WO2024105489A1

WO2024105489A1 - Acoustic article

Info

Publication number: WO2024105489A1
Application number: PCT/IB2023/061118
Authority: WO
Inventors: Peter A. Masterson
Original assignee: 3M Innovative Properties Company
Priority date: 2022-11-18
Filing date: 2023-11-03
Publication date: 2024-05-23

Abstract

Provided is an acoustic article that include a first porous layer having a first density, and a second porous layer having a second density that is disposed on the first porous layer. The first density is from 110 percent to 1200 percent of the second density or the second density is from 110 percent to 1200 percent of the first density. The first porous layer includes a plurality of apertures extending through the first porous layer, where the plurality of apertures are not considered when determining density. These acoustic articles can provide significant noise reduction in various applications, including server housings.

Description

ACOUSTIC ARTICLE

Field of the Invention

Provided are articles and methods thereof for absorbing sound energy. Such articles and methods can be useful, for example, in electronic applications.

Background

Computer networks have become an essential part of people's lives. Many enterprises have their own network servers for storing a large amount of research and development data, financial data, mails and the like. Enterprise-level servers can be used for hundreds of computers connected with the networks. A large amount of noise is generated in the operation process of the large network servers, and especially, by the cooling fans as they generate noise when operating at high RPM levels.

The negative impacts of environmental noise on mental and physical health are well documented. Noise issues are not only undesirable from a health perspective, they can also affect the operation of electronic equipment. As server hard drives have evolved to ever higher data density levels they are becoming increasingly sensitive to disruption from fan noise. Noise problems can arise internally within each server unit, and there is a need to reduce noise level between fans and hard drives. Ultimately, left unabated, fan noise can lead to degradation in hard drive performance.

Summary

There is a technical need to provide sound-absorbing panels including materials capable of absorbing sound associated with electronic equipment and cooling fans used to cool the equipment. There is also a need to provide an acoustic absorbing panel that accommodates the needs, such as sound absorption frequency, sound reduction, rigidity, weight, thickness, air flow, and fire resistance, of panels used with computers, servers, or server racks.

Provided herein is a multilayer article comprised of foam layers having different densities in which some layers include macroscopic air gaps and some do not. The multilayer article may be comprised of one or more continuous foam layers and one or more discontinuous foam layers. Acoustic absorption is enhanced when sound must pass though different density materials and when air gaps are present, as provided by apertures extending through a layer. Optionally, the layer containing the apertures can be disposed with a suitable adhesive on the surface (i.e., wall) of noise-generating device. As a further option, the continuous foam layer that lacks apertures has a greater density than the discontinuous foam layer containing the apertures. Advantageously, these articles display acoustic attenuation attributable to both density effects and air gap effects. Acoustic articles can be augmented by replication of these layer configurations to further enhance acoustic absorption.

In a first aspect, an acoustic article is provided. The acoustic article comprises: a first porous layer having a first density; and a second porous layer having a second density that is disposed on the first porous layer, wherein the first density is from 110 percent to 1200 percent of the second density or the second density is from 110 percent to 1200 percent of the first density, and wherein the first porous layer includes a plurality of apertures extending through the first porous layer and wherein the plurality of apertures are not considered when determining density.

In a second aspect, a sound-absorbing assembly is provided, comprising: a substrate; and the acoustic article extending across the substrate, wherein the first porous layer is exposed along a major surface of the sound-absorbing assembly.

In a third aspect, a method is provided for reducing noise in an enclosure in which there is air flow. The method comprises: providing an acoustic article comprising: a first porous layer having a first density; and a second porous layer having a second density that is disposed on the first porous layer, wherein the first density is from 110 percent to 1200 percent of the second density or the second density is from 110 percent to 1200 percent of the first density, wherein the first porous layer includes a plurality of apertures extending through the first porous layer and wherein the plurality of apertures are not considered when determining density; and disposing the acoustic article within the enclosure such that the air flow is guided along an exposed major surface of the acoustic article.

