WO2025105062A1 - Short fiber and spun yarn - Google Patents

Abstract

Short fibers according to the present invention are each characterized by comprising at least two polymers that have different melting points, and having a crimp number/crimp diameter of 75-500, and are each characterized in that the coefficient of variation CV% of the crimp number between the short fibers is 15-50%. This spun yarn is characterized by comprising flat short fibers made of at least two polymers having different melting points, and is characterized in that the coefficient of variation CV% of the void distance between the short fibers is 60-90%.　Provided are short fibers and a spun yarn that are suitable for textiles for clothing having excellent wearing comfort, and that have, by controlling the crimped form of each of the short fibers constituting the spun yarn, a moist and comfortable tactile sensation and a plump and soft texture such as those of cotton, and functions such as water absorption.

Description

Staple fibres and yarn

The present invention relates to staple fibers and spun yarns suitable for textiles for comfortable clothing.

Spun yarn is made by twisting together short fibers several tens of millimeters in length, and by using natural fibers such as cotton or wool, or regenerated fibers such as rayon, it is possible to obtain woven and knitted fabrics that feature excellent moisture absorption and heat retention. However, due to the nature of these fibers, they have disadvantages such as low strength, and when they absorb a large amount of sweat or moisture, it is absorbed deep into the fiber, making them difficult to dry and causing discomfort such as stickiness.

Synthetic fibers made from polyester, polyamide, etc. are materials with excellent mechanical properties and dimensional stability, and some are used as spun yarn by cutting short fibers to a certain length and spinning them. To solve the problems of natural fibers, spun yarn made from synthetic fibers with excellent mechanical properties, chemical properties, and moisture absorption and quick-drying properties, or spun yarn made by blending synthetic fibers with natural fibers or recycled fibers, is used. Due to the texture and natural appearance unique to spun yarn, it is used in a wide range of applications such as jackets, coats, shirts, underwear, and sportswear.

However, in today's world, where people's lives have become more diverse and people are seeking a better way of life, there is a demand for spun yarns that have a sophisticated feel closer to natural materials, while also providing the functionality and higher performance that only synthetic fibers can provide. As a result, spun yarns made from staple fibers with a side-by-side cross section in which different polymers are bonded together have been proposed as spun yarns with a more sophisticated feel and functionality.

The purpose of these staple fibers with a side-by-side cross section is to impart functionality such as bulkiness and texture, as well as stretchability, by causing shrinkage due to the difference in thermal shrinkage between the polymers. However, when spun yarn made from these staple fibers is used to make textiles, all of the staple fibers will exhibit the same shrinkage form, so the shrink phases of the staple fibers tend to be aligned, resulting in a lack of volume and stretch due to tight convergence, or wrinkles and spots appearing on the textile surface, impairing the appearance quality.

In response to this, various technologies have been proposed that not only improve the bulkiness, stretch, and appearance quality mentioned above by controlling the cross-sectional shape of short fibers, but also impart further functionality.

Patent Document 1 discloses an acrylic staple fiber in which two types of acrylonitrile-based polymers with different acrylonitrile content ratios are compounded in a side-by-side structure and the flatness is 1.5 to 8, and a spun yarn containing the acrylic staple fiber.

The flat shape of the acrylic staple fibers described above results in a lower moment of area in the short axis direction of the fiber compared to acrylic staple fibers with a cross-sectional shape close to circular, improving the softness of the fiber and making it easier for crimping to occur due to side-by-side compounding. As a result, spun yarn containing the acrylic staple fibers has excellent bulkiness, and when used in textiles, it has a fluffy texture and is less likely to become worn out even after repeated washing, resulting in textiles with excellent durability.

Patent Document 2 also discloses polyester staple fibers that are made by compounding polytrimethylene terephthalate (PTT) with at least one of polyethylene terephthalate (PET), PTT, and polytetramethylene terephthalate (PBT), have a flat cross section with a major axis length: minor axis length of 2:1 to 5:1, are side-by-side compounded or eccentric core-sheath compounded in a direction perpendicular to the major axis of the flat cross section, and have multiple longitudinal grooves, and a spun yarn that contains the polyester staple fibers.

In spun yarns containing polyester staple fibers as described above, the staple fibers have at least one component of PTT and are side-by-side composite or eccentric core-sheath composite in the direction perpendicular to the long axis of the flat cross section, resulting in high stretchability. In addition, the staple fibers have a flat cross section with a long axis length:short axis length ratio of 2:1 to 5:1, resulting in high homogeneity (uniformity). Furthermore, the staple fibers have multiple longitudinal grooves, which impart good water absorption (wicking properties). As a result, it is said that spun yarns containing the polyester staple fibers can produce textiles that combine high stretchability with a uniform woven appearance and good water absorption.

JP 2020-007667 A Special Publication No. 2009-510275

As in Patent Documents 1 and 2, by flattening the cross-sectional shape of short fibers having a side-by-side cross section, the fibers are less likely to be closely packed when twisted during spinning, and the crimp phases of adjacent short fibers are less likely to be aligned, which may improve the fullness, stretch, and appearance quality.

However, in Patent Document 1 and Patent Document 2, the short fibers exhibit the same crimp form, and the improvements in fluffiness and appearance quality obtained are not sufficient, and the texture can be monotonous.

Furthermore, in Patent Document 2, in order to obtain high stretchability, the short fibers need to have high shrinkage, but if the short fibers, which are restrained by twisting during spinning processing, exhibit high shrinkage, adjacent short fibers will pack closely together, resulting in the loss of gaps between the fibers. As a result, the fluffy, soft texture required for comfortable clothing may be lacking, and the water absorbency utilizing the capillary phenomenon caused by the gaps may be reduced.

The object of the present invention is to solve the problems of the conventional technology described above and provide staple fibers and spun yarns suitable for clothing textiles that have excellent wearability and functionality, such as water absorbency, in addition to a comfortable feel and soft, fluffy texture with a moist, cotton-like unevenness.

The object of the present invention is achieved by the following means:
(1) A staple fiber comprising at least two kinds of polymers having different melting points, a crimp number/crimp diameter of 75 to 500, and a coefficient of variation CV% of the crimp number among staple fibers of 15 to 50%.
(2) The staple fiber according to (1) above, characterized in that the coefficient of variation CV% of the value of (distance between the centers of gravity of polymers/fiber diameter) among the staple fibers is 5 to 30%.
(3) The staple fiber according to (1) or (2) above, characterized in that the flatness in the fiber cross section is 1.2 to 5.0.
(4) The staple fiber according to any one of (1) to (3) above, characterized in that the staple fiber has three or more convex portions in a fiber cross section.
(5) A textile product partially containing the short fiber according to any one of (1) to (4).
(6) A spun yarn containing the staple fiber according to any one of (1) to (4) above.
(7) A spun yarn comprising flat staple fibers made of at least two kinds of polymers having different melting points, the coefficient of variation CV% of the inter-fiber void distance being 60 to 90%.
(8) The spun yarn according to (7) above, characterized in that the inter-fiber gap distance is 4 to 10 μm.
(9) The spun yarn according to (7) or (8) above, characterized in that it has a void structure with a void ratio of 30 to 60%.
(10) The spun yarn according to any one of (7) to (9), characterized in that the mixing ratio of flat staple fibers is 30 to 100 mass%.
(11) A woven or knitted fabric partially comprising the spun yarn according to any one of (7) to (10) above.
It is.

The staple fibers and spun yarn of the present invention have the above-mentioned characteristics, and the crimp morphology of each staple fiber in the staple fibers that make up the spun yarn is precisely controlled, and the spun yarn has complex surface irregularities and interfiber voids. Therefore, by using the staple fibers and spun yarn of the present invention, it is possible to obtain clothing textiles that have excellent wearability, functionality such as water absorbency, in addition to a comfortable, fluffy, soft texture with a moist, cotton-like unevenness.

FIGS. 1A, 1B, 1C, and 1D are schematic diagrams showing examples of the cross-sectional structure of the short fibers of the present embodiment. 2(a) and (b) are schematic diagrams showing an example of a cross-sectional structure of the short fiber of the present embodiment. FIG. 3 is a schematic diagram showing an example of a cross-sectional structure of a conventional staple fiber. FIG. 4 is a schematic diagram showing an example of a cross-sectional structure of each staple fiber in the staple fiber of this embodiment. FIG. 5 is a diagram for understanding the method for measuring the inter-fiber gap distance in the spun yarn of this embodiment. FIG. 6 is a diagram for understanding the method for measuring the crimp diameter of the short fibers of this embodiment. FIG. 7 is a cross-sectional view for explaining the method for producing short fibers according to this embodiment.

The present invention will be described in detail below along with preferred embodiments.

(1) Staple Fibers When analyzing cotton, which is widely used as a natural material with functionality such as a comfortable touch due to its moist unevenness and water absorption, it is found that each staple fiber has a different twist. By twisting together multiple staple fibers with different twists, complex surface unevenness and interfiber voids are formed in the spun yarn, which is thought to achieve the unique touch and feel when made into a textile.

The inventors conducted extensive research to realize the complex surface irregularities and inter-fiber voids of cotton-like fibers in synthetic fibers, and discovered that by setting the relationship between the number of crimps and the crimp diameter in short fibers made of at least two polymers with different melting points within a specific range, and by controlling the distance between the polymer centers of gravity of each short fiber to change the number of crimps, it is possible to achieve a spun yarn with complex surface irregularities and inter-fiber voids that were difficult to achieve with conventional synthetic fibers.

In other words, in spun yarn obtained by twisting together staple fibers, the staple fibers are constrained by the twist. Therefore, if the staple fibers develop excessive crimps or small crimp diameters due to heat treatment, adjacent staple fibers tend to pack closely together, resulting in a loss of space between the fibers.

In contrast, if the number of crimps and crimp diameter during the crimping of staple fibers are controlled within a specific range, adjacent staple fibers will not be densely packed together, and voids will be formed due to the crimping in addition to the voids that were originally present between the staple fibers. Furthermore, by controlling the distance between the polymer centers of gravity of each staple fiber to change the number of crimps, differences in yarn length will appear between the staple fibers when the crimping occurs, creating complex inter-fiber voids with a mixture of void sizes, and creating complex irregularities on the surface of the spun yarn that have not been seen before. Therefore, when this spun yarn is made into a textile, it will be possible to create a unique feel and texture like that of natural materials.

The staple fibers of the present invention are constructed based on this idea, and specifically, they are made of at least two types of polymers with different melting points, and it is important that the crimp number/crimp diameter is 75-500 and the coefficient of variation CV% of the crimp number between staple fibers is 15-50%. A preferred embodiment is described below.

[Polymers with different melting points]
In the staple fiber of this embodiment, in order to control the crimp form, it is necessary for the staple fiber to be made of at least two kinds of polymers having different melting points.

If polymers with different melting points (low melting point polymer and high melting point polymer) are arranged so that their centers of gravity are different in the cross section of the short fiber, the short fiber will bend significantly toward the low melting point polymer side, which shrinks more after heat treatment, and this continuation will result in the appearance of a coil-like crimped morphology. Furthermore, by controlling the distance between the centers of gravity of the polymers, it is possible to create any crimped morphology, which is the object of the present invention to control the crimped morphology.

In other words, the fiber cross section of the staple fiber of this embodiment is preferably a composite cross section in which polymers with different melting points are arranged so that their centers of gravity are different. Examples of such composite cross sections include a side-by-side type as shown in FIG. 1(a) and an eccentric core-sheath type as shown in FIG. 1(b), as well as an island-in-the-sea type and a blend type.

In addition, in the fiber cross section of the short fiber of this embodiment, if the cross section has a hollow portion in the center of the fiber as shown in Figure 1 (d), the swelling can be further improved and a lightweight material can be obtained, which is more preferable.

[Thin film]
In this embodiment, the surface layer of the staple fiber is preferably covered with one type of polymer. By covering the surface layer of the staple fiber with one type of polymer, even if a polymer with low heat resistance or abrasion resistance is used as one component of the composite fiber, peeling does not occur at the interface due to friction or impact, and fiber properties can be well maintained, making it possible to improve processing stability during spinning and spun yarn quality.

