Modified polyamide, gray easy-to-dye nylon 66 fiber and preparation method and application of gray easy-to-dye nylon 66 fiber

Abstract

The invention relates to the technical field of high polymer materials, and particularly discloses a modified polyamide, a gray easily-dyed nylon 66 fiber and a preparation method and application of the gray easily-dyed nylon 66 fiber. According to the invention, a modified monomer, adipic acid and hexamethylenediamine are copolymerized, and the obtained modified polyamide and conventional nylon 66 are spun into the parallel composite fiber. Ion groups in the modified polyamide have dyeing resistance and can be white when being dyed to be black, and conventional nylon 66 can be normally dyed to be black, so that the obtained side-by-side composite fiber can comprehensively present a gray visual effect, is uniform in color development and adjustable in depth, and is simpler and more convenient than a conventional method. Besides, the modified monomer with the molecular size similar to that of the nylon 66 monomer is selected, adverse effects on the polymerization process and the mechanical property of the fiber are avoided, the implementation cost is low, the effect is remarkable, and the application prospect is wide.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer materials, and particularly relates to a modified polyamide, a gray easily-dyed nylon 66 fiber and a preparation method and application thereof. BACKGROUND

[0002] In the field of dyeing and finishing process, some colors such as beige, coffee, bright red, mouse gray, light blue, army green, grass green, turquoise and brown are quite sensitive to the differences in fiber structure and dyeing conditions, and are extremely prone to cause visible dyeing color difference, so they are called sensitive colors. Among them, gray, as a classic neutral color, is popular among consumers in many fields such as home furnishing and clothing due to its stable, simple and modern characteristics. However, the dyeing process of gray textiles is still a challenging topic.

[0003] The difficulty in dyeing gray is on the one hand due to its process particularity, mainly embodied in the following three points: (1) when dyeing gray, 0.0%5~0.5% owf (on weight the fabric, indicating the percentage of dye or auxiliary quality to fabric quality) of ultra-low dye concentration is needed, and a deviation of 0.01% in concentration can cause a significant shift in color light; (2) three primary color dyes are usually used to dye gray, and the difference in directness and fixation rate of dyes can easily cause color mottle; (3) the transfer dyeing effect of gray (especially light gray) is poor, and the hiding power for fiber imperfections is weak, so if the fiber structure itself is uneven, it is easy to be enlarged into visible color difference. On the other hand, gray is called sensitive color because of the physiological structure of human beings: in the human retina, the proportion of L-type cone cells responsible for perceiving red and M-type cone cells responsible for perceiving green is as high as 95% (blue-sensitive cells only account for 5%). As a low saturation hue, the slight hue shift of gray mainly depends on the antagonistic effect of red and green channels (i.e. L-M signal difference), so the slight color difference or color mottle will be significantly amplified and recognized by the visual system.

[0004] To solve the problem of difficult dyeing of gray, the research in the field of fiber engineering mainly develops in two directions: one is to develop new dyes and optimize the dyeing process; the other is to try to prepare gray yarn by mixing black and white fibers. The basic principle of the latter is to ply black and white filaments, and present gray by means of visual color mixing. However, it is difficult to mix fibers uniformly when plying, even if the same plate spinning technology is used to make the two fibers complete the mixing simultaneously during spinning, it is also difficult to achieve the ideal color development effect of mixed fibers. Therefore, this method is mostly used to produce bi-color yarns with special style. If black and white short fibers are used for blending, the uniformity of mixing can be improved, but it is still difficult to make the different fibers closely adhere to each other. Therefore, the final effect is usually limited to producing "gray" style yarns.

[0005] Nylon 66 fiber has high strength, wear resistance and excellent resilience due to its highly regular molecular chain structure. In addition, nylon 66 fiber has high melting point, good heat resistance, low hot water shrinkage and good dimensional stability. These characteristics make it have durability, comfort and functionality in high-end outdoor equipment, protective clothing and smart wear fields, especially suitable for high-performance clothing and high-end fabric scenarios that need to withstand mechanical stress and environmental pressure.

[0006] In summary, the development of gray easy-to-dye nylon 66 fiber has important practical significance for widening its application in clothing fabric field and improving product added value. SUMMARY

[0007] In view of the above problems, the present application provides a modified polyamide, a gray easy-to-dye nylon 66 fiber and a preparation method and application thereof. The gray easy-to-dye nylon 66 fiber prepared from the modified polyamide and conventional nylon 66 has uniform color development, adjustable depth, excellent mechanical properties, low preparation cost and simple process. In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme: The first aspect of the present application provides a modified polyamide, which is polymerized from a modified monomer, adipic acid and hexamethylene diamine; the molar ratio of the modified monomer to hexamethylene diamine is (10-15): 100; and the modified monomer is a diamine monomer containing carboxylate ion groups.

