Fiber Composite Acoustic Damping Material

Abstract

A damping material (11) in accordance with the invention consists of a ground material that is composed of fibers that are in loose connection with each other. For example, the fibers are minimally interlooped with each other or also glued to each other. This ground material is condensed in some areas in that the fibers are reoriented or interlooped with each other to a greater degree or glued to each other. Consequently, zones (17) and (18) of different densities are formed, thus making it possible to increase and adjust, as desired, the sound-damping effect of the damping material.

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the priority of European Patent Application No. 10 002 801.8, filed Mar. 17, 2010, the subject matter of which, in its entirety, is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to an acoustic damping or absorbing material in the manner of a body consisting of fibers. In particular, the invention relates to such a spatially configured, i.e., not simply planar, damping or absorbing material.

Acoustic damping materials consisting of the most diverse materials such as mineral wool, glass wool or natural or synthetic fibers have been known. In each case, the damping material is to absorb sound energy, i.e., the sound waves are to be attenuated in that the vibration energy of the sound waves is converted by friction into thermal energy. In doing so, the formation of resonances and the formation of standing waves is to be prevented.

Fiber materials with non-ordered fibers may display a high acoustic damping effect. In doing so, it is possible—in principle—to design the felt bodies so as to be relatively variable, as has been known from document EP 2 034 072 A1. This publication deals with a hygiene article such as, for example, sanitary materials. In order to produce such materials, a non-woven fibrous web is needled along strip-shaped areas with different strengths, so that elongated parallel-oriented zones displaying a higher fiber density are achieved in the material. The extent to which such a material can be employed for a use other than in the medical and nursing fields is open.

It is the object of the invention to provide an acoustic damping material displaying improved efficacy.

SUMMARY OF THE INVENTION

The damping material in accordance with the invention forms a random fiber non-woven body, i.e., a body consisting of non-ordered fibers. In this body, the fibers may be also be arranged parallel to each other in zones. The fibers may be interlooped, in which case the degree of interlooping may be different in at least two different zones. The random-fiber non-woven body may be produced, for example, in that a loose fibrous web or non-woven (for example of polyester) is condensed by mechanical or also thermal action in specified zones. In doing so, an acoustic damping material displaying spatially varying densities is produced. In this case, the invention offers a means to produce this damping material in a cost-favorable manner.

The acoustic damping material can be provided in the form of a mat. The mat may be made of glass fiber wool or of mineral wool or also of other materials, for example. The fibers of the mat in the fibrous web are preferably arranged next to each other, loosely but still holding together. This can be achieved in that the fibers are interlooped with each other in such a manner that at least a loose cohesion of the mat exists. The fibers may be aligned parallel or may be arranged so as to be crossed superimposed in layers by means of a cross-laying process.

For example, the fibrous web may first be made available by using carding methods or spunbonding processes, these being known per se. Due to a zone-wise condensation, the loose fibrous web is converted into the desired state in that zones are created, wherein the degree of fiber interlooping is greater compared with the remaining body or the remaining mat. Increased fiber interlooping may be achieved by mechanical needling, e.g., with the use of felting needles, by condensing with water jets or similar techniques. Alternatively, local condensing may be achieved, for example by thermal compression. By condensing the fiber body, the condensed zones become more compact, whereby more interlooped fibers are counted by unit of volume than in the non-condensed material.

The acoustic damping material may be provided in the form of random-fiber non-woven bodies displaying defined geometric shape or also in the form of mats that are cut to the desired size and dimensions prior to use. It is characteristic of the damping material that at least two, but preferably more, zones displaying at least two degrees of fiber interlooping do exist.

The zones displaying different degrees of fiber interlooping, preferably also have different fiber densities. As a result of this, zones of different pore volume and different acoustic hardness are formed in the damping material, so that a strong acoustic damping effect can be achieved.

The zones displaying differently strong fiber interlooping may be arranged in a regular or preferably irregular pattern, as a result of which a broad-spectrum acoustic damping effect can be achieved.

The damping material in accordance with the invention may be produced of uniform fibers or also of different fibers, for example, of fibers having different lengths and/or thicknesses, of fibers that consist of a uniform material or also of fibers that consist of different fibers, i.e., fiber mixtures. If necessary, fibers having different dimensions or consisting of different materials may also be concentrated in different zones so as to also form zones of different materials in addition to the zone-specific different degrees of fiber interlooping.

