CN117716074A - Method for spinning alkali cellulose - Google Patents

Method for spinning alkali cellulose Download PDF

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Publication number
CN117716074A
CN117716074A CN202280044808.2A CN202280044808A CN117716074A CN 117716074 A CN117716074 A CN 117716074A CN 202280044808 A CN202280044808 A CN 202280044808A CN 117716074 A CN117716074 A CN 117716074A
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CN
China
Prior art keywords
holes
spinneret die
spinneret
group
die
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CN202280044808.2A
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Chinese (zh)
Inventor
阿图尔·海德伦德
本特·哈格斯特龙
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Tritech
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Tritech
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Priority claimed from PCT/EP2022/068458 external-priority patent/WO2023280778A1/en
Publication of CN117716074A publication Critical patent/CN117716074A/en
Pending legal-status Critical Current

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    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F2/00—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D1/00—Treatment of filament-forming or like material
    • D01D1/02—Preparation of spinning solutions
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D4/00—Spinnerette packs; Cleaning thereof
    • D01D4/02—Spinnerettes
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/06—Wet spinning methods
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F2/00—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof
    • D01F2/02—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof from solutions of cellulose in acids, bases or salts

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  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Spinning Methods And Devices For Manufacturing Artificial Fibers (AREA)
  • Artificial Filaments (AREA)

Abstract

A process for spinning an alkali cellulose spinning dope comprising dissolved cellulose into an aqueous alkali coagulation bath liquid comprising a coagulation salt, thereby forming cellulose filaments. The method comprises the following steps: -feeding the alkali cellulose dope to a spinneret die (110) having a plurality of holes (120) arranged in at least one group (130) such that the distance (D1) from the centre 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 3mm, such as 2mm, each hole (120) having a diameter of 40 μm to 100 μm; -extruding the alkali cellulose dope through the orifice (120) into the aqueous alkali coagulation bath liquid, thereby forming cellulose filaments; -withdrawing the cellulose filaments from the aqueous alkaline coagulation bath liquid; wherein the holes (121) at the periphery (131) of the set (130) are in direct contact with an aqueous alkaline coagulation bath liquid.

Description

Method for spinning alkali cellulose
Technical Field
The present invention relates to a process for spinning cellulose dissolved in an aqueous solution of sodium hydroxide (NaOH) into cellulose fibers. In spinning the dissolved alkali cellulose, the alkali cellulose is extruded into a coagulation bath to precipitate cellulose, thereby forming cellulose fibers.
Background
Fibers have a wide range of applications in the textile industry. Historically, textile fibers have been natural fibers. For example, cotton fibers have long been used in the textile industry to make fabrics. In addition, other plant fibers, such as flax fibers, have been used. In the 20 th century, plastic fibers (such as nylon and polyester fibers) emerged as an inexpensive alternative to the production of fabrics. Cotton fibers still represent a very important fiber in the textile industry.
In view of the need to reduce the carbon footprint, the demand for natural fibers has restarted. However, the planting and processing of cotton also causes environmental problems. Accordingly, there is an increasing interest in alternative sources of cellulose for making fibers.
The viscose process has long been known to use wood as a raw material for the production of cellulose fibres. In the viscose process, regenerated cellulose fibres are passed through sodium cellulose xanthate, i.e. through CS 2 Regeneration of the (carbon disulphide) -derived cellulose is provided to increase the solubility. However, the use of carbon disulphide is associated with problems including its toxicity. Furthermore, as the dissolved sodium cellulose xanthate is spun into aqueous sulfuric acid to precipitate the cellulose fibers and regenerate carbon disulfide, there is currently no commercially valuable Na 2 SO 4 Inevitably formed as a by-product in the viscose process. Accordingly, it is desirable in the art to find alternative methods of providing cellulosic fibers from wood.
It is known in the art that underivatized cellulose is to some extent soluble in cold aqueous sodium hydroxide solution. Thus, aqueous sodium hydroxide was used as the cellulose solvent in the experimental procedure, but no commercially viable process for fiber spinning has been available to date.
In spinning of experimental spin dope comprising cellulose dissolved in aqueous sodium hydroxide, as in the viscose process, the spin dope has been wet spun into a coagulation bath comprising aqueous sulfuric acid. This procedure requires a large amount of sodium hydroxide when providing the fibers, and similar to the viscose process, sodium sulfate is produced as a residue.
To solve this problem, it has been proposed in the art (see for example WO 2020/171767, WO 2018/169479, WO 2017/178532, WO 2015/000820, WO2010/104458, issued to the applicant) to spin the dissolved cellulose to a solution comprising a coagulated sodium salt aqueous solution (for example Na 2 CO 3 Or Na (or) 2 SO 4 ) And recovering sodium hydroxide (NaOH) and sodium coagulating salt from the spinning bath, respectively. This method is considered promising because the chemicals (i.e. NaOH and coagulated sodium salt) can be recovered separately.
The applicant has indeed found that cellulose dissolved in an aqueous sodium hydroxide solution to produce a spinning dope can be spun onto a solid containing an aqueous solution of sodium salt (e.g. Na 2 CO 3 Or Na (or) 2 SO 4 ) Is used for the coagulation bath. When the dope is spun into a coagulation bath, a wet-swellable tow is provided. The regenerated fiber bundles may then be withdrawn from the coagulation bath to provide cellulosic fibers.
