JP4791844B2 - Polyester fiber - Google Patents

Description

  The present invention has high toughness particularly suitable for rubber reinforcement applications such as tire cords, belt applications, sling applications, net applications such as fishing nets, and industrial material applications such as ropes, etc., but also strength, elastic modulus and thermal stability. It relates to a polyester fiber excellent in both properties.

In recent years of high technology, structural materials (for rubber reinforcement applications such as tire cords, rubber hoses, rubber belts, belts such as seat belts, slings, nets such as fish nets and land nets, and industrial materials such as ropes) In order to improve the performance of the product, it is essential to improve the mechanical properties of the fibers used in the structural material.
In addition, fibers used for industrial materials are often used under harsh conditions such as repeated elongation and compression under high loads, and mechanical characteristics deteriorate over time due to abrasion and deformation (deterioration). ) Is also important.

In general, in order to suppress such deterioration over time, it is necessary to improve the energy absorption rate, that is, to have moderate elongation while having high strength and elastic modulus. This characteristic is called toughness, and is a value represented by toughness = strength × (elongation) ^1/2 .
In addition, in order to use fibers as a structural material, heat treatment such as heat setting and bonding with other materials is performed, so in order to link the mechanical properties of the fiber to the performance of the structural material, thermal stability is also required. This is a very important characteristic.

  Currently, environmental impacts in the manufacturing process are also attracting attention. Polyester fibers that can be recycled relatively easily and can be produced at low energy and at a lower cost than melt spinning / drawing and high-speed spinning are used not only for clothing but also for industrial materials. There is a demand for a wide range of applications, and it is strongly desired to improve the toughness, strength, elastic modulus, and thermal stability of polyester fibers.

  Also in the prior art, there is a disclosure relating to a polyester fiber having a strength of 10.0 g / d (8.82 cN / dtex) or more and a cut elongation of 15% or more as a high toughness polyester fiber (see Patent Document 1).

  However, although the polyester fiber is certainly a fiber having a high degree of toughness, there is a problem that the initial modulus is as low as 140 g / d (123 cN / dtex) or less. This indicates that the elastic deformation region of the fiber is low, and in applications where compression and extension are repeatedly performed under high loads, such as ropes, the fiber is likely to be deformed over time. Problems such as degradation occur.

Further, there is a disclosure relating to a polyester fiber having high toughness having a strength of 10.0 g / d (8.82 cN / dtex) or more and an elongation of 10% or more (see Patent Document 2).
However, the method for producing the fiber does not deviate from stretching the conventional low orientation fiber at a high magnification, and it is difficult to achieve both high toughness and high elastic modulus, in addition to deterioration due to deformation of a single fiber, Since the energy absorption rate is low, there is a problem that deterioration due to rubbing or the like easily proceeds.

  On the other hand, there is a disclosure relating to a polyester fiber having a cutting strength of 11 g / d (9.7 cN / dtex) or higher and an initial tensile elastic modulus of 160 g / d (141 cN / dtex) or higher as a high-strength high-elasticity fiber (see Patent Document 3).

  However, the polyester fiber certainly has excellent strength and elastic modulus, but in order to obtain a high molecular weight polymer in the production process, the heat medium swells with triphenyl hydride and performs solid phase polymerization. Yes. The polymer that has been solid-phase polymerized in the heat medium is free to enter the fiber structure because the heat medium exists in the polymer even during melt spinning, and the heat medium remaining in the polymer diverges from the fiber structure during the melt spinning and drawing process. There will be a lot of volume (such as microvoids). Therefore, when the free energy is increased by heat treatment or the like, there is a problem that the fiber structure is greatly deformed and the mechanical properties after the treatment are greatly deteriorated.

  Similarly, there is disclosure relating to obtaining a polyester fiber having excellent strength and elastic modulus by using an organic solvent to enable improvement in yarn production and stretching at a high magnification (see Patent Documents 4-6).

