Fine-denier dope-dyed fiber and method for preparing fine-denier dope-dyed fiber from waste polyester

Abstract

The invention provides a method for preparing fine-denier dope-dyed fibers from waste polyester, and relates to the field of high-added-value recycling of waste polyester. The method for preparing the fine denier stock solution colored fiber by using the waste polyester comprises the following steps: uniformly mixing a molecular weight regulator and carbon black to form a functional component with a certain mass fraction, and jointly feeding the waste polyester and the functional component into a double-screw extruder. The extruded product enters a vertical pre-polycondensation reaction kettle, a certain proportion of long-carbon-chain dihydric alcohol is introduced into the pre-polycondensation reaction kettle, a pre-polycondensation product is prepared through reaction, the pre-polycondensation product finally enters a horizontal polycondensation reaction kettle for tackifying, and the functional polyester is prepared. The functional polyester is subjected to melt spinning forming to obtain the fine denier stock solution colored fiber, and high-valued and efficient reutilization of the waste polyester raw material is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of waste polyester recycling, and relates to a method for preparing fine-denier dope-colored fibers from waste polyesters. BACKGROUND

[0002] The recycling of polymers can realize the reuse of resources and meet the requirements of green and low-carbon development. Polyester is an important variety of synthetic polymers. How to efficiently and highly value the waste polyesters after they are discarded is an important development direction.

[0003] Chinese patent CN119265740A discloses a preparation method of regenerated colored polyester fibers. The regenerated colored polyester comprises regenerated polyester and pigments. The preparation method comprises the following steps: the regenerated colored polyester is melted to obtain a regenerated colored polyester melt, the regenerated colored polyester melt is metered, extruded through a spinneret, cooled, oiled, stretched, heat set and wound to obtain the regenerated colored polyester fibers. The oil used in the oiling step comprises at least mineral oil and isomeric tridecanol polyoxyethylene ether. The application adjusts the static friction coefficient μs and the dynamic friction coefficient μd of the oil to obtain suitable cohesion of the fibers, increases the wear resistance of the fibers, reduces the broken ends of the fibers during the spinning process, and improves the processability of the fibers.

[0004] Chinese patent CN115726051B discloses a dope-colored regenerated colored flame-retardant polyester flat filament and a preparation method thereof. The raw materials include, by weight: 100 parts of PET regenerated powder, 5-12 parts of halogen-free flame retardant, 1-3 parts of oxidized polyethylene wax, and 9-16 parts of liquid color paste. The liquid color paste includes 2-3 parts of modified inorganic pigment, 2-5 parts of auxiliary agent, and 5-8 parts of solvent. The auxiliary agent includes a modified sol-type auxiliary agent, which is a pseudo-boehmite sol modified by nano-magnesium hydroxide and C6-C12 aromatic diamine. The application uses PET regenerated powder to prepare polyester fibers by the method of dope coloring, and has better environmental protection and energy saving. The modified sol-type auxiliary agent can improve the compatibility between the flame retardant and the polyester, improve the spinnability of the dope-colored polyester fibers, and obtain colored polyester filaments with better flame-retardant effect and higher dyeing color fastness.

[0005] Chinese patent CN117888231A discloses a regenerated colored polyester fiber and a preparation process thereof. A degradation agent and ethylene glycol are added to the regenerated polyethylene terephthalate for degradation reaction, and the reaction melt is filtered to obtain relatively pure oligomers. Nano-cellulose, color masterbatch and carbon black are added to the oligomers and mixed with the melt to perform vacuum polymerization reaction. The melt after reaction is processed by spinning, stretching and setting to obtain the regenerated colored polyester fiber. The composition of the application can be used to make environmentally friendly clothing, household goods, automotive interiors, packaging materials, etc., and has the advantages of environmental protection and high breaking strength. The degradation agent is composed of 0.1-0.5 parts of N,N-dimethylformamide, 0.2-0.5 parts of dimethyl sulfoxide and 1-2 parts of formic acid.

[0006] Chinese patent CN107326467B relates to a black washable polyester fiber, which has a wash fastness of 4-5 levels, a breaking strength of 3.0-3.5 dtex / cN, preferably 3.3-3.4 dtex / cN, and an elongation at break of 20-30%, preferably 25%. The application also provides a preparation method of the black washable polyester fiber. The continuous polymerization process effectively controls the intrinsic viscosity and the content of terminal hydroxyl groups of the polymer, stabilizes the quality of the fiber product, and uses the corresponding dispersion medium to make the carbon black dyeing more uniform.

