EP1797226A1

EP1797226A1 - Meltblown method for melt spinning fine non-woven fibres and device for carrying out said method

Info

Publication number: EP1797226A1
Application number: EP04804007A
Authority: EP
Inventors: Mathias GRÖNER; Henning Rave
Original assignee: Oerlikon Textile GmbH and Co KG; Saurer GmbH and Co KG
Current assignee: Oerlikon Textile GmbH and Co KG
Priority date: 2004-09-30
Filing date: 2004-12-17
Publication date: 2007-06-20
Also published as: CN101065521A; US20070202769A1; WO2006037371A1

Abstract

The invention relates to a meltblown method for melt spinning fine non-woven fibres and to a device for carrying out said method. According to the invention, a polymer melt is extruded, in order to form several fibre strands, through several nozzle bores of a spinning nozzle and twisted on the outlet side of the nozzle bores by means of a cold blow flow. According to the invention, the blow flow is fed to the fibre strands in an acceleration path wherein the fibre stands and the blow flow are accelerated in such a manner that the fibre strands are twisted in order to form continuous fine fibres. According to the inventive device, the inventive acceleration path is formed between the upper edges and the lower edges of the two blow nozzle openings below the spinning nozzle.

Description

Meltblown process for melt spinning of fine nonwoven fibers and Vorrich¬ device for performing the method

The invention relates to a meltblown process for melt-spinning fine nonwoven fibers according to the preamble of claim 1 and to an apparatus for carrying out the process according to the preamble of claim 14.

In the production of ultrafine fiber webs, a plurality of fiber strands are extruded from a polymer melt through nozzle bores of a spinneret and then drawn into ultrafine fibers with a blowing stream. Such fibers have an average fiber diameter of usually <10 microns. In the prior art, such processes are characterized as meltblown processes. The blowing stream is preferably formed from a hot air which is blown onto the fiber strands with high energy. The blowing stream leads to warping and tearing of the fiber strands, resulting in fine nonwoven fibers of finite length.

Such a method is known from DE 33 41 590 A1, wherein a non-heated fluid is used as the blow stream. Such relatively cold Blasströ¬ me basically have the advantage that heating of the fluid can be omitted. Here, too, fine fibers could be produced from thermoplastic polymers which have finenesses of less than 10 μm.

Regardless of whether the known meltblown process is carried out with a hot blowing medium or, as known from DE 33 41 590 A1, with a cold blowing medium, the fiber strands are usually torn into finite fibers. In addition to the disadvantageous formation of fluff, such fibers, after being deposited in a nonwoven, lead to regularities in the physical properties due to bonded pieces of fiber. In particular, such nonwovens can endure only low tensile strengths due to the finite fiber pieces. From DE 199 29 709 Al a further process for the production of fine nonwoven fibers is known in which the fiber strands are split by a gas flow to fine fibers. The known method, which is referred to in the art as the so-called nanoval process, based on the fact that on the fiber strand under the effect of gas flow and a nozzle device, a pressure effect is generated, which leads to bursting of the fiber strand, so that a variety of finer in the essential endless fibers arises. In this case, the hydrostatic pressure prevailing in the interior of the fiber is greater than the gas pressure surrounding the fiber strands, whereby the bursting of the fiber strand is achieved. The fibers are then guided under the action of the gas flow to a tray and stored as a nonwoven.

In all known meltblown processes, there is a risk that individual fibers will stick together before the final solidification and lead to undesirable points of discontinuity in the nonwoven.

Accordingly, it is an object of the invention to provide a meltblown process for melt-spinning fine non-woven fibers of the type mentioned at the beginning, with which a high-quality ultrafine fiber can be produced at a relatively low energy input.

Another object of the invention is to provide nonwoven fibers for making a nonwoven fabric with which improved physical properties are achieved.

In addition, it is the object of the invention to further develop a meltblown process and a meltblown apparatus for melt spinning fine nonwoven fibers in such a way that the most uniform and continuous fiber formation of very fine fibers takes place in order to ensure a uniform deposit distribution of the fiber during the subsequent nonwoven production receive. The object is achieved by a method with the features of claim 1 and by a device having the features of claim 14. A nonwoven fiber produced by the process of the invention is given with the features of claim 24 and a nonwoven formed therefrom with the features of claim 25.

Advantageous developments of the invention are defined by the features and feature combinations of the respective subclaims.

