Production method of 8-shaped nylon 66 hollow fiber

Abstract

The invention belongs to the technical field of nylon 66, and particularly relates to a production method of 8-shaped nylon 66 hollow fibers. The 8-shaped nylon 66 hollow fiber is prepared from four symmetrical C-shaped spinneret orifices, and the 8-shaped nylon 66 hollow fiber is obtained through nylon 66 slice solid-phase drying tackifying, melting, mixing, metering, spinning, cooling forming, oiling, stretching forming and winding forming. The breaking strength of the produced fiber is 2.8-3.1 cN.dtex-1, the elongation at break is 40-55%, the dry heat shrinkage rate is 3.5-4.5%, the hollow regularity is good, various physical indexes meet the requirements of customers, and the new market requirements are met.

Description

Technical Field

[0001] The invention belongs to the technical field of nylon 66, and particularly relates to a method for producing 8-shaped nylon 66 hollow fibers. Background Art

[0002] With the improvement of people's living standards and the localization of adiponitrile, the differentiation and functionalization of nylon 66 fiber is an important development direction. Nylon 66 hollow fiber is a high-functional and high-performance chemical fiber with a hollow rate of more than 30%. The fabric is fluffy, has good thermal insulation, and has waterproof and breathable effects. It has a good market prospect. The difficulties in the development and production of nylon 66 hollow fiber include: high spinning speed, relatively poor production stability and quality controllability, and it is relatively scarce in the market and cannot meet customer needs for a long time. Summary of the invention

[0003] The 8-shaped nylon 66 hollow fiber prepared by the present invention is a high-function, high-performance chemical fiber. Each monofilament of the fiber has two thin tubular cavities in the axial direction. The hollow holes inside the fiber are used to limit heat conduction, prevent the invasion of external cold and humid airflow, and prevent the internal heat from dissipating, thereby achieving the purpose of keeping warm. It can bring light elasticity, good moisture permeability and comfortable warming effect to the fabric. The product is widely used in thermal underwear, underwear, sportswear, casual clothing, shirts, outdoor sports and blankets, etc., meeting new market needs.

[0004] A method for producing 8-shaped nylon 66 hollow fibers, comprising the following contents:

[0005] Step 1: solid phase drying and viscosity enhancement of nylon 66 slices;

[0006] The drying temperature of the nylon 66 chips of the present invention is selected to be 158-162° C., the drying time is 22-26 hours, the moisture content of the chips after drying is 300-500 ppm, the relative viscosity of the dry chips is controlled within 74-78, the relative viscosity of the spinning melt is 78-82, the relative viscosity difference between the two is controlled within 8, and the chips have good spinnability.

[0007] Step 2: Melting (screw extruder);

[0008] The dried slices are melted by a screw extruder. According to the production control requirements of the hollow fiber, the temperature of each zone of the screw extruder is set at 288-300°C, and the temperature of each zone differs by 2-3°C.

[0009] Step 3: Mixing (static mixer);

[0010] A static mixer is used to mix the melt at the outlet of the screw extruder evenly, thereby enhancing the uniformity of the melt and reducing the difference in temperature and residence time between the tube wall and the center of the tube when the melt passes through the elbow.

[0011] Step 4: metering (metering pump);

[0012] The mixed melt is distributed by the spinning box distribution pipe to the metering pumps at each spinning position for metering to ensure consistent linear density and uniform dryness of the yarns; the metering pump can pressurize the melt to meet the needs of high-pressure spinning.

[0013] Step 5: Spinning;

[0014] Before spinning, filter sand and other filter materials are used to filter out impurities in the melt. Through multiple optimization tests, the filter screen before the sand uses a 100-mesh single-layer metal mesh, the filter screen under the sand uses a 20μm sintered metal felt, and the filter screen before the plate uses a 30μm sintered metal felt; a single component uses 260g of metal sand, and the metal sand ratio is as follows: 20-40 mesh 100g (accounting for about 38-40%), 40-60 mesh 120g (accounting for about 45-46%), 80-100 mesh 40g (accounting for about 14-15%), the initial pressure of the component is ≥14Mpa, the service life of the spinning component is 12-13 days, there is no floating silk, injection head, and the spinning condition is good.

