Polyester fibers and tricot knit fabrics

Abstract

The present invention provides a polyester fiber capable of realizing a tricot knitted fabric that prevents the occurrence of vertical streaks when knitted into a tricot fabric by dispersing the crimp of individual yarns without having to align the crimp phases, and that has excellent abrasion resistance and stretchability.　The present invention is a polyester fiber having an eccentric core-sheath cross-section in the fiber cross-section, wherein a degree of deformation (Y / X) calculated by a major diameter Y and a minor diameter X which is orthogonal to Y and which passes through the centroid of the fiber is 1.2 to 3.0 in a deformation cross-section, the ratio L / X of the minor diameter X and the circumference L of the core section is 2.6 to 5.0, and the degree of irregularity at the interface of the core section is 15% or less. Interface irregularity: a value indicated by the following equation, where W is a straight line passing through the most convex point of the core contour on the side where the thickness of the sheath is the greatest and parallel to the minor diameter X, and Z is the distance between line X and line W. Degree of irregularity = Z / X × 100

Description

Technical Field

[0001] The present invention relates to polyester fibers and tricot knitted fabrics. More specifically, the present invention relates to a tricot knitted fabric which is a conjugate cross-section fiber composed of two types of polyester polymers, has excellent abrasion resistance, high quality and excellent stretchability.

Background Art

[0002] In recent years, among woven and knitted fabrics, stretch woven and knitted fabrics imparted with stretch performance have been strongly demanded due to their wearing comfort. To satisfy this demand, for example, many woven and knitted fabrics imparted with stretchability by mixing polyurethane-based fibers with polyester-based fibers have been used. However, polyurethane-based fibers have problems such as the dyeing process being complicated because they are difficult to dye with disperse dyes used for polyester-based fibers, and the stretch performance decreases due to embrittlement after long-term use. For the purpose of avoiding such drawbacks, crimped yarn of polyester-based fibers is used instead of polyurethane-based fibers.

[0003] Polyester fibers containing polytrimethylene terephthalate (hereinafter referred to as PTT) as a main component have a high elongation recovery rate and a low Young's modulus, so they have excellent soft stretch properties. By using this PTT in side-by-side type or eccentric core-sheath type conjugate fibers, a soft stretch fabric can be obtained, and conjugate fibers using PTT have been actively researched and developed in a wide range from clothing applications to non-clothing applications.

[0004] For example, the invention described in Patent Document 1 proposes an aromatic polyester-based conjugate fiber that increases the interfacial perimeter of the sea-island component to disperse the stress applied to the yarn, has excellent abrasion resistance and interfacial peel resistance, and has latent crimping ability suitable for elastic woven fabrics.

[0005] Furthermore, the invention described in Patent Document 2 proposes a bulky polyester composite yarn that has excellent crimping ability, similar to false-twist yarn, when used as a raw yarn with a side-by-side or eccentric core-sheath cross-section, and has soft stretchability when made into a fabric.

[0006] Furthermore, the invention described in Patent Document 3 proposes a spunbond nonwoven fabric that is bulky and flexible, utilizing the high crimping properties of eccentric core-sheath composite fibers or bimetallic composite fibers, at least one of which is made of polybutylene terephthalate. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2018-9261 [Patent Document 2] Japanese Patent Publication No. 2002-61031 [Patent Document 3] Japanese Patent Publication No. 2003-13354 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, the composite fiber described in Patent Document 1 is a typical eccentric core-sheath yarn with a round cross-section. While it exhibits the high crimping performance characteristic of side-by-side and eccentric core-sheath composite fibers, the crimping torque generated during crimping causes the crimped coils of each single yarn to align, resulting in the multifilament forming a single large spring coil. When used to make a tricot knit fabric, this coil protrudes between the loops of the surface fabric, leading to a deterioration in the quality of the warp lines.

[0009] Furthermore, while Patent Document 2 proposes a side-by-side type irregular cross-section for composite fibers, it does not propose an eccentric core-sheath type irregular cross-section, and therefore has not proposed a cross-section that achieves both abrasion resistance and the quality of the warp lines in tricot knitted fabric.

