Cellulose fiber manufacturing method

Abstract

To provide a method for producing cellulose fibers that can produce high-strength regenerated cellulose fibers. [Solution] A method for producing cellulose fibers, characterized by comprising: a dissolution step of dissolving cellulose in a tetraalkylammonium hydroxide solution at a temperature of less than 45°C to produce a solution; and a spinning step of extruding the solution produced in the dissolution step into a coagulation solution at a temperature of less than 15°C to spin the fibers. Furthermore, it is preferable that the content of tetraalkylammonium hydroxide in the tetraalkylammonium hydroxide solution is 50% by mass or more and 60% by mass or less, and the content of water in the tetraalkylammonium hydroxide solution is 40% by mass or more and 50% by mass or less.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing cellulose fibers.

Background Art

[0002] A technique for chemically regenerating natural cellulose existing in nature, such as wood, to produce regenerated cellulose fibers is known. For example, Patent Document 1 discloses that cellulose as a raw material is dissolved using a solution containing tetraalkylammonium hydroxide. By discharging the cellulose-dissolved solution into a coagulation liquid, regenerated cellulose fibers can be produced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, conventionally, sufficient consideration has not been given to the conditions for producing regenerated cellulose fibers, and the strength of the obtained regenerated cellulose fibers has been insufficient.

Means for Solving the Problems

[0005] The method for manufacturing cellulose fibers according to an application example of the present invention includes a dissolution step of dissolving cellulose in a tetraalkylammonium hydroxide solution at a temperature lower than 45°C to produce a solution, and a spinning step of discharging and spinning the solution produced in the dissolution step into a coagulation liquid at a temperature lower than 15°C.

[0006] The method for manufacturing cellulose fibers according to an application example of the present invention includes a dissolution step of dissolving cellulose in a tetraalkylammonium hydroxide solution at a temperature lower than 30°C to produce a solution, The process includes a spinning step in which the dissolved solution produced in the dissolution step is extruded into a coagulation solution at a temperature of less than 20°C and spun. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram showing a cellulose fiber manufacturing apparatus that carries out the cellulose fiber manufacturing method according to the first embodiment of the present invention. [Figure 2] Figure 2 is a flowchart of a cellulose fiber manufacturing method according to the first embodiment of the present invention. [Figure 3] Figure 3 is a flowchart of a cellulose fiber production method according to a second embodiment of the present invention. [Figure 4] Figure 4 is a table summarizing the manufacturing conditions and evaluation results for each example and comparative example. [Modes for carrying out the invention]

[0008] The cellulose fiber manufacturing method of the present invention will be described in detail below based on preferred embodiments shown in the attached drawings.

[0009] <First Embodiment> Figure 1 is a schematic diagram showing a cellulose fiber manufacturing apparatus for carrying out the cellulose fiber manufacturing method according to the first embodiment of the present invention. Figure 2 is a flowchart of the cellulose fiber manufacturing method according to the first embodiment of the present invention.

[0010] [Cellulose fiber manufacturing apparatus, cellulose fiber manufacturing method] As shown in Figure 1, the cellulose fiber manufacturing apparatus 1 comprises a raw material supply unit 2 for supplying raw materials, a dissolution unit 3, a spinning unit 4, and a control unit (not shown), and is an apparatus for producing regenerated cellulose M5 by dissolving and solidifying cellulose as a raw material. The operation of the raw material supply unit 2, the dissolution unit 3, and the spinning unit 4 is controlled by the control unit (not shown). Furthermore, as shown in Figure 2, the cellulose fiber manufacturing method comprises a raw material supply step, a dissolution step, and a spinning step. Each part and each step will be described in detail below.

[0011] [1] Raw material supply department, raw material supply process The raw material supply unit 2 is the part that performs the raw material supply process, which supplies the solid raw material M1 to the dissolution unit 3. Although not shown in the figures, the raw material supply unit 2 includes, for example, a raw material storage unit for storing cellulose, a dispensing unit for dispensing cellulose, a weighing unit for weighing cellulose, and so on.

[0012] [1-1] Cellulose Raw material M1 contains cellulose.

