Eccentric sheath-core hollow composite fiber and manufacturing method thereof

Abstract

To provide an eccentric sheath-core hollow composite fiber that overcomes problems of prior arts and is capable of obtaining a textile having high stretch property, bulkiness, and light-weight property.SOLUTION: An eccentric sheath-core hollow composite fiber is characterized by, in a cross section of a composite fiber comprising two kinds of polyesters of an A component and a B component, having one hollow part where the A component is completely covered with the B component, is continuous in a fiber axis direction, and the following (1) to (6) are simultaneously satisfied. (1) A ratio S / D of a minimum thickness S of a thickness of the B component covering the A component and a fiber diameter D is 0.01 to 0.1. (2) A boundary length of a fiber at a part with a thickness of 1.05-fold the minimum thickness S is a boundary length of 1 / 3 or over of the whole fiber. (3) The number of crimps before heat treatment is 8 to 20 tops / 25 mm and a crimping degree is 8 to 25%. (4) A latent crimping ability where a crimping degree on non-loading heat treatment at 160°C is 2.0-fold or over of a crimping degree before the heat treatment exists. (5) A hollow ratio in the fiber cross section is 10% or over and 30% under. (6) A single fiber fineness is 1.0 to 2.5 dtex.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an eccentric sheath-core hollow composite fiber and a method for producing the same. [Background technology]

[0002] Synthetic fibers made from thermoplastic resins, such as polyester and polyamide, are widely used in clothing, industrial materials, and nonwoven fabrics because of their excellent properties, including strength, heat resistance, chemical resistance, and wash-and-wear properties.

[0003] Among clothing applications, woven and knitted fabrics made from spun yarns are widely used in jackets, coats, shirts, underwear, sportswear, and other products due to their texture and natural appearance. Spun yarns are threads made by twisting together several to several dozen short fibers with lengths of several tens of millimeters. By using natural fibers such as cotton, regenerated fibers such as rayon, and animal fibers such as wool as the short fibers, woven and knitted fabrics with excellent moisture absorption and heat retention properties can be obtained. However, due to the nature of these fibers, they have drawbacks, such as low strength and the tendency to absorb large amounts of sweat and moisture, which can trap the sweat and moisture deep into the fibers, resulting in poor drying times and discomfort, such as stickiness.

[0004] To solve these problems, spun yarns made of polyester fibers, which have excellent mechanical properties, chemical properties, and moisture absorption and quick-drying properties, or spun yarns made by blending polyester fibers with natural fibers or recycled fibers, are used.

[0005] In order to meet the various requirements for clothing applications, the development of spun yarns containing higher-performance polyester fibers is progressing. In recent years, there has been a growing demand for reduced restrictiveness when wearing clothing and for better movement, resulting in high demands for stretch performance. Stretch performance is particularly important for fabrics made with fine-count spun yarns (30-60 count), such as shirts, underwear, and sportswear. Generally, using thick staple fibers (single fiber fineness of 3 dtex or more) with fine-count spun yarns leads to unevenness and neps in the spun yarn, resulting in a decrease in the quality of the final fabric. Therefore, the development of fine staple fibers (single fiber fineness of less than 3 dtex) is progressing.

[0006] One method for achieving stretchability is to mix polyurethane-based fibers to impart stretchability. However, polyurethane-based fibers have the inherent stiffness of polyurethane, which can lead to problems such as poor texture and drapeability. Furthermore, polyurethane-based fibers are difficult to dye with dyes for polyester, and even when used in combination with polyester fibers, not only is the dyeing process complicated, but it is also difficult to dye them to the desired color.

[0007] As a method that does not use polyurethane fibers, various latent crimp-developing fibers using side-by-side composites have been proposed. Latent crimp-developing fibers are fibers that can develop crimps upon heat treatment or that have the ability to develop finer crimps than before heat treatment.

[0008] For example, Patent Document 1 proposes a latent crimpable conjugate fiber made of a conjugate fiber in which two component polymers (polyesters) having different viscosities are bonded side-by-side.

[0009] This potentially crimpable conjugate fiber takes on a three-dimensional spiral structure after heat treatment, as the fiber bends significantly toward the high-shrinkage component, allowing the structure to expand and contract like a spring, imparting stretchability to woven and knitted fabrics.

[0010] Patent Document 2 proposes apparently crimpable conjugate staple fibers in which the center of gravity of the second component in the cross section of the conjugate fiber containing a first component and a second component is shifted from the center of gravity of the fiber. Because of the core-sheath structure, yarn bending during extrusion is suppressed, and spinning stability is excellent. Apparently crimpable conjugate staple fibers having wavy crimps and spiral crimps are obtained.

[0011] The eccentric sheath-core fiber proposed in Patent Document 3 is a filament, but because it suppresses yarn bending just below the spinneret and provides good spinnability, it is possible to obtain fibers with a single fiber fineness of 1.0 dtex or less and with sufficient stretchability. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-148768 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-106188 [Patent Document 3] WO2018 / 110523 publication Summary of the Invention [Problem to be solved by the invention]

[0013] However, the side-by-side composite fiber proposed in Patent Document 1 exhibits significant yarn bending immediately after spinning due to the difference in melt viscosity between the two polymers. Even slight contamination of the spinneret surface can cause yarn breakage, resulting in poor spinning operability. For short fibers, spinning using a spinneret with a capacity of several hundred to several thousand helix is ​​required for production efficiency and cost reasons. However, rectification during the polymer cooling process after spinning from the spinneret is difficult, leading to problems such as increased yarn breakage at the bent portion. These problems become more pronounced as the fineness of the fiber increases. Patent Document 1 attempts to suppress yarn bending by minimizing the difference in viscosity between the two polymers. However, since a certain viscosity difference is necessary to achieve sufficient latent crimp expression, there is a limit to how much yarn bending can be suppressed, and the effect on spinning stability is limited. Furthermore, the broken portions and fused portions caused by yarn swaying are subjected to the heat history during the spinning process, shrinking to form fused fibers (thicker yarns than normal fibers or yarns formed by the fusion of multiple yarns). Fused fibers can be removed to some extent on the flat part of the flat card during the spinning process, but not all of them can be removed. Fused fibers that cannot be removed can cause sliver loss during the roving and fine spinning processes, reducing spinning processability, and if they are mixed into the spun yarn, they can cause defects such as neps, reducing the quality of the spun yarn.

[0014] Furthermore, in Patent Document 2, the number of crimps is at most 16 crimps per 25 mm, which is about the same as the number of crimps obtained using a stuffing box crimper with a fiber that does not exhibit normal latent or apparent crimps. Therefore, the crimping of a simple eccentric sheath-core composite fiber as in Patent Document 2 is poor in terms of the essential stretchability, and it is difficult to say that the material has satisfactory stretchability. Furthermore, when the fineness is reduced, there is the problem that the stretchability is even worse.

