Method and apparatus for making a spunbond nonwoven from endless filaments

Abstract

An apparatus for making a spunbond nonwoven from endless filaments of a thermoplastic synthetic resin has a spinneret for spinning the filaments in a filament-travel direction into a spinning zone and a monomer aspirator downstream of the spinneret and having two vacuum intake ports flanking the spinning zone zone, horizontally confronting each other, and each extending transversely to the direction opposite one another. Suction means connected to the two ports withdraws gas through both the vacuum intake ports. The suction and/or the ports are set up to vary the flow through the vacuum intake ports such that substantially more gas flows through one of the ports than through the other.

Claims

1. An apparatus for making a spunbond nonwoven from endless filaments of a thermoplastic synthetic resin, the apparatus comprising: a spinneret for spinning the filaments in a filament-travel direction into a spinning zone; a monomer aspirator downstream of the spinneret and having two ports serving for vacuum intake and flanking the spinning zone, open toward each other, and each extending transversely to the direction opposite one another; and means connected to the two ports for withdrawing gas through both the ports; means associated with the ports for varying the flow through the ports such that more gas flows through one of the ports than through the other port and a ratio of the volume flow removed by suction through the one port to the volume flow removed by suction through the other port on the opposite side of the spinning zone is 5.5:1 to 1.3:1; and a cooler downstream of the aspirator for cooling the filaments.

2. The apparatus defined in claim 1, wherein the means for varying is part of the means for withdrawing and operates such that more gas is pulled through the one port than through the other port.

3. The apparatus defined in claim 2, wherein the flow cross section of the one port is greater than the flow cross section of the other port.

4. The apparatus defined in claim 3, wherein both ports are slots extending transversely of the direction, a gap width measured in the direction of the one port being at least twice as large as a gap width measured in the direction of the other port.

5. The apparatus defined in claim 1, wherein a combined flow cross section of the two ports is more than 11,000 mm.sup.2/m of the spinning zone.

6. The apparatus defined in claim 1, wherein each of the ports extends transversely of the direction generally over a full width of the spinning zone.

7. The apparatus defined in claim 1, wherein the ports are slots extending transverse to the direction and at least one of the ports is formed by a row extending transverse to the direction of short slot-shaped subports.

8. The apparatus defined in claim 1, further comprising: at least one collecting chamber for the suction gases connected to each of the ports, the means for varying or means for withdrawing including at least one throttle element that provided in one of the collecting chambers or in or on a suction line connected to the one collecting chamber.

9. The apparatus defined in claim 1, wherein the means for varying or means for withdrawing alternates which of the ports aspirates more gas from one side to the other of the spinning zone.

10. The apparatus defined in claim 1, wherein each of the ports is formed as a row extending transversely of the direction of slot-shaped subports.

11. The apparatus defined in claim 1, wherein surfaces at risk of soiling at the ports are covered by covering materials and a covering web that absorbs or insulates by holding and absorbing dirt.

12. The apparatus defined in claim 1, further comprising: means for heating surfaces at risk of soiling at the ports to prevent soiling or to prevent formation of condensation.

13. The apparatus defined in claim 1, wherein the spinneret has a hole density of 1 to 6 hole/cm.sup.2.

14. The apparatus defined in claim 13, wherein the hole density of the spinneret is lower in the central region of the spinneret than in outer regions of the spinneret and the hole density in the central region of the spinneret is 0 to 1 hole/cm.sup.2.

15. The apparatus defined in claim 1, wherein a depth in the filament-travel direction of the spinning zone is 120 to 350 mm.

16. The apparatus defined in claim 1, wherein the cooler has at least two compartments provided one after the other in the direction and from which cooling air at different temperatures is projected at the filaments.

17. The apparatus defined in claim 1, further comprising: a stretcher connected downstream of the cooler in the direction of filament flow; and a deposition support for depositing the filaments to form the spunbond nonwoven downstream from the stretcher in the filament-travel direction, an assembly of a cooler and the stretcher being a closed system into which there is no further supply of air except for cooling air in the cooler.

18. A method of making a spunbond nonwoven from endless filaments made of a thermoplastic synthetic resin, the method comprising the steps of: spinning the filaments with a spinneret and passing the spun filaments in a filament-travel direction through a spinning zone; providing two ports serving for vacuum intake flanking the spinning zone and opening oppositely transversely into the zone; and aspirating from the zone a greater volume of gas through one of the ports than through the other of the ports with a ratio of the volume flow removed by suction through the one port to the volume flow removed by suction through the other port on the opposite side of the spinning zone being 5.5:1 to 1.3:1.

