Multifilament

Abstract

To provide a multifilament suitable for casual clothing applications such as a shirt, blouse and pant as a textile having not only stretching property for improving a movement following ability but also an excellent textile shape retention property and bending retuning property when folded, i.e., firmness.SOLUTION: There is provided a multifilament that is made of composite fibers composed of two types of polyester, wherein in a cross section of the composite fibers, the outermost fiber layer is covered with only one component polyester, a crimp elongation rate of the multifilament is 100% or more, and a 5% elongation stress is 2.5 cN / dtex or more.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a multifilament composed of composite fibers suitable for a textile having appropriate stretchability and stiffness that gives a comfortable feeling when worn.

Background Art

[0002] Synthetic fibers made of polyester, polyamide, etc. have characteristics such as excellent mechanical properties, dimensional stability, handleability, and functional processability, and are therefore widely used from clothing applications to non-clothing applications. Among them, as a basic characteristic in clothing textiles, in order to suppress the feeling of restraint when worn and enhance the followability of movements, the demand for stretch textiles aimed at the elongation and contraction of clothes that do not feel stress during movements has been high since ancient times, and various proposals have been made.

[0003] For example, from the viewpoint of imparting stretchability to the fiber itself, a composite fiber in which two types of polymers having different heat shrinkage characteristics are joined in a side-by-side type or an eccentric core-sheath type is a main example. The crimp structure exhibited by these composite fibers expands and contracts like a spring when an elongation deformation is applied, and can impart sufficient stretch performance to the fabric.

[0004] However, with the diversification of recent lifestyles, not only stretch performance but also further added value is required, and excellent stiffness is one of them. Here, "hari" refers to shape retention, meaning that the shape of the textile is not easily deformed when worn, and "koshi" refers to the bending return property when the textile is bent, that is, the resilience.

[0005] This stiffness is known to be highly related to the rigidity of the fibers and depends on the polymer type, fiber structure, etc. Generally, polyester has higher rigidity compared to polyamide, and among polyesters, polyethylene terephthalate (PET) has higher rigidity compared to polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT). Therefore, several composite fibers based on PET that can impart a stiffness feeling while having stretchability have been proposed.

[0006] In Patent Document 1, a composite fiber in which two types of PET with different molecular weights are joined side by side has been proposed. This composite fiber is suitable for obtaining a textile with stretchability and a stiffness feeling.

[0007] In Patent Document 2, a polyester composite fiber in which two different copolyester fibers are joined has been proposed.

[0008] In Patent Document 3, a composite fiber suitable for a textile with a soft texture like peach touch and good stiffness feeling has been proposed by composite false-twisting a side-by-side type polyester composite fiber with another polyester fiber.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] In Patent Document 1, a technique is disclosed in which a polyester composite fiber in which two types of polyesters having different molecular weights are joined can be stably spun by using a die in which the upstream portion of the die discharge hole merges symmetrically in terms of surface. The polymer composite flow immediately below the die discharge causes a discharge line curvature that greatly curves toward the high molecular weight component side due to the flow resistance difference caused by the molecular weight difference, leading to problems such as contacting the die surface or interfering with adjacent composite flows, which impairs the spinning stability. Applying the above-described die enables stable spinning.

[0011] However, when discharging the polymer composite flow from such a die, the flow resistance received by the high molecular weight component from the discharge hole wall surface inside the die hole is large, and excessive crystal nuclei are generated on the spinning line due to the deformation of the molecular chain, promoting orientation crystallization in the drawing process. As a result, the composite fiber has a low orientation in the amorphous part and low rigidity, so the stiffness feeling may be insufficient.

[0012] In Patent Document 2, by using a copolyester, it is possible to promote spinning stability and the orientation of the amorphous part in the drawing process. Certainly, by using a copolyester with excellent shrinkage properties, a composite fiber with excellent stretchability can be obtained. However, since the copolymer component responsible for the shrinkage properties is amorphous, the composite fiber has lower rigidity compared to the homopolymer, and the textile may have insufficient stiffness.

[0013] In Patent Document 3, a composite fiber that is a highly oriented undrawn yarn in which two types of polymers with different thermal shrinkage properties are joined and a mixed yarn obtained by composite false twisting with a fiber having a single fiber fineness of 0.2 to 0.9 dtex are used to impart properties such as stretchability and a peachy touch texture. Certainly, making a mixed yarn can improve the stiffness of the yarn bundle. However, for a composite fiber in which two types of polymers responsible for mechanical properties are joined, it may be difficult to sufficiently increase the orientation of the amorphous part in false twist drawing, and it may be difficult to achieve a stiffness feeling that satisfies the shape retention and bending recovery properties.

[0014] As described above, it is difficult to say that the composite fiber obtained by the prior art forms a satisfactory fiber structure, and there has been a demand for a fiber that can realize a textile excellent in a crispy feeling such as shape retention and bending resilience in addition to stretchability.

Means for Solving the Problems

[0015] The problems of the above-described prior art are solved as follows. (1) In a multifilament composed of a composite fiber composed of two types of polyesters, in the cross section of the composite fiber, the outermost layer of the fiber is covered only with one component of polyester, and the crimp elongation rate of the multifilament is 100% or more and the 5% elongation stress is 2.5 cN / dtex or more. (2) In the two types of polyesters constituting the composite fiber, the difference (MA - MB) between the weight average molecular weight MA of polyester A and the weight average molecular weight MB of polyester B is 5000 to 15000, and the multifilament according to (1) above. (3) The multifilament according to (1) or (2) above, wherein the single fiber fineness is 4.0 dtex to 8.0 dtex. (4) A fiber product containing the multifilament according to any one of (1) to (3) above.

Advantages of the Invention

[0016] The multifilament of the present invention is composed of a crimped composite fiber in which two types of polyesters having different molecular weights are joined, and can provide a multifilament having high rigidity by controlling the fiber structure. Therefore, not only stretchability for enhancing the followability of movement, but also shape retention of the textile and bending resilience when bent, that is, a multifilament suitable for casual clothing applications such as shirts, blouses, and pants fabrics can be provided as a textile having a high level of crispy feeling.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0018] Hereinafter, the present invention will be described together with preferred embodiments.

