Manufacture of spunbonded nonwovens from continuous filaments

Abstract

A spunbonded nonwovens is made by first spinning thermoplastic continuous filaments and emitting them from a spinneret in a direction and then passing the filaments in the direction through a cooling chamber. Meanwhile cooling air is fed from respective manifolds flanking the chamber into the chamber to cool the filaments and the cooling air is guided into the manifolds through respective manifolds and through respective planar homogenizing elements each having a plurality of openings forming a free open surface area constituting 1 to 40% of the total surface area of the respective planar homogenizing element. The cooling air passes from the planar homogenizing element into the cooling chamber through a flow straightener.

Claims

1. A method of making spunbonded nonwovens comprising the steps of: spinning thermoplastic continuous filaments and emitting them from a spinneret in a direction; passing the filaments in the direction through a cooling chamber; feeding cooling air from respective manifolds flanking the chamber into the chamber to cool the filaments; guiding the cooling air in the manifolds through respective planar homogenizing elements each having a plurality of openings forming a free open surface area constituting 1 to 40% of a total surface area of the respective planar homogenizing element; passing the cooling air from the planar homogenizing elements into the cooling chamber through a flow straightener; and subdividing the flow straightener into a plurality of flow passages oriented transverse to the direction and delimiting the flow passages by passage walls such that the open surface area of the flow straightener is greater than 85% a cross-sectional size of the flow straightener and a ratio of a length of the flow passages to an inner diameter of the flow passages being between 1 and 15, the homogenizing elements of the manifolds being substantially parallel to one another and substantially perpendicular to an air flow direction, at least one of the homogenizing elements of each manifold being spaced upstream in the air-flow direction at least 50 mm from the respective flow straightener and having a surface extending over at least a majority of the respective manifold cross-sectional area.

2. The method defined in claim 1, wherein the cooling air is applied in the chamber to the filaments at an air speed of from 0.15 to 3 m/s.

3. The method defined in claim 1, wherein the cooling air is in a stream at a rate of from 200 to 14000 m.sup.3/h/m to the filaments in the cooling chamber.

4. The method defined in claim 1, further comprising the step of: stretching the filaments in a stretcher extending in the direction from the cooling chamber while blocking air other than the cooling air from entry into a closed system formed by the cooling chamber and the stretcher.

5. The method defined in claim 1, wherein the manifolds each have a vertical height of from 400 to 1500 mm.

6. The method defined in claim 1, further comprising the step of: supplying the cooling air to the manifolds as a plurality of substreams from the respective conduits.

7. The method defined in claim 6, wherein the manifold conduit cross-sectional areas are each 3 to 15 times greater than cross-sectional areas of the respective conduits.

8. The method defined in claim 6, further comprising the step of: subdividing the cooling-air stream into two to five substreams.

9. The method defined in claim 6, further comprising the step of: imparting to the cooling air of at least two of the substreams respective different air speeds or different temperatures or different humidities.

10. The method defined in claim 6, further comprising the step of: subdividing each manifold into at least two manifold sections from which cooling air of different temperature is supplied as two respective substreams.

11. The method defined in claim 6, wherein a cross-sectional area of each conduit increases stepwise in a plurality of stages or continuously to the respective manifold.

12. The method defined in claim 1, wherein each homogenizing element has a plurality of holes with an opening diameter of from 1 to 10 mm.

13. The method defined in claim 1, wherein each homogenizing element is at least one screen or mesh with a plurality of the holes having mesh widths of from 0.1 to 0.5 mm.

14. The method defined in claim 1, wherein a spacing between two adjacent homogenizing elements in the respective manifold is at least 50 mm in the air-flow direction.

15. The method defined in claim 1, wherein a free open surface area of each of the homogenizing elements that are provided one after the other increases in the air-flow direction toward the respective flow straightener.

16. The method defined in claim 1, wherein a surface area of each homogenizing element extends over at least half of a manifold cross-sectional area of the respective manifold.

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 the apparatus according to the invention;

(3) FIG. 2 is a large-scale section through a detail of FIG. 1 showing the cooler of the cooling chamber and the manifolds;

(4) FIG. 3 is a section through a first embedment of a manifold;

(5) FIG. 4 is a view like FIG. 3 of a second embodiment;

(6) FIG. 5 is a section through a split supply conduit with connected manifold;

(7) FIG. 6 is a perspective view of a subassembly of a flow straightener with upstream and downstream flow screen; and

(8) FIG. 7 is a cross section through part of a flow straightener.

