JP2012251263A - Method for producing polyamide fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently producing a polyamide fiber excellent in mechanical properties.SOLUTION: There is provided a method for producing a polyamide fiber in which a yarn melt and extruded from a spinneret is cooled, solidified and took-off, and then water is imparted to the yarn before it is wound. In the method, an undrawn fiber which is obtained by a linear extrusion velocity Vp(m/min) and a take-off velocity Vt(m/min) satisfying the relation 10 Vp≤Vt≤500 Vp and to which water is adhered substantially in a rate of 0.1 wt.% to 10.0 wt.% is drawn.

Description

  The present invention relates to a method for producing a polyamide fiber, and more particularly to a method for stably producing a polyamide fiber having excellent mechanical properties.

  Fibers made of thermoplastic polymers such as polyester and polyamide have an excellent balance of properties, so they have extremely high industrial value and are widely used not only for clothing but also for non-garments (such as industrial materials). Has been. In particular, since polyamide fibers have characteristics such as wear resistance, weather resistance and durability, they can be used in applications that are subjected to relatively harsh conditions such as for automotive parts, fishery, materials, and agriculture. Many have been applied.

  As a method for fiberizing a polyamide resin, melt spinning is generally employed in which the resin is melted and then discharged from a spinneret, and the discharged yarn is cooled and solidified and wound. Furthermore, in order to generate a fiber structure and impart practical properties, it is common to heat-draw in a set with melt spinning.

  In fiber products, mechanical properties such as strength and elongation are properties that correlate with properties in the case of a fiber product, and are considered to be one of important properties. For this reason, various proposals have been made regarding methods for efficiently producing polyamide fibers having high mechanical properties, particularly for polyamide fibers for industrial materials.

  As described above, it is not an exaggeration to say that it is theoretically a stretching process to impart substantial mechanical properties, and it is important to set stretching conditions. Focusing on the technology related to the improvement of mechanical properties, the technology related to multi-stage stretching in which stretching is performed in multiple times for the purpose of highly orienting the fiber structure so as not to cause defects in the fiber structure etc. There are many.

In Patent Document 1, in a method for producing a high-strength polyamide fiber that is melt-spun and subjected to multi-stage drawing of two or more stages by a multi-stage roll, the draw ratio until the final draw is 80% or more of the total draw ratio, and the final stage draw Proposed a technique characterized by stretching at a low strain of 300 min ⁻¹ . The purpose of this technology is to slow the orientation of the fiber structure and reduce the generation of defects such as voids or cracks by reducing the strain rate in the final stage of stretching where the fiber structure is most oriented. It is said. Certainly, in the technique of Patent Document 1, by reducing the deformation of the fiber in a state in which the fiber structure is almost completed, by suppressing the generation of the above-described defects, it is possible to prevent the occurrence of yarn breakage and the like. Magnification stretching is possible. However, polyamide fibers that have high hydrophilicity and absorb moisture in the air during the spinning process and cause crystallization may cause the stretching behavior in the initial stage to become unstable, and this control cannot be ignored. . This is presumably because the water absorption behavior during the yarn making process is often non-uniform between the single fibers and the fiber cross section, and the fiber structure difference resulting from this causes the drawing behavior to fluctuate and generate defects. For this reason, in the technique described in Patent Document 1, the effect may be insufficient in terms of the stability of yarn production. In addition, since the final draw ratio at which the molecular chain (fiber structure) can be oriented with high efficiency is reduced, there are cases where the restriction can be made in terms of improving the mechanical properties.

  As a technique for suppressing the unevenness of the fiber structure in the unstretched stage as described above, there is a proposal for the purpose of forcibly causing crystallization by attaching moisture to the unstretched stage in advance.

  Patent Document 2 proposes a technique in which water is attached by a water-based emulsion when the polyamide fiber is not yet stretched, and is subsequently thermally stretched. The technique of Patent Document 2 discloses that a polyamide fiber having excellent mechanical properties can be obtained, and that a stable fiber structure that contributes to the development of these properties is easily formed.

  When water is applied to polyamide unstretched fibers and heat-stretched, a stable fiber structure is formed, and improvement in abrasion resistance and strength retention is expected, but it is difficult to obtain high-strength polyamide fibers Met. This is because the unstretched polyamide fiber is easily crystallized at the time of hot drawing, and the fiber structure is formed before substantial drawing, so that it becomes a low-oriented fiber structure. In Patent Document 2, such problems are solved by controlling the time from application of the aqueous emulsion to stretching to moderately and uniformly permeate water between single fibers and in the fiber cross section. ing. Certainly, in the method of Patent Document 2, it is possible to collect polyamide fibers having excellent mechanical properties. However, since heating roller stretching is adopted, even before the draw point, even if water adheres uniformly, moisture evaporates from the surface in contact with the heating roller in the preheating stage before stretching. It will be. For this reason, at the draw point, the moisture permeability is uneven between the single fibers and in the fiber cross section, and uniform stretching may be difficult. Furthermore, in order to precisely control the time to the draw point, there has been a problem that it is necessary to precisely control the behavior of the running yarn by the peripheral speed of the roller. Furthermore, a special device may be required for exhausting the oil or the like evaporated on the heating roller.

  On the other hand, in Patent Document 3, after the yarn melt-spun from the die is passed through a high-temperature atmosphere by a heating cylinder, the yarn is passed through a heating-drying atmosphere in which a substantially dry gas exists, There has been proposed a method characterized by attaching moisture and drawing after taking up at a take-up speed of 1000 m / min or less. In this method, the running yarn is once dried so that moisture adhesion to the running yarn can be easily and appropriately controlled. As a result, it is described that polyamide fibers excellent in strength retention and thermal dimensional stability can be collected in addition to excellent mechanical properties such as high strength and high elongation. Certainly, in the method of Patent Document 3, the orientation of the molecular chain can be promoted and the adhesion (penetration) of the water can be simplified by passing through the heat-dried atmosphere. For this reason, uniformization of moisture adhesion, that is, fiber structure formation by moisture adhesion can be easily controlled. However, since the birefringence control of the undrawn fiber described in Patent Document 3 is eventually performed by the spinning tension, it often varies easily due to roller vibration and dirt. In particular, in the case of multifilaments used for industrial material applications, since the number of filaments is very large, it is very difficult to make birefringence uniform between single fibers. Further, similarly to Patent Document 2, the method of Patent Document 3 is a technique that substantially uses a heating roller, and thus the water adhering to the unstretched fibers may be biased.

