JP7735866B2 - Island-in-sea composite fibers and textile products containing islands-in-sea composite fibers - Google Patents

Description

The present invention relates to a polyester fiber having moisture-absorbing properties.

Polyester fibers, typified by polyethylene terephthalate, are widely used in clothing and industrial applications due to their excellent mechanical properties, chemical resistance, and heat resistance, as well as their characteristic firm and resilient texture, low moisture absorption and minimal change in properties even when wet, wrinkle resistance, and excellent dimensional stability. However, as mentioned above, polyester fibers are not hygroscopic, and they can become stuffy and sticky, especially in hot and humid summer environments. Therefore, it has been proposed to conjugate polyester fibers with a hygroscopic polymer to impart hygroscopic properties to them.

For example, Patent Document 1 proposes a hygroscopic sea-island composite fiber in which the sea portion is made of polyethylene terephthalate and the island portion is made of polyether block amide copolymer.

Patent document 2 proposes a sea-island composite fiber in which cracking of the sea portion during hot water treatment is suppressed by imparting moisture absorption to the fiber by using a hygroscopic polymer in the island portion and controlling the thickness of the sea portion in the outermost layer of the fiber cross section.

JP 2016-69770 A International Publication No. 2018/012318

In the sea-island composite fibers disclosed in Patent Documents 1 and 2, the thickness of the sea region and the number of island regions are specified in relation to the arrangement of the island regions in the fiber cross section. However, if the single fiber fineness is reduced to achieve the soft texture required for clothing applications, the stress generated by the volumetric swelling of the hygroscopic polymer during hot water treatment cannot be dispersed, and cracks and other breakages may occur on the fiber surface. In this case, uneven dyeing and fuzz may occur, potentially reducing the quality of woven and knitted fabrics. Furthermore, surface cracks in the fiber may also cause the hygroscopic polymer to leach out, resulting in reduced hygroscopicity. Furthermore, such fibers may be prone to surface cracks when the fiber or a textile made from them is worn, posing challenges for their application in clothing that is repeatedly washed, such as innerwear, or clothing that is repeatedly subjected to abrasion, such as sportswear.

The present invention aims to solve the above problems by dispersing the stress that occurs as the fiber expands in volume upon moisture absorption, thereby dramatically reducing cracks that occur on the fiber surface. Furthermore, it is an object of the present invention to provide a polyester fiber that is excellent in quality and does not suffer from uneven dyeing or fuzz when made into woven or knitted fabrics, and whose moisture absorption properties do not decrease when subjected to hot water treatment, etc.

In order to solve the above problems, the present invention has the following configuration.
(1) A fiber characterized in that it is an islands-in-sea type composite fiber in which the main constituent component of the sea portion is an aromatic polyester, the fiber has a moisture absorption/desorption parameter ΔMR of 2.0% or more, the figure obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery in the fiber cross section with line segments is a regular polygon with the centers of gravity as vertices, and the ratio C/L of the radius of curvature C (μm) of the side of the outer periphery of the island portions arranged at the outermost periphery in the fiber cross section on the fiber surface side to the radius L (μm) of the circumscribed circle including the island portions arranged at the outermost periphery in the fiber cross section is 0.50 to 0.90 .
(2) The fiber according to (1), characterized in that the number of island portions arranged at the outermost periphery in the cross section of the fiber is odd.
(3) A textile product comprising the islands-in-the-sea type composite fiber according to (1) or (2) .

The present invention can disperse the stress that occurs as the fiber expands in volume upon moisture absorption, suppressing cracks on the fiber surface, resulting in a polyester fiber of excellent quality that is free of uneven dyeing or fuzz when woven or knitted. Furthermore, the fiber has excellent moisture absorption properties without any reduction in moisture absorption, making it particularly suitable for use in clothing.

1A, 1B, and 1C are schematic diagrams of the cross-sectional structure of a polyester fiber of the present invention. 1A, 1B, 1C, and 1D are schematic diagrams of cross-sectional structures of polyester fibers of the present invention. FIG. 1 is a cross-sectional view illustrating a method for producing a polyester fiber according to the present invention.

The polyester fiber of the present invention is primarily composed of an aromatic polyester. By using an aromatic polyester as the primary component, the fiber has excellent mechanical properties and heat resistance, resulting in a favorable texture, including firmness, stiffness, and a dry feel. Furthermore, the polyester fiber of the present invention has excellent moisture absorption, with a moisture absorption/release parameter ΔMR of 2.0% or more, allowing for the production of a fiber structure that is comfortable to wear as a cooling material.

Moisture-absorbing fibers incorporate water molecules through physical adsorption onto the fiber and/or through interactions between water molecules and functional groups in the molecular structure of the components that make up the fiber. In particular, when a fiber has high moisture absorption, water molecules are incorporated into the fiber, causing the fiber to swell in volume. However, aromatic polyesters are difficult to deform due to the presence of rigid aromatic rings in their polymer structure, and the stress generated when the fiber swells in volume due to moisture absorption cannot be fully dispersed, which can result in cracks on the fiber surface.

Therefore, in the polyester fibers of the present invention, which suppress cracking of the fiber surface due to volumetric swelling upon moisture absorption, it is important that the figure obtained by connecting the centers of gravity of the components arranged at the outermost periphery among the components arranged inside the fiber in the cross section of the fiber with line segments is a regular polygon with the centers of gravity as vertices.

The cross-sectional form of a fiber having components disposed inside the fiber in the fiber cross section is preferably a sea-island composite fiber composed of two or more types of polymers, and the components disposed inside the fiber are called island portions. The figure obtained by connecting the centers of gravity of the components disposed inside the fiber in the fiber cross section, i.e., the centers of gravity of the island portions disposed outside the fiber cross section, with line segments is drawn by selecting the center of gravity so that the line segments do not intersect except at the center of gravity, as shown in Figure 1(a). On the other hand, when the centers of gravity of the island portions are connected with line segments as shown in Figure 1(b), the line segments intersect at points other than the center of gravity of the island portions, and the figure drawn in this case is not included in the figure obtained by connecting the centers of gravity of the island portions disposed outside the fiber cross section. Furthermore, as shown in Figure 1(c), in island portion 2f, other island portions (2a, 2b, 2c, 2d, 2e) are disposed between the island portion and the fiber surface, so island portion 2f is not included in the island portions disposed outside the fiber cross section.

The definition of a regular polygon, which is the arrangement form of the island components that is a characteristic of this invention, is explained below.

A figure obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery in the fiber cross section with line segments is defined as an n-polygon, with the lengths of each line segment being A1, A2, A3... An. The average length of these line segments is defined as Lx. The ratio of each line segment length to the average Lx (A1/Lx, A2/Lx, A3/Lx... An/Lx) is calculated by rounding to two decimal places, and when all ratios are between 0.97 and 1.03, this means that the figure obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery in the fiber cross section with line segments is a regular n-polygon.