[0008] Compared with the prior art, the present application introduces ion groups into the polyamide molecular chain by copolymerization modification. The introduced ion groups have a dye-blocking property and will appear white when dyed black. The present application selects a modified monomer with a size similar to that of nylon 66 monomer molecules (adipic acid and hexamethylene diamine), which has little effect on the symmetry of the polyamide molecular chain and does not adversely affect the mechanical properties of the polyamide, so that the excellent mechanical properties of the polyamide can be maintained.

[0009] Preferably, the number average molecular weight of the modified polyamide is 15000-20000.

[0010] Preferably, the molar ratio of the modified monomer to hexamethylene diamine is (10-15): 100.

[0011] The present application adopts a specific molar ratio of the modified monomer to hexamethylene diamine, which does not affect the subsequent polymerization process. In addition, the modified monomer of the present application has a size similar to that of nylon 66 monomer molecules, which has little effect on the symmetry of the nylon 66 molecular chain.

[0012] Preferably, the modified monomer is 2,6-diaminoheptanedioic acid disodium salt.

[0013] The second aspect of the present application provides a preparation method of the modified polyamide, which comprises the following steps: S1. Mix the modified monomer, adipic acid, hexamethylenediamine and water evenly, add catalyst and antioxidant, and carry out a neutralization reaction under inert gas and 90~100℃ to obtain modified nylon 66 salt solution; S2. The modified nylon 66 salt solution is subjected to a polymerization reaction to obtain modified polyamide.

[0014] Preferably, in step S1, the catalyst is at least one of sodium hypophosphite, magnesium hypophosphite, calcium hypophosphite, or zinc hypophosphite.

[0015] More preferably, in step S1, the catalyst is sodium hypophosphite.

[0016] Preferably, in step S1, the antioxidant is at least one of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide, pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) or N,N'-1,6-hexylene-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide].

[0017] More preferably, in step S1, the antioxidant is N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide.

[0018] Preferably, in step S1, the ratio of the mass of the catalyst, the mass of the antioxidant, to the total mass of the modified monomer, adipic acid, and hexamethylenediamine is (0.01~0.05): (0.1~0.3): 100.

[0019] Preferably, in step S1, the neutralization reaction takes 20 to 40 minutes.

[0020] Preferably, in step S2, the polymerization reaction includes the following steps: S2-1. React for 1-3 h at 90~100℃→210~230℃ and atmospheric pressure→1.8~2.2 MPa; S2-2. Maintain a pressure of 1.8~2.2 MPa and react at 210~230℃→270~295℃ for 1~2 h; S2-3. React for 1-3 hours under the conditions of 270~285℃→290~300℃ and 1.8~2.2MPa→normal pressure; S2-4. Maintain a temperature of 290~300℃ and react at normal pressure for 5~15 min, then react under vacuum for another 5~15 min to obtain modified polyamide.

[0021] It should be noted that the "normal pressure" mentioned in this invention refers to ambient atmospheric pressure, and the specific value depends on the geographical environment. For example, the ambient atmospheric pressure is lower in high-altitude areas and higher in low-altitude areas. In this invention, "normal pressure" is defined as ambient atmospheric pressure of 86–106 kPa.

[0022] The third aspect of the present invention provides the application of the modified polyamide described above, or the modified polyamide prepared by the above-described method, in the preparation of nylon 66 fibers.

[0023] The fourth aspect of the present invention provides a gray easily dyeable nylon 66 fiber, wherein the gray easily dyeable nylon 66 fiber is made by composite spinning using the above-mentioned modified polyamide and polyamide as raw materials; wherein the polyamide is obtained by polymerization of adipic acid and hexamethylenediamine.

[0024] This invention introduces cationic groups into the nylon 66 molecular chain through copolymerization modification. The resulting modified polyamide and conventional nylon 66 (polyamide) are then melt-spun together to form side-by-side composite fibers. Due to the dye-resisting effect of the cationic groups, when the side-by-side composite fibers are dyed black, the conventional nylon 66 component is colored while the modified polyamide component remains white, thus producing a gray effect. Compared with conventional gray dyeing methods that are more difficult to process, this invention is simpler to operate, and produces uniform color development with adjustable shades. This invention uses modified monomers with molecular sizes similar to those of nylon 66 monomers, which has no adverse effects on the polymerization process and fiber mechanical properties.

[0025] This invention uses modified polyamide with dye-resistant properties instead of other polymer raw materials suitable for melt spinning but unable to be dyed with acid dyes (such as polypropylene), overcoming the problem of poor compatibility between dissimilar polymers. Even in polyester / nylon composite yarns where both components have polar groups, component delamination easily occurs. However, the modified polyamide of this invention has a chemical composition very similar to conventional nylon 66, exhibiting strong compatibility and preventing the delamination of parallel components that would lead to graying during black-and-white mixing and deterioration of fiber mechanical properties.

