An eccentric sheath-core type nylon-spandex composite fully drawn yarn and a preparation method thereof

Abstract

The present application provides an eccentric sheath-core type nylon-spandex composite fully drawn yarn and a preparation method thereof, which belongs to the technical field of filament preparation of sheath-core structure. It is an eccentric sheath-core structure with an opening in the cross section so that the core layer is partially exposed, the core layer is a thermoplastic polyurethane component, the sheath layer is a nylon 6 component, and the sheath-core composite volume ratio is 35-50:65-50. The fully drawn yarn of the present application has good spiral curling elasticity and high strength. The core layer of the sheath-core structure has an eccentric opening "exposed", and because the opening is small, it can effectively avoid whitening during dyeing and has good dyeing uniformity.

Description

Technical Field

[0001] The present application relates to an eccentric sheath-core nylon-spandex composite fully drawn yarn and a preparation method thereof, belonging to the technical field of preparation of filaments with a sheath-core structure. Background Art

[0002] The interweaving of nylon and spandex in weaving is mainly due to the similarities in dyeing and finishing conditions of the two, as well as the excellent hygroscopicity of nylon and the high elasticity of spandex. The interwoven fabrics are widely used in skin-friendly fabrics, such as underwear, swimwear and stockings. However, when exposed spandex is directly used for weaving, there are problems with spandex aging and dyeing color difference. In order to make up for this defect, nylon-coated spandex is usually processed into spandex-coated yarn, but nylon-spandex-coated yarn has problems such as long processing cycle, complicated process, and spandex whitening. In recent years, with the maturity of two-component composite spinning technology and breakthroughs in new materials, two-component composite elastic fibers such as T400&T800 have been developed. T400&T800 are still polyester fibers, which cannot be compared with nylon in terms of hygroscopicity and feel, and there is a certain gap in elasticity with nylon-spandex-coated yarn.

[0003] CN1936123A discloses a PA6 / PU composite three-dimensional curled fiber with a fiber strength of more than 2.8 cN / dtex, an elongation of more than 30%, a curl number of more than 10 / 25mm, an elastic elongation of more than 80%, and a tensile elasticity of more than 90%. However, the defects are: the eccentric skin-core structure of the composite fiber is a closed structure, the fiber elasticity will be affected to a certain extent, and the uniformity of the fiber cross-sectional shape is difficult to ensure.

[0004] CN202849648U discloses a spandex coated yarn, which prevents the problem of uneven color when the spandex coated yarn has a core exposure phenomenon, but has the following defects: the production process of the spandex coated yarn is long, the product cannot achieve fine denier, the curled coated yarn is not easy to weave, and there are limitations in the procurement of raw materials.

[0005] CN105887218A discloses a nylon high shrinkage fiber with the characteristics of soft drape, elegant luster, and delicate touch. However, the product adopts single-component spinning and cannot form the self-curling elastic effect produced by the different thermal shrinkage of the two components in the composite spinning.

[0006] CN109355716A discloses a method for producing a nylon 6 and nylon 66 parallel composite elastic fiber, but the composite structure provided is parallel, and the two materials are completely exposed. Since the two materials have different color absorption rates, color difference is likely to occur when the woven fabric is dyed; the two raw materials only differ in viscosity, and contribute less to the elastic curl variation range, and the resulting curl elasticity is subject to certain restrictions.

[0007] CN104975362A discloses a nylon high-shrinkage composite split-flap FDY, which does not contain spandex but has good elasticity. However, it is not specified what raw material its high-shrinkage component is made of. If it is a split-flap composite structure, it is generally used for polyester-nylon composites, and the fibers are opened by mechanical or alkali reduction method to process dense fabrics such as suede, rather than elastic fabrics. If the high-shrinkage component is nylon, the two components of the split-flap composite will produce weak curling elasticity. Summary of the invention

[0008] In view of this, the present application first provides an eccentric sheath-core nylon-spandex composite fully drawn yarn, which is a two-component product with good spiral curl elasticity and a strength higher than 3.5 cN / dtex. The core layer of the sheath-core structure has an eccentric opening "exposed". Due to the small opening, it can effectively avoid whitening during dyeing and has good dyeing uniformity.