In the polyester fiber of the present invention, the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery in the fiber cross section with line segments is a regular polygon with the center of gravity as a vertex. This means that the vectors of stress generated during volumetric swelling due to moisture absorption are opposite between adjacent island portions, and the stresses cancel each other out between the island portions, thereby reducing stress propagation to the sea portion on the fiber surface side. Because stress propagation to the sea portion on the fiber surface side is reduced, the fiber surface is less likely to crack, and uneven dyeing and fuzzing can be suppressed. On the other hand, if the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery in the fiber cross section with line segments is not a regular polygon with the center of gravity as a vertex, stress generated during volumetric swelling during moisture absorption is less likely to be dispersed, and points where stress concentrates are more likely to occur at the interface between the island portion and the sea portion. This can lead to cracking on the fiber surface, uneven dyeing, and fuzzing, which can reduce the quality of woven or knitted fabrics.

As described above, the polyester fiber of the present invention significantly improves upon the problems associated with conventional composite fibers containing moisture-absorbing components by arranging the island components at the outermost periphery in a regular polygonal shape, but it is preferable that the number of island components arranged at the outermost periphery in the fiber cross section is an odd number.

By making the number of island portions arranged at the outermost periphery an odd number, the stress generated by volumetric swelling due to moisture absorption is prevented from concentrating in a straight line, dispersing the stress and suppressing cracks on the fiber surface. This prevents uneven dyeing and fuzz caused by cracks on the fiber surface, resulting in superior quality when made into a woven or knitted fabric. The number of island portions arranged at the outermost periphery in the fiber cross section is more preferably an odd number of 9 or less, and even more preferably an odd number of 5 or less, with the minimum number of island portions being 3.

The polyester fiber of the present invention preferably has a total number of island portions in the fiber cross section of 15 or less. By keeping the total number of island portions within this range, stress generated by volumetric swelling due to moisture absorption is prevented from concentrating linearly, dispersing the stress and suppressing cracking on the fiber surface. This prevents uneven dyeing and fuzzing caused by cracking on the fiber surface, resulting in excellent quality when made into a woven or knitted fabric. The total number of island portions in the fiber cross section is more preferably 10 or less, and even more preferably 6 or less, with the minimum number of island portions being 3.

In the polyester fiber of the present invention, the ratio C/L of the radius of curvature C (μm) of the outer periphery of the island portion located at the outermost periphery in the fiber cross section, which is on the fiber surface side, to the radius L (μm) of the circumscribing circle including the island portion located at the outermost periphery in the fiber cross section, is preferably 0.50 to 0.90. Here, the circumscribing circle including the island portion located at the outermost periphery in the fiber cross section is circle 4 in Fig. 2(b), and L is the radius of circle 4. Furthermore, the radius of curvature C of the outer periphery of the island portion located at the outermost periphery in the fiber cross section, which is on the fiber surface side, is the radius of circle 5 in Fig. 2(c), which is determined by the method described in the Examples.
C/L indicates the sharpness of the curve of the outer peripheral fiber surface-side edge of the outermost island portion in the fiber cross section. When C/L is 0.50 or more, the stress generated by volumetric swelling upon moisture absorption is evenly distributed across the sea portion, making the fiber surface less likely to crack. It is more preferably 0.55 or more, and even more preferably 0.60 or more. When C/L is 0.90 or less, the curve of the outer peripheral fiber surface-side edge of the outermost island portion in the fiber cross section is not large and no corners are formed. Therefore, the stress generated by volumetric swelling upon moisture absorption does not concentrate in these areas, making the fiber surface less likely to crack. It is more preferably 0.85 or less, and even more preferably 0.80 or less. A C/L of 1.0 indicates that the curve of the outer peripheral fiber surface-side edge of the outermost island portion is equivalent to the curve of the fiber surface. A specific example of a fiber cross section in this case is a core-sheath composite fiber with a single island portion.

In the polyester fiber of the present invention, the ratio L/R of the radius L (μm) of a circumscribed circle including all the island portions arranged at the outermost periphery in the fiber cross section to the fiber radius R (μm) is preferably 0.50 to 0.90.
L/R indicates the thickness of the sea portion between the fiber surface and the island portions arranged at the outermost periphery in the fiber cross section. When L/R is 0.90 or less, the thickness of the sea portion is sufficiently secured relative to the fiber diameter, thereby suppressing sea portion cracking due to stress generated by volumetric swelling upon moisture absorption, and suppressing the occurrence of uneven dyeing and fluffing due to cracks on the fiber surface caused by sea portion cracking, resulting in excellent quality when made into a woven or knitted fabric. Based on this idea, the L/R is more preferably 0.80 or less, and even more preferably 0.60 or less. Furthermore, when L/R is 0.50 or more, the rigidity due to the thickness of the aromatic polyester arranged in the sea portion can be reduced, and the stress generated by volumetric swelling upon moisture absorption can be reduced.

The polyester fiber of the present invention preferably has a ratio S/L of 0.05 to 0.50, where S (μm) is the minimum distance between island portions in the fiber cross section and L (μm) is the radius of the circumscribed circle that includes all of the islands arranged at the outermost periphery in the fiber cross section. Here, the minimum distance between island portions in the fiber cross section is line segment 7 in Figure 2(d), determined by the method described in the Examples.

Here, the minimum distance between island portions in the fiber cross section refers to the thickness of the sea portion sandwiched between two adjacent island portions. When S/L is 0.05 or more, the stress generated by volumetric swelling upon moisture absorption is alleviated in the sea portion between the island portions, reducing stress propagation to the sea portion and suppressing cracking on the fiber surface. A ratio of 0.10 or more is more preferable, and 0.15 or more is even more preferable. Furthermore, when S/L is 0.50 or less, the distance between the island portions is not large enough, resulting in a stress alleviation effect from the sea portion between the island portions, reducing stress propagation to the sea portion on the fiber surface side and suppressing cracking on the fiber surface. Based on this concept, a ratio of 0.40 or less is more preferable, and 0.30 or less is even more preferable.

It is preferable that the polyester fiber of the present invention has a minimum thickness of the sea portion of 0.3 μm or more.

Here, the minimum thickness of the sea portion is the minimum distance between the intersection of the outer periphery of an island portion and the fiber surface when a straight line is drawn from the center of gravity of any island portion in the fiber cross section to the surface of any fiber, as described in the Examples, and the intersection of the line with the fiber surface and the outer periphery of the island portion. This is line segment 6 in Figure 2(c). A minimum thickness of 0.3 μm or more can suppress sea portion cracking due to stress generated by volumetric swelling upon moisture absorption, and can suppress the occurrence of uneven dyeing and fuzz due to cracks on the fiber surface caused by sea portion cracking, resulting in excellent quality when made into a woven or knitted fabric. A minimum thickness of 1.0 μm or more is more preferable, and 2.5 μm or more is even more preferable.

