Sound-absorbing materials and sound-absorbing systems

Abstract

The present invention provides a sound-absorbing material comprising a foamed resin mixed with magnetic powder, and a sound-absorbing system equipped therewith. [Solution] In the sound absorption system 100, the sound absorber 20, which is made by mixing magnetic powder 22 with foamed resin 21, is a sound absorber in which the sound absorption characteristics corresponding to frequency and sound absorption coefficient differ due to the difference in the magnetic force acting between it and other parts. The magnet 41 is arranged by a movable mechanism 43 so that the like poles of the sound absorber 20 and the magnet 41 are facing each other, and the sound absorption characteristics of the sound absorber can be changed by changing the magnetic force acting on the sound absorber. As a result, it is possible to achieve sound absorption performance over a wide frequency range with a single sound absorber, and the sound absorption characteristics can be changed according to the noise source even after the sound absorber has been installed.

Description

Technical Field

[0001] The present disclosure relates to a sound absorber and a sound absorption system including the same.

Background Art

[0002] Conventionally, sound absorbers made of foamed resin have been known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0012] , etc.)

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present disclosure provides a novel sound absorber.

Means for Solving the Problems

[0005] One aspect of the invention is a sound absorber in which magnetic powder is mixed with foamed resin, and the sound absorption characteristics in which the frequency and the sound absorption rate are made to correspond are different due to the difference in the magnetic force acting between other components.

Brief Description of the Drawings

[0006] [Figure 1] Conceptual diagram of the sound absorption system when a repulsive force occurs between the magnetized sound absorber and the magnet [Figure 2] Conceptual diagram of the sound absorption system when an attractive force occurs between the magnetized sound absorber and the magnet [Figure 3] Conceptual diagram of the sound absorption system including an electromagnet [Figure 4] Conceptual diagram of the sound absorption system when an attractive force occurs between the non-magnetized sound absorber and the N pole of the magnet [Figure 5]Conceptual diagram of a sound absorption system when an attractive force is generated between an unmagnetized sound absorber and the south pole of a magnet. [Figure 6] Conceptual diagram of the experimental apparatus [Figure 7] Graph showing the sound absorption characteristics of the sound absorber in Experimental Example 1. [Figure 8] Graph showing the sound absorption characteristics of the sound absorber in Experimental Example 2. [Figure 9] Graph showing the sound absorption characteristics of the sound absorber in Experimental Example 3. [Figure 10] Graph showing the sound absorption characteristics of the sound absorber in Experimental Example 4. [Figure 11] Graph showing the sound absorption characteristics of the sound absorber in Experimental Example 5. [Figure 12] Graph showing the sound absorption characteristics of the sound absorber in Experimental Example 6. [Modes for carrying out the invention]

[0007] [First Embodiment] Figure 1 shows a sound-absorbing body 20 according to the first embodiment. The sound-absorbing body 20 is formed by mixing and dispersing magnetic powder 22 in a foamed resin 21. The magnetic powder 22 is added to the raw materials of the foamed resin 21 and stirred and mixed, and when the raw materials foam and harden, it is dispersed within the foamed resin 21.

[0008] The foamed resin 21 preferably has an open-cell structure in order to exhibit sound absorption properties. The foamed resin 21 may have an open-cell structure in part, and it is preferable that the portion of the sound absorber 20 facing the noise source has an open-cell structure. In the example of this embodiment, the entire foamed resin 21 has an open-cell structure. In this disclosure, the term "resin" in "foamed resin 21" refers to resin in a broad sense and is used to include rubber and elastomers such as thermoplastic elastomers.

[0009] In this embodiment, the foamed resin 21 is latex foam. Latex foam is manufactured using latex, in which an uncrosslinked or partially crosslinked polymer of the resin is dispersed in water, as a raw material. The latex may contain additives such as crosslinking agents, crosslinking accelerators, crosslinking aids, plasticizers, surfactants, and gelling agents as appropriate. Latex foam is obtained by mixing the latex containing these additives (and magnetic powder 22) with a gas (e.g., air, nitrogen, carbon dioxide, etc.), stirring and mixing it to foam it, and then heating and molding it (crosslinking it).

