Polyurethane elastic fiber and preparation method thereof

Abstract

The present invention provides a polyurethane elastic fiber and a preparation method thereof, wherein the polyurethane elastic fiber is obtained by reacting a diol mixture consisting of polyester diol and polytetramethylene ether glycol with diisocyanate to obtain a prepolymer, the prepolymer reacts with mixed amine to obtain a polyurethane-polyurea solution, and the polyurethane-polyurea solution is used as a raw material for dry spinning to obtain the fiber, wherein the polyester diol is obtained by polycondensation of an aromatic diol and an aliphatic dibasic acid, or by polycondensation of an aliphatic diol and an aromatic dibasic acid, or by polycondensation of an aromatic diol and an aromatic dibasic acid. Part of the aromatic diol is introduced into the soft segment of the polyurethane elastic fiber of the present invention to replace the polyether diol, so that the product has the characteristics of excellent mechanical strength, heat resistance, etc., and excellent spinnability.

Description

Technical Field

[0001] The invention belongs to a method for preparing dry-process polyurethane elastic fiber, and particularly relates to a polyurethane elastic fiber and a preparation method thereof. Background Art

[0002] Polyurethane elastic fiber uses polytetramethylene ether glycol as the soft segment. Due to its good regularity, the microscopic phase separation degree of soft and hard segments is high, which can give polyurethane elastic fiber. Polyester diol, like polytetramethylene ether glycol, belongs to the polyurethane soft segment, which has the characteristics of low price, wide variety, and easy control of molecular weight. Due to its poor regularity, the microscopic phase separation degree of soft and hard segments is weakened, resulting in increased tensile strength and breaking strength, and decreased resilience. Such characteristics are conducive to the dyeing and finishing of polyurethane elastic fibers at high temperatures.

[0003] CN201811172376.5 uses alicyclic polyester diols to improve the placement stability of polyurethane elastic fibers, effectively solving the impact of environmental temperature and humidity changes on product performance. CN201210448865.5 uses a small amount of aliphatic polyester diols to reduce the shaping temperature of polyurethane elastic fibers, thereby ensuring that the organizational structure of other fibers is not destroyed when shaping with other fibers with poor heat resistance. CN201510170468.X uses aromatic polyester diols to enhance the crystallinity of polyurethane elastic fibers, thereby improving the strength and toughness of the product. It can be seen that the introduction of polyester diols can improve the quality of polyurethane elastic fibers to a certain extent and give the fibers differentiated characteristics. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing polyurethane elastic fibers. The preparation method of the present invention uses polyester diol to replace polyether diol in a high proportion, which can not only greatly reduce the production cost, but also help to achieve fiber dyeing and finishing at high temperature, and can overcome the adverse effects of polyester diol on the spinnability, unwinding performance and hydrolysis resistance of polyurethane elastic fibers, so that it can meet the needs of production, weaving, dyeing and finishing.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] On the one hand, the present invention provides a polyurethane elastic fiber, which is obtained by reacting a diol mixture consisting of polyester diol and polytetramethylene ether glycol with diisocyanate to obtain a prepolymer, and reacting the prepolymer with mixed amine to obtain a polyurethane-polyurea solution, and dry spinning the polyurethane-polyurea solution as a raw material, wherein the polyester diol is obtained by condensation polymerization of an aromatic diol and an aliphatic dibasic acid, or by condensation polymerization of an aliphatic diol and an aromatic dibasic acid, or by condensation polymerization of an aromatic diol and an aromatic dibasic acid.

[0007] In the present invention, the hydrolysis resistance of the polyurethane elastic fiber prepared by the reaction of polytetramethylene ether glycol, polyester diol and diisocyanate does not decrease significantly, and the fiber still has excellent mechanical properties after subsequent alkali washing. At the same time, the aromatic polyester diol can improve the heat resistance of spandex and reduce the degradation of ordinary spandex fibers when treated for a long time under high temperature conditions.

[0008] The polyester diol of the invention has a rigid benzene ring structure, which improves the rigidity of polyurethane elastic fiber molecules and gives the fibers excellent temperature resistance and mechanical properties.

[0009] Preferably, the number average molecular weight of the polytetramethylene ether glycol is 1500-2500, for example, 1500, 1800, 2000, 2500, etc.