19. The method defined in claim 18, wherein the filaments are spun at a throughput of 100 to 350 kg/h/m.

20. The method defined in claim 18, wherein the filaments are spun at a filament speed of 2000 to 4200 m/min.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

(2) FIG. 1 is a vertical section through an apparatus according to the invention;

(3) FIG. 2A is an enlarged detail from FIG. 1 showing suction removal of monomer according to the prior art;

(4) FIG. 2b is a view like FIG. 2A but with suction removal of monomer according to the invention; and

(5) FIG. 3 is a perspective view of a monomer aspirator according to the invention.

SPECIFIC DESCRIPTION OF THE INVENTION

(6) As seen in FIG. 1, an apparatus according to the invention for making a spunbond nonwoven 22 from endless filaments 23 that consist in particular and/or essentially of a thermoplastic synthetic resin. The filaments 23 are spun using a spinneret 1 and are passed downward in a filament-travel direction D D through a filament-forming space 29 beneath this spinneret 1 through a monomer aspirator 2 for suction removal of gases formed during the spinning process.

(7) A cooler 3 for toe filaments is provided downstream from and/or beneath the monomer aspirator 2, as seen in the filament-travel direction D. Preferably this cooler has an air-supply chamber that is subdivided into two compartments 13, 14. Preferably process air and/or cooling air at different temperatures can be projected from these two compartments 13, 14 toward the descending filament bundle.

(8) A stretcher 15 is connected to the cooler 3 downstream in the filament-travel direction D. This stretcher 15 preferably and in the illustrated embodiment has an intermediate passage 24 that converges in the filament-travel direction D as well as a stretching passage 25 connected thereto.

(9) As recommended and in the illustrated embodiment, the assembly formed from the cooler 3 and the stretcher 15 is a closed system. In addition to the supply of cooling air and/or process air to the cooler 3, there is no further supply of air into this closed system. According to the preferred embodiment of the invention, at least one diffuser 17, 18 is connected to the stretcher 15 downstream in the filament-travel direction D.

(10) Advantageously, two diffusers 17, 18 provided one after the other and/or side by side are provided. It is advisable for an ambient air inlet gap 28 to be provided between the two diffusers 17 and 18 for the admission of ambient air. Preferably the filaments 23 are deposited on a deposition support 16 to form the spunbond nonwoven downstream from the diffusers 17, 18. Preferably the deposition support 16 is designed as a continuously revolving endless screen belt.

(11) According to the invention, the monomer aspirator 2 for suction removal of the gases formed in the spinning process is provided at the spinneret 1. Preferably the monomer aspirator 2 is provided in the filament-forming space 29 beneath the spinneret 1. As recommended, this monomer aspirator 2 has two CD vacuum intake ports 5 and 6 provided one after the other in the machine direction MD, which here is the same as the filament-travel direction D, and each extending transversely to the machine direction and being on opposite sides of the spinning zone 4. Preferably the CD vacuum intake ports 5 and 6 are provided in side walls 26 on opposite sides and extend in the CD direction, that is open transversely of the direction D, bordering the filament-forming space 29. These CD vacuum intake ports 5 and 6 that are on opposite sides of the spinning zone 4 are preferably each designed as CD vacuum gaps 7 and 8 extending transversely and/or perpendicularly to the machine direction. Preferably the two CD vacuum gaps 7 and 8 are each subdivided into a plurality of CD vacuum gaps sections 7 and 8. These CD vacuum gap subsections 7 and 8 are preferably provided side by side as well as being at the same width vertically. It is within the scope of the invention for the two CD vacuum gaps 7 and 8 that are on opposite sides to be set up such that a higher volume flow of gases can be removed by suction through one of the two CD vacuum gaps 7 and 8 than through the other CD vacuum gaps 7 and 8 on the opposite side.

(12) In the illustrated embodiment, a higher volume flow V.sub.A can be removed by suction through the downstream CD vacuum gap 8, as seen in the machine direction (outlet side) of the spunbond nonwoven web than through the upstream CD vacuum gap 7 in the machine direction (inside of the spunbond nonwoven web). In the illustrated embodiment, the rate of the volume flow V.sub.A/V.sub.E may amount to 3:1. In the illustrated embodiment, the vertical gap width h.sub.A of the downstream CD vacuum gap 8, as seen in the machine direction (outlet side), is larger than the vertical gap width h.sub.A of the upstream CD vacuum gap 7, as seen in the machine direction (inlet side). However, it may be possible to vacuum up a higher volume flow V.sub.E through the upstream CD vacuum gap 7, as seen in the machine direction (inlet side of the spunbond nonwoven web) than through the downstream CD vacuum gap 8, as seen in the machine direction (outlet side of the spunbond nonwoven web). The ratio of the volume flows and the vertical gap widths can then be provided more or less as the converse to the above specifications.

