EP1358369B1 - Method and device for producing substantially endless fine threads - Google Patents

Abstract

The invention relates to a method and a device for producing substantially endless fine threads from polymer solutions, especially spinning material for lyocell, wherein the spinning material is spun from at least one spinning hole or a spinning slot. The spun thread or film is drawn by high-speed accelerated gas flows using a Laval nozzle whose narrowest cross-section is located beneath the point where the spinning material exists. The threads are arranged on a strip in the form of a non-woven or are taken up in the form of a yarn and are subsequently separated in spinning baths by means of solvents.

Description

The invention relates to a method for manufacturing of fine threads from solutions of polymers natural or synthetic origin and devices for their manufacture.

Fine threads, also called micro threads, mostly however Microfibers of finite length are made after a Hot air blow spinning process, so-called meltblown process, manufactured for many years, and it today there are different devices for this. It is all the same that in addition to a series of melt holes - also several rows parallel to each other have become known - hot air escapes the Warps. By mixing with the colder Ambient air cools and solidifies of these threads or finally long fibers, because often, Mostly undesirable, the threads break. The The disadvantage of this meltblown process is the high level Energy expenditure for heating the at high speed flowing hot air, limited flow through the individual spinning holes (even if these have become increasingly dense over time up to a distance of less than 0.6 mm at 0.25 mm in Hole diameter) that it is under thread diameters 3µm comes off, resulting in beads and protruding Fibers in the later textile composite leads, and that the polymers through the to produce fine threads necessary high air temperature well above the Melt temperature can be thermally damaged. The Spinnerets, a large number of which are proposed and have also been protected are complex Injection molds that are manufactured with high precision Need to become. They are expensive, operationally vulnerable and expensive to clean.

Such meltblown processes are also for education known from finally long fibers from Lyocell materials become, i.e. from a solvent, mostly NMMO (N-methylmorpholine-N-oxide), dissolved cellulose spun, e.g. WO98 / 26122, WO98 / 07911, WO99 / 47,733th

In French Patent 2,735,794 a Process described in which a cellulosic mass from one or more spinning holes by bursting (éclatement) split into individual particles becomes and this through the gas flow too finite long fibers are warped. The process of fiber formation happens in turbulent flow conditions.

A prevailing problem in spinning Lyocell threads from solution masses are spinning security. Undissolved particles or unequal to cellulose Enriched masses lead to thread breaks, which is why Take special care to avoid these two determining parameters must be set. The leads to special designs of the devices. Environmental requirements and an in sensitive, narrow limits to be carried out Spinning process.

The present invention is therefore the object based, improved methods and devices for Production of fine threads from solutions of polymers to create that are essentially endless not thermally damaged by gas streams drawing out will need little energy and by a spinning tool that is simple in its construction can be produced.

In the German patent DE 199 29 709 C2 a Methods and devices described, according to which Essentially endless threads made from polymer melts become. The molten polymer threads emerge from spinning bores in one or more parallel rows or rings are arranged in one with gas, usually air, from which Environment separate chamber and certain pressure get into an area of rapid acceleration this Gases at the exit from the chamber, this as Laval nozzle is running.

Those on the way there on the respective thread forces transmitted by shear stress increase, its diameter decreases sharply and the pressure conversely, in its still fluid interior rises proportional to its radius through the action of the Surface tension correspondingly strong. Through the Acceleration of the gas drops in fluid mechanics Lawfulness of its pressure. Here are the Conditions of the temperature of the dope, the Gas flow and its rapid acceleration so one on top of the other voted that the thread before its solidification a hydrostatic pressure inside reached, which is greater than the surrounding gas pressure, so that the thread bursts and turns into a multitude dividing fine threads side by side. Through a Gap and air leave the bottom of the chamber this. The bursting occurs in or after Gap and surprising under otherwise unchanged conditions stable at a certain point. Gas and gas run in the area of strong acceleration Thread flow parallel, the flow boundary layer around the threads is laminar. One succeeds continued splitting of the original thread monofilament without pearl formation and tears. From a Monofil is a multifilament of much finer threads using a gas flow from ambient temperature or slightly higher temperature.

The threads can continue to warp after the point of splice until they are frozen. This happens because of the suddenly created larger thread area very quickly. The threads are endless. It can be in child Dimensions due to technical interference finally long threads come, are predominant but the endless fine filaments.

The spinning masses used in DE 199 29 709 are meltable polymers. There are synthetic ones or of natural origin. Among those on natural Fibers based fibers are especially those of the of renewable raw material cellulose of interest.