[0026] Preferably, the number average molecular weight of the polyamide is 20,000 to 25,000; the mass ratio of the modified polyamide to the polyamide is (1 to 2): (1 to 4).

[0027] Preferably, the gray easily dyeable nylon 66 fiber has a single filament fineness of 2.3~2.7 dtex, a breaking strength ≥3.0 cN / dtex, a breaking elongation of 30%~40%, a crimp shrinkage of 1.5%~5.5%, a network density of 35~45, and a dyeing color difference ΔE<0.20.

[0028] The fifth aspect of this invention provides a method for preparing the above-mentioned gray easily dyeable nylon 66 fiber, comprising the following steps: Modified polyamide and polyamide are melted separately and then composite spun to obtain composite pre-oriented yarn; The pre-oriented yarn is guided, heated and stretched, false twisted, heat-set and wound to obtain gray easily dyeable nylon 66 fiber.

[0029] Preferably, the process parameters for preparing the composite pre-oriented yarn include: a spinning temperature of 295~305℃ for the modified polyamide, a spinning temperature of 290~300℃ for conventional nylon 66, a cooling air temperature of 18~22℃, and a winding speed of 2800~3000m / min.

[0030] Preferably, the process parameters for preparing the gray, easily dyeable nylon 66 fiber include: a first hot roller temperature of 90~95℃, a second hot roller temperature of 185~195℃, a draw ratio of 1.65~1.75, a D / Y ratio of 1.7~1.9, a deformation temperature of 200~215℃, a setting temperature of 170~180℃, a relaxation rate of 3%~5%, and a network pressure of 0.45~0.55MPa.

[0031] This invention copolymerizes modified monomers with adipic acid and hexamethylenediamine, then spins the resulting modified polyamide with conventional nylon 66 to form a side-by-side composite fiber. The ionic groups in the modified polyamide exhibit dye-resistant properties, appearing white when dyed black, while conventional nylon 66 can be dyed black normally. Therefore, the resulting side-by-side composite fiber exhibits a uniform gray visual effect with adjustable color depth, making it simpler than conventional methods. Furthermore, this invention uses modified monomers with molecular sizes similar to those of nylon 66, which does not adversely affect the polymerization process or fiber mechanical properties. It is cost-effective and yields significant results, demonstrating broad application prospects. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the dye-blocking mechanism of the modified polyamide of this invention.

[0033] Figure 2 The images show the dyeing effect of the nylon 66 fibers obtained in Comparative Example 1 (A) and Example 1 (B) of this invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] The dyeing resistance mechanism of the modified polyamide of this invention is as follows: Figure 1 As shown.

[0036] Nylon 66 fiber is typically dyed with acid dyes in an acidic dye bath, where its terminal amine groups combine with protons to form -NH3. +Cationic dyes, on the other hand, contain sulfonic acid groups, which ionize in the dye bath to form -SO3. - Anions, therefore dye molecules can pass through -SO3 - With -NH3 + The electrostatic attraction between the molecules anchors the dye into the interior of nylon 66, thus imparting its color. Taking disodium 2,6-diaminopimelic acid as an example, when disodium 2,6-diaminopimelic acid segments are introduced into the nylon molecular chain, they also ionize in the dye bath to produce -COO. - Anionic. The polymer macromolecules are in a random coil shape, with their ends encased within the molecular coil; therefore, the terminal amine group -NH3 in the modified nylon 66 of this invention... + It will be subject to a large number of -COOs - Surrounded by electrostatic repulsion, the -SO3 group... - The dye molecule with the group will be repelled at -COO - Unable to interact with -NH3 outside the encirclement + This combination achieves a dye-resistant effect, preventing modified nylon 66 from being dyed with acidic dyes and maintaining its natural white color. It is important to note that the amount of disodium 2,6-diaminopimelic acid salt must be within a suitable range (10-15 mol% of hexamethylenediamine): too small a amount will result in an insignificant dye-resistant effect; too large a amount will cause a sharp increase in the melt viscosity of the copolymer (ionomers are prone to forming ionic clusters), leading to spinning difficulties.

[0037] When a parallel composite fiber spun from modified nylon 66 and conventional nylon 66 is dyed with black dye, the conventional nylon in the parallel fiber is dyed black, while the modified nylon 66, unable to be dyed, remains white. Therefore, the overall visual appearance is gray. The minimum resolving distance for high-contrast black and white under daylight conditions is approximately 75-100 μm, while the thickness of a single filament in a fabric fiber is generally 10-20 μm (e.g., the single filament fineness of the nylon 66 fiber obtained in this embodiment of the invention is 2.3-2.7 dtex). This invention combines the black and white components within a range much smaller than the resolving distance of the human eye through composite spinning, thus resulting in a uniform gray fiber without any "whitening" effect. In dyeing practice, when dyeing black, the dye concentration is usually ≥3% owf, and a concentration fluctuation of ±0.2% only results in a color depth change of <5%, which is difficult to detect with the naked eye. However, dyeing gray requires an ultra-low concentration of 0.05~0.5% owf, and a concentration deviation of 0.01% can cause a significant color shift (such as gray turning blue). Therefore, developing a stable and simple dyeing process for gray textiles is challenging.

