Patent Application
20070090555
The present invention relates to a method and an apparatus for producing spunbonded fabrics of a thermoplastic material, wherein the filaments of the spunbonded fabric result from burst fibers, and undergo an additional treatment after leaving a Laval nozzle.
WO 0100909 A1 and WO 02/052070 A2 disclose methods and apparatus for producing substantially endless fine filaments from meltable polymers or polymer solutions, wherein polymer melts or polymer solutions are spun from at least one spinneret hole, and wherein the spun filament is drawn by gas flows that are accelerated to a high velocity by means of a Laval nozzle. With a given geometry of the melt bore and its position relative to the Laval nozzle, the temperature of the polymer melt, its throughput per spinneret hole, and the pressures that determine the velocity of the gas flows, are controlled upstream and downstream of the Laval nozzle in such a manner that before its solidification, the yarn reaches in its interior a hydrostatic pressure, which is greater than the gas pressure that surrounds it, such that the filament bursts and separates into a plurality of fine filaments. In this process, the gas flows that draw the filament have an ambient temperature or a temperature that is caused by their feed. The filament exiting from the Laval nozzle is heated in the region of the Laval nozzle.
Furthermore, WO 02/099176 A1 discloses a process for producing a bonded nonwoven from at least partly microfine endless filaments of meltable polymers, wherein a polymer melt of only one certain polymer is spun from a plurality of spinneret holes, and the spun filaments are drawn by substantially cold gas flows that are accelerated by an acceleration nozzle, for example, a Laval nozzle, and wherein as a result of further production conditions, each filament reaches, before solidifying, a hydrostatic inside pressure, which is greater than the surrounding gas pressure, such that each filament bursts in the longitudinal direction, and separates into a plurality of fine endless filaments. The microfibers are continuously laid to a nonwoven (web) of a desired width, and the web is continuously subjected to hydrodynamic water jets for entangling the microfibers, so as to bond the nonwoven of the longitudinally separated endless fibers. Furthermore, the entanglement and bonding occur, if need be, with other fibers, which have previously been laid below the microfibers, or are subsequently laid on top of the microfibers.
WO 92/10599 discloses a method and an apparatus for producing finest fibers from thermoplastic polymers by the meltblowing method, wherein a polymer melt flows through at least one outlet hole in a meltblowndie, and wherein directly after its emergence, the polymer melt is surrounded on both sides of the outlet hole by a gas flow, and burst and separated into fibers in such a manner that the gas is accelerated to ultrasonic speed in a Laval nozzle, which extends in mirror-symmetric relationship with the outlet hole, that downstream of the Laval nozzle, it is decelerated in flow channels with a constant cross section or a cross section narrowing in the flow direction, to a flow velocity just below the ultrasonic speed, and that the polymer melt is supplied into the gas flow that emerges from the flow channels.
Further known are apparatus and methods for flash spinning plexifilamentary strands of film fibrils that consist of fiber forming polymers.
EP 0 482 882 B1 discloses such a strand as a three-dimensional, integral network of a plurality of thin, tapelike film fibril elements having a statistic length and an average thickness of less than about 4 ìm, which are in general oriented in a far extending relationship along the longitudinal axis of the strand. The film fibril elements temporarily combine and separate at irregular intervals in different locations along the length, width, and thickness of the strand, while forming the three-dimensional network.
EP 0 431 801, for example, discloses a method, wherein strands of film fibrils of an ethylene vinyl alcohol copolymer, if need be, with polyolefin components develop by forming a spin mixture of water, carbon dioxide, and the copolymer at a temperature of at least 130° C. and under a pressure, which is greater than the autogenous pressure of the mixture, and by subsequently flash spinning the mixture at substantially lower temperatures and pressures.
Preferred uses for spunbonded fabrics of this type in the area of disposable products, in particular protective garments are disclosed in EP 0 669 994 B1. These nonwovens are produced on an industrial scale by E.I. du Pont de Nemours and Co., and marketed as a spunbonded olefin nonwoven under the trade name “Tyvek.”
