Making spunbond from continuous filaments

Abstract

Spunbonded nonwoven is made from continuous thermoplastic filaments emitted downwardly by a spinneret in a filament direction. A cooling chamber directly beneath the spinneret receives the filaments from the spinneret and cools the spun filaments with cooling air and has relative to a longitudinally extending machine direction a pair of longitudinal sides extending parallel to the machine direction and a pair of transverse sides extending substantially perpendicular to the machine direction between the longitudinal sides. Respective air-supply manifolds on the transverse sides feed cooling air therefrom into the cooling chamber. The cooling air is extracted from the cooling chamber at the longitudinal sides. A stretcher directly beneath the cooling chamber receives and elongates the cooled filaments, and a device deposits the stretched filaments as a band and conveys the band off in the machine direction.

Claims

1. A method of making spunbonded nonwoven in an apparatus having: a spinneret for downwardly emitting continuous filaments in a filament direction; a cooling chamber directly beneath the spinneret for receiving the filaments from the spinneret and cooling the spun filaments with cooling air and having relative to a longitudinally extending machine direction a pair of longitudinal side walls extending parallel to the machine direction and a pair of transverse side walls extending substantially perpendicular to the machine direction between the longitudinal side walls; respective air-supply manifolds on the transverse side walls; a stretcher directly beneath the cooling chamber for receiving and elongating the cooled filaments; and a device for depositing the stretched filaments as a nonwoven band and conveying the nonwoven band off in the machine direction, the method comprising the steps of: providing each of the side walls with a plurality of openings or gas-permeable regions; feeding cooling air through the openings or gas-permeable regions of at least one of the transverse side walls into the cooling chamber; and extracting cooling air through the openings or gas permeable regions of at least one of the longitudinal side walls out of the cooling chamber.

2. The method defined in claim 1, the cooling air is extracted through both longitudinal side walls.

3. The method defined in claim 1, further comprising: controlling a rate at which the cooling air is extracted through the at least one longitudinal side wall.

4. The method defined in claim 3, wherein the rate is controlled in accordance with a sensed state of the filaments in the cooling chamber.

5. The method defined in claim 4, wherein the cooling air is extracted through both longitudinal side walls and at different rates.

6. A method of making spunbonded nonwoven in an apparatus having: a spinneret for downwardly emitting continuous filaments in a filament direction; a cooling chamber directly beneath the spinneret for receiving the filaments from the spinneret and cooling the spun filaments with cooling air and having relative to a longitudinally extending machine direction a pair of longitudinal side walls extending parallel to the machine direction and a pair of transverse side walls extending substantially perpendicular to the machine direction between the longitudinal side walls; respective air-supply manifolds on the transverse side walls; a stretcher directly beneath the cooling chamber for receiving and elongating the cooled filaments; and a device for depositing the stretched filaments as a nonwoven band and conveying the nonwoven band off in the machine direction, the method comprising the steps of: feeding cooling air through at least one of the transverse side walls into the cooling chamber; extracting cooling air through at least one of the longitudinal side walls out of the cooling chamber; and passing the cooling air extracted through the at least one longitudinal side wall through a monomer extractor and then feeding the air from the extractor back into the chamber through the at least one transverse side wall.

7. The method defined in claim 6, further comprising the step of: providing the longitudinal and transverse side walls each with at least one opening or gas-permeable region through which the cooling air is introduced into or extracted from the cooling chamber.

8. The method defined in claim 7, wherein each of the side walls is formed with a plurality of the openings or gas-permeable regions.

9. The method defined in claim 1, wherein the cooling air is introduced through the transverse side walls at superatmospheric pressure.

10. The method defined in claim 1, wherein the cooling air is extracted through the longitudinal side walls at a rate of 1 to 400 m.sup.3/h.

11. The method defined in claim 1, further comprising the step of: providing an air-conducting element on at least one the longitudinal walls for guiding the extracted cooling air.