In addition, when producing the staple fiber of this embodiment, if a melt of polymers with a large melting point difference is spun from a spinneret as a composite flow, the high melting point polymer will bend toward the low melting point polymer due to the cooling difference after discharge, causing yarn bending, which will come into contact with the spinneret or interfere with the composite flow spun from another location, resulting in yarn breakage. However, since the surface layer of the staple fiber is covered with one type of polymer, the cooling difference is mitigated and yarn bending can be suppressed, making it possible to stably spin the fiber even if a combination of polymers with a large melting point difference is used.

Examples of one type of polymer that covers the surface layer of the staple fibers include polyesters such as polyethylene terephthalate, copolymerized polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate, polyamides such as nylon 6, nylon 66, and nylon 610, and polypropylene, etc. Among these, it is preferable to cover the surface layer of the staple fibers with polyethylene terephthalate or copolymerized polyethylene terephthalate from the viewpoint of excellent heat resistance and color development. It is preferable that the polymer that covers the surface layer is the same as one of the polymers with different melting points that constitute the staple fibers.

The thickness of the single type of polymer covering the surface layer of the staple fibers can be adjusted as appropriate, but for example, it is preferable that the ratio S/D of the minimum thickness S of the polymer covering the surface layer of the staple fibers to the fiber diameter D is 0.01 to 0.1. By setting it in this range, whitening or fluffing will not occur even if the staple fibers are subjected to friction or impact, and the operability during spinning processing will be good, and the quality of the spun yarn obtained will also be improved. Furthermore, if S/D is set to 0.02 to 0.08, the centers of gravity of the high melting point polymer and the low melting point polymer will be separated, and shrinkage due to shrinkage difference can be maximized, so this is considered to be a more preferable range.

In this embodiment, the ratio S/D of the minimum thickness S of the polymer covering the surface of the short fiber to the fiber diameter D is determined by embedding the short fiber in an embedding agent such as epoxy resin, taking an image of the cross section with a transmission electron microscope (TEM), and observing the composite cross section. In this case, metal dyeing is applied to create a dye difference between the polymers, making the contrast of the joints in the composite cross section clear.

Specifically, when the composite cross section in the photographed image is an eccentric core-sheath cross section as shown in Figure 1 (b), one short fiber is analyzed from the photographed image to determine the minimum thickness of the polymer covering the surface layer of the short fiber in μm units. The obtained minimum thickness S is divided by the fiber diameter D, which is obtained by measuring the area of each composite fiber and measuring the diameter calculated as a perfect circle in μm units to one decimal place. This operation is performed for 20 short fibers, and the average of the obtained values is rounded off to three decimal places to obtain the ratio S/D of the minimum thickness S of the polymer covering the surface layer of the short fiber to the fiber diameter D. [Area ratio]
The area ratio of the low melting point polymer to the high melting point polymer in the composite cross section of the staple fiber of this embodiment, i.e., the area of the low melting point polymer/the area of the high melting point polymer, is preferably 70/30 to 30/70, and more preferably 60/40 to 40/60. Within this range, the crimp form due to the shrinkage difference between the polymers can be fully expressed without being affected by the texture hardening that occurs when the low melting point polymer highly shrinks during heat treatment.

[Number of crimps/crimp diameter]
In the staple fibers of this embodiment, by controlling the crimp form developed by heat treatment and setting the number of crimps to a specific value according to the crimp diameter, adjacent staple fibers are not packed closely together, and gaps can be formed between the staple fibers, even in spun yarn in which the staple fibers are constrained by twist. Specifically, when the crimp diameter is large, the staple fibers are constrained by twist and crimp is difficult to develop, so the number of crimps needs to be large, whereas when the crimp diameter is small, crimp is easy to develop but the staple fibers tend to pack closely together, so the number of crimps needs to be small.

In other words, it is important that the number of crimps/crimp diameter of the short fibers in this embodiment is 75 to 500.

Here, the number of crimps and the crimp diameter are calculated using the following method.

First, the staple fibers are dry-heat treated at 180°C for 5 minutes without load, and then the number of crimps is determined from the crimp shape of one staple fiber observed according to the method in JIS L1015 (2010) 8.12.1. This is done for 20 different staple fibers, the average value is calculated, and the value rounded off to the nearest whole number is the number of crimps (peaks/25 mm).

Next, in the crimped form observed according to the same method as above, JIS L1015 (2010) 8.12.1, a straight line (S1) is used to connect the apex of the first peak (M1) and the last valley (V2) in the section where the sequence is peak (M1) → valley (V1) → peak (M2) → valley (V2) as shown in Figure 6. The distance Le (mm) between two points where a line that is parallel to this line (S1) and perpendicular to two lines (S2, S3) that pass through the apex of the valley (V1) and the peak (M2) intersects is calculated. This operation is performed at three or more arbitrary points per staple fiber, and a simple number average is calculated. Furthermore, the simple number average of the results obtained by performing this on 20 different staple fibers is calculated, and the value rounded off to three decimal places is defined as the crimped diameter (mm).

The number of crimps obtained is divided by the crimp diameter, and the value is rounded off to the nearest whole number to obtain the number of crimps/crimp diameter.

If the crimp number/crimp diameter is set to 75-500, in the spun yarn obtained by twisting together the short fibers, voids will be formed due to the crimping in addition to the voids that were originally present between the fibers. Therefore, when made into a textile, not only will the increase in coarse voids give the fabric a fluffy, soft feel, but the fine voids will also provide water absorption through the capillary action.

Moreover, it is more preferable to set the crimp number/crimp diameter to 100 to 300, since the voids caused by the crimping increase, and the fluffy soft texture and water absorbency can be accentuated.Furthermore, it is particularly preferable to set the crimp number/crimp diameter to 125 to 200, since the voids caused by the crimping can be formed even in the spun yarn obtained by strong twisting in which the staple fibers are strongly restrained.

[Crimped diameter] The short fibers of the present embodiment preferably have a crimped form with a crimped diameter of 0.10 to 0.40 mm.

If the crimped diameter is 0.10 mm or more, voids can be formed between the short fibers due to the crimping, and in the spun yarn made by twisting together the short fibers of the present invention, complex voids and uneven surfaces can be formed. Therefore, when made into a textile, not only can the increase in coarse voids give it a fluffy, soft feel, but the fine voids also provide water absorption through the capillary phenomenon. Furthermore, if the crimped diameter is 0.15 mm or more, the increased voids between the short fibers can also have the effect of improving the fluffiness.

From the viewpoint of swelling, the larger the crimp diameter, the more preferable it is, but if the crimp diameter exhibited by the short fibers becomes too large, the expression of crimp may be inhibited due to the constraint caused by twisting. Therefore, in this embodiment, the crimp diameter is preferably 0.40 mm or less, and more preferably 0.30 mm or less.

[Number of Crimps] The staple fibers of the present embodiment preferably have a crimp form with a number of crimps of 20 to 200 crimps/25 mm.

If the crimp number is 20 crimps/25 mm or more, voids can be formed between the short fibers due to the crimping, and complex voids and uneven surfaces can be formed in the spun yarn made by twisting together the short fibers of the present invention. Therefore, when made into a textile, not only can the increase in coarse voids give it a fluffy, soft feel, but the fine voids also provide water absorption through the capillary phenomenon. Furthermore, if the crimp number is 40 crimps/25 mm or more, stretch can also be imparted through the spiral structure.

In terms of stretchability, the more the number of crimps, the better; however, because the short fibers are constrained by twisting, if the short fibers exhibit an excessive number of crimps, adjacent short fibers may be packed closely together, resulting in the loss of spaces between the fibers. Therefore, in this embodiment, the number of crimps is preferably 200 crimps/25 mm or less, and more preferably 100 crimps/25 mm or less.

[Coefficient of variation of crimp number]
In the staple fibers of this embodiment, the number of crimps is changed by controlling the distance between the polymer centers of gravity of each staple fiber. In the spun yarn obtained by twisting these staple fibers together, differences in yarn length occur between the staple fibers when crimping occurs, and complex inter-fiber voids with a mixture of void sizes are created, so that when the yarn is made into a textile, a unique texture like that of natural materials can be achieved.

In order to form the above-mentioned complex inter-fiber voids in spun yarn, it is important that the coefficient of variation CV% of the number of crimps between short fibers is 15 to 50%.

The coefficient of variation CV% of the number of crimps between short fibers in this embodiment can be calculated by the following method.

First, the staple fibers are dry-heat treated at 180°C for 5 minutes without load, and then the number of crimps (peaks/25mm) is determined from the crimp shape of one staple fiber observed according to the method in JIS L1015 (2010) 8.12.1. This is performed on 20 different staple fibers, and the standard deviation and average value are calculated. The standard deviation is divided by the average value, multiplied by 100, and the value is rounded off to the nearest whole number to obtain the coefficient of variation CV% (%) of the number of crimps among the staple fibers.

If the coefficient of variation CV% of the number of crimps between short fibers is 15% or more, the spun yarn obtained by twisting together short fibers will have a mixture of short fibers with different numbers of crimps, which will create various inter-fiber gaps due to the difference in yarn length between the short fibers, and complex unevenness can be formed on the surface. As a result, when the spun yarn is made into a textile, the unevenness makes it easier for fingers to catch on it, increasing the degree of adhesion to the fingers, resulting in a moist feel, and a natural feel with a comfortable unevenness that provides moderate friction when running your fingers over the surface.

In addition, from the viewpoint of emphasizing the effect of the present invention, which is a comfortable feel due to the moist unevenness, it is preferable to increase the coefficient of variation CV% of the number of crimps between the short fibers and make the unevenness of the spun yarn surface more complex. Therefore, it is more preferable to set the coefficient of variation CV% of the number of crimps to 20% or more, and an especially preferable range is 25% or more.

However, if the coefficient of variation CV% of the crimp number becomes too large, the fibers will be polarized into those with a large number of crimps and those with a small number of crimps, resulting in a monotonous surface unevenness of the resulting spun yarn, which may cause a foreign body sensation or a rough surface feel. Therefore, the upper limit of the coefficient of variation CV% of the crimp number in this invention is 50%.

[Variation coefficient of (distance between polymer centers of gravity/fiber diameter)]
In the staple fibers of this embodiment, the crimp morphology can be controlled by the distance between the polymer centers of gravity and the fiber diameter, and the larger the distance between the polymer centers of gravity and the smaller the fiber diameter, the greater the crimp number that can be achieved. That is, the crimp number is expressed by (distance between the polymer centers of gravity/fiber diameter), and by varying this (distance between the polymer centers of gravity/fiber diameter) for each staple fiber to vary the crimp number, the void size and surface unevenness in the spun yarn can be controlled. Therefore, in this embodiment, the coefficient of variation CV% of the value of (distance between the polymer centers of gravity/fiber diameter) between staple fibers is preferably 5% or more.

The coefficient of variation CV% of the value of (distance between polymer centers of gravity/fiber diameter) between short fibers in this embodiment can be calculated by the following method.

First, the short fibers or spun yarn are embedded in an embedding agent such as epoxy resin, and an image of the fiber cross section perpendicular to the fiber axis is taken with a scanning electron microscope (SEM). Next, one short fiber is randomly selected from the image and analyzed using image analysis software to measure the area of the composite fiber, and the diameter calculated as a perfect circle is measured in μm units to one decimal place. The value obtained is the fiber diameter (μm).

Next, for the same short fibers as above, measure the length of the straight line connecting the centers of gravity (Gx, Gy) of the low melting point polymer x and the high melting point polymer y in the cross section of the composite fiber in μm units to one decimal place as shown in Figure 2 (a). The value obtained is the distance between the polymer centers of gravity (μm).

The simple number average of the ratio (distance between polymer centers of gravity/fiber diameter) of the fiber diameter and the distance between polymer centers of gravity obtained above is calculated, and this value is rounded to one decimal place to obtain (distance between polymer centers of gravity/fiber diameter). This evaluation is performed in the same way on 20 short fibers randomly selected, and the standard deviation and average value of the results are calculated. The standard deviation is divided by the average value, multiplied by 100, and the value is rounded to the nearest whole number. The obtained value is the coefficient of variation CV% (%) of the value of (distance between polymer centers of gravity/fiber diameter).