[0015] The spinneret of the present invention comprises two first C-shaped plate structures and two second C-shaped plate structures, the openings of the first C-shaped plate structure and the second C-shaped plate structure are opposite and symmetrically arranged, a gap is left between the first C-shaped plate structure and the second C-shaped plate structure, and the two first C-shaped plate structures are also symmetrically arranged with a gap left between them. The spinneret of the present invention is called a 4C symmetrical spinneret. The aperture D of the spinneret is 0.2-0.4 mm, the aperture depth (length) L is 0.6-1.2 mm, and the L / D (aspect ratio) is controlled at 3-4:1. The commonly used specifications in actual production are: aperture D: 0.29 mm, aperture length L is 0.89 mm, and aspect ratio L / D is 3:1.

[0016] In order to ensure the smooth closed loop of the hollow hole and the melt, and avoid hollow rupture, as well as the spinneret material, strength and other factors, the center distance of the 4C symmetrical spinneret is 6-7mm, the slit E of the arc-shaped first C-shaped plate structure or the second C-shaped plate structure is 0.10-0.20mm, the gap C between the first C-shaped plate structure and the second C-shaped plate structure is 0.06-0.15mm, and the spinneret aperture D is 0.2-0.4mm. This can reduce the orifice expansion effect of the spinning melt, which is beneficial to improving the degree of special-shaped fibers and the realization of a steady-state spinning process.

[0017] In order to ensure the quality of spinning fluid, it is necessary to control the appropriate temperature range of the spinning box. The temperature of the spinning box is 291-295℃ to ensure stable spinning conditions and high profile and regularity of the fiber cross section.

[0018] In addition, the initial pressure of the spinning assembly should be controlled at 14MPa.

[0019] Step 6: Cooling and forming to obtain primary fibers;

[0020] The process in which the melt stream is cooled by the cooling medium and solidified into a filament is called cooling forming.

[0021] The invention uses side blowing to perform spinning cooling and forming. The process control conditions of side blowing are mainly wind speed and wind temperature, which directly affect the cooling and forming of the nascent fiber. Finally, the cooling distance is selected to be 80-100cm, the side blowing humidity is 80±5%, the wind temperature is 18°C, and the wind speed is 0.8-0.9m / s.

[0022] When the wind speed reaches 0.8-0.9 m / s, the fiber cross-sectional profile is 31-32% and the cross-sectional regularity is good.

[0023] Step 7: Oiling;

[0024] The nascent fiber should be oiled before stretching, with an oiling rate of 1.0-1.6%.

[0025] Step 8: Stretch and shape;

[0026] In order to achieve a higher degree of orientation of nylon 66 hollow fibers, the spinning speed during stretching needs to be above 5000 m / min. The various conditions are controlled as follows:

[0027] (1) The temperature of the first wire guide plate is 50-70°C, which is controlled above the glass transition temperature; the temperature of the second wire guide plate is controlled at 60-140°C, and the temperature can be adjusted according to the requirements of the dry heat shrinkage rate;

[0028] (2) The spinning speed is 5000-5500 m / min, micro-stretching is performed, and the draft ratio is controlled at 1.05-1.15.

[0029] In addition, the invention performs compressed air blowing and twisting during stretching and shaping to control the network degree. It is better to control the network degree to be above 10 / m.

[0030] Step 9, winding and forming;

[0031] The overfeed rate is controlled at 1.6-1.8%, and the winding angle is controlled at 7-9°.

[0032] The beneficial effects of the present invention are:

[0033] The present invention adopts four symmetrical "C"-shaped spinnerets to prepare 8-shaped nylon 66 hollow fibers. The fiber breaking strength produced by the method of the present invention is 2.8-3.1 cN·dtex -1, elongation at break 40-55%, dry heat shrinkage 3.5-4.5%, good hollow regularity, hollowness above 30%, various physical indicators meet customer requirements and meet new market demands.

[0034] In specific practice, in order to ensure the degree of special shape, the relative viscosity of the spinning melt is controlled at 78-82 (relative viscosity of formic acid), the temperature of the spinning box is controlled at 291-295°C, the initial pressure of the spinning assembly is designed to be 14MP, the side wind humidity is 80±5%, the wind temperature is 18°C, the wind speed is 0.8-0.9m / s, the spinning speed is 5000-5500m / min, and the oil application rate is 1.0-1.6%. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a cross-sectional view of the figure-8 hollow fiber of the present invention.