[0015] Furthermore, in Patent Document 3, the number of spinneret holes actually used in the examples is less than 100H. If the number of spinneret holes is small, it is easier to rectify the flow in the polymer cooling process after spinning from the spinneret, and it is easy to suppress yarn sway and prevent yarn breakage at bent yarn portions. However, from the viewpoint of production efficiency, staple fibers need to be produced at several hundred to several thousand H, and this is even more so when fine fibers are required. In other words, even with this method, it is difficult to achieve fine fibers.

[0016] In recent years, aiming for further performance improvement, there has been a demand for spun yarns and fabrics made therefrom that have sufficient stretchability as well as bulkiness and lightness, but as mentioned above, Patent Documents 1 to 3 do not describe any specific means for providing these.

[0017] An object of the present invention is to provide an eccentric core-sheath hollow conjugate fiber which overcomes the problems of the prior art and enables fabrics to be obtained which are highly stretchable, bulky, and lightweight. [Means for solving the problem]

[0018] The present inventors have conducted research to solve the above problems and have arrived at the present invention. That is, the present invention is as follows. (1) An eccentric sheath-core hollow composite fiber, characterized in that in the cross section of the composite fiber made of two types of polyester, component A and component B, component A is completely covered with component B, and the following (i) to (f) are simultaneously satisfied, and the fiber has one continuous hollow portion in the axial direction. (a) The ratio S / D of the minimum thickness S of the B component covering the A component to the fiber diameter D is 0.01 to 0.1. (b) The perimeter of the fiber in the part that is within 1.05 times the minimum thickness S is at least 1 / 3 of the perimeter of the entire fiber. (c) The number of crimps before heat treatment is 8 to 20 crimps / 25 mm, and the degree of crimp is 8 to 25%. (d) It has latent crimping ability such that the degree of crimping when heat-treated without load at 160°C is 2.0 times or more the degree of crimping before heat-treatment. (e) The hollow ratio of the fiber cross section is 10% or more but less than 30%. (F) The single fiber fineness is 1.0 to 2.5 dtex. (2) The eccentric core-sheath hollow composite fiber according to claim 1, characterized in that component A is a copolymer polyester mainly composed of ethylene terephthalate units, which is obtained by copolymerizing 2 to 7 mol % of 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane and 5 to 13 mol % of isophthalic acid, and component B is a polyester essentially composed of ethylene terephthalate units. (3) A method for producing an eccentric core-sheath hollow composite fiber according to claim 1 or 2, characterized in that the cooling treatment of the filamentous fiber comprises rapidly cooling and solidifying the spun yarn by applying cooling air from a position 5 to 25 mm from the spinneret surface. [Effects of the Invention]

[0019] By using the eccentric core-sheath hollow composite fiber of the present invention, it is possible to obtain a fabric that is highly stretchable, bulky, and lightweight. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a cross section of an example of an eccentric sheath-core hollow composite fiber of the present invention, illustrating the position of the center of gravity in the fiber cross section. [Figure 2] FIG. 2 is a fiber cross section for explaining the fiber diameter (D) and minimum thickness (S) of the eccentric sheath-core hollow composite fiber of the present invention. [Figure 3] FIG. 3 is a cross section of the eccentric sheath-core composite short fiber of Example 2. [Figure 4] FIG. 4 is a cross section of the eccentric sheath-core composite short fiber of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in detail below.

[0022] The eccentric core-sheath hollow composite fiber of the present invention is composed of two polymers, component A and component B, and has a structure in which component A is completely covered with component B in the cross section of the fiber.

[0023] The polymer referred to here is preferably a fiber-forming thermoplastic polymer, and in view of the object of the present invention, a combination of polymers that causes a difference in shrinkage when subjected to heat treatment is preferred, and a combination of polymers with different molecular weights or compositions that results in a difference in melt viscosity of 40 Pa s or more is preferred.

[0024] The melt viscosity referred to in the present invention is measured by adjusting the moisture content of chip-shaped polymer to 200 ppm or less using a vacuum dryer, changing the strain rate stepwise, and measuring at a strain rate of 1216 s when the measurement temperature is the same as the spinning temperature. -1 This is the value at 100%. If the melt viscosities of the polymers that make up the composite fiber differ by 40 Pa·s or more, for example, stress will be concentrated on the polymer component with the higher melt viscosity at the spinning line. Therefore, in the case of sheath-core or islands-in-sea cross sections, stress will be concentrated on the main polymer, resulting in excellent mechanical properties, while in the case of laminated cross sections, a significant difference will arise depending on the orientation of the combined components, making it possible to achieve the desired crimp.

[0025] Suitable polymers for achieving the objectives of the present invention include polyethylenes such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, and polytrimethylene terephthalate, polyamides, polylactic acid, thermoplastic polyurethanes, polyphenylene sulfide, and copolymers thereof. The molecular weights of these polymers can be changed, for example, by using a high-molecular-weight polymer for component A and a low-molecular-weight polymer for component B as shown in Figure 1, or by using one component as a homopolymer and the other as a copolymer.

[0026] Furthermore, examples of combinations of different polymer compositions include various combinations such as polybutylene terephthalate / polyethylene terephthalate, polytrimethylene terephthalate / polyethylene terephthalate, thermoplastic polyurethane / polyethylene terephthalate, and polytrimethylene terephthalate / polybutylene terephthalate, for component A / component B.

[0027] In particular, polyester, polyamide, polyethylene, polypropylene, etc. are preferably used as the polymer, and among these, polyester is more preferred because it also has mechanical properties, etc. The polyester referred to here includes polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, copolymers thereof with a dicarboxylic acid component, a diol component, or an oxycarboxylic acid component, and blends of these polyesters.

[0028] Among the above polymers, one example of a suitable polymer combination for the conjugated fiber of the present invention is where Component A is a copolymer polyester containing ethylene terephthalate units as the main structural unit, and is preferably a polyethylene terephthalate copolymer polyester modified with 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane (BHPP) or its ester-forming derivative (hereinafter, the ester-forming derivative may also be referred to as BHPP) and isophthalic acid (IPA) as copolymerization components, and Component B is a polyester essentially consisting of ethylene terephthalate units. In the present invention, the copolymerization ratio of BHPP in polyester (A) is preferably 2 to 7 mol %. If the copolymerization ratio of BHPP is less than 2 mol %, the shrinkage characteristics will be insufficient, and when spun into a yarn, the elongation rate and elongation recovery rate will be low, and sufficient stretchability may not be obtained. On the other hand, if the copolymerization ratio exceeds 7 mol %, the melting point of the polymer will decrease, tending to impair thermal stability.

[0029] The copolymerization ratio of IPA in polyester (A) is preferably 5 to 13 mol %. If the copolymerization ratio of IPA is less than 5 mol %, it is difficult to obtain a substantially large crimp, while if it exceeds 13 mol %, the melting point of the polymer decreases, tending to impair thermal stability.