The invention is based on the finding that in the conventional meltblown process, the blowing stream is accelerated when hitting the fiber strand to a maximum speed. The coincidence of the blast stream with the fiber strand thus leads to a more or less sudden stretching of the fiber strands. This leads to warping and, if necessary, after exceeding a maximum spinning delay for tearing the fiber. In order to avoid such overstressing of the fibers, according to the invention the blowing flow is supplied to the fiber strands within an acceleration section, and then the blowing flow and the fiber strands are accelerated together in such a way that the fiber strands are warped into endless ultrafine fibers. An overuse of the fiber strand during Ver¬ pulling can be advantageously avoided. The maximum speed of the blowing flow is only reached at the end of the acceleration section and leads to the desired total stretching of the fiber strands.

Due to the acceleration of the blowing flow and the fiber strands within the acceleration section, the blowing flow can be supplied to the fiber strands with relatively low energies. It has been shown that even an overpressure in the range below 1000 mbar was sufficient to set the desired spinning delay on the fiber strands. This allows the consumption of the Blasstro¬ mes set to a minimum. The blowing stream is preferably formed of an air, which has a natural Luft¬ temperature ranging from 15 ° C to 110 ⁰ C. This makes it possible to obtain a rapid edge zone fixation of the fibers, which in particular favors the stability of the fibers for stretching. In addition, an improved cooling of the

Fine fibers. It is essential that no heating of the air is provided. The term "natural air temperature" here refers to the temperature which the air assumes without cooling or heating due to ambient conditions.

Preferably, the blowing stream is formed from an ambient air having an ambient temperature, which is drawn in from the environment below the spinneret. With an average consumption of about 600 m ³ / h * m ambient air and a maximum overpressure of 1 bar in a spinning device which is customary in practice, the blowing flow can thus be provided at low cost.

By the process variant in which the fiber strands are extruded with a mass flow of the polymer melt through the Düseribohrung the spinneret from 1.0 g / min to 10 g / min per nozzle holes, all common types of polymers such as polypropylene or polyamide can be extruded. Preferably, a flow rate of> 3 g / min, adjusted per bore of the nozzle, wherein the bore diameter can be in the range of 0.2 to 1.0 mm.

It is particularly advantageous if the polymer melt is tempered just before exiting the nozzle bores within the spinneret, so that the freshly extruded fiber strand has a relatively high melting temperature, which may be, for example, in a polypropylene fiber above 35O ⁰ C. Depending on the polymer type, the polymer melt to a temperature preferably in the range from Be¬ 300 ⁰ C to 400 ° C temperature-controlled. In order to always maintain an optimum setting as a function of the type of polymer, the capillary diameter of the nozzle bores and the desired fiber fineness, the length of the acceleration path for accelerating the blast stream and the fiber strands is formed in the range from 2 mm to 30 mm.

The fiber strands can be guided directly from the nozzle bore into the acceleration section or, however, only after passing through a short extrusion zone of max. 2mm, in which the fiber strands can escape from the nozzle bore without Blasstromeinfluss.

In order to be able to generate the highest possible distortion forces on fiber strands, the fiber strands and the blown stream are passed, after passing through the acceleration section, into a free space in which there is an atmosphere that is substantially equal to an ambient pressure. During the expansion of the blowing flow into the free space, vortex zones are created which improve the attack of the blowing flow on the fiber surface. This can also occur so-called whip cracking effects, which causes a further distortion of the fiber.

To intensify such effects, additional air vortex zones can also be generated by air-guiding means within the free space. In this way special effects in the fibers, such as thick-thin areas, can be produced.

However, it is also possible within the free space to provide an additional airflow for cooling. This variant of the method can be used advantageously in particular in cases in which the blowing stream has relatively high air temperatures.

The process according to the invention is suitable for processing all customary types of polymer, for example polypropylene, polyethylene, polyester or polyamide. to process and to a fleece fiber with the finest fiber cross-sections up to 0.5 microns. In particular, good results could be achieved with a polypropylene material, the fiber finenesses of the endless microfibers ranging from 1 .mu.m to 30 .mu.m.

The ultrafine fiber produced by the process according to the invention is thus particularly suitable as an endless fiber in order to be laid down to form a nonwoven.

The device according to the invention for carrying out the method according to the invention provides that a acceleration section is formed between the upper edges and the lower edges of the two blowing nozzle openings arranged below the spinneret. Thus, no additional tools are required to obtain a Be¬ schleunigungsstrecke formed immediately below the nozzle holes. The device according to the invention is characterized in particular by the fact that a multiplicity of fiber strands can be warped uniformly to form superfine fibers at a relatively close distance from each other, without any adhesion of adjacent fibers occurring. The device according to the invention is thus suitable for producing high-quality fine fibers in large numbers with high uniformity.

