Method for spinning alkali cellulose

Abstract

A method for spinning an alkali cellulose spinning dope comprising dissolved cellulose into an aqueous alkaline coagulation bath liquid comprising coagulation salt, thereby forming cellulose filaments. The method comprises the steps of: - feeding the alkali cellulose spinning dope to a spinneret (110) having a plurality of holes (120) arranged in at least one group (130) such that the distance (D1) from the center of any given hole (120) in the group (130) to the nearest point on the periphery (131) of the group (130) is no more than 3 mm, such as 2 mm, the diameter of each hole (120) being from 40 µm to 100 µm; - extruding the alkali cellulose spinning dope through the holes (120) into the aqueous alkaline coagulation bath liquid, thereby forming cellulose filaments; and - withdrawing the cellulose filaments from the aqueous alkaline coagulation bath liquid; wherein the holes (121) at the periphery (131) of the group (130) are in direct contact with the aqueous alkaline coagulation bath liquid.

Description

Technical Field

[0001] This invention relates to a method for spinning cellulose dissolved in an aqueous sodium hydroxide (NaOH) solution into cellulose fibers. During the spinning process, the dissolved alkali cellulose is extruded into a coagulation bath to precipitate the cellulose, thereby forming cellulose fibers. Background Technology

[0002] Fibers have a wide range of applications in the textile industry. Historically, textile fibers have always been natural fibers. For example, cotton fiber has long been used to produce fabrics in the textile industry. In addition, other plant fibers, such as flax fiber, have been used. In the 20th century, plastic fibers (such as nylon and polyester) emerged as inexpensive alternatives for fabric production. However, cotton fiber still represents a very important fiber within the textile industry.

[0003] Demand for natural fibers is beginning to grow again due to the need to reduce carbon footprint. However, cotton cultivation and processing also cause environmental problems. Therefore, interest is growing in alternative sources of cellulose for fiber production.

[0004] The viscose process, known for a long time, uses wood as a raw material for producing cellulose fibers. In the viscose process, regenerated cellulose fibers are provided through the regeneration of cellulose derived from sodium cellulose xanthate (CS2, carbon disulfide) to increase solubility. However, the use of carbon disulfide is associated with problems, including its toxicity. Furthermore, as the dissolved sodium cellulose xanthate is spun into an aqueous sulfuric acid solution to precipitate the cellulose fibers and regenerate the carbon disulfide, Na2SO4, which currently has no commercial value, inevitably forms as a byproduct in the viscose process. Therefore, it is desirable in the art to find alternative methods for providing cellulose fibers from wood.

[0005] It is known in the art that underived cellulose is soluble to some extent in cold aqueous sodium hydroxide solution. Therefore, aqueous sodium hydroxide solution is used as a cellulose solvent in experimental procedures; however, to date, no economically feasible industrial method for fiber spinning is available.

[0006] In experimental spinning solutions containing cellulose dissolved in an aqueous sodium hydroxide solution, as in the viscose process, the spinning solution has been wet-spun into a coagulation bath containing an aqueous sulfuric acid solution. This process requires a large amount of sodium hydroxide when supplying fibers and, similar to the viscose process, produces sodium sulfate as a residue.

[0007] To address this problem, a method has been proposed in the art (see, for example, WO 2020 / 171767, WO 2018 / 169479, WO 2017 / 178532, WO 2015 / 000820, WO 2010 / 104458 granted to the applicant) to spin dissolved cellulose into an alkaline spinning bath containing an aqueous solution of coagulated sodium salt (e.g., Na2CO3 or Na2SO4), and to recover sodium hydroxide (NaOH) and the coagulated sodium salt separately from the spinning bath. This method is considered promising because the chemicals (i.e., NaOH and the coagulated sodium salt) can be recovered separately.

[0008] The applicant has indeed discovered that cellulose dissolved in an aqueous sodium hydroxide solution to produce a spinning solution can be spun into a coagulation bath containing an aqueous solution of a coagulating sodium salt (e.g., Na₂CO₃ or Na₂SO₄). When the spinning solution is spun into the coagulation bath, a wet, swollen fiber bundle is provided. The regenerated fiber bundle can then be withdrawn from the coagulation bath to provide cellulose fibers.

[0009] In the viscose process, sodium cellulose xanthate is typically spun using a spinneret—a small metal plate, sleeve, or cap with fine holes—in which the spinning solution is forced through these holes into the acid coagulation bath during filament spinning. (See spinneret for details.) Figure 1 It shows a conventional spinning head with multiple spinnerets, such as Figure 2 As shown, each spinneret (with hundreds or thousands of orifices) is designed to form thousands of thin spin solution jets exiting the spinneret and entering the coagulation bath liquid. Upon contact with the coagulation liquid, a diffusion-based chemical exchange occurs between the spin solution jets and the coagulation liquid. This interdiffusion of chemicals is a rapid process because the spin solution jets exiting the spinneret capillary are thin (typically 40µm to 100µm in diameter). Upon contact between the spin solution jets and the coagulation liquid, protons rapidly enter the jet, neutralizing the alkali to form sodium sulfate. The solvation capacity of the alkali is thus abruptly reduced, and cellulose precipitates, forming a dense cellulose network. Because cellulose precipitates (coagulates) very rapidly under acidic conditions, the spin solution jets transform directly into thin, strong, and non-swelling filaments upon exiting the spinneret orifices. Unbound by any theory, rapid precipitation can be at least partially attributed to acidic conditions and hydrated hydrogen ions (H₃O₂). + This can be explained by the rapid spread of ( ).

[0010] These features allow for numerous and densely spaced orifices in each spinneret, such as Figure 2 As shown. Existing spinnerets (16 mm in diameter) can have 1800 to 2400 orifices, each with a diameter of approximately 60 µm. The exit velocity of the spinning solution jet is typically in the range of 30 m / min to 50 m / min (average velocity within the orifice). (Source: ...) Figure 1 The spinning head shown (with a diameter of 200 mm and 45 dies, each with 2000 holes) can produce at a rate of 30 kg / h to 50 kg / h (1.3 dtex fiber).