Preferably, the fibers in zones of minimal fiber interlooping are predominantly oriented in one plane (or in crossed position), whereby the fibers in the plane may be selectively oriented in parallel direction or also in different directions, i.e., they cross one or more times, but interloop minimally. If the damping material is provided in the form of a mat, the fibers—in particular in zones of minimal fiber interlooping—are preferably predominantly in the plane of this mat. In zones of more fiber interlooping, the fibers—at least preferably—are oriented in an increased proportion in a direction perpendicular to this plane. As a result of this, condensed zones are formed that impart the mat or the other fiber body with a particular mechanical stability and, specifically, with cohesion.

The zones of increased fiber interlooping may be arranged as regularly or irregularly formed islands in the damping material. Preferably, they have the form of strip-shaped—again preferably straight—regions that, for example, may extend in transverse direction of the mat and/or in longitudinal direction of the mat. Furthermore, they may extend in oblique directions, for example extend diagonally. Preferably, the condensed zones extend through the entire mat thickness, i.e., from the upper side to the underside of said mat.

Considering a particularly advantageous embodiment, the damping materials comprises at least two layers, wherein zones with different degrees of fiber interlooping are provided, in which case these two zones may be arranged differently in the two layers, for example, not in a registered manner. It is possible to provide in these layers condensed zones, i.e., zones with a greater degree of fiber interlooping, said zones being connected to the respectively other layer. For example, the condensed zones in these layers may be produced by needling, by water-jet condensing or the like. A fiber body or a corresponding mat can be produced as a layer. As previously described, such a layer is produced, for example, by zone-wise compacting the fiber body. After superimposing two or more such layers, they, in turn, may experience compacting in some areas, in which case the degree of fiber interlooping increases at certain points or in zones (regions) and, in doing so, a connection is also established between the layers.

Hereinafter, exemplary embodiments of the invention are explained. These exemplary embodiments as well as the corresponding drawings and subordinate claims show additional details of advantageous embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematic representation of a damping material with interspersed zones of increased fiber interloping.

FIG. 2 is a schematic perspective principle representation of a device for the production of a damping material in accordance with FIG. 1.

FIG. 3 is a perspective principle representation of a damping material with local condensed zones.

FIG. 4 is a perspective principle representation of a modified embodiment of an inventive damping material with strip-like condensed zones and interstices.

FIG. 5 is a perspective principle representation of another exemplary embodiment of an inventive damping material consisting of a multi-layer assembly and strip-shaped condensed zones.

FIG. 6 is a perspective principle representation of a modified embodiment of a damping material consisting of a multi-layer assembly.

FIG. 7 is a principle representation of a potential production process for a damping material in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a random-fiber non-woven body 10 that consists of an acoustic damping material 11 and, may be used, for example, for sound absorption or for sound damping in rooms, in or on room ceilings or walls, in loudspeaker boxes or other acoustic devices. The random-fiber non-woven body 10 is represented here as a flat, parallel-epipedal body. However, said body may also have a shape that is suitable for the respective purpose of use. In the present exemplary example, the random-fiber non-woven body 10 depicted as a section of a preferably continuously produced mat 12, as shown in FIG. 2.

The damping material 11 is made of an immeasurably large number of individual fibers 13, 14, 15, 16 that, for example, may consist of one uniform material or also of different materials. The fibers 13 through 16, as well as the remaining fibers indicated in FIG. 1, said fibers not being specifically referenced, may consist in full or in part of glass, ceramic, wool, cellulose, synthetic material, one or more elastomers, one or more polymers or the like. The fibers may consist of only one of these materials. However, it is also possible to have a homogeneous or inhomogeneous mixture of fibers that consist of different such mentioned materials.

At least some of the fibers 13 through 16 may consist of a metal or of a non-metallic material that may also be metallized. The fibers 13 through 16 may have uniform diameters, cross-sections and lengths or also different diameters and/or or different cross-sections and/or different lengths.