It has been shown that these methods of Also use splice threads on Lyocell spinning masses can by cellulose in N-methylmorpholine-N-oxide and Dissolved water and pressed into threads through spinning bores becomes. Other solvents can also be used but NMMO is the most suitable so far has proven. The solution Spinning mass is spun out as described above and the threads pass through the Laval nozzle predetermined air gap in which they become thinner diameters be warped, and then get into a water bath in which the cellulose coagulates into a thread and the solvent gets into the water bath, which is renewed because of the constant enrichment and the solution is withdrawn.

A special feature of the method according to the invention is that the accompanying gas, usually air flow the liquid filament threads shortly after their Accompany the exit from the spinning bore and through Distortion of shear stress. This gives them one Orientation and a cool down, both of which are increasing Strength and reducing the harmful Demolitions, even until they are completely prevented leads. By mixing the gas flow with the surrounding atmosphere, mostly also air, is delayed the gas flow and the threads are subject to each other no longer the initial tension due to the higher one Speed of the same, but remain endless and even when torn off by the air flow carried away. It is still the threads of the initial one Solution mass, if not already by blowing from e.g. Steam or water with the precipitation of the cellulose starts. These threads can be on a screen belt filed and from the accompanying gas flow, such as known in spunbonded nonwoven processes, separated, whereby the gas (air) passes through the screen belt and below the same is suctioned off and the threads for Fleece deposited now only fed to the precipitation bath become. One otherwise very much when spinning lyocell threads exact compliance starting with fine capillary diameters for the spin hole, subsequent Air gap and its temperature and renewal as well the requirements for the uniformity of the melt as free as possible of undissolved parts that only exist in a few ppm are allowed, is eliminated by the forced threading through the pulling out Air flow. The thread formation and storage room is easily accessible because of distances of 1 and 2 m between the nozzle outlet and the fall arrester are.

Instead of threading the solution into a fleece put it and then put it in a precipitation bath bring, you can in the same way according to the invention Process spinning threads and separating them from the accompanying gas flow by looking at this laterally aspirated in a device similar to that in German Patent 42 36 514 is provided. The individual threads or several as yarns are then used for coagulation fed to the cellulose case equipment and wound on spools.

In contrast to the production of fine threads from synthetic Polymers such as polyethylene, polypropylene, Polyamide, polyester and others is fanning out of the solution mass jet to produce fine and the finest threads are only required to a limited extent. As before noticed, arise after removal of the solvent by coagulation according to the cellulose content used in the solution mass already at good 10%, that is, in the spinning process for lyocell threads quite usual concentration, threads in the range of less than 10 µm in diameter without fanning, and it showed that only to a minor extent, too because of the special, of synthetic polymers very different viscosity behavior of the NMMO cellulose solutions splicing into multiple threads side by side only to a minor extent and at lower cellulose contents of the spinning mass possible is. While synthetic polymers have a Temperature increase is sufficient, so through the effect the surface tension by increasing the internal pressure burst in the thread and into individual threads fanning out, Lyocell quickly Damage to these sensitive masses at temperatures well above 100 ° C and the threads are missing later in strength and other desired properties.

In contrast, it has been shown that other natural polymers according to the method according to DE 199 29 709 and the present one is essentially endless Threads can be processed. they behave like the synthetic polymers in terms of fanning out or more like the cellulosic masses for Lyocell threads depending on the type.

Another naturally-based polymer that can be spun into threads is polylactide PLA (polylactic acid), which is obtained on the basis of starch, for example grain or corn starch, but also from whey or sugar. PLA materials have the special property that they are biodegradable, whereby the decomposition, ie the decomposition into CO ₂ and H ₂ O, can also be set for a certain period of time, and that they are body-friendly. Here too it is possible to produce very fine threads with the splice spinning process, which can otherwise only be obtained with the disadvantages of the melt-blown process - large amounts of air have to be raised to at least melt temperature, whereby the polymers are mostly damaged.

Another goal is to increase profitability in the manufacture of threads by higher Spinning mass throughput and lower specific air and thus energy consumption. It has been shown that thread forming plastic solutions natural or of synthetic origin of very different types not only can be deformed by threads pressed out of round or profiled individual openings and then distorted gas or air flows be, but that one splicing threads all over similar to that generated from single openings Can produce monofilaments from films. For this, the Spinning mass from an elongated slit-shaped Nozzle, as mentioned above, in a separate from the environment Chamber of certain pressure, the gas, e.g. Air, fed, squeezed, the film into an area rapid acceleration of the gas at the outlet the chamber enters a longitudinal gap. Below the Acceleration zone, i.e. in the relaxation zone the film splits open and piles are formed of essentially endless threads, however in contrast to those spliced from monofilaments of very different diameters and nodular Thickening. These still arise molten state of the textile materials and can within certain limits by the main process parameters Melt temperature, melt flow rate and extruding Gases - mostly air flows - within certain limits can be set. Individual threads that then can also be wound up by splicing not made from films, but nonwovens are. These spunbonded fabrics made of randomly deposited single threads Different thread diameters can have advantages have and are more like natural substances in which also a wider range of different ones that make them up individual elements, here fibers and threads, occurs like leather and wood, their different Single fibers their special and mostly identify advantageous properties.

