JP7797795B2 - Sound-absorbing structure, automotive interior parts and automobiles - Google Patents

Description

The present invention relates to sound-absorbing structures, automotive interior parts, and automobiles.

There are many sound sources within an automobile. To address the demand for quietness from noise both inside and outside the vehicle, automobiles are equipped with a variety of soundproofing measures. In particular, specialized soundproofing covers with excellent sound absorption and insulation performance are used for loud noise-generating components (intrinsic sound sources) such as the engine, transmission, and drivetrain. Furthermore, since reducing interior noise is directly linked to the value (luxury) of a vehicle, there is a high demand for low-noise components in automobiles. For example, even within an automobile's cabin, cavity resonance can be induced by engine vibration, intake and exhaust noise, and road surface irritation, resulting in problems such as muffled sounds and road noise. Measures to reduce such noise are essential. While various soundproofing components have been used in automobile interiors, such as roof trim, further performance improvements are required. Furthermore, from the perspective of improving fuel economy, it is preferable for soundproofing measures to also meet the demand for lightweight vehicles.

There are various known structures for sound-absorbing materials used in soundproofing. For example, foams such as urethane foam have traditionally been used as sound-absorbing materials, and are capable of absorbing airborne sound in the high-frequency range. In addition, porous materials such as glass wool and rock wool are used as sound-absorbing materials for noise in the frequency range above 500 Hz.

On the other hand, attempts have been made to deal with noise below 500 Hz by increasing the thickness of the porous sound-absorbing material, or by creating an air layer behind the sound-absorbing material for even lower frequency ranges. However, in order to achieve sufficient sound absorption, problems have arisen, such as the weight increasing and the need for a large space.

To address this issue, for example, Patent Document 1 discloses a sound-absorbing material made by laminating a foam and a porous material such as glass wool or rock wool into a single piece. This configuration is said to provide a high sound-absorbing effect in the low frequency range and excellent vibration damping.

Japanese Patent Application Laid-Open No. 2003-316364

However, the inventors' investigations have revealed that even using the technology described in Patent Document 1 does not necessarily result in sufficient sound absorption performance in the frequency range of 300 Hz or less. Therefore, an object of the present invention is to provide a means for achieving high sound absorption performance in the frequency range of 300 Hz or less.

The inventors conducted extensive research in light of the above-mentioned problems. As a result, they discovered that by laminating a porous sheet and a lattice plate made of resin or metal, and allowing the porous sheet to displace in the direction of sound incidence, it is possible to obtain a sound-absorbing structure that exhibits high sound-absorbing performance in the frequency range of 300 Hz or less, and thus completed the present invention.

In other words, the present invention is a sound-absorbing structure in which a porous body sheet and a lattice plate made of resin or metal are laminated in this order, the porous body sheet is fixed to the lattice plate at locations facing at least some of the lattice points of the lattice plate, and the areas other than the fixed locations are displaceable in the direction of incident sound.

According to the present invention, when sound is incident on a porous sheet, the portions of the porous sheet that are not fixed to the lattice plate are displaced in the direction of the sound, generating vibrations that cancel out the low-frequency components of the sound. As a result, sound absorption performance can be improved, particularly in the low-frequency range below 300 Hz.