The fibers 13 through 16 form a fiber web, wherein they are positioned next to each other in a loose but cohesive arrangement. In doing so, different zones may be distinguished in the random-fiber non-woven body 10. The fibers 13, 14 are in a loose zone 17 with minimal fiber interlooping, whereas the fibers 15, 16 are located in a compacted, more condensed zone 18 with an increased degree of fiber interlooping. For example, the zone 17 is formed by the afore-mentioned loose fiber web, whereas the zone 18 represents a compacted zone. Preferably, several zones with increased fiber interlooping exist in the random-fiber non-woven body 10, for example the zone 18, whereby these different zones may be formed and/or arranged regularly or irregularly. They may extend over the entire height of the fiber body 10 (vertically in FIG. 1) or the mat 12.

In the zone 17, the fibers 13, 14 are predominantly arranged in a plane that is essentially parallel to the upper side 19 or the underside 20 of the random-fiber non-woven body 10, whereby the fibers 13, 14 are preferably oriented essentially parallel and in mat longitudinal direction 21, i.e., with respect to FIG. 2. The fibers 13, 14, as well as any additional fibers oriented in mat longitudinal direction have been joined, for example, in a combing process, by carding a natural or synthetic fiber to produce a loose non-woven web with parallelized fibers. In order to produce the fiber body 10 in accordance with FIG. 1, the thusly obtained mat 12 is passed through a processing station 22, said station comprising one or more members 23, 24 that act permanently or at selected times on the mat 12 located or passing underneath, in order to effect a local increased interlooping of the fibers such as, for example the fibers 15, 16, and thus produce a zone 18 with increased fiber interlooping, respectively. The members 23, 24 may act on the mat 12 in a mechanical or non-mechanical manner. In particular, considering synthetic fibers, said members may be heat sources, radiation sources or also only members that dispense jets of organic or inorganic fluids such as, for example, water. Alternatively, the members 23, 24 may also comprise mechanical tools such as felting needles or the like, these being used to treat the mat 12.

For further explanation of the damping material 11 in accordance with the invention, reference is made to FIG. 3. Again, this damping material is initially a mat 12, wherein the fibers 13, 14 are largely parallelized in a loose fiber assembly or also oriented in a crossed manner essentially parallel to the upper side 19. In the zone 18, said zone having been created, for example, by local condensing of the mat 12 with water jets, the fibers 25, 26 have been reoriented out of the horizontal orientation into an approximately perpendicular orientation relative to the upper side 19. Consequently, a greater degree of interlooping of the fibers among each other occurs in the zones 18 than in the remaining zone 17. At the same time, this increased interlooping, as has been created by water-jet condensing for example, is accompanied by a compacting effect. FIGS. 3 and 4 show how, due to the treatment process, the fibers have been locally reoriented in the zones 18 out of their normal orientation in their predominantly horizontal position into an oblique or perpendicular position, whereby, at the same time, the material has been condensed. The reorientation of the fibers 25, 26 out of the horizontal direction (parallel to the upper side 19) into the vertical direction, at the same time, means a compacting of the fiber material at the affected location or in the zone 18. The upper side 19 and/or the underside 20 may have respectively one indentation in the condensed zone 18.

Inasmuch as the mat 12 is zone-wise condensed at certain locations and not condensed at other locations, a varying density structure is formed across the spatial segments. For example, outside the condensed zones 18, it is possible for (hollow spaces) interstices 27 displaying extremely low density, i.e., low proportion of fibers per unit of volume, to form, the fiber density in said interstices being lower than the density in the remaining fiber web of the mat 12. Such interstices 27 may be irregular and be approximately lentil-shaped, for example. Their form and arrangement depend on the form and arrangement of the condensed zones 18.

The random-fiber non-woven body 10 in accordance with FIG. 1 or FIG. 3 exhibits good sound damping properties. It also exhibits a high pore and air volume. Sound waves impinging on the damping material 11 penetrate the damping material 11 and are absorbed there, i.e., ultimately converted into heat. This effect is supported by the preferably irregular arrangement of the zones 18 that suppress the formation of standing waves and may achieve an additional wave extinction in a large frequency spectrum due to interference. Such interference may occur within the damping material 11 as well as outside said damping material. As is shown by FIG. 3, the condensed zones 18 may also be formed by indentations that are preferably irregularly arranged on the surface of the material, said indentations reflecting a certain percentage of the impinging sound energy and, together, contributing to the extinguishing interference.