  However, the polyester fiber treated with an organic solvent in the production process has a problem that the thermal stability is low because the free volume in the fiber structure is increased when the organic solvent is removed as in the above-described technique, and the swelling is also swollen. Since the effect is utilized and high magnification stretching is performed, the elongation is remarkably lowered and the toughness is reduced. In addition, the organic solvent remaining in the fiber after the manufacturing process oozes out on the fiber surface over time, so the adhesive surface with the material covering the surface changes in applications where it is buried in other materials such as tire cords. It is not preferable because a major problem such as peeling or partial alteration of the material may occur. In addition, the organic solvent used during the manufacturing process of these polyester fibers is substantially unrecoverable, so that the burden on manufacturing workers and the environment is very large, and the cost increases.

JP-A-2-289115 (see page 1) Japanese Examined Patent Publication No. 41-7892 (page 4, lines 36-37, see Examples) JP-A 63-196712 (refer to claim 1) JP-A-4-73212 (refer to page 1) JP 63-196713 A (see page 1) Japanese Patent Laid-Open No. 3-294539 (see page 1)

  The problem of the present invention is to solve the above-mentioned problems of the prior art, and relates to polyester fibers suitable for rubber reinforcement applications such as tire cords, belt applications, sling applications, net applications such as fishing nets, and industrial material applications such as ropes. An object of the present invention is to provide a novel polyester fiber having toughness and excellent strength, elastic modulus and thermal stability.

The polyester fiber of the present invention that achieves the above-described problems has the following configuration.
That is, it is a polyester fiber characterized by simultaneously satisfying the following requirements (1) to (4) obtained by drawing an undrawn yarn obtained by irradiating a melted and discharged resin with a laser .
(1) Strength ≧ 10.0 cN / dtex
(2) Elastic modulus ≧ 130 cN / dtex
(3) Toughness ≧ 30
Toughness = strength (cN / dtex) × (elongation (%)) ^1/2
(4) Elastic modulus change rate MC ≦ 10%
MC (%) = {(Mb−Ma) / Mb} × 100
MC: elastic modulus change rate Mb: elastic modulus before treatment (cN / dtex)
Ma: Elastic modulus after constant length heat treatment at 150 ° C. for 10 minutes (cN / dtex)

In the polyester fiber of the present invention, as a more specific embodiment, preferably, the polyester fiber has a strength of 12.0 cN / dtex or more, and more preferably, the toughness of the polyester fiber of the present invention is 35 or more. Is a polyester fiber. Furthermore, it is preferably a polyester fiber whose scattered image is two-point interference in small-angle X-ray analysis.

According to the present invention, it is suitable for rubber reinforcement applications such as tire cords, belt applications, sling applications, net applications such as fishing nets, and industrial material applications such as ropes, while having high toughness, strength, elastic modulus and heat. A novel polyester fiber excellent in both stability is provided.
According to the present invention, a polyester fiber excellent in processability to a structural material is provided because of its excellent thermal stability.

  Hereinafter, the polyester fiber of the present invention will be described in more detail below.

In the present invention, the polyester means a linear polymer having an ester bond in a repeating structure, and is not particularly limited, but is particularly preferably polyethylene terephthalate, polypropylene terephthalate, or polybutylene terephthalate. In particular, polyethylene terephthalate is more preferable.
Further, the polyester fiber of the present invention may be copolymerized with other components as long as the effects of the present invention are not impaired. Furthermore, the fiber of the present invention may contain a small amount of various additives such as a matting agent, a flame retardant, or a lubricant.

The polyester fiber of the present invention satisfies the following requirements (1) to (4) obtained by melt spinning at the same time.
In the present invention, the “fiber obtained by melt spinning” means a fiber obtained by specially setting the melt spinning conditions as described later, and means that the fiber is not obtained by solution spinning or the like. . In general, melt spinning refers to a method in which pellet-shaped raw materials manufactured through a polymer material polymerization process are charged into an extruder, melted by heating, extruded, and then solidified in air. The term “stretching” means that the rollers are continuously stretched while being heated to increase the deformability between rollers having different surface speeds. Therefore, the fiber of the present invention can be obtained by industrial production stable in terms of quality and performance.

