after the start of heating was 100 ° C. Further, the temperature of the polymer solution is changed to 65 ° C. within 3 minutes from the time when the polymer solution is obtained (after 8 minutes from the start of heating), and then immediately before the production of the carbon fiber precursor fiber. The temperature was kept at 65 ° C. The others were the same as in Example 1.
The filter replacement frequency and the number (number) of gels of 100 nm or more were also as shown in Table 1, and the obtained carbon fiber had a strand strength of 7.1 GPa.

(Example 15)
An acrylonitrile polymer dispersion was prepared by stirring and mixing 24% by mass of an acrylonitrile polymer and 78% by mass of -10 ° C. dimethylformamide with a biaxial mixer. When this dispersion is dissolved to obtain an acrylonitrile polymer solution, the dispersion temperature Y (° C.) after 1 minute from the start of heating and the solution temperature Z (° C.) after 10 minutes from the start of heating are the same as in Example 1. And Y = 125 (° C.) and Z = 95 (° C.) as shown in Table 1. In addition, the temperature of the dispersion liquid obtained after exceeding 1 minute from the start of heating until obtaining the polymer solution 10 minutes after the start of heating was changed to 90 ° C. or more and 125 ° C. or less. Further, the temperature of the polymer solution is changed to 80 ° C. within 3 minutes from the time when the polymer solution is obtained (after 10 minutes from the start of heating), and then until immediately before the production of the carbon fiber precursor fiber, The temperature was kept at 80 ° C. The others were the same as in Example 1.
The filter replacement frequency and the number (number) of gels of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 7.0 GPa.

(Example 16)
The same procedure as in Example 1 was conducted except that acrylonitrile-based polymer dispersion was prepared using -10 ° C dimethylacetamide (DMAc) instead of -10 ° C dimethylformamide.
The filter replacement frequency and the number of gels (number) of 100 nm or more were as shown in Table 1, and the strand strength of the obtained carbon fiber was 6.6 GPa.

(Example 17)
An acrylonitrile-based polymer dispersion was prepared by stirring and mixing 21% by mass of an acrylonitrile-based polymer and 79% by mass of dimethyl sulfoxide (DMSO) at 20 ° C. with a biaxial mixer. At this time, the temperature of the dispersion during preparation of the dispersion was not allowed to exceed 20 ° C. The dispersion temperature just before the start of heating was 30 ° C. Further, the temperature of the polymer solution is changed to 45 ° C. within 3 minutes from the time when the polymer solution is obtained (after 10 minutes from the start of heating), and then until immediately before the production of the carbon fiber precursor fiber, The temperature was kept at 45 ° C. The others were the same as in Example 1.
The filter replacement frequency and the number of gels (number) of 100 nm or more were as shown in Table 1, and the strand strength of the obtained carbon fiber was 6.6 GPa.

(Example 18)
The temperature of the polymer solution is changed to 60 ° C. within 3 minutes from the time when the polymer solution is obtained (10 minutes after the start of heating), and then the temperature of the polymer solution is changed until immediately before the production of the carbon fiber precursor fiber. The same operation as in Example 1 was performed except that the temperature was kept at 60 ° C.
The filter replacement frequency and the number of gels (numbers) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.8 GPa.

(Example 19)
The temperature of the polymer solution is changed to 80 ° C. within 3 minutes from the time when the polymer solution is obtained (after 10 minutes from the start of heating), and then the temperature of the polymer solution is changed until immediately before the production of the carbon fiber precursor fiber. The same procedure as in Example 1 was performed except that the temperature was kept at 80 ° C.
The filter replacement frequency and the number of gels (number) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.9 GPa.

(Example 20)
The same procedure as in Example 1 was conducted except that the acrylonitrile polymer dispersion was passed through the tube side of one shell-and-tube type multi-tube heat exchanger immediately after dispersion.
The filter replacement frequency and the number of gels (number) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.9 GPa.