[0010] Furthermore, although the composite fiber described in Patent Document 3 exhibits high crimping characteristics in spunbond nonwoven fabrics made of eccentric core-sheath type or bimetallic type composite fibers, it does not describe the viscosity difference between the two types of polyester polymers or the design of the discharge pore meter. As a result, the degree of unevenness at the polymer interface becomes large, and therefore the stretchability required for tricot knit fabrics cannot be obtained.

[0011] The present invention solves the above problems and provides a polyester fiber in which the crimping phase of the single yarn is not aligned after heat treatment due to the eccentric core-sheath irregular cross-section, resulting in a tricot knit fabric that is less prone to warp streaks, is of high quality, and has excellent abrasion resistance and stretchability. [Means for solving the problem]

[0012] The above problems can be solved by the following means. (1) It consists of two types of polyester polymers with different thermal shrinkage properties. In the fiber cross-section of an eccentric core-sheath polyester fiber, the degree of deformation (Y / X), calculated from the major axis Y and the minor axis X which is perpendicular to the major axis Y and passes through the centroid of the fiber, is between 1.1 and 3.0. Flat shape A polyester fiber having an irregular cross-section, a ratio L / X of the minor axis X to the circumference L of the core being 2.6 to 5.0, and a degree of roughness at the core interface being 15% or less. Degree of unevenness: This value is given by the following formula, where W is a straight line parallel to the minor axis X that passes through the most convex point of the core contour on the side where the thickness of the sheath is maximum, and Z is the distance between line X and line W. Unevenness=Z / X×100 (2) The polyester fiber according to (1), characterized in that, in the cross-section of the fiber, the ratio S / X of the minimum thickness S of the sheath to the minor axis X is 0.01 to 0.1. (3) The polyester fiber according to (1) or (2) above, wherein the main repeating structural unit of the polyester component of the core is trimethylene terephthalate or butylene terephthalate, and the main repeating structural unit of the polyester component of the sheath is ethylene terephthalate. (4) A tricot knit fabric made from polyester fibers as described in any of (1) to (3) above. [Effects of the Invention]

[0013] The polyester fiber of the present invention can provide a tricot knitted fabric that is excellent in abrasion resistance, has high quality without warp stripes, and is excellent in stretchability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] [Figure 1] FIG. 1 is a schematic diagram for explaining the composite morphology of a fiber cross-section. [Figure 2] FIG. 2 is an example of a composite spinneret for explaining the method for producing the polyester fiber of the present invention, and is a front cross-sectional view of a main part constituting the composite spinneret. [Figure 3] FIG. 3 is an example of the shape of discharge holes of a composite spinneret discharge plate for explaining the method for producing the polyester fiber of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing an example of a spinning step (direct spinning drawing method) that is preferably used in the present invention. MODE FOR CARRYING OUT THE INVENTION

[0015] The polyester fiber of the present invention is an eccentric core-sheath cross-section polyester fiber, and in the fiber cross-section, the degree of irregularity (Y / X) calculated from the major diameter Y and the minor diameter X that is orthogonal to the major diameter Y and passes through the center of gravity of the fiber is 1.1 to 3.0, the ratio L / X of the minor diameter X to the perimeter L of the core part is 2.6 to 5.0, and the degree of unevenness at the interface of the core part is 15% or less.

[0016] The polyester fiber of the present invention is composed of two types of polyester polymers, a core part and a sheath part. Examples of the polyester polymer include polyethylene terephthalate (PET) or copolymers thereof, polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), and polylactic acid (PLA).

[0017] The coil-shaped crimping property is developed by arranging two components with different heat shrinkages as a conjugate cross-section fiber. Since this property is exerted by the expansion-contraction behavior of the high-shrinkage component with the low-shrinkage component serving as a fulcrum, the polyester polymer used for the high-shrinkage component is required to have high stretchability and recovery properties. For the high-shrinkage component, polytrimethylene terephthalate and polybutylene terephthalate are preferable in view of mechanical properties and chemical properties. More preferably, polytrimethylene terephthalate is preferable for the high-shrinkage component because it can increase the difference in shrinkage, and polyethylene terephthalate is preferable for the low-shrinkage component.