When the coefficient of variation CV% of the value of (distance between polymer centers of gravity/fiber diameter) between short fibers is set to 5% or more, the coefficient of variation CV% of the number of crimps between short fibers becomes large, and by mixing short fibers with different numbers of crimps, various interfiber gaps are created due to the difference in yarn length between the short fibers, and complex unevenness can be formed on the surface.

Furthermore, it is more preferable to set the coefficient of variation CV% of the value (distance between polymer centers of gravity/fiber diameter) in the range of 10% or more, and even more preferable to set it in the range of 15% or more. By setting the coefficient of variation CV% in the above range, the coefficient of variation CV% of the number of crimps between short fibers can be increased, and the unevenness of the spun yarn surface can be made more complex, thereby emphasizing the comfortable feel of the cotton-like moist unevenness.

In addition, if the coefficient of variation CV% becomes too large, the crimp morphology will polarize into coarse fibers and fine fibers, resulting in a monotonous surface unevenness of the resulting spun yarn, which may result in a loss of the comfortable feel of a cotton-like, moist uneven surface. Therefore, it is preferable to set the coefficient of variation CV% to 30% or less.

[Flatness]

In the staple fibers of this embodiment, a method for controlling (distance between polymer centers of gravity/fiber diameter) can be considered by changing the cross-sectional shape or the conjugation ratio of each staple fiber, but from the viewpoint of controlling the crimp phase alignment and spinning stability, it is preferable that the cross-sectional shape of the staple fibers is flat and the flatness is 1.2 or more. In the present invention, the term "flat" refers to a long and narrow shape in a planar view, and specifically refers to a short fiber having a "flatness" of 1.1 or more in the cross section, which will be described later.

In this embodiment, the flatness is determined by the following method. First, the short fibers are embedded in an embedding agent such as epoxy resin, and an image of the fiber cross section perpendicular to the fiber axis is taken with a scanning electron microscope (SEM). Next, one short fiber randomly selected from the taken image is analyzed using image analysis software, and a value is calculated by dividing the length of the long axis by the length of the short axis, with the straight line connecting the two points (a1, a2) that are the farthest apart among any points on the circumference of the composite fiber as shown in FIG. 1(a) being the long axis, and the straight line connecting the intersection point (b1, b2) of the circumference of the fiber with the straight line that passes through the midpoint of the long axis and is perpendicular to the long axis being the short axis. This is performed on 20 short fibers in the same manner, and a simple number average is calculated, and the value rounded off to one decimal place is the flatness.

If the cross-sectional shape of the short fibers is flat (flat cross section), the distance between the polymer centers of gravity will be maximum when polymers with different melting points are bonded in the major axis direction of the flat cross section as shown in (a) of Fig. 2, and the distance between the polymer centers of gravity will be minimum when they are bonded in the minor axis direction of the flat cross section as shown in (b) of Fig. 2. In this way, by making the cross-sectional shape of the short fibers flat and changing the direction of the bonding surface for each short fiber, it is possible to control the value of (distance between polymer centers of gravity/fiber diameter).

For this reason, it is preferable that the flatness of the short fibers is 1.2 or more, and more preferably, the composite cross section is made such that the joining surface direction is changed for each short fiber, as shown in Figure 4. By having the short fibers have the above configuration, the coefficient of variation CV% of the value of (distance between the centers of gravity of polymers/fiber diameter) can be easily set within the desired range. Furthermore, compared to when the cross-sectional shape or composite ratio is changed for each short fiber, yarn breakage due to yarn interference caused by cooling unevenness is suppressed, and spinning stability can also be improved.

In order to further exert the above-mentioned effect, the flatness is preferably 1.4 or more, and even more preferably 1.6 or more. By making the flatness of the staple fibers 1.4 or more, not only can the coefficient of variation CV% of the value of (distance between the centers of gravity of the polymer/fiber diameter) be brought closer to the optimal range, but also, due to steric hindrance when staple fibers having a flat cross section exhibit crimping, the gaps between the staple fibers are increased in the spun yarn made of the staple fibers, and when the spun yarn is made into a textile, a fluffy and soft texture can be obtained.

As described above, the higher the flatness, the better, from the viewpoint of controlling the coefficient of variation CV% of the value of (distance between the centers of gravity of polymer/fiber diameter) and increasing the voids in the spun yarn made of short fibers. On the other hand, if the flatness is too high, the light reflected from the composite fiber surface becomes stronger, which may cause an uneven appearance (glare). In addition, the cross-sectional shape with edges may increase the bending rigidity more than necessary, which may impair flexibility, and the increased distance of the voids between fibers may reduce water absorption due to capillary action. For this reason, the flatness in this embodiment is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less.

[Cross-sectional shape]
The cross-sectional shape of the staple fiber of this embodiment may be flat as shown in FIG. 1(a), as well as multi-lobed as shown in FIG. 1(c), polygonal, gear-like, petal-like, star-like, etc.

In this embodiment, it is preferable to combine short fibers having a cross-sectional shape with three or more convex portions on the surface. By combining short fibers having a cross-sectional shape with three or more convex portions on the surface, it is possible to suppress uneven appearance (glare) caused by diffuse reflection of light and to increase water absorbency due to minute gaps between the short fibers. It is more preferable that the number of convex portions is five or more, and even more preferable that it is eight or more.

However, as the number of protrusions becomes too large, the effect gradually decreases, so the practical upper limit for the number of protrusions is 20, and 12 or less is more preferable.

[Fiber diameter] The short fibers of this embodiment preferably have a fiber diameter of 20 μm or less. This range not only suppresses light reflection on the short fiber surface and suppresses uneven appearance (glare) when made into a textile, but also provides a sufficient sense of resilience. This makes the fibers suitable for clothing applications such as pants and shirts that require a firm and resilient texture.

Furthermore, it is more preferable to set the fiber diameter to 12 μm or less. By setting the fiber diameter to 12 μm or less, the flexibility of the composite fiber bundle is increased, and it can be suitably used for clothing applications such as innerwear and blouses that come into contact with the skin.

From the viewpoint of suppressing deterioration in bending recovery and color development, the fiber diameter is preferably 5 μm or more, and more preferably 10 μm or more in order to improve carding properties during spinning processing.

(2) Spun Yarn In order to maximize the comfortable feel and fluffy soft texture of the spun yarn due to the moist cotton-like unevenness created by the complex voids and unevenness that are unique to natural materials, the inventors conducted extensive research and discovered that by including flat staple fibers with a controlled crimp morphology in the spun yarn, variation in the inter-fiber void distance is created, making it possible to form complex surface unevenness and inter-fiber voids like those of natural fibers, which were difficult to obtain with conventional spun yarns.

In other words, in spun yarns containing flat staple fibers that do not have a crimped morphology, the fibers are densely packed together with other staple fibers when twisted together during spinning, resulting in small inter-fiber voids and flat irregularities. On the other hand, in the case of spun yarns containing flat staple fibers that have been given the same crimped morphology, the crimped morphology of each staple fiber is uniform, so although inter-fiber voids and irregularities are obtained, they may end up being monotonous.

In contrast, spun yarn containing flat staple fibers with different crimp forms for each staple fiber creates variation in the inter-fiber gap distance due to the different crimp forms, which allows for the formation of complex surface irregularities and inter-fiber gaps. This not only allows for the creation of a comfortable feel with moist, cotton-like unevenness and a soft, fluffy texture, but also provides water absorption through capillary action.

The spun yarn of the present invention is constructed based on this idea, and specifically, the yarn contains flat staple fibers made of two types of polymers with different melting points, and the requirement of the present invention is that the coefficient of variation CV% of the inter-fiber gap distance is 60 to 90%. Preferred embodiments will be described below.

[Flat Staple Fibers] It is important that the spun yarn of the present embodiment contains flat staple fibers made of two types of polymers having different melting points.

If polymers with different melting points are arranged so that their centers of gravity are different in the cross section of the short fibers, the short fibers will bend significantly toward the low-melting-point polymer, which shrinks more after heat treatment, and this continuation will result in the appearance of a coiled crimped morphology. Furthermore, by controlling the distance between the centers of gravity of the polymers, it is possible to create any crimped morphology, which allows the objective of this invention to be achieved: control of the crimped morphology for each short fiber.

In other words, the cross section of the flat staple fiber used in the spun yarn of this embodiment is preferably a composite cross section in which polymers with different melting points are arranged so that their centers of gravity are different. Examples of such composite cross sections include a side-by-side type as shown in FIG. 1(a) and an eccentric core-sheath type as shown in FIG. 1(b), as well as an island-in-the-sea type and a blend type.

Furthermore, if the cross section of the flat staple fiber used in the spun yarn of this embodiment has a hollow portion at the center of the fiber, this is more preferable because it improves the volume and provides an even lighter feel.

One possible method for controlling the distance between the polymer centers of gravity is to change the cross-sectional shape or the conjugation ratio of each staple fiber. From the viewpoints of controlling the crimp phase alignment and spinning stability, however, in the spun yarn of this embodiment, it is important to make the staple fibers have a flat cross-sectional shape.

By using flat short fibers and changing the direction of the bonded surfaces of the short fibers, it is possible to control the distance between the centers of gravity of the polymers.

The flatness of the flat short fibers is preferably 1.2 or more, and more preferably, the composite cross section is made by changing the joining surface direction for each composite fiber, as shown in Figure 4. By having the short fibers have the above configuration, the difference in the crimp form due to the difference in the distance between the centers of gravity of the polymers becomes large, and the coefficient of variation CV% of the inter-fiber gap distance, which will be described later, can be increased. Furthermore, compared to the case where the cross-sectional shape and the composite ratio are changed for each short fiber, thread breakage due to thread interference caused by cooling unevenness is suppressed, and spinning stability can be improved. In order to further express the above effect, the flatness is more preferably 1.4 or more, and even more preferably 1.6 or more. By having a flatness of 1.4 or more between composite fibers, not only can the coefficient of variation CV% of the inter-fiber gap distance be increased, but also the steric hindrance when the flat short fibers express crimp becomes large, so that the voids in the spun yarn containing the flat short fibers are increased, and when the spun yarn is made into a textile, a fluffy and soft texture can be obtained.

From the viewpoint of the coefficient of variation CV% of the inter-fiber void distance and the increase in voids in the spun yarn, the higher the flatness, the better. However, if the flatness is too high, the light reflected from the composite fiber surface will be stronger, which may cause an uneven appearance (glare). In addition, the cross-sectional shape with edges may increase the bending rigidity more than necessary, which may impair flexibility, and the increase in the inter-fiber void distance may reduce water absorption due to capillary action. For this reason, the flatness in this embodiment is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less.

[Inter-fiber gap distance]
In the spun yarn of this embodiment, the inter-fiber gap distance is preferably 4 to 10 μm.

The longer the inter-fiber gap distance, the more space is created for the fibers fixed at the binding points of the woven or knitted fabric to be able to move, improving flexibility and providing water absorption through capillary action due to the fine gaps, so the inter-fiber gap distance is preferably 4 μm or more. Furthermore, if the inter-fiber gap distance is 6 μm or more, the apparent density decreases when the fabric is made into a fabric due to the development of bulkiness, and there is also an added effect of improving fluffiness, so this is considered to be a more preferable range.

From the standpoint of fluffiness and flexibility, the greater the inter-fiber gap distance, the more preferable it is; however, if the inter-fiber gap distance is too large, the texture becomes excessively soft, which may result in a loss of the firmness required for clothing applications. In addition, the water absorbency obtained by capillary action due to fine voids may also decrease. Therefore, in this embodiment, the inter-fiber gap distance is preferably 10 μm or less, and more preferably 8 μm or less.

