JP4757655B2 - Method for producing polyester fiber - Google Patents

Description

  The present invention relates to a method for producing a polyester fiber, and more particularly to a method for producing a polyester fiber that makes it possible to produce a polyester fiber having unprecedented mechanical properties.

  Polyester fibers have excellent balance in mechanical properties and dimensional stability, and can be manufactured at a lower cost than melt spinning / drawing and high-speed spinning, so they are widely used not only for clothing but also for industrial use. ing.

  When polyester fibers are used for industrial applications, the most important characteristic is that of mechanical characteristics such as high strength, and there is an increasing demand for further improvement of mechanical characteristics in order to expand the applications.

In general, a method for producing a fiber using a polyester resin is obtained by melting a polyester resin and guiding it to a melt spinneret pack attached to a spin block, melting and discharging the resin from the melt spinneret pack, It is well known that it is carried out in a melt spinning process which is cooled and solidified and taken up by a take-up roller. In addition, rubber cords such as tire cords, rubber hoses, rubber belts, belts such as seat belts, slings, nets such as fish nets and land nets, ropes, and other industrial polyester fibers that require high mechanical properties are generally used. Specifically, it is manufactured by a method in which a raw material resin having a high degree of polymerization is melt-spun and then stretched at a high magnification and heat-set as necessary. The obtained fiber is required to have a high breaking strength while having an appropriate breaking elongation. This characteristic is referred to as toughness and is expressed as strength × (elongation) ^½ .

  In order to improve the strength, one of the techniques is to make the molecular chain as low-oriented as possible in the undrawn yarn stage and to make a highly oriented fiber by performing high-strength drawing in the drawing process.

  As one of the low orientation technologies, there is a low draft technology (see Non-Patent Document 1). The draft in spinning is expressed by the take-up speed / discharge linear speed. In order to reduce the draft, the mainstream is usually low-speed spinning, and there are few technical study examples of the discharge linear velocity improvement technique, and there has been no knowledge that it is effective for lower orientation. In particular, when a raw material resin having a high degree of polymerization is used, the pressure loss of the die hole is extremely high, and there is a limit to improving the discharge linear velocity in a normal spinning device.

In addition to reducing the diameter of the die hole, laser irradiation is known as a technique for reducing the orientation. The resin can be heated instantaneously by laser irradiation, and the orientation can be lowered by lowering the melt viscosity. In polyester melt spinning, excellent stretchability, that is, low orientation, is achieved by irradiating a traveling resin with an energy density of 20 W / cm ² or more at a position from the spinneret surface to 15 cm along the spinning line. A method for obtaining an undrawn yarn is disclosed (see Patent Document 1: pages 2 to 4).

  In addition, a technique is disclosed in which a single-sided heating and single-sided cooling of a yarn are simultaneously performed by irradiating a laser until the thinning of the yarn is substantially finished (see, for example, Patent Document 2).

  In this technique, the intrinsic viscosity of the resin used is at most about 0.63, and a powerful laser (100 to 300 W in the embodiment) is short on the other side of the yarn while cooling one side of the spinning line. By irradiating for a time, a structural difference in the cross-sectional direction is forcibly generated, so that the strength of the obtained fiber becomes a very low level.

  As described above, the polyester fiber obtained from the melt spinning method is known, but there is still no method for producing a polyester fiber having high strength and high toughness in this fiber.

"Polyester fiber", p. 130 (issued by Corona, written by Ludewig) JP 2004-324017 A (page 2-4) Japanese Examined Patent Publication No. 56-11762 (page 3)

  An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing a polyester fiber having mechanical properties having high strength and high toughness which are not present in the past.

  As a result of intensive studies on the thinning behavior at high temperature in melt spinning, the present inventors have promoted the thinning behavior at high temperature by increasing the discharge linear velocity in the high molecular weight polyester resin. It has been found that fibers having an unprecedented mechanical property that affect the melt structure can be obtained, and the production method of the polyester fiber of the present invention has been reached.