[0010] In this embodiment, the polymer is rubber, and rubber latex foam is used as the foamed resin 21. The polymer may also be, for example, an elastomer or another resin.

[0011] If the above polymer is rubber, the rubber may be natural rubber or synthetic rubber. Examples of rubber include ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), butadiene rubber (BR), or silicone rubber.

[0012] If the above polymer is an elastomer, examples of elastomers include polyolefin elastomers (TPO), polyurethane elastomers (TPU), polyester elastomers (TPEE), polystyrene elastomers (TPS), and polyvinyl chloride elastomers (TPVC).

[0013] Other examples of the polymers mentioned above include polyurethane resins, polyolefin resins (polyethylene resins, polypropylene resins, etc.), polyvinyl chloride resins, and silicone resins.

[0014] Note that the foamed resin 21 may be a foam other than latex foam, for example, one obtained by chemical foaming or the like. Examples of foams other than latex foam include polyurethane foam, polyolefin foam (for example, polyethylene foam or polypropylene foam), polyvinyl chloride foam, foamed rubber, foamed elastomer, and the like.

[0015] The magnetic powder 22 may be a hard magnetic material or a soft magnetic material. Examples of powders of hard magnetic materials include neodymium-based magnetic powders, samarium-based magnetic powders, alnico-based magnetic powders, ferrite-based magnetic powders, and the like. When the magnetic powder 22 is a hard magnetic material, it can be permanently magnetized by magnetization. In the example of the present embodiment, the magnetic powder 22 is a hard magnetic material, and the magnetic powder of the entire sound absorber 20 is magnetized in one direction. When magnetizing the magnetic powder 22 to make it permanently magnetized, it is particularly preferable that the magnetic powder 22 is a neodymium-based magnetic powder that generates a strong magnetic force. Examples of powders of soft magnetic materials include powders of iron, carbonyl iron, silicon iron, Fe-Ni alloy (permalloy), Fe-Si-Al alloy (sendust), Fe-Co alloy (permenzyme), electromagnetic stainless steel, and the like.

[0016] The median diameter of the particles 23 of the magnetic powder 22 is preferably 50 μm or less, and more preferably 30 μm or less. By using the magnetic powder 22 having a median diameter of the particles 23 of 50 μm or less, the influence on the foaming and crosslinking of the foamed resin 21 (for example, latex foam) is reduced, so that it is possible to suppress a decrease in the foaming ratio and produce a foamed resin 21 having a finer and more uniform cell structure. The median diameter of the particles 23 of the magnetic powder 22 is preferably 0.5 μm or more, and more preferably 5 μm or more. Note that examples of the shape of the particles 23 of the magnetic powder 22 include spherical, flaky, needle-like, and the like.

[0017] The apparent density of the sound absorber 20 (the foamed resin 21 containing the magnetic powder 22) is 0.10 to 0.30 kg / m 3It is preferable that it is. The Asker C hardness of the sound absorber 20 is, for example, 60 or less, preferably 50 or less, and more preferably 40 or less. The Asker C hardness of the sound absorber 20 is, for example, 4 or more, but may be 10 or more, or may be 15 or more. The mass ratio of the magnetic powder to the foamed resin 21 is preferably 25 to 50 wt%.

[0018] The shape of the sound absorber 20 is not limited to a specific shape and may be determined according to the place of use and application. The shape of the sound absorber 20 may be, for example, plate-like (for example, plate-like with a thickness of 10 mm or more), columnar, spherical, or polyhedral such as cubic, rectangular, or prismatic.

[0019] Here, the sound absorber 20 has different sound absorption characteristics due to the difference in the magnetic force acting between it and other components. FIGS. 1 and 2 show a sound absorption system 100 of the present embodiment including a sound absorber 20 in which a magnetic powder 22 (for example, neodymium magnetic powder) is magnetized. The sound absorption system 100 includes a magnetic force generation unit 40 capable of generating a magnetic force acting on the sound absorber 20.