[0011] However, the coagulation method using an alkaline coagulation bath containing coagulating salts (such as Na₂SO₄ or Na₂CO₃) differs from the viscose method using an acid coagulation bath. Specifically, it has been found that the precipitated filaments remain swollen in the alkaline coagulation bath, resulting in lower initial filament structural integrity. These characteristics of the filaments limit the production rate using conventional spinning heads and spinnerets. To avoid filament breakage, leading to the formation of filament clumps / bands, the exit speed must be significantly reduced, thus decreasing the production rate.

[0012] Therefore, there is a need in the art for an efficient method for spinning cellulose dissolved in an aqueous sodium hydroxide (NaOH) solution into cellulose fibers. Summary of the Invention

[0013] In spinning studies using conventional circular spinnerets with orifices arranged in concentric circles, it was found that the softer nature and larger diameter of the swollen filaments in an alkaline coagulation bath resulted in a radially inward movement pattern of the spinning solution jet leaving the orifices in the spinneret, leading to bundle shrinkage (see [link to study]). Figure 4a If an acid coagulation bath is used, the corresponding filament shrinkage is not observed. In this case, the spinning solution jet generally follows an upward straight path. In the acid coagulation bath, the dense, thin, and strong filaments formed at the spinneret surface resist the dragging effect of the radial inward flow of the coagulation bath liquid.

[0014] Therefore, in the case of an alkaline coagulation bath, tow shrinkage is a result of the soft characteristics of the jet, and their significantly larger diameter generates a greater hydrodynamic interaction with the radial inflow of the coagulating liquid. The aforementioned phenomena (radial inflow of the coagulating liquid and tow shrinkage) tend to tear the formed filaments and cause them to break. The degree of coagulation is also sensitive to the high ratio of fiber volume to coagulating bath liquid volume in the upward-traveling tow. If the draw ratio is kept constant (draw ratio DR = take-up speed divided by dosing jet output speed), tow shrinkage in the case of an alkaline coagulation bath will increase with increasing spinning dosing flow rate. Therefore, it is concluded that in the case of an alkaline coagulation bath, both the orifice density and output speed of a conventional spinneret limit the possible production rate using conventional viscose spinneret technology.

[0015] Therefore, according to a first aspect, a method is provided for spinning an alkali cellulose spinning solution containing dissolved cellulose into an aqueous alkaline coagulation bath liquid containing a coagulation salt (such as a sodium coagulation salt), thereby forming cellulose filaments. The method includes the following steps: - Feed the alkali cellulose spinning solution into a spinneret with multiple holes; - The alkali cellulose spinning solution is extruded through a hole into an aqueous alkaline coagulation bath, thereby forming cellulose filaments; and - Extracting cellulose filaments from an alkaline coagulation bath containing water.

[0016] By providing a spinneret with the plurality of orifices, fiber shrinkage can be significantly reduced, thereby increasing the possible production rate. Each orifice has a diameter of 40µm to 100µm, arranged in at least one group such that the distance from the center of any given orifice in the group to the nearest point on the periphery of the group does not exceed 3mm (e.g., 2mm), and the orifices at the periphery of the group are in direct contact with an aqueous alkaline coagulation bath. Therefore, the spinneret has a plurality of orifices arranged in at least one group such that the distance from the center of any given orifice in the group to the nearest point on the periphery of the group does not exceed 3mm (e.g., 2mm). The periphery of the group of orifices is defined by the periphery of the outermost orifice in the group. The average center-to-center distance between adjacent orifices can be 200µm to 400µm, such as 250µm to 400µm.

[0017] According to one embodiment, the perimeter is defined by fitting a polygon (such as a quadrilateral) to the set of holes. Preferably, the quadrilateral is a rectangle or trapezoid (a pair of opposite sides are parallel), such as an isosceles trapezoid (a pair of opposite sides are parallel and have equal base angles). According to one embodiment, the polygon fitted to the set of holes is a rectangle.

[0018] According to another implementation, the perimeter is defined by a tangential straight line between the perimeters of the adjacent outermost holes in the group.

[0019] Typically, the plurality of holes are arranged in an elongated group. The elongated group can be substantially rectangular. Alternatively, the elongated group can taper at least partially along its longitudinal extension, such as taking the form of a substantially isosceles trapezoid (a pair of opposite sides are parallel and have equal base angles).

[0020] In embodiments where the plurality of holes are arranged in an elongated group, the width of the group (the dimension perpendicular to the longitudinal extension, i.e., the length, at half the length of the group) can range from 0.5 mm to 6 mm, preferably from 1 mm to 4 mm. Additionally, the length:width ratio of the elongated group (e.g., a substantially rectangular group) can be at least 2, such as at least 3. For a rectangular group, the length is the longest dimension of the group, and the width is, for example, the dimension of the group perpendicular to the length at half the length of the group. For elongated groups that are not rectangular, the width is defined as the dimension of the group perpendicular to the length (i.e., the longest dimension of the group) at half the length of the group.

[0021] For tapered elongated groups, such as those substantially in the form of isosceles trapezoids, the width can be at least 0.5 mm at one end and no more than 6 mm, such as no more than 4 mm, at the opposite end. Furthermore, the width of the tapered elongated group can gradually decrease, meaning the group can be considered as comprising two or more adjacent rectangles. The tapered elongated group can also be a wedge-shaped group that is very thin at one end of its longitudinal extension. For such an elongated group, the width at the thin end can even correspond to the diameter of a single hole.

[0022] The spinneret can take different forms. For example, it can be circular or rectangular. According to one embodiment, the spinneret is circular. According to another embodiment, the spinneret is rectangular. The minimum characteristic measure of the spinneret is in the range of 0.5 mm to 24 mm, such as in the range of 1.5 mm to 20 mm. For a circular spinneret, the minimum characteristic measure is the diameter. For a rectangular spinneret, the minimum characteristic measure is the width.

[0023] In embodiments where the spinneret is circular, the diameter of its minimum characteristic measure (i.e., diameter) can be in the range of 8 mm to 24 mm, such as in the range of 10 mm to 20 mm.