1A is a perspective view schematically illustrating an outline of a sound absorbing structure according to one embodiment of the present invention, and FIG. 1B is a cross-sectional view of the sound absorbing structure according to one embodiment of the present invention. FIG. 10 is a perspective view schematically illustrating an outline of a sound absorbing structure according to another embodiment of the present invention. FIG. 1A is a diagram showing an outline of an apparatus used to measure sound absorption coefficient, and FIG. 1B is a diagram showing an outline of an apparatus used to measure membrane vibration acceleration. 1 is a diagram showing the sound absorption coefficient and membrane vibration acceleration of the sound absorbing structure produced in Example 1. FIG. 1 is a photograph of the sound-absorbing structure samples produced in Examples 2-1 and 2-2. 1 is a graph showing the results of measuring the sound absorption coefficient of the sound absorbing structures produced in Comparative Examples 2-1 and 2-2 and Examples 2-1 and 2-2. FIG. 1 is a diagram showing the size and arrangement of openings in a lattice plate used in a sound-absorbing structure fabricated in the Examples section described later, as well as the opening area. 10 is a graph showing the results of measuring the sound absorption coefficient of the sound absorbing structures produced in Examples 3-1 to 3-6. 1 is a graph showing the results of measuring the sound absorption coefficient of the sound absorbing structures produced in Example 2-1, Examples 3-2 to 3-4, and Example 3-7. 10 is a graph showing the results of measuring the sound absorption coefficient of the sound absorbing structures produced in Examples 4-1 to 4-6. FIG. 2 is a diagram showing the adhesive positions of the porous sheet and the lattice plate in the sound-absorbing structure produced in the Examples section described later. 10 is a graph showing the results of measuring the sound absorption coefficient of the sound absorbing structures produced in Examples 5-1 to 5-5 and Comparative Examples 5-1 to 5-3.

One aspect of the present invention is a sound-absorbing structure in which a porous body sheet and a lattice plate made of resin or metal are laminated in this order, the porous body sheet is fixed to the lattice plate at locations facing at least some of the lattice points of the lattice plate, and the areas other than the fixed locations are displaceable in the direction of incident sound.

Embodiments of the present invention will be described below with reference to the drawings, but the technical scope of the present invention is not limited to the following embodiments. Note that the dimensional proportions in the drawings have been exaggerated for the sake of explanation and may differ from the actual proportions. In this specification, the range "X to Y" means "X or greater and Y or less." Furthermore, unless otherwise specified, operations and measurements of physical properties are performed at room temperature (20-25°C) and a relative humidity of 40-50%.

Figure 1(a) is a perspective view showing a schematic outline of a sound-absorbing structure according to one embodiment of the present invention. Figure 1(b) is a cross-sectional view of a sound-absorbing structure according to one embodiment of the present invention.

As shown in Figures 1(a) and (b), a sound-absorbing structure 1 according to one embodiment of the present invention has a configuration in which a porous body sheet 10 and a lattice plate 20 are laminated in this order from the sound incident side indicated by the arrow in Figure 1(b). The lattice plate 20 is made of resin or metal, and has regularly-spaced openings 22. The porous body sheet 10 is fixed to the lattice plate at portions (fixed positions) 21a that face at least some of the intersections (lattice points) 21 of the lattice plate 20, and is free at other portions, allowing it to move in the direction of incident sound.

When sound is incident on the porous body sheet 10, the portion of the porous body sheet 10 that is not fixed to the lattice plate displaces in the direction of the sound, causing membrane vibrations that cancel out the low-frequency components of the sound. This is thought to attenuate the low-frequency components of the sound and produce a sound-absorbing effect. Therefore, even if the porous body sheet 10 and the lattice plate 20 are stacked in the reverse order to that of this embodiment, it is thought that the same sound-absorbing effect as described above will be produced.

The sound-absorbing structure 1 of this embodiment is able to achieve excellent sound-absorbing performance with a very simple configuration. In particular, despite its lightweight and simple configuration, it is able to exhibit high sound-absorbing performance in the frequency range of 300 Hz or less (for example, the frequency range of 50 to 300 Hz or the frequency range of 100 to 300 Hz), a characteristic that could not be achieved with conventional technology.

It has been known that when sound enters a porous sheet with open cells, such as glass wool or urethane foam, the sound waves are affected by friction with the surrounding walls and viscous resistance within the pores, and some of the sound energy is dissipated as heat energy, resulting in sound absorption performance. However, because sound absorption characteristics are generally low in the low frequency range and high in the high frequency range, it has been difficult to achieve sufficient sound absorption characteristics in the low frequency range below 300 Hz, such as vibrations caused by cavity resonance within the vehicle body. Therefore, in order to improve sound absorption characteristics in the low frequency range, it has been thought that it is necessary to increase the thickness of the porous sheet in response to the longer wavelength of the sound waves.

Furthermore, with conventional soundproofing materials, there has been a performance trend in which soundproofing performance improves as the density of the constituent materials increases. For this reason, it was common knowledge in the prior art that in order to improve soundproofing performance, the density of the soundproofing material needed to be increased, i.e., its weight needed to be increased.