The sea/island composite ratio of the polyester fiber of the present invention is preferably 50/50 to 90/10 by weight. When the sea portion composite ratio is 50% by weight or more, the aromatic polyester in the sea portion provides excellent mechanical properties and heat resistance, firmness, stiffness, and a dry feel, resulting in a fiber structure with excellent wear comfort. Furthermore, sea portion cracking due to stress generated by volumetric swelling upon moisture absorption can be suppressed, and uneven dyeing and fuzzing due to cracks on the fiber surface caused by sea portion cracking can be suppressed, resulting in excellent quality when woven or knitted fabrics are produced. A sea portion composite ratio of 60% by weight or more is more preferred, and 70% by weight or more is even more preferred. On the other hand, when the sea portion composite ratio of the polyester fiber is 90% by weight or less, i.e., the island portion composite ratio is 10% by weight or more, the stiffness due to the thickness of the aromatic polyester disposed in the sea portion can be reduced, and the stress generated by volumetric swelling upon moisture absorption can be reduced. Based on this concept, a sea portion composite ratio of 85% by weight or less is more preferred, and 80% by weight or less is even more preferred.

The polyester fiber of the present invention has a moisture absorption/desorption parameter ΔMR, an index of moisture absorption, of 2.0% or more. ΔMR is the difference in the moisture absorption rate of a fiber at high temperature and humidity, typically 30°C x 90% RH, and at standard temperature and humidity, typically 20°C x 65% RH. The higher the ΔMR, the higher the moisture absorption of the fiber. A ΔMR of 2.0% or more reduces stuffiness inside the garment, resulting in comfortable wear. A more preferred ΔMR range is 2.5% or more, an even more preferred range is 3.0% or more, and an especially preferred range is 4.0% or more. While there is no particular upper limit to the ΔMR range, the level achievable with the present invention is approximately 10%, which is the practical upper limit. Furthermore, the polyester fiber of the present invention satisfies the above ΔMR range both before and after hot water treatment such as dyeing.

Aromatic polyester, the main component of the polyester fiber of the present invention, is a polymer formed from a combination of an aromatic dicarboxylic acid and an aliphatic diol, an aliphatic dicarboxylic acid and an aromatic diol, or an aromatic dicarboxylic acid and an aromatic diol. In general, from the standpoints of mechanical properties, heat resistance, and ease of handling during production, it is preferable to use an aromatic polyester formed from a combination of an aromatic dicarboxylic acid and an aliphatic diol.

Specific examples of aromatic dicarboxylic acids include, but are not limited to, terephthalic acid, isophthalic acid, phthalic acid, 5-sodium sulfoisophthalic acid, 5-lithium sulfoisophthalic acid, 5-(tetraalkyl)phosphonium sulfoisophthalic acid, 4,4'-diphenyldicarboxylic acid, and 2,6-naphthalenedicarboxylic acid.

Specific examples of aliphatic diols include, but are not limited to, ethylene glycol, 1,3-propanediol, 1,4-butanediol, hexanediol, cyclohexanediol, diethylene glycol, hexamethylene glycol, and neopentyl glycol.

The method for producing the aromatic polyester of the present invention is not limited, and if the raw materials used in production are collectively referred to as monomers, the aromatic polyester may be produced by synthesizing the monomers through general polycondensation reactions, addition polymerization reactions, etc. Examples of monomers include, but are not limited to, petroleum-derived monomers, biomass-derived monomers, and mixtures of petroleum-derived monomers and biomass-derived monomers.

In addition, the aromatic polyester of the present invention may be copolymerized or mixed with a second or third component in addition to the main component, as long as it does not deviate from the objectives of the present invention. For the main component to be an aromatic polyester, the copolymerization amount is 10 mol % or less, calculated as the amount of copolymerized monomers relative to the total amount of monomers.

As described above, the polyester fiber of the present invention has an aromatic polyester as the main component of the sea portion. However, aromatic polyesters generally do not have functional groups in their polymer structure that form strong interactions with water molecules. Therefore, examples of methods for adjusting the ΔMR of the polyester fiber of the present invention to the above range include adding a hygroscopic compound, disposing a highly hygroscopic polymer (hereinafter sometimes referred to as a hygroscopic polymer), and treating polymer molecules on the fiber surface with ozone or the like to generate hygroscopic functional groups. Among these, disposing a hygroscopic polymer in the island portion is preferred when aiming to obtain polyester fibers with excellent hygroscopicity.

Examples of hygroscopic polymers suitable for disposing in the island portions of the polyester fiber of the present invention include polyetheresters, polyetheramides, polyetheresteramides, polyamides, thermoplastic cellulose derivatives, and polyvinylpyrrolidone. Among these, polyetheresters, polyetheramides, and polyetheresteramides containing polyethers as copolymerization components are more preferably used for the polyester fiber of the present invention, as they have excellent stability during melt molding and the desired high hygroscopicity. Furthermore, polyetheresters have excellent affinity with the aromatic polyester of the sea portion and also provide excellent heat resistance for the hygroscopic polymer, thereby improving the mechanical properties of the resulting sea-island composite fiber. Therefore, they are particularly preferred for use in the present invention. Additionally, polyetheresters composed of polybutylene terephthalate and polyether, which have excellent crystallinity, are more preferred, as they can suppress the elution of the hygroscopic polymer in hot water.

These hygroscopic polymers have a high affinity for water and are prone to elution when they come into contact with water or hot water during dyeing. If cracks occur on the fiber surface due to stress caused by volumetric swelling during moisture absorption, the hygroscopic polymer in the island portions may elute from the fiber upon contact with hot water, reducing the hygroscopicity of the fiber. Therefore, when a hygroscopic polymer is placed in the island portions, the composite cross-sectional shape of the polyester fiber of the present invention significantly reduces cracks on the fiber surface, resulting in a polyester fiber with excellent hygroscopicity.

The hygroscopic polymer of the present invention may contain, in addition to the main component, a second or third component copolymerized or mixed therein, as long as it does not deviate from the objectives of the present invention, and the copolymerization amount is 10 mol % or less as the amount of monomer of the copolymerization component relative to the total amount of monomers.

The cross-sectional shape of the polyester fiber of the present invention can be not only round, but also a wide variety of cross-sectional shapes such as flat, Y-shaped, T-shaped, hollow, square-shaped, and square-shaped.

The polyester fibers of the present invention may be in any form, such as long fibers (filaments) or short fibers (staples). In the case of long fibers, they may be monofilaments consisting of a single yarn or multifilaments consisting of multiple single yarns. In the case of short fibers, there are no limitations on the cut length or number of crimps.

The total fineness of the polyester fiber of the present invention may be set appropriately depending on the application, but for long fibers for clothing, a value of 8 dtex or more and 150 dtex or less is practically preferred. Furthermore, while a strength of 1.5 cN/dtex or more is preferred for clothing, a strength of 1.5 cN/dtex or less can be used without problems by combining it with other fibers when producing fabrics. The elongation may be set appropriately depending on the application, but from the perspective of processability when processing into fabrics, it is preferably 25% or more and 60% or less.

