A high-strength filament for tire cord and its preparation method

Abstract

The present invention relates to the technical field of polyamide materials, and discloses a high-strength yarn for tire cord and a preparation method thereof. By optimizing the melt direct spinning process, a high-strength yarn for bio-based polyamide 56 tire cord with large capacity and high performance is prepared, which has stable production, few broken single filaments, high fiber forming rate, and excellent high-strength and heat-resistant properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyamide materials, and particularly relates to a high-strength yarn for tire cord and a preparation method thereof. Background Art

[0002] Melt spinning is one of the main forming methods of synthetic fibers, abbreviated 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 the polymer melt to go through pre-spinning preparation processes such as casting, pelletizing, and drying before being sent to spinning.

[0003] The monomer content in the polymer of polyamide 6 is relatively high (about 10wt%), and the chips need to be extracted before melt spinning can be achieved. Currently, industrial melt direct spinning cannot be realized. During the spinning process of polyamide 66, problems such as gel formation and difficult dyeing are likely 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 delivery 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 ≤1.5wt%, and the content of cyclic dimers is ≤0.2wt%. Then, after the polycondensation reaction kinetics strengthening ends, direct melt spinning is carried out for forming, but there is still no technical breakthrough and industrialization case.

[0005] CN103668510 A discloses a device and method for producing fine 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 as a nylon 66 melt through a polycondensation reaction, and then the nylon 66 melt is directly spun to prepare fine or superfine denier nylon 66 POY filaments. The spinning speed is 4200 - 4300m / 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 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, wear resistance, good softness, and easy dyeing at low temperatures, etc. 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 preparation of high-strength filaments for large-capacity bio-based polyamide 56 tire cord by melt direct spinning industrialization. Summary of the Invention

[0007] In order to meet the requirements of the industrial production of bio-based polyamide 56 by melt direct spinning, the present invention optimizes the melt direct spinning process to prepare high-strength filaments for large-capacity bio-based polyamide 56 tire cord, with stable production, few broken single filaments, high fiber forming rate, and excellent high strength and heat resistance.

[0008] The first object of the present invention is to provide a high-strength filament for tire cord, the fineness of the high-strength filament for tire cord is 600 - 3500 dtex, further 700 - 2500 dtex, and still further 800 - 2100 dtex; and / or

[0009] The breaking strength of the high-strength filament for tire cord is 7.5 - 10.0 cN / dtex, further 8.0 - 9.5 cN / dtex, and still further 8.3 - 9.0 cN / dtex; the coefficient of variation (CV)% of the breaking strength is ≤4%, further ≤3.8%, and still further ≤3.5%; and / or

[0010] The breaking elongation of the high-strength filament for tire cord is 12 - 28%, further 14 - 26%, and still further 16 - 24%; the coefficient of variation (CV)% of the breaking elongation is ≤5%, further ≤4.5%, and still further ≤4%; and / or

[0011] The initial modulus of the high-strength filament for tire cord is ≥38 cN / dtex, further ≥43 cN / dtex, and still further ≥48 cN / dtex; and / or

[0012] The dry heat shrinkage rate of the high-strength filament for tire cord is ≤8.5%, further ≤8.0%, and still further ≤7.5%; and / or

[0013] After the high-strength yarn for tire cord is heat-treated at 180°C for 4 hours, the heat-resistant breaking strength retention rate is ≥90%, further ≥91%, and even further ≥92%.

[0014] In some specific embodiments, the number of single-filament breaks of the high-strength yarn for tire cord 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.

[0015] In some specific embodiments, the production rate of the high-strength yarn for tire cord is ≥95%, preferably ≥96%, and more preferably ≥98%.

[0016] The second object of the present invention is to provide a method for preparing a high-strength yarn for tire cord, and the preparation method at least includes the following steps:

[0017] (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 filament;

[0018] (2) Subjecting 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 to obtain the high-strength yarn for tire cord.

[0019] In some specific embodiments, 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 filament.

[0020] In some specific embodiments, the temperature of the spinning box is 280 - 300°C, preferably 283 - 295°C, and more preferably 285 - 293°C.

[0021] In some specific embodiments, the pressure of the spinning component in the spinning box is ≥9 MPa, preferably ≥10 MPa, further preferably ≥11 MPa, and even further preferably ≥12 MPa.

[0022] In some specific embodiments, the spinneret draw ratio of the spinneret plate is 30 - 100, preferably 40 - 90.

[0023] In some specific embodiments, in step (1), the temperature of the melt conveying pipeline is controlled to be 265 - 295°C, preferably 268 - 293°C, further preferably 270 - 290°C, and even further preferably 273 - 288°C.

[0024] In some specific embodiments, in step (1), from the melt booster pump to the spinning box, the dynamic viscosity of the polyamide 56 melt is controlled to be ≥200 Pa·s, preferably ≥220 Pa·s, more preferably 230 - 350 Pa·s, and even more preferably 250 - 350 Pa·s.

[0025] In some specific embodiments, a saturated superheated steam device, a slow cooling device, and a monomer suction device are provided below the spinning box. By setting 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. 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 provided below the spinning box is used to increase the slow cooling temperature and inhibit its crystallization and precipitation, thereby preventing the oligomers from crystallizing and forming 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, extending the cleaning cycle of the spinning component shovel plate, reducing the phenomena of nozzle wire and single filament breakage caused by oligomers during spinning, and effectively improving the spinning production stability and the production rate.

[0026] In one embodiment, the temperature of the saturated superheated steam is 100 - 290 °C, further 110 - 280 °C, further 120 - 260 °C, and even more preferably 130 - 250 °C.

[0027] In one embodiment, the pressure of the saturated superheated steam is 0.5 - 3.0 bar, further 0.8 - 2.5 bar, further 1.0 - 2.0 bar, and even more preferably 1.2 - 1.8 bar.