The method for producing a polyester fiber according to the present invention that achieves the above-mentioned object is a method for producing a polyester fiber by melt spinning a polyester resin. A polyester resin having an intrinsic viscosity of 0.8 dl / g or more is less than the diameter of a die hole of Φ0.5 mm. The nozzle is melted and discharged at a discharge linear velocity of 0.25 m / s or more, and after cooling and solidification , it is taken out at a take-up speed of less than 1000 m / min .

  According to the present invention, it is possible to produce a polyester fiber having mechanical properties having high strength and high toughness, which has not been obtained conventionally.

  Hereinafter, the best mode for carrying out the method for producing a polyester fiber of the present invention and the effects thereof will be described.

  The polyester resin in the present invention is a linear polymer having an ester bond in a repeating structure, and is not particularly limited, but is preferably polyethylene terephthalate, polypropylene terephthalate, or polybutylene terephthalate, and has higher strength. In order to achieve this, polyethylene terephthalate is more preferable. The polyester resin used in the present invention may be copolymerized with other components as long as the effects of the present invention are not impaired. Furthermore, the polyester resin used in the present invention may contain a small amount of known additives such as a matting agent, a flame retardant, and a lubricant.

  In order to make the effect of the present invention sufficient, the intrinsic viscosity of the polyester resin needs to be 0.8 dl / g or more. When the intrinsic viscosity is less than 0.8 dl / g, the breaking strength and toughness level of the resulting fiber are lowered. In order to further improve the breaking strength, the intrinsic viscosity is preferably 1.0 dl / g or more, and more preferably 1.2 dl / g or more. The upper limit is not particularly limited, but is about 5.0 dl / g considering the spinning limit in the melt spinning process.

  Moreover, since the manufacturing method of the polyester fiber of this invention aims at industrial fiber, the discharge amount per single hole of resin is preferably 1.0 g / min or more, more preferably 2.0 g / min or more. . The upper limit is not particularly limited, but is practically up to about 5.0 g / min.

  The hole diameter of the spinneret used in the present invention needs to be less than φ0.5 mm. When the hole diameter of the spinneret is φ0.5 mm or more, it is difficult to achieve both improvements in strength and toughness when a drawn yarn is used. For this purpose, it is preferable to set the diameter to 0.3 mm or less. In the present invention, the diameter of the nozzle hole means the outlet diameter of the discharge hole formed in the nozzle, and when spinning with a deformed hole, the value obtained by converting the discharge hole cross-sectional area to a round hole is used. .

Since the discharge linear velocity depends on the die hole diameter and the discharge amount, by setting the die hole diameter to less than φ0.5 mm, the discharge linear velocity is greatly improved, and the deformation rate at a high temperature is greatly increased. In the present invention, a polyester resin having an intrinsic viscosity of 0.8 dl / g or more is melted and discharged from a nozzle having a nozzle hole diameter of less than Φ0.5 mm so that the discharge linear velocity is 0.25 m / s or more.

Generally, the entangled structure of molecular chains is fixed at about (melting point−20) ° C. on the spinning line. And since the structure once fixed does not change also in a drawing process, but they form a fiber structure by extending | stretching, it has big influence on a final fiber physical property. In other words, in order to obtain polyester fibers with unprecedented strength and toughness, it is important to control the entangled structure in the high temperature molten resin state, that is, the “melt structure” before fixing these structures. is there. As a result of intensive studies on the thinning behavior at high temperature in melt spinning, the present inventors have increased the discharge linear velocity and promoted thinning at high temperature in a high molecular weight resin. Found to affect. By making the hole diameter of the spinneret less than 0.5 mm based on this knowledge, the deformation rate can be 3.0 sec ⁻¹ or more in the entire temperature range of (resin melting point−20) ° C. or higher. It has been found that the homogeneity of the chain entanglement structure is improved. The deformation speed in the present invention means a change in speed per unit distance of the molten resin.

