MAKING A NONWOVEN FABRIC FROM FIBERS

Abstract

Method for producing a nonwoven fabric from fibres. Continuous filaments are produced from thermoplastic material by at least one meltblown spinneret. Chopped pulp fibres are also produced by at least one pulping device. In the pulping device, at least one chopped-fibre/air stream is produced from the chopped pulp fibres, is passed through and discharged from an outlet channel and flows with an initial volumetric flow V1 and a flow direction S1 in the direction of an air-permeable depositing screen belt. The continuous filaments flow from the at least one meltblown spinneret as a filament/air stream with an initial volumetric flow V2 in the direction of the chopped-fibre/air stream. The filament/air stream and the chopped-fibre/air stream are brought together above the depositing screen belt in a contact zone and deposited as a mixture of continuous filaments and chopped fibres in a depositing region on the depositing screen belt to form the nonwoven fabric or nonwoven web. In the depositing region of the fibres or of the mixture of continuous filaments and chopped fibres, air or process air is sucked through the depositing screen belt from below with a volumetric flow V4. The volumetric flow V4 is greater than the sum of the volumetric flows V1 and V2.

Claims

1. A method of making a nonwoven fabric from fibers, the method comprising the steps of: making continuous filaments of thermoplastic material by a meltblow spinneret; making pulp short fibers by a defibrator in which a short-fiber/air stream is made from the pulp short fibers and is guided through an outlet passage and emerges therefrom and flows with an initial volume flow V1 and a flow direction S1 toward an air-permeable foraminous deposition belt; flowing the continuous filaments from the meltblow spinneret as a filament-air stream with an initial volume flow V2 toward the short-fiber/air stream, combining the filament-air stream and the short-fiber/air stream above the foraminous deposition belt in a contact zone and depositing the combined streams as a continuous-filament/short-fiber mixture in a deposition zone on the foraminous deposition belt to form the nonwoven fabric; and aspirating air or process air with a volume flow V4 greater than the sum of the volume flows V1 and V2 from below through the foraminous deposition belt in the deposition zone of the fibers or of the continuous-filament/short-fiber mixture.

2. The method according to claim 1, wherein two meltblow spinnerets are provided and continuous filaments flow from the second meltblow spinneret as a second filament-air stream with an initial volume flow V3 to toward the short-fiber/air stream, the volume flow V4 is greater than the sum of the volume flows V1, V2, and V3, and the filament-air stream in the travel direction of the foraminous deposition belt flows upstream of the short-fiber/air stream and the second filament-air stream flows in the travel direction of the foraminous deposition belt flows downstream of the short-fiber/air stream.

3. The method according to claim 1, wherein the filament-air stream flows with respect to its flow direction S2 at least in regions or sections at an angle ?1 to the flow direction S1 of the short-fiber/air stream, the second filament-air stream flows with respect to its flow direction S3 at least in regions or sections at an angle ?2 to the flow direction S1 of the short-fiber/air stream, and the angle ?1 or the angle ?2 is greater than 10?.

4. The method according to claim 1, wherein the short-fiber/air stream flows from the outlet passage or an outlet passage end perpendicularly or substantially perpendicularly to a surface of the foraminous deposition belt with regard to its flow direction S1.

5. The method according to claim 1, further comprising the step of: aspirating secondary air in a space between the short-fiber/air stream and the filament-air stream and/or in a space between the short-fiber/air stream and the second filament-air stream.

6. The method according to claim 1, wherein the short-fiber/air stream is accelerated in the outlet passage by a blower of the defibrator.

7. The method according to claim 1, wherein the meltblow spinneret has a plurality of nozzle openings in a row and two air-flow slots running parallel to the row of nozzle openings on both sides, inclined relative to the nozzle openings, and from which blown air emerges.

8. The method according to claim 1, wherein the meltblow spinneret has a plurality of nozzle openings in several rows and each each adjacent an air outflow opening or its own air outflow opening from which blown air emerges.

9. The method according to claim 1, wherein the meltblow spinneret has a plurality of outlet openings in several rows in the form of nozzle openings and air outflow openings, the outlet openings or the nozzle openings and the air outflow openings are spaced apart from one another in a regular and/or irregular pattern, and each air outflow opening is flanked by at least two of the nozzle openings and/or each nozzle opening is flanked by at least two air outflow openings.

