Patent Application
20090221206
The invention relates to a spinning device for producing fine threads by splitting according to the preamble of the main claim.
Fine threads into the range below 1 micrometre (μm) can be produced by splitting a thread-forming fluid flow as a melt, solution or in general as liquids which are subsequently made to solidify, as has been described in DE 199 29 709 and DE 100 65 859. The mechanism of thread formation is fundamentally different from all the spinning methods which have become known to date where the spinning material is withdrawn by winding-up devices from the spinning nozzles to form threads or, in the case of spunbond methods, by accompanying airflows which exert a force on them and, in a special embodiment, in the so-called meltblown methods, where the air drawing the thread emerges right beside the spinning nozzle openings heated to approx. spinning material temperature. The thread speed thereby achieves that of the winding or is below that of the air- or gas flows drawing it. This applies to the average of thread diameters, however individual “mavericks” are discovered during the meltblown method where also finer diameters can arise than that from throughput and maximum possible withdrawal speed, the greatest air speed, but still not in a targeted manner as happens in the mentioned new method, also termed Nanoval method. Here the following effect is used according to a new mechanism, only explained recently from hydrodynamic basic rules, see L. Gerking in Chemical Fibers International 54 (2004) pp. 261-262 and 56 (2006), pp. 57-59: if a melt—or in general fluid thread or—film is impinged upon by shear stresses externally, then the result in the interior thereof is a pressure build-up if the speed on the outer skin of the fluid jet is greater than that in the interior thereof and this is even more the case the greater is the acceleration thereof that can be achieved after emergence from the spinning opening. This is, one can say, the reverse of flow in pipes or channels (Hagen-Poiseuille) where the pressure energy is used to overcome the friction on the channel walls whilst, in the case of the new spinning method, energy is transmitted to the thread by the shear stresses acting thereon from the exterior. Said thread attempts to counteract this by a pressure increase in the interior. If not only the outer skin is cooled by the gas flow surrounding it then the result can be solidification of the thread.
In the case of polymers and polymer solutions with their basically low heat conductivity, firstly however only an outer skin of increasing viscosity is formed and the hydrodynamic effects can act in the interior of the thread. The result then is, with good regularity and reproducibility, a bursting which is comparable with the bursting of pipe on its longitudinal join with astonishingly essentially continuous threads and, in view of the stochastic character of the splitting, of a low distribution width in the thread diameter. The number of individual threads produced in this way exceeds, in the production of particularly fine threads, in the range around and below 1 μm, up to several hundreds from one liquid jet.
The Nanoval method is carried out in lines of nozzles in its industrial applications, a series of spinning orifices being located above a gap. The gas, in general air, without particular conditioning after its production in fans or compressors (the energy requirement is fundamentally low compared with the meltblown methods) flows at both sides of the line of nozzles in constant acceleration towards the narrowest cross-section of the gap which then again generally rapidly widens, basically however has the configuration of a Laval nozzle. Also individual round nozzles were described surrounded by an annular gap which constantly reduces towards the narrowest cross-section.
It has been shown that the shear forces acting on the thread on all sides by a rotationally symmetrical gas flow lead to a smaller average diameter of the essentially continuous threads which are produced by splitting, which can be attributed to the more uniform impingement of the thread, irrespective of whether the air is also heated additionally or not. Also the cooling which, in interplay, causes the bursting effect with the hydrodynamic forces is distributed more uniformly around the thread than happens in the case of merely lateral impingement in the lines of nozzles with a linear Laval nozzle configuration and less air is consumed. In the case of the lines of nozzles, a part of the air is used more poorly in the intermediate spaces from thread to thread.
A further influential factor for the production of fine and ever finer threads, as can be produced otherwise for example only by electrospinning methods, however in very small throughputs and with a high spatial and safety expenditure because of the required high voltage, is the throughput per spinning nozzle opening, irrespective of whether with round or slot-shaped openings for the spinning material. The gas speed in the narrowest cross-section of the Laval nozzle can achieve the speed of sound, thereafter in the widened section even into ultrasound, which then, in the case of this flow laden with threads, generally leads rapidly to subsonic sound by means of compression shocks. However, only a specific shape changing operation can be performed by the shear stress forces in the case of a given running surface of the still deformable thread material. The throughputs are consequently fundamentally lower when producing very fine threads in the range around and below 1 μm. This leads to the fact that, for a specific total throughput when producing nonwovens according to the Nanoval method for finer threads, more spinning nozzles are used over the width. This applies correspondingly in the production of yarns.
The object underlying the invention is to produce a device for producing fine threads which is compact and constructionally simple, a good start to spinning being intended to be possible.
