JP2015030926A - Method of producing dope for acrylic fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve dispersibility and solubility of an acrylonitrile-based polymer in a solvent without modifying properties of the acrylonitrile-based polymer and step passability of a dope for polyacrylonitrile-based fibers in a dope filtration step.SOLUTION: A process of producing a dope for polyacrylonitrile-based fibers consists of a step of dispersing an acrylonitrile-based polymer in a solvent cooled to -20°C to 25°C and a step of heating the dispersion of the acrylonitrile-based polymer to dissolve the acrylonitrile-based polymer, and the acrylonitrile-based polymer is cooled to 0°C or lower to disperse in the solvent.

Description

  The present invention relates to a method for producing a spinning dope for acrylic fibers used in the production of clothing fibers, precursor fiber bundles for carbon fibers, and the like.

Acrylic fibers have excellent bulkiness similar to wool, texture, dyeing clarity, and the like, and are used in a wide range of applications. Furthermore, the acrylic fiber is also used as a carbon fiber precursor fiber bundle (precursor), and a polyacrylonitrile-based carbon fiber can be obtained by carbonizing the acrylic fiber in a firing step. Polyacrylonitrile-based carbon fiber is superior in strength, elastic modulus, heat resistance, etc., and as a reinforcing fiber for composite materials, it is used in general applications such as automobiles, civil engineering buildings, pressure vessels, windmill blades, in addition to sports and aerospace applications. Widely deployed for industrial use.

  Acrylic fibers are generally obtained by drawing a spinning stock solution obtained by dissolving an acrylonitrile polymer in an organic or inorganic solvent into wet or dry-wet spinning and shaping it into a fiber, and then drawing, washing, and drying and densifying. As the solvent, amide solvents such as dimethylformamide and dimethylacetamide and organic solvents such as dimethyl sulfoxide are widely used.

  The foreign matter such as dust contained in the spinning dope and the gel-like material generated by the thermal degradation of the spinning dope not only adversely affect the production of the carbon fiber precursor acrylic fiber. It becomes a surface defect point and an intrinsic defect point in the manufacturing process, and causes a decrease in strength of the carbon fiber. Therefore, it is common to remove the above-mentioned foreign matters and gels by filtering the spinning dope with a filter material.

  It is known that the solubility of the acrylonitrile-based polymer in the solvent has a great influence not only on the performance of the resulting fiber product but also on the process passability in the filtration process of the spinning dope. Therefore, the acrylonitrile-based polymer as a spinning raw material is required to have excellent solubility in a solvent.

Patent Document 1 includes 95 to 99.5% by mass of an acrylonitrile monomer unit, 0.5 to 5% by mass of an acrylamide monomer unit, and a vinyl monomer unit copolymerizable with acrylonitrile as an optional component. The bulk specific gravity is greater than 0.30 g / cm ³ and not greater than 0.40 g / cm ³ , the average particle size is not less than 30 μm and not more than 40 μm, and the thickness from the surface is 5 μm. It is disclosed that an acrylonitrile-based polymer having a surface layer portion porosity of 30% or less is improved in dispersibility in a solvent and easily dissolved. However, the production conditions for the acrylonitrile polymer must be changed, and if the monomer composition of the acrylonitrile polymer is changed, the solidification and stretchability in the spinning process and the reactivity in the firing process are large. May have an effect.

  In Patent Document 2, the dispersibility of the acrylonitrile polymer in the solvent is improved by allowing the acrylonitrile polymer to continuously and freely fall freely, ejecting the solvent, and mixing the acrylonitrile polymer in the middle of the dropping with a jet flow. A technique is disclosed.

JP 2009-185273 A JP 2003-340253 A

An object of the present invention is to improve the dispersibility and solubility of an acrylonitrile polymer in a solvent without changing the properties of the acrylonitrile polymer, and to improve the process passability in the filtration process of the spinning solution for acrylic fibers. And

The method for producing the spinning solution for polyacrylonitrile fiber of the present invention includes a step of cooling the temperature of the acrylonitrile polymer to 10 ° C. or less, a step of dispersing the acrylonitrile polymer in a solvent of −20 ° C. or more and 25 ° C. or less, This is a method for producing a spinning dope for acrylic fiber, which in turn includes a step of dissolving an acrylonitrile polymer by heating an acrylonitrile polymer dispersion.

The method for producing a spinning solution for polyacrylonitrile fiber of the present invention is preferably a step of cooling the temperature of the acrylonitrile polymer to -20 ° C or higher and 5 ° C or lower.

  By controlling not only the temperature of the solvent for dispersing the acrylonitrile polymer, but also the temperature of the acrylonitrile polymer at a low temperature, the properties of the acrylonitrile polymer are not changed, and the dispersibility of the acrylonitrile polymer in the solvent and Solubility can be improved and the process passability in the filtration process of the spinning solution for acrylic fibers can be improved.

Hereinafter, the present invention will be described in detail.

  The method for producing a spinning dope for acrylic fibers of the present invention is a method for producing a spinning dope by heating an acrylonitrile polymer dispersion (sometimes referred to simply as a dispersion) to dissolve the acrylonitrile polymer. The dispersion is obtained by dispersing an acrylonitrile-based polymer in a solvent.

