EP0051203A1 - Process for the production of dry spun hollow polyacrylonitrile filaments and fibres - Google Patents

Abstract

After the dry spinning process, acrylonitrile hollow fibers and filaments can be obtained by spinning the spinning solution through a nozzle with loop-shaped nozzle holes, the solution having a viscosity of at least 120 ball falling seconds, measured at 80 ° C or at least 75 ball falling seconds, measured at 100 ° C , wherein the nozzle hole area of the profile nozzle is less than 0.2 mm² and the leg width of the loop-shaped nozzle is a maximum of 0.1 mm and the overlap of the two leg ends of the loop-shaped nozzle measured from the center of the nozzle forms an angle of 10 to 30 ° and wherein the spinning air acts on the threads in the transverse direction to the thread take-off and the air direction forms an angle of 80 to 100 ° with a straight line which passes through the leg opening.

Description

The production of hollow fibers using the melt spinning process or wet spinning technology has been known for many years. The processes specified in numerous patents can essentially be traced back to 3 methods.

In the first method, a molten polymer, for example a polyester, is spun from nozzles with adjacent segment bends. By expanding the molten polymer below the nozzle and flowing together the segmental ends in a continuous form, synthetic hollow fibers are produced. In the second method, a hollow needle is used, which must be placed in the center of the nozzle hole opening, and gaseous substances or fillers are pumped through the hollow needle. The polymer flows around the needle and the gas fills the cavity in the center and stabilizes the shape until the polymer has cooled. In this way, viscose hollow threads are particularly popular prepared, for example castor oil is used as the lumen-filling medium. Finally, in the third method, a fixed pin extends into the nozzle hole opening. This is generally a difficult spinning process because the polymer wants to go into a closed form. The method is particularly suitable for cross-sectional modifications, but air must be supplied at the pin end or a vacuum must be applied in order to produce hollow fibers.

Hollow threads and fibers have now found many areas of application. So they will e.g. used for sea water desalination, for cleaning liquids and gases, as an ion exchanger, for reverse osmosis, dialysis and ultrafiltration (artificial kidneys) as well as for their low weight and high bulk for comfort clothing. Especially the cleaning of fabrics, e.g. of industrial gases has recently come to the fore. Summary articles on the production and meaning of synthetic hollow fibers can be found in Encyclopedia of Polymer Science and Technology 15, (1971), pages 258-272, in Acta Polymerica 30, (1979), pages 343-347 and in Chemical Engineering, Feb. 1980 , Page 54-55.

So far, there has been no lack of attempts to produce hollow acrylic fibers from a spinning solution after a dry spinning process. Because of the problems that arise, however, no technical process for the production of hollow acrylic fibers using this technology has become known to date.

Hollow fibers are understood here to mean fibers which have a continuous, continuously continuous channel arranged in the longitudinal direction inside the fiber.

While it is relatively easy to convert acrylonitrile polymers into hollow fibers using wet spinning technology using one of the abovementioned methods, this leads to considerable difficulties in a dry spinning process as a result of another thread-forming mechanism. In the wet spinning process, the thread formation is carried out by coagulation of the spinning solution in an aqueous precipitation bath which contains a solvent for polyacrylonitrile, the precipitation bath concentration, temperature and additional coagulating agents, such as, for example, aqueous salt solutions, being able to vary within wide limits. For example, DE-OS 2 346 011 describes the production of hollow acrylic fibers according to Method 2 for a wet spinning process with aqueous DMF as a precipitation bath and DE-OS 2 321 460 for aqueous nitric acid as a precipitation bath, spinning from nozzles with annular openings and a liquid introduces as an inner precipitant into the central part of the annular opening.

If you try to apply methods 1 to 3 to a dry spinning process, you will encounter considerable difficulties, since when spinning from a spinning solution, only part of the solvent has to evaporate after it has emerged from the nozzle opening in order to achieve thread formation and solidification. Because of the high tech African effort and the difficult process control in the case of the production of hollow acrylic fibers by dry spinning from spinning solutions, methods 2 and 3 were not followed up.

If you try to use method 1 to produce hollow fibers from profile nozzles with adjacent segment bends using the dry spinning process, you will generally only get dumbbell-shaped to irregular, bizarre cross-sections that have air pockets in an uneven form. If the polymer solids concentration is increased in order to obtain the predetermined cavity profile by increasing the intrinsic viscosity, unexpected problems arise. There are limits to the increase in the solids content due to gelation, flowability and handling of such spinning solutions. For example, an acrylonitrile copolymer with the chemical composition 93.6% acrylonitrile, 5.7% methyl acrylate and 0.7% sodium methallylsulfonate with a K value of 81 can only be dissolved in a spinning solvent such as dimethylformamide up to a maximum solids concentration of 32% by weight and spin it into threads. If an attempt is made to increase the solids content further, such spinning solutions gel on cooling even at temperatures around 50 to 80 ° C., so that trouble-free spinning becomes impossible.

