A melt direct spinning polyamide 56 industrial yarn and its preparation method and application

Abstract

The present invention relates to the technical field of polyamide materials, and discloses a melt direct spinning polyamide 56 industrial yarn and its preparation method and application. By optimizing the melt direct spinning process, a large-capacity and high-performance bio-based polyamide 56 industrial yarn is prepared, with stable production, few broken single filaments, high fiber forming rate, few hairiness, and excellent low shrinkage performance, and is mainly applied to fields such as release cloth, sewing thread, and water cloth.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyamide materials, and particularly relates to a melt direct spinning polyamide 56 industrial yarn and its preparation method and application. Background Art

[0002] Melt spinning is one of the main forming methods of synthetic fibers, simply referred to as melt spinning. Melt spinning is divided into direct spinning method and chip spinning method. Direct spinning is to directly send the polymer melt after polymerization to spinning; chip spinning requires pre-spinning preparation processes such as casting, pelletizing, and drying of the high polymer melt and then sending it to spinning.

[0003] The monomer content in the polymer of polyamide 6 is relatively high (about 10 wt%), and the chips need to be extracted before melt spinning can be achieved. Currently, industrialized melt direct spinning cannot be realized. In the spinning process of polyamide 66, problems such as easy generation of gels and difficult dyeing are prone to occur, and there are great difficulties in the melt direct spinning technology of civil yarns. Although melt direct spinning has been partially realized in the field of industrial yarns, the melt conveying pipeline and the spinning box need to be disassembled, calcined, and cleaned regularly, increasing the spinning cost.

[0004] CN105669969 B discloses a nylon 6 polymerization method and its melt direct spinning method. By first preparing a polyamide 6 prepolymer at a low temperature, controlling the content of oligomers in the melt in advance, and then through a method of strengthening the polycondensation reaction kinetics, polymerization is completed before a large amount of cyclic oligomers are generated, obtaining a nylon 6 polymer melt with a certain molecular weight. In the obtained product, the content of extractables is ≤ 1.5 wt%, and the content of cyclic dimers is ≤ 0.2 wt%. Then, after the polycondensation reaction kinetics strengthening ends, it is directly melt spun into shape, but there is still no technical breakthrough and industrialization case.

[0005] CN103668510 A discloses a device and method for producing fine denier or superfine denier nylon 66 filaments. The device includes an evaporator, a preheater, a reactor, a flash evaporator, and a post-polycondensation system. The nylon 66 brine solution is obtained through a polycondensation reaction to obtain a nylon 66 melt, and then the nylon 66 melt is directly spun to prepare fine denier or superfine denier nylon 66 POY filaments. The spinning speed is 4200 - 4300 m / min, the spinning speed is low, the output is low, and the fiber strength is low.

[0006] Bio-based polyamide 56 uses bio-based pentamethylenediamine as a monomer raw material. The carbon emissions per unit weight of bio-based polyamide 56 are reduced by more than 50% compared to the carbon emissions of the same weight of nylon 66 and nylon 6. The application and promotion of bio-based polyamide 56 will play a positive role in improving China's dependence on imported key materials and are of great significance for solving the sustainable development of fossil resource dependence and low-carbon emission reduction. Bio-based polyamide 56 materials have excellent mechanical properties, fast moisture absorption and drying, skin-friendly properties, abrasion resistance, good softness, and easy dyeing characteristics at low temperatures. Currently, they have broad application prospects in the fields of civil filament, staple fiber, industrial yarn, continuous bulk filament, monofilament, etc. However, there is currently no relevant research and report on the industrial production of large-capacity bio-based polyamide 56 industrial yarn by melt direct spinning. Summary of the Invention

[0007] In order to meet the industrial production requirements of melt direct spinning of bio-based polyamide 56, the present invention has prepared large-capacity and high-performance bio-based polyamide 56 industrial yarn by optimizing the melt direct spinning process, with stable production, few broken and single filaments, high fiber forming rate, few hairiness, and excellent low shrinkage properties.

[0008] The first object of the present invention is to provide a melt direct spinning polyamide 56 industrial yarn, which is prepared by the melt direct spinning one-step method. The dry heat shrinkage rate of the polyamide 56 industrial yarn is ≤9.0%, further ≤8.0%, and even further ≤7.5%; and / or

[0009] The boiling water shrinkage rate of the polyamide 56 industrial yarn is 4.0 - 12.0%, further 5.0 - 11.0%, and even further 6.0 - 10%; and / or

[0010] The breaking strength of the polyamide 56 industrial yarn is 6.0 - 9.0 cN / dtex, further 6.5 - 8.7 cN / dtex, and even further 7.0 - 8.5 cN / dtex; the coefficient of variation (CV)% of the breaking strength is ≤3.8%, further ≤3.5%, and even further ≤3.0%; and / or

[0011] The breaking elongation of the polyamide 56 industrial yarn is 13 - 26%, further 15 - 25%, and even further 18 - 23%; the coefficient of variation (CV)% of the breaking elongation is ≤4.8%, further ≤4.5%, and even further ≤4%; and / or

[0012] The breaking elongation of the polyamide 56 industrial yarn after being treated with hot water at 100°C for 30 min is 15 - 30%, further 18 - 28%, and even further 22 - 26%; and / or

[0013] The initial modulus of the polyamide 56 industrial yarn is ≥40 cN / dtex, further ≥42 cN / dtex, and still further ≥44 cN / dtex.

[0014] In some specific embodiments, the polyamide 56 industrial yarn is used for sewing threads, demolding fabrics or water cloths.

[0015] In some specific embodiments, the number of single broken filaments of the polyamide 56 industrial yarn is ≤3 per spinning position in 24 hours, preferably ≤2 per spinning position in 24 hours, and more preferably ≤1 per spinning position in 24 hours.

[0016] In some specific embodiments, the production rate of the polyamide 56 industrial yarn is ≥96%, preferably ≥97%, and more preferably ≥98%.

[0017] In some specific embodiments, the hairiness of the polyamide 56 industrial yarn is ≤8 per cake (10 kg package), preferably ≤6 per cake, and more preferably ≤5 per cake.

[0018] In some specific embodiments, the fineness of the polyamide 56 industrial yarn is 100 - 3000 dtex, preferably 150 - 2000 dtex, and more preferably 200 - 1500 dtex.

[0019] The second object of the present invention is to provide a method for preparing a melt direct spinning polyamide 56 industrial yarn, and the melt direct spinning at least includes the following steps:

[0020] (1) The polyamide 56 melt is drawn through a melt booster pump and a melt conveying pipeline into a spinning box to form a nascent yarn.

[0021] (2) The nascent yarn is subjected to slow cooling heating, cooling, oiling, pre-networking, multi-stage stretching, tension heat setting, two-stage relaxation heat setting, main networking, and winding to obtain the melt direct spinning polyamide 56 industrial yarn.

[0022] In some specific embodiments, in step (1), the relative viscosity of the polyamide 56 melt is 2.7 - 3.5, preferably 2.8 - 3.4, more preferably 2.9 - 3.3, and still more preferably 3.0 - 3.2.

[0023] In some specific embodiments, the amino group content of the polyamide 56 melt is 30 - 60 mmol / kg, preferably 33 - 55 mmol / kg, more preferably 36 - 50 mmol / kg, and further preferably 38 - 48 mmol / kg.

[0024] In some specific embodiments, the equilibrium moisture content of the polyamide 56 melt is 200 - 800 ppm, preferably 250 - 700 ppm, more preferably 300 - 600 ppm, and further preferably 350 - 500 ppm.

