METHOD FOR PRODUCING CELLULOSE FIBER

Description

The present application is based on, and claims priority from JP Application Serial Number 2024-201352, filed Nov. 19, 2024, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a method for producing a cellulose fiber.

2. Related Art

A technique for producing a regenerated cellulose fiber by chemically regenerating natural cellulose existing in nature, such as wood, is known. For example, JP-A-2022-169188 discloses that a solution containing tetraalkylammonium hydroxide is used to dissolve cellulose as a raw material. A regenerated cellulose fiber can be produced by discharging the dissolution liquid having the dissolved cellulose into a coagulation liquid.

However, conditions for producing a regenerated cellulose fiber were not sufficiently studied, and the strength of the obtained regenerated cellulose fiber was insufficient.

SUMMARY

A method for producing a cellulose fiber according to an application example of the present disclosure includes dissolving cellulose in a tetraalkylammonium hydroxide solution having a temperature of less than 45° C. to form a dissolution liquid and spinning the dissolution liquid by discharging the dissolution liquid formed by the dissolving into a coagulation liquid having a temperature of less than 15° C.

A method for producing a cellulose fiber according to an application example of the present disclosure includes dissolving cellulose in a tetraalkylammonium hydroxide solution having a temperature of less than 30° C. to form a dissolution liquid and spinning the dissolution liquid by discharging the dissolution liquid formed by the dissolving into a coagulation liquid having a temperature of less than 20° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically illustrating a cellulose fiber production apparatus that carries out a method for producing a cellulose fiber according to a first embodiment of the present disclosure.

FIG. 2 is a flowchart of the method for producing a cellulose fiber according to the first embodiment of the present disclosure.

FIG. 3 is a flowchart of the method for producing a cellulose fiber according to a second embodiment of the present disclosure.

FIG. 4 is a table collectively indicating production conditions and evaluation results of Examples and Comparative Examples.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a method for producing a cellulose fiber according to the present disclosure will be described in detail based on preferred embodiments illustrated in the accompanying drawings.

First Embodiment

FIG. 1 is a view schematically illustrating a cellulose fiber production apparatus that carries out a method for producing a cellulose fiber according to a first embodiment of the present disclosure. FIG. 2 is a flowchart of a method for producing a cellulose fiber according to the first embodiment of the present disclosure.

Cellulose Fiber Production Apparatus and Method for Producing Cellulose Fiber

As illustrated in FIG. 1, a cellulose fiber production apparatus 1 includes a raw material supply unit 2, which supplies a raw material, a dissolving unit 3, a spinning unit 4, and a control unit (not illustrated) and is an apparatus that produces a regenerated cellulose M5 by dissolving and coagulating cellulose as a raw material. Operations of the raw material supply unit 2, the dissolving unit 3, and the spinning unit 4 are controlled by the control unit (not illustrated). As illustrated in FIG. 2, the method for producing a cellulose fiber includes a raw material supply step, a dissolving step, and a spinning step. Hereinafter, the components and the steps will be described in detail.

1 Raw Material Supply Unit and Raw Material Supply Step

The raw material supply unit 2 is a component that carries out a raw material supply step of supplying a raw material M1, which is a solid, to the dissolving unit 3. Although not illustrated, the raw material supply unit 2 includes, for example, a raw material storage that stores cellulose, a delivery portion that delivers cellulose, and a measuring unit that measures cellulose.

1-1 Cellulose

The raw material M1 contains cellulose.

Cellulose is a material that is readily available and has high theoretical strength. Examples of the cellulose include, but are not limited to, natural cellulose such as animal cellulose and plant cellulose.

Among them, plant cellulose, particularly one produced by breaking cotton into small pieces, is preferred. This enables the cellulose to dissolve more efficiently in the dissolving step, and thus the strength of the regenerated cellulose M5 can be more effectively increased. This also improves the texture and air permeability of a product including the regenerated cellulose M5.

Furthermore, the cellulose may be subjected to a treatment, such as an ultraviolet irradiation treatment, an ozone treatment, and a plasma treatment.

The average fiber length (length-weighted average length) of the cellulose is not particularly limited, and is, for example, 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 enables the cellulose to dissolve more efficiently in the dissolving step.