In contrast, the sound-absorbing structure of this embodiment exhibits sound-absorbing performance by canceling out low-frequency sounds through membrane vibration of the porous sheet. Therefore, contrary to conventional performance trends, it can have excellent sound-absorbing performance in the frequency range of 300 Hz or less, even though it is lightweight and thin.

Figure 2 is a perspective view schematically illustrating a sound-absorbing structure according to another embodiment of the present invention. Similar to the sound-absorbing structure 1 described in Figures 1(a) and (b), the sound-absorbing structure 2 shown in Figure 2 comprises a porous body sheet 10 and a lattice plate 20 laminated in this order from the sound-incident side. The porous body sheet 10 is fixed to the lattice plate 20 at portions facing at least some of the lattice points, while remaining unfixed at other portions, allowing it to move in the direction of sound incidence. In addition, the sound-absorbing structure 2 shown in Figure 2 further comprises a film 30 laminated on the radiation/transmission side of the lattice plate 20, which is adhered to the lattice plate 20. This allows the vibration of the film 30 to be applied, changing the sound-absorbing characteristics of the sound-absorbing structure 2. For example, the sound absorption coefficient in the 200-700 Hz frequency range can be increased, enhancing sound-absorbing performance in that frequency range. Therefore, the sound-absorbing characteristics can be adjusted according to the application. In this case, it is preferable that the film 30 be bonded to the lattice plate 20 except for the outer periphery of the lattice plate 20.

The components of sound-absorbing structures 1 and 2 are described in more detail below. Note that in this specification, "sound absorption" means reducing reflected sound or absorbing sound (acoustics).

(Porous sheet)
The porous body sheet has sound absorption properties due to the presence of continuous holes, and attenuates sound by vibrating in the direction of sound incidence. There are no particular limitations on the material constituting the porous body sheet, and known materials can be used. Examples include porous body sheets made of fibrous materials; resin foams; metals, ceramics, glass, etc. Among these, resin foams are preferred because of their light weight.

The fibrous body is not particularly limited as long as it is an aggregate of fibers having voids on its surface and inside, and either woven fabric or nonwoven fabric such as felt can be used. Furthermore, the fibrous body may be made of organic fibers such as resin fibers, or inorganic fibers such as glass fibers.

Examples of resin foams include polyolefin foams such as polyurethane foam (hereinafter also referred to as urethane foam), polyethylene foam, and polypropylene foam; polystyrene foam; polyamide foam; polyester foams such as polyethylene terephthalate (PET) foam and polybutylene terephthalate (PBT); (meth)acrylic foam; phenolic foam; polyvinyl chloride foam; polyimide foam; silicone resin foam; urea resin foam; melamine resin foam; ethylene propylene diene rubber (EPDM) foam; styrene butadiene rubber (SBR) foam; nitrile butadiene rubber (NBR) foam; ethylene-vinyl acetate copolymer (EVA) foam; ethylene-acrylic acid copolymer foam; and ethylene-ethyl acrylate copolymer (EEA) foam. Among these, polyurethane foam is preferred from the standpoint of sound absorption performance. These foams can be flexible, semi-rigid, or rigid.

The thickness of the porous body sheet is not particularly limited, but from the viewpoint of the sound absorbing effect of the sound absorbing structure, it is preferably 1 to 100 mm, more preferably 5 to 50 mm. The density of the porous body sheet is also not particularly limited, but from the viewpoint of weight reduction, it is preferably 3 to 150 kg/ ^m3 .

(lattice board)
The lattice plate is a resin or metal plate having lattice-like compartments, and supports the porous sheet at at least some of the lattice intersections (lattice points). By making the lattice plate from resin or metal, it becomes easier to adjust the Young's modulus of the lattice plate to a desired value, and it becomes possible to improve the sound absorption characteristics of the sound absorbing structure.

The resin material that makes up the grid plate is not particularly limited, but conventionally known thermoplastic or thermosetting resins can be used.

