Patent Application
20070202769
The invention relates to a melt-blown method for melt spinning fine non-woven fibers, as well as to a device for carrying out said method.
In the production of non-woven microfibers a plurality of fiber strands are extruded from a polymer melt through nozzle holes of a spinneret and then drawn with a blowing stream into microfibers. Such fibers exhibit an average fiber diameter of usually <10 μm. In the state of the art such methods are called melt-blown methods. The blowing stream is preferably produced from hot air that is blown with a high expenditure of energy on the fiber strands. The blowing stream leads to drawing and bursting of the fiber strands so that fine non-woven fibers of finite length are produced.
DE 33 41 590 A1 and corresponding U.S. Pat. No. 4,526,733 disclose such a method, where a fluid, which is not heated up, is used as the blowing stream. In principle, such relatively cold blowing streams exhibit the advantage that there is no need to heat up the fluid. This method could also produce fine fibers made of thermoplastic polymers, which exhibit a fineness of less than 10 μm.
Irrespective of whether the prior art melt-blown method is carried out with a hot blowing medium or with a cold blowing medium, as disclosed in the DE 33 41 590 A1, the fiber strands are usually torn into finite fibers. In addition to the disadvantageous formation of fuzz, such fibers lead, upon being deposited to form a non-woven fabric, to irregularities in the physical properties due to the conglutinated fiber pieces. In particular, such non-woven fabrics can tolerate only slight tensile strengths owing to the finite fiber pieces.
DE 199 29 709 A1 discloses another method for producing fine non-woven fibers. In this method the fiber strands are split into fine fibers by means of a gas stream. The prior art method, which is referred to as the Nanoval method in professional circles, is based on generating a pressure effect on the fiber strand subject to the action of a gas stream and a nozzle unit. Said pressure effect causes the fiber strand to burst so that a plurality of fine, essentially endless fibers is produced. At the same time the hydrostatic pressure, prevailing in the interior of the fibers, is greater than the gas pressure that envelops the fiber strands and by means of which the bursting of the fiber strands is achieved. Then the fibers are guided—subject to the action of the gas stream—to a depositing area and are deposited as a non-woven fabric.
All of the state of the art melt-blown methods run the risk that the individual fibers will conglutinate before the final solidification and lead to undesired points of discontinuity in the non-woven fabric.
Therefore, an object of the invention is to provide a melt-blown method for melt spinning fine non-woven fibers of the type described in the introductory part. According to this method, a high quality microfiber could be produced at a relatively low expenditure of energy.
Another goal of the invention is to provide non-woven fibers for producing a non-woven fabric, which exhibits improved physical properties.
In addition, an object of the invention is to improve a melt-blown method and a melt-blown device for melt spinning fine non-woven fibers in such a manner that a microfiber is produced that exhibits maximum uniformity and continuity in order to attain, during their subsequent manufacture into a non-woven fabric, a uniform distribution of the fibers during the depositing process.
The above objectives and others are realized according to the invention by providing, in one embodiment, a method for melt spinning fine non-woven fibers, comprising extruding a polymer melt through several nozzle holes of a spinneret in order to form several fiber strands, and immediately after emerging from the nozzle holes, acting on the fiber strands with a cold blowing stream that, subject to the action of an overpressure, flows through at least one blowing nozzle orifice onto the fiber strands and draws the fiber strands, wherein the blowing stream is guided to the fiber strands inside an acceleration section, in which the fiber strands and the blowing stream are accelerated in such a manner that the fiber strands are drawn to form infinite microfibers. The present invention also provides a non-woven fiber and a resulting non-woven fabric produced according to the method.
The invention is based on the knowledge that in the conventional melt-blown methods, the blowing stream is accelerated, upon impinging on the fiber strand, to a maximum velocity. Therefore, the meeting of the blowing stream and the fiber strand results in a more or less sudden elongation of the fiber strands. This elongation leads to drafting and—optionally upon exceeding a maximum spinning draft—to tearing of the fibers. In order to avoid such overstressing of the fibers, the blowing stream is fed, according to the invention, to the fiber strands inside an acceleration section. In the acceleration section the blowing stream and the fiber strands are then accelerated together in such a manner that the fiber strands are drawn to form endless micro fibers. In this way overstressing the fiber strand while drawing can be avoided in an advantageous way. The maximum velocity of the blowing stream is not reached until the end of the acceleration section and leads to the desired total drawing of the fiber strands.