[0030] Another preferred embodiment of the copolymer polyester of component A is a copolymer polyester in which 5-sodium isophthalic acid (5-SIPA) is used as a copolymer component instead of or in combination with IPA.

[0031] A combination of polyethylene terephthalate copolymer polyester modified with BHPP and IPA as component A and polyester essentially consisting of ethylene terephthalate units as component B has better stiffness and strength when processed into fabric, making it suitable for shirts, etc., compared to the combinations of polybutylene terephthalate / polyethylene terephthalate and polytrimethylene terephthalate / polyethylene terephthalate in component A / component B. This is because polybutylene terephthalate and polytrimethylene terephthalate have lower stiffness than polyethylene terephthalate.

[0032] The polyester of component B, which is substantially ethylene terephthalate units, is a polyester mainly composed of ethylene terephthalate units, and preferably contains 85 mol % or more of ethylene terephthalate units. In order to achieve lower heat shrinkage than the above-mentioned copolymer polyesters, it is preferable that the polyester does not contain components that significantly inhibit crystallinity, or contain BHPP, IPA, sulfonate group compounds, etc.

[0033] On the other hand, if you want to obtain a soft and flexible fabric, it is preferable to use polybutylene terephthalate and polytrimethylene terephthalate as component A, so it is best to use them depending on the required properties.

[0034] The combination of component A / component B as polytrimethylene terephthalate / polyethylene terephthalate has superior fabric elongation and fabric elongation recovery rates when processed into fabric, compared to a combination in which both components A and B are polyethylene terephthalate, and fabrics with excellent stretch performance can be obtained.

[0035] Furthermore, since the conjugated fiber of the present invention is composed of a combination of polymers that undergo differential shrinkage upon heat treatment, it develops crimp during heat treatment. To obtain a stretchable fabric, however, it is necessary for the fiber to have a latent crimping ability such that the degree of crimping during no-load heat treatment at 160°C is at least 2.0 times the degree of crimping before heat treatment. If the degree of crimping during heat treatment is less than 2.0 times the degree of crimping before heat treatment, the fabric will have significantly reduced stretchability and low stretchability. There is no particular upper limit. The latent crimping ability can be achieved by adjusting the type of polymers to be combined, their area ratio (described below), the cross-sectional structure of the eccentric core-sheath, etc.

[0036] Regarding the composite area ratio of component A to component B in the fiber cross section in the composite fiber of the present invention, in view of crimp development, a fine spiral structure can be realized by increasing the ratio of the high-shrinkage component, component A. Furthermore, since the eccentric sheath-core hollow composite fiber must have excellent physical properties, the ratio of the two components, component A:component B, is preferably in the range of 70:30 to 30:70 (area ratio), and more preferably in the range of 65:35 to 45:55.

[0037] In the present invention, it is necessary for the composite cross section to be formed by bonding two different polymers, and the two polymers with different polymer properties must be present in a bonded state without being substantially separated, and must be of an eccentric core-sheath type in which component A completely covers component B.

[0038] Here, the term "eccentricity" as used in the present invention refers to the position of the center of gravity of the component A polymer in the cross section of the conjugate fiber being different from the center of the cross section of the conjugate fiber, and will be explained using FIG.

[0039] In FIG. 1, horizontal hatching represents component B, 45° hatching (diagonal lines rising to the right) represents component A, the center of gravity of component A in the cross section of the composite fiber is center of gravity a, and the center of gravity of the cross section of the composite fiber is center of gravity C.

[0040] In the present invention, it is important that the center of gravity a of component A is far from the center of gravity C of the cross section of the composite fiber, so that the fiber will bend significantly toward the high-shrinkage component after heat treatment. As a result, the composite fiber continues to bend from the fiber axis direction, forming a three-dimensional spiral structure and exhibiting good crimp. Here, the greater the distance between the centers of gravity, the better the crimp will be, and the better the stretchability will be.

[0041] In the present invention, because component A is completely covered by component B, even if the fibers or fabric are subjected to friction or impact, whitening or fuzzing does not occur, and the quality of the fabric can be maintained. In addition, high molecular weight polymers and highly elastic polymers, which are exposed on the surface in conventional simple bonded structures and cause defects in composite fibers, can also be used as one component of the composite fiber.

[0042] Furthermore, since one component A is completely covered by the other component B, it is possible to have the effect of maintaining good fiber properties even when using, for example, a polymer with low heat resistance or abrasion resistance, or a hygroscopic polymer.

[0043] In the composite fiber of the present invention, the ratio S / D of the minimum thickness S of the B component covering the A component to the fiber diameter D (diameter of the composite fiber) must be 0.01 to 0.1. Preferably, it is 0.02 to 0.08. Within this range, excellent abrasion resistance and sufficient crimp development ability and stretch performance can be obtained.

[0044] Although good stretchability can be achieved by the polymers being in contact only at the bonded interface, and the stretchability is reduced if the high-shrinkage component is completely covered by the low-shrinkage component, by keeping the thickness of component B within the range of the present invention, it is possible to obtain a composite fiber that satisfies both the stretchability and abrasion resistance.

[0045] This will be explained in more detail using the fiber cross section shown in Figure 2. Here, the thinnest part of the B component in the core-sheath hollow composite fiber is the minimum thickness S.

[0046] Furthermore, it is important that the length of the portion with a thickness within 1.05 times the minimum thickness S accounts for at least one-third of the overall perimeter of the composite fiber. This means that component A is present along the contour of the fiber, and compared to conventional eccentric sheath-core composite fibers with the same area ratio, the centers of gravity of the components of the present invention are farther apart in the fiber cross section, forming a fine spiral and exhibiting good crimp. More preferably, by making the perimeter of the portion with a thickness within 1.05 times the minimum thickness S at least two-fifths of the overall perimeter of the fiber, good stretch performance can be achieved without crimp irregularities.

[0047] The minimum thickness S of the B component covering the A component, the fiber diameter D, and the area ratio of the A component to the B component are calculated as follows.

[0048] Specifically, an eccentric core-sheath hollow composite fiber is embedded in an embedding medium such as epoxy resin, and an image of the cross section is taken with a transmission electron microscope (TEM) at a magnification that allows observation of 10 or more fibers. If metal staining is applied, the dye differences between the polymers can be utilized to clarify the contrast at the bond between component A and component B. The circumscribing circle diameter of 10 fibers randomly selected within each captured image is measured, and the value corresponds to the fiber diameter D referred to in this invention. If it is not possible to observe 10 or more fibers, a total of 10 or more fibers, including other fibers, can be observed. The circumscribing circle diameter referred to here means the diameter of the perfect circle that circumscribes the most at two or more points on a cross section perpendicular to the fiber axis in a two-dimensionally captured image.

[0049] Furthermore, using the images in which the fiber diameter D was measured, the smallest thickness of component B covering component A for 10 or more fibers was measured, and the value corresponds to the minimum thickness S referred to in the present invention. Furthermore, these fiber diameters D and minimum thicknesses S are measured in units of μm, and are rounded to two decimal places. For 10 images photographed after the above operation, the measured values ​​and the simple number average of the ratio (S / D) are calculated.

