EP0029949B1 - A dry-spinning process for the making of stable cross-section hygroscopic core-sheath fibres and filaments - Google Patents

Abstract

Hygroscopic filaments or fibers with a core-jacket structure of hydrophobic, filament-forming synthetic polymers having a water retention capacity of at least 10% and having uniform round to oval cross-sectional profiles are obtained by a dry-spinning process which comprises addition of a substance to the spinning solvent which (a) has a higher boiling point than the spinning solvent used, (b) is readily miscible with the spinning solvent and with water, (c) is a non-solvent for the polymer to be spun, and addition of another substance which (a) is soluble in the non-solvent for the polymer to be spun, (b) is soluble in the solvent for the polymer (c) remains dissolved in the non-solvent for the polymer during solidification of the filaments, (d) is insoluble in water, and (e) does not evaporate to any significant extent during the spinning process, to the system in quantities of at least 1% by weight, based on polymer solids/spinning solvent/non-solvent carrying out the spinning process in such a way that the non-solvent does not evaporate to any significant extent in the spinning duct and washing out the non-solvent from the solidified filaments.

Description

In DE-A-2 607 996 it has already been proposed to produce hygroscopic threads and fibers from hydrophobic thread-forming, synthetic polymers by a wet spinning process by adding 5-50% by weight, based on solvent and solids, of a substance to the spinning solvent which essentially represents a non-solvent for the polymer, which has a higher boiling point than the solvent used and which is readily miscible with the spinning solvent and a liquid suitable as a washing liquid for the threads, and subsequently washes this non-solvent out of the threads produced. Preferred non-solvents in this process are polyhydric alcohols such as glycerin, sugar and glycols.

The threads and fibers obtainable by this process have the round or oval cross-sectional shapes expected for a wet-spun product. The same applies to DE-A-2 854 314. According to the dry spinning process (DE-A-2 719 019), threads and fibers with such cross sections can only be obtained if certain conditions are met which again influence the desired water absorption capacity. Threads and fibers with round to oval cross sections show advantages in further processing, which lie in the avoidance of fluffy and hairy yarns, a rough handle or an increased proportion of short fibers due to breaks in the yarn.

The present invention was therefore based on the object of producing hygroscopic fibers and threads with largely uniform round to oval fiber cross sections by a dry spinning process, since a plant suitable for dry spinning cannot be converted to a wet spinning process.

• a) einen höheren Siedepunkt als das verwendete Spinnlösungsmittel aufweist,
• b) mit dem Spinnlösungsmittel und mit Wasser gut mischbar ist und
• c) ein Nicht-Lösungsmittel für das zu verspinnende Polymerisat ist

und vor dem Spinnprozess zusätzlich eine Substanz einbringt, die folgende Bedingungen erfüllt:

• 1. Sie ist löslich im Nichtlösungsmittel für den Polymerfeststoff, z.B. Glykole,
• 2. sie ist löslich im Spinnlösungsmittel, z.B. DMF,
• 3. sie ist löslich im Nichtlösungsmittel auch während der Fadenverfestigung,
• 4. sie ist unlöslich in Wasser und
• 5. sie verdampft nicht während des Spinnprozesses.

It has now surprisingly been found that such fibers and filaments having a hygroscopic core / sheath structure with largely uniform round to oval fiber cross sections can be produced by a dry spinning process by adding a substance to the spinning solvent which

• a) has a higher boiling point than the spinning solvent used,
• b) is readily miscible with the spinning solvent and with water and
• c) is a non-solvent for the polymer to be spun

and additionally introduces a substance before the spinning process that fulfills the following conditions:

• 1. It is soluble in the non-solvent for the polymer solid, for example glycols,
• 2. it is soluble in the spinning solvent, eg DMF,
• 3. it is soluble in the non-solvent even during thread consolidation,
• 4. it is insoluble in water and
• 5. it does not evaporate during the spinning process.

The spinning process is carried out in such a way that the non-solvent essentially does not evaporate in the spinning shaft and is washed out of the solidified threads after spinning.

Substances that meet these requirements are e.g. polymeric compounds from the series of polycarbonates, polystyrenes, polyvinyl acetates and cellulose esters.