[0019] The multifilament of the present invention is composed of composite fibers made of two different types of polyesters, and in the cross-section of the composite fiber, the outermost layer of the fiber is covered only with one component of polyester.

[0020] The two types of polyesters constituting the composite fiber in the present invention refer to those having different polymer compositions, amounts of copolymer components, molecular weights, etc. Considering the expression of crimp, they are polyesters with different heat shrinkage characteristics.

[0021] That is, examples of the combination of the two types of polyesters of the present invention include various combinations such as PET / PET, copolymerized PET / PET, PBT / PBT, PBT / PET, PTT / PTT, PTT / PET, polyester-based elastomer / PET, etc. However, from the viewpoint of increasing the rigidity of the composite fiber, combinations of polymers whose main chain is polyethylene terephthalate, that is, combinations of PET / PET and copolymerized PET / PET, are particularly preferable ranges.

[0022] In addition, examples of the copolymerization component in the copolymerized PET include succinic acid, adipic acid, azelaic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, maleic acid, phthalic acid, isophthalic acid, 5-sodium sulfoisophthalic acid, etc. From the viewpoint of obtaining the effect of high shrinkage due to the copolymerization component and not impairing the rigidity of the composite fiber, the copolymerization ratio of the copolymerization component is preferably less than 3 mol%.

[0023] In addition, various additives such as inorganic substances such as titanium oxide, silica, and barium oxide, colorants such as carbon black, dyes and pigments, flame retardants, fluorescent brighteners, or ultraviolet absorbers may be contained in the polymer. In particular, titanium oxide is preferably contained in an amount of 1.0% by weight or more because the fiber surface can suppress glare by diffusely reflecting light, and functions such as anti-see-through and ultraviolet shielding inside the fiber can be obtained.

[0024] From the viewpoint of reducing the environmental load, in the polyester of the present invention, plant-derived biopolymers or recycled polymers may be used. As the recycled polymer, a recycled polymer recycled by any of chemical recycling, material recycling, and thermal recycling methods may be used.

[0025] As the fiber cross-section of the composite fiber in the present invention, like the eccentric core-sheath type illustrated in FIG. 1, the outermost layer of the fiber is covered only with one component of polyester, so that stretchability and stiffness can be achieved at the same time.

[0026] When manufacturing a composite fiber in which two types of polyester are simply joined as illustrated in Fig. 2 by discharging a polymer from a die, it will receive flow resistance from the discharge hole wall surface in the die hole. As a result, crystal nuclei are generated due to the deformation of molecular chains, and orientation crystallization is promoted by the stress in the stretching process. As a result, since the amorphous part has low orientation and the composite fiber has low rigidity, a crisp feeling cannot be obtained. In particular, when different molecular weights and copolymer components are used to exhibit stretchability, the flow resistance received by the component that exhibits heat shrinkage becomes larger, which is disadvantageous in terms of increasing the fiber rigidity.

[0027] Therefore, a fiber cross-section completely covered only with one component of polyester at the outermost surface of the fiber was adopted to achieve both stretchability and crispness. By covering the fiber cross-section with one component of polyester, the one-component polymer bears the flow resistance from the vicinity of the die wall surface where the flow resistance is the greatest, so that the formation of the fiber structure of the remaining one component is not inhibited, and the rigidity of the fiber derived from polyester can be exhibited.

[0028] From this perspective, in order to minimize the flow resistance with the die discharge hole wall surface, suppress excessive crystal nucleus generation, and promote fiber structure formation in the spinning and stretching processes, the polymer B (Fig. 1(2)) covering the outermost surface of the fiber is preferably a polymer with a low molecular weight that does not contribute to heat shrinkage.

[0029] In addition, when manufacturing a composite fiber in which two different types of polymers are joined by discharging a polymer from a die, if a polymer composite flow with a large molecular weight difference is discharged from the die, a yarn bend occurs in which the high molecular weight component curves toward the low molecular weight component side due to the flow resistance difference after discharge, and it may interfere with the polymer composite flow in contact with or adjacent to the die discharge surface, causing yarn breakage. However, in the multifilament of the present invention, since the component receiving the flow resistance is one component, yarn bending is suppressed, which is also preferable in terms of good spinning stability.

[0030] In the present invention, in terms of exhibiting stretchability, it is preferable that the center of gravity point of polymer A in the fiber inner layer (point a in Fig. 1) is separated from the center point of the composite fiber cross-section (point c in Fig. 1). When the composite fiber is heat-treated, a three-dimensional spiral structure can be formed by greatly curving toward the high-shrinkage component side, and good stretchability can be exhibited.

[0031] Further, in the composite fiber constituting the multifilament of the present invention, it is preferable that the ratio S / D of the minimum thickness S of polymer B covering the outermost surface of the fiber to the fiber diameter D is 0.01 to 0.1. By setting it within such a range, the crimp structure due to the heat shrinkage difference can be maximally exhibited, enabling good stretchability. From the viewpoint of maintaining yarn processing stability and fabric quality while exhibiting stretchability, a more preferable range is that S / D is 0.02 to 0.08.

[0032] In the composite fiber constituting the multifilament of the present invention, it is preferable that the ratio of the length on the circumference having the minimum thickness S to the circumference of the fiber cross-section (referred to as the S ratio) is 30% or more. This means that polymer A in the fiber inner layer exists along the contour of the fiber. Although good crimp is exhibited when the center of gravity point of polymer A in the fiber inner layer is sufficiently separated from the center of the composite fiber cross-section, from the viewpoint of maximizing the potential for crimp expression, the S ratio is more preferably 40 to 60%. Here, the length on the circumference having the minimum thickness S refers to the length of the minimum thickness S where the aforementioned S / D is 0.01 to 0.1.