[0050] The area ratio of component A to component B was calculated by using the image captured above and the image analysis software "WinROOF2015" manufactured by Mitani Shoji Co., Ltd. to determine the area of ​​the entire fiber and the areas of component A and component B, and then calculating the area ratio.

[0051] The single fiber fineness of the eccentric sheath-core hollow composite fiber of the present invention is preferably 1.0 to 2.5 dtex, and more preferably 1.2 to 2.0 dtex. If the single fiber fineness is less than 1.0 dtex, the fiber will not pass through the card well, and may wind around the card cylinder, resulting in the generation of card neps. If the single fiber fineness is thicker, the number of fibers constituting one spun yarn will decrease, and the thickness irregularities and neps of the spun yarn will increase. However, in spun yarns (counts 30 to 60) used for shirts, underwear, sportswear, etc., if the single fiber fineness exceeds 2.5 dtex, the thickness irregularities and neps of the spun yarn will increase significantly.

[0052] The number of crimps in the eccentric sheath-core hollow composite fiber of the present invention before heat treatment is preferably 8 to 20 crimps / 25 mm, more preferably 10 to 17 crimps / 25 mm. If the number of crimps is less than 8 crimps / 25 mm, carding performance will be extremely poor. If the number of crimps exceeds 20 crimps / 25 mm, carding performance will be extremely poor, and neps will frequently occur after carding, and thickness unevenness in the spun yarn will increase significantly, significantly reducing advanced processability and spun yarn quality.

[0053] The crimp degree of the eccentric sheath-core hollow composite fiber of the present invention before heat treatment is preferably 8 to 25%, more preferably 10 to 20%. If the crimp degree is less than 8%, the carding property is extremely poor. If the crimp degree is more than 25%, the carding property is extremely poor, and neps occur frequently after carding, and the thickness of the spun yarn becomes extremely uneven, significantly reducing the advanced processability and the quality of the spun yarn.

[0054] The eccentric sheath-core hollow composite fiber of the present invention is characterized by having one continuous hollow portion in the fiber axial direction, and the hollow ratio is preferably 10% or more and less than 30%, more preferably 15% or more and 25% or less. The hollow ratio is necessary to achieve bulkiness and light weight, but a hollow ratio of less than 10% is not advantageous in terms of bulkiness or light weight, while a hollow ratio of 30% or more causes the hollow portion to collapse due to the strong binding force between the fibers generated during the spinning process, making it impossible to achieve sufficient bulkiness and light weight.

[0055] It is preferable that the hollow portion be in contact with both component A and component B, as shown in Figure 1. By forming a fiber cross section in which the hollow portion is in contact with both component A and component B, the interface between component A and component B becomes smaller, which is preferable because it is possible to suppress yarn bending.

[0056] The hollow portions are preferably arranged so that their center of gravity coincides with or is close to the center of gravity of the fiber cross section. In other words, the fact that the hollow portions are located at the center of the fiber cross section means that the hollow portions are not substantially eccentric. If the hollow portions are not located at the center of the fiber but are eccentrically located, the hollow portions may be crushed by the thin-walled portions during the fiber production process or nonwoven fabric production process, causing deformation of the fiber cross section, and sufficient bulkiness and light weight may not be obtained.

[0057] Next, the method for producing the eccentric sheath-core hollow composite fiber of the present invention will be described.

[0058] The polymers of components A and B are melted and formed into a composite stream at a predetermined mass ratio using a composite melt spinning device, and then melt-spun through a spinneret having 100 to 2,000 discharge holes with a diameter of 0.2 to 0.6 mm at a spinning temperature higher than the melting point. The spinning temperature is preferably set at a temperature 20 to 60°C higher than the polymer melting point. Setting the temperature at least 20°C higher than the polymer melting point prevents the polymer from solidifying and clogging the spinning machine piping, and setting the higher temperature to no more than +60°C is preferable because excessive thermal degradation of the polymer can be suppressed.

[0059] The melting method can be a pressure melter method or an extruder method, either of which is acceptable, but it is preferable to use a melting method using an extruder from the viewpoint of uniform melting and preventing retention. The molten polymer passes through a pipe, is measured, and then flows into a nozzle pack. In this case, the time it takes to pass through the pipe is preferably 30 minutes or less to prevent thermal degradation. The molten polymer that flows into the pack is spun out from a spinneret.

[0060] Furthermore, since the present invention relates to staple fibers, a multi-hole spinneret is usually used from the viewpoint of production efficiency, and it is necessary to use one with a thread count of 100H or more. Considering the market price of staple fibers, a thread count of 300H or more is more preferable, and a thread count of 600H or more is even more preferable.

[0061] Generally, the more holes there are, the more difficult it becomes to uniformly cool the spun yarn. Furthermore, turbulence occurs directly below the spinneret, making stable spinning difficult. Furthermore, in two-component eccentric sheath-core conjugate spinning and side-by-side conjugate spinning, yarn bending occurs after polymer discharge, making stable spinning even more difficult. However, by using the cross-section of the present invention, yarn bending caused by the difference in flow speed between the two polymers at the time of discharge from the spinneret can be suppressed. In other words, the presence of the sheath component generates a force in the opposite direction to the bending direction of the polymer flow, thereby suppressing the force perpendicular to the spin line caused by the difference in flow speed between the two polymers at the time of discharge from the spinneret. Additionally, by controlling the cooling of the yarn and the convergence position of the yarn from the spinneret discharge surface as described below, stable spinning becomes possible even when using a spinneret with a large number of spinneret holes.

[0062] The preferred method for cooling the yarn is rapid cooling directly below the spinneret. The cooling and solidification of the spun yarn (polymer) directly below the spinneret is preferably carried out using cooling air at a position 5 to 25 mm from the spinneret surface. If cooling starts more than 5 mm from the spinneret surface, the cooling air will cause a drop in the spinneret surface temperature, leading to yarn breakage. If cooling starts more than 25 mm from the spinneret surface, the timing of polymer cooling and solidification will be delayed, making it impossible to achieve the target hollowness. The cooling air temperature is preferably 10 to 50°C, and cooling is preferably carried out at a rate of 30 to 120 m / min using a cold air blower with a cooling length of 10 to 400 mm. This cooling process suppresses turbulence directly below the spinneret and reduces yarn sway. Rapidly cooling the yarn also raises the polymer solidification position, making yarn breakage due to yarn sway less likely. By using a cross section such as that of the present invention, it is possible to suppress bending of the fiber after polymer extrusion, and therefore it is possible to start cooling just below the spinneret even when spinning with a spinneret of 100H or more. As a result, it has become possible to produce composite fibers using a spinneret of 100H or more.