[0038] In this invention, the shade of gray can be controlled by adjusting the ratio of the black and white components, i.e., conventional nylon 66 and modified polyamide. For example, if the black content percentage is K and the white content percentage is W (K + W = 100%), then the lightness / darkness...L The theoretical calculation formula for * is: L * = 100×(W / 100) 0.43 Therefore, when it is necessary to spin a specific shade of gray, the required composite ratio of conventional nylon 66 and modified polyamide can be roughly calculated according to the above formula. Then, the dye concentration can be finely adjusted during dyeing to achieve a relatively accurate color.

[0039] The reagents and detection methods used for testing the dyeing properties of fibers in this embodiment of the invention are as follows: 1. Dyes CI Acid Black 172 2. Dyeing process The dye concentration is 3% owf, the dye bath pH is 5, the fiber is dyed at 40℃ and kept at the temperature for 10~15min, heated to boiling within 45min at a heating rate of 1.0~2.0℃ / min, and continued to boil for 45min. Then the temperature is gradually reduced to 40℃ and washed with cold water.

[0040] 3. Determination of dyeing percentage Perform the dyeing process as described above, and separately pipette 2 mL of the pre-dye solution and the residual solution after dyeing into 10 mL volumetric flasks. Add acetic acid aqueous solution with pH=5 to the mark, and then measure the λ using a spectrophotometer. max The absorbance A0 and A1 of the dye before and after staining are as follows: Percentage of dye uptake (%) = (l - A1 / A0) × 100% In the formula: A0 represents the absorbance of the pre-dye solution; A1 represents the absorbance of the residual solution.

[0041] 4. Determination of color fastness Test according to GB3920-83, GB251-64, and GB3921-83.

[0042] 5. Measurement of lightness and color difference A colorimeter was used for testing.

[0043] 6. Measurement of apparent color depth (K / S) Using the Kubelka-Munk function K / S = (1―R) 2 The formula is calculated as / 2R, where K is the absorption coefficient of the object being tested, S is the scattering coefficient of the object being tested, and R is the reflectance of the object being tested at infinite thickness. The SF600XDatacolor colorimeter was used for testing; each sample was tested 5 times in different areas, and the mathematical average was taken.

[0044] To better illustrate the present invention, further examples are provided below.

[0045] Example 1 This embodiment provides a gray, easily dyeable nylon 66 fiber, the preparation method of which includes the following steps: (1) At a stirring speed of 10 rpm, 1500 g of deionized water, 3000 g of 2,6-diaminopimelic acid disodium salt, hexamethylenediamine, and adipic acid were added to the polymerization reactor in sequence. The molar ratio of 2,6-diaminopimelic acid disodium salt to hexamethylenediamine was 10:100, and the molar ratio of total amine to acid in the system was 1:1. After adding 200 ppm of sodium hypophosphite catalyst and 0.15 wt% of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide antioxidant, nitrogen was injected to replace the air in the reactor and the stirring speed was increased to 80 rpm. Then the temperature was raised to 100 °C and the reaction was carried out for 30 min to complete the neutralization and salt formation, resulting in a modified nylon 66 salt solution.

[0046] (2) Heating and pressurizing stage: The temperature inside the reactor is raised to 220℃ within 2 hours, and the pressure is raised from 0MPa to 1.9MPa; Heating and pressurizing stage: The pressure inside the reactor is maintained at 1.9MPa by controlling the exhaust valve, and the temperature inside the reactor is gradually raised to 275℃ within 1.5 hours; Heating and depressurizing stage: After the temperature inside the reactor reaches 275℃, the pressure is depressurized to atmospheric pressure within 2 hours. When the pressure is depressurized, the temperature inside the reactor rises to 290℃; After the pressure inside the reactor drops to atmospheric pressure, the reaction is carried out for 10 minutes. Then the pressure inside the reactor is controlled at -0.06MPa and the reaction is carried out for 10 minutes. Then nitrogen is injected to a slightly positive pressure, and the material is discharged from the outlet. After cooling the casting strip in the water tank and cutting it into pellets, modified polyamide with a number average molecular weight of 20,000 is obtained.