[0033] Incidentally, the S / D and S ratios were calculated using image analysis software (WINROOF) by taking an image at a magnification at which 10 or more fibers could be observed with a transmission electron microscope (TEM) of the cross-section after embedding the fibers with an embedding agent such as an epoxy resin. At this time, metal staining was performed to clarify the contrast of the composite fibers by taking advantage of the fact that a staining difference between polymers could be created. For 10 or more fibers randomly extracted from each of the captured images, the minimum thickness indicated by the symbol S in Fig. 1 was measured for each fiber, and the average value was calculated in units of μm. The fiber diameter D was measured for each fiber in units of μm as the diameter obtained by converting the area of the fiber into a perfect circle, and the value obtained by rounding off the second decimal place of the average value was taken as the fiber diameter D. Also, the perimeter of the thickness portion within 1.05 times the minimum thickness S was determined, divided by the perimeter of the fiber cross-section, and multiplied by 100 to obtain the S ratio (%).

[0034] The multifilament of the present invention exhibits a crimp structure after heat treatment, and the crimp elongation rate, which is an index indicating stretchability, is 100% or more. The crimp elongation rate referred to here is obtained by preparing 10 multifilaments that have been kasen-wound so that the kasen length is 50 cm, tying the upper and lower two places with cotton thread, and bundling them together. This thread kasen is subjected to free heat treatment in water at 100°C for 15 minutes and air-dried for 5 hours or more. Then, an initial load of 0.0009 cN / dtex (1 mgf / d) is applied, the kasen length L0 after 30 seconds is measured, the load is removed, and then a load equivalent to 0.18 cN / dtex (0.2 gf / d) is applied. The value obtained by rounding off the decimal part of the value obtained from L0 and L1 measured for the kasen length L1 after 30 seconds according to the following formula was taken as the crimp elongation rate (%). Crimp elongation rate (%) = (L1 - L0) / L0 × 100 (%) If the crimp elongation rate is 100% or more, good crimp is developed, and good stretchability can be obtained even when made into a textile. From the viewpoint of appealing for better wearing comfort due to further stretchability, it is more preferable that the crimp elongation rate is 150% or more. Within such a range, it is more preferable in that it is excellent in swelling feeling due to a strong crimp structure. On the other hand, if the crimp elongation rate is too high, it may cause a hardening of the texture due to clogging. Therefore, the upper limit of the crimp elongation rate in the present invention is 250%.

[0035] In the multifilament of the present invention, in order to realize a textile excellent in stiffness and resilience, the 5% elongation stress is 2.5 cN / dtex or more. Here, stiffness means shape retention property, which means that the shape of the textile is hard to collapse during wearing. Resilience means the bending return property when the textile is bent, that is, the resilience. This stiffness and resilience is an element strongly correlated with the fiber rigidity. The greater the fiber rigidity, the more excellent the stiffness and resilience can be realized.

[0036] An example of the stress-strain curve of the multifilament of the present invention is shown in Fig. 3(3). In the curve shown here, the region up to the change in gradient (primary yield point) is the elastic deformation region, which refers to the region where the fiber structure can move reversibly. It has been found that the greater the deformation within this elastic deformation region is in terms of high elongation-high stress, the more excellent the bending return property and resilience are shown when made into a textile. That is, when the 5% elongation stress is 2.5 cN / dtex or more, a sufficient stiffness and resilience can be exhibited even when made into a textile, resulting in a textile excellent in wearing comfort. On the other hand, if the 5% elongation stress is too high, the fiber rigidity will increase excessively, resulting in a hard-textured textile. Therefore, the upper limit of the 5% elongation stress in the present invention is 3.5 cN / dtex.

[0037] Note that Fig. 3(4) shows an example of the stress-strain curve of a multifilament obtained by laminating two types of polymers side by side as illustrated in Fig. 2. In this case, due to insufficient formation of the fiber structure of the high molecular weight component, the rigidity of the fiber was insufficient, and it was difficult to sufficiently exhibit a crispy feeling as a textile.

[0038] The 5% elongation stress in the present invention was measured under the constant rate of elongation conditions shown in the standard test of JIS L1013(2010) 8.5.1 using a tensile testing machine for the sample. At this time, the grip interval was 200 mm, the tensile speed was 200 mm / min, and the test was carried out 10 times. The stress at 5% elongation was determined, and the value obtained by rounding off the second decimal place of the average value was defined as the 5% elongation stress. In addition, the strength was the value obtained by dividing the maximum strength in the measured stress-strain curve by the fineness, the elongation at the point indicating the maximum strength was defined as the elongation, and the toughness was determined from the following formula. Toughness = Strength (cN / dtex) × √(Elongation (%)) The multifilament of the present invention is preferably used as a high-value-added material that enjoys wearing comfort due to a crispy feeling such as excellent shape retention and bend-back property when bent while appealing to the followability of movements during wearing due to good stretchability. For this reason, it can be expected for casual clothing applications such as shirts, blouses, and trouser fabrics. From such a viewpoint, it is preferable that the strength of the multifilament of the present invention is 3.0 to 5.0 cN / dtex, the elongation is 20.0 to 40.0%, and the toughness is 18 or more. If it is within such a range, it is preferable from the viewpoints of high-order processing passability and repeated wearability as general clothing, and in addition, it is also preferable from the viewpoint of excellent yarn processing passability such as true twist and mixed fiber interlacing applied according to the application.

[0039] Here, in the case of actual twisting, the number of twists is preferably 500 to 2,500 turns / m. By performing actual twisting within such a range, not only latent crimp but also apparent crimp is imparted. By forming a more advanced crimp structure, not only the stretchability and resilience are improved, but also a swelling feeling is generated. Further, by mixing and interlacing the multifilament of the present invention with other fibers, while having the stretchability and stiffness which are the target effects of the multifilament of the present invention, aesthetic properties such as a texture can be imparted, or a feeling such as a smooth touch can be imparted, and multiple values can be imparted.

[0040] In view of maximizing the crimp characteristics and rigidity of the multifilament, for the two types of polyesters of the composite fiber constituting the multifilament of the present invention, the difference (MA - MB) between the weight average molecular weight MA of polyester A and the weight average molecular weight MB of polyester B is preferably 5,000 to 15,000. If the difference in molecular weight is 5,000 or more, a difference occurs in the stress applied to each component in the spinning and drawing process, and the high molecular weight component is highly oriented by being applied with high stress. Thus, the crimp characteristics and rigidity of the composite fiber constituting the multifilament of the present invention are improved. A more preferable difference in molecular weight (MA - MB) is 7,500 or more.

