Polyamide 56 fiber as well as preparation method and application thereof

Abstract

The invention relates to a polyamide 56 fiber as well as a preparation method and application thereof. The polyamide 56 fiber is prepared from polyamide 56 resin through melt spinning; wherein the polyamide 56 resin comprises titanium dioxide, the titanium dioxide is added in the polymerization reaction process of polyamide 56, the content of the titanium dioxide is 0.2-0.4 wt% or 1.2-2.0 wt%, the dispersion particle size of more than 98.5% of the titanium dioxide is 0.2-0.6 [mu] m, and the dispersion particle size of more than 96% of the titanium dioxide is 0.2-0.35 [mu] m; the relative viscosity of the polyamide 56 resin is 2.3-3.0, the content of an oligomer is less than 0.8 wt%, and the polymerization degree of the oligomer is less than 5; the coefficient of variation in breaking strength of the polyamide 56 fiber is 5.0% or less, and the crimp stability of the polyamide 56 fiber is 40-56%. The polyamide 56 fiber provided by one embodiment of the invention has good mechanical properties, hygroscopicity and dyeing properties.

Description

[0001] This application is a divisional application. The application number of its parent application is 2020104673862, the application date is May 28, 2020, and the invention title is "A Polyamide 56 Resin, Fiber, and Their Preparation Methods and Applications". Technical Field

[0002] The present invention relates to polyamides, specifically to a polyamide 56 resin, fiber, and their preparation methods and applications. Background Art

[0003] Polyamide fiber is one of the first synthetic fibers to be put into industrial production in the world and plays a crucial role in the field of synthetic fibers. There are many types of polyamide fibers. Currently, the most widely produced and applied industrially are polyamide 6 and polyamide 66. The main applications involve: socks, lace underwear, body shapers, sports underwear, wedding dresses, casual jackets, sportswear, windbreakers, hiking jackets, quick-drying clothes, cold-proof clothes, outdoor tents, sleeping bags, hiking backpacks, etc.; and industrial yarns are widely used in fields such as tire cords, conveyor belts, hoses, ropes, fishing nets, tires, parachutes, etc.

[0004] Polyamide fibers are divided into bright and dull types according to whether they contain a delustering agent. Fabrics made from bright fibers have a relatively obvious surface gloss and a strong surface wax texture, making it difficult to apply to high-demand casual clothing and high-end clothing. Fabrics made from dull fibers have a soft gloss, close to the natural effect, soft handfeel, bright colors, good drape, and strong shielding performance, and are increasingly favored by consumers.

[0005] Titanium dioxide (TiO2) is widely used as a delustering material in the field of chemical fiber dull fibers. Currently, the main production method of dull fibers is mainly the addition technology of online delustering masterbatch. In this method, first, delustering masterbatch is added during the spinning process, which requires the spinning mill to be equipped with a masterbatch addition device, resulting in large production investment; second, during the masterbatch addition process, it is necessary to strictly control the addition ratio of the masterbatch. If the mixing ratio is inappropriate or the mixing is uneven, it is easy to cause poor compatibility between the delustering masterbatch and the matrix resin, and problems such as broken single filaments, hairiness, low strength, and poor dyeing are likely to occur during the spinning process.

[0006] The invention patent application (publication number: CN105986327A) discloses a polyamide 56 fiber and its manufacturing method. The spinning step includes: providing a plurality of polyamide 6 matting resin particles and polyamide 56 resin particles that have undergone viscosity and moisture adjustment steps, melting and kneading them, and spinning at 275°C to 285°C to obtain matting 56 fibers. The above patent application selects a matting masterbatch as the polyamide 6 matrix material. In this material, first, the melting point of polyamide 6 is about 220°C, while the melting point of polyamide 56 is about 256°C. The large difference in melting points between the two makes it easy to cause phase separation if the spinning processing conditions are not properly controlled, resulting in a decrease in melt viscosity and fiber strength. Second, to prepare polyamide 56 fibers with a high proportion of titanium dioxide content, it is necessary to add polyamide 6 matting resin particles with a content greater than 10% by weight to the polyamide 56 resin particles, which will cause poor compatibility and lead to problems such as an increase in hairiness and breakage during spinning, a decrease in fiber strength, uneven dyeing, and a decrease in the M rate.

[0007] The invention patent application (publication number: CN 110054891 A) discloses a matting polyamide 56 masterbatch, matting fibers and a preparation method. It is necessary to first prepare the matting polyamide 56 masterbatch, and then blend and spin it with polyamide 56 to prepare matting fibers, resulting in relatively large production investment. Moreover, when using the method of blending and adding a matting masterbatch for spinning, it is required that the masterbatch be added evenly. Otherwise, it is easy to cause the compatibility between the matting masterbatch and the matrix spinning material, resulting in problems such as broken single filaments, poor dyeing, and a low M rate. Summary of the Invention

[0008] A main object of the present invention is to provide a polyamide 56 resin containing titanium dioxide, wherein the content of the titanium dioxide is 0.2 to 5.0 wt%, and the dispersion particle size of more than 98% of the titanium dioxide is 0.2 to 0.6 μm.

[0009] An embodiment of the present invention further provides a preparation method of a polyamide 56 resin, including obtaining the polyamide 56 resin by polymerizing monomers. The polyamide 56 resin contains titanium dioxide, and the titanium dioxide is added during the polymerization reaction.

[0010] An embodiment of the present invention further provides a polyamide 56 fiber, which is obtained by melt spinning the above polyamide 56 resin, or directly spun from the melt generated during the preparation process of the polyamide 56 resin.

[0011] One embodiment of the present invention further provides a polyamide 56 fiber, which is prepared by melt spinning from a polyamide 56 resin; wherein, the polyamide 56 resin contains titanium dioxide, and the titanium dioxide is added during the polymerization reaction of polyamide 56, and the content of the titanium dioxide is 0.2-0.4 wt% or 1.2-2.0 wt%, and the dispersion particle size of more than 98.5% of the titanium dioxide is 0.2-0.6 μm, and the dispersion particle size of more than 96% of the titanium dioxide is 0.2-0.35 μm;

[0012] The relative viscosity of the polyamide 56 resin is 2.3-3.0, the oligomer content is 0.8 wt% or less, and the degree of polymerization of the oligomer is 5 or less;

[0013] The coefficient of variation of the breaking strength of the polyamide 56 fiber is 5.0% or less, and the crimp stability of the polyamide 56 fiber is 40-56%.