In order to obtain a defined acceleration distance, the upper edge of the two Blasendüsenöffhungen are arranged according to an advantageous development of the inventive device to an inlet mouth and the lower edges of the two Blasdüsenöffhungen to an outlet orifice, wherein the outlet orifice has a free flow cross-section which is smaller than the flow cross-section the entrance mouth. Thus, after passing through the inlet mouth, the fibers can be accelerated continuously up to the outlet mouth by the blowing flow provided by the blow nozzle openings.

Depending on the fiber fineness and polymer type, the exit orifice is adjusted to a gap width in the range of 2 to 8 mm. The gap width is through the smallest distance between the opposite lower edges of the Blas- Düsenöffiiungen determined.

The inlet orifice, which has a larger gap width, can advantageously be formed directly at the level of the underside of the spinneret, so that the extruded fiber strands can enter directly into the acceleration section. However, it is also possible to form the inlet mouth with a small distance to the underside of the spinneret, so that the fiber strands only reach the acceleration section after passing through a short extrusion zone in the range of 0 to 2 mm.

The length of the acceleration section is determined by the distance of the inlet orifice to the outlet orifice, which, depending on the fiber type and fiber fineness, can be in the range from 2 mm to 20 mm.

For the air supply, a preferred embodiment of the device according to the invention in each case to each Blasöffhung an inflow, which is formed between the lower edge and the upper edge of the respective blowing nozzle. In this case, the lower edge and the upper edge are aligned or shaped relative to each other such that the inflow channel in the direction of the Blasöffhung at the end of the lower edge and the upper edge each have a tapered flow cross-section auf¬. Thus, a continuous acceleration of the supplied air can be achieved up to the entry into the acceleration section, so that a small power supply for generating the blowing flow is required.

The air provided is advantageously kept in the pressure chamber, which is connected to the Blasöffhungen.

In order to enable the most cost-effective provision of the air, the pressure chamber is connected to a suction device, through which a. According to a particularly advantageous embodiment of the invention Vor¬ direction an ambient air is sucked in and conveyed directly into the pressure chamber.

In order to permit intensive distortion of the fiber strands during the expansion of the blast flow on exiting the acceleration section, a free space is formed below the lower edges of the blast openings.

In this case, the free space may contain additional aids for guiding, for cooling and / or for drawing the fibers. This is a high flexibility of the device according to the invention, which allows the production of ultrafine fibers of any kind and application.

The nonwoven fiber of a polymer material produced by the process according to the invention is characterized in that, despite the finest fiber cross sections in the range from 0.5 μm to 30 μm, the fibers have an endless length. This makes it possible to provide an endless ultrafine fiber produced by a meltblown process for the production of nonwovens.

The nonwoven fabric according to the invention, which is formed by the nonwoven fiber according to the invention, is thus distinguished in particular by high uniformity both in the machine direction and in the transverse direction. Such nonwovens are therefore particularly suitable for barrier products in which on the one hand an air permeability is desired, but on the other hand represents a blocking effect for liquids. The nonwoven according to the invention is thus particularly suitable for hygiene products, medical products and filter applications.

The nonwoven according to the invention is distinguished, in particular, by a higher extensibility in comparison with conventional meltblown webs. In this way, the nonwoven according to the invention can advantageously be used in products in which smaller deformations occur during production or use. In particular, a nonwoven is suitable for these applications, in which the endless fine fibers a polypropylene to a basis weight in the range of 1.5 g / m ² to 50 g / m ^{2 are} laid and 2x1 an elongation at break of at least 60% lead or a maximum tensile load with an elongation of at least 40% can endure.

Due to the high strength and deformability of the nonwovens can thus also advantageously composite nonwovens produce having multiple nonwoven layers. In the composite nonwoven fabric according to the invention, at least one of the layers is formed from a nonwoven with the endless ultrafine fiber according to the invention.

Both the nonwoven according to the invention and the composite nonwoven are particularly suitable for hygiene products such as, for example, diapers or sanitary napkins, medical products such as, for example, wound dressings, filter products or household products such as, for example, wiping or dust flaps.

Bonding nonwoven webs in which at least one further layer is formed from a spunbond nonwoven are particularly preferred here.

The meltblown process according to the invention is explained in more detail with reference to some embodiments of the device according to the invention for carrying out the process, with reference to the enclosed figures.

They show:

1 shows schematically a view of an embodiment of the device according to the invention for carrying out the method according to the invention

2 schematically shows a detail view of the spinning nozzle underside of a further embodiment of the device according to the invention; FIG. 3 shows a schematic sectional view of a further embodiment of the device according to the invention; FIG. 4 schematically shows a longitudinal sectional view of a further embodiment of the device according to the invention 5 shows a diagram of the elongation as a function of the basis weight of a nonwoven according to the invention

6 shows a diagram of the tensile strength as a function of the surface weight of a nonwoven according to the invention

1 shows a first exemplary embodiment of the device according to the invention for carrying out the method according to the invention in a schematic view.

