Conjugate fiber and process for producing the same

Abstract

To obtain a conjugate fiber capable of providing a fabric or a nonwoven fabric having both high stretchability and softness.SOLUTION: The conjugate fiber is a flat multi-lobal fiber composed of two kinds of polyesters of an A component and a B component and having a flatness of 1.8-4.0 as a ratio of a major axis (a) to a minor axis (b), a plurality of convex parts symmetrical to the major axis (a) and composed of the A component, and a ratio of a maximum length (b) to a minimum length (c) of the convex part of 1.1-1.5, and has a side-by-side or eccentric sheath-core composite structure having a polymer interface perpendicular to the major axis (a).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a 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] However, among these synthetic fibers, polyester fibers have recently been increasingly used in the field of nonwoven fabrics, and have been widely used in particular for nonwoven applications in the field of hygienic materials such as baby diapers, diaper liners, and sanitary products; in the field of daily necessities such as counter cloths and wet tissues for the food service industry; in the field of nonhygienic materials such as draining bags for kitchen sinks; in the medical field such as base fabrics and fixing sheets for medicinal patches, hospital surgical gowns, and masks; and in the field of industrial materials such as automotive interior materials and filters.

[0004] Patent Document 1 proposes a method for imparting stretchability to polyester fibers, which involves bonding two polymer components (polyesters) with different viscosities side-by-side to form a potentially crimpable conjugate fiber. This potentially crimpable conjugate fiber bends significantly toward the high-shrinkage component after heat treatment, forming a continuous three-dimensional spiral structure. This structure therefore expands and contracts like a spring, resulting in a fiber with excellent stretchability and stretch recovery.

[0005] 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, resulting in apparently crimpable conjugate staple fibers with excellent spinning stability and wavy crimps and spiral crimps.

[0006] The eccentric sheath-core fiber proposed in Patent Document 3 is a filament, but the sheath-core structure suppresses yarn bending just below the spinneret, resulting in good spinnability, and thus fibers with a single fiber fineness of 1.0 dtex or less can be obtained, and the special eccentric sheath-core structure ensures sufficient stretchability. [Prior art documents] [Patent documents]

[0007] [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]

[0008] However, the side-by-side composite fiber proposed in Patent Document 1 exhibits significant yarn bending immediately after spinning from the spinneret due to the difference in melt viscosity between the two polymers, and even slight contamination of the spinneret surface causes yarn breakage, resulting in poor spinning operability. From the standpoints of production efficiency and cost, staple fibers require spinnerets with several hundred to several thousand holes for production. Therefore, rectification during the polymer cooling process after spinning from the spinneret is difficult, and significant yarn bending makes yarn breakage likely at the bent portion. Patent Document 1 attempts to minimize the difference in viscosity between the two polymers to suppress yarn bending, but a certain viscosity difference is necessary to achieve sufficient latent crimp expression, and the viscosity difference is insufficient to achieve the desired latent crimp.

[0009] 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 when a normal fiber (which does not exhibit latent or apparent crimps) is crimped using a stuffing box crimper. Therefore, the crimping of a simple eccentric core-sheath composite fiber such as that 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, there is also the issue that the stretchability is even worse when the fiber is made finer.

[0010] Furthermore, in Patent Document 3, the number of spinneret holes actually used in the examples is less than 100H. A smaller number of spinneret holes makes it easier to rectify the flow during the polymer cooling process after spinning, making it easier to suppress yarn sway and prevent yarn breakage at bent yarn portions. However, from the perspective of production efficiency, staple fibers require production with several hundred H (holes) to several thousand H, and this is even more difficult when it comes to finer fibers. In other words, even with this method, it is difficult to achieve finer fibers. Furthermore, the fibers in this invention have a round cross section, and the distance between the centers of gravity is close, so the expression of crimp after heat treatment is reduced, resulting in insufficient crimp potential.

[0011] In recent years, in an effort to further improve performance, there has been a demand for nonwoven fabrics that are both sufficiently stretchable and soft, but as mentioned above, Patent Documents 1 to 3 do not describe any specific means for providing these. [Means for solving the problem]

[0012] An object of the present invention is to provide a conjugated fiber which overcomes the problems of the prior art and can be used to obtain fabrics and nonwoven fabrics that are both highly stretchable and soft.

[0013] In order to achieve the above object, the present invention employs the following configuration.

