MAKING A NONWOVEN FROM FIBERS

Abstract

The invention relates to a method for producing a nonwoven fabric from fibres, wherein the fibres are spun by means of at least one spinneret, are cooled and then deposited on a collection device to form a nonwoven web. The nonwoven web undergoes hot fluid bonding during at least two consecutive bonding steps. In a first bonding step, the surface of the nonwoven web is subjected to a hot fluid and, in a second bonding step, the surface of the nonwoven web is also subsequently subjected to a hot fluid and, in addition and at the same time, surface pressure is exerted on the nonwoven web.

Claims

1. A method of making a nonwoven fabric from thermoplastic fibers, the method comprising the steps of: spinning the fibers with a spinneret; cooling the spun fibers; depositing the cooled fibers on a conveyor to form a nonwoven web; in a first consolidating step applying a hot fluid to a surface of the nonwoven web; in a subsequent second consolidating step applying a hot fluid to the surface of the nonwoven web in a dual-belt furnace; and applying pressure to the surface of the nonwoven web.

2. The method according to claim 1, wherein the surface pressure that is exerted on the nonwoven web occurs with a force of greater than 2 Pa.

3. The method according to claim 1, wherein the fibers are spun as multicomponent, bicomponent segmented pie, or as a mixture of at least two different types of fiber.

4. The method according 3, wherein multicomponent or bicomponent fibers have a component constituting more than 50% by weight by weight of the total fiber and consists of a polyolefin.

5. The method according to claim 1, wherein the first hot-fluid surface consolidating is performed on the conveyor.

6. The method according to claim 1, wherein, in the first consolidating step a fluid temperature is employed that is below a melting point of a highest-melting component of the fibers and at which a lower-melting component of the fibers fuses or melts.

7. The method according to claim 1, further comprising the steps, after passing through the first consolidating step, of: cooling the nonwoven web in a cooling zone; thereafter conveying the cooled nonwoven web through the second consolidating step.

8. The method according to claim 7, further comprising the step of: using a fluid temperature in the second consolidating step or in the dual-belt furnace that lies below a melting point of a highest-melting component of the fibers.

9. The method according to claim 1, wherein in the first consolidating step or in the second consolidating step or in the dual-belt furnace the hot fluid is flowed with an inflow rate of from 0.2 to 15 m/s against the nonwoven web.

10. The method according to claim 1, further comprising the step of: cooling the nonwoven web after passing through the second consolidating step or the dual-belt furnace.

11. The method according to claim 1, further comprising the steps of: electrically charging the nonwoven web after passing through the first and second consolidating steps; and thereafter winding up the electrically charged nonwoven web.

12. The method according to claim 1, wherein the fibers are spun with the spinneret as continuous filaments, the method further comprising the steps of: stretching the continuous filaments a stretcher after cooling in a cooler; depositing the stretched continuous filaments on the conveyor to form the nonwoven web, the conveyor being a mesh conveyor belt.

13. The method according to claim 12, further comprising the step of: passing the continuous filaments through a closed subassembly of the cooler and the stretcher; and excluding from the subassembly any further fluid supply or air supply apart from a supply of the cooling fluid or cooling air in the cooler.

14. An apparatus for making a nonwoven fabric from thermoplastic fibers, the apparatus comprising: a spinneret for spinning fibers; a cooler for cooling the fibers; a conveyor for depositing the fibers to form a nonwoven web; a first consolidating means for surface treating the nonwoven web with a hot fluid or hot air being conveyed on the conveyor belt; and a second consolidating having a dual-belt furnace in which the nonwoven web is passed between two circulating belts or continuous belts and for surface treating the nonwoven web (9) with a hot fluid or hot air and for applying surface pressure can be applied to the nonwoven web at the same time.

15. The apparatus according to claim 14, wherein the first consolidating means comprises a heated tunnel furnace for the surface treatment with a hot fluid or hot air of the nonwoven web being conveyed on the mesh conveyor belt.

16. The apparatus according 14, wherein the conveyor is free of compaction rollers and press rollers between where the fibers are deposited and the first consolidating means.