The exemplary embodiment has a spinneret 1, which is connected via a melt inlet 2 to a melt source (not shown here). The melt source used is usually an extruder which melts a thermoplastic material and supplies it as polymer melt to the spinneret under pressure. The spinneret 1 has on its underside a plurality of nozzle bores 5, which are connected within the spinneret 1 with the melt inlet 2. The nozzle bores 5 are formed on the underside of the spinneret 1 in a specific arrangement preferably in a row arrangement with one or more Rei¬ side by side. From each of the nozzle bores 5 can be extruded from the polymer melt in each case a fiber strand.

Below the spinneret 1, a blowing device 3 is provided, which has two opposite blowing nozzles 4.1 and 4.2 at a short distance below the spinneret 1. Each of the blowing nozzles 4.1 and 4.2 contains a Blasdüsenöffhung 7.1 and 7.2, which are each formed between an upper edge 9.1 or 9.2 and a lower edge 10.1 or 10.2. The upper edge 9.1 or 9.2 and the lower canals 10.1 and 10.2 are plate-shaped and extend with their free ends substantially parallel to the nozzle bores 5 of the spinneret 1. Here, the opposing upper edges 9.1 and 9.2 form an entry mouth and the lower edges lying opposite 10.1 and 10.2 an exit orifice for the fiber strands 6. Here, the inlet mouth and the outlet mouth is formed such that between the upper edges 9.1 and 9.2 and the lower edges 10.1 and 10.2 an acceleration section 15 is formed, in which an over the Blasdüsenöffiiung 7.1 and 7.2 emerging Blässtrom together with the fiber strands 6 are accelerated.

The upper edges 9.1 and 9.2 of the blowing nozzles 4.1 and 4.2 are generally arranged in such a way to the spinneret 1 that on the one hand no significant heat losses can occur at the spinneret 1 and on the other hand, no blowing air can escape outside of Be schleunigungsstrecke. The formation of the transition from the spinneret 1 to the upper edges 9.1 and 9.2, which is not shown in Figure 1, will be explained in more detail below.

The blowing nozzles 4.1 and 4.2 are each assigned a chamber space 8.1 and 8.2, in which a blowing medium held under an overpressure is stored. Air is preferably used as the blowing medium here. However, it is also possible to use a gas. The pressure chambers 8.1 and 8.2 can be connected together or separately with a pressure source, for example a compressed air network. Below the blowing device 3, a free space 12 is formed, which extends from the lower edges 10.1 and 10.2 of the nozzles 4.1 and 4.2 to a storage belt 13. The depositing belt 13 serves to deposit the delicately fine fibers 11 to form a nonwoven 14. For this purpose, the depositing belt 13 is connected to a drive in order to continuously remove the nonwoven 14 after the finest fibers 11 have been deposited. The direction of movement of the depositing belt 13 is here marked by arrows.

The exemplary embodiment of the device according to the invention shown in FIG. 1 is shown in an operating situation. During operation, the spinneret 1 is continuously supplied with a polymer melt, for example, from polypropylene. The spinneret 1 is designed to be heatable in order to keep the melt temperature of the polymer melt in a range above 300 ^° C., preferably in the range from 300 to 400 ^° C. The polymer melt is then extruded through the nozzle bores 5 to a respective fiber strand 6. After leaving the Fiber strands 6 from the nozzle bores 5 pass into the acceleration path 15 and are combined with a blowing stream. The fiber strands 6 and the blowing stream are continuously accelerated within the acceleration section 15 as far as an exit orifice. This results in an increasing stretching of the fiber strands 6, which leads, after expansion of the blow mill in the free space, to fine fibers having a fiber cross section in the range of 0.5 μm to 30 μm. The ultrafine fibers 11 are then deposited continuously on the storage belt 13 as nonwoven 14.

The blowing medium used for stripping and stretching the fiber strands 6 is a cold blowing medium, preferably a cold air. As a result, the fiber strands can be cooled to storage, so that no additional cooling of Fa¬ fibers is required. At air temperatures of, for example 25 ⁰ C can be re insbesonde¬ the free space 12 between the blower 3 and 13 ex- tremely hold the deposit belt small, so that the blast flow advantageously storing the Feinstfa¬ fibers into a nonwoven improved. In addition, the stability of the Faserfuhrung increased by the fact that a rapid edge zone cooling occurs at the fiber strands 6 already at the meeting of the cold blast air with the Irish extruded fiber strands. However, the stretchability is maintained essentially by the molten core regions of the fiber strands 6.