[0014] (1) A composite fiber having a single fiber fineness of 0.9 dtex to 3.0 dtex, which is a flattened multilobal fiber made of two polyesters, component A and component B, with a flatness of 1.8 to 4.0, which is the ratio of the major axis a to the minor axis b, and which has multiple convex portions made of component A that are symmetrical about the major axis a, and a ratio of the maximum length b of the convex portion to the minimum length c of the convex portion of 1.1 to 1.5, and which has a side-by-side or eccentric sheath-core composite structure with a polymer interface perpendicular to the major axis a.

[0015] (2) The composite fiber according to (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 essentially composed of ethylene terephthalate units.

[0016] (3) The composite fiber according to (1) or (2), wherein the intrinsic viscosity (IV) of component A is 0.620 or more and 0.690 or less, and the intrinsic viscosity (IV) of component B is 0.550 or more and 0.595 or less.

[0017] (4) The conjugated short fiber according to any one of (1) to (3) above, which has latent crimping ability such that the degree of crimping after heat treatment at 180°C under no load is 2.3 times or more the number of crimps before heat treatment.

[0018] (5) A nonwoven fabric or a cloth using the composite short fiber according to any one of (1) to (3) above. [Effects of the Invention]

[0019] By using the flat multi-lobe bimetal raw cotton of the present invention, a nonwoven fabric having both high stretchability and softness can be obtained. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 shows an example of the conjugate fiber of the present invention (flat multilobal shape and side-by-side structure), and is a fiber cross section for explaining the flatness and convex portion ratio in the fiber cross section. [Figure 2]FIG. 2 is an example of a composite fiber of the present invention (flat multi-lobal shape and side-by-side structure), and is a fiber cross section for explaining the center of gravity points p, q and the distance between the centers of gravity pq in the fiber cross section. [Figure 3] FIG. 3 shows an example of the composite fiber of the present invention (flat multi-lobal shape and eccentric core-sheath structure), and is a cross section of a fiber with a thin skin structure in which component A is completely covered with a thin skin of component B. DETAILED DESCRIPTION OF THE INVENTION

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

[0022] The composite fiber is a flat multilobal fiber made of two polyesters, component A and component B, with a flatness, which is the ratio of the major axis a to the minor axis b, of 1.8 to 4.0, with multiple convex portions made of component A that are symmetrical about the major axis a, and with a ratio of the maximum length b of the convex portion to the minimum length c of the convex portion of 1.1 to 1.5, and has a side-by-side or eccentric sheath-core composite structure with a polymer interface perpendicular to the major axis a, and a single fiber fineness of 0.9 dtex to 3.0 dtex.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] Among the above polymers, a suitable polymer combination for the conjugated fiber of the present invention is one in which both component A and component B are polyesters. For example, component A is a copolymerized polyester containing ethylene terephthalate units as the main structural unit, and is preferably a polyethylene terephthalate copolymerized 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 the copolymerization components, and component B is preferably a polyester essentially consisting of ethylene terephthalate units. The copolymerization ratio of BHPP in the copolymerized polyester of component A is preferably 2 to 7 mol %. If the copolymerization ratio of BHPP is less than 2 mol %, the shrinkage properties will be insufficient, and the elongation rate and elongation recovery rate will be low, resulting in insufficient stretchability. On the other hand, if the copolymerization ratio exceeds 7 mol %, the melting point of the polymer will decrease, tending to impair thermal stability.

[0027] The copolymerization ratio of IPA in the copolymer polyester of component A is preferably 5 to 13 mol %. If the copolymerization ratio of IPA is less than 5 mol %, it is difficult to obtain substantial crimp, while if it exceeds 13 mol %, the melting point of the polymer decreases, tending to impair thermal stability. 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.

[0028] 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.

[0029] 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.

[0030] On the other hand, if a soft fabric is desired, it is preferable to use polybutylene terephthalate and polytrimethylene terephthalate as component A, so it is advisable to use them according to the required properties.

[0031] 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.