The average width (average diameter) of the cellulose fibers is not particularly limited, and is, for example, preferably 0.5 μm or more and 200 μm or less, and more preferably 1.0 μm or more and 100 μm or less. This enables the cellulose to dissolve more efficiently in the dissolving step.

The raw material may contain a substance other than the cellulose. The substance other than cellulose is not particularly limited, and examples thereof include hemicellulose, which is a component derived from natural cotton.

The form of the cellulose supplied to the dissolving unit 3 is not particularly limited, and may be, for example, a powder form, a cotton form, or a sheet form. This enables the cellulose to dissolve more efficiently in the dissolving step.

When the cellulose is produced by breaking cotton into smaller pieces, the average fiber length is preferably less than 2.0 mm, and more preferably less than 1.0 mm. This enables the cellulose to dissolve more efficiently in the dissolving step and can more effectively increase the strength and quality of the obtained regenerated cellulose M5.

The raw material M1 may be obtained from materials other than cotton, for example, paper such as used paper or recycled paper, or cloth.

2 Dissolving Unit and Dissolving Step

The dissolving unit 3 is a component that carries out a dissolving step of dissolving the raw material M1 supplied from the raw material supply unit 2 in the tetraalkylammonium hydroxide solution M2 to form a dissolution liquid M3.

Although not illustrated, the dissolving unit 3 includes, for example, a dissolving tank that stores the tetraalkylammonium hydroxide solution M2 and dissolves cellulose, a delivery portion that delivers the dissolution liquid M3 in the dissolving tank, and a measuring unit. The dissolving tank preferably has a stirring function. This enables the cellulose to dissolve efficiently. The dissolving tank preferably has a bubble eliminating function. This can increase the shape formation accuracy of the regenerated cellulose M5 in the spinning step described later.

In addition, the dissolving tank is provided with a temperature sensor, a temperature adjuster, and the like (not illustrated) and is controlled so that the tetraalkylammonium hydroxide solution M2 has a constant temperature described below.

2-1 Tetraalkylammonium Hydroxide Solution

The tetraalkylammonium hydroxide solution M2 is a solution that dissolves cellulose to form a dissolution liquid M3 and contains at least tetraalkylammonium hydroxide.

2-1-1 Tetraalkylammonium Hydroxide

The tetraalkylammonium hydroxide is not particularly limited, and examples thereof include 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 preferred examples thereof include tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH). One or two or more kinds selected from these may be used in combination.

Among them, the tetraalkylammonium hydroxide is preferably tetrabutylammonium hydroxide. This enables the cellulose to dissolve efficiently.

The tetraalkylammonium hydroxide content of the tetraalkylammonium hydroxide solution M2 is not particularly limited and is, for example, preferably 50% by mass or more and 60% by mass or less, and more preferably 53% by mass or more and 58% by mass or less. This enables the cellulose to dissolve more efficiently and can increase the strength and shape formation accuracy of the regenerated cellulose M5 more effectively. If the tetraalkylammonium hydroxide content is too high, the shape formation accuracy of the regenerated cellulose M5 may decrease in the spinning step described below. In contrast, if the tetraalkylammonium hydroxide content is too low, it may take a relatively long time to dissolve cellulose.

2-1-2 Water

The tetraalkylammonium hydroxide solution M2 preferably contains water. This enables the concentration of the tetraalkylammonium hydroxide solution M2 to be readily adjusted at low cost.

When the tetraalkylammonium hydroxide solution M2 contains water, the water content of the tetraalkylammonium hydroxide solution M2 is not particularly limited and is, for example, preferably 40% by mass or more and 50% by mass or less, and more preferably 43% by mass or more and 48% by mass or less. This enables the cellulose to dissolve more efficiently and can increase the strength and shape formation accuracy of the regenerated cellulose M5 more effectively. If the water content is too high, the concentration of tetraalkylammonium hydroxide is likely to decrease, and it may take a relatively long time to dissolve cellulose. In contrast, if the water content is too low, the tetraalkylammonium hydroxide content is likely to be too high, and the shape formation accuracy of the regenerated cellulose M5 may decrease in the spinning step described below.