SPECIFIC DESCRIPTION OF THE INVENTION

(9) As seen in FIG. 1, an apparatus according to the invention for making spunbonded nonwovens from continuous filaments 1, particularly from continuous thermoplastic filaments 1 has a spinneret 2 for spinning the continuous filaments 1. These spun continuous filaments 1 are emitted into a cooler 3 with a cooling chamber 4 and with two manifolds 5 and 6 that are on opposite sides of the cooling chamber 4. The cooling chamber 4 and the manifolds 5 and 6 extend transverse to the machine direction MD and thus in the CD direction of the apparatus. Cooling air is fed from the oppositely situated manifolds 5 and 6 into the cooling chamber 4.

(10) Preferably and in this embodiment, a monomer extractor 7 is provided between the spinneret 2 and the cooler 3. With this monomer extractor 7, objectionable gases generated by the spinning process can be removed from the apparatus. These gases can be monomers, oligomers, or decomposition products and similar substances, for example.

(11) In the filament flow direction FS, the cooler 3 is followed by a stretcher 8 in which the filaments 1 are elongated. Preferably and in this embodiment, the stretcher 8 has an intermediate passage 9 that connects the cooler 3 to a stretch tunnel 10 of the stretcher 8. According to an especially preferred embodiment and in this embodiment, the subassembly of the cooler 3 and the stretcher 8 and/or the subassembly of the cooler 3, the intermediate passage 9, and the stretch tunnel 10 are a closed system. “Closed system” means particularly that, apart from the supply of cooling air into the cooler 3, no further air supply takes place in this subassembly.

(12) Preferably and in this embodiment, a diffuser 11 through which the filaments 1 are guided extends from the stretcher 8 in the direction of filament flow FS. According to a recommended embodiment, and in this embodiment, secondary air inlet gaps 12 are provided between the stretcher 8 and/or between the stretch tunnel 10 and the diffuser 11 for introducing secondary air into the diffuser 11. Preferably and in this embodiment, after passing through the diffuser 11, the filaments are deposited on a deposition device, here a mesh belt 13. The filament deposition or the nonwoven web 14 is then conveyed or transported away by the mesh belt 13 in the machine direction MD. Advantageously and in this embodiment, an extractor for sucking air or process air through the mesh belt 13 is provided beneath the deposition device or beneath the mesh belt 13. For this purpose, an aspiration zone 15 is preferably provided beneath the mesh belt 13 and, in this embodiment, beneath the diffuser outlet. Preferably, the aspiration zone 15 extends at least over the width B of the diffuser outlet. Recommendably and in this embodiment, the width b of the aspiration zone 15 is greater than the width B of the diffuser outlet.

(13) According to a preferred embodiment, and in this embodiment, each manifold 5 and 6 is divided into two manifold sections 16 and 17 from which cooling air of different temperatures can be fed. In this embodiment, cooling air can be supplied from each of the upper manifold sections 16 at a temperature T.sub.1, whereas cooling air can be supplied from each of the two lower manifold sections 17 at a temperature T.sub.2 different from the temperature T.sub.1.

(14) According to a preferred embodiment, and in this embodiment, a flow straightener 18 is provided in each manifold 5 and 6 on the cooling chamber side that, preferably and in this embodiment, extends over both manifold sections 16 and 17 of each manifold 5 and 6. The two flow straighteners 18 serve to rectify the cooling air flow incident on the filaments 1. The flow straighteners will be addressed in further detail below.

(15) According to the invention, at least one conduit 22 for feeding the cooling air is connected to each manifold 5 and 6. These conduits 22 each have a cross-sectional area Q.sub.Z that is enlarged to a cross-sectional area Q.sub.L of the manifold 5 and 6 when the cooling air passes into the manifold 5 and 6. The downstream cross-sectional area Q.sub.L is preferably at least three times as large and preferably at least four times as large as the upstream cross-sectional area Q.sub.Z of the conduit 22. It lies within the scope of the invention for the cross-sectional area Q.sub.Z of the conduit 22 to be increased to 3 to 15 times the cross-sectional area Q.sub.L of the manifold 5 and 6.

