JP2020015998A - Method for producing synthetic fiber - Google Patents

Abstract

To provide a method for producing a synthetic fiber capable of inhibiting air bubbles and undissolved matters in a spinning dope from being caused to produce synthetic fibers having a high quality.SOLUTION: In a method for producing a synthetic fiber by mixing and dissolving a solid polymer and a liquid solvent while maintaining them in a reduced pressure state from the beginning to prepare a spinning dope and then subjecting the spinning dope to spinning and drawing; the polymer and the solvent before mixing and dissolving stay preferably in a vacuum state of -0.02 MPa or less, and the polymer and the solvent before mixing and dissolving are preferably deaerated in advance respectively at -0.02 MPa or less; the polymer is preferably powdery or pelletized; the deaerated polymer is added preferably at a melting point of the solvent or higher to the melting point + 30°C, and the polymer is added to the solvent at a rate of 200 to 1200 g/min; and the synthetic fiber is preferably a carbon fiber precursor fiber.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a synthetic fiber using a solution spinning method.

  In the case of producing synthetic fibers using the solution spinning method, it is necessary to prepare a spinning dope first, but there are roughly the following two types. A method in which a polymer is solution-polymerized using a solvent used in spinning, and a method in which a spinning stock solution is used as it is, and a polymer which is once produced by suspension polymerization and solidified, is then redissolved in a solvent used in spinning. This method is used as a spinning solution. These methods are appropriately selected depending on cost, required time, handleability, and the like. However, when unreacted monomers and air bubbles are generated, there is a problem that not only adversely affects the production process of the synthetic fiber but also lowers the quality of the obtained synthetic fiber.

  In particular, this is a problem when producing acrylonitrile-based fibers that are precursor fibers for carbon fibers. This is because the deterioration of the quality of the acrylonitrile-based precursor fiber greatly affects not only the processability but also the physical properties of the final carbon fiber. Needless to say, carbon fibers have attracted attention in many fields as reinforcing fibers of composite materials, and high physical properties such as strength, elastic modulus and heat resistance are required. In particular, acrylonitrile-based carbon fiber using acrylonitrile-based fiber as the precursor fiber is excellent in strength, etc., so as a reinforcing fiber for composite materials, in addition to sports applications, aerospace applications, automobiles, civil engineering, pressure vessels , Wind turbine blades and other general industrial applications.

  The acrylonitrile-based fiber to be the precursor fiber is obtained by the solution spinning method described above, and when bubbles or undissolved substances are generated in the spinning solution preparation step, or when there is an excessive unreacted substance, This not only adversely affects the production process of the polyacrylonitrile-based fiber, but also degrades the acrylonitrile-based fiber itself. Then, there is a problem in that it becomes a defect in the subsequent process of manufacturing the carbon fiber and causes a decrease in the strength of the carbon fiber.

  For example, in order to solve this problem, Patent Literature 1 and the like propose a method of dispersing a polymer solution in a degassing tank that has been depressurized to reduce excessive unreacted substances. However, this polymer solution has a high viscosity, and such a treatment could not sufficiently suppress the generation of bubbles and the like. There is also a problem that the physical properties of the finally obtained synthetic fiber deteriorate.

JP-A-2002-363214

  An object of the present invention is to provide a method for producing high-quality synthetic fibers by suppressing the generation of bubbles and undissolved substances in a spinning dope.

  The method for producing a synthetic fiber according to the present invention is characterized in that a solid polymer and a liquid solvent are mixed and dissolved while maintaining a reduced pressure state from the beginning to form a stock spinning solution, and then spinning and drawing.

  Further, it is preferable that the polymer and the solvent before mixing are in a vacuum state of −0.02 MPa or less, and the polymer and the solvent before mixing and dissolving are each degassed in advance at −0.02 MPa or less. The polymer is preferably in the form of powder or pellets, and the degassed polymer is charged at a temperature equal to or higher than the melting point of the solvent to a melting point + 30 ° C., and the charging rate of the polymer to the solvent is 200 to 1200 g / min. Is preferred. And it is preferable that a synthetic fiber is a carbon fiber precursor fiber.

