METHOD AND APPARATUS FOR MAKING NONWOVEN FABRIC OF CRIMPED SYNTHETIC FIBERS

Abstract

A method for producing a nonwoven fabric made of crimped synthetic fibers, wherein the synthetic fibers are spun and are deposited on a conveyor as a nonwoven web. The deposited nonwoven web is pre-bonded by means of at least one first hot-air bonding device, wherein a main suction air is sucked from below through the conveyor in the area of fiber deposition. A first suction air is sucked from below through the conveyor in the region of the first hot-air bonding device. The air speed of the main suction air is greater than the air speed of the first suction air.

Claims

1-21. (canceled)

22. A method of making a nonwoven fabric of crimped synthetic filaments, the method comprising the steps of: spinning the synthetic filaments; depositing the spun filaments on a conveyor at a deposition location as a nonwoven web; drawing main suction air down through the web and the conveyor at a main suction-air speed at the deposition location; and prebonding the deposited nonwoven web with a first hot-air bonding device downstream in a travel direction of the conveyor from the deposition location by blowing first hot air down at the web on the conveyor at a first hot-air speed smaller than the main suction-air speed and simultaneously drawing air down through the conveyor and web beneath the first hot-air bonding device at a first suction-air speed smaller than the main suction-air speed and equal to or greater than the first hot-air speed.

23. The method according to claim 22, wherein the nonwoven web is a spunbond and the filaments are continuous, the method further comprising the steps between the steps of spinning and deposition of: cooling the spun filaments, stretching the cooled spun filaments.

24. The method according to claim 22, wherein the filaments are bicomponent or multicomponent and at least partially formed of polyolefin.

25. The method according to claim 22, wherein the filaments are spun with side-by-side configuration or with an eccentric core-sheath configuration.

26. The method according to claim 22, further comprising the step of: drawing second suction air down through the web and conveyor between the deposition location and the first hot-air bonding device at a second suction-air speed smaller than the main suction-air speed and greater than the first suction-air speed.

27. The method according to claim 22, further comprising the step of: bonding the deposited nonwoven web on the conveyor with a second hot-air bonding device downstream of the first hot-air bonding device by blowing second hot air down at the web on the conveyor at a second hot-air speed.

28. The method according to claim 27 wherein the first hot-air speed is greater than the second hot-air speed.

29. The method according to claim 27, wherein the first hot air has a higher temperature than the second hot air.

30. The method according to claim 27, wherein the first hot-air bonding device has a smaller air treatment area measured in the travel direction than the second hot-air bonding device.

31. The method according to claim 27, further comprising the step of: drawing third suction air down through the web and the conveyor beneath the second hot-air bonding device at a third suction-air speed smaller than the second suction-air speed.

32. The method according to claim 27, wherein the main suction-air speed and the first suction-air speed are each greater than the third suction-air speed.

33. The method according to claim 27, further comprising the step of: drawing fourth suction air down through the web and the conveyor between the first hot-air bonding device and the second hot-air bonding device at a fourth suction-air speed that is less than the first suction-air speed and greater than the third-suction air speed.

34. The method according to claim 27, further comprising the step of: heating the second hot air to between 80° C. and 180° C.

35. The method according to claim 27, wherein the first bonding device and the second bonding device precompact the web, the method further comprising the step of: finally consolidating the web with hot air downstream in the travel direction of the second bonding device.

36. The method according to claim 22, wherein the conveyor displaces the web in the travel direction at a speed of more than 120 m/min.

37. The method according to claim 22, further comprising the steps, after forming a first nonwoven web according to the steps of claim 22 of forming a second nonwoven web according to the steps of claim 22; and laminating the second web onto the first web.

38. The method according to claim 22, wherein the nonwoven web has downstream of the second bonding device a bulk density of at most 0.06 g/cm.sup.3 and a strength of more than 0.6 (N/5 cm)/(g/m.sup.2) .

39. An apparatus comprising: a conveyor moving in a travel direction; means for spinning the synthetic filaments; means for cooling the spun filaments; means for stretching the cooled filaments and for depositing the stretched filaments at a deposition location on the conveyor as a nonwoven web, the cooling and stretching means being a closed subassembly into which air entry is blocked except for cooling air; first means for drawing main suction air down through the web and the conveyor at the deposition location; a first hot-air prebonding device for prebonding the deposited nonwoven downstream in a travel direction of the conveyor from the deposition location by blowing first hot air down at the web on the conveyor; means beneath the hot-air prebonding device for drawing air down through the conveyor and web; and second means for drawing second suction air down through the web and the conveyor between the deposition location and the first hot-air prebonding device.