[0028] 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.

[0029] In one embodiment, the pressure of the monomer suction device is ≥6.0 bar, further ≥6.5 bar, further ≥7.0 bar, and even more preferably ≥7.5 bar.

[0030] In some specific embodiments, in step (1), the relative viscosity of the polyamide 56 melt is 3.2 - 4.0, preferably 3.3 - 3.9, more preferably 3.4 - 3.8, and even more preferably 3.5 - 3.7

[0031] In some specific embodiments, the amino group content of the polyamide 56 melt is 20 - 60 mmol / kg, preferably 25 - 55 mmol / kg, more preferably 28 - 50 mmol / kg, and further preferably 32 - 45 mmol / kg.

[0032] 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.

[0033] In some specific embodiments, the content of copper ions in the polyamide 56 melt is 50 - 300 ppm, preferably 60 - 200 ppm, and more preferably 65 - 100 ppm.

[0034] In some specific embodiments, the method for preparing the polyamide 56 melt comprises 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.

[0035] In some specific embodiments, the molar ratio of pentamethylenediamine to adipic acid is (1 - 1.08):1.

[0036] In some specific embodiments, the concentration of the polyamide 56 salt solution is 40 - 80 wt%.

[0037] In some specific embodiments, the pH value of the polyamide 56 salt solution is 6.0 - 9.5.

[0038] In some specific embodiments, the pressure of the prepolymerization is 0.8 - 2.6 MPa, preferably 1.0 - 2.4 MPa, further preferably 1.3 - 2.2 MPa, and still further preferably 1.5 - 2.0 MPa; the temperature of the prepolymerization is 180 - 275 °C, preferably 190 - 270 °C, further preferably 210 - 265 °C, and still further preferably 225 - 260 °C.

[0039] In some specific embodiments, the pressure of the polycondensation is -(0 - 0.08) MPa, preferably -(0.02 - 0.07) MPa, further preferably -(0.03 - 0.06) MPa, and still further preferably -(0.04 - 0.05) MPa; the temperature of the polycondensation is 265 - 295 °C, preferably 270 - 293 °C, further preferably 275 - 290 °C, and still further preferably 278 - 288 °C.

[0040] In the present invention, a heat stabilizer is added during the polymerization of pentamethylenediamine and adipic acid, or the heat stabilizer is added in the form of a heat-resistant masterbatch through an on-line masterbatch adding device and a dynamic mixer, and then melt direct spinning is carried out. In the present invention, the on-line masterbatch adding device and the dynamic mixer are arranged between the polyamide 56 melt polycondensation device and the melt booster pump.

[0041] In some specific embodiments, the heat stabilizer is selected from any one or a combination of copper acetate, potassium iodide, potassium bromide, copper chloride, cuprous iodide, copper oxide, and cuprous oxide, preferably a combination of copper acetate and potassium iodide or a combination of cuprous iodide and potassium iodide.

[0042] In some specific embodiments, the content of copper ions in the heat-resistant masterbatch is 1-10 wt%, preferably 2-8 wt%, and more preferably 3-6 wt%; the addition amount of the heat-resistant masterbatch accounts for 0.05-2.0 wt% of the total weight of the production raw materials, preferably 0.08-1.5 wt%, and more preferably 0.12-1.0 wt%.

[0043] 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 air temperature is preferably 16-25 °C, more preferably 18-22 °C; the humidity is preferably 50-90%, more preferably 60-85%.

[0044] In some specific embodiments, in step (2), the pre-network pressure is 1-2.5 bar, preferably 1.5-2.0 bar.

[0045] In some specific embodiments, in step (2), the multi-stage stretching process is carried out using five or more pairs of hot rollers, preferably six pairs of hot rollers, and is 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, and finally winding and forming are carried out using a winding head.

[0046] In one embodiment, the speed of the first pair of hot rollers is 400-800 m / min, preferably 450-750 m / min, and the temperature is 20-70 °C, preferably 30-60 °C.

[0047] 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.

[0048] In one embodiment, the speed of the third pair of hot rollers is 1300 - 2500 m / min, preferably 1500 - 2300 m / min, and the temperature is 130 - 210 °C, preferably 150 - 200 °C.

[0049] 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 - 230 °C.

[0050] 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 - 210 °C.

[0051] 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 140 - 210 °C, preferably 150 - 180 °C.

[0052] In one embodiment, the total draw ratio of the drawing is 4.5 - 6.0, preferably 4.8 - 5.7.

[0053] In one embodiment, the speed reduction between the fourth and fifth pairs of hot rollers is 30 - 200 m / min, preferably 50 - 150 m / min.

[0054] In one embodiment, the speed reduction between the fifth and sixth pairs of hot rollers is 30 - 200 m / min, preferably 50 - 150 m / min.

[0055] In one embodiment, the main network pressure is 2.5 - 4.5 bar, preferably 3.0 - 3.5 bar.

[0056] In one embodiment, the winding tension during winding forming is 40 - 250 cN, preferably 50 - 200 cN, more preferably 60 - 150 cN.

[0057] 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%, more preferably 1.5 - 3%.

[0058] In some specific embodiments, a humidifying device is provided during the retraction and winding process. The humidifying temperature is 18 - 30 °C, preferably 20 - 28 °C, more preferably 22 - 26 °C; the humidity is 60 - 95%, preferably 65 - 90%, more preferably 70 - 85%.

[0059] On the basis of conforming to 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.

[0060] The positive and progressive effects of the present invention are as follows:

[0061] First, by optimizing the polymerization process and formula adjustment, the present invention can directly prepare high-viscosity polyamide 56 melt for the production of high-strength industrial yarns, saving the processes of polymerization granulation, solid-phase polycondensation, and conditioning, and reducing production costs.