(1) Strength In the recent trend of high technology, considering the quality level required as a structural material for industrial materials, the strength should be at least 10.0 cN / dtex or higher. is there. Further, in order to satisfy a high level of demand and to enable application expansion in industrial materials, it is preferably 12.0 cN / dtex or more.
The upper limit is up to about 20 cN / dtex, which is difficult to manufacture according to the knowledge of the present inventors.

(2) Elastic modulus In industrial material applications, stretching and compression are often repeated, and fibers with a low elastic modulus, that is, with a narrow elastic deformation region, are subject to deterioration of mechanical properties due to the progress of plastic deformation of fibers over time. Breaking occurs and deterioration as a structural material proceeds. A fiber having an excellent elastic modulus can bear the stress of elongation and compression by elastic deformation, so that there is little plastic deformation and the deterioration of the fiber and the structural material can be minimized. In the polyester fiber of the present invention, the elastic modulus needs to be 130 cN / dtex or more, and preferably 150 cN / dtex or more.
According to the knowledge of the present invention, the upper limit is up to about 250 cN / dtex where the production becomes difficult.

(3) Toughness Fibers used for industrial materials are required to have a large energy absorption rate even under high stress. This is a characteristic generally regarded as toughness, and the toughness value is expressed by strength (cN / dtex) × (elongation (%)) ^1/2 and has no unit. In industrial materials such as belt reinforcements, tire cords, or ropes, the stress that a single fiber bears may increase momentarily, and the resulting breakage of the single fiber in the structural material results in the quality of the structural material. Cause a decline. Furthermore, under conditions where stretch and compression are repeatedly applied under high stress such as a rope, if the single fiber has low toughness, the structural material easily deteriorates due to abrasion or deformation. In order to suppress such deterioration, it is necessary that the toughness is 30 or more, and in order to make this characteristic remarkable, it is preferable that the toughness is 35 or more.
According to the knowledge of the present invention, the upper limit is up to around 60, which makes manufacture difficult.

(4) Elastic modulus change rate When using polyester fiber as a structural material, thermal stability of mechanical properties is important. For example, when used as a rubber reinforcing material such as a tire cord, heating at 150 ° C. or higher is performed in the step of burying in rubber after weaving. If the thermal stability is insufficient, the performance of the structural material will be significantly lower than that estimated from the mechanical properties of the fiber, and physical property irregularities will occur in any part of the structural material. Problems such as the loss of homogeneity occur.

The elastic modulus change rate (MC (%)) in the present invention refers to the rate of decrease in the elastic modulus of the polyester fiber after the constant-length heat treatment at 150 ° C. for 10 minutes, and is a value obtained by the following formula.
MC (%) = {(Mb−Ma) / Mb} × 100
MC: elastic modulus change rate Mb: elastic modulus before treatment (cN / dtex)
Ma: Elastic modulus after constant length heat treatment at 150 ° C. for 10 minutes (cN / dtex)

  Mb (elastic modulus before processing) in the present invention refers to a value obtained from an initial gradient in a stress-strain curve profile. In the present invention, the term “Ma” refers to stress-distortion in the same manner as the above-described method for obtaining Mb after a polyester fiber is heat-treated at 150 ° C. for 10 minutes at a constant temperature and the treated polyester fiber is sufficiently cooled at room temperature. A value obtained by measuring a line and determining its initial slope. The elastic modulus is an index indicating the elastic deformation region of the fiber, and has a deep correlation with the orientation of the crystal and amorphous repeating structure. Therefore, by measuring the rate of change, the structural orientation change before and after the heat treatment can be easily estimated. That is, when this elastic change rate is large, it means that the fiber structure change due to the heat treatment is large, and there are many free volumes such as loose amorphous parts not restricted by microvoids or crystals in the fiber structure. In the fiber having a large amount of free volume, the mechanical properties are significantly deteriorated by the heat treatment performed when the structural material or the structure is formed, and chemicals such as rubber covering the fiber surface are chemically treated. A large impact.