[0018] The polyester fiber of the present invention has a conjugate cross-section formed by bonding two different types of polymers. It is an eccentric core-sheath type in which two types of polymers having different polymer properties exist in a substantially unseparated and bonded state, and the B component completely covers the A component. Here, the term "eccentric" as used in the present invention means that the center of gravity of the A component polymer in the core part in the conjugate cross-section is different from the center of gravity of the conjugate cross-section fiber, which will be described with reference to FIG. 1.

[0019] In FIG. 1, the sheath part is B, the core part is A, the center of gravity of the core part A in the conjugate cross-section is the center of gravity a, and the center of gravity of the conjugate cross-section fiber is the center of gravity C.

[0020] In the present invention, it is important that the center of gravity a and the center of gravity C are separated from each other, whereby the fiber is greatly curved toward the high-shrinkage component side after heat treatment. Therefore, as the conjugate fiber continues to curve in the fiber axial direction, it forms a three-dimensional spiral structure and develops favorable crimps.

[0021] In the present invention, since the B component completely covers the A component, whitening, fuzzing and the like do not occur even when friction or impact is applied to the fiber or fabric, so the fabric quality can be maintained.

[0022] The polyester fibers of the present invention are long fibers and include processed yarns. The total fineness can range from 33 dtex to 167 dtex, and the number of filaments can range from 12 to 72. From the viewpoint of soft stretchability when woven, a total fineness of 56 dtex to 84 dtex and a number of filaments of 12 to 72 are preferred. More preferably, a total fineness of 56 dtex and a number of filaments of 24 are preferred.

[0023] The polyester fiber of this invention has a ratio L / X of 2.6 or higher, which is the relationship between the minor axis X in the composite cross-section and the circumference L of the core. L / X is a parameter that indicates the relationship between the minor axis X and the contour length of the core in the irregularly shaped eccentric core sheath cross-section. By setting L / X to 2.6 or higher, the stress applied per unit interface is distributed, thereby improving wear resistance. Preferably, L / X is 3.0 or higher.

[0024] The polyester fiber of the present invention has a deformation degree of 1.1 to 3.0. The deformation degree is the value obtained by dividing the major axis Y of the fiber cross-section by the minor axis X passing through the centroid point of the fiber. By setting the deformation degree Y / X to 3.0 or less, the crimped coil does not become too large, and the physical power of the crimped coil is maintained, so sufficient stretchability can be obtained in the tricot knitted fabric. In addition, since the movement of each single yarn in the same direction when the crimping torque is generated can be eliminated, the tendency for the crimped coil phase to align is reduced, and it is possible to prevent warp lines. On the other hand, the lower the deformation degree Y / X, the better the stretchability of the tricot knitted fabric, but when L / X becomes small, the abrasion resistance decreases, and the phase of the crimped coil tends to align, which tends to worsen the quality of the warp lines in the tricot knitted fabric. Therefore, the deformation degree Y / X is 1.1 or higher. A preferred deformation degree Y / X is 1.2 to 2.9, more preferably 1.4 to 2.3.

[0025] The polyester fiber of the present invention has a core roughness of 15% or less. The roughness is calculated by drawing a straight line W parallel to the minor axis X passing through the centroid C of the fiber, passing through the most convex point of the core contour on the side where the sheath thickness is maximum at the interface of the eccentric core-sheath cross-section, and taking the distance between the two lines (XW) as Z, then dividing Z by X. By making the roughness 15% or less, the distance between the centroids of the two components increases, improving the crimpability of the polyester fiber and maintaining sufficient stretchability in tricot knitted fabrics. A preferred roughness is 10% or less.

[0026] In the polyester fiber of the present invention, the ratio S / X of the minimum thickness S of the sheath portion to the minor axis X in the fiber cross-section is preferably 0.01 to 0.1. By setting S / X to 0.1 or less, it is possible to reduce the inhibition of yarn crimping by the sheath portion. Furthermore, by setting S / X to 0.01 or more, it is possible to suppress the deterioration of the quality of the tricot knitted fabric due to abrasion. A preferred S / X is 0.02 to 0.08.