[0009] Specifically, the present application is implemented through the following scheme:

[0010] The invention discloses an eccentric sheath-core type nylon-spandex composite fully drawn yarn, which is obtained by compounding a nylon 6 component and a thermoplastic polyurethane component, and has an eccentric sheath-core structure with an open cross section so that the core layer is partially exposed. The nylon 6 component is the sheath layer, the thermoplastic polyurethane component is the core layer, and the composite volume ratio of the sheath layer to the core layer is 35-50:65-50.

[0011] The composite fully drawn yarn of the present application is used as a substitute for the nylon-spandex coated yarn, which is a new type of elastic fiber. It overcomes the problems of spandex aging and difficulty in fine denier of the coated yarn. The eccentric skin-core structure with an opening can not only maintain a high strength of ≥3.5 cN / dtex, but also the appropriate eccentric opening "exposed" of the core layer ensures the uniformity of dyeing. The different thermal shrinkage and recovery force of the two components give the fully drawn yarn good spiral curl elasticity.

[0012] Further, as a preference:

[0013] The volume proportion of the nylon 6 component is 50%, and the volume proportion of the thermoplastic polyurethane component is 50%; alternatively, the volume proportion of the low-viscosity nylon 6 component is 35%, and the volume proportion of the thermoplastic polyurethane component is 65%.

[0014] The central angle θ of the eccentric opening is 10-35°. The central angle θ of the exposed part of the core layer is a key indicator affecting the degree of dye penetration. As the central angle increases, the more dye is infiltrated. However, if the central angle is too large, the color difference between the two components will become larger. When controlled within the above range, the dyeing uniformity is basically maintained above level 4.

[0015] At the same time, the applicant also provides a method for preparing the above-mentioned drawn yarn, comprising the following steps:

[0016] (1) Slice pretreatment: Low viscosity nylon 6 slices and thermoplastic polyurethane slices are used as raw materials. Low viscosity nylon 6 slices are dried by nitrogen heating to a moisture content of ≤800 ppm, and thermoplastic polyurethane slices are dried by nitrogen heating to a moisture content of ≤50 ppm. The dried low viscosity nylon 6 slices and thermoplastic polyurethane slices are respectively transported to their respective dry slice silos, and the silos are filled with nitrogen for protection. The nitrogen pressure is 0.02 Mpa and they are kept ready for use.

[0017] (2) Preparation of nylon-spandex composite undrawn yarn: Dried low-viscosity nylon 6 chips and thermoplastic polyurethane chips are respectively fed into the main screw and the auxiliary screw at a volume percentage of 35-50:65-50. The main screw extruder is melt-extruded to form nylon 6 melt, which is metered by a metering pump and fed into the main channel of the spinneret; the auxiliary screw extruder is melted and extruded to form thermoplastic polyurethane melt, which is accurately metered by a metering pump, fed into the auxiliary channel of the spinneret and compounded with the nylon 6 melt in the main channel, and then extruded through the spinneret hole, cooled, oiled, and wound to obtain UDY yarn cake, i.e. nylon-spandex composite undrawn yarn.

[0018] The main screw extruder is equipped with four heating zones in the melt extrusion process, with heating temperatures of 250-270°C in each zone, melt pressure of 10-15 MPa, and main box heating temperature of 235-260°C. By changing the heating temperature of the main screw extruder and the temperature of biphenyl vapor, the performance of the nylon 6 melt can be properly adjusted, which is then reflected in the difference with the thermoplastic polyurethane melt, and in terms of performance indicators, the elongation at break, breaking strength, boiling water shrinkage and fiber crimp number of the fully drawn yarn are changed.

[0019] The melt extrusion process of the secondary main screw extruder is equipped with four heating zones, each zone has a heating temperature of 215-235 ℃, a melt pressure of 10-15 Mpa, a melt residence time of ≤15 min, and a secondary box heating temperature of 220-240 ℃. The heating temperature of the secondary screw extruder and the biphenyl vapor temperature can be changed to appropriately adjust the performance of the thermoplastic polyurethane melt, which is then reflected in the difference with the nylon 6 melt, and the performance indicators are manifested in the changes in the elongation at break, breaking strength, boiling water shrinkage and fiber crimp number of the fully drawn yarn.