[0036] Figure 2 2A is a schematic diagram of the structure of the spinneret of the present invention. 2B is a structure of a single plate in the spinneret.

[0037] Figure 3 A is a schematic diagram of the structure of a conventional double C-type spinneret, and 3B is a cross-sectional view of a hollow fiber prepared using the conventional double C-type spinneret.

[0038] Figure 4 A is a schematic diagram of the structure of a conventional 8-shaped annular spinneret, and 4B is a cross-sectional view of a hollow fiber prepared by using the conventional 8-shaped annular spinneret. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The raw material used in the examples is nylon 66 chips.

[0041] Example 1

[0042] The present invention discloses a method for producing an "8"-shaped nylon 66 hollow fiber, which adopts an indirect (chip) spinning method. The nylon 66 chip raw material is dried, melted, metered and ejected, cooled, oiled, drawn, and wound to produce the nylon 66 hollow fiber. The process is as follows:

[0043] After pre-crystallization and drying, nylon 66 chips are added from the material hopper, melted by the screw extruder, and mixed by the static mixer. The mixed melt is sent to the metering pump at the spinning part through the material pipe in the spinning box. The metering pump metering and pressurizing the melt, quantitatively extruding the melt through the spinneret holes of the spinneret to form a melt stream. The melt stream enters the cooling air chamber, and is cooled, blown, and solidified to form primary fibers. The primary fibers are oiled, stretched, shaped, and networked, and then rolled into a silk cake to obtain a finished fiber with applicability.

[0044] Nylon 66 chips → solid phase drying and viscosity enhancement → screw extruder → static mixer → spinning box → metering pump (precise metering) → spinning assembly (4C symmetrical spinneret, such as Figure 2 (as shown) → side air cooling → oiling with nozzle → pre-network → first guide wire disk (pre-tension roller) → second guide wire disk (hot roller) → main network → winding and forming → quality grade determination → packaging.

[0045] The specific steps include:

[0046] Step 1: solid phase drying and viscosity enhancement of nylon 66 slices;

[0047] The quality of nylon 66 chips is closely related to the spinnability of the fiber and the quality of the product. In addition to the quality indicators of the chips - intrinsic viscosity, softening point, amine content, ash content and agglomerated particles, the appearance of the chips, the presence of carbon black particles, the distribution of relative molecular mass and the moisture content also affect the spinnability, especially the moisture content has a greater impact on high-speed spinning. When spinning industrial yarns and other varieties, the moisture content does not exceed 700ppm, and the quality between batches remains stable and consistent.

[0048] The drying temperature of the nylon 66 chips of the present invention is selected to be 158-162° C., the drying time is 22-26 hours, the moisture content of the chips after drying is 300-500 ppm, the relative viscosity of the dry chips is controlled within 74-78, the relative viscosity of the spinning melt is 78-82, and the relative viscosity difference between the two is controlled within 8, so as to have good spinnability. The present invention finds that the moisture content and viscosity of the chips are the conditions for stable production.

[0049] The drying process of nylon 66 chips is a simultaneous heat and mass transfer process, accompanied by changes in polymer structure (crystallization) and properties (softening point, etc.). Nylon 66 chips need to be heated to above 140°C during drying, while the softening point of ordinary chips is very low. They soften and become sticky below 80°C, and are easily bonded into blocks to block the drying device or feed pipe (commonly known as agglomeration). In order to improve the softening point of nylon 66 chips, the present invention increases the crystallinity of the chips by increasing the drying temperature and drying time of the chips, so that the softening point reaches about 200°C, so that the drying process can proceed smoothly; and the moisture content of the chips is further reduced to below the moisture content required by the process to meet the spinning requirements. During drying, the dehumidified dry air (dew point below -20°C) is heated to about 160°C, transported from the bottom of the drying tower to the drying tower to contact the chips in reverse to quickly dehydrate the chips, and the dry air takes the moisture out from the top of the drying tower, further reducing the moisture content of the chips to below the moisture content required by the process to meet the spinning requirements. If the drying temperature is too high, the slices will easily stick together, the macromolecules will degrade, and the color will turn yellow. Above 180°C, it will easily cause solid phase polycondensation reaction, affecting the uniformity of the melt. Finally, it was determined that the best effect would be achieved when the drying temperature was controlled at around 160°C (158-162°C).

