Eccentric sheath-core hollow composite fiber raw cotton and fiber spheroid made of the same

Abstract

To provide an eccentric sheath-core hollow composite raw cotton having not only light weight and excellent bulkiness, but also softness and a feeling similar to a feather, which is suitable for constituting a polyester hollow fiber spheroid for an inner cotton material of a cushion, a down jacket, etc., and a fiber spheroid made of the same.SOLUTION: In a cross-section of a composite raw cotton formed of 2 types of polyester, a component A and a component B, the component A is completely covered by the component B. The component A is a copolymerized polyester consisting essentially of an ethylene terephthalate unit obtained by copolymerizing 2 to 7 mol% of 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane and 5 to 13 mol% of isophthalic acid. The component B is the polyester which is substantially the ethylene terephthalate unit, having a single fiber fineness of 1.0 to 7.0 dtex, a fiber length of 15 to 50 mm, and one hollow part continuing in a fiber axis direction with a hollow degree of 10 to 50%. The composite raw cotton is used to obtain a fiber spheroid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an eccentric core-sheath hollow composite fiber raw fiber and a fiber sphere made using the same. [Background technology]

[0002] Conventionally, feathers and polyester staple fibers have been widely used as padding or cushioning materials for down jackets and sleeping bags.

[0003] The feathers generally used are those of waterfowl, which are known for their rich texture, light weight, excellent heat retention, ability to conform to the body, high bulk, and high recovery rate. However, when trying to obtain natural feathers, there is a problem that the supply is limited and that the supply fluctuates due to natural conditions and the effects of epidemics.

[0004] Furthermore, from the perspective of nature conservation, there are limits to capturing wild birds, and if one were to raise waterfowl to obtain feathers, it would be necessary to raise a large number of waterfowl, which would not only require a large amount of feed but would also raise issues such as water pollution due to the waterfowl's excrement and the outbreak and spread of infectious diseases.

[0005] Furthermore, in order to make feathers usable as stuffing, they must go through many processes, such as collecting, sorting, disinfecting, degreasing, and stuffing into futons. In addition, the process is complicated because the feathers tend to fly up, and as a result, the prices of products using feathers tend to be high.

[0006] Furthermore, when feathers are harvested, meat remains at the ends of the feathers, causing a rotten smell, so there is a movement in Europe and other places to eliminate feathers from the perspective of animal welfare.

[0007] On the other hand, polyester staple fibers are inexpensive and have excellent bulkiness, and are easy to spin during fiber production and to process into products such as nonwoven fabrics. Therefore, a well-known method involves covering a fibrous web laminate, which is made by laminating polyester staple fibers by carding or the like to form a fibrous web, with a side fabric. However, this method has the drawback of being time-consuming to cover the layered fibrous web laminate with the side fabric.

[0008] To address these issues, padding made of highly elastic fiber spheres (fiber balls) that have excellent elasticity, compression resistance, and shape stability has been proposed (Patent Document 1).

[0009] It has also been proposed that the use of fibers with three-dimensional spiral crimps can improve the formability of fiber spheres and produce fiber spheres with excellent bulkiness (Patent Documents 2 and 4).

[0010] Furthermore, Patent Documents 1 and 4 also propose making fiber spheres using composite fibers that are a mixture of multiple types of fibers, such as fine fibers and binder fibers, in order to form dense air layers and improve bulkiness. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-169846 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-160564 [Patent Document 3] WO2016 / 121643 publication [Patent Document 4] Japanese Patent Application Publication No. 2023-157431 Summary of the Invention [Problem to be solved by the invention]

[0012] However, in the proposal of Patent Document 1, the fiber material used is fiber spheres made of, for example, polyester fiber and binder fiber, and the binder fiber is thermally fused using hot air or the like during sphere formation, which causes the fibers to shrink during thermal formation, resulting in high-density fiber spheres, resulting in poor softness and bulkiness of the spheres, and the presence of thermally bonded portions results in poor softness of the spheres.The proposals of Patent Documents 2 to 4 have problems in that the fibers constituting the fiber spheres are too entangled, resulting in a hard texture, and further, the fibers are difficult to open during formation, making them difficult to process.

[0013] Furthermore, the methods proposed in Patent Documents 1 and 4 for producing fiber spheres using composite fibers that are a mixture of multiple types of fibers, such as fine fibers and binder fibers, have problems such as the time-consuming process of mixing multiple types of fibers and the difficulty in opening the fibers during the formation of the fiber spheres, making them difficult to process.

