Polyamide fiber and preparation method and application thereof

Abstract

The invention discloses a polyamide fiber and a preparation method and application thereof. And the melting point of the polyamide fiber is 275-310 DEG C. The polyamide fiber disclosed by the invention has the characteristics of high melting point and good heat resistance, the melting point of the polyamide fiber is far higher than that of the existing polyamide 6, polyamide 56 and polyamide 66 fibers, the high temperature resistance is better, and the polyamide fiber disclosed by the invention has better mechanical property, heat resistance, dimensional stability and dyeing property, and is suitable for industrial production. The method can be applied to the fields of knitted and woven fabrics, carpet yarns, blended yarns, monofilaments and industrial yarns, in particular to the fields of knitted and woven fabrics.

Description

Technical Field

[0001] The present invention relates to the technical field of polyamide materials, and specifically relates to a polyamide fiber, a preparation method thereof, and an application thereof. Background Art

[0002] Polyamide fiber is one of the earliest synthetic fibers put into industrial production in the world and plays a crucial role in the field of synthetic fibers. There are many types of polyamide fibers, and the most widely used in industrial production and application at present are polyamide 6 and polyamide 66. The main applications involve: socks, lace underwear, body shapers, sports underwear, wedding dresses, casual jackets, sportswear, windbreakers, hiking jackets, quick-drying clothes, cold-proof clothes, outdoor tents, sleeping bags, mountaineering bags, etc.; and industrial yarns are widely used in fields such as tyre cords, conveyor belts, hoses, ropes, fishing nets, tyres, parachutes, etc.

[0003] Bio-based polyamide 56 uses bio-based pentamethylenediamine as a monomer raw material, and the carbon emission per unit weight of bio-based polyamide 56 is reduced by more than 50% compared with 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 is 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 properties, skin-friendly properties, wear resistance, good softness, and low-temperature dyeing characteristics, etc., and currently have broad application prospects in the fields of civil filament yarns, staple fibers, industrial yarns, continuous bulked filament yarns, monofilaments, etc.

[0004] The melting points of nylon 6, nylon 66, and polyamide 56 are 220 °C, 260 °C, and 254 °C respectively. Currently, there is no relevant research and report on the preparation of a polyamide resin with a higher melting point and a polyamide fiber with heat resistance, good dimensional stability, low water absorption, good dyeing properties, and high fastness, as well as its downstream applications. Summary of the Invention

[0005] In the first aspect of the present invention, a polyamide fiber is provided, and the melting point of the polyamide fiber is 275 - 310 °C. The polyamide fiber of the present invention has a relatively high melting point and good high-temperature resistance.

[0006] In some embodiments, the fineness of the polyamide fiber is 10 - 300 dtex, preferably 20 - 200 dtex, and more preferably 30 - 100 dtex.

[0007] In some embodiments, the melting point of the polyamide fiber is 280 - 305 °C, and more preferably 285 - 300 °C.

[0008] In some embodiments, the boiling water shrinkage rate of the polyamide fiber is ≤7%, preferably ≤6%, and more preferably ≤5%.

[0009] In some embodiments, the moisture regain of the polyamide fiber is ≤3.8%, preferably ≤3.4%, more preferably ≤3.0%.

[0010] In some embodiments, the breaking strength of the polyamide fiber is ≥2.8 cN / dtex, preferably ≥3.2 cN / dtex, more preferably ≥3.5 cN / dtex.

[0011] In some embodiments, the initial modulus of the polyamide fiber is ≥35 cN / dtex, preferably ≥38 cN / dtex, more preferably ≥40 cN / dtex.

[0012] In some embodiments, the elongation at break of the polyamide fiber is ≤55%, preferably ≤50%, more preferably ≤45%.

[0013] In some embodiments, the dyeing uniformity (grey scale) of the polyamide fiber is ≥4.0 grade, preferably ≥4.5 grade, more preferably ≥5.0 grade.

[0014] In some embodiments, the soaping fastness of the polyamide fiber: the fastness to fading is ≥4.0 grade, preferably ≥4.5 grade, more preferably ≥5.0 grade; the fastness to staining is ≥4.0 grade, preferably ≥4.5 grade, more preferably ≥5.0 grade.

[0015] In some embodiments, the polyamide fiber includes undrawn yarn (UDY), pre-oriented yarn (POY), highly oriented yarn (HOY), fully oriented yarn (FOY), fully drawn yarn (FDY), draw textured yarn (DTY), continuous bulk filament (BCF), staple fiber, industrial yarn, monofilament, preferably fully drawn yarn.

[0016] In some embodiments, the raw material of the polyamide fiber includes PA56T resin.

[0017] In some embodiments, the raw materials of the PA56T resin include adipic acid, terephthalic acid, pentamethylenediamine and a capping agent.

