EP0541552B1 - Process and spinning device for making microfilaments - Google Patents

Abstract

PCT No. PCT/DE90/00941 Sec. 371 Date Jun. 19, 1992 Sec. 102(e) Date Jun. 19, 1992 PCT Filed Dec. 3, 1990 PCT Pub. No. WO91/09162 PCT Pub. Date Jun. 27, 1991.An improved process and apparatus are provided for producing fine microfilaments of a melt-spinnable polymeric material having a silk-like character. The molten polymeric material is melt extruded through a plurality of extrusion orifices, is passed from the extrusion orifices while surrounded by a stream of headed air that surrounds and flows parallel with the molten polymeric material, is passed through a solidification zone wherein cooling air is transversely blown to contact the same, and a pulling force is exerted on the resulting solidified microfilamentary material which is applied below the solidification zone so a to accomplish substantial drawing of the polymeric material intermediate the extrusion orifices and its transformation in to a solidified microfilamentary material. The formation at a high rate of 4,000 to 6,000 meters per minute of quality fine microfilaments of less than 1 dtex per filament (e.g., 0.33 dtex) is made possible. Preferably, the stream of heated air that surrounds the molten polymeric material immediately after the melt extrusion is provided at a temperature that approximates the temperature of the molten filamentary material.

Description

The invention relates to a method for producing microfilaments according to the preamble of claim 1, and the invention also relates to a spinning device for producing microfilaments.

Synthetic filaments with a single titer of less than 1 dtex are referred to as microfilaments (the specification 1 dtex means that 10 km of the thread or filament weighs 1 gram). The microfilaments therefore have a very small diameter and are twisted in a known manner to form microfilament yarns. These microfilament yarns can be woven or knitted to make a textile. Due to the single titer of less than 1 dtex, the textiles are characterized by a very soft feel and a noble case, so that they have a silk-like character and can follow the fashion trend of silk fabrics.

The production of microfilaments takes place in that the microfilament is drawn off and stretched at a high take-off speed from the spinning hole of a spinneret fed with a melt and is taken up on a roll after passing through an area blown transversely with cooling air. This is followed by twisting with a large number of microfilaments to form a microfilament yarn from which the desired textile can be produced by weaving.

In addition, it is also known to produce spunbonded nonwovens from the microfilaments by pulling the filaments emerging from spinnerets under the action of an injector after passing through an area blown transversely with cooling air and depositing them on a continuously moving deposit belt. Such spunbonded nonwovens made from microfilaments are also covered by the invention.

In the case of the microfilaments produced from synthetic polymers, the filament diameter, depending on the synthetic polymer used, is below 12 »m for polypropylene and below 11» m for polyamide or below 10 »m for polyester. The microfilament yarns obtained from it, which are mostly offered as polyamide and polyester yarns, generally have a single titer that is only slightly less than 1 dtex.

As already mentioned above, the microfilament yarns and textile products resemble the fashionably preferred natural silk due to their soft feel. In addition, the textile yarns made from microfilaments have yet another advantage that is due to the tightness of the fabric. Fabrics made from microfilament yarns can be woven so densely that their diffusion properties are similar to semi-permeable diaphragms. These fabrics breathe, that is, they let gases and vapors such as water vapor through easily, even though they are poorly wettable at the same time. The poor wettability is due to the small filament diameter and the resulting unfavorable angles between two filament surfaces.

The advantageous properties of the textiles made from filament yarns and also the corresponding spunbonded nonwovens can therefore be attributed to the relatively small diameter of the microfilaments, which are produced in the manner described above using the customary "rapid spinning process" and generally to "POY yarns" (POY = Partially Oriented Yarn) can be summarized. The polymer melt is extruded through the spinneret, cooled by an air stream below the spinneret and drawn off at high speed - usually around 6,000 m / min.