The polyester fiber of the present invention preferably has a single fiber fineness of 6.0 dtex or less. By achieving this range, the stiffness due to the thickness of the aromatic polyester disposed in the sea portion can be reduced, and in addition, a fiber structure with excellent mechanical properties and heat resistance, firmness, stiffness, and a dry feel can be obtained, resulting in an excellent wearing comfort. Furthermore, sea portion cracking due to stress generated by volumetric swelling upon moisture absorption can be suppressed, and uneven dyeing and fuzzing due to cracks on the fiber surface caused by sea portion cracking can be suppressed, resulting in excellent quality when made into woven or knitted fabrics. More preferably, the single fiber fineness is 4.0 dtex or less, and even more preferably 2.0 dtex or less.

The polyester fibers of the present invention can be obtained by known melt spinning and conjugate spinning techniques, examples of which are shown below. However, the spinning and conjugate methods are not limited to those exemplified here.

Polyester fibers of the present invention, which are made from two or more polymers, can be produced by melt spinning, which is intended to produce continuous fibers; wet and dry-wet solution spinning; and melt-blowing and spunbonding, which are suitable for obtaining sheet-like fiber structures. However, from the perspective of increasing productivity, melt spinning is preferred. Furthermore, the use of a composite spinneret, as described below, is preferred for melt spinning. When using melt spinning, the spinning temperature should be the temperature at which the polymers used, primarily those with high melting points or high viscosity, exhibit fluidity. While this fluidity temperature varies depending on the molecular weight, stable production is possible when it is set between the melting point of the polymer and melting point + 60°C.

In a melt spinning process, for example, the sea polymer and island polymer are melted separately, metered and transported using a gear pump, and then a composite flow is formed using conventional methods to form a specific composite structure. The composite flow is then discharged from a spinneret. The yarn is cooled to room temperature by blowing cooling air onto it using a yarn cooling device such as a chimney, oiled and focused using an oiling device, entangled using a fluid entangling nozzle, passed through a take-up roller and a stretching roller, and stretched according to the ratio of the peripheral speeds of the take-up roller and the stretching roller. Further examples include a method in which the yarn is heat-set using a stretching roller and wound on a winder (winding device). Another example is a two-step method in which the peripheral speeds of the take-up roller and the stretching roller are set to the same, and the yarn is wound on a winder operating at the same speed to form an unstretched yarn, which is then stretched in a separate process.

In the polyester fiber of the present invention, it is preferable to set the melt viscosity ratio of the two or more polymers used in the sea portion and the island portion to less than 5.0, as this allows a stable formation of a composite polymer flow and enables the production of fibers with a good composite cross section.

The composite spinneret used in producing the polyester fiber of the present invention is preferably the composite spinneret described in JP 2011-208313 A. The composite spinneret shown in Figure 3 of the present application is comprised of three main components stacked from top to bottom: a metering plate 8, a distribution plate 9, and a discharge plate 10, and is incorporated into a spinning pack for spinning. Incidentally, Figure 3 shows an example in which two types of polymers, A polymer and B polymer, are used. With conventional composite spinnerets, it is difficult to control the shape of the island portions as described above, and therefore it is preferable to use a composite spinneret that utilizes fine flow channels, as illustrated in Figure 3.

In the spinneret member illustrated in Figure 3, the metering plate 8 measures the amount of polymer per each discharge hole and each distribution hole, the distribution plate 9 controls the composite cross section and its cross-sectional shape of the single fiber, and the discharge plate 10 compresses the composite polymer flow formed by the distribution plate 9 and discharges it.

To avoid confusing the composite spinneret, components stacked above the metering plate 8 (not shown) can be components with flow paths formed to match the spinning machine and spin pack. By designing the metering plate 8 to match existing flow path components, existing spinning packs and their components can be used as is, eliminating the need to dedicate a spinning machine specifically to the spinneret. Multiple flow path plates can also be stacked between the flow path and metering plate 8 or between the metering plate 8 and distribution plate 9. This allows for efficient polymer transport in the cross-sectional direction of the spinneret and the cross-sectional direction of the single fiber, resulting in a configuration in which the polymer is introduced into the distribution plate 9. The composite polymer stream discharged from the discharge plate 10 is cooled and solidified according to the manufacturing method described above, and then an oil agent is applied. The composite polymer stream is then taken up by a roller at a specified peripheral speed, yielding a fiber with the desired composite cross section.

The polyester fibers of the present invention can be post-processed, such as by false twisting or twisting, and can be woven and knitted in the same way as ordinary fibers.

The polyester fibers and/or post-processed yarns of the present invention can be made into textile structures such as woven fabrics, knitted fabrics, pile fabrics, nonwoven fabrics, spun yarns, and wadding using known methods. Furthermore, textile structures made from the polyester fibers and/or post-processed yarns of the present invention may have any weave or knit structure, and suitable weaves include plain weave, twill weave, satin weave, or variations thereof, as well as warp knitting, weft knitting, circular knitting, lace knitting, or variations thereof.

When making a fiber structure, the polyester fiber of the present invention may be combined with other fibers by interweaving or interknitting, or it may be made into a blended yarn with other fibers and then used as a fiber structure.

The fiber structure made from the polyester fiber and/or post-processed yarn of the present invention has excellent moisture absorption properties and can therefore be suitably used in applications requiring comfort and quality. Examples include, but are not limited to, general clothing, sportswear, bedding, interior design, and materials.

The present invention will be described in detail using examples, but the present invention is not limited to these examples. The property values in the examples were measured using the following methods.

A. Melt Viscosity of Polymer A polymer sample whose moisture content was reduced to 300 ppm or less using a vacuum dryer was placed in a heating furnace set at the same temperature as the spinning temperature using a Toyo Seiki Capillograph, and melted in a nitrogen atmosphere. The sample was extruded from the capillary at the tip of the heating furnace while changing the strain rate in stages, and the viscosity was measured. The measurement was started after the sample had been placed in the heating furnace and allowed to reside for 5 minutes, and the value at a shear rate of 1216 sec ^-1 was taken as the melt viscosity of the polymer.

B. Polymer Melting Point (Tm)
Using a TA Instruments Q2000 differential scanning calorimeter, 20 mg of a polymer sample was heated from 20°C to 300°C at a heating rate of 20°C/min, held at 300°C for 5 minutes, then cooled from 300°C to 20°C at a cooling rate of 20°C/min, held at 20°C for 1 minute, and then heated from 20°C to 280°C at a heating rate of 20°C/min. The peak top temperature of the endothermic peak observed when this was measured was taken as the melting point. When multiple endothermic peaks were observed, the top of the endothermic peak with the highest temperature was taken as the melting point.

C. Total fineness A fiber sample was wound 200 times on a measuring machine with a frame circumference of 1.125 m to prepare a hank, and after drying in a hot air dryer (105±2°C x 60 minutes), the hank was weighed on a balance and multiplied by the official moisture regain to calculate the total fineness. The measurement was carried out four times, and the average value was taken as the total fineness.

D. Tensile Strength and Elongation Fiber samples were measured using a "TENSILON" (registered trademark) UCT-100 manufactured by Orientec Co., Ltd. as a measuring instrument under the constant-rate elongation conditions specified in the Test Method for Chemical Fiber Filament Yarns (JIS L1013 (2010)). The elongation was determined from the elongation at the point showing the maximum strength in the tensile strength-elongation curve. The tensile strength was determined as the value obtained by dividing the maximum strength by the total fineness. The measurement was performed 10 times, and the average values were used as the tensile strength and elongation.