The object of the present invention was, because of the versatile application possibilities of such hollow fibers and filaments to provide such a dry spinning process for the production of acrylonitrile hollow fibers.

It has now been found, surprisingly, that hollow acrylonitrile threads can also be spun using a dry spinning process, if spinning solutions with a viscosity exceeding a certain value are used, nozzles with loop-shaped nozzle holes are used, which are of certain dimensions and the spinning air in a certain way on the threads can act.

The invention therefore relates to dry-spun hollow polyacrylonitrile filaments. Suitable acrylonitrile polymers for the production of these threads and fibers obtainable therefrom are acrylonitrile homopolymers and copolymers, the copolymers containing at least 50% by weight, preferably at least 85% by weight, of copolymerized acrylonitrile units.

The invention further relates to a process for the production of hollow polyacrylonitrile threads and fibers, characterized in that the thread-forming synthetic polymers are spun from a solution through a nozzle with loop-shaped nozzle holes after a dry spinning process, the solution having a viscosity of at least 120 falling ball seconds, measured at 80 ° C or of at least 75 ball falling seconds, measured at 100 ° C, wherein the nozzle hole area is less than 0.2 mm2, the leg width of the loop-shaped nozzle is a maximum of 0.1 mm and the overlap of the measured both ends of the loop of the loop-shaped nozzle from the center of the nozzle at an angle of 10 to 30 ° and wherein the spinning air acts in the direction transverse to the thread take-off on the threads and the air direction with a straight line that goes through the leg opening, an angle of 80 to 100 ° forms.

Spinning is followed by the usual further process steps of the polyacrylonitrile dry spinning process.

The viscosity in falling ball seconds, measured at 80 or at 100 ° C., was determined by the method of K. Jost, Reologica Acta, Volume 1 (1958), page 303. The nozzle hole area is preferably less than 0.1 mm ² and the leg width is between 0.02 to 0.06 mm. If the nozzle hole area is larger than 0.2 mm, the cross-sectional shape will flow. You get fuzzy bulbous to formless deformed, bizarre structures.

Spinning solutions of the specified viscosity, which also contain a higher concentration of the thread-forming polymer than is customary, are obtained according to DE-OS 2 706 032 by preparing appropriately concentrated suspensions of the thread-forming polymer, which are easy to convey, in the desired solvent and these suspensions by brief heating to temperatures just below the boiling point point of the spinning solvent used in viscosity-stable spinning solutions.

The suspensions for the preparation of such spinning solutions are obtained by, if necessary, adding a non-solvent for the polymer to be spun to the spinning solvent and then adding the polymer with stirring.

As a non-solvent in the context of the invention there are suitable, which are for the polymer a non-solvent _'and can be mixed with the spinning solvent widely.

The boiling points of the non-solvents can be both below and above the boiling point of the spinning solvent used. Such substances, which can be in solid or liquid state, are, for example, alcohols, esters or ketones and mono- and polysubstituted alkyl ethers and esters of polyhydric alcohols, inorganic or organic acids, salts and the like. Water and, on the other hand, glycerol, mono- and tetraethylene glycol and sugar are used as preferred non-solvents because of their easy handling and removal in the spin shaft without residue formation and recovery.

When using non-solvents whose boiling point is below the boiling point of the spinning solvent, one obtains hollow acrylic fibers which are distinguished from the known compact types by a considerably increased water retention capacity. When using non-solvents whose boiling point is higher than that of the spinning solvent, acrylic fibers with a high water retention capacity are obtained, as already described in DE-OS 2 554 124. These fibers are characterized by their special wearing properties. While in the first case the non-solvent is removed in the spinning shaft, in the second case the non-solvent has to be washed out of the consolidated fiber in a further process step following the spinning process.

If water was used as the non-solvent, the acrylonitrile copolymer mentioned on page 2 with a K value of 81 could be obtained from the above-mentioned nozzles using the dry spinning process from a solids concentration of 36% by weight of hollow fibers.

The water content of such suspensions made of polyacrylonitrile and dimethylformamide is in the range between 2 to 10%, based on the total suspension. Below 2% by weight of water, a free-flowing, transportable suspension is no longer obtained, but rather a thick, sluggish paste. On the other hand, if the water content is more than 10% by weight, the threads burst during the spinning process below the nozzle because of the high water vapor partial pressure when it emerges from the nozzle holes. The percentage of water in the Spinning solution does not affect the profile at the nozzle. The only decisive factor is the polymer solids concentration. With solids contents of up to 40%, water proportions of 2 to 3% have proven to be optimal in order to obtain transportable suspensions that are still flowable at room temperature. If you use another non-solvent, such as propanol or butanol, instead of water, you will get the same results. For acrylonitrile copolymers with K values less than 81, of course, even more concentrated spinning solutions can be produced. For example, a suspension of 45% copolymer solids content, 4% water and 51% dimethylformamide can be produced from an acrylonitrile copolymer made of 92% acrylonitrile, 6% methyl acrylate and 2% sodium methallylsulfonate with a K value of 60, which has a viscosity of 142 ball falling seconds, measured at 80 ° C, which is still flowable at room temperature and can be converted into hollow fibers by loosening and spinning from a special profile nozzle. On the other hand, when using polymers with higher K values, even with a lower solids concentration than the indicated 36% spinning solutions of K value 81, hollow fibers can be obtained from special profile nozzles during dry spinning. The only decisive factor for the shape of the profile nozzle is the level of viscosity.