In the viscose process, sodium cellulose xanthate is usually spun by means of a spinneret die, a small metal plate, sleeve or cap with fine holes through which the spinning dope is forced into an acid coagulation bath in the spinning of filaments. A spinneret (see fig. 1, which shows a conventional spinneret with multiple spinneret dies, each having hundreds or thousands of fine holes as shown in fig. 2) is designed to form thousands of thin jets of dope exiting the spinneret and entering the coagulation bath liquid. There will be a diffusion-based chemical exchange between the dope jet and the coagulation liquid upon contact with the coagulation liquid. The interdiffusion of chemicals is a rapid process because the dope jet exiting the spinneret capillaries is thin (typically 40 μm to 100 μm in diameter). When the spinning dope jet contacts with the solidification liquid, protons quickly enter the jet and neutralize the alkali to form sodium sulfate. The solvating power of the base is thus suddenly reduced and the cellulose precipitates, forming a dense cellulose network. Since cellulose precipitates (solidifies) very rapidly under acidic conditions, the dope jet is converted directly into thin, tough and non-swelling filaments as it exits the spinneret orifice. Without being bound by any theory, the rapid precipitation may be at least partially mediated by acidic conditions and hydronium ions (H 3 O + ) Is explained by the rapid diffusion of (c).
These features allow for a number of and closely spaced holes in each spinneret die, as shown in fig. 2. The prior art spinneret die (16 mm in diameter) may have 1800 to 2400 holes, each hole having a diameter of about 60 μm. The exit velocity of the dope jet may typically be in the range of 30m/min to 50m/min (average velocity in the hole). The production rate from a spinneret as shown in fig. 1 (200 mm diameter, provided with 45 dies each having 2000 holes) may be in the range of 30kg/h to 50kg/h (1.3 dtex fiber).
However, in contrast to the viscose process using an acid coagulation bath, a process is used which comprises a coagulation salt (e.g. Na 2 SO 4 Or Na (or) 2 CO 3 ) The coagulation method of the alkali coagulation bath is different from the viscose method using the acid coagulation bath. In particular, the precipitated filaments have been found to solidify in alkaliThe bath remains swollen and thus the initial filaments have a lower structural integrity. These characteristics of filaments limit the production rate using conventional spinnerets and spinneret dies. To avoid breakage of the filaments, resulting in formation of filament masses/coils, the exit velocity must be significantly reduced, thereby reducing the production rate.
Accordingly, there is a need in the art for an efficient process for spinning cellulose dissolved in aqueous sodium hydroxide (NaOH) solution into cellulose fibers.
Disclosure of Invention
In spinning studies using a conventional circular spinneret die with holes arranged in concentric circles, it was found that the softer nature and larger diameter of the swollen filaments in the case of an alkali coagulation bath resulted in a radially inward moving pattern of the dope jet exiting the holes in the spinneret die, resulting in shrinkage of the filament bundle (see fig. 4 a). If an acid coagulation bath is used, no corresponding shrinkage of the filament bundle is seen, in which case the jet of spinning dope follows in principle a straight path in the upward direction. In the acid coagulation bath, the dense, thin and tough filaments formed at the spinneret die surface resist the drag action of the radially inward flow of the coagulation bath liquid.
Thus, in the case of an alkaline coagulation bath, the filament bundle shrinkage is a result of the soft character of the jet and their significantly larger diameter produces a greater hydrodynamic interaction with the radial inflow of the coagulating liquid. The phenomena described (radial inflow of the solidifying liquid and shrinkage of the strands) tend to tear and break the filaments formed. The degree of coagulation is also sensitive to the high ratio of fiber volume to coagulation bath liquid volume in the advancing tow. If the draw ratio is kept constant (draw ratio dr=take-up speed divided by stock jet output speed), the strand shrinkage in the case of an alkaline coagulation bath will increase with increasing flow rate of the dope. It follows that: in the case of an alkali coagulation bath, both the hole density and output speed of conventional spinneret dies limit the possible production rates using conventional viscose spinneret technology.
Thus, according to a first aspect, there is provided a process for spinning an alkali cellulose spinning dope comprising dissolved cellulose into an aqueous alkali coagulation bath liquid comprising a coagulation salt, such as sodium coagulation salt, thereby forming cellulose filaments. The method comprises the following steps:
-feeding an alkali cellulose spinning dope to a spinning die having a plurality of holes;
-extruding an alkali cellulose dope through an orifice into an aqueous alkali coagulation bath liquid, thereby forming cellulose filaments; and
-withdrawing cellulose filaments from the aqueous alkaline coagulation bath liquid.
By providing a spinneret die with said plurality of holes, the shrinkage of the filament bundle can be significantly reduced, thereby increasing the possible production rate, each hole having a diameter of 40 μm to 100 μm, being arranged in at least one group such that the distance from the center of any given hole in the group to the nearest point on the group's periphery is no more than 3mm (such as 2 mm), and such that the holes at the group's periphery are in direct contact with the aqueous alkaline coagulation bath liquid. Thus, the spinneret die has a plurality of holes arranged in at least one set such that the distance from the center of any given hole in the set to the nearest point on the periphery of the set is no more than 3mm (such as 2 mm). The perimeter of the set of holes is defined by the perimeter of the outermost holes in the set. The average center-to-center distance of adjacent holes may be 200 μm to 400 μm, such as 250 μm to 400 μm.
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 rectangular or trapezoidal (a pair of opposite sides parallel), such as an isosceles trapezoid (a pair of opposite sides parallel and with equal base angles). According to one embodiment, the polygon fitted to the set of holes is a rectangle.
According to another embodiment, the perimeter is defined by a tangential straight line between the perimeters of adjacent outermost holes in the set.
Typically, the plurality of holes are arranged in an elongated group. The elongate group may be substantially rectangular. In addition, the elongate group may taper at least partially along its longitudinal extension, such as substantially in the form of an isosceles trapezoid (a pair of opposing sides parallel and having equal base angles).