  Since the entangled structure of the molecular chains is fixed at room temperature, it is necessary to evaluate at a temperature at which the fiber softens, that is, at a temperature higher than the glass transition point. One method for evaluating the entangled structure is to evaluate the heat shrinkage stress relative to the network stretch ratio (see, for example, S. D. Long and I. M. Ward, J. Appl. Polym. Sci., 42, 1911 (1991)). The network stretch ratio is a parameter calculated from a stress-strain curve by a method described later, and represents the orientation of the entangled structure. In addition, the heat shrinkage stress above the glass transition point in amorphous fibers, that is, in the softened state, is caused by the shrinkage of the molecular chain entanglement (network) structure, and the increase in the peak value of the stress contributes to the shrinkage. This means that there are many molecular chains with the same degree of entanglement. Therefore, when evaluating the homogeneity of the entangled structure with respect to fibers of different production methods, it is only necessary to compare the heat shrinkage stress at the same network stretch ratio (orientation).

  FIG. 1 shows the relationship between the network stretch ratio and the heat shrinkage stress under various spinning conditions. When comparing Example 3 (die hole diameter φ0.3 mm), which will be described later in detail, and Comparative Example 3 (die hole diameter φ0.6 mm), the slope of the approximate line is greatly increased from 0.36 to 0.52. . That is, the heat shrinkage stress with respect to the network stretch ratio is remarkably increased by the promotion of the thinning at the high temperature due to the decrease in the diameter of the die hole. As described above, in the production method of the present invention, the fiber having improved entanglement structure homogeneity that cannot be obtained by the conventional technique in which the heat shrinkage stress value with respect to the network stretch ratio is increased. Fibers with improved entangled structure homogeneity have excellent fiber structure with highly efficient molecular chain orientation and fine microstructure because high stress is propagated to the molecular chain entangled structure in the drawing process Is formed.

  In particular, it is preferable to irradiate a high-temperature molten resin with a laser and heat it instantaneously from the viewpoint of further increasing the deformation speed at a high temperature. Looking at the relationship between the network stretching ratio and the heat shrinkage stress shown in FIG. 1, the slope of the approximate curve is further increased by laser irradiation (for example, Example 1 and Example 3). That is, by irradiating a high-temperature molten resin with a laser, thinning at a higher temperature is further promoted and the homogeneity of the entangled structure is improved. Further, when a high molecular weight resin is melt-spun, stable yarn production is possible even under conditions where the spinning stress is high, and energy efficiency can be saved because it is superior in heating efficiency to conventional methods such as a heating cylinder. The laser beam is preferably applied to the resin discharged from the die with an appropriate laser irradiation intensity within a range of 50 mm from the spinneret surface.

  The spinneret surface in the present invention means a position where the discharged resin has a free surface and can be deformed by extension. When laser light is irradiated downstream of 50 mm, cooling proceeds and the molten resin temperature often decreases to 250 ° C. or lower, so the effect of controlling the molten structure may be reduced. . Moreover, the pulsation accompanying a heating spot will generate | occur | produce and a physical spot may generate | occur | produce in the fiber axis direction. Therefore, the laser irradiation is preferably performed while the discharge resin is in the range of 50 mm from the spinneret surface, and in order to further increase the temperature at the irradiation position, it is more preferable to irradiate between 30 mm from the spinneret. preferable. The laser used in the present invention is a monochromatic light, a parallel light beam, and a coherent light beam. The type of laser is not particularly limited, but it is preferable to use a carbon dioxide gas laser because a large output can be obtained and it is inexpensive. Laser irradiation may be from one side, but it is also preferable to use reflection by a reflecting element or to irradiate from many directions in terms of improving energy efficiency and heating uniformity.