In the case of using monoethylene glycol as a non-solvent, spinning solutions could be obtained using the acrylonitrile copolymer mentioned on page 2 be prepared with solids concentrations of 36 wt .-% or greater, the viscosities were at least 75 falling seconds, measured at 100 ° C. Hollow threads and fibers were spun from these spinning solutions, which, after the non-solvent had been washed out and the usual aftertreatment, were distinguished by high water retention properties. The non-solvent content of such suspensions of polyacrylonitrile, dimethylformamide and monoethylene glycol must, as already communicated in DE-OS 2 554 124, be at least 5% by weight, based on solvent and solid, so that the threads and fibers have a water retention capacity of at least 10%. exhibit. As can be seen from Table II, the percentage of non-solvent in the spinning solution does not affect the profile at the nozzle. Rather, it is crucial that there is a minimum viscosity of the spinning solution. With solids contents of up to 40% by weight, non-solvent fractions of 5 to 10% by weight have proven to be optimal in order to obtain hollow acrylic fibers with a water retention capacity of greater than 10%. The solid mass surrounding the continuous continuous channel arranged in the longitudinal direction inside the fiber has a core / shell structure. The thickness of the fiber cladding can be varied within wide limits by the ratio of polymer solid to non-solvent content. According to the statements made when using water as a non-solvent, when using non-solvents whose boiling point is above the boiling point of the spinning solvent, it is also true that acrylonitrile copolymers with K values are small ner than 81 in higher concentration and acrylonitrile copolymers with K values greater than 81 in lower concentration in the spinning solution give the required minimum viscosity.

The minimum viscosity can be determined at two different temperatures, namely at 80 ° C and 100 ° C. This measure takes into account the fact that, on the one hand, the determination of the viscosity in spinning solutions which contain water as non-solvent is difficult because of the evaporation of the water at 100 ° C., while on the other hand in the determination of the viscosity in other spinning solutions which contain a substance as non-solvent whose boiling point is above that of the spinning solvent can become problematic at 80 ° C due to the tendency to gel. However, the viscosity of water-containing spinning solutions can also be determined at 100 ° C when working in a closed system.

As long as the spinning solution to be spun gives a finite falling ball seconds value, the production of hollow acrylic fibers from this spinning solution is possible in principle. For economic reasons, however, in conventional spinning systems, spinning solutions with viscosities over 300 falling ball seconds, measured at 80 or 100 ° C., can no longer be processed without problems, so that this results in a natural upper limit of the viscosity range.

In addition to dimethylformamide, the spinning solvents which can be used are also the higher-boiling solvents such as dimethylacetamide, dimethyl sulfoxide, ethylene carbonate and N-methylpyrrolidone and the like.

Another important factor in the production of hollow acrylic fibers after a dry spinning process according to the invention is the process control of the spinning air during thread formation and the special geometry, size and arrangement of the nozzle holes of the spinnerets suitable for the production of hollow acrylic fibers. It has been shown that for Production of round, uniformly shaped hollow fibers with mutually identical void portions, a spiral or loop nozzle according to FIG. 1 is particularly advantageous, the overlap angle of the two leg ends of the spiral nozzle holes being 10 to 30 °, preferably 20 °. If the leg end of the spiral nozzle holes is extended, the overlap angle of the two leg ends is 55 °, for example (see Fig. 4) or the leg opening of the spiral nozzle holes has a different position than the transverse position to the center of the spinning shaft (see Fig. 3) no hollow fibers obtained in shape and proportion of voids. Depending on the spinneret geometry and the arrangement of the leg opening to the center of the spinning shaft, bean-shaped and other undesirable cross-sectional shapes arise. In addition to this special nozzle hole geometry and arrangement, the type of air supply plays a role to the profile threads for the formation of hollow fibers. Uniform hollow fibers can only be obtained by targeted flow of spun air from the center of the spinning shaft. If the air flows through the threads in a different way, for example from the inside and outside, you get undefined bizarre fiber cross-sections with changing voids. Obviously, it is crucial that the spinning air does not hit the leg openings of the profile nozzle centrally, but is accessed in the transverse direction at an angle of 80 to 100 °, preferably 90 ° (cf. FIG. 2). If the spinning air arrives directly into the thigh openings (cf. FIG. 3), the threads swell strongly in order to then collapse under the influence of the delay. Discontinuous cross-sectional shapes and changing cavity parts are obtained.