[0062] Second, adopting the preparation method of high-strength yarn for polyamide 56 tire cord by direct melt spinning of the present invention, by optimizing the direct melt spinning process and controlling parameters such as the temperature of the melt conveying pipeline and the dynamic viscosity of the melt, not only can the production of high-strength yarn for polyamide 56 tire cord with a large capacity be realized, but also the gel content in the melt booster pump to the spinning box can be effectively reduced.

[0063] Specifically, the annual output of the high-strength yarn for polyamide 56 tire cord by direct melt spinning is ≤50,000 tons / line, preferably ≤40,000 tons / line, more preferably ≤30,000 tons / line, further preferably ≤20,000 tons / line. The number of spinning positions is ≤50 positions / line, preferably ≤40 positions / line, more preferably ≤30 positions / line, 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 processes of melt granulation, slice drying, and screw melting in the slice spinning process, greatly reducing the production cost of high-strength yarn for polyamide 56 tire cord. The gel content can be controlled to ≤1.0 wt% / 6 months, preferably ≤0.8 wt% / 6 months, more preferably ≤0.6 wt% / 6 months, further preferably ≤0.4 wt% / 6 months. The reduction of the gel content greatly reduces the number of disassembly, calcination, and cleaning of the melt pipeline and the spinning box, reducing the production cost.

[0064] Third, by providing a saturated superheated steam device, a slow cooling device, and a monomer suction device below the spinning box, the present invention can effectively reduce the oligomer content, reduce the phenomenon of single filament breakage caused by oligomers during the spinning process, improve the spinning production stability and the forming rate, and can further reduce the number of disassembly, calcination, and cleaning of the melt conveying pipeline and the spinning box, reducing the production cost.

[0065] Fourthly, the present invention can stabilize the polyamide 56 melt and reduce the viscosity and amino group fluctuations by optimizing the melt direct spinning process and controlling the temperature of the melt delivery pipeline and the dynamic viscosity of the melt and other parameters.

[0066] Specifically, the absolute value of the change in viscosity of the polyamide 56 tire cord 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.

[0067] Fifth, the present invention provides a humidifying device during the retraction and winding process, so that the high-strength yarn of the polyamide 56 tire cord absorbs water and retracts during the winding process, and the internal stress generated by the high-multiple drawing is fully released, the dimensional stability is good, and the fluctuations in breaking strength and elongation are small. DETAILED DESCRIPTION

[0068] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The experimental methods for which specific conditions are not specified in the following embodiments are selected according to conventional methods and conditions, or according to the product instructions.

[0069] Test method:

[0070] (1) Fineness: measured in accordance with GB / T 14343.

[0071] (2) Breaking strength, breaking strength variation coefficient (CV): measured in accordance with GB / T 14344-2008.

[0072] (3) Elongation at break, coefficient of variation of elongation at break (CV): measured in accordance with GB / T 14344-2008.

[0073] (4) Heat-resistant breaking strength retention rate: Heat-resistant breaking strength retention rate = (breaking strength after heat treatment / breaking strength before heat treatment) * 100%, breaking strength is measured according to GB / T 14344-2008, and the heat treatment equipment is an oven and a wire winding rack.

[0074] (5) Initial modulus: measured in accordance with GB / T 14344-2008.

[0075] (6) Relative viscosity: By the Ubbelohde viscometer concentrated sulfuric acid method: Accurately weigh 0.5 ± 0.0002 g of the polyamide melt sample taken online after drying, add 50 mL of concentrated sulfuric acid (96 wt%) to dissolve it; measure and record the flowing time t0 of the 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 viscosity number: Relative viscosity = t / t0; t - flowing time of the solution; t0 - flowing time of the solvent.

[0076] (7) Amino end group: Determined by an automatic titrator.

[0077] (8) Equilibrium moisture content: Determined by a Karl Fischer moisture titrator.

[0078] (9) Copper ion content: Measured by an elemental analyzer.

[0079] (10) Number of broken single filaments: Manually counted.

[0080] (11) Yield rate: Yield rate = (mass of the finished fiber prepared / total mass of the polyamide melt input) × 100%.

[0081] (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 formula for gel content: Gel content wt% = A2 / A1 * 100%.

[0082] (13) Dry heat shrinkage rate: Executed according to the provisions of FZ / T 50004, and the heat treatment temperature is 180°C.

[0083] High-strength yarn for polyamide 56 tire cord with a specification of 930 dtex in Example 1

[0084] Preparation of Polyamide 56 Melt

[0085] 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;

[0086] Among them, the molar ratio of the pentamethylenediamine to the adipic acid is 1.06:1; the concentration of the polyamide 56 salt solution is 55 wt%; the pH value of the polyamide 56 salt solution is 7.8;

[0087] The pressure of the prepolymerization is 1.76 MPa, and the temperature of the prepolymerization is 250°C;

[0088] The pressure of the polycondensation is -0.04 MPa, and the temperature of the polycondensation is 282°C;

[0089] During the polymerization of pentamethylenediamine and adipic acid, a heat stabilizer is added, and the heat stabilizer is a compound of copper acetate and potassium iodide;

[0090] The content of copper ions in the polyamide 56 melt is 65 ppm, the relative viscosity is 3.4, the amino group content is 35 mmol / kg, and the equilibrium moisture content is 400 ppm.