According to this process, threads and fibers are obtained from hydrophobic polymers which, in addition to the desired uniform round to oval cross-sectional profiles, have a water retention capacity of at least 10% and a core / shell structure in which the core is highly microporous, the pores predominantly with one another are connected and the jacket surrounding the core is considerably more compact compared to the core, but is penetrated by channels which allow the access of liquids to the pore system of the core.

The fact that the further spinning additives used in the process according to the invention in the non-solvent for the polymer solid, e.g. Glycerin for polyacrylonitrile, which remains dissolved during the thread hardening and is not precipitated until it comes into contact with water, fills the pores that arise as a result of washing out the non-solvent in the threads. The additives embedded in the pore system of the fibers stabilize the cavity structure of such threads, as shown by scanning electron micrographs, by forming strong cell walls inside the fibers. This effect continues from the fiber core to the outside, so that uniform cross-sectional structures are obtained. The following observation serves as evidence that such polymeric additives remain dissolved in the non-solvent during thread consolidation:

If one examines spinning material samples in a microscope with transmitted light, they appear bright white as long as they do not come into contact with water. When water is added, however, a dark fiber core and light outer jacket are obtained due to the precipitation of the polymeric additional substance. If, for example, polycarbonate is used as the polymeric additional compound, it can subsequently be recovered quantitatively from, for example, hygroscopic polyacrylonitrile fibers, for example by extraction with methylene chloride. If compounds are used which do not meet the stated conditions, there is no cross-sectional stabilizing effect. If, for example, an acrylonitrile homopolymer is used as the polymeric additive, this is probably soluble in the DMF spinning solvent, but not in the non-solvent, for example in glycerol or glycols. After carrying out the spinning material post-treatment to fibers or threads, bizarre to worm-like cross-sectional profiles are available. As test series with different concentrations of polymeric additives showed, 1-5% by weight, preferably 1.5-4% by weight, based on the weight of the polymer solid / spinning solvent and non-solvent system, is sufficient to include one to achieve cross-sectional stabilizing effect of the fibers.

Another important advantage of the present invention is that such fibers not only no longer have the disadvantages mentioned at the outset, but that they additionally have a very stable pore system which is far less sensitive to manufacturing processes such as steaming, ironing and the like. Furthermore, the additives spun in increase the water retention capacity, which contributes to the comfort properties of such fibers.

An additional advantage results from the fact that the fibers according to the invention are also less sensitive to shrinking processes during drying and largely retain their cross-sectional structure. In this way, it is possible to manufacture fibers and filaments having a hydrophilic core / sheath structure on an industrial scale, even in the form of cables.

In experiments, it also turned out to be a great advantage that such fiber tapes lose moisture much faster and more strongly than fiber tapes without such additives due to a drying process. As a result, the flake presentation could be improved and the production output increased significantly.

Determination of water retention (WR):

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_t, = Gewicht des trockenen Fasergutes

The fiber samples were immersed in water containing 0.1% wetting agent for 2 hours. The fibers were 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, was determined gravimetrically. To determine the dry weight, the fibers are dried to constant moisture at 105 ° C. The WR in weight percent is:

• m _f = weight of the moist fiber material
• m _t , = weight of the dry fiber material

The following examples serve to explain the invention in more detail. If. unless otherwise noted, parts and percentages are by weight.