JP-A-11-1725232 (Claims) JP-A-9-49112 (Claims) Japanese Patent Laid-Open No. 10-18126 (Claims)

  The subject of this invention is providing the method which can manufacture efficiently the polyamide fiber excellent in the mechanical characteristic in view of the trouble in the above prior arts.

The problems in the above prior art are solved by the following method according to the present invention.
(1) In a method for producing a polyamide fiber in which moisture is given after cooling and solidifying the yarn melted and discharged from the spinneret before winding, the relationship between the discharge linear speed and the take-off speed is expressed by the following formula 1. A process for producing a polyamide fiber, characterized in that an unstretched fiber obtained by satisfying and having a substantial water adhesion rate of 0.1 wt% to 10.0 wt% is drawn.
10 Vp ≦ Vt ≦ 500 Vp (Formula 1)
Here, Vp: discharge linear velocity (m / min), and Vt: take-up velocity (m / min).
(2) The method for producing a polyamide fiber according to (1), wherein the undrawn fiber is drawn by infrared light beam irradiation.
(3) The method for producing a polyamide fiber according to (2), wherein the infrared light flux is a carbon dioxide laser.
(4) The method for producing a polyamide fiber according to (3), wherein a carbon dioxide laser having a laser density of 10 W / cm ² to 1000 W / cm ² is irradiated for less than 100 ms from the neck generation position.
(5) The unstretched fiber is stretched by two or more stages of multistage stretching, and when performing the multistage stretching, the relationship between the stretch ratio before the final stretch and the total stretch ratio including the final stretch is expressed by the following formula 2 The method for producing a polyamide fiber according to any one of (1) to (4), wherein:
0.20 Rt ≦ Rf ≦ 0.70 Rt (Formula 2)
Here, Rf: stretch ratio before final stretching, Rt: total stretch ratio.

  According to the present invention, a polyamide having excellent strength retention and fatigue resistance by a stable fiber structure while overcoming the above-mentioned problems of the prior art and having high mechanical properties such as high strength and high elongation. A fiber can be manufactured efficiently.

It is a schematic block diagram which shows one embodiment of the spinning process for implementing this invention. It is a schematic block diagram which shows one embodiment of the extending process for implementing this invention. It is a schematic diagram of the image of the fiber for laser irradiation time calculation method explanation.

Hereinafter, the present invention will be described in detail together with preferred embodiments.
In the production method according to the present invention, it is necessary to use a polyamide resin. Examples of the polyamide herein include nylon 6, nylon 66, nylon 12, nylon 610, nylon 6/66 copolymer, nylon 56, and nylon 410. Copolymers having hexamethylene terephthalamide units such as nylon 6T / 66 copolymer, nylon 6T / 6I copolymer, nylon 6T / M5T copolymer, nylon 6T / 12 copolymer, nylon 66 / 6T / 6I copolymer and nylon 6T / 6 copolymer Coalescence is also preferred. Of these, nylon 6, nylon 66, and mixtures thereof are preferred as highly versatile polyamides. Moreover, while environmental problems are attracting attention, bio-derived polymers such as nylon 56 and nylon 410 are preferable from the viewpoint of environmental problems.

  The degree of polymerization of the polyamide resin used in the present invention has a relative viscosity (ηr) measured at 25 ° C. in a 98% concentrated sulfuric acid solution having a sample concentration of 0.01 g / ml and a range of 1.5 to 7.0. High molecular weight polyamide in the range of 3.5 to 7.0 is preferable from the viewpoint of obtaining mechanical properties that can be practically used for applications that require high strength even in clothing applications (for example, thin fabrics) and industrial applications. More preferred. These polyamide resins are usually used additives such as inorganic materials such as titanium oxide, silica and barium oxide, colorants such as carbon black, dyes and pigments, flame retardants, fluorescent whitening agents, antioxidants, or Various additives such as an ultraviolet absorber may be contained in the polymer.

  FIG. 1 is a schematic block diagram showing an embodiment of a spinning process for carrying out the present invention, and FIG. 2 is a schematic block diagram showing an embodiment of a drawing process for carrying out the present invention. The above-mentioned polyamide resin is fibrillated by the melt spinning machine of FIG. 1, and the fiber structure is highly oriented by the drawing machine of FIG. In FIG. 1 and FIG. 2, in order to simplify the description of the production method of the present invention, the spinning-stretching process is shown separately. Needless to say, it is possible to perform stretching following the spinning process. Yes.

A specific embodiment of the production method of the present invention will be described in detail below with reference to FIGS.
The polyamide resin used for spinning is dried by a vacuum dryer or a hot air dryer as necessary, and charged into the hopper 1. Here, since the polyamide resin has high water absorption, it is preferable to prevent water absorption by setting the hopper as nitrogen atmosphere as much as possible. The polyamide resin charged in the hopper 1 is introduced into the melt extruder 2 heated to the melting point or higher of the polyamide resin. Here, when it is necessary to add the above-mentioned additive later, there are a method of adding it to a hopper by dry blending, or a method of adding it while controlling it to a predetermined content by a side feeder or the like.

  The polyamide resin introduced into the melt extruder 2 is melted, measured by a gear pump or the like so as to obtain a desired discharge amount, and introduced into the spinning pack 3. The polyamide introduced into the spin pack 3 is discharged as a yarn 4 through a discharge hole of a spinneret installed in the spin pack 3. The discharged polyamide yarn 4 is cooled and solidified by a forced cooling device 5 (chimney) such as Uniflow, and after the oil agent is attached by the oil agent guide 6, it is taken up by the take-up roller 7.

Here, the first requirement of the present invention is that the relationship between the discharge linear velocity of the molten polymer and the take-off velocity satisfies the following formula 1.
10 Vp ≦ Vt ≦ 500 Vp (Formula 1)
Here, Vp: discharge linear velocity (m / min), Vt: take-up velocity (m / min)

The discharge linear velocity referred to in the present invention means the speed of polyamide discharged from the discharge holes, and can be uniquely determined from the discharge hole diameter and the single hole discharge amount by Vp = 4Q / (πρD ² ). Is. Here, Q: discharge amount (g / min) D: discharge hole diameter (mm) ρ: density (g / cm ³ ) (in the case of polyamide: 1.1 g / cm ³ ).