  ADVANTAGE OF THE INVENTION According to this invention, the production | generation of the bubble and the undissolved material in a spinning stock solution is suppressed, and the manufacturing method of a high quality synthetic fiber is provided.

  The method for producing a synthetic fiber of the present invention is a method of mixing and dissolving a solid polymer and a liquid solvent from the beginning while maintaining a reduced pressure to form a stock spinning solution, followed by spinning and drawing.

  Here, the polymer is a polymer necessary for the synthetic fiber, and the solvent is one that dissolves the polymer in a spinning solution during spinning. In the present invention, it is preferable that each of the polymers and the solvent is in a reduced pressure state before being mixed.

  Further, in the production method of the present invention, it is preferable that both the polymer and the solvent are kept in a vacuum state of -0.02 MPa or less. In particular, it is preferable that the polymer and the solvent are each degassed in advance at -0.02 MPa, and neither of them contains air. The state of the polymer used at this time is preferably a powder or a pellet.

  In the present invention, by thus dissolving the mixture of the polymer and the solvent under reduced pressure, it has become possible to minimize the generation of bubbles in the spinning dope. As a result, a high-quality synthetic fiber having no fluff and no break in the spinning process can be obtained. The present invention is particularly effective for carbon fiber precursor fibers composed of an acrylonitrile-based polymer, and in the subsequent flame-proofing step and carbonizing step, there are few defects such as generation of fluff, and finally high strength and high quality Can be obtained.

  Each requirement of the synthetic fiber production method of the present invention will be described in more detail.

(polymer)
The polymer used in the production method of the present invention is not particularly limited as long as it has a fiber-forming property, but the shape is preferably a powder or a pellet. As for the size of the powder, it is preferable that the diameter is 1000 μm or less, and it is particularly preferable that the powder be in the range of 1 to 800 μm. The size of the pellet is preferably 10 mm square or less, particularly preferably 5 mm square or less. Although a slurry polymer can be used, the effect of the present invention is limited because the spinning solution has a low viscosity.

  The polymer used in the present invention is a polymer that can be spun into a synthetic fiber, and is a polymer that can be dissolved in a solvent to form a spinning stock solution. In particular, the present invention is effectively used with an acrylonitrile-based polymer.

  The acrylonitrile-based polymer particularly preferably used in the present invention is a polymer containing acrylonitrile as a main component, and acrylonitrile is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95 to 99% by mass. It is preferable that the polymer is contained by mass%. The acrylonitrile-based polymer preferably contains a comonomer component that can be copolymerized with acrylonitrile having a vinyl skeleton, so that solubility in a solvent can be improved. At this time, the content of the copolymerizable comonomer component is preferably 1 to 20% by mass, more preferably 1 to 10% by mass. Specific examples of such a comonomer copolymerizable with acrylonitrile include, for example, acids such as acrylic acid and itaconic acid and salts thereof, acrylates such as methyl acrylate and ethyl acrylate, and amides such as acrylamide. The required composition can be adopted according to the desired fiber characteristics. In particular, it is preferable to copolymerize methyl acrylate and itaconic acid. On the other hand, if the copolymerization ratio is too high, for example, structural defects tend to increase in carbon fibers produced by subsequent firing, and the copolymerization ratio is determined in consideration of the carbon fiber structure and solubility, etc. It should be.

  The molecular weight of the polymer to be a polymer is preferably 100,000 or more by weight average molecular weight, more preferably 150,000 to 1,000,000, particularly preferably 200,000 to 800,000. The value of z-average molecular weight / weight-average molecular weight (Mz / Mw) is preferably greater than 1.4, and more preferably in the range of 1.5 to 2.0. In order to adjust the value of Mz / Mw, it is also a preferable method to mix two or more types of polymers having different molecular weight distributions with different degrees of polymerization. The production method of the present invention is particularly effective when the molecular weight distribution has a wide range. The polymer is preferably an acrylonitrile-based polymer.

  When an acrylonitrile-based polymer is used in the production method of the present invention, the polymerization step is preferably aqueous suspension polymerization. It is possible to improve the productivity and simplify the washing step of the residual monomer. In the case of aqueous suspension polymerization, an acrylonitrile polymer solid can be easily obtained at room temperature. Mixing of the solvent with the acrylonitrile-based polymer becomes easier.