[0063] Furthermore, it is preferable to straighten the yarn after rapid cooling just below the spinneret, using a cold air blowing cooling device with an air temperature of 10 to 50°C and a cooling length of 100 to 700 mm, and to cool at a speed of 20 to 90 m / min, preferably at or below the speed of the cooling air just below the spinneret. If the speed is higher than the speed of the cooling air just below the spinneret, yarn swaying will increase, causing yarn breakage and yarn fusion, which may prevent stable spinning. If there are many broken or fused yarns, they may be mixed into the spun yarn, resulting in a decrease in the quality of the spun yarn.

[0064] The distance from the nozzle discharge surface to the yarn convergence point is preferably 2000 mm or less. By setting the distance from the nozzle discharge surface to the yarn convergence point to 2000 mm or less, the width of yarn sway caused by cooling air can be suppressed and the accompanying airflow until the yarn converges can be suppressed, which is preferable because it makes it easier to achieve stable spinning with less yarn breakage. A more preferable range for the yarn convergence point in the spinning process is 1600 mm or less.

[0065] In the process of drawing the spun undrawn yarn, the undrawn yarn is bundled to 30 to 300 ktex and drawn 2 to 5 times in steam or hot water. After that, it is subjected to a tension heat treatment and crimped using a press-type crimper or the like.

[0066] Next, the crimped drawn tow is dried, an aqueous finishing oil solution is sprayed onto the tow, and the tow is cut to produce the conjugate fiber of the present invention.

[0067] In the case of a latent crimpable conjugate fiber bonded side-by-side, the spun undrawn yarn is prone to fusing with adjacent fibers due to the heat of drawing during the drawing process, increasing the risk of fused fibers being mixed in. This is a problem that is particularly evident in the staple fiber production process, and the conjugate fiber of the present invention solves this problem specific to staple fibers.

[0068] Although the detailed mechanism has not been elucidated, in the present invention, by applying an eccentric core-sheath type composite fiber in which component A is completely covered by component B, this decrease in fusion can be alleviated and the incorporation of fused fibers into the staple fibers can be suppressed. Since the lower the melting point, the easier it is for fibers to fuse together, it is expected that the number of fused fibers will be further reduced if a component with a lower melting point than component A is used for component B. If the number of fused fibers is reduced, the risk of fused fibers being mixed into the spun yarn can be reduced, and the quality of the spun yarn can be improved.

[0069] In addition, by preheating the undrawn yarn to 40 to 60°C before drawing, the formation of fused fibers can be further suppressed.

[0070] In order to obtain the number of crimps and degree of crimp of the present invention, it is important to set the tension heat treatment temperature, tension heat treatment time, temperature of the tow when it enters the push-type crimper, pushing pressure of the push-type crimper, and drying temperature of the tow after crimping.

[0071] In tension heat treatment, heat setting is performed while maintaining tension, and then cooling is performed with cooling water to below the glass transition temperature to fix the molecular chain structure. This makes it possible to suppress the occurrence of crimp in the subsequent drying process of the tow after crimping, and enables the fiber to exhibit high crimp occurrence ability through heat treatment in advanced processing steps such as spinning and nonwoven fabrics.

[0072] 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 or the treatment time is less than 3 seconds, the crimp may be excessively developed in the subsequent drying process of the tow after crimping, resulting in a decrease in the latent crimp properties. Furthermore, if the treatment temperature is higher than 190°C or the treatment time is longer than 20 seconds, the latent crimp properties may be decreased.

[0073] The temperature of the tow when it enters the push-in crimper is preferably 20 to 60° C. If the temperature is lower than 20° C., the degree of crimp may be low and the crimp degree of the present invention may not be obtained, and if the temperature is higher than 60° C., the degree of crimp may be high and the crimp degree of the present invention may not be obtained.

[0074] The pressure of the crimping machine is 1 to 3 kg / cm 2 G is preferred. 1kg / cm 2 If it is less than G, the number of crimps or the degree of crimping will be low, and 2 If it is higher than G, the number of crimps or the degree of crimping tends to be high.

[0075] The drying temperature for the tow after crimping is preferably 50 to 120° C. If the temperature is lower than 50° C., the tow may not be dried sufficiently, whereas if the temperature is higher than 120° C., crimping occurs during the drying process, and sufficient crimping cannot be achieved by heat treatment in advanced processing steps such as spinning and nonwoven fabrics.

[0076] The cross-sectional shape of the present invention adequately suppresses the occurrence of crimp during the spinning process, making it relatively easy to obtain the crimp of the present invention. Although the detailed mechanism has not been elucidated, it is thought that the thin portion of component B covering component A adequately suppresses the shrinkage of component A. In the case of a cross-section in which component A is exposed, such as a side-by-side cross-section, if the difference in melt viscosity between the two component polymers is large, crimp occurs during the spinning process, for example, when the tow is dried after crimping, and the number and degree of crimp after cutting the drawn tow tend to be high, making it relatively difficult to control crimp during the spinning process. The eccentric sheath-core hollow composite fiber of the present invention is preferably obtained by a melt spinning method. The spinneret may have any commonly used internal structure as long as it allows for spinning with good quality and stable operation. In particular, the spinnerets exemplified in JP-A Nos. 2011-174215, 2011-208313, and 2012-136804 can be suitably used to form a fiber with a desired cross-sectional shape.

[0077] The purpose of the outlet holes of the spinneret is to re-meter the flow rate of the composite polymer stream, i.e., the discharge rate, and to control the draft (=take-up speed / discharge linear velocity) on the spinning line. The hole diameter and hole length are preferably determined taking into consideration the viscosity of the polymer and the discharge rate. When producing the composite fiber of the present invention, the outlet hole diameter can be selected from the range of 0.1 to 2.0 mm, and the L / D (outlet hole length / outlet hole diameter) can be selected from the range of 0.1 to 5.0.

[0078] As described above, the conjugated fiber of the present invention preferably has the A component completely covered by the B component, as shown in Figure 1. The cross section of the present invention can suppress bending of the extrusion line (kneeing phenomenon) caused by the difference in flow speed between the two polymers when extruding from the spinneret. That is, the presence of the sheath component generates a force in the opposite direction to the bending direction of the polymer flow, thereby suppressing the force perpendicular to the spinning line caused by the difference in flow speed between the two polymers when extruding from the spinneret.

[0079] Furthermore, in the case of a conventional simple laminated structure (bimetal structure), differences occur in the balance of stresses applied to the respective polymers during thinning on the spinning line after discharge from the spinneret, which causes unevenness in elongation deformation and can manifest as fineness unevenness. This tendency is very noticeable when thinning is achieved by combining polymers with large differences in viscosity or by reducing the discharge rate, but in the present invention, the stress balance is balanced within the fiber cross section by covering the fiber with one of the polymers, and fineness unevenness can be suppressed.

[0080] Furthermore, it has been found that when a high-molecular-weight polymer is used as component A and a low-molecular-weight polymer is used as component B, the complete coverage of component B results in excellent high-speed spinning stability. This is because the low-molecular-weight polymer is positioned on the outside, making it easier for the high-molecular-weight polymer to follow the elongation deformation after extrusion from the spinneret.