[0050] Step 2: Melting (screw extruder);

[0051] The dried slices enter the screw extruder from the feed port by their own weight. The screw extruder is divided into a feeding section, a compression section and a metering section. The screw groove of the feeding section is deeper to accommodate more slices. The compression section compresses and plasticizes the slices, and the groove gradually becomes shallower, so that the material is subjected to gradually increasing pressure and shear force, thereby increasing the temperature and plasticization degree of the slices. Metering section: ensure that the extruded material has a uniform flow and pressure, and the groove depth is relatively stable. After the slices are fed, they are continuously pushed forward by the screw. The nylon 66 slices are subjected to the friction and shearing action of the screw, as well as the heating of the external heating device of the sleeve. The temperature gradually rises, and they begin to soften and partially melt. It is necessary to prevent the material from melting and bonding prematurely, which affects the normal feeding. The groove of the compression section gradually changes from deep to shallow, and the preheated slices melt and are compressed at the same time. The compressed melt in the metering section is further mixed and plasticized, and the melt temperature reaches the setting uniformly, and is quantitatively transported to the box at a certain pressure for spinning.

[0052] If the temperature of the feeding section is too high, the slices will melt too early, causing the gaps between the original solid particles to disappear, resulting in the inability to compress the melt, and thus losing the ability to move forward; and the material will generate a circulation with the screw's rotation force, and the unmelted slices may enter the circulating melt and bond with the melt, causing "ring knots" to block the material; if the temperature is too low, the slices will not melt after entering the compression section, affecting the compression, metering and mixing of the screw. In the compression section and metering section, the slices are gradually melted, compressed, metered and mixed. The temperature of the melt material should be close to the spinning process temperature, and the temperature of each zone should not be greatly increased or decreased.

[0053] Since high-speed spinning requires the melt to have good flow properties, the temperature control of each zone of the screw is generally 25-40°C higher than the melting point of the dry slice (the melting point of the slice is 260-264°C). According to the production control requirements of hollow fibers, the temperature of each zone of the screw extruder is set at 288-300°C, and the temperature of each zone differs by 2-3°C.

[0054] Step 3: Mixing (static mixer);

[0055] A static mixer is used to mix the melt at the outlet of the screw extruder evenly, thereby enhancing the uniformity of the melt and reducing the difference in temperature and residence time between the tube wall and the center of the tube when the melt passes through the elbow.

[0056] Step 4: metering and pressurization (metering pump);

[0057] The mixed melt is distributed by the spinning box distribution pipe to the metering pumps at each spinning position for metering to ensure consistent linear density and uniform dryness of the yarns; the metering pump can pressurize the melt to meet the needs of high-pressure spinning.

[0058] Step 5: Spinning;

[0059] The spinning assembly includes sealing materials, filter materials, distribution plates, spinnerets and other components. Its main function is to mix and filter the melt delivered by the metering pump and spray out filaments through the spinneret.

[0060] Before spinning, filter sand and other filter materials are used to filter out impurities in the melt. Filter materials include corundum, sea sand, ultrafine glass beads, filter mesh, etc. In high-pressure spinning, the filter layer will produce higher resistance, causing the melt to generate heat by friction, increase the temperature, and improve the rheological properties of the melt.

[0061] Through multiple optimization tests, the filter screen before sand uses a 100-mesh single-layer metal mesh, the filter screen under sand uses a 20μm sintered metal felt, and the filter screen before plate uses a 30μm sintered metal felt; a single component uses 260g of metal sand, and the metal sand ratio is as follows: 100g for 20-40 mesh (accounting for about 38-40%), 120g for 40-60 mesh (accounting for about 45-46%), 40g for 80-100 mesh (accounting for about 14-15%), the initial pressure of the component is ≥14Mpa, the service life of the spinning component is 12-13 days, there is no floating silk or injection head, and the spinning condition is good.

[0062] The pressure and filtration effect of the spinning assembly have an important influence on the quality of melt extrusion. The assembly pressure is mainly determined by the assembly filtration layer structure and the melt properties.

[0063] Low pressure in the spinning assembly will lead to thin filaments, leakage, stigma, etc. High pressure in the spinning assembly will lead to hairy filaments. The initial pressure of the spinning assembly on the machine should be controlled at 14MPa.