  The take-up speed referred to in the present invention means a speed at which the discharged yarn is taken up by the take-up roller 7, and substantially represents the peripheral speed of the take-up roller 7.

  If the take-up speed (Vt) is 10 times or more of the discharge linear speed (Vp), a suitable spinning tension can be applied to the running yarn. It is possible to prevent instability. From the viewpoint of increasing the spinning tension of the running yarn and stabilizing the spinning line, the ratio of the take-up speed to the discharge line speed may be increased by lowering the discharge line speed or increasing the take-up speed. However, when the spinning tension is excessively increased, the molecular orientation proceeds on the spinning line (between the die surface and the take-up roller), and a crystal structure (α crystal) is generated along with the orientation crystallization. When the α crystal is generated in the fiber, the α crystal has a stable structure, so that it becomes a starting point of defect generation in the stretching process, and it may be difficult to stretch at a high magnification. For this reason, in the present invention aiming at stable yarn production of polyamide fibers, the take-up speed (Vt) needs to be 500 times or less of the discharge linear speed (Vp). Moreover, by setting it as this range, there also exists an effect that water adhesion which is the 2nd requirement of this invention mentioned later can be performed more simply. Furthermore, from another viewpoint, by setting such a range, it is possible to prevent the formation of a non-uniform fiber structure on the spinning line (between the die and the take-up roller), and to suppress the yarn breakage and the influence of vibration of the take-up roller 7 and the like. The effect of doing is also great. From the viewpoint of improving the stability of the spinning line, it is more preferable that the take-up speed is in the range of 10 to 250 times the discharge linear speed, and considering the effect of moisture adhesion described later, the discharge linear speed It is a more preferable range to be in the range of 10 times to 100 times.

  The number of holes of the discharge holes drilled in the spinneret used in the present invention can be set as the number of holes entering the die surface as a concentric circle arrangement, a staggered arrangement or a linear arrangement, but when the number of holes is too large Since cooling unevenness may occur between the single yarns, and the single yarns may interfere with each other and the spinnability may be deteriorated. Although it is necessary to consider that the diameter of the discharge hole satisfies the relationship between the discharge linear velocity and the take-up speed described above, generally 0.1 to 5.0 mmφ is a guide for a round hole. In the case of obtaining fine fibers or in the case of using a low viscosity polymer, 0.1 to 0.4 mmφ is suitably used, and in the case of a high viscosity polymer, 0.3 to 5.0 mmφ is suitably used. Considering the meterability of the discharged polyamide, it is preferable that a metering hole with a reduced hole diameter is provided on the discharge hole when the discharge hole diameter is 2.0 mmφ or more. The L / D (= hole length / hole diameter) of the discharge hole and the measurement hole depends on the melt viscosity of the polyamide used, but is 0.1 to 5.0 as a guideline. 0.0 is preferable.

  The take-up speed is also determined by satisfying the above-mentioned first requirement of the present invention and the fineness and mechanical properties of the target undrawn fiber, but may be 100 to 2000 m / min. It becomes a standard. In the case of using a high molecular weight polyamide, the spinning tension tends to be high, and therefore 100 to 1000 m / min is preferable, and 100 to 500 m / min is a more preferable range in consideration of the ease of moisture adhesion.

  The taken running yarn (undrawn fiber) is guided to the water bath 8 via the roller 7 or the like, and moves in the water in the water bath 8 so that moisture adheres thereto. The running yarn that has exited the water bath 8 removes excess water adhering to the surface with a yarn path guide 9 and winds it as unstretched fiber 10 with a winder having substantially the same peripheral speed as the take-up roller 7. It is done.

  The second requirement of the present invention is that moisture is imparted to the taken-up yarn to obtain an unstretched fiber with a substantial moisture adhesion rate of 0.1% to 10.0% by weight. In order to make the polyamide fiber have high mechanical properties, it is necessary to perform high-strength stretching in a subsequent stretching step. For this reason, in the spinning process, it is preferable to take up at a low spinning tension to suppress the generation of the fiber structure (molecular chain orientation). However, polyamide fibers spun at a low spinning tension are highly hygroscopic and absorb moisture in the production atmosphere (in the air) to plasticize and cause crystallization. When this phenomenon is remarkable, undrawn fibers are elongated in the fiber axis direction and the behavior of the running yarn is destabilized. On the other hand, in order to suppress this behavior, when spinning at a high spinning tension, a fiber structure is generated by the spinning line, and thus it becomes difficult to stretch at a high magnification in the subsequent stretching step. This makes it difficult to produce a polyamide fiber having both mechanical properties and durability.

  The present inventors have intensively studied on this point, and have arrived at the present invention by conceiving the use of a crystal structure (γ crystal) that is structurally easily broken (unstable). That is, in the unstretched stage, γ crystals are generated and fixed once, and the molecular chain is brought into a semi-stable state. In the subsequent stretching step, the fiber structure is highly oriented by stretching at a high magnification, and the γ crystal is transferred to the α crystal, so that a highly oriented stable structure is generated in the stretched fiber. Although this can be said to be a phenomenon that has been achieved as a result in the prior art, the present inventors have taken the post-taken-up for collecting undrawn fibers suitable for high-magnification drawing by uniform formation of γ crystals. It was found that it is important to force moisture to adhere to the running yarn in a constant tension state. This is because, as in the prior art, in the case where moisture is adhered with an oil agent guide or the like before take-up, the moisture is adhered under the spinning tension, so that the moisture is artificially shut out with a single fiber or fiber bundle. It becomes. For this reason, the amount of water present in the surface layer and inner layer of the single fiber or fiber bundle changes, and as a result, the generation of γ crystals becomes non-uniform. On the other hand, in the present invention, since moisture adheres under low tension after take-up, the possibility that the inner layer and the outer layer are biased is extremely low without moisture being squeezed out from the single fiber or fiber bundle. In the present invention, it is of course possible to perform a stretching treatment without once winding the polyamide unstretched fiber. However, from the viewpoint of homogenization of γ crystal generation of the unstretched fiber, it is preferable that the polyamide is stretched after being wound once. . At this time, when aging is performed for 24 hours or more in a room where the humidity and temperature of the atmosphere are controlled, the migration of moisture attached to the package is completed, and the formation of γ crystals in the unstretched fibers is completed and stabilized.