In embodiments wherein the plurality of apertures are arranged in an elongated group, the width of the group (the dimension perpendicular to the longitudinal extension, i.e. length, at half the length of the group) may be in the range of 0.5mm to 6mm, preferably in the range of 1mm to 4 mm. In addition, the length of the elongated group (e.g., a substantially rectangular group): the width ratio may 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 the dimension of the group perpendicular to the length, e.g., at half the length of the group. For an elongated group that is not rectangular, the width is defined as the dimension of the group that is perpendicular to the length (i.e., the longest dimension of the group) at half the length of the group.
For a tapered elongate group, such as an elongate group substantially taking the form of an isosceles trapezoid, the width may be at least 0.5mm at one end and no more than 6mm, such as no more than 4mm, at the opposite end. In addition, the width of the tapered elongate group may be gradually reduced, i.e. the group may be regarded as comprising two or more adjacent rectangles. The tapered elongate group may also be a wedge-shaped group that is very thin at one end of its longitudinal extension. For such an elongated set, the width at the thin end may even correspond to the diameter of a single hole.
The spinneret die may have different forms. For example, it may be circular or rectangular. According to one embodiment, the spinneret die is circular. According to another embodiment, the spinneret die is rectangular. The minimum feature measurement of the spinneret die is in the range of 0.5mm to 24mm, such as in the range of 1.5mm to 20 mm. For a circular spinneret die, the minimum characteristic measure is the diameter. For rectangular spinneret dies, the smallest feature measure is width.
In embodiments where the spinneret die is circular, its smallest feature measure (i.e., diameter) may have a diameter in the range of 8mm to 24mm, such as in the range of 10mm to 20 mm.
In embodiments where the spinneret die is rectangular, its minimum feature measure (i.e., width) may be less than 10mm, for example in any of the ranges of 0.5mm to 7mm, 1mm to 6mm, or 1.5mm to 5 mm. For rectangular spinneret dies, the length to width ratio may be at least 5:1. The length to width ratio may be from 5:1 to 200:1, such as from 10:1 to 100:1. In addition, the holes in the rectangular spinneret die may be arranged in a set of rectangular holes. The holes may be arranged such that the width of a set of rectangular holes does not exceed 4mm, preferably does not exceed 3mm. According to one embodiment, the holes are arranged such that the width of a set of rectangular holes is 0.4mm to 4mm, such as 1mm to 3mm.
According to one embodiment, the spinneret die is arranged on the edge of the plate. The plate is provided with a flow channel for receiving, distributing and feeding the alkali cellulose dope to a spinneret die having holes. The plate may have a length of 5cm to 50 cm. Thus, the edge on which the spinneret die is disposed may be 5cm to 50cm long.
The dimension of the spinneret die perpendicular to the minimum feature measure may be longer than the minimum feature measure, such as in a rectangular spinneret die. However, in some embodiments, the spinneret die measure perpendicular to the minimum feature measure may also be in the range of 0.5mm to 24mm, such as in the range of 1.5mm to 20 mm. By definition, the spinneret die measure perpendicular to the minimum feature measure is equal to or longer than the minimum feature measure. For a circular spinneret die, these two measurements are identical.
In the art, a plurality of circular spinneret dies are generally arranged in a spinneret to which an alkali cellulose dope is fed to be extruded through each spinneret die. According to one embodiment, at least two (such as at least five) spinneret dies are arranged in the spinneret. In one embodiment, according to this embodiment, a circular spinneret die is arranged in the spinneret, and at least 5, such as at least 10, spinneret dies may be arranged in the spinneret.
According to one embodiment, the plurality of holes of a spinneret die (such as a circular spinneret die) are arranged in more than one set of holes. The sets of holes are arranged in such a way that flow channels for aqueous alkaline coagulation bath liquid are present on the spinneret die between adjacent sets. The flow channels are free of holes. By providing a spinneret die with a flow channel, holes at the periphery of the stack are directly fed with aqueous alkali coagulation bath liquid, as aqueous alkali coagulation bath liquid can flow in the flow channel to feed alkali coagulation bath liquid to holes that are not present along the periphery of the spinneret die. Each set of holes is arranged in such a way that the minimum distance between the perimeters 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 am. According to one embodiment, the groups of holes are arranged in such a way that the distance between the circumferences of two adjacent groups is at least 1.5 times the centre-to-centre distance of the smallest holes between holes in the group, such as at least 3 times the centre-to-centre distance of the smallest holes between holes in the group.
According to one embodiment, a spinneret die having more than one set of holes may be circular. The diameter of the circular spinneret die may be 8mm to 24mm, such as 10mm to 20mm in diameter. Thus, the diameter of the circular surface of the circular spinneret die on which each set of holes is arranged may be 8mm to 24mm, such as 10mm to 20mm in diameter. The sets of holes on the circular spinneret die may be elongated, such as substantially rectangular. In addition, the elongate sets of apertures may be at least partially tapered along their longitudinal extension. The groups of elongated orifices disposed on the circular spinneret die may be radially disposed to provide radially disposed flow channels between the groups of orifices. By radially arranging the substantially rectangular sets of holes, if each set is substantially rectangular, a flow channel tapering toward the center of the circular spinneret die can be radially provided on the circular spinneret die. In addition, the lengths of the elongated sets of holes disposed on the circular spinneret can be varied 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 die, i.e. the radius of the circular surface of the spinneret die on which they are arranged. Preferably, the length of the radially arranged group is shorter than the radius, such as not longer than 90%, 80% or 70% of the radius, i.e. the length of the radially arranged group does not exceed 90%, such as 80% or 70% of the radius. In addition, the length of the radially arranged group may be at least 40%, such as at least 50% or at least 60% of the radius.