(Example 21)
The same procedure as in Example 1 was conducted except that the acrylonitrile polymer dispersion was passed through the tube side of 10 shell-and-tube type multi-tube heat exchangers immediately after dispersion.
The filter replacement frequency and the number of gels (numbers) of 100 nm or more were also as shown in Table 1. The strand strength of the obtained carbon fiber was 6.8 GPa.

(Comparative Example 1)
Table 2 shows the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. It changed to Y = 135 (degreeC) and Z = 135 (degreeC) as shown. Further, the temperature of the dispersion liquid was maintained at 135 ° C. after 1 minute from the start of heating until 10 minutes after the start of heating until a polymer solution was obtained. Further, the temperature of the polymer solution is changed to 70 ° C. within 3 minutes from the time when the polymer solution is obtained (10 minutes after the start of heating), and then until just before the carbon fiber precursor fiber is produced. The temperature was kept at 70 ° C. The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are also as shown in Table 2. Compared with Example 1, the filter replacement frequency and the number of gels (numbers) of 100 nm or more were considerably large.
The strand strength of the obtained carbon fiber was 5.7 GPa, which was 1.3 GPa lower than that in Example 1.

(Comparative Example 2)
Table 2 shows the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 90 (° C.) and Z = 90 (° C.) as shown. Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed to 90 ° C. after exceeding 1 minute from the start of heating. The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are as shown in Table 2. Compared with Example 1, the number of gels (numbers) of 100 nm or more was not significantly different, but the filter replacement frequency There were many.
The obtained carbon fiber had a strand strength of 5.5 GPa, which was 1.5 GPa lower than that of Example 1.

(Comparative Example 3)
Table 2 shows the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. It changed to Y = 80 (degreeC) and Z = 80 (degreeC) as shown. Moreover, the temperature of the dispersion liquid obtained after exceeding 1 minute from the start of heating until obtaining the polymer solution 10 minutes after the start of heating was changed to 80 ° C. The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are as shown in Table 2. Compared with Example 1, the number of gels (numbers) of 100 nm or more was not significantly different, but the filter replacement frequency There were many.
The obtained carbon fiber had a strand strength of 5.6 GPa, which was 1.4 GPa lower than that of Example 1.

(Comparative Example 4)
When an acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution, the dispersion temperature Y (° C.) after 1 minute from the start of heating and the solution temperature Z (° C.) after 10 minutes after the heating are displayed. 2 was changed to Y = 80 (° C.) and Z = 130 (° C.). Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 130 ° C. after exceeding 1 minute from the start of heating. The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are as shown in Table 2. Compared with Example 1, the number of gels (numbers) of 100 nm or more is large, and the filter replacement frequency is slightly increased. It was.
The obtained carbon fiber had a strand strength of 6.3 GPa, which was 0.7 GPa lower than that of Example 1.

(Comparative Example 5)
When an acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution, the dispersion temperature Y (° C.) after 1 minute from the start of heating and the solution temperature Z (° C.) after 10 minutes after the heating are displayed. 2 was changed to Y = 35 (° C.) and Z = 135 (° C.). Moreover, the temperature of the dispersion liquid after obtaining the polymer solution after 1 minute from the start of heating until 10 minutes after the start of heating was changed from 35 ° C. to 135 ° C. The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are as shown in Table 2. Compared with Example 1, the number of gels (numbers) of 100 nm or more is considerably large, and the frequency of filter replacements is also slightly high. became.
The strand strength of the obtained carbon fiber was 5.7 GPa, which was 1.3 GPa lower than that in Example 1.

(Comparative Example 6)
When an acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution, the dispersion temperature Y (° C.) after 1 minute from the start of heating and the solution temperature Z (° C.) after 10 minutes after the heating are displayed. 2 was changed to Y = 80 (° C.) and Z = 130 (° C.). Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 135 ° C. after exceeding 1 minute from the start of heating. Furthermore, the average flow velocity C (m / min) was changed to C = 1.50 (m / min) as shown in Table 2. The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are as shown in Table 2. Compared with Example 1, the number of gels (numbers) of 100 nm or more is large, and the filter replacement frequency is slightly increased. It was.
The obtained carbon fiber was 6.1 GPa, which was 0.9 GPa lower than that in Example 1.