[0020] (3) Post-processing: The nylon-spandex composite undrawn yarn is drawn, heated, relaxed, shaped, oiled and wound to obtain the nylon-spandex composite fully drawn yarn.

[0021] The nylon 6 melt and the thermoplastic polyurethane melt first flow in their respective channels and finally flow into the spinneret, where they are compounded by injecting the thermoplastic polyurethane melt into the nylon 6 melt, thus solving the problems of the nylon-spandex coated yarn having many processing steps, long processing time and difficult weaving processing.

[0022] Further, as a preference:

[0023] The relative viscosity of the low-viscosity nylon 6 chips (i.e., the ratio of the flow time of 1% of the chips dissolved in 95.7% sulfuric acid solution to the flow time of sulfuric acid itself, measured by an Ubbelohde viscometer) is 2.2-2.45. The relative viscosity of nylon 6 chips used for FDY is generally distributed in the range of 2.51-2.53 (Tan Ziliang, The Effect of Nylon 6 Chip Quality on FDY Spinning, 1999-3, No. 1, p1-4), and some can even be as high as 3.4-3.6 (Yang Feng, Analysis of Polymerization Production Technology of High-viscosity Chips for Industrial Use of Nylon 6, 2004-4, Vol. 23, No. 2, p35-40). In this case, low-viscosity nylon 6 chips with a relative viscosity of 2.2-2.45 are used as the skin structure, and the setting of this viscosity is conducive to its good coating properties.

[0024] The hardness of the thermoplastic polyurethane slice is 75-80 HA (Shore hardness), and preferably 77 HA. The hardness of polyurethane is generally 25-98° Shore. The hardness of the thermoplastic polyurethane slice is set at a relatively high level. During composite molding, it can play a good supporting role as a core layer to avoid being crushed by the peripheral skin layer and affecting its molding effect.

[0025] The skin-core structure of this case has a nylon 6 component formed by low-viscosity nylon 6 slices as the skin layer, and a thermoplastic polyurethane component formed by high-hardness thermoplastic polyurethane slices as the core layer. The former gives the skin layer good inclusiveness and a wider deformable range, ensuring that the fully drawn yarn has good tensile properties; the latter gives the core layer good supporting properties and a relatively dense structure, ensuring that the fully drawn yarn has high strength. The combination of the two gives the composite fully drawn yarn a good molding effect, and the final product has high breaking strength, good breaking elongation and boiling water shrinkage, and a stable fiber curl number.

[0026] In step (2), the cooling temperature is 25-30°C, the cooling wind speed is 0.35-0.45 m / sec, and the monomer suction and discharge is 4-6 m / min.

[0027] In step (2), the oiling is carried out in multiple passes, firstly applying the nylon oil agent, and then applying the spandex oil agent. Multiple passes of oiling are beneficial to improving the bonding force of the composite fiber and improving the friction tension of unwinding and weaving.

[0028] In step (2), the winding speed is 400-650 m / min, and the winding angle is 5-7°. The winding speed is not easy to be too high during the undrawn yarn forming process, but setting the above winding angle is conducive to forming the curled primary form.

[0029] In step (3), the drafting ratio is 3-3.5, the temperature of the heated hot plate is 80-100°C, the temperature of the hot plate for relaxation and setting is 100-120°C, the winding speed is 500-800 m / min, and the winding angle is 6-8°. Heating and relaxing can eliminate the internal stress of the thermoplastic polyurethane component in the composite yarn caused by drawing, and improve the stability of the fully drawn yarn structure; while the winding speed mainly manifests itself as a stretching effect on the undrawn yarn, and is manifested as a breaking strength in terms of parameters, especially when combined with the drafting ratio, it changes the stretching effect on the fiber. At the same time, changes in the winding speed will also affect the number of three-dimensional curling structures, and are manifested in parameters as changes in the number of fiber curls, so the winding speed should not be too large.