[0025] In some specific embodiments, the melt pressure drop from the melt booster pump to the inlet of the spinning box is ≤10 MPa, preferably ≤9 MPa, further preferably ≤8 MPa, and even more preferably ≤7 MPa.

[0026] In some specific embodiments, the melt pressure at the inlet of the spinning box is ≥6.0 MPa, preferably ≥7.0 MPa, further preferably ≥8.0 MPa, and even more preferably ≥9.0 MPa.

[0027] In some specific embodiments, the melt residence time of the polyamide 56 melt from the melt booster pump to the spinning box is 7 - 45 min, preferably 10 - 40 min, further preferably 14 - 35 min, and even more preferably 16 - 30 min.

[0028] In some specific embodiments, the melt shear rate of the polyamide 56 melt from the melt booster pump to the spinning box is 8 - 35 s -1 , preferably 10 - 30 s -1 , further preferably 12 - 28 s -1 , even more preferably 14 - 25 s -1 .

[0029] In some specific embodiments, the wire drawing in step (1) is to eject the polyamide 56 melt through the spinneret of the spinning box to form the initial filament.

[0030] In some specific embodiments, the temperature of the spinning box is 280 - 300 °C, preferably 283 - 295 °C, and more preferably 285 - 293 °C.

[0031] In some specific embodiments, the pressure of the spinning pack in the spinning box is ≥9 MPa, preferably ≥10 MPa, further preferably ≥11 MPa, and even more preferably ≥12 MPa.

[0032] In some specific embodiments, the spinneret draw ratio of the spinneret is 40 - 100, preferably 45 - 75.

[0033] In some specific embodiments, the number of holes of the spinneret is 18 - 300 f, preferably 24 - 210 f, further preferably 30 - 192 f, and even more preferably 36 - 136 f.

[0034] In some specific embodiments, a saturated superheated steam device, a slow cooling device and a monomer suction device are arranged below the spinning box. By arranging the saturated superheated steam device, the slow cooling device and the monomer suction device, the inventors of the present invention can make the saturated superheated steam spray in from the periphery below the spinneret plate, and the polyamide oligomers overflowing from the spinneret holes and the fiber surface are dissolved in the saturated superheated steam. At the same time, the slow cooling device arranged below the spinning box is used to increase the slow cooling temperature and inhibit its crystallization and precipitation, thereby preventing the oligomers from crystallizing to form white flocculent crystals on the spinneret plate and below it. Then, the polyamide oligomers dissolved in the saturated superheated steam are taken away by monomer suction, keeping the spinneret plate and below it clean, prolonging the shoveling period of the spinning component, reducing the phenomena of nozzle yarn and broken single yarn caused by oligomers during the spinning process, and effectively improving the spinning production stability and the yield rate.

[0035] In one embodiment, the temperature of the saturated superheated steam is 100 - 290 °C, further 110 - 280 °C, further 120 - 260 °C, and still further 130 - 250 °C.

[0036] In one embodiment, the pressure of the saturated superheated steam is 0.4 - 3.0 bar, further 0.6 - 2.5 bar, further 0.8 - 2.0 bar, and still further 1.0 - 1.8 bar.

[0037] In one embodiment, the slow cooling height of the slow cooling device is 180 - 350 mm, preferably 200 - 300 mm; the slow cooling temperature is 220 - 320 °C, preferably 250 - 300 °C.

[0038] In one embodiment, the pressure of the monomer suction device is ≥6.0 bar, further ≥6.5 bar, further ≥7.0 bar, and still further ≥7.5 bar.

[0039] In some specific embodiments, the method for preparing the polyamide 56 melt includes the following steps: preparing a polyamide 56 salt solution from pentamethylenediamine, adipic acid and water, and then obtaining the polyamide 56 melt through prepolymerization, flash evaporation and polycondensation.

[0040] In some specific embodiments, the molar ratio of pentamethylenediamine to adipic acid is (1 - 1.08):1.

[0041] In some specific embodiments, the concentration of the polyamide 56 salt solution is 40 - 80 wt%.

[0042] In some specific embodiments, the pH value of the polyamide 56 salt solution is 6.0 - 9.5.

[0043] In some specific embodiments, the pressure for prepolymerization is 0.8 - 2.6 MPa, preferably 1.0 - 2.4 MPa, more preferably 1.3 - 2.2 MPa, and even more preferably 1.5 - 2.0 MPa; the temperature for prepolymerization is 180 - 275 °C, preferably 190 - 270 °C, more preferably 210 - 265 °C, and even more preferably 225 - 260 °C.

[0044] In some specific embodiments, the pressure for polycondensation is -(0 - 0.08) MPa, preferably -(0.02 - 0.07) MPa, more preferably -(0.03 - 0.06) MPa, and even more preferably -(0.04 - 0.05) MPa; the temperature for polycondensation is 265 - 295 °C, preferably 270 - 293 °C, more preferably 275 - 290 °C, and even more preferably 278 - 288 °C.

[0045] In some specific embodiments, in step (2), the cooling is carried out by side blowing or ring blowing; the wind speed is preferably 0.4 - 0.9 m / s, more preferably 0.5 - 0.8 m / s; the wind temperature is preferably 16 - 25 °C, more preferably 18 - 22 °C; the humidity is preferably 50 - 90%, more preferably 60 - 85%.

[0046] In some specific embodiments, in step (2), the pre-network pressure is 1 - 2.5 bar, preferably 1.5 - 2.0 bar.

[0047] In some specific embodiments, in step (2), the multi-stage stretching process is carried out using five pairs or more of hot rolls, preferably six pairs of hot rolls, and is stretched in five stages. The stretching process is as follows: the as-spun filament after oiling is first fed into the first pair of hot rolls, and the first-stage pre-stretching is carried out between the first pair of hot rolls and the second pair of hot rolls, then the second-stage main stretching is carried out between the second pair of hot rolls and the third pair of hot rolls, the third-stage main stretching and tension heat setting are carried out between the third pair of hot rolls and the fourth pair of hot rolls, the fourth-stage sub-stretching and the first relaxation heat setting are carried out between the fourth pair of hot rolls and the fifth pair of hot rolls, then the fifth-stage sub-stretching and the second relaxation heat setting are carried out between the fifth pair of hot rolls and the sixth pair of hot rolls, and finally winding and forming are carried out using a winding head.

[0048] In one embodiment, the speed of the first pair of hot rolls is 400 - 800 m / min, preferably 450 - 750 m / min, and the temperature is 20 - 70 °C, preferably 30 - 60 °C.

[0049] In one embodiment, the speed of the second pair of hot rollers is 450 - 950 m / min, preferably 500 - 900 m / min, and the temperature is 80 - 150 °C, preferably 90 - 130 °C.

[0050] In one embodiment, the speed of the third pair of hot rollers is 1500 - 2500 m / min, preferably 1700 - 2300 m / min, and the temperature is 130 - 210 °C, preferably 150 - 200 °C.

[0051] In one embodiment, the speed of the fourth pair of hot rollers is 2400 - 3500 m / min, preferably 2500 - 3450 m / min, and the temperature is 180 - 230 °C, preferably 190 - 220 °C.

[0052] In one embodiment, the speed of the fifth pair of hot rollers is 2350 - 3450 m / min, preferably 2450 - 3400 m / min, and the temperature is 160 - 220 °C, preferably 170 - 200 °C.

