Polyester fiber and tricot warp knitted fabric

Abstract

Provided is a polyester fiber which is capable of achieving a tricot warp knitting fabric that is excellent in wear resistance and stretchability and that suppresses the occurrence of vertical stripes when made into the tricot warp knitting fabric by means of dispersion of single yarn curl due to inconsistent curl phases. The present invention is a polyester fiber in which, in a fiber cross-section of an eccentric core-sheath cross-sectional polyester fiber, the degree of profile (Y / X) calculated from the long diameter (Y) and the short diameter (X) that is orthogonal to the Y and passes through the center of gravity of the fiber is 1.2-3.0, the ratio (L / X) of the short diameter (X) to the perimeter (L) of the core is 2.6-5.0, and the degree of unevenness at the interface of the core is 15% or less. The interface irregularity is a value represented by the following formula, where W is a straight line parallel to the minor axis X and passing through the most convex point of the core profile on the side where the thickness of the sheath is the largest, and Z is the distance between the line X and the line W. The concave-convex degree is equal to Z / X * 100.

Description

Technical Field

[0001] The present invention relates to a polyester fiber and a tricot warp knitted fabric, and more particularly to a tricot warp knitted fabric comprising a composite cross-section fiber of two polyester polymers, which has excellent abrasion resistance, high quality, and excellent stretchability. Background Art

[0002] In recent years, there has been a strong demand for stretchable knits, particularly for their wearability. To meet this demand, knits that have been given stretchability by blending polyurethane fibers with polyester fibers are often used. However, polyurethane fibers are difficult to dye with the disperse dyes used in polyester fibers, making the dyeing process complicated. They also become brittle with long-term use, leading to a decrease in stretchability. To overcome these drawbacks, crimped yarns made from polyester fibers are being used instead of polyurethane fibers.

[0003] Polyester fibers primarily composed of polytrimethylene terephthalate (PTT) exhibit excellent softness and stretchability due to their high elongation recovery and low Young's modulus. Using PTT in parallel or eccentric core-sheath composite fibers can create soft and stretchable fabrics. Research and development of composite fibers using PTT is actively underway for a wide range of applications, from clothing 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 island-in-the-sea component to disperse the stress applied to the yarn, resulting in excellent abrasion resistance and interfacial peeling resistance, and a potential crimping ability suitable for stretch fabric applications.

[0005] The invention described in Patent Document 2 proposes a bulky polyester composite yarn having excellent crimping performance similar to false twist yarn in a raw yarn with a parallel or eccentric core-sheath cross section and soft stretchability when made into a fabric.

[0006] Furthermore, the invention described in Patent Document 3 proposes a spunbonded nonwoven fabric having bulkiness and softness by utilizing the high crimp properties of at least one eccentric core-sheath composite fiber or bimetallic composite fiber containing polybutylene terephthalate.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2018-9261

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2002-61031

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 2003-13354 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] However, the composite fiber described in Patent Document 1 is a typical eccentric core-sheath yarn with a circular cross-section. Although it exhibits the high crimping performance unique to parallel or eccentric core-sheath composite fibers, it exhibits a crimping torque during crimping, and the crimping coils of each single yarn are oriented in the same direction, so the multifilament yarn becomes a large spring coil. When it is made into a tricot warp knitted fabric, there is a problem that the coils fly out between the loops on the surface of the fabric, resulting in deterioration of the quality of the longitudinal stripes.

[0014] Furthermore, the conjugate fiber described in Patent Document 2 proposes a side-by-side modified cross section, but does not propose an eccentric core-sheath modified cross section, nor does it propose a cross section that combines abrasion resistance with the longitudinal striation quality of a tricot fabric.

[0015] In addition, although the composite fiber described in Patent Document 3 exhibits high crimp properties in a spunbonded nonwoven fabric containing an eccentric core-sheath type or bimetallic composite fiber, since the viscosity difference between the two polyester polymers or the design of the ejection hole meter is not described, and the unevenness at the polymer interface becomes large, it is impossible to obtain the stretchability required for a tricot warp knitted fabric.