[0024] In embodiments where the spinneret is rectangular, its minimum characteristic measure (i.e., width) can be less than 10 mm, for example, within any range of 0.5 mm to 7 mm, 1 mm to 6 mm, or 1.5 mm to 5 mm. For a rectangular spinneret, the length:width ratio can be at least 5:1. The length:width ratio can be from 5:1 to 200:1, such as 10:1 to 100:1. Additionally, the holes in the rectangular spinneret can be arranged as a set of rectangular holes. The holes can be arranged such that the width of a set of rectangular holes does not exceed 4 mm, preferably not exceeding 3 mm. According to one embodiment, these holes are arranged such that the width of a set of rectangular holes is from 0.4 mm to 4 mm, such as 1 mm to 3 mm.

[0025] According to one embodiment, the spinneret is arranged on the edge of a plate. The plate is provided with flow channels for receiving, distributing, and feeding the alkali cellulose spinning solution into the perforated spinneret. The plate can have a length of 5 cm to 50 cm. Therefore, the edge on which the spinneret is arranged can be 5 cm to 50 cm long.

[0026] In rectangular spinnerets, for example, the spinneret dimension perpendicular to the minimum characteristic dimension can be longer than the minimum characteristic dimension. However, in some embodiments, the spinneret dimension perpendicular to the minimum characteristic dimension can also be in the range of 0.5 mm to 24 mm, such as in the range of 1.5 mm to 20 mm. By definition, the spinneret dimension perpendicular to the minimum characteristic dimension is equal to or longer than the minimum characteristic dimension. For circular spinnerets, these two dimensions are the same.

[0027] In this art, multiple circular spinnerets are typically arranged in a spinning head, to which alkali cellulose spinning solution is fed for extrusion through each spinneret. According to one embodiment, at least two (such as at least five) spinnerets are arranged in the spinning head. In one embodiment, according to this embodiment, circular spinnerets are arranged in the spinning head, and at least five, such as at least ten, spinnerets may be arranged in the spinning head.

[0028] According to one embodiment, the plurality of orifices in a spinneret (such as a circular spinneret) are arranged in more than one set of orifices. Each set of orifices is arranged such that a flow channel for an aqueous alkaline coagulation bath liquid exists on the spinneret between adjacent sets. The flow channel has no holes. By providing a spinneret with a flow channel, the orifices at the periphery of the set directly allow the aqueous alkaline coagulation bath liquid to flow in the flow channel to feed the alkaline coagulation bath liquid to orifices that are not present along the periphery of the spinneret. Each set of orifices is arranged such that the minimum distance between the peripheries of two adjacent sets is at least 450 µm, such as at least 500 µm or at least 1000 µm, i.e., the width of the flow channel is at least 450 µm. According to one embodiment, each set of orifices is arranged such that the distance between the peripheries of two adjacent sets is at least 1.5 times the minimum center-to-center distance between the orifices within the set, such as at least 3 times the minimum center-to-center distance between the orifices within the set.

[0029] According to one embodiment, a spinneret having more than one set of orifices can be circular. The diameter of the circular spinneret can be from 8 mm to 24 mm, such as from 10 mm to 20 mm. Therefore, the diameter of the circular surface of the circular spinneret on which the various sets of orifices are arranged can be from 8 mm to 24 mm, such as from 10 mm to 20 mm. The various sets of orifices on the circular spinneret can be elongated, such as substantially rectangular. In addition, the elongated sets of orifices can taper at least partially along their longitudinal extension. The sets of elongated orifices arranged on the circular spinneret can be arranged radially to provide radially arranged flow channels between the sets of orifices. By radially arranging substantially rectangular sets of orifices, if the sets are substantially rectangular, a flow channel that tapers radially toward the center of the circular spinneret can be provided on the circular spinneret. In addition, the lengths of the elongated sets of orifices arranged on the circular spinneret can be different to increase the number of sets on the spinneret while still maintaining a certain distance between adjacent sets. The length of the radially arranged groups typically does not exceed the radius of the circular spinneret, i.e., the radius of the circular surface of the spinneret on which they are arranged. Preferably, the length of the radially arranged groups is shorter than the radius, such as not exceeding 90%, 80%, or 70% of the radius, i.e., the length of the radially arranged groups does not exceed 90%, such as 80% or 70% of the radius. Alternatively, the length of the radially arranged groups can be at least 40%, such as at least 50% or at least 60% of the radius.

[0030] According to one embodiment, adjacent elongated groups arranged radially on a circular spinneret can have different lengths. Therefore, longer groups of orifices can be arranged close to shorter groups of orifices. By arranging groups of different lengths on the circular spinneret, the number of orifices present on the spinneret can be increased while still providing flow channels of sufficient width to allow the aqueous alkaline coagulation bath liquid to flow inwards through the spinneret. According to this embodiment, the length-to-width ratio of the first shorter group can be at least 2, and the length-to-width ratio of the second longer group can be at least 3. The width of each group can range from 0.5 mm to 6 mm; preferably, the width of each group is in the range of 1 mm to 4 mm.

[0031] According to one embodiment, elongated groups radially arranged on a circular spinneret may taper at least partially towards the center of the circular spinneret along their longitudinal extensions. Preferably, at least the portion of the elongated group facing the center of the circular spinneret is tapered, such as at least 15% of the elongated group along its longitudinal extension. The at least partial taper of the elongated groups radially arranged on the circular spinneret towards the center of the circular spinneret along their longitudinal extensions has the advantage that the distance between adjacent groups does not decrease or decreases only slightly in the radial direction.

[0032] According to one embodiment, elongated groups are radially arranged on a circular spinneret. These radially arranged groups can be arranged in a fan-shaped pattern to provide a main flow channel in addition to the aforementioned flow channel. The aqueous alkaline coagulation bath liquid can flow through this main flow channel onto the circular spinneret towards its center. The main flow channel can be used to increase the feed of the aqueous alkaline coagulation bath liquid into the orifice at the center of the spinneret.