17. The apparatus according to claim 14, further comprising: an electrical-charge unit for electrically charging the consolidated nonwoven web downstream from the first and second consolidating means.

18. The apparatus according to claim 14, further comprising: a stretcher for stretching the fibers is downstream from the cooler for cooling the fibers, and a diffuser is between the stretcher and the conveyor.

19. The apparatus according to claim 14, wherein the conveyor is a mesh conveyor belt and that between where the fibers are deposited and the first consolidating step there are no compaction or press rollers.

20. A nonwoven fabric made of fibers, by a method according to claim 1, wherein the spun-consolidated nonwoven has a weight per unit area of between 40 and 250 g/m.sup.2 and usable as insulation material and/or packaging material.

Description

[0024] The invention is explained in further detail below with reference to a schematic drawing, which illustrates only one embodiment. In the schematic figures:

[0025] FIG. 1 is a vertical section through the upstream portion of an apparatus according to the invention;

[0026] FIG. 2 is a vertical section through the downstream portion of the apparatus according to the invention,

[0027] FIG. 3 is a large-scale view of the detail shown at A [17] in FIG. 2;

[0028] FIG. 4 is a large scale view of the detail shown at B [23] in FIG. 2; and

[0029] FIGS. 5a, b, c, and d are sections through continuous or bicomponent filaments according to preferred embodiments of the invention.

[0030] The figures show an apparatus according to the invention for making spun-consolidated nonwovens from continuous filaments 1. According to a preferred embodiment of the invention, the continuous filaments 1 are made of thermoplastic and especially preferably of polyolefins. The apparatus shown in FIG. 1 is a spunbond apparatus for making spun-consolidated nonwovens from continuous filaments 1. With the apparatus according to the invention, the continuous filaments 1 are spun by a spinneret 2 and subsequently cooled in a cooler 3. According to a preferred embodiment and here, a monomer extractor 4 for extracting spinning vapors generated in this space is provided between the spinneret 2 and the cooler 3. Recommendably and here, the cooler 3 has two cooling chambers 3a and 3b that are one above the other or in the filament-travel direction in which cooling air of different temperatures is applied to the continuous filaments 1. A stretcher 5 downstream from the cooler 3 in the filament travel direction, and, preferably and here, has an intermediate passage 6 that converges in the direction of flow of the continuous filaments 1 as well as an adjoining stretch passage 7. According to a very preferred embodiment and here, the subassembly composed of the cooler 3 and the stretcher 5 is a closed unit to which no additional air is supplied apart from the cooling fluid or cooling air that is supplied to the cooler 3.

[0031] The continuous filaments 1 are deposited on a conveyor that is a mesh conveyor belt to form the nonwoven web 9. According to a recommended embodiment and here, the continuous filaments 1 are passed between the stretcher 5 and the mesh conveyor belt 8 through at least one diffuser 10, 11. Preferably and here, two successive diffusers 10 and 11 are provided in the flow direction of the continuous filaments 1. Recommendably and here, an ambient air inlet gap 12 is provided for introducing ambient air between the two diffusers 10, 11. Downstream from the diffusers 10, 11, the continuous filaments 1 are deposited on the mesh conveyor belt to form the nonwoven web 9. Preferably and here, the mesh conveyor belt 8 is a continuously circulating mesh conveyor belt 8.

[0032] Preferably and here, the nonwoven web 9 of the continuous filaments 1 that is deposited on the mesh conveyor belt 8 is then passed through the first consolidating step or through the initial hot-fluid consolidating in the form of the tunnel furnace 13 without the use of compaction or press rollers. Preferably and here, a first surface treatment of the nonwoven web 9 with hot air takes place here on the mesh conveyor belt 8. Advantageously and here, hot air is applied from above to the surface of the nonwoven web 9 for this purpose, this hot air preferably having an inflow rate of 1 to 3 m/s and preferably a temperature that is lower than the higher-melting plastic component of the continuous filaments 1. Preferably and here, the first consolidating step or the tunnel furnace 13 has two heating zones 14 and 15 that follow each other in the travel direction of the nonwoven web 9 in which hot air is applied to the nonwoven web 9. Advantageously and here, the heating zones 14 and 15 are followed by a cooling zone 16.