  The above phenomenon is naturally related to the amount of moisture applied to the unstretched fiber, and in the present invention, the moisture adhesion rate of the unstretched fiber needs to be 0.1 wt% to 10.0 wt%.

  When the moisture application rate mentioned here is 0.1% by weight or more, it means that water penetrates the entire fiber, and γ crystals are uniformly formed in the fiber cross section. From this point of view, the higher the moisture adhesion rate, the better. However, in consideration of reducing the scattering of water during winding and the contamination of the rollers and thread guides, the moisture adhesion rate needs to be 10.0% by weight or less. is there. In addition, when winding the unstretched fiber once, the moisture adhesion rate may be 0.1 wt% or more and 5.0 wt% or less from the viewpoint of preventing package collapse due to moisture that has not penetrated. preferable. Furthermore, in the case of a multifilament, considering the homogenization of moisture adhesion between single fibers, the moisture adhesion rate is more preferably 0.5 wt% or more and 5.0 wt% or less.

  The moisture adhesion rate mentioned here means the ratio of the amount of water adhering to the fiber weight, and is a value that can be measured by the following method. That is, 1000 m of the collected polyamide unstretched fiber is taken with a measuring machine, and the weight before drying is measured. After drying the sample with a hot air dryer, the weight after drying is measured, and the value obtained by dividing the weight difference by the weight before drying is multiplied by 100. The water adhesion rate of the present invention was a value obtained by rounding off the second decimal place of the average value obtained as a result of performing the same evaluation 10 times. The moisture adhesion can be controlled simply by the speed of the running yarn (the stay time in the water bath 8). To perform more precisely, the yarn path guide 9 is used as a nip roller, and is controlled by the pressing pressure of the nip roller. Or a non-contact heater such as a heating roller, a hot plate, a hot pin, or a slit heater after the water bath, and a method of adjusting moisture can be employed.

  The polyamide unstretched fiber obtained as described above is then stretched to highly align the fiber structure, and a stable highly oriented structure composed of α crystals is generated. The polyamide fiber having such a fiber structure becomes a polyamide fiber excellent in durability such as strength retention due to the α crystal in addition to excellent mechanical properties.

The stretching in the present invention is the same as in the normal stretching step, for example, as shown in FIG. 2, between each pair of stretching rollers (supply roller 11, first roller 12, second roller 15, third roller 16). The act of extending and deforming the fiber in the fiber axis direction at the peripheral speed ratio of the roller.
In the stretching of the present invention, it is possible to cold-draw between unheated rollers due to a decrease in glass transition temperature accompanying moisture adhesion of polyamide unstretched fibers. However, from the viewpoint of uniform stretching, it is preferable to perform heat stretching. The heat drawing mentioned here can also be performed by contact heating of a roller, a hot plate, a hot pin or the like heated to a temperature higher than the glass transition temperature of the polyamide undrawn fiber. However, from the viewpoint of improving the mechanical properties, considering high magnification stretching, a method using non-contact heating such as irradiation with an infrared light beam is preferable. The polyamide fiber in the present invention is in a state of containing moisture at an unstretched stage. Further, in the substantial stretching region between the rollers, the fibers are exposed to a high stress, so that the attached moisture tends to be shut out from the single fiber or the fiber bundle. Furthermore, in the case of the contact type, the stress may change on the surface that is in contrast with the contact surface with the roller or the like, and therefore, the non-contact type is preferable in consideration of uniform stretching. In the case of contact heating, since heat is transferred to a single fiber or the entire fiber bundle by heat conduction, there may be a change in the amount of attached water. On the other hand, in the case of irradiating the infrared light flux between the drawing rollers, since it is radiant heating, the heating with the single fiber and the fiber bundle is extremely homogeneous, and the fluctuation of the moisture adhesion rate is suppressed. From the above two viewpoints, it can be said that thermal stretching using a non-heating source by infrared irradiation is suitable for high magnification stretching. The term “infrared rays” as used herein refers to electromagnetic waves having a wavelength longer than that of visible red light having a wavelength of 1 to 100 μm and shorter than radio waves. This infrared ray can raise the yarn temperature in a short time and is capable of local rapid heating, and is therefore suitable for fixing the drawing point (neck point). Moreover, since it has the side surface with the high transmittance | permeability with respect to a polyamide fiber, it can be said that a temperature rise is uniform in the cross section of a single fiber and a fiber bundle, and it can be said that it is suitable for uniform extending | stretching also in this respect.

  Specifically, the infrared light beam irradiation used in the present invention is performed using a halogen lamp as its light source, a laser beam as its light source, or the like. Among these, it is preferable to use laser light because it is monochromatic light and has high energy. Among these, it is more preferable to use a carbon dioxide laser (wavelength 10.6 μm) because continuous oscillation, long-time use is possible, high output can be obtained, and it is relatively inexpensive.

In the drawing process in the present invention, for example, as shown in FIG. 2, when the traveling yarn is irradiated with the laser beam 14 from the laser oscillator 13 and energy necessary for deformation is accumulated, the single fiber is caused by the drawing stress. A neck point is formed in the film, and stretching is started. The laser light irradiation conditions in the present invention are preferably determined from the fineness of the undrawn fiber (thickness of single fiber, the number of filaments), the drawing speed, etc., but generally the laser density should be 10 W / cm ² or more. If so, stretching can be started. On the other hand, if the upper limit of the laser density is 1000 W / cm ² or less, it is preferable because continuous production is possible without causing unstretched fibers with an undeveloped fiber structure. Specifically, the laser spot diameter is preferably about 0.1 to 8.0 mm. Laser light generally has a Gaussian distribution within a spot, and the laser density differs greatly between the outermost layer and the innermost layer of the spot. For this reason, when the spot diameter is 0.2 to 3.0 mm, the stretching point can be fixed to a portion where the laser energy of the inner layer is strong, so that it can be said to be a more preferable range. By the way, laser light irradiation can be installed in a place away from the yarn by reflection by mirror, condensing by combining various lenses (for example, cylindrical lens), optical fiber etc. . The laser beam may be single-sided irradiation, but in the case of a multifilament or a monofilament having a large fiber diameter, it is preferable to irradiate the laser beam from many directions from the viewpoint of fixing the stretching point. As described above, the laser irradiation conditions are preferably determined from the above-mentioned range in consideration of unstretched fibers, stretching conditions, and the like. In order to perform drawing at a higher speed from the viewpoint of productivity improvement, the temperature rise is controlled to a temperature range above the glass transition temperature that triggers plasticization. Heating is also a preferred form.