The nonwovens that are produced in the art, exhibit in part undesired thick places in filament sections, which result not only from spin discontinuities that enter the deposited filaments, in an undrawn state, as polymer melt drops, namely so-called “spots,” but also in particular from relaxations of the filaments in the case of inadequate drawing and lacking tempering. Disadvantageous in this connection is in particular that the water column of such nonwovens is reduced by 20% to 80%, when compared with, for example, conventional meltblown nonwovens with a comparable basis weight. Likewise, the achievable textile-mechanical properties, such as strength and elongation are reduced by 10% to 50%, when compared with a conventional spunbonded fabric with a comparable basic weight. Essential characteristics of use, such as softness and hand, are deteriorated to the same extent. A further disadvantage lies in that the production of nonwovens, which contain both discontinuous and continuous filaments, requires additional steps, such as, for example, a separate supply and feed of discontinuous filaments or fibers. At this point, the invention sets in.
It is an object of the invention to improve a process for producing spunbonded fabrics of a thermoplastic material with filaments of burst fibers.
This object is accomplished by a method with the steps of claim 1, with an apparatus comprising the elements of claim 13, with filaments having the characteristics of claim 25, and with a nonwoven fabric having the characteristics of claim 29.
Advantageous further developments and improvements are defined in the respective dependent claims.
The present invention provides a method and an apparatus for producing a spunbonded fabric of a thermoplastic material, wherein the filaments of the spunbonded fabric originate from burst fibers. As to the production of the filaments, the entire contents of WO 01/00909 are herewith incorporated by reference.
However, it is also possible to use different methods and different apparatus, which utilize a thermoplastic material by way of forming fibers to filaments with the use of a pressure that prevails in the interior of the fibers. In particular, it is possible to use in this process a Laval nozzle. However, it is possible to use any other nozzle geometry, for example, a slot die or the like, as long as it remains ensured that from the fibers, filaments are formed by advancing the thermoplastic material through the nozzle.
Because of the action of the interior pressure in the fibers, the latter burst at least in part into a plurality of filaments. The filaments are tempered, in particular additionally tempered, and/or drawn, in particularly additionally drawn. Preferably, the filaments have different diameters and different lengths.
A further development provides that pressure is regulated via the nozzle such that the fibers burst in such a manner that they form at least 80%, preferably at least more than 90%, preferably at least approximately all filaments, in particular that 100% filaments are formed from the fibers.
Another development provides that only a certain percentage of the fibers burst and separate to result in filaments. Thus, the fibers form anchoring points for the individual filaments, so that the filaments are not loose, but still have cohesion at least in part among themselves. This is especially preferred, when the filaments are to be used for enabling an engagement of, for example, hooklike means, as may find a use, for example, in Velcro-type closures.
The method and the apparatus for producing the spunbonded fabric differ from methods and apparatus of the art, in that the filaments are additionally tempered, and/or additionally drawn, and that the filaments have different diameters.
Furthermore, the filaments may also have different lengths. Possibly because of the formation of fibers, the filaments are already surrounded by a gaseous fluid. Therefore, an additional tempering or an additional drawing means that when, for example, this gaseous fluid also continues to exert on the filaments a temperature effect or a drawing action, the filaments will then undergo in addition a tempering and/or a drawing downstream of the nozzle. The tempering or drawing that is imparted downstream of the nozzle has the advantage that it permits in this process exerting directly on the filaments a purposeful action in the absence of an influence by preceding process steps, in particular the formation of the fibers. With that, it becomes possible to perform a tempering or a drawing operation that is adapted to the filaments, while avoiding disturbing influences.
