Regenerated cellulose fiber, article containing same, and method for producing regenerated cellulose fiber

Abstract

The present invention addresses the problem of providing: a regenerated cellulose fiber that does not contain CS2 and has novel characteristics; and an article containing the same. The present invention also addresses the problem of providing a method for producing novel regenerated cellulose fibers that does not use CS2. [First embodiment] Provided is a regenerated cellulose fiber that does not contain CS2, in which the monofilament has a tensile elongation at break of 8% or more and a toughness of 25 MPa or more. [Second embodiment] Provided is an article containing the regenerated cellulose fiber according to the first embodiment. [Third embodiment] Provided is a method for producing a regenerated cellulose fiber using a solvent, the method including spinning a spinning solution in which a raw material cellulose having an average polymerization degree of 200 to 3000 is dissolved in the solvent by a wet spinning method or a dry spinning method at a draft ratio (take-up speed / discharge line speed of the spinning solution) of 20 or less to obtain a regenerated cellulose fiber having a monofilament fineness of 0.1-3 dtex.

Description

Regenerated cellulose fiber, article containing same, and method for producing regenerated cellulose fiber

[0001] The present disclosure relates to regenerated cellulose fibers and articles containing the same, as well as methods for producing the regenerated cellulose fibers.

[0002] Cellulose is the most abundant natural polymer compound on Earth. Given the finiteness of fossil fuels, the problem of synthetic resin disposal, and business sustainability, interest in renewable and highly biodegradable cellulose is growing. Regenerated cellulose fiber, in particular, is attracting attention as a sustainable material that not only possesses unique and excellent properties but is also environmentally friendly.

[0003] Regenerated cellulose fibers are used, for example, for woven carcasses for automobile tires, fiber-reinforced resin compositions, etc. In these applications, regenerated cellulose fibers (viscose rayon) obtained by the viscose method are mainly used. However, the existing viscose method has a problem in that carbon disulfide (CS), which is toxic to humans, is generated. ２ ) to use CS ２ Free or CS ２ There has been growing interest in solvent-processed regenerated cellulose fibers, which can reduce the amount of solvent used. Patent Documents 1 to 3 describe regenerated cellulose fibers produced using N-methylmorpholine-N-oxide (NMMO) as a solvent. The regenerated cellulose fibers described in these patent documents have a breaking elongation of about 4 to 6%, which is lower than that of viscose rayon.

[0004] JP-T-2005-530916A JP-A-2006-257616A WO 2008 / 143375A

[0005] This disclosure relates to CS ２ The present disclosure also provides a regenerated cellulose fiber that does not contain CS and has novel properties, and an article that includes the regenerated cellulose fiber. ２ The present invention addresses the problem of providing a novel method for producing regenerated cellulose fibers that does not use any additives.

[0006] The present disclosure includes the following embodiments. [First embodiment] CS ２A regenerated cellulose fiber that does not contain cellulose nitrile, and has a monofilament tensile breaking elongation of 8% or more and a toughness of 25 MPa or more. [Second embodiment] An article comprising the regenerated cellulose fiber of the first embodiment. [Third embodiment] A method for producing regenerated cellulose fiber using a solvent, the production method comprising: spinning a spinning solution obtained by dissolving raw material cellulose having an average degree of polymerization of 200 to 3000 in the solvent by a wet spinning method or a dry wet spinning method at a draft ratio (take-up speed / linear extrusion speed of the spinning solution) of 20 or less, to obtain regenerated cellulose fiber having a monofilament fineness of 0.1 to 3 dtex.

[0007] According to the present disclosure, CS ２ The present disclosure also provides a regenerated cellulose fiber that does not contain CS and has novel properties, and an article containing the same. ２ It is possible to provide a novel method for producing regenerated cellulose fibers without using any additives.

[0008] An embodiment of the present disclosure will be described in detail below. However, the scope of the present disclosure is not limited to the embodiment described herein, and various modifications can be made without departing from the spirit of the present disclosure. Each aspect disclosed in this specification can be combined with any other feature disclosed in this specification. Furthermore, when multiple upper and lower limits are described for a particular parameter, any of these upper and lower limits can be combined to form a suitable numerical range. Furthermore, the lower and / or upper limits of a numerical range described in this disclosure may be replaced with numerical values ​​within that range and shown in the examples. The expression "X to Y" indicating a numerical range means "X or greater and Y or less." Furthermore, unless otherwise noted, all test temperatures are room temperature (20°C ± 5°C). If a specific description described for one embodiment also applies to other embodiments, that description may be omitted in other embodiments.

[0009] The configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible as appropriate within the scope of the gist of the present disclosure. The present disclosure is not limited by the embodiments. Each aspect disclosed in this specification can be combined with any other feature disclosed in this specification. In this specification, "regenerated cellulose fiber" refers to a fiber obtained by dissolving raw cellulose and regenerating it into a fibrous form, and can include both monofilaments and multifilaments. Furthermore, in this disclosure, a "monofilament" refers to a single filament constituting a regenerated cellulose fiber, and is a single filament obtained by spinning from a single nozzle or a single filament extracted from a multifilament obtained from a multi-hole nozzle. A "multifilament" refers to a bundle or aggregate of two or more monofilaments.

[0010] [Regenerated cellulose fiber] The first embodiment of the present disclosure is a CS ２ The present invention relates to a regenerated cellulose fiber that does not contain CS, and has a monofilament tensile breaking elongation of 8% or more and a toughness of 25 MPa or more. As described above, the tensile breaking elongation of conventional solvent-process regenerated cellulose fibers is 4 to 6%. The regenerated cellulose fiber according to the first embodiment has a monofilament tensile breaking elongation of 8% or more, achieving a higher breaking elongation than conventional fibers. Furthermore, the regenerated cellulose fiber according to the first embodiment has a monofilament toughness of 25 MPa or more. CS ２ Among regenerated cellulose fibers not containing cellulose, fibers that can achieve such high breaking elongation and high tenacity have not been known up to now, and are therefore novel fibers.