In both processes, splicing a monofilament or of a film, the temperature of the spinning mass is greatest influence because they have viscosity and thus thread formation ability and surface tension and thus Determine pressure build-up in monofilament and film. A it is therefore not desirable to cool the thread too early, on the contrary, an increase in temperature shortly after exiting the spinning orifice of Be an advantage. The mechanism of the fanning out is similar for monofilament and film, but not equal. With monofilament there is a burst when the pressure inside is greater than that in the surrounding Gas flow. This happens with the splicing process in that the thread diameter next to the generally little influence by gravity an accompanying gas flow decreases, this. constantly accelerated and according to the fluid dynamics Law the pressure in the gas decreases. Through the Surface tension is the pressure in the liquid monofilament greater. Unraveling occurs in individual threads by bursting the monofilament when the fluid skin can no longer hold the thread together. At the Films are spun across the width of the film different pressures, and they are on the edges due to the surface tension because of the Curvature higher there. Such films are fundamental unstable even if the gas flow is according to the invention is kept laminar for as long as possible. It comes to Grooves, scoring across the width of the film and to breakthroughs with the formation of thread or band-shaped individual parts, also called ligaments.

The area of strong acceleration and pressure reduction in the gas flow according to the invention in Shape of a rotationally symmetrical or elongated Laval nozzle with a convergent contour to a narrowest Cross section there and then rapid expansion realized, the latter already side by side running newly formed single threads not to the Can stick to walls. The narrowest cross section can with appropriate selection of the pressure in the chamber (in air about twice as high as the ambient pressure behind it) speed of sound and in the extended Part of the Laval nozzle is supersonic.

For the production of thread fleeces (spun fleeces) become spinnerets with spinning bores arranged in rows and in rectangular or with slot shape and Laval nozzles with rectangular cross-section used. For the production of yarns and for special types nonwoven fabrication can also use round nozzles one or more spinning bores and rotationally symmetrical Laval nozzles are used.

The advantage of the present invention is that that in a simple and economical way fine threads in Range below 10 µm, for example between 2 and 5 µm, can be generated, what with pure warping through the meltblown process only with hot, gas (air) jets heated above the melting point Is brought about and thus considerably more energy requirement. In addition, the threads in their molecular Structure not damaged by overheating, which would result in reduced strength, causing they often rub themselves out of a textile bandage to let. Another advantage is that the threads are endless or quasi endless and from one textile bandage such as a fleece does not stick out and can be removed as lint. The device to implement the method according to the invention is simple. The spinning holes of the spinneret just like the slot nozzle can be bigger and therefore the Laval nozzle cross-section is less prone to failure its accuracy does not require the narrow tolerances the side louvers of the meltblown process. With a certain polymer you need only the solution temperature and pressure in the chamber to coordinate with each other and for a given throughput per spin hole and the geometric position of the Spinning nozzle to Laval nozzle there is fanning. at Lyocell dilutes the solution thread to the desired one Diameter, the splicing occurs only sporadically on.

A further development of the invention is the solution cone, round as a monofilament or wedge-shaped as a film cooling down as little as possible and above out to warm it up to a higher temperature. For this purpose, heaters are shielded from the gas flow on both sides of the outlet openings - row of holes or slot - attached. These heaters lead heat on the one hand in the area of the outlet opening to the spinning mass from the outside and give it to her where they have a higher speed and therefore higher heat transfer allowed, an increase in temperature, on the other hand, the heaters are of the type that they radiate heat at the conical or wedge-shaped Transfer part of the deforming spinning mass.

Fig. 1

eine schematische Schnittdarstellung eines Teils einer Vorrichtung zur Herstellung von Fäden nach der Erfindung,

Fig. 2

eine perspektivische Ansicht einer erfindungsgemäßen Vorrichtung nach einem Ausführungsbeispiel mit Zeilendüse und Spinnbohrungen zur Herstellung von Lyocell-Vliesen aus Mikrofäden,

Fig. 3

ein Foto einer mikroskopischen Aufnahme von PP-Spleißfäden, hergestellt nach Beispiel 3 durch Aufplatzen eines Schmelzefilms, und

Fig. 4

ein Foto von PP-Spleißfäden unter Bedingungen entsprechend Fig. 3, hergestellt durch Aufspleißen von Monofilen.