[0018] In some embodiments, the molar ratio of the structural units corresponding to adipic acid, terephthalic acid, and pentamethylenediamine in the PA56T resin is (35 - 65):(65 - 35):100, preferably (40 - 62):(60 - 38):100.

[0019] In some embodiments, the end-capping agent is any one of decanedioic acid, undecandioic acid, dodecanedioic acid, terephthalic acid, acetic acid, and adipic acid, or a combination thereof, and the added content of the end-capping agent is 50-2000ppm, preferably 100-1500ppm, and more preferably 200-1000ppm.

[0020] In some embodiments, the raw material of the PA56T resin further includes an additive, and the additive includes any one of sodium hypophosphite, calcium hypophosphite, phosphorous acid, antioxidant 1010, and antioxidant 1097, or a combination of two or more thereof, preferably any one of sodium hypophosphite, calcium hypophosphite, and antioxidant 1010, or a combination of two or more thereof.

[0021] In some embodiments, the content of the additive is 10-800 ppm, preferably 10-200 ppm, and more preferably 55-150 ppm.

[0022] In some embodiments, the melting point of the PA56T resin is 275-310°C, preferably 280-305°C, and more preferably 285-300°C.

[0023] In some embodiments, the relative viscosity of the PA56T resin is 2.4-3.0, preferably 2.5-2.9, and more preferably 2.6-2.8.

[0024] In some embodiments, the amino content of the PA56T resin is 40-80 mmol / kg, preferably 45-70 mmol / kg, and more preferably 48-60 mmol / kg.

[0025] A second aspect of the present invention provides a method for preparing a polyamide fiber, the method for preparing the polyamide fiber comprising:

[0026] 1) drying and heating the polyamide resin to a molten state to form a polyamide melt;

[0027] 2) transporting the polyamide melt to a spinning manifold through a melt pipe, and after being accurately metered by a metering pump, injecting the melt into a spinning assembly, and extruding the melt from a spinneret hole to form primary fibers;

[0028] 3) Preheating, cooling, oiling, stretching, heat-setting and winding the spun fibers to obtain the polyamide fibers, wherein the stretching is performed using two pairs of hot rollers, firstly stretching is performed between a first pair of hot rollers and a second pair of hot rollers, and then heat-setting is performed on the second pair of hot rollers.

[0029] In some embodiments, the raw material of the polyamide fiber includes PA56T resin.

[0030] In some embodiments, the raw materials of the PA56T resin include adipic acid, terephthalic acid, pentamethylenediamine, and a capping agent.

[0031] In some embodiments, the molar ratio of the structural units corresponding to adipic acid, terephthalic acid, and pentamethylenediamine in the PA56T resin is (35 - 65):(65 - 35):100, preferably (40 - 62):(60 - 38):100.

[0032] In some embodiments, the capping agent is any one or a combination of several of decanedioic acid, undecanedioic acid, dodecanedioic acid, terephthalic acid, acetic acid, and adipic acid. The addition content of the capping agent is 50 - 2000 ppm, preferably 100 - 1500 ppm, and more preferably 200 - 1000 ppm.

[0033] In some embodiments, the raw materials of the PA56T resin further include additives. The additives include any one or a combination of two or more of sodium hypophosphite, calcium hypophosphite, phosphorous acid, antioxidant 1010, and antioxidant 1097, preferably any one or a combination of two or more of sodium hypophosphite, calcium hypophosphite, and antioxidant 1010.

[0034] In some embodiments, the content of the additives is 10 - 800 ppm, preferably 10 - 200 ppm, and more preferably 55 - 150 ppm.

[0035] In some embodiments, the melting point of the PA56T resin is 275 - 310 °C, preferably 280 - 305 °C, and more preferably 285 - 300 °C.

[0036] In some embodiments, the relative viscosity of the PA56T resin is 2.4 - 3.0, preferably 2.5 - 2.9, and more preferably 2.6 - 2.8.

[0037] In some embodiments, the amino group content of the PA56T resin is 40 - 80 mmol / kg, preferably 45 - 70 mmol / kg, and more preferably 48 - 60 mmol / kg.

[0038] In some embodiments, in step 1), the drying temperature is 100 - 180 °C, preferably 120 - 160 °C; the drying time is 10 - 30 h, preferably 15 - 25 h; and the water content of the dried polyamide resin is ≤200 ppm, preferably ≤150 ppm.

[0039] In some embodiments, the heating in step 1) is carried out by a screw, where the temperature in zone 1 is 270 - 290 °C, preferably 275 - 285 °C; the temperature in zone 2 is 280 - 300 °C, preferably 285 - 295 °C; the temperature in zone 3 is 290 - 320 °C, preferably 295 - 315 °C; the temperature in zone 4 is 300 - 330 °C, preferably 305 - 325 °C.

[0040] In some embodiments, a monomer suction device is provided below the spinneret plate in step 2).