[0027] The cross-sectional shape of the polyester fiber of the present invention is not particularly limited as long as it is a flattened shape with an irregularity of 1.1 to 3.0, but a daruma-shaped cross-section or a mushroom-shaped cross-section with a constriction near the center is preferable from the viewpoint of avoiding the crimping phase becoming aligned.

[0028] The composite ratio of the polyester fibers of the present invention is preferably 70:30 to 30:70, and more preferably 60:40 to 40:60, in terms of spinnability, crimp performance, and dimensional uniformity of the coil pitch in the fiber length direction. The composite ratio is the area ratio of the two types of polyester polymer components in a photograph of the fiber cross-section.

[0029] Next, a preferred method for producing the polyester fiber of the present invention will be described. The present invention provides a method for producing polyester fibers, including a method in which the fiber yarn extruded from the spinneret is wound onto a drum and then stretched, and a method in which the fiber yarn is continuously stretched during the spinning stage. These production methods will be described in detail.

[0030] The polyester fiber of the present invention can be manufactured by a two-step method, in which two different polyester polymers are melted separately, fed into a predetermined composite pack using a composite spinning machine, filtered in the pack, composite spun into an eccentric core-sheath type using a composite die, the undrawn yarn is wound up, and then drawn to a predetermined breaking elongation using a conventional drawer. Alternatively, it can also be manufactured by a one-step method in which the fibers are discharged from the spinning die, composite spun, and then drawn without winding the fiber yarn up. Considering the ease of tension control from spinning to winding during fiber structure formation, the one-step direct spinning and drawing method (hereinafter referred to as the DSD method) shown in Figure 4 is preferred.

[0031] As a method for forming an eccentric core sheath cross section, a distribution plate type nozzle as exemplified in Japanese Patent Publication No. 2011-174215, Japanese Patent Publication No. 2011-208313, and Japanese Patent Publication No. 2012-136804 can be suitably used to achieve the desired cross-sectional shape.

[0032] The composite die shown in Figure 2 is assembled into a spinning pack with three main components stacked from top to bottom: a measuring plate 1, a distribution plate 2, and a discharge plate 3, and is used for spinning.

[0033] In the nozzle member illustrated in Figure 2, the metering plate 1 measures the amount of polymer per discharge hole 6 and allows it to flow in, the distribution plate 2 controls the composite cross-section and its cross-sectional shape in the cross-section of the single fiber, and the discharge plate 3 compresses the composite polymer flow formed by the distribution plate 2 and discharges it.

[0034] To avoid confusion in the explanation of the composite die, it is not shown in the diagram, but for the components stacked above the weighing plate 1, a component with a flow channel formed in accordance with the spinning machine and spinning pack can be used. By designing the weighing plate 1 to match the existing flow channel component, the existing spinning pack and its components can be used as is. Therefore, there is no need to exclusively use the spinning machine for this die.

[0035] Furthermore, it is preferable that the discharge hole shape of the discharge plate 3 be an asymmetrical slit shape as shown in Figure 3(a). In a cross-section where two components with different thermal shrinkage, i.e., different polymer viscosities, are joined, a flow velocity gradient is generated inside the discharge hole, and when this flow velocity gradient is relieved immediately after discharge, the polymer becomes twisted immediately after discharge, resulting in poor discharge stability. In addition, problems such as not being able to obtain the desired cross-section occur. By setting the discharge hole diameter to an appropriate range according to the viscosity of each component, it is possible to reduce the flow velocity difference between the two components, thereby ensuring stable discharge of the polymer immediately after discharge, dramatically improving the stability of cross-section formation in the distribution plate type nozzle, and enabling the acquisition of an accurate eccentric sheath cross-section.