[0081] This will dramatically increase the freedom of polymer selection to improve added value other than stretch performance and yarn reeling stability, even for fine-denier yarns, and will also contribute to improved productivity.

[0082] In addition, from the viewpoint of suppressing discharge line bending, the difference in melt viscosity of the polymers used in the conjugate fiber of the present invention is also important. When the two types of molten polymers constituting the conjugate fiber are contracted, the cross-sectional areas of the polymers in the direction of flow and the cross section perpendicular to the direction of flow are changed in order to match the pressure losses of the two types of polymers. As a result, a difference in flow velocity occurs, and these are discharged with a biased center of gravity, resulting in discharge line bending.

[0083] That is, a polymer with a high melt viscosity has a large cross-sectional area and therefore a slow flow rate, whereas a polymer with a low melt viscosity has a small cross-sectional area and therefore a fast flow rate. Therefore, by reducing the difference in melt viscosity between the polymers used, the difference in flow rate between the polymers can be alleviated, and extrusion line bending can be suppressed. From this perspective, it is preferable that the difference in melt viscosity between the combined polymers is small. However, in the case of the conjugated fiber of the present invention, taking into consideration the occurrence of crimp, etc., it is preferable that the difference in melt viscosity between the combined polymers is large.

[0084] When the bending of the discharge line is suppressed in this way, interference between single fibers on the spinning line can be suppressed, which makes it possible to increase the density of the discharge holes on the spinneret, i.e., the number of discharge holes per spinneret, thereby achieving higher sophistication and improved production efficiency through the use of multiple yarns.

[0085] In this case, it is preferable to set the spinning draft to 300 times or less, since this will result in uniform fibers with reduced variations in physical properties between the yarns.

[0086] The spinning draft of the conjugated fiber of the present invention, represented by the following formula, is preferably 50 to 300. Spinning draft = Vs / V0 Vs: spinning speed (m / min) V0: Discharge linear velocity (m / min).

[0087] By setting the spinning draft to 50 or more, the polymer flow discharged from the spinneret hole is prevented from remaining directly below the spinneret for a long period of time, and spinneret surface contamination can be suppressed, resulting in stable spinnability. Furthermore, by setting the spinning draft to 300 or less, it is possible to suppress yarn breakage due to excessive spinning tension, and eccentric sheath-core hollow composite fibers can be obtained with stable spinnability, which is preferable. A spinning draft of 80 to 250 is more preferable.

[0088] The eccentric sheath-core hollow conjugate fiber of the present invention can be used to make a spun yarn, but the type of other fibers constituting the spun yarn is not particularly limited, and the use of at least one of polyester fiber, acrylic fiber, polyamide fiber, rayon, cotton, linen, wool, and silk is preferred because it can exert the effects of the present invention. The spun yarn may also be composed solely of the conjugate fiber of the present invention. Particularly preferred are 100% conjugate fiber of the present invention, conjugate fiber of the present invention / cotton blends, conjugate fiber of the present invention / wool blends, etc.

[0089] When the conjugated fiber of the present invention is spun into a spun yarn, a conventional spinning method can be used. The preferred count of the spun yarn is 30 to 60, which is commonly used for thin fabrics such as shirts, underwear, and sportswear. A count below 30 results in a thick fabric, making it difficult to obtain the desired fabric. A count above 60 is rarely used for existing applications due to processability issues. The twist factor of the spun yarn is preferably in the range of 2.5 to 4.5. A twist factor of 2.5 or higher provides sufficient yarn strength, eliminating concerns about yarn breakage during spinning and reduced strength when woven or knitted. Furthermore, a twist factor of 4.5 or less reduces the risk of ripping due to twist reversion and reduces the risk of the fabric becoming coarse and stiff when woven or knitted. Furthermore, the fibers are strongly bound together, making them less likely to shrink, resulting in a loss of essential stretchability.

[0090] The stretchability of fabrics made from spun yarns using the conjugated fiber of the present invention can be evaluated by measuring the fabric elongation rate and fabric elongation recovery rate. If the elongation rate is 15% or more and the elongation recovery rate is 70% or more, the fabric feels stretchy and is less likely to feel restrictive when worn. Furthermore, when the spun yarn count, twist coefficient, and fabric composition are the same, a thicker fineness means fewer constituent fibers and less restriction between fibers, which can be expected to improve the fabric elongation rate, but conversely, the quality of the spun yarn will be reduced.

[0091] The elongation rate was measured by first preparing a spun yarn of 45S (single yarn) with a twist factor of 3.5 from the composite fiber of the present invention and using it as the weft in a woven fabric, and using a spun yarn of 45S with a twist factor of 3.5, a blend of polyester (manufactured by Toray Industries, Inc., product name: T403-1.45T x 38mm) and cotton, as the warp. A 1 / 3 twill fabric was produced using an air jet loom with a warp density of 110 threads / inch (2.54 cm) and a weft density of 76 threads / inch (2.54 cm). The fabric was then heat-treated for 10 minutes in a moist, heat-sensitive atmosphere at 130°C under no load, and cut into 30 cm x 5 cm samples with the weft threads aligned longitudinally. Three samples were then cut out. Next, using a constant-speed extension tensile tester with an automatic recording device (INSTRON: MODEL 5566), the grip spacing is set to 20 cm, and an initial load equivalent to a mass of 5 cm x 1 m is applied and fixed to the grips. The grip spacing at this time is designated as L0. The specimen is stretched to 14.7 N (1.5 kg) at a tensile speed of 20 cm / min, and the grip spacing (L1) at this time is measured. The elongation rate (%) is calculated using the following formula and expressed as the average value of three specimens. Fabric elongation rate (%)={(L1-L0) / L0}×100 L0: Grip spacing under initial load (mm) L1: Grip spacing (mm) when extended to 14.7N (1.5kg).

[0092] The elongation recovery rate was measured using the same woven fabric as used for the elongation rate measurement. The fabric was similarly heat-treated for 10 minutes in a humid, heat-sensitive atmosphere at 130°C under no load. Three 30cm x 5cm pieces were cut into samples with the weft threads aligned longitudinally. Using a tensile tester, the clamps were spaced 20cm apart, and an initial load equivalent to the mass of a 5cm x 1m sample was applied. The sample was then fixed to the clamps. The sample was stretched at a rate of 20cm / min to 80% of the elongation rate previously determined (L3), left for 1 minute, then returned to the original position at the same rate and left for 3 minutes. This procedure was repeated 10 times, and the sample was then stretched again at the same rate to the initial load condition. The residual elongation (L4) was measured, and the elongation recovery rate was calculated using the following formula, which was expressed as the average of the three samples. Fabric elongation recovery rate (%) = {(L3-L4) / L3} x 100 L3: Length at 80% of fabric elongation (mm) L4: Residual elongation length after 10 repeated elongations (mm).