[0007] From the above disclosed technology, the existing waste polyester recycling technology needs to strictly control the quality of the raw material to prepare high-quality fiber products by physical recycling. High-purity bottle chips can be used as raw materials to directly physically recycle fine denier fibers by using the excellent quality of bottle chips. However, the development of functional varieties is limited, and it is extremely dependent on the introduction of functional masterbatch components in spinning. When spinning the colored polyester fiber of the regenerated dope, bottle chip tail raw materials are usually used, and components including carbon black masterbatch are added for blending spinning. The uniform dispersion of the introduced color masterbatch in the high-viscosity bottle chip directly affects the coloring effect and the thickness specification of the spun fiber, and the challenge of regenerating polyester fiber from bottle chip dope is very difficult. Using waste polyester as raw material, the macromolecular polyester is depolymerized into small molecules or monomers by chemical or enzymatic method, and then purified to the purity of virgin raw material, and then polymerized. This technical route can ensure the quality of the spun fiber, but the process of depolymerizing into small molecules or monomers is long and the cost is very high, which limits the application and promotion.

[0008] The present application is to adjust the molecular weight of the polyester to the low molecular weight intermediate product by introducing the molecular weight regulator based on the ester exchange reaction mechanism between the molecular weight regulator and the waste polyester. SUMMARY

[0009] The present application aims at the problems of long process and low added value of the regenerated product in the existing waste polyester recycling functional polyester fiber process, and proposes a method for preparing fine denier dope colored fiber from waste polyester, which mixes waste polyester and molecular weight regulator and other components, directionally micro-depolymerizes the waste polyester with rich end hydroxyl intermediate product by combining physical and chemical characteristics, realizes homogeneous dispersion of carbon black containing carboxyl and re-polymerization with long carbon chain diol organic component, and obtains dope colored and flexible polyester fiber by melt spinning, realizing efficient and high value recycling of waste resources.

[0010] As a preferred technical solution:

[0011] A method for preparing fine denier dope colored fiber from waste polyester, the specific steps are as follows: mixing the molecular weight regulator and carbon black uniformly to form a functional component with a certain mass fraction, and putting the waste polyester and the functional component into a double screw extruder together; the extruded product enters a vertical pre-polycondensation reactor, a certain proportion of long carbon chain diol is introduced into the pre-polycondensation reactor, and a pre-polycondensation product is prepared by reaction, and the pre-polycondensation product finally enters a horizontal polycondensation reactor for tackifying to prepare a functional polyester; the functional polyester is melt spun to form a fine denier dope colored fiber; the molecular weight regulator is bis-hydroxyethyl terephthalate or a product with a polymerization degree of 2-5 prepared by reaction of terephthalic acid and diol.

[0012] The method for preparing fine denier dope colored fiber from waste polyester as described above, the waste polyester refers to polyester with a mass fraction of polyethylene terephthalate of 85% or more, which can contain other types of polyester with a mass fraction of 15% or less, and the intrinsic viscosity is 0.60-0.85 dL / g.

[0013] Among them, the type of polyester is polytrimethylene terephthalate, polybutylene terephthalate and its copolyester, etc.

[0014] The method for preparing fine denier dope colored fiber from waste polyester as described above, the molecular weight regulator is mixed uniformly with carbon black, which is a solid powder form of molecular weight regulator mixed uniformly with solid powder carbon black in a mixer.

[0015] The molecular weight regulator has a particle size of 10-50 microns in solid powder form, and the carbon black has a particle size of 100-500 nanometers.

[0016] The mass ratio of the carbon black to the molecular weight regulator is 2:8-8:2.

[0017] The molecular weight regulator is bis-hydroxyethyl terephthalate or a product obtained by reacting terephthalic acid with a dihydric alcohol, and the dihydric alcohol is one or more than two of ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol.

[0018] The waste polyester and the functional component are fed into a twin-screw extruder for blending extrusion.

[0019] The functional component accounts for 2-10% of the mass fraction of the waste polyester.

[0020] The twin-screw extrusion temperature is 240-260°C, the shear rate is 200-1000 Pa·s, and the intrinsic viscosity of the extrusion product is 0.35-0.45 dL / g.