[0013] Cellulose is a readily available material with high theoretical strength. The type of cellulose used is not particularly limited; for example, natural celluloses such as animal cellulose and plant cellulose can be used.

[0014] In particular, plant cellulose, especially that produced by crushing cotton, is preferred. This allows for more efficient dissolution of cellulose during the dissolution process, and more effectively increases the strength of regenerated cellulose M5. It also improves the feel and breathability of products using regenerated cellulose M5.

[0015] Furthermore, the cellulose may be treated with, for example, ultraviolet irradiation, ozone treatment, or plasma treatment.

[0016] The average fiber length (length-length weighted average) of cellulose is not particularly limited, but is preferably 0.05 mm or more and 50 mm or less, and more preferably 0.1 mm or more and 5.0 mm or less. This allows for more efficient dissolution of cellulose in the dissolution process.

[0017] The average width (average diameter) of the cellulose fibers is not particularly limited, but is preferably 0.5 μm to 200 μm, and more preferably 1.0 μm to 100 μm. This allows for more efficient dissolution of cellulose in the dissolution process.

[0018] The raw material may contain substances other than the above-mentioned cellulose. Substances other than cellulose are not particularly limited, and examples thereof include hemicellulose, which is a component of natural cotton origin.

[0019] Also, the form of cellulose supplied to the dissolution section 3 is not particularly limited, and for example, it may be in powder form, cotton form, or sheet form. Thereby, the dissolution of cellulose in the dissolution step can be carried out more efficiently.

[0020] When the cellulose is produced by pulverizing cotton, the average fiber length is preferably less than 2.0 mm, and more preferably less than 1.0 mm. Thereby, the dissolution of cellulose in the dissolution step can be carried out more efficiently, and the strength and quality of the obtained regenerated cellulose M5 can be more effectively improved.

[0021] Note that the raw material M1 may be obtained from substances other than cotton, such as paper like waste paper and recycled paper, or cloth.

[0022] [2] Dissolution section, dissolution step The dissolution section 3 is a part that executes a dissolution step of dissolving the raw material M1 supplied from the raw material supply section 2 in the tetraalkylammonium hydroxide solution M2 to generate a solution M3.

[0023] Although not shown in the figure, the dissolution section 3 has, for example, a dissolution tank that stores the tetraalkylammonium hydroxide solution M2 and dissolves cellulose, a delivery section that delivers the solution M3 in the dissolution tank, a metering section, etc. The dissolution tank preferably has a stirring function. Thereby, the dissolution of cellulose can be carried out efficiently. Also, the dissolution tank preferably has a function of removing bubbles. Thereby, the forming accuracy of the regenerated cellulose M5 in the spinning step described later can be improved.

[0024] Furthermore, the dissolution tank is equipped with a temperature sensor, a temperature control unit, etc. (not shown), and is controlled to ensure that the tetraalkylammonium hydroxide solution M2 remains constant at a temperature described later.

[0025] [2-1] Tetraalkylammonium hydroxide solution Tetraalkylammonium hydroxide solution M2 is a solution used to dissolve cellulose and produce dissolution M3, and is a solution containing at least tetraalkylammonium hydroxide.

[0026] [2-1-1] Tetraalkylammonium hydroxide Tetraalkylammonium hydroxide is not particularly limited and includes tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, methyltripropylammonium hydroxide, methyltributylammonium hydroxide, ethyltripropylammonium hydroxide, ethyltributylammonium hydroxide, propyltributylammonium hydroxide, dimethyldipropylammonium hydroxide, dimethyldibutylammonium hydroxide, diethyldipropylammonium hydroxide, and diethyldibutylammonium hydroxide. More preferably, examples include tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH). One or more selected from these can be used in combination.

[0027] In particular, tetraalkylammonium hydroxide is preferably tetrabutylammonium hydroxide. This allows for efficient dissolution of cellulose.

[0028] The content of tetraalkylammonium hydroxide in the tetraalkylammonium hydroxide solution M2 is not particularly limited, but is preferably 50% to 60% by mass, and more preferably 53% to 58% by mass. This allows for more efficient dissolution of cellulose and more effectively improves the strength and molding accuracy of the regenerated cellulose M5. If the content of tetraalkylammonium hydroxide is too high, the molding accuracy of the regenerated cellulose M5 may decrease in the spinning process described later. On the other hand, if the content of tetraalkylammonium hydroxide is too low, it may take a relatively long time to dissolve the cellulose.