In addition to the special process control of the spinning air during thread formation and the special geometry and arrangement of the nozzle hole openings of the profile nozzles to be used, the size of the nozzle hole diameter and the nozzle hole area, as stated, also play an important role. It has been shown that in the case of special geometric configurations, sharp contours of the thread cross-sections can only be spun up to a certain leg width as a function of the entire nozzle hole area. The leg width of a profile nozzle is understood here to mean the distance between the outer boundary of the predetermined profile shape in mm, but not the distance to the center of the nozzle hole.

In addition to the properties already mentioned for dialysis and ultrafiltration purposes, the fibers according to the invention are particularly notable for their high water retention capacity. As already mentioned in DE-OS 2 719 019, textile fabrics made of such fibers have good wearing comfort. The water retention capacity is at least 10% in all cases where there is a closed, self-contained hollow fiber with a constant void fraction. In the case of non-uniform hollow fiber cross-sectional shapes and partially open, partially closed shapes, fluctuating values for the water retention capacity are determined depending on the void fraction. The water retention capacity is determined on the basis of DIN regulation 53 814 (cf. Melliand Textile Reports 4, 1973, page 350). _-

m_{f =} Gewicht des feuchten Fasergutes m_tr = Gewicht des trockenen FasergutesThe fiber samples are immersed in water containing 0.1% wetting agent for 2 hours. The fibers are then centrifuged for 10 minutes at an acceleration of 10,000 m / sec ² and the amount of water, which is retained in and between the fibers, is determined gravimetrically. To determine the dry weight, the fibers are dried to constant moisture at 105 ° C. The water retention capacity (WR) in% by weight is:

m _{f =} weight of the moist fiber material m _tr = weight of the dry fiber material

Such hollow fibers tend to cross-sectional deformation due to their structure when exposed to high temperatures. If, for example, an endless cavity cable is dried at temperatures above 160 ° C, individual cavity capillaries burst with the formation of irregular, partly open fiber cross sections and high short fiber shares. The following post-treatment procedure has proven to be optimal for the after-treatment of the fibers according to the invention: washing-stretching-preparing-crimping-cutting-drying up to a maximum of 140 ° C. Preferred drying temperature is 110 to 130 ° C. If the acrylic hollow fibers according to the invention are aftertreated, as just mentioned, then self-contained, uniform hollow fibers with mutually identical void fractions are obtained.

example 1

59 kg of dimethylformamide (DMF) are mixed with 3 kg of water in a kettle at room temperature with stirring. 38 kg of an acrylonitrile copolymer composed of 93.6% acrylonitrile, 5.7% methyl acrylate and 0.7% sodium methallylsulfonate with a K value of 81 are then metered in with stirring at room temperature. The suspension is pumped via a gear pump into a spinning kettle equipped with an agitator. Then the suspension, which has a solids content of 38% by weight and a water content of 3% by weight, based on the total solution, is heated in a double-walled tube with steam of 4.0 bar. The dwell time in the tube is 7 minutes. The temperature of the solution at the pipe outlet is 138 ° C. There are several mixing combs in the tube for homogenizing the spinning solution. The spinning solution, which has a viscosity of 176 falling balls at 90 ° C, is filtered after leaving the heating device without intermediate cooling and fed directly to the spinning shaft.

The spinning solution is spun dry from a 36-hole nozzle with spiral nozzle holes (see FIG. 1). The nozzle holes are arranged on an annular nozzle so that the openings of the profile nozzle are aligned transversely to the air blowing (see FIG. 2). The nozzle hole area is 0.08 mm and the leg width is 0.06 mm. The shaft temperature is 160 ° C and. the air temperature is 150 ° C. The amount of air that flows through in the immediate vicinity of the spinneret this emerging bundle of threads flowing out in one direction from the center of the spinning shaft in all directions in the direction transverse to the thread take-off is 30 m ³ / h. The take-off speed is 125 m / min. The spun material with a titer of 790 dtex is collected on spools and folded into a band with a total titer of 158,000 dtex. The fiber cable is then washed in water at 80 ° C, stretched 1: 4 in boiling water, provided with antistatic preparation, crimped, cut into staple fibers of 60 mm in length and then dried on a belt dryer at 120 ° C. The hollow fibers, which have a final titer of 6.7 dtex, have a tensile strength of 2.7 cN / tex and an elongation at break of 31%. The water retention capacity is 37.6%. For the microscopic assessment of the cross-sectional geometry, the fiber capillaries were embedded in methyl methacrylate and cross-cut. The light microscopic images produced in the differential interference contrast method show that the sample cross sections have a perfectly uniform, round cavity structure. The void fraction is around 50% of the total cross-sectional area.

The following table I shows the limits of the process according to the invention for the production of hollow acrylic fibers according to the dry spinning process using further examples. In all cases, an acrylonitrile copolymer with the chemical composition of Example 1 is used again and transferred to a spinning solution as described there. The solids concentration and the type and pro were varied percentage of non-solvent for polyacrylonitrile. Was spun from a 36-hole nozzle with a loop shape (see. Fig. 1) with the hole arrangement shown in Fig. 2. The spinning and post-treatment conditions correspond to the information from Example 1. The viscosities were measured in falling ball seconds at 80 ° C.