[Coefficient of variation CV% of inter-fiber gap distance] In the spun yarn of the present embodiment, the inter-fiber gap distance resulting from the crimped form of the flat staple fibers can be varied to make the surface unevenness and inter-fiber gaps complex. In order to approach the comfortable touch with moist unevenness like cotton, which is the objective of the present invention, it is important that the coefficient of variation CV% of the inter-fiber gap distance is 60 to 90%.

In this embodiment, the interfiber gap distance and its coefficient of variation CV% can be calculated by the following method.

First, in a textile made of spun yarn, an image of the cross section of the fabric perpendicular to the fiber axis direction of the spun yarn is taken with a scanning electron microscope (SEM) at a magnification that allows more than 20 short fibers that make up the spun yarn to be observed. For each image taken, a perfect circle is drawn to fit 20 short fibers as shown in Figure 5, and of the 20 short fibers present inside the perfect circle, one short fiber is selected at random, and the intersection point between the line connecting the center of gravity G of the short fiber and the adjacent short fiber and the surface of each fiber is determined, and the distance between the intersection points is measured in μm units to one decimal place. "Adjacent" here means that no other short fibers are present on the line connecting the centers of gravity of any two fibers. This operation is performed on all adjacent short fibers in the 20 short fibers present inside the perfect circle as shown in Figure 5, and the average value and standard deviation are calculated. The average value is rounded off to the nearest whole number to determine the inter-fiber gap distance (μm), and the standard deviation is divided by the average value, multiplied by 100, and the value is rounded off to the nearest whole number to determine the coefficient of variation CV% (%) of the inter-fiber gap distance.

When the coefficient of variation CV% of the interfiber gap distance in spun yarn is 60% or more, the various interfiber gaps can form complex irregularities on the surface. As a result, when the spun yarn is made into a textile, the unevenness makes it easier for fingers to catch on it, increasing the degree of adhesion to the fingers and providing a moist feel, as well as a natural feel with a comfortable unevenness that provides moderate friction when a finger is slid across the surface.

In addition, from the viewpoint of emphasizing the comfortable cotton-like feel that is a characteristic of the present invention, it is preferable to increase the coefficient of variation CV% of the inter-fiber gap distance and make the unevenness of the spun yarn surface more complex, so it is preferable to set the coefficient of variation CV% of the inter-fiber gap distance to 65% or more, and more preferably 70% or more.

However, if the coefficient of variation CV% of the inter-fiber gap distance becomes too large, the inter-fiber gap distance will be polarized into small and large areas, the resulting surface irregularities will be monotonous, and the material may feel rough to the touch, so it is important that the coefficient of variation CV% is 90% or less, preferably 85% or less, and more preferably 80% or less.

[Porosity]
The spun yarn of the present embodiment preferably has a void structure with a void ratio of 30 to 60%.

In this embodiment, the porosity can be calculated by the following method.

First, in a textile made of spun yarn, an image of the cross section of the fabric perpendicular to the fiber axis direction of the spun yarn is taken with a scanning electron microscope (SEM) at a magnification that allows observation of 20 or more short fibers that constitute the spun yarn. For each image taken, a perfect circle that contains 20 short fibers is drawn as shown in Figure 5, and the total cross-sectional area of the 20 fibers present inside the perfect circle is subtracted from the cross-sectional area of the perfect circle to calculate the value. At this time, if 1/2 or more of the fiber is contained inside the perfect circle, it is counted as one fiber, and the cross-sectional area is measured to one decimal place in ^μm2 units. The obtained value is then divided by the cross-sectional area of the perfect circle to calculate the value, multiplied by 100, and rounded off to the nearest decimal place to obtain the void ratio (%).

If the spun yarn has a void structure with a void ratio of 30% or more inside, this is preferable because it creates enough space for the fibers fixed at the binding points of the woven or knitted fabric to move, improving flexibility. Furthermore, if the void structure has a void ratio of 40% or more, this is considered an even more preferable range because the high void ratio reduces the apparent density when made into a fabric and also improves fluffiness.

In terms of volume and flexibility, the higher the void ratio, the more suitable it is; however, if the void ratio is too high, the texture becomes excessively soft, which may result in a loss of the firmness required for clothing applications. In addition, when the fabric is rubbed, short fibers may be pulled out and tangled, resulting in pilling, which results in a poor appearance. Therefore, in this embodiment, the void ratio is preferably 60% or less, and more preferably 50% or less.

[Flat staple fiber blend ratio]
In the spun yarn of the present embodiment, the mixing ratio of the flat staple fibers is preferably 30 to 100 mass %.

When other fibers are blended, the blend ratio is preferably 30% by mass or more of the flat staple fibers and 70% by mass or less of the other fibers, from the viewpoint of fully exhibiting the characteristics of the flat staple fibers used in this embodiment, and more preferably 45% by mass or more of the flat staple fibers and 55% by mass or less of the other fibers. Also, from the viewpoint of fully exhibiting the characteristics of the other fibers, it is preferable that the blend ratio is 65% by mass or less of the flat staple fibers and 35% by mass or more of the other fibers.

By being in the above range, it is possible to obtain a spun yarn that exhibits the characteristics of the present invention, such as a comfortable feel due to the moist unevenness like cotton, a soft and fluffy texture, and water absorbency, while also having the characteristics of other fibers, which has an excellent practical advantage.

The type of other staple fibers that make up the spun yarn is not particularly limited, but it is preferable to use at least one of polyester staple fibers, acrylic staple fibers, polyamide staple fibers, rayon, cotton, linen, wool, and silk, as this will be effective in achieving the effects of the present invention.

In particular, 100% by mass of the flat staple fiber used in the present invention, a blend of the flat staple fiber used in the present invention/cotton, a blend of the flat staple fiber used in the present invention/rayon, etc. are preferred.

Furthermore, the process for mixing flat staple fibers with other fibers can be any process, such as beating, drawing, gill loom, or twisting.

(3) Polymer The polymer used in this embodiment is preferably a thermoplastic polymer because of its excellent processability. As the thermoplastic polymer, for example, a polyester-based, polyethylene-based, polypropylene-based, polystyrene-based, polyamide-based, polycarbonate-based, polymethyl methacrylate-based, polyphenylene sulfide-based polymer group and its copolymer are preferable. In particular, from the viewpoint of being able to impart high interfacial affinity and obtaining short fibers without abnormalities in the composite cross section, it is preferable that all of the thermoplastic polymers used in this embodiment are the same polymer group and its copolymer. Among these, from the viewpoint of obtaining good color development when dyeing the short fibers and spun yarn of this embodiment when they are tailored into textiles, it is more preferable that the thermoplastic polymer used is a polyester-based or polyamide-based polymer group and its copolymer, and among them, polyethylene terephthalate and its copolymer are even more preferable because they provide a moderate resilience due to their high bending recovery.

Furthermore, as environmental issues are gaining attention, the use of plant-derived biopolymers and recycled polymers in this embodiment is also suitable from the perspective of reducing the environmental impact. Therefore, the polymers used in this embodiment described above can be recycled polymers that have been recycled using any of the methods of chemical recycling, material recycling, and thermal recycling.

Even if biopolymers or recycled polymers are used, as mentioned above, polyester-based or polyamide-based polymers and their copolymers are preferred from the viewpoint of obtaining good color development when dyed, and among these, recycled polyethylene terephthalate and its copolymers are even more suitable because they provide a moderate bounce feeling due to their high bending recovery.

The polymer may also contain various additives such as inorganic compounds such as titanium oxide, silica, and barium oxide, colorants such as carbon black, dyes, and pigments, flame retardants, fluorescent brighteners, antioxidants, and ultraviolet absorbers.

Among these, it is preferable to incorporate titanium oxide into the polymer. By incorporating titanium oxide into the polymer, not only can the titanium oxide in the fiber diffusely reflect light, thereby improving the quality of appearance by suppressing uneven appearance (glare) caused by increases and decreases in reflection depending on the angle of incidence of light, but the titanium oxide inside the fiber also provides functionality such as anti-transparency and UV protection. To fully obtain the above effects, the content of titanium oxide in the composite fiber is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, and even more preferably 3.0 mass% or more. Furthermore, since increased diffuse reflection of light by titanium oxide can cause a decrease in color development, the content of titanium oxide in the fiber is preferably 10.0 mass% or less.

In this embodiment, a combination of polymers with different melting points refers to a combination of polymers whose melting points differ by 10°C or more from a group of melt-moldable thermoplastic polymers such as polyesters, polyethylenes, polypropylenes, polystyrenes, polyamides, polycarbonates, polymethyl methacrylates, and polyphenylene sulfide, and their copolymers, and a combination of polymers whose melting points differ by 5°C or more from a group of the same polymers with the same bonds in the main chain, such as polyesters with ester bonds and polyamides with amide bonds.

In the staple fibers and spun yarns of this embodiment, since the purpose is to create a crimped morphology by the difference in shrinkage between polymers with different melting points, it is preferable to combine polymers with different melting points such that one type is a high-shrinkage, low-melting-point polymer and the other is a low-shrinkage, high-melting-point polymer.

In particular, from the viewpoint of preventing peeling and imparting stability to advanced processing and durability to textiles, it is more preferable to select polymer combinations from the same polymer group in which the bonds present in the main chain are the same, such as polyesters with ester bonds and polyamides with amide bonds.

Combinations of low-melting point polymers and high-melting point polymers in the same polymer group include, for example, polyester-based copolymer polyethylene terephthalate/polyethylene terephthalate, polypropylene terephthalate/polyethylene terephthalate, polybutylene terephthalate/polyethylene terephthalate, thermoplastic polyurethane/polyethylene terephthalate, polyester-based elastomer/polyethylene terephthalate, polyester-based elastomer/polybutylene terephthalate, polyamide-based combinations of nylon 6/nylon 66, nylon 6/nylon 610, nylon 6-nylon 66 copolymer/nylon 6 or 610, PEG copolymer nylon 6/nylon 6 or 610, thermoplastic polyurethane/nylon 6 or 610, polyolefin-based combinations of ethylene-propylene rubber finely dispersed polypropylene/polypropylene, propylene-α-olefin copolymer/polypropylene, etc.

Among these, from the viewpoint of obtaining good color development by dyeing when the staple fiber and spun yarn of this embodiment are made into textiles, it is more preferable that the polymers having different melting points are a combination of polyesters or polyamides, and among these, the combination of copolymerized polyethylene terephthalate/polyethylene terephthalate as the polyester is a particularly preferable combination because it provides a moderate resilience due to its high bending recovery.

Furthermore, examples of the copolymerized components in the copolymerized polyethylene terephthalate include succinic acid, adipic acid, azelaic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, maleic acid, phthalic acid, isophthalic acid, and 5-sodium sulfoisophthalic acid. Among these, from the viewpoint of maximizing the difference in shrinkage with polyethylene terephthalate, it is preferable to use polyethylene terephthalate copolymerized with 5 to 15 mol% isophthalic acid.

(4) Applications In the staple fibers and spun yarn of the present embodiment, by controlling the crimp morphology of each staple fiber, it is possible to achieve a comfortable touch due to moist unevenness like cotton and a soft, fluffy texture, as well as functionality such as water absorbency.

The inclusion of the short fibers of this embodiment in part provides a unique fluffy, soft texture and water absorbency due to the voids, and the fibers can be used suitably in a wide range of textile products, from general clothing such as jackets, skirts, pants, and underwear, to sports clothing and clothing materials, and also in a wide range of textile products, such as interior products such as carpets and sofas, automotive interior products such as car seats, cosmetics, cosmetic masks, and health products, taking advantage of their comfort. However, from the viewpoint of being able to express a unique touch and texture like natural materials, it is particularly preferable to use the fibers as spun yarn for clothing applications.

The staple fiber of this embodiment can be used in various textiles such as nonwoven fabrics and woven and knitted fabrics, but from the viewpoint of suitability for the above-mentioned clothing applications, it is particularly preferable to use the spun yarn of this embodiment as a part of the woven and knitted fabric, which is a clothing textile with excellent wearing comfort.

Below is a detailed description of an example of a method for producing the staple fibers and spun yarn of this embodiment.