Embodiments of the invention are shown in the drawing and are explained in more detail in the following description. Show it

Fig. 1

2 shows a schematic sectional illustration of part of a device for producing threads according to the invention,

Fig. 2

2 shows a perspective view of a device according to the invention in accordance with an exemplary embodiment with a line nozzle and spinning bores for producing lyocell nonwovens from micro threads,

Fig. 3

a photo of a micrograph of PP splice threads made according to Example 3 by bursting a melt film, and

Fig. 4

a photo of PP splice threads under conditions corresponding to Fig. 3, made by splicing monofilaments.

In Fig. 1 is a section through the lower part of a Spinneret 1 and an associated Laval nozzle shown this cut being both for a rotatin-symmetrical Spinneret which is a thread or a Spins monofilament, and a rotationally symmetrical Laval nozzle, as well as for a slit or rectangular shape Spinneret that spins a film, and so on rectangular Laval nozzle applies. It can also a spinneret with several in a row Spinning bores with corresponding elongated Laval nozzle may be provided. Below the spinneret 1 there is a plate 11, 11 'with a gap 12 ', seen from the spinneret converging and then is slightly divergent and is at the bottom Edge of the plate 11, 11 'greatly expanded, whereby the Laval nozzle is formed. The spinneret or the spinning holes of the spinnerets end just above the Laval nozzle or in the upper level of the plate 11, 11 ', if necessary, the spinneret 1 can also easily protrude into the opening 12.

Between the spinneret 1 and plate 11, 11 'is a closed Space, according to arrows 6, 6 ', for example, gas supplied by a compressor becomes. The gas that can be air usually has Ambient temperature, but can also due to the heat of compression a slightly higher one from the compressor Have temperature, for example 70 ° to 80 °. The Spinneret 1 is surrounded by an insulating arrangement 8, 8 ', to shield the on spinning temperature heated spinneret serves against heat loss, whereby also advantageously an air gap 9 between the spinneret 1 and insulating arrangement 8, 8 'is provided. The spinneret 1 has an outlet opening 4, in the Area a heater 10, 10 'is attached, which in the Embodiment is designed as a flat heating tape and which advantageously against the insulating arrangement 8, 8 'to avoid heat loss is isolated by parts 13 and 13 '. The room below the plate 11, 11 'usually has ambient pressure, i.e. Atmospheric pressure while the Gas in the space between spinneret 1 and plate 11, 11 ' is under increased pressure. With immediately following Further processing into fleece, yarn or the space below the other thread structures Plate 11, 11 'a little against ambient pressure have increased pressure, for example by a few millibars, the one for further processing, such as fleece laying or other thread collecting devices is needed.

A polymer solution 2, for example Lyocell, flows against the outflow opening 4 of the nozzle 1 along the arrow 3 shown. A thread 5 or a film is formed, which in its further course due to the gas flow coming laterally from above along the arrows 6, 6 ′ drawn in between the contour of the surfaces of the plate 11, 11 ′ and the outer surfaces 7, 7 'of the insulating arrangement 8, 8' runs, reduced in diameter or in width. The heater 10, 10 'heats the capillary of the outlet opening 4 from the outside and can heat up the spinning mass flowing past it with its lower part by appropriate extension, essentially by radiation. The thread 5 or the film passes into the constriction 12 'of the flow cross section for the gas flow 6, 6' formed by the parts 11, 11 'of the plate, in the manner of the Laval nozzle with the narrowest cross section at 12. Until then, the flow velocity of the gas increases Constantly to and in the narrowest cross section 12, the speed of sound can prevail if the critical pressure ratio, for example in the idle state of the gas p ₁ in the chamber above the plate 11, 11 'to the pressure in the narrowest point p _e , is exceeded. By expanding the Laval nozzle towards the room with the pressure p ₂ below the plate 11, 11 ', supersonic speeds can also arise in the case of supercritical pressure conditions. In general, the Laval nozzle widens very much immediately after the narrowest cross-section 12 or shortly thereafter in order to prevent the threads from sticking to the plate 11, 11 'just below the Laval nozzle due to the fanning out that begins in this area.