Example 2

• a) A part of the spinning solution from Example 1 is dry spun as described there from a 36-hole nozzle with loop-shaped nozzle holes (see FIGS. 1 and 2), with only the spinning air of 30 m ³ / h both passed through under otherwise identical spinning conditions outside as well as inside in the immediate vicinity of the spinneret, which can act on the thread bundle emerging from it in the direction of the thread take-off. The spinning material is collected on bobbins and, as described in Example 1, folded into a tape with a total titer of 158,000 dtex and post-treated into fibers with a final titer of 6.7 dtex. The sample cross-sections of the fibers do not show a uniform shape and changing voids. Approx. 50% of the fiber cross-sections are completely compact.
• b) A further part of the spinning solution from Example 1 is dry spun as described there from a 36-hole nozzle with loop-shaped nozzle holes according to FIGS. 1 and 2, whereby under otherwise identical spinning conditions only the throughput air of 30 m ³ / h from the outside instead of from inside in the transverse direction on the emerging bundle of threads in the immediate vicinity of the spinneret.

The spinning material is again collected as described in Example 1, fanned and post-treated into fibers with a final titer of 6.7 dtex. The sample cross-sections of the fibers again do not show a uniform shape and changing voids. Approx. 60% of the fiber cross sections were completely compact.

Example 3

A part of the folded hollow fiber cable from Example 1 with a total titre of 158,000 dtex was washed in water at 80 ° C., stretched 1: 4 times in boiling water, provided with antistatic preparation and dried at 160 ° C. in a drum dryer under tension. It was then crimped and cut into staple fibers 60 mm long. The hollow fibers, which have a final titer of 6.7 dtex, have a water retention capacity of 14.1%. The sample cross-sections of the fibers show, in addition to approx. 30% in the form of uniform round hollow fibers, approx. 70% in the form of collapsed fibers with fluctuating void proportions, partially crescent-shaped to sickle-shaped structures and hollow fibers with several break points in cross section. Apparently, when hollow fiber cables are dried at high temperatures, an excess pressure of the air enclosed in the cavity arises, so that the hollow fibers burst and the cross-sectional structure collapses. The bursting of the hollow fibers announces itself in the dryer through crunching noises.

Example-4

An acrylonitrile copolymer with the chemical composition of Example 1 was dissolved as described there, filtered and dry spun from a 36-hole nozzle with spiral nozzle holes (see FIG. 3). In contrast to Example 1, the nozzle holes are arranged so that the opening of the legs is precise is oriented towards the center of the spinning shaft, so that the spinning air can flow centrally from the spinning shaft center (air flow angle = 0 °) into the nozzle hole openings. The overlapping of the leg ends of the nozzle holes is again 20 °, the nozzle hole area 0.08 mm ² and the leg width 0.06 mm. The remaining spinning and aftertreatment data correspond to the information in Example 1. The hollow fibers, which have a final titer of 6.7 dtex, have a water retention capacity of 16.4%. The sample cross-sections of the fibers show irregularly deformed tubular to loop-like collapsed hollow fibers with changing void proportions and partially completely compact cross-sectional structures.

Example 5

An acrylonitrile copolymer with the chemical composition of Example 1 was dissolved as described there, filtered and dry spun from a 36-hole nozzle with loop-shaped nozzle holes (see dep. 4). One leg end of the loop-shaped nozzle holes is elongated in comparison to the profile nozzle from Example 1 in such a way that the angle of overlap of the leg ends is 55 °, as a result of which the air flow no longer takes place transversely to the leg openings of the profile nozzle, but at an angle of 125 ° (cf. Fig. 5). The nozzle hole area is 0.095 mm2 and the leg width is 0.06 mm. The other spinning and aftertreatment conditions correspond to the information in Example 1. The fibers, which have a final titer of 6.7 dtex, have a water retention capacity of 10.7%. The sample cross sections of the fibers show none closed cavity shape, there are crescent-shaped to curved structures.

Example 6

An acrylonitrile copolymer with the chemical composition of Example 1 was dissolved as described there, filtered and dry spun from a 36-hole nozzle with loop-shaped nozzle holes (see FIG. 3). One leg end of the loop-shaped nozzle holes is extended as described in Example 5 so that the angle of overlap of the leg ends is 55 °. In contrast to Example 5, the nozzle holes are arranged so that the openings of the leg ends of the profile nozzle form an angle of 35 ° to the direction of the spinning air from the center of the spinning shaft, so that the spinning air can only flow obliquely from the inside into the nozzle openings ( see Fig. 6). The nozzle hole area is 0.095 mm 2 and the leg width is 0.06 mm. The other spinning and aftertreatment conditions correspond to the information in Example 1. The hollow fibers, which have a final titer of 6.7 dtex, have a water retention capacity of 20.5%. The sample cross-sections of the fibers show mostly closed, but irregularly deformed tube-like to loop-like structures.