[0093] The spun yarn using the conjugated fiber of the present invention is suitable for use in shirts, underwear, sportswear, etc., and can provide sufficient stretchability in addition to bulkiness and light weight. [Example]

[0094] Next, the eccentric sheath-core hollow composite fiber of the present invention will be described in detail using examples. The methods for measuring the fiber properties and the like are as follows.

[0095] (1) Melt viscosity of polymer The chip-shaped polymer was dried in a vacuum dryer to a moisture content of 200 ppm or less, and the melt viscosity was measured by a Capillograph 1B manufactured by Toyo Seiki Co., Ltd., while changing the strain rate stepwise. The measurement temperature was the same as the spinning temperature, and in the examples and comparative examples, the melt viscosity was measured at 1216 s -1 The melt viscosity is shown in Table 1. Incidentally, the measurement was carried out in a nitrogen atmosphere, with 5 minutes elapsed between the time the sample was placed in the heating furnace and the start of the measurement.

[0096] (2) Single fiber fineness, number of crimps and degree of crimp Fiber properties (single fiber fineness, number of crimps, and degree of crimp) were measured according to JIS L1015 (2010).

[0097] (3) Hollowness ratio The cross section of the obtained hollow composite fiber was photographed using a microscope at a magnification of 400x, and the cross section photograph was then copied at an enlargement of 2x. The cross section of the fiber and the hollow section were cut out from the copied paper, and the masses of each were measured using an electronic balance. The hollow ratio (%) was calculated by averaging N = 20.

[0098] (4) Spun yarn breakage (spinnability) The evaluation was based on the number of times yarn breakage occurred per ton (production amount) during melt spinning. Evaluation was made on the following two levels. ·Pass (good): less than 5 times / t ·Fail: 5 times / t or more.

[0099] (5) Fabric elongation rate (stretchability) A spun yarn with a count of 45S (single yarn) and a twist factor of 3.5 was prepared from the composite fiber to be measured and used as the weft in the woven fabric. The warp yarn was a spun yarn with a count of 45S and a twist factor of 3.5, made from a polyester (Toray Industries, Inc., product name: T403-1.45T x 38 mm) / cotton blend in a ratio of 65:35. A 1 / 3 twill fabric was woven using an air jet loom with a warp density of 110 threads / inch (2.54 cm) and a weft density of 76 threads / inch (2.54 cm). The fabric was heat-treated for 10 minutes in a moist, heat-treated atmosphere at 130°C under no load, and then cut into 30 cm x 5 cm samples with the weft threads running longitudinally. Three samples were then cut out. Next, using a constant-speed extension tensile tester with an automatic recording device (INSTRON: MODEL 5566), the grip spacing was set to 20 cm, and an initial load equivalent to the mass of a 5 cm x 1 m area was applied and fixed to the grips. The grip spacing at this time was designated L0. The specimen was stretched to 14.7 N (1.5 kg) at a tensile speed of 20 cm / min, and the grip spacing (L1) at this time was measured. The elongation rate (%) was calculated using the following formula, and the average of three specimens was used to evaluate the elongation rate using the following two-level scale. Fabric elongation rate (%)={(L1-L0) / L0}×100 L0: Grip spacing under initial load (mm) L1: Grip distance (mm) when extended to 14.7N (1.5kg) ·Pass (good): 15% or more · Fail: Less than 15%.

[0100] (6) Fabric stretch recovery rate (stretchability) The same woven fabric as used in the elongation measurement was used. As with the elongation measurement, the woven fabric was heat-treated for 10 minutes in a humid, heat-sensitive atmosphere at 130°C under no load. Three 30cm x 5cm samples were cut with the weft threads aligned longitudinally. Using a tensile tester, the grips were spaced 20cm apart, and an initial load equivalent to the mass of a 5cm x 1m sample was applied. The sample was then fixed to the grips. The sample was stretched at a tensile speed of 20cm / min to 80% of the previously determined elongation (L3), left for 1 minute, then returned to the original position at the same speed and left for 3 minutes. This procedure was repeated 10 times, and the sample was again stretched at the same speed to the initial load condition. The residual elongation (L4) was measured, and the elongation recovery (%) was calculated using the following formula. The average value of the three samples was calculated and rated on a two-level scale. Fabric elongation recovery rate (%) = {(L3-L4) / L3} x 100 L3: Length at 80% of fabric elongation (mm) L4: Residual elongation length after 10 repeated elongations (mm) ·Pass (good): 70% or more · Fail: Less than 70%.

[0101] (7) Bulky The obtained hollow composite fibers were used to produce air-through nonwoven fabrics with a basis weight of 20 g / m2, which were heat-treated at a temperature of 150°C. The thickness (mm) of the nonwoven fabrics under a load of 0.2 kPa was measured in accordance with JIS L 1913A, calculated as an average value for N=10, and evaluated using the following two-level scale. ·Pass (good): 1.5mm or more · Fail: Less than 1.5mm.

[0102] [Example 1] An eccentric sheath-core hollow composite fiber was produced in the following manner.

[0103] The component A polymer was polyethylene terephthalate (melt viscosity: 110 Pa s) copolymerized with 7.0 mol% IPA and 4.0 mol% 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane, and the component B polymer was polyethylene terephthalate (melt viscosity: 70 Pa s). Both the component A polymer and the component B polymer were melted at 280°C using an extruder, then metered using a pump to a melt temperature of 290°C. The melted polymer was then allowed to flow into a spinneret while maintaining the temperature. The area ratio of component A to component B was 50 / 50, and the polymers were allowed to flow into a spinneret with 600 spinneret holes for eccentric sheath-core hollow composite fibers. The polymers merged inside the spinneret to form an eccentric sheath-core hollow composite fiber in which the component A polymer was encased within the component B polymer, and the resulting fiber was extruded from the spinneret. Note that in the spinning of Example 1, a spinneret capable of producing the eccentric sheath-core hollow composite fiber shown in Figure 1 was used. The spun yarn was cooled while being taken up at a speed of 1300 m / min. The yarn was cooled using a cold air blower with an air temperature of 20°C, an air speed of 70 m / min, and a cooling length of 30 mm from a position 15 mm from the spinneret, and then using a cold air blower with an air temperature of 20°C, an air speed of 40 m / min, and a cooling length of 600 mm. After cooling the yarn, 0.1% by mass of process oil was added, and the yarn was passed through a free roller and combined with 20 other spindles using a convergence guide of 0.1% to obtain an undrawn yarn.