[0021] The end hydroxyl content of the blending extrusion product in the twin-screw extruder is 50-150 mgKOH / g.

[0022] The extrusion product in a molten state is further conveyed to a vertical pre-polycondensation reactor by screw extrusion pressure, a certain proportion of long-chain dihydric alcohol is introduced, and pre-polycondensation reaction is performed.

[0023] The pre-polycondensation reactant temperature is 255-265°C, the reaction pressure is 500-1000 Pa, and the reaction time is 20-40 min.

[0024] The intrinsic viscosity of the pre-polycondensation product is 0.45-0.55 dL / g.

[0025] The long-chain dihydric alcohol is one or both of polyethylene glycol and polytetrahydrofuran, and the number average molecular weight is 1000-4000 g / mol.

[0026] The pre-polycondensation product is further reacted in a horizontal polycondensation kettle to further increase the molecular weight and prepare a functional polyester.

[0027] The final polycondensation reactant temperature is 260-275°C, the reaction pressure is 0-100 Pa, and the reaction time is 20-40 min.

[0028] wherein the functional polyester obtained by the final polycondensation has an intrinsic viscosity of 0.65-0.70 dL / g and a filter pressure value FPFPV of not more than 0.2 bar / g.

[0029] The fine denier dope-colored fiber prepared according to the above technology has the characteristics of dope coloring and softness, the fiber single filament specification is 0.2-1.5 dtex, the root number is 36-144, the fiber breaking strength is 2.5-4.0 cN / dtex, the breaking elongation is 20-60%, and the modulus is 30-80 cN / dtex.

[0030] Invention principle

[0031] Polyester is one of the important varieties of synthetic polymers, with large output and wide application. In the face of a large amount of waste polyester, scientific and reasonable recycling is an important environmental protection measure. The current recycling methods developed for the characteristics of waste polyester include physical and chemical regeneration technologies. The physical method is mostly based on waste polyester bottle pieces as raw materials, which are melted, filtered and impurities are removed, and then cut into particles for reuse, which can be used to spin fibers, etc. The chemical recycling method is to depolymerize the waste polyester into monomers or other types of small molecules in the presence of a depolymerization agent, and then esterify and polycondensate to prepare regenerated polyester or functional polyester. The physical method has a high dependence on the quality of the raw materials. Although the chemical method can prepare copolymerized functional polyester, the long process and high energy consumption limit the promotion and application of waste polyester.

[0032] The waste polyester regeneration method proposed in the present application combines the technical principles of physical and chemical recycling, which can realize efficient regeneration of waste polyester and improve the added value of polyester. Compared with the monomer small molecules obtained by the current chemical depolymerization method, the present application is based on the micro-depolymerization of complex macromolecular polyester into low molecular weight polyester, which can realize the homogeneous mixing of polyester from different sources at the low molecular weight level. The recycled polyester is not possible to be the same type, and the raw materials are relatively complex, mainly reflected in the difference in molecular weight and chemical structure of the polyester. How to realize the uniform quality of polyester with different molecular weights and different chemical structures under certain process conditions has a significant influence on improving the spinning performance. Reducing the molecular weight is helpful to realize the mixing of materials. By introducing a functional depolymerization component with dihydric alcohol characteristics as a depolymerization agent, the waste polyester with different molecular weights and chemical structures is depolymerized into "intermediate" molecular weight polyester, which can realize the homogeneous mixing of polyester with different molecular weights at low molecular weight. The waste polyester suitable for the present application includes waste polyester with a mass fraction of polyethylene terephthalate of 85% or more, which can contain other types of polyester with a mass fraction of 15% or less, and the intrinsic viscosity is 0.60-0.85 dL / g.

[0033] The molecular weight regulator of the waste polyester in the application is BHET or a product with a polymerization degree of 2-5 formed by reacting terephthalic acid with a dihydric alcohol, which is essentially a type of dihydric alcohol. The mechanism of the molecular weight regulator to regulate the molecular weight of the polyester is that the dihydric alcohol at both ends attacks the ester bond of the macromolecular polyester, the ester bond in the polyester is broken to form a dihydric alcohol-terminated structure, the molecular weight is reduced, and the polyester with reduced molecular weight is dihydric alcohol-terminated to ensure its stability at high temperature and reactivity. The addition amount of the molecular weight regulator needs to be controlled. If the content of the introduced molecular weight regulator is too low, the molecular weight of the waste polyester cannot be significantly regulated, the molecular weight of the waste polyester is limitedly reduced, and it is difficult to achieve homogeneous mixing. If the content of the introduced molecular weight regulator is too large, the waste polyester will be depolymerized into small molecular structures with lower molecular weight, the time for re-polymerization is long, the sequence structure is severely destroyed, and the spinnability of the functional polyester prepared is obviously reduced.