The method and the apparatus permit producing both continuous filaments (endless fibers) and discontinuous filaments (short fibers). According to a further development, the spunbonded fabrics comprise different properties of different spunbonding processes, which are realizable in combination with one another in one production process. With that, essential disadvantages of known nonwovens are eliminated. On the one hand, the nonwoven has, for example, dimensions, which are otherwise known only from meltblown nonwovens. On the other hand, the plurality of fine filaments is produced in particular by a different mechanism, which in turn brings along freedoms with respect to the usable materials. Preferably, by bursting, filaments are produced, which have a diameter of less than 10 μm, preferably less than 1 μm.
A tempering and/or drawing of the filaments after the thermoplastic material leaves the nozzle, and before the filaments impact upon a web laying surface, make it possible to use the space between the nozzle and the web laying surface. Preferably, the tempering and/or the drawing steps can be differently adjustable along this path. It is likewise possible to provide one or more tempering steps or drawing steps along this path. A tempering may occur by way of radiation, convection, or via other active mechanisms. A drawing is possible in particular by frictional force acting upon the filament surface, as can be imparted, for example, by a moved medium that surrounds the filaments. Furthermore, there exists the possibility that a tension is active in the filaments themselves, for example, by a mechanical withdrawal from the nozzle.
When using a medium for drawing and/or tempering, in particular a gaseous medium, same may be both heated and cooled. In particular, the draw unit comprises conditioning facilities for this medium. Conditioning may, for example, relate to a moisture content of the medium, a composition of the medium, in particular a composition of one or more phases, different substances, as well as an addition of solid, liquid, and gaseous media. For example, the gaseous medium is supplied to the filaments at a velocity, which is approximately equal to, preferably higher than the speed of the filaments advancing from the nozzle. According to one embodiment, the medium has a velocity higher than 400 m/min, in particular a velocity higher than 300 m/min, preferably higher than 800 m/min.
An accurate adjustment of the apparatus makes it possible to suppress undesired thick places in filament segments to at least more than 95%, in particular more than 98%, in particular approximately 100%. On the one hand, the apparatus permits avoiding the classic “spots.” On the other hand, a suitable adjustment of the drawing or the tempering step makes it possible to cause the filaments to burst and separate totally and to prevent an undesired relaxation of the filaments.
According to one embodiment, it accomplished that a nonwoven that is totally produced from the thus-obtained filaments, has a water column, which is clearly above conventional water column values with a comparable basis weight and identical bonding of other nonwovens. In particular, it is accomplished that such a nonwoven has at least a 20% higher water column than a comparable nonwoven of this type on the basis of a meltblown or a spunbonded nonwoven. Furthermore, it is accomplished that a nonwoven of these filaments has an elongation, which is at least 10%, preferably at least 20%, in particular more than 35% higher than that of a comparable spunbonded nonwoven with the same basis weight and the same bonding. Moreover, in comparison with such a spunbonded fabric, the nonwoven of the filaments produced in accordance with the invention has the advantage of a softer surface.
In particular, a nonwoven that comprises filaments of the present invention, in particular consists of these filaments, is suitable for a preferred application as surface. Such a surface may come into contact with sensitive surfaces. These surfaces can be, for example, the skin of humans or animals, as well as polished surfaces or other scratch- and pressure-sensitive surfaces.
In the production of the fibers, the thermoplastic material according to one embodiment is heated to a temperature ranging from 150° C. to 350° C., preferably from 280° C. to 330° C. According to another embodiment, the thermoplastic material is heated to a temperature from more than 205° C. to about at least 280° C. According to a further embodiment, a temperature range from 250° C. to 320° C. is preferred. The temperature range for heating the thermoplastic material is influenced, for example, by the selection thereof. It is possible to spin a single polymer material. Furthermore, there exists the possibility that one or more polymers form the thermoplastic material. It is likewise possible that additives are present, which may be both meltable and solid. In particular, it is possible to use homopolymers, copolymers, as well as block polymers. The thermoplastic material may be both atactic and syndiotactic. In the production, it is possible to use polyolefins, such as polypropylene, polyisoprene, polystyrene, or polyethylene. Likewise, there exists the possibility of using polyester and polyamides, alone or in combination with other polymers or additives. In particular, it is possible to add additives, stabilizers, as well as pigments. There exists the possibility of using master batches.