The damping material 11 may be designed in various ways. While the zones 18 in the embodiments described so far are formed by local islands, for example having a rectangular, square, circular or another contour, they may also be strip-shaped, as shown by FIG. 4. The strips may have consistent or changing width. The strips may have one uniform width or they may have different widths.

The damping material 11 as in FIG. 4 has several zones 18, 28, 29 with increased fiber interlooping, three of these being shown. These zones extend at a distance parallel to each other along the transverse direction of the mat 12 (at a right angle to the mat longitudinal direction 21) in FIG. 2 for example, or also parallel to said mat longitudinal direction. Regarding the fiber orientation for the zones 18, 28, 29, the comments that have been made in conjunction with FIGS. 1 through 3 apply. Uncondensed zones 17, 30, 31 are formed between the zones 18, 28, 29, said uncondensed zones preferably accounting for the greater part of the volume of the damping material 11. In these zones, for example in zone 29, again one or more interstices 27 may be formed. For example, such an interstice 27 extends like a longitudinal channel parallel to the adjacent condensed zones 18, 28.

In the damping material 11, the distances between the parallel, strip-shaped condensed zones 18, 28, 29 has been selected so as to be irregular. FIG. 4 illustrates three such distances L1, L2, L3. Preferably, the distances are not equal. Ideally, none of the distances L1, L2, L3, etc. is identical. The widths of the zones 18, 28, 29 are preferably the same among each other.

The damping material 11 in accordance with FIG. 4 can be produced in an apparatus in accordance with FIG. 2 in that a mat 12 of a non-woven fibrous material is passed through the processing station 22. The fibers are loosely layered in predominantly horizontal orientation and are stacked in a specific height h. The width of the mat 12 is random. For practical purposes, these widths are between 50 cm and 5 meters. Preferably, the mat 12 is obtained by continuous production and can thus be adjusted as desired by cutting.

FIG. 5 shows a damping material 11 representing a multi-layer assembly. As illustrated, the material comprises two or also more layers 32, 33, of which at least one, preferably however more or all of them, have one or more condensed zones 34, 35, 36, 37. Considering the composition of the layer 32, all the explanations provided regarding the exemplary embodiment of FIG. 4 apply. Likewise applicable to the layer 33 are the explanations provided in conjunction with FIG. 4. Consequently, as explained in conjunction with FIG. 4, the layers 32, 33 may be first provided separately and then be superimposed. In doing so, the condensed zones 34,35 of the upper layer 32 may be oriented parallel to the condensed zones 36, 37 of the lower layer 33, whereby they, preferably, need not be moved in a registered manner. As a result of this, the distances of the condensed zones 34, 35 of the upper layer 32 may be different from the distances between the condensed zones 36, 37 of the lower layer 33. The layers 32, 33 may be different regarding the number and position of the condensed zones 34 through 37.

As many such layers as are desired may be placed on each other. If needed, layers without condensed zones may be interposed. The cohesion of the layers 32, 33, as well as all potentially additionally present layers can be created by continuously condensed zones 38 that extend parallel to the other condensed zones 34 through 37, or also in a direction transverse to them. The continuous condensed zones 38 are preferably produced in that the individual layers 32, 33 are placed on top of each other. For example, they can be produced by condensing with water jets or by any other mode of condensing as mentioned in this document. Preferably, as illustrated, they are strip-shaped. However, it is also possible to produce continuous condensed zones having a locally limited contour, said contour being round, oval or rectangular, for example. In the condensed zone 38, the fibers are transferred from the upper layer 32 into the lower layer 33. Additionally or alternatively, the fibers of the lower layer 33 may have been transferred from the lower layer 33 into the upper layer 32. Again, as in all the other condensed zones, there is a greater degree of interlooping of fibers in the condensed zone 38 than in the surrounding material of the first zone 17. The condensing or interlooping of fibers in the zone 38 may be the same as in the zones 34 through 37. However, it is also possible to specify different degrees of interlooping and condensing for the zones 34 through 37 and 38.