According to one embodiment, adjacent elongated groups radially disposed on a circular spinneret die may have different lengths. Thus, the longer set of holes may be arranged close to the shorter set of holes. By arranging groups of different lengths on the circular spinneret die, the number of holes present on the circular spinneret die can be increased while still providing a flow channel of sufficient width to allow the aqueous alkaline coagulation bath liquid to flow inwardly on the circular spinneret die. According to this embodiment, the length of the first shorter group: the width ratio may be at least 2, and the second longer group of lengths: the width ratio may be at least 3. The width of each group may be in the range of 0.5mm to 6 mm; preferably, the width of each group is in the range 1mm to 4 mm.
According to one embodiment, the elongated groups radially arranged on the circular spinneret die may taper at least partially along their longitudinal extension towards the center of the circular spinneret die. Preferably, at least the portion of the elongated set facing the center of the circular spinneret die is tapered, such as at least 15% of the elongated set is tapered along its longitudinal extension. The at least partial tapering of the elongated groups radially arranged on the circular spinneret die along their longitudinal extension towards the center of the circular spinneret die has the following advantages: the distance between adjacent groups does not decrease or decreases less in the radial direction.
According to one embodiment, wherein the elongated groups are radially arranged on the circular spinneret die, the radially arranged groups may be arranged in a fan pattern to provide a main flow channel in addition to said flow channel through which aqueous alkaline coagulation bath liquid may flow on the circular spinneret die towards the center of the circular spinneret die. The main flow channel can be used to increase the feed of aqueous alkaline coagulation bath liquid to the orifice in the center of the spinneret die.
According to one embodiment, wherein the elongated groups are radially arranged on the circular spinneret die, the holes are not arranged in the center of the circular spinneret die, whereby the radial flow channels between the elongated groups are in fluid communication with each other in the center of the circular spinneret die.
According to another embodiment, wherein the elongated groups are radially arranged on the circular spinneret die, the holes are also arranged in the center of the circular spinneret die, whereby the flow channels between the elongated groups are closed and not in fluid communication with each other in the center of the circular spinneret die. Thus, the elongated groups may be considered to be arranged in a star or asterisk pattern.
The holes in the group may be distributed in different ways. According to one embodiment, they are uniformly distributed in groups, for example in a hexagonal or square pattern. The distribution of the holes in a square pattern may improve the flow of aqueous alkaline coagulation bath liquid within the group.
In addition, the holes may also be unevenly distributed in the group. The non-uniform distribution of the pores may improve the flow of aqueous alkaline coagulation bath liquid within the group. The average center-to-center distance of two adjacent holes in a group may be 250 μm to 400 μm, also with unevenly distributed holes.
According to one embodiment, the holes in the set on the circular spinneret are unevenly arranged in such a way that the average center-to-center hole distance in the radial direction is greater than the average center-to-center hole distance in the direction perpendicular to the radial direction. The holes in the set that are unevenly arranged on the circular spinneret die may be arranged to provide micro-channels for the solidifying liquid to flow into the set.
According to another aspect, there is provided an alkali cellulose dope spinning die for spinning an alkali cellulose dope into an aqueous alkali coagulation bath liquid. The spinneret die has a plurality of holes, each hole having a diameter of 40 μm to 100 μm. The holes are arranged in at least two groups. The holes in each group are arranged such that the distance from the centre of any given hole in the group to the nearest point on the periphery of the group is no more than 3mm, such as 2mm. In addition, the holes in each set are arranged such that the flow channels for the aqueous alkaline coagulation bath liquid are arranged on the spinneret die between adjacent sets. The flow channels are free of holes. Preferably, the alkali cellulose dope spinning die is circular and has radially arranged sets of holes and radially arranged flow channels therebetween. In addition, preferred features of such circular spinneret dies have been described above.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. Accordingly, the above preferred embodiments should be understood as being merely exemplary and in no way limiting of the present disclosure.
Although the invention has been described above with reference to specific embodiments, it is not intended to be limited to the specific forms set forth herein. Rather, the invention is limited only by the accompanying claims and, other embodiments than the specific above are equally possible within the scope of these appended claims.
In the claims, the term "comprising" does not exclude the presence of other elements or steps. Furthermore, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous.
In addition, singular references do not exclude a plurality. The terms "a", "an", "the" first "," second "etc. do not preclude a plurality.
Drawings
These and other aspects, features and advantages that the present invention can achieve will be apparent from and elucidated with reference to the embodiments described hereinafter, with reference to the accompanying drawings, in which:
FIG. 1 shows a photograph of a conventional spinneret with several circular spinneret dies as known in the art;
fig. 2 shows one of the spinneret dies in the spinneret of fig. 1. The holes in a conventional spinneret die are arranged in concentric circles;
FIG. 3a illustrates a circular spinneret die with holes arranged in elongated groups according to one embodiment;
FIG. 3b illustrates a circular spinneret die with holes arranged in elongated groups according to one embodiment;
FIG. 4a shows a photograph of spinning from a conventional spinneret die (see FIG. 2);
FIG. 4b shows a photograph of spinning from a spinneret die according to one embodiment;
FIG. 5 shows a close-up of a circular spinneret die with orifices arranged in elongated groups and two adjacent groups of orifices, according to one embodiment;
FIG. 6 illustrates a die having radially arranged set of holes according to an embodiment;
FIG. 7 illustrates various ways of distributing holes in a given set of holes;
FIG. 8 illustrates a rectangular spinneret die according to one embodiment;
FIG. 9 illustrates a rectangular spinneret die according to one embodiment;
FIG. 10 illustrates a spinneret having two rectangular spinneret dies, each rectangular spinneret die having a set of holes, according to one embodiment; and is also provided with
Fig. 11 shows a photograph of a spinneret with four rectangular spinneret dies, each rectangular spinneret die having a set of holes, according to one embodiment.