(5) Manufacturing method of staple fibers The object of the present invention is to obtain a spun yarn having complex surface irregularities and inter-fiber voids like natural fibers, which is difficult to obtain with conventional spun yarns due to the inclusion of staple fibers with controlled crimp morphology, which causes variation in the inter-fiber void distance. To obtain such a spun yarn, it is important to set the relationship between the crimp number and the crimp diameter in staple fibers made of at least two polymers with different melting points within a specific range, and further to change the crimp number for each staple fiber. To change the crimp number for each staple fiber, various methods can be adopted, such as a method of changing the bonding surface direction for each staple fiber in flat staple fibers with the same cross section and the same compounding ratio to change the distance between the polymer centers of gravity, a method of changing the cross-sectional shape or compounding ratio for each staple fiber, and a method of mixing flat staple fibers with different crimp numbers that have been spun separately during spinning processing. In particular, from the viewpoints of yarn production stability during spinning, processing stability during spinning processing, and yarn quality, it is preferable to use a method of changing the bonding surface direction of each staple fiber in flat staple fibers having the same cross section and the same conjugation ratio to change the distance between the polymer centers of gravity.

The staple fibers of this embodiment can be produced by melt spinning, which is intended to produce staple fibers by taking a shortcut from long fibers, or by wet or dry-wet solution spinning methods, but from the standpoint of increasing productivity, melt spinning is preferred.

In addition, in the melt spinning method, production is possible by using a composite spinneret, which will be described later. The spinning temperature is preferably set to a temperature at which the polymers used, mainly the high melting point polymers and high viscosity polymers, exhibit fluidity. This fluidity temperature varies depending on the molecular weight, but stable production is possible if it is set between the melting point of the polymer and the melting point + 60°C.

The spinning speed can be set to about 500 to 6000 m/min, but can be changed as appropriate depending on the physical properties of the polymer and the intended use of the short fibers. In particular, from the perspective of achieving high orientation and improving mechanical properties, a spinning speed of 500 to 2000 m/min and subsequent drawing is more preferable, as this promotes uniaxial orientation of the fibers.

When stretching, it is preferable to set the preheating temperature appropriately, using the temperature at which the polymer can be softened, such as its glass transition temperature, as a guide. The upper limit of the preheating temperature is preferably set to a temperature at which the yarn path is not disturbed due to spontaneous elongation of the composite fiber bundle during the preheating process. For example, in the case of PET, which has a glass transition temperature of around 70°C, the preheating temperature is usually set to around 80 to 95°C.

The discharge rate per hole in the die for producing the staple fibers of this embodiment is preferably 0.1 to 10 g/min/hole. By setting the discharge rate within the above range, stable production is possible. The discharged polymer flow is cooled and solidified, and then an oil agent is applied and the flow is taken up by rollers at a specified peripheral speed. The flow is then stretched under heating, and further post-processing is added to produce a spun yarn in which the desired staple fibers are twisted together.

In addition, in the staple fibers of this embodiment that are made of at least two types of polymers with different melting points, it is preferable that the melt viscosity ratio of the composite polymers is less than 5.0. If the melt viscosity ratio is within this range, excessive crimping is suppressed, making it easier to control the crimping of the staple fibers, which is the object of the present invention, and allowing the formation of complex interfiber voids and surface irregularities.

In addition, when producing the short fibers of this embodiment, if melts of polymers with a large difference in melt viscosity are spun from a spinneret as a composite flow, the flow rate difference caused by the difference in resistance from the wall surface inside the spinneret hole can cause yarn bending in which the polymer on the lower viscosity side pushes out the polymer on the higher viscosity side, which can come into contact with the spinneret or interfere with the composite flow spun from another location, causing yarn breakage. From this perspective, it is preferable that the melt viscosity ratio of the composite polymers is less than 5.0.

It is also preferable that the difference in solubility parameters is less than 2.0, as this allows a stable composite polymer flow to be formed and composite fibers with a good composite cross section to be obtained.

As a spinneret used when manufacturing the composite fiber bundle of this embodiment, for example, the composite spinneret described in Japanese Patent Publication No. 2011-208313 is preferably used.

The composite spinneret shown in Figure 7 is assembled into a spinning pack with three main components stacked from the top: a metering plate 1, a distribution plate 2, and a discharge plate 3, and is used for spinning. Incidentally, Figure 7 shows an example in which three types of polymers, A polymer, B polymer, and C polymer, are used. Since it is difficult to combine three or more types of polymers with conventional composite spinnerets, it is preferable to use a composite spinneret that utilizes fine flow paths as shown in Figure 7 in the production of short fibers in this embodiment.

In the spinneret member shown in Figure 7, the metering plate 1 measures and introduces the amount of polymer per each discharge hole and each distribution hole, the distribution plate 2 controls the cross section and cross-sectional shape of each composite fiber, and the discharge plate 3 compresses the composite polymer flow formed by the distribution plate 2 and discharges it.

In this case, in order to achieve a composite cross section in which the short fibers have a flat cross section while varying the bonding surface direction for each short fiber, which is cited as a preferred range in this embodiment, the nozzle hole shape of the nozzle plate 3 is made flat, and the composite polymer flow is controlled in the distribution plate 2 so that the polymer bonding surface direction differs for each nozzle hole. From the viewpoint of being able to control an arbitrary composite cross section for each nozzle hole in this way, it is preferable in this embodiment to use a composite spinneret that utilizes fine flow paths as exemplified in Figure 7.

In addition, to avoid confusing the explanation of the composite spinneret, although this is not shown, for the components stacked above the metering plate 1, components with flow paths formed to match the spinning machine and spinning pack can be used. By designing the metering plate 1 to match the existing flow path components, the existing spinning pack and its components can be used as is. For this reason, there is no need to dedicate a spinning machine specifically for the spinneret.

In practice, it is advisable to stack multiple flow path plates between the flow path and metering plate 1, or between metering plate 1 and distribution plate 2. The purpose of this is to provide a flow path through which the polymer is efficiently transported in the cross-sectional direction of the spinneret and the cross-sectional direction of the composite fiber, and to configure it so that it is introduced into the distribution plate 2. The composite polymer flow discharged from the discharge plate 3 is cooled and solidified according to the manufacturing method described above, and then an oil agent is applied and the composite polymer flow is taken up by a roller that has a specified peripheral speed. It is then stretched under heat, and further post-processing is performed to produce a spun yarn in which the desired short fibers are twisted together.

In the process of stretching the spun unstretched yarn, the unstretched yarn is bundled to 30-300 ktex and stretched 2-5 times in steam or hot water to produce a stretched tow, which is then subjected to tension heat treatment and mechanically crimped using a crimping machine (crimper) or the like to obtain a crimped tow.

The crimped tow is then dried, a finishing oil solution is sprayed onto the tow, and the tow is cut to produce the short fibers of this embodiment.

[Fiber length]
The staple fiber of this embodiment preferably has a fiber length of 20 to 120 mm. This range allows for good processability in the spinning process and stable production of spun yarn. Furthermore, a fiber length of 30 to 90 mm is a more preferable range, since it suppresses fuzzing during twisting and provides a textile with excellent appearance quality.

[Number of crimps before heat treatment]
In the staple fiber of this embodiment, the number of crimps before heat treatment is preferably 5 to 30 crimps/25 mm.

The number of crimps before heat treatment referred to here is the number of crimps obtained by cutting the crimped tow and obtaining short fibers without heat treatment according to the method of JIS L1015 (2010) 8.12.1.

By having the number of crimps be 5 crimps/25mm or more, the short fibers are well entangled with each other, and excellent carding performance is obtained. From this viewpoint, the higher the number of crimps, the better, more preferably 8 crimps/25mm or more, and particularly preferably 10 crimps/25mm or more.

In addition, by keeping the number of crimps at 30 crimps/25 mm or less, the occurrence of frequent neps after passing through the card and the unevenness in the thickness of the spun yarn do not increase excessively, and the high-level processability and quality of the spun yarn can be improved. From this perspective, the fewer the number of crimps, the more preferable, with 25 crimps/25 mm or less being more preferable, and 20 crimps/25 mm or less being particularly preferable.

[Heat treatment conditions]
In order to control the crimp form, which is important for the staple fiber of the embodiment of the present invention, it is important to set the tension heat treatment temperature, the temperature of the stretched tow when it enters the push-type crimper, the pushing pressure of the push-type crimper, and the drying temperature of the crimped tow after crimping.

The tension heat treatment involves heat setting while maintaining tension, and then cooling the fibers with cooling water to below the glass transition temperature to fix the molecular chain structure. This suppresses the occurrence of crimping during the tow drying process after crimping, improves the carding ability of the short fibers, and allows the desired crimp shape to be expressed by heat treatment after spinning.

The tension heat treatment temperature is preferably 100 to 190°C, and the tension heat treatment time is preferably 3 to less than 20 seconds. If the treatment temperature is less than 100°C, excessive crimping may occur in the subsequent drying process of the crimped tow, which may deteriorate the carding ability of the short fibers. Also, if the treatment temperature is higher than 190°C, the desired crimp shape may not be achieved by the heat treatment after spinning.

The temperature of the stretched tow when it enters the push-in type crimping machine is preferably 20 to 60°C. If it is below 20°C, the number of crimps in the short fibers is small, which may result in poor carding properties, and if it is above 60°C, the number of crimps in the short fibers is large, which may result in frequent neps after carding or extremely increased thickness unevenness in the spun yarn.

The pressing pressure of the pressing type crimping machine is preferably 98 to 294 kPa. If it is less than 98 kPa, the number of crimps of the short fibers will be small, and if it is higher than 294 kPa, the number of crimps of the short fibers will tend to be large.

The drying temperature for the crimped tow after crimping is preferably 80 to 120°C. If it is lower than 80°C, the crimped tow may not be dried sufficiently, and if it is higher than 120°C, crimping may occur during the drying process, and the number of crimps in the short fibers may be high, resulting in frequent neps after passing through the card and extremely increased thickness unevenness in the spun yarn.

(7) Manufacturing method of spun yarn When the staple fiber of the present embodiment is made into a spun yarn, the spun yarn can be manufactured by a known spinning method, for example, the staple fiber is twisted into a spun yarn using a ring spinning machine (including a bundling/vortex method) or an air spinning machine, etc. When making the spun yarn, it may be compounded with a filament as necessary.

The staple fibers of this embodiment are twisted together to form a spun yarn, which is then subjected to advanced processing such as weaving and knitting, and then heat-treated to cause the staple fibers to shrink, forming complex surface irregularities and interfiber voids in the spun yarn. Due to the special fiber morphology of this spun yarn, it is possible to obtain clothing textiles that are comfortable to wear, with functionality such as water absorbency, in addition to a comfortable feel due to the moist unevenness of cotton and a soft, fluffy texture not found in conventional materials. In order to maximize the above effects, it is preferable that the twist coefficient of the spun yarn made from the staple fibers of this embodiment is 2 to 6.

The twist factor referred to here can be calculated using the following method.

First, the yarn count is measured according to the cotton yarn count measurement method for measuring the correct tex and yarn count of general spun yarn in JIS L1095 (2010) 9.4.1. Next, the number of twists is measured according to JIS L1095 (2010) 9.15.1A method, and the value obtained by the formula twist factor = twist number / (yarn count) ^1/2 is rounded off to the nearest whole number to obtain the twist factor.

A twist factor of 2 or more is preferable because the torque due to the manifestation of shrinkage of the staple fibers of this embodiment approaches the torque due to twisting during spinning, making it easier for the staple fibers to manifest shrinkage through heat treatment even under constraints from fabric structures such as weaving and knitting. Furthermore, a twist factor of 3 or more is more preferable from the viewpoint that stronger constraints from twisting can suppress pilling, which is a defect in appearance caused by staple fibers being pulled out and tangled when the fabric is rubbed.

However, if the twist factor is too large, the torque during spinning will be greater than the torque caused by the crimping of the short fibers, and the crimping of the short fibers during heat treatment may be suppressed, so the twist factor is preferably 6 or less, and more preferably 5 or less.