(Comparative Example 7)
Table 2 shows the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 80 (° C.) and Z = 130 (° C.) as shown. Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 130 ° C. after exceeding 1 minute from the start of heating. Furthermore, the average flow velocity C (m / min) was changed to C = 0.02 (m / min) as shown in Table 2. The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are also as shown in Table 2. Compared with Example 1, the number of gels (numbers) of 100 nm or more was large, and the filter replacement frequency was also increased. .
The strand strength of the obtained carbon fiber was 5.9 GPa, which was 1.1 GPa lower than that in Example 1.

(Comparative Example 8)
Table 2 shows the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 80 (° C.) and Z = 130 (° C.) as shown. Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 130 ° C. after exceeding 1 minute from the start of heating. Further, as shown in Table 2, the radius A (mm) of the inscribed circle with respect to the tube cross section, the inner peripheral length B (m) of the tube cross section, and the average flow velocity C (m / min) are A = 2.0 (mm). B = 0.015 (m) and C = 1.95 (m / min). The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are also as shown in Table 2. Compared with Example 1, the number of gels (numbers) of 100 nm or more was large, and the filter replacement frequency was also increased. .
The strand strength of the obtained carbon fiber was 6.5 GPa, which was 0.5 GPa lower than that in Example 1.

(Comparative Example 9)
Table 2 shows the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 80 (° C.) and Z = 130 (° C.) as shown. Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 135 ° C. after exceeding 1 minute from the start of heating. Further, the radius A (mm) of the inscribed circle with respect to the tube cross section, the inner peripheral length B (m) of the tube cross section, and the average flow velocity C (m / min), as shown in Table 2, A = 15.0 (mm) B = 0.095 (m) and C = 0.25 (m / min). The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are as shown in Table 2. Compared with Example 1, the number of gels (numbers) of 100 nm or more is large, and the filter replacement frequency is considerably increased. It was.
The obtained carbon fiber had a strand strength of 5.5 GPa, which was 1.5 GPa lower than that of Example 1.

(Comparative Example 10)
15 minutes after heating the acrylonitrile polymer dispersion, an acrylonitrile polymer solution was obtained. At that time, the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 15 minutes after the start of heating were as shown in Table 2, Y = 125 (° C.), Z = 100 (° C. )Met. Further, the temperature of the dispersion liquid from 100 ° C. to 125 ° C. from 1 minute after the start of heating until obtaining the polymer solution 15 minutes after the start of heating was 100 ° C. The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are also as shown in Table 2. Compared with Example 1, the filter replacement frequency and the number of gels (numbers) of 100 nm or more were considerably large.
The strand strength of the obtained carbon fiber was 5.7 GPa, which was 1.3 GPa lower than that in Example 1.

(Comparative Example 11)
15 minutes after heating the acrylonitrile polymer dispersion, an acrylonitrile polymer solution was obtained. At that time, the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 15 minutes after the start of heating were as shown in Table 2, Y = 135 (° C.), Z = 110 (° C. )Met. Further, the temperature of the dispersion liquid from 110 ° C. to 135 ° C. after 1 minute from the start of heating until 15 minutes after the start of heating until a polymer solution was obtained. The others were the same as in Example 1.

The filter replacement frequency and the number of gels (pieces) of 100 nm or more were also as shown in Table 2. Compared with Example 1, the filter replacement frequency and the number of gels (pieces) of 100 nm or more were large.
The strand strength of the obtained carbon fiber was 4.8 GPa, which was 2.2 GPa lower than that in Example 1.