In particular, the tetraalkylammonium hydroxide content of the tetraalkylammonium hydroxide solution M2 is preferably 50% by mass or more and 60% by mass or less, and the water content of the tetraalkylammonium hydroxide solution M2 is preferably 40% by mass or more and 50% by mass or less. This enables the cellulose to dissolve more efficiently and can increase the strength and shape formation accuracy of the regenerated cellulose M5 more effectively.

The tetraalkylammonium hydroxide solution M2 may contain dimethyl sulfoxide, alcohol, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, pyridine, or the like.

2-1-3 Urea

The tetraalkylammonium hydroxide solution M2 may contain urea.

When the tetraalkylammonium hydroxide solution M2 contains urea, the urea content of the tetraalkylammonium hydroxide solution M2 is preferably less than 5% by mass, and more preferably less than 4% by mass. This can increase the water retention of the obtained regenerated cellulose M5.

As described above, the tetraalkylammonium hydroxide solution M2 may contain urea, and the urea content of the tetraalkylammonium hydroxide solution M2 is preferably less than 5% by mass. This enables the cellulose to dissolve more efficiently and can improve the quality of the regenerated cellulose M5.

2-1-4 Other Components

The tetraalkylammonium hydroxide solution M2 may contain other components in addition to those described above. The other components are not particularly limited, and examples thereof include a viscosity modifier and a coloring agent.

2-2 Dissolution Condition

The temperature of the tetraalkylammonium hydroxide solution M2 when cellulose is dissolved is less than 45° C. This enables the strength of the regenerated cellulose S5 to sufficiently increase without excessively deteriorating the cellulose. In the present embodiment, when the temperature of the tetraalkylammonium hydroxide solution M2 is 45° C. or more, the cellulose may be excessively deteriorated, and the strength of the regenerated cellulose S5 may decrease.

In the present embodiment, the temperature of the tetraalkylammonium hydroxide solution M2 when cellulose is dissolved may be less than 45° C., preferably less than 40° C., and more preferably less than 20° C. This enables the cellulose to dissolve more efficiently.

The lower limit of the temperature of the tetraalkylammonium hydroxide solution M2 when cellulose is dissolved is not particularly limited.

The time taken for dissolving cellulose, that is, the time taken for the dissolving step is not particularly limited, and is preferably 10 minutes or more and 24 hours or less, and more preferably 1 hour or more and 16 hours or less. This enables the cellulose to dissolve more efficiently.

The pressure in the dissolving tank is atmospheric pressure. That is, the dissolving step is performed under atmospheric pressure. This enables the cellulose to dissolve more efficiently.

2-3 Dissolution Liquid

The dissolution liquid M3 is formed by dissolving cellulose in the tetraalkylammonium hydroxide solution M2. The cellulose content of the dissolution liquid M3 is not particularly limited and is, for example, preferably 1% by mass or more and 40% by mass or less, more preferably 4% by mass or more and 25% by mass or less. This can increase the strength of the obtained regenerated cellulose M5 more effectively.

The viscosity of the dissolution liquid M3 is not particularly limited, and is, for example, preferably 10 Pa·s or more and 600 Pa·s or less, and more preferably 50 Pa·s or more and 100 Pa·s or less. This can increase the strength of the obtained regenerated cellulose M5 more effectively and also can increase the shape formation accuracy of the regenerated cellulose M5 in the spinning step more effectively.

The viscosity of the dissolution liquid M3 is a value measured at a measurement temperature of 23° C. using, for example, a vibrating viscosity meter (VISOCOMATE MODEL VM-10A series) available from SEKONIC CORPORATION.

When the dissolution liquid M3 is stored for a long time (for example, 3 hours or more) after the completion of the dissolving step and before the spinning step, the temperature of the dissolution liquid M3 being stored is preferably 10° C. or more and less than 50° C., and more preferably 15° C. or more and less than 40° C. This can more effectively prevent the dissolved cellulose from precipitating or deteriorating. This can increase the strength of the regenerated cellulose M5 more effectively.

3 Spinning Unit and Spinning Step

The spinning unit 4 includes a coagulation liquid storage 41 that stores the coagulation liquid M4, a nozzle 42 that discharges the dissolution liquid M3 into the coagulation liquid M4, and a winding unit 43 that winds up the regenerated cellulose M5, which is formed by coagulating and shaping the dissolution liquid M3 discharged from the nozzle 42 with the coagulation liquid M4.