[0014] Therefore, an object of the present invention is to solve the problems of the prior art described above and to provide an eccentric core-sheath hollow composite raw fiber and fiber spheres that are not only lightweight and have excellent bulkiness, but also soft and have a texture similar to that of feathers, and are suitable for forming fiber spheres for use as padding materials for cushions, down jackets, etc. [Means for solving the problem]

[0015] The present inventors have considered that the use of an eccentric sheath-core hollow composite raw fiber is suitable for obtaining fiber spheres that are both lightweight and bulky. Furthermore, to obtain fiber spheres that are easy to process, have good resilience when compressed, and have high bulk recovery, it is necessary to effectively generate spiral crimp. They have also discovered that by incorporating a high-thermal-shrinkage polymer into the eccentric sheath-core hollow composite raw fiber, it is possible to effectively generate strong spiral crimp in both the raw fiber and the fiber spheres, leading to the completion of the present invention.

[0016] That is, the present invention is intended to achieve the above object and comprises the following components. (1) In the cross section of a composite raw cotton consisting of two types of polyester, component A and component B, component A is completely covered with component B, component A is a copolymer polyester mainly composed of ethylene terephthalate units copolymerized with 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 consisting of ethylene terephthalate units, and has the following characteristics: A. Single fiber fineness: 1.0 to 7.0 dtex B. Fiber length is 15 to 50 mm; C. It has one continuous hollow space in the fiber axis direction, and its hollowness is 10 to 50%. D. An oil containing polysiloxane is applied to the fiber surface at a rate of 0.2 to 0.8% by weight based on the fiber weight. The ratio S / D of the minimum thickness S of the B component covering the EA component to the fiber diameter D is 0.01 to 0.1. F. The perimeter of the fiber in the part that is within 1.05 times the minimum thickness S is 1 / 3 or more of the perimeter of the entire fiber G. Without mechanical crimping, when heat treated at 100-200°C for 3 minutes or more, it has the potential for crimping to occur at 3-20 crimps per 25mm. (2) A fiber sphere made using the above eccentric core-sheath hollow composite raw cotton. [Effects of the Invention]

[0017] It is possible to obtain an eccentric core-sheath hollow composite raw fiber and fiber spheres which are not only lightweight and have excellent bulkiness, but also soft and have a texture similar to that of feathers, and are suitable for forming fiber spheres for use as padding materials for cushions, down jackets, etc. [Brief explanation of the drawings]

[0018] [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 shows an example embodiment of a distribution arrangement in the final distribution plate. [Figure 4] FIG. 4 is a cross section of the eccentric core-sheath composite short fiber of Example 2. [Figure 5] FIG. 5 is a cross section of the eccentric sheath-core composite short fiber of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in detail below.

[0020] The eccentric core-sheath hollow composite raw fiber of the present invention has a fiber cross section composed of two types of polymers, component A and component B.

[0021] 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.

[0022] 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°C. If the melt viscosity of the polymers that make up the eccentric sheath-core hollow composite fiber differs by 40 Pa·s or more, this means that, 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 bonded cross sections, the orientation of the combined components will create significant differences, making it possible to achieve optimal crimp.

[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 preferred combination of polymers for the eccentric core-sheath hollow composite fiber of the present invention is as follows: Component A is a copolymerized polyester containing ethylene terephthalate units as the main structural unit, and is a polyethylene terephthalate-based copolymerized polyester (hereinafter also referred to as polyester (A)) 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 properties will be insufficient, and when made into a nonwoven fabric, 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.

[0027] 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 substantially large crimps, while if it exceeds 13 mol %, the melting point of the polymer decreases, tending to impair thermal stability.

[0028] 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.

[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] Furthermore, the combination of polybutylene terephthalate / polyethylene terephthalate or polytrimethylene terephthalate / polyethylene terephthalate as component A / component B can be said to achieve sufficient elongation and elongation recovery when processed into a nonwoven fabric, and to have excellent stretch performance. However, a combination of a polyethylene terephthalate-based copolymer polyester modified with BHPP and IPA as component A and a polyester substantially consisting of ethylene terephthalate units as component B is superior in terms of elongation recovery and is a more preferred form.