[0032] 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. However, to obtain a stretchable fabric, it is necessary for the conjugated fiber to have a latent crimp such that the crimp degree after heat treatment without load at 180°C is at least 2.3 times the crimp degree before heat treatment. If the crimp degree after heat treatment is less than 2.0 times the crimp degree before heat treatment, the stretchability of the fabric will be significantly reduced, resulting in low stretchability. There is no particular upper limit. The latent crimp degree can be achieved by adjusting the type of polymers to be combined, their area ratio, cross-sectional structure, etc. Among these, from the viewpoint of imparting the latent crimp degree, it is preferable to use a polymer with an intrinsic viscosity (IV) of 0.620 to 0.690 as component A and a polymer with an intrinsic viscosity (IV) of 0.550 to 0.595 as component B.

[0033] Regarding the composite area ratio of component A and 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, and since it is also necessary for the component B to have excellent physical properties, the ratio of both 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.

[0034] The flatness of the conjugated fiber of the present invention, which is the ratio (a / b) of the major axis a to the minor axis b, is 1.8 or more and 4.0 or less, more preferably 2.2 or more and 3.5 or less. If the flatness is less than 1.8, a sufficient distance between the centers of gravity cannot be secured, resulting in reduced stretch performance. If the flatness exceeds 3.5, the hole area in the spinneret decreases, the number of spinneret holes decreases, and sufficient performance cannot be obtained. Here, the flatness is the ratio of the major axis a to the minor axis b, where the major axis a is the longest line in the fiber cross section and the minor axis b is the longest line perpendicular to the major axis in the fiber cross section.

[0035] Fig. 1 is a cross-sectional view of an example of a fiber having a flat multilobal shape and a side-by-side structure, which is a preferred embodiment of the composite fiber of the present invention. In this cross-section, the longest diameter is the major axis a, and the longest diameter perpendicular to the major axis a is the minor axis b. The interface (polymer interface) between component A and component B is perpendicular to the major axis a (parallel to the minor axis b). Multiple convex portions are present on only one side (one of the components), symmetrically about the major axis a. The heights of the convex portions vary, and the distance between the apexes of the tallest convex portions is the longest diameter perpendicular to the major axis a = the minor axis b.

[0036] FIG. 2 is a cross-sectional view of an example of a fiber having the same flattened multi-lobal shape and side-by-side structure as FIG. 1. In FIG. 2, the white part is component A, the part with diagonal lines slanting upward to the right is component B, and the center of gravity of component A in the cross section of the composite fiber is center of gravity p, and the center of gravity of component B is center of gravity q.

[0037] In the present invention, it is important that the centers of gravity p and q of the cross section of the composite fiber are separated from each other, i.e., that the distance between the centers of gravity pq is as large as possible, 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, forming a three-dimensional spiral structure and exhibiting good crimp. Here, the larger the distance between the centers of gravity pq, the better the crimp will be, and the better the stretch performance will be.

[0038] In the present invention, the polymer interface is preferably perpendicular to the major axis. Here, "perpendicular to the major axis" does not necessarily mean completely perpendicular, and may be tilted by about ±5°. It has been found that when the polymer interface is perpendicular to the major axis, the distance between the centers of gravity can be made large, thereby achieving greater crimp development after heat treatment.

[0039] It is preferable that multiple convex portions exist on only one side of the cross section of the composite fiber of the present invention, preferably only on the component A side. If convex portions exist on both sides, when the fibers are adjacent to each other, the concave and convex portions will fit together and many areas will be completely blocked, resulting in a decrease in porosity, which will reduce the diffusion ability due to capillary action during water absorption and impair the feel and softness of the fabric. It is also preferable that multiple convex portions exist on both sides of the major axis. Figure 1 shows an embodiment in which two convex portions of different heights exist on each side of the major axis, but three or more convex portions of different heights may exist on both sides of the major axis.

[0040] It is preferable that the convex portions of the present invention are symmetrical with respect to the long axis. If the convex portions are asymmetrical with respect to the long axis, the design of the nozzle die requires the slits to be asymmetric with respect to the long axis, which makes clogging of the slits by minute foreign matter more likely to occur. Clogging by minute foreign matter raises concerns about spinning operability.