Brief Description of the Drawings

FIGS. 1-4 are exploded perspective views of an acoustic article according to various exemplary embodiments. FIGS. 5 and 6 display acoustic insertion loss test results for exemplary acoustic articles relative to those of comparative examples.

FIGS. 7A and 7B are top down and side views of an acoustic horn used for insertion loss testing the exemplary acoustic articles.

Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the disclosure. The figures may not be drawn to scale.

DEFINITIONS

“Ambient temperature” means at 21 degrees Centigrade.

Detailed Description

As used herein, the terms “preferred” and “preferably” refer to embodiments described herein that can afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” or “the” component may include one or more of the components and equivalents thereof known to those skilled in the art. Further, the term “and/or” means one or all of the listed elements or a combination of any two or more of the listed elements.

It is noted that the term “comprises”, and variations thereof do not have a limiting meaning where these terms appear in the accompanying description. Moreover, “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably herein. Relative terms such as left, right, forward, rearward, top, bottom, side, upper, lower, horizontal, vertical, and the like may be used herein and, if so, are from the perspective observed in the particular drawing. These terms are used only to simplify the description, however, and not to limit the scope of the invention in any way. Reference throughout this specification to “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment” means that a particular feature, structure, material, or characteristic described relating to the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention.

An acoustic article according to one exemplary embodiment is illustrated in FIG. 1 and designated by the numeral 100 herein. Acoustic article 100 has a bilayer configuration, and includes a first layer 102 and a second layer 104. Both the first and second layers 102, 104 are porous layers. In some embodiments, the bilayer configuration may be reversed, with the second layer being placed on top of the first layer.

The first layer 102 has a major surface 106 that is exposed along a top surface of the acoustic article 100. A plurality of apertures 108 extends through the first layer 102 along a direction perpendicular to the major surface 106. Optionally and as shown, the plurality of apertures 108 are arranged according to a two-dimensional pattern that is replicated across the major surface 106. A grid pattern is shown, but other aperture configurations (e.g., hexagonal, semi -random) are also possible. In contrast to the first layer 102, the second layer 104 does not include any apertures. In some embodiments, the plurality of apertures 108 extends through the second layer 104 along a direction perpendicular to the major surface 106.

The first layer 102 and second layer 104 can be made from porous materials with densities that are significantly different from each other. In some embodiments, the first layer 102 has a first density, the second layer 104 has a second density, where the first density is significantly greater than the second density. In other embodiments, the first layer 102 can have a first density, and the second layer 104 can have a second density, where the second density is significantly greater than the first density. For the purposes of this disclosure, the plurality of apertures 108 are deemed to be macroscopic features separate from the bulk of the first layer 102 and thus not considered in determining density.

More particularly, the first density can be from 110 percent to 1200 percent, from 115 percent to 400 percent, from 120 percent to 200 percent, or in some embodiments less than, equal to, or greater than 110 percent, 115, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1100, or 1200 percent of the second density. The first density itself can be from 16 kg/m³ to 400 kg/m³, from 48 kg/m³ to 160 kg/m³, from 80 kg/m³ to 130 kg/m³, or in some embodiments, less than, equal to, or greater than 16 kg/m³, 20, 30, 48, 50, 60, 70, 80, 90, 100, 130, 160, 200, 300, or 400 kg/m³. Similarly, the second density can be from 16 kg/m³ to 400 kg/m³, from 48 kg/m³ to 160 kg/m³, from 80 kg/m³ to 130 kg/m³, or in some embodiments, less than, equal to, or greater than 16 kg/m³, 20, 30, 48, 50, 60, 70, 80, 90, 100, 130, 160, 200, 300, or 400 kg/m³.

The porous layers described herein are comprised of materials containing a multiplicity of embedded pores, or voids. In some instances, the pores are interconnected, in which case the material is deemed to be open-celled. In other instances, the pores do not communicate with each other, in which case the material is deemed closed-cell. It is also possible that the material of a porous layer falls within a continuum between these two scenarios, where some but not all of the pores communicate with the pores around them. For the sake of clarity in this disclosure, the pores within the first and second layers 102, 104 are considered when determining the density of these layers.