[0031] However, the combination of polytrimethylene terephthalate / polyethylene terephthalate has low rigidity and therefore a soft texture, making it suitable for applications where a soft texture is required.

[0032] Furthermore, since the eccentric core-sheath hollow composite fiber fiber of the present invention is composed of a combination of polymers that undergo differential shrinkage upon heat treatment, it exhibits crimping during heat treatment. However, to improve processability during molding of fiber spheres and the bulkiness, resilience, and compression recovery properties after molding, it is preferable for the fiber fiber fiber to have a latent crimping capacity of 3 to 20 crimps / 25 mm when heated at 100 to 200°C for 3 minutes or more under no load without mechanical crimping. Regarding the number of crimps exhibited, in order to satisfy the required properties of molded fiber spheres, if the number is less than 3 crimps / 25 mm, the shape stability of the fiber spheres will be poor, and resilience and compression recovery will be poor due to the whisker-like fiber ends protruding from the fiber spheres and becoming entangled. On the other hand, if the number is more than 10 crimps / 25 mm, the processability during molding will be poor and the size of the finished fiber spheres will be too small, resulting in a hard feel and poor bulkiness. The number of crimps that can be expressed (potential crimping ability) can be achieved by adjusting the types of polymers to be combined, their area ratio (described later), the cross-sectional structure of the eccentric core-sheath structure, and the like.

[0033] Regarding the composite area ratio of component A and component B in the fiber cross section of the eccentric core-sheath hollow composite raw fiber of the present invention, in consideration of tendon development, a fine spiral structure can be realized by increasing the ratio of component A, which is the high-shrinkage component.In addition, since the eccentric core-sheath composite raw 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.

[0034] 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.

[0035] Here, the term "eccentricity" as used herein refers to the position of the center of gravity of the component A polymer in the cross section of the eccentric core-sheath hollow composite raw fiber being different from the center of the cross section of the eccentric core-sheath hollow composite raw fiber, and is explained using Figure 1.

[0036] In Figure 1, the horizontal hatching represents component B, the 45° hatching (diagonal lines rising to the right) represents component A, and the center of gravity of component A in the cross section of the eccentric core-sheath hollow composite raw cotton is center of gravity point a, and the center of gravity of the cross section of the eccentric core-sheath hollow composite raw cotton is center of gravity point C.

[0037] 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 eccentric sheath-core hollow composite raw fiber, so that the fiber will bend significantly toward the high-shrinkage component after heat treatment. As a result, the eccentric sheath-core hollow composite raw fiber continues to bend from the fiber axis, forming a three-dimensional spiral structure and achieving good crimp expression.

[0038] In the present invention, because component A is completely covered by component B, whitening or fuzzing does not occur even when friction or impact is applied to the fiber surface, and high molecular weight polymers and highly elastic polymers, which would be exposed to the surface and cause fiber defects in the conventional simple bonded structure, can also be used as one of the components of the composite raw cotton.

[0039] 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.

[0040] In the eccentric sheath-core hollow composite raw 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 (total diameter of the composite fiber) D 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 force can be obtained.

[0041] Although good crimping performance can be achieved by the polymers being in contact only at the bonding interface, if the high-shrinkage component is completely covered by the low-shrinkage component, stretch performance will decrease. On the other hand, by keeping the thickness of component B within the range of the present invention, it is possible to obtain a composite raw cotton that satisfies both good crimping performance and abrasion resistance.

[0042] 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 eccentric core-sheath hollow composite raw fiber is the minimum thickness S.

[0043] Furthermore, it is important that 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 eccentric sheath-core hollow composite raw fiber. This means that component A is present along the contour of the fiber, and compared to conventional eccentric sheath-core composite raw fiber of 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 crimp expression performance can be achieved without crimp irregularities.

[0044] 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.

[0045] Specifically, the eccentric core-sheath hollow composite raw cotton 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 for observation of 10 or more fibers. In this case, if metal staining is applied, the dye differences between the polymers can be utilized to clarify the contrast at the joint between component A and component B. The circumscribing circle diameter of 10 fibers randomly selected within each image is measured, and this 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.

[0046] 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.

[0047] 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.