[0104] Next, the obtained undrawn yarn was introduced into hot water at a temperature of 90°C, and the drawn yarn was drawn at a draw ratio of 2.8 times. The drawn yarn was then subjected to a tension heat treatment for 5 seconds with a heated roller at 160°C, and introduced into a crimper, where the temperature of the drawn tow was 30°C and the tow pressing pressure was 1.5 kg / cm. 2 The fibers were mechanically crimped at 1000 W / m² / min, dried, and cut at 80°C to obtain eccentric sheath-core hollow composite fibers. The results, shown in Table 1, demonstrate satisfactory spinnability, an S / D ratio of 0.02 in the fiber cross section, a minimum thickness (S) portion accounting for 45% of the fiber circumference, a single fiber fineness of 1.8 dtex, a crimp count of 14 crimps / 25 mm before heat treatment, a crimp degree of 16%, a crimp degree after no-load heat treatment at 160°C that was 2.7 times the crimp degree before heat treatment, and a hollowness of 20%. Fabrics using these fibers were confirmed to have both stretchability and bulkiness.

[0105] [Example 2] An eccentric sheath-core hollow composite fiber was produced by the following method. An eccentric sheath-core hollow composite fiber was obtained in the same manner as in Example 1, except that the composite morphology was as shown in Figure 3, the S / D ratio in the fiber cross section was 0.05, and the proportion of the minimum thickness S portion on the fiber circumference was 70%. As shown in Table 1, an eccentric sheath-core hollow composite fiber was obtained without any problems in spinnability, with a single fiber fineness of 1.8 dtex, the number of crimps before heat treatment of 12 crimps / 25 mm, a crimp degree of 14%, a crimp degree after no-load heat treatment at 160°C that was 2.3 times the crimp degree before heat treatment, and a hollow ratio of 20%. It was confirmed that a fabric using this fiber had both stretchability and bulkiness.

[0106] [Example 3] An eccentric sheath-core hollow composite fiber was produced by the following method. An eccentric sheath-core hollow composite fiber was obtained in the same manner as in Example 1, except that the cooling start position of the yarn was set 10 mm from the spinneret. As the results are shown in Table 1, an eccentric sheath-core hollow composite fiber was obtained without any problems in spinnability, with a single fiber fineness of 1.8 dtex, the number of crimps before heat treatment being 14 crimps / 25 mm, a crimp degree of 16%, a crimp degree after no-load heat treatment at 160°C that was 2.6 times the crimp degree before heat treatment, and a hollow ratio of 24%. It was confirmed that the fabric using this fiber had both stretchability and bulkiness.

[0107] [Example 4] An eccentric sheath-core hollow composite fiber was produced by the following method. An eccentric sheath-core hollow composite fiber was obtained in the same manner as in Example 1, except that the cooling start position of the yarn was set 20 mm from the spinneret. The results are shown in Table 1. There were no problems with spinnability, and an eccentric sheath-core hollow composite fiber was obtained with a fiber single fiber fineness of 1.8 dtex, the number of crimps before heat treatment was 14 crimps / 25 mm, a crimp degree of 16%, a crimp degree after no-load heat treatment at 160°C that was 2.7 times the crimp degree before heat treatment, and a hollow ratio of 16%. It was confirmed that the fabric using this fiber had both stretchability and bulkiness.

[0108] [Comparative Example 1] A hollow composite fiber was produced by the following method. Using the spinneret described in JP-A-09-157941, a hollow composite fiber was obtained in the same manner as in Example 1, except that composite fibers bonded side-by-side with a substantially straight boundary surface were formed into a hollow composite fiber with a hollow cross section (round cross section, the hollow portion being in contact with both component A and component B). The results are shown in Table 1. The spun fiber broke, the spinnability was poor, and it was not possible to obtain a hollow ratio and bulkiness within the allowable range.

[0109] Comparative Example 2 An eccentric sheath-core hollow composite fiber was produced in the following manner. The eccentric sheath-core hollow composite fiber was obtained in the same manner as in Example 1, except that the composite morphology was as shown in Figure 4, the S / D ratio in the fiber cross section was 0.01, and the proportion of the portion with minimum thickness S on the fiber circumference was 10%. The results are shown in Table 1. The crimp ratio and stretchability before and after the no-load heat treatment at 160°C were not within the allowable range.

[0110] Comparative Example 3 Concentric sheath-core hollow composite fibers were produced by the following method. Concentric sheath-core hollow composite fibers (circular cross section) were produced using a conventional sheath-core composite spinneret, and were obtained in the same manner as in Example 1, except that the S / D ratio in the fiber cross section was 0.04 and the proportion of the minimum thickness S portion on the fiber circumference was 100%. The results are shown in Table 1. The crimp ratio and stretchability before and after the no-load heat treatment at 160°C were not within the allowable range.

[0111] Comparative Example 4 Except for changing the position where the cooling of the yarn started from the spinneret to 3 mm, the same method as in Example 1 was used. As shown in Table 1, the results were as follows: frequent breakage of the spun yarn occurred, and spinnability was poor, so that the yarn was not turned into a fiber.

[0112] Comparative Example 5 An eccentric sheath-core hollow composite fiber was produced in the following manner. Except for changing the position at which the cooling of the yarn started from the spinneret to 30 mm, an eccentric sheath-core hollow composite fiber was obtained in the same manner as in Example 1. As shown in Table 1, the spun yarn broke, the spinnability was poor, and it was not possible to obtain a hollow ratio and bulkiness within the allowable range.

[0113] [Table 1] [Explanation of symbols]

[0114] A: Component A B:B component a: Center of gravity of component A in the cross section of the composite fiber C: Center of gravity of composite fiber cross section S: Minimum thickness of B component D: Fiber diameter H: Hollow part L: Length of the part with a thickness within 1.05 times the minimum thickness S

Claims

1. An eccentric sheath-core hollow conjugate fiber, characterized in that in a cross section of the conjugate fiber made of two kinds of polyester, component A and component B, component A is completely covered with component B, the following (1) to (6) are simultaneously satisfied, and the fiber has one continuous hollow portion in the axial direction: (1) The ratio S / D of the minimum thickness S of the B component covering the A component to the fiber diameter D is 0.01 to 0.

1. (2) The perimeter of the fiber in the portion within 1.05 times the minimum thickness S is at least 1 / 3 of the perimeter of the entire fiber. (3) The number of crimps before heat treatment is 8 to 20 crimps / 25 mm, and the degree of crimp is 8 to 25%. (4) The fiber has a latent crimping ability such that the degree of crimping when heat-treated under no load at 160°C is at least 2.0 times the degree of crimping before heat-treatment. (5) The hollow ratio of the fiber cross section is 10% or more but less than 30%. (6) The single fiber fineness is 1.0 to 2.5 dtex.

2. 2. The eccentric core-sheath hollow conjugate fiber according to claim 1, wherein component A is a copolymer polyester mainly composed of ethylene terephthalate units, which is obtained by copolymerizing 2 to 7 mol % of 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane and 5 to 13 mol % of isophthalic acid, and component B is a polyester substantially composed of ethylene terephthalate units.

3. 3. The method for producing an eccentric core-sheath hollow composite fiber according to claim 1 or 2, characterized in that the cooling treatment of the yarn comprises quenching the spun yarn with cooling air from a position 5 to 25 mm from the spinneret surface to cool and solidify it.

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