[0016] The present invention solves the above-mentioned problem and is a polyester fiber as follows: by making the crimp phase after heat treatment inconsistent in the eccentric core-sheath profile cross-section, the crimp of the single yarn is dispersed, thereby providing a tricot warp knitted fabric that is not prone to longitudinal stripes when made into a tricot warp knitted fabric, is high-quality, and has excellent wear resistance and stretchability.

[0017] Technical means to solve the problem

[0018] The above-mentioned problems are solved by the following means.

[0019] (1) A polyester fiber having an eccentric core-sheath cross-section, wherein the cross-section has a profile (Y / X) of 1.1 to 3.0 as calculated from the major diameter Y and the minor diameter X perpendicular to the major diameter Y and passing through the center of gravity of the fiber, the ratio L / X of the minor diameter X to the circumference L of the core is 2.6 to 5.0, and the concavity at the interface of the core is 15% or less.

[0020] Concavity: The value expressed by the following formula, where W is a straight line parallel to the minor diameter X and passing through the most convex point of the core contour on the side where the sheath thickness is the largest, and Z is the distance between the line X and the line W.

[0021] Convexity = Z / X×100

[0022] (2) The polyester fiber according to (1) above, wherein in the fiber cross section, a ratio S / X of the minimum thickness S of the sheath portion to the minor diameter X is 0.01 to 0.1.

[0023] (3) The polyester fiber according to (1) or (2), wherein the main repeating structural unit of the polyester component in the core is trimethylene terephthalate or butylene terephthalate, and the main repeating structural unit of the polyester component in the sheath is ethylene terephthalate.

[0024] (4) A tricot fabric comprising the polyester fiber according to any one of (1) to (3).

[0025] Effects of the Invention

[0026] The polyester fiber of the present invention can provide a high-quality tricot fabric having excellent abrasion resistance and no longitudinal streaks and excellent stretchability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] [ Figure 1 ] Figure 1 This is a schematic diagram for explaining the composite structure of the fiber cross section.

[0028] [ Figure 2 ] Figure 2 This is an example of a composite die for explaining the method for producing polyester fibers of the present invention, and is a front cross-sectional view of the main parts constituting the composite die.

[0029] [ Figure 3 ] Figure 3 This is an example of the shape of the ejection holes of the composite die ejection plate for explaining the method for producing polyester fibers of the present invention.

[0030] [ Figure 4 ] Figure 4 This is a schematic diagram showing an example of a yarn-making process (direct spinning and drawing method) preferably used in the present invention. DETAILED DESCRIPTION

[0031] The polyester fiber of the present invention has an eccentric core-sheath cross-section polyester fiber having a cross-section with a profiled cross-section having a degree of irregularity (Y / X) of 1.1 to 3.0, as calculated from a major diameter Y and a minor diameter X perpendicular to the major diameter Y and passing through the center of gravity of the fiber; a ratio (L / X) of the minor diameter X to the circumference L of the core portion is 2.6 to 5.0; and a degree of irregularity at the interface of the core portion is 15% or less.

[0032] The polyester fiber of the present invention is composed of two polyester polymers: a core and a sheath. Examples of these polyester polymers include polyethylene terephthalate (PET) or its copolymers, polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), and polylactic acid (PLA).

[0033] The coil-like crimping property is achieved by combining two components with different thermal shrinkage properties into a composite fiber cross-section. Because its performance is achieved through the expansion and contraction of the high-shrinkage component, the polyester polymer used for the high-shrinkage component requires high elongation and recovery. The high-shrinkage component is preferably poly(trimethylene terephthalate) or poly(butylene terephthalate) from the perspective of mechanical and chemical properties. Furthermore, poly(trimethylene terephthalate) is preferred for the high-shrinkage component due to its ability to maximize the difference in shrinkage, while the low-shrinkage component is preferably polyethylene terephthalate.