[0064] After being filtered, the spinning melt is distributed to the various spinneret holes on the spinneret by the distribution plate and is extruded from the spinneret holes to form a thin melt stream.

[0065] The first condition for producing hollow fibers is to design and process a hollow hole spinneret with excellent performance, which not only involves the feasibility of mechanical processing of the spinneret and the performance of the spinneret, but more importantly, the stability of the spinning process must be met to ensure that the performance of the final product meets the design requirements. Spinneret design is a key factor affecting the performance of "8" shaped nylon 66 hollow fibers. The spinneret hole type and size directly affect the spinning stability, fiber cross-sectional shape, physical quality, and spinneret service life.

[0066] The spinneret design of the present invention is based on the Barus effect, that is, the fluid orifice expansion effect occurs when the viscoelastic polymer fluid flows out of the orifice due to the elastic energy stored when the melt stream is released at the entrance. Figure 2As shown in A, the spinneret of the present invention includes two first C-shaped plate structures and two second C-shaped plate structures, the openings of the first C-shaped plate structure and the second C-shaped plate structure are opposite and symmetrically arranged, a gap is left between the first C-shaped plate structure and the second C-shaped plate structure, and the two first C-shaped plate structures are also symmetrically arranged with a gap left between them. The spinneret of the present invention is called a 4C symmetrical spinneret. The aperture D of the spinneret is 0.2-0.4 mm, the aperture depth (length) L is 0.6-1.2 mm, and the L / D (aspect ratio) is controlled at 3-4:1. The commonly used specifications in actual production are: aperture D: 0.29 mm, aperture length L is 0.89 mm, and aspect ratio L / D is 3:1. The spinneret of the present invention combines several discontinuous curved plate-like structural designs together to form a spinneret hole of a special shape, so that the polymer melt extruded from these combined slits undergoes the Barus effect and adheres together before solidification, so that the melt stream forms an "8"-shaped fiber with certain cross-sectional characteristics after cooling and solidification.

[0067] In order to ensure the smooth closure of the hollow hole shape and the melt, and avoid hollow rupture, as well as the spinneret material, strength and other factors, the center distance of the 4C symmetrical spinneret (the center distance between the spinneret hole of one 4C symmetrical spinneret and the spinneret hole of another 4C symmetrical spinneret) is 6-7mm, the slit E of the arc-shaped first C-shaped plate structure or the second C-shaped plate structure is 0.10-0.20mm, the gap C between the first C-shaped plate structure and the second C-shaped plate structure is 0.06-0.15mm, and the spinneret aperture D is 0.2-0.4mm. This can reduce the orifice expansion effect of the spinning melt, which is beneficial to improving the degree of special-shaped fibers and the realization of a steady-state spinning process. Figure 2 As shown in B.

[0068] The present invention has carried out the spinneret hole selection, and the specific table is as follows:

[0069] Hollow fibers obtained using different spinnerets

[0070]

[0071] When spinning hollow fibers, the relative viscosity of the melt is controlled between 78 and 82, which can achieve good spinnability and hollowness. The melt viscosity of nylon 66 polymer is greatly affected by temperature. When the temperature is too low, the melt fluidity becomes poor and spinning is difficult to achieve; when the temperature is too high, the polymer will be thermally cracked and cross-linked, generating bubbles and gels, causing broken ends and floating fibers. In order to ensure the quality of the spinning fluid, it is necessary to control the appropriate temperature range.

[0072] As the spinning box temperature increases, the hollowness tends to decrease; when the spinning temperature is low, the melt fluidity becomes poor, and problems such as hairy fibers and broken fibers are prone to occur. The spinning box temperature was finally determined to be 291-295°C to ensure stable spinning conditions and high profile and regularity of the fiber cross section.

[0073] Experimental results at different spinning box temperatures

[0074]

[0075]

[0076] Step 6: Cooling and forming;

[0077] The process of the melt stream being cooled by the cooling medium and solidified into filaments is called cooling forming. During cooling, the melt stream gradually becomes thinner before solidification due to the stretching effect of the spinneret. The cooling forming is completed in the spinning cold air chamber. The cooling air forced out by the blowing window at the upper end of the spinning tunnel can ensure uniform cooling conditions.