(Comparative Example 12)
Three minutes after heating the acrylonitrile polymer dispersion, an acrylonitrile polymer solution was obtained. At that time, the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 3 minutes after the start of heating are as shown in Table 2, Y = 125 (° C.), Z = 100 (° C. )Met. Further, the temperature of the dispersion liquid from 100 ° C. to 125 ° C. from 1 minute after the start of heating until 3 minutes after the start of heating until a polymer solution was obtained. The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are as shown in Table 2. Compared with Example 1, the number of gels (numbers) of 100 nm or more was not significantly different, but the filter replacement frequency There were many.
The strand strength of the obtained carbon fiber was 5.9 GPa, which was 1.1 GPa lower than that in Example 1.

(Comparative Example 13)
An acrylonitrile polymer dispersion was prepared by stirring and mixing 10% by mass of an acrylonitrile polymer and 90% by mass of dimethylformamide at −10 ° C. with a biaxial mixer. Table 2 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the obtained dispersion is dissolved to obtain an acrylonitrile polymer solution. It changed to Y = 80 (degreeC) as it was, and Z = 130 (degreeC). Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 130 ° C. after exceeding 1 minute from the start of heating. Further, the temperature of the polymer solution is changed to 20 ° C. within 3 minutes from the time when the polymer solution is obtained (after 10 minutes from the start of heating), and then until immediately before the production of the carbon fiber precursor fiber, The temperature was kept at 20 ° C. The others were the same as in Example 1.

The number of gels (pieces) of 100 nm or more is as shown in Table 2. Compared with Example 1, the number of gels (pieces) of 100 nm or more was considerably large.
Further, stable spinning could not be performed, and carbon fiber precursor fibers could not be obtained. For this reason, the filter replacement frequency and the strand strength of the carbon fiber could not be measured.

(Comparative Example 14)
An acrylonitrile polymer dispersion was prepared by stirring and mixing 30% by mass of an acrylonitrile polymer and 70% by mass of -10 ° C. dimethylformamide with a biaxial mixer. The dispersion temperature Y (° C.) 1 minute after the start of heating of the obtained dispersion and the solution temperature Z (° C.) 10 minutes after the start of heating are as shown in Table 2, Y = 80 (° C.), Z = The temperature was changed to 130 (° C). Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 130 ° C. after exceeding 1 minute from the start of heating. Furthermore, the temperature of the polymer solution is changed to 100 ° C. within 3 minutes from the time when the polymer solution is obtained (after 10 minutes from the start of heating), and then immediately before the production of the carbon fiber precursor fiber. The temperature was kept at 100 ° C. The others were the same as in Example 1.

The number of gels (pieces) of 100 nm or more is as shown in Table 2. Compared with Example 1, the number of gels (pieces) of 100 nm or more was considerably large.
Further, stable spinning could not be performed, and carbon fiber precursor fibers could not be obtained. For this reason, the filter replacement frequency and the strand strength of the carbon fiber could not be measured.

(Comparative Example 15)
Table 2 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain a polymer solution. Y = 80 (° C.) and Z = 130 (° C.). Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 130 ° C. after exceeding 1 minute from the start of heating. At this time, the temperature of the dispersion just before passing through the three-series multitubular heat exchanger was 70 ° C. The others were the same as in Example 1.

  During the passage of the dispersion through a multi-tube heat exchanger in series, the viscosity of the dispersion increased, the load of liquid feeding increased, and the heat exchanger was clogged, and operation was not possible. . For this reason, the light absorbency of the polymer solution, the number of gels, the filter replacement frequency, and the strand strength of the carbon fiber could not be measured.

(Comparative Example 16)
Table 2 shows the dispersion temperature Y (° C) 1 minute after the start of heating and the solution temperature Z (° C) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain a polymer solution. Y = 80 (° C.) and Z = 130 (° C.). Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 130 ° C. after exceeding 1 minute from the start of heating. At this time, the temperature of the dispersion just before passing through the three-series multitubular heat exchanger was −40 ° C. The others were the same as in Example 1.