[0033] According to one embodiment, elongated groups are radially arranged on a circular spinneret, with the orifice not arranged at the center of the circular spinneret, thereby allowing the radial flow channels between the elongated groups to be fluidly connected to each other at the center of the circular spinneret.

[0034] According to another embodiment, the elongated groups are radially arranged on a circular spinneret, and the orifices are also arranged at the center of the circular spinneret, thereby the flow channels between the elongated groups are closed and they are not fluidly connected to each other at the center of the circular spinneret. Therefore, the elongated groups can be regarded as being arranged in a star or asterisk pattern.

[0035] The pores in the assembly can be distributed in different ways. According to one embodiment, they are evenly distributed in the assembly, for example, in a hexagonal or square pattern. A square pattern of pores can improve the flow of the aqueous alkaline coagulation bath liquid within the assembly.

[0036] Alternatively, the pores can be unevenly distributed within the assembly. This uneven distribution can improve the flow of the aqueous alkaline coagulation bath liquid within the assembly. The average center-to-center distance between two adjacent pores in the assembly can range from 250 µm to 400 µm, also exhibiting an uneven pore distribution.

[0037] According to one embodiment, the orifices in the assembly of the circular spinneret are arranged non-uniformly such that the average center-to-center distance in the radial direction is greater than the average center-to-center distance in the direction perpendicular to the radial direction. The non-uniformly arranged orifices in the assembly of the circular spinneret can be configured to provide microchannels for the coagulated liquid to flow into the assembly.

[0038] According to another aspect, a spinneret for spinning alkali cellulose spinning solution into an aqueous alkali coagulation bath liquid is provided. The spinneret has a plurality of orifices, each with a diameter of 40 µm to 100 µm. The orifices are arranged in at least two groups. The orifices in each group are arranged such that the distance from the center of any given orifice in the group to the nearest point on the periphery of the group does not exceed 3 mm, such as 2 mm. Furthermore, the orifices in each group are arranged such that flow channels for the aqueous alkali coagulation bath liquid are arranged on the spinneret between adjacent groups. The flow channels have no orifices. Preferably, the alkali cellulose spinning solution spinneret is circular and has radially arranged groups of orifices and radially arranged flow channels between them. Furthermore, preferred features of this circular spinneret have already been described above.

[0039] Without further detailed description, it is believed that those skilled in the art can make full use of the invention using the foregoing description. Therefore, the preferred embodiments described above should be understood as merely exemplary and in no way intended to limit this disclosure.

[0040] Although the invention has been described above with reference to specific embodiments, it is not intended to limit the invention to the specific forms set forth herein. Rather, the invention is limited only by the appended claims, and other embodiments besides the specific embodiments described above are also within the scope of these appended claims.

[0041] In the claims, the term "comprising / including" does not exclude the presence of other elements or steps. Furthermore, while individual features may be included in different claims, these features may be advantageously combined, and inclusion in different claims does not mean that such combination of features is not feasible and / or advantageous.

[0042] Furthermore, singular references do not preclude multiple instances. Terms such as "a," "an," "first," and "second" do not preclude multiple instances. Attached Figure Description

[0043] Referring to the accompanying drawings, these and other aspects, features, and advantages of the present invention will become apparent and will be elucidated from the following description of embodiments thereof, wherein: Figure 1 A photograph of a conventional spinning head with several circular spinnerets, known in the art, is shown; Figure 2 It shows Figure 1 One of the spinnerets in a spinning head. The orifices in a conventional spinneret are arranged in concentric circles; Figure 3a A circular spinneret with orifices arranged in an elongated group is shown according to one embodiment; Figure 3bA circular spinneret with orifices arranged in an elongated group is shown according to one embodiment; Figure 4a A photograph of spinning from a conventional spinneret is shown (see Figure 2 ); Figure 4b A photograph shows spinning from a spinneret according to one embodiment; Figure 5 A close-up of a circular spinneret with orifices arranged in elongated groups, according to one embodiment, is shown; Figure 6 shows a die head with radially arranged group holes according to an embodiment; Figure 7 illustrates various ways of distributing holes with a given group of holes; Figure 8 A rectangular spinneret is shown according to one embodiment; Figure 9 A rectangular spinneret is shown according to one embodiment; Figure 10 A spinneret with two rectangular spinnerets is shown according to one embodiment, each rectangular spinneret having a set of orifices; and Figure 11 A photograph is shown of a spinning head with four rectangular spinnerets according to one embodiment, each rectangular spinneret having a set of orifices. Detailed Implementation

[0044] To provide an effective spinning solution for alkali cellulose spinning, multiple spinnerets 110 with orifices 120 (see [reference]) are typically used. Figure 2 Assembled into the spinning head 100, as in Figure 1 As is known in the art, an alkali cellulose spinning solution is fed into a spinneret 100 and extruded through orifices 120 into a coagulation bath liquid to form cellulose filaments. The spinneret is provided with a plurality of orifices 120 to provide efficient spinning. In spinnerets 110 of the art, the orifices 120 are typically arranged in concentric circles, as shown in… Figure 2 As can be seen in the text.

[0045] Figure 3a and Figure 3b A circular spinneret 110 according to one embodiment is shown. The orifices 120 on the spinneret 110 are arranged in elongated groups 130a, 130b to provide flow channels 135 for inward flow of the alkali coagulation bath liquid between groups 130a, 130b, as shown. Figure 3aAs shown. Groups 130a and 130b are elongated. Furthermore, the lengths of groups 130a and 130b can be different. These groups can be arranged radially as shown in Figure 3. Optionally, one or more groups in a radial pattern can be omitted to provide the main flow channel 136.

[0046] As in Figure 3b As can be seen, groups 130a, 130b, and 130c of different lengths can be combined to increase the number of holes 120 present on the spinneret 110, while still providing flow channels 135 that separate the groups 130.

[0047] As can be seen in Figure 4 (see double arrows), compared to a conventional spinneret with orifices arranged in concentric circles (see Figure 4), Figure 4a When spinning is performed using a spinneret with orifices arranged in a radial group, less filament shrinkage is observed (see [link]). Figure 4b This means that the filament experiences less force perpendicular to the flow direction.