As a result of the number and arrangement of condensed zones 34 through 37 and 38 and their degree of condensation, as well as the number of layers 32, 33, etc., it is possible to adjust the damping properties of the damping material 11 within wide limits as desired.

The damping material 11 in accordance with FIG. 5 may have interstices—like the already described interstice 27—within the layers 32, 33. In addition, interstices extending toward the respectively other layer are formed on the condensed zones 34, 35 as well as 36, 37. FIG. 5 shows such an interstice 39 between the condensed zone 35 and the layer 33. Such interstices can improve sound-damping properties. The distances of the condensed zones 34, 35, 36, 37, 38 from each other, as well as the geometric distances relative to the interstices 27, 39, are preferably within the range of half the wavelength of the sound waves to be attenuated or a multiple of half the wavelength. If, for example, in particular a frequency of 200 Hz is to be attenuated, the distances may be in the range of 85 cm. If the focus of the damping effect is to be at 2000 Hz, it is advantageous to specify the distances in the range of 8.5 cm. A broader frequency spectrum can be covered by varying these distances.

FIG. 6 shows another embodiment of the damping material 11 in accordance with the invention, said damping material having at least two layers 32, 33. In this case, the layers 32, 33 are oriented transversely with respect to each other. While the condensed zones 36, 37 of the lower layer 33 extend in a first direction, the condensed zones of the upper layer (zone 34) are oriented transversely with respect thereto. The connecting condensed zone 38 may extend parallel to the zone 34, transversely with respect to the zones 36, 37, or in a separate different direction. Due to the mutual crossing of both the condensed zones 34 and 36, as well as 37, additional interstices are formed in the damping material 11, said interstices being capable of affecting the sound-damping effect in a positive manner. In the layers 32, 33, the fibers in the uncondensed zones 17 may be oriented parallel to each other or also crossed with respect to each other.

In each of the presented embodiments representing a multi-layer assembly, the damping properties can be additionally influenced in that the geometric configuration of the obtained interstices and their relative distances are adjusted to the frequency that is to be attenuated.

Furthermore, the damping properties can be adjusted in that the layers 32, 33 and, optionally, additional layers are made of different ground fiber materials, so that different mass densities result in view of the spatial volume segment. In addition, it is possible to vary the density of the non-woven fibrous web in a direction transverse to the mat longitudinal direction 21.

FIG. 7 is a schematic illustration of the condensing process by means of the water jet method. Again, the mat 12 has been produced with a known method such as carding, optionally also by cross-laying or by producing a spunbonded fabric. This mat 12 moves in the direction of the mat longitudinal direction 21 under a nozzle bar 49 of a water-jet condensing system, said nozzle bar being known per se. The nozzle bar 49 may be part of one of the members 23, 24 shown in FIG. 2. Again, the nozzle bar 49 comprises at least one, preferably however more, nozzle clusters 40, 41, 42, 43 and, optionally, even more such nozzle clusters. Each of the nozzle clusters 40 through 43 that are schematically symbolized by circles in FIG. 7 may be individually formed by a group of smaller nozzle orifices that are arranged linearly or in an array. The distances between these nozzle clusters L1, L2, L3 are preferably not identical to one another.

Each nozzle cluster 40 through 43 produces a bundle 44, 45, 46, 47 of water jets that impinge on the surface of the mat 12 and penetrate the material of the mat. The impinging water jet bundles 44 through 47 cause a fluidizing of the fibers in the mat 12 and a reorientation, as well as the interlooping of said fibers. This is also accompanied by a condensing of the material of the mat 12 so that, as the work progresses, the strip-shaped condensed zones 18, 34, 35, 36 are formed. The diameter of the nozzle clusters 40 through 43 and the pressure of the water that is applied above the nozzle bar 49 are selected in such a manner that the water jet bundles 44 through 47 fluidize said fibers but do not cause a separation or even a destruction of the fibers. In doing so, it is important that, between the individual water jet bundles 44 through 47, there be at least one interstice in which no condensing of the mat 12 occurs so that here—in order to form zone 17—there is no increased density of the non-woven fabric. A condensing of the mat 12 occurs only in the region of action of the water jet bundles 44 through 47. Furthermore, measures may be taken to temporarily interrupt individual water jet bundles 44 through 47, for example the water jet bundle 45. This may be accomplished by means of a baffle that is pushed into the region of the water jet bundle 45 in order to interrupt the latter. This means that, with a forward movement of the mat 12 under the nozzle bar 49, a strip-shaped condensed zone is created through the entire height of the mat, said zone being interrupted in mat longitudinal direction 21.