The laser irradiation intensity in the present invention is not particularly limited as long as the resin at the laser irradiation position can be heated to the melting point or higher. According to various findings of the present inventors, the diameter of the die hole: D ( φmm) and the laser irradiation intensity: E (W / cm ² ) is preferably 20 ≦ D × E ≦ 100, and by setting the relationship within this range, the resin temperature can be controlled without causing pulsation. Can be increased. When the (D × E) value is less than 20, the heating effect is low, and when the (D × E) value is greater than 100, the molten resin surface layer is excessively heated, and the discharge resin is slightly shaken. Care must be taken because the fiber-making property may deteriorate, for example, the fibers may melt. The laser irradiation intensity in the present invention is calculated by dividing the laser output measured at the position irradiated with the molten resin by the spot area.

  The fibers that have been promoted to be thinned at high temperatures according to the present invention have sufficiently excellent mechanical properties, but are further provided with a conventional cooling delay measure, so-called heating cylinders and heat insulation cylinders, for the purpose of improving the yarn production and suppressing orientation. Use in combination is preferable.

In the production method of the present invention, the fiber take-up method is not particularly limited, and any method such as a so-called two-step method and a direct drawing method can be adopted. However, even in the entangled structure in which the homogeneity is improved by the technique of the present invention, when orientation crystallization occurs on the spinning line, the crystal becomes an inhibition point of orientation, and therefore the effect of efficiently orienting molecular chains is reduced. There is a possibility. Accordingly, it is preferable to set the take-up speed so that orientation crystallization does not occur in the spinning process. Specifically, it is important that the take-up speed is less than 1000 m / min. By setting it to less than 1000 m / min, the degree of orientation of unstretched fibers can be lowered, and high strength can be easily achieved. Furthermore, in order to make this tendency remarkable, it is preferable to set the take-up speed to 700 m / min or less. However, preferably from the industrial viewpoint, the lower limit of the take-up speed is 300 m / min. The take-off speed of the present invention refers to the rotation speed of the first roller with which the molten resin contacts after cooling and solidification.

  In order to obtain a fiber having excellent characteristics suitable for industrial fibers, in particular, strength, it is preferable to form a thermally stable fiber structure by orienting molecular chains by drawing heat setting. As a stretching method, for example, there is a method of stretching between a pair of rollers having different rotation speeds. In order to obtain excellent mechanical properties, it is preferable to stretch in two or more stages. The speed ratio and temperature between the rollers can be changed according to the required mechanical characteristics. The heating method can be selected from heating methods such as a heating roller, a hot plate, a heat pin, and laser beam irradiation. In addition, it is preferable to use a laser beam as a heating method in the stretching step because it can be stretched with high stress without generating an obstacle to molecular chain orientation such as microcrystals generated during heating in the stretching step. That is.

  The production method of the present invention can be applied to both monofilament and multifilament production methods.

  The method for producing the polyester fiber of the present invention will be described specifically and in detail with reference to Examples and Comparative Examples below. However, the present invention is not limited by the following examples. Each physical property value in Examples and Comparative Examples was measured by the following method. In any measurement, in the case of obtaining a numerical value, the n number is set to 20 and averaged. The n number may be further increased depending on how data is output.

A. Breaking strength, elongation Using an autograph manufactured by Shimadzu Corporation, the stress-strain curve was determined by measuring an initial sample length of 50 mm (unstretched fiber), an initial sample length of 100 mm (stretched fiber), and a tensile rate of 100% / min. It was.
B. Network stretch ratio A true stress-true strain curve is obtained from the stress-strain curve obtained at the time of measurement of breaking strength and elongation using the following formula.
True stress = (F × l) / (A ₀ × l ₀ )
True strain = ln {(l−l ₀ ) / l ₀ }
F: Load,
l: sample length (mm),
l ₀ : initial sample length (mm),
A ₀ : Initial sectional area