[0020] In the present embodiment, as described above, the entire magnetic powder 22 of the sound absorber 20 is magnetized in one direction (specifically, the synthetic magnetic moment obtained by synthesizing the magnetic moments of the particles 23 of the magnetic powder 22 is directed in one direction). This magnetization direction (magnetic direction) is downward in the examples of FIGS. 1 and 2. That is, the sound absorber 20 is a magnet with the lower side as the N pole and the upper side as the S pole.

[0021] In the present embodiment, the magnetic force generation unit includes a magnet 41, and the magnet 41 is a permanent magnet (for example, a ferrite magnet). In the present embodiment, the magnetic force generation unit 40 includes a movable mechanism 43 for relatively moving the magnet 41 with respect to the sound absorber 20. Further, the sound absorber 20 is fixed to a sound absorber support portion not shown. For example, in the sound absorption system 100, the magnet 41 is disposed on the side opposite to the side of the sound absorber 20 facing the noise source.

[0022] Here, as shown in Figure 1, when the magnet 41 is positioned by the movable mechanism 43 such that the same poles of the sound absorber 20 and the magnet 41 face each other (hereinafter referred to as "same-pole facing arrangement"), a repulsive force is generated between the sound absorber 20 and the magnet 41 (in the example in Figure 1, the north poles of the magnet 41 and the sound absorber 20 face each other, but the same is true if the south poles face each other). In the sound absorber 20, when a magnetic force acts as a repulsive force between the sound absorber 20 and the magnet 41 in this way, the sound absorption characteristics corresponding to frequency and sound absorption coefficient are different compared to when no magnetic force is acting. This is thought to be because when a repulsive force is generated, the magnetic powder 22 inside the sound absorber 20 is subjected to a force that moves it away from the magnet 41, causing the sound absorber 20 (foamed resin 21) to deform (for example, to compress) away from the magnet 41, and as a result, the bubble structure inside the sound absorber 20 changes.

[0023] On the other hand, as shown in Figure 2, when the magnet 41 is positioned by the movable mechanism 43 such that the opposite poles of the sound absorber 20 and the magnet 41 face each other (hereinafter referred to as "opposite pole facing arrangement"), an attractive force is generated between the sound absorber 20 and the magnet 41 (in the example in Figure 2, the south pole of the magnet 41 faces the north pole of the sound absorber 20, but the same is true if the north pole of the magnet 41 faces the south pole of the sound absorber 20). In the sound absorber 20, when a magnetic force acts as an attractive force between the sound absorber 20 and the magnet 41 in this way, the sound absorption characteristics corresponding to frequency and sound absorption coefficient are different compared to when no magnetic force is acting. This is thought to be because when an attractive force is generated, the magnetic powder 22 inside the sound absorber 20 deforms to move closer to the magnet 41 (for example, deforms to stretch), and as a result, the bubble structure inside the sound absorber 20 changes. Furthermore, in the sound absorber 20 of this embodiment, the sound absorption characteristics differ when the polarity is opposed to the polarity, compared to when the polarity is opposed as described above. As will be described later, for example, when comparing the sound absorption characteristics when the magnetic force acts as an attractive force with the sound absorption characteristics when the magnetic force acts as a repulsive force, it is possible to make the difference in sound absorption coefficient larger at a frequency of 4000 Hz than at a frequency of 2000 Hz.

[0024] As described above, the sound absorber 20 and sound absorption system 100 of this embodiment provide a novel sound absorber 20 in which the sound absorption characteristics corresponding to frequency and sound absorption coefficient can be varied by the difference in the magnetic force acting between the sound absorber 20 and other components (e.g., magnet 41). The movable mechanism 43 allows the magnetic force acting on the sound absorber 20 to be changed by moving the magnet 41 closer to or further away from the sound absorber 20, or by changing the orientation of the N and S poles of the magnet 41, thereby changing the sound absorption characteristics of the sound absorber 20. As a result, it is possible to achieve sound absorption performance across a wide frequency range with a single sound absorber 20, and the sound absorption characteristics can be changed according to the noise source even after the sound absorber 20 has been installed.