[0034] In the application, the molecular weight regulator is first mixed with carbon black powder uniformly, and then added together into the twin screw. The molecular weight regulator is quickly melted in the twin screw by temperature and shearing force. The molecular weight regulator is essentially a dihydric alcohol, which can be combined with the abundant carboxyl functional groups on the surface of carbon black, playing a role of pre-dispersing carbon black on the surface, preventing the agglomeration of nano-sized carbon black. The main role of the molecular weight regulator is to regulate the molecular weight of the waste polyester and to pre-disperse the introduced nano-sized carbon black. The application strictly controls the introduction amount of the molecular weight regulator, so that the intrinsic viscosity of the extrusion product is 0.35-0.45 dL / g, and the hydroxyl end group content is 50-150 mgKOH / g.

[0035] In the application, the waste polyester is extruded by a twin screw, the product in a molten state is further conveyed to a vertical pre-polycondensation reactor and a horizontal polycondensation reactor by the screw extrusion pressure, and pre-polycondensation and final polycondensation are carried out. At the same time, a certain proportion of long-chain dihydric alcohol is introduced at the pre-polycondensation stage. The long-chain dihydric alcohol is one or more of polyethylene glycol or polytetrahydrofuran, and the number average molecular weight is 1000-4000 g / mol. The long-chain dihydric alcohol and the product extruded by the twin screw are subjected to ester exchange reaction. The product extruded by the twin screw has a hydroxyl end group content of 50-150 mgKOH / g, and the hydroxyl end group content is rich, which can fully carry out ester exchange reaction with the long-chain dihydric alcohol. The long-chain dihydric alcohol is copolymerized into the polyester main chain during the pre-polycondensation reaction, which improves the flowability of the pre-polycondensation product and improves the common problem of hard hand feeling of the final spun dope colored fiber.

[0036] The double screw extrusion product in the application enters a polycondensation reactor, and the polycondensation is divided into a pre-polycondensation stage and a final polycondensation stage because the intrinsic viscosity of the product entering the polycondensation reactor is 0.35-0.45 dL / g, and long-chain diols are introduced. If the product directly enters the final polycondensation stage with high vacuum, the polyester with a relatively low intrinsic viscosity and the long-chain diols will be extracted and condensed in the pipeline, causing a blockage problem. The pre-polycondensation stage can increase the molecular weight, and the problem of being extracted and blocking the pipeline will not occur when entering the final polycondensation stage.

[0037] Advantages

[0038] (1) The recycling method of the application combines the technical principles of physical and chemical recycling. Under the action of the molecular weight regulator, the polyester with a complex molecular weight and molecular weight distribution can be quickly depolymerized into polyester with a lower molecular weight but not monomer small molecules by the double screw, and then the spinning grade polyester can be obtained through the polycondensation reaction. The recycled raw material has wider adaptability and higher efficiency.

[0039] (2) The molecular weight regulator can play a role in regulating the molecular weight of the complex polyester and pre-dispersing the nanometer-sized materials such as carbon black, avoiding the agglomeration problem caused by the high surface area. The prepared dope colored fiber has high color fastness and black depth, which is much better than the current carbon black masterbatch technology.

[0040] (3) The molecular weight regulator regulates the molecular weight of the polyester, and the low-viscosity polyester product extruded by the double screw contains rich hydroxyl functional groups, which can react with long-chain diols. The long-chain diols improve the flowability of the polyester and increase the softness of the dope colored polyester fiber, solving the common problem of hard hand caused by the introduction of carbon black. DETAILED DESCRIPTION

[0041] Examples 1-8:

[0042] A method for preparing fine denier dope colored fiber from waste polyester, a functional component is formed by uniformly mixing a molecular weight regulator in the form of a solid powder with a particle size of 20-40 microns and a solid powder carbon black with a particle size of 250-350 nanometers in a mass ratio according to different examples in Table 1, the waste polyester (polyethylene terephthalate with a mass fraction of more than 85%, and an intrinsic viscosity of 0.60-0.85 dL / g) and the functional component are jointly fed into a double screw extruder for blending and extrusion, and the mass fraction of the functional component in the waste polyester in different examples is shown in Table 1. The double screw extrusion temperature is 240-260℃, the shear rate is 500-7000 Pa.s, the intrinsic viscosity of the extrusion product is 0.35-0.45 dL / g, and the hydroxyl end group content is 50-150 mgKOH / g.