[0029] [2-1-2]Water The tetraalkylammonium hydroxide solution M2 preferably contains water. This allows for inexpensive and easy adjustment of the concentration of the tetraalkylammonium hydroxide solution M2.

[0030] When the tetraalkylammonium hydroxide solution M2 contains water, the water content in the tetraalkylammonium hydroxide solution M2 is not particularly limited, but is preferably 40% to 50% by mass, and more preferably 43% to 48% by mass. This allows for more efficient dissolution of cellulose and more effectively improves the strength and molding accuracy of the regenerated cellulose M5. If the water content is too high, the tetraalkylammonium hydroxide content tends to decrease, which may result in a relatively long time being required to dissolve the cellulose. On the other hand, if the water content is too low, the tetraalkylammonium hydroxide content tends to increase, which may reduce the molding accuracy of the regenerated cellulose M5 in the spinning process described later.

[0031] In particular, it is preferable that the tetraalkylammonium hydroxide content in the tetraalkylammonium hydroxide solution M2 is 50% to 60% by mass, and the water content in the tetraalkylammonium hydroxide solution M2 is 40% to 50% by mass. This allows for more efficient dissolution of cellulose, and more effectively improves the strength and molding accuracy of the regenerated cellulose M5.

[0032] Furthermore, the tetraalkylammonium hydroxide solution M2 may contain dimethyl sulfoxide, alcohol, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, pyridine, etc.

[0033] [2-1-3]Urea The tetraalkylammonium hydroxide solution M2 may contain urea.

[0034] When the tetraalkylammonium hydroxide solution M2 contains urea, the urea content in the tetraalkylammonium hydroxide solution M2 is preferably less than 5% by mass, and more preferably less than 4% by mass. This improves the water retention capacity of the resulting regenerated cellulose M5.

[0035] Thus, the tetraalkylammonium hydroxide solution M2 may contain urea, and it is preferable that the urea content in the tetraalkylammonium hydroxide solution M2 is less than 5% by mass. This allows for more efficient dissolution of cellulose and improves the quality of the regenerated cellulose M5.

[0036] [2-1-4] Other ingredients The tetraalkylammonium hydroxide solution M2 may contain other components besides those mentioned above. These other components are not particularly limited and include viscosity modifiers, colorants, and the like.

[0037] [2-2]Dissolution conditions The temperature of the tetraalkylammonium hydroxide solution M2 used to dissolve cellulose is set to less than 45°C. This allows for a sufficient increase in the strength of the regenerated cellulose S5 without excessively altering the cellulose. In this embodiment, if the temperature of the tetraalkylammonium hydroxide solution M2 is 45°C or higher, there is a risk of excessively altering the cellulose, which may lead to a decrease in the strength of the regenerated cellulose S5.

[0038] In this embodiment, the temperature of the tetraalkylammonium hydroxide solution M2 used to dissolve cellulose should be less than 45°C, but preferably less than 40°C, and more preferably less than 20°C. This allows for more efficient dissolution of cellulose.

[0039] The lower limit of the temperature of the tetraalkylammonium hydroxide solution M2 when dissolving cellulose is not particularly limited.

[0040] The time required to dissolve the cellulose, i.e., the duration of the dissolution process, is not particularly limited, but is preferably between 10 minutes and 24 hours, and more preferably between 1 hour and 16 hours. This allows for more efficient dissolution of the cellulose.

[0041] Furthermore, the dissolution tank is kept at atmospheric pressure. In other words, the dissolution process is carried out under atmospheric pressure. This allows for more efficient dissolution of cellulose.

[0042] [2-3]Dissolution solution The dissolution M3 is produced by dissolving cellulose in the tetraalkylammonium hydroxide solution M2. The cellulose content in the dissolution M3 is not particularly limited, but is preferably 1% to 40% by mass, and more preferably 4% to 25% by mass. This makes it possible to more effectively increase the strength of the resulting regenerated cellulose M5.