Since the blowing stream and the fiber strands are accelerated inside the acceleration section, the blowing stream can be fed to the fiber strands at a relatively low expenditure of energy. Thus, it has been demonstrated that merely an overpressure in a range below 1,000 mbar is sufficient to provide the fiber strands with the desired spinning draft. Consequently the consumption of the blowing stream can also be reduced to a minimum.
The blowing stream is preferably air that exhibits a natural air temperature in a range between 15° C. and 110° C. Thus, it is possible to quickly establish peripheral zones for the fibers, a feature that benefits in particular the stability of the fibers for drawing. In addition, the microfibers cool better. In this respect it is important that the air does not heat up. Therefore, the temperature that accepts the air without cooling or heating owing to the environmental conditions is called here the natural air temperature.
The blowing stream is produced preferably from the surrounding air at an ambient temperature. Said surrounding air is drawn in from the environment below the spinneret. At an average consumption of approximately 600 m3/h*m of surrounding air and at a maximum overpressure of 1 bar in a conventional spinning device, the blowing stream can be provided at a low cost.
Owing to the alternative method, with which the fiber strands are extruded at a mass flow of the polymer melt through the nozzle hole of the spinneret of 1.0 g/min. to 10 g/min. per nozzle hole, all of the current types of polymers, for example polypropylene or polyamide, may be extruded. Preferably a throughflow of >3 g/min. is set per nozzle hole. Therefore, the hole diameter may lie in a range between 0.2 and 1.0 mm.
Therefore, it is especially advantageous for the polymer melt to be heated inside the spinnerets just before emerging from the nozzle holes, so that the freshly extruded fiber strand exhibits a relatively high melting temperature that may be, for example, above 350° C. for a polypropylene fiber. Depending on the type of polymer, the polymer melt is heated preferably to a range between 300° C. and 400° C. in order to obtain a constant optimal setting as a function of the type of polymer, the capillary diameter of the nozzle holes and the desired fiber fineness, the length of the acceleration section for accelerating the blowing stream and the fiber strands ranges from 2 mm to 30 mm.
Thus, the fiber strands can be fed directly from the nozzle hole into the acceleration section or not until the fiber strands have passed through a short extrusion zone of a maximum 2 mm, in which the fiber strands may emerge from the nozzle hole without any influence of the blowing stream.
In order to generate high draft forces on the fiber strands, a preferred alternative of the method provides that the fiber strands and the blowing stream are fed, upon passing through the acceleration section, into a free space, where an atmosphere prevails that is in essence equal to an ambient pressure. The expansion of the blowing stream into the free space produces zones of turbulence, which improves the blowing stream's attack on the fiber surface. So-called whiplash effects may also occur with the result that the fibers continue to be drawn.
In order to intensify such effects, additional zones of air turbulence may be generated by air conductors inside the free space. This in turn also generates special effects in the fibers, such as thick and thin points.
However, there is also the possibility of providing an additional air stream inside the free space for the purpose of cooling. This alternative of the method is especially advantageous to implement in those cases, in which the blowing stream exhibits relatively high air temperatures.
The method, according to the invention, is suitable for processing all current types of polymers, such as polypropylene, polyethylene, polyester or polyamide, and to process into non-woven fibers with microfiber cross sections ranging up to 0.5 μm. In particular, good results could be attained with a polypropylene material, where the fiber fineness of the infinite microfibers was in a range between 1 μm and 30 μm.
The microfiber, produced with the method according to the invention, is suitable, as an infinite fiber, in particular for depositing in order to form a non-woven fabric.
The inventive device for carrying out the inventive method provides that an acceleration section is formed between the upper edges and the bottom edges of the two blowing nozzle orifices, which are arranged below the spinneret. Thus, there is no need for any additional aids in order to achieve an acceleration section, which is designed directly below the nozzle holes. The device, according to the invention, is characterized in particular in that a plurality of fiber strands can be drawn uniformly with relatively close spacing to form microfibers without the adjacent fibers conglutinating. Therefore, the device, according to the invention, is suitable for producing a large number of high quality microfibers of high uniformity.
According to an advantageous further development of the inventive device, the upper edge of the two blowing nozzle orifices is assigned to an entry throat; and the bottom edges of the two blowing nozzle orifices are assigned to an exit throat in order to achieve a defined acceleration section. The exit throat exhibits a free flow cross section that is smaller than the flow cross section of the entry throat. Thus, after the fibers have passed through the entry throat, they may be accelerated continuously by means of the blowing stream, emerging from the blowing nozzle orifices, as far as up to the exit throat.
