Method and apparatus for making a nonwoven from crimped filaments

Abstract

A nonwoven web is made by displacing an air-permeable mesh-belt conveyor in a horizontal travel direction and spinning and then depositing crimped continuous filaments as a web at a deposit region on the air-permeable mesh-belt conveyor. A first preconsolidation stage is provided downstream of the deposit region and a second preconsolidation separated by a suction gap from the first stage. Air is drawn air through the web and the conveyor at the deposit region at a first predetermined speed, the first and second consolidation stages at a second and third predetermined speeds, and at the suction gap either not at all or at a fourth predetermined equal to at most substantially less than the second predetermined speed.

Claims

1. An apparatus for making a nonwoven web, the apparatus comprising: an air-permeable deposit conveyor moving in a horizontal travel direction; a spinneret for spinning and depositing continuous filaments as the nonwoven web on a deposit region of the conveyor, whereby the filaments form a nonwoven web thereon and are transported downstream from the deposit region in the direction by the conveyor; a first preconsolidater for a first preconsolidation of the nonwoven web spaced downstream along the conveyor from the deposit region with air at a temperature of 80? C. to 250? C. a second preconsolidater for a second preconsolidation of the nonwoven web spaced downstream by a suction gap along the conveyor from the first preconsolidater by 400 mm to 5200 mm; and a suction device for draws air or process air through the deposit conveyor at the deposit region and/or at the first preconsolidater at a first predetermined speed, at the second preconsolidater at a second predetermined speed, and in the suction gap at a third predetermined speed equal to at most substantially less than the first or the second predetermined speeds.

2. The apparatus according to claim 1, wherein the entire suction gap is formed by the deposit conveyor on which the filaments for the nonwoven web are deposited and on which the first and second preconsolidation takes place.

3. The apparatus according to claim 1, wherein only the first preconsolidater is provided between the deposit region of the filaments and the suction gap.

4. The apparatus according to claim 1, wherein air or process air is sucked through the conveyor at the deposit region at a higher speed than at the first preconsolidater.

5. The apparatus according to claim 1, wherein the first preconsolidater is a hot-air knife.

6. The apparatus according to claim 1, further comprising: a third preconsolidater in the suction gap and movable between a position disengaged from the web and conveyor and a position engaging the web and conveyor and thereby consolidating the web.

7. The apparatus according to claim 6, wherein the third preconsolidater has a pair of compacting rollers one of which is movable between a position engaging the web and a position disengaged from the web, and the other of which is movable between a position engaging the conveyor and a position disengaged from the conveyor.

8. The apparatus according to claim 1, wherein the second preconsolidater is a hot-air oven.

9. The apparatus according to claim 1, wherein the second predetermined speed is lower than the first predetermined speed.

10. A method comprising the steps of: displacing an air-permeable mesh-belt conveyor in a horizontal travel direction; spinning and then depositing crimped continuous filaments each having a crimp of 1.5 to 3.5 loops per centimeter as a web at a deposit region on the air-permeable mesh-belt conveyor by drawing air through the web and the conveyor at the deposit region at a first predetermined speed such that a nonwoven web is formed on the conveyor; preconsolidating the web on the conveyor at a first preconsolidation stage downstream in the direction from the deposit region by drawing air at a temperature of 80? C. to 250? C. through the web and the conveyor at the first preconsolidation stage at a second predetermined speed; preconsolidating the web on the conveyor at a second preconsolidation stage spaced downstream in the direction by a suction gap from the first preconsolidation stage by drawing air through the web at the second preconsolidation stage at a third predetermined speed; and at the suction gap either not drawing air through the web and the conveyor, or drawing air through the web and the conveyor at a fourth predetermined speed equal at most to less than the second predetermined speed.

11. The method according to claim 10, wherein the fourth predetermined speed is less than the third predetermined speed.

12. The method according to claim 10, wherein the fourth predetermined speed is greater than the third predetermined speed.