[0010] Preferably, the aromatic diol is one or a combination of at least two of p-phenylenediol, m-phenylenediol, o-phenylenediol or p-phenylenediol, preferably p-phenylenediol;

[0011] Preferably, the aromatic dibasic acid is one or a combination of at least two of terephthalic acid, isophthalic acid, phthalic acid or terephthalic acid, preferably terephthalic acid.

[0012] Preferably, the diisocyanate is 4,4'-diphenylmethane diisocyanate.

[0013] Preferably, the number average molecular weight of the polyester diol is 1000-3000, for example, 1000, 1200, 1500, 1800, 2000, 2500 or 3000.

[0014] Preferably, the mixed amine comprises a diamine as a chain extender and a monoamine as a chain terminator, wherein the diamine as a chain extender is one or a combination of at least two of ethylenediamine, 1,2-propylenediamine, and 2-methyl-1,5-pentanediamine; and the monoamine as a chain terminator is one or a combination of at least two of dimethylamine, diethylamine, dipropylamine, ethanolamine, or diethanolamine.

[0015] In another aspect, the present invention provides a method for preparing the polyurethane elastic fiber as described above, the method comprising the following steps:

[0016] Step 1. Adding a solvent, polytetramethylene ether glycol, and polyester diol sequentially into a reactor and stirring and mixing them to form a diol mixture;

[0017] Step 2. Prepolymerizing 4,4'-diphenylmethane diisocyanate with a diol mixture to obtain an isocyanate-terminated prepolymer;

[0018] Step 3. reacting the mixed amine with the isocyanate-terminated prepolymer to obtain a polyurethane-polyurea solution;

[0019] Step 4. Fully stirring, dispersing and ripening the polyurethane-polyurea solution to obtain a spinning solution;

[0020] Step 5. Using a dry spinning system to perform spinning and stretching on the spinning solution to obtain the polyurethane elastic fiber;

[0021] The polyester diol is obtained by polycondensation of an aromatic diol and an aliphatic dibasic acid, or by polycondensation of an aliphatic diol and an aromatic dibasic acid, or by polycondensation of an aromatic diol and an aromatic dibasic acid.

[0022] Preferably, the molar ratio of the polytetramethylene ether glycol to the polyester diol is above 2:8.

[0023] Preferably, the molar ratio of the polytetramethylene ether glycol to the polyester diol is 2:8 to 8:2, for example, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, etc., preferably 4:6 to 6:4.

[0024] In polyester diols, the presence of side methyl groups can inhibit hydrolysis, but it will also further reduce the regularity of polyester diols, resulting in a weakened microphase separation of soft and hard segments, causing a significant decrease in modulus. In order to ensure the regularity of polyester diols, linear diols such as 1,3-propylene glycol, 1,4-butanediol, or 1,6-hexanediol are required to prepare polyester diols. Regulating the ratio of branched diols to linear diols in polyester diols, such as a molar ratio of branched diols to linear diols above 0.2:0.8, is the key to preparing polyurethane elastic fibers with excellent hydrolysis resistance and suitable modulus.

[0025] Preferably, the molar ratio of the 4,4'-diphenylmethane diisocyanate to the diol mixture is 1.3:1 to 2.6:1, for example, 1.3:1, 1.4:1, 1.45:1, 1.5:1, 1.8:1, 2.0:1, 2.2:1, 2.4:1 or 2.6:1.

[0026] Preferably, the temperature of the prepolymerization reaction in step 2 is 40-50°C, for example 40°C, 43°C, 45°C, 48°C or 50°C.

[0027] Preferably, the isocyanate content of the isocyanate terminated prepolymer is 1.5wt% to 5.0wt% of the isocyanate terminated prepolymer, for example 1.5wt%, 1.8wt%, 2.0wt%, 2.3wt%, 2.5wt%, 3.0wt%, 3.3wt%, 3.5wt%, 4.0wt% or 5.0wt%.

[0028] Preferably, before the reaction in step 3, the isocyanate-terminated prepolymer is dissolved in N,N-dimethylacetamide to obtain an isocyanate-terminated prepolymer solution;

[0029] Preferably, the concentration of the isocyanate-terminated prepolymer solution is 35wt% to 75wt%, for example, 35wt%, 38wt%, 40wt%, 45wt%, 48wt%, 50wt%, 55wt%, 58wt%, 60wt%, 65wt%, 68wt% or 70wt%, etc.