Detailed Description
To provide efficient spinning of the alkali cellulose dope, a plurality of spinneret dies 110 (see fig. 2) having holes 120 are typically assembled into a spinneret 100, as seen in fig. 1 and as known in the art. The alkali cellulose dope is fed to the spinneret 100, and the alkali cellulose dope is extruded into a coagulation bath liquid through the holes 120 to form cellulose filaments. The spinneret die is provided with a plurality of holes 120 to provide efficient spinning. In die 110 of the art, holes 120 are typically arranged in concentric circles, as can be seen in fig. 2.
Fig. 3a and 3b respectively illustrate a circular spinneret die 110 according to one embodiment. Orifices 120 on spinneret die 110 are arranged in elongated groupings 130a, 130b to provide flow channels 135 for the flow of the alkaline coagulation bath liquid inwardly between groupings 130a, 130b, as shown in fig. 3 a. The sets 130a, 130b are elongated. In addition, the lengths of the sets 130a, 130b may be different. These groups may be radially arranged as shown in fig. 3. Optionally, one or more groups in a radial pattern may be omitted to provide the primary flow channels 136.
As can be seen in fig. 3b, groups 130a, 130b, 130c of different lengths may be combined to increase the number of holes 120 present on spinneret die 110 while still providing flow channels 135 separating groups 130.
As can be seen in fig. 4 (see double arrow), less strand shrinkage is observed when spinning with a spinneret die having holes arranged in radially arranged groups (see fig. 4 b) compared to a conventional spinneret die having holes arranged in concentric circles (see fig. 4 a). This means that the filaments are subjected to less force perpendicular to the flow direction.
The elongate groups 130a, 130b, 130c in fig. 3 are substantially rectangular. By fitting a rectangle around the aperture 120, the perimeter 131 of the set may be defined, as can be seen in fig. 5. The length L and width W of the elongate set may be defined as the length L and width W of a rectangle fitted to the set of holes. When fitting a rectangle to the holes 120, all holes will be within the rectangle. In addition, the rectangle should be as short and as narrow as possible. The perimeter 121 is thus defined by the perimeter of the outermost aperture 121 in the set 130.
The closest distance between two adjacent groups 130a, 130b may be defined as the closest distance D2 between the perimeter 131a, 131b of each of the groups 130a, 130b. As an alternative to fitting a rectangle to a group, the perimeter may be defined by a tangential straight line between the perimeters of adjacent outermost holes 121 in the group 130. For the group in fig. 5, this provides a substantially rectangular arrow-shaped group 130a, 130b. In addition, the distance D1 from the center of the holes 122 in the center of the set 130 to the nearest point on the perimeter 131 of the set 130 is also shown in FIG. 5.
In radially arranging the holes 120 of the set 130, they may be arranged in different numbers (e.g. 6, 8, 10, 12 or 16) of radii, as can be seen in fig. 6 a-6 g. Group 130 has the same length with the tapered ends pointing toward the center of circular spinneret die 110. The hole is not disposed in the center of circular spinneret die 110. By tapering stack 130, the number of holes 120 present on spinneret die 110 may be increased while still providing flow channels 135 having a sufficient width to separate stack 130. In addition, as can be seen in fig. 6 e-6 g and 7, holes 120 in a given set may be distributed differently, regardless of the shape of spinneret die 110.
In fig. 8, a rectangular spinneret die 110 is shown according to one embodiment. A set 130 of holes 120 are present on spinneret die 110. According to this embodiment, the set 120 consists of two rows of holes 130. In fig. 7, a rectangular spinneret die 110 is shown according to one embodiment. This embodiment is similar to the embodiment in fig. 9. However, the apertures 130 of the set 120 are comprised of nine rows of apertures 130.
Similar to circular spinneret die 110, rectangular spinneret die 110 may also be arranged together in spinneret 100, as schematically shown in fig. 10, which shows rectangular spinneret die 110 from above. Fig. 11 shows a photograph of a spinneret 100 having four rectangular spinneret dies 110 arranged in parallel spaced apart relation.
Examples
Example 1-spinneret with two rows of holes
Using holes having rectangular groups arranged in two parallel rowsIs shown in fig. 8). The distance between the circumferences of two adjacent holes in a row is 140 μm (the distance between the centers of the holes is 200 μm).
The spinning dope comprising 6.0 wt% acid hydrolyzed birch pulp (intrinsic viscosity=210), 7.5 wt% NaOH and 0.95 wt% ZnO was spun using the spinning die. In preparing the dope, it is filtered through two consecutive PP nonwoven filter media (coarse and fine media) in a filter press.
The aqueous alkaline coagulation bath liquid used contained 21 wt% Na 2 CO 3 And 5.7 wt% NaOH. The temperature was 29 ℃. In the spinning, an on-line filtration of 20 μm metal fiber fleece by means of SIKA-FIL was used. The depth of the spinning bath was 80cm. Spinning with an output speed of 40m/min and a godet speed (take-up speed) of 35m/min works well (draft ratio=0.88).
Example 2-spinneret with two rows of holes
The same spinneret die as in example 1 was used. The spin dope contained 6.0 wt% cellulose, 7.5% NaOH, and 0.9% ZnO. The aqueous alkaline coagulation bath liquid used contained 21 wt% Na 2 CO 3 And 5% by weight NaOH. The temperature was 30 ℃.