  The filter replacement frequency and the number of gels (number) of 100 nm or more were also as shown in Table 2. Compared with Example 1, the filter replacement frequency was considerably high.

  The strand strength of the obtained carbon fiber was 5.8 GPa, which was 1.2 GPa lower than that in Example 1.

(Comparative Example 17)
Table 2 shows the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 80 (° C.) and Z = 130 (° C.) as shown. Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 130 ° C. after exceeding 1 minute from the start of heating. Further, the temperature of the polymer solution is changed to 20 ° C. within 3 minutes from the time when the polymer solution is obtained (after 10 minutes from the start of heating), and then until immediately before the production of the carbon fiber precursor fiber, The temperature was kept at 20 ° C. The others were the same as in Example 1.

The filter replacement frequency and the number of gelled substances (numbers) of 100 nm or more are also as shown in Table 2. Compared with Example 1, the number of gelled substances (numbers) of 100 nm or more and the filter replacement frequency were considerably increased.
The strand strength of the obtained carbon fiber was 5.2 GPa, which was 1.8 GPa lower than that in Example 1.

(Comparative Example 18)
Table 2 shows the dispersion temperature Y (° C.) 1 minute after the start of heating and the solution temperature Z (° C.) 10 minutes after the start of heating when the acrylonitrile polymer dispersion is dissolved to obtain an acrylonitrile polymer solution. Y = 80 (° C.) and Z = 130 (° C.) as shown. Moreover, the temperature of the dispersion liquid after obtaining the polymer solution 10 minutes after the start of heating was changed from 80 ° C. to 130 ° C. after exceeding 1 minute from the start of heating. Further, the temperature of the polymer solution is changed to 110 ° C. within 3 minutes from the time when the polymer solution is obtained (after 10 minutes from the start of heating), and then until immediately before the production of the carbon fiber precursor fiber, The temperature was kept at 110 ° C. The others were the same as in Example 1.

The filter replacement frequency and the number of gels (numbers) of 100 nm or more are also as shown in Table 2. Compared with Example 1, the filter replacement frequency and the number of gels (numbers) of 100 nm or more were considerably large.
The obtained carbon fiber had a strand strength of 3.3 GPa, which was 3.7 GPa lower than that of Example 1.

Claims (14)