[0011] The regenerated cellulose fiber according to the first embodiment is "CS ２ "Regenerated cellulose fiber that does not contain CS" means that the regenerated cellulose fiber is ２ and / or C.S. ２"Substantially free" means that the above components are not detected when the regenerated cellulose fiber is analyzed by GC-MS. When the regenerated cellulose fiber is prepared by a method other than the viscose method (preferably the solvent method), the fiber is not considered to be "CS"-derived. ２ The regenerated cellulose fiber according to the first embodiment can be said to be a "regenerated cellulose fiber that does not contain CS." ２ It does not contain any , so it has a small impact on the environment.

[0012] <Tensile Breaking Elongation of Monofilament> In the first embodiment, the tensile breaking elongation of the monofilament can be measured under the following conditions. The tensile breaking elongation of the regenerated cellulose fiber monofilament is measured in accordance with JIS L 1015. Specifically, a single fiber is extracted from the monofilament or the multifilament to be measured to form a monofilament. A tensile test is then performed using an automatic single-fiber fineness meter and a strength and elongation meter (e.g., manufactured by Lenzing Instruments / Austria, product names "Vibroskop Micro" and "Vibrodyn 500") at a temperature of 20°C and a relative humidity of 65% under conditions of a chuck distance of 20 mm and a pulling speed of 20 mm / min. In this tensile test, the elongation at which the monofilament breaks (breaks) is measured. The test is performed 15 or more times, and the average value is calculated. The average value is rounded to one decimal place.

[0013] In one embodiment, the tensile breaking elongation of the regenerated cellulose fiber monofilament is preferably 9% or more, more preferably 10% or more. There is no particular upper limit to the tensile breaking elongation of the monofilament, but from the viewpoint of easily controlling the tensile modulus of the monofilament, it is preferably 20% or less, more preferably 17% or less. In one embodiment, the tensile breaking elongation of the regenerated cellulose fiber monofilament may be 8 to 20%, or may be 10 to 17%.

[0014] <Toughness of Monofilament> The toughness (tenacity) of the monofilament in the first embodiment can be measured under the following conditions. A tensile test is conducted under the same conditions (JIS L 1015) as those for the tensile breaking elongation. Using the stress-strain curve (so-called SS curve) obtained by the tensile test, the toughness is calculated by determining the area enclosed by the curve from the origin to the breaking point. Note that the method for determining this area may be, for example, by analysis using analysis software for a tensile tester, or by integrating the measurement data of the tensile breaking strength and tensile breaking elongation. The tensile breaking strength can also be determined by conducting a tensile test under the same conditions as those for the tensile breaking elongation, and detailed conditions will be described later.

[0015] In one embodiment, the toughness of the regenerated cellulose fiber monofilament is preferably 30 MPa or more, more preferably 35 MPa or more, and even more preferably 40 MPa or more. If the toughness of the monofilament is 25 MPa or more, the fatigue resistance of the regenerated cellulose fiber is likely to be improved.

[0016] The regenerated cellulose fibers according to the first embodiment can be easily obtained by spinning a cellulose spinning solution prepared by dissolving raw cellulose in a solvent (preferably a solvent containing imidazolium ions) into fibers using a wet spinning method or a dry-wet spinning method, and then contacting the solution with a coagulation solution to regenerate (coagulate). A more preferred embodiment for achieving the fibers according to the first embodiment is a method comprising: using raw cellulose having an average degree of polymerization of 200 to 3,000, spinning the raw cellulose by a wet spinning method or a dry spinning method at a draft ratio (take-up speed / linear discharge speed of the spinning solution) of 20 or less (preferably 1 to 10, more preferably 1 or more but less than 10, and even more preferably 1 to 6) to obtain regenerated cellulose fibers having a monofilament fineness of 0.1 to 3 dtex.

[0017] In the regenerated cellulose fiber according to the first embodiment, the relationship between the tensile breaking strength of the monofilament and the tensile modulus of the monofilament preferably satisfies the following formula (1): 8≧M−5.29S (1) (In formula (1), M represents the tensile modulus of the monofilament (GPa), and S represents the tensile breaking strength of the monofilament (cN / dtex).) The tensile modulus (hereinafter referred to as "tensile modulus (M)") and the tensile breaking strength (hereinafter referred to as "tensile breaking strength (S)") in formula (1) are values ​​measured by the above-described method. When the regenerated cellulose fiber satisfies formula (1), thread breakage during spinning is less likely to occur, and productivity is likely to be improved. In one embodiment, (M−5.29S) in formula (1) is preferably 5 or less, and more preferably 2 or less. Note that (M−5.29S) in formula (1) may be less than 0 (a negative value). In one embodiment, (M-5.29S) is preferably -0.5 or less, more preferably -0.61 or less. The lower limit of (M-5.29S) is not particularly limited as long as the effects of the present disclosure are achieved, but may be, for example, -100 or more, -50 or more, or -10 or more. In one embodiment, the range of M-5.29S may be -100 or more and 8 or less, -50 or more and 5 or less, -10 or more and 2 or less, -10 or more and -0.5 or less, or -10 or more and -3.5 or less.

[0018] <Tensile Modulus (M) of Monofilament> In one embodiment, the tensile modulus (M) (Young's modulus) of the regenerated cellulose fiber monofilament is preferably within a range satisfying the relationship of the above formula (1). In one embodiment, the tensile modulus (M) may be 10 GPa or more, 15 GPa or more, or 19 GPa or more. If the tensile modulus (M) is too high, the tensile elongation at break tends to decrease. Therefore, from the viewpoint of easily achieving both the tensile modulus (M) and the tensile elongation at break, the tensile modulus (M) may be 40 GPa or less, 30 GPa or less, or 20 GPa or less. From the viewpoint of easily obtaining a molded product having good mechanical properties when the regenerated cellulose fiber according to the first embodiment is used for a fiber-reinforced resin composition, the tensile modulus (M) of the regenerated cellulose fiber may be 10 to 40 GPa, 15 to 30 GPa, 16 to 20 GPa, or 16 GPa or more but less than 20 GPa. The tensile modulus (M) of the regenerated cellulose fiber monofilament can be measured by the following method.