Example 7

• a) An acrylonitrile copolymer with the chemical composition of Example 1 was as there dissolved written, filtered and recrystallized from a 36-hole nozzle with a loop-shaped nozzle holes (see ig. _F. 1) spun dry. The nozzle hole arrangement and the overlap angle of the two leg ends correspond to the information in Example 1, so that the air flow angle between the center of the spinning shaft and the profile nozzle opening is again 90 °. In contrast to example 1, the leg width of the profile nozzle is 0.10 mm instead of 0.06 mm and the nozzle hole area = 1.33 mm ² . The other spinning and aftertreatment conditions correspond to the information in Example 1. The hollow fibers, which have a final titer of 6.7 dtex, have a water retention capacity of 35.3%. The sample cross-sections of the fibers are completely uniform and round, the void fraction is again around 50% of the total cross-sectional area.
• b) Part of the spinning solution from Example 7 is spun dry as described in Example 1 from a 36-hole nozzle with loop-shaped nozzle holes (see FIG. 1). The nozzle hole arrangement, the overlap angle of the leg ends and the air flow angle again correspond to the information from Example 1. The leg width of the profile nozzle is 0.12 mm and the nozzle hole area is 0.16 mm 2.

The spinning and aftertreatment conditions correspond to the data from Example 1. Hollow fibers are formed, but the shape is not uniform. In addition to completely round hollow fibers, you can also get loop-shaped and shaped tubes well-collapsed cross-sectional shapes with lower void volume. The water retention capacity is 23.1%.

c) Another part of the spinning solution from Example 7 is dry spun as described in Example 1 from a 36-hole nozzle with loop-shaped nozzle holes (cf. FIG. 1). Nozzle hole arrangement, overlap angle and air flow angle correspond to the information from Example 1. The leg width of the profile nozzle is 0.15 mm and the nozzle hole area is 0.20 mm ^2. Spinning and post-treatment conditions correspond to the data from Example 1.

Hollow fibers are no longer obtained. The profile shape flows, forming compact, irregular oval to bizarre cross-sectional structures. The water retention capacity is 6.3%.

Example 8

51 kg of DMF are mixed with 4 kg of water in a kettle with stirring. 45 kg of an acrylonitrile copolymer composed of 92% acrylonitrile, 6% methyl acrylate and 2% sodium methallylsulfonate with a K value of 60 are then metered in with stirring at room temperature. The suspension, which has a solids concentration of 45%, is dissolved as described in Example 1, filtered and dry spun from a loop-shaped profile nozzle with 36 holes according to FIGS. 1 and 2.

The viscosity of the spinning solution is 142 falling balls at 80 ° C. The other spinning and post-treatment conditions correspond to the explanations of Example 1. The sample cross sections of the hollow fibers, which have a final titer of 8.0 dtex, show a completely uniform, round profile with approximately 50% void content. The water retention capacity is 39%.

Example 9

57 kg of dimethylformamide (DMF) are mixed with 6 kg of monoethylene glycol in a kettle at room temperature with stirring. 37 kg of an acrylonitrile copolymer composed of 93.6% acrylonitrile, 5.7% methyl acrylate and 0.7% sodium methallylsulfonate with a K value of 81 are then metered in with stirring at room temperature. The suspension is pumped via a gear pump into a spinning kettle equipped with an agitator. Then the suspension, which has a solids content of 37% by weight, is heated in a double-walled tube with steam of 4.0 bar. The dwell time in the tube is 7 minutes. The temperature of the solution at the pipe outlet is 138 ° C. There are several mixing combs in the tube for homogenizing the spinning solution. The spinning solution, which has a viscosity of 186 falling seconds at 100 ° C, is filtered after leaving the heating device without intermediate cooling and fed directly to the spinning shaft.

The spinning solution is spun dry from a 36-hole nozzle with spiral nozzle holes (see FIG. 1). The nozzle holes are arranged on an annular nozzle so that the openings of the profile nozzle are aligned transversely to the air blowing (see FIG. 2). The nozzle hole area is 0.08 mm ² and the leg width is 0.06 mm. The shaft temperature was 160 ° C and the air temperature was 150 ° C. The amount of air that is passed, which in the immediate vicinity of the spinneret onto the thread bundle emerging from it in the transverse direction to the thread take-off on one side of the. Spinning shaft center flows out from all sides, is 30 m ³ / h. The take-off speed was 125 m / min. The spun material with a titer of 790 dtex is collected on spools and folded into a band with a total titer of 158,000 dtex. The fiber cable is then washed in water at 80 ° C, stretched 1: 4 in boiling water, provided with antistatic preparation, crimped, cut into staple fibers of 60 mm in length and then dried on a belt dryer at 120 ° C. The hollow fibers, which have a final titer of 6.7 dtex, have a tensile strength of 2.3 cN / tex and an elongation at break of 37%. The water retention capacity is 50.3%. The sample cross-sections have a completely uniform, round cavity structure. The void fraction is around 50% of the total cross-sectional area. The solid mass surrounding the cavity consists of a porous core / shell structure.