[0041] In some embodiments, the temperature of the spinning box is 290 - 330 °C, preferably 295 - 325 °C.

[0042] In some embodiments, the pressure of the spinning pack is 10 - 25 MPa, preferably 14 - 20 MPa; the mesh number of the metal sand in the pack is 10 - 60 mesh, preferably 20 - 40 mesh; the mesh number of the filter screen is 50 - 400 mesh, preferably 150 - 300 mesh.

[0043] In some embodiments, the preheating temperature in step 3) is 290 - 350 °C, preferably 300 - 330 °C.

[0044] In some embodiments, the cooling air velocity is 0.4 - 0.6 m / s, preferably 0.45 - 0.55 m / s; the air temperature is 16 - 22 °C, preferably 18 - 20 °C; the air humidity is 60 - 95%, preferably 70 - 90%.

[0045] In some embodiments, the oiling rate is 1.0 - 1.3%, preferably 1.1 - 1.2%.

[0046] In some embodiments, the draw ratio is 1.3 - 6.0, preferably 1.5 - 4.5.

[0047] In some embodiments, the heat setting temperature is 150 - 250 °C, preferably 180 - 230 °C.

[0048] In some embodiments, the winding speed is 2200 - 5500 m / min, preferably 2500 - 5000 m / min.

[0049] In some embodiments, the overfeed is 0.8 - 3.5%, preferably 1.0 - 3.0%.

[0050] In some embodiments, the production rate of the polyamide fiber is ≥95%, preferably ≥97%.

[0051] The third aspect of the present invention provides an application of a polyamide fiber: the polyamide fiber is applied to the fields of knitted and woven fabrics, carpet yarns, blended yarns, monofilaments, and industrial yarns, preferably in the field of knitted and woven fabrics.

[0052] The beneficial effects that can be achieved by adopting the technical solution of the present invention include:

[0053] First, the polyamide fiber of the present invention has the characteristics of high melting point and good heat resistance. The melting point of the polyamide fiber is 275-310°C. By adjusting the polymerization ratio of pentamethylenediamine, adipic acid and terephthalic acid monomers, a high melting point polyamide resin is obtained, which is much higher than the current melting points of polyamide 6, polyamide 56 and polyamide 66, and has better high temperature resistance.

[0054] Second, the polyamide fiber of the present invention has the characteristics of good dimensional stability, low water absorption, good dyeing performance and high fastness.

[0055] Third, the polyamide fiber of the present invention has good mechanical properties, heat resistance, dimensional stability and dyeing properties, and can be applied to knitted and woven fabrics, carpet yarns, blended yarns, monofilaments, industrial yarns, especially knitted and woven fabrics. DETAILED DESCRIPTION

[0056] The various properties of the products obtained in the following examples and comparative examples were measured according to the following methods:

[0057] (1) Fineness: measured in accordance with GB / T 14343.

[0058] (2) Breaking strength, initial modulus and elongation at break: measured in accordance with GB / T 14344-2008.

[0059] (3) Relative viscosity: The relative viscosity is measured by the concentrated sulfuric acid method using an Ubbelohde viscometer, and the steps are as follows: accurately weigh 0.5±0.0002 g of the dried polyamide resin or fiber sample, add 50 mL of concentrated sulfuric acid (96%) to dissolve it, and measure and record the flow time t of the concentrated sulfuric acid in a constant temperature water bath at 25°C. 0 and the flow time t of the polyamide 56 chips or its staple fiber sample solution.

[0060] The relative viscosity calculation formula is: relative viscosity VN = t / t 0 ; t—solution flow time; t 0 —Solvent flow time.

[0061] (4) Amino acid content: Determined by automatic titrator.

[0062] (5) Water content: Determined by Karl Fischer titrator.

[0063] (6) Moisture regain: The method for measuring moisture regain is as follows: After washing, the fibers are placed in an oven to dry in a loose state. Then, the dried fiber samples are placed in a standard atmosphere specified in GB / T 6529 to condition and reach equilibrium. For the washed and conditioned specimens, the moisture regain is measured. The moisture regain measurement method is carried out in accordance with GB / T 6503. The drying temperature of the oven is 105 °C, and the drying time is 1 h.

[0064] (7) Boiling water shrinkage rate: Measured in accordance with GB / 6505.

[0065] (8) Dyeing evenness (grey scale) / grade: Test method for dyeing evenness of polyamide filaments, FZ / T 50008

[0066] (9) Soaping fastness: Measured in accordance with the national standard GB / T 3921.1—1997.

[0067] (10) Yield rate: Yield rate = (mass of the prepared finished fiber / total mass of the polyamide melt input) × 100%.

[0068] (11) Limiting oxygen index: GB / T 5454-1997 Textiles - Test method for burning performance - Oxygen index method.