[0078] After the spinning melt is ejected from the spinneret, it is stretched by winding and transfers heat with the environment. When the temperature drops, the molten polymer crystallizes to form a solidification point. The position of the solidification point will affect the physical properties of the filaments, and the cooling conditions need to be strictly controlled. The cooling device controls the wind speed, wind temperature, wind volume, wind pressure, humidity and other parameters to achieve regulation of the fiber solidification point. Too fast or too slow a cooling rate will cause fluctuations in the spinning quality. Different spinning speeds correspond to different cooling conditions. High-speed spinning requires lower wind temperature and higher wind speed. The wind speed has a great influence on the uniformity of the spinning filaments. Too large or too small a wind speed will reduce the uniformity of the primary fiber.

[0079] The invention uses side blowing to perform spinning cooling and forming. The process control conditions of side blowing are mainly wind speed and wind temperature, which directly affect the cooling and forming of the nascent fiber. Finally, the cooling distance is selected to be 80-100cm, the side blowing humidity is 80±5%, the wind temperature is 18°C, and the wind speed is 0.8-0.9m / s.

[0080] The number of holes in the "8"-shaped hollow fiber is relatively small, and the fineness is relatively coarse. The side blowing speed is too low or the temperature is too high, the cooling speed of the filament bundle is slow, and the melt stream has no time to solidify, which makes the cavity part smaller and causes the fiber's profile to decrease. When the wind speed is 0.4-0.7m / s, the fiber cross-sectional profile is only about 15-17%. This is because the cooling speed is slow, the melt stream has no time to solidify, and the shape of the spinneret hole is offset, thereby making the cavity part smaller and causing the fiber's profile to decrease.

[0081] Higher wind speed can improve the hollowness of the fiber. When the cooling wind speed is high, the cavity formed in the cooling spinning process of the fiber has no time to shrink and solidifies quickly, and the cross-sectional irregularity increases. When the wind speed reaches 0.8-0.9m / s, the cross-sectional irregularity of the fiber is 31-32%, and the cross-sectional regularity is good.

[0082] When the wind speed reaches 0.9-1.1m / s, the fiber cross-section profile is 30-31%. The profile does not change significantly, but decreases slightly. This is mainly because the cooling speed is too fast, and there is a large temperature gradient between the fiber cortex and the interior, forming an obvious skin-core structure, which causes uneven stretching and increased breakage during the hot stretching process.

[0083] Step 7: Oiling;

[0084] Because the raw fiber is relatively dry, it is easy to generate static electricity, and the cohesion between the monofilaments is poor, the yarn is loose, the friction coefficient is large, and it is impossible to draw, shape and wind. The yarn must be oiled before stretching. When using different spinning processes, the oiling position and oil type are different. The purpose of oiling is to make the yarn bundle, reduce static electricity, and improve smoothness. The oiling rate is 1.0-1.6%.

[0085] Step 8: Stretch and shape;

[0086] Stretching is the secondary forming of the fiber. The stretching ratio and stretching temperature are important process parameters. The magnitude of the stretching tension has a significant impact on the stability and structure of nylon 66 fiber during the stretching process, which mainly depends on the friction coefficient between the fiber and the surface of the hot roller, and the wrap angle of the fiber on the hot roller. The greater the friction coefficient and the greater the wrap angle of the fiber, the greater the stretching tension, which will cause the fiber to have fuzz.

[0087] The tensile tension of the fiber is affected by the stretching speed and temperature. When the stretching speed increases, the tensile tension increases slowly, but the thermal effect also increases, resulting in a decrease in tensile stress. It is necessary to determine the optimal stretching speed and temperature. The stretching temperature should be higher than the glass transition temperature (49°C) and lower than the softening temperature. The temperature of the hot roller generally does not exceed 235°C. Nylon 66 molecular chains are easier to stretch, straighten and recrystallize at high temperatures, thereby enhancing fiber strength and dimensional stability. The stretching multiple increases with increasing temperature, and is lower than the elongation at break, and greater than the natural stretching multiple.

[0088] The spinning speed during stretching has a certain influence on the structure and tensile properties of nylon 66 fiber. When the winding speed is below 2000m / min, the maximum stretching ratio of the fiber will decrease significantly with the increase of the spinning speed. When the winding speed is higher than 2000m / min, the maximum stretching ratio is almost unaffected by the change of spinning speed. When the spinning speed reaches 4000m / min, the orientation and crystallinity of the filaments are stabilized at a high level, the expansion and deformation of the filaments after moisture absorption are significantly improved, and the quality of the silk cake forming is greatly improved. In order to achieve a higher orientation degree of nylon 66 hollow fibers, the spinning speed during stretching needs to reach more than 5000m / min.