[0048] The slender groups 130a, 130b, and 130c in Figure 3 are substantially rectangular. The perimeter 131 of this group can be defined by fitting a rectangle around the hole 120, as shown in... Figure 5 As can be seen, the length L and width W of the elongated group can be defined as the length L and width W of the rectangle fitted to the holes in that group. When fitting the rectangle to the holes 120, all holes will be within the rectangle. In addition, the rectangle should be as short and narrow as possible. The perimeter 121 is therefore defined by the perimeter of the outermost hole 121 in the group 130.

[0049] The closest distance between two adjacent groups 130a, 130b can be defined as the closest distance D2 between the perimeters 131a, 131b of each group in groups 130a, 130b. As an alternative to fitting a rectangle to the group, the perimeter can be defined by a tangential line between the perimeters of adjacent outermost holes 121 in group 130. Figure 5 The group provides groups 130a and 130b, which are basically rectangular arrow shapes. Additionally, in Figure 5 The distance D1 from the center of the hole 122 in the center of group 130 to the nearest point on the periphery 131 of group 130 is also shown.

[0050] When the holes 120 of the radially arranged group 130 are arranged, they can be arranged in different numbers (e.g., 6, 8, 10, 12, or 16) of radius, such as Figures 6a-6gAs can be seen in the image. Groups 130 have the same length, with the tapered end pointing towards the center of the circular spinneret 110. The orifices are not located at the center of the circular spinneret 110. By tapering group 130, the number of orifices 120 present on the spinneret 110 can be increased, while still providing flow channels 135 with sufficient width to separate groups 130. Additionally, as in... Figures 6e-6g As can be seen in Figure 7, the orifices 120 in a given group can be distributed differently, regardless of the shape of the spinneret 110.

[0051] exist Figure 8 Figure 7 shows a rectangular spinneret 110 according to one embodiment. A set of holes 120 of 130 are present on the spinneret 110. According to this embodiment, the set of holes 120 consists of two rows of holes 130. Figure 7 shows a rectangular spinneret 110 according to one embodiment. This embodiment is similar to... Figure 9 The implementation scheme is as follows. However, the holes 130 of group 120 consist of nine rows of holes 130.

[0052] Similar to the circular spinneret 110, rectangular spinnerets 110 can also be arranged together in the spinning head 100, such as... Figure 10 The figure schematically shows a rectangular spinneret 110 from above. Figure 11 A photograph of a spinning head 100 having four rectangular spinnerets 110 arranged in parallel and spaced apart is shown.

[0053] Example Example 1- Spinneret with two rows of holes Using rectangular sets of holes arranged in two parallel rows ( 60µm) spinneret (see Figure 8 The distance between the perimeters of two adjacent holes in a row is 140µm (the distance between the centers of the holes is 200µm).

[0054] The spinning doss was used to spin a spinning solution containing 6.0 wt% acid-hydrolyzed birch pulp (intrinsic viscosity = 210), 7.5 wt% NaOH, and 0.95 wt% ZnO. During the preparation of the spinning doss, it was filtered in a filter press through two continuous PP nonwoven filter media (coarse and fine media).

[0055] The aqueous alkaline coagulation bath liquid used contained 21% by weight Na₂CO₃ and 5.7% by weight NaOH. Its temperature was 29°C. In spinning, online filtration was used with SIKA-FIL 20µm metal fiber flocking. The spinning bath depth was 80cm. Spinning performed well at an output speed of 40m / min and a guide roller speed (winding speed) of 35m / min (draw ratio = 0.88).

[0056] Example 2- Spinneret with two rows of holes The same spinneret as in Example 1 was used. The spinning solution contained 6.0% by weight cellulose, 7.5% NaOH, and 0.9% ZnO. The aqueous alkaline coagulation bath liquid used contained 21% by weight Na₂CO₃ and 5% by weight NaOH. Its temperature was 30°C.

[0057] The following results were obtained by spinning in the same manner as in Example 1.

[0058] Table 1 - Spinnerets with two rows of holes Example 3 (Refer to the embodiment) Conventional spinneret cap Use a standard spinneret cap (see...) Figure 2 The spinning solution contains 6.3% by weight cellulose (IV = 220 mL / g) dissolved in cold alkali. The aqueous alkaline coagulation bath used contains 5.0% by weight NaOH and approximately 20% by weight Na₂CO₃. Its temperature is 30°C.

[0059] The following results were obtained by spinning in the same manner as in Example 1.

[0060] Table 2 - Spinnerets with two rows of holes In Example 3, it is shown that for a conventional spinneret cap, the draw ratio must be significantly reduced as the output speed increases to avoid filament breakage and the formation of clumps entrained by the filament bundle. Reducing the output speed results in a decrease in production rate. It is also shown that this effect (i.e., filament breakage and the formation of clumps entrained by the filament bundle) is stronger when the orifice density increases (900 compared to 300 on the same spinneret cap surface area).

[0061] However, if a spooled spinneret is used (see Examples 1 and 2), the problem of agglomeration can be overcome, and output speeds of up to 40 m / min-50 m / min and draw ratios in the range of 0.8 to 0.9 can be used. Low draw ratios are less preferred because the target linear density (1.3 dtex-1.5 dtex) cannot be achieved with a normal spinneret orifice diameter (productivity decreases as the orifice diameter decreases). There is also a practical lower limit to the orifice diameter that can be manufactured economically, which is approximately 40 micrometers.

[0062] Example 4- Compared to conventional spinnerets, spinnerets with nine rows of holes arranged in rectangular groups... A spinneret with nine rows of holes (541 holes in total) was compared with a conventional spinneret. This spinneret features rectangular groups of holes arranged in nine parallel rows in a hexagonal pattern. 60µm (see) Figure 9 The distance between the peripheries of two adjacent holes in a row is 140µm (the distance between the centers of the holes is 200µm). (See standard circular spinneret). Figure 2 It has 400 holes (Φ: 60µm), which are arranged such that the distance between the perimeters of two adjacent holes is about 540µm (the distance between the centers of the holes is 600µm).