Examples of thermoplastic resins include polyethylene (e.g., low-density polyethylene, high-density polyethylene, etc.), polyolefin resins such as polypropylene, polyvinyl chloride resin, acrylic resin, methacrylic resin, acrylonitrile-butadiene-styrene resin, vinyl acetate resin, ethylene-vinyl acetate resin, and styrene-butadiene resin. Examples of thermosetting resins that can be used include urethane resin, melamine resin, thermosetting acrylic resin, urea resin, phenolic resin, resorcinol resin, alkylresorcinol resin, epoxy resin, and thermosetting polyester. Resin precursors that produce these resins, such as prepolymers, oligomers, and monomers, may also be used, including urethane resin prepolymer, urea resin prepolymer (precondensate), phenolic resin prepolymer (precondensate), diallyl phthalate prepolymer, acrylic oligomer, polyisocyanate, methacrylic ester monomer, and diallyl phthalate monomer. Among these, thermoplastic resins are preferred from the perspective of ease of molding, and polyolefin resins are particularly preferred due to their lightweight, durable, and inexpensive properties.

Examples of metal materials include copper, aluminum, titanium, magnesium, tungsten, iron, chromium, and alloys thereof. SUS (stainless steel) and other metal materials may also be used.

It is more preferable that the lattice plate 20 has a plurality of openings 22 of the same shape arranged in a regular pattern. This configuration makes it easy to manufacture, and the presence of a large number of openings of the same shape makes it possible to specifically exhibit sound absorption performance for sound waves in the desired frequency range. In this case, there are no particular restrictions on the proportion of the area of the openings 22 to the area of the lattice plate 20. The shape of the openings 22 is not limited to square, and may be rectangular, hexagonal, triangular, etc.

There are no particular restrictions on the size of the openings 22 in the lattice plate 20. For example, if the openings are square, the length of one side is, for example, 1 to 50 mm, preferably 2 to 40 mm, and more preferably 3 to 39 mm. This can improve sound absorption characteristics in the frequency range below 300 Hz.

The area per opening 22 of the lattice plate 20 (opening area) is not particularly limited, but is preferably 10 to 1500 ^mm2 from the viewpoint of obtaining high sound absorption characteristics. In particular, in a sound absorbing structure composed of a porous body sheet 10 and a lattice plate 20, such as the sound absorbing structure 1 shown in Figures 1(a) and 1(b), an opening area of 10 ^mm2 or more can improve the sound absorption coefficient at frequencies below 200 Hz. Furthermore, an opening area of 1500 ^mm2 or less can improve the sound absorption coefficient in the frequency range from 200 to 300 Hz.

On the other hand, in a sound absorbing structure such as the sound absorbing structure 2 in Figure 2, in addition to the porous body sheet 10 and lattice plate 20, a film 30 is bonded to the radiation/transmission side of the lattice plate 20, it is more preferable that the opening area of the openings 22 in the lattice plate 20 is 10 to 225 ^mm2 . If the opening area is 10 ^mm2 or more, the sound absorption coefficient at 200 Hz or less can be improved. Furthermore, if the opening area is 225 ^mm2 or less, the sound absorption coefficient in the frequency range of 200 to 300 Hz can be improved.

The thickness of the lattice plate 20 is not particularly limited, but is, for example, 0.1 to 10 mm, and preferably 0.5 to 5 mm. If it is 0.1 mm or more, the effects of the present invention can be more easily achieved. Furthermore, if it is 10 mm or less, it is preferable from the perspective of weight reduction.

In the sound-absorbing structure of this embodiment, the bonding positions (fixing positions) between the porous body sheet and the lattice plate are not particularly limited, as long as the porous body sheet is fixed to the lattice plate at locations facing at least some of the lattice points, and the remaining locations are capable of vibrating in the direction of sound incidence. As long as the above-mentioned bonding positions (fixing positions) include locations facing at least some of the lattice points, and locations other than the bonding positions of the porous body sheet are capable of vibrating in the direction of sound incidence, the porous body sheet may be further bonded (fixed) to locations other than those facing the lattice points. Similarly, the bonding area is not particularly limited, as long as it meets the above requirements.