13. The method according to claim 10, wherein the fourth predetermined speed is less than the second predetermined speed.

14. The method according to claim 10, wherein the fourth predetermined speed is greater or smaller than the third predetermined speed.

15. The method according to claim 10, further comprising the step of; providing in the suction gap a pair of compaction rollers movable into and out of compressive engagement with the web and conveyor for, when engaged, a third preconsolidation of the web.

16. The method according to claim 10, wherein the crimped filaments are bicomponent or multicomponent filaments having an eccentric core-sheath configuration and are each formed by a sheath that has a region of uniform thickness and takes up at least 20% of a filament cross section.

17. An apparatus for making a nonwoven web, the apparatus comprising: an air-permeable deposit conveyor moving in a horizontal travel direction; a spinneret for spinning and depositing continuous filaments as the nonwoven web on a deposit region of the conveyor, whereby the filaments form a nonwoven web thereon and are transported downstream from the deposit region in the direction by the conveyor; a first preconsolidater for a first preconsolidation of the nonwoven web spaced downstream along the conveyor from the deposit region with air at a temperature of 80? C. to 250? C. a second preconsolidater for a second preconsolidation of the nonwoven web spaced downstream by a suction gap along the conveyor from the first preconsolidater by 400 mm to 5200 mm; and a suction device for draws air or process air through the deposit conveyor at the deposit region at a first upstream predetermined speed, at the first preconsolidater at a first downstream predetermined speed that is less than the first upstream predetermined speed, at the second preconsolidater at a second predetermined speed, and in the suction gap at a third predetermined speed equal to at most substantially less than the first or the second predetermined speeds.

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 largely schematic section through an apparatus according to the invention for making a spunbonded nonwoven web;

(3) FIG. 2 is a large-section view of a detail of FIG. 1 at the deposit conveyor and preconsolidaters; and

(4) FIG. 3 is a large-scale cross section through a continuous filament preferably used in the invention and having an eccentric core-sheath configuration.

SPECIFIC DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows an apparatus according to the invention for making a spunbonded nonwoven web 1 from continuous filaments 2 of thermoplastic resin. The apparatus has a spinneret 10 for spinning the continuous filaments 2 that then pass. downward through a cooler 11 having a cooling chamber 12. Preferably and in the embodiment according to FIG. 1, two vertically stacked air-supply manifolds 13 and 14 laterally flank the cooling chamber 12. Air of different temperatures is expediently introduced into the cooling chamber 12 from these air-supply manifolds 13 and 14. As recommended and in the embodiment, a monomer extractor 15 is provided between the spinneret 10 and the cooler 11. This monomer extractor 15 draws toxic gases made during the spinning process from the apparatus. These gases are, for example, monomers, oligomers, or decomposition products and the like.

(6) The cooler 11 is preferably and in this embodiment followed in the filament flow direction by a downstream stretcher 16 that plastically elongates the continuous filaments 2. Preferably and here, the stretcher 16 has an intermediate passage 17 that connects the cooler 11 to a shaft 18 of the stretcher 16. According to a preferred embodiment and here, the subassembly of the cooler 11 and the stretcher 16 or the subassembly of the cooler 11, the intermediate passage 17, and the stretch shaft 18 is a closed assembly and, apart from the supply of cooling air in the cooler 11, entry of further air outside into this subassembly is blocked.

(7) The stretcher 16 is preferably followed in this embodiment in the vertically downward filament flow direction by a diffuser 19 through which the continuous filaments 2 pass. After passing through the diffuser 19, the continuous filaments 2 are preferably and here deposited on a deposit conveyor a mesh belt 20. The mesh belt 20 is preferably and in this embodiment an endlessly rotating mesh belt 20. This mesh belt 20 is expediently foraminous so that suction of process air can take place from below through the mesh belt 20.