[0041] However, if the difference in molecular weight is too large, the low molecular weight component will be extremely poorly oriented, and yarn breakage and fuzz are likely to occur during high-order processing, easily causing defects in process passage. For this reason, the upper limit of the difference in molecular weight (MA - MB) is preferably 15,000.

[0042] Here, the molecular weight is measured using a gel permeation chromatography (GPC) device ("RI-104 type" manufactured by Showa Denko) by adding 5 mL of hexafluoroisopropanol as a solvent to 3 mg of the multifilament, gently stirring at room temperature, and then. From the obtained molecular weight distribution, the weight average molecular weight Mw calculated with the standard sample as monodisperse polymethyl methacrylate was taken as the molecular weight of the polymer. If the obtained molecular weight distribution is a single peak, the molecular weight difference (MA - MB) is 0, and if it is a double peak, the high molecular weight side is the high molecular weight polymer and the low molecular weight side is the low molecular weight polymer.

[0043] In the present invention, the molecular weight distribution adopts the differential molecular weight distribution. One type of polymer having a molecular weight within the range of ±30% of each peak value is defined, and the range from this peak value is defined as the distribution width. In the case of a double-peak molecular weight distribution as exemplified in FIG. 6, even though the peak values are clearly different, when the distribution widths overlap, the range of ±10% of the peak value is used as the distribution width to distinguish two types of polymers, and the molecular weight difference is calculated by measuring each molecular weight.

[0044] The fineness per filament of the multifilament of the present invention is preferably 4.0 dtex to 8.0 dtex. By setting the fineness per filament to 4.0 dtex or more, the rigidity as a multifilament becomes sufficiently high, resulting in a textile excellent in stiffness. Further, the fineness per filament of the multifilament of the present invention is preferably 8.0 dtex or less. Within such a range, since the rigidity of the multifilament is not too high, it does not become hard as a textile and does not impair the texture, and it is preferable because it has excellent processability until it becomes a final product.

[0045] In addition, the cross-sectional shape of the composite fiber constituting the multifilament of the present invention may be a circular cross-section, or may be a non-circular cross-section such as a flat or triangular shape as exemplified in FIG. 4. Generally, by making the fiber into a non-circular cross-section, the second moment of inertia of the cross-section, which is an index of the rigidity of the material, increases, so that the rigidity, gloss, crispness, etc. are improved. The multifilament of the present invention is no exception. By making it into a non-circular cross-section, it shows higher rigidity compared to a circular cross-section, can exhibit an excellent stiffness and crispness, and is preferable in that it can impart aesthetic properties such as a gloss and a unique texture such as crispness. When the composite fiber is made into a non-circular cross-section in this way, the degree of non-circularity is preferably 1.5 to 5.0, and from the viewpoint of the quality stability of the characteristics, the variation in the degree of non-circularity is preferably 1.0% to 20.0%. Within such a range, specific performance corresponding to the degree of non-circularity can be stably exhibited, indicating that the existing composite fibers have substantially the same cross-sectional shape. Furthermore, in order to exhibit a more remarkable effect compared to a circular cross-section, the degree of non-circularity is more preferably 2.0 to 5.0. In carrying out the present invention, considering the handleability, high-order passage properties, comfort, etc. during the processing of the composite fiber, the upper limit value of the degree of non-circularity is preferably 5.0.

[0046] Here, the degree of non-circularity is determined according to the method exemplified in FIG. 5. In the same way as the evaluation of the fiber diameter D, the cross-section of the composite fiber is two-dimensionally photographed. From the image, for 10 fibers arbitrarily extracted, using image processing software, the true circle that circumscribes the most convex tip of the outer periphery of the fiber cross-section is defined as the circumscribed circle (broken line 5 in FIG. 5), and further, the inscribed true circle is defined as the inscribed circle (broken line 6 in FIG. 5). The degree of non-circularity is the value obtained by rounding the third decimal place of (circumscribed circle diameter ÷ inscribed circle diameter). Also, the variation in the degree of non-circularity is a value calculated as the variation in the degree of non-circularity (coefficient of variation of the degree of non-circularity (CV%)) = (standard deviation of the degree of non-circularity / average value of the degree of non-circularity) × 100 (%), and the third decimal place is rounded off. The above operations are evaluated for the 10 photographed images, and the value obtained by rounding the second decimal place of the simple average value is taken as the degree of non-circularity and the variation in the degree of non-circularity.

[0047] The preferred manufacturing method of the multifilament of the present invention will be described in detail below.

[0048] As a method for producing the multifilament of the present invention, it is also possible to produce it by a melt spinning method for the purpose of producing long fibers, a solution spinning method such as a wet method and a dry-wet method, but from the viewpoint of enhancing productivity, the melt spinning method is preferable.

[0049] The multifilament of the present invention can be produced by a two-step method in which, after once winding up an undrawn yarn, it is drawn by a normal drawing machine so as to have a predetermined elongation at break. Further, it can also be produced by a direct spinning and drawing method (DSD method), which is a one-step method in which it is discharged from a spinneret, spun in a composite manner, and continuously drawn without once winding up the fiber yarn. It is important to control the fiber structure of the multifilament of the present invention at a high level. Considering the need to precisely control the tension from spinning to drawing and winding, the DSD method is most suitable as a method for producing the multifilament of the present invention.

[0050] Considering the object and effect of the present invention, the cross-section of the composite fiber constituting the multifilament of the present invention is most preferably an eccentric core-sheath type as illustrated in FIG. 1. From the viewpoints of the cross-sectional uniformity, quality, and stable production of the operation, it is preferable to use a distribution type spinneret as exemplified in JP-A-2011-174215, JP-A-2011-208313, and JP-A-2012-136804.

[0051] It is preferable that the polymer composite flow discharged from such a spinneret is such that the low molecular weight polymer B (FIG. 1(2)) completely covers the high molecular weight polymer A (FIG. 1(1)) as shown in FIG. 1. As a result, in addition to enabling the formation of a fiber structure according to the purpose without inhibiting the formation of the fiber structure in spinning and drawing, it is possible to suppress poor operability caused by the discharge line bending caused by the difference in the flow rates of the two types of polymers at the time of spinneret discharge.