According to a further development, the fibers formed in the spinneret are immediately surrounded after leaving the spinneret by the flow of a medium, in particular an oxygen-containing medium. The medium for tempering the fibers has, for example, a temperature above the melting point of the thermoplastic material, in particular the polymer or polymers in use.
By the method of the invention, the filaments of burst fibers are accelerated after leaving, for example, the Laval nozzle and before impacting upon a web laying surface, and/or additionally tempered, and/or drawn in desired locations. The acceleration and/or additional tempering and/or drawing may occur, for example, by compressed air upstream of the web laying surface in a channel, which preferably is a nozzle.
Besides the use of compressed air, which may in particular be conditioned, it is also possible to make use of multiphase mixtures. For example, a gas may be mixed with a liquid, a vapor, in particular water vapor, may be added to a gas, and the use of an aerosol may also be made possible. Preferably, this additional medium is supplied directly into an inlet opening of the channel for the filaments. A further embodiment provides for supplying the medium inside the channel. A yet further embodiment provides for distributing the supply of the medium. For example, a first volume is supplied upstream of an opening of the channel, while at least a second volume is supplied inside the channel. Both volumes may be differently conditioned.
Preferably, the opening of the channel is arranged in spaced relationship with the nozzle outlet, which enables an inflow of ambient air. In particular, a channel opening is arranged at a distance of preferably no more than 30 cm downstream of a nozzle opening. A further development provides that the channel opening is arranged, preferably no more than 15 cm, in particular less than 10 cm removed from the nozzle outlet. Likewise, it is possible to vary the spacing.
A further development provides for using a channel-shaped unit. The channel-shaped unit may be a closed channel in the form of a shaft. Preferably, the shaft is made nozzle-shaped. It may comprise an injector region and/or also a diffuser region. According to a further development, the channel-shaped unit may also be constructed to be at least similar to a spin beam. For example, the channel-shaped unit may have a geometry, as is known in meltblowing processes. A further embodiment provides that a geometry is present, as is used, for example, in spunbonding processes. Furthermore, the channel-shaped unit may be constructed at least approximately like a Lurgi-Docan draw unit. A further development provides that the channel-shaped unit enables an electrostatic charging, so that the filaments can be separated from one another on the one hand, and undergo themselves a lasting electrostatic charging on the other hand. This will be advantageous, for example, in industrial applications, such as for filter materials and the like.
A further development of the process provides that by generating a vacuum in a region directly below the web laying surface, the filaments are accelerated in a channel, and additionally tempered and/or drawn. According to the invention, it is possible to use as media for accelerating and additionally tempering and/or drawing the filaments not only air, but also air-liquid mixtures, or liquids. Preferably, these media possess specific heat capacities, which are greater than or equal to air under atmospheric pressure. Use is made, for example, of water vapor or aerosols.
According to a further embodiment, an additional mechanical drawing of the filaments is generated by providing, for example, pairs of temperable rolls, which have smooth and/or structured surfaces.
For the mechanical drawing of the filaments, one or also several pairs of rolls may be arranged one following the other. Preferably, one pair of rolls is arranged downstream of the nozzle, so that the filaments leaving the nozzle advance between the rolls, and can then be drawn in a mechanical way. A further development provides that both a system of paired rolls and individual rolls are used for enabling a mechanical drawing downstream of the exit from the nozzle, before a compacting, and in particular a thermobonding step. Preferably, at least one of the rolls is heatable to a temperature, which ranges from 30° C. to 180° C. A further development provides that at least one of the rolls can be cooled. It is also possible that successively arranged rolls are cooled on the one hand and heated on the other hand. In particular, the use of a pair of rolls presents the possibility that portions of the rolls engage and, in so doing, draw the filaments. There also exists the possibility that the filaments are crimped.