[0053] In one embodiment, the speed of the sixth pair of hot rollers is 2300 - 3400 m / min, preferably 2400 - 3350 m / min, and the temperature is 120 - 210 °C, preferably 130 - 180 °C.

[0054] In one embodiment, the total draw ratio of the drawing is 4.5 - 6.0, preferably 4.8 - 5.7.

[0055] In one embodiment, the speed retraction between the fourth and fifth pairs of hot rollers is 30 - 200 m / min, preferably 50 - 150 m / min.

[0056] In one embodiment, the speed retraction between the fifth and sixth pairs of hot rollers is 30 - 200 m / min, preferably 50 - 150 m / min.

[0057] In one embodiment, the main network pressure is 2.5 - 4.5 bar, preferably 3.0 - 3.5 bar.

[0058] In one embodiment, the winding tension during winding forming is 20 - 250 cN, preferably 30 - 200 cN, more preferably 50 - 150 cN.

[0059] In one embodiment, the winding speed is 2200 - 3300 m / min, preferably 2400 - 3250 m / min, more preferably 2500 - 3200 m / min; the winding overfeed ratio is 0.5 - 5%, preferably 1.0 - 4.5%, more preferably 1.5 - 4.0%.

[0060] In some specific embodiments, a humidifying device is provided during the retraction and winding process. The humidifying temperature is 16 - 26°C, preferably 18 - 25°C, more preferably 20 - 24°C; the humidity is 60 - 95%, preferably 65 - 90%, more preferably 70 - 85%.

[0061] The third object of the present invention is to provide an application of the melt direct spinning polyamide 56 industrial yarn in the fields of release cloth, sewing thread, water cloth, canvas, safety belt, rope, fishing net, industrial filter cloth, conveyor belt, parachute, tent, luggage, etc., preferably in the fields of release cloth, sewing thread and water cloth.

[0062] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention. The reagents and raw materials used in the present invention are all commercially available.

[0063] The positive and progressive effects of the present invention are as follows:

[0064] First, 1,5-pentanediamine, the production raw material of the polyamide 56 industrial yarn provided by the present invention, is made by a biological method, which is a green material, does not rely on petroleum resources, does not cause serious pollution to the environment, can reduce carbon dioxide emissions, reduce the generation of the greenhouse effect, and adapt to the development trend of carbon neutrality.

[0065] Second, by optimizing the polymerization process and formula adjustment, the present invention can directly prepare polyamide 56 melt for the production of industrial yarn, save the processes of polymerization granulation, solid-phase polycondensation, and conditioning, and reduce production costs.

[0066] Third, by adopting the preparation method of the melt direct spinning polyamide 56 industrial yarn of the present invention, by optimizing the melt direct spinning process and controlling parameters such as the melt pressure drop from the melt booster pump to the inlet of the spinning box, the melt pressure at the inlet of the spinning box, the melt residence time, and the melt shear rate, not only can the production of large-capacity polyamide 56 industrial yarn be realized, but also the gel content in the melt from the melt booster pump to the spinning box can be effectively reduced.

[0067] Specifically, the annual output of the melt-spun polyamide 56 industrial yarn is ≤50,000 tons / line, preferably ≤40,000 tons / line, more preferably ≤30,000 tons / line, and further preferably ≤20,000 tons / line; the spinning position is ≤50 positions / line, preferably ≤40 positions / line, more preferably ≤30 positions / line, and further preferably ≤25 positions / line; the number of spinning heads is 2-12 heads / position, preferably 4-8 heads / position. The preparation method of the present invention saves the melt pelletizing, slice drying, screw melting and other links in the slice spinning process, thereby greatly reducing the production cost of polyamide 56 industrial yarn. The gel content can be controlled to ≤1.0wt% / 6 months, preferably ≤0.8wt% / 6 months, more preferably ≤0.6wt% / 6 months, and further preferably ≤0.4wt% / 6 months. The reduction in gel content greatly reduces the number of times the melt pipe and the spinning box are disassembled, calcined, and cleaned, thereby reducing production costs.

[0068] Fourthly, the present invention can effectively reduce the oligomer content and the phenomenon of single-filament breakage caused by oligomers in the spinning process by arranging a saturated superheated steam device, a slow cooling device and a monomer suction device under the spinning box, thereby improving the spinning production stability and production rate, and can further reduce the number of times of disassembly, calcination and cleaning of the melt conveying pipeline and the spinning box, thereby reducing production costs.

[0069] Fifth, the present invention optimizes the melt direct spinning process, controls parameters such as the melt pressure drop from the melt booster pump to the spinning manifold inlet, the melt pressure at the spinning manifold inlet, the melt residence time, and the melt shear rate, and can also stabilize the polyamide 56 melt with small fluctuations in viscosity and amino groups.

[0070] Specifically, the absolute value of the change in viscosity of the polyamide 56 industrial yarn relative to the melt viscosity is controlled to be ≤0.1, preferably ≤0.08, more preferably ≤0.06, and further preferably ≤0.05; the absolute value of the change in amino group is controlled to be ≤3.0mmol / kg, preferably ≤2.5mmol / kg, more preferably ≤2.0mmol / kg, and further preferably ≤1.5mmol / kg.

[0071] Sixth, the present invention provides a humidifying device during the shrinking and winding process, so that the polyamide 56 industrial yarn absorbs water and shrinks during the winding process, and the internal stress generated by high-multiple stretching is fully released, the dimensional stability is good, and the breaking strength and elongation fluctuations are small. DETAILED DESCRIPTION

[0072] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, rather than all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention. For the experimental methods without specific conditions indicated in the following embodiments, they shall be carried out according to conventional methods and conditions, or selected according to the product specifications.

[0073] Testing method:

[0074] (1) Denier: Determined in accordance with GB / T 14343.

[0075] (2) Tensile strength, coefficient of variation of tensile strength (CV): Determined in accordance with GB / T 14344-2008.

[0076] (3) Elongation at break, coefficient of variation of elongation at break (CV): Determined in accordance with GB / T 14344-2008.

[0077] (4) Initial modulus: Determined in accordance with GB / T 14344-2008.

[0078] (5) Relative viscosity: By the Ubbelohde viscometer concentrated sulfuric acid method: Accurately weigh 0.5 ± 0.0002 g of the dried polyamide melt sample taken online, add 50 mL of concentrated sulfuric acid (96 wt%) to dissolve it; measure and record the flowing time t0 of concentrated sulfuric acid and the flowing time t of the polyamide sample solution in a constant temperature water bath at 25°C. The formula for calculating the viscosity number: Relative viscosity = t / t0; t - flowing time of the solution; t0 - flowing time of the solvent.

[0079] (6) Amino end group: Determined by an automatic titrator.

[0080] (7) Equilibrium moisture content: Determined by a Karl Fischer moisture titrator.

[0081] (8) Dry heat shrinkage rate: Executed in accordance with the provisions of FZ / T 50004, and the heat treatment temperature is 180°C.

[0082] (9) Boiling water shrinkage rate: Among them, the determination of the boiling water shrinkage rate refers to GB / 6505-2008 "Test Method for Heat Shrinkage Rate of Chemical Fiber Filaments", and the boiling water shrinkage rate = ((length before heat treatment - length after heat treatment) / length before heat treatment) * 100%.

[0083] (10) Number of single filament breaks: Manually counted.

[0084] (11) Yield rate: Yield rate = (mass of the prepared finished fiber / mass of the total polyamide melt input) × 100%.