As an example, as shown by the bold lines in the photograph of the sound-absorbing structure sample in Figure 10(a), the porous body sheet can be fixed to the lattice plate at the positions where the lattice is located. Alternatively, as shown in Figures 10(b) to 10(d), the porous body sheet can be fixed to the lattice plate at an arbitrarily selected portion of the positions where the lattice is located. Alternatively, as shown in Figure 10(e), the porous body sheet can be fixed to the lattice plate at some of the lattice points. The adhesive area is not particularly limited and can be selected arbitrarily. Figures 10(a) to 10(e) are photographs of sound-absorbing structure samples stacked with a 90 mm x 90 mm porous body sheet and a lattice plate with a line width of 7 mm and openings of 15 mm x 15 mm. The adhesive positions between the porous body sheet and the lattice plate in each sample are indicated by bold lines.

Furthermore, as shown in Figures 10(a) to (e), the spacing between adjacent bonded positions is not particularly limited. To achieve the effects of the present invention more significantly, for example, if the bonded positions are arranged in a strip pattern that is parallel to each other at regular intervals, the distance between adjacent parallel bonded positions is, for example, 200 mm or less, preferably 100 mm or less. For example, if the bonded positions are arranged in a grid pattern, the distance between adjacent parallel bonded positions is, for example, 200 mm or less, preferably 100 mm or less. For example, if the bonded positions are arranged in a dot pattern, the distance between the nearest bonded positions is, for example, 200 mm or less, preferably 100 mm or less.

(film)
The film is provided on the radiation/transmission side of the grid plate and is bonded to the grid plate. Preferably, the film is arranged so as to close the opening of the grid plate. Preferably, the film is bonded to the grid plate in a portion other than the outer periphery of the grid plate.

There are no particular restrictions on the material that can be used to make the film, but lightweight, rigid materials are preferred. For example, polyolefin resins such as polyethylene (e.g., low-density polyethylene, high-density polyethylene, etc.), polypropylene, polyethylene terephthalate resin, polyvinyl chloride resin, and polystyrene resin are preferably used.

The thickness of the film is not particularly limited, but is, for example, 1 to 100 μm, and preferably 2 to 50 μm. The effects of the present invention can be more easily achieved within this range. There are also no particular restrictions on the size of the film, but it is preferable that it be large enough to cover the entire surface of the grid plate.

The sound absorbing structure according to this embodiment is preferably lightweight. From this viewpoint, the overall density of the sound absorbing structure according to this embodiment is preferably 1 g/ ^cm3 or less, more preferably 0.5 g/ ^cm3 or less, even more preferably 0.3 g/ ^cm3 or less, and particularly preferably 0.2 g/ ^cm3 or less. The sound absorbing structure according to this embodiment is also preferably thin. From this viewpoint, the overall thickness of the sound absorbing structure according to this embodiment is preferably 50 mm or less, more preferably 30 mm or less, and even more preferably 20 mm or less.

When producing the sound-absorbing structure according to this embodiment, there are no particular restrictions on the method for bonding the porous sheet and the lattice plate, and methods such as using a known adhesive or double-sided tape, or fastening devices such as screws or bolts, can be used. Furthermore, there are no particular restrictions on the method for bonding the lattice plate and film, and they can be fixed using a known adhesive or double-sided tape.

The sound-absorbing structure of this embodiment can be suitably used to absorb noise from various sound sources. In particular, the sound-absorbing structure of this embodiment can be constructed to be extremely lightweight. Because of its lightweight design, the sound-absorbing structure of this embodiment is preferably mounted on a vehicle for use. Examples of application areas include dash insulators, dash panels, floor carpets, spacers, door trim, sound-absorbing structures within door trim, sound-absorbing structures within compartments, instrument panels, instrument center boxes, instrument upper boxes, air conditioner housings, roof trim, sound-absorbing structures within roof trim, sun visors, rear seat air conditioning ducts, cooling ducts for battery cooling systems in battery-powered vehicles, cooling fans, center console trim, sound-absorbing structures within consoles, parcel trim, parcel panels, seat headrests, front seat backs, and rear seat backs. Furthermore, in the trunk, the sound-absorbing structure can be applied to trunk floor trim, trunk boards, trunk side trim, sound-absorbing structures within trim, and draft cover. It can also be applied within the vehicle frame or between panels, for example, to pillar trim and fenders. It is particularly suitable for use in automotive interior parts, as it has excellent sound absorption performance in the frequency range of 300 Hz or less, is lightweight, and allows for a thin overall thickness.