[0041] Furthermore, the composite fiber of the present invention preferably has a plurality of convex portions in its cross section, with the ratio of the maximum length b of the convex portion to the minimum length c of the convex portion (convex portion ratio = b / c) being 1.1 or more and 1.5 or less. If the convex portion ratio exceeds 1.5, when fibers are adjacent to each other, the convex portions interlock with each other, completely blocking the concave portions, reducing the porosity, reducing the diffusion due to capillary action during water absorption and impairing the feel and softness of the fabric. If the convex portion ratio is less than 1.1, the convex portions are small, and the desired porosity cannot be achieved. Here, the maximum length b of the convex portions is the distance between the vertices of the tallest convex portions among the convex portions that are symmetrical about the major axis, and the minimum length c of the convex portions is the distance between the vertices of the smallest convex portions among the convex portions that are symmetrical about the major axis. In a flattened multilobal shape in which convex portions are symmetrical about the major axis as shown in Figures 1 to 3, the maximum length of the convex portions is the same as the length of the minor axis.

[0042] In the present invention, in addition to the side-by-side structure, an eccentric sheath-core flattened multi-lobe structure (Figure 3) may also be used. By completely covering the A component with the B component in the cross section, whitening and fuzzing do not occur even when the fiber or fabric is subjected to friction or impact, thereby maintaining fabric quality. In addition, in the side-by-side structure, high-molecular-weight polymers and highly elastic polymers, which would otherwise be a drawback of composite fibers due to surface exposure, can be used as one component of the composite fiber. Furthermore, the bending of the yarn immediately below the spinneret that occurs when spinning polymers with different intrinsic viscosities (IV) is suppressed, improving spinning operability.

[0043] 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.

[0044] When using the eccentric sheath-core flattened multi-lobate structure, a thin skin structure is preferred. That is, it is preferable that the thickness of the B component, which completely covers the A component, is nearly uniform. The skin thickness varies depending on the fineness, but is essentially 5.0 μm or less. If the thickness exceeds 5.0 μm, the characteristics of the B component become prominent, and the convex portions described below are not obtained. Furthermore, the influence of the center-of-gravity distance pq cannot be ignored, and as a result of the center-of-gravity distance pq becoming small, the crimp expression after heat treatment decreases. There is no particular lower limit for the skin thickness as long as it can be maintained as a raw cotton, but a realistic value that does not cause skin destruction during drawing is 0.05 μm. Furthermore, as a level of thickness uniformity, it is preferable that the perimeter of the fiber within 1.05 times the minimum thickness is at least 1 / 3 of the perimeter of the entire fiber.

[0045] The single fiber fineness of the conjugate fiber of the present invention is 0.9 dtex or more and 3.0 dtex or less, more preferably 1.0 dtex or more and 2.5 dtex or less. If the single fiber fineness is less than 0.9 dtex, the fiber will not pass through the card during the production of the nonwoven fabric, leading to wrapping around the card cylinder and the generation of card neps. It has also been found that a small single fiber fineness significantly deteriorates spinning operability. If the single fiber fineness exceeds 3.0 dtex, the single-hole output rate increases and the spinning cooling effect significantly decreases, making it impossible to obtain the desired peak ratio and impairing the softness of the nonwoven fabric.

[0046] The number of crimps of the conjugated fiber of the present invention before heat treatment is preferably 8 crimps / 25 mm or more and 20 crimps / 25 mm or less, more preferably 10 crimps / 25 mm or more and 17 crimps / 25 mm or less. If the number of crimps is less than 8 crimps / 25 mm, the carding ability is extremely poor. If the number of crimps exceeds 20 crimps / 25 mm, the carding ability 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.

[0047] The crimp degree of the conjugated fiber of the present invention before heat treatment is preferably 8% or more and 25% or less, more preferably 10% or more and 20% or less. 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 unevenness of the spun yarn increases significantly, significantly reducing the advanced processability and the quality of the spun yarn.

[0048] It is important that the conjugated fiber of the present invention has a form in which crimping occurs upon heat treatment. After the crimped conjugated fiber is opened and heat-treated at 180°C for 10 minutes, the fiber preferably has latent crimping ability such that the number of crimps is at least 2.3 times the number of crimps before heat treatment. Due to the crimping after heat treatment, when a nonwoven fabric is produced and then heat-treated, not only can a stretchable nonwoven fabric be obtained, but the form of the present invention also produces coil-shaped crimps, which have been shown to improve the water absorption and water retention properties of the nonwoven fabric. It has been found that if the number of crimps is less than 2.3 times the number of crimps before heat treatment, sufficient stretchability cannot be obtained. A crimping of at least 2.5 times is more preferable. While there is no particular upper limit, a crimping of at most 6.0 times is preferred in consideration of the stability of the nonwoven fabric form.