In the example shown, the thread 5 or bursts splits when the thread cladding the solution thread against the internal pressure that has grown with the thread constriction can no longer hold together. The monofilament then divides into individual threads, which are due to the temperature difference between solution and cold gas or air and suddenly suddenly strongly growing surface of the individual threads, based on the Thread mass, cool quickly. It is therefore a certain one Number of very fine, essentially endless Individual threads emerged. With a Lyocell solution the phenomenon of fanning often does not occur or only here and there, i.e. in Fig. 1 would continue spinning thread. The thread is through the laminar gas flow of ever increasing speed warped so that it ultimately becomes too fine Threads due to the cellulose content being around or below 10% comes.

The solution film also tears just below the Laval nozzle on, the pressure ratios in the film before the Fanning different across the width and the film becomes unstable. Just before fanning out there are furrows and marks the film width and then to break through threads small but larger diameters.

It follows from the nature of such burst processes that the number of threads created after the point of attachment, which is still in the Laval nozzle or for example 5 to 25 mm below the narrowest part of the Laval nozzle can lie, can not be constant. Because of the short distance, the thread or film and gas with each other to the point of splice up or to the final one The warpage of the thread is the flow boundary layer around the thread laminar. Also the Air from the supply lines as laminar as possible to the Area of the expansion. That has the Advantage of lower flow losses, but also a more even course of fanning out over time. The accelerated flow, as in the Cross-section of the Laval nozzle remains laminar and can even laminarize if there is one certain turbulence prevailed.

Fig. 2 shows the perspective view of a system for the method according to the invention, in which a Lyocell mass 130 is supplied to a device 30 and a fleece 20 is obtained therefrom. The device 30 for making essentially endless Threads corresponds to the arrangement of FIG. 1, wherein several spinnerets or spinning holes accordingly Fig. 1 are arranged in series and the Laval nozzle is elongated or formed in a rectangular shape. Thread monofilaments emerge from the individual spinning bores from, rejuvenate by the thrust of the Gas flow and splicing if necessary, at Lyocell however less, not in the lower part of the gap illustrated Laval nozzle or something below it to several Threads on. At Lyocell, essentially Single threads spun out.

The air flow accompanying them leads them to a catch belt 50 counter, where the threads are still dry be filed. That is with the present procedure possible and has great advantages over lyocell processes, in which the threads are immediately after a short Air gap of a few cm in the precipitation bath, mostly from water. Below the filing path there is a suction in the dry, represented by box 60 as in spunbond processes usual, so that the accompanying air through Suction devices, not shown, is discharged. Around an introduction below the level of the precipitation bath 70 without the threads coming off the sieve belt, can also carry out precipitation bath liquid, predominantly water, at this point through the sieve belt be sucked through, not shown in detail, or it is a roller 89 with or without touching the Water surface present that the fleece in the Precipitation bath 70 presses. While the fall arrester 50 is being returned the fleece 20 runs to its further Processing, for example, by calendering, drying and more like hydroentangling.

Some of the air can already advance along the arrows 120, 120 'are removed; the boxes show 110, 110 'facing the threads, not shown air-permeable surfaces.

Such suction can laterally to the thread sheet are used in a special way when the threads not to a fleece, but to a continuous yarn to be processed, what is wound on rolls or staple fibers to be cut, each after solvent and cellulose pulp Coagulation have been separated.

It is a special peculiarity of the invention Procedure that the threads after leaving the Spinning bores and if necessary after splicing Shear stresses due to the essentially parallel to experience gas flow, mostly air flow. It is different from the ones used for spinning applied forces by winding or any other type Extractors. The spinning solution from the Spinning bores only withstands low tensile forces and it is therefore with methods according to the prior art not possible to create very fine threads, because only in the air gap between the nozzle outlet and the coagulation bath the spinning mass can be reduced to a thread Pull out the diameter, then no more. To the present method are those for deformation necessary forces shear stress forces (besides the very little effect of gravity) that the thread do not use as tensile forces across the thread cross-section, which means that there is hardly any tearing off.

The coagulation of the dissolved thread polymer, here cellulose for lyocell threads, in a solvent, here NMMO, can already between spinning device 30 and Storage area 51 is initiated by water mist or steam is blown in laterally against the thread sheet be there, for example, where the previously described Suction boxes for air 110, 110 'are attached and thus exactly in the opposite way to the discharged air now moist air or steam is introduced into the thread sheet become. This causes the threads on her The exterior is already enriched in the cellulose part before it is planted are and not a bond with each other is as strong as if it became one without the like Fleece can be deposited. The fleece is then in one Precipitation bath introduced, but then only by press rolls or between a drum, too heated, and the screen belt to self-binding comes. Because the Lyocell threads are soft and already stick to each other if you put them under little Pressure connects. This autogenic Connection is another particular benefit at the production of nonwovens from lyocell threads. Is the Coagulation has already begun, so is the bond not so strong and you get softer fleeces textile grip compared to the previously not sprayed, only fleece drawn through the precipitation bath, the more compact are and have a harder, paper grip.