(solvent)
Here, the solvent used in the present invention is a solvent that dissolves the above-mentioned fiber-forming polymer and becomes a spinning stock solution. For example, when an acrylonitrile-based polymer is used as the polymer, an aqueous solution such as an aqueous zinc chloride solution and an organic solvent such as dimethylacetamide, dimethylsulfoxide, and dimethylformamide can be used. The solvent can be appropriately selected according to the purpose, but in the present invention, it is preferable to use an organic solvent, and particularly preferable to use dimethyl sulfoxide. In particular, when an acrylonitrile-based polymer is employed as the polymer, the copolymerization ratio can be reduced, the structural defects of the fiber are suppressed, and the strength of the finally obtained carbon fiber can be increased. In addition, when the dry-wet spinning method is employed to increase the polymer concentration, there is a problem that undissolved matter is easily generated. However, by using a highly soluble solvent such as dimethyl sulfoxide, it has become possible to further reduce such undissolved substances.

(Spinning stock solution preparation process)
In the synthetic fiber production method of the present invention, using the solid polymer as described above, further mixing and dissolving the solid polymer and the liquid solvent while maintaining the reduced pressure state from the beginning, the spinning stock solution Is very important. Further, in the present invention, it is preferable that the polymer and the solvent before mixing are each degassed at −0.02 MPa in advance, and that the air and the air are not contained in any of them. The deaeration time of the polymer is preferably 5 minutes or more, more preferably 10 to 90 minutes, and particularly preferably 30 to 60 minutes. Further, it is preferable that the pressure reducing condition is a condition under a pressure of −0.10 to −0.02 MPa. Unlike the present invention, when the polymer is not degassed in advance, it takes a long time for defoaming after dissolution, and complete degassing cannot be confirmed by visual observation, so that complete removal becomes difficult.

  When such a degassed polymer is mixed with a solvent, the temperature of the solvent is preferably from the melting point to the melting point + 30 ° C. or less, more preferably from the melting point to the melting point + 20 ° C. or less, more preferably from the melting point. Preferably, the temperature is 5 to 10 ° C. higher.

  Specifically, the temperature of the solvent or the spinning solution used in the polymerization is preferably in the range of 20 to 45 ° C. When the temperature of the spinning solution is lower than the melting point of the solvent, the solvent becomes solid, the power load of the stirrer increases, and a special stirrer is required. If the temperature is higher than necessary, the dissolution of the polymer starts immediately at the stage when the polymer is charged into the solvent, and the polymer may not be uniformly dispersed in the solvent and may form a lump. Once such lumps are generated, it becomes difficult to uniformly dissolve the polymer in the solvent.

  The charging rate of the polymer into the solvent is preferably from 200 to 1200 g / min, and more preferably from 200 to 600 g / min. If the charging speed is low, the spinning dope preparation time becomes long, and there is a problem in terms of productivity. If the charging rate is too high, the polymer is not uniformly dispersed in the solvent but forms a lump, and it is difficult to uniformly dissolve the polymer in the solvent.

  The concentration of the polymer at the time of preparing the spinning solution is not particularly limited, but is preferably 15 to 40% by mass, and more preferably 16 to 26% by mass. When the polymer concentration is high, good productivity can be obtained, and a coagulated yarn in which the inside of the fiber is dense can be obtained in the spinning step. Conversely, if the polymer concentration is too high, the dissolution in the solvent does not proceed, and a gel-like mass is likely to be generated. In the production method of the present invention, it is preferable to extract a small amount of the dope as a spinning dope and observe it with an optical microscope in order to confirm whether or not the deaeration is sufficient.

(Spinning process)
As the spinning step in the production method of the present invention, a dry spinning method of coagulating a spinning solution in a gas phase, a wet spinning method of coagulating a spinning solution in a coagulation solution, or a dry-wet spinning method using a gas phase and a coagulation solution is used. It can be performed using: In particular, the production method of the present invention is effective in a wet spinning method or a dry-wet spinning method in which fibers are coagulated in a solution.