Using the true stress-true strain curve of the reference sample (spinning speed 500 m / min) as a reference curve, each spinning is performed so that the true stress-true strain curve obtained from undrawn yarns with different spinning speeds overlaps the break point of the reference curve. The true stress-true strain curve of velocity is shifted along the horizontal axis. The shift amount is defined as the shift amount (S) of the true stress-true strain curve, and the network stretch ratio in each sample is determined according to the following formula.
λshift = exp (S)
λshrinkage = {100 / (100−BOS)}
λnet = λshift × λshrinkage
λshift: Stretch ratio relative to horizontal axis shift
λshrinkage: Stretch ratio relative to initial deformation λnet: Network stretch ratio S: Shift amount of true stress-true strain curve BOS: Boiling water shrinkage (%)

The boiling water shrinkage BOS (%) used here measures the skein length as a small skein using a measuring instrument. Subsequently, the skein is treated with boiling water at 98 ° C. for 30 minutes, air-dried, and the skein length is measured again. It calculated | required according to the following formula from the skein length before a process, and the skein length after a process.
BOS = {(l ₁ −l ₂ ) / l ₁ }
l ₁ : Skein length before processing l ₂ : Skein length after processing

C. Measurement of thermal shrinkage stress Using a thermal stress measuring device (Type: KE-2S) manufactured by Kanebo Engineering Co., Ltd., the sample length was 50 mm, the initial tension was 0.01 cN / dtex, and the temperature increase rate was 75 ° C./min.
D. Birefringence Using a BH-2 polarizing microscope manufactured by Olympus, the birefringence was measured by an interference fringe method using a Belek compensator.
E. Laser intensity With the resin not running, a laser power meter was installed at the resin running position to measure the laser irradiation energy, and this was divided by the cross-sectional area determined from the fiber diameter at the time of irradiation.
F. Intrinsic viscosity Measured at 25 ° C. orthochlorophenol. In this example, Shodex GPC-101 manufactured by Showa Denko KK was used to measure the eluent HFIP, column HFIP-806M × 2, detector RI, flow rate 1.0 mL / min, and polyethylene terephthalate with a known intrinsic viscosity. It converted using.

Example 1
Polyethylene terephthalate (intrinsic viscosity: 1.0 dl / g) was melted by a biaxial extruder and discharged at a spinning temperature of 300 ° C. and a spinneret (hole diameter φ0.3 mm, hole number 1) at a discharge rate of 3.0 g / min. A carbon dioxide laser with a laser intensity of 210 W / cm ² was irradiated 10 mm downstream from the spinneret surface, and after cooling and solidification, the fiber was taken out at a spinning speed of 500 m / min to obtain a polyester fiber. Table 1 shows the physical properties of the obtained fiber.

Comparative Example 1
Except that the intrinsic viscosity of the resin was 0.75 dl / g, melt spinning was performed in the same manner as in Example 1 to obtain polyester fibers. Table 1 shows the physical properties of the obtained fiber.

Comparative Example 2
Except that the diameter of the die hole was 0.6 mm and the laser intensity was 100 W / cm ² , melt spinning was performed in the same manner as in Example 1 to obtain a polyester fiber. Table 1 shows the physical properties of the obtained fiber.

Example 2
Except for the diameter of the die hole being φ0.45 mm, melt spinning was performed in the same manner as in Example 1 to obtain a polyester fiber. Table 1 shows the physical properties of the obtained fiber.

Example 3
Except for not irradiating the laser, melt spinning was performed in the same manner as in Example 1 to obtain a polyester fiber. Table 1 shows the physical properties of the obtained fiber.

Comparative Example 3
Spinning was carried out in the same manner as in Example 1 except that the diameter of the die hole was set to φ0.6 mm and the laser was not irradiated to obtain a polyester fiber. Table 1 shows the physical properties of the obtained fiber.

Example 4
Except that the intrinsic viscosity of the resin was 1.2 dl / g and the spinning temperature was 320 ° C., melt spinning was performed in the same manner as in Example 1 to obtain polyester fibers. Table 1 shows the physical properties of the obtained fiber.

Example 5
Except that the laser intensity was 400 W / cm ² , melt spinning was performed in the same manner as in Example 1 to obtain a polyester fiber. Table 1 shows the physical properties of the obtained fiber.

