Nonwoven Fabric For Acoustic Isolation Applications

Abstract

The invention relates to a method for manufacturing a nonwoven fabric having an air permeability of 2000 l/m.sup.2/s or less when measured at a pressure difference of 200 Pa according to EN ISO 9237, the method comprising the steps of: providing at least two sets of fibers, wherein a first fiber set comprises a significant level of splittable fibers and a second fiber set comprises a low level of splittable fibers or no splittable fibers; using the first fiber set to form at least one first fibrous web in a first web formation process and using the second fiber set to form at least one second fibrous web in a second web formation process; stacking the first and second webs so obtained to provide a multilayer web including two distinct layers of fibrous webs; and bonding the multilayer web. The invention further relates to a nonwoven fabric obtainable by such process and the use of such nonwoven fabric in acoustic isolation applications.

Claims

1-15. (canceled)

16. A method for manufacturing a nonwoven fabric having an air permeability of between 100 and 1500 l/m.sup.2/s when measured at a pressure difference of 200 Pa according to EN ISO 9237, the method comprising the steps of: providing at least two sets of fibers, wherein a first fiber set comprises at least 30 wt-% of splittable fibers and a second fiber set comprises less than 20 wt-% of splittable fibers or no splittable fibers; using the first fiber set to form at least one first fibrous web in a first web formation process and using the second fiber set to form at least one second fibrous web in a second web formation process; stacking the first and second webs so obtained to provide a multilayer web including two distinct layers of fibrous webs; bonding the multilayer web, wherein the bonding comprises spunlacing to direct high pressure fluid jets to the multilayer web; and impregnating the bonded multilayer web, the impregnating comprising adding a binder to stiffen and fixate the nonwoven fabric and a flame retardant.

17. The method of claim 16, wherein the nonwoven fabric has an air permeability of between 100 and 1000 l/m.sup.2/s, when measured at a pressure difference of 200 Pa according to EN ISO 9237.

18. The method of claim 16, wherein at least one of said first fiber set or said second fiber set are staple fibers.

19. The method of claim 16, wherein at least one of said first fiber set or said second fiber set further comprises nanofibers.

20. The method of claim 16, wherein the nonwoven is formed continuously and wherein the method involves continuously forming and stacking the webs on a moving conveyor belt, on which the multilayer web is continuously bonded.

21. The method of claim 16, wherein the webs are configured and oriented such that the fibers within each of the layers have different average directions in the plane of the nonwoven fabric.

22. The method of claim 18, wherein at least one of said first web formation process or said second web formation process is a carding process in which the respective said staple fibers are carded to provide the respective fibrous webs.

23. The method of claim 22, wherein the first fibrous web and the second fibrous web are laid on a conveyor belt in different orientations.

24. The method of claim 16, wherein the method further comprises thermomechanical processing the bonded multilayer web.

25. The method of claim 16, wherein the impregnating further comprises adding an oil- and water-repellent agent and/or particulate filler material.

26. The method of claim 16, wherein the method further comprises drying the multilayer web after said impregnating.

27. The method of claim 16, wherein the method further comprises adding an adhesive to at least one surface of the multilayer web.

28. A nonwoven fabric, wherein the fabric has an air permeability of between 100 and 1500 l/m.sup.2/s when measured at a pressure difference of 200 Pa according to EN ISO 9237 and comprises at least two distinct layers of nonwoven fiber webs, wherein a first web comprises at least 30 wt-% of splittable fibers and a second web comprises less than 20 wt-% of splittable fibers or no splittable fibers, wherein the splittable fibers of the first web are at least partially split into small filaments and wherein the fibers from the first and second fiber webs are interentangled, and wherein the fabric is impregnated with a binder that stiffens and fixates the fabric and with a flame retardant.

29. An acoustic isolation material that comprises the nonwoven fabric of claim 28.

30. The method of claim 16, wherein the nonwoven fabric has an air permeability of between 150 and 900 l/m.sup.2/s when measured at a pressure difference of 200 Pa according to EN ISO 9237.

31. The method of claim 16, wherein said first fiber set and said second fiber set are staple fibers.

32. The method of claim 16, wherein each of said first fiber set and said second fiber set further comprises nanofibers.

33. The method of claim 18, wherein said first web formation process and said second web formation process are each a carding process in which the respective said staple fibers are carded to provide the respective fibrous webs.