E. Boiling Water Shrinkage A fiber sample was wound 20 times on a measuring machine with a frame circumference of 1.125 m to prepare a hank, and the initial length _L0 was determined under a load of 0.09 cN/dtex. Next, the hank was treated in boiling water for 30 minutes without load and then air-dried. Next, the length L1 after treatment was determined under a load of 0.09 cN/dtex and calculated using the formula ( ₁ ).
Boiling water shrinkage rate (%) = [(L ₀ - L ₁ )/L ₀ ] x 100...(1)
was calculated.

F. ΔMR before hot water treatment
Approximately 1 to 2 g of a fiber sample or fabric sample was weighed into a weighing bottle and dried at 110°C for 2 hours, after which the mass was measured and designated as _w0 . Next, the dried fiber sample was held at a temperature of 20°C and a relative humidity of 65% for 24 hours, after which the mass was measured and designated as _w65% . Subsequently, the temperature was adjusted to 30°C and a relative humidity of 90%, and the fiber sample was held there for 24 hours, after which the mass was measured and designated as w90 _% .
MR ₁ = [(w _65% - w ₀ )/w ₀ ]×100...(2)
MR ₂ = [(w _90% - w ₀ )/w ₀ ]×100...(3)
ΔMR= _MR2 - _MR1 ...(4)
At this time, the value calculated using the formulas (2) to (4) was defined as ΔMR.

G. ΔMR after hot water treatment
A cylindrical knitted fabric was produced from the fiber sample using an Eiko Sangyo NCR-BL circular knitting machine (boiler diameter 3.5 inches (8.9 cm), 27 gauge) with the stitch count adjusted to 50. When the fiber fineness was less than 80 dtex, the fibers were appropriately combined so that the total fiber fineness fed to the cylindrical knitting machine was 80 to 160 dtex. When the total fiber fineness exceeded 80 dtex, only one yarn was fed to the cylindrical knitting machine, and the stitch count was adjusted to 50 in the same manner as above. Next, the obtained cylindrical knitted fabric was placed in an aqueous solution containing 1 g/L sodium carbonate and the surfactant Sunmol BK-80 manufactured by Nicca Chemical Co., Ltd. The aqueous solution was heated to 80°C and treated for 20 minutes, and then dried in a hot air dryer at 60°C for 60 minutes. The dried cylindrical knitted fabric was then subjected to a hot water treatment under conditions of a bath ratio of 1:100, a treatment temperature of 130°C, and a treatment time of 60 minutes, and then dried for 60 minutes in a hot air dryer at 60°C to obtain a hot water-treated cylindrical knitted fabric. ΔMR was calculated for the obtained hot water-treated cylindrical knitted fabric in accordance with the description in section F.

H. radius of curvature C
The fiber sample was embedded in an embedding agent such as epoxy resin, and an image of the fiber cross section perpendicular to the fiber axis was taken using a scanning electron microscope (SEM) manufactured by Hitachi at a magnification such that 10 or more single fibers could be observed. The obtained image was analyzed using computer software WinROOF manufactured by Mitani Shoji to determine the radius of curvature C of the outer periphery of the outermost island portion on the fiber surface side of the fiber cross section.

To determine the radius of curvature, first, referring to Figure 2(c), a straight line was drawn from the center of gravity G of the island portion toward the surface of any fiber. The length of line segment BF, consisting of intersection point B where the line intersects the periphery of the island portion and intersection point F where the line intersects the fiber surface, was measured to two decimal places to determine intersection point B where the length of line segment BF is the smallest. The smallest radius of the circle circumscribing and tangent to the island portion at intersection point B was determined to three decimal places. This procedure was performed for all islands contained in a single fiber, and then for three randomly selected single fibers. The average of the resulting radii was calculated and rounded to three decimal places to determine the radius of curvature C (μm).

I. Radius of the circumscribed circle L
As in Section H, an image of the fiber cross section was taken with an SEM, and the image was analyzed using WinROOF. The radius of the circumscribed circle that included all of the island portions arranged on the outermost periphery in the fiber cross section was measured to three decimal places. This operation was performed for 10 randomly selected single fibers, and the simple number average of the results was calculated. The value rounded to three decimal places was defined as the radius L (μm) of the circumscribed circle.

J. Fiber radius R
As in Section H, images of the fiber cross section were taken with an SEM, and the radius of a single fiber randomly sampled within each image was measured in μm units to three decimal places. This operation was performed for 10 randomly sampled single fibers, and the simple number average of the results was calculated and rounded to two decimal places to obtain the fiber radius R (μm). Here, if the fiber cross section perpendicular to the fiber axis was not a perfect circle, its area was measured and the value calculated in terms of a circle was used.

K. Minimum distance between islands S
As in Section H, an image of the fiber cross section was taken with an SEM, and the image was analyzed using WinROOF to determine the minimum distance S between island portions in the fiber cross section.

To determine the minimum distance between island portions, referring to Figure 2(d), a line was drawn from the center of gravity Ga of island portion 2a to island portion 2b for two adjacent island portions 2a and 2b. The intersections with the outer periphery of each island were designated Da and Db, and the minimum length of this line segment Da-Db was measured to three decimal places. This procedure was performed on 10 adjacent island portions randomly selected from the island portions contained in a single fiber. If there were fewer than 10 line segments Da-Db between adjacent island portions, the minimum length of the line segment Da-Db was measured for all island portions contained in a single fiber. This procedure was then performed on three randomly selected single fibers, and the average length of the resulting line segments Da-Db was calculated. This average was rounded to three decimal places and used as the minimum distance S (μm) between island portions.

L. Minimum Thickness of Sea Region In the same manner as in the method for determining the length of line segment BF described in Section H, with reference to Fig. 2(c), a straight line is drawn from the center of gravity Ga of an island region toward the surface of any fiber, and the length of line segment BF consisting of intersection point B between the periphery of the island region and the line and intersection point F between the line and the fiber surface is measured to two decimal places, and intersection point B where the length of line segment BF is the minimum value is determined. This measurement was performed for all island regions included in one single fiber, and further for three single fibers selected at random, and the average value of the obtained line segments BF was calculated and rounded to one decimal place to obtain the minimum thickness (µm) of the sea region.

M. Number of cracks in the sea portion A cylindrical knitted fabric produced by the method described in Section G and subjected to hot water treatment was vapor-deposited with a platinum-palladium alloy and observed at 1000x magnification using a Hitachi S-4000 scanning electron microscope (SEM), and micrographs of 10 random fields were taken. In the 10 photographs obtained, the fiber surfaces constituting the cylindrical knitted fabric were observed, and the number of cracks in the sea portion was counted. A test with 10 or fewer cracks in the sea portion was considered to be acceptable.