[0069] The preparation method of PA56T resin in the following examples and comparative examples is as follows:

[0070] Prepare a pentamethylenediamine adipate solution from pentamethylenediamine, adipic acid, a capping agent, and water. At the same time, prepare a pentamethylenediamine terephthalate solution from pentamethylenediamine, terephthalic acid, a capping agent, and water. Then, mix the pentamethylenediamine adipate solution and the pentamethylenediamine terephthalate solution according to a certain molar fraction ratio to obtain a mixed salt solution. Then, through concentration, prepolymerization under pressure, flash evaporation, and polycondensation, a polyamide melt is obtained;

[0071] The concentration of the mixed salt solution is 48 - 65 wt%, and the pH value is 7.5 - 8.8;

[0072] The pressure of the prepolymerization is 2.0 - 4.0 MPa, and the temperature is 230 - 270 °C;

[0073] The pressure of the polycondensation is -(0 - 0.1) MPa, and the temperature is 280 - 320 °C.

[0074] Example 1 (specification 78 dtex / 48 f)

[0075] The method for preparing the polyamide fiber includes:

[0076] 1) Dry the polyamide resin and heat it to a molten state to form a polyamide melt;

[0077] 2) Feed the polyamide melt into the spinning box through a melt pipeline. After accurate metering by a metering pump, inject it into the spinning pack and extrude it from the spinneret holes. A monomer suction device is arranged below the spinneret plate.

[0078] 3) Preheat, cool, oil, stretch, heat-set, and wind the extruded nascent fibers to obtain the polyamide fibers.

[0079] The polyamide resin is prepared by melt polycondensation of three monomers, namely pentamethylenediamine, adipic acid, and terephthalic acid, with a capping agent. The molar fraction ratio of pentamethylenediamine adipate to pentamethylenediamine terephthalate is 63:37. The capping agent is decanedioic acid, and the added content is 500 ppm. The melting point of the polyamide is 277 °C, the relative viscosity is 2.55, and the amino group content is 50 mmol / kg.

[0080] In step 1), the drying temperature is 120 °C, the drying time is 20 h, and the water content of the dried polyamide resin is 120 ppm.

[0081] In step 1), the heating is carried out by a screw. The temperature of zone 1 is 275 °C, the temperature of zone 2 is 285 °C, the temperature of zone 3 is 295 °C, and the temperature of zone 4 is 305 °C.

[0082] In step 2), the temperature of the spinning box is 295 °C.

[0083] The pressure of the spinning pack is 16 MPa. The mesh number of the metal sand in the pack is 60, and the mesh number of the filter screen is 300.

[0084] In step 3), the preheating temperature is 290 °C.

[0085] The cooling air velocity is 0.5 m / s, the air temperature is 18 °C, and the air humidity is 85%.

[0086] The oiling rate is 1.0%.

[0087] The drawing ratio is 2.5.

[0088] The heat-setting temperature is 200 °C.

[0089] The winding speed is 4500 m / min.

[0090] The overfeed is 1.2%.

[0091] Example 2 (Specification: 78 dtex / 48 f)

[0092] The method for preparing the polyamide fibers includes:

[0093] 1) Dry and heat the polyamide resin to a molten state to form a polyamide melt.

[0094] 2) Feed the polyamide melt into the spinning box through a melt pipeline. After accurate metering by a metering pump, inject it into the spinning pack and extrude it from the spinneret holes. A monomer suction device is arranged below the spinneret plate.

[0095] 3) Preheat, cool, oil, stretch, heat-set, and wind the extruded nascent fibers to obtain the polyamide fibers.

[0096] The polyamide resin is prepared by melt polycondensation of three monomers, namely pentamethylenediamine, adipic acid, and terephthalic acid, with a capping agent. The molar fraction ratio of pentamethylenediamine adipate to pentamethylenediamine terephthalate is 58:42. The capping agent is dodecanedioic acid, and the added content is 800 ppm. The melting point of the polyamide resin is 282 °C, the relative viscosity is 2.68, and the amino group content is 55 mmol / kg.

[0097] In step 1), the drying temperature is 130 °C, the drying time is 24 h, and the water content of the dried polyamide resin is 100 ppm.

[0098] In step 1), the heating is carried out by a screw. The temperature of zone 1 is 280 °C, the temperature of zone 2 is 290 °C, the temperature of zone 3 is 300 °C, and the temperature of zone 4 is 310 °C.

[0099] In step 2), the temperature of the spinning box is 300 °C.

[0100] The pressure of the spinning pack is 19 MPa. The mesh number of the metal sand in the pack is 40, and the mesh number of the filter screen is 250.

[0101] In step 3), the preheating temperature is 300 °C.

[0102] The cooling wind speed is 0.52 m / s, the wind temperature is 19 °C, and the wind humidity is 90%.