[0085] (12) Gel content: Randomly extract melt samples from 6 places in the melt transfer pipeline after 6 months of production line operation, measure and take the average value according to the following method. Weigh the mass of the melt sample after cooling and drying as A1. After reflux extraction using the Soxhlet extraction method, take out the sample and dry it, and weigh the mass of the sample in the filter paper bag as A2. The calculation formula for gel content: Gel content wt% = A2 / A1 * 100%.

[0086] Polyamide 56 industrial yarn with a specification of 235 dtex / 36 f in Example 1

[0087] Preparation of polyamide 56 melt

[0088] Prepare a polyamide 56 salt solution from pentamethylenediamine, adipic acid and water, and then obtain a polyamide 56 melt through prepolymerization, flash evaporation and polycondensation;

[0089] Among them, the molar ratio of the 1,5-pentamethylenediamine to adipic acid is 1.06:1; the concentration of the polyamide 56 salt solution is 52 wt%; the pH value of the polyamide 56 salt solution is 8.1;

[0090] The pressure of the prepolymerization is 1.75 MPa, and the temperature of the prepolymerization is 247 °C;

[0091] The pressure of the polycondensation is -0.06 MPa, and the temperature of the polycondensation is 282 °C;

[0092] The relative viscosity in the polyamide 56 melt is 3.2, the amino group content is 38 mmol / kg, and the equilibrium moisture content is 420 ppm.

[0093] Preparation of polyamide 56 industrial yarn

[0094] (1) Feed the above-obtained polyamide 56 melt into the spinning box through a melt booster pump and a melt transfer pipeline for wire drawing to form a nascent filament;

[0095] (2) Subject the nascent filament to slow cooling heating, cooling, oiling, pre-networking, multi-stage stretching, tension heat setting, two-stage relaxation heat setting, main networking, and winding;

[0096] The wire drawing in step (1) is to extrude the polyamide 56 melt through the spinneret of the spinning box to form the nascent filament;

[0097] The temperature of the spinning box is 287 °C;

[0098] The pressure of the spinning component in the spinning box is 16 MPa;

[0099] The spinneret draw ratio of the spinneret is 70;

[0100] The melt pressure drop from the melt booster pump to the inlet of the spinning box is 6 MPa;

[0101] The melt pressure at the inlet of the spinning box is 13.0 MPa;

[0102] The melt residence time of the polyamide 56 melt from the melt booster pump to the spinning box is 22 min;

[0103] The melt shear rate of the polyamide 56 melt from the melt booster pump to the spinning box is 25 s -1 ;

[0104] A saturated superheated steam device, a slow cooling device and a monomer suction device are arranged below the spinning box;

[0105] The temperature of the saturated superheated steam is 165 °C; the pressure of the saturated superheated steam is 0.8 bar;

[0106] The slow cooling height of the slow cooling device is 280 mm, and the slow cooling temperature is 290 °C;

[0107] The pressure of the monomer suction device is 6.8 bar;

[0108] The cooling is side blowing, the wind speed is 0.65 m / s, the wind temperature is 17 °C, and the humidity is 85%;

[0109] The pre-network pressure is 1.8 bar;

[0110] The multi-stage stretching process uses 6 pairs of hot rolls and is divided into five stages of stretching. The stretching process is as follows: The as-spun yarn after oiling is first fed into the first pair of hot rolls, and the first-stage pre-stretching is carried out between the first pair of hot rolls and the second pair of hot rolls. Then, the second-stage main stretching is carried out between the second pair of hot rolls and the third pair of hot rolls, and the third-stage main stretching and tension heat setting are carried out between the third pair of hot rolls and the fourth pair of hot rolls. The fourth-stage sub-stretching and the first relaxation heat setting are carried out between the fourth pair of hot rolls and the fifth pair of hot rolls. Then, the fifth-stage sub-stretching and the second relaxation heat setting are carried out between the fifth pair of hot rolls and the sixth pair of hot rolls; Finally, winding is carried out using a winding head;

[0111] Among them, the speed of the first pair of hot rolls is 560 m / min, and the temperature is 30 °C;

[0112] The speed of the second pair of hot rolls is 600 m / min, and the temperature is 120 °C;

[0113] The speed of the third pair of hot rolls is 1900 m / min, and the temperature is 200 °C;

[0114] The speed of the fourth pair of hot rolls is 2,800 m / min and the temperature is 220 °C;

[0115] The speed of the fifth pair of hot rolls is 2,700 m / min and the temperature is 190 °C;

[0116] The speed of the sixth pair of hot rolls is 2,650 m / min and the temperature is 150 °C;

[0117] The total draw ratio of the drawing is 5.0;

[0118] The speed reduction between the 4th and 5th pairs of hot rolls is 100 m / min;

[0119] The speed reduction between the 5th and 6th pairs of hot rolls is 50 m / min;

[0120] The main network pressure is 3.0 bar;

[0121] The winding tension during winding forming is 22 cN;

[0122] The winding speed is 2,600 m / min; the winding overfeed ratio is 1.9%;

[0123] A humidifying device is provided during the retraction and winding process, the humidifying temperature is 25 °C, and the humidity is 70%.

[0124] In this embodiment, the annual output of the polyamide 56 industrial yarn is 13,000 tons / line, the spinning unit is 48 units / line, and the number of spinning heads is 8 heads / unit.

[0125] Polyamide 56 industrial yarn with a specification of 315 dtex / 120f in Example 2

[0126] Preparation of polyamide 56 melt

[0127] Prepare a polyamide 56 salt solution from pentamethylenediamine, adipic acid and water, and then obtain a polyamide 56 melt through prepolymerization, flash evaporation and polycondensation;

[0128] Among them, the molar ratio of pentamethylenediamine to adipic acid is 1.05:1; the concentration of the polyamide 56 salt solution is 56 wt%; the pH value of the polyamide 56 salt solution is 8.0;

[0129] The pressure of the prepolymerization is 1.7 MPa and the temperature of the prepolymerization is 245 °C;

[0130] The pressure of the polycondensation is -0.05 MPa and the temperature of the polycondensation is 284 °C;

[0131] The relative viscosity of the polyamide 56 melt is 3.3, the amino group content is 43 mmol / kg, and the equilibrium moisture content is 380 ppm.

[0132] Preparation of polyamide 56 industrial yarn

[0133] (1) The obtained polyamide 56 melt is sent to a spinning box through a melt booster pump and a melt conveying pipeline for wire drawing to form a nascent filament;

[0134] (2) The nascent filament is subjected to slow cooling heating, cooling, oiling, pre-networking, multi-stage stretching, tension heat setting, two-stage relaxation heat setting, main networking, and winding;

[0135] The wire drawing in step (1) is to eject the polyamide 56 melt through a spinneret plate of the spinning box to form the initial filament;

[0136] The temperature of the spinning box is 288 °C;

[0137] The pressure of the spinning pack in the spinning box is 14 MPa;

[0138] The spinneret draw ratio of the spinneret plate is 62;

[0139] The melt pressure drop from the melt booster pump to the inlet of the spinning box is 4 MPa;

[0140] The melt pressure at the inlet of the spinning box is 15.0 MPa;

[0141] The melt residence time of the polyamide 56 melt from the melt booster pump to the spinning box is 23 min;

[0142] The melt shear rate of the polyamide 56 melt from the melt booster pump to the spinning box is 30 s -1 ;

[0143] A saturated superheated steam device, a slow cooling device, and a monomer suction device are arranged below the spinning box;