The first and second porous layers 102, 104 can be of any suitable porosity. In some embodiments, the first porous layer has a first porosity, the second porous layer has a second porosity, and the first porosity differs significantly from the second porosity. In some instances, the second porosity can be from 5 percent to 90 percent, from 10 percent to 80 percent, from 20 percent to 60 percent, or in some embodiments less than, equal to, or greater than 5 percent, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or 90 percent of the first porosity. Conversely, the first porosity can be from 5 percent to 90 percent, from 10 percent to 80 percent, from 20 percent to 60 percent, or in some embodiments less than, equal to, or greater than 5 percent, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or 90 percent of the second porosity.

The first porosity can be from 30 percent to 99.9 percent, from 65 percent to 98 percent, from 85 percent to 96 percent, or in some embodiments, less than, equal to, or greaterthan 30 percent, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.2, 99.5, 99.7, 99.8, or 99.9 percent. The second porosity can be from 30 percent to 99.9 percent, from 65 percent to 98 percent, from 85 percent to 96 percent, or in some embodiments, less than, equal to, or greater than 30 percent, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.2, 99.5, 99.7, 99.8, or 99.9 percent. In each case above, the plurality of apertures 180 are not considered when determining porosity.

The porous layers 102, 104 can be made of any suitable material. Suitable materials can include polymers, metals, ceramics, and combinations thereof. In some embodiments, both porous layers 102, 104 are made from polymeric foams. Each polymeric foam be, for example, a polyurethane foam that has viscoelastic properties at ambient temperature. These viscoelastic properties can be manifested by a peak tan delta of at least 1.0, the peak tan delta measured by dynamic mechanical analysis ranging from 1 to 10,000 Hertz and from - 20 to 70 degrees Centigrade, with an amplitude of 0.3% at 30% pre-compression.

The first and second layers 102, 104 can be thermally, sonically, or chemically welded to each other, adhesively bonded to each other, or otherwise fastened to each other by mechanical means. Suitable adhesives can include curable adhesives, hot melt adhesives, and pressure-sensitive adhesives. If an adhesive is used, the adhesive can extend continuously over the entire major surface of the second layer 104 facing the first layer 102, or alternatively, the adhesive can extend only along the bottom-facing surface of the first layer 102 such that no adhesive is disposed across the apertures 108. In some instances, the latter configuration might impart an acoustic benefit by allowing air penetration into exposed pores of the second porous layer 104.

It is to be further understood that while the first layer 102 is considered a top layer and the second layer 104 is considered a bottom layer as described herein, the acoustic article 100 could have any suitable orientation based on the desired installation and direction of incoming sound energy. Moreover, one or both of the first and second layers 102, 104 can be replicated, in alternating fashion (e.g., ABA, ABAB, BAB, or ABABA), to augment the layer structure of the acoustic article 100 and provide a configuration having 3, 4, 5, 6, or any other suitable number of layers. Such augmentation can further enhance the sound absorbing capability of the acoustic article 100.

The layers of the acoustic article 100, such as the first layer 102 or second layer 104, are not particularly limited and can have any suitable thickness. The thickness can be from 0.1 millimeters to 120 millimeters, 1 millimeters to 60 millimeters, 2 millimeters to 20 millimeters, or in some embodiments, less than, equal to, or greater than 0.1 millimeters, 0.2, 0.3, 0.4, 0.5, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, or 120 millimeters. FIG. 2 shows an acoustic article 200 that has, like the prior embodiment, a first layer 202 and a second layer 204. Unlike the prior embodiment, both of the first and second layers 202, 204 have apertures extending through them. As depicted, the first layer 202 includes a plurality of first apertures 208, 208’, 208”, while the second layer 204 includes a plurality of second apertures 210. Optionally and as shown, the apertures 208, 208’, 208” have different sizes, while the apertures 210 are generally uniform in their size and shape. As previously explained, the first and second layers 202, 204 are preferably porous layers and can have significantly differing degrees of density and/or porosity, depending on the application at hand.