example

a) 10 kg of dimethylformamide are dissolved with 2.5 kg of polycarbonate from 2,2-di- (4-hydroxyphenyl) propane and phosgene (MW approx. 80,000) in a kettle with stirring at 130 ° C. This solution is then metered into a mixture of 50 kg of DMF and 17.5 kg of tetraethylene glycol with stirring at room temperature. Then 20 kg of an acrylonitrile copolymer of chem. Composition 93.6% acrylonitrile, 5.7% methyl acrylate and 0.7% sodium methallylsulfonate were added with stirring at room temperature. The amount of polycarbonate added is 2.5%, based on polymer solid / spinning solvent / non-solvent. The suspension was fed to a heating device via a gear pump and heated to 130.degree. The residence time in the heating device was 3 minutes. The spinning solution was then filtered and dry-spun in a spinning shaft in a manner known per se from a 240-hole nozzle. The spinning material with a titer of 1580 dtex was collected on spools and folded into a band with a total titer of 110 600 dtex. The fiber cable was then stretched 1: 4.0 times in boiling water, washed with water at 80 ° C., provided with antistatic preparation and dried in a sieve drum dryer at 100 ° C. under tension. The fiber cable leaves the dryer with a moisture content of 41.5%. The cable is then crimped in a stuffer box and then cut into fibers with a stack length of 60 mm. The individual fibers with a final titer of 2.6 dtex have a strength of 2.2 centi Newton / dtex and an elongation of 32%. The water retention capacity is 46%. The fibers have a pronounced core / cladding structure with completely uniform round cross-sectional profiles, as shown by light microscope images in 700x magnification. As scanning electron micrographs in 1000x magnification also show, the pore system with strong cell walls is 2 - 5µ. Strength enforced.

b) A part of the fiber cable was branched off, stretched 1: 4.0 times in boiling water, washed, provided with antistatic preparation and then dried at various temperatures under tension or 20% shrinkage approval, crimped and processed to staple fibers. The individual measurands are shown in Table I. As can be seen from Table 1, uniform round to oval cross-sectional shapes are obtained in all cases.

c) In a further series of experiments, the amount of added polycarbonate was varied in order to determine from what amount by weight of added substance a cross-sectional stabilizing effect is achieved with the hygroscopic core / sheath fibers. The spinning tests were carried out as described under a). The fiber cross-sections were assessed by light microscopy in 700x magnification. The cross sections were obtained by embedding in methyl methacrylate. As can be seen from Table 11, a cross-sectional stabilizing effect occurs from about 1% by weight of added substance.

Example 2

a) 10 kg of dimethylformamide are dissolved with 2.5 kg of polyvinyl acetate (Movilith 30) in a kettle with stirring at 120 ° C. This solution is then metered into a mixture of 50 kg of DMF and 17.5 kg of triethylene glycol with stirring at room temperature. Then 20 kg of an acrylonitrile copolymer with the chem. The composition from Example 1 is added with stirring at room temperature. The amount of polyvinyl acetate added is 2.5%, based on polymer solid / spinning solvent / non-solvent. The suspension was then, as described in Example 1, transferred to a spinning solution, filtered and, as described there, spun into threads and aftertreated into fibers with a final titer of 2.2 dtex. The fiber cable left the dryer with a moisture content of 51%. The fiber strength is 2.6 centi Newton / dtex, the elongation 30% and the water retention capacity = 52%. The fibers have a pronounced core / cladding structure with uniform round cross-sectional shapes, as shown by light microscope images at a magnification of 700 times. In the scanning electron microscope, strong cell walls of 2 - 5µ thickness in the pore system can be seen at a magnification of 1000 times.

b) A part of the fiber cable was again branched off, 1: 4, stretched several times, washed, provided with antistatic preparation and dried, crimped and processed into staple fibers at various temperatures under tension and shrinkage approval. The individual measurands are shown in Table 111. As can be seen in Table 111, uniform round to oval cross-sectional profiles are again obtained in all cases.

Example 3

a) 60 kg of dimethylformamide with 2.5 kg of cellulose ester based on butyric acid (Cellit BP 900), 17.5 kg of glycerol and 20 kg of an acrylonitrile copolymer with the chem. The composition from Example 1 is stirred at room temperature in a kettle to form a suspension and then converted into a spinning solution as described in Example 1, filtered and the spinning solution is spun into threads and aftertreated into fibers with a final titer of 2.3 dtex. The fiber cable left the dryer with a moisture content of 54%. The fiber strength is 2.6 centi Newton / dtex, the elongation 29% and the water retention 45%. The fibers have a core / man, as shown by light microscope images in 700x magnification tel structure with uniform round cross-sectional profiles. In the scanning electron microscope, strong cell walls of 2 - 5µ thickness in the pore system can be seen at a magnification of 1000 times.

b) A part of the fiber cable was again branched off and, as described in Example 1b, treated in various ways. The individual measurands are shown in Table IV. In all cases, the result is again uniformly round to oval cross-sectional structures.