This object is achieved according to the invention by the characterising features of the main claim in conjunction with the features of the preamble.
As a result of the features represented in the sub-claims, advantageous developments and improvements are possible.
As a result of the fact that the device for producing fine threads has at least one spinning nozzle part which is equipped with spinning nozzles and at least one partially plate-shaped gas nozzle part with at least one gas supply chamber, the at least partially plate-shaped gas nozzle part having a plurality of funnel-shaped depressions as acceleration nozzles into which the spinning nozzles engage in such a manner that combinations of spinning nozzles/acceleration nozzles, in particular Laval nozzles, with rotationally symmetrical gas flow channels are formed, the device can be constructed compactly with a large number of closely adjacent combinations, gas nozzle part and spinning nozzle part being displaceable relative to each other so that the gas flow channels which are formed between gas nozzle part and spinning nozzles of the spinning nozzle part can have different flow cross-sections, as a result of which the height of the spinning openings can be adjusted to the narrowest cross-section of the acceleration nozzles, in particular Laval nozzles. As a result, the start of spinning is facilitated and made possible for the first time ever with a plurality of nozzles which are adjacent and in succession in that the gas nozzle part is withdrawn relative to the spinning nozzle part towards the latter in order not to impair the arriving thread run. At the same time, maintenance and cleaning of the spinning nozzles is facilitated as a result of the displaceability.
A particularly simple construction is provided if the gas chamber is formed between the underside of the spinning nozzle part, out of which the spinning nozzles or spinning nipples protrude, and the upper side of the plate-shaped region of the gas nozzle part, the gas, usually air, being supplied to the acceleration nozzles via said gas chamber.
It is particularly advantageous to provide a self-adjusting seal between the spinning nozzle part and gas nozzle part, which is compressed when introducing the gas during spinning by the then resulting pressure.
An advantageous embodiment, although somewhat more complex and in particular when supplying “cold” air, resides in configuring the gas nozzle part as a hollow body which is engaged by the depressions and the cavity of which between the depressions forms the gas chamber, the hollow body having openings which are directed towards the spinning nozzle part, preferably rotationally symmetrically about the depressions, via which the air or the gas passes towards the acceleration nozzles.
A plurality of nozzle parts and gas nozzle parts can be disposed adjacently, different spinning materials also being able to be spun.
Advantageously, a further plate with openings can be disposed below the plate-shaped region of the gas nozzle part, forming a distributor chamber for a further fluid. This fluid can be water for coagulating dissolved fibre materials, coolant for freezing the molecular orientation achieved during the splitting, means for heating, e.g. steam, for a second stretching or the like.
The invention is represented in the drawing and is explained in more detail in the subsequent description. There are shown:
The spinning device represented in
The lower plate-shaped region of the spinning nozzle part is received in a gas nozzle part 27 which comprises a frame-like edging 34 and a plate-like part 35, in the latter three respectively offset rows of Laval nozzles 36 being provided corresponding to the rows of spinning nipples 23. The edging 34 is provided with an upright edge, a seal 33 being disposed between this upright edge and a surface 32, which is situated opposite said upright edge, of the lower region of the spinning nozzle part 28.
The spinning- and the gas nozzle part 28, 27 are aligned relative to each other such that the tip of the spinning nipples 23 protrudes into the Laval nozzles 36, a gas chamber 22 being formed between the lower surface of the spinning nozzle part 28 and the upper surface of the plate-shaped region 35 of the gas nozzle part, through which gas chamber the spinning nipples 23 engage and which is connected to gas or air supply lines 20 provided in the edging.
In particular if the supplied air is cold, the spinning nipples 23 are preferably provided with a heating means 24, advantageously with a belt heating means, as is known from injection moulding tools in plastic material machine construction.
The device according to the invention has means for displacement of the spinning- and gas nozzle part 28, 27 relative to each other, a screw 29 being guided, in the present embodiment, in a split nut 30 which is securely connected to the spinning nozzle part and is connected in an anchor 31 in the frame 34 of the gas nozzle part 27 to the latter, the anchor 31 being able to exert a pressure or tension force according to the direction of rotation of the screw 29, as a result of which the gas nozzle part is displaced. Of course, other types of displacement means are possible.
For the start of spinning, the gas nozzle part 27 is raised, i.e. displaced upwards in
In order to clean the spinning nipples 23, the gas supply 21 is switched off, the gas nozzle part 27 is raised until the plate part 35 abuts against the spinning nipples 23 with the wall of the Laval nozzles 35. The air present in the region of the seal 33 and the surface 32 is thereby blown out. The nipples 23 protrude out of the Laval nozzles and can be cleaned.