  It can be seen that the undrawn yarn obtained by the method for producing a polyester fiber of the present invention has a high elongation at break and a fiber excellent in drawability can be obtained.

  In order to evaluate the homogeneity of the entangled structure by each production method, only the take-up speed was changed to 500, 1000, and 2000 m / min for Examples 1 to 3 and Comparative Examples 2 and 3, and undrawn yarns were obtained. The network stretch ratio and the heat shrinkage stress were measured for the obtained fibers, and the relationship between the network stretch ratio and the heat shrinkage stress in each production method was determined.

  The results are shown in FIG. From FIG. 1, the polyester fiber obtained by the method for producing a polyester fiber according to the present invention has a significantly increased heat shrinkage stress relative to the network stretch ratio as compared with the polyester fiber obtained by the comparative example from the inclination of the approximate straight line. I understand that. From this, it can be seen that the undrawn yarn obtained by the method for producing a polyester fiber of the present invention has excellent characteristics in which the homogeneity of the molecular chain entanglement structure is improved.

Example 5
Using the unstretched fiber obtained according to Example 1, heating roller stretching was performed. The undrawn yarn is guided to a supply roller, and after two-stage drawing is performed between the first drawing roller, the second drawing roller, and the third drawing roller, the drawn yarn is passed through the final roller by a tension control type winder. Winding and drawn yarn were obtained. The temperature of each stretching roller was 90 ° C., 140 ° C., and 230 ° C., the stretching ratio in the second stage was set to 1.6 times, and the stretching speed was set to 100 m / min. Table 2 shows the physical properties of the obtained fiber.

Example 6
All were stretched according to Example 5 except that the fiber used was Example 2. Table 2 shows the physical properties of the obtained fiber.

Example 7
All were stretched according to Example 5 except that the fiber used was Example 3. Table 2 shows the physical properties of the obtained fiber.

Example 8
All were stretched according to Example 5 except that the fiber used was Example 3. Table 2 shows the physical properties of the obtained fiber.

Comparative Example 6
All were stretched according to Example 5 except that the fiber used was Comparative Example 1. Table 2 shows the physical properties of the obtained fiber.

Comparative Example 7
All were stretched according to Example 5 except that the fiber used was Comparative Example 2. Table 2 shows the physical properties of the obtained fiber.

Comparative Example 8
All were stretched according to Example 5 except that the fiber used was Comparative Example 3. Table 2 shows the physical properties of the obtained fiber.

  From the above results, a polyester fiber having excellent strength and toughness that could not be obtained in the past by drawing and heat-setting undrawn yarn with improved molecular chain homogeneity by heating according to the production method of the present invention. It can be seen that can be obtained.

FIG. 1 shows the network stretching of unstretched polyester fibers obtained in each production method example by measuring the network stretching ratio and heat shrinkage stress of the unstretched polyester fibers obtained in Examples 1 to 3 and Comparative Examples 2 and 3. The relationship between the ratio and the heat shrinkage stress is illustrated.

Claims (4)

In a method for producing polyester fiber by melt spinning polyester resin, a polyester resin having an intrinsic viscosity of 0.8 dl / g or more is discharged from a nozzle having a nozzle hole diameter of less than Φ0.5 mm so as to have a discharge linear velocity of 0.25 m / s or more. A method for producing a polyester fiber, characterized in that the polyester fiber is melted and discharged, and after cooling and solidification, the polyester fiber is taken up at a take-up speed of less than 1000 m / min . 2. The method for producing a polyester fiber according to claim 1, wherein the diameter of the base hole is not more than 0.3 mm.   3. The method for producing a polyester fiber according to claim 1, wherein the resin discharged from the die is irradiated with a laser within a distance of 50 mm along the spinning line from the spinneret surface. 4. The method for producing a polyester fiber according to claim 1, wherein the resin discharged from the die is irradiated with a laser so as to satisfy the following conditions.
20 ≦ D × E ≦ 100
D: Base hole diameter (φmm), E: Laser intensity (W / cm ² )

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