[0025] In this embodiment, since the entire magnetic powder 22 of the sound absorber 20 is magnetized in one direction, the sound absorption characteristics when the magnetic force acts as an attractive force and the sound absorption characteristics when the magnetic force acts as a repulsive force are different from each other. In other words, the sound absorption characteristics of the sound absorber 20 differ due to the difference in the direction of the magnetic force acting on the sound absorber 20. Therefore, it is possible to realize a sound absorber 20 having these two sound absorption characteristics.

[0026] [Second Embodiment] Figure 3 shows a sound-absorbing body 20 of a second embodiment and a sound-absorbing system 100 equipped therewith. In this embodiment, the magnet 41 of the magnetic force generating unit 40 is an electromagnet, which differs from the first embodiment. The magnetic force generating unit 40 is equipped with a drive circuit 45 that can change the direction or magnitude of the current supplied to the electromagnet.

[0027] In the sound absorption system 100 of this embodiment, the drive circuit 45 can change the magnetic force of the magnet 41 (electromagnet) on the sound absorber 20 to a repulsive or attractive force. This makes it possible to change the sound absorption characteristics of the sound absorber 20, similar to the first embodiment. In this embodiment, since the magnet 41 is an electromagnet, it is possible to change the sound absorption characteristics of the sound absorber 20 without providing a movable mechanism 43 as in the first embodiment.

[0028] [Third Embodiment] Figures 4 and 5 show a sound absorber 20 of a third embodiment and a sound absorption system 100 equipped therewith. This embodiment differs from the first embodiment in that the magnetic powder 22 of the sound absorber 20 is a soft magnetic material (for example, carbonyl iron powder) and is not magnetized. In this embodiment, since the sound absorber 20 is not magnetized, an attractive force is generated between the sound absorber 20 and the magnet 41 whether the north pole of the magnet 41 is pointed toward the sound absorber 20 (see Figure 4) or the south pole of the magnet 41 is pointed toward it (see Figure 5). Therefore, the sound absorption characteristics of the sound absorber 20 are the same in the arrangement in Figure 4 and the arrangement in Figure 5. With this embodiment as well, the sound absorption characteristics of the sound absorber 20 can be changed by changing the magnetic force acting on the sound absorber 20, making it possible to achieve sound absorption performance over a wide frequency range with a single sound absorber 20. In this embodiment, since there is no need to change the orientation of the north and south poles of the magnet 41 in the movable mechanism 43, the configuration of the movable mechanism 43 can be simplified.

[0029] [Other embodiments] In the above embodiment, the magnetic force generating unit 40 generated a magnetic force acting on the sound-absorbing material 20 using a magnet 41, but it may also generate a magnetic force by passing an electric current through a coil, for example.

[0030] [Confirmation experiment] The sound absorption characteristics of the sound absorption systems in Experimental Examples 1 to 6 were evaluated below. The following experimental examples are just examples, and the sound absorber 20 and sound absorption system 100 of this disclosure are not limited to the configurations of the following experimental examples.

[0031] 1. Configuration of sound-absorbing materials and sound-absorbing systems <Experimental Examples 1-3> The sound absorbers in Experimental Examples 1-3 have the same configuration (a disc shape with a diameter of 40 mm and a thickness of 10 mm), and are sound absorbers 20 having magnetized magnetic powder 22 (neodymium powder), similar to the first embodiment described above (the magnetization direction is the axial direction of the disc-shaped sound absorber 20). The following materials were used. Foamed resin 21; rubber latex foam. "NBR Nipol LX531B" manufactured by Nippon Zeon Co., Ltd. was used. Magnetic powder 22; neodymium powder. Magnequench's "MQFP-14-12 (average particle size 25 μm)" was used.

[0032] In Experimental Example 1, the sound absorption system 100 is not equipped with a magnet 41 (no magnetic field).

[0033] In Experimental Example 2, in the sound absorption system 100, the sound absorber 20 and the magnet 41 are arranged opposite each other with the same poles (the north poles are facing each other), similar to Figure 1.

[0034] In Experimental Example 3, in the sound absorption system 100, the sound absorber 20 and the magnet 41 are arranged opposite each other with opposite poles, similar to Figure 2 (the north pole of the sound absorber 20 and the south pole of the magnet 41 are arranged opposite each other).