Depending on the fiber fineness and the type of polymer, the exit throat is set to a slit width ranging from 2 to 8 mm. The slit width is defined by the smallest distance between the bottom edges that are opposite each other and belong to the blowing nozzle orifices.
The entry throat, which exhibits a larger slit width, can be formed advantageously directly on a level with the underside of the spinneret, so that the extruded fiber strands can enter directly into the acceleration section. However, there is the possibility of forming the entry throat at a short distance from the underside of the spinneret, so that the fiber strands do not reach the acceleration section until after passing through a short extrusion zone ranging from 0 to 2 mm.
The length of the acceleration section is defined by the distance of the entry throat from the exit throat. Depending on the type of fiber and the fiber fineness this length may range from 2 mm to 20 mm.
A preferred design of the inventive device exhibits an inflow channel for each blowing orifice for the air supply. Said inflow channel is formed between the bottom edge and the upper edge of the respective blowing nozzle. Therefore, the upper edge and the bottom edge are aligned or formed in such a manner that the inflow channel exhibits in the direction of the blowing orifice a tapering flow cross section on the end of the bottom edge and the upper edge respectively. Thus, a continuous acceleration of the supplied air as far as up to the entry into the acceleration section can be achieved so that a small supply of energy is necessary to generate the blowing stream.
The air that is made available is held advantageously in reserve in a pressure chamber that is connected to the blowing orifices.
According to an especially advantageous further development of the inventive device, the pressure chamber is connected to a suction unit in order to provide air as inexpensively as possible. This suction unit takes in the surrounding air and conveys it directly into the pressure chamber.
A free space is formed below the bottom edges of the blowing orifices in order to facilitate an intensive draft of the fiber strands during the expansion of the blowing stream upon emerging from the acceleration section.
The free space may contain additional aids for guiding, cooling and/or drawing the fibers. This gives the inventive device a high degree of flexibility that makes it possible to produce microfibers of any type and for any application.
The non-woven fiber, which is made of a polymer material and produced according to the method of the invention, is characterized in that, despite the microfiber cross sections ranging from 0.5 μm to 30 μm, the fibers exhibit an infinite length. This makes it possible to provide infinite microfibers, produced by a melt-blown method, in order to produce non-woven fabrics.
Thus, the inventive non-woven fabric, which is formed from the non-woven fibers of the invention, is characterized in particular by a high uniformity both in the machine direction and in the cross direction. Therefore, such non-woven fabrics are especially suitable for barrier products, where, on the one hand, permeability to air is desired, but, on the other hand, such a non-woven fabric exhibits a blocking effect with respect to liquids. Therefore, the inventive non-woven fabric is especially suitable for hygienic products, medical products and filter applications.
The inventive non-woven fabric is characterized in particular by a higher stretching ability as compared to conventional melt-blown non-woven fabrics. Therefore, the inventive non-woven fabric can be used advantageously in products, where minor deformations occur during production or use. In particular for such applications a suitable non-woven fabric is one, where the infinite microfibers, which are made of a polypropylene, are deposited to form a weight per unit of area in a range between 1.5 g/m2 and 50 g/m2 and lead to an elongation at break of at least 60% or can tolerate a maximum tensile stress at an elongation of at least 40%.
The high strength and deformability of the non-woven fabrics make it possible to produce in an advantageous manner composite non-woven fabrics that exhibit a plurality of layers. In the composite non-woven fabric of the invention, at least one of the layers is made of a non-woven fabric exhibiting the infinite microfibers of the invention.
Both the inventive non-woven fabric and the composite non-woven fabric are especially suitable for hygienic products, such as diapers, sanitary napkins, medicinal products, such as wound dressings, filter products, or household products, such as cleaning cloths or dust cloths.
Therefore, for the above applications in particular composite non-woven fabrics, wherein at least one other layer is made of a spun bond non-woven fabric, are preferably used.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
The embodiment exhibits a spinneret 1, which is connected to a melt source (not illustrated here) by means of a melt feed 2. Usually an extruder is used as the melt source. Said extruder melts a thermoplastic material and feeds said material as the polymer melt under pressure to the spinneret. The underside of the spinneret 1 exhibits a plurality of nozzle holes 5, which are connected inside the spinneret 1 to the melt feed 2. The nozzle holes 5 are configured on the underside of the spinneret 1 in a specific arrangement, preferably in a series of rows with one or more rows next to one another. A fiber strand can be extruded out of the polymer melt emerging from each of the nozzle holes 5.