(16) It also lies within the scope of the invention for at least one planar element 23 in each manifold 5 and 6 to homogenize the cooling air flow introduced into the manifolds 5 and 6. Advantageously, at least one planar homogenizing element 23 is provided in each manifold section 16 and 17 of the manifolds 5 and 6. According to an especially preferred embodiment, the homogenizing elements 23 are perforated, particularly a perforated plate 24 with a plurality of holes 25 and/or a homogenizing screen 26 with a plurality or a multitude of meshes 27. According to an especially preferred embodiment of the invention, and in this embodiment, a plurality of homogenizing elements 23 are provided successively and spaced apart from one another in each manifold 5 and 6 or in each manifold section 16 and 17 at a spacing from the flow straightener 18 in the air-flow direction. Recommendably and in this embodiment, the spacing a.sub.1 between the flow straightener 18 and the homogenizing element 23 that is closest to the flow straightener 18 is at least 50 mm, preferably at least 100 mm. The mutual spacing a.sub.x between two homogenizing elements 23 that are provided successively in a manifold 5 and 6 or in a manifold section 16 and 17 in the flow direction is also at least 50 mm, preferably at least 100 mm.

(17) According to the invention, the free open surface area of a planar homogenizing element 23 that can be flowed through freely by the cooling air constitutes 1 to 40%, preferably 2 to 35%, and more preferably 2 to 30% of the total surface area of the planar homogenizing element 23. According to one design variant, the free open surface area of a planar homogenizing element 23 is 2 to 25%, advantageously 2 to 20%, and particularly 2 to 15%. Especially preferably and in this embodiment, the free open surface or the surface area of the successively provided homogenizing elements 23 through which the cooling air flows freely increases from homogenizing element 23 to homogenizing element 23 toward the respective flow straightener 18 or toward the cooling chamber 4. Advantageously and in this embodiment, the surface of a homogenizing element 23 also extends over the entire cross-sectional area Q.sub.L of the respective manifold 5 and 6 or of the respective manifold section 16 and 17.

(18) Each of FIGS. 3 and 4 shows a section through a manifold 5. Instead of for an entire manifold 5 and 6, the illustration can also be used for only one manifold section 16 and 17 of the manifolds 5 and 6. In this embodiment according to FIG. 3, the upstream cross section Q.sub.Z of the conduit 22 increases immediately and without gradation to the downstream cross-sectional area Q.sub.L of the manifold 5. Four homogenizing elements 23 are provided in this manifold 5 spaced in the air-flow direction upstream from the flow straightener 18. In this embodiment, the homogenizing element 23.0 is located in a transitional region between the conduit 22 and the manifold 5 and extends only over the cross section Q.sub.Z of the conduit 22. The other homogenizing elements 23.1, 23.2, and 23.3 are each provided in the manifold 4 at a spacing from one another and at a spacing from the flow straightener 18. They extend over the complete cross section Q.sub.L of the manifold 5. The following table shows exemplary typical parameters for the homogenizing elements 23.0 to 23.3 according to FIG. 3, namely for a system width (in the CD direction) of 1000 mm in each case. The left column of the tables first lists the vertical height h of the homogenizing elements 23 in mm, followed by the total area of each homogenizing element 23 next to that, and the two columns to the right indicate the free open surface area, or the surface area through which the cooling air can flow freely, in percent and in mm.sup.2. The relative free surface area is calculated using the following formula: Cross-sectional area of the homogenizing element×open surface area of the homogenizing element/surface area of the outflow cross section in the vicinity of the straightener. For the homogenizing elements 23.1, 23.2, and 23.3, the relative free surface area (in percent) thus coincides with the free open surface area (in percent). Just for the homogenizing element 23.0 with the cross-sectional area corresponding to the conduit 22, this yields a relative free surface area of only 1%. The spacing a (in mm) corresponds to the spacing a of the individual homogenizing elements 23 from the flow straightener 18. The integral value in the last column corresponds to the area below the curve when plotting the relative free surface area of the homogenizing elements 23 over the spacing a of these homogenizing elements 23 from the flow straightener 18.