[0043] The viscosity of the dissolving solution M3 is not particularly limited, but is preferably, for example, 100 mPa·s to 600 mPa·s, and more preferably 150 mPa·s to 500 mPa·s. This makes it possible to more effectively increase the strength of the resulting regenerated cellulose M5 and to more effectively improve the molding accuracy of the regenerated cellulose M5 in the spinning process.

[0044] The viscosity of the above-mentioned dissolving solution M3 was measured, for example, using a vibrating viscometer (VISOCOMATE MODEL VM-10A series) manufactured by Sekonic Corporation at a measurement temperature of 23°C.

[0045] When the dissolution solution M3 is stored for a long period (e.g., 3 hours or more) after the dissolution process is completed and before proceeding to the spinning process, the storage temperature is preferably between 10°C and 50°C, and more preferably between 15°C and 40°C. This more effectively prevents the dissolved cellulose from precipitating or degrading. Therefore, the strength of the regenerated cellulose M5 can be more effectively increased.

[0046] [3] Spinning section, spinning process The spinning unit 4 includes a coagulation liquid storage unit 41 for storing the coagulation liquid M4, a nozzle 42 for discharging the dissolving liquid M3 into the coagulation liquid M4, and a winding unit 43 for winding up the regenerated cellulose M5 formed by the coagulation of the dissolving liquid M3 discharged from the nozzle 42 by the coagulation liquid M4.

[0047] Furthermore, the coagulation liquid reservoir 41 is equipped with a temperature sensor, a temperature control unit, etc. (not shown), and is controlled to keep the coagulation liquid M4 at a constant temperature, as described later.

[0048] Furthermore, multiple coagulation liquid storage sections 41 may be provided. In this case, it is preferable that each coagulation liquid storage section 41 stores coagulation liquid M4 with different concentrations of components.

[0049] Furthermore, although there is one nozzle 42 in the illustrated configuration, the present invention is not limited to this and may have two or more nozzles. This can increase the productivity of regenerated cellulose M5.

[0050] The opening shape of the nozzle 42 may be, for example, a circle, a triangle, a polygon such as a square, or an ellipse. In particular, when the opening shape of the nozzle 42 has a straight line, the resulting plane can accentuate the glossiness of the regenerated cellulose M5, and the design of products manufactured using regenerated cellulose M5 can be more effectively enhanced.

[0051] The opening diameter (or maximum width if not circular) of the nozzle 42 is appropriately set according to the desired thickness of the regenerated cellulose M5, but is preferably 30 mm to 100 mm, and more preferably 40 mm to 60 mm. This makes it possible to more effectively increase the strength of the regenerated cellulose M5 and to further increase the versatility when manufacturing products using the regenerated cellulose M5.

[0052] Furthermore, the spinning section 4 may be configured to circulate the coagulation liquid M4 in the coagulation liquid reservoir 41 to maintain an appropriate pH value.

[0053] [3-1]Coagulation liquid The coagulation solution M4 is not particularly limited and can include liquids containing water, ethanol, sulfuric acid, sodium sulfate, etc., but it is preferable that the coagulation solution M4 is a liquid containing sulfuric acid and sodium sulfate. This effectively suppresses fluctuations in the pH of the coagulation solution M4 when coagulating cellulose, and allows for more effective coagulation of cellulose in the dissolving solution M3.

[0054] The sulfuric acid content in the coagulation solution M4 is not particularly limited, but is preferably, for example, 0.1 mol / L or more and 5.0 mol / L or less, and more preferably 0.2 mol / L or more and 3.0 mol / L or less.

[0055] The sodium sulfate content in the coagulation solution M4 is not particularly limited, but is preferably, for example, 0.1 mol / L or more and 3.0 mol / L or less, and more preferably 0.2 mol / L or more and 2.0 mol / L or less.

[0056] By setting the content of sulfuric acid and sodium sulfate within the above numerical range, fluctuations in the pH of the coagulation solution M4 during cellulose coagulation can be more effectively suppressed.

[0057] The pH of the coagulation solution M4 is preferably greater than 0 and less than or equal to 1.0. This allows for more effective coagulation of the cellulose in the dissolving solution M3.