  In the present invention, when performing multistage stretching of two or more stages, it is preferable that the laser light irradiation is completed in less than 100 ms from the neck occurrence position. This is because, as described above, when stretching is performed by irradiating with laser light, unstretched fibers heated to a temperature higher than the glass transition temperature by the laser light are quickly brought into a neck point (due to high stress in the stretching region). Stretch point) is generated and stretched. Since this neck point is generally completed at about 0.1 to 0.3 mm, the laser is irradiated even after the completion of stretching. For this reason, the fiber after drawing is heated to a temperature higher than the crystallization temperature by helping with crystallization heat generation and the like, and is subjected to tension heat treatment after the drawing is completed until the laser spot is emitted. When the molecular chains highly oriented by stretching are subjected to a tension heat treatment, α crystals having a stable structure are quickly generated. If α crystals are excessively generated at this stage, the second and subsequent stages of stretching are caused. May be an obstacle. With regard to this phenomenon, the present inventors have intensively studied, and when the laser irradiation time is less than 100 ms from the neck occurrence position, the generation of excess α crystals is prevented, and conversely, α crystals are appropriately generated, so that the second stage. In the subsequent stretching, it was found that the fiber structure is highly oriented efficiently. The polyamide fiber stretched as such a range shows a good stretchability even in the second and subsequent stretches, and by adding an additional stretch, the fiber structure is highly oriented and α crystals are formed, resulting in a dense fiber structure. Is formed. In addition, considering the reduction of the α crystal generation rate and the improvement of the draw ratio in the second and subsequent stages, the laser irradiation time is more preferably set to 70 ms or less from the neck point. It is preferable that only the neck point is generated, and a more preferable range is 20 ms or less. The laser irradiation time can be easily controlled by adjusting the stretching speed and the laser spot.

In addition, when multi-stage stretching of two or more stages is assumed, it is preferable that the stretching ratio before the final stretching satisfies the following formula 2 in addition to considering the laser irradiation time described above.
0.20 Rt ≦ Rf ≦ 0.70 Rf (Formula 2)
Here, Rt: total stretching ratio, Rf: stretching ratio until final stretching

  This is because in the production method of the present invention, the polyamide fiber in the unstretched stage has a lot of γ crystals generated by moisture adhesion in the spinning process. For this reason, even if the initial stage of multi-stage drawing is set to a high draw ratio, the fiber structure may not be efficiently aligned with the deformation rate (draw ratio). Therefore, it is preferable that the fiber structure is highly oriented and densified at once in the final drawing, and the draw ratio until the final draw (before the final draw) is 0.70 times or less of the total draw ratio. It is preferable to do. On the other hand, the lower limit of the draw ratio is preferably 0.20 times or more with respect to the total draw ratio in consideration of stability in the final draw field, that is, fixing of the neck point. In addition, from the viewpoint of forming a so-called precursor structure for satisfying the present invention in which α crystals and γ crystals are mixed in advance until final stretching, the stretching ratio until final stretching is 0.40 times or more of the total stretching ratio. A more preferable range is 0.70 times or less.

  The polyamide fiber obtained by the production method of the present invention preferably has a strength of 5.0 cN / dtex or more, and preferably 9.0 cN / dtex or more in view of mechanical properties required for industrial materials. A practical upper limit is 20.0 cN / dtex.

  Moreover, it is preferable that the elasticity modulus of the polyamide fiber of this invention is 40-200 cN / dtex. The elastic modulus of the fiber expresses the resistance to so-called deformation, in particular, the repeated compression and compression. When this value is high, for example, in an industrial application, a polyamide fiber is subjected to repeated elongation and compression under severe wet conditions. Even underneath, elongation deformation of the fibers is suppressed, and so-called settling is suppressed. For this reason, the polyamide fiber obtained by the production method of the present invention preferably has an elastic modulus of 40 cN / dtex or more, and if it is more than this, in addition to suppressing deterioration under the use conditions, The process passability in post-processing such as cloth is improved.

  Also, in industrial applications, for example, in applications where repeated elongation and compression are performed under wet conditions such as tire cords, ropes and felts, the elastic modulus is particularly preferably 60 cN / dtex or more as a range that exhibits excellent performance. . The substantial upper limit of the polyamide fiber obtained here is 200 cN / dtex. The elastic modulus mentioned here is obtained from a slope obtained by obtaining a load-elongation curve under the conditions shown in JIS L1013 (1999), linearly approximating an initial rising portion of the load-elongation curve. The elongation is preferably 2 to 60% for drawn yarn, particularly 2 to 25% in the industrial material field where high strength is required, and 25 to 60% for clothing.

  The above-mentioned polyamide fiber can be used in various fiber products such as fiber winding packages, tows, cut fibers, cotton, fiber balls, cords, piles, knitted fabrics, nonwoven fabrics, paper, and liquid dispersions.

  The polyamide fiber obtained by the production method of the present invention can be used without any particular limitation. In apparel use, for example, it is effective for textiles such as outerwear. In the outer using the polyamide fiber of the present invention, since the polyamide has abrasion resistance, it can be used with a strength of 4 cN / dtex or more particularly in a thin fabric used for outdoor clothing and the like. Since the polyamide fiber produced for this thin fabric is often low in fineness and naturally requires durability, it is suitable for exhibiting the effect of the polyamide fiber obtained by the production method of the present invention.

  In industrial applications, tire cords, fishnets, ropes, tents, industrial brushes, fishing lines, etc. can be used effectively even in severe conditions such as repeated rubbing, repeated tension and relaxation. it can.