(19) TABLE-US-00003 Relative Height Free open free Spacing H Surface surface area surface a Element mm mm2 % mm2 % mm Integral 23.0 350 350000  4% 14000  3% 1200 23.1 500 500000  6% 30000  6%  800 17.6 23.2 500 500000  8% 40000  8%  600 14 23.3 500 500000 10% 50000 10%  400 18 Sum: 49.6

(20) The height H of the manifold 5 according to FIG. 3 may be 500 mm in this embodiment, and the length l of the manifold 5 from the flow straightener 18 to the mouth of the conduit 22 may be 1000 mm. According to an especially preferred embodiment of the invention, the sum of the integral values explained above is greater than 45, preferably greater than 50, and more preferably greater than 65.

(21) FIG. 4 shows a second embodiment of a manifold 5 according to the invention. Here as well, four homogenizing elements 23.0 to 23.3 are used. In contrast to the embodiment according to FIG. 3, however, a stepped enlargement of the cross section Q.sub.Z of the conduit 22 to the total cross section Q.sub.L of the manifold 5 takes place here. This stepped expansion advantageously takes place in a cuboid-shaped manifold 5 over all four walls toward the flow straightener 18. Apart from the differences due to the stepped cross-sectional enlargement, the dimensions in this embodiment according to FIG. 4 correspond to the dimensions in this embodiment according to FIG. 3. Analogously to the table in relation to FIG. 3, the parameters for the embodiment of FIG. 4 are listed in the following table:

(22) TABLE-US-00004 Relative Height Free open free Spacing H Surface surface area surface a Element mm mm2 % mm2 % mm Integral 23.0 350 300000  3%  9000  2% 1000 23.1 400 400000  6% 24000  5%  800 6.6 23.2 450 450000  8% 36000  7%  600 12 23.3 500 500000 10% 50000 12%  300 28.8 Sum: 47.4

(23) FIG. 5 illustrates the connection region of a curved conduit 22 to the manifold 5. According to this embodiment, segmentation elements 28 are provided in the conduit 22 that split the conduit 22 into individual line segments. By virtue of this segmentation or vaning of the conduit section, an additional equalization of the cooling air flow can be achieved. In particular, the cooling air flow here is subjected here to a pre-equalization and is thus prepared for further equalization or homogenization, as it were, in the manifold 5.

(24) FIG. 6 shows a perspective view of a flow straightener 18 that is preferably used in the context of the invention. The flow straighteners 18 serve to rectify the cooling air flow that is incident on the filaments 1. Recommendably and in this embodiment, each flow straightener 18 has a plurality of flow passages 19 for this purpose that are oriented perpendicular to the direction of filament flow FS. These flow passages 19 are each delimited by passage walls 20 and are preferably straight. According to a preferred embodiment, and in this embodiment, the free or open surface area of each flow straightener 18 constitutes greater than 90% of the total area of the flow straightener 18. Advantageously and in this embodiment, the ratio of the length L of the flow passages 19 to the smallest inner diameter D.sub.i of the flow passages 19 lies in the range between 1 and 10, advantageously in the range between 1 and 9. As an example, and in this embodiment according to FIG. 7, the flow passages 19 of a flow straightener 18 can have a hexagonal or honeycomb-shaped cross section. The smallest inner diameter D.sub.i is measured here between opposite sides of the hexagon.

(25) According to a preferred embodiment, and in this embodiment, each flow straightener 18 has a flow screen 21 both on its cooling-air intake side ES and on its cooling-air output side AS. Preferably and in this embodiment, the two flow screens 21 of each flow straightener 18 are provided directly in front of or behind the flow straightener 18. In that regard, the flow screens 21 are to be distinguished from the homogenizing elements 23 that are homogenizing screens 26. Recommendably and in this embodiment, the two flow screens 21 of a flow straightener 18, more particularly the surfaces of these flow screens 21 are aligned perpendicular to the longitudinal direction of the flow passages 19 of the flow straightener 18. It has proven advantageous for the flow screen 21 to have mesh sizes of from 0.1 to 0.5 mm and preferably from 0.1 to 0.4 mm, as well as a wire thickness of from 0.05 to 0.35 and preferably from 0.05 to 0.32