It is understood that after that shown in Fig. 2 Trough still further levels of coagulation or Can wash out the solvent. Sieve drum washing machines can also be used for this as used in the textile industry be, the fleece the sieve drum in a certain Circumferential segment wraps around and the water through the fleece and the perforated drum jacket axially withdrawn and the bath or the separation of water and solvents, for example NMMO are fed. The fleece must then be dried are what drum driers are used for can. Since there is a general shrinkage here the Lyocell threads occurs, the fleece can between a suction drum through which warm air flows and one this wrapping around at the same speed moving sieve belt.

example 1

A solution was made using a screw press (extruder) of 13% cellulose in an aqueous NMMO solution of 75% and 12% water of a spinning device from a Spinneret with a hole and a round Laval nozzle fed, the single spinning bore a Had a diameter of 0.5 mm. On an industrial scale the solution is made and directly over it conveying pumps metered to the spinning device. The temperature of the Lyocell spinning mass at the extruder outlet was 94 ° C. At the bottom of the conical The tip of the nozzle was an electrical resistance heater attached to their heating with a Power between 50 and 300 W. The thread pull happened through air at room temperature of about 22 ° C, the pressure measured before acceleration in the Laval nozzle, was between 0.05 and 3 bar above atmospheric pressure set. The leakage of the lyocell mass only a little was varied from the tip of the nozzle and lay 1 to 2 mm above the plane where the Laval nozzle constricts, with further settings exactly in this plane or 1 to 2 mm below, so further downstream. The Laval nozzle was wide in the narrowest cross section of 4 mm and a total length, measured from the plane where their necking begins, until the strong expansion shortly after the narrowest Cross section, of 10 mm.

Table 1 shows the settings 1 - 11. You can see the special influence of the heater 10 of the nozzle tip, causing the spinning mass just before it emerges received an elevated temperature from the spinning bore, and clearly above their original temperature from 94 ° C. The threads were only partially spliced, for individual settings, in particular with lower air pressure and lower temperature essentially not. You can convince yourself of this by the thread speed is calculated from the measured throughput of the spinning mass and the mean End thread diameter, corrected for the reduction in diameter through the solvent removal with the highest occurring air speed, i.e. that in the Laval nozzle gap (if no supersonic speed occurs afterwards). Is this higher, the threads can be spliced - the more the speeds differ. Is she less than this calculated average thread speed, most of them are not spliced, if both are approximately the same size, there are some spliced, some not, because everything applies in each case Medium. The observation is common that lyocell threads less prone to splicing compared to the beginning synthetic polymers such as polypropylene already noticed.

Even with high throughputs per spinning bore above 4 g / min, threads around and below 10 µm could be produced. A higher air pressure p ₁ leads to finer threads within certain limits until the nozzle tip cools down more due to increased heat transfer to the air flow and the splicing was also more difficult. The influence of the increased air velocity due to increased air pressure in front of the Laval nozzle can be partially compensated for by increased temperature at the tip of the nozzle. There is also an influence from the position of the nozzle tip relative to the Laval nozzle. Here, too, the two main influencing variables, temperature of the spinning mass and shear effect of the air flow, are decisive for splicing. No. Mo
g / min p ₁
mbar P _h
W d ₅₀
microns CV
% 1 3.4 80 79 26.2 26 2 3.4 150 97 24.9 20 3 3.4 150 116 19.0 24 4 3.4 150 130 13.2 29 5 3.4 200 130 12.0 17 6 3.4 100 130 10.1 64 7 11.1 400 370 24.4 47 8th 6.65 1000 370 13.4 38 9 3.68 1500 276 11.1 36 10 2.33 1500 280 8.3 33 11 4.57 3000 208 9.1 54

Example 2

In a device such as that in Example 1, a Solution of 8% cellulose in 78% NMMO and the rest 14% water from diameter spinning holes spun of 0.6 mm. The temperature of the solution at the extruder outlet was 115 ° C and in the distribution room the solution to a total of twenty spinning holes 114 ° C. The heating power of the heating system on both sides of the Nozzle tip was 450 W. The throughput per spin bore was 3.6 g / min.