In addition, the coagulation liquid storage 41 is provided with a temperature sensor, a temperature adjuster, and the like (not illustrated) and is controlled so that the coagulation liquid M4 has a constant temperature described below.

The number of coagulation liquid storages 41 may be two or more. In this case, the coagulation liquids M4 stored in the respective coagulation liquid storages 41 preferably have different component concentrations.

Furthermore, the illustrated configuration has one nozzle 42, but the present disclosure is not limited to this, and the number of nozzles may be two or more. This can improve the productivity of the regenerated cellulose M5.

The opening shape of the nozzle 42 may be, for example, a circular shape, a polygonal shape, such as a triangular shape and a quadrangular shape, or an elliptical shape. In particular, when the opening shape of the nozzle 42 has a straight line, the glossy feeling of the regenerated cellulose M5 can be emphasized by the formed plane, improving the design property of the product produced using the regenerated cellulose M5 more effectively.

The opening diameter (if not circular, the maximum width) of the discharge port of the nozzle 42 is appropriately set depending on the desired thickness of the regenerated cellulose M5. For example, the opening diameter is preferably 30 mm or more and 100 mm or less, and more preferably 40 mm or more and 60 mm or less. This can increase the strength of the regenerated cellulose M5 more effectively and also makes the regenerated cellulose M5 more versatile when used to produce a product.

The spinning unit 4 may be configured to circulate the coagulation liquid M4 in the coagulation liquid storage 41 to keep the pH level at an appropriate value.

3-1 Coagulation Liquid

The coagulation liquid M4 is not particularly limited, and examples thereof include liquids containing water, ethanol, sulfuric acid, sodium sulfate, or the like. The coagulation liquid M4 is preferably a liquid containing sulfuric acid and sodium sulfate. This can effectively reduce fluctuation of the pH of the coagulation liquid M4 during the coagulation of the cellulose, and thus the cellulose in the dissolution liquid M3 can be more effectively coagulated.

The sulfuric acid content of the coagulation liquid M4 is not particularly limited and is, for example, preferably 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.

The sulfuric acid content of the coagulation liquid M4 is not particularly limited and is, for example, preferably 0.1 mol/L or more and 3.0 mol/L or less, more preferably 0.2 mol/L or more and 2.0 mol/L or less.

By setting the sulfuric acid content and sodium sulfate content within the above-described numerical ranges, fluctuation of the pH of the coagulation liquid M4 during the coagulation of the cellulose can be more effectively reduced.

The pH of the coagulation liquid M4 is preferably, for example, more than 0 and 1.0 or less. This enables more effective coagulation of the cellulose in the dissolution liquid M3.

3-2 Coagulation Condition

The temperature of the coagulation liquid M4 is less than 15° C. This can increase the shape formation accuracy of the regenerated cellulose M5 and thus can increase the strength of the obtained regenerated cellulose M5. In the present embodiment, when the temperature of the coagulation liquid M4 is 15° C. or more, the strength of the obtained regenerated cellulose M5 is insufficient.

In the present embodiment, the temperature of the coagulation liquid M4 may be less than 15° C., preferably less than 10° C., and more preferably less than 5° C. This can increase the strength of the obtained regenerated cellulose M5 more effectively.

The time taken for the spinning step, that is, the time taken from the moment the dissolution liquid M3 is discharged from the nozzle 42 to become the regenerated cellulose M5 until the regenerated cellulose M5 is pulled up from the coagulation liquid M4 is preferably 1 second or more and 300 seconds or less, and more preferably 10 seconds or more and 100 seconds or less. This enables more effective coagulation of the dissolution liquid M3, and thus the strength of the regenerated cellulose M5 can be more effectively increased. If the time taken for the spinning step is too short, the coagulation of the dissolution liquid M3 may be insufficient, and thus the strength of the regenerated cellulose M5 may be insufficient. If the time taken for the spinning step is too long, no further improvement in the strength of the regenerated cellulose M5 is expected. In addition, the productivity of the regenerated cellulose M5 is likely to decrease.

The time taken for the spinning step can be set to a desired value, for example, by adjusting the winding speed of the winding unit 43 and the discharge speed of the dissolution liquid M3 from the nozzle 42.