The count of the spun yarn of this embodiment is preferably 20 to 100, which is often used for denim and uniforms as well as thin fabrics such as shirts, underwear, and sportswear, but can be selected appropriately depending on the application. In addition, since the staple fibers of this embodiment are spun into yarn and then heat-treated to develop crimp, the crimp form can be suppressed to a form suitable for processing during spinning processing. Furthermore, unlike conventional staple fibers with a side-by-side cross section that develop a uniform crimp form, the different crimps of each staple fiber improve the opening property when passing through the card without the crimp phase being aligned, and even with a fine count of 60 to 100, a spun yarn with excellent operability and quality can be obtained.

(8) Manufacturing Method of Woven/Knitted Fabrics The spun yarn of the present embodiment can be used at least in part to manufacture a woven fabric having the above-mentioned weave structure and a knitted fabric having the above-mentioned knit structure by a known method.

The following provides a more detailed explanation of the staple fibers and spun yarn of the present invention using examples.

The following evaluations were carried out for the examples and comparative examples.

A. Melt Viscosity of Polymer The chip-shaped polymer was dried to a moisture content of 200 ppm or less using a vacuum dryer, and the melt viscosity was measured by changing the strain rate stepwise using a Capillograph manufactured by Toyo Seiki Seisaku-sha. The measurement temperature was the same as the spinning temperature, and the time from the introduction of the sample into the heating furnace in a nitrogen atmosphere to the start of the measurement was 5 minutes. The value at a shear rate of 1216 s ^-1 was evaluated as the melt viscosity of the polymer.

B. Melting point of polymer The chip-shaped polymer was dried in a vacuum dryer to a moisture content of 200 ppm or less, and about 5 mg was weighed out. Using a TA Instruments differential scanning calorimeter (DSC) Q2000 model, the temperature was raised from 0°C to 300°C at a heating rate of 16°C/min, and then the temperature was held at 300°C for 5 minutes to perform DSC measurement. The melting point was calculated from the melting peak observed during the heating process. The measurement was performed three times for each sample, and the average value was taken as the melting point. When multiple melting peaks were observed, the melting peak top on the highest temperature side was taken as the melting point.

C. Fineness and Fiber Length The fineness and fiber length of staple fibers were measured according to the methods set forth in JIS L1015 (2010) 8.4A and 8.5A.

D. Flatness The short fibers or spun yarns are embedded in an embedding agent such as epoxy resin, and an image of the fiber cross section perpendicular to the fiber axis is taken with a scanning electron microscope (SEM) manufactured by Hitachi. Next, one short fiber randomly selected from the taken image is analyzed using image analysis software (WinROOF) manufactured by Mitani Shoji, and the value is calculated by dividing the length of the long axis by the length of the short axis, with the straight line connecting the two points (a1, a2) that are the most distant among any points on the circumference of the composite fiber as shown in (a) of Figure 1, and the straight line connecting the intersection point (b1, b2) of the circumference of the fiber and the straight line passing through the midpoint of the long axis and perpendicular to the long axis being the short axis. This was performed on 20 short fibers in the same manner, and the simple number average was calculated, and the value rounded off to one decimal place was taken as the flatness.

E. Fiber diameter Short fibers or spun yarns are embedded in an embedding agent such as epoxy resin, and an image of the fiber cross section perpendicular to the fiber axis is taken using a scanning electron microscope (SEM) manufactured by Hitachi. Next, one short fiber randomly extracted from the taken image is analyzed using image analysis software (WinROOF) manufactured by Mitani Shoji to measure the area of the short fiber, and the diameter calculated as a perfect circle is measured in μm units to the first decimal place. This was performed on 20 short fibers in the same manner, and the simple number average was calculated, and the value rounded off to the first decimal place was taken as the fiber diameter (μm).

F. Coefficient of variation CV% of (distance between polymer centers of gravity/fiber diameter)
The short fibers or spun yarns are embedded in an embedding agent such as epoxy resin, and an image of the fiber cross section perpendicular to the fiber axis is taken using a scanning electron microscope (SEM) manufactured by Hitachi. Next, one short fiber randomly selected from the taken image is analyzed using computer software WinROOF manufactured by Mitani Shoji to measure the area of the composite fiber, and the diameter calculated as a perfect circle is measured in μm units to one decimal place. The obtained value is defined as the fiber diameter (μm).

In addition, for the same short fibers as above, the length of the straight line connecting the centers of gravity (Gx, Gy) of the low melting point polymer x and the high melting point polymer y in the cross section of the composite fiber was measured in μm units to one decimal place as shown in Figure 2 (a). The obtained value was taken as the distance between the polymer centers of gravity (μm).

The simple number average of the ratio (distance between polymer centers of gravity/fiber diameter) of the fiber diameter and the distance between polymer centers of gravity obtained above was calculated, and the value rounded to one decimal place was used as (distance between polymer centers of gravity/fiber diameter). This evaluation was performed in the same way on 20 short fibers randomly selected, and the standard deviation and average value of the results were calculated. The standard deviation was divided by the average value, multiplied by 100, and rounded to the nearest whole number. The value obtained was used as the coefficient of variation CV% (%) of the value of (distance between polymer centers of gravity/fiber diameter).

G. Number of crimps, coefficient of variation of number of crimps CV%
The staple fibers were dry-heated at 180°C for 5 minutes without load, and the number of crimps was determined from the crimp morphology of one staple fiber observed according to the method of JIS L1015 (2010) 8.12.1. This was performed on 20 different staple fibers to determine the average value and standard deviation, and the average value was rounded off to the nearest whole number to determine the number of crimps (peaks/25 mm). The standard deviation was divided by the average value, multiplied by 100, and the value was rounded off to the nearest whole number to determine the coefficient of variation CV% (%) of the number of crimps among the staple fibers.

The number of crimps obtained by cutting the crimped tow and not subjecting it to heat treatment was calculated according to the method of JIS L1015 (2010) 8.12.1, and this was taken as the number of crimps before heat treatment (peaks/25 mm).

H. Crimp diameter, number of crimps/crimp diameter After dry-heating the staple fiber at 180°C for 5 minutes without load, the crimped form of one staple fiber is observed according to the method of JIS L1015 (2010) 8.12.1. In the crimped form of one staple fiber, the apex of the first peak (M1) and the last valley (V2) in the part of peak (M1) → valley (V1) → peak (M2) → valley (V2) as shown in Figure 6 are connected by a straight line (S1). The distance Le (mm) between the intersection of two straight lines (S2, S3) that are parallel to this straight line (S1) and pass through the apex of the valley (V1) and the peak (M2) and one straight line that is perpendicular to S1 is calculated. This operation is measured at three or more arbitrary points per staple fiber, and a simple number average is calculated. Further, this was carried out for 20 different short fibers, and the simple number average of the results was calculated, and the value was rounded off to three decimal places to obtain the crimp diameter (mm).

The number of crimps obtained in section G was divided by the crimp diameter obtained above, and the value was rounded off to the nearest whole number to obtain the number of crimps/crimp diameter.

I. Spinning Stability In the spinning of each of the Examples and Comparative Examples, the spinning stability was evaluated based on the number of yarn breakages per 1 million meters (times/million meters) and rated into four stages according to the following criteria.
S: Excellent spinning stability (number of yarn breaks < 1.0)
A: Good spinning stability (1.0≦number of yarn breaks<5.0)
B: Spinning stability (5.0≦number of yarn breaks<10.0)
C: Poor spinning stability (number of yarn breakages 10.0 or less).

J. Yarn count and twist factor The value obtained according to the cotton yarn count measurement method for measuring the correct tex and yarn count of general spun yarn in JIS L1095 (2010) 9.4.1 was used as the yarn count.

Next, the number of twists was measured according to JIS L1095 (2010) 9.15.1A method, and the value obtained by the formula Twist factor = Twist factor / (yarn count) ^1/2 was rounded off to the nearest whole number to obtain the twist factor.

K. Interfiber gap distance, coefficient of variation of interfiber gap distance CV%
In a textile made of spun yarn, a cross section of the fabric perpendicular to the fiber axis direction of the spun yarn was photographed with a scanning electron microscope (SEM) manufactured by Hitachi at a magnification that allowed observation of 20 or more staple fibers constituting the spun yarn. For each photographed image, a perfect circle was drawn in which 20 staple fibers could fit, as shown in Figure 5, and one staple fiber was selected from the 20 staple fibers present inside the perfect circle. The intersections of the line connecting the center of gravity G of the staple fiber and the adjacent staple fiber with the surface of each fiber were determined, and the distance between the intersections was measured in μm units to the first decimal place. "Adjacent" here means that no other staple fiber is present on the line connecting the centers of gravity of any two fibers. This operation was performed on all adjacent short fibers of 20 short fibers present inside a perfect circle as shown in Figure 5 to determine their average value and standard deviation. The average value was rounded off to the nearest whole number to define the inter-fiber gap distance (µm). The standard deviation was divided by the average value, multiplied by 100, and the result was rounded off to the nearest whole number to define the coefficient of variation CV% (%) of the inter-fiber gap distance.

L. Void ratio In a textile made of spun yarn, an image was taken of the cross section of the fabric perpendicular to the fiber axis direction of the spun yarn with a scanning electron microscope (SEM) at a magnification such that 20 or more short fibers constituting the spun yarn could be observed. For each image taken, a perfect circle was drawn in which 20 short fibers could fit, as shown in FIG. 5, and the total cross-sectional area of the 20 fibers present inside the perfect circle was subtracted from the cross-sectional area of the perfect circle to calculate the value. In this case, if 1/2 or more of the fiber is contained inside the perfect circle, it was counted as one fiber, and the cross-sectional area was measured to the first decimal place in ^μm2 units. The value obtained was further divided by the cross-sectional area of the perfect circle to calculate the value, multiplied by 100, and rounded off to the first decimal place to obtain the void ratio (%).

M. Processing Stability In the spinning process of each Example and Comparative Example, the processing stability was evaluated based on the number of yarn breakages per 1 million meters (times/million meters) and rated into four stages according to the following criteria.
S: Excellent processing stability (number of thread breaks < 5.0)
A: Good processing stability (5.0≦number of yarn breakages<10.0)
B: Stable processing (10.0≦number of thread breaks<20.0)
C: Poor processing stability (number of yarn breakages is 20.0 or less).

N. Spun Yarn Quality For the spun yarns of each Example and Comparative Example, a yarn defect detector (Evene Tester (Tester 5) manufactured by USTER) was used to measure the number of thick irregularities, thin irregularities, and neps relative to the average thickness per 1,000 meters in accordance with JIS L1095 (2010) 9.20.2B method, and the yarn quality was evaluated into four levels based on the total number of yarn irregularities and neps, respectively, based on the following criteria.
S: Excellent yarn quality (yarn unevenness, nep count <100)
A: Good yarn quality (100≦yarn unevenness, number of neps<200)
B: Meets yarn quality requirements (200≦yarn unevenness, number of neps<500)
C: Poor yarn quality (500≦yarn unevenness, number of neps).

O. Textile texture evaluation (fullness, flexibility, moistness, unevenness)
A plain weave fabric was woven by adjusting the number of spun yarns so that the warp cover factor (CFA) was 20 and the weft cover factor (CFB) was 15. The CFA and CFB mentioned here are values calculated by measuring the warp density and weft density of the fabric in a 2.54 cm section in accordance with JIS L1096 (2010) 8.6.1, and using the formulas CFA = warp density / (warp count) ^1/2 and CFB = weft density / (weft count) ^1/2 .

The resulting fabric was dyed under the following conditions, and then evaluated for four texture aspects - fluffiness, flexibility, moistness, and unevenness - using the following methods.

(dyeing process)
After scouring for 10 minutes in 80°C warm water containing a surfactant, the yarn was relaxed for 30 minutes in 130°C warm water. It was then heat set for 5 minutes in dry heat at 180°C. Thereafter, finishing such as singeing, weight reduction, and polishing was performed as necessary.