The following table II shows the limits of the process according to the invention for the production of hollow acrylic fibers according to the dry spinning process using further examples. In all cases, an acrylonitrile copolymer with the chemical composition of Example 9 is used again and transferred to a spinning solution as described there. The solids concentration and the type and percentage of the non-solvent for polyacrylonitrile were varied. Was spun from a 36-hole nozzle ochanordnung with loop shape (see. FIG. 1) with the indicated in Fig. 2 _L. The spinning and aftertreatment conditions correspond to the information from Example 9. The viscosities were measured in the falling ball seconds at 100 ° C. as described at the beginning.

Example 10

• a) A part of the spinning solution from Example 9 is dry spun as described there from a 36-hole nozzle with loop-shaped nozzle holes (see FIGS. 1 and 2), with only the spinning air of 30 m ³ / h both passed through under otherwise identical spinning conditions outside, as well as from the inside in the immediate vicinity of the spinneret can act on the thread bundle emerging from it in the direction of the thread take-off. The spinning material is collected on bobbins and, as described in Example 9, folded into a tape with a total titer of 158,000 dtex and post-treated into fibers with a final titer of 6.7 dtex. The sample cross-sections of the fibers do not show a uniform shape and changing voids. Approx. 50% of the fiber cross-sections are completely - compact.
• b) A further part of the spinning solution from Example 9 is spun dry as described there from a 36-hole nozzle with loop-shaped nozzle holes according to FIGS. 1 and 2, whereby under otherwise identical spinning conditions only the throughput air of 30 m ³ / h from the outside instead of from inside in the transverse direction on the emerging bundle of threads in the immediate vicinity of the spinneret.

The spinning material is again collected as described in Example 9, fanned and post-treated into fibers with a final titer of 6.7 dtex. The sample cross-sections of the fibers again do not show a uniform shape and changing voids. Approx. 60% of the fiber cross sections were completely compact.

Example 11

A part of the folded hollow fiber cable from Example 9 with a total titer of 158,000 dtex was washed in water at 80 ° C., stretched 1: 4 in boiling water, provided with antistatic preparation and dried under tension at 160 ° C. in a drum dryer. It was then crimped and cut into staple fibers 60 mm long. The hollow fibers, which have a final titer of 6.7 dtex, have a water retention capacity of 17.1%. The sample cross-sections of the fibers show, in addition to approx. 30% in the form of uniform round hollow fibers, approx. 70% in the form of collapsed fibers with fluctuating void proportions, partly crescent-shaped to crescent-shaped structures and hollow fibers with several break points in cross section. Apparently, when these hollow fiber cables are dried at high temperatures, an excess pressure of the air enclosed in the cavity arises, so that the hollow fibers burst and the cross-sectional structure collapses. The bursting of the hollow fibers announces itself in the dryer through crunching noises. At the same time, the core / shell structure is largely lost. There are only compact hollow fibers without a pore system.

Example 12

An acrylonitrile copolymer with the chemical composition of Example 9 was dissolved as described there, filtered and from a 36-hole nozzle spiral-shaped nozzle holes (see. Fig. 1) spun dry. In contrast to Example 9, the nozzle holes are arranged so that the opening of the legs is exactly aligned with the center of the spinning shaft (see Fig. 3), so that the spinning air can flow centrally from the spinning shaft center (air inflow angle = 0 °) into the nozzle hole openings . The overlap of the leg ends of the nozzle holes is again 20 °, the _D üsenlochfläche 0.08 mm2 and 0.06 mm, the leg width. The remaining spinning and aftertreatment data correspond to the information in Example 9. The hollow fibers, which have a final titer of 6.7 dtex, have a water retention capacity of 22.4%. The sample cross-sections of the fibers show irregularly deformed tube-like or loop-like collapsed hollow fibers with changing void proportions and partially completely compact cross-sectional structures.

Example 13

An acrylonitrile copolymer with the chemical composition of Example 9 was dissolved as described there, filtered and dry spun from a 36-hole nozzle with loop-shaped nozzle holes (cf. FIG. 4). One leg end of the loop-shaped nozzle holes is elongated in comparison to the profile nozzle from Example 1 in such a way that the angle of overlap of the leg ends is 55 °, so that the air flow no longer takes place transversely to the leg openings of the profile nozzle, but at an angle of 125 ° C (cf. Fig. 5). The nozzle hole area is 0.095 mm and the Leg width 0.06 mm. The other spinning and aftertreatment conditions correspond to the information in Example 9. The fibers, which have a final titer of 6.7 dtex, have a water retention capacity of 13.7%. The sample cross-sections of the fibers show no closed cavity shape, there are crescent-shaped to curved structures.