[0089] When producing "8"-shaped hollow fibers, high-multiple stretching is not required. The speed difference between GR1 (pre-tension roller, or first godet) and GR2 (hot roller, or second godet) is used for micro-stretching. When the spinning speed reaches 4000m / min, the orientation and crystallinity of the filaments are both stable at a high level. High-speed spinning speed is the main influencing factor. When stretched at room temperature (turn off the hot roller temperature), the filaments shake violently on the godet and the package tension is large.

[0090] By using a low-temperature hot roller (the temperature of the hot roller is higher than the glass transition temperature of nylon 66), the molecular chain activity of the filament bundle is enhanced after passing through the low-temperature heated hot roller, which reduces the winding tension and improves the stability of the filament bundle operation.

[0091] The present invention optimizes various parameters during stretching, as follows:

[0092] Example 1:

[0093] The temperatures of the godet GR1 and GR2 were controlled at 60°C and 65°C respectively. The hair ratio of the fibers obtained under different spinning speeds, different first godet speeds, different second godet speeds, and different draft ratios was analyzed. The results showed that:

[0094] The temperature of the guide wire discs GR1 and GR2 is controlled at 60℃ and 65℃, the draft ratio is 1.08, the spinning speed is 5200m / min, the GR1 line speed is 4814m / min, and the GR2 line speed is 5200m / min. The production conditions are good.

[0095] Effects of different spinning speeds and draft ratios on wool yarn

[0096]

[0097] Example 2:

[0098] The physical properties (breaking strength, breaking strength variation coefficient, breaking elongation, breaking elongation variation coefficient, oil content, dry heat shrinkage) of the fibers prepared under process one and process two were analyzed.

[0099] Process 1: The temperature of the first wire guide disk is 60°C, the temperature of the second wire guide disk is 65°C, the speed of the first wire guide disk is 4727m / min, and the speed of the second wire guide disk is 5200m / min.

[0100] Process 2: The temperature of the first wire guide disk is 60°C, the temperature of the second wire guide disk is 140°C, the speed of the first wire guide disk is 4727m / min, and the speed of the second wire guide disk is 5200m / min.

[0101] The results show that when other process conditions remain unchanged, increasing the temperature of the second wire guide disk will increase the elongation at break, decrease the dry heat shrinkage, and the strength will not change much.

[0102] Effects of different spinning speeds and draft ratios on wool yarn

[0103] Serial number parameter Process 1 and corresponding properties Process 2 and corresponding properties 1 The first wire guide temperature / °C 60 60 2 Second godet temperature / ℃ 65 140 3 <![CDATA[First guide wire spool speed / (m·min -1 )]]> 4727 4727 4 <![CDATA[Second guide wire spool speed / (m·min -1 )]]> 5200 5200 5 <![CDATA[Breaking strength / (cN·dtex -1 )]]> 2.96 3.03 6 Coefficient of variation of breaking strength / % 2.23 2.17 7 Elongation at break / % 48.3 52.6 8 Coefficient of variation of elongation at break / % 2.76 2.49 9 Oil content / % 1.2 1.1 10 Dry heat shrinkage / % 4.1 3.2

[0104] Finalize:

[0105] (1) GR1 temperature is 50-70℃, which is controlled above the glass transition temperature; GR2 temperature is controlled at 60-140℃, and the temperature can be adjusted according to the requirements of dry heat shrinkage rate;

[0106] (2) The spinning speed is 5000-5500 m / min, micro-stretching is performed, and the draft ratio is controlled at 1.05-1.15.

[0107] In addition, the present invention performs interlacing during stretching and shaping to control the interlacing degree. The interlacing degree refers to the number of fibers interwoven and cohesive in each meter of the silk strip. Increasing the interlacing degree can increase the cohesive force between the monofilaments and avoid the phenomenon of monofilament looseness and splitting. It is necessary to give a certain interlacing degree during the manufacturing process.