[0058] [3-2] Coagulation conditions The temperature of the coagulation solution M4 is set to less than 15°C. This improves the molding accuracy of the regenerated cellulose M5 and increases the strength of the resulting regenerated cellulose M5. In this embodiment, if the temperature of the coagulation solution M4 is 15°C or higher, the strength of the resulting regenerated cellulose M5 will be insufficient.

[0059] In this embodiment, the temperature of the coagulation solution M4 may be less than 15°C, but it is preferably less than 10°C, and more preferably less than 5°C. This allows for a more effective increase in the strength of the resulting regenerated cellulose M5.

[0060] The spinning process time, that is, the time from when the dissolving solution M3 is discharged from the nozzle 42 to when it becomes regenerated cellulose M5 and is withdrawn from the coagulation solution M4, is preferably between 1 second and 300 seconds, and more preferably between 10 seconds and 100 seconds. This allows for more effective coagulation of the dissolving solution M3 and more effective improvement of the strength of the regenerated cellulose M5. If the spinning process time is too short, the coagulation of the dissolving solution M3 may be insufficient, and the strength of the regenerated cellulose M5 may be insufficient. If the spinning process time is too long, further improvement in the strength of the regenerated cellulose M5 cannot be expected. Furthermore, the productivity of regenerated cellulose M5 tends to decrease.

[0061] The spinning process time can be set to a desired value by adjusting the winding speed of the winding unit 43 and the discharge speed of the dissolving solution M3 from the nozzle 42.

[0062] Furthermore, the solidification liquid storage section 41 is installed under atmospheric pressure. In other words, the solidification process is carried out under atmospheric pressure. This allows for more efficient solidification of cellulose.

[0063] By carrying out the dissolution and spinning processes under atmospheric pressure in this manner, the dissolution of cellulose in the dissolution process and the coagulation of cellulose in the spinning process can be carried out efficiently, thereby more effectively increasing the strength of regenerated cellulose M5.

[0064] The stretching ratio of regenerated cellulose M5 is not particularly limited, but is preferably between 0.5 and 5.0 times, and more preferably between 1.0 and 3.0 times. This allows for a moderate alignment of the molecular orientation of the regenerated cellulose M5, thereby more effectively increasing the strength of the regenerated cellulose M5.

[0065] [3-3] Discharge conditions The flow rate of the dissolving liquid M3 discharged from the nozzle 42 is not particularly limited, but is preferably, for example, 1.0 m / min or more and 1500 m / min or less, and more preferably 3.0 m / min or more and 1000 m / min or less. This allows for more effective coagulation of the dissolving liquid M3 and more effective enhancement of the strength of the regenerated cellulose M5.

[0066] The temperature of the dissolving solution M3 at the time of discharge is not particularly limited, but is preferably, for example, 5°C or higher and less than 50°C, and more preferably 10°C or higher and less than 45°C. This allows for more effective coagulation of the dissolving solution M3 and more effectively increases the strength of the regenerated cellulose M5.

[0067] Note that the temperature of the dissolving solution M3 at the time of discharge and the temperature of the tetraalkylammonium hydroxide solution M2 used to dissolve the cellulose may be different.

[0068] The temperature T3 (°C) of the dissolving solution M3 at the time of discharge is preferably higher than the temperature T4 (°C) of the coagulating solution M4. That is, T3 > T4 is satisfied. This allows for more effective coagulation of the dissolving solution M3, and thus more effectively increases the strength of the regenerated cellulose M5.

[0069] When the temperature T3 (°C) of the dissolving solution M3 at the time of discharge is higher than the temperature T4 (°C) of the solidifying solution M4, the temperature difference T3-T4 (°C) is not particularly limited, but is preferably between 1°C and 50°C, and more preferably between 5°C and 40°C. This allows for more effective solidification of the dissolving solution M3 and more effective enhancement of the strength of the regenerated cellulose M5. Note that T3 = T4 is also acceptable, and T4 > T3 is also acceptable.