12. The method defined in claim 1, further comprising the steps of: drawing monomers with an extractor from between the spinneret and the cooling chamber, and feeding cooling air extracted from least one longitudinal side wall of the cooling chamber into the extractor.

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 section II-II through the object of FIG. 1,

(4) FIG. 3 is cross section through the apparatus of FIG. 1,

(5) FIG. 4 is a perspective view of air-conducting elements on an MD/longitudinal side wall of the apparatus according to the invention,

(6) FIG. 5 is a perspective view of a subassembly of a flow straightener with upstream and downstream flow screens, and

(7) FIG. 6 is a cross section through part of a flow straightener.

SPECIFIC DESCRIPTION OF THE INVENTION

(8) The drawing shows an apparatus according to the invention for making spunbonded nonwoven and that has a spinneret 2 for spinning continuous filaments 1 that are fed into a cooler 3 with a cooling chamber 4 and air supply manifolds 5, 6 provided on two opposite side walls of the cooling chamber 4. The cooling chamber 4 and the air supply manifolds 5, 6 have a long width dimension extending transverse to the machine direction MD and thus in the CD direction of the apparatus, which here is perpendicular to the view plane of FIG. 1. Cooling air is fed from the oppositely situated air supply manifolds 5, 6 into the cooling chamber 4. A flow straightener 18 is provided in each of the two air supply manifolds 5, 6 on the cooling chamber side wall through which the cooling air flows before entering the cooling chamber 4.

(9) A monomer extractor 7 is provided between the spinneret 2 and the cooler 3 and pulls gases occurring during the spinning process from the apparatus. These gases can be monomers, oligomers, or decomposition products and similar substances, for example. The monomer extractor 7 has a fan 22 for extracting the objectionable gases.

(10) The air supply manifolds 5, 6 with their flow straighteners 18 extend transverse to the machine direction MD along CD/transverse side walls 24 of the cooling chamber 4. Cooling air is supplied to the cooling chamber 4 from the air supply manifolds 5, 6 through the CD/transverse walls. According to the invention, cooling air is extracted at the end walls or on MD/longitudinal side walls 25 of the cooling chamber. These cooling-air streams are shown particularly in FIG. 3 by arrows. The discharge of cooling air through the MD/longitudinal side walls 25 will be explained in greater detail below. The end walls or the MD/longitudinal side walls 25 of the cooling chamber 4 are the short side walls of the cooling chamber 4, which are particularly substantially shorter than the CD/transverse walls 24. According to a design variant, side-wall doors 23 are provided on the MD/longitudinal side walls 25 of the cooling chamber 4.

(11) Down in the filament flow direction FS from the cooler 3 is a stretcher 8 in which the filaments 1 are elongated. The stretcher 8 has an intermediate passage 9 that connects the cooler 3 to a tunnel 10 of the stretcher 8. According to an especially preferred 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 tunnel 10 are a closed system. “Closed system” means particularly that, apart from the supply of cooling air in the cooler 3, no further air is fed into this subassembly. This closed system has proven to be particularly advantageous in connection with the inventive extraction of cooling air through the MD/longitudinal side walls 25 of the apparatus.

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

(13) According to a preferred embodiment, each air supply manifold 5, 6 is divided into two compartments 16, 17, from which cooling air of different temperatures can be fed into the cooling chamber 4. In this embodiment, cooling air can be supplied from each of the upper compartments 16 at a temperature T.sub.1, whereas cooling air can be supplied from each of the two lower compartments 17 at a temperature T.sub.2 different from the temperature T.sub.1. The air supply manifolds 5, 6 can also be subdivided into more than two manifold sections 16, 17 that are provided one above the other and from which cooling air of different temperature is advantageously supplied. This subdivision of the air supply manifolds 5, 6 and the inflow of cooling air of different temperatures is also of particular importance in combination with the inventive extraction of cooling air via the MD/longitudinal side walls 25. In this embodiment, very homogeneous edge portions of the deposited nonwoven band are formed, producing a very stable and compact edge of the nonwoven web 14h.