The coagulation liquid storage 41 is mounted under atmospheric pressure. That is, the coagulation step is performed under atmospheric pressure. This enables cellulose to be more efficiently coagulated.

By performing the dissolving step and the spinning step under atmospheric pressure as described above, the dissolution of cellulose in the dissolving step and the coagulation of cellulose in the spinning step can be efficiently performed, and the strength of the regenerated cellulose M5 can be more effectively increased.

The draw ratio of the regenerated cellulose M5 is not particularly limited, and is, for example, preferably 0.5 times or more and 5.0 times or less, and more preferably 1.0 times or more and 3.0 times or less. This enables the orientation of the molecules of the regenerated cellulose M5 to be appropriately aligned, increasing the strength of the regenerated cellulose M5 more effectively.

3-3 Discharge Condition

The flow rate of the dissolution liquid M3 discharged from the nozzle 42 is not particularly limited, and is, for example, preferably 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 enables more effective coagulation of the dissolution liquid M3, and thus the strength of the regenerated cellulose M5 can be more effectively increased.

The temperature of the dissolution liquid M3 at the time of being discharged is not particularly limited, and is, for example, preferably 5° C. or more and less than 50° C., and more preferably 10° C. or more and less than 45° C. This enables more effective coagulation of the dissolution liquid M3, and thus the strength of the regenerated cellulose M5 can be more effectively increased.

The temperature of the dissolution liquid M3 at the time of being discharged may be different from the temperature of the tetraalkylammonium hydroxide solution M2 at the time of dissolving cellulose.

The temperature T3 (° C.) of the dissolution liquid M3 at the time of being discharged is preferably higher than the temperature T4 (° C.) of the coagulation liquid M4. That is, T3>T4 is satisfied. This enables more effective coagulation of the dissolution liquid M3, and thus the strength of the regenerated cellulose M5 can be more effectively increased.

When the temperature T3 (° C.) of the dissolution liquid M3 at the time of being discharged is higher than the temperature T4 (° C.) of the coagulation liquid M4, the difference between these temperatures T3 and T4 (° C.) is not particularly limited, and is preferably 1° C. or more and 50° C. or less, and more preferably 5° C. or more and 40° C. or less. This enables more effective coagulation of the dissolution liquid M3, and thus the strength of the regenerated cellulose M5 can be more effectively increased.

It should be noted that T3 may be equal to T4 or T4 is greater than T3.

4 Summary of Present Embodiment

As described above, the method for producing a cellulose fiber according to the present embodiment includes dissolving cellulose, which is the raw material M1, in the tetraalkylammonium hydroxide solution M2 having a temperature of less than 45° C. to form the dissolution liquid M3, and spinning the dissolution liquid M3 by discharging the dissolution liquid M3 formed by the dissolving into the coagulation liquid M4 having a temperature of less than 15° C. In general, when cellulose is dissolved, spun, and regenerated in a wet process, the strength of regenerated cellulose is insufficient. However, by performing the dissolving step and the spinning step under the temperature conditions as described above, the strength of the regenerated cellulose M5 can be effectively increased.

In the present embodiment, even when the temperature of the tetraalkylammonium hydroxide solution M2 is less than 45° C., if the temperature of the coagulation liquid M4 is 15° C. or more, the shape formation of the regenerated cellulose M5 cannot be reliably performed, resulting in that the obtained regenerated cellulose M5 has insufficient strength. In addition, even when the temperature of the coagulation liquid M4 is less than 15° C., if the temperature of the tetraalkylammonium hydroxide solution M2 is 45° C. or more, the cellulose may be deteriorated in the dissolving step, resulting in that the obtained regenerated cellulose M5 has insufficient strength.

As described above, the regenerated cellulose M5 having high strength can be obtained by the combination of the temperature of the tetraalkylammonium hydroxide solution M2 being less than 45° C. and the temperature of the coagulation liquid M4 being less than 15° C.

More preferably, in the dissolving, cellulose is dissolved in the tetraalkylammonium hydroxide solution M2 having a temperature of less than 30° C. to form the dissolution liquid M3 and, in the spinning, the dissolution liquid M3 is discharged into a coagulation liquid M4 having a temperature of less than 15° C. Thus, the strength of the regenerated cellulose M5 can be more effectively increased.