In order to obtain the highest possible stretching forces through the blowing flow, the blowing nozzles 4.1 and 4.2 are preferably shaped such that the blowing flow flows out of the blowing nozzle openings already in the running direction of the fibers. For this purpose, a further exemplary embodiment of a device according to the invention is shown in a sectional view in FIG. The sectional view here shows only a part of the spinneret bottom with the underlying Blasdüsenöffhungen the tuyeres.

The section in FIG. 2 represents the exit situation of a fiber strand 6 on the spinneret 1 in a cross section. The spinneret 1 has a nozzle for this purpose. senbohrung 5 on. In the spinneret 1 a plurality of heating elements 19 are provided to heat the stirred polymer melt within the spinneret 1.

Below the spinning device 1, the blast nozzles 4.1 and 4.2 are arranged with the Blasdü- senöffhungen 7.1 and 7.2. The Blasdüsenöfmung 7.1 is zwi¬ tween the upper edge 9.1 and the lower edge 10.1 formed. The upper edge 9.1 and the lower edge 10.1 are formed as mold plates which form an inflow channel 18.1 between them. The inflow channel 18.1 has a flow cross-section tapering in the direction of the blow nozzle opening 7.1, so that a blow air supplied within the inflow channel 18.1 is accelerated continuously up to the blow nozzle opening 7.1. In this case, the shaping of the inlet channel 18.1 through the upper edge 9.1 and the lower edge 10.1 is designed in such a way that the blowing stream emerging from the blowing nozzle opening 7.1 is guided in the direction of fiber travel. It has been found to be particularly advantageous if the upper edge 9.1 in relation to the lower edge 10.1 has such a Formkrüm¬ determination, the theoretical incident beyond the free end imaginary extension in the middle of a formed by the opposite lower edges 10.1 and 10.2 exit port 17. In this case, the continuous reduction in the distance between the upper edge 9.1 and the lower edge 10.1 continues up to the middle of the outlet orifice 17. As a result of this design of the blowing nozzle 4. 1, the accelerating effect for pulling off the fiber strand can still be improved.

The Blasdüsenöfmung 7.2 of the nozzle 4.2 on the opposite side of the spinneret 1 is mirror-inverted identical to the first Blasdüsenöfmung 7.1 of the nozzle 4.1, wherein the inflow 18.2 formed between the shaped plates of the upper edge 9.2 and the lower edge 10.2 with a tapered flow cross-section. For further description, reference may therefore be made to the above. The upper edges 9.1 and 9.2 are below the underside of the spinneret 1 with a distance opposite and form an inlet mouth 16. The Spalt¬ width of the inlet orifice 16 is gekenn¬ in Fig. 2 with the capital letter E and characterized by the distance between the two upper edges 9.1 and 9.2 determined to each other. The gap width E is substantially constant over the entire spinning width of the spinneret 1.

Below the upper edges 9.1 and 9.2, the lower edges 10.1 and 10.2 are arranged opposite to the exit opening 17. The gap width of the outlet orifice 17 is identified in FIG. 2 by the capital letter A and is determined by the narrowest distance between the two lower edges 10. 1 and 10. 2 relative to one another. The gap width A of the outlet orifice 17 is also essentially constant over the entire spinning width of the spinneret 1. The gap width A of the outlet orifice 17 is smaller than the gap width E of the inlet orifice 16. Between the inlet orifice 16 and the outlet orifice 16 an acceleration section 15 is formed. In particular, through the inflow channels 18.1 and 18.2 of the tuyeres 4.1 and 4.2 opening directly into the acceleration section 15, the fiber strand 6 is fed together with the blowing air from the inlet mouth 16 at increasing speed along the acceleration path 15 to the outlet mouth 17 and into the below the exit port 17 formed free space 12 is blown. The distance between the inlet orifice 16 and the outlet orifice 17, which directly determines the outlet cross section of the blowing nozzle openings 7.1 and 7.2 and indicates the length of the acceleration zone 15, can be in the range from 2 mm to 30 mm, depending on the polymer type and fiber fineness. The gap widths of the Austritts¬ mouth 17 vary between 2 mm to 8 mm. Even with capillary diameters of 0.6 mm of the nozzle bores 5, it was possible with the device according to the invention to produce finest fibers in the range of 1 to 30 μ fiber fineness. On the side of the blowing nozzles 4.1 and 4.2 facing the spinneret 1, between the spinneret 1 and the upper edges 9.1 and 9.2, a sealing means 23.1 and 23.2 are respectively arranged. On the one hand, the sealing means 23.1 and 23.2 form, for the spinneret 1, an insulating layer for entrainment of heat losses and, on the other hand, a seal against the blast air stirred in the acceleration section 15. The sealing means 23.1 and 23.2 are preferably formed from Isoliermateria¬ lien.