[0063] The spinning solution contained 6.0% by weight cellulose (IV = 210 mL / g) dissolved in cold alkali. The aqueous alkaline coagulation bath used contained 20% by weight Na₂CO₃ and 5.6% by weight NaOH. Its temperature was 28°C. The spinning bath depth was 400 mm.

[0064] Spinning was started at a low extrusion speed (output speed) and gradually increased to find the maximum possible output speed that would produce stable spinning without agglomeration. Throughout the experiment, the draw ratio (take-up speed / output speed) was kept constant at 1.0.

[0065] The rectangular spinneret allows for significantly higher output speeds (26 m / min to 30 m / min, compared to 10 m / min for a conventional circular spinneret cap), even with a denser orifice arrangement (140 µm between the peripheries of two adjacent orifices compared to 540 µm). While maintaining high output speeds (=high production rates), the number of parallel rows can be increased from two rows (see Examples 1 and 2) to at least nine rows. The distance from the center of the orifice in the central row to the nearest point on the periphery of the rectangular group formed by the nine rows is 0.83 mm.

[0066] Example 5- Compared to conventional circular spinnerets, spinnerets with radially arranged groups of orifices... A spinneret with radially arranged groups of holes (each group comprising three rows of holes, each hole having a diameter of approximately 60 µm) is compared to a conventional circular spinneret used in Example 5. The first spinneret with radially arranged groups (see Example 5) Figure 3a It includes 303 holes (the distance between the peripheries of two adjacent holes is 340µm; the distance between the centers of the holes is 400µm), while the second spinneret (see...) Figure 3b It includes 1041 holes (the distance between the perimeters of two adjacent holes is 190µm; the distance between the centers of the holes is 250µm).

[0067] The spinning solution contained 6.0% by weight cellulose (IV = 210 mL / g) dissolved in cold alkali. The aqueous alkaline coagulation bath used contained 20% by weight Na₂CO₃ and 5.6% by weight NaOH. Its temperature was 28°C. The spinning bath depth was 400 mm.

[0068] Spinning was started at a low extrusion speed (output speed) and gradually increased to find the maximum possible output speed that would produce stable spinning without agglomeration. Throughout the experiment, the draw ratio (take-up speed / output speed) was kept constant at 1.0.

[0069] A spinneret with radially arranged groups of orifices allows for significantly higher output speeds (22 m / min and 20 m / min, respectively, compared to 10 m / min), even with a denser orifice arrangement. In fact, the number of orifices can be increased from 303 to 1041 without significantly affecting the maximum output speed.

[0070] The maximum output speed of the spinneret with a radially arranged group of 1041 holes (at a draw ratio of 1.0) is significantly higher than that of the spinneret cap with 900 uniformly distributed holes (see Examples 3 and 4), highlighting the importance of hole arrangement.

[0071] Example 6- A spinneret with radially arranged tapered orifices A 6% wt% cellulose slurry with an IV of 210 mL / g was filtered through a 20 µm nonwoven filter at 20 °C in a spinning solution containing 7.5% wt% NaOH and 0.95% wt% ZnO, and then spun at 30 °C into a coagulated liquid containing water, 18% wt% Na2CO3, 5.5% wt% NaOH and 0.7% wt% ZnO.

[0072] The ratio between the extrusion speed (the average velocity of the feed liquid through the spinneret capillary) and the take-up speed (the speed at which the formed filament is removed from the solidified liquid) is commonly referred to as the draw ratio. This means that the positive draw ratio between the die and the take-up guide roller is 60%. The use of a positive draw ratio is an effective way to distinguish spinnerets that suffer from bundle shrinkage and filament breakage at higher spinning speeds. However, a draw ratio of 1.6 is generally not used for large-scale production because the method becomes less stable and more demanding. Under these conditions, it is simply impossible to spin using a conventional spinneret with 300 holes evenly spaced over a circular area with a diameter of 12 mm (see [link to product description]). Figure 2 The maximum permissible and satisfactory extrusion speed (negligible number of broken filaments) of the new spinneret designed more or less based on the present invention is evaluated.

[0073] Additionally, when spinning at 10 m / min and a constant draw ratio of 1 (i.e., stretching from the die head to the take-up guide roller), the toughness of the wet filament bundle is measured online using a deflection roller connected to a Newton meter. This provides a good indication of the degree of coagulation achieved.

[0074] Different spinnerets with the orifice distributions shown in Figures 6 and 7 were tested. All spinnerets had orifices with a diameter of 60 µm.

[0075] Example 6A) 12mm rectangular area The 1.45mm diameter allows spinning at 14m / min and a draw ratio of 1.6, but results in poor coagulation at a maximum stress of <0.3cN / tex (calculated based on dry cellulose content). This rectangular region comprises 9 rows of parallel holes (541 holes in total) organized in a hexagonal pattern, such that all adjacent holes are equidistant from center to center at 200µm.

[0076] Example 6B) 12mm rectangular area The 3.5mm allows spinning only at 5m / min and a draw ratio of 1.6, but it solidifies well at a maximum stress of >1.3cN / tex (calculated based on the dry cellulose content). This rectangular area includes 9 rows of parallel holes (217 holes in total) organized in a hexagonal pattern, such that all adjacent holes are equidistant from center to center at 500µm.

[0077] Example 6C) Rectangular area 12.5mm The 2.4mm diameter allows for spinning only at 5m / min and a draw ratio of 1.6. This rectangular area comprises 11 rows of parallel holes (500 holes in total) organized in a hexagonal pattern (see [link]). Figure 7g This resulted in all adjacent holes being equidistant from center to center at a distance of 270 µm. However, the maximum stress increased slightly to 0.5 cN / tex (based on the dry cellulose content).

[0078] This illustrates how a larger orifice-to-orifice distance increases coagulation but reduces the permissible extrusion speed. More coagulating fluid is drawn closer to the filaments and improves coagulation, but the greater flow also increases the stress the coagulating fluid must pass through to reach the outermost filaments of the inner filaments. Even though an increased orifice-to-orifice distance will promote inflow, this cannot compensate for the greater flow required to fill the larger volume between the more distant orifices / filaments.