Example 14

An acrylonitrile copolymer with the chemical composition of Example 9 was dissolved as described there, filtered and dry spun from a 36-hole nozzle with loop-shaped nozzle holes (cf. FIG. 4). One leg end of the loop-shaped nozzle holes is extended as described in Example 13 so that the overlap angle of the leg ends is 55 °. In contrast to Example 13, the nozzle holes are arranged so that the openings of the leg ends of the profile nozzle form an angle of 35 ° to the direction of the spinning air from the center of the spinning shaft (see FIG. 6), so that the spinning air is only inclined from the inside the nozzle openings can flow. The nozzle hole area is 0.095 mm ² and the leg width is 0.06 mm. The other spinning and aftertreatment conditions correspond to the information in Example 9. The hollow fibers, which have a final titer of 6.7 dtex, have a water retention capacity of 24.5%. The sample cross-sections of the fibers show mostly closed, but irregularly deformed tube-like to loop-like structures with core / shell structures.

Example 15

• a) An acrylonitrile copolymer with the chemical composition of Example 9 was dissolved as described there, filtered and dry spun from a 36-hole nozzle with loop-shaped nozzle holes (see FIG. 1). The nozzle hole arrangement and the overlap angle of the two leg ends correspond to the information in Example 9, so that the air flow angle between the center of the spinning shaft and the profile nozzle opening is again 90 ° (cf. FIG. 2). In contrast to Example 9, the leg width of the profile nozzle is 0.10 mm instead of 0.06 mm and the nozzle hole area = 1.33 mm ² . The other spinning and post-treatment conditions correspond to the information in Example 9. The porous hollow fibers, which have a final titer of 6.7 dtex, have a water retention capacity of 45.3%. The sample cross-sections of the fibers are completely uniform and round, the void fraction is again around 50% of the total cross-sectional area.
• b) A portion of the spinning solution from Example 15 is spun dry as described in Example 9 from a 36-hole nozzle with loop-shaped nozzle holes (see FIG. 1). The nozzle hole arrangement, the overlap angle of the leg ends and the air flow angle again correspond to the information from Example 9. The leg width of the profile nozzle is 0.12 mm and the nozzle hole area 0.16 mm ² .

The spinning and aftertreatment conditions correspond to the data from Example 9. Hollow fibers are formed, but the shape is not uniform. In addition to perfectly round, porous hollow fibers, loop-shaped and tubular collapsed cross-sectional shapes with a smaller void volume are also obtained. The water retention capacity is 25.1%.

c) Another part of the spinning solution from Example 15 is dry spun as described in Example 9 from a 36-hole nozzle with loop-shaped nozzle holes (see FIG. 1). Nozzle hole arrangement, overlap angle and air flow angle correspond to the information from Example 9. The leg width of the profile nozzle is 0.15 mm and the nozzle hole area is 0.20 mm2. Spinning and post-treatment conditions correspond to the data in Example 9. No hollow fibers are obtained.

The profile shape flows, forming compact, irregular, oval to bizarre cross-sectional structures. The water retention capacity is 8.3%.

Claims (9)

1. Dry-spun hollow acrylonitrile fibers and threads. 2. Dry-spun acrylonitrile hollow fibers and filaments according to claim 1 with a water retention capacity of at least 10%. 3. Dry-spun acrylonitrile hollow fibers and filaments according to claim 1, which consist of acrylonitrile homo- and copolymers with at least 50% by weight of copolymerized acrylonitrile units. 4. A process for the production of acrylonitrile hollow fibers and threads, characterized in that the thread-forming synthetic polymers are spun from a solution through a nozzle with loop-shaped nozzle holes after a dry spinning process, the solution having a viscosity of at least 120 falling ball seconds, measured at 80 ° C or of at least 75 ball falling seconds, measured at 100 ° C, the nozzle hole area of the profile nozzle being less than 0.2 mm 2 and the leg width of the loop-shaped nozzle being a maximum of 0.1 mm, and the overlap of the two leg ends of the loop-shaped nozzle being measured from the center of the nozzle forms an angle of 10 to 30 ° and the spinning air acts on the threads in the transverse direction to the thread take-off and the air direction forms an angle of 80 to 100 ° with a straight line which passes through the leg opening. 5. The method according to claim 4, characterized in that the _D üsenlochfläche less than 0.1 mm2, and the limb width from 0.02 to 0.06 mm is. 6. The method according to claim 4, characterized in that the spinning solutions contain a non-solvent for the polymer, which is miscible with the spinning solvent within wide limits. 7. The method according to claim 6, characterized in that water, glycerol, monoethylene glycol, tetraethylene glycol or sugar are used as non-solvent. 8. The method according to claim 4, characterized in that the viscosity of the spinning solution, measured at 80 ° C 120-300 ball falling seconds and measured at 100 ° C is 75-300 ball falling seconds. 9. The method according to claim 4, characterized in that the overlap of the two leg ends forms an angle of 20 ° and the air direction with a straight line which passes through the leg opening forms an angle of 90 °.

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