[0052] When manufacturing the multifilament of the present invention, the spinning temperature is preferably set at a temperature of +20°C to +50°C higher than the polymer melting point. By setting the temperature more than +20°C higher than the polymer melting point, it is possible to prevent the polymer from solidifying and blocking in the spinning machine piping, and by setting the spinning temperature to +50°C or lower than the polymer melting point, excessive thermal degradation of the polymer can be suppressed.

[0053] Also, the discharge amount of the polymer is preferably 0.1 g / min / hole to 20.0 g / min / hole per discharge hole within the range where it can be melt-extruded while maintaining stability from the die discharge holes. At this time, it is preferable to consider the pressure loss at the die discharge holes, and it is preferable to determine the polymer discharge amount from the relationship between the melt viscosity of the polymer, the discharge hole diameter, and the discharge hole length so that the pressure loss is 0.1 MPa to 40 MPa.

[0054] When manufacturing the multifilament of the present invention, the ratio of polymer A to polymer B is preferably in the range of 30 / 70 to 70 / 30 in terms of weight ratio based on the discharge amount. From the viewpoint of stable production of multifilaments and long-term stability of the composite cross-section in addition to the object effects of the present invention, the ratio of polymer A / polymer B is more preferably in the range of 40 / 60 to 60 / 40.

[0055] When manufacturing the multifilament of the present invention, the spinning draft for spinning extruded from the die is preferably 250 or less. By suppressing excessive high orientation on the spinning line and sufficiently stretching in the stretching process to promote high crystallization and high orientation, the rigidity of the fiber is increased. In addition, in terms of manufacturing a composite fiber that satisfies the object effects of the present invention while suppressing poor yarn production due to the polymer flow discharged from the die holes staying on the lower surface of the die for a long time and the die surface being contaminated, the lower limit of the spinning draft is preferably 50. Here, the spinning draft is represented by the following formula. Spinning draft = Vs / V0 (Vs: Spinning speed (m / min), V0: Discharge linear speed (m / min)) When manufacturing the multifilament of the present invention, from the viewpoint of controlling the fiber structure, it is preferable to strictly control the cooling and solidification of the discharged polymer, and the cooling start point is preferably 130 mm to 200 mm from the lower surface of the die. In order to exhibit the excellent rigidity which is a characteristic of the multifilament of the present invention, it is preferable to gradually cool and solidify the high-temperature polymer composite flow discharged from the die as much as possible, induce thinning and elongation deformation in the high-temperature region, and subject it to the stretching process while homogenizing the orientation formation on the spinning line. The cooling start point is preferably 130 mm or more for gradual cooling and solidification. On the other hand, the rigidity of the fiber increases as the cooling start point is further downstream, but if the distance is excessively increased, the cooling and solidification of the fiber becomes inhomogeneous and appears as uneven fineness in the longitudinal direction of the yarn. This may damage the appearance of the textile such as dyeing unevenness, so the upper limit of the cooling start point is preferably 200 mm.

[0056] Also, in terms of controlling the cooling start point, in order to suppress the fluctuation of the die surface temperature as much as possible, it is preferable to install a heating device in the peripheral part of the die and control the die surface temperature, and the heating temperature of the heating device is preferably controlled within the range of ±15°C of the spinning temperature.

[0057] The distance from the die discharge surface to the oil supply position is preferably 2000 mm or less. By setting it within such a range, the sway of the yarn due to the cooling air can be suppressed and the yarn can be stably produced.

[0058] An undrawn yarn can be obtained by taking up the spun yarn discharged from the die surface. At this time, the spinning speed is preferably 500 m / min to 1500 m / min. By setting the spinning speed to 500 m / min or more, the spinning tension is moderately increased and the yarn sway is reduced. Also, in order to enable high magnification stretching and obtain fibers with high rigidity, the upper limit of the spinning speed is preferably 1500 m / min.

[0059] In the drawing process, it is preferable to perform drawing so that the elongation of the obtained fibers is 20.0% to 40.0%. The draw ratio may be selected within the range of 2.5 times to 6.0 times. By setting the draw ratio to 2.5 times or more, stable drawing becomes possible. Also, by setting the draw ratio to 6.0 times or less, the generation of fiber fuzz can be suppressed, and stable drawing becomes possible. Note that the draw ratio refers to the ratio between the first heating roller and the final heating roller (that is, the draw ratio is the final heating roller speed / the first heating roller speed ratio). The number of drawing stages may be 1 stage or multiple stages of 2 stages or more, and it may be appropriately selected according to the intended use.

[0060] The temperature of the first heating roller is preferably in the range of 30°C to 110°C, and from the point of stably and uniformly drawing polyethylene terephthalate, it is preferably set to 60°C to 95°C. Also, the temperature of the final heating roller is preferably 130°C to 180°C. By setting the temperature of the final heating roller to 130°C or higher, effective control of molecular orientation and promotion of crystallization can be achieved. Also, by setting the temperature of the final heating roller to 180°C or lower, fiber fusion on the heating roller does not occur, so the drawability does not decrease, and excessive molecular mobility is suppressed, and molecular orientation spots in the yarn longitudinal direction of the fiber can be suppressed.

[0061] Regarding the multifilament obtained as described above, it may be used as it is as a textile, or it may be used as a textile after imparting yarn processing such as true twisting or mixed fiber interlacing according to the application.

[0062] Here, for true twisting, the twist number is preferably 500 to 2500 turns / m. By applying true twisting within such a range, not only latent crimp but also apparent crimp is imparted.

[0063] Also, the method for mixed fiber interlacing of the multifilament of the present invention is not particularly limited, and general mixed fiber methods such as interlace mixed fiber and taslan mixed fiber can be used.

[0064] The multifilament of the present invention is preferably formed into a woven or knitted fabric, and further, if necessary, by performing post-processing involving heat treatments such as conventional scouring, relaxation treatment, intermediate heat setting, dyeing, and finishing heat setting, crimping due to the shrinkage difference is developed, and in addition to good stretchability, a woven or knitted fabric suitable for clothing textiles that exhibits appropriate stiffness can be obtained.