  The acrylonitrile-based polymer contains 90% by mass or more, preferably 95% by mass or more of acrylonitrile monomer units. When such an acrylonitrile-based polymer is used as a raw material, a high-quality carbon fiber having sufficient performance can be finally obtained. If the ratio of the acrylonitrile unit is less than the above range, the copolymer component other than the acrylonitrile unit tends to be a defect point, and the quality and performance of the obtained carbon fiber may be insufficient. A copolymerization component will not be specifically limited if it is a monomer which has an ethylenically unsaturated bond.

  The concentration of the acrylonitrile polymer in the spinning dope is preferably 13 to 25% by mass. If it is 13% by mass or more, it is possible to prevent a decrease in spinnability due to a decrease in elongational viscosity, to suppress the amount of solvent used, and when a spinning stock solution is solidified, voids are generated inside it. It is also possible to prevent the quality from deteriorating. Moreover, if it is 25 mass% or less, it can spin without making shear viscosity and elongation viscosity too high, and can also ensure the solubility of an acrylonitrile-type polymer.

As the solvent, it is preferable to use dimethylformamide, dimethylacetamide, or dimethylsulfoxide, which has a high solidification rate and is easy to improve productivity, and may be used alone or in combination.

  The temperature of the solvent when the acrylonitrile polymer is dispersed in the solvent is preferably -20 ° C or higher and 25 ° C or lower. By setting the temperature to −20 ° C. or higher, the viscosity of the dispersion liquid increases moderately due to the slight progress of dissolution, and density spots due to precipitation of the acrylonitrile-based polymer in the dispersion liquid can be prevented. Moreover, the excess viscosity increase of a dispersion liquid can be suppressed by setting it as 25 degrees C or less, and process passability improves.

The temperature of the acrylonitrile polymer when the acrylonitrile polymer is dispersed in the solvent is preferably -20 ° C or higher and 5 ° C or lower, more preferably 0 ° C or lower. By setting it as 5 degrees C or less, the progress of melt | dissolution of an acrylonitrile-type polymer can be suppressed, and the viscosity raise of a dispersion liquid can be suppressed. Moreover, by setting it as -20 degreeC or more, the viscosity of a dispersion liquid will increase moderately by progress of slight melt | dissolution, and the density spot by sedimentation of the acrylonitrile-type polymer in a dispersion liquid can be prevented.
The method for cooling the acrylonitrile polymer is preferably performed in dehumidified dry air to prevent condensation.
After the acrylonitrile-based polymer is cooled, it is preferable to continuously dissolve it in the solvent.

  The temperature for heating the dispersion is preferably 60 ° C. or more and 125 ° C. or less, and the heating time is preferably 5 minutes or more and 12 minutes or less. By setting the heating temperature 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, the amount of undissolved material can be reduced by setting the heating time to 5 minutes or longer, and the generation of gel-like material can be suppressed by setting the heating time to 12 minutes or shorter.

  The spinning dope obtained by heating the dispersion is filtered with a filter material to remove foreign matters such as dust contained in the spinning dope and gel-like substances generated by thermal degradation of the spinning dope itself. The spinning dope thus obtained is spun and used as clothing fibers, precursor fiber bundles for carbon fibers, or the like.

As described above, according to such a method for producing a spinning dope for acrylic fiber, the dispersibility and solubility of the acrylonitrile polymer in the solvent are improved without changing the properties of the acrylonitrile polymer. The process passability in the filtration process of the fiber spinning dope can be improved.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples.

(Dispersibility evaluation)
Evaluation of dispersibility of the acrylonitrile-based polymer in a solvent was performed using a rheometer AR550 manufactured by TA Instruments. The measurement was performed using a cone having a diameter of 40 mm and a cone angle of 2 ° at a shear rate of 0 ° C. and 0.1 to 1000 (/ sec), and using a shear viscosity (Pa · s) of 10 (/ sec) as an index. did. The smaller the shear viscosity, the higher the dispersibility of the acrylonitrile polymer.

(Filterability evaluation)
The filterability of the spinning dope is the value of the differential pressure increase when 0.65 kg is passed through a metal nonwoven fabric filter (Nasslon manufactured by Nippon Seisen) with a 90% collection efficiency at a rate of 1 kg / mm ² · hr. Was evaluated as the degree of pressure increase (MPa). The smaller the pressure increase, the better the filtration process passability.

(Example)
The acrylonitrile polymer cooled to 0 ° C. was uniformly dispersed at a solid content of 23% in dimethylformamide cooled to 0 ° C., and a dispersion was obtained to evaluate the dispersibility. Further, this dispersion was passed through a pipe having an inner diameter of 12 mm with a jacket capable of circulating the heat medium, heated to 110 ° C. and dissolved in a residence time of 9 minutes to obtain a spinning dope, and the filterability was evaluated. The results are shown in the table.

(Comparative example)
Evaluation was performed in the same manner as in the Examples except that the temperature of the acrylonitrile-based polymer was changed to 25 ° C.

Claims (2)

A step of cooling the temperature of the acrylonitrile polymer to 10 ° C. or lower, a step of dispersing the acrylonitrile polymer in a solvent of −20 ° C. or higher and 25 ° C. or lower, and heating the acrylonitrile polymer dispersion to obtain an acrylonitrile polymer. A method for producing a spinning dope for acrylic fiber, which has a step of dissolving in order. The method for producing an acrylic fiber spinning dope according to claim 1, wherein the temperature is a temperature of the acrylonitrile-based polymer cooled to -20 ° C or higher and 5 ° C or lower.