[0144] The temperature of the saturated superheated steam is 155 °C; the pressure of the saturated superheated steam is 0.6 bar;

[0145] The slow cooling height of the slow cooling device is 265 mm, and the slow cooling temperature is 275 °C;

[0146] The pressure of the monomer suction device is 6.0 bar;

[0147] The cooling is side blowing, the wind speed is 0.7 m / s, the wind temperature is 19 °C, and the humidity is 85%;

[0148] The pre-network pressure is 1.5 bar;

[0149] The multi-stage stretching process uses 6 pairs of hot rollers and is divided into five stages of stretching. The stretching process is as follows: The as-spun yarn after oiling is first fed into the first pair of hot rollers, and the first-stage pre-stretching is carried out between the first pair of hot rollers and the second pair of hot rollers. Then, the second-stage main stretching is carried out between the second pair of hot rollers and the third pair of hot rollers, and the third-stage main stretching and tension heat setting are carried out between the third pair of hot rollers and the fourth pair of hot rollers. The fourth-stage sub-stretching and the first relaxation heat setting are carried out between the fourth pair of hot rollers and the fifth pair of hot rollers. Then, the fifth-stage sub-stretching and the second relaxation heat setting are carried out between the fifth pair of hot rollers and the sixth pair of hot rollers. Finally, winding is carried out using a winding head.

[0150] Among them, the speed of the first pair of hot rollers is 650 m / min, and the temperature is 45 °C.

[0151] The speed of the second pair of hot rollers is 750 m / min, and the temperature is 100 °C.

[0152] The speed of the third pair of hot rollers is 1900 m / min, and the temperature is 180 °C.

[0153] The speed of the fourth pair of hot rollers is 3000 m / min, and the temperature is 210 °C.

[0154] The speed of the fifth pair of hot rollers is 2900 m / min, and the temperature is 190 °C.

[0155] The speed of the sixth pair of hot rollers is 2850 m / min, and the temperature is 140 °C.

[0156] The total stretching multiple of the stretching is 4.62.

[0157] The speed reduction between the 4th and 5th pairs of hot rollers is 100 m / min.

[0158] The speed reduction between the 5th and 6th pairs of hot rollers is 50 m / min.

[0159] The main network pressure is 3.2 bar.

[0160] The winding tension during winding forming is 30 cN.

[0161] The winding speed is 2750 m / min; the winding overfeed ratio is 3.6%.

[0162] A humidifying device is set during the retraction and winding process. The humidifying temperature is 21 °C, and the humidity is 82%.

[0163] In this embodiment, the annual output of the polyamide 56 industrial yarn is 18,000 tons / line, the spinning position is 48 positions / line, and the number of spinning heads is 8 heads / position.

[0164] Polyamide 56 industrial yarn with a specification of 420 dtex / 96 f in Example 3

[0165] Preparation of polyamide 56 melt

[0166] Prepare a polyamide 56 salt solution from pentamethylenediamine, adipic acid and water, and then obtain a polyamide 56 melt through prepolymerization, flash evaporation and polycondensation;

[0167] Among them, the molar ratio of the 1,5-pentamethylenediamine to adipic acid is 1.07:1; the concentration of the polyamide 56 salt solution is 62 wt%; the pH value of the polyamide 56 salt solution is 7.9;

[0168] The pressure of the prepolymerization is 1.78 MPa, and the temperature of the prepolymerization is 248 °C;

[0169] The pressure of the polycondensation is -0.06 MPa, and the temperature of the polycondensation is 285 °C;

[0170] The relative viscosity of the polyamide 56 melt is 3.4, the amino group content is 42 mmol / kg, and the equilibrium moisture content is 480 ppm.

[0171] Preparation of polyamide 56 industrial yarn

[0172] (1) Feed the obtained polyamide 56 melt into a spinning box through a melt booster pump and a melt conveying pipeline for wire drawing to form a nascent yarn;

[0173] (2) Subject the nascent yarn to slow cooling heating, cooling, oiling, pre-networking, multi-stage stretching, tension heat setting, two-stage relaxation heat setting, main networking and winding;

[0174] The wire drawing in step (1) is to eject the polyamide 56 melt through a spinneret plate of a spinning box to form the nascent yarn;

[0175] The temperature of the spinning box is 290 °C;

[0176] The pressure of the spinning pack in the spinning box is 15 MPa;

[0177] The spinneret draw ratio of the spinneret plate is 98;

[0178] The residence time of the polyamide 56 melt from the melt booster pump to the spinning box is 24 min;

[0179] The melt shear rate of the polyamide 56 melt from the melt booster pump to the spinning box is 23 s -1 ;

[0180] The melt pressure drop from the melt booster pump to the inlet of the spinning box is 5 MPa;

[0181] The melt pressure at the inlet of the spinning box is 14.0 MPa;

[0182] A saturated superheated steam device, a slow cooling device and a monomer suction device are arranged below the spinning box;

[0183] The temperature of the saturated superheated steam is 145 °C; the pressure of the saturated superheated steam is 1.0 bar;

[0184] The slow cooling height of the slow cooling device is 285 mm, and the slow cooling temperature is 280 °C;

[0185] The pressure of the monomer suction device is 6.5 bar;

[0186] The cooling is side blowing, the wind speed is 0.8 m / s, the wind temperature is 18 °C, and the humidity is 88%;

[0187] The pre-network pressure is 1.5 bar;

[0188] Six pairs of hot rollers are used in the multi-stage stretching process, and the stretching is divided into five stages. The stretching process is as follows: The as-spun yarn after oiling is first fed into the first pair of hot rollers, and the first-stage pre-stretching is carried out between the first pair of hot rollers and the second pair of hot rollers, then the second-stage main stretching is carried out between the second pair of hot rollers and the third pair of hot rollers, the third-stage main stretching and tension heat setting are carried out between the third pair of hot rollers and the fourth pair of hot rollers, the fourth-stage sub-stretching and the first relaxation heat setting are carried out between the fourth pair of hot rollers and the fifth pair of hot rollers, and then the fifth-stage sub-stretching and the second relaxation heat setting are carried out between the fifth pair of hot rollers and the sixth pair of hot rollers; finally, winding is carried out by using a winding head.

[0189] Among them, the speed of the first pair of hot rollers is 480 m / min, and the temperature is 50 °C;

[0190] The speed of the second pair of hot rollers is 550 m / min, and the temperature is 100 °C;

[0191] The speed of the third pair of hot rollers is 1800 m / min, and the temperature is 195 °C;

[0192] The speed of the fourth pair of hot rollers is 2600 m / min, and the temperature is 225 °C;

[0193] The speed of the fifth pair of hot rollers is 2500 m / min, and the temperature is 195 °C;

[0194] The speed of the sixth pair of hot rollers is 2450 m / min, and the temperature is 150 °C;

[0195] The total stretching multiple of the stretching is 5.42;

[0196] The speed retraction of the 4th and 5th pairs of hot rollers is 100 m / min;

[0197] The speed retraction of the 5th and 6th pairs of hot rollers is 50 m / min;

[0198] The main network pressure is 3.2 bar;

[0199] The winding tension during winding and forming is 40 cN;

[0200] The winding speed is 2400 m / min; the winding overfeed ratio is 2.1%;

[0201] A humidifying device is set during the retraction and winding process, and the humidifying temperature is 24 °C and the humidity is 80%.

[0202] In this embodiment, the annual output of the polyamide 56 industrial yarn is 20,000 tons / line, the spinning position is 48 positions / line, and the number of spinning heads is 8 heads / position.