[0030] In the present invention, the mixed amine includes a diamine as a chain extender and a monoamine as a chain terminator, wherein the diamine as a chain extender is one or a combination of at least two of ethylenediamine, 1,2-propylenediamine, and 2-methyl-1,5-pentanediamine; and the monoamine as a chain terminator is one or a combination of at least two of dimethylamine, diethylamine, dipropylamine, ethanolamine, or diethanolamine.

[0031] Preferably, the molar ratio of the amine groups of the diamine to the monoamine is 5:1 to 30:1, for example 5:1, 7:1, 8:1, 9:1, 10:1, 13:1, 15:1, 18:1, 20:1, 25:1 or 30:1.

[0032] Preferably, before the reaction in step 3, the mixed amine is dissolved in N,N-dimethylacetamide to obtain a mixed amine solution;

[0033] Preferably, the mass percentage of the mixed amines in the mixed amine solution is 4wt% to 8wt%, for example, 4wt%, 4.3wt%, 4.5wt%, 4.8wt%, 5wt%, 5.5wt%, 5.8wt%, 6wt%, 7wt% or 8wt%.

[0034] Preferably, the molar ratio of amine groups in the mixed amine solution to isocyanate groups in the isocyanate-terminated prepolymer is 1.00:1 to 1.15:1, for example, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.08:1, 1.1:1, 1.12:1, 1.14:1 or 1.15:1, etc.

[0035] In the present invention, preferably, in step 4, an alkali-resistant additive and / or an anti-adhesion agent and optionally other additives are added to the polyurethane-polyurea solution before stirring.

[0036] Preferably, the alkali-resistant additive is nano silicon dioxide and / or nano titanium dioxide.

[0037] Preferably, the added amount of the alkali-resistant additive is 0.5wt% to 2wt% of the polyurethane elastic fiber, for example, 0.5wt%, 0.8wt%, 1wt%, 1.3wt%, 1.5wt%, 1.8wt% or 2wt%.

[0038] Preferably, the anti-adhesion agent is polyethylene glycol with a molecular weight of 2000 and / or polyvinyl alcohol with a molecular weight of 2000.

[0039] Organic anti-adhesive agents such as polyethylene glycol with a molecular weight of 2000 and polyvinyl alcohol with a molecular weight of 2000 are used to ensure good molding while giving the polyurethane elastic fiber a lasting unwinding performance. Compared with inorganic lubricants, organic anti-adhesive agents have good compatibility with polyurethane elastic fibers and are not easy to enrich on the surface of polyurethane elastic fibers. Reasonable compounding can ensure that the monofilament is not affected by excessive slippage and the organic anti-adhesive agent will slowly enrich on the surface, thereby solving the problem of decreased unwinding performance caused by the volatilization of the oil.

[0040] Preferably, the anti-adhesion agent is added in an amount of 0.1 wt% to 0.2 wt% of the polyurethane elastic fiber.

[0041] Preferably, the other auxiliary agents include any one of antioxidants, ultraviolet absorbers, lubricants, matting agents or dyeing auxiliary agents, or a combination of at least two thereof.

[0042] Preferably, the addition amount of the other auxiliary agents is 0.1wt%-2.5wt% of the polyurethane elastic fiber.

[0043] Preferably, the spin-stretching in step 5 is dried, oiled, and wound to obtain the polyurethane elastic fiber.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The polyurethane elastic fiber soft segment of the present invention introduces part of aromatic diols to replace polyether diols. Although the regularity of the molecular chain is reduced to a certain extent and the microphase separation is reduced, the proportion of the hard segment is increased due to the presence of benzene ring rigid groups in the molecule, the crystallinity of the polyurethane elastic fiber is enhanced, and the product has excellent mechanical strength, heat resistance and other characteristics, and excellent spinnability. DETAILED DESCRIPTION

[0046] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0047] Example 1

[0048] Provided is a polyurethane elastic fiber, and the preparation method thereof is as follows:

[0049] 1. Add 60.00kg DMAc, 50.00kg polyester diol (obtained by polycondensation of terephthalic acid and terephthalic alcohol, molecular weight 1800), and 50.00kg polytetramethylene ether glycol PTG (molecular weight 1800) (the molar ratio of polytetramethylene ether glycol to polyester diol is 1:1) into the prepolymerization tank in sequence, and stir and mix well;

[0050] 2. When the temperature reaches about 25°C, add 23.46kg 4,4-MDI (4,4'-diphenylmethane diisocyanate), raise the temperature to 45°C, and react for 120 minutes to obtain the prepolymer product PPS;