[0049] The fiber length of the conjugated fiber of the present invention is preferably 30 to 64 mm, more preferably 35 to 51 mm, from the viewpoint of preventing fiber shedding when the fiber is made into a nonwoven fabric.

[0050] The form of the nonwoven fabric of the present invention is not particularly limited, but needle-punched or spunlaced nonwoven fabrics are preferred. 2 Preferably, the content is 20 to 50 g / m or less, more preferably 20 to 50 g / m 2 and particularly preferably 30 to 50 g / m 2 It is important that the obtained nonwoven fabric is highly soft, and although this can be quantitatively evaluated using KES evaluation, it can also be judged by a sensory test in which a paired comparison is made with a standard sample. In this study, the results of the sensory test were used, and the evaluation was carried out using polyester (PET) raw cotton with a round cross section and a fineness of 2.2 dtex as the standard sample.

[0051] Next, the method for producing the composite fiber of the present invention will be described.

[0052] 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 a length of 200 to 2000 H 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 +60°C or lower is preferable because it prevents excessive thermal degradation of the polymer.

[0053] 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.

[0054] Furthermore, since the present invention is primarily directed to short fibers, a multi-hole spinneret is usually used from the viewpoint of production efficiency, and it is necessary to use one with a spinneret of 200H or more. Considering the market price of short fibers, a spinneret of 300H or more is more preferable, and a spinneret of 600H or more is even more preferable.

[0055] Generally, the more holes there are, the more difficult it becomes to uniformly cool the spun yarn, and in addition, turbulence occurs just below the spinneret, making stable spinning difficult.

[0056] 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 flatness and groove ratio. 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 the cross section and intrinsic viscosity (IV) of the present invention, it is possible to suppress the bending of the polymer after extrusion to a spinnable range, and therefore it is possible to start cooling just below the spinneret even when spinning with a spinneret of 200H or more. As a result, it has become possible to produce composite fibers with a spinneret of 200H or more.

[0057] 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 cooling air speed just below the spinneret. If the cooling air speed is higher than that just below the spinneret, yarn swaying becomes greater, 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 nonwoven fabric, potentially reducing the quality of the nonwoven fabric.

[0058] 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.

[0059] A spinning draft of 300 or less is preferred because it allows for the production of homogeneous fibers with reduced variations in physical properties between yarns.

[0060] 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) 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 composite fibers can be obtained with stable spinnability, which is preferable. A spinning draft of 80 to 280 is more preferable.

[0061] 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.

[0062] 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.

[0063] By preheating the undrawn yarn to 40 to 60°C before drawing, the fusion of the fibers can be further suppressed.

[0064] In order to obtain the desired number of crimps and degree of crimp, 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.

[0065] 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.

[0066] 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.

[0067] 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 desired degree of crimp may not be obtained, and if the temperature is higher than 60° C., the degree of crimp may be high and the desired degree of crimp may not be obtained.

[0068] 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.

[0069] 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.

[0070] The resulting tow is cut to the desired length to obtain raw cotton made of composite fibers. To produce a spunlace nonwoven fabric, the resulting raw cotton is pre-opened using an opener and passed through a roller carding machine to form a fiber web. The fiber web formed by the carding is then sent to the spunlace process, where both sides are subjected to a high-pressure water jet entanglement treatment to process it into a sheet. After spunlace processing, the nonwoven fabric is sent to a drying process on a conveyor to remove moisture and obtain a spunlace nonwoven fabric. [Example]

[0071] Next, the conjugate 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.

[0072] <Polymer intrinsic viscosity (IV)> 0.8 g of a sample was dissolved in 10 ml of orthochlorophenol (hereinafter abbreviated as OCP), and the relative viscosity ηr was determined at 25°C using an Ostwald viscometer (B type) according to the following formula, and the IV was calculated. ηr=η / η0=(t×d) / (t0×d0) IV=0.0242ηr+0.2634 where η is the viscosity of the polymer solution, η0: viscosity of OCP, t: solution drop time (seconds), d: density of the solution (g / cm 3 ), t0: OCP fall time (seconds), d0: density of OCP (g / cm 3 ).

[0073] <Single fiber fineness (dtex)> Measurement was carried out according to the method of JIS-L1015 (2010).

[0074] <Breaking strength (cN / dtex) and breaking elongation (%)> Measurement was carried out according to the method of JIS-L1015 (2010).