As a measure of an unprecedented excellent fiber structure such as the polyester fiber of the present invention, the elastic modulus change rate before and after the heat treatment needs to be 10% or less , and the lower limit is preferably 0%.

  As described above, the polyester fiber of the present invention has high toughness, but has unprecedented properties, such as strength, elastic modulus, and thermal stability, and a balance thereof. It is a polyester fiber that is also excellent in processability.

  Therefore, the polyester fiber of the present invention is suitable for rubber reinforcement applications such as tire cords, belt applications, sling applications, net applications such as fishing nets, and industrial material applications such as ropes.

  The reason why the polyester fiber of the present invention has excellent characteristics is due to an excellent fiber structure that has not been formed by the prior art.

  Particularly, in order to have high toughness, excellent strength and elastic modulus, and improved thermal stability, it is important that the fibrillar structure (microfibril structure) is densified. In other words, due to the densification of the fibrillar structure, there are few free volumes such as loose amorphous regions that are not constrained by microvoids or crystals, and stress concentration is suppressed there, so that strength and elastic modulus are excellent. In addition, it has high toughness.

Further, in the fibrillar structure, since the fiber structure hardly changes even when the heat treatment is performed, the thermal stability is very excellent.
In addition, “the fibrillar structure (microfibril structure) in the polyester fiber structure is densified” refers to a structure in which fibrillar structures centering on tie molecular chains penetrating the crystal are arranged uniformly in the cross-sectional direction, Alternatively, it refers to a structure with a small free volume such as a molecular chain (loose amorphous region) that is not restricted by a crystal. In the present invention, as described later, this was realized for the first time without using the swelling effect of an organic solvent or the like, and could not be achieved by conventional melt spinning and stretching techniques.

The fibrillar structure can be confirmed by small angle X-ray analysis. That is, comparing the polyester fiber of the present invention and the small-angle X-ray scattering image of the polyester fiber obtained by the prior art, the scattered image of the polyester fiber of the prior art is four-point interference, whereas the polyester fiber of the present invention In a typical scattered image , two-point interference occurs.

  The two-point interference of the small-angle X-ray scattering image in the polyester fiber of the present invention generally means that the peak is substantial when the intensity distribution of the equator streak (streaky scattering perpendicular to the fiber axis) is measured in the equator direction. It means that it is a scattered image confirmed only at one place. In addition, two peaks are confirmed in the four-point interference obtained with the polyester fiber of the prior art. A polyester fiber exhibiting such four-point interference has a structure in which the crystal plane is inclined with respect to the fiber axis direction, and can be evaluated as having a so-called zigzag structure.

  On the other hand, the two-point interference seen in the polyester fiber of the present invention shows that the crystal plane exists at approximately 90 ° with respect to the fibril structure, and the fiber axis direction without tilting the fibril structure. In addition to being homogeneous and highly oriented, it can be evaluated as dense. Although the polyester fiber which can obtain two-point interference in the small-angle X-ray scattering image has excellent mechanical properties for the reasons described above, it utilizes the swelling effect by the organic solvent in the manufacturing process, and the obtained structure. Since the portion where the organic solvent exists becomes a free volume, the structural change by the heat treatment is large, and the thermal stability is low. This can be estimated from the elastic modulus change rate described above. From the above, it is preferable that the polyester fiber of the present invention exhibits two-point interference in a small-angle X-ray scattering image.

  In order to form the excellent fiber structure of the polyester fiber of the present invention, it is important to control the entanglement structure of molecular chains. The inventors of the present invention have made extensive studies on the control of the molecular chain entanglement structure during the melt spinning of the polyester, and have found that the structure is controlled by promoting the thinning of the molten resin at high temperatures. The unstretched yarn in which the molecular chain entanglement structure is controlled is then stretched and heat-set under heating, whereby an excellent fiber structure with a small free volume is formed, resulting in a polyester fiber having excellent characteristics.