N. Dyeing Unevenness A cylindrical knit fabric was prepared by the method described in Section G, and the resulting cylindrical knit fabric was placed in an aqueous solution containing 1 g/L sodium carbonate and the surfactant Sunmol BK-80 manufactured by Nicca Chemical. The aqueous solution was heated to 80°C and treated for 20 minutes, and then dried for 60 minutes in a hot air dryer at 60°C. Next, the fabric was dry-heat set at 160°C for 2 minutes. After dry-heat setting, the cylindrical knit fabric was placed in a dyeing solution prepared by adding 1.3 wt% of Nippon Kayaku Kayalon Polyester Blue UT-YA as a disperse dye and adjusting the pH to 5.0, or in a dyeing solution prepared by adding 1.0 wt% of Nippon Kayaku Kayacryl Blue 2RL-ED as a cationic dye and adjusting the pH to 4.0, and dyed under the conditions of a liquor ratio of 1:100, a dyeing temperature of 130°C, and a dyeing time of 60 minutes.

Using dyed cylindrical knit fabric as a sample, the L value was measured three times per sample using a Minolta CM-3700d spectrophotometer with a D65 light source, a viewing angle of 10°, and optical conditions of SCE (specular reflection excluded). The average of these measurements, rounded to two decimal places, was used as the L value of the sample. This procedure was performed on 10 randomly selected samples, and the rate of variation was calculated from the average and standard deviation of the L values of the 10 samples. If the rate of variation in the L values of these 10 samples was 5.0% or less, it was determined that there was no uneven dyeing.

O. Number of fluff Using a multipoint fluff counter (MFC-120 manufactured by Toray Engineering Co., Ltd.), the fiber sample was run at 600 m/min, measured for 10,000 m, and the number of fluffs displayed on the counter was counted. A warping reed (made of stainless steel, reed spacing 1 mm) was provided just before the measurement point, and the fiber was passed through it. This measurement was repeated 10 times, and the average value over 10,000 m was taken as the number of fluffs. A fluff count of 10 fluffs/10,000 m or less was deemed acceptable.

P. Moisture absorption and quick-drying properties A cylindrical knitted fabric prepared according to the method described in Section G and subjected to hot water treatment was held at a temperature of 20°C and a relative humidity of 65% for 24 hours, after which its mass was measured and designated as w _a . Next, 0.3 ml of water was dropped onto the center of the sample, and the mass was measured and designated as w _{0 minutes} . The moment water was dropped onto the sample was designated as 0 minutes, and the mass of the sample was measured at 5-minute intervals and designated as w _{n minutes} . Here, n minutes represents an arbitrary time at which the sample's mass was measured, and refers to 5, 10, 15 minutes, and other 5-minute intervals. The moisture residual rate WR at an arbitrary time was calculated using formula (5).
WR = [(w _{0 min} - _{w n min} ) / (w _{0 min} - _{w a} )] × 100 (5)
When the time during which the moisture residual rate WR calculated by the formula (5) falls below 30% is 60 minutes or less, the fabric is deemed to have moisture-absorbing and quick-drying properties.

Q. Maintenance of moisture absorption before and after hot water treatment The change in moisture absorption of the fiber before and after hot water treatment was evaluated as the difference in ΔMR, obtained by subtracting the ΔMR before hot water treatment calculated in section F from the ΔMR after hot water treatment calculated in section G. If the change in ΔMR was 2.0% or less, the moisture absorption of the fiber was considered to be maintained before and after hot water treatment.

Example 1
The sea portion was made of polyethylene terephthalate (melt viscosity 120 Pa s, melting point 254°C) and the island portion was made of polybutylene terephthalate (melt viscosity 50 Pa s, melting point 217°C) copolymerized with 50% by weight of polyethylene glycol (PEG6000S manufactured by Sanyo Chemical Industries, Ltd.) having a number average molecular weight of 8,300 g/mol. The sea portion and island portion polymers were separately melted at a spinning temperature of 285°C, and then weighed out so that the sea-island ratio was 80:20 by weight. The polymers were fed into a spinning pack equipped with the composite spinneret shown in Figure 3, and the fed polymers were discharged from a discharge hole (hole diameter 0.30 mm, number of holes 36) so as to form a sea-island composite structure in which the number of island portions located at the outermost periphery was three and the total number of island portions was three. The discharged composite polymer stream was cooled and solidified in a cooling device, and then a water-containing oil was added using an oiling device. The stream was then wound at a peripheral speed of 2000 m/min for the take-up roller (first roll), 2000 m/min for the drawing roller (second roll), and 2000 m/min for the winder take-up speed, yielding a polyester fiber undrawn yarn of 200 dtex-36 filaments. The undrawn yarn was then drawn at a first roller temperature of 90°C, a second roller temperature of 130°C, and a draw ratio of 2.38 times, which is expressed as the ratio of the peripheral speeds of the first roller and the second roller, to yield a drawn yarn of 84 dtex-36 filaments polyester fiber. In the cross section of the obtained polyester fiber, the ratios of the lengths of the line segments to the average length of the line segments were 0.97, 1.03, and 0.99, respectively, in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery. It was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with the line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 1.

Example 2
A drawn yarn of a polyester fiber having 84 dtex-36 filaments was obtained under the same conditions as in Example 1, except that the sea portion was made of polyethylene terephthalate (melt viscosity 170 Pa s, melting point 244°C) copolymerized with 1.5 mol% of 5-sodium sulfoisophthalate and 1.0 wt% of polyethylene glycol (PEG1000 manufactured by Sanyo Chemical Industries, Ltd.) having a number average molecular weight of 1000 g/mol. In the cross section of the obtained polyester fiber, the ratios of the lengths of the line segments to the average length of each line segment in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery were 0.99, 1.02, and 0.99, respectively, and it was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with the line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 1.

Example 3
A drawn yarn of 84 dtex-72 filament polyester fiber was obtained under the same conditions as in Example 2, except that the number of holes in the discharge holes was 72, an undrawn polyester fiber of 155 dtex-72 filaments was obtained, and the undrawn yarn obtained was drawn at a draw ratio of 1.84. In the cross section of the obtained polyester fiber, the ratios of the lengths of each line segment to the average length of each line segment in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments were 0.99, 0.99, and 1.02, confirming that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 1.

Example 4
A drawn yarn of 84 dtex-14 filament polyester fiber was obtained under the same conditions as in Example 2, except that the number of nozzle holes was 14, an undrawn polyester fiber of 258 dtex-14 filaments was obtained, and the undrawn yarn was drawn at a draw ratio of 3.07. In the cross section of the obtained polyester fiber, the ratios of the lengths of each line segment to the average length of each line segment in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments were 0.97, 1.00, and 1.03, respectively, and it was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 1.

Example 5
A drawn yarn of 84 dtex-72 filament polyester fiber was obtained under the same conditions as in Example 3, except that the sea-island ratio was set to 50:50 by weight. In the cross section of the obtained polyester fiber, the ratios of the lengths of the line segments to the average length of the line segments in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery were 1.00, 0.99, and 1.01, respectively, and it was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with the line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 1.