34. The method of claim 16, wherein the method further comprises calendering the bonded multilayer web.

35. The method of claim 16, wherein the method further comprises adding an adhesive to the surface of the multilayer web that goes back to the first fibrous web.

Description

[0040] Further details and advantages of the invention will become apparent from the figures and examples described in the following. The figures show:

[0041] FIG. 1: a schematic illustration of a machine setup for manufacturing a nonwoven fabric in agreement with the method of the invention;

[0042] FIG. 2: a schematic illustration of a layered nonwoven fabric of the invention;

[0043] FIG. 3: a microscopic image of a fabric as shown in FIG. 2;

[0044] FIG. 4: a schematic illustration of the function of a layered nonwoven fabric of the invention within an acoustic package;

[0045] FIG. 5: a picture of a thermoformed cladding for acoustic isolation applications comprising a nonwoven fabric on top of a substrate;

[0046] FIG. 6: a microscopic picture of a layered nonwoven fabric manufactured in agreement with a concrete example described herein.

[0047] An exemplary machine setup for carrying out the method of the invention is illustrated in FIG. 1.

[0048] The machine comprises a first reservoir 10 with means for opening and mixing a first fiber set and a second reservoir 20 with means for opening and mixing a second fiber set. When carrying out the inventive method, the first reservoir 10 is filled with a first fiber set that comprises a significant level of splittable fibers and the second reservoir 20 is filled with a second fiber set that comprises none or a low level of splittable fibers.

[0049] The machine further comprises two carding machines. A first carding machine 11 is associated with the first reservoir 10 and functions to card the fibers of the first fiber set to provide a first fibrous web during a first carding process. A second carding machine 21 is associated with the second reservoir 20 and functions to card the fibers of the second fiber set to provide a second fibrous web during a second carding process.

[0050] A crosslapper 22 works to cross-lay the second fibrous web onto the conveyor belt 30 of the machine. The conveyor belt 30 moves to the right direction in the drawing and transports the cross-laid layer of the second fibrous web towards a point where the first fibrous web is parallel-laid on top.

[0051] The two layers, i.e., the cross-laid layer of the second fibrous web and the parallel-laid layer of the first fibrous web together form a multilayer web that is then transported further to the right direction in the drawing on the conveyor belt 30. It then passes spunlacing zones 40 where the fibers are mechanically interentangled by a plurality of small high pressure water jets. The water jets also function to split the splittable fibers within the layer going back to the first fibrous web into smaller filaments.

[0052] The nonwoven web thus formed is transported further on the conveyor belt 30 through drying zone 50, impregnation zone 60 and powdering zone 70. In the drying zone 50 an increased temperature is used to remove water that remains in the nonwoven after spunlacing. In the impregnation zone 60, a binder mixture is added to the nonwoven for stiffening and fixation as well as to confer flame retardant or oil- and water repellent properties. Additionally, filler particles can be added to the nonwoven to lower air permeability. Impregnation is carried out on the side of the nonwoven that goes back to the second fibrous web, i.e., the lower side on the drawing.

[0053] The product can go through thermomechanical processing, either in-line or offline before it goes into the powdering zone 70, adhesive is disposed on the surface of the nonwoven that goes back to the first fibrous web, i.e., the upper side on the drawing. This step can be done in-line, as shown, or alternatively also off-line.

[0054] The nonwoven is finally rolled up for transportation purposes at station 80.

[0055] FIG. 2 shows a schematic illustration of a layered nonwoven fabric 1 of the invention.

[0056] The fabric 1 can be produced on a machine as illustrated in FIG. 1. It comprises two distinct layers, an aspect side layer A and a function side layer B. The aspect side layer A is the layer that goes back to the second fibrous web of normal, non-splittable fibers. The function side layer B is the layer that goes back to the first fibrous web of splittable fibers. Little dots inside the aspect side layer A illustrate that this layer is impregnated, inter alia, with filler particles.

[0057] When used in acoustic packages, the fabric 1 is intended to be attached to a substrate having the function side layer B facing the substrate and the aspect side layer A being visible. The adhesive is disposed on the surface of the function side layer B aids to attach the fabric to the substrate during a thermoforming process. The binder impregnation of the aspect side layer A makes the outer side flame retardant and oil- and water-repellent.

[0058] FIG. 3 is a microscopic image of a fabric as schematically illustrated in FIG. 2.