  The entangled structure of molecular chains in the present invention means a network structure formed by entanglement of molecular chains, and is generally fixed (freeze) at (melting point−20) ° C. In addition, the entangled structure once fixed does not change, and this structure stretches while maintaining the network in the drawing process, so that the final fiber structure is greatly affected. That is, in order to obtain a structure having a dense fibrillar structure as described above and a small free volume, it is necessary to homogenize the entangled structure of molecular chains and improve the substantial molecular chain orientation. This was achieved without the use of an organic solvent by promoting the thinning of the molten resin at high temperatures.

  A specific method for producing the polyester fiber of the present invention will be described below.

  Since the polyester fiber of the present invention is required to have high strength and elastic modulus, the polyester resin to be used preferably has a higher intrinsic viscosity, at least 0.8 dl / g or more, preferably 1.0 dl / g or more. Is used. In order to further increase the strength, the intrinsic viscosity of the resin is more preferably 1.2 dl / g.

  In the melt spinning step, molten resin melted and measured by a conventional method is melted and discharged from a spinneret. At this time, the diameter of the die hole is preferably less than φ0.5 mm. More preferably, it is φ0.3 mm or less. The diameter of the nozzle hole in the present invention means the outlet diameter of the discharge hole formed in the nozzle. In the case of a deformed hole, the value obtained by converting the sectional area of the discharge hole to a round hole is used. The number of ejection holes can be determined as appropriate according to the intended application. The discharge amount of the resin can be appropriately determined in consideration of the single yarn fineness at the drawn yarn stage according to the required use. However, since the polyester fiber of the present invention is intended for industrial fibers, the single-hole discharge rate is preferably 1.0 g / min or more, and more preferably 2.0 g / min or more in consideration of yarn-making properties. .

The resin melted and discharged from the spinneret is irradiated with laser at an appropriate intensity between 50 mm from the spinneret surface. By irradiating the resin with a laser, the melt viscosity is lowered and the thinning at a high temperature is promoted. The laser in the present invention is monochromatic light, parallel light, and light that is coherent. The type of laser is not particularly limited, but a carbon dioxide laser is preferable because a large output can be obtained and it is inexpensive. The laser intensity is calculated by grading the laser output measured at the position where the molten resin is irradiated with the spot area.
The spinneret surface in the present invention means a position where the discharged resin has a free surface and can be deformed by extension.

  The laser-irradiated resin is cooled and solidified, and then taken out to form an undrawn yarn. The 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 employed. 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. Therefore, it is preferable to set the take-up speed so that orientation crystallization does not occur in the spinning process. Specifically, the take-up speed is preferably 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, the take-up speed is preferably set to 700 m / min or less. From the industrial viewpoint, the lower limit of the take-up speed is preferably 300 m / min. Here, in the present invention, the take-up speed refers to the rotation speed of the first roller with which the molten resin contacts after cooling and solidification.

  In order to obtain the polyester fiber of the present invention, it is necessary to heat and set with stretching. As a stretching method, for example, there is a method of stretching between a pair of rollers having different rotation speeds. At this time, it is preferable to stretch in two or more stages. As the heating method, any heating method such as a heating roller, a hot plate, and a hot pin may be used. Since the polyester fiber of the present invention is used as a structural material, it is necessary to perform a process such as weaving. Even if the properties of the polyester fiber are extremely excellent, if the elongation is very low, the weaving speed may need to be limited. Considering this productivity, the elongation is 9.0% or more. It is preferable.

  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. In addition, the physical-property value in an Example and a comparative example was measured with 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. Intrinsic viscosity (dl / g)
Orthochlorophenol was measured at 25 ° C. 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.

B. Fineness (dtex)
The fineness was calculated from the weight of a small cocoon having a test total yarn length of 100 m using a measuring machine (HD-3) manufactured by Daiei Kagaku Seiki Co., Ltd.

C. Strength, elongation and elastic modulus (cN / dtex)
Using an autograph manufactured by Shimadzu Corporation, the stress-strain curve was measured and determined at an initial sample of 50 mm (unstretched fiber), 100 mm (stretched fiber), and a tensile rate of 100% / min.