[0203] Polyamide 56 industrial yarn with a specification of 500 dtex / 120 f in Example 4

[0204] Preparation of polyamide 56 melt

[0205] Prepare a polyamide 56 salt solution from pentamethylenediamine, adipic acid and water, and then obtain a polyamide 56 melt through prepolymerization, flash evaporation and polycondensation;

[0206] Among them, the molar ratio of 1,5-pentamethylenediamine to adipic acid is 1.08:1; the concentration of the polyamide 56 salt solution is 58 wt%; the pH value of the polyamide 56 salt solution is 7.8;

[0207] The pressure of the prepolymerization is 1.76 MPa, and the temperature of the prepolymerization is 252 °C;

[0208] The pressure of the polycondensation is -0.04 MPa, and the temperature of the polycondensation is 283 °C;

[0209] The relative viscosity of the polyamide 56 melt is 3.4, the amino group content is 40 mmol / kg, and the equilibrium moisture content is 460 ppm.

[0210] Preparation of polyamide 56 industrial yarn

[0211] (1) Feed the obtained polyamide 56 melt into the spinning box through a melt booster pump and a melt delivery pipeline for wire drawing to form a nascent filament;

[0212] (2) Subject the nascent filament to slow cooling heating, cooling, oiling, pre-networking, multi-stage stretching, tension heat setting, two-stage relaxation heat setting, main networking and winding;

[0213] The wire drawing in step (1) is to extrude the polyamide 56 melt through the spinneret of the spinning box to form the initial filament;

[0214] The temperature of the spinning box is 288 °C;

[0215] The spinning component pressure in the spinning box is 14 MPa;

[0216] The spinneret draw ratio of the spinneret is 87;

[0217] The residence time of the polyamide 56 melt from the melt booster pump to the spinning box is 22 min;

[0218] The melt shear rate of the polyamide 56 melt from the melt booster pump to the spinning box is 24 s -1 ;

[0219] The melt pressure drop from the melt booster pump to the inlet of the spinning box is 6 MPa;

[0220] The melt pressure at the inlet of the spinning box is 13.0 MPa;

[0221] A saturated superheated steam device, a slow cooling device and a monomer suction device are arranged below the spinning box;

[0222] The temperature of the saturated superheated steam is 162 °C; the pressure of the saturated superheated steam is 1.2 bar;

[0223] The slow cooling height of the slow cooling device is 295 mm, and the slow cooling temperature is 300 °C;

[0224] The pressure of the monomer suction device is 6.0 bar;

[0225] The cooling is side blowing, the wind speed is 0.6 m / s, the air temperature is 17 °C, and the humidity is 85%;

[0226] The pre-network pressure is 1.3 bar;

[0227] The multi-stage stretching process uses 6 pairs of hot rollers and is stretched in five stages. The stretching process is as follows: The as-spun filament after oiling is first fed into the first pair of hot rollers, and the first-stage pre-stretching is carried out between the first pair of hot rollers and the second pair of hot rollers, then the second-stage main stretching is carried out between the second pair of hot rollers and the third pair of hot rollers, the third-stage main stretching and tension heat setting are carried out between the third pair of hot rollers and the fourth pair of hot rollers, the fourth-stage sub-stretching and the first relaxation heat setting are carried out between the fourth pair of hot rollers and the fifth pair of hot rollers, and then the fifth-stage sub-stretching and the second relaxation heat setting are carried out between the fifth pair of hot rollers and the sixth pair of hot rollers; finally, winding is carried out using a winding head;

[0228] Among them, the speed of the first pair of hot rollers is 450 m / min, and the temperature is 55 °C;

[0229] The speed of the second pair of hot rollers is 550 m / min, and the temperature is 85 °C;

[0230] The speed of the third pair of hot rollers is 1900 m / min, and the temperature is 170 °C;

[0231] The speed of the fourth pair of hot rollers is 2500 m / min, and the temperature is 220 °C;

[0232] The speed of the fifth pair of hot rollers is 2400 m / min, and the temperature is 185 °C;

[0233] The speed of the sixth pair of hot rollers is 2350 m / min, and the temperature is 145 °C;

[0234] The total draw ratio of the drawing is 5.56;

[0235] The speed retraction between the 4th and 5th pairs of hot rollers is 100 m / min;

[0236] The speed retraction between the 5th and 6th pairs of hot rollers is 50 m / min;

[0237] The main network pressure is 3.0 bar;

[0238] The winding tension during winding and forming is 45 cN;

[0239] The winding speed is 2300 m / min; the winding overfeed ratio is 2.2%;

[0240] A humidifying device is set during the retraction and winding process, the humidifying temperature is 22 °C, and the humidity is 86%.

[0241] In this embodiment, the annual output of the polyamide 56 industrial yarn is 18,000 tons / line, the spinning position is 48 positions / line, and the number of spinning heads is 6 heads / position.

[0242] Polyamide 56 industrial yarn with a specification of 630 dtex / 136f in Example 5

[0243] Preparation of polyamide 56 melt

[0244] Prepare a polyamide 56 salt solution from pentamethylenediamine, adipic acid and water, and then obtain a polyamide 56 melt through prepolymerization, flash evaporation and polycondensation;

[0245] Among them, the molar ratio of 1,5-pentamethylenediamine to adipic acid is 1.06:1; the concentration of the polyamide 56 salt solution is 53 wt%; the pH value of the polyamide 56 salt solution is 8.2;

[0246] The pressure of the prepolymerization is 1.74 MPa, and the temperature of the prepolymerization is 254 °C;

[0247] The pressure of the polycondensation is -0.04 MPa, and the temperature of the polycondensation is 285 °C;

[0248] The relative viscosity of the polyamide 56 melt is 3.5, the amino group content is 38 mmol / kg, and the equilibrium moisture content is 400 ppm.

[0249] Preparation of polyamide 56 industrial yarn

[0250] (1) The obtained polyamide 56 melt is sent to a spinning box through a melt booster pump and a melt conveying pipeline for wire drawing to form a nascent fiber;

[0251] (2) The nascent fiber is subjected to slow cooling and heating, cooling, oiling, pre-networking, multi-stage stretching, tension heat setting, two-stage relaxation heat setting, main networking, and winding;

[0252] The wire drawing in step (1) is to eject the polyamide 56 melt through a spinneret plate of the spinning box to form the nascent fiber;

[0253] The temperature of the spinning box is 284 °C;

[0254] The pressure of the spinning component in the spinning box is 13 MPa;

[0255] The spinneret draw ratio of the spinneret plate is 62;

[0256] The residence time of the polyamide 56 melt from the melt booster pump to the spinning box is 20 min;

[0257] The melt shear rate of the polyamide 56 melt from the melt booster pump to the spinning box is 20 s -1 ;

[0258] The melt pressure drop from the melt booster pump to the inlet of the spinning box is 6 MPa;

[0259] The melt pressure at the inlet of the spinning box is 12.0 MPa;

[0260] A saturated superheated steam device, a slow cooling device, and a monomer suction device are arranged below the spinning box;

[0261] The temperature of the saturated superheated steam is 183 °C; the pressure of the saturated superheated steam is 1.3 bar;

[0262] The slow cooling height of the slow cooling device is 250 mm, and the slow cooling temperature is 285 °C;

[0263] The pressure of the monomer suction device is 6.0 bar;

[0264] The cooling is side blowing, the wind speed is 0.63 m / s, the wind temperature is 18 °C, and the humidity is preferably 85%;