[0047] (3) Composite spinning: The modified polyamide and conventional nylon 66 with a number average molecular weight of 20,000 are melted separately and extruded into the composite spinning assembly at a composite ratio of 1:4. After extrusion through the spinneret, the composite POY yarn (pre-oriented yarn) is obtained by cooling, oiling and winding. Then, it is further processed into DTY yarn (i.e., gray and easily dyed nylon 66 fiber) through steps such as yarn guiding, heating and stretching, false twisting, heat setting and winding. The parameters of the POY process are: spinning temperature of modified polyamide 295℃, spinning temperature of conventional nylon 66 290℃, cooling air temperature 20℃, and winding speed 3000m / min; the parameters of the DTY process are: first hot roller 95℃, second hot roller 195℃, stretch ratio 1.65, D / Y ratio 1.7, deformation temperature 215℃, setting temperature 180℃, relaxation rate 5%, and network pressure 0.55MPa.

[0048] Example 2 This embodiment provides a gray, easily dyeable nylon 66 fiber, the preparation method of which includes the following steps: (1) At a stirring speed of 10 rpm, 1500 g of deionized water, 3000 g of 2,6-diaminopimelic acid disodium salt, hexamethylenediamine, and adipic acid were added to the polymerization reactor in sequence. The molar ratio of 2,6-diaminopimelic acid disodium salt to hexamethylenediamine was 11:100, and the molar ratio of total amine to acid in the system was 1:1. After adding 200 ppm of sodium hypophosphite catalyst and 0.15 wt% of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide antioxidant, nitrogen was injected to replace the air in the reactor and the stirring speed was increased to 80 rpm. Then the temperature was raised to 98 ℃ and the reaction was carried out for 30 min to complete the neutralization and salt formation, resulting in a modified nylon 66 salt solution.

[0049] (2) Heating and pressurizing stage: The temperature inside the reactor is raised to 220℃ within 2 hours, and the pressure is raised from 0MPa to 2.0MPa; Heating and pressurizing stage: The pressure inside the reactor is maintained at 2.0MPa by controlling the exhaust valve, and the temperature inside the reactor is gradually raised to 276℃ within 1.5 hours; Heating and depressurizing stage: After the temperature inside the reactor reaches 276℃, the pressure is depressurized to atmospheric pressure within 2 hours. When the pressure is depressurized, the temperature inside the reactor rises to 291℃; After the pressure inside the reactor drops to atmospheric pressure, the reaction is carried out for 10 minutes. Then the pressure inside the reactor is controlled at -0.06MPa and the reaction is carried out for 10 minutes. Then nitrogen is injected to a slightly positive pressure, and the material is discharged from the outlet. After cooling the casting strip in the water tank and cutting it into pellets, modified polyamide with a number average molecular weight of 19000 is obtained.

[0050] (3) Composite spinning: The modified polyamide and conventional nylon 66 with a number average molecular weight of 21,000 are melted separately and extruded into the composite spinning assembly at a composite ratio of 1:3. After extrusion through the spinneret, the composite POY yarn is obtained by cooling, oiling and winding. Then, it is further processed into DTY yarn (i.e., gray and easily dyed nylon 66 fiber) through steps such as yarn guiding, heating and stretching, false twisting, heat setting and winding. The parameters of the POY process are: spinning temperature of modified polyamide 296℃, spinning temperature of conventional nylon 66 291℃, cooling air temperature 20℃, winding speed 2950m / min; the parameters of the DTY process are: first hot roller 92℃, second hot roller 190℃, stretch ratio 1.75, D / Y ratio 1.8, deformation temperature 210℃, setting temperature 175℃, relaxation rate 4.5%, network pressure 0.50MPa.

[0051] Example 3 This embodiment provides a gray, easily dyeable nylon 66 fiber, the preparation method of which includes the following steps: (1) At a stirring speed of 10 rpm, 1500 g of deionized water, 3000 g of 2,6-diaminopimelic acid disodium salt, hexamethylenediamine, and adipic acid were added to the polymerization reactor in sequence. The molar ratio of 2,6-diaminopimelic acid disodium salt to hexamethylenediamine was 12:100, and the molar ratio of total amine to acid in the system was 1:1. After adding 200 ppm of sodium hypophosphite catalyst and 0.15 wt% of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide antioxidant, nitrogen was injected to replace the air in the reactor and the stirring speed was increased to 80 rpm. Then the temperature was raised to 96 ℃ and the reaction was carried out for 30 min to complete the neutralization and salt formation, resulting in a modified nylon 66 salt solution.

[0052] (2) Heating and pressurizing stage: The temperature inside the reactor is raised to 220℃ within 2 hours, and the pressure is raised from 0MPa to 2.1MPa; Heating and pressurizing stage: The pressure inside the reactor is maintained at 2.1MPa by controlling the exhaust valve, and the temperature inside the reactor is gradually raised to 276℃ within 1.5 hours; Heating and depressurizing stage: After the temperature inside the reactor reaches 277℃, the pressure is depressurized to atmospheric pressure within 2 hours. When the pressure is depressurized, the temperature inside the reactor rises to 292℃; After the pressure inside the reactor drops to atmospheric pressure, the reaction is carried out for 10 minutes. Then the pressure inside the reactor is controlled at -0.06MPa and the reaction is carried out for 10 minutes. Then nitrogen is injected to a slightly positive pressure, and the material is discharged from the outlet. After cooling the casting strip in the water tank and cutting it into pellets, modified polyamide with a number average molecular weight of 18000 is obtained.