[0079] Example 6D) 12mm rectangular area The 2.6mm diameter allows for spinning at 6m / min and a draw ratio of 1.6. This rectangular area comprises 11 rows of parallel holes (a total of 506 holes) organized in a square pattern (see [link to relevant documentation]). Figure 7f This resulted in adjacent holes being equidistant from center to center at a distance of 260µm. The maximum stress was slightly increased to 0.65cN / tex (based on the dry cellulose content).

[0080] Density similar to the example 6C)The hexagonal pattern was compared to the hexagonal pattern, but both evaluation measures were improved, indicating that the square pattern was superior to the hexagonal one. When fluid flow within the group was improved, the square distribution between the liquid and the filament provided less inertial drag.

[0081] Example 6E) 12mm rectangular area The 2.5mm diameter allows for spinning at 14m / min and a draw ratio of 1.6. This rectangular area comprises 13 rows of parallel holes (520 holes in total) organized in a periodic rectangular pattern (see [link to relevant documentation]). Figure 7d This design ensures that the center-to-center distance between adjacent holes in the row is 200µm, and that adjacent holes are periodically spaced 200µm or 400µm apart along the length. The maximum stress is approximately 0.8 cN / tex (calculated based on the dry cellulose content).

[0082] Clearly, it is beneficial to distribute the holes in a concentrated manner on a larger rectangular group or even a smaller length scale to improve fluid flow within the group through microchannels perpendicular to the group's perimeter.

[0083] Example 6F) like Figure 6a The distribution comprises 630 pores, with center-to-center pore distances of 300µm radially and 200µm tangentially within the elongated groups (6 groups in total). This allows spinning at 10m / min and a draw ratio of 1.6. The maximum stress is approximately 1cN / tex (calculated based on dry cellulose content).

[0084] Example 6G) like Figure 6c The distribution comprises 920 pores, with center-to-center pore distances of 300µm radially and 200µm tangentially within the elongated groups (10 groups in total). This allows spinning at 10m / min and a draw ratio of 1.6. The maximum stress is 0.65cN / tex (calculated based on dry cellulose content).

[0085] Example 6H) like Figure 6d The distribution comprises 1020 holes, with center-to-center hole distances of 300 µm radially and 200 µm tangentially within the elongated groups (12 groups in total). However, this allows spinning at a speed of just 3 m / min and a draw ratio of 1.6. The maximum stress is 0.4 cN / tex (calculated based on dry cellulose content).

[0086] Examples 6F-6H illustrate that, considering the specific size of the group to which the coagulating liquid is supplied through the channels, there is a lower limit to the width of those channels, at which the degree of coagulation and spinning stability are negatively affected by further reducing the channel width. The lower limit of the channel width is approximately 450 µm. As already described herein, the channel width is preferably at least 1000 µm.

Claims

1. A method for spinning an alkali cellulose spinning solution containing dissolved cellulose into an aqueous alkaline coagulation bath liquid containing coagulation salts, thereby forming cellulose filaments, the method comprising the following steps: - The alkali cellulose spinning solution is fed into a spinneret (110) having a plurality of holes (120) arranged in at least one set (130) such that the distance D1 from the center of any given hole (120) in the set (130) to the nearest point on the periphery (131) of the set (130) does not exceed 3 mm, and the diameter of each hole (120) is 40 µm to 100 µm; The plurality of orifices of the spinneret (110) are arranged in more than one group, and the flow channels (135) for the aqueous alkaline coagulation bath liquid are arranged on the spinnerets (110) between adjacent groups to provide flow channels (135) for the aqueous alkaline coagulation bath liquid to flow inward between the groups (130), wherein the flow channels (135) have no orifices; - The alkali cellulose spinning solution is extruded through the orifice (120) into the water-containing alkaline coagulation bath liquid, thereby forming cellulose filaments; as well as - The cellulose filaments are extracted from the aqueous alkaline coagulation bath liquid; The holes at the periphery (131) of the group (130) are in direct contact with the water-containing alkaline coagulation bath liquid.

2. The method according to claim 1, wherein the distance D1 from the center of any given hole (120) in the group (130) to the nearest point on the periphery (131) of the group (130) does not exceed 2 mm.

3. The method according to claim 1, wherein the group (130) is elongated.

4. The method according to claim 2, wherein the group (130) is elongated.

5. The method of claim 3, wherein the elongated group (130) is substantially rectangular and / or tapered.

6. The method of claim 4, wherein the elongated group (130) is substantially rectangular and / or tapered.

7. The method according to any one of claims 3-6, wherein the width W of the group (130) is in the range of 0.5 mm to 6 mm, the width being the size of the group perpendicular to the length at half the length of the group; and / or wherein the length L:width W ratio of the group (130) is at least 2.

8. The method according to claim 7, wherein the width W of the group (130) is in the range of 1 mm to 4 mm.

9. The method according to claim 7, wherein the length L:width W ratio of the group (130) is at least 3.

10. The method according to any one of claims 1-6 and 8-9, wherein the minimum characteristic measure of the spinneret (110) is in the range of 0.5 mm to 24 mm.

11. The method according to claim 10, wherein the minimum feature measure of the spinneret (110) is in the range of 1.5 mm to 20 mm.

12. The method according to any one of claims 1-6, 8-9 and 11, wherein the flow channel (135) has no holes, thereby providing an opening at the periphery (131) of the assembly (130) for direct access to the aqueous alkaline coagulation bath liquid.

13. The method according to claim 12, wherein the spinneret (110) is circular.

14. The method of claim 12, wherein the width of the flow channel is at least 450 µm.

15. The method of claim 13, wherein the elongated group (130) is arranged radially.

16. The method according to claim 15, wherein the diameter of the spinneret (110) is 8 mm to 24 mm.

17. The method according to claim 16, wherein the diameter of the spinneret (110) is 10 mm to 20 mm.

18. The method according to any one of claims 15-17, wherein the elongated group (130) is substantially rectangular and the elongated group (130) is radially arranged on the spinneret (110).