  In the tire cord, it is used for a car ply, a cap ply, and the like that form a tire skeleton. In particular, polyamide fibers are often applied to cap plies because of their high resistance to vulcanization accelerators (amine compounds) contained in tire rubber. With this cap ply, since the centrifugal force acts on the tire while the automobile is running, the tire swells in the circumferential direction. When the bulge in the circumferential direction becomes excessive, a so-called burst phenomenon or the like occurs, so that a cap ply that suppresses the bulge in the circumferential direction is used in general-purpose tires due to increased safety awareness. Has also been adopted. In addition to repeated relaxation of tension on the cap ply, the tire has heat when it travels, so rain or water vapor attacks the cap ply, especially when it is raining, and it is coated with resorcin-latex etc. However, the polyamide fiber used for the cap ply is also required to have excellent mechanical properties and durability. In order to use for this tire cord, it can be used by setting the strength to 5.0 cN / dtex or more.

  In fish nets, a lot of amines are present in the water due to fermentation of underwater organisms and the like, and polyester fibers with low alkali resistance have a short product life, and polyamide fibers are often used. However, as described above, since the polyamide fiber is hygroscopic, its mechanical properties and dimensional stability are lowered in water, so there are problems such as elongation of fish nets and breakage due to deterioration of mechanical properties. Also in this application, the stable highly oriented structure formed by the production method of the present invention works effectively, and an excellent fish net with a long product life is obtained. In fish nets, the strength is 5.0 cN / dtex or more.

  In ropes and tents used in natural environments, polyamide fibers are often used because of their excellent wear resistance. Naturally, polyamides obtained by the production method of the present invention are also used in such applications. The fiber works effectively.

  The production method of the present invention can be used not only for multifilaments but also for monofilaments, and can be an excellent industrial brush or fishing line.

  As described above, the use in which the characteristics of the polyamide fiber of the present invention are particularly effective has been described. Naturally, the use of polyamide fiber is generally used in clothing such as pantyhose, or in industries such as seat belts and airbags. It can be used as an application fiber. Needless to say, these applications are also effective.

  Hereinafter, the present invention will be described in detail with reference to examples. In addition, the measuring method in an Example used the following method.

A. Relative viscosity of polyamide (ηr)
Nylon was dissolved in a 98% sulfuric acid aqueous solution and adjusted to a concentration of 0.01 g / mL, and then measured at 25 ° C. using an Ostwald viscometer.

B. The moisture content of the chip was measured by a coulometric titration method using a Karl Fischer moisture meter (AQ-2100) manufactured by Hiranuma Sangyo Co., Ltd. The average value of 3 trials was used.

C. In an atmosphere controlled to a single yarn fineness of fiber of 25 ° C. and 55% RH, the fiber was made into a 100-m small wrinkle with a measuring machine, and its weight was multiplied by 100 to obtain a total fineness. The single yarn fineness was calculated by dividing the total fineness by the number of filaments.

D. Fiber mechanical properties (strength, elongation, elastic modulus)
Under an atmosphere controlled at 25 ° C. and 55% RH, the initial sample length was 200 mm, the tensile speed was 100% mm / min, and a load-elongation curve was obtained under the conditions shown in JIS L1013 (1999). Next, the load value at the time of fracture was divided by the initial fineness, which was used as the strength, and the elongation at the time of fracture was determined as the elongation by the initial sample length. Further, the initial rising portion of the load-elongation curve was linearly approximated, and the elastic modulus was obtained from the slope. Similar evaluation was repeated 10 times to obtain an average value. Regarding the strength, the value rounded off the second decimal place was taken as the mechanical property of the sample, and regarding the elongation and elastic modulus, the value rounded off after the decimal point was taken as the mechanical property.

E. 1000 m of the polyamide fiber collected from the moisture adhesion rate of the fiber is taken with a measuring machine, and the weight before drying is measured. Subsequently, the casserole sample is dried in a hot air dryer at 110 ° C. for 30 minutes, and the weight is measured after drying. All the above-mentioned weights are measured by rounding off 4 decimal places in grams. The measured weight is determined according to the following formula 3 to determine the moisture adhesion rate of the polyamide fiber.
MR = (Wb−Wa) / Wb × 100 (%) (Formula 3)
Here, MR: moisture adhesion rate, Wb: weight before drying, Wa: weight after drying.
The value obtained by rounding off the second decimal place of the average value obtained as a result of performing the same evaluation 10 times was defined as the moisture adhesion rate. In addition, 0.04 weight% or less was not able to be detected.

F. Fiber durability (strength retention)
A load is applied to the annular polyamide fiber so as to be 0.5 cN / dtex, and a bending test is performed 1000 times using a rubbing tester. The strength of the sample after the bending test is measured by the method described in (D) above, and the strength retention is evaluated by the following formula 4.
TR = Sa / Sb × 100 (%) (Formula 4)
Here, TR: strength retention, Sb: strength before test, Sa: strength after test.
Regarding durability (strength retention), the average value obtained by repeating the same evaluation 10 times was rounded off after the decimal point.

G. Laser irradiation time For calculation of laser irradiation time, the laser irradiation position is photographed with a CCD camera, and the neck point is confirmed. As shown in FIG. 3, since the neck point 18 is confirmed as shown in the figure, the neck generation position point is between the deformation start position 19 and the deformation (stretching) end position 21 (fiber diameter deformation rate ± 0.05%). Laser irradiation distance 23 (time) was calculated by dividing the distance excluding the irradiation distance from the spot diameter (laser spot 22) to the neck generation position 20 by the stretching speed. Regarding the determination of the neck occurrence position 20, the neck point was photographed with a moving image, the above-described evaluation was performed on 10 images arbitrarily extracted from the moving image, and the average value was set as the neck occurrence position.

H. Stretching evaluation of fiber When threading was performed on a 6-strand stretching machine and continuous stretching was performed for 6 hours, the stretched fiber could be continuously collected without any breakage in any weight. Stretching is good (○) when there is a thread breakage with one spindle, stretching is possible when there is a thread breakage with 2-3 spindles (△), and stretching is impossible when there is a thread breakage with 4 spindles or more (×) It was.