[0034] The polyester fiber of the present invention has a composite cross-section formed by joining two different polymers. The two polymers with different polymer properties exist in a state of being substantially inseparable and joined, and are an eccentric core-sheath type in which the B component completely covers the A component. Here, the eccentricity mentioned in the present invention means that the center of gravity of the A component polymer in the core of the composite cross-section is different from the center of gravity of the composite cross-section fiber. Figure 1 Provide explanation.

[0035] exist Figure 1 In the figure, the sheath is B, the core is A, the center of gravity of the core A in the composite cross section is the center of gravity a, and the center of gravity of the composite cross section fiber is the center of gravity C.

[0036] The important thing in the present invention is that the center of gravity a is separated from the center of gravity C. This allows the fiber to bend significantly toward the high shrinkage component after heat treatment. Consequently, the composite fiber continuously bends in the fiber axis, forming a three-dimensional helical structure and exhibiting good crimping.

[0037] In the present invention, since component A is completely covered by component B, whitening and fuzzing will not occur even when friction or impact is applied to the fiber or fabric, and thus the quality of the fabric can be maintained.

[0038] The polyester fiber of the present invention is a filament, including processed yarn. The total fineness is 33 to 167 dtex, and the number of filaments can be 12 to 72. For the sake of softness and stretchability when made into a fabric, the total fineness is preferably 56 to 84 dtex, and the number of filaments is preferably 12 to 72. More preferably, the total fineness is 56 dtex, and the number of filaments is preferably 24.

[0039] In the polyester fiber of the present application, L / X, the relationship between the minor diameter X and the core circumference L in the composite cross-section, is 2.6 or greater. L / X is a parameter that represents the relationship between the minor diameter X of the eccentric core-sheath cross-section and the core profile length. By setting L / X to 2.6 or greater, the stress applied to each unit interface is dispersed, thereby improving wear resistance. Preferably, L / X is 3.0 or greater.

[0040] The polyester fiber of the present invention has a profile of 1.1 to 3.0. Profile is the value obtained by dividing the major diameter Y of the fiber's cross section by the minor diameter X passing through the fiber's center of gravity. By keeping the profile Y / X below 3.0, the crimping loops do not become excessively large, maintaining the physical strength of the crimping loops. This allows for sufficient stretchability in the tricot fabric. Furthermore, since the movement of the individual yarns in the same direction during crimping torque is eliminated, the phase alignment of the crimping loops is reduced, preventing the occurrence of longitudinal streaks. Meanwhile, a lower profile Y / X improves the stretchability of the tricot fabric. However, a smaller profile Y / X reduces abrasion resistance, makes it easier for the crimping loops to align, and reduces the quality of longitudinal streaks in the tricot fabric. Therefore, the profile Y / X should be 1.1 or higher. A preferred profile Y / X is 1.2 to 2.9, more preferably 1.4 to 2.3.

[0041] The core of the polyester fiber of the present invention has a convexity of 15% or less. The convexity is calculated by drawing a straight line W through the most convex point of the core contour, where the sheath thickness is greatest, at the interface of an eccentric core-sheath cross section, and parallel to the minor axis X passing through the fiber's center of gravity C. The distance between the two straight lines (XW) is defined as Z, and the result is divided by X. A convexity of 15% or less increases the distance between the centers of gravity of the two components, thereby improving the crimping properties of the polyester fiber and maintaining sufficient stretchability in tricot knitted fabrics. A preferred convexity is 10% or less.

[0042] The polyester fiber of the present invention preferably has a ratio (S / X) of the minimum thickness (S) of the sheath portion to the minor diameter (X) in the fiber cross section of 0.01 to 0.1. By setting S / X to 0.1 or less, the sheath portion can be less likely to hinder the yarn from crimping. Furthermore, by setting S / X to 0.01 or greater, deterioration in the quality of the tricot fabric due to abrasion can be suppressed. A preferred S / X ratio is 0.02 to 0.08.

[0043] The cross-sectional shape of the polyester fiber of the present invention is not particularly limited as long as it is a flat shape with a non-circularity of 1.1 to 3.0, but a tumbler-shaped cross-section or a mushroom-shaped cross-section with shrinkage near the center is preferred from the viewpoint of avoiding crimp phase alignment.