10. The method according to claim 1, wherein the continuous filaments of the filament-air stream between the meltblow spinneret and the foraminous deposition belt on a side of the filament-air stream facing away from the short-fiber/air stream is sprayed with water.

11. The method according to claim 1, wherein the short-fiber/air stream emerges from the outlet passage with a proportion of 0.0138 to 0.0833 kg of pulp short fibers per kg of air.

12. The method according to claim 1 wherein the filament-air stream or the filament-air streams emerges from the meltblow spinnerets with a proportion of 0.002 kg to 0.5 kg of the continuous filaments per kg of air.

13. The method according to claim 1, wherein the outlet passage is height-adjustable relative to an upper surface of the foraminous deposition belt, a spacing between the outlet passage end and a foraminous belt surface is between 200 and 1000 mm, and an amount of secondary air aspirated is controlled by adjusting a height of the outlet passage relative to the foraminous belt surface of the foraminous deposition belt.

14. The method according to claim 1, wherein the short-fiber/air stream relative to a width of the foraminous deposition belt carries or conveys at least 50 (kg/h)/m of the pulp short fibers.

15. The method according to claim 1, further comprising the step of: consolidating the nonwoven fabric by a calender such that an embossing pattern is introduced into the nonwoven fabric by the calender.

16. The method according to claim 15, wherein the embossing pattern is configured to be uninterrupted and a basic pattern geometry of the embossing pattern has a pressing area in the range from 20 to 50 mm.sup.2.

17. The method according to claim 16, wherein the embossing pattern has interruptions and consists of a plurality of elements that are not connected to one another and that each have a compressed area of less than 2 mm.sup.2.

18. An apparatus for making a nonwoven fabric from fibers by a method according to claim 1, the apparatus comprising: the meltblow spinneret for making continuous filaments of thermoplastic material, the defibrator for making pulp short fibers and having an outlet passage for guiding the pulp short fibers or a short-fiber/air stream, the air-permeable foraminous deposition belt for deposition of the pulp short fibers and the continuous filaments as a continuous-filament/short-fiber mixture to form a nonwoven fabric, and, and the suction device for aspirating air or process air through the foraminous deposition belt in the deposition zone of the fibers or the continuous-filament/short-fiber mixture.

19. The apparatus according to claim 18, wherein the apparatus has a first one of the meltblow spinnerets upstream in the travel direction of the foraminous deposition belt of the outlet passage and a second one of the meltblow spinnerets downstream of the outlet passage in the travel direction of the foraminous deposition belt.

20. A nonwoven fabric made from a continuous-filament/short-fiber mixture according to a method according to claim 1.

Description

[0050] The invention is explained in more detail hereinafter using a drawing that only shows an embodiment. In the figures in a schematic representation:

[0051] FIG. 1 is a vertical section through an apparatus according to the invention for carrying out the method according to the invention,

[0052] FIG. 2 is a bottom view of a meltblow spinneret according to the invention in a first embodiment,

[0053] FIG. 3 is a vertical section through the subject matter according to FIG. 2,

[0054] FIG. 4 is a bottom view of a meltblow spinneret according to the invention in a second embodiment,

[0055] FIG. 5 is a bottom view of a meltblow spinneret according to the invention in a third embodiment,

[0056] FIG. 6A is a top view of a section of a nonwoven fabric according to the invention with an embossing pattern,

[0057] FIG. 6B is a cross-section along line A-A according to FIG. 6A.

[0058] FIG. 1 shows an apparatus according to the invention for making a nonwoven fabric 1 of fibers. Two meltblow spinnerets 2, 3 make continuous filaments of thermoplastic material. Within the scope of the invention and in this embodiment, the thermoplastic material may be polypropylene. In FIG. 1 it can be seen that pulp short fibers are made from pulp, preferably and in this embodiment from solid pulp 19, by at least one defibrator 4. The defibrator 4 expediently and in this embodiment is a sawmill. According to the invention at least one short-fiber/air stream is made from the pulp short fibers in the defibrator 4. This short-fiber/air stream 5 is preferably and in this embodiment accelerated by a blower 7 of the defibrator 4 in the outlet passage 6. The blower 7 expediently and in this embodiment supplies air to the defibrator 4. The air flow for making the short-fiber/air stream 5 is made within the scope of the invention and in this embodiment from the grinding process in the defibrator 4 or the sawmill and by the blower 7.