[0070] [4] Summary of this embodiment As described above, the cellulose fiber manufacturing method in this embodiment comprises a dissolution step of dissolving cellulose, which is the raw material M1, in a tetraalkylammonium hydroxide solution M2 at a temperature of less than 45°C to produce a dissolution solution M3, and a spinning step of extruding the dissolution solution M3 produced in the dissolution step into a coagulation solution M4 at a temperature of less than 15°C to spin the fibers. Generally, when cellulose is dissolved and spun in a wet manner to regenerate it, the strength of the regenerated cellulose is insufficient. However, by performing the dissolution step and spinning step under the temperature conditions described above, the strength of the regenerated cellulose M5 can be effectively increased.

[0071] In this embodiment, even if the temperature of the tetraalkylammonium hydroxide solution M2 is below 45°C, if the temperature of the coagulation solution M4 is 15°C or higher, the regenerated cellulose M5 cannot be molded properly, and the strength of the resulting regenerated cellulose M5 will be insufficient. Furthermore, even if the temperature of the coagulation solution M4 is below 15°C, if the temperature of the tetraalkylammonium hydroxide solution M2 is 45°C or higher, the cellulose may be altered during the dissolution process, resulting in insufficient strength of the resulting regenerated cellulose M5.

[0072] Thus, by combining a tetraalkylammonium hydroxide solution M2 at a temperature of less than 45°C and a coagulation solution M4 at a temperature of less than 15°C, high-strength regenerated cellulose M5 can be obtained.

[0073] Furthermore, it is more preferable to dissolve cellulose in a tetraalkylammonium hydroxide solution M2 at a temperature below 30°C during the dissolution process to produce a dissolution solution M3, and then extrude the dissolution solution M3 into a coagulation solution M4 at a temperature below 15°C during the spinning process. This makes it possible to further effectively increase the strength of the regenerated cellulose M5.

[0074] Furthermore, it is preferable that in the dissolution step, cellulose is dissolved in a tetraalkylammonium hydroxide solution M2 at a temperature below 30°C to produce a dissolution M3, and in the spinning step, the dissolution M3 is extruded into a coagulation solution M4 at a temperature below 5°C for spinning. This makes it particularly effective to increase the strength of the regenerated cellulose M5.

[0075] <Second Embodiment> Figure 3 is a flowchart of a cellulose fiber production method according to a second embodiment of the present invention.

[0076] The second embodiment of the cellulose fiber production method of the present invention will be described below with reference to Figure 3, but the following description will focus on the differences from the first embodiment, and similar matters will be omitted.

[0077] [5] The present invention according to a second embodiment As shown in Figure 3, the cellulose fiber manufacturing method in this embodiment comprises a dissolution step of dissolving cellulose, which is the raw material M1, in a tetraalkylammonium hydroxide solution M2 at a temperature of less than 30°C to produce a dissolution solution M3, and a spinning step of extruding the dissolution solution M3 produced in the dissolution step into a coagulation solution M4 at a temperature of less than 20°C to spin the fibers. Generally, when cellulose is dissolved and spun in a wet manner to regenerate it, the strength of the regenerated cellulose is insufficient. However, by performing the dissolution step and spinning step under the above temperature conditions, the strength of the regenerated cellulose M5 can be effectively increased.

[0078] In this embodiment, even if the temperature of the tetraalkylammonium hydroxide solution M2 is below 30°C, if the temperature of the coagulation solution M4 is 20°C or higher, the regenerated cellulose M5 cannot be molded properly, and the strength of the resulting regenerated cellulose M5 will be insufficient. Furthermore, even if the temperature of the coagulation solution M4 is below 20°C, if the temperature of the tetraalkylammonium hydroxide solution M2 is 30°C or higher, the cellulose may be altered during the dissolution process, resulting in insufficient strength of the resulting regenerated cellulose M5.

[0079] Thus, by combining a tetraalkylammonium hydroxide solution M2 at a temperature of less than 30°C and a coagulation solution M4 at a temperature of less than 20°C, high-strength regenerated cellulose M5 can be obtained.

[0080] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto. [Examples]

[0081] Next, specific embodiments of the present invention will be described. [6] Preparation of raw materials, constituent materials of tetraalkylammonium hydroxide solution, and constituent materials of coagulation solution

[0082] The following materials were prepared as raw materials, constituent materials for the tetraalkylammonium hydroxide solution, and constituent materials for the coagulation solution.