An additional tempering, for example, by a gaseous medium, which surrounds the filaments, may assist a mechanical drawing. There also exists the possibility that the filaments reach the desired temperature or are maintained at this temperature by a different application of energy. For example, this may occur by means of heat radiation, as well as with the use of suitable wavelengths for applying energy to the filaments.
For carrying out the method of producing a spunbonded fabric from filaments, at least one device for additionally tempering and/or drawing the filaments is provided in any spaced relationship downstream of the Laval nozzle. In this case, both open and closed systems or combinations of both are used, which may surround the filaments both in symmetric and asymmetric relationship.
An open system means in particular a system of the type, which allows ambient air to enter. A closed system, however, avoids the entry of ambient air. This may occur, for example, by suitable seals. For example, one may provide such a seal at the inlet of the channel-shaped unit. In this instance, one should see that in cooperation with the outlet, a required pressure difference remains unchanged for causing the filaments to burst. In particular, a closed system makes it possible to adjust a pressure in a purposeful manner. With that, for example, it becomes possible to use overpressures and vacuums for influencing in particular a burst and separation of the filaments.
Depending on the polymer quality and the process conditions, the devices for additionally tempering and/or drawing the filaments are constructed as devices for generating a vacuum or pressure, or as a mechanical unit. The web laying surface in the region of the filament receiving area may be a belt, preferably a screen belt. It has also been found advantageous to deposit the filaments on a drum, preferably a screen drum.
The spunbonded fabrics produced by the method of the invention and its apparatus from filaments of burst fibers are continuous or discontinuous, or contain both fiber types, and have a filament diameter of a range between smaller than or equal to 1 μm and 80 μm, preferably from 2 μm to 5 μm. The filament length/filament diameter ratios are from 100:1 to 100,000,000:1, preferably 10,000:1 to 1,000,000:1.
The throughput rate of the production line is preferably from 0.15 to more than 2.00 grams per minute and hole. The used polymer may have an MFI from 1 to 500 g/10 min. (at 230° and a piston weight of 2.16 kg), preferably an MFI that ranges from 9 to 45 g/10 min.
Preferably, the method and apparatus are used to produce nonwoven fabrics or laminates that have at least one layer of a spunbonded fabric.
The laminates may include a nonwoven layer that entirely consists of the filaments. At least one adjacent nonwoven layer is, for example, a prefabricated nonwoven, for example, a spunbonded fabric with a larger filament diameter. In particular, it is possible to produce multilayer nonwovens, which have in each layer a different average filament diameter. For example, a first nonwoven layer has an average filament diameter from 0.3 μm to 0.7 μm. A second nonwoven layer has an average filament diameter that is higher. This diameter may be in a range from 1 μm to 3 μm. When a further nonwoven layer is added, same may have an average diameter, which ranges, for example, from 3 μm to 20 μm.
Furthermore, the apparatus may provide not only for the production of burst and separated filaments, but may also include at least one further spin beam and/or meltblown beam, so as to enable a simultaneous production of at least two-layer materials. To this end, at least the one spin beam and/or the meltblown beam may be arranged upstream or downstream of the filament production unit.
A further development provides that a film forms part of the laminate. The film may be directly or indirectly laminated with burst filaments, for example, on one side or both sides. To this end, the film layer may be prefabricated or also be directly produced in the apparatus. The film may be, for example, gas permeable, in particular microporous.
The nonwoven or the laminate, which contains burst and separated filaments, is made both as a semi-finished and a finished product. For example, the nonwoven may be bonded prior to further processing and be subsequently assembled.
The nonwoven or the laminate is used for clothing, preferably protective apparel, for example, in protective masks, protective suits, protective covers for shoes and hair. A further applicability includes the area of cleaning cloths, packaging, and household products, medical products, such as OR covers, smocks, sterile packs, bandage materials or, however, the use of hygienic products, such as sanitary pads, diapers, tampons, disposable products of the general type, and the like.