[0030] The preparation process of the above-mentioned nylon-spandex composite fully drawn yarn has completely changed the current situation. The production process flow is greatly shortened, and the fully drawn yarn can meet the requirements of nylon-spandex coated yarn in terms of performance. Thinner nylon-spandex composite yarn products can be achieved. The fibers are in a straight yarn state when the yarn bobbin is unwound and woven, and the problem of difficult weaving of curly coated yarn can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the cross-sectional structure of the spinneret in this application;

[0032] Figure 2 It is a schematic diagram of the cross-sectional structure of the nylon-spandex composite fully drawn yarn in this application.

[0033] Numbers in the figure: 1. core layer; 2. skin layer; 3. spinneret; 30. spinneret body; 31. main channel; 32. secondary channel; 33. spinneret hole. DETAILED DESCRIPTION

[0034] Example 1

[0035] The raw materials of this embodiment are: low-viscosity nylon 6 melt with a relative viscosity of 2.2 as the skin layer 2, and thermoplastic polyurethane melt with a hardness of 77HA as the core layer 1, and the skin-core composite volume percentage is 50:50.

[0036] 1. Slice processing: firstly process the low viscosity nylon 6 to the moisture content of the dry slice ≤800 ppm, and process the thermoplastic polyurethane to the moisture content of the dry slice ≤20 ppm. The nitrogen protection pressure of the dry slice is 0.02Mpa.

[0037] 2. Preparation of UDY (spinning):

[0038] The spinneret used in this embodiment is as follows Figure 1As shown, the spinneret 3 includes a spinneret body 30, a main channel 31, a secondary channel 32 and a spinneret hole 33. The spinneret body 30 is provided with the main channel 31 and the secondary channel 32. The main channel 31 is located at the center of the spinneret 3 and penetrates the spinneret body 31. The bottom of the main channel 31 is the spinneret hole 33. The secondary channel 32 is arranged at the periphery relative to the main channel 31. The secondary channel 32 is arranged obliquely, and the bottom of the secondary channel 32 is connected to the middle and lower part of the main channel 31.

[0039] The above spinnerets cooperate with various screw extruders (conventional structures are sufficient, not described in detail on the drawings) to perform spinning, and the specific process is as follows:

[0040] Low-viscosity nylon 6 dry chips enter the main screw extruder. Four heating zones are set in the melt extrusion process. The heating temperature of each zone is 265 / 260 / 255 / 250 ℃, and the melt pressure is 10 MPa. The main box is heated by medium-temperature biphenyl steam at a temperature of 245 ℃. The dry chips in the silo enter the main screw extruder for melt extrusion into nylon 6 melt, which is accurately measured by the metering pump and sent to the main channel 31 of the spinneret 3.

[0041] Thermoplastic polyurethane dry chips enter the secondary screw extruder, and four heating zones are set in the melt extrusion process. The heating temperature of each zone is 220 / 225 / 230 / 235 ℃, the melt pressure is 15 MPa, and the melt residence time is ≤10 min. The secondary box is heated by low-temperature biphenyl steam at a heating temperature of 235 ℃. The thermoplastic polyurethane melt obtained by melt extrusion is accurately measured by a metering pump and sent to the secondary channel 32 of the spinneret 3.

[0042] Combination Figure 1 In the spinneret 3 , the thermoplastic polyurethane melt entering the secondary channel 32 is compounded with the low-viscosity nylon 6 melt entering the primary channel 31 and then ejected through the spinneret hole 33 .

[0043] Since the low-viscosity nylon 6 melt as the skin layer has certain elasticity and coating properties in the main channel, and the thermoplastic polyurethane melt as the core layer has a certain hardness, it merges and compounds with the low-viscosity nylon 6 melt through the secondary channel 32 and is ejected from the spinneret hole 33 to form an eccentric skin-core structure with a small opening.

[0044] Fiber cooling air: temperature 26 ℃, wind speed 0.4 m / sec.

[0045] Single suction and exhaust: wind speed 5 m / min.

[0046] The fiber is oiled in multiple steps, firstly the nylon is oiled with oil agent, and then the second step of spandex oiling is performed.

[0047] Fiber winding with a winding speed of 450 m / min and a winding angle of 6°.