[0019] (Method for measuring tensile modulus (M)) The tensile modulus (M) of a monofilament of regenerated cellulose fiber is measured in accordance with JIS L1015. Specifically, a single fiber is taken out of the monofilament or multifilament to be measured to form a monofilament, and then a tensile test is carried out at a temperature of 20°C and a relative humidity of 65% using an automatic single-fiber fineness meter and a strength and elongation meter (e.g., manufactured by Lenzing Instruments / Austria, product names "Vibroskop Micro and Vibrodyn 500") at a chuck distance of 20 mm and a tensile speed of 20 mm / min to measure the tensile modulus. The test is carried out 15 or more times, and the average value is calculated, and the value rounded to one decimal place is used as the tensile modulus (M).

[0020] <Tensile Breaking Strength (S) of Monofilament> In one embodiment, the tensile breaking strength (S) of the regenerated cellulose fiber monofilament is preferably within a range that satisfies the relationship of the above formula (1). In one embodiment, the tensile breaking strength (S) may be 1.1 to 10.0 cN / dtex, 3.0 to 7.0 cN / dtex, or 4.8 to 5.5 cN / dtex. The tensile breaking strength (S) of the regenerated cellulose fiber monofilament can be measured by the following method.

[0021] (Method for measuring tensile breaking strength (S)) The tensile breaking strength (S) of a monofilament of regenerated cellulose fiber is measured in accordance with JIS L1015. Specifically, a single fiber is taken from the monofilament or multifilament to be measured to form a monofilament, and then a tensile test is carried out under conditions of a temperature of 20°C and a relative humidity of 65% using an automatic single-fiber fineness measuring device and a strength and elongation measuring device (e.g., manufactured by Lenzing Instruments / Austria, product names "Vibroskop Micro" and "Vibrodyn 500") at a chuck distance of 20 mm and a pulling speed of 20 mm / min. In this tensile test, the load (tensile breaking strength) at which the monofilament breaks (breaks) is measured. The test is carried out 15 or more times, and the average value is calculated, and the value rounded to one decimal place is used as the tensile breaking strength (S).

[0022] In one embodiment, the regenerated cellulose fiber preferably satisfies the following formula (2): 43≧M / S －０．２ ... (2) (In formula (2), M represents the tensile modulus (M) (GPa), and S represents the tensile breaking strength (S) (cN / dtex). When regenerated cellulose fibers satisfy formula (2), they tend to have good tensile breaking elongation. －０．２ may be 1 to 43, or may be 1 to 40. In one embodiment, M / S －０．２ may be 19 to 32, or may be 19 to 30.

[0023] <Monofilament Fineness> The fineness of the monofilament of the regenerated cellulose fiber can be adjusted as desired within a range that achieves the above-described tensile breaking elongation and toughness. In one embodiment, the monofilament fineness may be 0.1 to 30 dtex, 1 to 20 dtex, or 1 to 10 dtex. Note that when preparing the regenerated cellulose fiber of the first embodiment using the production method of the third embodiment described below, regenerated cellulose fiber having the above-described tensile breaking elongation and toughness is easily obtained. From this perspective, the monofilament fineness is preferably 0.1 to 3 dtex, more preferably 0.2 to 3 dtex, and even more preferably 1 to 3 dtex. In one embodiment, it may be 1.5 to 3.0 dtex or 1.8 to 2.8 dtex. The fineness refers to the weight (g) per 10,000 m of monofilament length and can be measured under the following conditions. (Method for Measuring Fineness) A single fiber is taken out from the monofilament or multifilament to be measured to make a monofilament, and then the fineness is measured using an automatic single-yarn fineness measuring device (for example, manufactured by Lenzing Instruments, product name "Vibroskop Micro") in an environment of a temperature of 20°C and a relative humidity of 65%.

[0024] <Average fiber diameter of monofilaments> The fineness of the regenerated cellulose fiber monofilaments can be adjusted as desired within a range that allows the above-mentioned tensile breaking elongation and toughness to be achieved. In one embodiment, the average fiber diameter of the regenerated cellulose fiber monofilaments is preferably 10 to 17 μm, more preferably 10 to 15.5 μm. The average fiber diameter can be measured from an SEM image of the cross section of the monofilament, but it may also be calculated from the fineness of the monofilament. When calculating from the fineness, it is calculated by the following formula, assuming that the cross section of the monofilament is a perfect circle: [(fineness (dtex) ÷ density (g / cm ３ ) ÷ 10,000 ÷ 1,000,000 ÷ π) ０．５ × 1,000,000 × 2]. The density represents the density of the monofilament, and the average fiber diameter is a value calculated assuming the density is 1.5.

[0025] <Major axis length / minor axis length> In one embodiment, the ratio of the major axis length to the minor axis length (major axis length / minor axis length) in the width direction cross section of a regenerated cellulose fiber monofilament is preferably 1.2 or less, more preferably 1.1 or less. Fibers with a major axis length / minor axis length of 1.2 or less have a substantially circular or substantially elliptical cross section in the width direction. The major axis length / minor axis length of a regenerated cellulose fiber can be measured by the following method. (Method for measuring major axis length / minor axis length) Regenerated cellulose fiber is embedded in epoxy resin, and the cross section is exposed with a microtome (or a razor) to take an SEM photograph. The length of the longest part of the cross section of the monofilament in the SEM photograph is defined as the "major axis length," and the length of the longest part of the line (axis) perpendicular to the major axis is defined as the "minor axis length," and the ratio of the major axis length to the minor axis length is calculated. The same measurement is performed on 100 monofilaments in the SEM photograph, and the average value is defined as the "major axis length / minor axis length."

[0026] <Nitrogen Content> In one embodiment, the nitrogen content of the regenerated cellulose fiber is preferably 1% by mass or less, and more preferably 0.5% by mass or less. If the nitrogen content of the regenerated cellulose fiber is 1% by mass or less, the amount of residual solvent in the regenerated cellulose fiber is reduced, and the tensile breaking elongation and toughness of the monofilament are likely to be good. The nitrogen content is likely to decrease during the production of regenerated cellulose fiber by extending the filament refining process (washing) (e.g., washing for 3 hours or more). However, from the perspective of productivity, a long washing process is not preferable. From the perspective of easily achieving both productivity and various physical properties such as tensile breaking elongation, the nitrogen content of the regenerated cellulose fiber may be 0.05 to 0.3% by mass, or even 0.05 to 0.2% by mass. The nitrogen content of the regenerated cellulose fiber can be measured by the following method.