19. The method of claim 18, wherein adjacent elongated groups have different lengths.

20. The method according to any one of claims 15-17, wherein the elongated group (130) is arranged radially on the spinneret (110), and wherein the elongated group (130) tapers at least partially toward the center of the spinneret (110) along its longitudinal extension.

21. The method according to any one of claims 15-17 and 19, wherein at least two circular spinnerets (110) are arranged in a spinning head (100), and the alkali cellulose spinning solution is fed into the spinning head to be extruded through each spinneret.

22. The method of claim 21, wherein at least five circular spinnerets (110) are arranged in the spinning head (100), and the alkali cellulose spinning solution is fed into the spinning head to be extruded through each spinneret.

23. The method according to any one of claims 1-6, 8-9, 11 and 14, wherein the spinneret (110) is rectangular and the width of the spinneret (110) is less than 10 mm.

24. The method according to claim 23, wherein the width of the spinneret (110) is in any range of 0.5 mm to 7 mm, 1 mm to 6 mm, or 1.5 mm to 5 mm.

25. The method according to claim 23, wherein the length:width ratio of the spinneret (110) is 5:1 to 200:

1.

26. The method according to claim 25, wherein the length:width ratio of the spinneret (110) is 10:1 to 100:

1.

27. The method of claim 23, wherein the holes in the spinneret are arranged in a rectangular group.

28. The method of claim 27, wherein the holes are arranged such that the width of the group of rectangles does not exceed 4 mm.

29. The method of claim 28, wherein the holes are arranged such that the width of the group of rectangles is 0.4 mm to 4 mm.

30. The method according to any one of claims 1-6, 8-9, 11, 13-17, 19, 22 and 24-29, wherein the holes (120) are unevenly distributed within the group (130).

31. A spinneret (110) for spinning an alkali cellulose spinning solution into an aqueous alkaline coagulation bath liquid, the spinneret (110) having a plurality of holes (120), each hole (120) having a diameter of 40µm to 100µm, wherein the holes (120) are arranged in at least two groups (130), the holes in each group being arranged such that the distance D1 from the center of any given hole (120) in the group (130) to the nearest point on the periphery (131) of the group (130) does not exceed 3mm, and wherein flow channels (135) for the aqueous alkaline coagulation bath liquid are arranged on the spinneret (110) between adjacent groups (130) to provide flow channels (135) for the aqueous alkaline coagulation bath liquid to flow inward between the groups (130), the flow channels (135) having no holes.

32. The alkali cellulose spinning solution spinneret (110) according to claim 31, wherein the holes in each group are arranged such that the distance D1 from the center of any given hole (120) in the group (130) to the nearest point on the periphery (131) of the group (130) does not exceed 2 mm.

33. The spinneret (110) for alkali cellulose spinning solution according to claim 31, wherein the minimum characteristic measurement of the spinneret (110) is in the range of 0.5 mm to 24 mm.

34. The spinneret (110) for alkali cellulose spinning solution according to claim 32, wherein the minimum characteristic measurement of the spinneret (110) is in the range of 0.5 mm to 24 mm.

35. The spinneret (110) for alkali cellulose spinning solution according to claim 33, wherein the minimum characteristic measurement of the spinneret (110) is in the range of 1.5 mm to 20 mm.

36. The spinneret (110) for alkali cellulose spinning solution according to claim 34, wherein the minimum characteristic measurement of the spinneret (110) is in the range of 1.5 mm to 20 mm.

37. The spinneret (110) for alkali cellulose spinning solution according to any one of claims 31-36, wherein the plurality of holes (120) are arranged in an elongated group (130), and wherein the spinneret (110) is circular.

38. The alkali cellulose spinning solution spinneret (110) according to claim 37, wherein the elongated group (130) is arranged radially.

39. The spinneret (110) for alkali cellulose spinning solution according to claim 37, wherein the diameter of the spinneret (110) is 8 mm to 24 mm.

40. The spinneret (110) for alkali cellulose spinning solution according to claim 39, wherein the diameter of the spinneret (110) is 10 mm to 20 mm.

41. The alkali cellulose spinning solution spinneret (110) according to claim 37, wherein the elongated group (130) is substantially rectangular and / or tapered.

42. The alkali cellulose spinning solution spinneret (110) according to claim 41, wherein: - The elongated group (130) is substantially rectangular, and the elongated group (130) is radially arranged on the spinneret (110); and / or - The elongated groups (130) are arranged radially on the spinneret (110), and wherein the elongated groups (130) taper at least partially toward the center of the spinneret along their longitudinal extensions.

43. The alkali cellulose spinning solution spinneret (110) according to claim 42, wherein when the elongated group (130) is substantially rectangular, adjacent elongated groups have different lengths.

44. The spinneret (110) for alkali cellulose spinning solution according to any one of claims 31-36, wherein the spinneret (110) is rectangular and the width of the spinneret (110) is less than 10 mm.

45. The spinneret (110) of alkali cellulose spinning solution according to claim 44, wherein the width of the spinneret (110) is in any range of 0.5 mm to 7 mm, 1 mm to 6 mm or 1.5 mm to 5 mm.

46. ​​The spinneret (110) for alkali cellulose spinning solution according to claim 44, wherein the length:width ratio of the spinneret is from 5:1 to 200:

1.

47. The spinneret (110) for alkali cellulose spinning solution according to claim 46, wherein the length:width ratio of the spinneret is 10:1 to 100:

1.

48. The spinneret (110) for alkali cellulose spinning solution according to claim 44, wherein the holes in the spinneret are arranged in a rectangular group.

49. The alkali cellulose spinning solution spinneret (110) according to claim 48, wherein the holes are arranged such that the width of the group of rectangles does not exceed 4 mm.

50. The alkali cellulose spinning solution spinneret (110) according to claim 49, wherein the holes are arranged such that the width of the group of rectangles is 0.4 mm to 4 mm.

51. The alkali cellulose spinning solution spinneret (110) according to any one of claims 31-36, 38-43 and 45-50, wherein the orifices (120) are unevenly distributed in the group (130).

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