[0014] One embodiment of the present invention further provides a method for preparing the above polyamide 56 fiber, comprising the following steps:

[0015] (a) Heating the polyamide 56 resin to a molten state to obtain a polyamide 56 melt;

[0016] (b) Feeding the polyamide 56 melt into a spinning box, injecting it into a spinning pack, and extruding a nascent fiber from a spinneret hole;

[0017] (c) Cooling, oiling, stretching, and winding the nascent fiber to obtain a polyamide 56 pre-oriented yarn;

[0018] (d) Thermally stretching the polyamide 56 pre-oriented yarn through a first roller, then cooling and shaping, and then passing it through a false twister, a second roller, an air-jet texturing device, oiling, and winding to obtain a polyamide 56 fiber.

[0019] One embodiment of the present invention further provides an application of the above polyamide 56 fiber in knitted or woven fabrics.

[0020] The polyamide 56 fiber of one embodiment of the present invention has good mechanical properties, moisture absorption, and dyeing properties. Detailed Embodiments

[0021] Typical embodiments demonstrating the features and advantages of the invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments, all of which do not depart from the scope of the present invention, and the descriptions therein are essentially for illustrative purposes and not for limiting the present invention.

[0022] An embodiment of the present invention provides a method for preparing polyamide 56 resin, which includes preparing polyamide 56 resin by polymerizing monomers, wherein the polyamide 56 resin contains titanium dioxide, and the titanium dioxide is added during the polymerization reaction.

[0023] In the method of an embodiment of the present invention, titanium dioxide is added during the polymerization of polyamide 56 for in-situ polymerization, so that the titanium dioxide can be evenly distributed in the polyamide 56 resin, effectively avoiding problems such as broken filaments and poor dyeability during subsequent spinning; at the same time, the preparation method is simple and easy to operate, and the production cost is low.

[0024] In the method of an embodiment of the present invention, TiO2 is directly added during the polymerization for in-situ polymerization. This method is relatively simple to operate and easy to control, does not require an additional masterbatch adding device, can reduce production investment, and adding TiO2 during the polymerization can make the mixing time of TiO2 and the resin longer, making the dispersion of TiO2 in the matrix resin more uniform. There are fewer broken single filaments and fly filaments during subsequent spinning, and the fiber has high strength and good dyeability.

[0025] In one embodiment, the particle size of the titanium dioxide powder added during the polymerization of polyamide 56 can be 0.15 - 0.5 μm, further can be 0.15 - 0.4 μm, further can be 0.15 - 0.3 μm, such as 0.18 μm, 0.20 μm, 0.22 μm, 0.23 μm, 0.25 μm, 0.27 μm, 0.28 μm.

[0026] Among them, the titanium dioxide can be added to the polymerization system of polyamide 56 in the form of particles, or can be added to the polymerization system of polyamide 56 in the form of a slurry of titanium dioxide.

[0027] In one embodiment, the addition amount of titanium dioxide is 0.2 - 5.0 wt% of the total weight of the polyamide 56 resin, and further is 0.2 - 3.0 wt%.

[0028] In one embodiment, the production raw materials of the polyamide 56 resin at least include 1,5-pentanediamine and adipic acid; or, polyamide 56 is polymerized using 1,5-pentanediamine and adipic acid as monomers.

[0029] In one embodiment, 1,5-pentanediamine is prepared from bio-based raw materials by fermentation or enzymatic conversion.

[0030] In the method for preparing polyamide 56 resin according to an embodiment of the present invention, the production raw materials adopt materials from non-petroleum-based sources, such as bio-based sources. The materials from bio-based sources do not cause large pollution and are beneficial to environmental protection.

[0031] In one embodiment, the method for preparing polyamide 56 resin includes:

[0032] (1) Prepare a polyamide 56 salt solution;

[0033] (2) Use the polyamide 56 salt solution as a raw material for polymerization to obtain a polyamide 56 melt;

[0034] (3) Filter the polyamide 56 melt through a melt filter, and finally pelletize and dry to obtain polyamide 56 resin.

[0035] In one embodiment, titanium dioxide can be added at any one or more stages of step (1) and step (2).

[0036] In one embodiment, step (1) includes: under nitrogen conditions, mixing 1,5-pentanediamine, adipic acid and water evenly to prepare a polyamide 56 salt solution.

[0037] In one embodiment, the molar ratio of 1,5-pentanediamine to adipic acid can be (1 to 1.08):1, such as 1.02:1, 1.04:1, 1.05:1, 1.06:1, etc.

[0038] In one embodiment, step (2) includes: heating the polyamide 56 salt solution to raise the pressure in the reaction system to 0.3 to 2.4 MPa (gauge pressure), exhausting and maintaining the pressure for 0.2 to 2.5 h, then reducing the pressure to make the pressure in the reaction system drop to 0 to 0.3 MPa (gauge pressure), and then evacuating to a vacuum degree of -0.001 to -0.08 MPa (gauge pressure) to obtain a polyamide 56 melt.

[0039] In one embodiment, the temperature of the reaction system at the end of the pressure maintenance in step (2) is 230 to 265 °C, such as 235 °C, 240 °C, 245 °C, 250 °C, 255 °C, etc.

[0040] In one embodiment, the pressure maintenance time in step (2) is 0.5 to 2 h, further 0.5 to 1.5 h, such as 0.8 h, 1 h, 1.2 h.

[0041] In one embodiment, the temperature of the reaction system after the pressure reduction in step (2) is 240 to 275 °C, such as 245 °C, 250 °C, 255 °C, 260 °C, 265 °C, 270 °C, etc.

[0042] In one embodiment, the temperature after evacuation in step (2) is 250 to 285 °C, such as 255 °C, 260 °C, 265 °C, 270 °C, 275 °C, 280 °C, etc.

[0043] In one embodiment, the time for maintaining the vacuum degree after evacuation in step (2) is 10 to 50 min; further 15 to 45 min.

[0044] In one embodiment, a second additive can be added to the reaction system, and it can be added at any one or more stages of step (1) and step (2). The second additive can be added simultaneously with titanium dioxide or not simultaneously.

[0045] In one embodiment, the second additive can include one or more of a flame retardant, an antioxidant, a capping agent, an ultraviolet absorber, an infrared absorber, a crystal nucleating agent, a fluorescent brightening agent, and an antistatic agent.

[0046] In one embodiment, the addition amount of the second additive accounts for 0 to 1% of the total weight of the raw materials for producing polyamide 56 resin, such as 0.05%, 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, etc.

[0047] In one embodiment, after the drying treatment in step (3), the moisture content of the resin is 300 to 1000 ppm, further it can be 300 to 800 ppm, and still further it can be 600 to 800 ppm.

[0048] In one embodiment, the temperature of the drying treatment in step (3) can be 80 to 130 °C, further it can be 100 to 110 °C, such as 90 °C, 95 °C, 98 °C, 102 °C, 104 °C, 105 °C, 106 °C, 108 °C, 115 °C, 120 °C, 125 °C, etc.