[0051] 3. Transfer the prepolymer product to the chain extension tank, add 128.6 kg DMAc to the prepolymer tank, add the cleaning solvent, and transfer to the chain extension tank;

[0052] 4. Cool to 10°C, slowly add a mixed chain extension amine DMAC solution containing 2.192 kg EDA and 0.255 kg diethylamine, and stir rapidly to allow chain extension and chain termination to occur simultaneously to prepare a 35% polyurethane-polyurea solution;

[0053] 5. Add 1.263 kg of nano-silicon dioxide, 0.126 kg of polyethylene glycol with a molecular weight of 2000, and antioxidant, ultraviolet absorber, lubricant, matting agent, and dyeing auxiliary agent to the above polyurethane-polyurea solution, stir, disperse, and ripen to obtain a spinning solution;

[0054] 6. The spinning solution is fed into the dry spinning system through a metering pump, and the spinning solution is stretched by a spinneret, wherein the specification is 40D, the spinneret is 3 holes and 36 heads, the upper chamber temperature is 260°C, the lower chamber temperature is 200°C, and the spinning speed is 900 m / min;

[0055] 7. Apply oil at an oiling rate of 5 wt %, and wind to obtain a polyurethane elastic fiber.

[0056] Example 2

[0057] The only difference from Example 1 is that the molar ratio of polytetramethylene ether glycol to polyester diol is 6:4.

[0058] Example 3

[0059] The only difference from Example 1 is that the molar ratio of polytetramethylene ether glycol to polyester diol is 4:6.

[0060] Example 4

[0061] 1. Add 74.00kg DMAc, 83.33kg polyester diol (obtained by polycondensation of terephthalic acid and terephthalic alcohol, molecular weight 3000), and 50.00kg polytetramethylene ether glycol (molecular weight 1800) into the prepolymerization tank in sequence, and stir and mix thoroughly;

[0062] 2. When the temperature reaches about 25°C, add 23.46kg 4,4-MDI, raise the temperature to 45°C, and react for 120 minutes to obtain the prepolymerized product PPS;

[0063] 3. Transfer the prepolymer product to the chain extension tank, add 176 kg DMAc to the prepolymer tank, add cleaning solvent, and transfer to the chain extension tank;

[0064] 4. Cool to 10°C, slowly add a mixed chain extension amine DMAC solution containing 2.16 kg EDA and 0.34 kg diethylamine, and stir rapidly to allow chain extension and chain termination to occur simultaneously to prepare a 35% polyurethane-polyurea solution;

[0065] 5. Add 1.6 kg of nano-silicon dioxide and 0.16 kg of polyethylene glycol with a molecular weight of 2000 to the above polyurethane-polyurea solution, and add antioxidant, ultraviolet absorber, lubricant, matting agent, dyeing auxiliary agent, and fully stir, disperse and ripen to obtain spinning solution;

[0066] 6. The spinning solution is fed into the dry spinning system through a metering pump, and the spinning solution is stretched by a spinneret, wherein the specification is 40D, the spinneret is 3 holes and 36 heads, the upper chamber temperature is 260°C, the lower chamber temperature is 200°C, and the spinning speed is 900 m / min;

[0067] 7. Apply oil at an oiling rate of 5 wt %, and wind to obtain a polyurethane elastic fiber.

[0068] Example 5

[0069] The only difference from Example 1 is that the polyester diol is obtained by condensation polymerization of terephthalic acid and terephthalic acid, and has a molecular weight of 1800.

[0070] Example 6

[0071] The only difference from Example 1 is that the polyester diol is obtained by polycondensation of isophthalic acid and isophthalic acid, and has a molecular weight of 1800.

[0072] Example 7

[0073] The only difference from Example 1 is that the polyester diol is obtained by polycondensation of o-phthalic alcohol and o-phthalic acid, and has a molecular weight of 1800.

[0074] Example 8

[0075] The only difference from Example 1 is that the polyester diol is obtained by polycondensation of 3-methyl-1,3-butanediol and terephthalic acid, and has a molecular weight of 1800.

[0076] Example 9

[0077] The only difference from Example 1 is that the polyester diol is obtained by polycondensation of 1,4-butanediol and terephthalic acid, and has a molecular weight of 1800.