[0027] (Method for Measuring Nitrogen Content) Measurement is performed using a combustion elemental analyzer (for example, Sumika Chemical Analysis Center, Ltd., product name "SUMIGRAPH (registered trademark) NC-220F"). A blank (empty sample) and a standard substance, DL-aspartic acid, are used to create a calibration curve. First, the weight of a sample of regenerated cellulose fiber is measured. Then, the regenerated cellulose fiber is pyrolyzed and oxidized, and the nitrogen and nitrogen oxide gases in the combustion gas are reduced to nitrogen in a reduction tube and detected and quantified using a thermal conductivity detector (TCD) gas chromatograph. The quantification is calculated as the total amount of nitrogen using the calibration curve. The temperatures (units: °C) of the furnace (FURNACE) used for pyrolysis and oxidation are set as follows: NC-L (reduction temperature): 600 °C, NC-H (reaction temperature): 870 °C. The various measurement times are set as follows: PURGE: 50 minutes, PUMP: 150 minutes, MEAS.: 100 minutes. The nitrogen content is calculated from the total nitrogen amount obtained and the weight of the regenerated cellulose fiber weighed during the measurement.

[0028] The regenerated cellulose fibers according to the first embodiment may be short fibers or long fibers. Here, "short fibers" refer to "long fibers" cut to an appropriate length, and are generally called "staple," "staple fiber," "staple staple," etc., with the length and thickness of the fibers being set according to the intended use. "Long fibers" refer to continuous fibers before cutting, and are called "filaments," etc. As with "short fibers," the length and thickness of the fibers are set according to the intended use. The regenerated cellulose fibers according to the first embodiment can be in the form of short fibers and / or long fibers depending on the intended use.

[0029] <Applications> The applications of the regenerated cellulose fibers according to the first embodiment are not particularly limited, and they can be used for a variety of applications. The regenerated cellulose fibers according to the first embodiment can achieve higher tensile elongation at break and higher toughness than conventional solvent-process regenerated cellulose fibers. Such regenerated cellulose fibers can be suitably used, for example, as fibers for resin compositions, tire cords, nonwoven fabrics, paper, fabrics, and clothing. Naturally, the applications are not limited to those mentioned above.

[0030] [Article] A second embodiment of the present disclosure is an article comprising the regenerated cellulose fiber according to the first embodiment. The article according to the second embodiment preferably comprises a nonwoven fabric, paper, fabric, clothing, or tire cord comprising the regenerated cellulose fiber according to the first embodiment. The proportion of the regenerated cellulose fiber in these articles is not particularly limited, and can be any proportion depending on the desired physical properties.

[0031] [Method for producing regenerated cellulose fibers] The third embodiment of the present disclosure is a method for producing regenerated cellulose fibers. ２ The third embodiment relates to a novel method for producing regenerated cellulose fibers using a solvent, the method comprising: spinning a spinning solution prepared by dissolving raw cellulose having an average degree of polymerization of 200 to 3000 in the solvent, by a wet spinning method or a dry-wet spinning method at a draft ratio (take-up speed / linear discharge speed of the spinning solution) of 20 or less, to obtain regenerated cellulose fibers having a monofilament fineness of 0.1 to 3 dtex. The production method according to the third embodiment relates to a method for producing regenerated cellulose fibers using a CS ２ Since this manufacturing method does not use any additives, it has a low environmental impact. Furthermore, this manufacturing method can produce regenerated cellulose fibers with higher tensile elongation at break and higher toughness than conventional methods. Preferably, the third embodiment is the method for producing regenerated cellulose fibers according to the first embodiment.

[0032] <Wet spinning method or dry wet spinning method> The production method according to the third embodiment includes spinning by a wet spinning method or a dry wet spinning method. The spinning method of the wet spinning method or the dry wet spinning method is not particularly limited, and known methods can be used. The wet spinning method is a method including discharging a spinning solution from a nozzle in a coagulation liquid to prepare a thread. The dry wet spinning method is a method including discharging a spinning solution from a nozzle into the atmosphere, and then introducing the spinning solution into a coagulation liquid to coagulate the spinning solution to prepare a thread. The production method according to the third embodiment is the above-mentioned wet spinning method or dry wet spinning method, and preferably includes a spinning step and a refining / drying step. Hereinafter, a method including a spinning step and a refining / drying step will be described.

[0033] <Spinning step> The spinning step is preferably a step of preparing threads by extruding a spinning solution, prepared by dissolving raw cellulose having an average degree of polymerization of 200 to 3,000 in a solvent, from a nozzle and bringing the spinning solution into contact with a coagulation liquid to coagulate it. The spinning step is also preferably carried out at a draft ratio of 20 or less.

[0034] (Spinning solution) The spinning solution is prepared by dissolving raw cellulose having an average degree of polymerization of 200 to 3000 in the solvent. The method for preparing the spinning solution is not particularly limited, and may include steps such as heating, cooling, stirring, shaking, concentrating, and diluting, as necessary. That is, the production method according to the third embodiment may include preparing a spinning solution before the spinning step (spinning solution preparation step). In a preferred embodiment, the spinning solution preparation step includes heating the solvent to dissolve the raw cellulose in the solvent.

[0035] The cellulose concentration in the spinning solution is not particularly limited and can be adjusted to a desired concentration as needed, and is, for example, 3 to 20% by weight, preferably 7 to 16% by weight, and more preferably 10 to 13% by weight.

[0036] (Raw Cellulose) The raw cellulose is a raw material containing cellulose, from which spinnable threads can be obtained by the aforementioned wet spinning method or dry-wet spinning method, and is not particularly limited as long as it has an average degree of polymerization of 200 to 3000. The raw cellulose may be an unprocessed cellulose raw material derived from natural plants such as wood, cotton, or hemp, or a processed cellulose raw material derived from plants such as pulp or paper, or may be a regenerated cellulose fiber such as rayon, lyocell, or solvent-processed cellulose. Clothing, fabrics, yarn, etc. made from these may be reused as raw cellulose, and any form such as fiber, powder, bulk, liquid, or slurry may be used. The properties of the raw cellulose can be appropriately selected depending on the application of the regenerated cellulose fiber. For example, cellulose fibers made of monofilaments having any desired fineness may be used as raw cellulose.