Underneath the spinneret 1 there is a blower 3, which exhibits two blowing nozzles 4.1 and 4.2, which lie opposite each other and are located a short distance underneath the spinneret 1. Each of the blowing nozzles 4.1 and 4.2 contains a blowing nozzle orifice 7.1 and 7.2, which is formed between a respective upper edge 9.1 or 9.2 and the respective bottom edge 10.1 or 10.2. The upper edge 9.1 and/or 9.2 and the bottom edge 10.1 and/or 10.2 are designed in the shape of plates and extend with their free end essentially parallel to the nozzle holes 5 of the spinneret 1. Thus, the upper edges 9.1 and 9.2, which lie opposite each other, form an entry throat; and the bottom edges 10.1 and 10.2, which lie opposite each other, form an exit throat for the fiber strands 6. The entry throat and the exit throat are designed in such a manner that between the upper edges 9.1 and 9.2 and the bottom edges 10.1 and 10.2 there is an acceleration section 15, in which a blowing stream, emerging from the blowing nozzle orifice 7.1 and 7.2, is accelerated together with the fiber strands 6.
The upper edges 9.1 and 9.2 of the blowing nozzles 4.1 an 4.2 are usually arranged in such a manner with respect 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 the acceleration section. The design (which is not shown in
Each of the blowing nozzles 4.1 and 4.2 is assigned a pressure chamber 8.1 and 8.2, in which is stored a blowing medium, which is held under an overpressure. Preferably air is used as the blowing medium. However, it is also possible to use a gas. The pressure chambers 8.1 and 8.2 may be connected jointly or separately to a pressure source, for example a compressed air ductwork system. Below the blower 3 there is a free space 12 that extends from the bottom edges 10.1 and/or 10.2 of the blowing nozzles 4.1 and 4.2 as far as to a depositing belt 13. The depositing belt 13 serves to deposit the drawn microfibers 11 to form a non-woven fabric 14. To this end, the depositing belt 13 is connected to a drive in order to carry away in a continuous mode the non-woven fabric 14 after the microfibers 11 have been deposited. The arrows show the direction of movement of the depositing belt 13.
The embodiment (shown in
A cold blowing medium, preferably cold air, is used as the blowing medium for taking off and stretching the fiber strands 6. This process allows the fiber strands to cool down until they are deposited, so that no additional cooling of the fibers is necessary. At air temperatures of, for example 25° C., in particular the free space 12 between the blower 3 and the depositing belt 13 can be held extremely small so that the blowing stream significantly improves the depositing of the microfibers so as to form a non-woven fabric. In addition, the stability of the fiber guide is enhanced in that, when the cold blowing air meets the freshly extruded fiber strands, rapid cooling of the peripheral zones of the fiber strands 6 takes place. However, the stretchability remains essentially preserved owing to the molten core areas of the fiber strands 6.
In order to attain maximum draft forces by means of the blowing stream, the blowing nozzles 4.1 and 4.2 are formed preferably in such a manner that the blowing stream already flows out of the blowing nozzle orifices in the direction of travel of the fibers. To this end,
The detail in
Below the spinneret 1 there are blowing nozzles 4.1 and 4.2 with blowing nozzle orifices 7.1 and 7.2. The blowing nozzle orifice 7.1 is placed between the upper edge 9.1 and the bottom edge 10.1. The upper edge 9.1 and the bottom edge 10.1 are designed as mold plates, which between themselves form the inflow channel 18.1. The inflow channel 18.1 exhibits a flow cross section that tapers off in the direction of the blowing nozzle orifice 7.1 so that the blowing air, supplied inside the inflow channel 18.1, is accelerated continuously as far as up to the blowing nozzle orifice 7.1. At the same time the inflow channel 18.1 is shaped by the upper edge 9.1 and the bottom edge 10.1 in such a manner that the blowing stream, emerging from the blowing nozzle orifice 7.1, is fed in the direction of travel of the fibers. It has proven to be especially advantageous if the upper edge 9.1 in relation to the bottom edge 10.1 exhibits such a physical curvature that its theoretical imaginary extension that projects beyond the free end strikes in the middle of an exit throat 17, which is formed by the bottom edges 10.1 and 10.2, which lie opposite each other. At the same time, the continuous decrease in the distance between the upper edge 9.1 and the bottom edge 10.1 continues as far as up to the middle of the exit throat 17. This design of the blowing nozzle 4.1 makes it possible to improve the accelerating effect for drawing off the fiber strand.