(13) In the illustrated embodiment, a depth t of the spinning zone 4 may amount to 200 mm and it is possible to work with a throughput of 230 kg/h/m and with a filament speed of 3300 m/min in this illustrated embodiment.

(14) According to a preferred embodiment, the monomer aspirator 2 also has two opposite MD vacuum intake ports 9 and 10 that extend in the machine direction MD and on opposite sides of the spinning zone 4. The MD vacuum intake ports 9 and 10 are preferably provided in opposite walls 27 that extend in the MD direction and border the filament-forming space. The walls 27 are advantageously connected to the side walls 26 that extend in the CD direction. The side walls 26 (in the CD direction) are as recommended longer or much longer than the side walls 27 (in the MD direction). Preferably the MD vacuum intake ports 9 and 10 are preferably designed as two opposite MD suction gaps 11 and 12 extending in the MD direction. Advantageously, the MD suction gaps 11 and 12 are also provided at the same vertical width as well as at the same vertical width as the CD vacuum gaps 7 and 8. The MD suction gaps 11 and 12 are preferably each subdivided into MD suction gap subsections 11 and 12, namely as recommended, each in two MD suction gap subsections 11 and 12.

(15) Advantageously, collecting chambers 19 and 20 for the gases removed by suction through the CD vacuum gaps 7 and 8 are provided at each CD vacuum gap 7 and 8. A plurality of suction lines 21 for suction removal of the gases as part of the suction removal of monomer is connected to each collecting chamber 19 and 20. Preferably each collecting chamber 19 and 20 is connected to a collecting duct 32, 33 via the suction lines 21. Advantageously at least one suction device (not shown)for example, in the form of a pumpis connected to the collecting duct 32, 33 for suction removal of the gases. Furthermore, the suction lines 21 may have cutoff elementsfor example, in the form of side valvesand the volume flow removed by suction through the CD vacuum gaps 7 and 8 on opposite sides can also be adjusted with these cutoff elements. The collecting ducts 32, 33 are preferably assigned not only to the CD vacuum gaps 7 and 8 but also to the two MD suction gaps 11 and 12 on opposite sides. The gases removed by suction through these MD suction gaps 11 and 12 can thus also be captured in the collecting ducts 32, 33. FIG. 3 also shows that baffles 30, 31 for the gases removed by suction are provided in the collecting chambers 19 and 20.

(16) A comparison of FIGS. 2A and 2B shows the gas flows during suction removal of monomer according to the prior art (FIG. 2A) and the gas flows with the monomer suction removal according to the invention (FIG. 2B). With the prior-art monomer aspirator 2 shown in FIG. 2A, the same volume flow of gases is removed by suction through each of the two CD vacuum intake ports 5 and 6 on opposite sides from the spinning zone 4. It can be seen here that the filament bundle spun by the spinneret 1 is not acted upon by the gas streams in its center. The invention is thus based on the discovery that to this extent this embodiment can result in the formation of drips and/or hard pieces on the filaments so thatas described in the introductiondefects and/or flaws result in the spunbond nonwoven web deposited. However, with the suction removal of monomer according to the inventionas can be seen in FIG. 2Ba higher volume flow is removed by suction on one side of the spinning zone 4. In this embodiment, a higher volume flow V.sub.A is removed by suction through the downstream CD vacuum gap 8 as seen in the machine direction MD (outlet side of the spunbond nonwoven web) than through the upstream CD vacuum gap 7 as seen in the machine direction (inlet side of the spunbond nonwoven web). As also shown in FIG. 2B, this results in the fact that even the filaments provided at the center of the spun filament bundle are acted upon by the gas flow. The invention is based on the discovery that this can effectively prevent the formation of drips and hard pieces on the filaments and thus also can prevent formation of defects and/or flaws in the deposited spunbond nonwoven. FIGS. 2A and 2B also show the introduction of cooling air in the cooler 3. The inflowing cooling air here is symbolized by the arrows pointing down.