Example 6
A drawn yarn of a polyester fiber having 84 dtex-36 filaments was obtained under the same conditions as in Example 1, except that the sea portion was made of polyethylene terephthalate (melt viscosity 40 Pa s, melting point 254°C). In the fiber cross section of the obtained polyester fiber, the ratios of the lengths of each line segment to the average length of each line segment in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments were 0.98, 1.03, and 0.99, respectively, and it was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 1.

Example 7
A drawn yarn of a polyester fiber having 84 dtex and 72 filaments was obtained under the same conditions as in Example 3, except that the sea portion was made of polyethylene terephthalate (melt viscosity 40 Pa s, melting point 254°C) and the sea-island ratio was set to 50:50 by weight. In the cross section of the obtained polyester fiber, the ratios of the lengths of the line segments to the average length of the line segments in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery were 1.03, 1.01, and 0.97, respectively, and it was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with the line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 1.

(Example 8)
A drawn yarn of 66 dtex-96 filament polyester fiber was obtained under the same conditions as in Example 3, except that the discharge holes had a hole diameter of 0.23 mm and the number of holes was 96, an undrawn polyester fiber of 115 dtex-96 filaments was obtained, and the undrawn yarn obtained was drawn at a draw ratio of 1.72. In the fiber cross section of the obtained polyester fiber, the ratios of the lengths of each line segment to the average length of each line segment in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments were 0.99, 1.01, and 0.99, respectively, and it was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 1.

Example 9
A drawn yarn of 56 dtex-144 filament polyester fiber was obtained under the same conditions as in Example 3, except that the discharge holes had a hole diameter of 0.20 mm and the number of holes was 144, an undrawn polyester fiber of 88 dtex-144 filaments was obtained, and the undrawn yarn obtained was drawn at a draw ratio of 1.57. In the fiber cross section of the obtained polyester fiber, the ratios of the lengths of each line segment to the average length of each line segment in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments were 0.98, 1.03, and 0.99, respectively, and it was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 2.

Example 10
The sea portion was made of polyethylene terephthalate (melt viscosity 68 Pa s, melting point 251°C) copolymerized with 16% by weight of polyethylene glycol (PEG6000S manufactured by Sanyo Chemical Industries, Ltd.) having a number average molecular weight of 8,300 g/mol, and the island portion was made of polyethylene terephthalate (melt viscosity 120 Pa s, melting point 254°C). The sea portion and island portion polymers were separately melted at a spinning temperature of 285°C, and then weighed out so that the sea-island ratio was 90:10 by weight. The polymers were fed into a spinning pack equipped with the composite spinneret shown in Figure 3, and the fed polymers were discharged from a discharge hole (hole diameter 0.30 mm, number of holes 36) so as to form a sea-island composite structure in which the number of island portions located at the outermost periphery was three and the total number of island portions was three. The discharged composite polymer stream was cooled and solidified in a cooling device, and then a water-containing oil was added using an oiling device. The stream was then wound at a peripheral speed of 2000 m/min for the take-up roller (first roll), 2000 m/min for the drawing roller (second roll), and 2000 m/min for the winder take-up speed, yielding an undrawn polyester fiber yarn of 215 dtex-36 filaments. The undrawn yarn was then drawn at a first roller temperature of 90°C, a second roller temperature of 130°C, and a draw ratio of 2.48 times, which is expressed as the ratio of the peripheral speeds of the first roller and the second roller, to yield a drawn polyester fiber yarn of 84 dtex-36 filaments. In the cross section of the obtained polyester fiber, the ratios of the lengths of the line segments to the average length of the line segments were 0.98, 1.02, and 0.99, respectively, in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery. It was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with the line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 2.

Example 11
The sea portion was made of polyethylene terephthalate (melt viscosity 170 Pa s, melting point 244 ° C) copolymerized with 1.5 mol% of 5-sulfoisophthalic acid sodium salt and 1.0 wt% of polyethylene glycol (PEG1000 manufactured by Sanyo Chemical Industries, Ltd.) having a number average molecular weight of 1000 g/mol. Next, a polycaprolactam master chip was prepared by adding 20 wt% of polyvinylpyrrolidone ("Ruviscol" K30SP manufactured by BASF, K value = 30) to additive-free polycaprolactam. Subsequently, the master chip was chip-blended with additive-free polycaprolactam (relative viscosity in sulfuric acid 2.71, melting point 220 ° C) to prepare a polycaprolactam blend polymer with a polyvinylpyrrolidone addition rate of 5.0 wt%, and this blend polymer (melt viscosity 130 Pa s, melting point 220 ° C) was used as the island portion. A drawn yarn of a polyester fiber having 84 dtex and 36 filaments was obtained under the same conditions as in Example 1, except that the polymers for the sea and island portions were combined as described above and the sea-island ratio was 50:50 by weight. In the cross section of the obtained polyester fiber, the ratios of the lengths of the line segments to the average length of each line segment in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery were 0.98, 1.02, and 0.99, respectively, and it was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with the line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 2.

Example 12
A drawn yarn of 84 dtex-36 filament polyester fiber was obtained under the same conditions as in Example 2, except that the island portions were made of "PEBAX MH1657" (melt viscosity 45 Pa s, melting point 203°C) manufactured by Arkema. In the fiber cross section of the obtained polyester fiber, the triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments had ratios of the lengths of each line segment to the average length of each line segment of 1.01, 1.01, and 0.98, confirming that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 2.

Example 13
A drawn yarn of a polyester fiber having 84 dtex and 72 filaments was obtained under the same conditions as in Example 3, except that the polymer was fed into a spin pack incorporating the composite spinneret shown in Figure 3 and discharged from an outlet hole (hole diameter: 0.30 mm, number of holes: 72) so as to form a sea-island composite structure in which the number of island portions arranged at the outermost periphery was 5 and the total number of island portions was 6. In the cross section of the obtained polyester fiber, the ratios of the lengths of the line segments to the average length of each line segment for a pentagon obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments were 1.01, 1.00, 0.98, 0.99, and 1.02, respectively, and it was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments was a regular pentagon. The evaluation results of the obtained polyester fiber are shown in Table 2.

Example 14
A drawn polyester fiber yarn of 84 dtex-36 filaments was obtained under the same conditions as in Example 2, except that the polymer was fed into a spin pack incorporating the composite spinneret shown in Figure 3 and discharged through a discharge hole (hole diameter 0.30 mm, number of holes 36) so as to form a sea-island composite structure with 9 island portions arranged at the outermost periphery and 12 island portions in total. In the cross section of the obtained polyester fiber, the nonagon obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments had the ratios of the lengths of the line segments to the average length of each line segment of 1.03, 1.01, 0.98, 0.99, 1.00, 1.00, 0.98, 0.99, and 1.02, confirming that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments was a regular nonagon. The evaluation results of the obtained polyester fiber are shown in Table 2.

Example 15
A drawn yarn of 84 dtex-36 filament polyester fiber was obtained under the same conditions as in Example 2, except that the sea-island ratio was set to a weight ratio of 65:35. In the cross section of the obtained polyester fiber, the ratios of the lengths of the line segments to the average length of the line segments in a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery were 1.01, 0.98, and 1.01, respectively, and it was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with the line segments was an equilateral triangle. The evaluation results of the obtained polyester fiber are shown in Table 2.