The following thread diameters of the essentially endless lyocell threads resulted depending on the pressure of the unheated air: No. P ₁
mbar d ₅₀
microns d _min
microns d _max
microns CV
% u _Le
m / s u _F50
m / s 5 160 8.5 2.8 21.1 59 156 67 7 200 8.0 3.7 14.7 39 173 78 9 250 9.7 2.7 16.3 39 192 52 11 300 9.2 5.1 18.4 43 209 61

Despite increasing air pressure p ₁ , measured in front of the Laval nozzle, the threads become thicker again from p ₁ = 200 mbar, which can be attributed to faster cooling due to the higher air flow.

The speed of the air in the narrowest cross section of the Laval nozzle u _Le and the speed u _F50 that a Lyocell thread would have before entering the precipitation bath with a later average diameter d _{50 are also listed} . If this is larger than u _Le , there may be a fanning out. To do this, the values would have to differ very significantly, since a finer diameter than the arithmetically corresponds to the maximum air speed during the spinning process, i.e. in the narrowest gap of the Laval nozzle, may also have resulted from the side peeling off of the main stream or poor cellulose concentration at this point.

The thread diameter can be further reduced by increasing the temperature of the solution before it emerges from the spinning bore, however the temperature is limited here because the solution decomposes, so that the shortest possible residence times under elevated temperature are chosen by appropriately designing the melting spaces in the lower part of the spinneret become. At a temperature there of 123 ° C instead of the previous 114 ° C, the proportion of individual threads with u _F> u _{Le increased} in one setting, roughly like No. 7 in Table 2.

The nozzle holes of this longitudinal nozzle (20 holes in a row) protruded 2 mm into the Laval nozzle in the direction of flow. There remains 3 mm of constricting distance to the narrowest cross section of the Laval nozzle. Thus there was a narrowing gap on both sides of the thread group. This creates a steadily accelerated gas flow over a very short distance from the inflow to the narrowest cross section of the Laval nozzle. Laminar flow prevails in the area of thread formation after it emerges from the spinning bore. Even with small disturbances, such a strong constriction and thus flow acceleration causes a relaminarization as is known in nozzle flows, with the effect that the thread, slowly emerging from the spinning bore, is warped under a steadily increasing gas (air) flow u _L and also constantly increasing in speed u _F. Fluctuating flow impulses of a turbulent nature would interfere with this process and, as with other methods which have become known, there would be separation of the dope thread (for example from a Lyocell solution) and the threads would no longer be essentially endless. The deformation to run lengths of a few mm in the method according to the invention also takes place at high shear stresses that increase up to the narrowest cross section - a reason for essentially tear-free thread formation, because the speed u _L (x) has its maximum = narrowest cross section of Laval nozzle below, not next to it the mass exit.

By setting certain values for the throughput the spinning mass, its temperature and the air speed in the flat gap in longitudinal nozzles or in An annular gap in the case of round nozzles can be used, as in Examples 1 and 2 show the diameter of the substantially control endless threads. The throughput per spin hole is higher than in all cases mentioned known meltblown process for Lyocell. The reason is the high shear stresses caused by the strongly accelerated flow, namely a start-up flow, with very thin boundary layers on the thread.

Example 3

In a spinning device, similar to that shown in Fig. 1, was a polypropylene melt with a Temperature of 355 ° C from a slot of 0.9 mm Width and 20 mm length from a bottom ending as a web Spinning nozzle spun out as a film. As a stretching gas air was used for the film. With a throughput of 11.5 g / min and an air pressure of Threads resulted at room temperature of 20 ° C and 250 mbar with an average diameter of 5.2 µm with a Scattering of s = 1.9 µm, corresponding to a coefficient of variation of CV = 37%. The thick ones Knots in the fleece not measured. The generated fleece is shown in Fig. 3, the photo a microscopic picture of the PP splice threads according to example 2 shows. 4 are for comparison Polypropylene splice threads shown below under otherwise same conditions from a round spinning hole with a diameter of 1 mm with a throughput were spun out of 3.6 g / min. The Threads in Fig. 4 had an average diameter of 8.6 mm, their coefficient of variation was 48%.

The present description of the invention The method and its devices can also be applied to others solvent-spun thread polymers applied be, for example, on conventional viscose or Rayon threads and their further processing Fleeces or yarns. In addition to the special features mentioned the spinning security is to be emphasized further, that the device is simple, the energy consumption much lower compared to meltblown processes is and surprisingly large diameter for spinning bores and slots can be applied through the high warping caused by the thrust at speeds up to speeds of sound and also above it by means of its production in a Laval nozzle. So there are impurities in the spinning mass no longer so critical with regard to thread breaks. With lyocell threads, higher proportions of hemicellulose processed into threads, and also the degree of polymerization the cellulose (DP) can be lower which generally makes the raw materials cheaper, because there are no high tensile forces on the lyocell threads in its original state as fine threads the release mass can be exercised. That basically only cold air or air with waste heat from the air atomization is used at Lyocell, especially but with solution polymers to be spun at a higher temperature much to the energy saving of the process at.