In the exemplary embodiment of the device according to the invention shown in FIG. 2, a gap is formed between the underside of the spinneret 1 and the acceleration section 15, which causes the fiber strands 6 to enter the acceleration section only after passing through a short extrusion zone. Such a return leads to an additional running stability of the fiber strands.

However, it is also possible to let the extruded fiber strands 6 run into the acceleration section 15 immediately after the nozzle bores 5 have been displaced. Such an embodiment of the device according to the invention is shown schematically in Fig. 3 in a sectional view. The design of the spinning nozzle 1 and of the blowing nozzles 4.1 and 4.2 is essentially identical to the preceding exemplary embodiment according to FIG. 2, so that reference is made to the preceding description and only the differences are explained.

The inlet mouth 16 between the upper edges 9.1 and 9.2 is formed directly on he level of the underside of the spinneret 1. This ensures that the fiber strands 6, after leaving the nozzle bore 5, enter the acceleration path 15 directly and come into contact with the blowing flow and thus obtain a different withdrawal behavior from the spinneret 1. On the side of the blowing nozzles 4.1 and 4.2 facing the spinneret 1, an air gap 24.1 and 24.2 are respectively formed between the spinneret 1 and the top edges 9.1 and 9.2. The air gaps 24.1 and 24.2 are dimensioned so narrow that essentially no blowing air can pass through, but a sufficient air layer for insulation with respect to the spinneret 1 remains.

In order to improve and increase the stretching of the ultra-fine fibers 11, in the embodiment shown in FIG. 3, a plurality of guide means 20 are arranged in the free space 12, which lead to the formation of a multiplicity of vortex zones and thus cause an intensification of the stretching. However, it is therefore also possible to produce ultrafine fibers with special effects, such as thin spots, for example.

4, a further embodiment of the device according to the invention is shown schematically in a longitudinal sectional view. The exemplary embodiment according to FIG. 4 is essentially identical to the exemplary embodiment according to FIG. 1, so that only the differences are explained below and otherwise reference is made to the preceding description.

In the exemplary embodiment illustrated in FIG. 4, the blowing device 3 has a suction device 21 below the spinneret 1. The suction device 21 is connected to the pressure chambers 8.1 and 8.2. By means of the suction device 21, ambient air is drawn in below the spinneret 1 and fed to the pressure chambers 8.1 and 8.2. Thus, the blower stream can advantageously be formed from an ambient air to distort it. The ambient air in this case has a room temperature, which may be between 15 ° C and 40 ° C, depending on the environment. This provides a particularly cost-effective provision and generation of the blowing stream.

In the exemplary embodiment shown in FIG. 4, a further improvement of the fiber guide below the blowing nozzles 4.1 and 4.2 in the free space 12 is a Injector 22 arranged. In this case, when the fiber strands pass through the injector device 22, the ambient air present in the free space 12 from the environment is included without any external power for guiding and cooling the fibers. However, it is also possible to suck in the free space 12 a climatic air. Thus, the climatic air can be predetermined as conditioned air with regard to air temperature, air humidity and air quantity, so that specific cooling conditions on the fibers can be set. However, such devices are preferably used in cases where the blowing stream has to be formed from a relatively warm air.

The process according to the invention and the device according to the invention for carrying out the process according to the invention are in principle suitable for use of polymer melts of all conventional polymers, for example polyester, polyamide, polypropylene or polyethylene.

In a process example, a polymer of a polypropylene was melted into a melt and extruded per nozzle bore by means of a nozzle bore with a capillary diameter of 0.6 mm and a melt throughput of 6 g / min. The number of nozzle bores was 36. The pressure chambers 8.1 and 8.2 were supplied with air at room temperature and an overpressure of 260 mbar. In this case, the arrangement of the device shown in FIG. 2 was used to make the extruded fiber strands into ultrafine fibers. The PP fine fiber was deposited after extrusion and drawing into a nonwoven fabric having a basis weight of 50 g / m ² . In the analysis of a non-woven sample, fiber finenesses of the ultra-fine fiber in the range from 2.5 to 25.1 μm could be determined. The average fiber cross section of the finest fibers was 5.2 μm. The subsequent determination of the elongation at break of a nonwoven sample of 40 mm length gave a value of 63% in the machine direction and 70% in the transverse direction. Maximum tensile strengths of 29 N in the machine direction and 17 N in the transverse direction were determined. Compared to conventional As a result, it was possible to ascertain an improvement in the physical properties of about 300% of meltblown webs with finite fiber pieces.