(Comparative Example 1)
The sea portion was made of polyethylene terephthalate (melt viscosity 120 Pa s, melting point 254°C) and the island portion was made of polybutylene terephthalate (melt viscosity 50 Pa s, melting point 217°C) copolymerized with 50% by weight of polyethylene glycol (PEG6000S manufactured by Sanyo Chemical Industries, Ltd.) having a number average molecular weight of 8,300 g/mol. The sea portion and island portion polymers were separately melted at a spinning temperature of 285°C, and then weighed so that the sea-island ratio was 80:20 by weight. The polymers were fed into a spinning pack equipped with the composite spinneret shown in Figure 3, and the fed polymers were extruded from a discharge hole (hole diameter 0.30 mm, number of holes 36) so as to form a core-sheath composite structure in which the number of island portions arranged at the outermost periphery was one and the total number of island portions was one. The discharged composite polymer flow was cooled and solidified in a cooling device, and then oiled with a water-containing oil agent using an oiling device. The flow was then wound at a peripheral speed of 2000 m/min for the take-up roller (first roll), 2000 m/min for the stretching roller (second roll), and 2000 m/min for the winder take-up speed, yielding a polyester fiber of undrawn yarn of 200 dtex-36 filaments. The undrawn yarn was then drawn at a first roller temperature of 90°C, a second roller temperature of 130°C, and a draw ratio of 2.38 (represented by the ratio of the peripheral speeds of the first roller and the second roller), yielding a drawn polyester fiber of 84 dtex-36 filaments. Since the total number of island portions in the cross section of the obtained polyester fiber was one, no line segment connecting the centers of gravity of the island portions arranged at the outermost periphery was obtained. Therefore, the resulting polyester fiber underwent sea portion cracking upon moisture absorption, resulting in uneven dyeing and fuzz when made into a fabric. Furthermore, the polymer in the island portion was eluted from the cracks in the sea portion, and the moisture absorption and desorption properties after hot water treatment were also poor. The evaluation results of the obtained polyester fiber are shown in Table 3.

(Comparative Example 2)
A drawn yarn of 84 dtex-36 filament polyester fiber was obtained under the same conditions as in Example 1, except that the sea portion was made of polyethylene terephthalate (melt viscosity 500 Pa s, melting point 254°C). In the cross section of the obtained polyester fiber, the ratios of the lengths of each line segment to the average length of each line segment for a triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments were 1.10, 1.04, and 0.86, respectively. Since the figure obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with line segments was not an equilateral triangle, the obtained polyester fiber experienced cracks in the sea portion upon moisture absorption, and uneven dyeing and fuzz occurred when the fabric was made. Furthermore, polymers from the island portions eluted from the cracks in the sea portion, and the moisture absorption and release properties after hot water treatment were also poor. The evaluation results of the obtained polyester fiber are shown in Table 3.

(Comparative Example 3)
A drawn yarn of 84 dtex-36 filament polyester fiber was obtained under the same conditions as in Example 1, except that the sea-island ratio was set to 40:60 by weight. In the cross section of the obtained polyester fiber, the ratios of the lengths of the line segments to the average lengths of the line segments in the triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery were 1.09, 0.96, and 0.95, respectively. Since the figure obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with the line segments was not an equilateral triangle, the obtained polyester fiber experienced cracking in the sea portion upon moisture absorption, and uneven dyeing and fuzz occurred when made into a fabric. Furthermore, since the amount of polyethylene terephthalate in the sea portion was small, the water absorption and quick-drying properties were poor. The evaluation results of the obtained polyester fiber are shown in Table 3.

(Comparative Example 4)
A drawn yarn of 84 dtex-10 filament polyester fiber was obtained under the same conditions as in Example 2, except that the number of nozzle holes was 10, an undrawn polyester fiber of 270 dtex-10 filaments was obtained, and the undrawn yarn was drawn at a draw ratio of 3.21. In the cross section of the obtained polyester fiber, the ratios of the lengths of each line segment to the average length of each line segment in the triangle obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery were 0.98, 1.02, and 1.00, respectively, and it was confirmed that the shape obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery with the line segments was an equilateral triangle. However, the moisture absorption and desorption properties were poor due to the thick sea portion, and the single fiber fineness was large, resulting in fiber stiffness, and the feel of the obtained fabric was also poor. The evaluation results of the obtained polyester fiber are shown in Table 3.

The polyester fiber of the present invention is able to disperse the stress that occurs as the fiber volume expands upon moisture absorption, suppressing cracks on the fiber surface. This results in no uneven dyeing or fuzz when made into woven or knitted fabrics, resulting in excellent quality. Furthermore, the fiber has excellent moisture absorption properties without any reduction in moisture absorption, making it particularly suitable for use in clothing applications.

1: Sea portion 2a, 2b, 2c, 2d, 2e, 2f: Island portion 3a, 3b, 3c: Line segment connecting the intersection points (centers of gravity) of any two straight lines that halve the area of adjacent island portions among the island portions arranged at the outermost periphery of the fiber cross section 4: Perfect circle (circumscribed circle) circumscribing two or more of all island portions arranged at the outermost periphery of the fiber cross section
5: A perfect circle that circumscribes one island at two or more points (circumscribed circle)
6: Minimum thickness of sea portion 7: Minimum distance between island portions 8: Metering plate 9: Distribution plate 10: Discharge plate B: Intersection of a line drawn from the intersection (center of gravity) of any two lines that halves the area of an island portion toward any fiber surface, with the periphery of the island portion Da, Db: Intersection of a line drawn from the intersection (center of gravity) of any two lines that halves the area of an island portion toward any adjacent island portion, with the periphery of the island portion F: Intersection of a line drawn from the intersection (center of gravity) of any two lines that halves the area of an island portion toward any fiber surface, with the fiber surface Ga, Gb, Gc, Gd, Ge: Intersection of a line drawn from the intersection (center of gravity) of any two lines that halves the area of an island portion toward any fiber surface, with the fiber surface

Claims (3)

A fiber characterized in that the fiber is an islands-in-sea type composite fiber in which the main constituent component of the sea portion is an aromatic polyester, the fiber has a moisture absorption/desorption parameter ΔMR of 2.0% or more, a figure obtained by connecting the centers of gravity of the island portions arranged at the outermost periphery in the fiber cross section with line segments is a regular polygon with the centers of gravity as vertices, and the ratio C/L of the radius of curvature C (μm) of the side of the outer periphery of the island portions arranged at the outermost periphery in the fiber cross section on the fiber surface side to the radius L (μm) of the circumscribed circle including the island portions arranged at the outermost periphery in the fiber cross section is 0.50 to 0.90 . The fiber described in claim 1, characterized in that the number of island portions arranged at the outermost periphery in the fiber cross section is odd. A textile product comprising the islands-in-sea type composite fiber according to claim 1 or 2 .