[0053] (3) Composite spinning: The modified polyamide and conventional nylon 66 with a number average molecular weight of 22,000 are melted separately and extruded into the composite spinning assembly at a composite ratio of 1:2. After extrusion through the spinneret, the composite POY yarn is obtained by cooling, oiling and winding. Then, it is further processed into DTY yarn (i.e., gray and easily dyed nylon 66 fiber) through steps such as yarn guiding, heating and stretching, false twisting, heat setting and winding. The parameters of the POY process are: spinning temperature of modified polyamide 297℃, spinning temperature of conventional nylon 66 292℃, cooling air temperature 20℃, winding speed 2900m / min; the parameters of the DTY process are: first hot roller 91℃, second hot roller 188℃, stretch ratio 1.65, D / Y ratio 1.8, deformation temperature 205℃, setting temperature 173℃, relaxation rate 4%, network pressure 0.50MPa.

[0054] Example 4 This embodiment provides a gray, easily dyeable nylon 66 fiber, the preparation method of which includes the following steps: (1) At a stirring speed of 10 rpm, 1500 g of deionized water, 3000 g of 2,6-diaminopimelic acid disodium salt, hexamethylenediamine, and adipic acid were added to the polymerization reactor in sequence. The molar ratio of 2,6-diaminopimelic acid disodium salt to hexamethylenediamine was 13:100, and the molar ratio of total amine to acid in the system was 1:1. After adding 200 ppm of sodium hypophosphite catalyst and 0.15 wt% of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide antioxidant, nitrogen was injected to replace the air in the reactor and the stirring speed was increased to 80 rpm. Then the temperature was raised to 92℃ and the reaction was carried out for 30 min to complete the neutralization and salt formation, resulting in a modified nylon 66 salt solution.

[0055] (2) Heating and pressurizing stage: The temperature inside the reactor is raised to 220℃ within 2 hours, and the pressure is raised from 0MPa to 2.0MPa; Heating and pressurizing stage: The pressure inside the reactor is maintained at 2.0MPa by controlling the exhaust valve, and the temperature inside the reactor is gradually raised to 278℃ within 1.5 hours; Heating and depressurizing stage: After the temperature inside the reactor reaches 278℃, the pressure is depressurized to atmospheric pressure within 2 hours. When the pressure is depressurized, the temperature inside the reactor rises to 295℃; After the pressure inside the reactor drops to atmospheric pressure, the reaction is carried out for 10 minutes. Then the pressure inside the reactor is controlled at -0.06MPa and the reaction is carried out for 10 minutes. Then nitrogen is injected to a slightly positive pressure, and the material is discharged from the outlet. After cooling the casting strip in the water tank and cutting it into pellets, modified polyamide with a number average molecular weight of 16500 is obtained.

[0056] (3) Composite spinning: The modified polyamide and conventional nylon 66 with a number average molecular weight of 24,000 are melted separately and extruded into the composite spinning assembly at a 1:1 composite ratio. After extrusion through the spinneret, the composite POY yarn is obtained by cooling, oiling, and winding. Then, it is further processed into DTY yarn (i.e., gray, easily dyed nylon 66 fiber) through steps such as yarn guiding, heating and stretching, false twisting, heat setting, and winding. The parameters of the POY process are: spinning temperature of modified polyamide 300℃, spinning temperature of conventional nylon 66 295℃, cooling air temperature 20℃, and winding speed 2850m / min; the parameters of the DTY process are: first hot roller 90℃, second hot roller 185℃, stretch ratio 1.7, D / Y ratio 1.7, deformation temperature 200℃, setting temperature 170℃, relaxation rate 3%, and network pressure 0.45MPa.

[0057] Example 5 This embodiment provides a gray, easily dyeable nylon 66 fiber, the preparation method of which includes the following steps: (1) At a stirring speed of 10 rpm, 1500 g of deionized water, 3000 g of 2,6-diaminopimelic acid disodium salt, hexamethylenediamine, and adipic acid were added to the polymerization reactor in sequence. The molar ratio of 2,6-diaminopimelic acid disodium salt to hexamethylenediamine was 15:100, and the molar ratio of total amine to acid in the system was 1:1. After adding 200 ppm of sodium hypophosphite catalyst and 0.15 wt% of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide antioxidant, nitrogen was injected to replace the air in the reactor and the stirring speed was increased to 80 rpm. Then the temperature was raised to 90 °C and the reaction was carried out for 30 min to complete the neutralization and salt formation, resulting in a modified nylon 66 salt solution.