[0037] The average degree of polymerization of the starting cellulose is preferably 400 to 2500, more preferably 500 to 2000, and even more preferably 600 to 1300. If the average degree of polymerization is too low (less than 200), the physical properties of the fiber (tensile strength at break, tensile modulus, toughness, tensile elongation at break, etc.) will be insufficient, while if the average degree of polymerization is too high (more than 3000), spinnability will be poor. By using a starting cellulose having an average degree of polymerization within the above range, it is possible to achieve both the physical properties of the fiber and spinnability.

[0038] (Solvent) As the solvent for dissolving the starting cellulose, the above-mentioned N-methylmorpholine-N-oxide (NMMO) or an ionic liquid can be used. Here, "ionic liquid" refers to a liquid salt consisting only of ions that has a melting point of 100°C or less, and refers to a salt in which the cation moiety and / or the anion moiety are composed of organic ions. In the production method according to the third embodiment, it is preferable to use an ionic liquid as the solvent. The ionic liquid will be described in detail below.

[0039] Ionic liquids are composed of a cation moiety and an anion moiety. The cation moiety of an ionic liquid is not particularly limited, and any cation moiety generally known as a cation moiety of an ionic liquid can be used. In a preferred embodiment, the cation moiety includes a nitrogen-containing aromatic ion, an ammonium ion, or a phosphonium ion.

[0040] Examples of nitrogen-containing aromatic cations include pyridinium ions, pyridazinium ions, pyrimidinium ions, pyrazinium ions, imidazolium ions, pyrazonium ions, oxazolium ions, 1,2,3-triazolium ions, 1,2,4-triazolium ions, thiazolium ions, piperidinium ions, pyrrolidinium ions, etc. Of these, the nitrogen-containing aromatic cations are preferably imidazolium ions and pyrimidinium ions, and more preferably imidazolium ions represented by the following formula (I):

[0041] [In formula (I), R ６ ~R ７are each independently an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, and R ８ ~R １０ each independently represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.

[0042] In formula (I), the alkyl group having 1 to 10 carbon atoms may be linear, branched, or cyclic, preferably linear or branched, and more preferably linear. Specific examples of linear alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl groups. Specific examples of branched alkyl groups include 1-methylethyl, 1,1-dimethylethyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, and 4-methylpentyl groups. The cyclic alkyl group may be a monocyclic group or a polycyclic group. Specific examples include monocyclic groups such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group; and polycyclic groups such as a norbornyl group, an adamantyl group, and an isobornyl group. In one embodiment, the alkyl group preferably has 1 to 8 carbon atoms.

[0043] In formula (I), the alkenyl group having 2 to 10 carbon atoms may be linear, branched, or cyclic, preferably linear or branched, and more preferably linear. In a preferred embodiment, the alkenyl group is an alkyl group having 2 to 10 carbon atoms in which one carbon-carbon single bond is substituted with a double bond, and preferred examples include a vinyl group and an allyl group. The position of the double bond is not particularly limited. In one embodiment, the alkenyl group preferably has 2 to 8 carbon atoms.

[0044] In one embodiment, R ６ ~R ７are each independently preferably an alkyl group having 1 to 8 carbon atoms, and particularly preferably an alkyl group having 1 to 4 carbon atoms. ８ ~R １０ are each independently preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and particularly preferably a hydrogen atom. A preferred specific example of the imidazolium ion represented by formula (I) is shown in formula (II) below.

[0045] [In formula (II), R １ represents an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 4 carbon atoms, and R ２ represents a hydrogen atom or a methyl group, and R ３ represents an alkyl group having 1 to 8 carbon atoms or an alkenyl group having 2 to 8 carbon atoms.]

[0046] Specific preferred examples of the imidazolium ion represented by formula (II) are shown as formulas (IIII) to (V) below. Of the imidazolium ions represented by formulas (III) to (V) below, those containing formula (IV) are particularly preferred.

[0047]

[0048]

[0049]

[0050] The phosphonium ion has P ＋ There are no particular limitations on the compounds as long as they have the general formula "(R) ４ P ＋ (wherein the multiple R's are each independently a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms.) The hydrocarbon group having 1 to 30 carbon atoms may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group.

[0051] The aliphatic hydrocarbon group is preferably a saturated hydrocarbon group (alkyl group), and the alkyl group may be linear, branched, or cyclic. The linear alkyl group preferably has 1 to 20 carbon atoms, and more preferably has 1 to 16 carbon atoms. Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, and a hexadecyl group.

[0052] The branched alkyl group has 3 to 30 carbon atoms, preferably 3 to 20 carbon atoms, and more preferably 3 to 16 carbon atoms. Specific examples include a 1-methylethyl group, a 1,1-dimethylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1,1-dimethylpropyl group, a 2,2-dimethylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, and a 4-methylpentyl group.

[0053] The cyclic alkyl group has 3 to 30 carbon atoms, preferably 3 to 20 carbon atoms, and more preferably 3 to 16 carbon atoms, and may be a monocyclic group or a polycyclic group. Specific examples include monocyclic groups such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group, and polycyclic groups such as a norbornyl group, an adamantyl group, and an isobornyl group.

[0054] The aromatic hydrocarbon group preferably has 6 to 30 carbon atoms, and specific examples thereof include allyl groups such as a phenyl group, a 1-naphthyl group, a 2-naphthyl group, a biphenyl group, and a tolyl group, and allylalkyl groups such as a benzyl group, a phenethyl group, a naphthylmethyl group, and a naphthylethyl group.

[0055] In one embodiment, the phosphonium ion is preferably a cation represented by the following formula (VI):

[0056] [In formula (VI), R １１ ~R１４ each independently represents an alkyl group having 1 to 16 carbon atoms.

[0057] In formula (VI), the alkyl group having 1 to 16 carbon atoms may be any of linear, branched, and cyclic, and is preferably linear or branched, and more preferably linear. Here, examples of the linear, branched, and cyclic alkyl group include the same as those described above. １１ ~R １４ may be the same or different, but for ease of availability, R １１ ~R １４ It is preferred that three or more of the above are the same substituent.

[0058] In one embodiment, R in formula (VI) １１ ~R １４ The alkyl group is preferably a linear or branched alkyl group having 1 to 14 carbon atoms, more preferably a linear or branched alkyl group having 1 to 10 carbon atoms, still more preferably a linear or branched alkyl group having 1 to 8 carbon atoms, and particularly preferably a linear or branched alkyl group having 1 to 4 carbon atoms. A preferred example of the cation represented by formula (VI) is shown in the following formula (VII).