In a series of experiments, the polypropylene fibers were laid down to nonwovens with different basis weights and then measured. The resulting results are shown in the diagrams in FIGS. 5 and 6. The diagram shown in FIG. 5 shows the relationship between the surface weight of the nonwoven and the elongation at break achieved. The capital letters MD and CD indicate the orientation of the nonwoven, MD (machine direction) being referred to as the machine direction and CD (gross direction) as the transverse direction in the nonwoven. In this case, as the basis weight decreases, an increasing elongation at break is found, which in particular suggests the high strength of the endless ultrafine fibers. Compared with conventional meltblown nonwoven materials, it has been possible to detect an increase in elongation at break of up to 300%.

FIG. 6 shows in a diagram the tensile strength of the nonwoven as a function of the basis weight. Here, too, a clear increase compared to conventional meltblown webs was found. The maximum tensile strength for nonwovens with basis weights was around 10 g / m ² above 5 N and for nonwovens with basis weights around 50 g / m ² above 25 N, irrespective of the tensile direction. Thus, such nonwovens are particularly suitable for applications in which deformations such. B. in Hy¬ gienematerialien or in which deformations occur in the production. In the case of the nonwoven according to the invention, the ultra-fine fiber characteristic on the one hand leads to an air or vapor permeability coupled with a low penetration tendency. Thus, the nonwoven materials can be preferably used as barrier products such as in the field of hygiene for Win¬ deln and sanitary napkins. Applications in medical technology such as wound dressings are also possible. Particularly advantageously, the nonwovens formed from such fibers can be included in composite materials. The absorbency and barrier effect of such nonwovens can thus be used advantageously in a composite nonwoven to form a barrier layer.

The significantly higher strains and tensile strengths of the meltblown process according to the invention also lead to improved processing. Also, applications with small deformation, such as in hygiene products are possible without problems.

LIST OF REFERENCE NUMBERS

1 spinneret

2 melt feed

3 blowing device

4.1, 4.2 Blow nozzle

5 nozzle bore

6 fiber strand

7.1, 7.2 Blast nozzle problem

8.1, 8.2 pressure chamber

9.1, 9.2 top edge

10.1, 10.2 lower edge

11 fine fiber

12 free space

13 storage belt

14 fleece

15 acceleration distance

16 entrance mouth

17 exit mouth

18.1, 18.2 inflow channel

19 heating element

20 conducting agents

21 suction device

22 ejector device

23.1, 23.2 Sealant

24.1, 24.2 airs;

Claims

claims

1. meltblown process for melt spinning of fine nonwoven fibers, in which a polymer melt is extruded through several nozzle holes of a spinneret to a plurality of fiber strands, in which acts on the fiber strands immediately after exiting the nozzle bores a cold blowing, which under the effect of an overpressure by at least one Blasdüsenöffhung flows on the fiber strands and this warps, characterized in that the blowing stream is fed within an acceleration section of the fiber strands, in which the fiber strands and the blowing stream are accelerated be¬ so that the fiber strands verzo¬ gene to endless fine fibers.

2. The method according to claim 1, characterized in that the overpressure of the blowing stream is set to a value of less than or equal to 1000 mbar.

3. The method according to claim 1 or 2, characterized in that the blowing stream is formed from an air having a natural Lufttem¬ temperature in the range of 15 ⁰ C to 120 ⁰ C.

4. The method according to claim 3, characterized in that the blowing stream is formed from an ambient air having an ambient temperature, which is sucked from the environment below the spinneret becomes.

5. The method according to any one of claims 1 to 4, characterized in that the fiber strands with a mass flow of the polymer melt through the

Nozzle holes of the spinneret of _. 1.0 g / min to 10 g / min per Düsen¬ bore, preferably> 3 g / min per nozzle bore extruded.

6. The method according to any one of claims 1 to 5, characterized in that the polymer melt before exiting the nozzle bore within the spinneret to a temperature in the range of 300 ° C to 400 ⁰ C tempe¬ ration.

7. The method according to any one of claims 1 to 6, characterized in that the acceleration section for accelerating the blowing flow and the fiber strands in the range of 2 mm to 30 mm long.

8. The method according to claim 7, characterized in that the acceleration section is followed immediately without clearance or with ei¬ nem small distance in the range of a maximum of 2 mm to the Mündun¬ conditions of the nozzle bores.

9. The method according to any one of claims 1 to 8, characterized in that the fiber strands and the blown stream after passing through the acceleration nigungsstrecke be performed in a free space and that the free space has a pressure which is substantially equal to the ambient pressure.