A method for producing an acrylonitrile polymer solution by heating an acrylonitrile polymer dispersion in which an acrylonitrile polymer containing an acrylonitrile monomer unit is dispersed in a dispersion medium, the production method satisfying the following conditions:
1. The temperature of the dispersion before heating is -20 ° C or higher and 40 ° C or lower,
2. The dispersion temperature Y (° C.) after 1 minute from the start of heating is 60 ° C. or more and 125 ° C. or less.
3. An acrylonitrile-based polymer solution in which the dispersion is dissolved is obtained within 5 minutes to 12 minutes after the start of heating. At this time, the temperature Z (° C.) of the obtained polymer solution is expressed by Formula 1. Fulfill,
4). The temperature of the polymer solution is controlled to 30 ° C. or more and 90 ° C. or less within 3 minutes from the time when the acrylonitrile-based polymer solution is obtained.
(Formula 1)
−0.006 × Y ² + 0.47 × Y + 112 (° C.) ≦ Z (° C.) ≦ −0.30 × Y + 145 (° C.).   The method for producing an acrylonitrile-based polymer solution according to claim 1, wherein the temperature of the dispersion from 1 minute after the start of heating until the acrylonitrile-based polymer solution is obtained is 60 ° C or higher and 130 ° C or lower.   The acrylonitrile polymer is a vinyl monomer unit 1.0 containing 95.0% by mass or less and 99.0% by mass or less of the acrylonitrile monomer unit and a carboxylic acid copolymerizable with the acrylonitrile monomer. The manufacturing method of the acrylonitrile-type polymer solution of Claim 1 or 2 comprised by mass% or more and 5.0 mass% or less.   The method for producing an acrylonitrile-based polymer solution according to any one of claims 1 to 3, wherein the dispersion medium is dimethylformamide, dimethylacetamide, or dimethylsulfoxide.   The method for producing an acrylonitrile-based polymer solution according to any one of claims 1 to 4, wherein a content of the acrylonitrile-based polymer in the acrylonitrile-based polymer dispersion is 18% by mass or more and 26% by mass or less.   The method for producing an acrylonitrile-based polymer solution according to any one of claims 1 to 5, wherein the means for heating the acrylonitrile-based polymer dispersion is a shell-and-tube type single tube or multi-tube heat exchanger. .   The acrylonitrile polymer according to claim 6, wherein the acrylonitrile polymer dispersion is passed through the tube side of the shell-and-tube type single tube or multi-tube heat exchanger, and the heating medium is passed through the shell side. A method for producing a solution. The method for producing an acrylonitrile-based polymer solution according to claim 7, wherein a radius A (mm) of an inscribed circle with respect to a cross section of the tube in the shell-and-tube type single-tube or multi-tube heat exchanger satisfies the following formula (2). :
(Formula 2)
4.0 (mm) ≦ A (mm) ≦ 10.0 (mm). The acrylonitrile-based weight according to claim 7 or 8, wherein an average flow rate C (m / min) of the acrylonitrile-based polymer dispersion in the shell-and-tube type single-tube or multi-tube heat exchanger satisfies the following formula (3). Method for producing coalescence solution:
(Formula 3)
0.0010 / B (m / min) ≦ C (m / min) ≦ 0.0500 / B (m / min)
(However, B represents the inner peripheral length (m) of the tube cross section in the shell-and-tube type single tube or multi-tube heat exchanger).   The method for producing an acrylonitrile-based polymer solution according to any one of claims 6 to 9, wherein a plurality of the shell-and-tube type single-tube or multi-tube heat exchangers are connected in series.   A carbon fiber precursor obtained by spinning the acrylonitrile-based polymer solution obtained by the production method according to claim 1 by a dry-wet spinning method or a wet-spinning method to obtain a carbon fiber precursor acrylonitrile-based fiber. A method for producing acrylonitrile fiber. In the dry-wet spinning method or the wet spinning method, when the acrylonitrile-based polymer solution is discharged from a nozzle for spinning,
The temperature of the polymer solution is kept at 30 ° C. or more and 90 ° C. or less until the temperature is controlled to 30 ° C. or more and 90 ° C. or less within 3 minutes from the time when the polymer solution is obtained, and then discharged from the nozzle. Item 12. A method for producing a carbon fiber precursor acrylonitrile fiber according to Item 11. 95.0% by mass or more and 99.0% by mass or less of acrylonitrile monomer unit, and 1.0% by mass or more and 5.0% by mass of vinyl monomer unit containing a carboxylic acid copolymerizable with the acrylonitrile monomer. A polymer solution in which an acrylonitrile polymer composed of:
An acrylonitrile polymer solution in which the concentration of the acrylonitrile polymer is 18% by mass or more and 26% by mass or less, and the absorbance calculated by the following method is 40 or more and 50 or less:
Method for calculating absorbance The acrylonitrile-based polymer solution is diluted 20-fold by mass with the solvent, placed in a cell having a thickness of 1 cm, the absorbance A ₃₅₀ at a wavelength of 350 nm is measured, and the absorbance is calculated using Equation 4 below. calculate:
(Formula 4)
Absorbance = absorbance A ₃₅₀ / (mass of acrylonitrile polymer in 1 g of acrylonitrile polymer solution before dilution (g) × mol amount of carboxylic acid (mol) in 1 mol of acrylonitrile polymer).   The acrylonitrile-based polymer solution according to claim 13, wherein the solvent is dimethylformamide, dimethylacetamide, or dimethylsulfoxide.