[0048] The single fiber fineness of the eccentric sheath-core hollow composite fiber fiber of the present invention is preferably 1.0 dtex to 7.0 dtex, more preferably 2.0 dtex to 5.0 dtex, and even more preferably 3.0 dtex to 4.0 dtex. A fiber fineness of less than 1.0 dtex can result in poor processing during fiber sphere molding and a decrease in the rigidity of the fiber itself, resulting in reduced bulkiness and resilience of the fiber spheres. Furthermore, the fiber spheres tend to be too small in size. Similarly, a fiber fineness of more than 7.0 dtex makes it difficult to obtain uniform fiber spheres during molding. Furthermore, the number of fibers constituting the fiber spheres is reduced for the same basis weight, resulting in reduced bulkiness. Furthermore, the fiber itself becomes too rigid, resulting in a hard texture, making it impossible to obtain fiber spheres with a soft, feather-like texture.

[0049] The hollowness of each hollow portion continuous in the fiber axis direction of the eccentric core-sheath hollow composite raw fiber of the present invention is preferably 10% or more and 50% or less. It is more preferably 15% or more and 45% or less, and even more preferably 20% or more and 40% or less. If the hollowness is less than 10%, the fiber loses its advantage over solid fibers in terms of lightness, and the distance between the centers of gravity becomes too close, resulting in reduced crimp expression. If the hollowness exceeds 50%, the fiber is more advantageous in terms of lightness, but the hollow portion is more likely to collapse during molding of the fiber spheres, and the fiber is more likely to crack.

[0050] The fiber length of the eccentric core-sheath hollow composite raw fiber in the present invention is preferably 15 mm to 50 mm, more preferably 20 mm to 45 mm, and even more preferably 25 mm to 40 mm. If the fiber length is less than 15 mm, the entanglement of the fibers during molding into fiber spheres becomes weak, making it difficult to obtain good fiber spheres. In addition, the size of the fiber spheres becomes too small, resulting in poor bulkiness. If the fiber length exceeds 50 mm, whisker-like fiber ends protrude from the fiber spheres and become entangled, resulting in poor compression recovery. Furthermore, the number of fibers constituting the fiber spheres becomes smaller for the same basis weight, resulting in poor bulkiness.

[0051] The eccentric core-sheath hollow composite raw cotton of the present invention preferably has a polysiloxane-containing oil agent adhered to it in an amount of 0.2 to 0.8% by weight, more preferably 0.3 to 0.7% by weight, and even more preferably 0.4 to 0.6% by weight. If the polysiloxane-containing oil agent is less than 0.2% by weight, the smoothness between the fibers is low, resulting in poor moldability during processing into fiber spheres and the resulting fiber spheres failing to achieve a soft, feather-like feel. If the polysiloxane-containing oil agent is more than 0.8% by weight, the fibers become too smooth, resulting in poor molding during processing into fiber spheres and a reduced rebound feel when compressed.

[0052] Next, the method for producing the eccentric sheath-core hollow composite fiber of the present invention will be described.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] In the process of drawing the spun undrawn yarn, the undrawn yarn is bundled to 30 to 300 ktex and drawn in steam or hot water at 2 to 5 times its original size, followed by a tension heat treatment at a temperature suitable for the development of crimp. While a push-type crimper is used to mechanically crimp the eccentric sheath-core hollow composite raw fiber of the present invention, no mechanical crimping is applied. Instead, an oil containing polysiloxane is applied, and the fiber is cut to a specified length with a cutter. The entanglement between the fibers is thoroughly opened with steam or the like, and the fiber is then dried in a conveyor-type dryer and heat-treated to develop a spiral crimp, thereby obtaining the eccentric sheath-core hollow composite raw fiber of the present invention.

[0061] Here, in the case of a latent winding composite raw fiber bonded side-by-side, in the process of drawing the spun undrawn yarn, the fiber tends to fuse with adjacent fibers due to the heat of drawing, increasing the risk of mixing in fused fibers. This is a problem that is particularly evident in the staple fiber manufacturing process, and the composite raw fiber of the present invention solves this problem specific to staple fibers.

[0062] Although the detailed mechanism has not been elucidated, in the present invention, by using 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 inclusion of fused fibers in the short 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 when 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 fiber spheres can be reduced, and the quality of the fiber spheres can be improved.

[0063] In addition, by preheating the undrawn yarn to 40 to 60°C before drawing, the formation of fused fibers can be further suppressed.

[0064] In order to obtain the crimp number of the present invention, it is important to set the temperature and time for heat treatment of the raw cotton after cutting, and if necessary, tension heat treatment can be carried out before cutting.