  Further, with respect to specific embodiments thereof, the details of the case of producing carbon fiber precursor fibers will be described below.

  In this case, the spinning dope prepared as described above becomes a spinning dope containing a polyacrylonitrile-based polymer as a polymer. The spinning solution is spun and drawn to produce a carbon fiber precursor fiber.

  As the spinning method, a known method can be used, and generally, a spinning solution is spun from a spinneret. More specific spinning methods include a dry spinning method in which the spinning solution is coagulated in a gas phase, a wet spinning method in which the spinning solution is coagulated in a coagulation solution, or a gas phase, depending on the type and use of the solvent used. And a dry-wet spinning method using a coagulation liquid.

  In this case, dimethyl sulfoxide is preferably used as a solvent for the polyacrylonitrile polymer. In particular, when the dry-wet spinning method is used, it is necessary to increase the viscosity of the spinning solution as compared with the wet spinning method, and it is preferable to use dimethyl sulfoxide having high solubility. Because of the high solubility, the degree of freedom of the content concentration is high, and a wider range of viscosity control is possible. Further, it is easy to keep the viscosity of the spinning stock solution low, and it is easy to completely remove bubbles after preparing the spinning stock solution, and the present invention is more effective.

(Solidification process)
When a wet or dry-wet spinning method is employed, the coagulation liquid used in the coagulation bath after the spinning is preferably an aqueous solution or an aqueous solution containing an organic solvent. More specifically, examples include an aqueous zinc chloride solution, dimethylacetamide, dimethylsulfoxide, dimethylformamide and the like. Particularly, the coagulating liquid is preferably dimethyl sulfoxide, since the melting point of dimethyl sulfoxide may be around room temperature.

  The spinneret for extruding the spinning dope preferably has 100 to 100,000 discharge holes, more preferably 1000 to 8000 discharge holes, and particularly preferably 3000 to 50,000 discharge holes. The diameter of the discharge hole of the die is 0.02 to 0.5 mm. If the pore size is 0.02 mm or more, the adhesion between the discharged yarns is unlikely to occur, so that acrylonitrile-based fibers having excellent homogeneity can be obtained. When the pore diameter is 0.5 mm or less, occurrence of spun yarn breakage is suppressed, and spinning stability can be maintained.

  Next, the coagulated yarn obtained by the above method is preferably subjected to washing and drawing. The stretching method is preferably performed in a coagulation bath or a washing bath, particularly when a wet spinning method or a dry-wet spinning method is employed. The maximum temperature for stretching in such a bath is preferably in the range of 60 to 100 ° C, more preferably in the range of 70 to 100 ° C, and particularly preferably in the range of 80 to 100 ° C. The stretching ratio is preferably 10 to 20 times, particularly preferably 13 to 17 times. In the present invention, since the spinning dope has no air bubbles, it is possible to draw at a higher magnification.

  The drawn yarn obtained by the above method is preferably applied with an oil agent in an oil agent applying step. The method of applying the oil agent is not particularly limited, but a method of dipping the yarn in an aqueous solution containing the oil agent to bring the fiber surface into contact with the oil agent or the like can be employed. The type of the oil agent is preferably a silicone oil agent as a main component from the viewpoint of adhesion between single fibers, heat resistance, releasability, and process passability.

  As the silicone oil agent preferably used in the present invention, amino-modified silicone, epoxy-modified silicone and ether-modified silicone are preferable, and two or more of these may be mixed. Further, the oil agent adhesion amount is preferably 0.01 to 10.0 wt%, more preferably 0.1 to 5.0 wt%, and more preferably 0.2 to 1.0 wt% with respect to the fiber weight. Is particularly preferred. By controlling the amount of the oil agent adhered in this range, yarn breakage in the spinning step and the subsequent flameproofing step, generation of fluff can be efficiently suppressed, and high-quality carbon fiber precursor fibers and carbon fibers can be obtained. it can. If the amount of the oil agent is small, the oil agent does not sufficiently adhere to the fiber surface, so that yarn breakage and fuzz in the spinning step and the subsequent flame-proofing step tend to increase, and on the other hand, the amount of the oil agent If the amount is too large, it tends to accumulate on the surface of a fiber transporting roller or a guide in a spinning step or a flame-proofing step, causing a problem that fibers are wound and cause a yarn breakage.