[0059]

[0060] In one embodiment, the cation moiety of the ionic liquid is preferably one or more selected from an imidazolium ion, a pyridinium ion, an ammonium ion, and a phosphonium ion, and more preferably includes an imidazolium ion. In a particularly preferred embodiment, the cation moiety is an imidazolium ion.

[0061] Examples of the anion moiety include halogen ions, carboxylate ions, phosphinate ions, phosphate ions, and phosphonate ions. Examples of halogen ions include chloride ions, bromide ions, and iodide ions, with chloride ions being preferred. Examples of carboxylate ions include formate ions, acetate ions, propionate ions, butyrate ions, hexanoate ions, maleate ions, fumarate ions, oxalate ions, lectate ions, and pyruvate ions, with formate ions, acetate ions, and propionate ions being preferred.

[0062] The anion moiety containing a phosphorus atom is preferably an ion represented by the following formula (VIII).

[0063] [In formula (VIII), X １ and X ２ each independently represents a hydrogen atom, a hydroxyl group, or an alkoxy group having 1 to 4 carbon atoms.

[0064] Among these, examples of the phosphate ion include those represented by the following formula (IX).

[0065] [In formula (IX), R １５ and R １６ each independently represents a hydrogen atom or an alkyl group.

[0066] In formula (XI), the alkyl group may be any of linear, branched, and cyclic, but is preferably a linear or branched alkyl group. １６ The number of carbon atoms in the alkyl group is preferably 1 to 10, more preferably 1 to 6, and even more preferably 1 to 4, and from industrial reasons, an alkyl group having 1 or 2 carbon atoms is particularly preferred. Of these phosphate ions, dimethyl phosphate ion and diethyl phosphate ion are preferred.

[0067] The phosphonate ion may be one represented by the following formula (X):

[0068] [In formula (X), R １５ is the same as formula (IX).

[0069] The phosphonate ion is preferably a methylphosphonate ion.

[0070] The phosphinate ion may be one represented by the following formula (XI):

[0071]

[0072] Other anion moieties include pseudohalogen ions, which have properties similar to those of halogen ions. Examples of pseudohalogen ions include cyanate ions, oxocyanate ions, thiocyanate ions, and selenocyanate ions.

[0073] The ionic liquid that can be used in the production method according to the third embodiment is preferably composed of the cation moiety and the anion moiety as described above. The combination of the cation moiety and the anion moiety is not particularly limited, and an ionic liquid that can suitably dissolve the cellulose raw material can be appropriately selected.

[0074] A preferred ionic liquid contains an imidazolium ion as the cation moiety. Preferred embodiments of the ionic liquid containing an imidazolium ion include, for example, 1-allyl-3-methylimidazolium chloride (AmimCl), 1-ethyl-3-methylimidazolium acetate (C ２ mimAc), 1-ethyl-3-methylimidazolium diethyl phosphate (C ２ mimDEP), 1-ethyl-3-methylimidazolium methylphosphonate (C ２ mimMEP), 1-ethyl-3-methylimidazolium phosphinate (C ２ mimHPO), 1-butyl-3-methylimidazolium acetate (C ４ mimAc), or 1-butyl-3-methylimidazolium chloride (C ４Among these, imidazolium salts containing an imidazolium ion and a halogen ion as the anion moiety are more preferred. A preferred imidazolium salt is imidazolium chloride, and particularly preferred is 1-butyl-3-methylimidazolium chloride (C ４ mimCl).

[0075] (Draft Ratio) In the production method according to the third embodiment, spinning is performed at a draft ratio of 20 or less. Here, the "draft ratio" is a spinning index defined by the relationship between the discharge speed (discharge linear velocity) of the spinning solution extruded from the nozzle and the take-up speed, and is expressed as the take-up speed / discharge linear velocity. A draft ratio of 20 or less allows the preparation of regenerated cellulose fibers with a monofilament tensile elongation at break of 8% or more and a toughness of 25 MPa or more. This is presumably because a draft ratio of 20 or less prevents the crystalline orientation of the fiber structure from becoming too high. Note that, when a yarn is prepared with a draft ratio set to less than 1, slack occurs in the yarn, making spinning difficult. Therefore, the lower limit of the draft ratio is essentially 1. In one embodiment, the draft ratio is preferably 1 to 10, more preferably 1 to 10 and even more preferably 1 to 6. According to the production method according to this embodiment, by setting the draft ratio to less than 10, more preferably 6 or less, regenerated cellulose fibers with both high break elongation and high toughness can be more easily obtained.

[0076] The linear discharge velocity and take-up velocity of the spinning solution are adjusted so that the draft ratio is not more than 20. In one embodiment, the take-up velocity is preferably 30 to 1000 m / min, more preferably 80 to 1000 m / min, and even more preferably 100 to 1000 m / min. The linear discharge velocity is set based on the draft ratio and the take-up velocity.

[0077] (Coagulation liquid) As the coagulation liquid, water, a lower alcohol, a polar solvent, a non-polar solvent, etc. can be used. The coagulation liquid may also contain a solvent such as an ionic liquid. From the viewpoint of reducing the environmental load, it is preferable that the coagulation liquid contains water.

[0078] In one embodiment, the temperature of the coagulation liquid is preferably 25° C. or less, and more preferably 15° C. or less. If the temperature of the coagulation liquid is 25° C. or less, the yarn is less likely to break, and stable spinning is facilitated.

[0079] In one embodiment, the concentration of the coagulation liquid is preferably 0 to 25% by weight from the viewpoint of equipment and shortening the coagulation time (i.e., the time from contact of the yarn with the coagulation liquid to completion of coagulation). Here, the "concentration of the coagulation liquid" refers to the concentration of the ionic liquid contained in the coagulation liquid.

[0080] In one embodiment, the coagulation liquid may be a fluidized bath, where "fluidized bath" refers to a coagulation liquid that is not stationary but flows in the direction of travel of the yarn.