[0049] In one embodiment, the time of the drying treatment in step (3) can be 10 to 30 h, further it can be 15 to 25 h, such as 12 h, 16 h, 18 h, 20 h, 22 h, 24 h, 28 h, etc.

[0050] In one embodiment, before pelletizing in step (3), a melt filter is used for filtration to remove large-sized particles generated by the agglomeration of TiO2 during the polymerization process, which can make the particle size of titanium dioxide in the polyamide 56 resin small and the distribution narrow, further improving the uniformity of the polyamide 56 melt, and thus avoiding the phenomena of broken single filaments and a large number of fuzz filaments generated during the stretching process due to too large particle size and the resulting impact on the mechanical properties and dyeing properties of the fiber, resulting in fewer broken single filaments and increased dyeing properties in the subsequent spinning process.

[0051] In one embodiment, after filtration by the melt filter, the dispersion particle size of titanium dioxide in the delustered polyamide 56 resin is 0.2 to 1.0 μm. Further, the dispersion particle size of more than 98% of the titanium dioxide particles is 0.2 to 0.6 μm, and still further, the dispersion particle size of more than 95% of the titanium dioxide particles is 0.2 to 0.35 μm.

[0052] In one embodiment, the mesh number of the filter screen of the melt filter is 5 to 15 μm.

[0053] In one embodiment of the preparation method of the polyamide 56 resin of the present invention, TiO2 is used for in-situ polymerization to prepare the matte polyamide 56 resin. By strictly controlling the particle size and distribution of TiO2 particles, TiO2 agglomerated particles can be avoided or removed, the particle size distribution range can be reduced, and the spinning performance can be improved.

[0054] One embodiment of the present invention provides a polyamide 56 resin, which can be prepared by the above method.

[0055] One embodiment of the present invention provides a polyamide 56 resin, the relative viscosity of which can be 2.3 to 3.0, further 2.5 to 2.8; the oligomer content is 1.5 wt% or less, further 1 wt% or less, further 0.8 wt% or less, such as 0.3 to 1.0 wt%, 0.3 to 0.8 wt%, etc.; the moisture content can be 300 to 1000 ppm, further 300 to 800 ppm, still further 600 to 800 ppm; the number average molecular weight is 15000 to 42000, further 18000 to 35000; the molecular weight distribution is 1.2 to 2.0, further 1.4 to 1.8. The degree of polymerization of the oligomer described in the present invention is 5 or less.

[0056] The polyamide 56 resin of one embodiment of the present invention has a low oligomer content, a narrow molecular weight distribution of the polyamide resin, and a moderate viscosity.

[0057] In one embodiment, the relative viscosity of the polyamide 56 resin can be 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, etc.

[0058] In one embodiment, the moisture content of the polyamide 56 resin can be 350 ppm, 550 ppm, 650 ppm, 700 ppm, 750 ppm, 850 ppm, 900 ppm, etc.

[0059] In one embodiment, the number average molecular weight of the polyamide 56 resin can be 16000, 20000, 22000, 25000, 28000, 30000, 32000, 34000, 38000, 40000, etc.

[0060] In one embodiment, the molecular weight distribution of the polyamide 56 resin can be 1.3, 1.5, 1.6, 1.7, 1.9, etc.

[0061] In one embodiment, the content of the polyamide 56 resin oligomer can be 0.3%, 0.6%, or 1.0%. The degree of polymerization of the oligomer described in the present invention is 10 or less. If the content of the oligomer in the resin is too high, during the spinning process, the oligomer will precipitate and condense under the spinneret. Excessive precipitation will affect the spinning, resulting in broken single filaments during spinning and reducing the service life of the spinning pack.

[0062] In one embodiment, the polyamide 56 resin contains a titanium dioxide matting agent.

[0063] In one embodiment, the polyamide 56 resin can be a semi-matt polyamide 56 resin, a matt polyamide 56 resin, or a full-matt polyamide 56 resin.

[0064] In one embodiment, the polyamide 56 resin is a semi-matt polyamide 56 resin, and its titanium dioxide content is 0.2 - 0.4 wt%, further can be 0.25 - 0.35 wt%, for example 0.3 wt%.

[0065] In one embodiment, the polyamide 56 resin is a full-matt polyamide 56 resin, and its titanium dioxide content is 1.2 - 2.0 wt%, further can be 1.4 - 1.8 wt%, for example 1.5 wt%, 1.6 wt%, 1.7 wt%.

[0066] In one embodiment, the polyamide 56 resin is a super-matt polyamide 56 resin, and its titanium dioxide content is 2.5 - 5.0 wt%, further can be 3.0 - 4.5 wt%, for example 2.8 wt%, 3.2 wt%, 3.5 wt%, 4.0 wt%, 4.2 wt%, 4.4 wt%, 4.8 wt%.

[0067] In one embodiment, the dispersion particle size of titanium dioxide in the polyamide 56 resin is 0.2 - 1.0 μm. Further, the particle distribution ratio of titanium dioxide with a dispersion particle size of 0.2 - 0.6 μm is above 98%. Further, the ratio of the dispersion particle size of titanium dioxide particles being 0.2 - 0.6 μm is above 98.5%. Further, the particle distribution ratio of titanium dioxide with a dispersion particle size of 0.2 - 0.35 μm is above 95%. Further, the ratio of the dispersion particle size of titanium dioxide particles being 0.2 - 0.35 μm is above 96%. Among them, the above description of the percentage content of titanium dioxide refers to the percentage content of the number of titanium dioxide particles.

[0068] One embodiment of the present invention provides a polyamide 56 fiber, which can be prepared by melt spinning from the above polyamide 56 resin.

[0069] In one embodiment, the polyamide 56 fiber can be a semi-dull polyamide 56 fiber, a dull polyamide 56 fiber, or a full dull polyamide 56 fiber; among them, the semi-dull polyamide 56 fiber, the dull polyamide 56 fiber, and the full dull polyamide 56 fiber can be prepared by melt spinning using semi-dull polyamide 56 resin, dull polyamide 56 resin, and full dull polyamide 56 resin, respectively.

[0070] In one embodiment, the polyamide 56 fiber includes undrawn yarn (UDY), fully drawn yarn (FDY), pre-oriented yarn (POY), highly oriented yarn (HOY), fully oriented yarn (FOY), drawn textured yarn (DTY), bulk continuous filament (BCF), monofilament, staple fiber, and industrial yarn, preferably pre-oriented yarn (POY) and drawn textured yarn (DTY). The drawn textured yarn is also known as drawn false twist yarn or drawn textured yarn.

[0071] The polyamide 56 fiber of one embodiment of the present invention has the advantages of high strength, low-temperature dyeability, moisture absorption, softness, wear resistance, and high elasticity, and has broad development prospects in the fields of civil yarn and industrial yarn.