[0035] <Experimental Examples 4-6> The sound absorbers in Experimental Examples 4-6 have the same configuration (disc shape with a diameter of 40 mm and a thickness of 10 mm) and are sound absorbers 20 having unmagnetized magnetic powder 22 (carbonyl iron powder), similar to the third embodiment described above. The following materials were used. Foamed resin 21; rubber latex foam. "NBR Nipol LX531B" manufactured by Nippon Zeon Co., Ltd. was used. Magnetic powder 22; carbonyl iron powder. BASF's "OM grade" was used.

[0036] In Experimental Example 4, the sound absorption system 100 is not equipped with a magnet 41 (no magnetic field).

[0037] In Experimental Example 5, in the sound absorption system 100, the north pole of the magnet 41 is directed towards the sound absorber 20, similar to Figure 4.

[0038] In Experimental Example 6, in the sound absorption system 100, the south pole of the magnet 41 is directed towards the sound absorber 20, similar to Figure 5.

[0039] 2. Test Method Based on JIS A 1405-2, the sound absorption coefficient corresponding to each frequency was measured using the acoustic tube 50 shown in Figure 6. Specifically, a speaker 51 (noise source) that generates white noise was placed at one end of the acoustic tube 50. The acoustic tube 50 was then sealed by placing a sound absorber 20 in the middle of the acoustic tube 50 so that the acoustic tube 50 and the sound absorber 20 were coaxially arranged, and the sound was measured with a microphone 52 placed between the speaker 51 and the sound absorber 20. In Examples 2, 3, 5, and 6, a magnet 41 was placed opposite the sound absorber 20 from the opposite side of the speaker 51 with a gap h between them, and the acoustic tube 50 was sealed with the magnet 41. In Examples 1 and 4, a sound barrier was placed opposite the sound absorber 20 from the opposite side of the speaker 51 with a gap h between them, and the acoustic tube 50 was sealed (the sound barrier was not provided with a magnetic force generating part 40 capable of generating a magnetic force that acts on the sound absorber 20). The orientation of the north and south poles of magnet 41 is as described above. The spacing h was set to three levels in each experimental example: 5 mm, 10 mm, and 15 mm.

[0040] 3. Test Results As shown in Figures 7 to 9, it was confirmed that the sound absorption characteristics of the magnetized sound absorber 20 differ significantly by varying the magnetic force. For example, in Experiment Example 1 under no magnetic field conditions, the sound absorption coefficient tends to be higher at low frequencies (see Figure 7), but in Experiment Example 2 with like-pole opposing arrangement, the sound absorption coefficient is low across all frequencies (see Figure 8). In Experiment Example 3 with opposite-pole opposing arrangement, the sound absorption coefficient is higher at high frequencies (see Figure 9). Comparing the sound absorption characteristics when the magnetic force acts as an attractive force and when the magnetic force acts as a repulsive force from Experiment Examples 2 and 3, the difference in sound absorption coefficient is larger at 4000 Hz than at 2000 Hz. Also, from Experiment Example 2, in the sound absorption characteristics when the magnetic force acts as a repulsive force, the sound absorption coefficient is 0.4 or less at frequencies in the range of 1000 to 4000 Hz. Furthermore, from Experimental Example 3, the sound absorption characteristics when magnetic force acts as an attractive force show that the sound absorption coefficient is higher at frequencies of 2000-4000 Hz than at frequencies of 1000 Hz.

[0041] As shown in Figures 10 to 12, it was confirmed that the sound absorption characteristics of the unmagnetized sound absorber 20 differed significantly depending on the magnetic force (depending on the presence or absence of magnetism). For example, in Experiment Example 4 under no magnetic field conditions, the sound absorption coefficient tended to be higher at low frequencies (see Figure 10), but in Experiment Examples 5 and 6, where a magnet 41 (N pole or S pole) was brought close, the sound absorption coefficient was higher at high frequencies (see Figures 11 and 12). It was confirmed that the sound absorption characteristics of the unmagnetized sound absorber 20 showed a similar trend whether the N pole or S pole of the magnet 41 was pointed towards it.