[0083] Material: Cotton (plain weave, 270 count) Tetrabutylammonium hydroxide aqueous solution: (Tetrabutylammonium hydroxide aqueous solution: (SACHEM Co., Ltd. (Tetrabutylammonium hydroxide, 55% (Aqueous solution))) (referred to as "TBAH" in Table 1) Urea: (Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) ("urea" in Table 1) Sulfuric acid: (Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. (sulfuric acid)) Sodium sulfate: (Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. (Sodium Sulfate))

[0084] [7] Preparation of raw materials, tetraalkylammonium hydroxide solution and coagulation solution First, the cotton used as raw material was crushed using a mill (screen diameter φ0.5 mm).

[0085] Furthermore, 250 ml of sulfuric acid and 535 mg of sodium sulfate were dissolved in 5549 ml of water to obtain a coagulation solution. The sulfuric acid content in the obtained coagulation solution was 0.75 mol / L, and the sodium sulfate content was 0.63 mol / L.

[0086] [8] Production of regenerated cellulose (Example 1) The raw materials obtained as described above were put into the raw material supply unit 2 shown in Figure 1, the tetraalkylammonium hydroxide solution obtained as described above was put into the dissolution tank of the dissolution unit 3 shown in Figure 1, and the coagulated liquid obtained as described above was put into the coagulated liquid storage unit 41 of the spinning unit 4 shown in Figure 1.

[0087] Then, regenerated cellulose was produced by operating a cellulose fiber manufacturing apparatus under the following conditions.

[0088] The temperature of the dissolution vessel was adjusted so that the tetraalkylammonium hydroxide solution reached 20°C, and the cellulose was dissolved for 16 hours.

[0089] The temperature of the obtained dissolution was set to 40°C, and the temperature of the coagulation solution reservoir 41 was adjusted so that the temperature of the coagulation solution was 0°C. The dissolution was then discharged from a nozzle 42 with an opening diameter of 100 μm at a flow rate of 6.4 m / min.

[0090] Furthermore, the winding speed of the regenerated cellulose by the winding unit 43 was 3.0 m / min, and the time from when the dissolving solution M3 was discharged from the nozzle 42 until it was lifted from the solidifying solution M4 was 40 seconds.

[0091] The regenerated cellulose was then washed with water and dried to obtain the regenerated cellulose of Example 1. The regenerated cellulose obtained had an average diameter of 10 dtex.

[0092] (Examples 2-16) Regenerated cellulose for Examples 2 to 16 was obtained in the same manner as in Example 1, except that the composition, quantity, temperature of the tetraalkylammonium hydroxide solution, and temperature of the coagulation solution were changed to those shown in Figure 4. In Examples 11 and 12, urea was added in the quantities indicated (indicated as "urea" in Table 1).

[0093] (Comparative Examples 1-7) Regenerated cellulose for Comparative Examples 1 to 7 was obtained in the same manner as in Example 1, except that the composition and quantity of the tetraalkylammonium hydroxide solution, the temperature of the tetraalkylammonium hydroxide solution, and the temperature of the coagulation solution were changed to those shown in Figure 4.

[0094] [9] Rating The regenerated cellulose produced by the cellulose fiber production methods described in each of the above examples and comparative examples was evaluated as follows.

[0095] [9-1] Tensile strength Measurements were performed in accordance with ASTM D 3822:07, and evaluations were conducted according to the following criteria. A:1.5cN / dtex or more B: 1.3 cN / dtex or more, less than 1.5 cN / dtex C: Greater than 1.1 cN / dtex and less than 1.3 cN / dtex D: 1.1cN / dtex or less

[0096] Here, a strength exceeding 1.1 cN / dtex, which is generally required for fibers, was designated as a passing strength with a rating of C. Furthermore, a strength of 1.3 cN / dtex or higher, equivalent to or greater than wool, was more preferable and designated as a rating of B. Even more preferable, a strength of 1.5 cN / dtex or higher, equivalent to or greater than viscose rayon, was designated as a rating of A. These results are shown in Table 1 of Figure 4. Note that "%" in Table 1 refers to "mass%".