[0048] After winding is completed, an eccentric sheath-core nylon-spandex composite undrawn yarn (UDY) is obtained.

[0049] 3. Post-processing:

[0050] UDY was post-processed by stretching, heating relaxation, oiling and winding, with a stretching ratio of 3.5, a hot plate temperature of 85 °C, a hot plate relaxation temperature of 100 °C, a winding speed of 550 m / min, and a winding angle of 7 °.

[0051] The eccentric sheath-core nylon-spandex composite fully drawn yarn prepared in this embodiment has a structure as follows: Figure 2 As shown: the nylon 6 component is the skin layer 2, the thermoplastic polyurethane component is the core layer 1, the central angle θ of the exposed part of the core layer 1 is 25°, and the skin-core composite volume percentage is 50:50.

[0052] The physical indicators of nylon-spandex composite sheath-core fully drawn yarn are: elongation at break is 60%, breaking strength ≥3.5 cN / dtex, boiling water shrinkage is 19%, fiber crimp number is 35 / 25mm, and dyeing uniformity is ≥level 4.

[0053] Example 2

[0054] The configuration of this embodiment is the same as that of embodiment 1, except that the relative viscosity of the low-viscosity nylon 6 chips is 2.45, the heating temperatures of the main screw extruder zones are 275 / 270 / 265 / 260°C, and the main box is heated by high-temperature biphenyl steam at a heating temperature of 255°C.

[0055] The physical indicators of the prepared nylon-spandex composite sheath-core fully drawn yarn are: elongation at break is 52%, breaking strength ≥2.8 cN / dtex, boiling water shrinkage is 15%, fiber crimp number is 16 / 25 mm; dyeing uniformity is ≥4 levels.

[0056] Compared with Example 1, the relative viscosity of the nylon 6 component is increased, the main screw extrusion temperature and the biphenyl steam heating temperature are increased, the parameters such as the elongation at break, the breaking strength, and the boiling water shrinkage are significantly reduced, and the fiber curl number is reduced; the central angle θ of the exposed part of the core layer 1 remains unchanged, the factors affecting dyeing do not change much, and the dyeing uniformity is ≥ level 4.

[0057] Example 3

[0058] The configuration of this embodiment is the same as that of embodiment 1, except that the volume percentage of the skin-core composite is 35:65.

[0059] The physical indicators of the prepared nylon-spandex composite sheath-core fully drawn yarn are: elongation at break of 75%, breaking strength ≥3.0 cN / dtex, boiling water shrinkage of 25%, fiber curl number of 50 / 25mm, and dyeing uniformity ≥level 4.

[0060] Compared with Example 1, the proportion of the skin layer 2 is relatively reduced, that is, the proportion of nylon 6 is reduced, the gap between the two components is increased, and the external manifestation is that the elongation at break, boiling water shrinkage and fiber curl number increase, and the breaking strength does not change much; however, the central angle θ of the exposed part of the core layer 1 remains unchanged, the factors affecting dyeing do not change much, and the dyeing uniformity is ≥ level 4.

[0061] Example 4

[0062] The configuration of this embodiment is the same as that of embodiment 1, except that the moisture content of the thermoplastic polyurethane dry slices is ≤50ppm.

[0063] The physical indicators of the prepared nylon-spandex composite sheath-core fully drawn yarn are: elongation at break of 50%, breaking strength ≥3.0 cN / dtex, boiling water shrinkage of 15%, fiber curl number of 18 / 25 mm, and dyeing uniformity ≥level 4.

[0064] Compared with Example 1, the required range of moisture content of the thermoplastic polyurethane dry slices is wider, the increase of water molecules leads to a decrease in the viscosity of the thermoplastic polyurethane melt, the viscosity difference between the two components becomes smaller, and the external manifestation is that the elongation at break, boiling water shrinkage and fiber curl number increase, and the breaking strength does not change much; however, the central angle θ of the exposed part of the core layer 1 remains unchanged, the factors affecting dyeing do not change much, and the dyeing uniformity is ≥ level 4.

[0065] Example 5

[0066] The configuration of this embodiment is the same as that of embodiment 1, except that the residence time of the thermoplastic polyurethane melt is ≤15 min.