[0044] In terms of yarn-forming properties, crimping performance, and dimensional uniformity of the coil pitch in the fiber length direction, the polyester fiber of the present invention preferably has a conjugation ratio of 70:30 to 30:70, and more preferably 60:40 to 40:60. The conjugation ratio refers to the area ratio of the two polyester polymer components in a photograph of a fiber cross section.

[0045] Next, a preferred method for producing the polyester fiber of the present invention will be described.

[0046] Examples of methods for producing the polyester fiber of the present invention include a method in which a fiber sliver ejected from a spinning die is temporarily wound around a drum and then stretched, and a method in which the fiber sliver is continuously stretched during the spinning process.

[0047] The polyester fiber of the present invention can be produced by the following two-step method: two different polyester polymers are melted separately, fed into a specified composite assembly using a composite spinning machine, the two polymers are filtered in the assembly, and then the composite yarn is spun into an eccentric core-sheath type through a composite die, and after temporarily winding the unstretched yarn, it is stretched to a specified breaking elongation through a conventional stretching machine. Alternatively, it can be produced by the following one-step method: the composite yarn is ejected from the spinning die and then continued to be stretched without temporarily winding the fiber yarn. Considering the ease of fiber structure formation, that is, the tension control from spinning to winding, it is preferred Figure 4 The one-step direct spinning and drawing method (hereinafter referred to as the DSD method) is shown.

[0048] As a method for forming an eccentric core-sheath cross section, a distributor plate die as exemplified in Japanese Patent Application Laid-Open No. 2011-174215, Japanese Patent Application Laid-Open No. 2011-208313, or Japanese Patent Application Laid-Open No. 2012-136804 can be appropriately used to form a desired cross-sectional shape.

[0049] Figure 2 The composite die shown is assembled in a spinning pack in a state where three components, namely a metering plate 1, a distribution plate 2, and a discharge plate 3, are stacked from top to bottom, and is provided for spinning.

[0050] exist Figure 2In the die mouth component shown in the example, the metering plate 1 is responsible for measuring the amount of polymer in each ejection hole 6 and allowing it to flow in, the distribution plate 2 is responsible for controlling the composite cross-section of the single fiber and its cross-sectional shape, and the ejection plate 3 is responsible for compressing and ejecting the composite polymer flow formed by the distribution plate 2.

[0051] To avoid overly complex descriptions of the composite die, although not shown, components stacked above the metering plate 1 can be used as components that form a flow path in conjunction with the spinning machine and spinning unit. By designing the metering plate 1 to accommodate existing flow path components, existing spinning units and their components can be directly and effectively utilized. Therefore, there is no need to dedicate a spinning machine specifically for this die.

[0052] In addition, the shape of the ejection hole of the ejection plate 3 is preferably set to Figure 3 (a) shows an asymmetric slit shape. In a cross-section formed by joining two components with different thermal shrinkage, i.e., different polymer viscosities, a flow velocity gradient is generated inside the ejection hole. When the flow velocity gradient is immediately relaxed after ejection, the polymer immediately after ejection becomes twisted and lacks ejection stability. In addition, problems such as the inability to obtain the desired cross-section arise. By setting the ejection hole diameter to an appropriate range according to the viscosity of each component, the flow velocity difference between the two components can be reduced, and stable ejection of the polymer immediately after ejection can be achieved. In addition, the cross-section formation stabilization of the die using the distribution plate method can be dramatically improved, and an accurate eccentric core-sheath cross-section can be obtained.

[0053] Furthermore, from the perspective of improving stable ejection and cross-sectional formability, the difference in melt viscosity between the polymers used in the fibers of the present invention is also important. To ensure uniform pressure loss during contraction, the two polymers that are melted to form a composite flow have their cross-sectional areas varied perpendicular to the polymer flow direction. This results in a flow velocity difference, causing the centers of gravity of the components to be ejected with deviations, leading to distortion in the ejected polymer flow. Specifically, a polymer with a higher melt viscosity has a slower flow rate due to its larger cross-sectional area, while a polymer with a lower melt viscosity has a faster flow rate due to its smaller cross-sectional area. Therefore, by reducing the melt viscosity difference between the polymers used, the flow velocity difference between the polymers is mitigated, thus suppressing distortion in the ejected polymer flow. To further this perspective, the melt viscosity difference between the combined polymers is preferably smaller. However, in the polyester fibers of the present invention, the melt viscosity difference between the combined polymers is preferably larger, taking into account factors such as crimping behavior. Given these considerations, a melt viscosity difference between the combined polymers of 100 Pa·s and 300 Pa·s is particularly preferred.