[0097]

[10] Overall rating In Examples 1-3 and 5-15, a cellulose fiber manufacturing method (first embodiment) was performed, which included a dissolution step of dissolving cellulose in a tetraalkylammonium hydroxide solution at a temperature of less than 45°C to produce a solution, and a spinning step of extruding the solution produced in the dissolution step into a coagulation solution at a temperature of less than 15°C to spin the fibers. As a result, regenerated cellulose with excellent strength was obtained.

[0098] Furthermore, in Examples 1-7 and 10-15, a cellulose fiber manufacturing method (second embodiment) was performed, which included a dissolution step of dissolving cellulose in a tetraalkylammonium hydroxide solution at a temperature of less than 30°C to produce a solution, and a spinning step of extruding the solution produced in the dissolution step into a coagulation solution at a temperature of less than 20°C to spin the fibers. As a result, regenerated cellulose with excellent strength was obtained.

[0099] On the other hand, in Comparative Examples 1 to 6, the manufacturing methods used did not satisfy the above-described method for producing cellulose fibers, and therefore, regenerated cellulose with excellent strength could not be obtained.

[0100] Furthermore, it has been confirmed that even when using cellulose other than cotton as a raw material, or when using a solution of tetraalkylammonium hydroxide other than TBAH, regenerated cellulose with excellent strength can be obtained by carrying out the cellulose fiber manufacturing method of the present invention. Furthermore, it is possible to provide multiple coagulation solutions with gradually changing concentrations. [Explanation of Symbols]

[0101] 1...Cellulose fiber manufacturing apparatus, 2...Raw material supply unit, 3...Dissolving unit, 4...Spinning unit, 41...Coagulation solution storage unit, 42...Nozzle, 43...Winding unit, M1...Raw material, M2...Tetraalkylammonium hydroxide solution, M3...Dissolving solution, M4...Coagulation solution, M5...Regenerated cellulose

Claims

1. A dissolution step in which cellulose is dissolved in a tetraalkylammonium hydroxide solution at a temperature below 45°C to produce a solution, A method for producing cellulose fibers, characterized by comprising a spinning step of discharging the dissolved solution generated in the dissolution step into a coagulation solution at a temperature of less than 15°C and spinning it.

2. A dissolution step in which cellulose is dissolved in a tetraalkylammonium hydroxide solution at a temperature below 30°C to produce a solution, A method for producing cellulose fibers, characterized by comprising a spinning step of discharging the dissolved solution generated in the dissolution step into a coagulation solution at a temperature of less than 20°C and spinning it.

3. In the dissolution step, the cellulose is dissolved in the tetraalkylammonium hydroxide solution at a temperature of less than 30°C to produce the solution. The method for producing cellulose fibers according to claim 1, wherein in the spinning step, the dissolving solution is discharged into the coagulation solution at a temperature of less than 15°C to produce the fibers.

4. In the dissolution step, the cellulose is dissolved in the tetraalkylammonium hydroxide solution at a temperature of less than 30°C to produce the solution. The method for producing cellulose fibers according to claim 3, wherein in the spinning step, the dissolving solution is discharged into the coagulation solution at a temperature of less than 5°C to produce the fibers.

5. The method for producing cellulose fibers according to any one of claims 1 to 4, wherein the tetraalkylammonium hydroxide solution comprises tetrabutylammonium hydroxide.

6. The content of tetraalkylammonium hydroxide in the tetraalkylammonium hydroxide solution is 50% by mass or more and 60% by mass or less. The method for producing cellulose fibers according to any one of claims 1 to 4, wherein the water content in the tetraalkylammonium hydroxide solution is 40% by mass or more and 50% by mass or less.

7. The cellulose fiber manufacturing method according to any one of claims 1 to 4, wherein the cellulose is produced by crushing cotton and has an average fiber length of less than 0.5 mm.

8. The method for producing cellulose fibers according to any one of claims 1 to 4, wherein the urea content in the tetraalkylammonium hydroxide solution is less than 5% by mass.

9. A method for producing cellulose fibers according to any one of claims 1 to 4, wherein the dissolution step and the spinning step are performed under atmospheric pressure.

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