[0036] Furthermore, from the perspective of improving stable discharge and cross-sectional formation, the difference in melt viscosity of the polymers used in the fibers of the present invention is also important. When two types of polymers that form a molten, combined flow are compressed, the cross-sectional area changes in a cross-section perpendicular to the polymer flow direction in order to equalize the pressure loss of the two types of polymers. As a result, a difference in flow velocity is created, and the center of gravity of each component is unevenly distributed during discharge, causing twisting of the discharged polymer flow. In other words, polymers with high melt viscosity have a larger cross-sectional area and therefore a slower flow velocity, while polymers with low melt viscosity have a smaller cross-sectional area and therefore a faster flow velocity. For this reason, by reducing the difference in melt viscosity of the polymers used, the difference in flow velocity between the polymers is mitigated, and the bending of the discharged polymer flow can be suppressed. Taking this perspective further, it is preferable that the difference in melt viscosity of the combined polymers be smaller, but in the case of the polyester fibers of the present invention, considering the occurrence of crimp, it is preferable that the difference in melt viscosity of the combined polymers be larger. Considering the above, a particularly preferable range for the difference in melt viscosity of the polymers to be combined is 100 Pa·s to 300 Pa·s.

[0037] By adopting these manufacturing conditions, it becomes possible to obtain polyester fibers with a degree of irregularity Y / X in the fiber cross-section of 1.1 to 3.0, a ratio L / X of the minor axis X to the circumference L of the core of 2.6 to 5.0, and a degree of unevenness at the core interface of 15% or less, as well as polyester fibers with a ratio S / X of the minimum thickness S of the sheath to the minor axis X of 0.01 to 0.1.

[0038] The polyester fibers of the present invention are warped in their raw state and knitted on a tricot knitting machine. Furthermore, the scouring and dyeing after knitting, as well as the subsequent preset and final set conditions, may be carried out according to known methods. [Examples]

[0039] The following evaluations were performed on the examples and comparative examples.

[0040] (1) Melt viscosity of polymers The chip-shaped polymer was dried in a vacuum dryer to a moisture content of 200 ppm or less, and the melt viscosity was measured using a Capillograph 1B manufactured by Toyo Seiki Seisakusho Co., Ltd., by gradually changing the strain rate. The measurement temperature was the same as the spinning temperature, and for the examples and comparative examples, 1216s -1 The melt viscosity is described. Incidentally, the time from placing the sample in the heating furnace to the start of measurement was set at 5 minutes, and the measurement was performed under a nitrogen atmosphere.

[0041] (2) Total fineness The fiber sample was prepared into 100 skeins using a measuring machine with a frame circumference of 1.0 m, and the total fineness was calculated from the values ​​obtained by weighing them on a balance using the following formula. Total fineness (dtex) = weight of skein (g) × 100 (3) In the cross-section of the fiber, the minor axis X, major axis Y, circumference L of the core, distance Z between two straight lines, and minimum thickness S of the sheath. A digital microscope (VHX-2000) manufactured by KEYENCE Corporation was used to photograph the cross-section of polyester fibers at magnifications of 100 to 500 times. The minor axis X, major axis Y, core circumference L, distance between two lines Z, and minimum sheath thickness S of a single filament were measured. Five arbitrary single filaments were measured. From the average values ​​of the measurements, the degree of irregularity Y / X, L / X, and the degree of unevenness = Z / X × 100, S / X were calculated.

[0042] (4)Stretching and elongation rate The stretch ratio was determined according to JIS L1013(2010) section 8.11 method C (simplified method).

[0043] (5) Evaluation of tricot knit fabric For both the front and back yarns, polyester fibers obtained in each example and comparative example were used to create a 28G tricot half-structure knitted fabric. The resulting fabric was scouring at 90°C for 1 minute and dyed at 130°C for 20 minutes. Then, it was pre-set at 130°C for 2 minutes and final-set at 170°C for 1 minute to obtain a tricot knitted fabric.

[0044] A. Stretchability (longitudinal elongation rate) The elongation rate in the warp direction of the tricot knitted fabric was determined according to JIS L1096(2010) Section 8.16.1 Method A (constant-speed elongation method). The following three evaluation levels were used, with S and A indicating good stretchability. S: Stretch rate of 15% or more A: Elongation rate of 10% or more C: Elongation rate less than 10%.