40. The apparatus according to claim 39, further comprising: a diffuser between the stretcher and the conveyor.

Description

[0038] The invention is explained in detail hereinafter by means of drawings showing merely one exemplary embodiment. In schematic view:

[0039] FIG. 1 shows a vertical section through an apparatus according to the invention for carrying out the method according to the invention, [0040] FIG. 2 shows a section from FIG. 1 in the region of the foraminous deposition belt, [0041] FIG. 3 shows the subject matter according to FIG. 2 in a different embodiment, [0042] FIG. 4 shows the subject matter according to FIG. 2 in a further embodiment, [0043] FIG. 5 shows the apparatus according to the invention in the form of a multibeam system for producing a nonwoven web laminate from a plurality of spunbond webs,

[0044] The figures show an apparatus according to the invention for carrying out the method according to the invention for producing a nonwoven web 14 in the form of a spunbond web made of crimped continuous filaments 1. These are crimped synthetic continuous filaments 1 which preferably and in the exemplary embodiment are formed as bicomponent filaments. It lies within the framework of the invention in this case that each of the two components comprises a polyolefin or consists of a polyolefin or substantially consists of a polyolefin. Preferably one component is a polypropylene and the other component is a polyethylene.

[0045] FIG. 1 show a very preferred embodiment of such an apparatus. This apparatus comprises a spinneret 2 for spinning the continuous filaments 1. The spun continuous filaments 1 are introduced into a cooling device with a cooling chamber 4 and with air supply cabins 5, 6 arranged on two opposite sides of the cooling chamber 4. The cooling chamber 4 and the air supply cabins 5, 6 extend transversely to the machine direction MD and therefore in the CD direction of the apparatus. Cooling air is introduced into the cooling chamber 4 from the opposite air supply cabins 5, 6.

[0046] According to a preferred embodiment and in the exemplary embodiment, each air supply cabin 5, 6 is divided into two cabin sections 16, 17 from which cooling air at different temperature is supplied in each case. In the exemplary embodiment cooling air at a first temperature can be supplied in each case from the upper cabin sections 16 whilst cooling air at a second temperature different from the first temperature can be supplied in each case from the two lower cabin sections 17. The division of the air supply cabins 5, 6 or the cooling chamber 4 into two has importance within the framework of the invention. It has been shown that the technical problem according to the invention can be solved particularly effectively and reliably with such a two-part or multipart cooling chamber.

[0047] In the filament flow direction FS a stretching device 8 is located downstream of the cooling device 3, by means of which the continuous filaments 1 are stretched. The stretching device 8 preferably and in the exemplary embodiment has an intermediate channel 9 which connects the cooling device 3 to a stretching shaft 10 of the stretching device 8. A particularly recommended embodiment of the invention is characterized in that the aggregate of the cooling device 3 and the stretching device 8 or the unit of the cooling device 3, the intermediate channel 9 and the stretching shaft 10 is configured as a closed system. Closed system means in this case in particular that apart from the supply of cooling air in the cooling device 3 there is no further supply of air in this aggregate. Accordingly the apparatus in FIG. 1 is constructed.

[0048] It has been proven and in the exemplary embodiment in the filament flow direction FS the stretching device 8 is followed by a diffuser 11 through which the continuous filaments 1 are guided. According to a preferred embodiment and in the exemplary embodiment, secondary air inlet gaps 12 for introducing secondary air into the diffuser 11 are provided between the stretching device 8 or between the stretching shaft 10 and the diffuser 11. This introduction of secondary air also has particularly advantageous importance within the framework of the invention. Instead of merely one diffuser 11 in FIG. 1, for example two diffusers 11 can also be arranged consecutively or above one another in the filament flow direction FS of the continuous filaments 1. A very recommended embodiment is characterized in that the distance between the diffuser 11 arranged directly above the foraminous deposition belt 13 and the foraminous deposition belt 13 can be adjusted. This adjustment of the distance between the lower edge of the diffuser 11 and the foraminous deposition belt 13 also has importance within the framework of the invention. Preferably the distance between the lower edge of the diffuser 11 and the foraminous deposition belt 13 is between 5 mm and 150 mm.

[0049] After running through the diffuser 11, the continuous filaments 1 are preferably and in the exemplary embodiment deposited on a conveyor configured as foraminous deposition belt 13. The foraminous deposition belt 13 is recommendedly and in the exemplary embodiment designed as a continuously circulating foraminous deposition belt 13. The filament deposition or the nonwoven web 14 is conveyed away or removed in the machine direction MD.