[0043] The molecular weight regulator is bis-hydroxyethyl terephthalate (BHET).

[0044] The extrusion product in a molten state is conveyed by screw extrusion pressure into a vertical pre-polycondensation reactor, a long carbon chain diol is introduced, and a pre-polycondensation reaction is performed. The pre-polycondensation reactant temperature is 255-265°C, the reaction pressure is 550-750 Pa, the reaction time is 20-40 min, and the pre-polycondensation product has a characteristic viscosity of 0.45-0.55 dL / g.

[0045] The long carbon chain diol is polyethylene glycol, and the number average molecular weight is 1000-3000 g / mol. The mass fraction of the long carbon chain diol in the screw extrusion product is 3-6%, and the mass fraction of the long carbon chain diol in different embodiments is shown in Table 1.

[0046] The pre-polycondensation product is introduced into a horizontal polycondensation reactor for reaction, further increasing the molecular weight, and a functional polyester is prepared. The final polycondensation reactant temperature is 260-275°C, the reaction pressure is 0-100 Pa, the reaction time is 20-40 min, the functional polyester obtained by the final polycondensation has a characteristic viscosity of 0.65-0.70 dL / g, and the functional polyester has a filter pressure value FPFPV of not more than 0.2 bar / g.

[0047] The functional polyester is melt spun into a fine denier dope colored fiber. The fiber has the characteristics of dope coloring and softness, and the fiber monofilament specification, number, and fiber performance parameters are shown in Table 1.

[0048] Examples 9-16:

[0049] Examples 9-16 differ from Examples 1-8 in that the molecular weight regulator is a product with a polymerization degree of 2-5 prepared by reacting terephthalic acid with 1,4-butanediol (the molar ratio of PTA to BDO is 1:1.8-1:2.5, the catalyst is tetrabutyl titanate, the amount used is 0.08-0.15% of the mass of PTA, the reaction temperature is 200-230°C, and the time is 60-120 min); the long carbon chain diol is polytetrahydrofuran, and the number average molecular weight is 2000-4000 g / mol; and the mass fraction of the long carbon chain diol in the screw extrusion product is 2-5%.

[0050] The mass fraction of the functional component in the waste polyester, the mass ratio of the molecular weight regulator to carbon black, the mass fraction of the long carbon chain diol in the screw extrusion product, and the performance parameters of the fine denier dope colored fiber prepared in different Examples 9-16 are shown in Table 2.

[0051] Table 1:

[0052] Example Functional component mass fraction (%) Mass ratio of molecular weight regulator to carbon black Long carbon chain diol mass fraction (%) Fiber filament gauge (dtex) Fiber filament number Fiber breaking strength (cN / dtex) Breaking elongation (%) Modulus (cN / dtex) 1 2 2:8 3 0.8 72 3.0 35 45 2 5 4:6 4 0.5 96 3.5 40 50 3 8 6:4 5 0.3 108 3.8 45 60 4 10 8:2 6 1.2 48 2.8 25 35 5 2 8:2 6 1.0 60 3.2 30 40 6 4 6:4 5 0.4 120 3.6 50 65 7 7 4:6 4 0.2 144 4.0 55 80 8 10 2:8 3 1.5 36 2.5 20 30

[0053] Table 2:

[0054] Example Functional component mass fraction (%) Mass ratio of molecular weight regulator to carbon black Long carbon chain diol mass fraction (%) Fiber filament gauge (dtex) Fiber filament number Fiber breaking strength (cN / dtex) Breaking elongation (%) Modulus (cN / dtex) 9 2 2:8 2 0.7 84 3.1 55 40 10 5 4:6 3 0.6 90 3.4 50 45 11 8 6:4 4 0.3 132 3.7 45 55 12 10 8:2 5 1.3 48 2.7 30 38 13 2 8:2 5 0.9 60 3.3 60 35 14 4 6:4 4 0.4 120 3.6 55 50 15 7 4:6 3 0.2 144 3.9 50 60 16 10 2:8 2 1.4 36 2.6 22 32