10. The method according to claim 9, characterized in that in the free space additional air vortex zones acting on the fibers are generated by at least one air guiding means.

11. The method according to any one of the preceding claims, characterized in that the fibers are cooled and guided by an additionally supplied below the acceleration section air flow.

12. The method according to any one of claims 1 to 10, characterized in that the Faserfeiriheit the endless ultrafine fibers in the range of 0.5 .mu.m to 30 .mu.m.

13. The method according to any one of claims 1 to 12, characterized in that the finest fibers are deposited to form a nonwoven.

14. An apparatus for carrying out the meltblown process according to one of claims 1 to 13, having a spinneret (1) which has a plurality of nozzle bores (5) in a serrated arrangement on an underside, and having a blowing device (3). , which has two opposite Blasdüsenöffhungen (7.1, 7.2), wherein each of the Blasdüsenöffiiung (7.1,7.2) between an upper edge (9.1, 9.2) and a lower edge (10.1, 10.2) is formed, which extend substantially parallel to the nozzle bores (5), characterized in that between the upper edges (9.1, 9.2) and the lower edges (10.1, 10.2) of the two Blasdüsenöffiiungen (7.1, 7.2) below the spinneret (1) an acceleration section (15) is formed, in which the fiber strands (6) and the blowing stream are accelerated such that the fiber strands (6). to endless fine fibers (11) are warped.

15. The apparatus according to claim 14, characterized in that between the lower edges (10.1, 10.2) of the two Blasdüsenöffiiungen (7.1, 7.2) an outlet mouth (17) and between the upper edges (9.1, 9.2) of the two Blasdüsenöffiiungen (7.1, 7.2) a Inlet mouth (16) are formed, wherein the outlet mouth (17) has a free Strömungs¬ cross-section which is smaller than the flow cross-section of the Ein¬ estuary (16).

16. The apparatus according to claim 15, characterized in that the outlet mouth (17) has a gap width (A) in the range of 2mm to 8mm.

17. The apparatus of claim 15 or 16, characterized in that the inlet mouth (16) is formed at the level of the underside of the spinneret (1) or with a small distance to the bottom of the spinneret.

18. Device according to one of claims 15 to 17, characterized in that the inlet mouth (16) and the Austrittsmüήdung (17) limit a length of the acceleration section (15), which is in the range of 2mm to 30mm.

19. Device according to one of claims 14 to 18, characterized in that one of the Blasöfmungen (7.1) associated lower edge (10.1) and upper edge (9.1) between them form an inlet channel (18.1) for air supply, and that the inflow channel (18.1) in the direction of Blasöffiiung (7.1) has a tapered flow cross-section.

20. Device according to one of claims 14 to 19, characterized in that the Blasöfmungen (7.1, 7.2) with at least one pressure chamber (8.1, 8.2) are connected, in which an air is maintained under an overpressure.

21. The apparatus according to claim 20, characterized in that the pressure chamber (8.1) is connected to a suction device (22) through which an ambient air sucked and in the pressure chamber (8.1) is required.

22. Device according to one of claims 14 to 21, characterized in that below the lower edges (10.1, 10.2) of the blowing nozzles (4.1, 4.2) a Frei¬ space (12) is formed.

23. The apparatus according to claim 22, characterized in that in the free space (12) additional aids (20, 22) are provided for guiding, for cooling and / or stretching of the fibers.

24. Nonwoven fiber of a polymer material, characterized in that the ultrafine fibers are made by a meltblown process according to any one of Ansprü¬ che 1 to 13 and have an endless length, the fiber fineness of the endless ultrafine fiber in the range of 0.5μm to

30μm lies.

25. A nonwoven formed from a nonwoven fiber, characterized in that the fibers are produced by a meltblown process according to any one of claims 1 to 13 and have an endless length, wherein the fiber fineness of the endless ultrafine fiber in the range of 0.5 .mu.m to 30 .mu.m lies.

26. Nonwoven according to claim 25, characterized in that the endless ultrafine fibers are laid to a basis weight in the range of 1.5 g / m ² to 50 g / m ² and lead to an elongation at break of at least 60%.

27 composite non-woven consisting of several nonwoven layers, characterized in that at least one of the layers of a non-woven with endless ultrafine fibers is formed according to claim 24.

28. The composite nonwoven according to claim 27, characterized in that the nonwoven of the layer has a basis weight in the range of 1.5 g / m ² to 50 g / m ² and an elongation at break of at least 60%.

29. The composite nonwoven according to claim 27 or 28, characterized in that at least one further layer is formed from a spunbonded nonwoven.