Use of the differently-sized apertures 208, 208’, 208” can provide Helmholtz resonators, which are resonant chambers tuned to operate at particular sound frequencies. Sizes of the apertures can be adjusted, as appropriate, according to multiple frequencies of sound energy for the application.

The apertures in the first layer 202 and the apertures in the second layer 204 may or may not overlap with each other when shown in plan view. For example, in FIG. 2, the centrally-located aperture 208” in the first layer 202 aligns with an aperture in the second layer 204, while many of the other apertures 208, 208’ do not.

Further options and related advantages associated with the first and second layers 202, 204 have been previously described and need not be repeated here.

FIG. 3 shows an acoustic article 300 according to yet another embodiment, which is comprised of a first layer 302, second layer 304, and third layer 305. The first and second layers 302, 304 are essentially analogous to those in the prior embodiment. The third layer 305 can be comprised of a porous layer having a density and/or porosity significantly different from that of either of the first layer 302 or second layer 304. Unlike the first and second layers 302, 304, the third layer 305 does not include any apertures. Augmentations of the acoustic article 300 are also possible by replicating one or more layers 302, 304, 305, as explained previously.

FIG. 4 provides yet another acoustic article 400 comprised of a first layer 402, a second layer 404, and a third layer 405 in a sandwich construction, the second layer 404 having a plurality of apertures 408 extending therethrough. The first layer 402 and third layer 405 have similar density (or porosity), while the second layer has a density (or porosity) that is significantly larger or smaller than that of the first layer 402 and the third layer 405. Alternatively, the first layer 402, second layer 404, and third layer 405 all have different densities (or porosities).

The acoustic articles described herein can be coupled to any of a number of suitable substrates to the purpose of mitigating noise. In one exemplary application, the substrate comprises the housing of a computer server. Coupling to the substrate can be achieved by bonding a major surface of the acoustic article to a surface of the substrate. The acoustic article can also be suspended from the substrate along one or more of its peripheral edges whereby one or both of its major surfaces are exposed. In this suspended configuration, there could be two or more acoustic articles arranged next to each other, with air gaps extending therebetween. The substrate can, in some cases, be an enclosure in which the acoustic articles are suspended from one or more walls of the enclosure. In each case above, the acoustic article can be mounted or fixtured relative to the substrate in a manner that guides air flow along an exposed major surface of the acoustic article.

EXAMPLES

Unless otherwise noted or readily apparent from the context, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. Where applicable, brand names and trademarked names are shown in all caps.

Table 1: Materials

Test Methods

Insertion Loss Test

The effect of the samples on sound propagation was measured using an acrylonitrile butadiene styrene (ABS) acoustic horn (inlet diameter of 10 cm (9.94 inches) and outlet cross section of 66.4 cm x 6.5 cm (26.14 inches x 2.56 inches)) as represented in FIGS. 7A and 7B. Three calibrated 4190 type free field (Hottinger Briiel & Kjaer of Nearum, Denmark) microphones were placed approximately 20 cm apart from each other and from the outlet of the acoustic horn with one microphone positioned in the center of the horn and the other two placed on either side of the center microphone on the same plane. Microphone data was collected and analyzed using a Hottinger Briiel & Kjaer data acquisition system and the associated PULSE Labshop software. Full spectrum white noise (total sound pressure level 82.547 dB(A)) was emitted from a Hottinger Briiel & Kjaer Type 4206 Impedance Sound Source speaker in the range of 20 - 20,000 Hz. A sample was placed in the acoustic horn without additional securement. The difference in the averaged measured sound pressure level (SPL) from the three microphones without a sample in the positioned in the acoustic horn versus with the sample in the acoustic horn is represented as the insertion loss.