[0058] (2) Heating and pressurizing stage: The temperature inside the reactor is raised to 220℃ within 2 hours, and the pressure is raised from 0MPa to 2.0MPa; Heating and pressurizing stage: The pressure inside the reactor is maintained at 2.0MPa by controlling the exhaust valve, and the temperature inside the reactor is gradually raised to 280℃ within 1.5 hours; Heating and depressurizing stage: After the temperature inside the reactor reaches 280℃, the pressure is depressurized to atmospheric pressure within 2 hours. When the pressure is depressurized, the temperature inside the reactor rises to 295℃; After the pressure inside the reactor drops to atmospheric pressure, the reaction is carried out for 10 minutes. Then the pressure inside the reactor is controlled at -0.06MPa and the reaction is carried out for 10 minutes. Then nitrogen is injected to a slightly positive pressure, and the material is discharged from the outlet. After cooling the casting strip in the water tank and cutting it into pellets, modified polyamide with a number average molecular weight of 15000 is obtained.

[0059] (3) Composite spinning: The modified polyamide and conventional nylon 66 with a number average molecular weight of 25,000 are melted separately and extruded into the composite spinning assembly at a composite ratio of 2:1. After extrusion through the spinneret, the composite POY yarn is obtained by cooling, oiling and winding. Then, it is further processed into DTY yarn (i.e., gray and easily dyed nylon 66 fiber) through steps such as yarn guiding, heating and stretching, false twisting, heat setting and winding. The parameters of the POY process are: spinning temperature of modified polyamide 305℃, spinning temperature of conventional nylon 66 300℃, cooling air temperature 20℃, and winding speed 2800m / min; the parameters of the DTY process are: first hot roller 90℃, second hot roller 185℃, stretch ratio 1.7, D / Y ratio 1.7, deformation temperature 200℃, setting temperature 170℃, relaxation rate 3%, and network pressure 0.45MPa.

[0060] Comparative Example 1 This comparative example provides a method for preparing nylon 66 fiber, the steps and parameters of which are similar to those of Example 1, except that the composite spinning process in step (3) is replaced by a twisted spinning process. The remaining steps and parameters are the same as those of Example 1 and will not be repeated here.

[0061] Comparative Example 2 This comparative example provides a method for preparing nylon 66 fiber, the steps and parameters of which are similar to those of Example 1, except that the amount of 2,6-diaminopimelic acid disodium salt in step (1) is replaced with 8 mol% of hexamethylenediamine. The remaining steps and parameters are the same as those of Example 1 and will not be repeated here.

[0062] Comparative Example 3 This comparative example provides a method for preparing nylon 66 fiber, with steps and parameters similar to those in Example 1, except that the amount of 2,6-diaminopimelic acid disodium salt in step (1) is replaced with 17 mol% of hexamethylenediamine. The remaining steps and parameters are the same as in Example 1. At the end of the polymerization process, in the vacuum reaction stage with a pressure of -0.06 MPa inside the reactor, the stirring power increases sharply within 5 minutes, and the polymer melt viscosity becomes extremely high, making normal discharge impossible. This demonstrates that excessive addition of ionic monomers can cause the formation of ionomers within the copolymer, resulting in excessively high melt viscosity and loss of spinnability.

[0063] Comparative Example 4 This comparative example provides a method for preparing nylon 66 fiber, the steps and parameters of which are similar to those in Example 2, except that the dye concentration during dyeing is replaced with 2.5% owf instead of 3% owf. The remaining steps and parameters are the same as in Example 2 and will not be repeated here.

[0064] Comparative Example 5 This comparative example provides a method for preparing nylon 66 fiber, the steps and parameters of which are similar to those of Example 1, except that in step (1), 2,6-diaminopimelic acid disodium salt is not added. The remaining steps and parameters are the same as those of Example 1 and will not be repeated here.

[0065] Detection Example 1 The nylon 66 fibers obtained in Examples 1-5 and Comparative Example 5 were tested according to GB / T 14343-2008 "Test Method for Linear Density of Chemical Fiber Filaments", GB / T 14344-2022 "Test Method for Tensile Properties of Chemical Fiber Filaments", GB / T 6506-2017 "Test Method for Curl Properties of Synthetic Fiber Textured Yarns" and FZ / T 50001-91 "Test Method for Network Degree of Synthetic Fiber Network Yarns". The results are shown in Table 1.

[0066] Table 1 Performance Tests of Nylon 66 Fiber

[0067] As shown in Table 1, the mechanical properties of the nylon 66 fibers obtained by the methods described in Examples 1-5 are similar to those of the nylon 66 fibers obtained in Comparative Example 5, proving that the addition of 2,6-diaminopimelic acid disodium salt has little effect on the mechanical properties of the modified nylon 66.