More preferably, in the dissolving, the cellulose is dissolved in the tetraalkylammonium hydroxide solution M2 having a temperature of less than 30° C. to form the dissolution liquid M3, and, in the spinning, the dissolution liquid M3 is discharged into the coagulation liquid M4 having a temperature of less than 5° C. Thus, the strength of the regenerated cellulose M5 can be particularly effectively increased.

Second Embodiment

FIG. 3 is a flowchart of a method for producing a cellulose fiber according to a second embodiment of the present disclosure.

Hereinafter, a second embodiment of the method for producing a cellulose fiber according to the present disclosure will be described with reference to FIG. 3, but hereinafter, differences from the first embodiment described above will be mainly described, and similarities will not be described.

5 Present Disclosure According to Second Embodiment

As illustrated in FIG. 3, the method for producing a cellulose fiber according to the present embodiment includes dissolving cellulose, which is the raw material M1, in the tetraalkylammonium hydroxide solution M2 having a temperature of less than 30° C. to form the dissolution liquid M3, and spinning the dissolution liquid M3 by discharging the dissolution liquid M3 formed by the dissolving into the coagulation liquid M4 having a temperature of less than 20° C. In general, when cellulose is dissolved, spun, and regenerated in a wet process, the strength of regenerated cellulose is insufficient. However, by performing the dissolving step and the spinning step under the temperature conditions as described above, the strength of the regenerated cellulose M5 can be effectively increased.

In the present embodiment, even when the temperature of the tetraalkylammonium hydroxide solution M2 is less than 30° C., if the temperature of the coagulation liquid M4 is 20° C. or more, the shape formation of the regenerated cellulose M5 cannot be reliably performed, resulting in that the obtained regenerated cellulose M5 has insufficient strength. In addition, even when the temperature of the coagulation liquid M4 is less than 20° C., if the temperature of the tetraalkylammonium hydroxide solution M2 is 30° C. or more, the cellulose may be deteriorated in the dissolving step, resulting in that the obtained regenerated cellulose M5 has insufficient strength.

As described above, the regenerated cellulose M5 having high strength can be obtained by the combination of the temperature of the tetraalkylammonium hydroxide solution M2 being less than 30° C. and the temperature of the coagulation liquid M4 being less than 20° C.

Although the preferred embodiments of the present disclosure have been described above, the present disclosure should not be limited to the embodiments.

EXAMPLES

Next, specific examples of the present disclosure will be described.

6 Preparation of Raw Material, Constituent Materials of Tetraalkylammonium Hydroxide Solution, and Constituent Materials of Coagulation Liquid

As raw material, constituent materials of the tetraalkylammonium hydroxide solution, and constituent materials of the coagulation liquid, the following materials were prepared.

• • Raw material: cotton (plain weave, 270 areal weight)
  • Tetrabutylammonium hydroxide solution: (tetrabutylammonium hydroxide solution: (available from SACHEM Inc (tetrabutylammonium hydroxide, 55% (aqueous solution))) (“TBAH” in Table 1)
  • Urea: (available from FUJIFILM Wako Pure Chemical Corporation) (“urea” in Table 1)
  • Sulfuric acid: (available from FUJIFILM Wako Pure Chemical Corporation (sulfuric acid))
  • Sodium sulfate: (available from FUJIFILM Wako Pure Chemical Corporation (sodium sulfate))

7 Production of Raw Material, Tetraalkylammonium Hydroxide Solution, and Coagulation Liquid

First, cotton as a raw material was broken into small pieces with a mill (screen diameter of 0.5 mm).

In addition, 0.250 l of sulfuric acid and 0.535 g of sodium sulfate were dissolved in 5.549 l of water to produce a coagulation liquid. The sulfuric acid content of the obtained coagulation liquid was 0.75 mol/L, and the sodium sulfate content was 0.63 mol/L.

8 Production of Regenerated Cellulose

Example 1

The raw material obtained as described above was charged into the raw material supply unit 2 illustrated in FIG. 1, the tetraalkylammonium hydroxide solution obtained as described above was charged into the dissolving tank of the dissolving unit 3 illustrated in FIG. 1, and the coagulation liquid obtained as described above was charged into the coagulation liquid storage 41 of the spinning unit 4 illustrated in FIG. 1.