The present invention will be described in more detail below using examples. However, the technical scope of the present invention is not limited to the following examples.

<<Sound absorption coefficient measurement>>
The sound absorption coefficient was measured in accordance with JIS A 1405-2 (Measurement of sound absorption coefficient and impedance using an acoustic tube - Part 2: Transfer function method). However, a spacer was used to hold the sample, a 10 mm back air space was created by the spacer behind the sample, and a 5 mm gap was provided between the spacer and the reflector. Figure 3(a) shows a schematic diagram of the sound absorption coefficient measurement device.

<<Measurement of membrane vibration acceleration>>
The membrane vibration acceleration was measured using a laser Doppler vibrometer (VibroOne manufactured by Polytec). The laser Doppler vibrometer consists of an optical head that emits laser light and a converter that processes the Doppler frequency from the reflected light. A voltage signal proportional to the sample's moving speed was input into an FFT analyzer and converted into acceleration. Figure 3(b) shows a schematic diagram of the membrane vibration acceleration measuring device. Note that both the sound absorption coefficient and membrane vibration acceleration can be measured using the device shown in Figure 3(b).

<<Creating a sound-absorbing structure>>
(Confirmation of sound absorption effect: 1)
[Example 1]
As a porous sheet, a 10 mm thick urethane foam (density: approximately 32.1 kg/m ³ , flow resistance: approximately 36000 Ns/m ⁴ ) cut into a size of 90 mm×90 mm was prepared.

A 1.0 mm thick polypropylene (PP) plate (manufactured by Acrylic Eye Co., Ltd., density: 0.9 g/cm ³ ) was cut into a size of 90 mm × 90 mm. This PP plate was cut so that the openings were squares with sides of 15 mm and the spacing between the openings was 7 mm, as shown in Figure 7(d), to produce a grid plate (d).

A lattice plate (d) was laminated on the porous body sheet, and the porous body sheet and lattice plate (d) were fixed with double-sided tape in the position shown in Figure 10(a), thereby obtaining the sound-absorbing structure of Example 1.

Using the sound-absorbing structure obtained above, the sound absorption coefficient and membrane vibration acceleration were measured using the device shown in Figure 3(b). The results are shown in Figure 4. As shown in Figure 4, in the sound-absorbing structure of the present invention, the sound absorption coefficient decreases in the frequency range from 100 Hz to around 250 Hz and increases from 800 Hz to 1000 Hz, and the membrane vibration acceleration also shows a similar trend. As the increase and decrease in the sound absorption coefficient and membrane vibration acceleration correspond in this way, it is thought that in the sound-absorbing structure of the present invention, sound is absorbed by consuming sound pressure energy due to membrane vibration.

(Confirmation of sound absorption effect: 2)
[Comparative Example 2-1]
A 10 mm thick urethane foam (density: approximately 32.1 kg/m ³ , flow resistance: approximately 36,000 Ns/m ⁴ ) cut into a 90 mm x 90 mm piece was prepared as a porous sheet. This porous sheet was used as the sound-absorbing structure of this comparative example.

[Comparative Example 2-2]
A 1.0 mm thick polypropylene (PP) plate (manufactured by Acrylic Eye Co., Ltd., density: 0.9 g/cm ³ ) was cut to 90 mm x 90 mm. This PP plate was cut so that the openings were square with sides of 15 mm and the spacing between the openings was 7 mm, as shown in Figure 7(d), to produce a lattice plate (d). This lattice plate (d) was used as the sound-absorbing structure of this comparative example.

[Example 2-1]
A lattice plate (d1) was produced in the same manner as the lattice plate (d) of Comparative Example 2-2, except that the thickness was changed to 2.0 mm. The lattice plate (d1) was laminated on the porous body sheet, and the porous body sheet and the lattice plate (d1) were fixed with double-sided tape at the position shown in Figure 10 (a), to form the sound-absorbing structure of this example.