[0072] In one embodiment, the fineness of the polyamide 56 fiber monofilament can be 0.5 to 5.0 dtex, further 0.8 to 4.0 dtex, still further 1.2 to 3.0 dtex, and even further 1.2 to 2.0 dtex, such as 1.0, 1.5, 1.8, 2.5, 3.5, 4.5 dtex, etc.

[0073] In one embodiment, the breaking strength of the polyamide 56 fiber can be 3.3 to 5.5 cN / dtex, further 3.5 to 4.8 cN / dtex, still further 3.7 to 4.5 cN / dtex, and even further 3.9 to 4.2 cN / dtex.

[0074] In one embodiment, the coefficient of variation of the breaking strength of the polyamide 56 fiber is 5.0% or less, further 3.0% or less, still further 2.5% or less, and even further 2.0% or less.

[0075] In one embodiment, the initial modulus of the polyamide 56 fiber can be 15 to 35 cN / dtex, further 22 to 33 cN / dtex, still further 24 to 30 cN / dtex, and even further 26 to 28 cN / dtex.

[0076] In one embodiment, the boiling water shrinkage rate of the polyamide 56 fiber can be ≤7%, further ≤6.8%, still further ≤6.5%, and even further ≤6.0%.

[0077] In one embodiment, the moisture regain of the polyamide 56 fiber may be ≥4.0%, further ≥4.5%, further ≥5.0%, and further ≥5.5%.

[0078] In one embodiment, the crimp shrinkage of the polyamide 56 fiber may be 35 to 60%, further 40 to 58%, and further 45 to 55%.

[0079] In one embodiment, the curl stability of the polyamide 56 fiber may be 38-58%, further may be 40-56%, further may be 48-54%, for example 45%, 50%, 52%.

[0080] In one embodiment, the dyeing uniformity (gray card) of the polyamide 56 fiber is ≥3.5, further ≥4.0, further ≥4.5, and further ≥5.0.

[0081] In one embodiment, the M rate of the polyamide 56 fiber is ≥92%, further ≥94%, further ≥96%, and further ≥98%.

[0082] In one embodiment, the soap fastness of polyamide 56 fiber: fading fastness can be ≥ grade 3.5, further can be ≥ grade 4.0, further can be ≥ grade 4.5, further can be ≥ grade 5.0; staining fastness can be ≥ grade 3.5, further can be ≥ grade 4.0, further can be ≥ grade 4.5, further can be ≥ grade 5.0.

[0083] One embodiment of the present invention provides a method for preparing the above-mentioned polyamide 56 fiber, comprising the following steps:

[0084] (a) heating a polyamide 56 resin to a molten state to form a polyamide 56 melt;

[0085] (b) transporting the polyamide 56 melt to the spinning manifold through a melt pipe, and after being accurately metered by a metering pump, injecting it into the spinning assembly, and extruding it from the spinneret hole under high pressure to obtain nascent fibers;

[0086] (c) The extruded spun fibers are cooled, oiled, stretched, and wound to obtain polyamide 56 pre-oriented fibers.

[0087] (d) The polyamide 56 pre-oriented yarn is passed through a yarn guide to the first roller, passed through a twist stopper, and heat-stretched in a first hot box. Then, the yarn is cooled and shaped using a cooling plate. The yarn is passed through a false twister, a second roller, a network device, oiled, and wound to obtain a polyamide 56 stretch yarn.

[0088] In one embodiment, the heating in step (a) is carried out by a screw, where the temperature in zone 1 can be 245 - 265°C, further can be 250 - 260°C; the temperature in zone 2 can be 260 - 280°C, further can be 265 - 275°C; the temperature in zone 3 can be 275 - 285°C, further can be 278 - 283°C; the temperature in zone 4 can be 280 - 290°C.

[0089] In one embodiment, the temperature of the spinning box in step (b) can be 278 - 290°C, further can be 282 - 285°C; the pressure of the spinning pack can be 13 - 22 MPa, further can be 15 - 18 MPa.

[0090] In one embodiment, the cooling in step (c) includes side air blowing cooling and ring air blowing cooling, preferably ring air blowing cooling; the wind speed can be 0.3 - 0.8 m / s, further can be 0.45 - 0.6 m / s; the wind temperature can be 18 - 23°C; the wind humidity can be 50 - 85%, further can be 55 - 70%.

[0091] In one embodiment, the oiling in step (c) is nozzle oiling; the oiling rate can be 0.4 - 0.6 wt%, further can be 0.45 - 0.55 wt%; the oiling height can be 80 - 150 cm, further can be 90 - 130 cm, and further can be 95 - 110 cm.

[0092] In one embodiment, the winding speed during winding and forming in step (c) can be 4000 - 5000 m / min, further can be 4200 - 4800 m / min, and further can be 4300 - 4500 m / min; the overfeed speed can be 10 - 100 m / min, further can be 20 - 80 m / min.

[0093] In one embodiment, the draw ratio of the hot drawing in step (d) can be 1.1 - 1.4, further can be 1.15 - 1.35; the temperature of the hot drawing can be 160 - 210°C, further can be 170 - 205°C, and further can be 180 - 195°C.

[0094] In one embodiment, the false twist ratio D / Y of the false twister in step (d) can be 1.3 - 2.2, further can be 1.5 - 2.0; the pressure of the compressed air in the texturing device can be 0.3 - 1.5 MPa, further can be 0.4 - 1.2 MPa, and further can be 0.5 - 1.0 MPa.

[0095] In one embodiment, the oiling in step (d) is nozzle oiling; the oiling rate can be 2.2 - 2.8 wt%, further can be 2.3 - 2.6 wt%.

[0096] In one embodiment, the winding speed during winding in step (d) can be 300 - 800 m / min, further can be 400 - 700 m / min; the overfeed speed during winding is 1 - 8%, further can be 1.5 - 6%, and still further can be 2 - 5%.

[0097] In one embodiment of the present invention, the raw materials for producing polyamide 56 fiber can be made by biological method, which are green materials, do not rely on petroleum resources and do not cause serious pollution to the environment. At the same time, it can reduce carbon dioxide emissions and the generation of greenhouse effect.

[0098] The polyamide 56 fiber of one embodiment of the present invention can be prepared by using the spinning equipment of conventional polyamide 6 and polyamide 66 without modifying the spinning equipment. By optimizing the quality of polyamide 56 fiber resin and the spinning process, the production rate can be improved.

[0099] The polyamide 56 fiber of one embodiment of the present invention has good mechanical properties, dimensional stability, moisture absorption and dyeing properties, and has a good dulling effect in the application of knitted or woven fabrics.

[0100] One embodiment of the present invention provides an application of the above polyamide 56 fiber in knitted or woven fabrics. Among them, the light transmittance of the polyamide 56 fabric can be ≤50%, further can be ≤48%, still further can be ≤35%, and even further can be ≤30%.