The blowing nozzle orifice 7.2 of the blowing nozzle 4.2 on the opposite side of the spinneret 1 is identical (as the mirror-image) to the first blowing nozzle orifice 7.1 of the blowing nozzle 4.1. The inflow channel 18.2 between the formed plates of the upper edge 9.2 and the bottom edge 10.2 is configured with a tapering flow cross section. Thus, with respect to a more detailed description reference is made to the aforesaid.
The upper edges 9.1 and 9.2 are spaced apart so as to lie opposite each other below the underside of the spinneret 1 and form an entry throat 16. The slit width of the entry throat 16 is labeled with the capital letter E in
Below the upper edges 9.1 and 9.2 the bottom edges 10.1 and 10.2 are arranged so as to lie opposite each other in relation to the exit throat 17. The slit width of the exit throat 17 is labeled with the capital letter A in
On the side of the blowing nozzles 4.1 and 4.2 that faces the spinneret 1, a sealant 23.1 and 23.2 is disposed between the spinneret 1 and the upper edges 9.1 and 9.2. The sealants 23.1 and 23.2 form, on the one hand, in relation to the spinneret 1 an insulating layer in order to avoid heat losses and, on the other hand, a seal with respect to the blowing air, conveyed in the acceleration section 15. The sealants 23.1 and 23.2 are made preferably of insulating materials.
In the embodiment of the inventive device, depicted in
However, it is also possible to let the extruded fiber strands 6 pass into the acceleration section 15 directly after leaving the nozzle holes 5. Such an embodiment of the inventive device is depicted as a schematic representation in a sectional view in
The entry throat 16 between the upper edges 9.1 and 9.2 is constructed directly on a level with the underside of the spinneret 1. The result is that upon leaving the nozzle hole 5, the fiber strands 6 enter directly into the acceleration section 15 and make contact with the blowing stream and thus acquire from the spinneret 1 a different take-off behavior.
On the side of the blowing nozzles 4.1 and 4.2 that faces the spinneret 1, there is one respective air gap 24.1 and 24.2 between the spinneret 1 and the upper edges 9.1 and 9.2. The air gaps 24.1 and 24.2 are dimensioned so closely that in essence no blowing air can pass through, but a sufficient layer of air remains in order to insulate it from the spinneret 1.
In order to improve and increase the drawing of the microfibers 11, the free space 12 in the embodiment, depicted in
In the embodiment, depicted in
The embodiment, depicted in
Therefore, when the fiber strands pass through the injector 22, the surrounding air pending in the free space 12 from the surrounding, is directly involved without any outside assistance in the guiding and cooling of the fibers. However, it is also possible for climate-controlled air to be drawn into the free space 12. Then, as the conditioned air, the climate-controlled air can be predetermined with respect to the air temperature, humidity and air quantity so that specific cooling conditions at the fibers can be set. However, such mechanisms are used preferably in those cases, in which the blowing stream must be produced from a relatively warm air.
In principle, the inventive method and the inventive device for carrying out the inventive method are suitable for use with polymer melts of all current polymers, such as polyester, polyamide, polypropylene or polyethylene.
In one example of the method, a polymer, which is made of a polypropylene, is melted to form a melt and extruded through a nozzle hole having a capillary diameter of 0.6 mm and a melt throughput of 6 g/min. per nozzle hole. The number of nozzle holes was 36. The pressure chambers 8.1 and 8.2 were supplied with air at room temperature and an overpressure of 260 mbar. Therefore, the configuration of the device, depicted in
In a series of experiments the polypropylene fibers were deposited to form non-woven fabric that exhibited a variety of different weights per unit of area. The results are plotted in the diagram in
The non-woven fabrics, made of such fibers, may be included in an especially advantageous manner in composite materials. The suction capability and blocking effect of such non-woven fabrics may be used advantageously in a composite non-woven fabric in order to form a barrier layer.
The significantly high elongation and tensile strength of the inventive melt-blown method also lead to improved processing. Even applications with small deformation, such as in hygienic products, are possible without any problems.
Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
| Number | Date | Country | Kind |
|---|---|---|---|
| DE102004047537.7 | Sep 2004 | DE | national |
The present application is a continuation of international application PCT/EP 2004/014403, filed 17 Dec. 2004, and which designates the U.S. The disclosure of the referenced application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP04/14403 | Dec 2004 | US |
| Child | 11693235 | Mar 2007 | US |