Example

[0065] The multifilament of the present invention will be specifically described below with reference to the following examples. The following evaluations were performed for the examples and comparative examples.

[0066] A. Molecular weight of polymer To 3 mg of the multifilament, 5 mL of hexafluoroisopropanol is added as a solvent, and it is gently stirred at room temperature. Then, it is measured using a gel permeation chromatography (GPC) apparatus (manufactured by Showa Denko, model "RI-104"). From the obtained molecular weight distribution, the weight average molecular weight Mw calculated with the standard sample as monodisperse polymethyl methacrylate was taken as the molecular weight of the polymer. The molecular weight distribution adopted the differential molecular weight distribution. One type of polymer having a molecular weight within the range of ±30% of each peak value was defined as one type, and the range from this peak value was defined as the distribution width. In the case of a double-peak molecular weight distribution as exemplified in FIG. 6, even though the peak values were clearly different, when the distribution widths overlapped, the range of ±10% of the peak value was used as the distribution width and distinguished into two types of polymers, and each molecular weight was measured to calculate the molecular weight difference.

[0067] B. Minimum thickness S, fiber diameter D, minimum thickness S ratio After embedding the multifilament with an embedding agent such as epoxy resin, an image was taken at a magnification at which 10 or more fibers could be observed with a transmission electron microscope (TEM) for this cross-section, and it was calculated using image analysis software (WINROOF). At this time, by taking advantage of the fact that a staining difference between polymers can be achieved by performing metal staining, the contrast of the composite fiber was clarified. For 10 or more fibers randomly extracted from each of the taken images, the minimum thickness indicated by the symbol "S" in Fig. 1 was measured for each fiber, and the average value was calculated in units of μm. The fiber diameter D was measured for each fiber in units of μm as the diameter obtained by converting the area of the fiber into a perfect circle, and the value obtained by rounding off the second decimal place of the average value was taken as the fiber diameter D. Also, the perimeter of the thickness portion within 1.05 times the minimum thickness S was obtained, divided by the perimeter of the entire fiber, and multiplied by 100, and the resulting value was taken as the ratio (%) of the minimum thickness S to the perimeter of the entire fiber.

[0068] C. Degree of irregularity, variation in degree of irregularity From the images taken in item B, for 10 fibers randomly extracted, using image processing software, the perfect circle that most circumscribes the tip of the convex part on the outer periphery of the fiber cross-section was defined as the circumscribed circle (broken line 5 in Fig. 5), and further, the diameter of the inscribed perfect circle was defined as the inscribed circle (broken line 6 in Fig. 5). Then, from the degree of irregularity = circumscribed circle diameter ÷ inscribed circle diameter, the value was obtained up to the third decimal place, and the value obtained by rounding off the third decimal place was taken as the degree of irregularity. Also, the variation in the degree of irregularity as referred to in the present invention is a value calculated as the variation in the degree of irregularity (degree of irregularity CV%) = (standard deviation of the degree of irregularity / average value of the degree of irregularity) × 100 (%) from the average value and standard deviation of the degree of irregularity, and the third decimal place is rounded off. The above operations were evaluated for the 10 images taken, and the values obtained by rounding off the second decimal place of the simple average value were taken as the degree of irregularity and the variation in the degree of irregularity.

[0069] D. Denier per filament Using the fiber diameter D calculated in item B and the known polymer density (PET: 1.38 g / cm 3 , PBT: 1.32 g / cm 3 ), the weight per 10,000 m was calculated, and the value obtained by rounding off the second decimal place was taken as the denier per filament (dtex) of the multifilament.

[0070] E. 5% Elongation Stress, Strength, Elongation, Toughness The 5% elongation stress in the present invention was measured under the constant rate of elongation conditions shown in the JIS L1013 (2010) 8.5.1 standard test using a tensile testing machine for a sample. At this time, the gripping interval was 200 mm, the tensile speed was 200 mm / min, and the test was carried out 10 times. The stress at 5% elongation was determined, and the value obtained by rounding the second decimal place of the average value was defined as the 5% elongation stress. Also, the value obtained by dividing the maximum strength in the measured stress-strain curve by the fineness was defined as the strength, the elongation at the point showing the maximum strength was defined as the elongation, and the toughness was determined from the following formula. Toughness = Strength (cN / dtex) × √(Elongation (%)) F. Crimp Elongation Rate Ten multifilaments were cased so that the cased length became 50 cm, and the upper and lower two places were tied with cotton thread and made into a bundle. This cased thread was subjected to free heat treatment in water at 100 °C for 15 minutes and air-dried for 5 hours or more. Then, an initial load of 0.0009 cN / dtex (1 mgf / d) was applied, the cased length L0 after 30 seconds was measured and the load was removed. Next, a load equivalent to 0.18 cN / dtex (0.2 gf / d) was applied, and the cased length L1 after 30 seconds was measured. The value obtained by rounding the decimal part of the value determined by the following formula from L0 and L1 was defined as the crimp elongation rate (%). Crimp elongation rate (%) = (L1 - L0) / L0 × 100 (%) G. Fabric Properties (Stretchability) The composite fiber wound up through the spinning and drawing process was subjected to a twisting process of 1300 turns / m using a double twister, and then used for warp and weft and woven into a 3 / 1 twill fabric using an air jet loom. Here, the fabric refers to the fabric woven in a 3 / 1 twill weave after adjusting the number of fibers so that the cover factor (CFA) in the warp direction is 1800 and the cover factor (CFB) in the weft direction is 1200. However, CFA and CFB are the values obtained by measuring the warp density and weft density of the fabric in a 2.54 cm section according to JIS-L-1096:2010 8.6.1, and CFA = warp density × (fineness of warp) 1 / 2 , CFB = weft density × (fineness of weft) 1 / 2 by the formula.

[0071] For this woven fabric, evaluation was carried out on a fabric that had been subjected to continuous scouring at 98°C, liquid flow relaxation at 130°C, intermediate setting at 180°C, and indigo dyeing at 130°C using disperse dyes, followed by a finishing set at 160°C.