(8) According to a preferred embodiment and here, the diffuser 19 has upstream and downstream diffuser walls extending transverse to a machine or travel direction MD and having respective lower diverging diffuser wall portions 21 and 22. These diverging diffuser wall portions 21 and 22 are preferably asymmetrical to the vertical center plane M of the apparatus or the diffuser 19. Appropriately and here, the upstream diffuser wall portion 21 forms a smaller angle ? with the center plane M than the downstream diffuser wall portion 22. It is recommended that the angle ? that the upstream diffuser portion 21 forms with the center plane M is at least 1? smaller than the angle ? that the downstream diffuser wall portion 22 forms with the center plane M. It is within the scope of the invention that the ends of the diverging diffuser wall portions 21 and 22 on at their upper end edges have different spacings e.sub.1 and e.sub.2 from the center plane M of the apparatus or of the diffuser 19. The spacing e.sub.1 of the upper end of the diffuser wall portion 21 upstream to the center plane M is preferred and in this embodiment less than the spacing e.sub.2 of the upper end of the downstream diffuser wall portion 22 to the center plane M. The terms upstream and downstream refer in particular to the horizontal travel direction MD of the mesh belt 20 or to the travel direction of the nonwoven web. According to a preferred embodiment of the invention, the ratio of the spacings e.sub.1:e.sub.2 is 0.6:1 to 0.95:1, preferably 0.65:1 to 0.9:1, and in particular 0.7:1 to 0.9:1. The asymmetrical configuration of the diffuser 19 with respect to the center plane M has proven particularly useful with regard to attaining the object of the invention.

(9) Furthermore, it is within the scope of the invention that two opposite secondary air inlet gaps 24 and 25 are provided at the upper intake end 23 of the diffuser 19, each at an upper end of a respective one of the two diffuser walls 21 and 22. A lower secondary air volume flow can preferably be introduced through the secondary air inlet gap 24 upstream relative to the travel direction of the mesh belt 20 or to the machine direction MD than through the secondary air inlet gap 25 downstream. It is recommended that the secondary air volume flow of the secondary air inlet gap 24 upstream is at least 5%, preferably at least 10% and in particular at least 15% lower than the secondary air volume flow through the secondary air inlet gap 25 downstream. The embodiment with the different secondary air volume flows has proven particularly useful with regard to attaining the object of the invention.

(10) It is within the scope of the invention that at least one suction apparatus (not shown in the figures) is provided that draws air or process air through the mesh belt 20 below the deposit region 26 of the filaments 2 in a main suction region 27. This air or process air is sucked through the mesh belt 20 at a suction velocity v.sub.H. The main suction region 27 is expediently delimited in this embodiment below the mesh belt 20 at an inlet region and in an outlet region of the mesh belt 20 by the upstream and downstream suction partition walls 28.1 and 28.2.

(11) A very recommended embodiment of the invention is characterized in that the lower upper end of the downstream suction partition 28.2 is at a vertical spacing A from the deposit conveyor or the mesh belt 20, this spacing A being preferably 25 mm to 200 mm and particularly preferably 28 mm to 150 mm. As recommended and here, a partition portion or spoiler 30 is connected to the suction partition 28.2 downstream at the upper end. Preferably and here, the spoiler 30 is, as it were, an integral part of the suction partition 28.2 downstream and is an angled partition portion on this suction partition 28.2. The spoiler 30 is expediently an obliquely angled spoiler 30 of planar or substantially planar shape. Preferably and here, the spoiler 30 is angled from the respective suction partition 28.2 facing away from the center plane M of the main suction region 27. It is within the scope of the invention that the upper end of the spoiler 30 is at the above-mentioned spacing A from the deposit conveyor or the mesh belt 20. The preferably provided vertical spacing A and in particular the embodiment with the spoiler 30 is of particular importance with regard to making defect-free nonwoven webs. With this configuration, it is possible for the relatively high suction velocity v.sub.H in the main suction region 27 to decrease gradually and linearly gradually to a lower suction velocity downstream. In this way, disadvantageous blow-back effects on the nonwoven web can be successfully avoided. As a result, nonwoven webs can be made without disruptive filament clumps and thus nonwoven webs with a very homogeneous surface or surface structure.