[0078] Example 10

[0079] The only difference from Example 1 is that the polyester diol is obtained by condensation polymerization of terephthalic acid and adipic acid, and has a molecular weight of 1800.

[0080] Blank example

[0081] In this blank example, the only difference from Example 1 is that polyester diol is not used in step 1, and only polytetramethylene ether glycol PTG (molecular weight 1800) is added to the prepolymerization tank and stirred thoroughly; the subsequent steps are the same as in Example 1.

[0082] Comparative Example 1

[0083] The only difference from Example 1 is that the molar ratio of polytetramethylene ether glycol to polyester diol is 1:9.

[0084] Comparative Example 2

[0085] The only difference from Example 1 is that the molar ratio of polytetramethylene ether glycol to polyester diol is 9:1.

[0086] The polyurethane elastic fibers obtained in the examples and comparative examples were subjected to performance tests, and the performance test methods were as follows:

[0087] Spinnability: It is judged according to the fault conditions that occur during the spinning process. The smaller the probability of broken yarns, twisted yarns, etc., the better the spinnability, otherwise the spinnability is poor;

[0088] Breaking strength (DS), breaking elongation (DE), 300% elongation stress (SS300): tested with reference to FZ / T50006-2013 standard;

[0089] Temperature resistance: The fiber is pulled to 2.3 times of its original length and then fixed. After being pre-set at 185°C for 1 minute, it is put into a dye solution containing disperse dyes, dispersants and leveling agents, immersed at 130°C for 40 minutes, and then pre-set at 190°C for 1 minute. The ratio of the DS of the fiber after the test to the DS before the test is the temperature resistance.

[0090] Chlorine resistance: Tested in accordance with FZ / T 50034-2016 standard.

[0091] Table 1

[0092] Spinnability SS300 cN dN DE / % Temperature resistance Blank example excellent 11.5 38 560 50％ Example 1 excellent 13.5 48 520 73％ Example 2 excellent 13.1 45 530 64％ Example 3 excellent 13.9 50 515 85％ Example 4 excellent 14.2 52 510 87％ Example 5 excellent 12.7 42 540 68％ Example 6 excellent 12.5 40 550 65％ Example 7 good 11.9 39 555 61％ Example 8 good 10.5 32 575 52％ Example 9 good 10.8 34 570 53％ Example 10 good 11 36 565 54％ Comparative Example 1 Difference 14.5 55 500 80％ Comparative Example 2 excellent 11.8 40 550 53％

[0093] It can be seen from the data in the table that the polyurethane elastic fiber prepared by using the polyester diol with a rigid structure in the present invention has excellent spinnability, excellent mechanical strength, and good heat resistance. Its 300% elongation stress can reach more than 10 cN, its breaking strength can reach more than 32 cN, its breaking elongation can reach more than 510%, and its temperature resistance can be as high as more than 52%.

[0094] The applicant declares that the present invention illustrates the preparation method of the polyurethane elastic fiber of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A polyurethane elastic fiber, characterized in that: The polyurethane elastic fiber is obtained by reacting a diol mixture consisting of polyester diol and polytetramethylene ether glycol with diisocyanate to obtain a prepolymer, reacting the prepolymer with a mixed amine to obtain a polyurethane-polyurea solution, and dry spinning the polyurethane-polyurea solution as a raw material, wherein the polyester diol is obtained by polycondensation of an aromatic diol and an aliphatic dibasic acid, or by polycondensation of an aliphatic diol and an aromatic dibasic acid, or by polycondensation of an aromatic diol and an aromatic dibasic acid; The molar ratio of the polytetramethylene ether glycol to the polyester diol is 4:6 to 6:4; The aromatic diol is one or a combination of at least two of p-phenylenediol, m-phenylenediol, o-phenylenediol or p-phenylenediol; The aromatic dibasic acid is one or a combination of at least two of terephthalic acid, isophthalic acid, phthalic acid or terephthalic acid; The diisocyanate is 4,4'-diphenylmethane diisocyanate.

2. The polyurethane elastic fiber according to claim 1, characterized in that: The number average molecular weight of the polytetramethylene ether glycol is 1500-2500.

3. The polyurethane elastic fiber according to claim 1, characterized in that: The aromatic diol is terephthalic acid.

4. The polyurethane elastic fiber according to claim 1, characterized in that: The aromatic dibasic acid is terephthalic acid.

5. The polyurethane elastic fiber according to claim 1, characterized in that: The number average molecular weight of the polyester diol is 1000-3000.