D. Elastic modulus change rate (%)
The sample is wound around a frame having a side of 200 mm so as not to shrink during the heat treatment, and the whole frame is put into a thermostatic bath set at 150 ° C. and subjected to heat treatment for 10 minutes. After the heat treatment, after taking out from the thermostatic chamber and sufficiently cooling in a room temperature atmosphere, the stress-strain curve is measured at an initial sample fiber length of 100 mm and a tensile rate of 100% / min by the same method as obtaining the fineness of B, The elastic modulus after heat treatment was determined. The elastic modulus change rate MC was calculated according to the following formula.
Elastic modulus change rate MC (%) = {(Mb−Ma) / Mb} × 100
Mb: elastic modulus before treatment (cN / dtex)
Ma: Elastic modulus after constant length heat treatment at 150 ° C. for 10 minutes (cN / dtex)

E. Small-angle X-ray scattering X-rays generated by a rotor flex RU-300 manufactured by Rigaku Corporation are monochromatized with a nickel filter and irradiated onto a sample. The target was operated with a copper counter cathode and a fine focus with an output of 30 kV × 30 mA. As a detector, an imaging plate (FDL UR-V) manufactured by Fuji Photo Film Co., Ltd. was used. The distance between the sample and the detector was set to an appropriate distance between 200 mm and 350 mm, and helium gas was filled between the sample and the detector in order to eliminate the influence of scattering such as air. The exposure time was set to an appropriate time for obtaining a scattered image from 2 hours to 24 hours. Reading of the scattered intensity signal recorded on the imaging plate was performed by digital micrography (FDL5000) manufactured by Fuji Photo Film Co., Ltd., and the intensity distribution of the equatorial streak was measured from the obtained data to evaluate the scattered image.

F. 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.

Example 1
Polyethylene terephthalate (inherent 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 single hole 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 yarn was taken out at a spinning speed of 500 m / min to obtain an undrawn yarn. The unstretched yarn is guided to a supply roller, and after two-stage stretching is performed between the first stretching roller, the second stretching roller, and the third stretching roller, the final roller is passed through a tension control type winder, A drawn yarn was 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 1 shows the physical properties of the obtained polyester fibers.

Example 2
Except that the intrinsic viscosity of the resin used was 1.2 dl / g and the spinning temperature was 320 ° C., yarn was produced in the same manner as in Example 1 to obtain a drawn yarn. Table 1 shows the physical properties of the obtained polyester fibers.

Comparative Example 1
Yarn production was performed in the same manner as in Example 1 except that the diameter of the nozzle hole was φ0.6 mm, the spinning speed was 200 m / min, and laser irradiation was not performed to obtain a drawn yarn. Table 1 shows the physical properties of the obtained polyester fibers.

Comparative Example 2
A polyethylene terephthalate chip having an intrinsic viscosity of 0.6 dl / g was heated to 230 ° C. while blowing nitrogen gas in a heating medium of triphenyl hydride, and heated and stirred for 20 hours to carry out heat medium polymerization. g of polyethylene terephthalate chip was obtained.

  Using the tip, spinning was performed in the same manner as in Example 1 except that the die diameter was 0.5 mm, the spinning temperature was 310 ° C., the single-hole discharge rate was 0.1 g / min, and the spinning speed was 20 m / min. A drawn yarn was obtained. Table 1 shows the physical properties of the obtained polyester fibers.

Comparative Example 3
A polyethylene terephthalate chip having an intrinsic viscosity of 0.6 dl / g was heated to 230 ° C. while blowing nitrogen gas in a heating medium of triphenyl hydride, and heated and stirred for 20 hours to carry out heat medium polymerization. g of polyethylene terephthalate chip was obtained. After the chip was dried under reduced pressure at 120 ° C. for 16 hours, 1-methylnaphthalene was added to the chip at a ratio of 4: 1, and the mixture was stirred under reduced pressure for 2 hours to contain 1-methylnaphthalene. A polyethylene terephthalate chip was obtained.