O-1. Fullness Using a Terotec constant pressure thickness gauge (PG-14J), the thickness (cm) of a 20 cm x 20 cm woven fabric was measured under a constant pressure (0.7 kPa) to calculate the volume of the woven fabric. The weight (g) of the woven fabric was then divided by the volume obtained, and the value was rounded off to one decimal place to obtain the apparent density (g/cm ³ ) of the woven fabric. The fullness was evaluated based on the apparent density obtained, and rated into four levels according to the following criteria:
S: Excellent fluffy feeling (apparent density ≦ 0.5)
A: Good fluffy feeling (0.5<apparent density≦0.7)
B: Feels fluffy (0.7<apparent density≦0.9)
C: Poor fluffy feeling (0.9<apparent density).

O-2. Flexibility Using a Kato Tech pure bending tester (KES-FB2), a 20 cm x 20 cm woven fabric was held with an effective sample length of 20 cm x 1 cm and bent in the warp direction under conditions of a maximum curvature of ±2.5 cm ^{-1. The} difference between the bending moment (gf cm/cm ⁾ per unit width at curvatures of 0.5 cm -1 and 1.5 cm -1 was divided by a curvature difference of 1 cm ^-1 , and the average value was calculated by dividing the difference between the bending moment (gf cm/cm) per unit width at curvatures of -0.5 cm ^-1 and -1.5 ^cm -1 by a curvature difference of 1 cm ^-1 . This operation was performed three times per location, and a simple number average of the results was obtained for a total of 10 locations, and the value was rounded off to the fourth decimal place and divided by 100 to obtain the bending hardness B x 10 ^-2 (gf cm ² /cm). From the obtained bending hardness B×10 ^−2, the flexibility was judged into four stages based on the following criteria.
S: Excellent flexibility (bending hardness B×10 ⁻² ≦2.0)
A: Good flexibility (2.0<bending hardness B×10 ⁻² ≦3.0)
B: Flexible (3.0<bending hardness B×10 ⁻² ≦4.0)
C: Poor flexibility (4.0<bending hardness B×10 ⁻² ).

O-3. Moist feeling, uneven feeling Using a static and dynamic friction measuring machine TL201Tt manufactured by Trinity Lab, an element in which a geometric fingerprint pattern was applied to a urethane having a hardness equivalent to a fingertip was set on a contact terminal having an area of ¹ cm2, and the surface of the measurement object was traced 30 mm at a speed of 10 mm/sec while applying a load of 20 g, and a friction curve showing the friction force (gf) relative to the moving distance was obtained. Based on the obtained friction curve, the static friction coefficient and the dynamic friction coefficient were calculated with reference to JIS K7125 (1999), and the value obtained by subtracting the dynamic friction coefficient from the obtained static friction coefficient was obtained, and the value rounded off to the third decimal place was taken as the difference between the static friction coefficient and the dynamic friction coefficient. The moist feeling was judged into four stages based on the following criteria from the difference between the obtained static friction coefficient and the dynamic friction coefficient.
S: Excellent moist feeling (difference between static and dynamic friction coefficients is 0.40 or less)
A: Good moist feeling (0.35≦difference between static friction coefficient and dynamic friction coefficient<0.40)
B: Moist feeling (0.30≦difference between static friction coefficient and dynamic friction coefficient<0.35)
C: Poor moist feeling (difference between static friction coefficient and dynamic friction coefficient <0.30).

The standard deviation of the dynamic friction coefficient values in the range of 5 to 25 mm was also calculated, and the value was rounded off to two decimal places to determine the dynamic friction fluctuation. From the obtained dynamic friction fluctuation, the unevenness feeling was judged into four stages based on the following criteria.
S: Excellent unevenness (0.70≦dynamic friction fluctuation)
A: Good unevenness (0.65≦dynamic friction fluctuation<0.70)
B: There is a feeling of unevenness (0.60≦dynamic friction fluctuation<0.65)
C: Poor unevenness (dynamic friction fluctuation <0.60).

P. Textile function evaluation (moisture absorption, quick drying, stretchability)
Fabrics were produced and dyed under the same conditions as for the textile texture evaluation, and then the two functions of water absorption, quick drying, and stretchability were evaluated using the following methods.

P-1. Water absorption and quick drying property Water absorption and quick drying property was measured by dropping 0.1 cc of water onto a 10 cm x 10 cm woven fabric, measuring the weight of the woven fabric every 5 minutes in an environment with a temperature of 20 degrees and a relative humidity of 65 RH%, and determining the time (minutes) until the residual moisture content was 1.0% or less. This operation was performed at a total of three locations, and a simple number average was calculated, and the value rounded off to the nearest whole number was used as the moisture diffusion time (minutes). The water absorption and quick drying property was evaluated based on the obtained moisture diffusion time and rated in four stages based on the following criteria.
S: Excellent water absorption and quick drying (water diffusion time ≦15)
A: Good water absorption and quick drying (15<moisture diffusion time≦30)
B: Absorbs water and dries quickly (30<water diffusion time≦60)
C: Poor water absorption and quick drying properties (60<moisture diffusion time).

P-2. Stretchability Stretchability was measured according to the elongation rate A method (constant speed elongation method) described in Section 8.16.1 of JIS L1096 (2010). The strip method was used with a load of 17.6 N (1.8 kg), and the test conditions were a sample width of 5 cm x length of 20 cm, clamp interval of 10 cm, and tensile speed of 20 cm/min. The initial load was a weight equivalent to a sample width of 1 m according to the method of JIS L1096 (2010). The simple number average of the results of three tests in the weft direction of the fabric was calculated, and the value rounded off to the nearest whole number was used as the elongation rate (%). The stretchability was evaluated based on the obtained elongation rate in four stages according to the following criteria.
S: Excellent stretchability (elongation rate ≦ 10)
A: Good stretchability (7≦elongation rate<10)
B: Stretchable (4≦elongation rate<7)
C: Poor stretchability (elongation rate < 4).

Q. Textile quality evaluation (appearance quality)
After fabric creation and dyeing under the same conditions as for the textile texture evaluation, light was irradiated onto each sample at an incident angle of 60° using an automatic variable angle photometer (GONIO PHOTOMETER GP-200 type) manufactured by Murakami Color Research Laboratory, and the light intensity at reception angles of 0° to 90° was measured in 0.1° increments by two-dimensional reflected light distribution measurement, and the maximum light intensity (specular reflection) near a reception angle of 60° was divided by the minimum light intensity (diffuse reflection) near a reception angle of 0° to calculate the value. This operation was performed three times per location, and a simple number average of the results was calculated for a total of 10 locations, and the value rounded off to one decimal place was used as the glare level. The appearance quality of the textile was evaluated on a four-level scale based on the following criteria from the glare level obtained.
S: Excellent appearance quality (glare level ≦1.2)
A: Good appearance quality (1.2<glare level≦1.6)
B: Appearance is elegant (1.6<glare level≦2.0)
C: Poor appearance quality (2.0<glare level).

R. Anti-pilling property After fabric creation and dyeing under the same conditions as for the textile texture evaluation, measurements were performed using the method specified in JIS L1076 (2012) Method A, and the degree of pilling was graded from 1 to 5 in 0.5 grade increments. From the results of the grading, the anti-pilling property was graded into 4 levels based on the following criteria.
S: Excellent anti-pilling properties (grade: 4.5 or higher)
A: Good anti-pilling properties (grade: 3.5, 4)
B: Good anti-pilling properties (grade: 2.5, 3)
C: Poor anti-pilling properties (grade: grade 2 or lower).

[Example 1]
As polymer 1, polyethylene terephthalate copolymerized with 7 mol % isophthalic acid (IPA copolymerized PET, melt viscosity: 140 Pa·s, melting point: 232° C.) was prepared, and as polymer 2, polyethylene terephthalate (PET, melt viscosity: 130 Pa·s, melting point: 254° C.) was prepared.

After melting these polymers separately at 290°C, polymer 1/polymer 2 were weighed out so that the area ratio in the composite cross section was 50/50. Next, the above polymers were poured into a spinning pack incorporating the composite spinneret shown in Figure 7, and the incoming polymers were discharged from the discharge holes so that the composite cross section was flat and had polymer 1 and polymer 2 bonded side-by-side as shown in Figure 1(a), with the bonded surface direction of each composite fiber changing (the six types in Figure 4 are examples of such composite cross sections). The number of discharge holes in this case was 500.

The discharged composite polymer flow was cooled and solidified, and then an oil was applied thereto, and the undrawn yarn was taken up at a spinning speed of 1300 m/min. Then, 20 undrawn yarns were aligned and introduced into hot water at a temperature of 90° C., and the drawn tow was subjected to tension heat treatment with a heating roller at 140° C. and introduced to a crimper, where mechanical crimping was given at a drawn tow temperature of 30° C. and a tow pressing pressure of 1.5 kg/cm ² G to obtain a crimped tow. The obtained crimped tow was dried at 80° C., and then a finishing oil was applied thereto, and the tow was cut to a fiber length of 38 mm with a rotary cutter to obtain a short fiber with a fineness of 1.5 dtex (fiber diameter 12 μm). The number of yarn breakages at this time was 2.5 times/million m, and good spinning stability was obtained.

All of the short fibers obtained had a flat cross-sectional shape, with a flatness of 1.8, and a coefficient of variation CV% of the value of (distance between polymer centers of gravity/fiber diameter) between short fibers was 18%. In addition, the number of crimps was 42 crimps/25 mm (number of crimps before heat treatment was 15 crimps/25 mm), the coefficient of variation CV% of the number of crimps was 25%, the crimp diameter was 0.21 mm, and the number of crimps/crinkle diameter was 200, confirming that they were short fibers of this embodiment.

Using 100% of the resulting short fibers, a spun yarn with a count of 40 and a twist factor of 4 was obtained. The number of yarn breaks during spinning was 6.7 times per million meters, demonstrating good processing stability, and the total number of unevenness and neps in the spun yarn was 155 per million meters, demonstrating good spun yarn quality.

The obtained spun yarn was used to weave a plain weave fabric by adjusting the number of spun yarns so that the warp cover factor (CFA) was 20 and the weft cover factor (CFB) was 15. The fabric was then scoured for 10 minutes in 80°C warm water containing a surfactant, and then relaxed for 30 minutes in 130°C warm water. It was then heat set for 5 minutes in dry heat at 180°C. Finishing processes such as singeing, weight reduction, and polishing were then carried out as necessary to obtain a fabric made from the spun yarn.

The fabric made from this spun yarn is composed of staple fibers having a specific number of crimps corresponding to the crimp diameter, so that even in spun yarns in which the staple fibers are constrained by twist, crimps can be expressed without adjacent staple fibers being densely packed together, and the gaps formed by the expression of crimp result in high voids (void ratio: 55%) and large inter-fiber gaps (inter-fiber gap distance: 8 μm), resulting in a fluffy (apparent density: 0.6 g/cm ³ ) and soft (bending stiffness B: 2.7 × 10 ^-2 gf cm ² /cm) texture and good stretchability (elongation rate: 9%).

Furthermore, the mixture of short fibers with different crimp numbers results in complex inter-fiber voids with a mixture of voids of various sizes, with the coefficient of variation CV% of the inter-fiber void distance being 80%, resulting in complex unevenness on the surface. As a result, the woven fabric has a pleasant feel with a cotton-like moist unevenness that combines a good moist feel (difference between static and dynamic friction coefficients: 0.37) and a good uneven feel (dynamic friction variation: 0.67), and also exhibits good water absorption and quick-drying properties (moisture diffusion time: 25 minutes) due to the fine voids. Therefore, the woven fabric made from this spun yarn was a clothing textile with excellent wearing comfort that combines texture and functionality that are directly related to human comfort.

Furthermore, in terms of the appearance of the woven fabric, uneven appearance (glare) caused by diffuse reflection of light due to the formation of complex interfiber voids was suppressed, resulting in good appearance quality (glare level: 1.3). In addition, because shrinkage can be expressed even at a twist number that sufficiently restrains the short fibers, it was found that the fabric has properties suitable for use as a clothing textile, such as little appearance defects caused by short fibers being pulled out and tangled when the fabric is rubbed, and good anti-pilling properties (grade 4). The above results are shown in Table 1-1.

[Comparative Example 1]
The same procedures as in Example 1 were repeated except that the bonding surface direction for each short fiber was not changed (only in FIG. 1(a)).