The following results were obtained by spinning in the same manner as in example 1.
TABLE 1 spinneret with two rows of holes
Example 3 (reference example) conventional spinneret cap
A conventional spinneret cap (see fig. 2) was used. The dope contained 6.3 wt% cellulose dissolved in cold base (iv=220 mL/g). The aqueous alkaline coagulation bath liquid used contained 5.0% by weight NaOH and about 20% by weight Na 2 CO 3 . The temperature was 30 ℃.
The following results were obtained by spinning in the same manner as in example 1.
TABLE 2 spinneret 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 formation of rolls entrained by the filament bundles. Decreasing the output speed results in a decrease in the production rate. It has also been shown that this effect (i.e., filament breakage and formation of a roll entrained by the filament bundle) is stronger as the hole density increases (900 vs. 300 on the same spinneret cap surface area).
However, if a line spinneret die (see examples 1 and 2) is used, the problem of lump formation can be overcome, and an output speed of up to 40m/min-50m/min and a draft ratio in the range of 0.8 to 0.9 can be used. Low draw ratios are less preferred because the target thread density (1.3 dtex-1.5 dtex) cannot be achieved with normal spinneret hole diameters (productivity decreases with decreasing hole diameter). There is also a practical lower limit to the pore diameter that can be economically manufactured, being about 40 microns.
Example 4-compared to a conventional spinneret die, a spinneret die having nine rows of holes arranged in rectangular groups
A spinneret die having nine rows of holes (541 holes in total) was compared with a conventional spinneret die. The spinneret die had rectangular sets of holes arranged in 9 parallel rows in a hexagonal pattern(see FIG. 9). The distance between the circumferences of two adjacent holes in a row is 140 μm (the distance between the centers of the holes is 200 μm). A conventional circular spinneret die (see fig. 2) has 400 holes (Φ:60 μm) arranged such that the distance between the circumferences of two adjacent holes is about 540 μm (the distance between the centers of the holes is 600 μm).
The dope contained 6.0 wt% cellulose dissolved in cold base (iv=210 mL/g). The aqueous alkaline coagulation bath liquid used contained 20% by weight of Na 2 CO 3 And 5.6 wt% NaOH. The temperature was 28 ℃. The depth of the spinning bath was 400mm.
Spinning starts at low extrusion speeds (output speeds) and gradually increases to find the maximum possible output speed that results in stable spinning without lump formation. During the experiment, the draft ratio (take-up speed/output speed) was kept constant at 1.0.
Rectangular spinneret dies allow significantly higher output speeds (26 m/min to 30m/min compared to 10m/min allowed by conventional round spinneret caps) even though the holes are more densely arranged (the distance between the circumferences of two adjacent holes is 140 μm versus 540 μm). The number of parallel rows can be increased from two rows (see examples 1 and 2) to at least nine rows while maintaining a high output speed (=high production rate). The distance from the center of the hole in the center row of holes to the nearest point on the periphery of the rectangular group formed by nine rows was 0.83mm.
EXAMPLE 5 and conventionalCompared with a circular spinning die head, the spinning die head with radial arranged group holes
A spinneret die having radially arranged sets (each set comprising three rows of holes, each hole having a diameter of about 60 μm) was compared with a conventional circular spinneret used in example 5. The first spinneret die (see fig. 3 a) with radially arranged sets comprised 303 holes (distance between the circumferences of two adjacent holes 340 μm; distance between the hole centers 400 μm), while the second spinneret die (see fig. 3 b) comprised 1041 holes (distance between the circumferences of two adjacent holes 190 μm; distance between the hole centers 250 μm).
The dope contained 6.0 wt% cellulose dissolved in cold base (iv=210 mL/g). The aqueous alkaline coagulation bath liquid used contained 20% by weight of Na 2 CO 3 And 5.6 wt% NaOH. The temperature was 28 ℃. The depth of the spinning bath was 400mm.
Spinning starts at low extrusion speeds (output speeds) and gradually increases to find the maximum possible output speed that results in stable spinning without lump formation. During the experiment, the draft ratio (take-up speed/output speed) was kept constant at 1.0.
A spinneret die with radially arranged sets of holes allows for significantly higher output speeds (22 m/min and 20m/min, respectively, compared to 10 m/min), even though the holes are more densely arranged. In practice, the number of holes can be increased from 303 to 1041 without significantly affecting the maximum output speed.
The maximum output speed (at a draw ratio of 1.0) of a spinneret die with a radial arrangement of holes comprising 1041 holes was significantly higher than the maximum output speed of a spinneret cap with 900 evenly distributed holes (see examples 3 and 4), emphasizing the importance of the hole arrangement.
Example 6-spinneret die with radially arranged tapered set of holes
The dope of 6 wt% cellulose slurry with IV of 210mL/g in 7.5 wt% NaOH and 0.95 wt% ZnO was filtered through 20 μ nonwoven filter at 20℃and then spun to a dope containing water, 18 wt% at 30 ℃Na of (2) 2 CO 3 5.5 wt% NaOH and 0.7 wt% ZnO.
The ratio (commonly referred to as the draw ratio) between the extrusion speed (average dope speed through the spinneret capillaries) and the take-up speed (speed at which the formed filaments are removed from the coagulation liquid) is 1.6. This means that the positive elongation between the die and the take-up godet is 60%. The use of a positive draft ratio is an effective way to distinguish between spinnerets that suffer from filament shrinkage and filament breakage at higher spinning speeds. However, a draft ratio of 1.6 is not generally used for large scale production, as the process becomes less stable and more demanding. Under these conditions, it was not possible at all to spin using a conventional spinneret with 300 holes uniformly spaced over a circular area of 12mm diameter (see fig. 2). The maximum speed (neglecting the number of broken filaments) of the new spinneret designed more or less based on the invention, allowing stable and satisfactory extrusion, was evaluated.