Example 1
The dried nylon 6 chip having a relative viscosity (ηr) of 3.5 was dried with a vacuum dryer so that the moisture content of the chip was 300 ppm or less, and charged in a hopper as a nitrogen atmosphere. The chips were melted while measuring the amount of chips in a twin-screw melt extruder (30 mmφ, L / D = 42) installed under the hopper. The screw rotation speed of the twin-screw extrusion kneader was 100 rpm, venting was performed on the discharge side of the twin-screw extrusion kneader to deaerate, thereby eliminating the bubbles and discharging the moisture generated during the extrusion kneading.

  The spinning temperature (kneading machine and spinning head) was 260 ° C., and the single-hole discharge rate was 2.45 g / min · hole, filtered through a metal nonwoven fabric with an absolute filtration diameter of 10 μm, and then the die (0.7 mmφ, L / D = 5). ) Was melted and discharged, passed through a uniflow cooling air zone, and then a non-hydrous oil agent was adhered, and taken up by a take-up roller having a peripheral speed of 125 m / min (Vs / Vp = 21.6). The taken yarn passes through a water bath (40 cm, water temperature 25 ° C.) installed after the take-up roller, passes through a yarn guide, and is sampled by a winder that circulates at the same speed as the take-up roller. Got. Although the take-up speed was as low as 125 m / min, the spinning wire was stable, and the package during winding and after winding did not loosen and collapse. When the unstretched fiber was allowed to stand for 24 hours and the moisture adhesion rate was confirmed, it was 5.0% by weight.

The collected polyamide unstretched fibers were subjected to two-stage stretching using a laser stretching machine as shown in FIG. The unstretched fibers are sent to a first stretching roller (room temperature) that circulates at 25 m / min by a supply roller having a nip roller. The unstretched fiber passes through a laser (irradiation) spot installed after the first stretching roller, and is sent to a second stretching roller (200 ° C.) that circulates at 94 m / min (stretching ratio between 1-2 rollers: 3.75). Times). When this laser spot was confirmed with a CCD camera, a clear neck point was generated, and it was confirmed that stretching was performed in the laser spot. This laser irradiation apparatus is equipped with a three-direction irradiation system using a reflection mirror, and this apparatus irradiated laser with a laser output of 4.0 W and a spot diameter of 5 mmφ (laser density of 5.1 W / cm ² ). . Subsequently, a stretched polyamide fiber was obtained by stretching 1.5 times with a second stretching roller and a third stretching roller (200 ° C.) and winding with a tension-controlled winder. In addition, when the above-mentioned two-stage stretching was continuously performed for 6 hours with a six-ply drawing machine, it was possible to continuously extract drawn fibers without any yarn breakage in any of the weights (drawing evaluation: ◎).

  The obtained stretched fiber had the mechanical properties and strength retention as shown in Table 1, and had excellent mechanical properties and excellent durability.

  When the wide angle X analysis (λ: 0.8 mm) was performed on the polyamide fiber in each step, a γ crystal ((010)) having a low orientation was observed in the undrawn fiber in the diffraction image, and after the first drawing Then, γ crystal ((010), (002)) and α crystal ((200), (002), (202)) are observed, and in the final drawn fiber, α crystal ((200), ( 002) and (202)) only. From this diffraction image result, in the unstretched stage, the crystals are substantially composed of γ crystals (95% or more), whereas α-crystal (60%) and γ-crystal ( 40%), and the final drawn fiber means that the crystals are composed of only α crystals. That is, in the production method of the present invention, in the unstretched stage, a γ crystal is generated to temporarily fix the fiber structure (molecular chain) and make the molecular chain semi-stable. This improves the stability of the spinning line even at low speed spinning. In the subsequent stretching step, the γ crystal is broken in the first stage stretching, and the α magnification and the γ crystal are mixed together as a draw ratio and laser irradiation to an appropriate degree to form an α crystal. It can be seen that this is a production method for obtaining a polyamide fiber having a highly oriented stable structure by highly stretching the fiber structure and transferring the γ crystal to the α crystal by stretching with stress.

Example 2
Except that the take-up speed was 500 m / min, everything was carried out according to Example 1.
It was found that even when the take-up speed was increased, a polyamide fiber excellent in mechanical properties and durability could be obtained. Further, the spinning line was stable, and even in Example 2, the yarn was not broken during the 6-hour drawing (drawing evaluation: A). The results are shown in Table 1.
In the wide-angle X-ray analysis of the process sample, it was found that the sample after one-stage stretching was in a state where α crystal and γ crystal were mixed.

Example 3
Except that the discharge hole diameter of the die was 0.5 mmφ and the total draw ratio was 6.5 times (first-stage draw ratio: 3.9 times), everything was carried out in accordance with Example 1.
Example 3 also had excellent mechanical properties and durability, and there was no problem with respect to spinnability and stretchability (stretching evaluation: ◎). The results are shown in Table 1.
In the wide-angle X-ray analysis of the process sample, it was found that the sample after one-stage stretching was in a state where α crystal and γ crystal were mixed.

Example 4
Except that the discharge hole diameter of the die was 1.0 mmφ, the take-up speed was 1000 m / min, and the total draw ratio was 5.5 times (first-stage draw ratio: 3.75 times), everything was carried out according to Example 1.
Example 4 also had excellent mechanical properties and durability, and there was no problem with respect to spinnability and stretchability (stretching evaluation: ◯). The results are shown in Table 1.
In the wide-angle X-ray analysis of the process sample, it was found that the sample after one-stage stretching was in a state where α crystal and γ crystal were mixed.

Example 5
The same procedure as in Example 1 was performed except that the discharge hole diameter of the die was 1.1 mmφ, the take-up speed was 1000 m / min, and the total draw ratio was 3.8 times (first-stage draw ratio: 1.52 times).
Also in Example 5, it had excellent mechanical properties and durability, and there was no problem with respect to spinnability and stretchability (stretching evaluation: ◯). The results are shown in Table 1.
In the wide-angle X-ray analysis of the process sample, it was found that the sample after one-stage stretching was in a state where α crystal and γ crystal were mixed.