[0067] The physical indicators of the prepared nylon-spandex composite sheath-core fully drawn yarn are: elongation at break of 55%, breaking strength ≥3.0 cN / dtex, boiling water shrinkage of 15%, fiber curl number of 18 / 25 mm, and dyeing uniformity ≥level 4.

[0068] Compared with Example 1, the residence time of the thermoplastic polyurethane melt is longer, and thermal degradation may occur, resulting in reduced viscosity and weakened elasticity, and the external manifestation is the loss of elongation at break and breaking strength, and the fiber curl number and boiling water shrinkage rate are reduced; the central angle θ of the exposed part of the core layer 1 remains unchanged, the factors affecting dyeing do not change much, and the dyeing uniformity is ≥ level 4.

[0069] Example 6

[0070] The configuration of this embodiment is the same as that of embodiment 1, except that the central angle of the opening of the core layer is 35°.

[0071] The physical indicators of the prepared nylon-spandex composite sheath-core fully drawn yarn are: elongation at break is 63%, breaking strength ≥3.3 cN / dtex, boiling water shrinkage is 21%, fiber curl number is 38 / 25 mm, and dyeing uniformity is ≥level 3.

[0072] Compared with Example 1, the factors affecting the mechanical properties of the drawn yarn, such as strength and elongation, have not changed, but the central angle θ increases, and the core layer 1, i.e., the thermoplastic polyurethane, is opened and exposed more, resulting in an increase in the dyeing area relative to the skin layer 2, which increases the probability of color difference and reduces the dyeing uniformity.

[0073] Example 7

[0074] The configuration of this embodiment is the same as that of embodiment 1, except that the thermoplastic polyurethane of the core layer 1 has no openings.

[0075] The physical indicators of the prepared nylon-spandex composite sheath-core fully drawn yarn are: elongation at break of 56%, breaking strength ≥3.0 cN / dtex, boiling water shrinkage of 17%, fiber curl number of 21 / 25mm, and dyeing uniformity ≥level 4.

[0076] Compared with Example 1, the core layer 1 in the present embodiment is completely wrapped inside the skin layer 2, and cannot produce high heat shrinkage three-dimensional curling elasticity during heat treatment, so its elasticity cannot be fully exerted, and thus the elongation at break and the number of fiber curls are both reduced to a certain extent.

[0077] Example 8

[0078] The configuration of this embodiment is the same as that of embodiment 1, except that only one layer of nylon oiling is provided.

[0079] The physical indicators of the prepared nylon-spandex composite sheath-core fully drawn yarn are: elongation at break of 58%, breaking strength ≥3.5 cN / dtex, boiling water shrinkage of 17%, fiber curl number of 25 / 25 mm, and dyeing uniformity ≥level 4.

[0080] Compared with Example 1, only one oiling step is provided, and parameters such as elongation at break and strength are not greatly affected. However, during the spinning process, there are phenomena such as composite fiber adhesion, difficulty in unwinding, and high weaving friction tension.

[0081] Example 9

[0082] The configuration of this embodiment is the same as that of embodiment 1, except that the fiber winding speed is 800 m / min and the post-processing draft ratio is 3.0.

[0083] The physical indicators of the prepared nylon-spandex composite sheath-core fully drawn yarn are: elongation at break of 56%, breaking strength ≥3.7 cN / dtex, boiling water shrinkage of 17%, fiber curl number of 30 / 25 mm, and dyeing uniformity ≥level 4.

[0084] As the winding speed increases, the post-processing drafting multiple decreases, and the tensile effect on the fiber increases, it is beneficial to improve the breaking strength. Therefore, the breaking strength of this embodiment is improved compared with that of Example 1, but the speed increase may destroy part of the three-dimensional curling structure, resulting in a decrease in the number of fiber curls, and a decrease in the breaking elongation and boiling water shrinkage.

[0085] Example 10

[0086] The configuration of this embodiment is the same as that of embodiment 1, except that no relaxation heating is provided in the post-stretching processing.