[0065] The heat treatment temperature for the cut raw cotton is preferably 100° C. or higher and 200° C. or lower. If the temperature is lower than 100° C., the crimping is too weak, causing processing defects when forming fiber spheres. If the temperature is higher than 200° C., the crimping is too strong, making it difficult to open the fibers when forming the fiber spheres, and making it difficult to obtain uniform spheres.

[0066] In tension heat treatment, the fiber is heat-set while maintaining tension, and then cooled with cooling water to below the glass transition temperature to fix the molecular chain structure, thereby preventing the occurrence of crimping during the heat treatment process of the cut raw cotton.

[0067] 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, extreme crimping may occur in the subsequent tow drying process, resulting in a decrease in 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 decrease.

[0068] 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 is able to adequately suppress 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 particularly large, the number of crimps and the degree of crimp tend to increase during the spinning process, for example, in the raw cotton after cutting, making it relatively difficult to control crimp during the spinning process.

[0069] For the eccentric sheath-core hollow composite raw fiber of the present invention, it is preferable to precisely control the sheath thickness and the perimeter of the thin skin portion, and methods using a distributor plate as exemplified in JP-A Nos. 2011-174215, 2011-208313, and 2012-136804 are preferably used. When a fiber having an eccentric sheath-core cross section is produced using a conventional composite spinneret, it is often very difficult to precisely control the position of the center of gravity of the core and the sheath thickness. For example, if the sheath thickness is too thin and the core component is exposed, this can cause whitening of the fabric and fuzz due to friction and impact. Conversely, if the sheath thickness is too thick, problems such as reduced crimp expression and reduced stretch performance can occur.

[0070] In the method using such a distributor plate, the cross-sectional form of the single fibers can be controlled by the arrangement of the distribution holes in the final distributor plate, which is the most downstream of the plurality of distributor plates.

[0071] The cross-sectional form of the eccentric sheath-core hollow composite raw fiber of the present invention can be controlled by the arrangement of distribution holes for the polymer (component A) constituting the core component and the polymer (component B) constituting the sheath component. Specifically, as shown in Figure 3, the eccentric sheath-core composite cross section required in the present invention can be preferably formed by arranging distribution holes 5-(a) and 5-(b) for the polymer (component B) constituting the sheath component so as to surround distribution hole 5-(c) for the polymer (component A) constituting the core component in the eccentric sheath-core composite cross section.

[0072] In addition, by changing the number of distribution holes 5-(a) that form the thin skin and the amount of polymer discharged per distribution hole, it is possible to control the S / D and the minimum thickness length in the cross section of the eccentric core-sheath hollow composite raw fiber.

[0073] The polymer stream thus formed by the distributor plate is contracted and discharged from the discharge holes of the spinneret. The purpose of the discharge holes 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 speed) on the spinning line. The hole diameter and length are preferably determined taking into consideration the viscosity of the polymer and the discharge rate. When producing the eccentric core-sheath hollow composite fiber of the present invention, the discharge hole diameter can be selected from the range of 0.1 to 2.0 mm, and the L / D (discharge hole length / discharge hole diameter) can be selected from the range of 0.1 to 5.0.

[0074] As described above, the eccentric sheath-core hollow composite fiber of the present invention preferably has the A component completely covered with the B component, as shown in Figure 1. By forming the cross section as in the present invention, it is possible to suppress bending of the extrusion line (kneeing phenomenon) caused by the difference in flow speed between the two polymers when extruding from the spinneret. 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 in the direction perpendicular to the spinning line caused by the difference in flow speed between the two polymers when extruding from the spinneret.

[0075] Furthermore, in the case of a conventional simple laminated structure (side-by-side structure), differences in the balance of stresses applied to the respective polymers during thinning on the spinning line after discharge from the spinneret occur, which can lead to unevenness in elongation deformation and manifest as fineness unevenness. This tendency is very pronounced 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, making it possible to suppress fineness unevenness.

[0076] 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.

[0077] 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.

[0078] In addition, from the viewpoint of suppressing the bending of the discharge line, the difference in melt viscosity of the polymers used in the eccentric core-sheath hollow composite fiber of the present invention is also important. When the two types of molten polymers that make up the composite fiber are contracted, in order to match the pressure losses of the two types of polymers, the cross-sectional area changes in the polymer flow direction and in the cross section perpendicular to the polymer flow direction, resulting in a difference in flow velocity, and these are discharged with a biased center of gravity, causing the bending of the discharge line.