[0059] FIG. 4 illustrates the function of such layered nonwoven fabric 1 of the invention within an acoustic package 100. The acoustic package 100 is comprised by a hard surface 105, which could be a car bonnet, a substrate 106 of acoustic absorbing foam and the layered nonwoven fabric 1 on top of the substrate 106.

[0060] The large arrow S illustrates the direction of incoming soundwaves 110. When the soundwaves 110 hit the nonwoven 1 on top of the acoustic package, it is partly reflected. The direction of the reflected soundwaves 111 is illustrated by arrow R. Another part 112 of the soundwave travels through the nonwoven and enters the substrate layer 106, where it is modified with regard to direction, amplitude and frequency before hitting the hard surface 105. At the hard surface the modified and damped soundwaves are reflected back and the soundwaves 113 thus reflected through the damping material. To the most part, the share 112 of the soundwave originally passing through the nonwoven hence becomes trapped between the hard surface 105 and the inner surface of the nonwoven 1. It oscillated in this area that is filled with the acoustic absorbing foam 106 and is steadily weakened deadened.

[0061] FIG. 5 shows a picture of a thermoformed cladding for acoustic isolation applications, comprising a nonwoven fabric on top of a substrate. The cladding can be mounted on a hard surface like the inside of a car bonnet to form an acoustic package as schematically illustrated in FIG. 4.

EXAMPLE 1

[0062] A nonwoven fabric as schematically illustrated in FIG. 2 is manufactured on a process line as schematically illustrated in FIG. 1.

[0063] The first fiber set consists of 100% splittable PET-PA fibers in 2.2 dTex and a cut length of between 28-51 mm that can split into 16 separate filaments. The second fiber set consists of a 70/30 mix between 1.7 dTex Viscose fibers with a cut length of 32-38 mm and a 1.3 dTex PET fiber with a cut length of 32-38 mm.

[0064] The resultant product is shown in the microscopic image of FIG. 6, where the loftier aspect side layer comprising the thicker fibers lies on top of the denser functional layer comprising the small filaments resulting from splitting of the splittable fibers.

Test Results:

[0065] The product has been tested for air permeability any yielded a value of 797 l/m.sup.2/s when measured at a pressure difference of 200 Pa according to EN ISO 9237.

[0066] Four tests for tensile strength (TS) and elongation (TE) properties were carried out in each machine direction (MD) and cross-machine direction (CD) according to WSP 110.4. The results are shown in Tables 1 and 2 below.

TABLE-US-00001 TABLE 1 Tensile Strength F (2.5%) F (5%) F (10%) F (20%) F (50%) F (Max) N N N N N N N 1.1 MD 61.35 86.72 123.74 207.19 263.75 1.2 69.99 95.78 135.09 227.77 282.69 1.3 73.55 100.43 141.03 237.37 288.10 1.4 66.97 92.10 129.52 214.74 264.42 2.1 CD 7.76 13.37 20.17 30.44 82.22 144.38 2.2 9.87 17.19 24.82 36.94 95.11 147.32 2.3 8.35 15.24 23.00 34.38 90.80 144.07 2.4 9.60 16.75 24.50 36.24 97.74 149.21

TABLE-US-00002 TABLE 2 Tensile Elongation All All All All All All All (5N) (10N) (20N) (50N) (100N) (200N) (Max) Nr % % % % % % % 1.1 MD 0.28 0.44 0.72 1.83 6.78 19.15 29.0 1.2 0.18 0.31 0.55 1.46 5.53 17.07 28.0 1.3 0.25 0.36 0.58 1.39 4.95 16.19 27.0 1.4 0.16 0.30 0.57 1.56 6.04 18.29 28.0 2.1 CD 1.47 3.41 9.84 33.82 58.05 81.0 2.2 1.24 2.53 6.50 28.51 52.09 76.0 2.3 1.46 3.03 7.70 30.58 53.86 74.5 2.4 1.23 2.62 6.71 29.14 52.16 75.0

[0067] As can be gathered, the average maximum tensile strength in machine direction (TSMD) was in the magnitude of 275 N/50 mm and the average maximum tensile strength in cross-machine direction (TSMD) was close to 150 N/50 mm. The average tensile elongation at break in machine direction (TSMD) was close to 30% and the average tensile elongation at break in cross-machine direction (TSMD) was close to 80%.