[0059] According to the invention, the accelerated short-fiber/air stream 5 emerges from the outlet passage 6 with an initial volume flow V1. In the context of the invention, initial volume flow V1 means in particular the volume flow of the short-fiber/air stream 5 directly or immediately after emerging from the outlet passage 6. The short-fiber/air stream 5 flows toward the foraminous deposition belts 8 in a flow direction S1 that is preferably and in this embodiment vertical or substantially perpendicular to the foraminous belt surface of an air-permeable foraminous deposition belt 8. The air-permeable foraminous deposition belt 8 is expediently designed as an endless continuously circulating foraminous deposition belt 8 in this embodiment.

[0060] The continuous filaments made by the meltblow spinnerets 2, 3 flow expediently and in this embodiment as filament-air streams 9, 10 with initial volume flow V2, V3 from the respective meltblow spinnerets 2, 3 parallel to the short-fiber/air stream 5. Initial volume flow V2 or V3 means in particular the volume flow of the filament-air streams 9, 10 present directly or immediately below the meltblow spinnerets 2, 3 after the continuous filaments have been exposed to blown air.

[0061] Within the scope of the invention and in this embodiment, a first filament-air stream 9 flows in a travel direction F of the foraminous deposition belt 8 upstream of the short-fiber/air stream 5. The filament-air stream 9 flows with respect to its flow direction S2 at an angle ?1 to the flow direction S1 of the short-fiber/air stream 5. The second filament-air stream 10 flows in the travel direction F of the foraminous deposition belt 8 downstream of the short-fiber/air stream 5. This second filament-air stream 10 flows with respect to its flow direction S3 at an angle ?2 to the flow direction S1 of the short-fiber/air stream 5. The filament-air streams 9, 10 thus flow preferably and in this embodiment from both sides of the central short-fiber/air stream 5 at the angles ?1 and ?2 toward the short-fiber/air stream 5. Within the scope of the invention, the angles ?1 and ?2 are preferably greater than 20?, particularly preferably greater than 25?. In this embodiment according to the figures, the angles ?1 and ?2 are each approximately 30?. Preferably and within the scope of this embodiment, the angles ?1 and ?2 have the same value or essentially the same value.

[0062] Expediently and in this embodiment, the filament-air streams 9, 10 and the short-fiber/air stream 5 are brought together above the foraminous deposition belt 8 in a contact zone 11 and are deposited as a continuous-filament/short-fiber mixture 12 in a deposition zone 13 on the foraminous deposition belt 8 to form the nonwoven fabric 1 or web. Preferably and in this embodiment, the filament-air streams 9, 10 flow in the area or just upstream of the contact zone 11 with regard to their flow direction S2 or S3 at the angle ?1 or ?2 to the flow direction S1 of the short-fiber/air stream 5. In the context of the invention and in this embodiment, the angles ?1 and ?2 mean in particular the angles of inclination at which the filament-air streams 9, 10 meet the short-fiber/air stream 5 in the contact zone 11. Preferably and in this embodiment, the two filament-air streams 9, 10 flow along the entire flow path from the respective meltblow spinneret 2, 3 to the contact zone 11 with regard to their flow directions S2 or S3 at the angles ?1 or ?2 to the flow direction S1 of the short-fiber/air stream 5. It is recommended that and in this embodiment the filament-air streams 9, 10 flow in a straight line or substantially in a straight line. Preferably and in this embodiment according to FIG. 1, the filament-air streams 9, 10 also flow symmetrically toward the short-fiber/air stream 5 and meet the short-fiber/air stream 5 symmetrically in the contact zone 11. The two filament-air streams 9, 10 and the short-fiber/air stream 5 preferably and in this embodiment flow without guides from the meltblow spinnerets 2, 3 or from the outlet passage 6 to the contact zone 11.

[0063] It is recommended in this embodiment that secondary air is aspirated in spaces between the filament-air streams 9, 10 and the short-fiber/air stream 5. The secondary air is aspirated in particular with a volume flow V.sub.sek, where V.sub.sek is expediently the total volume flow of the total aspirated secondary air. In addition, according to the invention, air or process air with a volume flow V4 is aspirated from below through the foraminous deposition belt 8. For this purpose, within the scope of the invention and in this embodiment, a suction device 16 or blower is provided below the foraminous deposition belt 8, in particular below the deposition zone 13. The volume flow V4 is preferably greater than the sum of the volume flows V1, V2 and V3. More preferably, the volume flow V4 is greater than or equal to the sum of the volume flows V1, V2, V3 and V.sub.sek.