[0054] By adopting these production conditions, it is possible to obtain a polyester fiber having a non-uniformity Y / X in the fiber cross section of 1.1 to 3.0, a ratio L / X of the minor diameter X to the circumference L of the core of 2.6 to 5.0, a core interface irregularity of 15% or less, and a ratio S / X of the minimum thickness S of the sheath to the minor diameter X of 0.01 to 0.1.

[0055] The polyester fiber of the present invention is warped in a raw yarn state and knitted using a tricot machine. Furthermore, the scouring, dyeing, and subsequent presetting and final setting conditions after knitting can be carried out according to conventional methods.

[0056] Example

[0057] The following evaluations were performed on Examples and Comparative Examples.

[0058] (1) Melt viscosity of polymer

[0059] The moisture regain of the polymer chips was reduced to 200 ppm or less by vacuum drying, and the melt viscosity was measured by changing the strain rate in stages using a Capilograph 1B manufactured by Toyo Seiki Co., Ltd. The measurement temperature was the same as the spinning temperature described in the Examples and Comparative Examples, i.e., 1216 s -1 Incidentally, the time from the time the sample was placed in the heating furnace to the start of measurement was set to 5 minutes, and the measurement was performed under a nitrogen atmosphere.

[0060] (2) Total fineness

[0061] For the fiber sample, 100 batches of hanks were produced using a measuring machine with a frame circumference of 1.0 m, and the value measured using a balance and calculated using the following formula was used as the total fineness.

[0062] Total fineness (dtex) = hank weight (g) × 100

[0063] (3) The short diameter X, long diameter Y, core circumference L, distance between two straight lines Z, and minimum thickness S of the sheath in the fiber cross section

[0064] A KEYENCE digital microscope (VHX-2000) was used to photograph a cross section of polyester fiber at 100x to 500x magnification. The short diameter (X), long diameter (Y), core circumference (L), distance between two straight lines (Z), and minimum sheath thickness (S) of each single yarn were measured. Five random single yarns were measured. The average values ​​of these values ​​were used to calculate the irregularity (Y / X), L / X, and the concavity (Z / X × 100) and S / X.

[0065] (4) Telescopic elongation

[0066] The expansion and contraction elongation was determined according to Japanese Industrial Standards (JIS) L1013 (2010), Item 8.11, Method C (Simplified Method).

[0067] (5) Evaluation of tricot warp knitted fabrics

[0068] A 28G tricot-warp plain weave fabric was produced using the polyester fibers obtained in each of the Examples and Comparative Examples for both the front and back yarns. The resulting fabric was scoured at 90°C for 1 minute and dyed at 130°C for 20 minutes. The fabric was then pre-set at 130°C for 2 minutes and final-set at 170°C for 1 minute to produce a tricot knit fabric.

[0069] A. Stretchability (warp elongation)

[0070] The elongation in the warp direction of the tricot fabric was determined according to JIS L1096 (2010) 8.16.1 Method A (Constant Elongation Method). Evaluation was performed based on the following three levels, with S and A being considered good elongation.

[0071] S: Warp elongation more than 15%

[0072] A: Warp elongation more than 10%

[0073] C: Warp elongation is less than 10%.

[0074] B. Abrasion resistance (Martindale)

[0075] Evaluation was conducted using tricot fabrics according to JIS L1096 (2010) 8.19.5 Method E (Martindale method). The test conditions involved using a standard polyester abrasion cloth as the friction material. The number of abrasions was measured under a compressive load of 9 kPa until the abrasion cloth's discoloration reached level 3 on the grayscale for discoloration. Evaluation was performed as follows. Acceptable grades were S and A.