  In the oil agent application step, a further stretching process (post-stretching process) may be performed on the drawn yarn to which the oil agent has been applied. The stretching method in the subsequent stretching step is not particularly limited, but is preferably steam stretching. When performing the steam stretching treatment, the saturated steam pressure is preferably set to 0.15 to 0.8 MPa.

  The stretching ratio in the steam stretching treatment is preferably 1.5 to 10 times, more preferably 1.8 to 5 times, and still more preferably 2.0 to 3.0 times. The temperature of the steam stretching treatment is preferably from 105 to 200C, more preferably from 110 to 180C.

  The stretching ratio is preferably 10 to 20 times, more preferably 13 to 17 times, as a total stretching ratio through wet stretching or the like immediately after spinning or through drying and post-stretching. The fineness of the precursor fiber after the steam drawing treatment is preferably 0.5 to 1.7 dtex.

  The production method of the synthetic fiber of the present invention as described above can suppress the generation of bubbles in the spinning dope, so that a high-quality synthetic fiber without fluff and single yarn breakage in the spinning process can be obtained. .

  And when the precursor fiber for carbon fiber such as acrylonitrile is obtained by the method for producing a synthetic fiber of the present invention, in particular, by performing a flame-resistant treatment at 180 to 300 ° C. in an oxidizing atmosphere. It can be a flame resistant fiber. Further, the flame-resistant fiber can be converted into a carbon fiber by performing a carbonization treatment at 400 to 2000 ° C. in an inert atmosphere. When the synthetic fiber obtained by the production method of the present invention is a precursor fiber for carbon fiber, the flame-resistant fiber or carbon fiber obtained by using the same does not have fusion, and the yarn breaks during the process. High-quality fiber with a small number of fibers, which can be produced more efficiently by the production method of the present invention.

  Hereinafter, the present invention will be described specifically with reference to examples and the like, but the present invention is not limited to these examples and the like. Various evaluations in the examples and comparative examples were performed by the following methods.

(1) Evaluation of air bubbles in the spinning stock solution After the spinning stock solution was prepared, the spinning stock solution was extracted and observed at 400 times magnification with an optical microscope to confirm the presence or absence of air bubbles.

(2) Viscosity The spinning stock solution was transferred into a 300 mL beaker, the temperature was adjusted in a thermostat so that the spinning stock temperature became 50 ° C., and the viscosity was measured using a viscometer VT-04F manufactured by Rion Co., Ltd., which is a rotational viscometer. .

(3) Single yarn break The number of single yarn breaks per 1 m of the polyacrylonitrile fiber bundle was measured 10 times and averaged. The number of filaments constituting the fiber bundle of the measurement sample was converted to 24000.

(Example 1)
Dimethyl sulfoxide (melting point: 18.5 ° C.) was charged into a stock solution tank, the temperature was adjusted to 25 ° C., and the mixture was stirred, and the pressure in the system was reduced to −0.095 MPa. Subsequently, a powdery acrylonitrile copolymer having an average particle size of 100 μm was charged into a hopper set in the stock solution tank via a ball valve so that the acrylonitrile-based polymer was in a proportion of 20% by mass, and the inside of the hopper was −0. 0.095 MPa and degassed for 10 minutes. The polyacrylonitrile copolymer used had a weight average molecular weight (Mw) of 420,000, a z average molecular weight / weight average molecular weight (Mz / Mw) of 1.7, acrylonitrile 95% by mass, methyl acrylate 4% by mass, and itaconic acid 1 % By mass.

  Next, while the stock solution tank and the hopper were both kept under reduced pressure, the opening degree of the ball valve was adjusted so that the polymer feeding speed was 300 g / min, and polyacrylonitrile in the hopper was fed into dimethyl sulfoxide in the stock solution tank.

  The temperature was raised to 80 ° C. while stirring while the pressure in the system was reduced to −0.095 MPa to prepare a spinning stock solution. The viscosity of the obtained spinning dope was 430 poise at 50 ° C., and no air bubbles and undissolved acrylonitrile-based polymer were found in the spinning dope.