The device represented in
Furthermore, a gas nozzle part 2 is provided which is configured for example as a hollow body which is formed by two plates provided with funnel-shaped depressions. Between the plates, a cavity 9 is formed which is interrupted by the funnel-shaped depressions. The cavity 9 serves as gas chamber which is in turn connected to a gas supply source. Around each funnel-shaped depression, an annular opening 4 is incorporated, the openings 4 represented in section in
The conical raised portions which form the spinning nozzles 13 engage in the depressions of the gas nozzle part 2 such that rotationally symmetrical gas flow channels 5 are produced. In the represented embodiment, respectively in the intermediate space between the spinning nozzles 13 which are represented in
The spinning nozzle part 1 and the gas nozzle part 2 are displaceable relative to each other, viewed according to
These sliding rods can absorb force produced at the same time with different expansions of the spinning nozzle-1 and of the gas nozzle part 2, as a result of which the positioning of both parts relative to each other is maintained.
In
The mode of operation is dealt with in the following.
In
Whilst the start of spinning with a line of nozzles takes place simply by pushing together two channel halves which form the Laval nozzles, this is not possible in the case of nozzle combinations in a plurality of rows. The part 2 can however be displaced in the direction of the thread emergence axis. As a result, it can be entirely drawn back when starting spinning towards the formed part 11, an expulsion of spinning air via the openings 4 can initially be stopped or permitted to a small extent. Then the part 2 is lowered, spinning of the thread is started, it is drawn and made to burst according to the setting data known from the method for the air speed from the applied pressure in the space 9 of part 2, for the flowing spinning material from the openings 3 and at the temperature of the spinning material required for splitting. Said material is advantageously heated in addition just before emergence from the spinning openings 3, indicated by heating means 10, the introduction and mounting of which has been dispensed with for the sake of clarity of the drawing. In order that the flowing air does not cool impermissibly at lower temperatures than the spinning material temperature, the formed part 11 is configured such that it, on the one hand, forms the inner wall of the rotationally symmetrical channel 5 for constant acceleration of the air until close to the spinning nozzle opening 3 but, via an air gap 12, also insulates the spinning nozzle 13 with respect to heat against the airflow in the flow channel 5. The formed part 11 can however also contain heating means of the spinning nozzles instead of the spinning nozzle part 1.
The two basic positions of the movable part 2 are indicated in
In the case of a greater air requirement, i.e. in the case of larger nonwoven and hence spinning beam widths, main distributor channels can be fitted between the nozzle openings, only the rows of individual nozzles moving apart slightly in the nonwoven running direction because the spinning nozzle device according to the invention has the advantage as spinning beam at the same time that it forms a plurality of spinning beams in succession viewed in the nonwoven running direction. Each has its specific irregularities, even from hole to hole, as in the case shown here with spinning nozzle and Laval nozzle beyond the nonwoven width. A statistical compensation for greater nonwoven uniformity can take place between the individual rows because the threads of the following rows increasingly cover the sparse positions of the preceding ones.
If in addition gas or air or a liquid medium for accompaniment of solutions is desired for cooling or keeping warm during spinning of said solutions also for coagulation of the threads, then this medium can easily be introduced as third fluid flow between the spinning and Laval nozzles and be made to flow out. This is illustrated in
The device is also fundamentally suitable for spinning different spinning materials in the individual spinning nozzles, for which purpose the melt- or spinning solution distribution must be correspondingly arranged, i.e. alternating transversely relative to the direction of travel or also differently from row to row. It is hence possible to produce mixed nonwovens in order to achieve special effects, such as the spinning of binding threads in matrix threads, e.g. polypropylene as binding threads and polyester as the matrix which provides strength or by means of a portion of more greatly shrinking threads in order, after the nonwoven deposition, to achieve higher volumes and softness as a result of shrinkage of the entire thread web and also other nonwoven properties by means of two or more different components. Also bicomponent or multicomponent threads can be produced without difficulty by supplying two or more spinning materials into the spinning nozzle part and into the channels 14. With different throughputs, adjusted by opening cross-sections of the spinning nozzle openings of different sizes or by controlled melt supply to the latter, a different type of mixed nonwoven can be produced.
The present device has in addition the advantage that it connects the melt-guiding spinning nozzle parts 1 or 28 to the colder gas nozzle parts 2 or 27, in fact in a mutually displaceable manner but securely transversely relative thereto. After heating part 1 with heating means, not shown here, part 1 will expand more relative to 2 if no particularly heated air is supplied from part 2 so that respectively spinning boring 3 and narrowest cross-section 6 show deviations over the width and length, the same is true for parts 28 and 27. The connection can take place by means of sliding rods, not shown, which prevent this deviation with respect to the forces, said sliding rods being able to be disposed in the plates of the spinning nozzle part 1 and of the gas nozzle part between the combinations of spinning nozzle/Laval nozzle. In order to prevent the different expansion, heating of the air flow in the flow channel 5 can however also be undertaken intentionally.