[0091] Preparation of High-Strength Yarn for Tire Cord

[0092] (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;

[0093] (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;

[0094] The wire drawing in step (1) is to eject the polyamide 56 melt through the spinneret of the spinning box to form the nascent filament;

[0095] The temperature of the spinning box is 290 °C;

[0096] The pressure of the spinning pack in the spinning box is 12 MPa;

[0097] The spinneret draw ratio of the spinneret is 60;

[0098] Control the temperature of the melt conveying pipeline to be 285 °C;

[0099] From the melt booster pump to the spinning box, control the dynamic viscosity of the polyamide 56 melt to be 260 Pa·s;

[0100] A saturated superheated steam device, a slow cooling device, and a monomer suction device are arranged below the spinning box;

[0101] The temperature of the saturated superheated steam is 180 °C; the pressure of the saturated superheated steam is 1.5 bar;

[0102] The slow cooling height of the slow cooling device is 250 mm, and the slow cooling temperature is 260 °C;

[0103] The pressure of the monomer suction device is 6.5 bar;

[0104] The cooling is side blowing, the wind speed is 0.6 m / s, the wind temperature is 18 °C, and the humidity is 80%;

[0105] The pre-network pressure is 1.5 bar;

[0106] 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. 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.

[0107] Among them, the speed of the first pair of hot rollers is 600 m / min, and the temperature is 30 °C.

[0108] The speed of the second pair of hot rollers is 650 m / min, and the temperature is 100 °C.

[0109] The speed of the third pair of hot rollers is 1800 m / min, and the temperature is 180 °C.

[0110] The speed of the fourth pair of hot rollers is 3000 m / min, and the temperature is 220 °C.

[0111] The speed of the fifth pair of hot rollers is 2900 m / min, and the temperature is 190 °C.

[0112] The speed of the sixth pair of hot rollers is 2850 m / min, and the temperature is 150 °C.

[0113] The total stretching multiple of the stretching is 5.0.

[0114] The speed reduction between the 4th and 5th pairs of hot rollers is 100 m / min.

[0115] The speed reduction between the 5th and 6th pairs of hot rollers is 50 m / min.

[0116] The main network pressure is 3.0 bar.

[0117] The winding tension during winding forming is 90 cN.

[0118] The winding speed is 2800 m / min; the winding overfeed ratio is 1.8%.

[0119] A humidifying device is set during the retraction and winding process. The humidifying temperature is 20 °C, and the humidity is 80%.

[0120] In this embodiment, the annual output of the high-strength yarn for polyamide 56 tire cord is 13,000 tons / line, the spinning positions are 24 positions / line, and the number of spinning heads is 4 heads / position.

[0121] High-strength yarn for polyamide 56 tire cord with a specification of 1400 dtex

[0122] Preparation of Polyamide 56 Melt

[0123] 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;

[0124] Among them, the molar ratio of the 1,5-pentamethylenediamine to adipic acid is 1.05:1; the concentration of the polyamide 56 salt solution is 50 wt%; the pH value of the polyamide 56 salt solution is 8.0;

[0125] The pressure of the prepolymerization is 1.78 MPa, and the temperature of the prepolymerization is 248 °C;

[0126] The pressure of the polycondensation is -0.06 MPa, and the temperature of the polycondensation is 280 °C;

[0127] Add a heat stabilizer during the polymerization of pentamethylenediamine and adipic acid, and the heat stabilizer is a compound of copper acetate and potassium iodide;

[0128] The content of copper ions in the polyamide 56 melt is 78 ppm, the relative viscosity is 3.6, the amino content is 38 mmol / kg, and the equilibrium moisture content is 420 ppm.

[0129] Preparation of High-Strength Yarn for Tire Cord

[0130] (1) Feed the obtained polyamide 56 melt into a spinning box through a melt booster pump and a melt transfer pipeline for wire drawing to form a nascent filament;

[0131] (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;

[0132] The wire drawing in step (1) is to extrude the polyamide 56 melt through a spinneret of the spinning box to form the nascent filament;

[0133] The temperature of the spinning box is 288 °C;

[0134] The pressure of the spinning component in the spinning box is 15 MPa;

[0135] The spinneret draw ratio of the spinneret is 70;

[0136] Control the temperature of the melt transfer pipeline to 282 °C;

[0137] From the melt booster pump to the spinning box, control the dynamic viscosity of the polyamide 56 melt to 280 pa*s;

[0138] A saturated superheated steam device, a slow cooling device, and a monomer suction device are provided below the spinning box body;

[0139] The temperature of the saturated superheated steam is 160 °C; the pressure of the saturated superheated steam is 1.4 bar;

[0140] The slow cooling height of the slow cooling device is 300 mm, and the slow cooling temperature is 300 °C;

[0141] The pressure of the monomer suction device is 6.5 bar;

[0142] The cooling is side blowing, the wind speed is 0.7 m / s, the wind temperature is 17 °C, and the humidity is 85%;

[0143] The pre-network pressure is 1.8 bar;

[0144] In the multi-stage stretching process, 6 pairs of hot rollers are used and 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, and the tension heat setting is 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;

[0145] Among them, the speed of the first pair of hot rollers is 550 m / min, and the temperature is 40 °C;

[0146] The speed of the second pair of hot rollers is 600 m / min, and the temperature is 110 °C;

[0147] The speed of the third pair of hot rollers is 1800 m / min, and the temperature is 200 °C;

[0148] The speed of the fourth pair of hot rollers is 2800 m / min, and the temperature is 220 °C;

[0149] The speed of the fifth pair of hot rollers is 2750 m / min, and the temperature is 190 °C;

[0150] The speed of the sixth pair of hot rollers is 2700 m / min, and the temperature is 160 °C;

[0151] The total stretching multiple of the stretching is 5.1;

[0152] The speed retraction between the 4th and 5th pairs of hot rollers is 50 m / min;

[0153] The speed retraction of the 5th and 6th pairs of hot rollers is 50 m / min;

[0154] The main network pressure is 3.0 bar;

[0155] The winding tension during winding and forming is 135 cN;

[0156] The winding speed is 2600 m / min; the winding overfeed ratio is 3.8%;

[0157] A humidifying device is set during the retraction and winding process, the humidifying temperature is 25 °C, and the humidity is 70%.

[0158] The annual output of the high-strength yarn for polyamide 56 tire cord in this example is 18,000 tons / line, the spinning positions are 24 positions / line, and the number of spinning heads is 4 heads / position.