6. The polyurethane elastic fiber according to claim 1, characterized in that: The mixed amine includes a diamine as a chain extender and a monoamine as a chain terminator, wherein the diamine as the chain extender is one of ethylenediamine, 1,2-propylenediamine, and 2-methyl-1,5-pentanediamine, or a combination of at least two thereof; and the monoamine as the chain terminator is one of dimethylamine, diethylamine, dipropylamine, ethanolamine, or a combination of at least two thereof.

7. The method for preparing polyurethane elastic fiber according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: Step 1. Add a solvent, polytetramethylene ether glycol, and polyester diol into a reactor in sequence and stir and mix them evenly to form a diol mixture; Step 2. Prepolymerizing 4,4'-diphenylmethane diisocyanate with a diol mixture to obtain an isocyanate-terminated prepolymer; Step 3. reacting the mixed amine with the isocyanate-terminated prepolymer to obtain a polyurethane-polyurea solution; Step 4. Fully stirring, dispersing and ripening the polyurethane-polyurea solution to obtain a spinning solution; Step 5. Use a dry spinning system to perform spin stretching on the spinning solution to obtain the polyurethane elastic fiber.

8. The preparation method according to claim 7, characterized in that: The molar ratio of the polytetramethylene ether glycol to the polyester diol is 4:6 to 6:

4.

9. The preparation method according to claim 7, characterized in that: The molar ratio of the 4,4'-diphenylmethane diisocyanate to the diol mixture is 1.3:1 to 2.6:

1.

10. The preparation method according to claim 7, characterized in that: The temperature of the prepolymerization reaction in step 2 is 40-50°C.

11. The preparation method according to claim 7, characterized in that: The isocyanate group content in the isocyanate-terminated prepolymer is 1.5 wt % to 5.0 wt % of the isocyanate-terminated prepolymer.

12. The preparation method according to claim 7, characterized in that: Before the reaction in step 3, the isocyanate-terminated prepolymer is dissolved in N,N-dimethylacetamide to obtain an isocyanate-terminated prepolymer solution.

13. The preparation method according to claim 12, characterized in that: The concentration of the isocyanate-terminated prepolymer solution is 35 wt % to 75 wt %.

14. The preparation method according to claim 7, characterized in that: The mixed amine in step 3 comprises a diamine as a chain extender and a monoamine as a chain terminator, and the molar ratio of the amine groups of the diamine to the monoamine in the mixed amine is 5:1 to 30:

1.

15. The preparation method according to claim 7, characterized in that: Before the reaction in step 3, the mixed amine is dissolved in N,N-dimethylacetamide to obtain a mixed amine solution.

16. The preparation method according to claim 15, characterized in that: The mass percentage of the mixed amine in the mixed amine solution is 4wt%-8wt%.

17. The preparation method according to claim 15, characterized in that: The molar ratio of the amine groups in the mixed amine solution to the isocyanate groups in the isocyanate-terminated prepolymer is 1.00:1 to 1.15:

1.

18. The preparation method according to claim 7, characterized in that: In step 4, an alkali-resistant additive and / or an anti-blocking agent and optionally other additives are added to the polyurethane-polyurea solution before stirring.

19. The preparation method according to claim 18, characterized in that: The alkali-resistant auxiliary agent is nano silicon dioxide and / or nano titanium dioxide.

20. The preparation method according to claim 18, characterized in that: The added amount of the alkali-resistant additive is 0.5wt% to 2wt% of the polyurethane elastic fiber.

21. The preparation method according to claim 18, characterized in that: The anti-adhesion agent is polyethylene glycol with a molecular weight of 2000 and / or polyvinyl alcohol with a molecular weight of 2000.

22. The preparation method according to claim 18, characterized in that: The added amount of the anti-adhesion agent is 0.1wt% to 0.2wt% of the polyurethane elastic fiber.

23. The preparation method according to claim 18, characterized in that: The other auxiliary agents include any one of antioxidants, ultraviolet absorbers, lubricants, matting agents or dyeing auxiliary agents, or a combination of at least two of them.

24. The preparation method according to claim 18, characterized in that: The addition amount of the other auxiliary agents is 0.1wt%-2.5wt% of the polyurethane elastic fiber.

25. The preparation method according to claim 7, characterized in that: In step 5, the spinning and stretching are dried, oiled, and wound to obtain the polyurethane elastic fiber.