In Comparative Example 1, the coefficient of variation CV% of the number of crimps between short fibers was 14%, and because there were few short fibers with different numbers of crimps, the coefficient of variation CV% of the interfiber gap distance of the resulting spun yarn was also 57%, with small variation in gap size. As a result, the fabric made from this spun yarn had small surface irregularities and lacked the comfortable feel that comes from moist irregularities. The results are shown in Table 1-1.

[Comparative Example 2]
The same procedures as in Example 1 were repeated except that the cross-sectional shape of the short fibers was changed to a circular cross-section as shown in FIG. 3 (the bonding surface direction for each composite fiber was not changed).

In Comparative Example 2, the coefficient of variation CV% of the number of crimps between short fibers was 11%, meaning that there were few short fibers with different crimp numbers, and because the short fibers had a round cross section, the crimp phases of the short fibers with the same crimp form were easily aligned. As a result, the inter-fiber gap distance of the obtained spun yarn was small at 3 μm, and the coefficient of variation CV% of the inter-fiber gap distance was also 49%, meaning that the variation in gap size was small. As a result, the fabric made from this spun yarn not only lacked fluffiness, but also had small surface irregularities and lacked a comfortable feel due to the moist irregularities. The results are shown in Table 1-1.

[Comparative Example 3]
The same procedure as in Comparative Example 1 was repeated except that Polymer 1 was changed to the same PET as in Polymer 2.

In Comparative Example 3, staple fibers made from the same polymer were used, so no voids due to shrinkage were obtained in the spun yarn. As a result, the fabric made from this spun yarn not only lacked a fluffy, soft feel, but also failed to express surface irregularities, lacking the comfortable feel of a moist uneven surface, and also lacking in water absorption, quick-drying properties, stretchability, and appearance quality. The results are shown in Table 1-1.

[Example 2]
The procedure of Example 1 was repeated except that the surface layer of the short fibers was covered with the same PET as polymer 2, and the composite cross section was changed to that shown in Fig. 1(b). The ratio S/D of the minimum thickness S of the PET to the fiber diameter D, determined by the above-mentioned method, was 0.03.

In Example 2, the surface layer of the short fibers was made of only PET, so that no peeling occurred at the interface due to friction or impact, and the fiber characteristics were well maintained, resulting in excellent processing stability during spinning and excellent spun yarn quality. Furthermore, the cooling difference between the PET and copolymerized PET was mitigated, which reduced yarn bending after discharge from the spinneret, and also resulted in excellent spinning stability. The results are shown in Table 1-1.

[Example 3]
The same procedures as in Example 1 were repeated except that the cross-sectional shape of the short fibers was changed to a flattened multi-lobed shape having four projections on the surface as shown in FIG. 1(c).

In Example 3, the irregularities formed on the surface of the short fibers increased the diffuse reflection of light, and the uneven appearance (glare) of the fabric made from the spun yarn was suppressed, resulting in an excellent appearance quality. Furthermore, by combining short fibers with an irregular surface, fine irregularities were added to the surface of the spun yarn, and the moist irregularities gave the fabric a comfortable feel and improved water absorption and quick-drying properties. The results are shown in Table 1-2.

[Example 4]
The same procedures as in Example 1 were repeated except that the cross-sectional shape of the short fibers was changed to a flat hollow shape having a hollow ratio of 20% in the center of the fiber as shown in FIG. 1(d).

In Example 4, the formation of hollow spaces inside the short fibers increased the diffuse reflection of light, and in the fabric made from the spun yarn, uneven appearance (glare) was suppressed, resulting in an excellent appearance quality. Furthermore, by combining short fibers with hollow spaces inside, fine interfiber spaces were added to the spun yarn, which also increased fluffiness and water absorption and quick-drying properties. The results are shown in Table 1-2.

[Examples 5 and 6]
The same procedures as in Example 1 were repeated except that the flatness of the short fibers was changed to 1.3 (Example 5) or 3.5 (Example 6).

In Example 5, as the flatness of the staple fibers decreased, the number of crimps that appeared in the staple fibers upon heat treatment increased. As a result, not only did the stretchability of the fabric made from the spun yarn increase, but the flat areas became smaller, reducing the specular reflection of light, suppressing unevenness in appearance (glare), and achieving excellent appearance quality. The results are shown in Table 1-2.

In Example 6, as the flatness of the staple fibers increases, the change in the crimp morphology that occurs during heat treatment for each staple fiber increases, and the coefficient of variation CV% of the number of crimps between staple fibers increases, as well as the inter-fiber gap distance in the spun yarn and the coefficient of variation CV% of the inter-fiber gap distance. This improves the fluffiness of the fabric made from the spun yarn, and also enhances the comfortable feel due to the moist unevenness. The results are shown in Table 1-2.

[Example 7]
The same procedure as in Example 1 was repeated except that polymer 2 was changed to PET having a melt viscosity of 31 Pa·s.

In Example 7, the strong expression of the crimp in the short fibers not only increased the stretchability of the resulting fabric, but also reduced unevenness in appearance (glare) due to the diffuse reflection of light caused by the crimp, resulting in an excellent appearance quality. The results are shown in Table 1-2.

[Examples 8 and 9]
The same procedures as in Example 1 were carried out except that the discharge amount was changed so that the fiber diameter of the short fibers was 9 μm (Example 8) or 15 μm (Example 9).

In Example 8, by setting the fiber diameter of the short fibers to 9 μm, the bending rigidity of each short fiber was reduced, and the softness of the fabric made from the spun yarn was improved. In addition, by increasing the number of fibers that make up the spun yarn, the diffuse reflection of light increased and uneven appearance (glare) was suppressed, resulting in an excellent appearance quality. In addition, by increasing the number of crimps that appear in the short fibers by heat treatment, the stretchability of the fabric made from the spun yarn was also improved. The results are shown in Table 2-1.

In Example 9, by setting the fiber diameter to 15 μm, the change in the crimp morphology that occurs during heat treatment for each short fiber becomes greater, and the coefficient of variation CV% of the number of crimps between short fibers increases, and the inter-fiber gap distance in the spun yarn and the coefficient of variation CV% of the inter-fiber gap distance also increase. As a result, the fluffiness of the fabric made from the spun yarn is improved, and the moist unevenness of the fabric gives it a comfortable feel. The results are shown in Table 2-1.

[Examples 10 and 11]
The same procedure as in Example 1 was repeated except that the twist factor of the spun yarn was changed to 2 (Example 10) or 6 (Example 11).

In Example 10, by loosening the twist of the spun yarn, the short fibers were more likely to develop crimps, and the inter-fiber gap distance and the coefficient of variation of the inter-fiber gap distance CV% in the spun yarn were also increased. As a result, the fabric made from the spun yarn had an improved fluffy and soft texture, and the moist unevenness gave it a more comfortable feel. The results are shown in Table 2-1.

In Example 11, by tightening the twist of the spun yarn, the short fibers are densely packed, which not only gives a unique feeling of resilience, but also reduces the amount of short fibers that are pulled out and tangled when the fabric is rubbed, resulting in excellent anti-pilling properties with no poor appearance. The results are shown in Table 2-1.

[Example 12]
The same procedure as in Example 1 was repeated except that the count of the spun yarn was changed to 60.

In Example 12, by using a fine count, the number of short fibers that make up the spun yarn was reduced, which improved the softness of the fabric woven from the spun yarn and resulted in a textile that is more suitable for clothing. The results are shown in Table 2-1.

[Example 13]
The same procedure as in Example 1 was repeated except that polymer 2 was changed to polyethylene terephthalate containing 5.0 wt % titanium oxide ( _TiO2 -containing PET).

In Example 13, the titanium oxide inside the short fibers diffusely reflected light, suppressing unevenness in appearance (glare) and resulting in excellent appearance quality. In addition, the titanium oxide also reflected ultraviolet and infrared rays, providing functionality such as anti-transparency and ultraviolet shielding. The results are shown in Table 2-2.

[Example 14]
The same procedure as in Example 1 was repeated except that Polymer 1 was changed to polypropylene terephthalate (PPT).

In Example 14, due to the rubber elastic properties of the PPT used as polymer 1, the fabric made from the spun yarn not only exhibited a soft and flexible feel, but also had significantly improved stretchability. The results are shown in Table 2-2.

[Example 15]
The same procedure as in Example 1 was repeated except that nylon 610 (N610, melt viscosity: 84 Pa s, melting point: 220°C) was prepared as polymer 1 and nylon 6 (N6, melt viscosity: 96 Pa s, melting point: 225°C) was prepared as polymer 2. These polymers were melted separately at 260°C and spun.

The fabric made from the obtained spun yarn was made of low-elasticity nylon, so it had excellent flexibility, and because it was made of low-density nylon, it had a low apparent density and excellent fluffiness. The results are shown in Table 2-2.

[Examples 16 and 17]
The same procedure as in Example 1 was repeated, except that the staple fibers of the present invention described in Example 1 and cotton were mixed at 80%/20% (Example 16) and 20%/80% (Example 17) to obtain a spun yarn having a count of 40 and a twist factor of 4.

In Examples 16 and 17, by blending the staple fibers of the present invention with cotton, the shrinkage of the staple fibers occurs, resulting in a difference in thread length between the staple fibers and the cotton. In the fabric made from spun yarn, the greater the cotton blend ratio, the more fluffy and soft the texture becomes, and the more comfortable the texture becomes due to the moist unevenness. The results are shown in Table 2-2.

The inclusion of the short fibers of this embodiment in part provides a unique fluffy, soft texture and water absorbency due to the voids, and as such can be used suitably for a wide range of textile products, from general clothing such as jackets, skirts, pants, and underwear, to sports clothing and clothing materials, and by taking advantage of their comfort, can be used for interior products such as carpets and sofas, vehicle interior products such as car seats, cosmetics, cosmetic masks, health products, and other daily life applications. In particular, it is preferable to use the fibers as spun yarn for clothing applications.

In addition, it is preferable that the spun yarn of this embodiment is partially contained in a woven or knitted fabric, which is a clothing textile that is highly comfortable to wear.

x: low melting point polymer y: high melting point polymer a1, a2: two points on the outer periphery of the fiber that are the furthest apart b1, b2: intersection point of the line that passes through the midpoint of the line connecting the two points on the outer periphery of the fiber and intersects at right angles with the outer periphery of the fiber Gx: center of gravity of low melting point polymer Gy: center of gravity of high melting point polymer G: center of gravity of short fiber M1, M2: crimp peak V1, V2: crimp valley S1: lines S2, S3 connecting the apexes of M1 and V2: line parallel to S1 and passing through the apexes of V1 and M2 Le: distance between the intersection points of S2 and S3 with a line that is perpendicular to S1 1: metering plate 2: distribution plate 3: discharge plate

Claims (11)

A short fiber made of at least two types of polymers with different melting points, characterized in that the number of crimps/crimp diameter is 75-500, and the coefficient of variation CV% of the number of crimps among short fibers is 15-50%. The short fibers described in claim 1, characterized in that the coefficient of variation CV% of (distance between polymer centers of gravity/fiber diameter) between short fibers is 5 to 30%. Short fibers according to claim 1 or 2, characterized in that the flatness in the cross section of the fiber is 1.2 to 5.0. The short fiber according to claim 1 or 2, characterized in that it has three or more convex portions in the fiber cross section. A textile product that contains, in part, the short fibers described in claim 1 or 2. Spun yarn characterized by containing the staple fiber described in claim 1 or 2. A spun yarn that contains flat short fibers made of at least two types of polymers with different melting points, and is characterized by a coefficient of variation CV% of the interfiber gap distance being 60-90%. The spun yarn according to claim 7, characterized in that the interfiber gap distance is 4 to 10 μm. The spun yarn according to claim 7 or 8, characterized in that it has a void structure with a void ratio of 30 to 60%. The spun yarn according to claim 7 or 8, characterized in that the mixing ratio of the flat short fibers is 30 to 100% by mass. A woven or knitted fabric comprising in part the spun yarn according to claim 6 or 7.

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