  Using the tip, spinning was performed in the same manner as in Example 1 except that the spinning temperature was 310 ° C., the single hole discharge rate was 0.3 g / min, and the spinning speed was 100 m / min, and a drawn yarn was obtained. Table 1 shows the physical properties of the obtained polyester fibers.

Comparative Example 4
A polyethylene terephthalate chip having an intrinsic viscosity of 1.0 dl / g is freeze-pulverized in liquid nitrogen, and the resulting fine particle resin is pre-crystallized in a vacuum dryer under reduced pressure at 120 ° C. for 10 hours, and then heated to 230 ° C. For 30 hours to obtain a particulate resin having an intrinsic viscosity of 1.5 dl / g.

  The resin was dissolved in hexafluoroisopropanol at room temperature (23 ° C.) so as to have a resin concentration of 15% by weight, and discharged from a die having a hole diameter of 0.3 mm so that the single hole discharge rate was 1.0 g / min. The discharged resin was introduced into a drying cylinder in which 100 ° C. dry air flows at 30 m / sec, and the gel fiber was wound up at 15 m / min. The gel-like fiber was stretched 9 times between three non-heated rollers with a speed ratio, and then hexafluoroisopropanol was completely removed from the gel-like fiber with a dryer to obtain a stretched yarn. Table 1 shows the physical properties of the obtained polyester fibers.

Example 3
Polyethylene terephthalate (inherent 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, number of holes 24) at a single hole discharge rate of 2.0 g / min. Irradiation was performed from the direction of carbon dioxide laser 4 with a laser intensity of 60 W / cm ² per direction at 10 mm downstream from the spinneret surface, and after cooling and solidification, the undrawn yarn was obtained at a spinning speed of 500 m / min. The stretching method was the same as in Example 1. Table 1 shows the physical properties of the obtained polyester fibers.

Example 4
Except that the intrinsic viscosity was 1.2 dl / g and the spinning temperature was 320 ° C., yarn was produced in the same manner as in Example 3 to obtain a drawn yarn. Table 1 shows the physical properties of the obtained polyester fibers.

Comparative Example 5
Except that the single hole discharge rate was 2.0 g / min and the number of holes in the spinneret was 24, yarn was produced in the same manner as in Comparative Example 1 to obtain a drawn yarn. Table 1 shows the physical properties of the obtained polyester fibers.

Comparative Example 6
Except that the number of holes in the spinneret was 24, all yarns were produced in the same manner as in Comparative Example 3 to obtain drawn yarns. Table 1 shows the physical properties of the obtained polyester fibers.

  As can be seen from Table 1, the polyester fiber according to the present invention has high toughness, high strength and elastic modulus, and low elastic modulus change rate.

  Since the polyester fiber of the present invention has excellent thermal stability, it is excellent in processability to a structural material. This is due to the fact that the fiber structure of the polyester fiber of the present invention is essentially excellent, and is apparent from the difference in small-angle X-ray scattering images.

Claims (4)

A polyester fiber characterized by simultaneously satisfying the following requirements (1) to (4) obtained by drawing an undrawn yarn obtained by irradiating a melted and discharged resin with a laser .
(1) Strength ≧ 10.0 cN / dtex
(2) Elastic modulus ≧ 130 cN / dtex
(3) Toughness ≧ 30
Toughness = strength (cN / dtex) × (elongation (%)) ^1/2
(4) Elastic modulus change rate MC ≦ 10%
MC (%) = {(Mb−Ma) / Mb} × 100
MC: elastic modulus change rate Mb: elastic modulus before treatment (cN / dtex)
Ma: Elastic modulus after constant length heat treatment at 150 ° C. for 10 minutes (cN / dtex)   The polyester fiber according to claim 1, wherein the strength is 12.0 cN / dtex or more.   The polyester fiber according to claim 1 or 2, wherein the toughness is 35 or more. The polyester fiber according to any one of claims 1 to 3, wherein the scattered image is two-point interference in small-angle X-ray analysis.