Examples 1-16 (EX1-EX16) and Comparative Examples 1-2 (CE1-CE2)

Samples were assembled as identified in Table 2. The length of each porous layer was 50 cm (19.69 inches), and the width was 7.5 cm (2.95 inches) for each sample. Various size (either 1 cm x 1 cm or 2.2 cm x 2.2 cm) square holes /apertures were patterned in the porous layer by die cutting techniques as known to those of skill in the art. 1 cm x 1 cm apertures were patterned as a 3 x 10 grid in the porous layer. 2.2 cm x 2.2 cm apertures were patterned as a 2 x 7 grid in the porous layer. Sample testing was conducted with the apertures either oriented up or down in the testing apparatus. Orientation is identified in Table 2.

Table 2: Sample Construction

Insertion Loss testing was conducted, and the results are represented in Table 3A (for CE1 and EXI - EX8) and Table 3B (for CE2 and EX9 - EX16). CE1 and EXI are represented visually in FIG. 5. CE2 and EX9 are represented visually in FIG. 6. Table 3A: Insertion Loss Test Results

Table 3B: Insertion Loss Test Results

All cited references, patents, and patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.

Claims

CLAIMS What is claimed is:

1. An acoustic article comprising: a first porous layer having a first density; and a second porous layer having a second density that is disposed on the first porous layer, wherein the first density is from 110 percent to 1200 percent of the second density or the second density is from 110 percent to 1200 percent of the first density, and wherein the first porous layer includes a plurality of apertures extending through the first porous layer and wherein the plurality of apertures are not considered when determining density.

2. The acoustic article of claim 1, wherein the first density is from 16 kg/m³ to 400 kg/m³.

3. The acoustic article of claim 2, wherein the second density is from 16 kg/m³ to 400 kg/m³.

4. The acoustic article of any one of claims 1-3, wherein the first porous layer has a first porosity, the second porous layer has a second porosity, and the first porosity is from 5 percent to 90 percent of the second porosity, wherein the plurality of apertures are not considered when determining porosity.

5. The acoustic article of any one of claims 1-4, wherein the first porous layer and/or second porous layer has a thickness of from 0.1 millimeters to 120 millimeters.

6. The acoustic article of any one of claims 1-5, wherein the second porous layer is a layer that does not include any apertures.

7. The acoustic article of any one of claims 1-6, wherein the plurality of apertures are arranged according to a replicated two-dimensional pattern.

8. The acoustic article of any one of claims 1-7, wherein the first and second porous layers are adhesively bonded to each other.

9. The acoustic article of any one of claims 1-8, wherein the first porous layer, the second porous layer, or both, comprise a polymeric foam.

10. The acoustic article of claim 9, wherein the polymeric foam comprises a polyurethane.

11. The acoustic article of claim 9 or 10, wherein the polymeric foam has a peak tan delta of at least 1.0, the peak tan delta measured by dynamic mechanical analysis ranging from 1 to 10,000 Hertz and from -20 to 70 degrees Centigrade, with an amplitude of 0.3% at 30% pre-compression.

12. A sound-absorbing assembly comprising: a substrate; and the acoustic article of any one of claims 1-11 extending across the substrate, wherein the first porous layer is exposed along a major surface of the soundabsorbing assembly.

13. A sound-absorbing assembly of claim 12, wherein the acoustic article is bonded to the substrate.

14. The sound-absorbing assembly of claim 12, wherein the acoustic article is fixtured next to the substrate with a gap therebetween.

15. The sound-absorbing assembly of any one of claims 12-14, wherein the substrate comprises a server housing.

16. A method of reducing noise in an enclosure in which there is air flow, the method comprising: providing an acoustic article comprising: a first porous layer having a first density; and a second porous layer having a second density that is disposed on the first porous layer, wherein the first density is from 110 percent to 1200 percent of the second density or the second density is from 110 percent to 1200 percent of the first density, wherein the first porous layer includes a plurality of apertures extending through the first porous layer and wherein the plurality of apertures are not considered when determining density; and disposing the acoustic article within the enclosure such that the air flow is guided along an exposed major surface of the acoustic article.