[0103] The oiling rate is 1.2%.

[0104] The drawing ratio is 3.0.

[0105] The heat-setting temperature is 220 °C.

[0106] The winding speed is 4700 m / min, and the overfeed is 1.5%.

[0107] Example 3 (specification 78 dtex / 48 f)

[0108] The method for preparing the polyamide fibers includes:

[0109] 1) Dry and heat the polyamide resin to a molten state to form a polyamide melt.

[0110] 2) Transport the polyamide melt through a melt pipeline into a spinning box. After being accurately metered by a metering pump, it is injected into a spinning pack and extruded from spinneret holes. A monomer suction device is arranged below the spinneret plate;

[0111] 3) Preheat, cool, oil, stretch, heat-set, and wind the extruded nascent fibers to obtain the polyamide fibers;

[0112] The polyamide resin is prepared by melt polycondensation of three monomers, namely pentamethylenediamine, adipic acid, and terephthalic acid, with a capping agent. The molar fraction ratio of pentamethylenediamine adipate to pentamethylenediamine terephthalate is 53:47; the capping agent is dodecanedioic acid, and the addition amount is 1000 ppm; the melting point of the polyamide resin is 288 °C, the relative viscosity is 2.75, and the amino group content is 53 mmol / kg;

[0113] In step 1), the drying temperature is 130 °C; the drying time is 30 h; the water content of the dried polyamide resin is 80 ppm;

[0114] The heating is carried out by a screw. Among them, the temperature of zone 1 is 285 °C; the temperature of zone 2 is 295 °C; the temperature of zone 3 is 305 °C; the temperature of zone 4 is 315 °C;

[0115] In step 2), the temperature of the spinning box is 305 °C;

[0116] The pressure of the spinning pack is 22 MPa, the mesh number of the metal sand in the pack is 30 meshes, and the mesh number of the filter screen is 200 meshes;

[0117] In step 3), the preheating temperature is 310 °C;

[0118] The cooling wind speed is 0.55 m / s, the wind temperature is 20 °C, and the wind humidity is 80%;

[0119] The oiling rate is 1.2%;

[0120] The draw ratio is 3.2;

[0121] The heat-setting temperature is 230 °C;

[0122] The winding speed is 4800 m / min, and the overfeed is 1.8%.

[0123] Example 4 (specification 78 dtex / 48 f)

[0124] The method for preparing the polyamide fibers includes:

[0125] 1) Dry and heat the polyamide resin to a molten state to form a polyamide melt;

[0126] 2) Feed the polyamide melt into the spinning box through a melt pipeline. After accurate metering by a metering pump, inject it into the spinning pack and extrude it from the spinneret holes. A monomer suction device is arranged below the spinneret plate;

[0127] 3) Preheat, cool, oil, stretch, heat-set, and wind the extruded nascent fibers to obtain the polyamide fibers;

[0128] The polyamide resin is prepared by melt polycondensation of three monomers, namely pentamethylenediamine, adipic acid, and terephthalic acid, with a capping agent. The molar fraction ratio of pentamethylenediamine adipate to pentamethylenediamine terephthalate is 50:50; the capping agent is adipic acid, and the added content is 700 ppm; the melting point of the polyamide resin is 292 °C, the relative viscosity is 2.85, and the amino group content is 56 mmol / kg;

[0129] In step (1), the drying temperature is 120 °C; the drying time is 30 h; the water content of the dried polyamide resin is 110 ppm;

[0130] In step 1), the heating is carried out by a screw. Among them, the temperature of zone 1 is 285 °C; the temperature of zone 2 is 295 °C; the temperature of zone 3 is 315 °C; the temperature of zone 4 is 320 °C;

[0131] In step 2), the temperature of the spinning box is 310 °C;

[0132] The pressure of the spinning pack is 20 MPa. The mesh number of the metal sand in the pack is 30 meshes, and the mesh number of the filter screen is 150 meshes;

[0133] In step 3), the preheating temperature is 320 °C;

[0134] The cooling air speed is 0.51 m / s, the air temperature is 21 °C, and the air humidity is 70%;

[0135] The oiling rate is 1.05%;

[0136] The draw ratio is 3.5;

[0137] The heat-setting temperature is 235 °C;

[0138] The winding speed is 4900 m / min, and the overfeed is 2.2%.

[0139] Example 5 (Specification 78 dtex / 48 f)

[0140] The method for preparing the polyamide fibers includes:

[0141] 1) Dry and heat the polyamide resin to a molten state to form a polyamide melt;

[0142] 2) Feed the polyamide melt into the spinning box through a melt pipeline. After being accurately metered by a metering pump, it is injected into the spinning pack and extruded from the spinneret holes, where a monomer suction device is arranged below the spinneret plate.

[0143] 3) Preheat, cool, oil, stretch, heat-set, and wind the extruded nascent fibers to obtain the polyamide fibers.