[0159] High-strength yarn for polyamide 56 tire cord in Example 3 with a specification of 1870 dtex

[0160] Preparation of Polyamide 56 Melt

[0161] 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;

[0162] Among them, the molar ratio of pentamethylenediamine to adipic acid is 1.03:1; the concentration of the polyamide 56 salt solution is 56 wt%; the pH value of the polyamide 56 salt solution is 8.1;

[0163] The pressure of the prepolymerization is 1.74 MPa, and the temperature of the prepolymerization is 246 °C;

[0164] The pressure of the polycondensation is -0.04 MPa, and the temperature of the polycondensation is 283 °C;

[0165] During the polymerization of the polyamide 56 melt, a heat stabilizer is added in the form of a heat-resistant masterbatch through a masterbatch in-line addition device and a dynamic mixer. The heat stabilizer is a compound of cuprous iodide and potassium iodide. The content of copper ions in the heat-resistant masterbatch is 3.5 wt%, and the addition amount of the heat-resistant masterbatch accounts for 0.2 wt% of the total weight of the production raw materials;

[0166] The content of copper ions in the obtained polyamide 56 melt is 70 ppm, the relative viscosity is 3.5, the amino group content is 40 mmol / kg, and the equilibrium moisture content is 400 ppm.

[0167] Preparation of High-Strength Yarn for Tire Cord

[0168] (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;

[0169] (2) The nascent fiber 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;

[0170] 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;

[0171] The temperature of the spinning box is 286 °C;

[0172] The pressure of the spinning component in the spinning box is 14 MPa;

[0173] The spinneret draw ratio of the spinneret plate is 75;

[0174] The temperature of the melt conveying pipeline is controlled at 281 °C;

[0175] From the melt booster pump to the spinning box, the dynamic viscosity of the polyamide 56 melt is controlled at 270 Pa·s;

[0176] A saturated superheated steam device, a slow cooling device, and a monomer suction device are arranged below the spinning box;

[0177] The temperature of the saturated superheated steam is 140 °C, and the pressure of the saturated superheated steam is 1.6 bar;

[0178] The slow cooling height of the slow cooling device is 280 mm, and the slow cooling temperature is 300 °C;

[0179] The pressure of the monomer suction device is 6.0 bar;

[0180] The cooling is side blowing, the wind speed is 0.6 m / s, the wind temperature is 18 °C, and the humidity is 88%;

[0181] The pre-network pressure is 1.5 bar;

[0182] Six pairs of hot rollers are used in the stretching process, and it 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, 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;

[0183] Among them, the speed of the first pair of hot rollers is 580 m / min and the temperature is 50 °C;

[0184] The speed of the second pair of hot rollers is 630 m / min and the temperature is 120 °C;

[0185] The speed of the third pair of hot rollers is 1850 m / min and the temperature is 180 °C;

[0186] The speed of the fourth pair of hot rollers is 2850 m / min and the temperature is 210 °C;

[0187] The speed of the fifth pair of hot rollers is 2800 m / min and the temperature is 190 °C;

[0188] The speed of the sixth pair of hot rollers is 2750 m / min and the temperature is 150 °C;

[0189] The total draw ratio of the drawing is 4.9;

[0190] The speed retraction between the 4th and 5th pairs of hot rollers is 50 m / min;

[0191] The speed retraction between the 5th and 6th pairs of hot rollers is 50 m / min;

[0192] The main network pressure is 3.2 bar;

[0193] The winding tension during winding and forming is 180 cN;

[0194] The winding speed is 2680 m / min; the winding overfeed ratio is 2.6%;

[0195] A humidifying device is provided during retraction and winding, the humidifying temperature is 19 °C, and the humidity is 80%.

[0196] In this embodiment, the annual output of the high-strength yarn for polyamide 56 tire cord is 13,000 tons / line, the spinning positions are 24 positions / line, and the number of spinning heads is 2 heads / position.

[0197] High-strength yarn for polyamide 56 melt tire cord with a specification of 2100 dtex in Example 4

[0198] Preparation of Polyamide 56 Melt

[0199] Prepare a polyamide 56 salt solution from pentamethylenediamine, adipic acid and water, and then obtain polyamide 56 melt through prepolymerization, flash evaporation and polycondensation;

[0200] Among them, the molar ratio of pentamethylenediamine to adipic acid is 1.04:1; the concentration of the polyamide 56 salt solution is 55 wt%; the pH value of the polyamide 56 salt solution is 8.0;

[0201] The pressure of the prepolymerization is 1.72 MPa, and the temperature of the prepolymerization is 243 °C;

[0202] The pressure of the polycondensation is -0.05 MPa, and the temperature of the polycondensation is 285 °C;

[0203] A heat stabilizer is added during the polymerization of pentamethylenediamine and adipic acid, and the heat stabilizer is a compound of copper acetate and potassium iodide;

[0204] The content of copper ions in the polyamide 56 melt is 80 ppm, the relative viscosity is 3.4, the amino group content is 43 mmol / kg, and the equilibrium moisture content is 380 ppm.