  A spin-drying solution is withdrawn from the bottom of the stock solution tank, the obtained spinning solution is discharged from a spinneret having a hole diameter of 150 μm and a number of holes of 3,000, and the distance between the spinneret and the surface of the coagulating liquid is set to 10 mm. Spinning was performed to obtain a coagulated yarn. The coagulated yarn was then desolvated in a water washing tank and stretched 4.0 times, and then immersed in a silicone oil bath to apply an oil. Then, it was dried by a heating roller and post-stretched 3.0 times in steam at a pressure of 0.25 MPa to obtain an acrylonitrile fiber bundle.

  The obtained acrylonitrile-based fiber bundle was a high-grade acrylonitrile-based fiber with zero breakage of single yarn.

(Example 2)
An acrylonitrile-based fiber for a carbon fiber precursor was obtained in the same manner as in Example 1, except that the solvent temperature at the time of charging the polymer was increased from 25 ° C to 40 ° C in Example 1. No air bubbles and undissolved acrylonitrile-based polymer were found in the spinning solution before spinning, and the obtained acrylonitrile-based fiber bundle was a high-quality acrylonitrile-based fiber with no single yarn breakage. Was.

  In addition, from Example 2, when the dissolving step was performed at 60 ° C. with the temperature further increased, the spinning was not performed because the polymer was not completely dissolved due to the formation of lumps.

(Example 3)
An acrylonitrile fiber for a carbon fiber precursor was obtained in the same manner as in Example 1 except that the pressure in the system was changed from -0.095 MPa to -0.070 MPa in Example 1.

  No air bubbles and undissolved acrylonitrile-based polymer were found in the spinning solution before spinning, and the obtained acrylonitrile-based fiber bundle was a high-quality acrylonitrile-based fiber with no single yarn breakage. Was.

(Example 4)
An acrylonitrile fiber for a carbon fiber precursor was obtained in the same manner as in Example 1, except that the charging rate of the polymer into the stock solution tank was changed from 300 g / min to 600 g / min in Example 1.

  No air bubbles and undissolved acrylonitrile-based polymer were found in the spinning solution before spinning, and the obtained acrylonitrile-based fiber bundle was a high-quality acrylonitrile-based fiber with no single yarn breakage. Was.

  In addition, from Example 4, when the dissolving step was performed by further increasing the polymer charging rate, the spinning was not performed because the lumps were formed and the polymer could not be completely dissolved.

(Comparative Example 1)
An acrylonitrile-based fiber for a carbon fiber precursor was obtained in the same manner as in Example 1, except that the pressure in the system was changed to 0.00 MPa (normal pressure). Bubbles having a diameter of 2 μm to 40 μm were observed in the obtained spinning dope, and spinning was not performed.

  Subsequently, the pressure in the system after the preparation of the stock solution was degassed from 0.00 MPa (normal pressure) to −0.095 MPa. However, bubbles having a diameter of 2 μm to 20 μm remained in the stock solution for spinning. Implementation was discontinued.

Claims (6)

  A method for producing synthetic fibers, comprising mixing and dissolving a solid polymer and a liquid solvent from the beginning while maintaining a reduced pressure to form a stock spinning solution, followed by spinning and drawing.   The method for producing a synthetic fiber according to claim 1, wherein the polymer and the solvent before mixing are in a vacuum state of -0.02 MPa or less.   The method for producing a synthetic fiber according to claim 1 or 2, wherein the polymer and the solvent before mixing and dissolving are degassed in advance at -0.02 MPa or less, and none of them contains air.   The method for producing a synthetic fiber according to any one of claims 1 to 3, wherein the polymer is in a powder form or a pellet form.   The method for producing a synthetic fiber according to any one of claims 1 to 4, wherein the degassed polymer is charged at a temperature equal to or higher than the melting point of the solvent to a melting point + 30 ° C, and the rate of charging the polymer into the solvent is 200 to 1200 g / min. .   The method for producing a synthetic fiber according to any one of claims 1 to 5, wherein the synthetic fiber is a carbon fiber precursor fiber.