Claims

1. A method for preparing fine denier solution-dyed fiber using waste polyester, characterized in that: The molecular weight regulator and carbon black are mixed evenly to form a functional component, and the waste polyester and the functional component are fed into a twin-screw extruder for blending and extrusion; The extruded product enters a vertical pre-condensation reactor, into which a long carbon chain diol is introduced for reaction to prepare a pre-condensation product, which enters a horizontal polycondensation reactor for viscosity enhancement to prepare a functional polyester; the functional polyester is melt-spun to obtain a fine-denier solution-dyed fiber; the molecular weight regulator is a product with a degree of polymerization of 2-5 prepared by reacting dihydroxyethyl terephthalate or terephthalic acid with a diol.

2. The method for preparing fine denier solution-dyed fiber using waste polyester according to claim 1, characterized in that: Waste polyester refers to polyester with a mass fraction of polyethylene terephthalate of more than 85%, and may contain other types of polyester with a mass fraction of less than 15%, with an intrinsic viscosity of 0.60-0.85dL / g.

3. The method for preparing fine denier solution-dyed fiber using waste polyester according to claim 1, characterized in that: The molecular weight regulator and carbon black are mixed evenly by mixing the molecular weight regulator in solid powder form and the solid powder carbon black evenly in a mixer, wherein the particle size of the molecular weight regulator in solid powder form is 10-50 microns, the particle size of the carbon black is 100-500 nanometers, and the mass ratio of carbon black to molecular weight regulator is 2:8-8:

2.

4. The method for preparing fine denier solution-dyed fiber using waste polyester according to claim 1, characterized in that: The molecular weight regulator is a product with a polymerization degree of 2-5 obtained by reacting dihydroxyethyl terephthalate or terephthalic acid with one or more diols selected from ethylene glycol, 1,3-propylene glycol, 1,4-butanediol and 1,5-pentanediol.

5. The method for preparing fine denier solution-dyed fiber using waste polyester according to claim 1, characterized in that: The waste polyester and the functional components are fed into a twin-screw extruder for blending and extrusion, and the functional components account for 2-10% of the mass fraction of the waste polyester.

6. The method for preparing fine denier solution-dyed fiber using waste polyester according to claim 1, characterized in that: The extrusion temperature of the twin-screw extruder is 240-260° C., the shear rate is 200-1000 Pa.s, the intrinsic viscosity of the extruded product is 0.35-0.45 dL / g, and the terminal hydroxyl content is 50-150 mgKOH / g.

7. The method for preparing fine denier solution-dyed fiber using waste polyester according to claim 1, characterized in that: The extruded product is in a molten state and is conveyed to a vertical pre-polycondensation reactor through screw extrusion pressure, and a long carbon chain diol is introduced for pre-polycondensation reaction. The pre-polycondensation reactant temperature is 255-265°C, the reaction pressure is 500-1000 Pa, the reaction time is 20-40 minutes, and the intrinsic viscosity of the pre-polycondensation product is 0.45-0.55 dL / g.

8. The method for preparing fine denier solution-dyed fiber using waste polyester according to claim 1, characterized in that: The long carbon chain diol is one or both of polyethylene glycol and polytetrahydrofuran, and has a number average molecular weight of 1000-4000 g / mol.

9. The method for preparing fine denier solution-dyed fiber using waste polyester according to claim 1, characterized in that: The pre-polycondensation product enters the horizontal polycondensation kettle for final polycondensation reaction to increase the molecular weight. The final polycondensation temperature is 260-275°C, the reaction pressure is 0-100Pa, the reaction time is 20-40min, and the functional polyester obtained by the final polycondensation has an intrinsic viscosity of 0.65-0.70dL / g and a filter pressure value FPFPV of no more than 0.2bar / g.

10. Fine denier solution-dyed fiber produced according to the method of any one of claims 1 to 9, the fiber being solution-dyed and soft, with a single filament specification of 0.2-1.5 dtex, a fiber count of 36-144, a fiber breaking strength of 2.5-4.0 cN / dtex, an elongation at break of 20-60%, and a modulus of 30-80 cN / dtex.