[0205] Preparation of High-Strength Yarn for Tire Cord

[0206] (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;

[0207] (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;

[0208] The wire drawing in step (1) is to eject the polyamide 56 melt through the spinneret plate of the spinning box to form the nascent filament;

[0209] The temperature of the spinning box is 290 °C;

[0210] The pressure of the spinning component in the spinning box is 13 MPa;

[0211] The spinneret draw ratio of the spinneret plate is 80;

[0212] Control the temperature of the melt conveying pipeline to 284 °C;

[0213] From the melt booster pump to the spinning box, control the dynamic viscosity of the polyamide 56 melt to 250 pa*s;

[0214] A saturated superheated steam device, a slow cooling device, and a monomer suction device are arranged below the spinning box;

[0215] The temperature of the saturated superheated steam is 150 °C; the pressure of the saturated superheated steam is 1.2 bar;

[0216] The slow cooling height of the slow cooling device is 260 mm, and the slow cooling temperature is 270 °C;

[0217] The pressure of the monomer suction device is 6.0 bar;

[0218] The cooling is side blowing, the wind speed is 0.7 m / s, the wind temperature is 19 °C, and the humidity is 85%;

[0219] The pre-network pressure is 1.5 bar;

[0220] 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. 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;

[0221] Among them, the speed of the first pair of hot rollers is 600 m / min and the temperature is 55 °C;

[0222] The speed of the second pair of hot rollers is 700 m / min and the temperature is 110 °C;

[0223] The speed of the third pair of hot rollers is 1900 m / min and the temperature is 190 °C;

[0224] The speed of the fourth pair of hot rollers is 2950 m / min and the temperature is 210 °C;

[0225] The speed of the fifth pair of hot rollers is 2900 m / min and the temperature is 180 °C;

[0226] The speed of the sixth pair of hot rollers is 2850 m / min and the temperature is 130 °C;

[0227] The total stretching multiple of the stretching is 4.92;

[0228] The speed retraction between the 4th and 5th pairs of hot rollers is 50 m / min;

[0229] The speed retraction between the 5th and 6th pairs of hot rollers is 50 m / min;

[0230] The main network pressure is 3.2 bar;

[0231] The winding tension during winding forming is 200 cN;

[0232] The winding speed is 2750 m / min; the winding overfeed ratio is 3.6%;

[0233] A humidifying device is provided during the retraction and winding process, with the humidifying temperature being 21°C and the humidity being 82%.

[0234] In this embodiment, the annual output of the high-strength yarn for polyamide 56 tire cord is 14,500 tons / line, the spinning positions are 24 positions / line, and the number of spinning heads is 2 heads / position.

[0235] High-strength yarn for polyamide 56 tire cord with a specification of 1670 dtex in Example 5

[0236] Preparation of Polyamide 56 Melt

[0237] 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;

[0238] Among them, the molar ratio of the 1,5-pentamethylenediamine to adipic acid is 1.05:1; the concentration of the polyamide 56 salt solution is 60 wt%; the pH value of the polyamide 56 salt solution is 7.8;

[0239] The pressure of the prepolymerization is 1.75 MPa, and the temperature of the prepolymerization is 248°C;

[0240] The pressure of the polycondensation is -0.06 MPa, and the temperature of the polycondensation is 282°C;

[0241] Add a heat stabilizer during the polymerization of pentamethylenediamine and adipic acid, and the heat stabilizer is a compound of copper acetate and potassium iodide;

[0242] The content of copper ions in the polyamide 56 melt is 85 ppm, the relative viscosity is 3.5, the amino group content is 42 mmol / kg, and the equilibrium moisture content is 480 ppm.

[0243] Preparation of High-Strength Yarn for Tire Cord

[0244] (1) Feed the obtained polyamide 56 melt through a melt booster pump and a melt transfer pipeline into a spinning box for wire drawing to form a nascent filament;

[0245] (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;

[0246] 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 filament;

[0247] The temperature of the spinning box is 293°C;

[0248] The pressure of the spinning component in the spinning box is 12 MPa;

[0249] The draw ratio of the spinneret of the spinneret plate is 100;

[0250] Control the temperature of the melt delivery pipeline to 282 °C;

[0251] From the melt booster pump to the spinning box, control the dynamic viscosity of the polyamide 56 melt to 255 Pa·s;

[0252] A saturated superheated steam device, a slow cooling device and a monomer suction device are arranged below the spinning box;

[0253] The temperature of the saturated superheated steam is 140 °C; the pressure of the saturated superheated steam is 1.4 bar;

[0254] The slow cooling height of the slow cooling device is 280 mm, and the slow cooling temperature is 280 °C;

[0255] The pressure of the monomer suction device is 6.5 bar;

[0256] The cooling is side blowing, the wind speed is 0.8 m / s, the wind temperature is 18 °C, and the humidity is 88%;

[0257] The pre-network pressure is 1.5 bar;

[0258] In the multi-stage stretching process, 6 pairs of hot rolls are used and 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, and the tension heat setting is 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;

[0259] Among them, the speed of the first pair of hot rolls is 450 m / min, and the temperature is 50 °C;

[0260] The speed of the second pair of hot rolls is 500 m / min, and the temperature is 100 °C;

[0261] The speed of the third pair of hot rolls is 1800 m / min, and the temperature is 195 °C;

[0262] The speed of the fourth pair of hot rolls is 2550 m / min, and the temperature is 215 °C;

[0263] The speed of the fifth pair of hot rolls is 2500 m / min, and the temperature is 185 °C;

[0264] The speed of the sixth pair of hot rollers is 2450 m / min, and the temperature is 120 °C;

[0265] The total draw ratio of the drawing is 5.67;

[0266] The speed retraction between the fourth and fifth pairs of hot rollers is 50 m / min;

[0267] The speed retraction between the fifth and sixth pairs of hot rollers is 50 m / min;

[0268] The main network pressure is 3.2 bar;

[0269] The winding tension during winding and forming is 160 cN;

[0270] The winding speed is 2400 m / min; the winding overfeed ratio is 2.1%;

[0271] A humidifying device is provided during the retraction and winding process, and the humidifying temperature is 24 °C and the humidity is 80%.

[0272] The annual output of the high-strength yarn for polyamide 56 tire cord in this example is 10,000 tons / line, the spinning positions are 24 positions / line, and the number of spinning heads is 2 heads / position.

[0273] Example 6

[0274] The high-strength yarn for polyamide 56 tire cord is prepared by the same process as in Example 2, except that the relative viscosity of the polyamide 56 melt is 2.65.