[0101] In one embodiment, the polyamide 56 fiber has high strength, softness, moisture absorption, fluffiness (crimp stability), easy dyeing and dulling properties, and is more suitable for application in the knitting field and civilian clothing. The applications for knitted and woven fabrics include, but are not limited to, applications in underwear, shirts, suits, yoga clothes, down jackets, windbreakers, socks, luggage, curtains, shoe materials, embroidery threads, trademarks, sofa fabrics, work clothes, sportswear, elastic bands, etc.

[0102] The fabric prepared from the polyamide 56 fiber of one embodiment of the present invention has good dulling properties. With the same TiO2 content, the dulling effect is better than that of polyamide 6 fiber and polyamide 66 fiber. And for preparing the polyamide 56 fabric with the same dulling effect, the required added TiO2 content is lower, which can reduce the production cost.

[0103] The light transmittance of the semi-dull polyamide 56 fabric of one embodiment of the present invention can be ≤48%, the light transmittance of the full-dull polyamide 56 fabric can be ≤33%, and the light transmittance of the super-dull polyamide 56 fabric can be ≤25%.

[0104] The following further describes the polyamide 56 resin, polyamide 56 fiber and their preparation according to an embodiment of the present invention in conjunction with specific embodiments. Among them, unless otherwise specified, the raw materials used can be obtained commercially, and the details of the relevant tests involved are as follows; in addition, the parameters involved in the present invention are measured according to the following methods.

[0105] 1) Denier:

[0106] It is measured according to GB / T 14343.

[0107] 2) Tensile strength and modulus: The measurement of tensile strength can refer to GB / T 14344-2008 Test Method for Tensile Properties of Chemical Fibers; apply a pre-tension of 0.05 ± 0.005 cN / dtex, a gripping distance of 500 mm, and a tensile speed of 500 mm / min; modulus = the tensile strength corresponding to a fracture elongation of 1% × 100.

[0108] 3) Moisture regain measurement method: After washing the fiber, dry it in a loose state in an oven, and then place the dried fiber sample in a standard atmosphere specified in GB / T6529 to condition it to equilibrium; perform moisture regain measurement, and the moisture regain measurement method is carried out according to GB / T6503, where the drying temperature of the oven is 105°C for drying.

[0109] 4) Boiling water shrinkage rate:

[0110] It is measured according to GB / 6505, and the pre-tension is 0.05 ± 0.005 cN / dtex.

[0111] 5) Dyeing evenness (grey scale) / grade:

[0112] Refer to FZ / T 50008 Test Method for Dyeing Evenness of Nylon Filament Yarns, keep it at 98°C for 30 min, and judge the dyeing evenness.

[0113] 6) Resin moisture content:

[0114] It is measured by a Karl Fischer moisture titrator.

[0115] 7) Crimp shrinkage rate and crimp stability: GB / T 6506-2001 Test Method for Crimp Properties of Synthetic Fiber Textured Yarns.

[0116] 8) Soaping fastness:

[0117] It is measured according to GB / T 3921.1-1997.

[0118] 9) Relative viscosity of the resin: by the concentrated sulfuric acid method using an Ubbelohde viscometer: accurately weigh 0.25±0.0002 g of the dried polyamide resin slices, add 50 mL of concentrated sulfuric acid (96 wt%) to dissolve; measure and record the concentrated sulfuric acid flow time t0 and the polyamide sample solution flow time t in a 25°C constant temperature water bath;

[0119] Viscosity calculation formula: relative viscosity = t / t0;

[0120] t—solution flow time;

[0121] t0—Solvent flow time.

[0122] 10) Number average molecular weight and molecular weight distribution of resin: measured by gel permeation chromatography (GPC).

[0123] 11) Dispersed particle size of titanium dioxide: The dispersed particle size of titanium dioxide was measured and counted from transmission electron microscopy images of polyamide resin slices.

[0124] 12) M rate: M rate = ((weight of fibers with dyeing uniformity ≥ 4.5) / total weight of all dyed fibers) × 100%.

[0125] 13) Matting property: The fibers prepared in the examples and comparative examples were woven on the same air-jet loom, rinsed on an open-width soaping machine, and dyed on a liquid jet dyeing machine to prepare fabrics of uniform specifications. A specific inspection team (10 people) was set up to visually evaluate the matting level of the fabrics and take the average value, that is, by comparing the surface matting of the fabrics under a halogen lamp simulating sunlight and a temperature of 25°C, the matting evaluation levels were divided into 1, 2, 3, 4, and 5, indicating that the matting properties ranged from low to very high, respectively.

[0126] 14) Transmittance: measured by UV-visible spectrophotometer, scanning wavelength is 300-800nm, and the transmittance of fabric refers to the transmittance at a wavelength of 550nm.

[0127] 15) Fiber production rate: Production rate = (weight of finished fiber prepared / total weight of resin input) × 100%.

[0128] 16) Test of oligomer content in resin:

[0129] The polyamide sample was dried in a forced-air oven at 130 °C for 7 hours, then placed in an aluminum-plastic bag, sealed, and cooled in a desiccator. Then, 2 g of the polyamide sample was accurately weighed and placed in a 250 mL round-bottom flask. 100 mL of water was added, and the mixture was heated under reflux at 100 °C for 24 hours using a heating mantle. The polyamide sample was taken out and washed three times with pure water. The polyamide sample was dried in a forced-air oven at 130 °C for 7 hours, then transferred to a pre-weighed aluminum-plastic bag, sealed, and cooled in a desiccator. The total weight of the aluminum-plastic bag and the polyamide sample was weighed and subtracted from the weight of the aluminum-plastic bag to obtain the weight of the polyamide sample after boiling. The oligomer content was calculated by comparing the weight difference of the polyamide sample before and after boiling. Parallel samples were taken for testing of each sample.

[0130] 17) Testing the titanium dioxide content in the resin: Calcination method. 10 g of the sample was placed in a crucible and calcined in a muffle furnace at 480 °C for 10 h, and the weight of the residue in the crucible was weighed.

[0131] 18) Testing the coefficient of variation (CV) of the breaking strength: Refer to GB / T 14344-2008 Test method for tensile properties of chemical fibers. If the titanium dioxide is evenly distributed in the fiber, then during the stretching process, different numbers of fibers break simultaneously, and the corresponding breaking strength at break is the same, which is reflected by a small coefficient of variation.

[0132] 19) Number of broken filaments: During the preparation of polyamide fibers from the nascent fibers, the number of broken filaments was manually counted.

[0133] Example 1

[0134] Preparation of polyamide 56 resin

[0135] (1) Under nitrogen conditions, 1,5-pentanediamine, adipic acid, and water were mixed evenly to obtain a polyamide 56 salt solution; among them, the molar ratio of 1,5-pentanediamine to adipic acid was 1.05:1.