[0050] FIG. 2 shows a first preferred embodiment of the apparatus according to the invention. The deposited nonwoven web is here precompacted using a (first) hot-air bonding device 7. In this case, the nonwoven web 14 is acted upon from above by (first) hot air by means of the (first) hot-air bonding device 7 and thereby precompacted. This (first) hot air 15 is preferably adjustable with respect to its temperature and/or with respect to its air speed v.sub.VH1. It is recommended and in the exemplary embodiment that the angle of the first hot-air bonding device 7 or the angle of the (first) hot air 15 with respect to the nonwoven web 14 or with respect to the foraminous deposition belt 13 is adjustable.

[0051] According to the invention, in the area 18 of fiber deposition a main suction air 19 is sucked through the foraminous deposition belt 13. Furthermore, according to the invention in the area of the (first) hot-air bonding device 7 a first suction air 20 is sucked through the foraminous deposition belt 13 or through the nonwoven web 14 resting on the foraminous deposition belt 13. For suction of the air flows, expediently fans 21, 22 are provided underneath the foraminous deposition belt 13.

[0052] It lies within the framework of the invention that the air speed v.sub.M of the main suction air 19 is greater than the air speed v.sub.1 of the first suction air 20. Furthermore the air speed v.sub.M of the main suction air 19 is preferably and in the exemplary embodiment greater than the air speed v.sub.H1 of the (first) hot air 15. According to one embodiment the air speed v.sub.M is between 10 m/s and 25 m/s and speed v.sub.H1 of the (first) hot air is between 1,5 m/s and 3 m/s. It is recommended and in the exemplary embodiment that the air speed v.sub.1 of the first suction air 20 is greater than the air speed v.sub.H1 of the (first) hot air 15.

[0053] Preferably and in the exemplary embodiment of FIG. 2, a second suction air 23 is sucked between the suction of the main suction air 19 and the suction of the first suction air 20. Expediently the air speed v.sub.2 of this second suction air 23 is lower than the air speed v.sub.M of the main suction air 19 and preferably greater than the air speed v.sub.1 of the first suction air 20. According to a preferred embodiment the air speed v.sub.2 of the second suction air 23 is in the range of 2-13 m/s, more preferably in the range of 3-12 m/s. In the lower region of FIG. 2 an air speed profile is shown in which the respective air speed v of the air sucked through the nonwoven web 14 and through the foraminous deposition belt 13 with the aid of the fans 21, 22 is shown as a function of the respective location in the conveying direction. It can be seen that the air speed v below the area 18 of fiber deposition is greatest and then decreases as far as the hot-air bonding device 7. Thus, a reduction in speed from the air speed v.sub.M of the main suction air 19 via the air speed v.sub.2 of the second suction air 23 to the air speed v.sub.1 of the first suction air 20 can be observed. The suction areas of the air flows 19, 23, 20 are preferably and in the exemplary embodiment delimited by dividing walls 29 or separated from one another. According to a preferred embodiment of the invention, these dividing walls 29 are adapted to be adjustable or settable and in this way influence is exerted on the suction or on the suction air speeds.

[0054] FIG. 3 shows a further embodiment of the apparatus according to the invention. Firstly the components and air flows as far as the first hot-air bonding device 7 are implemented as in the embodiment according to FIG. 2. In addition, in this embodiment according to FIG. 3 a second hot-air bonding device 24 is provided which preferably and in the exemplary embodiment is configured as a hot air oven. Both hot-air bonding devices 7 and 24 are used for precompaction of the nonwoven web 14. After these two precompactions the nonwoven web 14 is preferably subjected to a final solidification which was not shown in FIG. 3. Expediently this final solidification of the nonwoven web 14 is also accomplished by means of hot air. In the second hot-air bonding device 24 the nonwoven web 14 is precompacted by means of a second hot air 25 acting on the surface of the nonwoven web 14. This second hot air 25 has an air speed v.sub.H2. It lies within the framework of the invention that the air speed v.sub.H1 of the first hot air 15 of the first hot-air bonding device 7 is greater than the air speed v.sub.H2 of the second hot air 25 of the second hot-air bonding device 24. According to a preferred embodiment the air speed v.sub.H2 of the second hot air 25 is at least 20% below the air speed v.sub.H1 of the first hot air 15. Preferably and in the exemplary embodiment furthermore the first hot air 15 of the first hot-air bonding device 7 has a higher temperature than the second hot air 25 of the second hot-air bonding device 24. According to a recommended embodiment and in the exemplary embodiment according to FIG. 3, the first hot-air bonding device 7 has a narrower air treatment region 26 when viewed in the conveying direction of the nonwoven web 14 than the second hot-air bonding device 24. It is recommended that the width of the air treatment region 26 of the first hot-air bonding device 7 viewed in the conveying direction of the nonwoven web 14 is between 35 and 110 mm. According to a preferred embodiment 5 the width of the air treatment region of the second hot air bonding device 24 viewed in the conveying direction of the nonwoven web 14 is between 110 and 1100 mm.