[0081] In one embodiment, where Vf is the take-up speed of the yarn in the fluidized bath and VL is the flow speed of the coagulation liquid at the outlet of the fluidized bath, the spinning may be carried out so as to satisfy the following formula (3): Vf - VL < 160 m / min (provided that VL ≦ Vf) (3) When formula (3) is satisfied, spinning is easily performed by a conventional wet spinning method or dry wet spinning method without the need for a special modified cross-section nozzle. If Vf - VL is less than 160 m / min, a normal microstructure of the fiber structure is easily formed, the cross-sectional shape is less likely to be modified, and the breaking strength is less likely to decrease. Furthermore, if VL ≦ Vf, the yarn in the coagulation liquid is less likely to break.

[0082] In the spinning process, the thread is prepared so that the final regenerated cellulose fiber monofilament fineness is 0.1 to 3 dtex. The monofilament fineness is preferably 0.2 to 3 dtex, and more preferably 1 to 3 dtex. By preparing the thread so that the monofilament fineness is 0.1 to 3 dtex, it is possible to obtain regenerated cellulose fibers having a monofilament tensile breaking elongation of 8% or more and a toughness of 25 MPa or more. Furthermore, if the monofilament fineness is 3 dtex or less, the amount of solvent residues, etc., in the thread and regenerated cellulose fiber described below is likely to be reduced without reducing productivity.

[0083] In one embodiment, the diameter of the nozzle for discharging the spinning solution is preferably 0.05 mm or more and 1.0 mm or less, and more preferably 0.1 to 0.3 mm.

[0084] In one embodiment, when spinning a yarn at high speed, it is preferable to heat the spinning solution from the viewpoint of easily suppressing the occurrence of unstable flow (i.e., fracture) on the spinning line and stabilizing spinnability. By heating the spinning solution to a high temperature and spinning it, the fluidity of the spinning solution is improved, making it easier to effectively align cellulose molecules and adjust the crystal orientation to an appropriate level. As a result, it is easier to obtain regenerated cellulose fibers with improved monofilament toughness, tensile breaking strength (S), and tensile breaking elongation. In one embodiment, the temperature of the spinning solution is preferably 80 to 160°C, more preferably 90 to 160°C, and even more preferably 100 to 160°C. In one embodiment, the temperature of the spinning solution may be greater than 130°C and equal to or less than 160°C.

[0085] <Refining and Drying Process> The refining and drying process is preferably a process of washing and drying the yarn prepared in the spinning process. In one embodiment, the refining and drying processes can be performed using conventional techniques used in wet spinning or dry-wet spinning. In a preferred embodiment, the refining process is preferably adjusted so that the nitrogen content in the final regenerated cellulose fibers is 1% by mass or less, more preferably 0.05 to 0.7% by mass, and even more preferably 0.05 to 0.3% by mass. By performing the refining process so that the nitrogen content falls within the above range, it is easy to achieve both the tensile elongation at break and the toughness of the regenerated cellulose fibers. From the above perspective, the refining process may be performed for 10 minutes to 1 hour, for 10 to 50 minutes, or for 10 to 30 minutes. The drying process time (drying time) is not particularly limited, but is preferably performed until the moisture content of the final regenerated cellulose fibers reaches the official moisture content. The method for recovering the regenerated cellulose fibers after drying is not particularly limited, and known methods such as winding the fibers onto a thread pipe or bobbin can be used.

[0086] A non-limiting list of exemplary embodiments and combinations of exemplary embodiments of the present disclosure is set forth below: [1] CS ２ A regenerated cellulose fiber that does not contain , and has a tensile breaking elongation of the monofilament of 8% or more and a toughness of 25 MPa or more. [2] The regenerated cellulose fiber according to [1], which satisfies the following formula (1): 8≧M−5.29S (1) (In formula (1), M represents the tensile modulus of elasticity (GPa) of the monofilament, and S represents the tensile breaking strength (cN / dtex) of the monofilament.) [3] The regenerated cellulose fiber according to [1] or [2], which is a long fiber or a short fiber. [4] The regenerated cellulose fiber according to any of [1] to [3], which is for use in a resin composition. [5] An article comprising the regenerated cellulose fiber according to any of [1] to [4]. [6] The article according to [5], which comprises a nonwoven fabric, paper, fabric, clothing, or tire cord. [7] A method for producing regenerated cellulose fibers using a solvent, the method comprising: dissolving raw cellulose having an average degree of polymerization of 200 to 3000 in the solvent, and spinning a spinning solution using a wet spinning method or a dry spinning method at a draft ratio (take-up speed / linear extrusion speed of the spinning solution) of 20 or less to obtain regenerated cellulose fibers having a monofilament fineness of 0.1 to 3 dtex. [8] The method for producing regenerated cellulose fibers according to [7], wherein the solvent contains imidazolium ions. [9] The method for producing regenerated cellulose fibers according to [7] or [8], wherein the take-up speed is 30 to 1000 m / min.

[10] The method for producing regenerated cellulose fibers according to any of [7] to [9], wherein the temperature of the spinning solution is 80 to 160°C.

[0087] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following description.

[0088] Example 1 Raw cellulose (pulp, degree of polymerization 1180, manufactured by Georgia-Pacific) was added to an aqueous solution (solvent) containing an imidazolium salt (1-butyl-3-methylimidazolium chloride (ionic liquid)), and the mixture was mixed at 140°C to prepare a spinning solution (raw cellulose concentration: 11%). The spinning solution was discharged from a nozzle (nozzle diameter: 0.1 mm) at a take-up speed of 100 m / min and coagulated by contact with a coagulation solution (water containing the imidazolium salt). The resulting mixture was then refined (washed with water for approximately 1 hour) and dried (hot air dried), after which it was taken up to prepare regenerated cellulose fibers. The draft ratio (take-up speed / extrusion linear velocity) was 5.9. The resulting regenerated cellulose fiber monofilament had a fineness of 1.98 dtex. The tensile breaking elongation, toughness, tensile modulus (M), tensile breaking strength (S), average fiber diameter, and nitrogen content of the regenerated cellulose fibers were measured under the following conditions. The results are shown in Table 1.