[0275] Example 7

[0276] The high-strength yarn for polyamide 56 tire cord is prepared by the same process as in Example 2, except that the equilibrium moisture content of the polyamide 56 melt is 1300 ppm.

[0277] Example 8

[0278] The high-strength yarn for polyamide 56 tire cord is prepared by the same process as in Example 2, except that the temperature of the melt transfer pipeline is controlled at 305 °C.

[0279] Example 9

[0280] The high-strength yarn for polyamide 56 tire cord is prepared by the same process as in Example 2, except that from the melt booster pump to the spinning box, the dynamic viscosity of the polyamide 56 melt is controlled at 140 Pa·s.

[0281] Example 10

[0282] The high-strength yarn for polyamide 56 tire cord is prepared by the same process as in Example 2, except that no heat stabilizer is added during the polymerization process.

[0283] Example 11

[0284] The high-strength yarn for polyamide 56 tire cord is prepared by the same process as in Example 2, except that there is no humidifying device during the retraction and winding process.

[0285] Example 12

[0286] The high-strength yarn for polyamide 56 tire cord is prepared by the same process as in Example 2, except that no saturated superheated steam device, slow cooling device and monomer suction device are provided below the spinning box.

[0287] Comparative Example 1

[0288] The high-strength yarn for polyamide 56 tire cord is prepared by the same process as in Example 2, except that the polyamide 56 melt obtained in step (1) is first granulated and dried to obtain chips, and then melted by a single screw and sent to the spinning box through a melt conveying pipeline, and the high-strength yarn for polyamide 56 tire cord is prepared by chip spinning.

[0289] Table 1 Parameters of the high-strength yarn for polyamide 56 tire cord prepared in Examples and Comparative Examples

[0290]

[0291] By adopting the preparation method of the high-strength yarn for polyamide 56 tire cord of the present invention, through optimizing the melt direct spinning process and controlling parameters such as the temperature of the melt conveying pipeline and the dynamic viscosity of the melt, the polyamide 56 melt can be stabilized, and the viscosity and amino group fluctuation are small. It can not only realize the production of high-strength yarn for large-capacity polyamide 56 tire cord, endow the high-strength yarn for polyamide 56 tire cord with high strength and heat resistance, but also effectively reduce the gel content in the melt booster pump to the spinning box.

[0292] 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. Those skilled in the art can obviously make various modifications to these embodiments easily 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 the 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 preparation method of high-strength yarn for tire cord, characterized in that, The breaking elongation of the high-strength yarn for tire cord is 12-28%, and the coefficient of variation of the breaking elongation is ≤5%; the preparation method 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) Cooling slowly and heating, cooling, oiling, pre-networking, multi-stage stretching, tension heat setting, two-stage relaxation heat setting, main networking, and winding of the nascent yarn to obtain the high-strength yarn for tire cord; Among them, in step (1), the temperature of the melt conveying pipeline is controlled at 265-295°C. From the melt booster pump to the spinning box, the dynamic viscosity of the polyamide 56 melt is controlled to be ≥200 Pa·s. A saturated superheated steam device, a slow cooling device, and a monomer suction device are arranged below the spinning box; A heat stabilizer is added during the polymerization of pentamethylenediamine and adipic acid to prepare polyamide 56; the relative viscosity of the polyamide 56 melt is 3.2-4.0, and the equilibrium moisture content of the polyamide 56 melt is 200-800 ppm.

2. The preparation method according to claim 1, wherein The wire drawing in step (1) is to spray the polyamide 56 melt through the spinneret of the spinning box to form the nascent yarn; The temperature of the spinning box is 280-300°C; and / or, The pressure of the spinning pack in the spinning box is ≥9 MPa.

3. The preparation method according to claim 2, characterized in that, The temperature of the spinning box is 283-295°C; and / or, The pressure of the spinning pack in the spinning box is ≥10 MPa; and / or, In step (1), the temperature of the melt conveying pipeline is controlled at 268-293°C; and / or, In step (1), from the melt booster pump to the spinning box, the dynamic viscosity of the polyamide 56 melt is controlled to be ≥220 Pa·s.

4. The preparation method according to claim 1, wherein The temperature of the spinning box is 285-293°C; and / or, The pressure of the spinning pack in the spinning box is ≥11 MPa; and / or, In step (1), from the melt booster pump to the spinning box, the dynamic viscosity of the polyamide 56 melt is 230-350 Pa·s; and / or, In step (1), the temperature of the melt conveying pipeline is controlled at 270-290°C.

5. The preparation method according to claim 1, wherein In step (1), the temperature of the melt conveying pipeline is controlled at 273-288°C; and / or, In step (1), from the melt booster pump to the spinning box, the dynamic viscosity of the polyamide 56 melt is 250-350 Pa·s; and / or, The pressure of the spinning pack in the spinning box is ≥12 MPa.

6. The preparation method according to claim 1, characterized in that, The temperature of the saturated superheated steam is 100-290°C; and / or, The pressure of the saturated superheated steam is 0.5-3.0 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.

7. The preparation method according to claim 6, characterized in that, The temperature of the saturated superheated steam is 110-280°C; and / or, The pressure of the saturated superheated steam is 0.8-2.5 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.

8. The preparation method according to claim 6, wherein The temperature of the saturated superheated steam is 120 to 260 °C; and / or, The pressure of the saturated superheated steam is 1.0 to 2.0 bar; and / or, The slow cooling temperature of the slow cooling device is 250 to 300 °C; and / or, The pressure of the monomer suction device is ≥7.0 bar.

9. The preparation method according to claim 6, characterized in that The temperature of the saturated superheated steam is 130 to 250 °C; and / or, The pressure of the saturated superheated steam is 1.2 to 1.8 bar; and / or, The pressure of the monomer suction device is ≥7.5 bar.