[0033] According to a very preferred embodiment and here, after the first consolidating step or after passing through the tunnel furnace 13, the nonwoven web 9 is introduced into the second consolidating step or into second hot-fluid consolidating, which is instantiated as a dual-belt furnace 17. In this second consolidating step, or in the dual-belt furnace 17, a hot fluid, particularly hot air here, is applied to the nonwoven web 9, and pressure is additionally applied to the surface of the nonwoven web 9 at the same time. Preferably and here, this pressure is applied by a calibration belt 18 that preferably and here is height-adjustable relative to the mesh conveyor belt 8. Advantageously and here, the calibration belt 18 is also a continuous belt. The nonwoven web 9 is clamped, as it were, between the mesh conveyor belt 8 and the calibration belt 18, and a defined pressure is exerted on the nonwoven web 9. At the same time, hot air is applied to the nonwoven web 9 in the dual-belt furnace 17. The nonwoven web 9 is able to be impinged from above and/or from below with hot air. Preferably and here, the inflow rate of the hot air is 1 to 3 m/s, and the temperature of the hot air is advantageously lower than the melting temperature of the higher-melting plastic component of the continuous filaments 1. Recommendably and here, the dual-belt furnace 17 has two heating panels 19 and 20 that direct hot air against the nonwoven web 9. Preferably and here, two cooling panels 21 and 22 follow the heating panels 19 and 20 in the travel direction of the nonwoven web 9. Preferably, the two heating panels 19 and 20 are controlled individually and/or separately. In particular, the cooling panels 21 and 22 are provided for the purpose of cooling the nonwoven web 9 again before electrical charging and interrupting the shrinking process in a defined manner.

[0034] According to a preferred embodiment and here, an electrical-charge unit 23 for electrically charging the nonwoven web 9 is downstream from the second consolidating step, or downstream of the dual-belt furnace 17 in the travel direction. Here, the nonwoven web 9 is electrically charged by a plurality of electrical charging bars 24. A large-scale view of the electrical-charge unit 23 is shown in FIG. 4. Downstream of the electrical-charge unit 23 in the travel direction, the nonwoven web 9 is preferably wound up (not shown in the figures). It also lies within the scope of the invention for a sensor (not shown in the figures) to be provided in a suitable location, for example downstream of the electrical-charge unit 23 in the travel direction, with which the air permeability of the nonwoven web 9 can be determined, particularly online. As a result, errors or deviations from a set point are detected immediately on the nonwoven web 9, and a correction can be made directly by adjusting system parameters.

[0035] FIG. 5[a-c] shows preferred cross-sectional configurations of continuous filaments 1 made by the method according to the invention. FIGS. 5a, b, and c show cross-sectional configurations of bicomponent filaments used in accordance with a recommended embodiment of the invention. The segmented pie configuration shown in FIG. 5a is especially preferred in the context of the invention. In principle, however, the continuous filaments can also have the core/sheath configuration illustrated in FIG. 5b. Here, the first plastic component 25 forms the sheath of the continuous filament 1, and the second plastic component 26 forms the core. Another preferred embodiment is the side-by-side configuration of the continuous filaments 1 shown in FIG. 5c, in which the two plastic components 25 and 26 each fill one half (side) of the cross section. According to an especially preferred embodiment of the invention, the two plastic components 25, 26 are composed of at least one polyolefin, for example polypropylene. FIG. 5d shows cross-sectional configurations of two different continuous filaments 1a, 1b, which are part of a mixture of two different types of filament used according to one embodiment of the invention. The plastics of the two continuous filaments 1a and 1b preferably have different melting points. One of the types of continuous filament 1b can act here as a binder fiber component, in which case these continuous filaments 1b are melted or at least partially melted during consolidating or hot-fluid consolidating.