[0079] In other words, a polymer with a high melt viscosity has a large cross-sectional area and therefore a slow flow rate, while 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 the bending of the discharge line can be suppressed. From this perspective, it is preferable that the difference in melt viscosity between the combined polymers is small, but in the case of the eccentric core-sheath hollow composite raw 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.

[0080] 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.

[0081] 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.

[0082] 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)

[0083] 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.

[0084] In the method for forming fiber spheres of the present invention, the eccentric core-sheath hollow composite raw fiber obtained as described above is thoroughly opened using a card equipped with a plurality of rollers each having a garnet wire on its surface, and the fully opened fibers are then spheronized (formed into spheroids) using a device that blows the fully opened fibers into a cylindrical chamber equipped with a rotating body with a plurality of fins in a cylindrical space where turbulent air is likely to occur, and removes them after a predetermined period of turbulent agitation. Alternatively, the fully opened fibers are retained in a fairly large chamber while creating an air vortex, and then spheronized. The mechanical force from the rigid body (fins) and air further promotes the loop-shaped crimp, forming fiber spheres.

[0085] The polyester hollow fiber spheres of the present invention preferably have an average diameter of 3 to 8 mm, more preferably 4 to 6 mm. Fiber spheres with an average diameter of less than 3 mm are difficult to process, while fiber spheres with an average diameter of more than 8 mm are not suitable for product processing, such as blowing.

[0086] Furthermore, by subjecting the fiber spheres obtained above to a heat treatment at a temperature in the range of 100°C to 200°C for 3 minutes or longer, latent crimp is generated, resulting in fiber spheres that are elastic and have excellent shape stability. The degree of crimp generation may be any within a range that satisfies the desired function.

[0087] The fiber spheres obtained using the eccentric core-sheath hollow composite raw cotton of the present invention not only have excellent bulkiness, elasticity, compression recovery, and light weight, but also have a soft texture similar to that of feathers, making them suitable for use as filling materials for clothing, bedding, cushioning materials, etc. [Example]

[0088] <Evaluation method> (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.

[0089] (2) Number of crimps (ridges / 25mm) Measurement was carried out according to the method of JIS-L1015 (2010).

[0090] (3) 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.

[0091] (4) Hollowness The cross section of the obtained eccentric core-sheath hollow composite raw cotton is photographed at 400x magnification using a microscope, and the cross section photograph is then enlarged and copied. From the copied paper, the cross section of the fiber part is cut out and the mass is measured at N=20 on an electronic balance. Next, the hollow part is cut out and the mass is measured at N=20 on an electronic balance, and the mass is calculated from the arithmetic mean using the following formula (3). Hollowness (%) = (mass of hollow part / cross-sectional mass of fiber part) × 100 (3) The mass ratio was calculated as shown below.

[0092] [Example 1] An eccentric sheath-core hollow composite fiber was produced in the following manner.

[0093] 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 the 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 discharged from the spinneret. In Example 1, a distributor plate-type spinneret was used to obtain the eccentric sheath-core hollow composite fiber shown in Figure 1. 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.

[0094] The undrawn yarn obtained was then 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 with a heated roller at 160°C for 5 seconds, and an oil solution containing polysiloxane was applied using a shower nozzle to an amount equivalent to 0.5% by weight. After cutting to a fiber length of 44 mm, the yarn was subjected to a tension heat treatment with a 2.0 kgf / cm 2 The fibers were opened by spraying steam of this kind onto the fibers, and then dried for 5 minutes with circulating hot air at 130°C. As a result, as shown in Table 1, eccentric sheath-core composite staple fibers were obtained which had no problems with spinnability, an S / D ratio in the fiber cross section of 0.02, the minimum thickness S portion accounting for 45% of the fiber circumference, a single fiber fineness of 1.8 dtex, a crimp number of 4 peaks / 25 mm, and a hollowness of 20%.

[0095] [Example 2] An eccentric sheath-core hollow composite raw fiber was produced in the following manner. An eccentric sheath-core hollow composite raw 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 0.05, and the proportion of the portion with the smallest thickness S on the fiber circumference was 70%. As the results are shown in Table 1, there were no problems with spinnability, and an eccentric sheath-core hollow composite raw fiber was obtained with a fiber single fiber fineness of 1.8 dtex, a crimp number of 3 crimps / 25 mm, and a hollowness of 20%.