[0045] B. Abrasion resistance (Martindale (cycles)) The evaluation was conducted using tricot knit fabric in accordance with JIS L1096(2010) Section 8.19.5 Method E (Martindale method). The test conditions were as follows: a standard polyester abrasion cloth was used as the abrasion element, and the number of abrasion cycles was measured at a pressing load of 9 kPa until the degree of discoloration of the abrasion target fabric reached grade 3 on the grayscale for discoloration. The evaluation was as follows. The passing levels are S and A. S: Over 5000 times A: Less than 5000 times, more than 2000 times C: Less than 2000 times.

[0046] C. Dignity The resulting tricot knitted fabric was inspected by skilled inspectors, who visually evaluated the presence of vertical streaks. The passing grades were S and A. S: No vertical streaks, extremely good condition. A: There are some vertical lines, but it's at an acceptable level. C: There are many vertical lines, making it a failing grade.

[0047] Example 1 Polytrimethylene terephthalate (PTT) with a melt viscosity of 100 Pa·s was used as the core component, and polyethylene terephthalate (PET) with a melt viscosity of 30 Pa·s was used as the sheath component. Both the PTT polymer and the PET polymer were melted using an extruder at 260°C and 280°C, respectively, and then metered using a pump. The spinning temperature was set to 275°C, and the mixture was fed into the spinneret while maintaining the temperature. The composite ratio of the PTT and PET components was 50 / 50, and the mixture was fed into a composite spinneret with an eccentric core-sheath cross-section and 24 discharge holes. The polymers merged inside the spinneret to form a composite cross-section, and were extruded from the spinneret with the desired eccentric core-sheath cross-section illustrated in Figure 1(a).

[0048] As shown in Figure 2, the spinneret used consisted of three types of components stacked from top to bottom: a metering plate 1, a distribution plate 2, and an extrusion plate 3. The distribution plate was stacked in multiple layers to form a microchannel. The extrusion hole shape of the extrusion plate 3 was set as follows: the extrusion hole diameter on the side mainly composed of PTT was Φ0.25, the extrusion hole diameter on the PET side was Φ0.18, the slit width was 0.13 mm, and the slit length was 1.05 mm (Figure 3(a)).

[0049] The yarn discharged from the die was spun and drawn using the melt spinning equipment shown in Figure 4. Specifically, the fiber yarn discharged from the composite die i was cooled by a yarn cooling air blower ii, and an oil application device iii was used to apply 0.8% by weight of oil based on the fiber weight. Pre-entanglement was then applied by a pre-entanglement device iv at an air pressure of 0.03 MPa. The yarn was then taken up by a first hot roller (1HR) v heated to 60°C at a speed of 1070 m / min, and without winding, it was passed to a second hot roller (2HR) vi heated to 155°C at a speed of 3780 m / min, where it was drawn and heat-set at a draw ratio of 3.5 times. Furthermore, the entanglement was applied using the entanglement device vii at an air pressure of 0.15 MPa, and the filament was routed to two godet rollers (third godet roller (3GR) viiii, fourth godet roller (4GR) ix) at a speed of 3700 m / min. It was then wound onto package x at a package winding speed of 3670 m / min to obtain a 56 dtex-24 polyester multifilament. The properties of this polyester multifilament are shown in Table 1.

[0050] The obtained polyester multifilaments were used as both the front and back yarns to create a 28G tricot half-structure knitted fabric on a tricot knitting machine. The resulting fabric was then scouring at 90°C for 1 minute and dyed at 130°C for 20 minutes. After that, it was pre-set at 130°C for 2 minutes and then final-set at 170°C for 1 minute to obtain a tricot knitted fabric. The resulting tricot knitted fabric had excellent stretchability and abrasion resistance, and the knitted fabric was free of warp lines and had good texture.

[0051] Examples 2-7, Comparative Example 1 Polyester multifilament was obtained in the same manner as in Example 1, except that the slit length of the extrusion plate 3 was changed. The results are shown in Table 1.

[0052] Comparative Example 2 Polyester multifilament was obtained in the same manner as in Example 1, except that the extrusion plate 3 was changed to the circular shape shown in Figure 3(b) and the material was extruded from the spinneret with the eccentric core sheath cross-section illustrated in Figure 1(b). The results are shown in Table 1.

[0053] [Table 1]

[0054] In Comparative Example 1, the degree of deformation of the polyester fibers was large, and the crimped coils became large, preventing the physical power of the coils from being maintained. As a result, the warp elongation rate of the tricot knit fabric was low at 8%, and sufficient stretchability could not be obtained.