[0064] According to a preferred embodiment of the invention, the meltblow spinnerets 2, 3 each have a plurality of nozzle openings 17 arranged in a row and that extrude the molten plastic filaments as part of the method according to the invention. Two air-flow slots 18 preferably run parallel to the row of nozzle openings 17 on both sides. This can be seen in FIGS. 2 and 3. Air under pressure preferably emerges from the air-flow slots 18. The plastic filaments extruded from the nozzle openings 17 are expediently extruded into the blown air stream. Within the scope of the invention and in this embodiment according to FIGS. 2 and 3, the meltblow spinnerets 2, 3 only have a single row of nozzle openings 17 and are therefore configured as single-row nozzles. The fact that the air-flow slots 18 run parallel to the row of nozzle openings 17 on both sides means within the scope of the invention in particular that the longitudinal extension of the air-flow slot 18 runs parallel to the longitudinal extension of the row of nozzle openings 17 (FIG. 2). The air-flow slots 18 are preferably and within the scope of the embodiment according to FIGS. 2 and 3 inclined relative to the nozzle openings 17 or parallel to the row of nozzle openings 17. The blown air emerging from the air-flow slots 18 or the flat blown-air stream then acts on the extruded continuous filaments from the side at an angle of attack (FIG. 3).

[0065] FIG. 4 is a bottom view of a further preferred embodiment of the meltblow spinnerets 2, 3. In the preferred embodiment of the meltblow spinnerets 2, 3 according to FIG. 4, a plurality of nozzle openings 17 arranged in several rows are provided, with each nozzle opening 17 having an air outflow opening 21 from which blown air emerges. Such a meltblow spinneret having nozzle openings 17 in several rows for expelling the molten plastic filaments is also designated as a multirow nozzle. Preferably and in this embodiment according to FIG. 4, each air outflow opening 21 is has a respective nozzle opening 17. The air outflow openings 21 preferably and in this embodiment according to FIG. 4 surround the respective nozzle opening 17 coaxially. In this way, blown air flows coaxially parallel to the plastic melt or the molten plastic filaments from the air outflow opening 21 assigned to the respective nozzle opening 17.

[0066] A further preferred embodiment of the meltblow spinnerets 2, 3 is shown in FIG. 5. According to this preferred embodiment, the meltblow spinneret 2 or the meltblow spinnerets 2, 3 have a plurality of outlet openings in several rows in the form of nozzle openings 17 (shown as unfilled circles in FIG. 5) and air outflow openings 21 (shown as filled circles in FIG. 5). Expediently and in this embodiment, the outlet openings or the nozzle openings 17 and the air outflow openings 21 are spaced apart from one another in a regular pattern. Each nozzle opening 17 is assigned at least two air outflow openings 21. This means in particular that at least two air outflow openings 21 transversely flank each nozzle opening 17. Preferably and in this embodiment, at least two nozzle openings 17 also longitudinally flank each air outflow opening 21. Within the scope of the preferred embodiment according to FIG. 5, only blown air emerges from the air outflow openings 21. It is preferred that the nozzle openings 17 are configured in such a way that only the polymer melt emerges from them and that the polymer melt emerges from the nozzle opening 17 in particular without a blown air stream emerging from the respective nozzle opening 17 or coaxially to the nozzle opening 17. Expediently and in this embodiment according to FIG. 5, some of the outlet openings of the meltblow spinneret 2 or the meltblow spinnerets 2, 3 are configured in the form of nozzle openings 17 and the other outlet openings are configured in the form of air outflow openings 21. In the context of this embodiment and in this embodiment, the spacings between directly adjacent outlet openings of the meltblow spinneret from one another in the longitudinal and transverse directions of the meltblow spinneret 2, 3 are the same or substantially the same over the entire nozzle 2, 3.