The activation and deactivation of the condensing effect cannot only be achieved by temporarily covering the individual nozzle cluster 40 through 43 but also in that the entire nozzle bar, for example of the members 23, 24, etc., is activated and deactivated.

The method is suitable, in particular, for mats 12 of polyester fibers. However, it is not restricted to a specific fiber material. In addition, the manufacture of the damping material 11 is possible not only by water jet condensing but also by other methods for locally condensing the mat 12. Methods using mechanical needling or thermal condensing can be used. Essential is that zones exhibiting varying spatial densities be produced in the damping material 11 in a targeted manner.

A damping material 11 in accordance with the invention consists of a ground material that is composed of fibers that are in loose connection with each other. For example, the fibers are minimally interlooped with each other or also glued to each other. This ground material is condensed in some areas in that the fibers are reoriented or interlooped with each other to a greater degree or glued to each other. Consequently, zones 17 and 18 of different densities are formed, thus making it possible to increase and adjust, as desired, the sound-damping effect of the damping material.

It will be appreciated that the above description of the present invention is susceptible to various modifications, changes and modifications, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

List of Reference Numerials:
10                     Random-fiber non-woven body
11                     Damping material
12                     Mat
13, 14, 15, 16, 25, 26 Fiber
17                     Zone with minimal fiber interlooping
18                     Zone with increased fiber interlooping
19                     Upper side
20                     Underside
21                     Mat longitudinal direction
22                     Processing station
23, 24                 Member
27, 39                 Interstice
28, 29, 34, 35, 36, 37 Linear zone with increased fiber interlooping
30, 31                 Linear zone with minimal fiber interlooping
32                     Upper layer
33                     Lower layer
38                     Condensed zone traversing the layers 32, 33
40                     First nozzle cluster
41                     Second nozzle cluster
42                     Third nozzle cluster
43                     Forth nozzle cluster
44                     First water jet bundle
45                     Second water jet bundle
46                     Third water jet bundle
47                     Fourth water jet bundle
49                     Nozzle bar

Claims

1. Acoustic damping material (11) consisting of a random-fiber non-woven body (10) that is made of interlooped fibers (13, 14, 15, 16) and has at least two spatial zones (17, 18, 28, 29) displaying different degrees of fiber interlooping.

2. Damping material as in claim 1, characterized in that the two zones (17, 18, 28, 29) displaying different degrees of fiber interlooping have different fiber densities.

3. Damping material as in claim 1, characterized in that the spatial zones (17, 18, 28, 29) are arranged in an irregular pattern.

4. Damping material as in claim 1, characterized in that the fibers in the zones (17) displaying a lower degree of fiber interlooping are oriented predominantly in one plane, while, in the zones (18, 28, 29) displaying a greater degree of interlooping, a larger proportion of said fibers is oriented in a direction perpendicular to said plane.

5. Damping material as in claim 1, characterized in that the zones (18, 28, 29) displaying the greater degree of fiber interlooping have the form of strip-shaped regions.

6. Damping material as in claim 5, characterized in that the zones (18, 28, 29) are arranged at different distances from each other and parallel to each other.

7. Damping material as in claim 1, characterized in that the random-fiber non-woven body (10) comprises several layers (32, 33) that are made of interlooped fibers (25, 26), whereby at least one layer (32) of said layers has the zones (17, 34, 35) displaying different degree of fiber interlooping.

8. Damping material as in claim 7, characterized in that at least two of said layers (32, 33) have zones (17, 34, 35, 36, 37) displaying different degrees of fiber interlooping, said zones being arranged differently.

9. Damping material as in claim 8, characterized in that the zones (17, 34, 35, 36, 37) of the layers (32, 33) are strip-shaped and are superimposed in a manner so as to cross each other.

10. Damping material as in claim 1, characterized in that the fiber body (10) contains interstices (27, 39) that are free of fibers or have a fiber density that is considerably reduced compared to the surrounding fiber body (10).