[0144] The polyamide resin is prepared by melt polycondensation of three monomers, namely pentamethylenediamine, adipic acid, and terephthalic acid, with a capping agent. The molar fraction ratio of pentamethylenediamine adipate to pentamethylenediamine terephthalate is 47:53. The capping agent is decanedioic acid, and the added content is 500 ppm. The melting point of the polyamide resin is 296 °C, the relative viscosity is 2.9, and the amino group content is 58 mmol / kg.

[0145] In step 1), the drying temperature is 130 °C, the drying time is 25 h, and the water content of the dried polyamide resin is 100 ppm.

[0146] In step 1), the heating is carried out by a screw. Among them, the temperature of zone 1 is 290 °C, the temperature of zone 2 is 300 °C, the temperature of zone 3 is 310 °C, and the temperature of zone 4 is 325 °C.

[0147] In step 2), the temperature of the spinning box is 315 °C.

[0148] The pressure of the spinning pack is 24 MPa. The mesh number of the metal sand in the pack is 20, and the mesh number of the filter screen is 200.

[0149] In step 3), the preheating temperature is 330 °C.

[0150] The cooling air velocity is 0.56 m / s, the air temperature is 22 °C, and the air humidity is 75%.

[0151] The oiling rate is 1.15%.

[0152] The draw ratio is 3.0.

[0153] The heat-setting temperature is 230 °C.

[0154] The winding speed is 4300 m / min, and the overfeed is 1.4%.

[0155] Example 6 (specification 78 dtex / 48 f)

[0156] The method for preparing the polyamide fibers includes:

[0157] Prepare polyamide fibers using the same process as in Example 1, except that the amino group content of the polyamide resin is 60 mmol / kg.

[0158] Example 7 (Specification: 78 dtex / 48 f)

[0159] The method for preparing the polyamide fiber comprises the following steps:

[0160] The polyamide fiber is prepared by the same process as in Example 1, except that the heat setting temperature is 220 °C.

[0161] Comparative Example 1 (Specification: 78 dtex / 48 f)

[0162] The method for preparing the polyamide fiber comprises the following steps:

[0163] The polyamide fiber is prepared by the same process as in Example 1, except that the addition content of the end-capping agent is 0 ppm.

[0164] Comparative Example 2 (Specification: 78 dtex / 48 f)

[0165] The method for preparing the polyamide fiber comprises the following steps:

[0166] The polyamide fiber is prepared by the same process as in Example 1, except that the polyamide resin is polyamide 6 with a melting point of 220 °C;

[0167] The heating in step 1) is carried out in a screw extruder, and the screw extruder is divided into four zones for heating; among them, the temperature of zone 1 is 225 °C, the temperature of zone 2 is 235 °C, the temperature of zone 3 is 245 °C, and the temperature of zone 4 is 255 °C;

[0168] The temperature of the spinning box in step 2) is 255 °C.

[0169] Comparative Example 3 (Specification: 78 dtex / 48 f)

[0170] The method for preparing the polyamide fiber comprises the following steps:

[0171] The polyamide fiber is prepared by the same process as in Example 1, except that the polyamide resin is polyamide 56 with a melting point of 254 °C;

[0172] The heating in step 1) is carried out in a screw extruder, and the screw extruder is divided into four zones for heating; among them, the temperature of zone 1 is 270 °C, the temperature of zone 2 is 280 °C, the temperature of zone 3 is 285 °C, and the temperature of zone 4 is 290 °C;

[0173] The temperature of the spinning box in step (2) is 288 °C.

[0174] Comparative Example 4 (Specification: 78 dtex / 48 f)

[0175] The method for preparing the polyamide fiber comprises the following steps:

[0176] The polyamide fiber was prepared by the same process as in Example 1, except that the polyamide resin was polyamide 66 with a melting point of 262 °C;

[0177] The heating in step (1) was carried out in a screw extruder, which was divided into four zones for heating; among them, the temperature of zone 1 was 280 °C, the temperature of zone 2 was 290 °C, the temperature of zone 3 was 295 °C, and the temperature of zone 4 was 295 °C;

[0178] The temperature of the spinning box in step (2) was 293 °C.

[0179] Comparative Example 5 (specification 78 dtex / 48 f)

[0180] The method for preparing the polyamide fiber includes:

[0181] The polyamide fiber was prepared by the same process as in Example 1, except that the spinning pack pressure was 35 MPa, the mesh number of the metal sand in the pack was 80 mesh, and the mesh number of the filter screen was 600 mesh.

[0182] Comparative Example 6 (specification 78 dtex / 48 f)

[0183] The method for preparing the polyamide fiber includes:

[0184] The polyamide fiber was prepared by the same process as in Example 1, except that the overfeed was 0.5%.