Example 6
The first stretching roller was heated to 50 ° C. without performing laser irradiation, and all operations were performed in accordance with Example 1 except that the total stretching ratio was 5.3 times (first stage stretching ratio: 4.00 times).
In Example 6, since laser irradiation was not performed, it was confirmed by observation of the neck point by CCD that the neck point was on the stretching roller.
Although the total draw ratio is 5.3 times (first stage draw ratio: 4.00 times), which is a slightly lower setting as compared to Example 1, in Example 5, the mechanical properties and A drawn fiber having excellent durability could be collected (drawing evaluation: ◯). The results are shown in Table 1.
In the wide-angle X-ray analysis of the process sample, it was found that the sample after one-stage stretching was in a state where α crystal and γ crystal were mixed.

Comparative Example 1
Spinning was carried out in accordance with Example 1 except that the melted and discharged yarn was cooled and solidified, a water-containing oil agent was adhered, and the water bath treatment after take-up was not performed. In addition, the stretching was performed by the heating stretching described in Example 5 without performing laser irradiation.
In Comparative Example 1, the running yarn swayed before the take-up roller, and the behavior of the spinning line was slightly unstable. Further, in the stretching, compared with Example 1, even when the total draw ratio is 4.6 times (first-stage draw ratio: 3.75), the running yarn wraps around the roller during the 6-hour drawing. As stretchability, it was inferior to Example 1 (stretch evaluation: Δ). The results are shown in Table 2.
In the wide-angle X-ray analysis of the process sample, it was found that the sample after one-step stretching was in a state composed of only α crystals.

Comparative Example 2
All were carried out according to Comparative Example 1 except that the take-up speed was 2000 m / min and laser stretching was performed under the conditions described in Example 1.
In Comparative Example 2, it was confirmed that stretching was possible by lowering the total stretching ratio compared to Example 1, and sampling was performed at a total stretching ratio of 4.60 times (first-stage stretching ratio of 4.00 times). Went. Incidentally, wide-angle X-ray analysis of the process sample revealed that the sample after one-stage stretching was in a state composed of only α crystals. The results are shown in Table 2.

Comparative Example 3
All the operations were performed according to Comparative Example 1 except that the non-hydrated oil agent was adhered to the melt-discharged yarn after cooling and solidification.
In Comparative Example 3, undrawn fibers could not be collected because the yarn was loosened between the take-up roller and the winder and the yarn was removed from the take-up roller. This is probably because moisture was not attached forcibly, and the moisture that was present in the atmosphere was absorbed by the yarn running at a constant tension before winding, causing longitudinal swelling. For reference, even when laser stretching was performed in the same manner as in Example 1 using a small amount of unstretched fibers collected, the unraveling property was low and decent stretching could not be performed (stretching evaluation: x).

Comparative Example 4
After taking up with a take-up roller at a take-up speed of 2000 m / min, and then without taking up once, subsequently, one-stage drawing between the first drawing roller and the second drawing roller, and further between the second drawing roller and the third drawing roller Then, 1.1-fold two-stage stretching was performed (total stretching ratio: 2.75 times). The stretching temperature was 50 ° C. for the first stretching roller and 200 ° C. for the second and third stretching rollers.
In Comparative Example 4, since the oriented crystallization was caused by drawing at a high take-up speed with the spinning line, the spinning line was stable. For reference, when the crystal structure was analyzed by the method described in Example 1, the crystals generated at the time of the take-up roller were substantially composed of α crystals. For this reason, the draw ratio is limited, and the reachable strength is limited to 7.0 cN / dtex and the elongation is 20% at most. During drawing, thread breakage was observed with a two-piece drawing machine (drawing evaluation: ◯).

Comparative Example 5
All were carried out in accordance with Comparative Example 1 except that the discharge diameter of the spinneret was 0.4 mmφ. In Comparative Example 5, as in Comparative Example 3, the spinning line was not stable, and it was difficult to collect unstretched fibers. In addition, even in the stretching performed for reference, decent stretching was not possible (stretching evaluation: × ).

Comparative Example 6
All were carried out according to Comparative Example 1 except that the oil agent was not adhered to the running yarn after cooling and solidification. In Comparative Example 6, as in Comparative Example 3, the spinning line was not stable, and it was difficult to collect undrawn fibers. In addition, even in the drawing performed for reference, decent drawing could not be performed (drawing evaluation: × ).

  The method according to the present invention can be applied to any case where it is desired to efficiently produce polyamide fibers having excellent mechanical properties.

1: Hopper 2: Melt extruder 3: Spin pack 4: Yarn 5: Cooling device (chimney)
6: Oil guide 7: Take-off roller 8: Water bath 9: Yarn path guide 10: Undrawn fiber 11: Supply roller 12: First roller 13: Laser oscillator 14: Laser light 15: Second roller 16: Third roller 17: Stretched fiber 18: Neck point 19: Stretch start position 20: Neck generation position 21: Stretch end position 22: Laser spot 23: Laser irradiation distance

Claims (5)

In the method for producing a polyamide fiber in which moisture is given before winding after the yarn melted and discharged from the spinneret is cooled and solidified, the relationship between the discharge linear speed and the take-off speed satisfies the following formula 1, A method for producing a polyamide fiber, comprising drawing an undrawn fiber obtained with a substantial moisture adhesion rate of 0.1 wt% to 10.0 wt%.
10 Vp ≦ Vt ≦ 500 Vp (Formula 1)
Here, Vp: discharge linear velocity (m / min), and Vt: take-up velocity (m / min).   The method for producing a polyamide fiber according to claim 1, wherein the unstretched fiber is stretched by infrared light beam irradiation.   The method for producing a polyamide fiber according to claim 2, wherein the infrared light flux is a carbon dioxide laser. The method for producing a polyamide fiber according to claim 3, wherein a carbon dioxide laser having a laser density of 10 W / cm ² to 1000 W / cm ² is irradiated for less than 100 ms from the neck generation position. The unstretched fiber is stretched by two or more stages of multistage stretching, and when the multistage stretching is performed, the relationship between the stretch ratio before the final stretch and the total stretch ratio including the final stretch satisfies the following formula 2. The manufacturing method of the polyamide fiber in any one of Claims 1-4 characterized by the above-mentioned.
0.20 Rt ≦ Rf ≦ 0.70 Rt (Formula 2)
Here, Rf: stretch ratio before final stretching, Rt: total stretch ratio.

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