In addition, when spinning at 10m/min and constant draw ratio 1 (i.e., no die to take-up godet draw), the tenacity of the wet tow was measured on-line by using a deflection roll connected to a newtonmeter. This is a good indication of the degree of coagulation achieved.
Different spinnerets were tested with the hole distribution shown in fig. 6 and 7. All spinnerets had holes with a diameter of 60 mu.
Example 6A) rectangular area 12mm x 1.45mm, which includes 9 rows of parallel holes (541 holes total) organized in a hexagonal pattern such that all adjacent holes are equidistant from 200 μm center to center, allows spinning at 14m/min and draft ratio 1.6, but poorly solidifies at maximum stress (calculated based on dry cellulose content) of < 0.3 cN/tex.
Example 6B) rectangular area 12mm x 3.5mm, which includes 9 rows of parallel holes (217 holes in total) organized in a hexagonal pattern such that all adjacent holes are equidistant from 500 μm center to center, allows spinning at only 5m/min and draft ratio 1.6, but solidifies well at maximum stress (calculated on dry cellulose content) of > 1.3 cN/tex.
Example 6G) rectangular area 12.5mm x 2.4mm, which includes 11 rows of parallel holes (500 holes total) organized in a hexagonal pattern (see fig. 7G) such that all adjacent holes are equidistant from 270 μm center to center, allows spinning at only 5m/min and draft ratio 1.6. However, the maximum stress was slightly increased to 0.5cN/tex (calculated on dry cellulose content).
This shows how a larger hole-to-hole distance increases solidification but decreases the allowable extrusion speed. More coagulation liquid is pulled into the vicinity of the filaments and coagulation is improved, but the greater flow also increases the stress on the outermost filaments that the coagulation liquid must pass through to reach the inner filaments. Even though an increase in hole-to-hole distance will promote inflow, this cannot compensate for the greater flow required to fill the greater volume between the more distant holes/filaments.
Example 6D) rectangular area 12mm x 2.6mm, which includes 11 rows of parallel holes (506 holes total) organized in a square pattern (see fig. 7 f) such that adjacent holes are equidistant from center to center at 260 μm, allows spinning at 6m/min and draft ratio 1.6. The maximum stress was slightly increased to 0.65cN/tex (calculated on dry cellulose content).
The density was similar to that of the hexagon in example 6C), but both evaluation metrics improved, indicating that square patterns outperform hexagons. The square distribution provides less inertial resistance between the liquid and the filaments when the fluid flow within the group is improved.
Example 6E) rectangular area 12mm x 2.5mm, which includes 13 rows of parallel holes (520 holes in total) organized in a periodic rectangular pattern (see fig. 7 d) such that adjacent holes between rows are 200 μm center-to-center apart and adjacent holes are periodically 200 μm or 400 μm apart in the length direction, allows spinning at 14m/min and draft ratio 1.6. The maximum stress was almost 0.8cN/tex (calculated on dry cellulose content).
Clearly, it is beneficial to distribute the holes in a concentrated manner over an even smaller length scale than the size of a larger rectangular group to improve fluid flow within the group through the microchannels perpendicular to the periphery of the group.
Example 6F) the distribution as in fig. 6a comprises 630 holes, wherein the center-to-center hole distance within the elongated group (6 groups total) is 300 μm radial and 200 μm tangential. Which allows spinning at 10m/min and a draft ratio of 1.6. The maximum stress was almost 1cN/tex (calculated on the basis of the dry cellulose content).
Example 6G) the distribution as in fig. 6c comprises 920 holes, wherein the center-to-center hole distance within the elongated group (total 10 groups) is 300 μm radial and 200 μm tangential. Which allows spinning at 10m/min and a draft ratio of 1.6. The maximum stress was 0.65cN/tex (calculated on dry cellulose content).
Example 6H) the distribution as in fig. 6d comprises 1020 holes, wherein the center-to-center hole distance within the elongated group (total 12 groups) is 300 μm radial and 200 μm tangential. However, it allows spinning at just 3m/min and a draft ratio of 1.6. The maximum stress was 0.4cN/tex (calculated on the basis of the dry cellulose content).
Examples 6F-6H show that, given the specific size of the group to which the coagulation liquid is supplied through the channels, there is a lower limit to the width of those channels, at which the extent of coagulation and the spinning stability can be negatively affected by a further reduction of the channel width. The lower limit of the channel width is about 450 μm. As already set forth herein, the width of the channels is preferably at least 1000 μm.

Claims (25)

1. A process for spinning an alkali cellulose spinning dope comprising dissolved cellulose into an aqueous alkali coagulation bath liquid comprising a coagulation salt, thereby forming cellulose filaments, the process comprising the steps of:
-feeding the alkali cellulose dope to a spinneret die (110) having a plurality of holes (120) arranged in at least one group (130) such that the distance (D1) from the centre 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 3mm, such as 2mm, each hole (120) having a diameter of 40 to 100 μm;
-extruding the alkali cellulose dope through the holes (120) into the aqueous alkali 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 perimeter (131) of the set (130) are in direct contact with an aqueous alkaline coagulation bath liquid.
2. The method of claim 1, wherein the group (130) is elongated; preferably, the elongate group (130) is substantially rectangular or tapered.
3. The method according to claim 2, wherein the width (W) of the group (130) is in the range of 0.5mm to 6mm, preferably the width (W) of the group (130) is in the range of 1mm to 4mm, the width being the dimension of the group perpendicular to the length at half the length of the group; and/or wherein the length (L) to width (W) ratio of the set (130) is at least 2, such as at least 3.