[0136] (2) Titanium dioxide with a particle size of 0.2 μm was added to the polyamide 56 salt solution, and the salt solution system was heated to raise the pressure in the reaction system to 2.4 MPa, exhaust and maintain the pressure for 1.2 h, then reduce the pressure to make the pressure in the reaction system drop to a gauge pressure of 0 MPa, and then evacuate to a vacuum degree of -0.04 MPa. The time to maintain the above vacuum degree was 35 min to obtain a polyamide 56 melt; among them, the addition amount of titanium dioxide was 0.27 wt% of the resin mass prepared without adding titanium dioxide under the same conditions. The temperature of the reaction system at the end of pressure maintenance was 260 °C, the temperature of the reaction system after pressure reduction was 275 °C, and the temperature of the reaction system after evacuation was 280 °C.

[0137] (3) Filter the polyamide 56 melt through a melt filter with a screen mesh size of 10 μm in the melt filter, and then pelletize and dry to obtain polyamide 56 resin; among them, the drying temperature is 110 °C and the drying time is 20 h.

[0138] Preparation of polyamide 56 fiber

[0139] (a) Heat the above-prepared polyamide 56 resin to a molten state to form a polyamide 56 melt; the heating is carried out by a screw, where the temperature of the first zone is 253 °C, the temperature of the second zone is 266 °C, the temperature of the third zone is 278 °C, and the temperature of the fourth zone is 288 °C.

[0140] (b) Transport the polyamide 56 melt to the spinning box through a melt pipe. After accurate metering by a metering pump, it is injected into the spinning pack and extruded under high pressure from the spinneret holes; among them, the temperature of the spinning box is 285 °C and the pressure of the spinning pack is 16.2 MPa.

[0141] (c) Cool, oil, stretch, and wind the extruded nascent fiber to obtain polyamide 56 pre-oriented yarn; among them, the cooling is carried out by ring blowing, the wind speed is 0.48 m / s, the wind temperature is 20 °C, and the wind humidity is 80%; the oiling is carried out by oiling at the oil nozzle, the oiling rate is 0.5 wt%, and the oiling height is 110 cm; the winding speed during winding is 4300 m / min and the overfeed speed is 60 m / min.

[0142] (d) Feed the polyamide 56 pre-oriented yarn through a thread guide to the first roller, pass through a twist stopper, and perform hot stretching in the first hot box, then cool and shape it with a cooling plate, and pass through a false twister, the second roller, a texturing device, oiling at the oil nozzle, and winding to obtain polyamide 56 drawn textured yarn;

[0143] Among them, the multiple of hot stretching is 1.3, the temperature of hot stretching is 185 °C; the speed ratio D / Y of the false twister is 1.8; the pressure of compressed air in the texturing device is 0.8 MPa; the oiling is carried out by oiling at the oil nozzle, the oiling rate is 2.5 wt%; the winding speed during winding is 600 m / min and the winding overfeed speed during winding is 2.5%.

[0144] Example 2

[0145] Preparation of polyamide 56 resin

[0146] Prepare polyamide 56 resin using substantially the same raw materials and process as in Example 1, with the only difference being that: the addition amount of titanium dioxide in step (2) is 0.34 wt%.

[0147] Preparation of polyamide 56 fiber

[0148] The polyamide 56 resin prepared above is used as the raw material for spinning, and the specific spinning process is the same as that in Example 1.

[0149] Example 3

[0150] Preparation of polyamide 56 resin

[0151] The same raw materials as in Example 1 are used, with the only differences being that the vacuum degree in step (2) is -0.07 MPa and the holding time is 10 min, and the addition amount of titanium dioxide in step (2) is 0.35 wt%.

[0152] Preparation of polyamide 56 fiber

[0153] The polyamide 56 resin prepared above is used as the raw material for spinning, and the specific spinning process is the same as that in Example 1.

[0154] Example 4

[0155] Preparation of polyamide 56 resin

[0156] Polyamide 56 resin is prepared using the same raw materials and process as in Example 1, with the only differences being that the addition amount of titanium dioxide in step (2) is 1.23 wt% and the mesh number of the filter screen in the melt filter in step (3) is 5 μm.

[0157] Preparation of polyamide 56 fiber

[0158] The polyamide 56 resin prepared above is used as the raw material for spinning, and the specific spinning process is the same as that in Example 1.

[0159] Example 5

[0160] Preparation of polyamide 56 resin

[0161] Polyamide 56 resin is prepared using the same raw materials and process as in Example 1, with the only differences being that the addition amount of titanium dioxide in step (2) is 1.56 wt% and the mesh number of the filter screen in the melt filter in step (3) is 15 μm.

[0162] Preparation of polyamide 56 fiber

[0163] The polyamide 56 resin prepared above is used as the raw material for spinning, and the specific spinning process is the same as that in Example 1.

[0164] Example 6

[0165] Preparation of polyamide 56 resin

[0166] Polyamide 56 resin is prepared using the same raw materials and process as in Example 1, with the only difference being that the addition amount of titanium dioxide in step (2) is 1.84 wt%.

[0167] Preparation of Polyamide 56 Fiber

[0168] Using the polyamide 56 resin obtained above as raw material for spinning, the specific spinning process is the same as that in Example 1.

[0169] Example 7

[0170] Preparation of Polyamide 56 Resin

[0171] Preparing polyamide 56 resin using substantially the same raw materials and process as in Example 1, with the only difference being that the addition amount of titanium dioxide in step (2) is 2.56 wt%.

[0172] Preparation of Polyamide 56 Fiber

[0173] Using the polyamide 56 resin obtained above as raw material for spinning, the specific spinning process is the same as that in Example 1.

[0174] Example 8

[0175] Preparation of Polyamide 56 Resin

[0176] Preparing polyamide 56 resin using substantially the same raw materials and process as in Example 1, with the only difference being that the addition amount of titanium dioxide in step (2) is 3.05 wt%.

[0177] Preparation of Polyamide 56 Fiber

[0178] Using the polyamide 56 resin obtained above as raw material for spinning, the specific spinning process is the same as that in Example 1.

[0179] Example 9

[0180] Preparation of Polyamide 56 Resin

[0181] Preparing polyamide 56 resin using substantially the same raw materials and process as in Example 1, with the only difference being that the addition amount of titanium dioxide in step (2) is 4.05 wt%.

[0182] Preparation of Polyamide 56 Fiber

[0183] Using the polyamide 56 resin obtained above as raw material for spinning, the specific spinning process is the same as that in Example 1.

[0184] Example 10

[0185] Preparation of Polyamide 56 Resin

[0186] The polyamide 56 resin was prepared using substantially the same raw materials and process as in Example 1, except that: the addition amount of titanium dioxide in step (2) was 0.34 wt%, the vacuum was pumped to a vacuum degree of -0.06 MPa, and the temperature of the reaction system after vacuum pumping was 285 °C.