[0055] Preferably and in the exemplary embodiment a third suction air 27 is sucked through the nonwoven web 14 or through the foraminous deposition belt 13 underneath the second hot-air bonding device 24. This third suction air 27 has an air speed v.sub.3 which preferably and in the exemplary embodiment is lower than the air speed v.sub.H2 of the second hot air 25. According to a recommended embodiment and in the exemplary embodiment, furthermore the air speed v.sub.M of the main suction air 19 and the air speed v.sub.1 of the first suction air 20 are each greater than the air speed v.sub.3 of the third suction air 27.

[0056] In FIG. 3 it can also be identified that according to a preferred embodiment and in the exemplary embodiment, between the first hot-air bonding device 7 and the second hot-air bonding device 24 a fourth suction air 28 is sucked through the nonwoven web 14 and through the foraminous deposition belt 13. This fourth suction air 28 has an air speed v.sub.4. Expediently this air speed v.sub.4 of the fourth suction air 28 is lower than the air speed v.sub.1 of the first suction air 20 and greater than the air speed v.sub.3 of the third suction air 27. According to a preferred embodiment the air speed v.sub.4 of the fourth suction air 28 is smaller than 3 m/s, more preferably smaller than 2 m/s. In the lower region of FIG. 3 a preferred air speed profile is shown which in turn shows the air speed v as a function of the location underneath the conveyor or the foraminous deposition belt 13. It can be seen that according to a preferred embodiment and in the exemplary embodiment, the air speed v decreases from the air speed v.sub.M of the main suction air 19 towards the air speed v3 of the third suction air 27. It is also shown in FIG. 3 that the individual suction areas—as in the exemplary embodiment of FIG. 2—are again separated from one another by dividing walls 29. It is recommended and in the exemplary embodiment that these dividing walls 29 are provided to be adjustable so that the suction cross-section of the individual suction air flows can be varied and thus the suction or the suction speed can be varied. This adjustment possibility has proved particularly successful within the framework of the invention. The suction or the suction speeds can furthermore also be controlled and/or regulated via the fans 21, 22.

[0057] FIG. 4 shows a further recommended embodiment of the invention. This embodiment differs from the embodiment according to FIG. 3 merely in that the second hot-air bonding device 24 is here not configured as a hot air oven but like the first hot-air bonding device 7 as a hot air knife. Both hot-air bonding devices 7, 24 or both hot air knives are provided for the precompaction of the nonwoven web 14. Expediently here after the two precompactions, a final solidification of the nonwoven web 14—not shown in FIG. 4—takes place, which is preferably carried out with hot air.

[0058] The air speed profiles in FIGS. 2, 3 and 4 show that the air speed v of the sucked air decreases or decreases continuously from the area 18 of fiber deposition in the conveying direction. As a result of this adjustment of the air speeds v according to the invention, negative blow-back effects onto the nonwoven web 14 can be avoided which particularly occur in transition regions between different suctions or in transition regions between different air flows. The invention is in this respect based on the finding that a defect-free homogeneous nonwoven web 14 can be produced with the measures according to the invention.

[0059] FIG. 5 illustrates a preferred embodiment of an apparatus according to the invention for producing a multilayer nonwoven web 14 made of a plurality of spunbond webs S, in the exemplary embodiment of three spunbond webs S1, S2 and S3. In order to produce the individual spunbond webs S for the multilayer nonwoven web 14, in each case a spinning beam or a spinneret 2 is used for spinning the respective continuous filaments 1. In this case, in order to produce each spunbond web 51, S2 and S3, in each case a spunbond apparatus explained above is used. After deposition of each spunbond web S1, S2 and S3, a pre-compaction takes place in each case with two hot-air bonding devices 7, 24 in the form of hot air knives. The air flows and air speeds preferably each correspond to those which were explained in connection with FIGS. 3 and 4. Each spunbond web S1, S2 and S3 therefore undergoes a double precompaction with the hot-air bonding devices 7, 24 after deposition on the foraminous deposition belt 13. Only after a laminate made of the three spunbond webs Si, S2 and S3 has been completed does a final solidification then preferably take place with a final solidification device 30.