Guiding part 1, which is initially set back relative to the spinning boring opening 3, and later is displaced in the running direction of the thread 7 in order to produce the splitting effect, must take place by means of guides or sliding rods which are known in tool construction. The introduction of air, likewise not shown here, takes place from the exterior to the front, rear or side on the spinning beam, a seal requiring to be present between spinning nozzle part 1 and gas nozzle part 2 or because a few millimetres of guidance length between 1 and 2 suffice, the chambers 9 shown in
It is now also possible in a simple manner to divide spinning beam of a larger width into a plurality of nozzle fields, these in turn comprising numerous individual spinning nozzle/Laval nozzle combinations so that individual ones of these packets (spinning packs) can be exchanged in the case of blockages of the spinning openings or other disruptions. The separating gaps are then arranged diagonally relative to the running direction, the spinning nozzle openings, as shown in
The following example shows the use of the device in the splitting spinning method according to Nanoval and the thread values achieved for example. A polypropylene melt was distributed to nineteen spinning nozzles 13, disposed in a row, with inlet borings for the melt 14 and spinning nozzle openings with a diameter of 0.3 mm. In the thread running direction, there was situated thereafter for each of these openings a Laval nozzle with the narrowest cross-section of 3 mm diameter which was guided back to the spinning opening after the start of spinning. The polymer throughput was changed in regions as reproduced in Table 1, likewise the air pressure and hence the flowing air speed in the region of the shear stresses on the thread leading to splitting. The temperature of the polypropylene melt could be heated in the spinning nozzles 13 by approx. a further 20° C. shortly before emergence thereof from the spinning opening via electrical heating elements.
For a device according to
It is obvious that, not necessarily only at higher air pressures, i.e. higher air speeds, higher air temperatures and lower throughputs, the fine threads could be produced down to approx. 0.5 μm=500 nanometres (nm) but that this was also achieved at greater throughputs of 3 g/min and hole, for which purpose the temperature of the melt was however increased before emergence thereof from 335 to 352° C., the air temperature remained initially, at the higher throughput of 3.0 g/min, still in the range of that produced by the compression and the increase at otherwise constant values to 180° C. produced no measurable influence in the direction of higher fineness. Only an air temperature increased to 220° C. then produced the value d50=1 μm with minimum diameters of 0.44 measured in the microscope. A thread measurement as here with the microscope can however no longer claim high precision since the range is already that of lightwave length. In any case, unequivocal dependencies are there which initially are surprising from the point of view of conventional spinning. If it is recalled however that here threads are produced by bursting, i.e. fragmentation, then rules other than those of pure length drawing, are in operation as described above, which lead to the fact that individual parameters can be changed, such as for example the melt temperature relative to the gas speed, with the same effect on the resulting average thread diameter and even its scatter.
Although the device according to the invention is intended primarily for the production of fine threads, also coarser ones can be spun with it, as a result of which the versatility thereof is displayed. Thus, threads made of polyester and polylactide were produced, as reproduced in Tables 2 and 3. The diameter of the spinning nozzle openings was 1.0 mm.
When spinning polyester threads, it proved to be of advantage to withdraw the threads after they had burst through an injector channel which was situated a good 1 metre lower, as described in L. Gerking, Change in Filament Properties of Polymer and in the Spinning Line, Chemical Fibres/Textile Industry 43/95 (1993) on pages 874/875. By repeated heating in between, as described in DE 19 65 054 column 4, lines 44 to 57, the tensile strength of the threads could be increased with both measures but primarily the shrinkage was able to be significantly reduced.
The polymer polylactide produced from natural raw materials showed in splitting spinning for coarser threads the values reproduced in table 3.
In Table 3, the value characterised with (1) emerges from the otherwise detectable dependencies, also as the greatest value. In this adjustment, the aerodynamic ratios were changed by changing the Laval nozzle geometry, likewise with the value characterised with (2). In the case of (1), absolutely no splitting of the melt thread took place, at (2) now and again.
The device according to the invention can be used for thread-forming melts or solutions but also in general for liquids if it is a question for example of applying thin layers, such as colours, paints, finishers. It then serves for atomising the liquids into as fine as possible droplets with as uniform as possible a distribution on the surface to be coated. The conditions can be found easily respectively by the given geometric adjustment possibilities of the device.
The devices (according to
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 012 052.3 | Mar 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP06/10320 | 10/23/2006 | WO | 00 | 11/20/2008 |