In order to further increase the silk-like character of the products made from the microfilaments (textile or spunbond) and to further improve the described advantages, the aim in practice is to reduce the diameter of the microfilaments during their manufacture to a single titer of significantly less than 1 dtex. Under the assumption that it is practically always desired that the same total titer of the microfilament yarn should be maintained even with the finer microfilaments, the number of microfilaments in the yarn or the number of nozzle holes per microfilament yarn must be used increase proportionally to the reduction in the individual titer in d-tex, because several microfilaments are then required to produce a microfilament yarn with the same diameter. In order to achieve the smaller diameter of the microfilaments, it is necessary to reduce the mass flow through the unchanged nozzle bore (spinning hole).

In a practical implementation of a method for producing microfilaments with smaller diameters, however, it must also be taken into account that the filament surface is inversely proportional to the third power of the filament diameter for the same volume. If, for example, the individual titer is halved, the thinner filament has an eightfold surface.

The larger surface area can be seen in connection with the cooling of the microfilament. Basically, the stretching of the microfilament requires a certain temperature, and if it cools down too much, there is a risk that the microfilament will become brittle and tear off, especially at the usual high take-off speeds of 6,000 m / min.

If the cooling rate is too rapid, hypothermic skin will form on the surface of the microfilament. This skin is responsible for the filament breaks. The skin is already rigid, while the inner mass, which is surrounded by the skin, is still in a stretchable state.

A cut-off is only possible here if the take-off speed is considerably reduced, and at the same time the mass flow of the melt through the spinneret must be reduced accordingly. In the other case, if the mass flow remains constant, the reduction in the draw-off speed would result in the filaments not being able to be produced with the desired small diameter.

The required reduction in the take-off speed leads to values of around 2,000 m / min (compared to the usual value of 6,000 m / min). In connection with the correspondingly reduced mass flow, however, this results in a considerably reduced performance of the spinning device, which can no longer be operated economically. Since one is otherwise in the implementation of an appropriately dimensioned spinning device with the spinning conditions to be taken into account in the usual way up to the still just acceptable limit with regard to filament tears, the quality of the microfilament yarn is additionally impaired, apart from the fact that the economy of a corresponding spinning device suffers from the fact that - compared to filaments with larger diameters and with increased take-off speed - fewer yarns can be produced per unit of time.

From EP-A-0 244 217 a process for the production of filaments is known which deals with the problem of treating freshly drawn and drawn filaments from a spinneret at high take-off speeds. A cylindrical pressure chamber is provided directly underneath a spinning hole of the spinneret, into which the filaments immediately come out of the spinning hole.

A cylindrical screen is arranged concentrically within the pressure chamber, and warm air under pressure is supplied to the pressure chamber from outside and pressed through the cylindrical screen, in which the filaments freshly extruded from the spinneret are drawn. The warm air is supplied in a direction which is predominantly transverse to the direction in which the filaments are drawn off, as a result of which the filaments are subjected to a load within the pressure chamber or within the cylindrical screen. In addition, turbulence inevitably occurs in the cylindrical sieve, which places an additional load on the freshly drawn filaments.

Only after the pressure chamber, which opens into an outlet tube, does the direction of the warm air run parallel to the direction of the filaments. This means that the filaments can only be enveloped by the warm air in a jacket-like manner after they have left the outlet pipe adjoining the pressure chamber below. The known method is not suitable for the production of microfilaments, i.e. filaments with a single titer of less than 1 dtex, because the stresses mentioned are within the pressure chamber or within the cylindrical sieve, i.e. in an area that is directly adjacent to the outlet opening of the Spinning hole connects, are too large. Otherwise, the filaments in a cooling area are not blown with cooling air parallel to the direction of the filaments.

EP-A-0 245 011 also discloses a similar process for the production of filaments, the filaments being drawn off and stretched from a spinneret fed with a melt through a spinning hole after passing through a cooling area at a high take-off speed. Here, too, a chamber with a cylindrical sieve immediately adjoins the spinning hole, through which warm air is fed under pressure transversely to the direction of the filaments. Only after leaving the chamber mentioned does the warm air supplied run in one direction parallel to the filaments. The disadvantages mentioned above apply to the area directly at the outlet opening of the spinning hole when it comes to the production of microfilaments with a very small diameter.