[0089] <Measurement of tensile breaking elongation, tensile modulus (M), and tensile breaking strength (S)> The tensile breaking elongation, tensile modulus (M), and tensile breaking strength (S) of regenerated cellulose fiber monofilaments were measured in accordance with JIS L 1015. Specifically, a single fiber was taken out of the monofilament or the multifilament to be measured to form a monofilament, and then a tensile test was carried out under conditions of a temperature of 20°C and a relative humidity of 65% using an automatic single-fiber fineness measuring instrument and a strength and elongation measuring instrument (manufactured by Lenzing Instruments / Austria, product names "Vibroskop Micro" and "Vibrodyn 500") at a chuck distance of 20 mm and a pulling speed of 20 mm / min, to measure the tensile breaking elongation, tensile modulus (M), and tensile breaking strength (S). The test was carried out 15 or more times, and the average value was calculated, and the value obtained by rounding off the first decimal place was used.

[0090] <Method of measuring toughness> Using the stress-strain curve (so-called SS curve) obtained by the tensile test such as the tensile elongation at break, the toughness was calculated by determining the area enclosed by the curve from the origin to the breaking point. The area was determined by analysis using the analysis software of the tensile tester.

[0091] <Measurement of average fiber diameter> From the fineness of the monofilament, [(fineness (dtex) ÷ density (g / cm ３ ) ÷ 10,000 ÷ 1,000,000 ÷ π) ０．５ The average fiber diameter was calculated as follows: [×1,000,000×2]. The density was calculated as 1.5.

[0092] <Measurement of Nitrogen Content> Measurement was performed using a combustion method elemental analyzer (manufactured by Sumika Chemical Analysis Center, Ltd., product name "SUMIGRAPH (registered trademark) NC-220F"). A blank (empty sample) and a standard substance, DL-aspartic acid, were used to create a calibration curve. First, the weight of a regenerated cellulose fiber sample was measured. The fiber was then pyrolyzed and oxidized, and the nitrogen and nitrogen oxide gases in the combustion gas were reduced to nitrogen in a reduction tube and detected and quantified using a thermal conductivity detector (TCD) gas chromatograph. The quantification was calculated as the total amount of nitrogen using the calibration curve. The temperatures (unit: °C) of the furnace (FURNACE) used for pyrolysis and oxidation were set to NC-L (reduction temperature): 600 °C and NC-H (reaction temperature): 870 °C. The various measurement times were set to PURGE: 50 minutes, PUMP: 150 minutes, and MEAS.: 100 minutes. The nitrogen content was calculated from the total nitrogen amount obtained and the weight of the regenerated cellulose fiber weighed at the time of measurement.

[0093] [Example 2] Regenerated cellulose fibers were produced in the same manner as in Example 1, except that the temperature of the spinning solution was 150°C and the take-up speed was 200 m / min. The fineness of the resulting regenerated cellulose fibers was 2.01 dtex. The tensile breaking elongation, toughness, tensile modulus (M), tensile breaking strength (S), average fiber diameter, and nitrogen content of the regenerated cellulose fibers were measured under the same conditions as in Example 1. The results are shown in Table 1.

[0094] Comparative Example 1 Regenerated cellulose fibers were prepared in the same manner as in Example 1, except that raw cellulose with an average degree of polymerization of 630 was used, the nozzle diameter was 0.3 mm, and the draft ratio was 47.9. The monofilament fineness of the resulting regenerated cellulose fibers was 1.92 dtex. The tensile breaking elongation, toughness, tensile modulus (M), tensile breaking strength (S), average fiber diameter, and nitrogen content of the regenerated cellulose fibers were measured under the same conditions as in Example 1. The results are shown in Table 1.

[0095] Reference Example 1: Solvent-process regenerated cellulose fiber (BioMid Fiber). Reference Example 2: Viscose-process regenerated cellulose fiber (viscose rayon (product name "CR500TEX"), manufactured by Kodenka Corporation).

[0096]

[0097] As shown in Table 1, the regenerated cellulose fibers of Examples 1 and 2 achieved higher tensile elongation at break than the conventional solvent-process regenerated cellulose fiber (Reference Example 1), and also had higher toughness. It was also confirmed that the manufacturing method according to the third embodiment makes it possible to prepare regenerated cellulose fibers that achieve both high tensile elongation at break and high toughness. Regenerated cellulose fibers and manufacturing methods for regenerated cellulose fibers that can achieve such physical properties are not known, and these are novel fibers and manufacturing methods. In each example in Table 1, 1-butyl-3-methylimidazolium chloride (C ４ However, it is presumed that similar results would be obtained even if other imidazolium ions were included as the cation moiety.

[0098] The regenerated cellulose fiber according to the first embodiment is a novel fiber that can achieve higher breaking elongation and toughness than conventional solvent-process regenerated cellulose fibers, and can therefore be suitably used as a fiber for resin compositions, tire cords, nonwoven fabrics, paper, fabrics, and clothing.

Claims

1. CS ２ The regenerated cellulose fiber does not contain cellulose, and the tensile breaking elongation of the monofilament is 8% or more and the toughness is 25 MPa or more.

2. The regenerated cellulose fiber according to claim 1, which satisfies the following formula (1): 8≧M−5.29S (1) (In formula (1), M represents the tensile modulus (GPa) of the monofilament, and S represents the tensile breaking strength (cN / dtex) of the monofilament.) 3. Regenerated cellulose fibers according to claim 1 or 2, which are long or short fibers.

4. Regenerated cellulose fibers according to claim 1 or 2, which are for use in resin compositions.

5. An article comprising the regenerated cellulose fibers according to claim 1 or 2.

6. The article of claim 5, comprising a nonwoven fabric, paper, fabric, clothing, or tire cord.

7. A method for producing regenerated cellulose fibers using a solvent, the method comprising: spinning a spinning solution prepared by dissolving raw material cellulose having an average degree of polymerization of 200 to 3000 in the solvent, using a wet spinning method or a dry wet spinning method at a draft ratio (take-up speed / linear discharge speed of the spinning solution) of 20 or less, to obtain regenerated cellulose fibers having a monofilament fineness of 0.1 to 3 dtex.

8. The method for producing regenerated cellulose fibers according to claim 7, wherein the solvent contains imidazolium ions.

9. The method for producing regenerated cellulose fibers according to claim 7 or 8, wherein the take-up speed is 30 to 1000 m / min.

10. The method for producing regenerated cellulose fibers according to claim 7 or 8, wherein the temperature of the spinning solution is 80 to 160°C.

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