[0042] As described above, it was confirmed that in the sound absorption system 100, the sound absorption characteristics of the sound absorber 20 can be significantly altered simply by changing the magnetic force acting on the sound absorber 20.

[0043] [Note] The following describes the features extracted from the above embodiment, explaining their effects and other aspects as needed. For ease of understanding, corresponding configurations in the above embodiment will be indicated in parentheses as appropriate, but these features are not limited to the specific configurations indicated in parentheses.

[0044] For example, the following set of features, relating to sound absorbers and sound absorption systems equipped therewith, can be considered to have been conceived with the objective of "providing a novel sound absorber," given the background technology that "conventionally, sound absorbers made of foamed resin are known (see, for example, Japanese Patent Application Publication No. 2021-116411 (paragraph

[0012] , etc.))."

[0045] [Feature 1] A sound-absorbing material in which magnetic powder is mixed with foamed resin, A sound-absorbing material in which the sound absorption characteristics, corresponding to frequency and sound absorption coefficient, differ due to differences in the magnetic force acting between it and other components.

[0046] [Feature 2] The sound-absorbing material according to Feature 1, wherein the sound-absorbing characteristics differ due to the difference in the direction of the magnetic force.

[0047] [Feature 3] The sound-absorbing material according to feature 1 or 2, wherein the magnetic powder of the entire sound-absorbing material is magnetized in one direction.

[0048] [Feature 4] The sound-absorbing material according to Feature 3, wherein, when comparing the sound absorption characteristics when the magnetic force acts as an attractive force with the sound absorption characteristics when the magnetic force acts as a repulsive force, the difference in sound absorption coefficient is greater at a frequency of 4000 Hz than at a frequency of 2000 Hz.

[0049] [Feature 5] The sound-absorbing material described in any one of the features 1 to 4, A sound absorption system comprising a magnetic force generating unit capable of changing the magnetic force acting on the sound absorber.

[0050] [Feature 6] The magnetic force generating unit includes, The sound absorption system according to feature 5, comprising a magnet and a movable mechanism for moving the magnet relative to the sound absorber.

[0051] [Feature 7] The magnetic force generating unit includes, The sound absorption system according to feature 5, comprising an electromagnet and a drive circuit capable of changing the direction or magnitude of the current supplied to the electromagnet.

[0052] Based on the above features, a novel sound-absorbing material is provided.

[0053] While this specification and drawings disclose specific examples of the technology included in the claims, the technology described in the claims is not limited to these specific examples, but also includes various modifications and changes to these examples, as well as parts of the examples taken individually. [Explanation of Symbols]

[0054] 20 Sound absorbers 21 Foamed resin 22 Magnetic powder 23 particles 40 Magnetic field generating section 41 Magnets 43 Movable mechanism 45 Drive Circuit 50 sound tube 51 speakers 52 Mike 100 sound absorption systems

Claims

1. A sound-absorbing material in which magnetic powder is mixed with foamed resin, A sound-absorbing material in which the sound absorption characteristics, corresponding to frequency and sound absorption coefficient, differ due to differences in the magnetic force acting between it and other components.

2. The sound-absorbing material according to claim 1, wherein the sound-absorbing characteristics differ depending on the direction of the magnetic force.

3. The sound absorber according to claim 1, wherein the magnetic powder of the entire sound absorber is magnetized in one direction.

4. The sound-absorbing material according to claim 3, wherein, when comparing the sound absorption characteristics when the magnetic force acts as an attractive force with the sound absorption characteristics when the magnetic force acts as a repulsive force, the difference in sound absorption coefficient is greater at a frequency of 4000 Hz than at a frequency of 2000 Hz.

5. A sound-absorbing body according to any one of claims 1 to 4, A sound absorption system comprising a magnetic force generating unit capable of changing the magnetic force acting on the sound absorber.

6. The magnetic force generating unit includes, The sound absorption system according to claim 5, further comprising a magnet and a movable mechanism for moving the magnet relative to the sound absorber.

7. The magnetic force generating unit includes, The sound absorption system according to claim 5, further comprising an electromagnet and a drive circuit capable of changing the direction or magnitude of the current supplied to the electromagnet.

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