[0185] Comparative Example 7 (specification 78 dtex / 48 f)

[0186] The method for preparing the polyamide fiber includes:

[0187] The polyamide fiber was prepared by the same process as in Example 1, except that the preheating temperature was 200 °C.

[0188] The performance indexes of the polyamide fibers prepared in Examples 1 - 7 and Comparative Examples 1 - 7 were tested, and they were made into suspenders. The dyeing uniformity, soaping fastness and flame retardant performance of the suspenders were tested, and the results are shown in Table 1.

[0189] Table 1 Indexes of Polyamide Fibers and Suspenders Prepared in Examples and Comparative Examples

[0190]

[0191] As can be seen from Table 1, the polyamide resin of the present invention has a relatively high melting point and amino group content. Therefore, the polyamide fiber has better strength and dyeing effect; overfeeding is beneficial to molecular relaxation, so the polyamide fiber of the present invention has good dimensional stability; by setting preheating, the cooling crystallization rate of the high-temperature melt can be slowed down, improving the drawing performance; due to the poor fluidity of the high-temperature melt, using fine metal sand and fine filter screen to filter the melt will cause too high pressure in the melt assembly, and the melt temperature in the spinning box will increase accordingly. If the temperature is too high, the melt will be partially degraded, resulting in low fiber strength. However, the present invention uses coarse metal sand and coarse filter screen to filter the melt, improving the fiber strength.

[0192] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polyamide fiber, characterized in that, the melting point of the polyamide fiber is 275 - 310 °C.

2. The polyamide fiber according to claim 1, characterized in that, the fineness of the polyamide fiber is 10 - 300 dtex, preferably 20 - 200 dtex, more preferably 30 - 100 dtex; and / or, the melting point of the polyamide fiber is 280 - 305 °C, more preferably 285 - 300 °C; and / or, the boiling water shrinkage rate of the polyamide fiber is ≤7%, preferably ≤6%, more preferably ≤5%; and / or, the moisture regain of the polyamide fiber is ≤3.8%, preferably ≤3.4%, more preferably ≤3.0%; and / or, the breaking strength of the polyamide fiber is ≥2.8 cN / dtex, preferably ≥3.2 cN / dtex, more preferably ≥3.5 cN / dtex; and / or, the initial modulus of the polyamide fiber is ≥35 cN / dtex, preferably ≥38 cN / dtex, more preferably ≥40 cN / dtex; and / or, the elongation at break of the polyamide fiber is ≤55%, preferably ≤50%, more preferably ≤45%; and / or, the dyeing uniformity (gray scale) of the polyamide fiber is ≥4.0 grade, preferably ≥4.5 grade, more preferably ≥5.0 grade; and / or, the soaping fastness of the polyamide fiber: the color fading fastness is ≥4.0 grade, preferably ≥4.5 grade, more preferably ≥5.0 grade; the staining fastness is ≥4.0 grade, preferably ≥4.5 grade, more preferably ≥5.0 grade.

3. The polyamide fiber as claimed in claim 1, characterized in that, the polyamide fiber includes undrawn yarn (UDY), pre-oriented yarn (POY), highly oriented yarn (HOY), fully oriented yarn (FOY), fully drawn yarn (FDY), drawn textured yarn (DTY), continuous bulked filament (BCF), staple fiber, industrial yarn, monofilament, preferably fully drawn yarn.

4. The polyamide fiber according to any one of claims 1 - 3, characterized in that, the raw material of the polyamide fiber includes PA56T resin; and / or, the raw material of the PA56T resin includes adipic acid, terephthalic acid, pentamethylenediamine and capping agent; and / or, the molar ratio of the structural units corresponding to adipic acid, terephthalic acid and pentamethylenediamine in the PA56T resin is (35 - 65):(65 - 35):100, preferably (40 - 62):(60 - 38):100; and / or, the capping agent is any one or a combination of several of decanedicarboxylic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, terephthalic acid, acetic acid and adipic acid, and the addition content of the capping agent is 50 - 2000 ppm, preferably 100 - 1500 ppm, more preferably 200 - 1000 ppm; and / or, The raw material of the PA56T resin further includes an additive, and the additive includes any one or a combination of two or more of sodium hypophosphite, calcium hypophosphite, phosphorous acid, antioxidant 1010, and antioxidant 1097, preferably any one or a combination of two or more of sodium hypophosphite, calcium hypophosphite and antioxidant 1010; and / or, The content of the additive is 10-800 ppm, preferably 10-200 ppm, more preferably 55-150 ppm; and / or, The melting point of the PA56T resin is 275-310°C, preferably 280-305°C, more preferably 285-300°C; and / or, The relative viscosity of the PA56T resin is 2.4-3.0, preferably 2.5-2.9, more preferably 2.6-2.8; and / or, The amino content of the PA56T resin is 40-80 mmol / kg, preferably 45-70 mmol / kg, and more preferably 48-60 mmol / kg.