Example4 comparison

a) 60 kg of dimethylformamide are mixed with 17.5 kg of tetraethylene glycol at room temperature with stirring in a kettle. Then 20 kg of an acrylonitrile copolymer with the chem. The composition from Example 1 was added and the suspension, as described in Example 1, transferred to a spinning solution, filtered and spun into threads. The collected spinning material is then, as shown in Example 1, post-treated into fibers with a final titer of 2.7 dtex. The fiber cable left the dryer with a moisture content of 75%. The fiber strength is 2.5 centi Newton / dtex, the elongation 39% and the water retention capacity = 30%. As shown by light microscope images at 700x magnification, the fibers have a distinctive core / shell structure with bizarre to asterisk-shaped, non-uniform cross-sectional profiles. In the scanning electron microscope at 10OOf magnification relatively thin cell walls of 1 - 2µ thickness can be seen in the pore system.

b) A part of the fiber cable was again branched off and, as described in Example 1b, treated in various ways. The individual findings are shown in Table V. The result is bizarre non-uniform to asterisk-shaped fiber cross-sectional structures in all cases.

Example 5 Comparison

a) 62.5 kg of dimethylformamide with 2.5 kg of acrylonitrile homopolymer with a K value of 90, 15 kg of triethylene glycol and 20 kg of an acrylonitrile copolymer with the chem. The composition from Example 1 is stirred into a suspension at room temperature in a kettle and then, as described in Example 1, transferred to a spinning solution, filtered and the spinning solution is spun into threads. As can be seen from preliminary tests, the acrylonitrile homopolymer used as a cross-section stabilizing additive in triethylene glycol is completely insoluble even in the heat. The threads are collected again, folded into a cable and, as stated in Example 1, treated to give fibers with a final titer of 2.3 dtex. The fiber cable left the dryer with a moisture content of 83%. The fiber strength is 2.7 centi Newton / dtex, the elongation 35% and the water retention capacity = 38%. The fibers have a core / shell structure with non-uniform worm to rod-shaped bizarre cross-sectional profiles, as shown by light microscope images in 700x magnification. In the scanning electron microscope, at 1000x magnification, relatively thin cell walls of 1 - 2µ thickness in the pore system can be seen.

b) Part of the fiber cable was removed again branches and, as explained in Example 1 b, treated in various ways. The individual findings are shown in Table Vi. As can be seen from the table, inconsistent, bizarre, worm-like cross-sectional profiles arise in all cases. An addition to the polymer solid / spinning solvent / non-solvent system only has a cross-sectional stabilizing effect if it is soluble in the non-solvent, remains in the system during the spinning process, and is only precipitated in the course of the aftertreatment, e.g. by washing, and the pore system of the hydrophilic core / Filled with sheath fibers from the inside. This also explains the stronger framework structure of the pore system in the form of stronger cell walls compared to a porous fiber without such addition.

Claims (3)

1. Process for the production of hygroscopic filaments or fibres which have a core/sheath structure and uniform round to oval cross-sectional profiles from hydrophobic, filament-forming synthetic polymers by a dry-spinning process, by adding to the spinning solvent a substance which

a) has a higher boiling point than the spinning solvent used,

b) is readily miscible with the spinning solvent and with water,

c) is a non-solvent for the polymer to be spun, carrying out the spinning process in such a way that the non-solvent does not evaporate to any significant extent in the spinning duct, and then washing out the non-solvent from the solidified filaments, characterised in that another substance which

a) is soluble in the non-solvent for the polymer to be spun,

b) is soluble in the solvent for the polymer,

c) remains dissolved in the non-solvent for the polymer during solidification of the filaments,

d) is insoluble in water and

e) does not evaporate to any significant extent during the spinning process

is added to the system in quantities of at least 1 percent by weight, based on polymer solids/spinning solvent /non-solvent.

2. Process according to claim 1, characterised in that the polymer is an acrylonitrile polymer containing at least 40% by weight of acrylonitrile units.

3. Process according to claim 1, characterised in that the polymer is an acrylonitrile polymer containing at least 80% by weight of acrylonitrile units.