[0265] The pre-network pressure is 1.5 bar;

[0266] In the stretching process, 6 pairs of hot rollers are used and stretched in five stages. The stretching process is as follows: The as-spun yarn after oiling is first fed into the first pair of hot rollers, and the first-stage pre-stretching is carried out between the first pair of hot rollers and the second pair of hot rollers. Then, the second-stage main stretching is carried out between the second pair of hot rollers and the third pair of hot rollers. The third-stage main stretching and tension heat setting are carried out between the third pair of hot rollers and the fourth pair of hot rollers. The fourth-stage sub-stretching and the first relaxation heat setting are carried out between the fourth pair of hot rollers and the fifth pair of hot rollers. Then, the fifth-stage sub-stretching and the second relaxation heat setting are carried out between the fifth pair of hot rollers and the sixth pair of hot rollers; finally, winding is carried out using a winding head;

[0267] Among them, the speed of the first pair of hot rollers is 580 m / min, and the temperature is 50 °C;

[0268] The speed of the second pair of hot rollers is 620 m / min, and the temperature is 90 °C;

[0269] The speed of the third pair of hot rollers is 1900 m / min, and the temperature is 160 °C;

[0270] The speed of the fourth pair of hot rollers is 2800 m / min, and the temperature is 220 °C;

[0271] The speed of the fifth pair of hot rollers is 2750 m / min, and the temperature is 170 °C;

[0272] The speed of the sixth pair of hot rollers is 2700 m / min, and the temperature is 130 °C;

[0273] The total stretching multiple of the stretching is 4.83;

[0274] The speed retraction between the 4th and 5th pairs of hot rollers is 50 m / min;

[0275] The speed retraction between the 5th and 6th pairs of hot rollers is 50 m / min;

[0276] The main network pressure is 3.0 bar;

[0277] The winding tension during winding and forming is 60 cN;

[0278] The winding speed is 2600 m / min; the winding overfeed ratio is 3.8%;

[0279] A humidifying device is provided during the retraction and winding process, with the humidifying temperature being 19°C and the humidity being 85%.

[0280] In this embodiment, the annual output of the polyamide 56 industrial yarn is 16,000 tons per line, the spinning position is 32 positions per line, and the number of spinning heads is 6 heads per position.

[0281] Example 6

[0282] The polyamide 56 industrial yarn is prepared using the same process as in Example 1, except that the relative viscosity of the polyamide 56 melt is 2.4.

[0283] Example 7

[0284] The polyamide 56 industrial yarn is prepared using the same process as in Example 1, except that the equilibrium moisture content of the polyamide 56 melt is 1250 ppm.

[0285] Example 8

[0286] The polyamide 56 industrial yarn is prepared using the same process as in Example 1, except that the melt pressure drop from the melt booster pump to the inlet of the spinning box is 12 MPa, and the melt pressure at the inlet of the spinning box is 6.0 MPa.

[0287] Example 9

[0288] The polyamide 56 industrial yarn is prepared using the same process as in Example 1, except that the melt residence time of the polyamide 56 melt from the melt booster pump to the spinning box is 58 min.

[0289] Example 10

[0290] The polyamide 56 industrial yarn is prepared using the same process as in Example 1, except that the melt shear rate of the polyamide 56 melt from the melt booster pump to the spinning box is 45 s -1 。

[0291] Example 11

[0292] The polyamide 56 industrial yarn is prepared using the same process as in Example 1, except that no saturated superheated steam device, slow cooling device, and monomer suction device are provided below the spinning box.

[0293] Example 12

[0294] The polyamide 56 industrial yarn is prepared using the same process as in Example 1, except that there is no humidifying device during the retraction and winding process.

[0295] Comparative Example 1

[0296] The polyamide 56 industrial yarn was prepared by the same process as in Example 1, except that the polyamide 56 melt obtained in step (1) was first granulated and dried to obtain chips, which were melted by a single screw and then transported to the spinning box through a melt transfer pipeline, and the polyamide 56 industrial yarn was prepared by chip spinning.

[0297] Table 1 Parameters of the polyamide 56 industrial yarns prepared in the examples and comparative examples

[0298]

[0299]

[0300] By using the method for preparing the polyamide 56 industrial yarn of the present invention, through optimizing the direct melt spinning process and controlling parameters such as the melt pressure drop from the melt booster pump to the inlet of the spinning box, the melt pressure at the inlet of the spinning box, the melt residence time, and the melt shear rate, the polyamide 56 melt can be stabilized, with small fluctuations in viscosity and amino group. It can not only realize the production of large-capacity polyamide 56 industrial yarn, endowing the polyamide 56 industrial yarn with the properties of less hairiness and low shrinkage, but also effectively reduce the gel content in the melt from the melt booster pump to the spinning box.

[0301] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the present invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A melt direct spinning polyamide 56 industrial yarn, which is obtained by a one-step melt direct spinning method, is characterized in that, The breaking strength of the polyamide 56 industrial yarn is 7.0 - 8.7 cN / dtex, and the coefficient of variation of the breaking strength is ≤3.0%; the elongation at break of the polyamide 56 industrial yarn is 18 - 23%, and the coefficient of variation of the elongation at break is ≤4%; The melt direct spinning process at least includes the following steps: (1) Feeding the polyamide 56 melt through a melt booster pump and a melt conveying pipeline into a spinning box for wire drawing to form a nascent yarn; (2) Subjecting the nascent yarn to slow cooling heating, cooling, oiling, pre-networking, multi-stage stretching, tension heat setting, two-stage relaxation heat setting, main networking, and winding to obtain the melt direct spun polyamide 56 industrial yarn; Among them, the melt pressure drop from the melt booster pump to the inlet of the spinning box is ≤ 10 MPa, the melt residence time of the polyamide 56 melt from the melt booster pump to the spinning box is 7 - 45 min, the melt pressure at the inlet of the spinning box is ≥ 7.0 MPa, and the melt shear rate of the polyamide 56 melt from the melt booster pump to the spinning box is 8 - 35 s -1 .

2. The melt direct spinning polyamide 56 industrial yarn according to claim 1, characterized in that, The dry heat shrinkage rate of the polyamide 56 industrial yarn is ≤7.5%; and / or, The boiling water shrinkage rate of the polyamide 56 industrial yarn is 6.0 - 10%; and / or, The elongation at break of the polyamide 56 industrial yarn after being treated with hot water at 100°C for 30 min is 22 - 28%; and / or, The initial modulus of the polyamide 56 industrial yarn is ≥44 cN / dtex.

3. The melt direct spinning polyamide 56 industrial yarn according to claim 1, wherein, In step (1), the relative viscosity of the polyamide 56 melt is 2.7 - 3.5; and / or, The amino group content of the polyamide 56 melt is 30 - 60 mmol / kg; and / or, The equilibrium moisture content of the polyamide 56 melt is 200 - 800 ppm.

4. The melt direct spinning polyamide 56 industrial yarn according to claim 1, characterized in that, In step (1), the relative viscosity of the polyamide 56 melt is 2.8 - 3.4; and / or, The amino group content of the polyamide 56 melt is 33 - 55 mmol / kg; and / or, The equilibrium moisture content of the polyamide 56 melt is 250 - 700 ppm.