The invention has for its object to provide a method which allows the production of microfilaments with very small diameters without deterioration of economy and quality, and also to be created by the invention, a spinning device which allows economical production of microfilaments with small diameters .

With regard to the method, this object is achieved in the method presupposed in the preamble of patent claim 1 by the features of the characterizing part, and with regard to the spinning device, the object in a spinning apparatus according to the preamble of patent claim 10 is achieved by the method characteristic features solved.

In a novel manner, the invention provides that the microfilaments are accompanied by a downward flow of hot air immediately after they exit the spinning hole. The extruded filament is thus embedded in a warm air stream after exiting the spinning hole, which preferably surrounds the filament in the form of a jacket. The hot air coating compensates for the negative influence of the large surface area of the microfilaments, which leads to rapid cooling. This prevents the filament from cooling too quickly - due to the much higher specific surface area. A major advantage of the invention is therefore that the filament can be drawn off easily even at the usual high speeds of 4,000-6,000 n / min.

Because of this high take-off speed, it is then also possible to improve the mass output of the melt even with extremely fine microfilaments, thereby ensuring the economy of the process according to the invention.

At the same time, the tendency to filament breaks is considerably reduced and the uniformity of the filament diameters over the entire nozzle bore is improved. The microfilament yarns produced by the method according to the invention thus guarantee a significantly better quality, the disadvantages described at the outset being eliminated.

The protective jacket made of hot air protects the just extruded and formed filament from cooling too quickly immediately after it emerges from the spinning hole of the spinneret. Thus, no rapidly cooled outer skin of the filament can arise, which would be damaged by the shear stress caused by the rapid filament draw-off without cracks and would lead to a filament breakage.

Rather, care is taken in the invention that the filament cools gradually, so that - viewed radially - a uniform structure is formed. This allows the very fine microfilament with a small diameter to be stretched optimally. Furthermore, differences between the individual filaments of a multifilament spinneret are largely suppressed, which leads to a significant improvement in quality.

Since the cooling of the microfilament in the invention does not take place suddenly, but continuously, the risk is eliminated that if the cooling is too rapid, an undercooled skin is formed on the surface of the filament, which is responsible for filament breaks.

Using the method according to the invention or with the spinning device according to the invention, the cooling of the microfilament is under control, so that the risk of microfilaments with different diameters being avoided is avoided. Although such deviations in the diameters in the prior art are only slight, they are nevertheless noticeable, e.g. in that when the microfilaments or the textile are colored, the color of the different microfilaments with different diameters is also taken up differently. As a result, the uniform color impression of the product used as a high-quality textile suffers.

In an expedient embodiment of the invention, the method for producing microfilaments also includes known very small diameter
Polymers used that are spinnable from a melt. In particular, polyolefins, especially polypropylene, furthermore polyester and polyamide 6 and 6,6 can be spun by the process according to the invention.

Known bicomponent nozzles can advantageously be used, whereby it must be ensured that the outer part of the combined spinneret is modified in such a way that a uniform distribution of the hot air over all bores is ensured. Furthermore, the outer holes of the combined nozzle must be adapted to the air flow.

Such bicomponent nozzles have a jacket-core arrangement, in which case only the core nozzle is used for spinning the polymer melt and the hot air flow is generated at the jacket nozzle.

The spinning conditions with regard to the polymer melt can essentially be maintained in the invention as they are set when spinning a conventional spinning device. The air temperatures in the outer part of the spinneret (bicomponent nozzle) depend on the melting temperature Embodiment of the invention is provided that the temperature difference between the two components should not be exceeded ± 10 ° C. In the optimal case, the temperatures of the two components, melt and air, are equal.

The amount of air in the hot air can be adjusted in a simple manner, a minimum setting being necessary in order to ensure that a clean free jet is formed at each spinning hole at least just below the spinneret.