[0187] Preparation of polyamide 56 fiber

[0188] The polyamide 56 resin prepared above was used as the raw material for spinning, and the specific spinning process was the same as that in Example 1.

[0189] Example 11

[0190] Preparation of polyamide 56 resin

[0191] The polyamide 56 resin was prepared using substantially the same raw materials and process as in Example 10, except that: the addition amount of titanium dioxide in step (2) was 1.54 wt%.

[0192] Preparation of polyamide 56 fiber

[0193] The polyamide 56 resin prepared above was used as the raw material for spinning, and the specific spinning process was the same as that in Example 1.

[0194] Example 12

[0195] Preparation of polyamide 56 resin

[0196] The polyamide 56 resin was prepared using substantially the same raw materials and process as in Example 10, except that: the addition amount of titanium dioxide in step (2) was 2.53 wt%.

[0197] Preparation of polyamide 56 fiber

[0198] The polyamide 56 resin prepared above was used as the raw material for spinning, and the specific spinning process was the same as that in Example 1.

[0199] Example 13

[0200] Preparation of polyamide 56 fiber

[0201] The polyamide 56 resin prepared in Example 10 was used as the raw material for spinning, and the specific spinning process was substantially the same as that in Example 1: the only difference was that the spinning pack contained a 10 μm non-woven fabric filter.

[0202] Example 14

[0203] Preparation of polyamide 56 fiber

[0204] Using the polyamide 56 resin prepared in Example 11 as the raw material for spinning, the specific spinning process is basically the same as that in Example 1: the only difference is that the spinning pack contains a 15-μm nonwoven fabric filter screen.

[0205] Example 15

[0206] Preparation of polyamide 56 fiber

[0207] Using the polyamide 56 resin prepared in Example 11 as the raw material for spinning, the specific spinning process is basically the same as that in Example 1: the only difference is that the spinning pack contains a 20-μm nonwoven fabric filter screen.

[0208] Comparative Example 1

[0209] Preparation of polyamide 56 resin

[0210] Using basically the same raw materials and process as in Example 2 to prepare polyamide 56 resin, the only difference is that in step (3), filtration through a melt filter was not carried out, and the polyamide 56 resin was directly pelletized.

[0211] Preparation of polyamide 56 fiber

[0212] Using the above-prepared polyamide 56 resin as the raw material for spinning, the specific spinning process is the same as that in Example 1.

[0213] Comparative Example 2

[0214] Preparation of polyamide 56 resin

[0215] Using basically the same raw materials and process as in Example 5 to prepare polyamide 56 resin, the only difference is that in step (3), filtration through a melt filter was not carried out, and the polyamide 56 resin was directly pelletized.

[0216] Preparation of polyamide 56 fiber

[0217] Using the above-prepared polyamide 56 resin as the raw material for spinning, the specific spinning process is the same as that in Example 1.

[0218] Comparative Example 3

[0219] Preparation of polyamide 56 resin

[0220] Using basically the same raw materials and process as in Example 7 to prepare polyamide 56 resin, the only difference is that in step (3), filtration through a melt filter was not carried out, and the polyamide 56 resin was directly pelletized.

[0221] Preparation of polyamide 56 fiber

[0222] Using the above-prepared polyamide 56 resin as the raw material for spinning, the specific spinning process is the same as that in Example 1.

[0223] Comparative Example 4

[0224] Preparation of Polyamide 6 Fibers

[0225] Polyamide 6 resin (viscosity 2.7, molecular weight distribution 1.59, oligomer content 0.61%, water content 612 ppm) was mixed with 0.33 wt% of titanium dioxide (particle size 0.2 um) as the spinning material, and spun through the same spinning process as in Example 1 to obtain polyamide 6 fibers; wherein the content of titanium dioxide was based on the mass of the polyamide 6 resin.

[0226] Comparative Example 5

[0227] Preparation of Polyamide 66 Fibers

[0228] Polyamide 66 resin (viscosity 2.68, molecular weight distribution 1.61, oligomer content 0.62%, water content 605 ppm) was mixed with 0.32 wt% of titanium dioxide (particle size 0.2 um) as the spinning material, and spun through the same spinning process as in Example 1 to obtain polyamide 66 fibers; wherein the content of titanium dioxide was based on the mass of the polyamide 66 resin.

[0229] Comparative Example 6

[0230] Preparation of Polyamide 56 Fibers

[0231] Polyamide 56 resin (viscosity 2.68, molecular weight distribution 1.61, oligomer content 0.61%, water content 607 ppm) was mixed with 0.26 wt% of titanium dioxide (particle size 0.2 um) as the spinning material, and spun through the same spinning process as in Example 1 to obtain polyamide 56 fibers; wherein the content of titanium dioxide was based on the mass of the polyamide 56 resin.

[0232] Comparative Example 7

[0233] Preparation of Polyamide 56 Resin

[0234] Polyamide 56 resin was prepared using substantially the same raw materials and process as in Example 5, except that: the mesh number of the filter screen in the melt filter in step (3) was 20 μm.

[0235] Preparation of Polyamide 56 Fibers

[0236] The above-prepared polyamide 56 resin was used as the raw material for spinning, and the specific spinning process was the same as in Example 1.

[0237] The polyamide 56 resins prepared in Examples 1 - 12 and Comparative Examples 1 - 3 were subjected to relevant performance tests, and the results are shown in Table 1.

[0238] Table 1 Performance of Polyamide 56 Resins in Examples and Comparative Examples

[0239]

[0240] The relevant performance tests were carried out on the polyamide fibers prepared in Examples 1-15 and Comparative Examples 1-7, and the results are shown in Table 2 and Table 3

[0241] Table 2 Performance of Polyamide Fibers in Examples and Comparative Examples

[0242]

[0243]

[0244] Table 3 Performance of Polyamide Fibers in Examples and Comparative Examples

[0245]

[0246] Unless otherwise specified, the terms used in the present invention have the meanings commonly understood by those skilled in the art

[0247] The embodiments described in the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above embodiments, but is only defined by the claims