(14) FIGS. 2, 3 and 4 in particular illustrate the inventive extraction of cooling air through the MD/longitudinal side walls 25 of the cooling chamber 4. The cooling-air streams are extracted here transverse to the machine direction MD and thus in the CD direction or substantially in the CD direction. The directions of the flow vectors correspond to the arrows showing the cooling-air streams in the figures. As a result of the features of to the invention, the cooling air is given a preferred direction of flow (in the CD direction) here at the edges, is responsible for the advantages of the invention.

(15) According to one embodiment of the invention, the cooling-air streams extracted through the two MD/longitudinal side walls 25 of the cooling chamber 4 can be set differently. As a result, disruptive manufacturing and assembly tolerances and/or different process air streams or monomer streams can be compensated for in order to achieve a homogeneous deposited nonwoven band. Apart from that, differences between the two edges of the deposited nonwoven band due to unevenness as a result of different heat input through the plastic melt or due to different per-hole throughputs on the spinneret or due to different mixing ratios can be compensated for.

(16) FIG. 4 shows a preferred example of an embodiment of an MD/longitudinal side wall 25 of the cooling chamber 4 serving for inventive extraction of cooling air. Twenty-five angular air-conducting elements 26 that extend over the height of the cooling chamber 4 are provided here on the MD/longitudinal side walls. These air-conducting elements 26 form the edge profiles of the side-wall doors 23 in the embodiment. These air-conducting elements 26 have holes 27 that are distributed vertically along the height of the cooling chamber 4. The extraction of the cooling air on the MD/longitudinal side walls takes place via these holes 27 of the air-conducting elements 26. This extraction can occur passively due to an overpressure in the cooling chamber 4 and/or actively through active extraction of the cooling air, for example by an unillustrated blower. Preferably, extraction of the cooling air takes place over the entire height of the cooling chamber 4. It lies within the scope of the invention for the cooling-air streams that flow out through the holes 27 to be brought together in a conduit and/or in a chamber and regulated, for example by a gate valve. One embodiment is characterized in that the cooling air partial streams that are drawn off on both MD/longitudinal side walls 25 of the cooling chamber 4 are merged, for example in a chamber and/or conduit, and set and/or regulated together particularly using an actuator and/or regulator.

(17) Special inventive significance is given to the combination of the cooling-air discharge through the MD/longitudinal side walls 25 of the cooling chamber 4 with the flow straighteners 18 provided in the air supply manifolds 5, 6 of the cooling chamber 4. The flow straighteners 18 extend over both compartments 16, 17 of each air supply manifold 5, 6. The flow straighteners 18 serve to rectify the cooling-air stream that is incident on the filaments 1. FIG. 5 shows a perspective view of a flow straightener 18 that is more preferably used in the context of the invention. Recommendably, this flow straightener 18 has a plurality of flow passages 19 that are oriented perpendicular to the filament flow FS. These flow passages 19 are advantageously each delimited by passage walls 20 and are preferably straight.

(18) According to a preferred embodiment, the free-flowable open surface area of each flow straightener 18 constitutes greater than 90% of the total area of the flow straightener 18. The ratio of a length L of the flow passages 19 to a 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 here according to FIG. 6, the flow passages 19 of a flow straightener 18 can have a hexagonal or honeycomb cross section. The smallest inner diameter D.sub.i is measured here between opposite side walls of the hexagon.

(19) Recommendably, each flow straightener 18 has a flow screen 21 both on its cooling air inflow side wall ES and on its cooling air outflow side wall AS. The two flow screens 21 of each flow straightener 18 are provided directly upstream or downstream of the flow straightener 18. Recommendably, 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 04 mm, as well as a wire thickness of from 0.05 to 0.35 and preferably from 0.05 to 0.32. It was demonstrated in the foregoing that, according to a preferred embodiment, the free-flowable open surface area of each flow straightener 18 constitutes greater than 90% of the total area of the flow straightener 18. The flow screens are not included in the calculation of the free-flowable open surface area of the flow straightener 18.