After running a distance of approximately 100 to 500 mm below the spinneret, the microfilaments can be cooled more intensely by cross-blowing, whereby the usual blowing chutes can be used here.

In addition to the mechanical take-off devices in the form of a roll, which are suitable for producing microfilament yarns from microfilaments, aerodynamic take-off devices in the form of an injector can also be used expediently within the scope of the invention, so that the microfilaments formed according to the invention can be used in a known manner and Wise also a spunbond can be formed.

Other expedient refinements and advantageous developments of the invention result from the subclaims, the description and the drawing.

Fig. 1

eine schematische Darstellung einer bekannten Spinnvorrichtung mit einer mechanischen Abzugsvorrichtung in Form einer Rolle,

Fig. 2

eine Spinnvorrichtung gemäß Fig. 1, jedoch mit einer aerodynamischen Abzugsvorrichtung,

Fig. 3

eine schematische Darstellung einer Ausführungsform der Spinnvorrichtung nach der Erfindung, und

Fig. 4

eine Detaildarstellung einer in Fig. 3 verwendeten Bikomponentdüse.

For a better understanding, the invention is explained in more detail below with reference to the drawing. Show it:

Fig. 1

1 shows a schematic illustration of a known spinning device with a mechanical take-off device in the form of a roll,

Fig. 2

1, but with an aerodynamic take-off device,

Fig. 3

is a schematic representation of an embodiment of the spinning device according to the invention, and

Fig. 4

a detailed view of a bicomponent nozzle used in Fig. 3.

The spinning device designated as a whole with the reference number 10 in FIG. 1 is known per se. It has a spinneret 12 with a spinning hole 14, through which melt 16 exits and is stretched into a microfilament 18. A rotating roller 20, on which the microfilaments 18 are rolled up, serves as the take-off device. For the sake of clarity, the representation according to FIG. 1 shows only the case of a single microfilament. In practice, if a large number of microfilaments are produced, the spinneret 12 has a corresponding number of spinning holes 14.

When leaving the spinning hole 14, the melt 16 has a temperature of approximately 280 ° C. A transverse blowing with cooling air is indicated by the arrow 22, and the microfilament 18 cools down to such an extent that it still has a temperature of about 60 ° C. at the bottom of the roll.

The microfilament 18 is thus stretched by the roll, the rotational speed of which is decisive for the take-off speed. A usual value of the take-off speed in FIG. 1 is 4000 to 6000 m / min.

1 shows a spinning device for production clarified by microfilament yarns from which a textile can be woven or knitted, FIG. 2 shows a spinning device for the production of spunbonded webs known per se. The take-off device is designed aerodynamically and is formed by an injector 24. The microfilaments are deposited on a laterally moving catch belt 36.

A practical embodiment of the method according to the invention results from the exemplary embodiment of the spinning device according to FIG. 3. Immediately at the outlet from a bicomponent nozzle 26 acting as a spinneret, the extruded microfilament 18 is embedded in a warm air flow indicated by the arrows A. This warm air flow A accompanies the microfilament essentially within the stretching area 38, which is the main stretching area with a length of approximately 30 to 50 cm. The total distance 1 between the bicomponent nozzle 26 and the roller 20 is approximately 1 m.

Below the stretching area 38, the microfilament 18 is blown transversely with cooling air 22 as in FIGS. 1 and 2. By supplying the warm air stream A, the temperature of which is the melt temperature of 280 ° C at the exit through the spinning hole 14 should not exceed or differ by ± 10 ° C., too rapid cooling of the microfilament 18 is prevented. Rather, the cooling of the microfilament 18 is delayed and carried out continuously in the invention.

The fact that the cooling does not occur suddenly, but continuously, counteracts the risk that an undercooled skin forms on the surface of the microfilament 18 and that filament breaks off as a result.

Furthermore, the invention ensures that, despite a reduction in the diameter of the microfilament 18, it is possible to work with the usual take-off speed of 4000-6000 m / min, so that the economy of a spinning system is not lost if smaller diameters of the microfilaments are desired.