10. The preparation method according to claim 1, characterized in that, In step (1), the amino group content of the polyamide 56 melt is 20 to 60 mmol / kg; and / or, The content of copper ions in the polyamide 56 melt is 50 to 300 ppm.

11. The preparation method according to claim 1, characterized in that, In step (1), the relative viscosity of the polyamide 56 melt is 3.3 to 3.9; and / or, The amino group content of the polyamide 56 melt is 25 to 55 mmol / kg; and / or, The equilibrium moisture content of the polyamide 56 melt is 250 to 700 ppm; and / or, The content of copper ions in the polyamide 56 melt is 60 to 200 ppm.

12. The preparation method according to claim 1, wherein In step (1), the relative viscosity of the polyamide 56 melt is 3.4 to 3.8; and / or, The amino group content of the polyamide 56 melt is 28 to 50 mmol / kg; and / or, The equilibrium moisture content of the polyamide 56 melt is 300 to 600 ppm; and / or, The content of copper ions in the polyamide 56 melt is 65 to 100 ppm.

13. The preparation method according to claim 1, wherein In step (1), the relative viscosity of the polyamide 56 melt is 3.5 to 3.7; and / or, The amino group content of the polyamide 56 melt is 32 to 45 mmol / kg; and / or, The equilibrium moisture content of the polyamide 56 melt is 350 to 500 ppm.

14. The preparation method according to claim 1, wherein In step (2), the multi-stage stretching process is carried out using five or more pairs of hot rollers.

15. The preparation method according to claim 14, wherein, In step (2), the multi-stage stretching process uses six 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, and tension heat setting is 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 and forming are carried out using a winding head; The total stretching ratio of the stretching is 4.5 to 6.0; The speed retraction between the fourth and fifth pairs of hot rollers is 30 to 200 m / min; The speed retraction between the fifth and sixth pairs of hot rollers is 30 to 200 m / min; The winding tension during winding and forming is 40 to 250 cN; The winding speed is 2200 to 3300 m / min; The winding overfeed ratio is 0.5 to 5%.

16. The preparation method according to claim 15, characterized in that, The total stretching ratio of the stretching is 4.8 to 5.7; and / or, The speed retraction of the fourth and fifth pairs of hot rollers is 50 - 150 m / min; and / or, The speed retraction of the fifth and sixth pairs of hot rollers is 50 - 150 m / min; and / or, The winding tension during winding and forming is 50 - 200 cN; and / or, The winding speed is 2400 - 3250 m / min; and / or, The winding overfeed ratio is 1.0 - 4%.

17. The preparation method according to claim 15, wherein, The winding tension during winding and forming is 60 - 150 cN; and / or, The winding speed is 2500 - 3200 m / min; and / or, The winding overfeed ratio is 1.5 - 3%.

18. The preparation method according to claim 15, characterized in that, A humidifying device is provided during the retraction and winding process, with the humidifying temperature being 18 - 30 °C and the humidity being 60 - 95%.

19. The preparation method according to claim 18, wherein, The humidifying temperature is 20 - 28 °C; and / or, The humidity is 65 - 90%.

20. The preparation method according to claim 18, wherein The humidifying temperature is 22 - 26 °C; and / or, The humidity is 70 - 85%.

21. A high-strength yarn for tire cord, prepared by the preparation method according to any one of claims 1 to 20.

22. The high-strength yarn for tire cord according to claim 21, characterized in that, The fineness of the high-strength yarn for tire cord is 600 - 3500 dtex; and / or, The breaking strength of the high-strength yarn for tire cord is 7.5 - 10.0 cN / dtex; and / or, The coefficient of variation of the breaking strength of the high-strength yarn for tire cord is ≤4%; and / or, The breaking elongation of the high-strength yarn for tire cord is 14 - 26%; and / or, The coefficient of variation of the breaking elongation of the high-strength yarn for tire cord is ≤4.5%; and / or, The initial modulus of the high-strength yarn for tire cord is ≥38 cN / dtex; and / or, The dry heat shrinkage rate of the high-strength yarn for tire cord is ≤8.5%; and / or, After the high-strength yarn for tire cord is heat-treated at 180 °C for 4 h, the heat-resistant breaking strength retention rate is ≥90%.

23. The high-strength yarn for tire cord according to claim 21, characterized in that, The fineness of the high-strength yarn for tire cord is 700 - 2500 dtex; and / or, The breaking strength of the high-strength yarn for tire cord is 8.0 - 9.5 cN / dtex; and / or, The coefficient of variation of the breaking strength of the high-strength yarn for tire cord is ≤3.8%; and / or, The breaking elongation of the high-strength yarn for tire cord is 16 - 24%; and / or, The coefficient of variation of the breaking elongation of the high-strength yarn for tire cord is ≤4%; and / or, The initial modulus of the high-strength yarn for tire cord is ≥43 cN / dtex; and / or, The dry heat shrinkage rate of the high-strength yarn for tire cord is ≤8.0%; and / or, After the high-strength yarn for tire cord is heat-treated at 180 °C for 4 h, the heat-resistant breaking strength retention rate is ≥91%.

24. The high-strength yarn for tire cord according to claim 21, wherein The fineness of the high-strength yarn for tire cord is 800 - 2100 dtex; and / or, The breaking strength of the high-strength yarn for tire cord is 8.3 - 9.0 cN / dtex; and / or, The coefficient of variation of the breaking strength of the high-strength yarn for tire cord is ≤3.5%; and / or, The initial modulus of the high-strength yarn for tire cord is ≥48 cN / dtex; and / or, The dry heat shrinkage rate of the high-strength yarn for tire cord is ≤ 7.5%; and / or, After heat treatment at 180°C for 4 hours, the heat-resistant breaking strength retention rate of the high-strength yarn for tire cord is ≥ 92%.

Images