[0087] The physical indicators of the prepared nylon-spandex composite sheath-core fully drawn yarn are: elongation at break of 55%, breaking strength ≥3.5 cN / dtex, boiling water shrinkage of 15%, fiber crimp number of 27 / 25 mm, and dyeing uniformity ≥level 4.

[0088] By comparing the processing process with that of Example 1, it can be seen that heating relaxation can eliminate the internal stress of the thermoplastic polyurethane component in the composite yarn caused by drawing, and improve the stability of the fully drawn yarn structure. Therefore, the breaking strength in this case does not change much, but the boiling water shrinkage and elongation at break are reduced, and the fiber curl number is significantly reduced.

[0089] Embodiment 11

[0090] The configuration of this embodiment is the same as that of embodiment 1, except that no oiling is performed in the post-processing drafting.

[0091] The physical indicators of the prepared nylon-spandex composite sheath-core fully drawn yarn are: elongation at break of 60%, breaking strength ≥3.5 cN / dtex, boiling water shrinkage of 17%, fiber curl number of 32 / 25 mm, and dyeing uniformity ≥level 4.

[0092] By comparing the processing process with that of Example 1, it can be seen that the strength and elongation properties are basically fixed after post-processing stretching, so whether the oiling treatment is done in the winding stage does not affect the breaking elongation and breaking strength; but when the winding oiling treatment is not performed, the fiber cohesion is relatively weak, the composite effect is not as ideal as in Example 1, and the boiling water shrinkage rate and the number of fiber curls are reduced.

Claims

1. A method for preparing an eccentric sheath-core nylon-spandex composite fully drawn yarn. It is characterized in that The method uses a low-viscosity nylon 6 melt with a relative viscosity of 2.2 as the skin layer and a thermoplastic polyurethane melt with a hardness of 77 HA as the core layer, and the skin-core composite volume percentage is 50:50, including the following steps: Step 1, slice processing: firstly, the low viscosity nylon 6 is processed to the moisture content of the dry slice ≤800 ppm, and the thermoplastic polyurethane is processed to the moisture content of the dry slice ≤20 ppm, and the nitrogen protection pressure of the dry slice is 0.02 MPa; Step 2, spinning: Low-viscosity nylon 6 dry chips enter the main screw extruder. Four heating zones are set in the melt extrusion process. The heating temperature of each zone is 265 / 260 / 255 / 250 ℃, and the melt pressure is 10 MPa. The main box is heated by medium-temperature biphenyl steam at a temperature of 245 ℃. The dry chips in the silo enter the main screw extruder for melt extrusion into nylon 6 melt, which is accurately measured by the metering pump and sent to the main channel of the spinneret. Thermoplastic polyurethane dry chips enter the secondary screw extruder. Four heating zones are set in the melt extrusion process. The heating temperature of each zone is 220 / 225 / 230 / 235 ℃, the melt pressure is 15 MPa, and the melt residence time is ≤10 min. The secondary box is heated by low-temperature biphenyl steam at a heating temperature of 235 ℃. The thermoplastic polyurethane melt obtained by melt extrusion is accurately measured by a metering pump and sent to the secondary channel of the spinneret. In the spinneret, the thermoplastic polyurethane melt entering the secondary channel is compounded with the low-viscosity nylon 6 melt entering the primary channel and then ejected through the spinneret hole to form an eccentric skin-core structure with a small opening. Fiber cooling air: temperature 26 ℃, wind speed 0.4 m / sec, Single suction and exhaust: wind speed 5 m / min, Oiling method: First apply nylon oil, then apply a second layer of spandex oil. The fiber winding speed is 450 m / min, the winding angle is 6°, and after winding, an eccentric sheath-core nylon-spandex composite undrawn yarn is obtained; Step three, post-treatment: stretching, heating relaxation, oiling and winding, stretching ratio of 3.5, hot plate temperature of 85 ℃, hot plate relaxation temperature of 100 ℃, winding speed of 550 m / min, winding angle of 7°, the obtained eccentric sheath-core nylon-spandex composite fully drawn yarn structure has a central angle θ of 25° for the exposed part of the core layer.

2. The method for preparing an eccentric sheath-core nylon-spandex composite fully drawn yarn according to claim 1, Features: The volume percentage of the skin-core composite is 35:65.

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