A bicomponent nozzle 26, which is shown in more detail in FIG. 4 and which has a core nozzle 28 and a jacket nozzle 30 and also has an annular gap 32, can be used to generate the hot air flow A which is decisive in the invention. The annular gap 32 surrounds an annular shape the spinning hole 34 from which the melt emerges.

While in the known use of the bicomponent nozzle 26, melt is extruded both through the spinning hole 34 of the core nozzle 28 and through the annular gap 32 of the jacket nozzle 30, it is provided according to FIG. 4 that the melt exits exclusively via the inner core nozzle 28. By contrast, the hot air flow is supplied or generated through the annular gap 36 under pressure p and temperature T, which then surrounds the microfilament 18 in the form of a jacket.

Of course, using the bicomponent nozzle 26, the invention can also be used for the production of spunbonded fabric in a spinning device according to FIG. 2.

With the method according to the invention or the new spinning device, microfilament yarns with a super fine single titer of 0.33 dtex can be produced without sacrificing the economy of a spinning system, so that it is possible to produce textiles that are practically equivalent to natural silk.

Claims (13)

1. Method of making microfilaments of small diameter for synthetic yarns or for spun tissues, wherein the microfilaments from spinning nozzles supplied with a melt are pulled at high drawing speed and stretched through a spinning orifice (nozzle bore) after passing through a region across which cooling air is transversely blown, characterized in that the microfilaments, immediately after issuing from the spinning orifice, are subjected to a hot air stream in such a manner that the hot air stream surrounds the microfilament in the manner of a sheath immediately after it issues from the spinning orifice.
2. Method according to Claim 1, characterized in that the hot air stream is supplied under pressure and at an air temperature corresponding approximately to the temperature of the melt.
3. Method according to one of the preceding Claims 1 to 2, characterized in that the difference between the temperature of the melt and the air temperature of the hot air is up to about ± 10°C.
4. Method according to one of the preceding Claims 1 to 3, characterized in that the microfilaments are transversely blown with cooling air at a distance underneath the spinning nozzle for the purpose of cooling them.
5. Method according to Claim 4, characterized in that the distance is at least about 100 mm, preferably 500 mm.
6. Method according to one of the preceding Claims 1 to 5, characterized in that the drawn and stretched filaments are twisted or wound up to form a microfilament yarn.
7. Method according to one of the preceding claims 1 to 5, characterized in that the drawn and stretched microfilaments are deposited or layed down to form a spun tissue.
8. Method according to claim 7, characterized in that the microfilaments are pulled by an aerodynamic pulling device.
9. Spinning apparatus for the production of microfilaments of small diameter for synthetic yarns or spun tissues, wherein the microfilaments from a spinning nozzle supplied with a melt are pulled and stretched at a high drawing speed through a spinning orifice (nozzle bore) after passing through a region across which cooling air is transversely blown, characterized in that the spinning apparatus (10) contains a multiple spinning nozzle (26) having a plurality of spinning orifices (34), through which the melt issues, and that the multiple spinning nozzle is provided, concentrically to each spinning orifice (34), with an opening (32), through which a hot air stream (A) issues.
10. A Spinning apparatus according to Claim 9, characterizd in that the multiple spinning nozzle (26) is constructed in the manner of a two-part nozzle having a core nozzle (28) and a casing nozzle (30).
11. Spinning apparatus according to Claim 10, characterized in that the casing nozzle (30) possesses an annular gap (32), concentrically surrounding the core nozzle (28) provided for the discharge of the melt (16), through which gap the hot air (A) issues at a pressure (p).
12. Spinning apparatus according to one of the preceding Claims 9 to 11, characterized in that the spinning apparatus contains a roller (20) as mechanical pulling device for the microfilaments (18).
13. Spinning apparatus according to one of the preceding Claims 9 to 11, characterized in that the spinning apparatus contains an injector (24) as aerodynamic pulling device for the micro-filaments (18) and a receiving belt for forming a spun tissue.

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