[0108] The interlacing degree affects both the physical properties and unwinding properties of the fiber. The higher the interlacing degree, the better the physical properties and the lower the unwinding abnormality rate; if the interlacing degree is too high, the fiber will break and become fuzzy, which will affect the physical properties of the finished fiber; if the interlacing degree is too low, the frequency of broken ends will increase, making subsequent processing difficult. According to production experience, it is better to control the interlacing degree above 10 / m.

[0109] Step 9: Winding and forming;

[0110] Winding is the last processing step of nylon 66 fiber products. The winding tension is proportional to the stretching ratio and the winding angle, and inversely proportional to the winding overfeed rate. The overfeed rate is controlled at 1.6-1.8%, and the winding angle is controlled at 7-9°. If the winding tension is too high or too low, it will affect the breakage of the yarn, the formation of the yarn, and the hardness of the package. If the contact pressure (P1) of the winding head is too high or too low, it will affect the hardness of the yarn.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing 8-shaped nylon 66 hollow fibers, characterized in that: include: Step 1: solid phase drying and viscosity enhancement of nylon 66 slices; After drying, the moisture content of the slices is 300-500ppm, and the relative viscosity of the dried slices is controlled at 74-78; Step 2: Melting the dried slices; Step 3: mixing the melt obtained in step 2; Step 4: Measuring the mixed melt; Step 5: spinning the melt; The spinneret for spinning is a 4 C-symmetrical spinneret, including two first C-shaped plate structures and two second C-shaped plate structures, the first C-shaped plate structure and the second C-shaped plate structure have openings facing each other and are symmetrically arranged, a gap is left between the first C-shaped plate structure and the second C-shaped plate structure, and the two first C-shaped plate structures are symmetrically arranged with a gap left between them; The relative viscosity of the spinning melt is 78-82, and the difference between the relative viscosity of the dry slice in step 1 and the relative viscosity of the spinning melt is less than 8; Step 6: Cooling and forming to obtain primary fibers; Step 7: Oiling the nascent fibers; Step 8: Stretch and shape; The temperature of the first wire guide plate is 50-70°C; the temperature of the second wire guide plate is controlled at 60-140°C; Spinning speed 5000-5500 m / min, draft ratio controlled at 1.05-1.15; Step 9: Roll to shape.

2. The method for producing a figure-8 nylon 66 hollow fiber according to claim 1, characterized in that: The drying temperature of the nylon 66 chips in step 1 is selected to be 158-162° C., and the drying time is 22-26 hours.

3. The method for producing a figure-8 nylon 66 hollow fiber according to claim 1, characterized in that: A screw extruder is used for melting, and the temperature of each zone of the screw extruder is set at 288-300° C., and the temperature of each zone differs by 2-3° C.

4. The method for producing a figure-8 nylon 66 hollow fiber according to claim 1, characterized in that: Step 5: Before spinning, filter material is used to filter out impurities in the melt.

5. The method for producing a figure-8 nylon 66 hollow fiber according to claim 1, characterized in that: The hole diameter D of the spinneret in step 5 is 0.2-0.4 mm, the hole depth L is 0.6-1.2 mm, and the aspect ratio is 3-4:1; the center distance between the two 4 C-symmetrical spinnerets is 6-7 mm, and the gap C between the first C-shaped plate structure and the second C-shaped plate structure is 0.06-0.15 mm.

6. The method for producing a figure-8 nylon 66 hollow fiber according to claim 1, characterized in that: In step 5, the spinning box temperature is 291-295°C during spinning.

7. The method for producing a figure-8 nylon 66 hollow fiber according to claim 1, characterized in that: In step 6, spinning cooling and forming are carried out by side blowing, the cooling distance of the side blowing is 80-100 cm, the side blowing humidity is 80±5%, the wind temperature is 18°C, and the wind speed is 0.8-0.9 m / s.

8. The method for producing a figure-8 nylon 66 hollow fiber according to claim 1, characterized in that: The oiling rate in step 7 is 1.0-1.6%.

9. The method for producing a figure-8 nylon 66 hollow fiber according to claim 1, characterized in that: During the stretching and shaping in step 8, the network degree is controlled to be above 10 / m.

10. The method for producing a figure-8 nylon 66 hollow fiber according to claim 1, characterized in that: During winding and shaping in step 9, the overfeed rate is controlled at 1.6-1.8%, and the winding angle is controlled at 7-9°.

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