[0072] The stretchability was evaluated in accordance with the elongation rate A method (low-speed elongation method) described in Clause 8.16.1 of JIS L1096:2012. The load at 17.6 N (1.8 kg) in the strip method was adopted, and the test conditions were a sample width of 5 cm × length of 20 cm, a clamp interval of 10 cm, and a tensile speed of 20 cm / min. The simple arithmetic mean of the results of conducting the test three times in the transverse direction of the fabric was obtained, and the value obtained by rounding off the decimal part was taken as the fabric elongation rate (%), and the stretchability was determined in three grades based on the following criteria from the obtained fabric elongation rate. A: Excellent stretchability (30 ≤ fabric elongation rate) B: Stretchability (20 ≤ fabric elongation rate < 30) C: Poor stretchability (fabric elongation rate < 20) H. Fabric properties (stiffness, firmness) For the fabric produced in Item G, using a pure bending tester (KES-FB2) manufactured by Kato Tech, a 20 cm × 20 cm fabric was gripped with an effective sample length of 20 cm × 1 cm for evaluation. The stiffness was determined by the difference in bending moment per unit width (gf·cm / cm) between a curvature of 0.5 cm -1 and 1.5 cm -1 when bent under the condition of a maximum curvature of ±2.5 cm in the weft direction -1 divided by the curvature difference of 1 cm -1 and the difference in bending moment per unit width (gf·cm / cm) between a curvature of -0.5 cm -1 and -1.5 cm -1 divided by the curvature difference of 1 cm -1 The average value of these was calculated. This operation was performed three times for each location, and the simple arithmetic mean of the results for a total of 10 locations was obtained. After rounding off the fourth decimal place, the value divided by 100 was taken as the bending stiffness B×10 -2 (gf·cm 2 / cm). The obtained bending stiffness B×10 -2Based on the following, the rigidity, i.e., the stiffness, was determined in three stages. A: Excellent stiffness (2.0 ≤ flexural rigidity B × 10 -2 ) B: Having stiffness (1.5 ≤ flexural rigidity B × 10 -2 < 2.0) C: Inferior in stiffness (flexural rigidity B × 10 -2 < 1.5) The resilience was calculated as the width (gf·cm / cm) of the hysteresis at a curvature of ±1.0 cm when bent in the weft direction. This operation was performed three times for each location, and the simple arithmetic mean of the results for a total of 10 locations was obtained. After rounding the fourth decimal place, the value divided by 100 was taken as the flexural recovery 2HB × 10 -1 (gf·cm / cm). Based on the following, the resilience, i.e., the resilience, was determined in three stages from the obtained flexural recovery 2HB × 10 -2 (gf·cm / cm). -2 Based on the following, the resilience, i.e., the resilience, was determined in three stages. A: Excellent resilience (flexural recovery 2HB × 10 -2 ≤ 0.8) B: Having resilience (0.8 < flexural recovery 2HB × 10 -2 ≤ 1.4) C: Inferior in resilience (1.4 < flexural recovery 2HB × 10 -2 ) [Example 1] Using the technology of the composite die described in JP-A-2011-174215 so as to obtain the fiber cross-section shown in FIG. 1, polyethylene terephthalate (PET1) as the A component having a high molecular weight and polyethylene terephthalate (PET2) as the polymer B having a low molecular weight were used. The volume ratio was adjusted to PET1 / PET2 = 50 / 50, and it was discharged from the die at a spinning temperature of 295°C. The cooling start point of the discharged composite polymer stream was 140 mm, and the heating temperature of the heating device installed between the die surface and the cooling start point was 295°C. After cooling by an air cooling device, an oil agent was applied, and composite fibers were produced by the DSD method. At this time, the oil supply position was 1600 mm from the die discharge surface.

[0073] The yarn extruded from the nozzle was drawn at a draw ratio of 3.66 times between heating rollers with a spinning speed of 1000 m / min (spinning draft 90), a first heating roller temperature set at 90 °C, and a final heating roller temperature set at 145 °C, and a 56 detx - 12 - filament multifilament was collected.

[0074] The composite fiber constituting the obtained multifilament has an eccentric core - sheath cross - section illustrated in Fig. 1. The ratio S / D of the minimum thickness S to the fiber diameter D is 0.03, the ratio of the minimum thickness S to the entire perimeter of the fiber is 50%, and the degree of irregularity is 1.0. Also, since the multifilament has undergone the spinning and drawing processes without impairing the fiber structure formation, it has sufficient mechanical properties to withstand practical use, with a strength of 4.2 cN / dtex, an elongation of 25.6%, and a toughness of 21. The 5% elongation stress is 3.1 cN / dtex, the crimp elongation rate is 188%, and it has a high rigidity derived from PET while having excellent stretchability due to the manifestation of crimp by the heat shrinkage difference.

[0075] When the molecular weight of the multifilament was measured by GPC, it had a molecular weight distribution with a double peak as shown in Fig. 6. The polymers were distinguished by taking the distribution width from each peak value, with the high - molecular - weight side being polymer A and the low - molecular - weight side being polymer B, and the molecular weights were calculated. The molecular weight of polymer A is 25,700, the molecular weight of polymer B is 16,900, and the weight - average molecular weight difference is 8,800.

[0076] Next, the obtained multifilament was twisted at 1300 turns / m with a double twister and then woven into a 3 / 1 twill fabric on an air - jet loom using it as the warp and weft. For this woven fabric, continuous scouring at 98 °C, liquid - flow relaxation at 130 °C, intermediate setting at 180 °C, and indigo dyeing at 130 °C using disperse dyes were carried out, and further a finishing set at 160 °C was applied to collect the fabric. The obtained fabric shows good stretchability (fabric elongation rate: 33%) due to the crimp structure of the multifilament, while also showing good stiffness (bending hardness B: 2.3×10-2 gf·cm 2 / cm) and stiffness (flexural recovery 2HB: 0.6×10 -2 gf·cm / cm), and it was a fabric with excellent stiffness. The results are shown in Table 1.

[0077] [Comparative Example 1] Unlike the examples, it was carried out according to Example 1 except that it was produced using a co-extrusion die that resulted in a side-by-side type fiber cross-section as illustrated in Fig. 2(a).