4. A method according to any of claims 1 to 3, wherein the minimum feature measure of the spinneret die (110) is in the range of 0.5mm to 24mm, such as in the range of 1.5mm to 20mm.
5. The method of any of claims 1 to 4, wherein the plurality of holes (120) are arranged in more than one set (130), and wherein flow channels (135) for aqueous base coagulation bath liquid are arranged on the spinneret die (110) between adjacent sets (130), the flow channels (135) being devoid of holes, thereby providing holes (121) directly into the aqueous base coagulation bath liquid at the perimeter (131) of the sets (130); preferably, the spinneret die (110) is circular; preferably, the width of the flow channel is at least 450 μm.
6. The method of claim 5, wherein the plurality of holes (120) are arranged in an elongated set (130), and wherein the spinneret die (110) is circular; preferably, the elongated groups (130) are radially arranged.
7. The method of claim 6, wherein the circular spinneret die (110) has a diameter of 8mm to 24mm, such as a diameter of 10mm to 20mm.
8. The method of claim 6 or 7, wherein the elongate group (130) is substantially rectangular and/or tapered.
9. The method of claim 8, wherein the elongated groups (130) are substantially rectangular groups, the elongated groups (130) being radially arranged on the circular spinneret die (110), and wherein adjacent elongated groups preferably have different lengths.
10. The method of claim 8, wherein the elongated groups (130) are radially arranged on the circular spinneret die (110), and wherein the elongated groups (130) taper at least partially along their longitudinal extension toward the center of the circular spinneret die (110).
11. The method according to any one of claims 6 to 10, wherein at least two (such as at least five) circular spinneret dies (110) are arranged in a spinneret (100) to which alkali cellulose dope is fed for extrusion through each spinneret die.
12. The alkali cellulose dope spinneret die (110) according to any one of claims 1 to 5, wherein the spinneret die (110) is rectangular, the width of the spinneret die (110) being less than 10mm, such as in any one of the ranges of 0.5mm to 7mm, 1mm to 6mm, or 1.5mm to 5 mm.
13. The alkali cellulose dope spinneret die (110) according to claim 12, wherein its length to width ratio is from 5:1 to 200:1, such as from 10:1 to 100:1.
14. The alkali cellulose dope spinneret die (110) according to claim 12 or 13, wherein the holes in the rectangular spinneret die are arranged in a set of rectangular holes; preferably, the holes are arranged such that the width of the rectangular set of holes does not exceed 4mm; more preferably, the holes are arranged such that the width of a rectangular set of holes is 0.4mm to 4mm.
15. The method of any one of claims 1 to 14, wherein the holes (120) are unevenly distributed within the group (130).
16. An alkali cellulose dope spinneret die (110) for spinning an alkali cellulose dope into an aqueous alkali coagulation bath liquid, the spinneret die (110) having a plurality of holes (120), each hole (120) having a diameter of 40 μm to 100 μm, wherein the holes (120) are arranged in at least two groups (130), the holes in each group being arranged such that a distance (D1) from a center of any given hole (120) in the group (130) to a closest point on a periphery (131) of the group (130) is no more than 3mm, such as 2mm, and wherein a flow channel (135) for an aqueous alkali coagulation bath liquid is arranged on the spinneret die (110) between adjacent groups (130), the flow channel (135) being free of holes.
17. The method of claim 16, wherein the minimum feature metric of the spinneret die (110) is in the range of 0.5mm to 24mm, such as in the range of 1.5mm to 20mm.
18. The alkali cellulose dope spinneret die (110) of claim 16 or 17, wherein the plurality of holes (120) are arranged in an elongated set (130), and wherein the spinneret die (110) is circular; preferably, the elongated groups (130) are radially arranged.
19. The alkali cellulose dope spinneret die (110) according to claim 18, wherein the diameter of the circular spinneret die (110) is 8mm to 24mm, such as 10mm to 20mm.
20. The alkali cellulose dope spinneret die (110) according to any one of claims 18 to 19, wherein the elongate set (130) is substantially rectangular and/or tapered.
21. The alkali cellulose dope spinneret die (110) of claim 20, wherein: -the elongated groups (130) are substantially rectangular groups, the elongated groups (130) being radially arranged on the circular spinneret die (110), and wherein adjacent elongated groups preferably have different lengths; and/or
-the elongated groups (130) are radially arranged on the circular spinneret die (110), and wherein the elongated groups (130) taper at least partially along their longitudinal extension towards the center of the circular spinneret.
22. The alkali cellulose dope spinneret die (110) according to claim 16 or 17, wherein the spinneret die (110) is rectangular, the width of the spinneret die (110) being less than 10mm, such as in any one of the ranges of 0.5mm to 7mm, 1mm to 6mm, or 1.5mm to 5 mm.
23. The alkali cellulose dope spinneret die (110) according to claim 22, wherein its length to width ratio is from 5:1 to 200:1, such as from 10:1 to 100:1.
24. The alkali cellulose dope spinneret die (110) according to claim 22 or 23, wherein the holes in the rectangular spinneret die are arranged in a set of rectangular holes; preferably, the holes are arranged such that the width of the rectangular set of holes does not exceed 4mm; more preferably, the holes are arranged such that the width of a rectangular set of holes is 0.4mm to 4mm.
25. The alkali cellulose dope spinneret (110) according to any one of claims 16 to 24, wherein the holes (120) are unevenly distributed in the group (130).
CN202280044808.2A 2021-07-05 2022-07-04 Method for spinning alkali cellulose Pending CN117716074A (en)

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