The cellulose fiber production apparatus was operated under the following conditions to produce regenerated cellulose.

The temperature of the dissolving tank was adjusted so that the temperature of the tetraalkylammonium hydroxide solution was 20° C., and the cellulose was dissolved for 16 hours.

The temperature of the obtained dissolution liquid was set to 40° C., the temperature of the coagulation liquid storage 41 was adjusted so that the temperature of the coagulation liquid was 0° C., and the dissolution liquid was discharged from the nozzle 42 having an opening diameter of 100 μm at a flow rate of 6.4 m/min.

The winding speed of the regenerated cellulose by the winding unit 43 was 3.0 m/min, and the time taken from the moment the dissolution liquid M3 was discharged from the nozzle 42 until the dissolution liquid M3 was pulled up from the coagulation liquid M4 was 40 seconds.

Then, the regenerated cellulose was washed with water and dried to produce regenerated cellulose of Example 1.

The obtained regenerated cellulose had an average diameter of 10 dtex.

Examples 2 to 16

Regenerated celluloses of Examples 2 to 16 were obtained in the same manner as in Example 1 except that the composition and amount of the tetraalkylammonium hydroxide solution, the temperature of the tetraalkylammonium hydroxide solution, and the temperature of the coagulation liquid were changed as indicated in FIG. 4. In Examples 11 and 12, urea was blended in the indicated amount (“urea” in Table 1).

Comparative Examples 1 to 7

Regenerated celluloses of Comparative Examples 1 to 7 were obtained in the same manner as in Example 1 except that the composition and amount of the tetraalkylammonium hydroxide solution, the temperature of the tetraalkylammonium hydroxide solution, and the temperature of the coagulation liquid were changed as indicated in FIG. 4.

9 Evaluation

The regenerated celluloses of Examples and Comparative Examples produced by the method for producing a cellulose fiber were evaluated as follows.

9-1 Tensile Strength

The tensile strength was measured in accordance with ASTM D 3822:07 and evaluated according to the following criteria.

• • A: 1.5 cN/dtex or more
  • B: 1.3 cN/dtex or more and less than 1.5 cN/dtex
  • C: more than 1.1 cN/dtex and less than 1.3 cN/dtex
  • D: 1.1 cN/dtex or less

Here, a strength of more than 1.1 cN/dtex, which is a strength generally required for a fiber, was evaluated as C and regarded as an acceptable strength. Furthermore, 1.3 cN/dtex or more, which is a strength equal to or higher than that of wool, was more preferable and evaluated as B. Furthermore, 1.5 cN/dtex or more, which is a strength equal to or more than that of viscose rayon, was still more preferable and evaluated as A.

The results are indicated in Table 1 of FIG. 4. In Table 1, “%” means “% by mass”.

10 Comprehensive Evaluation

In Examples 1 to 3 and 5 to 15, the method for producing a cellulose fiber (first embodiment) including dissolving cellulose in a tetraalkylammonium hydroxide solution having a temperature of less than 45° C. to form a dissolution liquid and spinning the dissolution liquid by discharging the dissolution liquid formed by the dissolving into a coagulation liquid having a temperature of less than 15° C. was carried out, and thus regenerated cellulose having high strength was successfully produced.

In addition, in Examples 1 to 7 and 10 to 15, the method for producing a cellulose fiber (second embodiment) including dissolving cellulose in a tetraalkylammonium hydroxide solution having a temperature of less than 30° C. to form a dissolution liquid and spinning the dissolution liquid by discharging the dissolution liquid formed by the dissolving into a coagulation liquid having a temperature of less than 20° C. was carried out, and thus regenerated cellulose having high strength was successfully produced.

In contrast, in Comparative Examples 1 to 6, regenerated cellulose having high strength was not obtained because the production method that does not comply with the above-described method for producing a cellulose fiber was carried out.

It has been confirmed that regenerated cellulose having high strength can be obtained by carrying out the method for producing a cellulose fiber according to the present disclosure even when cellulose other than cotton is used as a raw material or a solution of tetraalkylammonium hydroxide other than TBAH is used.

It is also possible to provide a plurality of coagulation liquids whose concentrations are varied stepwise.