5. A method for preparing the polyamide fiber according to claims 1-4, It is characterized in that The method comprises: 1) drying and heating the polyamide resin to a molten state to form a polyamide melt; 2) transporting the polyamide melt to a spinning manifold through a melt pipe, and after being accurately metered by a metering pump, injecting the melt into a spinning assembly, and extruding the melt from a spinneret hole to form primary fibers; 3) Preheating, cooling, oiling, stretching, heat-setting and winding the spun fibers to obtain the polyamide fibers, wherein the stretching is performed using two pairs of hot rollers, firstly stretching is performed between a first pair of hot rollers and a second pair of hot rollers, and then heat-setting is performed on the second pair of hot rollers.

6. The method according to claim 5, It is characterized in that The polyamide resin in step 1) is PA56T resin; and / or, The raw materials of the PA56T resin include adipic acid, terephthalic acid, pentamethylenediamine and a capping agent; and / or, The molar ratio of the structural units corresponding to adipic acid, terephthalic acid and pentamethylenediamine in the PA56T resin is (35-65): (65-35): 100, preferably (40-62): (60-38): 100; and / or, The end-capping agent is any one of deca-dicarboxylic acid, undeca-dicarboxylic acid, dodeca-dicarboxylic acid, terephthalic acid, acetic acid, and adipic acid, or a combination thereof, and the added content of the end-capping agent is 50-2000 ppm, preferably 100-1500 ppm, and more preferably 200-1000 ppm; and / or, The raw material of the PA56T resin further includes an additive, and the additive includes any one or a combination of two or more of sodium hypophosphite, calcium hypophosphite, phosphorous acid, antioxidant 1010, and antioxidant 1097, preferably any one or a combination of two or more of sodium hypophosphite, calcium hypophosphite and antioxidant 1010; and / or, The content of the additive is 10-800 ppm, preferably 10-200 ppm, more preferably 55-150 ppm; and / or, The melting point of the PA56T resin is 275 - 310 °C, preferably 280 - 305 °C, more preferably 285 - 300 °C; and / or, The relative viscosity of the PA56T resin is 2.4 - 3.0, preferably 2.5 - 2.9, more preferably 2.6 - 2.8; and / or, The amino content of the PA56T resin is 40 - 80 mmol / kg, preferably 45 - 70 mmol / kg, more preferably 48 - 60 mmol / kg.

7. According to the method described in claim 5, characterized in that in step 1), the drying temperature is 100 - 180 °C, preferably 120 - 160 °C; and / or, the drying time is 10 - 30 h, preferably 15 - 25 h; and / or, the water content of the dried polyamide resin is ≤200 ppm, preferably ≤150 ppm; and / or, the heating is carried out by a screw, wherein the temperature of the first zone is 270 - 290 °C, preferably 275 - 285 °C; the temperature of the second zone is 280 - 300 °C, preferably 285 - 295 °C; the temperature of the third zone is 290 - 320 °C, preferably 295 - 315 °C; the temperature of the fourth zone is 300 - 330 °C, preferably 305 - 325 °C.

8. According to the method described in claim 5, characterized in that in step 2), a monomer suction device is provided below the spinneret; and / or, the temperature of the spinning box is 290 - 330 °C, preferably 295 - 325 °C; and / or, the pressure of the spinning pack is 10 - 25 MPa, preferably 14 - 20 MPa; and / or, the mesh number of the metal sand in the pack is 10 - 60 mesh, preferably 20 - 40 mesh; and / or, the mesh number of the filter screen in the pack is 50 - 400 mesh, preferably 150 - 300 mesh.

9. According to the method described in claim 5, characterized in that in step 3), the preheating temperature is 290 - 350 °C, preferably 300 - 330 °C; and / or, the cooling air speed is 0.4 - 0.6 m / s, preferably 0.45 - 0.55 m / s; the air temperature is 16 - 22 °C, preferably 18 - 20 °C; the air humidity is 60 - 95%, preferably 70 - 90%; and / or, the oiling rate is 1.0 - 1.3%, preferably 1.1 - 1.2%; and / or, the draw ratio is 1.3 - 6.0, preferably 1.5 - 4.5; and / or, the heat setting temperature is 150 - 250 °C, preferably 180 - 230 °C; and / or, the winding speed is 2200 - 5500 m / min, preferably 2500 - 5000 m / min; and / or, the overfeed is 0.8 - 3.5%, preferably 1.0 - 3.0%; and / or, the production rate of the polyamide fiber is ≥95%, preferably ≥97%.

10. A polyamide fiber according to any one of claims 1 - 4 is applied to the fields of knitted and woven fabrics, carpet yarns, blended yarns, monofilaments, and industrial yarns, preferably to the field of knitted and woven fabrics.

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