[Example 2-2]
For the sound-absorbing structure of Example 2-1, the lattice plate (d1) was replaced with the lattice plate (d), which was laminated and fixed in the same manner. A 0.01 mm thick polyethylene (PE) film (Hook Poly, manufactured by System Polymer Co., Ltd.) was cut to 100 mm x 100 mm, and this PE film was fixed to the lattice plate (d) with double-sided tape in a portion excluding the outer periphery of the lattice plate (d) (as shown in Figure 10 (a) , the lattice portion excluding the outer periphery of the lattice), forming the sound-absorbing structure of this example. Figure 5 shows photographs of the samples of the sound-absorbing structures produced in Examples 2-1 and 2-2.

The specifications for the above examples and comparative examples are shown in Table 1 below, and the sound absorption coefficient results obtained by evaluating sound absorption performance using the device shown in Figure 3(a) are shown in Figure 6. The sound absorbing structures of Examples 2-1 and 2-2 were found to exhibit superior sound absorption performance compared to urethane foam alone (Comparative Example 2-1) or lattice board alone (Comparative Example 2-2). It was also found that the sound absorbing structure of Example 2-2, which further includes a film layer, can enhance sound absorption performance in the 200 to 700 Hz range. Therefore, it was found that a structure without a film can be used in applications where sound absorption performance in the 100 to 200 Hz range is particularly important, while a structure with a film can be used in applications where sound absorption performance over a relatively wide frequency range of 200 to 700 Hz is required.

(Effect of the opening area of the grid plate: 1)
[Examples 3-4]
The sound absorbing structure of this example was obtained in the same manner as in the sound absorbing structure of Example 2-1 described above, except that the thickness of the lattice plate was changed to 1.0 mm.

[Examples 3-1 to 3-3, 3-5, and 3-6]
The sound absorbing structures of Examples 3-1 to 3-3, 3-5, and 3-6 were obtained in the same manner as in Example 3-4, except that the opening area of the openings in the lattice plate was changed as shown in Table 2 below. The size and arrangement of the openings in the lattice plate are shown in Figure 7. (a) to (f) in Figure 7 correspond to Examples 3-1 to 3-6, respectively.

[Examples 3-7]
The sound absorbing structure of this example was obtained in the same manner as in the sound absorbing structure of Example 2-1 described above, except that the lattice plate was changed to a 2.0 mm thick SUS plate cut so that the openings were square with sides of 15 mm and the spacing between the openings was 7 mm, as shown in Figure 7(d).

The specifications of the above examples are shown in Table 2 below, and the sound absorption coefficient results obtained by evaluating the sound absorption performance are shown in Figures 8A and 8B. Figure 8A shows the sound absorption performance of the sound-absorbing structures of Examples 3-1 to 3-6, and Figure 8B shows the sound absorption performance of the sound-absorbing structures of Examples 2-1, 3-2 to 3-4, and 3-7. Note that in Figure 8B, the sound absorption performance data for Examples 2-1 and 3-2 to 3-4 are the same as those shown in Figures 6 and 8A, respectively. These results demonstrate that the frequency range with high sound absorption coefficients and the sound absorption coefficient can be controlled by changing the opening area of the lattice plate. In the sound-absorbing structures composed of a porous sheet and a lattice plate, Examples 3-2 to 3-6, which have an opening area of 10 ^mm2 or more, have a high sound absorption coefficient in the low frequency range below around 200 Hz. Furthermore, it was found that Examples 3-1 to 3-5, which have an opening area of 1500 ^mm2 or less, have a high sound absorption coefficient in the frequency range from 200 to 300 Hz. Furthermore, as shown in FIG. 8B, it was confirmed that the sound absorbing structure of Example 3-7, which uses a metal lattice plate, also exhibits excellent sound absorbing performance, similar to the sound absorbing structures of Examples 2-1 and 3-1 to 3-6, which use a resin lattice plate.