[0096] [Example 3] An eccentric sheath-core hollow composite raw fiber was produced in the following manner. Except for changing the position at which the cooling of the yarn started from the spinneret to 10 mm from the spinneret, an eccentric sheath-core hollow composite fiber was obtained in the same manner as in Example 1. As the results are shown in Table 1, there were no problems with spinnability, and an eccentric sheath-core hollow composite raw fiber was obtained with a fiber single fiber fineness of 1.8 dtex, a crimp number of 4 peaks / 25 mm, and a hollowness of 24%.

[0097] [Example 4] An eccentric sheath-core hollow composite raw fiber was produced in the following manner. Except for changing the position at which the cooling of the yarn started from the spinneret to 20 mm from the spinneret, an eccentric sheath-core hollow composite fiber was obtained in the same manner as in Example 1. As the results are shown in Table 1, there were no problems with spinnability, and an eccentric sheath-core hollow composite raw fiber was obtained with a fiber single fiber fineness of 1.8 dtex, a crimp number of 4 peaks / 25 mm, and a hollowness of 16%.

[0098] [Comparative Example 1] Hollow composite raw cotton was produced by the following method. Using the spinneret described in JP-A-09-157941, hollow composite raw cotton 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 made into hollow composite raw cotton with a hollow cross section (round cross section, the hollow part contacting both component A and component B). As the results are shown in Table 1, spun yarn breakage occurred, spinnability was poor, and a hollowness within the acceptable range could not be obtained.

[0099] Comparative Example 2 An eccentric sheath-core hollow composite raw fiber was produced in the following manner. The eccentric sheath-core hollow composite raw fiber was obtained in the same manner as in Example 1, except that the composite morphology was as shown in Figure 5, the S / D ratio in the fiber cross section was 0.01, and the proportion of the minimum thickness S portion on the fiber circumference was 10%. As the results are shown in Table 1, it was not possible to obtain a crimp number within the allowable range.

[0100] Comparative Example 3 Concentric sheath-core hollow composite raw cotton was produced in the following manner. A concentric sheath-core hollow composite raw cotton was obtained in the same manner as in Example 1, except that a conventional sheath-core composite spinneret was used to form concentric sheath-core fibers (circular cross section), 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%. As the results are shown in Table 1, it was not possible to obtain a crimp number within the allowable range.

[0101] Comparative Example 4 An eccentric core-sheath hollow composite raw fiber was produced in the same manner as in Example 1, except that the cooling start position of the yarn was set 3 mm from the spinneret. As shown in Table 1, the results showed frequent spun yarn breakage and poor spinnability, so that the fiber could not be produced.

[0102] Comparative Example 5 An eccentric sheath-core hollow composite raw fiber was produced in the following manner. 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 to 30 mm from the spinneret. As shown in Table 1, spun yarn breakage occurred, spinnability was poor, and a hollowness within the allowable range could not be achieved.

[0103] [Table 1] [Explanation of symbols]

[0104] 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 5-(a): Among the distribution holes in the final distribution plate, the distribution holes for component B that form a thin skin 5-(b): Among the distribution holes in the final distribution plate, distribution holes for component B other than 5-(a) 5-(c): Among the distribution holes in the final distribution plate, the distribution hole for component A

Claims

1. In the cross section of a composite fiber made of two kinds of polyesters, component A and component B, component A is completely covered with component B, 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, and an eccentric core-sheath hollow composite raw cotton simultaneously satisfies the following (1) to (7): (1) Single fiber fineness is 1.0 to 7.0 dtex (2) Fiber length is 15 to 50 mm (3) It has one continuous hollow portion in the fiber axial direction, and its hollowness is 10 to 50%. (4) An oil agent containing polysiloxane is applied to the fiber surface in an amount of 0.2 to 0.8% by weight based on the weight of the fiber. (5) 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 (6) The perimeter of the fiber in the portion within 1.05 times the minimum thickness S is 1 / 3 or more of the perimeter of the entire fiber. (7) The fiber has a latent crimping ability that allows the number of spiral crimps to be 3 to 20 crimps / 25 mm when heat-treated at 100 to 200°C for 3 minutes or more without mechanical crimping.

2. A fiber sphere obtained by using the eccentric core-sheath hollow composite raw fiber according to claim 1.

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