Claims (19)

1. Method for producing substantially endless fine threads from a spinning substance of dissolved polymers of synthetic or natural origin, where the spinning substance is spun through at least one spinning bore, and the spun thread is drawn by gas flows which are constantly accelerated by means of a Laval nozzle, and the gas flow in the area of thread development is substantially laminar.
2. Method according to Claim 1, characterised in that the maximum speed of the gas flow lies below the outlet of the spinning substance from the spinning bore.
3. Method according to Claim 1 or 2, characterised in that the gas flows which draw the thread are at environmental temperature or at a temperature caused by its production and delivery.
4. Method according to one of Claims 1 to 3, characterised in that the spinning substance is cellulose dissolved in a solvent, such as aminoxide.
5. Method according to one of Claims 1 to 3, characterised in that, with a given geometry of the spinning bore and its position relative to the Laval nozzle, the temperature of the spinning substance or of the thread exiting through the spinning bore and/or the pressures in front of and behind the Laval nozzle are controlled in such a manner that the thread arrives prior to solidification at a hydrostatic pressure in its interior which is greater than its surrounding gas pressure, so that the thread bursts and splices itself into a plurality of fine threads.
6. Method according to one of Claims 1 to 5, characterised in that the area behind the Laval nozzle is at environmental pressure or, in the event of further processing of the threads. at a pressure somewhat above environmental pressure as required for further processing.
7. Method according to one of Claims 1 to 6, characterised in that the ratio of pressures in the space above and below the Laval nozzle during the use of air is selected in dependence of the polymer the throughput and temperature of which lies between 1.02 and 3.
8. Method according to one of Claims 1 to 7, characterised in that the spinning substance in the area of the exit point and/or the thread exiting from the spinning bore is/are heated.
9. Method according to one of Claims 1 to 7, characterised in that a plurality of threads is spun out and, if appropriate, spliced, stored as a fleece or processed further into yarns.
10. Method according to one of Claims 1 to 8, characterised in that the threads are spun out, separated from the accompanying gas flow, delivered to a precipitation device and spooled onto spools.
11. Method according to one of Claims 1 to 10, characterised in that threads spun from a cellulose solution are stored in the dry and subsequently guided through a precipitation bath.
12. Method according to one of Claims 1 to 11, characterised in that into the drawing area of the threads is blown water or water vapour for controlling bonding of the threads relative to each other in a fleece.
13. Method for production of fine threads from a spinning substance of soluble polymers of synthetic or natural origin, in which the spinning substance is spun in form of a film out of a long stretched slotlike spinning nozzle, and the spun film is drawn by means of gas flows which are accelerated by means of a long stretched Laval nozzle to high speed, and the film is at the exit from the Laval nozzle and shortly thereafter broken up into a plurality of threads which are deposited as a fleece.
14. Device for production of substantially endless fine threads of solution spun polymers of natural or synthetic origin comprising a spinning head which is linked to a feeding device for the spinning substance, a spinning nozzle arrangement accommodated in the spinning head with at least one spinning bore, which spins a solution thread, a round Laval nozzle arranged below the spinning head in fixed geometric association to the spinning nozzle, and the narrowest cross-section of the Laval nozzle is located below the spinning substance outlet.
15. Device for production of fine threads from solution spun polymers of natural or synthetic origin, comprising a spinning head which is linked to a feeding device for the spinning substance, a spinning nozzle arrangement accommodated in the spinning head, which comprises at least one long stretched slotlike spinning nozzle which spins a solution film, a long stretched Laval nozzle arranged below the spinning head in a fixed geometric association to the spinning nozzle, and the narrowest cross-section of the Laval nozzle is located below the spinning substance outlet.
16. Device according to Claim 14 or 15, characterised in that the spinning arrangement in the area of the at least one spinning bore or the at least one spinning slot is insulated by an insulating arrangement and/or heated.
17. Device according to one of Claims 14 to 16, characterised in that the distance between spinning substance outlet and narrowest cross-section of the Laval nozzle ≥ 5 mm.
18. Device according to one of Claims 14 to 17, characterised in that a depositing band is provided for depositing the threads and forming a fleece.
19. Device according to Claim 18, characterised in that the depositing band at least partially intrudes into a precipitation bath for coagulation of the fibre materials from the solution.

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