(12) Preferably and here, in a second suction region 29 downstream of the main suction region 27 air or process air is sucked through the deposit conveyor or through the mesh belt 20 at a suction velocity v.sub.2. This suction velocity v.sub.2 is lower or significantly lower than the suction velocity v.sub.H in the main suction region 27. The preferably provided vertical spacing A and in particular the spoiler 30 thus ensures a gradual, continuous transition of the suction velocities from the high suction velocity v.sub.H in the main suction region to the lower suction velocity v.sub.2 in the second suction region 29.

(13) In particular, FIG. 2 shows a particularly preferred embodiment with respect to the preconsolidaters and to the suction gap 34 at the deposit conveyor or the mesh belt 20. Preferably and here, an upstream hot-air preconsolidater provided in the travel direction downstream of the deposit region 26 of the filaments, is a hot-air knife 31 as recommended in this embodiment. This upstream hot-air preconsolidater or this hot-air knife 31 is, as has been proven and as in this embodiment, above the second suction region 29 where process air is sucked through the mesh belt 20 at the suction velocity v.sub.2. It is recommended that the spacing B between the upstream hot-air preconsolidater or the hot-air knife 31 and the center plane M of the apparatus be 100 mm to 1000 mm, preferably 110 mm to 600 mm, and preferably 120 mm to 550 mm. The spacing B is measured in particular between this center plane M and the first component or structural component of the upstream hot-air preconsolidater or the hot-air knife 31 following it in the travel direction.

(14) A downstream hot-air preconsolidater is downstream of the upstream hot-air preconsolidater or the hot-air knife 31 in the machine direction MD, which is preferred and here is a hot-air oven 32. The horizontal spacing C in the direction MD between the upstream hot-air preconsolidater and the downstream hot-air preconsolidater, or between the hot-air knife 31 and the hot-air oven 32, is expediently 400 mm to 5200 mm and in particular 1100 mm to 4700 mm. At the downstream hot-air preconsolidater or at the hot-air oven 32, a further suction of process air takes place preferably and here through the mesh belt 20, specifically process air is suctioned here at a suction velocity v.sub.3 in a third suction region 33. The individual suction regions below the mesh belt 20 are otherwise preferred and are separated from one another in this embodiment according to FIG. 2 by partitions 35. It is within the scope of the invention that the suction velocity v.sub.3 in the third suction region 33 below the hot-air oven 32 is lower than the suction velocity v.sub.2 in the second suction region 29.

(15) The suction gap 34 according to the invention is between the upstream hot-air preconsolidater and the downstream hot-air preconsolidater. The length L of the suction gap 34 in the machine direction MD is preferably and here at least 80% of the spacing C between the upstream hot-air preconsolidater and the downstream hot-air preconsolidater. According to a recommended embodiment of the invention, no suction of process air takes place in the suction gap 34 through the mesh belt 20, so that the suction velocity v.sub.L is zero or approximately zero here. According to another embodiment, a little suction of process air takes place in the suction gap 34 through the mesh belt 20. The suction velocity v.sub.L in the suction gap 34 is then preferably lower or significantly lower than the suction velocity v.sub.2 in the second suction region 29. According to a recommended embodiment of the invention, the suction velocity v.sub.L is also lower than the suction velocity v.sub.3 in the third suction region 33 below the downstream hot-air preconsolidater.