A further field of application is the use in filters, in particular microfilters for room air up to the highest degree of safety. It may likewise be used as preliminary or end filter material. Besides the filtration of gaseous media, in particular filtration of dust particles, there is also the possibility of use in filtering liquid media, such as, for example, oil. Furthermore, the nonwoven or the laminate may be used in the field of construction or as a geotextile. In particular, there is the possibility of using it in pillows. Because of the very fine filament diameters, it is possible to apply it as covering of finely powdered materials.
The nonwoven may be made antibacterial and/or antistatic, and likewise be finished in a different manner. It may also be used to store a material, for example, a fluid. For example, a material is absorbed and/or dispensed or released.
Further advantageous embodiments, features, and further developments are described in greater detail in the following. The therein described features, however, are not restricted or limited to there embodiments, but may be combined with further, in particular the above-described features to further embodiments. For a better understanding, the invention is described in greater detail with reference to drawings, in which:
Upstream of this draw unit, a device 15 for generating compressed air is arranged. Below the filament web laying surface, a vacuum source 8 is arranged for generating suction air 7. The tempered and drawn filaments 4 that are deposited on the web laying surface 5, form a nonwoven web 11, which contains filaments with filament length/filament cross section ratios from 100:1 to 100,000,000:1, preferably 10,000:1 to 100,000:1.
A further development of this apparatus may be equipped without a nozzle unit 13. In this development, the filaments 4 are accelerated and drawn by means of compressed air 15 and suction air 7, or by means of an injector. In this instance, the produced nonwoven web 11 comprises either exclusively continuous filaments, or continuous filaments with portions of discontinuous filaments. Subsequently, a pair of rolls 10 bonds the nonwoven web.
Via an extruder 25 and a melt line 26, a polymer melt of polypropylene with an MFI of 13 g/10 min. (at 230° C. and a piston weight of 2.16 kg) advances to a spin device 1 (with spin pack and spinneret). At a melt temperature of 325° C., a yarn 2 forms, which bursts in a known manner into filaments 4 after leaving the Laval nozzle 3. The burst filaments 4 are unilaterally cooled by means of a gas 18, preferably air or an air-liquid aerosol at a temperature from about 5° to 25° C. In a channel 6, the filaments are drawn, with a vacuum from −500 to −3000 Pa being adjusted in the region upstream of the screen belt by the vacuum source 8 depending on the desired filament fineness or the desired textile-mechanical properties of the nonwoven. The filaments are collected on the screen belt 5 and advanced through pressure rolls 10. The nonwoven web 11 predominantly comprises endless filaments with diameters ranging from 0.5 to 12 ìm, and it is bonded in a usual manner by a thermal bonding (calendering) step. Thus, after thermobonding, one obtains with a specific nonwoven weight of 11 g/m2, a strength from 0.5 to 12.5 N crosswise to the machine direction (CD) (according to DIN 53455 (German Industrial Standards), with a free clamping length of 100 mm; width of 50 mm; testing speed of 200 mm/min.). Without further finish, this spunbonded nonwoven has a water column from 15 to 20 mbar, which normally corresponds to a meltblown nonwoven with a basis weight of 9 g/m2.
Under the same conditions as used in Example 1, a nonwoven web is produced with a basis weight of 20 g/m2. The nonwoven has strength values in the MD from 25 to 30 N (according to DIN 53455, with a free clamping length of 100 mm; width of 50 mm; testing speed of 200 mm/min.) In the case of this nonwoven, the water column is 30 to 40 mbar, which normally corresponds to a 16-g/m2 meltblown nonwoven.
| Number | Date | Country | Kind |
|---|---|---|---|
| 103 22 460.2 | May 2003 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP04/05056 | 5/12/2004 | WO | 11/8/2006 |