[0068] Detection Example 2 The dyeing properties of the nylon 66 fibers obtained in Examples 1-5 and Comparative Examples 1-4 were tested respectively, and the results are shown in Table 2.

[0069] Table 2 Dyeing performance test of Nylon 66 fiber

[0070] As shown in Table 1, the nylon 66 fibers obtained according to the methods described in Examples 1-5 exhibit uniform color development, strong dyeing, and adjustable color depth. Comparing the dyeing effects of the nylon 66 fibers obtained in Example 1 and Comparative Example 1, it can be seen from... Figure 2 It is evident that although the mixed fiber obtained by the twisting spinning process in Comparative Example 1 is gray overall, it has obvious white spots, giving it a mottled gray color; while the parallel composite fiber obtained by the composite spinning process of this invention presents a uniform dark gray color, proving that this invention can obtain uniform gray fiber by spinning the black and white components together to a very small distance.

[0071] Comparing the dyeing effects of the nylon 66 fibers obtained in Example 1 and Comparative Example 2, the lightness of Comparative Example 2 was 19.5, which was darker than the required dyeing grayness. This indicates that when the amount of modified monomer added is too small, the dyeing resistance effect of the introduced ionic groups becomes poor, which will cause the predetermined white component to be dyed, affecting the color matching effect.

[0072] The nylon 66 fiber obtained in Comparative Example 4 had a dyeing lightness of 23.5, appearing as a dark gray, but slightly lighter than that of Example 2, with a color difference of 0.131. This indicates that in addition to adjusting the fiber composite ratio, the depth of the dyed gray can also be controlled by changing the dye concentration. The present invention can produce a relatively wide gray spectrum.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A modified polyamide, characterized in that, The modified polyamide is polymerized from modified monomers, adipic acid and hexamethylenediamine; the molar ratio of the modified monomer to hexamethylenediamine is (10~15):100; the modified monomer is a diamine monomer containing carboxylate ion groups.

2. The modified polyamide according to claim 1, characterized in that, The number average molecular weight of the modified polyamide is 15,000 to 20,000.

3. The modified polyamide according to claim 1, characterized in that, The modified monomer is 2,6-diaminopimelic acid disodium salt.

4. The method for preparing the modified polyamide according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Mix the modified monomer, adipic acid, hexamethylenediamine and water evenly, add catalyst and antioxidant, and carry out a neutralization reaction under inert gas and 90~100℃ to obtain modified nylon 66 salt solution; S2. The modified nylon 66 salt solution is subjected to a polymerization reaction to obtain modified polyamide.

5. The method for preparing the modified polyamide according to claim 4, characterized in that, In step S1, the catalyst is at least one of sodium hypophosphite, magnesium hypophosphite, calcium hypophosphite, or zinc hypophosphite; the antioxidant is at least one of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide, pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), or N,N'-1,6-hexylene-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide]. In step S1, the ratio of the mass of the catalyst, the mass of the antioxidant, to the total mass of the modified monomer, adipic acid, and hexamethylenediamine is (0.01~0.05): (0.1~0.3): 100; In step S1, the neutralization reaction takes 20 to 40 minutes.

6. The method for preparing the modified polyamide according to claim 4, characterized in that, In step S2, the polymerization reaction includes the following steps: S2-1. React for 1-3 h at 90~100℃→210~230℃ and atmospheric pressure→1.8~2.2 MPa; S2-2. Maintain a pressure of 1.8~2.2 MPa and react at 210~230℃→270~295℃ for 1~2 h; S2-3. React for 1-3 hours under the conditions of 270~285℃→290~300℃ and 1.8~2.2MPa→normal pressure; S2-4. Maintain a temperature of 290~300℃ and react at normal pressure for 5~15 min, then react under vacuum for another 5~15 min to obtain modified polyamide.

7. The use of the modified polyamide according to any one of claims 1 to 3 or the modified polyamide prepared by the method according to any one of claims 4 to 6 in the preparation of nylon 66 fiber.

8. A gray, easily dyeable nylon 66 fiber, characterized in that, The gray, easily dyeable nylon 66 fiber is made by composite spinning using the modified polyamide and polyamide as raw materials according to any one of claims 1 to 3; the polyamide is obtained by polymerization of adipic acid and hexamethylenediamine.

9. The gray, easily dyeable nylon 66 fiber according to claim 8, characterized in that, The number average molecular weight of the polyamide is 20,000 to 25,000; the mass ratio of the modified polyamide to the polyamide is (1 to 2): (1 to 4).

10. The method for preparing gray, easily dyeable nylon 66 fiber according to claim 8 or 9, characterized in that, Includes the following steps: Modified polyamide and polyamide are melted separately and then composite spun to obtain composite pre-oriented yarn; The pre-oriented yarn is guided, heated and stretched, false twisted, heat-set and wound to obtain gray easily dyeable nylon 66 fiber.

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