(16) FIG. 2 also shows a very particularly preferred embodiment of an apparatus according to the invention. In this embodiment, a third preconsolidater can be introduced into the suction gap 34 that is a compacting roller pair 36 in this embodiment according to FIG. 2. An upper compacting roller 37 can, if necessary, be pivoted from above down to the mesh belt 20, while a lower compacting roller 38 is pivoted from below up against the mesh belt 20. With the help of the compacting roller pair 36, the nonwoven web can be compacted in the suction gap 34. If compacting of the nonwoven web is not desired, the compacting roller pair 36 can be spread or swung out again from the region of the mesh belt 20 or the suction gap 34. In this respect, the apparatus according to the invention having the suction gap 34 according to the invention is also distinguished by a high degree of flexibility and variability with regard to the preconsolidation options. The consolidating rollers 37 and 38 expediently each have a diameter Z of 200 mm to 500 mm, preferably of 250 mm to 450 mm. It is within the scope of the invention that the diameters Z of the compacting rollers 37, 38 are not greater than the length L of the suction gap 34 and is expediently smaller than the length L of the suction gap 34. Basically, according to one embodiment, a maintenance catwalk (not shown in the figures) can also be provided at the suction gap 34 that extends transversely to the machine direction MD and ensures easy access to the system components for the maintenance personnel or operating personnel. This embodiment can be provided in particular if there is no suction of process air in the suction gap 34 and if the suction velocity v.sub.L is zero or approximately zero there.

(17) If, according to the embodiment of the invention described above, an upper compacting roller 37 is provided in the suction gap 34, this compacting roller 37 has spacings X and Y from the adjacent hot-air preconsolidaters 31 and 32. It is within the scope of the invention that the spacing X and/or the spacing Y is smaller than the diameter Z of the compacting roller 37. The spacing X is the spacing from the upper compacting roller 37 to the upstream hot-air preconsolidater or to the hot-air knife 31 and the spacing Y is the spacing from the upper compacting roller 37 to the downstream hot-air preconsolidater or the hot-air oven 32. Both spacings X and Y are measured like the length L of the suction gap 34 and the spacing C between the two hot-air preconsolidaters in the machine direction MD and expediently in the horizontal machine direction MD. It is within the scope of the invention that the spacing X between the hot-air knife 31 and the upper compacting roller 37 is 100 mm to 500 mm, preferably 150 mm to 450 mm. Furthermore, it is within the scope of the invention that the spacing Y between the upper compacting roller 37 and the hot-air oven 32 is 50 mm to 1500 mm and preferably 100 mm to 1000 mm.

(18) The filaments or continuous filaments made with the apparatus according to the invention or with the method according to the invention are expediently 2 bicomponent filaments or multicomponent filaments. These are preferably bicomponent filaments or multicomponent filaments with side-by-side configuration or with eccentric core-sheath configuration. In the scope of the invention, bicomponent filaments or multicomponent filaments having an eccentric core-sheath configuration and very particularly preferably having an eccentric core-sheath configuration of the type shown in FIG. 3 are particularly preferred. In FIG. 3, a cross section through a continuous filament 2 having the preferred special core-sheath configuration is shown. In the case of these continuous filaments 2, the sheath 3 has a region of uniform thickness d or a substantially region of uniform thickness d in the filament cross section, preferably in this embodiment over more than 50%, preferably over more than 55% of the filament circumference. Preferably and here, the core 4 of the filaments 2 occupies more than 65% of the filament cross section of the filaments 2. As recommended and here, the core 4, seen in the filament cross section, is of pie-shaped like a segment of a circle. Expediently and here, this core 4 has a circular arcuate peripheral portion 5 and a secantal peripheral portion 6 with regard to its circumference. Preferably and here, the arcuate peripheral portion of the core 4 takes up over 50%, preferably over 55% of the circumference of the core 4. Expediently and here, the sheath 3 of the filaments 2, seen in the filament cross section, is formed outside the sheath region with the region of uniform thickness d in the shape of a segment of a circle. This circular segment 7 of the sheath 3 has, as recommended and here, an arcuate peripheral portion 8 and a linear peripheral portion 9 with regard to its circumference. The thickness d or the average thickness d of the sheath 3 at its part of uniform thickness is preferably 0.5% to 8%, in particular 2% to 10% of the filament diameter D. In this embodiment, the thickness d of the sheath 3 may be at its region of uniform thickness of 0.05 ?m to 3 ?m.