[0075] <Number of crimps ( / 25mm)> Measurement was performed according to the method of JIS-L1015 (2010). The number of crimps was measured after dry heat treatment of the short fibers at 180°C for 5 minutes.

[0076] <Flatness> The cross section of the obtained composite fiber is photographed using a microscope at a magnification of 400 times, and the cross section photograph is then copied at a magnification of 2 times. The major axis of the copied paper is measured as a and the minor axis as b, and the following formula is used: Flatness = a / b The flatness was determined.

[0077] <Protrusion ratio> The cross section of the obtained composite fiber is photographed at a magnification of 400 times using a microscope, and the cross section photograph is then copied at a magnification of 2 times. The maximum length (minor axis) of the convex portion on the copied paper is measured as b and the minimum length of the convex portion as c, and the difference is calculated using the following formula: Convexity ratio = b / c The convexity ratio was calculated using the formula:

[0078] <Softness> The resulting composite fiber was 50 g / m 2 Spunlace nonwoven fabrics with a basis weight of 100g were prepared and cut into 10cm square pieces. These were then heat treated at 180°C for 5 minutes and subjected to a sensory test in which the fabric was compared pairwise with a reference sample. The results were rated on a four-point scale: ○○ for "extremely excellent," ○ for "excellent," △ for "average (no change)," and × for "inferior."

[0079] The reference sample was a nonwoven fabric made of polyester (PET) round cross section raw cotton with a fineness of 2.2 dtex, and subjected to the same heat treatment as above.

[0080] <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.

[0081] Example 1 It was prepared in the following manner.

[0082] The component A polymer was polyethylene terephthalate (intrinsic viscosity (IV): 0.667) obtained by copolymerizing 7.0 mol% IPA and 4.0 mol% BHPP, and the component B polymer was polyethylene terephthalate (intrinsic viscosity (IV): 0.586). Both the component A polymer and the component B polymer were melted at 280°C using an extruder, and then metered using a pump to bring the melting temperature to 290°C. The temperature was maintained while the polymers were flowed into a spinneret. The area ratio of component A to component B was 50 / 50, and the polymers were flowed into a flat multilobal side-by-side spinneret with 500 spinneret holes. The polymers merged inside the spinneret and were discharged from the spinneret. Note that a spinneret capable of obtaining the flat multilobal side-by-side structure shown in Figure 1 was used for spinning in Example 1. The spun yarn was cooled while being withdrawn at a speed of 1,300 m / min. The yarn was cooled from a position 15 mm from the spinneret using a cold air blower with an air temperature of 20°C, an air speed of 45 m / min, and a cooling length of 30 mm, and then cooled using a cold air blower with an air temperature of 20°C, an air speed of 60 m / min, and a cooling length of 600 mm. After cooling the yarn, 0.1% by mass of process oil was applied, 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.

[0083] The undrawn yarn was then introduced into hot water at 90°C and drawn to a draw ratio of 2.8. The drawn yarn was then heat-treated under tension with a 160°C heating roller for 5 seconds and then introduced into a crimper. The drawn tow was mechanically crimped at a temperature of 30°C and a tow pressure of 1.5 kg / cm2G, dried at 80°C, and cut to a length of 51 mm to obtain a flat multilobal side-by-side composite fiber. The results, as shown in Table 1, showed no problems with spinnability, a single fiber fineness of 2.2 dtex, a crimp count of 14 crimps / 25 mm before heat treatment, a crimp degree of 16%, and a crimp degree after no-load heat treatment at 180°C that was 2.7 times the crimp degree before heat treatment.

[0084] Example 2 The same procedure as in Example 1 was carried out, except that polyethylene terephthalate (intrinsic viscosity (IV): 0.563) was used as the polymer for component B, the single fiber fineness was 2.8 dtex, the number of crimps before heat treatment was 12 crimps / 25 mm, and the crimp degree was 16%.

[0085] Example 3 The procedure was the same as in Example 1, except that a spinneret capable of obtaining the eccentric sheath-core flattened multilobal structure shown in Figure 3 was used. The obtained composite fiber had the component A polymer encompassed in the component B polymer, and the component B in the thin skin portion had an eccentric sheath-core flattened multilobal structure with a thickness of 2 µm.

[0086] Example 4 The same procedure as in Example 3 was carried out, except that polyethylene terephthalate (intrinsic viscosity (IV): 0.592) was used as the polymer of component B and the single fiber fineness was 1.2 dtex.