[0076] S: more than 5000 times

[0077] A: Less than 5000 times and more than 2000 times

[0078] C: Less than 2000 times.

[0079] C.Quality

[0080] The obtained tricot fabric was inspected by a skilled inspector and visually evaluated for the occurrence of longitudinal streaks. The pass levels were S and A.

[0081] S: No vertical streaks, very good

[0082] A: Although there are some vertical stripes, it is acceptable.

[0083] C: There are many vertical streaks, which is an unacceptable level.

[0084] Example 1

[0085] As the core component, polytrimethylene terephthalate (PTT) with a melt viscosity of 100 Pa·s was used, and as the sheath component, polyethylene terephthalate (PET) with a melt viscosity of 30 Pa·s was used. Both the PTT polymer and the PET polymer were melted at 260°C and 280°C respectively using an extruder, and then metered by a pump. 275°C was set as the spinning temperature, and the polymers were flowed into the die while maintaining the temperature. The composite ratio of the PTT component and the PET component was set to 50 / 50, and the polymers were flowed into an eccentric core-sheath cross-section composite die with 24 ejection holes. The polymers merged inside the die to form a composite cross-section to present a Figure 1 The desired eccentric core-sheath cross-section illustrated in (a) is ejected from the spinning die.

[0086] Spinning die mouth Figure 2 As shown, a metering plate 1, a distribution plate 2, and a discharge plate 3 are stacked from top to bottom. The distribution plate forms a spinning die with a multi-layered fine flow path. Furthermore, the discharge hole shape of the discharge plate 3 is set to a discharge hole diameter of 0.25 mm on the side containing the PTT as the main component, a discharge hole diameter of 0.18 mm on the side containing the PET as the main component, a slit width of 0.13 mm, and a slit length of 1.05 mm ( Figure 3 (a)).

[0087] The yarn ejected from the die is used Figure 4 The melt spinning equipment is used for spinning and stretching. Specifically, the fiber sliver ejected from the composite die orifice i is cooled by the sliver cooling air supply device ii, and the oil is applied to the sliver by the oil applying device iii at a rate of 0.8% by weight based on the fiber weight. After pre-interlacing by the pre-interlacing device iv at an air pressure of 0.03 MPa, the sliver is drawn at a speed of 1070 m / min by the first hot roller (1HR) v heated to 60°C. The sliver is not wound temporarily, but is drawn at a speed of 3780 m / min by the second hot roller (2HR) vi heated to 155°C, and stretched and heat-set at a stretch ratio of 3.5 times. The yarn was then interwoven using a final interweaving device vii at an air pressure of 0.15 MPa. The yarn was then taken up by two godet rollers (the third godet roller (3GR) viiii and the fourth godet roller (4GR) ix) at a speed of 3700 m / min and wound into a package x at a package winding speed of 3670 m / min, yielding a 56 dtex, 24-filament polyester multifilament yarn. The properties of this polyester multifilament yarn are shown in Table 1.

[0088] The resulting polyester multifilament yarn was used as both the front and back yarns, and a 28G tricot pile-warp plain weave fabric was knitted using a tricot knitting machine. The resulting fabric was then scoured at 90°C for 1 minute and dyed at 130°C for 20 minutes. The fabric was then pre-set at 130°C for 2 minutes and final-set at 170°C for 1 minute to produce a tricot knitted fabric. The resulting tricot knitted fabric exhibited excellent stretchability and abrasion resistance, lacked longitudinal streaks, and exhibited excellent knit quality.

[0089] Examples 2 to 7, Comparative Example 1

[0090] A polyester multifilament was obtained in the same manner as in Example 1 except that the slit length of the ejection plate 3 was changed. The results are shown in Table 1.

[0091] Comparative Example 2

[0092] In addition to changing the ejection plate 3 to Figure 3 (b) The circular shape shown in Figure 1 The eccentric core-sheath cross section shown in (b) was obtained by the same method as in Example 1 except for the spinning die. The results are shown in Table 1.