5. The melt direct spinning polyamide 56 industrial yarn according to claim 1, characterized in that, In step (1), the relative viscosity of the polyamide 56 melt is 2.9 - 3.3; and / or, The amino group content of the polyamide 56 melt is 36 - 50 mmol / kg; and / or, The equilibrium moisture content of the polyamide 56 melt is 300 - 600 ppm; and / or, The melt pressure drop from the melt booster pump to the inlet of the spinning box is ≤9 MPa; and / or, The melt residence time of the polyamide 56 melt from the melt booster pump to the spinning box is 10 - 40 min.

6. The melt direct spinning polyamide 56 industrial yarn according to claim 1, characterized in that, In step (1), the relative viscosity of the polyamide 56 melt is 3.0 - 3.2; and / or, The amino group content of the polyamide 56 melt is 38 - 48 mmol / kg; and / or, The equilibrium moisture content of the polyamide 56 melt is 350 - 500 ppm; and / or, The melt pressure drop from the melt booster pump to the inlet of the spinning box is ≤8 MPa; and / or, The melt pressure at the inlet of the spinning box is ≥8.0 MPa; and / or, The melt residence time of the polyamide 56 melt from the melt booster pump to the spinning box is 14 - 35 min.

7. The direct melt spinning polyamide 56 industrial yarn according to claim 1, characterized in that, The melt pressure drop from the melt booster pump to the inlet of the spinning box is ≤7 MPa; and / or, The melt pressure at the inlet of the spinning box is ≥9.0 MPa; and / or, The melt residence time of the polyamide 56 melt from the melt booster pump to the spinning box is 16 - 30 min.

8. The melt direct spinning polyamide 56 industrial yarn according to claim 1, characterized in that, The melt shear rate of the polyamide 56 melt from the melt booster pump to the spinning box is 10 to 30 s -1 ; and / or, The wire drawing in step (1) is to extrude the polyamide 56 melt through the spinneret of the spinning box to form the nascent fiber; The temperature of the spinning box is 280 - 300 °C; and / or, The pressure of the spinning component in the spinning box is ≥ 9 MPa.

9. The direct melt spinning polyamide 56 industrial yarn according to claim 8, characterized in that The melt shear rate of the polyamide 56 melt from the melt booster pump to the spinning box is 12 to 28 s -1 ; and / or, The temperature of the spinning box is 283 - 295 °C; and / or, The pressure of the spinning component in the spinning box is ≥ 10 MPa.

10. The melt direct spinning polyamide 56 industrial yarn according to claim 8, characterized in that, The temperature of the spinning box is 285 - 293 °C; and / or, The pressure of the spinning component in the spinning box is ≥ 11 MPa; and / or, The melt shear rate of the polyamide 56 melt from the melt booster pump to the spinning box is 14-25 s -1 .

11. The melt direct spinning polyamide 56 industrial yarn according to claim 8, wherein The pressure of the spinning component in the spinning box is ≥ 12 MPa.

12. The melt direct spinning polyamide 56 industrial yarn according to claim 1, characterized in that, A saturated superheated steam device, a slow cooling device and a monomer suction device are arranged below the spinning box; where, The temperature of the saturated superheated steam of the saturated superheated steam device is 100 - 290 °C; and / or, The pressure of the saturated superheated steam of the saturated superheated steam device is 0.4 - 3.0 bar; and / or, The slow cooling height of the slow cooling device is 180 - 350 mm, and the slow cooling temperature is 220 - 320 °C; and / or, The pressure of the monomer suction device is ≥ 6.0 bar.

13. The melt direct spinning polyamide 56 industrial yarn according to claim 12, wherein The temperature of the saturated superheated steam is 110 - 280 °C; and / or, The pressure of the saturated superheated steam is 0.6 - 2.5 bar; and / or, The slow cooling height of the slow cooling device is 200 - 300 mm; and / or, The pressure of the monomer suction device is ≥ 6.5 bar.

14. The melt direct spinning polyamide 56 industrial yarn according to claim 12, characterized in that, The temperature of the saturated superheated steam is 120 - 260 °C; and / or, The pressure of the saturated superheated steam is 0.8 - 2.0 bar; and / or, The slow cooling temperature of the slow cooling device is 250 - 300 °C; and / or, The pressure of the monomer suction device is ≥ 7.0 bar.

15. The melt direct spinning polyamide 56 industrial yarn according to claim 12, characterized in that, The temperature of the saturated superheated steam is 130 - 250 °C; and / or, The pressure of the saturated superheated steam is 1.0 - 1.8 bar; and / or, The pressure of the monomer suction device is ≥ 7.5 bar.

16. The melt direct spinning polyamide 56 industrial yarn according to claim 1, characterized in that, In step (2), the multi-stage stretching process is carried out using five or more pairs of hot rollers.

17. The melt direct spinning polyamide 56 industrial yarn according to claim 16, characterized in that, The multi-stage stretching process uses six pairs of hot rollers and is stretched in five stages. The stretching process is as follows: the nascent fiber after oiling is first fed into the first pair of hot rollers, and the first-stage pre-stretching is carried out between the first pair of hot rollers and the second pair of hot rollers, then the second-stage main stretching is carried out between the second pair of hot rollers and the third pair of hot rollers, the third-stage main stretching and tension heat setting are carried out between the third pair of hot rollers and the fourth pair of hot rollers, the fourth-stage sub-stretching and the first relaxation heat setting are carried out between the fourth pair of hot rollers and the fifth pair of hot rollers, then the fifth-stage sub-stretching and the second relaxation heat setting are carried out between the fifth pair of hot rollers and the sixth pair of hot rollers, and finally winding and forming are carried out using a winding head; The total stretching ratio of the stretching is 4.5 - 6.0; The speed retraction between the fourth and fifth pairs of hot rollers is 30 - 200 m / min; The speed retraction between the fifth and sixth pairs of hot rollers is 30 - 200 m / min; The winding tension during winding and forming is 20 - 250 cN; The winding speed is 2,200 - 3,300 m / min; the winding overfeed ratio is 0.5 - 5%.

18. The melt direct spinning polyamide 56 industrial yarn according to claim 17, characterized in that, The total draw ratio of the drawing is 4.8 - 5.7; and / or, The speed retraction of the fourth and fifth hot rollers is 50 - 150 m / min; and / or, The speed retraction of the fifth and sixth hot rollers is 50 - 150 m / min; and / or, The winding tension during winding forming is 30 - 200 cN; and / or, The winding speed is 2,400 - 3,250 m / min; and / or, The winding overfeed ratio is 1.0 - 4.5%.

19. The melt direct spinning polyamide 56 industrial yarn according to claim 17, characterized in that, The winding tension during winding forming is 50 - 150 cN; and / or, The winding speed is 2,500 - 3,200 m / min; and / or, The winding overfeed ratio is 1.5 - 4.0%.

20. The direct melt spinning polyamide 56 industrial yarn according to claim 17, characterized in that, A humidifying device is provided during the retraction and winding process, the temperature of the humidification is 16 - 26 °C, and the humidity is 60 - 95%.

21. The melt direct spinning polyamide 56 industrial yarn according to claim 20, characterized in that, The temperature of the humidification is 18 - 25 °C; and / or, The humidity of the humidification is 65 - 90%.

22. The melt direct spinning polyamide 56 industrial yarn according to claim 20, wherein, The temperature of the humidification is 20 - 24 °C; and / or, The humidity of the humidification is 70 - 85%.

23. Use of the melt direct spinning polyamide 56 industrial yarn according to any one of claims 1 - 22 in the fields of release cloth, sewing thread, water cloth, canvas, safety belt, rope, fishing net, industrial filter cloth, conveyor belt, parachute, tent or luggage.

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