Claims

1. A polyamide 56 fiber, which is prepared by melt spinning from polyamide 56 resin; wherein, The polyamide 56 resin contains titanium dioxide, which is added during the polymerization reaction of polyamide 56. The content of the titanium dioxide is 0.2 - 0.4 wt% or 1.2 - 2.0 wt%. The dispersion particle size of more than 98.5% of the titanium dioxide is 0.2 - 0.6 μm, and the dispersion particle size of more than 96% of the titanium dioxide is 0.2 - 0.35 μm; The relative viscosity of the polyamide 56 resin is 2.3 - 3.0, the oligomer content is 0.8 wt% or less, and the degree of polymerization of the oligomer is 5 or less; The coefficient of variation of the breaking strength of the polyamide 56 fiber is 5.0% or less, and the crimp stability of the polyamide 56 fiber is 40 - 56%; 2. The polyamide 56 fiber according to claim 1, having a monofilament fineness of 0.5 - 5.0 dtex; and / or, The breaking strength of the polyamide 56 fiber is 3.3 - 5.5 cN / dtex, further can be 3.5 - 4.8 cN / dtex, still further can be 3.7 - 4.5 cN / dtex, and even further can be 3.9 - 4.2 cN / dtex; and / or, The coefficient of variation of the breaking strength of the polyamide 56 fiber is 3.0% or less, further is 2.5% or less, and still further is 2.0% or less; and / or, The initial modulus of the polyamide 56 fiber is 15 - 35 cN / dtex, further can be 22 - 33 cN / dtex, still further can be 24 - 30 cN / dtex, and even further can be 26 - 28 cN / dtex; and / or, The boiling water shrinkage rate of the polyamide 56 fiber is ≤7%, further can be ≤6.8%, still further can be ≤6.5%, and even further can be ≤6.0%; and / or, The moisture regain rate of the polyamide 56 fiber is ≥4.0%, further can be ≥4.5%, still further can be ≥5.0%, and even further can be ≥5.5%; and / or, The crimp shrinkage rate of the polyamide 56 fiber is 35 - 60%, further can be 40 - 58%, still further can be 45 - 55%; and / or, The crimp stability of the polyamide 56 fiber is 48 - 54%; and / or, The dyeing uniformity of the polyamide 56 fiber is ≥3.5 grade, further can be ≥4.0 grade, still further can be ≥4.5 grade, and even further can be ≥5.0 grade; and / or, The M rate of the polyamide 56 fiber is ≥92%, further can be ≥94%, still further can be ≥96%, and even further can be ≥98%; and / or, The color fastness to fading of the polyamide 56 fiber is ≥3.5 grade, further can be ≥4.0 grade, still further can be ≥4.5 grade, and even further can be ≥5.0 grade; and / or, The color fastness to staining of the polyamide 56 fiber is ≥3.5 grade, further can be ≥4.0 grade, still further can be ≥4.5 grade, and even further can be ≥5.0 grade.

3. The polyamide 56 fiber according to claim 1, which comprises one or more of undrawn yarn, fully drawn yarn, pre-oriented yarn, highly oriented yarn, fully oriented yarn, texturized yarn, continuous bulked filament, staple fiber, monofilament and industrial yarn; and / or, the relative viscosity of the polyamide 56 resin is 2.5 to 2.8; and / or, the moisture content of the polyamide 56 resin can be 300 to 1000 ppm, further can be 300 to 800 ppm, and still further can be 600 to 800 ppm; and / or, the number-average molecular weight of the polyamide 56 resin is 15000 to 42000, further can be 18000 to 35000; and / or, the molecular weight distribution of the polyamide 56 resin is 1.2 to 2.0, further can be 1.4 to 1.

8.

4. The polyamide 56 fiber according to claim 3, which is pre-oriented yarn or texturized yarn.

5. A method for preparing the polyamide 56 fiber according to any one of claims 1 to 4, comprising the following steps: (a) Heating the polyamide 56 resin to a molten state to obtain a polyamide 56 melt; (b) Feeding the polyamide 56 melt into a spinning box, injecting it into a spinning pack, and extruding a nascent fiber from a spinneret hole; (c) Cooling, oiling, stretching and winding the nascent fiber to obtain a polyamide 56 pre-oriented yarn; (d) Subjecting the polyamide 56 pre-oriented yarn to hot stretching treatment by a first roller, then cooling and shaping, and then passing through a false twister, a second roller, an air entangler, oiling treatment and winding treatment to obtain a polyamide 56 fiber.

6. The method according to claim 5, wherein, In the step (a), the heating is carried out by a screw, the temperature of the first zone is 245 to 265 °C; the temperature of the second zone is 260 to 280 °C; the temperature of the third zone is 275 to 285 °C; the temperature of the fourth zone is 280 to 290 °C; and / or, In the step (b), the temperature of the spinning box is 278 to 290 °C, and the pressure of the spinning pack is 13 to 22 MPa.

7. The method according to claim 5, wherein In the step (c), the cooling treatment is carried out by side blowing cooling or ring blowing cooling, the air temperature is 18 to 23 °C, and the air humidity is 50 to 85%; and / or, the oiling treatment is oiling by an oil nozzle, and the oiling rate is 0.4 to 0.6 wt%; and / or, the winding speed of the winding treatment is 4200 to 5000 m / min, and the overfeed speed is 10 to 100 m / min.

8. The method according to claim 5, wherein In the step (d), the multiple of the hot stretching treatment is 1.1 to 1.4, and the temperature of the hot stretching treatment is 160 to 210 °C; the false twister speed ratio D / Y is 1.3 to 2.2; the pressure of the compressed air in the air entangler is 0.3 to 1.5 MPa; the oiling treatment is oiling by an oil nozzle, and the oiling rate is 2.2 to 2.8 wt%; the winding speed of the winding treatment is 300 to 800 m / min, and the winding overfeed speed during winding is 1 to 8%.

9. The method according to claim 5, wherein, The polyamide 56 resin is prepared by a polymerization reaction of monomers, the monomers include 1,5-pentanediamine and adipic acid, and the polymerization reaction process comprises the following steps: (1) Prepare a polyamide 56 salt solution; (2) Use the polyamide 56 salt solution as a raw material for polymerization to obtain a polyamide 56 melt; Add the titanium dioxide in the step (1) and / or the step (2).

10. The method according to claim 9, wherein, The step (2) includes: heating the polyamide 56 salt solution to raise the pressure of the reaction system of the polyamide 56 salt solution to 0.3 - 2.4 MPa, exhausting and maintaining the pressure for 0.2 - 2.5 h, then reducing the pressure to make the pressure in the reaction system drop to 0 - 0.3 MPa, and then evacuating to make the vacuum degree in the reaction system be -0.001 - -0.08 MPa.

11. The method according to claim 10, wherein, The temperature of the reaction system at the end of the pressure maintenance process is 230 - 265 °C; and / or, The temperature of the reaction system after the pressure reduction process is 240 - 275 °C; and / or, The temperature of the reaction system after evacuation is 250 - 285 °C; and / or, the time for maintaining the vacuum degree after evacuation is 10 - 50 min.

12. The method according to claim 9, including obtaining the polyamide 56 resin by filtering, pelletizing, and drying the polyamide 56 melt.

13. An application of the polyamide 56 fiber according to any one of claims 1 to 4 in a knitted or woven fabric.

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