[0093] [Table 1]

[0094]

[0095] In Comparative Example 1, the polyester fiber had a large irregularity and the crimped loops became large, which made it impossible to maintain the physical strength of the loops. As a result, the warp elongation of the tricot fabric was as low as 8%, and sufficient stretchability could not be obtained.

[0096] In Comparative Example 2, the irregularity was small and L / X became small, so the Martindale of the tricot fabric was 1500 times and the abrasion resistance was low. The crimp phase was aligned, resulting in significant deterioration in the quality of the longitudinal stripes.

[0097] Examples 8 to 11, Comparative Example 3

[0098] Except for changing the distribution plate 2 and the unevenness, the polyester fiber was obtained in the same manner as in Example 1. Figure 1 The eccentric core-sheath composite cross-section shown in (c) was ejected from the spinning die. The results are shown in Table 2.

[0099] In Comparative Example 3, the degree of irregularity was large, and the distance between the centers of gravity of the polyester fiber was increased, so the crimping property was reduced, and the warp elongation of the tricot fabric was as low as 6%, and sufficient stretchability could not be obtained.

[0100] [Table 2]

[0101]

[0102] Examples 12 to 14, Comparative Examples 4 and 5

[0103] The polyester fibers were obtained in the same manner as in Example 1 except that the distribution plate 2 and the minimum thickness of the sheath portion were changed. The results are shown in Table 3.

[0104] In Comparative Example 4, the minimum thickness of the sheath portion was small, and the Martindale test of the tricot fabric was 1000 times, resulting in poor abrasion resistance.

[0105] In Comparative Example 5, the minimum thickness of the sheath portion was large, the crimping properties of the polyester fiber were reduced, and the warp elongation of the tricot fabric was as low as 8%, and sufficient stretchability could not be obtained.

[0106] Example 15

[0107] A polyester fiber was obtained in the same manner as in Example 1 except that the core component was changed to polybutylene terephthalate (PBT) having a melt viscosity of 250 Pa·s. The evaluation results of the obtained polyester multifilament are shown in Table 3.

[0108] [Table 3]

[0109]

[0110] While the present invention has been described in detail and with reference to specific embodiments, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the present invention.

[0111] 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.

[0112] Industrial applicability

[0113] The polyester fiber of the present invention can provide a high-quality tricot fabric having excellent abrasion resistance, no longitudinal streaks, and excellent stretchability.

[0114] Explanation of Figure Numbers

[0115] A: core

[0116] B: Sheath

[0117] a: The center of gravity of the core A in the composite cross section

[0118] C: Center of gravity of composite cross-section fiber

[0119] 1: Metering board

[0120] 2: Distribution board

[0121] 3: ejection plate

[0122] 4: Measuring tank A

[0123] 5: Measuring tank B

[0124] 6: Spout hole

[0125] i: Compound die

[0126] ii: Yarn cooling air supply device

[0127] iii: Oil applying device

[0128] iv: Front interweaving device

[0129] v: First hot roller

[0130] vi: Second hot roller

[0131] vii: Formal Interweaving Device

[0132] viii: The third godet roller

[0133] ix: Fourth Godet Roller

[0134] x: roll

[0135] xi: contact roller

Claims

1. A polyester fiber, wherein in a fiber cross section of an eccentric core-sheath cross-section polyester fiber, The cross-section has a profile ratio (Y / X) of 1.1 to 3.0, calculated from the major axis Y and the minor axis X perpendicular to the major axis Y and passing through the center of gravity of the fiber. The ratio L / X of the minor diameter X to the circumference L of the core is 2.6 to 5.0, The concavity and convexity at the interface of the core is less than 15%, Concavity: The value expressed by the following formula, where W is a straight line parallel to the minor diameter X and passing through the most convex point of the core contour on the side where the sheath thickness is the largest, and Z is the distance between the line X and the line W. Convexity = 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 diameter X is 0.01 to 0.

1.

3. The polyester fiber according to claim 1 or 2, 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 knitted fabric, comprising the polyester fiber according to claim 1 .

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