[0078] The resulting multifilament had a low 5% elongation stress because the amorphous part on the high molecular weight side was poorly oriented and the composite fiber had low rigidity due to the flow resistance received from the wall surface of the discharge holes in the die. In the fabric, it was inferior in stiffness compared to Example 1. The results are shown in Table 1.

[0079] [Examples 2, Comparative Example 2] In Example 2, the composite fiber was produced with a spinning speed of 1500 m / min, and in Comparative Example 2, the composite fiber was produced with a spinning speed of 2000 m / min, and otherwise it was carried out according to Example 1.

[0080] In Example 2, even when the spinning speed was changed, it showed good 5% elongation stress and crimp elongation rate. Also, in the fabric, it exhibited good stretchability and stiffness. On the other hand, in Comparative Example 2, due to the too high spinning speed, the fiber structure formation in the drawing process was insufficient, and the resulting composite fiber had a low crimp elongation rate and 5% elongation stress. The fabric was significantly inferior in stretchability and stiffness compared to Example 1. The results are shown in Table 1.

[0081] [Examples 3, 4] In Examples 3 and 4, it was carried out according to Example 1 except that the polymer discharge amount was changed so that the fineness of the single filament of the multifilament was 7.0 and 2.8, respectively.

[0082] In the multifilament of Example 3, due to the increase in the fineness of the single filament, it exhibited high rigidity even when compared with Example 1, and was a stretch fabric that demonstrated an excellent crispness when made into a woven fabric.

[0083] In the multifilament of Example 4, by reducing the fineness of the single filament, it was a stretch fabric that had an appropriate crispness and a soft touch when made into a woven fabric. The results are shown in Table 1.

[0084] [Comparative Example 3] In Comparative Example 3, the polymer discharge amount was changed so that the fineness of the single filament of the multifilament was 0.8, and it was carried out according to Example 1 except that the cooling start point was changed to 97 mm to suppress yarn unevenness.

[0085] In Comparative Example 3, in addition to the fact that the fineness of the single filament was too thin, the polymer flow discharged from the die was rapidly cooled, so that satisfactory stretching was not performed, the 5% elongation stress was low, and it was greatly inferior in crispness when made into a woven fabric. The results are shown in Table 1.

[0086] [Examples 5 and 6] In Example 5, the polymer molecular weight of Component A was changed (PET3), and in Example 6, it was changed to 7 mol% isophthalic acid copolymerized polyethylene terephthalate (co-PET), and it was carried out according to Example 1.

[0087] In Example 5, from the GPC measurement results, the molecular weight of Polymer A was 30,900, and the molecular weight difference between Component A and Component B was 14,000, which was higher than that of Example 1. As a result, the rigidity of the multifilament increased, and the shrinkage characteristics also increased, so the crimp elongation rate also increased. Therefore, the fabric was also a fabric that achieved both excellent stretchability and crispness.

[0088] In Example 6, by introducing a copolymer component, it was a multifilament that exhibited high crimp properties while having the rigidity derived from PET, and was a fabric rich in stretchability compared to Example 1. The results are shown in Table 1.

[0089] [Comparative Example 4] It was carried out according to Example 1 except that polybutylene terephthalate (PBT) was used as Component A.

[0090] In Comparative Example 4, due to the molecular structure of PBT, although the stretchability was good, the fiber rigidity was much inferior compared to Example 1. As a fabric, it was a stretch fabric rich in flexibility, but was much inferior in the feeling of stiffness. The results are shown in Table 1.

[0091] [Examples 7, 8] In Example 7, it was carried out according to Example 1 except that the die orifice shape was changed so that the fiber cross-section became the flat shape illustrated in Fig. 4(a), and in Example 8, so that it became the triangular shape illustrated in Fig. 4(b).

[0092] In the multifilament of Example 7, since the center of gravity of Polymer A and the center of the composite fiber cross-section are separated by making the fiber cross-section flat compared to Example 1, a high crimp elongation rate is exhibited compared to Example 1, and due to the improvement in rigidity by the increase in the second moment of the cross-section, as a fabric, it exhibited excellent stretchability and a feeling of stiffness.

[0093] In the multifilament of Example 8, by making the fiber cross-section triangular, the rigidity was increased compared to Example 1, so it was an excellent value-added material with an excellent feeling of stiffness in the fabric and a crisp feeling in the texture. The results are shown in Table 1.

[0094] [Comparative Example 5] It was carried out according to Example 1 except that it was produced using a composite die that resulted in a side-by-side type fiber cross-section with a flat shape as illustrated in Fig. 2(b).

[0095] In Comparative Example 5, although it exhibited stretchability comparable to that of Example 1 due to its flat shape, it showed low rigidity due to the flow resistance received from the wall surface of the discharge hole in the die, similar to Comparative Example 1, and the stiffness feeling was inferior to that of Example 1. The results are shown in Table 1.

[0096]

Table 1

Explanation of Signs

[0097] 1: Polymer A 2: Polymer B a: Center of gravity point of Polymer A in the cross-section of the composite fiber c: Center of gravity point of the cross-section of the composite fiber S: Minimum thickness of Polymer B in the eccentric core-sheath cross-section D: Fiber diameter 3: An example of the stress-strain curve of the multifilament of the present invention 4: An example of the stress-strain curve of the multifilament composed of composite fibers laminated in a side-by-side type 5: Circumscribed circle 6: Inscribed circle 7: Distribution width

Claims

1. In a multifilament composed of conjugate fibers made of two types of polyester, in the cross-section of the conjugate fiber, the outermost layer of the fiber is covered only with one component of polyester, a multifilament having a crimp elongation rate of 100% or more and a 5% elongation stress of 2.5 cN / dtex or more.

2. In the two types of polyester constituting the conjugate fiber, the multifilament according to claim 1, wherein the difference (MA - MB) between the weight average molecular weight MA of polyester A and the weight average molecular weight MB of polyester B is 5000 to 15000.

3. The multifilament according to claim 1 or 2, wherein the single fiber fineness is 4.0 dtex to 8.0 dtex.

4. A fiber product containing the multifilament according to claim 1 or 2.

Images