[0087] (Comparative Example 1) The same procedure as in Example 1 was carried out except that the spinneret was a round cross-section side-by-side spinneret, the number of crimps before heat treatment was 16 crimps / 25 mm, and the crimp degree was 18%.

[0088] (Comparative Example 2) The same procedure as in Example 1 was carried out, except that polyethylene terephthalate (intrinsic viscosity (IV): 0.600) copolymerized with 7.0 mol% IPA and 4.0 mol% BHPP was used as the polymer for component A, the number of crimps before heat treatment was 10 crimps / 25 mm, and the crimp degree was 12%.

[0089] (Comparative Example 3) Polyethylene terephthalate (intrinsic viscosity (IV): 0.605) was used as the polymer of component B. The same method as in Example 1 was used except that the number of crimps before heat treatment was 10 crimps / 25 mm and the degree of crimp was 12%.

[0090] Comparative Example 4 The same procedure as in Example 1 was carried out, except that polyethylene terephthalate (intrinsic viscosity (IV): 0.600) copolymerized with 7.0 mol% IPA and 1.3 mol% BHPP was used as the polymer for component A, and the number of crimps before heat treatment was 12 crimps / 25 mm and the crimp degree was 16%.

[0091] (Comparative Example 5) The same procedure as in Example 3 was carried out, except that polyethylene terephthalate (intrinsic viscosity (IV): 0.592) was used as the polymer for component B, the single fiber fineness was 0.8 dtex, the number of crimps before heat treatment was 14 crimps / 25 mm, and the crimp degree was 15%.

[0092] [Table 1]

[0093] Examples 1 and 2, which are in accordance with the present invention, have a flat multilobal shape and a side-by-side structure, while Examples 3 and 4 have a flat multilobal shape and an eccentric sheath-core structure, and it can be seen that these nonwoven fabrics have excellent softness. Furthermore, the crimp ratio before and after heat treatment is large, suggesting high stretchability. On the other hand, Comparative Example 1 has a round cross section rather than a flat cross section, so the crimping upon heat treatment is small, and high stretchability cannot be expected. In Comparative Example 2, the intrinsic viscosity of Component A was low, so convex portions were not formed well using the same spinneret as in Example 1, resulting in a convex portion ratio of 1.0, and therefore sufficient softness was not obtained. In Comparative Example 3, the difference in intrinsic viscosity between Component A and Component B was small, resulting in insufficient flatness and high stretchability. In Comparative Example 4, the shrinkability of the B component polymer was insufficient, and therefore high stretchability was not obtained. In Comparative Example 5, although the flat multilobal shape and eccentric sheath-core structure were obtained, the spinning operability deteriorated due to the low fineness. [Explanation of symbols]

[0094] a: long axis b: Minor axis = Maximum length of convex part c: Minimum length of convex part p: Center of gravity of component A q: Center of gravity of B component pq: Distance between centers of gravity 1: Convex parts that exist symmetrically with respect to the major axis a 2: Multiple protrusions of different heights 3: Component A 4:B component 5: Thin skin

Claims

1. A composite fiber having a single fiber fineness of 0.9 dtex or more and 3.0 dtex or less, which is a flattened multilobal fiber made of two polyesters, component A and component B, and which has a flatness, which is the ratio of the major axis a to the minor axis b, of 1.8 to 4.0, and which has a plurality of convex portions made of component A that are symmetrical about the major axis a, and in which the ratio of the maximum length b of the convex portion to the minimum length c of the convex portion is 1.1 to 1.5, and which has a side-by-side or eccentric sheath-core composite structure with a polymer interface perpendicular to the major axis a.

2. 2. The conjugated fiber according to claim 1, wherein component A is a copolymer polyester mainly composed of ethylene terephthalate units, 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 composite fiber according to claim 2, wherein the intrinsic viscosity (IV) of component A is 0.620 or more and 0.690 or less, and the intrinsic viscosity (IV) of component B is 0.550 or more and 0.595 or less.

4. 3. The composite staple fiber according to claim 1, which has latent crimping ability such that the degree of crimping after heat treatment at 180° C. under no load is at least 2.3 times the number of crimps before heat treatment.

5. A nonwoven fabric or cloth using the composite staple fiber according to claim 1 or 2.

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