(Effect of the opening area of the grid plate: 2)
[Example 4-4]
The sound absorbing structure of Example 2-2 described above was used as the sound absorbing structure of this example.

[Examples 4-1 to 4-3, 4-5, and 4-6]
The sound absorbing structures of Examples 4-1 to 4-3, 4-5, and 4-6 were obtained in the same manner as in Example 4-4, except that the opening area of the openings in the lattice plate was changed as shown in Table 3 below. The size and arrangement of the openings in the lattice plate are as shown in Figure 7. (a) to (f) in Figure 7 correspond to Examples 4-1 to 4-6, respectively.

The specifications of the above examples are shown in Table 3 below, and the sound absorption coefficient results obtained by evaluating the sound absorption performance are shown in Figure 9. These results show that in the sound absorbing structure in which a film is further laminated on the radiation/transmission side of the lattice plate, Examples 4-2 to 4-6, which have an opening area of 10 ^mm2 or more, have a high sound absorption coefficient in the low frequency range below around 200 Hz. Furthermore, it was found that Examples 4-2 to 4-4, which have an opening area of 10 ^mm2 or more and 225 ^mm2 or less, have a high sound absorption coefficient in the frequency range from 200 to 300 Hz.

(Influence of adhesive position)
[Example 5-1]
The sound absorbing structure of Example 3-4 described above was used as the sound absorbing structure of this example.

[Examples 5-2 to 5-5]
In the sound-absorbing structure of Example 5-1, the adhesive position between the porous sheet and the lattice plate was changed from the position shown in Figure 10(a) to the positions shown in Figures 10(b) to (d). The sound-absorbing structures of Examples 5-2 to 5-5 were obtained in the same manner, except that

[Comparative Examples 5-1 to 5-3]
The sound-absorbing structure of Comparative Example 5-1 was obtained in the same manner as in Example 5-1, except that the porous body sheet and the lattice plate were not bonded. In Comparative Example 5-2, only the porous body sheet of Example 5-1 was used as the sound-absorbing structure, and in Comparative Example 5-3, only the lattice plate of Example 5-1 was used as the sound-absorbing structure.

The specifications of the above examples and comparative examples are shown in Table 4 below, and the sound absorption coefficient results obtained by evaluating sound absorption performance are shown in Figure 11. As shown in Figure 10, from Example 5-1 to Example 5-5, the spacing between the bonded portions of the porous sheet and the lattice plate is gradually increased, and the bonded area is gradually decreased. However, as shown in Figure 11, all examples show high sound absorption coefficients in the frequency range of 300 Hz or less, and it was found that the influence of the spacing and bonded area of the bonded portions is small.

Therefore, when creating a large-area sound-absorbing structure for use in a vehicle, it is believed that it can be used without any problems even if the distance between adjacent bonding positions is increased to approximately 90 mm.

1, 2 Sound absorbing structure 10 Porous sheet 20 Lattice plate 21 Lattice point 21a Adhesion position (fixing position)
22 opening 30 film

Claims (5)

A porous sheet and a grid plate made of resin or metal are laminated together ,
The opening of the lattice plate on the opposite side to the porous body sheet is not closed,
the porous sheet is fixed to the lattice plate at a portion facing at least a part of the lattice points of the lattice plate,
A sound absorbing method comprising: absorbing sound in a frequency range of 300 Hz or less by causing sound to be incident on the sound absorbing structure from the porous sheet side, wherein portions other than the fixed portions are displaceable in the stacking direction . The sound absorbing method according to claim 1, wherein the opening area of each opening of the lattice plate is 10 mm ² or more and 1500 mm ² or less. 3. The sound absorbing method according to claim 1, wherein the sound absorbing structure consists of only the porous sheet, the lattice plate, and an adhesive, double-sided tape, or fixture for fixing them together. The sound absorbing method according to any one of claims 1 to 3, wherein the thickness of the porous body sheet is 5 mm or more, the thickness of the lattice plate is 0.1 to 5 mm, and the overall thickness of the sound absorbing structure is 20 mm or less. The sound absorbing method according to any one of claims 1 to 4, wherein the lattice plate is not fixed to the porous sheet at its outer periphery.