[0067] Within the scope of the invention and in this embodiment, the filament-air streams 9, 10 are sprayed laterally with water between the meltblow spinneret 2, 3 and the foraminous deposition belt 8 on the sides of the filament-air stream 9, 10 facing away from the short-fiber/air stream 5. For this purpose water nozzles 20 are provided that expediently and in this embodiment on the sides of the respective filament-air stream 9, 10 facing away from the short-fiber/air stream 5. It is recommended that and in this embodiment the water nozzles 20 are therefore located on the outer side of the filament-air streams 9, 10 and are particularly preferably in the filament flow direction below or directly below the meltblow spinnerets 2, 3.

[0068] The amount of aspirated secondary air can be controlled with or without feedback in the context of the method according to the invention or with the apparatus according to the invention, preferably by adjusting the height of the outlet passage 6 or the outlet passage end 14 relative to the surface of the foraminous deposition belt 8. It is recommended that the height of the outlet passage 6 be set such that: V4?(V1+V2+V.sub.sek). The outlet passage 6 is preferably configured to be height-adjustable relative to the surface of the foraminous deposition belt 8. The spacing a between an outlet passage end 14 and the foraminous belt surface is expediently between 200 and 1000 mm, preferably between 300 and 750 mm. In the context of the invention, the spacing a is measured between the outlet passage end 14 and the foraminous belt surface perpendicular to the foraminous belt surface. The walls of the outlet passage 6 in the area of the outlet passage end 14 are preferably and in this embodiment configured in such a way that the outlet passage end 14 is configured to be divergent in the internal cross-section. Due to the height adjustability or height adjustment of the outlet passage 6 and the configuration of the walls of the outlet passage 6 or the outlet passage end 14 the position of the contact zone 11 can be controlled with or without feedback within the scope of the invention, especially in combination with the choice of the angles ?1 and ?2. As a result, the mixing of the continuous filaments and the pulp short fibers can be advantageously influenced.

[0069] It is preferred that the continuous-filament/short-fiber mixture 12 flows from the contact zone 11 to the foraminous deposition belt 8 as a homogeneous or substantially homogeneous mixture. The homogeneous continuous-filament/short-fiber mixture 12 is then expediently deposited in the deposition zone 13 on the foraminous deposition belt 8 to form the nonwoven fabric 1 or the nonwoven web. It is recommended in this embodiment that according to FIG. 1, the continuous-filament/short-fiber mixture 12 flows from the contact zone 11 to the foraminous deposition belt 8 or to the deposition zone 13 with regard to its flow direction perpendicularly or substantially perpendicular to the foraminous belt surface.

[0070] The nonwoven fabric 1 is consolidated according to a preferred embodiment of the method according to the invention and in this embodiment inline by at least one calender 15. In this embodiment, the at least one calender 15 has at least one pair of calender rollers through which the nonwoven fabric 1 is preferably guided under a contact pressure. It is further preferred that an embossing pattern is introduced into the nonwoven fabric 1 or into the nonwoven web by the at least one calender 15. For this purpose, at least one of the calender rolls of the calender 15 can have an embossing pattern on its outer surface.

[0071] FIG. 6A shows a top view of a section of a nonwoven fabric according to the invention with an embossing pattern. FIG. 6B shows a cross-section through the subject according to FIG. 6A along line A-A. Preferably and in this embodiment according to FIG. 6A, the embossing pattern is configured to be uninterrupted. The basic pattern geometry or the repeating element of the embossing pattern is preferably a regular hexagon, so that the embossing pattern preferably and in this embodiment consists of a large number of regular hexagons of the same size that adjoin one another and is therefore configured in particular as a honeycomb-shaped embossing pattern. FIG. 6B shows that the inner hexagon surface expediently forms the uncompressed part of the embossing pattern.

[0072] It is recommended that a height h of the basic pattern geometry or the elements of the embossing pattern is between 0.3 and 2.0 mm. In this embodiment according to FIGS. 6A and 6B, the height of the basic pattern geometry or the regular hexagons may be approximately 1.5 mm. The height h of the basic pattern geometry means the height difference or the average height difference between the pressing area and the non-pressed areas of the embossing pattern. It is also within the scope of the invention that the proportion of the pressing area of the embossing pattern to the total surface of the nonwoven is between 2.5% and 25%, preferably between 5% and 15%. It is also understood that the corresponding roll of the pair of calender rolls, which has the embossing pattern, has a complementary embossing pattern on the outer surface.