[0055] In Comparative Example 2, the degree of deformation was small and the L / X ratio was small, resulting in low abrasion resistance of 1500 cycles for the Martindale tricot knit fabric, and a noticeable deterioration in the quality of the vertical ribs due to the alignment of the crimping phase.

[0056] Examples 8-11, Comparative Example 3 Polyester fibers were obtained in the same manner as in Example 1, except that the distribution plate 2 was changed and the degree of unevenness was altered. In Example 11, the fibers were extruded from the spinneret using the eccentric core-sheath composite cross-section illustrated in Figure 1(c). The results are shown in Table 2.

[0057] In Comparative Example 3, the degree of unevenness was large, and the distance between the centers of gravity of the polyester fibers was large, resulting in reduced crimpability. The warp elongation rate of the tricot knit fabric was low at 6%, and sufficient stretchability could not be obtained.

[0058] [Table 2]

[0059] Examples 12-14, Comparative Examples 4, 5 Polyester fibers were obtained in the same manner as in Example 1, except that the distribution plate 2 was changed and the minimum thickness of the sheath portion was modified. The results are shown in Table 3.

[0060] In Comparative Example 4, the minimum thickness of the sheath was small, resulting in inferior abrasion resistance for the tricot knitted Martindale fabric, with only 1000 cycles.

[0061] In Comparative Example 5, the minimum thickness of the sheath was large, reducing the crimpability of the polyester fibers, resulting in a low warp elongation rate of 8% for the tricot knit fabric, and insufficient stretchability was obtained.

[0062] Example 15 Polyester fibers were obtained in the same manner as in Example 1, except that the core component was changed to polybutylene terephthalate (PBT) with a melt viscosity of 250 Pa·s. The evaluation results of the obtained polyester multifilaments are shown in Table 3.

[0063] [Table 3]

[0064] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2023-57259 filed on March 31, 2023, the contents of which are incorporated herein by reference. [Industrial applicability]

[0065] The polyester fiber of the present invention provides a tricot knitted fabric that is highly abrasion-resistant, free of warp lines, and has excellent stretchability. [Explanation of Symbols]

[0066] A: Core B: Scabbard part a: Center of gravity of core A in the composite cross-section C: Center of gravity of composite cross-sectional fibers 1: Measuring plate 2: Distribution plate 3: Discharge plate 4:Measuring groove A 5:Measuring groove B 6:Discharge hole i: Composite nozzle ii: Fibre cooling and blowing device iii: Oil dispenser iv: pre-confounding device v: 1st Hot Roller vi: 2nd Hot Roller vii: This entangling device viii: The 3rd Godetlora ix: The 4th Godetlor x: package xi: Contact roller

Claims

1. In the fiber cross-section of an eccentric core-sheath cross-section polyester fiber made of two types of polyester polymers with different thermal shrinkage properties, The irregular cross-section is a flattened shape with a degree of irregularity (Y / X) of 1.1 to 3.0, calculated from the major axis Y and the minor axis X which is perpendicular to the major axis Y and passes through the centroid point of the fiber. The ratio L / X of the minor axis X to the circumference L of the core is 2.6 to 5.

0. Polyester fiber having a core interface with a degree of unevenness of 15% or less. Degree of unevenness: This value is given by the following formula, where W is a straight line parallel to the minor axis X that passes through the most convex point of the core contour on the side where the thickness of the sheath is maximum, and Z is the distance between line X and line W. Unevenness=Z / X×100

2. The polyester fiber according to claim 1, characterized in that, in the cross-section of the fiber, the ratio S / X of the minimum thickness S of the sheath to the minor axis X is 0.01 to 0.

1.

3. The polyester fiber according to claim 1 or claim 2, wherein the polyester component of the core is mainly composed of trimethylene terephthalate or butylene terephthalate as the repeating structural unit, and the polyester component of the sheath is mainly composed of ethylene terephthalate as the repeating structural unit.

4. A tricot knitted fabric made from polyester fibers as described in claim 1 or claim 2.

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